Proton depth dose distribution: 3-D calculation of dose distributions from solar flare irradiation

NASA Astrophysics Data System (ADS)

Leavitt, Dennis D.

1990-11-01

Relative depth dose distribution to the head from 3 typical solar flare proton events were calculated for 3 different exposure geometries: (1) single directional radiation incident upon a fixed head; (2) single directional radiation incident upon head rotating axially (2-D rotation); and (3) omnidirectional radiation incident upon head (3-D rotation). Isodose distributions in the transverse plane intersecting isocenter are presented for each of the 3 solar flare events in all 3 exposure geometries. In all 3 calculation configurations the maximum predicted dose occurred on the surface of the head. The dose at the isocenter of the head relative to the surface dose for the 2-D and 3-D rotation geometries ranged from 2 to 19 percent, increasing with increasing energy of the event. The calculations suggest the superficially located organs (lens of the eye and skin) are at greatest risk for the proton events studied here.

Does Choice of Head Size and Neck Geometry Affect Stem Migration in Modular Large-Diameter Metal-on-Metal Total Hip Arthroplasty? A Preliminary Analysis

PubMed Central

Georgiou, CS; Evangelou, KG; Theodorou, EG; Provatidis, CG; Megas, PD

2012-01-01

Due to their theoretical advantages, hip systems combining modular necks and large diameter femoral heads have gradually gained popularity. However, among others, concerns regarding changes in the load transfer patterns were raised. Recent stress analyses have indeed shown that the use of modular necks and big femoral heads causes significant changes in the strain distribution along the femur. Our original hypothesis was that these changes may affect early distal migration of a modular stem. We examined the effect of head diameter and neck geometry on migration at two years of follow-up in a case series of 116 patients (125 hips), who have undergone primary Metal-on-Metal total hip arthroplasty with the modular grit-blasted Profemur®E stem combined with large-diameter heads (>36 mm). We found that choice of neck geometry and head diameter has no effect on stem migration. A multivariate regression analysis including the potential confounding variables of the body mass index, bone quality, canal fill and stem positioning revealed only a negative correlation between subsidence and canal fill in midstem area. Statistical analysis, despite its limitations, did not confirm our hypothesis that choice of neck geometry and/or head diameter affects early distal migration of a modular stem. However, the importance of correct stem sizing was revealed. PMID:23284597

Does Choice of Head Size and Neck Geometry Affect Stem Migration in Modular Large-Diameter Metal-on-Metal Total Hip Arthroplasty? A Preliminary Analysis.

PubMed

Georgiou, Cs; Evangelou, Kg; Theodorou, Eg; Provatidis, Cg; Megas, Pd

2012-01-01

Due to their theoretical advantages, hip systems combining modular necks and large diameter femoral heads have gradually gained popularity. However, among others, concerns regarding changes in the load transfer patterns were raised. Recent stress analyses have indeed shown that the use of modular necks and big femoral heads causes significant changes in the strain distribution along the femur. Our original hypothesis was that these changes may affect early distal migration of a modular stem. We examined the effect of head diameter and neck geometry on migration at two years of follow-up in a case series of 116 patients (125 hips), who have undergone primary Metal-on-Metal total hip arthroplasty with the modular grit-blasted Profemur®E stem combined with large-diameter heads (>36 mm). We found that choice of neck geometry and head diameter has no effect on stem migration. A multivariate regression analysis including the potential confounding variables of the body mass index, bone quality, canal fill and stem positioning revealed only a negative correlation between subsidence and canal fill in midstem area. Statistical analysis, despite its limitations, did not confirm our hypothesis that choice of neck geometry and/or head diameter affects early distal migration of a modular stem. However, the importance of correct stem sizing was revealed.

Development of a child head analytical dynamic model considering cranial nonuniform thickness and curvature - Applying to children aged 0-1 years old.

PubMed

Li, Zhigang; Ji, Cheng; Wang, Lishu

2018-07-01

Although analytical models have been used to quickly predict head response under impact condition, the existing models generally took the head as regular shell with uniform thickness which cannot account for the actual head geometry with varied cranial thickness and curvature at different locations. The objective of this study is to develop and validate an analytical model incorporating actual cranial thickness and curvature for child aged 0-1YO and investigate their effects on child head dynamic responses at different head locations. To develop the new analytical model, the child head was simplified into an irregular fluid-filled shell with non-uniform thickness and the cranial thickness and curvature at different locations were automatically obtained from CT scans using a procedure developed in this study. The implicit equation of maximum impact force was derived as a function of elastic modulus, thickness and radius of curvature of cranium. The proposed analytical model are compared with cadaver test data of children aged 0-1 years old and it is shown to be accurate in predicting head injury metrics. According to this model, obvious difference in injury metrics were observed among subjects with the same age, but different cranial thickness and curvature; and the injury metrics at forehead location are significant higher than those at other locations due to large thickness it owns. The proposed model shows good biofidelity and can be used in quickly predicting the dynamics response at any location of head for child younger than 1 YO. Copyright © 2018 Elsevier B.V. All rights reserved.

Comparison of radio frequency energy absorption in ear and eye region of children and adults at 900, 1800 and 2450 MHz.

PubMed

Keshvari, J; Lang, S

2005-09-21

The increasing use of mobile communication devices, especially mobile phones by children, has triggered discussions on whether there is a larger radio frequency (RF) energy absorption in the heads of children compared to that of adults. The objective of this study was to clarify possible differences in RF energy absorption in the head region of children and adults using computational techniques. Using the finite-difference time-domain (FDTD) computational method, a set of specific absorption rate (SAR) calculations were performed for anatomically correct adult and child head models. A half-wave dipole was used as an exposure source at 900, 1800 and 2450 MHz frequencies. The ear and eye regions were studied representing realistic exposure scenarios to current and upcoming mobile wireless communication devices. The differences in absorption were compared with the maximum energy absorption of the head model. Four magnetic resonance imaging (MRI) based head models, one female, one adult, two child head models, aged 3 and 7 years, were used. The head models greatly differ from each other in terms of size, external shape and the internal anatomy. The same tissue dielectric parameters were applied for all models. The analyses suggest that the SAR difference between adults and children is more likely caused by the general differences in the head anatomy and geometry of the individuals rather than age. It seems that the external shape of the head and the distribution of different tissues within the head play a significant role in the RF energy absorption.

Creating a normative database of age-specific 3D geometrical data, bone density, and bone thickness of the developing skull: a pilot study.

PubMed

Delye, Hans; Clijmans, Tim; Mommaerts, Maurice Yves; Sloten, Jos Vnder; Goffin, Jan

2015-12-01

Finite element models (FEMs) of the head are used to study the biomechanics of traumatic brain injury and depend heavily on the use of accurate material properties and head geometry. Any FEM aimed at investigating traumatic head injury in children should therefore use age-specific dimensions of the head, as well as age-specific material properties of the different tissues. In this study, the authors built a database of age-corrected skull geometry, skull thickness, and bone density of the developing skull to aid in the development of an age-specific FEM of a child's head. Such a database, containing age-corrected normative skull geometry data, can also be used for preoperative surgical planning and postoperative long-term follow-up of craniosynostosis surgery results. Computed tomography data were processed for 187 patients (age range 0-20 years old). A 3D surface model was calculated from segmented skull surfaces. Skull models, reference points, and sutures were processed into a MATLAB-supported database. This process included automatic calculation of 2D measurements as well as 3D measurements: length of the coronal suture, length of the lambdoid suture, and the 3D anterior-posterior length, defined as the sum of the metopic and sagittal suture. Skull thickness and skull bone density calculations were included. Cephalic length, cephalic width, intercoronal distance, lateral orbital distance, intertemporal distance, and 3D measurements were obtained, confirming the well-established general growth pattern of the skull. Skull thickness increases rapidly in the first year of life, slowing down during the second year of life, while skull density increases with a fast but steady pace during the first 3 years of life. Both skull thickness and density continue to increase up to adulthood. This is the first report of normative data on 2D and 3D measurements, skull bone thickness, and skull bone density for children aged 0-20 years. This database can help build an age-specific FEM of a child's head. It can also help to tailor preoperative virtual planning in craniosynostosis surgery toward patient-specific normative target values and to perform objective long-term follow-up in craniosynostosis surgery.

New Geometry of Worm Face Gear Drives with Conical and Cylindrical Worms: Generation, Simulation of Meshing, and Stress Analysis

NASA Technical Reports Server (NTRS)

Litvin, Faydor L.; Nava, Alessandro; Fan, Qi; Fuentes, Alfonso

2002-01-01

New geometry of face worm gear drives with conical and cylindrical worms is proposed. The generation of the face worm-gear is based on application of a tilted head-cutter (grinding tool) instead of application of a hob applied at present. The generation of a conjugated worm is based on application of a tilted head-cutter (grinding tool) as well. The bearing contact of the gear drive is localized and is oriented longitudinally. A predesigned parabolic function of transmission errors for reduction of noise and vibration is provided. The stress analysis of the gear drive is performed using a three-dimensional finite element analysis. The contacting model is automatically generated. The developed theory is illustrated with numerical examples.

A new model for the surface arrangement of myosin molecules in tarantula thick filaments.

PubMed

Offer, G; Knight, P J; Burgess, S A; Alamo, L; Padrón, R

2000-04-28

Three-dimensional reconstructions of the negatively stained thick filaments of tarantula muscle with a resolution of 50 A have previously suggested that the helical tracks of myosin heads are zigzagged, short diagonal ridges being connected by nearly axial links. However, surface views of lower contour levels reveal an additional J-shaped feature approximately the size and shape of a myosin head. We have modelled the surface array of myosin heads on the filaments using as a building block a model of a two-headed regulated myosin molecule in which the regulatory light chains of the two heads together form a compact head-tail junction. Four parameters defining the radius, orientation and rotation of each myosin molecule were varied. In addition, the heads were allowed independently to bend in a plane perpendicular to the coiled-coil tail at three sites, and to tilt with respect to the tail and to twist at one of these sites. After low-pass filtering, models were aligned with the reconstruction, scored by cross-correlation and refined by simulated annealing. Comparison of the geometry of the reconstruction and the distance between domains in the myosin molecule narrowed the choice of models to two main classes. A good match to the reconstruction was obtained with a model in which each ridge is formed from the motor domain of a head pointing to the bare zone together with the head-tail junction of a neighbouring molecule. The heads pointing to the Z-disc intermittently occupy the J-position. Each motor domain interacts with the essential and regulatory light chains of the neighbouring heads. A near-radial spoke in the reconstruction connecting the backbone to one end of the ridge can be identified as the start of the coiled-coil tail. Copyright 2000 Academic Press.

Photon migration through fetal head in utero using continuous wave, near infrared spectroscopy: clinical and experimental model studies

NASA Astrophysics Data System (ADS)

Ramanujam, Nirmala; Vishnoi, Gargi; Hielscher, Andreas H.; Rode, Martha; Forouzan, Iraj; Chance, Britton

2000-04-01

Near infrared (NIR) measurements were made from the maternal abdomen (clinical studies) and laboratory tissue phantoms (experimental studies) to gain insight into photon migration through the fetal head in utero. Specifically, a continuous wave spectrometer was modified and employed to make NIR measurements at 760 and 850 nm, at a large (10 cm) and small (2.5/4 cm) source-detector separation, simultaneously, on the maternal abdomen, directly above the fetal head. A total of 19 patients were evaluated, whose average gestational age and fetal head depth, were 37 weeks +/- 3 and 2.25 cm +/- 0.7, respectively. At the large source-detector separation, the photons are expected to migrate through both the underlying maternal and fetal tissues before being detected at the surface, while at the short source-detector separation, the photons are expected to migrate primarily through the superficial maternal tissues before being detected. Second, similar NIR measurements were made on laboratory tissue phantoms, with variable optical properties and physical geometries. The variable optical properties were obtained using different concentrations of India ink and Intralipid in water, while the variable physical geometries were realized by employing glass containers of different shapes and sizes. Third, the NIR measurements, which were made on the laboratory tissue phantoms, were compared to the NIR measurements made on the maternal abdomen to determine which tissue phantom best simulates the photon migration path through the fetal head in utero. The results of the comparison were used to provide insight into the optical properties and physical geometry of the maternal and fetal tissues in the photon migration path.

Monte Carlo study of the effects of system geometry and antiscatter grids on cone-beam CT scatter distributions

PubMed Central

Sisniega, A.; Zbijewski, W.; Badal, A.; Kyprianou, I. S.; Stayman, J. W.; Vaquero, J. J.; Siewerdsen, J. H.

2013-01-01

Purpose: The proliferation of cone-beam CT (CBCT) has created interest in performance optimization, with x-ray scatter identified among the main limitations to image quality. CBCT often contends with elevated scatter, but the wide variety of imaging geometry in different CBCT configurations suggests that not all configurations are affected to the same extent. Graphics processing unit (GPU) accelerated Monte Carlo (MC) simulations are employed over a range of imaging geometries to elucidate the factors governing scatter characteristics, efficacy of antiscatter grids, guide system design, and augment development of scatter correction. Methods: A MC x-ray simulator implemented on GPU was accelerated by inclusion of variance reduction techniques (interaction splitting, forced scattering, and forced detection) and extended to include x-ray spectra and analytical models of antiscatter grids and flat-panel detectors. The simulator was applied to small animal (SA), musculoskeletal (MSK) extremity, otolaryngology (Head), breast, interventional C-arm, and on-board (kilovoltage) linear accelerator (Linac) imaging, with an axis-to-detector distance (ADD) of 5, 12, 22, 32, 60, and 50 cm, respectively. Each configuration was modeled with and without an antiscatter grid and with (i) an elliptical cylinder varying 70–280 mm in major axis; and (ii) digital murine and anthropomorphic models. The effects of scatter were evaluated in terms of the angular distribution of scatter incident upon the detector, scatter-to-primary ratio (SPR), artifact magnitude, contrast, contrast-to-noise ratio (CNR), and visual assessment. Results: Variance reduction yielded improvements in MC simulation efficiency ranging from ∼17-fold (for SA CBCT) to ∼35-fold (for Head and C-arm), with the most significant acceleration due to interaction splitting (∼6 to ∼10-fold increase in efficiency). The benefit of a more extended geometry was evident by virtue of a larger air gap—e.g., for a 16 cm diameter object, the SPR reduced from 1.5 for ADD = 12 cm (MSK geometry) to 1.1 for ADD = 22 cm (Head) and to 0.5 for ADD = 60 cm (C-arm). Grid efficiency was higher for configurations with shorter air gap due to a broader angular distribution of scattered photons—e.g., scatter rejection factor ∼0.8 for MSK geometry versus ∼0.65 for C-arm. Grids reduced cupping for all configurations but had limited improvement on scatter-induced streaks and resulted in a loss of CNR for the SA, Breast, and C-arm. Relative contribution of forward-directed scatter increased with a grid (e.g., Rayleigh scatter fraction increasing from ∼0.15 without a grid to ∼0.25 with a grid for the MSK configuration), resulting in scatter distributions with greater spatial variation (the form of which depended on grid orientation). Conclusions: A fast MC simulator combining GPU acceleration with variance reduction provided a systematic examination of a range of CBCT configurations in relation to scatter, highlighting the magnitude and spatial uniformity of individual scatter components, illustrating tradeoffs in CNR and artifacts and identifying the system geometries for which grids are more beneficial (e.g., MSK) from those in which an extended geometry is the better defense (e.g., C-arm head imaging). Compact geometries with an antiscatter grid challenge assumptions of slowly varying scatter distributions due to increased contribution of Rayleigh scatter. PMID:23635285

A DTI-based model for TMS using the independent impedance method with frequency-dependent tissue parameters

NASA Astrophysics Data System (ADS)

De Geeter, N.; Crevecoeur, G.; Dupré, L.; Van Hecke, W.; Leemans, A.

2012-04-01

Accurate simulations on detailed realistic head models are necessary to gain a better understanding of the response to transcranial magnetic stimulation (TMS). Hitherto, head models with simplified geometries and constant isotropic material properties are often used, whereas some biological tissues have anisotropic characteristics which vary naturally with frequency. Moreover, most computational methods do not take the tissue permittivity into account. Therefore, we calculate the electromagnetic behaviour due to TMS in a head model with realistic geometry and where realistic dispersive anisotropic tissue properties are incorporated, based on T1-weighted and diffusion-weighted magnetic resonance images. This paper studies the impact of tissue anisotropy, permittivity and frequency dependence, using the anisotropic independent impedance method. The results show that anisotropy yields differences up to 32% and 19% of the maximum induced currents and electric field, respectively. Neglecting the permittivity values leads to a decrease of about 72% and 24% of the maximum currents and field, respectively. Implementing the dispersive effects of biological tissues results in a difference of 6% of the maximum currents. The cerebral voxels show limited sensitivity of the induced electric field to changes in conductivity and permittivity, whereas the field varies approximately linearly with frequency. These findings illustrate the importance of including each of the above parameters in the model and confirm the need for accuracy in the applied patient-specific method, which can be used in computer-assisted TMS.

Theoretical and experimental investigation of near-infrared light propagation in a model of the adult head.

PubMed

Okada, E; Firbank, M; Schweiger, M; Arridge, S R; Cope, M; Delpy, D T

1997-01-01

Near-infrared light propagation in various models of the adult head is analyzed by both time-of-flight measurements and mathematical prediction. The models consist of three- or four-layered slabs, the latter incorporating a clear cerebrospinal fluid (CSF) layer. The most sophisticated model also incorporates slots that imitate sulci on the brain surface. For each model, the experimentally measured mean optical path length as a function of source-detector spacing agrees well with predictions from either a Monte Carlo model or a finite-element method based on diffusion theory or a hybrid radiosity-diffusion theory. Light propagation in the adult head is shown to be highly affected by the presence of the clear CSF layer, and both the optical path length and the spatial sensitivity profile of the models with a CSF layer are quite different from those without the CSF layer. However, the geometry of the sulci and the boundary between the gray and the white matter have little effect on the detected light distribution.

Computer-aided multiple-head 3D printing system for printing of heterogeneous organ/tissue constructs

NASA Astrophysics Data System (ADS)

Jung, Jin Woo; Lee, Jung-Seob; Cho, Dong-Woo

2016-02-01

Recently, much attention has focused on replacement or/and enhancement of biological tissues via the use of cell-laden hydrogel scaffolds with an architecture that mimics the tissue matrix, and with the desired three-dimensional (3D) external geometry. However, mimicking the heterogeneous tissues that most organs and tissues are formed of is challenging. Although multiple-head 3D printing systems have been proposed for fabricating heterogeneous cell-laden hydrogel scaffolds, to date only the simple exterior form has been realized. Here we describe a computer-aided design and manufacturing (CAD/CAM) system for this application. We aim to develop an algorithm to enable easy, intuitive design and fabrication of a heterogeneous cell-laden hydrogel scaffolds with a free-form 3D geometry. The printing paths of the scaffold are automatically generated from the 3D CAD model, and the scaffold is then printed by dispensing four materials; i.e., a frame, two kinds of cell-laden hydrogel and a support. We demonstrated printing of heterogeneous tissue models formed of hydrogel scaffolds using this approach, including the outer ear, kidney and tooth tissue. These results indicate that this approach is particularly promising for tissue engineering and 3D printing applications to regenerate heterogeneous organs and tissues with tailored geometries to treat specific defects or injuries.

Computer-aided multiple-head 3D printing system for printing of heterogeneous organ/tissue constructs.

PubMed

Jung, Jin Woo; Lee, Jung-Seob; Cho, Dong-Woo

2016-02-22

Recently, much attention has focused on replacement or/and enhancement of biological tissues via the use of cell-laden hydrogel scaffolds with an architecture that mimics the tissue matrix, and with the desired three-dimensional (3D) external geometry. However, mimicking the heterogeneous tissues that most organs and tissues are formed of is challenging. Although multiple-head 3D printing systems have been proposed for fabricating heterogeneous cell-laden hydrogel scaffolds, to date only the simple exterior form has been realized. Here we describe a computer-aided design and manufacturing (CAD/CAM) system for this application. We aim to develop an algorithm to enable easy, intuitive design and fabrication of a heterogeneous cell-laden hydrogel scaffolds with a free-form 3D geometry. The printing paths of the scaffold are automatically generated from the 3D CAD model, and the scaffold is then printed by dispensing four materials; i.e., a frame, two kinds of cell-laden hydrogel and a support. We demonstrated printing of heterogeneous tissue models formed of hydrogel scaffolds using this approach, including the outer ear, kidney and tooth tissue. These results indicate that this approach is particularly promising for tissue engineering and 3D printing applications to regenerate heterogeneous organs and tissues with tailored geometries to treat specific defects or injuries.

Fast in-situ tool inspection based on inverse fringe projection and compact sensor heads

NASA Astrophysics Data System (ADS)

Matthias, Steffen; Kästner, Markus; Reithmeier, Eduard

2016-11-01

Inspection of machine elements is an important task in production processes in order to ensure the quality of produced parts and to gather feedback for the continuous improvement process. A new measuring system is presented, which is capable of performing the inspection of critical tool geometries, such as gearing elements, inside the forming machine. To meet the constraints on sensor head size and inspection time imposed by the limited space inside the machine and the cycle time of the process, the measuring device employs a combination of endoscopy techniques with the fringe projection principle. Compact gradient index lenses enable a compact design of the sensor head, which is connected to a CMOS camera and a flexible micro-mirror based projector via flexible fiber bundles. Using common fringe projection patterns, the system achieves measuring times of less than five seconds. To further reduce the time required for inspection, the generation of inverse fringe projection patterns has been implemented for the system. Inverse fringe projection speeds up the inspection process by employing object-adapted patterns, which enable the detection of geometry deviations in a single image. Two different approaches to generate object adapted patterns are presented. The first approach uses a reference measurement of a manufactured tool master to generate the inverse pattern. The second approach is based on a virtual master geometry in the form of a CAD file and a ray-tracing model of the measuring system. Virtual modeling of the measuring device and inspection setup allows for geometric tolerancing for free-form surfaces by the tool designer in the CAD-file. A new approach is presented, which uses virtual tolerance specifications and additional simulation steps to enable fast checking of metric tolerances. Following the description of the pattern generation process, the image processing steps required for inspection are demonstrated on captures of gearing geometries.

MODELING THE ANATOMICAL DISTRIBUTION OF SUNLIGHT

EPA Science Inventory

One of the major technical challenges in calculating solar irradiance on the human form has been the complexity of the surface geometry (i.e. the surface normal vis a vis the incident radiation. Over 80 percent of skin cancers occur on the face, head, and back of the hands. The...

Validating a new methodology for optical probe design and image registration in fNIRS studies

PubMed Central

Wijeakumar, Sobanawartiny; Spencer, John P.; Bohache, Kevin; Boas, David A.; Magnotta, Vincent A.

2015-01-01

Functional near-infrared spectroscopy (fNIRS) is an imaging technique that relies on the principle of shining near-infrared light through tissue to detect changes in hemodynamic activation. An important methodological issue encountered is the creation of optimized probe geometry for fNIRS recordings. Here, across three experiments, we describe and validate a processing pipeline designed to create an optimized, yet scalable probe geometry based on selected regions of interest (ROIs) from the functional magnetic resonance imaging (fMRI) literature. In experiment 1, we created a probe geometry optimized to record changes in activation from target ROIs important for visual working memory. Positions of the sources and detectors of the probe geometry on an adult head were digitized using a motion sensor and projected onto a generic adult atlas and a segmented head obtained from the subject's MRI scan. In experiment 2, the same probe geometry was scaled down to fit a child's head and later digitized and projected onto the generic adult atlas and a segmented volume obtained from the child's MRI scan. Using visualization tools and by quantifying the amount of intersection between target ROIs and channels, we show that out of 21 ROIs, 17 and 19 ROIs intersected with fNIRS channels from the adult and child probe geometries, respectively. Further, both the adult atlas and adult subject-specific MRI approaches yielded similar results and can be used interchangeably. However, results suggest that segmented heads obtained from MRI scans be used for registering children's data. Finally, in experiment 3, we further validated our processing pipeline by creating a different probe geometry designed to record from target ROIs involved in language and motor processing. PMID:25705757

Rotating and translating anthropomorphic head voxel models to establish an horizontal Frankfort plane for dental CBCT Monte Carlo simulations: a dose comparison study

NASA Astrophysics Data System (ADS)

Stratis, A.; Zhang, G.; Jacobs, R.; Bogaerts, R.; Bosmans, H.

2016-12-01

In order to carry out Monte Carlo (MC) dosimetry studies, voxel phantoms, modeling human anatomy, and organ-based segmentation of CT image data sets are applied to simulation frameworks. The resulting voxel phantoms preserve patient CT acquisition geometry; in the case of head voxel models built upon head CT images, the head support with which CT scanners are equipped introduces an inclination to the head, and hence to the head voxel model. In dental cone beam CT (CBCT) imaging, patients are always positioned in such a way that the Frankfort line is horizontal, implying that there is no head inclination. The orientation of the head is important, as it influences the distance of critical radiosensitive organs like the thyroid and the esophagus from the x-ray tube. This work aims to propose a procedure to adjust head voxel phantom orientation, and to investigate the impact of head inclination on organ doses in dental CBCT MC dosimetry studies. The female adult ICRP, and three in-house-built paediatric voxel phantoms were in this study. An EGSnrc MC framework was employed to simulate two commonly used protocols; a Morita Accuitomo 170 dental CBCT scanner (FOVs: 60  ×  60 mm2 and 80  ×  80 mm2, standard resolution), and a 3D Teeth protocol (FOV: 100  ×  90 mm2) in a Planmeca Promax 3D MAX scanner. Result analysis revealed large absorbed organ dose differences in radiosensitive organs between the original and the geometrically corrected voxel models of this study, ranging from  -45.6% to 39.3%. Therefore, accurate dental CBCT MC dose calculations require geometrical adjustments to be applied to head voxel models.

Effect of intake swirl on the performance of single cylinder direct injection diesel engine

NASA Astrophysics Data System (ADS)

Sharma, Vinod Kumar; Mohan, Man; Mouli, Chandra

2017-11-01

In the present work, the effect of inlet manifold geometry and swirl intensity on the direct injection (DI) diesel engine performance was investigated experimentally. Modifications in inlet manifold geometry have been suggested to achieve optimized swirl for the better mixing of fuel with air. The intake swirl intensities of modified cylinder head were measured in swirl test rig at different valve lifts. Later, the overall performance of 435 CC DI diesel engine was measured using modified cylinder head. In addition, the performance of engine was compared for both modified and old cylinder head. For same operating conditions, the brake power and brake specific fuel consumption was improved by 6% and 7% respectively with modified cylinder head compared to old cylinder head. The maximum brake power of 9 HP was achieved for modified cylinder head. The results revealed that the intake swirl has great influence on engine performance.

Computer-aided multiple-head 3D printing system for printing of heterogeneous organ/tissue constructs

PubMed Central

Jung, Jin Woo; Lee, Jung-Seob; Cho, Dong-Woo

2016-01-01

Recently, much attention has focused on replacement or/and enhancement of biological tissues via the use of cell-laden hydrogel scaffolds with an architecture that mimics the tissue matrix, and with the desired three-dimensional (3D) external geometry. However, mimicking the heterogeneous tissues that most organs and tissues are formed of is challenging. Although multiple-head 3D printing systems have been proposed for fabricating heterogeneous cell-laden hydrogel scaffolds, to date only the simple exterior form has been realized. Here we describe a computer-aided design and manufacturing (CAD/CAM) system for this application. We aim to develop an algorithm to enable easy, intuitive design and fabrication of a heterogeneous cell-laden hydrogel scaffolds with a free-form 3D geometry. The printing paths of the scaffold are automatically generated from the 3D CAD model, and the scaffold is then printed by dispensing four materials; i.e., a frame, two kinds of cell-laden hydrogel and a support. We demonstrated printing of heterogeneous tissue models formed of hydrogel scaffolds using this approach, including the outer ear, kidney and tooth tissue. These results indicate that this approach is particularly promising for tissue engineering and 3D printing applications to regenerate heterogeneous organs and tissues with tailored geometries to treat specific defects or injuries. PMID:26899876

Cross-borehole flowmeter tests for transient heads in heterogeneous aquifers.

PubMed

Le Borgne, Tanguy; Paillet, Frederick; Bour, Olivier; Caudal, Jean-Pierre

2006-01-01

Cross-borehole flowmeter tests have been proposed as an efficient method to investigate preferential flowpaths in heterogeneous aquifers, which is a major task in the characterization of fractured aquifers. Cross-borehole flowmeter tests are based on the idea that changing the pumping conditions in a given aquifer will modify the hydraulic head distribution in large-scale flowpaths, producing measurable changes in the vertical flow profiles in observation boreholes. However, inversion of flow measurements to derive flowpath geometry and connectivity and to characterize their hydraulic properties is still a subject of research. In this study, we propose a framework for cross-borehole flowmeter test interpretation that is based on a two-scale conceptual model: discrete fractures at the borehole scale and zones of interconnected fractures at the aquifer scale. We propose that the two problems may be solved independently. The first inverse problem consists of estimating the hydraulic head variations that drive the transient borehole flow observed in the cross-borehole flowmeter experiments. The second inverse problem is related to estimating the geometry and hydraulic properties of large-scale flowpaths in the region between pumping and observation wells that are compatible with the head variations deduced from the first problem. To solve the borehole-scale problem, we treat the transient flow data as a series of quasi-steady flow conditions and solve for the hydraulic head changes in individual fractures required to produce these data. The consistency of the method is verified using field experiments performed in a fractured-rock aquifer.

Practical and adequate approach to modeling light propagation in an adult head with low-scattering regions by use of diffusion theory.

PubMed

Koyama, Tatsuya; Iwasaki, Atsushi; Ogoshi, Yosuke; Okada, Eiji

2005-04-10

A practical and adequate approach to modeling light propagation in an adult head with a low-scattering cerebrospinal fluid (CSF) region by use of diffusion theory was investigated. The diffusion approximation does not hold in a nonscattering or low-scattering regions. The hybrid radiosity-diffusion method was adopted to model the light propagation in the head with a nonscattering region. In the hybrid method the geometry of the nonscattering region is acquired as a priori information. In reality, low-level scattering occurs in the CSF region and may reduce the error caused by the diffusion approximation. The partial optical path length and the spatial sensitivity profile calculated by the finite-element method agree well with those calculated by the Monte Carlo method in the case in which the transport scattering coefficient of the CSF layer is greater than 0.3 mm(-1). Because it is feasible to assume that the transport scattering coefficient of a CSF layer is 0.3 mm(-1), it is practical to adopt diffusion theory to the modeling of light propagation in an adult head as an alternative to the hybrid method.

Practical and adequate approach to modeling light propagation in an adult head with low-scattering regions by use of diffusion theory

NASA Astrophysics Data System (ADS)

Koyama, Tatsuya; Iwasaki, Atsushi; Ogoshi, Yosuke; Okada, Eiji

2005-04-01

A practical and adequate approach to modeling light propagation in an adult head with a low-scattering cerebrospinal fluid (CSF) region by use of diffusion theory was investigated. The diffusion approximation does not hold in a nonscattering or low-scattering regions. The hybrid radiosity-diffusion method was adopted to model the light propagation in the head with a nonscattering region. In the hybrid method the geometry of the nonscattering region is acquired as a priori information. In reality, low-level scattering occurs in the CSF region and may reduce the error caused by the diffusion approximation. The partial optical path length and the spatial sensitivity profile calculated by the finite-element method agree well with those calculated by the Monte Carlo method in the case in which the transport scattering coefficient of the CSF layer is greater than 0.3 mm^-1. Because it is feasible to assume that the transport scattering coefficient of a CSF layer is 0.3 mm^-1, it is practical to adopt diffusion theory to the modeling of light propagation in an adult head as an alternative to the hybrid method.

Numerical model (switchable/dual model) of the human head for rigid body and finite elements applications.

PubMed

Tabacu, Stefan

2015-01-01

In this paper, a methodology for the development and validation of a numerical model of the human head using generic procedures is presented. All steps required, starting with the model generation, model validation and applications will be discussed. The proposed model may be considered as a dual one due to its capabilities to switch from deformable to a rigid body according to the application's requirements. The first step is to generate the numerical model of the human head using geometry files or medical images. The required stiffness and damping for the elastic connection used for the rigid body model are identified by performing a natural frequency analysis. The presented applications for model validation are related to impact analysis. The first case is related to Nahum's (Nahum and Smith 1970) experiments pressure data being evaluated and a pressure map generated using the results from discrete elements. For the second case, the relative displacement between the brain and the skull is evaluated according to Hardy's (Hardy WH, Foster CD, Mason, MJ, Yang KH, King A, Tashman S. 2001.Investigation of head injury mechanisms using neutral density technology and high-speed biplanar X-ray. Stapp Car Crash J. 45:337-368, SAE Paper 2001-22-0016) experiments. The main objective is to validate the rigid model as a quick and versatile tool for acquiring the input data for specific brain analyses.

Statistical thermodynamics of amphiphile chains in micelles

PubMed Central

Ben-Shaul, A.; Szleifer, I.; Gelbart, W. M.

1984-01-01

The probability distribution of amphiphile chain conformations in micelles of different geometries is derived through maximization of their packing entropy. A lattice model, first suggested by Dill and Flory, is used to represent the possible chain conformations in the micellar core. The polar heads of the chains are assumed to be anchored to the micellar surface, with the other chain segments occupying all lattice sites in the interior of the micelle. This “volume-filling” requirement, the connectivity of the chains, and the geometry of the micelle define constraints on the possible probability distributions of chain conformations. The actual distribution is derived by maximizing the chain's entropy subject to these constraints; “reversals” of the chains back towards the micellar surface are explicitly included. Results are presented for amphiphiles organized in planar bilayers and in cylindrical and spherical micelles of different sizes. It is found that, for all three geometries, the bond order parameters decrease as a function of the bond distance from the polar head, in accordance with recent experimental data. The entropy differences associated with geometrical changes are shown to be significant, suggesting thereby the need to include curvature (environmental)-dependent “tail” contributions in statistical thermodynamic treatments of micellization. PMID:16593492

Study of the influence of the laterality of mobile phone use on the SAR induced in two head models

NASA Astrophysics Data System (ADS)

Ghanmi, Amal; Varsier, Nadège; Hadjem, Abdelhamid; Conil, Emmanuelle; Picon, Odile; Wiart, Joe

2013-05-01

The objective of this paper is to investigate and to analyse the influence of the laterality of mobile phone use on the exposure of the brain to radio-frequencies (RF) and electromagnetic fields (EMF) from different mobile phone models using the finite-difference time-domain (FDTD) method. The study focuses on the comparison of the specific absorption rate (SAR) induced on the right and left sides of two numerical adult and child head models. The heads are exposed by both phone models operating in GSM frequency bands for both ipsilateral and contralateral configurations. A slight SAR difference between the two sides of the heads is noted. The results show that the variation between the left and the right sides is more important at 1800 MHz for an ipsilateral use. Indeed, at this frequency, the variation can even reach 20% for the SAR10g and the SAR1g induced in the head and in the brain, respectively. Moreover, the average SAR induced by the mobile phone in the half hemisphere of the brain in ipsilateral exposure is higher than in contralateral exposure. Owing to the superficial character of energy deposition at 1800 MHz, this difference in the SAR induced for the ipsilateral and contralateral usages is more significant at 1800 MHz than at 900 MHz. The results have shown that depending on the phantom head models, the SAR distribution in the brain can vary because of differences in anatomical proportions and in the geometry of the head models. The induced SAR in child head and in sub-regions of the brain is significantly higher (up to 30%) compared to the adult head. This paper confirms also that the shape/design of the mobile and the location of the antenna can have a large influence at high frequency on the exposure of the brain, particularly on the SAR distribution and on the distinguished brain regions.

Understanding the unique flowering sequence in Dipsacus fullonum: Evidence from geometrical changes during head development

PubMed Central

Naghiloo, Somayeh; Claßen-Bockhoff, Regine

2017-01-01

The genus Dipsacus is characterized by a remarkable bidirectional flowering sequence and a rare phyllotactic pattern. Considering that flower initiation and flowering sequence may be interconnected, we document the development of the head meristem in Dipsacus fullonum. Our results indicate a gradual change in the geometry of the head meristem beginning with a dome shaped stage, continuing with a remarkable widening in the middle part of the head meristem and ending in a spindle-like form. Quantitative data confirm that meristem expansion is higher in the middle part than at the base of the meristem. Likewise, the size of the flower primordia in the middle part of the young head is significantly larger than at the base soon after initiation. We conclude that the change in the geometry of the meristem and the availability of newly generated space result in the promotion of the middle flowers and the bidirectional flowering sequence at anthesis. Our investigation on phyllotactic patterns reveals a high tendency (30%) of the head meristem to insert or lose parastichies. This finding can also be attributed to changes in the expansion rate of the meristem. Dependent on the spatio-temporal relation between meristem expansion and primordia initiation, either flower primordia are promoted or additional parastichies appear. Our results emphasize the important role of geometry in flower development and phyllotactic pattern formation. PMID:28328952

Experimental verification of a Monte Carlo-based MLC simulation model for IMRT dose calculations in heterogeneous media

NASA Astrophysics Data System (ADS)

Tyagi, N.; Curran, B. H.; Roberson, P. L.; Moran, J. M.; Acosta, E.; Fraass, B. A.

2008-02-01

IMRT often requires delivering small fields which may suffer from electronic disequilibrium effects. The presence of heterogeneities, particularly low-density tissues in patients, complicates such situations. In this study, we report on verification of the DPM MC code for IMRT treatment planning in heterogeneous media, using a previously developed model of the Varian 120-leaf MLC. The purpose of this study is twofold: (a) design a comprehensive list of experiments in heterogeneous media for verification of any dose calculation algorithm and (b) verify our MLC model in these heterogeneous type geometries that mimic an actual patient geometry for IMRT treatment. The measurements have been done using an IMRT head and neck phantom (CIRS phantom) and slab phantom geometries. Verification of the MLC model has been carried out using point doses measured with an A14 slim line (SL) ion chamber inside a tissue-equivalent and a bone-equivalent material using the CIRS phantom. Planar doses using lung and bone equivalent slabs have been measured and compared using EDR films (Kodak, Rochester, NY).

Particle sedimentation in curved tubes: A 3D simulation and optimization for treatment of vestibular vertigo

NASA Astrophysics Data System (ADS)

White, Brian; Squires, Todd M.; Hain, Timothy C.; Stone, Howard A.

2003-11-01

Benign paroxysmal positional vertigo (BPPV) is a mechanical disorder of the vestibular system where micron-size crystals abnormally drift into the semicircular canals of the inner ear that sense angular motion of the head. Sedimentation of these crystals causes sensation of motion after true head motion has stopped: vertigo results. The usual clinical treatment is through a series of head maneuvers designed to move the particles into a less sensitive region of the canal system. We present a three-dimensional model to simulate treatment of BPPV by determining the complete hydrodynamic motion of the particles through the course of a therapeutic maneuver while using a realistic representation of the actual geometry. Analyses of clinical maneuvers show the parameter range for which they are effective, and indicate inefficiencies in current practice. In addition, an optimization process determines the most effective head maneuver, which significantly differs from those currently in practice.

Systematic evaluation of a time-domain Monte Carlo fitting routine to estimate the adult brain optical properties

NASA Astrophysics Data System (ADS)

Selb, Juliette; Ogden, Tyler M.; Dubb, Jay; Fang, Qianqian; Boas, David A.

2013-03-01

Time-domain near-infrared spectroscopy (TD-NIRS) offers the ability to measure the absolute baseline optical properties of a tissue. Specifically, for brain imaging, the robust assessment of cerebral blood volume and oxygenation based on measurement of cerebral hemoglobin concentrations is essential for reliable cross-sectional and longitudinal studies. In adult heads, these baseline measurements are complicated by the presence of thick extra-cerebral tissue (scalp, skull, CSF). A simple semi-infinite homogeneous model of the head has proven to have limited use because of the large errors it introduces in the recovered brain absorption. Analytical solutions for layered media have shown improved performance on Monte-Carlo simulated data and layered phantom experiments, but their validity on real adult head data has never been demonstrated. With the advance of fast Monte Carlo approaches based on GPU computation, numerical methods to solve the radiative transfer equation become viable alternatives to analytical solutions of the diffusion equation. Monte Carlo approaches provide the additional advantage to be adaptable to any geometry, in particular more realistic head models. The goals of the present study were twofold: (1) to implement a fast and flexible Monte Carlo-based fitting routine to retrieve the brain optical properties; (2) to characterize the performances of this fitting method on realistic adult head data. We generated time-resolved data at various locations over the head, and fitted them with different models of light propagation: the homogeneous analytical model, and Monte Carlo simulations for three head models: a two-layer slab, the true subject's anatomy, and that of a generic atlas head. We found that the homogeneous model introduced a median 20 to 25% error on the recovered brain absorption, with large variations over the range of true optical properties. The two-layer slab model only improved moderately the results over the homogeneous one. On the other hand, using a generic atlas head registered to the subject's head surface decreased the error by a factor of 2. When the information is available, using the true subject anatomy offers the best performance.

Numerical study of the motion of a flagellated swimmer inside a tube in the Stokes regime

NASA Astrophysics Data System (ADS)

Zhang, Ji; Jiao, Yusheng; Xu, Xinliang; Ding, Yang

2017-11-01

Confined environments are common to micro-swimmers such bacteria and previous studies have shown that confinements such as a wall can influenced the trajectory of the micro-swimmers. Here we study whether some micro-swimmers can achieve a higher speed and energetic efficiency within a long tube comparing to the free-space case using a numerical model. The swimmer consists of an elliptical head and two helical flagella. To solve the governing Stokes equations inside an infinite tube, we combine the method of fundamental solution (MSF) and the method of Stokeslet. The geometry parameters, including shape and size of head and flagella, and relative spatial position of these components, are varied. Our results show that the geometry of the swimmer and the tube can greatly affect the speed of the micro-swimmer. For certain geometric parameters of the micro-swimmer, a greater confinement leads to a higher speed, which is consistent with the results from our robotic experiments.

Fluorescence Diffusion in the Presence of Optically Clear Tissues in a Mouse Head Model.

PubMed

Ancora, Daniele; Zacharopoulos, Athanasios; Ripoll, Jorge; Zacharakis, Giannis

2017-05-01

Diffuse Optical Tomography commonly neglects or assumes as insignificant the presence of optically clear regions in biological tissues, estimating their contribution as a small perturbation to light transport. The inaccuracy introduced by this practice is examined in detail in the context of a complete, based on realistic geometry, virtual fluorescence Diffuse Optical Tomography experiment where a mouse head is imaged in the presence of cerebral spinal fluid. Despite the small thickness of such layer, we point out that an error is introduced when neglecting it from the model with possibly reduction in the accuracy of the reconstruction and localization of the fluorescence distribution within the brain. The results obtained in the extensive study presented here suggest that fluorescence diffuse neuroimaging studies can be improved in terms of quantitative and qualitative reconstruction by accurately taking into account optically transparent regions especially in the cases where the reconstruction is aided by the prior knowledge of the structural geometry of the specimen. Thus, this has only recently become an affordable choice, thanks to novel computation paradigms that allow to run Monte Carlo photon propagation on a simple graphic card, hence speeding up the process a thousand folds compared to CPU-based solutions.

Automated Planar Tracking the Waving Bodies of Multiple Zebrafish Swimming in Shallow Water.

PubMed

Wang, Shuo Hong; Cheng, Xi En; Qian, Zhi-Ming; Liu, Ye; Chen, Yan Qiu

2016-01-01

Zebrafish (Danio rerio) is one of the most widely used model organisms in collective behavior research. Multi-object tracking with high speed camera is currently the most feasible way to accurately measure their motion states for quantitative study of their collective behavior. However, due to difficulties such as their similar appearance, complex body deformation and frequent occlusions, it is a big challenge for an automated system to be able to reliably track the body geometry of each individual fish. To accomplish this task, we propose a novel fish body model that uses a chain of rectangles to represent fish body. Then in detection stage, the point of maximum curvature along fish boundary is detected and set as fish nose point. Afterwards, in tracking stage, we firstly apply Kalman filter to track fish head, then use rectangle chain fitting to fit fish body, which at the same time further judge the head tracking results and remove the incorrect ones. At last, a tracklets relinking stage further solves trajectory fragmentation due to occlusion. Experiment results show that the proposed tracking system can track a group of zebrafish with their body geometry accurately even when occlusion occurs from time to time.

Automated Planar Tracking the Waving Bodies of Multiple Zebrafish Swimming in Shallow Water

PubMed Central

Wang, Shuo Hong; Cheng, Xi En; Qian, Zhi-Ming; Liu, Ye; Chen, Yan Qiu

2016-01-01

Zebrafish (Danio rerio) is one of the most widely used model organisms in collective behavior research. Multi-object tracking with high speed camera is currently the most feasible way to accurately measure their motion states for quantitative study of their collective behavior. However, due to difficulties such as their similar appearance, complex body deformation and frequent occlusions, it is a big challenge for an automated system to be able to reliably track the body geometry of each individual fish. To accomplish this task, we propose a novel fish body model that uses a chain of rectangles to represent fish body. Then in detection stage, the point of maximum curvature along fish boundary is detected and set as fish nose point. Afterwards, in tracking stage, we firstly apply Kalman filter to track fish head, then use rectangle chain fitting to fit fish body, which at the same time further judge the head tracking results and remove the incorrect ones. At last, a tracklets relinking stage further solves trajectory fragmentation due to occlusion. Experiment results show that the proposed tracking system can track a group of zebrafish with their body geometry accurately even when occlusion occurs from time to time. PMID:27128096

Estimation of computed tomography dose index in cone beam computed tomography: MOSFET measurements and Monte Carlo simulations.

PubMed

Kim, Sangroh; Yoshizumi, Terry; Toncheva, Greta; Yoo, Sua; Yin, Fang-Fang; Frush, Donald

2010-05-01

To address the lack of accurate dose estimation method in cone beam computed tomography (CBCT), we performed point dose metal oxide semiconductor field-effect transistor (MOSFET) measurements and Monte Carlo (MC) simulations. A Varian On-Board Imager (OBI) was employed to measure point doses in the polymethyl methacrylate (PMMA) CT phantoms with MOSFETs for standard and low dose modes. A MC model of the OBI x-ray tube was developed using BEAMnrc/EGSnrc MC system and validated by the half value layer, x-ray spectrum and lateral and depth dose profiles. We compared the weighted computed tomography dose index (CTDIw) between MOSFET measurements and MC simulations. The CTDIw was found to be 8.39 cGy for the head scan and 4.58 cGy for the body scan from the MOSFET measurements in standard dose mode, and 1.89 cGy for the head and 1.11 cGy for the body in low dose mode, respectively. The CTDIw from MC compared well to the MOSFET measurements within 5% differences. In conclusion, a MC model for Varian CBCT has been established and this approach may be easily extended from the CBCT geometry to multi-detector CT geometry.

Influence of particle geometry and PEGylation on phagocytosis of particulate carriers.

PubMed

Mathaes, Roman; Winter, Gerhard; Besheer, Ahmed; Engert, Julia

2014-04-25

Particle geometry of micro- and nanoparticles has been identified as an important design parameter to influence the interaction with cells such as macrophages. A head to head comparison of elongated, non-spherical and spherical micro- and nanoparticles with and without PEGylation was carried out to benchmark two phagocytosis inhibiting techniques. J774.A1 macrophages were incubated with fluorescently labeled PLGA micro- and nanoparticles and analyzed by confocal laser scanning microscope (CLSM) and flow cytometry (FACS). Particle uptake into macrophages was significantly reduced upon PEGylation or elongated particle geometry. A combination of both, an elongated shape and PEGylation, had the strongest phagocytosis inhibiting effect for nanoparticles. Copyright © 2014 Elsevier B.V. All rights reserved.

SU-G-TeP1-08: LINAC Head Geometry Modeling for Cyber Knife System

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liang, B; Li, Y; Liu, B

Purpose: Knowledge of the LINAC head information is critical for model based dose calculation algorithms. However, the geometries are difficult to measure precisely. The purpose of this study is to develop linac head models for Cyber Knife system (CKS). Methods: For CKS, the commissioning data were measured in water at 800mm SAD. The measured full width at half maximum (FWHM) for each cone was found greater than the nominal value, this was further confirmed by additional film measurement in air. Diameter correction, cone shift and source shift models (DCM, CSM and SSM) are proposed to account for the differences. Inmore » DCM, a cone-specific correction is applied. For CSM and SSM, a single shift is applied to the cone or source physical position. All three models were validated with an in-house developed pencil beam dose calculation algorithm, and further evaluated by the collimator scatter factor (Sc) correction. Results: The mean square error (MSE) between nominal diameter and the FWHM derived from commissioning data and in-air measurement are 0.54mm and 0.44mm, with the discrepancy increasing with cone size. Optimal shift for CSM and SSM is found to be 9mm upward and 18mm downward, respectively. The MSE in FWHM is reduced to 0.04mm and 0.14mm for DCM and CSM (SSM). Both DCM and CSM result in the same set of Sc values. Combining all cones at SAD 600–1000mm, the average deviation from 1 in Sc of DCM (CSM) and SSM is 2.6% and 2.2%, and reduced to 0.9% and 0.7% for the cones with diameter greater than 15mm. Conclusion: We developed three geometrical models for CKS. All models can handle the discrepancy between vendor specifications and commissioning data. And SSM has the best performance for Sc correction. The study also validated that a point source can be used in CKS dose calculation algorithms.« less

How does a three-dimensional continuum muscle model affect the kinematics and muscle strains of a finite element neck model compared to a discrete muscle model in rear-end, frontal, and lateral impacts.

PubMed

Hedenstierna, Sofia; Halldin, Peter

2008-04-15

A finite element (FE) model of the human neck with incorporated continuum or discrete muscles was used to simulate experimental impacts in rear, frontal, and lateral directions. The aim of this study was to determine how a continuum muscle model influences the impact behavior of a FE human neck model compared with a discrete muscle model. Most FE neck models used for impact analysis today include a spring element musculature and are limited to discrete geometries and nodal output results. A solid-element muscle model was thought to improve the behavior of the model by adding properties such as tissue inertia and compressive stiffness and by improving the geometry. It would also predict the strain distribution within the continuum elements. A passive continuum muscle model with nonlinear viscoelastic materials was incorporated into the KTH neck model together with active spring muscles and used in impact simulations. The resulting head and vertebral kinematics was compared with the results from a discrete muscle model as well as volunteer corridors. The muscle strain prediction was compared between the 2 muscle models. The head and vertebral kinematics were within the volunteer corridors for both models when activated. The continuum model behaved more stiffly than the discrete model and needed less active force to fit the experimental results. The largest difference was seen in the rear impact. The strain predicted by the continuum model was lower than for the discrete model. The continuum muscle model stiffened the response of the KTH neck model compared with a discrete model, and the strain prediction in the muscles was improved.

A Navigation Safety Support Model for the Strait of Istanbul

NASA Astrophysics Data System (ADS)

Yazici, M. Anil; Otay, Emre N.

In this study, a real time maritime traffic support model is developed for safe navigation in the Strait of Istanbul, also known as the Bosporus. The present model simulates vessel trajectories corresponding to possible headings, using channel geometry, counter traffic, and surface currents as input. A new MATLAB code is developed for the simulation and the Marine GNC Toolbox (Fossen and Perez, 2004) is used for the vessel hydrodynamics and the auto-pilot model. After computing the trajectory tree of the vessel by forward-mapping its position distribution with respect to the initial position vector, the casualty probabilities of each trajectory are found. Within certain restrictions on vessel geometry, the proposed model predicts the safest possible intended course for the transit vessels based on the navigational parameters including position, speed, and course of the vessel. The model is tested for the Strait of Istanbul for validation. Without loss of generality, the model can be used for any narrow channel with a vessel traffic system providing the necessary input.

Impact of meander geometry and stream flow events on residence times and solute transport in the intra-meander flow

NASA Astrophysics Data System (ADS)

Nasir Mahmood, Muhammad; Schmidt, Christian; Trauth, Nico

2017-04-01

Stream morphological features, in combination with hydrological variability play a key role in water and solute exchange across surface and subsurface waters. Meanders are prominent morphological features within stream systems which exhibit unique hydrodynamics. The water surface elevation difference across the inner bank of a meander induces lateral hyporheic exchange within the intra-meander region. This hyporheic flow is characterized by considerably prolonged flow paths and residence times (RT) compared to smaller scales of hyporheic exchange. In this study we examine the impact of different meander geometries on the intra-meander hyporheic flow field and solute mobilization under both steady state and transient flow conditions. We developed a number of artificial meander shape scenarios, representing various meander evolution stages, ranging from a typical initial to advanced stage (near cut off ) meander. Three dimensional steady state numerical groundwater flow simulations including the unsaturated zone were performed for the intra-meander region. The meandering stream was implemented in the model by adjusting the top layers of the modelling domain to the streambed elevation and assigning linearly decreasing head boundary conditions to the streambed cells. Residence times for the intra-meander region were computed by advective particle tracking across the inner bank of meander. Selected steady state cases were extended to transient flow simulations to evaluate the impact of stream discharge events on the temporal behavior of the water exchange and solute transport in the intra-meander region. The transient stream discharge was simulated for a number of discharge events of variable duration and peak height using the surface water model HEC-RAS. Transient hydraulic heads obtained from the surface water model were applied as transient head boundary conditions to the streambed cells of the groundwater model. A solute concentration source was added in the unsaturated zone to evaluate the effect of transient flow conditions on solute mobilization. Our preliminary results indicate that residence times ranging from 0.5 to 250 hours are influenced by meander geometry, as well as the size of the intra-meander area. In general, we found that larger intra-meander areas lead to longer flow paths and higher mean intra-meander residence times (MRTs). The shortest RTs were observed near the meander neck in all scenarios, a feature most predominant in more developed meander resulting shorter MRTs. Transient modelling results show that fluctuations in stream hydraulic head influence the transport and zonation of the solute concentration in the intra-meander area with higher and longer stream discharge events leading to stronger mobilization and removal of solutes dominated mainly around meander neck area.

Design of a Kaplan turbine for a wide range of operating head -Curved draft tube design and model test verification-

NASA Astrophysics Data System (ADS)

KO, Pohan; MATSUMOTO, Kiyoshi; OHTAKE, Norio; DING, Hua

2016-11-01

As for turbomachine off-design performance improvement is challenging but critical for maximising the performing area. In this paper, a curved draft tube for a medium head Kaplan type hydro turbine is introduced and discussed for its significant effect on expanding operating head range. Without adding any extra structure and working fluid for swirl destruction and damping, a carefully designed outline shape of draft tube with the selected placement of center-piers successfully supresses the growth of turbulence eddy and the transport of the swirl to the outlet. Also, more kinetic energy is recovered and the head lost is improved. Finally, the model test results are also presented. The obvious performance improvement was found in the lower net head area, where the maximum efficiency improvement was measured up to 20% without compromising the best efficiency point. Additionally, this design results in a new draft tube more compact in size and so leads to better construction and manufacturing cost performance for prototype. The draft tube geometry parameter designing process was concerning the best efficiency point together with the off-design points covering various water net heads and discharges. The hydraulic performance and flow behavior was numerically previewed and visualized by solving Reynolds-Averaged Navier-Stokes equations with Shear Stress Transport turbulence model. The simulation was under the assumption of steady-state incompressible turbulence flow inside the flow passage, and the inlet boundary condition was the carefully simulated flow pattern from the runner outlet. For confirmation, the corresponding turbine efficiency performance of the entire operating area was verified by model test.

Application of differential game theory to role-determination in aerial combat

NASA Technical Reports Server (NTRS)

Merz, A. W.

1975-01-01

The development of criteria which specify the roles of pursuer and evader as functions of the relative geometry and of the important parameters of the problem are discussed. A reduced-order model of the relative motion is derived and discussed. In this model, the two aircraft move in the same plane at unequal but constant speeds, and with different maximum turn rates. The equations of relative motion are of third order, the dependent variables being the relative range, bearing, and heading of the two aircraft. Termination of the pursuit-evasion game is defined by either the heading-limited or the range-limited end condition. These are geometric conditions for which the evading aircraft is in front of the other, with the relative heading and relative range satisfying certain inequalities. Retrograde solutions to the equations of relative motion were used with the derived optimal terminal maneuvers to find where an assumed set of end conditions could have begun.

Sediment dispersal in modern and mid-Holocene basins: implications for shoreline progradation and sediment bypassing, Poverty Bay, New Zealand

NASA Astrophysics Data System (ADS)

Bever, A. J.; Harris, C. K.; McNinch, J.

2006-12-01

Poverty Bay is a small embayment located on the eastern shore of New Zealand's North Island. The modern Waipaoa River, a small mountainous river that drains highly erodible mudstone and siltstone, discharges ~15 million tons of sediment per year to Poverty Bay. Rates of bay infilling from fluvial sediment have varied since the maximum shoreline transgression, ~7000 kya. The evolving geometry of Poverty Bay has likely impacted sediment dispersal over these timescales, and thereby influenced the stratigraphic architecture, rates of shoreline progradation, and sediment supply to the continental shelf. This modeling study investigates sediment transport within both modern and paleo, ~7000 kya, Poverty Bays. The Regional Ocean Modeling System was used to examine sediment transport within modern and ~7000 kya Poverty Bay basin geometries. The numerical model includes hydrodynamics driven by winds and buoyancy, and sediment resuspension from energetic waves and currents. Strong winds and waves from the southeast were used, along with high Waipaoa freshwater and sediment discharge, consistent with storm conditions. Besides shedding light on short term transport mechanisms, these results are being incorporated into a stratigraphic model by Wolinsky and Swenson. The paleo basin geometry narrowed at the head of the bay, causing currents to converge and promoting near- field sediment deposition. Buoyancy and wind driven across-shelf currents in the modern bay transport sediment away from the river mouth. Sediment was deposited closer to the river mouth in the paleo than the modern bay, and the modern bay exported much more sediment to the continental shelf than predicted for the middle Holocene bay. Net across-shelf fluxes decreased from a maximum at the head of the bay to nearly zero at the mouth during the paleo run. The modern run, however, had net across-shelf fluxes still half the maximum at the bay mouth. Results from short term model runs indicated that, with similar river discharges, the 7000 kya Poverty Bay shoreline should have prograded rapidly as sediment was deposited near the river mouth at the head of the bay, an area of little accommodation space. The trapping of sediment within the bay would have lead to a relatively sediment starved continental shelf. As the river mouth progressed towards the wider section of the bay, progradation should have been reduced as both proximal accommodation space and sediment export to the continental shelf increased.

Ignition transient analysis of solid rocket motor

NASA Technical Reports Server (NTRS)

Han, Samuel S.

1990-01-01

To predict pressure-time and thrust-time behavior of solid rocket motors, a one-dimensional numerical model is developed. The ignition phase of solid rocket motors (time less than 0.4 sec) depends critically on complex interactions among many elements, such as rocket geometry, heat and mass transfer, flow development, and chemical reactions. The present model solves the mass, momentum, and energy equations governing the transfer processes in the rocket chamber as well as the attached converging-diverging nozzle. A qualitative agreement with the SRM test data in terms of head-end pressure gradient and the total thrust build-up is obtained. Numerical results show that the burning rate in the star-segmented head-end section and the erosive burning are two important parameters in the ignition transient of the solid rocket motor (SRM).

New Computer Simulation Procedure of Heading Face Mining Process with Transverse Cutting Heads for Roadheader Automation

NASA Astrophysics Data System (ADS)

Dolipski, Marian; Cheluszka, Piotr; Sobota, Piotr; Remiorz, Eryk

2017-03-01

The key working process carried out by roadheaders is rock mining. For this reason, the mathematical modelling of the mining process is underlying the prediction of a dynamic load on the main components of a roadheader, the prediction of power demand for rock cutting with given properties or the prediction of energy consumption of this process. The theoretical and experimental investigations conducted point out - especially in relation to the technical parameters of roadheaders used these days in underground mining and their operating conditions - that the mathematical models of the process employed to date have many limitations, and in many cases the results obtained using such models deviate largely from the reality. This is due to the fact that certain factors strongly influencing cutting process progress have not been considered at the modelling stage, or have been approached in an oversimplified fashion. The article presents a new model of a rock cutting process using conical picks of cutting heads of boom-type roadheaders. An important novelty with respect to the models applied to date is, firstly, that the actual shape of cuts has been modelled with such shape resulting from the geometry of the currently used conical picks, and, secondly, variations in the depth of cuts in the cutting path of individual picks have been considered with such variations resulting from the picks' kinematics during the advancement of transverse cutting heads parallel to the floor surface. The work presents examples of simulation results for mining with a roadheader's transverse head equipped with 80 conical picks and compares them with the outcomes obtained using the existing model.

Measurement and Finite Element Model Validation of Immature Porcine Brain-Skull Displacement during Rapid Sagittal Head Rotations.

PubMed

Pasquesi, Stephanie A; Margulies, Susan S

2018-01-01

Computational models are valuable tools for studying tissue-level mechanisms of traumatic brain injury, but to produce more accurate estimates of tissue deformation, these models must be validated against experimental data. In this study, we present in situ measurements of brain-skull displacement in the neonatal piglet head ( n  = 3) at the sagittal midline during six rapid non-impact rotations (two rotations per specimen) with peak angular velocities averaging 51.7 ± 1.4 rad/s. Marks on the sagittally cut brain and skull/rigid potting surfaces were tracked, and peak values of relative brain-skull displacement were extracted and found to be significantly less than values extracted from a previous axial plane model. In a finite element model of the sagittally transected neonatal porcine head, the brain-skull boundary condition was matched to the measured physical experiment data. Despite smaller sagittal plane displacements at the brain-skull boundary, the corresponding finite element boundary condition optimized for sagittal plane rotations is far less stiff than its axial counterpart, likely due to the prominent role of the boundary geometry in restricting interface movement. Finally, bridging veins were included in the finite element model. Varying the bridging vein mechanical behavior over a previously reported range had no influence on the brain-skull boundary displacements. This direction-specific sagittal plane boundary condition can be employed in finite element models of rapid sagittal head rotations.

Measurement and Finite Element Model Validation of Immature Porcine Brain–Skull Displacement during Rapid Sagittal Head Rotations

PubMed Central

Pasquesi, Stephanie A.; Margulies, Susan S.

2018-01-01

Computational models are valuable tools for studying tissue-level mechanisms of traumatic brain injury, but to produce more accurate estimates of tissue deformation, these models must be validated against experimental data. In this study, we present in situ measurements of brain–skull displacement in the neonatal piglet head (n = 3) at the sagittal midline during six rapid non-impact rotations (two rotations per specimen) with peak angular velocities averaging 51.7 ± 1.4 rad/s. Marks on the sagittally cut brain and skull/rigid potting surfaces were tracked, and peak values of relative brain–skull displacement were extracted and found to be significantly less than values extracted from a previous axial plane model. In a finite element model of the sagittally transected neonatal porcine head, the brain–skull boundary condition was matched to the measured physical experiment data. Despite smaller sagittal plane displacements at the brain–skull boundary, the corresponding finite element boundary condition optimized for sagittal plane rotations is far less stiff than its axial counterpart, likely due to the prominent role of the boundary geometry in restricting interface movement. Finally, bridging veins were included in the finite element model. Varying the bridging vein mechanical behavior over a previously reported range had no influence on the brain–skull boundary displacements. This direction-specific sagittal plane boundary condition can be employed in finite element models of rapid sagittal head rotations. PMID:29515995

Advanced stitching head for making stitches in a textile article having variable thickness

NASA Technical Reports Server (NTRS)

Thrash, Patrick J. (Inventor); Miller, Jeffrey L. (Inventor); Codos, Richard (Inventor)

1999-01-01

A stitching head for a computer numerically controlled stitching machine includes a thread tensioning mechanism for automatically adjusting thread tension according to the thickness of the material being stitched. The stitching head also includes a mechanism for automatically adjusting thread path geometry according to the thickness of the material being stitched.

The role of blood vessels in high-resolution volume conductor head modeling of EEG.

PubMed

Fiederer, L D J; Vorwerk, J; Lucka, F; Dannhauer, M; Yang, S; Dümpelmann, M; Schulze-Bonhage, A; Aertsen, A; Speck, O; Wolters, C H; Ball, T

2016-03-01

Reconstruction of the electrical sources of human EEG activity at high spatio-temporal accuracy is an important aim in neuroscience and neurological diagnostics. Over the last decades, numerous studies have demonstrated that realistic modeling of head anatomy improves the accuracy of source reconstruction of EEG signals. For example, including a cerebro-spinal fluid compartment and the anisotropy of white matter electrical conductivity were both shown to significantly reduce modeling errors. Here, we for the first time quantify the role of detailed reconstructions of the cerebral blood vessels in volume conductor head modeling for EEG. To study the role of the highly arborized cerebral blood vessels, we created a submillimeter head model based on ultra-high-field-strength (7T) structural MRI datasets. Blood vessels (arteries and emissary/intraosseous veins) were segmented using Frangi multi-scale vesselness filtering. The final head model consisted of a geometry-adapted cubic mesh with over 17×10(6) nodes. We solved the forward model using a finite-element-method (FEM) transfer matrix approach, which allowed reducing computation times substantially and quantified the importance of the blood vessel compartment by computing forward and inverse errors resulting from ignoring the blood vessels. Our results show that ignoring emissary veins piercing the skull leads to focal localization errors of approx. 5 to 15mm. Large errors (>2cm) were observed due to the carotid arteries and the dense arterial vasculature in areas such as in the insula or in the medial temporal lobe. Thus, in such predisposed areas, errors caused by neglecting blood vessels can reach similar magnitudes as those previously reported for neglecting white matter anisotropy, the CSF or the dura - structures which are generally considered important components of realistic EEG head models. Our findings thus imply that including a realistic blood vessel compartment in EEG head models will be helpful to improve the accuracy of EEG source analyses particularly when high accuracies in brain areas with dense vasculature are required. Copyright © 2016 The Authors. Published by Elsevier Inc. All rights reserved.

Development of a head-phantom and measurement setup for lightning effects.

PubMed

Machts, Rene; Hunold, Alexander; Leu, Carsten; Haueisen, Jens; Rock, Michael

2016-08-01

Direct lightning strikes to human heads lead to various effects ranging from Lichtenberg figures, over loss of consciousness to death. The evolution of the induced current distribution in the head is of great interest to understand the effect mechanisms. This work describes a technique to model a simplified head-phantom to investigate effects during direct lightning strike. The head-phantom geometry, conductive and dielectric parameters were chosen similar to that of a human head. Three layers (brain, skull, and scalp) were created for the phantom using agarose hydrogel doped with sodium chloride and carbon. The head-phantom was tested on two different impulse generators, which reproduce approximate lightning impulses. The effective current and the current distribution in each layer were analyzed. The biggest part of the current flowed through the brain layer, approx. 70 % in cases without external flashover. Approx. 23 % of the current flowed through skull layer and 6 % through the scalp layer. However, the current decreased within the head-phantom to almost zero after a complete flashover on the phantom occurred. The flashover formed faster with a higher impulse current level. Exposition time of current through the head decreases with a higher current level of the lightning impulse. This mechanism might explain the fact that people can survive a lightning strike. The experiments help to understand lightning effects on humans.

Raman Monte Carlo simulation for light propagation for tissue with embedded objects

NASA Astrophysics Data System (ADS)

Periyasamy, Vijitha; Jaafar, Humaira Bte; Pramanik, Manojit

2018-02-01

Monte Carlo (MC) stimulation is one of the prominent simulation technique and is rapidly becoming the model of choice to study light-tissue interaction. Monte Carlo simulation for light transport in multi-layered tissue (MCML) is adapted and modelled with different geometry by integrating embedded objects of various shapes (i.e., sphere, cylinder, cuboid and ellipsoid) into the multi-layered structure. These geometries would be useful in providing a realistic tissue structure such as modelling for lymph nodes, tumors, blood vessels, head and other simulation medium. MC simulations were performed on various geometric medium. Simulation of MCML with embedded object (MCML-EO) was improvised for propagation of the photon in the defined medium with Raman scattering. The location of Raman photon generation is recorded. Simulations were experimented on a modelled breast tissue with tumor (spherical and ellipsoidal) and blood vessels (cylindrical). Results were presented in both A-line and B-line scans for embedded objects to determine spatial location where Raman photons were generated. Studies were done for different Raman probabilities.

Dipole estimation errors due to not incorporating anisotropic conductivities in realistic head models for EEG source analysis

NASA Astrophysics Data System (ADS)

Hallez, Hans; Staelens, Steven; Lemahieu, Ignace

2009-10-01

EEG source analysis is a valuable tool for brain functionality research and for diagnosing neurological disorders, such as epilepsy. It requires a geometrical representation of the human head or a head model, which is often modeled as an isotropic conductor. However, it is known that some brain tissues, such as the skull or white matter, have an anisotropic conductivity. Many studies reported that the anisotropic conductivities have an influence on the calculated electrode potentials. However, few studies have assessed the influence of anisotropic conductivities on the dipole estimations. In this study, we want to determine the dipole estimation errors due to not taking into account the anisotropic conductivities of the skull and/or brain tissues. Therefore, head models are constructed with the same geometry, but with an anisotropically conducting skull and/or brain tissue compartment. These head models are used in simulation studies where the dipole location and orientation error is calculated due to neglecting anisotropic conductivities of the skull and brain tissue. Results show that not taking into account the anisotropic conductivities of the skull yields a dipole location error between 2 and 25 mm, with an average of 10 mm. When the anisotropic conductivities of the brain tissues are neglected, the dipole location error ranges between 0 and 5 mm. In this case, the average dipole location error was 2.3 mm. In all simulations, the dipole orientation error was smaller than 10°. We can conclude that the anisotropic conductivities of the skull have to be incorporated to improve the accuracy of EEG source analysis. The results of the simulation, as presented here, also suggest that incorporation of the anisotropic conductivities of brain tissues is not necessary. However, more studies are needed to confirm these suggestions.

Levels of detail analysis of microwave scattering from human head models for brain stroke detection

PubMed Central

2017-01-01

In this paper, we have presented a microwave scattering analysis from multiple human head models. This study incorporates different levels of detail in the human head models and its effect on microwave scattering phenomenon. Two levels of detail are taken into account; (i) Simplified ellipse shaped head model (ii) Anatomically realistic head model, implemented using 2-D geometry. In addition, heterogenic and frequency-dispersive behavior of the brain tissues has also been incorporated in our head models. It is identified during this study that the microwave scattering phenomenon changes significantly once the complexity of head model is increased by incorporating more details using magnetic resonance imaging database. It is also found out that the microwave scattering results match in both types of head model (i.e., geometrically simple and anatomically realistic), once the measurements are made in the structurally simplified regions. However, the results diverge considerably in the complex areas of brain due to the arbitrary shape interface of tissue layers in the anatomically realistic head model. After incorporating various levels of detail, the solution of subject microwave scattering problem and the measurement of transmitted and backscattered signals were obtained using finite element method. Mesh convergence analysis was also performed to achieve error free results with a minimum number of mesh elements and a lesser degree of freedom in the fast computational time. The results were promising and the E-Field values converged for both simple and complex geometrical models. However, the E-Field difference between both types of head model at the same reference point differentiated a lot in terms of magnitude. At complex location, a high difference value of 0.04236 V/m was measured compared to the simple location, where it turned out to be 0.00197 V/m. This study also contributes to provide a comparison analysis between the direct and iterative solvers so as to find out the solution of subject microwave scattering problem in a minimum computational time along with memory resources requirement. It is seen from this study that the microwave imaging may effectively be utilized for the detection, localization and differentiation of different types of brain stroke. The simulation results verified that the microwave imaging can be efficiently exploited to study the significant contrast between electric field values of the normal and abnormal brain tissues for the investigation of brain anomalies. In the end, a specific absorption rate analysis was carried out to compare the ionizing effects of microwave signals to different types of head model using a factor of safety for brain tissues. It is also suggested after careful study of various inversion methods in practice for microwave head imaging, that the contrast source inversion method may be more suitable and computationally efficient for such problems. PMID:29177115

Neutron radiography experiments for verification of soluble boron mixing and transport modeling under natural circulation conditions

DOE Office of Scientific and Technical Information (OSTI.GOV)

Feltus, M.A.; Morlang, G.M.

1996-06-01

The use of neutron radiography for visualization of fluid flow through flow visualization modules has been very successful. Current experiments at the Penn State Breazeale Reactor serve to verify the mixing and transport of soluble boron under natural flow conditions as would be experienced in a pressurized water reactor. Different flow geometries have been modeled including holes, slots, and baffles. Flow modules are constructed of aluminum box material 1 1/2 inches by 4 inches in varying lengths. An experimental flow system was built which pumps fluid to a head tank and natural circulation flow occurs from the head tank throughmore » the flow visualization module to be radiographed. The entire flow system is mounted on a portable assembly to allow placement of the flow visualization module in front of the neutron beam port. A neutron-transparent fluorinert fluid is used to simulate water at different densities. Boron is modeled by gadolinium oxide powder as a tracer element, which is placed in a mixing assembly and injected into the system by remote operated electric valve, once the reactor is at power. The entire sequence is recorded on real-time video. Still photographs are made frame-by-frame from the video tape. Computers are used to digitally enhance the video and still photographs. The data obtained from the enhancement will be used for verification of simple geometry predictions using the TRAC and RELAP thermal-hydraulic codes. A detailed model of a reactor vessel inlet plenum, downcomer region, flow distribution area and core inlet is being constructed to model the AP600 plenum. Successive radiography experiments of each section of the model under identical conditions will provide a complete vessel/core model for comparison with the thermal-hydraulic codes.« less

High resolution, MRI-based, segmented, computerized head phantom

DOE Office of Scientific and Technical Information (OSTI.GOV)

Zubal, I.G.; Harrell, C.R.; Smith, E.O.

1999-01-01

The authors have created a high-resolution software phantom of the human brain which is applicable to voxel-based radiation transport calculations yielding nuclear medicine simulated images and/or internal dose estimates. A software head phantom was created from 124 transverse MRI images of a healthy normal individual. The transverse T2 slices, recorded in a 256x256 matrix from a GE Signa 2 scanner, have isotropic voxel dimensions of 1.5 mm and were manually segmented by the clinical staff. Each voxel of the phantom contains one of 62 index numbers designating anatomical, neurological, and taxonomical structures. The result is stored as a 256x256x128 bytemore » array. Internal volumes compare favorably to those described in the ICRP Reference Man. The computerized array represents a high resolution model of a typical human brain and serves as a voxel-based anthropomorphic head phantom suitable for computer-based modeling and simulation calculations. It offers an improved realism over previous mathematically described software brain phantoms, and creates a reference standard for comparing results of newly emerging voxel-based computations. Such voxel-based computations lead the way to developing diagnostic and dosimetry calculations which can utilize patient-specific diagnostic images. However, such individualized approaches lack fast, automatic segmentation schemes for routine use; therefore, the high resolution, typical head geometry gives the most realistic patient model currently available.« less

Computational Electromagnetic Analysis in a Human Head Model with EEG Electrodes and Leads Exposed to RF-Field Sources at 915 MHz and 1748 MHz

PubMed Central

Angelone, Leonardo M.; Bit-Babik, Giorgi; Chou, Chung-Kwang

2010-01-01

An electromagnetic analysis of a human head with EEG electrodes and leads exposed to RF-field sources was performed by means of Finite-Difference Time-Domain simulations on a 1-mm3 MRI-based human head model. RF-field source models included a half-wave dipole, a patch antenna, and a realistic CAD-based mobile phone at 915 MHz and 1748 MHz. EEG electrodes/leads models included two configurations of EEG leads, both a standard 10–20 montage with 19 electrodes and a 32-electrode cap, and metallic and high resistive leads. Whole-head and peak 10-g average SAR showed less than 20% changes with and without leads. Peak 1-g and 10-g average SARs were below the ICNIRP and IEEE guideline limits. Conversely, a comprehensive volumetric assessment of changes in the RF field with and without metallic EEG leads showed an increase of two orders of magnitude in single-voxel power absorption in the epidermis and a 40-fold increase in the brain during exposure to the 915 MHz mobile phone. Results varied with the geometry and conductivity of EEG electrodes/leads. This enhancement confirms the validity of the question whether any observed effects in studies involving EEG recordings during RF-field exposure are directly related to the RF fields generated by the source or indirectly to the RF-field-induced currents due to the presence of conductive EEG leads. PMID:20681803

The numerical study of the coextrusion process of polymer melts in the cable head

NASA Astrophysics Data System (ADS)

Kozitsyna, M. V.; Trufanova, N. M.

2017-06-01

The process of coextrusion consists in a simultaneous creation of all necessary insulating layers of different polymers in the channel of a special forming tool. The main focus of this study is the analysis of technological, geometrical and rheological characteristics on the values of the layer’s thickness. In this paper are considered three geometries of cable head on the three-dimensional and two-dimensional representation. The mathematical models of separate and joint flow of polymer melts have been implemented by the finite element method in Ansys software package. The velocity fields, temperature, pressure in the cross-sections of the channel and by the length have been obtained. The influence of some thickness characteristics of insulation layers has been identified.

MODFLOW equipped with a new method for the accurate simulation of axisymmetric flow

NASA Astrophysics Data System (ADS)

Samani, N.; Kompani-Zare, M.; Barry, D. A.

2004-01-01

Axisymmetric flow to a well is an important topic of groundwater hydraulics, the simulation of which depends on accurate computation of head gradients. Groundwater numerical models with conventional rectilinear grid geometry such as MODFLOW (in contrast to analytical models) generally have not been used to simulate aquifer test results at a pumping well because they are not designed or expected to closely simulate the head gradient near the well. A scaling method is proposed based on mapping the governing flow equation from cylindrical to Cartesian coordinates, and vice versa. A set of relationships and scales is derived to implement the conversion. The proposed scaling method is then embedded in MODFLOW 2000. To verify the accuracy of the method steady and unsteady flows in confined and unconfined aquifers with fully or partially penetrating pumping wells are simulated and compared with the corresponding analytical solutions. In all cases a high degree of accuracy is achieved.

Using noble gas tracers to constrain a groundwater flow model with recharge elevations: A novel approach for mountainous terrain

USGS Publications Warehouse

Doyle, Jessica M.; Gleeson, Tom; Manning, Andrew H.; Mayer, K. Ulrich

2015-01-01

Environmental tracers provide information on groundwater age, recharge conditions, and flow processes which can be helpful for evaluating groundwater sustainability and vulnerability. Dissolved noble gas data have proven particularly useful in mountainous terrain because they can be used to determine recharge elevation. However, tracer-derived recharge elevations have not been utilized as calibration targets for numerical groundwater flow models. Herein, we constrain and calibrate a regional groundwater flow model with noble-gas-derived recharge elevations for the first time. Tritium and noble gas tracer results improved the site conceptual model by identifying a previously uncertain contribution of mountain block recharge from the Coast Mountains to an alluvial coastal aquifer in humid southwestern British Columbia. The revised conceptual model was integrated into a three-dimensional numerical groundwater flow model and calibrated to hydraulic head data in addition to recharge elevations estimated from noble gas recharge temperatures. Recharge elevations proved to be imperative for constraining hydraulic conductivity, recharge location, and bedrock geometry, and thus minimizing model nonuniqueness. Results indicate that 45% of recharge to the aquifer is mountain block recharge. A similar match between measured and modeled heads was achieved in a second numerical model that excludes the mountain block (no mountain block recharge), demonstrating that hydraulic head data alone are incapable of quantifying mountain block recharge. This result has significant implications for understanding and managing source water protection in recharge areas, potential effects of climate change, the overall water budget, and ultimately ensuring groundwater sustainability.

Ellipsoidal head model for fetal magnetoencephalography: forward and inverse solutions

NASA Astrophysics Data System (ADS)

Gutiérrez, David; Nehorai, Arye; Preissl, Hubert

2005-05-01

Fetal magnetoencephalography (fMEG) is a non-invasive technique where measurements of the magnetic field outside the maternal abdomen are used to infer the source location and signals of the fetus' neural activity. There are a number of aspects related to fMEG modelling that must be addressed, such as the conductor volume, fetal position and orientation, gestation period, etc. We propose a solution to the forward problem of fMEG based on an ellipsoidal head geometry. This model has the advantage of highlighting special characteristics of the field that are inherent to the anisotropy of the human head, such as the spread and orientation of the field in relationship with the localization and position of the fetal head. Our forward solution is presented in the form of a kernel matrix that facilitates the solution of the inverse problem through decoupling of the dipole localization parameters from the source signals. Then, we use this model and the maximum likelihood technique to solve the inverse problem assuming the availability of measurements from multiple trials. The applicability and performance of our methods are illustrated through numerical examples based on a real 151-channel SQUID fMEG measurement system (SARA). SARA is an MEG system especially designed for fetal assessment and is currently used for heart and brain studies. Finally, since our model requires knowledge of the best-fitting ellipsoid's centre location and semiaxes lengths, we propose a method for estimating these parameters through a least-squares fit on anatomical information obtained from three-dimensional ultrasound images.

The Impact of Ocular Pressures, Material Properties and Geometry on Optic Nerve Head Deformation

NASA Technical Reports Server (NTRS)

Feola, Andrew J.; Myers, Jerry G.; Raykin, Julia; Nelson, Emily S.; Samuels, Brian C.; Ethier C. Ross

2017-01-01

Alteration in intracranial pressure (ICP) has been associated with various diseases that cause visual impairment, including glaucoma, idiopathic intracranial hypertension and Visual Impairment and Intracranial Pressure (VIIP) syndrome. However, how changes in ICP lead to vision loss is unclear, although it is hypothesized to involve deformations of the tissues in the optic nerve head (ONH). Recently, understanding the effect of ICP alterations on ocular tissues has become a major concern for NASA, where 42 of astronauts that partake in long duration space missions suffer from VIIP syndrome. Astronauts with VIIP syndrome suffer from visual impairment and changes in ocular anatomy that persist after returning to earth (1). It is hypothesized that the cephalad fluid shift that occurs upon entering microgravity increases ICP, which leads to an altered biomechanical environment in the posterior globe and optic nerve sheath, and subsequently VIIP syndrome. Our goal was to develop a finite element (FE) model to simulate the acute effects of elevated ICP on the posterior eye. Here, we simulated how inter-individual differences affect the deformation of ONH tissues. Further, we examined how several different geometries influenced deformations when exposed to elevated ICP.

Geometry in the Secondary School, A Compendium of Papers Presented in Houston, Texas, January 29, 1967, at a Joint Session of The Mathematical Association of America and The National Council of Teachers of Mathematics.

ERIC Educational Resources Information Center

McNabb, W. K.

This booklet is a collection of the papers presented at a joint session of the Mathematical Association of America and the National Council of Teachers of Mathematics during the fiftieth annual meeting of the MAA. These papers were presented under the headings of "Geometry and School Mathematics,""High School Geometry," and…

Simultaneous multi-headed imager geometry calibration method

DOEpatents

Tran, Vi-Hoa [Newport News, VA; Meikle, Steven Richard [Penshurst, AU; Smith, Mark Frederick [Yorktown, VA

2008-02-19

A method for calibrating multi-headed high sensitivity and high spatial resolution dynamic imaging systems, especially those useful in the acquisition of tomographic images of small animals. The method of the present invention comprises: simultaneously calibrating two or more detectors to the same coordinate system; and functionally correcting for unwanted detector movement due to gantry flexing.

On the Coupling Between the Incus and the Stapes in the Cat

PubMed Central

Heng Siah, T.; McKee, Marc D.; Daniel, Sam J.; Decraemer, Willem F.

2005-01-01

The connection between the long process and the lenticular process of the incus is extremely fine, so much so that some authors have treated the lenticular process as a separate bone. We review descriptions of the lenticular process that have appeared in the literature, and present some new histological observations. We discuss the dimensions and composition of the lenticular process and of the incudostapedial joint, and present estimates of the material properties for the bone, cartilage, and ligament of which they are composed. We present a preliminary finite-element model which includes the lenticular plate, the bony pedicle connecting the lenticular plate to the long process, the head of the stapes, and the incudostapedial joint. The model has a much simplified geometry. We present simulation results for ranges of values for the material properties. We then present simulation results for this model when it is incorporated into an overall model of the middle ear of the cat. For the geometries and material properties used here, the bony pedicle is found to contribute significant flexibility to the coupling between the incus and the stapes. PMID:15735938

Properties of a monopivot centrifugal blood pump manufactured by 3D printing.

PubMed

Nishida, Masahiro; Negishi, Takumi; Sakota, Daisuke; Kosaka, Ryo; Maruyama, Osamu; Hyakutake, Toru; Kuwana, Katsuyuki; Yamane, Takashi

2016-12-01

An impeller the same geometry as the impeller of a commercial monopivot cardiopulmonary bypass pump was manufactured using 3D printing. The 3D-printed impeller was integrated into the pump casing of the commercially available pump to form a 3D-printed pump model. The surface roughness of the impeller, the hydraulic performance, the axial displacement of the rotating impeller, and the hemolytic properties of the 3D-printed model were measured and compared with those of the commercially available model. Although the surface roughness of the 3D-printed model was significantly larger than that of the commercially available model, the hydraulic performance of the two models almost coincided. The hemolysis level of the 3D-printed model roughly coincided with that of the commercially available model under low-pressure head conditions, but increased greatly under high-pressure head conditions, as a result of the narrow gap between the rotating impeller and the pump casing. The gap became narrow under high-pressure head conditions, because the axial thrust applied to the impeller increased with increasing impeller rotational speed. Moreover, the axial displacement of the rotating impeller was twice that of the commercially available model, confirming that the elastic deformation of the 3D-printed impeller was larger than that of the commercially available impeller. These results suggest that trial models manufactured by 3D printing can reproduce the hydraulic performance of the commercial product. However, both the surface roughness and the deformation of the trial models must be considered to precisely evaluate the hemolytic properties of the model.

Development of HEATHER for cochlear implant stimulation using a new modeling workflow.

PubMed

Tran, Phillip; Sue, Andrian; Wong, Paul; Li, Qing; Carter, Paul

2015-02-01

The current conduction pathways resulting from monopolar stimulation of the cochlear implant were studied by developing a human electroanatomical total head reconstruction (namely, HEATHER). HEATHER was created from serially sectioned images of the female Visible Human Project dataset to encompass a total of 12 different tissues, and included computer-aided design geometries of the cochlear implant. Since existing methods were unable to generate the required complexity for HEATHER, a new modeling workflow was proposed. The results of the finite-element analysis agree with the literature, showing that the injected current exits the cochlea via the modiolus (14%), the basal end of the cochlea (22%), and through the cochlear walls (64%). It was also found that, once leaving the cochlea, the current travels to the implant body via the cranial cavity or scalp. The modeling workflow proved to be robust and flexible, allowing for meshes to be generated with substantial user control. Furthermore, the workflow could easily be employed to create realistic anatomical models of the human head for different bioelectric applications, such as deep brain stimulation, electroencephalography, and other biophysical phenomena.

Finite element model focused on stress distribution in the levator ani muscle during vaginal delivery.

PubMed

Krofta, Ladislav; Havelková, Linda; Urbánková, Iva; Krčmář, Michal; Hynčík, Luděk; Feyereisl, Jaroslav

2017-02-01

During vaginal delivery, the levator ani muscle (LAM) undergoes severe deformation. This stress can lead to stretch-related LAM injuries. The objective of this study was to develop a sophisticated MRI-based model to simulate changes in the LAM during vaginal delivery. A 3D finite element model of the female pelvic floor and fetal head was developed. The model geometry was based on MRI data from a nulliparous woman and 1-day-old neonate. Material parameters were estimated using uniaxial test data from the literature and by least-square minimization method. The boundary conditions reflected all anatomical constraints and supports. A simulation of vaginal delivery with regard to the cardinal movements of labor was then performed. The mean stress values in the iliococcygeus portion of the LAM during fetal head extension were 4.91-7.93 MPa. The highest stress values were induced in the pubovisceral and puborectal LAM portions (mean 27.46 MPa) at the outset of fetal head extension. The last LAM subdivision engaged in the changes in stress was the posteromedial section of the puborectal muscle. The mean stress values were 16.89 MPa at the end of fetal head extension. The LAM was elongated by nearly 2.5 times from its initial resting position. The cardinal movements of labor significantly affect the subsequent heterogeneous stress distribution in the LAM. The absolute stress values were highest in portions of the muscle that arise from the pubic bone. These areas are at the highest risk for muscle injuries with long-term complications.

Stochastic and deterministic causes of streamer branching in liquid dielectrics

NASA Astrophysics Data System (ADS)

Jadidian, Jouya; Zahn, Markus; Lavesson, Nils; Widlund, Ola; Borg, Karl

2013-08-01

Streamer branching in liquid dielectrics is driven by stochastic and deterministic factors. The presence of stochastic causes of streamer branching such as inhomogeneities inherited from noisy initial states, impurities, or charge carrier density fluctuations is inevitable in any dielectric. A fully three-dimensional streamer model presented in this paper indicates that deterministic origins of branching are intrinsic attributes of streamers, which in some cases make the branching inevitable depending on shape and velocity of the volume charge at the streamer frontier. Specifically, any given inhomogeneous perturbation can result in streamer branching if the volume charge layer at the original streamer head is relatively thin and slow enough. Furthermore, discrete nature of electrons at the leading edge of an ionization front always guarantees the existence of a non-zero inhomogeneous perturbation ahead of the streamer head propagating even in perfectly homogeneous dielectric. Based on the modeling results for streamers propagating in a liquid dielectric, a gauge on the streamer head geometry is introduced that determines whether the branching occurs under particular inhomogeneous circumstances. Estimated number, diameter, and velocity of the born branches agree qualitatively with experimental images of the streamer branching.

MCNP6 unstructured mesh application to estimate the photoneutron distribution and induced activity inside a linac bunker

NASA Astrophysics Data System (ADS)

Juste, B.; Morató, S.; Miró, R.; Verdú, G.; Díez, S.

2017-08-01

Unwanted neutrons in radiation therapy treatments are typically generated by photonuclear reactions. High-energy beams emitted by medical Linear Accelerators (LinAcs) interact with high atomic number materials situated in the accelerator head and release neutrons. Since neutrons have a high relative biological effectiveness, even low neutron doses may imply significant exposure of patients. It is also important to study radioactivity induced by these photoneutrons when interacting with the different materials and components of the treatment head facility and the shielding room walls, since persons not present during irradiation (e.g. medical staff) may be exposed to them even when the accelerator is not operating. These problems are studied in this work in order to contribute to challenge the radiation protection in these treatment locations. The work has been performed by simulation using the latest state of the art of Monte-Carlo computer code MCNP6. To that, a detailed model of particles transport inside the bunker and treatment head has been carried out using a meshed geometry model. The LinAc studied is an Elekta Precise accelerator with a treatment photon energy of 15 MeV used at the Hospital Clinic Universitari de Valencia, Spain.

Estimation of electrical conductivity distribution within the human head from magnetic flux density measurement.

PubMed

Gao, Nuo; Zhu, S A; He, Bin

2005-06-07

We have developed a new algorithm for magnetic resonance electrical impedance tomography (MREIT), which uses only one component of the magnetic flux density to reconstruct the electrical conductivity distribution within the body. The radial basis function (RBF) network and simplex method are used in the present approach to estimate the conductivity distribution by minimizing the errors between the 'measured' and model-predicted magnetic flux densities. Computer simulations were conducted in a realistic-geometry head model to test the feasibility of the proposed approach. Single-variable and three-variable simulations were performed to estimate the brain-skull conductivity ratio and the conductivity values of the brain, skull and scalp layers. When SNR = 15 for magnetic flux density measurements with the target skull-to-brain conductivity ratio being 1/15, the relative error (RE) between the target and estimated conductivity was 0.0737 +/- 0.0746 in the single-variable simulations. In the three-variable simulations, the RE was 0.1676 +/- 0.0317. Effects of electrode position uncertainty were also assessed by computer simulations. The present promising results suggest the feasibility of estimating important conductivity values within the head from noninvasive magnetic flux density measurements.

Effective scattering coefficient of the cerebral spinal fluid in adult head models for diffuse optical imaging

NASA Astrophysics Data System (ADS)

Custo, Anna; Wells, William M., III; Barnett, Alex H.; Hillman, Elizabeth M. C.; Boas, David A.

2006-07-01

An efficient computation of the time-dependent forward solution for photon transport in a head model is a key capability for performing accurate inversion for functional diffuse optical imaging of the brain. The diffusion approximation to photon transport is much faster to simulate than the physically correct radiative transport equation (RTE); however, it is commonly assumed that scattering lengths must be much smaller than all system dimensions and all absorption lengths for the approximation to be accurate. Neither of these conditions is satisfied in the cerebrospinal fluid (CSF). Since line-of-sight distances in the CSF are small, of the order of a few millimeters, we explore the idea that the CSF scattering coefficient may be modeled by any value from zero up to the order of the typical inverse line-of-sight distance, or approximately 0.3 mm-1, without significantly altering the calculated detector signals or the partial path lengths relevant for functional measurements. We demonstrate this in detail by using a Monte Carlo simulation of the RTE in a three-dimensional head model based on clinical magnetic resonance imaging data, with realistic optode geometries. Our findings lead us to expect that the diffusion approximation will be valid even in the presence of the CSF, with consequences for faster solution of the inverse problem.

Excitations of interface pinned domain walls in constrained geometries

NASA Astrophysics Data System (ADS)

Martins, S. M. S. B.; Oliveira, L. L.; Rebouças, G. O. G.; Dantas, Ana L.; Carriço, A. S.

2018-05-01

We report a theoretical investigation of the equilibrium pattern and the spectra of head-to-head and Neel domain walls of flat Fe and Py stripes, exchange coupled with a vicinal antiferromagnetic substrate. We show that the domain wall excitation spectrum is tunable by the strength of the interface field. Furthermore, strong interface coupling favors localized wall excitations.

Structural Benchmark Testing for Stirling Convertor Heater Heads

NASA Technical Reports Server (NTRS)

Krause, David L.; Kalluri, Sreeramesh; Bowman, Randy R.

2007-01-01

The National Aeronautics and Space Administration (NASA) has identified high efficiency Stirling technology for potential use on long duration Space Science missions such as Mars rovers, deep space missions, and lunar applications. For the long life times required, a structurally significant design limit for the Stirling convertor heater head is creep deformation induced even under relatively low stress levels at high material temperatures. Conventional investigations of creep behavior adequately rely on experimental results from uniaxial creep specimens, and much creep data is available for the proposed Inconel-718 (IN-718) and MarM-247 nickel-based superalloy materials of construction. However, very little experimental creep information is available that directly applies to the atypical thin walls, the specific microstructures, and the low stress levels. In addition, the geometry and loading conditions apply multiaxial stress states on the heater head components, far from the conditions of uniaxial testing. For these reasons, experimental benchmark testing is underway to aid in accurately assessing the durability of Stirling heater heads. The investigation supplements uniaxial creep testing with pneumatic testing of heater head test articles at elevated temperatures and with stress levels ranging from one to seven times design stresses. This paper presents experimental methods, results, post-test microstructural analyses, and conclusions for both accelerated and non-accelerated tests. The Stirling projects use the results to calibrate deterministic and probabilistic analytical creep models of the heater heads to predict their life times.

Accelerated Life Structural Benchmark Testing for a Stirling Convertor Heater Head

NASA Technical Reports Server (NTRS)

Krause, David L.; Kantzos, Pete T.

2006-01-01

For proposed long-duration NASA Space Science missions, the Department of Energy, Lockheed Martin, Infinia Corporation, and NASA Glenn Research Center are developing a high-efficiency, 110 W Stirling Radioisotope Generator (SRG110). A structurally significant limit state for the SRG110 heater head component is creep deformation induced at high material temperature and low stress level. Conventional investigations of creep behavior adequately rely on experimental results from uniaxial creep specimens, and a wealth of creep data is available for the Inconel 718 material of construction. However, the specified atypical thin heater head material is fine-grained with a heat treatment that limits precipitate growth, and little creep property data for this microstructure is available in the literature. In addition, the geometry and loading conditions apply a multiaxial stress state on the component, far from the conditions of uniaxial testing. For these reasons, an extensive experimental investigation is ongoing to aid in accurately assessing the durability of the SRG110 heater head. This investigation supplements uniaxial creep testing with pneumatic testing of heater head-like pressure vessels at design temperature with stress levels ranging from approximately the design stress to several times that. This paper presents experimental results, post-test microstructural analyses, and conclusions for four higher-stress, accelerated life tests. Analysts are using these results to calibrate deterministic and probabilistic analytical creep models of the SRG110 heater head.

Simultaneous head tissue conductivity and EEG source location estimation.

PubMed

Akalin Acar, Zeynep; Acar, Can E; Makeig, Scott

2016-01-01

Accurate electroencephalographic (EEG) source localization requires an electrical head model incorporating accurate geometries and conductivity values for the major head tissues. While consistent conductivity values have been reported for scalp, brain, and cerebrospinal fluid, measured brain-to-skull conductivity ratio (BSCR) estimates have varied between 8 and 80, likely reflecting both inter-subject and measurement method differences. In simulations, mis-estimation of skull conductivity can produce source localization errors as large as 3cm. Here, we describe an iterative gradient-based approach to Simultaneous tissue Conductivity And source Location Estimation (SCALE). The scalp projection maps used by SCALE are obtained from near-dipolar effective EEG sources found by adequate independent component analysis (ICA) decomposition of sufficient high-density EEG data. We applied SCALE to simulated scalp projections of 15cm(2)-scale cortical patch sources in an MR image-based electrical head model with simulated BSCR of 30. Initialized either with a BSCR of 80 or 20, SCALE estimated BSCR as 32.6. In Adaptive Mixture ICA (AMICA) decompositions of (45-min, 128-channel) EEG data from two young adults we identified sets of 13 independent components having near-dipolar scalp maps compatible with a single cortical source patch. Again initialized with either BSCR 80 or 25, SCALE gave BSCR estimates of 34 and 54 for the two subjects respectively. The ability to accurately estimate skull conductivity non-invasively from any well-recorded EEG data in combination with a stable and non-invasively acquired MR imaging-derived electrical head model could remove a critical barrier to using EEG as a sub-cm(2)-scale accurate 3-D functional cortical imaging modality. Copyright © 2015 Elsevier Inc. All rights reserved.

The effects of boundary conditions on the steady-state response of three hypothetical ground-water systems; results and implications of numerical experiments

USGS Publications Warehouse

Franke, O. Lehn; Reilly, Thomas E.

1987-01-01

The most critical and difficult aspect of defining a groundwater system or problem for conceptual analysis or numerical simulation is the selection of boundary conditions . This report demonstrates the effects of different boundary conditions on the steady-state response of otherwise similar ground-water systems to a pumping stress. Three series of numerical experiments illustrate the behavior of three hypothetical groundwater systems that are rectangular sand prisms with the same dimensions but with different combinations of constant-head, specified-head, no-flow, and constant-flux boundary conditions. In the first series of numerical experiments, the heads and flows in all three systems are identical, as are the hydraulic conductivity and system geometry . However, when the systems are subjected to an equal stress by a pumping well in the third series, each differs significantly in its response . The highest heads (smallest drawdowns) and flows occur in the systems most constrained by constant- or specified-head boundaries. These and other observations described herein are important in steady-state calibration, which is an integral part of simulating many ground-water systems. Because the effects of boundary conditions on model response often become evident only when the system is stressed, a close match between the potential distribution in the model and that in the unstressed natural system does not guarantee that the model boundary conditions correctly represent those in the natural system . In conclusion, the boundary conditions that are selected for simulation of a ground-water system are fundamentally important to groundwater systems analysis and warrant continual reevaluation and modification as investigation proceeds and new information and understanding are acquired.

Simultaneous head tissue conductivity and EEG source location estimation

PubMed Central

Acar, Can E.; Makeig, Scott

2015-01-01

Accurate electroencephalographic (EEG) source localization requires an electrical head model incorporating accurate geometries and conductivity values for the major head tissues. While consistent conductivity values have been reported for scalp, brain, and cerebrospinal fluid, measured brain-to-skull conductivity ratio (BSCR) estimates have varied between 8 and 80, likely reflecting both inter-subject and measurement method differences. In simulations, mis-estimation of skull conductivity can produce source localization errors as large as 3 cm. Here, we describe an iterative gradient-based approach to Simultaneous tissue Conductivity And source Location Estimation (SCALE). The scalp projection maps used by SCALE are obtained from near-dipolar effective EEG sources found by adequate independent component analysis (ICA) decomposition of sufficient high-density EEG data. We applied SCALE to simulated scalp projections of 15 cm2-scale cortical patch sources in an MR image-based electrical head model with simulated BSCR of 30. Initialized either with a BSCR of 80 or 20, SCALE estimated BSCR as 32.6. In Adaptive Mixture ICA (AMICA) decompositions of (45-min, 128-channel) EEG data from two young adults we identified sets of 13 independent components having near-dipolar scalp maps compatible with a single cortical source patch. Again initialized with either BSCR 80 or 25, SCALE gave BSCR estimates of 34 and 54 for the two subjects respectively. The ability to accurately estimate skull conductivity non-invasively from any well-recorded EEG data in combination with a stable and non-invasively acquired MR imaging-derived electrical head model could remove a critical barrier to using EEG as a sub-cm2-scale accurate 3-D functional cortical imaging modality. PMID:26302675

Mitral Valve Chordae Tendineae: Topological and Geometrical Characterization.

PubMed

Khalighi, Amir H; Drach, Andrew; Bloodworth, Charles H; Pierce, Eric L; Yoganathan, Ajit P; Gorman, Robert C; Gorman, Joseph H; Sacks, Michael S

2017-02-01

Mitral valve (MV) closure depends upon the proper function of each component of the valve apparatus, which includes the annulus, leaflets, and chordae tendineae (CT). Geometry plays a major role in MV mechanics and thus highly impacts the accuracy of computational models simulating MV function and repair. While the physiological geometry of the leaflets and annulus have been previously investigated, little effort has been made to quantitatively and objectively describe CT geometry. The CT constitute a fibrous tendon-like structure projecting from the papillary muscles (PMs) to the leaflets, thereby evenly distributing the loads placed on the MV during closure. Because CT play a major role in determining the shape and stress state of the MV as a whole, their geometry must be well characterized. In the present work, a novel and comprehensive investigation of MV CT geometry was performed to more fully quantify CT anatomy. In vitro micro-tomography 3D images of ovine MVs were acquired, segmented, then analyzed using a curve-skeleton transform. The resulting data was used to construct B-spline geometric representations of the CT structures, enriched with a continuous field of cross-sectional area (CSA) data. Next, Reeb graph models were developed to analyze overall topological patterns, along with dimensional attributes such as segment lengths, 3D orientations, and CSA. Reeb graph results revealed that the topology of ovine MV CT followed a full binary tree structure. Moreover, individual chords are mostly planar geometries that together form a 3D load-bearing support for the MV leaflets. We further demonstrated that, unlike flow-based branching patterns, while individual CT branches became thinner as they propagated further away from the PM heads towards the leaflets, the total CSA almost doubled. Overall, our findings indicate a certain level of regularity in structure, and suggest that population-based MV CT geometric models can be generated to improve current MV repair procedures.

Brain Response to Primary Blast Wave Using Validated Finite Element Models of Human Head and Advanced Combat Helmet

PubMed Central

Zhang, Liying; Makwana, Rahul; Sharma, Sumit

2013-01-01

Blast-induced traumatic brain injury has emerged as a “signature injury” in combat casualty care. Present combat helmets are designed primarily to protect against ballistic and blunt impacts, but the current issue with helmets is protection concerning blasts. In order to delineate the blast wave attenuating capability of the Advanced Combat Helmet (ACH), a finite element (FE) study was undertaken to evaluate the head response against blast loadings with and without helmet using a partially validated FE model of the human head and ACH. Four levels of overpressures (0.27–0.66 MPa) from the Bowen’s lung iso-damage threshold curves were used to simulate blast insults. Effectiveness of the helmet with respect to head orientation was also investigated. The resulting biomechanical responses of the brain to blast threats were compared for human head with and without the helmet. For all Bowen’s cases, the peak intracranial pressures (ICP) in the head ranged from 0.68 to 1.8 MPa in the coup cortical region. ACH was found to mitigate ICP in the head by 10–35%. Helmeted head resulted in 30% lower average peak brain strains and product of strain and strain rate. Among three blast loading directions with ACH, highest reduction in peak ICP (44%) was due to backward blasts whereas the lowest reduction in peak ICP and brain strains was due to forward blast (27%). The biomechanical responses of a human head to primary blast insult exhibited directional sensitivity owing to the different geometry contours and coverage of the helmet construction and asymmetric anatomy of the head. Thus, direction-specific tolerances are needed in helmet design in order to offer omni-directional protection for the human head. The blasts of varying peak overpressures and durations that are believed to produce the same level of lung injury produce different levels of mechanical responses in the brain, and hence “iso-damage” curves for brain injury are likely different than the Bowen curves for lung injury. PMID:23935591

Measurement of eye lens dose for Varian On-Board Imaging with different cone-beam computed tomography acquisition techniques

PubMed Central

Deshpande, Sudesh; Dhote, Deepak; Thakur, Kalpna; Pawar, Amol; Kumar, Rajesh; Kumar, Munish; Kulkarni, M. S.; Sharma, S. D.; Kannan, V.

2016-01-01

The objective of this work was to measure patient eye lens dose for different cone-beam computed tomography (CBCT) acquisition protocols of Varian's On-Board Imaging (OBI) system using optically stimulated luminescence dosimeter (OSLD) and to study the variation in eye lens dose with patient geometry and distance of isocenter to the eye lens. During the experimental measurements, OSLD was placed on the patient between the eyebrows of both eyes in line of nose during CBCT image acquisition to measure eye lens doses. The eye lens dose measurements were carried out for three different cone-beam acquisition protocols (standard dose head, low-dose head [LDH], and high-quality head [HQH]) of Varian OBI. Measured doses were correlated with patient geometry and distance between isocenter and eye lens. Measured eye lens doses for standard head and HQH protocols were in the range of 1.8–3.2 mGy and 4.5–9.9 mGy, respectively. However, the measured eye lens dose for the LDH protocol was in the range of 0.3–0.7 mGy. The measured data indicate that eye lens dose to patient depends on the selected imaging protocol. It was also observed that eye lens dose does not depend on patient geometry but strongly depends on distance between eye lens and treatment field isocenter. However, undoubted advantages of imaging system should not be counterbalanced by inappropriate selection of imaging protocol, especially for very intense imaging protocol. PMID:27651564

Resistance Heater Helps Stirling-Engine Research

NASA Technical Reports Server (NTRS)

Hoehn, F. W.

1982-01-01

Stirling engine heater head consists of 18 double-turn coils of tubing, each of which is tightly wrapped with resistance-heating element, through which working gas flows. Coils form a toroid about periphery of heater-head body. With new resistance heater, total circuit resistance can be selected independently of tube geometry by changing size of wires and/or number of wire wraps around each tube.

Annular beam shaping system for advanced 3D laser brazing

NASA Astrophysics Data System (ADS)

Pütsch, Oliver; Stollenwerk, Jochen; Kogel-Hollacher, Markus; Traub, Martin

2012-10-01

As laser brazing benefits from advantages such as smooth joints and small heat-affected zones, it has become established as a joining technology that is widely used in the automotive industry. With the processing of complex-shaped geometries, recent developed brazing heads suffer, however, from the need for continuous reorientation of the optical system and/or limited accessibility due to lateral wire feeding. This motivates the development of a laser brazing head with coaxial wire feeding and enhanced functionality. An optical system is designed that allows to generate an annular intensity distribution in the working zone. The utilization of complex optical components avoids obscuration of the optical path by the wire feeding. The new design overcomes the disadvantages of the state-of-the-art brazing heads with lateral wire feeding and benefits from the independence of direction while processing complex geometries. To increase the robustness of the brazing process, the beam path also includes a seam tracking system, leading to a more challenging design of the whole optical train. This paper mainly discusses the concept and the optical design of the coaxial brazing head, and also presents the results obtained with a prototype and selected application results.

Effect of crystallographical and geometrical changes of a ferrite head on magnetic signals during the sliding process with magnetic tape

NASA Technical Reports Server (NTRS)

Miyoshi, K.; Buckley, D. H.; Tanaka, K.

1986-01-01

This paper reviews changes in the crystalline structure and geometry of lapped Mn-Zn ferrite heads in sliding contact with magnetic tape and the effects of these changes on magnetic signals. A highly textured, polycrystalline structure was produced on the surface of a single-crystal Mn-Zn ferrite head when it was finished with an aluminum oxide lapping tape. Sliding this lapped surface against a magnetic tape produced a nearly amorphous structure. The sliding process led to a degradation in readback signal of 1 to 2 dB (short-wavelength recording). Furthermore, wear of the magnetic head caused geometrical changes in the head surface. The signal read back with the worn magnetic head was sensitive to operating parameters such as head displacement and tape tension. A change in operating parameters created head-to-tape spacings and, consequently, excessive gains or losses in the readback signal.

First metatarsophalangeal joint motion in Homo sapiens: theoretical association of two-axis kinematics and specific morphometrics.

PubMed

Durrant, Michael N; McElroy, Tucker; Durrant, Lara

2012-01-01

The metatarsal head and proximal phalanx exhibit considerable asymmetry in their shape and geometry, but there is little documentation in the literature regarding the prevalence of structural characteristics that occur in a given population. Although there is a considerable volume of in vivo and in vitro experiments demonstrating first metatarsal inversion around its longitudinal axis with dorsiflexion, little is known regarding the applicability of specific morphometrics to these motions. Nine distinctive osseous characteristics in the metatarsal head and phalanx were selected based on their location, geometry, and perceived functional relationship to previous studies describing metatarsal motion as inversion with dorsiflexion. The prevalences of the chosen characteristics were determined in a cohort of 21 randomly selected skeletal specimens, 19 of which were provided by the anatomical preparation office at the University of California, San Diego, and two of which were in the possession of one of us (M.D.). The frequency of occurrence of each selected morphological characteristic in this sample and the relevant summary statistics confirm a strong association between the selected features and a conceptual two-axis kinematic model of the metatarsophalangeal joint. The selected morphometrics are consistent with inversion of the metatarsal around its longitudinal axis as it dorsiflexes.

Exit blade geometry and part-load performance of small axial flow propeller turbines: An experimental investigation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Singh, Punit; Nestmann, Franz

2010-09-15

A detailed experimental investigation of the effects of exit blade geometry on the part-load performance of low-head, axial flow propeller turbines is presented. Even as these turbines find important applications in small-scale energy generation using micro-hydro, the relationship between the layout of blade profile, geometry and turbine performance continues to be poorly characterized. The experimental results presented here help understand the relationship between exit tip angle, discharge through the turbine, shaft power, and efficiency. The modification was implemented on two different propeller runners and it was found that the power and efficiency gains from decreasing the exit tip angle couldmore » be explained by a theoretical model presented here based on classical theory of turbomachines. In particular, the focus is on the behaviour of internal parameters like the runner loss coefficient, relative flow angle at exit, mean axial flow velocity and net tangential flow velocity. The study concluded that the effects of exit tip modification were significant. The introspective discussion on the theoretical model's limitation and test facility suggests wider and continued experimentation pertaining to the internal parameters like inlet vortex profile and exit swirl profile. It also recommends thorough validation of the model and its improvement so that it can be made capable for accurate characterization of blade geometric effects. (author)« less

A numerical investigation of the interplay between fireline length, geometry, and rate of spread

Treesearch

J. M. Canfield; R. R. Linn; J. A. Sauer; M. Finney; J. Forthofer

2014-01-01

The current study focuses on coupled dynamics and resultant geometry of fireline segments of various ignition lengths. As an example, for ignition lines of length scales typical for field experiments, fireline curvature is the result of a competition between the head fire and the flanks of the fire. A number of physical features (i.e. buoyancy and wind field divergence...

Kinematics of pediatric crash dummies seated on vehicle seats with realistic belt geometry.

PubMed

Klinich, Kathleen D; Reed, Matthew P; Ebert, Sheila M; Rupp, Jonathan D

2014-01-01

A series of sled tests was performed using vehicle seats and Hybrid-III 6-year-old (6YO) and 10YO anthropomorphic test devices (ATDs) to explore possibilities for improving occupant protection for children who are not using belt-positioning booster seats. Cushion length was varied from production length of 450 mm to a shorter length of 350 mm. Lap belt geometry was set to rear, mid, and forward anchorage locations that span the range of lap belt angles found in vehicles. Six tests each were performed with the 6YO and 10YO Hybrid III ATDs. One additional test was performed using a booster seat with the 6YO. The ATDs were positioned using an updated version of the University of Michigan Transportation Research Institute (UMTRI) seating procedure that positions the ATD hips further forward with longer seat cushions to reflect the effect of cushion length on posture that has been measured with child volunteers. ATD kinematics were evaluated using peak head excursion, peak knee excursion, the difference between peak head and peak knee excursion, and the maximum torso angle. Shortening the seat cushion improved kinematic outcomes, particularly for the 10YO. Lap belt geometry had a greater effect on kinematics with the longer cushion length, with mid or forward belt geometries producing better kinematics than the rearward belt geometry. The worst kinematics for both ATDs occurred with the long cushion length and rearward lap belt geometry. The improvements in kinematics from shorter cushion length or more forward belt geometry are smaller than those provided by a booster seat. The results show potential benefits in occupant protection from shortening cushion length and increasing lap belt angles, particularly for children the size of the 10YO ATD.

An investigation of light transport through scattering bodies with non-scattering regions.

PubMed

Firbank, M; Arridge, S R; Schweiger, M; Delpy, D T

1996-04-01

Near-infra-red (NIR) spectroscopy is increasingly being used for monitoring cerebral oxygenation and haemodynamics. One current concern is the effect of the clear cerebrospinal fluid upon the distribution of light in the head. There are difficulties in modelling clear layers in scattering systems. The Monte Carlo model should handle clear regions accurately, but is too slow to be used for realistic geometries. The diffusion equation can be solved quickly for realistic geometries, but is only valid in scattering regions. In this paper we describe experiments carried out on a solid slab phantom to investigate the effect of clear regions. The experimental results were compared with the different models of light propagation. We found that the presence of a clear layer had a significant effect upon the light distribution, which was modelled correctly by Monte Carlo techniques, but not by diffusion theory. A novel approach to calculating the light transport was developed, using diffusion theory to analyze the scattering regions combined with a radiosity approach to analyze the propagation through the clear region. Results from this approach were found to agree with both the Monte Carlo and experimental data.

SU-F-BRD-01: A Logistic Regression Model to Predict Objective Function Weights in Prostate Cancer IMRT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Boutilier, J; Chan, T; Lee, T

2014-06-15

Purpose: To develop a statistical model that predicts optimization objective function weights from patient geometry for intensity-modulation radiotherapy (IMRT) of prostate cancer. Methods: A previously developed inverse optimization method (IOM) is applied retrospectively to determine optimal weights for 51 treated patients. We use an overlap volume ratio (OVR) of bladder and rectum for different PTV expansions in order to quantify patient geometry in explanatory variables. Using the optimal weights as ground truth, we develop and train a logistic regression (LR) model to predict the rectum weight and thus the bladder weight. Post hoc, we fix the weights of the leftmore » femoral head, right femoral head, and an artificial structure that encourages conformity to the population average while normalizing the bladder and rectum weights accordingly. The population average of objective function weights is used for comparison. Results: The OVR at 0.7cm was found to be the most predictive of the rectum weights. The LR model performance is statistically significant when compared to the population average over a range of clinical metrics including bladder/rectum V53Gy, bladder/rectum V70Gy, and mean voxel dose to the bladder, rectum, CTV, and PTV. On average, the LR model predicted bladder and rectum weights that are both 63% closer to the optimal weights compared to the population average. The treatment plans resulting from the LR weights have, on average, a rectum V70Gy that is 35% closer to the clinical plan and a bladder V70Gy that is 43% closer. Similar results are seen for bladder V54Gy and rectum V54Gy. Conclusion: Statistical modelling from patient anatomy can be used to determine objective function weights in IMRT for prostate cancer. Our method allows the treatment planners to begin the personalization process from an informed starting point, which may lead to more consistent clinical plans and reduce overall planning time.« less

Experimental verification of a CT-based Monte Carlo dose-calculation method in heterogeneous phantoms.

PubMed

Wang, L; Lovelock, M; Chui, C S

1999-12-01

To further validate the Monte Carlo dose-calculation method [Med. Phys. 25, 867-878 (1998)] developed at the Memorial Sloan-Kettering Cancer Center, we have performed experimental verification in various inhomogeneous phantoms. The phantom geometries included simple layered slabs, a simulated bone column, a simulated missing-tissue hemisphere, and an anthropomorphic head geometry (Alderson Rando Phantom). The densities of the inhomogeneity range from 0.14 to 1.86 g/cm3, simulating both clinically relevant lunglike and bonelike materials. The data are reported as central axis depth doses, dose profiles, dose values at points of interest, such as points at the interface of two different media and in the "nasopharynx" region of the Rando head. The dosimeters used in the measurement included dosimetry film, TLD chips, and rods. The measured data were compared to that of Monte Carlo calculations for the same geometrical configurations. In the case of the Rando head phantom, a CT scan of the phantom was used to define the calculation geometry and to locate the points of interest. The agreement between the calculation and measurement is generally within 2.5%. This work validates the accuracy of the Monte Carlo method. While Monte Carlo, at present, is still too slow for routine treatment planning, it can be used as a benchmark against which other dose calculation methods can be compared.

[Are Higher Prices for Larger Femoral Heads in Total Hip Arthroplasty Justified from the Perspective of Health Care Economics? An Analysis of Costs and Effects in Germany].

PubMed

Grunert, R; Schleifenbaum, S; Möbius, R; Sommer, G; Zajonz, D; Hammer, N; Prietzel, T

2017-02-01

Background: In total hip arthroplasty (THA), femoral head diameter has not been regarded as a key parameter which should be restored when reconstructing joint biomechanics and geometry. Apart from the controversial discussion on the advantages and disadvantages of using larger diameter heads, their higher cost is another important reason that they have only been used to a limited extent. The goal of this study was to analyse the price structure of prosthetic heads in comparison to other components used in THA. A large group of patients with hip endoprostheses were evaluated with respect to the implanted socket diameter and thus the theoretically attainable head diameter. Materials and Methods: The relative prices of various THA components (cups, inserts, stems and ball heads) distributed by two leading German manufacturers were determined and analysed. Special attention was paid to different sizes and varieties in a series of components. A large patient population treated with THA was evaluated with respect to the implanted cup diameter and therefore the theoretically attainable head diameter. Results: The pricing analysis of the THA components of two manufacturers showed identical prices for cups, inserts and stems in a series. In contrast to this, the prices for prosthetic heads with a diameter of 36-44 mm were 11-50 % higher than for 28 mm heads. Identical prices for larger heads were the exception. The distribution of the head diameter in 2719 THA cases showed significant differences between the actually implanted and the theoretically attainable heads. Conclusion: There are proven advantages in using larger diameter ball heads in THA and the remaining problems can be solved. It is therefore desirable to correct the current pricing practice of charging higher prices for larger components. Instead, identical prices should be charged for all head diameters in a series, as is currently established practice for all other THA components. Thus when reconstructing biomechanics and joint geometry in THA, it should be possible to recover not only leg length, femoral offset and antetorsion of the femoral neck, but also to approximately restore the diameter of the femoral head and thereby optimise the functional outcome. Georg Thieme Verlag KG Stuttgart · New York.

Computational modeling of blast wave interaction with a human body and assessment of traumatic brain injury

NASA Astrophysics Data System (ADS)

Tan, X. G.; Przekwas, A. J.; Gupta, R. K.

2017-11-01

The modeling of human body biomechanics resulting from blast exposure poses great challenges because of the complex geometry and the substantial material heterogeneity. We developed a detailed human body finite element model representing both the geometry and the materials realistically. The model includes the detailed head (face, skull, brain and spinal cord), the neck, the skeleton, air cavities (lungs) and the tissues. Hence, it can be used to properly model the stress wave propagation in the human body subjected to blast loading. The blast loading on the human was generated from a simulated C4 explosion. We used the highly scalable solvers in the multi-physics code CoBi for both the blast simulation and the human body biomechanics. The meshes generated for these simulations are of good quality so that relatively large time-step sizes can be used without resorting to artificial time scaling treatments. The coupled gas dynamics and biomechanics solutions were validated against the shock tube test data. The human body models were used to conduct parametric simulations to find the biomechanical response and the brain injury mechanism due to blasts impacting the human body. Under the same blast loading condition, we showed the importance of inclusion of the whole body.

Selective evaporation of focusing fluid in two-fluid hydrodynamic print head.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Keicher, David M.; Cook, Adam W.

The work performed in this project has demonstrated the feasibility to use hydrodynamic focusing of two fluid steams to create a novel micro printing technology for electronics and other high performance applications. Initial efforts focused solely on selective evaporation of the sheath fluid from print stream provided insight in developing a unique print head geometry allowing excess sheath fluid to be separated from the print flow stream for recycling/reuse. Fluid flow models suggest that more than 81 percent of the sheath fluid can be removed without affecting the print stream. Further development and optimization is required to demonstrate this capabilitymore » in operation. Print results using two-fluid hydrodynamic focusing yielded a 30 micrometers wide by 0.5 micrometers tall line that suggests that the cross-section of the printed feature from the print head was approximately 2 micrometers in diameter. Printing results also demonstrated that complete removal of the sheath fluid is not necessary for all material systems. The two-fluid printing technology could enable printing of insulated conductors and clad optical interconnects. Further development of this concept should be pursued.« less

Efficacy of radiation safety glasses in interventional radiology.

PubMed

van Rooijen, Bart D; de Haan, Michiel W; Das, Marco; Arnoldussen, Carsten W K P; de Graaf, R; van Zwam, Wim H; Backes, Walter H; Jeukens, Cécile R L P N

2014-10-01

This study was designed to evaluate the reduction of the eye lens dose when wearing protective eyewear in interventional radiology and to identify conditions that optimize the efficacy of radiation safety glasses. The dose reduction provided by different models of radiation safety glasses was measured on an anthropomorphic phantom head. The influence of the orientation of the phantom head on the dose reduction was studied in detail. The dose reduction in interventional radiological practice was assessed by dose measurements on radiologists wearing either leaded or no glasses or using a ceiling suspended screen. The different models of radiation safety glasses provided a dose reduction in the range of a factor of 7.9-10.0 for frontal exposure of the phantom. The dose reduction was strongly reduced when the head is turned to the side relative to the irradiated volume. The eye closest to the tube was better protected due to side shielding and eyewear curvature. In clinical practice, the mean dose reduction was a factor of 2.1. Using a ceiling suspended lead glass shield resulted in a mean dose reduction of a factor of 5.7. The efficacy of radiation protection glasses depends on the orientation of the operator's head relative to the irradiated volume. Glasses can offer good protection to the eye under clinically relevant conditions. However, the performance in clinical practice in our study was lower than expected. This is likely related to nonoptimized room geometry and training of the staff as well as measurement methodology.

Positron emission particle tracking using a modular positron camera

NASA Astrophysics Data System (ADS)

Parker, D. J.; Leadbeater, T. W.; Fan, X.; Hausard, M. N.; Ingram, A.; Yang, Z.

2009-06-01

The technique of positron emission particle tracking (PEPT), developed at Birmingham in the early 1990s, enables a radioactively labelled tracer particle to be accurately tracked as it moves between the detectors of a "positron camera". In 1999 the original Birmingham positron camera, which consisted of a pair of MWPCs, was replaced by a system comprising two NaI(Tl) gamma camera heads operating in coincidence. This system has been successfully used for PEPT studies of a wide range of granular and fluid flow processes. More recently a modular positron camera has been developed using a number of the bismuth germanate (BGO) block detectors from standard PET scanners (CTI ECAT 930 and 950 series). This camera has flexible geometry, is transportable, and is capable of delivering high data rates. This paper presents simple models of its performance, and initial experience of its use in a range of geometries and applications.

A differential game solution to the Coplanar tail-chase aerial combat problem

NASA Technical Reports Server (NTRS)

Merz, A. W.; Hague, D. S.

1976-01-01

Numerical results obtained in a simplified version of the one on one aerial combat problem are presented. The primary aim of the data is to specify the roles of pursuer and evader as functions of the relative geometry and of the significant physical parameters of the problem. Numerical results are given in a case in which the slower aircraft is more maneuverable than the faster aircraft. A third order dynamic model of the relative motion is described, for which the state variables are relative range, bearing, and heading. The ranges at termination are arbitary in the present version of the problem, so the weapon systems of both aircraft can be visualized as forward firing high velocity weapons, which must be aimed at the tail pipe of the evader. It was found that, for the great majority of the ralative geometries, each aircraft can evade the weapon system of the other.

Development and validation of a modified Hybrid-III six-year-old dummy model for simulating submarining in motor-vehicle crashes.

PubMed

Hu, Jingwen; Klinich, Kathleen D; Reed, Matthew P; Kokkolaras, Michael; Rupp, Jonathan D

2012-06-01

In motor-vehicle crashes, young school-aged children restrained by vehicle seat belt systems often suffer from abdominal injuries due to submarining. However, the current anthropomorphic test device, so-called "crash dummy", is not adequate for proper simulation of submarining. In this study, a modified Hybrid-III six-year-old dummy model capable of simulating and predicting submarining was developed using MADYMO (TNO Automotive Safety Solutions). The model incorporated improved pelvis and abdomen geometry and properties previously tested in a modified physical dummy. The model was calibrated and validated against four sled tests under two test conditions with and without submarining using a multi-objective optimization method. A sensitivity analysis using this validated child dummy model showed that dummy knee excursion, torso rotation angle, and the difference between head and knee excursions were good predictors for submarining status. It was also shown that restraint system design variables, such as lap belt angle, D-ring height, and seat coefficient of friction (COF), may have opposite effects on head and abdomen injury risks; therefore child dummies and dummy models capable of simulating submarining are crucial for future restraint system design optimization for young school-aged children. Copyright © 2011 IPEM. Published by Elsevier Ltd. All rights reserved.

TU-FG-209-09: Mathematical Estimation and Experimental Measurement of Patient Free-In-Air Skin Entrance Exposure During a Panoramic Dental X-Ray Procedure

DOE Office of Scientific and Technical Information (OSTI.GOV)

Errico, A; Behrman, R; Li, B

Purpose: To develop a simple mathematical model for estimating the patient free-in-air skin entrance exposure (SEE) during a panoramic dental x-ray that does not require the use of a head phantom. This eliminates issues associated with phantom centering and the mounting of a detector on the phantom for routine QC testing. Methods: We used a Sirona Orthophos XG panoramic radiographic unit and a Radcal Accu-Gold system for this study. A solid state detector was attached over the slit of the Orthophos’ sensor with the help of a custom-built jig. A single measurement of the free-in-air exposure at this position wasmore » taken over a full panoramic scan. A mathematical model for estimating the SEE was developed based upon this measurement, the system geometry, x-ray field beam width, and x-ray sweep angle. To validate the model, patient geometry was simulated by a 16 cm diameter PMMA CTDI phantom centered at the machine’s isocenter. Measurements taken on the phantom’s surface were made using a solid state detector with lead backing, an ion chamber, and the ion chamber with the phantom wrapped in lead to mitigate backscatter. Measurements were taken near the start position of the tube and at 90 degrees from the start position. Results: Using the solid state detector, the average SEE was 23.5+/−0.02 mR and 55.5+/−0.08 mR at 64 kVp and 73 kVp, respectively. With the lead-wrapping, the measurements from the ion chamber matched those of the solid state detector to within 0.1%. Preliminary results gave the difference between the mathematical model and the phantom measurements to be approximately 5% at both kVps. Conclusion: Reasonable estimates of patient SEE for panoramic dental radiography can be made using a simple mathematical model without the need for a head phantom.« less

Finite element analysis of mechanical behavior of human dysplastic hip joints: a systematic review.

PubMed

Vafaeian, B; Zonoobi, D; Mabee, M; Hareendranathan, A R; El-Rich, M; Adeeb, S; Jaremko, J L

2017-04-01

Developmental dysplasia of the hip (DDH) is a common condition predisposing to osteoarthritis (OA). Especially since DDH is best identified and treated in infancy before bones ossify, there is surprisingly a near-complete absence of literature examining mechanical behavior of infant dysplastic hips. We sought to identify current practice in finite element modeling (FEM) of DDH, to inform future modeling of infant dysplastic hips. We performed multi-database systematic review using PRISMA criteria. Abstracts (n = 126) fulfilling inclusion criteria were screened for methodological quality, and results were analyzed and summarized for eligible articles (n = 12). The majority of the studies modeled human adult dysplastic hips. Two studies focused on etiology of DDH through simulating mechanobiological growth of prenatal hips; we found no FEM-based studies in infants or children. Finite element models used either patient-specific geometry or idealized average geometry. Diversities in choice of material properties, boundary conditions, and loading scenarios were found in the finite-element models. FEM of adult dysplastic hips demonstrated generally smaller cartilage contact area in dysplastic hips than in normal joints. Contact pressure (CP) may be higher or lower in dysplastic hips depending on joint geometry and mechanical contribution of labrum (Lb). FEM of mechanobiological growth of prenatal hip joints revealed evidence for effects of the joint mechanical environment on formation of coxa valga, asymmetrically shallow acetabulum and malformed femoral head associated with DDH. Future modeling informed by the results of this review may yield valuable insights into optimal treatment of DDH, and into how and why OA develops early in DDH. Copyright © 2016 Osteoarthritis Research Society International. Published by Elsevier Ltd. All rights reserved.

The influence of sulcus width on simulated electric fields induced by transcranial magnetic stimulation

PubMed Central

Janssen, A M; Rampersad, S M; Lucka, F; Lanfer, B; Lew, S; Aydin, Ü; Wolters, C H; Stegeman, D F; Oostendorp, T F

2013-01-01

Volume conduction models can help in acquiring knowledge about the distribution of the electric field induced by transcranial magnetic stimulation (TMS). One aspect of a detailed model is an accurate description of the cortical surface geometry. Since its estimation is difficult, it is important to know how accurate the geometry has to be represented. Previous studies only looked at the differences caused by neglecting the complete boundary between the CSF and GM (Thielscher et al. 2011; Bijsterbosch et al. 2012), or by resizing the whole brain (Wagner et al. 2008). However, due to the high conductive properties of the CSF, it can be expected that alterations in sulcus width can already have a significant effect on the distribution of the electric field. To answer this question, the sulcus width of a highly realistic head model, based on T1-, T2- and diffusion-weighted magnetic resonance images (MRI), was altered systematically. This study shows that alterations in the sulcus width do not cause large differences in the majority of the electric field values. However, considerable overestimation of sulcus width produces an overestimation of the calculated field strength, also at locations distant from the target location. PMID:23787706

Marvin: an anatomical phantom for dosimetric evaluation of complex radiotherapy of the head and neck.

PubMed

Aitkenhead, A H; Rowbottom, C G; Mackay, R I

2013-10-07

We report on the design of Marvin, a Model Anatomy for Radiotherapy Verification and audit In the head and Neck and present results demonstrating its use in the development of the Elekta volumetric modulated arc therapy (VMAT) technique at the Christie, and in the audit of TomoTherapy and Varian RapidArc at other institutions. The geometry of Marvin was generated from CT datasets of eight male and female patients lying in the treatment position, with removable inhomogeneities modelling the sinuses and mandible. A modular system allows the phantom to be used with a range of detectors, with the locations of the modules being based on an analysis of a range of typical treatment plans (27 in total) which were mapped onto the phantom geometry. Results demonstrate the use of Gafchromic EBT2/EBT3 film for measurement of relative dose in a plane through the target and organs-at-risk, and the use of a small-volume ionization chamber for measurement of absolute dose in the target and spinal cord. Measurements made during the development of the head and neck VMAT protocol at the Christie quantified the improvement in plan delivery resulting from the installation of the Elekta Integrity upgrade (which permits an effectively continuously variable dose rate), with plans delivered before and after the upgrade having 88.5 ± 9.4% and 98.0 ± 2.2% respectively of points passing a gamma analysis (at 4%, 4 mm, global). Audits of TomoTherapy and Varian RapidArc neck techniques at other institutions showed a similar quality of plan delivery as for post-Integrity Elekta VMAT: film measurements for both techniques had >99% of points passing a gamma analysis at the clinical criteria of 4%, 4 mm, global, and >95% of points passing at tighter criteria of 3%, 3 mm, global; and absolute dose measurements in the PTV and spinal cord were within 1.5% and 3.5% of the planned doses respectively for both techniques. The results demonstrate that Marvin is an efficient and effective means of assessing the quality of delivery of complex radiotherapy in the head and neck, and is a useful tool to assist development and audit of these techniques.

Marvin: an anatomical phantom for dosimetric evaluation of complex radiotherapy of the head and neck

NASA Astrophysics Data System (ADS)

Aitkenhead, A. H.; Rowbottom, C. G.; Mackay, R. I.

2013-10-01

We report on the design of Marvin, a Model Anatomy for Radiotherapy Verification and audit In the head and Neck and present results demonstrating its use in the development of the Elekta volumetric modulated arc therapy (VMAT) technique at the Christie, and in the audit of TomoTherapy and Varian RapidArc at other institutions. The geometry of Marvin was generated from CT datasets of eight male and female patients lying in the treatment position, with removable inhomogeneities modelling the sinuses and mandible. A modular system allows the phantom to be used with a range of detectors, with the locations of the modules being based on an analysis of a range of typical treatment plans (27 in total) which were mapped onto the phantom geometry. Results demonstrate the use of Gafchromic EBT2/EBT3 film for measurement of relative dose in a plane through the target and organs-at-risk, and the use of a small-volume ionization chamber for measurement of absolute dose in the target and spinal cord. Measurements made during the development of the head and neck VMAT protocol at the Christie quantified the improvement in plan delivery resulting from the installation of the Elekta Integrity upgrade (which permits an effectively continuously variable dose rate), with plans delivered before and after the upgrade having 88.5 ± 9.4% and 98.0 ± 2.2% respectively of points passing a gamma analysis (at 4%, 4 mm, global). Audits of TomoTherapy and Varian RapidArc neck techniques at other institutions showed a similar quality of plan delivery as for post-Integrity Elekta VMAT: film measurements for both techniques had >99% of points passing a gamma analysis at the clinical criteria of 4%, 4 mm, global, and >95% of points passing at tighter criteria of 3%, 3 mm, global; and absolute dose measurements in the PTV and spinal cord were within 1.5% and 3.5% of the planned doses respectively for both techniques. The results demonstrate that Marvin is an efficient and effective means of assessing the quality of delivery of complex radiotherapy in the head and neck, and is a useful tool to assist development and audit of these techniques.

Predicting objective function weights from patient anatomy in prostate IMRT treatment planning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Taewoo, E-mail: taewoo.lee@utoronto.ca; Hammad, Muhannad; Chan, Timothy C. Y.

2013-12-15

Purpose: Intensity-modulated radiation therapy (IMRT) treatment planning typically combines multiple criteria into a single objective function by taking a weighted sum. The authors propose a statistical model that predicts objective function weights from patient anatomy for prostate IMRT treatment planning. This study provides a proof of concept for geometry-driven weight determination. Methods: A previously developed inverse optimization method (IOM) was used to generate optimal objective function weights for 24 patients using their historical treatment plans (i.e., dose distributions). These IOM weights were around 1% for each of the femoral heads, while bladder and rectum weights varied greatly between patients. Amore » regression model was developed to predict a patient's rectum weight using the ratio of the overlap volume of the rectum and bladder with the planning target volume at a 1 cm expansion as the independent variable. The femoral head weights were fixed to 1% each and the bladder weight was calculated as one minus the rectum and femoral head weights. The model was validated using leave-one-out cross validation. Objective values and dose distributions generated through inverse planning using the predicted weights were compared to those generated using the original IOM weights, as well as an average of the IOM weights across all patients. Results: The IOM weight vectors were on average six times closer to the predicted weight vectors than to the average weight vector, usingl{sub 2} distance. Likewise, the bladder and rectum objective values achieved by the predicted weights were more similar to the objective values achieved by the IOM weights. The difference in objective value performance between the predicted and average weights was statistically significant according to a one-sided sign test. For all patients, the difference in rectum V54.3 Gy, rectum V70.0 Gy, bladder V54.3 Gy, and bladder V70.0 Gy values between the dose distributions generated by the predicted weights and IOM weights was less than 5 percentage points. Similarly, the difference in femoral head V54.3 Gy values between the two dose distributions was less than 5 percentage points for all but one patient. Conclusions: This study demonstrates a proof of concept that patient anatomy can be used to predict appropriate objective function weights for treatment planning. In the long term, such geometry-driven weights may serve as a starting point for iterative treatment plan design or may provide information about the most clinically relevant region of the Pareto surface to explore.« less

Predicting objective function weights from patient anatomy in prostate IMRT treatment planning

DOE Office of Scientific and Technical Information (OSTI.GOV)

Lee, Taewoo, E-mail: taewoo.lee@utoronto.ca; Hammad, Muhannad; Chan, Timothy C. Y.

Purpose: Intensity-modulated radiation therapy (IMRT) treatment planning typically combines multiple criteria into a single objective function by taking a weighted sum. The authors propose a statistical model that predicts objective function weights from patient anatomy for prostate IMRT treatment planning. This study provides a proof of concept for geometry-driven weight determination. Methods: A previously developed inverse optimization method (IOM) was used to generate optimal objective function weights for 24 patients using their historical treatment plans (i.e., dose distributions). These IOM weights were around 1% for each of the femoral heads, while bladder and rectum weights varied greatly between patients. Amore » regression model was developed to predict a patient's rectum weight using the ratio of the overlap volume of the rectum and bladder with the planning target volume at a 1 cm expansion as the independent variable. The femoral head weights were fixed to 1% each and the bladder weight was calculated as one minus the rectum and femoral head weights. The model was validated using leave-one-out cross validation. Objective values and dose distributions generated through inverse planning using the predicted weights were compared to those generated using the original IOM weights, as well as an average of the IOM weights across all patients. Results: The IOM weight vectors were on average six times closer to the predicted weight vectors than to the average weight vector, usingl{sub 2} distance. Likewise, the bladder and rectum objective values achieved by the predicted weights were more similar to the objective values achieved by the IOM weights. The difference in objective value performance between the predicted and average weights was statistically significant according to a one-sided sign test. For all patients, the difference in rectum V54.3 Gy, rectum V70.0 Gy, bladder V54.3 Gy, and bladder V70.0 Gy values between the dose distributions generated by the predicted weights and IOM weights was less than 5 percentage points. Similarly, the difference in femoral head V54.3 Gy values between the two dose distributions was less than 5 percentage points for all but one patient. Conclusions: This study demonstrates a proof of concept that patient anatomy can be used to predict appropriate objective function weights for treatment planning. In the long term, such geometry-driven weights may serve as a starting point for iterative treatment plan design or may provide information about the most clinically relevant region of the Pareto surface to explore.« less

DOE Office of Scientific and Technical Information (OSTI.GOV)

Jadidian, Jouya; Zahn, Markus; Lavesson, Nils

Streamer branching in liquid dielectrics is driven by stochastic and deterministic factors. The presence of stochastic causes of streamer branching such as inhomogeneities inherited from noisy initial states, impurities, or charge carrier density fluctuations is inevitable in any dielectric. A fully three-dimensional streamer model presented in this paper indicates that deterministic origins of branching are intrinsic attributes of streamers, which in some cases make the branching inevitable depending on shape and velocity of the volume charge at the streamer frontier. Specifically, any given inhomogeneous perturbation can result in streamer branching if the volume charge layer at the original streamer headmore » is relatively thin and slow enough. Furthermore, discrete nature of electrons at the leading edge of an ionization front always guarantees the existence of a non-zero inhomogeneous perturbation ahead of the streamer head propagating even in perfectly homogeneous dielectric. Based on the modeling results for streamers propagating in a liquid dielectric, a gauge on the streamer head geometry is introduced that determines whether the branching occurs under particular inhomogeneous circumstances. Estimated number, diameter, and velocity of the born branches agree qualitatively with experimental images of the streamer branching.« less

Quadruple Cone Coil with improved focality than Figure-8 coil in Transcranial Magnetic Stimulation

NASA Astrophysics Data System (ADS)

Rastogi, Priyam; Lee, Erik G.; Hadimani, Ravi L.; Jiles, David C.

Transcranial Magnetic Stimulation (TMS) is a non-invasive therapy which uses a time varying magnetic field to induce an electric field in the brain and to cause neuron depolarization. Magnetic coils play an important role in the TMS therapy since their coil geometry determines the focality and penetration's depth of the induced electric field in the brain. Quadruple Cone Coil (QCC) is a novel coil with an improved focality when compared to commercial Figure-8 coil. The results of this newly designed QCC coil are compared with the Figure-8 coil at two different positions of the head - vertex and dorsolateral prefrontal cortex, over the 50 anatomically realistic MRI derived head models. Parameters such as volume of stimulation, maximum electric, area of stimulation and location of maximum electric field are determined with the help of computer modelling of both coils. There is a decrease in volume of brain stimulated by 11.6 % and a modest improvement of 8 % in the location of maximum electric field due to QCC in comparison to the Figure-8 coil. The Carver Charitable Trust and The Galloway Foundation.

Transcranial Magnetic Stimulation-coil design with improved focality

NASA Astrophysics Data System (ADS)

Rastogi, P.; Lee, E. G.; Hadimani, R. L.; Jiles, D. C.

2017-05-01

Transcranial Magnetic Stimulation (TMS) is a technique for neuromodulation that can be used as a non-invasive therapy for various neurological disorders. In TMS, a time varying magnetic field generated from an electromagnetic coil placed on the scalp is used to induce an electric field inside the brain. TMS coil geometry plays an important role in determining the focality and depth of penetration of the induced electric field responsible for stimulation. Clinicians and basic scientists are interested in stimulating a localized area of the brain, while minimizing the stimulation of surrounding neural networks. In this paper, a novel coil has been proposed, namely Quadruple Butterfly Coil (QBC) with an improved focality over the commercial Figure-8 coil. Finite element simulations were conducted with both the QBC and the conventional Figure-8 coil. The two coil's stimulation profiles were assessed with 50 anatomically realistic MRI derived head models. The coils were positioned on the vertex and the scalp over the dorsolateral prefrontal cortex to stimulate the brain. Computer modeling of the coils has been done to determine the parameters of interest-volume of stimulation, maximum electric field, location of maximum electric field and area of stimulation across all 50 head models for both coils.

Modeling and simulation of blast-induced, early-time intracranial wave physics leading to traumatic brain injury.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Ford, Corey C.; Taylor, Paul Allen

The objective of this modeling and simulation study was to establish the role of stress wave interactions in the genesis of traumatic brain injury (TBI) from exposure to explosive blast. A high resolution (1 mm{sup 3} voxels), 5 material model of the human head was created by segmentation of color cryosections from the Visible Human Female dataset. Tissue material properties were assigned from literature values. The model was inserted into the shock physics wave code, CTH, and subjected to a simulated blast wave of 1.3 MPa (13 bars) peak pressure from anterior, posterior and lateral directions. Three dimensional plots ofmore » maximum pressure, volumetric tension, and deviatoric (shear) stress demonstrated significant differences related to the incident blast geometry. In particular, the calculations revealed focal brain regions of elevated pressure and deviatoric (shear) stress within the first 2 milliseconds of blast exposure. Calculated maximum levels of 15 KPa deviatoric, 3.3 MPa pressure, and 0.8 MPa volumetric tension were observed before the onset of significant head accelerations. Over a 2 msec time course, the head model moved only 1 mm in response to the blast loading. Doubling the blast strength changed the resulting intracranial stress magnitudes but not their distribution. We conclude that stress localization, due to early time wave interactions, may contribute to the development of multifocal axonal injury underlying TBI. We propose that a contribution to traumatic brain injury from blast exposure, and most likely blunt impact, can occur on a time scale shorter than previous model predictions and before the onset of linear or rotational accelerations traditionally associated with the development of TBI.« less

Modeling and design of a cone-beam CT head scanner using task-based imaging performance optimization

NASA Astrophysics Data System (ADS)

Xu, J.; Sisniega, A.; Zbijewski, W.; Dang, H.; Stayman, J. W.; Wang, X.; Foos, D. H.; Aygun, N.; Koliatsos, V. E.; Siewerdsen, J. H.

2016-04-01

Detection of acute intracranial hemorrhage (ICH) is important for diagnosis and treatment of traumatic brain injury, stroke, postoperative bleeding, and other head and neck injuries. This paper details the design and development of a cone-beam CT (CBCT) system developed specifically for the detection of low-contrast ICH in a form suitable for application at the point of care. Recognizing such a low-contrast imaging task to be a major challenge in CBCT, the system design began with a rigorous analysis of task-based detectability including critical aspects of system geometry, hardware configuration, and artifact correction. The imaging performance model described the three-dimensional (3D) noise-equivalent quanta using a cascaded systems model that included the effects of scatter, scatter correction, hardware considerations of complementary metal-oxide semiconductor (CMOS) and flat-panel detectors (FPDs), and digitization bit depth. The performance was analyzed with respect to a low-contrast (40-80 HU), medium-frequency task representing acute ICH detection. The task-based detectability index was computed using a non-prewhitening observer model. The optimization was performed with respect to four major design considerations: (1) system geometry (including source-to-detector distance (SDD) and source-to-axis distance (SAD)); (2) factors related to the x-ray source (including focal spot size, kVp, dose, and tube power); (3) scatter correction and selection of an antiscatter grid; and (4) x-ray detector configuration (including pixel size, additive electronics noise, field of view (FOV), and frame rate, including both CMOS and a-Si:H FPDs). Optimal design choices were also considered with respect to practical constraints and available hardware components. The model was verified in comparison to measurements on a CBCT imaging bench as a function of the numerous design parameters mentioned above. An extended geometry (SAD  =  750 mm, SDD  =  1100 mm) was found to be advantageous in terms of patient dose (20 mGy) and scatter reduction, while a more isocentric configuration (SAD  =  550 mm, SDD  =  1000 mm) was found to give a more compact and mechanically favorable configuration with minor tradeoff in detectability. An x-ray source with a 0.6 mm focal spot size provided the best compromise between spatial resolution requirements and x-ray tube power. Use of a modest anti-scatter grid (8:1 GR) at a 20 mGy dose provided slight improvement (~5-10%) in the detectability index, but the benefit was lost at reduced dose. The potential advantages of CMOS detectors over FPDs were quantified, showing that both detectors provided sufficient spatial resolution for ICH detection, while the former provided a potentially superior low-dose performance, and the latter provided the requisite FOV for volumetric imaging in a centered-detector geometry. Task-based imaging performance modeling provides an important starting point for CBCT system design, especially for the challenging task of ICH detection, which is somewhat beyond the capabilities of existing CBCT platforms. The model identifies important tradeoffs in system geometry and hardware configuration, and it supports the development of a dedicated CBCT system for point-of-care application. A prototype suitable for clinical studies is in development based on this analysis.

Automatic Fontanel Extraction from Newborns' CT Images Using Variational Level Set

NASA Astrophysics Data System (ADS)

Kazemi, Kamran; Ghadimi, Sona; Lyaghat, Alireza; Tarighati, Alla; Golshaeyan, Narjes; Abrishami-Moghaddam, Hamid; Grebe, Reinhard; Gondary-Jouet, Catherine; Wallois, Fabrice

A realistic head model is needed for source localization methods used for the study of epilepsy in neonates applying Electroencephalographic (EEG) measurements from the scalp. The earliest models consider the head as a series of concentric spheres, each layer corresponding to a different tissue whose conductivity is assumed to be homogeneous. The results of the source reconstruction depend highly on the electric conductivities of the tissues forming the head.The most used model is constituted of three layers (scalp, skull, and intracranial). Most of the major bones of the neonates’ skull are ossified at birth but can slightly move relative to each other. This is due to the sutures, fibrous membranes that at this stage of development connect the already ossified flat bones of the neurocranium. These weak parts of the neurocranium are called fontanels. Thus it is important to enter the exact geometry of fontaneles and flat bone in a source reconstruction because they show pronounced in conductivity. Computer Tomography (CT) imaging provides an excellent tool for non-invasive investigation of the skull which expresses itself in high contrast to all other tissues while the fontanels only can be identified as absence of bone, gaps in the skull formed by flat bone. Therefore, the aim of this paper is to extract the fontanels from CT images applying a variational level set method. We applied the proposed method to CT-images of five different subjects. The automatically extracted fontanels show good agreement with the manually extracted ones.

SU-E-J-11: Measurement of Eye Lens Dose for Varian On-Board Imaging with Different CBCT Acquisition Techniques

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deshpande, S; Dhote, D; Kumar, R

Purpose: To measure actual patient eye lens dose for different cone beam computed tomography (CBCT) acquisition protocol of Varian’s On Board Imagining (OBI) system using Optically Stimulated Luminescence (OSL) dosimeter and study the eye lens dose with patient geometry and distance of isocenter to the eye lens Methods: OSL dosimeter was used to measure eye lens dose of patient. OSL dosimeter was placed on patient forehead center during CBCT image acquisition to measure eye lens dose. For three different cone beam acquisition protocol (standard dose head, low dose head and high quality head) of Varian On-Board Imaging, eye lens dosesmore » were measured. Measured doses were correlated with patient geometry and distance between isocenter to eye lens. Results: Measured eye lens dose for standard dose head was in the range of 1.8 mGy to 3.2 mGy, for high quality head protocol dose was in range of 4.5mGy to 9.9 mGy whereas for low dose head was in the range of 0.3mGy to 0.7mGy. Dose to eye lens is depends upon position of isocenter. For posterioraly located tumor eye lens dose is less. Conclusion: From measured doses it can be concluded that by proper selection of imagining protocol and frequency of imaging, it is possible to restrict the eye lens dose below the new limit set by ICRP. However, undoubted advantages of imaging system should be counter balanced by careful consideration of imaging protocol especially for very intense imaging sequences for Adoptive Radiotherapy or IMRT.« less

Gravity-Driven Hydraulic Fractures

NASA Astrophysics Data System (ADS)

Germanovich, L. N.; Garagash, D.; Murdoch, L. C.; Robinowitz, M.

2014-12-01

This study is motived by a new method for disposing of nuclear waste by injecting it as a dense slurry into a hydraulic fracture that grows downward to great enough depth to permanently isolate the waste. Disposing of nuclear waste using gravity-driven hydraulic fractures is mechanically similar to the upward growth of dikes filled with low density magma. A fundamental question in both applications is how the injected fluid controls the propagation dynamics and fracture geometry (depth and breadth) in three dimensions. Analog experiments in gelatin [e.g., Heimpel and Olson, 1994; Taisne and Tait, 2009] show that fracture breadth (the short horizontal dimension) remains nearly stationary when the process in the fracture "head" (where breadth is controlled) is dominated by solid toughness, whereas viscous fluid dissipation is dominant in the fracture tail. We model propagation of the resulting gravity-driven (buoyant or sinking), finger-like fracture of stationary breadth with slowly varying opening along the crack length. The elastic response to fluid loading in a horizontal cross-section is local and can be treated similar to the classical Perkins-Kern-Nordgren (PKN) model of hydraulic fracturing. The propagation condition for a finger-like crack is based on balancing the global energy release rate due to a unit crack extension with the rock fracture toughness. It allows us to relate the net fluid pressure at the tip to the fracture breadth and rock toughness. Unlike the PKN fracture, where breadth is known a priori, the final breadth of a finger-like fracture is a result of processes in the fracture head. Because the head is much more open than the tail, viscous pressure drop in the head can be neglected leading to a 3D analog of Weertman's hydrostatic pulse. This requires relaxing the local elasticity assumption of the PKN model in the fracture head. As a result, we resolve the breadth, and then match the viscosity-dominated tail with the 3-D, toughness-dominated head to obtain a complete closed-form solution. We then analyze the gravity fracture propagation in conditions of either continuous injection or finite volume release for sets of parameters representative of dense waste injection technique and low viscosity magma diking.

Reassessment of the Necessity of the Proton Gantry: Analysis of Beam Orientations From 4332 Treatments at the Massachusetts General Hospital Proton Center Over the Past 10 Years

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yan, Susu, E-mail: syan5@mgh.harvard.edu; Lu, Hsiao-Ming; Flanz, Jay

2016-05-01

Purpose: To retrospectively analyze the beam approaches used in gantry-based proton treatments, and to reassess the practical advantages of the gantry, compared with beam approaches that are achievable without a gantry, in the context of present-day technology. Methods and Materials: We reviewed the proton therapy plans of 4332 patients treated on gantries at our hospital, delivered by the double scattering technique (n=4228) and, more recently, pencil beam scanning (PBS) (n=104). Beam approaches, relative to the patient frame, were analyzed individually to identify cases that could be treated without a gantry. Three treatment configurations were considered, with the patient in lying position,more » sitting position, or both. The FIXED geometry includes a fixed horizontal portal. The BEND geometry enables a limited vertical inflection of the beam by up to 20°. The MOVE geometry allows for flexibility of the patient head and body setup. Results: The percentage of patients with head and neck tumors that could be treated without a gantry using double scattering was 44% in FIXED, 70% in 20° BEND, and 100% in 90° MOVE. For torso regions, 99% of patients could be treated in 20° BEND. Of 104 PBS treatments, all but 1 could be reproduced with FIXED geometry. The only exception would require a 10° BEND capability. Note here that the PBS treatments were applied to select anatomic sites, including only 2 patients with skull-base tumors. Conclusions: The majority of practical beam approaches can be realized with gantry-less delivery, aided by limited beam bending and patient movements. Practical limitations of the MOVE geometry, and treatments requiring a combination of lying and sitting positions, may lower the percentage of head and neck patients who could be treated without a gantry. Further investigation into planning, immobilization, and imaging is needed to remove the practical limitations and to facilitate proton treatment without a gantry.« less

Accounting for intracell flow in models with emphasis on water table recharge and stream-aquifer interaction: 1. Problems and concepts

USGS Publications Warehouse

Jorgensen, Donald G.; Signor, Donald C.; Imes, Jeffrey L.

1989-01-01

Intracell flow is important in modeling cells that contain both sources and sinks. Special attention is needed if recharge through the water table is a source. One method of modeling multiple sources and sinks is to determine the net recharge per cell. For example, for a model cell containing both a sink and recharge through the water table, the amount of recharge should be reduced by the ratio of the area of influence of the sink within the cell to the area of the cell. The reduction is the intercepted portion of the recharge. In a multilayer model this amount is further reduced by a proportion factor, which is a function of the depth of the flow lines from the water table boundary to the internal sink. A gaining section of a stream is a typical sink. The aquifer contribution to a gaining stream can be conceptualized as having two parts; the first part is the intercepted lateral flow from the water table and the second is the flow across the streambed due to differences in head between the water level in the stream and the aquifer below. The amount intercepted is a function of the geometry of the cell, but the amount due to difference in head across the stream bed is largely independent of cell geometry. A discharging well can intercept recharge through the water table within a model cell. The net recharge to the cell would be reduced in proportion to the area of influence of the well within the cell. The area of influence generally changes with time. Thus the amount of intercepted recharge and net recharge may not be constant with time. During periods when the well is not discharging there will be no intercepted recharge even though the area of influence from previous pumping may still exist. The reduction of net recharge per cell due to internal interception of flow will result in a model-calculated mass balance less than the prototype. Additionally the “effective transmissivity” along the intercell flow paths may be altered when flow paths are occupied by intercepted recharge.

Influence of anisotropic conductivity in the skull and white matter on transcranial direct current stimulation via an anatomically realistic finite element head model

NASA Astrophysics Data System (ADS)

Suh, Hyun Sang; Lee, Won Hee; Kim, Tae-Seong

2012-11-01

To establish safe and efficient transcranial direct current stimulation (tDCS), it is of particular importance to understand the electrical effects of tDCS in the brain. Since the current density (CD) and electric field (EF) in the brain generated by tDCS depend on various factors including complex head geometries and electrical tissue properties, in this work, we investigated the influence of anisotropic conductivity in the skull and white matter (WM) on tDCS via a 3D anatomically realistic finite element head model. We systematically incorporated various anisotropic conductivity ratios into the skull and WM. The effects of anisotropic tissue conductivity on the CD and EF were subsequently assessed through comparisons to the conventional isotropic solutions. Our results show that the anisotropic skull conductivity significantly affects the CD and EF distribution: there is a significant reduction in the ratio of the target versus non-target total CD and EF on the order of 12-14%. In contrast, the WM anisotropy does not significantly influence the CD and EF on the targeted cortical surface, only on the order of 1-3%. However, the WM anisotropy highly alters the spatial distribution of both the CD and EF inside the brain. This study shows that it is critical to incorporate anisotropic conductivities in planning of tDCS for improved efficacy and safety.

Conebeam CT of the head and neck, part 1: physical principles.

PubMed

Miracle, A C; Mukherji, S K

2009-06-01

Conebeam x-ray CT (CBCT) is a developing imaging technique designed to provide relatively low-dose high-spatial-resolution visualization of high-contrast structures in the head and neck and other anatomic areas. This first installment in a 2-part review will address the physical principles underlying CBCT imaging as it is used in dedicated head and neck scanners. Concepts related to CBCT acquisition geometry, flat panel detection, and image quality will be explored in detail. Particular emphasis will be placed on technical limitations to low-contrast detectability and radiation dose. Proposed methods of x-ray scatter reduction will also be discussed.

Simulation of blast-induced early-time intracranial wave physics leading to traumatic brain injury.

PubMed

Taylor, Paul A; Ford, Corey C

2009-06-01

The objective of this modeling and simulation study was to establish the role of stress wave interactions in the genesis of traumatic brain injury (TBI) from exposure to explosive blast. A high resolution (1 mm3 voxels) five material model of the human head was created by segmentation of color cryosections from the Visible Human Female data set. Tissue material properties were assigned from literature values. The model was inserted into the shock physics wave code, CTH, and subjected to a simulated blast wave of 1.3 MPa (13 bars) peak pressure from anterior, posterior, and lateral directions. Three-dimensional plots of maximum pressure, volumetric tension, and deviatoric (shear) stress demonstrated significant differences related to the incident blast geometry. In particular, the calculations revealed focal brain regions of elevated pressure and deviatoric stress within the first 2 ms of blast exposure. Calculated maximum levels of 15 KPa deviatoric, 3.3 MPa pressure, and 0.8 MPa volumetric tension were observed before the onset of significant head accelerations. Over a 2 ms time course, the head model moved only 1 mm in response to the blast loading. Doubling the blast strength changed the resulting intracranial stress magnitudes but not their distribution. We conclude that stress localization, due to early-time wave interactions, may contribute to the development of multifocal axonal injury underlying TBI. We propose that a contribution to traumatic brain injury from blast exposure, and most likely blunt impact, can occur on a time scale shorter than previous model predictions and before the onset of linear or rotational accelerations traditionally associated with the development of TBI.

Now you see me, now you don't: iridescence increases the efficacy of lizard chromatic signals

NASA Astrophysics Data System (ADS)

Pérez i de Lanuza, Guillem; Font, Enrique

2014-10-01

The selective forces imposed by primary receivers and unintended eavesdroppers of animal signals often act in opposite directions, constraining the development of conspicuous coloration. Because iridescent colours change their chromatic properties with viewer angle, iridescence offers a potential mechanism to relax this trade-off when the relevant observers involved in the evolution of signal design adopt different viewer geometries. We used reflectance spectrophotometry and visual modelling to test if the striking blue head coloration of males of the lizard Lacerta schreibeiri (1) is iridescent and (2) is more conspicuous when viewed from the perspective of conspecifics than from that of the main predators of adult L. schreibeiri (raptors). We demonstrate that the blue heads of L. schreiberi show angle-dependent changes in their chromatic properties. This variation allows the blue heads to be relatively conspicuous to conspecific viewers located in the same horizontal plane as the sender, while simultaneously being relatively cryptic to birds that see it from above. This study is the first to suggest the use of angle-dependent chromatic signals in lizards, and provides the first evidence of the adaptive function of iridescent coloration based on its detectability to different observers.

Optimizing the performance of a solar liquid piston pump

NASA Astrophysics Data System (ADS)

Murphy, C. L.

Utilization of solar energy for pumping water for irrigation or storage is discussed. Oscillations of a Freon 113 liquid column are generated in a working tube when a continuous flow of hot water, and cooling water, are supplied to heated and cooling coils located in the tube. The oscillations are converted into a pump (SLPP) model exhibited self starting, stable operation over a wide range of conditions, provides the inlet hot water heat source and inlet cooling water heat sink are above and below the critical values for stalling at a given pump head. The operation of the SLPP model, is primarily affected by the heating coil position within the working tube, and the geometries of the inlet and outlet water tubes.

A new head phantom with realistic shape and spatially varying skull resistivity distribution.

PubMed

Li, Jian-Bo; Tang, Chi; Dai, Meng; Liu, Geng; Shi, Xue-Tao; Yang, Bin; Xu, Can-Hua; Fu, Feng; You, Fu-Sheng; Tang, Meng-Xing; Dong, Xiu-Zhen

2014-02-01

Brain electrical impedance tomography (EIT) is an emerging method for monitoring brain injuries. To effectively evaluate brain EIT systems and reconstruction algorithms, we have developed a novel head phantom that features realistic anatomy and spatially varying skull resistivity. The head phantom was created with three layers, representing scalp, skull, and brain tissues. The fabrication process entailed 3-D printing of the anatomical geometry for mold creation followed by casting to ensure high geometrical precision and accuracy of the resistivity distribution. We evaluated the accuracy and stability of the phantom. Results showed that the head phantom achieved high geometric accuracy, accurate skull resistivity values, and good stability over time and in the frequency domain. Experimental impedance reconstructions performed using the head phantom and computer simulations were found to be consistent for the same perturbation object. In conclusion, this new phantom could provide a more accurate test platform for brain EIT research.

3D reconstruction and spatial auralization of the "Painted Dolmen" of Antelas

NASA Astrophysics Data System (ADS)

Dias, Paulo; Campos, Guilherme; Santos, Vítor; Casaleiro, Ricardo; Seco, Ricardo; Sousa Santos, Beatriz

2008-02-01

This paper presents preliminary results on the development of a 3D audiovisual model of the Anta Pintada (painted dolmen) of Antelas, a Neolithic chamber tomb located in Oliveira de Frades and listed as Portuguese national monument. The final aim of the project is to create a highly accurate Virtual Reality (VR) model of this unique archaeological site, capable of providing not only visual but also acoustic immersion based on its actual geometry and physical properties. The project started in May 2006 with in situ data acquisition. The 3D geometry of the chamber was captured using a Laser Range Finder. In order to combine the different scans into a complete 3D visual model, reconstruction software based on the Iterative Closest Point (ICP) algorithm was developed using the Visualization Toolkit (VTK). This software computes the boundaries of the room on a 3D uniform grid and populates its interior with "free-space nodes", through an iterative algorithm operating like a torchlight illuminating a dark room. The envelope of the resulting set of "free-space nodes" is used to generate a 3D iso-surface approximating the interior shape of the chamber. Each polygon of this surface is then assigned the acoustic absorption coefficient of the corresponding boundary material. A 3D audiovisual model operating in real-time was developed for a VR Environment comprising head-mounted display (HMD) I-glasses SVGAPro, an orientation sensor (tracker) InterTrax 2 with 3 Degrees Of Freedom (3DOF) and stereo headphones. The auralisation software is based on a geometric model. This constitutes a first approach, since geometric acoustics have well-known limitations in rooms with irregular surfaces. The immediate advantage lies in their inherent computational efficiency, which allows real-time operation. The program computes the early reflections forming the initial part of the chamber's impulse response (IR), which carry the most significant cues for source localisation. These early reflections are processed through Head Related Transfer Functions (HRTF) updated in real-time according to the orientation of the user's head, so that sound waves appear to come from the correct location in space, in agreement with the visual scene. The late-reverberation tail of the IR is generated by an algorithm designed to match the reverberation time of the chamber, calculated from the actual acoustic absorption coefficients of its surfaces. The sound output to the headphones is obtained by convolving the IR with anechoic recordings of the virtual audio source.

Linac head scatter factor for asymmetric radiation field

NASA Astrophysics Data System (ADS)

Soubra, Mazen Ahmed

1997-11-01

The head scatter factor, Sh is an important dosimetric quantity used in radiation therapy dose calculation. It is empirically determined and its field size dependence reflects changes in photon scatter from components in the linac treatment head. In this work a detailed study of the physical factors influencing the determination of Sh was performed with particular attention given to asymmetric field geometries. Ionization measurements for 6 and 18 MV photon beams were made to examine the factors which determine Sh. These include: phantom size and material, collimator backscatter, non-lateral electronic equilibrium (LEE) conditions, electron contamination, collimator-exchange, photon energy, flattening filter and off-axis distance (OAD). Results indicated that LEE is not required for Sh measurements if electron contamination is minimized. Brass caps or polystyrene miniphantoms can both be used in Sh measurements provided the phantom thickness is large enough to stop contaminant electrons. Backscatter radiation effects into the monitor chamber were found to be negligible for the Siemens linac. It was found that the presence and shape of the flattening filter had a significant effect on the empirically determined value of Sh was also shown to be a function of OAD, particularly for small fields. For fields larger than 12×12 cm2/ Sh was independent of OAD. A flattening filter mass model was introduced to explain qualitatively the above results. A detailed Monte Carlo simulation of the Siemens KD2 linac head in 6 MV mode was performed to investigate the sources of head scatter which contribute to the measured Sh. The simulated head components include the flattening filter, the electron beam stopper, the primary collimator, the photon monitor chamber and the secondary collimators. The simulations showed that the scatter from the head of the Siemens linac is a complex function of the head components. On the central axis the flattening filter played the dominant role in the contributing to scatter. However this role was significantly reduced off- axis and other head components, such as the electron beam stopper and the primary collimator, became more important. The role of the mirror and ion chamber was relatively minor. Scatter from the secondary collimators was shown to be a function of the filed size and the position of the collimators in the treatment head. They were also found to play a dual role, both as a scatter source and as an attenuator for scatter produced upstream in the linac head. A closed form model, based on the work of Yu and Slobada, was developed to estimate head scatter factors for on- and off-axis asymmetric fields. The model requires three parameters to fit the measured data. The first, a constant c, has a physical significance and is independent of energy and off-axis distance. The second, g, shows a small variation with the energy and OAD while the third parameter, the primary-to-scatter ratio, is strongly dependent on energy and off-axis distance. Comparison of Sh, predicted by the model, to measurement for a large range of symmetric and asymmetric fields showed excellent agreement. A maximum of 0.7% discrepancy was observed at 12 cm OAD.

Kinematic behavior of the human body during deceleration.

DOT National Transportation Integrated Search

1962-06-01

The geometry of motion of the head, trunk and appendages was established for one hundred male subjects restrained by a safety belt during forward and side dynamic loadings. Lethal structures of present aircraft seating and cockpit arrangements are re...

Impact of extraneous mispositioned events on motion-corrected brain SPECT images of freely moving animals

DOE Office of Scientific and Technical Information (OSTI.GOV)

Angelis, Georgios I., E-mail: georgios.angelis@sydney.edu.au; Ryder, William J.; Bashar, Rezaul

Purpose: Single photon emission computed tomography (SPECT) brain imaging of freely moving small animals would allow a wide range of important neurological processes and behaviors to be studied, which are normally inhibited by anesthetic drugs or precluded due to the animal being restrained. While rigid body motion of the head can be tracked and accounted for in the reconstruction, activity in the torso may confound brain measurements, especially since motion of the torso is more complex (i.e., nonrigid) and not well correlated with that of the head. The authors investigated the impact of mispositioned events and attenuation due to themore » torso on the accuracy of motion corrected brain images of freely moving mice. Methods: Monte Carlo simulations of a realistic voxelized mouse phantom and a dual compartment phantom were performed. Each phantom comprised a target and an extraneous compartment which were able to move independently of each other. Motion correction was performed based on the known motion of the target compartment only. Two SPECT camera geometries were investigated: a rotating single head detector and a stationary full ring detector. The effects of motion, detector geometry, and energy of the emitted photons (hence, attenuation) on bias and noise in reconstructed brain regions were evaluated. Results: The authors observed two main sources of bias: (a) motion-related inconsistencies in the projection data and (b) the mismatch between attenuation and emission. Both effects are caused by the assumption that the orientation of the torso is difficult to track and model, and therefore cannot be conveniently corrected for. The motion induced bias in some regions was up to 12% when no attenuation effects were considered, while it reached 40% when also combined with attenuation related inconsistencies. The detector geometry (i.e., rotating vs full ring) has a big impact on the accuracy of the reconstructed images, with the full ring detector being more advantageous. Conclusions: Motion-induced inconsistencies in the projection data and attenuation/emission mismatch are the two main causes of bias in reconstructed brain images when there is complex motion. It appears that these two factors have a synergistic effect on the qualitative and quantitative accuracy of the reconstructed images.« less

The influence of sulcus width on simulated electric fields induced by transcranial magnetic stimulation

NASA Astrophysics Data System (ADS)

Janssen, A. M.; Rampersad, S. M.; Lucka, F.; Lanfer, B.; Lew, S.; Aydin, Ü.; Wolters, C. H.; Stegeman, D. F.; Oostendorp, T. F.

2013-07-01

Volume conduction models can help in acquiring knowledge about the distribution of the electric field induced by transcranial magnetic stimulation. One aspect of a detailed model is an accurate description of the cortical surface geometry. Since its estimation is difficult, it is important to know how accurate the geometry has to be represented. Previous studies only looked at the differences caused by neglecting the complete boundary between cerebrospinal fluid (CSF) and grey matter (Thielscher et al 2011 NeuroImage 54 234-43, Bijsterbosch et al 2012 Med. Biol. Eng. Comput. 50 671-81), or by resizing the whole brain (Wagner et al 2008 Exp. Brain Res. 186 539-50). However, due to the high conductive properties of the CSF, it can be expected that alterations in sulcus width can already have a significant effect on the distribution of the electric field. To answer this question, the sulcus width of a highly realistic head model, based on T1-, T2- and diffusion-weighted magnetic resonance images, was altered systematically. This study shows that alterations in the sulcus width do not cause large differences in the majority of the electric field values. However, considerable overestimation of sulcus width produces an overestimation of the calculated field strength, also at locations distant from the target location.

Gender Differences in Hip Anatomy: Possible Implications for Injury Tolerance in Frontal Collisions

PubMed Central

Wang, Stewart C.; Brede, Chris; Lange, David; Poster, Craig S.; Lange, Aaron W.; Kohoyda-Inglis, Carla; Sochor, Mark R.; Ipaktchi, Kyros; Rowe, Stephen A.; Patel, Smita; Garton, Hugh J.

2004-01-01

Male occupants in frontal motor vehicle collisions have reduced tolerance for hip fractures than females in similar crashes. We studied 92 adult pelvic CT scans and found significant gender differences in bony pelvic geometry, including acetabular socket depth and femoral head width. Significant differences were also noted in the presentation angle of the acetabular socket to frontal loading. The observed differences provide biomechanical insight into why hip injury tolerance may differ with gender. These findings have implications for the future design of vehicle countermeasures as well as finite element models capable of more accurately predicting body tolerances to injury. PMID:15319131

Finite Element Modeling Techniques for Analysis of VIIP

NASA Technical Reports Server (NTRS)

Feola, Andrew J.; Raykin, J.; Gleason, R.; Mulugeta, Lealem; Myers, Jerry G.; Nelson, Emily S.; Samuels, Brian C.; Ethier, C. Ross

2015-01-01

Visual Impairment and Intracranial Pressure (VIIP) syndrome is a major health concern for long-duration space missions. Currently, it is thought that a cephalad fluid shift in microgravity causes elevated intracranial pressure (ICP) that is transmitted along the optic nerve sheath (ONS). We hypothesize that this in turn leads to alteration and remodeling of connective tissue in the posterior eye which impacts vision. Finite element (FE) analysis is a powerful tool for examining the effects of mechanical loads in complex geometries. Our goal is to build a FE analysis framework to understand the response of the lamina cribrosa and optic nerve head to elevations in ICP in VIIP.

A three-part geometric model to predict the radar backscatter from wheat, corn, and sorghum

NASA Technical Reports Server (NTRS)

Ulaby, F. T. (Principal Investigator); Eger, G. W., III; Kanemasu, E. T.

1982-01-01

A model to predict the radar backscattering coefficient from crops must include the geometry of the canopy. Radar and ground-truth data taken on wheat in 1979 indicate that the model must include contributions from the leaves, from the wheat head, and from the soil moisture. For sorghum and corn, radar and ground-truth data obtained in 1979 and 1980 support the necessity of a soil moisture term and a leaf water term. The Leaf Area Index (LAI) is an appropriate input for the leaf contribution to the radar response for wheat and sorghum, however the LAI generates less accurate values for the backscattering coefficient for corn. Also, the data for corn and sorghum illustrate the importance of the water contained in the stalks in estimating the radar response.

Local plantar pressure relief in therapeutic footwear: design guidelines from finite element models.

PubMed

Erdemir, Ahmet; Saucerman, Jeffrey J; Lemmon, David; Loppnow, Bryan; Turso, Brie; Ulbrecht, Jan S; Cavanagh, Peter Re

2005-09-01

A major goal of therapeutic footwear in patients with pain or those at risk for skin injury is to relieve focal loading under prominent metatarsal heads. One frequent approach is to place plugs of compliant material into the midsole of the shoe. This study investigated 36 plug designs, a combination of three materials, six geometries, and two placements using a two-dimensional (2D) finite element model. Realistic loading conditions were obtained from plantar pressures (PP) recorded during walking in five subjects who wore control midsoles manufactured using Microcell Puff. Measured peak pressures underneath the second metatarsal head were similar to the results of the control model. PP obtained from simulations with the plugs built into a firm midsole were compared to the simulation results of the control midsole. Large plugs (e.g. 40 mm width), made out of Microcell Puff Lite or Plastazote Medium, placed at peak pressure sites, resulted in highest reductions in peak pressures (18-28%). Smaller plugs benefited from tapering when placed at high pressure areas. Case studies were completed on a healthy male subject and a diabetic female patient to address the efficacy of a plug design favored by our simulations (pressure based placement, 40 x 20 mm, Plastazote Medium). Successful reductions of second metatarsal head pressures were observed with a mediolateral load redistribution that was not represented by our model. 2D computer simulations allowed systematic investigation of plug properties without the need for high volume experimentation on human subjects and established basic guidelines for plug selection. In particular, plugs that are placed based on plantar pressure measurements were proven to be more effective when compared to those positioned according to the projection of the bony landmark on the foot-shoe plantar contact area.

Compact and mobile high resolution PET brain imager

DOEpatents

Majewski, Stanislaw [Yorktown, VA; Proffitt, James [Newport News, VA

2011-02-08

A brain imager includes a compact ring-like static PET imager mounted in a helmet-like structure. When attached to a patient's head, the helmet-like brain imager maintains the relative head-to-imager geometry fixed through the whole imaging procedure. The brain imaging helmet contains radiation sensors and minimal front-end electronics. A flexible mechanical suspension/harness system supports the weight of the helmet thereby allowing for patient to have limited movements of the head during imaging scans. The compact ring-like PET imager enables very high resolution imaging of neurological brain functions, cancer, and effects of trauma using a rather simple mobile scanner with limited space needs for use and storage.

SU-E-T-352: Effects of Skull Attenuation and Missing Backscatter On Brain Dose in HDR Treatment of the Head with Surface Applicators

DOE Office of Scientific and Technical Information (OSTI.GOV)

Cifter, F; Dhou, S; Lewis, J

2015-06-15

Purpose: To calculate the effect of lack of backscatter from air and attenuation of bone on dose distributions in brachytherapy surface treatment of head. Existing treatment planning systems based on TG43 do not account for heterogeneities, and thus may overestimate the dose to the brain. While brachytherapy generally has rapid dose falloff, the dose to the deeper tissues (in this case, the brain) can become significant when treating large curved surfaces. Methods: Applicator geometries representing a range of clinical cases were simulated in MCNP5. An Ir-192 source was modeled using the energy spectrum presented by TG-43. The head phantom wasmore » modeled as a 7.5-cm radius water sphere, with a 7 -mm thick skull embedded 5-mm beneath the surface. Dose values were calculated at 20 points inside the head, in which 10 of them were on the central axis and the other 10 on the axis connecting the central of the phantom with the second to last source from the applicator edge. Results: Central and peripheral dose distributions for a range of applicator and head sizes are presented. The distance along the central axis at which the dose falls to 80% of the prescribed dose (D80) was 7 mm for a representative small applicator and 9 mm for a large applicator. Corresponding D50 and D30 for the same small applicator were 17 mm and 32 mm respectively. D50 and D30 for the larger applicator were 32 mm and 60 mm respectively. These results reflect the slower falloff expected for larger applicators on a curved surface. Conclusion: Our results can provide guidance for clinicians to calculate the dose reduction effect due to bone attenuation and the lack of backscatter from air to estimate the brain dose for the HDR treatments of surface lesions.« less

Endoscopic fringe projection for in-situ inspection of a sheet-bulk metal forming process

NASA Astrophysics Data System (ADS)

Matthias, Steffen; Kästner, Markus; Reithmeier, Eduard

2015-05-01

Sheet-bulk metal forming is a new production process capable of performing deep-drawing and massive forming steps in a single operation. However, due to the high forming forces of the forming process, continuous process control is required in order to detect wear on the forming tool before production quality is impacted. To be able to measure the geometry of the forming tool in the limited space of forming presses, a new inspection system is being developed within the SFB/TR 73 collaborative research center. In addition to the limited space, the process restricts the amount of time available for inspection. Existing areal optical measurement systems suffer from shadowing when measuring the tool's inner elements, as they cannot be placed in the limited space next to the tool, while tactile measurement systems cannot meet the time restrictions for measuring the areal geometries. The new inspection system uses the fringe projection optical measurement principle to capture areal geometry data from relevant parts of the forming tool in short time. Highresolution image fibers are used to connect the system's compact sensor head to a base unit containing both camera and projector of the fringe projection system, which can be positioned outside of the moving parts of the press. To enable short measurement times, a high intensity laser source is used in the projector in combination with a digital micro-mirror device. Gradient index lenses are featured in the sensor head to allow for a very compact design that can be used in the narrow space above the forming tool inside the press. The sensor head is attached to an extended arm, which also guides the image fibers to the base unit. A rotation stage offers the possibility to capture measurements of different functional elements on the circular forming tool by changing the orientation of the sensor head next to the forming tool. During operation of the press, the arm can be travelled out of the moving parts of the forming press. To further reduce the measurement times of the fringe projection system, the inverse fringe projection principle has been adapted to the system to detect geometry deviations in a single camera image. Challenges arise from vibrations of both the forming machine and the positioning stages, which are transferred via the extended arm to the sensor head. Vibrations interfere with the analysis algorithms of both encoded and inverse fringe projection and thus impair measurement accuracy. To evaluate the impact of vibrations on the endoscopic system, results of measurements of simple geometries under the influence of vibrations are discussed. The effect of vibrations is imitated by displacing the measurement specimen during the measurement with a linear positioning stage. The concept of the new inspection system is presented within the scope of the TR 73 demonstrational sheet-bulk metal forming process. Finally, the capabilities of the endoscopic fringe projection system are shown by measurements of gearing structures on a forming tool compared to a CAD-reference.

Review on solving the forward problem in EEG source analysis

PubMed Central

Hallez, Hans; Vanrumste, Bart; Grech, Roberta; Muscat, Joseph; De Clercq, Wim; Vergult, Anneleen; D'Asseler, Yves; Camilleri, Kenneth P; Fabri, Simon G; Van Huffel, Sabine; Lemahieu, Ignace

2007-01-01

Background The aim of electroencephalogram (EEG) source localization is to find the brain areas responsible for EEG waves of interest. It consists of solving forward and inverse problems. The forward problem is solved by starting from a given electrical source and calculating the potentials at the electrodes. These evaluations are necessary to solve the inverse problem which is defined as finding brain sources which are responsible for the measured potentials at the EEG electrodes. Methods While other reviews give an extensive summary of the both forward and inverse problem, this review article focuses on different aspects of solving the forward problem and it is intended for newcomers in this research field. Results It starts with focusing on the generators of the EEG: the post-synaptic potentials in the apical dendrites of pyramidal neurons. These cells generate an extracellular current which can be modeled by Poisson's differential equation, and Neumann and Dirichlet boundary conditions. The compartments in which these currents flow can be anisotropic (e.g. skull and white matter). In a three-shell spherical head model an analytical expression exists to solve the forward problem. During the last two decades researchers have tried to solve Poisson's equation in a realistically shaped head model obtained from 3D medical images, which requires numerical methods. The following methods are compared with each other: the boundary element method (BEM), the finite element method (FEM) and the finite difference method (FDM). In the last two methods anisotropic conducting compartments can conveniently be introduced. Then the focus will be set on the use of reciprocity in EEG source localization. It is introduced to speed up the forward calculations which are here performed for each electrode position rather than for each dipole position. Solving Poisson's equation utilizing FEM and FDM corresponds to solving a large sparse linear system. Iterative methods are required to solve these sparse linear systems. The following iterative methods are discussed: successive over-relaxation, conjugate gradients method and algebraic multigrid method. Conclusion Solving the forward problem has been well documented in the past decades. In the past simplified spherical head models are used, whereas nowadays a combination of imaging modalities are used to accurately describe the geometry of the head model. Efforts have been done on realistically describing the shape of the head model, as well as the heterogenity of the tissue types and realistically determining the conductivity. However, the determination and validation of the in vivo conductivity values is still an important topic in this field. In addition, more studies have to be done on the influence of all the parameters of the head model and of the numerical techniques on the solution of the forward problem. PMID:18053144

Trap geometry in three giant montane pitcher plant species from Borneo is a function of tree shrew body size.

PubMed

Chin, Lijin; Moran, Jonathan A; Clarke, Charles

2010-04-01

*Three Bornean pitcher plant species, Nepenthes lowii, N. rajah and N. macrophylla, produce modified pitchers that 'capture' tree shrew faeces for nutritional benefit. Tree shrews (Tupaia montana) feed on exudates produced by glands on the inner surfaces of the pitcher lids and defecate into the pitchers. *Here, we tested the hypothesis that pitcher geometry in these species is related to tree shrew body size by comparing the pitcher characteristics with those of five other 'typical' (arthropod-trapping) Nepenthes species. *We found that only pitchers with large orifices and lids that are concave, elongated and oriented approximately at right angles to the orifice capture faeces. The distance from the tree shrews' food source (that is, the lid nectar glands) to the front of the pitcher orifice precisely matches the head plus body length of T. montana in the faeces-trapping species, and is a function of orifice size and the angle of lid reflexion. *Substantial changes to nutrient acquisition strategies in carnivorous plants may occur through simple modifications to trap geometry. This extraordinary plant-animal interaction adds to a growing body of evidence that Nepenthes represents a candidate model for adaptive radiation with regard to nitrogen sequestration strategies.

Does haptic robot-assisted total hip arthroplasty better restore native acetabular and femoral anatomy?

PubMed

Tsai, Tsung-Yuan; Dimitriou, Dimitris; Li, Jing-Sheng; Kwon, Young-Min

2016-06-01

The objective was to evaluate whether total hip arthroplasty (THA) using haptic robot assistance restores hip geometry better than the free-hand technique. Twelve robot-assisted and 14 free-hand unilateral THA patients underwent CT scan for three-dimensional (3D) hip models. The anteversion, inclination and hip joint centre locations of the native and implanted hips in each patient were quantified and compared. Significant increase of combined anteversion by 19.1 ± 11.7° and 23.5 ± 23.6° and decrease of cup inclination by 16.5 ± 6.0° and 10.2 ± 6.8° were observed in the robot-assisted and the free-hand THAs, respectively. Less variation in the difference of the component orientations (max 11.1 vs 18.3°) and the femoral head centre (max 4.5 vs 6.3 mm) were found in the robot-assisted group. This study demonstrated that neither robot-assisted nor free-hand THAs had fully restored native hip geometry. However, the higher precision of the robot-assisted THA suggested that it has potential utility in restoring the native hip geometry. Copyright © 2015 John Wiley & Sons, Ltd. Copyright © 2015 John Wiley & Sons, Ltd.

Decoupling of a tight-fit transceiver phased array for human brain imaging at 9.4T: Loop overlapping rediscovered.

PubMed

Avdievich, Nikolai I; Giapitzakis, Ioannis-Angelos; Pfrommer, Andreas; Henning, Anke

2018-02-01

To improve the decoupling of a transceiver human head phased array at ultra-high fields (UHF, ≥ 7T) and to optimize its transmit (Tx) and receive (Rx) performance, a single-row eight-element (1 × 8) tight-fit transceiver overlapped loop array was developed and constructed. Overlapping the loops increases the RF field penetration depth but can compromise decoupling by generating substantial mutual resistance. Based on analytical modeling, we optimized the loop geometry and relative positioning to simultaneously minimize the resistive and inductive coupling and constructed a 9.4T eight-loop transceiver head phased array decoupled entirely by overlapping loops. We demonstrated that both the magnetic and electric coupling between adjacent loops is compensated at the same time by overlapping and nearly perfect decoupling (below -30 dB) can be obtained without additional decoupling strategies. Tx-efficiency and SNR of the overlapped array outperformed that of a common UHF gapped array of similar dimensions. Parallel Rx-performance was also not compromised due to overlapping the loops. As a proof of concept we developed and constructed a 9.4T (400 MHz) overlapped transceiver head array based on results of the analytical modeling. We demonstrated that at UHF overlapping loops not only provides excellent decoupling but also improves both Tx- and Rx-performance. Magn Reson Med 79:1200-1211, 2018. © 2017 International Society for Magnetic Resonance in Medicine. © 2017 International Society for Magnetic Resonance in Medicine.

Computation of high-resolution SAR distributions in a head due to a radiating dipole antenna representing a hand-held mobile phone.

PubMed

Van de Kamer, J B; Lagendijk, J J W

2002-05-21

SAR distributions in a healthy female adult head as a result of a radiating vertical dipole antenna (frequency 915 MHz) representing a hand-held mobile phone have been computed for three different resolutions: 2 mm, 1 mm and 0.4 mm. The extremely high resolution of 0.4 mm was obtained with our quasistatic zooming technique, which is briefly described in this paper. For an effectively transmitted power of 0.25 W, the maximum averaged SAR values in both cubic- and arbitrary-shaped volumes are, respectively, about 1.72 and 2.55 W kg(-1) for 1 g and 0.98 and 1.73 W kg(-1) for 10 g of tissue. These numbers do not vary much (<8%) for the different resolutions, indicating that SAR computations at a resolution of 2 mm are sufficiently accurate to describe the large-scale distribution. However, considering the detailed SAR pattern in the head, large differences may occur if high-resolution computations are performed rather than low-resolution ones. These deviations are caused by both increased modelling accuracy and improved anatomical description in higher resolution simulations. For example, the SAR profile across a boundary between tissues with high dielectric contrast is much more accurately described at higher resolutions. Furthermore, low-resolution dielectric geometries may suffer from loss of anatomical detail, which greatly affects small-scale SAR distributions. Thus. for strongly inhomogeneous regions high-resolution SAR modelling is an absolute necessity.

A preliminary Monte Carlo study for the treatment head of a carbon-ion radiotherapy facility using TOPAS

NASA Astrophysics Data System (ADS)

Liu, Hongdong; Zhang, Lian; Chen, Zhi; Liu, Xinguo; Dai, Zhongying; Li, Qiang; Xu, Xie George

2017-09-01

In medical physics it is desirable to have a Monte Carlo code that is less complex, reliable yet flexible for dose verification, optimization, and component design. TOPAS is a newly developed Monte Carlo simulation tool which combines extensive radiation physics libraries available in Geant4 code, easyto-use geometry and support for visualization. Although TOPAS has been widely tested and verified in simulations of proton therapy, there has been no reported application for carbon ion therapy. To evaluate the feasibility and accuracy of TOPAS simulations for carbon ion therapy, a licensed TOPAS code (version 3_0_p1) was used to carry out a dosimetric study of therapeutic carbon ions. Results of depth dose profile based on different physics models have been obtained and compared with the measurements. It is found that the G4QMD model is at least as accurate as the TOPAS default BIC physics model for carbon ions, but when the energy is increased to relatively high levels such as 400 MeV/u, the G4QMD model shows preferable performance. Also, simulations of special components used in the treatment head at the Institute of Modern Physics facility was conducted to investigate the Spread-Out dose distribution in water. The physical dose in water of SOBP was found to be consistent with the aim of the 6 cm ridge filter.

Finite element analysis of moment-rotation relationships for human cervical spine.

PubMed

Zhang, Qing Hang; Teo, Ee Chon; Ng, Hong Wan; Lee, Vee Sin

2006-01-01

A comprehensive, geometrically accurate, nonlinear C0-C7 FE model of head and cervical spine based on the actual geometry of a human cadaver specimen was developed. The motions of each cervical vertebral level under pure moment loading of 1.0 Nm applied incrementally on the skull to simulate the movements of the head and cervical spine under flexion, tension, axial rotation and lateral bending with the inferior surface of the C7 vertebral body fully constrained were analysed. The predicted range of motion (ROM) for each motion segment were computed and compared with published experimental data. The model predicted the nonlinear moment-rotation relationship of human cervical spine. Under the same loading magnitude, the model predicted the largest rotation in extension, followed by flexion and axial rotation, and least ROM in lateral bending. The upper cervical spines are more flexible than the lower cervical levels. The motions of the two uppermost motion segments account for half (or even higher) of the whole cervical spine motion under rotational loadings. The differences in the ROMs among the lower cervical spines (C3-C7) were relatively small. The FE predicted segmental motions effectively reflect the behavior of human cervical spine and were in agreement with the experimental data. The C0-C7 FE model offers potentials for biomedical and injury studies.

Quantifying the relationship between vehicle interior geometry and child restraint systems.

PubMed

Sherwood, C P; Abdelilah, Y; Crandall, J R

2006-01-01

The prevention of interactions of children or child restraints with other vehicle structures is critical to child passenger safety. Fifteen current vehicles and seven rear and forward facing child restraint systems were measured in an attempt to quantify the available distance between child restraints and these vehicle structures. Rear facing child restraints exhibited such small amounts of clearance that contact would be expected in the majority of frontal crashes. Upper tethers are critical in the prevention of head contact, while head contact is likely when the upper tether is not used.

Hybrid Parallel-Slant Hole Collimators for SPECT Imaging

NASA Astrophysics Data System (ADS)

Bai, Chuanyong; Shao, Ling; Ye, Jinghan; Durbin, M.; Petrillo, M.

2004-06-01

We propose a new collimator geometry, the hybrid parallel-slant (HPS) hole geometry, to improve sensitivity for SPECT imaging with large field of view (LFOV) gamma cameras. A HPS collimator has one segment with parallel holes and one or more segments with slant holes. The collimator can be mounted on a conventional SPECT LFOV system that uses parallel-beam collimators, and no additional detector or collimator motion is required for data acquisition. The parallel segment of the collimator allows for the acquisition of a complete data set of the organs-of-interest and the slant segments provide additional data. In this work, simulation studies of an MCAT phantom were performed with a HPS collimator with one slant segment. The slant direction points from patient head to patient feet with a slant angle of 30/spl deg/. We simulated 64 projection views over 180/spl deg/ with the modeling of nonuniform attenuation effect, and then reconstructed images using an MLEM algorithm that incorporated the hybrid geometry. It was shown that sensitivity to the cardiac region of the phantom was increased by approximately 50% when using the HPS collimator compared with a parallel-hole collimator. No visible artifacts were observed in the myocardium and the signal-to-noise ratio (SNR) of the myocardium walls was improved. Compared with collimators with other geometries, using a HPS collimator has the following advantages: (a) significant sensitivity increase; (b) a complete data set obtained from the parallel segment that allows for artifact-free image reconstruction; and (c) no additional collimator or detector motion. This work demonstrates the potential value of hybrid geometry in collimator design for LFOV SPECT imaging.

Target Tracking Onboard an Autonomous Underwater Vehicle: Determining Optimal Towed Array Heading in an Anisotropic Noise Field

DTIC Science & Technology

2007-09-01

The geometry depicted in Figure 2-1 and defined in (9) governs the relationship between the two coordinate systems. We obtain the three-dimensional...node = ’ Unicorn ’ else if (v_id == 4) node = ’Macrura

49 CFR 213.53 - Gage.

Code of Federal Regulations, 2010 CFR

2010-10-01

... 49 Transportation 4 2010-10-01 2010-10-01 false Gage. 213.53 Section 213.53 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Track Geometry § 213.53 Gage. (a) Gage is measured between the heads of the...

49 CFR 213.53 - Gage.

Code of Federal Regulations, 2011 CFR

2011-10-01

... 49 Transportation 4 2011-10-01 2011-10-01 false Gage. 213.53 Section 213.53 Transportation Other Regulations Relating to Transportation (Continued) FEDERAL RAILROAD ADMINISTRATION, DEPARTMENT OF TRANSPORTATION TRACK SAFETY STANDARDS Track Geometry § 213.53 Gage. (a) Gage is measured between the heads of the...

32-channel 3 Tesla receive-only phased-array head coil with soccer-ball element geometry.

PubMed

Wiggins, G C; Triantafyllou, C; Potthast, A; Reykowski, A; Nittka, M; Wald, L L

2006-07-01

A 32-channel 3T receive-only phased-array head coil was developed for human brain imaging. The helmet-shaped array was designed to closely fit the head with individual overlapping circular elements arranged in patterns of hexagonal and pentagonal symmetry similar to that of a soccer ball. The signal-to-noise ratio (SNR) and noise amplification (g-factor) in accelerated imaging applications were quantitatively evaluated in phantom and human images and compared with commercially available head coils. The 32-channel coil showed SNR gains of up to 3.5-fold in the cortex and 1.4-fold in the corpus callosum compared to a (larger) commercial eight-channel head coil. The experimentally measured g-factor performance of the helmet array showed significant improvement compared to the eight-channel array (peak g-factor 59% and 26% of the eight-channel values for four- and fivefold acceleration). The performance of the arrays is demonstrated in high-resolution and highly accelerated brain images. Copyright (c) 2006 Wiley-Liss, Inc.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shang, Yu; Yu, Guoqiang, E-mail: guoqiang.yu@uky.edu

Conventional semi-infinite analytical solutions of correlation diffusion equation may lead to errors when calculating blood flow index (BFI) from diffuse correlation spectroscopy (DCS) measurements in tissues with irregular geometries. Very recently, we created an algorithm integrating a Nth-order linear model of autocorrelation function with the Monte Carlo simulation of photon migrations in homogenous tissues with arbitrary geometries for extraction of BFI (i.e., αD{sub B}). The purpose of this study is to extend the capability of the Nth-order linear algorithm for extracting BFI in heterogeneous tissues with arbitrary geometries. The previous linear algorithm was modified to extract BFIs in different typesmore » of tissues simultaneously through utilizing DCS data at multiple source-detector separations. We compared the proposed linear algorithm with the semi-infinite homogenous solution in a computer model of adult head with heterogeneous tissue layers of scalp, skull, cerebrospinal fluid, and brain. To test the capability of the linear algorithm for extracting relative changes of cerebral blood flow (rCBF) in deep brain, we assigned ten levels of αD{sub B} in the brain layer with a step decrement of 10% while maintaining αD{sub B} values constant in other layers. Simulation results demonstrate the accuracy (errors < 3%) of high-order (N ≥ 5) linear algorithm in extracting BFIs in different tissue layers and rCBF in deep brain. By contrast, the semi-infinite homogenous solution resulted in substantial errors in rCBF (34.5% ≤ errors ≤ 60.2%) and BFIs in different layers. The Nth-order linear model simplifies data analysis, thus allowing for online data processing and displaying. Future study will test this linear algorithm in heterogeneous tissues with different levels of blood flow variations and noises.« less

A Nth-order linear algorithm for extracting diffuse correlation spectroscopy blood flow indices in heterogeneous tissues.

PubMed

Shang, Yu; Yu, Guoqiang

2014-09-29

Conventional semi-infinite analytical solutions of correlation diffusion equation may lead to errors when calculating blood flow index (BFI) from diffuse correlation spectroscopy (DCS) measurements in tissues with irregular geometries. Very recently, we created an algorithm integrating a N th-order linear model of autocorrelation function with the Monte Carlo simulation of photon migrations in homogenous tissues with arbitrary geometries for extraction of BFI (i.e., αD B ). The purpose of this study is to extend the capability of the N th-order linear algorithm for extracting BFI in heterogeneous tissues with arbitrary geometries. The previous linear algorithm was modified to extract BFIs in different types of tissues simultaneously through utilizing DCS data at multiple source-detector separations. We compared the proposed linear algorithm with the semi-infinite homogenous solution in a computer model of adult head with heterogeneous tissue layers of scalp, skull, cerebrospinal fluid, and brain. To test the capability of the linear algorithm for extracting relative changes of cerebral blood flow (rCBF) in deep brain, we assigned ten levels of αD B in the brain layer with a step decrement of 10% while maintaining αD B values constant in other layers. Simulation results demonstrate the accuracy (errors < 3%) of high-order ( N  ≥ 5) linear algorithm in extracting BFIs in different tissue layers and rCBF in deep brain. By contrast, the semi-infinite homogenous solution resulted in substantial errors in rCBF (34.5% ≤ errors ≤ 60.2%) and BFIs in different layers. The N th-order linear model simplifies data analysis, thus allowing for online data processing and displaying. Future study will test this linear algorithm in heterogeneous tissues with different levels of blood flow variations and noises.

Centrifugal and Axial Pump Design and Off-Design Performance Prediction

NASA Technical Reports Server (NTRS)

Veres, Joseph P.

1995-01-01

A meanline pump-flow modeling method has been developed to provide a fast capability for modeling pumps of cryogenic rocket engines. Based on this method, a meanline pump-flow code PUMPA was written that can predict the performance of pumps at off-design operating conditions, given the loss of the diffusion system at the design point. The design-point rotor efficiency and slip factors are obtained from empirical correlations to rotor-specific speed and geometry. The pump code can model axial, inducer, mixed-flow, and centrifugal pumps and can model multistage pumps in series. The rapid input setup and computer run time for this meanline pump flow code make it an effective analysis and conceptual design tool. The map-generation capabilities of the code provide the information needed for interfacing with a rocket engine system modeling code. The off-design and multistage modeling capabilities of PUMPA permit the user to do parametric design space exploration of candidate pump configurations and to provide head-flow maps for engine system evaluation.

Development of a finite element/multi-body model of a newborn infant for restraint analysis and design.

PubMed

Bondy, Matthew; Altenhof, William; Chen, Xilin; Snowdon, Anne; Vrkljan, Brenda

2014-01-01

A finite element/multi-body model of a newborn infant has been developed by researchers at the University of Windsor. The geometry of this model is derived from a Nita newborn hospital training mannequin. It consists of 17 parts: eight upper and lower limb segments, the torso, head, and a seven-segment neck with seven translational and eight rotational joints. Anthropometry is consistent with hospital growth charts, measurements requested from health professionals and data from the open literature. The biomechanical properties of the model (i.e. joint stiffnesses) are implementations of data identified in the open literature. The model has been validated with respect to studies of the biomechanics of shaken baby syndrome, infant falls and the Q0 anthropomorphic testing device. A significant conclusion of this study is that the kinetics of the Q0 neck is not biofidelic. This model is currently used in an analysis of airway patency for infants in modern automotive child restraints.

Modeling the truebeam linac using a CAD to Geant4 geometry implementation: dose and IAEA-compliant phase space calculations.

PubMed

Constantin, Magdalena; Perl, Joseph; LoSasso, Tom; Salop, Arthur; Whittum, David; Narula, Anisha; Svatos, Michelle; Keall, Paul J

2011-07-01

To create an accurate 6 MV Monte Carlo simulation phase space for the Varian TrueBeam treatment head geometry imported from CAD (computer aided design) without adjusting the input electron phase space parameters. GEANT4 v4.9.2.p01 was employed to simulate the 6 MV beam treatment head geometry of the Varian TrueBeam linac. The electron tracks in the linear accelerator were simulated with Parmela, and the obtained electron phase space was used as an input to the Monte Carlo beam transport and dose calculations. The geometry components are tessellated solids included in GEANT4 as GDML (generalized dynamic markup language) files obtained via STEP (standard for the exchange of product) export from Pro/Engineering, followed by STEP import in Fastrad, a STEP-GDML converter. The linac has a compact treatment head and the small space between the shielding collimator and the divergent are of the upper jaws forbids the implementation of a plane for storing the phase space. Instead, an IAEA (International Atomic Energy Agency) compliant phase space writer was implemented on a cylindrical surface. The simulation was run in parallel on a 1200 node Linux cluster. The 6 MV dose calculations were performed for field sizes varying from 4 x 4 to 40 x 40 cm2. The voxel size for the 60 x 60 x 40 cm3 water phantom was 4 x 4 x 4 mm3. For the 10 x 10 cm2 field, surface buildup calculations were performed using 4 x 4 x 2 mm3 voxels within 20 mm of the surface. For the depth dose curves, 98% of the calculated data points agree within 2% with the experimental measurements for depths between 2 and 40 cm. For depths between 5 and 30 cm, agreement within 1% is obtained for 99% (4 x 4), 95% (10 x 10), 94% (20 x 20 and 30 x 30), and 89% (40 x 40) of the data points, respectively. In the buildup region, the agreement is within 2%, except at 1 mm depth where the deviation is 5% for the 10 x 10 cm2 open field. For the lateral dose profiles, within the field size for fields up to 30 x 30 cm2, the agreement is within 2% for depths up to 10 cm. At 20 cm depth, the in-field maximum dose difference for the 30 x 30 cm2 open field is within 4%, while the smaller field sizes agree within 2%. Outside the field size, agreement within 1% of the maximum dose difference is obtained for all fields. The calculated output factors varied from 0.938 +/- 0.015 for the 4 x 4 cm2 field to 1.088 +/- 0.024 for the 40 x 40 cm2 field. Their agreement with the experimental output factors is within 1%. The authors have validated a GEANT4 simulated IAEA-compliant phase space of the TrueBeam linac for the 6 MV beam obtained using a high accuracy geometry implementation from CAD. These files are publicly available and can be used for further research.

Effect of injection screen slot geometry on hydraulic conductivity tests

NASA Astrophysics Data System (ADS)

Klammler, Harald; Nemer, Bassel; Hatfield, Kirk

2014-04-01

Hydraulic conductivity and its spatial variability are important hydrogeological parameters and are typically determined through injection tests at different scales. For injection test interpretation, shape factors are required to account for injection screen geometry. Shape factors act as proportionality constants between hydraulic conductivity and observed ratios of injection flow rate and injection head at steady-state. Existing results for such shape factors assume either an ideal screen (i.e., ignoring effects of screen slot geometry) or infinite screen length (i.e., ignoring effects of screen extremes). In the present work, we investigate the combined effects of circumferential screen slot geometry and finite screen length on injection shape factors. This is done in terms of a screen entrance resistance by solving a steady-state potential flow mixed type boundary value problem in a homogeneous axi-symmetric flow domain using a semi-analytical solution approach. Results are compared to existing analytical solutions for circumferential and longitudinal slots on infinite screens, which are found to be identical. Based on an existing approximation, an expression is developed for a dimensionless screen entrance resistance of infinite screens, which is a function of the relative slot area only. For anisotropic conditions, e.g., when conductivity is smaller in the vertical direction than in the horizontal, screen entrance losses for circumferential slots increase, while they remain unaffected for longitudinal slots. This work is not concerned with investigating the effects of (possibly turbulent) head losses inside the injection device including the passage through the injection slots prior to entering the porous aquifer.

Determination of the average orientation of DNA in the octopus sperm [ital Eledone] [ital cirrhossa] through polarized light scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shapiro, D.B.; Maestre, M.F.; McClain, W.M.

1994-08-20

The coupled-dipole approximation has been used to model polarized light-scattering data obtained from the sperm of the octopus [ital Eledone] [ital cirrhosa]. Mueller scattering-matrix elements (which describe how a sample alters the intensity and degree of polarization of scattered light) were measured as a function of angle. The sample was modeled as a helical fiber believed to correspond to a DNA protein complex. It was necessary to propose an inherent anisotropy in the polarizability of the fiber in order to fit the data. The direction of the principle axes of the polarizability were determined by comparing the model with experimentalmore » data. The results suggest that the 2-nm DNA fibers are perpendicular to the thick fiber that defines the helical geometry of the octopus sperm head.« less

The geometry of high angle of attack maneuvers and the implications for Gy-induced neck injuries.

PubMed

Newman, David G; Ostler, David

2011-08-01

Modern super agile fighter aircraft have significantly expanded maneuverability envelopes, often involving very high angles of attack (AOA) in the post-stall region. One such maneuver is the high AOA velocity vector roll. The geometry of this flight maneuver is such that during the roll there is a significant lateral C load imposed on the unrestrained head-neck complex of the pilot. A mathematical analysis of the geometric relationship determining the magnitude of +/- Gy acceleration during high AOA maneuvering was conducted. This preliminary mathematical model is able to predict the Gy load imposed on the head-neck complex of the pilot for a given set of flight maneuver parameters. The analysis predicts that at an AOA of 700 and with a roll rate of 100 degrees x s(-1), the lateral G developed will be approximately 3.5 Gy. Increasing the roll rate increases the lateral G component: at 200 degrees x s(-1) the Gy, load is more than 6 Gy. There are serious potential implications of super agile maneuvers on the neck of the pilot. The G environment experienced by the pilot of super agile aircraft is increasingly multiaxial, involving +/- Gx, +/- Gy, and +/- Gz. The level of lateral G developed during these dynamic flight maneuvers should not be underestimated, as such G loads can potentially lead to neck injuries. While aircraft become ever more capable, a full understanding of the biodynamic effects on the pilot while exploiting the agility of the aircraft still needs to be developed.

A geometrically adjustable receive array for imaging marmoset cohorts.

PubMed

Gilbert, Kyle M; Gati, Joseph S; Klassen, L Martyn; Zeman, Peter; Schaeffer, David J; Everling, Stefan; Menon, Ravi S

2017-08-01

The common marmoset (Callithrix jacchus) is an increasingly popular animal model for translational neuroscience studies, during which anatomical and functional MRI can be useful investigative tools. To attain the requisite SNR for high-resolution acquisitions, the radiofrequency coil must be optimized for the marmoset; however, relatively few custom coils have been developed that maximize SNR and are compatible with accelerated acquisitions. For the study of large populations of animals, the heterogeneity in animal size reduces the effectiveness of a "one size fits all" approach to coil sizing and makes coils tailored to individual animals cost and time prohibitive. The approach taken in this study was to create an 8-channel phased-array receive coil that was adjustable to the width of the marmoset head, thereby negating the need for tailored coils while still maintaining high SNR. Two marmosets of different size were imaged on a 9.4-T small-animal scanner. Consistent SNR was achieved in the periphery of the brain between head sizes. When compared to a 15-channel, "one size fits all" receive coil, the adjustable coil achieved 57% higher SNR in the superior frontal and parietal cortices and 29% higher SNR in the centre of the brain. The mean geometry factor of the adjustable coil was less than 1.2 for a 2-fold reduction factor in the left-right and anterior-posterior directions. Geometry factors were compared to the 15-channel coil to guide future designs. The adjustable coil was shown to be a practical means for anatomical and echo-planar imaging of marmoset cohorts. Copyright © 2017 Elsevier Inc. All rights reserved.

Evaluation of a cone beam computed tomography geometry for image guided small animal irradiation.

PubMed

Yang, Yidong; Armour, Michael; Wang, Ken Kang-Hsin; Gandhi, Nishant; Iordachita, Iulian; Siewerdsen, Jeffrey; Wong, John

2015-07-07

The conventional imaging geometry for small animal cone beam computed tomography (CBCT) is that a detector panel rotates around the head-to-tail axis of an imaged animal ('tubular' geometry). Another unusual but possible imaging geometry is that the detector panel rotates around the anterior-to-posterior axis of the animal ('pancake' geometry). The small animal radiation research platform developed at Johns Hopkins University employs the pancake geometry where a prone-positioned animal is rotated horizontally between an x-ray source and detector panel. This study is to assess the CBCT image quality in the pancake geometry and investigate potential methods for improvement. We compared CBCT images acquired in the pancake geometry with those acquired in the tubular geometry when the phantom/animal was placed upright simulating the conventional CBCT geometry. Results showed signal-to-noise and contrast-to-noise ratios in the pancake geometry were reduced in comparison to the tubular geometry at the same dose level. But the overall spatial resolution within the transverse plane of the imaged cylinder/animal was better in the pancake geometry. A modest exposure increase to two folds in the pancake geometry can improve image quality to a level close to the tubular geometry. Image quality can also be improved by inclining the animal, which reduces streak artifacts caused by bony structures. The major factor resulting in the inferior image quality in the pancake geometry is the elevated beam attenuation along the long axis of the phantom/animal and consequently increased scatter-to-primary ratio in that orientation. Not withstanding, the image quality in the pancake-geometry CBCT is adequate to support image guided animal positioning, while providing unique advantages of non-coplanar and multiple mice irradiation. This study also provides useful knowledge about the image quality in the two very different imaging geometries, i.e. pancake and tubular geometry, respectively.

Evaluation of a Cone Beam Computed Tomography Geometry for Image Guided Small Animal Irradiation

PubMed Central

Yang, Yidong; Armour, Michael; Wang, Ken Kang-Hsin; Gandhi, Nishant; Iordachita, Iulian; Siewerdsen, Jeffrey; Wong, John

2015-01-01

The conventional imaging geometry for small animal cone beam computed tomography (CBCT) is that a detector panel rotates around the head-to-tail axis of an imaged animal (“tubular” geometry). Another unusual but possible imaging geometry is that the detector panel rotates around the anterior-to-posterior axis of the animal (“pancake” geometry). The small animal radiation research platform (SARRP) developed at Johns Hopkins University employs the pancake geometry where a prone-positioned animal is rotated horizontally between an x-ray source and detector panel. This study is to assess the CBCT image quality in the pancake geometry and investigate potential methods for improvement. We compared CBCT images acquired in the pancake geometry with those acquired in the tubular geometry when the phantom/animal was placed upright simulating the conventional CBCT geometry. Results showed signal-to-noise and contrast-to-noise ratios in the pancake geometry were reduced in comparison to the tubular geometry at the same dose level. But the overall spatial resolution within the transverse plane of the imaged cylinder/animal was better in the pancake geometry. A modest exposure increase to two folds in the pancake geometry can improve image quality to a level close to the tubular geometry. Image quality can also be improved by inclining the animal, which reduces streak artifacts caused by bony structures. The major factor resulting in the inferior image quality in the pancake geometry is the elevated beam attenuation along the long axis of the phantom/animal and consequently increased scatter-to-primary ratio in that orientation. Notwithstanding, the image quality in the pancake-geometry CBCT is adequate to support image guided animal positioning, while providing unique advantages of non-coplanar and multiple mice irradiation. This study also provides useful knowledge about the image quality in the two very different imaging geometries, i.e., pancake and tubular geometry, respectively. PMID:26083659

Nonlinear nature of composite structure induced by the interaction of nonplanar solitons in a nonextensive plasma

NASA Astrophysics Data System (ADS)

Han, Jiu-Ning; Luo, Jun-Hua; Liu, Zhen-Lai; Shi, Jun; Xiang, Gen-Xiang; Li, Jun-Xiu

2015-06-01

The nonlinear properties of composite structure induced by the head-on collision of electron-acoustic solitons in a general plasma composed of cold fluid electrons, hot nonextensive distributed electron, and stationary ions are studied. We have made a detailed investigation on the time-evolution process of this merged wave structure. It is found that the structure survives during some time interval, and there are obviously different for the properties of the composite structures which are induced in cylindrical and spherical geometries. Moreover, it is shown that there are both positive and negative phase shifts for each colliding soliton after the interaction. For fixed plasma parameters, the soliton received the largest phase shift in spherical geometry, followed by the cylindrical and one-dimensional planar geometries.

Investigation of tDCS volume conduction effects in a highly realistic head model

NASA Astrophysics Data System (ADS)

Wagner, S.; Rampersad, S. M.; Aydin, Ü.; Vorwerk, J.; Oostendorp, T. F.; Neuling, T.; Herrmann, C. S.; Stegeman, D. F.; Wolters, C. H.

2014-02-01

Objective. We investigate volume conduction effects in transcranial direct current stimulation (tDCS) and present a guideline for efficient and yet accurate volume conductor modeling in tDCS using our newly-developed finite element (FE) approach. Approach. We developed a new, accurate and fast isoparametric FE approach for high-resolution geometry-adapted hexahedral meshes and tissue anisotropy. To attain a deeper insight into tDCS, we performed computer simulations, starting with a homogenized three-compartment head model and extending this step by step to a six-compartment anisotropic model. Main results. We are able to demonstrate important tDCS effects. First, we find channeling effects of the skin, the skull spongiosa and the cerebrospinal fluid compartments. Second, current vectors tend to be oriented towards the closest higher conducting region. Third, anisotropic WM conductivity causes current flow in directions more parallel to the WM fiber tracts. Fourth, the highest cortical current magnitudes are not only found close to the stimulation sites. Fifth, the median brain current density decreases with increasing distance from the electrodes. Significance. Our results allow us to formulate a guideline for volume conductor modeling in tDCS. We recommend to accurately model the major tissues between the stimulating electrodes and the target areas, while for efficient yet accurate modeling, an exact representation of other tissues is less important. Because for the low-frequency regime in electrophysiology the quasi-static approach is justified, our results should also be valid for at least low-frequency (e.g., below 100 Hz) transcranial alternating current stimulation.

Design considerations for a C-shaped PET system, dedicated to small animal brain imaging, using GATE Monte Carlo simulations

NASA Astrophysics Data System (ADS)

Efthimiou, N.; Papadimitroulas, P.; Kostou, T.; Loudos, G.

2015-09-01

Commercial clinical and preclinical PET scanners rely on the full cylindrical geometry for whole body scans as well as for dedicated organs. In this study we propose the construction of a low cost dual-head C-shaped PET system dedicated for small animal brain imaging. Monte Carlo simulation studies were performed using GATE toolkit to evaluate the optimum design in terms of sensitivity, distortions in the FOV and spatial resolution. The PET model is based on SiPMs and BGO pixelated arrays. Four different configurations with C- angle 0°, 15°, 30° and 45° within the modules, were considered. Geometrical phantoms were used for the evaluation process. STIR software, extended by an efficient multi-threaded ray tracing technique, was used for the image reconstruction. The algorithm automatically adjusts the size of the FOV according to the shape of the detector's geometry. The results showed improvement in sensitivity of ∼15% in case of 45° C-angle compared to the 0° case. The spatial resolution was found 2 mm for 45° C-angle.

Generation of noncircular gears for variable motion of the crank-slider mechanism

NASA Astrophysics Data System (ADS)

Niculescu, M.; Andrei, L.; Cristescu, A.

2016-08-01

The paper proposes a modified kinematics for the crank-slider mechanism of a nails machine. The variable rotational motion of the driven gear allows to slow down the velocity of the slider in the head forming phase and increases the period for the forming forces to be applied, improving the quality of the final product. The noncircular gears are designed based on a hybrid function for the gear transmission ratio whose parameters enable multiple variations of the noncircular driven gears and crack-slider mechanism kinematics, respectively. The AutoCAD graphical and programming facilities are used (i) to analyse and optimize the slider-crank mechanism output functions, in correlation with the predefined noncircular gears transmission ratio, (ii) to generate the noncircular centrodes using the kinematics hypothesis, (iii) to generate the variable geometry of the gear teeth profiles, based on the rolling method, and (iv) to produce the gears solid virtual models. The study highlights the benefits/limits that the noncircular gears transmission ratio defining hybrid functions have on both crank-slider mechanism kinematics and gears geometry.

77 FR 59941 - Prospective Grant of Exclusive License: Terahertz Scanning Systems for Cancer Pathology

Federal Register 2010, 2011, 2012, 2013, 2014

2012-10-01

... Computer-Controlled Adaptive Near Field Imaging of Biological Systems'' Patent application No. Territory... licensure describe and claim a terahertz (THz) imaging system that may overcome the limitations of existing.... Additionally, the THz imaging system describes a sensor head geometry that eliminates the requirement to...

Filtration by eyelashes

NASA Astrophysics Data System (ADS)

Vistarakula, Krishna; Bergin, Mike; Hu, David

2010-11-01

Nearly every mammalian and avian eye is rimmed with lashes. We investigate experimentally the ability of lashes to reduce airborne particle deposition in the eye. We hypothesize that there is an optimum eyelash length that maximizes both filtration ability and extent of peripheral vision. This hypothesis is tested using a dual approach. Using preserved heads from 36 species of animals at the American Museum of Natural History, we determine the relationship between eye size and eyelash geometry (length and spacing). We test the filtration efficacy of these geometries by deploying outdoor manikins and measuring particle deposition rate as a function of eyelash length.

Is Canyon Width a Diagnostic Indicator of the Discharge of Megafloods on Earth and Mars?

NASA Astrophysics Data System (ADS)

Lapotre, M. G.; Lamb, M. P.

2013-12-01

On Earth, large floods have carved steep-walled and amphitheater-headed canyons from the Pleistocene (e.g. Box Canyon, ID) through the Holocene (e.g. Asbyrgi Canyon, Iceland), to historic times (e.g. Canyon Lake Gorge, TX). The geologic record on Mars suggests that similar floods have carved canyons by waterfall retreat about 3.5 billion years ago, when the red planet was wetter and possibly warmer. We currently lack robust paleo-hydraulic tools to reconstruct the discharge of ancient floods, especially on Mars where sediment sizes are obscured from observation. To address this issue, we hypothesize that the width of canyon escarpment is controlled by the hydraulics of the canyon-carving flood due to focusing of the flood into the canyon head. We compiled field data from multiple canyons and floods on Earth and Mars and show that there is a correlation between estimated flood discharge and canyon headwall width. To explore what sets this relationship, we identified five important parameters using dimensional analysis: the Froude number, the ratio of backwater length to canyon length, the ratio of backwater length to flood width, the ratio of canyon width to flood width, and the topographic slope upstream of the canyon. We used the hydraulic numerical modeling suite ANUGA to simulate overland flow over different canyon geometries and flood parameters to systematically explore the relative bed shear stresses along the canyon rim as a metric for flow focusing. Results show that canyons that exceed a certain length, scaling with the hydraulic backwater length, have shear stresses at their heads that are significantly higher than near the canyon mouth. Shear stresses along the rim of the canyon sidewalls are limited, in comparison to stresses along the canyon head, when the flood width is of the order of the backwater length. Flow focusing only occurs for subcritical flow. Together, these results suggest that canyons may only grow from a perturbation that is large enough to instigate flow focusing. Once canyon growth is initiated, the equilibrium width of canyons may arise from the competition between the cross-stream backwater effects along the canyon sidewalls, which promote widening of the escarpment, and the geometry of the canyon flood system, which promote a drying of the canyon sidewalls. These results show promise for a new paleohydraulic tool to infer discharges of ancient floods on Earth and Mars.

Linking fault pattern with groundwater flow in crystalline rocks at the Grimsel Test Site (Switzerland)

NASA Astrophysics Data System (ADS)

Schneeberger, Raphael; Berger, Alfons; Mäder, Urs K.; Niklaus Waber, H.; Kober, Florian; Herwegh, Marco

2017-04-01

Water flow across crystalline bedrock is of major interest for deep-seated geothermal energy projects as well as for underground disposal of radioactive waste. In crystalline rocks enhanced fluid flow is related to zones of increased permeability, i.e. to fractures that are associated to fault zones. The flow regime around the Grimsel Test Site (GTS, Central Aar massif) was assessed by establishing a 3D fault zone pattern on a local scale in the GTS underground facility (deca-meter scale) and on a regional scale at the surface (km-scale). The study reveals the existence of a dense fault zone network consisting of several km long and few tens of cm to meter wide, sub-vertically oriented major faults that are connected by tens to hundreds of meters long minor bridging faults. This geometrical information was used as input for the generation of a 3D fault zone network model. The faults originate from ductile shear zones that were reactivated as brittle faults under retrograde conditions during exhumation. Embrittlement and associated dilatancy along the faults provide the pathways for today's groundwater flow. Detection of the actual 3D flow paths is, however, challenging since flow seem to be not planar but rather tube-like. Two strategies are applied to constrain the 3D geometry of the flow tubes: (i) Characterization of the groundwater infiltrating into the GTS (location, yield, hydraulic head, and chemical composition) and (ii) stress modelling on the base of the 3D structural model to unravel potential domains of enhanced fluid flow such as fault plane intersections and domains of dilatancy. At the Grimsel Test Site, hydraulic and structural data demonstrate that the groundwater flow is head-driven from the surface towards the GTS located some 450 m below the surface. The residence time of the groundwater in this surface-near section is >60 years as evidenced by absence of detectable tritium. However, hydraulic heads obtained from interval pressure measurements within boreholes are variable and do not correspond to the overburden above the interval. Underground mapping revealed close spatial relation between water inflow points and faults, major water inflows occur in strongly deformed areas of the GTS. Furthermore, persistent differences in the groundwater chemical composition between infiltration points indicate that connectivity between different water flow paths is poor. Different findings indicate complex flow path geometries. However, domains of enhanced dilatancy and domains with increased number of fault intersections correlate with areas in the underground with 'high' water inflow.

Development of Advanced In-Cylinder Components and Tribological Systems for Low Heat Rejection Diesel Engines

NASA Technical Reports Server (NTRS)

Yonushonis, T. M.; Wiczynski, P. D.; Myers, M. R.; Anderson, D. D.; McDonald, A. C.; Weber, H. G.; Richardson, D. E.; Stafford, R. J.; Naylor, M. G.

1999-01-01

In-cylinder components and tribological system concepts were designed, fabricated and tested at conditions anticipated for a 55% thermal efficiency heavy duty diesel engine for the year 2000 and beyond. A Cummins L10 single cylinder research engine was used to evaluate a spherical joint piston and connecting rod with 19.3 MPa (2800 psi) peak cylinder pressure capability, a thermal fatigue resistant insulated cylinder head, radial combustion seal cylinder liners, a highly compliant steel top compression ring, a variable geometry turbocharger, and a microwave heated particulate trap. Components successfully demonstrated in the final test included spherical joint connecting rod with a fiber reinforced piston, high conformability steel top rings with wear resistant coatings, ceramic exhaust ports with strategic oil cooling and radial combustion seal cylinder liner with cooling jacket transfer fins. A Cummins 6B diesel was used to develop the analytical methods, materials, manufacturing technology and engine components for lighter weight diesel engines without sacrificing performance or durability. A 6B diesel engine was built and tested to calibrate analytical models for the aluminum cylinder head and aluminum block.

Evaluation of a Spiral Groove Geometry for Improvement of Hemolysis Level in a Hydrodynamically Levitated Centrifugal Blood Pump.

PubMed

Murashige, Tomotaka; Kosaka, Ryo; Sakota, Daisuke; Nishida, Masahiro; Kawaguchi, Yasuo; Yamane, Takashi; Maruyama, Osamu

2015-08-01

The purpose of this study is to evaluate a spiral groove geometry for a thrust bearing to improve the hemolysis level in a hydrodynamically levitated centrifugal blood pump. We compared three geometric models: (i) the groove width is the same as the ridge width at any given polar coordinate (conventional model); (ii) the groove width contracts inward from 9.7 to 0.5 mm (contraction model); and (iii) the groove width expands inward from 0.5 to 4.2 mm (expansion model). To evaluate the hemolysis level, an impeller levitation performance test and in vitro hemolysis test were conducted using a mock circulation loop. In these tests, the driving conditions were set at a pressure head of 200 mm Hg and a flow rate of 4.0 L/min. As a result of the impeller levitation performance test, the bottom bearing gaps of the contraction and conventional models were 88 and 25 μm, respectively. The impeller of the expansion model touched the bottom housing. In the hemolysis test, the relative normalized index of hemolysis (NIH) ratios of the contraction model in comparison with BPX-80 and HPM-15 were 0.6 and 0.9, respectively. In contrast, the relative NIH ratios of the conventional model in comparison with BPX-80 and HPM-15 were 9.6 and 13.7, respectively. We confirmed that the contraction model achieved a large bearing gap and improved the hemolysis level in a hydrodynamically levitated centrifugal blood pump. Copyright © 2015 International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc.

Nozzle geometry for organic vapor jet printing

DOE Office of Scientific and Technical Information (OSTI.GOV)

Forrest, Stephen R.; McGraw, Gregory

A first device is provided. The device includes a print head. The print head further includes a first nozzle hermetically sealed to a first source of gas. The first nozzle has an aperture having a smallest dimension of 0.5 to 500 microns in a direction perpendicular to a flow direction of the first nozzle. At a distance from the aperture into the first nozzle that is 5 times the smallest dimension of the aperture of the first nozzle, the smallest dimension perpendicular to the flow direction is at least twice the smallest dimension of the aperture of the first nozzle.

Nozzle geometry for organic vapor jet printing

DOEpatents

Forrest, Stephen R; McGraw, Gregory

2015-01-13

A first device is provided. The device includes a print head. The print head further includes a first nozzle hermetically sealed to a first source of gas. The first nozzle has an aperture having a smallest dimension of 0.5 to 500 microns in a direction perpendicular to a flow direction of the first nozzle. At a distance from the aperture into the first nozzle that is 5 times the smallest dimension of the aperture of the first nozzle, the smallest dimension perpendicular to the flow direction is at least twice the smallest dimension of the aperture of the first nozzle.

SU-D-BRA-04: Computerized Framework for Marker-Less Localization of Anatomical Feature Points in Range Images Based On Differential Geometry Features for Image-Guided Radiation Therapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Soufi, M; Arimura, H; Toyofuku, F

Purpose: To propose a computerized framework for localization of anatomical feature points on the patient surface in infrared-ray based range images by using differential geometry (curvature) features. Methods: The general concept was to reconstruct the patient surface by using a mathematical modeling technique for the computation of differential geometry features that characterize the local shapes of the patient surfaces. A region of interest (ROI) was firstly extracted based on a template matching technique applied on amplitude (grayscale) images. The extracted ROI was preprocessed for reducing temporal and spatial noises by using Kalman and bilateral filters, respectively. Next, a smooth patientmore » surface was reconstructed by using a non-uniform rational basis spline (NURBS) model. Finally, differential geometry features, i.e. the shape index and curvedness features were computed for localizing the anatomical feature points. The proposed framework was trained for optimizing shape index and curvedness thresholds and tested on range images of an anthropomorphic head phantom. The range images were acquired by an infrared ray-based time-of-flight (TOF) camera. The localization accuracy was evaluated by measuring the mean of minimum Euclidean distances (MMED) between reference (ground truth) points and the feature points localized by the proposed framework. The evaluation was performed for points localized on convex regions (e.g. apex of nose) and concave regions (e.g. nasofacial sulcus). Results: The proposed framework has localized anatomical feature points on convex and concave anatomical landmarks with MMEDs of 1.91±0.50 mm and 3.70±0.92 mm, respectively. A statistically significant difference was obtained between the feature points on the convex and concave regions (P<0.001). Conclusion: Our study has shown the feasibility of differential geometry features for localization of anatomical feature points on the patient surface in range images. The proposed framework might be useful for tasks involving feature-based image registration in range-image guided radiation therapy.« less

Two-stage high frequency pulse tube cooler for refrigeration at 25 K

NASA Astrophysics Data System (ADS)

Dietrich, M.; Thummes, G.

2010-04-01

A two-stage Stirling-type U-shape pulse tube cryocooler driven by a 10 kW-class linear compressor was designed, built and tested. A special feature of the cold head is the absence of a heat exchanger at the cold end of the first-stage, since the intended application requires no cooling power at this intermediate temperature. Simulations where done using SAGE-software to find optimum operating conditions and cold head geometry. Flow-impedance matching was required to connect the compressor designed for 60 Hz operation to the 40 Hz cold head. A cooling power of 12.9 W at 25 K with an electrical input power of 4.6 kW has been achieved up to now. The lowest temperature reached is 13.7 K.

Structure of gel phase DMPC determined by X-ray diffraction.

PubMed Central

Tristram-Nagle, Stephanie; Liu, Yufeng; Legleiter, Justin; Nagle, John F

2002-01-01

The structure of fully hydrated gel phase dimyristoylphosphatidylcholine lipid bilayers was obtained at 10 degrees C. Oriented lipid multilayers were used to obtain high signal-to-noise intensity data. The chain tilt angle and an estimate of the methylene electron density were obtained from wide angle reflections. The chain tilt angle is measured to be 32.3 +/- 0.6 degrees near full hydration, and it does not change as the sample is mildly dehydrated from a repeat spacing of D = 59.9 A to D = 56.5 A. Low angle diffraction peaks were obtained up to the tenth order for 17 samples with variable D and prepared by three different methods with different geometries. In addition to the usual Fourier reconstructions of the electron density profiles, model electron density profiles were fit to all the low angle data simultaneously while constraining the model to include the wide-angle data and the measured lipid volume. Results are obtained for area/lipid (A = 47.2 +/- 0.5 A(2)), the compressibility modulus (K(A) = 500 +/- 100 dyn/cm), various thicknesses, such as the hydrocarbon thickness (2D(C) = 30.3 +/- 0.2 A), and the head-to-head spacing (D(HH) = 40.1 +/- 0.1 A). PMID:12496100

Geometry induced sequence of nanoscale Frank–Kasper and quasicrystal mesophases in giant surfactants

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yue, Kan; Huang, Mingjun; Marson, Ryan L.

Frank–Kasper (F-K) and quasicrystal phases were originally identified in metal alloys and only sporadically reported in soft materials. These unconventional sphere-packing schemes open up possibilities to design materials with different properties. The challenge in soft materials is how to correlate complex phases built from spheres with the tunable parameters of chemical composition and molecular architecture. Here, we report a complete sequence of various highly ordered mesophases by the self-assembly of specifically designed and synthesized giant surfactants, which are conjugates of hydrophilic polyhedral oligomeric silsesquioxane cages tethered with hydrophobic polystyrene tails. We show that the occurrence of these mesophases results frommore » nanophase separation between the heads and tails and thus is critically dependent on molecular geometry. Variations in molecular geometry achieved by changing the number of tails from one to four not only shift compositional phase boundaries but also stabilize F-K and quasicrystal phases in regions where simple phases of spheroidal micelles are typically observed. These complex self-assembled nanostructures have been identified by combining X-ray scattering techniques and real-space electron microscopy images. Brownian dynamics simulations based on a simplified molecular model confirm the architecture-induced sequence of phases. Our results demonstrate the critical role of molecular architecture in dictating the formation of supramolecular crystals with “soft” spheroidal motifs and provide guidelines to the design of unconventional self-assembled nanostructures.« less

Geometry induced sequence of nanoscale Frank–Kasper and quasicrystal mesophases in giant surfactants

PubMed Central

Yue, Kan; Huang, Mingjun; Marson, Ryan L.; He, Jinlin; Huang, Jiahao; Zhou, Zhe; Wang, Jing; Liu, Chang; Yan, Xuesheng; Wu, Kan; Guo, Zaihong; Liu, Hao; Ni, Peihong; Wesdemiotis, Chrys; Zhang, Wen-Bin; Glotzer, Sharon C.; Cheng, Stephen Z. D.

2016-01-01

Frank–Kasper (F-K) and quasicrystal phases were originally identified in metal alloys and only sporadically reported in soft materials. These unconventional sphere-packing schemes open up possibilities to design materials with different properties. The challenge in soft materials is how to correlate complex phases built from spheres with the tunable parameters of chemical composition and molecular architecture. Here, we report a complete sequence of various highly ordered mesophases by the self-assembly of specifically designed and synthesized giant surfactants, which are conjugates of hydrophilic polyhedral oligomeric silsesquioxane cages tethered with hydrophobic polystyrene tails. We show that the occurrence of these mesophases results from nanophase separation between the heads and tails and thus is critically dependent on molecular geometry. Variations in molecular geometry achieved by changing the number of tails from one to four not only shift compositional phase boundaries but also stabilize F-K and quasicrystal phases in regions where simple phases of spheroidal micelles are typically observed. These complex self-assembled nanostructures have been identified by combining X-ray scattering techniques and real-space electron microscopy images. Brownian dynamics simulations based on a simplified molecular model confirm the architecture-induced sequence of phases. Our results demonstrate the critical role of molecular architecture in dictating the formation of supramolecular crystals with “soft” spheroidal motifs and provide guidelines to the design of unconventional self-assembled nanostructures. PMID:27911786

SU-E-T-168: Characterization of Neutrons From the TrueBeam Treatment Head

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sawkey, D; Svatos, M

2015-06-15

Purpose: Calculate neutron production and transport in the TrueBeam treatment head, as input for vault design and phantom dose calculations. Methods: A detailed model of the treatment head, including shielding components off the beam axis, was created from manufacturer’s engineering drawings. Simulations were done with Geant4 for the 18X, 15X, 10X and 10FFF beams, tuned to match measured dose distributions inside the treatment field. Particles were recorded on a 70 cm radius sphere surrounding the treatment head enabling input into simulations of vaults. Results: For the 18X beam, 11×10{sup 9} neutrons/MU were observed. The energy spectrum was a broad peakmore » with average energy 0.37 MeV. With jaws closed, 48% of the neutrons were generated in the primary collimator, 18% in the jaws, 12% in the target, and 10% in the flattening filter. With wide open jaws, few neutrons were produced in the jaws and consequently total neutron production dropped to 8.5×10{sup 9} neutrons/MU. Angular distributions were greatest along the beam axis (12×10{sup 9} neutrons/MU/sr, within 2 deg of the beam axis) and antiparallel to the beam axis (7×10{sup 9} neutrons/MU/sr). Peaks were observed in the neutron energy spectrum, corresponding to elastic scattering resonances in the shielding materials. Neutron production was lower for the other beams studied: 4.1×10{sup 9} neutrons/MU for 15X, 0.38×10{sup 9} neutrons/MU for 10X, and 0.22×10{sup 9} neutrons/MU for 10FFF. Despite dissimilar treatment head geometries and materials, the neutron production and energy spectrum were similar to those reported for Clinac accelerators. Conclusion: Detailed neutron production and leakage calculations for the TrueBeam treatment head were done. Unlike other studies, results are independent of the surrounding vault, enabling vault design calculations.« less

Semi-automatic 10/20 Identification Method for MRI-Free Probe Placement in Transcranial Brain Mapping Techniques.

PubMed

Xiao, Xiang; Zhu, Hao; Liu, Wei-Jie; Yu, Xiao-Ting; Duan, Lian; Li, Zheng; Zhu, Chao-Zhe

2017-01-01

The International 10/20 system is an important head-surface-based positioning system for transcranial brain mapping techniques, e.g., fNIRS and TMS. As guidance for probe placement, the 10/20 system permits both proper ROI coverage and spatial consistency among multiple subjects and experiments in a MRI-free context. However, the traditional manual approach to the identification of 10/20 landmarks faces problems in reliability and time cost. In this study, we propose a semi-automatic method to address these problems. First, a novel head surface reconstruction algorithm reconstructs head geometry from a set of points uniformly and sparsely sampled on the subject's head. Second, virtual 10/20 landmarks are determined on the reconstructed head surface in computational space. Finally, a visually-guided real-time navigation system guides the experimenter to each of the identified 10/20 landmarks on the physical head of the subject. Compared with the traditional manual approach, our proposed method provides a significant improvement both in reliability and time cost and thus could contribute to improving both the effectiveness and efficiency of 10/20-guided MRI-free probe placement.

Integrated Model of the Eye/Optic Nerve Head Biomechanical Environment

NASA Technical Reports Server (NTRS)

Ethier, C. R.; Feola, A.; Myers, J. G.; Nelson, E.; Raykin, J.; Samuels, B.

2017-01-01

Visual Impairment and Intracranial Pressure (VIIP) syndrome is a concern for long-duration space flight. Previously, it has been suggested that ocular changes observed in VIIP syndrome are related to the cephalad fluid shift that results in altered fluid pressures [1]. We are investigating the impact of changes in intracranial pressure (ICP) using a combination of numerical models, which simulate the effects of various environment conditions, including finite element (FE) models of the posterior eye. The specific interest is to understand how altered pressures due to gravitational changes affect the biomechanical environment of tissues of the posterior eye and optic nerve sheath. METHODS: Additional description of the numerical modeling is provided in the IWS abstract by Nelson et al. In brief, to simulate the effects of a cephalad fluid shift on the cardiovascular and ocular systems, we utilized a lumped-parameter compartment model of these systems. The outputs of this lumped-parameter model then inform boundary conditions (pressures) for a finite element model of the optic nerve head (Figure 1). As an example, we show here a simulation of postural change from supine to 15 degree head-down tilt (HDT), with primary outcomes being the predicted change in strains at the optic nerve head (ONH) region, specifically in the lamina cribrosa (LC), retrolaminar optic nerve, and prelaminar neural tissue (PLNT). The strain field can be decomposed into three orthogonal components, denoted as the first, second and third principal strains. We compare the peak tensile (first principal) and compressive (third principal) strains, since elevated strain alters cell phenotype and induces tissue remodeling. RESULTS AND CONCLUSIONS: Our lumped-parameter model predicted an IOP increase of c. 7 mmHg after 21 minutes of 15 degree HDT, which agreed with previous reports of IOP in HDT [1]. The corresponding FEM simulations predicted a relative increase in the magnitudes of the peak tensile and compressive strains in the lamina cribrosa of 42 and 43, respectively (Fig. 2). The corresponding changes in the optic nerve strains were 17 and 39, while in the PLNT they were 47 and 43. These magnitudes of relative elevations in peak strains may induce a phenotypic response in resident mechano-responsive resident cells [2]. This approach may be expanded to investigate other environmental changes (e.g. parabolic flight). Through our VIIP SCHOLAR project, we will validate and improve these integrated models by measuring patient-specific changes in optic nerve sheath geometry in patients with idiopathic intracranial hypertension before and after lumbar puncture and CSF removal.

Effectiveness of Collision-Involved Motorcycle Helmets in Thailand

PubMed Central

Wobrock, Jesse; Smith, Terry; Kasantikul, Vira; Whiting, William

2003-01-01

The purpose of this study was to analyze variables present in selected motorcycle crashes involving helmeted riders to find the best injury predictors. The helmets used in this study were collected from motorcycle crashes in Thailand. Pertinent data were collected, a conventional helmet impact drop test apparatus was used to quantify the head impact forces, and stepwise multiple regression analyses were performed. The results indicate that the geometry of the object impacting the head and GSI were the best predictors for MAIS (R2=.875) while geometry of the object, liner thickness and impact energy were the best predictors for ISS (R2=.911). Analysis of motor vehicle crashes in the United States in the year 2001 reveals that motorcyclist fatalities increased 7.2%, from 2,862 fatalities in 2000 to 3,067 in 2001 [NHTSA 2002]. In 2001, 59,000 motorcyclists were injured, which represents an increase of 2.0% from 2000. These statistics are indicative of the risk that motorcycle riders face in the traffic environment and warrant the need for further research focusing on injury potential in motorcycle crashes. PMID:12941212

Optical measurement of sound using time-varying laser speckle patterns

NASA Astrophysics Data System (ADS)

Leung, Terence S.; Jiang, Shihong; Hebden, Jeremy

2011-02-01

In this work, we introduce an optical technique to measure sound. The technique involves pointing a coherent pulsed laser beam on the surface of the measurement site and capturing the time-varying speckle patterns using a CCD camera. Sound manifests itself as vibrations on the surface which induce a periodic translation of the speckle pattern over time. Using a parallel speckle detection scheme, the dynamics of the time-varying speckle patterns can be captured and processed to produce spectral information of the sound. One potential clinical application is to measure pathological sounds from the brain as a screening test. We performed experiments to demonstrate the principle of the detection scheme using head phantoms. The results show that the detection scheme can measure the spectra of single frequency sounds between 100 and 2000 Hz. The detection scheme worked equally well in both a flat geometry and an anatomical head geometry. However, the current detection scheme is too slow for use in living biological tissues which has a decorrelation time of a few milliseconds. Further improvements have been suggested.

Parametric analysis of the biomechanical response of head subjected to the primary blast loading--a data mining approach.

PubMed

Zhu, Feng; Kalra, Anil; Saif, Tal; Yang, Zaihan; Yang, King H; King, Albert I

2016-01-01

Traumatic brain injury due to primary blast loading has become a signature injury in recent military conflicts and terrorist activities. Extensive experimental and computational investigations have been conducted to study the interrelationships between intracranial pressure response and intrinsic or 'input' parameters such as the head geometry and loading conditions. However, these relationships are very complicated and are usually implicit and 'hidden' in a large amount of simulation/test data. In this study, a data mining method is proposed to explore such underlying information from the numerical simulation results. The heads of different species are described as a highly simplified two-part (skull and brain) finite element model with varying geometric parameters. The parameters considered include peak incident pressure, skull thickness, brain radius and snout length. Their interrelationship and coupling effect are discovered by developing a decision tree based on the large simulation data-set. The results show that the proposed data-driven method is superior to the conventional linear regression method and is comparable to the nonlinear regression method. Considering its capability of exploring implicit information and the relatively simple relationships between response and input variables, the data mining method is considered to be a good tool for an in-depth understanding of the mechanisms of blast-induced brain injury. As a general method, this approach can also be applied to other nonlinear complex biomechanical systems.

Deformation Prediction and Geometrical Modeling of Head and Neck Cancer Tumor: A Data Mining Approach

NASA Astrophysics Data System (ADS)

Azimi, Maryam

Radiation therapy has been used in the treatment of cancer tumors for several years and many cancer patients receive radiotherapy. It may be used as primary therapy or with a combination of surgery or other kinds of therapy such as chemotherapy, hormone therapy or some mixture of the three. The treatment objective is to destroy cancer cells or shrink the tumor by planning an adequate radiation dose to the desired target without damaging the normal tissues. By using the pre-treatment Computer Tomography (CT) images, most of the radiotherapy planning systems design the target and assume that the size of the tumor will not change throughout the treatment course, which takes 5 to 7 weeks. Based on this assumption, the total amount of radiation is planned and fractionated for the daily dose required to be delivered to the patient's body. However, this assumption is flawed because the patients receiving radiotherapy have marked changes in tumor geometry during the treatment period. Therefore, there is a critical need to understand the changes of the tumor shape and size over time during the course of radiotherapy in order to prevent significant effects of inaccuracy in the planning. In this research, a methodology is proposed in order to monitor and predict daily (fraction day) tumor volume and surface changes of head and neck cancer tumors during the entire treatment period. In the proposed method, geometrical modeling and data mining techniques will be used rather than repetitive CT scans data to predict the tumor deformation for radiation planning. Clinical patient data were obtained from the University of Texas-MD Anderson Cancer Center (MDACC). In the first step, by using CT scan data, the tumor's progressive geometric changes during the treatment period are quantified. The next step relates to using regression analysis in order to develop predictive models for tumor geometry based on the geometric analysis results and the patients' selected attributes (age, weight, stage, etc.). Moreover, repeated measure analyses have been applied to identify the effects of patients' selected attributes on tumor deformation. The main goal of the proposed methodology is increasing the accuracy of each therapy and quality of life for patients.

Quantifying the Dynamics of Field Cancerization in Tobacco-Related Head and Neck Cancer: A Multiscale Modeling Approach.

PubMed

Ryser, Marc D; Lee, Walter T; Ready, Neal E; Leder, Kevin Z; Foo, Jasmine

2016-12-15

High rates of local recurrence in tobacco-related head and neck squamous cell carcinoma (HNSCC) are commonly attributed to unresected fields of precancerous tissue. Because they are not easily detectable at the time of surgery without additional biopsies, there is a need for noninvasive methods to predict the extent and dynamics of these fields. Here, we developed a spatial stochastic model of tobacco-related HNSCC at the tissue level and calibrated the model using a Bayesian framework and population-level incidence data from the Surveillance, Epidemiology, and End Results (SEER) registry. Probabilistic model analyses were performed to predict the field geometry at time of diagnosis, and model predictions of age-specific recurrence risks were tested against outcome data from SEER. The calibrated models predicted a strong dependence of the local field size on age at diagnosis, with a doubling of the expected field diameter between ages at diagnosis of 50 and 90 years, respectively. Similarly, the probability of harboring multiple, clonally unrelated fields at the time of diagnosis was found to increase substantially with patient age. On the basis of these findings, we hypothesized a higher recurrence risk in older than in younger patients when treated by surgery alone; we successfully tested this hypothesis using age-stratified outcome data. Further clinical studies are needed to validate the model predictions in a patient-specific setting. This work highlights the importance of spatial structure in models of epithelial carcinogenesis and suggests that patient age at diagnosis may be a critical predictor of the size and multiplicity of precancerous lesions. Cancer Res; 76(24); 7078-88. ©2016 AACR. ©2016 American Association for Cancer Research.

Quantifying the dynamics of field cancerization in tobacco-related head and neck cancer: a multi-scale modeling approach

PubMed Central

Ryser, Marc D.; Lee, Walter T.; Readyz, Neal E.; Leder, Kevin Z.; Foo, Jasmine

2017-01-01

High rates of local recurrence in tobacco-related head and neck squamous cell carcinoma (HNSCC) are commonly attributed to unresected fields of precancerous tissue. Since they are not easily detectable at the time of surgery without additional biopsies, there is a need for non-invasive methods to predict the extent and dynamics of these fields. Here we developed a spatial stochastic model of tobacco-related HNSCC at the tissue level and calibrated the model using a Bayesian framework and population-level incidence data from the Surveillance, Epidemiology, and End Results (SEER) registry. Probabilistic model analyses were performed to predict the field geometry at time of diagnosis, and model predictions of age-specific recurrence risks were tested against outcome data from SEER. The calibrated models predicted a strong dependence of the local field size on age at diagnosis, with a doubling of the expected field diameter between ages at diagnosis of 50 and 90 years, respectively. Similarly, the probability of harboring multiple, clonally unrelated fields at the time of diagnosis were found to increase substantially with patient age. Based on these findings, we hypothesized a higher recurrence risk in older compared to younger patients when treated by surgery alone; we successfully tested this hypothesis using age-stratified outcome data. Further clinical studies are needed to validate the model predictions in a patient-specific setting. This work highlights the importance of spatial structure in models of epithelial carcinogenesis, and suggests that patient age at diagnosis may be a critical predictor of the size and multiplicity of precancerous lesions. Major Findings Patient age at diagnosis was found to be a critical predictor of the size and multiplicity of precancerous lesions. This finding challenges the current one-size-fits-all approach to surgical excision margins. PMID:27913438

Freshwater-Brine Mixing Zone Hydrodynamics in Salt Flats (Salar de Atacama)

NASA Astrophysics Data System (ADS)

Marazuela, M. A.; Vázquez-Suñé, E.; Custodio, E.; Palma, T.; García-Gil, A.

2017-12-01

The increase in the demand of strategic minerals for the development of medicines and batteries require detailed knowledge of the salt flats freshwater-brine interface to make its exploitation efficient. The interface zone is the result of a physical balance between the recharged and evaporated water. The sharp interface approach assumes the immiscibility of the fluids and thus neglects the mixing between them. As a consequence, for miscible fluids it is more accurate and often needed to use the mixing zone concept, which results from the dynamic equilibrium of flowing freshwater and brine. In this study, we consider two and three-dimensional scale approaches for the management of the mixing zone. The two-dimensional approach is used to understand the dynamics and the characteristics of the salt flat mixing zone, especially in the Salar de Atacama (Atacama salt flat) case. By making use of this model we analyze and quantify the effects of the aquitards on the mixing zone geometry. However, the understanding of the complex physical processes occurring in the salt flats and the management of these environments requires the adoption of three-dimensional regional scale numerical models. The models that take into account the effects of variable density represent the best management tool, but they require large computational resources, especially in the three-dimensional case. In order to avoid these computational limitations in the modeling of salt flats and their valuable ecosystems, we propose a three-step methodology, consisting of: (1) collection, validation and interpretation of the hydrogeochemical data, (2) identification and three-dimensional mapping of the mixing zone on the land surface and in depth, and (3) application of a water head correction to the freshwater and mixed water heads in order to compensate the density variations and to transform them to brine water heads. Finally, an evaluation of the sensibility of the mixing zone to anthropogenic and climate changes is included.

Water exchange, mixing and transient storage between a saturated karstic conduit and the surrounding aquifer: Groundwater flow modeling and inputs from stable water isotopes

NASA Astrophysics Data System (ADS)

Binet, S.; Joigneaux, E.; Pauwels, H.; Albéric, P.; Fléhoc, Ch.; Bruand, A.

2017-01-01

Water exchanges between a karstic conduit and the surrounding aquifer are driven by hydraulic head gradient at the interface between these two domains. The case-study presented in this paper investigates the impact of the geometry and interface conditions around a conduit on the spatial distribution of these exchanges. Isotopic (δ18O and δD), discharge and water head measurements were conducted at the resurgences of a karst system with a strong allogenic recharge component (Val d'Orléans, France), to estimate the amounts of water exchanged and the mixings between a saturated karstic conduit and the surrounding aquifer. The spatio-temporal variability of the observed exchanges was explored using a 2D coupled continuum-conduit flow model under saturated conditions (Feflow®). The inputs from the water heads and stable water isotopes in the groundwater flow model suggest that the amounts of water flowing from the aquifer are significant if the conduit flow discharges are less than the conduit flow capacity. This condition creates a spatial distribution of exchanges from upstream where the aquifer feeds the conduit (recharge area) to downstream where the conduit reaches its maximum discharge capacity and can feed the aquifer (discharge area). In the intermediate transport zone no exchange between the two domains takes place that brings a new criterion to delineate the vulnerable zones to surface water. On average, 4% of the water comes from the local recharge, 80% is recent river water and 16% is old river water. During the November 2008 flood, both isotopic signatures and model suggest that exchanges fluctuate around this steady state, limited when the river water level increases and intensified when the river water level decreases. The existence of old water from the river suggests a transient storage at the aquifer/conduit interface that can be considered as an underground hyporheic zone.

Modeling the TrueBeam linac using a CAD to Geant4 geometry implementation: Dose and IAEA-compliant phase space calculations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Constantin, Magdalena; Perl, Joseph; LoSasso, Tom

2011-07-15

Purpose: To create an accurate 6 MV Monte Carlo simulation phase space for the Varian TrueBeam treatment head geometry imported from cad (computer aided design) without adjusting the input electron phase space parameters. Methods: geant4 v4.9.2.p01 was employed to simulate the 6 MV beam treatment head geometry of the Varian TrueBeam linac. The electron tracks in the linear accelerator were simulated with Parmela, and the obtained electron phase space was used as an input to the Monte Carlo beam transport and dose calculations. The geometry components are tessellated solids included in geant4 as gdml (generalized dynamic markup language) files obtainedmore » via STEP (standard for the exchange of product) export from Pro/Engineering, followed by STEP import in Fastrad, a STEP-gdml converter. The linac has a compact treatment head and the small space between the shielding collimator and the divergent arc of the upper jaws forbids the implementation of a plane for storing the phase space. Instead, an IAEA (International Atomic Energy Agency) compliant phase space writer was implemented on a cylindrical surface. The simulation was run in parallel on a 1200 node Linux cluster. The 6 MV dose calculations were performed for field sizes varying from 4 x 4 to 40 x 40 cm{sup 2}. The voxel size for the 60x60x40 cm{sup 3} water phantom was 4x4x4 mm{sup 3}. For the 10x10 cm{sup 2} field, surface buildup calculations were performed using 4x4x2 mm{sup 3} voxels within 20 mm of the surface. Results: For the depth dose curves, 98% of the calculated data points agree within 2% with the experimental measurements for depths between 2 and 40 cm. For depths between 5 and 30 cm, agreement within 1% is obtained for 99% (4x4), 95% (10x10), 94% (20x20 and 30x30), and 89% (40x40) of the data points, respectively. In the buildup region, the agreement is within 2%, except at 1 mm depth where the deviation is 5% for the 10x10 cm{sup 2} open field. For the lateral dose profiles, within the field size for fields up to 30x30 cm{sup 2}, the agreement is within 2% for depths up to 10 cm. At 20 cm depth, the in-field maximum dose difference for the 30x30 cm{sup 2} open field is within 4%, while the smaller field sizes agree within 2%. Outside the field size, agreement within 1% of the maximum dose difference is obtained for all fields. The calculated output factors varied from 0.938{+-}0.015 for the 4x4 cm{sup 2} field to 1.088{+-}0.024 for the 40x40 cm{sup 2} field. Their agreement with the experimental output factors is within 1%. Conclusions: The authors have validated a geant4 simulated IAEA-compliant phase space of the TrueBeam linac for the 6 MV beam obtained using a high accuracy geometry implementation from cad. These files are publicly available and can be used for further research.« less

Computation of leading edge film cooling from a CONSOLE geometry (CONverging Slot hOLE)

NASA Astrophysics Data System (ADS)

Guelailia, A.; Khorsi, A.; Hamidou, M. K.

2016-01-01

The aim of this study is to investigate the effect of mass flow rate on film cooling effectiveness and heat transfer over a gas turbine rotor blade with three staggered rows of shower-head holes which are inclined at 30° to the spanwise direction, and are normal to the streamwise direction on the blade. To improve film cooling effectiveness, the standard cylindrical holes, located on the leading edge region, are replaced with the converging slot holes (console). The ANSYS CFX has been used for this computational simulation. The turbulence is approximated by a k-ɛ model. Detailed film effectiveness distributions are presented for different mass flow rate. The numerical results are compared with experimental data.

An alternative arrangement of metered dosing fluid using centrifugal pump

NASA Astrophysics Data System (ADS)

Islam, Md. Arafat; Ehsan, Md.

2017-06-01

Positive displacement dosing pumps are extensively used in various types of process industries. They are widely used for metering small flow rates of a dosing fluid into a main flow. High head and low controllable flow rates make these pumps suitable for industrial flow metering applications. However their pulsating flow is not very suitable for proper mixing of fluids and they are relatively more expensive to buy and maintain. Considering such problems, alternative techniques to control the fluid flow from a low cost centrifugal pump is practiced. These include - throttling, variable speed drive, impeller geometry control and bypass control. Variable speed drive and impeller geometry control are comparatively costly and the flow control by throttling is not an energy efficient process. In this study an arrangement of metered dosing flow was developed using a typical low cost centrifugal pump using bypass flow technique. Using bypass flow control technique a wide range of metered dosing flows under a range of heads were attained using fixed pump geometry and drive speed. The bulk flow returning from the system into the main tank ensures better mixing which may eliminate the need of separate agitators. Comparative performance study was made between the bypass flow control arrangement of centrifugal pump and a diaphragm type dosing pump. Similar heads and flow rates were attainable using the bypass control system compared to the diaphragm dosing pump, but using relatively more energy. Geometrical optimization of the centrifugal pump impeller was further carried out to make the bypass flow arrangement more energy efficient. Although both the systems run at low overall efficiencies but the capital cost could be reduced by about 87% compared to the dosing pump. The savings in capital investment and lower maintenance cost very significantly exceeds the relatively higher energy cost of the bypass system. This technique can be used as a cost effective solution for industries in Bangladesh and have been implemented in two salt iodization plants at Narayangang.

Design and clinical outcome of a novel 3D-printed prosthetic joint replacement for the human temporomandibular joint.

PubMed

Ackland, David; Robinson, Dale; Lee, Peter Vee Sin; Dimitroulis, George

2018-05-11

Stock prosthetic temporomandibular joint replacements come in limited sizes, and do not always encompass the joint anatomy that presents clinically. The aims of this study were twofold. Firstly, to design a personalized prosthetic total joint replacement for the treatment of a patient's end-stage temporomandibular joint osteoarthritis, to implant the prosthesis into the patient, and assess clinical outcome 12-months post-operatively; and secondly, to evaluate the influence of changes in prosthetic condyle geometry on implant load response during mastication. A 48-year-old female patient with Grade-5 osteoarthritis to the left temporomandibular joint was recruited, and a prosthesis developed to match the native temporomandibular joint anatomy. The prosthesis was 3D printed, sterilized and implanted into the patient, and pain and function measured 12-months post-operatively. The prosthesis load response during a chewing-bite and maximum-force bite was evaluated using a personalized multi-body musculoskeletal model. Simulations were performed after perturbing condyle thickness, neck length and head sphericity. Increases in prosthetic condyle neck length malaligned the mandible and perturbed temporomandibular joint force. Changes in condylar component thickness greatly influenced fixation screw stress response, while a more eccentric condylar head increased prosthetic joint-contact loading. Post-operatively, the prosthetic temporomandibular joint surgery reduced patient pain from 7/10 to 1/10 on a visual analog scale, and increased intercisal opening distance from 22 mm to 38 mm. This study demonstrates effectiveness of a personalized prosthesis that may ultimately be adapted to treat a wide-range of end-stage temporomandibular joint conditions, and highlights sensitivity of prosthesis load response to changes in condylar geometry. Copyright © 2018 Elsevier Ltd. All rights reserved.

Field of view of limitations in see-through HMD using geometric waveguides.

PubMed

DeHoog, Edward; Holmstedt, Jason; Aye, Tin

2016-08-01

Geometric waveguides are being integrated into head-mounted display (HMD) systems, where having see-through capability in a compact, lightweight form factor is required. We developed methods for determining the field of view (FOV) of such waveguide HMD systems and have analytically derived the FOV for waveguides using planar and curved geometries. By using real ray-tracing methods, we are able to show how the geometry and index of refraction of the waveguide, as well as the properties of the coupling optics, impact the FOV. Use of this analysis allows one to determine the maximum theoretical FOV of a planar or curved waveguide-based system.

Effects of volute geometry and impeller orbit on the hydraulic performance of a centrifugal pump

NASA Technical Reports Server (NTRS)

Flack, R. D.; Lanes, R. F.

1983-01-01

Overall performance data was taken for a Plexiglas water pump with a logarithmic spiral volute and rectangular cross sectioned flow channels. Parametric studies were made in which the center of the impeller was offset from the design center of the volute. The rig was also designed such that the impeller was allowed to synchronously orbit by a fixed amount about any center. The studies indicate that decreasing the tongue clearance decreases the head at low flowrates and increases the head at high flowrates. Also, decreasing the volute area in the first half of the volute and holding the tongue clearance the same, resulted in a decreased head for low flowrates but performance at high flowrates was not affected. Finally, the overall hydraulic performance was not affected by the impeller orbitting about the volute center.

Numerical simulation of transient temperature profiles for canned apple puree in semi-rigid aluminum based packaging during pasteurization.

PubMed

Shafiekhani, Soraya; Zamindar, Nafiseh; Hojatoleslami, Mohammad; Toghraie, Davood

2016-06-01

Pasteurization of canned apple puree was simulated for a 3-D geometry in a semi-rigid aluminum based container which was heated from all sides at 378 K. The computational fluid dynamics code Ansys Fluent 14.0 was used and the governing equations for energy, momentum, and continuity were computed using a finite volume method. The food model was assumed to have temperature-dependent properties. To validate the simulation, the apple puree was pasteurized in a water cascading retort. The effect of the mesh structures was studied for the temperature profiles during thermal processing. The experimental temperature in the slowest heating zone in the container was compared with the temperature predicted by the model and the difference was not significant. The study also investigated the impact of head space (water-vapor) on heat transfer.

Generating Facial Expressions Using an Anatomically Accurate Biomechanical Model.

PubMed

Wu, Tim; Hung, Alice; Mithraratne, Kumar

2014-11-01

This paper presents a computational framework for modelling the biomechanics of human facial expressions. A detailed high-order (Cubic-Hermite) finite element model of the human head was constructed using anatomical data segmented from magnetic resonance images. The model includes a superficial soft-tissue continuum consisting of skin, the subcutaneous layer and the superficial Musculo-Aponeurotic system. Embedded within this continuum mesh, are 20 pairs of facial muscles which drive facial expressions. These muscles were treated as transversely-isotropic and their anatomical geometries and fibre orientations were accurately depicted. In order to capture the relative composition of muscles and fat, material heterogeneity was also introduced into the model. Complex contact interactions between the lips, eyelids, and between superficial soft tissue continuum and deep rigid skeletal bones were also computed. In addition, this paper investigates the impact of incorporating material heterogeneity and contact interactions, which are often neglected in similar studies. Four facial expressions were simulated using the developed model and the results were compared with surface data obtained from a 3D structured-light scanner. Predicted expressions showed good agreement with the experimental data.

Integrated multiple-model adaptive fault identification and reconfigurable fault-tolerant control for Lead-Wing close formation systems

NASA Astrophysics Data System (ADS)

Liu, Chun; Jiang, Bin; Zhang, Ke

2018-03-01

This paper investigates the attitude and position tracking control problem for Lead-Wing close formation systems in the presence of loss of effectiveness and lock-in-place or hardover failure. In close formation flight, Wing unmanned aerial vehicle movements are influenced by vortex effects of the neighbouring Lead unmanned aerial vehicle. This situation allows modelling of aerodynamic coupling vortex-effects and linearisation based on optimal close formation geometry. Linearised Lead-Wing close formation model is transformed into nominal robust H-infinity models with respect to Mach hold, Heading hold, and Altitude hold autopilots; static feedback H-infinity controller is designed to guarantee effective tracking of attitude and position while manoeuvring Lead unmanned aerial vehicle. Based on H-infinity control design, an integrated multiple-model adaptive fault identification and reconfigurable fault-tolerant control scheme is developed to guarantee asymptotic stability of close-loop systems, error signal boundedness, and attitude and position tracking properties. Simulation results for Lead-Wing close formation systems validate the efficiency of the proposed integrated multiple-model adaptive control algorithm.

Postural abnormalities and contraversive pushing following right hemisphere brain damage.

PubMed

Lafosse, C; Kerckhofs, E; Vereeck, L; Troch, M; Van Hoydonck, G; Moeremans, M; Sneyers, C; Broeckx, J; Dereymaeker, L

2007-06-01

We investigated the presence of postural abnormalities in a consecutive sample of stroke patients, with either left or right brain damage, in relation to their perceived body position in space. The presence or absence of posture-related symptoms was judged by two trained therapists and subsequently analysed by hierarchical classes analysis (HICLAS). The subject classes resulting from the HICLAS model were further validated with respect to posture-related measurements, such as centre of gravity position and head position, as well as measurements related to the postural body scheme, such as the perception of postural and visual verticality. The results of the classification analysis clearly demonstrated a relation between the presence of right brain damage and abnormalities in body geometry. The HICLAS model revealed three classes of subjects: The first class contained almost all the patients without neglect and without any signs of contraversive pushing. They were mainly characterised by a normal body axis in any position. The second class were all neglect patients but predominantly without any contraversive pushing. The third class contained right brain damaged patients, all showing neglect and mostly exhibiting contraversive pushing. The patients in the third class showed a clear resistance to bringing the weight over to the ipsilesional side when the therapist attempted to make the subject achieve a vertical posture across the midline. The clear correspondence between abnormalities of the observed body geometry and the tilt of the subjective postural and visual vertical suggests that a patient's postural body geometry is characterised by leaning towards the side of space where he/she feels aligned with an altered postural body scheme. The presence of contraversive pushing after right brain damage points in to a spatial higher-order processing deficit underlying the higher frequency and severity of the axial postural abnormalities found after right brain lesions.

Computer-Aided Geometry Modeling

NASA Technical Reports Server (NTRS)

Shoosmith, J. N. (Compiler); Fulton, R. E. (Compiler)

1984-01-01

Techniques in computer-aided geometry modeling and their application are addressed. Mathematical modeling, solid geometry models, management of geometric data, development of geometry standards, and interactive and graphic procedures are discussed. The applications include aeronautical and aerospace structures design, fluid flow modeling, and gas turbine design.

Spatial calibration of an optical see-through head mounted display

PubMed Central

Gilson, Stuart J.; Fitzgibbon, Andrew W.; Glennerster, Andrew

2010-01-01

We present here a method for calibrating an optical see-through Head Mounted Display (HMD) using techniques usually applied to camera calibration (photogrammetry). Using a camera placed inside the HMD to take pictures simultaneously of a tracked object and features in the HMD display, we could exploit established camera calibration techniques to recover both the intrinsic and extrinsic properties of the HMD (width, height, focal length, optic centre and principal ray of the display). Our method gives low re-projection errors and, unlike existing methods, involves no time-consuming and error-prone human measurements, nor any prior estimates about the HMD geometry. PMID:18599125

Probability, geometry, and dynamics in the toss of a thick coin

NASA Astrophysics Data System (ADS)

Yong, Ee Hou; Mahadevan, L.

2011-12-01

When a thick cylindrical coin is tossed in the air and lands without bouncing on an inelastic substrate, it ends up on its face or its side. We account for the rigid body dynamics of spin and precession and calculate the probability distribution of heads, tails, and sides for a thick coin as a function of its dimensions and the distribution of its initial conditions. Our theory yields a simple expression for the aspect ratio of homogeneous coins with a prescribed frequency of heads or tails compared to sides, which we validate using data from the results of tossing coins of different aspect ratios.

Bulb turbine operating at medium head: XIA JIANG case study

NASA Astrophysics Data System (ADS)

Loiseau, F.; Desrats, C.; Petit, P.; Liu, J.

2012-11-01

With lots of references for 4-blade bulb turbines, such as these of Wu Jin Xia (4 units - 36.1 MW per unit - 9.2 m rated head), Chang Zhou (15 units - 46.7 MW per unit - 9.5 m rated head) and Tong Wan (4 units - 46.2 MW per unit - 11 m rated head), ALSTOM Power Hydro is one of the major suppliers of bulb turbines operating under medium head for the Chinese market. ALSTOM Power Hydro has been awarded in November 2010 a contract by Jiang Xi Province Xia Jiang Water Control Project Headquarters to equip Xia Jiang's new hydropower plant. The power dam is located on the Gan Jiang river, at about 160 km away from Nan Chang town in South Eastern China. The supply will consist in 5 bulb units including the furniture of both the turbine and its generator, for a total capacity of 200 MW, under a rated net head of 8.6 m. The prototype turbine is a 7.8 m diameter runner, rotating at 71.4 rpm speed. For this project, ALSTOM has proposed a fully new design of 4-blade bulb runner. This paper outlines the main steps of the hydraulic development. First of all, a fine tuning of the blade geometry was performed to enhance the runner behaviour at high loads and low heads, so that to fulfill the demanding requirements of efficiencies and maximum output. The challenge was also to keep an excellent cavitation behaviour, especially at the outer blade diameter in order to avoid cavitation erosion on the prototype. The shape of the blade was optimized by using the latest tools in computational fluid dynamics. Steady state simulations of the distributor and the runner were performed, in order to simulate more accurately the pressure fields on the blade and the velocity distribution at the outlet of the runner. Moreover, draft tube computations have been performed close to the design point and at higher loads. Then, a model fully homologous with the prototype was manufactured and tested at ALSTOM's laboratory in Grenoble (France). The model test results confirmed the predicted ones: the expected weighted average efficiency is higher than the guaranteed value and the maximum output was reached with a comfortable safety margin. A comparison of the experimental and numerical velocity probings under the runner is also proposed as an insight into the prediction of flow behaviour at the inlet of the draft tube.

The interaction of plume heads with compositional discontinuities in the Earth's mantle

NASA Technical Reports Server (NTRS)

Manga, Michael; Stone, Howard A.; O'Connell, Richard J.

1993-01-01

The effects of compositional discontinuities of density and viscosity in the Earth's mantle on the ascent of mantle plume heads is studied using a boundary integral numerical technique. Three specific problems are considered: (1) a plume head rising away from a deformable interface, (2) a plume head passing through an interface, and (3) a plume head approaching the surface of the Earth. For the case of a plume attached to a free-surface, the calculated time-dependent plume shapesare compared with experimental results. Two principle modes of plume head deformation are observed: plume head elingation or the formation of a cavity inside the plume head. The inferred structure of mantle plumes, namely, a large plume head with a long tail, is characteristic of plumes attached to their source region, and also of buoyant material moving away from an interface and of buoyant material moving through an interface from a high- to low-viscosity region. As a rising plume head approaches the upper mantle, most of the lower mantle will quickly drain from the gap between the plume head and the upper mantle if the plume head enters the upper mantle. If the plume head moves from a high- to low-viscosity region, the plume head becomes significantly elongated and, for the viscosity contrasts thought to exist in the Earth, could extend from the 670 km discontinuity to the surface. Plume heads that are extended owing to a viscosity decrease in the upper mantle have a cylindrical geometry. The dynamic surface topography induced by plume heads is bell-shaped when the top of the plume head is at depths greater than about 0.1 plume head radii. As the plume head approaches the surface and spreads, the dynamic topography becomes plateau-shaped. The largest stresses are produced in the early stages of plume spreading when the plume head is still nearly spherical, and the surface expression of these stresses is likely to be dominated by radial extension. As the plume spreads, compressional stresses on the surface are produced beyond the edges of the plume; consequently, extensional features will be produced above the plume head and may be surrounded by a ring of compressional features.

SABRINA: an interactive solid geometry modeling program for Monte Carlo

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, J.T.

SABRINA is a fully interactive three-dimensional geometry modeling program for MCNP. In SABRINA, a user interactively constructs either body geometry, or surface geometry models, and interactively debugs spatial descriptions for the resulting objects. This enhanced capability significantly reduces the effort in constructing and debugging complicated three-dimensional geometry models for Monte Carlo Analysis.

Poster — Thur Eve — 46: Monte Carlo model of the Novalis Classic 6MV stereotactic linear accelerator using the GATE simulation platform

DOE Office of Scientific and Technical Information (OSTI.GOV)

Wiebe, J; Department of Physics and Astronomy, University of Calgary, Calgary, AB; Ploquin, N

2014-08-15

Monte Carlo (MC) simulation is accepted as the most accurate method to predict dose deposition when compared to other methods in radiation treatment planning. Current dose calculation algorithms used for treatment planning can become inaccurate when small radiation fields and tissue inhomogeneities are present. At our centre the Novalis Classic linear accelerator (linac) is used for Stereotactic Radiosurgery (SRS). The first MC model to date of the Novalis Classic linac was developed at our centre using the Geant4 Application for Tomographic Emission (GATE) simulation platform. GATE is relatively new, open source MC software built from CERN's Geometry and Tracking 4more » (Geant4) toolkit. The linac geometry was modeled using manufacturer specifications, as well as in-house measurements of the micro MLC's. Among multiple model parameters, the initial electron beam was adjusted so that calculated depth dose curves agreed with measured values. Simulations were run on the European Grid Infrastructure through GateLab. Simulation time is approximately 8 hours on GateLab for a complete head model simulation to acquire a phase space file. Current results have a majority of points within 3% of the measured dose values for square field sizes ranging from 6×6 mm{sup 2} to 98×98 mm{sup 2} (maximum field size on the Novalis Classic linac) at 100 cm SSD. The x-ray spectrum was determined from the MC data as well. The model provides an investigation into GATE'S capabilities and has the potential to be used as a research tool and an independent dose calculation engine for clinical treatment plans.« less

A virtual photon energy fluence model for Monte Carlo dose calculation.

PubMed

Fippel, Matthias; Haryanto, Freddy; Dohm, Oliver; Nüsslin, Fridtjof; Kriesen, Stephan

2003-03-01

The presented virtual energy fluence (VEF) model of the patient-independent part of the medical linear accelerator heads, consists of two Gaussian-shaped photon sources and one uniform electron source. The planar photon sources are located close to the bremsstrahlung target (primary source) and to the flattening filter (secondary source), respectively. The electron contamination source is located in the plane defining the lower end of the filter. The standard deviations or widths and the relative weights of each source are free parameters. Five other parameters correct for fluence variations, i.e., the horn or central depression effect. If these parameters and the field widths in the X and Y directions are given, the corresponding energy fluence distribution can be calculated analytically and compared to measured dose distributions in air. This provides a method of fitting the free parameters using the measurements for various square and rectangular fields and a fixed number of monitor units. The next step in generating the whole set of base data is to calculate monoenergetic central axis depth dose distributions in water which are used to derive the energy spectrum by deconvolving the measured depth dose curves. This spectrum is also corrected to take the off-axis softening into account. The VEF model is implemented together with geometry modules for the patient specific part of the treatment head (jaws, multileaf collimator) into the XVMC dose calculation engine. The implementation into other Monte Carlo codes is possible based on the information in this paper. Experiments are performed to verify the model by comparing measured and calculated dose distributions and output factors in water. It is demonstrated that open photon beams of linear accelerators from two different vendors are accurately simulated using the VEF model. The commissioning procedure of the VEF model is clinically feasible because it is based on standard measurements in air and water. It is also useful for IMRT applications because a full Monte Carlo simulation of the treatment head would be too time-consuming for many small fields.

TH-E-BRE-07: Development of Dose Calculation Error Predictors for a Widely Implemented Clinical Algorithm

DOE Office of Scientific and Technical Information (OSTI.GOV)

Egan, A; Laub, W

2014-06-15

Purpose: Several shortcomings of the current implementation of the analytic anisotropic algorithm (AAA) may lead to dose calculation errors in highly modulated treatments delivered to highly heterogeneous geometries. Here we introduce a set of dosimetric error predictors that can be applied to a clinical treatment plan and patient geometry in order to identify high risk plans. Once a problematic plan is identified, the treatment can be recalculated with more accurate algorithm in order to better assess its viability. Methods: Here we focus on three distinct sources dosimetric error in the AAA algorithm. First, due to a combination of discrepancies inmore » smallfield beam modeling as well as volume averaging effects, dose calculated through small MLC apertures can be underestimated, while that behind small MLC blocks can overestimated. Second, due the rectilinear scaling of the Monte Carlo generated pencil beam kernel, energy is not properly transported through heterogeneities near, but not impeding, the central axis of the beamlet. And third, AAA overestimates dose in regions very low density (< 0.2 g/cm{sup 3}). We have developed an algorithm to detect the location and magnitude of each scenario within the patient geometry, namely the field-size index (FSI), the heterogeneous scatter index (HSI), and the lowdensity index (LDI) respectively. Results: Error indices successfully identify deviations between AAA and Monte Carlo dose distributions in simple phantom geometries. Algorithms are currently implemented in the MATLAB computing environment and are able to run on a typical RapidArc head and neck geometry in less than an hour. Conclusion: Because these error indices successfully identify each type of error in contrived cases, with sufficient benchmarking, this method can be developed into a clinical tool that may be able to help estimate AAA dose calculation errors and when it might be advisable to use Monte Carlo calculations.« less

Data integrity systems for organ contours in radiation therapy planning.

PubMed

Shah, Veeraj P; Lakshminarayanan, Pranav; Moore, Joseph; Tran, Phuoc T; Quon, Harry; Deville, Curtiland; McNutt, Todd R

2018-06-12

The purpose of this research is to develop effective data integrity models for contoured anatomy in a radiotherapy workflow for both real-time and retrospective analysis. Within this study, two classes of contour integrity models were developed: data driven models and contiguousness models. The data driven models aim to highlight contours which deviate from a gross set of contours from similar disease sites and encompass the following regions of interest (ROI): bladder, femoral heads, spinal cord, and rectum. The contiguousness models, which individually analyze the geometry of contours to detect possible errors, are applied across many different ROI's and are divided into two metrics: Extent and Region Growing over volume. After analysis, we found that 70% of detected bladder contours were verified as suspicious. The spinal cord and rectum models verified that 73% and 80% of contours were suspicious respectively. The contiguousness models were the most accurate models and the Region Growing model was the most accurate submodel. 100% of the detected noncontiguous contours were verified as suspicious, but in the cases of spinal cord, femoral heads, bladder, and rectum, the Region Growing model detected additional two to five suspicious contours that the Extent model failed to detect. When conducting a blind review to detect false negatives, it was found that all the data driven models failed to detect all suspicious contours. The Region Growing contiguousness model produced zero false negatives in all regions of interest other than prostate. With regards to runtime, the contiguousness via extent model took an average of 0.2 s per contour. On the other hand, the region growing method had a longer runtime which was dependent on the number of voxels in the contour. Both contiguousness models have potential for real-time use in clinical radiotherapy while the data driven models are better suited for retrospective use. © 2018 The Authors. Journal of Applied Clinical Medical Physics published by Wiley Periodicals, Inc. on behalf of American Association of Physicists in Medicine.

VARIAN CLINAC 6 MeV Photon Spectra Unfolding using a Monte Carlo Meshed Model

NASA Astrophysics Data System (ADS)

Morató, S.; Juste, B.; Miró, R.; Verdú, G.

2017-09-01

Energy spectrum is the best descriptive function to determine photon beam quality of a Medical Linear Accelerator (LinAc). The use of realistic photon spectra in Monte Carlo simulations has a great importance to obtain precise dose calculations in Radiotherapy Treatment Planning (RTP). Reconstruction of photon spectra emitted by medical accelerators from measured depth dose distributions in a water cube is an important tool for commissioning a Monte Carlo treatment planning system. Regarding this, the reconstruction problem is an inverse radiation transport function which is ill conditioned and its solution may become unstable due to small perturbations in the input data. This paper presents a more stable spectral reconstruction method which can be used to provide an independent confirmation of source models for a given machine without any prior knowledge of the spectral distribution. Monte Carlo models used in this work are built with unstructured meshes to simulate with realism the linear accelerator head geometry.

Organ and effective dose coefficients for cranial and caudal irradiation geometries: Neutrons

DOE Office of Scientific and Technical Information (OSTI.GOV)

Veinot, K. G.; Eckerman, K. F.; Hertel, N. E.

Dose coefficients based on the recommendations of International Commission on Radiological Protection (ICRP) Publication 103 were reported in ICRP Publication 116, the revision of ICRP Publication 74 and ICRU Publication 57 for the six reference irradiation geometries: anterior–posterior, posterior–anterior, right and left lateral, rotational and isotropic. In this work, dose coefficients for neutron irradiation of the body with parallel beams directed upward from below the feet (caudal) and downward from above the head (cranial) using the ICRP 103 methodology were computed using the MCNP 6.1 radiation transport code. The dose coefficients were determined for neutrons ranging in energy from 10more » –9 MeV to 10 GeV. Here, at energies below about 500 MeV, the cranial and caudal dose coefficients are less than those for the six reference geometries reported in ICRP Publication 116.« less

Organ and effective dose coefficients for cranial and caudal irradiation geometries: Neutrons

DOE PAGES

Veinot, K. G.; Eckerman, K. F.; Hertel, N. E.; ...

2016-08-29

Dose coefficients based on the recommendations of International Commission on Radiological Protection (ICRP) Publication 103 were reported in ICRP Publication 116, the revision of ICRP Publication 74 and ICRU Publication 57 for the six reference irradiation geometries: anterior–posterior, posterior–anterior, right and left lateral, rotational and isotropic. In this work, dose coefficients for neutron irradiation of the body with parallel beams directed upward from below the feet (caudal) and downward from above the head (cranial) using the ICRP 103 methodology were computed using the MCNP 6.1 radiation transport code. The dose coefficients were determined for neutrons ranging in energy from 10more » –9 MeV to 10 GeV. Here, at energies below about 500 MeV, the cranial and caudal dose coefficients are less than those for the six reference geometries reported in ICRP Publication 116.« less

Phase space methods in HMD systems

NASA Astrophysics Data System (ADS)

Babington, James

2017-06-01

We consider using phase space techniques and methods in analysing optical ray propagation in head mounted display systems. Two examples are considered that illustrate the concepts and methods. Firstly, a shark tooth freeform geometry, and secondly, a waveguide geometry that replicates a pupil in one dimension. Classical optics and imaging in particular provide a natural stage to employ phase space techniques, albeit as a constrained system. We consider how phase space provides a global picture of the physical ray trace data. As such, this gives a complete optical world history of all of the rays propagating through the system. Using this data one can look at, for example, how aberrations arise on a surface by surface basis. These can be extracted numerically from phase space diagrams in the example of a freeform imaging prism. For the waveguide geometry, phase space diagrams provide a way of illustrating how replicated pupils behave and what these imply for design considerations such as tolerances.

Coplanar tail-chase aerial combat as a differential game

NASA Technical Reports Server (NTRS)

Merz, A. W.; Hague, D. S.

1977-01-01

A reduced-order version of the one-on-one aerial combat problem is studied as a pursuit-evasion differential game. The coplanar motion takes place at given speeds and given maximum available turn rates, and is described by three state equations which are equivalent to the range, bearing, and heading of one aircraft relative to the other. The purpose of the study is to determine those relative geometries from which either aircraft can be guaranteed a win, regardless of the maneuver strategies of the other. Termination is specified by the tail-chase geometry, at which time the roles of pursuer and evader are known. The roles are found in general, together with the associated optimal turn maneuvers, by solution of the differential game of kind. For the numerical parameters chosen, neither aircraft can win from the majority of possible initial conditions if the other turns optimally in certain critical geometries.

A Bluetooth/PDR Integration Algorithm for an Indoor Positioning System.

PubMed

Li, Xin; Wang, Jian; Liu, Chunyan

2015-09-25

This paper proposes two schemes for indoor positioning by fusing Bluetooth beacons and a pedestrian dead reckoning (PDR) technique to provide meter-level positioning without additional infrastructure. As to the PDR approach, a more effective multi-threshold step detection algorithm is used to improve the positioning accuracy. According to pedestrians' different walking patterns such as walking or running, this paper makes a comparative analysis of multiple step length calculation models to determine a linear computation model and the relevant parameters. In consideration of the deviation between the real heading and the value of the orientation sensor, a heading estimation method with real-time compensation is proposed, which is based on a Kalman filter with map geometry information. The corrected heading can inhibit the positioning error accumulation and improve the positioning accuracy of PDR. Moreover, this paper has implemented two positioning approaches integrated with Bluetooth and PDR. One is the PDR-based positioning method based on map matching and position correction through Bluetooth. There will not be too much calculation work or too high maintenance costs using this method. The other method is a fusion calculation method based on the pedestrians' moving status (direct movement or making a turn) to determine adaptively the noise parameters in an Extended Kalman Filter (EKF) system. This method has worked very well in the elimination of various phenomena, including the "go and back" phenomenon caused by the instability of the Bluetooth-based positioning system and the "cross-wall" phenomenon due to the accumulative errors caused by the PDR algorithm. Experiments performed on the fourth floor of the School of Environmental Science and Spatial Informatics (SESSI) building in the China University of Mining and Technology (CUMT) campus showed that the proposed scheme can reliably achieve a 2-meter precision.

A Bluetooth/PDR Integration Algorithm for an Indoor Positioning System

PubMed Central

Li, Xin; Wang, Jian; Liu, Chunyan

2015-01-01

This paper proposes two schemes for indoor positioning by fusing Bluetooth beacons and a pedestrian dead reckoning (PDR) technique to provide meter-level positioning without additional infrastructure. As to the PDR approach, a more effective multi-threshold step detection algorithm is used to improve the positioning accuracy. According to pedestrians’ different walking patterns such as walking or running, this paper makes a comparative analysis of multiple step length calculation models to determine a linear computation model and the relevant parameters. In consideration of the deviation between the real heading and the value of the orientation sensor, a heading estimation method with real-time compensation is proposed, which is based on a Kalman filter with map geometry information. The corrected heading can inhibit the positioning error accumulation and improve the positioning accuracy of PDR. Moreover, this paper has implemented two positioning approaches integrated with Bluetooth and PDR. One is the PDR-based positioning method based on map matching and position correction through Bluetooth. There will not be too much calculation work or too high maintenance costs using this method. The other method is a fusion calculation method based on the pedestrians’ moving status (direct movement or making a turn) to determine adaptively the noise parameters in an Extended Kalman Filter (EKF) system. This method has worked very well in the elimination of various phenomena, including the “go and back” phenomenon caused by the instability of the Bluetooth-based positioning system and the “cross-wall” phenomenon due to the accumulative errors caused by the PDR algorithm. Experiments performed on the fourth floor of the School of Environmental Science and Spatial Informatics (SESSI) building in the China University of Mining and Technology (CUMT) campus showed that the proposed scheme can reliably achieve a 2-meter precision. PMID:26404277

The Planetary Data System Information Model for Geometry Metadata

NASA Astrophysics Data System (ADS)

Guinness, E. A.; Gordon, M. K.

2014-12-01

The NASA Planetary Data System (PDS) has recently developed a new set of archiving standards based on a rigorously defined information model. An important part of the new PDS information model is the model for geometry metadata, which includes, for example, attributes of the lighting and viewing angles of observations, position and velocity vectors of a spacecraft relative to Sun and observing body at the time of observation and the location and orientation of an observation on the target. The PDS geometry model is based on requirements gathered from the planetary research community, data producers, and software engineers who build search tools. A key requirement for the model is that it fully supports the breadth of PDS archives that include a wide range of data types from missions and instruments observing many types of solar system bodies such as planets, ring systems, and smaller bodies (moons, comets, and asteroids). Thus, important design aspects of the geometry model are that it standardizes the definition of the geometry attributes and provides consistency of geometry metadata across planetary science disciplines. The model specification also includes parameters so that the context of values can be unambiguously interpreted. For example, the reference frame used for specifying geographic locations on a planetary body is explicitly included with the other geometry metadata parameters. The structure and content of the new PDS geometry model is designed to enable both science analysis and efficient development of search tools. The geometry model is implemented in XML, as is the main PDS information model, and uses XML schema for validation. The initial version of the geometry model is focused on geometry for remote sensing observations conducted by flyby and orbiting spacecraft. Future releases of the PDS geometry model will be expanded to include metadata for landed and rover spacecraft.

Electroactive polymer and shape memory alloy actuators in biomimetics and humanoids

NASA Astrophysics Data System (ADS)

Tadesse, Yonas

2013-04-01

There is a strong need to replicate natural muscles with artificial materials as the structure and function of natural muscle is optimum for articulation. Particularly, the cylindrical shape of natural muscle fiber and its interconnected structure promote the critical investigation of artificial muscles geometry and implementation in the design phase of certain platforms. Biomimetic robots and Humanoid Robot heads with Facial Expressions (HRwFE) are some of the typical platforms that can be used to study the geometrical effects of artificial muscles. It has been shown that electroactive polymer and shape memory alloy artificial muscles and their composites are some of the candidate materials that may replicate natural muscles and showed great promise for biomimetics and humanoid robots. The application of these materials to these systems reveals the challenges and associated technologies that need to be developed in parallel. This paper will focus on the computer aided design (CAD) models of conductive polymer and shape memory alloys in various biomimetic systems and Humanoid Robot with Facial Expressions (HRwFE). The design of these systems will be presented in a comparative manner primarily focusing on three critical parameters: the stress, the strain and the geometry of the artificial muscle.

Measurement and simulation of millimeter wave scattering cross-sections from steel-reinforced concrete

NASA Astrophysics Data System (ADS)

Hassan, A. M.; Martys, N. S.; Garboczi, E. J.; McMichael, R. D.; Stiles, M. D.; Plusquellic, D. F.; Stutzman, P. E.; Wang, S.; Provenzano, V.; Surek, J. T.; Novotny, D. R.; Coder, J. B.; Janezic, M. D.; Kim, S.

2014-02-01

Some iron oxide corrosion products exhibit antiferromagnetic magnetic resonances (AFMR) at frequencies on the order of 100 GHz at ambient temperatures. AFMR can be detected in laboratory conditions, which serves as the basis for a new non-destructive spectroscopic method for detecting early corrosion. When attempting to measure the steel corrosion in reinforced concrete in the field, rebar geometry must be taken into account. Experiments and numerical simulations have been developed at frequencies near 100 GHz to sort out these effects. The experimental setup involves a vector network analyzer with converter heads to up-convert the output frequency, which is then connected to a horn antenna followed by a 7.5 cm diameter polymer lens to focus the waves on the sample. Two sets of samples were studied: uniform cylindrical rods and rebar corrosion samples broken out of concrete with different kinds of coatings. Electromagnetic scattering from uniform rods were calculated numerically using classical modal expansion. A finite-element electromagnetic solver was used to model more complex rebar geometry and non-uniform corrosion layers. Experimental and numerical data were compared to help quantify and understand the anticipated effect of local geometrical features on AFMR measurements.

Place recognition and heading retrieval are mediated by dissociable cognitive systems in mice.

PubMed

Julian, Joshua B; Keinath, Alexander T; Muzzio, Isabel A; Epstein, Russell A

2015-05-19

A lost navigator must identify its current location and recover its facing direction to restore its bearings. We tested the idea that these two tasks--place recognition and heading retrieval--might be mediated by distinct cognitive systems in mice. Previous work has shown that numerous species, including young children and rodents, use the geometric shape of local space to regain their sense of direction after disorientation, often ignoring nongeometric cues even when they are informative. Notably, these experiments have almost always been performed in single-chamber environments in which there is no ambiguity about place identity. We examined the navigational behavior of mice in a two-chamber paradigm in which animals had to both recognize the chamber in which they were located (place recognition) and recover their facing direction within that chamber (heading retrieval). In two experiments, we found that mice used nongeometric features for place recognition, but simultaneously failed to use these same features for heading retrieval, instead relying exclusively on spatial geometry. These results suggest the existence of separate systems for place recognition and heading retrieval in mice that are differentially sensitive to geometric and nongeometric cues. We speculate that a similar cognitive architecture may underlie human navigational behavior.

Cerebrospinal Fluid Pressure: Revisiting Factors Influencing Optic Nerve Head Biomechanics

PubMed Central

Hua, Yi; Voorhees, Andrew P.; Sigal, Ian A.

2018-01-01

Purpose To model the sensitivity of the optic nerve head (ONH) biomechanical environment to acute variations in IOP, cerebrospinal fluid pressure (CSFP), and central retinal artery blood pressure (BP). Methods We extended a previously published numerical model of the ONH to include 24 factors representing tissue anatomy and mechanical properties, all three pressures, and constraints on the optic nerve (CON). A total of 8340 models were studied to predict factor influences on 98 responses in a two-step process: a fractional factorial screening analysis to identify the 16 most influential factors, followed by a response surface methodology to predict factor effects in detail. Results The six most influential factors were, in order: IOP, CON, moduli of the sclera, lamina cribrosa (LC) and dura, and CSFP. IOP and CSFP affected different aspects of ONH biomechanics. The strongest influence of CSFP, more than twice that of IOP, was on the rotation of the peripapillary sclera. CSFP had similar influence on LC stretch and compression to moduli of sclera and LC. On some ONHs, CSFP caused large retrolamina deformations and subarachnoid expansion. CON had a strong influence on LC displacement. BP overall influence was 633 times smaller than that of IOP. Conclusions Models predict that IOP and CSFP are the top and sixth most influential factors on ONH biomechanics. Different IOP and CSFP effects suggest that translaminar pressure difference may not be a good parameter to predict biomechanics-related glaucomatous neuropathy. CON may drastically affect the responses relating to gross ONH geometry and should be determined experimentally. PMID:29332130

Two-dimensional, steady-state model of ground-water flow, Nevada Test Site and vicinity, Nevada-California

USGS Publications Warehouse

Waddell, R.K.

1982-01-01

A two-dimensional, steady-state model of ground-water flow beneath the Nevada Test Site and vicinity has been developed using inverse techniques. The area is underlain by clastic and carbonate rocks of Precambrian and Paleozoic age and by volcanic rocks and alluvium of Tertiary and Quaternary age that have been juxtaposed by normal and strike-slip faulting. Aquifers are composed of carbonate and volcanic rocks and alluvium. Characteristics of the flow system are determined by distribution of low-conductivity rocks (barriers); by recharge originating in the Spring Mountains, Pahranagat, Timpahute, and Sheep Ranges, and in Pahute Mesa; and by underflow beneath Pahute Mesa from Gold Flat and Kawich Valley. Discharge areas (Ash Meadows, Oasis Valley, Alkali Flat, and Furnace Creek Ranch) are upgradient from barriers. Sensitivities of simulated hydraulic heads and fluxes to variations in model parameters were calculated to guide field studies and to help estimate errors in predictions from transport modeling. Hydraulic heads and fluxes are very sensitive to variations in the greater magnitude recharge/discharge terms. Transmissivity at a location may not be the most important transmissivity for determining flux there. Transmissivities and geometries of large barriers that impede flow from Pahute Mesa have major effects on fluxes elsewhere; as their transmissivities are decreased, flux beneath western Jackass Flats and Yucca Mountains is increased as water is diverted around the barriers. Fortymile Canyon is underlain by highly transmissive rocks that cause potentiometric contours to vee upgradient; increasing their transmissivity increases flow through them, and decreases it beneath Yucca Mountain. (USGS)

The Influence of Environment Geometry on Injury Outcome: II. Lumbosacral Spine

NASA Astrophysics Data System (ADS)

Shaibani, Saami J.

2006-03-01

It is widely agreed that the type of motor vehicle in which an occupant is situated can sometimes make a noticeable difference in injury potential even when the insult suffered is the same. A simple example might be the same occupant being in a sports car as opposed to a minivan, but such anecdotal experience does not usually help to distinguish the effect of particular features within the same category of vehicle. Other research has addressed the role of environment geometry in neck injury,[1] and this paper adopts the same methodology for the low back. The heights, lengths and angles of the seat cushion and seat back (including head rest) are all examined as descriptors of passenger compartment geometry, and any changes caused by these are determined. Useful results are feasible with the large patient population available even if clear patterns in these are not always present. As in earlier work, there is still the option of finding individual outcomes on a case-by-case basis. [1] The influence of environment geometry on injury outcome: I. Cervical spine, Bull Am Phys Soc, in press (2006).

A programmable DNA origami nanospring that reveals force-induced adjacent binding of myosin VI heads

PubMed Central

Iwaki, M.; Wickham, S. F.; Ikezaki, K.; Yanagida, T.; Shih, W. M.

2016-01-01

Mechanosensitive biological nanomachines such as motor proteins and ion channels regulate diverse cellular behaviour. Combined optical trapping with single-molecule fluorescence imaging provides a powerful methodology to clearly characterize the mechanoresponse, structural dynamics and stability of such nanomachines. However, this system requires complicated experimental geometry, preparation and optics, and is limited by low data-acquisition efficiency. Here we develop a programmable DNA origami nanospring that overcomes these issues. We apply our nanospring to human myosin VI, a mechanosensory motor protein, and demonstrate nanometre-precision single-molecule fluorescence imaging of the individual motor domains (heads) under force. We observe force-induced transitions of myosin VI heads from non-adjacent to adjacent binding, which correspond to adapted roles for low-load and high-load transport, respectively. Our technique extends single-molecule studies under force and clarifies the effect of force on biological processes. PMID:27941751

A programmable DNA origami nanospring that reveals force-induced adjacent binding of myosin VI heads.

PubMed

Iwaki, M; Wickham, S F; Ikezaki, K; Yanagida, T; Shih, W M

2016-12-12

Mechanosensitive biological nanomachines such as motor proteins and ion channels regulate diverse cellular behaviour. Combined optical trapping with single-molecule fluorescence imaging provides a powerful methodology to clearly characterize the mechanoresponse, structural dynamics and stability of such nanomachines. However, this system requires complicated experimental geometry, preparation and optics, and is limited by low data-acquisition efficiency. Here we develop a programmable DNA origami nanospring that overcomes these issues. We apply our nanospring to human myosin VI, a mechanosensory motor protein, and demonstrate nanometre-precision single-molecule fluorescence imaging of the individual motor domains (heads) under force. We observe force-induced transitions of myosin VI heads from non-adjacent to adjacent binding, which correspond to adapted roles for low-load and high-load transport, respectively. Our technique extends single-molecule studies under force and clarifies the effect of force on biological processes.

Analysis of wall shear stress around a competitive swimmer using 3D Navier-Stokes equations in CFD.

PubMed

Popa, C V; Zaidi, H; Arfaoui, A; Polidori, G; Taiar, R; Fohanno, S

2011-01-01

This paper deals with the flow dynamics around a competitive swimmer during underwater glide phases occurring at the start and at every turn. The influence of the head position, namely lifted up, aligned and lowered, on the wall shear stress and the static pressure distributions is analyzed. The problem is considered as 3D and in steady hydrodynamic state. Three velocities (1.4 m/s, 2.2 m/s and 3.1 m/s) that correspond to inter-regional, national and international swimming levels are studied. The flow around the swimmer is assumed turbulent. The Reynolds-averaged Navier-Stokes (RANS) equations are solved with the standard k-ω turbulent model by using the CFD (computational fluid dynamics) numerical method based on a volume control approach. Numerical simulations are carried out with the ANSYS FLUENT® CFD code. The results show that the wall shear stress increases with the velocity and consequently the drag force opposing the movement of the swimmer increases as well. Also, high wall shear stresses are observed in the areas where the body shape, globally rigid in form, presents complex surface geometries such as the head, shoulders, buttocks, heel and chest.

Linking suckling biomechanics to the development of the palate

NASA Astrophysics Data System (ADS)

Li, Jingtao; Johnson, Chelsey A.; Smith, Andrew A.; Hunter, Daniel J.; Singh, Gurpreet; Brunski, John B.; Helms, Jill A.

2016-02-01

Skulls are amongst the most informative documents of evolutionary history but a complex geometry, coupled with composite material properties and complicated biomechanics, have made it particularly challenging to identify mechanical principles guiding the skull’s morphogenesis. Despite this challenge, multiple lines of evidence, for example the relationship between masticatory function and the evolution of jaw shape, nonetheless suggest that mechanobiology plays a major role in skull morphogenesis. To begin to tackle this persistent challenge, cellular, molecular and tissue-level analyses of the developing mouse palate were coupled with finite element modeling to demonstrate that patterns of strain created by mammalian-specific oral behaviors produce complementary patterns of chondrogenic gene expression in an initially homogeneous population of cranial neural crest cells. Neural crest cells change from an osteogenic to a chondrogenic fate, leading to the materialization of cartilaginous growth plate-like structures in the palatal midline. These growth plates contribute to lateral expansion of the head but are transient structures; when the strain patterns associated with suckling dissipate at weaning, the growth plates disappear and the palate ossifies. Thus, mechanical cues such as strain appear to co-regulate cell fate specification and ultimately, help drive large-scale morphogenetic changes in head shape.

A patterned microtexture to reduce friction and increase longevity of prosthetic hip joints

PubMed Central

Chyr, Anthony; Qiu, Mingfeng; Speltz, Jared; Jacobsen, Ronald L.; Sanders, Anthony P.; Raeymaekers, Bart

2014-01-01

More than 285,000 total hip replacement surgeries are performed in the US each year. Most prosthetic hip joints consist of a cobalt-chromium (CoCr) femoral head that articulates with a polyethylene acetabular component, lubricated with synovial fluid. The statistical survivorship of these metal-on-polyethylene prosthetic hip joints declines significantly after 10 to 15 years of use, primarily as a result of polyethylene wear and wear debris incited disease. The current engineering paradigm to increase the longevity of prosthetic hip joints is to improve the mechanical properties of the polyethylene component, and to manufacture ultra-smooth articulating surfaces. In contrast, we show that adding a patterned microtexture to the ultra-smooth CoCr femoral head reduces friction when articulating with the polyethylene acetabular liner. The microtexture increases the load-carrying capacity and the thickness of the joint lubricant film, which reduces contact between the articulating surfaces. As a result, friction and wear is reduced. We have used a lubrication model to design the geometry of the patterned microtexture, and experimentally demonstrate reduced friction for the microtextured compared to conventional smooth surrogate prosthetic hip joints. PMID:25013240

Optical profilometer using laser based conical triangulation for inspection of inner geometry of corroded pipes in cylindrical coordinates

NASA Astrophysics Data System (ADS)

Buschinelli, Pedro D. V.; Melo, João. Ricardo C.; Albertazzi, Armando; Santos, João. M. C.; Camerini, Claudio S.

2013-04-01

An axis-symmetrical optical laser triangulation system was developed by the authors to measure the inner geometry of long pipes used in the oil industry. It has a special optical configuration able to acquire shape information of the inner geometry of a section of a pipe from a single image frame. A collimated laser beam is pointed to the tip of a 45° conical mirror. The laser light is reflected in such a way that a radial light sheet is formed and intercepts the inner geometry and forms a bright laser line on a section of the inspected pipe. A camera acquires the image of the laser line through a wide angle lens. An odometer-based triggering system is used to shot the camera to acquire a set of equally spaced images at high speed while the device is moved along the pipe's axis. Image processing is done in real-time (between images acquisitions) thanks to the use of parallel computing technology. The measured geometry is analyzed to identify corrosion damages. The measured geometry and results are graphically presented using virtual reality techniques and devices as 3D glasses and head-mounted displays. The paper describes the measurement principles, calibration strategies, laboratory evaluation of the developed device, as well as, a practical example of a corroded pipe used in an industrial gas production plant.

Diffracted and head waves associated with waves on nonseparable surfaces

NASA Technical Reports Server (NTRS)

Barger, Raymond L.

1992-01-01

A theory is presented for computing waves radiated from waves on a smooth surface. With the assumption that attention of the surface wave is due only to radiation and not to dissipation in the surface material, the radiation coefficient is derived in terms of the attenuation factor. The excitation coefficient is determined by the reciprocity condition. Formulas for the shape and the spreading of the radiated wave are derived, and some sample calculations are presented. An investigation of resonant phase matching for nonseparable surfaces is presented with a sample calculation. A discussion of how such calculations might be related to resonant frequencies of nonseparable thin shell structures is included. A description is given of nonseparable surfaces that can be modeled in the vector that facilitates use of the appropriate formulas of differential geometry.

Design of multihundredwatt DIPS for robotic space missions

NASA Technical Reports Server (NTRS)

Bents, D. J.; Geng, S. M.; Schreiber, J. G.; Withrow, C. A.; Schmitz, P. C.; Mccomas, Thomas J.

1991-01-01

Design of a dynamic isotope power system (DIPS) general purpose heat source (GPHS) and small free piston Stirling engine (FPSE) is being pursued as a potential lower cost alternative to radioisotope thermoelectric generators (RTG's). The design is targeted at the power needs of future unmanned deep space and planetary surface exploration missions ranging from scientific probes to SEI precursor missions. These are multihundredwatt missions. The incentive for any dynamic system is that it can save fuel which reduces cost and radiological hazard. However, unlike a conventional DIPS based on turbomachinery converions, the small Stirling DIPS can be advantageously scaled to multihundred watt unit size while preserving size and weight competitiveness with RTG's. Stirling conversion extends the range where dynamic systems are competitive to hundreds of watts (a power range not previously considered for dynamic systems). The challenge of course is to demonstrate reliability similar to RTG experience. Since the competative potential of FPSE as an isotope converter was first identified, work has focused on the feasibility of directly integrating GPHS with the Stirling heater head. Extensive thermal modeling of various radiatively coupled heat source/heater head geometries were performed using data furnished by the developers of FPSE and GPHS. The analysis indicates that, for the 1050 K heater head configurations considered, GPHS fuel clad temperatures remain within safe operating limits under all conditions including shutdown of one engine. Based on these results, preliminary characterizations of multihundred watt units were established.

Neutron H*(10) estimation and measurements around 18MV linac.

PubMed

Cerón Ramírez, Pablo Víctor; Díaz Góngora, José Antonio Irán; Paredes Gutiérrez, Lydia Concepción; Rivera Montalvo, Teodoro; Vega Carrillo, Héctor René

2016-11-01

Thermoluminescent dosimetry, analytical techniques and Monte Carlo calculations were used to estimate the dose of neutron radiation in a treatment room with a linear electron accelerator of 18MV. Measurements were carried out through neutron ambient dose monitors which include pairs of thermoluminescent dosimeters TLD 600 ( 6 LiF: Mg, Ti) and TLD 700 ( 7 LiF: Mg, Ti), which were placed inside a paraffin spheres. The measurements has allowed to use NCRP 151 equations, these expressions are useful to find relevant dosimetric quantities. In addition, photoneutrons produced by linac head were calculated through MCNPX code taking into account the geometry and composition of the linac head principal parts. Copyright © 2016 Elsevier Ltd. All rights reserved.

A comparison between EGS4 and MCNP computer modeling of an in vivo X-ray fluorescence system.

PubMed

Al-Ghorabie, F H; Natto, S S; Al-Lyhiani, S H

2001-03-01

The Monte Carlo computer codes EGS4 and MCNP were used to develop a theoretical model of a 180 degrees geometry in vivo X-ray fluorescence system for the measurement of platinum concentration in head and neck tumors. The model included specification of the photon source, collimators, phantoms and detector. Theoretical results were compared and evaluated against X-ray fluorescence data obtained experimentally from an existing system developed by the Swansea In Vivo Analysis and Cancer Research Group. The EGS4 results agreed well with the MCNP results. However, agreement between the measured spectral shape obtained using the experimental X-ray fluorescence system and the simulated spectral shape obtained using the two Monte Carlo codes was relatively poor. The main reason for the disagreement between the results arises from the basic assumptions which the two codes used in their calculations. Both codes assume a "free" electron model for Compton interactions. This assumption will underestimate the results and invalidates any predicted and experimental spectra when compared with each other.

Coil optimisation for transcranial magnetic stimulation in realistic head geometry.

PubMed

Koponen, Lari M; Nieminen, Jaakko O; Mutanen, Tuomas P; Stenroos, Matti; Ilmoniemi, Risto J

Transcranial magnetic stimulation (TMS) allows focal, non-invasive stimulation of the cortex. A TMS pulse is inherently weakly coupled to the cortex; thus, magnetic stimulation requires both high current and high voltage to reach sufficient intensity. These requirements limit, for example, the maximum repetition rate and the maximum number of consecutive pulses with the same coil due to the rise of its temperature. To develop methods to optimise, design, and manufacture energy-efficient TMS coils in realistic head geometry with an arbitrary overall coil shape. We derive a semi-analytical integration scheme for computing the magnetic field energy of an arbitrary surface current distribution, compute the electric field induced by this distribution with a boundary element method, and optimise a TMS coil for focal stimulation. Additionally, we introduce a method for manufacturing such a coil by using Litz wire and a coil former machined from polyvinyl chloride. We designed, manufactured, and validated an optimised TMS coil and applied it to brain stimulation. Our simulations indicate that this coil requires less than half the power of a commercial figure-of-eight coil, with a 41% reduction due to the optimised winding geometry and a partial contribution due to our thinner coil former and reduced conductor height. With the optimised coil, the resting motor threshold of abductor pollicis brevis was reached with the capacitor voltage below 600 V and peak current below 3000 A. The described method allows designing practical TMS coils that have considerably higher efficiency than conventional figure-of-eight coils. Copyright © 2017 Elsevier Inc. All rights reserved.

The applicability of a computer model for predicting head injury incurred during actual motor vehicle collisions.

PubMed

Moran, Stephan G; Key, Jason S; McGwin, Gerald; Keeley, Jason W; Davidson, James S; Rue, Loring W

2004-07-01

Head injury is a significant cause of both morbidity and mortality. Motor vehicle collisions (MVCs) are the most common source of head injury in the United States. No studies have conclusively determined the applicability of computer models for accurate prediction of head injuries sustained in actual MVCs. This study sought to determine the applicability of such models for predicting head injuries sustained by MVC occupants. The Crash Injury Research and Engineering Network (CIREN) database was queried for restrained drivers who sustained a head injury. These collisions were modeled using occupant dynamic modeling (MADYMO) software, and head injury scores were generated. The computer-generated head injury scores then were evaluated with respect to the actual head injuries sustained by the occupants to determine the applicability of MADYMO computer modeling for predicting head injury. Five occupants meeting the selection criteria for the study were selected from the CIREN database. The head injury scores generated by MADYMO were lower than expected given the actual injuries sustained. In only one case did the computer analysis predict a head injury of a severity similar to that actually sustained by the occupant. Although computer modeling accurately simulates experimental crash tests, it may not be applicable for predicting head injury in actual MVCs. Many complicating factors surrounding actual MVCs make accurate computer modeling difficult. Future modeling efforts should consider variables such as age of the occupant and should account for a wider variety of crash scenarios.

Flight display dynamics and compensatory head movements in pilots.

PubMed

Beer, Jeremy; Freeman, David

2007-06-01

Experiments measured the optokinetic cervical reflex (OKCR), wherein the banking pilot aligns the head with the horizon. In a synthetic cockpit, the flight display was manipulated to test whether changing the visual reference frame would alter OKCR. Eight subjects (five rated pilots) flew a route in simulated visual meteorological conditions that required them to bank the aircraft frequently. Pilots' head tilt was characterized using both the conventional method of regressing against simultaneous aircraft bank, and also an event-based analysis, which identified head movements before, during, and after each turn. Three display configurations were compared to determine whether pilots' orientation would ever migrate from the horizon to the aircraft symbol. The first was a conventional "Inside-Out" condition. A "Frequency-Separated" condition combined Inside-Out horizon geometry with Outside-In dynamics for the aircraft symbol, which depicted joystick bank inputs. In the "Outside-In" condition, the aircraft symbol rolled against a static horizon. Regressions identified an interaction (p < 0.001) between display condition and aircraft bank: head tilt followed horizon tilt in Inside-Out and Frequency-Separated conditions, while remaining mostly level in the Outside-In condition. The event-based analysis identified anticipatory head movements in Inside-Out and Frequency-Separated conditions: 95% CI indicated that before each turn, head tilt favored the direction of the imminent bank. While the conventional analysis confirmed that the horizon comprises a primary spatial reference, the finer-grained event-based analysis indicated that pilots' reference can migrate at least temporarily to the vehicle, and that OKCR can be preceded by anticipatory head movements in the opposite direction.

The Articulation of Sauropod Necks: Methodology and Mythology

PubMed Central

Stevens, Kent A.

2013-01-01

Sauropods are often imagined to have held their heads high atop necks that ascended in a sweeping curve that was formed either intrinsically because of the shape of their vertebrae, or behaviorally by lifting the head, or both. Their necks are also popularly depicted in life with poses suggesting avian flexibility. The grounds for such interpretations are examined in terms of vertebral osteology, inferences about missing soft tissues, intervertebral flexibility, and behavior. Osteologically, the pronounced opisthocoely and conformal central and zygapophyseal articular surfaces strongly constrain the reconstruction of the cervical vertebral column. The sauropod cervico-dorsal vertebral column is essentially straight, in contrast to the curvature exhibited in those extant vertebrates that naturally hold their heads above rising necks. Regarding flexibility, extant vertebrates with homologous articular geometries preserve a degree of zygapophyseal overlap at the limits of deflection, a constraint that is further restricted by soft tissues. Sauropod necks, if similarly constrained, were capable of sweeping out large feeding surfaces, yet much less capable of retracting the head to explore the enclosed volume in an avian manner. Behaviorally, modern vertebrates generally assume characteristic neck postures which are close to the intrinsic curvature of the undeflected neck. With the exception of some vertebrates that can retract their heads to balance above their shoulders at rest (e.g., felids, lagomorphs, and some ratites), the undeflected neck generally predicts the default head height at rest and during locomotion. PMID:24205266

The articulation of sauropod necks: methodology and mythology.

PubMed

Stevens, Kent A

2013-01-01

Sauropods are often imagined to have held their heads high atop necks that ascended in a sweeping curve that was formed either intrinsically because of the shape of their vertebrae, or behaviorally by lifting the head, or both. Their necks are also popularly depicted in life with poses suggesting avian flexibility. The grounds for such interpretations are examined in terms of vertebral osteology, inferences about missing soft tissues, intervertebral flexibility, and behavior. Osteologically, the pronounced opisthocoely and conformal central and zygapophyseal articular surfaces strongly constrain the reconstruction of the cervical vertebral column. The sauropod cervico-dorsal vertebral column is essentially straight, in contrast to the curvature exhibited in those extant vertebrates that naturally hold their heads above rising necks. Regarding flexibility, extant vertebrates with homologous articular geometries preserve a degree of zygapophyseal overlap at the limits of deflection, a constraint that is further restricted by soft tissues. Sauropod necks, if similarly constrained, were capable of sweeping out large feeding surfaces, yet much less capable of retracting the head to explore the enclosed volume in an avian manner. Behaviorally, modern vertebrates generally assume characteristic neck postures which are close to the intrinsic curvature of the undeflected neck. With the exception of some vertebrates that can retract their heads to balance above their shoulders at rest (e.g., felids, lagomorphs, and some ratites), the undeflected neck generally predicts the default head height at rest and during locomotion.

SABRINA: an interactive three-dimensional geometry-mnodeling program for MCNP

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, J.T. III

SABRINA is a fully interactive three-dimensional geometry-modeling program for MCNP, a Los Alamos Monte Carlo code for neutron and photon transport. In SABRINA, a user constructs either body geometry or surface geometry models and debugs spatial descriptions for the resulting objects. This enhanced capability significantly reduces effort in constructing and debugging complicated three-dimensional geometry models for Monte Carlo analysis. 2 refs., 33 figs.

SU-F-J-192: A Quick and Effective Method to Validate Patient’s Daily Setup and Geometry Changes Prior to Proton Treatment Delivery Based On Water Equivalent Thickness Projection Imaging (WETPI) for Head Neck Cancer (HNC) Patient

DOE Office of Scientific and Technical Information (OSTI.GOV)

Liu, G; Qin, A; Zhang, J

Purpose: With the implementation of Cone-beam Computed-Tomography (CBCT) in proton treatment, we introduces a quick and effective tool to verify the patient’s daily setup and geometry changes based on the Water-Equivalent-Thickness Projection-Image(WETPI) from individual beam angle. Methods: A bilateral head neck cancer(HNC) patient previously treated via VMAT was used in this study. The patient received 35 daily CBCT during the whole treatment and there is no significant weight change. The CT numbers of daily CBCTs were corrected by mapping the CT numbers from simulation CT via Deformable Image Registration(DIR). IMPT plan was generated using 4-field IMPT robust optimization (3.5% rangemore » and 3mm setup uncertainties) with beam angle 60, 135, 300, 225 degree. WETPI within CTV through all beam directions were calculated. 3%/3mm gamma index(GI) were used to provide a quantitative comparison between initial sim-CT and mapped daily CBCT. To simulate an extreme case where human error is involved, a couch bar was manually inserted in front of beam angle 225 degree of one CBCT. WETPI was compared in this scenario. Results: The average of GI passing rate of this patient from different beam angles throughout the treatment course is 91.5 ± 8.6. In the cases with low passing rate, it was found that the difference between shoulder and neck angle as well as the head rest often causes major deviation. This indicates that the most challenge in treating HNC is the setup around neck area. In the extreme case where a couch bar is accidently inserted in the beam line, GI passing rate drops to 52 from 95. Conclusion: WETPI and quantitative gamma analysis give clinicians, therapists and physicists a quick feedback of the patient’s setup accuracy or geometry changes. The tool could effectively avoid some human errors. Furthermore, this tool could be used potentially as an initial signal to trigger plan adaptation.« less

Calibration and Validation of a Finite ELement Model of THor-K Anthropomorphic Test Device for Aerospace Safety Applications

NASA Technical Reports Server (NTRS)

Putnam, J. B.; Unataroiu, C. D.; Somers, J. T.

2014-01-01

The THOR anthropomorphic test device (ATD) has been developed and continuously improved by the National Highway Traffic Safety Administration to provide automotive manufacturers an advanced tool that can be used to assess the injury risk of vehicle occupants in crash tests. Recently, a series of modifications were completed to improve the biofidelity of THOR ATD [1]. The updated THOR Modification Kit (THOR-K) ATD was employed at Wright-Patterson Air Base in 22 impact tests in three configurations: vertical, lateral, and spinal [2]. Although a computational finite element (FE) model of the THOR had been previously developed [3], updates to the model were needed to incorporate the recent changes in the modification kit. The main goal of this study was to develop and validate a FE model of the THOR-K ATD. The CAD drawings of the THOR-K ATD were reviewed and FE models were developed for the updated parts. For example, the head-skin geometry was found to change significantly, so its model was re-meshed (Fig. 1a). A protocol was developed to calibrate each component identified as key to the kinematic and kinetic response of the THOR-K head/neck ATD FE model (Fig. 1b). The available ATD tests were divided in two groups: a) calibration tests where the unknown material parameters of deformable parts (e.g., head skin, pelvis foam) were optimized to match the data and b) validation tests where the model response was only compared with test data by calculating their score using CORrelation and Analysis (CORA) rating system. Finally, the whole ATD model was validated under horizontal-, vertical-, and lateral-loading conditions against data recorded in the Wright Patterson tests [2]. Overall, the final THOR-K ATD model developed in this study is shown to respond similarly to the ATD in all validation tests. This good performance indicates that the optimization performed during calibration by using the CORA score as objective function is not test specific. Therefore confidence is provided in the ATD model for uses in predicting response in test conditions not performed in this study such those observed in the spacecraft landing. Comparison studies with ATD and human models may also be performed to contribute to future changes in THOR ATD design in an effort to improve its biofidelity, which has been traditionally based on post-mortem human subject testing and designer experience.

On the geometry dependence of differential pathlength factor for near-infrared spectroscopy. I. Steady-state with homogeneous medium

PubMed Central

Piao, Daqing; Barbour, Randall L.; Graber, Harry L.; Lee, Daniel C.

2015-01-01

Abstract. This work analytically examines some dependences of the differential pathlength factor (DPF) for steady-state photon diffusion in a homogeneous medium on the shape, dimension, and absorption and reduced scattering coefficients of the medium. The medium geometries considered include a semi-infinite geometry, an infinite-length cylinder evaluated along the azimuthal direction, and a sphere. Steady-state photon fluence rate in the cylinder and sphere geometries is represented by a form involving the physical source, its image with respect to the associated extrapolated half-plane, and a radius-dependent term, leading to simplified formula for estimating the DPFs. With the source-detector distance and medium optical properties held fixed across all three geometries, and equal radii for the cylinder and sphere, the DPF is the greatest in the semi-infinite and the smallest in the sphere geometry. When compared to the results from finite-element method, the DPFs analytically estimated for 10 to 25 mm source–detector separations on a sphere of 50 mm radius with μa=0.01  mm−1 and μs′=1.0  mm−1 are on average less than 5% different. The approximation for sphere, generally valid for a diameter ≥20 times of the effective attenuation pathlength, may be useful for rapid estimation of DPFs in near-infrared spectroscopy of an infant head and for short source–detector separation. PMID:26465613

[Stereovideographic evaluation of the postural geometry of healthy and scoliotic patients].

PubMed

De la Huerta, F; Leroux, M A; Zabjek, K F; Coillard, C; Rivard, C H

1998-01-01

Idiopathic scoliosis principally characterised by a deformation of the vertebral column can also be associated to postural abnormalities. The validity and reliability of current quantitative postural evaluations has not been thoroughly documented, frequently limited by a two dimensional view of the patient, and do not include the whole posture of the patient. The purpose of this study is to 1) quantify within and between-session reliability of a stereovideographic Postural Geometry (PG) evaluation and 2) to investigate the sensitivity of this technique for the postural evaluation of scoliosis patients. The PG of 14 control subjects and 9 untreated scoliosis patients were evaluated with 5 repeat trials, on two occasions. Postural geometry parameters that describe the position and orientation of the pelvis, trunk, scapular girdle and head were calculated based on the 3-dimensional co-ordinates of anatomical landmarks. The mean between and within-session variability across all parameters were 12.5 mm, 2.8 degrees and 5.4 mm and 1.4 degrees respectively. The patient group was heterogeneous with some noted pathological characteristics. This global stereovideographic postural geometry evaluation appears to demonstrate sufficient reliability and sensitivity to follow-up on the posture of scoliosis patients.

Channel geometry change of a first-order stream after a small debris flow in Ashio Mountains of central Japan

NASA Astrophysics Data System (ADS)

Hattanji, T.; Wasklewicz, T.

2006-12-01

We examined geometry change of a steep first-order channel with a laserscanner before and after a small debris flow. The study site is located in chert area, Ashio Mountains, Japan. On August 12, 2005, a 20-year storm event with maximum 1-hour rainfall of 75.4 mm/h triggered a small landslide at a steep channel head. The sliding material moved as a debris flow along the first-order channel (C3) to the mouth. We successfully measured high-resolution channel topography with the Leica Geosystems High-Definition Surveying Laser Scanner before (April 30) and after the debris-flow event (October 9-11). Width, depth and other related parameters were measured for 30 selected cross sections. Bankfull stage of this first-order channel after the debris-flow event is much higher than two-year flood stage. The magnitude of channel geometry change varies non-linearly in downstream direction. The non-linear variability is attributed to differences in stream bed and bank characteristics. Bedrock-channel reach is less impacted by the debris flow. The largest magnitude changes in the channel geometry parameters occur along colluvially confined channel reaches.

Analytical calculation of proton linear energy transfer in voxelized geometries including secondary protons

NASA Astrophysics Data System (ADS)

Sanchez-Parcerisa, D.; Cortés-Giraldo, M. A.; Dolney, D.; Kondrla, M.; Fager, M.; Carabe, A.

2016-02-01

In order to integrate radiobiological modelling with clinical treatment planning for proton radiotherapy, we extended our in-house treatment planning system FoCa with a 3D analytical algorithm to calculate linear energy transfer (LET) in voxelized patient geometries. Both active scanning and passive scattering delivery modalities are supported. The analytical calculation is much faster than the Monte-Carlo (MC) method and it can be implemented in the inverse treatment planning optimization suite, allowing us to create LET-based objectives in inverse planning. The LET was calculated by combining a 1D analytical approach including a novel correction for secondary protons with pencil-beam type LET-kernels. Then, these LET kernels were inserted into the proton-convolution-superposition algorithm in FoCa. The analytical LET distributions were benchmarked against MC simulations carried out in Geant4. A cohort of simple phantom and patient plans representing a wide variety of sites (prostate, lung, brain, head and neck) was selected. The calculation algorithm was able to reproduce the MC LET to within 6% (1 standard deviation) for low-LET areas (under 1.7 keV μm-1) and within 22% for the high-LET areas above that threshold. The dose and LET distributions can be further extended, using radiobiological models, to include radiobiological effectiveness (RBE) calculations in the treatment planning system. This implementation also allows for radiobiological optimization of treatments by including RBE-weighted dose constraints in the inverse treatment planning process.

Analytical calculation of proton linear energy transfer in voxelized geometries including secondary protons.

PubMed

Sanchez-Parcerisa, D; Cortés-Giraldo, M A; Dolney, D; Kondrla, M; Fager, M; Carabe, A

2016-02-21

In order to integrate radiobiological modelling with clinical treatment planning for proton radiotherapy, we extended our in-house treatment planning system FoCa with a 3D analytical algorithm to calculate linear energy transfer (LET) in voxelized patient geometries. Both active scanning and passive scattering delivery modalities are supported. The analytical calculation is much faster than the Monte-Carlo (MC) method and it can be implemented in the inverse treatment planning optimization suite, allowing us to create LET-based objectives in inverse planning. The LET was calculated by combining a 1D analytical approach including a novel correction for secondary protons with pencil-beam type LET-kernels. Then, these LET kernels were inserted into the proton-convolution-superposition algorithm in FoCa. The analytical LET distributions were benchmarked against MC simulations carried out in Geant4. A cohort of simple phantom and patient plans representing a wide variety of sites (prostate, lung, brain, head and neck) was selected. The calculation algorithm was able to reproduce the MC LET to within 6% (1 standard deviation) for low-LET areas (under 1.7 keV μm(-1)) and within 22% for the high-LET areas above that threshold. The dose and LET distributions can be further extended, using radiobiological models, to include radiobiological effectiveness (RBE) calculations in the treatment planning system. This implementation also allows for radiobiological optimization of treatments by including RBE-weighted dose constraints in the inverse treatment planning process.

Comparisons of Computed Mobile Phone Induced SAR in the SAM Phantom to That in Anatomically Correct Models of the Human Head.

PubMed

Beard, Brian B; Kainz, Wolfgang; Onishi, Teruo; Iyama, Takahiro; Watanabe, Soichi; Fujiwara, Osamu; Wang, Jianqing; Bit-Babik, Giorgi; Faraone, Antonio; Wiart, Joe; Christ, Andreas; Kuster, Niels; Lee, Ae-Kyoung; Kroeze, Hugo; Siegbahn, Martin; Keshvari, Jafar; Abrishamkar, Houman; Simon, Winfried; Manteuffel, Dirk; Nikoloski, Neviana

2006-06-05

The specific absorption rates (SAR) determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct models of the human head when exposed to a mobile phone model are compared as part of a study organized by IEEE Standards Coordinating Committee 34, SubCommittee 2, and Working Group 2, and carried out by an international task force comprising 14 government, academic, and industrial research institutions. The detailed study protocol defined the computational head and mobile phone models. The participants used different finite-difference time-domain software and independently positioned the mobile phone and head models in accordance with the protocol. The results show that when the pinna SAR is calculated separately from the head SAR, SAM produced a higher SAR in the head than the anatomically correct head models. Also the larger (adult) head produced a statistically significant higher peak SAR for both the 1- and 10-g averages than did the smaller (child) head for all conditions of frequency and position.

Chain architecture and micellization: A mean-field coarse-grained model for poly(ethylene oxide) alkyl ether surfactants

DOE Office of Scientific and Technical Information (OSTI.GOV)

García Daza, Fabián A.; Mackie, Allan D., E-mail: allan.mackie@urv.cat; Colville, Alexander J.

2015-03-21

Microscopic modeling of surfactant systems is expected to be an important tool to describe, understand, and take full advantage of the micellization process for different molecular architectures. Here, we implement a single chain mean field theory to study the relevant equilibrium properties such as the critical micelle concentration (CMC) and aggregation number for three sets of surfactants with different geometries maintaining constant the number of hydrophobic and hydrophilic monomers. The results demonstrate the direct effect of the block organization for the surfactants under study by means of an analysis of the excess energy and entropy which can be accurately determinedmore » from the mean-field scheme. Our analysis reveals that the CMC values are sensitive to branching in the hydrophilic head part of the surfactant and can be observed in the entropy-enthalpy balance, while aggregation numbers are also affected by splitting the hydrophobic tail of the surfactant and are manifested by slight changes in the packing entropy.« less

Chain architecture and micellization: A mean-field coarse-grained model for poly(ethylene oxide) alkyl ether surfactants

NASA Astrophysics Data System (ADS)

García Daza, Fabián A.; Colville, Alexander J.; Mackie, Allan D.

2015-03-01

Microscopic modeling of surfactant systems is expected to be an important tool to describe, understand, and take full advantage of the micellization process for different molecular architectures. Here, we implement a single chain mean field theory to study the relevant equilibrium properties such as the critical micelle concentration (CMC) and aggregation number for three sets of surfactants with different geometries maintaining constant the number of hydrophobic and hydrophilic monomers. The results demonstrate the direct effect of the block organization for the surfactants under study by means of an analysis of the excess energy and entropy which can be accurately determined from the mean-field scheme. Our analysis reveals that the CMC values are sensitive to branching in the hydrophilic head part of the surfactant and can be observed in the entropy-enthalpy balance, while aggregation numbers are also affected by splitting the hydrophobic tail of the surfactant and are manifested by slight changes in the packing entropy.

Suzaku Observations of the HMXB 1A 1118-61

NASA Technical Reports Server (NTRS)

Suchy, Slawomir; Pottschmidt, Katja; Rothschild, Richard E.; Wilms, Joern; Fuerst, Felis; Barragan, Laura; Caballero, Isabel; Grinberg, Victoria; Kreykenbohm, Ingo; Doroshenko, Victor;

Feasibility of fast neutron analysis for the detection of explosives buried in soil

NASA Astrophysics Data System (ADS)

Faust, A. A.; McFee, J. E.; Bowman, C. L.; Mosquera, C.; Andrews, H. R.; Kovaltchouk, V. D.; Ing, H.

2011-12-01

A commercialized thermal neutron analysis (TNA) sensor has been developed to confirm the presence of buried bulk explosives as part of a multi-sensor anti-tank landmine detection system. Continuing improvements to the TNA system have included the use of an electronic pulsed neutron generator that offers the possibility of applying fast neutron analysis (FNA) methods to improve the system's detection capability. This paper describes an investigation into the use of FNA as a complementary component in such a TNA system. The results of a modeling study using simple geometries and a full model of the TNA sensor head are presented, as well as preliminary results from an experimental associated particle imaging (API) system that supports the modeling study results. The investigation has concluded that the pulsed beam FNA approach would not improve the detection performance of a TNA system for landmine or buried IED detection in a confirmation role, and could not be made into a practical stand-alone detection system for buried anti-tank landmines. Detection of buried landmines and IEDs by FNA remains a possibility, however, through the use of the API technique.

Numerical simulation of droplet impact onto a solid sphere in mid-air

NASA Astrophysics Data System (ADS)

Banitabaei, Sayed Abdolhossein; Amirfazli, Alidad

2017-11-01

Collision of a droplet and a particle in mid-air has applications in chemical, petrochemical, and pharmaceutical industries. As a result of a head-on collision between a droplet and a hydrophobic particle with a relative diameter of a thin liquid film is created in the form of a hallow truncated cone (i.e. lamella). In this work, a numerical simulation was developed based on VOF method for head-on collision of a falling droplet and a moving particle. Impact outcomes predicted by the model shows a fair agreement with the experimental images of lamellas (Vp = 6.8 and Vd = 0.68 m/s). Using the simulation model, the effect of liquid viscosity and surface tension on impact outcomes were studied. As viscosity increases, the lamella thickness increases accordingly. This happens as more energy transfer is required to move the liquid layers against each other to create a longer, and therefore thinner, lamella. However, a small decrease in viscosity halts the lamella formation as the boundary layer thickness in the spreading liquid gets so small that a crown cannot be developed. Moreover, investigation of the effect of particle wettability on the impact outcomes indicates that a lamella only forms due to impact of a droplet onto a hydrophobic particle. The lamella geometry is not affected by the particle wettability after contact angle reaches a certain threshold. These results show a good agreement with the literature of drop impact on a stationary particle.

Characterization of tribological sealing system componenets using Scanning Electron Microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Shuster, M.; Deis, M.

1996-12-31

A system approach to solving the tribological problems associated with sealing joints implies comprehensive investigation of all the components. Any measurable parameters, including geometry, density (porosity), hardness distributions, microstructure and grain size changes observed during routine metallurgical analysis could provide evidence of the root cause of failure. In the head-gasket-block sealing system of the internal combustion engine, the EDS evaluation of the chlorine and sulfur distribution through the head gasket flange fracture in conjunction with analysis of the sludge between the head, block and gasket surfaces pointed to the corrosive nature of the gasket flange cracking. This approach is evenmore » more useful for the closed tribological system of telescopic hydraulic cylinders or rotary axle shaft oil seals. In these cases in addition to the routine metallurgical analysis of the metal shaft surface, we have to analyze the rubber or plastic sealing elements. The influence of oil contamination as a destructive mechanism must also be evaluated.« less

Design and evaluation of an imaging informatics system for analytics-based decision support in radiation therapy

NASA Astrophysics Data System (ADS)

Deshpande, Ruchi; DeMarco, John; Liu, Brent J.

2015-03-01

We have developed a comprehensive DICOM RT specific database of retrospective treatment planning data for radiation therapy of head and neck cancer. Further, we have designed and built an imaging informatics module that utilizes this database to perform data mining. The end-goal of this data mining system is to provide radiation therapy decision support for incoming head and neck cancer patients, by identifying best practices from previous patients who had the most similar tumor geometries. Since the performance of such systems often depends on the size and quality of the retrospective database, we have also placed an emphasis on developing infrastructure and strategies to encourage data sharing and participation from multiple institutions. The infrastructure and decision support algorithm have both been tested and evaluated with 51 sets of retrospective treatment planning data of head and neck cancer patients. We will present the overall design and architecture of our system, an overview of our decision support mechanism as well as the results of our evaluation.

Long term three dimensional tracking of orthodontic patients using registered cone beam CT and photogrammetry.

PubMed

Boulanger, Pierre; Flores-Mir, Carlos; Ramirez, Juan F; Mesa, Elizabeth; Branch, John W

2009-01-01

The measurements from registered images obtained from Cone Beam Computed Tomography (CBCT) and a photogrammetric sensor are used to track three-dimensional shape variations of orthodontic patients before and after their treatments. The methodology consists of five main steps: (1) the patient's bone and skin shapes are measured in 3D using the fusion of images from a CBCT and a photogrammetric sensor. (2) The bone shape is extracted from the CBCT data using a standard marching cube algorithm. (3) The bone and skin shape measurements are registered using titanium targets located on the head of the patient. (4) Using a manual segmentation technique the head and lower jaw geometry are extracted separately to deal with jaw motion at the different record visits. (5) Using natural features of the upper head the two datasets are then registered with each other and then compared to evaluate bone, teeth, and skin displacements before and after treatments. This procedure is now used at the University of Alberta orthodontic clinic.

Three-dimensional printing (3DP) of neonatal head phantom for ultrasound: thermocouple embedding and simulation of bone.

PubMed

Gatto, Matteo; Memoli, Gianluca; Shaw, Adam; Sadhoo, Neelaksh; Gelat, Pierre; Harris, Russell A

2012-09-01

A neonatal head phantom, comprising of an ellipsoidal geometry and including a circular aperture for simulating the fontanel was designed and fabricated, in order to allow an objective assessment of thermal rise in tissues during trans-cranial ultrasonic scanning of pre-term neonates. The precise position of a series of thermocouples was determined on the basis of finite-element analysis, which identified crucial target points for the thermal monitoring within the phantom geometry. Three-Dimensional Printing (3DP) was employed for the manufacture of the skull phantom, which was subsequently filled with dedicated brain-mimic material. A novel 3DP material combination was found to be able to mimic the acoustic properties of neonatal skull bone. Similarly, variations of a standard recipe for tissue mimic were examined, until one was found to mimic the brain of an infant. A specific strategy was successfully pursued to embed a thermocouple within the 3DP skull phantom during the manufacturing process. An in-process machine vision system was used to assess the correct position of the deposited thermocouple inside the fabricated skull phantom. An external silicone-made skin-like covering completed the phantom and was manufactured through a Direct Rapid Tooling (DRT) technique. Copyright © 2011 IPEM. Published by Elsevier Ltd. All rights reserved.

Long-term hydrodynamic response induced by past climatic and geomorphologic forcing: The case of the Paris basin, France

NASA Astrophysics Data System (ADS)

Jost, A.; Violette, S.; Gonçalvès, J.; Ledoux, E.; Guyomard, Y.; Guillocheau, F.; Kageyama, M.; Ramstein, G.; Suc, J.-P.

In the framework of safe underground storage of radioactive waste in low-permeability layers, it is essential to evaluate the mobility of deep groundwaters over timescales of several million years. On these timescales, the environmental evolution of a repository should depend upon a range of natural processes that are primarily driven by climate and geomorphologic variations. In this paper, the response of the Paris basin groundwater system to variations in its hydrodynamic boundary conditions induced by past climate and geodynamic changes over the last five million years is investigated. A three-dimensional transient modelling of the Paris basin aquifer/aquitard system was developed using the code NEWSAM (Ecole des Mines de Paris, ENSMP). The geometry and hydrodynamic parameters of the model originate from a basin model, NEWBAS (ENSMP), built to simulate the geological history of the basin. Geomorphologic evolution is deduced from digital elevation model analysis, which allows to estimate river-valley incision and alpine surrection. Climate forcing results from palaeoclimate modelling experiments using the LMDz atmospheric general circulation model (Institut Pierre Simon Laplace) with a refined spatial resolution, for the present, the Last Glacial Maximum (21 ka) and the Middle Pliocene Warmth (˜3 Ma). The water balance is computed by the distributed hydrological model MODSUR (ENSMP). Results about the simulated evolution of piezometric heads in the system in response to the altered boundary conditions are presented, in particular in the vicinity of ANDRA’s Bure potential repository site within the Callovo-Oxfordian argillaceous layer. For the present, the comparison of head patterns between steady state and time dependent simulation shows little differences for aquifer layers close to the surface but suggests a transient state of the current system in the main aquitards of the basin and in the deep aquifers, characterized by abnormally low fluid potentials. The dependence of the boundary-induced transient effects on the hydraulic diffusivity is illustrated by means of a sensitivity study.

Small Stirling dynamic isotope power system for robotic space missions

NASA Technical Reports Server (NTRS)

Bents, D. J.

1992-01-01

The design of a multihundred-watt Dynamic Isotope Power System (DIPS), based on the U.S. Department of Energy (DOE) General Purpose Heat Source (GPHS) and small (multihundred-watt) free-piston Stirling engine (FPSE), is being pursued as a potential lower cost alternative to radioisotope thermoelectric generators (RTG's). The design is targeted at the power needs of future unmanned deep space and planetary surface exploration missions ranging from scientific probes to Space Exploration Initiative precursor missions. Power level for these missions is less than a kilowatt. The incentive for any dynamic system is that it can save fuel and reduce costs and radiological hazard. Unlike DIPS based on turbomachinery conversion (e.g. Brayton), this small Stirling DIPS can be advantageously scaled to multihundred-watt unit size while preserving size and mass competitiveness with RTG's. Stirling conversion extends the competitive range for dynamic systems down to a few hundred watts--a power level not previously considered for dynamic systems. The challenge for Stirling conversion will be to demonstrate reliability and life similar to RTG experience. Since the competitive potential of FPSE as an isotope converter was first identified, work has focused on feasibility of directly integrating GPHS with the Stirling heater head. Thermal modeling of various radiatively coupled heat source/heater head geometries has been performed using data furnished by the developers of FPSE and GPHS. The analysis indicates that, for the 1050 K heater head configurations considered, GPHS fuel clad temperatures remain within acceptable operating limits. Based on these results, preliminary characterizations of multihundred-watt units have been established.

Fabrication and characterization of a 3-D non-homogeneous tissue-like mouse phantom for optical imaging

NASA Astrophysics Data System (ADS)

Avtzi, Stella; Zacharopoulos, Athanasios; Psycharakis, Stylianos; Zacharakis, Giannis

2013-11-01

In vivo optical imaging of biological tissue not only requires the development of new theoretical models and experimental procedures, but also the design and construction of realistic tissue-mimicking phantoms. However, most of the phantoms available currently in literature or the market, have either simple geometrical shapes (cubes, slabs, cylinders) or when realistic in shape they use homogeneous approximations of the tissue or animal under investigation. The goal of this study is to develop a non-homogeneous realistic phantom that matches the anatomical geometry and optical characteristics of the mouse head in the visible and near-infrared spectral range. The fabrication of the phantom consisted of three stages. Initially, anatomical information extracted from either mouse head atlases or structural imaging modalities (MRI, XCT) was used to design a digital phantom comprising of the three main layers of the mouse head; the brain, skull and skin. Based on that, initial prototypes were manufactured by using accurate 3D printing, allowing complex objects to be built layer by layer with sub-millimeter resolution. During the second stage the fabrication of individual molds was performed by embedding the prototypes into a rubber-like silicone mixture. In the final stage the detailed phantom was constructed by loading the molds with epoxy resin of controlled optical properties. The optical properties of the resin were regulated by using appropriate quantities of India ink and intralipid. The final phantom consisted of 3 layers, each one with different absorption and scattering coefficient (μa,μs) to simulate the region of the mouse brain, skull and skin.

Three-dimensional analysis of the proximal humeral and glenoid geometry using MicroScribe 3D digitizer.

PubMed

Owaydhah, Wejdan H; Alobaidy, Mohammad A; Alraddadi, Abdulrahman S; Soames, Roger W

2017-07-01

To understand the geometry of the proximal humerus and glenoid fossa to facilitate the design of components used in shoulder arthroplasty. The aim is to evaluate the geometry of the proximal humerus and glenoid fossa and their relationship using a MicroScribe 3D digitizer. Scans and measurements were obtained from 20 pairs of dry proximal humeri and scapulae [10 female and 10 male cadavers: median age 81 years (range 70-94 years)] using a MicroScribe 3D digitizer and Rhinoceros software. Means (±SD) of humeral inclination, medial wall angle of the bicipital groove, and radius of the humeral head values were 135 ± 11°, 39 ± 19°, and 14 ± 3 mm, respectively. Means (±SD) of glenoid height and width were 35 ± 4 and 26 ± 4 mm, while the means (±SD) of the angles of glenoid inclination, retroversion, and rotation were 87 ± 32°, 96 ± 10°, and 9 ± 6°, respectively. A significant difference in glenoid height (P ≤ 0.002) and width (P ≤ 0.0001) was observed between males and females, despite them having almost an identical radius of the humeral head, glenoid inclination, retroversion, and angle of rotation. There was also a significant difference (P ≤ 0.01) in the angle of glenoid retroversion between the right and left sides. Using a MicroScribe 3D digitizer, the glenoid fossa was observed to be significantly smaller in females than males; furthermore, there was a difference in glenoid retroversion between the right and left sides.

Fault Diagnostics and Prognostics for Large Segmented SRMs

NASA Technical Reports Server (NTRS)

Luchinsky, Dmitry; Osipov, Viatcheslav V.; Smelyanskiy, Vadim N.; Timucin, Dogan A.; Uckun, Serdar; Hayashida, Ben; Watson, Michael; McMillin, Joshua; Shook, David; Johnson, Mont;

A Geometric Capacity–Demand Analysis of Maternal Levator Muscle Stretch Required for Vaginal Delivery

PubMed Central

Tracy, Paige V.; DeLancey, John O.; Ashton-Miller, James A.

2016-01-01

Because levator ani (LA) muscle injuries occur in approximately 13% of all vaginal births, insights are needed to better prevent them. In Part I of this paper, we conducted an analysis of the bony and soft tissue factors contributing to the geometric “capacity” of the maternal pelvis and pelvic floor to deliver a fetal head without incurring stretch injury of the maternal soft tissue. In Part II, we quantified the range in demand, represented by the variation in fetal head size and shape, placed on the maternal pelvic floor. In Part III, we analyzed the capacity-to-demand geometric ratio, g, in order to determine whether a mother can deliver a head of given size without stretch injury. The results of a Part I sensitivity analysis showed that initial soft tissue loop length (SL) had the greatest effect on maternal capacity, followed by the length of the soft tissue loop above the inferior pubic rami at ultimate crowning, then subpubic arch angle (SPAA) and head size, and finally the levator origin separation distance. We found the more caudal origin of the puborectal portion of the levator muscle helps to protect it from the stretch injuries commonly observed in the pubovisceral portion. Part II fetal head molding index (MI) and fetal head size revealed fetal head circumference values ranging from 253 to 351 mm, which would increase up to 11 mm upon face presentation. The Part III capacity-demand analysis of g revealed that, based on geometry alone, the 10th percentile maternal capacity predicted injury for all head sizes, the 25th percentile maternal capacity could deliver half of all head sizes, while the 50th percentile maternal capacity could deliver a head of any size without injury. If ultrasound imaging could be operationalized to make measurements of ratio g, it might be used to usefully inform women on their level of risk for levator injury during vaginal birth. PMID:26746116

A Geometric Capacity-Demand Analysis of Maternal Levator Muscle Stretch Required for Vaginal Delivery.

PubMed

Tracy, Paige V; DeLancey, John O; Ashton-Miller, James A

2016-02-01

Because levator ani (LA) muscle injuries occur in approximately 13% of all vaginal births, insights are needed to better prevent them. In Part I of this paper, we conducted an analysis of the bony and soft tissue factors contributing to the geometric "capacity" of the maternal pelvis and pelvic floor to deliver a fetal head without incurring stretch injury of the maternal soft tissue. In Part II, we quantified the range in demand, represented by the variation in fetal head size and shape, placed on the maternal pelvic floor. In Part III, we analyzed the capacity-to-demand geometric ratio, g, in order to determine whether a mother can deliver a head of given size without stretch injury. The results of a Part I sensitivity analysis showed that initial soft tissue loop length (SL) had the greatest effect on maternal capacity, followed by the length of the soft tissue loop above the inferior pubic rami at ultimate crowning, then subpubic arch angle (SPAA) and head size, and finally the levator origin separation distance. We found the more caudal origin of the puborectal portion of the levator muscle helps to protect it from the stretch injuries commonly observed in the pubovisceral portion. Part II fetal head molding index (MI) and fetal head size revealed fetal head circumference values ranging from 253 to 351 mm, which would increase up to 11 mm upon face presentation. The Part III capacity-demand analysis of g revealed that, based on geometry alone, the 10th percentile maternal capacity predicted injury for all head sizes, the 25th percentile maternal capacity could deliver half of all head sizes, while the 50th percentile maternal capacity could deliver a head of any size without injury. If ultrasound imaging could be operationalized to make measurements of ratio g, it might be used to usefully inform women on their level of risk for levator injury during vaginal birth.

3D printing of MRI compatible components: why every MRI research group should have a low-budget 3D printer.

PubMed

Herrmann, Karl-Heinz; Gärtner, Clemens; Güllmar, Daniel; Krämer, Martin; Reichenbach, Jürgen R

2014-10-01

To evaluate low budget 3D printing technology to create MRI compatible components. A 3D printer is used to create customized MRI compatible components, a loop-coil platform and a multipart mouse fixation. The mouse fixation is custom fit for a dedicated coil and facilitates head fixation with bite bar, anesthetic gas supply and biomonitoring sensors. The mouse fixation was tested in a clinical 3T scanner. All parts were successfully printed and proved MR compatible. Both design and printing were accomplished within a few days and the final print results were functional with well defined details and accurate dimensions (Δ<0.4mm). MR images of the mouse head clearly showed reduced motion artifacts, ghosting and signal loss when using the fixation. We have demonstrated that a low budget 3D printer can be used to quickly progress from a concept to a functional device at very low production cost. While 3D printing technology does impose some restrictions on model geometry, additive printing technology can create objects with complex internal structures that can otherwise not be created by using lathe technology. Thus, we consider a 3D printer a valuable asset for MRI research groups. Copyright © 2014 IPEM. Published by Elsevier Ltd. All rights reserved.

Comparisons of Computed Mobile Phone Induced SAR in the SAM Phantom to That in Anatomically Correct Models of the Human Head

PubMed Central

Beard, Brian B.; Kainz, Wolfgang; Onishi, Teruo; Iyama, Takahiro; Watanabe, Soichi; Fujiwara, Osamu; Wang, Jianqing; Bit-Babik, Giorgi; Faraone, Antonio; Wiart, Joe; Christ, Andreas; Kuster, Niels; Lee, Ae-Kyoung; Kroeze, Hugo; Siegbahn, Martin; Keshvari, Jafar; Abrishamkar, Houman; Simon, Winfried; Manteuffel, Dirk; Nikoloski, Neviana

2018-01-01

The specific absorption rates (SAR) determined computationally in the specific anthropomorphic mannequin (SAM) and anatomically correct models of the human head when exposed to a mobile phone model are compared as part of a study organized by IEEE Standards Coordinating Committee 34, SubCommittee 2, and Working Group 2, and carried out by an international task force comprising 14 government, academic, and industrial research institutions. The detailed study protocol defined the computational head and mobile phone models. The participants used different finite-difference time-domain software and independently positioned the mobile phone and head models in accordance with the protocol. The results show that when the pinna SAR is calculated separately from the head SAR, SAM produced a higher SAR in the head than the anatomically correct head models. Also the larger (adult) head produced a statistically significant higher peak SAR for both the 1- and 10-g averages than did the smaller (child) head for all conditions of frequency and position. PMID:29515260

Morphometric analysis of acetabular dysplasia in cerebral palsy: three-dimensional CT study.

PubMed

Gose, Shinichi; Sakai, Takashi; Shibata, Toru; Murase, Tsuyoshi; Yoshikawa, Hideki; Sugamoto, Kazuomi

2009-12-01

Three-dimensional computed tomography (3D-CT) eliminates the positioning errors and allows the clinician to more accurately assess the radiographic parameters present. To elucidate the 3D geometry of the acetabulum and the extent of hip subluxation/dislocation in patients with cerebral palsy (CP), quantitative morphometric analysis was performed using 3D-CT data. We evaluated 150 hips in 75 patients with bilateral spastic CP. The mean age of the patients was 5.4 years (range: 2.7 to 6.9 y). The fitting plane of the ilium was projected onto the coronal plane and then onto the sagittal plane, and then the angle formed with a horizontal line was defined as CTalpha (the lateral opening angle) and CTbeta (the sagittal inclination angle), respectively. The center of the acetabulum and the femoral head were defined, and the distance between these centers was divided by the femoral head diameter, defined as CT migration percentage (CTMP, %). In 123 (82%) of the 150 hips, the femoral head center was located posteriorly, superiorly, and laterally relative to the acetabular center. Large CTalpha cases tended to show large CTMP. CTalpha and CTMP were significantly larger in the cases with Gross Motor Functional Classification System (GMFCS) level IV/V and spastic quadriplegia, than in the cases with GMFCS level II/III and spastic diplegia. CTbeta showed significant correlation with the acetabular defect on the lateral 3D reconstructed images. Three-dimensional acetabular geometry and migration percentage in CP patients can be analyzed quantitatively using 3D-CT regardless of the abnormal spastic posture. The extent of acetabular dysplasia and subluxation is more severe in patients with GMFCS level IV/V and spastic quadriplesia. Level 4.

Coupling of a finite element human head model with a lumped parameter Hybrid III dummy model: preliminary results.

PubMed

Ruan, J S; Prasad, P

1995-08-01

A skull-brain finite element model of the human head has been coupled with a multilink rigid body model of the Hybrid III dummy. The experimental coupled model is intended to represent anatomically a 50th percentile human to the extent the dummy and the skull-brain model represent a human. It has been verified by simulating several human cadaver head impact tests as well as dummy head 'impacts" during barrier crashes in an automotive environment. Skull-isostress and brain-isostrain response curves were established based on model calibration of experimental human cadaver tolerance data. The skull-isostress response curve agrees with the JARI Human Head Impact Tolerance Curve for skull fracture. The brain-isostrain response curve predicts a higher G level for concussion than does the JARI concussion curve and the Wayne State Tolerance Curve at the longer time duration range. Barrier crash simulations consist of belted dummies impacting an airbag, a hard and soft steering wheel hub, and no head contact with vehicle interior components. Head impact force, intracranial pressures and strains, skull stress, and head center-of-gravity acceleration were investigated as injury parameters. Head injury criterion (HIC) was also calculated along with these parameters. Preliminary results of the model simulations in those impact conditions are discussed.

Upgrade to MODFLOW-GUI; addition of MODPATH, ZONEBDGT, and additional MODFLOW packages to the U.S. Geological Survey MODFLOW-96 Graphical-User Interface

USGS Publications Warehouse

Winston, R.B.

1999-01-01

This report describes enhancements to a Graphical-User Interface (GUI) for MODFLOW-96, the U.S. Geological Survey (USGS) modular, three-dimensional, finitedifference ground-water flow model, and MOC3D, the USGS three-dimensional, method-ofcharacteristics solute-transport model. The GUI is a plug-in extension (PIE) for the commercial program Argus ONEe. The GUI has been modified to support MODPATH (a particle tracking post-processing package for MODFLOW), ZONEBDGT (a computer program for calculating subregional water budgets), and the Stream, Horizontal-Flow Barrier, and Flow and Head Boundary packages in MODFLOW. Context-sensitive help has been added to make the GUI easier to use and to understand. In large part, the help consists of quotations from the relevant sections of this report and its predecessors. The revised interface includes automatic creation of geospatial information layers required for the added programs and packages, and menus and dialog boxes for input of parameters for simulation control. The GUI creates formatted ASCII files that can be read by MODFLOW-96, MOC3D, MODPATH, and ZONEBDGT. All four programs can be executed within the Argus ONEe application (Argus Interware, Inc., 1997). Spatial results of MODFLOW-96, MOC3D, and MODPATH can be visualized within Argus ONEe. Results from ZONEBDGT can be visualized in an independent program that can also be used to view budget data from MODFLOW, MOC3D, and SUTRA. Another independent program extracts hydrographs of head or drawdown at individual cells from formatted MODFLOW head and drawdown files. A web-based tutorial on the use of MODFLOW with Argus ONE has also been updated. The internal structure of the GUI has been modified to make it possible for advanced users to easily customize the GUI. Two additional, independent PIE?s were developed to allow users to edit the positions of nodes and to facilitate exporting the grid geometry to external programs.

Correlating High Resolution Radar Reflectors with Visible Layering of the Polar Layered Deposits, Mars

NASA Astrophysics Data System (ADS)

Christian, S.; Holt, J. W.; Choudhary, P.; Fishbaugh, K. E.; Plaut, J. J.

2010-12-01

The Shallow Radar (SHARAD) onboard NASA’s Mars Reconnaissance Orbiter (MRO) has successfully detected many subsurface reflectors in the North Polar Layered Deposits (NPLD) of Mars. Confirming that these reflectors are caused by varying fractions of dust within the ice will be of primary importance in any attempt to model the composition of the NPLD, particularly if such a study incorporates optical data based on the assumption of a shared mechanism between layering and radar reflectance. As a first step towards examining this assumption, we have quantitatively studied the relationship between radar reflectors and adjacent visible layers exposed in an NPLD outcrop using statistical analyses and geometric comparisons. A clustering analysis of vertical separation distances between radar reflectors returned strong values at 11.8, 15.8, 20.3, 27.9, and 35.3 m, which strongly agree with published visible layer clusters [Fishbaugh et al., LPSC, 2009] and known frequency analysis results [Milkovich and Head, JGR, 2005]. Furthermore, in order to understand subsurface structures and reflector geometry we have gridded reflector surfaces in three dimensions, taking into account the influence of surface slopes to obtain accurate subsurface geometries. These geometries reveal average reflector dips of 0.4°, which are consistent with optical layer slopes on the order of 1.0°. Unexpected long wavelength topography resulting from subsurface structures visible to SHARAD complicated the attempt to compare radar reflector geometries with layer boundary elevation profiles obtained from the stratigraphic column produced using a digital elevation model (DEM) of High Resolution Imaging Science Experiment (HiRISE) stereo imagery [Fishbaugh et al., GRL, 2010]. The limitation imposed by the small extent of the DEM was resolved by increasing exposure coverage through the incorporation of images from Context Camera (CTX), also on MRO. In doing so, we were able to resolve the disparity between geometries and have now determined visible layers demonstrate similar subsurface topographic features as those revealed by SHARAD. Direct elevation comparisons between individual reflectors and discrete optical layers, while considered necessary for a correlation, are complicated by variations in subsurface structure that exist between the outcrop and the SHARAD tracks, as inferred from our mapping. While a direct correlation has not yet been accomplished, we have confirmed a genetic link between radar reflectors and visible layers; furthermore, we have generalized and improved the techniques for conducting such correlations so this can be undertaken at additional locations.

Head motion in humans alternating between straight and curved walking path: combination of stabilizing and anticipatory orienting mechanisms.

PubMed

Hicheur, Halim; Vieilledent, Stéphane; Berthoz, Alain

Anticipatory head orientation relative to walking direction was investigated in humans. Subjects were asked to walk along a 20 m perimeter, figure of eight. The geometry of this path required subjects to steer their body according to both curvature variations (alternate straight with curved walking) and walking direction (clock wise and counter clock wise). In agreement with previous results obtained during different locomotor tasks [R. Grasso, S. Glasauer, Y. Takei, A. Berthoz, The predictive brain: anticipatory control of head direction for the steering of locomotion, NeuroReport 7 (1996) 1170-1174; R. Grasso, P. Prevost, Y.P. Ivanenko, A. Berthoz, Eye-head coordination for the steering of locomotion in humans: an anticipatory synergy, Neurosci. Lett. 253 (2) (1998) 115-118; T. Imai, S.T. Moore, T. Raphan, B. Cohen, Interaction of body, head, and eyes during walking and turning, Exp. Brain Res. 136 (2001) 1-18; P. Prevost, Y. Ivanenko, R. Grasso, A. Berthoz, Spatial invariance in anticipatory orienting behaviour during human navigation, Neurosci. Lett. 339 (2002) 243-247; G. Courtine, M. Schieppati, Human walking along a curved path. I. Body trajectory, segment orientation and the effect of vision, Eur. J. Neurosci. 18 (2003) 177-190], the head turned toward the future walking direction. This anticipatory head behaviour was continuously modulated by the geometrical variations of the path. Two main components were observed in the anticipatory head behaviour. One was related to the geometrical form of the path, the other to the transfer of body mass from one foot to the other during stepping. A clear modulation of the head deviation pattern was observed between walking on curved versus straight parts of the path: head orientation was influenced to a lesser extent by step alternation for curved path where a transient head fixation was observed. We also observed good symmetry in the head deviation profile, i.e. the head tended to anticipate the future walking direction with the same amplitude when turning to the left (29.75 +/- 7.41 degrees of maximum head deviation) or to the right (30.86 +/- 9.92 degrees ). These findings suggest a combination of motor strategies underlying head stabilization in space and more global orienting mechanisms for steering the whole body in the desired direction.

Does Head Start differentially benefit children with risks targeted by the program’s service model?☆

PubMed Central

Miller, Elizabeth B.; Farkas, George; Duncan, Greg J.

2015-01-01

Data from the Head Start Impact Study (N = 3540) were used to test for differential benefits of Head Start after one program year and after kindergarten on pre-academic and behavior outcomes for children at risk in the domains targeted by the program’s comprehensive services. Although random assignment to Head Start produced positive treatment main effects on children’s pre-academic skills and behavior problems, residualized growth models showed that random assignment to Head Start did not differentially benefit the pre-academic skills of children with risk factors targeted by the Head Start service model. The models showed detrimental impacts of Head Start for maternal-reported behavior problems of high-risk children, but slightly more positive impacts for teacher-reported behavior. Policy implications for Head Start are discussed. PMID:26379369

THM large spatial-temporal model to simulate the past 2 Ma hydrogeological evolution of Paris Basin including natural tracer transport as part of site characterization for radwaste repository project Cigéo - France

NASA Astrophysics Data System (ADS)

Benabderrahmane, A., Sr.

2017-12-01

Hydrogeological site characterization for deep geological high level and intermediate level long lived radioactive waste repository cover a large time scale needed for safety analysis and calculation. Hydrogeological performance of a site relies also on the effects of geodynamic evolution as tectonic uplift, erosion/sedimentation and climate including glaciation on the groundwater flow and solute and heat transfer. Thermo-Hydro-Mechanical model of multilayered aquifer system of Paris Basin is developed to reproduce the present time flow and the natural tracer (Helium) concentration profiles based on the last 2 Ma of geodynamic evolution. Present time geological conceptual model consist of 27 layers at Paris Basin (Triassic-Tertiary) with refinement at project site scale (29 layers from Triassic to Portlandian). Target layers are the clay host formation of Callovo-Oxfrodian age (160 Ma) and the surrounding aquifer layers of Oxfordian and Dogger. Modelled processes are: groundwater flow, heat and solutes (natural tracers) transport, freezing and thawing of groundwater (expansion and retreat of permafrost), deformation of the multilayered aquifer system induced by differential tectonic uplift and the hydro-mechanical stress effect as caused by erosion of the outcropping layers. Numerical simulation considers a period from 2 Ma BP and up to the present. Transient boundary conditions are governed by geodynamic processes: (i) modification of the geometry of the basin and (ii) temperatures along the topography will change according to a series of 15 identical climate cycles with multiple permafrost (glaciation) periods. Numerical model contains 71 layers and 18 million cells. The solution procedure solves three coupled systems of equations, head, temperature and concentrations, by the use of a finite difference method, and by applying extensive parallel processing. The major modelling results related to the processes of importance for site characterization as hydraulic head distribution, flow velocity, heat and natural tracer transport impacted by geodynamic past evolution are discussed.

A kinematic model for 3-D head-free gaze-shifts

PubMed Central

Daemi, Mehdi; Crawford, J. Douglas

2015-01-01

Rotations of the line of sight are mainly implemented by coordinated motion of the eyes and head. Here, we propose a model for the kinematics of three-dimensional (3-D) head-unrestrained gaze-shifts. The model was designed to account for major principles in the known behavior, such as gaze accuracy, spatiotemporal coordination of saccades with vestibulo-ocular reflex (VOR), relative eye and head contributions, the non-commutativity of rotations, and Listing's and Fick constraints for the eyes and head, respectively. The internal design of the model was inspired by known and hypothesized elements of gaze control physiology. Inputs included retinocentric location of the visual target and internal representations of initial 3-D eye and head orientation, whereas outputs were 3-D displacements of eye relative to the head and head relative to shoulder. Internal transformations decomposed the 2-D gaze command into 3-D eye and head commands with the use of three coordinated circuits: (1) a saccade generator, (2) a head rotation generator, (3) a VOR predictor. Simulations illustrate that the model can implement: (1) the correct 3-D reference frame transformations to generate accurate gaze shifts (despite variability in other parameters), (2) the experimentally verified constraints on static eye and head orientations during fixation, and (3) the experimentally observed 3-D trajectories of eye and head motion during gaze-shifts. We then use this model to simulate how 2-D eye-head coordination strategies interact with 3-D constraints to influence 3-D orientations of the eye-in-space, and the implications of this for spatial vision. PMID:26113816

Response of hyporheic zones to transient forcing

NASA Astrophysics Data System (ADS)

Singh, T.; Wu, L.; Gomez-Velez, J. D.; Krause, S.; Hannah, D. M.; Lewandowski, J.; Nuetzmann, G.

2017-12-01

Exchange of water, solutes, and energy between river channels and hyporheic zones (HZs) modulates biogeochemical cycling, regulates stream temperature and impacts ecological structure and function. Numerical modelling of HZ processes is required as field observations are challenging for transient flow. To gain a deeper mechanistic understanding of the effects of transient discharge on hyporheic exchange, we performed a systematic analysis using numerical experiments. In this case, we vary (i) the characteristics of time-varying flood events; (ii) river bedform geometry; (iii) river hydraulic geometry; and (iv) the magnitude and direction of groundwater fluxes (neutral, gaining and losing conditions). We conceptualize the stream bed as a two-dimensional system. Whereby the flow is driven by a dynamically changing head distribution at the water-sediment interface and is modulated by steady groundwater flow. Our model estimates both net values for a single bedform and spatial distributions of (i) the flow field; (ii) mean residence times; and (iii) the concentration of a conservative tracer. A detailed sensitivity analysis was performed by changing channel slope, flood characteristics, groundwater upwelling/downwelling fluxes and biogeochemical time-scales in different bedforms such as ripples, dunes and alternating bars. Results show that change of parameters can have a substantial impact on exchange fluxes which can lead to the expansion, contraction, emergence and/or dissipation of HZs . Our results also reveal that groundwater fluxes have different impacts on HZs during flood events, depending on the channel slope and bedform topography. It is found that topographies with smaller aspect ratios and shallower slopes are more affected by groundwater upwelling/downwelling fluxes during flood events. The analysis of biogeochemical transformations shows that discharge events can potentially affects the efficiencies of nitrate removal. Taking into consideration multiple morphological characteristics along with hydrological controls are important to improve model conceptualizations at the reach and watershed scale.

Risk assessment of occupational exposure to benzene using numerical simulation in a complex geometry of a reforming unit of petroleum refinery.

PubMed

Bayatian, Majid; Ashrafi, Khosro; Azari, Mansour Rezazadeh; Jafari, Mohammad Javad; Mehrabi, Yadollah

2018-04-01

There has been an increasing concern about the continuous and the sudden release of volatile organic pollutants from petroleum refineries and occupational and environmental exposures. Benzene is one of the most prevalent volatile compounds, and it has been addressed by many authors for its potential toxicity in occupational and environmental settings. Due to the complexities of sampling and analysis of benzene in routine and accidental situations, a reliable estimation of the benzene concentration in the outdoor setting of refinery using a computational fluid dynamics (CFD) could be instrumental for risk assessment of occupational exposure. In the present work, a computational fluid dynamic model was applied for exposure risk assessment with consideration of benzene being released continuously from a reforming unit of a refinery. For simulation of benzene dispersion, GAMBIT, FLUENT, and CFD post software are used as preprocessing, processing, and post-processing, respectively. Computational fluid dynamic validation was carried out by comparing the computed data with the experimental measurements. Eventually, chronic daily intake and lifetime cancer risk for routine operations through the two seasons of a year are estimated through the simulation model. Root mean square errors are 0.19 and 0.17 for wind speed and concentration, respectively. Lifetime risk assessments of workers are 0.4-3.8 and 0.0096-0.25 per 1000 workers in stable and unstable atmospheric conditions, respectively. Exposure risk is unacceptable for the head of shift work, chief engineer, and general workers in 141 days (38.77%) in a year. The results of this study show that computational fluid dynamics is a useful tool for modeling of benzene exposure in a complex geometry and can be used to estimate lifetime risks of occupation groups in a refinery setting.

Hydraulic development of high specific-speed pump-turbines by means of an inverse design method, numerical flow-simulation (CFD) and model testing

NASA Astrophysics Data System (ADS)

Kerschberger, P.; Gehrer, A.

2010-08-01

In recent years an increased interest in pump-turbines has been recognized in the market. The rapid availability of pumped storage schemes and the benefits to the power system by peak lopping, providing reserve and rapid response for frequency control are becoming of growing advantage. In that context it is requested to develop pump-turbines that reliably stand dynamic operation modes, fast changes of the discharge rate by adjusting the variable diffuser vanes as well as fast changes from pump to turbine operation. Within the present study various flow patterns linked to the operation of a pump-turbine system are discussed. In that context pump and turbine mode are presented separately and different load cases at both operation modes are shown. In order to achieve modern, competitive pump-turbine designs it is further explained which design challenges should be considered during the geometry definition of a pump-turbine impeller. Within the present study a runner-blade profile for a low head pump-turbine has been developed. For the initial hydraulic runner-blade design, an inverse design method has been applied. Within this design procedure, a first blade geometry is generated by imposing the pressure loading-distribution and by means of an inverse 3D potential-flow-solution. The hydraulic behavior of both, pump-mode and turbine-mode is then evaluated by solving the full 3D Navier-Stokes equations in combination with a robust turbulence model. Based on this initial design the blade profile has been further optimized and redesigned considering various hydraulic pump-turbine requirements. Finally, the progress in hydraulic design is demonstrated by model test results which show a significant improvement in hydraulic performance compared to an existing reference design.

Research study on neck injury lessening with active head restraint using human body FE model.

PubMed

Kitagawa, Yuichi; Yasuki, Tsuyoshi; Hasegawa, Junji

2008-12-01

The objective of this study is to examine the effectiveness of the active head restraint system in reducing neck injury risk of car occupants in low-speed rear impacts. A human body FE model "THUMS" was used to simulate head and neck kinematics of the occupant and to evaluate loading to the neck. Joint capsule strain was calculated to predict neck injury risk as well as NIC. The validity of the model was confirmed comparing its mechanical responses to those in human subjects in the literatures. Seat FE models were also prepared representing one with a fixed head restraint and the other one with an active head restraint system. The active head restraint system was designed to move the head restraint forward and upward when the lower unit was lower unit was loaded by the pelvis. Rear impact simulations were performed assuming a triangular acceleration pulse at a delta-V of 25 km/h. The model reproduced similar head and neck motions to those measured in the human volunteer test, except for active muscular responses. The calculated joint capsule strain also showed a good match with those of PMHS tests in the literature. A rear-impact simulation was conducted using the model with the fixed head restraint. The result revealed that NIC was strongly correlated with the relative acceleration between the head and the torso and that its maximum peak appeared when the head contacted the head restraint. It was also found that joint capsule strain grew in later timing synchronizing with the relative displacement. Another simulation with the active head restraint system showed that both NIC and joint capsule strain were lowered owing to the forward and upward motion of the head restraint. A close investigation of the vertebral motion indicated that the active head restraint reduced the magnitude of shear deformation in the facet joint, which contributed to the strain growth in the fixed head restraint case. Rear-impact simulations were conducted using a human body FE model, THUMS, representing an average-size male occupant. The cervical system including the facet joint capsules was incorporated to the model. The validity of the model was examined comparing its mechanical responses to those in the literature such as the whole body motion of the volunteer subject and the vertebral motion in the PMHS tests. Rear-impact simulations were conducted using the validated THUMS model and two prototype seat models; one had a fixed head restraint and the other one was equipped with an active head restraint system. The active head restraint system works moving the head restraint forward and upward when the lower unit is loaded by the pelvis. The head and neck kinematics and responses were analyzed from the simulation results. The force and acceleration rose at the pelvis first, followed by T1 and the head. The early timing of force rise and its magnitude indicated that the pelvis force was a good trigger for the active head restraint system. The results showed that the head was supported earlier in a case with the active head restraint system, and both NIC and joint capsule strain were lowered. The study also analyzed the mechanism of strain growth in the joint capsules. Relatively greater strain was observed in the direction of the facet joint surface, which was around 45 degrees inclined to the spinal column. The forward and upward motion of the active head restraint were aligned with the direction of the joint deformation and contributed to lower strain in the joint capsules. The results indicated that the active head restraint could help reduce the neck injury risk not only by supporting the head at an early timing but also through its trajectory stopping the joint deformation.

PowerWheel - A new look at waterwheels

DOE Office of Scientific and Technical Information (OSTI.GOV)

Weisman, R.N.; Broome, K.R.; Mayo, H.A.

1995-12-31

The PowerWheel is an advanced overshot water wheel, designed to generate electric power at drop structures on canals or on overflow spillways. Unlike the wheels of the 18th and 19th century which were designed to have maximum efficiency at a single flow rate, the current applications demand a wheel that can operate efficiently over a wide range of flows. The prototype PowerWheel will have a width to diameter ratio of 3 or more, in contrast to the wheels of the 19th century, which had large diameters and narrow widths. A model PowerWheel was built of plexiglass and delivered for testingmore » to the Imbt Hydraulics Laboratory at Lehigh University. The wheel has a diameter of 3.5 ft and is 16 in wide. The wheel contains 20 buckets and the bucket depth can be varied from a shallow depth of 4 in to a mid depth of 7 in to 10 in for the deep bucket. The blades have a rather simple geometry with a 4 in radius quarter circle at the outside of the wheel and then straight to the bottom of the bucket. The flume in which the wheel was tested has a width of 18 in. A hole was cut in the head box of the flume and a delivery chute was connected to the head box. The position of the chute can readily be moved up or down in relation to the wheel; for a fixed position of the chute on the head box, the slope of the chute can be changed because the chute was attached to the head box with a piano hinge. The laboratory flow system can deliver flow up to 6 cfs through a calibrated Venturi meter. The PowerWheel was subjected to flows ranging from 0.3 to 3.5 cfs.« less

Head flying characteristics in heat assisted magnetic recording considering various nanoscale heat transfer models

NASA Astrophysics Data System (ADS)

Hu, Yueqiang; Wu, Haoyu; Meng, Yonggang; Wang, Yu; Bogy, David

2018-01-01

The thermal issues in heat-assisted magnetic recording (HAMR) technology have drawn much attention in the recent literature. In this paper, the head flying characteristics and thermal performance of a HAMR system during the touch-down process considering different nanoscale heat transfer models across the head-disk interface are numerically studied. An optical-thermal-mechanical coupled model is first described. The coupling efficiency of the near field transducer is found to be dependent on the head disk clearance. The shortcomings of a constant disk-temperature model are investigated, which reveals the importance of considering the disk temperature as a variable. A study of the head flying on the disk is carried out using an air conduction model and additional near-field heat transfer models. It is shown that when the head disk interface is filled with a solid material caused by the laser-induced accumulation, the heat transfer coefficient can become unexpectedly large and the head's temperature can rise beyond desirable levels. Finally, the additional head protrusion due to the laser heating is investigated.

Biomechanical Analyses of the Efficacy of Patterns of Maternal Effort on Second-Stage Progress

PubMed Central

Lien, Kuo-Cheng; DeLancey, John O.L.; Ashton-Miller, James A.

2009-01-01

OBJECTIVE To develop and use a biomechanical computer model to simulate the effect of varying the timing of voluntary maternal pushes during uterine contraction on second-stage labor duration. METHODS Published initial pelvic floor geometry was imported into technical computing software to build a simplified 3-D biomechanical model with six representative viscoelastic levator muscle bands interconnected by a hyperelastic iliococcygeal raphé. An incompressible sphere simulated the molded fetal head. Forces from uterine contraction and voluntary expulsive efforts were summed to push the model fetal head along the Curve of Carus opposed by the resistance of the pelvic floor structures to stretch. Holding uterine maximal contraction force and push strength constant, pushes were timed before (“Pre”), at (“Peak”), and after (“Post”) maximal uterine contraction force. The effect of different combinations of pushes on second stage duration and the number of pushes required for delivery were evaluated. RESULTS Calculated second stage durations ranged from 57.5 minutes (“triple” or Pre-Peak-Post pattern) to 75.8 minutes (“pre-push” and “post-push” patterns). Delivery with the “triple push” pattern required 59 voluntary pushes, while the “peak push” pattern required 23 voluntary pushes, a 61% reduction. The corresponding reduction for the “pre-and-peak push” pattern was 29%, the “peak-and-post push” pattern was 30%, the “pre-push” pattern was 54%, and the “post-push” pattern was 56%. CONCLUSION Although the “triple push” pattern resulted in a 16% shorter second stage, this came at the energetic expense of a 61% increase in the number of pushes required. PMID:19305333

Generalized Kähler geometry and current algebras in classical N=2 superconformal WZW model

NASA Astrophysics Data System (ADS)

Parkhomenko, S. E.

2018-04-01

I examine the Generalized Kähler (GK) geometry of classical N = (2, 2) superconformal WZW model on a compact group and relate the right-moving and left-moving Kac-Moody superalgebra currents to the GK geometry data using biholomorphic gerbe formulation and Hamiltonian formalism. It is shown that the canonical Poisson homogeneous space structure induced by the GK geometry of the group manifold is crucial to provide N = (2, 2) superconformal σ-model with the Kac-Moody superalgebra symmetries. Then, the biholomorphic gerbe geometry is used to prove that Kac-Moody superalgebra currents are globally defined.

Optical discharge with absorption of repetitive CO{sub 2} laser pulses in supersonic air flow: wave structure and condition of a quasi-steady state

DOE Office of Scientific and Technical Information (OSTI.GOV)

Bobarykina, T A; Malov, A N; Orishich, A M

We report a study of the wave structure formed by an optical discharge plasma upon the absorption of repetitively pulsed CO{sub 2} laser radiation in a supersonic (M = 1.36) air flow. Experimental data are presented on the configuration of the head shock wave and the geometry and characteristic dimensions of breakdown regions behind a laser plasma pulsating in the flow at a frequency of up to 150 kHz. The data are compared to calculation in a point explosion model with allowance for counterpressure, which makes it possible to identify the relationship between laser radiation and supersonic flow parameters thatmore » ensures quasisteady- state energy delivery and is necessary for extending the possibilities of controlling the structure of supersonic flows. (interaction of laser radiation with matter)« less

Modeling of weld bead geometry for rapid manufacturing by robotic GMAW

NASA Astrophysics Data System (ADS)

Yang, Tao; Xiong, Jun; Chen, Hui; Chen, Yong

2015-03-01

Weld-based rapid prototyping (RP) has shown great promises for fabricating 3D complex parts. During the layered deposition of forming metallic parts with robotic gas metal arc welding, the geometry of a single weld bead has an important influence on surface finish quality, layer thickness and dimensional accuracy of the deposited layer. In order to obtain accurate, predictable and controllable bead geometry, it is essential to understand the relationships between the process variables with the bead geometry (bead width, bead height and ratio of bead width to bead height). This paper highlights an experimental study carried out to develop mathematical models to predict deposited bead geometry through the quadratic general rotary unitized design. The adequacy and significance of the models were verified via the analysis of variance. Complicated cause-effect relationships between the process parameters and the bead geometry were revealed. Results show that the developed models can be applied to predict the desired bead geometry with great accuracy in layered deposition with accordance to the slicing process of RP.

Morphing the feature-based multi-blocks of normative/healthy vertebral geometries to scoliosis vertebral geometries: development of personalized finite element models.

PubMed

Hadagali, Prasannaah; Peters, James R; Balasubramanian, Sriram

2018-03-01

Personalized Finite Element (FE) models and hexahedral elements are preferred for biomechanical investigations. Feature-based multi-block methods are used to develop anatomically accurate personalized FE models with hexahedral mesh. It is tedious to manually construct multi-blocks for large number of geometries on an individual basis to develop personalized FE models. Mesh-morphing method mitigates the aforementioned tediousness in meshing personalized geometries every time, but leads to element warping and loss of geometrical data. Such issues increase in magnitude when normative spine FE model is morphed to scoliosis-affected spinal geometry. The only way to bypass the issue of hex-mesh distortion or loss of geometry as a result of morphing is to rely on manually constructing the multi-blocks for scoliosis-affected spine geometry of each individual, which is time intensive. A method to semi-automate the construction of multi-blocks on the geometry of scoliosis vertebrae from the existing multi-blocks of normative vertebrae is demonstrated in this paper. High-quality hexahedral elements were generated on the scoliosis vertebrae from the morphed multi-blocks of normative vertebrae. Time taken was 3 months to construct the multi-blocks for normative spine and less than a day for scoliosis. Efforts taken to construct multi-blocks on personalized scoliosis spinal geometries are significantly reduced by morphing existing multi-blocks.

Experimental conical-head abutment screws on the microbial leakage through the implant-abutment interface: an in vitro analysis using target-specific DNA probes.

PubMed

Pita, Murillo S; do Nascimento, Cássio; Dos Santos, Carla G P; Pires, Isabela M; Pedrazzi, Vinícius

2017-07-01

The aim of this in vitro study was to identify and quantify up to 38 microbial species from human saliva penetrating through the implant-abutment interface in two different implant connections, external hexagon and tri-channel internal connection, both with conventional flat-head or experimental conical-head abutment screws. Forty-eight two-part implants with external hexagon (EH; n = 24) or tri-channel internal (TI; n = 24) connections were investigated. Abutments were attached to implants with conventional flat-head or experimental conical-head screws. After saliva incubation, Checkerboard DNA-DNA hybridization was used to identify and quantify up to 38 bacterial colonizing the internal parts of the implants. Kruskal-Wallis test followed by Bonferroni's post-tests for multiple comparisons was used for statistical analysis. Twenty-four of thirty-eight species, including putative periodontal pathogens, were found colonizing the inner surfaces of both EH and TI implants. Peptostreptococcus anaerobios (P = 0.003), Prevotella melaninogenica (P < 0.0001), and Candida dubliniensis (P < 0.0001) presented significant differences between different groups. Means of total microbial count (×10 4 , ±SD) for each group were recorded as follows: G1 (0.27 ± 2.04), G2 (0 ± 0), G3 (1.81 ± 7.50), and G4 (0.35 ± 1.81). Differences in the geometry of implant connections and abutment screws have impacted the microbial leakage through the implant-abutment interface. Implants attached with experimental conical-head abutment screws showed lower counts of microorganisms when compared with conventional flat-head screws. © 2016 John Wiley & Sons A/S. Published by John Wiley & Sons Ltd.

Automated muscle wrapping using finite element contact detection.

PubMed

Favre, Philippe; Gerber, Christian; Snedeker, Jess G

2010-07-20

Realistic muscle path representation is essential to musculoskeletal modeling of joint function. Algorithms predicting these muscle paths typically rely on a labor intensive predefinition of via points or underlying geometries to guide wrapping for given joint positions. While muscle wrapping using anatomically precise three-dimensional (3D) finite element (FE) models of bone and muscle has been achieved, computational expense and pre-processing associated with this approach exclude its use in applications such as subject-specific modeling. With the intention of combining advantageous features of both approaches, an intermediate technique relying on contact detection capabilities of commercial FE packages is presented. We applied the approach to the glenohumeral joint, and validated the method by comparison against existing experimental data. Individual muscles were modeled as a straight series of deformable beam elements and bones as anatomically precise 3D rigid bodies. Only the attachment locations and a default orientation of the undeformed muscle segment were pre-defined. The joint was then oriented in a static position of interest. The muscle segment free end was then moved along the shortest Euclidean path to its origin on the scapula, wrapping the muscle along bone surfaces by relying on software contact detection. After wrapping for a given position, the resulting moment arm was computed as the perpendicular distance from the line of action vector to the humeral head center of rotation. This approach reasonably predicted muscle length and moment arm for 27 muscle segments when compared to experimental measurements over a wide range of shoulder motion. Artificial via points or underlying contact geometries were avoided, contact detection and multiobject wrapping on the bone surfaces were automatic, and low computational cost permitted wrapping of individual muscles within seconds on a standard desktop PC. These advantages may be valuable for both general and subject-specific musculoskeletal modeling. 2010 Elsevier Ltd. All rights reserved.

A Multivariate Model of Achievement in Geometry

ERIC Educational Resources Information Center

Bailey, MarLynn; Taasoobshirazi, Gita; Carr, Martha

2014-01-01

Previous studies have shown that several key variables influence student achievement in geometry, but no research has been conducted to determine how these variables interact. A model of achievement in geometry was tested on a sample of 102 high school students. Structural equation modeling was used to test hypothesized relationships among…

An experimental investigation on the thermal field of overlapping layers in laser-assisted tape winding process

NASA Astrophysics Data System (ADS)

Hosseini, S. M. A.; Baran, I.; Akkerman, R.

2018-05-01

The laser-assisted tape winding (LATW) is an automated process for manufacturing fiber-reinforced thermoplastic tubular products, such as pipes and pressure vessels. Multi-physical phenomena such as heat transfer, mechanical bonding, phase changes and solid mechanics take place during the process. These phenomena need to be understood and described well for an improved product reliability. Temperature is one of the important parameters in this process to control and optimize the product quality which can be employed in an intelligent model-based inline control system. The incoming tape can overlap with the already wounded layer during the process based on the lay-up configuration. In this situation, the incoming tape can step-on or step-off to an already deposited layer/laminate. During the overlapping, the part temperature changes due to the variation of the geometry caused by previously deposited layer, i.e. a bump geometry. In order to qualify the temperature behavior at the bump regions, an experimental set up is designed on a flat laminate. Artificial bumps/steps are formed on the laminate with various thicknesses and fiber orientations. As the laser head experiences the step-on and step-off, the IR (Infra-Red) camera and the embedded thermocouples measure the temperature on the surface and inside the laminate, respectively. During the step-on, a small drop in temperature is observed while in step-off a higher peak in temperature is observed. It can be concluded that the change in the temperature during overlapping is due to the change in laser incident angle made by the bump geometry. The effect of the step thickness on the temperature peak is quantified and found to be significant.

Using groundwater temperature data to constrain parameter estimation in a groundwater flow model of a wetland system

USGS Publications Warehouse

Bravo, Hector R.; Jiang, Feng; Hunt, Randall J.

2002-01-01

Parameter estimation is a powerful way to calibrate models. While head data alone are often insufficient to estimate unique parameters due to model nonuniqueness, flow‐and‐heat‐transport modeling can constrain estimation and allow simultaneous estimation of boundary fluxes and hydraulic conductivity. In this work, synthetic and field models that did not converge when head data were used did converge when head and temperature were used. Furthermore, frequency domain analyses of head and temperature data allowed selection of appropriate modeling timescales. Inflows in the Wilton, Wisconsin, wetlands could be estimated over periods such as a growing season and over periods of a few days when heads were nearly steady and groundwater temperature varied during the day. While this methodology is computationally more demanding than traditional head calibration, the results gained are unobtainable using the traditional approach. These results suggest that temperature can efficiently supplement head data in systems where accurate flux calibration targets are unavailable.

Micro-tomography based Geometry Modeling of Three-Dimensional Braided Composites

NASA Astrophysics Data System (ADS)

Fang, Guodong; Chen, Chenghua; Yuan, Shenggang; Meng, Songhe; Liang, Jun

2018-06-01

A tracking and recognizing algorithm is proposed to automatically generate irregular cross-sections and central path of braid yarn within the 3D braided composites by using sets of high resolution tomography images. Only the initial cross-sections of braid yarns in a tomography image after treatment are required to be calibrated manually as searching cross-section template. The virtual geometry of 3D braided composites including some detailed geometry information, such as the braid yarn squeezing deformation, braid yarn distortion and braid yarn path deviation etc., can be reconstructed. The reconstructed geometry model can reflect the change of braid configurations during solidification process. The geometry configurations and mechanical properties of the braided composites are analyzed by using the reconstructed geometry model.

Time-accurate unsteady flow simulations supporting the SRM T+68-second pressure spike anomaly investigation (STS-54B)

NASA Astrophysics Data System (ADS)

Dougherty, N. S.; Burnette, D. W.; Holt, J. B.; Matienzo, Jose

1993-07-01

Time-accurate unsteady flow simulations are being performed supporting the SRM T+68sec pressure 'spike' anomaly investigation. The anomaly occurred in the RH SRM during the STS-54 flight (STS-54B) but not in the LH SRM (STS-54A) causing a momentary thrust mismatch approaching the allowable limit at that time into the flight. Full-motor internal flow simulations using the USA-2D axisymmetric code are in progress for the nominal propellant burn-back geometry and flow conditions at T+68-sec--Pc = 630 psi, gamma = 1.1381, T(sub c) = 6200 R, perfect gas without aluminum particulate. In a cooperative effort with other investigation team members, CFD-derived pressure loading on the NBR and castable inhibitors was used iteratively to obtain nominal deformed geometry of each inhibitor, and the deformed (bent back) inhibitor geometry was entered into this model. Deformed geometry was computed using structural finite-element models. A solution for the unsteady flow has been obtained for the nominal flow conditions (existing prior to the occurrence of the anomaly) showing sustained standing pressure oscillations at nominally 14.5 Hz in the motor IL acoustic mode that flight and static test data confirm to be normally present at this time. Average mass flow discharged from the nozzle was confirmed to be the nominal expected (9550 lbm/sec). The local inlet boundary condition is being perturbed at the location of the presumed reconstructed anomaly as identified by interior ballistics performance specialist team members. A time variation in local mass flow is used to simulate sudden increase in burning area due to localized propellant grain cracks. The solution will proceed to develop a pressure rise (proportional to total mass flow rate change squared). The volume-filling time constant (equivalent to 0.5 Hz) comes into play in shaping the rise rate of the developing pressure 'spike' as it propagates at the speed of sound in both directions to the motor head end and nozzle. The objectives of the present analysis are to: (1) capture the dynamic responses of the motor combustion gas flow to correlate with available low-frequency (less than 12.5 sample/sec) data and (2) observe the high-frequency (up to 50 Hz) characteristics of the response to determine any potentials for dynamic coupling.

Electrical Advantages of Dendritic Spines

PubMed Central

Gulledge, Allan T.; Carnevale, Nicholas T.; Stuart, Greg J.

2012-01-01

Many neurons receive excitatory glutamatergic input almost exclusively onto dendritic spines. In the absence of spines, the amplitudes and kinetics of excitatory postsynaptic potentials (EPSPs) at the site of synaptic input are highly variable and depend on dendritic location. We hypothesized that dendritic spines standardize the local geometry at the site of synaptic input, thereby reducing location-dependent variability of local EPSP properties. We tested this hypothesis using computational models of simplified and morphologically realistic spiny neurons that allow direct comparison of EPSPs generated on spine heads with EPSPs generated on dendritic shafts at the same dendritic locations. In all morphologies tested, spines greatly reduced location-dependent variability of local EPSP amplitude and kinetics, while having minimal impact on EPSPs measured at the soma. Spine-dependent standardization of local EPSP properties persisted across a range of physiologically relevant spine neck resistances, and in models with variable neck resistances. By reducing the variability of local EPSPs, spines standardized synaptic activation of NMDA receptors and voltage-gated calcium channels. Furthermore, spines enhanced activation of NMDA receptors and facilitated the generation of NMDA spikes and axonal action potentials in response to synaptic input. Finally, we show that dynamic regulation of spine neck geometry can preserve local EPSP properties following plasticity-driven changes in synaptic strength, but is inefficient in modifying the amplitude of EPSPs in other cellular compartments. These observations suggest that one function of dendritic spines is to standardize local EPSP properties throughout the dendritic tree, thereby allowing neurons to use similar voltage-sensitive postsynaptic mechanisms at all dendritic locations. PMID:22532875

Assignment of boundary conditions in embedded ground water flow models

USGS Publications Warehouse

Leake, S.A.

1998-01-01

Many small-scale ground water models are too small to incorporate distant aquifer boundaries. If a larger-scale model exists for the area of interest, flow and head values can be specified for boundaries in the smaller-scale model using values from the larger-scale model. Flow components along rows and columns of a large-scale block-centered finite-difference model can be interpolated to compute horizontal flow across any segment of a perimeter of a small-scale model. Head at cell centers of the larger-scale model can be interpolated to compute head at points on a model perimeter. Simple linear interpolation is proposed for horizontal interpolation of horizontal-flow components. Bilinear interpolation is proposed for horizontal interpolation of head values. The methods of interpolation provided satisfactory boundary conditions in tests using models of hypothetical aquifers.Many small-scale ground water models are too small to incorporate distant aquifer boundaries. If a larger-scale model exists for the area of interest, flow and head values can be specified for boundaries in the smaller-scale model using values from the larger-scale model. Flow components along rows and columns of a large-scale block-centered finite-difference model can be interpolated to compute horizontal flow across any segment of a perimeter of a small-scale model. Head at cell centers of the larger.scale model can be interpolated to compute head at points on a model perimeter. Simple linear interpolation is proposed for horizontal interpolation of horizontal-flow components. Bilinear interpolation is proposed for horizontal interpolation of head values. The methods of interpolation provided satisfactory boundary conditions in tests using models of hypothetical aquifers.

Site-specific range uncertainties caused by dose calculation algorithms for proton therapy

NASA Astrophysics Data System (ADS)

Schuemann, J.; Dowdell, S.; Grassberger, C.; Min, C. H.; Paganetti, H.

2014-08-01

The purpose of this study was to assess the possibility of introducing site-specific range margins to replace current generic margins in proton therapy. Further, the goal was to study the potential of reducing margins with current analytical dose calculations methods. For this purpose we investigate the impact of complex patient geometries on the capability of analytical dose calculation algorithms to accurately predict the range of proton fields. Dose distributions predicted by an analytical pencil-beam algorithm were compared with those obtained using Monte Carlo (MC) simulations (TOPAS). A total of 508 passively scattered treatment fields were analyzed for seven disease sites (liver, prostate, breast, medulloblastoma-spine, medulloblastoma-whole brain, lung and head and neck). Voxel-by-voxel comparisons were performed on two-dimensional distal dose surfaces calculated by pencil-beam and MC algorithms to obtain the average range differences and root mean square deviation for each field for the distal position of the 90% dose level (R90) and the 50% dose level (R50). The average dose degradation of the distal falloff region, defined as the distance between the distal position of the 80% and 20% dose levels (R80-R20), was also analyzed. All ranges were calculated in water-equivalent distances. Considering total range uncertainties and uncertainties from dose calculation alone, we were able to deduce site-specific estimations. For liver, prostate and whole brain fields our results demonstrate that a reduction of currently used uncertainty margins is feasible even without introducing MC dose calculations. We recommend range margins of 2.8% + 1.2 mm for liver and prostate treatments and 3.1% + 1.2 mm for whole brain treatments, respectively. On the other hand, current margins seem to be insufficient for some breast, lung and head and neck patients, at least if used generically. If no case specific adjustments are applied, a generic margin of 6.3% + 1.2 mm would be needed for breast, lung and head and neck treatments. We conclude that the currently used generic range uncertainty margins in proton therapy should be redefined site specific and that complex geometries may require a field specific adjustment. Routine verifications of treatment plans using MC simulations are recommended for patients with heterogeneous geometries.

Accurate and efficient modeling of the detector response in small animal multi-head PET systems.

PubMed

Cecchetti, Matteo; Moehrs, Sascha; Belcari, Nicola; Del Guerra, Alberto

2013-10-07

In fully three-dimensional PET imaging, iterative image reconstruction techniques usually outperform analytical algorithms in terms of image quality provided that an appropriate system model is used. In this study we concentrate on the calculation of an accurate system model for the YAP-(S)PET II small animal scanner, with the aim to obtain fully resolution- and contrast-recovered images at low levels of image roughness. For this purpose we calculate the system model by decomposing it into a product of five matrices: (1) a detector response component obtained via Monte Carlo simulations, (2) a geometric component which describes the scanner geometry and which is calculated via a multi-ray method, (3) a detector normalization component derived from the acquisition of a planar source, (4) a photon attenuation component calculated from x-ray computed tomography data, and finally, (5) a positron range component is formally included. This system model factorization allows the optimization of each component in terms of computation time, storage requirements and accuracy. The main contribution of this work is a new, efficient way to calculate the detector response component for rotating, planar detectors, that consists of a GEANT4 based simulation of a subset of lines of flight (LOFs) for a single detector head whereas the missing LOFs are obtained by using intrinsic detector symmetries. Additionally, we introduce and analyze a probability threshold for matrix elements of the detector component to optimize the trade-off between the matrix size in terms of non-zero elements and the resulting quality of the reconstructed images. In order to evaluate our proposed system model we reconstructed various images of objects, acquired according to the NEMA NU 4-2008 standard, and we compared them to the images reconstructed with two other system models: a model that does not include any detector response component and a model that approximates analytically the depth of interaction as detector response component. The comparisons confirm previous research results, showing that the usage of an accurate system model with a realistic detector response leads to reconstructed images with better resolution and contrast recovery at low levels of image roughness.

Accurate and efficient modeling of the detector response in small animal multi-head PET systems

NASA Astrophysics Data System (ADS)

Cecchetti, Matteo; Moehrs, Sascha; Belcari, Nicola; Del Guerra, Alberto

2013-10-01

In fully three-dimensional PET imaging, iterative image reconstruction techniques usually outperform analytical algorithms in terms of image quality provided that an appropriate system model is used. In this study we concentrate on the calculation of an accurate system model for the YAP-(S)PET II small animal scanner, with the aim to obtain fully resolution- and contrast-recovered images at low levels of image roughness. For this purpose we calculate the system model by decomposing it into a product of five matrices: (1) a detector response component obtained via Monte Carlo simulations, (2) a geometric component which describes the scanner geometry and which is calculated via a multi-ray method, (3) a detector normalization component derived from the acquisition of a planar source, (4) a photon attenuation component calculated from x-ray computed tomography data, and finally, (5) a positron range component is formally included. This system model factorization allows the optimization of each component in terms of computation time, storage requirements and accuracy. The main contribution of this work is a new, efficient way to calculate the detector response component for rotating, planar detectors, that consists of a GEANT4 based simulation of a subset of lines of flight (LOFs) for a single detector head whereas the missing LOFs are obtained by using intrinsic detector symmetries. Additionally, we introduce and analyze a probability threshold for matrix elements of the detector component to optimize the trade-off between the matrix size in terms of non-zero elements and the resulting quality of the reconstructed images. In order to evaluate our proposed system model we reconstructed various images of objects, acquired according to the NEMA NU 4-2008 standard, and we compared them to the images reconstructed with two other system models: a model that does not include any detector response component and a model that approximates analytically the depth of interaction as detector response component. The comparisons confirm previous research results, showing that the usage of an accurate system model with a realistic detector response leads to reconstructed images with better resolution and contrast recovery at low levels of image roughness.

Head orientation affects the intracranial pressure response resulting from shock wave loading in the rat.

PubMed

Dal Cengio Leonardi, Alessandra; Keane, Nickolas J; Bir, Cynthia A; Ryan, Anne G; Xu, Liaosa; Vandevord, Pamela J

2012-10-11

Since an increasing number of returning military personnel are presenting with neurological manifestations of traumatic brain injury (TBI), there has been a great focus on the effects resulting from blast exposure. It is paramount to resolve the physical mechanism by which the critical stress is being inflicted on brain tissue from blast wave encounters with the head. This study quantitatively measured the effect of head orientation on intracranial pressure (ICP) of rats exposed to a shock wave. Furthermore, the study examined how skull maturity affects ICP response of animals exposed to shock waves at various orientations. Results showed a significant increase in ICP values in larger rats at any orientation. Furthermore, when side-ICP values were compared to the other orientations, the peak pressures were significantly lower suggesting a relation between ICP and orientation of the head due to geometry of the skull and location of sutures. This finding accentuates the importance of skull dynamics in explaining possible injury mechanisms during blast. Also, the rate of pressure change was measured and indicated that the rate was significantly higher when the top of the head was facing the shock front. The results confirm that the biomechanical response of the superior rat skull is distinctive compared to other areas of the skull, suggesting a skull flexure mechanism. These results not only present insights into the mechanism of brain injury, but also provide information which can be used for designing more effective protective head gear. Copyright © 2012 Elsevier Ltd. All rights reserved.

Lower extremity EMG-driven modeling of walking with automated adjustment of musculoskeletal geometry

PubMed Central

Meyer, Andrew J.; Patten, Carolynn

2017-01-01

Neuromusculoskeletal disorders affecting walking ability are often difficult to manage, in part due to limited understanding of how a patient’s lower extremity muscle excitations contribute to the patient’s lower extremity joint moments. To assist in the study of these disorders, researchers have developed electromyography (EMG) driven neuromusculoskeletal models utilizing scaled generic musculoskeletal geometry. While these models can predict individual muscle contributions to lower extremity joint moments during walking, the accuracy of the predictions can be hindered by errors in the scaled geometry. This study presents a novel EMG-driven modeling method that automatically adjusts surrogate representations of the patient’s musculoskeletal geometry to improve prediction of lower extremity joint moments during walking. In addition to commonly adjusted neuromusculoskeletal model parameters, the proposed method adjusts model parameters defining muscle-tendon lengths, velocities, and moment arms. We evaluated our EMG-driven modeling method using data collected from a high-functioning hemiparetic subject walking on an instrumented treadmill at speeds ranging from 0.4 to 0.8 m/s. EMG-driven model parameter values were calibrated to match inverse dynamic moments for five degrees of freedom in each leg while keeping musculoskeletal geometry close to that of an initial scaled musculoskeletal model. We found that our EMG-driven modeling method incorporating automated adjustment of musculoskeletal geometry predicted net joint moments during walking more accurately than did the same method without geometric adjustments. Geometric adjustments improved moment prediction errors by 25% on average and up to 52%, with the largest improvements occurring at the hip. Predicted adjustments to musculoskeletal geometry were comparable to errors reported in the literature between scaled generic geometric models and measurements made from imaging data. Our results demonstrate that with appropriate experimental data, joint moment predictions for walking generated by an EMG-driven model can be improved significantly when automated adjustment of musculoskeletal geometry is included in the model calibration process. PMID:28700708

Extending rule-based methods to model molecular geometry and 3D model resolution.

PubMed

Hoard, Brittany; Jacobson, Bruna; Manavi, Kasra; Tapia, Lydia

2016-08-01

Computational modeling is an important tool for the study of complex biochemical processes associated with cell signaling networks. However, it is challenging to simulate processes that involve hundreds of large molecules due to the high computational cost of such simulations. Rule-based modeling is a method that can be used to simulate these processes with reasonably low computational cost, but traditional rule-based modeling approaches do not include details of molecular geometry. The incorporation of geometry into biochemical models can more accurately capture details of these processes, and may lead to insights into how geometry affects the products that form. Furthermore, geometric rule-based modeling can be used to complement other computational methods that explicitly represent molecular geometry in order to quantify binding site accessibility and steric effects. We propose a novel implementation of rule-based modeling that encodes details of molecular geometry into the rules and binding rates. We demonstrate how rules are constructed according to the molecular curvature. We then perform a study of antigen-antibody aggregation using our proposed method. We simulate the binding of antibody complexes to binding regions of the shrimp allergen Pen a 1 using a previously developed 3D rigid-body Monte Carlo simulation, and we analyze the aggregate sizes. Then, using our novel approach, we optimize a rule-based model according to the geometry of the Pen a 1 molecule and the data from the Monte Carlo simulation. We use the distances between the binding regions of Pen a 1 to optimize the rules and binding rates. We perform this procedure for multiple conformations of Pen a 1 and analyze the impact of conformation and resolution on the optimal rule-based model. We find that the optimized rule-based models provide information about the average steric hindrance between binding regions and the probability that antibodies will bind to these regions. These optimized models quantify the variation in aggregate size that results from differences in molecular geometry and from model resolution.

Towards adaptive radiotherapy for head and neck patients: validation of an in-house deformable registration algorithm

NASA Astrophysics Data System (ADS)

Veiga, C.; McClelland, J.; Moinuddin, S.; Ricketts, K.; Modat, M.; Ourselin, S.; D'Souza, D.; Royle, G.

2014-03-01

The purpose of this work is to validate an in-house deformable image registration (DIR) algorithm for adaptive radiotherapy for head and neck patients. We aim to use the registrations to estimate the "dose of the day" and assess the need to replan. NiftyReg is an open-source implementation of the B-splines deformable registration algorithm, developed in our institution. We registered a planning CT to a CBCT acquired midway through treatment for 5 HN patients that required replanning. We investigated 16 different parameter settings that previously showed promising results. To assess the registrations, structures delineated in the CT were warped and compared with contours manually drawn by the same clinical expert on the CBCT. This structure set contained vertebral bodies and soft tissue. Dice similarity coefficient (DSC), overlap index (OI), centroid position and distance between structures' surfaces were calculated for every registration, and a set of parameters that produces good results for all datasets was found. We achieve a median value of 0.845 in DSC, 0.889 in OI, error smaller than 2 mm in centroid position and over 90% of the warped surface pixels are distanced less than 2 mm of the manually drawn ones. By using appropriate DIR parameters, we are able to register the planning geometry (pCT) to the daily geometry (CBCT).

Quasi-steady Bingham plastic analysis of an electrorheological flow mode bypass damper with piston bleed

NASA Astrophysics Data System (ADS)

Lindler, Jason; Wereley, Norman M.

2003-06-01

We present an improved experimental validation of our nonlinear quasi-steady electrorheological (ER) and magnetorheological damper analysis, using an idealized Bingham plastic shear flow mechanism, for the flow mode of damper operation with leakage effect. To validate the model, a double-acting ER valve or bypass damper was designed and fabricated. Both the hydraulic cylinder and the bypass duct have cylindrical geometry, and damping forces are developed in the annular bypass via Poiseuille flow. The ER fluid damper contains a controlled amount of leakage around the piston head. The leakage allows ER fluid to flow from one side of the piston head to the opposite side without passing through the ER bypass. For this flow mode damper, the damping coefficient, defined as the ratio of equivalent viscous damping of the Bingham plastic material, Ceq, to the Newtonian viscous damping, C, is a function of the non-dimensional plug thickness only. The damper was tested for varying conditions of applied electric field and frequency using a mechanical damper dynamometer. In this analysis, the leakage damping coefficient with incorporated leakage effects, predict the amount of energy dissipated for a complete cycle of the piston rod. Measured force verses displacement cycles for multiple frequencies and electric fields validate the ability of the non-dimensional groups and the leakage damping coefficient to predict the damping levels for an ER bypass damper with leakage. Based on the experimental validation of the model using these data, the Bingham plastic analysis is shown to be an effective tool for the analysis-based design of double-acting ER bypass dampers.

Stability of infinite slopes under transient partially saturated seepage conditions

NASA Astrophysics Data System (ADS)

Godt, Jonathan W.; ŞEner-Kaya, BaşAk; Lu, Ning; Baum, Rex L.

2012-05-01

Prediction of the location and timing of rainfall-induced shallow landslides is desired by organizations responsible for hazard management and warnings. However, hydrologic and mechanical processes in the vadose zone complicate such predictions. Infiltrating rainfall must typically pass through an unsaturated layer before reaching the irregular and usually discontinuous shallow water table. This process is dynamic and a function of precipitation intensity and duration, the initial moisture conditions and hydrologic properties of the hillside materials, and the geometry, stratigraphy, and vegetation of the hillslope. As a result, pore water pressures, volumetric water content, effective stress, and thus the propensity for landsliding vary over seasonal and shorter time scales. We apply a general framework for assessing the stability of infinite slopes under transient variably saturated conditions. The framework includes profiles of pressure head and volumetric water content combined with a general effective stress for slope stability analysis. The general effective stress, or suction stress, provides a means for rigorous quantification of stress changes due to rainfall and infiltration and thus the analysis of slope stability over the range of volumetric water contents and pressure heads relevant to shallow landslide initiation. We present results using an analytical solution for transient infiltration for a range of soil texture and hydrological properties typical of landslide-prone hillslopes and show the effect of these properties on the timing and depth of slope failure. We follow by analyzing field-monitoring data acquired prior to shallow landslide failure of a hillside near Seattle, Washington, and show that the timing of the slide was predictable using measured pressure head and volumetric water content and show how the approach can be used in a forward manner using a numerical model for transient infiltration.

In-vessel coolability and retention of a core melt

DOE Office of Scientific and Technical Information (OSTI.GOV)

Theofanous, T.G.; Liu, C.; Additon, S.

1997-02-01

The efficacy of external flooding of a reactor vessel as a severe accident management strategy is assessed for an AP600-like reactor design. The overall approach is based on the Risk Oriented Accident Analysis Methodology (ROAAM), and the assessment includes consideration of bounding scenarios and sensitivity studies, as well as arbitrary parametric evaluations that allow the delineation of the failure boundaries. The technical treatment in this assessment includes: (a) new data on energy flow from either volumetrically heated pools or non-heated layers on top, boiling and critical heat flux in inverted, curved geometries, emissivity of molten (superheated) samples of steel, andmore » chemical reactivity proof tests, (b) a simple but accurate mathematical formulation that allows prediction of thermal loads by means of convenient hand calculations, (c) a detailed model programmed on the computer to sample input parameters over the uncertainty ranges, and to produce probability distributions of thermal loads and margins for departure from nucleate boiling at each angular position on the lower head, and (d) detailed structural evaluations that demonstrate that departure from nucleate boiling is a necessary and sufficient criterion for failure. Quantification of the input parameters is carried out for an AP600-like design, and the results of the assessment demonstrate that lower head failure is {open_quotes}physically unreasonable.{close_quotes} Use of this conclusion for any specific application is subject to verifying the required reliability of the depressurization and cavity-flooding systems, and to showing the appropriateness (in relation to the database presented here, or by further testing as necessary) of the thermal insulation design and of the external surface properties of the lower head, including any applicable coatings.« less

A statistical human rib cage geometry model accounting for variations by age, sex, stature and body mass index.

PubMed

Shi, Xiangnan; Cao, Libo; Reed, Matthew P; Rupp, Jonathan D; Hoff, Carrie N; Hu, Jingwen

2014-07-18

In this study, we developed a statistical rib cage geometry model accounting for variations by age, sex, stature and body mass index (BMI). Thorax CT scans were obtained from 89 subjects approximately evenly distributed among 8 age groups and both sexes. Threshold-based CT image segmentation was performed to extract the rib geometries, and a total of 464 landmarks on the left side of each subject׳s ribcage were collected to describe the size and shape of the rib cage as well as the cross-sectional geometry of each rib. Principal component analysis and multivariate regression analysis were conducted to predict rib cage geometry as a function of age, sex, stature, and BMI, all of which showed strong effects on rib cage geometry. Except for BMI, all parameters also showed significant effects on rib cross-sectional area using a linear mixed model. This statistical rib cage geometry model can serve as a geometric basis for developing a parametric human thorax finite element model for quantifying effects from different human attributes on thoracic injury risks. Copyright © 2014 Elsevier Ltd. All rights reserved.

Kinematics of a Head-Neck Model Simulating Whiplash

ERIC Educational Resources Information Center

Colicchia, Giuseppe; Zollman, Dean; Wiesner, Hartmut; Sen, Ahmet Ilhan

2008-01-01

A whiplash event is a relative motion between the head and torso that occurs in rear-end automobile collisions. In particular, the large inertia of the head results in a horizontal translation relative to the thorax. This paper describes a simulation of the motion of the head and neck during a rear-end (whiplash) collision. A head-neck model that…

Optimum Design of a Ceramic Tensile Creep Specimen Using a Finite Element Method

PubMed Central

Wang, Z.; Chiang, C. K.; Chuang, T.-J.

1997-01-01

An optimization procedure for designing a ceramic tensile creep specimen to minimize stress concentration is carried out using a finite element method. The effect of pin loading and the specimen geometry are considered in the stress distribution calculations. A growing contact zone between the pin and the specimen has been incorporated into the problem solution scheme as the load is increased to its full value. The optimization procedures are performed for the specimen, and all design variables including pinhole location and pinhole diameter, head width, neck radius, and gauge length are determined based on a set of constraints imposed on the problem. In addition, for the purpose of assessing the possibility of delayed failure outside the gage section, power-law creep in the tensile specimen is considered in the analysis. Using a particular grade of advanced ceramics as an example, it is found that if the specimen is not designed properly, significant creep deformation and stress redistribution may occur in the head of the specimen resulting in undesirable (delayed) head failure of the specimen during the creep test. PMID:27805126

The FieldTrip-SimBio pipeline for EEG forward solutions.

PubMed

Vorwerk, Johannes; Oostenveld, Robert; Piastra, Maria Carla; Magyari, Lilla; Wolters, Carsten H

2018-03-27

Accurately solving the electroencephalography (EEG) forward problem is crucial for precise EEG source analysis. Previous studies have shown that the use of multicompartment head models in combination with the finite element method (FEM) can yield high accuracies both numerically and with regard to the geometrical approximation of the human head. However, the workload for the generation of multicompartment head models has often been too high and the use of publicly available FEM implementations too complicated for a wider application of FEM in research studies. In this paper, we present a MATLAB-based pipeline that aims to resolve this lack of easy-to-use integrated software solutions. The presented pipeline allows for the easy application of five-compartment head models with the FEM within the FieldTrip toolbox for EEG source analysis. The FEM from the SimBio toolbox, more specifically the St. Venant approach, was integrated into the FieldTrip toolbox. We give a short sketch of the implementation and its application, and we perform a source localization of somatosensory evoked potentials (SEPs) using this pipeline. We then evaluate the accuracy that can be achieved using the automatically generated five-compartment hexahedral head model [skin, skull, cerebrospinal fluid (CSF), gray matter, white matter] in comparison to a highly accurate tetrahedral head model that was generated on the basis of a semiautomatic segmentation with very careful and time-consuming manual corrections. The source analysis of the SEP data correctly localizes the P20 component and achieves a high goodness of fit. The subsequent comparison to the highly detailed tetrahedral head model shows that the automatically generated five-compartment head model performs about as well as a highly detailed four-compartment head model (skin, skull, CSF, brain). This is a significant improvement in comparison to a three-compartment head model, which is frequently used in praxis, since the importance of modeling the CSF compartment has been shown in a variety of studies. The presented pipeline facilitates the use of five-compartment head models with the FEM for EEG source analysis. The accuracy with which the EEG forward problem can thereby be solved is increased compared to the commonly used three-compartment head models, and more reliable EEG source reconstruction results can be obtained.

Background-independent condensed matter models for quantum gravity

NASA Astrophysics Data System (ADS)

Hamma, Alioscia; Markopoulou, Fotini

2011-09-01

A number of recent proposals on a quantum theory of gravity are based on the idea that spacetime geometry and gravity are derivative concepts and only apply at an approximate level. There are two fundamental challenges to any such approach. At the conceptual level, there is a clash between the 'timelessness' of general relativity and emergence. Secondly, the lack of a fundamental spacetime renders difficult the straightforward application of well-known methods of statistical physics to the problem. We recently initiated a study of such problems using spin systems based on the evolution of quantum networks with no a priori geometric notions as models for emergent geometry and gravity. In this paper, we review two such models. The first model is a model of emergent (flat) space and matter, and we show how to use methods from quantum information theory to derive features such as the speed of light from a non-geometric quantum system. The second model exhibits interacting matter and geometry, with the geometry defined by the behavior of matter. This model has primitive notions of gravitational attraction that we illustrate with a toy black hole, and exhibits entanglement between matter and geometry and thermalization of the quantum geometry.

Monte Carlo simulation of electron beams from an accelerator head using PENELOPE.

PubMed

Sempau, J; Sánchez-Reyes, A; Salvat, F; ben Tahar, H O; Jiang, S B; Fernández-Varea, J M

2001-04-01

The Monte Carlo code PENELOPE has been used to simulate electron beams from a Siemens Mevatron KDS linac with nominal energies of 6, 12 and 18 MeV. Owing to its accuracy, which stems from that of the underlying physical interaction models, PENELOPE is suitable for simulating problems of interest to the medical physics community. It includes a geometry package that allows the definition of complex quadric geometries, such as those of irradiation instruments, in a straightforward manner. Dose distributions in water simulated with PENELOPE agree well with experimental measurements using a silicon detector and a monitoring ionization chamber. Insertion of a lead slab in the incident beam at the surface of the water phantom produces sharp variations in the dose distributions, which are correctly reproduced by the simulation code. Results from PENELOPE are also compared with those of equivalent simulations with the EGS4-based user codes BEAM and DOSXYZ. Angular and energy distributions of electrons and photons in the phase-space plane (at the downstream end of the applicator) obtained from both simulation codes are similar, although significant differences do appear in some cases. These differences, however, are shown to have a negligible effect on the calculated dose distributions. Various practical aspects of the simulations, such as the calculation of statistical uncertainties and the effect of the 'latent' variance in the phase-space file, are discussed in detail.

Atomic Forces for Geometry-Dependent Point Multipole and Gaussian Multipole Models

PubMed Central

Elking, Dennis M.; Perera, Lalith; Duke, Robert; Darden, Thomas; Pedersen, Lee G.

2010-01-01

In standard treatments of atomic multipole models, interaction energies, total molecular forces, and total molecular torques are given for multipolar interactions between rigid molecules. However, if the molecules are assumed to be flexible, two additional multipolar atomic forces arise due to 1) the transfer of torque between neighboring atoms, and 2) the dependence of multipole moment on internal geometry (bond lengths, bond angles, etc.) for geometry-dependent multipole models. In the current study, atomic force expressions for geometry-dependent multipoles are presented for use in simulations of flexible molecules. The atomic forces are derived by first proposing a new general expression for Wigner function derivatives ∂Dlm′m/∂Ω. The force equations can be applied to electrostatic models based on atomic point multipoles or Gaussian multipole charge density. Hydrogen bonded dimers are used to test the inter-molecular electrostatic energies and atomic forces calculated by geometry-dependent multipoles fit to the ab initio electrostatic potential (ESP). The electrostatic energies and forces are compared to their reference ab initio values. It is shown that both static and geometry-dependent multipole models are able to reproduce total molecular forces and torques with respect to ab initio, while geometry-dependent multipoles are needed to reproduce ab initio atomic forces. The expressions for atomic force can be used in simulations of flexible molecules with atomic multipoles. In addition, the results presented in this work should lead to further development of next generation force fields composed of geometry-dependent multipole models. PMID:20839297

Design and Analysis Tools for Supersonic Inlets

NASA Technical Reports Server (NTRS)

Slater, John W.; Folk, Thomas C.

2009-01-01

Computational tools are being developed for the design and analysis of supersonic inlets. The objective is to update existing tools and provide design and low-order aerodynamic analysis capability for advanced inlet concepts. The Inlet Tools effort includes aspects of creating an electronic database of inlet design information, a document describing inlet design and analysis methods, a geometry model for describing the shape of inlets, and computer tools that implement the geometry model and methods. The geometry model has a set of basic inlet shapes that include pitot, two-dimensional, axisymmetric, and stream-traced inlet shapes. The inlet model divides the inlet flow field into parts that facilitate the design and analysis methods. The inlet geometry model constructs the inlet surfaces through the generation and transformation of planar entities based on key inlet design factors. Future efforts will focus on developing the inlet geometry model, the inlet design and analysis methods, a Fortran 95 code to implement the model and methods. Other computational platforms, such as Java, will also be explored.

Putting Cocrystal Stoichiometry to Work: A Reactive Hydrogen-Bonded "Superassembly" Enables Nanoscale Enlargement of a Metal-Organic Rhomboid via a Solid-State Photocycloaddition.

PubMed

Chu, Qianli; Duncan, Andrew J E; Papaefstathiou, Giannis S; Hamilton, Tamara D; Atkinson, Manza B J; Mariappan, S V Santhana; MacGillivray, Leonard R

2018-04-11

Enlargement of a self-assembled metal-organic rhomboid is achieved via the organic solid state. The solid-state synthesis of an elongated organic ligand was achieved by a template directed [2 + 2] photodimerization in a cocrystal. Initial cocrystals obtained of resorcinol template and reactant alkene afforded a 1:2 cocrystal with the alkene in a stacked yet photostable geometry. Cocrystallization performed in the presence of excess template resulted in a 3:2 cocrystal composed of novel discrete 10-component hydrogen-bonded "superassemblies" wherein the alkenes undergo a head-to-head [2 + 2] photodimerization. Isolation and reaction of elongated photoproduct with Cu(II) ions afforded a metal-organic rhomboid of nanoscale dimensions that hosts small molecules in the solid state as guests.

The impact of surface and geometry on coefficient of friction of artificial hip joints.

PubMed

Choudhury, Dipankar; Vrbka, Martin; Mamat, Azuddin Bin; Stavness, Ian; Roy, Chanchal K; Mootanah, Rajshree; Krupka, Ivan

2017-08-01

Coefficient of friction (COF) tests were conducted on 28-mm and 36-mm-diameter hip joint prostheses for four different material combinations, with or without the presence of Ultra High Molecular Weight Polyethylene (UHMWPE) particles using a novel pendulum hip simulator. The effects of three micro dimpled arrays on femoral head against a polyethylene and a metallic cup were also investigated. Clearance played a vital role in the COF of ceramic on polyethylene and ceramic on ceramic artificial hip joints. Micro dimpled metallic femoral heads yielded higher COF against a polyethylene cup; however, with metal on metal prostheses the dimpled arrays significantly reduced the COF. In situ images revealed evidence that the dimple arrays enhanced film formation, which was the main mechanism that contributed to reduced friction. Copyright © 2017 Elsevier Ltd. All rights reserved.

Optimization of a reversible hood for protecting a pedestrian's head during car collisions.

PubMed

Huang, Sunan; Yang, Jikuang

2010-07-01

This study evaluated and optimized the performance of a reversible hood (RH) for the prevention of the head injuries of an adult pedestrian from car collisions. The FE model of a production car front was introduced and validated. The baseline RH was developed from the original hood in the validated car front model. In order to evaluate the protective performance of the baseline RH, the FE models of an adult headform and a 50th percentile human head were used in parallel to impact the baseline RH. Based on the evaluation, the response surface method was applied to optimize the RH in terms of the material stiffness, lifting speed, and lifted height. Finally, the headform model and the human head model were again used to evaluate the protective performance of the optimized RH. It was found that the lifted baseline RH can obviously reduce the impact responses of the headform model and the human head model by comparing with the retracted and lifting baseline RH. When the optimized RH was lifted, the HIC values of the headform model and the human head model were further reduced to much lower than 1000. The risk of pedestrian head injuries can be prevented as required by EEVC WG17. Copyright 2009 Elsevier Ltd. All rights reserved.

Simulation of the Francis-99 Hydro Turbine During Steady and Transient Operation

NASA Astrophysics Data System (ADS)

Dewan, Yuvraj; Custer, Chad; Ivashchenko, Artem

2017-01-01

Numerical simulation of the Francis-99 hydroturbine with correlation to experimental measurements are presented. Steady operation of the hydroturbine is analyzed at three operating conditions: the best efficiency point (BEP), high load (HL), and part load (PL). It is shown that global quantities such as net head, discharge and efficiency are well predicted. Additionally, time-averaged velocity predictions compare well with PIV measurements obtained in the draft tube immediately downstream of the runner. Differences in vortex rope structure between operating points are discussed. Unsteady operation of the hydroturbine from BEP to HL and from BEP to PL are modeled. It is shown that simulation methods used to model the steady operation produce predictions that correlate well with experiment for transient operation. Time-domain unsteady simulation is used for both steady and unsteady operation. The full-fidelity geometry including all components is meshed using an unstructured polyhedral mesh with body-fitted prism layers. Guide vane rotation for transient operation is imposed using fully-conservative, computationally efficient mesh morphing. The commercial solver STAR-CCM+ is used for all portions of the analysis including meshing, solving and post-processing.

On the flow through the normal fetal aortic arc at late gestation

NASA Astrophysics Data System (ADS)

Pekkan, Kerem; Nourparvar, Paymon; Yerneni, Srinivasu; Dasi, Lakshmi; de Zelicourt, Diane; Fogel, Mark; Yoganathan, Ajit

2006-11-01

During the fetal stage, the aortic arc is a complex junction of great vessels (right and left ventricular outflow tracks (RVOT, LVOT), pulmonary arteries (PA), ductus, head-neck vessels, decending aorta (Dao)) delicately distributing the oxygenated blood flow to the lungs and the body -preferential to the brain. Experimental and computational studies are performed in idealized models of the fetal aorta to understand and visualize the unsteady hemodynamics. Unsteady in vitro flow, generated by two peristaltic pumps (RVOT and LVOT) is visualized with two colored dyes and a red laser in a rigid glass model with physiological diameters. Helical flow patterns at the PA's and ductal shunting to the Dao are visualized. Computational fluid dynamics of the same geometry is modeled using the commercial code Fidap with porous boundary conditions representing systemic and pulmonary resistances (˜400000 tetrahedral elements). Combined (RVOT+LVOT) average flow rates ranging from 1.9 to 2.1-L/min for 34 to 38-weeks gestation were simulated with the Reynolds and Womersly numbers (Dao) of 500 and 8. Computational results are compared qualitatively with the flow visualizations at this target flow condition. Understanding fetal hemodynamics is critical for congenital heart defects, tissue engineering, fetal cardiac MRI and surgeries.

Assessment of thermal effects in a model of the human head implanted with a wireless active microvalve for the treatment of glaucoma creating a filtering bleb

NASA Astrophysics Data System (ADS)

Schaumburg, F.; Guarnieri, F. A.

2017-05-01

A 3D anatomical computational model is developed to assess thermal effects due to exposure to the electromagnetic field required to power a new investigational active implantable microvalve for the treatment of glaucoma. Such a device, located in the temporal superior eye quadrant, produces a filtering bleb, which is included in the geometry of the model, together with the relevant ocular structures. The electromagnetic field source—a planar coil—as well as the microvalve antenna and casing are also included. Exposure to the electromagnetic field source of an implanted and a non-implanted subject are simulated by solving a magnetic potential formulation, using the finite element method. The maximum SAR10 is reached in the eyebrow and remains within the limits suggested by the IEEE and ICNIRP standards. The anterior chamber, filtering bleb, iris and ciliary body are the ocular structures where more absorption occurs. The temperature rise distribution is also obtained by solving the bioheat equation with the finite element method. The numerical results are compared with the in vivo measurements obtained from four rabbits implanted with the microvalve and exposed to the electromagnetic field source.

Assessment of thermal effects in a model of the human head implanted with a wireless active microvalve for the treatment of glaucoma creating a filtering bleb.

PubMed

Schaumburg, F; Guarnieri, F A

2017-05-07

A 3D anatomical computational model is developed to assess thermal effects due to exposure to the electromagnetic field required to power a new investigational active implantable microvalve for the treatment of glaucoma. Such a device, located in the temporal superior eye quadrant, produces a filtering bleb, which is included in the geometry of the model, together with the relevant ocular structures. The electromagnetic field source-a planar coil-as well as the microvalve antenna and casing are also included. Exposure to the electromagnetic field source of an implanted and a non-implanted subject are simulated by solving a magnetic potential formulation, using the finite element method. The maximum SAR 10 is reached in the eyebrow and remains within the limits suggested by the IEEE and ICNIRP standards. The anterior chamber, filtering bleb, iris and ciliary body are the ocular structures where more absorption occurs. The temperature rise distribution is also obtained by solving the bioheat equation with the finite element method. The numerical results are compared with the in vivo measurements obtained from four rabbits implanted with the microvalve and exposed to the electromagnetic field source.

Multiregion bicentric-spheres models of the head for the simulation of bioelectric phenomena.

PubMed

Vatta, Federica; Bruno, Paolo; Inchingolo, Paolo

2005-03-01

Equations are derived for the electric potentials [electroencephalogram (EEG)] produced by dipolar sources in a multiregion bicentric-spheres volume-conductor head model. Being the equations valid for an arbitrary number of regions, our proposal is a generalization of many spherical models presented so far in literature, each of those regarded as a particular case of our multiregion model. Moreover, our approach allows considering new features of the head volume-conductor to better approximate electrical properties of the real head.

Developments in deep brain stimulation using time dependent magnetic fields

DOE Office of Scientific and Technical Information (OSTI.GOV)

Crowther, L.J.; Nlebedim, I.C.; Jiles, D.C.

2012-03-07

The effect of head model complexity upon the strength of field in different brain regions for transcranial magnetic stimulation (TMS) has been investigated. Experimental measurements were used to verify the validity of magnetic field calculations and induced electric field calculations for three 3D human head models of varying complexity. Results show the inability for simplified head models to accurately determine the site of high fields that lead to neuronal stimulation and highlight the necessity for realistic head modeling for TMS applications.

Developments in deep brain stimulation using time dependent magnetic fields

NASA Astrophysics Data System (ADS)

Crowther, L. J.; Nlebedim, I. C.; Jiles, D. C.

2012-04-01

The effect of head model complexity upon the strength of field in different brain regions for transcranial magnetic stimulation (TMS) has been investigated. Experimental measurements were used to verify the validity of magnetic field calculations and induced electric field calculations for three 3D human head models of varying complexity. Results show the inability for simplified head models to accurately determine the site of high fields that lead to neuronal stimulation and highlight the necessity for realistic head modeling for TMS applications.

[RESEARCH PROGRESS OF EXPERIMENTAL ANIMAL MODELS OF AVASCULAR NECROSIS OF FEMORAL HEAD].

PubMed

Yu, Kaifu; Tan, Hongbo; Xu, Yongqing

2015-12-01

To summarize the current researches and progress on experimental animal models of avascular necrosis of the femoral head. Domestic and internation literature concerning experimental animal models of avascular necrosis of the femoral head was reviewed and analyzed. The methods to prepare the experimental animal models of avascular necrosis of the femoral head can be mainly concluded as traumatic methods (including surgical, physical, and chemical insult), and non-traumatic methods (including steroid, lipopolysaccharide, steroid combined with lipopolysaccharide, steroid combined with horse serum, etc). Each method has both merits and demerits, yet no ideal methods have been developed. There are many methods to prepare the experimental animal models of avascular necrosis of the femoral head, but proper model should be selected based on the aim of research. The establishment of ideal experimental animal models needs further research in future.

Adaptation of the Carter-Tracy water influx calculation to groundwater flow simulation

USGS Publications Warehouse

Kipp, Kenneth L.

1986-01-01

The Carter-Tracy calculation for water influx is adapted to groundwater flow simulation with additional clarifying explanation not present in the original papers. The Van Everdingen and Hurst aquifer-influence functions for radial flow from an outer aquifer region are employed. This technique, based on convolution of unit-step response functions, offers a simple but approximate method for embedding an inner region of groundwater flow simulation within a much larger aquifer region where flow can be treated in an approximate fashion. The use of aquifer-influence functions in groundwater flow modeling reduces the size of the computational grid with a corresponding reduction in computer storage and execution time. The Carter-Tracy approximation to the convolution integral enables the aquifer influence function calculation to be made with an additional storage requirement of only two times the number of boundary nodes more than that required for the inner region simulation. It is a good approximation for constant flow rates but is poor for time-varying flow rates where the variation is large relative to the mean. A variety of outer aquifer region geometries, exterior boundary conditions, and flow rate versus potentiometric head relations can be used. The radial, transient-flow case presented is representative. An analytical approximation to the functions of Van Everdingen and Hurst for the dimensionless potentiometric head versus dimensionless time is given.

The Influence of Organized Physical Activity (including Gymnastics) on Young Adult Skeletal Traits: Is Maturity Phase Important?

PubMed Central

Bernardoni, Brittney; Scerpella, Tamara A.; Rosenbaum, Paula F.; Kanaley, Jill A.; Raab, Lindsay N.; Li, Quefeng; Wang, Sijian; Dowthwaite, Jodi N.

2015-01-01

We prospectively evaluated adolescent organized physical activity (PA) as a factor in adult female bone traits. Annual DXA scans accompanied semi-annual records of anthropometry, maturity and PA for 42 participants in this preliminary analysis (criteria: appropriately timed DXA scans at ~1 year pre-menarche [predictor] and ~5 years post-menarche [dependent variable]). Regression analysis evaluated total adolescent inter-scan PA and PA over 3 maturity sub-phases as predictors of young adult bone outcomes: 1) bone mineral content (BMC), geometry and strength indices at non-dominant distal radius and femoral neck; 2) sub-head BMC; 3) lumbar spine BMC. Analyses accounted for baseline gynecological age (years pre- or post-menarche), baseline bone status, adult body size and inter-scan body size change. Gymnastics training was evaluated as a potentially independent predictor, but did not improve models for any outcomes (p<0.07). Pre-menarcheal bone traits were strong predictors of most adult outcomes (semi-partial r2 = 0.21-0.59, p≤0.001). Adult 1/3 radius and sub-head BMC were predicted by both total PA and PA 1-3 years post-menarche (p<0.03). PA 3-5 years post-menarche predicted femoral narrow neck width, endosteal diameter and buckling ratio (p<0.05). Thus, participation in organized physical activity programs throughout middle and high school may reduce lifetime fracture risk in females. PMID:25386845

The Influence of Neck Muscle Activation on Head and Neck Injuries of Occupants in Frontal Impacts.

PubMed

Li, Fan; Lu, Ronggui; Hu, Wei; Li, Honggeng; Hu, Shiping; Hu, Jiangzhong; Wang, Haibin; Xie, He

2018-01-01

The aim of the present paper was to study the influence of neck muscle activation on head and neck injuries of vehicle occupants in frontal impacts. A mixed dummy-human finite element model was developed to simulate a frontal impact. The head-neck part of a Hybrid III dummy model was replaced by a well-validated head-neck FE model with passive and active muscle characteristics. The mixed dummy-human FE model was validated by 15 G frontal volunteer tests conducted in the Naval Biodynamics Laboratory. The effects of neck muscle activation on the head dynamic responses and neck injuries of occupants in three frontal impact intensities, low speed (10 km/h), medium speed (30 km/h), and high speed (50 km/h), were studied. The results showed that the mixed dummy-human FE model has good biofidelity. The activation of neck muscles can not only lower the head resultant acceleration under different impact intensities and the head angular acceleration in medium- and high-speed impacts, thereby reducing the risks of head injury, but also protect the neck from injury in low-speed impacts.

Geometric Model for a Parametric Study of the Blended-Wing-Body Airplane

NASA Technical Reports Server (NTRS)

Mastin, C. Wayne; Smith, Robert E.; Sadrehaghighi, Ideen; Wiese, Micharl R.

1996-01-01

A parametric model is presented for the blended-wing-body airplane, one concept being proposed for the next generation of large subsonic transports. The model is defined in terms of a small set of parameters which facilitates analysis and optimization during the conceptual design process. The model is generated from a preliminary CAD geometry. From this geometry, airfoil cross sections are cut at selected locations and fitted with analytic curves. The airfoils are then used as boundaries for surfaces defined as the solution of partial differential equations. Both the airfoil curves and the surfaces are generated with free parameters selected to give a good representation of the original geometry. The original surface is compared with the parametric model, and solutions of the Euler equations for compressible flow are computed for both geometries. The parametric model is a good approximation of the CAD model and the computed solutions are qualitatively similar. An optimal NURBS approximation is constructed and can be used by a CAD model for further refinement or modification of the original geometry.

Kinematic analyses of the golf swing hub path and its role in golfer/club kinetic transfers.

PubMed

Nesbit, Steven M; McGinnis, Ryan

2009-01-01

This study analyzed the fundamental geometric and kinematic characteristics of the swing hub path of the golf shot for four diverse subjects. In addition, the role of the hub path geometry in transferring the kinetic quantities from the golfer to the club were investigated. The hub path was found to have a complex geometry with significantly changing radii, and a constantly moving center-of-curvature during the downswing for all subjects. While the size and shape of the hub path differed considerably among the subjects, a three phase radius-based pattern was revealed that aligned with distinct stages of the downswing. Artificially controlling and optimizing the hub path of the better golfer in the group indicated that a non-circular hub path was superior to a constant radius path in minimizing the kinetic loading while generating the highest possible club head velocity. The shape and purpose of the hub path geometry appears to result from a complex combination of achieving equilibrium between the golfer and the club, and a purposeful configuring of the path to control the outward movement of the club while minimizing the kinetic loading on the golfer yet transferring the maximum kinetic quantities to the club. Describing the downswing relative to the hub path phasing is presented and was found to be informative since the phases align with significant swing, kinetic and kinematic markers. These findings challenge golf swing modeling methodologies which fix the center-of-curvature of the hub path thus constraining it to constant radius motion. Key pointsThe golf swing hub path was found to have a complex geometry with significantly changing radii, and a constantly moving center-of-curvature during the downswing.The hub path differed considerably among subjects, however a three phase radius-based pattern was revealed that aligned with distinct stages of the downswing.The shape and purpose of the hub path geometry appears to result from a complex combination of achieving equilibrium between the golfer and the club, and a purposeful configuring of the path to control the outward movement of the club while minimizing the kinetic loading on the golfer yet transferring the maximum kinetic quantities to the club.

Tensionless Strings and Supersymmetric Sigma Models: Aspects of the Target Space Geometry

NASA Astrophysics Data System (ADS)

Bredthauer, Andreas

2007-01-01

In this thesis, two aspects of string theory are discussed, tensionless strings and supersymmetric sigma models. The equivalent to a massless particle in string theory is a tensionless string. Even almost 30 years after it was first mentioned, it is still quite poorly understood. We discuss how tensionless strings give rise to exact solutions to supergravity and solve closed tensionless string theory in the ten dimensional maximally supersymmetric plane wave background, a contraction of AdS(5)xS(5) where tensionless strings are of great interest due to their proposed relation to higher spin gauge theory via the AdS/CFT correspondence. For a sigma model, the amount of supersymmetry on its worldsheet restricts the geometry of the target space. For N=(2,2) supersymmetry, for example, the target space has to be bi-hermitian. Recently, with generalized complex geometry, a new mathematical framework was developed that is especially suited to discuss the target space geometry of sigma models in a Hamiltonian formulation. Bi-hermitian geometry is so-called generalized Kaehler geometry but the relation is involved. We discuss various amounts of supersymmetry in phase space and show that this relation can be established by considering the equivalence between the Hamilton and Lagrange formulation of the sigma model. In the study of generalized supersymmetric sigma models, we find objects that favor a geometrical interpretation beyond generalized complex geometry.

Competitive Dynamics in MSTd: A Mechanism for Robust Heading Perception Based on Optic Flow

PubMed Central

Layton, Oliver W.; Fajen, Brett R.

2016-01-01

Human heading perception based on optic flow is not only accurate, it is also remarkably robust and stable. These qualities are especially apparent when observers move through environments containing other moving objects, which introduce optic flow that is inconsistent with observer self-motion and therefore uninformative about heading direction. Moving objects may also occupy large portions of the visual field and occlude regions of the background optic flow that are most informative about heading perception. The fact that heading perception is biased by no more than a few degrees under such conditions attests to the robustness of the visual system and warrants further investigation. The aim of the present study was to investigate whether recurrent, competitive dynamics among MSTd neurons that serve to reduce uncertainty about heading over time offer a plausible mechanism for capturing the robustness of human heading perception. Simulations of existing heading models that do not contain competitive dynamics yield heading estimates that are far more erratic and unstable than human judgments. We present a dynamical model of primate visual areas V1, MT, and MSTd based on that of Layton, Mingolla, and Browning that is similar to the other models, except that the model includes recurrent interactions among model MSTd neurons. Competitive dynamics stabilize the model’s heading estimate over time, even when a moving object crosses the future path. Soft winner-take-all dynamics enhance units that code a heading direction consistent with the time history and suppress responses to transient changes to the optic flow field. Our findings support recurrent competitive temporal dynamics as a crucial mechanism underlying the robustness and stability of perception of heading. PMID:27341686

A nitrogen-rich septage-effluent plume in a glacial aquifer, Cape Cod, Massachusetts, February 1990 through December 1992

USGS Publications Warehouse

Desimone, Leslie A.; Barlow, Paul M.; Howes, Brian L.

1996-01-01

Physical, chemical, and microbial processes controlled transport of a nitrogen-rich ground-water plume through a glacial aquifer. Lithologic heterogeneity and vertical head gradients influenced plume movement and geometry. Nitrate was the predominant nitrogen form and oxygen was depleted in the ground-water plume. However, denitrification transformed only 2 percent of plume nitrogen because of limited organic-carbon availability. Aerobic respiration, nitrification and cation exchange (unsaturated zone) and ammonium sorption (saturated zone) had larger effects.

Journal of Rehabilitation Research and Development Progress Reports 1994, Volume 32, June 1995

DTIC Science & Technology

1995-06-01

Stepping Over an Obstacle: Effect of Reduced Visual Field 50 Effect of Reduced Optic Flow on Gait 51 Effects of Robotic-Assisted Weight Support on Gait...Geometry in Hip Replacement 240 Wear Debris Generation in Hip Modular Head and Neck Components 241 Changes in Bone Blood Flow Associated with...rectangular cross-section to form a continuously flowing ribbon of melted plastic. Rib- bon dimensions are 0.75 mm thick and 5 mm wide, corresponding to

Downforce variation dependence of angle of incidence modification for the rear wing of high speed vehicles

NASA Astrophysics Data System (ADS)

Tarulescu, R.; Tarulescu, S.; Leahu, C.

2017-10-01

The conventional downforce devices (with fixed geometry) of high speed vehicles have parameters such as area, angle of incidence and head resistance coefficients, all with constant values. The downforce is proportional with the square of movement speed and the power consumed for the neutralization of aerodynamic road resistance is proportional with the cube of speed. The authors carried out an analytical study of downforce, adjustable/monitored by optimum incidence (modification of incidence angle of rear wing for performance improvement).

Live Speech Driven Head-and-Eye Motion Generators.

PubMed

Le, Binh H; Ma, Xiaohan; Deng, Zhigang

2012-11-01

This paper describes a fully automated framework to generate realistic head motion, eye gaze, and eyelid motion simultaneously based on live (or recorded) speech input. Its central idea is to learn separate yet interrelated statistical models for each component (head motion, gaze, or eyelid motion) from a prerecorded facial motion data set: 1) Gaussian Mixture Models and gradient descent optimization algorithm are employed to generate head motion from speech features; 2) Nonlinear Dynamic Canonical Correlation Analysis model is used to synthesize eye gaze from head motion and speech features, and 3) nonnegative linear regression is used to model voluntary eye lid motion and log-normal distribution is used to describe involuntary eye blinks. Several user studies are conducted to evaluate the effectiveness of the proposed speech-driven head and eye motion generator using the well-established paired comparison methodology. Our evaluation results clearly show that this approach can significantly outperform the state-of-the-art head and eye motion generation algorithms. In addition, a novel mocap+video hybrid data acquisition technique is introduced to record high-fidelity head movement, eye gaze, and eyelid motion simultaneously.

SAR Simulation with Magneto Chiral Effects for Human Head Radiated from Cellular Phones

NASA Astrophysics Data System (ADS)

Torres-Silva, H.

2008-09-01

A numerical method for a microwave signal emitted by a cellular phone, propagating in a magneto-chiral media, characterized by an extended Born-Fedorov formalism, is presented. It is shown that the use of a cell model, combined with a real model of the human head, derived from the magnetic resonance of images allows a good determination of the near fields induced in the head when the brain chirality and the battery magnetic field are considered together. The results on a 2-Dim human head model show the evolution of the specific absorption rate, (SAR coefficient) and the spatial peak specific absorption rate which are sensitives to the magneto-chiral factor, which is important in the brain layer. For GSM/PCN phones, extremely low frequency real pulsed magnetic fields (in the order of 10 to 60 milligauss) are added to the model through the whole of the user's head. The more important conclusion of our work is that the head absorption is bigger than the results for a classical model without the magneto chiral effect. Hot spots are produced due to the combination of microwave and the magnetic field produced by the phone's operation. The FDTD method was used to compute the SARs inside the MRI based head models consisting of various tissues for 1.8 GHz. As a result, we found that in the head model having more than four kinds of tissue, the localized peak SAR reaches maximum inside the head for over five tissues including skin, bone, blood and brain cells.

A geometric modeler based on a dual-geometry representation polyhedra and rational b-splines

NASA Technical Reports Server (NTRS)

Klosterman, A. L.

1984-01-01

For speed and data base reasons, solid geometric modeling of large complex practical systems is usually approximated by a polyhedra representation. Precise parametric surface and implicit algebraic modelers are available but it is not yet practical to model the same level of system complexity with these precise modelers. In response to this contrast the GEOMOD geometric modeling system was built so that a polyhedra abstraction of the geometry would be available for interactive modeling without losing the precise definition of the geometry. Part of the reason that polyhedra modelers are effective is that all bounded surfaces can be represented in a single canonical format (i.e., sets of planar polygons). This permits a very simple and compact data structure. Nonuniform rational B-splines are currently the best representation to describe a very large class of geometry precisely with one canonical format. The specific capabilities of the modeler are described.

Heading in football. Part 3: Effect of ball properties on head response

PubMed Central

Shewchenko, N; Withnall, C; Keown, M; Gittens, R; Dvorak, J

2005-01-01

Objectives: Head impacts from footballs are an essential part of the game but have been implicated in mild and acute neuropsychological impairment. Ball characteristics have been noted in literature to affect the impact response of the head; however, the biomechanics are not well understood. The present study determined whether ball mass, pressure, and construction characteristics help reduce head and neck can impact response. Methods: Head responses under ball impact (6–7 m/s) were measured with a biofidelic numerical human model and controlled human subject trials (n = 3). Three ball masses and four ball pressures were investigated for frontal heading. Further, the effect of ball construction in wet/dry conditions was studied with the numerical model. The dynamic ball characteristics were determined experimentally. Head linear and angular accelerations were measured and compared with injury assessment functions comprising peak values and head impact power. Neck responses were assessed with the numerical model. Results: Ball mass reductions up to 35% resulted in decreased head responses up to 23–35% for the numerical and subject trials. Similar decreases in neck axial and shear responses were observed. Ball pressure reductions of 50% resulted in head and neck response reductions up to 10–31% for the subject trials and numerical model. Head response reductions up to 15% were observed between different ball constructions. The wet condition generally resulted in greater head and neck responses of up to 20%. Conclusion: Ball mass, pressure, and construction can reduce the impact severity to the head and neck. It is foreseeable that the benefits can be extended to players of all ages and skill levels. PMID:16046354

Thermal therapy of pancreatic tumors using endoluminal ultrasound: parametric and patient-specific modeling

PubMed Central

Adams, Matthew S.; Scott, Serena J.; Salgaonkar, Vasant A.; Sommer, Graham; Diederich, Chris J.

2016-01-01

Purpose To investigate endoluminal ultrasound applicator configurations for volumetric thermal ablation and hyperthermia of pancreatic tumors using 3D acoustic and biothermal finite element models. Materials and Methods Parametric studies compared endoluminal heating performance for varying applicator transducer configurations (planar, curvilinear-focused, or radial-diverging), frequencies (1–5 MHz), and anatomical conditions. Patient-specific pancreatic head and body tumor models were used to evaluate feasibility of generating hyperthermia and thermal ablation using an applicator positioned in the duodenal or stomach lumen. Temperature and thermal dose were calculated to define ablation (>240 EM43°C) and moderate hyperthermia (40–45 °C) boundaries, and to assess sparing of sensitive tissues. Proportional-integral control was incorporated to regulate maximum temperature to 70–80 °C for ablation and 45 °C for hyperthermia in target regions. Results Parametric studies indicated that 1–3 MHz planar transducers are most suitable for volumetric ablation, producing 5–8 cm3 lesion volumes for a stationary 5 minute sonication. Curvilinear-focused geometries produce more localized ablation to 20–45 mm depth from the GI tract and enhance thermal sparing (Tmax<42 °C) of the luminal wall. Patient anatomy simulations show feasibility in ablating 60.1–92.9% of head/body tumor volumes (4.3–37.2 cm3) with dose <15 EM43°C in the luminal wall for 18–48 min treatment durations, using 1–3 applicator placements in GI lumen. For hyperthermia, planar and radial-diverging transducers could maintain up to 8 cm3 and 15 cm3 of tissue, respectively, between 40–45 °C for a single applicator placement. Conclusions Modeling studies indicate the feasibility of endoluminal ultrasound for volumetric thermal ablation or hyperthermia treatment of pancreatic tumor tissue. PMID:27097663

Development, Validation and Parametric study of a 3-Year-Old Child Head Finite Element Model

NASA Astrophysics Data System (ADS)

Cui, Shihai; Chen, Yue; Li, Haiyan; Ruan, ShiJie

2015-12-01

Traumatic brain injury caused by drop and traffic accidents is an important reason for children's death and disability. Recently, the computer finite element (FE) head model has been developed to investigate brain injury mechanism and biomechanical responses. Based on CT data of a healthy 3-year-old child head, the FE head model with detailed anatomical structure was developed. The deep brain structures such as white matter, gray matter, cerebral ventricle, hippocampus, were firstly created in this FE model. The FE model was validated by comparing the simulation results with that of cadaver experiments based on reconstructing the child and adult cadaver experiments. In addition, the effects of skull stiffness on the child head dynamic responses were further investigated. All the simulation results confirmed the good biofidelity of the FE model.

The National Shipbuilding Research Program. Photogrammetric Dimensioning of Distributive Systems Models. Phase 1

DTIC Science & Technology

1978-08-01

21- accepts piping geometry as one of its basic inputs; whether this geometry comes from arrangement drawings or models is of no real consequence. c ... computer . Geometric data is taken from the catalogue and automatically merged with the piping geometry data. Also, fitting orientation is automatically...systems require a number of data manipulation routines to convert raw digitized data into logical pipe geometry acceptable to a computer -aided piping design

Comparison of calculated and measured model rotor loading and wake geometry

NASA Technical Reports Server (NTRS)

Johnson, W.

1980-01-01

The calculated blade bound circulation and wake geometry are compared with measured results for a model helicopter rotor in hover and forward flight. Hover results are presented for rectangular tip and ogee tip planform blades. The correlation is quite good when the measured wake geometry characteristics are used in the analysis. Available prescribed wake geometry models are found to give fair predictions of the loading, but they do not produce a reasonable prediction of the induced power. Forward flight results are presented for twisted and untwisted blades. Fair correlation between measurements and calculations is found for the bound circulation distribution on the advancing side. The tip vortex geometry in the vicinity of the advancing blade in forward flight was predicted well by the free wake calculation used, although the wake geometry did not have a significant influence on the calculated loading and performance for the cases considered.

Numerical Investigation on Head and Brain Injuries Caused by Windshield Impact on Riders Using Electric Self-Balancing Scooters

PubMed Central

Zheng, Yanting; Shen, Ming; Yang, Xianfeng

2018-01-01

To investigate head-brain injuries caused by windshield impact on riders using electric self-balancing scooters (ESS). Numerical vehicle ESS crash scenarios are constructed by combining the finite element (FE) vehicle model and multibody scooter/rider models. Impact kinematic postures of the head-windshield contact under various impact conditions are captured. Then, the processes during head-windshield contact are reconstructed using validated FE head/laminated windshield models to assess the severity of brain injury caused by the head-windshield contact. Governing factors, such as vehicle speed, ESS speed, and the initial orientation of ESS rider, have nontrivial influences over the severity of a rider's brain injuries. Results also show positive correlations between vehicle speed and head-windshield impact speeds (linear and angular). Meanwhile, the time of head-windshield contact happens earlier when the vehicle speed is faster. According to the intensive study, windshield-head contact speed (linear and angular), impact location on the windshield, and head collision area are found to be direct factors on ESS riders' brain injuries during an impact. The von Mises stress and shear stress rise when relative contact speed of head-windshield increases. Brain injury indices vary widely when the head impacting the windshield from center to the edge or impacting with different areas. PMID:29770161

Analytical correlation of centrifugal compressor design geometry for maximum efficiency with specific speed

NASA Technical Reports Server (NTRS)

Galvas, M. R.

1972-01-01

Centrifugal compressor performance was examined analytically to determine optimum geometry for various applications as characterized by specific speed. Seven specific losses were calculated for various combinations of inlet tip-exit diameter ratio, inlet hub-tip diameter ratio, blade exit backsweep, and inlet-tip absolute tangential velocity for solid body prewhirl. The losses considered were inlet guide vane loss, blade loading loss, skin friction loss, recirculation loss, disk friction loss, vaneless diffuser loss, and vaned diffuser loss. Maximum total efficiencies ranged from 0.497 to 0.868 for a specific speed range of 0.257 to 1.346. Curves of rotor exit absolute flow angle, inlet tip-exit diameter ratio, inlet hub-tip diameter ratio, head coefficient and blade exit backsweep are presented over a range of specific speeds for various inducer tip speeds to permit rapid selection of optimum compressor size and shape for a variety of applications.

Performance evaluation of a LYSO-based PET scanner for monitoring of dose delivery in hadrontherapy

NASA Astrophysics Data System (ADS)

Fabbiani, E.; Belcari, N.; Camarlinghi, N.; Del Guerra, A.; Ferretti, S.; Kraan, A.; Panetta, D.; Sportelli, G.; Rosso, V.

2015-12-01

The DoPET scanner is a compact positron emission tomography (PET) device. It has been developed for monitoring the range of charged particles during therapy with hadron beams. Previous works have focused on the development and upgrade of the device and on data analysis. In this paper, a full performance characterization of the DoPET system in terms of the energy resolution, spatial resolution, sensitivity, uniformity, and noise equivalent count rate is reported. All measurements refer to an adapted version of the National Electrical Manufacturers Association (NEMA) NU 4 - 2008 protocol, which was written originally for small animal PET systems. Since DoPET is a dual head planar system, it requires a modified characterisation procedure with respect to those described for ring geometries as in the NEMA NU 4 - 2008 protocol. The presented procedure may be of interest for any other PET system with a similar geometry as DoPET.

A combined experimental and finite element approach to analyse the fretting mechanism of the head-stem taper junction in total hip replacement.

PubMed

Bitter, Thom; Khan, Imran; Marriott, Tim; Lovelady, Elaine; Verdonschot, Nico; Janssen, Dennis

2017-09-01

Fretting corrosion at the taper interface of modular hip implants has been implicated as a possible cause of implant failure. This study was set up to gain more insight in the taper mechanics that lead to fretting corrosion. The objectives of this study therefore were (1) to select experimental loading conditions to reproduce clinically relevant fretting corrosion features observed in retrieved components, (2) to develop a finite element model consistent with the fretting experiments and (3) to apply more complicated loading conditions of activities of daily living to the finite element model to study the taper mechanics. The experiments showed similar wear patterns on the taper surface as observed in retrievals. The finite element wear score based on Archard's law did not correlate well with the amount of material loss measured in the experiments. However, similar patterns were observed between the simulated micromotions and the experimental wear measurements. Although the finite element model could not be validated, the loading conditions based on activities of daily living demonstrate the importance of assembly load on the wear potential. These findings suggest that finite element models that do not incorporate geometry updates to account for wear loss may not be appropriate to predict wear volumes of taper connections.

SU-F-J-205: Effect of Cone Beam Factor On Cone Beam CT Number Accuracy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yao, W; Hua, C; Farr, J

Purpose: To examine the suitability of a Catphan™ 700 phantom for image quality QA of a cone beam computed tomography (CBCT) system deployed for proton therapy. Methods: Catphan phantoms, particularly Catphan™ 504, are commonly used in image quality QA for CBCT. As a newer product, Catphan™ 700 offers more tissue equivalent inserts which may be useful for generating the electron density – CT number curve for CBCT based treatment planning. The sensitometry-and-geometry module used in Catphan™ 700 is located at the end of the phantom and after the resolution line pair module. In Catphan™ 504 the line pair module ismore » located at the end of the phantom and after the sensitometry-and-geometry module. To investigate the effect of difference in location on CT number accuracy due to the cone beam factor, we scanned the Catphan™ 700 with the central plane of CBCT at the center of the phantom, line pair and sensitometry-andgeometry modules of the phantom, respectively. The protocol head and thorax scan modes were used. For each position, scans were repeated 4 times. Results: For the head scan mode, the standard deviation (SD) of the CT numbers of each insert under 4 repeated scans was up to 20 HU, 11 HU, and 11 HU, respectively, for the central plane of CBCT located at the center of the phantom, line pair, and sensitometry-and-geometry modules of the phantom. The mean of the SD was 9.9 HU, 5.7 HU, and 5.9 HU, respectively. For the thorax mode, the mean of the SD was 4.5 HU, 4.4 HU, and 4.4 HU, respectively. The assessment of image quality based on resolution and spatial linearity was not affected by imaging location changes. Conclusion: When the Catphan™ 700 was aligned to the center of imaging region, the CT number accuracy test may not meet expectations. We recommend reconfiguration of the modules.« less

Ellipsoidal geometry in asteroid thermal models - The standard radiometric model

NASA Technical Reports Server (NTRS)

Brown, R. H.

1985-01-01

The major consequences of ellipsoidal geometry in an othewise standard radiometric model for asteroids are explored. It is shown that for small deviations from spherical shape a spherical model of the same projected area gives a reasonable aproximation to the thermal flux from an ellipsoidal body. It is suggested that large departures from spherical shape require that some correction be made for geometry. Systematic differences in the radii of asteroids derived radiometrically at 10 and 20 microns may result partly from nonspherical geometry. It is also suggested that extrapolations of the rotational variation of thermal flux from a nonspherical body based solely on the change in cross-sectional area are in error.

Accurate Analysis of the Change in Volume, Location, and Shape of Metastatic Cervical Lymph Nodes During Radiotherapy

DOE Office of Scientific and Technical Information (OSTI.GOV)

Takao, Seishin, E-mail: takao@mech-me.eng.hokudai.ac.jp; Tadano, Shigeru; Taguchi, Hiroshi

2011-11-01

Purpose: To establish a method for the accurate acquisition and analysis of the variations in tumor volume, location, and three-dimensional (3D) shape of tumors during radiotherapy in the era of image-guided radiotherapy. Methods and Materials: Finite element models of lymph nodes were developed based on computed tomography (CT) images taken before the start of treatment and every week during the treatment period. A surface geometry map with a volumetric scale was adopted and used for the analysis. Six metastatic cervical lymph nodes, 3.5 to 55.1 cm{sup 3} before treatment, in 6 patients with head and neck carcinomas were analyzed inmore » this study. Three fiducial markers implanted in mouthpieces were used for the fusion of CT images. Changes in the location of the lymph nodes were measured on the basis of these fiducial markers. Results: The surface geometry maps showed convex regions in red and concave regions in blue to ensure that the characteristics of the 3D tumor geometries are simply understood visually. After the irradiation of 66 to 70 Gy in 2 Gy daily doses, the patterns of the colors had not changed significantly, and the maps before and during treatment were strongly correlated (average correlation coefficient was 0.808), suggesting that the tumors shrank uniformly, maintaining the original characteristics of the shapes in all 6 patients. The movement of the gravitational center of the lymph nodes during the treatment period was everywhere less than {+-}5 mm except in 1 patient, in whom the change reached nearly 10 mm. Conclusions: The surface geometry map was useful for an accurate evaluation of the changes in volume and 3D shapes of metastatic lymph nodes. The fusion of the initial and follow-up CT images based on fiducial markers enabled an analysis of changes in the location of the targets. Metastatic cervical lymph nodes in patients were suggested to decrease in size without significant changes in the 3D shape during radiotherapy. The movements of the gravitational center of the lymph nodes were almost all less than {+-}5 mm.« less

Progress in the Development of CdZnTe Unipolar Detectors for Different Anode Geometries and Data Corrections

PubMed Central

Zhang, Qiushi; Zhang, Congzhe; Lu, Yanye; Yang, Kun; Ren, Qiushi

2013-01-01

CdZnTe detectors have been under development for the past two decades, providing good stopping power for gamma rays, lightweight camera heads and improved energy resolution. However, the performance of this type of detector is limited primarily by incomplete charge collection problems resulting from charge carriers trapping. This paper is a review of the progress in the development of CdZnTe unipolar detectors with some data correction techniques for improving performance of the detectors. We will first briefly review the relevant theories. Thereafter, two aspects of the techniques for overcoming the hole trapping issue are summarized, including irradiation direction configuration and pulse shape correction methods. CdZnTe detectors of different geometries are discussed in detail, covering the principal of the electrode geometry design, the design and performance characteristics, some detector prototypes development and special correction techniques to improve the energy resolution. Finally, the state of art development of 3-D position sensing and Compton imaging technique are also discussed. Spectroscopic performance of CdZnTe semiconductor detector will be greatly improved even to approach the statistical limit on energy resolution with the combination of some of these techniques. PMID:23429509

Visualization of light propagation in visible Chinese human head for functional near-infrared spectroscopy

NASA Astrophysics Data System (ADS)

Li, Ting; Gong, Hui; Luo, Qingming

2011-04-01

Using the visible Chinese human data set, which faithfully represents human anatomy, we visualize the light propagation in the head in detail based on Monte Carlo simulation. The simulation is verified to agree with published experimental results in terms of a differential path-length factor. The spatial sensitivity profile turns out to seem like a fat tropical fish with strong distortion along the folding cerebral surface. The sensitive brain region covers the gray matter and extends to the superficial white matter, leading to a large penetration depth (>3 cm). Finally, the optimal source-detector separation is suggested to be narrowed down to 3-3.5 cm, while the sensitivity of the detected signal to brain activation reaches the peak of 8%. These results indicate that the cerebral cortex folding geometry actually has substantial effects on light propagation, which should be necessarily considered for applications of functional near-infrared spectroscopy.

CFD based draft tube hydraulic design optimization

NASA Astrophysics Data System (ADS)

McNabb, J.; Devals, C.; Kyriacou, S. A.; Murry, N.; Mullins, B. F.

2014-03-01

The draft tube design of a hydraulic turbine, particularly in low to medium head applications, plays an important role in determining the efficiency and power characteristics of the overall machine, since an important proportion of the available energy, being in kinetic form leaving the runner, needs to be recovered by the draft tube into static head. For large units, these efficiency and power characteristics can equate to large sums of money when considering the anticipated selling price of the energy produced over the machine's life-cycle. This same draft tube design is also a key factor in determining the overall civil costs of the powerhouse, primarily in excavation and concreting, which can amount to similar orders of magnitude as the price of the energy produced. Therefore, there is a need to find the optimum compromise between these two conflicting requirements. In this paper, an elaborate approach is described for dealing with this optimization problem. First, the draft tube's detailed geometry is defined as a function of a comprehensive set of design parameters (about 20 of which a subset is allowed to vary during the optimization process) and are then used in a non-uniform rational B-spline based geometric modeller to fully define the wetted surfaces geometry. Since the performance of the draft tube is largely governed by 3D viscous effects, such as boundary layer separation from the walls and swirling flow characteristics, which in turn governs the portion of the available kinetic energy which will be converted into pressure, a full 3D meshing and Navier-Stokes analysis is performed for each design. What makes this even more challenging is the fact that the inlet velocity distribution to the draft tube is governed by the runner at each of the various operating conditions that are of interest for the exploitation of the powerhouse. In order to determine these inlet conditions, a combined steady-state runner and an initial draft tube analysis, using a stage interface between them, must first be performed for each operating condition. Due to the computationally intensive nature of the evaluation process, the efficiency of the optimization algorithm becomes important. Therefore, a state-of-the-art hierarchical-metamodel-assisted evolutionary algorithm is used.

Measurement of Pressure Responses in a Physical Model of a Human Head with High Shape Fidelity Based on Ct/mri Data

NASA Astrophysics Data System (ADS)

Miyazaki, Yusuke; Tachiya, Hiroshi; Anata, Kenji; Hojo, Akihiro

This study discusses a head injury mechanism in case of a human head subjected to impact, from results of impact experiments by using a physical model of a human head with high-shape fidelity. The physical model was constructed by using rapid prototyping technology from the three-dimensional CAD data, which obtained from CT/MRI images of a subject's head. As results of the experiments, positive pressure responses occurred at the impacted site, whereas negative pressure responses occurred at opposite the impacted site. Moreover, the absolute maximum value of pressure occurring at the frontal region of the intracranial space of the head model resulted in same or higher than that at the occipital site in each case that the impact force was imposed on frontal or occipital region. This result has not been showed in other study using simple shape physical models. And, the result corresponds with clinical evidences that brain contusion mainly occurs at the frontal part in each impact direction. Thus, physical model with accurate skull shape is needed to clarify the mechanism of brain contusion.

A chaotic-dynamical conceptual model to describe fluid flow and contaminant transport in a fractured vadose zone. 1997 progress report and presentations at the annual meeting, Ernest Orlando Lawrence Berkeley National Laboratory, December 3--4, 1997

DOE Office of Scientific and Technical Information (OSTI.GOV)

Faybishenko, B.; Doughty, C.; Geller, J.

1998-07-01

Understanding subsurface flow and transport processes is critical for effective assessment, decision-making, and remediation activities for contaminated sites. However, for fluid flow and contaminant transport through fractured vadose zones, traditional hydrogeological approaches are often found to be inadequate. In this project, the authors examine flow and transport through a fractured vadose zone as a deterministic chaotic dynamical process, and develop a model of it in these terms. Initially, the authors examine separately the geometric model of fractured rock and the flow dynamics model needed to describe chaotic behavior. Ultimately they will put the geometry and flow dynamics together to developmore » a chaotic-dynamical model of flow and transport in a fractured vadose zone. They investigate water flow and contaminant transport on several scales, ranging from small-scale laboratory experiments in fracture replicas and fractured cores, to field experiments conducted in a single exposed fracture at a basalt outcrop, and finally to a ponded infiltration test using a pond of 7 by 8 m. In the field experiments, they measure the time-variation of water flux, moisture content, and hydraulic head at various locations, as well as the total inflow rate to the subsurface. Such variations reflect the changes in the geometry and physics of water flow that display chaotic behavior, which they try to reconstruct using the data obtained. In the analysis of experimental data, a chaotic model can be used to predict the long-term bounds on fluid flow and transport behavior, known as the attractor of the system, and to examine the limits of short-term predictability within these bounds. This approach is especially well suited to the need for short-term predictions to support remediation decisions and long-term bounding studies. View-graphs from ten presentations made at the annual meeting held December 3--4, 1997 are included in an appendix to this report.« less

Modeling eye-head gaze shifts in multiple contexts without motor planning

PubMed Central

Haji-Abolhassani, Iman; Guitton, Daniel

2016-01-01

During gaze shifts, the eyes and head collaborate to rapidly capture a target (saccade) and fixate it. Accordingly, models of gaze shift control should embed both saccadic and fixation modes and a mechanism for switching between them. We demonstrate a model in which the eye and head platforms are driven by a shared gaze error signal. To limit the number of free parameters, we implement a model reduction approach in which steady-state cerebellar effects at each of their projection sites are lumped with the parameter of that site. The model topology is consistent with anatomy and neurophysiology, and can replicate eye-head responses observed in multiple experimental contexts: 1) observed gaze characteristics across species and subjects can emerge from this structure with minor parametric changes; 2) gaze can move to a goal while in the fixation mode; 3) ocular compensation for head perturbations during saccades could rely on vestibular-only cells in the vestibular nuclei with postulated projections to burst neurons; 4) two nonlinearities suffice, i.e., the experimentally-determined mapping of tectoreticular cells onto brain stem targets and the increased recruitment of the head for larger target eccentricities; 5) the effects of initial conditions on eye/head trajectories are due to neural circuit dynamics, not planning; and 6) “compensatory” ocular slow phases exist even after semicircular canal plugging, because of interconnections linking eye-head circuits. Our model structure also simulates classical vestibulo-ocular reflex and pursuit nystagmus, and provides novel neural circuit and behavioral predictions, notably that both eye-head coordination and segmental limb coordination are possible without trajectory planning. PMID:27440248

Biomechanical characterisation of osteosyntheses for proximal femur fractures: helical blade versus screw.

PubMed

Al-Munajjed, Amir A; Hammer, Joachim; Mayr, Edgar; Nerlich, Michael; Lenich, Andreas

2008-01-01

Proximal femur fractures are of main concern for elderly and especially osteoporotic patients. Despite advanced implant modifications and surgical techniques, serious mechanical complication rates between 4-18% are found in conventional osteosyntheses of proximal femur fractures. Clinical complications such as the rotation of the femoral head and the cut-out phenomenon of the fracture fixation bolt are often diagnosed during post-operative treatments. Therefore, efforts in new intramedulary techniques focus on the load bearing characteristics of the implant by developing new geometries to improve the implant-tissue interface. The objective of this investigation was to analyse the osteosynthesis/femur head interaction of two commonly used osteosyntheses, one with a helical blade and the other one with a screw design under different loading conditions. For the comparative investigation the helical blade of the Proximal Femur Nail Antirotation was investigated versus the screw system of the Dynamic Hip Screw. After implantation in a femoral head the loads for rotational overwinding of the implants were analysed. Pull-out forces with suppressed rotation were investigated with analysis of the influence of the previous overwinding. All investigations were performed on human femoral heads taken of patients with average age of 70.3+/-11.8. The bone mineral densities of the human specimens were detected by QCT-scans (average BMD: 338.9+/- 61.3$\\frac[\\mathit[mg

Simplified realistic human head model for simulating Tumor Treating Fields (TTFields).

PubMed

Wenger, Cornelia; Bomzon, Ze'ev; Salvador, Ricardo; Basser, Peter J; Miranda, Pedro C

2016-08-01

Tumor Treating Fields (TTFields) are alternating electric fields in the intermediate frequency range (100-300 kHz) of low-intensity (1-3 V/cm). TTFields are an anti-mitotic treatment against solid tumors, which are approved for Glioblastoma Multiforme (GBM) patients. These electric fields are induced non-invasively by transducer arrays placed directly on the patient's scalp. Cell culture experiments showed that treatment efficacy is dependent on the induced field intensity. In clinical practice, a software called NovoTalTM uses head measurements to estimate the optimal array placement to maximize the electric field delivery to the tumor. Computational studies predict an increase in the tumor's electric field strength when adapting transducer arrays to its location. Ideally, a personalized head model could be created for each patient, to calculate the electric field distribution for the specific situation. Thus, the optimal transducer layout could be inferred from field calculation rather than distance measurements. Nonetheless, creating realistic head models of patients is time-consuming and often needs user interaction, because automated image segmentation is prone to failure. This study presents a first approach to creating simplified head models consisting of convex hulls of the tissue layers. The model is able to account for anisotropic conductivity in the cortical tissues by using a tensor representation estimated from Diffusion Tensor Imaging. The induced electric field distribution is compared in the simplified and realistic head models. The average field intensities in the brain and tumor are generally slightly higher in the realistic head model, with a maximal ratio of 114% for a simplified model with reasonable layer thicknesses. Thus, the present pipeline is a fast and efficient means towards personalized head models with less complexity involved in characterizing tissue interfaces, while enabling accurate predictions of electric field distribution.

Principle Study of Head Meridian Acupoint Massage to Stress Release via Grey Data Model Analysis.

PubMed

Lee, Ya-Ting

2016-01-01

This paper presents the scientific study of the effectiveness and action principle of head meridian acupoint massage by applying the grey data model analysis approach. First, the head massage procedure for massaging the important head meridian acupuncture points including Taiyang, Fengfu, Tianzhu, Fengqi, and Jianjing is formulated in a standard manner. Second, the status of the autonomic nervous system of each subject is evaluated by using the heart rate variability analyzer before and after the head massage following four weeks. Afterward, the physiological factors of autonomic nerves are quantitatively analyzed by using the grey data modeling theory. The grey data analysis can point out that the status of autonomic nervous system is greatly improved after the massage. The order change of the grey relationship weighting of physiological factors shows the action principle of the sympathetic and parasympathetic nerves when performing head massage. In other words, the grey data model is able to distinguish the detailed interaction of the autonomic nervous system and the head meridian acupoint massage. Thus, the stress relaxing effect of massaging head meridian acupoints is proved, which is lacked in literature. The results can be a reference principle for massage health care in practice.

Principle Study of Head Meridian Acupoint Massage to Stress Release via Grey Data Model Analysis

PubMed Central

Lee, Ya-Ting

2016-01-01

This paper presents the scientific study of the effectiveness and action principle of head meridian acupoint massage by applying the grey data model analysis approach. First, the head massage procedure for massaging the important head meridian acupuncture points including Taiyang, Fengfu, Tianzhu, Fengqi, and Jianjing is formulated in a standard manner. Second, the status of the autonomic nervous system of each subject is evaluated by using the heart rate variability analyzer before and after the head massage following four weeks. Afterward, the physiological factors of autonomic nerves are quantitatively analyzed by using the grey data modeling theory. The grey data analysis can point out that the status of autonomic nervous system is greatly improved after the massage. The order change of the grey relationship weighting of physiological factors shows the action principle of the sympathetic and parasympathetic nerves when performing head massage. In other words, the grey data model is able to distinguish the detailed interaction of the autonomic nervous system and the head meridian acupoint massage. Thus, the stress relaxing effect of massaging head meridian acupoints is proved, which is lacked in literature. The results can be a reference principle for massage health care in practice. PMID:26904144

Photon migration through fetal head in utero using continuous wave, near infrared spectroscopy: development and evaluation of experimental and numerical models

NASA Astrophysics Data System (ADS)

Vishnoi, Gargi; Hielscher, Andreas H.; Ramanujam, Nirmala; Chance, Britton

2000-04-01

In this work experimental tissue phantoms and numerical models were developed to estimate photon migration through the fetal head in utero. The tissue phantoms incorporate a fetal head within an amniotic fluid sac surrounded by a maternal tissue layer. A continuous wave, dual-wavelength ((lambda) equals 760 and 850 nm) spectrometer was employed to make near-infrared measurements on the tissue phantoms for various source-detector separations, fetal-head positions, and fetal-head optical properties. In addition, numerical simulations of photon propagation were performed with finite-difference algorithms that provide solutions to the equation of radiative transfer as well as the diffusion equation. The simulations were compared with measurements on tissue phantoms to determine the best numerical model to describe photon migration through the fetal head in utero. Evaluation of the results indicates that tissue phantoms in which the contact between fetal head and uterine wall is uniform best simulates the fetal head in utero for near-term pregnancies. Furthermore, we found that maximum sensitivity to the head can be achieved if the source of the probe is positioned directly above the fetal head. By optimizing the source-detector separation, this signal originating from photons that have traveled through the fetal head can drastically be increased.

Influence of Head Motion on the Accuracy of 3D Reconstruction with Cone-Beam CT: Landmark Identification Errors in Maxillofacial Surface Model.

PubMed

Lee, Kyung-Min; Song, Jin-Myoung; Cho, Jin-Hyoung; Hwang, Hyeon-Shik

2016-01-01

The purpose of this study was to investigate the influence of head motion on the accuracy of three-dimensional (3D) reconstruction with cone-beam computed tomography (CBCT) scan. Fifteen dry skulls were incorporated into a motion controller which simulated four types of head motion during CBCT scan: 2 horizontal rotations (to the right/to the left) and 2 vertical rotations (upward/downward). Each movement was triggered to occur at the start of the scan for 1 second by remote control. Four maxillofacial surface models with head motion and one control surface model without motion were obtained for each skull. Nine landmarks were identified on the five maxillofacial surface models for each skull, and landmark identification errors were compared between the control model and each of the models with head motion. Rendered surface models with head motion were similar to the control model in appearance; however, the landmark identification errors showed larger values in models with head motion than in the control. In particular, the Porion in the horizontal rotation models presented statistically significant differences (P < .05). Statistically significant difference in the errors between the right and left side landmark was present in the left side rotation which was opposite direction to the scanner rotation (P < .05). Patient movement during CBCT scan might cause landmark identification errors on the 3D surface model in relation to the direction of the scanner rotation. Clinicians should take this into consideration to prevent patient movement during CBCT scan, particularly horizontal movement.

Modeling length-tension properties of RCPm muscles during voluntary retraction of the head.

PubMed

Hallgren, Richard C

2014-08-01

Head retraction exercises are one of several commonly used clinical tools that are used to assess and treat patients with head and neck pain and to aid in restoration of a normal neutral head posture. Retraction of the head results in flexion of the occipitoatlantal (OA) joint and stretching of rectus capitis posterior minor (RCPm) muscles. The role that retraction of the head might have in treating head and neck pain patients is currently unknown. RCPm muscles arise from the posterior tubercle of the posterior arch of C1 and insert into the occipital bone inferior to the inferior nuchal line and lateral to the midline. RCPm muscles are the only muscles that attach to the posterior arch of C1. The functional role of RCPm muscles has not been clearly defined. The goal of this project was to develop a three-dimensional, computer-based biomechanical model of the posterior aspect of the OA joint. This model should help clarify why voluntary head retraction exercises seem to contribute to the resolution of head and neck pain and restoration of a normal head posture in some patients. The model documents that length-tension properties of RCPm muscles are significantly affected by variations in the physical properties of the musculotendonous unit. The model suggests that variations in the cross sectional area of RCPm muscles due to pathologies that weaken the muscle, such as muscle atrophy, may reduce the ability of these muscles to generate levels of force that are necessary for the performance of normal, daily activities. The model suggests that the main benefit of the initial phase of head retraction exercises may be to strengthen RCPm muscles through eccentric contractions, and that the main benefit of the final phase of retraction may be to stretch the muscles as the final position is held. Copyright © 2014 Elsevier Ltd. All rights reserved.

The Smallest Drops of the Hottest Matter? New Investigations at the Relativistic Heavy Ion Collider (493rd Brookhaven Lecture)

DOE Office of Scientific and Technical Information (OSTI.GOV)

Sickles, Anne

2014-03-19

Pool sharks at the billiards hall know that sometimes you aim to rocket the cue ball for a head-on collision, and other times, a mere glance will do. Physicists need to know more than a thing or two about collision geometry too, as they sift through data from the billions of ions that smash together at the Relativistic Heavy Ion Collider (RHIC). Determining whether ions crash head-on or just glance is crucial for the physicists analyzing data to study quark-gluon plasma—the ultra-hot, "perfect" liquid of quarks and gluons that existed more than 13 billion years ago, before the first protonsmore » and neutrons formed. For these physicists, collision geometry data provides insights about quark-gluon plasma's extremely low viscosity and other unusual properties, which are essential for understanding more about the "strong force" that holds together the nucleus, protons, and neutrons of every atom in the universe. Dr. Sickles explains how physicists use data collected at house-sized detectors like PHENIX and STAR to determine what happens before, during, and after individual particle collisions among billions at RHIC. She also explains how the ability to collide different "species" of nuclei at RHIC—including protons and gold ions today and possibly more with a proposed future electron-ion collider upgrade (eRHIC)—enables physicists to probe deeper into the mysteries of quark-gluon plasma and the strong force.« less

The effect of skin entry site, needle angulation and soft tissue compression on simulated antegrade and retrograde femoral arterial punctures: an anatomical study using Cartesian co-ordinates derived from CT angiography.

PubMed

Tam, Matthew D B S; Lewis, Mark

2012-10-01

Safe femoral arterial access is an important procedural step in many interventional procedures and variations of the anatomy of the region are well known. The aim of this study was to redefine the anatomy relevant to the femoral arterial puncture and simulate the results of different puncture techniques. A total of 100 consecutive CT angiograms were used and regions of interest were labelled giving Cartesian co-ordinates which allowed determination of arterial puncture site relative to skin puncture site, the bifurcation and inguinal ligament (ING). The ING was lower than defined by bony landmarks by 16.6 mm. The femoral bifurcation was above the inferior aspect of the femoral head in 51% and entirely medial to the femoral head in 1%. Simulated antegrade and retrograde punctures with dogmatic technique, using a 45-degree angle would result in a significant rate of high and low arterial punctures. Simulated 50% soft tissue compression also resulted in decreased rate of high retrograde punctures but an increased rate of low antegrade punctures. Use of dogmatic access techniques is predicted to result in an unacceptably high rate of dangerous high and low punctures. Puncture angle and geometry can be severely affected by patient obesity. The combination of fluoroscopy to identify entry point, ultrasound-guidance to identify the femoral bifurcation and soft tissue compression to improve puncture geometry are critical for safe femoral arterial access.

Path integration of head direction: updating a packet of neural activity at the correct speed using axonal conduction delays.

PubMed

Walters, Daniel; Stringer, Simon; Rolls, Edmund

2013-01-01

The head direction cell system is capable of accurately updating its current representation of head direction in the absence of visual input. This is known as the path integration of head direction. An important question is how the head direction cell system learns to perform accurate path integration of head direction. In this paper we propose a model of velocity path integration of head direction in which the natural time delay of axonal transmission between a linked continuous attractor network and competitive network acts as a timing mechanism to facilitate the correct speed of path integration. The model effectively learns a "look-up" table for the correct speed of path integration. In simulation, we show that the model is able to successfully learn two different speeds of path integration across two different axonal conduction delays, and without the need to alter any other model parameters. An implication of this model is that, by learning look-up tables for each speed of path integration, the model should exhibit a degree of robustness to damage. In simulations, we show that the speed of path integration is not significantly affected by degrading the network through removing a proportion of the cells that signal rotational velocity.

Path Integration of Head Direction: Updating a Packet of Neural Activity at the Correct Speed Using Axonal Conduction Delays

PubMed Central

Walters, Daniel; Stringer, Simon; Rolls, Edmund

2013-01-01

The head direction cell system is capable of accurately updating its current representation of head direction in the absence of visual input. This is known as the path integration of head direction. An important question is how the head direction cell system learns to perform accurate path integration of head direction. In this paper we propose a model of velocity path integration of head direction in which the natural time delay of axonal transmission between a linked continuous attractor network and competitive network acts as a timing mechanism to facilitate the correct speed of path integration. The model effectively learns a “look-up” table for the correct speed of path integration. In simulation, we show that the model is able to successfully learn two different speeds of path integration across two different axonal conduction delays, and without the need to alter any other model parameters. An implication of this model is that, by learning look-up tables for each speed of path integration, the model should exhibit a degree of robustness to damage. In simulations, we show that the speed of path integration is not significantly affected by degrading the network through removing a proportion of the cells that signal rotational velocity. PMID:23526976

[Establishment of a 3D finite element model of human skull using MSCT images and mimics software].

PubMed

Huang, Ping; Li, Zheng-dong; Shao, Yu; Zou, Dong-hua; Liu, Ning-guo; Li, Li; Chen, Yuan-yuan; Wan, Lei; Chen, Yi-jiu

2011-02-01

To establish a human 3D finite element skull model, and to explore its value in biomechanics analysis. The cadaveric head was scanned and then 3D skull model was created using Mimics software based on 2D CT axial images. The 3D skull model was optimized by preprocessor along with creation of the surface and volume meshes. The stress changes, after the head was struck by an object or the head hit the ground directly, were analyzed using ANSYS software. The original 3D skull model showed a large number of triangles with a poor quality and high similarity with the real head, while the optimized model showed high quality surface and volume meshes with a small number of triangles comparatively. The model could show the local and global stress changes effectively. The human 3D skull model can be established using MSCT and Mimics software and provides a good finite element model for biomechanics analysis. This model may also provide a base for the study of head stress changes following different forces.

SABRINA - an interactive geometry modeler for MCNP

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, J.T.; Murphy, J.

One of the most difficult tasks when analyzing a complex three-dimensional system with Monte Carlo is geometry model development. SABRINA attempts to make the modeling process more user-friendly and less of an obstacle. It accepts both combinatorial solid bodies and MCNP surfaces and produces MCNP cells. The model development process in SABRINA is highly interactive and gives the user immediate feedback on errors. Users can view their geometry from arbitrary perspectives while the model is under development and interactively find and correct modeling errors. An example of a SABRINA display is shown. It represents a complex three-dimensional shape.

Efficient voxel navigation for proton therapy dose calculation in TOPAS and Geant4

NASA Astrophysics Data System (ADS)

Schümann, J.; Paganetti, H.; Shin, J.; Faddegon, B.; Perl, J.

2012-06-01

A key task within all Monte Carlo particle transport codes is ‘navigation’, the calculation to determine at each particle step what volume the particle may be leaving and what volume the particle may be entering. Navigation should be optimized to the specific geometry at hand. For patient dose calculation, this geometry generally involves voxelized computed tomography (CT) data. We investigated the efficiency of navigation algorithms on currently available voxel geometry parameterizations in the Monte Carlo simulation package Geant4: G4VPVParameterisation, G4VNestedParameterisation and G4PhantomParameterisation, the last with and without boundary skipping, a method where neighboring voxels with the same Hounsfield unit are combined into one larger voxel. A fourth parameterization approach (MGHParameterization), developed in-house before the latter two parameterizations became available in Geant4, was also included in this study. All simulations were performed using TOPAS, a tool for particle simulations layered on top of Geant4. Runtime comparisons were made on three distinct patient CT data sets: a head and neck, a liver and a prostate patient. We included an additional version of these three patients where all voxels, including the air voxels outside of the patient, were uniformly set to water in the runtime study. The G4VPVParameterisation offers two optimization options. One option has a 60-150 times slower simulation speed. The other is compatible in speed but requires 15-19 times more memory compared to the other parameterizations. We found the average CPU time used for the simulation relative to G4VNestedParameterisation to be 1.014 for G4PhantomParameterisation without boundary skipping and 1.015 for MGHParameterization. The average runtime ratio for G4PhantomParameterisation with and without boundary skipping for our heterogeneous data was equal to 0.97: 1. The calculated dose distributions agreed with the reference distribution for all but the G4PhantomParameterisation with boundary skipping for the head and neck patient. The maximum memory usage ranged from 0.8 to 1.8 GB depending on the CT volume independent of parameterizations, except for the 15-19 times greater memory usage with the G4VPVParameterisation when using the option with a higher simulation speed. The G4VNestedParameterisation was selected as the preferred choice for the patient geometries and treatment plans studied.

Model of head-neck joint fast movements in the frontal plane.

PubMed

Pedrocchi, A; Ferrigno, G

2004-06-01

The objective of this work is to develop a model representing the physiological systems driving fast head movements in frontal plane. All the contributions occurring mechanically in the head movement are considered: damping, stiffness, physiological limit of range of motion, gravitational field, and muscular torques due to voluntary activation as well as to stretch reflex depending on fusal afferences. Model parameters are partly derived from the literature, when possible, whereas undetermined block parameters are determined by optimising the model output, fitting to real kinematics data acquired by a motion capture system in specific experimental set-ups. The optimisation for parameter identification is performed by genetic algorithms. Results show that the model represents very well fast head movements in the whole range of inclination in the frontal plane. Such a model could be proposed as a tool for transforming kinematics data on head movements in 'neural equivalent data', especially for assessing head control disease and properly planning the rehabilitation process. In addition, the use of genetic algorithms seems to fit well the problem of parameter identification, allowing for the use of a very simple experimental set-up and granting model robustness.

Advanced Stirling Convertor Heater Head Durability and Reliability Quantification

NASA Technical Reports Server (NTRS)

Krause, David L.; Shah, Ashwin R.; Korovaichuk, Igor; Kalluri, Sreeramesh

2008-01-01

The National Aeronautics and Space Administration (NASA) has identified the high efficiency Advanced Stirling Radioisotope Generator (ASRG) as a candidate power source for long duration Science missions, such as lunar applications, Mars rovers, and deep space missions, that require reliable design lifetimes of up to 17 years. Resistance to creep deformation of the MarM-247 heater head (HH), a structurally critical component of the ASRG Advanced Stirling Convertor (ASC), under high temperatures (up to 850 C) is a key design driver for durability. Inherent uncertainties in the creep behavior of the thin-walled HH and the variations in the wall thickness, control temperature, and working gas pressure need to be accounted for in the life and reliability prediction. Due to the availability of very limited test data, assuring life and reliability of the HH is a challenging task. The NASA Glenn Research Center (GRC) has adopted an integrated approach combining available uniaxial MarM-247 material behavior testing, HH benchmark testing and advanced analysis in order to demonstrate the integrity, life and reliability of the HH under expected mission conditions. The proposed paper describes analytical aspects of the deterministic and probabilistic approaches and results. The deterministic approach involves development of the creep constitutive model for the MarM-247 (akin to the Oak Ridge National Laboratory master curve model used previously for Inconel 718 (Special Metals Corporation)) and nonlinear finite element analysis to predict the mean life. The probabilistic approach includes evaluation of the effect of design variable uncertainties in material creep behavior, geometry and operating conditions on life and reliability for the expected life. The sensitivity of the uncertainties in the design variables on the HH reliability is also quantified, and guidelines to improve reliability are discussed.

Investigation of different simulation approaches on a high-head Francis turbine and comparison with model test data: Francis-99

NASA Astrophysics Data System (ADS)

Mössinger, Peter; Jester-Zürker, Roland; Jung, Alexander

2015-01-01

Numerical investigations of hydraulic turbo machines under steady-state conditions are state of the art in current product development processes. Nevertheless allow increasing computational resources refined discretization methods, more sophisticated turbulence models and therefore better predictions of results as well as the quantification of existing uncertainties. Single stage investigations are done using in-house tools for meshing and set-up procedure. Beside different model domains and a mesh study to reduce mesh dependencies, the variation of several eddy viscosity and Reynolds stress turbulence models are investigated. All obtained results are compared with available model test data. In addition to global values, measured magnitudes in the vaneless space, at runner blade and draft tube positions in term of pressure and velocity are considered. From there it is possible to estimate the influence and relevance of various model domains depending on different operating points and numerical variations. Good agreement can be found for pressure and velocity measurements with all model configurations and, except the BSL-RSM model, all turbulence models. At part load, deviations in hydraulic efficiency are at a large magnitude, whereas at best efficiency and high load operating point efficiencies are close to the measurement. A consideration of the runner side gap geometry as well as a refined mesh is able to improve the results either in relation to hydraulic efficiency or velocity distribution with the drawbacks of less stable numerics and increasing computational time.

A Reliable Method of Completing and Compensating the Results of Measurements of Flow Parameters in a Network of Headings / O Pewnej Metodzie Uzupełniania I Wyrównywania Wyników Pomiarów Parametrów Przepływu W Sieci Wyrobisk Górniczych

NASA Astrophysics Data System (ADS)

Dziurzyński, Wacław; Krach, Andrzej; Pałka, Teresa

2015-03-01

Forecasting a ventilation process is based on two factors: using a validated software (Dziurzyński et al., 2011; Pritchard, 2010) and a properly prepared database encompassing the parameters describing the flow of air and gases, compatible with the adopted mathematical model of the VentGraph software (Dziurzyński, 2002). With a body of measurement data and a mathematical model for computer calculations and air flow simulation at our disposal, we proceed to develop a numerical model for a chosen network of mine headings. Preparing a numerical model of a ventilation network of a given mine requires providing a collection of data regarding the structure of the network and the physical properties of its elements, such as headings, fans, or stoppings. In the case of fire simulations, it is also necessary to specify the parameters describing the seat of a fire and the properties of the rocks of which the rock mass is comprised. The methods which are currently applied to this task involve manual ventilation measurements performed in headings; the results obtained in the course of these measurements constitute a basis for determining physical parameters, such as the aerodynamic resistance of a heading, density of the flow of air, or natural depression. Experience shows that - due to difficulties regarding accessibility of headings, as well as the considerable lengths of the latter - there are some nodes and headings in mines where such measurements are not performed. Thus, an attempt was made to develop a new methodology that would provide the missing data on the basis of some other available information concerning - for example - the air density, the geometry of headings and elevations. The adopted methodology suggests that one should start with balancing the air mass fluxes within the structure of a network of headings. The next step is to compile a database concerning the pressure values in the network nodes, based on the measurement results - and provide the missing pressure values on the basis of the available results of measurements carried out in adjacent nodes, as well as the pressure value calculated on the basis of the heading geometry and the given volumetric flow rate. The present paper discusses the methodology of compensating and balancing the volumetric air flow rates within a network of headings (Chapter 2) and the methodology of determining pressure values (Chapter 3) in the nodes of the network. The developed calculation algorithms - verified by means of sample calculations performed for a selected area of a mine ventilation network - were introduced into the VentGraph software system. The calculation results were presented in tabular form. The Summary section discusses the minuses and pluses of the adopted methodology. Podstawą prognozy procesu przewietrzania jest posługiwanie się zwalidowanym programem komputerowym (Dziurzyński i in., 2011; Pritchard, 2010) oraz poprawnie przygotowaną bazą danych zawierającą parametry opisujące przepływ powietrza i gazów, zgodną z przyjętym modelem matematycznym w programie komputerowym VentGraph (Dziurzyński, 2002). Dysponując bazą danych pomiarowych oraz przyjętym do obliczeń komputerowych i symulacji procesu przewietrzania modelem matematycznym przystępujemy do opracowania modelu numerycznego dla wybranej sieci wyrobisk kopalni. Przygotowanie modelu numerycznego sieci wentylacyjnej danej kopalni wymaga dostarczenia zestawu danych dotyczących struktury sieci i własności fizycznych jej elementów, tj. wyrobisk, wentylatorów, tam, a przy symulacji pożaru dodatkowo wymagane jest podanie parametrów opisujących ognisko pożaru oraz własności skał górotworu. Obecna praktyka postępowania polega na tym, że wykonuje się ręczne pomiary wentylacyjne w wyrobiskach górniczych, a uzyskane wyniki stanowią podstawę do wyznaczenia parametrów fizycznych takich jak: opór aerodynamiczny wyrobiska, gęstość przepływającego powietrza i naturalna depresja. Z uwagi na występujące trudności w dostępności wyrobisk jak również na znaczne ich długości, praktyka pokazuje, że pomiary nie są realizowane we wszystkich węzłach i wyrobiskach kopalni. Dlatego podjęto próbę opracowania nowej metodyki prowadzącej do uzupełnienia brakujących danych na podstawie innych dostępnych danych dotyczących np. gęstości powietrza, geometrii wyrobisk i kot niwelacyjnych. Z przyjętej metodyki wynika, że w pierwszej kolejności należy wykonać bilans strumieni masy powietrza w strukturze sieci wyrobisk. Następnie zbudować bazę danych ciśnień w węzłach sieci w oparciu o pomiary i uzupełnić brakujące ciśnienia na podstawie dostępnych wyników pomiarów w sąsiednich węzłach oraz ciśnienia obliczonego z wartości oporu aerodynamicznego wyznaczonego na podstawie geometrii wyrobiska i znanego strumienia objętości. W artykule przedstawiono metodykę wyrównywania i bilansowania strumieni objętości powietrza w sieci wyrobisk (rozdz. 2) oraz metodykę wyznaczania ciśnień (rozdz. 3) w węzłach sieci wyrobisk. Opracowane algorytmy obliczeń wprowadzono do systemu programów VentGraph, które zostały sprawdzone poprzez obliczenia dla przykładu wybranego rejonu kopalnianej sieci wentylacyjnej. Wyniki obliczeń przedstawiono w postaci tabelarycznej. W podsumowaniu omówiono wady i zalety przyjętej metodyki.

Head Motion Modeling for Human Behavior Analysis in Dyadic Interaction

PubMed Central

Xiao, Bo; Georgiou, Panayiotis; Baucom, Brian; Narayanan, Shrikanth S.

2015-01-01

This paper presents a computational study of head motion in human interaction, notably of its role in conveying interlocutors’ behavioral characteristics. Head motion is physically complex and carries rich information; current modeling approaches based on visual signals, however, are still limited in their ability to adequately capture these important properties. Guided by the methodology of kinesics, we propose a data driven approach to identify typical head motion patterns. The approach follows the steps of first segmenting motion events, then parametrically representing the motion by linear predictive features, and finally generalizing the motion types using Gaussian mixture models. The proposed approach is experimentally validated using video recordings of communication sessions from real couples involved in a couples therapy study. In particular we use the head motion model to classify binarized expert judgments of the interactants’ specific behavioral characteristics where entrainment in head motion is hypothesized to play a role: Acceptance, Blame, Positive, and Negative behavior. We achieve accuracies in the range of 60% to 70% for the various experimental settings and conditions. In addition, we describe a measure of motion similarity between the interaction partners based on the proposed model. We show that the relative change of head motion similarity during the interaction significantly correlates with the expert judgments of the interactants’ behavioral characteristics. These findings demonstrate the effectiveness of the proposed head motion model, and underscore the promise of analyzing human behavioral characteristics through signal processing methods. PMID:26557047

Large scale study on the variation of RF energy absorption in the head & brain regions of adults and children and evaluation of the SAM phantom conservativeness.

PubMed

Keshvari, J; Kivento, M; Christ, A; Bit-Babik, G

2016-04-21

This paper presents the results of two computational large scale studies using highly realistic exposure scenarios, MRI based human head and hand models, and two mobile phone models. The objectives are (i) to study the relevance of age when people are exposed to RF by comparing adult and child heads and (ii) to analyze and discuss the conservativeness of the SAM phantom for all age groups. Representative use conditions were simulated using detailed CAD models of two mobile phones operating between 900 MHz and 1950 MHz including configurations with the hand holding the phone, which were not considered in most previous studies. The peak spatial-average specific absorption rate (psSAR) in the head and the pinna tissues is assessed using anatomically accurate head and hand models. The first of the two mentioned studies involved nine head-, four hand- and two phone-models, the second study included six head-, four hand- and three simplified phone-models (over 400 configurations in total). In addition, both studies also evaluated the exposure using the SAM phantom. Results show no systematic differences between psSAR induced in the adult and child heads. The exposure level and its variation for different age groups may be different for particular phones, but no correlation between psSAR and model age was found. The psSAR from all exposure conditions was compared to the corresponding configurations using SAM, which was found to be conservative in the large majority of cases.

Large scale study on the variation of RF energy absorption in the head & brain regions of adults and children and evaluation of the SAM phantom conservativeness

NASA Astrophysics Data System (ADS)

Keshvari, J.; Kivento, M.; Christ, A.; Bit-Babik, G.

2016-04-01

This paper presents the results of two computational large scale studies using highly realistic exposure scenarios, MRI based human head and hand models, and two mobile phone models. The objectives are (i) to study the relevance of age when people are exposed to RF by comparing adult and child heads and (ii) to analyze and discuss the conservativeness of the SAM phantom for all age groups. Representative use conditions were simulated using detailed CAD models of two mobile phones operating between 900 MHz and 1950 MHz including configurations with the hand holding the phone, which were not considered in most previous studies. The peak spatial-average specific absorption rate (psSAR) in the head and the pinna tissues is assessed using anatomically accurate head and hand models. The first of the two mentioned studies involved nine head-, four hand- and two phone-models, the second study included six head-, four hand- and three simplified phone-models (over 400 configurations in total). In addition, both studies also evaluated the exposure using the SAM phantom. Results show no systematic differences between psSAR induced in the adult and child heads. The exposure level and its variation for different age groups may be different for particular phones, but no correlation between psSAR and model age was found. The psSAR from all exposure conditions was compared to the corresponding configurations using SAM, which was found to be conservative in the large majority of cases.

Analysis of RF exposure in the head tissues of children and adults

NASA Astrophysics Data System (ADS)

Wiart, J.; Hadjem, A.; Wong, M. F.; Bloch, I.

2008-07-01

This paper analyzes the radio frequencies (RF) exposure in the head tissues of children using a cellular handset or RF sources (a dipole and a generic handset) at 900, 1800, 2100 and 2400 MHz. Based on magnetic resonance imaging, child head models have been developed. The maximum specific absorption rate (SAR) over 10 g in the head has been analyzed in seven child and six adult heterogeneous head models. The influence of the variability in the same age class is carried out using models based on a morphing technique. The SAR over 1 g in specific tissues has also been assessed in the different types of child and adult head models. Comparisons are performed but nevertheless need to be confirmed since they have been derived from data sets of limited size. The simulations that have been performed show that the differences between the maximum SAR over 10 g estimated in the head models of the adults and the ones of the children are small compared to the standard deviations. But they indicate that the maximum SAR in 1 g of peripheral brain tissues of the child models aged between 5 and 8 years is about two times higher than in adult models. This difference is not observed for the child models of children above 8 years old: the maximum SAR in 1 g of peripheral brain tissues is about the same as the one in adult models. Such differences can be explained by the lower thicknesses of pinna, skin and skull of the younger child models.

Influence of length and conformation of saccharide head groups on the mechanics of glycolipid membranes: Unraveled by off-specular neutron scattering

NASA Astrophysics Data System (ADS)

Yamamoto, Akihisa; Abuillan, Wasim; Burk, Alexandra S.; Körner, Alexander; Ries, Annika; Werz, Daniel B.; Demé, Bruno; Tanaka, Motomu

2015-04-01

The mechanical properties of multilayer stacks of Gb3 glycolipid that play key roles in metabolic disorders (Fabry disease) were determined quantitatively by using specular and off-specular neutron scattering. Because of the geometry of membrane stacks deposited on planar substrates, the scattered intensity profile was analyzed in a 2D reciprocal space map as a function of in-plane and out-of-plane scattering vector components. The two principal mechanical parameters of the membranes, namely, bending rigidity and compression modulus, can be quantified by full calculation of scattering functions with the aid of an effective cut-off radius that takes the finite sample size into consideration. The bulkier "bent" Gb3 trisaccharide group makes the membrane mechanics distinctly different from cylindrical disaccharide (lactose) head groups and shorter "bent" disaccharide (gentiobiose) head groups. The mechanical characterization of membranes enriched with complex glycolipids has high importance in understanding the mechanisms of diseases such as sphingolipidoses caused by the accumulation of non-degenerated glycosphingolipids in lysosomes or inhibition of protein synthesis triggered by the specific binding of Shiga toxin to Gb3.

Towards the estimation of the scattered energy spectra reaching the head of the medical staff during interventional radiology: A Monte Carlo simulation study

NASA Astrophysics Data System (ADS)

Zagorska, A.; Bliznakova, K.; Buchakliev, Z.

2015-09-01

In 2012, the International Commission on Radiological Protection has recommended a reduction of the dose limits to the eye lens for occupational exposure. Recent studies showed that in interventional rooms is possible to reach these limits especially without using protective equipment. The aim of this study was to calculate the scattered energy spectra distribution at the level of the operator's head. For this purpose, an in-house developed Monte Carlo-based computer application was used to design computational phantoms (patient and operator), the acquisition geometry as well as to simulate the photon transport through the designed system. The initial spectra from 70 kV tube voltage and 8 different filtrations were calculated according to the IPEM Report 78. An experimental study was carried out to verify the results from the simulations. The calculated scattered radiation distributions were compared to the initial incident on the patient spectra. Results showed that there is no large difference between the effective energies of the scattered spectra registered in front of the operator's head obtained from simulations of all 8 incident spectra. The results from the experimental study agreed well to simulations as well.

Extrinsic Calibration of Camera Networks Based on Pedestrians

PubMed Central

Guan, Junzhi; Deboeverie, Francis; Slembrouck, Maarten; Van Haerenborgh, Dirk; Van Cauwelaert, Dimitri; Veelaert, Peter; Philips, Wilfried

2016-01-01

In this paper, we propose a novel extrinsic calibration method for camera networks by analyzing tracks of pedestrians. First of all, we extract the center lines of walking persons by detecting their heads and feet in the camera images. We propose an easy and accurate method to estimate the 3D positions of the head and feet w.r.t. a local camera coordinate system from these center lines. We also propose a RANSAC-based orthogonal Procrustes approach to compute relative extrinsic parameters connecting the coordinate systems of cameras in a pairwise fashion. Finally, we refine the extrinsic calibration matrices using a method that minimizes the reprojection error. While existing state-of-the-art calibration methods explore epipolar geometry and use image positions directly, the proposed method first computes 3D positions per camera and then fuses the data. This results in simpler computations and a more flexible and accurate calibration method. Another advantage of our method is that it can also handle the case of persons walking along straight lines, which cannot be handled by most of the existing state-of-the-art calibration methods since all head and feet positions are co-planar. This situation often happens in real life. PMID:27171080

DOE Office of Scientific and Technical Information (OSTI.GOV)

Krieg, R.

For future pressurized-water reactors, which should be designed against core-meltdown accidents, missiles generated inside the containment present a severe problem for its integrity. The masses and geometries of the missiles, as well as their velocities, may vary to a great extent. Therefore a reliable proof of the containment integrity is very difficult. In this article the potential sources of missiles are discussed, and the conclusion was reached that the generation of heavy missiles must be prevented. Steam explosions must not damage the reactor vessel head. Thus fragments of the head cannot become missiles that endanger the containment shell. Furthermore, duringmore » a melt-through failure of the reactor vessel under high pressure, the resulting forces must not catapult the whole vessel against the containment shell. Only missiles caused by hydrogen explosions may be tolerable, but shielding structures that protect the containment shell may be required. Further investigations are necessary. Finally, measures are described showing that the generation of heavy missiles can indeed be prevented. Investigations are currently being carried out that will confirm the strength of the reactor vessel head. In addition, a device for retaining the fragments of a failing reactor vessel is discussed.« less

Influence of length and conformation of saccharide head groups on the mechanics of glycolipid membranes: Unraveled by off-specular neutron scattering

DOE Office of Scientific and Technical Information (OSTI.GOV)

Yamamoto, Akihisa, E-mail: ayamamoto@icems.kyoto-u.ac.jp, E-mail: tanaka@uni-heidelberg.de; Tanaka, Motomu, E-mail: ayamamoto@icems.kyoto-u.ac.jp, E-mail: tanaka@uni-heidelberg.de; Institute for Integrated Cell-Material Sciences

2015-04-21

The mechanical properties of multilayer stacks of Gb3 glycolipid that play key roles in metabolic disorders (Fabry disease) were determined quantitatively by using specular and off-specular neutron scattering. Because of the geometry of membrane stacks deposited on planar substrates, the scattered intensity profile was analyzed in a 2D reciprocal space map as a function of in-plane and out-of-plane scattering vector components. The two principal mechanical parameters of the membranes, namely, bending rigidity and compression modulus, can be quantified by full calculation of scattering functions with the aid of an effective cut-off radius that takes the finite sample size into consideration.more » The bulkier “bent” Gb3 trisaccharide group makes the membrane mechanics distinctly different from cylindrical disaccharide (lactose) head groups and shorter “bent” disaccharide (gentiobiose) head groups. The mechanical characterization of membranes enriched with complex glycolipids has high importance in understanding the mechanisms of diseases such as sphingolipidoses caused by the accumulation of non-degenerated glycosphingolipids in lysosomes or inhibition of protein synthesis triggered by the specific binding of Shiga toxin to Gb3.« less

Human recognition based on head-shoulder contour extraction and BP neural network

NASA Astrophysics Data System (ADS)

Kong, Xiao-fang; Wang, Xiu-qin; Gu, Guohua; Chen, Qian; Qian, Wei-xian

2014-11-01

In practical application scenarios like video surveillance and human-computer interaction, human body movements are uncertain because the human body is a non-rigid object. Based on the fact that the head-shoulder part of human body can be less affected by the movement, and will seldom be obscured by other objects, in human detection and recognition, a head-shoulder model with its stable characteristics can be applied as a detection feature to describe the human body. In order to extract the head-shoulder contour accurately, a head-shoulder model establish method with combination of edge detection and the mean-shift algorithm in image clustering has been proposed in this paper. First, an adaptive method of mixture Gaussian background update has been used to extract targets from the video sequence. Second, edge detection has been used to extract the contour of moving objects, and the mean-shift algorithm has been combined to cluster parts of target's contour. Third, the head-shoulder model can be established, according to the width and height ratio of human head-shoulder combined with the projection histogram of the binary image, and the eigenvectors of the head-shoulder contour can be acquired. Finally, the relationship between head-shoulder contour eigenvectors and the moving objects will be formed by the training of back-propagation (BP) neural network classifier, and the human head-shoulder model can be clustered for human detection and recognition. Experiments have shown that the method combined with edge detection and mean-shift algorithm proposed in this paper can extract the complete head-shoulder contour, with low calculating complexity and high efficiency.

A General, Synthetic Model for Predicting Biodiversity Gradients from Environmental Geometry.

PubMed

Gross, Kevin; Snyder-Beattie, Andrew

2016-10-01

Latitudinal and elevational biodiversity gradients fascinate ecologists, and have inspired dozens of explanations. The geometry of the abiotic environment is sometimes thought to contribute to these gradients, yet evaluations of geometric explanations are limited by a fragmented understanding of the diversity patterns they predict. This article presents a mathematical model that synthesizes multiple pathways by which environmental geometry can drive diversity gradients. The model characterizes species ranges by their environmental niches and limits on range sizes and places those ranges onto the simplified geometries of a sphere or cone. The model predicts nuanced and realistic species-richness gradients, including latitudinal diversity gradients with tropical plateaus and mid-latitude inflection points and elevational diversity gradients with low-elevation diversity maxima. The model also illustrates the importance of a mid-environment effect that augments species richness at locations with intermediate environments. Model predictions match multiple empirical biodiversity gradients, depend on ecological traits in a testable fashion, and formally synthesize elements of several geometric models. Together, these results suggest that previous assessments of geometric hypotheses should be reconsidered and that environmental geometry may play a deeper role in driving biodiversity gradients than is currently appreciated.

Development and application of CATIA-GDML geometry builder

NASA Astrophysics Data System (ADS)

Belogurov, S.; Berchun, Yu; Chernogorov, A.; Malzacher, P.; Ovcharenko, E.; Schetinin, V.

2014-06-01

Due to conceptual difference between geometry descriptions in Computer-Aided Design (CAD) systems and particle transport Monte Carlo (MC) codes direct conversion of detector geometry in either direction is not feasible. The paper presents an update on functionality and application practice of the CATIA-GDML geometry builder first introduced at CHEP2010. This set of CATIAv5 tools has been developed for building a MC optimized GEANT4/ROOT compatible geometry based on the existing CAD model. The model can be exported via Geometry Description Markup Language (GDML). The builder allows also import and visualization of GEANT4/ROOT geometries in CATIA. The structure of a GDML file, including replicated volumes, volume assemblies and variables, is mapped into a part specification tree. A dedicated file template, a wide range of primitives, tools for measurement and implicit calculation of parameters, different types of multiple volume instantiation, mirroring, positioning and quality check have been implemented. Several use cases are discussed.

DOE Office of Scientific and Technical Information (OSTI.GOV)

Rybicki, E.F.; Luiskutty, C.T.; Sutrick, J.S.

This research is part of a larger program sponsored by the United States Department of Energy with the objective of developing better methods to produce gas from low permeability formations in western gas sands. This large research program involves several universities and research centers. Each group is involved in a different area of study to answer specific questions. The hydraulic fracturing computer model has three components---a model for fracture geometry, a model for proppant transport, and a computer program that couples the two models. The fracture geometry model was developed at Oral Roberts University and the proppant transport model wasmore » developed at The University of Tulsa prior to the start of the present work. The present work is directed at enhancing the capabilities of these two models and coupling them to obtain a single model for evaluating the final fracture geometry and proppant distribution within the fracture. The report is organized into four parts. Part 1 describes the fracture geometry modeling effort accomplished at Oral Roberts University, NIPER and recently at The University of Tulsa. The proppant transport model, developed for constant height fractures at the University of Tulsa, is contained in Part 2. The coupling of the Proppant Transport Model and the model for the variable height fracture geometry constitutes Part 3 of this report. Part 4 presents a summary of accomplishments and recommendations of this study. 112 refs., 147 figs., 70 tabs.« less

Simulate speleogenesis processes with an approach based on fracturing and hydrogeological processes: effect of various hydraulic boundary conditions

NASA Astrophysics Data System (ADS)

Lafare, A.; Jourde, H.; Leonardi, V.; Pistre, S.; Dörfliger, N.

2012-04-01

Several numerical modeling approaches attempted to simulate the processes of karst conduit genesis. These existing methods are mainly based on the physical and chemical laws driving the carbonate dissolution processes (taking account of calcite saturation of the water and the partial pressure of carbon dioxide). As a consequence, these works bring a well-documented knowledge on the kinetics of the carbonate dissolution processes in karst systems. Nevertheless, these models are mainly applied on simplified initial void networks, which do not match the fracturing and geological reality. Considering that the initial geometry of the void network (fractures, bedding planes) would have an influence on the final pattern of the speleological network, taking account of it could improve the understanding of speleogenesis. In the aim to take into account the geometry of the initial void network (fracture networks of several orders), a numerical model is developed, which involves a pseudo-statistic fracturing generator (REZO3D, Jourde 1999, Josnin et al. 2002, Jourde et al. 2002) coupled to a finite element groundwater simulator (GROUNDWATER, F. Cornaton, CHYN, University of Neuchâtel). The principle of the modeling of the genesis of the karst drainage system is based on an analogical empirical polynomial equation considering the pore velocity and the mean age of the water as main parameters. The computation is carried out on the basis of a time step, whose duration depends on the simulated scenario (from 100 to 5000 years). The mean age of the water is used in order to simulate the decrease of the chemical dissolving potential of the water within the aquifer, in contact with the carbonate rock. The first simulator -REZO3D- allows producing three-dimensional discrete fracture networks constituted by plane fractures, whose spatial distribution respects mechanical and statistical laws. These networks are then processed in order to write finite element meshes which constitute the bases of groundwater flow and transport simulations. The polynomial parameters of the equation are calibrated with former speleogenesis studies (Dreybrodt 1996, Dreybrodt et al. 2005, Palmer 1991). The presented study involves two orthogonal families of fractures embedded in a carbonate matrix, in a mono-stratum setting. For each simulation, several settings of boundary conditions are tested, in terms of recharge (diffuse or concentrated, hydraulic head or flux limited) and discharge (spatial position, punctual or diffuse). The results are interpreted in terms of head fields, mean groundwater age distributions and total flow rates as a function of time. The aim is to assess the influence of the hydraulic boundary conditions on the finally obtained morphologies of the karstic networks, and on the velocity of the evolution of the drainage system. Results are discussed and perspectives are given on the application of such model to real case studies.

What Do Kinematic Models Imply About the Constitutive Properties of Rocks Deformed in Flat-Ramp-Flat Folds?

NASA Astrophysics Data System (ADS)

Cruz, L.; Nevitt, J. M.; Seixas, G.; Hilley, G. E.

2017-10-01

Kinematic theories of flat-ramp-flat folds relate fault angles to stratal dips in a way that allows prediction of structural geometries in areas of economic or scientific interest. However, these geometric descriptions imply constitutive properties of rocks that might be discordant with field and laboratory measurements. In this study, we compare deformation resulting from kinematic and mechanical models of flat-ramp-flat folds with identical geometries to determine the conditions over which kinematic models may be reasonably applied to folded rocks. Results show that most mechanical models do not conform to the geometries predicted by the kinematic models, and only low basal friction (μ ≤ 0.1) and shallow ramps (ramp angle ≤10°) produce geometries consistent with kinematic predictions. This implies that the kinematic models might be appropriate for a narrow set of geometric and basal fault friction parameters.

An Accurate and Dynamic Computer Graphics Muscle Model

NASA Technical Reports Server (NTRS)

Levine, David Asher

1997-01-01

A computer based musculo-skeletal model was developed at the University in the departments of Mechanical and Biomedical Engineering. This model accurately represents human shoulder kinematics. The result of this model is the graphical display of bones moving through an appropriate range of motion based on inputs of EMGs and external forces. The need existed to incorporate a geometric muscle model in the larger musculo-skeletal model. Previous muscle models did not accurately represent muscle geometries, nor did they account for the kinematics of tendons. This thesis covers the creation of a new muscle model for use in the above musculo-skeletal model. This muscle model was based on anatomical data from the Visible Human Project (VHP) cadaver study. Two-dimensional digital images from the VHP were analyzed and reconstructed to recreate the three-dimensional muscle geometries. The recreated geometries were smoothed, reduced, and sliced to form data files defining the surfaces of each muscle. The muscle modeling function opened these files during run-time and recreated the muscle surface. The modeling function applied constant volume limitations to the muscle and constant geometry limitations to the tendons.

Designing an educative curriculum unit for teaching molecular geometry in high school chemistry

NASA Astrophysics Data System (ADS)

Makarious, Nader N.

Chemistry is a highly abstract discipline that is taught and learned with the aid of various models. Among the most challenging, yet a fundamental topic in general chemistry at the high school level, is molecular geometry. This study focused on developing exemplary educative curriculum materials pertaining to the topic of molecular geometry. The methodology used in this study consisted of several steps. First, a diverse set of models were analyzed to determine to what extent each model serves its purpose in teaching molecular geometry. Second, a number of high school teachers and college chemistry professors were asked to share their experiences on using models in teaching molecular geometry through an online questionnaire. Third, findings from the comparative analysis of models, teachers’ experiences, literature review on models and students’ misconceptions, the curriculum expectations of the Next Generation Science Standards and their emphasis on three-dimensional learning and nature of science (NOS) contributed to the development of the molecular geometry unit. Fourth, the developed unit was reviewed by fellow teachers and doctoral-level science education experts and was revised to further improve its coherence and clarity in support of teaching and learning of the molecular geometry concepts. The produced educative curriculum materials focus on the scientific practice of developing and using models as promoted in the Next Generations Science Standards (NGSS) while also addressing nature of science (NOS) goals. The educative features of the newly developed unit support teachers’ pedagogical knowledge (PK) and pedagogical content knowledge (PCK). The unit includes an overview, teacher’s guide, and eight detailed lesson plans with inquiry oriented modeling activities replete with models and suggestions for teachers, as well as formative and summative assessment tasks. The unit design process serves as a model for redesigning other instructional units in science disciplines in general and chemistry courses in particular.

A machine learning approach as a surrogate of finite element analysis-based inverse method to estimate the zero-pressure geometry of human thoracic aorta.

PubMed

Liang, Liang; Liu, Minliang; Martin, Caitlin; Sun, Wei

2018-05-09

Advances in structural finite element analysis (FEA) and medical imaging have made it possible to investigate the in vivo biomechanics of human organs such as blood vessels, for which organ geometries at the zero-pressure level need to be recovered. Although FEA-based inverse methods are available for zero-pressure geometry estimation, these methods typically require iterative computation, which are time-consuming and may be not suitable for time-sensitive clinical applications. In this study, by using machine learning (ML) techniques, we developed an ML model to estimate the zero-pressure geometry of human thoracic aorta given 2 pressurized geometries of the same patient at 2 different blood pressure levels. For the ML model development, a FEA-based method was used to generate a dataset of aorta geometries of 3125 virtual patients. The ML model, which was trained and tested on the dataset, is capable of recovering zero-pressure geometries consistent with those generated by the FEA-based method. Thus, this study demonstrates the feasibility and great potential of using ML techniques as a fast surrogate of FEA-based inverse methods to recover zero-pressure geometries of human organs. Copyright © 2018 John Wiley & Sons, Ltd.

Simulations of Cavitating Cryogenic Inducers

NASA Technical Reports Server (NTRS)

Dorney, Dan (Technical Monitor); Hosangadi, Ashvin; Ahuja, Vineet; Ungewitter, Ronald J.

2004-01-01

Simulations of cavitating turbopump inducers at their design flow rate are presented. Results over a broad range of Nss, numbers extending from single-phase flow conditions through the critical head break down point are discussed. The flow characteristics and performance of a subscale geometry designed for water testing are compared with the fullscale configuration that employs LOX. In particular, thermal depression effects arising from cavitation in cryogenic fluids are identified and their impact on the suction performance of the inducer quantified. The simulations have been performed using the CRUNCH CFD[R] code that has a generalized multi-element unstructured framework suitable for turbomachinery applications. An advanced multi-phase formulation for cryogenic fluids that models temperature depression and real fluid property variations is employed. The formulation has been extensively validated for both liquid nitrogen and liquid hydrogen by simulating the experiments of Hord on hydrofoils; excellent estimates of the leading edge temperature and pressure depression were obtained while the comparisons in the cavity closure region were reasonable.

Uncoupling apical constriction from tissue invagination

PubMed Central

Chung, SeYeon; Kim, Sangjoon; Andrew, Deborah J

2017-01-01

Apical constriction is a widely utilized cell shape change linked to folding, bending and invagination of polarized epithelia. It remains unclear how apical constriction is regulated spatiotemporally during tissue invagination and how this cellular process contributes to tube formation in different developmental contexts. Using Drosophila salivary gland (SG) invagination as a model, we show that regulation of folded gastrulation expression by the Fork head transcription factor is required for apicomedial accumulation of Rho kinase and non-muscle myosin II, which coordinate apical constriction. We demonstrate that neither loss of spatially coordinated apical constriction nor its complete blockage prevent internalization and tube formation, although such manipulations affect the geometry of invagination. When apical constriction is disrupted, compressing force generated by a tissue-level myosin cable contributes to SG invagination. We demonstrate that fully elongated polarized SGs can form outside the embryo, suggesting that tube formation and elongation are intrinsic properties of the SG. DOI: http://dx.doi.org/10.7554/eLife.22235.001 PMID:28263180

Mechanistic modeling study on process optimization and precursor utilization with atmospheric spatial atomic layer deposition

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deng, Zhang; He, Wenjie; Duan, Chenlong

2016-01-15

Spatial atomic layer deposition (SALD) is a promising technology with the aim of combining the advantages of excellent uniformity and conformity of temporal atomic layer deposition (ALD), and an industrial scalable and continuous process. In this manuscript, an experimental and numerical combined model of atmospheric SALD system is presented. To establish the connection between the process parameters and the growth efficiency, a quantitative model on reactant isolation, throughput, and precursor utilization is performed based on the separation gas flow rate, carrier gas flow rate, and precursor mass fraction. The simulation results based on this model show an inverse relation betweenmore » the precursor usage and the carrier gas flow rate. With the constant carrier gas flow, the relationship of precursor usage and precursor mass fraction follows monotonic function. The precursor concentration, regardless of gas velocity, is the determinant factor of the minimal residual time. The narrow gap between precursor injecting heads and the substrate surface in general SALD system leads to a low Péclet number. In this situation, the gas diffusion act as a leading role in the precursor transport in the small gap rather than the convection. Fluid kinetics from the numerical model is independent of the specific structure, which is instructive for the SALD geometry design as well as its process optimization.« less

Feedbacks Between Shallow Groundwater Dynamics and Surface Topography on Runoff Generation in Flat Fields

NASA Astrophysics Data System (ADS)

Appels, Willemijn M.; Bogaart, Patrick W.; van der Zee, Sjoerd E. A. T. M.

2017-12-01

In winter, saturation excess (SE) ponding is observed regularly in temperate lowland regions. Surface runoff dynamics are controlled by small topographical features that are unaccounted for in hydrological models. To better understand storage and routing effects of small-scale topography and their interaction with shallow groundwater under SE conditions, we developed a model of reduced complexity to investigate SE runoff generation, emphasizing feedbacks between shallow groundwater dynamics and mesotopography. The dynamic specific yield affected unsaturated zone water storage, causing rapid switches between negative and positive head and a flatter groundwater mound than predicted by analytical agrohydrological models. Accordingly, saturated areas were larger and local groundwater fluxes smaller than predicted, leading to surface runoff generation. Mesotopographic features routed water over larger distances, providing a feedback mechanism that amplified changes to the shape of the groundwater mound. This in turn enhanced runoff generation, but whether it also resulted in runoff events depended on the geometry and location of the depressions. Whereas conditions favorable to runoff generation may abound during winter, these feedbacks profoundly reduce the predictability of SE runoff: statistically identical rainfall series may result in completely different runoff generation. The model results indicate that waterlogged areas in any given rainfall event are larger than those predicted by current analytical groundwater models used for drainage design. This change in the groundwater mound extent has implications for crop growth and damage assessments.

Development and validation of a human biomechanical model for rib fracture and thorax injuries in blunt impact.

PubMed

Cai, Zhihua; Lan, Fengchong; Chen, Jiqing

2015-07-01

From 1990 to approximately 50,000-120,000 people die annually of road traffic accidents in China. Traffic accidents are the main cause of death of Chinese adults aged 15-45 years. This study aimed to determine the biomechanical response and injury tolerance of the human body in traffic accidents. The subject was a 35-year-old male with a height of 170 cm, weight of 70 kg and Chinese characteristics at the 50th percentile. Geometry was generated by computed tomography and magnetic resonance imaging. A human-body biomechanical model was then developed. The model featured in great detail the main anatomical characteristics of skeletal tissues, soft tissues and internal organs, including the head, neck, shoulder, thoracic cage, abdomen, spine, pelvis, pleurae and lungs, heart, aorta, arms, legs, and other muscle tissues and skeletons. The material properties of all tissues in the human body model were obtained from the literature. Material properties were developed in the LS-DYNA code to simulate the mechanical behaviour of the biological tissues in the human body. The model was validated against cadaver responses to frontal and side impact. The predicted model response reasonably agreed with the experimental data, and the model can further be used to evaluate thoracic injury in real-world crashes. We believe that the transportation industry can use numerical models in the future to simultaneously reduce physical testing and improve automotive safety.

Hydraulic tomography of discrete networks of conduits and fractures in a karstic aquifer by using a deterministic inversion algorithm

NASA Astrophysics Data System (ADS)

Fischer, P.; Jardani, A.; Lecoq, N.

2018-02-01

In this paper, we present a novel inverse modeling method called Discrete Network Deterministic Inversion (DNDI) for mapping the geometry and property of the discrete network of conduits and fractures in the karstified aquifers. The DNDI algorithm is based on a coupled discrete-continuum concept to simulate numerically water flows in a model and a deterministic optimization algorithm to invert a set of observed piezometric data recorded during multiple pumping tests. In this method, the model is partioned in subspaces piloted by a set of parameters (matrix transmissivity, and geometry and equivalent transmissivity of the conduits) that are considered as unknown. In this way, the deterministic optimization process can iteratively correct the geometry of the network and the values of the properties, until it converges to a global network geometry in a solution model able to reproduce the set of data. An uncertainty analysis of this result can be performed from the maps of posterior uncertainties on the network geometry or on the property values. This method has been successfully tested for three different theoretical and simplified study cases with hydraulic responses data generated from hypothetical karstic models with an increasing complexity of the network geometry, and of the matrix heterogeneity.

Countermanding eye-head gaze shifts in humans: marching orders are delivered to the head first.

PubMed

Corneil, Brian D; Elsley, James K

2005-07-01

The countermanding task requires subjects to cancel a planned movement on appearance of a stop signal, providing insights into response generation and suppression. Here, we studied human eye-head gaze shifts in a countermanding task with targets located beyond the horizontal oculomotor range. Consistent with head-restrained saccadic countermanding studies, the proportion of gaze shifts on stop trials increased the longer the stop signal was delayed after target presentation, and gaze shift stop-signal reaction times (SSRTs: a derived statistic measuring how long it takes to cancel a movement) averaged approximately 120 ms across seven subjects. We also observed a marked proportion of trials (13% of all stop trials) during which gaze remained stable but the head moved toward the target. Such head movements were more common at intermediate stop signal delays. We never observed the converse sequence wherein gaze moved while the head remained stable. SSRTs for head movements averaged approximately 190 ms or approximately 70-75 ms longer than gaze SSRTs. Although our findings are inconsistent with a single race to threshold as proposed for controlling saccadic eye movements, movement parameters on stop trials attested to interactions consistent with a race model architecture. To explain our data, we tested two extensions to the saccadic race model. The first assumed that gaze shifts and head movements are controlled by parallel but independent races. The second model assumed that gaze shifts and head movements are controlled by a single race, preceded by terminal ballistic intervals not under inhibitory control, and that the head-movement branch is activated at a lower threshold. Although simulations of both models produced acceptable fits to the empirical data, we favor the second alternative as it is more parsimonious with recent findings in the oculomotor system. Using the second model, estimates for gaze and head ballistic intervals were approximately 25 and 90 ms, respectively, consistent with the known physiology of the final motor paths. Further, the threshold of the head movement branch was estimated to be 85% of that required to activate gaze shifts. From these results, we conclude that a commitment to a head movement is made in advance of gaze shifts and that the comparative SSRT differences result primarily from biomechanical differences inherent to eye and head motion.

Study on Brain Injury Biomechanics Based on the Real Pedestrian Traffic Accidents

NASA Astrophysics Data System (ADS)

Feng, Chengjian; Yin, Zhiyong

This paper aimed to research the dynamic response and injury mechanisms of head based on real pedestrian traffic accidents with video. The kinematics of head contact with the vehicle was reconstructed by using multi-body dynamics models. These calculated parameters such as head impact velocity and impact location and head orientation were applied to the THUMS-4 FE head model as initial conditions. The intracranial pressure and stress of brain were calculated from simulations of head contact with the vehicle. These results were consistent with that of others. It was proved that real traffic accidents combined with simulation analysis can be used to study head injury biomechanics. Increasing in the number of cases, a tolerance limit of brain injury will be put forward.

Accurate reconstruction of 3D cardiac geometry from coarsely-sliced MRI.

PubMed

Ringenberg, Jordan; Deo, Makarand; Devabhaktuni, Vijay; Berenfeld, Omer; Snyder, Brett; Boyers, Pamela; Gold, Jeffrey

2014-02-01

We present a comprehensive validation analysis to assess the geometric impact of using coarsely-sliced short-axis images to reconstruct patient-specific cardiac geometry. The methods utilize high-resolution diffusion tensor MRI (DTMRI) datasets as reference geometries from which synthesized coarsely-sliced datasets simulating in vivo MRI were produced. 3D models are reconstructed from the coarse data using variational implicit surfaces through a commonly used modeling tool, CardioViz3D. The resulting geometries were then compared to the reference DTMRI models from which they were derived to analyze how well the synthesized geometries approximate the reference anatomy. Averaged over seven hearts, 95% spatial overlap, less than 3% volume variability, and normal-to-surface distance of 0.32 mm was observed between the synthesized myocardial geometries reconstructed from 8 mm sliced images and the reference data. The results provide strong supportive evidence to validate the hypothesis that coarsely-sliced MRI may be used to accurately reconstruct geometric ventricular models. Furthermore, the use of DTMRI for validation of in vivo MRI presents a novel benchmark procedure for studies which aim to substantiate their modeling and simulation methods using coarsely-sliced cardiac data. In addition, the paper outlines a suggested original procedure for deriving image-based ventricular models using the CardioViz3D software. Copyright © 2013 Elsevier Ireland Ltd. All rights reserved.

SABRINA - An interactive geometry modeler for MCNP (Monte Carlo Neutron Photon)

DOE Office of Scientific and Technical Information (OSTI.GOV)

West, J.T.; Murphy, J.

SABRINA is an interactive three-dimensional geometry modeler developed to produce complicated models for the Los Alamos Monte Carlo Neutron Photon program MCNP. SABRINA produces line drawings and color-shaded drawings for a wide variety of interactive graphics terminals. It is used as a geometry preprocessor in model development and as a Monte Carlo particle-track postprocessor in the visualization of complicated particle transport problem. SABRINA is written in Fortran 77 and is based on the Los Alamos Common Graphics System, CGS. 5 refs., 2 figs.

Image-based 3D reconstruction and virtual environmental walk-through

NASA Astrophysics Data System (ADS)

Sun, Jifeng; Fang, Lixiong; Luo, Ying

2001-09-01

We present a 3D reconstruction method, which combines geometry-based modeling, image-based modeling and rendering techniques. The first component is an interactive geometry modeling method which recovery of the basic geometry of the photographed scene. The second component is model-based stereo algorithm. We discus the image processing problems and algorithms of walking through in virtual space, then designs and implement a high performance multi-thread wandering algorithm. The applications range from architectural planning and archaeological reconstruction to virtual environments and cinematic special effects.

Empirical intrinsic geometry for nonlinear modeling and time series filtering.

PubMed

Talmon, Ronen; Coifman, Ronald R

2013-07-30

In this paper, we present a method for time series analysis based on empirical intrinsic geometry (EIG). EIG enables one to reveal the low-dimensional parametric manifold as well as to infer the underlying dynamics of high-dimensional time series. By incorporating concepts of information geometry, this method extends existing geometric analysis tools to support stochastic settings and parametrizes the geometry of empirical distributions. However, the statistical models are not required as priors; hence, EIG may be applied to a wide range of real signals without existing definitive models. We show that the inferred model is noise-resilient and invariant under different observation and instrumental modalities. In addition, we show that it can be extended efficiently to newly acquired measurements in a sequential manner. These two advantages enable us to revisit the Bayesian approach and incorporate empirical dynamics and intrinsic geometry into a nonlinear filtering framework. We show applications to nonlinear and non-Gaussian tracking problems as well as to acoustic signal localization.

Performance characterization of complex fuel port geometries for hybrid rocket fuel grains

NASA Astrophysics Data System (ADS)

Bath, Andrew

This research investigated the 3D printing and burning of fuel grains with complex geometry and the development of software capable of modeling and predicting the regression of a cross-section of these complex fuel grains. The software developed did predict the geometry to a fair degree of accuracy, especially when enhanced corner rounding was turned on. The model does have some drawbacks, notably being relatively slow, and does not perfectly predict the regression. If corner rounding is turned off, however, the model does become much faster; although less accurate, this method does still predict a relatively accurate resulting burn geometry, and is fast enough to be used for performance-tuning or genetic algorithms. In addition to the modeling method, preliminary investigations into the burning behavior of fuel grains with a helical flow path were performed. The helix fuel grains have a regression rate of nearly 3 times that of any other fuel grain geometry, primarily due to the enhancement of the friction coefficient between the flow and flow path.

Automated, Parametric Geometry Modeling and Grid Generation for Turbomachinery Applications

NASA Technical Reports Server (NTRS)

Harrand, Vincent J.; Uchitel, Vadim G.; Whitmire, John B.

2000-01-01

The objective of this Phase I project is to develop a highly automated software system for rapid geometry modeling and grid generation for turbomachinery applications. The proposed system features a graphical user interface for interactive control, a direct interface to commercial CAD/PDM systems, support for IGES geometry output, and a scripting capability for obtaining a high level of automation and end-user customization of the tool. The developed system is fully parametric and highly automated, and, therefore, significantly reduces the turnaround time for 3D geometry modeling, grid generation and model setup. This facilitates design environments in which a large number of cases need to be generated, such as for parametric analysis and design optimization of turbomachinery equipment. In Phase I we have successfully demonstrated the feasibility of the approach. The system has been tested on a wide variety of turbomachinery geometries, including several impellers and a multi stage rotor-stator combination. In Phase II, we plan to integrate the developed system with turbomachinery design software and with commercial CAD/PDM software.

A free geometry model-independent neural eye-gaze tracking system

PubMed Central

2012-01-01

Background Eye Gaze Tracking Systems (EGTSs) estimate the Point Of Gaze (POG) of a user. In diagnostic applications EGTSs are used to study oculomotor characteristics and abnormalities, whereas in interactive applications EGTSs are proposed as input devices for human computer interfaces (HCI), e.g. to move a cursor on the screen when mouse control is not possible, such as in the case of assistive devices for people suffering from locked-in syndrome. If the user’s head remains still and the cornea rotates around its fixed centre, the pupil follows the eye in the images captured from one or more cameras, whereas the outer corneal reflection generated by an IR light source, i.e. glint, can be assumed as a fixed reference point. According to the so-called pupil centre corneal reflection method (PCCR), the POG can be thus estimated from the pupil-glint vector. Methods A new model-independent EGTS based on the PCCR is proposed. The mapping function based on artificial neural networks allows to avoid any specific model assumption and approximation either for the user’s eye physiology or for the system initial setup admitting a free geometry positioning for the user and the system components. The robustness of the proposed EGTS is proven by assessing its accuracy when tested on real data coming from: i) different healthy users; ii) different geometric settings of the camera and the light sources; iii) different protocols based on the observation of points on a calibration grid and halfway points of a test grid. Results The achieved accuracy is approximately 0.49°, 0.41°, and 0.62° for respectively the horizontal, vertical and radial error of the POG. Conclusions The results prove the validity of the proposed approach as the proposed system performs better than EGTSs designed for HCI which, even if equipped with superior hardware, show accuracy values in the range 0.6°-1°. PMID:23158726

Stability analysis of an F/A-18 E/F cable mount m odel

NASA Technical Reports Server (NTRS)

Thompson, Nancy; Farmer, Moses

1994-01-01

A full-span F/A-18 E/F cable mounted wind tunnel model is part of a flutter clearance program at the NASA Langley Transonic Dynamics Tunnel. Parametric analysis of this model using GRUMCBL software was conducted to assess stability for wind tunnel tests. Two configurations of the F/A-18 E/F were examined. The parameters examined were pulley-cable friction, mach number, dynamic pressure, cable geometry, center of gravity location, cable tension, snubbing the model, drag, and test medium. For the nominal cable geometry (Cable Geometry 1), Configuration One was unstable for cases with higher pulley-cable friction coefficients. A new cable geometry (Cable Geometry 3) was determined in which Configuration One was stable for all cases evaluated. Configuration Two with the nominal center of gravity position was found to be unstable for cases with higher pulley-cable friction coefficients; however, the model was stable when the center of gravity moved forward 1/2. The model was tested using the cable mount system during the initial wind tunnel entry and was stable as predicted.

Are patient specific meshes required for EIT head imaging?

PubMed

Jehl, Markus; Aristovich, Kirill; Faulkner, Mayo; Holder, David

2016-06-01

Head imaging with electrical impedance tomography (EIT) is usually done with time-differential measurements, to reduce time-invariant modelling errors. Previous research suggested that more accurate head models improved image quality, but no thorough analysis has been done on the required accuracy. We propose a novel pipeline for creation of precise head meshes from magnetic resonance imaging and computed tomography scans, which was applied to four different heads. Voltages were simulated on all four heads for perturbations of different magnitude, haemorrhage and ischaemia, in five different positions and for three levels of instrumentation noise. Statistical analysis showed that reconstructions on the correct mesh were on average 25% better than on the other meshes. However, the stroke detection rates were not improved. We conclude that a generic head mesh is sufficient for monitoring patients for secondary strokes following head trauma.

Multiple sparse volumetric priors for distributed EEG source reconstruction.

PubMed

Strobbe, Gregor; van Mierlo, Pieter; De Vos, Maarten; Mijović, Bogdan; Hallez, Hans; Van Huffel, Sabine; López, José David; Vandenberghe, Stefaan

2014-10-15

We revisit the multiple sparse priors (MSP) algorithm implemented in the statistical parametric mapping software (SPM) for distributed EEG source reconstruction (Friston et al., 2008). In the present implementation, multiple cortical patches are introduced as source priors based on a dipole source space restricted to a cortical surface mesh. In this note, we present a technique to construct volumetric cortical regions to introduce as source priors by restricting the dipole source space to a segmented gray matter layer and using a region growing approach. This extension allows to reconstruct brain structures besides the cortical surface and facilitates the use of more realistic volumetric head models including more layers, such as cerebrospinal fluid (CSF), compared to the standard 3-layered scalp-skull-brain head models. We illustrated the technique with ERP data and anatomical MR images in 12 subjects. Based on the segmented gray matter for each of the subjects, cortical regions were created and introduced as source priors for MSP-inversion assuming two types of head models. The standard 3-layered scalp-skull-brain head models and extended 4-layered head models including CSF. We compared these models with the current implementation by assessing the free energy corresponding with each of the reconstructions using Bayesian model selection for group studies. Strong evidence was found in favor of the volumetric MSP approach compared to the MSP approach based on cortical patches for both types of head models. Overall, the strongest evidence was found in favor of the volumetric MSP reconstructions based on the extended head models including CSF. These results were verified by comparing the reconstructed activity. The use of volumetric cortical regions as source priors is a useful complement to the present implementation as it allows to introduce more complex head models and volumetric source priors in future studies. Copyright © 2014 Elsevier Inc. All rights reserved.

An Instrument for Measuring Performance in Geometry Based on the Van Hiele Model

ERIC Educational Resources Information Center

Sánchez-García, Ana B.; Cabello, Ana Belén

2016-01-01

In this paper we present the process of constructing a test for assessing student performance in geometry corresponding to the first year of Secondary Education. The main goal was to detect student errors in the understanding of geometry in order to develop a proposal according to the Van Hiele teaching model, explained in this paper. Our research…

Head and neck surgical subspecialty training in Africa: Sustainable models to improve cancer care in developing countries.

PubMed

Fagan, Johannes J; Zafereo, Mark; Aswani, Joyce; Netterville, James L; Koch, Wayne

2017-03-01

Cancer poses a health crisis in the developing world where surgery is the mainstay of treatment for head and neck cancers. However, a shortage of surgeons with appropriate skills exists. How do we train head and neck surgeons in developing countries and avoid a brain drain? The ideal model provides appropriate affordable training leading to establishment of head and neck cancer centers that teach and train others. Different head and neck surgery training models are presented based on the personal experiences of the authors. Surgical exposure of head and neck fellows in Cape Town and (potentially) in Nairobi is benchmarked against programs in the United States. Surgical exposure in Cape Town is equivalent to that in the United States, but more appropriate to a developing world setting. Training can be achieved in a number of ways, which may be complimentary. Fellowship training is possible in developing countries. © 2016 Wiley Periodicals, Inc. Head Neck 39: 605-611, 2017. © 2016 Wiley Periodicals, Inc.

Investigation of detection limits for diffuse optical tomography systems: II. Analysis of slab and cup geometry for breast imaging.

PubMed

Ziegler, Ronny; Brendel, Bernhard; Rinneberg, Herbert; Nielsen, Tim

2009-01-21

Using a statistical (chi-square) test on simulated data and a realistic noise model derived from the system's hardware we study the performance of diffuse optical tomography systems for fluorescence imaging. We compare the predicted smallest size of detectable lesions at various positions in slab and cup geometry and model how detection sensitivity depends on breast compression and lesion fluorescence contrast. Our investigation shows that lesion detection is limited by relative noise in slab geometry and by absolute noise in cup geometry.

Fracture characterization from near-offset VSP inversion

DOE Office of Scientific and Technical Information (OSTI.GOV)

Horne, S.; MacBeth, C.; Queen, J.

1997-01-01

A global optimization method incorporating a ray-tracing scheme is used to invert observations of shear-wave splitting from two near-offset VSPs recorded at the Conoco Borehole Test Facility, Kay County, Oklahoma. Inversion results suggest that the seismic anisotropy is due to a non-vertical fracture system. This interpretation is constrained by the VSP acquisition geometry for which two sources are employed along near diametrically opposite azimuths about the well heads. A correlation is noted between the time-delay variations between the fast and slow split shear waves and the sandstone formations.

Miniature drag-force anemometer

NASA Technical Reports Server (NTRS)

Krause, L. N.; Fralick, G. C.

1981-01-01

A miniature drag force anemometer is described which is capable of measuring unsteady as well as steady state velocity head and flow direction. It consists of a cantilevered beam with strain gages located at the base of the beam as the force measuring element. The dynamics of the beam are like those of lightly damped second order system with a natural frequency as high as 40 kilohertz depending on beam geometry and material. The anemometer is used in both forward and reversed flow. Anemometer characteristics and several designs are presented along with discussions of several applications.

Heading-vector navigation based on head-direction cells and path integration.

PubMed

Kubie, John L; Fenton, André A

2009-05-01

Insect navigation is guided by heading vectors that are computed by path integration. Mammalian navigation models, on the other hand, are typically based on map-like place representations provided by hippocampal place cells. Such models compute optimal routes as a continuous series of locations that connect the current location to a goal. We propose a "heading-vector" model in which head-direction cells or their derivatives serve both as key elements in constructing the optimal route and as the straight-line guidance during route execution. The model is based on a memory structure termed the "shortcut matrix," which is constructed during the initial exploration of an environment when a set of shortcut vectors between sequential pairs of visited waypoint locations is stored. A mechanism is proposed for calculating and storing these vectors that relies on a hypothesized cell type termed an "accumulating head-direction cell." Following exploration, shortcut vectors connecting all pairs of waypoint locations are computed by vector arithmetic and stored in the shortcut matrix. On re-entry, when local view or place representations query the shortcut matrix with a current waypoint and goal, a shortcut trajectory is retrieved. Since the trajectory direction is in head-direction compass coordinates, navigation is accomplished by tracking the firing of head-direction cells that are tuned to the heading angle. Section 1 of the manuscript describes the properties of accumulating head-direction cells. It then shows how accumulating head-direction cells can store local vectors and perform vector arithmetic to perform path-integration-based homing. Section 2 describes the construction and use of the shortcut matrix for computing direct paths between any pair of locations that have been registered in the shortcut matrix. In the discussion, we analyze the advantages of heading-based navigation over map-based navigation. Finally, we survey behavioral evidence that nonhippocampal, heading-based navigation is used in small mammals and humans. Copyright 2008 Wiley-Liss, Inc.

Include dispersion in quantum chemical modeling of enzymatic reactions: the case of isoaspartyl dipeptidase.

PubMed

Zhang, Hai-Mei; Chen, Shi-Lu

2015-06-09

The lack of dispersion in the B3LYP functional has been proposed to be the main origin of big errors in quantum chemical modeling of a few enzymes and transition metal complexes. In this work, the essential dispersion effects that affect quantum chemical modeling are investigated. With binuclear zinc isoaspartyl dipeptidase (IAD) as an example, dispersion is included in the modeling of enzymatic reactions by two different procedures, i.e., (i) geometry optimizations followed by single-point calculations of dispersion (approach I) and (ii) the inclusion of dispersion throughout geometry optimization and energy evaluation (approach II). Based on a 169-atom chemical model, the calculations show a qualitative consistency between approaches I and II in energetics and most key geometries, demonstrating that both approaches are available with the latter preferential since both geometry and energy are dispersion-corrected in approach II. When a smaller model without Arg233 (147 atoms) was used, an inconsistency was observed, indicating that the missing dispersion interactions are essentially responsible for determining equilibrium geometries. Other technical issues and mechanistic characteristics of IAD are also discussed, in particular with respect to the effects of Arg233.

CAD-based Automatic Modeling Method for Geant4 geometry model Through MCAM

NASA Astrophysics Data System (ADS)

Wang, Dong; Nie, Fanzhi; Wang, Guozhong; Long, Pengcheng; LV, Zhongliang; LV, Zhongliang

2014-06-01

Geant4 is a widely used Monte Carlo transport simulation package. Before calculating using Geant4, the calculation model need be established which could be described by using Geometry Description Markup Language (GDML) or C++ language. However, it is time-consuming and error-prone to manually describe the models by GDML. Automatic modeling methods have been developed recently, but there are some problem existed in most of present modeling programs, specially some of them were not accurate or adapted to specifically CAD format. To convert the GDML format models to CAD format accurately, a Geant4 Computer Aided Design (CAD) based modeling method was developed for automatically converting complex CAD geometry model into GDML geometry model. The essence of this method was dealing with CAD model represented with boundary representation (B-REP) and GDML model represented with constructive solid geometry (CSG). At first, CAD model was decomposed to several simple solids which had only one close shell. And then the simple solid was decomposed to convex shell set. Then corresponding GDML convex basic solids were generated by the boundary surfaces getting from the topological characteristic of a convex shell. After the generation of these solids, GDML model was accomplished with series boolean operations. This method was adopted in CAD/Image-based Automatic Modeling Program for Neutronics & Radiation Transport (MCAM), and tested with several models including the examples in Geant4 install package. The results showed that this method could convert standard CAD model accurately, and can be used for Geant4 automatic modeling.

Synergism of the method of characteristics and CAD technology for neutron transport calculation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chen, Z.; Wang, D.; He, T.

2013-07-01

The method of characteristics (MOC) is a very popular methodology in neutron transport calculation and numerical simulation in recent decades for its unique advantages. One of the key problems determining whether the MOC can be applied in complicated and highly heterogeneous geometry is how to combine an effective geometry processing method with MOC. Most of the existing MOC codes describe the geometry by lines and arcs with extensive input data, such as circles, ellipses, regular polygons and combination of them. Thus they have difficulty in geometry modeling, background meshing and ray tracing for complicated geometry domains. In this study, amore » new idea making use of a CAD solid modeler MCAM which is a CAD/Image-based Automatic Modeling Program for Neutronics and Radiation Transport developed by FDS Team in China was introduced for geometry modeling and ray tracing of particle transport to remove these geometrical limitations mentioned above. The diamond-difference scheme was applied to MOC to reduce the spatial discretization error of the flat flux approximation in theory. Based on MCAM and MOC, a new MOC code was developed and integrated into SuperMC system, which is a Super Multi-function Computational system for neutronics and radiation simulation. The numerical testing results demonstrated the feasibility and effectiveness of the new idea for geometry treatment in SuperMC. (authors)« less

Digital dental surface registration with laser scanner for orthodontics set-up planning

NASA Astrophysics Data System (ADS)

Alcaniz-Raya, Mariano L.; Albalat, Salvador E.; Grau Colomer, Vincente; Monserrat, Carlos A.

1997-05-01

We present an optical measuring system based on laser structured light suitable for its diary use in orthodontics clinics that fit four main requirements: (1) to avoid use of stone models, (2) to automatically discriminate geometric points belonging to teeth and gum, (3) to automatically calculate diagnostic parameters used by orthodontists, (4) to make use of low cost and easy to use technology for future commercial use. Proposed technique is based in the use of hydrocolloids mould used by orthodontists for stone model obtention. These mould of the inside of patient's mouth are composed of very fluent materials like alginate or hydrocolloids that reveal fine details of dental anatomy. Alginate mould are both very easy to obtain and very low costly. Once captured, alginate moulds are digitized by mean of a newly developed and patented 3D dental scanner. Developed scanner is based in the optical triangulation method based in the projection of a laser line on the alginate mould surface. Line deformation gives uncalibrated shape information. Relative linear movements of the mould with respect to the sensor head gives more sections thus obtaining a full 3D uncalibrated dentition model. Developed device makes use of redundant CCD in the sensor head and servocontrolled linear axis for mould movement. Last step is calibration to get a real and precise X, Y, Z image. All the process is done automatically. The scanner has been specially adapted for 3D dental anatomy capturing in order to fulfill specific requirements such as: scanning time, accuracy, security and correct acquisition of 'hidden points' in alginate mould. Measurement realized on phantoms with known geometry quite similar to dental anatomy present errors less than 0,1 mm. Scanning of global dental anatomy is 2 minutes, and generation of 3D graphics of dental cast takes approximately 30 seconds in a Pentium-based PC.

The Parameterization of Top-Hat Particle Sensors with Microchannel-Plate-Based Detection Systems and its Application to the Fast Plasma Investigation on NASA's Magnetospheric MultiScale Mission

NASA Technical Reports Server (NTRS)

Gershman, Daniel J.; Gliese, Ulrik; Dorelli, John C.; Avanov, Levon A.; Barrie, Alexander C.; Chornay, Dennis J.; MacDonald, Elizabeth A.; Holland, Matthew P.; Pollock, Craig J.

2015-01-01

The most common instrument for low energy plasmas consists of a top-hat electrostatic analyzer geometry coupled with a microchannel-plate (MCP)-based detection system. While the electrostatic optics for such sensors are readily simulated and parameterized during the laboratory calibration process, the detection system is often less well characterized. Furthermore, due to finite resources, for large sensor suites such as the Fast Plasma Investigation (FPI) on NASA's Magnetospheric Multiscale (MMS) mission, calibration data are increasingly sparse. Measurements must be interpolated and extrapolated to understand instrument behavior for untestable operating modes and yet sensor inter-calibration is critical to mission success. To characterize instruments from a minimal set of parameters we have developed the first comprehensive mathematical description of both sensor electrostatic optics and particle detection systems. We include effects of MCP efficiency, gain, scattering, capacitive crosstalk, and charge cloud spreading at the detector output. Our parameterization enables the interpolation and extrapolation of instrument response to all relevant particle energies, detector high voltage settings, and polar angles from a small set of calibration data. We apply this model to the 32 sensor heads in the Dual Electron Sensor (DES) and 32 sensor heads in the Dual Ion Sensor (DIS) instruments on the 4 MMS observatories and use least squares fitting of calibration data to extract all key instrument parameters. Parameters that will evolve in flight, namely MCP gain, will be determined daily through application of this model to specifically tailored in-flight calibration activities, providing a robust characterization of sensor suite performance throughout mission lifetime. Beyond FPI, our model provides a valuable framework for the simulation and evaluation of future detection system designs and can be used to maximize instrument understanding with minimal calibration resources.

A Preprocessor for Modeling Nonpoint Sources in Fractured Media using MODFLOW and MT3D

NASA Astrophysics Data System (ADS)

Mun, Y.; Uchrin, C. G.

2002-05-01

There are a multitude of fractures in the geological structure of fractured media which act as conduits for subsurface fluid flow. The hydraulic properties of this flow are very heterogeneous even within a single unit and this heterogeneity is very localized. As a result, modeling flow in fractured media is difficult due to this heterogeneity. There are two major approaches to simulate the flow and transport of fluid flow in fractured media: the discrete fracture approach and the continuum approach. Precise characteristics such as geometry are required to use the discrete fracture approach. It, however, is difficult to determine the fluid flow through the fractures because of inaccessibility. In the continuum approach, although head distributions can match to well data, chemical concentration distributions are hard to match well sample concentration observations, because some aquifers are dominated by advective transport and others are likely to serve as reservoirs for immobile solutes. The MODFLOW preprocessor described in this paper has been developed and applied to the Cranberry Lake system in Northwestern New Jersey. Cranberry Lake has exhibited eutrophic characteristics for some time by nonpoint sources including surface water runoff, leaching from local septic systems and direct deposition. It has been estimated that 70% of the nutrient loading to the lake flows through fractured media from septic systems. The preprocessor presented in this paper utilizes percolation theory, which is concerned with the existence of ­ropen paths­_. The percolation threshold of a body-centered cubic lattice (3D), a square lattice (2D) and several other percolation numbers are applied to make the model system represent the fractured media. The distribution of hydraulic head within groundwater is simulated by MODFLOW and the advection-dispersion equation of nitrate transport is solved by MT3D. This study also simulates boron transport as an indicator.

From a Point Cloud Survey to a Mass 3d Modelling: Renaissance Hbim in Poggio a Caiano

NASA Astrophysics Data System (ADS)

Bolognesi, C.; Garagnani, S.

2018-05-01

This paper introduces some studies developed regarding the Medicea Villa at Poggio a Caiano, in Italy. The monumental building was built by Lorenzo de' Medici and his heirs following the design of the famous architect Giuliano da Sangallo, between 1485 and 1520. The Villa embodies many of the typical features of the Italian Renaissance, added a monumental double circular stairway in the front façade during neoclassical times, heading to the upper balcony surrounded by a balustrade. The Villa was surveyed taking advantage of Terrestrial Laser Scanning and Digital Photogrammetry, in order to produce a detailed model to be translated into a HBIM digital prototype then. The Scan-to-BIM approach was obtained with a generation of semantics and components proper of Sangallo's architectural grammar, first of all defining the object, then geometry, and then their parametrization. This process led to a model of the exteriors, used to better understand the architectural composition of the volumes, to make some hypothesis on its shape according to the original architect's drawing in the Taccuino Senese, on its general structural behaviours, to understand the limits of a process and the perspective of a research that goes from a digital survey to the HBIM environment.

Development of the software tool for generation and visualization of the finite element head model with bone conduction sounds

NASA Astrophysics Data System (ADS)

Nikolić, Dalibor; Milošević, Žarko; Saveljić, Igor; Filipović, Nenad

2015-12-01

Vibration of the skull causes a hearing sensation. We call it Bone Conduction (BC) sound. There are several investigations about transmission properties of bone conducted sound. The aim of this study was to develop a software tool for easy generation of the finite element (FE) model of the human head with different materials based on human head anatomy and to calculate sound conduction through the head. Developed software tool generates a model in a few steps. The first step is to do segmentation of CT medical images (DICOM) and to generate a surface mesh files (STL). Each STL file presents a different layer of human head with different material properties (brain, CSF, different layers of the skull bone, skin, etc.). The next steps are to make tetrahedral mesh from obtained STL files, to define FE model boundary conditions and to solve FE equations. This tool uses PAK solver, which is the open source software implemented in SIFEM FP7 project, for calculations of the head vibration. Purpose of this tool is to show impact of the bone conduction sound of the head on the hearing system and to estimate matching of obtained results with experimental measurements.

Modeling and Simulation Network Data Standards

DTIC Science & Technology

2011-09-30

COMBATXXI Movement Logger Data Output Dictionary. Field # Geocentric Coordinates (GCC) Heading Geodetic Coordinates (GDC) Heading Universal...B-8 Field # Geocentric Coordinates (GCC) Heading Geodetic Coordinates (GDC) Heading Universal Transverse Mercator (UTM) Heading...FKSM Fort Knox Supplemental Material FM field manual GCC geocentric coordinates GDC geodetic coordinates GIG global information grid

Grundwasserfließgeschehen Mecklenburg-Vorpommerns - Geohydraulische Modellierung mit Detrended Kriging

NASA Astrophysics Data System (ADS)

Hilgert, Toralf; Hennig, Heiko

2017-03-01

Groundwater heads were mapped for the entire State of Mecklenburg-Western Pomerania by applying a Detrended Kriging method based on a numerical geohydraulic model. The general groundwater flow system (trend surface) was represented by a two-dimensional horizontal flow model. Thus deviations of observed groundwater heads from simulated groundwater heads are no longer subject to a regional trend and can be interpolated by means of Ordinary Kriging. Subsequently, the groundwater heads were obtained from the sum of the simulated trend surface and interpolated residuals. Furthermore, the described procedure allowed a plausibility check of observed groundwater heads by comparing them to results of the hydraulic model. If significant deviations were seen, the observation wells could be allocated to different aquifers. The final results are two hydraulically established groundwater head distributions - one for the regional main aquifer and one for the upper aquifer which may differ locally from the main aquifer.

Chromaticity effects on head-tail instabilities for broadband impedance using two particle model, Vlasov analysis, and simulations

DOE Office of Scientific and Technical Information (OSTI.GOV)

Chin, Yong Ho; Chao, Alexander Wu; Blaskiewicz, Michael M.

Effects of the chromaticity on head-tail instabilities for broadband impedances are comprehensively studied, using the two particle model, the Vlasov analysis and computer simulations. We show both in the two particle model and the Vlasov analysis with the trapezoidal (semiconstant) wake model that we can derive universal contour plots for the growth factor as a function of the two dimensionless parameters: the wakefield strength, Υ, and the difference of the betatron phase advances between the head and the tail, χ. They reveal how the chromaticity affects strong head-tail instabilities and excites head-tail instabilities. We also apply the LEP (Large Electron-Positronmore » Collider) broadband resonator model to the Vlasov approach and find that the results are in very good agreement with those of the trapezoidal wake model. The theoretical findings are also reinforced by the simulation results. In conclusion, the trapezoidal wake model turns out to be a very useful tool since it significantly simplifies the time domain analysis and provides well-behaved impedance at the same time.« less

Chromaticity effects on head-tail instabilities for broadband impedance using two particle model, Vlasov analysis, and simulations

DOE PAGES

Chin, Yong Ho; Chao, Alexander Wu; Blaskiewicz, Michael M.; ...

2017-07-28

Effects of the chromaticity on head-tail instabilities for broadband impedances are comprehensively studied, using the two particle model, the Vlasov analysis and computer simulations. We show both in the two particle model and the Vlasov analysis with the trapezoidal (semiconstant) wake model that we can derive universal contour plots for the growth factor as a function of the two dimensionless parameters: the wakefield strength, Υ, and the difference of the betatron phase advances between the head and the tail, χ. They reveal how the chromaticity affects strong head-tail instabilities and excites head-tail instabilities. We also apply the LEP (Large Electron-Positronmore » Collider) broadband resonator model to the Vlasov approach and find that the results are in very good agreement with those of the trapezoidal wake model. The theoretical findings are also reinforced by the simulation results. In conclusion, the trapezoidal wake model turns out to be a very useful tool since it significantly simplifies the time domain analysis and provides well-behaved impedance at the same time.« less

Shock wave attenuation by grids and orifice plates

NASA Astrophysics Data System (ADS)

Britan, A.; Igra, O.; Ben-Dor, G.; Shapiro, H.

2006-11-01

The interaction of weak shock waves with porous barriers of different geometries and porosities is examined. Installing a barrier inside the shock tube test section will cause the development of the following wave pattern upon a head-on collision between the incident shock wave and the barrier: a reflected shock from the barrier and a transmitted shock propagating towards the shock tube end wall. Once the transmitted shock wave reaches the end wall it is reflected back towards the barrier. This is the beginning of multiple reflections between the barrier and the end wall. This full cycle of shock reflections/interactions resulting from the incident shock wave collision with the barrier can be studied in a single shock tube test. A one-dimensional (1D), inviscid flow model was proposed for simulating the flow resulting from the initial collision of the incident shock wave with the barrier. Fairly good agreement is found between experimental findings and simulations based on a 1D flow model. Based on obtained numerical and experimental findings an optimal design procedure for shock wave attenuator is suggested. The suggested attenuator may ensure the safety of the shelter’s ventilation systems.

Can we calibrate simultaneously groundwater recharge and aquifer hydrodynamic parameters ?

NASA Astrophysics Data System (ADS)

Hassane Maina, Fadji; Ackerer, Philippe; Bildstein, Olivier

2017-04-01

By groundwater model calibration, we consider here fitting the measured piezometric heads by estimating the hydrodynamic parameters (storage term and hydraulic conductivity) and the recharge. It is traditionally recommended to avoid simultaneous calibration of groundwater recharge and flow parameters because of correlation between recharge and the flow parameters. From a physical point of view, little recharge associated with low hydraulic conductivity can provide very similar piezometric changes than higher recharge and higher hydraulic conductivity. If this correlation is true under steady state conditions, we assume that this correlation is much weaker under transient conditions because recharge varies in time and the parameters do not. Moreover, the recharge is negligible during summer time for many climatic conditions due to reduced precipitation, increased evaporation and transpiration by vegetation cover. We analyze our hypothesis through global sensitivity analysis (GSA) in conjunction with the polynomial chaos expansion (PCE) methodology. We perform GSA by calculating the Sobol indices, which provide a variance-based 'measure' of the effects of uncertain parameters (storage and hydraulic conductivity) and recharge on the piezometric heads computed by the flow model. The choice of PCE has the following two benefits: (i) it provides the global sensitivity indices in a straightforward manner, and (ii) PCE can serve as a surrogate model for the calibration of parameters. The coefficients of the PCE are computed by probabilistic collocation. We perform the GSA on simplified real conditions coming from an already built groundwater model dedicated to a subdomain of the Upper-Rhine aquifer (geometry, boundary conditions, climatic data). GSA shows that the simultaneous calibration of recharge and flow parameters is possible if the calibration is performed over at least one year. It provides also the valuable information of the sensitivity versus time, depending on the aquifer inertia and climatic conditions. The groundwater levels variations during recharge (increase) are sensitive to the storage coefficient whereas the groundwater levels variations after recharge (decrease) are sensitive to the hydraulic conductivity. The performed model calibration on synthetic data sets shows that the parameters and recharge are estimated quite accurately.

Changing head model extent affects finite element predictions of transcranial direct current stimulation distributions

NASA Astrophysics Data System (ADS)

Indahlastari, Aprinda; Chauhan, Munish; Schwartz, Benjamin; Sadleir, Rosalind J.

2016-12-01

Objective. In this study, we determined efficient head model sizes relative to predicted current densities in transcranial direct current stimulation (tDCS). Approach. Efficiency measures were defined based on a finite element (FE) simulations performed using nine human head models derived from a single MRI data set, having extents varying from 60%-100% of the original axial range. Eleven tissue types, including anisotropic white matter, and three electrode montages (T7-T8, F3-right supraorbital, Cz-Oz) were used in the models. Main results. Reducing head volume extent from 100% to 60%, that is, varying the model’s axial range from between the apex and C3 vertebra to one encompassing only apex to the superior cerebellum, was found to decrease the total modeling time by up to half. Differences between current density predictions in each model were quantified by using a relative difference measure (RDM). Our simulation results showed that {RDM} was the least affected (a maximum of 10% error) for head volumes modeled from the apex to the base of the skull (60%-75% volume). Significance. This finding suggested that the bone could act as a bioelectricity boundary and thus performing FE simulations of tDCS on the human head with models extending beyond the inferior skull may not be necessary in most cases to obtain reasonable precision in current density results.

Modeling Spin Creation and Mass Generation in the Electron Motivated by an Angle Doubler Mechanism

DTIC Science & Technology

2017-11-01

electricity. The second author and project manager (W. Liu), suggested the use of an angle doubler mechanism to improve the length of the movements...to present an attempt to explain this effect using geometry. The model is extended by projective geometry, which provides a deeper understanding of...LANGUAGE OF PROJECTIVE GEOMETRY ...................21 10. CONNECTION WITH MATHEMATICAL PHYSICS

Geometry control of long-span continuous girder concrete bridge during construction through finite element model updating

NASA Astrophysics Data System (ADS)

Wu, Jie; Yan, Quan-sheng; Li, Jian; Hu, Min-yi

2016-04-01

In bridge construction, geometry control is critical to ensure that the final constructed bridge has the consistent shape as design. A common method is by predicting the deflections of the bridge during each construction phase through the associated finite element models. Therefore, the cambers of the bridge during different construction phases can be determined beforehand. These finite element models are mostly based on the design drawings and nominal material properties. However, the accuracy of these bridge models can be large due to significant uncertainties of the actual properties of the materials used in construction. Therefore, the predicted cambers may not be accurate to ensure agreement of bridge geometry with design, especially for long-span bridges. In this paper, an improved geometry control method is described, which incorporates finite element (FE) model updating during the construction process based on measured bridge deflections. A method based on the Kriging model and Latin hypercube sampling is proposed to perform the FE model updating due to its simplicity and efficiency. The proposed method has been applied to a long-span continuous girder concrete bridge during its construction. Results show that the method is effective in reducing construction error and ensuring the accuracy of the geometry of the final constructed bridge.

Measuring striving for understanding and learning value of geometry: a validity study

NASA Astrophysics Data System (ADS)

Ubuz, Behiye; Aydınyer, Yurdagül

2017-11-01

The current study aimed to construct a questionnaire that measures students' personality traits related to striving for understanding and learning value of geometry and then examine its psychometric properties. Through the use of multiple methods on two independent samples of 402 and 521 middle school students, two studies were performed to address this issue to provide support for its validity. In Study 1, exploratory factor analysis indicated the two-factor model. In Study 2, confirmatory factor analysis indicated the better fit of two-factor model compared to one or three-factor model. Convergent and discriminant validity evidence provided insight into the distinctiveness of the two factors. Subgroup validity evidence revealed gender differences for striving for understanding geometry trait favouring girls and grade level differences for learning value of geometry trait favouring the sixth- and seventh-grade students. Predictive validity evidence demonstrated that the striving for understanding geometry trait but not learning value of geometry trait was significantly correlated with prior mathematics achievement. In both studies, each factor and the entire questionnaire showed satisfactory reliability. In conclusion, the questionnaire was psychometrically sound.

Convection in Slab and Spheroidal Geometries

NASA Technical Reports Server (NTRS)

Porter, David H.; Woodward, Paul R.; Jacobs, Michael L.

2000-01-01

Three-dimensional numerical simulations of compressible turbulent thermally driven convection, in both slab and spheroidal geometries, are reviewed and analyzed in terms of velocity spectra and mixing-length theory. The same ideal gas model is used in both geometries, and resulting flows are compared. The piecewise-parabolic method (PPM), with either thermal conductivity or photospheric boundary conditions, is used to solve the fluid equations of motion. Fluid motions in both geometries exhibit a Kolmogorov-like k(sup -5/3) range in their velocity spectra. The longest wavelength modes are energetically dominant in both geometries, typically leading to one convection cell dominating the flow. In spheroidal geometry, a dipolar flow dominates the largest scale convective motions. Downflows are intensely turbulent and up drafts are relatively laminar in both geometries. In slab geometry, correlations between temperature and velocity fluctuations, which lead to the enthalpy flux, are fairly independent of depth. In spheroidal geometry this same correlation increases linearly with radius over the inner 70 percent by radius, in which the local pressure scale heights are a sizable fraction of the radius. The effects from the impenetrable boundary conditions in the slab geometry models are confused with the effects from non-local convection. In spheroidal geometry nonlocal effects, due to coherent plumes, are seen as far as several pressure scale heights from the lower boundary and are clearly distinguishable from boundary effects.

Real-time inversions for finite fault slip models and rupture geometry based on high-rate GPS data

USGS Publications Warehouse

Minson, Sarah E.; Murray, Jessica R.; Langbein, John O.; Gomberg, Joan S.

2015-01-01

We present an inversion strategy capable of using real-time high-rate GPS data to simultaneously solve for a distributed slip model and fault geometry in real time as a rupture unfolds. We employ Bayesian inference to find the optimal fault geometry and the distribution of possible slip models for that geometry using a simple analytical solution. By adopting an analytical Bayesian approach, we can solve this complex inversion problem (including calculating the uncertainties on our results) in real time. Furthermore, since the joint inversion for distributed slip and fault geometry can be computed in real time, the time required to obtain a source model of the earthquake does not depend on the computational cost. Instead, the time required is controlled by the duration of the rupture and the time required for information to propagate from the source to the receivers. We apply our modeling approach, called Bayesian Evidence-based Fault Orientation and Real-time Earthquake Slip, to the 2011 Tohoku-oki earthquake, 2003 Tokachi-oki earthquake, and a simulated Hayward fault earthquake. In all three cases, the inversion recovers the magnitude, spatial distribution of slip, and fault geometry in real time. Since our inversion relies on static offsets estimated from real-time high-rate GPS data, we also present performance tests of various approaches to estimating quasi-static offsets in real time. We find that the raw high-rate time series are the best data to use for determining the moment magnitude of the event, but slightly smoothing the raw time series helps stabilize the inversion for fault geometry.

A Novel Closed-Head Model of Mild Traumatic Brain Injury Using Focal Primary Overpressure Blast to the Cranium in Mice

PubMed Central

Guley, Natalie H.; Rogers, Joshua T.; Del Mar, Nobel A.; Deng, Yunping; Islam, Rafiqul M.; D'Surney, Lauren; Ferrell, Jessica; Deng, Bowei; Hines-Beard, Jessica; Bu, Wei; Ren, Huiling; Elberger, Andrea J.; Marchetta, Jeffrey G.; Rex, Tonia S.; Honig, Marcia G.

2016-01-01

Abstract Mild traumatic brain injury (TBI) from focal head impact is the most common form of TBI in humans. Animal models, however, typically use direct impact to the exposed dura or skull, or blast to the entire head. We present a detailed characterization of a novel overpressure blast system to create focal closed-head mild TBI in mice. A high-pressure air pulse limited to a 7.5 mm diameter area on the left side of the head overlying the forebrain is delivered to anesthetized mice. The mouse eyes and ears are shielded, and its head and body are cushioned to minimize movement. This approach creates mild TBI by a pressure wave that acts on the brain, with minimal accompanying head acceleration-deceleration. A single 20-psi blast yields no functional deficits or brain injury, while a single 25–40 psi blast yields only slight motor deficits and brain damage. By contrast, a single 50–60 psi blast produces significant visual, motor, and neuropsychiatric impairments and axonal damage and microglial activation in major fiber tracts, but no contusive brain injury. This model thus reproduces the widespread axonal injury and functional impairments characteristic of closed-head mild TBI, without the complications of systemic or ocular blast effects or head acceleration that typically occur in other blast or impact models of closed-skull mild TBI. Accordingly, our model provides a simple way to examine the biomechanics, pathophysiology, and functional deficits that result from TBI and can serve as a reliable platform for testing therapies that reduce brain pathology and deficits. PMID:26414413

Optical properties of light absorbing carbon aggregates mixed with sulfate: assessment of different model geometries for climate forcing calculations.

PubMed

Kahnert, Michael; Nousiainen, Timo; Lindqvist, Hannakaisa; Ebert, Martin

2012-04-23

Light scattering by light absorbing carbon (LAC) aggregates encapsulated into sulfate shells is computed by use of the discrete dipole method. Computations are performed for a UV, visible, and IR wavelength, different particle sizes, and volume fractions. Reference computations are compared to three classes of simplified model particles that have been proposed for climate modeling purposes. Neither model matches the reference results sufficiently well. Remarkably, more realistic core-shell geometries fall behind homogeneous mixture models. An extended model based on a core-shell-shell geometry is proposed and tested. Good agreement is found for total optical cross sections and the asymmetry parameter. © 2012 Optical Society of America

An efficient use of mixing model for computing the effective dielectric and thermal properties of the human head.

PubMed

Mishra, Varsha; Puthucheri, Smitha; Singh, Dharmendra

2018-05-07

As a preventive measure against the electromagnetic (EM) wave exposure to human body, EM radiation regulatory authorities such as ICNIRP and FCC defined the value of specific absorption rate (SAR) for the human head during EM wave exposure from mobile phone. SAR quantifies the absorption of EM waves in the human body and it mainly depends on the dielectric properties (ε', σ) of the corresponding tissues. The head part of the human body is more susceptible to EM wave exposure due to the usage of mobile phones. The human head is a complex structure made up of multiple tissues with intermixing of many layers; thus, the accurate measurement of permittivity (ε') and conductivity (σ) of the tissues of the human head is still a challenge. For computing the SAR, researchers are using multilayer model, which has some challenges for defining the boundary for layers. Therefore, in this paper, an attempt has been made to propose a method to compute effective complex permittivity of the human head in the range of 0.3 to 3.0 GHz by applying De-Loor mixing model. Similarly, for defining the thermal effect in the tissue, thermal properties of the human head have also been computed using the De-Loor mixing method. The effective dielectric and thermal properties of equivalent human head model are compared with the IEEE Std. 1528. Graphical abstract ᅟ.

Lattice gas simulations of dynamical geometry in two dimensions.

PubMed

Klales, Anna; Cianci, Donato; Needell, Zachary; Meyer, David A; Love, Peter J

2010-10-01

We present a hydrodynamic lattice gas model for two-dimensional flows on curved surfaces with dynamical geometry. This model is an extension to two dimensions of the dynamical geometry lattice gas model previously studied in one dimension. We expand upon a variation of the two-dimensional flat space Frisch-Hasslacher-Pomeau (FHP) model created by Frisch [Phys. Rev. Lett. 56, 1505 (1986)] and independently by Wolfram, and modified by Boghosian [Philos. Trans. R. Soc. London, Ser. A 360, 333 (2002)]. We define a hydrodynamic lattice gas model on an arbitrary triangulation whose flat space limit is the FHP model. Rules that change the geometry are constructed using the Pachner moves, which alter the triangulation but not the topology. We present results on the growth of the number of triangles as a function of time. Simulations show that the number of triangles grows with time as t(1/3), in agreement with a mean-field prediction. We also present preliminary results on the distribution of curvature for a typical triangulation in these simulations.

Constant Head Evaluation of Full Scale Soil Absorption Fields

NASA Astrophysics Data System (ADS)

Dix, S. P.

2001-05-01

Design loading rates for septic tank effluent in trenches of various designs with different geometry and media has been debated for decades. The role of bottom and sidewall is a hot topic with many opinion by experts in the field of agricultural and environmental engineering. Research institutions have conducted numerous studies and developed procedures for measuring both test systems and fundamental of soil hydraulics. Falling head tests have been used more recently to evaluate mature test cells and evaluate both sidewall and basal absorption, (Keys et al). The proposed paper will discuss the design and testing of a constant head permeameter. Testing this equipment and developing the test protocol followed the application of the procedure to on a number of residential systems in both sandy and clay loam soil. Results from this testing showed the relability step that must be taken to successfully use this equipment. Result of the testing show the variability and consistency of absorption, the changes in absorption when systems are flooded above their equilibrium condition and the longer-term changes that occur when trenches are rested in a warm climate. More recent application of the test procedure evaluated affects of head and increased depth sidewall on absorption rates when the effluent level in the trenches was raised. Future modification of the test equipment and procedure by integrating a data logger will permits more exact recording of dose cycles and improved estimate of soil absorption efficiency over time.

Vehicle Related Factors that Influence Injury Outcome in Head-On Collisions

PubMed Central

Blum, Jeremy J.; Scullion, Paul; Morgan, Richard M.; Digges, Kennerly; Kan, Cing-Dao; Park, Shinhee; Bae, Hanil

2008-01-01

This study specifically investigated a range of vehicle-related factors that are associated with a lower risk of serious or fatal injury to a belted driver in a head-on collision. This analysis investigated a range of structural characteristics, quantities that describes the physical features of a passenger vehicle, e.g., stiffness or frontal geometry. The study used a data-mining approach (classification tree algorithm) to find the most significant relationships between injury outcome and the structural variables. The algorithm was applied to 120,000 real-world, head-on collisions, from the National Highway Traffic Safety Administration’s (NHTSA’s) State Crash data files, that were linked to structural attributes derived from frontal crash tests performed as part of the USA New Car Assessment Program. As with previous literature, the analysis found that the heavier vehicles were correlated with lower injury risk to their drivers. This analysis also found a new and significant correlation between the vehicle’s stiffness and injury risk. When an airbag deployed, the vehicle’s stiffness has the most statistically significant correlation with injury risk. These results suggest that in severe collisions, lower intrusion in the occupant cabin associated with higher stiffness is at least as important to occupant protection as vehicle weight for self-protection of the occupant. Consequently, the safety community might better improve self-protection by a renewed focus on increasing vehicle stiffness in order to improve crashworthiness in head-on collisions. PMID:19026230

Head-and-face shape variations of U.S. civilian workers

PubMed Central

Zhuang, Ziqing; Shu, Chang; Xi, Pengcheng; Bergman, Michael; Joseph, Michael

2016-01-01

The objective of this study was to quantify head-and-face shape variations of U.S. civilian workers using modern methods of shape analysis. The purpose of this study was based on previously highlighted changes in U.S. civilian worker head-and-face shape over the last few decades – touting the need for new and better fitting respirators – as well as the study's usefulness in designing more effective personal protective equipment (PPE) – specifically in the field of respirator design. The raw scan three-dimensional (3D) data for 1169 subjects were parameterized using geometry processing techniques. This process allowed the individual scans to be put in correspondence with each other in such a way that statistical shape analysis could be performed on a dense set of 3D points. This process also cleaned up the original scan data such that the noise was reduced and holes were filled in. The next step, statistical analysis of the variability of the head-and-face shape in the 3D database, was conducted using Principal Component Analysis (PCA) techniques. Through these analyses, it was shown that the space of the head-and-face shape was spanned by a small number of basis vectors. Less than 50 components explained more than 90% of the variability. Furthermore, the main mode of variations could be visualized through animating the shape changes along the PCA axes with computer software in executable form for Windows XP. The results from this study in turn could feed back into respirator design to achieve safer, more efficient product style and sizing. Future study is needed to determine the overall utility of the point cloud-based approach for the quantification of facial morphology variation and its relationship to respirator performance. PMID:23399025

Head-and-face shape variations of U.S. civilian workers.

PubMed

Zhuang, Ziqing; Shu, Chang; Xi, Pengcheng; Bergman, Michael; Joseph, Michael

2013-09-01

The objective of this study was to quantify head-and-face shape variations of U.S. civilian workers using modern methods of shape analysis. The purpose of this study was based on previously highlighted changes in U.S. civilian worker head-and-face shape over the last few decades - touting the need for new and better fitting respirators - as well as the study's usefulness in designing more effective personal protective equipment (PPE) - specifically in the field of respirator design. The raw scan three-dimensional (3D) data for 1169 subjects were parameterized using geometry processing techniques. This process allowed the individual scans to be put in correspondence with each other in such a way that statistical shape analysis could be performed on a dense set of 3D points. This process also cleaned up the original scan data such that the noise was reduced and holes were filled in. The next step, statistical analysis of the variability of the head-and-face shape in the 3D database, was conducted using Principal Component Analysis (PCA) techniques. Through these analyses, it was shown that the space of the head-and-face shape was spanned by a small number of basis vectors. Less than 50 components explained more than 90% of the variability. Furthermore, the main mode of variations could be visualized through animating the shape changes along the PCA axes with computer software in executable form for Windows XP. The results from this study in turn could feed back into respirator design to achieve safer, more efficient product style and sizing. Future study is needed to determine the overall utility of the point cloud-based approach for the quantification of facial morphology variation and its relationship to respirator performance. Copyright © 2013 Elsevier Ltd and The Ergonomics Society. All rights reserved.

SU-F-J-48: Effect of Scan Length On Magnitude of Imaging Dose in KV CBCT

DOE Office of Scientific and Technical Information (OSTI.GOV)

Deshpande, S; Naidu, S; Sutar, A

Purpose: To study effect of scan length on magnitude of imaging dose deposition in Varian kV CBCT for head & neck and pelvis CBCT. Methods: To study effect of scan length we measured imaging dose at depth of 8 cm for head and neck Cone Beam Computed Tomography (CBCT) acquisition ( X ray beam energy is used 100kV and 200 degree of gantry rotation) and at 16 cm depth for pelvis CBCT acquisition ( X ray beam energy used is 125 kV and 360 degree of gantry rotation) in specially designed phantom. We used farmer chamber which was calibrated inmore » kV X ray range for measurements .Dose was measured with default field size, and reducing field size along y direction to 10 cm and 5 cm. Results: As the energy of the beam decreases the scattered radiation increases and this contributes significantly to the dose deposited in the patient. By reducing the scan length to 10 Cm from default 20.6 cm we found a dose reduction of 14% for head and neck CBCT protocol and a reduction of 26% for pelvis CBCT protocol. Similarly for a scan length of 5cm compared to default the dose reduction in head and neck CBCT protocol is 36% while in the pelvis CBCT protocol the dose reduction is 50%. Conclusion: By limiting the scan length we can control the scatter radiation generated and hence the dose to the patient. However the variation in dose reduction for same length used in two protocols is because of the scan geometry. The pelvis CBCT protocol uses a full rotation and head and neck CBCT protocol uses partial rotation.« less

Brain Injury Differences in Frontal Impact Crash Using Different Simulation Strategies

PubMed Central

Ma, Chunsheng; Shen, Ming; Li, Peiyu; Zhang, Jinhuan

2015-01-01

In the real world crashes, brain injury is one of the leading causes of deaths. Using isolated human head finite element (FE) model to study the brain injury patterns and metrics has been a simplified methodology widely adopted, since it costs significantly lower computation resources than a whole human body model does. However, the degree of precision of this simplification remains questionable. This study compared these two kinds of methods: (1) using a whole human body model carried on the sled model and (2) using an isolated head model with prescribed head motions, to study the brain injury. The distribution of the von Mises stress (VMS), maximum principal strain (MPS), and cumulative strain damage measure (CSDM) was used to compare the two methods. The results showed that the VMS of brain mainly concentrated at the lower cerebrum and occipitotemporal region close to the cerebellum. The isolated head modelling strategy predicted higher levels of MPS and CSDM 5%, while the difference is small in CSDM 10% comparison. It suggests that isolated head model may not equivalently reflect the strain levels below the 10% compared to the whole human body model. PMID:26495029

Predicting brain acceleration during heading of soccer ball

NASA Astrophysics Data System (ADS)

Taha, Zahari; Hasnun Arif Hassan, Mohd; Azri Aris, Mohd; Anuar, Zulfika

2013-12-01

There has been a long debate whether purposeful heading could cause harm to the brain. Studies have shown that repetitive heading could lead to degeneration of brain cells, which is similarly found in patients with mild traumatic brain injury. A two-degree of freedom linear mathematical model was developed to study the impact of soccer ball to the brain during ball-to-head impact in soccer. From the model, the acceleration of the brain upon impact can be obtained. The model is a mass-spring-damper system, in which the skull is modelled as a mass and the neck is modelled as a spring-damper system. The brain is a mass with suspension characteristics that are also defined by a spring and a damper. The model was validated by experiment, in which a ball was dropped from different heights onto an instrumented dummy skull. The validation shows that the results obtained from the model are in a good agreement with the brain acceleration measured from the experiment. This findings show that a simple linear mathematical model can be useful in giving a preliminary insight on what human brain endures during a ball-to-head impact.

Modeling heading and path perception from optic flow in the case of independently moving objects

PubMed Central

Raudies, Florian; Neumann, Heiko

2013-01-01

Humans are usually accurate when estimating heading or path from optic flow, even in the presence of independently moving objects (IMOs) in an otherwise rigid scene. To invoke significant biases in perceived heading, IMOs have to be large and obscure the focus of expansion (FOE) in the image plane, which is the point of approach. For the estimation of path during curvilinear self-motion no significant biases were found in the presence of IMOs. What makes humans robust in their estimation of heading or path using optic flow? We derive analytical models of optic flow for linear and curvilinear self-motion using geometric scene models. Heading biases of a linear least squares method, which builds upon these analytical models, are large, larger than those reported for humans. This motivated us to study segmentation cues that are available from optic flow. We derive models of accretion/deletion, expansion/contraction, acceleration/deceleration, local spatial curvature, and local temporal curvature, to be used as cues to segment an IMO from the background. Integrating these segmentation cues into our method of estimating heading or path now explains human psychophysical data and extends, as well as unifies, previous investigations. Our analysis suggests that various cues available from optic flow help to segment IMOs and, thus, make humans' heading and path perception robust in the presence of such IMOs. PMID:23554589

Parameters of thermochemical plumes responsible for the formation of batholiths: Results of experimental simulation

NASA Astrophysics Data System (ADS)

Kirdyashkin, A. A.; Kirdyashkin, A. G.; Gurov, V. V.

2017-07-01

Based on laboratory and theoretical modeling results, we present the thermal and hydrodynamical structure of the plume conduit during plume ascent and eruption on the Earth's surface. The modeling results show that a mushroom-shaped plume head forms after melt eruption on the surface for 1.9 < Ka < 10. Such plumes can be responsible for the formation of large intrusive bodies, including batholiths. The results of laboratory modeling of plumes with mushroom-shaped heads are presented for Ka = 8.7 for a constant viscosity and uniform melt composition. Images of flow patterns are obtained, as well as flow velocity profiles in the melt of the conduit and the head of the model plume. Based on the laboratory modeling data, we present a scheme of a thermochemical plume with a mushroom-shaped head responsible for the formation of a large intrusive body (batholith). After plume eruption to the surface, melting occurs along the base of the massif above the plume head, resulting in a mushroom-shaped plume head. A possible mechanism for the formation of localized surface manifestations of batholiths is presented. The parameters of some plumes with mushroom-shaped heads (plumes of the Altay-Sayan and Barguzin-Vitim large-igneous provinces, and Khangai and Khentei plumes) are estimated using geological data, including age intervals and volumes of magma melts.

The point spread function of the human head and its implications for transcranial current stimulation

NASA Astrophysics Data System (ADS)

Dmochowski, Jacek P.; Bikson, Marom; Parra, Lucas C.

2012-10-01

Rational development of transcranial current stimulation (tCS) requires solving the ‘forward problem’: the computation of the electric field distribution in the head resulting from the application of scalp currents. Derivation of forward models has represented a major effort in brain stimulation research, with model complexity ranging from spherical shells to individualized head models based on magnetic resonance imagery. Despite such effort, an easily accessible benchmark head model is greatly needed when individualized modeling is either undesired (to observe general population trends as opposed to individual differences) or unfeasible. Here, we derive a closed-form linear system which relates the applied current to the induced electric potential. It is shown that in the spherical harmonic (Fourier) domain, a simple scalar multiplication relates the current density on the scalp to the electric potential in the brain. Equivalently, the current density in the head follows as the spherical convolution between the scalp current distribution and the point spread function of the head, which we derive. Thus, if one knows the spherical harmonic representation of the scalp current (i.e. the electrode locations and current intensity to be employed), one can easily compute the resulting electric field at any point inside the head. Conversely, one may also readily determine the scalp current distribution required to generate an arbitrary electric field in the brain (the ‘backward problem’ in tCS). We demonstrate the simplicity and utility of the model with a series of characteristic curves which sweep across a variety of stimulation parameters: electrode size, depth of stimulation, head size and anode-cathode separation. Finally, theoretically optimal montages for targeting an infinitesimal point in the brain are shown.

Modeling gravity-dependent plasticity of the angular vestibuloocular reflex with a physiologically based neural network.

PubMed

Xiang, Yongqing; Yakushin, Sergei B; Cohen, Bernard; Raphan, Theodore

2006-12-01

A neural network model was developed to explain the gravity-dependent properties of gain adaptation of the angular vestibuloocular reflex (aVOR). Gain changes are maximal at the head orientation where the gain is adapted and decrease as the head is tilted away from that position and can be described by the sum of gravity-independent and gravity-dependent components. The adaptation process was modeled by modifying the weights and bias values of a three-dimensional physiologically based neural network of canal-otolith-convergent neurons that drive the aVOR. Model parameters were trained using experimental vertical aVOR gain values. The learning rule aimed to reduce the error between eye velocities obtained from experimental gain values and model output in the position of adaptation. Although the model was trained only at specific head positions, the model predicted the experimental data at all head positions in three dimensions. Altering the relative learning rates of the weights and bias improved the model-data fits. Model predictions in three dimensions compared favorably with those of a double-sinusoid function, which is a fit that minimized the mean square error at every head position and served as the standard by which we compared the model predictions. The model supports the hypothesis that gravity-dependent adaptation of the aVOR is realized in three dimensions by a direct otolith input to canal-otolith neurons, whose canal sensitivities are adapted by the visual-vestibular mismatch. The adaptation is tuned by how the weights from otolith input to the canal-otolith-convergent neurons are adapted for a given head orientation.

Experimental and Analytical Investigation of the Coolant Flow Characteristics in Cooled Turbine Airfoils

NASA Technical Reports Server (NTRS)

Damerow, W. P.; Murtaugh, J. P.; Burggraf, F.

1972-01-01

The flow characteristics of turbine airfoil cooling system components were experimentally investigated. Flow models representative of leading edge impingement, impingement with crossflow (midchord cooling), pin fins, feeder supply tube, and a composite model of a complete airfoil flow system were tested. Test conditions were set by varying pressure level to cover the Mach number and Reynolds number range of interest in advanced turbine applications. Selected geometrical variations were studied on each component model to determine these effects. Results of these tests were correlated and compared with data available in the literature. Orifice flow was correlated in terms of discharge coefficients. For the leading edge model this was found to be a weak function of hole Mach number and orifice-to-impinged wall spacing. In the impingement with crossflow tests, the discharge coefficient was found to be constant and thus independent of orifice Mach number, Reynolds number, crossflow rate, and impingement geometry. Crossflow channel pressure drop showed reasonable agreement with a simple one-dimensional momentum balance. Feeder tube orifice discharge coefficients correlated as a function of orifice Mach number and the ratio of the orifice-to-approach velocity heads. Pin fin data was correlated in terms of equivalent friction factor, which was found to be a function of Reynolds number and pin spacing but independent of pin height in the range tested.

Multi-objective parametric optimization of Inertance type pulse tube refrigerator using response surface methodology and non-dominated sorting genetic algorithm

NASA Astrophysics Data System (ADS)

Rout, Sachindra K.; Choudhury, Balaji K.; Sahoo, Ranjit K.; Sarangi, Sunil K.

2014-07-01

The modeling and optimization of a Pulse Tube Refrigerator is a complicated task, due to its complexity of geometry and nature. The aim of the present work is to optimize the dimensions of pulse tube and regenerator for an Inertance-Type Pulse Tube Refrigerator (ITPTR) by using Response Surface Methodology (RSM) and Non-Sorted Genetic Algorithm II (NSGA II). The Box-Behnken design of the response surface methodology is used in an experimental matrix, with four factors and two levels. The diameter and length of the pulse tube and regenerator are chosen as the design variables where the rest of the dimensions and operating conditions of the ITPTR are constant. The required output responses are the cold head temperature (Tcold) and compressor input power (Wcomp). Computational fluid dynamics (CFD) have been used to model and solve the ITPTR. The CFD results agreed well with those of the previously published paper. Also using the results from the 1-D simulation, RSM is conducted to analyse the effect of the independent variables on the responses. To check the accuracy of the model, the analysis of variance (ANOVA) method has been used. Based on the proposed mathematical RSM models a multi-objective optimization study, using the Non-sorted genetic algorithm II (NSGA-II) has been performed to optimize the responses.

Development and Verification of Body Armor Target Geometry Created Using Computed Tomography Scans

DTIC Science & Technology

2017-07-13

designated by other authorized documents. Citation of manufacturer’s or trade names does not constitute an official endorsement or approval of...modeling consisted of manual measurement of armor systems and translating those measurements to computer-aided design geometry, which can be tedious and...computer-aided design (CAD) human geometry model (referred to throughout as ORCA man) that is used in the Operational Requirement-based Casualty Assessment

A Generalization of Pythagoras's Theorem and Application to Explanations of Variance Contributions in Linear Models. Research Report. ETS RR-14-18

ERIC Educational Resources Information Center

Carlson, James E.

2014-01-01

Many aspects of the geometry of linear statistical models and least squares estimation are well known. Discussions of the geometry may be found in many sources. Some aspects of the geometry relating to the partitioning of variation that can be explained using a little-known theorem of Pappus and have not been discussed previously are the topic of…

DOE Office of Scientific and Technical Information (OSTI.GOV)

Popov, Emilian L.; Pointer, William David

This work assesses the influence of assumptions made when generating a mesh of a wire-wrappedgeometry. The contact region between a wire and its adjacent pin is commonly modeled by eitherembedding the wire to the adjacent pin or trimming the wire so that a gap separates the wire from itsadjacent pin. These models are referred to as close-gap and open-gap approaches herein and are applied totwo geometries. The first geometry consists of a single pin wire-wrapped subchannel. A polyhedral meshand a hexahedral mesh are generated. The second and third geometry are a 7-pin and a 19-pinwire-wrapped bundles meshed with polyhedral elementsmore » only. Pressure drops are obtained with theSTAR-CCM+computational fluid dynamic package. Sensitivity analyses of the mesh density, the meshtype, and the turbulent models are performed. Numerical results show that the best match to theexperimental data and to the Cheng-Todreas correlation is obtained with the combination of a hexahedralmesh, the shear stress transport (SST) turbulent model, and the open-gap approach. In the case of the 7-pingeometry, the best results are obtained with the open-gap approach and the SST turbulent model. The19-pin geometry yields contradictory results to the 7-pin geometry results, and thus will require furtherinvestigations.« less

Applying Turbulence Models to Hydroturbine Flows: A Sensitivity Analysis Using the GAMM Francis Turbine

NASA Astrophysics Data System (ADS)

Lewis, Bryan; Cimbala, John; Wouden, Alex

2011-11-01

Turbulence models are generally developed to study common academic geometries, such as flat plates and channels. Creating quality computational grids for such geometries is trivial, and allows stringent requirements to be met for boundary layer grid refinement. However, engineering applications, such as flow through hydroturbines, require the analysis of complex, highly curved geometries. To produce body-fitted grids for such geometries, the mesh quality requirements must be relaxed. Relaxing these requirements, along with the complexity of rotating flows, forces turbulence models to be employed beyond their developed scope. This study explores the solution sensitivity to boundary layer grid quality for various turbulence models and boundary conditions currently implemented in OpenFOAM. The following models are resented: k-omega, k-omega SST, k-epsilon, realizable k-epsilon, and RNG k-epsilon. Standard wall functions, adaptive wall functions, and sub-grid integration are compared using various grid refinements. The chosen geometry is the GAMM Francis Turbine because experimental data and comparison computational results are available for this turbine. This research was supported by a grant from the DoE and a National Defense Science and Engineering Graduate Fellowship.

TOPAS Tool for Particle Simulation

DOE Office of Scientific and Technical Information (OSTI.GOV)

Perl, Joseph

2013-05-30

TOPAS lets users simulate the passage of subatomic particles moving through any kind of radiation therapy treatment system, can import a patient geometry, can record dose and other quantities, has advanced graphics, and is fully four-dimensional (3D plus time) to handle the most challenging time-dependent aspects of modern cancer treatments.TOPAS unlocks the power of the most accurate particle transport simulation technique, the Monte Carlo (MC) method, while removing the painstaking coding work such methods used to require. Research physicists can use TOPAS to improve delivery systems towards safer and more effective radiation therapy treatments, easily setting up and running complexmore » simulations that previously used to take months of preparation. Clinical physicists can use TOPAS to increase accuracy while reducing side effects, simulating patient-specific treatment plans at the touch of a button. TOPAS is designed as a “user code” layered on top of the Geant4 Simulation Toolkit. TOPAS includes the standard Geant4 toolkit, plus additional code to make Geant4 easier to control and to extend Geant4 functionality. TOPAS aims to make proton simulation both “reliable” and “repeatable.” “Reliable” means both accurate physics and a high likelihood to simulate precisely what the user intended to simulate, reducing issues of wrong units, wrong materials, wrong scoring locations, etc. “Repeatable” means not just getting the same result from one simulation to another, but being able to easily restore a previously used setup and reducing sources of error when a setup is passed from one user to another. TOPAS control system incorporates key lessons from safety management, proactively removing possible sources of user error such as line-ordering mistakes In control files. TOPAS has been used to model proton therapy treatment examples including the UCSF eye treatment head, the MGH stereotactic alignment in radiosurgery treatment head and the MGH gantry treatment heads in passive scattering and scanning modes, and has demonstrated dose calculation based on patient-specific CT data.« less

Spectral photosensitivity of an organic semiconductor in a submicron metal grating

DOE Office of Scientific and Technical Information (OSTI.GOV)

Blinov, L. M., E-mail: lev39blinov@gmail.com; Lazarev, V. V.; Yudin, S. G.

The photoelectric effect in films of the copper phthalocyanine organic semiconductor (α-CuPc) has been experimentally studied for two fundamentally different geometries. A sample in the first, normal geometry is fabricated in the form of a sandwich with an α-CuPc film between a transparent SnO{sub 2} electrode on a substrate and an upper reflecting Al electrode. In the second case of the planar geometry, the semiconductor is deposited on the substrate with a system of submicron chromium interdigital electrodes. It has been found that the effective photoconductivity in the planar geometry is more than two orders of magnitude higher than thatmore » in the normal geometry. In addition to the classical model (without excitons), a simple exciton model has been proposed within which a relation has been obtained between the probability of the formation of electron–hole pairs and the characteristic recombination and dissociation times of excitons. An increase in the photoconductivity in the planar geometry has been explained within the exciton model by an increase in the rate of dissociation of excitons into electron–hole pairs owing to acceptor oxygen molecules, which diffuse more efficiently into the film in the case of the planar geometry where the upper electrode is absent.« less

Dynamic hyperbolic geometry: building intuition and understanding mediated by a Euclidean model

NASA Astrophysics Data System (ADS)

Moreno-Armella, Luis; Brady, Corey; Elizondo-Ramirez, Rubén

2018-05-01

This paper explores a deep transformation in mathematical epistemology and its consequences for teaching and learning. With the advent of non-Euclidean geometries, direct, iconic correspondences between physical space and the deductive structures of mathematical inquiry were broken. For non-Euclidean ideas even to become thinkable the mathematical community needed to accumulate over twenty centuries of reflection and effort: a precious instance of distributed intelligence at the cultural level. In geometry education after this crisis, relations between intuitions and geometrical reasoning must be established philosophically, rather than taken for granted. One approach seeks intuitive supports only for Euclidean explorations, viewing non-Euclidean inquiry as fundamentally non-intuitive in nature. We argue for moving beyond such an impoverished approach, using dynamic geometry environments to develop new intuitions even in the extremely challenging setting of hyperbolic geometry. Our efforts reverse the typical direction, using formal structures as a source for a new family of intuitions that emerge from exploring a digital model of hyperbolic geometry. This digital model is elaborated within a Euclidean dynamic geometry environment, enabling a conceptual dance that re-configures Euclidean knowledge as a support for building intuitions in hyperbolic space-intuitions based not directly on physical experience but on analogies extending Euclidean concepts.

Modeling Active Contraction and Relaxation of Left Ventricle Using Different Zero-load Diastole and Systole Geometries for Better Material Parameter Estimation and Stress/Strain Calculations

PubMed Central

Fan, Longling; Yao, Jing; Yang, Chun; Xu, Di; Tang, Dalin

2018-01-01

Modeling ventricle active contraction based on in vivo data is extremely challenging because of complex ventricle geometry, dynamic heart motion and active contraction where the reference geometry (zero-stress geometry) changes constantly. A new modeling approach using different diastole and systole zero-load geometries was introduced to handle the changing zero-load geometries for more accurate stress/strain calculations. Echo image data were acquired from 5 patients with infarction (Infarct Group) and 10 without (Non-Infarcted Group). Echo-based computational two-layer left ventricle models using one zero-load geometry (1G) and two zero-load geometries (2G) were constructed. Material parameter values in Mooney-Rivlin models were adjusted to match echo volume data. Effective Young’s moduli (YM) were calculated for easy comparison. For diastole phase, begin-filling (BF) mean YM value in the fiber direction (YMf) was 738% higher than its end-diastole (ED) value (645.39 kPa vs. 76.97 kPa, p=3.38E-06). For systole phase, end-systole (ES) YMf was 903% higher than its begin-ejection (BE) value (1025.10 kPa vs. 102.11 kPa, p=6.10E-05). Comparing systolic and diastolic material properties, ES YMf was 59% higher than its BF value (1025.10 kPa vs. 645.39 kPa. p=0.0002). BE mean stress value was 514% higher than its ED value (299.69 kPa vs. 48.81 kPa, p=3.39E-06), while BE mean strain value was 31.5% higher than its ED value (0.9417 vs. 0.7162, p=0.004). Similarly, ES mean stress value was 562% higher than its BF value (19.74 kPa vs. 2.98 kPa, p=6.22E-05), and ES mean strain value was 264% higher than its BF value (0.1985 vs. 0.0546, p=3.42E-06). 2G models improved over 1G model limitations and may provide better material parameter estimation and stress/strain calculations. PMID:29399004

Modeling Active Contraction and Relaxation of Left Ventricle Using Different Zero-load Diastole and Systole Geometries for Better Material Parameter Estimation and Stress/Strain Calculations.

PubMed

Fan, Longling; Yao, Jing; Yang, Chun; Xu, Di; Tang, Dalin

2016-01-01

Modeling ventricle active contraction based on in vivo data is extremely challenging because of complex ventricle geometry, dynamic heart motion and active contraction where the reference geometry (zero-stress geometry) changes constantly. A new modeling approach using different diastole and systole zero-load geometries was introduced to handle the changing zero-load geometries for more accurate stress/strain calculations. Echo image data were acquired from 5 patients with infarction (Infarct Group) and 10 without (Non-Infarcted Group). Echo-based computational two-layer left ventricle models using one zero-load geometry (1G) and two zero-load geometries (2G) were constructed. Material parameter values in Mooney-Rivlin models were adjusted to match echo volume data. Effective Young's moduli (YM) were calculated for easy comparison. For diastole phase, begin-filling (BF) mean YM value in the fiber direction (YM f ) was 738% higher than its end-diastole (ED) value (645.39 kPa vs. 76.97 kPa, p=3.38E-06). For systole phase, end-systole (ES) YM f was 903% higher than its begin-ejection (BE) value (1025.10 kPa vs. 102.11 kPa, p=6.10E-05). Comparing systolic and diastolic material properties, ES YM f was 59% higher than its BF value (1025.10 kPa vs. 645.39 kPa. p=0.0002). BE mean stress value was 514% higher than its ED value (299.69 kPa vs. 48.81 kPa, p=3.39E-06), while BE mean strain value was 31.5% higher than its ED value (0.9417 vs. 0.7162, p=0.004). Similarly, ES mean stress value was 562% higher than its BF value (19.74 kPa vs. 2.98 kPa, p=6.22E-05), and ES mean strain value was 264% higher than its BF value (0.1985 vs. 0.0546, p=3.42E-06). 2G models improved over 1G model limitations and may provide better material parameter estimation and stress/strain calculations.

A Unified Model of Heading and Path Perception in Primate MSTd

PubMed Central

Layton, Oliver W.; Browning, N. Andrew

2014-01-01

Self-motion, steering, and obstacle avoidance during navigation in the real world require humans to travel along curved paths. Many perceptual models have been proposed that focus on heading, which specifies the direction of travel along straight paths, but not on path curvature, which humans accurately perceive and is critical to everyday locomotion. In primates, including humans, dorsal medial superior temporal area (MSTd) has been implicated in heading perception. However, the majority of MSTd neurons respond optimally to spiral patterns, rather than to the radial expansion patterns associated with heading. No existing theory of curved path perception explains the neural mechanisms by which humans accurately assess path and no functional role for spiral-tuned cells has yet been proposed. Here we present a computational model that demonstrates how the continuum of observed cells (radial to circular) in MSTd can simultaneously code curvature and heading across the neural population. Curvature is encoded through the spirality of the most active cell, and heading is encoded through the visuotopic location of the center of the most active cell's receptive field. Model curvature and heading errors fit those made by humans. Our model challenges the view that the function of MSTd is heading estimation, based on our analysis we claim that it is primarily concerned with trajectory estimation and the simultaneous representation of both curvature and heading. In our model, temporal dynamics afford time-history in the neural representation of optic flow, which may modulate its structure. This has far-reaching implications for the interpretation of studies that assume that optic flow is, and should be, represented as an instantaneous vector field. Our results suggest that spiral motion patterns that emerge in spatio-temporal optic flow are essential for guiding self-motion along complex trajectories, and that cells in MSTd are specifically tuned to extract complex trajectory estimation from flow. PMID:24586130

Efficacy of visor and helmet for blast protection assessed using a computational head model

NASA Astrophysics Data System (ADS)

Singh, D.; Cronin, D. S.

2017-11-01

Head injury resulting from blast exposure has been identified as a challenge that may be addressed, in part, through improved protective systems. Existing detailed head models validated for blast loading were applied to investigate the influence of helmet visor configuration, liner properties, and shell material stiffness. Response metrics including head acceleration and intracranial pressures (ICPs) generated in brain tissue during primary blast exposure were used to assess and compare helmet configurations. The addition of a visor was found to reduce peak head acceleration and positive ICPs. However, negative ICPs associated with a potential for injury were increased when a visor and a foam liner were present. In general, the foam liner material was found to be more significant in affecting the negative ICP response than positive ICP or acceleration. Shell stiffness was found to have relatively small effects on either metric. A strap suspension system, modeled as an air gap between the head and helmet, was more effective in reducing response metrics compared to a foam liner. In cases with a foam liner, lower-density foam offered a greater reduction of negative ICPs. The models demonstrated the "underwash" effect in cases where no foam liner was present; however, the reflected pressures generated between the helmet and head did not translate to significant ICPs in adjacent tissue, when compared to peak ICPs from initial blast wave interaction. This study demonstrated that the efficacy of head protection can be expressed in terms of load transmission pathways when assessed with a detailed computational model.

Computation of peak discharge at culverts

USGS Publications Warehouse

Carter, Rolland William

1957-01-01

Methods for computing peak flood flow through culverts on the basis of a field survey of highwater marks and culvert geometry are presented. These methods are derived from investigations of culvert flow as reported in the literature and on extensive laboratory studies of culvert flow. For convenience in computation, culvert flow has been classified into six types, according to the location of the control section and the relative heights of the head-water and tail-water levels. The type of flow which occurred at any site can be determined from the field data and the criteria given in this report. A discharge equation has been developed for each flow type by combining the energy and continuity equations for the distance between an approach section upstream from the culvert and a terminal section within the culvert barrel. The discharge coefficient applicable to each flow type is listed for the more common entrance geometries. Procedures for computing peak discharge through culverts are outlined in detail for each of the six flow types.

A Literature Review of Musculoskeletal Injuries to the Human Neck and the Effects of Head-Supported Mass Worn by Soldier

DTIC Science & Technology

2005-10-01

in whiplash -type injury studies (Table 1). At the time it was the most sophisticated head - neck model available. This model uses a series of rigid...phase of rear-end whiplash loading (i.e. the extension phase). In this initial phase, the head translates backward, putting the upper spine in local...work to characterize neck response in impact scenarios has been performed, the effect of musculature on head -neck whiplash -type response is still

Development and application of a 3-D geometry/mass model for LDEF satellite ionizing radiation assessments

NASA Technical Reports Server (NTRS)

Colborn, B. L.; Armstong, T. W.

1993-01-01

A three-dimensional geometry and mass model of the Long Duration Exposure Facility (LDEF) spacecraft and experiment trays was developed for use in predictions and data interpretation related to ionizing radiation measurements. The modeling approach, level of detail incorporated, example models for specific experiments and radiation dosimeters, and example applications of the model are described.

[MODEL ESTABLISHMENT, MRI AND PATHOLOGICAL FEATURES OF EARLY STEROID-INDUCED AVASCULAR NECROSIS OF FEMORAL HEAD IN RABBIT].

PubMed

Zhang, Liyan; Sun, Xin; Tian, Dan; Xu, Rui; Lei, Hao; Al, Jinhui; Zhao, Bo; Chen, Jiying; Chai, Wei; Ma, Shoucheng; Liu, Weijia; Shen, Siyuan

2015-10-01

To establish an rabbit model of early steroid-induced avascular necrosis of the femoral head (SANFH) and evaluate its validity with MRI and pathological examination. Twenty 6-month-old rabbits (weighing, 2-3 kg) were randomly divided into 2 groups (control group and model group), 10 rabbits in each group. Dexamethasone sodium phosphate solution (10 mg/kg) was injected into bilateral gluteus in model group, and the same amount of saline was injected in control group, every 3 days for 14 times. General observation was done after modelling. Osteonecrosis was verified by pathological observation and MRI findings at 6 weeks. After 6 weeks, rabbits did not show obvious changes in control group; increased hair removal, decreased food intake, and slight limp were observed in model group. The MRI results showed normal shape of the bilateral femoral head and no abnormal signals in control group; irregular shape of the bilateral femoral head and a slice of irregular abnormal signals were observed, and necrosis and cystolization of the subchondral bone and sparse changes of trabecular bone were shown in model group. General observation from coronal section of femoral head showed smooth red cartilage surface in control group; on the contrary, the cartilage surface of the femoral head became dull, thin even visible hemorrhage under articular cartilage and necrosis of the femoral head were observed. The histopathological examination indicated that trabecular bone of the femoral head in control group was massive, thick, and close and osteocytes in the bone lacunae had normal shapes. The osseous trabecular became thinner and broken; karyopyknosis of osteocytes and bone empty lacunae could be obviously seen in model. group. The rates of empty lacunae were 8.0% ± 0.5% in control group and 49.0% ± 0.3% in model group, showing significant difference (t = 21.940, P = 0.000). Establishing a model of early SANFH through injecting short-term, shock, and high dose of dexamethasone, and it can been evaluated effectively with MRI and pathological examination.

Finite element micro-modelling of a human ankle bone reveals the importance of the trabecular network to mechanical performance: new methods for the generation and comparison of 3D models.

PubMed

Parr, W C H; Chamoli, U; Jones, A; Walsh, W R; Wroe, S

2013-01-04

Most modelling of whole bones does not incorporate trabecular geometry and treats bone as a solid non-porous structure. Some studies have modelled trabecular networks in isolation. One study has modelled the performance of whole human bones incorporating trabeculae, although this required considerable computer resources and purpose-written code. The difference between mechanical behaviour in models that incorporate trabecular geometry and non-porous models has not been explored. The ability to easily model trabecular networks may shed light on the mechanical consequences of bone loss in osteoporosis and remodelling after implant insertion. Here we present a Finite Element Analysis (FEA) of a human ankle bone that includes trabecular network geometry. We compare results from this model with results from non-porous models and introduce protocols achievable on desktop computers using widely available softwares. Our findings show that models including trabecular geometry are considerably stiffer than non-porous whole bone models wherein the non-cortical component has the same mass as the trabecular network, suggesting inclusion of trabecular geometry is desirable. We further present new methods for the construction and analysis of 3D models permitting: (1) construction of multi-property, non-porous models wherein cortical layer thickness can be manipulated; (2) maintenance of the same triangle network for the outer cortical bone surface in both 3D reconstruction and non-porous models allowing exact replication of load and restraint cases; and (3) creation of an internal landmark point grid allowing direct comparison between 3D FE Models (FEMs). Copyright © 2012 Elsevier Ltd. All rights reserved.

Morphology and stratal geometry of the Antarctic continental shelf: Insights from models

USGS Publications Warehouse

Cooper, Alan K.; Barker, Peter F.; Brancolini, Giuliano

1997-01-01

Reconstruction of past ice-sheet fluctuations from the stratigraphy of glaciated continental shelves requires understanding of the relationships among the stratal geometry, glacial and marine sedimentary processes, and ice dynamics. We investigate the formation of the morphology and the broad stratal geometry of topsets on the Antarctic continental shelf with numerical models. Our models assume that the stratal geometry and morphology are principally the results of time-integrated effects of glacial erosion and sedimentation related to the location of the seaward edge of the grounded ice. The location of the grounding line varies with time almost randomly across the shelf. With these simple assumptions, the models can successfully mimic salient features of the morphology and the stratal geometry. The models suggest that the current shelf has gradually evolved to its present geometry by many glacial advances and retreats of the grounding line to different locations across the shelf. The locations of the grounding line do not appear to be linearly correlated with either fluctuations in the 5 l s O record (which presumably represents changes in the global ice volume) or with the global sea-level curve, suggesting that either a more complex relationship exists or local effects dominate. The models suggest that erosion of preglacial sediments is confined to the inner shelf, and erosion decreases and deposition increases toward the shelf edge. Some of the deposited glacial sediments must be derived from continental erosion. The sediments probably undergo extensive transport and reworking obliterating much of the evidence for their original depositional environment. The flexural rigidity and the tectonic subsidence of the underlying lithosphere modify the bathymetry of the shelf, but probably have little effect on the stratal geometry. Our models provide several guidelines for the interpretation of unconformities, the nature of preserved topset deposits, and the significance of progradation versus aggradation of shelf sediments.

Parameter study for child injury mitigation in near-side impacts through FE simulations.

PubMed

Andersson, Marianne; Pipkorn, Bengt; Lövsund, Per

2012-01-01

The objective of this study is to investigate the effects of crash-related car parameters on head and chest injury measures for 3- and 12-year-old children in near-side impacts. The evaluation was made using a model of a complete passenger car that was impacted laterally by a barrier. The car model was validated in 2 crash conditions: the Insurance Institute for Highway Safety (IIHS) and the US New Car Assessment Program (NCAP) side impact tests. The Small Side Impact Dummy (SID-IIs) and the human body model 3 (HBM3) (Total HUman Model for Safety [THUMS] 3-year-old) finite element models were used for the parametric investigation (HBM3 on a booster). The car parameters were as follows: vehicle mass, side impact structure stiffness, a head air bag, a thorax-pelvis air bag, and a seat belt with pretensioner. The studied dependent variables were as follows: resultant head linear acceleration, resultant head rotational acceleration, chest viscous criterion, rib deflection, and relative velocity at head impact. The chest measurements were only considered for the SID-IIs. The head air bag had the greatest effect on the head measurements for both of the occupant models. On average, it reduced the peak head linear acceleration by 54 g for the HBM3 and 78 g for the SID-IIs. The seat belt had the second greatest effect on the head measurements; the peak head linear accelerations were reduced on average by 39 g (HBM3) and 44 g (SID-IIs). The high stiffness side structure increased the SID-IIs' head acceleration, whereas it had marginal effect on the HBM3. The vehicle mass had a marginal effect on SID-IIs' head accelerations, whereas the lower vehicle mass caused 18 g higher head acceleration for HBM3 and the greatest rotational acceleration. The thorax-pelvis air bag, vehicle mass, and seat belt pretensioner affected the chest measurements the most. The presence of a thorax-pelvis air bag, high vehicle mass, and a seat belt pretensioner all reduced the chest viscous criterion (VC) and peak rib deflection in the SID-IIs. The head and thorax-pelvis air bags have the potential to reduce injury measurements for both the SID-IIs and the HBM3, provided that the air bag properties are designed to consider these occupant sizes also. The seat belt pretensioner is also effective, provided that the lateral translation of the torso is managed by other features. The importance of lateral movement management is greater the smaller the occupant is. Light vehicles require interior restraint systems of higher performance than heavy vehicles do to achieve the same level of injury measures for a given side structure. Copyright © 2012 Taylor & Francis Group, LLC

Skull Defects in Finite Element Head Models for Source Reconstruction from Magnetoencephalography Signals

PubMed Central

Lau, Stephan; Güllmar, Daniel; Flemming, Lars; Grayden, David B.; Cook, Mark J.; Wolters, Carsten H.; Haueisen, Jens

2016-01-01

Magnetoencephalography (MEG) signals are influenced by skull defects. However, there is a lack of evidence of this influence during source reconstruction. Our objectives are to characterize errors in source reconstruction from MEG signals due to ignoring skull defects and to assess the ability of an exact finite element head model to eliminate such errors. A detailed finite element model of the head of a rabbit used in a physical experiment was constructed from magnetic resonance and co-registered computer tomography imaging that differentiated nine tissue types. Sources of the MEG measurements above intact skull and above skull defects respectively were reconstructed using a finite element model with the intact skull and one incorporating the skull defects. The forward simulation of the MEG signals reproduced the experimentally observed characteristic magnitude and topography changes due to skull defects. Sources reconstructed from measured MEG signals above intact skull matched the known physical locations and orientations. Ignoring skull defects in the head model during reconstruction displaced sources under a skull defect away from that defect. Sources next to a defect were reoriented. When skull defects, with their physical conductivity, were incorporated in the head model, the location and orientation errors were mostly eliminated. The conductivity of the skull defect material non-uniformly modulated the influence on MEG signals. We propose concrete guidelines for taking into account conducting skull defects during MEG coil placement and modeling. Exact finite element head models can improve localization of brain function, specifically after surgery. PMID:27092044

Unit cell geometry of multiaxial preforms for structural composites

NASA Technical Reports Server (NTRS)

Ko, Frank; Lei, Charles; Rahman, Anisur; Du, G. W.; Cai, Yun-Jia

1993-01-01

The objective of this study is to investigate the yarn geometry of multiaxial preforms. The importance of multiaxial preforms for structural composites is well recognized by the industry but, to exploit their full potential, engineering design rules must be established. This study is a step in that direction. In this work the preform geometry for knitted and braided preforms was studied by making a range of well designed samples and studying them by photo microscopy. The structural geometry of the preforms is related to the processing parameters. Based on solid modeling and B-spline methodology a software package is developed. This computer code enables real time structural representations of complex fiber architecture based on the rule of preform manufacturing. The code has the capability of zooming and section plotting. These capabilities provide a powerful means to study the effect of processing variables on the preform geometry. the code also can be extended to an auto mesh generator for downstream structural analysis using finite element method. This report is organized into six sections. In the first section the scope and background of this work is elaborated. In section two the unit cell geometries of braided and multi-axial warp knitted preforms is discussed. The theoretical frame work of yarn path modeling and solid modeling is presented in section three. The thin section microscopy carried out to observe the structural geometry of the preforms is the subject in section four. The structural geometry is related to the processing parameters in section five. Section six documents the implementation of the modeling techniques into the computer code MP-CAD. A user manual for the software is also presented here. The source codes and published papers are listed in the Appendices.

On the Influence of Material Parameters in a Complex Material Model for Powder Compaction

NASA Astrophysics Data System (ADS)

Staf, Hjalmar; Lindskog, Per; Andersson, Daniel C.; Larsson, Per-Lennart

2016-10-01

Parameters in a complex material model for powder compaction, based on a continuum mechanics approach, are evaluated using real insert geometries. The parameter sensitivity with respect to density and stress after compaction, pertinent to a wide range of geometries, is studied in order to investigate completeness and limitations of the material model. Finite element simulations with varied material parameters are used to build surrogate models for the sensitivity study. The conclusion from this analysis is that a simplification of the material model is relevant, especially for simple insert geometries. Parameters linked to anisotropy and the plastic strain evolution angle have a small impact on the final result.

Experimental investigation and numerical simulation of 3He gas diffusion in simple geometries: implications for analytical models of 3He MR lung morphometry.

PubMed

Parra-Robles, J; Ajraoui, S; Deppe, M H; Parnell, S R; Wild, J M

2010-06-01

Models of lung acinar geometry have been proposed to analytically describe the diffusion of (3)He in the lung (as measured with pulsed gradient spin echo (PGSE) methods) as a possible means of characterizing lung microstructure from measurement of the (3)He ADC. In this work, major limitations in these analytical models are highlighted in simple diffusion weighted experiments with (3)He in cylindrical models of known geometry. The findings are substantiated with numerical simulations based on the same geometry using finite difference representation of the Bloch-Torrey equation. The validity of the existing "cylinder model" is discussed in terms of the physical diffusion regimes experienced and the basic reliance of the cylinder model and other ADC-based approaches on a Gaussian diffusion behaviour is highlighted. The results presented here demonstrate that physical assumptions of the cylinder model are not valid for large diffusion gradient strengths (above approximately 15 mT/m), which are commonly used for (3)He ADC measurements in human lungs. (c) 2010 Elsevier Inc. All rights reserved.

Microbial mutualism at a distance: The role of geometry in diffusive exchanges

NASA Astrophysics Data System (ADS)

Peaudecerf, François J.; Bunbury, Freddy; Bhardwaj, Vaibhav; Bees, Martin A.; Smith, Alison G.; Goldstein, Raymond E.; Croze, Ottavio A.

2018-02-01

The exchange of diffusive metabolites is known to control the spatial patterns formed by microbial populations, as revealed by recent studies in the laboratory. However, the matrices used, such as agarose pads, lack the structured geometry of many natural microbial habitats, including in the soil or on the surfaces of plants or animals. Here we address the important question of how such geometry may control diffusive exchanges and microbial interaction. We model mathematically mutualistic interactions within a minimal unit of structure: two growing reservoirs linked by a diffusive channel through which metabolites are exchanged. The model is applied to study a synthetic mutualism, experimentally parametrized on a model algal-bacterial co-culture. Analytical and numerical solutions of the model predict conditions for the successful establishment of remote mutualisms, and how this depends, often counterintuitively, on diffusion geometry. We connect our findings to understanding complex behavior in synthetic and naturally occurring microbial communities.

Volume Diffusion Growth Kinetics and Step Geometry in Crystal Growth

NASA Technical Reports Server (NTRS)

Mazuruk, Konstantin; Ramachandran, Narayanan

1998-01-01

The role of step geometry in two-dimensional stationary volume diff4sion process used in crystal growth kinetics models is investigated. Three different interface shapes: a) a planar interface, b) an equidistant hemispherical bumps train tAx interface, and c) a train of right angled steps, are used in this comparative study. The ratio of the super-saturation to the diffusive flux at the step position is used as a control parameter. The value of this parameter can vary as much as 50% for different geometries. An approximate analytical formula is derived for the right angled steps geometry. In addition to the kinetic models, this formula can be utilized in macrostep growth models. Finally, numerical modeling of the diffusive and convective transport for equidistant steps is conducted. In particular, the role of fluid flow resulting from the advancement of steps and its contribution to the transport of species to the steps is investigated.

Methods for Expanding Rotary Wing Aircraft Health and Usage Monitoring Systems to the Rotating Frame through Real-time Rotor Blade Kinematics Estimation

NASA Astrophysics Data System (ADS)

Allred, Charles Jefferson

Since the advent of Health and Usage Monitoring Systems (HUMS) in the early 1990's, there has been a steady decrease in the number of component failure related helicopter accidents. Additionally, measurable cost benefits due to improved maintenance practices based on HUMS data has led to a desire to expand HUMS from its traditional area of helicopter drive train monitoring. One of the areas of greatest interest for this expansion of HUMS is monitoring of the helicopter rotor head loads. Studies of rotor head load and blade motions have primarily focused on wind tunnel testing with technology which would not be applicable for production helicopter HUMS deployment, or measuring bending along the blade, rather than where it is attached to the rotor head and the location through which all the helicopter loads pass. This dissertation details research into finding methods for real time methods of estimating rotor blade motion which could be applied across helicopter fleets as an expansion of current HUMS technology. First, there is a brief exploration of supporting technologies which will be crucial in enabling the expansion of HUMS from the fuselage of helicopters to the rotor head: wireless data transmission and energy harvesting. A brief overview of the commercially available low power wireless technology selected for this research is presented. The development of a relatively high-powered energy harvester specific to the motion of helicopter rotor blades is presented and two different prototypes of the device are shown. Following the overview of supporting technologies, two novel methods of monitoring rotor blade motion in real time are developed. The first method employs linear displacement sensors embedded in the elastomer layers of a high-capacity laminate bearing of the type commonly used in fully articulated rotors throughout the helicopter industry. The configuration of these displacement sensors allows modeling of the sensing system as a robotic parallel mechanism, similar to a Stewart Platform. A calibration method for this device is developed and the improved orientation estimation results are shown. The second method is not specific to the fully articulated rotor head mounting geometry of the first method. Rather, it utilizes micro-electromechanical (MEMS) accelerometers and gyroscopes configured to measure the centrifugal acceleration and rotation rate induced through rotor head rotation differentially. By measuring these quantities differentially, other accelerations from the fuselage reference frame are removed from the measurement, resulting in acceleration and rate quantities that are impacted only by the angle of the sensors relative to the plane of rotation. By mounting these sensors strategically and symmetrically about the rotor blade root center of rotation, the orientation of the rotor blade can be estimated in real time.

On supermatrix models, Poisson geometry, and noncommutative supersymmetric gauge theories

DOE Office of Scientific and Technical Information (OSTI.GOV)

Klimčík, Ctirad

2015-12-15

We construct a new supermatrix model which represents a manifestly supersymmetric noncommutative regularisation of the UOSp(2|1) supersymmetric Schwinger model on the supersphere. Our construction is much simpler than those already existing in the literature and it was found by using Poisson geometry in a substantial way.

A 3D Geometry Model Search Engine to Support Learning

ERIC Educational Resources Information Center

Tam, Gary K. L.; Lau, Rynson W. H.; Zhao, Jianmin

2009-01-01

Due to the popularity of 3D graphics in animation and games, usage of 3D geometry deformable models increases dramatically. Despite their growing importance, these models are difficult and time consuming to build. A distance learning system for the construction of these models could greatly facilitate students to learn and practice at different…

Implementation of Structured Inquiry Based Model Learning toward Students' Understanding of Geometry

ERIC Educational Resources Information Center

Salim, Kalbin; Tiawa, Dayang Hjh

2015-01-01

The purpose of this study is implementation of a structured inquiry learning model in instruction of geometry. The model used is a model with a quasi-experimental study amounted to two classes of samples selected from the population of the ten classes with cluster random sampling technique. Data collection tool consists of a test item…

Geometry-dependent atomic multipole models for the water molecule.

PubMed

Loboda, O; Millot, C

2017-10-28

Models of atomic electric multipoles for the water molecule have been optimized in order to reproduce the electric potential around the molecule computed by ab initio calculations at the coupled cluster level of theory with up to noniterative triple excitations in an augmented triple-zeta quality basis set. Different models of increasing complexity, from atomic charges up to models containing atomic charges, dipoles, and quadrupoles, have been obtained. The geometry dependence of these atomic multipole models has been investigated by changing bond lengths and HOH angle to generate 125 molecular structures (reduced to 75 symmetry-unique ones). For several models, the atomic multipole components have been fitted as a function of the geometry by a Taylor series of fourth order in monomer coordinate displacements.

Geometry-dependent atomic multipole models for the water molecule

NASA Astrophysics Data System (ADS)

Loboda, O.; Millot, C.

2017-10-01

Models of atomic electric multipoles for the water molecule have been optimized in order to reproduce the electric potential around the molecule computed by ab initio calculations at the coupled cluster level of theory with up to noniterative triple excitations in an augmented triple-zeta quality basis set. Different models of increasing complexity, from atomic charges up to models containing atomic charges, dipoles, and quadrupoles, have been obtained. The geometry dependence of these atomic multipole models has been investigated by changing bond lengths and HOH angle to generate 125 molecular structures (reduced to 75 symmetry-unique ones). For several models, the atomic multipole components have been fitted as a function of the geometry by a Taylor series of fourth order in monomer coordinate displacements.

S-values calculated from a tomographic head/brain model for brain imaging

NASA Astrophysics Data System (ADS)

Chao, Tsi-chian; Xu, X. George

2004-11-01

A tomographic head/brain model was developed from the Visible Human images and used to calculate S-values for brain imaging procedures. This model contains 15 segmented sub-regions including caudate nucleus, cerebellum, cerebral cortex, cerebral white matter, corpus callosum, eyes, lateral ventricles, lenses, lentiform nucleus, optic chiasma, optic nerve, pons and middle cerebellar peduncle, skull CSF, thalamus and thyroid. S-values for C-11, O-15, F-18, Tc-99m and I-123 have been calculated using this model and a Monte Carlo code, EGS4. Comparison of the calculated S-values with those calculated from the MIRD (1999) stylized head/brain model shows significant differences. In many cases, the stylized head/brain model resulted in smaller S-values (as much as 88%), suggesting that the doses to a specific patient similar to the Visible Man could have been underestimated using the existing clinical dosimetry.

A new osteonecrosis animal model of the femoral head induced by microwave heating and repaired with tissue engineered bone

PubMed Central

Han, Rui; Geng, Chengkui; Wang, Yongnian; Wei, Lei

2008-01-01

The objective of this research was to induce a new animal model of osteonecrosis of the femoral head (ONFH) by microwave heating and then repair with tissue engineered bone. The bilateral femoral heads of 84 rabbits were heated by microwave at various temperatures. Tissue engineered bone was used to repair the osteonecrosis of femoral heads induced by microwave heating. The roentgenographic and histological examinations were used to evaluate the results. The femoral heads heated at 55°C for ten minutes showed low density and cystic changes in X-ray photographs, osteonecrosis and repair occurred simultaneously in histology at four and eight weeks, and 69% femoral heads collapsed at 12 weeks. The ability of tissue engineered bone to repair the osteonecrosis was close to that of cancellous bone autograft. The new animal model of ONFH could be induced by microwave heating, and the tissue engineering technique will provide an effective treatment. PMID:18956184

The role of passive avian head stabilization in flapping flight

PubMed Central

Pete, Ashley E.; Kress, Daniel; Dimitrov, Marina A.; Lentink, David

2015-01-01

Birds improve vision by stabilizing head position relative to their surroundings, while their body is forced up and down during flapping flight. Stabilization is facilitated by compensatory motion of the sophisticated avian head–neck system. While relative head motion has been studied in stationary and walking birds, little is known about how birds accomplish head stabilization during flapping flight. To unravel this, we approximate the avian neck with a linear mass–spring–damper system for vertical displacements, analogous to proven head stabilization models for walking humans. We corroborate the model's dimensionless natural frequency and damping ratios from high-speed video recordings of whooper swans (Cygnus cygnus) flying over a lake. The data show that flap-induced body oscillations can be passively attenuated through the neck. We find that the passive model robustly attenuates large body oscillations, even in response to head mass and gust perturbations. Our proof of principle shows that bird-inspired drones with flapping wings could record better images with a swan-inspired passive camera suspension. PMID:26311316

A new method to include the gravitational forces in a finite element model of the scoliotic spine.

PubMed

Clin, Julien; Aubin, Carl-Éric; Lalonde, Nadine; Parent, Stefan; Labelle, Hubert

2011-08-01

The distribution of stresses in the scoliotic spine is still not well known despite its biomechanical importance in the pathomechanisms and treatment of scoliosis. Gravitational forces are one of the sources of these stresses. Existing finite element models (FEMs), when considering gravity, applied these forces on a geometry acquired from radiographs while the patient was already subjected to gravity, which resulted in a deformed spine different from the actual one. A new method to include gravitational forces on a scoliotic trunk FEM and compute the stresses in the spine was consequently developed. The 3D geometry of three scoliotic patients was acquired using a multi-view X-ray 3D reconstruction technique and surface topography. The FEM of the patients' trunk was created using this geometry. A simulation process was developed to apply the gravitational forces at the centers of gravity of each vertebra level. First the "zero-gravity" geometry was determined by applying adequate upwards forces on the initial geometry. The stresses were reset to zero and then the gravity forces were applied to compute the geometry of the spine subjected to gravity. An optimization process was necessary to find the appropriate zero-gravity and gravity geometries. The design variables were the forces applied on the model to find the zero-gravity geometry. After optimization the difference between the vertebral positions acquired from radiographs and the vertebral positions simulated with the model was inferior to 3 mm. The forces and compressive stresses in the scoliotic spine were then computed. There was an asymmetrical load in the coronal plane, particularly, at the apices of the scoliotic curves. Difference of mean compressive stresses between concavity and convexity of the scoliotic curves ranged between 0.1 and 0.2 MPa. In conclusion, a realistic way of integrating gravity in a scoliotic trunk FEM was developed and stresses due to gravity were explicitly computed. This is a valuable improvement for further biomechanical modeling studies of scoliosis.

Computational Investigation of a Boundary-Layer Ingesting Propulsion System for the Common Research Model

NASA Technical Reports Server (NTRS)

Blumenthal, Brennan T.; Elmiligui, Alaa; Geiselhart, Karl A.; Campbell, Richard L.; Maughmer, Mark D.; Schmitz, Sven

2016-01-01

The present paper examines potential propulsive and aerodynamic benefits of integrating a Boundary-Layer Ingestion (BLI) propulsion system into a typical commercial aircraft using the Common Research Model (CRM) geometry and the NASA Tetrahedral Unstructured Software System (TetrUSS). The Numerical Propulsion System Simulation (NPSS) environment is used to generate engine conditions for CFD analysis. Improvements to the BLI geometry are made using the Constrained Direct Iterative Surface Curvature (CDISC) design method. Previous studies have shown reductions of up to 25% in terms of propulsive power required for cruise for other axisymmetric geometries using the BLI concept. An analysis of engine power requirements, drag, and lift coefficients using the baseline and BLI geometries coupled with the NPSS model are shown. Potential benefits of the BLI system relating to cruise propulsive power are quantified using a power balance method, and a comparison to the baseline case is made. Iterations of the BLI geometric design are shown and any improvements between subsequent BLI designs presented. Simulations are conducted for a cruise flight condition of Mach 0.85 at an altitude of 38,500 feet and an angle of attack of 2 deg for all geometries. A comparison between available wind tunnel data, previous computational results, and the original CRM model is presented for model verification purposes along with full results for BLI power savings. Results indicate a 14.4% reduction in engine power requirements at cruise for the BLI configuration over the baseline geometry. Minor shaping of the aft portion of the fuselage using CDISC has been shown to increase the benefit from Boundary-Layer Ingestion further, resulting in a 15.6% reduction in power requirements for cruise as well as a drag reduction of eighteen counts over the baseline geometry.