Detonation front curvatures and detonation rates
NASA Astrophysics Data System (ADS)
Lauderbach, Lisa M.; Lorenz, K. Thomas; Lee, Edward L.; Souers, P. Clark
2017-01-01
Many detonation front curvatures are reviewed. Most are of the Shock Dynamics type, which are described as a combination of quadratic and 8th power-of-the-radius curves. The integrated fraction of the 8th power curve is taken as a measure of curvature, which we are able to relate to the logarithm of the detonation rate. This provides a means of estimating the rates of some unknown explosives from the curvature. Using the edge lag divided by the radius is an even better way. A second group of curvatures are almost or purely quadratic. This is probably not associated with density gradients but may be caused by low sound speeds. A final group of "sombreros" show curvy fronts for ideal explosives, which appear to be caused by density gradients.
Hill, L.G.; Bdzil, J.B.; Aslam, T.D.
1998-12-31
Detonation velocity and wave shape are measured for PBX 9502 (95 wt.% TATB, 5 wt.% Kel-F 800) rate sticks at the temperatures {minus}55, 25, and 75 C. At each temperature three different diameters were fired: 50 mm, 18 mm, and 8, 10, and 12 mm respectively for the hot, ambient, and cold sticks. The measured wave shapes are fit with an analytic form and the fitting parameters are tabulated along with thermal expansion and diameter effect data. The simplest detonation shock dynamics (DSD) model assumes a unique calibration function relating the local normal wave speed D{sub n} to the local total curvature {kappa}. The data confirm this notion for sufficiently small curvature, but at large curvature the curves for different charge diameters diverge. Global optimization is used to determine a best single D{sub n}-{kappa} function at each initial temperature T{sub 0}. From these curves a D{sub n}({kappa},T{sub 0}) calibration surface is generated that allows computation of problems with temperature gradients.
Theory for the curvature dependence of delta front progradation
NASA Astrophysics Data System (ADS)
Ke, Wun-Tao; Capart, Hervé
2015-12-01
When Gilbert-type deltas respond to uneven sediment supply or advance over irregular basin bathymetry, they develop curved, creased fronts prograding at speeds that vary with location along the shoreline. Relations governing the progradation rate, however, have so far been proposed only for simple special cases. In this paper, we exploit the special properties of solutions to the eikonal equation to derive a general progradation relation, applicable to delta fronts of finite angle of repose and arbitrary shoreline planform. In these circumstances, the theory explicitly relates the progradation rate to the local shoreline curvature. We illustrate the resulting morphodynamics with numerical and analytical solutions for a sinuous delta front. The proposed relation can be used to model deltaic evolution or deduce spanwise distributions of sediment supply rates from observations of foreset evolution.
Effects of curvature and compressibility on the stability of thermal fronts
Ibanez S, Miguel H.; Bessega L, Maria C.; Shchekinov, Yuri
2006-06-15
The stability of subsonic thermal fronts against corrugation is analyzed and an exact dispersion relation is obtained taking into account the effects of the curvature of the distorted front as well as the compressibility of the gas. At a certain value of the Mach number ahead of the thermal front, unstable rates show a maximum; these rates drop to zero when a Chapman-Jouguet regime is established behind heat fronts. It is shown that curvature effects tend to stabilize conductive heat fronts propagating in a compressible gas.
Influence of the bonding front propagation on the wafer stack curvature
Navarro, E.; Bréchet, Y.; Barthelemy, A.; Radu, I.; Pardoen, T.; Raskin, J.-P.
2014-08-11
The influence of the dynamics of the direct wafer bonding process on the curvature of the final wafer stack is investigated. An analytical model for the final curvature of the bonded wafers is developed, as a function of the different load components acting during the bonding front propagation, using thin plate theory and considering a strain discontinuity locked at the bonding interface. Experimental profiles are measured for different bonding conditions and wafer thicknesses. A very good agreement with the model prediction is obtained and the influence of the thin air layer trapped in-between the two wafers is demonstrated. The proposed model contributes to further improvement of the bonding process, in particular, for the stacking of layers of electronic devices, which requires a high accuracy of wafer-to-wafer alignment and a very low distortion level.
Instant curvature measurement for microcantilever sensors
Jeon, Sangmin; Thundat, Thomas
2004-08-09
A multiple-point deflection technique has been developed for the instant measurement of microcantilever curvature. Eight light-emitting diodes are focused on various positions of a gold-coated silicon cantilever through optical fibers, and temperature change or chemical adsorption induces cantilever bending. The deflection at each point on the cantilever is measured with subnanometer precision by a position-sensitive detector, and thus the curvature of the cantilever is obtained.
Fronts propagating with curvature dependent speed: Algorithms based on Hamilton-Jacobi formulations
NASA Technical Reports Server (NTRS)
Osher, Stanley; Sethian, James A.
1987-01-01
New numerical algorithms are devised (PSC algorithms) for following fronts propagating with curvature-dependent speed. The speed may be an arbitrary function of curvature, and the front can also be passively advected by an underlying flow. These algorithms approximate the equations of motion, which resemble Hamilton-Jacobi equations with parabolic right-hand-sides, by using techniques from the hyperbolic conservation laws. Non-oscillatory schemes of various orders of accuracy are used to solve the equations, providing methods that accurately capture the formation of sharp gradients and cusps in the moving fronts. The algorithms handle topological merging and breaking naturally, work in any number of space dimensions, and do not require that the moving surface be written as a function. The methods can be used also for more general Hamilton-Jacobi-type problems. The algorithms are demonstrated by computing the solution to a variety of surface motion problems.
Tube curvature measuring probe and method
Sokol, George J.
1990-01-01
The present invention is directed to a probe and method for measuring the radius of curvature of a bend in a section of tubing. The probe includes a member with a pair of guide means, one located at each end of the member. A strain gauge is operatively connected to the member for detecting bending stress exrted on the member as the probe is drawn through and in engagement with the inner surface of a section of tubing having a bend. The method of the present invention includes steps utilizing a probe, like the aforementioned probe, which can be made to detect bends only in a single plane when having a fixed orientation relative the section of tubing to determine the maximum radius of curvature of the bend.
Curvature sensor for ocular wavefront measurement.
Díaz-Doutón, Fernando; Pujol, Jaume; Arjona, Montserrat; Luque, Sergio O
2006-08-01
We describe a new wavefront sensor for ocular aberration determination, based on the curvature sensing principle, which adapts the classical system used in astronomy for the living eye's measurements. The actual experimental setup is presented and designed following a process guided by computer simulations to adjust the design parameters for optimal performance. We present results for artificial and real young eyes, compared with the Hartmann-Shack estimations. Both methods show a similar performance for these cases. This system will allow for the measurement of higher order aberrations than the currently used wavefront sensors in situations in which they are supposed to be significant, such as postsurgery eyes.
Local curvature measurements of a lean, partially premixed swirl-stabilised flame
NASA Astrophysics Data System (ADS)
Bayley, Alan E.; Hardalupas, Yannis; Taylor, Alex M. K. P.
2012-04-01
A swirl-stabilised, lean, partially premixed combustor operating at atmospheric conditions has been used to investigate the local curvature distributions in lifted, stable and thermoacoustically oscillating CH4-air partially premixed flames for bulk cold-flow Reynolds numbers of 15,000 and 23,000. Single-shot OH planar laser-induced fluorescence has been used to capture instantaneous images of these three different flame types. Use of binary thresholding to identify the reactant and product regions in the OH planar laser-induced fluorescence images, in order to extract accurate flame-front locations, is shown to be unsatisfactory for the examined flames. The Canny-Deriche edge detection filter has also been examined and is seen to still leave an unacceptable quantity of artificial flame-fronts. A novel approach has been developed for image analysis where a combination of a non-linear diffusion filter, Sobel gradient and threshold-based curve elimination routines have been used to extract traces of the flame-front to obtain local curvature distributions. A visual comparison of the effectiveness of flame-front identification is made between the novel approach, the threshold binarisation filter and the Canny-Deriche filter. The novel approach appears to most accurately identify the flame-fronts. Example histograms of the curvature for six flame conditions and of the total image area are presented and are found to have a broader range of local flame curvatures for increasing bulk Reynolds numbers. Significantly positive values of mean curvature and marginally positive values of skewness of the histogram have been measured for one lifted flame case, but this is generally accounted for by the effect of flame brush curvature. The mean local flame-front curvature reduces with increasing axial distance from the burner exit plane for all flame types. These changes are more pronounced in the lifted flames but are marginal for the thermoacoustically oscillating flames. It is
Measuring Intrinsic Curvature of Space with Electromagnetism
NASA Astrophysics Data System (ADS)
Mabin, Mason; Becker, Maria; Batelaan, Herman
2016-10-01
The concept of curved space is not readily observable in everyday life. The educational movie "Sphereland" attempts to illuminate the idea. The main character, a hexagon, has to go to great lengths to prove that her world is in fact curved. We present an experiment that demonstrates a new way to determine if a two-dimensional surface, the 2-sphere, is curved. The behavior of an electric field, placed on a spherical surface, is shown to be related to the intrinsic Gaussian curvature. This approach allows students to gain some understanding of Einstein's theory of general relativity, which relates the curvature of spacetime to the presence of mass and energy. Additionally, an opportunity is provided to investigate the dimensionality of Gauss's law.
Measurement of the gravity-field curvature by atom interferometry.
Rosi, G; Cacciapuoti, L; Sorrentino, F; Menchetti, M; Prevedelli, M; Tino, G M
2015-01-09
We present the first direct measurement of the gravity-field curvature based on three conjugated atom interferometers. Three atomic clouds launched in the vertical direction are simultaneously interrogated by the same atom interferometry sequence and used to probe the gravity field at three equally spaced positions. The vertical component of the gravity-field curvature generated by nearby source masses is measured from the difference between adjacent gravity gradient values. Curvature measurements are of interest in geodesy studies and for the validation of gravitational models of the surrounding environment. The possibility of using such a scheme for a new determination of the Newtonian constant of gravity is also discussed.
Clinical workflow for spinal curvature measurement with portable ultrasound
NASA Astrophysics Data System (ADS)
Tabanfar, Reza; Yan, Christina; Kempston, Michael; Borschneck, Daniel; Ungi, Tamas; Fichtinger, Gabor
2016-03-01
PURPOSE: Spinal curvature monitoring is essential in making treatment decisions in scoliosis. Monitoring entails radiographic examinations, however repeated ionizing radiation exposure has been shown to increase cancer risk. Ultrasound does not emit ionizing radiation and is safer for spinal curvature monitoring. We investigated a clinical sonography protocol and challenges associated with position-tracked ultrasound in spinal curvature measurement in scoliosis. METHODS: Transverse processes were landmarked along each vertebra using tracked ultrasound snapshots. The transverse process angle was used to determine the orientation of each vertebra. We tested our methodology on five patients in a local pediatric scoliosis clinic, comparing ultrasound to radiographic curvature measurements. RESULTS: Despite strong correlation between radiographic and ultrasound curvature angles in phantom studies, we encountered new challenges in the clinical setting. Our main challenge was differentiating transverse processes from ribs and other structures during landmarking. We observed up to 13° angle variability for a single vertebra and a 9.85° +/- 10.81° difference between ultrasound and radiographic Cobb angles for thoracic curvatures. Additionally, we were unable to visualize anatomical landmarks in the lumbar region where soft tissue depth was 25-35mm. In volunteers with large Cobb angles (greater than 40° thoracic and 60° lumbar), we observed spinal protrusions resulting in incomplete probe-skin contact and partial ultrasound images not suitable for landmarking. CONCLUSION: Spinal curvature measurement using tracked ultrasound is viable on phantom spine models. In the clinic, new challenges were encountered which must be resolved before a universal sonography protocol can be developed.
NASA Astrophysics Data System (ADS)
Ma, Shuang; Yi, Shengzhen; Chen, Shenghao; Wang, Zhanshan
2014-11-01
Monochromatic energy multilayer Kirkpatrick-Baez microscope is one of key diagnostic tools for researches on inertial confinement fusion. It is composed by two orthogonal concave spherical mirrors with small curvature and aperture, and produce the image of an object by collecting X-rays in each orthogonal direction, independently. Accurate measurement of radius of curvature of concave spherical mirrors is very important to achieve its design optical properties including imaging quality, optical throughput and energy resolution. However, it is difficult to measure the radius of curvature of spherical optical surfaces with small curvature and aperture by conventional methods, for the produced reflective intensity of glass is too low to correctly test. In this paper, we propose an improved measuring method of optical profiler to accomplish accurate measurement of radius of curvature of spherical optical surfaces with small curvature and aperture used in the monochromatic energy multilayer Kirkpatrick-Baez microscope. Firstly, we use a standard super-smooth optical flat to calibrate reference mirror before each experiment. Following, deviation of central position between measurement area and interference pattern is corrected by the theory of Newton's rings, and the zero-order fringe position is derived from the principle of interference in which surface roughness has minimum values in the position of zero light path difference. Measured results by optical profiler show the low relative errors and high repeatability. Eventually, an imaging experiment of monochromatic energy multilayer Kirkpatrick-Baez microscope determines the measurement accuracy of radius of curvature.
Direct and alignment-insensitive measurement of cantilever curvature
Hermans, Rodolfo I.; Aeppli, Gabriel; Bailey, Joe M.
2013-07-15
We analytically derive and experimentally demonstrate a method for the simultaneous measurement of deflection for large arrays of cantilevers. The Fresnel diffraction patterns of a cantilever independently reveal tilt, curvature, cubic, and higher order bending of the cantilever. It provides a calibrated absolute measurement of the polynomial coefficients describing the cantilever shape, without careful alignment and could be applied to several cantilevers simultaneously with no added complexity. We show that the method is easily implemented, works in both liquid media and in air, for a broad range of displacements and is especially suited to the requirements for multi-marker biosensors.
Characterizing Suspension Plasma Spray Coating Formation Dynamics through Curvature Measurements
NASA Astrophysics Data System (ADS)
Chidambaram Seshadri, Ramachandran; Dwivedi, Gopal; Viswanathan, Vaishak; Sampath, Sanjay
2016-12-01
Suspension plasma spraying (SPS) enables the production of variety of microstructures with unique mechanical and thermal properties. In SPS, a liquid carrier (ethanol/water) is used to transport the sub-micrometric feedstock into the plasma jet. Considering complex deposition dynamics of SPS technique, there is a need to better understand the relationships among spray conditions, ensuing particle behavior, deposition stress evolution and resultant properties. In this study, submicron yttria-stabilized zirconia particles suspended in ethanol were sprayed using a cascaded arc plasma torch. The stresses generated during the deposition of the layers (termed evolving stress) were monitored via the change in curvature of the substrate measured using an in situ measurement apparatus. Depending on the deposition conditions, coating microstructures ranged from feathery porous to dense/cracked deposits. The evolving stresses and modulus were correlated with the observed microstructures and visualized via process maps. Post-deposition bi-layer curvature measurement via low temperature thermal cycling was carried out to quantify the thermo-elastic response of different coatings. Lastly, preliminary data on furnace cycle durability of different coating microstructures were evaluated. This integrated study involving in situ diagnostics and ex situ characterization along with process maps provides a framework to describe coating formation mechanisms, process parametrics and microstructure description.
Residual Stress Determination from a Laser-Based Curvature Measurement
Swank, William David; Gavalya, Rick Allen; Wright, Julie Knibloe; Wright, Richard Neil
2000-05-01
Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and that the spinel coating produces a larger CTE mismatch stress than quench stress.
Residual stress determination from a laser-based curvature measurement
W. D. Swank; R. A. Gavalya; J. K. Wright; R. N. Wright
2000-05-08
Thermally sprayed coating characteristics and mechanical properties are in part a result of the residual stress developed during the fabrication process. The total stress state in a coating/substrate is comprised of the quench stress and the coefficient of thermal expansion (CTE) mismatch stress. The quench stress is developed when molten particles impact the substrate and rapidly cool and solidify. The CTE mismatch stress results from a large difference in the thermal expansion coefficients of the coating and substrate material. It comes into effect when the substrate/coating combination cools from the equilibrated deposit temperature to room temperature. This paper describes a laser-based technique for measuring the curvature of a coated substrate and the analysis required to determine residual stress from curvature measurements. Quench stresses were determined by heating the specimen back to the deposit temperature thus removing the CTE mismatch stress. By subtracting the quench stress from the total residual stress at room temperature, the CTE mismatch stress was estimated. Residual stress measurements for thick (>1mm) spinel coatings with a Ni-Al bond coat on 304 stainless steel substrates were made. It was determined that a significant portion of the residual stress results from the quenching stress of the bond coat and that the spinel coating produces a larger CTE mismatch stress than quench stress.
A novel setup for wafer curvature measurement at very high heating rates
NASA Astrophysics Data System (ADS)
Islam, T.; Zechner, J.; Bernardoni, M.; Nelhiebel, M.; Pippan, R.
2017-02-01
The curvature evolution of a thin film layer stack containing a top Al layer is measured during temperature cycles with very high heating rates. The temperature cycles are generated by means of programmable electrical power pulses applied to miniaturized polysilicon heater systems embedded inside a semiconductor chip and the curvature is measured by a fast wafer curvature measurement setup. Fast temperature cycles with heating duration of 100 ms are created to heat the specimen up to 270 °C providing an average heating rate of 2500 K/s. As a second approach, curvature measurement utilizing laser scanning Doppler vibrometry is also demonstrated which verifies the results obtained from the fast wafer curvature measurement setup. Film stresses calculated from the measured curvature values compare well to literature results, indicating that the new method can be used to measure curvature during fast temperature cycling.
An Improved Method to Measure the Cosmic Curvature
NASA Astrophysics Data System (ADS)
Wei, Jun-Jie; Wu, Xue-Feng
2017-04-01
In this paper, we propose an improved model-independent method to constrain the cosmic curvature by combining the most recent Hubble parameter H(z) and supernovae Ia (SNe Ia) data. Based on the H(z) data, we first use the model-independent smoothing technique, Gaussian processes, to construct a distance modulus μ H (z), which is susceptible to the cosmic curvature parameter Ω k . In contrary to previous studies, the light-curve-fitting parameters, which account for the distance estimation of SN (μ SN(z)), are set free to investigate whether Ω k has a dependence on them. By comparing μ H (z) to μ SN(z), we put limits on Ω k . Our results confirm that Ω k is independent of the SN light-curve parameters. Moreover, we show that the measured Ω k is in good agreement with zero cosmic curvature, implying that there is no significant deviation from a flat universe at the current observational data level. We also test the influence of different H(z) samples and different Hubble constant H 0 values, finding that different H(z) samples do not have a significant impact on the constraints. However, different H 0 priors can affect the constraints of Ω k to some degree. The prior of H 0 = 73.24 ± 1.74 km s‑1 Mpc‑1 gives a value of Ω k , a little bit above the 1σ confidence level away from 0, but H 0 = 69.6 ± 0.7 km s‑1 Mpc‑1 gives it below 1σ.
Camera-based curvature measurement of a large incandescent object
NASA Astrophysics Data System (ADS)
Ollikkala, Arttu V. H.; Kananen, Timo P.; Mäkynen, Anssi J.; Holappa, Markus
2013-04-01
The goal of this work was to implement a low-cost machine vision system to help the roller operator to estimate the amount of strip camber during the rolling process. The machine vision system composing of a single camera, a standard PC-computer and a LabVIEW written program using straightforward image analysis determines the magnitude and direction of camber and presents the results both in numerical and graphical form on the computer screen. The system was calibrated with LED set-up which was also used to validate the accuracy of the system by mimicking the strip curvatures. The validation showed that the maximum difference between the true and measured values was less than +/-4 mm (k=0.95) within the 22 meter long test pattern.
Coherent gradient sensing method and system for measuring surface curvature
NASA Technical Reports Server (NTRS)
Rosakis, Ares J. (Inventor); Singh, Ramen P. (Inventor); Kolawa, Elizabeth (Inventor); Moore, Jr., Nicholas R. (Inventor)
2000-01-01
A system and method for determining a curvature of a specularly reflective surface based on optical interference. Two optical gratings are used to produce a spatial displacement in an interference field of two different diffraction components produced by one grating from different diffraction components produced by another grating. Thus, the curvature of the surface can be determined.
Radius of Curvature Measurements: An Independent Look at Accuracy Using Novel Optical Metrology
NASA Technical Reports Server (NTRS)
Taylor, Bryon; Kahan, Mark; Russell, Kevin (Technical Monitor)
2002-01-01
The AMSD (Advanced Mirror System Demonstrator) program mirror specifications include the ability to manufacture the mirror to a radius of curvature of 10 m +/- 1 mm and to control its radius at 30K to the same specification. Therefore, it is necessary for the Government Team to be able to measure mirror radius of curvature to an accuracy of better than 0.5 mm. This presentation discusses a novel optical metrology system for measuring radius of curvature.
Measurement of spinal sagittal curvatures using the laser triangulation method.
Celan, Dusan; Palfy, Miroslav; Bracun, Drago; Turk, Zmago; Mozina, Janez; Komadina, Radko
2012-03-01
The purpose of the first part of the study was to establish the variability of repeated measurements in different measuring conditions. In the second part, we performed in a large number of patients, a measurement of thoracic kyphosis and lumbar lordosis and compared them to age, gender, and level of nourishment. In the first part, measurements were performed on a plastic model of the back of a patient with a rigid and a normal spine. In the second part, 250 patients participated in the study (126 men and 124 women). For measuring spinal curvatures we used an apparatus for laser triangulation constructed at the Faculty of Mechanical Engineering, University of Ljubljana. A comparison of 30 repeated measurements was shown as the average value +/- 2 SD which included 95% of the results. Thirty repeated readings of one 3D measurement: thoracic kyphosis 41.2 degrees +/- 0.6 degrees, lumbar lordosis 4.4 degrees +/- 1.2 degrees; 30 measurements on a plastic model: thoracic kyphosis 36.8 degrees +/- 1.2 degrees, lumbar lordosis 30.9 degrees +/- 2.0 degrees; 30 measurements on a patient with a rigid spine: thoracic kyphosis 41.5 degrees +/- 2.4 degrees, lumbar lordosis 4.0 degrees +/- 1.8 degrees; 30 measurements on a patient with a normal spine: thoracic kyphosis 48.8 degrees +/- 7.4 degrees, lumbar lordosis 21.1 degrees +/- 4.4 degrees. The average size of thoracic kyphosis in 250 patients was 46.8 degrees (SD 10.1 degrees) and lumbar lordosis 31.7 degrees (SD 12.5 degrees). The angle size was statistically significantly correlated to gender (increased thoracic kyphosis and lumbar lordosis in women) and body mass index (increased thoracic kyphosis and lumbar lordosis in more nourished patients). Age was not significantly correlated to the observed angles. During measurements of the spinal angles it was important to pay attention to relaxation and the patient's position as well as to perform more measurements providing the average value. The age and the level of
Measurement of curvature and twist of a deformed object using digital holography
Chen Wen; Quan Chenggen; Cho Jui Tay
2008-05-20
Measurement of curvature and twist is an important aspect in the study of object deformation. In recent years, several methods have been proposed to determine curvature and twist of a deformed object using digital shearography. Here we propose a novel method to determine the curvature and twist of a deformed object using digital holography and a complex phasor. A sine/cosine transformation method and two-dimensional short time Fourier transform are proposed subsequently to process the wrapped phase maps. It is shown that high-quality phase maps corresponding to curvature and twist can be obtained. An experiment is conducted to demonstrate the validity of the proposed method.
Non-scanning measurement of convex and concave curvature with an annular array
NASA Astrophysics Data System (ADS)
Lenz, Michael; Kühnicke, Elfgard
2012-05-01
The paper describes a novel ultrasonic method for measuring local object curvature radii without scanning. For the measurements, an ultrasonic annular array is used, where the phase and amplitude differences on the different receivers are used to determine the object curvature radius and its distance from the transducer simultaneously. The method aims at measurements of spherical or oval inclusions in fluids and solids in general, and of the curvature radius of eye lens and retina in particular. It is intended to work as a supplement to conventional imaging applications. To verify the measurement method, theoretical and experimental results with steel spheres as reflectors are presented. After measuring and taking into account the acoustically effective size of the single transducer elements, good agreement between measurements and simulations could be achieved.
Curvature adaptive optics and low light imaging
NASA Astrophysics Data System (ADS)
Ftaclas, C.; Chun, M.; Kuhn, J.; Ritter, J.
We review the basic approach of curvature adaptive optics (AO) and show how its many advantages arise. A curvature wave front sensor (WFS) measures exactly what a curvature deformable mirror (DM) generates. This leads to the computational and operational simplicity of a nearly diagonal control matrix. The DM automatically reconstructs the wave front based on WFS curvature measurements. Thus, there is no formal wave front reconstruction. This poses an interesting challenge to post-processing of AO images. Physical continuity of the DM and the reconstruction of phase from wave front curvature data assure that each actuated region of the DM corrects local phase, tip-tilt and focus. This gain in per-channel correction efficiency, combined with the need for only one pixel per channel detector reads in the WFS allows the use of photon counting detectors for wave front sensing. We note that the use of photon counting detectors implies penalty-free combination of correction channels either in the WFS or on the DM. This effectively decouples bright and faint source performance in that one no longer predicts the other. The application of curvature AO to the low light moving target detection problem, and explore the resulting challenges to components and control systems. Rapidly moving targets impose high-speed operation posing new requirements unique to curvature components. On the plus side, curvature wave front sensors, unlike their Shack-Hartmann counterparts, are tunable for optimum sensitivity to seeing and we are examining autonomous optimization of the WFS to respond to rapid changes in seeing.
The coherent gradient sensor for film curvature measurements at cryogenic temperature.
Liu, Cong; Zhang, Xingyi; Zhou, Jun; Zhou, Youhe; Feng, Xue
2013-11-04
Coherent Gradient Sensor (CGS) system is presented for measurement of curvatures and nonuniform curvatures changes in film-substrate systems at cryogenic temperature. The influences of the interface of refrigerator and itself on the interferograms which are accounting for the temperature effect are successfully eliminated. Based on the measurement technique, the thermal stresses (including the radial stress, circumferential stress and shear stress) of superconducting YBCO thin-film are obtained by the extended Stoney's formula during the heating process from 30K to 150K. Take the superconducting YBCO thin film as an example, the thermal stresses of which are gained successfully.
FY 2016 Status Report: CIRFT Testing Data Analyses and Updated Curvature Measurements
Wang, Jy-An John; Wang, Hong
2016-08-01
This report provides a detailed description of FY15 test result corrections/analysis based on the FY16 Cyclic Integrated Reversible-Bending Fatigue Tester (CIRFT) test program methodology update used to evaluate the vibration integrity of spent nuclear fuel (SNF) under normal transportation conditions. The CIRFT consists of a U-frame testing setup and a real-time curvature measurement method. The three-component U-frame setup of the CIRFT has two rigid arms and linkages to a universal testing machine. The curvature of rod bending is obtained through a three-point deflection measurement method. Three linear variable differential transformers (LVDTs) are used and clamped to the side connecting plates of the U-frame to capture the deformation of the rod. The contact-based measurement, or three-LVDT-based curvature measurement system, on SNF rods has been proven to be quite reliable in CIRFT testing. However, how the LVDT head contacts the SNF rod may have a significant effect on the curvature measurement, depending on the magnitude and direction of rod curvature. It has been demonstrated that the contact/curvature issues can be corrected by using a correction on the sensor spacing. The sensor spacing defines the separation of the three LVDT probes and is a critical quantity in calculating the rod curvature once the deflections are obtained. The sensor spacing correction can be determined by using chisel-type probes. The method has been critically examined this year and has been shown to be difficult to implement in a hot cell environment, and thus cannot be implemented effectively. A correction based on the proposed equivalent gauge-length has the required flexibility and accuracy and can be appropriately used as a correction factor. The correction method based on the equivalent gauge length has been successfully demonstrated in CIRFT data analysis for the dynamic tests conducted on Limerick (LMK) (17 tests), North Anna (NA) (6 tests), and Catawba mixed oxide (MOX
Aligning and measuring the curvature and thickness of high-precision lens
NASA Astrophysics Data System (ADS)
Wu, Kun-Huan; Chang, Shenq-Tsong; Hsu, Ming-Ying; Huang, Ting-Ming; Hsu, Wei-Yao; Tseng, Shih-Feng
2015-09-01
The radius of curvature is one of the most important specifications for spherical optics [1]. There are several methods and devices currently on the market that can be used to measure it, including optical level, non-contact laser interferometer (Interferometer), a probe-contact profiler (Profilometer), the centering machine and three-point contact ball diameter meter (Spherometer). The amount that can be measured with a radius of curvature of the lens aperture range depends on the interferometer standard lens f / number and lens of R / number (radius of curvature divided by the clear aperture of the spherical surface ratio between them). Unfortunately, for lens with diameter greater than 300 mm, the device is limited by the size of the holding fixture lenses or space. This paper aims to provide a novel surface contour detection method and machine, named "CMM spherometry by probe compensation," to measure the radius and thickness of the curvature of the optical surface by a coordinate measurement machine (CMM). In order to obtain more accurate optimization results, we used probe and temperature compensation to discuss the effect. The trace samples and the measurement results of CMM and the centering machine, which has top and bottom autocollimators, are compared.
In-fiber directional coupler for high-sensitivity curvature measurement.
Guzman-Sepulveda, J R; May-Arrioja, D A
2013-05-20
A curvature fiber optic sensor using a two-core fiber (TCF) is proposed and demonstrated. The TCF is designed to operate as a directional coupler with one core located exactly at the center of the fiber and the other off-axis, but close to the center of the fiber. This design allows straightforward splicing of the TCF to single mode fibers (SMF), and alignment of the off-axis core is not strictly required for optimum operation. The sensor is fabricated by simply splicing a 5 cm long section of TCF between two SMF sections, which provides a sinusoidal spectral response. When the fiber is bent, the coupling parameters are modified due to stress-optic and effective length effects, effectively blue-shifting the sinusoidal spectral response of the sensor and allowing for the measurement of curvature. The sensor exhibits linear response and a sensitivity of -137.87 nm/m(-1) for curvature ranging from 0 to 0.27 m(-1), making it suitable to measure small curvatures with high sensitivity.
Radius of Curvature Measurement of Large Optics Using Interferometry and Laser Tracker
NASA Technical Reports Server (NTRS)
Hagopian, John; Connelly, Joseph
2011-01-01
The determination of radius of curvature (ROC) of optics typically uses either a phase measuring interferometer on an adjustable stage to determine the position of the ROC and the optics surface under test. Alternatively, a spherometer or a profilometer are used for this measurement. The difficulty of this approach is that for large optics, translation of the interferometer or optic under test is problematic because of the distance of translation required and the mass of the optic. Profilometry and spherometry are alternative techniques that can work, but require a profilometer or a measurement of subapertures of the optic. The proposed approach allows a measurement of the optic figure simultaneous with the full aperture radius of curvature.
Effect of Grain Curvature on Nano-Indentation Measurements of Thin Films
NASA Astrophysics Data System (ADS)
Tsai, Kuang-Yue; Chin, Tsung-Shune; Shieh, Han-Ping D.
2004-09-01
Grain curvature effect on the measurement of nano-indentation has been observed for the first time, taking VO2 thin film as an example. As the grain size of thin film is comparable to the diameter of indenter tip, the maximum penetration depths under the same maximum load (Pmax) vary and lead to deviations in estimated hardness and Young’s modulus. Under the same Pmax, larger penetration depth leads to a larger projected area, and a decrease in hardness. The large deviation of stiffness, affected by surface roughness under low Pmax, produces fluctuation of Young’s modulus. Increase in penetration depth diminishes the roughness effect so that deviations in penetration depths dominate the variations in Young’s modulus. The hardness and Young’s modulus curves measured at lowest penetration depth, being thought to be free from effect of grain curvature, coincide very well to the curves measured by continuous stiffness measurements mode.
Villa, Chiara; Gaudio, Daniel; Cattaneo, Cristina; Buckberry, Jo; Wilson, Andrew S; Lynnerup, Niels
2015-03-01
Recent studies have reported that quantifying symphyseal and auricular surface curvature changes on 3D models acquired by laser scanners has a potential for age estimation. However, no tests have been carried out to evaluate the repeatability of the results between different laser scanners. 3D models of the two pelvic joints were generated using three laser scanners (Custom, Faro, and Minolta). The surface curvature, the surface area, and the distance between co-registered meshes were investigated. Close results were found for surface areas (differences between 0.3% and 2.4%) and for distance deviations (average <20 μm, SD <200 μm). The curvature values were found to be systematically biased between different laser scanners, but still showing similar trends with increasing phases/scores. Applying a smoothing factor to the 3D models, it was possible to separate anatomy from the measurement error of each instrument, so that similar curvature values could be obtained (p < 0.05) independent of the specific laser scanner.
Assessment of the effect of vessel curvature on Doppler measurements in steady flow.
Balbis, S; Guiot, C; Roatta, S; Arina, R; Todros, T
2004-05-01
Blood vessel curvature is responsible for the appearance of nonaxial velocity components and for minor changes in the pattern of the axial flow. All the velocity components are expected to contribute to the Doppler signal produced by the ultrasound (US) backscattered by the insonated blood cells, the axial velocity, contributing to the actual volumetric blood flow, and the transverse velocity, causing the recirculating vortices. A detailed, separate analysis of the velocity components is, therefore, mandatory to quantify how vessel curvature can affect results and clinical diagnosis. Both experimental in vitro measures and numerical simulations were performed on a curved tube and the Doppler power spectra so obtained were compared. The satisfactorily agreement of the above spectra shows that the nonaxial velocity components are easily detectable with clinical equipment and that their amplitude, as expected, is not negligible and can bias Doppler measurements and resulting clinical diagnosis.
Real time measurement of epilayer strain using a simplified wafer curvature technique
Floro, J.A.; Chason, E.; Lee, S.R.
1995-12-31
We describe a technique for measuring thin film stress using wafer curvature that is robust, compact, easy to setup, and sufficiently sensitive to serve as a routine diagnostic of semiconductor epilayer strain in real time during MBE or CVD growth. We demonstrate, using growth of SiGe alloys on Si, that the critical thickness for misfit dislocation can clearly be resolved, and that the subsequent strain relaxation kinetics during growth or post-growth annealing are readily obtained.
Simple yet accurate noncontact device for measuring the radius of curvature of a spherical mirror
Spiridonov, Maxim; Toebaert, David
2006-09-10
An easily reproducible device is demonstrated to be capable of measuring the radii of curvature of spherical mirrors, both convex and concave, without resorting to high-end interferometric or tactile devices. The former are too elaborate for our purposes,and the latter cannot be used due to the delicate nature of the coatings applied to mirrors used in high-power CO2 laser applications. The proposed apparatus is accurate enough to be useful to anyone using curved optics and needing a quick way to assess the values of the radii of curvature, be it for entrance quality control or trouble shooting an apparently malfunctioning optical system. Specifically, the apparatus was designed for checking 50 mm diameter resonator(typically flat or tens of meters concave) and telescope (typically some meters convex and concave) mirrors for a high-power CO2 laser, but it can easily be adapted to any other type of spherical mirror by a straightforward resizing.
Measurement of the curvature of a surface using parallel light beams
Chason, Eric H.; Floro, Jerrold A.; Seager, Carleton H.; Sinclair, Michael B.
1999-01-01
Apparatus for measuring curvature of a surface wherein a beam of collimated light is passed through means for producing a plurality of parallel light beams each separated by a common distance which then reflect off the surface to fall upon a detector that measures the separation of the reflected beams of light. This means can be an etalon and the combination of a diffractive element and a converging lens. The curvature of the surface along the line onto which the multiple beams fall can be calculated from this information. A two-dimensional map of the curvature can be obtained by adding a second etalon (or a second combination of a diffractive element and a converging lens) which is rotated 90.degree. about the optical axis relative to the first etalon and inclined at the same angle. The second etalon creates an individual set of parallel light beams from each of the individual beams created by the first etalon with the sets of parallel light beams from the second etalon rotated 90.degree. relative to the line onto which the single set of parallel beams from the first etalon would have fallen.
Measurement of the curvature of a surface using parallel light beams
Chason, E.H.; Floro, J.A.; Seager, C.H.; Sinclair, M.B.
1999-06-15
Apparatus is disclosed for measuring curvature of a surface wherein a beam of collimated light is passed through a means for producing a plurality of parallel light beams each separated by a common distance which then reflect off the surface to fall upon a detector that measures the separation of the reflected beams of light. This means can be an etalon and the combination of a diffractive element and a converging lens. The curvature of the surface along the line onto which the multiple beams fall can be calculated from this information. A two-dimensional map of the curvature can be obtained by adding a second etalon (or a second combination of a diffractive element and a converging lens) which is rotated 90[degree] about the optical axis relative to the first etalon and inclined at the same angle. The second etalon creates an individual set of parallel light beams from each of the individual beams created by the first etalon with the sets of parallel light beams from the second etalon rotated 90[degree] relative to the line onto which the single set of parallel beams from the first etalon would have fallen. 5 figs.
Laser confocal measurement system for curvature radius of lenses based on grating ruler
NASA Astrophysics Data System (ADS)
Tian, Jiwei; Wang, Yun; Zhou, Nan; Zhao, Weirui; Zhao, Weiqian
2015-02-01
In the modern optical measurement field, the radius of curvature (ROC) is one of the fundamental parameters of optical lens. Its measurement accuracy directly affects the other optical parameters, such as focal length, aberration and so on, which significantly affect the overall performance of the optical system. To meet the demand of measurement instruments for radius of curvature (ROC) with high accuracy in the market, we develop a laser confocal radius measurement system with grating ruler. The system uses the peak point of the confocal intensity curve to precisely identify the cat-eye and confocal positions and then measure the distance between these two positions by using the grating ruler, thereby achieving the high-precision measurement for the ROC. The system has advantages of high focusing sensitivity and anti-environment disturbance ability. And the preliminary theoretical analysis and experiments show that the measuring repeatability can be up to 0.8 um, which can provide an effective way for the accurate measurement of ROC.
Wave-front aberration measurements on GRIN-rod lenses.
Cline, T W; Jander, R B
1982-03-15
A survey of the optical quality of commercial and experimental Selfoc GRIN-rod lenses was made using a digital Twyman-Green wave-front interferometer. The technique provides an accurate and reproducible method for predicting lens performance in microoptic devices. Wave-front aberrations are reported for (1/4) pitch lenses measured in a double-pass configuration. It was found that spherical aberration is dominant in commercial lenses. SLW (1/4) pitch lenses have lower aberrations than SLS lenses and are quite suitable for microoptic devices based on fiber-to-fiber coupling. Measured multimode coupling efficiency under steady-state modal propagation is compared to measured spherical aberration for a number of lenses. The slope of the coupling dependence on spherical aberration was found to be -0.1 dB/wave. Effects due to mechanical alignment and the modal distribution in the fibers had a greater influence on the measured coupling efficiency than the contribution due the intrinsic lens aberrations, especially for the SLW lenses. Comparison of this empirical dependence with theoretical predictions for a uniform distribution, which suggests a stronger dependence, is discussed. This work suggests that commercially available GRIN-rod lenses are suitable for use in microoptic components.
177-207 GHz Radiometer Front End: Single Sideband Measurements
NASA Technical Reports Server (NTRS)
Galin, I.; Schnitzer, C. A.; Dengler, R. J.; Quintero, O.
1999-01-01
Twenty years of progress in 200 GHz receivers for spaceborne remote sensing has yielded a 180-220 GHz technology with maturing characteristics, as evident by increasing availability of relevant hardware, paralleled by further refinement in receiver performance requirements at this spectrum band. The 177-207 GHz superheterodyne receiver, for the Earth observing system (EOS) microwave limb sounder (MLS), effectively illustrates such technology developments. This MLS receiver simultaneously detects six different signals, located at sidebands below and above its 191.95 GHZ local-oscillator (LO). The paper describes the MLS 177-207 GHz receiver front-end (RFE), and provides measured data for its lower and upper sidebands. Sideband ratio data is provided as a function of IF frequency, at different LO power drive, and for variation in the ambient temperature.
Measurement of the absolute wavefront curvature radius in a heterodyne interferometer.
Hechenblaikner, Gerald
2010-09-01
We present an analytical derivation of the coupling parameter relating the angle between two interfering beams in a heterodyne interferometer to the differential phase signals detected by a quadrant photodiode. This technique, also referred to as differential wavefront sensing, is commonly used in space-based gravitational wave detectors to determine the attitude of a test mass in one of the interferometer arms from the quadrant diode signals. Successive approximations to the analytical expression are made to simplify the investigation of parameter dependencies. Motivated by our findings, we propose what we believe to be a new measurement method to accurately determine the absolute wavefront curvature of a single measurement beam. We also investigate the change in the coupling parameter when the interferometer "test mirror" is moved from its nominal position, an effect which mediates the coupling of mirror displacement noise into differential phase measurements.
Comparison of portable and conventional ultrasound imaging in spinal curvature measurement
NASA Astrophysics Data System (ADS)
Yan, Christina; Tabanfar, Reza; Kempston, Michael; Borschneck, Daniel; Ungi, Tamas; Fichtinger, Gabor
2016-03-01
PURPOSE: In scoliosis monitoring, tracked ultrasound has been explored as a safer imaging alternative to traditional radiography. The use of ultrasound in spinal curvature measurement requires identification of vertebral landmarks, but bones have reduced visibility in ultrasound imaging and high quality ultrasound machines are often expensive and not portable. In this work, we investigate the image quality and measurement accuracy of a low cost and portable ultrasound machine in comparison to a standard ultrasound machine in scoliosis monitoring. METHODS: Two different kinds of ultrasound machines were tested on three human subjects, using the same position tracker and software. Spinal curves were measured in the same reference coordinate system using both ultrasound machines. Lines were defined by connecting two symmetric landmarks identified on the left and right transverse process of the same vertebrae, and spinal curvature was defined as the transverse process angle between two such lines, projected on the coronal plane. RESULTS: Three healthy volunteers were scanned by both ultrasound configurations. Three experienced observers localized transverse processes as skeletal landmarks and obtained transverse process angles in images obtained from both ultrasounds. The mean difference per transverse process angle measured was 3.00 +/-2.1°. 94% of transverse processes visualized in the Sonix Touch were also visible in the Telemed. Inter-observer error in the Telemed was 4.5° and 4.3° in the Sonix Touch. CONCLUSION: Price, convenience and accessibility suggest the Telemed to be a viable alternative in scoliosis monitoring, however further improvements in measurement protocol and image noise reduction must be completed before implementing the Telemed in the clinical setting.
Measurement of the shock front velocity produced in a T-tube
Djurović, S.; Mijatović, Z.; Vujičić, B.; Kobilarov, R.; Savić, I.; Gavanski, L.
2015-01-15
A set of shock front velocity measurements is described in this paper. The shock waves were produced in a small electromagnetically driven shock T-tube. Most of the measurements were performed in hydrogen. The shock front velocity measurements in other gases and the velocity of the gas behind the shock front were also analyzed, as well as the velocity dependence on applied input energy. Some measurements with an applied external magnetic field were also performed. The used method of shock front velocity is simple and was shown to be very reliable. Measured values were compared with the calculated ones for the incident and reflected shock waves.
New approach to accuracy enhancement and traceability realization of radius of curvature measurement
NASA Astrophysics Data System (ADS)
Ding, Xiang; Li, Fei; Liu, Wenli
2012-10-01
High accuracy radius of curvature (ROC) measurement of optical surfaces is usually realized by techniques such as autocollimation, interferometry and profilometry, with theoretical accuracy as high as 10-6. In practical application, significant discrepancy may exist in results obtained by different methods owing to figure error of measured surfaces. In this paper, mathematical models are built up to characterize the relationship between the ROC and the figure error as well as the aperture angle. Based on the models, equations for calculating the ROC accuracy are derived and tested on several ROC measuring methods. Experiments are carried out on a set of high quality spheres whose diameters are from 11mm to 93mm and roundness is from 0.03μm to 0.07μm, measured by instruments with top level accuracy, which are a length measuring machine, a profilometer and a homemade differential confocal system. Uncertainties are calculated and analyzed against several factors. The reason for the discrepancy between different methods is explained. An approach is also proposed which could reduce the uncertainty of ROC by 1~2 scales, making it possible to trace the results of ROC measuring instruments to the primary standard of length via diameter and roundness measurement method.
NASA Astrophysics Data System (ADS)
Mutter, Markus; Mauer, Georg; Mücke, Robert; Vaßen, Robert; Back, Hyoung Chul; Gibmeier, Jens
2016-04-01
The residual stresses within plasma-sprayed coatings are an important factor that can influence the lifetime as well as the performance in operation. The investigation of stresses evolving during deposition and post-deposition cooling for atmospheric plasma spraying of yttria-stabilized zirconia coatings using in situ measurement of the samples curvature is a powerful tool for identifying the factors that contribute to stress generation. Under various spray conditions, the first deposition pass leads to a significantly larger increase in samples curvature than the subsequent passes. It is shown in this work that the amount of curvature change at the onset of spraying is significantly influenced by the spray conditions, as well as by the substrate material. More information on the origin of this steep curvature increase at the onset of spraying was obtained by single splat experiments, which yielded information on the splat bonding behavior under various conditions. A comparison of the compressive yield strength for different substrate materials indicated the influence of substrate residual stress relaxation. Residual stress measurements using the incremental hole-drilling method and x-ray diffraction confirmed that the coating deposition affects the substrate residual stress level. The yield strength data were combined with the substrate near-surface temperature during deposition, obtained by finite element simulations, and with the measured residual stress-profile. This revealed that residual stress relaxation is the key factor for the initial curvature increase.
AC-coupled front-end for biopotential measurements.
Spinelli, Enrique Mario; Pallàs-Areny, Ramon; Mayosky, Miguel Angel
2003-03-01
AC coupling is essential in biopotential measurements. Electrode offset potentials can be several orders of magnitude larger than the amplitudes of the biological signals of interest, thus limiting the admissible gain of a dc-coupled front end to prevent amplifier saturation. A high-gain input stage needs ac input coupling. This can be achieved by series capacitors, but in order to provide a bias path, grounded resistors are usually included, which degrade the common mode rejection ratio (CMRR). This paper proposes a novel balanced input ac-coupling network that provides a bias path without any connection to ground, thus resulting in a high CMRR. The circuit being passive, it does not limit the differential dc input voltage. Furthermore, differential signals are ac coupled, whereas common-mode voltages are dc coupled, thus allowing the closed-loop control of the dc common mode voltage by means of a driven-right-leg circuit. This makes the circuit compatible with common-mode dc shifting strategies intended for single-supply biopotential amplifiers. The proposed circuit allows the implementation of high-gain biopotential amplifiers with a reduced number of parts, thus resulting in low power consumption. An electrocardiogram amplifier built according to the proposed design achieves a CMRR of 123 dB at 50 Hz.
Observation of atmospheric fronts using Raman lidar moisture measurements
NASA Technical Reports Server (NTRS)
Melfi, S. H.; Whiteman, D.; Ferrare, R.
1989-01-01
This paper presents the results of a field program using a ground-based Raman lidar system to observe changes in moisture profiles as a cold and a warm front passed over the NASA/Goddard Space Flight Center in Greenbelt, Maryland. The lidar operating only during darkness is capable of providing continuous high vertical resolution profiles of water vapor mixing ratio and aerosol scattering ratio from near the surface to about 7 km altitude. The lidar data acquired on three consecutive nights from shortly after sunset to shortly before sunrise, along with upper air data from specially launched rawinsondes, have provided a unique visualization of the detailed structure of the two fronts.
Laser Phase Front Measurements Using a Phase Conjugate Twyman-Green Interferometer
1992-12-01
34 AD-A258 821 AFIT/GEP/ENP/92-D-08 LASER PHASE FRONT MEASUREMENTS USING A PHASE CONJUGATE TWYMAN -GREEN INTERFEROMETER THESIS William J. Mandeville...LASER PHASE FRONT MEASUREMENTS USING A PHASE CONJUGATE TWYMAN -GREEN INTERFEROMETER THESIS Presented to the Faculty of the School of Engineering of the... Interferometer .............................................. 19 8. Phase conjugate Twyman -Green Interferometer .................................. 21
Measuring the composition-curvature coupling in binary lipid membranes by computer simulations
Barragán Vidal, I. A. Müller, M.; Rosetti, C. M.; Pastorino, C.
2014-11-21
The coupling between local composition fluctuations in binary lipid membranes and curvature affects the lateral membrane structure. We propose an efficient method to compute the composition-curvature coupling in molecular simulations and apply it to two coarse-grained membrane models—a minimal, implicit-solvent model and the MARTINI model. Both the weak-curvature behavior that is typical for thermal fluctuations of planar bilayer membranes as well as the strong-curvature regime corresponding to narrow cylindrical membrane tubes are studied by molecular dynamics simulation. The simulation results are analyzed by using a phenomenological model of the thermodynamics of curved, mixed bilayer membranes that accounts for the change of the monolayer area upon bending. Additionally the role of thermodynamic characteristics such as the incompatibility between the two lipid species and asymmetry of composition are investigated.
Measurement of Cut Front Properties in Laser Cutting
NASA Astrophysics Data System (ADS)
Thombansen, Ulrich; Hermanns, Torsten; Molitor, Thomas; Pereira, Milton; Schulz, Wolfgang
Cut-front properties are a key variable in laser-cutting and thus of major importance for self-optimization. Within the Cluster of Excellence at RWTH Aachen University, several achievements were made in setting up sensor-systems that provide information on the operating-point of this melt-based manufacturing process. These achievements contribute to a gradual increase in system-transparency which is seen as an enabler for self-optimization. Instead of searching for a single measurand to characterize the course of the process, an approach is being presented which establishesa surrogate criterion to allow determination of the current operating-point. In the depicted area, this is done by joining sources of information from process observation, determining boundary-conditions such as actual feed-rate and modeling of process-variables. Although process-variables like properties of the cutting-front are influenced through more than one process parameter, a concept for a sensor-system is reported showing the correlation between properties of the melt-front and the current feed-rate. The results are compared to a solution derived from process-simulation.
NASA Astrophysics Data System (ADS)
Gruppetta, Steve; Koechlin, Laurent; Lacombe, François; Puget, Pascal
2005-10-01
A system to measure the topography of the first optical surface of the human eye noninvasively by using a curvature sensor is described. The static corneal topography and the dynamic topography of the tear film can both be measured, and the topographies obtained are presented. The system makes possible the study of the dynamic aberrations introduced by the tear film to determine their contribution to the overall ocular aberrations in healthy eyes, eyes with corneal pathologies, and eyes wearing contact lenses.
The effects of thermal field in interferometric measurements of radius of curvature
NASA Astrophysics Data System (ADS)
Mao, Jie; Hou, Xi; Wu, Fan
2014-09-01
The radius of curvature is one of the most important parameters to determine the properties of spherical surfaces. Based on the interferometric method, the importance of thermal analysis of spherical optical elements is stated in the paper. And then using different material, such as K9 and fused silica, the change of the curvature radius of spherical elements in different static temperature field is calculated and analyzed theoretically in the change of sag and surface. Finally, the theoretic results and simulated results by ANSYS have been compared. It is found that the radius of curvature of spherical optical elements is not only connected with the magnitude and direction of the temperature gradient, but also directly connected with material and structural parameters.
NASA Astrophysics Data System (ADS)
Dai, Lei; Zhang, Jian; Gu, Yongqiang; Miao, Erlong
2016-10-01
The radius of curvature (ROC) is one of the most important parameters of sphere optic components. In optic fine grinding process, radius of curvature accuracy requires up to 0.1%. We propose a method based on high precision CNC grinding machine, develop ROC online measurement method for fine grinding optics. This rapid method only takes few measurement points based on spiral route path, attaining enough accuracy and reduce the time cost, furthermore, can greatly reduce the repeated installation error. Analyzing the uncertainty sources that affect to the ROC measurement results, calculates the combined standard uncertainty 32.8 micron. Completed comparison experiments with CMM, the standard deviation of the experiment result are about 18 micron that approaches to CMM results.
Measurement of the Earth's Radius Based on Historical Evidence of Its Curvature
ERIC Educational Resources Information Center
Roura, Pere; Josep, Calbo
2005-01-01
Probably the most direct observation of the Earth's curvature is how objects appear from over the horizon when we approach them and disappear as we get further away from them. Similarly, the portion of a high object (a building or a mountain) that is visible depends on the height of the site where the observation is made. Based upon these very…
NASA Astrophysics Data System (ADS)
Lee, Stephen; Breiland, William; Koleske, Dan
2003-03-01
Wafer-curvature measurements of thin-film stress during chemical-vapor deposition of epitaxial GaN films on sapphire substrates are made using a multi-beam optical stress sensor (MOSS). The stress measurements are impacted by thickness nonuniformities in the growing film; lateral variations in film thickness produce optical diffraction effects that steer the reflected laser beams of the MOSS sensor away from the normally specular direction. These unintended beam-steering effects oscillate with film thickness and superimpose on the desired time-dependent beam deflections due to the wafer-curvature produced by true stress variations in the growing film. The oscillations can substantially impact stress-measurement accuracy, but allow the film nonuniformity to be assessed in real time. We develop a Fresnel-Kirchhoff diffraction model of laser-beam steering by nonuniform films that we compare to MOSS wafer-curvature measurements. Steering effects vary with the degree of film nonuniformity, the film thickness, the wavelength dispersion of the light source, the illuminated spot size, and the refractive indices of the film and substrate. Lockheed-Martin operates Sandia National Laboratories for the U. S. Dept. of Energy (Contract No. DE-AC04-94AL85000).
NASA Astrophysics Data System (ADS)
Coghlan, Leslie; Singleton, H. R.; Dell'Italia, L. J.; Linderholm, C. E.; Pohost, G. M.
1995-05-01
We have developed a method for measuring the detailed in vivo three dimensional geometry of the left and right ventricles using cine-magnetic resonance imaging. From data in the form of digitized short axis outlines, the normal vectors, principal curvatures and directions, and wall thickness were computed. The method was evaluated on simulated ellipsoids and on human MRI data. Measurements of normal vectors and of wall thickness were very accurate in simulated data and appeared appropriate in patient data. On simulated data, measurements of the principal curvature k1 (corresponding approximately to the short axis direction of the left ventricle) and of principal directions were quite accurate, but measurements of the other principal curvature (k2) were less accurate. The reasons behind this are considered. We expect improvements in the accuracy with thinner slices and improved representation of the surface data. Gradient echo images were acquired from 8 dogs with a 1.5T system (Philips Gyroscan) at baseline and four months after closed chest experimentally produced mitral regurgitation (MR). The product (k1 + k2) X wall thickness averaged over all slices at end-diastole was significantly lower after surgery (n equals 8, p < 0.005). These geometry changes were consistent with the expected increase in wall stress after MR.
Mirror with thermally controlled radius of curvature
Neil, George R.; Shinn, Michelle D.
2010-06-22
A radius of curvature controlled mirror for controlling precisely the focal point of a laser beam or other light beam. The radius of curvature controlled mirror provides nearly spherical distortion of the mirror in response to differential expansion between the front and rear surfaces of the mirror. The radius of curvature controlled mirror compensates for changes in other optical components due to heating or other physical changes. The radius of curvature controlled mirror includes an arrangement for adjusting the temperature of the front surface and separately adjusting the temperature of the rear surface to control the radius of curvature. The temperature adjustment arrangements can include cooling channels within the mirror body or convection of a gas upon the surface of the mirror. A control system controls the differential expansion between the front and rear surfaces to achieve the desired radius of curvature.
Wilcox, Rand R
2010-05-01
This paper considers the problem of estimating the overall strength of an association, including situations where there is curvature. The general strategy is to fit a robust regression line, or some type of smoother that allows curvature, and then use a robust analogue of explanatory power, say eta(2). When the regression surface is a plane, an estimate of eta(2) via the Theil-Sen estimator is found to perform well, relative to some other robust regression estimators, in terms of mean squared error and bias. When there is curvature, a generalization of a kernel estimator derived by Fan performs relatively well, but two alternative smoothers have certain practical advantages. When eta(2) is approximately equal to zero, estimation using smoothers has relatively high bias. A variation of eta(2) is suggested for dealing with this problem. Methods for testing H(0): eta(2)=0 are examined that are based in part on smoothers. Two methods are found that control Type I error probabilities reasonably well in simulations. Software for applying the more successful methods is provided.
HIGH RESOLUTION EMITTANCE MEASUREMENTS AT SNS FRONT END
Aleksandrov, Alexander V; Zhukov, Alexander P
2013-01-01
The Spallation Neutron Source (SNS) linac accelerates an H- beam from 2.5MeV up to 1GeV. Recently the emittance scanner in the MEBT (2.5 MeV) was upgraded. In addition to the slit - harp measurement, we now can use a slit installed on the same actuator as the harp. In combination with a faraday cup located downstream in DTL part of the linac, it represents a classical slit-slit emittance measurement device. While a slit slit scan takes much longer, it is immune to harp related problems such as wire cross talk, and thus looks promising for accurate halo measurements. Time resolution of the new device seems to be sufficient to estimate the amount of beam in the chopper gap (the scanner is downstream of the chopper), and probably to measure its emittance. This paper describes the initial measurements with the new device and some model validation data.
Direct measurement of the wetting front capillary pressure in a clay brick ceramic
NASA Astrophysics Data System (ADS)
Ioannou, Ioannis; Hall, Christopher; Wilson, Moira A.; Hoff, William D.; Carter, Margaret A.
2003-12-01
The absorption of a liquid into a rectangular bar of an initially dry porous material that is sealed on all surfaces except the inflow face is analysed in terms of Sharp Front theory. Sharp Front models are developed for both complete and incomplete displacement of air ahead of the advancing wetting front. Experiments are described from which a characteristic capillary potential of the material is obtained by measuring the equilibrium pressure of the air displaced and compressed ahead of the advancing wetting front. Results for the absorption of water and n-heptane by a fired clay brick ceramic suggest that this wetting front capillary pressure (or capillary potential) scales approximately with the surface tension and also that the permeability scales inversely with the liquid viscosity. The pressure of the air trapped in the wetted region is found to be the same as the pressure of the displaced air. For this material the wetting front capillary pressure for water at 20°C is 0.113 MPa, equivalent to a hydraulic tension head of 11.5 m and to a Young-Laplace pore diameter of 2.6 µm. The capillary pressure so measured is apparently a fundamental percolation property of the material that can be interpreted as the air pressure at which liquid phase continuity and unsaturated conductivity both vanish. The method described can be applied generally to porous materials.
NASA Astrophysics Data System (ADS)
Tung, Y. T.; Hsu, C. Y.; Yeh, J. A.; Wang, P. J.
2012-10-01
Liquid lenses based on the principle of driving two dielectric fluids via controlled electric field were investigated with an experimental apparatus designed for analysis of wave front read from a Shack-Hartmann sensor. Due to small available aperture and requirements in dynamic responses, wave front measurement was selected for study of optical characteristics in dielectric lenses. With the advent of commercial electro-optics sensors in wave front measurement, the experimental apparatus was first designed and simulated with the help of ASAP program. The simulated results proved the conceptual design with handful of engineering insights so that less trial and error efforts could be relieved from building the optics system on the bench. In-house built liquid lens modules with driving circuits were then set on the apparatus for initial calibration and functional tests. Since the electric field generated for the control of liquid profile must be alternating current, various frequency and modulation schemes were put through the liquid lens module to further study the influences on dynamic responses in terms of optical characteristics. Furthermore, effects due to material impurity and ambient effects were also carefully studied for established the fundamental phenomena of liquid lenses made of dielectric fluids. More detailed observations were possible with the measured wave-front data. In conclusion, the wave-front measurement proved to be more reliable and less expensive compared to measurement based on interferometer.
NASA Astrophysics Data System (ADS)
Rodriguez-Carranza, Claudia E.; Mukherjee, P.; Vigneron, Daniel; Barkovich, James; Studholme, Colin
2007-03-01
In this work we compare 3D Gyrification Index and our recently proposed area-independent curvature-based surface measures [26] for the in-vivo quantification of brain surface folding in clinically acquired neonatal MR image data. A meaningful comparison of gyrification across brains of different sizes and their subregions will only be possible through the quantification of folding with measures that are independent of the area of the region of analysis. This work uses a 3D implementation of the classical Gyrification Index, a 2D measure that quantifies folding based on the ratio of the inner and outer contours of the brain and which has been used to study gyral patterns in adults with schizophrenia, among other conditions. The new surface curvature-based measures and the 3D Gyrification Index were calculated on twelve premature infants (age 28-37 weeks) from which surfaces of cerebrospinal fluid/gray matter (CSF/GM) interface and gray matter/white matter (GM/WM) interface were extracted. Experimental results show that our measures better quantify folding on the CSF/GM interface than Gyrification Index, and perform similarly on the GM/WM interface.
Forman curvature for complex networks
NASA Astrophysics Data System (ADS)
Sreejith, R. P.; Mohanraj, Karthikeyan; Jost, Jürgen; Saucan, Emil; Samal, Areejit
2016-06-01
We adapt Forman’s discretization of Ricci curvature to the case of undirected networks, both weighted and unweighted, and investigate the measure in a variety of model and real-world networks. We find that most nodes and edges in model and real networks have a negative curvature. Furthermore, the distribution of Forman curvature of nodes and edges is narrow in random and small-world networks, while the distribution is broad in scale-free and real-world networks. In most networks, Forman curvature is found to display significant negative correlation with degree and centrality measures. However, Forman curvature is uncorrelated with clustering coefficient in most networks. Importantly, we find that both model and real networks are vulnerable to targeted deletion of nodes with highly negative Forman curvature. Our results suggest that Forman curvature can be employed to gain novel insights on the organization of complex networks.
Measurement of the Earth's radius based on historical evidence of its curvature
NASA Astrophysics Data System (ADS)
Roura, Pere; Calbó, Josep
2005-09-01
Probably the most direct observation of the Earth’s curvature is how objects appear from over the horizon when we approach them and disappear as we get further away from them. Similarly, the portion of a high object (a building or a mountain) that is visible depends on the height of the site where the observation is made. Based upon these very obvious facts, a simple method to estimate the Earth's radius R has been applied. The method does not need either sophisticated instrumentation or complex mathematics. In our application of the method presented here, the result is R = 6600 +/- 600 km in the best case. A discussion is presented about the possible use of this method in ancient times. Surprisingly enough, we have not found any reference to the use of this method despite its being simpler than, for example, the classical approach of Eratosthenes.
Subbarayalu, Arun Vijay
2016-01-01
The Modified Head Posture Spinal Curvature Instrument (MHPSCI) is an extension of the Head Posture Spinal Curvature Instrument. Two specific modifications were made in the original design by adding a third arm projecting horizontally from the protractor to objectively fix the pivot exactly over the C7 vertebra and the addition of a spirit-level to properly align the instrument. In order to demonstrate reliability and validity, this study was conducted using patients with postural neck pain (N = 65) and healthy subjects (N = 20). All the subjects were working at a selected Information Technology Industry in India and had been recruited using a criterion-based sampling approach. The craniovertebral (CV) angle of each subject was evaluated by two raters consecutively. The measurements were taken by using both MHPSCI and the standard photographic method in a standardized sitting posture for the purpose of establishing criterion-validity of the instrument. The results of this study indicate a good inter-rater reliability (ICC = 0.76; CI = 0.65-0.84) as well as intra-rater reliability (ICC = 0.87; CI = 0.82-0.91) between three successive CV angle measurements (with 2 minutes interval between each measurement) through MHPSCI. While keeping the digital photographic measurement as a standard, this study established that the MHPSCI is a valid tool for measuring the CV angle as shown by non-significant difference (p > 0.01) and high correlation between the two methods (r = 0.79-0.84). This study demonstrates that the MHPSCI is a reliable and valid instrument for measuring CV angle in subjects with or without postural neck pain.
Front-end Electronics for Unattended Measurement (FEUM). Prototype Test Plan
Conrad, Ryan C.; Morris, Scott J.; Smith, Leon E.; Keller, Daniel T.
2015-09-16
The IAEA has requested that PNNL perform an initial set of tests on front-end electronics for unattended measurement (FEUM) prototypes. The FEUM prototype test plan details the tests to be performed, the criteria for evaluation, and the procedures used to execute the tests.
NASA Astrophysics Data System (ADS)
Chen, S. H.; Lee, D. D.; Kimishima, K.; Jinnai, H.; Hashimoto, T.
1996-12-01
Small-angle x-ray and neutron-scattering (SAXS and SANS) measurements are made of a three-component isometric microemulsion, C10E4-D2O-octane, in the one-phase channel around the hydrophile-lipophile balance temperature of the system. A previous SANS contrast variation experiment indicated that the microstructure of this isometric microemulsion is bicontinuous in water and oil, with the surfactant film having a zero mean curvature. We analyze the SAXS and SANS data taken with a bulk contrast in terms of a modified Berk's random wave model. We choose a spectral function which is an inverse sixth-order polynomial, with three parameters a, b, and c, as introduced by Lee and Chen earlier. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function for the microemulsion. The analysis gives an excellent agreement with the intensity data in an absolute scale. We then use the three parameters so obtained to calculate the mean Gaussian curvature of the surfactant film. We also show a three-dimensional-reconstructed morphology of the microemulsion.
Measurements of shock-front structure in multi-species plasmas on OMEGA
NASA Astrophysics Data System (ADS)
Rinderknecht, Hans G.; Park, H.-S.; Ross, J. S.; Wilks, S. C.; Amendt, P. A.; Heeter, R. F.; Katz, J.; Hoffman, N. M.; Vold, E.; Taitano, W.; Simakov, A.; Chacon, L.
2016-10-01
The structure of a shock front in a plasma with multiple ion species is measured for the first time in experiments on the OMEGA laser. Thomson scattering of a 263.25 nm probe beam is used to diagnose electron density, electron and ion temperature, ion species concentration, and flow velocity in strong shocks (M 5) propagating through low-density (ρ 0.1 mg/cc) plasmas composed of H(98%)+Ne(2%) and H(98%)+C(2%). Separation of the ion species within the shock front is inferred. Although shocks play an important role in ICF and astrophysical plasmas, the intrinsically kinetic nature of the shock front indicates the need for experiments to benchmark hydrodynamic models. Comparison with PIC, Vlasov-Fokker-Planck, and multi-component hydrodynamic simulations will be presented. This work performed under auspices of U.S. DOE by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
NASA Astrophysics Data System (ADS)
Jiazhen, Wang; Jun, Xu; Lirong, Zheng; Junyan, Ren
2010-10-01
A continuously tunable gain and bandwidth analog front-end for ambulatory biopotential measurement systems is presented. The front-end circuit is capable of amplifying and conditioning different biosignals. To optimize the power consumption and simplify the system architecture, the front-end only adopts two-stage amplifiers. In addition, careful design eliminates the need for chopping circuits. The input-referred noise of the system is only 1.19 μVrms (0.48-2000 Hz). The chip is fabricated via a SMIC 0.18 μm CMOS process. Although the power consumption is only 32.1 μW under a 3 V voltage supply, test results show that the chip can successfully extract biopotential signals.
NASA Astrophysics Data System (ADS)
Candoré, Jean Charles; Bodnar, J. L.; Detalle, Vincent; Remy, B.; Grossel, Philippe
2010-03-01
In this paper we present, in an experimental way, the possibilities of front face photothermal radiometry to measure, in situ, the longitudinal thermal diffusivity of mural paintings. First, we present the principle of the method of measurement. Then, we present the experimental device implemented for the study. Finally, we show, using the experimental study of a plaster sample, the photothermal method allows in a particular case, a good approximation of the parameter longitudinal thermal diffusivity.
Sparse aperture differential piston measurements using the pyramid wave-front sensor
NASA Astrophysics Data System (ADS)
Arcidiacono, Carmelo; Chen, Xinyang; Yan, Zhaojun; Zheng, Lixin; Agapito, Guido; Wang, Chaoyan; Zhu, Nenghong; Zhu, Liyun; Cai, Jianqing; Tang, Zhenghong
2016-07-01
In this paper we report on the laboratory experiment we settled in the Shanghai Astronomical Observatory (SHAO) to investigate the pyramid wave-front sensor (WFS) ability to measure the differential piston on a sparse aperture. The ultimate goal is to verify the ability of the pyramid WFS work in close loop to perform the phasing of the primary mirrors of a sparse Fizeau imaging telescope. In the experiment we installed on the optical bench we performed various test checking the ability to flat the wave-front using a deformable mirror and to measure the signal of the differential piston on a two pupils setup. These steps represent the background from which we start to perform full close loop operation on multiple apertures. These steps were also useful to characterize the achromatic double pyramids (double prisms) manufactured in the SHAO optical workshop.
Liquid-Crystal Point-Diffraction Interferometer for Wave-Front Measurements
NASA Technical Reports Server (NTRS)
Mercer, Carolyn R.; Creath, Katherine
1996-01-01
A new instrument, the liquid-crystal point-diffraction interferometer (LCPDI), is developed for the measurement of phase objects. This instrument maintains the compact, robust design of Linnik's point-diffraction interferometer and adds to it a phase-stepping capability for quantitative interferogram analysis. The result is a compact, simple to align, environmentally insensitive interferometer capable of accurately measuring optical wave fronts with very high data density and with automated data reduction. We describe the theory and design of the LCPDI. A focus shift was measured with the LCPDI, and the results are compared with theoretical results,
NASA Astrophysics Data System (ADS)
Sharma, Haripriya; Golla, Ramsri G.; Zhang, Yu; Kendall, Christopher B.; Hurst, R. Todd; Tajbakhsh, Nima; Liang, Jianming
2014-03-01
Carotid intima-media thickness (CIMT) has proven to be sensitive for predicting individual risk of cardiovascular diseases (CVD). The CIMT is measured based on region of interest (ROIs) in end-diastolic ultrasound frames (EUFs). To interpret CIMT videos, in the current practice, the EUFs and ROIs must be manually selected, a process that is tedious and time consuming. To reduce CIMT interpretation time, this paper presents a novel method for automatically selecting EUFs and determining ROIs in ultrasound videos. The EUFs are selected based on the QRS complex of the electrocardiogram (ECG) signal associated with the ultrasound video, and the ROI is detected based on image intensity and curvature of the carotid artery bulb. Once a EUF is selected and its corresponding ROI is determined, our system measures CIMT using the snake algorithm extended with hard constraints [1,6-7] by computing the average thickness and maximum thickness, calculating the vascular age, and generating a patient's report. In this study, we utilize 23 subjects. Each subject has 4 videos, and 3 EUFs are selected in each video, resulting in a total of 272 ROIs. By comparing with the reference provided by an expert for both frame selection and ROI detection, we achieve 92.96% sensitivity and 97.62% specificity for EUF selection, and 81.25% accuracy in ROI detection.
Approach to nonphotoperturbed differential capacitance measurements: A front-wing cantilever
NASA Astrophysics Data System (ADS)
Chang, M. N.; Chen, C. Y.; Huang, W. J.; Cheng, T. C.
2005-07-01
We have developed a front-wing (FW) cantilever structure that can significantly suppress photoperturbation effects during scanning capacitance microscopy (SCM) and scanning capacitance spectroscopy (SCS) measurements. The FW cantilever provides an effective shadow area that fully covers the scan region, allowing us to synchronously obtain SCM images and the corresponding topographic images without photoperturbation problems. Nonphotoperturbed differential capacitance characteristics versus tip biases were also obtained for SCS by the use of these FW cantilevers. This means that nonphotoperturbed SCM and SCS measurements can be carried out during the typical SCM operations.
Measurement of corneal topography through Hartmann-Shack wave-front sensor
NASA Astrophysics Data System (ADS)
Yang, Jinsheng; Rao, Xuejun; Rao, Changhui
2008-12-01
A corneal topography based on Hartmann-Shack Sensor is presented in this paper. In the system, the focus of an objective lens is precisely positioned on cornea's curve center. Wave-front of the reflecting beam can be measured by the Hartmann-Shack sensor which is conjugate to the cornea plane. If the corneal surface is a perfect sphere, wave-front detected by the Hartmann-Shack sensor is a plane. As a result, data measured by Hartmann-Shacks sensor is the deviation between the sphere and the real cornea surface. This paper describes a methodology for designing instrument based on Hartmann-Shack sensor. Then, applying this method, an instrument is developed for accurate measurement of corneal topography. In addition, measuring principle of Hartmann-Shack sensor which determined system parameters is also introduced. Repeatability is demonstrated by a series of data. The instrument was able to accurately measure simulative cornea's reflective aberrations, from which corneal topography and corneal refractive aberrations were derived.
Ground based mobile isotopic methane measurements in the Front Range, Colorado
NASA Astrophysics Data System (ADS)
Vaughn, B. H.; Rella, C.; Petron, G.; Sherwood, O.; Mielke-Maday, I.; Schwietzke, S.
2014-12-01
Increased development of unconventional oil and gas resources in North America has given rise to attempts to monitor and quantify fugitive emissions of methane from the industry. Emission estimates of methane from oil and gas basins can vary significantly from one study to another as well as from EPA or State estimates. New efforts are aimed at reconciling bottom-up, or inventory-based, emission estimates of methane with top-down estimates based on atmospheric measurements from aircraft, towers, mobile ground-based vehicles, and atmospheric models. Attributing airborne measurements of regional methane fluxes to specific sources is informed by ground-based measurements of methane. Stable isotopic measurements (δ13C) of methane help distinguish between emissions from the O&G industry, Confined Animal Feed Operations (CAFO), and landfills, but analytical challenges typically limit meaningful isotopic measurements to individual point sampling. We are developing a toolbox to use δ13CH4 measurements to assess the partitioning of methane emissions for regions with multiple methane sources. The method was applied to the Denver-Julesberg Basin. Here we present data from continuous isotopic measurements obtained over a wide geographic area by using MegaCore, a 1500 ft. tube that is constantly filled with sample air while driving, then subsequently analyzed at slower rates using cavity ring down spectroscopy (CRDS). Pressure, flow and calibration are tightly controlled allowing precise attribution of methane enhancements to their point of collection. Comparisons with point measurements are needed to confirm regional values and further constrain flux estimates and models. This effort was made in conjunction with several major field campaigns in the Colorado Front Range in July-August 2014, including FRAPPÉ (Front Range Air Pollution and Photochemistry Experiment), DISCOVER-AQ, and the Air Water Gas NSF Sustainability Research Network at the University of Colorado.
Front-crawl instantaneous velocity estimation using a wearable inertial measurement unit.
Dadashi, Farzin; Crettenand, Florent; Millet, Grégoire P; Aminian, Kamiar
2012-09-25
Monitoring the performance is a crucial task for elite sports during both training and competition. Velocity is the key parameter of performance in swimming, but swimming performance evaluation remains immature due to the complexities of measurements in water. The purpose of this study is to use a single inertial measurement unit (IMU) to estimate front crawl velocity. Thirty swimmers, equipped with an IMU on the sacrum, each performed four different velocity trials of 25 m in ascending order. A tethered speedometer was used as the velocity measurement reference. Deployment of biomechanical constraints of front crawl locomotion and change detection framework on acceleration signal paved the way for a drift-free integration of forward acceleration using IMU to estimate the swimmers velocity. A difference of 0.6 ± 5.4 cm · s(-1) on mean cycle velocity and an RMS difference of 11.3 cm · s(-1) in instantaneous velocity estimation were observed between IMU and the reference. The most important contribution of the study is a new practical tool for objective evaluation of swimming performance. A single body-worn IMU provides timely feedback for coaches and sport scientists without any complicated setup or restraining the swimmer's natural technique.
ANALOG FRONT-END ELECTRONICS FOR BEAM POSITION MEASUREMENT ON THE BEAM HALO MEASUREMENT
R.B. SHURTER; T.J. COTE; J.D. GILPATRICK
2001-06-01
Enhancements have been made to the log-ratio analog front-end electronics based on the Analog Devices 8307 logarithmic amplifier as used on the LEDA accelerator. The dynamic range of greater than 85 dB, has been extended to nearly the full capability of the AD8307 from the previous design of approximately 65 dB through the addition of a 350 MHz band-pass filter, careful use of ground and power plane placement, signal routing, and power supply bypassing. Additionally, selection of high-isolation RF switches (55dB) has been an integral part of a new calibration technique, which is fully described in another paper submitted to this conference. Provision has also been made for insertion of a first-stage low-noise amplifier for using the circuit under low-signal conditions.
NASA Astrophysics Data System (ADS)
Leusink, G. J.; Oosterlaken, T. G. M.; Janssen, G. C. A. M.; Radelaar, S.
1993-09-01
An in situ study of the evolution of the biaxial state of intrinsic stress during nucleation and growth of polycrystalline tungsten chemical vapor deposition films deposited by the hydrogen reduction of tungsten hexafluoride is presented. The evolution of biaxial stress was determined from in situ wafer curvature measurements. It is shown that the intrinsic stress is a growth stress, i.e., a stress developing in close vicinity to the advancing surface of the film due to metastable film growth processes. The stress developing depends strongly on the thickness of the film. High tensile stress (≊4 GPa) is observed during the initial stage of growth, compressive stress (up to -1 GPa) is observed in an intermediate thickness regime after film closure and tensile stress (0.1-1 GPa) is observed in the thick film regime. The associated stress gradients in the film are preserved during and after growth. The development of growth stress is determined by deposition temperature and growth rate. The tensile stress in the thick film regime is larger at a higher growth rate or a lower deposition temperature, while the compressive stress in the intermediate thickness regime showed the opposite dependency. Film properties as the evolution of grain size, impurity content, and resistivity are found not to vary significantly with the growth conditions. Therefore, the development of growth stress is ascribed to kinetical processes. The development of tensile stress in the thick film regime is described with a (kinetic) grain boundary formation and relaxation model. The compressive stress in the intermediate thickness regime is tentatively ascribed to compressive coherency strains induced by interfacial tensions of the grains in the stage of island growth.
Aerial and in situ Measurements of Submesoscale Eddies, Fronts, and Filaments
NASA Astrophysics Data System (ADS)
Baschek, Burkard; Maarten Molemaker, Jeroen
2010-05-01
Submesoscale eddies, fronts, and filaments on scales of 10 m to 20 km are common features of many coastal regions of the world. Modeling results suggest that these submesoscale phenomena play an important role in local energy cascades, transferring energy from the large-scale ocean circulation to turbulence. It is also likely that submesoscale features are important for mixing, vertical transport, or biogeochemical processes. While submesoscale features have been observed using SAR satellite imagery, only very limited in situ measurements exist that reveal the dynamically relevant internal structure. Submesoscale features have a life time of several hours to a few days and advective speeds of up to 0.5 ms-1, which makes it very hard to measure them with traditional in situ sampling. Also satellite sea surface temperature (SST) data cannot sufficiently resolve the small scales of these features. We present aerial and in situ measurements of submesoscale eddies, fronts, and filaments, and believe to have carried out the first time in situ measurements of a spiral eddy (~2.5 km diameter) during a 5-day experiment in September 2009 off Catalina Island, CA. The observations are taken with a cost efficient and pragmatic observational approach for repeat quasi-synoptic measurements of submesoscale features in real-time and on the required small spatial and temporal scales of ~30min and ~20m. An IR camera mounted on a small plane is used to derive fine-resolution SST maps of this area and to guide a fast response vessel to distinct submesoscale features. A temperature/pressure array is towed in the upper 45m at speeds of 5 ms-1 through the features. The properties of the submesoscale features are examined within the context of the larger-scale circulation patterns of this highly variable coastal region combined with the analysis of satellite SST, coastal radar, and mooring data.
Front-end Electronics for Unattended Measurement (FEUM). Results of Prototype Evaluation
Conrad, Ryan C.; Keller, Daniel T.; Morris, Scott J.; Smith, Leon E.
2015-07-01
The International Atomic Energy Agency (IAEA) deploys unattended monitoring systems to provide continuous monitoring of nuclear material within safeguarded facilities around the world. As the number of unattended monitoring instruments increases, the IAEA is challenged to become more efficient in the implementation of those systems. In 2010, the IAEA initiated the Front-End Electronics for Unattended Measurement (FEUM) project with the goals of greater flexibility in the interfaces to various sensors and data acquisition systems, and improved capabilities for remotely located sensors (e.g., where sensor and front-end electronics might be separated by tens of meters). In consultation with the IAEA, a technical evaluation of a candidate FEUM device produced by a commercial vendor has been performed. This evaluation assessed the device against the IAEA’s original technical specifications and a broad range of important parameters that include sensor types, cable lengths and types, industrial electromagnetic noise that can degrade signals from remotely located detectors, and high radiation fields. Testing data, interpretation, findings and recommendations are provided.
Poyneer, Lisa A; Bauman, Brian J
2015-03-31
Reference-free compensated imaging makes an estimation of the Fourier phase of a series of images of a target. The Fourier magnitude of the series of images is obtained by dividing the power spectral density of the series of images by an estimate of the power spectral density of atmospheric turbulence from a series of scene based wave front sensor (SBWFS) measurements of the target. A high-resolution image of the target is recovered from the Fourier phase and the Fourier magnitude.
Ferreira, João C P; Fujihara, Caroline J; Fruhvald, Erika; Trevisol, Eduardo; Destro, Flavia C; Teixeira, Carlos R; Pantoja, José C F; Schmidt, Elizabeth M S; Palme, Rupert
2015-01-01
Parrots kept in zoos and private households often develop psychological and behavioural disorders. Despite knowing that such disorders have a multifactorial aetiology and that chronic stress is involved, little is known about their development mainly due to a poor understanding of the parrots' physiology and the lack of validated methods to measure stress in these species. In birds, blood corticosterone concentrations provide information about adrenocortical activity. However, blood sampling techniques are difficult, highly invasive and inappropriate to investigate stressful situations and welfare conditions. Thus, a non-invasive method to measure steroid hormones is critically needed. Aiming to perform a physiological validation of a cortisone enzyme immunoassay (EIA) to measure glucocorticoid metabolites (GCM) in droppings of 24 Blue-fronted parrots (Amazona aestiva), two experiments were designed. During the experiments all droppings were collected at 3-h intervals. Initially, birds were sampled for 24 h (experiment 1) and one week later assigned to four different treatments (experiment 2): Control (undisturbed), Saline (0.2 mL of 0.9% NaCl IM), Dexamethasone (1 mg/kg IM) and Adrenocorticotropic hormone (ACTH; 25 IU IM). Treatments (always one week apart) were applied to all animals in a cross-over study design. A daily rhythm pattern in GCM excretion was detected but there were no sex differences (first experiment). Saline and dexamethasone treatments had no effect on GCM (not different from control concentrations). Following ACTH injection, GCM concentration increased about 13.1-fold (median) at the peak (after 3-9 h), and then dropped to pre-treatment concentrations. By a successful physiological validation, we demonstrated the suitability of the cortisone EIA to non-invasively monitor increased adrenocortical activity, and thus, stress in the Blue-fronted parrot. This method opens up new perspectives for investigating the connection between behavioural
Ferreira, João C. P.; Fujihara, Caroline J.; Fruhvald, Erika; Trevisol, Eduardo; Destro, Flavia C.; Teixeira, Carlos R.; Pantoja, José C. F.; Schmidt, Elizabeth M. S.; Palme, Rupert
2015-01-01
Parrots kept in zoos and private households often develop psychological and behavioural disorders. Despite knowing that such disorders have a multifactorial aetiology and that chronic stress is involved, little is known about their development mainly due to a poor understanding of the parrots’ physiology and the lack of validated methods to measure stress in these species. In birds, blood corticosterone concentrations provide information about adrenocortical activity. However, blood sampling techniques are difficult, highly invasive and inappropriate to investigate stressful situations and welfare conditions. Thus, a non-invasive method to measure steroid hormones is critically needed. Aiming to perform a physiological validation of a cortisone enzyme immunoassay (EIA) to measure glucocorticoid metabolites (GCM) in droppings of 24 Blue-fronted parrots (Amazona aestiva), two experiments were designed. During the experiments all droppings were collected at 3-h intervals. Initially, birds were sampled for 24 h (experiment 1) and one week later assigned to four different treatments (experiment 2): Control (undisturbed), Saline (0.2 mL of 0.9% NaCl IM), Dexamethasone (1 mg/kg IM) and Adrenocorticotropic hormone (ACTH; 25 IU IM). Treatments (always one week apart) were applied to all animals in a cross-over study design. A daily rhythm pattern in GCM excretion was detected but there were no sex differences (first experiment). Saline and dexamethasone treatments had no effect on GCM (not different from control concentrations). Following ACTH injection, GCM concentration increased about 13.1-fold (median) at the peak (after 3–9 h), and then dropped to pre-treatment concentrations. By a successful physiological validation, we demonstrated the suitability of the cortisone EIA to non-invasively monitor increased adrenocortical activity, and thus, stress in the Blue-fronted parrot. This method opens up new perspectives for investigating the connection between behavioural
NASA Astrophysics Data System (ADS)
Aliverti, Matteo; Pariani, Giorgio; Moschetti, Manuele; Riva, Marco
2016-08-01
Traditional techniques usually rely on optical feedback to align optical elements over all the degrees of freedom needed. This strongly iterative process implies the use of bulky and/or flexible adjustable mountings. Another solution under study consists in the characterization of every optomechanical elements and the integration of the parts without any optical feedback. The characterization can be performed using different 3D Coordinate Measuring Machines (like Laser Tracker, Articulated Arms and Cartesian ones) and referencing different parts like the optomechanical mounts or the optical surfaces. The alignment of the system is done adjusting the six degrees of freedom of every element with metallic shims. Those calibrated elements are used to correct the interfaces position of the semikinematic system composed by 3 screws and 3 pins. In this paper, the integration and alignment of the ESPRESSO Front End Units (FEUs) will be used as pathfinder to test different alignment methods and evaluate their performances.
Theoretical and measured power density in front of VHF/UHF broadcasting antennas.
Jokela, K
1988-05-01
A simple and easy-to-use model based on more rigorous computations was formulated for the prediction of power density levels in front of dipole array-type VHF (very high frequency) and UHF (ultra high frequency) broadcasting antennas. Measurements on site verified the usefulness of the model. The distance at which the power density begins to exceed 10 W.m-2--the value established by standards as a limit--is roughly 40 m for UHF-TV antennas, 30 m for FM (frequency modulated) radio antennas and 15 m for VHF-TV antennas. Typical average input powers of antennas are 20 kW, 4 kW and 10 kW for FM radio, VHF-TV and UHF transmissions, respectively.
Measures of the environmental footprint of the front end of the nuclear fuel cycle
E. Schneider; B. Carlsen; E. Tavrides; C. van der Hoeven; U. Phathanapirom
2013-11-01
Previous estimates of environmental impacts associated with the front end of the nuclear fuel cycle (FEFC) have focused primarily on energy consumption and CO2 emissions. Results have varied widely. This work builds upon reports from operating facilities and other primary data sources to build a database of front end environmental impacts. This work also addresses land transformation and water withdrawals associated with the processes of the FEFC. These processes include uranium extraction, conversion, enrichment, fuel fabrication, depleted uranium disposition, and transportation. To allow summing the impacts across processes, all impacts were normalized per tonne of natural uranium mined as well as per MWh(e) of electricity produced, a more conventional unit for measuring environmental impacts that facilitates comparison with other studies. This conversion was based on mass balances and process efficiencies associated with the current once-through LWR fuel cycle. Total energy input is calculated at 8.7 x 10- 3 GJ(e)/MWh(e) of electricity and 5.9 x 10- 3 GJ(t)/MWh(e) of thermal energy. It is dominated by the energy required for uranium extraction, conversion to fluoride compound for subsequent enrichment, and enrichment. An estimate of the carbon footprint is made from the direct energy consumption at 1.7 kg CO2/MWh(e). Water use is likewise dominated by requirements of uranium extraction, totaling 154 L/MWh(e). Land use is calculated at 8 x 10- 3 m2/MWh(e), over 90% of which is due to uranium extraction. Quantified impacts are limited to those resulting from activities performed within the FEFC process facilities (i.e. within the plant gates). Energy embodied in material inputs such as process chemicals and fuel cladding is identified but not explicitly quantified in this study. Inclusion of indirect energy associated with embodied energy as well as construction and decommissioning of facilities could increase the FEFC energy intensity estimate by a factor of up
Spatial curvature falsifies eternal inflation
Kleban, Matthew; Schillo, Marjorie E-mail: mls604@nyu.edu
2012-06-01
Inflation creates large-scale cosmological density perturbations that are characterized by an isotropic, homogeneous, and Gaussian random distribution about a locally flat background. Even in a flat universe, the spatial curvature measured within one Hubble volume receives contributions from long wavelength perturbations, and will not in general be zero. These same perturbations determine the Cosmic Microwave Background (CMB) temperature fluctuations, which are O(10{sup −5}). Consequently, the low-l multipole moments in the CMB temperature map predict the value of the measured spatial curvature Ω{sub k}. On this basis we argue that a measurement of |Ω{sub k}| > 10{sup −4} would rule out slow-roll eternal inflation in our past with high confidence, while a measurement of Ω{sub k} < −10{sup −4} (which is positive curvature, a locally closed universe) rules out false-vacuum eternal inflation as well, at the same confidence level. In other words, negative curvature (a locally open universe) is consistent with false-vacuum eternal inflation but not with slow-roll eternal inflation, and positive curvature falsifies both. Near-future experiments will dramatically extend the sensitivity of Ω{sub k} measurements and constitute a sharp test of these predictions.
Nedzelnitsky, Victor; Wagner, Randall P.
2008-01-01
To achieve an acceptable degree of accuracy at high frequencies in some standardized methods for primary calibration of laboratory standard (LS) microphones, the front cavity depth lfc of each microphone must be known. This dimension must be measured using non-contact methods to prevent damage to the microphone diaphragm. The basic capabilities of an optical depth-measuring microscope were demonstrated by the agreement of its measurements within 0.7 μm of the known values of reference gage blocks. Using this microscope, two basic methods were applied to measure lfc. One (D) uses direct measurements at the microphone front surface annulus and conventional data reduction techniques. The other (GB) uses measurements at the surface of a gage block placed on the annulus, and plane-fitting data reduction techniques intended to reduce the effects of the slightly imperfect geometries of the microphones. The GB method was developed to provide a smoother surface of measurement than the relatively rough surface of the annulus, and to simulate the contact that occurs between the annulus and the smooth, plane surface of an acoustic coupler during microphone calibration. Using these methods, full data sets were obtained at 33 measurement positions (D), or 25 positions (GB). In addition, D and GB subsampling methods were applied by using subsamples of either the D or the GB full data sets. All these methods were applied to six LS microphones, three each of two different types. The GB subsampling methods are preferred for several reasons. The measurement results for lfc obtained by these methods agree well with those obtained by the GB method using the full data set. The expanded uncertainties of results from the GB subsampling methods are not very different from the expanded uncertainty of results from the GB method using the full data set, and are smaller than the expanded uncertainties of results from the D subsampling methods. Measurements of lfc using the GB subsampling
Excitation ahead of shock fronts in krypton measured by single line laser absorption
NASA Astrophysics Data System (ADS)
Boetticher, W.; Kilpin, D.
1984-12-01
The absorption of single-mode radiation (from a dye laser tuned to 587.25 and 557.18 nm) by Kr in front of shock waves with Mach numbers 12-21 in a 50-mm-diameter 4.4-m-long free-position driver shock tube at preshock pressures 0.7-2.7 kPa is measured to determine the number densities of the metastable 5s(1 1/2)2 and 5s(1 1/2)1 precursor states (1s5 and 1s4 in Paschen notation, respectively). The measurement technique and calculations follow those of Ernst (1982). The results are presented in tables and graphs and characterized in comparison with previous findings. The time constant of the exponential rise of the precursor is found to be about 8 microsec, and the concentration of 1s5 + 1s4 for Mach 20 is calculated as about 10 ppm, in agreement (to within a factor of 5) with model predictions for Ar and Xe.
Spatial curvature endgame: Reaching the limit of curvature determination
NASA Astrophysics Data System (ADS)
Leonard, C. Danielle; Bull, Philip; Allison, Rupert
2016-07-01
Current constraints on spatial curvature show that it is dynamically negligible: |ΩK|≲5 ×10-3 (95% C.L.). Neglecting it as a cosmological parameter would be premature however, as more stringent constraints on ΩK at around the 10-4 level would offer valuable tests of eternal inflation models and probe novel large-scale structure phenomena. This precision also represents the "curvature floor," beyond which constraints cannot be meaningfully improved due to the cosmic variance of horizon-scale perturbations. In this paper, we discuss what future experiments will need to do in order to measure spatial curvature to this maximum accuracy. Our conservative forecasts show that the curvature floor is unreachable—by an order of magnitude—even with Stage IV experiments, unless strong assumptions are made about dark energy evolution and the Λ CDM parameter values. We also discuss some of the novel problems that arise when attempting to constrain a global cosmological parameter like ΩK with such high precision. Measuring curvature down to this level would be an important validation of systematics characterization in high-precision cosmological analyses.
NASA Technical Reports Server (NTRS)
Demoz, Belay; Miller, David; Schwemmer, Geary; Starr, David OC (Technical Monitor)
2001-01-01
Lidar atmospheric systems have required large telescope for receiving atmospheric backscatter signals. Thus, the relative complexity in size and ease of operation has limited their wider use in the atmospheric science and meteorology community. The Holographic Airborne Rotating Lidar Instrument Experiment (HARLIE) uses a scanning holographic receiver and demonstrates that these issues can be overcome. HARLIE participated at the DOE-ARM Southern Great Plains site (CART) during the Water Vapor Intensive Operation Period (WVIOP2000) held September-October 2000. It provided exceptional high temporal and spatial resolution measurements of aerosol and cloud backscatter in three dimensions. HARLIE recorded over 110 hours of data were recorded on 16 days between 17 September and 6 October 2000. Placed in a ground-based trailer for upward looking scanning measurements of clouds and aerosols, HARLIE provided a unique record of time-resolved atmospheric backscatter at 1-micron wavelength. The conical scanning lidar measures atmospheric backscatter on the surface of an inverted 90 degree (full angle) cone up to an altitude of 20 km, 360-degree scans having spatial resolutions of 20 meters in the vertical and 1 degree in azimuth were obtained every 36 seconds during the daily, operating period. In this study we present highlights of HARLIE-based measurements of the boundary layer and cloud parameters as well as atmospheric wind vectors where there is sufficiently resolved structure in the backscatter. In particular we present data and discussions from a bore-front case observed on 23 September 2000.
Pech-May, Nelson Wilbur; Mendioroz, Arantza; Salazar, Agustín
2014-10-15
In this work, we have extended the front-face flash method to retrieve simultaneously the thermal diffusivity and the optical absorption coefficient of semitransparent plates. A complete theoretical model that allows calculating the front surface temperature rise of the sample has been developed. It takes into consideration additional effects, such as multiple reflections of the heating light beam inside the sample, heat losses by convection and radiation, transparency of the sample to infrared wavelengths, and heating pulse duration. Measurements performed on calibrated solids, covering a wide range of absorption coefficients (from transparent to opaque) and thermal diffusivities, validate the proposed method.
Wide Dynamic Range Front-end Electronics for Beam Current and Position Measurement
Rawnsley, W. R.; Potter, R. J.; Verzilov, V. A.; Root, L.
2006-11-20
An Analog Devices log detector, AD8306, and a Digital Signal Processor (DSP), ADSP-21992, have been found useful for building wide dynamic range, accurate and inexpensive front-end electronics to measure and process the RF signals from TRIUMF's beam monitors. The high-precision log detector has a useful dynamic range of over 100 dB. The 160 MHz mixed-signal DSP is used to digitize the log detector output, linearize it via a lookup table, perform temperature compensation, and remove the variable duty cycle 1 kHz pulse structure of the beam. This approach has been applied to two types of devices in a 500 MeV proton beamline. The 0.1% DC to CW total current monitor is based on a capacitive pickup resonant at 46.11 MHz, the second harmonic of the bunch frequency. The DSP software provides low pass filtering, calculates the antilog of the data and passes the output to a CAMAC input register. The BPM electronics process data from inductive pickup loops. The DSP controls a GaAs switch which multiplexes signals from four adjacent pickups to a single log detector. The DSP performs difference-over-sum or log-ratio data analysis along with averaging over an arbitrary number of samples.
NASA Astrophysics Data System (ADS)
Meyer, Eileen T.
The effects of modeling the intrinsic curvature of the spectral energy distributions of BL Lacertae objects in the soft x-ray on the V/V M evolutionary statistic were studied. It was found that the power law approximations in the soft x-ray could cause a significant bias in V/V M towards values supporting either negative or positive evolution for BL Lacs. The effects of such a bias on the Sedentary Survey, a large sample of 150 BL Lacertae objects, were found to be negligible on average though individual effects were appreciable. The luminosity function and parametric values of evolution for pure luminosity and pure density evolution were computed for the Sedentary Sample.
NASA Astrophysics Data System (ADS)
Zisman, Alexander
2016-04-01
Starting from Nye's tensor, alternative characteristics of crystal curvature indicative of dislocation content are considered subject to very low thickness of investigated matter under the free surface and discreteness of orientation sampling. Analysis within the framework of continuum mechanics, undertaken to allow for such conditions peculiar to the electron backscatter diffraction (EBSD) technique, has shown the variable part of orientations expressed in a vector form to be most sensitive to lattice defects when projected to the free surface plane. Hence, as verified with EBSD data on a grain junction in a low deformed IF steel, magnitude of the projected field allows one to map plastic strains inhomogeneous within grains whereas divergence of this field distinctly images and quantifies low-angle dislocation boundaries formed at low strains.
ERIC Educational Resources Information Center
Ngo, Duc Minh
2009-01-01
Current methodologies used for the inference of thin film stresses through curvatures are strictly restricted to stress and curvature states which are assumed to remain uniform over the entire film/substrate system. In this dissertation, we extend these methodologies to non-uniform stress and curvature states for the single layer of thin film or…
NASA Astrophysics Data System (ADS)
Verlinden, Pierre; Van de Wiele, Fernand
1985-03-01
A method is proposed for measuring the diffusion length and surface recombination velocity of Interdigitated Back Contact (IBC) solar cells by means of a simple linear regression on experimental quantum efficiency values versus the inverse of the absorption coefficient. This method is extended to the case of Front Surface Field (FSF) solar cells. Under certain conditions, the real or the effective surface recombination velocity may be measured.
Measures of the Environmental Footprint of the Front End of the Nuclear Fuel Cycle
Brett Carlsen; Emily Tavrides; Erich Schneider
2010-08-01
Previous estimates of environmental impacts associated with the front end of the nuclear fuel cycle have focused primarily on energy consumption and CO2 emissions. Results have varied widely. Section 2 of this report provides a summary of historical estimates. This study revises existing empirical correlations and their underlying assumptions to fit to a more complete set of existing data. This study also addresses land transformation, water withdrawals, and occupational and public health impacts associated with the processes of the front end of the once-through nuclear fuel cycle. These processes include uranium mining, milling, refining, conversion, enrichment, and fuel fabrication. Metrics are developed to allow environmental impacts to be summed across the full set of front end processes, including transportation and disposition of the resulting depleted uranium.
Curvatures Estimation in Orientation Selection
1991-01-31
than is-obtained in length-tuning measurements . Hence, over a limited range, increasing the size or gain of the small RF has a similar effect . The...the remaining larger, lower curvature units to represent the curve. An indirect test involves measuring the time for the effect to set in, with and...31Jan 91 By, Steen .Zcke * ax . Cnadr tDistribution/ Steen .Zcke *MaxS. ynaer ~ Availability Codes Dist Special Computer Vision and Robotics Laboratory
Kim, Do-Hyun; Shi, Dexiu; Ilev, Ilko K
2011-09-10
We present a simple method for measuring the effective focal length without determining the location of principle plane of the lens. The method is based on the measurement of confocal backreflection axial responses from the front and back surfaces of a reference plate with known refractive index and thickness. We proved the concept by measuring the effective focal lengths of thin singlet lenses and complex microscope objectives. The theoretical limit of measurement precision varies depending on the numerical aperture of the lens. This method can provide an alternative focal length measurement method for complex lenses or lenses that are permanently attached to other structures. Measurement errors were analyzed theoretically and improvements in measurement accuracy were discussed.
Determining wave direction using curvature parameters.
de Queiroz, Eduardo Vitarelli; de Carvalho, João Luiz Baptista
2016-01-01
The curvature of the sea wave was tested as a parameter for estimating wave direction in the search for better results in estimates of wave direction in shallow waters, where waves of different sizes, frequencies and directions intersect and it is difficult to characterize. We used numerical simulations of the sea surface to determine wave direction calculated from the curvature of the waves. Using 1000 numerical simulations, the statistical variability of the wave direction was determined. The results showed good performance by the curvature parameter for estimating wave direction. Accuracy in the estimates was improved by including wave slope parameters in addition to curvature. The results indicate that the curvature is a promising technique to estimate wave directions.•In this study, the accuracy and precision of curvature parameters to measure wave direction are analyzed using a model simulation that generates 1000 wave records with directional resolution.•The model allows the simultaneous simulation of time-series wave properties such as sea surface elevation, slope and curvature and they were used to analyze the variability of estimated directions.•The simultaneous acquisition of slope and curvature parameters can contribute to estimates wave direction, thus increasing accuracy and precision of results.
NASA Astrophysics Data System (ADS)
Shishkovskiy, I.; Sherbakov, V.; Morozov, Yu.
2007-06-01
Rapid prototyping (RP) and manufacturing (M) is a novel layer-by-layer fabrication technique which has become increasingly popular due to its inherent flexibility for the manufacture of simple and complex 3D parts. Early we had been shown opportunity of selective laser sintering (SLS) of different type powder systems (intermetallics, ceramics, ferrites, high-temperature superconductors), traditional use for self-propagated high-temperature synthesis (SHS). The non-thermal heating affect of an external electromagnetic field during SHS is related to the specific system under study due to differences in movement of defects and ions at the 'plasma-like' molten combustion wave front. We have developed and refined the testing scheme for electro-thermal phenomena studies which can directly influence on the SHS combustion wave front. This work studies electromotive force (EMF) measurements across the front of combustion wave during layer by layer surface laser sintering of exothermal powder compositions (Ni-Ti, Ni-Al). Analysis using an analog-digital-analog computer converter allowed some control of the laser movement and hence some control of the exothermal reaction - in so doing it provided near optimum conditions for forming layered 3D articles. Comparative results of structural-phase transformation during laser control SHS in reaction-capable compositions are presented.
NASA Astrophysics Data System (ADS)
Semmelroth, K.; Berwian, P.; Schröter, C.; Leibiger, G.; Schönleber, M.; Friedrich, J.
2015-10-01
For improved real-time process control we integrated a novel optical in-situ monitoring system in a vertical reactor for hydride vapor phase epitaxy (HVPE) growth of gallium nitride (GaN) bulk crystals. The in-situ monitoring system consists of a fiber-optical interferometric sensor in combination with an optimized differential measuring head. The system only needs one small optical path perpendicular to the center of the layer stack typically consisting of sapphire as substrate and GaN. It can handle sample distances up to 1 m without difficulty. The in-situ monitoring system is simultaneously measuring the optical layer thicknesses of the GaN/sapphire layer stack and the absolute change of the distance between the measuring head and the backside of the layer stack. From this data it is possible to calculate the thickness of the growing GaN up to a thickness of about 1000 μm and the absolute change in curvature of the layer stack. The performance of the in-situ monitoring system is shown and discussed based on the measured interference signals recorded during a short-time and a long-time HVPE growth run.
Vasquez, Dionicio; Scharcanski, Jacob; Wong, Alexander
2015-01-01
This paper presents a new automatic framework for extracting and characterizing the dynamic shape of the 3D wetting front and its propagation, based in a sequence of tomographic images acquired as water (moisture) infiltrates in unsaturated soils. To the best of the authors’ knowledge, the shape of the 3D wetting front and its propagation and progress over time has not been previously produced as a whole by methods in existing literature. The proposed automatic framework is composed two important and integrated modules: i) extraction of the 3D wetting front, and ii) characterization and description of the 3D wetting front to obtain important information about infiltration process. The 3D wetting front surface is segmented from 3D CT imagery provided as input via a 3D stochastic region merging strategy using quadric-regressed bilateral space-scale representations. Based on the 3D segmentation results, the normal directions at local curvature maxima of the wetting front surface are computed for 3D images of soil moisture, and its propagation is analyzed at the local directions in sites of maximal water adsorption, and described using histograms of curvature changes over time in response to sample saturation. These curvature change descriptors provide indirect measurements of moisture infiltration in soils, and soil saturation. Results using a field tomograph equipment specific for soil studies are encouraging, and suggest that the proposed automatic framework can be applied to estimate the infiltration of water in soils in 3D and in time. PMID:25602498
Vasquez, Dionicio; Scharcanski, Jacob; Wong, Alexander
2015-01-01
This paper presents a new automatic framework for extracting and characterizing the dynamic shape of the 3D wetting front and its propagation, based in a sequence of tomographic images acquired as water (moisture) infiltrates in unsaturated soils. To the best of the authors' knowledge, the shape of the 3D wetting front and its propagation and progress over time has not been previously produced as a whole by methods in existing literature. The proposed automatic framework is composed two important and integrated modules: i) extraction of the 3D wetting front, and ii) characterization and description of the 3D wetting front to obtain important information about infiltration process. The 3D wetting front surface is segmented from 3D CT imagery provided as input via a 3D stochastic region merging strategy using quadric-regressed bilateral space-scale representations. Based on the 3D segmentation results, the normal directions at local curvature maxima of the wetting front surface are computed for 3D images of soil moisture, and its propagation is analyzed at the local directions in sites of maximal water adsorption, and described using histograms of curvature changes over time in response to sample saturation. These curvature change descriptors provide indirect measurements of moisture infiltration in soils, and soil saturation. Results using a field tomograph equipment specific for soil studies are encouraging, and suggest that the proposed automatic framework can be applied to estimate the infiltration of water in soils in 3D and in time.
Front lighted optical tooling method and apparatus
Stone, William J.
1985-06-18
An optical tooling method and apparatus uses a front lighted shadowgraphic technique to enhance visual contrast of reflected light. The apparatus includes an optical assembly including a fiducial mark, such as cross hairs, reflecting polarized light with a first polarization, a polarizing element backing the fiducial mark and a reflective surface backing the polarizing element for reflecting polarized light bypassing the fiducial mark and traveling through the polarizing element. The light reflected by the reflecting surface is directed through a second pass of the polarizing element toward the frontal direction with a polarization differing from the polarization of the light reflected by the fiducial mark. When used as a tooling target, the optical assembly may be mounted directly to a reference surface or may be secured in a mounting, such as a magnetic mounting. The optical assembly may also be mounted in a plane defining structure and used as a spherometer in conjunction with an optical depth measuring instrument. A method of measuring a radius of curvature of an unknown surface includes positioning the spherometer on a surface between the surface and a depth measuring optical instrument. As the spherometer is frontally illuminated, the distance from the depth measuring instrument to the fiducial mark and the underlying surface are alternately measured and the difference in these measurements is used as the sagittal height to calculate a radius of curvature.
Ruppel, F.R.
1991-01-01
An evaluation of the novel self-calibrating thermocouple was performed to determine whether the sensor would be acceptable as a front end to a smart temperature measurement system. The evaluation consisted of a fast-ramp test, long-term drift tests, and physical examinations including X rays, microphotography, and energy-dispersive spectrometry. The results of the tests show that the sensor is a viable industrial-grade device worthy for use in this application. However, recommendations for improving fabrication of the assembly are made and caveats are given for conditions that may constrain the use of the sensor in certain situations. 4 refs., 17 figs., 1 tab.
NASA Astrophysics Data System (ADS)
Wu, Fenxiang; Xu, Yi; Yu, Linpeng; Yang, Xiaojun; Li, Wenkai; Lu, Jun; Leng, Yuxin
2016-11-01
Pulse front distortion (PFD) is mainly induced by the chromatic aberration in femtosecond high-peak power laser systems, and it can temporally distort the pulse in the focus and therefore decrease the peak intensity. A novel measurement scheme is proposed to directly measure the PFD of ultra-intensity ultra-short laser pulses, which can work not only without any extra struggle for the desired reference pulse, but also largely reduce the size of the required optical elements in measurement. The measured PFD in an experimental 200TW/27fs laser system is in good agreement with the calculated result, which demonstrates the validity and feasibility of this method effectively. In addition, a simple compensation scheme based on the combination of concave lens and parabolic lens is also designed and proposed to correct the PFD. Based on the theoretical calculation, the PFD of above experimental laser system can almost be completely corrected by using this compensator with proper parameters.
NASA Astrophysics Data System (ADS)
Monga, Olivier; Ayache, Nicholas; Sander, Peter T.
1991-09-01
Modern medical image techniques, such as magnetic resonance image (MRI) or x-ray computed tomography provide three dimensional images of internal structures of the body, usually by means of a stack of tomographic images. The first stage in the automatic analysis of such data is 3-D edge detection1,2 which provides points corresponding to the boundaries of the surfaces forming the 3-D structure. The next stage is to characterize the local geometry of these surfaces in order to extract points or lines on which registration and/or tracking procedures can rely.3,4,5,6 This paper presents a pipeline of processes which define a hierarchical description of the second order differential characteristics of the surfaces. The focus is on the theoretical coherence of these levels of representation. Using uncertainty, a link is established between the edge detection and the local surface approximation by addressing the uncertainties inherent to edge detection in 2-D or 3-D images; and how to incorporate these uncertainties into the computation of local geometric models. In particular, calculate the uncertainty of edge location, direction, and magnitude for the 3-D Deriche operator is calculated.1,2 Statistical results are then used as a solid theoretical foundation on which to base subsequent computations, such as the determination of local surface curvature using local geometric models for surface segmentation. From the local fitting, for each edge point the mean and Gaussian curvature, principal curvatures and directions, curvature singularities, lines of curvature singularities, and covariance matrices defining the uncertainties are calculated. Experimental results for real data using two 3-D scanner images of the same organ taken at different positions demonstrate the stability of the mean and Gaussian curvatures. Experimental results for real data showing the determination of local curvature extremes of surfaces extracted from MR images are presented.
NASA Astrophysics Data System (ADS)
Farooq, Omer; Ranjeet Madiyar, Foram; Crandall, Sara; Ratra, Bharat
2017-01-01
We compile an updated list of 38 measurements of the Hubble parameter H(z) between redshifts 0.07 ≤ z ≤ 2.36 and use them to place constraints on model parameters of constant and time-varying dark energy cosmological models, both spatially flat and curved. We use five models to measure the redshift of the cosmological deceleration–acceleration transition, zda, from these H(z) data. Within the error bars, the measured zda are insensitive to the model used, depending only on the value assumed for the Hubble constant H0. The weighted mean of our measurements is zda = 0.72 ± 0.05 (0.84 ± 0.03) for H0 = 68 ± 2.8 (73.24 ± 1.74) km s‑1 Mpc‑1 and should provide a reasonably model-independent estimate of this cosmological parameter. The H(z) data are consistent with the standard spatially flat ΛCDM cosmological model but do not rule out nonflat models or dynamical dark energy models.
NASA Astrophysics Data System (ADS)
Block, Martin M.; Durand, Loyal; Ha, Phuoc; Halzen, Francis
2016-06-01
We study the effects of curvature in the expansion of the logarithm of the differential elastic scattering cross section near t =0 as d σ (s ,t )/d t =d σ (s ,0 )/d t ×exp (B t +C t2+D t3⋯) in an eikonal model for p p and p ¯p scattering, and use the results to discuss the extrapolation of measured differential cross sections and the slope parameters B to t =-q2=0 . We find that the curvature effects represented by the parameters C and D , while small, lead to significant changes in the forward slope parameter relative to that determined in a purely exponential fit, and to smaller but still significant changes in the forward elastic scattering and total cross sections. Curvature effects should therefore be considered in future analyses or reanalyses of the elastic scattering data.
Barenboim, Gabriela; Martínez, Enrique Fernández; Mena, Olga; Verde, Licia E-mail: enfmarti@mppmu.mpg.de E-mail: liciaverde@icc.ub.edu
2010-03-01
Geometrical tests such as the combination of the Hubble parameter H(z) and the angular diameter distance d{sub A}(z) can, in principle, break the degeneracy between the dark energy equation of state parameter w(z), and the spatial curvature Ω{sub k} in a direct, model-independent way. In practice, constraints on these quantities achievable from realistic experiments, such as those to be provided by Baryon Acoustic Oscillation (BAO) galaxy surveys in combination with CMB data, can resolve the cosmic confusion between the dark energy equation of state parameter and curvature only statistically and within a parameterized model for w(z). Combining measurements of both H(z) and d{sub A}(z) up to sufficiently high redshifts z ∼ 2 and employing a parameterization of the redshift evolution of the dark energy equation of state are the keys to resolve the w(z)−Ω{sub k} degeneracy.
A new front-end ASIC for GEM detectors with time and charge measurement capabilities
NASA Astrophysics Data System (ADS)
Ciciriello, F.; Corsi, F.; De Robertis, G.; Felici, G.; Loddo, F.; Marzocca, C.; Matarrese, G.; Ranieri, A.
2016-07-01
A 32 channel CMOS front-end ASIC has been designed to read out the GEM detectors intended to be used for beam monitoring in a new proton-therapy facility currently under construction. In order to improve the spatial resolution by exploiting charge centroid algorithms, the analog channels, based on the classic CSA+shaper architecture, are equipped with a peak detector (PD) which works as an analog memory during the read-out phase. The outputs of the PDs are multiplexed towards an integrated 8-bit subranging ADC. An accurate trigger signal marks the arrival of a valid event and is generated by fast-ORing the outputs of 32 voltage discriminators which compare the shaper outputs with a programmable threshold. The digital part of the ASIC manages the read-out of the channels, the A/D conversion and the configuration of the ASIC. A 100 Mbit/s LVDS serial link is used for data communication. The sensitivity of the analog channel is 15 mV/fC and the dynamic range is 80 fC. The simulated ENC is about 650 e- for a detector capacitance of 10 pF. © 2001 Elsevier Science. All rights reserved
Fleas on operations in Afghanistan--environmental health measures on the front line.
Naumann, D N; Baird-Clarke, C D; Ross, D A
2011-09-01
Flea bites can cause irritating symptoms, secondary infections, and may potentiate the spread of vector-borne disease. Flea infestation and bites may also cause significant psychological distress, and can reduce the morale and fighting fitness of deployed military personnel. The problem of flea infestation was highlighted during Op HERRICK 12 in two 'front line' Check Points (CPs) where the entire population of soldiers suffered from multiple symptoms due to flea infestation and bites. Several attempts at infestation control initially succeeded but later lead to recurrence. Such failure was due to the incomplete killing of all stages of the flea life cycle, and due to constraints on education, training, communication, and resupply in the isolated and austere environment of the CPs. A dedicated operation (designated Op Insecticide) was put into action in order to eradicate the problem and return the affected troops back to full fighting fitness. Op Insecticide was thorough, systematic and sustainable, and lead to an eradication of the flea infestation problem at the affected CPs.
NASA Astrophysics Data System (ADS)
Andrew, Matthew; Bijeljic, Branko; Blunt, Martin J.
2014-11-01
X-ray microtomography was used to image the shape and size of residual ganglia of supercritical CO2 at resolutions of 3.5 and 2 μm and at representative subsurface conditions of temperature and pressure. The capillary pressure for each ganglion was found by measuring the curvature of the CO2-brine interface, while the pore structure was parameterized using distance maps of the pore space. The formation of the residual clusters by snap-off was examined by comparing the ganglion capillary pressure to local pore topography. The capillary pressure was found to be inversely proportional to the radius of the largest restriction (throat) surrounding the ganglion, which validates the imbibition mechanisms used in pore-network modeling. The potential mobilization of residual ganglia was assessed using a reformulation of both the capillary (Ncmacro) and Bond numbers (Nbmacro), rigorously based on a balance of pore-scale forces, with the majority of ganglia remobilized at Ncmacro around 1. Buoyancy forces were found to be small in this system (Nbmacro << 1), meaning the gravitational remobilization of CO2 after residual trapping would be extremely difficult.
The front end electronics of the NA62 Gigatracker: challenges, design and experimental measurements
NASA Astrophysics Data System (ADS)
Noy, M.; Aglieri Rinella, G.; Ceccucci, A.; Dellacasa, G.; Fiorini, M.; Garbolino, S.; Jarron, P.; Kaplon, J.; Kluge, A.; Marchetto, F.; Martin, E.; Mazza, G.; Martoiu, S.; Morel, M.; Perktold, L.; Rivetti, A.; Tiuraniemi, S.
2011-06-01
The beam spectrometer of the NA62 experiment consists of 3 Gigatracker (GTK) stations. Each station comprises a pixel detector of 16 cm active area made of an assembly of 10 readout ASICs bump bonded to a 200 μm thick pixel silicon sensor, comprising 18000 pixels of 300 μm×300 μm. The main challenge of the NA62 pixel GTK station is the combination of an extremely high kaon/pion beam rate, where the intensity in the center of the beam reaches up to 1.5 Mhit s mm together with an extreme time resolution of 100 ps. To date, it is the first silicon tracking system with this time resolution. To face this challenge, the pixel analogue front end has been designed with a peaking time of 4 ns, with a planar silicon sensor operating up to 300 V over depletion. Moreover, the radiation level is severe, 2×10 1 MeV n cm per year of operation. Easy replacement of the GTK stations is foreseen as a design requirement. The amount of material of a single station should also be less than 0.5% X to minimize the background, which imposes strong constraints on the mechanics and the cooling system. We report upon the design and architecture of the 2 prototype demonstrator chips both designed in 130 nm CMOS technology, one with a constant fraction discriminator and the time stamp digitisation in each pixel (In-Pixel), and the other with a time-over-threshold discriminator and the processing of the time stamp located in the End of Column (EoC) region at the chip periphery. Some preliminary results are presented.
Spline-Based Smoothing of Airfoil Curvatures
NASA Technical Reports Server (NTRS)
Li, W.; Krist, S.
2008-01-01
Constrained fitting for airfoil curvature smoothing (CFACS) is a splinebased method of interpolating airfoil surface coordinates (and, concomitantly, airfoil thicknesses) between specified discrete design points so as to obtain smoothing of surface-curvature profiles in addition to basic smoothing of surfaces. CFACS was developed in recognition of the fact that the performance of a transonic airfoil is directly related to both the curvature profile and the smoothness of the airfoil surface. Older methods of interpolation of airfoil surfaces involve various compromises between smoothing of surfaces and exact fitting of surfaces to specified discrete design points. While some of the older methods take curvature profiles into account, they nevertheless sometimes yield unfavorable results, including curvature oscillations near end points and substantial deviations from desired leading-edge shapes. In CFACS as in most of the older methods, one seeks a compromise between smoothing and exact fitting. Unlike in the older methods, the airfoil surface is modified as little as possible from its original specified form and, instead, is smoothed in such a way that the curvature profile becomes a smooth fit of the curvature profile of the original airfoil specification. CFACS involves a combination of rigorous mathematical modeling and knowledge-based heuristics. Rigorous mathematical formulation provides assurance of removal of undesirable curvature oscillations with minimum modification of the airfoil geometry. Knowledge-based heuristics bridge the gap between theory and designers best practices. In CFACS, one of the measures of the deviation of an airfoil surface from smoothness is the sum of squares of the jumps in the third derivatives of a cubicspline interpolation of the airfoil data. This measure is incorporated into a formulation for minimizing an overall deviation- from-smoothness measure of the airfoil data within a specified fitting error tolerance. CFACS has been
Fiber Fabry-Perot interferometer for curvature sensing
NASA Astrophysics Data System (ADS)
Monteiro, Catarina S.; Ferreira, Marta S.; Silva, Susana O.; Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Frazão, Orlando
2016-12-01
A curvature sensor based on an Fabry-Perot (FP) interferometer was proposed. A capillary silica tube was fusion spliced between two single mode fibers, producing an FP cavity. Two FP sensors with different cavity lengths were developed and subjected to curvature and temperature. The FP sensor with longer cavity showed three distinct operating regions for the curvature measurement. Namely, a linear response was shown for an intermediate curvature radius range, presenting a maximum sensitivity of 68.52 pm/m-1. When subjected to temperature, the sensing head produced a similar response for different curvature radii, with a sensitivity varying from 0.84 pm/°C to 0.89 pm/°C, which resulted in a small cross-sensitivity to temperature when the FP sensor was subjected to curvature. The FP cavity with shorter length presented low sensitivity to curvature.
Radius of Curvature of Off-Axis Paraboloids
NASA Technical Reports Server (NTRS)
Robinson, Brian; Reardon, Patrick; Hadaway, James; Geary, Joseph; Russell, Kevin (Technical Monitor)
2002-01-01
We present several methods for measuring the vertex radius of curvature of off-axis paraboloidal mirrors. One is based on least-squares fitting of interferometer output, one on comparison of sagittal and tangential radii of curvature, and another on measurement of displacement of the nulled test article from the ideal reference wave. Each method defines radius of curvature differently and, as a consequence, produces its own sort of errors.
In-use measurement of the activity, fuel use, and emissions of front-loader refuse trucks
NASA Astrophysics Data System (ADS)
Sandhu, Gurdas S.; Frey, H. Christopher; Bartelt-Hunt, Shannon; Jones, Elizabeth
2014-08-01
Field measurements were made for six front-loader refuse trucks for over 560 miles (901 km) and 47 h of operation using a portable emissions measurement system, electronic control unit data logger, and global positioning system receivers. Daily activity, fuel use rates, and emission rates are quantified in terms of operating mode bins defined by the U.S. Environmental Protection Agency for the MOVES emission factor model. On average, 44 (±4) percent of time was spent at idle, 5 (±1) percent braking or decelerating, 11 (±2) percent coasting, 23 (±3) percent cruising or accelerating at low speed (up to 25 mph, 40.2 kmph), 10 (±2) percent cruising or accelerating at moderate speed (25-50 mph, 40.2 to 80.4 kmph), and 7 (±3) percent cruising or accelerating at high speed (50 mph, 80.4 kmph or higher). Fuel use and emission rates varied among operating modes by factors of 6-24. The estimated daily activity cycle average fuel economy ranges from 2.3 to 3.2 mpg (0.98-1.4 kmpl). The PM emission rates for trucks with diesel particulate filters are 98 percent lower compared to those without. Variation in truck weight lead to differences in average fuel use and emission rates of 20 percent or less, except for hydrocarbons. The variation in the empirically-based daily activity cycle average rates were highly correlated with MOVES estimates, except for hydrocarbons. The data collected here are useful for quantifying daily activity specific to front-loaders, and for developing fuel use and emission estimates and models for this type of vehicle.
NASA Technical Reports Server (NTRS)
Kim, J.; Simon, T. W.
1987-01-01
The effects of streamwise convex curvature, recovery, and freestream turbulence intensity on the turbulent transport of heat and momentum in a mature boundary layer are studied using a specially designed three-wire hot-wire probe. Increased freestream turbulence is found to increase the profiles throughout the boundary layer on the flat developing wall. Curvature effects were found to dominate turbulence intensity effects for the present cases considered. For the higher TI (turbulence intensity) case, negative values of the turbulent Prandtl number are found in the outer half of the boundary layer, indicating a breakdown in Reynolds analogy.
NASA Astrophysics Data System (ADS)
Chambolle, Antonin; Morini, Massimiliano; Ponsiglione, Marcello
2015-12-01
This paper aims at building a unified framework to deal with a wide class of local and nonlocal translation-invariant geometric flows. We introduce a class of nonlocal generalized mean curvatures and prove the existence and uniqueness for the level set formulation of the corresponding geometric flows. We then introduce a class of generalized perimeters, whose first variation is an admissible generalized curvature. Within this class, we implement a minimizing movements scheme and we prove that it approximates the viscosity solution of the corresponding level set PDE. We also describe several examples and applications. Besides recovering and presenting in a unified way existence, uniqueness, and approximation results for several geometric motions already studied and scattered in the literature, the theory developed in this paper also allows us to establish new results.
Veberg, A; Olsen, E; Nilsen, A N; Wold, J P
2007-05-01
This paper shows that fluorescence spectroscopy can measure both degradation of photosensitizers and formation of lipid oxidation products in light-exposed butter. The photosensitizers were already notably degraded after 4 h of light exposure, whereas fluorescent lipid oxidation products were detected after 5 d. The fluorescence measurements were highly correlated with sensory assessments of acidic and rancid flavor. Photosensitizer degradation is therefore a promising indirect indicator of the onset of lipid oxidation in butter. Sensory analysis and measurement of peroxide value showed that the level of lipid oxidation was significantly higher for butter stored in air compared with butter stored in nitrogen (N2). This might be explained by the formation of singlet oxygen from direct photooxidation and type II photosensitized oxidation. Addition of the singlet oxygen quencher beta-carotene reduced the rancid flavor intensity in the air and N2 packages from 9.0 to 4.9 and from 6.5 to 4.7, respectively. Results indicate that lipid oxidation in the butter stored in N2 was mainly caused by type I photosensitized reactions, because addition of beta-carotene had little effect on the rancid flavor intensity.
Liu, Zhihong; Muldrew, Ken; Wan, Richard G; Elliott, Janet A W
2003-06-01
Variations of the Kelvin equation [W. Thomson, Philos. Mag. 42, 448 (1871)] to describe the freezing point depression of water in capillaries exist in the literature. The differing equations, coupled with the uncertainty in input parameters, lead to various predictions. The difference between the predictions may become substantial when the capillary size decreases much below micron dimensions. An experiment was designed to investigate the predicted values using a customized directional solidification stage. The capillary freezing point depression for glass tubes with radii of 87 microm-3 microm was successfully measured. The image of the ice-water interface at equilibrium was also digitally captured and analyzed to examine the contact angle and the interface shape as well. Both are important for examining the hemispherical interface assumption that was exclusively used in the theoretical derivations. Finally, an equilibrium analysis of the thermodynamic system leads to a theoretical discussion of the problem. The effect of the temperature gradient on the interface shape is addressed, and an engineering criterion for the critical temperature gradient above which the effect must be considered for the interface shape calculation is derived.
NASA Astrophysics Data System (ADS)
Zhang, Wei; ASDEX Upgrade Team; Eurofusion MST1 Team
2016-10-01
Plasma heating with waves in the Ion Cyclotron Range of Frequency (ICRF) is one of the standard heating methods in tokamaks. The parallel (to the magnetic field) component of the electric field of the waves enhances the edge plasma potential nonlinearly through radio-frequency-sheath (rf-sheath) rectification. The gradient of this potential across magnetic field drives plasma convection in the Scrape-Off Layer. To reduce the rf-sheath driven close to ICRF antennas, the parallel electric near-field has to be decreased. This can be achieved by minimization of undesired parasitic currents induced in the antenna box by the antenna currents. New antennas with a novel approach to reduce those undesired currents through the proper phase and amplitude of the current in 3-straps have been installed and validated on ASDEX Upgrade. With reflectometers embedded in one 3-strap antenna at different poloidal locations, the density profiles in front of the antenna can be measured in when the antenna is either active or passive. The ICRF induced edge plasma convection in different antenna feeding configurations (different phasing, different power ratio between the central and the side straps) has thus been studied. Also we have carried out comprehensive simulations by running the EMC3EIRENE, RAPLICASOL and SSWICH codes in an iterative and quasi self-consistent way. The steadystate ICRF induced plasma density convection can clearly be reproduced in the models and compared with the ones measured in experiments.
NASA Technical Reports Server (NTRS)
Bever, R. S.
1976-01-01
Internal embedment stress measurements were performed, using tiny ferrite core transformers, whose voltage output was calibrated versus pressure by the manufacturer. Comparative internal strain measurements were made by attaching conventional strain gages to the same type of resistors and encapsulating these in various potting compounds. Both types of determinations were carried out while temperature cycling from 77 C to -50 C.
Fringes of equal tangential inclination by curvature-induced birefringence
NASA Astrophysics Data System (ADS)
Medhat, M.; Hendawy, N. I.; Zaki, A. A.
2003-02-01
A new kind of interference fringes, fringes of equal tangential inclination by curvature-induced birefringence, is presented. These are two-beam interference fringes produced by bending a thin sheet of birefringent material into a part of an exact cylinder such that the curvature is constant. Due to this curvature there is a uniform birefringence being induced. The change in birefringence induced by applying different radii of curvatures to a Fortepan sheet is measured. The stored (fixed) or natural birefringence of this sheet is deduced.
The curvature index and synchronization of dynamical systems.
Chen, Yen-Sheng; Chang, Chien-Cheng
2012-06-01
We develop a quantity, named the curvature index, for dynamical systems. This index is defined as the limit of the average curvature of the trajectory during evolution, which measures the bending of the curve on an attractor. The curvature index has the ability to differentiate the topological change of an attractor, as its alterations exhibit the structural changes of a dynamical system. Thus, the curvature index may indicate thresholds of some synchronization regimes. The Rössler system and a time-delay system are simulated to demonstrate the effectiveness of the index, respectively.
Mannion, Anne F; Knecht, Katrin; Balaban, Gordana; Dvorak, Jiri; Grob, Dieter
2004-03-01
There is an increasing awareness of the risks and dangers of exposure to radiation associated with repeated radiographic assessment of spinal curvature and spinal movements. As such, attempts are continuously being made to develop skin-surface devices for use in examining the progression and response to treatment of various spinal disorders. However, the reliability and validity of measurements recorded with such devices must be established before they can be recommended for use in the research or clinical environment. The aim of this study was to examine the reliability of measurements using a newly developed skin-surface device, the Spinal Mouse. Twenty healthy volunteers (mean age 41 +/- 12 years, nine males, 11 females) took part. On 2 separate days, spinal curvature was measured with the Spinal Mouse during standing, full flexion, and full extension (each three times by each of two examiners). Paired t-tests, intraclass correlation coefficients (ICC), and standard errors of measurement (SEM) with 95% confidence intervals were used to characterise between-day and interexaminer reliability for: standing sacral angle, lumbar lordosis, thoracic kyphosis, and ranges of motion (flexion, extension) of the thoracic spine, lumbar spine, hips, and trunk. The between-day reliability for segmental ranges of flexion was also determined for each motion segment from T1-2 to L5-S1. The majority of parameters measured for the 'global regions' (thoracic, lumbar, or hips) showed good between-day reliability. Depending on the parameter of interest, between-day ICCs ranged from 0.67 to 0.92 for examiner 1 (average 0.82) and 0.57 to 0.95 for examiner 2 (average 0.83); for 70% of the parameters measured, the ICCs were greater than 0.8 and generally highest for the lumbar spine and whole trunk measures. For lumbar spine range of flexion, the SEM was approximately 3 degrees. The ICCs were also good for the interexaminer comparisons, ranging from 0.62 to 0.93 on day 1 (average 0
NASA Astrophysics Data System (ADS)
Eselevich, V. G.; Borodkova, N. L.; Eselevich, M. V.; Zastenker, G. N.; Šafránkova, Y.; Němeček, Z.; Přech, L.
2017-01-01
According to the data of the BMSW/ SPEKTR-R instrument, which measured the density and velocity of solar wind plasma with a record time resolution, up to 3 ×10-2 s, the structure of the front of interplanetary shocks has been investigated. The results of these first investigations were compared with the results of studying the structure of the bow shocks obtained in previous years. A comparison has shown that the quasi-stationary (averaged over the rapid oscillations) distribution of plasma behind the interplanetary shock front was significantly more inhomogeneous than that behind the bow-shock front, i.e., in the magnetosheath. It has also been shown that, to determine the size of internal structures of the fronts of quasi-perpendicular (θBN > 45°) shocks, one could use the magnetic field magnitude, the proton density, and the proton flux of the solar wind on almost equal terms. A comparison of low Mach ( M A < 2), low beta (β1 < 1) fronts of interplanetary and bow shocks has shown that the dispersion of oblique magnetosonic waves plays an essential role in their formation.
Cosmic curvature from de Sitter equilibrium cosmology.
Albrecht, Andreas
2011-10-07
I show that the de Sitter equilibrium cosmology generically predicts observable levels of curvature in the Universe today. The predicted value of the curvature, Ω(k), depends only on the ratio of the density of nonrelativistic matter to cosmological constant density ρ(m)(0)/ρ(Λ) and the value of the curvature from the initial bubble that starts the inflation, Ω(k)(B). The result is independent of the scale of inflation, the shape of the potential during inflation, and many other details of the cosmology. Future cosmological measurements of ρ(m)(0)/ρ(Λ) and Ω(k) will open up a window on the very beginning of our Universe and offer an opportunity to support or falsify the de Sitter equilibrium cosmology.
Suyu, S.H.; Marshall, P.J.; Auger, M.W.; Hilbert, S.; Blandford, R.D.; Koopmans, L.V.E.; Fassnacht, C.D.; Treu, T.; /UC, Santa Barbara
2009-12-11
Strong gravitational lens systems with measured time delays between the multiple images provide a method for measuring the 'time-delay distance' to the lens, and thus the Hubble constant. We present a Bayesian analysis of the strong gravitational lens system B1608+656, incorporating (1) new, deep Hubble Space Telescope (HST) observations, (2) a new velocity dispersion measurement of 260 {+-} 15 km s{sup -1} for the primary lens galaxy, and (3) an updated study of the lens environment. Our analysis of the HST images takes into account the extended source surface brightness, and the dust extinction and optical emission by the interacting lens galaxies. When modeling the stellar dynamics of the primary lens galaxy, the lensing effect, and the environment of the lens, we explicitly include the total mass distribution profile logarithmic slope {gamma}{prime} and the external convergence {kappa}{sub ext}; we marginalize over these parameters, assigning well-motivated priors for them, and so turn the major systematic errors into statistical ones. The HST images provide one such prior, constraining the lens mass density profile logarithmic slope to be {gamma}{prime} = 2.08 {+-} 0.03; a combination of numerical simulations and photometric observations of the B1608+656 field provides an estimate of the prior for {kappa}{sub ext}: 0.10{sub -0.05}{sup +0.08}. This latter distribution dominates the final uncertainty on H{sub 0}. Fixing the cosmological parameters at {Omega}{sub m} = 0.3, {Omega}{sub {Lambda}} = 0.7, and w = -1 in order to compare with previous work on this system, we find H{sub 0} = 70.6{sub -3.1}{sup +3.1} km s{sup -1} Mpc{sup -1}. The new data provide an increase in precision of more than a factor of two, even including the marginalization over {kappa}{sub ext}. Relaxing the prior probability density function for the cosmological parameters to that derived from the WMAP 5-year data set, we find that the B1608+656 data set breaks the degeneracy between {Omega
Advanced Curvature Deformable Mirrors
2010-09-01
designs using just a glass wafer and a wafer of Carbon Fiber Reinforced Polymer ( CFRP ). In both cases minimum bend radius decreases and the resonant... matrix is consequently nearly diagonal. The long actuators at the outer edge of the deformable mirror are largely outside the working pupil so their...formal reconstruction of the wave front either explicitly or implicitly in the control matrix . The WFS-DM combination is acting like an analog computer
Multi-scale curvature tensor analysis of machined surfaces
NASA Astrophysics Data System (ADS)
Bartkowiak, Tomasz; Brown, Christopher
2016-12-01
This paper demonstrates the use of multi-scale curvature analysis, an areal new surface characterization technique for better understanding topographies, for analyzing surfaces created by conventional machining and grinding. Curvature, like slope and area, changes with scale of observation, or calculation, on irregular surfaces, therefore it can be used for multi-scale geometric analysis. Curvatures on a surface should be indicative of topographically dependent behavior of a surface and curvatures are, in turn, influenced by the processing and use of the surface. Curvatures have not been well characterized previously. Curvature has been used for calculations in contact mechanics and for the evaluation of cutting edges. In the current work two parts were machined and then one of them was ground. The surface topographies were measured with a scanning laser confocal microscope. Plots of curvatures as a function of position and scale are presented, and the means and standard deviations of principal curvatures are plotted as a function of scale. Statistical analyses show the relations between curvature and these two manufacturing processes at multiple scales.
NASA Astrophysics Data System (ADS)
Anderlini, L.; Anelli, M.; Archilli, F.; Auriemma, G.; Baldini, W.; Bencivenni, G.; Bizzeti, A.; Bocci, V.; Bondar, N.; Bonivento, W.; Bochin, B.; Bozzi, C.; Brundu, D.; Cadeddu, S.; Campana, P.; Carboni, G.; Cardini, A.; Carletti, M.; Casu, L.; Chubykin, A.; Ciambrone, P.; Dané, E.; De Simone, P.; Falabella, A.; Felici, G.; Fiore, M.; Fontana, M.; Fresch, P.; Furfaro, E.; Graziani, G.; Kashchuk, A.; Kotriakhova, S.; Lai, A.; Lanfranchi, G.; Loi, A.; Maev, O.; Manca, G.; Martellotti, G.; Neustroev, P.; Oldeman, R. G. C.; Palutan, M.; Passaleva, G.; Penso, G.; Pinci, D.; Polycarpo, E.; Saitta, B.; Santacesaria, R.; Santimaria, M.; Santovetti, E.; Saputi, A.; Sarti, A.; Satriano, C.; Satta, A.; Schmidt, B.; Schneider, T.; Sciascia, B.; Sciubba, A.; Siddi, B. G.; Tellarini, G.; Vacca, C.; Vazquez-Gomez, R.; Vecchi, S.; Veltri, M.; Vorobyev, A.
2016-04-01
A method is described which allows to deduce the dead-time of the front-end electronics of the LHCb muon detector from a series of measurements performed at different luminosities at a bunch-crossing rate of 20 MHz. The measured values of the dead-time range from ~ 70 ns to ~ 100 ns. These results allow to estimate the performance of the muon detector at the future bunch-crossing rate of 40 MHz and at higher luminosity.
On nonlinear higher spin curvature
NASA Astrophysics Data System (ADS)
Manvelyan, Ruben; Mkrtchyan, Karapet; Rühl, Werner; Tovmasyan, Murad
2011-05-01
We present the first nonlinear term of the higher spin curvature which is covariant with respect to deformed gauge transformations that are linear in the field. We consider the case of spin 3 after presenting spin 2 as an example, and then construct the general spin s quadratic term of the de Wit-Freedman curvature.
NASA Astrophysics Data System (ADS)
Hasegawa, Hiroki; Kowatari, Takaya; Shiroki, Yasuhiro; Shibata, Hiroyuki; Ohta, Hiromichi; Waseda, Yoshio
2012-12-01
Thermal conductivity values have been systematically obtained for molten silicates containing Al2O3, CaO, Na2O, and SiO2 by means of a front heating-front detection laser flash method. The measurements were made for 13 samples in the temperature range between 1073 K and 1823 K (800 °C and 1550 °C), depending on the composition. Thermal conductivities of the silicate melts are found to be relatively insensitive to the variation of temperature, but they depend on the composition ratio, particularly the ratio of Non-Bridging Oxygen ions per Tetrahedrally coordinated cation—NBO/T. The thermal conductivity values decrease from 2.8 W/mK to 1.5 W/mK with the NBO/T value until it reaches about 1. Thermal conductivity values become constant for silicate melts with a higher value of NBO/T. It is known that the length of the silicate chain decreases with disconnection by the addition of alkaline earth cation or alkaline cation. The strong correlation between thermal conductivity and NBO/T is quite likely to suggest that silicate chain is a preferential path for heat transport in silicate melts.
John Paul Wallace, Ganapati Rao Myneni, and Robert Pike
2011-03-01
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Wallace, John Paul; Myneni, Ganapati Rao; Pike, Robert
2011-03-31
The manufacturing of niobium SRF accelerator cavities is plagued by a mobile point defect, hydrogen. For efficient accelerator operation, niobium must function at both high electric and magnetic fields, and is compromised if magnetic impurities are located in the surface regions of the material. The finding that trace hydrogen in niobium can produce structures with magnetic properties is a feature that is not acceptable for a high performance cavity. X-ray diffraction has proved to be the key tool in assessing irreversible process damage to the niobium substrate. In future generations of accelerators, niobium will actually be merely the substrate for more effective superconductors that will allow for more efficient operation. The substrate analogy to the silicon wafer industry is useful since for niobium it may be possible to avoid some of the mistakes made in silicon technology. Because hydrogen attacks niobium on a number of different size scales, there is an inherent complexity in the trouble sources. There are also features in cavity design that are benign, such as local curvature considerations, requiring a fully non symmetric analysis of current flow to be appreciated.
Cosmic curvature and condensation
NASA Technical Reports Server (NTRS)
Harwit, Martin
1992-01-01
It is shown that the universe may consist of a patchwork of domains with different Riemann curvature constants k = 0, +/-1. Features of a phase transition in which flat space breaks up in a transition 2k0 - k(-) + k(+) with initial scale factors R(-) = R(+) are postulated and explored. It is shown that such a transition is energetically permitted, has the equivalent of a Curie temperature, and can lead in a natural way to the formation of voids and galaxies. It is predicted that, if the ambient universe on average is well fitted by a purely k(-) space, with only occasional domains of k(+) containing galaxies, a density parameter of (A(z sub c + 1)) super -1 should be expected, where z sub c represents the redshift of the earliest objects to have condensed, and A takes on values ranging from about 5 to 3. Present observations of quasars would suggest a density of about 0.03 or 0.05, respectively, but it could be lower if earlier condensation took place.
Graph Curvature for Differentiating Cancer Networks
Sandhu, Romeil; Georgiou, Tryphon; Reznik, Ed; Zhu, Liangjia; Kolesov, Ivan; Senbabaoglu, Yasin; Tannenbaum, Allen
2015-01-01
Cellular interactions can be modeled as complex dynamical systems represented by weighted graphs. The functionality of such networks, including measures of robustness, reliability, performance, and efficiency, are intrinsically tied to the topology and geometry of the underlying graph. Utilizing recently proposed geometric notions of curvature on weighted graphs, we investigate the features of gene co-expression networks derived from large-scale genomic studies of cancer. We find that the curvature of these networks reliably distinguishes between cancer and normal samples, with cancer networks exhibiting higher curvature than their normal counterparts. We establish a quantitative relationship between our findings and prior investigations of network entropy. Furthermore, we demonstrate how our approach yields additional, non-trivial pair-wise (i.e. gene-gene) interactions which may be disrupted in cancer samples. The mathematical formulation of our approach yields an exact solution to calculating pair-wise changes in curvature which was computationally infeasible using prior methods. As such, our findings lay the foundation for an analytical approach to studying complex biological networks. PMID:26169480
Modeling normal shock velocity curvature relations for heterogeneous explosives
NASA Astrophysics Data System (ADS)
Yoo, Sunhee; Crochet, Michael; Pemberton, Steven
2017-01-01
The theory of Detonation Shock Dynamics (DSD) is, in part, an asymptotic method to model a functional form of the relation between the shock normal, its time rate and shock curvature κ. In addition, the shock polar analysis provides a relation between shock angle θ and the detonation velocity Dn that is dependent on the equations of state (EOS) of two adjacent materials. For the axial detonation of an explosive material confined by a cylinder, the shock angle is defined as the angle between the shock normal and the normal to the cylinder liner, located at the intersection of the shock front and cylinder inner wall. Therefore, given an ideal explosive such as PBX-9501 with two functional models determined, a unique, smooth detonation front shape ψ can be determined that approximates the steady state detonation shock front of the explosive. However, experimental measurements of the Dn(κ) relation for heterogeneous explosives such as PBXN-111 [D. K. Kennedy, 2000] are challenging due to the non-smoothness and asymmetry usually observed in the experimental streak records of explosion fronts. Out of many possibilities the asymmetric character may be attributed to the heterogeneity of the explosives; here, material heterogeneity refers to compositions with multiple components and having a grain morphology that can be modeled statistically. Therefore in extending the formulation of DSD to modern novel explosives, we pose two questions: (1) is there any simple hydrodynamic model that can simulate such an asymmetric shock evolution, and (2) what statistics can be derived for the asymmetry using simulations with defined structural heterogeneity in the unreacted explosive? Saenz, Taylor and Stewart [1] studied constitutive models for derivation of the Dn(κ) relation for porous homogeneous explosives and carried out simulations in a spherical coordinate frame. In this paper we extend their model to account for heterogeneity and present shock evolutions in heterogeneous
Effects of Iris Surface Curvature on Iris Recognition
Thompson, Joseph T; Flynn, Patrick J; Bowyer, Kevin W; Santos-Villalobos, Hector J
2013-01-01
To focus on objects at various distances, the lens of the eye must change shape to adjust its refractive power. This change in lens shape causes a change in the shape of the iris surface which can be measured by examining the curvature of the iris. This work isolates the variable of iris curvature in the recognition process and shows that differences in iris curvature degrade matching ability. To our knowledge, no other work has examined the effects of varying iris curvature on matching ability. To examine this degradation, we conduct a matching experiment across pairs of images with varying degrees of iris curvature differences. The results show a statistically signi cant degradation in matching ability. Finally, the real world impact of these ndings is discussed
Curvature sensor based on a Fabry-Perot interferometer
NASA Astrophysics Data System (ADS)
Monteiro, Catarina; Ferreira, Marta S.; Kobelke, Jens; Schuster, Kay; Bierlich, Jörg; Frazão, Orlando
2016-05-01
A curvature sensor based on a Fabry-Perot interferometer is proposed. A capillary tube of silica is fusion spliced between two single mode fibers, producing a Fabry-Perot cavity. The light propagates in air, when passing through the capillary tube. Two different cavities are subjected to curvature and temperature. The cavity with shorter length shows insensitivity to both measurands. The larger cavity shows two operating regions for curvature measurement, where a linear response is shown, with a maximum sensitivity of 18.77pm/m-1 for the high curvature radius range. When subjected to temperature, the sensing head produces a similar response for different curvature radius, with a sensitivity of 0.87pm/°C.
Modeling Normal Shock Velocity Curvature Relation for Heterogeneous Explosives
NASA Astrophysics Data System (ADS)
Yoo, Sunhee; Crochet, Michael; Pemberton, Steve
2015-06-01
The normal shock velocity and curvature, Dn(κ) , relation on a detonation shock surface has been an important functional quantity to measure to understand the shock strength exerted against the material interface between a main explosive charge and the case of an explosive munition. The Dn(κ) relation is considered an intrinsic property of an explosive, and can be experimentally deduced by rate stick tests at various charge diameters. However, experimental measurements of the Dn(κ) relation for heterogeneous explosives such as PBXN-111 are challenging due to the non-smoothness and asymmetry usually observed in the experimental streak records of explosion fronts. Out of the many possibilities, the asymmetric character may be attributed to the heterogeneity of the explosives, a hypothesis which begs two questions: (1) is there any simple hydrodynamic model that can explain such an asymmetric shock evolution, and (2) what statistics can be derived for the asymmetry using simulations with defined structural heterogeneity in the unreacted explosive? Saenz, Taylor and Stewart studied constitutive models for derivation of the Dn(κ) relation on porous `homogeneous' explosives and carried out simulations in a spherical coordinate frame. In this paper, we extend their model to account for `heterogeneity' and present shock evolutions in heterogeneous explosives using 2-D hydrodynamic simulations with some statistical examination. (96TW-2015-0004)
Michel, D. T.; Davis, A. K.; Armstrong, W.; ...
2015-07-08
Self-emission x-ray shadowgraphy provides a method to measure the ablation-front trajectory and low-mode nonuniformity of a target imploded by directly illuminating a fusion capsule with laser beams. The technique uses time-resolved images of soft x-rays (> 1 keV) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. Methods used to accurately measure the ablation-front radius (more » $${\\it\\delta}R=\\pm 1.15~{\\rm\\mu}\\text{m}$$), image-to-image timing ($${\\it\\delta}({\\rm\\Delta}t)=\\pm 2.5$$ ps) and absolute timing ($${\\it\\delta}t=\\pm 10$$ ps) are presented. Angular averaging of the images provides an average radius measurement of$${\\it\\delta}(R_{\\text{av}})=\\pm 0.15~{\\rm\\mu}\\text{m}$$and an error in velocity of$${\\it\\delta}V/V=\\pm 3\\%$$. This technique was applied on the Omega Laser Facility and the National Ignition Facility.« less
Propagation of curved activation fronts in anisotropic excitable media.
Morozov, V G; Davydov, N V; Davydov, V A
1999-06-01
We study theoretical and numerical propagation of autowave fronts in excitable two-variable (activator-inhibitor) systems with anisotropic diffusion. A general curvature-velocity relation is derived for the case that the inhibitor diffusion is neglected. This relation predicts the break of an activation front when the front curvature exceeds a critical value, which is corroborated by computer simulations of a particular reaction-diffusion model. Some qualitative effects associated with the inhibitor diffusion are studied numerically. It is found that the critical value of curvature decreases with an increase in the inhibitor diffusion coefficient. The core of a spiral wave increases in size and turns through an angle which depends on the inhibitor diffusion coefficient. PACS Numbers: 05.50. +q, 05.70. Ln., 82.40. -g, 87.10. +e.
Curvature Interaction in Collective Space
NASA Astrophysics Data System (ADS)
Herrmann, Richard
2012-12-01
For the Riemannian space, built from the collective coordinates used within nuclear models, an additional interaction with the metric is investigated, using the collective equivalent to Einstein's curvature scalar. The coupling strength is determined using a fit with the AME2003 ground state masses. An extended finite-range droplet model including curvature is introduced, which generates significant improvements for light nuclei and nuclei in the trans-fermium region.
Curvature of spacetime: A simple student activity
NASA Astrophysics Data System (ADS)
Wood, Monika; Smith, Warren; Jackson, Matthew
2016-12-01
The following is a description of an inexpensive and simple student experiment for measuring the differences between the three types of spacetime topology—Euclidean (flat), Riemann (spherical), and Lobachevskian (saddle) curvatures. It makes use of commonly available tools and materials, and requires only a small amount of construction. The experiment applies to astronomical topics such as gravity, spacetime, general relativity, as well as geometry and mathematics.
NASA Technical Reports Server (NTRS)
2006-01-01
[figure removed for brevity, see original site] Context image for PIA02171 Cloud Front
These clouds formed in the south polar region. The faintness of the cloud system likely indicates that these are mainly ice clouds, with relatively little dust content.
Image information: VIS instrument. Latitude -86.7N, Longitude 212.3E. 17 meter/pixel resolution.
Note: this THEMIS visual image has not been radiometrically nor geometrically calibrated for this preliminary release. An empirical correction has been performed to remove instrumental effects. A linear shift has been applied in the cross-track and down-track direction to approximate spacecraft and planetary motion. Fully calibrated and geometrically projected images will be released through the Planetary Data System in accordance with Project policies at a later time.
NASA's Jet Propulsion Laboratory manages the 2001 Mars Odyssey mission for NASA's Office of Space Science, Washington, D.C. The Thermal Emission Imaging System (THEMIS) was developed by Arizona State University, Tempe, in collaboration with Raytheon Santa Barbara Remote Sensing. The THEMIS investigation is led by Dr. Philip Christensen at Arizona State University. Lockheed Martin Astronautics, Denver, is the prime contractor for the Odyssey project, and developed and built the orbiter. Mission operations are conducted jointly from Lockheed Martin and from JPL, a division of the California Institute of Technology in Pasadena.
Surface tension driven flow on a thin reaction front
NASA Astrophysics Data System (ADS)
Guzman, Roberto; Vasquez, Desiderio A.
2016-11-01
Surface tension driven convection affects the propagation of chemical reaction fronts in liquids. The changes in surface tension across the front generate this type of convection. The resulting fluid motion increases the speed and changes the shape of fronts as observed in the iodate-arsenous acid reaction. We calculate these effects using a thin front approximation, where the reaction front is modeled by an abrupt discontinuity between reacted and unreacted substances. We analyze the propagation of reaction fronts of small curvature. In this case the front propagation equation becomes the deterministic Kardar-Parisi-Zhang (KPZ) equation with the addition of fluid flow. These results are compared to calculations based on a set of reaction-diffusion-convection equations.
Magnetophoretic Induction of Root Curvature
NASA Technical Reports Server (NTRS)
Hasenstein, Karl H.
1997-01-01
The last year of the grant period concerned the consolidation of previous experiments to ascertain that the theoretical premise apply not just to root but also to shoots. In addition, we verified that high gradient magnetic fields do not interfere with regular cellular activities. Previous results have established that: (1) intracellular magnetophoresis is possible; and (2) HGMF lead to root curvature. In order to investigate whether HGMF affect the assembly and/or organization of structural proteins, we examined the arrangement of microtubules in roots exposed to HGMF. The cytoskeletal investigations were performed with fomaldehyde-fixed, nonembedded tissue segments that were cut with a vibratome. Microtubules (MTs) were stained with rat anti-yeast tubulin (YOL 1/34) and DTAF-labeled antibody against rat IgG. Microfilaments (MFs) were visualized by incubation in rhodamine-labeled phalloidin. The distribution and arrangement of both components of the cytoskeleton were examined with a confocal microscope. Measurements of growth rates and graviresponse were done using a video-digitizer. Since HGMF repel diamagnetic substances including starch-filled amyloplasts and most The second aspect of the work includes studies of the effect of cytoskeletal inhibitors on MTs and MFs. The analysis of the effect of micotubular inhibitors on the auxin transport in roots showed that there is very little effect of MT-depolymerizing or stabilizing drugs on auxin transport. This is in line with observations that application of such drugs is not immediately affecting the graviresponsiveness of roots.
Ionic liquid tunes microemulsion curvature.
Liu, Liping; Bauduin, Pierre; Zemb, Thomas; Eastoe, Julian; Hao, Jingcheng
2009-02-17
Middle-phase microemulsions formed from cationic dioctadecyldimethylammonium chloride (DODMAC), anionic sodium dodecylsulfate (SDS), n-butanol, and n-heptane were studied. An ionic liquid (IL), 1-butyl-3-methylimidazolium tetrafluoroborate ([bmim][BF4]), was employed as the electrolyte in the aqueous media instead of inorganic salts usually used in microemulsion formulation. Studies have been carried out as a function of the concentrations of [bmim][BF4], n-butanol, total surfactant (cDODMAC+SDS), and temperature on the phase behavior and the ultralow interfacial tensions in which the anionic component is present in excess in the catanionic film. Ultralow interfacial tension measurements confirmed the formation of middle-phase microemulsions and the necessary conditions for stabilizing middle-phase microemulsions. Electrical conductivity, small-angle X-ray scattering (SAXS), and small-angle neutron scattering (SANS) experiments were also performed, indicating that the typical heptane domain size has an average radius of 360 A and the ionic liquid induces softening of the charged catanionic film. Most interestingly, the IL concentration (cIL) is shown to act as an effective interfacial curvature-control parameter, representing a new approach to tuning the formulation of microemulsions and emulsions. The results expand the potential uses of ILs but also point to the design of new ILs that may achieve superefficient control over interfacial and self-assembly systems.
3D curvature of muscle fascicles in triceps surae.
Rana, Manku; Hamarneh, Ghassan; Wakeling, James M
2014-12-01
Muscle fascicles curve along their length, with the curvatures occurring around regions of high intramuscular pressure, and are necessary for mechanical stability. Fascicles are typically considered to lie in fascicle planes that are the planes visualized during dissection or two-dimensional (2D) ultrasound scans. However, it has previously been predicted that fascicles must curve in three-dimensional (3D) and thus the fascicle planes may actually exist as 3D sheets. 3D fascicle curvatures have not been explored in human musculature. Furthermore, if the fascicles do not lie in 2D planes, then this has implications for architectural measures that are derived from 2D ultrasound scans. The purpose of this study was to quantify the 3D curvatures of the muscle fascicles and fascicle sheets within the triceps surae muscles and to test whether these curvatures varied among different contraction levels, muscle length, and regions within the muscle. Six male subjects were tested for three torque levels (0, 30, and 60% maximal voluntary contraction) and four ankle angles (-15, 0, 15, and 30° plantar flexion), and fascicles were imaged using 3D ultrasound techniques. The fascicle curvatures significantly increased at higher ankle torques and shorter muscle lengths. The fascicle sheet curvatures were of similar magnitude to the fascicle curvatures but did not vary between contractions. Fascicle curvatures were regionalized within each muscle with the curvature facing the deeper aponeuroses, and this indicates a greater intramuscular pressure in the deeper layers of muscles. Muscle architectural measures may be in error when using 2D images for complex geometries such as the soleus.
Static optical designs for Wavefront Curvature Sensing
NASA Astrophysics Data System (ADS)
Bharmal, Nazim A.
2006-06-01
A bulk optic is presented, the Parallel Output Beamsplitter, which allows simultaneous imaging of two planes either side of the focus using static imaging optics. The POB is used to create novel optical configurations for Wavefront Curvature Sensing and two designs are presented. The first is suited to small-amplitude aberration measurements in situations where compactness, a large field of view, and high optical throughput are desirable. A laboratory experiment using a POB to make such a wavefront sensor was undertaken, and results are presented. The second design is a conceptual idea which offers image-scale invariant imaging of two planes whose conjugation satisfies the requirements of a conventional Wavefront Curvature Sensor concept.
Membrane curvature at a glance
McMahon, Harvey T.; Boucrot, Emmanuel
2015-01-01
ABSTRACT Membrane curvature is an important parameter in defining the morphology of cells, organelles and local membrane subdomains. Transport intermediates have simpler shapes, being either spheres or tubules. The generation and maintenance of curvature is of central importance for maintaining trafficking and cellular functions. It is possible that local shapes in complex membranes could help to define local subregions. In this Cell Science at a Glance article and accompanying poster, we summarize how generating, sensing and maintaining high local membrane curvature is an active process that is mediated and controlled by specialized proteins using general mechanisms: (i) changes in lipid composition and asymmetry, (ii) partitioning of shaped transmembrane domains of integral membrane proteins or protein or domain crowding, (iii) reversible insertion of hydrophobic protein motifs, (iv) nanoscopic scaffolding by oligomerized hydrophilic protein domains and, finally, (v) macroscopic scaffolding by the cytoskeleton with forces generated by polymerization and by molecular motors. We also summarize some of the discoveries about the functions of membrane curvature, where in addition to providing cell or organelle shape, local curvature can affect processes like membrane scission and fusion as well as protein concentration and enzyme activation on membranes. PMID:25774051
On the Weyl curvature hypothesis
Stoica, Ovidiu Cristinel
2013-11-15
The Weyl curvature hypothesis of Penrose attempts to explain the high homogeneity and isotropy, and the very low entropy of the early universe, by conjecturing the vanishing of the Weyl tensor at the Big-Bang singularity. In previous papers it has been proposed an equivalent form of Einstein’s equation, which extends it and remains valid at an important class of singularities (including in particular the Schwarzschild, FLRW, and isotropic singularities). Here it is shown that if the Big-Bang singularity is from this class, it also satisfies the Weyl curvature hypothesis. As an application, we study a very general example of cosmological models, which generalizes the FLRW model by dropping the isotropy and homogeneity constraints. This model also generalizes isotropic singularities, and a class of singularities occurring in Bianchi cosmologies. We show that the Big-Bang singularity of this model is of the type under consideration, and satisfies therefore the Weyl curvature hypothesis. -- Highlights: •The singularities we introduce are described by finite geometric/physical objects. •Our singularities have smooth Riemann and Weyl curvatures. •We show they satisfy Penrose’s Weyl curvature hypothesis (Weyl=0 at singularities). •Examples: FLRW, isotropic singularities, an extension of Schwarzschild’s metric. •Example: a large class of singularities which may be anisotropic and inhomogeneous.
Effect of crack curvature on stress intensity factors for ASTM standard compact tension specimens
NASA Technical Reports Server (NTRS)
Alam, J.; Mendelson, A.
1983-01-01
The stress intensity factors (SIF) are calculated using the method of lines for the compact tension specimen in tensile and shear loading for curved crack fronts. For the purely elastic case, it was found that as the crack front curvature increases, the SIF value at the center of the specimen decreases while increasing at the surface. For the higher values of crack front curvatures, the maximum value of the SIF occurs at an interior point located adjacent to the surface. A thickness average SIF was computed for parabolically applied shear loading. These results were used to assess the requirements of ASTM standards E399-71 and E399-81 on the shape of crack fronts. The SIF is assumed to reflect the average stress environment near the crack edge.
Michel, D. T.; Davis, A. K.; Armstrong, W.; Bahr, R.; Epstein, R.; Goncharov, V. N.; Hohenberger, M.; Igumenshchev, I. V.; Jungquist, R.; Meyerhofer, D. D.; Radha, P. B.; Sangster, T. C.; Sorce, C.; Froula, D. H.
2015-07-08
Self-emission x-ray shadowgraphy provides a method to measure the ablation-front trajectory and low-mode nonuniformity of a target imploded by directly illuminating a fusion capsule with laser beams. The technique uses time-resolved images of soft x-rays (> 1 keV) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. Methods used to accurately measure the ablation-front radius (
Sorting of amphiphile membrane components in curvature and composition gradients
NASA Astrophysics Data System (ADS)
Tian, Aiwei
Phase and shape heterogeneities in biomembranes are of functional importance. However, it is difficult to elucidate the roles membrane heterogeneities play in maintaining cellular function due to the complexity of biomembranes. Therefore, investigations of phase behavior and composition/curvature coupling in lipid and polymer model membranes offer some advantages. In this thesis, phase properties in lipid and polymer giant vesicles were studied. Line tension at the fluid/fluid phase boundary of giant lipid unilamellar vesicles was determined directly by micropipette aspiration, and found to be composition-dependent. Dynamics of calcium-induced domains within polyanionic vesicles subject to chemical stimuli were investigated, which revealed the strength of molecular interaction and suggested applications in triggered delivery. In addition, curvature sorting of lipids and proteins was examined. Lipid membrane tethers were pulled from giant unilamellar vesicles using two micropipettes and a bead. Tether radius can be controlled and measured in this system. By examining fluorescence intensity of labeled molecules as a function of curvature, we found that DiI dyes (lipid analogues with spontaneous curvatures) had no curvature preference down to radii of 10 nm. Theoretical calculation predicted that the distribution of small lipids was dominated by entropy instead of bending energy. However protein Cholera toxin subunit B was efficiently sorted away from the high positive curvature due to its negative spontaneous curvature. Bending stiffness was determined to decrease as curvature increased in homogeneous membranes with ternary lipid mixtures near a critical consulate point, revealing the strong preferential intermolecular interactions of such mixtures. In addition, diffusion controlled domain growth was observed in tethers pulled from phase-separated vesicles, which provides a new dynamic sorting principle for lipids and proteins in curvature gradients.
Curvature of the localized surface plasmon resonance peak.
Chen, Peng; Liedberg, Bo
2014-08-05
Localized surface plasmon resonance (LSPR) occurring in noble metal nanoparticles (e.g., Au) is a widely used phenomenon to report molecular interactions. Traditional LSPR sensors typically monitor shifts in the peak position or extinction in response to local refractive index changes in the close vicinity of the nanoparticle surface. The ability to resolve minute shifts/extinction changes is to a large extent limited by instrumental noise. A new strategy to evaluate LSPR responses utilizing changes in the shape of the extinction spectrum (the curvature) is proposed. The response of curvature to refractive index changes is investigated theoretically using Mie theory and an analytical expression relating the curvature to the refractive index is presented. The experimentally derived curvatures for 13 nm spherical gold nanoparticles (AuNPs) exposed to solvents with different bulk refractive indices confirm the theoretical predictions. Moreover, both the calculated and experimental findings suggest that the curvature is approximately a linear function of refractive index in regimes relevant to bio and chemical sensing. We demonstrate that curvature is superior over peak shift and extinction both in terms of signal-to-noise (S/N) ratio and reliability of LSPR sensors. With a curvature, one could readily monitor submonolayer adsorption of a low molecular weight thiol molecule (M(w) = 458.6) onto 13 nm AuNPs. It is also worthwhile mentioning that curvature is virtually insensitive to instrumental instabilities and artifacts occurring during measurement. Instabilities such as baseline tilt and shift, shift in peak position as well as sharp spikes/steps in the extinction spectra do not induce artifacts in the sensorgrams of curvature.
Curvature generation in nematic surfaces
NASA Astrophysics Data System (ADS)
Mostajeran, Cyrus
2015-06-01
In recent years there has been a growing interest in the study of shape formation using modern responsive materials that can be preprogrammed to undergo spatially inhomogeneous local deformations. In particular, nematic liquid crystalline solids offer exciting possibilities in this context. Considerable recent progress has been made in achieving a variety of shape transitions in thin sheets of nematic solids by engineering isolated points of concentrated Gaussian curvature using topological defects in the nematic director field across textured surfaces. In this paper, we consider ways of achieving shape transitions in thin sheets of nematic glass by generation of nonlocalized Gaussian curvature in the absence of topological defects in the director field. We show how one can blueprint any desired Gaussian curvature in a thin nematic sheet by controlling the nematic alignment angle across the surface and highlight specific patterns which present feasible initial targets for experimental verification of the theory.
Intrinsically disordered proteins drive membrane curvature
NASA Astrophysics Data System (ADS)
Busch, David J.; Houser, Justin R.; Hayden, Carl C.; Sherman, Michael B.; Lafer, Eileen M.; Stachowiak, Jeanne C.
2015-07-01
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures.
Intrinsically disordered proteins drive membrane curvature
Busch, David J.; Houser, Justin R.; Hayden, Carl C.; Sherman, Michael B.; Lafer, Eileen M.; Stachowiak, Jeanne C.
2015-01-01
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures. PMID:26204806
Intrinsically disordered proteins drive membrane curvature.
Busch, David J; Houser, Justin R; Hayden, Carl C; Sherman, Michael B; Lafer, Eileen M; Stachowiak, Jeanne C
2015-07-24
Assembly of highly curved membrane structures is essential to cellular physiology. The prevailing view has been that proteins with curvature-promoting structural motifs, such as wedge-like amphipathic helices and crescent-shaped BAR domains, are required for bending membranes. Here we report that intrinsically disordered domains of the endocytic adaptor proteins, Epsin1 and AP180 are highly potent drivers of membrane curvature. This result is unexpected since intrinsically disordered domains lack a well-defined three-dimensional structure. However, in vitro measurements of membrane curvature and protein diffusivity demonstrate that the large hydrodynamic radii of these domains generate steric pressure that drives membrane bending. When disordered adaptor domains are expressed as transmembrane cargo in mammalian cells, they are excluded from clathrin-coated pits. We propose that a balance of steric pressure on the two surfaces of the membrane drives this exclusion. These results provide quantitative evidence for the influence of steric pressure on the content and assembly of curved cellular membrane structures.
Changes on the corneal thickness and curvature after orthokeratology
NASA Astrophysics Data System (ADS)
Mitsui, Iwane; Yamada, Yoshiya
2004-07-01
To evaluate the corneal thickness and curvature changes after Orthokeratology contact lens wear, using the ORBSCAN II corneal topography system, corneal thickness and corneal curvature were measured on one hundred and twenty eyes of sixty patients before and after wearing the custom rigid gas permeable contact lenses for Orthokeratology. The contact lenses were specially designed for each eye. The subjects wore the orthokeratology lenses for approximately Four hours with their eyes closed. The corneal thickness of the subjects was increased on fifty-five eyes at not only the peripheral zone but also the center of the cornea. The average increase of central and peripheral corneal thickness was 18 micrometer and 22micrometer, respectively. The mean anterior curvature of corneal surface changed 1.25D. The mean posterior curvature of corneal endothelium side changed 0.75D.
DSD front models : nonideal explosive detonation
Bdzil, J. B.; Short, M.; Aslam, T. D.; Catanach, R. A.; Hill, L. G.
2001-01-01
The Detonation Shock Dynamics (DSD) method for propagating detonation in numerical simulation of detonation in high explosive (HE) is based on three elements: (1) a subscale theory of multi-dimensional detonation that treats the evolving detonation as a front with dynamics that depends only on metrics of the front (such as curvature, etc.), (2) high-resolution direct numerical sirnuliltion of detonation serving both to test existing subscale theories and suggest modifications, and (3) physical experiments to characterize multi-dimensional detonation propagation on real explosives and to calibrate the front models for use in engineering simulations. In this paper we describe our work on all three of these elements of the DSD method as it applies to detonation in nonideal explosives.
Correlation between thoracolumbar curvatures and respiratory function in older adults.
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were -46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=-0.23, P<0.05; forced vital capacity: r=-0.32, P<0.05), quiet expiration intercostal thickness (r=-0.22, P<0.05) and deep expiration diaphragm muscle thickness (r=-0.21, P<0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=-0.29, P<0.05) and diaphragm muscle thickness at deep inspiration (r=-0.22, P<0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and lumbar curvatures
Correlation between thoracolumbar curvatures and respiratory function in older adults
Rahman, Nor Najwatul Akmal Ab; Singh, Devinder Kaur Ajit; Lee, Raymond
2017-01-01
Aging is associated with alterations in thoracolumbar curvatures and respiratory function. Research information regarding the correlation between thoracolumbar curvatures and a comprehensive examination of respiratory function parameters in older adults is limited. The aim of the present study was to examine the correlation between thoracolumbar curvatures and respiratory function in community-dwelling older adults. Thoracolumbar curvatures (thoracic and lumbar) were measured using a motion tracker. Respiratory function parameters such as lung function, respiratory rate, respiratory muscle strength and respiratory muscle thickness (diaphragm and intercostal) were measured using a spirometer, triaxial accelerometer, respiratory pressure meter and ultrasound imaging, respectively. Sixty-eight community-dwelling older males and females from Kuala Lumpur, Malaysia, with mean (standard deviation) age of 66.63 (5.16) years participated in this cross-sectional study. The results showed that mean (standard deviation) thoracic curvature angle and lumbar curvature angles were −46.30° (14.66°) and 14.10° (10.58°), respectively. There was a significant negative correlation between thoracic curvature angle and lung function (forced expiratory volume in 1 second: r=−0.23, P<0.05; forced vital capacity: r=−0.32, P<0.05), quiet expiration intercostal thickness (r=−0.22, P<0.05) and deep expiration diaphragm muscle thickness (r=−0.21, P<0.05). The lumbar curvature angle had a significant negative correlation with respiratory muscle strength (r=−0.29, P<0.05) and diaphragm muscle thickness at deep inspiration (r=−0.22, P<0.05). However, respiratory rate was correlated neither with thoracic nor with lumbar curvatures. The findings of this study suggest that increase in both thoracic and lumbar curvatures is correlated with decrease in respiratory muscle strength, respiratory muscle thickness and some parameters of lung function. Clinically, both thoracic and lumbar
A novel curvature-controllable steerable needle for percutaneous intervention.
Bui, Van Khuyen; Park, Sukho; Park, Jong-Oh; Ko, Seong Young
2016-08-01
Over the last few decades, flexible steerable robotic needles for percutaneous intervention have been the subject of significant interest. However, there still remain issues related to (a) steering the needle's direction with less damage to surrounding tissues and (b) increasing the needle's maximum curvature for better controllability. One widely used approach is to control the fixed-angled bevel-tip needle using a "duty-cycle" algorithm. While this algorithm has shown its applicability, it can potentially damage surrounding tissue, which has prevented the widespread adoption of this technology. This situation has motivated the development of a new steerable flexible needle that can change its curvature without axial rotation, while at the same time producing a larger curvature. In this article, we propose a novel curvature-controllable steerable needle. The proposed robotic needle consists of two parts: a cannula and a stylet with a bevel-tip. The curvature of the needle's path is controlled by a control offset, defined by the offset between the bevel-tip and the cannula. As a result, the necessity of rotating the whole needle's body is decreased. The duty-cycle algorithm is utilized to a limited degree to obtain a larger radius of curvature, which is similar to a straight path. The first prototype of 0.46 mm (outer diameter) was fabricated and tested with both in vitro gelatin phantom and ex vivo cow liver tissue. The maximum curvatures measured 0.008 mm(-1) in 6 wt% gelatin phantom, 0.0139 mm(-1) in 10 wt% gelatin phantom, and 0.0038 mm(-1) in cow liver. The experimental results show a linear relationship between the curvature and the control offset, which can be utilized for future implementation of this control algorithm.
The effect of illuminant position on perceived curvature.
Curran, W; Johnston, A
1996-05-01
In shaded scenes surface features can appear either concave or convex, depending upon the viewer's judgement about the direction of the prevailing illumination. If other curvature cues are added to the image this ambiguity can be removed. However, it is not clear to what extent, if any, illuminant position exerts an influence on the perceived magnitude of surface curvature. Subjects were presented with pairs of spherical surface patches in a curvature matching task. The patches were defined by shading and texture cues. The perceived curvature of a standard patch was measured as a function of light source position. We found a clear effect of light source position on apparent curvature. Perceived curvature decreased as light source tilt increased and as light source slant decreased. We also found that the strength of this effect is determined partly by a surface's reflectance function and partly by the relative weight of the texture cue. When a specular component was added to the stimuli, the effect of light source orientation was weakened. The weight of the texture cue was manipulated by disrupting the regular distribution of texture elements. We found an inverse relationship between the strength of the effect and the weight of the texture cue: lowering the texture cue weight resulted in an enhancement of the illuminant position effect.
Space Curvature and the "Heavy Banana 'Paradox.'"
ERIC Educational Resources Information Center
Gruber, Ronald P.; And Others
1991-01-01
Two ways to visually enhance the concept of space curvature are described. Viewing space curvature as a meterstick contraction and the heavy banana "paradox" are discussed. The meterstick contraction is mathematically explained. (KR)
Curvature-induced lipid segregation
NASA Astrophysics Data System (ADS)
Zheng, Bin; Meng, Qing-Tian; B. Selinger Robin, L.; V. Selinger, Jonathan; Ye, Fang-Fu
2015-06-01
We investigate how an externally imposed curvature influences lipid segregation on two-phase-coexistent membranes. We show that the bending-modulus contrast of the two phases and the curvature act together to yield a reduced effective line tension. On largely curved membranes, a state of multiple domains (or rafts) forms due to a mechanism analogous to that causing magnetic-vortex formation in type-II superconductors. We determine the criterion for such a multi-domain state to occur; we then calculate respectively the size of the domains formed on cylindrically and spherically curved membranes. Project supported by the Hundred-Talent Program of the Chinese Academy of Sciences (FY) and the National Science Foundation of USA via Grant DMR-1106014 (RLBS, JVS).
Quantum complexity and negative curvature
NASA Astrophysics Data System (ADS)
Brown, Adam R.; Susskind, Leonard; Zhao, Ying
2017-02-01
As time passes, once simple quantum states tend to become more complex. For strongly coupled k -local Hamiltonians, this growth of computational complexity has been conjectured to follow a distinctive and universal pattern. In this paper we show that the same pattern is exhibited by a much simpler system—classical geodesics on a compact two-dimensional geometry of uniform negative curvature. This striking parallel persists whether the system is allowed to evolve naturally or is perturbed from the outside.
Disformal invariance of curvature perturbation
Motohashi, Hayato; White, Jonathan E-mail: jwhite@post.kek.jp
2016-02-01
We show that under a general disformal transformation the linear comoving curvature perturbation is not identically invariant, but is invariant on superhorizon scales for any theory that is disformally related to Horndeski's theory. The difference between disformally related curvature perturbations is found to be given in terms of the comoving density perturbation associated with a single canonical scalar field. In General Relativity it is well-known that this quantity vanishes on superhorizon scales through the Poisson equation that is obtained on combining the Hamiltonian and momentum constraints, and we confirm that a similar result holds for any theory that is disformally related to Horndeski's scalar-tensor theory so long as the invertibility condition for the disformal transformation is satisfied. We also consider the curvature perturbation at full nonlinear order in the unitary gauge, and find that it is invariant under a general disformal transformation if we assume that an attractor regime has been reached. Finally, we also discuss the counting of degrees of freedom in theories disformally related to Horndeski's.
Turning maneuvers in sharks: Predicting body curvature from axial morphology.
Porter, Marianne E; Roque, Cassandra M; Long, John H
2009-08-01
Given the diversity of vertebral morphologies among fishes, it is tempting to propose causal links between axial morphology and body curvature. We propose that shape and size of the vertebrae, intervertebral joints, and the body will more accurately predict differences in body curvature during swimming rather than a single meristic such as total vertebral number alone. We examined the correlation between morphological features and maximum body curvature seen during routine turns in five species of shark: Triakis semifasciata, Heterodontus francisci, Chiloscyllium plagiosum, Chiloscyllium punctatum, and Hemiscyllium ocellatum. We quantified overall body curvature using three different metrics. From a separate group of size-matched individuals, we measured 16 morphological features from precaudal vertebrae and the body. As predicted, a larger pool of morphological features yielded a more robust prediction of maximal body curvature than vertebral number alone. Stepwise linear regression showed that up to 11 features were significant predictors of the three measures of body curvature, yielding highly significant multiple regressions with r(2) values of 0.523, 0.537, and 0.584. The second moment of area of the centrum was always the best predictor, followed by either centrum length or transverse height. Ranking as the fifth most important variable in three different models, the body's total length, fineness ratio, and width were the most important non-vertebral morphologies. Without considering the effects of muscle activity, these correlations suggest a dominant role for the vertebral column in providing the passive mechanical properties of the body that control, in part, body curvature during swimming.
NASA Astrophysics Data System (ADS)
Estep, J. D.; Shaw, J.; Edmonds, D. A.
2015-12-01
Quantifying the progradation of the Wax Lake Delta (WLD), a sub-delta of the Mississippi River Delta, can lend valuable insight into coastal land-building patterns. Previous studies of WLD progradation have relied on subaerially-exposed land for indicating delta extent, but an inherent problem with this method lies in the high variability of exposed land due to vegetative, hydrologic, and atmospheric fluctuations. By mapping water surface films observed in remote imagery which form streaklines along flow paths in the delta, we show that the shallow delta front flow patterns are relatively unaffected by short term water level changes and can be used to evaluate WLD progradation over time. Remotely sensed imagery from multiple sources (infrared aerial photography, SPOT, UAVSAR) spanning from 1988 to 2015 was used to map streaklines from which we calculate a flow direction divergence field across the delta. Measuring the translation of this field through time, such as areas containing extreme divergence values along the delta front, quantifies the progradation over the time elapsed. Preliminary measurements of WLD progradation were subdivided into the eastern, southern, and western thirds of the delta. The eastern third prograded at 110 ±20m/yr from 1988 - 1997, 100 ±40m/yr from 1997 - 2002, and then remained relatively constant to 2015. The southern third prograded at 130 ±20m/yr from 1988 - 1997, 200 ±40m/yr from 1997 - 2002, and remained relatively constant to 2015. The western third prograded at 130 ±30m/yr from 1988 - 1997, 220 ±60 m from 1997 - 2002, and then remained relatively constant from 2002 - 2015. Also of note is the retrogradation on the average of 700 ±400m observed from January to August, 1992 which we interpret as being caused by the impact of Hurricane Andrew. The streakline methodology of evaluating WLD progradation could provide new methods for analysis of land change in other deltas around the world.
Design and Measurement of a Low-Noise 64-Channels Front-End Readout ASIC for CdZnTe Detectors
Gan, Bo; Wei, Tingcun; Gao, Wu; Liu, Hui; Hu, Yann
2015-07-01
Cadmium zinc telluride (CdZnTe) detectors, as one of the principal detectors for the next-generation X-ray and γ-ray imagers, have high energy resolution and supporting electrode patterning in the radiation environment at room-temperature. In the present, a number of internationally renowned research institutions and universities are actively using these detector systems to carry out researches of energy spectrum analysis, medical imaging, materials characterization, high-energy physics, nuclear plant monitoring, and astrophysics. As the most important part of the readout system for the CdZnTe detector, the front-end readout application specific integrated circuit (ASIC) would have an important impact on the performances of the whole detector system. In order to ensure the small signal to noise ratio (SNR) and sufficient range of the output signal, it is necessary to design a front-end readout ASIC with very low noise and very high dynamic range. In addition, radiation hardness should be considered when the detectors are utilized in the space applications and high energy physics experiments. In this paper, we present measurements and performances of a novel multi-channel radiation-hardness low-noise front-end readout ASIC for CdZnTe detectors. The readout circuits in each channel consist of charge sensitive amplifier, leakage current compensation circuit (LCC), CR-RC shaper, S-K filter, inverse proportional amplifier, peak detect and hold circuit (PDH), discriminator and trigger logic, time sequence control circuit and driving buffer. All of 64 readout channels' outputs enter corresponding inputs of a 64 channel multiplexer. The output of the mux goes directly out of the chip via the output buffer. The 64-channel readout ASIC is implemented using the TSMC 0.35 μm mixed-signal CMOS technology. The die size of the prototype chip is 2.7 mm x 8 mm. At room temperature, the equivalent noise level of a typical channel reaches 66 e{sup -} (rms) at zero farad for a power
A novel approach in assessment of root canal curvature
Sadeghi, Shiva; Poryousef, Vahideh
2009-01-01
Introduction: The purpose of this in vitro study was to introduce a new method to describe root canal curvatures and to assess the degree of curvature of human permanent mandibular teeth with curved root canals. Materials and Methods: One hundred and thirty five mesial root canals of mandibular first and second molar teeth were selected. Access cavities were prepared. After inserting a K-file size #10 into each canal, radiographs were taken. Canal curvature was determined by measuring the Schneider angle, canal access angle, as well as the canal radius, length, height and curvature starting distance on scanned radiographs using a computerized image processing system. Data was evaluated statistically using Pearson correlation. Results: The mean canal access angle (CAA) and Schneider angle (S) were 8.04◦ (3.46) and 19◦ (6.99), respectively. The Pearson correlation analysis found significant positive correlation between S and CAA (r=0.826, P<0.0001). Negative correlations were found between radius and length (r= –0.4, P<0.0001), radius and Schneider angle (r= –0.4, P<0.0001), radius and CAA (r= –0.24, P=0.004) and CAA and curvature starting distance (r= 0.4, P<0.0001). There was no correlation between height and distance (r=0.013, P=0.789), as well as CAA and height (r=0.654, P=0.001). Conclusion: Under the limitations of this study, the results indicated that the shape of root canal curvature can be more accurately described using two angles, Schneider in combination with Canal access angle. The related parameters included radius, length, distance and height of curvature. [Iranian Endodontic Journal 2009;4(4):131-4] PMID:24019833
Almond, P. M.; Kaplan, D. I.; Langton, C. A.; Stefanko, D. B.; Spencer, W. A.; Hatfield, A.; Arai, Y.
2012-08-23
The objective of this work was to develop and evaluate a series of methods and validate their capability to measure differences in oxidized versus reduced saltstone. Validated methods were then applied to samples cured under field conditions to simulate Performance Assessment (PA) needs for the Saltstone Disposal Facility (SDF). Four analytical approaches were evaluated using laboratory-cured saltstone samples. These methods were X-ray absorption spectroscopy (XAS), diffuse reflectance spectroscopy (DRS), chemical redox indicators, and thin-section leaching methods. XAS and thin-section leaching methods were validated as viable methods for studying oxidation movement in saltstone. Each method used samples that were spiked with chromium (Cr) as a tracer for oxidation of the saltstone. The two methods were subsequently applied to field-cured samples containing chromium to characterize the oxidation state of chromium as a function of distance from the exposed air/cementitious material surface.
Status of the front-end-electronics for the time-of-flight measurements at the MPD experiment
NASA Astrophysics Data System (ADS)
Buryakov, M. G.; Babkin, V. A.; Golovatyuk, V. M.; Volgin, S. V.; Rumyantsev, M. M.
2016-09-01
The preamplifier based on the ASIC NINO for the Time of Flight system (TOF) of MPD/NICA was developed and tested. The signal is read from both sides of the strip of the multi gap Resistive Plate Chamber (MRPC). In total there are around 14000 channels of electronics. To measure time of flight of secondary particles from collision of heavy ions on the collider NICA the Time over Threshold (ToT) method is used. According to the bench tests the preamplifier board showed stable work and good time resolution <10 ps for one channel. It was also tested at the test beam facility of the Nuclotron. The time resolution of the TOF detector which used the described preamplifier was reached ˜42 ps.
NASA Astrophysics Data System (ADS)
Abeleira, A.; Farmer, D.; Fischer, E. V.; Pollack, I. B.; Zaragoza, J.
2015-12-01
Authors: Ilana Pollock1,2, Jake Zaragoza2, Emily V. Fischer2, Delphine K. Farmer11. Department of Chemistry, Colorado State University, Fort Collins, CO 2. Department of Atmospheric Science, Colorado State University, Fort Collins, CO During summer months, the Northern Front Range Metropolitan Area (NFRMA) of Colorado consistently violates the 75 ppbv 8-hour EPA National Ambient Air Quality Standard (NAAQS) for ambient ozone (O3), despite continued reduction in anthropogenic emissions. The region has been deemed an O3 non-attainment zone since 2008. Ground-level O3 is produced from photochemical catalytic cycles involving OH radicals, volatile organic compounds (VOCs), and NOx (NO + NO2). VOC emissions in the NFRMA are dominated by anthropogenic sources and influenced by biogenic and agricultural sources, while NOx emissions are mainly from automobile exhaust. A growing concern in the region is the role of oil and natural gas (ONG) on VOC concentrations and the potential for O3 production. Increases in local VOC emissions will likely cause subsequent increase in local O3 concentrations as PO3 increases in a region that is already affected by high O3episodes. As a part of the SONGNEX 2015 (Shale Oil and Natural Gas Nexus) campaign, we measured a broad suite of speciated VOCs during two 8-week deployments (March-May 2015, July-September 2015) at the Boulder Atmospheric Observatory in Erie, CO. VOC measurements were made with a custom-online multichannel gas chromatography system (50+ compounds hourly), along with measurements of O3, SO2, NOx, NOy, PAN, CO, CO2, and CH4. We use these data to investigate the role of different VOC sources, and ONG in particular, in contributing to VOC reactivity and thus instantaneous O3 production. Preliminary analysis of the Spring VOC data indicates that VOC reactivity is dominated by light alkanes typical of ONG emissions - specifically propane, consistent with previous winter-time studies. We will use the observed temperature
Measuring Intrinsic Curvature of Space with Electromagnetism
ERIC Educational Resources Information Center
Mabin, Mason; Becker, Maria; Batelaan, Herman
2016-01-01
The concept of curved space is not readily observable in everyday life. The educational movie "Sphereland" attempts to illuminate the idea. The main character, a hexagon, has to go to great lengths to prove that her world is in fact curved. We present an experiment that demonstrates a new way to determine if a two-dimensional surface,…
Geometric curvature and phase of the Rabi model
Mao, Lijun; Huai, Sainan; Guo, Liping; Zhang, Yunbo
2015-11-15
We study the geometric curvature and phase of the Rabi model. Under the rotating-wave approximation (RWA), we apply the gauge independent Berry curvature over a surface integral to calculate the Berry phase of the eigenstates for both single and two-qubit systems, which is found to be identical with the system of spin-1/2 particle in a magnetic field. We extend the idea to define a vacuum-induced geometric curvature when the system starts from an initial state with pure vacuum bosonic field. The induced geometric phase is related to the average photon number in a period which is possible to measure in the qubit–cavity system. We also calculate the geometric phase beyond the RWA and find an anomalous sudden change, which implies the breakdown of the adiabatic theorem and the Berry phases in an adiabatic cyclic evolution are ill-defined near the anti-crossing point in the spectrum.
NASA Astrophysics Data System (ADS)
Asakura, N.; Tsuji-Iio, S.; Ikeda, Y.; Neyatani, Y.; Seki, M.
1995-12-01
A fast reciprocating probe system with a long drive shaft was incorporated into a multi-junction lower hybrid (LH) wave launcher on JT-60U in order to investigate an improved coupling mechanism of the radio frequency wave to the core plasma. The system has been operated reliably over a horizontal scan of 25 cm in 1.5 s using a compact pneumatic cylinder drive and springs. A double probe measurement provided the scrape-off layer plasma profile between the last closed flux surface and the first wall with the spatial resolution of 1-2 mm measured with a laser displacement gauge. The profiles of the electron density ne and temperature Te were in good agreement with those obtained with a triple probe method. During the LH wave injection with good coupling to the core plasma, an increase in the local Te was observed in front of the LH launcher mouth. The local ne was (7-10)×1016 m-3, consistent values needed for the good coupling.
Asakura, N.; Tsuji-Iio, S.; Ikeda, Y.; Neyatani, Y.; Seki, M.
1995-12-01
A fast reciprocating probe system with a long drive shaft was incorporated into a multi-junction lower hybrid (LH) wave launcher on JT-60U in order to investigate an improved coupling mechanism of the radio frequency wave to the core plasma. The system has been operated reliably over a horizontal scan of 25 cm in 1.5 s using a compact pneumatic cylinder drive and springs. A double probe measurement provided the scrape-off layer plasma profile between the last closed flux surface and the first wall with the spatial resolution of 1{minus}2 mm measured with a laser displacement gauge. The profiles of the electron density {ital n}{sub {ital e}} and temperature {ital T}{sub {ital e}} were in good agreement with those obtained with a triple probe method. During the LH wave injection with good coupling to the core plasma, an increase in the local {ital T}{sub {ital e}} was observed in front of the LH launcher mouth. The local {ital n}{sub {ital e}} was (7{minus}10){times}10{sup 16} m{sup {minus}3}, consistent values needed for the good coupling. {copyright} {ital 1995} {ital American} {ital Institute} {ital of} {ital Physics}.
Biostereometric Analysis Of Spine Curvatures On Living Human Body
NASA Astrophysics Data System (ADS)
Pineau, J.-C.; Ignazi, G.; Prudent, J.
1986-07-01
An analysis of the external and internal curvatures of spine was carried out on a sample of nine males from biostereometric measurements for different imposed postures. The results concerning the modifications of the external shape of the curves are used for the 3-D human body modeling in C.A.D. applications.
NASA Technical Reports Server (NTRS)
Bagshaw, S. L.; Cleland, R. E.
1990-01-01
Gravitropic curvature results from unequal growth rates on the upper and lower sides of horizontal stems. These unequal growth rates could be due to differences in wall extensibility between the two sides. To test this, the time course of curvature of horizontal sunflower (Helianthus annuus L.) hypocotyls was determined and compared with the time courses of changes in Instron-measured wall extensibility (PEx) of the upper and lower epidermal layers. As gravicurvature developed, so did the difference in PEx between the upper and lower epidermis. The enhanced growth rate on the lower side during the period of maximum increase in curvature was matched by PEx values greater than those of the vertical control, while the inhibited growth rate on the upper side was accompanied by PEx values below that of the control. The close correlation between changes in growth rates and alterations in PEx demonstrates that changes in wall extensibility play a major role in controlling gravicurvature.
Radius of curvature controlled mirror
Neil, George R.; Rathke, John Wickham; Schultheiss, Thomas John; Shinn, Michelle D.; Dillon-Townes, Lawrence A.
2006-01-17
A controlled radius of curvature mirror assembly comprising: a distortable mirror having a reflective surface and a rear surface; and in descending order from the rear surface; a counter-distortion plate; a flow diverter having a flow diverter aperture at the center thereof; a flow return plate having a flow return aperture at the center thereof; a thermal isolation plate having a thermal isolation plate aperture at the center thereof and a flexible heater having a rear surface and a flexible heater aperture at the center thereof; a double walled tube defining a coolant feed chamber and a coolant return chamber; said coolant feed chamber extending to and through the flow diverter aperture and terminating at the counter-distortion plate and the coolant return chamber extending to and through the thermal isolation backplate and terminating at the flow diverter; and a coolant feed and a coolant return exit at the rear of said flexible heater.
NASA Astrophysics Data System (ADS)
Kuang, Shi; Newchurch, Michael J.; Johnson, Matthew S.; Wang, Lihua; Burris, John; Pierce, Robert B.; Eloranta, Edwin W.; Pollack, Ilana B.; Graus, Martin; Gouw, Joost; Warneke, Carsten; Ryerson, Thomas B.; Markovic, Milos Z.; Holloway, John S.; Pour-Biazar, Arastoo; Huang, Guanyu; Liu, Xiong; Feng, Nan
2017-01-01
Stratosphere-to-troposphere transport (STT) and biomass burning (BB) are two important natural sources for tropospheric ozone that can result in elevated ozone and air-quality episode events. High-resolution observations of multiple related species are critical for complex ozone source attribution. In this article, we present an analysis of coinciding ground-based and airborne observations, including ozone lidar, ozonesonde, high spectral resolution lidar (HSRL), and multiple airborne in situ measurements, made on 28 and 29 June 2013 during the Southeast Nexus field campaign. The ozone lidar and HSRL reveal detailed ozone and aerosol structures as well as the temporal evolution associated with a cold front passage. The observations also captured two enhanced (+30 ppbv) ozone layers in the free troposphere (FT), which were determined from this study to be caused by a mixture of BB and stratospheric sources. The mechanism for this STT is tropopause folding associated with a cutoff upper level low-pressure system according to the analysis of its potential vorticity structure. The depth of the tropopause fold appears to be shallow for this case compared to events observed in other seasons; however, the impact on lower tropospheric ozone was clearly observed. This event suggests that strong STT may occur in the southeast United States during the summer and can potentially impact lower troposphere during these times. Statistical analysis of the airborne observations of trace gases suggests a coincident influence of BB transport in the FT impacting the vertical structure of ozone during this case study.
Flame front geometry in premixed turbulent flames
Shepherd, I.G.; Ashurst, W.T.
1991-12-01
Experimental and numerical determinations of flame front curvature and orientation in premixed turbulent flames are presented. The experimental data is obtained from planar, cross sectional images of stagnation point flames at high Damkoehler number. A direct numerical simulation of a constant energy flow is combined with a zero-thickness, constant density flame model to provide the numerical results. The computational domain is a 32{sup 3} cube with periodic boundary conditions. The two-dimensional curvature distributions of the experiments and numerical simulations compare well at similar q{prime}/S{sub L} values with means close to zero and marked negative skewness. At higher turbulence levels the simulations show that the distributions become symmetric about zero. These features are also found in the three dimensional distributions of curvature. The simulations support assumptions which make it possible to determine the mean direction cosines from the experimental data. This leads to a reduction of 12% in the estimated flame surface area density in the middle of the flame brush. 18 refs.
Curvature of the spectral energy distributions of blazars
Chen, Liang
2014-06-20
In this paper, spectral energy distributions (SED) of both synchrotron and inverse Compton (IC) components of a sample of Fermi bright blazars are fitted by a log-parabolic law. The second-degree term of the log parabola measures the curvature of an SED. We find a statistically significant correlation between the synchrotron peak frequency and its curvature. This result is in agreement with the theoretical prediction and confirms previous studies that dealt with a single source with observations at various epochs or a small sample. If a broken power law is employed to fit the SED, the difference between the two spectral indices (i.e., |α{sub 2} – α{sub 1}|) can be considered a 'surrogate' of the SED curvature. We collect data from the literature and find a correlation between the synchrotron peak frequency and the spectral difference. We do not find a significant correlation between the IC peak frequency and its curvature, which may be caused by a complicated seed photon field. It is also found that the synchrotron curvatures are on average larger than those of IC curvatures, and there is no correlation between these two parameters. As suggested by previous works, both the log-parabolic law of the SED and the above correlation can be explained by statistical and/or stochastic particle accelerations. Based on a comparison of the slops of the correlation, our result seems to favor stochastic acceleration mechanisms and emission processes. Additional evidence, including SED modeling, particle acceleration simulation, and comparisons between some predictions and empirical relations/correlations, also seems to support the idea that the electron energy distribution (and/or synchrotron SED) may be log-parabolic.
Interaction of a cold front with a sea-breeze front Observations
NASA Astrophysics Data System (ADS)
Brümmer, B.; Hennemuth, B.; Rhodin, A.; Thiemann, S.
1995-08-01
On 9 May 1989, during the field experiment FRONTEX, a synoptic-scale cold front was observed which moved from the North Sea to Northern Germany and interacted with a sea-breeze front. The modification of the cold front is documented by satellite images and measurements over the sea, at the coast and further inland. The synoptic-scale front was characterized by weak frontal gradients over the sea. It was aligned approximately parallel to the coast as was approximately the wind ahead of it. While the synoptic-scale front approached the coast during the forenoon hours, a strong temperature contrast developed between sea and land due to solar heating of the land surface. This led to the formation of a sea-breeze front associated with a stronger temperature gradient than the synoptic-scale front. At about noon, when the synoptic-scale front almost reached the coast, the sea-breeze front began to move inland. The onshore wind behind the sea-breeze front and ahead of the synoptic-scale front was so large that the wind field at the synoptic-scale front changed from confluence to difluence. This process was supported by a shallow inversion ahead of the synoptic-scale front which confined the vertical depth of the sea-breeze. The former sea-breeze front overtook the main frontal characteristics, continued its inland propagation and was the only frontal event observed over the land. As a result of the interaction, the synoptic-scale front was significantly intensified in the boundary layer.
Single Lipid Molecule Dynamics on Supported Lipid Bilayers with Membrane Curvature
Cheney, Philip P.; Weisgerber, Alan W.; Feuerbach, Alec M.; Knowles, Michelle K.
2017-01-01
The plasma membrane is a highly compartmentalized, dynamic material and this organization is essential for a wide variety of cellular processes. Nanoscale domains allow proteins to organize for cell signaling, endo- and exocytosis, and other essential processes. Even in the absence of proteins, lipids have the ability to organize into domains as a result of a variety of chemical and physical interactions. One feature of membranes that affects lipid domain formation is membrane curvature. To directly test the role of curvature in lipid sorting, we measured the accumulation of two similar lipids, 1,2-Dihexadecanoyl-sn-glycero-3-phosphoethanolamine (DHPE) and hexadecanoic acid (HDA), using a supported lipid bilayer that was assembled over a nanopatterned surface to obtain regions of membrane curvature. Both lipids studied contain 16 carbon, saturated tails and a head group tag for fluorescence microscopy measurements. The accumulation of lipids at curvatures ranging from 28 nm to 55 nm radii was measured and fluorescein labeled DHPE accumulated more than fluorescein labeled HDA at regions of membrane curvature. We then tested whether single biotinylated DHPE molecules sense curvature using single particle tracking methods. Similar to groups of fluorescein labeled DHPE accumulating at curvature, the dynamics of single molecules of biotinylated DHPE was also affected by membrane curvature and highly confined motion was observed. PMID:28294967
Rapid acceleration of protons upstream of earthward propagating dipolarization fronts
Ukhorskiy, AY; Sitnov, MI; Merkin, VG; Artemyev, AV
2013-01-01
[1] Transport and acceleration of ions in the magnetotail largely occurs in the form of discrete impulsive events associated with a steep increase of the tail magnetic field normal to the neutral plane (Bz), which are referred to as dipolarization fronts. The goal of this paper is to investigate how protons initially located upstream of earthward moving fronts are accelerated at their encounter. According to our analytical analysis and simplified two-dimensional test-particle simulations of equatorially mirroring particles, there are two regimes of proton acceleration: trapping and quasi-trapping, which are realized depending on whether the front is preceded by a negative depletion in Bz. We then use three-dimensional test-particle simulations to investigate how these acceleration processes operate in a realistic magnetotail geometry. For this purpose we construct an analytical model of the front which is superimposed onto the ambient field of the magnetotail. According to our numerical simulations, both trapping and quasi-trapping can produce rapid acceleration of protons by more than an order of magnitude. In the case of trapping, the acceleration levels depend on the amount of time particles stay in phase with the front which is controlled by the magnetic field curvature ahead of the front and the front width. Quasi-trapping does not cause particle scattering out of the equatorial plane. Energization levels in this case are limited by the number of encounters particles have with the front before they get magnetized behind it. PMID:26167430
Streamline curvature effects on turbulent boundary layers
NASA Technical Reports Server (NTRS)
Wilcox, D. C.; Chambers, T. L.
1976-01-01
A theoretical tool has been developed for predicting, in a nonempirical manner, effects of streamline curvature and coordinate-system rotation on turbulent boundary layers. The second-order closure scheme developed by Wilcox and Traci has been generalized for curved streamline flow and for flow in a rotating coordinate system. A physically based straightforward argument shows that curvature/rotation primarily affects the turbulent mixing energy; the argument yields suitable curvature/rotation terms which are added to the mixing-energy equation. Singular-perturbation solutions valid in the wall layer of a curved-wall boundary layer and a fully developed rotating channel flow demonstrate that, with the curvature/rotation terms, the model predicts the curved-wall and the rotating coordinate system laws of the wall. Results of numerical computations of curved-wall boundary layers and of rotating channel flow show that curvature/rotation effects can be computed accurately with second-order closure.
Gao, Dengliang
2013-03-01
In 3D seismic interpretation, curvature is a popular attribute that depicts the geometry of seismic reflectors and has been widely used to detect faults in the subsurface; however, it provides only part of the solutions to subsurface structure analysis. This study extends the curvature algorithm to a new curvature gradient algorithm, and integrates both algorithms for fracture detection using a 3D seismic test data set over Teapot Dome (Wyoming). In fractured reservoirs at Teapot Dome known to be formed by tectonic folding and faulting, curvature helps define the crestal portion of the reservoirs that is associated with strong seismic amplitude and high oil productivity. In contrast, curvature gradient helps better define the regional northwest-trending and the cross-regional northeast-trending lineaments that are associated with weak seismic amplitude and low oil productivity. In concert with previous reports from image logs, cores, and outcrops, the current study based on an integrated seismic curvature and curvature gradient analysis suggests that curvature might help define areas of enhanced potential to form tensile fractures, whereas curvature gradient might help define zones of enhanced potential to develop shear fractures. In certain fractured reservoirs such as at Teapot Dome where faulting and fault-related folding contribute dominantly to the formation and evolution of fractures, curvature and curvature gradient attributes can be potentially applied to differentiate fracture mode, to predict fracture intensity and orientation, to detect fracture volume and connectivity, and to model fracture networks.
A Phased-Array Stimulator System for Studying Planar and Curved Cardiac Activation Wave Fronts
Abbas, Rashida A.; Lin, Shien Fong; Mashburn, David; Xu, Junkai; Wikswo, John P.
2009-01-01
Wave front propagation in cardiac tissue is affected greatly by the geometry of the wave front. We describe a computer-controlled stimulator system that creates reproducible wave fronts of a predetermined shape and orientation for the investigation of the effects of wave front geometry. We conducted demonstration experiments on isolated perfused rabbit hearts, which were stained with the voltage-sensitive dye, di-4-ANEPPS. The wave fronts were imaged using a laser and a CCD camera. The stimulator and imaging systems have been used to characterize the relationship between wave front velocity and fiber orientation. This approach has potential applications in investigating curvature effects, testing numerical models of cardiac tissue, and creating complex wave fronts using one-, twoor three-dimensional electrode arrays. PMID:18232365
Programming curvature using origami tessellations
NASA Astrophysics Data System (ADS)
Dudte, Levi H.; Vouga, Etienne; Tachi, Tomohiro; Mahadevan, L.
2016-05-01
Origami describes rules for creating folded structures from patterns on a flat sheet, but does not prescribe how patterns can be designed to fit target shapes. Here, starting from the simplest periodic origami pattern that yields one-degree-of-freedom collapsible structures--we show that scale-independent elementary geometric constructions and constrained optimization algorithms can be used to determine spatially modulated patterns that yield approximations to given surfaces of constant or varying curvature. Paper models confirm the feasibility of our calculations. We also assess the difficulty of realizing these geometric structures by quantifying the energetic barrier that separates the metastable flat and folded states. Moreover, we characterize the trade-off between the accuracy to which the pattern conforms to the target surface, and the effort associated with creating finer folds. Our approach enables the tailoring of origami patterns to drape complex surfaces independent of absolute scale, as well as the quantification of the energetic and material cost of doing so.
Curvature function and coarse graining
Diaz-Marin, Homero; Zapata, Jose A.
2010-12-15
A classic theorem in the theory of connections on principal fiber bundles states that the evaluation of all holonomy functions gives enough information to characterize the bundle structure (among those sharing the same structure group and base manifold) and the connection up to a bundle equivalence map. This result and other important properties of holonomy functions have encouraged their use as the primary ingredient for the construction of families of quantum gauge theories. However, in these applications often the set of holonomy functions used is a discrete proper subset of the set of holonomy functions needed for the characterization theorem to hold. We show that the evaluation of a discrete set of holonomy functions does not characterize the bundle and does not constrain the connection modulo gauge appropriately. We exhibit a discrete set of functions of the connection and prove that in the abelian case their evaluation characterizes the bundle structure (up to equivalence), and constrains the connection modulo gauge up to ''local details'' ignored when working at a given scale. The main ingredient is the Lie algebra valued curvature function F{sub S}(A) defined below. It covers the holonomy function in the sense that expF{sub S}(A)=Hol(l={partial_derivative}S,A).
NASA Astrophysics Data System (ADS)
Lapenta, Giovanni; Goldman, Martin; Newman, David; olshevskyi, Vyacheslav; Markidis, Stefano
2016-04-01
Dipolarization fronts (DF) are formed by reconnection outflows interacting with the pre-existing environment. These regions are host of important energy exchanges [1], particle acceleration [2] and a complex structure and evolution [3]. Our recent work has investigated these regions via fully kinetic 3D simulations [4]. As reported recently on Nature Physics [3], based on 3D fully kinetic simulations started with a well defined x-line, we observe that in the DF reconnection transitions towards a more chaotic regime. In the fronts an instability devel- ops caused by the local gradients of the density and by the unfavourable acceleration and field line curvature. The consequence is the break up of the fronts in a fashion similar to the classical fluid Rayleigh-Taylor instability with the formation of "fingers" of plasma and embedded magnetic fields. These fingers interact and produce secondary reconnection sites. We present several different diagnostics that prove the existence of these secondary reconnection sites. Each site is surrounded by its own electron diffusion region. At the fronts the ions are generally not magnetized and considerable ion slippage is present. The discovery we present is that electrons are also slipping, forming localized diffusion regions near secondary reconnection sites [1]. The consequence of this discovery is twofold. First, the instability in the fronts has strong energetic implications. We observe that the energy transfer locally is very strong, an order of magnitude stronger than in the "X" line. However, this energy transfer is of both signs as it is natural for a wavy rippling with regions of magnetic to kinetic and regions of kinetic to magnetic energy conversion. Second, and most important for this session, is that MMS should not limit the search for electron diffusion regions to the location marked with X in all reconnection cartoons. Our simulations predict more numerous and perhaps more easily measurable electron diffusion
NASA Technical Reports Server (NTRS)
Morrison, John R.; Sosik, Heidi M.
2003-01-01
Fronts in the coastal ocean describe areas of strong horizontal gradients in both physical and biological properties associated with tidal mixing and freshwater estuarine output (e.g. Simpson, 1981 and O Donnell, 1993). Related gradients in optically important constituents mean that fronts can be observed from space as changes in ocean color as well as sea surface temperature (e.g., Dupouy et al., 1986). This research program is designed to determine which processes and optically important constituents must be considered to explain ocean color variations associated with coastal fronts on the New England continental shelf, in particular the National Ocean Partnership Program (NOPP) Front Resolving Observational Network with Telemetry (FRONT) site. This site is located at the mouth of Long Island sound and was selected after the analysis of 12 years of AVHRR data showed the region to be an area of strong frontal activity (Ullman and Cornillon, 1999). FRONT consists of a network of modem nodes that link bottom mounted Acoustic Doppler Current Profilers (ADCPs) and profiling arrays. At the center of the network is the Autonomous Vertically Profiling Plankton Observatory (AVPPO) (Thwaites et al. 1998). The AVPPO consists of buoyant sampling vehicle and a trawl-resistant bottom-mounted enclosure, which holds a winch, the vehicle (when not sampling), batteries, and controller. Three sampling systems are present on the vehicle, a video plankton recorder, a CTD with accessory sensors, and a suite of bio-optical sensors including Satlantic OCI-200 and OCR-200 spectral radiometers and a WetLabs ac-9 dual path absorption and attenuation meter. At preprogrammed times the vehicle is released, floats to the surface, and is then winched back into the enclosure with power and data connection maintained through the winch cable. Communication to shore is possible through a bottom cable and nearby surface telemetry buoy, equipped with a mobile modem, giving the capability for near
In vitro dimensions and curvatures of human lenses.
Rosen, Alexandre M; Denham, David B; Fernandez, Viviana; Borja, David; Ho, Arthur; Manns, Fabrice; Parel, Jean-Marie; Augusteyn, Robert C
2006-03-01
The purpose of this study was to determine dimensions and curvatures of excised human lenses using the technique of shadowphotogrammetry. A modified optical comparator and digital camera were used to photograph magnified sagittal and coronal lens profiles. Equatorial diameter, anterior and posterior sagittal thickness, anterior and posterior curvatures, and shape factors were obtained from these images. The data were used to calculate lens volumes, which were compared with the lens weights. Measurements were made on 37 human lenses ranging in age from 20 to 99 years. These showed that lens dimensions and the anterior radius of curvature increase linearly throughout adult life while posterior curvature remains constant. The relative shape (or aspect ratio) of the posterior lens is unchanged through adult life since both equatorial diameter and posterior thickness increase at the same rate. The ratio of anterior thickness to posterior thickness is constant at 0.70. It is suggested that in vivo forces alter the apparent location of the lens equator, that the in vitro lens shape corresponds to the maximally accommodated shape in vivo and that the shapes of the accommodated and unaccommodated lens progressively converge toward each other due to lens growth with age, with a convergence point located near the age of total loss of accommodation (55-60 years). Together, these observations provide additional support for the Helmholtz theory of accommodation.
Curvature in solid oxide fuel cells
NASA Astrophysics Data System (ADS)
Li, Wenxia; Hasinska, Kathy; Seabaugh, Matt; Swartz, Scott; Lannutti, John
At this point in history, curvature is inherent to the laminated components that comprise solid oxide fuel cells (SOFCs). Surprisingly, however, this fact has never been previously quantified in the literature. In addition, potential curvature changes associated with NiO reduction and re-oxidation during operation have not been investigated. In this report, an optical profilometer was employed to non-destructively quantify the surface curvature or cracking behavior observed on a large scale in industrially manufactured cells. This provides insights into the challenges that the component materials face as well as additional appreciation for why, in spite of a concerted effort to commercialize SOFC power generation, all currently manufactured SOFC stacks fail. Our results demonstrate that cracked electrolyte areas (caused by differential sintering) are flatter than uncracked regions. The height of the electrolyte surface ranged from 86 to 289 μm above the baseline following sintering. Reduction typically results in increases in curvature of up to 214 μm. Initial crack density appears to affect curvature evolution during reduction; the higher the crack density, the smaller the curvature increase following reduction at 600 °C. In general, however, we observed that the electrolyte layer is remarkably resistant to further cracking during these typographic changes. Following oxidation at 750 °C, large changes in curvature (up to 280 μm) are noted that appear to be related to the strength of the bond between the electrolyte and the underlying anode.
Curvature and torsion in growing actin networks
Shaevitz, Joshua W; Fletcher, Daniel A
2011-01-01
Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 s. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a three-dimensional (3D) space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature, possibly associated with filament debranching, rather than a fixed torque. PMID:18560043
Curvature and torsion in growing actin networks
NASA Astrophysics Data System (ADS)
Shaevitz, Joshua W.; Fletcher, Daniel A.
2008-06-01
Intracellular pathogens such as Listeria monocytogenes and Rickettsia rickettsii move within a host cell by polymerizing a comet-tail of actin fibers that ultimately pushes the cell forward. This dense network of cross-linked actin polymers typically exhibits a striking curvature that causes bacteria to move in gently looping paths. Theoretically, tail curvature has been linked to details of motility by considering force and torque balances from a finite number of polymerizing filaments. Here we track beads coated with a prokaryotic activator of actin polymerization in three dimensions to directly quantify the curvature and torsion of bead motility paths. We find that bead paths are more likely to have low rather than high curvature at any given time. Furthermore, path curvature changes very slowly in time, with an autocorrelation decay time of 200 s. Paths with a small radius of curvature, therefore, remain so for an extended period resulting in loops when confined to two dimensions. When allowed to explore a three-dimensional (3D) space, path loops are less evident. Finally, we quantify the torsion in the bead paths and show that beads do not exhibit a significant left- or right-handed bias to their motion in 3D. These results suggest that paths of actin-propelled objects may be attributed to slow changes in curvature, possibly associated with filament debranching, rather than a fixed torque.
Igor Kaganovich
2000-12-18
Negative ions tend to stratify in electronegative plasmas with hot electrons (electron temperature Te much larger than ion temperature Ti, Te > Ti ). The boundary separating a plasma containing negative ions, and a plasma, without negative ions, is usually thin, so that the negative ion density falls rapidly to zero-forming a negative ion density front. We review theoretical, experimental and numerical results giving the spatio-temporal evolution of negative ion density fronts during plasma ignition, the steady state, and extinction (afterglow). During plasma ignition, negative ion fronts are the result of the break of smooth plasma density profiles during nonlinear convection. In a steady-state plasma, the fronts are boundary layers with steepening of ion density profiles due to nonlinear convection also. But during plasma extinction, the ion fronts are of a completely different nature. Negative ions diffuse freely in the plasma core (no convection), whereas the negative ion front propagates towards the chamber walls with a nearly constant velocity. The concept of fronts turns out to be very effective in analysis of plasma density profile evolution in strongly non-isothermal plasmas.
The role of the epidermis and cortex in gravitropic curvature of maize roots
NASA Technical Reports Server (NTRS)
Bjorkman, T.; Cleland, R. E.
1988-01-01
In order to determine the role of the epidermis and cortex in gravitropic curvature of seedling roots of maize (Zea mays L. cv. Merit), the cortex on the two opposite flanks was removed from the meristem through the growing zone; gravitropic curvature was measured with the roots oriented horizontally with the cut flanks either on the upper and lower side, or on the lateral sides as a wound control. Curvature was slower in both these treatments (53 degrees in 5 h) than in intact roots (82 degrees), but there was no difference between the two orientations in extent and rate of curvature, nor in the latent time, showing that epidermis and cortex were not the site of action of the growth-regulating signal. The amount of cortex removed made no difference in the extent of curvature. Curvature was eliminated when the endodermis was damaged, raising the possibility that the endodermis or the stele-cortex interface controls gravitropic curvature in roots. The elongation rate of roots from which just the epidermis had been peeled was reduced by 0.01 mM auxin (indole-3-acetic acid) from 0.42 to 0.27 mm h-1, contradicting the hypothesis that only the epidermis responds to changes in auxin activity during gravistimulation. These observations indicate that gravitropic curvature in maize roots is not driven by differential cortical cell enlargement, and that movement of growth regulator(s) from the tip to the elongating zone is unlikely to occur in the cortex.
The role of the epidermis and cortex in gravitropic curvature of maize roots.
Björkman, T; Cleland, R E
1988-12-01
In order to determine the role of the epidermis and cortex in gravitropic curvature of seedling roots of maize (Zea mays L. cv. Merit), the cortex on the two opposite flanks was removed from the meristem through the growing zone; gravitropic curvature was measured with the roots oriented horizontally with the cut flanks either on the upper and lower side, or on the lateral sides as a wound control. Curvature was slower in both these treatments (53 degrees in 5 h) than in intact roots (82 degrees), but there was no difference between the two orientations in extent and rate of curvature, nor in the latent time, showing that epidermis and cortex were not the site of action of the growth-regulating signal. The amount of cortex removed made no difference in the extent of curvature. Curvature was eliminated when the endodermis was damaged, raising the possibility that the endodermis or the stele-cortex interface controls gravitropic curvature in roots. The elongation rate of roots from which just the epidermis had been peeled was reduced by 0.01 mM auxin (indole-3-acetic acid) from 0.42 to 0.27 mm h-1, contradicting the hypothesis that only the epidermis responds to changes in auxin activity during gravistimulation. These observations indicate that gravitropic curvature in maize roots is not driven by differential cortical cell enlargement, and that movement of growth regulator(s) from the tip to the elongating zone is unlikely to occur in the cortex.
Sequence-dependent DNA curvature and flexibility from scanning force microscopy images.
Scipioni, Anita; Anselmi, Claudio; Zuccheri, Giampaolo; Samori, Bruno; De Santis, Pasquale
2002-01-01
This paper reports a study of the sequence-dependent DNA curvature and flexibility based on scanning force microscopy (SFM) images. We used a palindromic dimer of a 1878-bp pBR322 fragment and collected a large pool of SFM images. The curvature of each imaged chain was measured in modulus and direction. It was found that the ensemble curvature modulus does not allow the separation of static and dynamic contributions to the curvature, whereas the curvature, when its direction in the two dimensions is taken into account, permits the direct separation of the intrinsic curvature contributions static and dynamic contributions. The palindromic symmetry also acted as an internal gauge of the validity of the SFM images statistical analysis. DNA static curvature resulted in good agreement with the predicted sequence-dependent intrinsic curvature. Furthermore, DNA sequence-dependent flexibility was found to correlate with the occurrence of A.T-rich dinucleotide steps along the chain and, in general, with the normalized basepair stacking energy distribution. PMID:12414677
Impact of curvature on topological defects
NASA Astrophysics Data System (ADS)
Mesarec, L.; Góźdź, W.; Iglič, A.; Kralj, S.
2017-01-01
We analyze the impact of extrinsic and intrinsic curvature on positions of topological defects (TDs) in two-dimensional (2D) nematic films. We demonstrate that both these curvature contributions are commonly present and are expected to be weighted by comparable elastic constants. A simple Landau-de Gennes approach in terms of tensor nematic order parameter is used to numerically demonstrate impact of the curvatures on position of TDs on 2D ellipsoidal nematic shells. In particular, in oblate ellipsoids the extrinsic and intrinsic elastic terms enforce conflicting tendencies to positions of TDs.
The Gaussian curvature elastic energy of intermediates in membrane fusion.
Siegel, David P
2008-12-01
The Gaussian curvature elastic energy contribution to the energy of membrane fusion intermediates has usually been neglected because the Gaussian curvature elastic modulus, kappa, was unknown. It is now possible to measure kappa for phospholipids that form bicontinuous inverted cubic (Q(II)) phases. Here, it is shown that one can estimate kappa for lipids that do not form Q(II) phases by studying the phase behavior of lipid mixtures. The method is used to estimate kappa for several lipid compositions in excess water. The values of kappa are used to compute the curvature elastic energies of stalks and catenoidal fusion pores according to recent models. The Gaussian curvature elastic contribution is positive and similar in magnitude to the bending energy contribution: it increases the total curvature energy of all the fusion intermediates by 100 units of k(B)T or more. It is important to note that this contribution makes the predicted intermediate energies compatible with observed lipid phase behavior in excess water. An order-of-magnitude fusion rate equation is used to estimate whether the predicted stalk energies are consistent with the observed rates of stalk-mediated processes in pure lipid systems. The current theory predicts a stalk energy that is slightly too large, by approximately 30 k(B)T, to rationalize the observed rates of stalk-mediated processes in phosphatidylethanolamine or N-monomethylated dioleoylphosphatidylethanolamine systems. Despite this discrepancy, the results show that models of fusion intermediate energy are accurate enough to make semiquantitative predictions about how proteins mediate biomembrane fusion. The same rate model shows that for proteins to drive biomembrane fusion at observed rates, they have to perform mediating functions corresponding to a reduction in the energy of a purely lipidic stalk by several tens of k(B)T. By binding particular peptide sequences to the monolayer surface, proteins could lower fusion intermediate
Anisotropic Membrane Curvature Sensing by Amphipathic Peptides
Gómez-Llobregat, Jordi; Elías-Wolff, Federico; Lindén, Martin
2016-01-01
Many proteins and peptides have an intrinsic capacity to sense and induce membrane curvature, and play crucial roles for organizing and remodeling cell membranes. However, the molecular driving forces behind these processes are not well understood. Here, we describe an approach to study curvature sensing by simulating the interactions of single molecules with a buckled lipid bilayer. We analyze three amphipathic antimicrobial peptides, a class of membrane-associated molecules that specifically target and destabilize bacterial membranes, and find qualitatively different sensing characteristics that would be difficult to resolve with other methods. Our findings provide evidence for direction-dependent curvature sensing mechanisms in amphipathic peptides and challenge existing theories of hydrophobic insertion. The buckling approach is generally applicable to a wide range of curvature-sensing molecules, and our results provide strong motivation to develop new experimental methods to track position and orientation of membrane proteins. PMID:26745422
Helical Microfilaments with Alternating Imprinted Intrinsic Curvatures.
Silva, Pedro Emanuel Santos; Godinho, Maria Helena
2017-03-01
There has been an intense research for developing techniques that can produce filaments with helical shapes, given the widespread of potential applications. In this work, how helices with different curvatures can be precisely imprinted in microfilaments is shown. It is also shown that using this technique, it is possible to produce, in a single fiber, helices with different curvatures. This striking and innovative behavior is observed when one side of the stretched filaments is irradiated with UV light, modifying the mechanical properties at surface. Upon release, the regions with higher curvature start to curl first, while regions with lower intrinsic curvature remain stretched until start to curl later. The results presented here can be important to understand why structures adopt a helical shape in general, which can be of interest in nanotechnology, biomolecular science, or even to understand why plant filaments curl.
Role of feature curvature in contact guidance
Mathur, Anurag; Moore, Simon W.; Sheetz, Michael P.; Hone, James
2012-01-01
This study examines the role of feature curvature in cellular topography sensing. To separate the effects of feature size and curvature, we have developed a method to fabricate grooved substrates whose radius of curvature (r) is varied from under 10 nm to 400 nm, while all other dimensions are kept constant. With increasing r up to 200 nm, mouse embryonic fibroblasts increased their spread area, but reduced their polarization (aspect ratio). Interestingly, on features with an r of 200 and 400 nm - where there was very little effect on spreading area and polarization - we find that internal structures such as stress fibers are nevertheless still strongly aligned to the topography. These findings are of importance to studies of both tissue engineering and curvature sensing proteins. PMID:22426288
Curvature Analysis of Cardiac Excitation Wavefronts
2013-04-01
computational cardiac-cell network accurately reproduces a particular kind of cardiac arrhythmia , such as ventricular fibrillation. Curvature Analysis of Cardiac...network accurately reproduces a particular kind of cardiac arrhythmia , such as ventricular fibrillation. Index Terms Cardiac excitation waves...isopotentials, Bézier curves, curvature, cardiac arrhythmia and fibrillation Ç 1 INTRODUCTION AN estimated 81,000,000 American adults, more than onein three
Experimental determination of the radius of curvature of an isotropic Gaussian Schell-model beam.
Zhu, Shijun; Chen, Yahong; Cai, Yangjian
2013-02-01
We propose a method to determine the radius of curvature of an isotropic Gaussian Schell-model (GSM) beam by measuring the transverse beam widths and the transverse coherence widths at two different planes. Furthermore, we carry out experimental determination of the radius of curvature of a GSM beam. Using the measured beam parameters, we carry out a comparative study of the propagation properties of a GSM beam both theoretically and experimentally. Our experimental results agree well with theoretical predictions.
Nonadditive Compositional Curvature Energetics of Lipid Bilayers
NASA Astrophysics Data System (ADS)
Sodt, A. J.; Venable, R. M.; Lyman, E.; Pastor, R. W.
2016-09-01
The unique properties of the individual lipids that compose biological membranes together determine the energetics of the surface. The energetics of the surface, in turn, govern the formation of membrane structures and membrane reshaping processes, and thus they will underlie cellular-scale models of viral fusion, vesicle-dependent transport, and lateral organization relevant to signaling. The spontaneous curvature, to the best of our knowledge, is always assumed to be additive. We describe observations from simulations of unexpected nonadditive compositional curvature energetics of two lipids essential to the plasma membrane: sphingomyelin and cholesterol. A model is developed that connects molecular interactions to curvature stress, and which explains the role of local composition. Cholesterol is shown to lower the number of effective Kuhn segments of saturated acyl chains, reducing lateral pressure below the neutral surface of bending and favoring positive curvature. The effect is not observed for unsaturated (flexible) acyl chains. Likewise, hydrogen bonding between sphingomyelin lipids leads to positive curvature, but only at sufficient concentration, below which the lipid prefers negative curvature.
The role of curvature in entanglement
NASA Astrophysics Data System (ADS)
Buck, Gregory
2015-10-01
Which tangles more readily: curly hair or straight hair? A perhaps natural thought, supported by some theoretical evidence, is to associate curvature and entanglement, and assume that they would grow together-that an increase in one fosters an increase in the other. However we have biological examples such as DNA in the chromosome, and mechanical examples such as coiled telephone cords, in which much more curvature is employed than is required for the packing, and in which tangling is presumably detrimental. We offer a resolution to this conundrum. We show, that at least for simple but generally applicable models, the relationship between curvature and entanglement is subtle: if we keep filament density constant and increase curvature, the entanglement initially increases, passes through a maximum, then decreases, so there is a regime where increasing curvature increases entanglement, and there is also a regime where increasing curvature decreases entanglement. This has implications for filament packing in many circumstances, and in particular for the compaction structure of DNA in the cell-it provides a straightforward argument for the view that one purpose of DNA coiling and supercoiling is to inhibit entanglement. It also tells us to expect that wavy hair-neither the straightest nor the curliest-tangles most readily.
Spherical gravitational curvature boundary-value problem
NASA Astrophysics Data System (ADS)
Šprlák, Michal; Novák, Pavel
2016-08-01
Values of scalar, vector and second-order tensor parameters of the Earth's gravitational field have been collected by various sensors in geodesy and geophysics. Such observables have been widely exploited in different parametrization methods for the gravitational field modelling. Moreover, theoretical aspects of these quantities have extensively been studied and well understood. On the other hand, new sensors for observing gravitational curvatures, i.e., components of the third-order gravitational tensor, are currently under development. As the gravitational curvatures represent new types of observables, their exploitation for modelling of the Earth's gravitational field is a subject of this study. Firstly, the gravitational curvature tensor is decomposed into six parts which are expanded in terms of third-order tensor spherical harmonics. Secondly, gravitational curvature boundary-value problems defined for four combinations of the gravitational curvatures are formulated and solved in spectral and spatial domains. Thirdly, properties of the corresponding sub-integral kernels are investigated. The presented mathematical formulations reveal some important properties of the gravitational curvatures and extend the so-called Meissl scheme, i.e., an important theoretical framework that relates various parameters of the Earth's gravitational field.
NASA Technical Reports Server (NTRS)
Lee, J. S.; Evans, M. L.
1990-01-01
We tested the involvement of ethylene in maize (Zea mays L.) root gravitropism by measuring the kinetics of curvature and lateral auxin movement in roots treated with ethylene, inhibitors of ethylene synthesis, or inhibitors of ethylene action. In the presence of ethylene the latent period of gravitropic curvature appeared to be increased somewhat. However, ethylene-treated roots continued to curve after control roots had reached their final angle of curvature. Consequently, maximum curvature in the presence of ethylene was much greater in ethylene-treated roots than in controls. Inhibitors of ethylene biosynthesis or action had effects on the kinetics of curvature opposite to that of ethylene, i.e. the latent period appeared to be shortened somewhat while total curvature was reduced relative to that of controls. Label from applied 3H-indole-3-acetic acid was preferentially transported toward the lower side of stimulated roots. In parallel with effects on curvature, ethylene treatment delayed the development of gravity-induced asymmetric auxin movement across the root but extended its duration once initiated. The auxin transport inhibitor, 1-N-naphthylphthalamic acid reduced both gravitropic curvature and the effect of ethylene on curvature. Since neither ethylene nor inhibitors of ethylene biosynthesis or action prevented curvature, we conclude that ethylene does not mediate the primary differential growth response causing curvature. Because ethylene affects curvature and auxin transport in parallel, we suggest that ethylene modifies curvature by affecting gravity-induced lateral transport of auxin, perhaps by interfering with adaptation of the auxin transport system to the gravistimulus.
Cosmic acceleration from matter-curvature coupling
NASA Astrophysics Data System (ADS)
Zaregonbadi, Raziyeh; Farhoudi, Mehrdad
2016-10-01
We consider f( {R,T} ) modified theory of gravity in which, in general, the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and the trace of the energy-momentum tensor. We indicate that in this type of the theory, the coupling energy-momentum tensor is not conserved. However, we mainly focus on a particular model that matter is minimally coupled to the geometry in the metric formalism and wherein, its coupling energy-momentum tensor is also conserved. We obtain the corresponding Raychaudhuri dynamical equation that presents the evolution of the kinematic quantities. Then for the chosen model, we derive the behavior of the deceleration parameter, and show that the coupling term can lead to an acceleration phase after the matter dominated phase. On the other hand, the curvature of the universe corresponds with the deviation from parallelism in the geodesic motion. Thus, we also scrutinize the motion of the free test particles on their geodesics, and derive the geodesic deviation equation in this modified theory to study the accelerating universe within the spatially flat FLRW background. Actually, this equation gives the relative accelerations of adjacent particles as a measurable physical quantity, and provides an elegant tool to investigate the timelike and the null structures of spacetime geometries. Then, through the null deviation vector, we find the observer area-distance as a function of the redshift for the chosen model, and compare the results with the corresponding results obtained in the literature.
DSD front models: nonideal explosive detonation in ANFO
Bdzil, J. B.; Aslam, T. D.; Catanach, R. A.; Hill, L. G.; Short, M.
2002-01-01
The DSD method for modeling propagating detonation is based on three elements: (1) a subscale theory of multi-dimensional detonation that treats the detonation as a front whose dynamics depends only on metrics of the front (such as curvature, etc.), (2) high-resolution, direct numerical simulation of detonation using Euler equation models, and (3) physical experiments to characterize multi-dimensional detonation propagation in real explosives and to provide data to calibrate DSD front models. In this paper, we describe our work on elements (1) and (3), develop a DSD calibration for the nonideal explosive ANFO and then demonstrate the utility of the ANFO calibration, with an example 3D detonation propagation calculation.
Effects of Berry Curvature on the Collective Modes of Ultracold Gases
NASA Astrophysics Data System (ADS)
Price, Hannah M.; Cooper, Nigel R.
2013-11-01
Topological energy bands have important geometrical properties described by the Berry curvature. We show that the Berry curvature changes the hydrodynamic equations of motion for a trapped Bose-Einstein condensate, and causes significant modifications to the collective mode frequencies. We illustrate our results for the case of two-dimensional Rashba spin-orbit coupling in a Zeeman field. Using an operator approach, we derive the effects of Berry curvature on the dipole mode in very general settings. We show that the sizes of these effects can be large and readily detected in experiment. Collective modes therefore provide a sensitive way to measure geometrical properties of energy bands.
Shape and curvature error estimation in polished surfaces of ground glass molds
NASA Astrophysics Data System (ADS)
Savio, Gianpaolo; Pal, Raj Kumar; Meneghello, Roberto; D'Angelo, Luciano; Concheri, Gianmaria
2017-02-01
In the fabrication process of aspheric glass lens and molds, shape characterization is a fundamental task to control geometrical errors. Nevertheless, the more significant geometrical functional aspect related to the optical properties is the curvature, which is rarely investigated in the manufacturing process of lenses. Algorithms for the assessment of shape and curvature errors on aspheric surface profile are presented. The method has been investigated on profiles measured before and at different steps of the membrane polishing process. The results show how surface roughness, shape, and curvature change during the polishing process as a function of the machining time.
Strong curvature effects in Neumann wave problems
Willatzen, M.; Pors, A.; Gravesen, J.
2012-08-15
Waveguide phenomena play a major role in basic sciences and engineering. The Helmholtz equation is the governing equation for the electric field in electromagnetic wave propagation and the acoustic pressure in the study of pressure dynamics. The Schroedinger equation simplifies to the Helmholtz equation for a quantum-mechanical particle confined by infinite barriers relevant in semiconductor physics. With this in mind and the interest to tailor waveguides towards a desired spectrum and modal pattern structure in classical structures and nanostructures, it becomes increasingly important to understand the influence of curvature effects in waveguides. In this work, we demonstrate analytically strong curvature effects for the eigenvalue spectrum of the Helmholtz equation with Neumann boundary conditions in cases where the waveguide cross section is a circular sector. It is found that the linear-in-curvature contribution originates from parity symmetry breaking of eigenstates in circular-sector tori and hence vanishes in a torus with a complete circular cross section. The same strong curvature effect is not present in waveguides subject to Dirichlet boundary conditions where curvature contributions contribute to second-order in the curvature only. We demonstrate this finding by considering wave propagation in a circular-sector torus corresponding to Neumann and Dirichlet boundary conditions, respectively. Results for relative eigenfrequency shifts and modes are determined and compared with three-dimensional finite element method results. Good agreement is found between the present analytical method using a combination of differential geometry with perturbation theory and finite element results for a large range of curvature ratios.
Stress-induced curvature engineering in surface-micromachined devices
NASA Astrophysics Data System (ADS)
Aksyuk, Vladimir A.; Pardo, Flavio; Bishop, David J.
1999-03-01
Residual stress and stress gradients play an important role in determining equilibrium shape and behavior of various Si surface-micromachined devices under applied loads. This is particularly true for system having large-area plates and long beams where curvature resulting from stress can lead to significant deviations from stress-free shape. To gain better understanding of these properties, we have measured the equilibrium shapes of various structures built on the MCNC MUMPs using an interferometric profiler. The structures were square plates and long beams composed of various combinations of polysilicon an oxide layers. Some of the structures had additional MUMPs metal layer on top, while on others in-house chromium-gold stacks of varying thickness have been deposited. Temperature dependence of the curvature was measured for some plates. We have used these data in conjunction with simple models to significantly improve the performance of our micromachined devices. While for some structures such as large area reflectors the curvature had to be minimized, it could be advantageously exploited by others, for example vertical actuators for self-assembly.
Lipids, curvature, and nano-medicine*
Mouritsen, Ole G
2011-01-01
The physical properties of the lamellar lipid-bilayer component of biological membranes are controlled by a host of thermodynamic forces leading to overall tensionless bilayers with a conspicuous lateral pressure profile and build-in curvature-stress instabilities that may be released locally or globally in terms of morphological changes. In particular, the average molecular shape and the propensity of the different lipid and protein species for forming non-lamellar and curved structures are a source of structural transitions and control of biological function. The effects of different lipids, sterols, and proteins on membrane structure are discussed and it is shown how one can take advantage of the curvature-stress modulations brought about by specific molecular agents, such as fatty acids, lysolipids, and other amphiphilic solutes, to construct intelligent drug-delivery systems that function by enzymatic triggering via curvature. Practical applications: The simple concept of lipid molecular shape and how it impacts on the structure of lipid aggregates, in particular the curvature and curvature stress in lipid bilayers and liposomes, can be exploited to construct liposome-based drug-delivery systems, e.g., for use as nano-medicine in cancer therapy. Non-lamellar-forming lysolipids and fatty acids, some of which may be designed to be prodrugs, can be created by phospholipase action in diseased tissues thereby providing for targeted drug release and proliferation of molecular entities with conical shape that break down the permeability barrier of the target cells and may hence enhance efficacy. PMID:22164124
ORNL Interim Progress Report on Static CIRFT Testing Curvature Data Update
Wang, Jy-An John; Wang, Hong
2016-10-10
Since the CIRFT tests reported in NUREG-7198 were generated, a number of factors that influence the recorded curvature measurement data were identified. In 2016, a data reanalysis task was undertaken to implement the lessons learned. This letter report provides the revised results of previous CIRFT tests, after implementing the following data reanalysis procedures: (A) experimental data smoothing and LVDT reset, (B) LVDT probe contact and sensor spacing correction for curvature data, and (C) LVDT probe dynamic vibration adjustment procedure development.
Perturbative High Harmonic Wave Front Control
NASA Astrophysics Data System (ADS)
Li, Zhengyan; Brown, Graham; Ko, Dong Hyuk; Kong, Fanqi; Arissian, Ladan; Corkum, P. B.
2017-01-01
We pattern the wave front of a high harmonic beam by intersecting the intense driving laser pulse that generates the high harmonic with a weak control pulse. To illustrate the potential of wave-front control, we imprint a Fresnel zone plate pattern on a harmonic beam, causing the harmonics to focus and defocus. The quality of the focus that we achieve is measured using the spectral wave-front optical reconstruction by diffraction method. We will show that it is possible to enhance the peak intensity by orders of magnitude without a physical optical element in the path of the extreme ultraviolet (XUV) beam. Through perturbative wave-front control, XUV beams can be created with a flexibility approaching what technology allows for visible and infrared light.
Eigenstates of Moebius nanostructures including curvature effects
Gravesen, J.; Willatzen, M.
2005-09-15
Moebius-shell structures and their physical properties have recently received considerable attention experimentally and theoretically. In this work, eigenstates and associated eigenenergies are determined for a quantum-mechanical particle bounded to a Moebius shell including curvature contributions to the kinetic-energy operator. This is done using a parametrization of the Moebius shell-found by minimizing the elastic energy of the full structure-and employing differential-geometry methods. It is shown that inclusion of curvature contributions to the kinetic energy leads to splitting of the otherwise doubly degenerate groundstate and significantly alters the form of the groundstate and excited-state wavefunctions. Hence, we anticipate qualitative changes in the physical properties of Moebius-shell structures due to surface confinement and curvature effects.
HEREDITARY DISTAL FORELEG CURVATURE IN THE RABBIT
Pearce, Louise
1960-01-01
An inwardly directed curvature of the distal segment of both forelegs of the rabbit has been described. The condition was detected at 2 to 3 weeks of age, developed rapidly, and reached its final and permanent stage at 2 to 3 months of age. Only the distal epiphysis of the ulna was primarily affected and this in the form of a massive chondrodystrophic lesion accompanied by a progressive curvature of the shaft. The curvature of the growing radius was a secondary effect due to the firm, immovable, anatomical connection of the ulna and radius. The positional changes of the wrist and paw were likewise effects secondary to the changed form of the ulna and radius. The bowing abnormality occurred only in certain families of pure bred Beveren, Belgian, French Silver, and Dutch rabbits and was found to be inherited. The mode of inheritance was on the basis of a single recessive unit factor (5). PMID:13733755
On the curvature effect of thin membranes
NASA Astrophysics Data System (ADS)
Wang, Duo; Jiao, Xiangmin; Conley, Rebecca; Glimm, James
2013-01-01
We investigate the curvature effect of a thin, curved elastic interface that separates two subdomains and exerts a pressure due to a curvature effect. This pressure, which we refer to as interface pressure, is similar to the surface tension in fluid mechanics. It is important in some applications, such as the canopy of parachutes, biological membranes of cells, balloons, airbags, etc., as it partially balances a pressure jump between the two sides of an interface. In this paper, we show that the interface pressure is equal to the trace of the matrix product of the curvature tensor and the Cauchy stress tensor in the tangent plane. We derive the theory for interfaces in both 2-D and 3-D, and present numerical discretizations for computing the quality over triangulated surfaces.
NASA Astrophysics Data System (ADS)
The Front Range Branch of AGU has installed officers for 1990: Ray Noble, National Center for Atmospheric Research, chair; Sherry Oaks, U.S. Geological Survey, chair-elect; Howard Garcia, NOAA, treasurer; Catharine Skokan, Colorado School of Mines, secretary. JoAnn Joselyn of NOAA is past chair. Members at large are Wallace Campbell, NOAA; William Neff, USGS; and Stephen Schneider, NCAR.
ERIC Educational Resources Information Center
Melnick, Blake
2002-01-01
Shares some of the author's personal experiences from the "front line" to illustrate the potential of computer-supported learning environments. Concludes that technology, if used in conjunction with sound pedagogy, allows students to tep outside the confines of the traditional classroom and school structure and take responsibility for both their…
Instability in bacterial populations and the curvature tensor
NASA Astrophysics Data System (ADS)
Melgarejo, Augusto; Langoni, Laura; Ruscitti, Claudia
2016-09-01
In the geometry associated with equilibrium thermodynamics the scalar curvature Rs is a measure of the volume of correlation, and therefore the singularities of Rs indicates the system instabilities. We explore the use of a similar approach to study instabilities in non-equilibrium systems and we choose as a test example, a colony of bacteria. In this regard we follow the proposal made by Obata et al. of using the curvature tensor for studying system instabilities. Bacterial colonies are often found in nature in concentrated biofilms, or other colony types, which can grow into spectacular patterns visible under the microscope. For instance, it is known that a decrease of bacterial motility with density can promote separation into bulk phases of two coexisting densities; this is opposed to the logistic law for birth and death that allows only a single uniform density to be stable. Although this homogeneous configuration is stable in the absence of bacterial interactions, without logistic growth, a density-dependent swim speed v(ρ) leads to phase separation via a spinodal instability. Thus we relate the singularities in the curvature tensor R to the spinodal instability, that is the appearance of regions of different densities of bacteria.
NASTRAN modifications for recovering strains and curvatures
NASA Technical Reports Server (NTRS)
Hennrich, C. W.
1975-01-01
Modifications to the NASTRAN structural analysis computer program are described. The modifications allow the recovery of strain and curvature data for the general two-dimensional elements, in addition to the usual stress data. Option features allow the transformation of the strain/curvature (or stress) data to a common coordinate system and representation at the grid points of the structural model rather than at the conventional element center locations. Usage information is provided which will allow present users of NASTRAN to easily utilize the new capability.
Equal-Curvature X-Ray Telescopes
NASA Technical Reports Server (NTRS)
Saha, Timo T.; Zhang, William
2002-01-01
We introduce a new type of x-ray telescope design; an Equal-Curvature telescope. We simply add a second order axial sag to the base grazing incidence cone-cone telescope. The radius of curvature of the sag terms is the same on the primary surface and on the secondary surface. The design is optimized so that the on-axis image spot at the focal plane is minimized. The on-axis RMS (root mean square) spot diameter of two studied telescopes is less than 0.2 arc-seconds. The off-axis performance is comparable to equivalent Wolter type 1 telescopes.
Cholesterol Mediates Membrane Curvature during Fusion Events
NASA Astrophysics Data System (ADS)
Ivankin, Andrey; Kuzmenko, Ivan; Gidalevitz, David
2012-06-01
Biomembranes undergo extensive shape changes as they perform vital cellular functions. The mechanisms by which lipids and proteins control membrane curvature remain unclear. We use x-ray reflectivity, grazing incidence x-ray diffraction, and epifluorescence microscopy to study binding of HIV-1 glycoprotein gp41’s membrane-bending domain to DPPC/cholesterol monolayers of various compositions at the air-liquid interface. The results offer a new insight into how membrane curvature could be regulated by cholesterol during fusion of the viral lipid envelope and the host cell membranes.
Ray Curvature and Refraction of Wave Packets.
1978-09-01
1!~~~~~ _ ‘ AD AOM 302 FLORIDA STATE UNIV TALLAHASSEE DEPT OF OCEANOGRAPHY FIG B/3 RAY CURVATURE AND REFRACTION OF WAVE PACKETS. (U) SEP 78 .J E...BREEDING N00014—77—C—0329 UNCLASSIFIED TR JE6 3 NL _ _ _ rwii__ _ ~iU ir!I I -~~ RAYOJR\\1L~[UREAND REFRACI ION OF WAVE F1~\\CKET~S ~y J. Ernest Breeding...01 29 014 -~ Technical Report No. JEB-3 Department of Oceanography • Florida State University RAY CURVATURE AND REFRACTION OF WAVE PACKETS b O G • J
Thermodynamics and mechanics of membrane curvature generation and sensing by proteins and lipids.
Baumgart, Tobias; Capraro, Benjamin R; Zhu, Chen; Das, Sovan L
2011-01-01
Research investigating lipid membrane curvature generation and sensing is a rapidly developing frontier in membrane physical chemistry and biophysics. The fast recent progress is based on the discovery of a plethora of proteins involved in coupling membrane shape to cellular membrane function, the design of new quantitative experimental techniques to study aspects of membrane curvature, and the development of analytical theories and simulation techniques that allow a mechanistic interpretation of quantitative measurements. The present review first provides an overview of important classes of membrane proteins for which function is coupled to membrane curvature. We then survey several mechanisms that are assumed to underlie membrane curvature sensing and generation. Finally, we discuss relatively simple thermodynamic/mechanical models that allow quantitative interpretation of experimental observations.
Infrared glass-based negative-curvature anti-resonant fibers fabricated through extrusion.
Gattass, Rafael R; Rhonehouse, Daniel; Gibson, Daniel; McClain, Collin C; Thapa, Rajesh; Nguyen, Vinh Q; Bayya, Shyam S; Weiblen, R Joseph; Menyuk, Curtis R; Shaw, L Brandon; Sanghera, Jasbinder S
2016-10-31
Negative curvature fibers have been gaining attention as fibers for high power infrared light. Currently, these fibers have been made of silica glass and infrared glasses solely through stack and draw. Infrared glasses' lower softening point presents the opportunity to perform low-temperature processing methods such as direct extrusion of pre-forms. We demonstrate an infrared-glass based negative curvature fiber fabricated through extrusion. The fiber shows record low losses in 9.75 - 10.5 µm range (which overlaps with the CO_{2} emission bands). We show the fiber's lowest order mode and measure the numerical aperture in the longwave infrared transmission band. The possibility to directly extrude a negative curvature fiber with no penalties in losses is a strong motivation to think beyond the limitations of stack-and-draw to novel shapes for negative curvature fibers.
3. VIEW NORTH, SOUTHWEST FRONT, SOUTHEAST SIDE Front and side ...
3. VIEW NORTH, SOUTHWEST FRONT, SOUTHEAST SIDE Front and side elevation. Note gasoline sign post added. Flush store window not altered, 1900 clapboard siding and panelling remaining. - 510 Central Avenue (Commercial Building), Ridgely, Caroline County, MD
9. DETAIL OF INTERIOR OF FRONT PORCH SHOWING FRONT ENTRY ...
9. DETAIL OF INTERIOR OF FRONT PORCH SHOWING FRONT ENTRY (LEFT) AND BLANK WALL (CENTER) CORRESPONDING TO LOCATION OF INTERIOR VAULTS. VIEW TO SOUTHEAST. - Boise Project, Boise Project Office, 214 Broadway, Boise, Ada County, ID
35. EAST FRONT OF POWERHOUSE AND CAR BARN: East front ...
35. EAST FRONT OF POWERHOUSE AND CAR BARN: East front of powerhouse and car barn. 'Annex' is right end of building. - San Francisco Cable Railway, Washington & Mason Streets, San Francisco, San Francisco County, CA
Mehta, Rujul; Keawwattana, Wirunya; Guenthner, Andrew L; Kyu, Thein
2004-06-01
The present article focuses on theoretical elucidation of possible effect of mechanical deformation on spatio-temporal emergence of unusual polymer morphology subjected to quiescent isothermal crystallization conditions. The present theory developed is based on a phase field model consisted of non-conserved time dependent Ginzburg-Landau equation having an asymmetric double well potential in the crystal order parameter signifying metastability for crystallization, coupled with the chain tilt angle involving curvature elasticity and strain recovery potentials. Under quiescent crystallization conditions, the curvature elasticity term is needed to discern the emergence of sectorized single crystals. Upon coupling with the strain recovery potential, the numerical calculation captures ripple formation running across the long lamellar growth front, which may be attributed to lamellar buckling caused by the volume shrinkage. Of particular interest is that these simulated topologies of the single crystals are in good accord with the growth character of syndiotactic polypropylene single crystals observed experimentally by us during isothermal crystallization from the melt.
Riemann curvature of a boosted spacetime geometry
NASA Astrophysics Data System (ADS)
Battista, Emmanuele; Esposito, Giampiero; Scudellaro, Paolo; Tramontano, Francesco
2016-10-01
The ultrarelativistic boosting procedure had been applied in the literature to map the metric of Schwarzschild-de Sitter spacetime into a metric describing de Sitter spacetime plus a shock-wave singularity located on a null hypersurface. This paper evaluates the Riemann curvature tensor of the boosted Schwarzschild-de Sitter metric by means of numerical calculations, which make it possible to reach the ultrarelativistic regime gradually by letting the boost velocity approach the speed of light. Thus, for the first time in the literature, the singular limit of curvature, through Dirac’s δ distribution and its derivatives, is numerically evaluated for this class of spacetimes. Moreover, the analysis of the Kretschmann invariant and the geodesic equation shows that the spacetime possesses a “scalar curvature singularity” within a 3-sphere and it is possible to define what we here call “boosted horizon”, a sort of elastic wall where all particles are surprisingly pushed away, as numerical analysis demonstrates. This seems to suggest that such “boosted geometries” are ruled by a sort of “antigravity effect” since all geodesics seem to refuse to enter the “boosted horizon” and are “reflected” by it, even though their initial conditions are aimed at driving the particles toward the “boosted horizon” itself. Eventually, the equivalence with the coordinate shift method is invoked in order to demonstrate that all δ2 terms appearing in the Riemann curvature tensor give vanishing contribution in distributional sense.
NASA Astrophysics Data System (ADS)
Marchetto, M.; Baartman, R. A.; Laxdal, R. E.
2014-01-01
The ARIEL project at TRIUMF will greatly expand the variety and availability of radioactive ion beams (RIBs) (Laxdal, Nucl Inst Methods Phys Res B 204:400-409, 2003). The ARIEL front end connects the two ARIEL target stations to the existing ISAC facility to expand delivery to two and eventually three simultaneous RIB beams with up to two simultaneous accelerated beams (Laxdal et al. 2008). The low-energy beam transport lines and mass separators are designed for maximum flexibility to allow a variety of operational modes in order to optimize the radioactive ion beam delivery. A new accelerator path is conceived for high mass delivery from an EBIS charge state breeder. The front-end design utilizes the experience gained in 15 years of ISAC beam delivery.
CURVATURE EFFECT QUANTIFICATION FOR IN-VIVO IR THERMOGRAPHY
Cheng, Tze-Yuan; Deng, Daxiang; Herman, Cila
2013-01-01
Medical Infrared (IR) Imaging has become an important diagnostic tool over recent years. However, one underlying problem in medical diagnostics is associated with accurate quantification of body surface temperatures. This problem is caused by the artifacts induced by the curvature of objects, which leads to inaccurate temperature mapping and biased diagnostic results. Therefore, in our study, an experiment-based analysis is conducted to address the curvature effects toward the 3D temperature reconstruction of the IR thermography image. For quantification purposes, an isothermal copper plate with flat surface, and a cylindrical metal container filled with water are imaged. For the flat surface, the tilting angle measured from camera axis was varied incrementally from 0° to 60 °, such that the effects of surface viewing angle and travel distance on the measured temperature can be explored. On the cylindrical curved surface, the points viewed from 0° to 90° with respect to the camera axis are simultaneously imaged at different temperature levels. The experimental data obtained for the flat surface indicate that both viewing angle and distance effects become noticeable for angles over 40 °. The travel distance contributes a minor change when compared with viewing angle. The experimental results from the curved surface indicate that the curvature effect becomes pronounced when the viewing angle is larger than 60 °. The measurement error on the curved surface is compared with the simulation using the non-dielectric model, and the normalized temperature difference relative to 0° viewing angle was analyzed at six temperature levels. These results indicate that the linear formula associated with directional emissivity is a reasonable approximation for the measurement error, and the normalized error curves change consistently with viewing angle at various temperatures. Therefore, the analysis in this study implies that the directional emissivity based on the non
NASA Astrophysics Data System (ADS)
Keller, Brad M.; Reeves, Anthony P.; Barr, R. Graham; Yankelevitz, David F.; Henschke, Claudia I.
2010-03-01
CT scans allow for the quantitative evaluation of the anatomical bases of emphysema. Recently, a non-density based geometric measurement of lung diagphragm curvature has been proposed as a method for the quantification of emphysema from CT. This work analyzes variability of diaphragm curvature and evaluates the effectiveness of a compensation methodology for the reduction of this variability as compared to emphysema index. Using a dataset of 43 scan-pairs with less than a 100 day time-interval between scans, we find that the diaphragm curvature had a trend towards lower overall variability over emphysema index (95% CI:-9.7 to + 14.7 vs. -15.8 to +12.0), and that the variation of both measures was reduced after compensation. We conclude that the variation of the new measure can be considered comparable to the established measure and the compensation can reduce the apparent variation of quantitative measures successfully.
Seismological Constraints on Fault Plane Curvature
NASA Astrophysics Data System (ADS)
Reynolds, K.
2015-12-01
The down-dip geometry of seismically active normal faults is not well known. Many examples of normal faults with down-dip curvature exist, such as listric faults revealed in cross-section or in seismic reflection data, or the exposed domes of core complexes. However, it is not understood: (1) whether curved faults fail in earthquakes, and (2) if those faults have generated earthquakes, is the curvature a primary feature of the rupture or due to later modification of the plane? Even if an event is surface-rupturing, because of the limited depth-extent over which observations can be made, it is difficult to reliably constrain the change in dip with depth (if any) and therefore the fault curvature. Despite the uncertainty in seismogenic normal fault geometries, published slip inversions most commonly use planar fault models. We investigate the seismological constraints on normal fault geometry using a forward-modelling approach and present a seismological technique for determining down-dip geometry. We demonstrate that complexity in the shape of teleseismic body waveforms may be used to investigate the presence of down-dip fault plane curvature. We have applied this method to a catalogue of continental and oceanic normal faulting events. Synthetic models demonstrate that the shapes of SH waveforms at along-strike stations are particularly sensitive to fault plane geometry. It is therefore important to consider the azimuthal station coverage before modelling an event. We find that none of the data require significant down-dip curvature, although the modelling results for some events remain ambiguous. In some cases we can constrain that the down-dip fault geometry is within 20° of planar.
NASA Astrophysics Data System (ADS)
Weissmann, Haim; Shnerb, Nadav M.; Kessler, David A.
2016-01-01
The properties of a front between two different phases in the presence of a smoothly inhomogeneous external field that takes its critical value at the crossing point is analyzed. Two generic scenarios are studied. In the first, the system admits a bistable solution and the external field governs the rate in which one phase invades the other. The second mechanism corresponds to a continuous transition that, in the case of reactive systems, takes the form of a transcritical bifurcation at the crossing point. We solve for the front shape and for the response of competitive fronts to external noise, showing that static properties and also some of the dynamical features cannot discriminate between the two scenarios. A reliable indicator turns out to be the fluctuation statistics. These take a Gaussian form in the bifurcation case and a double-peaked shape in a bistable system. Our results are discussed in the context of biological processes, such as species and communities dynamics in the presence of a resource gradient.
Radiative thermal conduction fronts
NASA Astrophysics Data System (ADS)
Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.
1990-07-01
The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence.
NASA Astrophysics Data System (ADS)
Spence, William
The second regional conference of the Front Range Branch, AGU, was attended by more than 80 professionals and some 20 outstanding high school students. The conference included 2 days of interdisciplinary talks, and lots of discussion, that primarily were keyed to geophysical studies of Colorado, Wyoming, and New Mexico. Other talks reported on nonregional, and sometimes global, studies being done by geophypsicists of the Front Range region.Topics included tectonics of the Front Range and the Colorado Plateau, pollution of the Arkansas and Mississippi rivers, and a supreme polluting event that caused the late-Cretaceous extinctions. Other notable talks were on toxic cleanup, microburst (wind shear) detection at U.S. airports, and other meteorological studies. Several talks treated the audience to the excitement of new work and surprise discoveries. The meeting was multimedia, including the playing of two videos through a projection TV and the playing of a fascinating tape between an airport control tower and incoming pilots during a severe microburst event.
Radiative thermal conduction fronts
NASA Technical Reports Server (NTRS)
Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.
1990-01-01
The discovery of the O VI interstellar absorption lines in our Galaxy by the Copernicus observatory was a turning point in our understanding of the Interstellar Medium (ISM). It implied the presence of widespread hot (approx. 10 to the 6th power K) gas in disk galaxies. The detection of highly ionized species in quasi-stellar objects' absorption spectra may be the first indirect observation of this hot phase in external disk galaxies. Previous efforts to understand extensive O VI absorption line data from our Galaxy were not very successful in locating the regions where this absorption originates. The location at interfaces between evaporating ISM clouds and hot gas was favored, but recent studies of steady-state conduction fronts in spherical clouds by Ballet, Arnaud, and Rothenflug (1986) and Bohringer and Hartquist (1987) rejected evaporative fronts as the absorption sites. Researchers report here on time-dependent nonequilibrium calculations of planar conductive fronts whose properties match well with observations, and suggest reasons for the difference between the researchers' results and the above. They included magnetic fields in additional models, not reported here, and the conclusions are not affected by their presence.
How to calculate normal curvatures of sampled geological surfaces
NASA Astrophysics Data System (ADS)
Bergbauer, Stephan; Pollard, David D.
2003-02-01
Curvature has been used both to describe geological surfaces and to predict the distribution of deformation in folded or domed strata. Several methods have been proposed in the geoscience literature to approximate the curvature of surfaces; however we advocate a technique for the exact calculation of normal curvature for single-valued gridded surfaces. This technique, based on the First and Second Fundamental Forms of differential geometry, allows for the analytical calculation of the magnitudes and directions of principal curvatures, as well as Gaussian and mean curvature. This approach is an improvement over previous methods to calculate surface curvatures because it avoids common mathematical approximations, which introduce significant errors when calculated over sloped horizons. Moreover, the technique is easily implemented numerically as it calculates curvatures directly from gridded surface data (e.g. seismic or GPS data) without prior surface triangulation. In geological curvature analyses, problems arise because of the sampled nature of geological horizons, which introduces a dependence of calculated curvatures on the sample grid. This dependence makes curvature analysis without prior data manipulation problematic. To ensure a meaningful curvature analysis, surface data should be filtered to extract only those surface wavelengths that scale with the feature under investigation. A curvature analysis of the top-Pennsylvanian horizon at Goose Egg dome, Wyoming shows that sampled surfaces can be smoothed using a moving average low-pass filter to extract curvature information associated with the true morphology of the structure.
THERMAL FRONTS IN SOLAR FLARES
Karlický, Marian
2015-12-01
We studied the formation of a thermal front during the expansion of hot plasma into colder plasma. We used a three-dimensional electromagnetic particle-in-cell model that includes inductive effects. In early phases, in the area of the expanding hot plasma, we found several thermal fronts, which are defined as a sudden decrease of the local electron kinetic energy. The fronts formed a cascade. Thermal fronts with higher temperature contrast were located near plasma density depressions, generated during the hot plasma expansion. The formation of the main thermal front was associated with the return-current process induced by hot electron expansion and electrons backscattered at the front. A part of the hot plasma was trapped by the thermal front while another part, mainly with the most energetic electrons, escaped and generated Langmuir and electromagnetic waves in front of the thermal front, as shown by the dispersion diagrams. Considering all of these processes and those described in the literature, we show that anomalous electric resistivity is produced at the location of the thermal front. Thus, the thermal front can contribute to energy dissipation in the current-carrying loops of solar flares. We estimated the values of such anomalous resistivity in the solar atmosphere together with collisional resistivity and electric fields. We propose that the slowly drifting reverse drift bursts, observed at the beginning of some solar flares, could be signatures of the thermal front.
Hydrogen peroxide treatment results in reduced curvature values in the Arabidopsis root apex.
Noriega, Arturo; Tocino, Angel; Cervantes, Emilio
2009-03-15
Curvature of a plane curve is a measurement related to its shape. A Mathematica code was developed [Cervantes E, Tocino A. J Plant Physiol 2005;162:1038-1045] to obtain parametric equations from microscopic images of the Arabidopsis thaliana root apex. In addition, curvature values for these curves were given. It was shown that ethylene-insensitive mutants (etr1-1 and ein2-1) have reduced curvature values in the root apex. It has also been shown that blocking ethylene action by norbornadiene, an ethylene inhibitor, results in reduced curvature values in the two outer cell layers of the root apex [Noriega A, Cervantes E, Tocino A. J Plant Physiol 2008, in press]. Because ethylene action has been related with hydrogen peroxide [Desikan R, Hancock JT, Bright J, Harrison J, Weir I, Hooley R, Neill SJ. Plant Physiol 2005;137:831-834], the effect of a treatment with hydrogen peroxide in the curvature values of three successive layers of the root apex in Arabidopsis thaliana was investigated by confocal microscopy. Treatment with 10mM hydrogen peroxide resulted in reduced curvature values in the three layers. The effect was associated with smaller cells having higher circularity indices. The results are discussed in the context of the role of ethylene in development.
Micron-scale plasma membrane curvature is recognized by the septin cytoskeleton
Bridges, Andrew A.; Jentzsch, Maximilian S.; Oakes, Patrick W.; Occhipinti, Patricia
2016-01-01
Cells change shape in response to diverse environmental and developmental conditions, creating topologies with micron-scale features. Although individual proteins can sense nanometer-scale membrane curvature, it is unclear if a cell could also use nanometer-scale components to sense micron-scale contours, such as the cytokinetic furrow and base of neuronal branches. Septins are filament-forming proteins that serve as signaling platforms and are frequently associated with areas of the plasma membrane where there is micron-scale curvature, including the cytokinetic furrow and the base of cell protrusions. We report here that fungal and human septins are able to distinguish between different degrees of micron-scale curvature in cells. By preparing supported lipid bilayers on beads of different curvature, we reconstitute and measure the intrinsic septin curvature preference. We conclude that micron-scale curvature recognition is a fundamental property of the septin cytoskeleton that provides the cell with a mechanism to know its local shape. PMID:27044896
Stress compensation for arbitrary curvature control in vanadium dioxide phase transition actuators
NASA Astrophysics Data System (ADS)
Dong, Kaichen; Lou, Shuai; Choe, Hwan Sung; Liu, Kai; You, Zheng; Yao, Jie; Wu, Junqiao
2016-07-01
Due to its thermally driven structural phase transition, vanadium dioxide (VO2) has emerged as a promising material for micro/nano-actuators with superior volumetric work density, actuation amplitude, and repetition frequency. However, the high initial curvature of VO2 actuators severely obstructs the actuation performance and application. Here, we introduce a "seesaw" method of fabricating tri-layer cantilevers to compensate for the residual stress and realize nearly arbitrary curvature control of VO2 actuators. By simply adjusting the thicknesses of the individual layers, cantilevers with positive, zero, or negative curvatures can be engineered. The actuation amplitude can be decoupled from the curvature and controlled independently as well. Based on the experimentally measured residual stresses, we demonstrate sub-micron thick VO2 actuators with nearly zero final curvature and a high actuation amplitude simultaneously. This "seesaw" method can be further extended to the curvature engineering of other microelectromechanical system multi-layer structures where large stress-mismatch between layers are inevitable.
Investigation of catheter curvature and genetic algorithms in conductance catheter optimization.
Thaijiam, C; Gale, T J
2007-01-01
Catheter curvature affects accuracy of intra-ventricular blood volume measurement when using conductance catheter techniques, especially with irregular geometries, such as in the right ventricle. To investigate this effect, we present results from using different curved catheter configurations and different numbers of electrodes in a simple Finite Element model. It was found that there is an apparent increase in accuracy with curvature, due to greater linearity in the field in the region of the measurement electrodes, which are located farther from the source electrodes as curvature increases. Also, optimization using Genetic Algorithms is presented as a method to find the optimal distribution of measurement electrodes. We plan to extend these results to develop improved electrode configurations for using in blood volume measurement in the right ventricle.
Fronts under arrest: Nonlocal boundary dynamics in biology
NASA Astrophysics Data System (ADS)
McCalla, Scott G.; von Brecht, James H.
2016-12-01
We introduce a minimal geometric partial differential equation framework to understand pattern formation from interacting, counterpropagating fronts. Our approach concentrates on the interfaces between different states in a system, and relies on both nonlocal interactions and mean-curvature flow to track their evolution. As an illustration, we use this approach to describe a phenomenon in bacterial colony formation wherein sibling colonies can arrest each other's growth. This arrested motion leads to static separations between healthy, growing colonies. As our minimal model faithfully recovers the geometry of these competing colonies, it captures and elucidates the key leading-order mechanisms responsible for such patterned growth.
Fronts under arrest: Nonlocal boundary dynamics in biology.
McCalla, Scott G; von Brecht, James H
2016-12-01
We introduce a minimal geometric partial differential equation framework to understand pattern formation from interacting, counterpropagating fronts. Our approach concentrates on the interfaces between different states in a system, and relies on both nonlocal interactions and mean-curvature flow to track their evolution. As an illustration, we use this approach to describe a phenomenon in bacterial colony formation wherein sibling colonies can arrest each other's growth. This arrested motion leads to static separations between healthy, growing colonies. As our minimal model faithfully recovers the geometry of these competing colonies, it captures and elucidates the key leading-order mechanisms responsible for such patterned growth.
Inequalities for scalar curvature of pseudo-Riemannian submanifolds
NASA Astrophysics Data System (ADS)
Tripathi, Mukut Mani; Gülbahar, Mehmet; Kılıç, Erol; Keleş, Sadık
2017-02-01
Some basic inequalities, involving the scalar curvature and the mean curvature, for a pseudo-Riemannian submanifold of a pseudo-Riemannian manifold are obtained. We also find inequalities for spacelike submanifolds. Equality cases are also discussed.
Crustal thickening drives arc front migration
NASA Astrophysics Data System (ADS)
Karlstrom, L.; Lee, C.; Manga, M.
2012-12-01
The position of active volcanism relative to the trench in arcs depends on melt focusing processes within the mantle wedge and the geometric parameters of subduction. Arc front migration has been observed in relic (Sierra Nevada, Andes) as well as active (Cascades) arcs, sometimes with cycles of retreat and return of the front towards the trench over millions of years. Other arcs, particularly where backarc extension dominates, exhibit a more stationary front in time relative to the trench. In addition, crustal indices of magmatism as measured by the ratio of trace elements La/Yb or isotopes 87}Sr/{86Sr covary with arc front migration (e.g., Haschke et al., 2002). Arc front migration is commonly attributed to variation in dip angle of the downgoing slab, delamination of overthickened crust, or to subduction erosion. Here we present an alternative hypothesis. Assuming mantle wedge melting is a largely temperature-dependant process, the maximum isotherm in the wedge sets arc front location. Isotherm location depends on slab angle, subduction velocity and wedge thermal diffusivity (England and Katz, 2010). It also depends on crustal thickness, which evolves as melt is transferred from the wedge to the crust. Arc front migration can thus occur purely through magmatic thickening of crust. Thickening proceeds through intrusive as well as extrusive volcanism, modulated by tectonics and surface erosion. Migration rate is set by the mantle melt flux into the crust, which decreases as thickening occurs. Thus slab angle need not change, and in the absence of other contribution processes front location and crustal thickness have long-time steady state values. We develop an analytic model of this process that produces migration rates consistent with published data and explains arc fronts that do not move (dominated by extension, such as in the case of intra-oceanic arcs). We present new geochemical and age data from the Peninsular Ranges Batholith that are also consistent with
[Instabilities of autowaves in excitable media associated with critical curvature phenomena].
Pertsov, A M; Panfilov, A V; Medvedeva, F U
1983-01-01
While studying a two-dimensional excitable medium described by the Fitz--Hugh equation on a digital computer a new type of instabilities was discovered which had no analogy in one-dimensional systems. It has been shown that when the wave encounters upon an obstacle the front breaks, diverge, thus destroying the excitation waves. Initiation of such instabilities is associated with critical curvative phenomenon. The instabilities appear when the front curvature in the region of wave break is greater than the critical one for the given medium. The instabilities found are observed when medium excitability is suppressed. This phenomenon may be related to the processes which occur in the damage regions of the myocardium tissue.
Glimm, J.; Grove, J.W.; Li, X.; Zhao, N.
1999-04-01
A new and simplified front tracking algorithm has been developed as an aspect of the extension of this algorithm to three dimensions. Here the authors emphasize two main results: (1) a simplified description of the microtopology of the interface, based on interface crossings with cell block edges, and (2) an improved algorithm for the interaction of a tracked contact discontinuity with an untracked shock wave. For the latter question, they focus on the post interaction jump at the contact, which is a purely 1D issue. Comparisons to other methods, including the level set method, are included.
Streamline curvature in supersonic shear layers
NASA Technical Reports Server (NTRS)
Kibens, V.
1992-01-01
Results of an experimental investigation in which a curved shear layer was generated between supersonic flow from a rectangular converging/diverging nozzle and the freestream in a series of open channels with varying radii of curvature are reported. The shear layers exhibit unsteady large-scale activity at supersonic pressure ratios, indicating increased mixing efficiency. This effect contrasts with supersonic flow in a straight channel, for which no large-scale vortical structure development occurs. Curvature must exceed a minimum level before it begins to affect the dynamics of the supersonic shear layer appreciably. The curved channel flows are compared with reference flows consisting of a free jet, a straight channel, and wall jets without sidewalls on a flat and a curved plate.
Cosmological signatures of anisotropic spatial curvature
Pereira, Thiago S.; Marugán, Guillermo A. Mena; Carneiro, Saulo E-mail: mena@iem.cfmac.csic.es
2015-07-01
If one is willing to give up the cherished hypothesis of spatial isotropy, many interesting cosmological models can be developed beyond the simple anisotropically expanding scenarios. One interesting possibility is presented by shear-free models in which the anisotropy emerges at the level of the curvature of the homogeneous spatial sections, whereas the expansion is dictated by a single scale factor. We show that such models represent viable alternatives to describe the large-scale structure of the inflationary universe, leading to a kinematically equivalent Sachs-Wolfe effect. Through the definition of a complete set of spatial eigenfunctions we compute the two-point correlation function of scalar perturbations in these models. In addition, we show how such scenarios would modify the spectrum of the CMB assuming that the observations take place in a small patch of a universe with anisotropic curvature.
Constraining inverse-curvature gravity with supernovae.
Mena, Olga; Santiago, José; Weller, Jochen
2006-02-03
We show that models of generalized modified gravity, with inverse powers of the curvature, can explain the current accelerated expansion of the Universe without resorting to dark energy and without conflicting with solar system experiments. We have solved the Friedmann equations for the full dynamical range of the evolution of the Universe and performed a detailed analysis of supernovae data in the context of such models that results in an excellent fit. If we further include constraints on the current expansion of the Universe and on its age, we obtain that the matter content of the Universe is 0.07
Breeding curvature from extended gauge covariance
NASA Astrophysics Data System (ADS)
Aldrovandi, R.
1991-05-01
Independence between spacetime and “internal” space in gauge theories is related to the adjoint-covariant behaviour of the gauge potential. The usual gauge scheme is modified to allow a coupling between both spaces. Gauging spacetime translations produce field equations similar to Einstein equations. A curvature-like quantity of mixed differential-algebraic character emerges. Enlarged conservation laws are present, pointing to the presence of an covariance.
Brodsky, Stanley J.; de Teramond, Guy F.; /SLAC /Southern Denmark U., CP3-Origins /Costa Rica U.
2011-01-10
AdS/QCD, the correspondence between theories in a dilaton-modified five-dimensional anti-de Sitter space and confining field theories in physical space-time, provides a remarkable semiclassical model for hadron physics. Light-front holography allows hadronic amplitudes in the AdS fifth dimension to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The result is a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time and determines the off-shell dynamics of the bound state wavefunctions as a function of the invariant mass of the constituents. The hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. Higher Fock states with extra quark-anti quark pairs also arise. The soft-wall model also predicts the form of the nonperturbative effective coupling and its {beta}-function. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method to systematically include QCD interaction terms. Some novel features of QCD are discussed, including the consequences of confinement for quark and gluon condensates. A method for computing the hadronization of quark and gluon jets at the amplitude level is outlined.
Superintegrable systems on spaces of constant curvature
Gonera, Cezary Kaszubska, Magdalena
2014-07-15
Construction and classification of two-dimensional (2D) superintegrable systems (i.e. systems admitting, in addition to two global integrals of motion guaranteeing the Liouville integrability, the third global and independent one) defined on 2D spaces of constant curvature and separable in the so-called geodesic polar coordinates are presented. The method proposed is applicable to any value of curvature including the case of Euclidean plane, sphere and hyperbolic plane. The main result is a generalization of Bertrand’s theorem on 2D spaces of constant curvature and covers most of the known separable and superintegrable models on such spaces (in particular, the so-called Tremblay–Turbiner–Winternitz (TTW) and Post–Winternitz (PW) models which have recently attracted some interest). -- Highlights: •Classifying 2D superintegrable, separable (polar coordinates) systems on S{sup 2}, R{sup 2}, H{sup 2}. •Construction of radial, angular potentials leading to superintegrability. •Generalization of Bertrand’s theorem covering known models, e.g. Higgs, TTW, PW, and Coulomb.
Stiffness Modulation of Rayed Fins by Curvature
NASA Astrophysics Data System (ADS)
Nguyen, Khoi; Yu, Ning; Venkadesan, Madhusudhan; Bandi, Mahesh; Mandre, Shreyas
2016-11-01
Fishes with rayed fins comprise over 99% of all extant fish species. Multifunctional use of fins, from propulsion to station holding, requires substantial modulation of stiffness. We propose that fishes stiffen the fin by curving it transverse to its length. This effect is similar to stiffening a dollar bill by curling it because of curvature-induced coupling of out-of-plane bending with in-plane stretching. Unlike a piece of paper, rayed fins are a composite of rays and membranes. We model this as parallel elastic beams (rays) with springy interconnections (membranes). Our analysis shows that the key parameters stiffening the fin are the ray anisotropy to bending, the misalignment of principal bending directions of adjacent rays, and the membrane elasticity. The composite fin stiffens when the principal bending directions of adjacent rays are misaligned due to fin curvature, which necessarily causes the membrane to stretch. Unlike a homogenous thin sheet, composite rayed structures are able to mimic curvature-induced stiffening by using misaligned rays even if the fin appears geometrically flat. Preliminary radiographic evidence from the rays of fish fins supports such a mechanism. Funding by Human Frontier Science Program.
Multiple Manifold Clustering Using Curvature Constrained Path
Babaeian, Amir; Bayestehtashk, Alireza; Bandarabadi, Mojtaba
2015-01-01
The problem of multiple surface clustering is a challenging task, particularly when the surfaces intersect. Available methods such as Isomap fail to capture the true shape of the surface near by the intersection and result in incorrect clustering. The Isomap algorithm uses shortest path between points. The main draw back of the shortest path algorithm is due to the lack of curvature constrained where causes to have a path between points on different surfaces. In this paper we tackle this problem by imposing a curvature constraint to the shortest path algorithm used in Isomap. The algorithm chooses several landmark nodes at random and then checks whether there is a curvature constrained path between each landmark node and every other node in the neighborhood graph. We build a binary feature vector for each point where each entry represents the connectivity of that point to a particular landmark. Then the binary feature vectors could be used as a input of conventional clustering algorithm such as hierarchical clustering. We apply our method to simulated and some real datasets and show, it performs comparably to the best methods such as K-manifold and spectral multi-manifold clustering. PMID:26375819
Desertification by front propagation?
Zelnik, Yuval R; Uecker, Hannes; Feudel, Ulrike; Meron, Ehud
2017-04-07
Understanding how desertification takes place in different ecosystems is an important step in attempting to forecast and prevent such transitions. Dryland ecosystems often exhibit patchy vegetation, which has been shown to be an important factor on the possible regime shifts that occur in arid regions in several model studies. In particular, both gradual shifts that occur by front propagation, and abrupt shifts where patches of vegetation vanish at once, are a possibility in dryland ecosystems due to their emergent spatial heterogeneity. However, recent theoretical work has suggested that the final step of desertification - the transition from spotted vegetation to bare soil - occurs only as an abrupt shift, but the generality of this result, and its underlying origin, remain unclear. We investigate two models that detail the dynamics of dryland vegetation using a markedly different functional structure, and find that in both models the final step of desertification can only be abrupt. Using a careful numerical analysis, we show that this behavior is associated with the disappearance of confined spot-pattern domains as stationary states, and identify the mathematical origin of this behavior. Our findings show that a gradual desertification to bare soil due to a front propagation process can not occur in these and similar models, and opens the question of whether these dynamics can take place in nature.
Pennington, D; Jovanovic, I; Comaskey, B J
2001-02-01
The next generation of Petawatt class lasers will require the development of new laser technology. Optical parametric chirped pulse amplification (OPCPA) holds a potential to increase the peak power level to >10 PW with existing grating technology through ultrashort pulses. Furthermore, by utilizing a new type of front-end system based on optical parametric amplification, pulses can be produced with substantially higher contrast than with Ti:sapphire regenerative amplifier technology. We performed extensive study of OPCPA using a single crystal-based OPA. We developed a replacement for Ti:sapphire regenerative amplifier for high peak power lasers based on OPCPA, with an output of 30 mJ, at 10 Hz repetition rate and 16.5 nm spectral bandwidth. We developed a 3D numerical model for OPCPA and we performed a theoretical study of influences of pump laser beam quality on optical parametric amplification. Our results indicate that OPCPA represents a valid replacement for Ti:sapphire in the front end of high energy short pulse lasers.
Price, Stephen
2009-01-01
The causes of recent dynamic thinning of Greenland's outlet glaciers have been debated. Realistic simulations suggest that changes at the marine fronts of these glaciers are to blame, implying that dynamic thinning will cease once the glaciers retreat to higher ground. For the last decade, many outlet glaciers in Greenland that terminate in the ocean have accelerated, thinned, and retreated. To explain these dynamic changes, two hypotheses have been discussed. Atmospheric warming has increased surface melting and may also have increased the amount of meltwater reaching the glacier bed, increasing lubrication at the base and hence the rate of glacier sliding. Alternatively, a change in the delicate balance of forces where the glacier fronts meet the ocean could trigger the changes. Faezeh Nick and colleagues5 present ice-sheet modeling experiments that mimic the observations on Helheim glacier, East Greenland, and suggest that the dynamic behaviour of outlet glaciers follows from perturbations at their marine fronts. Greenland's ice sheet loses mass partly through surface melting and partly through fast flowing outlet glaciers that connect the vast plateau of inland ice with the ocean. Earlier ice sheet models have failed to reproduce the dynamic variability exhibited by ice sheets over time. It has therefore not been possible to distinguish with confidence between basal lubrication from surface meltwater and changes at the glaciers' marine fronts as causes for the observed changes on Greenland's outlet glaciers. But this distinction bears directly on future sea-level rise, the raison d'etre of much of modern-day glaciology: If the recent dynamic mass loss Greenland's outlet glaciers is linked to changing atmospheric temperatures, it may continue for as long as temperatures continue to increase. On the other hand, if the source of the dynamic mass loss is a perturbation at the ice-ocean boundary, these glaciers will lose contact with that perturbation after a finite
Speed of fast and slow rupture fronts along frictional interfaces
NASA Astrophysics Data System (ADS)
Trømborg, Jørgen Kjoshagen; Sveinsson, Henrik Andersen; Thøgersen, Kjetil; Scheibert, Julien; Malthe-Sørenssen, Anders
2015-07-01
The transition from stick to slip at a dry frictional interface occurs through the breaking of microjunctions between the two contacting surfaces. Typically, interactions between junctions through the bulk lead to rupture fronts propagating from weak and/or highly stressed regions, whose junctions break first. Experiments find rupture fronts ranging from quasistatic fronts, via fronts much slower than elastic wave speeds, to fronts faster than the shear wave speed. The mechanisms behind and selection between these fronts are still imperfectly understood. Here we perform simulations in an elastic two-dimensional spring-block model where the frictional interaction between each interfacial block and the substrate arises from a set of junctions modeled explicitly. We find that material slip speed and rupture front speed are proportional across the full range of front speeds we observe. We revisit a mechanism for slow slip in the model and demonstrate that fast slip and fast fronts have a different, inertial origin. We highlight the long transients in front speed even along homogeneous interfaces, and we study how both the local shear to normal stress ratio and the local strength are involved in the selection of front type and front speed. Last, we introduce an experimentally accessible integrated measure of block slip history, the Gini coefficient, and demonstrate that in the model it is a good predictor of the history-dependent local static friction coefficient of the interface. These results will contribute both to building a physically based classification of the various types of fronts and to identifying the important mechanisms involved in the selection of their propagation speed.
Free-streaming radiation in cosmological models with spatial curvature
NASA Technical Reports Server (NTRS)
Wilson, M. L.
1982-01-01
The effects of spatial curvature on radiation anisotropy are examined for the standard Friedmann-Robertson-Walker model universes. The effect of curvature is found to be very important when considering fluctuations with wavelengths comparable to the horizon. It is concluded that the behavior of radiation fluctuations in models with spatial curvature is quite different from that in spatially flat models, and that models with negative curvature are most strikingly different. It is therefore necessary to take the curvature into account in careful studies of the anisotropy of the microwave background.
Determination of biplane geometry and centerline curvature in vascular imaging
NASA Astrophysics Data System (ADS)
Nazareth, Daryl; Hoffmann, Kenneth R.; Walczak, Alan; Dmochowski, Jacek; Guterman, Lee R.; Rudin, Stephen; Bednarek, Daniel R.
2002-05-01
Three-dimensional (3-D) vessel trees can provide useful visual and quantitative information during interventional procedures. To calculate the 3-D vasculature from biplane images, the transformation relating the imaging systems (i.e., the rotation matrix R and the translation vector t) must be determined. We have developed a technique to calculate these parameters, which requires only the identification of approximately corresponding vessel regions in the two images. Initial estimates of R and t are generated based on the gantry angles, and then refined using an optimization technique. The objective function to be minimized is determined as follows. For each endpoint of each vessel in the first image, an epipolar line in the second image is generated. The intersection points between these two epipolar lines and the corresponding vessel centerline in the second image are determined. The vessel arclength between these intersection points is calculated as a fraction of the entire vessel region length in the image. This procedure is repeated for every vessel in each image. The value of the objective function is calculated from the sum of these fractions, and is smallest when the total fractional arclength is greatest. The 3-D vasculature is obtained from the optimal R and t using triangulation, and vessel curvature is then determined. This technique was evaluated using simulated curves and vessel centerlines obtained from clinical images, and provided rotational, magnification and relative curvature errors of 1 degree(s), 1% and 14% respectively. Accurate 3-D and curvature measures may be useful in clinical decision making, such as in assessing vessel tortuousity and access, during interventional procedures.
Bragg gratings in surface-core fibers: Refractive index and directional curvature sensing
NASA Astrophysics Data System (ADS)
Osório, Jonas H.; Oliveira, Ricardo; Aristilde, Stenio; Chesini, Giancarlo; Franco, Marcos A. R.; Nogueira, Rogério N.; Cordeiro, Cristiano M. B.
2017-03-01
In this paper, we report, to our knowledge, the first extended study of the inscription of Bragg gratings in surface-core fibers and their application in refractive index and directional curvature sensing. The research ranges from fiber fabrication and grating inscription in untapered and tapered fibers to the performance of simulations and sensing measurements. Maximum sensitivities of 40 nm/RIU and 202.7 pm/m-1 were attained in refractive index and curvature measurements respectively. The obtained results compares well to other fiber Bragg grating based devices. Ease of fabrication, robustness and versatility makes surface-core fibers an interesting platform when exploring fiber sensing devices.
Optimal Spatial Scale for Curvature Calculations in Multiphase Flows
NASA Astrophysics Data System (ADS)
Senecal, Jacob; Owkes, Mark
2016-11-01
In gas-liquid flows, the surface tension force often controls the dynamics of the flow and an accurate calculation of this force is necessary for predictive simulations. The surface tension force is directly proportional to the curvature of the gas-liquid interface, making accurate curvature calculations an essential consideration. Multiple methods have been developed to calculate the curvature of volume of fluid (VoF) interface capturing schemes, such as the height function method. These methods have been extensively tested. However, the impact of the scale or size of computational stencil on which the curvature is computed, has not been correlated with the rate at which interface perturbations relax under the surface tension force. In this work, the effect of varying the scale on which the curvature is computed has been tested and quantified. An optimal curvature scale is identified that leads to accurate and converging curvatures, and accurate timescales for surface tension induced, interface dynamics.
Curvature inducing macroion condensation driven shape changes of fluid vesicles.
Sreeja, K K; Ipsen, John H; Sunil Kumar, P B
2015-11-21
We study the effect of curvature inducing macroion condensation on the shapes of charged deformable fluid interfaces using dynamically triangulated Monte Carlo simulations. In the weak electrostatic coupling regime, surface charges are weakly screened and the conformations of a vesicle, with fixed spherical topology, depend on the charge-charge interaction on the surface. While in the strong coupling regime, condensation driven curvature induction plays a dominant role in determining the conformations of these surfaces. Condensation itself is observed to be dependent on the induced curvature, with larger induced curvatures favoring increased condensation. We show that both curvature generation and curvature sensing, induced by the interplay of electrostatics and curvature energy, contribute to determination of the vesicle configurations.
NASA Astrophysics Data System (ADS)
Karimi, Davood; Ward, Rabab K.
2016-03-01
Reducing the radiation dose in computed tomography (CT) requires reducing the number or the energy of the photons that pass through the patient's body. An image reconstructed from such noisy or undersampled measurements will contain much noise and artifacts that can significantly reduce the diagnostic value of the image. Effective sinogram denoising or interpolation can reduce these noise and artifacts. In this paper, we present a novel approach to sinogram smoothing and interpolation. The proposed method iteratively estimates the local slope and curvature of the sinogam and forces the sinogram to follow the estimated slope and curvature. This is performed by projection onto the set of constraints that define the slope and the curvature. The constraints on the slope and curvature correspond to very simple convex sets. Projection onto these sets have simple analytical solutions. Moreover, these operations are highly parallelizable because the equations defining the slope and curvature constraints for all the points in a sinogram can be summarized as five convex sets, regardless of the length of the sinogram. We apply the proposed method on simulated and real data and examine its effect on the quality of the reconstructed image. Our results show that the proposed method is highly effective and can lead to a substantial improvement in the quality of the images reconstructed from noisy sinogram measurements. A comparison with the K-SVD denoising algorithm shows that the proposed algorithm achieves better results. We suggest that the proposed method can be a useful tool for low-dose CT.
Front tracking for characterizing and quantifying reactive mixing
NASA Astrophysics Data System (ADS)
Kelley, Douglas; Nevins, Thomas
2016-11-01
Mixing in industrial chemical reactors involves complicated interactions between advection, reaction, and diffusion that are difficult to simulate or measure in detail. However, in large-Damköhler-number systems which show sharp fronts between reacted and unreacted regions, reactor dynamics might be more simply and usefully characterized in terms of the reaction fronts themselves. In fact, prior work has already shown that the reaction rate and material diffusivity can be calculated directly if front speed and front thickness are known. We have developed methods to optically track reaction fronts, measuring their speed and thickness throughout space and time. We will present such measurements in both simulation and experiment, consider their statistics, and discuss future efforts to characterize and quantify mixing in chemical reactors.
Jones, L.
1995-01-01
Like the patients, doctors in Sarajevo depend largely on humanitarian aid; everyone in the public sector has worked without pay for almost three years. The hospital is on a front line; yet the psychiatric department continues to function, even conducting large scale studies of psychosocial aspects of war in Bosnia-Hercegovina. The type of inpatient morbidity and treatment patterns have changed. A plethora of psychosocial rehabilitation programmes has emerged, including counselling, drop in centres, and attending to special needs of elderly people, schoolchildren, and women. The most prominent psychological symptoms were exhaustion at the prospect of a third winter of war and bewilderment at the Western stereotype of Bosnians as Muslim fundamentalists. Images p1052-a p1053-a PMID:7728062
Experimental study of curvature-driven flute instability in the gas-dynamic trap
Ivanov, A.A.; Anikeev, A.V.; Bagryansky, P.A.; Bocharov, V.N.; Deichuli, P.P.; Karpushov, A.N.; Maximov, V.V.; Pod'minogin, A.A.; Rogozin, A.I.; Salikova, T.V.; Tsidulko, Y.A. )
1994-05-01
A curvature-driven flute instability will be excited in the magnetized plasmas if the magnetic field lines curve toward the entire plasma boundary. Conditions under which it can be effectively stabilized in axisymmetric geometry have been experimentally studied in a gas-dynamic trap (GDT) at Novosibirsk. Flexible design of the experimental device and the availability of neutral beams and ion cyclotron heating enabled the pressure-weighted curvature to be varied over a wide range. The stability limits were thus measured and compared with those predicted by the modified Rosenbluth--Longmire criterion. Characteristics of unstable curvature-driven flute modes were also measured and found to conform to a theory including finite ion Larmor radius (FLR) effects. Stable operation during neutral beam injection was achieved with a cusp end cell, resulting in an increase in [ital T][sub [ital e
Damage Identification Dependence on Number of Vibration Modes Using Mode Shape Curvature Squares
NASA Astrophysics Data System (ADS)
Janeliukstis, R.; Rucevskis, S.; Wesolowski, M.; Chate, A.
2016-09-01
In this paper a damage identification algorithm for multiple damage sites based on mode shape curvature square method of vibration mode shapes in aluminium beam is reported. The required mode shape curvature of a healthy structure was obtained via interpolation of mode shape curvature of a damaged structure with Fourier series functions of different orders. Algorithm employed calculations of standardized damage index distributions over beam coordinate. Finite element simulations of proposed methodology involving various artificial noise levels and reduction of mode shape input data points were validated on the damage identification results of experimentally measured mode shapes which were measured using scanning laser vibrometer. Results show that the algorithm is capable of capturing the areas of damage. The term called damage estimate reliability was introduced in terms of likelihood of the chosen approximation function to capture the location of damage.
NASA Astrophysics Data System (ADS)
Liu, Jin; Tourdot, Richard; Ramanan, Vyas; Agrawal, Neeraj J.; Radhakrishanan, Ravi
2012-06-01
The membrane-surface migration of curvature-inducing proteins in response to membrane curvature gradients has been investigated using Monte Carlo simulations of a curvilinear membrane model based on the Helfrich Hamiltonian. Consistent with theoretical and experimental data, we find the proteins that generate curvature can also sense the background membrane curvature, wherein they preferentially partition to the high curvature regions. The partitioning strength depends linearly on local membrane curvature and the slope (or the coupling constant) of the partitioning probability versus mean curvature depends on the membrane bending rigidity and instantaneous curvature field caused by different proteins. Our simulation study allows us to quantitatively characterize and identify the important factors affecting the coupling constant (slope), which may be difficult to determine in experiments. Furthermore, the membrane model is used to study budding of vesicles where it is found that in order to stabilize a mature vesicle with a stable 'neck-region' (or stable membrane overhangs), the area (extent) of the intrinsic curvature region needs to exceed a threshold-critical value. The migration and partitioning of curvature-inducing proteins in a budding vesicle with a stable neck (with a characteristic negative value of the Gaussian curvature) is investigated.
Comparison between a propane-air combustion front and a helium-air simulated combustion front
Barraclough, S.
1983-12-01
Turbulent combustion experiments were performed in a right cylindrical combustion bomb using a premixed propane-air gaseous fuel. The initial conditions inside the combustion chamber were three psig and room temperature. Prior to spark firing, the turbulence intensity inside the combustion chamber was measured and could be varied over a ten fold range. The effect of initial turbulence intensity on turbulent flame propagation was investigated. Two regimes of turbulent combustion were identified, which is in agreement with a previous investigator's results. One of them, a ''transition regime'' occurs when the turbulence intensity is approximately twice the laminar flame speed. Within the transition regime, the turbulent burning speed is linearly proportional to initial turbulence intensity and independent of laminar flame speed and turbulence length scale. A high pressure helium front was injected into the combustion chamber to simulate the combustion front. Since the helium front is isothermal, hot-wire anemometry can be used to quantify the change in turbulence intensity ahead of the propagating front. The helium front was found to have different characteristics than the combustion front.
FACILITY 1042. FRONT OBLIQUE SHOWING ROYAL PALMS LINING FRONT WALK. ...
FACILITY 1042. FRONT OBLIQUE SHOWING ROYAL PALMS LINING FRONT WALK. VIEW FACING SOUTHEAST - U.S. Naval Base, Pearl Harbor, Naval Housing Area Hale Alii, Junior Officers' Quarters Type, 9-10 Hale Alii Avenue, 1-2 Eighth Street, Pearl City, Honolulu County, HI
Steering electromagnetic beams with conical curvature singularities.
Zhang, Yong-Liang; Dong, Xian-Zi; Zheng, Mei-Ling; Zhao, Zhen-Sheng; Duan, Xuan-Ming
2015-10-15
We describe how the transformation-optics technique can be used to design an effective medium mimicking the conical curvature singularity. Anholonomic coordinate transformation gives rise to linear topological defects that break the rotational symmetry. The bending and splitting of the optical beams are found analytically and numerically, depending on the incident direction and the topological charge. Beyond their practical applications to omnidirectional beam steering for photonics, our findings set forth an attractive realm to simulate the relevant physical phenomena in the optical laboratory.
Spacetime Curvature and Higgs Stability after Inflation.
Herranen, M; Markkanen, T; Nurmi, S; Rajantie, A
2015-12-11
We investigate the dynamics of the Higgs field at the end of inflation in the minimal scenario consisting of an inflaton field coupled to the standard model only through the nonminimal gravitational coupling ξ of the Higgs field. Such a coupling is required by renormalization of the standard model in curved space, and in the current scenario also by vacuum stability during high-scale inflation. We find that for ξ≳1, rapidly changing spacetime curvature at the end of inflation leads to significant production of Higgs particles, potentially triggering a transition to a negative-energy Planck scale vacuum state and causing an immediate collapse of the Universe.
Solitons in curved space of constant curvature
Batz, Sascha; Peschel, Ulf
2010-05-15
We consider spatial solitons as, for example, self-confined optical beams in spaces of constant curvature, which are a natural generalization of flat space. Due to the symmetries of these spaces we are able to define respective dynamical parameters, for example, velocity and position. For positively curved space we find stable multiple-hump solitons as a continuation from the linear modes. In the case of negatively curved space we show that no localized solution exists and a bright soliton will always decay through a nonlinear tunneling process.
Double curvature mirrors for linear concentrators
NASA Astrophysics Data System (ADS)
Lance, Tamir; Ackler, Harold; Finot, Marc
2012-10-01
Skyline Solar's medium concentration photovoltaic system uses quasi-parabolic mirrors and one axis tracking. Improvements in levelized cost of energy can be achieved by effective management of non-uniformity of the flux line on the panels. To reduce non uniformity of the flux line due to mirror to mirror gaps, Skyline developed a dual curvature mirror that stretches the flux line along the panel. Extensive modeling and experiments have been conducted to analyze the impact of this new design and to optimize the design.
Lipid membrane-mediated attraction between curvature inducing objects
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J.
2016-01-01
The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (−3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles. PMID:27618764
Lipid membrane-mediated attraction between curvature inducing objects
NASA Astrophysics Data System (ADS)
van der Wel, Casper; Vahid, Afshin; Šarić, Anđela; Idema, Timon; Heinrich, Doris; Kraft, Daniela J.
2016-09-01
The interplay of membrane proteins is vital for many biological processes, such as cellular transport, cell division, and signal transduction between nerve cells. Theoretical considerations have led to the idea that the membrane itself mediates protein self-organization in these processes through minimization of membrane curvature energy. Here, we present a combined experimental and numerical study in which we quantify these interactions directly for the first time. In our experimental model system we control the deformation of a lipid membrane by adhering colloidal particles. Using confocal microscopy, we establish that these membrane deformations cause an attractive interaction force leading to reversible binding. The attraction extends over 2.5 times the particle diameter and has a strength of three times the thermal energy (‑3.3 kBT). Coarse-grained Monte-Carlo simulations of the system are in excellent agreement with the experimental results and prove that the measured interaction is independent of length scale. Our combined experimental and numerical results reveal membrane curvature as a common physical origin for interactions between any membrane-deforming objects, from nanometre-sized proteins to micrometre-sized particles.
Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U.
2012-02-16
QCD Hamiltonian 'Light-Front Holography'. Light-Front Holography is in fact one of the most remarkable features of the AdS/CFT correspondence. The Hamiltonian equation of motion in the light-front (LF) is frame independent and has a structure similar to eigenmode equations in AdS space. This makes a direct connection of QCD with AdS/CFT methods possible. Remarkably, the AdS equations correspond to the kinetic energy terms of the partons inside a hadron, whereas the interaction terms build confinement and correspond to the truncation of AdS space in an effective dual gravity approximation. One can also study the gauge/gravity duality starting from the bound-state structure of hadrons in QCD quantized in the light-front. The LF Lorentz-invariant Hamiltonian equation for the relativistic bound-state system is P{sub {mu}}P{sup {mu}}|{psi}(P)> = (P{sup +}P{sup -} - P{sub {perpendicular}}{sup 2})|{psi}(P)> = M{sup 2}|{psi}(P)>, P{sup {+-}} = P{sup 0} {+-} P{sup 3}, where the LF time evolution operator P{sup -} is determined canonically from the QCD Lagrangian. To a first semiclassical approximation, where quantum loops and quark masses are not included, this leads to a LF Hamiltonian equation which describes the bound-state dynamics of light hadrons in terms of an invariant impact variable {zeta} which measures the separation of the partons within the hadron at equal light-front time {tau} = x{sup 0} + x{sup 3}. This allows us to identify the holographic variable z in AdS space with an impact variable {zeta}. The resulting Lorentz-invariant Schroedinger equation for general spin incorporates color confinement and is systematically improvable. Light-front holographic methods were originally introduced by matching the electromagnetic current matrix elements in AdS space with the corresponding expression using LF theory in physical space time. It was also shown that one obtains identical holographic mapping using the matrix elements of the energy-momentum tensor by perturbing
Topological implications of negative curvature for biological and social networks
NASA Astrophysics Data System (ADS)
Albert, Réka; DasGupta, Bhaskar; Mobasheri, Nasim
2014-03-01
Network measures that reflect the most salient properties of complex large-scale networks are in high demand in the network research community. In this paper we adapt a combinatorial measure of negative curvature (also called hyperbolicity) to parametrized finite networks, and show that a variety of biological and social networks are hyperbolic. This hyperbolicity property has strong implications on the higher-order connectivity and other topological properties of these networks. Specifically, we derive and prove bounds on the distance among shortest or approximately shortest paths in hyperbolic networks. We describe two implications of these bounds to crosstalk in biological networks, and to the existence of central, influential neighborhoods in both biological and social networks.
Curvature detection by entanglement generation using a beam splitter
NASA Astrophysics Data System (ADS)
Mahdifar, Ali; Dehdashti, Shahram; Roknizadeh, Rasoul; Chen, Hongsheng
2015-08-01
In this paper, we investigate the behavior of radiation field, whose state is described by the so-called sphere coherent state, through a beam splitter. These states are realization of coherent states of two-dimensional harmonic oscillator, which lives on a sphere, as radiation field. By using the linear entropy as a measure of entanglement, we show that the entanglement depends on the curvature of the sphere. So, by using the appropriating sphere coherent states, we can control the entanglement of the output states of the beam splitter in the laboratory. In addition, as the convince measures of non-classical behaviors, we consider Mandel parameters of the output states of the beam splitter and their quadrature squeezing.
A SANS study of the interfacial curvatures and the phase behavior in bicontinuous microemulsions
NASA Astrophysics Data System (ADS)
Choi, Sung-Min
A microemulsion is a three-component system in which oil and water are solubilized via an interfacial surfactant monolayer. Depending on the composition and various external conditions, it exhibits a wide variety of phases with corresponding mesoscopic scale interfacial structures. For scientific as well as industrial purposes, knowledge of the relation between the interfacial structure and the phase behavior is crucial but its quantitative measure is lacking. To identify the relation in a quantitative way, the natural parameters to be measured are the interfacial curvatures: Gaussian, mean, and square mean curvatures. A new small-angle neutron scattering (SANS) data analysis method to extract the interfacial curvatures was developed and applied to various microemulsions. The method involves the use of a clipped random wave model with an inverse 8th order polynomial spectral function. The spectral density function contains three basic length scales: the inter- domain distance, the coherence length, and the surface roughness parameter. These three length scales are essential to describe mesoscopic scale interfaces. A series of SANS experiments were performed at various phase points of isometric and non-isometric microemulsions. Using the developed model, the three interfacial curvatures at each phase point were determined for the first time in a practical way. In isometric bicontinuous microemulsions, the Gaussian curvature is negative and has a parabolic dependence on the surfactant volume fraction. In non-isometric systems, based on the measured interfacial curvatures, a characteristic structural transformation was identified. As the water and oil volume ratio moves away from unity, the bicontinuous structure transforms to a spherical structure through an intermediate cylindrical structure. (Copies available exclusively from MIT Libraries, Rm. 14- 0551, Cambridge, MA 02139-4307. Ph. 617-253-5668; Fax 617-253-1690.)
Using Single-Scattering Albedo Spectral Curvature to Characterize East Asian Aerosol Mixtures
NASA Technical Reports Server (NTRS)
Li, Jing; Carlson, Barbara E.; Lacis, Andrew A.
2015-01-01
Spectral dependence of aerosol single-scattering albedo (SSA) has been used to infer aerosol composition. In particular, aerosol mixtures dominated by dust absorption will have monotonically increasing SSA with wavelength while that dominated by black carbon absorption has monotonically decreasing SSA spectra. However, by analyzing SSA measured at four wavelengths, 440, 675, 870, and 1020 nm from the Aerosol Robotic Network data set, we find that the SSA spectra over East Asia are frequently peaked at 675 nm. In these cases, we suggest that SSA spectral curvature, defined as the negative of the second derivative of SSA as a function of wavelength, can provide additional information on the composition of these aerosol mixtures. Aerosol SSA spectral curvatures for East Asia during fall and winter are considerably larger than those found in places primarily dominated by biomass burning or dust aerosols. SSA curvature is found to increase as the SSA magnitude decreases. The curvature increases with coarse mode fraction (CMF) to a CMF value of about 0.4, then slightly decreases or remains constant at larger CMF. Mie calculations further verify that the strongest SSA curvature occurs at approx. 40% dust fraction, with 10% scattering aerosol fraction. The nonmonotonic SSA spectral dependence is likely associated with enhanced absorption in the shortwave by dust, absorption by black carbon at longer wavelengths, and also the flattened absorption optical depth spectral dependence due to the increased particle size.
2007-09-01
TH T d TT ρ κγλ −⎟ ⎠ ⎞ ⎜ ⎝ ⎛−= 3 (5) The last term on the right accounts for the Gibbs- Thomson effect . The γsl is the solid-liquid interfacial...fusion per unit mass. The Gibbs- Thomson effect reduces the magnitude of the curvature of the solidification front (i.e. it tends to flatten the...affects the temperature at which the solidification front solidifies through the Gibbs- Thomson effect , viz.: mm sl sl mi Td T H TT 3 ⎟ ⎠ ⎞ ⎜ ⎝ ⎛−−= λ
Surface properties of ocean fronts
NASA Technical Reports Server (NTRS)
Wolff, P. M.; Hubert, W. E.
1976-01-01
Background information on oceanic fronts is presented and the results of several models which were developed to study the dynamics of oceanic fronts and their effects on various surface properties are described. The details of the four numerical models used in these studies are given in separate appendices which contain all of the physical equations, program documentation and running instructions for the models.
You, Jae Eung; Lee, Hye Young; Kim, Kyoung
2015-06-01
[Purpose] Degree of curvature on the spine is known to affect respiratory function and back muscle activation. We compared pulmonary function and back muscle strength according to the degree of curvature of the spine of healthy adults. [Subjects and Methods] Twenty-three healthy volunteers were enrolled. They were divided into two groups according to the degree of curvature of the spine: the below 2° group, and the above 2° group. The degree of curvature was assessed using the Adams forward bending test and a scoliometer. A pulmonary function test (PFT) was conducted, and back muscle strength was measured. [Results] No significant differences in PFT were found between the below 2° group and the above 2° group, in terms of forced vital capacity (FVC), forced expiratory volume in one second (FEV1), ratio of forced expiratory volume in one second to forced vital capacity (FEV1/FVC), or peak expiratory flow (PEF). However, back muscle strength in the below 2 group was significantly higher than that of the above 2 group. [Conclusion] Our findings indicate that the degree of curvature of the spine is associated with back muscle strength in subjects who have spinal curvature within the normal range. Therefore, evaluation and treatment of back muscle strength might be helpful for preventing the progress of curvature of the spine in adolescents with potential scoliosis.
Effects of streamline curvature on separation prediction
NASA Astrophysics Data System (ADS)
Arolla, Sunil K.; Durbin, Paul A.
2009-11-01
In this study, the effects of streamline curvature on prediction of flow separation are investigated. The geometry is a circulation control airfoil, a high-lift configuration that has been under extensive research for more than two decades. A tangential jet is blown over a thick, rounded trailing edge, using the Coanda effect to delay separation. An attempt is made to understand, through numerical simulations, the dynamics of turbulent separation and reattachment on the Coanda surface. Highly curved, attached recirculation regions are seen to form. A physics based curvature correction proposed by Pettersson-Reif et al. (1999) is used in conjunction with ζ-f turbulence model. The chord-based Reynolds number is Re = 10^6. Two jet momentum coefficients of Cμ=0.03 and 0.1 are computed. In this paper, comparisons between the computed and experimental pressure distributions, velocity profiles and the position of flow detachment are presented. Comparisons with other closures such as Menter's SST model are also discussed.
ODE/PDE analysis of corneal curvature.
Płociniczak, Lukasz; Griffiths, Graham W; Schiesser, William E
2014-10-01
The starting point for this paper is a nonlinear, two-point boundary value ordinary differential equation (BVODE) that defines corneal curvature according to a static force balance. A numerical solution to the BVODE is computed by first converting the BVODE to a parabolic partial differential equation (PDE) by adding an initial value (t, pseudo-time) derivative to the BVODE. A numerical solution to the PDE is then computed by the method of lines (MOL) with the calculation proceeding to a sufficiently large value of t such that the derivative in t reduces to essentially zero. The PDE solution at this point is also the solution for the BVODE. This procedure is implemented in R (an open source scientific programming system) and the programming is discussed in some detail. A series approximation to the solution is derived from which an estimate for the rate of convergence is obtained. This is compared to a fitted exponential model. Also, two linear approximations are derived, one of which leads to a closed form solution. Both provide solutions very close to that obtained from the full nonlinear model. An estimate for the cornea radius of curvature is also derived. The paper concludes with a discussion of the features of the solution to the ODE/PDE system.
Vortex motion on surfaces of small curvature
Dorigoni, Daniele Dunajski, Maciej Manton, Nicholas S.
2013-12-15
We consider a single Abelian Higgs vortex on a surface Σ whose Gaussian curvature K is small relative to the size of the vortex, and analyse vortex motion by using geodesics on the moduli space of static solutions. The moduli space is Σ with a modified metric, and we propose that this metric has a universal expansion, in terms of K and its derivatives, around the initial metric on Σ. Using an integral expression for the Kähler potential on the moduli space, we calculate the leading coefficients of this expansion numerically, and find some evidence for their universality. The expansion agrees to first order with the metric resulting from the Ricci flow starting from the initial metric on Σ, but differs at higher order. We compare the vortex motion with the motion of a point particle along geodesics of Σ. Relative to a particle geodesic, the vortex experiences an additional force, which to leading order is proportional to the gradient of K. This force is analogous to the self-force on bodies of finite size that occurs in gravitational motion. -- Highlights: •We study an Abelian Higgs vortex on a surface with small curvature. •A universal expansion for the moduli space metric is proposed. •We numerically check the universality at low orders. •Vortex motion differs from point particle motion because a vortex has a finite size. •Moduli space geometry has similarities with the geometry arising from Ricci flow.
Particles and curvatures in nematic liquid crystals
NASA Astrophysics Data System (ADS)
Serra, Francesca; Luo, Yimin; Yang, Shu; Kamien, Randall D.; Stebe, Kathleen J.
Elastic interactions in anisotropic fluids can be harnessed to direct particle interactions. A strategy to smoothly manipulate the director field in nematic liquid crystals is to vary the topography of the bounding surfaces. A rugged landscape with peaks and valleys create local deformations of the director field which can interact with particles in solution. We study this complex interaction in two different settings. The first consists of an array of shallow pores in a poly-dimethyl-siloxane (PDMS) membrane, whose curvature can be tuned either by swelling the PDMS membrane or by mechanical stretching. The second is a set of grooves with wavy walls, fabricated by photolithography, with various parameters of curvature and shapes. In this contexts we study how the motion of colloidal particles in nematic liquid crystals can be influenced by their interaction with the peaks and valleys of the bottom substrate or of the side walls. Particles with different associated topological defects (hedgehogs or Saturn rings) behave differently as they interact with the topographical features, favoring the docking on peaks or valleys. These experimental systems are also ideal to study the ``lock and key'' mechanism of particles in holes and to investigate a possible route for particle sorting.
Emergent gravity in spaces of constant curvature
NASA Astrophysics Data System (ADS)
Alvarez, Orlando; Haddad, Matthew
2017-03-01
In physical theories where the energy (action) is localized near a submanifold of a constant curvature space, there is a universal expression for the energy (or the action). We derive a multipole expansion for the energy that has a finite number of terms, and depends on intrinsic geometric invariants of the submanifold and extrinsic invariants of the embedding of the submanifold. This is the second of a pair of articles in which we try to develop a theory of emergent gravity arising from the embedding of a submanifold into an ambient space equipped with a quantum field theory. Our theoretical method requires a generalization of a formula due to by Hermann Weyl. While the first paper discussed the framework in Euclidean (Minkowski) space, here we discuss how this framework generalizes to spaces of constant sectional curvature. We focus primarily on anti de Sitter space. We then discuss how such a theory can give rise to a cosmological constant and Planck mass that are within reasonable bounds of the experimental values.
Efficient CT Metal Artifact Reduction Based on Fractional-Order Curvature Diffusion
Zhang, Yi; Pu, Yi-Fei; Hu, Jin-Rong; Liu, Yan; Chen, Qing-Li; Zhou, Ji-Liu
2011-01-01
We propose a novel metal artifact reduction method based on a fractional-order curvature driven diffusion model for X-ray computed tomography. Our method treats projection data with metal regions as a damaged image and uses the fractional-order curvature-driven diffusion model to recover the lost information caused by the metal region. The numerical scheme for our method is also analyzed. We use the peak signal-to-noise ratio as a reference measure. The simulation results demonstrate that our method achieves better performance than existing projection interpolation methods, including linear interpolation and total variation. PMID:21941593
Snowplow Injection Front Effects
NASA Technical Reports Server (NTRS)
Moore, T. E.; Chandler, M. O.; Buzulukova, N.; Collinson, G. A.; Kepko, E. L.; Garcia-Sage, K. S.; Henderson, M. G.; Sitnov, M. I.
2013-01-01
As the Polar spacecraft apogee precessed through the magnetic equator in 2001, Polar encountered numerous substorm events in the region between geosynchronous orbit and 10 RE geocentric distance; most of them in the plasma sheet boundary layers. Of these, a small number was recorded near the neutral sheet in the evening sector. Polar/Thermal Ion Dynamics Experiment provides a unique perspective on the lowest-energy ion plasma, showing that these events exhibited a damped wavelike character, initiated by a burst of radially outward flow transverse to the local magnetic field at approximately 80 km/s. They then exhibit strongly damped cycles of inward/outward flow with a period of several minutes. After one or two cycles, they culminated in a hot plasma electron and ion injection, quite similar to those observed at geosynchronous orbit. Cold plasmaspheric plasmas comprise the outward flow cycles, while the inward flow cycles contain counterstreaming field-parallel polar wind-like flows. The observed wavelike structure, preceding the arrival of an earthward moving substorm injection front, suggests an outward displacement driven by the inward motion at local times closer to midnight, that is, a "snowplow" effect. The damped in/out flows are consistent with interchange oscillations driven by the arrival at the observed local time by an injection originating at greater radius and local time.
Kinetics for Phototropic Curvature by Etiolated Seedlings of Arabidopsis thaliana 1
Orbović, Vladimir; Poff, Kenneth L.
1991-01-01
An infrared-imaging system has been used to study the influence of gravity on the kinetics of first positive phototropism. The development of phototropic curvature of etiolated seedlings of Arabidopsis thaliana was measured in the absence of visible radiation. Following a pulse of blue light, stationary seedlings curved to a maximum of approximately 16° about 80 minutes after stimulation. The seedlings then curved upward again or straightened by about 6° during the subsequent 100 minutes. Seedlings rotated on a clinostat reached a similar maximum curvature following photostimulation. These seedlings maintained that curvature for 30 to 40 minutes before subsequently straightening to the same extent as the stationary seedlings. It is concluded that straightening is not a consequence of gravitropism, although gravity has some effect on the phototropism kinetics. PMID:11538373
Curvature rate approach to the evaluation of the stiffness distribution in plate-like structures
NASA Astrophysics Data System (ADS)
Goldfeld, Yiska
2014-09-01
A procedure for identifying the bending stiffness distribution in plate-like structures is presented. The algorithm is based on the correlation between a parameter called curvature increased factor (CIF) and the bending stiffness of the plate, D. Accurate correlation can be achieved only by considering the effect of the redistribution of internal forces and moments due to the damage on the curvature distribution. In order to achieve this goal, the study offers an iterative procedure, which eliminates the effect of the moment redistribution from the CIF and eventually correlates accurately between CIF and D. The curvature rate is evaluated from the displacement mode shape using a 2D smoothing technique. The procedure takes into account the presence of random errors and the limited number of measured nodes. The procedure's effectiveness, reliability, and range of applicability are demonstrated using numerical examples.
The curvature elastic-energy function of the lipid-water cubic mesophase
NASA Astrophysics Data System (ADS)
Chung, Hesson; Caffrey, Martin
1994-03-01
CELL and lipid membranes are able to bend, as manifested during membrane fusion and the formation of non-lamellar lyotropic mesopbases in water. But there is an energy cost to bending of lipid layers, called the curvature elastic energy. Although the functional form of this energy is known1, a complete quantitative knowledge of the curvature elastic energy, which is central to predicting the relative stability of the large number of phases that lipid membranes can adopt, has been lacking. Here we use X-ray synchrotron diffraction measurements of the variation of lattice parameter with pressure and temperature for the periodic Ia3d (Q230) cubic phase of hydrated monoolein to calculate the complete curvature elastic-energy function for the lipid cubic mesophase. This allows us to predict the stabilities of different cubic and lamellar phases for this system as a function of composition.
Engineering curvature in graphene ribbons using ultrathin polymer films.
Li, Chunyu; Koslowski, Marisol; Strachan, Alejandro
2014-12-10
We propose a method to induce curvature in graphene nanoribbons in a controlled manner using an ultrathin thermoset polymer in a bimaterial strip setup and test it via molecular dynamics (MD) simulations. Continuum mechanics shows that curvature develops to release the residual stress caused by the chemical and thermal shrinkage of the polymer during processing and that this curvature increases with decreasing film thickness; however, significant deformation is only achieved for ultrathin polymer films. Quite surprisingly, explicit MD simulations of the curing and annealing processes show that the predicted trend not just continues down to film thicknesses of 1-2 nm but that the curvature development is enhanced significantly in such ultrathin films due to surface tension effects. This combination of effects leads to very large curvatures of over 0.14 nm(-1) that can be tuned via film thickness. This provides a new avenue to engineer curvature and, thus, electromagnetic properties of graphene.
Ihlow, Dankmar; Kubein-Meesenburg, Dietmar; Hunze, Justus; Dathe, Henning; Planert, Jens; Schwestka-Polly, Rainer; Nägerl, Hans
2002-07-01
Radii for concave-convex vertical stripping instruments can be derived from measurements of the natural curvature morphology in the horizontal contact area of the mandibular dentition. The concave-convex adjustment of contacts in the anterior dental arch with a newly developed set of concave-convex stripping instruments should enable orthodontic crowding problems to be alleviated biomechanically.
Curvature and Tangency Handles for Control of Convex Cubic Shapes
2000-01-01
looked at A-splines constructed with segments of singular al- gebraic cubics, which are just rational cubics, with new, geometrically more meaningful...contact interpolation , and curvatures at three prescribed points, see Figures 1-4. Curve and Surface Design: Saint-Malo 1999 91 Pierre-Jean Laurent...curvature at one contact point. §2. Barycentric Coordinates and Curvature at the Endpoints The general algebraic cubic in cartesian coordinates x, y is
Wrinkles and splay conspire to give positive disclinations negative curvature
Matsumoto, Elisabetta A.; Vega, Daniel A.; Pezzutti, Aldo D.; García, Nicolás A.; Chaikin, Paul M.; Register, Richard A.
2015-01-01
Recently, there has been renewed interest in the coupling between geometry and topological defects in crystalline and striped systems. Standard lore dictates that positive disclinations are associated with positive Gaussian curvature, whereas negative disclinations give rise to negative curvature. Here, we present a diblock copolymer system exhibiting a striped columnar phase that preferentially forms wrinkles perpendicular to the underlying stripes. In free-standing films this wrinkling behavior induces negative Gaussian curvature to form in the vicinity of positive disclinations. PMID:26420873
NASA Astrophysics Data System (ADS)
Gerilowski, K.; Krautwurst, S.; Kolyer, R.; Jonsson, H.; Krings, T.; Horstjann, M.; Leifer, I.; Schuettemeyer, D.; Fladeland, M. M.; Burrows, J. P.; Bovensmann, H.
2014-12-01
During three flights performed with the MAMAP (Methane Airborne MAPper) airborne remote sensing instrument in the framework of the CO2 and MEthane Experiment (COMEX) - a NASA and ESA funded campaign in support of HyspIRI and CarbonSat mission definition activities - large scale methane plumes were detected over the Kern River and Kern Front Oil fields in the period between June 3 and 13, 2014. MAMAP was installed for these flights aboard of the Center for Interdisciplinary Remotely-Piloted Aircraft Studies (CIRPAS) Twin Otter aircraft, together with a Picarro fast in-situ greenhouse gas (GHG) analyzer (operate by the Ames Research Center, ARC), a 5 hole turbulence probe as well as a atmospheric measurement package (operated by CIRPAS), measuring aerosols, temperature, dew-point and other atmospheric parameters. Data collected with the in-situ GHG analyzer will be used for validation of MAMAP remotely sensed data by acquiring vertical cross sections of the discovered plumes at a fixed downwind distance. Precise airborne wind information from the turbulence probe together with ground based wind data from the nearby airport will be used to estimate emission rates from the remote sensed and in-situ measured data. Remote sensed and in-situ data as well as initial flux estimates for the three flights will be presented.
Inconsistency of scale invariant curvature coupled to gravity
Zoller, D.
1990-01-01
We show that the scale invariant curvature action for paths, the point particle version of Polyakov's extrinsic curvature action for surfaces, does not couple consistently to gravity. Although the curvature action for paths yields a massless representation of the Poincare group with fixed helicity and so potentially provides a description of single photons and gravitons, the inconsistent coupling to gravity apparently suggests such a description is not viable. We present a physical interpretation of the inconsistency in terms of the non-localizability of the photon and point out a conceptual kinship between the local symmetry of the curvature theory and the local supersymmetry of a spinning particle or spinning string. 11 refs.
Evolving extrinsic curvature and the cosmological constant problem
NASA Astrophysics Data System (ADS)
Capistrano, Abraão J. S.; Cabral, Luis A.
2016-10-01
The concept of smooth deformation of Riemannian manifolds associated with the extrinsic curvature is explained and applied to the Friedmann-Lemaître-Robertson-Walker cosmology. We show that such deformation can be derived from the Einstein-Hilbert-like dynamical principle may produce an observable effect in the sense of Noether. As a result, we show how the extrinsic curvature compensates both quantitative and qualitative differences between the cosmological constant Λ and the vacuum energy {ρ }{vac} obtaining the observed upper bound for the cosmological constant problem at electroweak scale. The topological characteristics of the extrinsic curvature are discussed showing that the produced extrinsic scalar curvature is an evolving dynamical quantity.
Plane wave gravitons, curvature singularities and string physics
Brooks, R. . Center for Theoretical Physics)
1991-03-21
This paper discusses bounded (compactifying) potentials arising from a conspiracy between plane wave graviton and dilaton condensates. So are string propagation and supersymmetry in spacetimes with curvature singularities.
NASA Technical Reports Server (NTRS)
Rosenbauer, H.; Schwenn, R.; Bame, S. J.
1978-01-01
The problems involved in the prediction of the arrival of fast solar wind streams at the earth on the basis of measurements made by space probes in the region between 0.3 and 1 AU are discussed. It is shown that arrival time predictions accurate to within a few hours that can be made at least as long as the large scale conditions on the Sun are relatively stationary as observed near the time of solar minimum. However, the latitudinal extent of the respective high speed streams is found to be important for making quantitative predictions. Coronal data sufficient for locating the sources of high speed streams can improve the precision of these predictions.
Thermodynamic curvature for attractive and repulsive intermolecular forces.
May, Helge-Otmar; Mausbach, Peter; Ruppeiner, George
2013-09-01
The thermodynamic curvature scalar R for the Lennard-Jones system is evaluated in phase space, including vapor, liquid, and solid state. We paid special attention to the investigation of R along vapor-liquid, liquid-solid, and vapor-solid equilibria. Because R is a measure of interaction strength, we traced out the line R=0 dividing the phase space into regions with effectively attractive (R<0) or repulsive (R>0) interactions. Furthermore, we analyzed the dependence of R on the strength of attraction applying a perturbation ansatz proposed by Weeks-Chandler-Anderson. Our results show clearly a transition from R>0 (for poorly repulsive interaction) to R<0 when loading attraction in the intermolecular potential.
Wang,W.; Yang, L.; Huang, H.
2007-01-01
Recent experiments suggested that cholesterol and other lipid components of high negative spontaneous curvature facilitate membrane fusion. This is taken as evidence supporting the stalk-pore model of membrane fusion in which the lipid bilayers go through intermediate structures of high curvature. How do the high-curvature lipid components lower the free energy of the curved structure? Do the high-curvature lipid components modify the average spontaneous curvature of the relevant monolayer, thereby facilitate its bending, or do the lipid components redistribute in the curved structure so as to lower the free energy? This question is fundamental to the curvature elastic energy for lipid mixtures. Here we investigate the lipid distribution in a monolayer of a binary lipid mixture before and after bending, or more precisely in the lamellar, hexagonal, and distorted hexagonal phases. The lipid mixture is composed of 2:1 ratio of brominated di18:0PC and cholesterol. Using a newly developed procedure for the multiwavelength anomalous diffraction method, we are able to isolate the bromine distribution and reconstruct the electron density distribution of the lipid mixture in the three phases. We found that the lipid distribution is homogenous and uniform in the lamellar and hexagonal phases. But in the distorted hexagonal phase, the lipid monolayer has nonuniform curvature, and cholesterol almost entirely concentrates in the high curvature region. This finding demonstrates that the association energies between lipid molecules vary with the curvature of membrane. Thus, lipid components in a mixture may redistribute under conditions of nonuniform curvature, such as in the stalk structure. In such cases, the spontaneous curvature depends on the local lipid composition and the free energy minimum is determined by lipid distribution as well as curvature.
Hawking temperature of constant curvature black holes
Cai Ronggen; Myung, Yun Soo
2011-05-15
The constant curvature (CC) black holes are higher dimensional generalizations of Banados-Teitelboim-Zanelli black holes. It is known that these black holes have the unusual topology of M{sub D-1}xS{sup 1}, where D is the spacetime dimension and M{sub D-1} stands for a conformal Minkowski spacetime in D-1 dimensions. The unusual topology and time-dependence for the exterior of these black holes cause some difficulties to derive their thermodynamic quantities. In this work, by using a globally embedding approach, we obtain the Hawking temperature of the CC black holes. We find that the Hawking temperature takes the same form when using both the static and global coordinates. Also, it is identical to the Gibbons-Hawking temperature of the boundary de Sitter spaces of these CC black holes.
Band geometry, Berry curvature, and superfluid weight
NASA Astrophysics Data System (ADS)
Liang, Long; Vanhala, Tuomas I.; Peotta, Sebastiano; Siro, Topi; Harju, Ari; Törmä, Päivi
2017-01-01
We present a theory of the superfluid weight in multiband attractive Hubbard models within the Bardeen-Cooper-Schrieffer (BCS) mean-field framework. We show how to separate the geometric contribution to the superfluid weight from the conventional one, and that the geometric contribution is associated with the interband matrix elements of the current operator. Our theory can be applied to systems with or without time-reversal symmetry. In both cases the geometric superfluid weight can be related to the quantum metric of the corresponding noninteracting systems. This leads to a lower bound on the superfluid weight given by the absolute value of the Berry curvature. We apply our theory to the attractive Kane-Mele-Hubbard and Haldane-Hubbard models, which can be realized in ultracold atom gases. Quantitative comparisons are made to state of the art dynamical mean-field theory and exact diagonalization results.
Asymmetric counterpropagating fronts without flow
NASA Astrophysics Data System (ADS)
Andrade-Silva, I.; Clerc, M. G.; Odent, V.
2015-06-01
Out-of-equilibrium systems exhibit domain walls between different states. These walls, depending on the type of connected states, can display rich spatiotemporal dynamics. In this Rapid Communication, we investigate the asymmetrical counterpropagation of fronts in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the different front shapes and propagation speeds. These fronts present dissimilar elastic deformations that are responsible for their asymmetric speeds. Theoretically, using a phenomenological model, we describe the observed dynamics with fair agreement.
Asymmetric counterpropagating fronts without flow.
Andrade-Silva, I; Clerc, M G; Odent, V
2015-06-01
Out-of-equilibrium systems exhibit domain walls between different states. These walls, depending on the type of connected states, can display rich spatiotemporal dynamics. In this Rapid Communication, we investigate the asymmetrical counterpropagation of fronts in an in-plane-switching cell filled with a nematic liquid crystal. Experimentally, we characterize the different front shapes and propagation speeds. These fronts present dissimilar elastic deformations that are responsible for their asymmetric speeds. Theoretically, using a phenomenological model, we describe the observed dynamics with fair agreement.
NASA Astrophysics Data System (ADS)
Casey, D.; Smalyuk, V.; Peterson, L.; Berzak Hopkins, L.; Bunn, T.; Carlson, L.; Haan, S.; Ho, D.; Hoover, D.; Kroll, J.; Landen, O.; Le Pape, S.; MacKinnon, A.; Macphee, A.; Meezan, N.; Milovich, J.; Nikroo, A.; Remington, B.; Robey, H.; Ross, S.
2014-10-01
High-density carbon (HDC) has emerged as a promising ablator for ignition experiments at the National Ignition Facility (NIF) partly because of its efficient coupling of the drive energy to fuel. Experiments during the National Ignition Campaign using a CH plastic ablator have shown that instability growth and the resultant mix of plastic into the hotspot was a significant source of overall the observed performance degradation. Likewise, mix of HDC ablator into the hotspot may also be a concern, as growth rates for HDC are comparable to CH and ablator/dopant is higher Z than CH ablators making the consequences potentially more severe. To help understand this issue, we plan to perform the first instability growth measurements of W-doped HDC implosions with preimposed mode 60 and mode 90 perturbations in convergent geometry using actual ignition targets and drives. These results will be presented and compared to ignition design simulations. This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
NASA Astrophysics Data System (ADS)
Toyota, H.; Takiyama, K.; Oda, T.
1998-10-01
Metastable atoms of rare gases affect on the etching processes and the radical formation processes in a reactive plasma because of their high internal energy. Fundamental understanding is required of the creation and annihilation mechanisms of the metastable atoms in the plasma, especially in the boundary region between plasma and substrate. We have measured spatial profile of He metastable (2^1S) atom density in plasma flow from an ECR plasma source by polarized laser-induced fluorescence (LIF) spectroscopy [1]. It has been shown that the metastable atoms near the outlet of the plasma flow are created by collisional-radiative processes. However, the remarkable decrease near the substrate placed in the downstream has not been clearly understood. Observation of the polarized LIF due to forbidden excitation is made with high spatial resolution in the vicinity of the substrate to obtain the detailed density profile. Based on these results, possible annihilation mechanism of the metastable atoms will be briefly discussed. [1] H. Toyota et al.; Jpn. J. Appl. Phys. 36 (1997) 4670.
Novel Laplacian scheme and multiresolution modal curvatures for structural damage identification
NASA Astrophysics Data System (ADS)
Cao, Maosen; Qiao, Pizhong
2009-05-01
Modal curvature is more sensitive to structural damage than directly measured mode shape, and the standard Laplace operator is commonly used to acquire the modal curvatures from the mode shapes. However, the standard Laplace operator is very prone to noise, which often leads to the degraded modal curvatures incapable of identifying damage. To overcome this problem, a novel Laplacian scheme is proposed, from which an improved damage identification algorithm is developed. The proposed step-by-step procedures in the algorithm include: (1) By progressively upsampling the standard Laplace operator, a new Laplace operator is constructed, from which a Laplace operator array is formed; (2) by applying the Laplace operator array to the retrieved mode shape of a damaged structure, the multiresolution curvature mode shapes are produced, on which the damage trait, previously shadowed under the standard Laplace operator, can be revealed by a ridge of multiresolution modal curvatures; (3) a Gaussian filter is then incorporated into the new Laplace operator to produce a more versatile Laplace operator with properties of both the smoothness and differential capabilities, in which the damage feature is effectively strengthened; and (4) a smoothened nonlinear energy operator is introduced to further enhance the damage feature by eliminating the trend interference of the multiresolution modal curvatures, and it results in a significantly improved damage trait. The proposed algorithm is tested using the data generated by an analytical crack beam model, and its applicability is validated with an experimental program of a delaminated composite beam using scanning laser vibrometer (SLV) to acquire mode shapes. The results are compared in each step, showing increasing degree of improvement for damage effect. Numerical and experimental results demonstrate that the proposed novel Laplacian scheme provides a promising damage identification algorithm, which exhibits apparent advantages (e
QCD and Light-Front Holography
Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U.
2010-10-27
The soft-wall AdS/QCD model, modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics. The model predicts a zero-mass pion for zero-mass quarks and a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number N. Light-Front Holography maps the amplitudes which are functions of the fifth dimension variable z of anti-de Sitter space to a corresponding hadron theory quantized on the light front. The resulting Lorentz-invariant relativistic light-front wave equations are functions of an invariant impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron at equal light-front time. The result is to a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryon light-quark bound states, which in turn predict the behavior of the pion and nucleon form factors. The theory implements chiral symmetry in a novel way: the effects of chiral symmetry breaking increase as one goes toward large interquark separation, consistent with spectroscopic data, and the the hadron eigenstates generally have components with different orbital angular momentum; e.g., the proton eigenstate in AdS/QCD with massless quarks has L = 0 and L = 1 light-front Fock components with equal probability. The soft-wall model also predicts the form of the non-perturbative effective coupling {alpha}{sub s}{sup AdS} (Q) and its {beta}-function which agrees with the effective coupling {alpha}{sub g1} extracted from the Bjorken sum rule. The AdS/QCD model can be systematically improved by using its complete orthonormal solutions to diagonalize the full QCD light-front Hamiltonian or by applying the Lippmann-Schwinger method in order to systematically include the QCD interaction terms. A new perspective on quark and gluon condensates is also reviewed.
Front interaction induces excitable behavior
NASA Astrophysics Data System (ADS)
Parra-Rivas, P.; Matías, M. A.; Colet, P.; Gelens, L.; Walgraef, D.; Gomila, D.
2017-02-01
Spatially extended systems can support local transient excitations in which just a part of the system is excited. The mechanisms reported so far are local excitability and excitation of a localized structure. Here we introduce an alternative mechanism based on the coexistence of two homogeneous stable states and spatial coupling. We show the existence of a threshold for perturbations of the homogeneous state. Subthreshold perturbations decay exponentially. Superthreshold perturbations induce the emergence of a long-lived structure formed by two back to back fronts that join the two homogeneous states. While in typical excitability the trajectory follows the remnants of a limit cycle, here reinjection is provided by front interaction, such that fronts slowly approach each other until eventually annihilating. This front-mediated mechanism shows that extended systems with no oscillatory regimes can display excitability.
Energy conversion at dipolarization fronts
NASA Astrophysics Data System (ADS)
Khotyaintsev, Yu. V.; Divin, A.; Vaivads, A.; André, M.; Markidis, S.
2017-02-01
We use multispacecraft observations by Cluster in the Earth's magnetotail and 3-D particle-in-cell simulations to investigate conversion of electromagnetic energy at the front of a fast plasma jet. We find that the major energy conversion is happening in the Earth (laboratory) frame, where the electromagnetic energy is being transferred from the electromagnetic field to particles. This process operates in a region with size of the order several ion inertial lengths across the jet front, and the primary contribution to E·j is coming from the motional electric field and the ion current. In the frame of the front we find fluctuating energy conversion with localized loads and generators at sub-ion scales which are primarily related to the lower hybrid drift instability excited at the front; however, these provide relatively small net energy conversion.
The association between cervical spine curvature and neck pain
Grob, D.; Frauenfelder, H.
2006-01-01
Degenerative changes of the cervical spine are commonly accompanied by a reduction or loss of the segmental or global lordosis, and are often considered to be a cause of neck pain. Nonetheless, such changes may also remain clinically silent. The aim of this study was to examine the correlation between the presence of neck pain and alterations of the normal cervical lordosis in people aged over 45 years. One hundred and seven volunteers, who were otherwise undergoing treatment for lower extremity problems in our hospital, took part. Sagittal radiographs of the cervical spine were taken and a questionnaire was completed, enquiring about neck pain and disability in the last 12 months. Based on the latter, subjects were divided into a group with neck pain (N = 54) and a group without neck pain (N = 53). The global curvature of the cervical spine (C2–C7) and each segmental angle were measured from the radiographs, using the posterior tangent method, and examined in relation to neck complaints. No significant difference between the two groups could be found in relation to the global curvature, the segmental angles, or the incidence of straight-spine or kyphotic deformity (P > 0.05). Twenty-three per cent of the people with neck pain and 17% of those without neck pain showed a segmental kyphosis deformity of more than 4° in at least one segment—most frequently at C4/5, closely followed by C5/6 and C3/4. The average segmental angle at the kyphotic level was 6.5° in the pain group and 6.3° in the group without pain, with a range of 5–10° in each group. In the group with neck pain, there was no association between any of the clinical characteristics (duration, frequency, intensity of pain; radiating pain; sensory/motor disturbances; disability; healthcare utilisation) and either global cervical curvature or segmental angles. The presence of such structural abnormalities in the patient with neck pain must be considered coincidental, i.e. not necessarily
Radiative magnetized thermal conduction fronts
NASA Technical Reports Server (NTRS)
Borkowski, Kazimierz J.; Balbus, Steven A.; Fristrom, Carl C.
1990-01-01
The evolution of plane-parallel magnetized thermal conduction fronts in the interstellar medium (ISM) was studied. Separating the coronal ISM phase and interstellar clouds, these fronts have been thought to be the site of the intermediate-temperature regions whose presence was inferred from O VI absorption-line studies. The front evolution was followed numerically, starting from the initial discontinuous temperature distribution between the hot and cold medium, and ending in the final cooling stage of the hot medium. It was found that, for the typical ISM pressure of 4000 K/cu cm and the hot medium temperature of 10 to the 6th K, the transition from evaporation to condensation in a nonmagnetized front occurs when the front thickness is 15 pc. This thickness is a factor of 5 smaller than previously estimated. The O VI column densities in both evaporative and condensation stages agree with observations if the initial hot medium temperature Th exceeds 750,000 K. Condensing conduction fronts give better agreement with observed O VI line profiles because of lower gas temperatures.
Gaussian and mean curvatures for discrete asymptotic nets
NASA Astrophysics Data System (ADS)
Schief, W. K.
2017-04-01
We propose discretisations of Gaussian and mean curvatures of surfaces parametrised in terms of asymptotic coordinates and examine their relevance in the context of integrable discretisations of classical classes of surfaces and their underlying integrable systems. We also record discrete analogues of the classical relation between the Gaussian curvature of hyperbolic surfaces and the torsion of their asymptotic lines.
An analytical approach to estimate curvature effect of coseismic deformations
NASA Astrophysics Data System (ADS)
Dong, Jie; Sun, Wenke; Zhou, Xin; Wang, Rongjiang
2016-08-01
We present an analytical approach to compute the curvature effect by the new analytical solutions of coseismic deformation derived for the homogeneous sphere model. We consider two spheres with different radii: one is the same as earth and the other with a larger radius can approximate a half-space model. Then, we calculate the coseismic displacements for the two spheres and define the relative percentage of the displacements as the curvature effect. The near-field curvature effect is defined relative to the maximum coseismic displacement. The results show that the maximum curvature effect is about 4 per cent for source depths of less than 100 km, and about 30 per cent for source depths of less than 600 km. For the far-field curvature effect, we define it relative to the observing point. The curvature effect is extremely large and sometimes exceeds 100 per cent. Moreover, this new approach can be used to estimate any planet's curvature effect quantitatively. For a smaller sphere, such as the Moon, the curvature effect is much larger than that of the Earth, with an inverse ratio to the earth's radius.
Wang, Q.; Li, M.; Lou, Edmond H. M.; Wong, M. S.
2015-01-01
Background Non-ionizing radiation imaging assessment has been advocated for the patients with adolescent idiopathic scoliosis (AIS). As one of the radiation-free methods, ultrasound imaging has gained growing attention in scoliosis assessment over the past decade. The center of laminae (COL) method has been proposed to measure the spinal curvature in the coronal plane of ultrasound image. However, the reliability and validity of this ultrasound method have not been validated in the clinical setting. Objectives To evaluate the reliability and validity of clinical ultrasound imaging on lateral curvature measurements of AIS with their corresponding magnetic resonance imaging (MRI) measurements. Methods Thirty curves (ranged 10.2°–68.2°) from sixteen patients with AIS were eligible for this study. The ultrasound scan was performed using a 3-D ultrasound unit within the same morning of MRI examination. Two researchers were involved in data collection of these two examinations. The COL method was used to measure the coronal curvature in ultrasound image, compared with the Cobb method in MRI. The intra- and inter-rater reliability of the COL method was evaluated by intra-class correlation coefficient (ICC). The validity of this method was analyzed by paired Student’s t-test, Bland–Altman statistics and Pearson correlation coefficient. The level of significance was set as 0.05. Results The COL method showed high intra- and inter-rater reliabilities (both with ICC (2, K) >0.9, p<0.05) to measure the coronal curvature. Compared with Cobb method, COL method showed no significant difference (p<0.05) when measuring coronal curvature. Furthermore, Bland-Altman method demonstrated an agreement between these two methods, and Pearson’s correlation coefficient (r) was high (r>0.9, p<0.05). Conclusion The ultrasound imaging could provide a reliable and valid measurement of spinal curvature in the coronal plane using the COL method. Further research is needed to validate the
Curvature dependence of the interfacial heat and mass transfer coefficients
NASA Astrophysics Data System (ADS)
Glavatskiy, K. S.; Bedeaux, D.
2014-03-01
Nucleation is often accompanied by heat transfer between the surroundings and a nucleus of a new phase. The interface between two phases gives an additional resistance to this transfer. For small nuclei the interfacial curvature is high, which affects not only equilibrium quantities such as surface tension, but also the transport properties. In particular, high curvature affects the interfacial resistance to heat and mass transfer. We develop a framework for determining the curvature dependence of the interfacial heat and mass transfer resistances. We determine the interfacial resistances as a function of a curvature. The analysis is performed for a bubble of a one-component fluid and may be extended to various nuclei of multicomponent systems. The curvature dependence of the interfacial resistances is important in modeling transport processes in multiphase systems.
Effect of curvature on cholesteric liquid crystals in toroidal geometries
NASA Astrophysics Data System (ADS)
Fialho, Ana R.; Bernardino, Nelson R.; Silvestre, Nuno M.; Telo da Gama, Margarida M.
2017-01-01
The confinement of liquid crystals inside curved geometries leads to exotic structures, with applications ranging from biosensors to optical switches and privacy windows. Here we study how curvature affects the alignment of a cholesteric liquid crystal. We model the system on the mesoscale using the Landau-de Gennes model. Our study was performed in three stages, analyzing different curved geometries from cylindrical walls and pores, to toroidal domains, in order to isolate the curvature effects. Our results show that the stresses introduced by the curvature influence the orientation of the liquid crystal molecules, and cause distortions in the natural periodicity of the cholesteric that depend on the radius of curvature, on the pitch, and on the dimensions of the system. In particular, the cholesteric layers of toroidal droplets exhibit a symmetry breaking not seen in cylindrical pores and that is driven by the additional curvature.
Nastic curvatures of wheat coleoptiles that develop in true microgravity
NASA Technical Reports Server (NTRS)
Heathcote, D. G.; Chapman, D. K.; Brown, A. H.
1995-01-01
Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML-1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non-random, and directed away from the caryopsis (the coleptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with phototropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Curvature-processing network in macaque visual cortex
Yue, Xiaomin; Pourladian, Irene S.; Tootell, Roger B. H.; Ungerleider, Leslie G.
2014-01-01
Our visual environment abounds with curved features. Thus, the goal of understanding visual processing should include the processing of curved features. Using functional magnetic resonance imaging in behaving monkeys, we demonstrated a network of cortical areas selective for the processing of curved features. This network includes three distinct hierarchically organized regions within the ventral visual pathway: a posterior curvature-biased patch (PCP) located in the near-foveal representation of dorsal V4, a middle curvature-biased patch (MCP) located on the ventral lip of the posterior superior temporal sulcus (STS) in area TEO, and an anterior curvature-biased patch (ACP) located just below the STS in anterior area TE. Our results further indicate that the processing of curvature becomes increasingly complex from PCP to ACP. The proximity of the curvature-processing network to the well-known face-processing network suggests a possible functional link between them. PMID:25092328
Nastic curvatures of wheat coleoptiles that develop in true microgravity.
Heathcote, D G; Chapman, D K; Brown, A H
1995-07-01
Dark-grown wheat coleoptiles developed strong curvatures within 5 h of being transferred in orbit from a 1 g centrifuge to microgravity during an experiment flown on the IML-1 shuttle mission. The curving tendency was strongest in seedlings that were immature, with coleoptiles shorter than 10 mm at the time of transfer. The curvature direction was non-random, and directed away from the caryopsis (the coleptile face adjacent to the caryopsis becoming convex). The curvatures were most marked in the basal third of the coleoptiles, contrasting with phototropic responses, which occur in the apical third. We interpret these curvatures as being nastic, and related to the curvatures commonly reported to occur during clinostat rotation treatments.
Robust pupil center detection using a curvature algorithm
NASA Technical Reports Server (NTRS)
Zhu, D.; Moore, S. T.; Raphan, T.; Wall, C. C. (Principal Investigator)
1999-01-01
Determining the pupil center is fundamental for calculating eye orientation in video-based systems. Existing techniques are error prone and not robust because eyelids, eyelashes, corneal reflections or shadows in many instances occlude the pupil. We have developed a new algorithm which utilizes curvature characteristics of the pupil boundary to eliminate these artifacts. Pupil center is computed based solely on points related to the pupil boundary. For each boundary point, a curvature value is computed. Occlusion of the boundary induces characteristic peaks in the curvature function. Curvature values for normal pupil sizes were determined and a threshold was found which together with heuristics discriminated normal from abnormal curvature. Remaining boundary points were fit with an ellipse using a least squares error criterion. The center of the ellipse is an estimate of the pupil center. This technique is robust and accurately estimates pupil center with less than 40% of the pupil boundary points visible.
Thermodynamic curvature from the critical point to the triple point.
Ruppeiner, George
2012-08-01
I evaluate the thermodynamic curvature R for fourteen pure fluids along their liquid-vapor coexistence curves, from the critical point to the triple point, using thermodynamic input from the NIST Chemistry WebBook. In this broad overview, R is evaluated in both the coexisting liquid and vapor phases. R is an invariant whose magnitude |R| is a measure of the size of mesoscopic organized structures in a fluid, and whose sign specifies whether intermolecular interactions are effectively attractive (R<0) or repulsive (R>0). I discuss five principles for R in pure fluids: (1) Near the critical point, the attractive part of the interactions forms loose structures of size |R| proportional to the correlation volume ξ(3), and the sign of R is negative. (2) In the vapor phase, there are instances of compact clusters of size |R| formed by the attractive part of the interactions and prevented from collapse by the repulsive part of the interactions, and the sign of R is positive. (3) In the asymptotic critical point regime, the R's in the coexisting liquid and vapor phases are equal to each other, i.e., commensurate. (4) Outside the asymptotic critical-point regime incommensurate R's may be associated with metastability. (5) The compact liquid phase has |R| on the order of the volume of a molecule, with the sign of R being negative for a liquidlike state held together by attractive interactions and the sign of R being positive for a solidlike state held up by repulsive interactions. These considerations amplify and extend the application of thermodynamic curvature in pure fluids.
Effect of Microscopic Noise on Front Propagation
NASA Astrophysics Data System (ADS)
Brunet, Éric; Derrida, Bernard
2001-04-01
We study the effect of the noise due to microscopic fluctuations on the position of a one dimensional front propagating from a stable to an unstable region in the "linearly marginal stability case." By simulating a very simple system for which the effective number N of particles can be as large as N=10150, we measure the N dependence of the diffusion constant DN of the front and the shift of its velocity vN. Our results indicate that DN˜(log N)-3. They also confirm our recent claim that the shift of velocity scales like vmin-vN≃K(log N)-2 and indicate that the numerical value of K is very close to the analytical expression Kapprox obtained in our previous work using a simple cut-off approximation.
NASA Astrophysics Data System (ADS)
Keshet, Uri; Naor, Yossi
2016-10-01
Compressible flows around blunt objects have diverse applications, but current analytic treatments are inaccurate and limited to narrow parameter regimes. We show that the gas-dynamic flow in front of an axisymmetric blunt body is accurately derived analytically using a low order expansion of the perpendicular gradients in terms of the parallel velocity. This reproduces both subsonic and supersonic flows measured and simulated for a sphere, including the transonic regime and the bow shock properties. Some astrophysical implications are outlined, in particular for planets in the solar wind and for clumps and bubbles in the intergalactic medium. The bow shock standoff distance normalized by the obstacle curvature is ∼ 2/(3g) in the strong shock limit, where g is the compression ratio. For a subsonic Mach number M approaching unity, the thickness δ of an initially weak, draped magnetic layer is a few times larger than in the incompressible limit, with amplification ∼ (1+1.3{M}2.6)/(3δ ).
Surface Curvature in Island Groups and Discontinuous Cratonic Structures
NASA Astrophysics Data System (ADS)
McDowell, M. S.
2002-05-01
distance separations, perhaps related to geologic time scale. What could this mean? 1) Two-dimensional expansion of an original Precambrian craton can be justified as rupture in some non explosive way (apparently not volcanic or quake action) with resulting cracks subsequently filled in from below. The cause of the initial cracking is problematic - consider an eggshell: a good whack on the outside, or a good chick on the inside, could make it happen. But 2) the tightened arc? The propensity to "curl up"? Is there something freaky about connecting flat map projections to make this happen, or has it really been there all along and we never realized it? If this is applied in reverse, curvature flattening further with time, the significance could be interesting. For idle speculation, the Atlantic mid-ocean ridge is calculated opening at 3cms/year. That's 3 km in 100,000 years. At that rate it would have taken 2.2 x 109 to open the Canadian archipelago this far. Which puts it almost into the Archean, matching Slave Province, not Wopmay, associated with the Huronian. So what WAS the early sea floor spreading rate? Monster speculations. Scientific research has created a fortress of opinion on Archean land masses and how they grew. This study proposes a phenomenon that has the advantage of measurability, one we can literally get our hands on, in our effort to know.
Madsen, K L; Bhatia, V K; Gether, U; Stamou, D
2010-05-03
The internal membranes of eukaryotic cells are all twists and bends characterized by high curvature. During recent years it has become clear that specific proteins sustain these curvatures while others simply recognize membrane shape and use it as "molecular information" to organize cellular processes in space and time. Here we discuss this new important recognition process termed membrane curvature sensing (MCS). First, we review a new fluorescence-based experimental method that allows characterization of MCS using measurements on single vesicles and compare it to sensing assays that use bulk/ensemble liposome samples of different mean diameter. Next, we describe two different MCS protein motifs (amphipathic helices and BAR domains) and suggest that in both cases curvature sensitive membrane binding results from asymmetric insertion of hydrophobic amino acids in the lipid membrane. This mechanism can be extended to include the insertion of alkyl chain in the lipid membrane and consequently palmitoylated and myristoylated proteins are predicted to display similar curvature sensitive binding. Surprisingly, in all the aforementioned cases, MCS is predominantly mediated by a higher density of binding sites on curved membranes instead of higher affinity as assumed so far. Finally, we integrate these new insights into the debate about which motifs are involved in sensing versus induction of membrane curvature and what role MCS proteins may play in biology.
NASA Astrophysics Data System (ADS)
Cao, Mao-Sen; Xu, Wei; Ren, Wei-Xin; Ostachowicz, Wiesław; Sha, Gang-Gang; Pan, Li-Xia
2016-08-01
Detection of multiple damage using modal curvature in noisy environments has become a research focus of considerable challenge and great significance over the last few years. However, a noticeable deficiency of modal curvature is its susceptibility to noise, which usually results in a noisy modal curvature with obscured damage signature. To address this deficiency, this study formulates a new concept of complex-wavelet modal curvature. Complex-wavelet modal curvature features the ability to reveal and delineate damage under noisy conditions. The effectiveness of the concept is analytically verified using cracked beams with various types of boundary conditions. The applicability is further experimentally validated by an aluminum beam with a single crack and a carbon-fiber-reinforced polymer composite beam with three cracks in the laboratory with mode shapes measured by a scanning laser vibrometer. Both analytical and experimental results have demonstrated that the complex-wavelet modal curvature is capable of revealing slight damage by eliminating noise interference, with no need for prior knowledge of either material properties or boundary conditions of the beam under inspection.
A generalized front marching algorithm for the solution of the eikonal equation
NASA Astrophysics Data System (ADS)
Covello, Paul; Rodrigue, Garry
2003-07-01
A new front marching algorithm for solving the eikonal equation is presented. An important property of the algorithm is that it can be used on nodes that are located on highly distorted grids or on nodes that are randomly located. When the nodes are located on an orthogonal grid, the method is first-order accurate and is shown to be a generalization of the front marching algorithm in (Proc. Natl. Acad. Sci. 93 (4) (1996) 1591). The accuracy of the method is also shown to be dependent on the principle curvature of the wave front solution. Numerical results on a variety of node configurations as well as on shadow, nonconvex and nondifferentiable solutions are presented.
Detonative propagation and accelerative expansion of the Crab Nebula shock front.
Gao, Yang; Law, Chung K
2011-10-21
The accelerative expansion of the Crab Nebula's outer envelope is a mystery in dynamics, as a conventional expanding blast wave decelerates when bumping into the surrounding interstellar medium. Here we show that the strong relativistic pulsar wind bumping into its surrounding nebula induces energy-generating processes and initiates a detonation wave that propagates outward to form the current outer edge, namely, the shock front, of the nebula. The resulting detonation wave, with a reactive downstream, then provides the needed power to maintain propagation of the shock front. Furthermore, relaxation of the curvature-induced reduction of the propagation velocity from the initial state of formation to the asymptotic, planar state of Chapman-Jouguet propagation explains the observed accelerative expansion. Potential richness in incorporating reactive fronts in the description of various astronomical phenomena is expected.
A Theoretical Study of Propagation and Extinction of Nonsteady Spherical Flame Fronts
NASA Technical Reports Server (NTRS)
Ronney, P. D.; Sivashinsky, G. I.
1989-01-01
Freely propagating expanding spherical flame fronts are studied analytically using the method of activation energy asymptotics. Effects of Lewis number (Le), curvature, heat loss, and thermal expansion on propagation rates and extinction conditions are examined. The behavior of spherical flame fronts is found to be determined primarily by the values of Le and a heat-loss parameter. Results are compared to recent experimental observations of spherical flame fronts in mixtures near the flammability limits; for Le less than 1, it is found that many of the features of these experimental results are described by the analysis presented here. For Le greater than 1, however, unrealistic dynamic behavior is predicted due to the nature of diffusive-thermal instabilities under these conditions.
Mean curvature flow of a hyperbolic surface
Ovchinnikov, Yu. N.; Sigal, I. M.
2011-12-15
A four-parameter family of self-similar solutions is obtained to the mean curvature flow equation for a surface. This family is shown to be stable with respect to a small deformation of a hyperbolic surface. At time instant t*, a singular point is formed within a finite time interval, that is accompanied by a change in the topology of the surface. The solution is continued beyond the singular point. A relationship between the parameters describing the hyperbolic surface before and after the change in the surface topology is obtained. A particular case is analyzed when the unperturbed surface is a cylinder. A cylindrical surface is weakly unstable with respect to a perturbation in the form of a 'wide neck.' At the final stage of the development of the neck when its transverse size becomes much less than the cylinder radius at large distances from the neck, the surface flow in a wide region in the neighborhood of the neck is described by a universal two-parameter family of self-similar solutions. These solutions are stable with respect to small perturbations of the surface.
Actin filament curvature biases branching direction
NASA Astrophysics Data System (ADS)
Wang, Evan; Risca, Viviana; Chaudhuri, Ovijit; Chia, Jia-Jun; Geissler, Phillip; Fletcher, Daniel
2012-02-01
Actin filaments are key components of the cellular machinery, vital for a wide range of processes ranging from cell motility to endocytosis. Actin filaments can branch, and essential in this process is a protein complex known as the Arp2/3 complex, which nucleate new ``daughter'' filaments from pre-existing ``mother'' filaments by attaching itself to the mother filament. Though much progress has been made in understanding the Arp2/3-actin junction, some very interesting questions remain. In particular, F-actin is a dynamic polymer that undergoes a wide range of fluctuations. Prior studies of the Arp2/3-actin junction provides a very static notion of Arp2/3 binding. The question we ask is how differently does the Arp2/3 complex interact with a straight filament compared to a bent filament? In this study, we used Monte Carlo simulations of a surface-tethered worm-like chain to explore possible mechanisms underlying the experimental observation that there exists preferential branch formation by the Arp2/3 complex on the convex face of a curved filament. We show that a fluctuation gating model in which Arp2/3 binding to the actin filament is dependent upon a rare high-local-curvature shape fluctuation of the filament is consistent with the experimental data.
Berry curvature and various thermal Hall effects
NASA Astrophysics Data System (ADS)
Zhang, Lifa
2016-10-01
Applying the approach of semiclassical wave packet dynamics, we study various thermal Hall effects where carriers can be electron, phonon, magnon, etc. A general formula of thermal Hall conductivity is obtained to provide an essential physics for various thermal Hall effects, where the Berry phase effect manifests naturally. All the formulas of electron thermal Hall effect, phonon Hall effect, and magnon Hall effect can be directly reproduced from the general formula. It is also found that the Strěda formula can not be directly applied to the thermal Hall effects, where only the edge magnetization contributes to the Hall effects. Furthermore, we obtain a combined formula for anomalous Hall conductivity, thermal Hall electronic conductivity and thermal Hall conductivity for electron systems, where the Berry curvature is weighted by a different function. Finally, we discuss particle magnetization and its relation to angular momentum of the carrier, change of which could induce a mechanical rotation; and possible experiments for thermal Hall effect associated with a mechanical rotation are also proposed.
BICEP2, the curvature perturbation and supersymmetry
Lyth, David H.
2014-11-01
The tensor fraction r ≅ 0.16 found by BICEP2 corresponds to a Hubble parameter H ≅ 1.0 × 10{sup 14} GeV during inflation. This has two implications for the (single-field) slow-roll inflation hypothesis. First, the inflaton perturbation must account for much more than 10% of the curvature perturbation ζ, which barring fine-tuning means that it accounts for practically all of it. It follows that a curvaton-like mechanism for generating ζ requires an alternative to slow roll such as k-inflation. Second, accepting slow-roll inflation, the excursion of the inflaton field is at least of order Planck scale. As a result, the flatness of the inflaton presumably requires a shift symmetry. I point out that if such is the case, the resulting potential is likely to have at least approximately the quadratic form suggested in 1983 by Linde, which is known to be compatible with the observed r as well as the observed spectral index n{sub s}. The shift symmetry does not require supersymmetry. Also, the big H may rule out a GUT by restoring the symmetry and producing fatal cosmic strings. The absence of a GUT would correspond to the absence of superpartners for the Standard Model particles, which indeed have yet to be found at the LHC.
Cosmological spatial curvature probed by microwave polarization
Matzner, R.A.; Tolman, B.W.
1982-11-15
If there is a large-scale anisotropy in the expansion of the universe, the microwave background radiation is expected to be linearly polarized. This communication shows that spatial curvature is capable of rotating the polarization of the microwaves relative to its direction at last scattering, which is directly correlated with the expansion anisotropy (and so also the observed intensity anisotropy). In Friedmann-Robertson-Walker models of the universe with additional small expansion anisotropy, the observed rotation relative to the intensity anisotropy would be appreciable and constant over the celestial sphere in the closed (type IX) model, but in the flat and open models, it must either vanish (types I and V) or vary ina complicated way over the celestial sphere (type VII/sub h/). These facts suggest a clear observational test of the closure of the universe. Also, an ambiguity inherent in the homogeneity of the universe does not allow prediction of the direction of rotation; thus homogeneous universes possess a property which might be called ''handedness.''
Programming curvature using origami tessellations.
Dudte, Levi H; Vouga, Etienne; Tachi, Tomohiro; Mahadevan, L
2016-05-01
Origami describes rules for creating folded structures from patterns on a flat sheet, but does not prescribe how patterns can be designed to fit target shapes. Here, starting from the simplest periodic origami pattern that yields one-degree-of-freedom collapsible structures-we show that scale-independent elementary geometric constructions and constrained optimization algorithms can be used to determine spatially modulated patterns that yield approximations to given surfaces of constant or varying curvature. Paper models confirm the feasibility of our calculations. We also assess the difficulty of realizing these geometric structures by quantifying the energetic barrier that separates the metastable flat and folded states. Moreover, we characterize the trade-off between the accuracy to which the pattern conforms to the target surface, and the effort associated with creating finer folds. Our approach enables the tailoring of origami patterns to drape complex surfaces independent of absolute scale, as well as the quantification of the energetic and material cost of doing so.
Gradient expansion, curvature perturbations, and magnetized plasmas
Giovannini, Massimo; Rezaei, Zahra
2011-04-15
The properties of magnetized plasmas are always investigated under the hypothesis that the relativistic inhomogeneities stemming from the fluid sources and from the geometry itself are sufficiently small to allow for a perturbative description prior to photon decoupling. The latter assumption is hereby relaxed and predecoupling plasmas are described within a suitable expansion where the inhomogeneities are treated to a given order in the spatial gradients. It is argued that the (general relativistic) gradient expansion shares the same features of the drift approximation, customarily employed in the description of cold plasmas, so that the two schemes are physically complementary in the large-scale limit and for the low-frequency branch of the spectrum of plasma modes. The two-fluid description, as well as the magnetohydrodynamical reduction, is derived and studied in the presence of the spatial gradients of the geometry. Various solutions of the coupled system of evolution equations in the anti-Newtonian regime and in the quasi-isotropic approximation are presented. The relation of this analysis to the so-called separate universe paradigm is outlined. The evolution of the magnetized curvature perturbations in the nonlinear regime is addressed for the magnetized adiabatic mode in the plasma frame.
Slow axis collimation lens with variable curvature radius for semiconductor laser bars
NASA Astrophysics Data System (ADS)
Xiong, Ling-Ling; Cai, Lei; Zheng, Yan-Fang; Liu, Hui; Zhang, Pu; Nie, Zhi-Qiang; Liu, Xing-Sheng
2016-03-01
Based on Snell's law and the constant phase in the front of optical field, a design method of the slow axis collimation lens with variable curvature radius is proposed for semiconductor laser bars. Variable radius of the collimator is designed by the transmission angle, and it is demonstrated that the collimator has good beam collimation ability by material with low refractive index. Resorting to the design thought of finite element method, the surface of the collimator has been divided, and it is feasible to be fabricated. This method is applied as an example in collimation of a 976 nm semiconductor laser bar. 6 mrad divergence angle of collimated beam at slow axis is realized by the designed collimation lens with refraction index of 1.51.
Refraction and reflection of diffusion fronts.
Remhof, A; Wijngaarden, R J; Griessen, R
2003-04-11
Diffusion waves form the basis of several measurement technologies in materials science as well as in biological systems. They are, however, so heavily damped that their observation is a real challenge to the experimentalist. We show that accurate information about the refraction-like and reflection-like behavior of diffusion waves can be obtained by studying diffusion fronts. For this we use hydrogen in a metal as a model system and visualize its 2D migration with an optical indicator. The similarities between classical optics and diffusion, in particular, the applicability of Snell's law to diffusive systems are discussed. Our measurements are in good agreement with numerical simulations.
Probing interaction and spatial curvature in the holographic dark energy model
Li, Miao; Li, Xiao-Dong; Wang, Shuang; Wang, Yi; Zhang, Xin E-mail: renzhe@mail.ustc.edu.cn E-mail: wangyi@hep.physics.mcgill.ca
2009-12-01
In this paper we place observational constraints on the interaction and spatial curvature in the holographic dark energy model. We consider three kinds of phenomenological interactions between holographic dark energy and matter, i.e., the interaction term Q is proportional to the energy densities of dark energy (ρ{sub Λ}), matter (ρ{sub m}), and matter plus dark energy (ρ{sub m}+ρ{sub Λ}). For probing the interaction and spatial curvature in the holographic dark energy model, we use the latest observational data including the type Ia supernovae (SNIa) Constitution data, the shift parameter of the cosmic microwave background (CMB) given by the five-year Wilkinson Microwave Anisotropy Probe (WMAP5) observations, and the baryon acoustic oscillation (BAO) measurement from the Sloan Digital Sky Survey (SDSS). Our results show that the interaction and spatial curvature in the holographic dark energy model are both rather small. Besides, it is interesting to find that there exists significant degeneracy between the phenomenological interaction and the spatial curvature in the holographic dark energy model.
Damage Detection in Bridges Using Modal Curvatures: Application to a Real Damage Scenario
NASA Astrophysics Data System (ADS)
ABDEL WAHAB, M. M.; DE ROECK, G.
1999-09-01
Damage detection in civil engineering constructions using the dynamic system parameters has become an important research topic. A direct, fast and inexpensive method is therefore required to evaluate and localize damage using the change in dynamic parameters between the intact and damage states. This paper investigates the application of the change in modal curvatures to detect damage in a prestressed concrete bridge. To establish the method simply supported and continuous beams containing damaged parts at different locations are tested using simulated data. Some important conclusions concerning the computation of the modal curvatures are drawn. A damage indicator called “curvature damage factor” is introduced, in which the difference in curvature mode shape for all modes can be summarized in one number for each measured point. The technique is further applied to a real structure, namely bridge Z24 which lies between the villages Koppigen and Utzenstorf and crosses the highway A1 between Bern and Zurich in Switzerland. In the framework of a Brite-Euram project, the bridge is used as a full-scale specimen and subjected to different damage scenarios in order to introduce damage.
Sim, SeungWoo; Kang, Seung-Ho; Lee, Sang-Hee
2015-02-01
Subterranean termites live underground and build tunnel networks to obtain food and nesting space. After obtaining food, termites return to their nests to transfer it. The efficiency of termite movement through the tunnels is directly connected to their survival. Tunnels should therefore be optimized to ensure highly efficient returns. An optimization factor that strongly affects movement efficiency is tunnel curvature. In the present study, we investigated traveling behavior in tunnels with different curvatures. We then characterized traveling behavior at the level of the individual using hidden Markov models (HMMs) constructed from the experimental data. To observe traveling behavior, we designed 5-cm long artificial tunnels that had different curvatures. The tunnels had widths (W) of 2, 3, or 4mm, and the linear distances between the two ends of the tunnels were (D) 20, 30, 40, or 50mm. High values of D indicate low curvature. We systematically observed the traveling behavior of Coptotermes formosanus shiraki and Reticulitermes speratus kyushuensis and measured the time (τ) required for a termite to pass through the tunnel. Using HMM models, we calculated τ for different tunnels and compared the results with the τ of real termites. We characterized the traveling behavior in terms of transition probability matrices (TPM) and emission probability matrices (EPM) of HMMs. We briefly discussed the construction of a sinusoidal-like tunnels in relation to the energy required for termites to pass through tunnels and provided suggestions for the development of more sophisticated HMMs to better understand termite foraging behavior.
Effect of contact angle on capillary displacement curvatures in pore throats formed by spheres
Mason, G. . Dept. of Chemical Engineering); Morrow, N.R. )
1994-11-01
The curvature of an interface in a pore depends upon the shape of the pore and the operative contact angle that the interface makes with the solid surface. Even relatively simple pores formed by the surfaces of equal spheres have a complex shape including nonaxisymmetric cross-section and converging-diverging geometry. For such pores, a theory for meniscus behavior has been devised that uses a combination of a theory for meniscus curvature in rods together with the toroidal approximation of Purcell. The results of the theory show that converging-diverging geometry tends to compensate for the effect of contact angle. This is because the position at which the nonzero contact angle meniscus has maximum curvature in a converging-diverging pore is not the narrowest part of the pore throat. Due to this compensation, the effect of contact angle on maximum meniscus curvatures for drainage is approximately proportional to cos 2/3 [theta] (rather than the cos [theta] appropriate for cylindrical tubes). Experiments on pores formed by PTFE spheres using partially wetting liquids confirmed the theoretical prediction. Contact angle measurements on the PTFE spheres also demonstrated that, because of microscopic surface roughness, receding contact angles (these being operative with respect to drainage) on ground surfaces are significantly lower than values for smooth surfaces.
Using Surface Curvature to Control the Dimerization of a Surface-Active Protein
NASA Astrophysics Data System (ADS)
Kurylowicz, Martin; Giuliani, Maximiliano; Dutcher, John
2012-02-01
Understanding the influence of surface geometry on adsorbed proteins promises new possibilities in biophysics, such as topographical catalysis, molecular recognition of geometric cues, and modulations of oligomerization or ligand binding. We have created nano-textured hydrophobic surfaces that are stable in buffer by spin coating polystyrene (PS) nanoparticles (NPs) to form patchy NP monolayers on a PS substrate, yielding flat and highly curved areas on the same sample. Moreover, we have separated surface chemistry from texture by floating a 10 nm thick film of monodisperse PS onto the NP-functionalized surface. Using Single Molecule Force Spectroscopy we have compared in situ the distribution of detachment lengths for proteins on curved surfaces to that measured on flat surfaces. We have shown that β-Lactoglobulin (β-LG), a surface-active protein which helps to stabilize oil droplets in milk, forms dimers on both flat PS surfaces and surfaces with a radius of curvature of 100 nm, whereas β-LG monomers exist for more highly curved surfaces with radii of curvature of 25 and 40 nm. It is surprising that rather large radii of curvature have such a strong influence on proteins whose radius is only ˜2 nm. Furthermore, the transition from dimer to monomer with changes in surface curvature offers promising applications for proteins whose function can be modified by their oligomerization state.
Flow structure in front of the broad-crested weir
NASA Astrophysics Data System (ADS)
Zachoval, Zbyněk; Roušar, Ladislav
2015-05-01
The paper deals with research focused on description of flow structure in front of broad-crested weir. Based on experimental measurement, the flow structure in front of the weir (the recirculation zone of flow and tornado vortices) and flow structure on the weir crest has been described. The determined flow character has been simulated using numerical model and based on comparing results the suitable model of turbulence has been recommended.
Controllable curvature from planar polymer sheets in response to light.
Hubbard, Amber M; Mailen, Russell W; Zikry, Mohammed A; Dickey, Michael D; Genzer, Jan
2017-02-24
The ability to change shape and control curvature in 3D structures starting from planar sheets can aid in assembly and add functionality to an object. Herein, we convert planar sheets of shape memory polymers (SMPs) into 3D objects with controllable curvature by dictating where the sheets shrink. Ink patterned on the surface of the sheet absorbs infrared (IR) light, resulting in localized heating, and the material shrinks locally wherever the temperature exceeds the activation temperature, Ta. We introduce two different mechanisms for controlling curvature within SMP sheets. The 'direct' mechanism uses localized shrinkage to induce curvature only in regions patterned with ink. The 'indirect' mechanism uses localized shrinkage in regions patterned with ink to induce curvature in neighboring regions without ink through a balance of internal stresses. Finite element analysis predicts the final shape of the polymer sheets with excellent qualitative agreement with experimental studies. Results from this study show that curvature can be controlled by the distribution and darkness of the ink pattern on the polymer sheet. Additionally, we utilize the direct and indirect curvature mechanisms to demonstrate the formation and actuation of gripper devices, which represent the potential utility of this approach.
Effect of curvature on domain wall motion in elliptical nanorings
NASA Astrophysics Data System (ADS)
Kaya, Fikriye Idil; Bickel, Jessica; Aidala, Katherine
2014-03-01
Understanding domain wall (DW) motion in ferromagnetic nanostructures is important to realize proposed magnetic data storage and logic devices. We investigate the effect of curvature on DW pinning and motion by studying elliptical rings using micromagnetic simulations. Elliptical rings with constant width have varying curvature, with the lowest curvature at the minor axis, and the greatest curvature at the major axis. DWs can be created at any angular position within the ellipse by the application of an appropriate uniform magnetic field. However, only some of these positions are stable when the field is removed. We study the stability and depinning of the DWs by applying a slowly increasing elliptical magnetic field to determine the magnitude of the field at which the DWs begin to move. By varying the major to minor axis ratio, we examine the effect of curvature on DW pinning. A larger field is required to move DWs in regions of higher curvature (near the major axis) than lower curvature (near the minor axis). Overall, we see that increasing the major to minor axis ratio of elliptical nanorings requires increasing field strength to depin the DWs along the major axis. Work supported in part by NSF DMR-1207924 and NSF CMMI-1025020. Simulations performed at the CNS computational facilities at Harvard University, a member of the NNIN supported by NSF Award No. ECS-0335765.
On 3-gauge transformations, 3-curvatures, and Gray-categories
Wang, Wei
2014-04-15
In the 3-gauge theory, a 3-connection is given by a 1-form A valued in the Lie algebra g, a 2-form B valued in the Lie algebra h, and a 3-form C valued in the Lie algebra l, where (g,h,l) constitutes a differential 2-crossed module. We give the 3-gauge transformations from one 3-connection to another, and show the transformation formulae of the 1-curvature 2-form, the 2-curvature 3-form, and the 3-curvature 4-form. The gauge configurations can be interpreted as smooth Gray-functors between two Gray 3-groupoids: the path 3-groupoid P{sub 3}(X) and the 3-gauge group G{sup L} associated to the 2-crossed module L, whose differential is (g,h,l). The derivatives of Gray-functors are 3-connections, and the derivatives of lax-natural transformations between two such Gray-functors are 3-gauge transformations. We give the 3-dimensional holonomy, the lattice version of the 3-curvature, whose derivative gives the 3-curvature 4-form. The covariance of 3-curvatures easily follows from this construction. This Gray-categorical construction explains why 3-gauge transformations and 3-curvatures have the given forms. The interchanging 3-arrows are responsible for the appearance of terms with the Peiffer commutator (, )
Active optics: variable curvature mirrors for ELT laser guide star refocusing systems
NASA Astrophysics Data System (ADS)
Challita, Zalpha; Hugot, Emmanuel; Madec, Fabrice; Ferrari, Marc; Le Mignant, David; Vivès, Sébastien; Cuby, Jean-Gabriel
2011-10-01
The future generation of Extremely Large Telescopes will require a complex combination of technologies for adaptive optics (AO) systems assisted by laser guide stars (LGS). In this context, the distance from the LGS spot to the telescope pupil ranges from about 80 to 200 km, depending on the Sodium layer altitude and the elevation of the telescope. This variation leads to a defocusing effect on the LGS wave-front sensor which needs to be compensated. We propose an active mirror able to compensate for this variation, based on an original optical design including this active optics component. This LGS Variable Curvature Mirror (LGS-VCM) is a 120 mm spherical active mirror able to achieve 820 μm deflection sag with an optical quality better than 150 nm RMS, allowing the radius of curvature variation from F/12 to F/2. Based on elasticity theory, the deformation of the metallic mirror is provided by an air pressure applied on a thin meniscus with a variable thickness distribution. In this article, we detail the analytical development leading to the specific geometry of the active component, the results of finite element analysis and the expected performances in terms of surface error versus the range of refocalisation. Three prototypes have been manufactured to compare the real behavior of the mirror and the simulations data. Results obtained on the prototypes are detailed, showing that the deformation of the VCM is very close to the simulation, and leads to a realistic active concept.
Influence of Coanda surface curvature on performance of bladeless fan
NASA Astrophysics Data System (ADS)
Li, Guoqi; Hu, Yongjun; Jin, Yingzi; Setoguchi, Toshiaki; Kim, Heuy Dong
2014-10-01
The unique Coanda surface has a great influence on the performance of bladeless fan. However, there is few studies to explain the relationship between the performance and Coanda surface curvature at present. In order to gain a qualitative understanding of effect of the curvature on the performance of bladeless fan, numerical studies are performed in this paper. Firstly, three-dimensional numerical simulation is done by Fluent software. For the purpose to obtain detailed information of the flow field around the Coanda surface, two-dimensional numerical simulation is also conducted. Five types of Coanda surfaces with different curvature are designed, and the flow behaviour and the performance of them are analyzed and compared with those of the prototype. The analysis indicates that the curvature of Coanda surface is strongly related to blowing performance, It is found that there is an optimal curvature of Coanda surfaces among the studied models. Simulation result shows that there is a special low pressure region. With increasing curvature in Y direction, several low pressure regions gradually enlarged, then begin to merge slowly, and finally form a large area of low pressure. From the analyses of streamlines and velocity angle, it is found that the magnitude of the curvature affects the flow direction and reasonable curvature can induce fluid flow close to the wall. Thus, it leads to that the curvature of the streamlines is consistent with that of Coanda surface. Meanwhile, it also causes the fluid movement towards the most suitable direction. This study will provide useful information to performance improvements of bladeless fans.
A modeling study of convection initiation prior to the merger of a sea-breeze front and a gust front
NASA Astrophysics Data System (ADS)
Abulikemu, Abuduwaili; Xu, Xin; Wang, Yuan; Ding, Jinfeng; Zhang, Shushi; Shen, Wenqiang
2016-12-01
Convection initiation (CI) prior to the merger of a sea-breeze front (SBF) with a gust front (GF) in North China is investigated using a real-data Weather Research and Forecasting (WRF) simulation with a high resolution of 444.4 m. The overall evolution of the GF and SBF is well reproduced by the simulation. The GF was produced by the decaying convective storm over northern Beijing, while the SBF came from the Bohai Sea. Several convective cells were generated between the two fronts even though they were still about 25-30 km far away from each other. During the development of these cells, the low-level convergence and conditional instability averaged within the intermediate area between the two fronts were enhanced significantly, both of which favored the initiation of convection. Vertical momentum budgets were conducted in the intermediate area as well as along the backward trajectories of parcels within a selected convective cell. The vertical acceleration was decomposed into dynamic and buoyant components, respectively. The diagnostic results showed that the dynamic acceleration dominated in the low level, while buoyant acceleration became evident only when the parcel reached a high altitude above 2 km. Therefore the dynamic forcing appeared to be more relevant to CI. The dynamic acceleration was further decomposed into four terms based on anelastic approximation. The positive dynamic acceleration was mainly caused by fluid extension associated with the low-level convergence, while fluid twisting in the vertical contributed negatively to the dynamic acceleration. The other two terms related to horizontal curvature and height variation of density were negligibly small.
Holomorphic bisectional curvatures, supersymmetry breaking, and Affleck-Dine baryogenesis
NASA Astrophysics Data System (ADS)
Dutta, Bhaskar; Sinha, Kuver
2012-11-01
Working in D=4, N=1 supergravity, we utilize relations between holomorphic sectional and bisectional curvatures of Kahler manifolds to constrain Affleck-Dine baryogenesis. We show the following no-go result: Affleck-Dine baryogenesis cannot be performed if the holomorphic sectional curvature at the origin is isotropic in tangent space; as a special case, this rules out spaces of constant holomorphic sectional curvature (defined in the above sense) and in particular maximally symmetric coset spaces. We also investigate scenarios where inflationary supersymmetry breaking is identified with the supersymmetry breaking responsible for mass splitting in the visible sector, using conditions of sequestering to constrain manifolds where inflation can be performed.
Dynamic Curvature Steering Control for Autonomous Vehicle: Performance Analysis
NASA Astrophysics Data System (ADS)
Aizzat Zakaria, Muhammad; Zamzuri, Hairi; Amri Mazlan, Saiful
2016-02-01
This paper discusses the design of dynamic curvature steering control for autonomous vehicle. The lateral control and longitudinal control are discussed in this paper. The controller is designed based on the dynamic curvature calculation to estimate the path condition and modify the vehicle speed and steering wheel angle accordingly. In this paper, the simulation results are presented to show the capability of the controller to track the reference path. The controller is able to predict the path and modify the vehicle speed to suit the path condition. The effectiveness of the controller is shown in this paper whereby identical performance is achieved with the benchmark but with extra curvature adaptation capabilites.
Motion on constant curvature spaces and quantization using Noether symmetries.
Bracken, Paul
2014-12-01
A general approach is presented for quantizing a metric nonlinear system on a manifold of constant curvature. It makes use of a curvature dependent procedure which relies on determining Noether symmetries from the metric. The curvature of the space functions as a constant parameter. For a specific metric which defines the manifold, Lie differentiation of the metric gives these symmetries. A metric is used such that the resulting Schrödinger equation can be solved in terms of hypergeometric functions. This permits the investigation of both the energy spectrum and wave functions exactly for this system.
LPG-based sensor for curvature and vibration
NASA Astrophysics Data System (ADS)
Nascimento, I. M.; Chesini, G.; Baptista, J. M.; Cordeiro, Cristiano M. B.; Jorge, P. A. S.
2016-05-01
A long-period grating (LPG) written on a standard single mode fiber is investigated as a curvature and vibration sensor. It is demonstrated a high sensitivity to applied curvature and the possibility to monitor vibration in a wide range of frequencies from 30 Hz to 2000 Hz. The system was tested using an intensity based interrogation scheme with the LPG sensor operating in the curvature regime. Results have shown a reproducible frequency discrimination in the 30 Hz to 2000 Hz, with resolutions between 11 mHz and 913 mHz. Frequency retrieval could be performed independent of temperature up to 86 °C.
Inconsistency of scale-invariant curvature coupled to gravity
Zoller, D. )
1990-10-29
We show that the scale-invariant curvature action for paths, the point-particle version of Polyakov's extrinsic-curvature action for surfaces, does not couple consistently to gravity. The curvature action for paths yields a massless representation of the Poincare group with fixed helicity and so potentially provides a description of single photons and gravitons. We present a physical interpretation of the inconsistency in terms of the nonlocalizability of the photon and point out a conceptual kinship with the local supersymmetry of a spinning particle.
Inconsistency of scale-invariant curvature coupled to gravity
NASA Astrophysics Data System (ADS)
Zoller, D.
1990-10-01
We show that the scale-invariant curvature action for paths, the point-particle version of Polyakov's extrinsic-curvature action for surfaces, does not couple consistently to gravity. The curvature action for paths yields a massless representation of the Poincaré group with fixed helicity and so potentially provides a description of single photons and gravitons. We present a physical interpretation of the inconsistency in terms of the nonlocalizability of the photon and point out a conceptual kinship with the local supersymmetry of a spinning particle.
Characterizing the curvature and its first derivative for imperfect fluids
NASA Astrophysics Data System (ADS)
Machado Ramos, Maria da Piedade
2017-04-01
The curvature tensor and its derivatives up to any order can be covariantly characterized by a minimal set of spinor quantities. On the other hand it might be useful, particularly in cosmology, to describe the geometry of a spacetime in a (1+3) formalism, based on an invariantly defined fluid velocity. In this work, we consider an imperfect fluid possessing both isotropic and anisotropic pressure. For these fluids, we determine the (1+3) matter terms of the curvature as well as the parts of the first order covariant derivative of the curvature (\
Enhancing magnetoelectric effect via the curvature of composite cylinder
NASA Astrophysics Data System (ADS)
Wang, H. M.; Pan, E.; Chen, W. Q.
2010-05-01
We solved analytically the magnetoelectric (ME) effect in a bilayered piezoelectric/piezomagnetic cylinder under harmonic excitation. We revealed that at a fixed thickness ratio of the layers, the static or low-frequency ME effect can be substantially enhanced by increasing the curvature of the cylinder. In the megahertz frequency domain, on the other hand, we observed that the peak ME effect can be considerably increased by decreasing the curvature. We further showed that at a fixed curvature, the ME effect can be tuned to be around the resonant frequency for giant output by varying the boundary condition and thickness ratio.
Curvature-driven assembly in soft matter.
Liu, Iris B; Sharifi-Mood, Nima; Stebe, Kathleen J
2016-07-28
Control over the spatial arrangement of colloids in soft matter hosts implies control over a wide variety of properties, ranging from the system's rheology, optics, and catalytic activity. In directed assembly, colloids are typically manipulated using external fields to form well-defined structures at given locations. We have been developing alternative strategies based on fields that arise when a colloid is placed within soft matter to form an inclusion that generates a potential field. Such potential fields allow particles to interact with each other. If the soft matter host is deformed in some way, the potential allows the particles to interact with the global system distortion. One important example is capillary assembly of colloids on curved fluid interfaces. Upon attaching, the particle distorts that interface, with an associated energy field, given by the product of its interfacial area and the surface tension. The particle's capillary energy depends on the local interface curvature. We explore this coupling in experiment and theory. There are important analogies in liquid crystals. Colloids in liquid crystals elicit an elastic energy response. When director fields are moulded by confinement, the imposed elastic energy field can couple to that of the colloid to define particle paths and sites for assembly. By improving our understanding of these and related systems, we seek to develop new, parallelizable routes for particle assembly to form reconfigurable systems in soft matter that go far beyond the usual close-packed colloidal structures.This article is part of the themed issue 'Soft interfacial materials: from fundamentals to formulation'.
The Arctic Front in the Fram Strait in autumn 2011
NASA Astrophysics Data System (ADS)
Ullgren, Jenny; Falck, Eva; Beszczynska-Möller, Agnieszka; Sagen, Hanne
2016-04-01
The front between Atlantic water carried northward by the main branch of the West Spitsbergen Current and the cooler, fresher Arctic domain in the central Fram Strait, here called the Arctic Front, is important because of the exchange of heat and salt across it. The marked water mass boundary and the dynamics of the front also profoundly affect the living conditions for marine organisms. A northwest-to-southeast transect across the Arctic Front with concurrent shipboard and glider measurements was done in September 2011. The CTD data, nutrient and pigment samples, and underway ADCP data from the research cruise are complemented by the glider observations of temperature and salinity at higher horizontal resolution. In addition, images from the ship's scientific echo sounder are used to qualitatively describe the water column structure and distribution of marine organisms along the transect. Crossing the front from northwest to southeast, the near-surface (5 m) temperature increased by more than 4°C and salinity increased by 0.98 PSU between stations 19 km apart. The front was thus clearly marked in salinity and temperature in the upper 200 m, but below the surface layer it was largely density compensated. The highest chlorophyll-a concentrations were found in subsurface maxima on the Arctic side of the front. We investigate the hydrographic structure of the front, considering properties relevant to cross-frontal exchange and mixing. We also assess the environmental conditions on each side of the front - for example mixed layer depths, nutrient availability, and bio-optical properties - and their implications for marine life.
Estimation of surface curvature from full-field shape data using principal component analysis
NASA Astrophysics Data System (ADS)
Sharma, Sameer; Vinuchakravarthy, S.; Subramanian, S. J.
2017-01-01
Three-dimensional digital image correlation (3D-DIC) is a popular image-based experimental technique for estimating surface shape, displacements and strains of deforming objects. In this technique, a calibrated stereo rig is used to obtain and stereo-match pairs of images of the object of interest from which the shapes of the imaged surface are then computed using the calibration parameters of the rig. Displacements are obtained by performing an additional temporal correlation of the shapes obtained at various stages of deformation and strains by smoothing and numerically differentiating the displacement data. Since strains are of primary importance in solid mechanics, significant efforts have been put into computation of strains from the measured displacement fields; however, much less attention has been paid to date to computation of curvature from the measured 3D surfaces. In this work, we address this gap by proposing a new method of computing curvature from full-field shape measurements using principal component analysis (PCA) along the lines of a similar work recently proposed to measure strains (Grama and Subramanian 2014 Exp. Mech. 54 913-33). PCA is a multivariate analysis tool that is widely used to reveal relationships between a large number of variables, reduce dimensionality and achieve significant denoising. This technique is applied here to identify dominant principal components in the shape fields measured by 3D-DIC and these principal components are then differentiated systematically to obtain the first and second fundamental forms used in the curvature calculation. The proposed method is first verified using synthetically generated noisy surfaces and then validated experimentally on some real world objects with known ground-truth curvatures.
Antarctic Ice-Shelf Front Dynamics from ICESat
NASA Technical Reports Server (NTRS)
Robbins, John W.; Zwally, H. Jay; Saba, Jack L.; Yi, Donghui
2012-01-01
Time variable elevation profiles from ICESat Laser Altimetry over the period 2003-2009 provide a means to quantitatively detect and track topographic features on polar ice surfaces. The results of this study provide a measure of the horizontal motion of ice-shelf fronts. We examine the time histories of elevation profiles crossing the ice fronts of the Ross, Ronne, Filchner, Riiser-Larson and Fimbul shelves. This provides a basis for estimating dynamics in two dimensions, i.e. in elevation and horizontally in the along-track direction. Ice front velocities, corrected for ground-track intersection angle, range from nearly static to 1.1 km/yr. In many examples, a decrease in elevation up to 1 m/yr near the shelf frontis also detectable. Examples of tabular calving along shelf fronts are seen in some elevation profiles and are confirmed by corresponding MODIS imagery.
Stability of the cylindrical shell of variable curvature
NASA Technical Reports Server (NTRS)
Marguerre, Karl
1951-01-01
This report is a first attempt to devise a calculation method for representing the buckling behavior of cylindrical shells of variable curvature. The problem occurs, for instance, in dimensioning wing noses, the stability of which is decisively influenced by the variability of curvature. The calculation is made possible by simplifying the stability equations (permissible for the shell of small curvature) and by assuming that the curvature 1/R as a function of the arc lengths can be represented by a very few Fourier terms. The formulas for the special case of an ellipse-like half oval with an axis ratio 1/3 ?= e ?= 1 under compression in longitudinal direction,shear, and a combination of shear and compression were evaluated. However, the results can also be applied approximately to an unsymmetrical oval-shell segment under compression, shear, and bending so that the numerical values contained in the diagrams 10 to 12 represent directly dimensioning data for the wing nose.
Curvature Control of Silicon Microlens for THz Dielectric Antenna
NASA Technical Reports Server (NTRS)
Lee, Choonsup; Chattopadhyay, Goutam; Cooper, Ken; Mehdi, Imran
2012-01-01
We have controlled the curvature of silicon microlens by changing the amount of photoresist in order to microfabricate hemispherical silicon microlens which can improve the directivity and reduce substrate mode losses.
Raft Formation in Lipid Bilayers Coupled to Curvature
Sadeghi, Sina; Müller, Marcus; Vink, Richard L.C.
2014-01-01
We present computer simulations of a membrane in which the local composition is coupled to the local membrane curvature. At high temperatures (i.e., above the temperature of macroscopic phase separation), finite-sized transient domains are observed, reminiscent of lipid rafts. The domain size is in the range of hundred nanometers, and set by the membrane elastic properties. These findings are in line with the notion of the membrane as a curvature-induced microemulsion. At low temperature, the membrane phase separates. The transition to the phase-separated regime is continuous and belongs to the two-dimensional Ising universality class when the coupling to curvature is weak, but becomes first-order for strong curvature-composition coupling. PMID:25296311
Spacetime curvature and the Higgs stability during inflation.
Herranen, M; Markkanen, T; Nurmi, S; Rajantie, A
2014-11-21
It has been claimed that the electroweak vacuum may be unstable during inflation due to large fluctuations of the order H in the case of a high inflationary scale as suggested by BICEP2. We compute the standard model Higgs effective potential including UV-induced curvature corrections at one-loop level. We find that for a high inflationary scale a large curvature mass is generated due to renormalization group running of nonminimal coupling ξ, which either stabilizes the potential against fluctuations for ξEW≳6×10(-2), or destabilizes it for ξEW≲2×10(-2) when the generated curvature mass is negative. Only in the narrow intermediate region may the effect of the curvature mass be significantly smaller.
16. Detail of curvature of northern parapet, with 1932 concrete ...
16. Detail of curvature of northern parapet, with 1932 concrete extension of parapet in foreground, facing east. - Dubbs Bridge, Spinnerstown Road (State Route 2031) spanning Hosensack Creek, Dillingerville, Lehigh County, PA
Bacterial cell curvature through mechanical control of cell growth
Cabeen, Matthew T; Charbon, Godefroid; Vollmer, Waldemar; Born, Petra; Ausmees, Nora; Weibel, Douglas B; Jacobs-Wagner, Christine
2009-01-01
The cytoskeleton is a key regulator of cell morphogenesis. Crescentin, a bacterial intermediate filament-like protein, is required for the curved shape of Caulobacter crescentus and localizes to the inner cell curvature. Here, we show that crescentin forms a single filamentous structure that collapses into a helix when detached from the cell membrane, suggesting that it is normally maintained in a stretched configuration. Crescentin causes an elongation rate gradient around the circumference of the sidewall, creating a longitudinal cell length differential and hence curvature. Such curvature can be produced by physical force alone when cells are grown in circular microchambers. Production of crescentin in Escherichia coli is sufficient to generate cell curvature. Our data argue for a model in which physical strain borne by the crescentin structure anisotropically alters the kinetics of cell wall insertion to produce curved growth. Our study suggests that bacteria may use the cytoskeleton for mechanical control of growth to alter morphology. PMID:19279668
Curvature-Squared Cosmology In The First-Order Formalism
NASA Technical Reports Server (NTRS)
Shahid-Saless, Bahman
1993-01-01
Paper presents theoretical study of some of general-relativistic ramifications of gravitational-field energy density proportional to R - alpha R(exp 2) (where R is local scalar curvature of space-time and alpha is a constant).
Uniform background curvature: Foam families and frustrated discs
NASA Astrophysics Data System (ADS)
Modes, Carl Douglas
The introduction of background curvature to systems in soft condensed matter, and across all of physics, has a long standing history of success. Particularly in cases where the role of curvature is a surprise, a great deal of new insight may be derived from this technique. This thesis carries on in that tradition, applying uniform background curvature to study varied systems. The glass transition of amorphous materials, and the hard sphere interactions that underlie it, is modeled with hard discs in a space of constant negative curvature. We examine random packing on negatively curved, triply periodic surfaces. Continuous families of Plateau's Laws-commensurate foam bubbles are generated by conformal projection of regular foams in positively-curved space.
Three dimensional computer vision: Potential applications with curvature tracking
Sanford, Adam
1996-05-01
The purpose of this project is to develop a method of tracking data points for computer vision systems using curvature analysis. This is of particular importance to fellow researchers at the Lab, who have developed a markerless video computer vision system and are in need of such a method to track data points. A three dimensional viewing program was created to analyze the geometry of surface patches. Virtual surfaces were plotted and processed by the program to determine the Mean and Gaussian Curvature parameters for each point on the surface, thus defining each point`s surface geometry type. The same computer processes are then applied to each frame of data acquired by the computer vision system to find surface {open_quotes}landmarks{close_quotes} that hold constant curvature during motion. Preliminary results indicate that curvature analysis shows great promise and could solve the tracking dilemma faced by those in the field of markerless imaging systems.
Modeling of stress-induced curvature in surface-micromachined devices
NASA Astrophysics Data System (ADS)
Cowan, William D.; Bright, Victor M.; Elvin, Alex A.; Koester, David A.
1997-09-01
This paper compares measured to modeled stress-induced curvature of simple piston micromirrors. Two similar flexure-beam micromirror designs were fabricate using the 11th DARPA-supported multi-user MEMS processes (MUMPs) run. The test devices vary only in the MUMPs layers used for fabrication. In one case the mirror plate is the 1.5 micrometers thick Poly2 layer. The other mirror design employs stacked Poly1 and Poly2 layers for a total thickness of 3.5 micrometers . Both mirror structures are covered with the standard MUMPs metallization of approximately 200 angstrom of chromium and 0.5 micrometers of gold. Curvature of these devices was measured to within +/- 5 nm with a computer controlled microscope laser interferometer system. As intended, the increased thickness of the stacked polysilicon layers reduces the mirror curvature by a factor of 4. The two micromirror designs were modeled using IntelliCAD, a commercial CAD system for MEMS. The basis of analysis was the finite element method. Simulated results using MUMPs 11 film parameters showed qualitative agreement with measured data, but obvious quantitative differences. Subsequent remeasurement of the metal stress and use of the new value significantly improved model agreement with the measured data. The paper explores the effect of several film parameters on the modeled structures. Implications for MEMS film metrology, and test structures are considered.
ERIC Educational Resources Information Center
Perry, Jim
1995-01-01
Discussion of management styles and front-end analysis focuses on a review of Douglas McGregor's theories. Topics include Theories X, Y, and Z; leadership skills; motivational needs of employees; intrinsic and extrinsic rewards; and faulty implementation of instructional systems design processes. (LRW)
Multiple WH-Fronting Constructions.
ERIC Educational Resources Information Center
Rudin, Catherine
The unique position of WH words in Slavic languages is discussed, with specific reference to Bulgarian and Serbo-Croatian. The multiple fronting characteristics of Bulgarian and Serbo-Croatian differ in terms of the following positions and behaviors: extraction from embedded questions; clitic placement and other indications of constituent status;…
Biological Activity at Oceanic Fronts.
1985-12-01
al. (1974) in a tidal (shallow sea) front in the English Channel. Most interestingly, a small *-. S jellyfish caught in the downwelling zone sank 28 m...and R.P. Harris. 1984. Photosynthesis, respiration and nitrogen supply of plankton populations in stratified, frontal, and tidally mixed she’-; waters
Fluctuation-controlled front propagation
NASA Astrophysics Data System (ADS)
Ridgway, Douglas Thacher
1997-09-01
A number of fundamental pattern-forming systems are controlled by fluctuations at the front. These problems involve the interaction of an infinite dimensional probability distribution with a strongly nonlinear, spatially extended pattern-forming system. We have examined fluctuation-controlled growth in the context of the specific problems of diffusion-limited growth and biological evolution. Mean field theory of diffusion-limited growth exhibits a finite time singularity. Near the leading edge of a diffusion-limited front, this leads to acceleration and blowup. This may be resolved, in an ad hoc manner, by introducing a cutoff below which growth is weakened or eliminated (8). This model, referred to as the BLT model, captures a number of qualitative features of global pattern formation in diffusion-limited aggregation: contours of the mean field match contours of averaged particle density in simulation, and the modified mean field theory can form dendritic features not possible in the naive mean field theory. The morphology transition between dendritic and non-dendritic global patterns requires that BLT fronts have a Mullins-Sekerka instability of the wavefront shape, in order to form concave patterns. We compute the stability of BLT fronts numerically, and compare the results to fronts without a cutoff. A significant morphological instability of the BLT fronts exists, with a dominant wavenumber on the scale of the front width. For standard mean field fronts, no instability is found. The naive and ad hoc mean field theories are continuum-deterministic models intended to capture the behavior of a discrete stochastic system. A transformation which maps discrete systems into a continuum model with a singular multiplicative noise is known, however numerical simulations of the continuum stochastic system often give mean field behavior instead of the critical behavior of the discrete system. We have found a new interpretation of the singular noise, based on maintaining
Curvature-driven acceleration: a utopia or a reality?
NASA Astrophysics Data System (ADS)
Das, Sudipta; Banerjee, Narayan; Dadhich, Naresh
2006-06-01
The present work shows that a combination of nonlinear contributions from the Ricci curvature in Einstein field equations can drive a late time acceleration of expansion of the universe. The transit from the decelerated to the accelerated phase of expansion takes place smoothly without having to resort to a study of asymptotic behaviour. This result emphasizes the need for thorough and critical examination of models with nonlinear contribution from the curvature.
Hedgehogs in higher dimensional gravity with curvature self-interactions
NASA Astrophysics Data System (ADS)
Giovannini, Massimo
2001-04-01
Static solutions of the higher dimensional Einstein-Hilbert gravity supplemented by quadratic curvature self-interactions are discussed in the presence of hedgehog configurations along the transverse dimensions. The quadratic part of the action is parametrized in terms of the (ghost-free) Euler-Gauss-Bonnet curvature invariant. Spherically symmetric profiles of the transverse metric admit exponentially decaying warp factors both for positive and negative bulk cosmological constants.
Fresnel diffractive imaging: Experimental study of coherence and curvature
Whitehead, L. W.; Williams, G. J.; Quiney, H. M.; Nugent, K. A.; Peele, A. G.; Paterson, D.; Jonge, M. D. de; McNulty, I.
2008-03-01
A Fresnel coherent diffractive imaging experiment is performed using a pinhole as a test object. The experimental parameters of the beam curvature and coherence length of the illuminating radiation are varied to investigate their effects on the reconstruction process. It is found that a sufficient amount of curvature across the sample strongly ameliorates the effects of low coherence, even when the sample size exceeds the coherence length.
Non-additive compositional curvature energetics of lipid bilayers
Sodt, A.J.; Venable, R.M.; Lyman, E.; Pastor, R.W.
2016-01-01
The unique properties of the individual lipids that compose biological membranes together determine the energetics of the surface. The energetics of the surface in turn govern the formation of membrane structures and membrane reshaping processes, and will thus underlie cellular-scale models of viral fusion, vesicle-dependent transport, and lateral organization relevant to signaling. The spontaneous curvature, to the best of our knowledge, is always assumed to be additive. The letter describes observations from simulations of unexpected non-additive compositional curvature energetics of two lipids essential to the plasma membrane: sphingomyelin and cholesterol. A model is developed that connects molecular interactions to curvature stress, and which explains the role of local composition. Cholesterol is shown to lower the number of effective Kuhn segments of saturated acyl chains, reducing lateral pressure below the neutral surface of bending and favoring positive curvature. The effect is not observed for unsaturated (flexible) acyl chains. Likewise, hydrogen bonding between sphingomyelin lipids leads to positive curvature, but only at sufficient concentration, below which the lipid prefers negative curvature. PMID:27715135
Curvature reduces bending strains in the quokka femur
McCabe, Kyle; Henderson, Keith; Pantinople, Jess; Milne, Nick
2017-01-01
This study explores how curvature in the quokka femur may help to reduce bending strain during locomotion. The quokka is a small wallaby, but the curvature of the femur and the muscles active during stance phase are similar to most quadrupedal mammals. Our hypothesis is that the action of hip extensor and ankle plantarflexor muscles during stance phase place cranial bending strains that act to reduce the caudal curvature of the femur. Knee extensors and biarticular muscles that span the femur longitudinally create caudal bending strains in the caudally curved (concave caudal side) bone. These opposing strains can balance each other and result in less strain on the bone. We test this idea by comparing the performance of a normally curved finite element model of the quokka femur to a digitally straightened version of the same bone. The normally curved model is indeed less strained than the straightened version. To further examine the relationship between curvature and the strains in the femoral models, we also tested an extra-curved and a reverse-curved version with the same loads. There appears to be a linear relationship between the curvature and the strains experienced by the models. These results demonstrate that longitudinal curvature in bones may be a manipulable mechanism whereby bone can induce a strain gradient to oppose strains induced by habitual loading. PMID:28348929
Nanoscale Membrane Curvature detected by Polarized Localization Microscopy
NASA Astrophysics Data System (ADS)
Kelly, Christopher; Maarouf, Abir; Woodward, Xinxin
Nanoscale membrane curvature is a necessary component of countless cellular processes. Here we present Polarized Localization Microscopy (PLM), a super-resolution optical imaging technique that enables the detection of nanoscale membrane curvature with order-of-magnitude improvements over comparable optical techniques. PLM combines the advantages of polarized total internal reflection fluorescence microscopy and fluorescence localization microscopy to reveal single-fluorophore locations and orientations without reducing localization precision by point spread function manipulation. PLM resolved nanoscale membrane curvature of a supported lipid bilayer draped over polystyrene nanoparticles on a glass coverslip, thus creating a model membrane with coexisting flat and curved regions and membrane radii of curvature as small as 20 nm. Further, PLM provides single-molecule trajectories and the aggregation of curvature-inducing proteins with super-resolution to reveal the correlated effects of membrane curvature, dynamics, and molecular sorting. For example, cholera toxin subunit B has been observed to induce nanoscale membrane budding and concentrate at the bud neck. PLM reveals a previously hidden and critical information of membrane topology.
NASA Astrophysics Data System (ADS)
RóŻycki, Bartosz; Lipowsky, Reinhard
2016-08-01
Biomimetic and biological membranes consist of molecular bilayers with two leaflets that are typically exposed to different aqueous solutions. We consider solutions of "particles" that experience effectively repulsive interactions with these membranes and form depletion layers in front of the membrane leaflets. The particles considered here are water-soluble, have a size between a few angstrom and a few nanometers as well as a rigid, more or less globular shape, and do neither adsorb onto the membranes nor permeate these membranes. Examples are provided by ions, small sugar molecules, globular proteins, or inorganic nanoparticles with a hydrophilic surface. We first study depletion layers in a hard-core system based on ideal particle solutions as well as hard-wall interactions between these particles and the membrane. For this system, we obtain exact expressions for the coverages and tensions of the two leaflets as well as for the spontaneous curvature of the bilayer membrane. All of these quantities depend linearly on the particle concentrations. The exact results for the hard-core system also show that the spontaneous curvature can be directly deduced from the planar membrane geometry. Our results for the hard-core system apply both to ions and solutes that are small compared to the membrane thickness and to nanoparticles with a size that is comparable to the membrane thickness, provided the particle solutions are sufficiently dilute. We then corroborate the different relationships found for the hard-core system by extensive simulations of a soft-core particle system using dissipative particle dynamics. The simulations confirm the linear relationships obtained for the hard-core system. Both our analytical and our simulation results show that the spontaneous curvature induced by a single particle species can be quite large. When one leaflet of the membrane is exposed, e.g., to a 100 mM solution of glucose, a lipid bilayer can acquire a spontaneous curvature of ±1
Karidas, Premananda; Challa, Krishna Reddy; Nath, Utpal
2015-01-01
The leaf surface usually stays flat, maintained by coordinated growth. Growth perturbation can introduce overall surface curvature, which can be negative, giving a saddle-shaped leaf, or positive, giving a cup-like leaf. Little is known about the molecular mechanisms that underlie leaf flatness, primarily because only a few mutants with altered surface curvature have been isolated and studied. Characterization of mutants of the CINCINNATA-like TCP genes in Antirrhinum and Arabidopsis have revealed that their products help maintain flatness by balancing the pattern of cell proliferation and surface expansion between the margin and the central zone during leaf morphogenesis. On the other hand, deletion of two homologous PEAPOD genes causes cup-shaped leaves in Arabidopsis due to excess division of dispersed meristemoid cells. Here, we report the isolation and characterization of an Arabidopsis mutant, tarani (tni), with enlarged, cup-shaped leaves. Morphometric analyses showed that the positive curvature of the tni leaf is linked to excess growth at the centre compared to the margin. By monitoring the dynamic pattern of CYCLIN D3;2 expression, we show that the shape of the primary arrest front is strongly convex in growing tni leaves, leading to excess mitotic expansion synchronized with excess cell proliferation at the centre. Reduction of cell proliferation and of endogenous gibberellic acid levels rescued the tni phenotype. Genetic interactions demonstrated that TNI maintains leaf flatness independent of TCPs and PEAPODs. PMID:25711708
Karidas, Premananda; Challa, Krishna Reddy; Nath, Utpal
2015-04-01
The leaf surface usually stays flat, maintained by coordinated growth. Growth perturbation can introduce overall surface curvature, which can be negative, giving a saddle-shaped leaf, or positive, giving a cup-like leaf. Little is known about the molecular mechanisms that underlie leaf flatness, primarily because only a few mutants with altered surface curvature have been isolated and studied. Characterization of mutants of the CINCINNATA-like TCP genes in Antirrhinum and Arabidopsis have revealed that their products help maintain flatness by balancing the pattern of cell proliferation and surface expansion between the margin and the central zone during leaf morphogenesis. On the other hand, deletion of two homologous PEAPOD genes causes cup-shaped leaves in Arabidopsis due to excess division of dispersed meristemoid cells. Here, we report the isolation and characterization of an Arabidopsis mutant, tarani (tni), with enlarged, cup-shaped leaves. Morphometric analyses showed that the positive curvature of the tni leaf is linked to excess growth at the centre compared to the margin. By monitoring the dynamic pattern of CYCLIN D3;2 expression, we show that the shape of the primary arrest front is strongly convex in growing tni leaves, leading to excess mitotic expansion synchronized with excess cell proliferation at the centre. Reduction of cell proliferation and of endogenous gibberellic acid levels rescued the tni phenotype. Genetic interactions demonstrated that TNI maintains leaf flatness independent of TCPs and PEAPODs.
NASA Technical Reports Server (NTRS)
Allen, R. W.; Mcruer, D. T.
1977-01-01
A simulation experiment was conducted to determine the effect of reduced visibility on driver lateral (steering) control. The simulator included a real car cab and a single lane road image projected on a screen six feet in front of the driver. Simulated equations of motion controlled apparent car lane position in response to driver steering actions, wind gusts, and road curvature. Six drivers experienced a range of visibility conditions at various speeds with assorted roadmaking configurations (mark and gap lengths). Driver describing functions were measured and detailed parametric model fits were determined. A pursuit model employing a road curvature feedforward was very effective in explaining driver behavior in following randomly curving roads. Sampled-data concepts were also effective in explaining the combined effects of reduced visibility and intermittent road markings on the driver's dynamic time delay. The results indicate the relative importance of various perceptual variables as the visual input to the driver's steering control process is changed.
NASA Astrophysics Data System (ADS)
Pallã S-Sanz, E.; Johnston, T. M. S.; Rudnick, D. L.
2010-12-01
The three-dimensional dynamics in a shallow front are examined using density and current data from two surveys 100 km offshore of Monterey Bay, California. Survey 1 is forced by down-front winds, and both surveys have considerable cross-front density gradients and flow curvature. The maximum Rossby numbers on the dense side reached maxima of +0.60 in survey 1 and +0.45 in survey 2. Downwelling occurs in regions of confluence (frontogenesis) associated with potential vorticity (PV) change and thermal wind imbalance. Streamers of particulate matter and PV are advected southeastward by the frontal jet and downward. Nonlinear Ekman currents advect dense water over light water in the presence of down-front winds, which leads to upwelling along the front and downwelling on the light side of the front. At sites of active ageostrophic secondary circulation (ASC), induced by frontogenesis or Ekman effects, the observed cross-front ageostrophic velocity is consistent with the diagnosed vertical velocity. Furthermore, in survey 2, ageostrophic divergence may play an important role at the curved front, presumably counteracting quasi-geostrophic frontogenesis due to isopycnal confluence. Downward frictional vertical PV flux below the surface extracts PV from the pycnocline and reinforces the frontogenetic vertical PV flux. PV destruction at the surface is inferred from a low PV anomaly below the mixed layer in survey 2. Since the magnitude of the frontogenetic ASC is only twice the magnitude of Ekman suction, external forcing may have a considerable impact on the vertical heat and PV fluxes.
The stability of the iodate-arsenous acid reaction front while advected by Poiseuille flow
NASA Astrophysics Data System (ADS)
Spangler, Robert S.
The competition between stabilizing and destabilizing effects is a motif that occurs in every aspect of the human experience. The coupling between the dynamics of chemical reactions and fluids offers a fruitful context in which to examine the patterns that arise in the presence of this competition. The upward-propagating iodate-arsenous acid front is an example of a system in constant struggle. As it moves upward, it leaves a reacted solution of lesser density behind (and below) it. The system is thus subjected to a Raleigh-Taylor-like instability. On the other hand, the well understood (experimentally and theoretically) relationship between the front speed and the curvature of the front is such that the higher a section of front peaks, the slower it goes. The lower a valley of the front, the faster it goes. Thus, the front has a stabilizing tendency. So a natural question is, will the front remain stable, or will it suffer the fate of a convective instability? The answer is a resounding "it depends." Previous research has shown that the onset of instability occurs when a driving parameter exceeds some critical value Sc. This driving parameter involves the fractional difference in density between the chemical species, the acceleration due to gravity, the wall separation, the viscosity, and the chemical diffusivity. The only variable that the earthbound experimenter is free to alter is the wall separation, and experiments have agreed very well with the predicted value of Sc. These successful experimental and theoretical developments were for the case of a stationary fluid. The next step is to extend the understanding of this dynamic to the case of a moving fluid. In a fluid moving between two no-slip boundaries, the fluid velocity assumes a parabolic (or Poiseuille) profile. An interesting question to ask is how is the stability of the chemical reaction front affected by the imposed fluid motion? The answer is contained in this text.
Reaction front formation in contaminant plumes.
Cribbin, Laura B; Winstanley, Henry F; Mitchell, Sarah L; Fowler, Andrew C; Sander, Graham C
2014-12-15
The formation of successive fronts in contaminated groundwater plumes by subsoil bacterial action is a commonly accepted feature of their propagation, but it is not obviously clear from a mathematical standpoint quite how such fronts are formed or propagate. In this paper we show that these can be explained by combining classical reaction-diffusion theory involving just two reactants (oxidant and reductant), and a secondary reaction in which a reactant on one side of such a front is (re-)formed on the other side of the front via diffusion of its product across the front. We give approximate asymptotic solutions for the reactant profiles, and the propagation rate of the front.
Schwarz, Thomas A.
2006-01-01
Quarks, along with leptons and force carrying particles, are predicted by the Standard Model to be the fundamental constituents of nature. In distinction from the leptons, the quarks interact strongly through the chromodynamic force and are bound together within the hadrons. The familiar proton and neutron are bound states of the light ''up'' and ''down'' quarks. The most massive quark by far, the ''top'' quark, was discovered by the CDF and D0 experiments in March, 1995. The new quark was observed in p$\\bar{p}$ collisions at 1.8 TeV at the Fermilab Tevatron. The mass of the top quark was measured to be 176 ± 13 GeV/c^{2} and the cross section 6.8$+3.6\\atop{-2.4}$ pb. It is the Q = 2/3, T_{3} = +1/2 member of the third generation weak-isospin doublet along with the bottom quark. The top quark is the final Standard Model quark to be discovered. Along with whatever is responsible for electroweak symmetry breaking, top quark physics is considered one of the least understood sectors of the Standard Model and represents a front line of our understanding of particle physics. Currently, the only direct measurements of top quark properties come from the CDF and D0 experiments observing p$\\bar{p}$ collisions at the Tevatron. Top quark production at the Tevatron is almost exclusively by quark-antiquark annihilation, q$\\bar{q}$ → t$\\bar{t}$ (85%), and gluon fusion, gg → t$\\bar{t}$ (15%), mediated by the strong force. The theoretical cross-section for this process is σ_{t$\\bar{t}$} = 6.7 ± 0.8 pb for m_{t} = 175 GeV/c^{2}. Top quarks can also be produced at the Tevatron via q$\\bar{b}$' → tb and qg → q'tb through the weak interaction. The cross section for these processes is lower (3pb) and the signal is much more difficult to isolate as backgrounds are much higher. The top quark is predicted to decay almost exclusively into a W-boson and a bottom quark (t → Wb). The total decay width t → Wb is Λ = 1.50 GeV. This
The influence of reed curvature on the tone quality of lingual organ pipes
NASA Astrophysics Data System (ADS)
Plitnik, G. R.; Angster, J.
2002-11-01
Given certain design constraints, such as the type of stop being voiced and the desired tone quality, reed voicers must use consummate skill to curve each tongue so as to produce the best and most stable tone, as well as maintaining a consistent tone quality across an entire rank of pipes. The curvature given to a reed tongue influences not only the harmonic structure of the steady-state sound, but also the attack. Two fundamentally different types of curvature are typically employed, the chorus reed (trompette) curve (which yields a bright sound) and the smooth-toned curve employed for solo reeds such as the clarinet. This study investigated the effect of reed curvature on the vibration and tone of reed tongues of both types. Two F2 pipes (a trompette and a clarinet) were constructed and voiced with 6 different tongues each to produce a variety of tones. The reed's vibration was measured under typical conditions by laser vibrometer; the pressure waves in the boot and in the shallot were measured by means of one-eighth inch microphones and the emitted sound was recorded at the egress. By performing various measurements simultaneously, phase differences were also determined.
Aslam, T.D.; Bdzil, J.B.
1998-02-01
When the detonation reaction-zone length, {eta}{sub r}, is short in comparison to the dimensions of the explosive piece being burnt, the detonation can be viewed as a propagating surface (or front) separating burnt from unburnt material. If the product of the shock curvature, {kappa} and {eta}{sub r} is small (i.e., the scaled shock curvature satisfies the {vert_bar}{kappa}{eta}{sub r}{vert_bar} {much_lt} 1), then to leading order the speed of this surface, D{sub n}({kappa}) is a function only of {kappa}. It is in this limit that the original version of the asymptotic detonation front theory, called detonation shock dynamics (DSD), derives the propagation law, D{sub n}({kappa}). In this lecture, the authors compare D{sub n}({kappa})-theory with the results obtained with high-resolution direct numerical simulations (DNS), and then use the DNS results to guide the development of extended asymptotic front theories with enhanced predictive capabilities.
System Estimates Radius of Curvature of a Segmented Mirror
NASA Technical Reports Server (NTRS)
Rakoczy, John
2008-01-01
A system that estimates the global radius of curvature (GRoC) of a segmented telescope mirror has been developed for use as one of the subsystems of a larger system that exerts precise control over the displacements of the mirror segments. This GRoC-estimating system, when integrated into the overall control system along with a mirror-segment- actuation subsystem and edge sensors (sensors that measure displacements at selected points on the edges of the segments), makes it possible to control the GROC mirror-deformation mode, to which mode contemporary edge sensors are insufficiently sensitive. This system thus makes it possible to control the GRoC of the mirror with sufficient precision to obtain the best possible image quality and/or to impose a required wavefront correction on incoming or outgoing light. In its mathematical aspect, the system utilizes all the information available from the edge-sensor subsystem in a unique manner that yields estimates of all the states of the segmented mirror. The system does this by exploiting a special set of mirror boundary conditions and mirror influence functions in such a way as to sense displacements in degrees of freedom that would otherwise be unobservable by means of an edge-sensor subsystem, all without need to augment the edge-sensor system with additional metrological hardware. Moreover, the accuracy of the estimates increases with the number of mirror segments.
Waves, instabilities and turbulence properties in Depolarisation Fronts
NASA Astrophysics Data System (ADS)
Lapenta, Giovanni; Goldman, Martin; Newman, David L.; Olshevskyi, Vyacheslav; Eastwood, Jonathan; Divin, Andrey; Pucci, Francesco
2016-04-01
The new mission MMS is currently focusing on the magnetopause but we need to be ready for the study of the tail. An aspect of great importance there are the Dipolarization fronts (DF), formed by reconnection outflows interacting with the pre-existing environment. These regions are host of important energy and wave phenomena [1-3]. Our recent work has investigated these regions via fully kinetic 3D simulations [4-5]. As reported recently on Nature Physics [3], based on 3D fully kinetic simulations started with a well defined x-line, we observe that in the DF reconnection transitions towards a more chaotic regime. In the fronts an instability develops caused by the local gradients of the density and by the unfavourable acceleration and field line curvature. The consequence is the break up of the fronts in a fashion similar to the classical fluid Rayleigh-Taylor instability and the onset of waves and secondary instabilities, transitioning towards a turbulent state. We investigate here especially the wave signatures that are observed in fully 3D simulations, looking for signatures of interchange-type lower hybrid waves [8], of whistler waves [7]. The end result present a vast array of waves and it is best analysed relying on concepts mutated by the turbulence theory. The end result of these waves and particle flows [2,6] are energy exchanges. We evaluate the different terms of the energy exchanges (energy deposition, J.E, and energy fluxes) and evaluate their relative improtance. The results presented are contrasted against existing results [1,9] and will provided useful guidance in analysis of future MMS data. [1] Hamrin, Maria, et al. "The evolution of flux pileup regions in the plasma sheet: Cluster observations." Journal of Geophysical Research: Space Physics 118.10 (2013): 6279-6290. [2] Angelopoulos, V., et al. "Electromagnetic energy conversion at reconnection fronts." Science 341.6153 (2013): 1478-1482. [3] Zhou, Meng, et al. "THEMIS observation of multiple
Weather fronts and acute myocardial infarction
NASA Astrophysics Data System (ADS)
Kveton, Vit
1991-03-01
Some methodological aspects are discussed of the investigation of acute infarct myocarditis (AIM) in relation to weather fronts. Results of a new method of analysis are given. Data were analysed from about the hour of the onset of symptoms, and led to the diagnosis of AIM either immediately or within a few hours or days (3019 cases observed over 4.5 years during 1982 1986 in Plzen, Czechoslovakia). Weather classification was based on three factors (the type of the foregoing front, the type of the subsequent front, the time section of the time interval demarcated by the passage of the surfaces of the fronts). AIM occurrence increased in particular types of weather fronts: (i) by 30% during 7 12 h after a warm front, if the time span between fronts exceeded 24 h; (ii) by 10% in time at least 36 h distant from the foregoing cold or occlusion front and from the succeeding warm or occlusion front; (iii) by 20% during 0 2 h before the passage of the front, provided the foregoing front was not warm and the interval between fronts exceeded 5 h. AIM occurrence decreased by 15% 20% for time span between fronts > 24 h at times 6 11, 6 23 and 6 35 h before a coming warm or occlusion front (for interfrontal intervals 25 48, 49 72 and possibly > 72 h), and also at 12 23 and possibly 12 35 h before a cold front (for intervals 49 72 and possibly > 72 h), if the foregoing front was cold or an occlusion front.
Absence of splash singularities for surface quasi-geostrophic sharp fronts and the Muskat problem.
Gancedo, Francisco; Strain, Robert M
2014-01-14
In this paper, for both the sharp front surface quasi-geostrophic equation and the Muskat problem, we rule out the "splash singularity" blow-up scenario; in other words, we prove that the contours evolving from either of these systems cannot intersect at a single point while the free boundary remains smooth. Splash singularities have been shown to hold for the free boundary incompressible Euler equation in the form of the water waves contour evolution problem. Our result confirms the numerical simulations in earlier work, in which it was shown that the curvature blows up because the contours collapse at a point. Here, we prove that maintaining control of the curvature will remove the possibility of pointwise interphase collapse. Another conclusion that we provide is a better understanding of earlier work in which squirt singularities are ruled out; in this case, a positive volume of fluid between the contours cannot be ejected in finite time.
Absence of splash singularities for surface quasi-geostrophic sharp fronts and the Muskat problem
Gancedo, Francisco; Strain, Robert M.
2014-01-01
In this paper, for both the sharp front surface quasi-geostrophic equation and the Muskat problem, we rule out the “splash singularity” blow-up scenario; in other words, we prove that the contours evolving from either of these systems cannot intersect at a single point while the free boundary remains smooth. Splash singularities have been shown to hold for the free boundary incompressible Euler equation in the form of the water waves contour evolution problem. Our result confirms the numerical simulations in earlier work, in which it was shown that the curvature blows up because the contours collapse at a point. Here, we prove that maintaining control of the curvature will remove the possibility of pointwise interphase collapse. Another conclusion that we provide is a better understanding of earlier work in which squirt singularities are ruled out; in this case, a positive volume of fluid between the contours cannot be ejected in finite time. PMID:24347645
Light-Front Holography and AdS/QCD Correspondence
Brodsky, Stanley J.; de Teramond, Guy F.
2008-04-23
Light-Front Holography is a remarkable consequence of the correspondence between string theory in AdS space and conformal field theories in physical-space time. It allows string modes {Phi}(z) in the AdS fifth dimension to be precisely mapped to the light-front wavefunctions of hadrons in terms of a specific light-front impact variable {zeta} which measures the separation of the quark and gluonic constituents within the hadron. This mapping was originally obtained by matching the exact expression for electromagnetic current matrix elements in AdS space with the corresponding exact expression for the current matrix element using light-front theory in physical space-time. More recently we have shown that one obtains the identical holographic mapping using matrix elements of the energy-momentum tensor, thus providing an important consistency test and verification of holographic mapping from AdS to physical observables defined on the light-front. The resulting light-front Schrodinger equations predicted from AdS/QCD give a good representation of the observed meson and baryon spectra and give excellent phenomenological predictions for amplitudes such as electromagnetic form factors and decay constants.
Microstrip-Transmission-Line Shock-Front Sensor
NASA Technical Reports Server (NTRS)
Leiweke, Robert J.; Smith, William C.
1993-01-01
Microstrip-transmission-line sensor measures velocities of low-overpressure shock fronts and offers dynamic range needed for measurements both far from and near explosions. Fabricated easily, relatively inexpensive, and repaired in field. In addition, basic geometry modified easily, as needed.
Light-Front Holography, Light-Front Wavefunctions, and Novel QCD Phenomena
Brodsky, Stanley J.; de Teramond, Guy F.; /Costa Rica U.
2012-02-16
Light-Front Holography is one of the most remarkable features of the AdS/CFT correspondence. In spite of its present limitations it provides important physical insights into the nonperturbative regime of QCD and its transition to the perturbative domain. This novel framework allows hadronic amplitudes in a higher dimensional anti-de Sitter (AdS) space to be mapped to frame-independent light-front wavefunctions of hadrons in physical space-time. The model leads to an effective confining light-front QCD Hamiltonian and a single-variable light-front Schroedinger equation which determines the eigenspectrum and the light-front wavefunctions of hadrons for general spin and orbital angular momentum. The coordinate z in AdS space is uniquely identified with a Lorentz-invariant coordinate {zeta} which measures the separation of the constituents within a hadron at equal light-front time and determines the off-shell dynamics of the bound-state wavefunctions, and thus the fall-off as a function of the invariant mass of the constituents. The soft-wall holographic model modified by a positive-sign dilaton metric, leads to a remarkable one-parameter description of nonperturbative hadron dynamics - a semi-classical frame-independent first approximation to the spectra and light-front wavefunctions of meson and baryons. The model predicts a Regge spectrum of linear trajectories with the same slope in the leading orbital angular momentum L of hadrons and the radial quantum number n. The hadron eigensolutions projected on the free Fock basis provides the complete set of valence and non-valence light-front Fock state wavefunctions {Psi}{sub n/H} (x{sub i}, k{sub {perpendicular}i}, {lambda}{sub i}) which describe the hadron's momentum and spin distributions needed to compute the direct measures of hadron structure at the quark and gluon level, such as elastic and transition form factors, distribution amplitudes, structure functions, generalized parton distributions and transverse
The curvature of material surfaces in isotropic turbulence
NASA Astrophysics Data System (ADS)
Pope, S. B.; Yeung, P. K.; Girimaji, S. S.
1989-12-01
Direct numerical simulation is used to study the curvature of material surfaces in isotropic turbulence. The Navier-Stokes equation is solved by a 643 pseudospectral code for constant-density homogeneous isotropic turbulence, which is made statistically stationary by low-wavenumber forcing. The Taylor-scale Reynolds number is 39. An ensemble of 8192 infinitesimal material surface elements is tracked through the turbulence. For each element, a set of exact ordinary differential equations is integrated in time to determine, primarily, the two principal curvatures k1 and k2. Statistics are then deduced of the mean-square curvature M= (1)/(2) (k21+k22), and of the mean radius of curvature R=(k21+k22)-1/2. Curvature statistics attain an essentially stationary state after about 15 Kolmogorov time scales. Then the area-weighted expectation of R is found to be 12η, where η is the Kolmogorov length scale. For moderate and small radii (less than 10η) the probability density function (pdf) of R is approximately uniform, there being about 5% probability of R being less than η. The uniformity of the pdf of R, for small R, implies that the expectation of M is infinite. It is found that the surface elements with large curvatures are nearly cylindrical in shape (i.e., ‖k1‖≫‖k2‖ or ‖k2‖≫‖k1‖), consistent with the folding of the surface along nearly straight lines. Nevertheless the variance of the Gauss curvature K=k1k2 is infinite.
On the determination of curvature and dynamical dark energy
Virey, J-M; Taxil, P; Talon-Esmieu, D; Ealet, A; Tilquin, A E-mail: talon@cppm.in2p3.fr E-mail: taxil@cpt.univ-mrs.fr
2008-12-15
Constraining simultaneously the dark energy (DE) equation of state and the curvature of the universe is difficult due to strong degeneracies. To circumvent this problem when analyzing data it is usual to assume flatness to constrain the DE or, conversely, to assume that the DE is a cosmological constant to constrain the curvature. In this paper, we quantify the impact of such assumptions with an eye to future large surveys. We simulate future data for type Ia supernovae, the cosmic microwave background and baryon acoustic oscillations for a large range of fiducial cosmologies allowing a small spatial curvature. We take into account a possible time evolution of DE through a parameterized equation of state: w(a) = w{sub 0}+(1-a)w{sub a}. We then fit the simulated data with a wrong assumption on the curvature or on the DE parameters. For a fiducial {Lambda}CDM cosmology, if flatness is incorrectly assumed in the fit and if the true curvature is within the ranges 0.01<{Omega}{sub k}<0.03 and -0.07<{Omega}{sub k}<-0.01, one will be led to conclude erroneously that an evolving DE is present, even with high statistics. On the other hand, models with curvature and dynamical DE can be confused with a flat {Lambda}CDM model when the fit ignores a possible DE evolution. We find that, in the future, with high statistics, such risks of confusion should be limited, but they are still possible, and biases in the cosmological parameters might be important. We conclude by recalling that, in the future, it will be mandatory to perform some complete multi-probe analyses, leaving the DE parameters as well as the curvature as free parameters.
Katzenbach, J R; Santamaria, J A
1999-01-01
For many organizations, achieving competitive advantage means eliciting superior performance from employees on the front line--the burger flippers, hotel room cleaners, and baggage handlers whose work has an enormous effect on customers. That's no easy task. Front line workers are paid low wages, have scant hope of advancement, and--not surprisingly--often care little about the company's performance. But then how do some companies succeed in engaging the emotional energy of rank-and-file workers? A team of researchers at McKinsey & Company and the Conference Board recently explored that question and discovered that one highly effective route is demonstrated by the U.S. Marine Corps. The Marines' approach to motivation follows the "mission, values, and pride" path, which researchers say is practical and relevant for the business world. More specifically, the authors say the Marines follow five practices: they over-invest in cultivating core value; prepare every person to lead, including front line supervisors; learn when to create teams and when to create single-leader work groups; attend to all employees, not just the top half; and encourage self-discipline as a way of building pride. The authors admit there are critical differences between the Marines and most businesses. But using vivid examples from companies such as KFC and Marriott International, the authors illustrate how the Marines' approach can be translated for corporate use. Sometimes, the authors maintain, minor changes in a company's standard operating procedure can have a powerful effect on front line pride and can result in substantial payoffs in company performance.
Effect of Tension and Curvature of Skin on Insertion Characteristics of Microneedle Array
NASA Astrophysics Data System (ADS)
Tachikawa, Hiroto; Takano, Naoki; Nishiyabu, Kazuaki; Miki, Norihisa; Ami, Yoshimichi
Recent MEMS (micro electro mechanical system) fabrication techniques have made it possible to produce painless microneedles precisely enough to be inserted into epidermis layer penetrating the stratum corneum of human skin. This paper presents a testing procedure to evaluate the insertion characteristics of microneedle array using cultured human skin considering the tension and the curvature. First, the biaxial strain applied to the cultured human skin was measured by optical technique with image processing. It was found that almost constant strain could be successfully given within a certain area and that error factors in the experiment except the thickness variation of the cultured skin were negligible. Next, using a microneedle square array for brain machine interface (BMI) application, the effects of biaxial tension and the curvature on insertion characteristics were discussed. Within the above mentioned area with high strain, the needles were successfully inserted.
Seo, Na Jin; Armstrong, Thomas J
2009-05-01
This study investigated the effect of object curvature, normal force and material on skin friction coefficient. Twelve subjects slid their middle fingertip pad against a test object with small (11 mm), medium (18, 21 mm) or large (flat object) radii of curvature, while maintaining a normal force of 1, 10 or 20 N. Tested materials were aluminium and four rubber hoses. The average friction coefficient was 0.6 for aluminium and 0.9 for the rubber hoses. As normal force increased from 1 to 20 N, the average friction coefficient decreased 46%. Friction coefficient did not vary significantly with object curvature. The citation of friction coefficient data requires careful attention to normal force levels with which they are measured, but not so much to object curvature between 11 mm and infinity. This study provides skin friction coefficient data that are needed for design of objects that are manipulated with the hands. The investigation of the effect of object curvature on skin friction coefficient has important implications to ergonomics practices as many objects handled in everyday activities have curved surfaces.
Lumbar spine disc heights and curvature: upright posture vs. supine compression harness
NASA Technical Reports Server (NTRS)
Lee, Shi-Uk; Hargens, Alan R.; Fredericson, Michael; Lang, Philipp K.
2003-01-01
INTRODUCTION: Spinal lengthening in microgravity is thought to cause back pain in astronauts. A spinal compression harness can compress the spine to eliminate lengthening but the loading condition with harness is different than physiologic conditions. Our purpose was to compare the effect of spine compression with a harness in supine position on disk height and spinal curvature in the lumbar spine to that of upright position as measured using a vertically open magnetic resonance imaging system. METHODS: Fifteen healthy subjects volunteered. On day 1, each subject lay supine for an hour and a baseline scan of the lumbar spine was performed. After applying a load of fifty percent of body weight with the harness for thirty minutes, the lumbar spine was scanned again. On day 2, after a baseline scan, a follow up scan was performed after kneeling for thirty minutes within the gap between two vertically oriented magnetic coils. Anterior and posterior disk heights, posterior disk bulging, and spinal curvature were measured from the baseline and follow up scans. RESULTS: Anterior disk heights increased and posterior disk heights decreased compared with baseline scans both after spinal compression with harness and upright posture. The spinal curvature increased by both loading conditions of the spine. DISCUSSION: The spinal compression with specially designed harness has the same effect as the physiologic loading of the spine in the kneeling upright position. The harness shows some promise as a tool to increase the diagnostic capabilities of a conventional MR system.
Curvature Sorting of Peripheral Proteins on Solid-Supported Wavy Membranes
Hsieh, Wan-Ting; Hsu, Chih-Jung; Capraro, Benjamin R.; Wu, Tingting; Chen, Chi-Mon; Yang, Shu; Baumgart, Tobias
2013-01-01
Cellular membrane deformation and the associated redistribution of membrane-bound proteins are important aspects of membrane function. Current model membrane approaches for studying curvature sensing are limited to positive curvatures, and often require complex and delicate experimental setups. To overcome these challenges, we fabricated a wavy substrate imposing a range of curvatures onto an adhering lipid bilayer membrane. We examined the curvature sorting of several peripheral proteins binding to the wavy membrane and observed them to partition into distinct regions of curvature. Furthermore, single molecule imaging experiments suggested that curvature sensing of proteins on low-curvature substrates requires cooperative interactions. PMID:22881196
NASA Technical Reports Server (NTRS)
Hadaway, James B.; Wells, Conrad; Olczak, Gene; Waldman, Mark; Whitman, Tony; Cosentino, Joseph; Connolly, Mark; Chaney, David; Telfer, Randal
2016-01-01
The JWST primary mirror consists of 18 1.5 m hexagonal segments, each with 6-DoF and RoC adjustment. The telescope will be tested at its cryogenic operating temperature at Johnson Space Center. The testing will include center-of-curvature measurements of the PM, using the Center-of-Curvature Optical Assembly (COCOA) and the Absolute Distance Meter Assembly (ADMA). The performance of these metrology systems, including hardware, software, procedures, was assessed during two cryogenic tests at JSC, using the JWST Pathfinder telescope. This paper describes the test setup, the testing performed, and the resulting metrology system performance.
NASA Astrophysics Data System (ADS)
Narayan Dash, Jitendra; Jha, Rajan
2016-10-01
We propose a Mach-Zehnder interferometric sensor based on tapered Photonic Crystal Fiber (PCF) with up-tapered collapsed region for measurement of parameters such as curvature, strain and temperature. The up-tapered collapsed region helps in excitation of the cladding modes in PCF and these modes interfere with each other at the tapered region of PCF which is completely collapsed. Three tapered PCFs with varying geometry are fabricated and their effect on curvature sensitivity is analyzed. Experimental results show that the proposed sensor has a curvature sensitivity of 7.56 nm m-1 with negligible hysteresis effect. Moreover, the proposed sensor shows a strain sensitivity of 1.6 pm/μɛ along with a maximum temperature sensitivity of 51.6 pm °C-1. In addition to this, the response of the interference pattern to all these parameters is found to be linear.
The role of curvature in silica mesoporous crystals
Miyasaka, Keiichi; Garcia Bennett, Alfonso; Han, Lu; Han, Yu; Xiao, Changhong; Fujita, Nobuhisa; Castle, Toen; Sakamoto, Yasuhiro; Che, Shunai; Terasaki, Osamu
2012-01-01
Silica mesoporous crystals (SMCs) offer a unique opportunity to study micellar mesophases. Replication of non-equilibrium mesophases into porous silica structures allows the characterization of surfactant phases under a variety of chemical and physical perturbations, through methods not typically accessible to liquid crystal chemists. A poignant example is the use of electron microscopy and crystallography, as discussed herein, for the purpose of determining the fundamental role of amphiphile curvature, namely mean curvature and Gaussian curvature, which have been extensively studied in various fields such as polymer, liquid crystal, biological membrane, etc. The present work aims to highlight some current studies devoted to the interface curvature on SMCs, in which electron microscopy and electron crystallography (EC) are used to understand the geometry of silica wall surface in bicontinuous and cage-type mesostructures through the investigation of electrostatic potential maps. Additionally, we show that by altering the synthesis conditions during the preparation of SMCs, it is possible to isolate particles during micellar mesophase transformations in the cubic bicontinuous system, allowing us to view and study epitaxial relations under the specific synthesis conditions. By studying the relationship between mesoporous structure, interface curvature and micellar mesophases using electron microscopy and EC, we hope to bring new insights into the formation mechanism of these unique materials but also contribute a new way of understanding periodic liquid crystal systems. PMID:24098848
Representation of tactile curvature in macaque somatosensory area 2
Connor, Charles E.; Hsiao, Steven S.
2013-01-01
Tactile shape information is elaborated in a cortical hierarchy spanning primary (SI) and secondary somatosensory cortex (SII). Indeed, SI neurons in areas 3b and 1 encode simple contour features such as small oriented bars and edges, whereas higher order SII neurons represent large curved contour features such as angles and arcs. However, neural coding of these contour features has not been systematically characterized in area 2, the most caudal SI subdivision in the postcentral gyrus. In the present study, we analyzed area 2 neural responses to embossed oriented bars and curved contour fragments to establish whether curvature representations are generated in the postcentral gyrus. We found that many area 2 neurons (26 of 112) exhibit clear curvature tuning, preferring contours pointing in a particular direction. Fewer area 2 neurons (15 of 112) show preferences for oriented bars. Because area 2 response patterns closely resembled SII patterns, we also compared area 2 and SII response time courses to characterize the temporal dynamics of curvature synthesis in the somatosensory system. We found that curvature representations develop and peak concurrently in area 2 and SII. These results reveal that transitions from orientation tuning to curvature selectivity in the somatosensory cortical hierarchy occur within SI rather than between SI and SII. PMID:23536717
Curvature properties of some class of warped product manifolds
NASA Astrophysics Data System (ADS)
Deszcz, Ryszard; Głogowska, Małgorzata; Jełowicki, Jan; Zafindratafa, Georges
2016-10-01
We prove that warped product manifolds with p-dimensional base, p = 1, 2, satisfy some pseudosymmetry type curvature conditions. These conditions are formed from the metric tensor g, the Riemann-Christoffel curvature tensor R, the Ricci tensor S and the Weyl conformal curvature C of the considered manifolds. The main result of the paper states that if p = 2 and the fiber is a semi-Riemannian space of constant curvature (when n is greater or equal to 5) then the (0, 6)-tensors R ṡ R - Q(S,R) and C ṡ C of such warped products are proportional to the (0, 6)-tensor Q(g,C) and the tensor C is a linear combination of some Kulkarni-Nomizu products formed from the tensors g and S. We also obtain curvature properties of this kind of quasi-Einstein and 2-quasi-Einstein manifolds, and in particular, of the Goedel metric, generalized spherically symmetric metrics and generalized Vaidya metrics.
Sculpting membranes: a mechanism of curvature generation by proteins
NASA Astrophysics Data System (ADS)
Campelo, Felix
2010-03-01
A wide spectrum of intracellular processes is dependent on the ability of cells to dynamically regulate membrane shape. Membrane bending by proteins is necessary for the generation of intracellular transport carriers and for the maintenance of otherwise intrinsically unstable regions of high membrane curvature in cell organelles. Understanding the mechanisms by which proteins curve membranes is therefore of primary importance. Crescent shaped N-BAR domains containing amphipathic helices can induce membrane curvature by two mechanisms: the scaffolding mechanism due to the very shape of the BAR dimer, and the hydrophobic insertion mechanism by which small shallow inclusions penetrate the membrane matrix and act as a wedge changing the local membrane curvature. We will focus on this latter mechanism, and study it from a quantitative point of view. We use an elastic model of the lipid bilayer, taking into account the internal strains and stresses generated by the presence of an inclusion. We show that large membrane curvatures found in in vitro experiments can be ascribed to this mechanism, and that shallow insertions are more powerful curvature generators than lipids.
Cloud, Beth A; Zhao, Kristin D; Breighner, Ryan; Giambini, Hugo; An, Kai-Nan
2014-07-01
Spinal posture affects how individuals function from a manual wheelchair. There is a need to directly quantify spinal posture in this population to ultimately improve function. A fiber optic system, comprised of an attached series of sensors, is promising for measuring large regions of the spine in individuals sitting in a wheelchair. The purpose of this study was to determine the agreement between fiber optic and optoelectronic systems for measuring spinal curvature, and describe the range of sagittal plane spinal curvatures in natural sitting. Able-bodied adults (n = 26, 13 male) participated. Each participant assumed three sitting postures: natural, slouched (accentuated kyphosis), and extension (accentuated lordosis) sitting. Fiber optic (ShapeTape) and optoelectronic (Optotrak) systems were applied to the skin over spinous processes from S1 to C7 and used to measure sagittal plane spinal curvature. Regions of kyphosis and lordosis were identified. A Cobb angle-like method was used to quantify lordosis and kyphosis. Generalized linear model and Bland-Altman analyses were used to assess agreement. A strong correlation exists between curvature values obtained with Optotrak and ShapeTape (R(2) = 0.98). The mean difference between Optotrak and ShapeTape for kyphosis in natural, extension, and slouched postures was 4.30° (95% LOA: -3.43 to 12.04°), 3.64° (95% LOA: -1.07 to 8.36°), and 4.02° (95% LOA: -2.80 to 10.84°), respectively. The mean difference for lordosis, when present, in natural and extension postures was 2.86° (95% LOA: -1.18 to 6.90°) and 2.55° (95% LOA: -3.38 to 8.48°), respectively. In natural sitting, the mean ± SD of kyphosis values was 35.07 ± 6.75°. Lordosis was detected in 8/26 participants: 11.72 ± 7.32°. The fiber optic and optoelectronic systems demonstrate acceptable agreement for measuring sagittal plane thoracolumbar spinal curvature.
Tomographic wave-front sensing with a single guide star
NASA Astrophysics Data System (ADS)
Hart, Michael; Jefferies, Stuart; Hope, Douglas
2016-09-01
Adaptive optics or numerical restoration algorithms that restore high resolution imaging through atmospheric turbulence are subject to isoplanatic wave-front errors. Mitigating those errors requires that the wave-front aberrations be estimated within the 3D volume of the atmosphere. Present techniques rely on multiple beacons, either natural stars or laser guide stars, to probe the atmospheric aberration along different lines of sight, followed by tomographic projection of the measurements onto layers at defined ranges. In this paper we show that a three-dimensional estimate of the wave-front aberration can be recovered from measurements by a single guide star in the case where the aberration is stratified, provided that the telescope tracks across the sky with non-uniform angular velocity. This is generally the case for observations of artificial earth-orbiting satellites, and the new method is likely to find application in ground-based telescopes used for space situational awareness.
Curvature affects Doppler investigation of vessels: implications for clinical practice.
Balbis, S; Roatta, S; Guiot, C
2005-01-01
In clinical practice, blood velocity estimations from Doppler examination of curved vascular segments are normally different from those of nearby straight segments. The observed "accelerations," sometimes considered as a sort of stochastic disturbances, can actually be related to very specific physical effects due to vessel curvature (i.e., the development of nonaxial velocity [NAV] components) and the spreading of the axial velocity direction in the Doppler sample volume with respect to the insonation axis. The relevant phenomena and their dependence on the radius of curvature of the vessels and on the insonation angle are investigated with a beam-vessel geometry as close as possible to clinical setting, with the simplifying assumptions of steady flow, mild vessel curvature, uniform ultrasonic beam and complete vessel insonation. The insonation angles that minimize the errors are provided on the basis of the study results.
Curvature-dependent surface energy and implications for nanostructures
NASA Astrophysics Data System (ADS)
Chhapadia, P.; Mohammadi, P.; Sharma, P.
2011-10-01
At small length scales, several size-effects in both physical phenomena and properties can be rationalized by invoking the concept of surface energy. Conventional theoretical frameworks of surface energy, in both the mechanics and physics communities, assume curvature independence. In this work we adopt a simplified and linearized version of a theory proposed by Steigmann-Ogden to capture curvature-dependence of surface energy. Connecting the theory to atomistic calculations and the solution to an illustrative paradigmatical problem of a bent cantilever beam, we catalog the influence of curvature-dependence of surface energy on the effective elastic modulus of nanostructures. The observation in atomistic calculations that the elastic modulus of bent nanostructures is dramatically different than under tension - sometimes softer, sometimes stiffer - has been a source of puzzlement to the scientific community. We show that the corrected surface mechanics framework provides a resolution to this issue. Finally, we propose an unambiguous definition of the thickness of a crystalline surface.
Spinor description of the curvatures of D = 5 gauge fields
NASA Astrophysics Data System (ADS)
Uvarov, D. V.
2017-03-01
Spinor description of the curvatures of D = 5 Yang-Mills, Rarita-Schwinger and gravitational fields is considered. Restrictions imposed on the curvature spinors by the dynamical equations and Bianchi identities are studied. In the absence of sources symmetric curvature spinors with 2 s indices obey first-order equations that in the linearized limit reduce to Dirac-type equations for massless free fields. These equations allow for a higher-spin generalization similarly to 4 d case. Their solution in the form of the integral over Lorentz-harmonic variables parametrizing coset manifold SO(1, 4)/( SO(1,1) × ISO(3)) isomorphic to the three-sphere is considered.
Relationship between peptide membrane curvature generation and bactericidal activities
NASA Astrophysics Data System (ADS)
Schmidt, Nathan; Lee, Michelle; Kuo, David; Ouellette, Andre; Wong, Gerard
2013-03-01
Many amphipathic peptides and amphipathic domains in proteins can restructure biological membranes. Two examples are host defense antimicrobial peptides (AMPs) which disrupt and destabilize the cell membranes of microbes, and apolipoproteins which help stabilize nanoscale lipid aggregates. We use complementary x-ray and bacterial cell assays to elucidate the molecular length scale membrane deformations generated by amphipathic peptides with different structural motifs and relate these deformations to their activities on bacteria. Small angle x-ray scattering is used to study the interactions of model membranes with prototypical AMPs and consensus peptides from the amphipathic domains in apolipoproteins. By characterizing the nanoscale curvature deformations induced by these two distinct classes of membrane restructuring peptides we will discuss the role of amino acid composition on curvature generation. Bactericidal assays are used to access the in vivo activities of different amphipathic peptide motifs in order to understand the relationships between cell viability and membrane curvature generation.
Total Gaussian curvature, drop shapes and the range of applicability of drop shape techniques.
Saad, Sameh M I; Neumann, A Wilhelm
2014-02-01
Drop shape techniques are used extensively for surface tension measurement. It is well-documented that, as the drop/bubble shape becomes close to spherical, the performance of all drop shape techniques deteriorates. There have been efforts quantifying the range of applicability of drop techniques by studying the deviation of Laplacian drops from the spherical shape. A shape parameter was introduced in the literature and was modified several times to accommodate different drop constellations. However, new problems arise every time a new configuration is considered. Therefore, there is a need for a universal shape parameter applicable to pendant drops, sessile drops, liquid bridges as well as captive bubbles. In this work, the use of the total Gaussian curvature in a unified approach for the shape parameter is introduced for that purpose. The total Gaussian curvature is a dimensionless quantity that is commonly used in differential geometry and surface thermodynamics, and can be easily calculated for different Laplacian drop shapes. The new definition of the shape parameter using the total Gaussian curvature is applied here to both pendant and constrained sessile drops as an illustration. The analysis showed that the new definition is superior and reflects experimental results better than previous definitions, especially at extreme values of the Bond number.
The Gaussian curvature of the oil-water interface in an isometric bicontinuous microemulsion
NASA Astrophysics Data System (ADS)
Chen, Sow-Hsin; Choi, Sung-Min
1997-02-01
Small-angle neutron scattering (SANS) measurements are made on a three-component isometric (equal volume fractions of water and oil) microemulsion system, composed of AOT/water (0.4% NaCl)/D-octane, in the one-phase channel near the three-phase region at and around the hydrophile-lipophile balance temperature. A previous SANS contrast variation experiment indicated that the microstructure of this type of isometric microemulsion is bicontinuous in water and oil with the surfactant film at the interface having a zero mean curvature. We analyze SANS data taken with an oil-water contrast in terms of a modified Berk's random wave model. We choose a spectral function which is an inverse sixth-order polynomial, with three parameters a, b and c, as introduced by Lee and Chen earlier. This three-parameter spectral function is then used in conjunction with Cahn's clipping scheme to obtain the Debye correlation function appropriate for the microemulsion system. The model analysis results in good agreement with the intensity data in an absolute scale. We then use the three parameters so obtained to calculate the average Gaussian curvature of the interface. We discuss the variation of the average Gaussian curvature as a function of the surfactant volume fraction and its implication on the degree of local order of the bicontinuous structure. We also show a 3-D reconstructed morphology of the most disordered microemulsion.
Curvature-enhanced Spin-orbit Coupling and Spinterface Effect in Fullerene-based Spin Valves
Liang, Shiheng; Geng, Rugang; Yang, Baishun; Zhao, Wenbo; Chandra Subedi, Ram; Li, Xiaoguang; Han, Xiufeng; Nguyen, Tho Duc
2016-01-01
We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface. PMID:26786047
Curvature-enhanced Spin-orbit Coupling and Spinterface Effect in Fullerene-based Spin Valves
NASA Astrophysics Data System (ADS)
Liang, Shiheng; Geng, Rugang; Yang, Baishun; Zhao, Wenbo; Chandra Subedi, Ram; Li, Xiaoguang; Han, Xiufeng; Nguyen, Tho Duc
2016-01-01
We investigated curvature-enhanced spin-orbit coupling (SOC) and spinterface effect in carbon-based organic spin valves (OSVs) using buckyball C60 and C70 molecules. Since the naturally abundant 12C has spinless nuclear, the materials have negligible hyperfine interaction (HFI) and the same intrinsic SOC, but different curvature SOC due to their distinct curvatures. We fitted the thickness dependence of magnetoresistance (MR) in OSVs at various temperatures using the modified Jullière equation. We found that the spin diffusion length in the C70 film is above 120 nm, clearly longer than that in C60 film at all temperatures. The effective SOC ratio of the C70 film to the C60 film was estimated to be about 0.8. This was confirmed by the magneto-electroluminescence (MEL) measurement in fullerene-based light emitting diodes (LED). Next, the effective spin polarization in C70-based OSVs is smaller than that in C60-based OSVs implying that they have different spinterface effect. First principle calculation study shows that the spin polarization of the dz2 orbital electrons of Co atoms contacted with C60 is larger causing better effective spin polarization at the interface.
Three-Dimensional Analysis of the Curvature of the Femoral Canal in 426 Chinese Femurs
Su, Xiu-Yun; Zhao, Zhe; Zhao, Jing-Xin; Zhang, Li-Cheng; Long, An-Hua; Zhang, Li-Hai; Tang, Pei-Fu
2015-01-01
Purpose. The human femur has long been considered to have an anatomical anterior curvature in the sagittal plane. We established a new method to evaluate the femoral curvature in three-dimensional (3D) space and reveal its influencing factors in Chinese population. Methods. 3D models of 426 femurs and the medullary canal were constructed using Mimics software. We standardized the positions of all femurs using 3ds Max software. After measuring the anatomical parameters, including the radius of femoral curvature (RFC) and banking angle, of the femurs using the established femur-specific coordinate system, we analyzed and determined the relationships between the anatomical parameters of the femur and the general characteristics of the population. Results. Pearson's correlation analyses showed that there were positive correlations between the RFC and height (r = 0.339, p < 0.001) and the femoral length and RFC (r = 0.369, p < 0.001) and a negative correlation between the femoral length and banking angle (r = −0.223, p < 0.001). Stepwise linear regression analyses showed that the most relevant factors for the RFC and banking angle were the femoral length and gender, respectively. Conclusions. This study concluded that the banking angle of the femur was significantly larger in female than in male. PMID:26640785
The effect of spinal curvature on the photogrammetric assessment on static balance in elderly women
2014-01-01
Background Involutional changes to the body in elderly patients affect the shape of the spine and the activity of postural muscles. The purpose of this study was to assess the influence of age-related changes in spinal curvature on postural balance in elderly women. Methods The study population consisted of 90 women, with a mean age of 70 ± 8.01 years. Static balance assessments were conducted on a tensometric platform, and posturographic assessments of body posture were performed using a photogrammetric method based on the Projection Moiré method. Results The results obtained were analysed using the Spearman’s rank correlation coefficient test. We found a statistically significant correlation between body posture and the quality of the balance system response based on the corrective function of the visual system. The shape of the spinal curvature influenced postural stability, as measured by static posturography. Improvement in the quality of the balance system response depended on corrective information from the visual system and proprioceptive information from the paraspinal muscles. Conclusions The sensitivity of the balance system to the change of centre of pressure location was influenced by the direction of the change in rotation of the shoulder girdle and spine. Development of spinal curvature in the sagittal plane and maintenance of symmetry in the coronal and transverse planes are essential for correct balance control, which in turn is essential for the development of a properly proportioned locomotor system. PMID:24885433
Experimental validation of normalized uniform load surface curvature method for damage localization.
Jung, Ho-Yeon; Sung, Seung-Hoon; Jung, Hyung-Jo
2015-10-16
In this study, we experimentally validated the normalized uniform load surface (NULS) curvature method, which has been developed recently to assess damage localization in beam-type structures. The normalization technique allows for the accurate assessment of damage localization with greater sensitivity irrespective of the damage location. In this study, damage to a simply supported beam was numerically and experimentally investigated on the basis of the changes in the NULS curvatures, which were estimated from the modal flexibility matrices obtained from the acceleration responses under an ambient excitation. Two damage scenarios were considered for the single damage case as well as the multiple damages case by reducing the bending stiffness (EI) of the affected element(s). Numerical simulations were performed using MATLAB as a preliminary step. During the validation experiments, a series of tests were performed. It was found that the damage locations could be identified successfully without any false-positive or false-negative detections using the proposed method. For comparison, the damage detection performances were compared with those of two other well-known methods based on the modal flexibility matrix, namely, the uniform load surface (ULS) method and the ULS curvature method. It was confirmed that the proposed method is more effective for investigating the damage locations of simply supported beams than the two conventional methods in terms of sensitivity to damage under measurement noise.
The Effect of Cooling Passage Aspect Ratio on Curvature Heat Transfer Enhancement
NASA Technical Reports Server (NTRS)
Meyer, Michael L.
1997-01-01
A series of electrically heated tube experiments was performed to investigate the effect of high aspect ratio on curvature heat transfer enhancement in uniformly heated rectangular cooling passages. Three hardware geometries were tested: a baseline straight aspect ratio 10 tube, an aspect ratio 1 (square) tube with a 45 deg. curve, and an aspect ratio 10 tube with a 45 deg. curve. Gaseous nitrogen with the following properties was used as the coolant: ambient inlet temperature, pressures to 8.3 MPa, wall-to-bulk temperature ratios less than two, and Reynolds numbers based on hydraulic diameter ranging from 250,000 to 1,600,000. The measured curvature enhancement factors were compared to values predicted by three previously published models which had been developed for low aspect ratio tubes. The models were shown to be valid for the high aspect ratio tube as well the low aspect ratio tube, indicating that aspect ratio had little impact on the curvature heat transfer enhancement in these tests.
Adiabatic approximation via hodograph translation and zero-curvature equations
NASA Astrophysics Data System (ADS)
Karasev, M. V.
2014-04-01
For quantum as well classical slow-fast systems, we develop a general method which allows one to compute the adiabatic invariant (approximate integral of motion), its symmetries, the adiabatic guiding center coordinates and the effective scalar Hamiltonian in all orders of a small parameter. The scheme does not exploit eigenvectors or diagonalization, but is based on the ideas of isospectral deformation and zero-curvature equations, where the role of "time" is played by the adiabatic (quantization) parameter. The algorithm includes the construction of the zero-curvature adiabatic connection and its splitting generated by averaging up to an arbitrary order in the small parameter.
Ion acceleration in dipolarization fronts
NASA Astrophysics Data System (ADS)
Birn, J.; Hesse, M.
2014-12-01
The electric field associated with flow bursts and dipolarization fronts has been shown to be an efficient mechanism for producing energetic ions and electrons. Using an MHD simulation of magnetotail reconnection, flow bursts and dipolarization, we investigate the acceleration of test particles to suprathermal energies. Particular emphasis of this presentation is on spatial, temporal, and angular variations of the modeled energetic ion fluxes. The test particle simulations reproduce characteristic features of observed injection events, such as a fast rise of energetic particle fluxes, limitations in energy, and demonstrate the large variability of energetic ion features.
NASA Astrophysics Data System (ADS)
Raji, Y. M.; Lin, H. S.; Ibrahim, S. A.; Mokhtar, M. R.; Yusoff, Z.
2016-12-01
An abrupt tapered fiber In-Line Mach-Zehnder Interferometer sensor for simultaneous measurement of temperature and curvature is proposed and experimentally demonstrated. The sensor head is fabricated by arcing Corning SMF-28 using a commercial arc fusion splicer. The individual parameters discrimination was achieved by manipulating the unequal sensitivities of optical power to temperature and curvature obtained at two wavelengths within the sensing spectrum. The curvature and temperature sensitivities at λ1 (1537 nm) and λ2 (1568.7 nm) were found to be 11.8264 dBm/m-1, 12.4885 dBm/m-1 and 0.0829 dBm/°C, 0.0833 dBm/°C, respectively. The experimental results show unperturbed readings with rms deviation of ±0.1801 m-1 and ±0.0826 °C, for curvature and temperature measurements, respectively, through measurement of optical power response of the sensor. With this simultaneous sensing technique, the proposed sensor can be deployed for many field applications such as nondestructive structural health monitoring of civil infrastructure.
1. VIEW SOUTHWARD FROM SOUTHWEST CORNER FRONT AND ARCH STREETS ...
1. VIEW SOUTHWARD FROM SOUTHWEST CORNER FRONT AND ARCH STREETS (2. N. Front Street starts at left) - North Front Street Area Study, 2-66 North Front Street (Commercial Buildings), Philadelphia, Philadelphia County, PA
NASA Astrophysics Data System (ADS)
Gubin, S. A.; Sumskoi, S. I.; Victorov, S. B.
According to the theory of detonation, in a detonation wave there is a sound plane, named Chapman-Jouguet (CJ) plane. There are certain stationary parameters for this plane. In this work the possibility of the second CJ plane is shown. This second CJ plane is stationary as well. The physical mechanism of non-equilibrium transition providing the existence of the second CJ plane is presented. There is a non-equilibrium state, when the heat is removed from the reaction zone and the heat capacity decreases sharply. As a result of this non-equilibrium state, the sound velocity increases, and the local supersonic zone with second sonic plane (second CJ plane) appears. So the new mode of detonation wave is predicted. Equations describing this mode of detonation are presented. The exact analytical solution for the second CJ plane parameters is obtained. The example of double-front detonation in high explosive (TNT) is presented. In this double-front structure "nanodiamond-nanographite" phase transition takes place in condensed particles of detonation products.
The effect of nanoscale surface curvature on the oligomerization of surface-bound proteins
Kurylowicz, M.; Paulin, H.; Mogyoros, J.; Giuliani, M.; Dutcher, J. R.
2014-01-01
The influence of surface topography on protein conformation and association is used routinely in biological cells to orchestrate and coordinate biomolecular events. In the laboratory, controlling the surface curvature at the nanoscale offers new possibilities for manipulating protein–protein interactions and protein function at surfaces. We have studied the effect of surface curvature on the association of two proteins, α-lactalbumin (α-LA) and β-lactoglobulin (β-LG), which perform their function at the oil–water interface in milk emulsions. To control the surface curvature at the nanoscale, we have used a combination of polystyrene (PS) nanoparticles (NPs) and ultrathin PS films to fabricate chemically pure, hydrophobic surfaces that are highly curved and are stable in aqueous buffer. We have used single-molecule force spectroscopy to measure the contour lengths Lc for α-LA and β-LG adsorbed on highly curved PS surfaces (NP diameters of 27 and 50 nm, capped with a 10 nm thick PS film), and we have compared these values in situ with those measured for the same proteins adsorbed onto flat PS surfaces in the same samples. The Lc distributions for β-LG adsorbed onto a flat PS surface contain monomer and dimer peaks at 60 and 120 nm, respectively, while α-LA contains a large monomer peak near 50 nm and a dimer peak at 100 nm, with a tail extending out to 200 nm, corresponding to higher order oligomers, e.g. trimers and tetramers. When β-LG or α-LA is adsorbed onto the most highly curved surfaces, both monomer peaks are shifted to much smaller values of Lc. Furthermore, for β-LG, the dimer peak is strongly suppressed on the highly curved surface, whereas for α-LA the trimer and tetramer tail is suppressed with no significant change in the dimer peak. For both proteins, the number of higher order oligomers is significantly reduced as the curvature of the underlying surface is increased. These results suggest that the surface curvature provides a new
HINS Linac front end focusing system R&D
Apollinari, G.; Carcagno, R.H.; Dimarco, J.; Huang, Y.; Kashikhin, V.V.; Orris, D.F.; Page, T.M.; Rabehl, R.; Sylvester, C.; Tartaglia, M.A.; Terechkine, I.; /Fermilab /Argonne
2008-08-01
This report summarizes current status of an R&D program to develop a focusing system for the front end of a superconducting RF linac. Superconducting solenoids will be used as focusing lenses in the low energy accelerating sections of the front end. The development of focusing lenses for the first accelerating section is in the production stage, and lens certification activities are in preparation at FNAL. The report contains information about the focusing lens design and performance, including solenoid, dipole corrector, and power leads, and about cryogenic system design and performance. It also describes the lens magnetic axis position measurement technique and discusses scope of an acceptance/certification process.
Flows in the Tasman Front south of Norfolk Island
NASA Astrophysics Data System (ADS)
Sutton, Philip J. H.; Bowen, Melissa
2014-05-01
The Tasman Front is a narrow band of eastward flowing subtropical water crossing the Tasman Sea from Australia to North Cape, New Zealand. It is the link between the two subtropical western boundary currents of the South Pacific, the East Australian Current (EAC) off eastern Australia, and the East Auckland Current (EAUC) off northeastern New Zealand. Here we report the first direct measurements of flow in the Tasman Front from a moored array deployed across gaps in the submarine ridges south of Norfolk Island and hydrographic and ADCP measurements during the deployment and recovery voyages. The mean flow through the array over July 2003 to August 2004 was found to be eastward only in the upper 800 m with a transport of ˜6 Sv. Below 800 m a weak westward mean flow (˜1.5 Sv) was measured, associated with Antarctic Intermediate Water (AAIW). Using sea surface height to account for additional transport south of the moored array results in a total mean eastward transport between Norfolk Island and North Cape, New Zealand of ˜8 Sv, varying between -4 and 18 Sv. The measurements show that the Tasman Front is much shallower than either the EAC or EAUC, both of which extend below 2000 m depth, has less transport than either the EAC or EAUC and has instances of flow reversal. Thus, the Tasman Front is a weaker connection between the EAC and EAUC than the paradigm of a contiguous South Pacific western boundary current system would suggest.
Surface roughness of rock faces through the curvature of triangulated meshes
NASA Astrophysics Data System (ADS)
Lai, P.; Samson, C.; Bose, P.
2014-09-01
In this paper, we examine three different measures of roughness based on a geometric property of surfaces known as curvature. These methods were demonstrated using an image of a large rock face made up of a smooth blocky limestone in contact with a rough friable dolostone. The point cloud analysed contained 10,334,288 points and was acquired at a distance of 3 m from the rock face. The point cloud was first decimated using an epsilon-net and then meshed using the Poisson surface reconstruction method before the proposed measures of roughness were applied. The first measure of roughness is defined as the difference in curvature between a mesh and a smoothed version of the same mesh. The second measure of roughness is a voting system applied to each vertex which identifies the subset of vertices which represent rough regions within the mesh. The third measure of roughness uses a combination of spatial partitioning data structures and data clustering in order to define roughness for a region in the mesh. The spatial partitioning data structure allows for a hierarchy of roughness values which is related to the size of the region being considered. All of the proposed measures of roughness are visualised using colour-coded displays which allows for an intuitive interpretation.
Methods for enhancing mapping of thermal fronts in oil recovery
Lee, David O.; Montoya, Paul C.; Wayland, Jr., James R.
1987-01-01
A method for enhancing the resistivity contrasts of a thermal front in an oil recovery production field as measured by the CSAMT technique is disclosed. This method includes the steps of: (a) preparing a CSAMT-determined topological resistivity map of the production field; (b) introducing a solution of a dopant material into the production field at a concentration effective to alter the resistivity associated with the thermal front; said dopant material having a high cation exchange capacity which might be selected from the group consisting of montmorillonite, illite, and chlorite clays; said material being soluble in the connate water of the production field; (c) preparing a CSAMT-determined topological resistivity map of the production field while said dopant material is moving therethrough; and (d) mathematically comparing the maps from step (a) and step (c) to determine the location of the thermal front. This method is effective with the steam flood, fire flood and water flood techniques.
Methods for enhancing mapping of thermal fronts in oil recovery
Lee, D.O.; Montoya, P.C.; Wayland, J.R. Jr.
1984-03-30
A method for enhancing the resistivity contrasts of a thermal front in an oil recovery production field as measured by the controlled source audio frequency magnetotelluric (CSAMT) technique is disclosed. This method includes the steps of: (1) preparing a CSAMT-determined topological resistivity map of the production field; (2) introducing a solution of a dopant material into the production field at a concentration effective to alter the resistivity associated with the thermal front; said dopant material having a high cation exchange capacity which might be selected from the group consisting of montmorillonite, illite, and chlorite clays; said material being soluble in the conate water of the production field; (3) preparing a CSAMT-determined topological resistivity map of the production field while said dopant material is moving therethrough; and (4) mathematically comparing the maps from step (1) and step (3) to determine the location of the thermal front. This method is effective with the steam flood, fire flood and water flood techniques.
Directable weathering of concave rock using curvature estimation.
Jones, Michael D; Farley, McKay; Butler, Joseph; Beardall, Matthew
2010-01-01
We address the problem of directable weathering of exposed concave rock for use in computer-generated animation or games. Previous weathering models that admit concave surfaces are computationally inefficient and difficult to control. In nature, the spheroidal and cavernous weathering rates depend on the surface curvature. Spheroidal weathering is fastest in areas with large positive mean curvature and cavernous weathering is fastest in areas with large negative mean curvature. We simulate both processes using an approximation of mean curvature on a voxel grid. Both weathering rates are also influenced by rock durability. The user controls rock durability by editing a durability graph before and during weathering simulation. Simulations of rockfall and colluvium deposition further improve realism. The profile of the final weathered rock matches the shape of the durability graph up to the effects of weathering and colluvium deposition. We demonstrate the top-down directability and visual plausibility of the resulting model through a series of screenshots and rendered images. The results include the weathering of a cube into a sphere and of a sheltered inside corner into a cavern as predicted by the underlying geomorphological models.
Effect of asymmetric auxin application on Helianthus hypocotyl curvature
NASA Technical Reports Server (NTRS)
Migliaccio, F.; Rayle, D. L.
1989-01-01
Indole-3-acetic acid was applied asymmetrically to the hypocotyls of sunflower (Helianthus annuus L.) seedlings. After 5 hours on a clinostat, auxin gradients as small as 1 to 1.3 produced substantial (more than 60 degrees) hypocotyl curvature. This result suggests the asymmetric growth underlying hypocotyl gravitropism can be explained by lateral auxin redistribution.
Frustration and curvature - Glasses and the cholesteric blue phase
NASA Technical Reports Server (NTRS)
Sethna, J. P.
1983-01-01
An analogy is drawn between continuum elastic theories of the blue phase of cholesteric liquid crystals and recent theories of frustration in configurational glasses. Both involve the introduction of a lattice of disclination lines to relieve frustration; the frustration is due to an intrinsic curvature in the natural form of parallel transport. A continuum theory of configurational glasses is proposed.
Equilibrium models of coronal loops that involve curvature and buoyancy
Hindman, Bradley W.; Jain, Rekha
2013-12-01
We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.
Active optics for high-dynamic variable curvature mirrors.
Hugot, Emmanuel; Ferrari, Marc; Lemaitre, Gérard R; Madec, Fabrice; Vives, Sébastien; Chardin, Elodie; Le Mignant, David; Cuby, Jean-Gabriel
2009-10-01
Variable curvature mirrors of large amplitude are designed by using finite element analysis. The specific case studied reaches at least a 800 mum sag with an optical quality better than lambda/5 over a 120 mm clear aperture. We highlight the geometrical nonlinearity and the plasticity effect.
Origins of chemoreceptor curvature sorting in Escherichia coli
Draper, Will; Liphardt, Jan
2017-01-01
Bacterial chemoreceptors organize into large clusters at the cell poles. Despite a wealth of structural and biochemical information on the system's components, it is not clear how chemoreceptor clusters are reliably targeted to the cell pole. Here, we quantify the curvature-dependent localization of chemoreceptors in live cells by artificially deforming growing cells of Escherichia coli in curved agar microchambers, and find that chemoreceptor cluster localization is highly sensitive to membrane curvature. Through analysis of multiple mutants, we conclude that curvature sensitivity is intrinsic to chemoreceptor trimers-of-dimers, and results from conformational entropy within the trimer-of-dimers geometry. We use the principles of the conformational entropy model to engineer curvature sensitivity into a series of multi-component synthetic protein complexes. When expressed in E. coli, the synthetic complexes form large polar clusters, and a complex with inverted geometry avoids the cell poles. This demonstrates the successful rational design of both polar and anti-polar clustering, and provides a synthetic platform on which to build new systems. PMID:28322223
Positivity of Curvature-Squared Corrections in Gravity.
Cheung, Clifford; Remmen, Grant N
2017-02-03
We study the Gauss-Bonnet (GB) term as the leading higher-curvature correction to pure Einstein gravity. Assuming a tree-level ultraviolet completion free of ghosts or tachyons, we prove that the GB term has a nonnegative coefficient in dimensions greater than 4. Our result follows from unitarity of the spectral representation for a general ultraviolet completion of the GB term.
Simple partitions of a hyperbolic plane of positive curvature
Romakina, Lyudmila N
2012-09-30
We construct special monohedral isotropic partitions with symmetries of the hyperbolic plane H of positive curvature with a simple 4-contour as a cell. An analogue of mosaic in these partitions called a tiling is introduced. Also we consider some fractal tilings. The existence of band tilings in each homological series with code (m, n) is proved. Bibliography: 14 titles.
Determination of light beam curvature in a rotating Luneburg lens
NASA Astrophysics Data System (ADS)
Gladyshev, V. O.; Bazleva, D. D.; Tereshin, A. A.; Gladysheva, T. M.
2016-09-01
We have determined the curvature of a beam of coherent electromagnetic radiation and its angular and linear deviation in a rotating microsatellite representing a Luneburg lens in the optical segment of accuracy augmentation for new-generation global navigation satellite systems.
Equilibrium Models of Coronal Loops That Involve Curvature and Buoyancy
NASA Astrophysics Data System (ADS)
Hindman, Bradley W.; Jain, Rekha
2013-12-01
We construct magnetostatic models of coronal loops in which the thermodynamics of the loop is fully consistent with the shape and geometry of the loop. This is achieved by treating the loop as a thin, compact, magnetic fibril that is a small departure from a force-free state. The density along the loop is related to the loop's curvature by requiring that the Lorentz force arising from this deviation is balanced by buoyancy. This equilibrium, coupled with hydrostatic balance and the ideal gas law, then connects the temperature of the loop with the curvature of the loop without resorting to a detailed treatment of heating and cooling. We present two example solutions: one with a spatially invariant magnetic Bond number (the dimensionless ratio of buoyancy to Lorentz forces) and the other with a constant radius of the curvature of the loop's axis. We find that the density and temperature profiles are quite sensitive to curvature variations along the loop, even for loops with similar aspect ratios.
Intracellular magnetophoresis of amyloplasts and induction of root curvature
NASA Technical Reports Server (NTRS)
Kuznetsov, O. A.; Hasenstein, K. H.
1996-01-01
High-gradient magnetic fields (HGMFs) were used to induce intracellular magnetophoresis of amyloplasts. The HGMFs were generated by placing a small ferromagnetic wedge into a uniform magnetic field or at the gap edge between two permanent magnets. In the vicinity of the tip of the wedge the dynamic factor of the magnetic field, delta(H2/2), was about 10(9) Oe2.cm-1, which subjected the amyloplasts to a force comparable to that of gravity. When roots of 2-d-old seedlings of flax (Linum usitatissimum L.) were positioned vertically and exposed to an HGMF, curvature away from the wedge was transient and lasted approximately 1 h. Average curvature obtained after placing magnets, wedge and seedlings on a 1-rpm clinostat for 2 h was 33 +/- 5 degrees. Roots of horizontally placed control seedlings without rotation curved about 47 +/- 4 degrees. The time course of curvature and changes in growth rate were similar for gravicurvature and for root curvature induced by HGMFs. Microscopy showed displacement of amyloplasts in vitro and in vivo. Studies with Arabidopsis thaliana (L.) Heynh. showed that the wild type responded to HGMFs but the starchless mutant TC7 did not. The data indicate that a magnetic force can be used to study the gravisensing and response system of roots.
Intracellular magnetophoresis of amyloplasts and induction of root curvature.
Kuznetsov, O A; Hasenstein, K H
1996-01-01
High-gradient magnetic fields (HGMFs) were used to induce intracellular magnetophoresis of amyloplasts. The HGMFs were generated by placing a small ferromagnetic wedge into a uniform magnetic field or at the gap edge between two permanent magnets. In the vicinity of the tip of the wedge the dynamic factor of the magnetic field, delta(H2/2), was about 10(9) Oe2.cm-1, which subjected the amyloplasts to a force comparable to that of gravity. When roots of 2-d-old seedlings of flax (Linum usitatissimum L.) were positioned vertically and exposed to an HGMF, curvature away from the wedge was transient and lasted approximately 1 h. Average curvature obtained after placing magnets, wedge and seedlings on a 1-rpm clinostat for 2 h was 33 +/- 5 degrees. Roots of horizontally placed control seedlings without rotation curved about 47 +/- 4 degrees. The time course of curvature and changes in growth rate were similar for gravicurvature and for root curvature induced by HGMFs. Microscopy showed displacement of amyloplasts in vitro and in vivo. Studies with Arabidopsis thaliana (L.) Heynh. showed that the wild type responded to HGMFs but the starchless mutant TC7 did not. The data indicate that a magnetic force can be used to study the gravisensing and response system of roots.
Effect of topological defects and curvature on anisotropic crystal growth
NASA Astrophysics Data System (ADS)
Azadi, Amir; Grason, Gregory M.
2015-03-01
The equilibrium shapes and symmetries of crystals are vestiges of the physical principles underlying their formation. We perform particle-based simulations guided by analytical analysis to investigate the structure of crystalline domains on curved substrates, a focus on the impact of topological defects on domain morphology. We find at low area fraction, as has been argued previously, that isotropic crystal growth with relatively compact domains generates large curvature-induced strains accommodated by relative ductile interactions, while the formation of anisotropic ribbon-like structures with lower-curvature induced stresses, introduces a larger line tension cost, and is thus favored for brittle crystals. Our results show that for ductile crystals with large surface coverage, appearance of stable topological defects precludes the formation of anisotropic, ribbon domains. However branch-like structures with large interfacial area are stable for certain values of intermediate curvature and crystalline ductility. These processes are guided by the interplay between elastic shape instability, defects, and curvature, where pattern formations are not related to kinetic instabilities.
Negative voltage bandgap reference with multilevel curvature compensation technique
NASA Astrophysics Data System (ADS)
Xi, Liu; Qian, Liu; Xiaoshi, Jin; Yongrui, Zhao; Lee, Jong-Ho
2016-05-01
A novel high-order curvature compensation negative voltage bandgap reference (NBGR) based on a novel multilevel compensation technique is introduced. Employing an exponential curvature compensation (ECC) term with many high order terms in itself, in a lower temperature range (TR) and a multilevel curvature compensation (MLCC) term in a higher TR, a flattened and better effect of curvature compensation over the TR of 165 °C (-40 to 125 °C) is realised. The MLCC circuit adds two convex curves by using two sub-threshold operated NMOS. The proposed NBGR implemented in the Central Semiconductor Manufacturing Corporation (CSMC) 0.5 μm BCD technology demonstrates an accurate voltage of -1.183 V with a temperature coefficient (TC) as low as 2.45 ppm/°C over the TR of 165 °C at a -5.0 V power supply; the line regulation is 3 mV/V from a -5 to -2 V supply voltage. The active area of the presented NBGR is 370 × 180 μm2. Project supported by the Fund of Liaoning Province Education Department (No. L2013045).
Special-holonomy manifolds and quartic-curvature string corrections
NASA Astrophysics Data System (ADS)
Stelle, K. S.
2004-06-01
The quartic-curvature corrections derived from string theory have a very specific impact on the geometry of target-space manifolds of special holonomy. In the cases of Calabi-Yau manifolds and D = 7 manifolds of G2 holonomy, we show how the corrections conspire to preserve the unbroken supersymmetry of these backgrounds.
Controlling Protein Oligomerization with Surface Curvature on the Nanoscale
NASA Astrophysics Data System (ADS)
Kurylowicz, Marty; Dutcher, John
2011-03-01
We investigate the effect of surface curvature on the conformation of beta-lactoglobulin (β LG) using Single Molecule Force Spectroscopy. β LG is a model interfacial protein which stabilizes oil droplets in milk and is known to undergo structural rearrangement when adsorbed onto a surface. We reliably control nanoscale surface curvature by creating close-packed monolayers of monodisperse polystyrene (PS) nanoparticles with diameters of 20, 40, 60, 80 and 140 nm, which are stable in aqueous buffer. By adsorbing β LG onto these hydrophobic surfaces and collecting force-extension curves in the fluid phase we can compare the conformation of β LG on 5 different surface curvatures with that on a flat PS film. We demonstrate a transition from oligomeric to monomeric β LG as the surface curvature is increased. Histograms of contour length from fits to peaks in the force-extension curves show a single maximum near 30 nm for β LG adsorbed onto nanoparticles with diameters less than 80 nm. For the larger nanoparticles, the histogram approaches that observed for β LG adsorbed onto a flat PS film, with maxima indicative of β LG dimers and trimers.
Symmetric curvature descriptors for label-free analysis of DNA
Buzio, Renato; Repetto, Luca; Giacopelli, Francesca; Ravazzolo, Roberto; Valbusa, Ugo
2014-01-01
High-resolution microscopy techniques such as electron microscopy, scanning tunnelling microscopy and atomic force microscopy represent well-established, powerful tools for the structural characterization of adsorbed DNA molecules at the nanoscale. Notably, the analysis of DNA contours allows mapping intrinsic curvature and flexibility along the molecular backbone. This is particularly suited to address the impact of the base-pairs sequence on the local conformation of the strands and plays a pivotal role for investigations relating the inherent DNA shape and flexibility to other functional properties. Here, we introduce novel chain descriptors aimed to characterize the local intrinsic curvature and flexibility of adsorbed DNA molecules with unknown orientation. They consist of stochastic functions that couple the curvatures of two nanosized segments, symmetrically placed on the DNA contour. We show that the fine mapping of the ensemble-averaged functions along the molecular backbone generates characteristic patterns of variation that highlight all pairs of tracts with large intrinsic curvature or enhanced flexibility. We demonstrate the practical applicability of the method for DNA chains imaged by atomic force microscopy. Our approach paves the way for the label-free comparative analysis of duplexes, aimed to detect nanoscale conformational changes of physical or biological relevance in large sample numbers. PMID:25248631
Cosmological models with positive scalar spatial curvature and Λ>0
NASA Astrophysics Data System (ADS)
Ponce de Leon, J.
1987-12-01
Some exact spherically symmetric solutions of the Einstein field equations with Λ>0 and positive three-curvature are given. They have reasonable physical properties and represent universes which do not undergo inflation but have a non-de Sitter behaviour for large times. This paper extends some previous results in the literature. Permanent address: Apartado 2816, Caracas 1010-A, Venezuela.
Positivity of Curvature-Squared Corrections in Gravity
NASA Astrophysics Data System (ADS)
Cheung, Clifford; Remmen, Grant N.
2017-02-01
We study the Gauss-Bonnet (GB) term as the leading higher-curvature correction to pure Einstein gravity. Assuming a tree-level ultraviolet completion free of ghosts or tachyons, we prove that the GB term has a nonnegative coefficient in dimensions greater than 4. Our result follows from unitarity of the spectral representation for a general ultraviolet completion of the GB term.
Three-dimensional ultrasound palmprint recognition using curvature methods
NASA Astrophysics Data System (ADS)
Iula, Antonio; Nardiello, Donatella
2016-05-01
Palmprint recognition systems that use three-dimensional (3-D) information of the palm surface are the most recently explored techniques to overcome some two-dimensional palmprint difficulties. These techniques are based on light structural imaging. In this work, a 3-D ultrasound palmprint recognition system is proposed and evaluated. Volumetric images of a region of the human hand are obtained by moving an ultrasound linear array along its elevation direction and one by one acquiring a number of B-mode images, which are then grouped in a 3-D matrix. The acquisition time was contained in about 5 s. Much information that can be exploited for 3-D palmprint recognition is extracted from the ultrasound volumetric images, including palm curvature and other under-skin information as the depth of the various traits. The recognition procedure developed in this work is based on the analysis of the principal curvatures of palm surface, i.e., mean curvature image, Gaussian curvature image, and surface type. The proposed method is evaluated by performing verification and identification experiments. Preliminary results have shown that the proposed system exhibits an acceptable recognition rate. Further possible improvements of the proposed technique are finally highlighted and discussed.
On the Surprising Salience of Curvature in Grouping by Proximity
ERIC Educational Resources Information Center
Strother, Lars; Kubovy, Michael
2006-01-01
The authors conducted 3 experiments to explore the roles of curvature, density, and relative proximity in the perceptual organization of ambiguous dot patterns. To this end, they developed a new family of regular dot patterns that tend to be perceptually grouped into parallel contours, dot-sampled structured grids (DSGs). DSGs are similar to the…
Front-end electronics development at BNL
O`Connor, P.
1995-09-01
AT BNL the monolithic front-end electronics development effort is an outgrowth of work in discrete and hybrid circuits over the past 30 years. BNL`s area of specialization centers on circuits for precision amplitude measurement, with signal-to-noise ratios of 100:1 and calibration to the same level of precision. Circuits are predominantly classical, continuous-time implementation of the functions now performed by hybrids, with little or no loss of performance. Included in this category are charge and current-sensitive preamplifiers, pulse shapers, sample/hold, multiplexing, and associated calibration and control circuits. Presently integration densities are limited to 16 channels per chip. Two examples are presented to illustrate the techniques needed to adopt hybrid circuits to the constraints of monolithic CMOS technology. They are programmable pulse shapes and a charge-sensitive preamp for very low detector capacitance.
Covert contrast in velar fronting: An acoustic and ultrasound study
Byun, Tara McAllister; Buchwald, Adam; Mizoguchi, Ai
2016-01-01
There is growing evidence that speech sound acquisition is a gradual process, with instrumental measures frequently revealing covert contrast in errors perceived to involve phonemic substitution. Ultrasound imaging has the potential to expand our understanding of covert contrast by showing whether a child uses different tongue shapes while producing sounds that are perceived as neutralized. This study used an ultrasound measure (Dorsum Excursion Index) and acoustic measures (VOT and spectral moments of the burst) to investigate overt and covert contrast between velar and alveolar stops in child speech. Participants were two children who produced a perceptually overt velar-alveolar contrast and two children who neutralized the contrast via velar fronting. Both acoustic and ultrasound measures revealed significant differences between perceptually distinct velar and alveolar targets. One child with velar fronting demonstrated covert contrast in one acoustic and one ultrasound measure; the other showed no evidence of contrast. Clinical implications are discussed. PMID:26325303
Traking of Laboratory Debris Flow Fronts with Image Analysis
NASA Astrophysics Data System (ADS)
Queiroz de Oliveira, Gustavo; Kulisch, Helmut; Fischer, Jan-Thomas; Scheidl, Christian; Pudasaini, Shiva P.
2015-04-01
Image analysis technique is applied to track the time evolution of rapid debris flow fronts and their velocities in laboratory experiments. These experiments are parts of the project avaflow.org that intends to develop a GIS-based open source computational tool to describe wide spectrum of rapid geophysical mass flows, including avalanches and real two-phase debris flows down complex natural slopes. The laboratory model consists of a large rectangular channel 1.4m wide and 10m long, with adjustable inclination and other flow configurations. The setup allows investigate different two phase material compositions including large fluid fractions. The large size enables to transfer the results to large-scale natural events providing increased measurement accuracy. The images are captured by a high speed camera, a standard digital camera. The fronts are tracked by the camera to obtain data in debris flow experiments. The reflectance analysis detects the debris front in every image frame; its presence changes the reflectance at a certain pixel location during the flow. The accuracy of the measurements was improved with a camera calibration procedure. As one of the great problems in imaging and analysis, the systematic distortions of the camera lens are contained in terms of radial and tangential parameters. The calibration procedure estimates the optimal values for these parameters. This allows us to obtain physically correct and undistorted image pixels. Then, we map the images onto a physical model geometry, which is the projective photogrammetry, in which the image coordinates are connected with the object space coordinates of the flow. Finally, the physical model geometry is rewritten in the direct linear transformation form, which allows for the conversion from one to another coordinate system. With our approach, the debris front position can then be estimated by combining the reflectance, calibration and the linear transformation. The consecutive debris front
Stimulation of root elongation and curvature by calcium.
Takahashi, H; Scott, T K; Suge, H
1992-01-01
Ca2+ has been proposed to mediate inhibition of root elongation. However, exogenous Ca2+ at 10 or 20 millimolar, applied directly to the root cap, significantly stimulated root elongation in pea (Pisum sativum L.) and corn (Zea mays L.) seedlings. Furthermore, Ca2+ at 1 to 20 millimolar, applied unilaterally to the caps of Alaska pea roots, caused root curvature away from the Ca2+ source, which was caused by an acceleration of elongation growth on the convex side (Ca2+ side) of the roots. Roots of an agravitropic pea mutant, ageotropum, responded to a greater extent. Roots of Merit and Silver Queen corn also responded to Ca2+ in similar ways but required a higher Ca2+ concentration than that of pea roots. Roots of all other cultivars tested (additional four cultivars of pea and one of corn) curved away from the unilateral Ca2+ source as well. The Ca(2+)-stimulated curvature was substantially enhanced by light. A Ca2+ ionophore, A23187, at 20 micromolar or abscisic acid at 0.1 to 100 micromolar partially substituted for the light effect and enhanced the Ca(2+)-stimulated curvature in the dark. Unilateral application of Ca2+ to the elongation zone of intact roots or to the cut end of detipped roots caused either no curvature or very slight curvature toward the Ca2+. Thus, Ca2+ action on root elongation differs depending on its site of application. The stimulatory action of Ca2+ may involve an elevation of cytoplasmic Ca2+ in root cap cells and may partipate in root tropisms.
Stimulation of root elongation and curvature by calcium
NASA Technical Reports Server (NTRS)
Takahashi, H.; Scott, T. K.; Suge, H.
1992-01-01
Ca2+ has been proposed to mediate inhibition of root elongation. However, exogenous Ca2+ at 10 or 20 millimolar, applied directly to the root cap, significantly stimulated root elongation in pea (Pisum sativum L.) and corn (Zea mays L.) seedlings. Furthermore, Ca2+ at 1 to 20 millimolar, applied unilaterally to the caps of Alaska pea roots, caused root curvature away from the Ca2+ source, which was caused by an acceleration of elongation growth on the convex side (Ca2+ side) of the roots. Roots of an agravitropic pea mutant, ageotropum, responded to a greater extent. Roots of Merit and Silver Queen corn also responded to Ca2+ in similar ways but required a higher Ca2+ concentration than that of pea roots. Roots of all other cultivars tested (additional four cultivars of pea and one of corn) curved away from the unilateral Ca2+ source as well. The Ca(2+)-stimulated curvature was substantially enhanced by light. A Ca2+ ionophore, A23187, at 20 micromolar or abscisic acid at 0.1 to 100 micromolar partially substituted for the light effect and enhanced the Ca(2+)-stimulated curvature in the dark. Unilateral application of Ca2+ to the elongation zone of intact roots or to the cut end of detipped roots caused either no curvature or very slight curvature toward the Ca2+. Thus, Ca2+ action on root elongation differs depending on its site of application. The stimulatory action of Ca2+ may involve an elevation of cytoplasmic Ca2+ in root cap cells and may partipate in root tropisms.
Polarization and wavelength diversities of Gulf Stream fronts imaged by AIRSAR
NASA Technical Reports Server (NTRS)
Lee, J. S.; Jansen, R. W.; Marmorino, G. O.; Chubb, S. R.
1995-01-01
During the 1990 Gulf Stream Experiment, NASA/JPL AIRSAR imaged the north edge of the Gulf Stream near the coast of Virginia. Simultaneous in-situ measurements of currents, temperatures, salinities, etc. were made for several crossings of the north edge by the R/V Cape Henlopen. Measurements identified two fronts with shearing and converging flows. The polarimetric SAR images from the fronts showed two bright linear features. One of them corresponds to the temperature front, which separated the warm Gulf Stream water to the south from a cool, freshwater filament to the north. The other line, located about 8 km north of the temperature front, is believed to correspond to the velocity front between the filament and the slope water. At these fronts, wave-current interactions produced narrow bands of steep and breaking waves manifesting higher radar returns in polarimetric SAR images. In general, our AIRSAR imagery shows that the signal-to-clutter ratio of radar cross sections for the temperature front is higher than that of the velocity front. In this paper, we study the polarization and wavelength diversities of radar response of these two fronts using the P-, L-, and C-Band Polarimetric SAR data. The north-south flight path of the AIRSAR crossed the temperature front several times and provided valuable data for analysis. Three individual passes are investigated. We found that for the temperature front, the cross-pol (HV) responses are much higher than co-pol responses (VV and HH), and that P-Band HV has the highest signal to clutter ratio. For the velocity front, the ratio is the strongest in P-Band VV, and it is indistinguishable for all polarizations in C-Band. The radar cross sections for all three polarization (HH, HV, and VV) and for all three bands are modelled using an ocean wave model and a composite Bragg scattering model. In our initial investigations, the theoretical model agrees qualitatively with the AIRSAR observations.
Condensation Front Migration in a Protoplanetary Nebula
NASA Technical Reports Server (NTRS)
Davis, Sanford S.
2004-01-01
Condensation front dynamics are investigated in the mid-solar nebula region. A quasi-steady model of the evolving nebula is combined with equilibrium vapor pressure curves to determine evolutionary condensation fronts for selected species. These fronts are found to migrate inwards from the far-nebula to final positions during a period of 10(exp 7) years. The physical process governing this movement is a combination of local viscous heating and luminescent heating from the central star. Two luminescent heating models are used and their effects on the ultimate radial position of the condensation front are discussed. At first the fronts move much faster than the nebular accretion velocity, but after a time the accreting gas and dust overtakes the slowing condensation front.
Yau, Michelle S; Demissie, Serkalem; Zhou, Yanhua; Anderson, Dennis E; Lorbergs, Amanda L; Kiel, Douglas P; Allaire, Brett T; Yang, Laiji; Cupples, L Adrienne; Travison, Thomas G; Bouxsein, Mary L; Karasik, David; Samelson, Elizabeth J
2017-01-01
Hyperkyphosis is a common spinal disorder in older adults, characterized by excessive forward curvature of the thoracic spine and adverse health outcomes. The etiology of hyperkyphosis has not been firmly established, but may be related to changes that occur with aging in the vertebrae, discs, joints, and muscles, which function as a unit to support the spine. Determining the contribution of genetics to thoracic spine curvature and the degree of genetic sharing among co-occurring measures of spine health may provide insight into the etiology of hyperkyphosis. The purpose of our study was to estimate heritability of thoracic spine curvature using T4–T12 kyphosis (Cobb) angle and genetic correlations between thoracic spine curvature and vertebral fracture, intervertebral disc height narrowing, facet joint osteoarthritis (OA), lumbar spine volumetric bone mineral density (vBMD), and paraspinal muscle area and density, which were all assessed from computed tomography (CT) images. Participants included 2063 women and men in the second and third generation offspring of the original cohort of the Framingham Study. Heritability of kyphosis angle, adjusted for age, sex, and weight, was 54% (95% confidence interval [CI], 43% to 64%). We found moderate genetic correlations between kyphosis angle and paraspinal muscle area ( ρ^G, −0.46; 95% CI, −0.67 to −0.26), vertebral fracture ( ρ^G, 0.39; 95% CI, 0.18 to 0.61), vBMD ( ρ^G,−0.23; 95% CI, −0.41 to −0.04), and paraspinal muscle density ( ρ^G,−0.22; 95% CI, −0.48 to 0.03). Genetic correlations between kyphosis angle and disc height narrowing ( ρ^G, 0.17; 95% CI, −0.05 to 0.38) and facet joint OA ( ρ^G, 0.05; 95% CI, −0.15 to 0.24) were low. Thoracic spine curvature may be heritable and share genetic factors with other age-related spine traits including trunk muscle size, vertebral fracture, and bone mineral density. PMID:27455046
Electrical double layers at shock fronts in glow discharges and afterglows
Siefert, Nicholas S.
2010-12-15
This paper examines the propagation of spark-generated shockwaves (1.0
PHYSICS RESULTS OF THE NSLS-II LINAC FRONT END TEST STAND
Fliller R. P.; Gao, F.; Yang, X.; Rose, J.; Shaftan, T.; Piel, C
2012-05-20
The Linac Front End Test Stand (LFETS) was installed at the Source Development Laboratory (SDL) in the fall of 2011 in order to test the Linac Front End. The goal of these tests was to test the electron source against the specifications of the linac. In this report, we discuss the results of these measurements and the effect on linac performance.