X-ray and optical emission-line filaments in the cooling flow cluster 2A 0335 + 096

NASA Technical Reports Server (NTRS)

Sarazin, Craig L.; O'Connell, Robert W.; Mcnamara, Brian R.

1992-01-01

We present a new high-resolution X-ray image of the 2A 0335 + 096 cluster of galaxies obtained with the High Resolution Imager (HRI) aboard the ROSAT satellite. The presence of dense gas having a very short cooling time in the central regions confirms its earlier identification as a cooling flow. The X-ray emission from the central regions of the cooling flow shows a great deal of filamentary structure. Using the crude spectral resolution of the HRI, we show that these filaments are the result of excess emission, rather than foreground X-ray absorption. Although there are uncertainties in the pointing, many of the X-ray features in the cooling flow region correspond to features in H-alpha optical line emission. This suggests that the optical emission line gas has resulted directly from the cooling of X-ray-emitting gas. The filament material cannot be in hydrostatic equilibrium, and it is likely that other forces such as rotation, turbulence, and magnetic fields influence the dynamical state of the gas.

Towards breaking the spatial resolution barriers: An optical flow and super-resolution approach for sea ice motion estimation

NASA Astrophysics Data System (ADS)

Petrou, Zisis I.; Xian, Yang; Tian, YingLi

2018-04-01

Estimation of sea ice motion at fine scales is important for a number of regional and local level applications, including modeling of sea ice distribution, ocean-atmosphere and climate dynamics, as well as safe navigation and sea operations. In this study, we propose an optical flow and super-resolution approach to accurately estimate motion from remote sensing images at a higher spatial resolution than the original data. First, an external example learning-based super-resolution method is applied on the original images to generate higher resolution versions. Then, an optical flow approach is applied on the higher resolution images, identifying sparse correspondences and interpolating them to extract a dense motion vector field with continuous values and subpixel accuracies. Our proposed approach is successfully evaluated on passive microwave, optical, and Synthetic Aperture Radar data, proving appropriate for multi-sensor applications and different spatial resolutions. The approach estimates motion with similar or higher accuracy than the original data, while increasing the spatial resolution of up to eight times. In addition, the adopted optical flow component outperforms a state-of-the-art pattern matching method. Overall, the proposed approach results in accurate motion vectors with unprecedented spatial resolutions of up to 1.5 km for passive microwave data covering the entire Arctic and 20 m for radar data, and proves promising for numerous scientific and operational applications.

Vertical Optical Scanning with Panoramic Vision for Tree Trunk Reconstruction

PubMed Central

Berveglieri, Adilson; Liang, Xinlian; Honkavaara, Eija

2017-01-01

This paper presents a practical application of a technique that uses a vertical optical flow with a fisheye camera to generate dense point clouds from a single planimetric station. Accurate data can be extracted to enable the measurement of tree trunks or branches. The images that are collected with this technique can be oriented in photogrammetric software (using fisheye models) and used to generate dense point clouds, provided that some constraints on the camera positions are adopted. A set of images was captured in a forest plot in the experiments. Weighted geometric constraints were imposed in the photogrammetric software to calculate the image orientation, perform dense image matching, and accurately generate a 3D point cloud. The tree trunks in the scenes were reconstructed and mapped in a local reference system. The accuracy assessment was based on differences between measured and estimated trunk diameters at different heights. Trunk sections from an image-based point cloud were also compared to the corresponding sections that were extracted from a dense terrestrial laser scanning (TLS) point cloud. Cylindrical fitting of the trunk sections allowed the assessment of the accuracies of the trunk geometric shapes in both clouds. The average difference between the cylinders that were fitted to the photogrammetric cloud and those to the TLS cloud was less than 1 cm, which indicates the potential of the proposed technique. The point densities that were obtained with vertical optical scanning were 1/3 less than those that were obtained with TLS. However, the point density can be improved by using higher resolution cameras. PMID:29207468

Vertical Optical Scanning with Panoramic Vision for Tree Trunk Reconstruction.

PubMed

Berveglieri, Adilson; Tommaselli, Antonio M G; Liang, Xinlian; Honkavaara, Eija

2017-12-02

This paper presents a practical application of a technique that uses a vertical optical flow with a fisheye camera to generate dense point clouds from a single planimetric station. Accurate data can be extracted to enable the measurement of tree trunks or branches. The images that are collected with this technique can be oriented in photogrammetric software (using fisheye models) and used to generate dense point clouds, provided that some constraints on the camera positions are adopted. A set of images was captured in a forest plot in the experiments. Weighted geometric constraints were imposed in the photogrammetric software to calculate the image orientation, perform dense image matching, and accurately generate a 3D point cloud. The tree trunks in the scenes were reconstructed and mapped in a local reference system. The accuracy assessment was based on differences between measured and estimated trunk diameters at different heights. Trunk sections from an image-based point cloud were also compared to the corresponding sections that were extracted from a dense terrestrial laser scanning (TLS) point cloud. Cylindrical fitting of the trunk sections allowed the assessment of the accuracies of the trunk geometric shapes in both clouds. The average difference between the cylinders that were fitted to the photogrammetric cloud and those to the TLS cloud was less than 1 cm, which indicates the potential of the proposed technique. The point densities that were obtained with vertical optical scanning were 1/3 less than those that were obtained with TLS. However, the point density can be improved by using higher resolution cameras.

Fibre-optic distributed temperature sensing in combined sewer systems.

PubMed

Schilperoort, R P S; Clemens, F H L R

2009-01-01

This paper introduces the application of fibre-optic distributed temperature sensing (DTS) in combined sewer systems. The DTS-technique uses a fibre-optic cable that is inserted into a combined sewer system in combination with a laser instrument that performs measurements and logs the data. The DTS-technique allows monitoring in-sewer temperatures with dense spatial and temporal resolutions. The installation of a fibre-optic cable in a combined sewer system has proven feasible. The use of a single instrument in an easy accessible and safe location that can simultaneously monitor up to several hundreds of monitoring locations makes the DTS set-up easy in use and nearly free of maintenance. Temperature data from a one-week monitoring campaign in an 1,850 m combined sewer system shows the level of detail with which in-sewer processes that affect wastewater temperatures can be studied. Individual discharges from house-connections can be tracked in time and space. With a dedicated cable configuration the confluence of wastewater flows can be observed with a potential to derive the relative contributions of contributary flows to a total flow. Also, the inflow and in-sewer propagation of stormwater can be monitored.

Variational optical flow computation in real time.

PubMed

Bruhn, Andrés; Weickert, Joachim; Feddern, Christian; Kohlberger, Timo; Schnörr, Christoph

2005-05-01

This paper investigates the usefulness of bidirectional multigrid methods for variational optical flow computations. Although these numerical schemes are among the fastest methods for solving equation systems, they are rarely applied in the field of computer vision. We demonstrate how to employ those numerical methods for the treatment of variational optical flow formulations and show that the efficiency of this approach even allows for real-time performance on standard PCs. As a representative for variational optic flow methods, we consider the recently introduced combined local-global method. It can be considered as a noise-robust generalization of the Horn and Schunck technique. We present a decoupled, as well as a coupled, version of the classical Gauss-Seidel solver, and we develop several multgrid implementations based on a discretization coarse grid approximation. In contrast, with standard bidirectional multigrid algorithms, we take advantage of intergrid transfer operators that allow for nondyadic grid hierarchies. As a consequence, no restrictions concerning the image size or the number of traversed levels have to be imposed. In the experimental section, we juxtapose the developed multigrid schemes and demonstrate their superior performance when compared to unidirectional multgrid methods and nonhierachical solvers. For the well-known 316 x 252 Yosemite sequence, we succeeded in computing the complete set of dense flow fields in three quarters of a second on a 3.06-GHz Pentium4 PC. This corresponds to a frame rate of 18 flow fields per second which outperforms the widely-used Gauss-Seidel method by almost three orders of magnitude.

Evaluation of Event-Based Algorithms for Optical Flow with Ground-Truth from Inertial Measurement Sensor

PubMed Central

Rueckauer, Bodo; Delbruck, Tobi

2016-01-01

In this study we compare nine optical flow algorithms that locally measure the flow normal to edges according to accuracy and computation cost. In contrast to conventional, frame-based motion flow algorithms, our open-source implementations compute optical flow based on address-events from a neuromorphic Dynamic Vision Sensor (DVS). For this benchmarking we created a dataset of two synthesized and three real samples recorded from a 240 × 180 pixel Dynamic and Active-pixel Vision Sensor (DAVIS). This dataset contains events from the DVS as well as conventional frames to support testing state-of-the-art frame-based methods. We introduce a new source for the ground truth: In the special case that the perceived motion stems solely from a rotation of the vision sensor around its three camera axes, the true optical flow can be estimated using gyro data from the inertial measurement unit integrated with the DAVIS camera. This provides a ground-truth to which we can compare algorithms that measure optical flow by means of motion cues. An analysis of error sources led to the use of a refractory period, more accurate numerical derivatives and a Savitzky-Golay filter to achieve significant improvements in accuracy. Our pure Java implementations of two recently published algorithms reduce computational cost by up to 29% compared to the original implementations. Two of the algorithms introduced in this paper further speed up processing by a factor of 10 compared with the original implementations, at equal or better accuracy. On a desktop PC, they run in real-time on dense natural input recorded by a DAVIS camera. PMID:27199639

Optical Coherence Tomography Angiography of Optic Disc Perfusion in Glaucoma

PubMed Central

Jia, Yali; Wei, Eric; Wang, Xiaogang; Zhang, Xinbo; Morrison, John C.; Parikh, Mansi; Lombardi, Lori H.; Gattey, Devin M.; Armour, Rebecca L.; Edmunds, Beth; Kraus, Martin F.; Fujimoto, James G.; Huang, David

2014-01-01

Purpose To compare optic disc perfusion between normal and glaucoma subjects using optical coherence tomography (OCT) angiography and detect optic disc perfusion changes in glaucoma. Design Observational, cross-sectional study. Participants Twenty-four normal subjects and 11 glaucoma patients were included. Methods One eye of each subject was scanned by a high-speed 1050 nm wavelength swept-source OCT instrument. The split-spectrum amplitude-decorrelation angiography algorithm (SSADA) was used to compute three-dimensional optic disc angiography. A disc flow index was computed from four registered scans. Confocal scanning laser ophthalmoscopy (cSLO) was used to measure disc rim area, and stereo photography was used to evaluate cup/disc ratios. Wide field OCT scans over the discs were used to measure retinal nerve fiber layer (NFL) thickness. Main Outcome Measurements Variability was assessed by coefficient of variation (CV). Diagnostic accuracy was assessed by sensitivity and specificity. Comparisons between glaucoma and normal groups were analyzed by Wilcoxon rank-sum test. Correlations between disc flow index, structural assessments, and visual field (VF) parameters were assessed by linear regression. Results In normal discs, a dense microvascular network was visible on OCT angiography. This network was visibly attenuated in glaucoma subjects. The intra-visit repeatability, inter-visit reproducibility, and normal population variability of the optic disc flow index were 1.2%, 4.2%, and 5.0% CV respectively. The disc flow index was reduced by 25% in the glaucoma group (p = 0.003). Sensitivity and specificity were both 100% using an optimized cutoff. The flow index was highly correlated with VF pattern standard deviation (R2 = 0.752, p = 0.001). These correlations were significant even after accounting for age, cup/disc area ratio, NFL, and rim area. Conclusions OCT angiography, generated by the new SSADA algorithm, repeatably measures optic disc perfusion. OCT angiography could be useful in the evaluation of glaucoma and glaucoma progression. PMID:24629312

Experimental realization of the analogy of quantum dense coding in classical optics

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

Yang, Zhenwei; Sun, Yifan; Li, Pengyun

2016-06-15

We report on the experimental realization of the analogy of quantum dense coding in classical optical communication using classical optical correlations. Compared to quantum dense coding that uses pairs of photons entangled in polarization, we find that the proposed design exhibits many advantages. Considering that it is convenient to realize in optical communication, the attainable channel capacity in the experiment for dense coding can reach 2 bits, which is higher than that of the usual quantum coding capacity (1.585 bits). This increased channel capacity has been proven experimentally by transmitting ASCII characters in 12 quaternary digitals instead of the usualmore » 24 bits.« less

Vision based obstacle detection and grouping for helicopter guidance

NASA Technical Reports Server (NTRS)

Sridhar, Banavar; Chatterji, Gano

1993-01-01

Electro-optical sensors can be used to compute range to objects in the flight path of a helicopter. The computation is based on the optical flow/motion at different points in the image. The motion algorithms provide a sparse set of ranges to discrete features in the image sequence as a function of azimuth and elevation. For obstacle avoidance guidance and display purposes, these discrete set of ranges, varying from a few hundreds to several thousands, need to be grouped into sets which correspond to objects in the real world. This paper presents a new method for object segmentation based on clustering the sparse range information provided by motion algorithms together with the spatial relation provided by the static image. The range values are initially grouped into clusters based on depth. Subsequently, the clusters are modified by using the K-means algorithm in the inertial horizontal plane and the minimum spanning tree algorithms in the image plane. The object grouping allows interpolation within a group and enables the creation of dense range maps. Researchers in robotics have used densely scanned sequence of laser range images to build three-dimensional representation of the outside world. Thus, modeling techniques developed for dense range images can be extended to sparse range images. The paper presents object segmentation results for a sequence of flight images.

The dense gas mass fraction of molecular clouds in the Milky Way

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

Battisti, Andrew J.; Heyer, Mark H., E-mail: abattist@astro.umass.edu, E-mail: heyer@astro.umass.edu

2014-01-10

The mass fraction of dense gas within giant molecular clouds (GMCs) of the Milky Way is investigated using {sup 13}CO data from the Five College Radio Astronomy Observatory Galactic Plane Surveys and the Bolocam Galactic Plane Survey (BGPS) of 1.1 mm dust continuum emission. A sample of 860 compact dust sources are selected from the BGPS catalog and kinematically linked to 344 clouds of extended (>3') {sup 13}CO J = 1-0 emission. Gas masses are tabulated for the full dust source and subregions within the dust sources with mass surface densities greater than 200 M {sub ☉} pc{sup –2}, whichmore » are assumed to be regions of enhanced volume density. Masses of the parent GMCs are calculated assuming optically thin {sup 13}CO J = 1-0 emission and local thermodynamic equilibrium conditions. The mean fractional mass of dust sources to host GMC mass is 0.11{sub −0.06}{sup +0.12}. The high column density subregions comprise 0.07{sub −0.05}{sup +0.13} of the mass of the cloud. Owing to our assumptions, these values are upper limits to the true mass fractions. The fractional mass of dense gas is independent of GMC mass and gas surface density. The low dense gas mass fraction suggests that the formation of dense structures within GMCs is the primary bottleneck for star formation. The distribution of velocity differences between the dense gas and the low density material along the line of sight is also examined. We find a strong, centrally peaked distribution centered on zero velocity displacement. This distribution of velocity differences is modeled with radially converging flows toward the dense gas position that are randomly oriented with respect to the observed line of sight. These models constrain the infall velocities to be 2-4 km s{sup –1} for various flow configurations.« less

Optical flow estimation on image sequences with differently exposed frames

NASA Astrophysics Data System (ADS)

Bengtsson, Tomas; McKelvey, Tomas; Lindström, Konstantin

2015-09-01

Optical flow (OF) methods are used to estimate dense motion information between consecutive frames in image sequences. In addition to the specific OF estimation method itself, the quality of the input image sequence is of crucial importance to the quality of the resulting flow estimates. For instance, lack of texture in image frames caused by saturation of the camera sensor during exposure can significantly deteriorate the performance. An approach to avoid this negative effect is to use different camera settings when capturing the individual frames. We provide a framework for OF estimation on such sequences that contain differently exposed frames. Information from multiple frames are combined into a total cost functional such that the lack of an active data term for saturated image areas is avoided. Experimental results demonstrate that using alternate camera settings to capture the full dynamic range of an underlying scene can clearly improve the quality of flow estimates. When saturation of image data is significant, the proposed methods show superior performance in terms of lower endpoint errors of the flow vectors compared to a set of baseline methods. Furthermore, we provide some qualitative examples of how and when our method should be used.

Flash X-Ray measurements on the shock-induced dispersal of a dense particle curtain

DOE PAGES

Wagner, Justin L.; Kearney, Sean P.; Beresh, Steven J.; ...

2015-11-23

The interaction of a Mach 1.67 shock wave with a dense particle curtain is quantified using flash radiography. These new data provide a view of particle transport inside a compressible, dense gas–solid flow of high optical opacity. The curtain, composed of 115-µm glass spheres, initially spans 87 % of the test section width and has a streamwise thickness of about 2 mm. Radiograph intensities are converted to particle volume fraction distributions using the Beer–Lambert law. The mass in the particle curtain, as determined from the X-ray data, is in reasonable agreement with that given from a simpler method using amore » load cell and particle imaging. Following shock impingement, the curtain propagates downstream and the peak volume fraction decreases from about 23 to about 4 % over a time of 340 µs. The propagation occurs asymmetrically, with the downstream side of the particle curtain experiencing a greater volume fraction gradient than the upstream side, attributable to the dependence of particle drag on volume fraction. Bulk particle transport is quantified from the time-dependent center of mass of the curtain. Furthermore, the bulk acceleration of the curtain is shown to be greater than that predicted for a single 115-µm particle in a Mach 1.67 shock-induced flow.« less

Flash X-Ray measurements on the shock-induced dispersal of a dense particle curtain

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

Wagner, Justin L.; Kearney, Sean P.; Beresh, Steven J.

The interaction of a Mach 1.67 shock wave with a dense particle curtain is quantified using flash radiography. These new data provide a view of particle transport inside a compressible, dense gas–solid flow of high optical opacity. The curtain, composed of 115-µm glass spheres, initially spans 87 % of the test section width and has a streamwise thickness of about 2 mm. Radiograph intensities are converted to particle volume fraction distributions using the Beer–Lambert law. The mass in the particle curtain, as determined from the X-ray data, is in reasonable agreement with that given from a simpler method using amore » load cell and particle imaging. Following shock impingement, the curtain propagates downstream and the peak volume fraction decreases from about 23 to about 4 % over a time of 340 µs. The propagation occurs asymmetrically, with the downstream side of the particle curtain experiencing a greater volume fraction gradient than the upstream side, attributable to the dependence of particle drag on volume fraction. Bulk particle transport is quantified from the time-dependent center of mass of the curtain. Furthermore, the bulk acceleration of the curtain is shown to be greater than that predicted for a single 115-µm particle in a Mach 1.67 shock-induced flow.« less

Flash X-ray measurements on the shock-induced dispersal of a dense particle curtain

NASA Astrophysics Data System (ADS)

Wagner, Justin L.; Kearney, Sean P.; Beresh, Steven J.; DeMauro, Edward P.; Pruett, Brian O.

2015-12-01

The interaction of a Mach 1.67 shock wave with a dense particle curtain is quantified using flash radiography. These new data provide a view of particle transport inside a compressible, dense gas-solid flow of high optical opacity. The curtain, composed of 115-µm glass spheres, initially spans 87 % of the test section width and has a streamwise thickness of about 2 mm. Radiograph intensities are converted to particle volume fraction distributions using the Beer-Lambert law. The mass in the particle curtain, as determined from the X-ray data, is in reasonable agreement with that given from a simpler method using a load cell and particle imaging. Following shock impingement, the curtain propagates downstream and the peak volume fraction decreases from about 23 to about 4 % over a time of 340 µs. The propagation occurs asymmetrically, with the downstream side of the particle curtain experiencing a greater volume fraction gradient than the upstream side, attributable to the dependence of particle drag on volume fraction. Bulk particle transport is quantified from the time-dependent center of mass of the curtain. The bulk acceleration of the curtain is shown to be greater than that predicted for a single 115-µm particle in a Mach 1.67 shock-induced flow.

Recent progress in InP/polymer-based devices for telecom and data center applications

NASA Astrophysics Data System (ADS)

Kleinert, Moritz; Zhang, Ziyang; de Felipe, David; Zawadzki, Crispin; Maese Novo, Alejandro; Brinker, Walter; Möhrle, Martin; Keil, Norbert

2015-02-01

Recent progress on polymer-based photonic devices and hybrid photonic integration technology using InP-based active components is presented. High performance thermo-optic components, including compact polymer variable optical attenuators and switches are powerful tools to regulate and control the light flow in the optical backbone. Polymer arrayed waveguide gratings integrated with InP laser and detector arrays function as low-cost optical line terminals (OLTs) in the WDM-PON network. External cavity tunable lasers combined with C/L band thinfilm filter, on-chip U-groove and 45° mirrors construct a compact, bi-directional and color-less optical network unit (ONU). A tunable laser integrated with VOAs, TFEs and two 90° hybrids builds the optical front-end of a colorless, dual-polarization coherent receiver. Multicore polymer waveguides and multi-step 45°mirrors are demonstrated as bridging devices between the spatialdivision- multiplexing transmission technology using multi-core fibers and the conventional PLCbased photonic platforms, appealing to the fast development of dense 3D photonic integration.

Apparatus and method for creating a photonic densely-accumulated ray-point

NASA Technical Reports Server (NTRS)

Park, Yeonjoon (Inventor); Choi, Sang H. (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

2012-01-01

An optical apparatus includes an optical diffraction device configured for diffracting a predetermined wavelength of incident light onto adjacent optical focal points, and a photon detector for detecting a spectral characteristic of the predetermined wavelength. One of the optical focal points is a constructive interference point and the other optical focal point is a destructive interference point. The diffraction device, which may be a micro-zone plate (MZP) of micro-ring gratings or an optical lens, generates a constructive ray point using phase-contrasting of the destructive interference point. The ray point is located between adjacent optical focal points. A method of generating a densely-accumulated ray point includes directing incident light onto the optical diffraction device, diffracting the selected wavelength onto the constructive interference focal point and the destructive interference focal point, and generating the densely-accumulated ray point in a narrow region.

Speckle contrast diffuse correlation tomography of complex turbid medium flow

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

Huang, Chong; Irwin, Daniel; Lin, Yu

2015-07-15

Purpose: Developed herein is a three-dimensional (3D) flow contrast imaging system leveraging advancements in the extension of laser speckle contrast imaging theories to deep tissues along with our recently developed finite-element diffuse correlation tomography (DCT) reconstruction scheme. This technique, termed speckle contrast diffuse correlation tomography (scDCT), enables incorporation of complex optical property heterogeneities and sample boundaries. When combined with a reflectance-based design, this system facilitates a rapid segue into flow contrast imaging of larger, in vivo applications such as humans. Methods: A highly sensitive CCD camera was integrated into a reflectance-based optical system. Four long-coherence laser source positions were coupledmore » to an optical switch for sequencing of tomographic data acquisition providing multiple projections through the sample. This system was investigated through incorporation of liquid and solid tissue-like phantoms exhibiting optical properties and flow characteristics typical of human tissues. Computer simulations were also performed for comparisons. A uniquely encountered smear correction algorithm was employed to correct point-source illumination contributions during image capture with the frame-transfer CCD and reflectance setup. Results: Measurements with scDCT on a homogeneous liquid phantom showed that speckle contrast-based deep flow indices were within 12% of those from standard DCT. Inclusion of a solid phantom submerged below the liquid phantom surface allowed for heterogeneity detection and validation. The heterogeneity was identified successfully by reconstructed 3D flow contrast tomography with scDCT. The heterogeneity center and dimensions and averaged relative flow (within 3%) and localization were in agreement with actuality and computer simulations, respectively. Conclusions: A custom cost-effective CCD-based reflectance 3D flow imaging system demonstrated rapid acquisition of dense boundary data and, with further studies, a high potential for translatability to real tissues with arbitrary boundaries. A requisite correction was also found for measurements in the fashion of scDCT to recover accurate speckle contrast of deep tissues.« less

Estimation of Discontinuous Displacement Vector Fields with the Minimum Description Length Criterion.

DTIC Science & Technology

1990-10-01

type of approach for finding a dense displacement vector field has a time complexity that allows a real - time implementation when an appropriate control...hardly vector fields as they appear in Stereo or motion. The reason for this is the fact that local displacement vector field ( DVF ) esti- mates bave...2 objects’ motion, but that the quantitative optical flow is not a reliable measure of the real motion [VP87, SU87]. This applies even more to the

Jammed Clusters and Non-locality in Dense Granular Flows

NASA Astrophysics Data System (ADS)

Kharel, Prashidha; Rognon, Pierre

We investigate the micro-mechanisms underpinning dense granular flow behaviour from a series of DEM simulations of pure shear flows of dry grains. We observe the development of transient clusters of jammed particles within the flow. Typical size of such clusters is found to scale with the inertial number with a power law that is similar to the scaling of shear-rate profile relaxation lengths observed previously. Based on the simple argument that transient clusters of size l exist in the dense flow regime, the formulation of steady state condition for non-homogeneous shear flow results in a general non-local relation, which is similar in form to the non-local relation conjectured for soft glassy flows. These findings suggest the formation of jammed clusters to be the key micro-mechanism underpinning non-local behaviour in dense granular flows. Particles and Grains Laboratory, School of Civil Engineering, The University of Sydney, Sydney, NSW 2006, Australia.

Microbial alignment in flow changes ocean light climate.

PubMed

Marcos; Seymour, Justin R; Luhar, Mitul; Durham, William M; Mitchell, James G; Macke, Andreas; Stocker, Roman

2011-03-08

The growth of microbial cultures in the laboratory often is assessed informally with a quick flick of the wrist: dense suspensions of microorganisms produce translucent "swirls" when agitated. Here, we rationalize the mechanism behind this phenomenon and show that the same process may affect the propagation of light through the upper ocean. Analogous to the shaken test tubes, the ocean can be characterized by intense fluid motion and abundant microorganisms. We demonstrate that the swirl patterns arise when elongated microorganisms align preferentially in the direction of fluid flow and alter light scattering. Using a combination of experiments and mathematical modeling, we find that this phenomenon can be recurrent under typical marine conditions. Moderate shear rates (0.1 s(-1)) can increase optical backscattering of natural microbial assemblages by more than 20%, and even small shear rates (0.001 s(-1)) can increase backscattering from blooms of large phytoplankton by more than 30%. These results imply that fluid flow, currently neglected in models of marine optics, may exert an important control on light propagation, influencing rates of global carbon fixation and how we estimate these rates via remote sensing.

Hugoniot measurements of double-shocked precompressed dense xenon plasmas

NASA Astrophysics Data System (ADS)

Zheng, J.; Chen, Q. F.; Gu, Y. J.; Chen, Z. Y.

2012-12-01

The current partially ionized plasmas models for xenon show substantial differences since the description of pressure and thermal ionization region becomes a formidable task, prompting the need for an improved understanding of dense xenon plasmas behavior at above 100 GPa. We performed double-shock compression experiments on dense xenon to determine accurately the Hugoniot up to 172 GPa using a time-resolved optical radiation method. The planar strong shock wave was produced using a flyer plate impactor accelerated up to ˜6 km/s with a two-stage light-gas gun. The time-resolved optical radiation histories were acquired by using a multiwavelength channel optical transience radiance pyrometer. Shock velocity was measured and mass velocity was determined by the impedance-matching methods. The experimental equation of state of dense xenon plasmas are compared with the self-consistent fluid variational calculations of dense xenon in the region of partial ionization over a wide range of pressures and temperatures.

A Review of Recent Developments in X-Ray Diagnostics for Turbulent and Optically Dense Rocket Sprays

NASA Technical Reports Server (NTRS)

Radke, Christopher; Halls, Benjamin; Kastengren, Alan; Meyer, Terrence

2017-01-01

Highly efficient mixing and atomization of fuel and oxidizers is an important factor in many propulsion and power generating applications. To better quantify breakup and mixing in atomizing sprays, several diagnostic techniques have been developed to collect droplet information and spray statistics. Several optical based techniques, such as Ballistic Imaging and SLIPI have previously demonstrated qualitative measurements in optically dense sprays, however these techniques have produced limited quantitative information in the near injector region. To complement to these advances, a recent wave of developments utilizing synchrotron based x-rays have been successful been implemented facilitating the collection of quantitative measurements in optically dense sprays.

Detection of dilute sperm samples using photoacoustic flowmetry

NASA Astrophysics Data System (ADS)

Viator, J. A.; Sutovsky, P.; Weight, R. M.

2008-02-01

Detection of sperm cells in dilute samples may have application in forensic testing and diagnosis of male reproductive health. Due to the optically dense subcellular structures in sperm cells, irradiation by nanosecond laser pulses induces a photoacoustic response detectable using a custom flow cytometer. We determined the detection threshold of bull sperm using various concentrations, from 200 to 1,000,000 sperm cells per milliliter. Using a tunable laser system set to 450nm with a 5 ns pulse duration and 11-12 mJ/pulse, we obtained a detection threshold of 3 sperm cells. The flow rate was 4 ml/minute through the flow chamber. The acoustic sensor was a 100 μm PVDF film attached to the glass flow chamber. The acoustic signal was preamplified and sent to an oscilloscope. The threshold signal indicated a signal to noise ratio of approximately 6 to 1. Improved system design may decrease the threshold to single sperm cells.

Thermal conductivity study of warm dense matter by differential heating on LCLS and Titan

NASA Astrophysics Data System (ADS)

Hill, M.; McKelvey, A.; Jiang, S.; Shepherd, R.; Hau-Riege, S.; Whitley, H.; Sterne, P.; Hamel, S.; Collins, G.; Ping, Y.; Brown, C.; Floyd, E.; Fyrth, J.; Hoarty, D.; Hua, R.; Bailly-Grandvaux, M.; Beg, F.; Cho, B.; Kim, M.; Lee, J.; Lee, H.; Galtier, E.

2017-10-01

A differential heating platform has been developed for thermal conduction study, where a temperature gradient is induced and subsequent heat flow is probed by time-resolved diagnostics. Multiple experiment using this platform have been carried out at LCLS-MEC and Titan laser facilities for warm dense Al, Fe, amorphous carbon and diamond. Two single-shot time-resolved diagnostics are employed, SOP (streaked optical pyrometry) for surface temperature and FDI (Fourier Domain Interferometry) for surface expansion. Both diagnostics provided excellent data to constrain release equation-of-state (EOS) and thermal conductivity. Data sets with varying target thickness and comparison between simulations with different thermal conductivity models are presented. This work was performed under DOE contract DE-AC52-07NA27344 with support from DOE OFES Early Career program and LLNL LDRD program.

Confocal Imaging of Confined Quiescent and Flowing Colloid-polymer Mixtures

PubMed Central

Conrad, Jacinta C.

2014-01-01

The behavior of confined colloidal suspensions with attractive interparticle interactions is critical to the rational design of materials for directed assembly1-3, drug delivery4, improved hydrocarbon recovery5-7, and flowable electrodes for energy storage8. Suspensions containing fluorescent colloids and non-adsorbing polymers are appealing model systems, as the ratio of the polymer radius of gyration to the particle radius and concentration of polymer control the range and strength of the interparticle attraction, respectively. By tuning the polymer properties and the volume fraction of the colloids, colloid fluids, fluids of clusters, gels, crystals, and glasses can be obtained9. Confocal microscopy, a variant of fluorescence microscopy, allows an optically transparent and fluorescent sample to be imaged with high spatial and temporal resolution in three dimensions. In this technique, a small pinhole or slit blocks the emitted fluorescent light from regions of the sample that are outside the focal volume of the microscope optical system. As a result, only a thin section of the sample in the focal plane is imaged. This technique is particularly well suited to probe the structure and dynamics in dense colloidal suspensions at the single-particle scale: the particles are large enough to be resolved using visible light and diffuse slowly enough to be captured at typical scan speeds of commercial confocal systems10. Improvements in scan speeds and analysis algorithms have also enabled quantitative confocal imaging of flowing suspensions11-16,37. In this paper, we demonstrate confocal microscopy experiments to probe the confined phase behavior and flow properties of colloid-polymer mixtures. We first prepare colloid-polymer mixtures that are density- and refractive-index matched. Next, we report a standard protocol for imaging quiescent dense colloid-polymer mixtures under varying confinement in thin wedge-shaped cells. Finally, we demonstrate a protocol for imaging colloid-polymer mixtures during microchannel flow. PMID:24894062

People detection method using graphics processing units for a mobile robot with an omnidirectional camera

NASA Astrophysics Data System (ADS)

Kang, Sungil; Roh, Annah; Nam, Bodam; Hong, Hyunki

2011-12-01

This paper presents a novel vision system for people detection using an omnidirectional camera mounted on a mobile robot. In order to determine regions of interest (ROI), we compute a dense optical flow map using graphics processing units, which enable us to examine compliance with the ego-motion of the robot in a dynamic environment. Shape-based classification algorithms are employed to sort ROIs into human beings and nonhumans. The experimental results show that the proposed system detects people more precisely than previous methods.

Interpenetration and deflection phenomena in collisions between supersonic, magnetized, tungsten plasma flows diagnosed using high resolution optical Thomson scattering

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

Swadling, G. F.; Lebedev, S. V.; Burdiak, G.

An optical Thomson scattering diagnostic has been used to investigate collisions between supersonic, magnetized plasma flows, in particular the transition from collisionless to collisional interaction dynamics. These flows were produced using tungsten wire array z-pinches, driven by the 1.4 MA 240 ns Magpie generator at Imperial College London. Measurements of the collective-mode Thomson scattering ion-feature clearly indicate that the ablation flows are interpenetrating at 100 ns (after current start), and this interpenetration continues until at least 140 ns. The Thomson spectrum at 150 ns shows a clear change in the dynamics of the stream interactions, transitioning towards a collisional, shock-like interaction of the streamsmore » near the axis. The Thomson scattering data also provide indirect evidence of the presence of a significant toroidal magnetic field embedded in the “precursor” plasma near the axis of the array over the period 100–140 ns; these observations are in agreement with previous measurements [Swadling et al., Phys. Rev. Lett. 113, 035003 (2014)]. The Thomson scattering measurements at 150 ns suggest that this magnetic field must collapse at around the time the dense precursor column begins to form.« less

Micro-Fresnel Zone Plate Optical Devices Using Densely Accumulated Ray Points

NASA Technical Reports Server (NTRS)

Choi, Sang H. (Inventor); Park, Yeonjoon (Inventor); King, Glen C. (Inventor); Elliott, James R. (Inventor)

2011-01-01

An embodiment generally relates to an optical device suitable for use with an optical medium for the storage and retrieval of data. The optical device includes an illumination means for providing a beam of optical radiation of wavelength .lamda. and an optical path that the beam of optical radiation follows. The optical device also includes a diffractive optical element defined by a plurality of annular sections. The plurality of annular sections having a first material alternately disposed with a plurality of annular sections comprising a second material. The diffractive optical element generates a plurality of focal points and densely accumulated ray points with phase contrast phenomena and the optical medium is positioned at a selected focal point or ray point of the diffractive optical element.

Dense motion estimation using regularization constraints on local parametric models.

PubMed

Patras, Ioannis; Worring, Marcel; van den Boomgaard, Rein

2004-11-01

This paper presents a method for dense optical flow estimation in which the motion field within patches that result from an initial intensity segmentation is parametrized with models of different order. We propose a novel formulation which introduces regularization constraints between the model parameters of neighboring patches. In this way, we provide the additional constraints for very small patches and for patches whose intensity variation cannot sufficiently constrain the estimation of their motion parameters. In order to preserve motion discontinuities, we use robust functions as a regularization mean. We adopt a three-frame approach and control the balance between the backward and forward constraints by a real-valued direction field on which regularization constraints are applied. An iterative deterministic relaxation method is employed in order to solve the corresponding optimization problem. Experimental results show that the proposed method deals successfully with motions large in magnitude, motion discontinuities, and produces accurate piecewise-smooth motion fields.

Maser mechanism of optical pulsations from anomalous X-ray pulsar 4U 0142+61

NASA Astrophysics Data System (ADS)

Lu, Y.; Zhang, S. N.

2004-11-01

Based on the work of Luo & Melrose from the early 1990s, a maser curvature emission mechanism in the presence of curvature drift is used to explain the optical pulsations from anomalous X-ray pulsars (AXPs). The model comprises a rotating neutron star with a strong surface magnetic field, i.e. a magnetar. Assuming the space-charge-limited flow acceleration mechanism, in which the strongly magnetized neutron star induces strong electric fields that pull the charges from its surface and flow along the open field lines, the neutron star generates a dense flow of electrons and positrons (relativistic pair plasma) by either two-photon pair production or one-photon pair creation resulting from inverse Compton scattering of the thermal photons above the pulsar polar cap (PC). The motion of the pair plasma is essentially one-dimensional along the field lines. We propose that optical pulsations from AXPs are generated by a curvature-drift-induced maser developing in the PC of magnetars. Pair plasma is considered as an active medium that can amplify its normal modes. The curvature drift, which is energy-dependent, is another essential ingredient in allowing negative absorption (maser action) to occur. For the source AXP 4U 0142+61, we find that the optical pulsation triggered by curvature-drift maser radiation occurs at the radial distance R(νM) ~ 4.75 × 109 cm to the neutron star. The corresponding curvature maser frequency is about νM~ 1.39 × 1014 Hz, and the pulse component from the maser amplification is about 27 per cent. The result is consistent with the observation of the optical pulsations from AXP 4U 0142+61.

Two-phase SLIPI for instantaneous LIF and Mie imaging of transient fuel sprays.

PubMed

Storch, Michael; Mishra, Yogeshwar Nath; Koegl, Matthias; Kristensson, Elias; Will, Stefan; Zigan, Lars; Berrocal, Edouard

2016-12-01

We report in this Letter a two-phase structured laser illumination planar imaging [two-pulse SLIPI (2p-SLIPI)] optical setup where the "lines structure" is spatially shifted by exploiting the birefringence property of a calcite crystal. By using this optical component and two cross-polarized laser pulses, the shift of the modulated pattern is not "time-limited" anymore. Consequently, two sub-images with spatially mismatched phases can be recorded within a few hundred of nanoseconds only, freezing the motion of the illuminated transient flow. In comparison with previous setups for instantaneous imaging based on structured illumination, the current optical design presents the advantage of having a single optical path, greatly simplifying its complexity. Due to its virtue of suppressing the effects from multiple light scattering, the 2p-SLIPI technique is applied here in an optically dense multi-jet direct-injection spark-ignition (DISI) ethanol spray. The fast formation of polydispersed droplets and appearance of voids after fuel injection are investigated by simultaneous detection of Mie scattering and liquid laser-induced fluorescence. The results allow for significantly improved analysis of the spray structure.

Intercomparison of granular stress and turbulence models for unidirectional sheet flow applications

NASA Astrophysics Data System (ADS)

Chauchat, J.; Cheng, Z.; Hsu, T. J.

2016-12-01

The intergranular stresses are one of the key elements in two-phase sediment transport models. There are two main existing approaches, the kinetic theory of granular flows (Jenkins and Hanes, 1998; Hsu et al., 2004) and the phenomenological rheology such as the one proposed by Bagnold (Hanes and Bowen, 1985) or the μ(I) dense granular flow rheology (Revil-Baudard and Chauchat, 2013). Concerning the turbulent Reynolds stress, mixing length and k-ɛ turbulence models have been validated by previous studies (Revil-Baudard and Chauchat, 2013; Hsu et al., 2004). Recently, sedFoam was developed based on kinetic theory of granular flows and k-ɛ turbulence models (Cheng and Hsu, 2014). In this study, we further extended sedFoam by implementing the mixing length and the dense granular flow rheology by following Revil-Baudard and Chauchat (2013). This allows us to objectively compare the different combinations of intergranular stresses (kinetic theory or the dense granular flow rheology) and turbulence models (mixing length or k-ɛ) under unidirectional sheet flow conditions. We found that the calibrated mixing length and k-ɛ models predicts similar velocity and concentration profiles. The differences observed between the kinetic theory and the dense granular flow rheology requires further investigation. In particular, we hypothesize that the extended kinetic theory proposed by Berzi (2011) would probably improve the existing combination of the kinetic theory with a simple Coulomb frictional model in sedFoam. A semi-analytical solution proposed by Berzi and Fraccarollo(2013) for sediment transport rate and sheet layer thickness versus the Shields number is compared with the results obtained by using the dense granular flow rheology and the mixing length model. The results are similar which demonstrate that both the extended kinetic theory and the dense granular flow rheology can be used to model intergranular stresses under sheet flow conditions.

DEVELOPMENT OF LOW-DIFFUSION FLUX-SPLITTING METHODS FOR DENSE GAS-SOLID FLOWS

EPA Science Inventory

The development of a class of low-diffusion upwinding methods for computing dense gas-solid flows is presented in this work. An artificial compressibility/low-Mach preconditioning strategy is developed for a hyperbolic two-phase flow equation system consisting of separate solids ...

Detecting dominant motion patterns in crowds of pedestrians

NASA Astrophysics Data System (ADS)

Saqib, Muhammad; Khan, Sultan Daud; Blumenstein, Michael

2017-02-01

As the population of the world increases, urbanization generates crowding situations which poses challenges to public safety and security. Manual analysis of crowded situations is a tedious job and usually prone to errors. In this paper, we propose a novel technique of crowd analysis, the aim of which is to detect different dominant motion patterns in real-time videos. A motion field is generated by computing the dense optical flow. The motion field is then divided into blocks. For each block, we adopt an Intra-clustering algorithm for detecting different flows within the block. Later on, we employ Inter-clustering for clustering the flow vectors among different blocks. We evaluate the performance of our approach on different real-time videos. The experimental results show that our proposed method is capable of detecting distinct motion patterns in crowded videos. Moreover, our algorithm outperforms state-of-the-art methods.

Coaxial gas-liquid jet: Dispersion and dynamics

NASA Astrophysics Data System (ADS)

Poplavski, S. V.; Boiko, V. M.; Lotov, V. V.; Nesterov, A. Yu.

2018-03-01

The aim of the work was to study the pneumatic spraying of liquids in a gas jet with reference to the creation of high-flow nozzles. A complex experimental study of a coaxial jet was performed with a central supply of liquid beyond the cutoff of the confusor nozzle at subsonic and supersonic flow conditions. A set of optical methods for flows diagnostics that can function in dense gas-liquid jets provides new data on the structure of the spray: the gas velocity field without liquid, shadow visualization of the geometry and wave structure of the jet with and without fluid, the velocity profiles of the liquid phase, size distribution of the droplets. The key parameters of the liquid breakup processes for the We numbers are obtained. A dynamic approach to the determination of average droplet sizes is considered. A physical model of a coaxial gas-liquid jet with a central fluid supply is proposed.

Towards co-packaging of photonics and microelectronics in existing manufacturing facilities

NASA Astrophysics Data System (ADS)

Janta-Polczynski, Alexander; Cyr, Elaine; Bougie, Jerome; Drouin, Alain; Langlois, Richard; Childers, Darrell; Takenobu, Shotaro; Taira, Yoichi; Lichoulas, Ted W.; Kamlapurkar, Swetha; Engelmann, Sebastian; Fortier, Paul; Boyer, Nicolas; Barwicz, Tymon

2018-02-01

The impact of integrated photonics on optical interconnects is currently muted by challenges in photonic packaging and in the dense integration of photonic modules with microelectronic components on printed circuit boards. Single mode optics requires tight alignment tolerance for optical coupling and maintaining this alignment in a cost-efficient package can be challenging during thermal excursions arising from downstream microelectronic assembly processes. In addition, the form factor of typical fiber connectors is incompatible with the dense module integration expected on printed circuit boards. We have implemented novel approaches to interfacing photonic chips to standard optical fibers. These leverage standard high throughput microelectronic assembly tooling and self-alignment techniques resulting in photonic packaging that is scalable in manufacturing volume and in the number of optical IOs per chip. In addition, using dense optical fiber connectors with space-efficient latching of fiber patch cables results in compact module size and efficient board integration, bringing the optics closer to the logic chip to alleviate bandwidth bottlenecks. This packaging direction is also well suited for embedding optics in multi-chip modules, including both photonic and microelectronic chips. We discuss the challenges and rewards in this type of configuration such as thermal management and signal integrity.

Dynamics of dense granular flows of small-and-large-grain mixtures in an ambient fluid.

PubMed

Meruane, C; Tamburrino, A; Roche, O

2012-08-01

Dense grain flows in nature consist of a mixture of solid constituents that are immersed in an ambient fluid. In order to obtain a good representation of these flows, the interaction mechanisms between the different constituents of the mixture should be considered. In this article, we study the dynamics of a dense granular flow composed of a binary mixture of small and large grains immersed in an ambient fluid. In this context, we extend the two-phase approach proposed by Meruane et al. [J. Fluid Mech. 648, 381 (2010)] to the case of flowing dense binary mixtures of solid particles, by including in the momentum equations a constitutive relation that describes the interaction mechanisms between the solid constituents in a dense regime. These coupled equations are solved numerically and validated by comparing the numerical results with experimental measurements of the front speed of gravitational granular flows resulting from the collapse, in ambient air or water, of two-dimensional granular columns that consisted of mixtures of small and large spherical particles of equal mass density. Our results suggest that the model equations include the essential features that describe the dynamics of grains flows of binary mixtures in an ambient fluid. In particular, it is shown that segregation of small and large grains can increase the front speed because of the volumetric expansion of the flow. This increase in flow speed is damped by the interaction forces with the ambient fluid, and this behavior is more pronounced in water than in air.

Modeling the purging of dense fluid from a street canyon driven by an interfacial mixing flow and skimming flow

NASA Astrophysics Data System (ADS)

Baratian-Ghorghi, Z.; Kaye, N. B.

2013-07-01

An experimental study is presented to investigate the mechanism of flushing a trapped dense contaminant from a canyon by turbulent boundary layer flow. The results of a series of steady-state experiments are used to parameterize the flushing mechanisms. The steady-state experimental results for a canyon with aspect ratio one indicate that dense fluid is removed from the canyon by two different processes, skimming of dense fluid from the top of the dense layer; and by an interfacial mixing flow that mixes fresh fluid down into the dense lower layer (entrainment) while mixing dense fluid into the flow above the canyon (detrainment). A model is developed for the time varying buoyancy profile within the canyon as a function of the Richardson number which parameterizes both the interfacial mixing and skimming processes observed. The continuous release steady-state experiments allowed for the direct measurement of the skimming and interfacial mixing flow rates for any layer depth and Richardson number. Both the skimming rate and the interfacial mixing rate were found to be power-law functions of the Richardson number of the layer. The model results were compared to the results of previously published finite release experiments [Z. Baratian-Ghorghi and N. B. Kaye, Atmos. Environ. 60, 392-402 (2012)], 10.1016/j.atmosenv.2012.06.077. A high degree of consistency was found between the finite release data and the continuous release data. This agreement acts as an excellent check on the measurement techniques used, as the finite release data was based on curve fitting through buoyancy versus time data, while the continuous release data was calculated directly by measuring the rate of addition of volume and buoyancy once a steady-state was established. Finally, a system of ordinary differential equations is presented to model the removal of dense fluid from the canyon based on empirical correlations of the skimming and interfacial mixing taken form the steady-state experiments. The ODE model predicts well the time taken for a finite volume of dense fluid to be flushed from a canyon.

Dense depth maps from correspondences derived from perceived motion

NASA Astrophysics Data System (ADS)

Kirby, Richard; Whitaker, Ross

2017-01-01

Many computer vision applications require finding corresponding points between images and using the corresponding points to estimate disparity. Today's correspondence finding algorithms primarily use image features or pixel intensities common between image pairs. Some 3-D computer vision applications, however, do not produce the desired results using correspondences derived from image features or pixel intensities. Two examples are the multimodal camera rig and the center region of a coaxial camera rig. We present an image correspondence finding technique that aligns pairs of image sequences using optical flow fields. The optical flow fields provide information about the structure and motion of the scene, which are not available in still images but can be used in image alignment. We apply the technique to a dual focal length stereo camera rig consisting of a visible light-infrared camera pair and to a coaxial camera rig. We test our method on real image sequences and compare our results with the state-of-the-art multimodal and structure from motion (SfM) algorithms. Our method produces more accurate depth and scene velocity reconstruction estimates than the state-of-the-art multimodal and SfM algorithms.

Three-dimensional reconstruction of highly complex microscopic samples using scanning electron microscopy and optical flow estimation.

PubMed

Baghaie, Ahmadreza; Pahlavan Tafti, Ahmad; Owen, Heather A; D'Souza, Roshan M; Yu, Zeyun

2017-01-01

Scanning Electron Microscope (SEM) as one of the major research and industrial equipment for imaging of micro-scale samples and surfaces has gained extensive attention from its emerge. However, the acquired micrographs still remain two-dimensional (2D). In the current work a novel and highly accurate approach is proposed to recover the hidden third-dimension by use of multi-view image acquisition of the microscopic samples combined with pre/post-processing steps including sparse feature-based stereo rectification, nonlocal-based optical flow estimation for dense matching and finally depth estimation. Employing the proposed approach, three-dimensional (3D) reconstructions of highly complex microscopic samples were achieved to facilitate the interpretation of topology and geometry of surface/shape attributes of the samples. As a byproduct of the proposed approach, high-definition 3D printed models of the samples can be generated as a tangible means of physical understanding. Extensive comparisons with the state-of-the-art reveal the strength and superiority of the proposed method in uncovering the details of the highly complex microscopic samples.

An investigation on characterizing dense coal-water slurry with ultrasound: theoretical and experimental method

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

Xue, M.H.; Su, M.X.; Dong, L.L.

2010-07-01

Particle size distribution and concentration in particulate two-phase flow are important parameters in a wide variety of industrial areas. For the purpose of online characterization in dense coal-water slurries, ultrasonic methods have many advantages such as avoiding dilution, the capability for being used in real time, and noninvasive testing, while light-based techniques are not capable of providing information because optical methods often require the slurry to be diluted. In this article, the modified Urick equation including temperature modification, which can be used to determine the concentration by means of the measurement of ultrasonic velocity in a coal-water slurry, is evaluatedmore » on the basis of theoretical analysis and experimental study. A combination of the coupled-phase model and the Bouguer-Lambert-Beer law is employed in this work, and the attenuation spectrum is measured within the frequency region from 3 to 12 MHz. Particle size distributions of the coal-water slurry at different volume fractions are obtained with the optimum regularization technique. Therefore, the ultrasonic technique presented in this work brings the possibility of using ultrasound for online measurements of dense slurries.« less

Effect of temperature on the shape of spatial quasi-periodic oscillations of the refractive index of alkali atoms in an optically dense medium with a closed excitation contour of Δ type

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

Barantsev, K A; Litvinov, A N

2014-10-31

A theory of a closed excitation contour (Δ system) of a three-level atom in an optically dense medium is constructed with allowance for temperature. The spatial quasi-periodic oscillations of the refractive index in the system under study are shown to damp with increasing temperature. The range of temperatures at which these oscillations are most pronounced is found. (quantum optics)

Growth of thin films of dicyanovinylanisole on quartz and teflon-coated quartz by physical vapor transport

NASA Technical Reports Server (NTRS)

Pearson, Earl F.

1994-01-01

Organic compounds offer the possibility of molecular engineering in order to optimize the nonlinearity and minimize damage due to the high-power lasers used in nonlinear optical devices. Recently dicyanovinylanisole (DIVA), ((2-methoxyphenyl) methylenepropanedinitrile) has been shown to have a second order nonlinearity 40 times that of alpha-quartz. Debe et. al. have shown that a high degree of orientational order exists for thin films of phthalocyanine grown by physical vapor transport in microgravity. The microgravity environment eliminates convective flow and was critical to the formation of highly ordered dense continuous films in these samples. This work seeks to discover the parameters necessary for the production of thin continuous films of high optical quality in Earth gravity. These parameters must be known before the experiment can be planned for growing DIVA in a microgravity environment. The microgravity grown films are expected to be denser and of better optical quality than the unit gravity films as was observed in the phthalocyanine films.

Effect of soil temperature on optical frequency transfer through unidirectional dense-wavelength-division-multiplexing fiber-optic links.

PubMed

Pinkert, T J; Böll, O; Willmann, L; Jansen, G S M; Dijck, E A; Groeneveld, B G H M; Smets, R; Bosveld, F C; Ubachs, W; Jungmann, K; Eikema, K S E; Koelemeij, J C J

2015-02-01

Results of optical frequency transfer over a carrier-grade dense-wavelength-division-multiplexing (DWDM) optical fiber network are presented. The relation between soil temperature changes on a buried optical fiber and frequency changes of an optical carrier through the fiber is modeled. Soil temperatures, measured at various depths by the Royal Netherlands Meteorology Institute (KNMI) are compared with observed frequency variations through this model. A comparison of a nine-day record of optical frequency measurements through the 2×298  km fiber link with soil temperature data shows qualitative agreement. A soil temperature model is used to predict the link stability over longer periods (days-months-years). We show that optical frequency dissemination is sufficiently stable to distribute and compare, e.g., rubidium frequency standards over standard DWDM optical fiber networks using unidirectional fibers.

Generation of dense plume fingers in saturated-unsaturated homogeneous porous media

NASA Astrophysics Data System (ADS)

Cremer, Clemens J. M.; Graf, Thomas

2015-02-01

Flow under variable-density conditions is widespread, occurring in geothermal reservoirs, at waste disposal sites or due to saltwater intrusion. The migration of dense plumes typically results in the formation of vertical plume fingers which are known to be triggered by material heterogeneity or by variations in source concentration that causes the density variation. Using a numerical groundwater model, six perturbation methods are tested under saturated and unsaturated flow conditions to mimic heterogeneity and concentration variations on the pore scale in order to realistically generate dense fingers. A laboratory-scale sand tank experiment is numerically simulated, and the perturbation methods are evaluated by comparing plume fingers obtained from the laboratory experiment with numerically simulated fingers. Dense plume fingering for saturated flow can best be reproduced with a spatially random, time-constant perturbation of the solute source. For unsaturated flow, a spatially and temporally random noise of solute concentration or a random conductivity field adequately simulate plume fingering.

Why P/OF should look for evidences of over-dense structures in solar flare hard X-ray sources

NASA Technical Reports Server (NTRS)

Neidig, D. F.; Kane, S. R.; Love, J. J.; Cliver, E. W.

1986-01-01

White-light and hard X-ray (HXR) observations of two white-light flares (WLFs) show that if the radiative losses in the optical continuum are powered by fast electrons directly heating the WLF source, then the column density constraints imposed by the finite range of the electrons requires that the WLF consist of an over-dense region in the chromosphere, with density exceeding 10 to the 14th power/cu cm. Thus, we recommend that P/OF search for evidences of over-dense structures in HXR images obtained simultaneously with optical observations of flares.

Investigation of Alien Wavelength Quality in Live Multi-Domain, Multi-Vendor Link Using Advanced Simulation Tool

NASA Astrophysics Data System (ADS)

Nordal Petersen, Martin; Nuijts, Roeland; Lange Bjørn, Lars

2014-05-01

This article presents an advanced optical model for simulation of alien wavelengths in multi-domain and multi-vendor dense wavelength-division multiplexing networks. The model aids optical network planners with a better understanding of the non-linear effects present in dense wavelength-division multiplexing systems and better utilization of alien wavelengths in future applications. The limiting physical effects for alien wavelengths are investigated in relation to power levels, channel spacing, and other factors. The simulation results are verified through experimental setup in live multi-domain dense wavelength-division multiplexing systems between two national research networks: SURFnet in Holland and NORDUnet in Denmark.

Exploring warm dense matter using quantum molecular dynamics

NASA Astrophysics Data System (ADS)

Clérouin, J.; Mazevet, S.

2006-06-01

For dense plasmas produced in shock experiments, the influence of the media on the isolated atomic properties can no longer be treated as a perturbation and conventional atomic physics approaches usually fail. Recently, quantum molecular dynamics (QMD) has been used to successfully predict static, dynamical and optical properties in this regime within the framework of a first principle method. In this short report, we illustrate the usefulness of the method for dense plasmas with a few selected examples: the equation of state of liquid deuterium, the electrical properties of expanded metals, the optical properties of shocked insulators, and the interaction of femto-second lasers with gold thin films.

Transonic aerodynamics of dense gases. M.S. Thesis - Virginia Polytechnic Inst. and State Univ., Apr. 1990

NASA Technical Reports Server (NTRS)

Morren, Sybil Huang

1991-01-01

Transonic flow of dense gases for two-dimensional, steady-state, flow over a NACA 0012 airfoil was predicted analytically. The computer code used to model the dense gas behavior was a modified version of Jameson's FL052 airfoil code. The modifications to the code enabled modeling the dense gas behavior near the saturated vapor curve and critical pressure region where the fundamental derivative, Gamma, is negative. This negative Gamma region is of interest because the nonclassical gas behavior such as formation and propagation of expansion shocks, and the disintegration of inadmissible compression shocks may exist. The results indicated that dense gases with undisturbed thermodynamic states in the negative Gamma region show a significant reduction in the extent of the transonic regime as compared to that predicted by the perfect gas theory. The results support existing theories and predictions of the nonclassical, dense gas behavior from previous investigations.

OpenFlow arbitrated programmable network channels for managing quantum metadata

DOE PAGES

Dasari, Venkat R.; Humble, Travis S.

2016-10-10

Quantum networks must classically exchange complex metadata between devices in order to carry out information for protocols such as teleportation, super-dense coding, and quantum key distribution. Demonstrating the integration of these new communication methods with existing network protocols, channels, and data forwarding mechanisms remains an open challenge. Software-defined networking (SDN) offers robust and flexible strategies for managing diverse network devices and uses. We adapt the principles of SDN to the deployment of quantum networks, which are composed from unique devices that operate according to the laws of quantum mechanics. We show how quantum metadata can be managed within a software-definedmore » network using the OpenFlow protocol, and we describe how OpenFlow management of classical optical channels is compatible with emerging quantum communication protocols. We next give an example specification of the metadata needed to manage and control quantum physical layer (QPHY) behavior and we extend the OpenFlow interface to accommodate this quantum metadata. Here, we conclude by discussing near-term experimental efforts that can realize SDN’s principles for quantum communication.« less

OpenFlow arbitrated programmable network channels for managing quantum metadata

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

Dasari, Venkat R.; Humble, Travis S.

Quantum networks must classically exchange complex metadata between devices in order to carry out information for protocols such as teleportation, super-dense coding, and quantum key distribution. Demonstrating the integration of these new communication methods with existing network protocols, channels, and data forwarding mechanisms remains an open challenge. Software-defined networking (SDN) offers robust and flexible strategies for managing diverse network devices and uses. We adapt the principles of SDN to the deployment of quantum networks, which are composed from unique devices that operate according to the laws of quantum mechanics. We show how quantum metadata can be managed within a software-definedmore » network using the OpenFlow protocol, and we describe how OpenFlow management of classical optical channels is compatible with emerging quantum communication protocols. We next give an example specification of the metadata needed to manage and control quantum physical layer (QPHY) behavior and we extend the OpenFlow interface to accommodate this quantum metadata. Here, we conclude by discussing near-term experimental efforts that can realize SDN’s principles for quantum communication.« less

Mather-type dense plasma focus as a new optical pump for short-wavelength high-power lasers

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

Fanning, J.J.; Kim, K.

For the first time, a Mather-type dense plasma focus (MDPF) is successfully operated as an optical pump for lasers. Rhodamine-6G dye is optically pumped using the MDPF fluorescence, producing a laser pulse 1 ..mu..s in duration and more than 50 kW in output power. No optimization is attempted either of the laser cavity or of the lasing medium concentration and volume. A brief description of the experimental setup is presented, along with a summary and discussion of the results. The advantages of the present optical pump source and, in particular, their implications for the pumping of short-wavelength lasers are discussed.

Shear dispersion in dense granular flows

DOE PAGES

Christov, Ivan C.; Stone, Howard A.

2014-04-18

We formulate and solve a model problem of dispersion of dense granular materials in rapid shear flow down an incline. The effective dispersivity of the depth-averaged concentration of the dispersing powder is shown to vary as the Péclet number squared, as in classical Taylor–Aris dispersion of molecular solutes. An extension to generic shear profiles is presented, and possible applications to industrial and geological granular flows are noted.

Flexible fiber in interaction with a dense granular flow close to the jamming transition

NASA Astrophysics Data System (ADS)

Algarra, Nicolas; Leang, Marguerite; Lazarus, Arnaud; Vandembroucq, Damien; Kolb, Evelyne

2017-06-01

We propose a new fluid/structure interaction in the unusual case of a dense granular medium flowing against an elastic fiber acting as a flexible intruder. We study experimentally the reconfiguration and the forces exerted on the flexible fiber produced by the flow at a constant and low velocity of a two-dimensional disordered packing of grains close but below the jamming transition.

Direct Numerical Simulation of dense particle-laden turbulent flows using immersed boundaries

NASA Astrophysics Data System (ADS)

Wang, Fan; Desjardins, Olivier

2009-11-01

Dense particle-laden turbulent flows play an important role in many engineering applications, ranging from pharmaceutical coating and chemical synthesis to fluidized bed reactors. Because of the complexity of the physics involved in these flows, current computational models for gas-particle processes, such as drag and heat transfer, rely on empirical correlations and have been shown to lack accuracy. In this work, direct numerical simulations (DNS) of dense particle-laden flows are conducted, using immersed boundaries (IB) to resolve the flow around each particle. First, the accuracy of the proposed approach is tested on a range of 2D and 3D flows at various Reynolds numbers, and resolution requirements are discussed. Then, various particle arrangements and number densities are simulated, the impact on particle wake interaction is assessed, and existing drag models are evaluated in the case of fixed particles. In addition, the impact of the particles on turbulence dissipation is investigated. Finally, a strategy for handling moving and colliding particles is discussed.

Generation of electromagnetic emission during the injection of dense supersonic plasma flows into arched magnetic field

NASA Astrophysics Data System (ADS)

Viktorov, Mikhail; Golubev, Sergey; Mansfeld, Dmitry; Vodopyanov, Alexander

2016-04-01

Interaction of dense supersonic plasma flows with an inhomogeneous arched magnetic field is one of the key problems in near-Earth and space plasma physics. It can influence on the energetic electron population formation in magnetosphere of the Earth, movement of plasma flows in magnetospheres of planets, energy release during magnetic reconnection, generation of electromagnetic radiation and particle precipitation during solar flares eruption. Laboratory study of this interaction is of big interest to determine the physical mechanisms of processes in space plasmas and their detailed investigation under reproducible conditions. In this work a new experimental approach is suggested to study interaction of supersonic (ion Mach number up to 2.7) dense (up to 1015 cm-3) plasma flows with inhomogeneous magnetic field (an arched magnetic trap with a field strength up to 3.3 T) which opens wide opportunities to model space plasma processes in laboratory conditions. Fully ionized plasma flows with density from 1013 cm-3 to 1015 cm-3 are created by plasma generator on the basis of pulsed vacuum arc discharge. Then plasma is injected in an arched open magnetic trap along or across magnetic field lines. The filling of the arched magnetic trap with dense plasma and further magnetic field lines break by dense plasma flow were experimentally demonstrated. The process of plasma deceleration during the injection of plasma flow across the magnetic field lines was experimentally demonstrated. Pulsed plasma microwave emission at the electron cyclotron frequency range was observed. It was shown that frequency spectrum of plasma emission is determined by position of deceleration region in the magnetic field of the magnetic arc, and is affected by plasma density. Frequency spectrum shifts to higher frequencies with increasing of arc current (plasma density) because the deceleration region of plasma flow moves into higher magnetic field. The observed emission can be related to the cyclotron mechanism of generation by non-equilibrium energetic electrons in dense plasma. The reported study was funded by RFBR, according to the research project No. 16-32-60056 mol_a_dk.

The thermal evolution of pyroclastic density currents: Exploring the thermal histories of juvenile clasts of Tungurahua and Cotopaxi, Ecuador

NASA Astrophysics Data System (ADS)

Benage, M. C.; Dufek, J.; Degruyter, W.

2010-12-01

The thermal history of pyroclastic density currents (PDCs) is critical in determining flow dynamics and deposit characteristics. The thermal history of these flows depends on the particles’ internal rate of heat transfer and heat exchange between discrete particles and a gas phase. We examine the thermal history of a class of dense PDC exemplified by the eruption of Tungurahua (2006) and Cotopaxi (1877) that have abundant breadcrust bombs segregated in levees and in flow snouts. An open question in this type of PDC is the amount of air entrainment (and cooling) during transport. To understand the entrainment and cooling history of these flows we use a multiphase numerical model coupled with a Lagrangian model (Eulerian-Eulerian-Lagrangian [EEL]) that tracks the internal heat transfer and post-eruption bubble evolution in juvenile clasts. We combine the numerical study with the observation of the morphology and vesicularity of breadcrust bombs from dense pyroclastic density currents from Tungurahua and Cotopaxi. Breadcrust bombs are common in many deposits from mafic explosive eruptions, e.g. Montserrat, Cotopaxi, Guagua Pichincha, and Tungurahua volcanoes. At many locations these bombs have likely been transported as ballistics (interacting mostly with ambient air), although several instances of dense scoria bomb flows have been noted (e.g. Cotopaxi and Tungurahua, Ecuador). The dense flow deposits are generally rich in unabraided breadcrust bombs along the flow levee and occasionally along the entire transect of the flow. The breadcrust bombs range in size from tens of centimeters to meters. They can also be found draping around previous deposits suggesting a high temperature of deposition. We discuss the use of clast morphology with other thermal proxies to better understand the thermal evolution of individual PDC and the proportion of time clasts underwent transport in dense flows as compared to ballistic transport.

Effect of electron-beam deposition process variables on the film characteristics of the CrOx films

NASA Astrophysics Data System (ADS)

Chiu, Po-kai; Liao, Yi-Ting; Tsai, Hung-Yin; Chiang, Donyau

2018-02-01

The film characteristics and optical properties of the chromium oxide films on the glass substrates prepared by electron-beam deposition with different process variables were investigated. The process variables included are the various oxygen flow rates, the different applied substrate temperatures, and the preparation process in Ar or O2 surrounding environment with and without ion-assisted deposition. The optical constants of the deposited films are determined from the reflectance and transmittance measurements obtained using a spectrophotometer with wavelengths ranging from 350 nm to 2000 nm. The microstructures of the films were examined by the XRD, SEM, and XPS. The electrical conductivity was measured by a four-point probe instrument. The resulting microstructures of all the prepared films are amorphous and the features of the films are dense, uniform and no pillar structure is observed. The refractive index of deposited films decrease with oxygen flow rate increase within studied wavelengths and the extinction coefficients have the same trend in wavelengths of UV/Vis ranges. Increasing substrate temperature to 200 oC results in increase of both refractive index and extinction coefficient, but substrate temperatures below 150 oC show negligible effect on optical constants. The optical and electrical properties in the prepared CrOx films are illustrated by the analyzed XPS results, which decompose the enveloped curve of chromium electron energy status into the constituents of metal Cr, oxides CrO2 and Cr2O3. The relative occupied area contributed from metal Cr and area contributed from the other oxides can express the concentration ratio of free electron to covalent bonds in deposited films and the ratio is applied to explain the film characteristics, including the optical constants and sheet resistance.

Measurements of the principal Hugoniots of dense gaseous deuterium-helium mixtures: Combined multi-channel optical pyrometry, velocity interferometry, and streak optical pyrometry measurements

NASA Astrophysics Data System (ADS)

Li, Zhi-Guo; Chen, Qi-Feng; Gu, Yun-Jun; Zheng, Jun; Chen, Xiang-Rong

2016-10-01

The accurate hydrodynamic description of an event or system that addresses the equations of state, phase transitions, dissociations, ionizations, and compressions, determines how materials respond to a wide range of physical environments. To understand dense matter behavior in extreme conditions requires the continual development of diagnostic methods for accurate measurements of the physical parameters. Here, we present a comprehensive diagnostic technique that comprises optical pyrometry, velocity interferometry, and time-resolved spectroscopy. This technique was applied to shock compression experiments of dense gaseous deuterium-helium mixtures driven via a two-stage light gas gun. The advantage of this approach lies in providing measurements of multiple physical parameters in a single experiment, such as light radiation histories, particle velocity profiles, and time-resolved spectra, which enables simultaneous measurements of shock velocity, particle velocity, pressure, density, and temperature and expands understanding of dense high pressure shock situations. The combination of multiple diagnostics also allows different experimental observables to be measured and cross-checked. Additionally, it implements an accurate measurement of the principal Hugoniots of deuterium-helium mixtures, which provides a benchmark for the impedance matching measurement technique.

Turbulent dusty boundary layer in an ANFO surface-burst explosion

NASA Astrophysics Data System (ADS)

Kuhl, A. L.; Ferguson, R. E.; Chien, K. Y.; Collins, J. P.

1992-01-01

This paper describes the results of numerical simulations of the dusty, turbulent boundary layer created by a surface burst explosion. The blast wave was generated by the detonation of a 600-T hemisphere of ANFO, similar to those used in large-scale field tests. The surface was assumed to be ideally noncratering but contained an initial loose layer of dust. The dust-air mixture in this fluidized bed was modeled as a dense gas (i.e., an equilibrium model, valid for very small-diameter dust particles). The evolution of the flow was calculated by a high-order Godunov code that solves the nonsteady conservation laws. Shock interactions with dense layer generated vorticity near the wall, a result that is similar to viscous, no-slip effects found in clean flows. The resulting wall shear layer was unstable, and rolled up into large-scale rotational structures. These structures entrained dense material from the wall layer and created a chaotically striated flow. The boundary layer grew due to merging of the large-scale structures and due to local entrainment of the dense material from the fluidized bed. The chaotic flow was averaged along similarity lines (i.e., lines of constant values of x = r/Rs and y = z/Rs where R(sub s) = ct(exp alpha)) to establish the mean-flow profiles and the r.m.s. fluctuating-flow profiles of the boundary layer.

Two-layer displacement flow of miscible fluids with viscosity ratio: Experiments

NASA Astrophysics Data System (ADS)

Etrati, Ali; Alba, Kamran; Frigaard, Ian A.

2018-05-01

We investigate experimentally the density-unstable displacement flow of two miscible fluids along an inclined pipe. This means that the flow is from the top to bottom of the pipe (downwards), with the more dense fluid above the less dense. Whereas past studies have focused on iso-viscous displacements, here we consider viscosity ratios in the range 1/10-10. Our focus is on displacements where the degree of transverse mixing is low-moderate, and thus a two-layer, stratified flow is observed. A wide range of parameters is covered in order to observe the resulting flow regimes and to understand the effect of the viscosity contrast. The inclination of the pipe (β) is varied from near horizontal β = 85° to near vertical β = 10°. At each angle, the flow rate and viscosity ratio are varied at fixed density contrast. Flow regimes are mapped in the (Fr, Re cos β/Fr)-plane, delineated in terms of interfacial instability, front dynamics, and front velocity. Amongst the many observations, we find that viscosifying the less dense fluid tends to significantly destabilize the flow. Different instabilities develop at the interface and in the wall-layers.

Benchmarking variable-density flow in saturated and unsaturated porous media

NASA Astrophysics Data System (ADS)

Guevara Morel, Carlos Roberto; Cremer, Clemens; Graf, Thomas

2015-04-01

In natural environments, fluid density and viscosity can be affected by spatial and temporal variations of solute concentration and/or temperature. These variations can occur, for example, due to salt water intrusion in coastal aquifers, leachate infiltration from waste disposal sites and upconing of saline water from deep aquifers. As a consequence, potentially unstable situations may exist in which a dense fluid overlies a less dense fluid. This situation can produce instabilities that manifest as dense plume fingers that move vertically downwards counterbalanced by vertical upwards flow of the less dense fluid. Resulting free convection increases solute transport rates over large distances and times relative to constant-density flow. Therefore, the understanding of free convection is relevant for the protection of freshwater aquifer systems. The results from a laboratory experiment of saturated and unsaturated variable-density flow and solute transport (Simmons et al., Transp. Porous Medium, 2002) are used as the physical basis to define a mathematical benchmark. The HydroGeoSphere code coupled with PEST are used to estimate the optimal parameter set capable of reproducing the physical model. A grid convergency analysis (in space and time) is also undertaken in order to obtain the adequate spatial and temporal discretizations. The new mathematical benchmark is useful for model comparison and testing of variable-density variably saturated flow in porous media.

Extinction measurement of dense media by an optical coherence tomography technique

NASA Astrophysics Data System (ADS)

Ago, Tomoki; Iwai, Toshiaki; Yokota, Ryoko

2016-10-01

The optical coherence tomography will make progress as the next stage toward a spectroscopic analysis technique. The spectroscopic analysis is based on the Beer-Lambert law. The absorption and scattering coefficients even for the dense medium can be measured by the Beer-Lambert law because the OCT can detect only the light keeping the coherency which propagated rectilinearly and retro-reflected from scatters. This study is concerned with the quantitative verification of Beer-Lambert law in the OCT imaging.

On the multi-scale description of micro-structured fluids composed of aggregating rods

NASA Astrophysics Data System (ADS)

Perez, Marta; Scheuer, Adrien; Abisset-Chavanne, Emmanuelle; Ammar, Amine; Chinesta, Francisco; Keunings, Roland

2018-05-01

When addressing the flow of concentrated suspensions composed of rods, dense clusters are observed. Thus, the adequate modelling and simulation of such a flow requires addressing the kinematics of these dense clusters and their impact on the flow in which they are immersed. In a former work, we addressed a first modelling framework of these clusters, assumed so dense that they were considered rigid and their kinematics (flow-induced rotation) were totally defined by a symmetric tensor c with unit trace representing the cluster conformation. Then, the rigid nature of the clusters was relaxed, assuming them deformable, and a model giving the evolution of both the cluster shape and its microstructural orientation descriptor (the so-called shape and orientation tensors) was proposed. This paper compares the predictions coming from those models with finer-scale discrete simulations inspired from molecular dynamics modelling.

Numerical modeling of the early interaction of a planar shock with a dense particle field

NASA Astrophysics Data System (ADS)

Regele, Jonathan; Blanquart, Guillaume

2011-11-01

Dense compressible multiphase flows are of interest for multiphase turbomachinary and energetic material detonations. Still, there is little understanding of the detailed interaction mechanisms between shock waves and dense (particle volume fraction αd > 0 . 001) particle fields. A recent experimental study [Wagner et al, AIAA Aero. Sci., Orlando, 2011-188] has focused on the impingement of a planar shock wave on a dense particle curtain. In the present work, numerical solutions of the Euler equations in one and two dimensions are performed for a planar shock wave impinging on a fixed particle curtain and are compared to the experimental data for early times. Comparison of the one- and two-dimensional results demonstrate that the one-dimensional description captures the large scale flow behavior, but is inadequate to capture all the details observed in the experiments. The two-dimensional solutions are shown to reproduce the experimentally observed flow structures and provide insight into how these details originate.

Turbulent Mixing and Afterburn in Post-Detonation Flow with Dense Particle Clouds

NASA Astrophysics Data System (ADS)

Menon, Suresh

2015-06-01

Reactive metal particles are used as additives in most explosives to enhance afterburn and augment the impact of the explosive. The afterburn is highly dependent on the particle dispersal and mixing in the post-detonation flow. The post-detonation flow is generally characterized by hydrodynamic instabilities emanating from the interaction of the blast waves with the detonation product gases and the ambient air. Further, influenced by the particles, the flow evolves and develops turbulent structures, which play vital role in determining mixing and combustion. Past studies in the field in open literature are reviewed along with some recent studies conducted using three dimensional numerical simulations of particle dispersal and combustion in the post-detonation flow. Spherical nitromethane charges enveloped by particle shells of varying thickness are considered along with dense loading effects. In dense flows, the particles block the flow of the gases and therefore, the role of the inter-particle interactions on particle dispersal cannot be ignored. Thus, both dense and dilute effects must be modeled simultaneously to simulate the post-detonation flow. A hybrid equation of state is employed to study the evolution of flow from detonation initiation till the late time mixing and afterburn. The particle dispersal pattern in each case is compared with the available experimental results. The burn rate and the energy release in each case is quantified and the effect of total mass of the particles and the particle size is analyzed in detail. Strengths and limitations of the various methods used for such studies as well as the uncertainties in the modeling strategies are also highlighted. Supported by Defense Threat Reduction Agency.

Development and utilization of new diagnostics for dense-phase pneumatic transport

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

Not Available

Dense-phase pneumatic transport is an attractive means of conveying solids. Unfortunately, because of the high solid concentrations, this transport method is a difficult regime in which to carry out detailed measurements. Hence most details of the flow are unknown. In this context, the main objective of this work is to develop probes for local measurements of solid velocity and holdup in dense gas-solid flows. Because we anticipate the recent theories of rapid granular flows will bring insight to the dense pneumatic transport of particles, we have sought to substantiate these theories through computer simulations. There we have verified the theorymore » of Hanes, Jenkins Richman (1988) for the rapid, steady shear flow of identical, smooth, nearly elastics disks driven by identical, parallel, bumpy boundaries. Because granular flows depend strongly on the nature of their interaction with a boundary, we have verified the boundary conditions calculated by Jenkins (1991) for spheres interacting with a flat, frictional surface. During the previous reporting period, we began a study of the time relaxation of the second moment of velocity fluctuations for a collection of disks undergoing simple shear. In the present reporting period, we have completed this study of relaxation by comparing results of simulations with the theoretical predictions of Jenkins and Richman (1988). In addition, we have concluded a series of experiments with flour plugs in the dense-phase pneumatic setup. Finally, we have established several industrial contacts to transfer the diagnostic techniques developed under this contract. 7 refs., 11 figs.« less

Excitonic effects in dense media: breakdown of intrinsic optical bistability

NASA Astrophysics Data System (ADS)

Yudson, V. I.; Reineker, P.

1994-12-01

The steady-state nonlinear response to optical excitation is studied for a thin layer containing “two-level-atoms” (TLA). For a high density of TLAs their dipole-dipole interaction and finite excitonic bandwidth effects become important. We demonstrate that the commonly used local-field approximation ignoring excitonic band effects breaks down. Considering a system of ordered TLAs corresponding to Frenkel excitons in molecular crystals we show that excitonic effects cause an instability of spatially uniform solutions and decrease drastically the existence range of the intrinsic optical bistability of a layer. The possibility of “fast instability”, developing with an increment large in comparison with relaxation rates and the Rabi frequency, also raises the question whether the local field approximation still holds for the description of transient optical phenomena in dense media.

Excitonic effects in dense media: breakdown of intrinsic optical bistability

NASA Astrophysics Data System (ADS)

Yudson, V. I.; Reineker, P.

The steady-state nonlinear response to optical excitation is studied for a thin layer containing “two-level-atoms” (TLA). For a high density of TLAs their dipole-dipole interaction and finite excitonic bandwidth effects become important. We demonstrate that the commonly used local-field approximation ignoring excitonic band effects breaks down. Considering a system of ordered TLAs corresponding to Frenkel excitons in molecular crystals we show that excitonic effects cause an instability of spatially uniform solutions and decrease drastically the existence range of the intrinsic optical bistability of a layer. The possibility of “fast instability”, developing with an increment large in comparison with relaxation rates and the Rabi frequency, also raises the question whether the local field approximation still holds for the description of transient optical phenomena in dense media.

Mesoscopic Length Scale Controls the Rheology of Dense Suspensions

NASA Astrophysics Data System (ADS)

Bonnoit, Claire; Lanuza, Jose; Lindner, Anke; Clement, Eric

2010-09-01

From the flow properties of dense granular suspensions on an inclined plane, we identify a mesoscopic length scale strongly increasing with volume fraction. When the flowing layer height is larger than this length scale, a diverging Newtonian viscosity is determined. However, when the flowing layer height drops below this scale, we evidence a nonlocal effective viscosity, decreasing as a power law of the flow height. We establish a scaling relation between this mesoscopic length scale and the suspension viscosity. These results support recent theoretical and numerical results implying collective and clustered granular motion when the jamming point is approached from below.

Mesoscopic length scale controls the rheology of dense suspensions.

PubMed

Bonnoit, Claire; Lanuza, Jose; Lindner, Anke; Clement, Eric

2010-09-03

From the flow properties of dense granular suspensions on an inclined plane, we identify a mesoscopic length scale strongly increasing with volume fraction. When the flowing layer height is larger than this length scale, a diverging Newtonian viscosity is determined. However, when the flowing layer height drops below this scale, we evidence a nonlocal effective viscosity, decreasing as a power law of the flow height. We establish a scaling relation between this mesoscopic length scale and the suspension viscosity. These results support recent theoretical and numerical results implying collective and clustered granular motion when the jamming point is approached from below.

Large-eddy simulation of dense gas dispersion over a simplified urban area

NASA Astrophysics Data System (ADS)

Wingstedt, E. M. M.; Osnes, A. N.; Åkervik, E.; Eriksson, D.; Reif, B. A. Pettersson

2017-03-01

Dispersion of neutral and dense gas over a simplified urban area, comprising four cubes, has been investigated by the means of large-eddy simulations (LES). The results have been compared to wind tunnel experiments and both mean and fluctuating quantities of velocity and concentration are in very good agreement. High-quality inflow profiles are necessary to achieve physically realistic LES results. In this study, profiles matching the atmospheric boundary layer flow in the wind tunnel, are generated by means of a separate precursor simulation. Emission of dense gas dramatically alters the flow in the near source region and introduces an upstream dispersion. The resulting dispersion patterns of neutral and dense gas differ significantly, where the plume in the latter case is wider and shallower. The dense gas is highly affected by the cube array, which seems to act as a barrier, effectively deflecting the plume. This leads to higher concentrations outside of the array than inside. On the contrary, the neutral gas plume has a Gaussian-type shape, with highest concentrations along the centreline. It is found that the dense gas reduces the vertical and spanwise turbulent momentum transport and, as a consequence, the turbulence kinetic energy. The reduction coincides with the area where the gradient Richardson number exceeds its critical value, i.e. where the flow may be characterized as stably stratified. Interestingly, this region does not correspond to where the concentration of dense gas is the highest (close to the ground), as this is also where the largest velocity gradients are to be found. Instead there is a layer in the middle of the dense gas cloud where buoyancy is dynamically dominant.

Application of polydimethylsiloxane-based optical system for measuring optical density of microbial culture.

PubMed

Takahashi, Yurika

2016-12-01

The performance of recently developed polydimethylsiloxane (PDMS)-based optical system was tested for measuring optical density of microbial culture. The data showed that PDMS-based spectrometer is superior to "one drop" spectrometers in the accuracy, and has an advantage over conventional spectrometers in measuring dense culture without dilution.

Dictionary learning-based spatiotemporal regularization for 3D dense speckle tracking

NASA Astrophysics Data System (ADS)

Lu, Allen; Zontak, Maria; Parajuli, Nripesh; Stendahl, John C.; Boutagy, Nabil; Eberle, Melissa; O'Donnell, Matthew; Sinusas, Albert J.; Duncan, James S.

2017-03-01

Speckle tracking is a common method for non-rigid tissue motion analysis in 3D echocardiography, where unique texture patterns are tracked through the cardiac cycle. However, poor tracking often occurs due to inherent ultrasound issues, such as image artifacts and speckle decorrelation; thus regularization is required. Various methods, such as optical flow, elastic registration, and block matching techniques have been proposed to track speckle motion. Such methods typically apply spatial and temporal regularization in a separate manner. In this paper, we propose a joint spatiotemporal regularization method based on an adaptive dictionary representation of the dense 3D+time Lagrangian motion field. Sparse dictionaries have good signal adaptive and noise-reduction properties; however, they are prone to quantization errors. Our method takes advantage of the desirable noise suppression, while avoiding the undesirable quantization error. The idea is to enforce regularization only on the poorly tracked trajectories. Specifically, our method 1.) builds data-driven 4-dimensional dictionary of Lagrangian displacements using sparse learning, 2.) automatically identifies poorly tracked trajectories (outliers) based on sparse reconstruction errors, and 3.) performs sparse reconstruction of the outliers only. Our approach can be applied on dense Lagrangian motion fields calculated by any method. We demonstrate the effectiveness of our approach on a baseline block matching speckle tracking and evaluate performance of the proposed algorithm using tracking and strain accuracy analysis.

Light-field-characterization in a continuous hydrogen-producing photobioreactor by optical simulation and computational fluid dynamics.

PubMed

Krujatz, Felix; Illing, Rico; Krautwer, Tobias; Liao, Jing; Helbig, Karsten; Goy, Katharina; Opitz, Jörg; Cuniberti, Gianaurelio; Bley, Thomas; Weber, Jost

2015-12-01

Externally illuminated photobioreactors (PBRs) are widely used in studies on the use of phototrophic microorganisms as sources of bioenergy and other photobiotechnology research. In this work, straightforward simulation techniques were used to describe effects of varying fluid flow conditions in a continuous hydrogen-producing PBR on the rate of photofermentative hydrogen production (rH2 ) by Rhodobacter sphaeroides DSM 158. A ZEMAX optical ray tracing simulation was performed to quantify the illumination intensity reaching the interior of the cylindrical PBR vessel. 24.2% of the emitted energy was lost through optical effects, or did not reach the PBR surface. In a dense culture of continuously producing bacteria during chemostatic cultivation, the illumination intensity became completely attenuated within the first centimeter of the PBR radius as described by an empirical three-parametric model implemented in Mathcad. The bacterial movement in chemostatic steady-state conditions was influenced by varying the fluid Reynolds number. The "Computational Fluid Dynamics" and "Particle Tracing" tools of COMSOL Multiphysics were used to visualize the fluid flow pattern and cellular trajectories through well-illuminated zones near the PBR periphery and dark zones in the center of the PBR. A moderate turbulence (Reynolds number = 12,600) and fluctuating illumination of 1.5 Hz were found to yield the highest continuous rH2 by R. sphaeroides DSM 158 (170.5 mL L(-1) h(-1) ) in this study. © 2015 Wiley Periodicals, Inc.

Two-dimensional modeling of density and thermal structure of dense circumstellar outflowing disks

NASA Astrophysics Data System (ADS)

Kurfürst, P.; Feldmeier, A.; Krtička, J.

2018-06-01

Context. Evolution of massive stars is affected by a significant loss of mass either via (nearly) spherically symmetric stellar winds or by aspherical mass-loss mechanisms, namely the outflowing equatorial disks. However, the scenario that leads to the formation of a disk or rings of gas and dust around massive stars is still under debate. It is also unclear how various forming physical mechanisms of the circumstellar environment affect its shape and density, as well as its kinematic and thermal structure. Aims: We study the hydrodynamic and thermal structure of optically thick, dense parts of outflowing circumstellar disks that may be formed around various types of critically rotating massive stars, for example, Be stars, B[e] supergiant (sgB[e]) stars or Pop III stars. We calculate self-consistent time-dependent models of temperature and density structure in the disk's inner dense region that is strongly affected by irradiation from a rotationally oblate central star and by viscous heating. Methods: Using the method of short characteristics, we specify the optical depth of the disk along the line-of-sight from stellar poles. Within the optically thick dense region with an optical depth of τ > 2/3 we calculate the vertical disk thermal structure using the diffusion approximation while for the optically thin outer layers we assume a local thermodynamic equilibrium with the impinging stellar irradiation. For time-dependent hydrodynamic modeling, we use two of our own types of hydrodynamic codes: two-dimensional operator-split numerical code based on an explicit Eulerian finite volume scheme on a staggered grid, and unsplit code based on the Roe's method, both including full second-order Navier-Stokes shear viscosity. Results: Our models show the geometric distribution and contribution of viscous heating that begins to dominate in the central part of the disk for mass-loss rates higher than Ṁ ≳ 10-10 M⊙ yr-1. In the models of dense viscous disks with Ṁ > 10-8 M⊙ yr-1, the viscosity increases the central temperature up to several tens of thousands of Kelvins, however the temperature rapidly drops with radius and with distance from the disk midplane. The high mass-loss rates and high viscosity lead to instabilities with significant waves or bumps in density and temperature in the very inner disk region. Conclusions: The two-dimensional radial-vertical models of dense outflowing disks including the full Navier-Stokes viscosity terms show very high temperatures that are however limited to only the central disk cores inside the optically thick area, while near the edge of the optically thick region the temperature may be low enough for the existence of neutral hydrogen, for example.

Dense electro-optic frequency comb generated by two-stage modulation for dual-comb spectroscopy.

PubMed

Wang, Shuai; Fan, Xinyu; Xu, Bingxin; He, Zuyuan

2017-10-01

An electro-optic frequency comb enables frequency-agile comb-based spectroscopy without using sophisticated phase-locking electronics. Nevertheless, dense electro-optic frequency combs over broad spans have yet to be developed. In this Letter, we propose a straightforward and efficient method for electro-optic frequency comb generation with a small line spacing and a large span. This method is based on two-stage modulation: generating an 18 GHz line-spacing comb at the first stage and a 250 MHz line-spacing comb at the second stage. After generating an electro-optic frequency comb covering 1500 lines, we set up an easily established mutually coherent hybrid dual-comb interferometer, which combines the generated electro-optic frequency comb and a free-running mode-locked laser. As a proof of concept, this hybrid dual-comb interferometer is used to measure the absorption and dispersion profiles of the molecular transition of H 13 CN with a spectral resolution of 250 MHz.

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

Ozaki, N.; Nellis, W. J.; Mashimo, T.

Materials at high pressures and temperatures are of great current interest for warm dense matter physics, planetary sciences, and inertial fusion energy research. Shock-compression equation-of-state data and optical reflectivities of the fluid dense oxide, Gd 3Ga 5O 12 (GGG), were measured at extremely high pressures up to 2.6 TPa (26 Mbar) generated by high-power laser irradiation and magnetically-driven hypervelocity impacts. Above 0.75 TPa, the GGG Hugoniot data approach/reach a universal linear line of fluid metals, and the optical reflectivity most likely reaches a constant value indicating that GGG undergoes a crossover from fluid semiconductor to poor metal with minimum metallicmore » conductivity (MMC). These results suggest that most fluid compounds, e.g., strong planetary oxides, reach a common state on the universal Hugoniot of fluid metals (UHFM) with MMC at sufficiently extreme pressures and temperatures. Lastly, the systematic behaviors of warm dense fluid would be useful benchmarks for developing theoretical equation-of-state and transport models in the warm dense matter regime in determining computational predictions.« less

Dynamic conductivity and partial ionization in dense fluid hydrogen

NASA Astrophysics Data System (ADS)

Zaghoo, Mohamed

2018-04-01

A theoretical description for optical conduction experiments in dense fluid hydrogen is presented. Different quantum statistical approaches are used to describe the mechanism of electronic transport in hydrogen's high-temperature dense phase. We show that at the onset of the metallic transition, optical conduction could be described by a strong rise in atomic polarizability, due to increased ionization, whereas in the highly degenerate limit, the Ziman weak scattering model better accounts for the observed saturation of reflectance. The inclusion of effects of partial ionization in the highly degenerate region provides great agreement with experimental results. Hydrogen's fluid metallic state is revealed to be a partially ionized free-electron plasma. Our results provide some of the first theoretical transport models that are experimentally benchmarked, as well as an important guide for future studies.

Constitutive model development for flows of granular materials

NASA Astrophysics Data System (ADS)

Chialvo, Sebastian

Granular flows are ubiquitous in both natural and industrial processes. When com- posed of dry, noncohesive particles, they manifest three different flow regimes---commonly referred to as the quasistatic, inertial, and intermediate regimes---each of which exhibits its own dependences on solids volume fraction, shear rate, and particle-level properties. The differences in these regimes can be attributed to microscale phenomena, with quasistatic flows being dominated by enduring, frictional contacts between grains, inertial flows by grain collisions, and intermediate flows by a combination of the two. Existing constitutive models for the solids-phase stress tend to focus on one or two regimes at a time, with a limited degree of success; the same is true of models for wall-boundary conditions for granular flows. Moreover, these models tend not to be based on detailed particle-level flow data, either from experiment or simulation. Clearly, a comprehensive modeling framework is lacking. The work in this thesis aims to address these issues by proposing continuum models constructed on the basis of discrete element method (DEM) simulations of granular shear flows. Specifically, we propose (a) a constitutive stress model that bridges the three dense flow regimes, (b) an modified kinetic-theory model that covers both the dense and dilute ends of the inertial regime, and (c) a boundary-condition model for dense, wall-bounded flows. These models facilitate the modeling of a wide range of flow systems of practical interest and provide ideas for further model development and refinement.

The simulation and experimental validation on gas-solid two phase flow in the riser of a dense fluidized bed

NASA Astrophysics Data System (ADS)

Wang, Xue-Yao; Jiang, Fan; Xu, Xiang; Wang, Sheng-Dian; Fan, Bao-Guo; Xiao, Yun-Han

2009-06-01

Gas-solid flow in dense CFB (circulating fluidized bed)) riser under the operating condition, superficial gas 15.5 m/s and solid flux 140 kg/m2s using Geldart B particles (sand) was investigated by experiments and CFD (computational fluid dynamics) simulation. The overall and local flow characteristics are determined using the axial pressure profiles and solid concentration profiles. The cold experimental results indicate that the axial solid concentration distribution contains a dilute region towards the up-middle zone and a dense region near the bottom and the top exit zones. The typical core-annulus structure and the back-mixing phenomenon near the wall of the riser can be observed. In addition, owing to the key role of the drag force of gas-solid phase, a revised drag force coefficient, based on the EMMS (energy-minimization multi-scale) model which can depict the heterogeneous character of gas-solid two phase flow, was proposed and coupled into the CFD control equations. In order to find an appropriate drag force model for the simulation of dense CFB riser, not only the revised drag force model but some other kinds of drag force model were used in the CFD. The flow structure, solid concentration, clusters phenomenon, fluctuation of two phases and axial pressure drop were analyzed. By comparing the experiment with the simulation, the results predicted by the EMMS drag model showed a better agreement with the experimental axial average pressure drop and apparent solid volume fraction, which proves that the revised drag force based on the EMMS model is an appropriate model for the dense CFB simulation.

Architectural transitions in Vibrio cholerae biofilms at single-cell resolution

PubMed Central

Drescher, Knut; Dunkel, Jörn; Nadell, Carey D.; van Teeffelen, Sven; Grnja, Ivan; Wingreen, Ned S.; Stone, Howard A.; Bassler, Bonnie L.

2016-01-01

Many bacterial species colonize surfaces and form dense 3D structures, known as biofilms, which are highly tolerant to antibiotics and constitute one of the major forms of bacterial biomass on Earth. Bacterial biofilms display remarkable changes during their development from initial attachment to maturity, yet the cellular architecture that gives rise to collective biofilm morphology during growth is largely unknown. Here, we use high-resolution optical microscopy to image all individual cells in Vibrio cholerae biofilms at different stages of development, including colonies that range in size from 2 to 4,500 cells. From these data, we extracted the precise 3D cellular arrangements, cell shapes, sizes, and global morphological features during biofilm growth on submerged glass substrates under flow. We discovered several critical transitions of the internal and external biofilm architectures that separate the major phases of V. cholerae biofilm growth. Optical imaging of biofilms with single-cell resolution provides a new window into biofilm formation that will prove invaluable to understanding the mechanics underlying biofilm development. PMID:26933214

Dynamic compression of dense oxide (Gd3Ga5O12) from 0.4 to 2.6 TPa: Universal Hugoniot of fluid metals

PubMed Central

Ozaki, N.; Nellis, W. J.; Mashimo, T.; Ramzan, M.; Ahuja, R.; Kaewmaraya, T.; Kimura, T.; Knudson, M.; Miyanishi, K.; Sakawa, Y.; Sano, T.; Kodama, R.

2016-01-01

Materials at high pressures and temperatures are of great current interest for warm dense matter physics, planetary sciences, and inertial fusion energy research. Shock-compression equation-of-state data and optical reflectivities of the fluid dense oxide, Gd3Ga5O12 (GGG), were measured at extremely high pressures up to 2.6 TPa (26 Mbar) generated by high-power laser irradiation and magnetically-driven hypervelocity impacts. Above 0.75 TPa, the GGG Hugoniot data approach/reach a universal linear line of fluid metals, and the optical reflectivity most likely reaches a constant value indicating that GGG undergoes a crossover from fluid semiconductor to poor metal with minimum metallic conductivity (MMC). These results suggest that most fluid compounds, e.g., strong planetary oxides, reach a common state on the universal Hugoniot of fluid metals (UHFM) with MMC at sufficiently extreme pressures and temperatures. The systematic behaviors of warm dense fluid would be useful benchmarks for developing theoretical equation-of-state and transport models in the warm dense matter regime in determining computational predictions. PMID:27193942

Dynamic compression of dense oxide (Gd 3Ga 5O 12) from 0.4 to 2.6 TPa: Universal Hugoniot of fluid metals

DOE PAGES

Ozaki, N.; Nellis, W. J.; Mashimo, T.; ...

2016-05-19

Materials at high pressures and temperatures are of great current interest for warm dense matter physics, planetary sciences, and inertial fusion energy research. Shock-compression equation-of-state data and optical reflectivities of the fluid dense oxide, Gd 3Ga 5O 12 (GGG), were measured at extremely high pressures up to 2.6 TPa (26 Mbar) generated by high-power laser irradiation and magnetically-driven hypervelocity impacts. Above 0.75 TPa, the GGG Hugoniot data approach/reach a universal linear line of fluid metals, and the optical reflectivity most likely reaches a constant value indicating that GGG undergoes a crossover from fluid semiconductor to poor metal with minimum metallicmore » conductivity (MMC). These results suggest that most fluid compounds, e.g., strong planetary oxides, reach a common state on the universal Hugoniot of fluid metals (UHFM) with MMC at sufficiently extreme pressures and temperatures. Lastly, the systematic behaviors of warm dense fluid would be useful benchmarks for developing theoretical equation-of-state and transport models in the warm dense matter regime in determining computational predictions.« less

Dynamic compression of dense oxide (Gd3Ga5O12) from 0.4 to 2.6 TPa: Universal Hugoniot of fluid metals.

PubMed

Ozaki, N; Nellis, W J; Mashimo, T; Ramzan, M; Ahuja, R; Kaewmaraya, T; Kimura, T; Knudson, M; Miyanishi, K; Sakawa, Y; Sano, T; Kodama, R

2016-05-19

Materials at high pressures and temperatures are of great current interest for warm dense matter physics, planetary sciences, and inertial fusion energy research. Shock-compression equation-of-state data and optical reflectivities of the fluid dense oxide, Gd3Ga5O12 (GGG), were measured at extremely high pressures up to 2.6 TPa (26 Mbar) generated by high-power laser irradiation and magnetically-driven hypervelocity impacts. Above 0.75 TPa, the GGG Hugoniot data approach/reach a universal linear line of fluid metals, and the optical reflectivity most likely reaches a constant value indicating that GGG undergoes a crossover from fluid semiconductor to poor metal with minimum metallic conductivity (MMC). These results suggest that most fluid compounds, e.g., strong planetary oxides, reach a common state on the universal Hugoniot of fluid metals (UHFM) with MMC at sufficiently extreme pressures and temperatures. The systematic behaviors of warm dense fluid would be useful benchmarks for developing theoretical equation-of-state and transport models in the warm dense matter regime in determining computational predictions.

A constitutive law for dense granular flows.

PubMed

Jop, Pierre; Forterre, Yoël; Pouliquen, Olivier

2006-06-08

A continuum description of granular flows would be of considerable help in predicting natural geophysical hazards or in designing industrial processes. However, the constitutive equations for dry granular flows, which govern how the material moves under shear, are still a matter of debate. One difficulty is that grains can behave like a solid (in a sand pile), a liquid (when poured from a silo) or a gas (when strongly agitated). For the two extreme regimes, constitutive equations have been proposed based on kinetic theory for collisional rapid flows, and soil mechanics for slow plastic flows. However, the intermediate dense regime, where the granular material flows like a liquid, still lacks a unified view and has motivated many studies over the past decade. The main characteristics of granular liquids are: a yield criterion (a critical shear stress below which flow is not possible) and a complex dependence on shear rate when flowing. In this sense, granular matter shares similarities with classical visco-plastic fluids such as Bingham fluids. Here we propose a new constitutive relation for dense granular flows, inspired by this analogy and recent numerical and experimental work. We then test our three-dimensional (3D) model through experiments on granular flows on a pile between rough sidewalls, in which a complex 3D flow pattern develops. We show that, without any fitting parameter, the model gives quantitative predictions for the flow shape and velocity profiles. Our results support the idea that a simple visco-plastic approach can quantitatively capture granular flow properties, and could serve as a basic tool for modelling more complex flows in geophysical or industrial applications.

The Presence of Dense Material in the Deep Mantle: Implications for Plate Motion

NASA Astrophysics Data System (ADS)

Stein, C.; Hansen, U.

2017-12-01

The dense material in the deep mantle strongly interacts with the convective flow in the mantle. On the one hand, it has a restoring effect on rising plumes. On the other hand, the dense material is swept about by the flow forming dense piles. Consequently this affects the plate motion and, in particular, the onset time and the style of plate tectonics varies considerably for different model scenarios. In this study we apply a thermochemical mantle convection model combined with a rheological model (temperature- and stress-dependent viscosity) that allows for plate formation according to the convective flow. The model's starting condition is the post-magma ocean period. We analyse a large number of model scenarios ranging from variations in thickness, density and depth of a layer of dense material to different initial temperatures.Furthermore, we present a mechanism in which the dense layer at the core-mantle boundary forms without prescribing the thickness or the density contrast. Due to advection-assisted diffusion, long-lived piles can be established that act on the style of convection and therefore on plate motion. We distinguish between the subduction-triggered regime with early plate tectonics and the plume-triggered regime with a late onset of plate tectonics. The formation of piles by advection-assisted diffusion is a typical phenomenon that appears not only at the lower boundary, but also at internal boundaries that form in the layering phase during the evolution of the system.

Embedded 100 Gbps Photonic Components

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

Kuznia, Charlie

This innovation to fiber optic component technology increases the performance, reduces the size and reduces the power consumption of optical communications within dense network systems, such as advanced distributed computing systems and data centers. VCSEL technology is enabling short-reach (< 100 m) and >100 Gbps optical interconnections over multi-mode fiber in commercial applications.

Thin film instabilities: Rayleigh-Taylor with thermocapillarity and Kolmogorov flow in a soap film

NASA Astrophysics Data System (ADS)

Burgess, John Matthew

The Rayleigh-Taylor instability occurs when a more dense fluid layer is suspended above a less dense fluid layer in a gravitational field. The horizontal interface between the two fluids is unstable to infinitesimal deformations and the dense fluid falls. To counteract the destabilizing effects of gravity on the interface between two thin fluid layers, we apply a vertical temperature gradient, heating from below. The dependence of surface tension on temperature (``thermocapillarity'') can cause spatially-varying interfacial forces between two immiscible fluid layers if a variation in temperature along the interface is introduced. With an applied vertical temperature gradient, the deforming interface spontaneously develops temperature variations which locally adjust the surface tension to restore a flat interface. We find that these surface tension gradients can stabilize a more dense thin fluid layer (silicone oil, 0.015 cm thick) above a less dense thin fluid layer (air, 0.025 cm thick) in a gravitational field, in qualitative agreement with linear stability analysis. This is the first experimental observation of the stabilization of Rayleigh-Taylor instability by thermocapillary forces. We also examine the instability of a soap film flow driven by a time-independent force that is spatially periodic in the direction perpendicular to the forcing (Kolmogorov flow). The film is in the x- y plane, where the forcing approximates a shape sin (y)x̂. Linear stability analysis of an idealized model of this flow predicts a critical Reynolds number Rc~2 . In our soap film experiment, we find a critical value Rc~70 . This discrepancy can be ascribed to frictional effects from viscous coupling of gas to the film, which is neglected in the idealized model. The kinematic viscosity of the surrounding gas and the thickness of gas layers on each side of the soap film are varied in the experiments to better understand these frictional effects. We conclude that flows in soap films cannot be decoupled from flows in the surrounding gas.

Optical Pumping of High Power Lasers with an Array of Plasma Pinches.

DTIC Science & Technology

1986-04-01

Two dense plasma focus systems, the hypocycloidal pinch and the Mather type were investigated as the potential excitation light sources for high...was also performed for the first time using the Mather type dense plasma focus (MDPF) sucsessfully. Results thus fare indicate that both HCP and MDPF

Design of CMOS compatible and compact, thermally-compensated electro-optic modulator based on off-axis microring resonator for dense wavelength division multiplexing applications.

PubMed

Haldar, Raktim; Banik, Abhik D; Varshney, Shailendra K

2014-09-22

In this work, we propose and demonstrate the performance of silicon-on-insulator (SOI) off-axis microring resonator (MRR) as electro-optic modulator (EOM). Adding an extra off-axis inner-ring in conventional microring structure provides control to compensate thermal effects on EOM. It is shown that dynamically controlled bias-voltage applied to the outer ring has the potency to quell the thermal effects over a wide range of temperature. Thus, besides the appositely biased conventional microring, off-axis inner microring with pre-emphasized electrical input message signal enables our proposed structure suitable for high data-rate dense wavelength division multiplexing scheme of optical communication within a very compact device size.

A review of the basic concepts of dense gas dispersion with special regard to modelling of heat transfer

NASA Astrophysics Data System (ADS)

Tasker, M. N.

1984-01-01

Dense gas dispersion is the study of the spreading and dilution of a gas that has a density greater than that of ambient air. Models to predict the dispersion of such dense gases as chlorine, sulfur dioxide, liquefied natural gas, and liquid propane are necessary to prevent a catastrophe in environmental and/or human terms. A basic physical picture of dense gas dispersion is provided. Mathematical and wind tunnel models of dense gas flow are presented and discussed, including the constraints and disadvantages of modelling techniques. Special emphasis is given to heat transfer during dense gas dispersion.

Multiband observations of Cygnus A: A study of pressure balance in the core of a powerful radio galaxy

NASA Technical Reports Server (NTRS)

Carilli, Chris; Conner, Sam; Dreher, John; Perley, Rick

1990-01-01

Cygnus A is a powerful double radio source associated with a giant elliptical galaxy at the center of a poor cluster of galaxies. The radio source also sits within the core radius of a dense, cooling flow, x ray emitting cluster gas. Optical spectroscopy and narrow band imaging have revealed copious amounts of narrow line emission from the inner 20 kpc of the associated galaxy. Researchers assume H sub o = 75 km sec (-1) Mpc(-1). Discussed here are the pressures in the three components of the Interstellar Medium (ISM) (i.e., the radio, x ray, and line emitting fluids) within a radius of about 15 kpc of the active nucleus of the Cygnus A galaxy.

Object Scene Flow

NASA Astrophysics Data System (ADS)

Menze, Moritz; Heipke, Christian; Geiger, Andreas

2018-06-01

This work investigates the estimation of dense three-dimensional motion fields, commonly referred to as scene flow. While great progress has been made in recent years, large displacements and adverse imaging conditions as observed in natural outdoor environments are still very challenging for current approaches to reconstruction and motion estimation. In this paper, we propose a unified random field model which reasons jointly about 3D scene flow as well as the location, shape and motion of vehicles in the observed scene. We formulate the problem as the task of decomposing the scene into a small number of rigidly moving objects sharing the same motion parameters. Thus, our formulation effectively introduces long-range spatial dependencies which commonly employed local rigidity priors are lacking. Our inference algorithm then estimates the association of image segments and object hypotheses together with their three-dimensional shape and motion. We demonstrate the potential of the proposed approach by introducing a novel challenging scene flow benchmark which allows for a thorough comparison of the proposed scene flow approach with respect to various baseline models. In contrast to previous benchmarks, our evaluation is the first to provide stereo and optical flow ground truth for dynamic real-world urban scenes at large scale. Our experiments reveal that rigid motion segmentation can be utilized as an effective regularizer for the scene flow problem, improving upon existing two-frame scene flow methods. At the same time, our method yields plausible object segmentations without requiring an explicitly trained recognition model for a specific object class.

Theoretical analysis of tsunami generation by pyroclastic flows

USGS Publications Warehouse

Watts, P.; Waythomas, C.F.

2003-01-01

Pyroclastic flows are a common product of explosive volcanism and have the potential to initiate tsunamis whenever thick, dense flows encounter bodies of water. We evaluate the process of tsunami generation by pyroclastic flow by decomposing the pyroclastic flow into two components, the dense underflow portion, which we term the pyroclastic debris flow, and the plume, which includes the surge and coignimbrite ash cloud parts of the flow. We consider five possible wave generation mechanisms. These mechanisms consist of steam explosion, pyroclastic debris flow, plume pressure, plume shear, and pressure impulse wave generation. Our theoretical analysis of tsunami generation by these mechanisms provides an estimate of tsunami features such as a characteristic wave amplitude and wavelength. We find that in most situations, tsunami generation is dominated by the pyroclastic debris flow component of a pyroclastic flow. This work presents information sufficient to construct tsunami sources for an arbitrary pyroclastic flow interacting with most bodies of water. Copyright 2003 by the American Geophysical Union.

Meniscus-assisted solution printing of large-grained perovskite films for high-efficiency solar cells

NASA Astrophysics Data System (ADS)

He, Ming; Li, Bo; Cui, Xun; Jiang, Beibei; He, Yanjie; Chen, Yihuang; O'Neil, Daniel; Szymanski, Paul; Ei-Sayed, Mostafa A.; Huang, Jinsong; Lin, Zhiqun

2017-07-01

Control over morphology and crystallinity of metal halide perovskite films is of key importance to enable high-performance optoelectronics. However, this remains particularly challenging for solution-printed devices due to the complex crystallization kinetics of semiconductor materials within dynamic flow of inks. Here we report a simple yet effective meniscus-assisted solution printing (MASP) strategy to yield large-grained dense perovskite film with good crystallization and preferred orientation. Intriguingly, the outward convective flow triggered by fast solvent evaporation at the edge of the meniscus ink imparts the transport of perovskite solutes, thus facilitating the growth of micrometre-scale perovskite grains. The growth kinetics of perovskite crystals is scrutinized by in situ optical microscopy tracking to understand the crystallization mechanism. The perovskite films produced by MASP exhibit excellent optoelectronic properties with efficiencies approaching 20% in planar perovskite solar cells. This robust MASP strategy may in principle be easily extended to craft other solution-printed perovskite-based optoelectronics.

Meniscus-assisted solution printing of large-grained perovskite films for high-efficiency solar cells

PubMed Central

He, Ming; Li, Bo; Cui, Xun; Jiang, Beibei; He, Yanjie; Chen, Yihuang; O’Neil, Daniel; Szymanski, Paul; EI-Sayed, Mostafa A.; Huang, Jinsong; Lin, Zhiqun

2017-01-01

Control over morphology and crystallinity of metal halide perovskite films is of key importance to enable high-performance optoelectronics. However, this remains particularly challenging for solution-printed devices due to the complex crystallization kinetics of semiconductor materials within dynamic flow of inks. Here we report a simple yet effective meniscus-assisted solution printing (MASP) strategy to yield large-grained dense perovskite film with good crystallization and preferred orientation. Intriguingly, the outward convective flow triggered by fast solvent evaporation at the edge of the meniscus ink imparts the transport of perovskite solutes, thus facilitating the growth of micrometre-scale perovskite grains. The growth kinetics of perovskite crystals is scrutinized by in situ optical microscopy tracking to understand the crystallization mechanism. The perovskite films produced by MASP exhibit excellent optoelectronic properties with efficiencies approaching 20% in planar perovskite solar cells. This robust MASP strategy may in principle be easily extended to craft other solution-printed perovskite-based optoelectronics. PMID:28685751

Devaney chaos, Li-Yorke chaos, and multi-dimensional Li-Yorke chaos for topological dynamics

NASA Astrophysics Data System (ADS)

Dai, Xiongping; Tang, Xinjia

2017-11-01

Let π : T × X → X, written T↷π X, be a topological semiflow/flow on a uniform space X with T a multiplicative topological semigroup/group not necessarily discrete. We then prove: If T↷π X is non-minimal topologically transitive with dense almost periodic points, then it is sensitive to initial conditions. As a result of this, Devaney chaos ⇒ Sensitivity to initial conditions, for this very general setting. Let R+↷π X be a C0-semiflow on a Polish space; then we show: If R+↷π X is topologically transitive with at least one periodic point p and there is a dense orbit with no nonempty interior, then it is multi-dimensional Li-Yorke chaotic; that is, there is a uncountable set Θ ⊆ X such that for any k ≥ 2 and any distinct points x1 , … ,xk ∈ Θ, one can find two time sequences sn → ∞ ,tn → ∞ with Moreover, let X be a non-singleton Polish space; then we prove: Any weakly-mixing C0-semiflow R+↷π X is densely multi-dimensional Li-Yorke chaotic. Any minimal weakly-mixing topological flow T↷π X with T abelian is densely multi-dimensional Li-Yorke chaotic. Any weakly-mixing topological flow T↷π X is densely Li-Yorke chaotic. We in addition construct a completely Li-Yorke chaotic minimal SL (2 , R)-acting flow on the compact metric space R ∪ { ∞ }. Our various chaotic dynamics are sensitive to the choices of the topology of the phase semigroup/group T.

Optical and transport properties of dense liquid silica

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

Qi, Tingting; Millot, Marius; Kraus, Richard G.

2015-06-15

Using density-functional-theory based molecular dynamics and the Kubo-Greenwood linear response theory, we evaluated the high-pressure equation of state and the optical and transport properties of quartz and fused silica shock-compressed to 2000 GPa. The computed Hugoniots and corresponding optical reflectivity values are in very good agreement with published data for quartz, and new data that we obtained on fused silica using magnetically launched flyer plate experiments. The rise of optical reflectivity upon shock compression appears to be primarily a temperature-driven mechanism, which is relatively insensitive to small density variation. We observed that the electrical conductivity does not display Drude-like frequencymore » dependence, especially at lower temperatures. In addition, the Wiedemann-Franz relation between electrical and thermal conductivities was found to be invalid. It suggests that even at three-fold compression, warm dense liquid silica on the Hugoniot curve is still far away from the degenerate limit.« less

Luminescent characteristics study of Mather-type dense plasma focus and applications to short-wavelength optical pumping. Final technical report, 1 May 1984-30 September 1985

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

Kim, K.K.

A Mather-type dense plasma focus (MDPF) system was designed, built, and tested specifically to study its luminescent characteristics and to assess its potential as a new light source of high-energy, short-wavelength lasers. The luminescence study of MDPF showed that the conversion efficiency from the electrical input to the optical output energies is at least 50%, up to the time the plasma compression is complete. Using the system, for the first time as an optical pump, laser activities were successfully obtained from a variety of liquid organic dyes. Diagnostic capabilities included an optical multichannel analyzer system complete with a computer control,more » a nitrogen-pumped tunable dye-laser system, a high-speed streak/framing camera, a digital laser energy meter, voltage and current probes, and a computer-based data-acquisition system.« less

Mesoscopic coherence in light scattering from cold, optically dense and disordered atomic systems

NASA Astrophysics Data System (ADS)

Kupriyanov, D. V.; Sokolov, I. M.; Havey, M. D.

2017-02-01

Coherent effects manifested in light scattering from cold, optically dense and disordered atomic systems are reviewed from a primarily theoretical point of view. Development of the basic theoretical tools is then elaborated through several physical atomic physics based processes which have been at least partly explored experimentally. These include illustrations drawn from the coherent backscattering effect, random lasing in atomic gases, quantum memories and light-atoms interface assisted by the light trapping mechanism. Current understanding and challenges associated with the transition to high atomic densities and cooperativity in the scattering process are also discussed in some detail.

Free-free opacity in dense plasmas with an average atom model

DOE PAGES

Shaffer, Nathaniel R.; Ferris, Natalie G.; Colgan, James Patrick; ...

2017-02-28

A model for the free-free opacity of dense plasmas is presented. The model uses a previously developed average atom model, together with the Kubo-Greenwood model for optical conductivity. This, in turn, is used to calculate the opacity with the Kramers-Kronig dispersion relations. Furthermore, comparisons to other methods for dense deuterium results in excellent agreement with DFT-MD simulations, and reasonable agreement with a simple Yukawa screening model corrected to satisfy the conductivity sum rule.

Free-free opacity in dense plasmas with an average atom model

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

Shaffer, Nathaniel R.; Ferris, Natalie G.; Colgan, James Patrick

A model for the free-free opacity of dense plasmas is presented. The model uses a previously developed average atom model, together with the Kubo-Greenwood model for optical conductivity. This, in turn, is used to calculate the opacity with the Kramers-Kronig dispersion relations. Furthermore, comparisons to other methods for dense deuterium results in excellent agreement with DFT-MD simulations, and reasonable agreement with a simple Yukawa screening model corrected to satisfy the conductivity sum rule.

Experimental evidence of exciton-plasmon coupling in densely packed dye doped core-shell nanoparticles obtained via microfluidic technique

NASA Astrophysics Data System (ADS)

De Luca, A.; Iazzolino, A.; Salmon, J.-B.; Leng, J.; Ravaine, S.; Grigorenko, A. N.; Strangi, G.

2014-09-01

The interplay between plasmons and excitons in bulk metamaterials are investigated by performing spectroscopic studies, including variable angle pump-probe ellipsometry. Gain functionalized gold nanoparticles have been densely packed through a microfluidic chip, representing a scalable process towards bulk metamaterials based on self-assembly approach. Chromophores placed at the hearth of plasmonic subunits ensure exciton-plasmon coupling to convey excitation energy to the quasi-static electric field of the plasmon states. The overall complex polarizability of the system, probed by variable angle spectroscopic ellipsometry, shows a significant modification under optical excitation, as demonstrated by the behavior of the ellipsometric angles Ψ and Δ as a function of suitable excitation fields. The plasmon resonances observed in densely packed gain functionalized core-shell gold nanoparticles represent a promising step to enable a wide range of electromagnetic properties and fascinating applications of plasmonic bulk systems for advanced optical materials.

Dynamic Conductivity and Partial Ionization in Warm, Dense Hydrogen

NASA Astrophysics Data System (ADS)

Zaghoo, M.; Silvera, I. F.

2017-10-01

A theoretical description for optical conduction experiments in dense fluid hydrogen is presented. Different quantum statistical approaches are used to describe the mechanism of electron transport in hydrogen's high-temperature dense phase. We show that at the onset of the metallic transition, optical conduction could be described by a strong rise in the atomic polarizability, resulting from increased ionization; whereas in the highly degenerate limit, the Ziman weak-scattering model better describes the observed saturation of reflectance. In the highly degenerate region, the inclusion of partial ionization effects provides excellent agreement with experimental results. Hydrogen's fluid metallic state is revealed to be a partially ionized free-electron plasma. These results provide a crucial benchmark for ab initio calculations as well as an important guide for future experiments. Research supported by DOE Stockpile Stewardship Academic Alliance Program, Grant DE-FG52-10NA29656, and NASA Earth and Space Science Fellowship Program, Award NNX14AP17H.

Fiber optic sensors for sub-centimeter spatially resolved measurements: Review and biomedical applications

NASA Astrophysics Data System (ADS)

Tosi, Daniele; Schena, Emiliano; Molardi, Carlo; Korganbayev, Sanzhar

2018-07-01

One of the current frontier of optical fiber sensors, and a unique asset of this sensing technology is the possibility to use a whole optical fiber, or optical fiber device, as a sensor. This solution allows shifting the whole sensing paradigm, from the measurement of a single physical parameter (such as temperature, strain, vibrations, pressure) to the measurement of a spatial distribution, or profiling, of a physical parameter along the fiber length. In the recent years, several technologies are achieving this task with unprecedentedly narrow spatial resolution, ranging from the sub-millimeter to the centimeter-level. In this work, we review the main fiber optic sensing technologies that achieve a narrow spatial resolution: Fiber Bragg Grating (FBG) dense arrays, chirped FBG (CFBG) sensors, optical frequency domain reflectometry (OFDR) based on either Rayleigh scattering or reflective elements, and microwave photonics (MWP). In the second part of the work, we present the impact of spatially dense fiber optic sensors in biomedical applications, where they find the main impact, presenting the key results obtained in thermo-therapies monitoring, high-resolution diagnostic, catheters monitoring, smart textiles, and other emerging applicative fields.

The Relationship between the Dense Neutral and Diffuse Ionized Gas in the Thick Disks of Two Edge-on Spiral Galaxies

NASA Astrophysics Data System (ADS)

Rueff, Katherine M.; Howk, J. Christopher; Pitterle, Marissa; Hirschauer, Alec S.; Fox, Andrew J.; Savage, Blair D.

2013-03-01

We present high-resolution, optical images (BVI + Hα) of the multiphase interstellar medium (ISM) in the thick disks of the edge-on spiral galaxies NGC 4013 and NGC 4302. Our images from the Hubble Space Telescope (HST), Large Binocular Telescope, and WIYN 3.5 m telescope reveal an extensive population of filamentary dust absorption seen to z ~2-2.5 kpc. Many of these dusty thick disk structures have characteristics reminiscent of molecular clouds found in the Milky Way disk. Our Hα images show that the extraplanar diffuse ionized gas (DIG) in these galaxies is dominated by a smooth, diffuse component. The strongly filamentary morphologies of the dust absorption have no counterpart in the smoothly distributed Hα emission. We argue that the thick disk DIG and dust-bearing filaments trace physically distinct phases of the thick disk ISM, the latter tracing a dense, warm or cold neutral medium. The dense, dusty matter in the thick disks of spiral galaxies is largely tracing matter ejected from the thin disk via energetic feedback from massive stars. The high densities of the gas may be a result of converging gas flows. This dense material fuels some thick disk star formation, as evidenced by the presence of thick disk H II regions. Based on observations obtained with the NASA/ESA Hubble Space Telescope operated at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS5-26555. Also, based on data acquired using the Large Binocular Telescope (LBT). The LBT is an international collaboration among institutions in the US, Italy, and Germany. LBT Corporation partners are the University of Arizona, on behalf of the Arizona University System; Instituto Nazionale do Astrofisica, Italy; LBT Beteiligungsgesellschaft, Germany, representing the Max Planck Society, the Astrophysical Institute of Potsdam, and Heidelberg University; Ohio State University, and the Research Corporation, on behalf of the University of Notre Dame, the University of Minnesota, and the University of Virginia. Also, based on observations obtained by the WIYN Observatory which is a joint facility of the University of Wisconsin-Madison, Yale University, Indiana University, and the National Optical Astronomy Observatories.

Effects of Noise and Vibration on the Solid to Liquid Fluidization Transition in Small Dense Granular Systems Under Shear

NASA Astrophysics Data System (ADS)

Melhus, Martin Frederic

2011-07-01

Granular materials exhibit bulk properties that are distinct from conventional solids, liq- uids, and gases, due to the dissipative nature of the inter-granular forces. Understanding the fundamentals of granular materials draws upon and gives insight into many fields at the current frontiers of physics, such as plasticity of solids, fracture and friction, com- plex systems such as colloids, foams and suspensions, and a variety of biological systems. Particulate flows are widespread in geophysics, and are also essential to many industries. Despite the importance of these phenomena, we lack a theoretical model that explains most behaviors of granular materials. Since granular assemblies are highly dissipative, they are often far from mechanical equilibrium, making most classical analyses inappli- cable. A theory for dilute granular systems exists, but for dense granular systems (by far the majority of granular systems in the real world) no comparable theory is accepted. We approach this problem by examining the fluidization, or transition from solid to liquid, in dense granular systems. In this study, the separate effects of random noise and vibration on the static to flowing transition of a dense granular assembly under planar shear is studied numerically using soft contact particle dynamics simulations in two dimensions. We focus on small systems in a thin planar Couette cell, examining the bistable region while increasing shear, with varying amounts of random noise or vibration, and determine the statistics of the shear required for the onset of flow. We find that the applied power is the key parameter in determining the magnitude of the effects of the noise or vibration, with vibration frequency also having an influence. Similarities and differences between noise and vibration are determined, and the results compare favorably with a two phase model for dense granular flow.

Self-sustained focusing of high-density streaming plasma

NASA Astrophysics Data System (ADS)

Bugaev, A.; Dobrovolskiy, A.; Goncharov, A.; Gushenets, V.; Litovko, I.; Naiko, I.; Oks, E.

2017-01-01

We describe our observations of the transport through an electrostatic plasma lens of a wide-aperture, high-current, low energy, metal-ion plasma flow produced by a cathodic arc discharge. The lens input aperture was 80 mm, the length of the lens was 140 mm, and there were three electrostatic ring electrodes located in a magnetic field formed by permanent magnets. The lens outer electrodes were grounded and the central electrode was biased up to -3 kV. The plasma was a copper plasma with directed (streaming) ion energy 20-40 eV, and the equivalent ion current was up to several amperes depending on the potential applied to the central lens electrode. We find that when the central lens electrode is electrically floating, the current density of the plasma flow at the lens focus increases by up to 40%-50%, a result that is in good agreement with a theoretical treatment based on plasma-optical principles of magnetic insulation of electrons and equipotentialization along magnetic field lines. When the central lens electrode is biased negatively, an on-axis stream of energetic electrons is formed, which can also provide a mechanism for focusing of the plasma flow. Optical emission spectra under these conditions show an increase in intensity of lines corresponding to both copper atoms and singly charged copper ions, indicating the presence of fast electrons within the lens volume. These energetic electrons, as well as accumulating on-axis and providing ion focusing, can also assist in reducing the microdroplet component in the dense, low-temperature, metal plasma.

A novel automated method for doing registration and 3D reconstruction from multi-modal RGB/IR image sequences

NASA Astrophysics Data System (ADS)

Kirby, Richard; Whitaker, Ross

2016-09-01

In recent years, the use of multi-modal camera rigs consisting of an RGB sensor and an infrared (IR) sensor have become increasingly popular for use in surveillance and robotics applications. The advantages of using multi-modal camera rigs include improved foreground/background segmentation, wider range of lighting conditions under which the system works, and richer information (e.g. visible light and heat signature) for target identification. However, the traditional computer vision method of mapping pairs of images using pixel intensities or image features is often not possible with an RGB/IR image pair. We introduce a novel method to overcome the lack of common features in RGB/IR image pairs by using a variational methods optimization algorithm to map the optical flow fields computed from different wavelength images. This results in the alignment of the flow fields, which in turn produce correspondences similar to those found in a stereo RGB/RGB camera rig using pixel intensities or image features. In addition to aligning the different wavelength images, these correspondences are used to generate dense disparity and depth maps. We obtain accuracies similar to other multi-modal image alignment methodologies as long as the scene contains sufficient depth variations, although a direct comparison is not possible because of the lack of standard image sets from moving multi-modal camera rigs. We test our method on synthetic optical flow fields and on real image sequences that we created with a multi-modal binocular stereo RGB/IR camera rig. We determine our method's accuracy by comparing against a ground truth.

Correlated motion in the bulk of dense granular flows.

PubMed

Staron, Lydie

2008-05-01

Numerical simulations of two-dimensional stationary dense granular flows are performed. We check that the system obeys the h_{stop} phenomenology. Focusing on the spatial correlations of the instantaneous velocity fluctuations of the grains, we give evidence of the existence of correlated motion over several grain diameters in the bulk of the flow. Investigating the role of contact friction and restitution, we show that the associated typical length scale lambda is essentially independent of the grain properties. Moreover, we show that lambda is not controlled by the packing compacity. However, in agreement with previous experimental work, we observe that the correlation length decreases with the shear rate. Computing the flows inertia number I , we show a first-order dependence of lambda on I .

Bacterial turbulence in motion

NASA Astrophysics Data System (ADS)

Rusconi, Roberto; Smriga, Steven; Stocker, Roman; Secchi, Eleonora; Buzzaccaro, Stefano; Piazza, Roberto

2014-11-01

Dense suspensions of motile bacteria exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence, yet this analogy has remained largely qualitative. Here we present experiments in which a dense suspension of Bacillus subtilis bacteria was flown through narrow microchannels and the velocity statistics of the flowing suspension were accurately quantified with a recently developed velocimetry technique. This revealed a robust intermittency phenomenon, whereby the average velocity profile of the flowing suspension oscillated between a plug-like flow and a parabolic flow. This intermittency is a hallmark of classic turbulence and was associated with the presence of collective structures in the suspension. Furthermore, quantification of the Reynolds stress profile revealed a direct link between the turbulent nature of the suspension and its anomalous viscosity.

Iterative reconstruction of volumetric particle distribution

NASA Astrophysics Data System (ADS)

Wieneke, Bernhard

2013-02-01

For tracking the motion of illuminated particles in space and time several volumetric flow measurement techniques are available like 3D-particle tracking velocimetry (3D-PTV) recording images from typically three to four viewing directions. For higher seeding densities and the same experimental setup, tomographic PIV (Tomo-PIV) reconstructs voxel intensities using an iterative tomographic reconstruction algorithm (e.g. multiplicative algebraic reconstruction technique, MART) followed by cross-correlation of sub-volumes computing instantaneous 3D flow fields on a regular grid. A novel hybrid algorithm is proposed here that similar to MART iteratively reconstructs 3D-particle locations by comparing the recorded images with the projections calculated from the particle distribution in the volume. But like 3D-PTV, particles are represented by 3D-positions instead of voxel-based intensity blobs as in MART. Detailed knowledge of the optical transfer function and the particle image shape is mandatory, which may differ for different positions in the volume and for each camera. Using synthetic data it is shown that this method is capable of reconstructing densely seeded flows up to about 0.05 ppp with similar accuracy as Tomo-PIV. Finally the method is validated with experimental data.

Corrosion, optical and magnetic properties of flexible iron nitride nano thin films deposited on polymer substrate

NASA Astrophysics Data System (ADS)

Khan, W. Q.; Wang, Qun; Jin, Xin; Yasin, G.

2017-11-01

Iron nitride thin films of different compositions and thicknesses were deposited on flexible polymer substrate in Ar/N2 atmosphere by reactive magnetron sputtering under varying nitrogen flow rates. The nano structured films were characterized by X-ray diffraction, UV-visible spectrophotometer, electrochemical impedance (EIS), atomic force (AFM) and transmission electron microscopies. The dependence of their functional properties on coating and growth conditions was studied in detail. It was found that the thin films show a uniform permeability in the frequency range of 200 MHz to 1 Ghz and can be used in this range without appreciable changes. Decrease of nitrogen flow rate resulted in the smoother surfaces which in turn increase transmittance quality and corrosion resistance. Functional properties are dependent of nature, relative concentration of the iron nitride phases and film thickness. Surface integrity is excellent for180 nm thick sample because the films appear to be very dense and free from open pores. By keeping sputtering power stable at 110 W, nitrogen flow rate of 10 sccm was ideal to develop the ferromagnetic γʹFe4N phase at room temperature.

Gas and particle motions in a rapidly decompressed flow

NASA Astrophysics Data System (ADS)

Johnson, Blair; Zunino, Heather; Adrian, Ronald; Clarke, Amanda

2017-11-01

To understand the behavior of a rapidly decompressed particle bed in response to a shock, an experimental study is performed in a cylindrical (D = 4.1 cm) glass vertical shock tube of a densely packed (ρ = 61%) particle bed. The bed is comprised of spherical glass particles, ranging from D50 = 44-297 μm between experiments. High-speed pressure sensors are incorporated to capture shock speeds and strengths. High-speed video and particle image velocimetry (PIV) measurements are collected to examine vertical and radial velocities of both the particles and gas to elucidate features of the shock wave and resultant expansion wave in the lateral center of the tube, away from boundaries. In addition to optically analyzing the front velocity of the rising particle bed, interaction between the particle and gas phases are investigated as the flow accelerates and the particle front becomes more dilute. Particle and gas interactions are also considered in exploring mechanisms through which turbulence develops in the flow. This work is supported by the U.S. Department of Energy, National Nuclear Security Administration, Advanced Simulation and Computing Program, as a Cooperative Agreement under the Predictive Science and Academic Alliance Program, under Contract No. DE-NA0002378.

A Massive, Cooling-Flow-Induced Starburst in the Core of a Highly Luminous Galaxy Cluster

NASA Technical Reports Server (NTRS)

McDonald, M.; Bayliss, M.; Benson, B. A.; Foley, R. J.; Ruel, J.; Sullivan, P.; Veilleux, S.; Aird, K. A.; Ashby, M. L. N.; Bautz, M.;

Parallel and perpendicular velocity sheared flows driven tripolar vortices in an inhomogeneous electron-ion quantum magnetoplasma

NASA Astrophysics Data System (ADS)

Mirza, Arshad M.; Masood, W.

2011-12-01

Nonlinear equations governing the dynamics of finite amplitude drift-ion acoustic-waves are derived by taking into account sheared ion flows parallel and perpendicular to the ambient magnetic field in a quantum magnetoplasma comprised of electrons and ions. It is shown that stationary solution of the nonlinear equations can be represented in the form of a tripolar vortex for specific profiles of the equilibrium sheared flows. The tripolar vortices are, however, observed to form on very short scales in dense quantum plasmas. The relevance of the present investigation with regard to dense astrophysical environments is also pointed out.

Supersonic minimum length nozzle design for dense gases

NASA Technical Reports Server (NTRS)

Aldo, Andrew C.; Argrow, Brian M.

1993-01-01

Recently, dense gases have been investigated for many engineering applications such as for turbomachinery and wind tunnels. Supersonic nozzle design for these gases is complicated by their nonclassical behavior in the transonic flow regime. In this paper a method of characteristics (MOC) is developed for two-dimensional (planar) and, primarily, axisymmetric flow of a van der Waals gas. Using a straight aortic line assumption, a centered expansion is used to generate an inviscid wall contour of minimum length. The van der Waals results are compared to previous perfect gas results to show the real gas effects on the flow properties and inviscid wall contours.

A study of the methods for the production and confinement of high energy plasmas. [injection of dense plasma into long magnetic field

NASA Technical Reports Server (NTRS)

Cheng, D. Y.; Wang, P.

1972-01-01

The injection of dense plasmas into a B sub z long magnetic field from both ends of the field coil was investigated. Deflagration plasma guns and continuous flow Z-pinch are discussed along with the possibility of a continuous flow Z-pinch fusion reactor. The injection experiments are described with emphasis on the synchronization of the two plasma deflagration guns, the collision of the two plasma beams, and the determination of plasma density.

The numerical simulation study of hemodynamics of the new dense-mesh stent

NASA Astrophysics Data System (ADS)

Ma, Jiali; Yuan, Zhishan; Yu, Xuebao; Feng, Zhaowei; Miao, Weidong; Xu, Xueli; Li, Juntao

2017-09-01

The treatment of aortic aneurysm in new dense mesh stent is based on the principle of hemodynamic changes. But the mechanism is not yet very clear. This paper analyzed and calculated the hemodynamic situation before and after the new dense mesh stent implanting by the method of numerical simulation. The results show the dense mesh stent changed and impacted the blood flow in the aortic aneurysm. The changes include significant decrement of blood velocity, pressure and shear forces, while ensuring blood can supply branches, which means the new dense mesh stent's hemodynamic mechanism in the treatment of aortic aneurysm is clearer. It has very important significance in developing new dense mesh stent in order to cure aortic aneurysm.

Electron-ion temperature equilibration in warm dense tantalum

DOE PAGES

Doppner, T; LePape, S.; Ma, T.; ...

2014-11-05

We present measurements of electron-ion temperature equilibration in proton-heated tantalum, under warm dense matter conditions. Our results agree with theoretical predictions for metals calculated using input data from ab initio simulations. Furthermore, the fast relaxation observed in the experiment contrasts with much longer equilibration times found in proton heated carbon, indicating that the energy flow pathways in warm dense matter are far from being fully understood.

Dense water plumes modulate richness and productivity of deep sea microbes.

PubMed

Luna, Gian Marco; Chiggiato, Jacopo; Quero, Grazia Marina; Schroeder, Katrin; Bongiorni, Lucia; Kalenitchenko, Dimitri; Galand, Pierre E

2016-12-01

Growing evidence indicates that dense water formation and flow over the continental shelf is a globally relevant oceanographic process, potentially affecting microbial assemblages down to the deep ocean. However, the extent and consequences of this influence have yet to be investigated. Here it is shown that dense water propagation to the deep ocean increases the abundance of prokaryotic plankton, and stimulates carbon production and organic matter degradation rates. Dense waters spilling off the shelf modifies community composition of deep sea microbial assemblages, leading to the increased relevance of taxa likely originating from the sea surface and the seafloor. This phenomenon can be explained by a combination of factors that interplay during the dense waters propagation, such as the transport of surface microbes to the ocean floor (delivering in our site 0.1 megatons of C), the stimulation of microbial metabolism due to increased ventilation and nutrients availability, the sediment re-suspension, and the mixing with ambient waters along the path. Thus, these results highlight a hitherto unidentified role for dense currents flowing over continental shelves in influencing deep sea microbes. In light of climate projections, this process will affect significantly the microbial functioning and biogeochemical cycling of large sectors of the ocean interior. © 2016 Society for Applied Microbiology and John Wiley & Sons Ltd.

Influence of the finite linewidth of the laser radiation spectrum on the shape of the coherent population trapping resonance line in an optically dense medium with a buffer gas

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

Barantsev, K. A., E-mail: kostmann@yandex.ru; Popov, E. N.; Litvinov, A. N., E-mail: andrey.litvinov@mail.ru

2015-11-15

The theory of coherent population trapping resonance is developed for the finite linewidth of the laser radiation spectrum in an optically dense medium of Λ atoms in a cell with a buffer gas. Equations are derived for the atomic density matrix and laser emission spectrum transfer in a cell with working and buffer gases at a finite temperature. The dependence of the quality factor of coherent population trapping resonance on the linewidth of the laser radiation spectrum is studied by measuring transmitted radiation and fluorescence signals.

Acousto-Optical Vector Matrix Product Processor: Implementation Issues

DTIC Science & Technology

1989-04-25

power by a factor of 3.8. The acoustic velocity in longitudinal TeO2 is 4200 m/s, almost the same as the 4100 m/s acoustic velocity in dense flint glass ...field via an Interaction Model AOD150 dense flint glass Bragg Cell. The cell’s specifications are listed in the table below. BRAGG CELL SPECIFICATIONS...39 ns intervals). Since the speed of sound in dense flint glass is 4100 m/s, the acoustic field generated in a 10 As interval is distributed over a 4.1

Quasidistributed temperature sensor based on dense wavelength-division multiplexing optical fiber delay

NASA Astrophysics Data System (ADS)

Su, Jun; Yang, Ning; Fan, Zhiqiang; Qiu, Qi

2017-10-01

We report on a fiber-optic delay-based quasidistributed temperature sensor with high precision. The device works by detecting the delay induced by the temperature instead of the spectrum. To analyze the working principle of this sensor, the thermal dependence of the fiber-optic delay was theoretically investigated and the delay-temperature coefficient was measured to be 42.2 ps/km°C. In this sensor, quasidistributed measurement of temperature could be easily realized by dense wavelength-division multiplexing and wavelength addressing. We built and tested a prototype quasidistributed temperature sensor with eight testing points equally distributed along a 32.61-km-long fiber. The experimental results demonstrate an average error of <0.1°C. These results prove that this quasidistributed temperature sensor is feasible and that it is a viable option for simple and economic temperature measurements.

Optical characterization of nonimaging dish concentrator for the application of dense-array concentrator photovoltaic system.

PubMed

Tan, Ming-Hui; Chong, Kok-Keong; Wong, Chee-Woon

2014-01-20

Optimization of the design of a nonimaging dish concentrator (NIDC) for a dense-array concentrator photovoltaic system is presented. A new algorithm has been developed to determine configuration of facet mirrors in a NIDC. Analytical formulas were derived to analyze the optical performance of a NIDC and then compared with a simulated result obtained from a numerical method. Comprehensive analysis of optical performance via analytical method has been carried out based on facet dimension and focal distance of the concentrator with a total reflective area of 120 m2. The result shows that a facet dimension of 49.8 cm, focal distance of 8 m, and solar concentration ratio of 411.8 suns is the most optimized design for the lowest cost-per-output power, which is US$1.93 per watt.

Numerical Modeling of Deep Mantle Flow: Thermochemical Convection and Entrainment

NASA Astrophysics Data System (ADS)

Mulyukova, Elvira; Steinberger, Bernhard; Dabrowski, Marcin; Sobolev, Stephan

2013-04-01

One of the most robust results from tomographic studies is the existence of two antipodally located Large Low Shear Velocity Provinces (LLSVPs) at the base of the mantle, which appear to be chemically denser than the ambient mantle. Results from reconstruction studies (Torsvik et al., 2006) infer that the LLSVPs are stable, long-lived, and are sampled by deep mantle plumes that rise predominantly from their margins. The origin of the dense material is debated, but generally falls within three categories: (i) a primitive layer that formed during magma ocean crystallization, (ii) accumulation of a dense eclogitic component from the recycled oceanic crust, and (iii) outer core material leaking into the lower mantle. A dense layer underlying a less dense ambient mantle is gravitationally stable. However, the flow due to thermal density variations, i.e. hot rising plumes and cold downwelling slabs, may deform the layer into piles with higher topography. Further deformation may lead to entrainment of the dense layer, its mixing with the ambient material, and even complete homogenisation with the rest of the mantle. The amount of the anomalous LLSVP-material that gets entrained into the rising plumes poses a constraint on the survival time of the LLSVPs, as well as on the plume buoyancy, on the lithospheric uplift associated with plume interaction and geochemical signature of the erupted lavas observed at the Earth's surface. Recent estimates for the plume responsible for the formation of the Siberian Flood Basalts give about 15% of entrained dense recycled oceanic crust, which made the hot mantle plume almost neutrally buoyant (Sobolev et al., 2011). In this numerical study we investigate the mechanics of entrainment of a dense basal layer by convective mantle flow. We observe that the types of flow that promote entrainment of the dense layer are (i) upwelling of the dense layer when it gets heated enough to overcome its stabilizing chemical density anomaly, (ii) upwelling of the ambient material in the vicinity of the dense material (mechanism of selective withdrawal (Lister, 1989)), and (iii) cold downwellings sliding along the bottom boundary, and forcing the dense material upwards. The objective of this study is to compare the efficiency of entrainment by each of these mechanisms, and its dependence on the density and viscosity anomaly of the dense material with respect to the ambient mantle. To perform this study, we have developed a two-dimensional FEM code to model thermal convection in a hollow cylinder domain with presence of chemical heterogeneities, and using a realistic viscosity profile. We present the results of the simulations that demonstrate the entrainment mechanisms described above. In addition, we perfom numerical experiments in a Cartesian box domain, where the bottom right boundary of the box is deformed to resemble the geometry of an LLSVP edge. In some of the experiments, the bottom left part of the boundary is moving towards the right boundary, simulating a slab sliding along the core-mantle boundary towards an LLSVP. These experiments allow a detailed study of the process of entrainment, and its role in the thermochemical evolution of the Earth.

An incompressible two-dimensional multiphase particle-in-cell model for dense particle flows

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

Snider, D.M.; O`Rourke, P.J.; Andrews, M.J.

1997-06-01

A two-dimensional, incompressible, multiphase particle-in-cell (MP-PIC) method is presented for dense particle flows. The numerical technique solves the governing equations of the fluid phase using a continuum model and those of the particle phase using a Lagrangian model. Difficulties associated with calculating interparticle interactions for dense particle flows with volume fractions above 5% have been eliminated by mapping particle properties to a Eulerian grid and then mapping back computed stress tensors to particle positions. This approach utilizes the best of Eulerian/Eulerian continuum models and Eulerian/Lagrangian discrete models. The solution scheme allows for distributions of types, sizes, and density of particles,more » with no numerical diffusion from the Lagrangian particle calculations. The computational method is implicit with respect to pressure, velocity, and volume fraction in the continuum solution thus avoiding courant limits on computational time advancement. MP-PIC simulations are compared with one-dimensional problems that have analytical solutions and with two-dimensional problems for which there are experimental data.« less

Numerical investigation of influence on heat transfer characteristics to pneumatically conveyed dense phase flow by selecting models and boundary conditions

NASA Astrophysics Data System (ADS)

Zheng, Y.; Liu, Q.; Li, Y.

2012-03-01

Solids moving with a gas stream in a pipeline can be found in many industrial processes, such as power generation, chemical, pharmaceutical, food and commodity transfer processes. A mass flow rate of the solids is important characteristic that is often required to be measured (and controlled) to achieve efficient utilization of energy and raw materials in pneumatic conveying systems. The methods of measuring the mass flow rate of solids in a pneumatic pipeline can be divided into direct and indirect (inferential) measurements. A thermal solids' mass flow-meter, in principle, should ideally provide a direct measurement of solids flow rate, regardless of inhomogeneities in solids' distribution and environmental impacts. One key issue in developing a thermal solids' mass flow-meter is to characterize the heat transfer between the hot pipe wall and the gas-solids dense phase flow. The Eulerian continuum modeling with gas-solid two phases is the most common method for pneumatic transport. To model a gas-solid dense phase flow passing through a heated region, the gas phase is described as a continuous phase and the particles as the second phase. This study aims to describe the heat transfer characteristics between the hot wall and the gas-solids dense phase flow in pneumatic pipelines by modeling a turbulence gas-solid plug passing through the heated region which involves several actual and crucial issues: selections of interphase exchange coefficient, near-wall region functions and different wall surface temperatures. A sensitivity analysis was discussed to identify the influence on the heat transfer characteristics by selecting different interphase exchange coefficient models and different boundary conditions. Simulation results suggest that sensitivity analysis in the choice of models is very significant. The simulation results appear to show that a combination of choosing the Syamlal-O'Brien interphase exchange coefficient model and the standard k-ɛ model along with the standard wall function model might be the best approach, by which, the simulation data seems to be closest to the experimental results.

Coherent ultra dense wavelength division multiplexing passive optical networks

NASA Astrophysics Data System (ADS)

Shahpari, Ali; Ferreira, Ricardo; Ribeiro, Vitor; Sousa, Artur; Ziaie, Somayeh; Tavares, Ana; Vujicic, Zoran; Guiomar, Fernando P.; Reis, Jacklyn D.; Pinto, Armando N.; Teixeira, António

2015-12-01

In this paper, we firstly review the progress in ultra-dense wavelength division multiplexing passive optical network (UDWDM-PON), by making use of the key attributes of this technology in the context of optical access and metro networks. Besides the inherit properties of coherent technology, we explore different modulation formats and pulse shaping. The performance is experimentally demonstrated through a 12 × 10 Gb/s bidirectional UDWDM-PON over hybrid 80 km standard single mode fiber (SSMF) and optical wireless link. High density, 6.25 GHz grid, Nyquist shaped 16-ary quadrature amplitude modulation (16QAM) and digital frequency shifting are some of the properties exploited together in the tests. Also, bidirectional transmission in fiber, relevant in the context, is analyzed in terms of nonlinear and back-reflection effects on receiver sensitivity. In addition, as a basis for the discussion on market readiness, we experimentally demonstrate real-time detection of a Nyquist-shaped quaternary phase-shift keying (QPSK) signal using simple 8-bit digital signal processing (DSP) on a field-programmable gate array (FPGA).

A light and faster regional convolutional neural network for object detection in optical remote sensing images

NASA Astrophysics Data System (ADS)

Ding, Peng; Zhang, Ye; Deng, Wei-Jian; Jia, Ping; Kuijper, Arjan

2018-07-01

Detection of objects from satellite optical remote sensing images is very important for many commercial and governmental applications. With the development of deep convolutional neural networks (deep CNNs), the field of object detection has seen tremendous advances. Currently, objects in satellite remote sensing images can be detected using deep CNNs. In general, optical remote sensing images contain many dense and small objects, and the use of the original Faster Regional CNN framework does not yield a suitably high precision. Therefore, after careful analysis we adopt dense convoluted networks, a multi-scale representation and various combinations of improvement schemes to enhance the structure of the base VGG16-Net for improving the precision. We propose an approach to reduce the test-time (detection time) and memory requirements. To validate the effectiveness of our approach, we perform experiments using satellite remote sensing image datasets of aircraft and automobiles. The results show that the improved network structure can detect objects in satellite optical remote sensing images more accurately and efficiently.

Multichannel optical mapping: investigation of depth information

NASA Astrophysics Data System (ADS)

Sase, Ichiro; Eda, Hideo; Seiyama, Akitoshi; Tanabe, Hiroki C.; Takatsuki, Akira; Yanagida, Toshio

2001-06-01

Near infrared (NIR) light has become a powerful tool for non-invasive imaging of human brain activity. Many systems have been developed to capture the changes in regional brain blood flow and hemoglobin oxygenation, which occur in the human cortex in response to neural activity. We have developed a multi-channel reflectance imaging system, which can be used as a `mapping device' and also as a `multi-channel spectrophotometer'. In the present study, we visualized changes in the hemodynamics of the human occipital region in multiple ways. (1) Stimulating left and right primary visual cortex independently by showing sector shaped checkerboards sequentially over the contralateral visual field, resulted in corresponding changes in the hemodynamics observed by `mapping' measurement. (2) Simultaneous measurement of functional-MRI and NIR (changes in total hemoglobin) during visual stimulation showed good spatial and temporal correlation with each other. (3) Placing multiple channels densely over the occipital region demonstrated spatial patterns more precisely, and depth information was also acquired by placing each pair of illumination and detection fibers at various distances. These results indicate that optical method can provide data for 3D analysis of human brain functions.

A new numerical benchmark for variably saturated variable-density flow and transport in porous media

NASA Astrophysics Data System (ADS)

Guevara, Carlos; Graf, Thomas

2016-04-01

In subsurface hydrological systems, spatial and temporal variations in solute concentration and/or temperature may affect fluid density and viscosity. These variations could lead to potentially unstable situations, in which a dense fluid overlies a less dense fluid. These situations could produce instabilities that appear as dense plume fingers migrating downwards counteracted by vertical upwards flow of freshwater (Simmons et al., Transp. Porous Medium, 2002). As a result of unstable variable-density flow, solute transport rates are increased over large distances and times as compared to constant-density flow. The numerical simulation of variable-density flow in saturated and unsaturated media requires corresponding benchmark problems against which a computer model is validated (Diersch and Kolditz, Adv. Water Resour, 2002). Recorded data from a laboratory-scale experiment of variable-density flow and solute transport in saturated and unsaturated porous media (Simmons et al., Transp. Porous Medium, 2002) is used to define a new numerical benchmark. The HydroGeoSphere code (Therrien et al., 2004) coupled with PEST (www.pesthomepage.org) are used to obtain an optimized parameter set capable of adequately representing the data set by Simmons et al., (2002). Fingering in the numerical model is triggered using random hydraulic conductivity fields. Due to the inherent randomness, a large number of simulations were conducted in this study. The optimized benchmark model adequately predicts the plume behavior and the fate of solutes. This benchmark is useful for model verification of variable-density flow problems in saturated and/or unsaturated media.

A photogrammetric technique for generation of an accurate multispectral optical flow dataset

NASA Astrophysics Data System (ADS)

Kniaz, V. V.

2017-06-01

A presence of an accurate dataset is the key requirement for a successful development of an optical flow estimation algorithm. A large number of freely available optical flow datasets were developed in recent years and gave rise for many powerful algorithms. However most of the datasets include only images captured in the visible spectrum. This paper is focused on the creation of a multispectral optical flow dataset with an accurate ground truth. The generation of an accurate ground truth optical flow is a rather complex problem, as no device for error-free optical flow measurement was developed to date. Existing methods for ground truth optical flow estimation are based on hidden textures, 3D modelling or laser scanning. Such techniques are either work only with a synthetic optical flow or provide a sparse ground truth optical flow. In this paper a new photogrammetric method for generation of an accurate ground truth optical flow is proposed. The method combines the benefits of the accuracy and density of a synthetic optical flow datasets with the flexibility of laser scanning based techniques. A multispectral dataset including various image sequences was generated using the developed method. The dataset is freely available on the accompanying web site.

Flow of Dense Granular Suspensions on an Inclined Plane

NASA Astrophysics Data System (ADS)

Bonnoit, C.; Lanuza, J.; Lindner, A.; Clément, E.

2008-07-01

We investigate the flow behavior of dense granular suspensions, by the use of an inclined plane. The suspensions are prepared at high packing fractions and consist of spherical non-Brownian particles density matched with the suspending fluid. On the inclined plane, we perform a systematic study of the surface velocity as a function of the layer thickness for various flow rates and tilt angles. We perform measurements on a classical rheometer (parallel-plate rheometer) that is shown to be in good agreement with existing models, up to a volume fraction of 50%. Comparing these results, we show that the flow on an inclined plane can, up to a volume fraction of 50%, indeed be described by a purely viscous model in agreement with the results from classical rheometry.

The Hydrodynamical Models of the Cometary Compact HII Region

NASA Astrophysics Data System (ADS)

Zhu, Feng-Yao; Zhu, Qing-Feng; Li, Juan; Zhang, Jiang-Shui; Wang, Jun-Zhi

2015-10-01

We have developed a full numerical method to study the gas dynamics of cometary ultracompact H ii regions, and associated photodissociation regions (PDRs). The bow-shock and champagne-flow models with a 40.9/21.9 M⊙ star are simulated. In the bow-shock models, the massive star is assumed to move through dense (n = 8000 cm-3) molecular material with a stellar velocity of 15 km s-1. In the champagne-flow models, an exponential distribution of density with a scale height of 0.2 pc is assumed. The profiles of the [Ne ii] 12.81 μm and H2 S(2) lines from the ionized regions and PDRs are compared for two sets of models. In champagne-flow models, emission lines from the ionized gas clearly show the effect of acceleration along the direction toward the tail due to the density gradient. The kinematics of the molecular gas inside the dense shell are mainly due to the expansion of the H ii region. However, in bow-shock models the ionized gas mainly moves in the same direction as the stellar motion. The kinematics of the molecular gas inside the dense shell simply reflects the motion of the dense shell with respect to the star. These differences can be used to distinguish two sets of models.

Fast fluidized bed steam generator

DOEpatents

Bryers, Richard W.; Taylor, Thomas E.

1980-01-01

A steam generator in which a high-velocity, combustion-supporting gas is passed through a bed of particulate material to provide a fluidized bed having a dense-phase portion and an entrained-phase portion for the combustion of fuel material. A first set of heat transfer elements connected to a steam drum is vertically disposed above the dense-phase fluidized bed to form a first flow circuit for heat transfer fluid which is heated primarily by the entrained-phase fluidized bed. A second set of heat transfer elements connected to the steam drum and forming the wall structure of the furnace provides a second flow circuit for the heat transfer fluid, the lower portion of which is heated by the dense-phase fluidized bed and the upper portion by the entrained-phase fluidized bed.

Sedimentology and geomorphology of the deposits from the August 2006 pyroclastic density currents at Tungurahua volcano, Ecuador.

PubMed

Douillet, Guilhem Amin; Tsang-Hin-Sun, Ève; Kueppers, Ulrich; Letort, Jean; Pacheco, Daniel Alejandro; Goldstein, Fabian; Von Aulock, Felix; Lavallée, Yan; Hanson, Jonathan Bruce; Bustillos, Jorge; Robin, Claude; Ramón, Patricio; Hall, Minard; Dingwell, Donald B

The deposits of the pyroclastic density currents from the August 2006 eruption of Tungurahua show three facies associations depending on the topographic setting: the massive, proximal cross-stratified, and distal cross-stratified facies. (1) The massive facies is confined to valleys on the slopes of the volcano. It contains clasts of >1 m diameter to fine ash material, is massive, and interpreted as deposited from dense pyroclastic flows. Its surface can exhibit lobes and levees covered with disk-shaped and vesicular large clasts. These fragile large clasts must have rafted at the surface of the flows all along the path in order to be preserved, and thus imply a sharp density boundary near the surface of these flows. (2) The proximal cross-stratified facies is exposed on valley overbanks on the upper part of the volcano and contains both massive coarse-grained layers and cross-stratified ash and lapilli bedsets. It is interpreted as deposited from (a) dense pyroclastic flows that overflowed the gentle ridges of valleys of the upper part of the volcano and (b) dilute pyroclastic density currents created from the dense flows by the entrainment of air on the steep upper flanks. (3) The distal cross-stratified facies outcrops as spatially limited, isolated, and wedge-shaped bodies of cross-stratified ash deposits located downstream of cliffs on valleys overbanks. It contains numerous aggrading dune bedforms, whose crest orientations reveal parental flow directions. A downstream decrease in the size of the dune bedforms, together with a downstream fining trend in the grain size distribution are observed on a 100-m scale. This facies is interpreted to have been deposited from dilute pyroclastic density currents with basal tractional boundary layers. We suggest that the parental flows were produced from the dense flows by entrainment of air at cliffs, and that these diluted currents might rapidly deposit through "pneumatic jumps". Three modes are present in the grain size distribution of all samples independently of the facies, which further supports the interpretation that all three facies derive from the same initial flows. This study emphasizes the influence of topography on small volume pyroclastic density currents, and the importance of flow transformation and flow-stripping processes.

Abyssal ocean overturning shaped by seafloor distribution.

PubMed

de Lavergne, C; Madec, G; Roquet, F; Holmes, R M; McDougall, T J

2017-11-08

The abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less-dense waters above them. Understanding what controls the strength and structure of these interhemispheric flows-referred to as the abyssal overturning circulation-is key to quantifying the ocean's ability to store carbon and heat on timescales exceeding a century. Here we show that, north of 32° S, the depth distribution of the seafloor compels dense southern-origin waters to flow northward below a depth of about 4 kilometres and to return southward predominantly at depths greater than 2.5 kilometres. Unless ventilated from the north, the overlying mid-depths (1 to 2.5 kilometres deep) host comparatively weak mean meridional flow. Backed by analysis of historical radiocarbon measurements, the findings imply that the geometry of the Pacific, Indian and Atlantic basins places a major external constraint on the overturning structure.

Volume fraction instability in an oscillating non-Brownian iso-dense suspension.

NASA Astrophysics Data System (ADS)

Roht, Y. L.; Gauthier, G.; Hulin, J. P.; Salin, D.; Chertcoff, R.; Auradou, H.; Ippolito, I.

2017-06-01

The instability of an iso-dense non-Brownian suspension of polystyrene beads of diameter 40 μm dispersed in a water-glycerol mixture submitted to a periodic square wave oscillating flow in a Hele-Shaw cell is studied experimentally. The instability gives rise to stationary bead concentration waves transverse to the flow. It has been observed for average particle volume fractions between 0.25 and 0.4, for periods of the square wave flow variation between 0.4 and 10 s and in finite intervals of the amplitude of the fluid displacement. The study shows that the wavelength λ increases roughly linearly with the amplitude of the oscillatory flow; on the other hand, λ is independent of the particle concentration and of the period of oscillation of the flow although the minimum threshold amplitude for observing the instability increases with the period.

Full distortion induced by dispersion evaluation and optical bandwidth constraining of fiber Bragg grating demultiplexers over analogue SCM systems.

PubMed

Martinez, Alfonso; Pastor, Daniel; Capmany, Jose

2002-12-30

We provide a full analysis of the distortion effects produced by the first and second order in-band dispersion of fiber Bragg grating based optical demultiplexers over analogue SCM (Sub Carrier Multiplexed) signals. Optical bandwidth utilization ranges for Dense WDM network are calculated considering different SCM system cases of frequency extension and modulation conditions.

On the possibilities of large-scale radio and fiber optics detectors in cosmic rays

NASA Technical Reports Server (NTRS)

Gusev, G. A.; Markov, M. A.; Zheleznykh, I. M.

1985-01-01

Different variants of radio and fiber optics detectors for registration of super high energy cascades in the atmosphere and in dense media are discussed. Particularly the possibilities for investigation of quasi horizontal cosmic ray showers (CRS) and simulated muons from these CRS with the help of radio detectors and fiber optics detectors located on the ice surface are considered.

Multi-modal diffuse optical techniques for breast cancer neoadjuvant chemotherapy monitoring (Conference Presentation)

NASA Astrophysics Data System (ADS)

Cochran, Jeffrey M.; Busch, David R.; Ban, Han Y.; Kavuri, Venkaiah C.; Schweiger, Martin J.; Arridge, Simon R.; Yodh, Arjun G.

2017-02-01

We present high spatial density, multi-modal, parallel-plate Diffuse Optical Tomography (DOT) imaging systems for the purpose of breast tumor detection. One hybrid instrument provides time domain (TD) and continuous wave (CW) DOT at 64 source fiber positions. The TD diffuse optical spectroscopy with PMT- detection produces low-resolution images of absolute tissue scattering and absorption while the spatially dense array of CCD-coupled detector fibers (108 detectors) provides higher-resolution CW images of relative tissue optical properties. Reconstruction of the tissue optical properties, along with total hemoglobin concentration and tissue oxygen saturation, is performed using the TOAST software suite. Comparison of the spatially-dense DOT images and MR images allows for a robust validation of DOT against an accepted clinical modality. Additionally, the structural information from co-registered MR images is used as a spatial prior to improve the quality of the functional optical images and provide more accurate quantification of the optical and hemodynamic properties of tumors. We also present an optical-only imaging system that provides frequency domain (FD) DOT at 209 source positions with full CCD detection and incorporates optical fringe projection profilometry to determine the breast boundary. This profilometry serves as a spatial constraint, improving the quality of the DOT reconstructions while retaining the benefits of an optical-only device. We present initial images from both human subjects and phantoms to display the utility of high spatial density data and multi-modal information in DOT reconstruction with the two systems.

Interaction of Interstellar Shocks with Dense Obstacles: Formation of ``Bullets''

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.

The so-called cumulative effect take place in converging conical shock waves arising behind dense obstacles overtaken by incident interstellar shock. A significant part of energy of converging flow of matter swept-up by a radiative conical shock can be transferred to a dense jet-like ejection (``bullet'') directed along the cone axis. Possible applications of this effect for star-forming regions (e.g., OMC-1) and supernova remnants (e.g., Vela SNR) are discussed.

Near re-entrant dense pattern optical multipass cell

NASA Technical Reports Server (NTRS)

Silver, Joel A. (Inventor)

2007-01-01

A multiple pass optical cell and method comprising providing a pair of opposed mirrors, one cylindrical and one spherical, introducing light into the cell via an entrance mechanism, and extracting light from the cell via an exit mechanism, wherein the entrance mechanism and exit mechanism are coextensive or non-coextensive.

A Simple Analytical Model for Asynchronous Dense WDM/OOK Systems

DTIC Science & Technology

1994-06-01

asynchronous dense WDM systems employing an external OOK modulator. Our model is based upon a close approximation of the optical Fabry - Perot filter in the...receiver as a single-pole RC filter for signals that are bandlimitr i, & -equency band approximately equal to one sixtieth of the Fabry - Perot filter’s...4 A. INPUT SIGNAL ............................................................................................... 4 B. FABRY - PEROT FILTERED OUTPUT

Progress on Ultra-Dense Quantum Communication Using Integrated Photonic Architecture

DTIC Science & Technology

2012-05-09

REPORT Progress on Ultra-Dense Quantum Communication Using Integrated Photonic Architecture 14. ABSTRACT 16. SECURITY CLASSIFICATION OF: The goal of...including the development of a large-alphabet quantum key distribution protocol that uses measurements in mutually unbiased bases. 1. REPORT DATE (DD-MM... quantum information, integrated optics, photonic integrated chip Dirk Englund, Karl Berggren, Jeffrey Shapiro, Chee Wei Wong, Franco Wong, and Gregory

Insulator-to-conducting transition in dense fluid helium.

PubMed

Celliers, P M; Loubeyre, P; Eggert, J H; Brygoo, S; McWilliams, R S; Hicks, D G; Boehly, T R; Jeanloz, R; Collins, G W

2010-05-07

By combining diamond-anvil-cell and laser-driven shock wave techniques, we produced dense He samples up to 1.5 g/cm(3) at temperatures reaching 60 kK. Optical measurements of reflectivity and temperature show that electronic conduction in He at these conditions is temperature-activated (semiconducting). A fit to the data suggests that the mobility gap closes with increasing density, and that hot dense He becomes metallic above approximately 1.9 g/cm(3). These data provide a benchmark to test models that describe He ionization at conditions found in astrophysical objects, such as cold white dwarf atmospheres.

Intermittent turbulence in flowing bacterial suspensions

PubMed Central

Secchi, Eleonora; Rusconi, Roberto; Buzzaccaro, Stefano; Salek, M. Mehdi; Smriga, Steven; Piazza, Roberto; Stocker, Roman

2016-01-01

Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence with important implications for chemical and biological transport, yet this analogy has remained primarily qualitative. Here, we present experiments in which a dense suspension of Bacillus subtilis bacteria was flowed through microchannels and the velocity statistics of the flowing suspension were quantified using a recently developed velocimetry technique coupled with vortex identification methods. Observations revealed a robust intermittency phenomenon, whereby the average velocity profile of the suspension fluctuated between a plug-like flow and a parabolic flow profile. This intermittency is a hallmark of the onset of classic turbulence and Lagrangian tracking revealed that it here originates from the presence of transient vortices in the active, collective motion of the bacteria locally reinforcing the externally imposed flow. These results link together two entirely different manifestations of turbulence and show the potential of the microfluidic approach to mimic the environment characteristic of certain niches of the human microbiome. PMID:27307513

Intermittent turbulence in flowing bacterial suspensions.

PubMed

Secchi, Eleonora; Rusconi, Roberto; Buzzaccaro, Stefano; Salek, M Mehdi; Smriga, Steven; Piazza, Roberto; Stocker, Roman

2016-06-01

Dense suspensions of motile bacteria, possibly including the human gut microbiome, exhibit collective dynamics akin to those observed in classic, high Reynolds number turbulence with important implications for chemical and biological transport, yet this analogy has remained primarily qualitative. Here, we present experiments in which a dense suspension of Bacillus subtilis bacteria was flowed through microchannels and the velocity statistics of the flowing suspension were quantified using a recently developed velocimetry technique coupled with vortex identification methods. Observations revealed a robust intermittency phenomenon, whereby the average velocity profile of the suspension fluctuated between a plug-like flow and a parabolic flow profile. This intermittency is a hallmark of the onset of classic turbulence and Lagrangian tracking revealed that it here originates from the presence of transient vortices in the active, collective motion of the bacteria locally reinforcing the externally imposed flow. These results link together two entirely different manifestations of turbulence and show the potential of the microfluidic approach to mimic the environment characteristic of certain niches of the human microbiome. © 2016 The Author(s).

Dense Array Optimization of Cross-Flow Turbines

NASA Astrophysics Data System (ADS)

Scherl, Isabel; Strom, Benjamin; Brunton, Steven; Polagye, Brian

2017-11-01

Cross-flow turbines, where the axis of rotation is perpendicular to the freestream flow, can be used to convert the kinetic energy in wind or water currents to electrical power. By taking advantage of mean and time-resolved wake structures, the optimal density of an array of cross-flow turbines has the potential for higher power output per unit area of land or sea-floor than an equivalent array of axial-flow turbines. In addition, dense arrays in tidal or river channels may be able to further elevate efficiency by exploiting flow confinement and surface proximity. In this work, a two-turbine array is optimized experimentally in a recirculating water channel. The spacing between turbines, as well as individual and coordinated turbine control strategies are optimized. Array efficiency is found to exceed the maximum efficiency for a sparse array (i.e., no interaction between turbines) for stream-wise rotor spacing of less than two diameters. Results are discussed in the context of wake measurements made behind a single rotor.

Numerical Generation of Dense Plume Fingers in Unsaturated Homogeneous Porous Media

NASA Astrophysics Data System (ADS)

Cremer, C.; Graf, T.

2012-04-01

In nature, the migration of dense plumes typically results in the formation of vertical plume fingers. Flow direction in fingers is downwards, which is counterbalanced by upwards flow of less dense fluid between fingers. In heterogeneous media, heterogeneity itself is known to trigger the formation of fingers. In homogeneous media, however, fingers are also created even if all grains had the same diameter. The reason is that pore-scale heterogeneity leading to different flow velocities also exists in homogeneous media due to two effects: (i) Grains of identical size may randomly arrange differently, e.g. forming tetrahedrons, hexahedrons or octahedrons. Each arrangement creates pores of varying diameter, thus resulting in different average flow velocities. (ii) Random variations of solute concentration lead to varying buoyancy effects, thus also resulting in different velocities. As a continuation of previously made efforts to incorporate pore-scale heterogeneity into fully saturated soil such that dense fingers are realistically generated (Cremer and Graf, EGU Assembly, 2011), the current paper extends the research scope from saturated to unsaturated soil. Perturbation methods are evaluated by numerically re-simulating a laboratory-scale experiment of plume transport in homogeneous unsaturated sand (Simmons et al., Transp. Porous Media, 2002). The following 5 methods are being discussed: (i) homogeneous sand, (ii) initial perturbation of solute concentration, (iii) spatially random, time-constant perturbation of solute source, (iv) spatially and temporally random noise of simulated solute concentration, and (v) random K-field that introduces physically insignificant but numerically significant heterogeneity. Results demonstrate that, as opposed to saturated flow, perturbing the solute source will not result in plume fingering. This is because the location of the perturbed source (domain top) and the location of finger generation (groundwater surface) do not coincide. Alternatively, similar to saturated flow, applying either a random concentration noise (iv) or a random K-field (v) generates realistic plume fingering. Future work will focus on the generation mechanisms of plume finger splitting.

Noninvasive Imaging of Retinal Morphology and Microvasculature in Obese Mice Using Optical Coherence Tomography and Optical Microangiography

PubMed Central

Zhi, Zhongwei; Chao, Jennifer R.; Wietecha, Tomasz; Hudkins, Kelly L.; Alpers, Charles E.; Wang, Ruikang K.

2014-01-01

Purpose. To evaluate early diabetes-induced changes in retinal thickness and microvasculature in a type 2 diabetic mouse model by using optical coherence tomography (OCT)/optical microangiography (OMAG). Methods. Twenty-two-week-old obese (OB) BTBR mice (n = 10) and wild-type (WT) control mice (n = 10) were imaged. Three-dimensional (3D) data volumes were captured with spectral domain OCT using an ultrahigh-sensitive OMAG scanning protocol for 3D volumetric angiography of the retina and dense A-scan protocol for measurement of the total retinal blood flow (RBF) rate. The thicknesses of the nerve fiber layer (NFL) and that of the NFL to the inner plexiform layer (IPL) were measured and compared between OB and WT mice. The linear capillary densities within intermediate and deep capillary layers were determined by the number of capillaries crossing a 500-μm line. The RBF rate was evaluated using an en face Doppler approach. These quantitative measurements were compared between OB and WT mice. Results. The retinal thickness of the NFL to IPL was significantly reduced in OB mice (P < 0.01) compared to that in WT mice, whereas the NFL thickness between the two was unchanged. 3D depth-resolved OMAG angiography revealed the first in vivo 3D model of mouse retinal microcirculation. Although no obvious differences in capillary vessel densities of the intermediate and deep capillary layers were detected between normal and OB mice, the total RBF rate was significantly lower (P < 0.05) in OB mice than in WT mice. Conclusions. We conclude that OB BTBR mice have significantly reduced NFL–IPL thicknesses and total RBF rates compared with those of WT mice, as imaged by OCT/OMAG. OMAG provides an unprecedented capability for high-resolution depth-resolved imaging of mouse retinal vessels and blood flow that may play a pivotal role in providing a noninvasive method for detecting early microvascular changes in patients with diabetic retinopathy. PMID:24458155

Thermal conduction study of warm dense aluminum by proton differential heating

NASA Astrophysics Data System (ADS)

Ping, Y.; Kemp, G.; McKelvey, A.; Fernandez-Panella, A.; Shepherd, R.; Collins, G.; Sio, H.; King, J.; Freeman, R.; Hua, R.; McGuffey, C.; Kim, J.; Beg, F.

2016-10-01

A differential heating platform has been developed for thermal conduction study (Ping et al. PoP 2015), where a temperature gradient is induced and subsequent heat flow is probed by time-resolved diagnostics. An experiment using proton differential heating has been carried out at Titan laser for Au/Al targets. Two single-shot time-resolved diagnostics are employed, SOP (streaked optical pyrometry) for surface temperature and FDI (Fourier Domain Interferometry) for surface expansion. Hydrodynamic simulations show that after 15ps, absorption in underdense plasma needs to be taken into account to correctly interpret SOP data. Comparison between simulations with different thermal conductivity models and a set of data with varying target thickness will be presented. This work was performed under DOE contract DE-AC52-07NA27344 with support from OFES Early Career program and LLNL LDRD program.

Long reach DWDM-PON with 12.5 GHz channel spacing based on comb source seeding

NASA Astrophysics Data System (ADS)

Zhou, Zhao; Nie, Hai-tao; Wang, Yao-jun

2016-07-01

A long reach dense wavelength division multiplexing passive optical network (DWDM-PON) with 12.5 GHz channel spacing is proposed and experimentally demonstrated. An optical frequency comb source is used to provide the multiwavelength seeding light, while reflective semiconductor optical amplifiers (RSOAs) are installed in both optical line terminal (OLT) and optical network units (ONUs) as colorless transmitter. The experimental results show that the bidirectional transmission for 1.2 Gbit/s data rate is achieved over 80 km single mode fiber (SMF).

Effects of the bottom boundary condition in numerical investigations of dense water cascading on a slope

NASA Astrophysics Data System (ADS)

Berntsen, Jarle; Alendal, Guttorm; Avlesen, Helge; Thiem, Øyvind

2018-05-01

The flow of dense water along continental slopes is considered. There is a large literature on the topic based on observations and laboratory experiments. In addition, there are many analytical and numerical studies of dense water flows. In particular, there is a sequence of numerical investigations using the dynamics of overflow mixing and entrainment (DOME) setup. In these papers, the sensitivity of the solutions to numerical parameters such as grid size and numerical viscosity coefficients and to the choices of methods and models is investigated. In earlier DOME studies, three different bottom boundary conditions and a range of vertical grid sizes are applied. In other parts of the literature on numerical studies of oceanic gravity currents, there are statements that appear to contradict choices made on bottom boundary conditions in some of the DOME papers. In the present study, we therefore address the effects of the bottom boundary condition and vertical resolution in numerical investigations of dense water cascading on a slope. The main finding of the present paper is that it is feasible to capture the bottom Ekman layer dynamics adequately and cost efficiently by using a terrain-following model system using a quadratic drag law with a drag coefficient computed to give near-bottom velocity profiles in agreement with the logarithmic law of the wall. Many studies of dense water flows are performed with a quadratic bottom drag law and a constant drag coefficient. It is shown that when using this bottom boundary condition, Ekman drainage will not be adequately represented. In other studies of gravity flow, a no-slip bottom boundary condition is applied. With no-slip and a very fine resolution near the seabed, the solutions are essentially equal to the solutions obtained with a quadratic drag law and a drag coefficient computed to produce velocity profiles matching the logarithmic law of the wall. However, with coarser resolution near the seabed, there may be a substantial artificial blocking effect when using no-slip.

A continuous stochastic model for non-equilibrium dense gases

NASA Astrophysics Data System (ADS)

Sadr, M.; Gorji, M. H.

2017-12-01

While accurate simulations of dense gas flows far from the equilibrium can be achieved by direct simulation adapted to the Enskog equation, the significant computational demand required for collisions appears as a major constraint. In order to cope with that, an efficient yet accurate solution algorithm based on the Fokker-Planck approximation of the Enskog equation is devised in this paper; the approximation is very much associated with the Fokker-Planck model derived from the Boltzmann equation by Jenny et al. ["A solution algorithm for the fluid dynamic equations based on a stochastic model for molecular motion," J. Comput. Phys. 229, 1077-1098 (2010)] and Gorji et al. ["Fokker-Planck model for computational studies of monatomic rarefied gas flows," J. Fluid Mech. 680, 574-601 (2011)]. The idea behind these Fokker-Planck descriptions is to project the dynamics of discrete collisions implied by the molecular encounters into a set of continuous Markovian processes subject to the drift and diffusion. Thereby, the evolution of particles representing the governing stochastic process becomes independent from each other and thus very efficient numerical schemes can be constructed. By close inspection of the Enskog operator, it is observed that the dense gas effects contribute further to the advection of molecular quantities. That motivates a modelling approach where the dense gas corrections can be cast in the extra advection of particles. Therefore, the corresponding Fokker-Planck approximation is derived such that the evolution in the physical space accounts for the dense effects present in the pressure, stress tensor, and heat fluxes. Hence the consistency between the devised Fokker-Planck approximation and the Enskog operator is shown for the velocity moments up to the heat fluxes. For validation studies, a homogeneous gas inside a box besides Fourier, Couette, and lid-driven cavity flow setups is considered. The results based on the Fokker-Planck model are compared with respect to benchmark simulations, where good agreement is found for the flow field along with the transport properties.

Robust optical flow using adaptive Lorentzian filter for image reconstruction under noisy condition

NASA Astrophysics Data System (ADS)

Kesrarat, Darun; Patanavijit, Vorapoj

2017-02-01

In optical flow for motion allocation, the efficient result in Motion Vector (MV) is an important issue. Several noisy conditions may cause the unreliable result in optical flow algorithms. We discover that many classical optical flows algorithms perform better result under noisy condition when combined with modern optimized model. This paper introduces effective robust models of optical flow by using Robust high reliability spatial based optical flow algorithms using the adaptive Lorentzian norm influence function in computation on simple spatial temporal optical flows algorithm. Experiment on our proposed models confirm better noise tolerance in optical flow's MV under noisy condition when they are applied over simple spatial temporal optical flow algorithms as a filtering model in simple frame-to-frame correlation technique. We illustrate the performance of our models by performing an experiment on several typical sequences with differences in movement speed of foreground and background where the experiment sequences are contaminated by the additive white Gaussian noise (AWGN) at different noise decibels (dB). This paper shows very high effectiveness of noise tolerance models that they are indicated by peak signal to noise ratio (PSNR).

Ultra-dense WDM-PON delivering carrier-centralized Nyquist-WDM uplink with digital coherent detection.

PubMed

Dong, Ze; Yu, Jianjun; Chien, Hung-Chang; Chi, Nan; Chen, Lin; Chang, Gee-Kung

2011-06-06

We introduce an "ultra-dense" concept into next-generation WDM-PON systems, which transmits a Nyquist-WDM uplink with centralized uplink optical carriers and digital coherent detection for the future access network requiring both high capacity and high spectral efficiency. 80-km standard single mode fiber (SSMF) transmission of Nyquist-WDM signal with 13 coherent 25-GHz spaced wavelength shaped optical carriers individually carrying 100-Gbit/s polarization-multiplexing quadrature phase-shift keying (PM-QPSK) upstream data has been experimentally demonstrated with negligible transmission penalty. The 13 frequency-locked wavelengths with a uniform optical power level of -10 dBm and OSNR of more than 50 dB are generated from a single lightwave via a multi-carrier generator consists of an optical phase modulator (PM), a Mach-Zehnder modulator (MZM), and a WSS. Following spacing the carriers at the baud rate, sub-carriers are individually spectral shaped to form Nyquist-WDM. The Nyquist-WDM channels have less than 1-dB crosstalk penalty of optical signal-to-noise ratio (OSNR) at 2 × 10(-3) bit-error rate (BER). Performance of a traditional coherent optical OFDM scheme and its restrictions on symbol synchronization and power difference are also experimentally compared and studied.

Rheology of dense suspensions of non colloidal particles

NASA Astrophysics Data System (ADS)

Guazzelli, Élisabeth

2017-06-01

Dense suspensions are materials with broad applications both in industrial processes (e.g. waste disposal, concrete, drilling muds, metalworking chip transport, and food processing) and in natural phenomena (e.g. flows of slurries, debris, and lava). Despite its long research history and its practical relevance, the mechanics of dense suspensions remain poorly understood. The major difficulty is that the grains interact both by hydrodynamic interactions through the liquid and by mechanical contact. These systems thus belong to an intermediate regime between pure suspensions and granular flows. We show that we can unify suspension and granular rheology under a common framework by transferring the frictional approach of dry granular media to wet suspensions of spherical particles. We also discuss non-Newtonian behavior such as normal-stress differences and shear-induced migration. Beyond the classical problem of dense suspension of hard spheres which is far from being completely resolved, there are also entirely novel avenues of study concerning more complex mixtures of particles and fluids such as those involving other types of particles (e.g. fibers) or non-Newtonian fluids that we will also address.

THE HYDRODYNAMICAL MODELS OF THE COMETARY COMPACT H ii REGION

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

Zhu, Feng-Yao; Zhu, Qing-Feng; Li, Juan

2015-10-10

We have developed a full numerical method to study the gas dynamics of cometary ultracompact H ii regions, and associated photodissociation regions (PDRs). The bow-shock and champagne-flow models with a 40.9/21.9 M{sub ⊙} star are simulated. In the bow-shock models, the massive star is assumed to move through dense (n = 8000 cm{sup −3}) molecular material with a stellar velocity of 15 km s{sup −1}. In the champagne-flow models, an exponential distribution of density with a scale height of 0.2 pc is assumed. The profiles of the [Ne ii] 12.81 μm and H{sub 2} S(2) lines from the ionized regionsmore » and PDRs are compared for two sets of models. In champagne-flow models, emission lines from the ionized gas clearly show the effect of acceleration along the direction toward the tail due to the density gradient. The kinematics of the molecular gas inside the dense shell are mainly due to the expansion of the H ii region. However, in bow-shock models the ionized gas mainly moves in the same direction as the stellar motion. The kinematics of the molecular gas inside the dense shell simply reflects the motion of the dense shell with respect to the star. These differences can be used to distinguish two sets of models.« less

Dense Plasma Focus-Based Nanofabrication of III–V Semiconductors: Unique Features and Recent Advances

PubMed Central

Mangla, Onkar; Roy, Savita; Ostrikov, Kostya (Ken)

2015-01-01

The hot and dense plasma formed in modified dense plasma focus (DPF) device has been used worldwide for the nanofabrication of several materials. In this paper, we summarize the fabrication of III–V semiconductor nanostructures using the high fluence material ions produced by hot, dense and extremely non-equilibrium plasma generated in a modified DPF device. In addition, we present the recent results on the fabrication of porous nano-gallium arsenide (GaAs). The details of morphological, structural and optical properties of the fabricated nano-GaAs are provided. The effect of rapid thermal annealing on the above properties of porous nano-GaAs is studied. The study reveals that it is possible to tailor the size of pores with annealing temperature. The optical properties of these porous nano-GaAs also confirm the possibility to tailor the pore sizes upon annealing. Possible applications of the fabricated and subsequently annealed porous nano-GaAs in transmission-type photo-cathodes and visible optoelectronic devices are discussed. These results suggest that the modified DPF is an effective tool for nanofabrication of continuous and porous III–V semiconductor nanomaterials. Further opportunities for using the modified DPF device for the fabrication of novel nanostructures are discussed as well. PMID:28344261

Dense Plasma Focus-Based Nanofabrication of III-V Semiconductors: Unique Features and Recent Advances.

PubMed

Mangla, Onkar; Roy, Savita; Ostrikov, Kostya Ken

2015-12-29

The hot and dense plasma formed in modified dense plasma focus (DPF) device has been used worldwide for the nanofabrication of several materials. In this paper, we summarize the fabrication of III-V semiconductor nanostructures using the high fluence material ions produced by hot, dense and extremely non-equilibrium plasma generated in a modified DPF device. In addition, we present the recent results on the fabrication of porous nano-gallium arsenide (GaAs). The details of morphological, structural and optical properties of the fabricated nano-GaAs are provided. The effect of rapid thermal annealing on the above properties of porous nano-GaAs is studied. The study reveals that it is possible to tailor the size of pores with annealing temperature. The optical properties of these porous nano-GaAs also confirm the possibility to tailor the pore sizes upon annealing. Possible applications of the fabricated and subsequently annealed porous nano-GaAs in transmission-type photo-cathodes and visible optoelectronic devices are discussed. These results suggest that the modified DPF is an effective tool for nanofabrication of continuous and porous III-V semiconductor nanomaterials. Further opportunities for using the modified DPF device for the fabrication of novel nanostructures are discussed as well.

Differences in overland flow, hydrophobicity and soil moisture dynamics between Mediterranean woodland types in a peri-urban catchment in Portugal

NASA Astrophysics Data System (ADS)

Ferreira, C. S. S.; Walsh, R. P. D.; Shakesby, R. A.; Keizer, J. J.; Soares, D.; González-Pelayo, O.; Coelho, C. O. A.; Ferreira, A. J. D.

2016-02-01

Forest hydrology has been widely investigated, but the impacts of different woodland types on hydrological processes within a peri-urban catchment mosaic are poorly understood. This paper investigates overland flow generation processes in three different types of woodland in a small (6.2 km2) catchment in central Portugal that has undergone strong urban development over the past 50 years. A semi-natural oak stand and a sparse eucalyptus stand on partly abandoned peri-urban land and a dense eucalyptus plantation were each instrumented with three 16 m2 runoff plots and 15 throughfall gauges, which were monitored at c. 1- to 2-week intervals over two hydrological years. In addition, surface soil moisture content (0-5 cm) and hydrophobicity (0-2 cm, 2-5 cm and 5-7 cm) were measured at the same time as overland flow and throughfall. Although all three woodland types produced relatively little overland flow (<3% of the incident rainfall overall), the dense eucalypt stand produced twice as much overland flow as the sparse eucalypt and oak woodland types. This contrast in overland flow can be attributed to infiltration-excess processes operating in storms following dry antecedent weather when severe hydrophobicity was widespread in the dense eucalypt plantation, whereas it was of moderate and low severity and less widespread in the sparse eucalypt and oak woodlands, respectively. In contrast, under wet conditions greater (albeit still small) percentages of overland flow were produced in oak woodland than in the two eucalypt plantations; this was probably linked to saturation-excess overland flow being generated more readily at the oak site as a result of its shallower soil. Differences in water retention in surface depressions affected overland flow generation and downslope flow transport. Implications of the seasonal differentials in overland flow generation between the three distinct woodland types for the hydrological response of peri-urban catchments are addressed.

Assessing the future of diffuse optical imaging technologies for breast cancer management

PubMed Central

Tromberg, Bruce J.; Pogue, Brian W.; Paulsen, Keith D.; Yodh, Arjun G.; Boas, David A.; Cerussi, Albert E.

2008-01-01

Diffuse optical imaging (DOI) is a noninvasive optical technique that employs near-infrared (NIR) light to quantitatively characterize the optical properties of thick tissues. Although NIR methods were first applied to breast transillumination (also called diaphanography) nearly 80 years ago, quantitative DOI methods employing time- or frequency-domain photon migration technologies have only recently been used for breast imaging (i.e., since the mid-1990s). In this review, the state of the art in DOI for breast cancer is outlined and a multi-institutional Network for Translational Research in Optical Imaging (NTROI) is described, which has been formed by the National Cancer Institute to advance diffuse optical spectroscopy and imaging (DOSI) for the purpose of improving breast cancer detection and clinical management. DOSI employs broadband technology both in near-infrared spectral and temporal signal domains in order to separate absorption from scattering and quantify uptake of multiple molecular probes based on absorption or fluorescence contrast. Additional dimensionality in the data is provided by integrating and co-registering the functional information of DOSI with x-ray mammography and magnetic resonance imaging (MRI), which provide structural information or vascular flow information, respectively. Factors affecting DOSI performance, such as intrinsic and extrinsic contrast mechanisms, quantitation of biochemical components, image formation∕visualization, and multimodality co-registration are under investigation in the ongoing research NTROI sites. One of the goals is to develop standardized DOSI platforms that can be used as stand-alone devices or in conjunction with MRI, mammography, or ultrasound. This broad-based, multidisciplinary effort is expected to provide new insight regarding the origins of breast disease and practical approaches for addressing several key challenges in breast cancer, including: Detecting disease in mammographically dense tissue, distinguishing between malignant and benign lesions, and understanding the impact of neoadjuvant chemotherapies. PMID:18649477

Optical Response of Warm Dense Matter Using Real-Time Electron Dynamics

NASA Astrophysics Data System (ADS)

Baczewski, Andrew; Shulenburger, Luke; Desjarlais, Michael; Magyar, Rudolph

2014-03-01

The extreme temperatures and solid-like densities in warm dense matter present a unique challenge for theory, wherein neither conventional models from condensed matter nor plasma physics capture all of the relevant phenomenology. While Kubo-Greenwood DFT calculations have proven capable of reproducing optical properties of WDM, they require a significant number of virtual orbitals to reach convergence due to their perturbative nature. Real-time TDDFT presents a complementary framework with a number of computationally favorable properties, including reduced cost complexity and better scalability, and has been used to reproduce the optical response of finite and ordered extended systems. We will describe the use of Ehrenfest-TDDFT to evolve coupled electron-nuclear dynamics in WDM systems, and the subsequent evaluation of optical response functions from the real-time electron dynamics. The advantages and disadvantages of this approach will be discussed relative to the current state-of-the-art. Sandia National Laboratories is a multi-program laboratory managed and operated by Sandia Corporation, a wholly owned subsidiary of Lockheed Martin Corporation, for the U.S. Department of Energy's National Security Administration under contract DE-AC04-94AL85000.

Feasibility of 3D Reconstruction of Neural Morphology Using Expansion Microscopy and Barcode-Guided Agglomeration

PubMed Central

Yoon, Young-Gyu; Dai, Peilun; Wohlwend, Jeremy; Chang, Jae-Byum; Marblestone, Adam H.; Boyden, Edward S.

2017-01-01

We here introduce and study the properties, via computer simulation, of a candidate automated approach to algorithmic reconstruction of dense neural morphology, based on simulated data of the kind that would be obtained via two emerging molecular technologies—expansion microscopy (ExM) and in-situ molecular barcoding. We utilize a convolutional neural network to detect neuronal boundaries from protein-tagged plasma membrane images obtained via ExM, as well as a subsequent supervoxel-merging pipeline guided by optical readout of information-rich, cell-specific nucleic acid barcodes. We attempt to use conservative imaging and labeling parameters, with the goal of establishing a baseline case that points to the potential feasibility of optical circuit reconstruction, leaving open the possibility of higher-performance labeling technologies and algorithms. We find that, even with these conservative assumptions, an all-optical approach to dense neural morphology reconstruction may be possible via the proposed algorithmic framework. Future work should explore both the design-space of chemical labels and barcodes, as well as algorithms, to ultimately enable routine, high-performance optical circuit reconstruction. PMID:29114215

Feasibility of 3D Reconstruction of Neural Morphology Using Expansion Microscopy and Barcode-Guided Agglomeration.

PubMed

Yoon, Young-Gyu; Dai, Peilun; Wohlwend, Jeremy; Chang, Jae-Byum; Marblestone, Adam H; Boyden, Edward S

2017-01-01

We here introduce and study the properties, via computer simulation, of a candidate automated approach to algorithmic reconstruction of dense neural morphology, based on simulated data of the kind that would be obtained via two emerging molecular technologies-expansion microscopy (ExM) and in-situ molecular barcoding. We utilize a convolutional neural network to detect neuronal boundaries from protein-tagged plasma membrane images obtained via ExM, as well as a subsequent supervoxel-merging pipeline guided by optical readout of information-rich, cell-specific nucleic acid barcodes. We attempt to use conservative imaging and labeling parameters, with the goal of establishing a baseline case that points to the potential feasibility of optical circuit reconstruction, leaving open the possibility of higher-performance labeling technologies and algorithms. We find that, even with these conservative assumptions, an all-optical approach to dense neural morphology reconstruction may be possible via the proposed algorithmic framework. Future work should explore both the design-space of chemical labels and barcodes, as well as algorithms, to ultimately enable routine, high-performance optical circuit reconstruction.

Towards a universal description of cohesive-particle flows

NASA Astrophysics Data System (ADS)

Lamarche, Casey; Liu, Peiyuan; Kellogg, Kevin; Lattanzi, Aaron; Hrenya, Christine

2017-11-01

A universal framework for describing cohesive granular flows seems unattainable based on prior works, making a fundamental continuum theory to predict such flows appear unachievable. For the first time, universal behavior of cohesive-grain flows is demonstrated by linking the macroscopic (many-grain) behavior to grain-grain interactions via two dimensionless groups: a generalized Bond number BoG - ratio of maximum cohesive force to the force driving flow - and a new Agglomerate number Ag - ratio of critical cohesive energy to the granular energy. Cohesive-grain flow is investigated in several systems, and universal behavior is determined via collapse of a cohesion-dependent output variable from each system with the appropriate dimensionless group. Universal behavior is observed using BoG for dense (enduring-contact-dominated) flows and Ag for dilute (collision-dominated) flows, as BoG accounts for the cohesive contact force and Ag for increased collisional dissipation due to cohesion. Hence, a new physical picture is presented, namely, BoG dominates in dense flows, where force chains drive momentum transfer, and Ag dominates in dilute systems, where the dissipative collisions dominate momentum transfer. Apparent discrepancies with past treatments are resolved. Dow Corning Corporation.

Perils at the heart of the Milky Way: Systematic effects for studying low-luminosity accretion onto Sgr A*

NASA Astrophysics Data System (ADS)

Corrales, Lia; Mon, Brayden; Haggard, Daryl; Baganoff, Frederick K.; Garmire, Gordon; Degenaar, Nathalie; Reynolds, Mark

2017-08-01

The supermassive black hole at the center of our galaxy, Sgr A*, is surprisingly under-luminous. This problem has motivated a host of theoretical models to explain low-level radiatively inefficient accretion flows onto compact objects. We discuss how the Galactic Center sight line, which is optically thick to the scattering of soft X-rays (tau ~ 5), affects high resolution studies of the accretion flow around Sgr A*. X-ray light from compact objects in the dense GC environment is scattered by foreground dust, producing scattering echoes that are time delayed relative to the X-ray source's light curve. We discuss the scattering halo of SWIFT J174540.7-290015, which underwent the brightest X-ray outburst within 30’' of Sgr A*. Preliminary fits to the scattering halo suggest that a small amount of foreground dust, within 250 pc of the GC, affects the X-ray surface brightness profile within 10’' of any GC point source. The associated time delay is on the order of several hours, which is important for understanding the quiescent accretion flow of Sgr A*. We take advantage of the Chandra Galactic Center XVP dataset to explore the effect of the interstellar medium on the inferred characteristics of Sgr A*.

Response of the Atmospheric Boundary Layer and Soil Layer to a High Altitude, Dense Aerosol Cover.

NASA Astrophysics Data System (ADS)

Garratt, J. R.; Pittock, A. B.; Walsh, K.

1990-01-01

The response of the atmospheric boundary layer to the appearance of a high-altitude smoke layer has been investigated in a mesoscale numerical model of the atmosphere. Emphasis is placed on the changes in mean boundary-layer structure and near-surface temperatures when smoke of absorption optical depth (AOD) in the, range 0 to 1 is introduced. Calculations have been made at 30°S, for different soil thermal properties and degrees of surface wetness, over a time period of several days during which major smoke-induced cooling occurs. The presence of smoke reduces the daytime mixed-layer depth and, for large enough values of AOD, results in a daytime surface inversion with large cooling confined to heights of less than a few hundred meters. Smoke-induced reductions in daytime soil and air temperatures of several degrees are typical, dependent critically upon soil wetness and smoke AOD. Locations near the coast experience reduced cooling whenever there is a significant onshore flow related to a sea breeze (this would also be the case with a large-scale onshore flow). The sea breeze itself disappears for large enough smoke AOD and, over sloping coastal terrain, a smoke-induced, offshore drainage flow may exist throughout the diurnal cycle.

Architecture Design and Experimental Platform Demonstration of Optical Network based on OpenFlow Protocol

NASA Astrophysics Data System (ADS)

Xing, Fangyuan; Wang, Honghuan; Yin, Hongxi; Li, Ming; Luo, Shenzi; Wu, Chenguang

2016-02-01

With the extensive application of cloud computing and data centres, as well as the constantly emerging services, the big data with the burst characteristic has brought huge challenges to optical networks. Consequently, the software defined optical network (SDON) that combines optical networks with software defined network (SDN), has attracted much attention. In this paper, an OpenFlow-enabled optical node employed in optical cross-connect (OXC) and reconfigurable optical add/drop multiplexer (ROADM), is proposed. An open source OpenFlow controller is extended on routing strategies. In addition, the experiment platform based on OpenFlow protocol for software defined optical network, is designed. The feasibility and availability of the OpenFlow-enabled optical nodes and the extended OpenFlow controller are validated by the connectivity test, protection switching and load balancing experiments in this test platform.

Turbulent flows over sparse canopies

NASA Astrophysics Data System (ADS)

Sharma, Akshath; García-Mayoral, Ricardo

2018-04-01

Turbulent flows over sparse and dense canopies exerting a similar drag force on the flow are investigated using Direct Numerical Simulations. The dense canopies are modelled using a homogeneous drag force, while for the sparse canopy, the geometry of the canopy elements is represented. It is found that on using the friction velocity based on the local shear at each height, the streamwise velocity fluctuations and the Reynolds stress within the sparse canopy are similar to those from a comparable smooth-wall case. In addition, when scaled with the local friction velocity, the intensity of the off-wall peak in the streamwise vorticity for sparse canopies also recovers a value similar to a smooth-wall. This indicates that the sparse canopy does not significantly disturb the near-wall turbulence cycle, but causes its rescaling to an intensity consistent with a lower friction velocity within the canopy. In comparison, the dense canopy is found to have a higher damping effect on the turbulent fluctuations. For the case of the sparse canopy, a peak in the spectral energy density of the wall-normal velocity, and Reynolds stress is observed, which may indicate the formation of Kelvin-Helmholtz-like instabilities. It is also found that a sparse canopy is better modelled by a homogeneous drag applied on the mean flow alone, and not the turbulent fluctuations.

An assessment of optical properties of dissolved organic material as quantitative source indicators in the Santa Ana River basin, Southern California

USGS Publications Warehouse

Bergamaschi, Brian A.; Kalve, Erica; Guenther, Larry; Mendez, Gregory O.; Belitz, Kenneth

2005-01-01

The ability to rapidly, reliably, and inexpensively characterize sources of dissolved organic material (DOM) in watersheds would allow water management agencies to more quickly identify problems in water sources, and to more efficiently allocate water resources by, for example, permitting real-time identification of high-quality water suitable for ground-water recharge, or poor-quality water in need of mitigation. This study examined the feasibility of using easily measurable intrinsic optical properties' absorbance and fluorescence spectra, as quantitative indicators of DOM sources and, thus, a predictor of water quality. The study focused on the Santa Ana River Basin, in southern California, USA, which comprises an area of dense urban development and an area of intense dairy production. Base flow in the Santa Ana Basin is primarily tertiary treated wastewater discharge. Available hydrologic data indicate that urban and agricultural runoff degrades water quality during storm events by introducing pathogens, nutrients, and other contaminants, including significant amounts of DOM. These conditions provide the basis for evaluating the use of DOM optical properties as a tracer of DOM from different sources. Sample spectra representing four principal DOM sources were identified among all samples collected in 1999 on the basis of basin hydrology, and the distribution of spectral variability within all the sample data. A linear mixing model provided quantitative estimates of relative endmember contribution to sample spectra for monthly, storm, and diurnal samples. The spectral properties of the four sources (endmembers), Pristine Water, Wastewater, Urban Water, and Dairy Water, accounted for 94 percent of the variability in optical properties observed in the study, suggesting that all important DOM sources were represented. The scale and distribution of the residual spectra, that not explained by the endmembers, suggested that the endmember spectra selected did not adequately represent Urban Water base flow. However, model assignments of sources generally agreed well with those expected, based on sampling location and hydrology. The results suggest that with a fuller characterization of the endmember spectra, analysis of optical properties will provide rapid quantitative estimates of the relative contribution of DOM sources in the Santa Ana Basin.

OAM-labeled free-space optical flow routing.

PubMed

Gao, Shecheng; Lei, Ting; Li, Yangjin; Yuan, Yangsheng; Xie, Zhenwei; Li, Zhaohui; Yuan, Xiaocong

2016-09-19

Space-division multiplexing allows unprecedented scaling of bandwidth density for optical communication. Routing spatial channels among transmission ports is critical for future scalable optical network, however, there is still no characteristic parameter to label the overlapped optical carriers. Here we propose a free-space optical flow routing (OFR) scheme by using optical orbital angular moment (OAM) states to label optical flows and simultaneously steer each flow according to their OAM states. With an OAM multiplexer and a reconfigurable OAM demultiplexer, massive individual optical flows can be routed to the demanded optical ports. In the routing process, the OAM beams act as data carriers at the same time their topological charges act as each carrier's labels. Using this scheme, we experimentally demonstrate switching, multicasting and filtering network functions by simultaneously steer 10 input optical flows on demand to 10 output ports. The demonstration of data-carrying OFR with nonreturn-to-zero signals shows that this process enables synchronous processing of massive spatial channels and flexible optical network.

Universal Scaling Laws for Dense Particle Suspensions in Turbulent Wall-Bounded Flows.

PubMed

Costa, Pedro; Picano, Francesco; Brandt, Luca; Breugem, Wim-Paul

2016-09-23

The macroscopic behavior of dense suspensions of neutrally buoyant spheres in turbulent plane channel flow is examined. We show that particles larger than the smallest turbulence scales cause the suspension to deviate from the continuum limit in which its dynamics is well described by an effective suspension viscosity. This deviation is caused by the formation of a particle layer close to the wall with significant slip velocity. By assuming two distinct transport mechanisms in the near-wall layer and the turbulence in the bulk, we define an effective wall location such that the flow in the bulk can still be accurately described by an effective suspension viscosity. We thus propose scaling laws for the mean velocity profile of the suspension flow, together with a master equation able to predict the increase in drag as a function of the particle size and volume fraction.

Abyssal ocean overturning shaped by seafloor distribution

NASA Astrophysics Data System (ADS)

de Lavergne, C.; Madec, G.; Roquet, F.; Holmes, R. M.; McDougall, T. J.

2017-11-01

The abyssal ocean is broadly characterized by northward flow of the densest waters and southward flow of less-dense waters above them. Understanding what controls the strength and structure of these interhemispheric flows—referred to as the abyssal overturning circulation—is key to quantifying the ocean’s ability to store carbon and heat on timescales exceeding a century. Here we show that, north of 32° S, the depth distribution of the seafloor compels dense southern-origin waters to flow northward below a depth of about 4 kilometres and to return southward predominantly at depths greater than 2.5 kilometres. Unless ventilated from the north, the overlying mid-depths (1 to 2.5 kilometres deep) host comparatively weak mean meridional flow. Backed by analysis of historical radiocarbon measurements, the findings imply that the geometry of the Pacific, Indian and Atlantic basins places a major external constraint on the overturning structure.

Dynamically generated patterns in dense suspensions of active filaments

NASA Astrophysics Data System (ADS)

Prathyusha, K. R.; Henkes, Silke; Sknepnek, Rastko

2018-02-01

We use Langevin dynamics simulations to study dynamical behavior of a dense planar layer of active semiflexible filaments. Using the strength of active force and the thermal persistence length as parameters, we map a detailed phase diagram and identify several nonequilibrium phases in this system. In addition to a slowly flowing melt phase, we observe that, for sufficiently high activity, collective flow accompanied by signatures of local polar and nematic order appears in the system. This state is also characterized by strong density fluctuations. Furthermore, we identify an activity-driven crossover from this state of coherently flowing bundles of filaments to a phase with no global flow, formed by individual filaments coiled into rotating spirals. This suggests a mechanism where the system responds to activity by changing the shape of active agents, an effect with no analog in systems of active particles without internal degrees of freedom.

Warm Dense Matter Demonstrating Non-Drude Conductivity from Observations of Nonlinear Plasmon Damping

NASA Astrophysics Data System (ADS)

Witte, B. B. L.; Fletcher, L. B.; Galtier, E.; Gamboa, E.; Lee, H. J.; Zastrau, U.; Redmer, R.; Glenzer, S. H.; Sperling, P.

2017-06-01

We present simulations using finite-temperature density-functional-theory molecular dynamics to calculate the dynamic electrical conductivity in warm dense aluminum. The comparison between exchange-correlation functionals in the Perdew-Burke-Enzerhof and Heyd-Scuseria-Enzerhof (HSE) approximation indicates evident differences in the density of states and the dc conductivity. The HSE calculations show excellent agreement with experimental Linac Coherent Light Source x-ray plasmon scattering spectra revealing plasmon damping below the widely used random phase approximation. These findings demonstrate non-Drude-like behavior of the dynamic conductivity that needs to be taken into account to determine the optical properties of warm dense matter.

Flow splitting in numerical simulations of oceanic dense-water outflows

NASA Astrophysics Data System (ADS)

Marques, Gustavo M.; Wells, Mathew G.; Padman, Laurie; Özgökmen, Tamay M.

2017-05-01

Flow splitting occurs when part of a gravity current becomes neutrally buoyant and separates from the bottom-trapped plume as an interflow. This phenomenon has been previously observed in laboratory experiments, small-scale water bodies (e.g., lakes) and numerical studies of small-scale systems. Here, the potential for flow splitting in oceanic gravity currents is investigated using high-resolution (Δx = Δz = 5 m) two-dimensional numerical simulations of gravity flows into linearly stratified environments. The model is configured to solve the non-hydrostatic Boussinesq equations without rotation. A set of experiments is conducted by varying the initial buoyancy number B0 =Q0N3 /g‧2 (where Q0 is the volume flux of the dense water flow per unit width, N is the ambient stratification and g‧ is the reduced gravity), the bottom slope (α) and the turbulent Prandtl number (Pr). Regardless of α or Pr, when B0 ≤ 0.002 the outflow always reaches the deep ocean forming an underflow. Similarly, when B0 ≥ 0.13 the outflow always equilibrates at intermediate depths, forming an interflow. However, when B0 ∼ 0.016, flow splitting always occurs when Pr ≥ 10, while interflows always occur for Pr = 1. An important characteristic of simulations that result in flow splitting is the development of Holmboe-like interfacial instabilities and flow transition from a supercritical condition, where the Froude number (Fr) is greater than one, to a slower and more uniform subcritical condition (Fr < 1). This transition is associated with an internal hydraulic jump and consequent mixing enhancement. Although our experiments do not take into account three-dimensionality and rotation, which are likely to influence mixing and the transition between flow regimes, a comparison between our results and oceanic observations suggests that flow splitting may occur in dense-water outflows with weak ambient stratification, such as Antarctic outflows.

The thermodynamics of dense granular flow and jamming

NASA Astrophysics Data System (ADS)

Lu, Shih Yu

The scope of the thesis is to propose, based on experimental evidence and theoretical validation, a quantifiable connection between systems that exhibit the jamming phenomenon. When jammed, some materials that flow are able to resist deformation so that they appear solid-like on the laboratory scale. But unlike ordinary fusion, which has a critically defined criterion in pressure and temperature, jamming occurs under a wide range of conditions. These condition have been rigorously investigated but at the moment, no self-consistent framework can apply to grains, foam and colloids that may have suddenly ceased to flow. To quantify the jamming behavior, a constitutive model of dense granular flows is deduced from shear-flow experiments. The empirical equations are then generalized, via a thermodynamic approach, into an equation-of-state for jamming. Notably, the unifying theory also predicts the experimental data on the behavior of molecular glassy liquids. This analogy paves a crucial road map for a unifying theoretical framework in condensed matter, for example, ranging from sand to fire retardants to toothpaste.

Slow-moving and far-travelled dense pyroclastic flows during the Peach Spring super-eruption.

PubMed

Roche, O; Buesch, D C; Valentine, G A

2016-03-07

Explosive volcanic super-eruptions of several hundred cubic kilometres or more generate long run-out pyroclastic density currents the dynamics of which are poorly understood and controversial. Deposits of one such event in the southwestern USA, the 18.8 Ma Peach Spring Tuff, were formed by pyroclastic flows that travelled >170 km from the eruptive centre and entrained blocks up to ∼ 70-90 cm diameter from the substrates along the flow paths. Here we combine these data with new experimental results to show that the flow's base had high-particle concentration and relatively modest speeds of ∼ 5-20 m s(-1), fed by an eruption discharging magma at rates up to ∼ 10(7)-10(8) m(3) s(-1) for a minimum of 2.5-10 h. We conclude that sustained high-eruption discharge and long-lived high-pore pressure in dense granular dispersion can be more important than large initial velocity and turbulent transport with dilute suspension in promoting long pyroclastic flow distance.

Dissipationless Hall current in dense quark matter in a magnetic field

DOE PAGES

Ferrer, Efrain J.; de la Incera, V.

2017-03-29

Here, we show the realization of axion electrodynamics within the Dual Chiral Density Wave phase of dense quark matter in the presence of a magnetic field. This system exhibits an anomalous dissipationless Hall current perpendicular to the magnetic field and an anomalous electric charge density. This connection to topological insulators and 3D optical lattices, as well as possible implications for heavy-ion collisions and neutron stars are outlined.

Design of Experiments Relevant to Accreting Stream-Disk Impact in Interacting Binaries

NASA Astrophysics Data System (ADS)

Krauland, Christine; Drake, R. P.; Kuranz, C. C.; Grosskopf, M. J.; Young, R.; Plewa, T.

2010-05-01

In many Cataclysmic Binary systems, mass transfer via Roche lobe overflow onto an accretion disk occurs. This produces a hot spot from the heating created by the supersonic impact of the infalling flow with the rotating accretion disk, which can produce a radiative reverse shock in the infalling flow. This collision region has many ambiguities as a radiation hydrodynamic system. Depending upon conditions, it has been argued (Armitgae & Livio, ApJ 493, 898) that the shocked region may be optically thin, thick, or intermediate, which has the potential to significantly alter its structure and emissions. Laboratory experiments have yet to produce colliding flows that create a radiative reverse shock or to produce obliquely incident colliding flows, both of which are aspects of these Binary systems. We have undertaken the design of such an experiment, aimed at the Omega-60 laser facility. The design elements include the production of postshock flows within a dense material layer or ejecta flows by release of material from a shocked layer. Obtaining a radiative reverse shock in the laboratory requires producing a sufficiently fast flow (> 100 km/s) within a material whose opacity is large enough to produce energetically significant emission from experimentally achievable layers. In this poster we will discuss the astrophysical context, the experimental design work we have done, and the challenges of implementing and diagnosing an actual experiment. This work is funded by the NNSA-DS and SC-OFES Joint Program in High-Energy-Density Laboratory Plasmas, by the National Laser User Facility Program in NNSA-DS and by the Predictive Sciences Academic Alliances Program in NNSA-ASC. The corresponding grant numbers are DE-FG52-09NA29548, DE-FG52-09NA29034, and DE-FC52-08NA28616.

Application of UDWDM technology in FTTH networks

NASA Astrophysics Data System (ADS)

Lamperski, Jan; Stepczak, Piotr

2015-12-01

In the paper we presented results of investigation of an original ultra dense wavelength division technology based on optical comb generator and its implementation for FTTH networks. The optical comb generator used a ring configuration with an acousto-optic frequency shifter (AOFS) which ensured obtaining very stable optical carrier frequency distances. Properties of an optical comb generator module determined stability of the UDWDM transmitter. Key properties of a selective components based on all fiber Fabry-Perot resonant cavity were presented. Operation of direct and coherent detection DWDM systems were shown. New configurations of FTTH UDWDM architecture have been proposed.

Optical tomography of fluorophores in dense scattering media based on ultrasound-enhanced chemiluminescence

NASA Astrophysics Data System (ADS)

Kobayashi, Masaki; Kikuchi, Naoto; Sato, Akihiro

2015-01-01

This letter proposes and demonstrates ultrasound-combined optical imaging in dense scattering media. A peroxyoxalate chemiluminescence system that includes fluorophores to chemically excite the pigment is stimulated by ultrasound irradiation with power of less than 0.14 W/cm2. Using focused ultrasound, the chemiluminescence is selectively spatially enhanced, which leads to imaging of the pigment when embedded in a light-scattering medium via scanning of the focal point. The ultrasonically enhanced intensity of the chemiluminescence depends on the base intensity of the chemiluminescence without the applied ultrasound irradiation, which thereby enables quantitative determination of the fluorophore concentration. The authors demonstrate the potential of this method to resolve chemiluminescent targets in a dense scattering medium that is comparable to biological tissue. An image was acquired of a chemiluminescent target that included indocyanine green as the fluorophore embedded at a depth of 20 mm in an Intralipid-10% 200 ml/l solution scattering medium (the reduced scattering coefficient was estimated to be approximately 1.3 mm-1), indicating the potential for expansion of this technique for use in biological applications.

Highlights from the previous volumes

NASA Astrophysics Data System (ADS)

-C., Liu K.; al., Kumar N. et; al., Anishchenko V. et; al., Jaeckel J. et; et al.

2009-10-01

The physics of pizza tossing and the next generation of micromotors Is diamagnetism possible classically? Phase dynamics of two coupled oscillators under external periodic force Optical communications through dense matter

Channel-capacity gain in entanglement-assisted communication protocols based exclusively on linear optics, single-photon inputs, and coincidence photon counting

DOE PAGES

Lougovski, P.; Uskov, D. B.

2015-08-04

Entanglement can effectively increase communication channel capacity as evidenced by dense coding that predicts a capacity gain of 1 bit when compared to entanglement-free protocols. However, dense coding relies on Bell states and when implemented using photons the capacity gain is bounded by 0.585 bits due to one's inability to discriminate between the four optically encoded Bell states. In this research we study the following question: Are there alternative entanglement-assisted protocols that rely only on linear optics, coincidence photon counting, and separable single-photon input states and at the same time provide a greater capacity gain than 0.585 bits? In thismore » study, we show that besides the Bell states there is a class of bipartite four-mode two-photon entangled states that facilitate an increase in channel capacity. We also discuss how the proposed scheme can be generalized to the case of two-photon N-mode entangled states for N=6,8.« less

Spatial height directed microfluidic synthesis of transparent inorganic upconversion nano film

NASA Astrophysics Data System (ADS)

Liu, Xiaoxia; Zhu, Cheng; Liao, Wei; Jin, Junyang; Ni, Yaru; Lu, Chunhua; Xu, Zhongzi

2017-11-01

A microfluidic-based synthesis of an inorganic upconversion nano film has been developed with a large area of dense-distributed NaYF4 crystal grains in a silica glass micro-reactor and the film exhibits high transparence, strong upconversion luminescence and robust adhesion with the substrate. The spatial heights of micro-reactors are tuned between 31 and 227 mm, which can regulate flow regimes. The synergistic effect of spatial height and fluid regime is put forward, which influences diffusion paths and assembly ways of different precursor molecules and consequently directs final distributions and morphologies of crystal grains, as well as optical properties due to diversity of surface and thickness of films. The spatial height of 110 mm is advantageous for high transmittance of upconversion film due to the flat surface and appropriate film thickness of 67 nm. The height of 150 mm is in favor of uniform distribution of upconversion fluorescence and achieving the strongest fluorescence due to minimized optical loss. Such a transparent upconversion film with a large area of uniform distribution is promising to promote the application of upconversion materials and spatial height directed microfluidic regime have a certain significance on many microfluidic synthesis.

Using UAS optical imagery and SfM photogrammetry to characterize the surface grain size of gravel bars in a braided river (Vénéon River, French Alps)

NASA Astrophysics Data System (ADS)

Vázquez-Tarrío, Daniel; Borgniet, Laurent; Liébault, Frédéric; Recking, Alain

2017-05-01

This paper explores the potential of unmanned aerial system (UAS) optical aerial imagery to characterize grain roughness and size distribution in a braided, gravel-bed river (Vénéon River, French Alps). With this aim in view, a Wolman field campaign (19 samples) and five UAS surveys were conducted over the Vénéon braided channel during summer 2015. The UAS consisted of a small quadcopter carrying a GoPro camera. Structure-from-Motion (SfM) photogrammetry was used to extract dense and accurate three-dimensional point clouds. Roughness descriptors (roughness heights, standard deviation of elevation) were computed from the SfM point clouds and were correlated with the median grain size of the Wolman samples. A strong relationship was found between UAS-SfM-derived grain roughness and Wolman grain size. The procedure employed has potential for the rapid and continuous characterization of grain size distribution in exposed bars of gravel-bed rivers. The workflow described in this paper has been successfully used to produce spatially continuous grain size information on exposed gravel bars and to explore textural changes following flow events.

Strain and ground-motion monitoring at magmatic areas: ultra-long and ultra-dense networks using fibre optic sensing systems

NASA Astrophysics Data System (ADS)

Jousset, Philippe; Reinsch, Thomas; Henninges, Jan; Blanck, Hanna; Ryberg, Trond

2016-04-01

The fibre optic distributed acoustic sensing technology (DAS) is a "new" sensing system for exploring earth crustal elastic properties and monitoring both strain and seismic waves with unprecedented acquisition characteristics. The DAS technology principle lies in sending successive and coherent pulses of light in an optical fibre and measuring the back-scattered light issued from elastic scattering at random defaults within the fibre. The read-out unit includes an interferometer, which measures light interference patterns continuously. The changes are related to the distance between such defaults and therefore the strain within the fibre can be detected. Along an optical fibre, DAS can be used to acquire acoustic signals with a high spatial (every meter over kilometres) and high temporal resolution (thousand of Hz). Fibre optic technologies were, up to now, mainly applied in perimeter surveillance applications and pipeline monitoring and in boreholes. Previous experiments in boreholes have shown that the DAS technology is well suited for probing subsurface elastic properties, showing new ways for cheaper VSP investigations of the Earth crust. Here, we demonstrate that a cable deployed at ground surface can also help in exploring subsurface properties at crustal scale and monitor earthquake activity in a volcanic environment. Within the framework of the EC funded project IMAGE, we observed a >15 km-long fibre optic cable at the surface connected to a DAS read-out unit. Acoustic data was acquired continuously for 9 days. Hammer shots were performed along the surface cable in order to locate individual acoustic traces and calibrate the spatial distribution of the acoustic information. During the monitoring period both signals from on- and offshore explosive sources and natural seismic events could be recorded. We compare the fibre optic data to conventional seismic records from a dense seismic network deployed on Reykjanes. We show that we can probe and monitor earth crust subsurface with dense acquisition of the ground motion, both in space and in time and over a broad band frequency range.

Heat and Groundwater Flow in the San Gabriel Mountains, California

NASA Astrophysics Data System (ADS)

Newman, A. A.; Becker, M.; Laton, W. R., Jr.

2017-12-01

Groundwater flow paths in mountainous terrain often vary widely in both time and space. Such systems remain difficult to characterize due to fracture-dominated flow paths, high topographic relief, and sparse hydrologic data. We develop a hydrogeologic conceptual model of the Western San Gabriel Mountains in Southern California based on geophysical, thermal, and hydraulic head data. Boreholes are located along the San Gabriel Fault Zone (SGFZ) and cover a wide range of elevations to capture the heterogeneity of the hydrogeologic system. Long term (2016-2017) monitoring of temperature and hydraulic head was carried out in four shallow (300-600m depth) boreholes within the study area using fiber-optic distributed temperature sensing (DTS). Borehole temperature profiles were used to assess the regional groundwater flow system and local flows in fractures intersecting the borehole. DTS temperature profiles were compared with available borehole geophysical logs and head measurements collected with grouted vibrating wire pressure transducers (VWPT). Spatial and temporal variations in borehole temperature profiles suggest that advective heat transfer due to fluid flow affected the subsurface thermal regime. Thermal evidence of groundwater recharge and/or discharge and flow through discrete fractures was found in all four boreholes. Analysis of temporal changes to the flow system in response to seasonal and drilling-induced hydraulic forcing was useful in reducing ambiguities in noisy datasets and estimating interborehole relationships. Acoustic televiewer logs indicate fractures were primarily concentrated in densely fractured intervals, and only a minor decrease of fracture density was observed with depth. Anomalously high hydraulic gradients across the SGFZ suggest that the feature is a potential barrier to lateral flow. However, transient thermal anomalies consistent with groundwater flow within the SGFZ indicate this feature may be a potential conduit to vertical flow. This study builds upon the limited hydrogeologic understanding of the region and demonstrates the value of DTS in characterization efforts.

A characterization of Parkinson's disease by describing the visual field motion during gait

NASA Astrophysics Data System (ADS)

Trujillo, David; Martínez, Fabio; Atehortúa, Angélica; Alvarez, Charlens; Romero, Eduardo

2015-12-01

An early diagnosis of Parkinson's Disease (PD) is crucial towards devising successful rehabilitation programs. Typically, the PD diagnosis is performed by characterizing typical symptoms, namely bradykinesia, rigidity, tremor, postural instability or freezing gait. However, traditional examination tests are usually incapable of detecting slight motor changes, specially for early stages of the pathology. Recently, eye movement abnormalities have correlated with early onset of some neurodegenerative disorders. This work introduces a new characterization of the Parkinson disease by describing the ocular motion during a common daily activity as the gait. This paper proposes a fully automatic eye motion analysis using a dense optical flow that tracks the ocular direction. The eye motion is then summarized using orientation histograms constructed during a whole gait cycle. The proposed approach was evaluated by measuring the χ2 distance between the orientation histograms, showing substantial differences between control and PD patients.

Fast Calcium Imaging with Optical Sectioning via HiLo Microscopy.

PubMed

Lauterbach, Marcel A; Ronzitti, Emiliano; Sternberg, Jenna R; Wyart, Claire; Emiliani, Valentina

2015-01-01

Imaging intracellular calcium concentration via reporters that change their fluorescence properties upon binding of calcium, referred to as calcium imaging, has revolutionized our way to probe neuronal activity non-invasively. To reach neurons densely located deep in the tissue, optical sectioning at high rate of acquisition is necessary but difficult to achieve in a cost effective manner. Here we implement an accessible solution relying on HiLo microscopy to provide robust optical sectioning with a high frame rate in vivo. We show that large calcium signals can be recorded from dense neuronal populations at high acquisition rates. We quantify the optical sectioning capabilities and demonstrate the benefits of HiLo microscopy compared to wide-field microscopy for calcium imaging and 3D reconstruction. We apply HiLo microscopy to functional calcium imaging at 100 frames per second deep in biological tissues. This approach enables us to discriminate neuronal activity of motor neurons from different depths in the spinal cord of zebrafish embryos. We observe distinct time courses of calcium signals in somata and axons. We show that our method enables to remove large fluctuations of the background fluorescence. All together our setup can be implemented to provide efficient optical sectioning in vivo at low cost on a wide range of existing microscopes.

Fast Calcium Imaging with Optical Sectioning via HiLo Microscopy

PubMed Central

Sternberg, Jenna R.; Wyart, Claire; Emiliani, Valentina

2015-01-01

Imaging intracellular calcium concentration via reporters that change their fluorescence properties upon binding of calcium, referred to as calcium imaging, has revolutionized our way to probe neuronal activity non-invasively. To reach neurons densely located deep in the tissue, optical sectioning at high rate of acquisition is necessary but difficult to achieve in a cost effective manner. Here we implement an accessible solution relying on HiLo microscopy to provide robust optical sectioning with a high frame rate in vivo. We show that large calcium signals can be recorded from dense neuronal populations at high acquisition rates. We quantify the optical sectioning capabilities and demonstrate the benefits of HiLo microscopy compared to wide-field microscopy for calcium imaging and 3D reconstruction. We apply HiLo microscopy to functional calcium imaging at 100 frames per second deep in biological tissues. This approach enables us to discriminate neuronal activity of motor neurons from different depths in the spinal cord of zebrafish embryos. We observe distinct time courses of calcium signals in somata and axons. We show that our method enables to remove large fluctuations of the background fluorescence. All together our setup can be implemented to provide efficient optical sectioning in vivo at low cost on a wide range of existing microscopes. PMID:26625116

Integrated reactor and centrifugal separator and uses thereof

DOEpatents

Birdwell, Jr., Joseph F; Jennings, Harold L [Clinton, TN; McFarlane, Joanna [Oak Ridge, TN; Tsouris, Constantino [Oak Ridge, TN

2012-01-17

An apparatus for providing reaction of fluids and separation of products with increased residence time. The apparatus includes a stationary shell, a rotating hollow cylindrical component disposed in the stationary shell, a residence-time increasing device external to the stationary shell, a standpipe for introducing fluid into an interior cavity of the hollow cylindrical component from the residence-time increasing device, a first outlet in fluid flow communication with the interior cavity of the hollow cylindrical component for a less dense phase fluid, and a second outlet in fluid flow communication with the interior cavity of the hollow cylindrical component for a more dense phase fluid.

Comparison of entrainment in constant volume and constant flux dense currents over sloping bottoms

NASA Astrophysics Data System (ADS)

Bhaganagar, K.; Nayamatullah, M.; Cenedese, C.

2014-12-01

Three dimensional high resolution large eddy simulations (LES) are employed to simulate lock-exchange and constant flux dense flows over inclined surface with the aim of investigating, visualizing and describing the turbulent structure and the evolution of bottom-propagating compositional density current at the channel bottom. The understanding of dynamics of density current is largely determined by the amount of interfacial mixing or entrainment between the ambient and dense fluids. No previous experimental or numerical studies have been done to estimate entrainment in classical lock-exchange system. The differences in entrainment between the lock-exchange and constant flux are explored. Comparing the results of flat bed with inclined surface results, flow exhibits significant differences near the leading edge or nose of the front of the density currents due to inclination of surface. Further, the instabilities are remarkably enhanced resulting Kelvin-Helmholtz and lobe-cleft type of instabilities arises much earlier in time. In this study, a brief analysis of entrainment on lock-exchange density current is presented using different bed slopes and a set of reduced gravity values (g'). We relate the entrainment value with different flow parameters such as Froude number (Fr) and Reynolds number (Re).

Optical flow versus retinal flow as sources of information for flight guidance

NASA Technical Reports Server (NTRS)

Cutting, James E.

1991-01-01

The appropriate description is considered of visual information for flight guidance, optical flow vs. retinal flow. Most descriptions in the psychological literature are based on the optical flow. However, human eyes move and this movement complicates the issues at stake, particularly when movement of the observer is involved. The question addressed is whether an observer, whose eyes register only retinal flow, use information in optical flow. It is suggested that the observer cannot and does not reconstruct the image in optical flow; instead they use retinal flow. Retinal array is defined as the projections of a three space onto a point and beyond to a movable, nearly hemispheric sensing device, like the retina. Optical array is defined as the projection of a three space environment to a point within that space. And flow is defined as global motion as a field of vectors, best placed on a spherical projection surface. Specifically, flow is the mapping of the field of changes in position of corresponding points on objects in three space onto a point, where that point has moved in position.

Benthic Ecology from Space: Optics and Net Primary Production in Seagrass and Benthic Algae Across the Great Bahama Bank

DTIC Science & Technology

2010-01-01

prevailing benthic habitat was mapped as sediment with little to no microalgal biofilm. Moderate to dense sea- grass meadows of Thalassia testudinum were...dense seagrass meadows of Thalassia testudinum were the dominant primary producers and contributed over 80% of NPP in the region. If the vast majority of...density of the seagrasses Thalassia testudinum (turtle grass), Syringodium filiforme (manatee grass), and Halodule wrightii (shoal grass) were estimated

A Sector Capacity Assessment Method Based on Airspace Utilization Efficiency

NASA Astrophysics Data System (ADS)

Zhang, Jianping; Zhang, Ping; Li, Zhen; Zou, Xiang

2018-02-01

Sector capacity is one of the core factors affecting the safety and the efficiency of the air traffic system. Most of previous sector capacity assessment methods only considered the air traffic controller’s (ATCO’s) workload. These methods are not only limited which only concern about the safety, but also not accurate enough. In this paper, we employ the integrated quantitative index system proposed in one of our previous literatures. We use the principal component analysis (PCA) to find out the principal indicators among the indicators so as to calculate the airspace utilization efficiency. In addition, we use a series of fitting functions to test and define the correlation between the dense of air traffic flow and the airspace utilization efficiency. The sector capacity is then decided as the value of the dense of air traffic flow corresponding to the maximum airspace utilization efficiency. We also use the same series of fitting functions to test the correlation between the dese of air traffic flow and the ATCOs’ workload. We examine our method with a large amount of empirical operating data of Chengdu Controlling Center and obtain a reliable sector capacity value. Experiment results also show superiority of our method against those only consider the ATCO’s workload in terms of better correlation between the airspace utilization efficiency and the dense of air traffic flow.

Observations of non-linear plasmon damping in dense plasmas

NASA Astrophysics Data System (ADS)

Witte, B. B. L.; Sperling, P.; French, M.; Recoules, V.; Glenzer, S. H.; Redmer, R.

2018-05-01

We present simulations using finite-temperature density-functional-theory molecular-dynamics to calculate dynamic dielectric properties in warm dense aluminum. The comparison between exchange-correlation functionals in the Perdew, Burke, Ernzerhof approximation, Strongly Constrained and Appropriately Normed Semilocal Density Functional, and Heyd, Scuseria, Ernzerhof (HSE) approximation indicates evident differences in the electron transition energies, dc conductivity, and Lorenz number. The HSE calculations show excellent agreement with x-ray scattering data [Witte et al., Phys. Rev. Lett. 118, 225001 (2017)] as well as dc conductivity and absorption measurements. These findings demonstrate non-Drude behavior of the dynamic conductivity above the Cooper minimum that needs to be taken into account to determine optical properties in the warm dense matter regime.

Sediment transport processes at the head of Halibut Canyon, Eastern Canada margin: An interplay between internal tides and dense shelf water cascading.

NASA Astrophysics Data System (ADS)

Puig, Pere; Greenan, Blair J. W.; Li, Michael Z.; Prescott, Robert H.; Piper, David J. W.

2013-04-01

To investigate the processes by which sediment is transported through a submarine canyon incised in a glaciated margin, the bottom boundary layer quadrapod RALPH was deployed at 276-m depth in the West Halibut Canyon (off Newfoundland) during winter 2008-2009. Two main sediment transport processes were identified throughout the deployment. Firstly, periodic increases of near-bottom suspended-sediment concentrations (SSC) were recorded associated with the up-canyon propagation of the semidiurnal internal tidal bore along the canyon axis, carrying fine sediment particles resuspended from deeper canyon regions. The recorded SSC peaks, lasting less than one hour, were observed sporadically and were linked to bottom intensified up-canyon flows concomitant with sharp drops in temperature. Secondly, sediment transport was also observed during events of intensified down-canyon current velocities that occurred during periods of sustained heat loss from surface waters, but were not associated with large storms. High-resolution velocity profiles throughout the water column during these events revealed that the highest current speeds (~1 m s-1) were centered several meters above the sea floor and corresponded to the region of maximum velocities of a gravity flow. Such flows had associated low SSC and cold water temperatures and have been interpreted as dense shelf water cascading events channelized along the canyon axis. Sediment transport during these events was largely restricted to bedload and saltation, producing winnowing of sands and fine sediments around larger gravel particles. Analysis of historical hydrographic data suggests that the origin of such gravity flows is not related to the formation of coastal dense waters advected towards the canyon head. Rather, the dense shelf waters appear to be generated around the outer shelf, where convection during winter is able to reach the sea floor and generate a pool of near-bottom dense water that cascades into the canyon during one or two tidal cycles. A similar transport mechanism can occur in other submarine canyons along the eastern Canadian margin, as well in other canyoned regions elsewhere, where winter convection generally reaches the shelf-edge.

Experimental strain modal analysis for beam-like structure by using distributed fiber optics and its damage detection

NASA Astrophysics Data System (ADS)

Cheng, Liangliang; Busca, Giorgio; Cigada, Alfredo

2017-07-01

Modal analysis is commonly considered as an effective tool to obtain the intrinsic characteristics of structures including natural frequencies, modal damping ratios, and mode shapes, which are significant indicators for monitoring the health status of engineering structures. The complex mode indicator function (CMIF) can be regarded as an effective numerical tool to perform modal analysis. In this paper, experimental strain modal analysis based on the CMIF has been introduced. Moreover, a distributed fiber-optic sensor, as a dense measuring device, has been applied to acquire strain data along a beam surface. Thanks to the dense spatial resolution of the distributed fiber optics, more detailed mode shapes could be obtained. In order to test the effectiveness of the method, a mass lump—considered as a linear damage component—has been attached to the surface of the beam, and damage detection based on strain mode shape has been carried out. The results manifest that strain modal parameters can be estimated effectively by utilizing the CMIF based on the corresponding simulations and experiments. Furthermore, damage detection based on strain mode shapes benefits from the accuracy of strain mode shape recognition and the excellent performance of the distributed fiber optics.

Comparative efficiency analysis of fiber-array and conventional beam director systems in volume turbulence.

PubMed

Vorontsov, Mikhail; Filimonov, Grigory; Ovchinnikov, Vladimir; Polnau, Ernst; Lachinova, Svetlana; Weyrauch, Thomas; Mangano, Joseph

2016-05-20

The performance of two prominent laser beam projection system types is analyzed through wave-optics numerical simulations for various atmospheric turbulence conditions, propagation distances, and adaptive optics (AO) mitigation techniques. Comparisons are made between different configurations of both a conventional beam director (BD) using a monolithic-optics-based Cassegrain telescope and a fiber-array BD that uses an array of densely packed fiber collimators. The BD systems considered have equal input power and aperture diameters. The projected laser beam power inside the Airy size disk at the target plane is used as the performance metric. For the fiber-array system, both incoherent and coherent beam combining regimes are considered. We also present preliminary results of side-by-side atmospheric beam projection experiments over a 7-km propagation path using both the AO-enhanced beam projection system with a Cassegrain telescope and the coherent fiber-array BD composed of 21 densely packed fiber collimators. Both wave-optics numerical simulation and experimental results demonstrate that, for similar system architectures and turbulence conditions, coherent fiber-array systems are more efficient in mitigation of atmospheric turbulence effects and generation of a hit spot of the smallest possible size on a remotely located target.

Control of a Quadcopter Aerial Robot Using Optic Flow Sensing

NASA Astrophysics Data System (ADS)

Hurd, Michael Brandon

This thesis focuses on the motion control of a custom-built quadcopter aerial robot using optic flow sensing. Optic flow sensing is a vision-based approach that can provide a robot the ability to fly in global positioning system (GPS) denied environments, such as indoor environments. In this work, optic flow sensors are used to stabilize the motion of quadcopter robot, where an optic flow algorithm is applied to provide odometry measurements to the quadcopter's central processing unit to monitor the flight heading. The optic-flow sensor and algorithm are capable of gathering and processing the images at 250 frames/sec, and the sensor package weighs 2.5 g and has a footprint of 6 cm2 in area. The odometry value from the optic flow sensor is then used a feedback information in a simple proportional-integral-derivative (PID) controller on the quadcopter. Experimental results are presented to demonstrate the effectiveness of using optic flow for controlling the motion of the quadcopter aerial robot. The technique presented herein can be applied to different types of aerial robotic systems or unmanned aerial vehicles (UAVs), as well as unmanned ground vehicles (UGV).

Optimal Filter Estimation for Lucas-Kanade Optical Flow

PubMed Central

Sharmin, Nusrat; Brad, Remus

2012-01-01

Optical flow algorithms offer a way to estimate motion from a sequence of images. The computation of optical flow plays a key-role in several computer vision applications, including motion detection and segmentation, frame interpolation, three-dimensional scene reconstruction, robot navigation and video compression. In the case of gradient based optical flow implementation, the pre-filtering step plays a vital role, not only for accurate computation of optical flow, but also for the improvement of performance. Generally, in optical flow computation, filtering is used at the initial level on original input images and afterwards, the images are resized. In this paper, we propose an image filtering approach as a pre-processing step for the Lucas-Kanade pyramidal optical flow algorithm. Based on a study of different types of filtering methods and applied on the Iterative Refined Lucas-Kanade, we have concluded on the best filtering practice. As the Gaussian smoothing filter was selected, an empirical approach for the Gaussian variance estimation was introduced. Tested on the Middlebury image sequences, a correlation between the image intensity value and the standard deviation value of the Gaussian function was established. Finally, we have found that our selection method offers a better performance for the Lucas-Kanade optical flow algorithm.

A new generation of ultra-dense optical I/O for silicon photonics

NASA Astrophysics Data System (ADS)

Wlodawski, Mitchell S.; Kopp, Victor I.; Park, Jongchul; Singer, Jonathan; Hubner, Eric E.; Neugroschl, Daniel; Chao, Norman; Genack, Azriel Z.

2014-03-01

In response to the optical packaging needs of a rapidly growing silicon photonics market, Chiral Photonics, Inc. (CPI) has developed a new generation of ultra-dense-channel, bi-directional, all-optical, input/output (I/O) couplers that bridge the data transport gap between standard optical fibers and photonic integrated circuits. These couplers, called Pitch Reducing Optical Fiber Arrays (PROFAs), provide a means to simultaneously match both the mode field and channel spacing (i.e. pitch) between an optical fiber array and a photonic integrated circuit (PIC). Both primary methods for optically interfacing with PICs, via vertical grating couplers (VGCs) and edge couplers, can be addressed with PROFAs. PROFAs bring the signal-carrying cores, either multimode or singlemode, of many optical fibers into close proximity within an all-glass device that can provide low loss coupling to on-chip components, including waveguides, gratings, detectors and emitters. Two-dimensional (2D) PROFAs offer more than an order of magnitude enhancement in channel density compared to conventional one-dimensional (1D) fiber arrays. PROFAs can also be used with low vertical profile solutions that simplify optoelectronic packaging while reducing PIC I/O real estate usage requirements. PROFA technology is based on a scalable production process for microforming glass preform assemblies as they are pulled through a small oven. An innovative fiber design, called the "vanishing core," enables tailoring the mode field along the length of the PROFA to meet the coupling needs of disparate waveguide technologies, such as fiber and onchip. Examples of single- and multi-channel couplers fabricated using this technology will be presented.

Development of a Computational Framework for Big Data-Driven Prediction of Long-Term Bridge Performance and Traffic Flow

DOT National Transportation Integrated Search

2018-04-01

Consistent efforts with dense sensor deployment and data gathering processes for bridge big data have accumulated profound information regarding bridge performance, associated environments, and traffic flows. However, direct applications of bridge bi...

X-Ray Emission from Supernovae in Dense Circumstellar Matter Environments: A Search for Collisionless Shock

NASA Technical Reports Server (NTRS)

Ofek, E.O; Fox, D.; Cenko, B.; Sullivan, M.; Gnat, O.; Frail A.; Horesh, A.; Corsi, A; Quimby, R. M.; Gehrels, N.;

Dense granular flow around a rigid or flexible intruder

NASA Astrophysics Data System (ADS)

Kolb, Evelyne; Adda-Bedia, Mokhtar

2012-02-01

We experimentally studied the flow of a dense granular material around an obstacle (rigid cylinder or flexible plate) placed in a 2 dimensional confined cell at a packing fraction near the 2D jamming threshold. In the case of the rigid obstacle, the displacement field of grains as well as the drag force experienced by the obstacle were simultaneously recorded and a parametric study was done by changing the cell size, the intruder diameter or the packing fraction. The drag force experienced by the intruder and the formation of a wake behind the obstacle were very sensitive to the approach to jamming. The same experimental set-up was adapted to a flexible intruder and coupling between the granular flow and fibre deflexion were imaged. The deformation of the fibre could be compared with theoretical predictions from elastica.

Externally Induced Evaporation of Young Stellar Disks: The Case for HST 10 in Orion's Trapezium.

NASA Astrophysics Data System (ADS)

Johnstone, D.; Hollenbach, D.; Storzer, H.; Bally, J.; Sutherland, R.

1996-12-01

The Trapezium region in Orion is composed of a few high-mass stars, responsible for the ionization of the surrounding gas, and a plethora of low-mass stars with disks. Observations at infrared, optical, and radio wavelengths have led to the discovery of extended ionized envelopes around many of the young low-mass stars requiring evaporation rates dot M ~ 10(-7) Modot/yr. In this poster we explain these observations through a model for the evaporation of disks around young low-mass stars by an external source of high energy photons. In particular, the externally produced ultraviolet continuum longward of the Lyman limit is used to heat the disk surface and produce a warm neutral flow. The model results in an offset ionization front, where the neutral flow encounters Lyman continuum radiation, and a mass-loss rate which is fixed due to the self-regulating nature of FUV heating. Applying this model to the Trapezium region evaporating objects, particularly HST 10, produces a satisfactory solution to both the mass-loss rate and the size of the ionized envelopes. The resulting short destruction times for these disks constrain the gestation period for planet embryos around stars in dense clusters.

Broadband X-ray Imaging in the Near-Field Region of an Airblast Atomizer

NASA Astrophysics Data System (ADS)

Li, Danyu; Bothell, Julie; Morgan, Timothy; Heindel, Theodore

2017-11-01

The atomization process has a close connection to the efficiency of many spray applications. Examples include improved fuel atomization increasing the combustion efficiency of aircraft engines, or controlled droplet size and spray angle enhancing the quality and speed of the painting process. Therefore, it is vital to understand the physics of the atomization process, but the near-field region is typically optically dense and difficult to probe with laser-based or intrusive measurement techniques. In this project, broadband X-ray radiography and X-ray computed tomography (CT) imaging were performed in the near-field region of a canonical coaxial airblast atomizer. The X-ray absorption rate was enhanced by adding 20% by weight of Potassium Iodide to the liquid phase to increase image contrast. The radiographs provided an estimate of the liquid effective mean path length and spray angle at the nozzle exit for different flow conditions. The reconstructed CT images provided a 3D map of the time-average liquid spray distribution. X-ray imaging was used to quantify the changes in the near-field spray characteristics for various coaxial airblast atomizer flow conditions. Office of Naval Research.

Self-diffusion in dense granular shear flows.

PubMed

Utter, Brian; Behringer, R P

2004-03-01

Diffusivity is a key quantity in describing velocity fluctuations in granular materials. These fluctuations are the basis of many thermodynamic and hydrodynamic models which aim to provide a statistical description of granular systems. We present experimental results on diffusivity in dense, granular shear flows in a two-dimensional Couette geometry. We find that self-diffusivities D are proportional to the local shear rate gamma; with diffusivities along the direction of the mean flow approximately twice as large as those in the perpendicular direction. The magnitude of the diffusivity is D approximately gamma;a(2), where a is the particle radius. However, the gradient in shear rate, coupling to the mean flow, and strong drag at the moving boundary lead to particle displacements that can appear subdiffusive or superdiffusive. In particular, diffusion appears to be superdiffusive along the mean flow direction due to Taylor dispersion effects and subdiffusive along the perpendicular direction due to the gradient in shear rate. The anisotropic force network leads to an additional anisotropy in the diffusivity that is a property of dense systems and has no obvious analog in rapid flows. Specifically, the diffusivity is suppressed along the direction of the strong force network. A simple random walk simulation reproduces the key features of the data, such as the apparent superdiffusive and subdiffusive behavior arising from the mean velocity field, confirming the underlying diffusive motion. The additional anisotropy is not observed in the simulation since the strong force network is not included. Examples of correlated motion, such as transient vortices, and Lévy flights are also observed. Although correlated motion creates velocity fields which are qualitatively different from collisional Brownian motion and can introduce nondiffusive effects, on average the system appears simply diffusive.

Condition of Development of Channeled Flow in Analogue Partially Molten Medium

NASA Astrophysics Data System (ADS)

Takashima, S.; Kumagai, I.; Kurita, K.

2003-12-01

Melt migration in partially molten medium is conceptually classified into two contrasting models; homogeneous permeable flow and localized channeled flow. The transition from homogeneous flow to localized one is promoted with advance of melting and deformation of the medium, but the physics behind this transition is not yet clarified well. Here we show two kinds of experimental results which are mutually related. One is a development of the channeled flow in a so-called Rayleigh-Taylor Instability experiments. Dense viscous fluid is poured at the top of the matrix fluid; homogeneous mixture of soft transparent gel and viscous fluid having equal density. Liquid fraction is varied for this matrix fluid to see how the fraction controls the development. At the intermediate gel fraction (between70% to about 40%) the dense fluid at first migrates through the grain boundary as permeable flow. But local heterogeneity in the gel fraction induces relative movement of solid phase, which in turns enhances the localization of the flow and deformation. We measured the motion of fluid phase and solid phase separately by PIV/PTV methods. Estimated relative motion and divergence of velocity field of the solid phase show that the state in the relative movement of the solid phase could cause heterogeneous distribution of the solid fraction. The deformation-induced compaction plays an important role. The second experimental result is rheology of the dense suspension of soft gel and viscous fluid. Deformation experiment with concentric cylinders shows that the mixture system has yield strength at the intermediate gel fraction. In the stress state above the yield strength the region where deformation rate is large has low viscosity and its internal structure evolves to the state in heterogeneous distribution of viscosity. We would like to show that this nature is critical in the development of flow from homogeneous one to localized one.

Combined in-depth, 3D, en face imaging of the optic disc, optic disc pits and optic disc pit maculopathy using swept-source megahertz OCT at 1050 nm.

PubMed

Maertz, Josef; Kolb, Jan Philip; Klein, Thomas; Mohler, Kathrin J; Eibl, Matthias; Wieser, Wolfgang; Huber, Robert; Priglinger, Siegfried; Wolf, Armin

2018-02-01

To demonstrate papillary imaging of eyes with optic disc pits (ODP) or optic disc pit associated maculopathy (ODP-M) with ultrahigh-speed swept-source optical coherence tomography (SS-OCT) at 1.68 million A-scans/s. To generate 3D-renderings of the papillary area with 3D volume-reconstructions of the ODP and highly resolved en face images from a single densely-sampled megahertz-OCT (MHz-OCT) dataset for investigation of ODP-characteristics. A 1.68 MHz-prototype SS-MHz-OCT system at 1050 nm based on a Fourier-domain mode-locked laser was employed to acquire high-definition, 3D datasets with a dense sampling of 1600 × 1600 A-scans over a 45° field of view. Six eyes with ODPs, and two further eyes with glaucomatous alteration or without ocular pathology are presented. 3D-rendering of the deep papillary structures, virtual 3D-reconstructions of the ODPs and depth resolved isotropic en face images were generated using semiautomatic segmentation. 3D-rendering and en face imaging of the optic disc, ODPs and ODP associated pathologies showed a broad spectrum regarding ODP characteristics. Between individuals the shape of the ODP and the appending pathologies varied considerably. MHz-OCT en face imaging generates distinct top-view images of ODPs and ODP-M. MHz-OCT generates high resolution images of retinal pathologies associated with ODP-M and allows visualizing ODPs with depths of up to 2.7 mm. Different patterns of ODPs can be visualized in patients for the first time using 3D-reconstructions and co-registered high-definition en face images extracted from a single densely sampled 1050 nm megahertz-OCT (MHz-OCT) dataset. As the immediate vicinity to the SAS and the site of intrapapillary proliferation is located at the bottom of the ODP it is crucial to image the complete structure and the whole depth of ODPs. Especially in very deep pits, where non-swept-source OCT fails to reach the bottom, conventional swept-source devices and the MHz-OCT alike are feasible and beneficial methods to examine deep details of optic disc pathologies, while the MHz-OCT bears the advantage of an essentially swifter imaging process.

Landsat Time-Series Analysis Opens New Approaches for Regional Glacier Mapping

NASA Astrophysics Data System (ADS)

Winsvold, S. H.; Kääb, A.; Nuth, C.; Altena, B.

2016-12-01

The archive of Landsat satellite scenes is important for mapping of glaciers, especially as it represents the longest running and continuous satellite record of sufficient resolution to track glacier changes over time. Contributing optical sensors newly launched (Landsat 8 and Sentinel-2A) or upcoming in the near future (Sentinel-2B), will promote very high temporal resolution of optical satellite images especially in high-latitude regions. Because of the potential that lies within such near-future dense time series, methods for mapping glaciers from space should be revisited. We present application scenarios that utilize and explore dense time series of optical data for automatic mapping of glacier outlines and glacier facies. Throughout the season, glaciers display a temporal sequence of properties in optical reflection as the seasonal snow melts away, and glacier ice appears in the ablation area and firn in the accumulation area. In one application scenario presented we simulated potential future seasonal resolution using several years of Landsat 5TM/7ETM+ data, and found a sinusoidal evolution of the spectral reflectance for on-glacier pixels throughout a year. We believe this is because of the short wave infrared band and its sensitivity to snow grain size. The parameters retrieved from the fitting sinus curve can be used for glacier mapping purposes, thus we also found similar results using e.g. the mean of summer band ratio images. In individual optical mapping scenes, conditions will vary (e.g., snow, ice, and clouds) and will not be equally optimal over the entire scene. Using robust statistics on stacked pixels reveals a potential for synthesizing optimal mapping scenes from a temporal stack, as we present in a further application scenario. The dense time series available from satellite imagery will also promote multi-temporal and multi-sensor based analyses. The seasonal pattern of snow and ice on a glacier seen in the optical time series can in the summer season also be observed using radar backscatter series. Optical sensors reveal the reflective properties at the surface, while radar sensors may penetrate the surface revealing properties from a certain volume.In an outlook to this contribution we have explored how we can combine information from SAR and optical sensor systems for different purposes.

Deployment of a Testbed in a Brazilian Research Network using IPv6 and Optical Access Technologies

NASA Astrophysics Data System (ADS)

Martins, Luciano; Ferramola Pozzuto, João; Olimpio Tognolli, João; Chaves, Niudomar Siqueira De A.; Reggiani, Atilio Eduardo; Hortêncio, Claudio Antonio

2012-04-01

This article presents the implementation of a testbed and the experimental results obtained with it on the Brazilian Experimental Network of the government-sponsored "GIGA Project." The use of IPv6 integrated to current and emerging optical architectures and technologies, such as dense wavelength division multiplexing and 10-gigabit Ethernet on the core and gigabit capable passive optical network and optical distribution network on access, were tested. These protocols, architectures, and optical technologies are promising and part of a brand new worldwide technological scenario that has being fairly adopted in the networks of enterprises and providers of the world.

Fiber-Optic/Photoelastic Flow Sensors

NASA Technical Reports Server (NTRS)

Wesson, Laurence N.; Cabato, Nellie L.; Brooks, Edward F.

1995-01-01

Simple, rugged, lightweight transducers detect periodic vortices. Fiber-optic-coupled transducers developed to measure flows over wide dynamic ranges and over wide temperature ranges in severe environments. Used to measure flows of fuel in advanced aircraft engines. Feasibility of sensors demonstrated in tests of prototype sensor in water flowing at various temperatures and speeds. Particularly attractive for aircraft applications because optical fibers compact and make possible transmission of sensor signals at high rates with immunity from electromagnetic interference at suboptical frequencies. Sensors utilize optical-to-optical conversion via photoelastic effect.

Video Salient Object Detection via Fully Convolutional Networks.

PubMed

Wang, Wenguan; Shen, Jianbing; Shao, Ling

This paper proposes a deep learning model to efficiently detect salient regions in videos. It addresses two important issues: 1) deep video saliency model training with the absence of sufficiently large and pixel-wise annotated video data and 2) fast video saliency training and detection. The proposed deep video saliency network consists of two modules, for capturing the spatial and temporal saliency information, respectively. The dynamic saliency model, explicitly incorporating saliency estimates from the static saliency model, directly produces spatiotemporal saliency inference without time-consuming optical flow computation. We further propose a novel data augmentation technique that simulates video training data from existing annotated image data sets, which enables our network to learn diverse saliency information and prevents overfitting with the limited number of training videos. Leveraging our synthetic video data (150K video sequences) and real videos, our deep video saliency model successfully learns both spatial and temporal saliency cues, thus producing accurate spatiotemporal saliency estimate. We advance the state-of-the-art on the densely annotated video segmentation data set (MAE of .06) and the Freiburg-Berkeley Motion Segmentation data set (MAE of .07), and do so with much improved speed (2 fps with all steps).This paper proposes a deep learning model to efficiently detect salient regions in videos. It addresses two important issues: 1) deep video saliency model training with the absence of sufficiently large and pixel-wise annotated video data and 2) fast video saliency training and detection. The proposed deep video saliency network consists of two modules, for capturing the spatial and temporal saliency information, respectively. The dynamic saliency model, explicitly incorporating saliency estimates from the static saliency model, directly produces spatiotemporal saliency inference without time-consuming optical flow computation. We further propose a novel data augmentation technique that simulates video training data from existing annotated image data sets, which enables our network to learn diverse saliency information and prevents overfitting with the limited number of training videos. Leveraging our synthetic video data (150K video sequences) and real videos, our deep video saliency model successfully learns both spatial and temporal saliency cues, thus producing accurate spatiotemporal saliency estimate. We advance the state-of-the-art on the densely annotated video segmentation data set (MAE of .06) and the Freiburg-Berkeley Motion Segmentation data set (MAE of .07), and do so with much improved speed (2 fps with all steps).

Snow, Firn and Ice Heterogeneity within Larsen C Ice Shelf Revealed by Borehole Optical-televiewing

NASA Astrophysics Data System (ADS)

Hubbard, B. P.; Ashmore, D.; Luckman, A. J.; Kulessa, B.; Bevan, S. L.; Booth, A.; Kuipers Munneke, P.; O'Leary, M.; Sevestre, H.

2016-12-01

The north-western sector of Larsen C Ice Shelf (LCIS), Antarctica, hosts intermittent surface ponds resulting from intense melting, largely driven by warm föhn winds. The fate of such surface melt water is largely controlled by the shelf's firn structure, which also dictates shelf density (widely used to reconstruct ice shelf thickness from altimetric data) and preconditioning to hydrofracture. Here, we report a suite of five 90 m long optical-televiewer (OPTV) borehole logs from the northern and central regions of LCIS recorded in spring 2014 and 2015. For each OPTV log we reconstruct vertical variations in material density via an empirical OPTV log-ice core calibration, and apply a thresholding technique to estimate refrozen ice content within the firn column. These data are combined to define five material facies present within this sector of LCIS. The firn/ice column is anomalously dense at all five sites, having an overall mean depth-averaged density of 873 +/-32 kg m-3. In terms of spatial variability, our findings generally support previous estimates of firn air content fields and implied infiltration ice content. However, they also highlight finer-resolution complexity of ice shelf structure. For example, the most dense ice, with the lowest equivalent firn air content, is not located within the most westerly inlets, where firn-driven melting and ponding are most active, but some tens of km down-flow of these areas. We interpret this effect in terms of the inheritance nearer the grounding line of relatively low-density glacial ice (e.g., 52 m thick with a density of 852 +/-21 kg m-3 in northernmost Cabinet Inlet) advected from inland. This inherited ice forms one of five facies identified across the study region. These are, extending broadly downwards into the shelf, and with different representation at each site: local accumulation (F1); local accumulation hosting substantial infiltration ice, i.e. influenced by intense melt but insufficient to form surface ponds (F2); massive refrozen pond ice (F3); ice composed of both metamorphosed host ice and infiltration ice, the origin of which is difficult to determine due to the facies being located at depth within our logs (F4); and glacial ice inherited from up-flow (F5).

X-ray Emission from Supernovae in Dense Circumstellar Matter Environments: a Search for Collisionless Shocks

NASA Technical Reports Server (NTRS)

Ofek, E. O.; Fox, D.; Cenko, Stephen B.; Sullivan, M; Gnat, O.; Frail, D. A.; Horesh, A.; Corsi, A.; Quimby, R. M.; Gehrels, N.;

Treatment of dystrophic calcification on a silicone intraocular lens with pars plana vitrectomy

PubMed Central

Mehta, Nitish; Goldberg, Roger A; Shah, Chirag P

2014-01-01

Purpose Dense, vision-obscuring calcification on the posterior aspect of silicone intraocular lenses (IOLs) is often not amenable to neodymium:yttrium-aluminum-garnet capsulotomy, and, in prior reports, has required IOL exchange. We report the successful removal of dense calcium deposition on the posterior surface of a three-piece silicone lens using pars plana vitrectomy (PPV). Materials and methods A 23-gauge PPV was performed using the Stellaris® vitrectomy system. A light pipe was used to retroilluminate the IOL, and a dense fibrous tissue setting with a low cut-rate and high aspiration rate was able to clear the visual axis of the dystrophic calcification without damaging the IOL optic. Results Visual acuity improved from 20/100 to 20/25. Conclusion Small-gauge PPV may be utilized to remove dense dystrophic calcium deposits on the lens surface in lieu of IOL exchange. PMID:25045246

Test of a new heat-flow equation for dense-fluid shock waves.

PubMed

Holian, Brad Lee; Mareschal, Michel; Ravelo, Ramon

2010-09-21

Using a recently proposed equation for the heat-flux vector that goes beyond Fourier's Law of heat conduction, we model shockwave propagation in the dense Lennard-Jones fluid. Disequilibrium among the three components of temperature, namely, the difference between the kinetic temperature in the direction of a planar shock wave and those in the transverse directions, particularly in the region near the shock front, gives rise to a new transport (equilibration) mechanism not seen in usual one-dimensional heat-flow situations. The modification of the heat-flow equation was tested earlier for the case of strong shock waves in the ideal gas, which had been studied in the past and compared to Navier-Stokes-Fourier solutions. Now, the Lennard-Jones fluid, whose equation of state and transport properties have been determined from independent calculations, allows us to study the case where potential, as well as kinetic contributions are important. The new heat-flow treatment improves the agreement with nonequilibrium molecular-dynamics simulations under strong shock wave conditions, compared to Navier-Stokes.

Real-time optical flow estimation on a GPU for a skied-steered mobile robot

NASA Astrophysics Data System (ADS)

Kniaz, V. V.

2016-04-01

Accurate egomotion estimation is required for mobile robot navigation. Often the egomotion is estimated using optical flow algorithms. For an accurate estimation of optical flow most of modern algorithms require high memory resources and processor speed. However simple single-board computers that control the motion of the robot usually do not provide such resources. On the other hand, most of modern single-board computers are equipped with an embedded GPU that could be used in parallel with a CPU to improve the performance of the optical flow estimation algorithm. This paper presents a new Z-flow algorithm for efficient computation of an optical flow using an embedded GPU. The algorithm is based on the phase correlation optical flow estimation and provide a real-time performance on a low cost embedded GPU. The layered optical flow model is used. Layer segmentation is performed using graph-cut algorithm with a time derivative based energy function. Such approach makes the algorithm both fast and robust in low light and low texture conditions. The algorithm implementation for a Raspberry Pi Model B computer is discussed. For evaluation of the algorithm the computer was mounted on a Hercules mobile skied-steered robot equipped with a monocular camera. The evaluation was performed using a hardware-in-the-loop simulation and experiments with Hercules mobile robot. Also the algorithm was evaluated using KITTY Optical Flow 2015 dataset. The resulting endpoint error of the optical flow calculated with the developed algorithm was low enough for navigation of the robot along the desired trajectory.

Dense matter at RHIC: Anisotropic flow

DOE PAGES

Voloshin, S. A.

2005-02-01

In this talk I discuss recent results on elliptic flow in Au+Au collisions at RHIC and how these results help us to understand the properties and evolution dynamics of the system created in such collisions. In particular, I discuss if and how the elliptic flow results obtained at RHIC indicate the system thermalization, deconfinement, and how much it tells us about the hadronization process.

Enterprise virtual private network (VPN) with dense wavelength division multiplexing (DWDM) design

NASA Astrophysics Data System (ADS)

Carranza, Aparicio

An innovative computer simulation and modeling tool for metropolitan area optical data communication networks is presented. These models address the unique requirements of Virtual Private Networks for enterprise data centers, which may comprise a mixture of protocols including ESCON, FICON, Fibre Channel, Sysplex protocols (ETR, CLO, ISC); and other links interconnected over dark fiber using Dense Wavelength Division Multiplexing (DWDM). Our models have the capability of designing a network with minimal inputs; to compute optical link budgets; suggest alternative configurations; and also optimize the design based on user-defined performance metrics. The models make use of Time Division Multiplexing (TDM) wherever possible for lower data rate traffics. Simulation results for several configurations are presented and they have been validated by means of experiments conducted on the IBM enterprise network testbed in Poughkeepsie, N.Y.

Preliminary research on flow rate and free surface of the accelerator driven subcritical system gravity-driven dense granular-flow target

PubMed Central

Li, Xiaodong; Wan, Jiangfeng; Zhang, Sheng; Lin, Ping; Zhang, Yanshi; Yang, Guanghui; Wang, Mengke; Duan, Wenshan; Sun, Jian’an

2017-01-01

A spallation target is one of the three core parts of the accelerator driven subcritical system (ADS), which has already been investigated for decades. Recently, a gravity-driven Dense Granular-flow Target (DGT) is proposed, which consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. The research on the flow rate and free surface are important for the design of the target whether in Heavy Liquid Metal (HLM) targets or the DGT. In this paper, the relations of flow rate and the geometry of the DGT are investigated. Simulations based on the discrete element method (DEM) implementing on Graphics Processing Units (GPUs) and experiments are both performed. It is found that the existence of an internal pipe doesn’t influence the flow rate when the distance from the bottom of the pipe to orifice is large enough even in a larger system. Meanwhile, snapshots of the free surface formed just below the beam pipe are given. It is observed that the free surface is stable over time. The entire research is meaningful for the design of DGT. PMID:29095910

High frequency flow-structural interaction in dense subsonic fluids

NASA Technical Reports Server (NTRS)

Liu, Baw-Lin; Ofarrell, J. M.

1995-01-01

Prediction of the detailed dynamic behavior in rocket propellant feed systems and engines and other such high-energy fluid systems requires precise analysis to assure structural performance. Designs sometimes require placement of bluff bodies in a flow passage. Additionally, there are flexibilities in ducts, liners, and piping systems. A design handbook and interactive data base have been developed for assessing flow/structural interactions to be used as a tool in design and development, to evaluate applicable geometries before problems develop, or to eliminate or minimize problems with existing hardware. This is a compilation of analytical/empirical data and techniques to evaluate detailed dynamic characteristics of both the fluid and structures. These techniques have direct applicability to rocket engine internal flow passages, hot gas drive systems, and vehicle propellant feed systems. Organization of the handbook is by basic geometries for estimating Strouhal numbers, added mass effects, mode shapes for various end constraints, critical onset flow conditions, and possible structural response amplitudes. Emphasis is on dense fluids and high structural loading potential for fatigue at low subsonic flow speeds where high-frequency excitations are possible. Avoidance and corrective measure illustrations are presented together with analytical curve fits for predictions compiled from a comprehensive data base.

Preliminary research on flow rate and free surface of the accelerator driven subcritical system gravity-driven dense granular-flow target.

PubMed

Li, Xiaodong; Wan, Jiangfeng; Zhang, Sheng; Lin, Ping; Zhang, Yanshi; Yang, Guanghui; Wang, Mengke; Duan, Wenshan; Sun, Jian'an; Yang, Lei

2017-01-01

A spallation target is one of the three core parts of the accelerator driven subcritical system (ADS), which has already been investigated for decades. Recently, a gravity-driven Dense Granular-flow Target (DGT) is proposed, which consists of a cylindrical hopper and an internal coaxial cylindrical beam pipe. The research on the flow rate and free surface are important for the design of the target whether in Heavy Liquid Metal (HLM) targets or the DGT. In this paper, the relations of flow rate and the geometry of the DGT are investigated. Simulations based on the discrete element method (DEM) implementing on Graphics Processing Units (GPUs) and experiments are both performed. It is found that the existence of an internal pipe doesn't influence the flow rate when the distance from the bottom of the pipe to orifice is large enough even in a larger system. Meanwhile, snapshots of the free surface formed just below the beam pipe are given. It is observed that the free surface is stable over time. The entire research is meaningful for the design of DGT.

Modified kinetic theory applied to the shear flows of granular materials

DOE PAGES

Duan, Yifei; Feng, Zhi -Gang; Michaelides, Efstathios E.; ...

2017-04-11

Here, granular materials are characterized by large collections of discrete particles, where the particle-particle interactions are significantly more important than the particle-fluid interactions. The current kinetic theory captures fairly accurately the granular flow behavior in the dilute case, when only binary interactions are significant, but is not accurate at all in the dense flow regime, where multi-particle interactions and contacts must be modeled. To improve the kinetic theory results for granular flows in the dense flow regime, we propose a Modified Kinetic Theory (MKT) model that utilizes the contact duration or cut-off time to account for the complex particle-particle interactionsmore » in the dense regime. The contact duration model, also called TC model, is originally proposed by Luding and McNamara to solve the inelastic collapse issue existing in the Inelastic Hard Sphere (IHS) model. This model defines a cut-off time t c such that dissipation is not counted if the time between two consecutive contacts is less than t c. As shown in their study, the use of a cut-off time t c can also reduce the dissipation during multi-particle contacts. In this paper we relate the TC model with the Discrete Element Method (DEM) by choosing the cut-off time t c to be the duration of contact calculated from the linear-spring-dashpot soft-sphere model of the DEM. We examine two types of granular flows: simple shear flow and the plane shear flow, and compare the results of the classical Kinetic Theory (KT) model, the present MKT model, and the DEM model. Here, we show that the MKT model entails a significant improvement over the KT model for simple shear flows at inertial regimes. With the MKT model the calculations are close to the DEM results at solid fractions as high as 0.57. Even for the plane shear flows, where shear rate and solid fraction are inhomogeneous, the results of the MKT model agree very well with the DEM results.« less

Modified kinetic theory applied to the shear flows of granular materials

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

Duan, Yifei; Feng, Zhi -Gang; Michaelides, Efstathios E.

Here, granular materials are characterized by large collections of discrete particles, where the particle-particle interactions are significantly more important than the particle-fluid interactions. The current kinetic theory captures fairly accurately the granular flow behavior in the dilute case, when only binary interactions are significant, but is not accurate at all in the dense flow regime, where multi-particle interactions and contacts must be modeled. To improve the kinetic theory results for granular flows in the dense flow regime, we propose a Modified Kinetic Theory (MKT) model that utilizes the contact duration or cut-off time to account for the complex particle-particle interactionsmore » in the dense regime. The contact duration model, also called TC model, is originally proposed by Luding and McNamara to solve the inelastic collapse issue existing in the Inelastic Hard Sphere (IHS) model. This model defines a cut-off time t c such that dissipation is not counted if the time between two consecutive contacts is less than t c. As shown in their study, the use of a cut-off time t c can also reduce the dissipation during multi-particle contacts. In this paper we relate the TC model with the Discrete Element Method (DEM) by choosing the cut-off time t c to be the duration of contact calculated from the linear-spring-dashpot soft-sphere model of the DEM. We examine two types of granular flows: simple shear flow and the plane shear flow, and compare the results of the classical Kinetic Theory (KT) model, the present MKT model, and the DEM model. Here, we show that the MKT model entails a significant improvement over the KT model for simple shear flows at inertial regimes. With the MKT model the calculations are close to the DEM results at solid fractions as high as 0.57. Even for the plane shear flows, where shear rate and solid fraction are inhomogeneous, the results of the MKT model agree very well with the DEM results.« less

Optical Processing.

DTIC Science & Technology

1986-06-01

Further improvements are clearly necessary. 2.2.2 Future Work It would appear that transverse cross-talk is a serious problem in thermally based bistable... manufacturing purposes except under an agreement or with the consent in writing of Ferranti pic and then only on the condition that this notice is...applications which might: (a) appear to benefit from the advantages offered by optical processing (such as large parallelism and dense global inter

An Algorithm for Pedestrian Detection in Multispectral Image Sequences

NASA Astrophysics Data System (ADS)

Kniaz, V. V.; Fedorenko, V. V.

2017-05-01

The growing interest for self-driving cars provides a demand for scene understanding and obstacle detection algorithms. One of the most challenging problems in this field is the problem of pedestrian detection. Main difficulties arise from a diverse appearances of pedestrians. Poor visibility conditions such as fog and low light conditions also significantly decrease the quality of pedestrian detection. This paper presents a new optical flow based algorithm BipedDetet that provides robust pedestrian detection on a single-borad computer. The algorithm is based on the idea of simplified Kalman filtering suitable for realization on modern single-board computers. To detect a pedestrian a synthetic optical flow of the scene without pedestrians is generated using slanted-plane model. The estimate of a real optical flow is generated using a multispectral image sequence. The difference of the synthetic optical flow and the real optical flow provides the optical flow induced by pedestrians. The final detection of pedestrians is done by the segmentation of the difference of optical flows. To evaluate the BipedDetect algorithm a multispectral dataset was collected using a mobile robot.

Optical tomography of fluorophores in dense scattering media based on ultrasound-enhanced chemiluminescence

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

Kobayashi, Masaki, E-mail: masaki@tohtech.ac.jp; Kikuchi, Naoto; Sato, Akihiro

This letter proposes and demonstrates ultrasound-combined optical imaging in dense scattering media. A peroxyoxalate chemiluminescence system that includes fluorophores to chemically excite the pigment is stimulated by ultrasound irradiation with power of less than 0.14 W/cm{sup 2}. Using focused ultrasound, the chemiluminescence is selectively spatially enhanced, which leads to imaging of the pigment when embedded in a light-scattering medium via scanning of the focal point. The ultrasonically enhanced intensity of the chemiluminescence depends on the base intensity of the chemiluminescence without the applied ultrasound irradiation, which thereby enables quantitative determination of the fluorophore concentration. The authors demonstrate the potential of thismore » method to resolve chemiluminescent targets in a dense scattering medium that is comparable to biological tissue. An image was acquired of a chemiluminescent target that included indocyanine green as the fluorophore embedded at a depth of 20 mm in an Intralipid-10% 200 ml/l solution scattering medium (the reduced scattering coefficient was estimated to be approximately 1.3 mm{sup −1}), indicating the potential for expansion of this technique for use in biological applications.« less

A framework for estimating potential fluid flow from digital imagery

NASA Astrophysics Data System (ADS)

Luttman, Aaron; Bollt, Erik M.; Basnayake, Ranil; Kramer, Sean; Tufillaro, Nicholas B.

2013-09-01

Given image data of a fluid flow, the flow field, ⟨u,v⟩, governing the evolution of the system can be estimated using a variational approach to optical flow. Assuming that the flow field governing the advection is the symplectic gradient of a stream function or the gradient of a potential function—both falling under the category of a potential flow—it is natural to re-frame the optical flow problem to reconstruct the stream or potential function directly rather than the components of the flow individually. There are several advantages to this framework. Minimizing a functional based on the stream or potential function rather than based on the components of the flow will ensure that the computed flow is a potential flow. Next, this approach allows a more natural method for imposing scientific priors on the computed flow, via regularization of the optical flow functional. Also, this paradigm shift gives a framework—rather than an algorithm—and can be applied to nearly any existing variational optical flow technique. In this work, we develop the mathematical formulation of the potential optical flow framework and demonstrate the technique on synthetic flows that represent important dynamics for mass transport in fluid flows, as well as a flow generated by a satellite data-verified ocean model of temperature transport.

Longitudinal optical monitoring of blood flow in breast tumors during neoadjuvant chemotherapy

NASA Astrophysics Data System (ADS)

Cochran, J. M.; Chung, S. H.; Leproux, A.; Baker, W. B.; Busch, D. R.; DeMichele, A. M.; Tchou, J.; Tromberg, B. J.; Yodh, A. G.

2017-06-01

We measure tissue blood flow markers in breast tumors during neoadjuvant chemotherapy and investigate their correlation to pathologic complete response in a pilot longitudinal patient study (n  =  4). Tumor blood flow is quantified optically by diffuse correlation spectroscopy (DCS), and tissue optical properties, blood oxygen saturation, and total hemoglobin concentration are derived from concurrent diffuse optical spectroscopic imaging (DOSI). The study represents the first longitudinal DCS measurement of neoadjuvant chemotherapy in humans over the entire course of treatment; it therefore offers a first correlation between DCS flow indices and pathologic complete response. The use of absolute optical properties measured by DOSI facilitates significant improvement of DCS blood flow calculation, which typically assumes optical properties based on literature values. Additionally, the combination of the DCS blood flow index and the tissue oxygen saturation from DOSI permits investigation of tissue oxygen metabolism. Pilot results from four patients suggest that lower blood flow in the lesion-bearing breast is correlated with pathologic complete response. Both absolute lesion blood flow and lesion flow relative to the contralateral breast exhibit potential for characterization of pathological response. This initial demonstration of the combined optical approach for chemotherapy monitoring provides incentive for more comprehensive studies in the future and can help power those investigations.

Implementation and Re nement of a Comprehensive Model for Dense Granular Flows

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

Sundaresan, Sankaran

2015-09-30

Dense granular ows are ubiquitous in both natural and industrial processes. They manifest three di erent ow regimes, each exhibiting its own dependence on solids volume fraction, shear rate, and particle-level properties. This research project sought to develop continuum rheological models for dense granular ows that bridges multiple regimes of ow, implement them in open-source platforms for gas-particle ows and perform test simulations. The rst phase of the research covered in this project involved implementation of a steady- shear rheological model that bridges quasi-static, intermediate and inertial regimes of ow into MFIX (Multiphase Flow with Interphase eXchanges - a generalmore » purpose computer code developed at the National Energy Technology Laboratory). MFIX simulations of dense granular ows in hourglass-shaped hopper were then performed as test examples. The second phase focused on formulation of a modi ed kinetic theory for frictional particles that can be used over a wider range of particle volume fractions and also apply for dynamic, multi- dimensional ow conditions. To guide this work, simulations of simple shear ows of identical mono-disperse spheres were also performed using the discrete element method. The third phase of this project sought to develop and implement a more rigorous treatment of boundary e ects. Towards this end, simulations of simple shear ows of identical mono-disperse spheres con ned between parallel plates were performed and analyzed to formulate compact wall boundary conditions that can be used for dense frictional ows at at frictional boundaries. The fourth phase explored the role of modest levels of cohesive interactions between particles on the dense phase rheology. The nal phase of this project focused on implementation and testing of the modi ed kinetic theory in MFIX and running bin-discharge simulations as test examples.« less

Making Optic Flow Robust to Dynamic Lighting Conditions for Real-Time Operation

DTIC Science & Technology

2016-03-17

ARL-TR-7629 ● MAR 2016 US Army Research Laboratory Making Optic Flow Robust to Dynamic Lighting Conditions for Real-Time...ARL-TR-7629 ● MAR 2016 US Army Research Laboratory Making Optic Flow Robust to Dynamic Lighting Conditions for Real-Time Operation...SUBTITLE Making Optic Flow Robust to Dynamic Lighting Conditions for Real-Time Operation 5a. CONTRACT NUMBER 5b. GRANT NUMBER 5c. PROGRAM ELEMENT

Onset of sediment transport is a continuous transition driven by fluid shear and granular creep.

PubMed

Houssais, Morgane; Ortiz, Carlos P; Durian, Douglas J; Jerolmack, Douglas J

2015-03-09

Fluid-sheared granular transport sculpts landscapes and undermines infrastructure, yet predicting the onset of sediment transport remains notoriously unreliable. For almost a century, this onset has been treated as a discontinuous transition at which hydrodynamic forces overcome gravity-loaded grain-grain friction. Using a custom laminar-shear flume to image slow granular dynamics deep into the bed, here we find that the onset is instead a continuous transition from creeping to granular flow. This transition occurs inside the dense granular bed at a critical viscous number, similar to granular flows and colloidal suspensions and inconsistent with hydrodynamic frameworks. We propose a new phase diagram for sediment transport, where 'bed load' is a dense granular flow bounded by creep below and suspension above. Creep is characteristic of disordered solids and reminiscent of soil diffusion on hillslopes. Results provide new predictions for the onset and dynamics of sediment transport that challenge existing models.

Fabrication of dense wavelength division multiplexing filters with large useful area

NASA Astrophysics Data System (ADS)

Lee, Cheng-Chung; Chen, Sheng-Hui; Hsu, Jin-Cherng; Kuo, Chien-Cheng

2006-08-01

Dense Wavelength Division Multiplexers (DWDM), a kind of narrow band-pass filter, are extremely sensitive to the optical thickness error in each composite layer. Therefore to have a large useful coating area is extreme difficult because of the uniformity problem. To enlarge the useful coating area it is necessary to improve their design and their fabrication. In this study, we discuss how the tooling factors at different positions and for different materials are related to the optical performance of the design. 100GHz DWDM filters were fabricated by E-gun evaporation with ion-assisted deposition (IAD). To improve the coating uniformity, an analysis technique called shaping tooling factor (STF) was used to analyze the deviation of the optical thickness in different materials so as to enlarge the useful coating area. Also a technique of etching the deposited layers with oxygen ions was introduced. When the above techniques were applied in the fabrication of 100 GHz DWDM filters, the uniformity was better than +/-0.002% over an area of 72 mm in diameter and better than +/-0.0006% over 20mm in diameter.

Optical and microphysical parameters of dense stratocumulus clouds during mission 206 of EUCREX '94 as retrieved from measurements made with the airborne lidar LEANDRE 1

NASA Astrophysics Data System (ADS)

Pelon, J.; Flamant, C.; Trouillet, V.; Flamant, P. H.

Cloud parameters derived from measurements performed with the airborne backscatter lidar LEANDRE 1 during mission 206 of the EUCREX '94 campaign are reported. A new method has been developed to retrieve the extinction coefficient at the top of the dense stratocumulus deck under scrutiny during this mission. The largest extinction values are found to be related to the highest cloud top altitude revealing the small-scale structure of vertical motions within the stratocumulus field. Cloud optical depth (COD) is estimated from extinction retrievals, as well as cloud top and cloud base altitude using nadir and zenith lidar observations, respectively. Lidar-derived CODs are compared with CODs deduced from radiometric measurements made onboard the French research aircraft Avion de Recherche Atmosphérique et de Télédétection (ARAT/F27). A fair agreement is obtained (within 20%) for COD's larger than 10. Our results show the potential of lidar measurements to analyze cloud properties at optical depths larger than 5.

Excitation of atoms and ions in plasmas by ultra-short electromagnetic pulses

NASA Astrophysics Data System (ADS)

Astapenko, V. A.; Sakhno, S. V.; Svita, S. Yu; Lisitsa, V. S.

2017-02-01

The problem of atoms and ions diagnostics in rarefied and dense plasmas by ultrashort laser pulses (USP) is under consideration. The application of USP provides: 1) excitation from ground states due to their carrier frequency high enough, 2) penetration into optically dense media due to short pulses duration. The excitation from ground atomic states increases sharply populations of excited atomic states in contrast with standard laser induced fluorescence spectroscopy based on radiative transitions between excited atomic states. New broadening parameter in radiation absorption, namely inverse pulse duration time 1/τ appears in addition to standard line-shape width in the profile G(ω). The Lyman-beta absorption spectra for USP are calculated for Holtsmark static broadening mechanism. Excitation of highly charged H-like ions in hot plasmas is described by both Gaussian shapes for Doppler broadening and pulse spectrum resulting in analytical absorption line-shape. USP penetration into optically thick media and corresponding excitation probability are calculated. It is shown a great effect of USP duration on excitation probabilities in optically thick media. The typical situations for plasma diagnostics by USP are discussed in details.

Optical response of nanostructured metal/dielectric composites and multilayers

NASA Astrophysics Data System (ADS)

Smith, Geoffrey B.; Maaroof, Abbas I.; Allan, Rodney S.; Schelm, Stefan; Anstis, Geoffrey R.; Cortie, Michael B.

2004-08-01

The homogeneous optical response in conducting nanostructured layers, and in insulating layers containing dense arrays of self assembled conducting nanoparticles separated by organic linkers, is examined experimentally through their effective complex indices (n*, k*). Classical effective medium models, modified to account for the 3-phase nanostructure, are shown to explain (n*, k*) in dense particulate systems but not inhomogeneous layers with macroscopic conductance for which a different approach to homogenisation is discussed. (n*, k*) data on thin granular metal films, thin mesoporous gold, and on thin metal layers containing ordered arrays of voids, is linked to properties of the surface plasmon states which span the nanostructured film. Coupling between evanescent waves at either surface counterbalanced by electron scattering losses must be considered. Virtual bound states for resonant photons result, with the associated transit delay leading to a large rise in n* in many nanostructures. Overcoating n-Ag with alumina is shown to alter (n*, k*) through its impact on the SP coupling. In contrast to classical optical homogenisation, effective indices depend on film thickness. Supporting high resolution SEM images are presented.

A two-phase flow model for submarine granular flows: With an application to collapse of deeply-submerged granular columns

NASA Astrophysics Data System (ADS)

Lee, Cheng-Hsien; Huang, Zhenhua

2018-05-01

The collapse process of a submerged granular column is strongly affected by its initial packing. Previous models for particle response time, which is used to quantify the drag force between the solid and liquid phases in rheology-based two-phase flow models, have difficulty in simulating the collapse process of granular columns with different initial concentrations (initial packing conditions). This study introduces a new model for particle response time, which enables us to satisfactorily model the drag force between the two phases for a wide range of volume concentration. The present model can give satisfactory results for both loose and dense packing conditions. The numerical results have shown that (i) the initial packing affects the occurrence of contractancy/diltancy behavior during the collapse process, (ii) the general buoyancy and drag force are strongly affected by the initial packing through contractancy and diltancy, and (iii) the general buoyancy and drag force can destabilize the granular material in loose packing condition but stabilize the granular material in dense packing condition. The results have shown that the collapse process of a densely-packed granular column is more sensitive to particle response time than that of a loosely-packed granular column.

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

Renaut, R.W.; Tiercelin, J.J.

Lake Bogoria is a meromictic, saline (90 g/l TDS), alkaline (pH: 10.3) lake with Na-CO[sub 3]-Cl waters, located in a narrow half-graben in the central Kenya Rift. It is fed by hot springs, direct precipitation, and a series of ephemeral streams that discharge into the lake via small deltas and fan-deltas. Examination of the exposed deltas and >50 short cores from the lake floor, have revealed a wide range of deltaic and prodeltaic sediments, including turbidites and subaqueous debris-flow deposits. Studies of 3 long cores and the exposed delta stratigraphy have shown how the style of deltaic sedimentation has respondedmore » to environmental changes during the last 30,000 years. During humid periods when lake level is high the lake waters are fresher and less dense. Theoretically, high sediment yield and more constant discharge may promote underflow (hyperpycnal flow), generating low-density turbidity currents. In contrast, during low stages with dense brine, the less dense, inflowing waters carry fine sediment plumes toward the center of the lake where they settle from suspension (hypopycnal flow). Although applicable as a general model, the sediment record shows that reality is more complex. Variations in meromixis and level of the chemocline, together with local and temporal differences in sediment yield and discharge, may permit density flows even when the lake is under a predominant hypopycnal regime. During periods of aridity when sodium carbonate evaporites were forming, exposed delta plains were subject to desiccation with local development of calcrete and zeolitic paleosols.« less

On the star-forming ability of Molecular Clouds

NASA Astrophysics Data System (ADS)

Anathpindika, S.; Burkert, A.; Kuiper, R.

2018-02-01

The star-forming ability of a molecular cloud depends on the fraction of gas it can cycle into the dense-phase. Consequently, one of the crucial questions in reconciling star formation in clouds is to understand the factors that control this process. While it is widely accepted that the variation in ambient conditions can alter significantly the ability of a cloud to spawn stars, the observed variation in the star-formation rate in nearby clouds that experience similar ambient conditions, presents an interesting question. In this work, we attempted to reconcile this variation within the paradigm of colliding flows. To this end we develop self-gravitating, hydrodynamic realizations of identical flows, but allowed to collide off-centre. Typical observational diagnostics such as the gas-velocity dispersion, the fraction of dense-gas, the column density distribution (N-PDF), the distribution of gas mass as a function of K-band extinction and the strength of compressional/solenoidal modes in the post-collision cloud were deduced for different choices of the impact parameter of collision. We find that a strongly sheared cloud is terribly inefficient in cycling gas into the dense phase and that such a cloud can possibly reconcile the sluggish nature of star formation reported for some clouds. Within the paradigm of cloud formation via colliding flows this is possible in case of flows colliding with a relatively large impact parameter. We conclude that compressional modes - though probably essential - are insufficient to ensure a relatively higher star-formation efficiency in a cloud.

How humans use visual optic flow to regulate stepping during walking.

PubMed

Salinas, Mandy M; Wilken, Jason M; Dingwell, Jonathan B

2017-09-01

Humans use visual optic flow to regulate average walking speed. Among many possible strategies available, healthy humans walking on motorized treadmills allow fluctuations in stride length (L n ) and stride time (T n ) to persist across multiple consecutive strides, but rapidly correct deviations in stride speed (S n =L n /T n ) at each successive stride, n. Several experiments verified this stepping strategy when participants walked with no optic flow. This study determined how removing or systematically altering optic flow influenced peoples' stride-to-stride stepping control strategies. Participants walked on a treadmill with a virtual reality (VR) scene projected onto a 3m tall, 180° semi-cylindrical screen in front of the treadmill. Five conditions were tested: blank screen ("BLANK"), static scene ("STATIC"), or moving scene with optic flow speed slower than ("SLOW"), matched to ("MATCH"), or faster than ("FAST") walking speed. Participants took shorter and faster strides and demonstrated increased stepping variability during the BLANK condition compared to the other conditions. Thus, when visual information was removed, individuals appeared to walk more cautiously. Optic flow influenced both how quickly humans corrected stride speed deviations and how successful they were at enacting this strategy to try to maintain approximately constant speed at each stride. These results were consistent with Weber's law: healthy adults more-rapidly corrected stride speed deviations in a no optic flow condition (the lower intensity stimuli) compared to contexts with non-zero optic flow. These results demonstrate how the temporal characteristics of optic flow influence ability to correct speed fluctuations during walking. Copyright © 2017 Elsevier B.V. All rights reserved.

Empirical study of a unidirectional dense crowd during a real mass event

NASA Astrophysics Data System (ADS)

Zhang, X. L.; Weng, W. G.; Yuan, H. Y.; Chen, J. G.

2013-06-01

Many tragic crowd disasters have happened across the world in recent years, such as the Phnom Penh stampede in Cambodia, crowd disaster in Mina/Makkah, and the Love Parade disaster in Germany, showing that management of mass events is a tough task for organizers. The study of unidirectional flow, one of the most common forms of motion in mass activities, is essential for safe organization of such events. In this paper, the properties of unidirectional flow in a crowded street during a real mass event in China are quantitatively investigated with sophisticated active infrared counters and an image processing method. A complete dataset of flow rates during the whole celebration is recorded, and a time series analysis gives new insight into such activities. The spatial analysis shows that the velocity and density of the crowd are inhomogeneous due to the boundary effect, whereas the flux is uniform. The estimated capacity of the street indicates that the maximum flow rate under normal condition should be between 1.73 and 1.98 /m/s, which is in good agreement with several field studies available in the existing literature. In consideration of the significant deviation among different studies, fundamental diagrams of dense crowds are also re-verified, and the results here are consistent with those from other field studies of unidirectional flow, but different from the bidirectional and experimental results. It is suggested that the data from multidirectional flow and experiments cannot be directly applied to unidirectional dense flow in a real mass event. The results also imply that the density of a similar unidirectional marching crowd should be controlled to be under 5 /m2, which can produce optimal efficiency and have more possibility to ensure safety. The field study data given here provide a good example of a database for crowd studies.

All optical OFDM transmission for passive optical networks

NASA Astrophysics Data System (ADS)

Kachare, Nitin; Ashik T., J.; Bai, K. Kalyani; Kumar, D. Sriram

2017-06-01

This paper demonstrates the idea of data transmission at a very higher rate (Tbits/s) through optical fibers in a passive optical network using the most efficient data transmission technique widely used in wireless communication that is orthogonal frequency division multiplexing. With an increase in internet users, data traffic has also increased significantly and the current dense wavelength division multiplexing (DWDM) systems may not support the next generation passive optical networks (PONs) requirements. The approach discussed in this paper allows to increase the downstream data rate per user and extend the standard single-mode fiber reach for future long-haul applications. All-optical OFDM is a promising solution for terabit per second capable single wavelength transmission, with high spectral efficiency and high tolerance to chromatic dispersion.

Mapping the Sedna-Lavinia Region of Venus

NASA Technical Reports Server (NTRS)

Campbell, Bruce A.; Anderson, Ross F.

2008-01-01

Geologic mapping of Venus at 1:5 M scale has shown in great detail the flow complexes of volcanoes, coronae, and shield fields, and the varying structural patterns that differentiate tesserae from corona rims and isolated patches of densely lineated terrain. In most cases, however, the lower-elevation plains between the higher-standing landforms are discriminated only on the basis of potentially secondary features such as late-stage lava flooding or tectonic overprinting. This result, in which volcanoes and tesserae appear as "islands in the sea," places weak constraints on the relative age of large upland regions and the nature of the basement terrain. In this work, we focus on the spatial distribution and topography of densely lineated and tessera units over a large region of Venus, and their relationship to apparently later corona and shield flow complexes. The goal is to identify likely connections between patches of deformed terrain that suggest earlier features of regional extent, and to compare the topography of linked patches with other such clusters as a guide to whether they form larger tracts beneath the plains. Mapping Approach. We are mapping the region from 57S to 57N, 300E-60E. Since the 1:5 M quadrangles emphasize detail of tessera structure and corona/edifice flows, we simply adopt the outlines of these features as they relate to the outcrops of either "densely lineated terrain" or tessera (Fig. 1). The densely lineated material is mapped in many quadrangles based on pervasive structural deformation, typically with a single major axis (in contrast to the overlapping orthogonal patterns on tesserae). This unit definition is often extended to include material of corona rims. We do not at present differentiate between plains units, since earlier efforts show that their most defining attributes may be secondary to the original emplacement (e.g., lobate or sheet-like flooding by thin flow units, tectonic patterns related to regional and localized stress regimes) [1].

Harbor seals (Phoca vitulina) can perceive optic flow under water.

PubMed

Gläser, Nele; Mauck, Björn; Kandil, Farid I; Lappe, Markus; Dehnhardt, Guido; Hanke, Frederike D

2014-01-01

Optic flow, the pattern of apparent motion elicited on the retina during movement, has been demonstrated to be widely used by animals living in the aerial habitat, whereas underwater optic flow has not been intensively studied so far. However optic flow would also provide aquatic animals with valuable information about their own movement relative to the environment; even under conditions in which vision is generally thought to be drastically impaired, e. g. in turbid waters. Here, we tested underwater optic flow perception for the first time in a semi-aquatic mammal, the harbor seal, by simulating a forward movement on a straight path through a cloud of dots on an underwater projection. The translatory motion pattern expanded radially out of a singular point along the direction of heading, the focus of expansion. We assessed the seal's accuracy in determining the simulated heading in a task, in which the seal had to judge whether a cross superimposed on the flow field was deviating from or congruent with the actual focus of expansion. The seal perceived optic flow and determined deviations from the simulated heading with a threshold of 0.6 deg of visual angle. Optic flow is thus a source of information seals, fish and most likely aquatic species in general may rely on for e. g. controlling locomotion and orientation under water. This leads to the notion that optic flow seems to be a tool universally used by any moving organism possessing eyes.

Harbor Seals (Phoca vitulina) Can Perceive Optic Flow under Water

PubMed Central

Gläser, Nele; Mauck, Björn; Kandil, Farid I.; Lappe, Markus; Dehnhardt, Guido; Hanke, Frederike D.

2014-01-01

Optic flow, the pattern of apparent motion elicited on the retina during movement, has been demonstrated to be widely used by animals living in the aerial habitat, whereas underwater optic flow has not been intensively studied so far. However optic flow would also provide aquatic animals with valuable information about their own movement relative to the environment; even under conditions in which vision is generally thought to be drastically impaired, e. g. in turbid waters. Here, we tested underwater optic flow perception for the first time in a semi-aquatic mammal, the harbor seal, by simulating a forward movement on a straight path through a cloud of dots on an underwater projection. The translatory motion pattern expanded radially out of a singular point along the direction of heading, the focus of expansion. We assessed the seal's accuracy in determining the simulated heading in a task, in which the seal had to judge whether a cross superimposed on the flow field was deviating from or congruent with the actual focus of expansion. The seal perceived optic flow and determined deviations from the simulated heading with a threshold of 0.6 deg of visual angle. Optic flow is thus a source of information seals, fish and most likely aquatic species in general may rely on for e. g. controlling locomotion and orientation under water. This leads to the notion that optic flow seems to be a tool universally used by any moving organism possessing eyes. PMID:25058490

Bumblebees measure optic flow for position and speed control flexibly within the frontal visual field.

PubMed

Linander, Nellie; Dacke, Marie; Baird, Emily

2015-04-01

When flying through narrow spaces, insects control their position by balancing the magnitude of apparent image motion (optic flow) experienced in each eye and their speed by holding this value about a desired set point. Previously, it has been shown that when bumblebees encounter sudden changes in the proximity to nearby surfaces - as indicated by a change in the magnitude of optic flow on each side of the visual field - they adjust their flight speed well before the change, suggesting that they measure optic flow for speed control at low visual angles in the frontal visual field. Here, we investigated the effect that sudden changes in the magnitude of translational optic flow have on both position and speed control in bumblebees if these changes are asymmetrical; that is, if they occur only on one side of the visual field. Our results reveal that the visual region over which bumblebees respond to optic flow cues for flight control is not dictated by a set viewing angle. Instead, bumblebees appear to use the maximum magnitude of translational optic flow experienced in the frontal visual field. This strategy ensures that bumblebees use the translational optic flow generated by the nearest obstacles - that is, those with which they have the highest risk of colliding - to control flight. © 2015. Published by The Company of Biologists Ltd.

Feasibility of flow studies at NICA/MPD

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

Geraksiev, N. S., E-mail: nikolay.geraksiev@gmail.com; Collaboration: MPD Collaboration

In the light of recent developments in heavy ion physic, anisotropic flow measurements play a key role in a better understanding of the hot and dense barionic matter. In the presented article a short introduction to the proposed NICA/MPD project is given, as well as a brief description of the event-plane method used to estimate the elliptic flow of reconstructed and identified hadrons (p, π, Λ)

The perfect ash-storm: large-scale Pyroclastic Density Current experiments reveal highly mobile, self-fluidising and air-cushioned flow transport regime

NASA Astrophysics Data System (ADS)

Lube, G.; Cronin, S. J.; Breard, E.; Valentine, G.; Bursik, M. I.; Hort, M. K.; Freundt, A.

2013-12-01

We report on the first systematic series of large-scale Pyroclastic Density Current (PDC) experiments using the New Zealand PDC Generator, a novel international research facility in Physical Volcanology recently commissioned at Massey University. Repeatable highly energetic and hot PDCs are synthesized by the controlled ';eruption column-collapse' of up to 3500 kg of homogenously aerated Taupo ignimbrite material from a 15 m-elevated hopper onto an instrumented inclined flume. At discharge rates between 250-1300 kg/s and low- to moderate gas injection rates (yielding initial solids concentration of 15-70 vol%) channelized gas-particle mixture flows life-scaled to dense PDCs can be generated. The flow fronts of the currents reach velocities of up to 9.5 m/s over their first 12 m of travel and rapidly develop strong vertical density stratification. The PDCs typically form a highly mobile, <60 cm-thick dense and channel-confined underflow, with an overriding dilute and turbulent ash cloud surge that also laterally escapes the flume boundaries. Depending on the PDC starting conditions underflows with 1-45 vol% solids concentration are formed, while the upper surge contains <<1 vol.% solids. A characteristic feature of the underflow is the occurrence of 'ignitive' front breakouts, producing jetted lobes that accelerate outward from the flow front, initially forming a lobe-cleft structure, followed by segregation downslope into multiple flow pulses. Depending on initial solids concentration and discharge rate, stratified, dune-bedded and inversely graded bedforms are created whose thicknesses are remarkably uniform along the medial to distal runout path characterising highly mobile flow runout. Along with high-speed video footage we present time-series data of basal arrays of load- and gas-pore pressure transducers to characterise the mobile dense underflows. Data shows that the PDCs are comprised of a turbulent coarse-grained and air-ingesting front with particle-solids concentrations of 1-5 vol%. The front shows a brief phase of negative pore pressure due to the entrainment and upward elutriation of ambient air inside this front. It is immediately followed by the fine-ash rich and highly impermeable main flow body. Passage of the flow body is accompanied by strongly increasing pore-pressures of 1-3 kPa that almost fully supports the weight of the entire underflow - depicting flow-induced fluidisation of the main flow part. The remainder of the flow body shows further increases in pore-pressure aside with strong reductions in flow mass. This suggests the occurrence of zones of air-cushions forming at the base of the underflow that largely aid its inviscid runout. This sequence is repeated during arrival and passage of up to three more flow pulses. The low-permeability deposits maintain high internal gas pore pressures for several minutes after emplacement, before sudden deaeration, settling and gas loss is caused by fracturing. Flow-induced fluidisation and basal air-cushioning provide key processes behind the enigmatic long runout behaviour of dense PDCs.

Flight control of fruit flies: dynamic response to optic flow and headwind.

PubMed

Lawson, Kiaran K K; Srinivasan, Mandyam V

2017-06-01

Insects are magnificent fliers that are capable of performing many complex tasks such as speed regulation, smooth landings and collision avoidance, even though their computational abilities are limited by their small brain. To investigate how flying insects respond to changes in wind speed and surrounding optic flow, the open-loop sensorimotor response of female Queensland fruit flies ( Bactrocera tryoni ) was examined. A total of 136 flies were exposed to stimuli comprising sinusoidally varying optic flow and air flow (simulating forward movement) under tethered conditions in a virtual reality arena. Two responses were measured: the thrust and the abdomen pitch. The dynamics of the responses to optic flow and air flow were measured at various frequencies, and modelled as a multicompartment linear system, which accurately captured the behavioural responses of the fruit flies. The results indicate that these two behavioural responses are concurrently sensitive to changes of optic flow as well as wind. The abdomen pitch showed a streamlining response, where the abdomen was raised higher as the magnitude of either stimulus was increased. The thrust, in contrast, exhibited a counter-phase response where maximum thrust occurred when the optic flow or wind flow was at a minimum, indicating that the flies were attempting to maintain an ideal flight speed. When the changes in the wind and optic flow were in phase (i.e. did not contradict each other), the net responses (thrust and abdomen pitch) were well approximated by an equally weighted sum of the responses to the individual stimuli. However, when the optic flow and wind stimuli were presented in counterphase, the flies seemed to respond to only one stimulus or the other, demonstrating a form of 'selective attention'. © 2017. Published by The Company of Biologists Ltd.

The Dynamics of Dense Planetary Rings.

NASA Astrophysics Data System (ADS)

Mosqueira, Ignacio

1995-01-01

We study the dynamics of a two-mode narrow ring in the case that one of the modes dominates the overall ring perturbation. We use a simple two-streamline self -gravity model, including viscosity, and shepherd satellites. As might be expected, we find that n m = 1 mode appears to be a natural end state for the rings, inasmuch as the presence of a dominant eccentric mode inhibits the growth of other modes, but the reverse is not true. Why some rings exhibit other m values only remains unexplained. Using a modified N-body code to include periodic boundary conditions in a perturbed shear flow, we investigate the role of viscosity on the dynamics of perturbed rings with optical depth tau ~ 1. In particular, we are concerned with rings such that qe = a{de over da} ne 0, where a is the semi-major axis and e is the eccentricity. We confirm the possibility that, for a sufficiently perturbed ring, the angular momentum luminosity may reverse direction with respect to the unperturbed ring (Borderies et al. 1983a). We use observationally constrained parameters for the delta and epsilon Uranian rings, as well as the outer portion of Saturn's B ring. We find that understanding the effects of viscosity for the Uranian rings requires that both local and non-local transport terms be considered if the coefficient of restitution experimentally obtained by Bridges et al. (1984) is appropriate for ring particles. We also find evidence that the criterion for viscous overstability is satisfied in the case of high optical depth rings, as originally proposed by Borderies et al. (1985), making viscous overstability a leading candidate mechanism to explain the non-axisymmetric structure present in the outer portion of Saturn's B ring. To better understand our path-code results we extend a non-local and incompressible fluid model used by Borderies et al. (1985) for dense rings. We incorporate local and non-local transport terms as well as compressibility, while retaining the same number of arbitrary model parameters.

Viscous Overstability in Saturn's B-Ring. II. Hydrodynamic Theory and Comparison to Simulations

NASA Astrophysics Data System (ADS)

Schmidt, Jürgen; Salo, Heikki; Spahn, Frank; Petzschmann, Olaf

2001-10-01

We investigate the viscous oscillatory instability (overstability) of an unperturbed dense planetary ring, an instability that might play a role in the formation of radial structure in Saturn's B-ring. We generalize existing hydrodynamic models by including the heat flow equation in the analysis and compare our results to the development of overstable modes in local particle simulations. With the heat flow, in addition to the balance equations for mass and momentum, we take into account the balance law for the energy of the random motion; i.e., we allow for a thermal mode in a stability analysis of the stationary Keplerian flow. We also incorporate the effects of nonlocal transport of momentum and energy on the stability of the ring. In a companion paper (Salo, H., J. Schmidt, and F. Spahn 2001. Icarus, doi:10.1006/icar.2001.6680) we describe the determination of the local and nonlocal parts of the viscosity, the heat conductivity, the pressure, as well as the collisional cooling, together with their dependences on temperature and density, in local event-driven simulations of a planetary ring. The ring's self-gravity is taken into account in these simulations by an enhancement of the frequency of vertical oscillations Ω z>Ω. We use these values as parameters in our hydrodynamic model for the comparison to overstability in simulated rings of meter-sized inelastic particles of large optical depth with Ω z/Ω=3.6. We find that the inclusion of the energy-balance equation has a stabilizing influence on the overstable modes, shifting the stability boundary to higher optical depths, and moderating the growth rates of the instability, as compared to a purely isothermal treatment. The non-isothermal model predicts correctly the growth rates and oscillation frequencies of overstable modes in the simulations, as well as the phase shifts and relative amplitudes of the perturbations in density and radial and tangential velocity.

A media maniac's guide to removable mass storage media

NASA Technical Reports Server (NTRS)

Kempster, Linda S.

1996-01-01

This paper addresses at a high level, the many individual technologies available today in the removable storage arena including removable magnetic tapes, magnetic floppies, optical disks and optical tape. Tape recorders represented below discuss logitudinal, serpantine, logitudinal serpantine,and helical scan technologies. The magnetic floppies discussed will be used for personal electronic in-box applications.Optical disks still fill the role for dense long-term storage. The media capacities quoted are for native data. In some cases, 2 KB ASC2 pages or 50 KB document images will be referenced.

Dense Pattern Optical Multipass Cell

NASA Technical Reports Server (NTRS)

Silver, Joel A. (Inventor)

2009-01-01

A multiple pass optical cell and method comprising providing a pair of opposed cylindrical mirrors having curved axes with substantially equal focal lengths, positioning an entrance hole for introducing light into the cell and an exit hole for extracting light from the cell, wherein the entrance hole and exit hole are coextensive or non-coextensive, introducing light into the cell through the entrance hole, and extracting light from the cell through the exit hole.

Dense pattern optical multipass cell

DOEpatents

Silver, Joel A [Santa Fe, NM

2009-01-13

A multiple pass optical cell and method comprising providing a pair of opposed cylindrical mirrors having curved axes with substantially equal focal lengths, positioning an entrance hole for introducing light into the cell and an exit hole for extracting light from the cell, wherein the entrance hole and exit hole are coextensive or non-coextensive, introducing light into the cell through the entrance hole, and extracting light from the cell through the exit hole.

A SUPER-EDDINGTON, COMPTON-THICK WIND IN GRO J1655–40?

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

Neilsen, J.; Homan, J.; Rahoui, F.

2016-05-01

During its 2005 outburst, GRO J1655–40 was observed at high spectral resolution with the Chandra High-Energy Transmission Grating Spectrometer, revealing a spectrum rich with blueshifted absorption lines indicative of an accretion disk wind—apparently too hot, too dense, and too close to the black hole to be driven by radiation pressure or thermal pressure (Miller et al.). However, this exotic wind represents just one piece of the puzzle in this outburst, as its presence coincides with an extremely soft and curved X-ray continuum spectrum, remarkable X-ray variability (Uttley and Klein-Wolt), and a bright, unexpected optical/infrared blackbody component that varies on themore » orbital period. Focusing on the X-ray continuum and the optical/infrared/UV spectral energy distribution, we argue that the unusual features of this “hypersoft state” are natural consequences of a super-Eddington Compton-thick wind from the disk: the optical/infrared blackbody represents the cool photosphere of a dense, extended outflow, while the X-ray emission is explained as Compton scattering by the relatively cool, optically thick wind. This wind obscures the intrinsic luminosity of the inner disk, which we suggest may have been at or above the Eddington limit.« less

Bumblebee flight performance in environments of different proximity.

PubMed

Linander, Nellie; Baird, Emily; Dacke, Marie

2016-02-01

Flying animals are capable of navigating through environments of different complexity with high precision. To control their flight when negotiating narrow tunnels, bees and birds use the magnitude of apparent image motion (known as optic flow) generated by the walls. In their natural habitat, however, these animals would encounter both cluttered and open environments. Here, we investigate how large changes in the proximity of nearby surfaces affect optic flow-based flight control strategies. We trained bumblebees to fly along a flight and recorded how the distance between the walls--from 60 cm to 240 cm--affected their flight control. Our results reveal that, as tunnel width increases, both lateral position and ground speed become increasingly variable. We also find that optic flow information from the ground has an increasing influence on flight control, suggesting that bumblebees measure optic flow flexibly over a large lateral and ventral field of view, depending on where the highest magnitude of optic flow occurs. A consequence of this strategy is that, when flying in narrow spaces, bumblebees use optic flow information from the nearby obstacles to control flight, while in more open spaces they rely primarily on optic flow cues from the ground.

Gravity-driven dense granular flows

NASA Astrophysics Data System (ADS)

Ertas, Deniz

2002-03-01

Despite their importance in many areas of science and technology, the emergent physics of hard granular systems remain largely obscure, especially when the packing density approaches that of a jammed system. In particular, I will focus on the rheology of gravity-driven dense granular flows on an incline with a ``rough" bottom in two and three dimensions. We have conducted large-scale molecular dynamics simulations of spheres that interact through linear damped spring or Hertzian force laws with a Coulomb failure criterion(D. Ertaş) et al., Europhys. Lett. 56, 214 (2001); L.E. Silbert et al., Phys. Rev. E 64, 051302 (2001).. This flow geometry produces a constant density profile, and reproduces key features of such flows that have been observed experimentally(O. Pouliquen, Phys. Fluids 11), 542 (1999), such as an angle of repose that depends on flow thickness, steady-state solutions at varying heights for a given inclination angle, and the scaling of the mean particle velocity with pile height (< v > ∝ H^3/2). These successes prompted us to carefully examine the rheology in the interior of the pile by measuring the full stress and strain tensors, which are generally unavailable through experiments. The type of force law has little impact on the behavior of the system. The bulk rheology can be approximately described in terms of extensions of Chapman-Enskog theory to dense packings(L. Bocquet et al.), cond-mat/0112072. However, close to the angle of repose, this description fails near the free surface, which exhibits a rheology dominated by normal stress differences that are small in the bulk. This change in rheology can be qualitatively understood in terms of stress-bearing force networks that are continuously formed by ``gravitational inelastic collapse" and destroyed by the imposed strain.

Laser anemometry - Advances and applications 1991; Proceedings of the 4th International Conference, Cleveland, OH, Aug. 5-9, 1991. Vols. 1 & 2

NASA Technical Reports Server (NTRS)

Dybbs, Alexander (Editor); Ghorashi, Bahman (Editor)

1991-01-01

The papers presented in this volume provide an overview of the latest advances in laser anemometry and optical flow diagnostics. Topics discussed include turbulence, jets, and chaos; novel optical techniques for velocity measurements; chemical reactions and combusting flows; and LDA/CFD interface. Attention is also given to particle image velocimetry, high speed flows and aerodynamic flows, internal flows, particle sizing, optics and signal processing, two-phase flows, and general fluid mechanics applications.

Velocity filtering applied to optical flow calculations

NASA Technical Reports Server (NTRS)

Barniv, Yair

1990-01-01

Optical flow is a method by which a stream of two-dimensional images obtained from a forward-looking passive sensor is used to map the three-dimensional volume in front of a moving vehicle. Passive ranging via optical flow is applied here to the helicopter obstacle-avoidance problem. Velocity filtering is used as a field-based method to determine range to all pixels in the initial image. The theoretical understanding and performance analysis of velocity filtering as applied to optical flow is expanded and experimental results are presented.

Insect-Inspired Optical-Flow Navigation Sensors

NASA Technical Reports Server (NTRS)

Thakoor, Sarita; Morookian, John M.; Chahl, Javan; Soccol, Dean; Hines, Butler; Zornetzer, Steven

2005-01-01

Integrated circuits that exploit optical flow to sense motions of computer mice on or near surfaces ( optical mouse chips ) are used as navigation sensors in a class of small flying robots now undergoing development for potential use in such applications as exploration, search, and surveillance. The basic principles of these robots were described briefly in Insect-Inspired Flight Control for Small Flying Robots (NPO-30545), NASA Tech Briefs, Vol. 29, No. 1 (January 2005), page 61. To recapitulate from the cited prior article: The concept of optical flow can be defined, loosely, as the use of texture in images as a source of motion cues. The flight-control and navigation systems of these robots are inspired largely by the designs and functions of the vision systems and brains of insects, which have been demonstrated to utilize optical flow (as detected by their eyes and brains) resulting from their own motions in the environment. Optical flow has been shown to be very effective as a means of avoiding obstacles and controlling speeds and altitudes in robotic navigation. Prior systems used in experiments on navigating by means of optical flow have involved the use of panoramic optics, high-resolution image sensors, and programmable imagedata- processing computers.

Optical Air Flow Measurements for Flight Tests and Flight Testing Optical Air Flow Meters

NASA Technical Reports Server (NTRS)

Jentink, Henk W.; Bogue, Rodney K.

2005-01-01

Optical air flow measurements can support the testing of aircraft and can be instrumental to in-flight investigations of the atmosphere or atmospheric phenomena. Furthermore, optical air flow meters potentially contribute as avionics systems to flight safety and as air data systems. The qualification of these instruments for the flight environment is where we encounter the systems in flight testing. An overview is presented of different optical air flow measurement techniques applied in flight and what can be achieved with the techniques for flight test purposes is reviewed. All in-flight optical airflow velocity measurements use light scattering. Light is scattered on both air molecules and aerosols entrained in the air. Basic principles of making optical measurements in flight, some basic optical concepts, electronic concepts, optoelectronic interfaces, and some atmospheric processes associated with natural aerosols are reviewed. Safety aspects in applying the technique are shortly addressed. The different applications of the technique are listed and some typical examples are presented. Recently NASA acquired new data on mountain rotors, mountain induced turbulence, with the ACLAIM system. Rotor position was identified using the lidar system and the potentially hazardous air flow profile was monitored by the ACLAIM system.

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

Lougovski, P.; Uskov, D. B.

Entanglement can effectively increase communication channel capacity as evidenced by dense coding that predicts a capacity gain of 1 bit when compared to entanglement-free protocols. However, dense coding relies on Bell states and when implemented using photons the capacity gain is bounded by 0.585 bits due to one's inability to discriminate between the four optically encoded Bell states. In this research we study the following question: Are there alternative entanglement-assisted protocols that rely only on linear optics, coincidence photon counting, and separable single-photon input states and at the same time provide a greater capacity gain than 0.585 bits? In thismore » study, we show that besides the Bell states there is a class of bipartite four-mode two-photon entangled states that facilitate an increase in channel capacity. We also discuss how the proposed scheme can be generalized to the case of two-photon N-mode entangled states for N=6,8.« less

Breaking camouflage and detecting targets require optic flow and image structure information.

PubMed

Pan, Jing Samantha; Bingham, Ned; Chen, Chang; Bingham, Geoffrey P

2017-08-01

Use of motion to break camouflage extends back to the Cambrian [In the Blink of an Eye: How Vision Sparked the Big Bang of Evolution (New York Basic Books, 2003)]. We investigated the ability to break camouflage and continue to see camouflaged targets after motion stops. This is crucial for the survival of hunting predators. With camouflage, visual targets and distracters cannot be distinguished using only static image structure (i.e., appearance). Motion generates another source of optical information, optic flow, which breaks camouflage and specifies target locations. Optic flow calibrates image structure with respect to spatial relations among targets and distracters, and calibrated image structure makes previously camouflaged targets perceptible in a temporally stable fashion after motion stops. We investigated this proposal using laboratory experiments and compared how many camouflaged targets were identified either with optic flow information alone or with combined optic flow and image structure information. Our results show that the combination of motion-generated optic flow and target-projected image structure information yielded efficient and stable perception of camouflaged targets.

Minimum viewing angle for visually guided ground speed control in bumblebees.

PubMed

Baird, Emily; Kornfeldt, Torill; Dacke, Marie

2010-05-01

To control flight, flying insects extract information from the pattern of visual motion generated during flight, known as optic flow. To regulate their ground speed, insects such as honeybees and Drosophila hold the rate of optic flow in the axial direction (front-to-back) constant. A consequence of this strategy is that its performance varies with the minimum viewing angle (the deviation from the frontal direction of the longitudinal axis of the insect) at which changes in axial optic flow are detected. The greater this angle, the later changes in the rate of optic flow, caused by changes in the density of the environment, will be detected. The aim of the present study is to examine the mechanisms of ground speed control in bumblebees and to identify the extent of the visual range over which optic flow for ground speed control is measured. Bumblebees were trained to fly through an experimental tunnel consisting of parallel vertical walls. Flights were recorded when (1) the distance between the tunnel walls was either 15 or 30 cm, (2) the visual texture on the tunnel walls provided either strong or weak optic flow cues and (3) the distance between the walls changed abruptly halfway along the tunnel's length. The results reveal that bumblebees regulate ground speed using optic flow cues and that changes in the rate of optic flow are detected at a minimum viewing angle of 23-30 deg., with a visual field that extends to approximately 155 deg. By measuring optic flow over a visual field that has a low minimum viewing angle, bumblebees are able to detect and respond to changes in the proximity of the environment well before they are encountered.

Optical probe

DOEpatents

Hencken, Kenneth; Flower, William L.

1999-01-01

A compact optical probe is disclosed particularly useful for analysis of emissions in industrial environments. The instant invention provides a geometry for optically-based measurements that allows all optical components (source, detector, rely optics, etc.) to be located in proximity to one another. The geometry of the probe disclosed herein provides a means for making optical measurements in environments where it is difficult and/or expensive to gain access to the vicinity of a flow stream to be measured. Significantly, the lens geometry of the optical probe allows the analysis location within a flow stream being monitored to be moved while maintaining optical alignment of all components even when the optical probe is focused on a plurality of different analysis points within the flow stream.

IRAS 18153-1651: an H II region with a possible wind bubble blown by a young main-sequence B star

NASA Astrophysics Data System (ADS)

Gvaramadze, V. V.; Mackey, J.; Kniazev, A. Y.; Langer, N.; Chené, A.-N.; Castro, N.; Haworth, T. J.; Grebel, E. K.

2017-04-01

We report the results of spectroscopic observations and numerical modelling of the H II region IRAS 18153-1651. Our study was motivated by the discovery of an optical arc and two main-sequence stars of spectral type B1 and B3 near the centre of IRAS 18153-1651. We interpret the arc as the edge of the wind bubble (blown by the B1 star), whose brightness is enhanced by the interaction with a photoevaporation flow from a nearby molecular cloud. This interpretation implies that we deal with a unique case of a young massive star (the most massive member of a recently formed low-mass star cluster) caught just tens of thousands of years after its stellar wind has begun to blow a bubble into the surrounding dense medium. Our 2D, radiation-hydrodynamics simulations of the wind bubble and the H II region around the B1 star provide a reasonable match to observations, both in terms of morphology and absolute brightness of the optical and mid-infrared emission, and verify the young age of IRAS 18153-1651. Taken together our results strongly suggest that we have revealed the first example of a wind bubble blown by a main-sequence B star.

Toward high-efficiency and detailed Monte Carlo simulation study of the granular flow spallation target

NASA Astrophysics Data System (ADS)

Cai, Han-Jie; Zhang, Zhi-Lei; Fu, Fen; Li, Jian-Yang; Zhang, Xun-Chao; Zhang, Ya-Ling; Yan, Xue-Song; Lin, Ping; Xv, Jian-Ya; Yang, Lei

2018-02-01

The dense granular flow spallation target is a new target concept chosen for the Accelerator-Driven Subcritical (ADS) project in China. For the R&D of this kind of target concept, a dedicated Monte Carlo (MC) program named GMT was developed to perform the simulation study of the beam-target interaction. Owing to the complexities of the target geometry, the computational cost of the MC simulation of particle tracks is highly expensive. Thus, improvement of computational efficiency will be essential for the detailed MC simulation studies of the dense granular target. Here we present the special design of the GMT program and its high efficiency performance. In addition, the speedup potential of the GPU-accelerated spallation models is discussed.

Normal stress differences and beyond-Navier-Stokes hydrodynamics

NASA Astrophysics Data System (ADS)

Alam, Meheboob; Saha, Saikat

2017-06-01

A recently proposed beyond-Navier-Stokes order hydrodynamic theory for dry granular fluids is revisited by focussing on the behaviour of the stress tensor and the scaling of related transport coefficients in the dense limit. For the homogeneous shear flow, it is shown that the eigen-directions of the second-moment tensor and those of the shear tensor become co-axial, thus making the first normal stress difference (N1) to zero in the same limit. In contrast, the origin of the second normal stress difference (N2) is tied to the `excess' temperature along the mean-vorticity direction and the imposed shear field, respectively, in the dilute and dense flows. The scaling relations for transport coefficients are suggested based on the present theory.

Energy Flow in Dense Off-Equilibrium Plasma

DTIC Science & Technology

2016-07-15

akT e in our system100 i e T T Teller 1966 Smoking Gun Experiment: Laser Breakdown in COLD gas In going from room to liquid Nitrogen temperature...oflaser breakdown have revealed a new phase of off-equilibrium plasma that has a tensile strength similar to a liquid , and reduced ion-electron...approved for public release. Part 1: Energy Balance in Sonoluminescing Dense Plasma Sonoluminescence occurs from rapid implosion of gas bubbles caused to

New intravascular flow sensor using fiber optics

NASA Astrophysics Data System (ADS)

Stenow, Erik N. D.

1994-12-01

A new sensor using fiber optics is suggested for blood flow measurements in small vessels. The sensor principle and a first evaluation on a flow model are presented. The new sensor uses small CO2 gas bubbles as flow markers for optical detection. When the bubbles pass an optical window, light emitted from one fiber is reflected and scattered into another fiber. The sensor has been proven to work in a 3 mm flow model using two 110 micrometers optical fibers and a 100 micrometers steel capillary inserted into a 1 mm guide wire. The evaluation of a sensor archetype shows that the new sensor provides a promising method for intravascular blood flow measurement in small vessels. The linearity for steady state flow is studied in the flow interval 30 - 130 ml/min. comparison with ultrasound Doppler flowmetry was performed for pulsatile flow in the interval 25 - 125 ml/min. with a pulse length between 0.5 and 2 s. The use of intravascular administered CO2 in small volumes is harmless because the gas is rapidly dissolved in whole blood.

A 2.7 Myr record of sedimentary processes on a high-latitude continental slope: 3D seismic evidence from the mid-Norwegian margin

NASA Astrophysics Data System (ADS)

Montelli, A.; Dowdeswell, J. A.; Ottesen, D.; Johansen, S. E.

2017-12-01

An extensive three-dimensional seismic dataset is used to investigate the sedimentary processes and morphological evolution of the mid-Norwegian continental slope through the Quaternary. These data reveal hundreds of buried landforms, including channels and debris flows of variable morphology, as well as gullies, iceberg ploughmarks, slide scars and sediment waves. Slide scars, turbidity currents and debris flows comprise slope systems controlled by local slope morphology, showing the spatial variability of high-latitude sedimentation. Channels dominate the Early Pleistocene ( 2.7-0.8 Ma) morphological record of the mid-Norwegian slope. During Early Plesitocene, glacimarine sedimentation on the slope was influenced by dense bottom-water flow and turbidity currents. Glacigenic debris-flows appear within the Middle-Late Pleistocene ( 0.8-0 Ma) succession. Their abundance increases on Late Pleistocene palaeo-surfaces, marking a paleo-environmental change characterised by decreasing role for channelized turbidity currents and dense water flows. This transition coincides with the gradual shift to full-glacial ice-sheet conditions marked by the appearance of the first erosive fast-flowing ice streams and an associated increase in sediment flux to the shelf edge, emphasizing first-order climate control on the temporal variability of high-latitude sedimentary slope records.

Effect of Residence Time on Net Nitrate Retention in Flow-Regulated Backwaters of the Upper Mississippi River

DTIC Science & Technology

2006-02-01

include Ceratophyllum demersum, Myriophyllum spicatum, and Nymphaea odorata . METHODS: In late April 2004, vertical slide gates were adjusted to...due to a shallow water column and dense N. odorata beds. Flows into Schmokers Lake could not be directly measured because it was not connected to the

Slow-moving and far-travelled dense pyroclastic flows during the Peach Spring super-eruption

USGS Publications Warehouse

Roche, Olivier; Buesch, David C.; Valentine, Greg A.

2016-01-01

Explosive volcanic super-eruptions of several hundred cubic kilometres or more generate long run-out pyroclastic density currents the dynamics of which are poorly understood and controversial. Deposits of one such event in the southwestern USA, the 18.8 Ma Peach Spring Tuff, were formed by pyroclastic flows that travelled >170 km from the eruptive centre and entrained blocks up to ~70–90 cm diameter from the substrates along the flow paths. Here we combine these data with new experimental results to show that the flow’s base had high-particle concentration and relatively modest speeds of ~5–20 m s−1, fed by an eruption discharging magma at rates up to ~107–108 m3 s−1 for a minimum of 2.5–10 h. We conclude that sustained high-eruption discharge and long-lived high-pore pressure in dense granular dispersion can be more important than large initial velocity and turbulent transport with dilute suspension in promoting long pyroclastic flow distance.

Enhanced Microfluidic Electromagnetic Measurements

NASA Technical Reports Server (NTRS)

Ricco, Antonio J. (Inventor); Kovacs, Gregory (Inventor); Giovangrandi, Laurent (Inventor)

2015-01-01

Techniques for enhanced microfluidic impedance spectroscopy include causing a core fluid to flow into a channel between two sheath flows of one or more sheath fluids different from the core fluid. Flow in the channel is laminar. A dielectric constant of a fluid constituting either sheath flow is much less than a dielectric constant of the core fluid. Electrical impedance is measured in the channel between at least a first pair of electrodes. In some embodiments, enhanced optical measurements include causing a core fluid to flow into a channel between two sheath flows of one or more sheath fluids different from the core fluid. An optical index of refraction of a fluid constituting either sheath flow is much less than an optical index of refraction of the core fluid. An optical property is measured in the channel.

Linear dependence of surface expansion speed on initial plasma temperature in warm dense matter

DOE PAGES

Bang, Woosuk; Albright, Brian James; Bradley, Paul Andrew; ...

2016-07-12

Recent progress in laser-driven quasi-monoenergetic ion beams enabled the production of uniformly heated warm dense matter. Matter heated rapidly with this technique is under extreme temperatures and pressures, and promptly expands outward. While the expansion speed of an ideal plasma is known to have a square-root dependence on temperature, computer simulations presented here show a linear dependence of expansion speed on initial plasma temperature in the warm dense matter regime. The expansion of uniformly heated 1–100 eV solid density gold foils was modeled with the RAGE radiation-hydrodynamics code, and the average surface expansion speed was found to increase linearly withmore » temperature. The origin of this linear dependence is explained by comparing predictions from the SESAME equation-of-state tables with those from the ideal gas equation-of-state. In conclusion, these simulations offer useful insight into the expansion of warm dense matter and motivate the application of optical shadowgraphy for temperature measurement.« less

Interband and intraband electron kinetics in non-thermal warm dense gold

NASA Astrophysics Data System (ADS)

Brennan Brown, Shaughnessy; Chen, Zhijiang; Curry, Chandra; Hering, Philippe; Hoffmann, Matthias C.; Ng, Andrew; Reid, Matthew; Tsui, Ying Y.; Glenzer, Siegfried H.

2015-11-01

Single-state warm dense matter may be produced via isochoric heating of thin metal foils using ultrafast high-power lasers. Previous experiments have confirmed that electron temperatures exceed ion temperatures during the initial picoseconds following excitation; however, electron kinetics in non-thermal states preceding establishment of a well-defined electron thermal distribution remain little understood. X-ray and optical probing techniques provide necessary resolution to investigate these electronic properties. Here, we will present a study of electron kinetics in warm dense gold produced by irradiating free-standing 30 nm Au foils with a 400 nm FWHM, 45 fs Ti:Sapphire laser system at SLAC National Accelerator Laboratory. The temporal evolutions of AC conductivity for 400 nm and 800 nm laser pulses are simultaneously determined with sub-100 fs resolution, providing insight into the 5 d-6 s/ p interband and 6 s / p intraband transitions respectively. Our results suggest that Auger decay and three-body recombination play important roles in electron thermalization of warm dense gold.

Pore-scale Modeling of CO2 Local Trapping in Heterogeneous Porous Media with Inter-granular Cements

NASA Astrophysics Data System (ADS)

Wang, D.; Li, Y.

2017-12-01

Based on pore-scale modeling of CO2/brine multiphase flow in heterogeneous porous media with inter-granular cements, we numerically analyze the effects of cement-modified pore structure on CO2 local trapping. Results indicate: 1) small pore throat is the main reason for causing CO2 local trapping in front of low-porosity layers (namely dense layers) formed by inter-granular cements; 2) in the case of the same pore throat size, the smaller particle size can increase the number of flow paths for CO2 plume and equivalently enhances local permeability, which may counteract the impediment of high capillary pressure on CO2 migration to some extent and consequently disables CO2 local capillary trapping; 3) the isolated pores by inter-granular cements can lead to dramatic reduction of CO2 saturation inside the dense layers, whereas the change of connectivity of some pores due to the cements can increase CO2 accumulation in front of the dense layers by lowering the displacement area of CO2 plume.

The effect of dense gas dynamics on loss in ORC transonic turbines

NASA Astrophysics Data System (ADS)

Durá Galiana, FJ; Wheeler, APS; Ong, J.; Ventura, CA de M.

2017-03-01

This paper describes a number of recent investigations into the effect of dense gas dynamics on ORC transonic turbine performance. We describe a combination of experimental, analytical and computational studies which are used to determine how, in-particular, trailing-edge loss changes with choice of working fluid. A Ludwieg tube transient wind-tunnel is used to simulate a supersonic base flow which mimics an ORC turbine vane trailing-edge flow. Experimental measurements of wake profiles and trailing-edge base pressure with different working fluids are used to validate high-order CFD simulations. In order to capture the correct mixing in the base region, Large-Eddy Simulations (LES) are performed and verified against the experimental data by comparing the LES with different spatial and temporal resolutions. RANS and Detached-Eddy Simulation (DES) are also compared with experimental data. The effect of different modelling methods and working fluid on mixed-out loss is then determined. Current results point at LES predicting the closest agreement with experimental results, and dense gas effects are consistently predicted to increase loss.

Collective motion of squirmers in a quasi-2D geometry

NASA Astrophysics Data System (ADS)

Zöttl, Andreas; Stark, Holger

2013-03-01

Microorganisms like bacteria, algae or spermatozoa typically move in an aqueous environment where they interact via hydrodynamic flow fields. Recent experiments studied the collective motion of dense suspensions of bacteria where swarming and large-scale turbulence emerged. Moreover, spherical artificial microswimmers, so-called squirmers, have been constructed and studied in a quasi-2D geometry. Here we present a numerical study of the collective dynamics of squirmers confined in quasi-2D between two parallel walls. Because of their spherical shape the reorientation of squirmers is solely due to noise and hydrodynamic interactions via induced flow fields. This is in contrast to elongated swimmers like bacteria which locally align due to steric interactions. We study the collective motion of pushers, pullers and potential swimmers at different densities. At small densities the squirmers are oriented parallel to the walls and pairwise collisions determine the reorientation rate. In dense suspensions rotational diffusion is greatly enhanced and pushers, in particular, tend to orient perpendicular to the walls. This effects the dynamics of the emerging clusters. In very dense suspensions we observe active jamming and long-lived crystalline structures.

New Variable Porosity Flow Diverter (VPOD) Stent Design for Treatment of Cerebrovascular Aneurysms

PubMed Central

Ionita, Ciprian; Baier, Robert; Rudin, Stephen

2012-01-01

Using flow diverting Stents for intracranial aneurysm repair has been an area of recent active research. While current commercial flow diverting stents rely on a dense mesh of braided coils for flow diversion, our group has been developing a method to selectively occlude the aneurysm neck, without endangering nearby perforator vessels. In this paper, we present a new method of fabricating the low porosity patch, a key element of such asymmetric vascular stents (AVS). PMID:22254507

Aqueous carrier waveguide in a flow cytometer

DOEpatents

Mariella, Jr., Raymond P.; van den Engh, Gerrit; Northrup, M. Allen

1995-01-01

The liquid of a flow cytometer itself acts as an optical waveguide, thus transmitting the light to an optical filter/detector combination. This alternative apparatus and method for detecting scattered light in a flow cytometer is provided by a device which views and detects the light trapped within the optical waveguide formed by the flow stream. A fiber optic or other light collecting device is positioned within the flow stream. This provides enormous advantages over the standard light collection technique which uses a microscope objective. The signal-to-noise ratio is greatly increased over that for right-angle-scattered light collected by a microscope objective, and the alignment requirements are simplified.

Pilot Study of Optical Coherence Tomography Measurement of Retinal Blood Flow in Retinal and Optic Nerve Diseases

PubMed Central

Wang, Yimin; Fawzi, Amani A.; Varma, Rohit; Sadun, Alfredo A.; Zhang, Xinbo; Tan, Ou; Izatt, Joseph A.

2011-01-01

Purpose. To investigate blood flow changes in retinal and optic nerve diseases with Doppler Fourier domain optical coherence tomography (OCT). Methods. Sixty-two participants were divided into five groups: normal, glaucoma, nonarteritic ischemic optic neuropathy (NAION), treated proliferative diabetic retinopathy (PDR), and branch retinal vein occlusion (BRVO). Doppler OCT was used to scan concentric circles of 3.4- and 3.75-mm diameters around the optic nerve head. Flow in retinal veins was calculated from the OCT velocity profiles. Arterial and venous diameters were measured from OCT Doppler and reflectance images. Results. Total retinal blood flow in normal subjects averaged 47.6 μL/min. The coefficient of variation of repeated measurements was 11% in normal eyes and 14% in diseased eyes. Eyes with glaucoma, NAION, treated PDR, and BRVO had significantly decreased retinal blood flow compared with normal eyes (P < 0.001). In glaucoma patients, the decrease in blood flow was highly correlated with the severity of visual field loss (P = 0.003). In NAION and BRVO patients, the hemisphere with more severe disease also had lower blood flow. Conclusions. Doppler OCT retinal blood flow measurements showed good repeatability and excellent correlation with visual field and clinical presentations. This approach could enhance our understanding of retinal and optic nerve diseases and facilitate the development of new therapies. PMID:21051715

Silicon photonics integrated circuits: a manufacturing platform for high density, low power optical I/O's.

PubMed

Absil, Philippe P; Verheyen, Peter; De Heyn, Peter; Pantouvaki, Marianna; Lepage, Guy; De Coster, Jeroen; Van Campenhout, Joris

2015-04-06

Silicon photonics integrated circuits are considered to enable future computing systems with optical input-outputs co-packaged with CMOS chips to circumvent the limitations of electrical interfaces. In this paper we present the recent progress made to enable dense multiplexing by exploiting the integration advantage of silicon photonics integrated circuits. We also discuss the manufacturability of such circuits, a key factor for a wide adoption of this technology.

The Relationship between Climate and Iceland Scotland Overflow Water During Mid-Late Pleistocene Interglacials

NASA Astrophysics Data System (ADS)

Nuber, S.; Thornalley, D.; Forman, M.; Barker, S.; Oppo, D.

2016-12-01

Ocean circulation has been identified as an important climate feedback mechanism in a warming world. An area of particular importance in global ocean circulation is the high latitude North Atlantic and the Nordic Seas. Here, cooling of northward flowing warm surface water produces dense deep water which sinks to the ocean floor and returns southward as part of the Atlantic Meridional Overturning Circulation (AMOC). Density structures in the Nordic Seas can change as a response to enhanced freshwater input (e.g. from the melting Greenland Ice Sheet or a stronger hydrological cycle) which in turn may perturb the AMOC. It is therefore important that we develop our understanding of the relationship between climate and the return flow of dense water formed in the high latitude North Atlantic, focusing in particular on past warm climates that can act as partial analogues for future global warming scenarios. Previous work investigating the Holocene has revealed long-term trends in the strength of the dense overflow from the Nordic Seas into the North Atlantic via Iceland Scotland Overflow Water (ISOW). These changes have been related to variations in the freshwater budget and the water densities in the Nordic Seas (Thornalley et al., 2013). Across earlier interglacials, ISOW dynamics remain poorly constrained. To gain a more complete understanding of the coupling of climate and ISOW during past warm climates, we reconstructed ISOW flow speeds across an additional five Pleistocene interglacials, using the sortable silt proxy and a newly developed calibration curve. We find that there is large variability in inferred ISOW flow speeds between interglacials, as well as different temporal evolution of flow speed through the various interglacials. Our results suggest that preceded deglacial dynamics may be an important influence on the interglacial ISOW flow structure and highlight the tight coupling between climate and the ISOW.

Ground and Space-Based Measurement of Rocket Engine Burns in the Ionosphere

NASA Technical Reports Server (NTRS)

Bernhardt, P. A.; Ballenthin, J. O.; Baumgardner, J. L.; Bhatt, A.; Boyd, I. D.; Burt, J. M.; Caton, R. G.; Coster, A.; Erickson, P. J.; Huba, J. D.;

Unifying Suspension and Granular flows near Jamming

NASA Astrophysics Data System (ADS)

DeGiuli, Eric; Wyart, Matthieu

2017-06-01

Rheological properties of dense flows of hard particles are singular as one approaches the jamming threshold where flow ceases, both for granular flows dominated by inertia, and for over-damped suspensions. Concomitantly, the lengthscale characterizing velocity correlations appears to diverge at jamming. Here we review a theoretical framework that gives a scaling description of stationary flows of frictionless particles. Our analysis applies both to suspensions and inertial flows of hard particles. We report numerical results in support of the theory, and show the phase diagram that results when friction is added, delineating the regime of validity of the frictionless theory.

Smart Application of Direct Gas Injection using a new conceptual model on Coherent and Incoherent Flow: From Bench Scale to Field Scale.

NASA Astrophysics Data System (ADS)

Geistlinger, H.; Samani, S.; Pohlert, M.; Martienssen, M.; Engelmann, F.; Hüttmann, S.

2008-12-01

Within the framework of the OXYWALL field experiment we developed the direct gas injection (DGI) of oxygen as a remediation technology, which allows the cost-efficient and large-scale cleaning of groundwater contaminated with organic contaminants. That technology can be used as wide-banded, unselective remediation method for complex contaminant mixtures. Particularly, it could be proofed in field experiments that mineral oil hydrocarbons, aromatic hydrocarbons (BTEX), the rather persistent gasoline component Methyl tertiary-butyl ether (MTBE), and chlorinated aliphatic and aromatic hydrocarbons, like Trichloroethene and Monochlorobenzene, can be aerobically metabolized by autochthon microorganisms. Over the last 8 years the field site was investigated and a dense monitoring network was installed using Geoprobe direct- push technology and standard hydrogeological investigations were conducted, like EC-Logs, Injections-Logs, Gamma-Logs, TDR-probes, oxygen measurements with in-situ optodes, and tracer test with test gases SF6, Ar, and Oxygen. The key parameter for controling and regulating the DGI is the spatial and temporal distribution of the gas phase. High-resolution optical bench scale experiments were conducted in order to investigate local gas flow pattern and integral flow properties caused by point-like gas injection into water-saturated glass beads and natural sands. We observed a grain-size (dk)- and flow-rate (Q) dependent transition from incoherent to coherent flow. Conceptualizing the stationary tortuous gas flow as core-annulus flow and applying Hagen- Poiseuille flow for a straight capillary, we propose a flow-rate- and grain-size dependent stability criterion that could describe our experimental results and was used for classifying the experiments in a dk-Q-diagram (flow chart). Since DGI simulations are mainly based on continuum models, we also test the validity of the continuum approach for two-fluid flow in macroscopic homogeneous media by comparing our experimental flow pattern with the theoretical ones. It was found that a pulse-like function yields the best fit for the lateral gas saturation profile. This strange behaviour of a relatively sharp saturation transition is in contradiction to the widely anticipated picture of a smooth Gaussian-like transition, which is obtained by the continuum approach. Based on lab experiments, the proposed flow chart, and computer simulations the DGI-technology will be advanced and optimized at the field scale. A proper application of continuum models to direct gas injection should check, whether stable coherent flow is achieved; estimate the coherence length, and account for the channelized flow pattern by a realistic capillary pressure - saturation relationship. Further research is needed for modeling of direct gas injection to include appropriate stability criteria, the transition from coherent to incoherent flow, and bubble trapping. Geistlinger, H., Krauss, G., Lazik, D., and Luckner, L. (2006) Direct gas injection into saturated glass beads: transition from incoherent to coherent gas flow pattern. Water Resour. Res., 42 (7) W07403. Lazik, D., G. Krauss, H. Geistlinger, and H.-J. Vogel (2008) Multi-scale optical analyses of dynamic gas saturation during air sparging into glass beads, Transp. Porous Media. 74, 87-104.

IRAS galaxies and the large-scale structure in the CfA slice

NASA Technical Reports Server (NTRS)

Babul, Arif; Postman, Marc

1990-01-01

The spatial distributions of the IRAS and the optical galaxies in the first CfA slice are compared. The IRAS galaxies are generally less clustered than optical ones, but their distribution is essentially identical to that of late-type optical galaxies. The discrepancy between the clustering properties of the IRAS and optical samples in the CfA slice region is found to be entirely due to the paucity of IRAS galaxies in the core of the Coma cluster. The spatial distributions of the IRAS and the optical galaxies, both late and early types, outside the dense core of the Coma cluster are entirely consistent with each other. This conflicts with the prediction of the linear biasing scenario.

An imaging system based on laser optical feedback for fog vision applications

NASA Astrophysics Data System (ADS)

Belin, E.; Boucher, V.

2008-08-01

The Laboratoire Régional des Ponts et Chaussées d'Angers - LRPC of Angers is currently studying the feasability of applying an optical technique based on the principle of the laser optical feedback to long distance fog vision. Optical feedback set up allows the creation of images on roadsigns. To create artificial fog conditions we used a vibrating cell that produces a micro-spray of water according to the principle of acoustic cavitation. To scale the sensitivity of the system under duplicatible conditions we also used optical densities linked to first-sight visibility distances. The current system produces, in a few seconds, 200 × 200 pixel images of a roadsign seen through dense artificial fog.

Wave optics theory and 3-D deconvolution for the light field microscope

PubMed Central

Broxton, Michael; Grosenick, Logan; Yang, Samuel; Cohen, Noy; Andalman, Aaron; Deisseroth, Karl; Levoy, Marc

2013-01-01

Light field microscopy is a new technique for high-speed volumetric imaging of weakly scattering or fluorescent specimens. It employs an array of microlenses to trade off spatial resolution against angular resolution, thereby allowing a 4-D light field to be captured using a single photographic exposure without the need for scanning. The recorded light field can then be used to computationally reconstruct a full volume. In this paper, we present an optical model for light field microscopy based on wave optics, instead of previously reported ray optics models. We also present a 3-D deconvolution method for light field microscopy that is able to reconstruct volumes at higher spatial resolution, and with better optical sectioning, than previously reported. To accomplish this, we take advantage of the dense spatio-angular sampling provided by a microlens array at axial positions away from the native object plane. This dense sampling permits us to decode aliasing present in the light field to reconstruct high-frequency information. We formulate our method as an inverse problem for reconstructing the 3-D volume, which we solve using a GPU-accelerated iterative algorithm. Theoretical limits on the depth-dependent lateral resolution of the reconstructed volumes are derived. We show that these limits are in good agreement with experimental results on a standard USAF 1951 resolution target. Finally, we present 3-D reconstructions of pollen grains that demonstrate the improvements in fidelity made possible by our method. PMID:24150383

Drifting while stepping in place in old adults: Association of self-motion perception with reference frame reliance and ground optic flow sensitivity.

PubMed

Agathos, Catherine P; Bernardin, Delphine; Baranton, Konogan; Assaiante, Christine; Isableu, Brice

2017-04-07

Optic flow provides visual self-motion information and is shown to modulate gait and provoke postural reactions. We have previously reported an increased reliance on the visual, as opposed to the somatosensory-based egocentric, frame of reference (FoR) for spatial orientation with age. In this study, we evaluated FoR reliance for self-motion perception with respect to the ground surface. We examined how effects of ground optic flow direction on posture may be enhanced by an intermittent podal contact with the ground, and reliance on the visual FoR and aging. Young, middle-aged and old adults stood quietly (QS) or stepped in place (SIP) for 30s under static stimulation, approaching and receding optic flow on the ground and a control condition. We calculated center of pressure (COP) translation and optic flow sensitivity was defined as the ratio of COP translation velocity over absolute optic flow velocity: the visual self-motion quotient (VSQ). COP translation was more influenced by receding flow during QS and by approaching flow during SIP. In addition, old adults drifted forward while SIP without any imposed visual stimulation. Approaching flow limited this natural drift and receding flow enhanced it, as indicated by the VSQ. The VSQ appears to be a motor index of reliance on the visual FoR during SIP and is associated with greater reliance on the visual and reduced reliance on the egocentric FoR. Exploitation of the egocentric FoR for self-motion perception with respect to the ground surface is compromised by age and associated with greater sensitivity to optic flow. Copyright © 2017 IBRO. Published by Elsevier Ltd. All rights reserved.

Influence of galactic arm scale dynamics on the molecular composition of the cold and dense ISM. I. Observed abundance gradients in dense clouds

NASA Astrophysics Data System (ADS)

Ruaud, M.; Wakelam, V.; Gratier, P.; Bonnell, I. A.

2018-04-01

Aim. We study the effect of large scale dynamics on the molecular composition of the dense interstellar medium during the transition between diffuse to dense clouds. Methods: We followed the formation of dense clouds (on sub-parsec scales) through the dynamics of the interstellar medium at galactic scales. We used results from smoothed particle hydrodynamics (SPH) simulations from which we extracted physical parameters that are used as inputs for our full gas-grain chemical model. In these simulations, the evolution of the interstellar matter is followed for 50 Myr. The warm low-density interstellar medium gas flows into spiral arms where orbit crowding produces the shock formation of dense clouds, which are held together temporarily by the external pressure. Results: We show that depending on the physical history of each SPH particle, the molecular composition of the modeled dense clouds presents a high dispersion in the computed abundances even if the local physical properties are similar. We find that carbon chains are the most affected species and show that these differences are directly connected to differences in (1) the electronic fraction, (2) the C/O ratio, and (3) the local physical conditions. We argue that differences in the dynamical evolution of the gas that formed dense clouds could account for the molecular diversity observed between and within these clouds. Conclusions: This study shows the importance of past physical conditions in establishing the chemical composition of the dense medium.

Perceiving Collision Impacts in Alzheimer's Disease: The Effect of Retinal Eccentricity on Optic Flow Deficits.

PubMed

Kim, Nam-Gyoon

2015-01-01

The present study explored whether the optic flow deficit in Alzheimer's disease (AD) reported in the literature transfers to different types of optic flow, in particular, one that specifies collision impacts with upcoming surfaces, with a special focus on the effect of retinal eccentricity. Displays simulated observer movement over a ground plane toward obstacles lying in the observer's path. Optical expansion was modulated by varying [Formula: see text]. The visual field was masked either centrally (peripheral vision) or peripherally (central vision) using masks ranging from 10° to 30° in diameter in steps of 10°. Participants were asked to indicate whether their approach would result in "collision" or "no collision" with the obstacles. Results showed that AD patients' sensitivity to [Formula: see text] was severely compromised, not only for central vision but also for peripheral vision, compared to age- and education-matched elderly controls. The results demonstrated that AD patients' optic flow deficit is not limited to radial optic flow but includes also the optical pattern engendered by [Formula: see text]. Further deterioration in the capacity to extract [Formula: see text] to determine potential collisions in conjunction with the inability to extract heading information from radial optic flow would exacerbate AD patients' difficulties in navigation and visuospatial orientation.

Delayed Shock-induced Dust Formation in the Dense Circumstellar Shell Surrounding the Type IIn Supernova SN 2010jl

NASA Astrophysics Data System (ADS)

Sarangi, Arkaprabha; Dwek, Eli; Arendt, Richard G.

2018-05-01

The light curves of Type IIn supernovae are dominated by the radiative energy released through the interaction of the supernova shock waves with their dense circumstellar medium (CSM). The ultraluminous Type IIn supernova SN 2010jl exhibits an infrared emission component that is in excess of the extrapolated UV–optical spectrum as early as few weeks postexplosion. This emission has been considered by some as evidence for the rapid formation of dust in the cooling postshock CSM. We investigate the physical processes that may inhibit or facilitate the formation of dust in the CSM. When only radiative cooling is considered, the temperature of the dense shocked gas rapidly drops below the dust condensation temperature. However, by accounting for the heating of the postshock gas by the downstream radiation from the shock, we show that dust formation is inhibited until the radiation from the shock weakens as it propagates into the less dense outer regions of the CSM. In SN 2010jl, dust formation can therefore only commence after day ∼380. Only the IR emission since that epoch can be attributed to the newly formed CSM dust. Observations on day 460 and later show that the IR luminosity exceeds the UV–optical luminosity. The postshock dust cannot extinct the radiation emitted by the expanding SN shock. Therefore, its IR emission must be powered by an interior source, which we identify as the reverse shock propagating through the SN ejecta. IR emission before day 380 must therefore be an IR echo from preexisting CSM dust.

Modeling Type II-P/II-L Supernovae Interacting with Recent Episodic Mass Ejections from Their Presupernova Stars with MESA and SNEC

NASA Astrophysics Data System (ADS)

Das, Sanskriti; Ray, Alak

2017-12-01

We show how dense, compact, discrete shells of circumstellar gas immediately outside of red supergiants affect the optical light curves of Type II-P/II-L supernovae (SNe), using the example of SN 2013ej. Earlier efforts in the literature had used an artificial circumstellar medium (CSM) stitched to the surface of an evolved star that had not gone through a phase of late-stage heavy mass loss, which, in essence, is the original source of the CSM. In contrast, we allow enhanced mass-loss rate from the modeled star during the 16O and 28Si burning stages and construct the CSM from the resulting mass-loss history in a self-consistent way. Once such evolved pre-SN stars are exploded, we find that the models with early interaction between the shock and the dense CSM reproduce light curves far better than those without that mass loss and, hence, having no nearby dense CSM. The required explosion energy for the progenitors with a dense CSM is reduced by almost a factor of two compared to those without the CSM. Our model, with a more realistic CSM profile and presupernova and explosion parameters, fits observed data much better throughout the rise, plateau, and radioactive tail phases as compared to previous studies. This points to an intermediate class of supernovae between Type II-P/II-L and Type II-n SNe with the characteristics of simultaneous UV and optical peak, slow decline after peak, and a longer plateau.

Wave-optics modeling of the optical-transport line for passive optical stochastic cooling

NASA Astrophysics Data System (ADS)

Andorf, M. B.; Lebedev, V. A.; Piot, P.; Ruan, J.

2018-03-01

Optical stochastic cooling (OSC) is expected to enable fast cooling of dense particle beams. Transition from microwave to optical frequencies enables an achievement of stochastic cooling rates which are orders of magnitude higher than ones achievable with the classical microwave based stochastic cooling systems. A subsystemcritical to the OSC scheme is the focusing optics used to image radiation from the upstream "pickup" undulator to the downstream "kicker" undulator. In this paper, we present simulation results using wave-optics calculation carried out with the SYNCHROTRON RADIATION WORKSHOP (SRW). Our simulations are performed in support to a proof-of-principle experiment planned at the Integrable Optics Test Accelerator (IOTA) at Fermilab. The calculations provide an estimate of the energy kick received by a 100-MeV electron as it propagates in the kicker undulator and interacts with the electromagnetic pulse it radiated at an earlier time while traveling through the pickup undulator.

Effects of adenosine on intraocular pressure, optic nerve head blood flow, and choroidal blood flow in healthy humans.

PubMed

Polska, Elzbieta; Ehrlich, Paulina; Luksch, Alexandra; Fuchsjäger-Mayrl, Gabriele; Schmetterer, Leopold

2003-07-01

There is evidence from a variety of animal studies that the adenosine system plays a role in the control of intraocular pressure (IOP) and ocular blood flow. However, human data on the effect of adenosine on IOP and choroidal and optic nerve blood flow are not available. The effect of stepwise increases in doses of adenosine (10, 20, and 40 micro g/kg per minute, 30 minutes per infusion step) on optic nerve head blood flow, choroidal blood flow, and IOP was determined in a placebo-controlled double-masked clinical trial in 12 healthy male volunteers. Blood flow in the optic nerve head and choroid was measured with laser Doppler flowmetry. In addition, fundus pulsation amplitude in the macula (FPAM) and the optic nerve head (FPAO) were assessed with laser interferometry. Adenosine induced a small but significant decrease in IOP (at 40 microg/kg per minute: 12% +/- 13%), which was significant versus placebo (P = 0.046). In addition, adenosine induced a significant increase in choroidal blood flow (P < 0.001) and optic nerve head blood flow (P = 0.037), and FPAM (P = 0.0014) and tended to increase FPAO (P = 0.057). At the highest administered dose, the effect on choroidal hemodynamic parameters between 14% and 17%, whereas the effect on optic nerve hemodynamic parameters was between 3% and 11%. These data are consistent with adenosine inducing choroidal and optic nerve head vasodilatation and reducing IOP in healthy humans. Considering the neuroprotective properties of adenosine described in previous animal experiments the adenosine system is an attractive target system for therapeutic approaches in glaucoma.

Measurements in the bottom boundary layer on the Amazon subaqueous delta

USGS Publications Warehouse

Cacchione, D.A.; Drake, D.E.; Kayen, R.W.; Sternberg, R.W.; Kineke, G.C.; Tate, G.B.

1995-01-01

An instrumented bottom tripod (GEOPROBE) recorded flow and suspended sediment data in the bottom boundary layer above the lower foresets of the Amazon subaqueous delta in 65 m mean water depth in February, 1990. After about two weeks of operation the apparent seafloor at the tripod site rapidly elevated over a 14-hour period by about 44 cm. This sudden change, which was detected by an acoustic altimeter and which caused the loss of signals from the lowermost GEOPROBE current and optical sensors, is though to have been caused by the incursion of a dense bottom layer of fluid mud that migrated downslope from shallower sections of the foresets. The fluid-mud migration across the outer part of the foresets, if a repetitive and occasional process in this region, could be a major mechanism for episodic seaward growth of the delta. Current velocity profiles are used to estimate shear velocities, u*, and roughness lengths, zo, during the first two weeks of measurements. -from Authors

Microcapsules with a pH responsive polymer: influence of the encapsulated oil on the capsule morphology.

PubMed

Wagdare, Nagesh A; Marcelis, Antonius T M; Boom, Remko M; van Rijn, Cees J M

2011-11-01

Microcapsules were prepared by microsieve membrane cross flow emulsification of Eudragit FS 30D/dichloromethane/edible oil mixtures in water, and subsequent phase separation induced by extraction of the dichloromethane through an aqueous phase. For long-chain triglycerides and jojoba oil, core-shell particles were obtained with the oil as core, surrounded by a shell of Eudragit. Medium chain triglyceride (MCT oil) was encapsulated as relatively small droplets in the Eudragit matrix. The morphology of the formed capsules was investigated with optical and SEM microscopy. Extraction of the oil from the core-shell capsules with hexane resulted in hollow Eudragit capsules with porous shells. It was shown that the differences are related to the compatibility of the oils with the shell-forming Eudragit. An oil with poor compatibility yields microcapsules with a dense Eudragit shell on a single oil droplet as the core; oils having better compatibility yield porous Eudragit spheres with several oil droplets trapped inside. Copyright © 2011 Elsevier B.V. All rights reserved.

Video stereolization: combining motion analysis with user interaction.

PubMed

Liao, Miao; Gao, Jizhou; Yang, Ruigang; Gong, Minglun

2012-07-01

We present a semiautomatic system that converts conventional videos into stereoscopic videos by combining motion analysis with user interaction, aiming to transfer as much as possible labeling work from the user to the computer. In addition to the widely used structure from motion (SFM) techniques, we develop two new methods that analyze the optical flow to provide additional qualitative depth constraints. They remove the camera movement restriction imposed by SFM so that general motions can be used in scene depth estimation-the central problem in mono-to-stereo conversion. With these algorithms, the user's labeling task is significantly simplified. We further developed a quadratic programming approach to incorporate both quantitative depth and qualitative depth (such as these from user scribbling) to recover dense depth maps for all frames, from which stereoscopic view can be synthesized. In addition to visual results, we present user study results showing that our approach is more intuitive and less labor intensive, while producing 3D effect comparable to that from current state-of-the-art interactive algorithms.

High energy radiation from jets and accretion disks near rotating black holes

NASA Astrophysics Data System (ADS)

O'Riordan, Michael; Pe'er, Asaf; McKinney, Jonathan C.

2017-01-01

We model the low/hard state in X-ray binaries as a magnetically arrested accretion flow, and calculate the resulting radiation using a general-relativistic radiative transport code. Firstly, we investigate the origin of the high-energy emission. We find the following indications of a significant jet contribution at high energies: (i) a pronounced γ-ray peak at ˜ 1023 Hz, (ii) a break in the optical/UV band where the spectrum changes from disk to jet dominated, and (iii) a low-frequency synchrotron peak ≲ 1014 Hz implies that a significant fraction of any observed X-ray and γ-ray emission originates in the jet. Secondly, we investigate the effects of black hole spin on the high-energy emission. We find that the X-ray and γ-ray power depend strongly on spin and inclination angle. Surprisingly, this dependence is not a result of the Blandford-Znajek mechanism, but instead can be understood as a redshift effect. For rapidly rotating black holes, observers with large inclinations see deeper into the hot, dense, highly-magnetized inner regions of the accretion flow. Since the lower frequency emission originates at larger radii, it is not significantly affected by the spin. Therefore, the ratio of the X-ray to near-infrared power is an observational probe of black hole spin.

Real-time eye motion correction in phase-resolved OCT angiography with tracking SLO

PubMed Central

Braaf, Boy; Vienola, Kari V.; Sheehy, Christy K.; Yang, Qiang; Vermeer, Koenraad A.; Tiruveedhula, Pavan; Arathorn, David W.; Roorda, Austin; de Boer, Johannes F.

2012-01-01

In phase-resolved OCT angiography blood flow is detected from phase changes in between A-scans that are obtained from the same location. In ophthalmology, this technique is vulnerable to eye motion. We address this problem by combining inter-B-scan phase-resolved OCT angiography with real-time eye tracking. A tracking scanning laser ophthalmoscope (TSLO) at 840 nm provided eye tracking functionality and was combined with a phase-stabilized optical frequency domain imaging (OFDI) system at 1040 nm. Real-time eye tracking corrected eye drift and prevented discontinuity artifacts from (micro)saccadic eye motion in OCT angiograms. This improved the OCT spot stability on the retina and consequently reduced the phase-noise, thereby enabling the detection of slower blood flows by extending the inter-B-scan time interval. In addition, eye tracking enabled the easy compounding of multiple data sets from the fovea of a healthy volunteer to create high-quality eye motion artifact-free angiograms. High-quality images are presented of two distinct layers of vasculature in the retina and the dense vasculature of the choroid. Additionally we present, for the first time, a phase-resolved OCT angiogram of the mesh-like network of the choriocapillaris containing typical pore openings. PMID:23304647

Design, simulation and characterisation of integrated optics for a microfabricated flow cytometer

NASA Astrophysics Data System (ADS)

Barat, David; Benazzi, Giuseppe; Mowlem, Matthew Charles; Ruano, Jesus Miguel; Morgan, Hywel

2010-05-01

Flow cytometry is widely used for analyzing micro-particles such as cells and bacteria. Microfabricated flow cytometers promise reduced instrument size and cost with increased robustness and have application in medicine, life sciences and environmental metrology. Further miniaturisation and robustness can be achieved if integrated optics are used instead of traditional free space optics. We present designs simulation and experimental characterisation of integrated optics for a microfabricated cytometer made from SU-8 resin on a glass substrate. The optics constructed from combinations of optical fibres (positioned with microgrooves), waveguides, and microlenses enable analysis of scattered light and fluorescence from particles positioned near the centre of a microchannel using one dimensional sheath flow. Four different methods for directing the incident light onto the particles are examined and the optimum design discussed.

Optic flow detection is not influenced by visual-vestibular congruency.

PubMed

Holten, Vivian; MacNeilage, Paul R

2018-01-01

Optic flow patterns generated by self-motion relative to the stationary environment result in congruent visual-vestibular self-motion signals. Incongruent signals can arise due to object motion, vestibular dysfunction, or artificial stimulation, which are less common. Hence, we are predominantly exposed to congruent rather than incongruent visual-vestibular stimulation. If the brain takes advantage of this probabilistic association, we expect observers to be more sensitive to visual optic flow that is congruent with ongoing vestibular stimulation. We tested this expectation by measuring the motion coherence threshold, which is the percentage of signal versus noise dots, necessary to detect an optic flow pattern. Observers seated on a hexapod motion platform in front of a screen experienced two sequential intervals. One interval contained optic flow with a given motion coherence and the other contained noise dots only. Observers had to indicate which interval contained the optic flow pattern. The motion coherence threshold was measured for detection of laminar and radial optic flow during leftward/rightward and fore/aft linear self-motion, respectively. We observed no dependence of coherence thresholds on vestibular congruency for either radial or laminar optic flow. Prior studies using similar methods reported both decreases and increases in coherence thresholds in response to congruent vestibular stimulation; our results do not confirm either of these prior reports. While methodological differences may explain the diversity of results, another possibility is that motion coherence thresholds are mediated by neural populations that are either not modulated by vestibular stimulation or that are modulated in a manner that does not depend on congruency.

Green Icebergs: a Problem in Geophysics and Atmospheric Optics

NASA Astrophysics Data System (ADS)

Lee, Raymond L., Jr.

The curious phenomenon of green icebergs has intrigued polar travelers for centuries. Although some researchers have speculated that this ice contains colorants, an investigator who has actually examined a green iceberg sample found very little intrinsically green material. This supports our idea that at least some green icebergs are due to the combined effects of reddened sunlight illuminating intrinsically blue-green ice. In this case, "intrinsic" refers to the blue-green absorption minimum of pure ice. Naturally occurring ice containing a few inclusions that scatter light with little or no spectral selectivity also exhibits this same absorption minimum. Artists' and travelers' accounts of colored ice tell us that, while remarkable, it is not uncommon. The few 20th-century scientific reports on green icebergs agree with the earlier accounts on the unusual denseness and translucence of highly colored ice. We see the same correlation between ice colors and ice denseness in accounts of glacier ice. When we examine the optical properties of dense, relatively bubble-free ice, we find that we can nearly match its reflectance spectra with either of two multiple -scattering models for ice optics. If we pair these models' reflectance spectra with estimates of polar daylight spectra, we can duplicate the observed colors of green icebergs. Our psychophysical model of human color perception is the 1931 CIE chromaticity space. Although this form of colorimetry has some perceptual faults, we may nonetheless use it as a means of comparing the observed and theoretical colors of green icebergs. In the absence of in situ spectral reflectance measurements, we use video digitizing and spectrodensitometry to extract colorimetric information from color photographs of green icebergs. However, before using these remote sensing techniques, first we must solve the intricate problem of calibrating them against known color standards. After doing this, we find that our analyses of green iceberg photographs support the idea that some of these icebergs result from the combination of ice's intrinsic optical properties and its illumination by reddened sunlight.

Laser speckle contrast imaging of cerebral blood flow of newborn mice at optical clearing

NASA Astrophysics Data System (ADS)

Timoshina, Polina A.; Zinchenko, Ekaterina M.; Tuchina, Daria K.; Sagatova, Madina M.; Semyachkina-Glushkovskaya, Oxana V.; Tuchin, Valery V.

2017-03-01

In this work, we consider the use of optical clearing agents to improve imaging quality of the cerebral blood flow of newborn mice. Aqueous 60%-glycerol solution, aqueous 70%-OmnipaqueTM(300) solution and OmnipaqueTM (300) solution in water/DMSO(25%/5%) were selected as the optical clearing agents. Laser speckle contrast imaging (LSCI) was used for imaging of cerebral blood flow in newborn mice brain during topical optical clearing of tissuesin the area of the fontanelle. These results demonstrate the effectiveness of glycerol and Omnipaque solutions as optical clearing agents for investigation of cerebral blood flow in newborn mice without scalp removing and skull thinning.

Ultrafast visualization of the structural evolution of dense hydrogen towards warm dense matter

NASA Astrophysics Data System (ADS)

Fletcher, Luke

2016-10-01

Hot dense hydrogen far from equilibrium is ubiquitous in nature occurring during some of the most violent and least understood events in our universe such as during star formation, supernova explosions, and the creation of cosmic rays. It is also a state of matter important for applications in inertial confinement fusion research and in laser particle acceleration. Rapid progress occurred in recent years characterizing the high-pressure structural properties of dense hydrogen under static or dynamic compression. Here, we show that spectrally and angularly resolved x-ray scattering measure the thermodynamic properties of dense hydrogen and resolve the ultrafast evolution and relaxation towards thermodynamic equilibrium. These studies apply ultra-bright x-ray pulses from the Linac Coherent Light (LCLS) source. The interaction of rapidly heated cryogenic hydrogen with a high-peak power optical laser is visualized with intense LCLS x-ray pulses in a high-repetition rate pump-probe setting. We demonstrate that electron-ion coupling is affected by the small number of particles in the Debye screening cloud resulting in much slower ion temperature equilibration than predicted by standard theory. This work was supported by the DOE Office of Science, Fusion Energy Science under FWP 100182.

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

NASA Astrophysics Data System (ADS)

Hansen, S. B.; Harding, E. C.; Knapp, P. F.; Gomez, M. R.; Nagayama, T.; Bailey, J. E.

2018-05-01

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. We show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated by the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 1024 e/cm3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.

Theoretical analysis for scaling law of thermal blooming based on optical phase deference

NASA Astrophysics Data System (ADS)

Sun, Yunqiang; Huang, Zhilong; Ren, Zebin; Chen, Zhiqiang; Guo, Longde; Xi, Fengjie

2016-10-01

In order to explore the laser propagation influence of thermal blooming effect of pipe flow and to analysis the influencing factors, scaling law theoretical analysis of the thermal blooming effects in pipe flow are carry out in detail based on the optical path difference caused by thermal blooming effects in pipe flow. Firstly, by solving the energy coupling equation of laser beam propagation, the temperature of the flow is obtained, and then the optical path difference caused by the thermal blooming is deduced. Through the analysis of the influence of pipe size, flow field and laser parameters on the optical path difference, energy scaling parameters Ne=nTαLPR2/(ρɛCpπR02) and geometric scaling parameters Nc=νR2/(ɛL) of thermal blooming for the pipe flow are derived. Secondly, for the direct solution method, the energy coupled equations have analytic solutions only for the straight tube with Gauss beam. Considering the limitation of directly solving the coupled equations, the dimensionless analysis method is adopted, the analysis is also based on the change of optical path difference, same scaling parameters for the pipe flow thermal blooming are derived, which makes energy scaling parameters Ne and geometric scaling parameters Nc have good universality. The research results indicate that when the laser power and the laser beam diameter are changed, thermal blooming effects of the pipeline axial flow caused by optical path difference will not change, as long as you keep energy scaling parameters constant. When diameter or length of the pipe changes, just keep the geometric scaling parameters constant, the pipeline axial flow gas thermal blooming effects caused by optical path difference distribution will not change. That is to say, when the pipe size and laser parameters change, if keeping two scaling parameters with constant, the pipeline axial flow thermal blooming effects caused by the optical path difference will not change. Therefore, the energy scaling parameters and the geometric scaling parameters can really describe the gas thermal blooming effect in the axial pipe flow. These conclusions can give a good reference for the construction of the thermal blooming test system of laser system. Contrasted with the thermal blooming scaling parameters of the Bradley-Hermann distortion number ND and Fresnel number NF, which were derived based on the change of far field beam intensity distortion, the scaling parameters of pipe flow thermal blooming deduced from the optical path deference variation are very suitable for the optical system with short laser propagation distance, large Fresnel number and obviously changed optical path deference.

Responses to deceleration during car following: roles of optic flow, warnings, expectations, and interruptions.

PubMed

DeLucia, Patricia R; Tharanathan, Anand

2009-12-01

More than 25% of accidents are rear-end collisions. It is essential to identify the factors that contribute to such collisions. One such factor is a driver's ability to respond to the deceleration of the car ahead. In Experiment 1, we measured effects of optic flow information and discrete visual and auditory warnings (brake lights, tones) on responses to deceleration during car following. With computer simulations of car-following scenes, university students pressed a button when the lead car decelerated. Both classes of information affected responses. Observers relied on discrete warnings when optic flow information was relatively less effective as determined by the lead car's headway and deceleration rate. This is consistent with DeLucia's (2008) conceptual framework of space perception that emphasized the importance of viewing distance and motion (and task). In Experiment 2, we measured responses to deceleration after a visual interruption. Scenes were designed to tease apart the role of expectations and optic flow. Responses mostly were consistent with optic flow information presented after the interruption rather than with putative mental expectations that were set up by the lead car's motion prior to the interruption. The theoretical implication of the present results is that responses to deceleration are based on multiple sources of information, including optical size, optical expansion rate and tau, and discrete warnings that are independent of optic flow. The practical implication is that in-vehicle collision-avoidance warning systems may be more useful when optic flow is less effective (e.g., slow deceleration rates), implicating a role for adaptive collision-warning systems. Copyright 2009 APA

On the high fidelity simulation of chemical explosions and their interaction with solid particle clouds

NASA Astrophysics Data System (ADS)

Balakrishnan, Kaushik

The flow field behind chemical explosions in multiphase environments is investigated using a robust, state-of-the-art simulation strategy that accounts for the thermodynamics, gas dynamics and fluid mechanics of relevance to the problem. Focus is laid on the investigation of blast wave propagation, growth of hydrodynamic instabilities behind explosive blasts, the mixing aspects behind explosions, the effects of afterburn and its quantification, and the role played by solid particles in these phenomena. In particular, the confluence and interplay of these different physical phenomena are explored from a fundamental perspective, and applied to the problem of chemical explosions. A solid phase solver suited for the study of high-speed, two-phase flows has been developed and validated. This solver accounts for the inter-phase mass, momentum and energy transfer through empirical laws, and ensures two-way coupling between the two phases, viz. solid particles and gas. For dense flow fields, i.e., when the solid volume fraction becomes non-negligible (˜60%), the finite volume method with a Godunov type shock-capturing scheme requires modifications to account for volume fraction gradients during the computation of cell interface gas fluxes. To this end, the simulation methodology is extended with the formulation of an Eulerian gas, Lagrangian solid approach, thereby ensuring that the so developed two-phase simulation strategy can be applied for both flow conditions, dilute and dense alike. Moreover, under dense loading conditions the solid particles inevitably collide, which is accounted for in the current research effort with the use of an empirical collision/contact model from literature. Furthermore, the post-detonation flow field consists of gases under extreme temperature and pressure conditions, necessitating the use of real gas equations of state in the multiphase model. This overall simulation strategy is then extended to the investigation of chemical explosions in multiphase environments, with emphasis on the study of hydrodynamic instability growth, mixing, afterburn effects ensuing from the process, particle ignition and combustion (if reactive), dispersion, and their interaction with the vortices in the mixing layer. The post-detonation behavior of heterogeneous explosives is addressed by using three parts to the investigation. In the first part, only one-dimensional effects are considered, with the goal to assess the presently developed dense two-phase formulation. The total deliverable impulsive loading from heterogeneous explosive charges containing inert steel particles is estimated for a suite of operating parameters and compared, and it is demonstrated that heterogeneous explosive charges deliver a higher near-field impulse than homogeneous explosive charges containing the same mass of the high explosive. In the second part, three-dimensional effects such as hydrodynamic instabilities are accounted for, with the focus on characterizing the mixing layer ensuing from the detonation of heterogeneous explosive charges containing inert steel particles. It is shown that particles introduce significant amounts of hydrodynamic instabilities in the mixing layer, resulting in additional physical phenomena that play a prominent role in the flow features. In particular, the fluctuation intensities, fireball size and growth rates are augmented for heterogeneous explosions vis-a-vis homogeneous explosions, thereby demonstrating that solid particles enhance the perturbation intensities in the flow. In the third part of the investigation of heterogeneous explosions, dense, aluminized explosions are considered, and the particles are observed to burn in two phases, with an initial quenching due to the rarefaction wave, and a final quenching outside the fireball. Due to faster response time scales, smaller particles are observed to heat and accelerate more during early times, and also cool and decelerate more at late times, compared to counterpart larger particle sizes. Furthermore, the average particle velocities at late times are observed to be independent of the initial solid volume fraction in the explosive charge, as the particles eventually reach an equilibrium with the local gas. These studies have provided some crucial insights to the flow physics of dense, aluminized explosives. (Abstract shortened by UMI.)

Effect of Self-Produced Locomotion on Infant Postural Compensation to Optic Flow.

ERIC Educational Resources Information Center

Higgins, Carol I.; And Others

1996-01-01

Compared the postural responsiveness of seven-, eight-, and nine-month-old infants. Results indicated greater use of optic flow for postural control after a self-produced locomotor experience. Infants with endogenous (creeping) or artificial (walker) self-produced locomotor experience responded to portions of the optic flow field, whereas…

Stability in Young Infants' Discrimination of Optic Flow

ERIC Educational Resources Information Center

Gilmore, Rick O.; Baker, Thomas J.; Grobman, K. H.

2004-01-01

Although considerable progress has been made in understanding how adults perceive their direction of self-motion, or heading, from optic flow, little is known about how these perceptual processes develop in infants. In 3 experiments, the authors explored how well 3- to 6-month-old infants could discriminate between optic flow patterns that…

Backscatter particle image velocimetry via optical time-of-flight sectioning

DOE PAGES

Paciaroni, Megan E.; Chen, Yi; Lynch, Kyle Patrick; ...

2018-01-11

Conventional particle image velocimetry (PIV) configurations require a minimum of two optical access ports, inherently restricting the technique to a limited class of flows. Here, the development and application of a novel method of backscattered time-gated PIV requiring a single-optical-access port is described along with preliminary results. The light backscattered from a seeded flow is imaged over a narrow optical depth selected by an optical Kerr effect (OKE) time gate. The picosecond duration of the OKE time gate essentially replicates the width of the laser sheet of conventional PIV by limiting detected photons to a narrow time-of-flight within the flow.more » Thus, scattering noise from outside the measurement volume is eliminated. In conclusion, this PIV via the optical time-of-flight sectioning technique can be useful in systems with limited optical access and in flows near walls or other scattering surfaces.« less

Backscatter particle image velocimetry via optical time-of-flight sectioning

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

Paciaroni, Megan E.; Chen, Yi; Lynch, Kyle Patrick

Conventional particle image velocimetry (PIV) configurations require a minimum of two optical access ports, inherently restricting the technique to a limited class of flows. Here, the development and application of a novel method of backscattered time-gated PIV requiring a single-optical-access port is described along with preliminary results. The light backscattered from a seeded flow is imaged over a narrow optical depth selected by an optical Kerr effect (OKE) time gate. The picosecond duration of the OKE time gate essentially replicates the width of the laser sheet of conventional PIV by limiting detected photons to a narrow time-of-flight within the flow.more » Thus, scattering noise from outside the measurement volume is eliminated. In conclusion, this PIV via the optical time-of-flight sectioning technique can be useful in systems with limited optical access and in flows near walls or other scattering surfaces.« less

Theoretical analysis of stack gas emission velocity measurement by optical scintillation

NASA Astrophysics Data System (ADS)

Yang, Yang; Dong, Feng-Zhong; Ni, Zhi-Bo; Pang, Tao; Zeng, Zong-Yong; Wu, Bian; Zhang, Zhi-Rong

2014-04-01

Theoretical analysis for an online measurement of the stack gas flow velocity based on the optical scintillation method with a structure of two parallel optical paths is performed. The causes of optical scintillation in a stack are first introduced. Then, the principle of flow velocity measurement and its mathematical expression based on cross correlation of the optical scintillation are presented. The field test results show that the flow velocity measured by the proposed technique in this article is consistent with the value tested by the Pitot tube. It verifies the effectiveness of this method. Finally, by use of the structure function of logarithmic light intensity fluctuations, the theoretical explanation of optical scintillation spectral characteristic in low frequency is given. The analysis of the optical scintillation spectrum provides the basis for the measurement of the stack gas flow velocity and particle concentration simultaneously.

Fast incorporation of optical flow into active polygons.

PubMed

Unal, Gozde; Krim, Hamid; Yezzi, Anthony

2005-06-01

In this paper, we first reconsider, in a different light, the addition of a prediction step to active contour-based visual tracking using an optical flow and clarify the local computation of the latter along the boundaries of continuous active contours with appropriate regularizers. We subsequently detail our contribution of computing an optical flow-based prediction step directly from the parameters of an active polygon, and of exploiting it in object tracking. This is in contrast to an explicitly separate computation of the optical flow and its ad hoc application. It also provides an inherent regularization effect resulting from integrating measurements along polygon edges. As a result, we completely avoid the need of adding ad hoc regularizing terms to the optical flow computations, and the inevitably arbitrary associated weighting parameters. This direct integration of optical flow into the active polygon framework distinguishes this technique from most previous contour-based approaches, where regularization terms are theoretically, as well as practically, essential. The greater robustness and speed due to a reduced number of parameters of this technique are additional and appealing features.

Study on polarized optical flow algorithm for imaging bionic polarization navigation micro sensor

NASA Astrophysics Data System (ADS)

Guan, Le; Liu, Sheng; Li, Shi-qi; Lin, Wei; Zhai, Li-yuan; Chu, Jin-kui

2018-05-01

At present, both the point source and the imaging polarization navigation devices only can output the angle information, which means that the velocity information of the carrier cannot be extracted from the polarization field pattern directly. Optical flow is an image-based method for calculating the velocity of pixel point movement in an image. However, for ordinary optical flow, the difference in pixel value as well as the calculation accuracy can be reduced in weak light. Polarization imaging technology has the ability to improve both the detection accuracy and the recognition probability of the target because it can acquire the extra polarization multi-dimensional information of target radiation or reflection. In this paper, combining the polarization imaging technique with the traditional optical flow algorithm, a polarization optical flow algorithm is proposed, and it is verified that the polarized optical flow algorithm has good adaptation in weak light and can improve the application range of polarization navigation sensors. This research lays the foundation for day and night all-weather polarization navigation applications in future.

Shear-induced organization of forces in dense suspensions: signatures of discontinuous shear thickening

NASA Astrophysics Data System (ADS)

Sarkar, Sumantra; Shatoff, Elan; Ramola, Kabir; Mari, Romain; Morris, Jeffrey; Chakraborty, Bulbul

2017-06-01

Dense suspensions can exhibit an abrupt change in their viscosity in response to increasing shear rate. The origin of this discontinuous shear thickening (DST) has been ascribed to the transformation of lubricated contacts to frictional, particle-on-particle contacts. Recent research on the flowing and jamming behavior of dense suspensions has explored the intersection of ideas from granular physics and Stokesian fluid dynamics to better understand this transition from lubricated to frictional rheology. DST is reminiscent of classical phase transitions, and a key question is how interactions between the microscopic constituents give rise to a macroscopic transition. In this paper, we extend a formalism that has proven to be successful in understanding shear jamming of dry grains to dense suspensions. Quantitative analysis of the collective evolution of the contactforce network accompanying the DST transition demonstrates clear changes in the distribution of microscopic variables, and leads to the identification of an "order parameter" characterizing DST.

Enhanced Mobility in Concentrated Pyroclastic Density Currents: An Examination of a Self-Fluidization Mechanism

NASA Astrophysics Data System (ADS)

Breard, Eric C. P.; Dufek, Josef; Lube, Gert

2018-01-01

Pyroclastic density currents (PDCs) are a significant volcanic hazard. However, their dominant transport mechanisms remain poorly understood, in part because of the large variability of PDC types and deposits. Here we combine field data with experimental and numerical simulations to illuminate the twofold fate of particles settling from an ash cloud to form the dense PDC basal flow. At solid fractions >1 vol %, heterogeneous drag leads to formation of mesoscale particle clusters that favor rapid particle settling and result in a mobile dense layer with significant bed weight support. Conversely, at lower concentrations the absence of particle clusters typically leads to formation of poorly mobile dense beds that deposit massive layers. Based on this transport dichotomy, we present a numerical dense-dilute parameter that allows a PDC's dominant transport mechanism to be determined directly from the deposit geometry and grainsize characteristics.

Effect of cross-phase-modulation-induced polarization scattering on optical polarization mode dispersion compensation in wavelength-division-multiplexed systems

NASA Astrophysics Data System (ADS)

Xie, Chongjin; Möller, Lothar; Kilper, Daniel C.; Mollenauer, Linn F.

2003-12-01

Interchannel cross-phase-modulation-induced polarization scattering (XPMIPS) and its effect on the performance of optical polarization mode dispersion (PMD) compensation in wavelength-division-multiplexed (WDM) systems are studied. The level of XPMIPS in long-haul WDM transmission systems is theoretically quantified, and its effect on optical PMD compensation is evaluated with numerical simulations. We show that in 10-Gbit/s ultra-long-haul dense WDM systems XPMIPS could reduce the PMD compensation efficiency by 50%, whereas for 40-Gbit/s systems the effect of XPMIPS is smaller.

High Average Power Laser Gain Medium With Low Optical Distortion Using A Transverse Flowing Liquid Host

DOEpatents

Comaskey, Brian J.; Ault, Earl R.; Kuklo, Thomas C.

2005-07-05

A high average power, low optical distortion laser gain media is based on a flowing liquid media. A diode laser pumping device with tailored irradiance excites the laser active atom, ion or molecule within the liquid media. A laser active component of the liquid media exhibits energy storage times longer than or comparable to the thermal optical response time of the liquid. A circulation system that provides a closed loop for mixing and circulating the lasing liquid into and out of the optical cavity includes a pump, a diffuser, and a heat exchanger. A liquid flow gain cell includes flow straighteners and flow channel compression.

Aqueous carrier waveguide in a flow cytometer

DOEpatents

Mariella, R.P. Jr.; Engh, G. van den; Northrup, M.A.

1995-12-12

The liquid of a flow cytometer itself acts as an optical waveguide, thus transmitting the light to an optical filter/detector combination. This alternative apparatus and method for detecting scattered light in a flow cytometer is provided by a device which views and detects the light trapped within the optical waveguide formed by the flow stream. A fiber optic or other light collecting device is positioned within the flow stream. This provides enormous advantages over the standard light collection technique which uses a microscope objective. The signal-to-noise ratio is greatly increased over that for right-angle-scattered light collected by a microscope objective, and the alignment requirements are simplified. 6 figs.

Processing, Mechanical and Optical Properties of Additive-Free ZrC Ceramics Prepared by Spark Plasma Sintering.

PubMed

Musa, Clara; Licheri, Roberta; Orrù, Roberto; Cao, Giacomo; Sciti, Diletta; Silvestroni, Laura; Zoli, Luca; Balbo, Andrea; Mercatelli, Luca; Meucci, Marco; Sani, Elisa

2016-06-18

In the present study, nearly fully dense monolithic ZrC samples are produced and broadly characterized from microstructural, mechanical and optical points of view. Specifically, 98% dense products are obtained by Spark Plasma Sintering (SPS) after 20 min dwell time at 1850 °C starting from powders preliminarily prepared by Self-propagating High-temperature Synthesis (SHS) followed by 20 min ball milling. A prolonged mechanical treatment up to 2 h of SHS powders does not lead to appreciable benefits. Vickers hardness of the resulting samples (17.5 ± 0.4 GPa) is reasonably good for monolithic ceramics, but the mechanical strength (about 250 MPa up to 1000 °C) could be further improved by suitable optimization of the starting powder characteristics. The very smoothly polished ZrC specimen subjected to optical measurements displays high absorption in the visible-near infrared region and low thermal emittance at longer wavelengths. Moreover, the sample exhibits goodspectral selectivity (2.1-2.4) in the 1000-1400 K temperature range. These preliminary results suggest that ZrC ceramics produced through the two-step SHS/SPS processing route can be considered as attractive reference materials for the development of innovative solar energy absorbers.

Waveguide detection of right-angle-scattered light in flow cytometry

DOEpatents

Mariella, Jr., Raymond P.

2000-01-01

A transparent flow cell is used as an index-guided optical waveguide. A detector for the flow cell but not the liquid stream detects the Right-Angle-Scattered (RAS) Light exiting from one end of the flow cell. The detector(s) could view the trapped RAS light from the flow cell either directly or through intermediate optical light guides. If the light exits one end of the flow cell, then the other end of the flow cell can be given a high-reflectivity coating to approximately double the amount of light collected. This system is more robust in its alignment than the traditional flow cytometry systems which use imaging optics, such as microscope objectives.

Onset of sediment transport is a continuous transition driven by fluid shear and granular creep

PubMed Central

Houssais, Morgane; Ortiz, Carlos P.; Durian, Douglas J.; Jerolmack, Douglas J.

2015-01-01

Fluid-sheared granular transport sculpts landscapes and undermines infrastructure, yet predicting the onset of sediment transport remains notoriously unreliable. For almost a century, this onset has been treated as a discontinuous transition at which hydrodynamic forces overcome gravity-loaded grain–grain friction. Using a custom laminar-shear flume to image slow granular dynamics deep into the bed, here we find that the onset is instead a continuous transition from creeping to granular flow. This transition occurs inside the dense granular bed at a critical viscous number, similar to granular flows and colloidal suspensions and inconsistent with hydrodynamic frameworks. We propose a new phase diagram for sediment transport, where ‘bed load’ is a dense granular flow bounded by creep below and suspension above. Creep is characteristic of disordered solids and reminiscent of soil diffusion on hillslopes. Results provide new predictions for the onset and dynamics of sediment transport that challenge existing models. PMID:25751296

A frictionally and hydraulically constrained model of the convectively driven mean flow in partially enclosed seas

NASA Astrophysics Data System (ADS)

Maxworthy, T.

1997-08-01

A simple three-layer model of the dynamics of partially enclosed seas, driven by a surface buoyancy flux, is presented. It contains two major elements, a hydraulic constraint at the exit contraction and friction in the interior of the main body of the sea; both together determine the vertical structure and magnitudes of the interior flow variables, i.e. velocity and density. Application of the model to the large-scale dynamics of the Red Sea gives results that are not in disagreement with observation once the model is applied, also, to predict the dense outflow from the Gulf of Suez. The latter appears to be the agent responsible for the formation of dense bottom water in this system. Also, the model is reasonably successful in predicting the density of the outflow from the Persian Gulf, and can be applied to any number of other examples of convectively driven flow in long, narrow channels, with or without sills and constrictions at their exits.

Chemical vapor deposition of mullite coatings

DOEpatents

Sarin, Vinod; Mulpuri, Rao

1998-01-01

This invention is directed to the creation of crystalline mullite coatings having uniform microstructure by chemical vapor deposition (CVD). The process comprises the steps of establishing a flow of reactants which will yield mullite in a CVD reactor, and depositing a crystalline coating from the reactant flow. The process will yield crystalline coatings which are dense and of uniform thickness.

Magnesium-Aluminum-Zirconium Oxide Amorphous Ternary Composite: A Dense and Stable Optical Coating

NASA Technical Reports Server (NTRS)

Sahoo, N. K.; Shapiro, A. P.

1998-01-01

In the present work, the process parameter dependent optical and structural properties of MgO-Al(2)O(3)-ZrO(2) ternary mixed-composite material have been investigated. Optical properties were derived from spectrophotometric measurements. The surface morphology, grain size distributions, crystallographic phases and process dependent material composition of films have been investigated through the use of Atomic Force Microscopy (AFM), X-ray diffraction analysis and Energy Dispersive X- ray (EDX) analysis. EDX analysis made evident the correlation between the optical constants and the process dependent compositions in the films. It is possible to achieve environmentally stable amorphous films with high packing density under certain optimized process conditions.

MgO-Al2O3-ZrO2 Amorphous Ternary Composite: A Dense and Stable Optical Coating

NASA Technical Reports Server (NTRS)

Shaoo, Naba K.; Shapiro, Alan P.

1998-01-01

The process-parameter-dependent optical and structural properties of MgO-Al2O3-ZrO2 ternary mixed-composite material were investigated. Optical properties were derived from spectrophotometric measurements. The surface morphology, grain size distributions, crystallographic phases, and process- dependent material composition of films were investigated through the use of atomic force microscopy, x-ray diffraction analysis, and energy-dispersive x-ray analysis. Energy-dispersive x-ray analysis made evident the correlation between the optical constants and the process-dependent compositions in the films. It is possible to achieve environmentally stable amorphous films with high packing density under certain optimized process conditions.

An Index-Mismatch Scattering Approach to Optical Limiting

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

Exarhos, Gregory J.; Ferris, Kim F.; Windisch, Charles F.

A densely packed bed of alkaline earth fluoride particles percolated by a fluid medium has been investigated as a potential index-matched optical limiter in the spirit of a Christiansen-Shelyubskii filter. Marked optical limiting was observed through this transparent medium under conditions where the focused second-harmonic output of a Q-swtiched Nd: YAG laser was on the order of about 1 J/cm2. An open-aperture Z-scan technique was used to quantify the limiting behavior. In this case, the mechanism of optical limiting is thought to be a nonlinear shift in the fluid index of refraction, resulting in an index mismatch between the disparatemore » phases at high laser fluence.« less

Agonist and antagonist effects of diadenosine tetraphosphate, a platelet dense granule constituent, on platelet P2Y1, P2Y12 and P2X1 receptors.

PubMed

Chang, Hung; Yanachkov, Ivan B; Michelson, Alan D; Li, YouFu; Barnard, M R; Wright, George E; Frelinger, Andrew L

2010-02-01

Diadenosine 5',5'''-P(1),P(4)- tetraphosphate (Ap(4)A) is stored in platelet dense granules, but its effects on platelet function are not well understood. We examined the effects of Ap(4)A on platelet purinergic receptors P2Y(1), P2Y(12) and P2X(1). Flow cytometry was used to measure the effects of Ap(4)A in the presence or absence of ADP on: a) P2Y(12)-mediated decrease in intraplatelet phosphorylated vasodilator stimulated phosphoprotein (VASP), b) P2Y(1)-mediated increase in platelet cytosolic Ca(2+), and c) P2X(1)-mediated intraplatelet entry of extracellular Ca(2+). ADP-stimulated platelet shape change (P2Y(1)-mediated) and aggregation (P2Y(1)- and P2Y(12)-mediated) were measured optically. Ap(4)A inhibited 3 microM ADP-induced: a) platelet aggregation (IC(50) 9.8+/-2.8 microM), b) P2Y(1)-mediated shape change, c) P2Y(1)-mediated increase in platelet cytosolic Ca(2+) (IC(50) 40.8+/-12.3 microM), and d) P2Y(12)-mediated decrease in VASP phosphorylation (IC(50)>250 microM). In the absence of added ADP, Ap(4)A had agonist effects on platelet P2X(1) and P2Y(12), but not P2Y(1), receptors. Ap(4)A, a constituent of platelet dense granules, is a) an antagonist of platelet P2Y(1) and P2Y(12) receptors, where it inhibits the effects of ADP, and b) an agonist of platelet P2X(1) and P2Y(12) receptors. Copyright 2009 Elsevier Ltd. All rights reserved.

Agonist and Antagonist Effects of Diadenosine Tetraphosphate, a Platelet Dense Granule Constituent, on Platelet P2Y1, P2Y12 and P2X1 Receptors

PubMed Central

Chang, Hung; Yanachkov, Ivan B.; Michelson, Alan D.; Li, YouFu; Barnard, M.R.; Wright, George E.; Frelinger, Andrew L.

2010-01-01

Introduction Diadenosine 5',5"'-P1,P4-tetraphosphate (Ap4A) is stored in platelet dense granules, but its effects on platelet function are not well understood. Methods and Results We examined the effects of Ap4A on platelet purinergic receptors P2Y1, P2Y12 and P2X1. Flow cytometry was used to measure the effects of Ap4A in the presence or absence of ADP on: a) P2Y12-mediated decrease in intraplatelet phosphorylated vasodilator stimulated phosphoprotein (VASP), b) P2Y1-mediated increase in platelet cytosolic Ca2+, and c) P2X1-mediated intraplatelet entry of extracellular Ca2+. ADP-stimulated platelet shape change (P2Y1-mediated) and aggregation (P2Y1- and P2Y12-mediated) were measured optically. Ap4A inhibited 3 µM ADP-induced: a) platelet aggregation (IC50 9.8 ± 2.8 µM), b) P2Y1-mediated shape change, c) P2Y1-mediated increase in platelet cytosolic Ca2+ (IC50 40.8 ± 12.3 µM), and d) P2Y12-mediated decrease in VASP phosphorylation (IC50 >250 µM). In the absence of added ADP, Ap4A had agonist effects on platelet P2X1 and P2Y12, but not P2Y1, receptors. Conclusion Ap4A, a constituent of platelet dense granules, is a) an antagonist of platelet P2Y1 and P2Y12 receptors, where it inhibits the effects of ADP, and b) an agonist of platelet P2X1 and P2Y12 receptors. PMID:19945153

Lateral migration of a microdroplet under optical forces in a uniform flow

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

Cho, Hyunjun; Chang, Cheong Bong; Jung, Jin Ho

2014-12-15

The behavior of a microdroplet in a uniform flow and subjected to a vertical optical force applied by a loosely focused Gaussian laser beam was studied numerically. The lattice Boltzmann method was applied to obtain the two-phase flow field, and the dynamic ray tracing method was adopted to calculate the optical force. The optical forces acting on the spherical droplets agreed well with the analytical values. The numerically predicted droplet migration distances agreed well with the experimentally obtained values. Simulations of the various flow and optical parameters showed that the droplet migration distance nondimensionalized by the droplet radius is proportionalmore » to the S number (z{sub d}/r{sub p} = 0.377S), which is the ratio of the optical force to the viscous drag. The effect of the surface tension was also examined. These results indicated that the surface tension influenced the droplet migration distance to a lesser degree than the flow and optical parameters. The results of the present work hold for the refractive indices of the mean fluid and the droplet being 1.33 and 1.59, respectively.« less

Flow cytometry without alignment of collection optics.

PubMed

Sitton, Greg; Srienc, Friedrich

2009-12-01

This study describes the performance of a new waveguide flow cell constructed from Teflon AF (TFC) and the potential use of fiber optic splitters to replace collection objectives and dichroic mirrors. The TFC has the unique optical property that the refractive index of the polymer is lower than water and therefore, water filled TFC behaves and functions as a liquid core waveguide. Thus, as cells flow through the TFC and are illuminated by a laser orthogonal to the flow direction, scattered and fluorescent light is directed down the axis of the TFC to a fiber optic. The total signal in the fiber optic is then split into multiple fibers by fiber optic splitters to enable measurement of signal intensities at different wavelengths. Optical filters are placed at the terminus of each fiber before measurement of specific wavelengths by a PMT. The constructed system was used to measure DNA content of CHO and yeast cells. Polystyrene beads were used for alignment and to assess the performance of the system. Polystyrene beads were observed to produce light scattering signals with unique bimodal characteristics dependent on the direction of flow relative to the collecting fiber optic.

Fiber-optic-based laser vapor screen flow visualization system for aerodynamic research in larger scale subsonic and transonic wind tunnels

NASA Technical Reports Server (NTRS)

Erickson, Gary E.; Inenaga, Andrew S.

1994-01-01

Laser vapor screen (LVS) flow visualization systems that are fiber-optic based were developed and installed for aerodynamic research in the Langley 8-Foot Transonic Pressure Tunnel and the Langley 7- by 10-Foot High Speed Tunnel. Fiber optics are used to deliver the laser beam through the plenum shell that surrounds the test section of each facility and to the light-sheet-generating optics positioned in the ceiling window of the test section. Water is injected into the wind tunnel diffuser section to increase the relative humidity and promote condensation of the water vapor in the flow field about the model. The condensed water vapor is then illuminated with an intense sheet of laser light to reveal features of the flow field. The plenum shells are optically sealed; therefore, video-based systems are used to observe and document the flow field. Operational experience shows that the fiber-optic-based systems provide safe, reliable, and high-quality off-surface flow visualization in smaller and larger scale subsonic and transonic wind tunnels. The design, the installation, and the application of the Langley Research Center (LaRC) LVS flow visualization systems in larger scale wind tunnels are highlighted. The efficiency of the fiber optic LVS systems and their insensitivity to wind tunnel vibration, the tunnel operating temperature and pressure variations, and the airborne contaminants are discussed.

Control of self-motion in dynamic fluids: fish do it differently from bees.

PubMed

Scholtyssek, Christine; Dacke, Marie; Kröger, Ronald; Baird, Emily

2014-05-01

To detect and avoid collisions, animals need to perceive and control the distance and the speed with which they are moving relative to obstacles. This is especially challenging for swimming and flying animals that must control movement in a dynamic fluid without reference from physical contact to the ground. Flying animals primarily rely on optic flow to control flight speed and distance to obstacles. Here, we investigate whether swimming animals use similar strategies for self-motion control to flying animals by directly comparing the trajectories of zebrafish (Danio rerio) and bumblebees (Bombus terrestris) moving through the same experimental tunnel. While moving through the tunnel, black and white patterns produced (i) strong horizontal optic flow cues on both walls, (ii) weak horizontal optic flow cues on both walls and (iii) strong optic flow cues on one wall and weak optic flow cues on the other. We find that the mean speed of zebrafish does not depend on the amount of optic flow perceived from the walls. We further show that zebrafish, unlike bumblebees, move closer to the wall that provides the strongest visual feedback. This unexpected preference for strong optic flow cues may reflect an adaptation for self-motion control in water or in environments where visibility is limited. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

Dense pattern multiple pass cells

DOEpatents

Silver, Joel A.; Bomse, David S.

2010-09-21

An optical cell and a method of operating an optical cell comprising employing a first mirror comprising a first hole therein at approximately a center of the first mirror and through which laser light enters the cell, employing a second mirror comprising a second hole therein at approximately a center of the second mirror and through which laser light exits the cell, and forming a Lissajous pattern of spots on the mirrors by repeated reflection of laser light entering the cell.

Emission Spectroscopy of the Interior of Optically Dense Post-Detonation Fireballs

DTIC Science & Technology

2013-03-01

sample. Light from the fiber optics was sent to spectrograph located in a shielded observation room several meters away from the explosive charge. The...spectrograph was constructed from a 1/8 m spectrometer (Oriel) interfaced to a 4096 pixel line-scan camera (Basler Sprint ) with a data collection rate... 400 ) 45 4000 (200) … FIG. 3. Time-resolved emission spectra obtained from detonation of 20 g charges of RDX containing 20 wt. % aluminum nanoparticles

Power budget of direct-detection ultra-dense WDM-Nyquist-SCM PON with low-complexity SSBI mitigation

NASA Astrophysics Data System (ADS)

Soeiro, Ricardo O. J.; Alves, Tiago M. F.; Cartaxo, Adolfo V. T.

2017-07-01

The power budget (PB) of a direct-detection ultra-dense wavelength division/subcarrier multiplexing (SCM) passive optical network (PON) is assessed numerically for downstream, when a low-complexity iterative signal-to-signal beat interference (SSBI) mitigation technique is employed. Each SCM signal, inserted in a 12.5 GHz width optical channel, is comprised of two or three electrically generated and multiplexed 16-quadrature-amplitude-modulation (QAM) or 32-QAM Nyquist pulse-shaped subcarriers, each with a 7% forward error correction bit rate of 10.7 Gbit/s. The PB and maximum number of optical network units (ONUs) served by each optical line terminal (OLT) are compared with and without SSBI mitigation. When SSBI mitigation is realized, PB gains up to 4.5 dB are attained relative to the PB in the absence of SSBI mitigation. The PB gain enabled by the SSBI mitigation technique proposed in this work increases the number of ONUs served per OLT at least by a factor of 2, for the cases of higher spectral efficiency. In particular, for a SCM signal comprised of three subcarriers, the maximum number of ONUs served per OLT is between 2 and 32, and between 8 and 64, in the absence of SSBI mitigation, and when SSBI mitigation is employed, respectively, depending on the fiber length (up to 50 km) and order of QAM.

MAPPING THE DYNAMICS OF COLD GAS AROUND SGR A* THROUGH 21 cm ABSORPTION

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

Christian, Pierre; Loeb, Abraham, E-mail: pchristian@cfa.harvard.edu

2015-11-20

The presence of a circumnuclear stellar disk around Sgr A* and megamaser systems near other black holes indicates that dense neutral disks can be found in galactic nuclei. We show that depending on their inclination angle, optical depth, and spin temperature, these disks could be observed spectroscopically through 21 cm absorption. Related spectroscopic observations of Sgr A* can determine its HI disk parameters and the possible presence of gaps in the disk. Clumps of dense gas similar to the G2 could could also be detected in 21 cm absorption against Sgr A* radio emission.

Effects of absorption on multiple scattering by random particulate media: exact results.

PubMed

Mishchenko, Michael I; Liu, Li; Hovenier, Joop W

2007-10-01

We employ the numerically exact superposition T-matrix method to perform extensive computations of elec nottromagnetic scattering by a volume of discrete random medium densely filled with increasingly absorbing as well as non-absorbing particles. Our numerical data demonstrate that increasing absorption diminishes and nearly extinguishes certain optical effects such as depolarization and coherent backscattering and increases the angular width of coherent backscattering patterns. This result corroborates the multiple-scattering origin of such effects and further demonstrates the heuristic value of the concept of multiple scattering even in application to densely packed particulate media.

Downslope flow across the Ross Sea shelf break (Antarctica)

NASA Astrophysics Data System (ADS)

Bergamasco, A.; Budillon, G.; Carniel, S.; Defendi, V.; Meloni, R.; Paschini, E.; Sclavo, M.; Spezie, G.

2003-12-01

The analysis of some high-resolution hydrological data sets acquired during the 1997, 1998, 2001 and 2003 austral summers across the Ross Sea continental shelf break are here presented. The main focus of these cruises carried out in the framework of the Italian National Antarctic Program was the investigation of the downslope flow of the dense waters originated inside the Ross Sea. Such dense waters, flow near the bottom and, reaching the continental shelf break, ventilate the deep ocean. Two Antarctic continental shelf mechanisms can originate dense and deep waters. The former mechanism involves the formation, along the Victoria Land coasts, of a dense and saline water mass, the High Salinity Shelf Water (HSSW). The HSSW formation is linked to the rejection of salt into the water column as sea ice freezes, especially during winter, in the polynya areas, where the ice is continuously pushed offshore by the strong katabatic winds. The latter one is responsible of the formation of a supercold water mass, the Ice Shelf Water (ISW). The salt supplied by the HSSW recirculated below the Ross Ice Shelf, the latent heat of melting and the heat sink provided by the Ross Ice Shelf give rise to plumes of ISW, characterized by temperatures below the sea-surface freezing point. The dense shelf waters migrate to the continental shelf-break, spill over the shelf edge and descend the continental slope as a shelf-break gravity current, subject to friction and possibly enhanced by topographic channelling. Friction, in particular, breaks the constraint of potential vorticity conservation, counteracting the geostrophic tendency for along slope flow. The density-driven downslope motion or cascading entrains ambient water, namely the lower layer of the CDW, reaches a depth where density is the same and spreads off-slope. In fact, the cascading event is inhibited by friction without entrainment. The downslope processes are important for the ocean and climate system because they play a crucial role in the formation of oceanic deep water responsible for ocean/continental shelf exchange of organic carbon, suspended material and dissolved gases around Antarctica. In this context, this work presents the analysis of the 1997, 2001 and 2003 high-resolution surveys carried out in the western Ross Sea near Cape Adare, where the HSSW flows down the continental slope. The second study area was investigated during the 1998 survey of the Italian National Programme for Antarctic Research of the CLIMA Project, in order to follow the ISW overflow path at the shelf break in the central Ross Sea. A 3D primitive equation model was also implemented as a first step in the construction of a high-resolution process study model to explore the dynamical constraints involved in the downslope motion.

Computation and analysis of backward ray-tracing in aero-optics flow fields.

PubMed

Xu, Liang; Xue, Deting; Lv, Xiaoyi

2018-01-08

A backward ray-tracing method is proposed for aero-optics simulation. Different from forward tracing, the backward tracing direction is from the internal sensor to the distant target. Along this direction, the tracing in turn goes through the internal gas region, the aero-optics flow field, and the freestream. The coordinate value, the density, and the refractive index are calculated at each tracing step. A stopping criterion is developed to ensure the tracing stops at the outer edge of the aero-optics flow field. As a demonstration, the analysis is carried out for a typical blunt nosed vehicle. The backward tracing method and stopping criterion greatly simplify the ray-tracing computations in the aero-optics flow field, and they can be extended to our active laser illumination aero-optics study because of the reciprocity principle.

Voluminous lava-like precursor to a major ash-flow tuff: Low-column pyroclastic eruption of the Pagosa Peak Dacite, San Juan volcanic field, Colorado

USGS Publications Warehouse

Bachmann, Olivier; Dungan, M.A.; Lipman, P.W.

2000-01-01

The Pagosa Peak Dacite is an unusual pyroclastic deposit that immediately predated eruption of the enormous Fish Canyon Tuff (~5000 km3) from the La Garita caldera at 28 Ma. The Pagosa Peak Dacite is thick (to 1 km), voluminous (>200 km3), and has a high aspect ratio (1:50) similar to those of silicic lava flows. It contains a high proportion (40-60%) of juvenile clasts (to 3-4 m) emplaced as viscous magma that was less vesiculated than typical pumice. Accidental lithic fragments are absent above the basal 5-10% of the unit. Thick densely welded proximal deposits flowed rheomorphically due to gravitational spreading, despite the very high viscosity of the crystal-rich magma, resulting in a macroscopic appearance similar to flow-layered silicic lava. Although it is a separate depositional unit, the Pagosa Peak Dacite is indistinguishable from the overlying Fish Canyon Tuff in bulk-rock chemistry, phenocryst compositions, and 40Ar/39Ar age. The unusual characteristics of this deposit are interpreted as consequences of eruption by low-column pyroclastic fountaining and lateral transport as dense, poorly inflated pyroclastic flows. The inferred eruptive style may be in part related to synchronous disruption of the southern margin of the Fish Canyon magma chamber by block faulting. The Pagosa Peak eruptive sources are apparently buried in the southern La Garita caldera, where northerly extensions of observed syneruptive faults served as fissure vents. Cumulative vent cross-sections were large, leading to relatively low emission velocities for a given discharge rate. Many successive pyroclastic flows accumulated sufficiently rapidly to weld densely as a cooling unit up to 1000 m thick and to retain heat adequately to permit rheomorphic flow. Explosive potential of the magma may have been reduced by degassing during ascent through fissure conduits, leading to fracture-dominated magma fragmentation at low vesicularity. Subsequent collapse of the 75 x 35 km2 La Garita caldera and eruption of the Fish Canyon Tuff were probably triggered by destabilization of the chamber roof as magma was withdrawn during the Pagosa Peak eruption. (C) 2000 Elsevier Science B.V. All rights reserved.

Design and performance evaluation of an OpenFlow-based control plane for software-defined elastic optical networks with direct-detection optical OFDM (DDO-OFDM) transmission.

PubMed

Liu, Lei; Peng, Wei-Ren; Casellas, Ramon; Tsuritani, Takehiro; Morita, Itsuro; Martínez, Ricardo; Muñoz, Raül; Yoo, S J B

2014-01-13

Optical Orthogonal Frequency Division Multiplexing (O-OFDM), which transmits high speed optical signals using multiple spectrally overlapped lower-speed subcarriers, is a promising candidate for supporting future elastic optical networks. In contrast to previous works which focus on Coherent Optical OFDM (CO-OFDM), in this paper, we consider the direct-detection optical OFDM (DDO-OFDM) as the transport technique, which leads to simpler hardware and software realizations, potentially offering a low-cost solution for elastic optical networks, especially in metro networks, and short or medium distance core networks. Based on this network scenario, we design and deploy a software-defined networking (SDN) control plane enabled by extending OpenFlow, detailing the network architecture, the routing and spectrum assignment algorithm, OpenFlow protocol extensions and the experimental validation. To the best of our knowledge, it is the first time that an OpenFlow-based control plane is reported and its performance is quantitatively measured in an elastic optical network with DDO-OFDM transmission.

Cascaded multiplexed optical link on a telecommunication network for frequency dissemination.

PubMed

Lopez, Olivier; Haboucha, Adil; Kéfélian, Fabien; Jiang, Haifeng; Chanteau, Bruno; Roncin, Vincent; Chardonnet, Christian; Amy-Klein, Anne; Santarelli, Giorgio

2010-08-02

We demonstrate a cascaded optical link for ultrastable frequency dissemination comprised of two compensated links of 150 km and a repeater station. Each link includes 114 km of Internet fiber simultaneously carrying data traffic through a dense wavelength division multiplexing technology, and passes through two routing centers of the telecommunication network. The optical reference signal is inserted in and extracted from the communication network using bidirectional optical add-drop multiplexers. The repeater station operates autonomously ensuring noise compensation on the two links and the ultra-stable signal optical regeneration. The compensated link shows a fractional frequency instability of 3 x 10(-15) at one second measurement time and 5 x 10(-20) at 20 hours. This work paves the way to a wide dissemination of ultra-stable optical clock signals between distant laboratories via the Internet network.

Optical and sensing properties of sol-gel derived vanadium pentoxide thin films with porous and dense structures

NASA Astrophysics Data System (ADS)

Babeva, T.; Awala, H.; Grand, J.; Lazarova, K.; Vasileva, M.; Mintova, S.

2018-03-01

The sol-gel and spin-coating methods were used for deposition of thin transparent V2O5 films on optical glass substrates and silicon wafers. Different synthesis and deposition conditions, including synthesis temperatures and post-deposition annealing, were used aiming at obtaining transparent films with high refractive index and good optical quality. The surface morphology and structure of the films were studied by SEM and XRD. The optical properties (refractive index, extinction coefficient and optical band gap) and thickness of the V2O5 films were determined from their transmittance and reflectance spectra. The potential application of the films as building blocks of optical sensors was demonstrated by preparation of multilayered structures comprising both V2O5 and BEA-type zeolite films and testing their response towards acetone vapors.

A fast low-power optical memory based on coupled micro-ring lasers

NASA Astrophysics Data System (ADS)

Hill, Martin T.; Dorren, Harmen J. S.; de Vries, Tjibbe; Leijtens, Xaveer J. M.; den Besten, Jan Hendrik; Smalbrugge, Barry; Oei, Yok-Siang; Binsma, Hans; Khoe, Giok-Djan; Smit, Meint K.

2004-11-01

The increasing speed of fibre-optic-based telecommunications has focused attention on high-speed optical processing of digital information. Complex optical processing requires a high-density, high-speed, low-power optical memory that can be integrated with planar semiconductor technology for buffering of decisions and telecommunication data. Recently, ring lasers with extremely small size and low operating power have been made, and we demonstrate here a memory element constructed by interconnecting these microscopic lasers. Our device occupies an area of 18 × 40µm2 on an InP/InGaAsP photonic integrated circuit, and switches within 20ps with 5.5fJ optical switching energy. Simulations show that the element has the potential for much smaller dimensions and switching times. Large numbers of such memory elements can be densely integrated and interconnected on a photonic integrated circuit: fast digital optical information processing systems employing large-scale integration should now be viable.

Single- and two-phase flow characterization using optical fiber bragg gratings.

PubMed

Baroncini, Virgínia H V; Martelli, Cicero; da Silva, Marco José; Morales, Rigoberto E M

2015-03-17

Single- and two-phase flow characterization using optical fiber Bragg gratings (FBGs) is presented. The sensor unit consists of the optical fiber Bragg grating positioned transversely to the flow and fixed in the pipe walls. The hydrodynamic pressure applied by the liquid or air/liquid flow to the optical fiber induces deformation that can be detected by the FBG. Given that the applied pressure is directly related to the mass flow, it is possible to establish a relationship using the grating resonance wavelength shift to determine the mass flow when the flow velocity is well known. For two phase flows of air and liquid, there is a significant change in the force applied to the fiber that accounts for the very distinct densities of these substances. As a consequence, the optical fiber deformation and the correspondent grating wavelength shift as a function of the flow will be very different for an air bubble or a liquid slug, allowing their detection as they flow through the pipe. A quasi-distributed sensing tool with 18 sensors evenly spread along the pipe is developed and characterized, making possible the characterization of the flow, as well as the tracking of the bubbles over a large section of the test bed. Results show good agreement with standard measurement methods and open up plenty of opportunities to both laboratory measurement tools and field applications.

Optic flow-based collision-free strategies: From insects to robots.

PubMed

Serres, Julien R; Ruffier, Franck

2017-09-01

Flying insects are able to fly smartly in an unpredictable environment. It has been found that flying insects have smart neurons inside their tiny brains that are sensitive to visual motion also called optic flow. Consequently, flying insects rely mainly on visual motion during their flight maneuvers such as: takeoff or landing, terrain following, tunnel crossing, lateral and frontal obstacle avoidance, and adjusting flight speed in a cluttered environment. Optic flow can be defined as the vector field of the apparent motion of objects, surfaces, and edges in a visual scene generated by the relative motion between an observer (an eye or a camera) and the scene. Translational optic flow is particularly interesting for short-range navigation because it depends on the ratio between (i) the relative linear speed of the visual scene with respect to the observer and (ii) the distance of the observer from obstacles in the surrounding environment without any direct measurement of either speed or distance. In flying insects, roll stabilization reflex and yaw saccades attenuate any rotation at the eye level in roll and yaw respectively (i.e. to cancel any rotational optic flow) in order to ensure pure translational optic flow between two successive saccades. Our survey focuses on feedback-loops which use the translational optic flow that insects employ for collision-free navigation. Optic flow is likely, over the next decade to be one of the most important visual cues that can explain flying insects' behaviors for short-range navigation maneuvers in complex tunnels. Conversely, the biorobotic approach can therefore help to develop innovative flight control systems for flying robots with the aim of mimicking flying insects' abilities and better understanding their flight. Copyright © 2017 The Authors. Published by Elsevier Ltd.. All rights reserved.

Bio-inspired multi-mode optic flow sensors for micro air vehicles

NASA Astrophysics Data System (ADS)

Park, Seokjun; Choi, Jaehyuk; Cho, Jihyun; Yoon, Euisik

2013-06-01

Monitoring wide-field surrounding information is essential for vision-based autonomous navigation in micro-air-vehicles (MAV). Our image-cube (iCube) module, which consists of multiple sensors that are facing different angles in 3-D space, can be applied to the wide-field of view optic flows estimation (μ-Compound eyes) and to attitude control (μ- Ocelli) in the Micro Autonomous Systems and Technology (MAST) platforms. In this paper, we report an analog/digital (A/D) mixed-mode optic-flow sensor, which generates both optic flows and normal images in different modes for μ- Compound eyes and μ-Ocelli applications. The sensor employs a time-stamp based optic flow algorithm which is modified from the conventional EMD (Elementary Motion Detector) algorithm to give an optimum partitioning of hardware blocks in analog and digital domains as well as adequate allocation of pixel-level, column-parallel, and chip-level signal processing. Temporal filtering, which may require huge hardware resources if implemented in digital domain, is remained in a pixel-level analog processing unit. The rest of the blocks, including feature detection and timestamp latching, are implemented using digital circuits in a column-parallel processing unit. Finally, time-stamp information is decoded into velocity from look-up tables, multiplications, and simple subtraction circuits in a chip-level processing unit, thus significantly reducing core digital processing power consumption. In the normal image mode, the sensor generates 8-b digital images using single slope ADCs in the column unit. In the optic flow mode, the sensor estimates 8-b 1-D optic flows from the integrated mixed-mode algorithm core and 2-D optic flows with an external timestamp processing, respectively.

Mixed-mode VLSI optic flow sensors for micro air vehicles

NASA Astrophysics Data System (ADS)

Barrows, Geoffrey Louis

We develop practical, compact optic flow sensors. To achieve the desired weight of 1--2 grams, mixed-mode and mixed-signal VLSI techniques are used to develop compact circuits that directly perform computations necessary to measure optic flow. We discuss several implementations, including a version fully integrated in VLSI, and several "hybrid sensors" in which the front end processing is performed with an analog chip and the back end processing is performed with a microcontroller. We extensively discuss one-dimensional optic flow sensors based on the linear competitive feature tracker (LCFT) algorithm. Hardware implementations of this algorithm are shown able to measure visual motion with contrast levels on the order of several percent. We argue that the development of one-dimensional optic flow sensors is therefore reduced to a problem of engineering. We also introduce two related two-dimensional optic flow algorithms that are amenable to implementation in VLSI. This includes the planar competitive feature tracker (PCFT) algorithm and the trajectory method. These sensors are being developed to solve small-scale navigation problems in micro air vehicles, which are autonomous aircraft whose maximum dimension is on the order of 15 cm. We obtain a proof-of-principle of small-scale navigation by mounting a prototype sensor onto a toy glider and programming the sensor to control a rudder or an elevator to affect the glider's path during flight. We demonstrate the determination of altitude by measuring optic flow in the downward direction. We also demonstrate steering to avoid a collision with a wall, when the glider is tossed towards the wall at a shallow angle, by measuring the optic flow in the direction of the glider's left and right side.

Effects of radial direction and eccentricity on acceleration perception.

PubMed

Mueller, Alexandra S; Timney, Brian

2014-01-01

Radial optic flow can elicit impressions of self-motion--vection--or of objects moving relative to the observer, but there is disagreement as to whether humans have greater sensitivity to expanding or to contracting optic flow. Although most studies agree there is an anisotropy in sensitivity to radial optic flow, it is unclear whether this asymmetry is a function of eccentricity. The issue is further complicated by the fact that few studies have examined how acceleration sensitivity is affected, even though observers and objects in the environment seldom move at a constant speed. To address these issues, we investigated the effects of direction and eccentricity on the ability to detect acceleration in radial optic flow. Our results indicate that observers are better at detecting acceleration when viewing contraction compared with expansion and that eccentricity has no effect on the ability to detect accelerating radial optic flow. Ecological interpretations are discussed.

The visual control of stability in children and adults: postural readjustments in a ground optical flow.

PubMed

Baumberger, Bernard; Isableu, Brice; Flückiger, Michelangelo

2004-11-01

The aim of this research was to analyse the development of postural reactions to approaching (AOF) and receding (ROF) ground rectilinear optical flows. Optical flows were shaped by a pattern of circular spots of light projected on the ground surface by a texture flow generator. The geometrical structure of the projected scenes corresponded to the spatial organisation of visual flows encountered in open outdoor settings. Postural readjustments of 56 children, ranging from 7 to 11 years old, and 12 adults were recorded by the changes of the centre of foot pressure (CoP) on a force platform during 44-s exposures to the moving texture. Before and after the optical flows exposure, a 24-s motionless texture served as a reference condition. Effect of ground rectilinear optical flows on postural control development was assessed by analysing sway latencies (SL), stability performances and postural orientation. The main results that emerge from this experiment show that postural responses are directionally specific to optical flow pattern and that they vary as a function of the motion onset and offset. Results showed that greater developmental changes in postural control occurred in an AOF (both at the onset and offset of the optical flow) than in an ROF. Onset of an approaching flow induced postural instability, canonical shifts in postural orientation and long latencies in children which were stronger than in the receding flow. This pattern of responses evolved with age towards an improvement in stability performances and shorter SL. The backward decreasing shift of the CoP in children evolved in adults towards forward postural tilt, i.show $132#e. in the opposite direction of the texture's motion. Offset of an AOF motion induced very short SL in children (which became longer in adult subjects), strong postural instability, but weaker shift of orientation compared to the receding one. Postural stability improved and orientation shift evolved to forward inclinations with age. SL remained almost constant across age at both onset and offset of the receding flow. Critical developmental periods seem to occur by the age of 8 and 10 years, as suggested by the transient 'neglect' of the children to optical flows. Linear vection was felt by 90% of the 7 year olds and decreased with age to reach 55% in adult subjects. The mature sensorimotor coordination subserving the postural organisation shown in adult subjects is an example aiming at reducing the postural effects induced by optical flows. The data are discussed in relation to the perceptual importance of mobile visual references on a ground support.

Non-local rheology for dense granular flows in avalanches

NASA Astrophysics Data System (ADS)

Izzet, Adrien; Clement, Eric; Andreotti, Bruno

A local constitutive relation was proposed to describe dense granular flows (GDR MiDi, EPJE 2004). It provides a rather good prediction of the flowing regime but does not foresee the existence of a ``creep regime'' as observed by Komatsu et al. (PRL 2001). In the context of a 2D shear cell, a relaxation length for the velocity profile was measured (Bouzid et al., PRL 2013) which confirmed the existence of a flow below the standard Coulomb yield threshold. A correction for the local rheology was proposed. To test further this non-local constitutive relation, we built an inclined narrow channel within which we monitor the flow from the side. We managed to observe the ``creep regime'' over five orders of magnitude in velocity and fit the velocity profiles in the depth with an asymptotic solution of the non-local equation. However, the boundary condition at the free surface needs to be selected in order to calibrate the non-local rheology over the whole range of stresses in the system. In this perspective, we complement the experimental results with 2D simulations of hard and frictional discs on an inclined plane in which we introduce a surface friction force proportional to the effective pressure in the granular. We analyze these results in the light of the non-local rheology.

LASER APPLICATIONS IN MEDICINE: Analysis of distortions in the velocity profiles of suspension flows inside a light-scattering medium upon their reconstruction from the optical coherence Doppler tomograph signal

NASA Astrophysics Data System (ADS)

Bykov, A. V.; Kirillin, M. Yu; Priezzhev, A. V.

2005-11-01

Model signals from one and two plane flows of a particle suspension are obtained for an optical coherence Doppler tomograph (OCDT) by the Monte-Carlo method. The optical properties of particles mimic the properties of non-aggregating erythrocytes. The flows are considered in a stationary scattering medium with optical properties close to those of the skin. It is shown that, as the flow position depth increases, the flow velocity determined from the OCDT signal becomes smaller than the specified velocity and the reconstructed profile extends in the direction of the distant boundary, which is accompanied by the shift of its maximum. In the case of two flows, an increase in the velocity of the near-surface flow leads to the overestimated values of velocity of the reconstructed profile of the second flow. Numerical simulations were performed by using a multiprocessor parallel-architecture computer.

A Real-Time Method to Estimate Speed of Object Based on Object Detection and Optical Flow Calculation

NASA Astrophysics Data System (ADS)

Liu, Kaizhan; Ye, Yunming; Li, Xutao; Li, Yan

2018-04-01

In recent years Convolutional Neural Network (CNN) has been widely used in computer vision field and makes great progress in lots of contents like object detection and classification. Even so, combining Convolutional Neural Network, which means making multiple CNN frameworks working synchronously and sharing their output information, could figure out useful message that each of them cannot provide singly. Here we introduce a method to real-time estimate speed of object by combining two CNN: YOLOv2 and FlowNet. In every frame, YOLOv2 provides object size; object location and object type while FlowNet providing the optical flow of whole image. On one hand, object size and object location help to select out the object part of optical flow image thus calculating out the average optical flow of every object. On the other hand, object type and object size help to figure out the relationship between optical flow and true speed by means of optics theory and priori knowledge. Therefore, with these two key information, speed of object can be estimated. This method manages to estimate multiple objects at real-time speed by only using a normal camera even in moving status, whose error is acceptable in most application fields like manless driving or robot vision.

Dusty Cloud Acceleration by Radiation Pressure in Rapidly Star-forming Galaxies

NASA Astrophysics Data System (ADS)

Zhang, Dong; Davis, Shane W.; Jiang, Yan-Fei; Stone, James M.

2018-02-01

We perform two-dimensional and three-dimensional radiation hydrodynamic simulations to study cold clouds accelerated by radiation pressure on dust in the environment of rapidly star-forming galaxies dominated by infrared flux. We utilize the reduced speed of light approximation to solve the frequency-averaged, time-dependent radiative transfer equation. We find that radiation pressure is capable of accelerating the clouds to hundreds of kilometers per second while remaining dense and cold, consistent with observations. We compare these results to simulations where acceleration is provided by entrainment in a hot wind, where the momentum injection of the hot flow is comparable to the momentum in the radiation field. We find that the survival time of the cloud accelerated by the radiation field is significantly longer than that of a cloud entrained in a hot outflow. We show that the dynamics of the irradiated cloud depends on the initial optical depth, temperature of the cloud, and intensity of the flux. Additionally, gas pressure from the background may limit cloud acceleration if the density ratio between the cloud and background is ≲ {10}2. In general, a 10 pc-scale optically thin cloud forms a pancake structure elongated perpendicular to the direction of motion, while optically thick clouds form a filamentary structure elongated parallel to the direction of motion. The details of accelerated cloud morphology and geometry can also be affected by other factors, such as the cloud lengthscale, reduced speed of light approximation, spatial resolution, initial cloud structure, and dimensionality of the run, but these have relatively little affect on the cloud velocity or survival time.

Highly Efficient Coherent Optical Memory Based on Electromagnetically Induced Transparency

NASA Astrophysics Data System (ADS)

Hsiao, Ya-Fen; Tsai, Pin-Ju; Chen, Hung-Shiue; Lin, Sheng-Xiang; Hung, Chih-Chiao; Lee, Chih-Hsi; Chen, Yi-Hsin; Chen, Yong-Fan; Yu, Ite A.; Chen, Ying-Cheng

2018-05-01

Quantum memory is an important component in the long-distance quantum communication based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 92.0 (1.5)% for a coherent optical memory based on the electromagnetically induced transparency scheme in optically dense cold atomic media. We also obtain a useful time-bandwidth product of 1200, considering only storage where the retrieval efficiency remains above 50%. Both are the best record to date in all kinds of schemes for the realization of optical memory. Our work significantly advances the pursuit of a high-performance optical memory and should have important applications in quantum information science.

Highly Efficient Coherent Optical Memory Based on Electromagnetically Induced Transparency.

PubMed

Hsiao, Ya-Fen; Tsai, Pin-Ju; Chen, Hung-Shiue; Lin, Sheng-Xiang; Hung, Chih-Chiao; Lee, Chih-Hsi; Chen, Yi-Hsin; Chen, Yong-Fan; Yu, Ite A; Chen, Ying-Cheng

2018-05-04

Quantum memory is an important component in the long-distance quantum communication based on the quantum repeater protocol. To outperform the direct transmission of photons with quantum repeaters, it is crucial to develop quantum memories with high fidelity, high efficiency and a long storage time. Here, we achieve a storage efficiency of 92.0 (1.5)% for a coherent optical memory based on the electromagnetically induced transparency scheme in optically dense cold atomic media. We also obtain a useful time-bandwidth product of 1200, considering only storage where the retrieval efficiency remains above 50%. Both are the best record to date in all kinds of schemes for the realization of optical memory. Our work significantly advances the pursuit of a high-performance optical memory and should have important applications in quantum information science.

A three-dimensional structured/unstructured hybrid Navier-Stokes method for turbine blade rows

NASA Technical Reports Server (NTRS)

Tsung, F.-L.; Loellbach, J.; Kwon, O.; Hah, C.

1994-01-01

A three-dimensional viscous structured/unstructured hybrid scheme has been developed for numerical computation of high Reynolds number turbomachinery flows. The procedure allows an efficient structured solver to be employed in the densely clustered, high aspect-ratio grid around the viscous regions near solid surfaces, while employing an unstructured solver elsewhere in the flow domain to add flexibility in mesh generation. Test results for an inviscid flow over an external transonic wing and a Navier-Stokes flow for an internal annular cascade are presented.

The evolution of cooling flows. I - Self-similar cluster flows. [of gas in intergalactic medium

NASA Technical Reports Server (NTRS)

Chevalier, Roger A.

1987-01-01

The evolution of a cooling flow from an initial state of hydrostatic equilibrium in a cluster of galaxies is investigated. After gas mass and energy are injected into the cluster at an early phase, the gas approaches hydrostatic equilibrium over most of the cluster and cooling becomes important in the dense central regions. As time passes, cooling strongly affects an increasing amount of gas. The effects of mass removal from the flow, the inclusion of magnetic or cosmic-ray pressure, and heat conduction are considered individually.

Development of an optical fiber flow velocity sensor.

PubMed

Harada, Toshio; Kamoto, Kenji; Abe, Kyutaro; Izumo, Masaki

2009-01-01

A new optical fiber flow velocity sensor was developed by using an optical fiber information network system in sewer drainage pipes. The optical fiber flow velocity sensor operates without electric power, and the signals from the sensor can be transmitted over a long distance through the telecommunication system in the optical fiber network. Field tests were conducted to check the performance of the sensor in conduits in the pumping station and sewage pond managed by the Tokyo Metropolitan Government. Test results confirmed that the velocity sensor can be used for more than six months without any trouble even in sewer drainage pipes.

Flow Regime Study in a High Density Circulating Fluidized Bed Riser with an Abrupt Exit

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

Mei, J.S.; Shadle, L.J.; Yue, P.C.

2007-01-01

Flow regime study was conducted in a 0.3 m diameter, 15.5 m height circulating fluidized bed (CFB) riser with an abrupt exit at the National Energy Technology Laboratory of the U.S. Department of Energy. Local particle velocities were measured at various radial positions and riser heights using an optical fiber probe. On-line measurement of solid circulating rate was continuously recorded by the Spiral. Glass beads of mean diameter 61 μm and particle density of 2,500 kg/m3 were used as bed material. The CFB riser was operated at various superficial gas velocities ranging from 3 to 7.6 m/s and solid massmore » flux from 20 to 550 kg/m2-s. At a constant riser gas velocity, transition from fast fluidization to dense suspension upflow (DSU) regime started at the bottom of the riser with increasing solid flux. Except at comparatively low riser gas velocity and solid flux, the apparent solid holdup at the top exit region was higher than the middle section of the riser. The solid fraction at this top region could be much higher than 7% under high riser gas velocity and solid mass flux. The local particle velocity showed downward flow near the wall at the top of the riser due to its abrupt exit. This abrupt geometry reflected the solids and, therefore, caused solid particles traveling downward along the wall. However, at location below, but near, the top of the riser the local particle velocities were observed flowing upward at the wall. Therefore, DSU was identified in the upper region of the riser with an abrupt exit while the fully developed region, lower in the riser, was still exhibiting core-annular flow structure. Our data were compared with the flow regime boundaries proposed by Kim et al. [1] for distinguishing the dilute pneumatic transport, fast fluidization, and DSU.« less

Exploring the use of optical flow for the study of functional NIRS signals

NASA Astrophysics Data System (ADS)

Fernandez Rojas, Raul; Huang, Xu; Ou, Keng-Liang; Hernandez-Juarez, Jesus

2017-03-01

Near infrared spectroscopy (NIRS) is an optical imaging technique that allows real-time measurements of Oxy and Deoxy-hemoglobin concentrations in human body tissue. In functional NIRS (fNIRS), this technique is used to study cortical activation in response to changes in neural activity. However, analysis of activation regions using NIRS is a challenging task in the field of medical image analysis and despite existing solutions, no homogeneous analysis method has yet been determined. For that reason, the aim of our present study is to report the use of an optical flow method for the analysis of cortical activation using near-infrared spectroscopy signals. We used real fNIRS data recorded from a noxious stimulation experiment as base of our implementation. To compute the optical flow algorithm, we first arrange NIRS signals (Oxy-hemoglobin) following our 24 channels (12 channels per hemisphere) head-probe configuration to create image-like samples. We then used two consecutive fNIRS samples per hemisphere as input frames for the optical flow algorithm, making one computation per hemisphere. The output from these two computations is the velocity field representing cortical activation from each hemisphere. The experimental results showed that the radial structure of flow vectors exhibited the origin of cortical activity, the development of stimulation as expansion or contraction of such flow vectors, and the flow of activation patterns may suggest prediction in cortical activity. The present study demonstrates that optical flow provides a power tool for the analysis of NIRS signals. Finally, we suggested a novel idea to identify pain status in nonverbal patients by using optical flow motion vectors; however, this idea will be study further in our future research.

Fine structure of the vapor field in evaporating dense sprays

NASA Astrophysics Data System (ADS)

Villermaux, Emmanuel; Moutte, Alexandre; Amielh, Muriel; Meunier, Patrice

2017-11-01

Making use of an original technique which permits the simultaneous measurement of both the displacement field of evaporating droplets in a spray, and of their vapor, we investigate the relevance of a scenario introduced earlier to describe the evaporation dynamics of dense sprays. A plume of dense acetone droplets evaporating in air is studied, for which the stirring field is measured by particle image velocimetry of the droplets, and the vapor field is imaged quantitatively by laser-induced fluorescence. We show, thanks to these unique in situ measurements, that the spray boundary with the diluting environment is slaved to the dynamics of its saturating vapor concentration field, whose structure is analyzed for different well defined local flow topologies.

Importance of perceptual representation in the visual control of action

NASA Astrophysics Data System (ADS)

Loomis, Jack M.; Beall, Andrew C.; Kelly, Jonathan W.; Macuga, Kristen L.

2005-03-01

In recent years, many experiments have demonstrated that optic flow is sufficient for visually controlled action, with the suggestion that perceptual representations of 3-D space are superfluous. In contrast, recent research in our lab indicates that some visually controlled actions, including some thought to be based on optic flow, are indeed mediated by perceptual representations. For example, we have demonstrated that people are able to perform complex spatial behaviors, like walking, driving, and object interception, in virtual environments which are rendered visible solely by cyclopean stimulation (random-dot cinematograms). In such situations, the absence of any retinal optic flow that is correlated with the objects and surfaces within the virtual environment means that people are using stereo-based perceptual representations to perform the behavior. The fact that people can perform such behaviors without training suggests that the perceptual representations are likely the same as those used when retinal optic flow is present. Other research indicates that optic flow, whether retinal or a more abstract property of the perceptual representation, is not the basis for postural control, because postural instability is related to perceived relative motion between self and the visual surroundings rather than to optic flow, even in the abstract sense.

Optic flow informs distance but not profitability for honeybees.

PubMed

Shafir, Sharoni; Barron, Andrew B

2010-04-22

How do flying insects monitor foraging efficiency? Honeybees (Apis mellifera) use optic flow information as an odometer to estimate distance travelled, but here we tested whether optic flow informs estimation of foraging costs also. Bees were trained to feeders in flight tunnels such that bees experienced the greatest optic flow en route to the feeder closest to the hive. Analyses of dance communication showed that, as expected, bees indicated the close feeder as being further, but they also indicated this feeder as the more profitable, and preferentially visited this feeder when given a choice. We show that honeybee estimates of foraging cost are not reliant on optic flow information. Rather, bees can assess distance and profitability independently and signal these aspects as separate elements of their dances. The optic flow signal is sensitive to the nature of the environment travelled by the bee, and is therefore not a good index of flight energetic costs, but it provides a good indication of distance travelled for purpose of navigation and communication, as long as the dancer and recruit travel similar routes. This study suggests an adaptive dual processing system in honeybees for communicating and navigating distance flown and for evaluating its energetic costs.

Optic flow informs distance but not profitability for honeybees

PubMed Central

Shafir, Sharoni; Barron, Andrew B.

2010-01-01

How do flying insects monitor foraging efficiency? Honeybees (Apis mellifera) use optic flow information as an odometer to estimate distance travelled, but here we tested whether optic flow informs estimation of foraging costs also. Bees were trained to feeders in flight tunnels such that bees experienced the greatest optic flow en route to the feeder closest to the hive. Analyses of dance communication showed that, as expected, bees indicated the close feeder as being further, but they also indicated this feeder as the more profitable, and preferentially visited this feeder when given a choice. We show that honeybee estimates of foraging cost are not reliant on optic flow information. Rather, bees can assess distance and profitability independently and signal these aspects as separate elements of their dances. The optic flow signal is sensitive to the nature of the environment travelled by the bee, and is therefore not a good index of flight energetic costs, but it provides a good indication of distance travelled for purpose of navigation and communication, as long as the dancer and recruit travel similar routes. This study suggests an adaptive dual processing system in honeybees for communicating and navigating distance flown and for evaluating its energetic costs. PMID:20018787

A novel all-fiber optic flow cytometer technology for Point-of Care and Remote Environments

NASA Astrophysics Data System (ADS)

Mermut, Ozzy

Traditional flow cytometry designs tend to be bulky systems with a complex optical-fluidic sub-system and often require trained personnel for operation. This makes them difficult to readily translate to remote site testing applications. A new compact and portable fiber-optic flow cell (FOFC) technology has been developed at INO. We designed and engineered a specialty optical fiber through which a square hole is transversally bored by laser micromachining. A capillary is fitted into that hole to flow analyte within the fiber square cross-section for detection and counting. With demonstrated performance benchmarks potentially comparable to commercial flow cytometers, our FOFC provides several advantages compared to classic free-space con-figurations, e.g., sheathless flow, low cost, reduced number of optical components, no need for alignment (occurring in the fabrication process only), ease-of-use, miniaturization, portability, and robustness. This sheathless configuration, based on a fiber optic flow module, renders this cytometer amenable to space-grade microgravity environments. We present our recent results for an all-fiber approach to achieve a miniature FOFC to translate flow cytometry from bench to a portable, point-of-care device for deployment in remote settings. Our unique fiber approach provides the capability to illuminate a large surface with a uniform intensity distri-bution, independently of the initial shape originating from the light source, and without loss of optical power. The CVs and sensitivities are measured and compared to industry benchmarks. Finally, integration of LEDs enable several advantages in cost, compactness, and wavelength availability.

Role of submerged vegetation in the retention processes of three plant protection products in flow-through stream mesocosms.

PubMed

Stang, Christoph; Wieczorek, Matthias Valentin; Noss, Christian; Lorke, Andreas; Scherr, Frank; Goerlitz, Gerhard; Schulz, Ralf

2014-07-01

Quantitative information on the processes leading to the retention of plant protection products (PPPs) in surface waters is not available, particularly for flow-through systems. The influence of aquatic vegetation on the hydraulic- and sorption-mediated mitigation processes of three PPPs (triflumuron, pencycuron, and penflufen; logKOW 3.3-4.9) in 45-m slow-flowing stream mesocosms was investigated. Peak reductions were 35-38% in an unvegetated stream mesocosm, 60-62% in a sparsely vegetated stream mesocosm (13% coverage with Elodea nuttallii), and in a similar range of 57-69% in a densely vegetated stream mesocosm (100% coverage). Between 89% and 93% of the measured total peak reductions in the sparsely vegetated stream can be explained by an increase of vegetation-induced dispersion (estimated with the one-dimensional solute transport model OTIS), while 7-11% of the peak reduction can be attributed to sorption processes. However, dispersion contributed only 59-71% of the peak reductions in the densely vegetated stream mesocosm, where 29% to 41% of the total peak reductions can be attributed to sorption processes. In the densely vegetated stream, 8-27% of the applied PPPs, depending on the logKOW values of the compounds, were temporarily retained by macrophytes. Increasing PPP recoveries in the aqueous phase were accompanied by a decrease of PPP concentrations in macrophytes indicating kinetic desorption over time. This is the first study to provide quantitative data on how the interaction of dispersion and sorption, driven by aquatic macrophytes, influences the mitigation of PPP concentrations in flowing vegetated stream systems. Copyright © 2014 Elsevier Ltd. All rights reserved.

Instability-induced ordering, universal unfolding and the role of gravity in granular Couette flow

NASA Astrophysics Data System (ADS)

Alam, Meheboob; Arakeri, V. H.; Nott, P. R.; Goddard, J. D.; Herrmann, H. J.

2005-01-01

Linear stability theory and bifurcation analysis are used to investigate the role of gravity in shear-band formation in granular Couette flow, considering a kinetic-theory rheological model. We show that the only possible state, at low shear rates, corresponds to a "plug" near the bottom wall, in which the particles are densely packed and the shear rate is close to zero, and a uniformly sheared dilute region above it. The origin of such plugged states is shown to be tied to the spontaneous symmetry-breaking instabilities of the gravity-free uniform shear flow, leading to the formation of ordered bands of alternating dilute and dense regions in the transverse direction, via an infinite hierarchy of pitchfork bifurcations. Gravity plays the role of an "imperfection", thus destroying the "perfect" bifurcation structure of uniform shear. The present bifurcation problem admits universal unfolding of pitchfork bifurcations which subsequently leads to the formation of a sequence of a countably infinite number of "isolas", with the solution structures being a modulated version of their gravity-free counterpart. While the solution with a plug near the bottom wall looks remarkably similar to the shear-banding phenomenon in dense slow granular Couette flows, a "floating" plug near the top wall is also a solution of these equations at high shear rates. A two-dimensional linear stability analysis suggests that these floating plugged states are unstable to long-wave travelling disturbances.The unique solution having a bottom plug can also be unstable to long waves, but remains stable at sufficiently low shear rates. The implications and realizability of the present results are discussed in the light of shear-cell experiments under "microgravity" conditions.

Characterization of subpopulations and immune-related parameters of hemocytes in the green-lipped mussel Perna viridis.

PubMed

Wang, Youji; Hu, Menghong; Chiang, M W L; Shin, P K S; Cheung, S G

2012-03-01

The green-lipped mussel Perna viridis is distributed widely in the estuarine and coastal areas of the Indo-Pacific region and extensively cultured as an inexpensive protein source. Morphology and immunological activities of hemocytes of P. viridis were investigated using flow cytometry and light and electron microscopy. Three major types of hemocytes were identified in the hemolymph, including dense-granulocyte, semi-granulocyte (small and large size) and hyalinocyte. Other hemocytes, which occurred in low numbers, included granulocytes with different electron-dense/lucent granules and hemoblast-like cells. Based on flow cytometry, two subpopulations were identified. Granulocytes were larger cells, and the more abundant, containing numerous granules in the cytoplasm, and hyalinocytes were the smaller and less abundant with the fewest granules. Flow cytometry revealed that the granulocytes were more active in cell phagocytosis, contained the higher lysosomal content, and showed higher esterase activity and reactive oxygen species (ROS) generation compared with hyalinocytes. Immune functions assessed by the flow cytometry indicated that the granulocytes were the main hemocytes involved in the cellular defence in P. viridis. Copyright © 2011. Published by Elsevier Ltd.

Interferometry using subnanosecond pulses from TEA nitrogen lasers.

PubMed

Schmidt, H; Salzmann, H; Strohwald, H

1975-09-01

The applicability of TEA nitrogen lasers emitting at 3371 A for high speed optical plasma interferometry of short lived plasmas is demonstrated. Interferograms of the dense phase of a 30-kJ plasma focus are obtained with an exposure time of less than 500 psec.

Enhanced cell trapping throughput using DC-biased AC electric field in a dielectrophoresis-based fluidic device with densely packed silica beads.

PubMed

Lewpiriyawong, Nuttawut; Xu, Guolin; Yang, Chun

2018-03-01

This paper presents the use of DC-biased AC electric field for enhancing cell trapping throughput in an insulator-based dielectrophoretic (iDEP) fluidic device with densely packed silica beads. Cell suspension is carried through the iDEP device by a pressure-driven flow. Under an applied DC-biased AC electric field, DEP trapping force is produced as a result of non-uniform electric field induced by the gap of electrically insulating silica beads packed between two mesh electrodes that allow both fluid and cells to pass through. While the AC component is mainly to control the magnitude of DEP trapping force, the DC component generates local electroosmotic (EO) flow in the cavity between the beads and the EO flow can be set to move along or against the main pressure-driven flow. Our experimental and simulation results show that desirable trapping is achieved when the EO flow direction is along (not against) the main flow direction. Using our proposed DC-biased AC field, the device can enhance the trapping throughput (in terms of the flowrate of cell suspension) up to five times while yielding almost the same cell capture rates as compared to the pure AC field case. Additionally, the device was demonstrated to selectively trap dead yeast cells from a mixture of flowing live and dead yeast cells. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Retrieval and Validation of Aerosol Optical Depth by using the GF-1 Remote Sensing Data

NASA Astrophysics Data System (ADS)

Zhang, L.; Xu, S.; Wang, L.; Cai, K.; Ge, Q.

2017-05-01

Based on the characteristics of GF-1 remote sensing data, the method and data processing procedure to retrieve the Aerosol Optical Depth (AOD) are developed in this study. The surface contribution over dense vegetation and urban bright target areas are respectively removed by using the dark target and deep blue algorithms. Our method is applied for the three serious polluted Beijing-Tianjin-Hebei (BTH), Yangtze River Delta (YRD) and Pearl River Delta (PRD) regions. The retrieved AOD are validated by ground-based AERONET data from Beijing, Hangzhou, Hong Kong sites. Our results show that, 1) the heavy aerosol loadings are usually distributed in high industrial emission and dense populated cities, with the AOD value near 1. 2) There is a good agreement between satellite-retrievals and in-site observations, with the coefficient factors of 0.71 (BTH), 0.55 (YRD) and 0.54(PRD). 3) The GF-1 retrieval uncertainties are mainly from the impact of cloud contamination, high surface reflectance and assumed aerosol model.

Digital services using quadrature amplitude modulation (QAM) over CATV analog DWDM system

NASA Astrophysics Data System (ADS)

Yeh, JengRong; Selker, Mark D.; Trail, J.; Piehler, David; Levi, Israel

2000-04-01

Dense Wavelength Division Multiplexing (DWDM) has recently gained great popularity as it provides a cost effective way to increase the transmission capacity of the existing fiber cable plant. For a long time, Dense WDM was exclusively used for baseband digital applications, predominantly in terrestrial long haul networks and in some cases in metropolitan and enterprise networks. Recently, the performance of DWDM components and frequency-stabilized lasers has substantially improved while the costs have down significantly. This makes a variety of new optical network architectures economically viable. The first commercial 8- wavelength DWDM system designed for Hybrid Fiber Coax networks was reported in 1998. This type of DWDM system utilizes Sub-Carrier Multiplexing (SCM) of Quadrature Amplitude Modulated (QAM) signals to transport IP data digital video broadcast and Video on Demand on ITU grid lightwave carriers. The ability of DWDM to provide scalable transmission capacity in the optical layer with SCM granularity is now considered by many to be the most promising technology for future transport and distribution of broadband multimedia services.

Massively parallel algorithms for real-time wavefront control of a dense adaptive optics system

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

Fijany, A.; Milman, M.; Redding, D.

1994-12-31

In this paper massively parallel algorithms and architectures for real-time wavefront control of a dense adaptive optic system (SELENE) are presented. The authors have already shown that the computation of a near optimal control algorithm for SELENE can be reduced to the solution of a discrete Poisson equation on a regular domain. Although, this represents an optimal computation, due the large size of the system and the high sampling rate requirement, the implementation of this control algorithm poses a computationally challenging problem since it demands a sustained computational throughput of the order of 10 GFlops. They develop a novel algorithm,more » designated as Fast Invariant Imbedding algorithm, which offers a massive degree of parallelism with simple communication and synchronization requirements. Due to these features, this algorithm is significantly more efficient than other Fast Poisson Solvers for implementation on massively parallel architectures. The authors also discuss two massively parallel, algorithmically specialized, architectures for low-cost and optimal implementation of the Fast Invariant Imbedding algorithm.« less

Speckle contrast optical tomography: A new method for deep tissue three-dimensional tomography of blood flow

PubMed Central

Varma, Hari M.; Valdes, Claudia P.; Kristoffersen, Anna K.; Culver, Joseph P.; Durduran, Turgut

2014-01-01

A novel tomographic method based on the laser speckle contrast, speckle contrast optical tomography (SCOT) is introduced that allows us to reconstruct three dimensional distribution of blood flow in deep tissues. This method is analogous to the diffuse optical tomography (DOT) but for deep tissue blood flow. We develop a reconstruction algorithm based on first Born approximation to generate three dimensional distribution of flow using the experimental data obtained from tissue simulating phantoms. PMID:24761306

Enhanced backscattering of optical waves due to densely distributed scatterers

NASA Astrophysics Data System (ADS)

Ma, Yushieh; Varadan, Vijay K.; Varadan, Vasundara V.

1988-01-01

Using multiple scattering theory, the T matrix of a pair of scatterers which takes all back-and-forth scattering between the pair members into account and considers multiple scattering effects in the intensity calculation is used to calculate the magnitude and the width of the backscattered intensity peak. Generally, at low concentrations, both the magnitude of the scattered intensity and multiple scattering contributions are not sufficiently strong to reach the enhanced-backscattering threshold. The results obtained are consistent with those yielded by optical experiments.

Spectroscopic Feedback for High Density Data Storage and Micromachining

DOEpatents

Carr, Christopher W.; Demos, Stavros; Feit, Michael D.; Rubenchik, Alexander M.

2008-09-16

Optical breakdown by predetermined laser pulses in transparent dielectrics produces an ionized region of dense plasma confined within the bulk of the material. Such an ionized region is responsible for broadband radiation that accompanies a desired breakdown process. Spectroscopic monitoring of the accompanying light in real-time is utilized to ascertain the morphology of the radiated interaction volume. Such a method and apparatus as presented herein, provides commercial realization of rapid prototyping of optoelectronic devices, optical three-dimensional data storage devices, and waveguide writing.

CFD-based aero-optical analysis of flow fields over two-dimensional cavities with active flow control

NASA Astrophysics Data System (ADS)

Tan, Yan

Prediction and control of optical wave front distortions and aberrations in a high energy laser beam due to interaction with an unsteady highly non-uniform flow field is of great importance in the development of directed energy weapon systems for Unmanned Air Vehicles (UAV). The unsteady shear layer over the weapons bay cavity is the primary cause of this distortion of the optical wave front. The large scale vortical structure of the shear layer over the cavity can be significantly reduced by employing an active flow control technique combined with passive flow control. This dissertation explores various active and passive control methods to suppress the cavity oscillations and thereby improve the aero-optics of cavity flow. In active flow control technique, a steady or a pulsed jet is applied at the sharp leading edge of cavities of different aspect ratios L/D (=2, 4, 15), where L and D are the width and the depth of a cavity respectively. In the passive flow control approach, the sharp leading or trailing edge of the cavity is modified into a round edge of different radii. Both of these active and passive flow control approaches are studied independently and in combination. Numerical simulations are performed, with and without active flow control for subsonic free stream flow past two-dimensional sharp and round leading or trailing edge cavities using Unsteady Reynolds-Averaged Navier-Stokes (URANS) equations with a two-equation Shear Stress Transport (SST) turbulence model or a hybrid SST/Large Eddy Simulation (LES) model. Aero-optical analysis is developed and applied to all the simulation cases. Index of refraction and Optical Path Difference (OPD) are compared for flow fields without and with active flow control. Root-Mean-Square (RMS) value of OPD is calculated and compared with the experimental data, where available. The effect of steady and pulsed blowing on buffet loading on the downstream face of the cavity is also computed. Using the numerical simulations, the most effective approach for controlling the cavity oscillations and aero-optical signatures is determined.

Shear-induced crystallization of a dense rapid granular flow: hydrodynamics beyond the melting point.

PubMed

Khain, Evgeniy; Meerson, Baruch

2006-06-01

We investigate shear-induced crystallization in a very dense flow of monodisperse inelastic hard spheres. We consider a steady plane Couette flow under constant pressure and neglect gravity. We assume that the granular density is greater than the melting point of the equilibrium phase diagram of elastic hard spheres. We employ a Navier-Stokes hydrodynamics with constitutive relations all of which (except the shear viscosity) diverge at the crystal-packing density, while the shear viscosity diverges at a smaller density. The phase diagram of the steady flow is described by three parameters: an effective Mach number, a scaled energy loss parameter, and an integer number m: the number of half-oscillations in a mechanical analogy that appears in this problem. In a steady shear flow the viscous heating is balanced by energy dissipation via inelastic collisions. This balance can have different forms, producing either a uniform shear flow or a variety of more complicated, nonlinear density, velocity, and temperature profiles. In particular, the model predicts a variety of multilayer two-phase steady shear flows with sharp interphase boundaries. Such a flow may include a few zero-shear (solidlike) layers, each of which moving as a whole, separated by fluidlike regions. As we are dealing with a hard sphere model, the granulate is fluidized within the "solid" layers: the granular temperature is nonzero there, and there is energy flow through the boundaries of the solid layers. A linear stability analysis of the uniform steady shear flow is performed, and a plausible bifurcation diagram of the system, for a fixed m, is suggested. The problem of selection of m remains open.

Conspecific aggregations mitigate the effects of ocean acidification on calcification of the coral Pocillopora verrucosa.

PubMed

Evensen, Nicolas R; Edmunds, Peter J

2017-03-15

In densely populated communities, such as coral reefs, organisms can modify the physical and chemical environment for neighbouring individuals. We tested the hypothesis that colony density (12 colonies each placed ∼0.5 cm apart versus ∼8 cm apart) can modulate the physiological response (measured through rates of calcification, photosynthesis and respiration in the light and dark) of the coral Pocillopora verrucosa to partial pressure of CO 2 ( P CO 2 ) treatments (∼400 μatm and ∼1200 μatm) by altering the seawater flow regimes experienced by colonies placed in aggregations within a flume at a single flow speed. While light calcification decreased 20% under elevated versus ambient P CO 2  for colonies in low-density aggregations, light calcification of high-density aggregations increased 23% at elevated versus ambient P CO 2 As a result, densely aggregated corals maintained calcification rates over 24 h that were comparable to those maintained under ambient P CO 2 , despite a 45% decrease in dark calcification at elevated versus ambient P CO 2 Additionally, densely aggregated corals experienced reduced flow speeds and higher seawater retention times between colonies owing to the formation of eddies. These results support recent indications that neighbouring organisms, such as the conspecific coral colonies in the present example, can create small-scale refugia from the negative effects of ocean acidification. © 2017. Published by The Company of Biologists Ltd.

Parametric dense stereovision implementation on a system-on chip (SoC).

PubMed

Gardel, Alfredo; Montejo, Pablo; García, Jorge; Bravo, Ignacio; Lázaro, José L

2012-01-01

This paper proposes a novel hardware implementation of a dense recovery of stereovision 3D measurements. Traditionally 3D stereo systems have imposed the maximum number of stereo correspondences, introducing a large restriction on artificial vision algorithms. The proposed system-on-chip (SoC) provides great performance and efficiency, with a scalable architecture available for many different situations, addressing real time processing of stereo image flow. Using double buffering techniques properly combined with pipelined processing, the use of reconfigurable hardware achieves a parametrisable SoC which gives the designer the opportunity to decide its right dimension and features. The proposed architecture does not need any external memory because the processing is done as image flow arrives. Our SoC provides 3D data directly without the storage of whole stereo images. Our goal is to obtain high processing speed while maintaining the accuracy of 3D data using minimum resources. Configurable parameters may be controlled by later/parallel stages of the vision algorithm executed on an embedded processor. Considering hardware FPGA clock of 100 MHz, image flows up to 50 frames per second (fps) of dense stereo maps of more than 30,000 depth points could be obtained considering 2 Mpix images, with a minimum initial latency. The implementation of computer vision algorithms on reconfigurable hardware, explicitly low level processing, opens up the prospect of its use in autonomous systems, and they can act as a coprocessor to reconstruct 3D images with high density information in real time.

A numerical framework for the direct simulation of dense particulate flow under explosive dispersal

NASA Astrophysics Data System (ADS)

Mo, H.; Lien, F.-S.; Zhang, F.; Cronin, D. S.

2018-05-01

In this paper, we present a Cartesian grid-based numerical framework for the direct simulation of dense particulate flow under explosive dispersal. This numerical framework is established through the integration of the following numerical techniques: (1) operator splitting for partitioned fluid-solid interaction in the time domain, (2) the second-order SSP Runge-Kutta method and third-order WENO scheme for temporal and spatial discretization of governing equations, (3) the front-tracking method for evolving phase interfaces, (4) a field function proposed for low-memory-cost multimaterial mesh generation and fast collision detection, (5) an immersed boundary method developed for treating arbitrarily irregular and changing boundaries, and (6) a deterministic multibody contact and collision model. Employing the developed framework, this paper further studies particle jet formation under explosive dispersal by considering the effects of particle properties, particulate payload morphologies, and burster pressures. By the simulation of the dispersal processes of dense particle systems driven by pressurized gas, in which the driver pressure reaches 1.01325× 10^{10} Pa (10^5 times the ambient pressure) and particles are impulsively accelerated from stationary to a speed that is more than 12000 m/s within 15 μ s, it is demonstrated that the presented framework is able to effectively resolve coupled shock-shock, shock-particle, and particle-particle interactions in complex fluid-solid systems with shocked flow conditions, arbitrarily irregular particle shapes, and realistic multibody collisions.

Extrapolating regional probability of drying of headwater streams using discrete observations and gauging networks

NASA Astrophysics Data System (ADS)

Beaufort, Aurélien; Lamouroux, Nicolas; Pella, Hervé; Datry, Thibault; Sauquet, Eric

2018-05-01

Headwater streams represent a substantial proportion of river systems and many of them have intermittent flows due to their upstream position in the network. These intermittent rivers and ephemeral streams have recently seen a marked increase in interest, especially to assess the impact of drying on aquatic ecosystems. The objective of this paper is to quantify how discrete (in space and time) field observations of flow intermittence help to extrapolate over time the daily probability of drying (defined at the regional scale). Two empirical models based on linear or logistic regressions have been developed to predict the daily probability of intermittence at the regional scale across France. Explanatory variables were derived from available daily discharge and groundwater-level data of a dense gauging/piezometer network, and models were calibrated using discrete series of field observations of flow intermittence. The robustness of the models was tested using an independent, dense regional dataset of intermittence observations and observations of the year 2017 excluded from the calibration. The resulting models were used to extrapolate the daily regional probability of drying in France: (i) over the period 2011-2017 to identify the regions most affected by flow intermittence; (ii) over the period 1989-2017, using a reduced input dataset, to analyse temporal variability of flow intermittence at the national level. The two empirical regression models performed equally well between 2011 and 2017. The accuracy of predictions depended on the number of continuous gauging/piezometer stations and intermittence observations available to calibrate the regressions. Regions with the highest performance were located in sedimentary plains, where the monitoring network was dense and where the regional probability of drying was the highest. Conversely, the worst performances were obtained in mountainous regions. Finally, temporal projections (1989-2016) suggested the highest probabilities of intermittence (> 35 %) in 1989-1991, 2003 and 2005. A high density of intermittence observations improved the information provided by gauging stations and piezometers to extrapolate the temporal variability of intermittent rivers and ephemeral streams.

Optical multicast system for data center networks.

PubMed

Samadi, Payman; Gupta, Varun; Xu, Junjie; Wang, Howard; Zussman, Gil; Bergman, Keren

2015-08-24

We present the design and experimental evaluation of an Optical Multicast System for Data Center Networks, a hardware-software system architecture that uniquely integrates passive optical splitters in a hybrid network architecture for faster and simpler delivery of multicast traffic flows. An application-driven control plane manages the integrated optical and electronic switched traffic routing in the data plane layer. The control plane includes a resource allocation algorithm to optimally assign optical splitters to the flows. The hardware architecture is built on a hybrid network with both Electronic Packet Switching (EPS) and Optical Circuit Switching (OCS) networks to aggregate Top-of-Rack switches. The OCS is also the connectivity substrate of splitters to the optical network. The optical multicast system implementation requires only commodity optical components. We built a prototype and developed a simulation environment to evaluate the performance of the system for bulk multicasting. Experimental and numerical results show simultaneous delivery of multicast flows to all receivers with steady throughput. Compared to IP multicast that is the electronic counterpart, optical multicast performs with less protocol complexity and reduced energy consumption. Compared to peer-to-peer multicast methods, it achieves at minimum an order of magnitude higher throughput for flows under 250 MB with significantly less connection overheads. Furthermore, for delivering 20 TB of data containing only 15% multicast flows, it reduces the total delivery energy consumption by 50% and improves latency by 55% compared to a data center with a sole non-blocking EPS network.

AWG-based WDM-PON monitoring system using an optical switch and a WDM filter

NASA Astrophysics Data System (ADS)

Liaw, S.-K.; Lai, Y.-T.; Chang, C.-L.; Shung, O.

2008-09-01

A new WDM-PON scheme with real-time monitoring based on a time-sharing method is proposed. It uses an optical time domain reflectometer (OTDR) to monitor multiple ports by integrating an optical switch (OSW) with a dense wavelength division multiplexer (DWDM) at the optical line terminal (OLT) site. Each downstream signal and its corresponding monitoring signal are separated by m times the free-space range (FSR) of an array waveguide grating (AWG). A bit error rate (BER) test in 2.5 Gb/s × 27 km is performed with and without turning on the OTDR. A small power penalty of 0.7 dB is observed compared to the back-to-back measurement.

Investigation of the Static and Dynamic Characteristics for a Wafer-Fused C-band VCSEL in the Mode of the Optical-Electric Converter

NASA Astrophysics Data System (ADS)

Belkin, M. E.

2018-01-01

The results of an experimental study for a long wavelength vertical cavity surface-emitting laser of a wafer-fused construction as an effective resonant cavity enhanced photodetector of analog optical signals are described. The device is of interest for a number of promising microwave photonics applications and for creation of a low-cost photoreceiver in a high-speed fiber optics telecommunication system with dense wavelength division multiplexing. The schematic of the testbed, the original technique allowing to calculate the passband of the built-in optical cavity, and the results of measuring dark current, current responsivity, amplitude- and phase-frequency characteristics during the process of photo-detection are demonstrated.

Thermophysical properties of multi-shock compressed dense argon.

PubMed

Chen, Q F; Zheng, J; Gu, Y J; Chen, Y L; Cai, L C; Shen, Z J

2014-02-21

In contrast to the single shock compression state that can be obtained directly via experimental measurements, the multi-shock compression states, however, have to be calculated with the aid of theoretical models. In order to determine experimentally the multiple shock states, a diagnostic approach with the Doppler pins system (DPS) and the pyrometer was used to probe multiple shocks in dense argon plasmas. Plasma was generated by a shock reverberation technique. The shock was produced using the flyer plate impact accelerated up to ∼6.1 km/s by a two-stage light gas gun and introduced into the plenum argon gas sample, which was pre-compressed from the environmental pressure to about 20 MPa. The time-resolved optical radiation histories were determined using a multi-wavelength channel optical transience radiance pyrometer. Simultaneously, the particle velocity profiles of the LiF window was measured with multi-DPS. The states of multi-shock compression argon plasma were determined from the measured shock velocities combining the particle velocity profiles. We performed the experiments on dense argon plasmas to determine the principal Hugonoit up to 21 GPa, the re-shock pressure up to 73 GPa, and the maximum measure pressure of the fourth shock up to 158 GPa. The results are used to validate the existing self-consistent variational theory model in the partial ionization region and create new theoretical models.

Thermophysical properties of multi-shock compressed dense argon

NASA Astrophysics Data System (ADS)

Chen, Q. F.; Zheng, J.; Gu, Y. J.; Chen, Y. L.; Cai, L. C.; Shen, Z. J.

2014-02-01

In contrast to the single shock compression state that can be obtained directly via experimental measurements, the multi-shock compression states, however, have to be calculated with the aid of theoretical models. In order to determine experimentally the multiple shock states, a diagnostic approach with the Doppler pins system (DPS) and the pyrometer was used to probe multiple shocks in dense argon plasmas. Plasma was generated by a shock reverberation technique. The shock was produced using the flyer plate impact accelerated up to ˜6.1 km/s by a two-stage light gas gun and introduced into the plenum argon gas sample, which was pre-compressed from the environmental pressure to about 20 MPa. The time-resolved optical radiation histories were determined using a multi-wavelength channel optical transience radiance pyrometer. Simultaneously, the particle velocity profiles of the LiF window was measured with multi-DPS. The states of multi-shock compression argon plasma were determined from the measured shock velocities combining the particle velocity profiles. We performed the experiments on dense argon plasmas to determine the principal Hugonoit up to 21 GPa, the re-shock pressure up to 73 GPa, and the maximum measure pressure of the fourth shock up to 158 GPa. The results are used to validate the existing self-consistent variational theory model in the partial ionization region and create new theoretical models.

Retinal blood flow detection in diabetic patients by Doppler Fourier domain optical coherence tomography◊

PubMed Central

Wang, Yimin; Fawzi, Amani; Tan, Ou; Gil-Flamer, John; Huang, David

2010-01-01

We present human retinal blood flow investigation for diabetic patients using Doppler Fourier domain optical coherence tomography (FD-OCT). The scanning pattern consisted of two concentric circles around the optic nerve head. The blood flow in one patient with diabetes and no retinpathy and another patient with treated proliferative diabetic retinopathy were measured. The patient without retinopathy showed a total blood flow value at the lower level of the normal range. The flow distribution between superior and inferior retina was balanced. The patient with diabetic retinopathy had a flow value lower than the normal people. Our study shows that Doppler FD-OCT can be used to evaluate the total retinal blood flow in patients with retinal diseases. PMID:19259246

Axial-Stereo 3-D Optical Metrology for Inner Profile of Pipes Using a Scanning Laser Endoscope

NASA Astrophysics Data System (ADS)

Gong, Yuanzheng; Johnston, Richard S.; Melville, C. David; Seibel, Eric J.

2015-07-01

As the rapid progress in the development of optoelectronic components and computational power, 3-D optical metrology becomes more and more popular in manufacturing and quality control due to its flexibility and high speed. However, most of the optical metrology methods are limited to external surfaces. This article proposed a new approach to measure tiny internal 3-D surfaces with a scanning fiber endoscope and axial-stereo vision algorithm. A dense, accurate point cloud of internally machined threads was generated to compare with its corresponding X-ray 3-D data as ground truth, and the quantification was analyzed by Iterative Closest Points algorithm.

Hot Corrosion Behavior of Arc-Sprayed Highly Dense NiCr-Based Coatings in Chloride Salt Deposit

NASA Astrophysics Data System (ADS)

Qin, Enwei; Yin, Song; Ji, Hua; Huang, Qian; Liu, Zekun; Wu, Shuhui

2017-04-01

To make cities more environmentally friendly, combustible wastes tend to be incinerated in waste-to-energy power plant boilers. However, release of chlorine gas (Cl2) during incineration causes serious problems related to hot corrosion of boiler tubes and poses a safety threat for such plants. In this study, a pseudo-de Laval nozzle was employed in a twin-wire arc spray system to enhance the velocity of in-flight particles. Highly dense NiCr-based coatings were obtained using the modified nozzle gun. The coating morphology was characterized by optical microscopy and scanning electron microscopy, and hot corrosion testing was carried out in a synthetic molten chloride salt environment. Results showed that the dense NiCr-based coatings exhibited high resistance against corrosion by chlorine, which can be related to the typical splat lamellar microstructure and chemical composition as well as minor alloying elements such as Ti and Mo.

Measurement of Preheat Due to Nonlocal Electron Transport in Warm Dense Matter

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

Falk, K.; Holec, M.; Fontes, C. J.

This work presents a novel approach to study electron transport in warm dense matter. It also includes the first x-ray Thomson scattering (XRTS) measurement from low-density CH foams compressed by a strong laser-driven shock at the OMEGA laser facility. The XRTS measurement is combined with velocity interferometry (VISAR) and optical pyrometry (SOP) providing a robust measurement of thermodynamic conditions in the shock. Evidence of significant preheat contributing to elevated temperatures reaching 17.5–35 eV in shocked CH foam is measured by XRTS. These measurements are complemented by abnormally high shock velocities observed by VISAR and early emission seen by SOP. Thesemore » results are compared to radiation hydrodynamics simulations that include first-principles treatment of nonlocal electron transport in warm dense matter with excellent agreement. Additional simulations confirm that the x-ray contribution to this preheat is negligible.« less

Measurement of Preheat Due to Nonlocal Electron Transport in Warm Dense Matter

DOE PAGES

Falk, K.; Holec, M.; Fontes, C. J.; ...

2018-01-10

This work presents a novel approach to study electron transport in warm dense matter. It also includes the first x-ray Thomson scattering (XRTS) measurement from low-density CH foams compressed by a strong laser-driven shock at the OMEGA laser facility. The XRTS measurement is combined with velocity interferometry (VISAR) and optical pyrometry (SOP) providing a robust measurement of thermodynamic conditions in the shock. Evidence of significant preheat contributing to elevated temperatures reaching 17.5–35 eV in shocked CH foam is measured by XRTS. These measurements are complemented by abnormally high shock velocities observed by VISAR and early emission seen by SOP. Thesemore » results are compared to radiation hydrodynamics simulations that include first-principles treatment of nonlocal electron transport in warm dense matter with excellent agreement. Additional simulations confirm that the x-ray contribution to this preheat is negligible.« less

Pulsar-irradiated stars in dense globular clusters

NASA Technical Reports Server (NTRS)

Tavani, Marco

1992-01-01

We discuss the properties of stars irradiated by millisecond pulsars in 'hard' binaries of dense globular clusters. Irradiation by a relativistic pulsar wind as in the case of the eclipsing millisecond pulsar PSR 1957+20 alter both the magnitude and color of the companion star. Some of the blue stragglers (BSs) recently discovered in dense globular clusters can be irradiated stars in binaries containing powerful millisecond pulsars. The discovery of pulsar-driven orbital modulations of BS brightness and color with periods of a few hours together with evidence for radio and/or gamma-ray emission from BS binaries would valuably contribute to the understanding of the evolution of collapsed stars in globular clusters. Pulsar-driven optical modulation of cluster stars might be the only observable effect of a new class of binary pulsars, i.e., hidden millisecond pulsars enshrouded in the evaporated material lifted off from the irradiated companion star.

Measurement of Preheat Due to Nonlocal Electron Transport in Warm Dense Matter

NASA Astrophysics Data System (ADS)

Falk, K.; Holec, M.; Fontes, C. J.; Fryer, C. L.; Greeff, C. W.; Johns, H. M.; Montgomery, D. S.; Schmidt, D. W.; Šmíd, M.

2018-01-01

This Letter presents a novel approach to study electron transport in warm dense matter. It also includes the first x-ray Thomson scattering (XRTS) measurement from low-density CH foams compressed by a strong laser-driven shock at the OMEGA laser facility. The XRTS measurement is combined with velocity interferometry (VISAR) and optical pyrometry (SOP) providing a robust measurement of thermodynamic conditions in the shock. Evidence of significant preheat contributing to elevated temperatures reaching 17.5-35 eV in shocked CH foam is measured by XRTS. These measurements are complemented by abnormally high shock velocities observed by VISAR and early emission seen by SOP. These results are compared to radiation hydrodynamics simulations that include first-principles treatment of nonlocal electron transport in warm dense matter with excellent agreement. Additional simulations confirm that the x-ray contribution to this preheat is negligible.

Measurements of ionization states in warm dense aluminum with betatron radiation

NASA Astrophysics Data System (ADS)

Mo, M. Z.; Chen, Z.; Fourmaux, S.; Saraf, A.; Kerr, S.; Otani, K.; Masoud, R.; Kieffer, J.-C.; Tsui, Y.; Ng, A.; Fedosejevs, R.

2017-05-01

Time-resolved measurements of the ionization states of warm dense aluminum via K-shell absorption spectroscopy are demonstrated using betatron radiation generated from laser wakefield acceleration as a probe. The warm dense aluminum is generated by irradiating a free-standing nanofoil with a femtosecond optical laser pulse and was heated to an electron temperature of ˜20 -25 eV at a close-to-solid mass density. Absorption dips in the transmitted x-ray spectrum due to the Al4 + and Al5 + ions are clearly seen during the experiments. The measured absorption spectra are compared to simulations with various ionization potential depression models, including the commonly used Stewart-Pyatt model and an alternative modified Ecker-Kröll model. The observed absorption spectra are in approximate agreement with these models, though indicating a slightly higher state of ionization and closer agreement for simulations with the modified Ecker-Kröll model.

Elliptic flow in Au+Au collisions at RHIC

NASA Astrophysics Data System (ADS)

Vale, Carla M.; PHOBOS Collaboration; Back, B. B.; Baker, M. D.; Ballintijn, M.; Barton, D. S.; Betts, R. R.; Bickley, A. A.; Bindel, R.; Budzanowski, A.; Busza, W.; Carroll, A.; Decowski, M. P.; García, E.; George, N.; Gulbrandsen, K.; Gushue, S.; Halliwell, C.; Hamblen, J.; Heintzelman, G. A.; Henderson, C.; Hofman, D. J.; Hollis, R. S.; Holynski, R.; Holzman, B.; Iordanova, A.; Johnson, E.; Kane, J. L.; Katzy, J.; Khan, N.; Kucewicz, W.; Kulinich, P.; Kuo, C. M.; Lin, W. T.; Manly, S.; McLeod, D.; Mignerey, A. C.; Ngyuen, M.; Nouicer, R.; Olszewski, A.; Pak, R.; Park, I. C.; Pernegger, H.; Reed, C.; Remsberg, L. P.; Reuter, M.; Roland, C.; Roland, G.; Rosenberg, L.; Sagerer, J.; Sarin, P.; Sawicki, P.; Skulski, W.; Steinberg, P.; Stephans, G. S. F.; Sukhanov, A.; Tang, J.-L.; Tonjes, M. B.; Trzupek, A.; van Nieuwenhuizen, G. J.; Verdier, R.; Veres, G.; Wolfs, F. L. H.; Wosiek, B.; Wozniak, K.; Wuosmaa, A. H.; Wyslouch, B.

2005-04-01

Elliptic flow is an interesting probe of the dynamical evolution of the dense system formed in the ultrarelativistic heavy ion collisions at the relativistic heavy ion collider (RHIC). The elliptic flow dependences on transverse momentum, centrality and pseudorapidity were measured using data collected by the PHOBOS detector, which offers a unique opportunity to study the azimuthal anisotropies of charged particles over a wide range of pseudorapidity. These measurements are presented, together with an overview of the analysis methods and a discussion of the results.

Development of Elasto-Acoustic Integral Equation Based Solver to Assess/Simulate Sound Conducting Mechanisms in Human Head

DTIC Science & Technology

2013-09-09

indicates energy flowing into and out of the bone. (b) The average energy flux density through the surface of the cochlear cavity (relative to the incident...simulation tool capable of handling a variety of aspects of wave propagation and the resulting energy flow in a human head subject to an incident...small amounts of energy transferred from air to a dense inhomogeneous object: such small energy flows are relevant only because of the exceedingly high

Cryogenic Flow Sensor

NASA Technical Reports Server (NTRS)

Justak, John

2010-01-01

An acousto-optic cryogenic flow sensor (CFS) determines mass flow of cryogens for spacecraft propellant management. The CFS operates unobtrusively in a high-pressure, high-flowrate cryogenic environment to provide measurements for fluid quality as well as mass flow rate. Experimental hardware uses an optical plane-of-light (POL) to detect the onset of two-phase flow, and the presence of particles in the flow of water. Acousto-optic devices are used in laser equipment for electronic control of the intensity and position of the laser beam. Acousto-optic interaction occurs in all optical media when an acoustic wave and a laser beam are present. When an acoustic wave is launched into the optical medium, it generates a refractive index wave that behaves like a sinusoidal grating. An incident laser beam passing through this grating will diffract the laser beam into several orders. Its angular position is linearly proportional to the acoustic frequency, so that the higher the frequency, the larger the diffracted angle. If the acoustic wave is traveling in a moving fluid, the fluid velocity will affect the frequency of the traveling wave, relative to a stationary sensor. This frequency shift changes the angle of diffraction, hence, fluid velocity can be determined from the diffraction angle. The CFS acoustic Bragg grating data test indicates that it is capable of accurately determining flow from 0 to 10 meters per second. The same sensor can be used in flow velocities exceeding 100 m/s. The POL module has successfully determined the onset of two-phase flow, and can distinguish vapor bubbles from debris.

Visualization of expanding warm dense gold and diamond heated rapidly by laser-generated ion beams

DOE PAGES

Bang, W.; Albright, B. J.; Bradley, P. A.; ...

2015-09-22

With the development of several novel heating sources, scientists can now heat a small sample isochorically above 10,000 K. Although matter at such an extreme state, known as warm dense matter, is commonly found in astrophysics (e.g., in planetary cores) as well as in high energy density physics experiments, its properties are not well understood and are difficult to predict theoretically. This is because the approximations made to describe condensed matter or high-temperature plasmas are invalid in this intermediate regime. A sufficiently large warm dense matter sample that is uniformly heated would be ideal for these studies, but has beenmore » unavailable to date. We have used a beam of quasi-monoenergetic aluminum ions to heat gold and diamond foils uniformly and isochorically. For the first time, we visualized directly the expanding warm dense gold and diamond with an optical streak camera. Furthermore, we present a new technique to determine the initial temperature of these heated samples from the measured expansion speeds of gold and diamond into vacuum. We anticipate the uniformly heated solid density target will allow for direct quantitative measurements of equation-of-state, conductivity, opacity, and stopping power of warm dense matter, benefiting plasma physics, astrophysics, and nuclear physics.« less

Visualization of expanding warm dense gold and diamond heated rapidly by laser-generated ion beams.

PubMed

Bang, W; Albright, B J; Bradley, P A; Gautier, D C; Palaniyappan, S; Vold, E L; Santiago Cordoba, M A; Hamilton, C E; Fernández, J C

2015-09-22

With the development of several novel heating sources, scientists can now heat a small sample isochorically above 10,000 K. Although matter at such an extreme state, known as warm dense matter, is commonly found in astrophysics (e.g., in planetary cores) as well as in high energy density physics experiments, its properties are not well understood and are difficult to predict theoretically. This is because the approximations made to describe condensed matter or high-temperature plasmas are invalid in this intermediate regime. A sufficiently large warm dense matter sample that is uniformly heated would be ideal for these studies, but has been unavailable to date. Here we have used a beam of quasi-monoenergetic aluminum ions to heat gold and diamond foils uniformly and isochorically. For the first time, we visualized directly the expanding warm dense gold and diamond with an optical streak camera. Furthermore, we present a new technique to determine the initial temperature of these heated samples from the measured expansion speeds of gold and diamond into vacuum. We anticipate the uniformly heated solid density target will allow for direct quantitative measurements of equation-of-state, conductivity, opacity, and stopping power of warm dense matter, benefiting plasma physics, astrophysics, and nuclear physics.

Fluorescence and absorption spectroscopy for warm dense matter studies and ICF plasma diagnostics

DOE PAGES

Hansen, Stephanie B.; Harding, Eric C.; Knapp, Patrick F.; ...

2018-03-07

The burning core of an inertial confinement fusion (ICF) plasma produces bright x-rays at stagnation that can directly diagnose core conditions essential for comparison to simulations and understanding fusion yields. These x-rays also backlight the surrounding shell of warm, dense matter, whose properties are critical to understanding the efficacy of the inertial confinement and global morphology. In this work, we show that the absorption and fluorescence spectra of mid-Z impurities or dopants in the warm dense shell can reveal the optical depth, temperature, and density of the shell and help constrain models of warm, dense matter. This is illustrated bymore » the example of a high-resolution spectrum collected from an ICF plasma with a beryllium shell containing native iron impurities. Lastly, analysis of the iron K-edge provides model-independent diagnostics of the shell density (2.3 × 10 24 e/cm 3) and temperature (10 eV), while a 12-eV red shift in Kβ and 5-eV blue shift in the K-edge discriminate among models of warm dense matter: Both shifts are well described by a self-consistent field model based on density functional theory but are not fully consistent with isolated-atom models using ad-hoc density effects.« less

Visualization of expanding warm dense gold and diamond heated rapidly by laser-generated ion beams

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

Bang, W.; Albright, B. J.; Bradley, P. A.

With the development of several novel heating sources, scientists can now heat a small sample isochorically above 10,000 K. Although matter at such an extreme state, known as warm dense matter, is commonly found in astrophysics (e.g., in planetary cores) as well as in high energy density physics experiments, its properties are not well understood and are difficult to predict theoretically. This is because the approximations made to describe condensed matter or high-temperature plasmas are invalid in this intermediate regime. A sufficiently large warm dense matter sample that is uniformly heated would be ideal for these studies, but has beenmore » unavailable to date. We have used a beam of quasi-monoenergetic aluminum ions to heat gold and diamond foils uniformly and isochorically. For the first time, we visualized directly the expanding warm dense gold and diamond with an optical streak camera. Furthermore, we present a new technique to determine the initial temperature of these heated samples from the measured expansion speeds of gold and diamond into vacuum. We anticipate the uniformly heated solid density target will allow for direct quantitative measurements of equation-of-state, conductivity, opacity, and stopping power of warm dense matter, benefiting plasma physics, astrophysics, and nuclear physics.« less

Visualization of expanding warm dense gold and diamond heated rapidly by laser-generated ion beams

NASA Astrophysics Data System (ADS)

Bang, W.; Albright, B. J.; Bradley, P. A.; Gautier, D. C.; Palaniyappan, S.; Vold, E. L.; Cordoba, M. A. Santiago; Hamilton, C. E.; Fernández, J. C.

2015-09-01

With the development of several novel heating sources, scientists can now heat a small sample isochorically above 10,000 K. Although matter at such an extreme state, known as warm dense matter, is commonly found in astrophysics (e.g., in planetary cores) as well as in high energy density physics experiments, its properties are not well understood and are difficult to predict theoretically. This is because the approximations made to describe condensed matter or high-temperature plasmas are invalid in this intermediate regime. A sufficiently large warm dense matter sample that is uniformly heated would be ideal for these studies, but has been unavailable to date. Here we have used a beam of quasi-monoenergetic aluminum ions to heat gold and diamond foils uniformly and isochorically. For the first time, we visualized directly the expanding warm dense gold and diamond with an optical streak camera. Furthermore, we present a new technique to determine the initial temperature of these heated samples from the measured expansion speeds of gold and diamond into vacuum. We anticipate the uniformly heated solid density target will allow for direct quantitative measurements of equation-of-state, conductivity, opacity, and stopping power of warm dense matter, benefiting plasma physics, astrophysics, and nuclear physics.

On the dense water spreading off the Ross Sea shelf (Southern Ocean)

NASA Astrophysics Data System (ADS)

Budillon, G.; Gremes Cordero, S.; Salusti, E.

2002-07-01

In this study, current meter and hydrological data obtained during the X Italian Expedition in the Ross Sea (CLIMA Project) are analyzed. Our data show a nice agreement with previous data referring to the water masses present in this area and their dynamics. Here, they are used to further analyze the mixing and deepening processes of Deep Ice Shelf Water (DISW) over the northern shelf break of the Ross Sea. In more detail, our work is focused on the elementary mechanisms that are the most efficient in removing dense water from the shelf: either classical mixing effects or density currents that interact with some topographic irregularity in order to drop to deeper levels, or also the variability of the Antarctic Circumpolar Current (ACC) which, in its meandering, can push the dense water off the shelf, thus interrupting its geostrophic flow. We also discuss in detail the (partial) evidence of dramatic interactions of the dense water with bottom particulate, of geological or biological origin, thus generating impulsive or quasi-steady density-turbidity currents. This complex interaction allows one to consider bottom particular and dense water as a unique self-interacting system. In synthesis, this is a first tentative analysis of the effect of bottom particulate on the dense water dynamics in the Ross Sea.

Optical vector network analysis of ultranarrow transitions in 166Er3+ : 7LiYF4 crystal.

PubMed

Kukharchyk, N; Sholokhov, D; Morozov, O; Korableva, S L; Cole, J H; Kalachev, A A; Bushev, P A

2018-02-15

We present optical vector network analysis (OVNA) of an isotopically purified Er166 3+ :LiYF 4 7 crystal. The OVNA method is based on generation and detection of a modulated optical sideband by using a radio-frequency vector network analyzer. This technique is widely used in the field of microwave photonics for the characterization of optical responses of optical devices such as filters and high-Q resonators. However, dense solid-state atomic ensembles induce a large phase shift on one of the optical sidebands that results in the appearance of extra features on the measured transmission response. We present a simple theoretical model that accurately describes the observed spectra and helps to reconstruct the absorption profile of a solid-state atomic ensemble as well as corresponding change of the refractive index in the vicinity of atomic resonances.

Doppler optical coherence tomography of retinal circulation.

PubMed

Tan, Ou; Wang, Yimin; Konduru, Ranjith K; Zhang, Xinbo; Sadda, SriniVas R; Huang, David

2012-09-18

Noncontact retinal blood flow measurements are performed with a Fourier domain optical coherence tomography (OCT) system using a circumpapillary double circular scan (CDCS) that scans around the optic nerve head at 3.40 mm and 3.75 mm diameters. The double concentric circles are performed 6 times consecutively over 2 sec. The CDCS scan is saved with Doppler shift information from which flow can be calculated. The standard clinical protocol calls for 3 CDCS scans made with the OCT beam passing through the superonasal edge of the pupil and 3 CDCS scan through the inferonal pupil. This double-angle protocol ensures that acceptable Doppler angle is obtained on each retinal branch vessel in at least 1 scan. The CDCS scan data, a 3-dimensional volumetric OCT scan of the optic disc scan, and a color photograph of the optic disc are used together to obtain retinal blood flow measurement on an eye. We have developed a blood flow measurement software called "Doppler optical coherence tomography of retinal circulation" (DOCTORC). This semi-automated software is used to measure total retinal blood flow, vessel cross section area, and average blood velocity. The flow of each vessel is calculated from the Doppler shift in the vessel cross-sectional area and the Doppler angle between the vessel and the OCT beam. Total retinal blood flow measurement is summed from the veins around the optic disc. The results obtained at our Doppler OCT reading center showed good reproducibility between graders and methods (<10%). Total retinal blood flow could be useful in the management of glaucoma, other retinal diseases, and retinal diseases. In glaucoma patients, OCT retinal blood flow measurement was highly correlated with visual field loss (R(2)>0.57 with visual field pattern deviation). Doppler OCT is a new method to perform rapid, noncontact, and repeatable measurement of total retinal blood flow using widely available Fourier-domain OCT instrumentation. This new technology may improve the practicality of making these measurements in clinical studies and routine clinical practice.

Fabrication Studies of Ternary Rare Earth Sulfides for Infrared Applications.

DTIC Science & Technology

1982-05-01

crystal growth by vapor transport. The objective was to achieve small , high purity, theoretically dense crystals for optical property characterization...Weapons Center White Oak Silver Spring MD 20910 Dr. S. Musikant General Electric Co - RESD 3198 Chestnut Street Philadelphia PA 19101 Dr. W. White

Use of Proper Orthogonal Decomposition Towards Time-resolved Image Analysis of Sprays

DTIC Science & Technology

2011-03-15

High-speed movies of optically dense sprays exiting a Gas-Centered Swirl Coaxial (GCSC) injector are subjected to image analysis to determine spray...sequence prior to image analysis . Results of spray morphology including spray boundary, widths, angles and boundary oscillation frequencies, are

Nonlinear Optics in Dense Frequency Narrow Supersonic Beams

DTIC Science & Technology

1991-12-01

supersonic beams suggested that it might be fruitful to pursue other applications of field gradients. Motivated by the lack of position measurement...to the velocity of the moving atoms along the measument axis. Much higher resolution will be obtained with the next generation systems which employ

Wave-Optics Modeling of the Optical-Transport Line for Passive Optical Stochastic Cooling

DOE PAGES

Andorf, M. B.; Lebedev, V. A.; Piot, P.; ...

2018-03-01

Optical stochastic cooling (OSC) is expected to enable fast cooling of dense particle beams. Transition from microwave to optical frequencies enables an achievement of stochastic cooling rates which are orders of magnitude higher than ones achievable with the classical microwave based stochastic cooling systems. A subsystemcritical to the OSC scheme is the focusing optics used to image radiation from the upstream “pickup” undulator to the downstream “kicker” undulator. In this paper, we present simulation results using wave-optics calculation carried out with the Synchrotron Radiation Workshop (SRW). Our simulations are performed in support to a proof-of-principle experiment planned at the Integrablemore » Optics Test Accelerator (IOTA) at Fermilab. The calculations provide an estimate of the energy kick received by a 100-MeV electron as it propagates in the kicker undulator and interacts with the electromagnetic pulse it radiated at an earlier time while traveling through the pickup undulator.« less

TOWARD QUANTITATIVE OPTICAL COHERENCE TOMOGRAPHY ANGIOGRAPHY: Visualizing Blood Flow Speeds in Ocular Pathology Using Variable Interscan Time Analysis.

PubMed

Ploner, Stefan B; Moult, Eric M; Choi, WooJhon; Waheed, Nadia K; Lee, ByungKun; Novais, Eduardo A; Cole, Emily D; Potsaid, Benjamin; Husvogt, Lennart; Schottenhamml, Julia; Maier, Andreas; Rosenfeld, Philip J; Duker, Jay S; Hornegger, Joachim; Fujimoto, James G

2016-12-01

Currently available optical coherence tomography angiography systems provide information about blood flux but only limited information about blood flow speed. The authors develop a method for mapping the previously proposed variable interscan time analysis (VISTA) algorithm into a color display that encodes relative blood flow speed. Optical coherence tomography angiography was performed with a 1,050 nm, 400 kHz A-scan rate, swept source optical coherence tomography system using a 5 repeated B-scan protocol. Variable interscan time analysis was used to compute the optical coherence tomography angiography signal from B-scan pairs having 1.5 millisecond and 3.0 milliseconds interscan times. The resulting VISTA data were then mapped to a color space for display. The authors evaluated the VISTA visualization algorithm in normal eyes (n = 2), nonproliferative diabetic retinopathy eyes (n = 6), proliferative diabetic retinopathy eyes (n = 3), geographic atrophy eyes (n = 4), and exudative age-related macular degeneration eyes (n = 2). All eyes showed blood flow speed variations, and all eyes with pathology showed abnormal blood flow speeds compared with controls. The authors developed a novel method for mapping VISTA into a color display, allowing visualization of relative blood flow speeds. The method was found useful, in a small case series, for visualizing blood flow speeds in a variety of ocular diseases and serves as a step toward quantitative optical coherence tomography angiography.

Observations of Antarctic Slope Current Transport and Dense Water Flow in the Northwestern Weddell Sea

NASA Astrophysics Data System (ADS)

Azaneu, M. V. C.; Heywood, K. J.; Queste, B. Y.; Thompson, A. F.

2016-02-01

In early 2012 the GENTOO project deployed three Seagliders in the northwest Weddell Sea, acquiring high temporal and spatial resolution measurements around Powell Basin for a period of 10 weeks. The Antarctic Slope Front and associated currents form a physical and dynamical barrier to the cross-slope exchange of properties, influencing local and global ocean dynamics. The Seaglider dataset comprises 1598 temperature and salinity profiles and is used to better understand cross-slope processes. From this dataset, 582 glider profiles with altimetric information at the east Antarctic Peninsula continental slope are used to investigate the properties and thickness of the dense bottom water spilling off the shelf. The dense water is identified mostly over the slope, between the 500 and 1000 m isobaths. The dense layer is thickest around ˜ 63.33 °S, along the 1000 m isobath, becoming thinner onshore and towards northern areas. We also evaluate with unprecedented resolution the along-stream velocity and potential vorticity fields along the 17 transects across the eastern Antarctic Peninsula shelf-break and the 4 transects that cross the South Orkney Islands plateau. Using an improved hydrodynamic flight model, we reference the geostrophic shear to the glider-derived depth-averaged currents corrected for tides. In the western Weddell Sea, the geostrophic velocities fields indicate the presence of a surprisingly weakened Antarctic Slope Current (ASC) around 63.5 °S, possibly indicative of high eddy activity in the area. ASC transport in this southernmost section is less than 0.2 Sv. In a more northerly section (˜ 63.1 °S), the ASC transport reaches 6 Sv. The transects west of the South Orkney Island indicate a northward flow, opposite to the previously assumed regime. The results also show intensified northward bottom flows close to the slope, which can be related to processes occurring in the bottom boundary layer. The potential vorticity fields are used to identify potential instability mechanisms contributing to the cross-slope exchange of water mass properties.

Optical Imaging of Flow Pattern and Phantom

NASA Technical Reports Server (NTRS)

Galland, Pierre A.; Liang, X.; Wang, L.; Ho, P. P.; Alfano, R. R.; Breisacher, K.

1999-01-01

Time-resolved optical imaging technique has been used to image the spatial distribution of small droplets and jet sprays in a highly scattering environment. The snake and ballistic components of the transmitted pulse are less scattered, and contain direct information about the sample to facilitate image formation as opposed to the diffusive components which are due to multiple collisions as a light pulse propagates through a scattering medium. In a time-gated imaging scheme, these early-arriving, image-bearing components of the incident pulse are selected by opening a gate for an ultrashort period of time and a shadowgram image is detected. Using a single shot cooled CCD camera system, the formation of water droplets is monitored as a function of time. Picosecond time-gated image of drop in scattering cells, spray droplets as a function of let speed and gas pressure, and model calcification samples consisted of calcium carbonate particles of irregular shapes ranging in size from 0. 1 to 1.5 mm affixed to a microscope slide have been measured. Formation produced by an impinging jet will be further monitored using a CCD with 1 kHz framing illuminated with pulsed light. The desired image resolution of the fuel droplets is on the 20 pm scale using early light through a highly scattering medium. A 10(exp -6)m displacement from a jet spray with a flow speed of 100 m/sec introduced by the ns grating pulse used in the imaging is negligible. Early ballistic/snake light imaging offers nondestructive and noninvasive method to observe the spatial distribution of hidden objects inside a highly scattering environment for space, biomedical, and materials applications. In this paper, the techniques we will present are time-resolved K-F transillumination imaging and time-gated scattered light imaging. With a large dynamic range and high resolution, time-gated early light imaging has the potential for improving rocket/aircraft design by determining jets shape and particle sizes. Refinements to these techniques may enable drop size measurements in the highly scattering, optically dense region of multi-element rocket injectors. These types of measurements should greatly enhance the design of stable, and higher performing rocket engines.

Characterizing relationship between optical microangiography signals and capillary flow using microfluidic channels.

PubMed

Choi, Woo June; Qin, Wan; Chen, Chieh-Li; Wang, Jingang; Zhang, Qinqin; Yang, Xiaoqi; Gao, Bruce Z; Wang, Ruikang K

2016-07-01

Optical microangiography (OMAG) is a powerful optical angio-graphic tool to visualize micro-vascular flow in vivo. Despite numerous demonstrations for the past several years of the qualitative relationship between OMAG and flow, no convincing quantitative relationship has been proven. In this paper, we attempt to quantitatively correlate the OMAG signal with flow. Specifically, we develop a simplified analytical model of the complex OMAG, suggesting that the OMAG signal is a product of the number of particles in an imaging voxel and the decorrelation of OCT (optical coherence tomography) signal, determined by flow velocity, inter-frame time interval, and wavelength of the light source. Numerical simulation with the proposed model reveals that if the OCT amplitudes are correlated, the OMAG signal is related to a total number of particles across the imaging voxel cross-section per unit time (flux); otherwise it would be saturated but its strength is proportional to the number of particles in the imaging voxel (concentration). The relationship is validated using microfluidic flow phantoms with various preset flow metrics. This work suggests OMAG is a promising quantitative tool for the assessment of vascular flow.

Photometric detection of high proper motions in dense stellar fields using difference image analysis

NASA Astrophysics Data System (ADS)

Eyer, L.; Woźniak, P. R.

2001-10-01

The difference image analysis (DIA) of the images obtained by the Optical Gravitational Lensing Experiment (OGLE-II) revealed a peculiar artefact in the sample of stars proposed as variable by Woźniak in one of the Galactic bulge fields: the occurrence of pairs of candidate variables showing anti-correlated light curves monotonic over a period of 3yr. This effect can be understood, quantified and related to the stellar proper motions. DIA photometry supplemented with a simple model offers an effective and easy way to detect high proper motion stars in very dense stellar fields, where conventional astrometric searches are extremely inefficient.

Dense modifiable interconnections utilizing photorefractive volume holograms

NASA Astrophysics Data System (ADS)

Psaltis, Demetri; Qiao, Yong

1990-11-01

This report describes an experimental two-layer optical neural network built at Caltech. The system uses photorefractive volume holograms to implement dense, modifiable synaptic interconnections and liquid crystal light valves (LCVS) to perform nonlinear thresholding operations. Kanerva's Sparse, Distributed Memory was implemented using this network and its ability to recognize handwritten character-alphabet (A-Z) has been demonstrated experimentally. According to Kanerva's model, the first layer has fixed, random weights of interconnections and the second layer is trained by sum-of-outer-products rule. After training, the recognition rates of the network on the training set (104 patterns) and test set (520 patterns) are 100 and 50 percent, respectively.

Nanoimprinting on optical fiber end faces for chemical sensing

NASA Astrophysics Data System (ADS)

Kostovski, G.; White, D. J.; Mitchell, A.; Austin, M. W.; Stoddart, P. R.

2008-04-01

Optical fiber surface-enhanced Raman scattering (SERS) sensors offer a potential solution to monitoring low chemical concentrations in-situ or in remote sensing scenarios. We demonstrate the use of nanoimprint lithography to fabricate SERS-compatible nanoarrays on the end faces of standard silica optical fibers. The antireflective nanostructure found on cicada wings was used as a convenient template for the nanoarray, as high sensitivity SERS substrates have previously been demonstrated on these surfaces. Coating the high fidelity replicas with silver creates a dense array of regular nanoscale plasmonic resonators. A monolayer of thiophenol was used as a low concentration analyte, from which strong Raman spectra were collected using both direct endface illumination and through-fiber interrogation. This unique combination of nanoscale replication with optical fibers demonstrates a high-resolution, low-cost approach to fabricating high-performance optical fiber chemical sensors.

Optics and Nonlinear Buckling Mechanics in Large-Area, Highly Stretchable Arrays of Plasmonic Nanostructures.

PubMed

Gao, Li; Zhang, Yihui; Zhang, Hui; Doshay, Sage; Xie, Xu; Luo, Hongying; Shah, Deesha; Shi, Yan; Xu, Siyi; Fang, Hui; Fan, Jonathan A; Nordlander, Peter; Huang, Yonggang; Rogers, John A

2015-06-23

Large-scale, dense arrays of plasmonic nanodisks on low-modulus, high-elongation elastomeric substrates represent a class of tunable optical systems, with reversible ability to shift key optical resonances over a range of nearly 600 nm at near-infrared wavelengths. At the most extreme levels of mechanical deformation (strains >100%), nonlinear buckling processes transform initially planar arrays into three-dimensional configurations, in which the nanodisks rotate out of the plane to form linear arrays with "wavy" geometries. Analytical, finite-element, and finite-difference time-domain models capture not only the physics of these buckling processes, including all of the observed modes, but also the quantitative effects of these deformations on the plasmonic responses. The results have relevance to mechanically tunable optical systems, particularly to soft optical sensors that integrate on or in the human body.

Applied optics. Multiwavelength achromatic metasurfaces by dispersive phase compensation.

PubMed

Aieta, Francesco; Kats, Mikhail A; Genevet, Patrice; Capasso, Federico

2015-03-20

The replacement of bulk refractive optical elements with diffractive planar components enables the miniaturization of optical systems. However, diffractive optics suffers from large chromatic aberrations due to the dispersion of the phase accumulated by light during propagation. We show that this limitation can be overcome with an engineered wavelength-dependent phase shift imparted by a metasurface, and we demonstrate a design that deflects three wavelengths by the same angle. A planar lens without chromatic aberrations at three wavelengths is also presented. Our designs are based on low-loss dielectric resonators, which introduce a dense spectrum of optical modes to enable dispersive phase compensation. The suppression of chromatic aberrations in metasurface-based planar photonics will find applications in lightweight collimators for displays, as well as chromatically corrected imaging systems. Copyright © 2015, American Association for the Advancement of Science.

Grouping of optic flow stimuli during binocular rivalry is driven by monocular information.

PubMed

Holten, Vivian; Stuit, Sjoerd M; Verstraten, Frans A J; van der Smagt, Maarten J

2016-10-01

During binocular rivalry, perception alternates between two dissimilar images, presented dichoptically. Although binocular rivalry is thought to result from competition at a local level, neighboring image parts with similar features tend to be perceived together for longer durations than image parts with dissimilar features. This simultaneous dominance of two image parts is called grouping during rivalry. Previous studies have shown that this grouping depends on a shared eye-of-origin to a much larger extent than on image content, irrespective of the complexity of a static image. In the current study, we examine whether grouping of dynamic optic flow patterns is also primarily driven by monocular (eye-of-origin) information. In addition, we examine whether image parameters, such as optic flow direction, and partial versus full visibility of the optic flow pattern, affect grouping durations during rivalry. The results show that grouping of optic flow is, as is known for static images, primarily affected by its eye-of-origin. Furthermore, global motion can affect grouping durations, but only under specific conditions. Namely, only when the two full optic flow patterns were presented locally. These results suggest that grouping during rivalry is primarily driven by monocular information even for motion stimuli thought to rely on higher-level motion areas. Copyright © 2016 Elsevier Ltd. All rights reserved.

Quantitative Analysis of Intracellular Motility Based on Optical Flow Model

PubMed Central

Li, Heng

2017-01-01

Analysis of cell mobility is a key issue for abnormality identification and classification in cell biology research. However, since cell deformation induced by various biological processes is random and cell protrusion is irregular, it is difficult to measure cell morphology and motility in microscopic images. To address this dilemma, we propose an improved variation optical flow model for quantitative analysis of intracellular motility, which not only extracts intracellular motion fields effectively but also deals with optical flow computation problem at the border by taking advantages of the formulation based on L1 and L2 norm, respectively. In the energy functional of our proposed optical flow model, the data term is in the form of L2 norm; the smoothness of the data changes with regional features through an adaptive parameter, using L1 norm near the edge of the cell and L2 norm away from the edge. We further extract histograms of oriented optical flow (HOOF) after optical flow field of intracellular motion is computed. Then distances of different HOOFs are calculated as the intracellular motion features to grade the intracellular motion. Experimental results show that the features extracted from HOOFs provide new insights into the relationship between the cell motility and the special pathological conditions. PMID:29065574

Head sway response to optic flow: effect of age is more important than the presence of unilateral vestibular hypofunction

PubMed Central

Sparto, Patrick J.; Furman, Joseph M.; Redfern, Mark S.

2014-01-01

Background The purpose of this study was to examine how older adults with vestibular impairment use sensory feedback for postural control. Methods Nine older adult subjects with unilateral vestibular hypofunction (UVH, mean age 69 y) and 14 older (mean age 70 y) and 8 young adult controls (CON, mean age 28 y) viewed full-field optic flow scenes while standing on a fixed or sway-referenced support surface. The subjects with UVH had 100% caloric asymmetry. Optic flow consisted of sinusoidal anterior-posterior movement of the visual surround at three frequencies and three amplitudes of stimulation. The anterior-posterior head sway was measured. The number of head sway responses that were coupled to the optic flow and magnitude of head sway during optic flow relative to during quiet stance on fixed floor was quantified. Results The number of trials in which the head sway response was significantly coupled to the optic flow was significantly greater in the Older UVH and Older CON subjects compared with the Young CON subjects. Furthermore, the magnitude of head sway was two to three times greater in Older UVH and CON compared with Young CON subjects. There was no difference in coupling or magnitude of head sway between Older UVH and Older CON subjects. The amplitude of sway was also dependent on the amount of surface support, stimulus frequency, and stimulus amplitude. Conclusions Older adults with unilateral vestibular hypofunction who are able to effectively compensate show no difference in postural responses elicited by optic flow compared with age-matched controls. PMID:17312341

Processing, Mechanical and Optical Properties of Additive-Free ZrC Ceramics Prepared by Spark Plasma Sintering

PubMed Central

Musa, Clara; Licheri, Roberta; Orrù, Roberto; Cao, Giacomo; Sciti, Diletta; Silvestroni, Laura; Zoli, Luca; Balbo, Andrea; Mercatelli, Luca; Meucci, Marco; Sani, Elisa

2016-01-01

In the present study, nearly fully dense monolithic ZrC samples are produced and broadly characterized from microstructural, mechanical and optical points of view. Specifically, 98% dense products are obtained by Spark Plasma Sintering (SPS) after 20 min dwell time at 1850 °C starting from powders preliminarily prepared by Self-propagating High-temperature Synthesis (SHS) followed by 20 min ball milling. A prolonged mechanical treatment up to 2 h of SHS powders does not lead to appreciable benefits. Vickers hardness of the resulting samples (17.5 ± 0.4 GPa) is reasonably good for monolithic ceramics, but the mechanical strength (about 250 MPa up to 1000 °C) could be further improved by suitable optimization of the starting powder characteristics. The very smoothly polished ZrC specimen subjected to optical measurements displays high absorption in the visible-near infrared region and low thermal emittance at longer wavelengths. Moreover, the sample exhibits goodspectral selectivity (2.1–2.4) in the 1000–1400 K temperature range. These preliminary results suggest that ZrC ceramics produced through the two-step SHS/SPS processing route can be considered as attractive reference materials for the development of innovative solar energy absorbers. PMID:28773611

Optical method and apparatus for detection of surface and near-subsurface defects in dense ceramics

DOEpatents

Ellingson, William A.; Brada, Mark P.

1995-01-01

A laser is used in a non-destructive manner to detect surface and near-subsurface defects in dense ceramics and particularly in ceramic bodies with complex shapes such as ceramic bearings, turbine blades, races, and the like. The laser's wavelength is selected based upon the composition of the ceramic sample and the laser can be directed on the sample while the sample is static or in dynamic rotate or translate motion. Light is scattered off surface and subsurface defects using a preselected polarization. The change in polarization angle is used to select the depth and characteristics of surface/subsurface defects. The scattered light is detected by an optical train consisting of a charge coupled device (CCD), or vidicon, television camera which, in turn, is coupled to a video monitor and a computer for digitizing the image. An analyzing polarizer in the optical train allows scattered light at a given polarization angle to be observed for enhancing sensitivity to either surface or near-subsurface defects. Application of digital image processing allows subtraction of digitized images in near real-time providing enhanced sensitivity to subsurface defects. Storing known "feature masks" of identified defects in the computer and comparing the detected scatter pattern (Fourier images) with the stored feature masks allows for automatic classification of detected defects.

Light-field camera-based 3D volumetric particle image velocimetry with dense ray tracing reconstruction technique

NASA Astrophysics Data System (ADS)

Shi, Shengxian; Ding, Junfei; New, T. H.; Soria, Julio

2017-07-01

This paper presents a dense ray tracing reconstruction technique for a single light-field camera-based particle image velocimetry. The new approach pre-determines the location of a particle through inverse dense ray tracing and reconstructs the voxel value using multiplicative algebraic reconstruction technique (MART). Simulation studies were undertaken to identify the effects of iteration number, relaxation factor, particle density, voxel-pixel ratio and the effect of the velocity gradient on the performance of the proposed dense ray tracing-based MART method (DRT-MART). The results demonstrate that the DRT-MART method achieves higher reconstruction resolution at significantly better computational efficiency than the MART method (4-50 times faster). Both DRT-MART and MART approaches were applied to measure the velocity field of a low speed jet flow which revealed that for the same computational cost, the DRT-MART method accurately resolves the jet velocity field with improved precision, especially for the velocity component along the depth direction.

An Analog Macroscopic Technique for Studying Molecular Hydrodynamic Processes in Dense Gases and Liquids.

PubMed

Dahlberg, Jerry; Tkacik, Peter T; Mullany, Brigid; Fleischhauer, Eric; Shahinian, Hossein; Azimi, Farzad; Navare, Jayesh; Owen, Spencer; Bisel, Tucker; Martin, Tony; Sholar, Jodie; Keanini, Russell G

2017-12-04

An analog, macroscopic method for studying molecular-scale hydrodynamic processes in dense gases and liquids is described. The technique applies a standard fluid dynamic diagnostic, particle image velocimetry (PIV), to measure: i) velocities of individual particles (grains), extant on short, grain-collision time-scales, ii) velocities of systems of particles, on both short collision-time- and long, continuum-flow-time-scales, iii) collective hydrodynamic modes known to exist in dense molecular fluids, and iv) short- and long-time-scale velocity autocorrelation functions, central to understanding particle-scale dynamics in strongly interacting, dense fluid systems. The basic system is composed of an imaging system, light source, vibrational sensors, vibrational system with a known media, and PIV and analysis software. Required experimental measurements and an outline of the theoretical tools needed when using the analog technique to study molecular-scale hydrodynamic processes are highlighted. The proposed technique provides a relatively straightforward alternative to photonic and neutron beam scattering methods traditionally used in molecular hydrodynamic studies.

Dynamic Echo Information Guides Flight in the Big Brown Bat

PubMed Central

Warnecke, Michaela; Lee, Wu-Jung; Krishnan, Anand; Moss, Cynthia F.

2016-01-01

Animals rely on sensory feedback from their environment to guide locomotion. For instance, visually guided animals use patterns of optic flow to control their velocity and to estimate their distance to objects (e.g., Srinivasan et al., 1991, 1996). In this study, we investigated how acoustic information guides locomotion of animals that use hearing as a primary sensory modality to orient and navigate in the dark, where visual information is unavailable. We studied flight and echolocation behaviors of big brown bats as they flew under infrared illumination through a corridor with walls constructed from a series of individual vertical wooden poles. The spacing between poles on opposite walls of the corridor was experimentally manipulated to create dense/sparse and balanced/imbalanced spatial structure. The bats’ flight trajectories and echolocation signals were recorded with high-speed infrared motion-capture cameras and ultrasound microphones, respectively. As bats flew through the corridor, successive biosonar emissions returned cascades of echoes from the walls of the corridor. The bats flew through the center of the corridor when the pole spacing on opposite walls was balanced and closer to the side with wider pole spacing when opposite walls had an imbalanced density. Moreover, bats produced shorter duration echolocation calls when they flew through corridors with smaller spacing between poles, suggesting that clutter density influences features of the bat’s sonar signals. Flight speed and echolocation call rate did not, however, vary with dense and sparse spacing between the poles forming the corridor walls. Overall, these data demonstrate that bats adapt their flight and echolocation behavior dynamically when flying through acoustically complex environments. PMID:27199690

Dense flow around a sphere moving into a cloud of grains

NASA Astrophysics Data System (ADS)

Gondret, Philippe; Faure, Sylvain; Lefebvre-Lepot, Aline; Seguin, Antoine

2017-06-01

A bidimensional simulation of a sphere moving at constant velocity into a cloud of smaller spherical grains without gravity is presented with a non-smooth contact dynamics method. A dense granular "cluster" zone of about constant solid fraction builds progressively around the moving sphere until a stationary regime appears with a constant upstream cluster size that increases with the initial solid fraction ϕ0 of the cloud. A detailed analysis of the local strain rate and local stress fields inside the cluster reveals that, despite different spatial variations of strain and stresses, the local friction coeffcient μ appears to depend only on the local inertial number I as well as the local solid fraction ϕ, which means that a local rheology does exist in the present non parallel flow. The key point is that the spatial variations of I inside the cluster does not depend on the sphere velocity and explore only a small range between about 10-2 and 10-1. The influence of sidewalls is then investigated on the flow and the forces.

Numerical approaches to combustion modeling. Progress in Astronautics and Aeronautics. Vol. 135

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

Oran, E.S.; Boris, J.P.

1991-01-01

Various papers on numerical approaches to combustion modeling are presented. The topics addressed include; ab initio quantum chemistry for combustion; rate coefficient calculations for combustion modeling; numerical modeling of combustion of complex hydrocarbons; combustion kinetics and sensitivity analysis computations; reduction of chemical reaction models; length scales in laminar and turbulent flames; numerical modeling of laminar diffusion flames; laminar flames in premixed gases; spectral simulations of turbulent reacting flows; vortex simulation of reacting shear flow; combustion modeling using PDF methods. Also considered are: supersonic reacting internal flow fields; studies of detonation initiation, propagation, and quenching; numerical modeling of heterogeneous detonations, deflagration-to-detonationmore » transition to reactive granular materials; toward a microscopic theory of detonations in energetic crystals; overview of spray modeling; liquid drop behavior in dense and dilute clusters; spray combustion in idealized configurations: parallel drop streams; comparisons of deterministic and stochastic computations of drop collisions in dense sprays; ignition and flame spread across solid fuels; numerical study of pulse combustor dynamics; mathematical modeling of enclosure fires; nuclear systems.« less

Fine-grained linings of leveed channels facilitate runout of granular flows

NASA Astrophysics Data System (ADS)

Kokelaar, B. P.; Graham, R. L.; Gray, J. M. N. T.; Vallance, J. W.

2014-01-01

Catastrophic dense granular flows, such as occur in rock avalanches, debris flows and pyroclastic flows, move as fully shearing mixtures that have approximately 60 vol.% solids and tend to segregate to form coarse-grained fronts and leveed channels. Levees restrict spreading of unconfined flows and form as coarse particles that become concentrated in the top of the flow are transported to the front and then advect to the sides in the flow head. Channels from which most material has drained away down slope are commonly lined with fine-grained deposit, widely thought to remain from the tail of the waning flow. We show how segregation in experimental dense flows of carborundum or sand (300-425 μm) mixed with spherical fine ballotini (150-250 μm), on rough slopes of 27-29°, produces fine-grained channel linings that are deposited with the levees, into which they grade laterally. Maximum runout distance is attained with mixtures containing 30-40% sand, just sufficient to segregate and form levees that are adequately robust to restrict the spreading attributable to the low-friction fines. Resin impregnation and serial sectioning of deliberately arrested experimental flows shows how fines-lined levees form from the flow head; the flows create their own stable ‘conduit’ entirely from the front, which in a geophysical context can play an important mechanistic role in facilitating runout. The flow self-organization ensures that low-friction fines at the base of the segregated channel flow shear over fine-grained substrate in the channel, thus reducing frictional energy losses. We propose that in pyroclastic flows and debris flows, which have considerable mobility attributable to pore-fluid pressures, such fine-grained flow-contact zones form similarly and not only reduce frictional energy losses but also reduce flow-substrate permeability so as to enhance pore-fluid pressure retention. Thus the granular flow self-organization that produces fine-grained channel linings can be an important factor in facilitating long runout of catastrophic geophysical flows on the low slopes (few degrees) of depositional fans and aprons around mountains and volcanoes.

Geophysical granular and particle-laden flows: review of the field.

PubMed

Hutter, Kolumban

2005-07-15

An introduction is given to the title theme, in general, and the specific topics treated in detail in the articles of this theme issue of the Philosophical Transactions. They fit into the following broader subjects: (i) dense, dry and wet granular flows as avalanche and debris flow events, (ii) air-borne particle-laden turbulent flows in air over a granular base as exemplified in gravity currents, aeolian transport of sand, dust and snow and (iii) transport of a granular mass on a two-dimensional surface in ripple formations of estuaries and rivers and the motion of sea ice.

High throughput analysis of samples in flowing liquid

DOEpatents

Ambrose, W. Patrick; Grace, W. Kevin; Goodwin, Peter M.; Jett, James H.; Orden, Alan Van; Keller, Richard A.

2001-01-01

Apparatus and method enable imaging multiple fluorescent sample particles in a single flow channel. A flow channel defines a flow direction for samples in a flow stream and has a viewing plane perpendicular to the flow direction. A laser beam is formed as a ribbon having a width effective to cover the viewing plane. Imaging optics are arranged to view the viewing plane to form an image of the fluorescent sample particles in the flow stream, and a camera records the image formed by the imaging optics.

Device and nondestructive method to determine subsurface micro-structure in dense materials

DOEpatents

Sun, Jiangang [Westmont, IL

2006-05-09

A method and a device to detect subsurface three-dimensional micro-structure in a sample by illuminating the sample with light of a given polarization and detecting light emanating from the sample that has a different direction of polarization by means of a confocal optical system.

Optical breakdown of air triggered by femtosecond laser filaments

NASA Astrophysics Data System (ADS)

Polynkin, Pavel; Moloney, Jerome V.

2011-10-01

We report experiments on the generation of dense plasma channels in ambient air using a dual laser pulse excitation scheme. The dilute plasma produced through the filamentation of an ultraintense femtosecond laser pulse is densified via avalanche ionization driven by a co-propagating multi-Joule nanosecond pulse.

Efficacy of predictive wavefront control for compensating aero-optical aberrations

NASA Astrophysics Data System (ADS)

Goorskey, David J.; Schmidt, Jason; Whiteley, Matthew R.

2013-07-01

Imaging and laser beam propagation from airborne platforms are degraded by dynamic aberrations due to air flow around the aircraft, aero-mechanical distortions and jitter, and free atmospheric turbulence. For certain applications, like dim-object imaging, free-space optical communications, and laser weapons, adaptive optics (AO) is necessary to compensate for the aberrations in real time. Aero-optical flow is a particularly interesting source of aberrations whose flowing structures can be exploited by adaptive and predictive AO controllers, thereby realizing significant performance gains. We analyze dynamic aero-optical wavefronts to determine the pointing angles at which predictive wavefront control is more effective than conventional, fixed-gain, linear-filter control. It was found that properties of the spatial decompositions and temporal statistics of the wavefronts are directly traceable to specific features in the air flow. Furthermore, the aero-optical wavefront aberrations at the side- and aft-looking angles were the most severe, but they also benefited the most from predictive AO.

Experimental study of stratified jet by simultaneous measurements of velocity and density fields

NASA Astrophysics Data System (ADS)

Xu, Duo; Chen, Jun

2012-07-01

Stratified flows with small density difference commonly exist in geophysical and engineering applications, which often involve interaction of turbulence and buoyancy effect. A combined particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) system is developed to measure the velocity and density fields in a dense jet discharged horizontally into a tank filled with light fluid. The illumination of PIV particles and excitation of PLIF dye are achieved by a dual-head pulsed Nd:YAG laser and two CCD cameras with a set of optical filters. The procedure for matching refractive indexes of two fluids and calibration of the combined system are presented, as well as a quantitative analysis of the measurement uncertainties. The flow structures and mixing dynamics within the central vertical plane are studied by examining the averaged parameters, turbulent kinetic energy budget, and modeling of momentum flux and buoyancy flux. At downstream, profiles of velocity and density display strong asymmetry with respect to its center. This is attributed to the fact that stable stratification reduces mixing and unstable stratification enhances mixing. In stable stratification region, most of turbulence production is consumed by mean-flow convection, whereas in unstable stratification region, turbulence production is nearly balanced by viscous dissipation. Experimental data also indicate that at downstream locations, mixing length model performs better in mixing zone of stable stratification regions, whereas in other regions, eddy viscosity/diffusivity models with static model coefficients represent effectively momentum and buoyancy flux terms. The measured turbulent Prandtl number displays strong spatial variation in the stratified jet.

Fine-grained linings of leveed channels facilitate runout of granular flows

USGS Publications Warehouse

Kokelaar, B.P.; Graham, R. L.; Gray, J.M.N.T.; Vallance, James W.

2014-01-01

Catastrophic dense granular flows, such as occur in rock avalanches, debris flows and pyroclastic flows, move as fully shearing mixtures that have approximately 60 vol.% solids and tend to segregate to form coarse-grained fronts and leveed channels. Levees restrict spreading of unconfined flows and form as coarse particles that become concentrated in the top of the flow are transported to the front and then advect to the sides in the flow head. Channels from which most material has drained away down slope are commonly lined with fine-grained deposit, widely thought to remain from the tail of the waning flow. We show how segregation in experimental dense flows of carborundum or sand (300–425 μm) mixed with spherical fine ballotini (150–250 μm), on rough slopes of 27–29°, produces fine-grained channel linings that are deposited with the levees, into which they grade laterally. Maximum runout distance is attained with mixtures containing 30–40% sand, just sufficient to segregate and form levees that are adequately robust to restrict the spreading attributable to the low-friction fines. Resin impregnation and serial sectioning of deliberately arrested experimental flows shows how fines-lined levees form from the flow head; the flows create their own stable ‘conduit’ entirely from the front, which in a geophysical context can play an important mechanistic role in facilitating runout. The flow self-organization ensures that low-friction fines at the base of the segregated channel flow shear over fine-grained substrate in the channel, thus reducing frictional energy losses. We propose that in pyroclastic flows and debris flows, which have considerable mobility attributable to pore-fluid pressures, such fine-grained flow-contact zones form similarly and not only reduce frictional energy losses but also reduce flow–substrate permeability so as to enhance pore-fluid pressure retention. Thus the granular flow self-organization that produces fine-grained channel linings can be an important factor in facilitating long runout of catastrophic geophysical flows on the low slopes (few degrees) of depositional fans and aprons around mountains and volcanoes.

Two problems in multiphase biological flows: Blood flow and particulate transport in microvascular network, and pseudopod-driven motility of amoeboid cells

NASA Astrophysics Data System (ADS)

Bagchi, Prosenjit

2016-11-01

In this talk, two problems in multiphase biological flows will be discussed. The first is the direct numerical simulation of whole blood and drug particulates in microvascular networks. Blood in microcirculation behaves as a dense suspension of heterogeneous cells. The erythrocytes are extremely deformable, while inactivated platelets and leukocytes are nearly rigid. A significant progress has been made in recent years in modeling blood as a dense cellular suspension. However, many of these studies considered the blood flow in simple geometry, e.g., straight tubes of uniform cross-section. In contrast, the architecture of a microvascular network is very complex with bifurcating, merging and winding vessels, posing a further challenge to numerical modeling. We have developed an immersed-boundary-based method that can consider blood cell flow in physiologically realistic and complex microvascular network. In addition to addressing many physiological issues related to network hemodynamics, this tool can be used to optimize the transport properties of drug particulates for effective organ-specific delivery. Our second problem is pseudopod-driven motility as often observed in metastatic cancer cells and other amoeboid cells. We have developed a multiscale hydrodynamic model to simulate such motility. We study the effect of cell stiffness on motility as the former has been considered as a biomarker for metastatic potential. Funded by the National Science Foundation.

Effects of background stimulation upon eye-movement information.

PubMed

Nakamura, S

1996-04-01

To investigate the effects of background stimulation upon eye-movement information (EMI), the perceived deceleration of the target motion during pursuit eye movement (Aubert-Fleishl paradox) was analyzed. In the experiment, a striped pattern was used as a background stimulus with various brightness contrasts and spatial frequencies for serially manipulating the attributions of the background stimulus. Analysis showed that the retinal-image motion of the background stimulus (optic flow) affected eye-movement information and that the effects of optic flow became stronger when high contrast and low spatial frequency stripes were presented as the background stimulus. In conclusion, optic flow is one source of eye-movement information in determining real object motion, and the effectiveness of optic flow depends on the attributes of the background stimulus.

Tunable top-down fabrication and functional surface coating of single-crystal titanium dioxide nanostructures and nanoparticles

NASA Astrophysics Data System (ADS)

Ha, Seungkyu; Janissen, Richard; Ussembayev, Yera Ye.; van Oene, Maarten M.; Solano, Belen; Dekker, Nynke H.

2016-05-01

Titanium dioxide (TiO2) is a key component of diverse optical and electronic applications that exploit its exceptional material properties. In particular, the use of TiO2 in its single-crystalline phase can offer substantial advantages over its amorphous and polycrystalline phases for existing and yet-to-be-developed applications. However, the implementation of single-crystal TiO2 has been hampered by challenges in its fabrication and subsequent surface functionalization. Here, we introduce a novel top-down approach that allows for batch fabrication of uniform high-aspect-ratio single-crystal TiO2 nanostructures with targeted sidewall profiles. We complement our fabrication approach with a functionalization strategy that achieves dense, uniform, and area-selective coating with a variety of biomolecules. This allows us to fabricate single-crystal rutile TiO2 nanocylinders tethered with individual DNA molecules for use as force- and torque-transducers in an optical torque wrench. These developments provide the means for increased exploitation of the superior material properties of single-crystal TiO2 at the nanoscale.Titanium dioxide (TiO2) is a key component of diverse optical and electronic applications that exploit its exceptional material properties. In particular, the use of TiO2 in its single-crystalline phase can offer substantial advantages over its amorphous and polycrystalline phases for existing and yet-to-be-developed applications. However, the implementation of single-crystal TiO2 has been hampered by challenges in its fabrication and subsequent surface functionalization. Here, we introduce a novel top-down approach that allows for batch fabrication of uniform high-aspect-ratio single-crystal TiO2 nanostructures with targeted sidewall profiles. We complement our fabrication approach with a functionalization strategy that achieves dense, uniform, and area-selective coating with a variety of biomolecules. This allows us to fabricate single-crystal rutile TiO2 nanocylinders tethered with individual DNA molecules for use as force- and torque-transducers in an optical torque wrench. These developments provide the means for increased exploitation of the superior material properties of single-crystal TiO2 at the nanoscale. Electronic supplementary information (ESI) available: Experimental details (ESI Methods) of the optic axis orientation of TiO2 nanocylinders, Cr etch mask fabrication, surface functionalization and its evaluation using fluorescence microscopy, preparation of DNA constructs, assembly of flow cells, bioconjugation of TiO2 nanocylinders, OTW instrumentation and measurements; TiO2 dry etching optimization and the etching parameters employed (Tables S1 and S2); dimensional analysis of TiO2 nanocylinders (Table S3); diverse applications of TiO2 at the nanoscale (Fig. S1); selection of etch mask material (Fig. S2); control of sidewall profiles in TiO2 etching (Fig. S3); size distributions of TiO2 nanocylinders (Fig. S4); quantitative comparisons of different surface linker molecules (Fig. S5); DLS measurements on TiO2 nanocylinders (Fig. S6); optical trap calibration (Fig. S7); and supplementary references. See DOI: 10.1039/c6nr00898d

Self-Consolidating Concrete for Prestressed Bridge Girders : Research Brief

DOT National Transportation Integrated Search

2017-08-01

Self-consolidating concrete (SCC) is commonly used as an alternative to conventional concrete (CC) in precast, prestressed concrete (PSC) bridge girders. The high strength, highly workable mixture can flow through dense reinforcement to fill formwork...

An artificial elementary eye with optic flow detection and compositional properties.

PubMed

Pericet-Camara, Ramon; Dobrzynski, Michal K; Juston, Raphaël; Viollet, Stéphane; Leitel, Robert; Mallot, Hanspeter A; Floreano, Dario

2015-08-06

We describe a 2 mg artificial elementary eye whose structure and functionality is inspired by compound eye ommatidia. Its optical sensitivity and electronic architecture are sufficient to generate the required signals for the measurement of local optic flow vectors in multiple directions. Multiple elementary eyes can be assembled to create a compound vision system of desired shape and curvature spanning large fields of view. The system configurability is validated with the fabrication of a flexible linear array of artificial elementary eyes capable of extracting optic flow over multiple visual directions. © 2015 The Author(s).

THE OPTICAL STRUCTURE OF THE STARBURST GALAXY M82. II. NEBULAR PROPERTIES OF THE DISK AND INNER WIND

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

Westmoquette, M. S.; Smith, L. J.; Konstantopoulos, I. S.

2009-12-01

In this second paper of the series, we present the results from optical Gemini-North GMOS-IFU and WIYN DensePak IFU spectroscopic observations of the starburst and inner wind zones of M82, with a focus on the state of the T approx 10{sup 4} K ionized interstellar medium. Our electron density maps show peaks of a few 1000 cm{sup -3} (implying very high thermal pressures), local small spatial-scale variations, and a falloff in the minor axis direction. We discuss the implications of these results with regards to the conditions/locations that may favor the escape of individual cluster winds that ultimately power themore » large-scale superwind. Our findings, when combined with the body of literature built up over the last decade on the state of the interstellar medium (ISM) in M82, imply that the starburst environment is highly fragmented into a range of clouds from small/dense clumps with low-filling factors (<1 pc, n {sub e} approx> 10{sup 4} cm{sup -3}) to larger filling factor, less dense gas. The most compact clouds seem to be found in the cores of the star cluster complexes, whereas the cloud sizes in the inter-complex region are larger. These dense clouds are bathed with an intense radiation field and embedded in an extensive high temperature (T approx> 10{sup 6} K), X-ray-emitting ISM that is a product of the high star formation rates in the starburst zones of M82. The near-constant state of the ionization state of the approx10{sup 4} K gas throughout the M82 starburst zone can be explained as a consequence of the small cloud sizes, which allow the gas conditions to respond quickly to any changes. In Paper I, we found that the observed emission lines are composed of multiple components, including a broad (FWHM approx 150-350 km s{sup -1}) feature that we associate with emission from turbulent mixing layers on the surfaces of the gas clouds, resulting from the interaction of the fast wind outflows from the synchrotron self-Comptons. The large number of compact clouds and wind sources provides an ideal environment for broad line emission, and explains the large observed broad/narrow-line flux ratios. We have examined in more detail the discrete outflow channel identified within the inner wind in Paper I. The channel appears as a coherent, expanding cylindrical structure of length >120 pc and width 35-50 pc. The walls maintain an approximately constant (but subsonic) expansion velocity of approx60 km s{sup -1}, and are defined by peaks and troughs in the densities of the different line components. We hypothesize that as the hot wind fluid flows down the channel cavity, it interacts with the cooler, denser walls of the channel and with entrained material within the flow to produce broad-line emission, while the walls themselves emit primarily the narrow lines. We use the channel to examine further the relationship between the narrow and broad component emitting gas within the inner wind. Within the starburst energy injection zone, we find that turbulent motions (as traced by the broad component) appear to play an increasing role with height. Finally, we have argued that a point-like knot identified in GMOS position 4, exhibiting blueshifted (by approx140 km s{sup -1}), broad (approx<350 km s{sup -1}) Halpha emission and enhanced [S II]/Halpha and [N II]/Halpha ratios, is most likely an ejected luminous blue variable-type object.« less

Creation of the reduced-density region by a pulsing optical discharge in the supersonic air flow

NASA Astrophysics Data System (ADS)

Kiseleva, T. A.; Orishich, A. M.; Chirkashenko, V. F.; Yakovlev, V. I.

2016-10-01

As a result of optical and pneumometric measurements is defined the flow shock wave structure that is formed by the optical breakdown, due to focused repetitively pulsed CO2 laser radiation when entering perpendicular to a supersonic (M = 1.36, 1.9) air flow direction. The dynamics of the bow shock formation in front of the energy input area is shown, depending on the frequency of energy impulse sequence. A flow structure is defined in the thermal wake behind pulsing laser plasma as well as wake's length with low thermal heterogeneity. A three-dimensional configuration of the energy area is defined in accordance with pneumometric and optical measuring results. It is shown that Pitot pressure decreases in thermal wake at a substantially constant static pressure, averaged flow parameters weakly depend on the energy impulse's frequency in range of 45-150 kHz.

Flow line asymmetric nonimaging concentrating optics

NASA Astrophysics Data System (ADS)

Jiang, Lun; Winston, Roland

2016-09-01

Nonimaging Optics has shown that it achieves the theoretical limits by utilizing thermodynamic principles rather than conventional optics. Hence in this paper the condition of the "best" design are both defined and fulfilled in the framework of thermodynamic arguments, which we believe has profound consequences for the designs of thermal and even photovoltaic systems, even illumination and optical communication tasks. This new way of looking at the problem of efficient concentration depends on probabilities, geometric flux field and radiative heat transfer while "optics" in the conventional sense recedes into the background. Some of the new development of flow line designs will be introduced and the connection between the thermodynamics and flow line design will be officially formulated in the framework of geometric flux field. A new way of using geometric flux to design nonimaging optics will be introduced. And finally, we discuss the possibility of 3D ideal nonimaing optics.

Limits on Optical Polarization during the Prompt Phase of GRB 140430A

NASA Astrophysics Data System (ADS)

Kopač, D.; Mundell, C. G.; Japelj, J.; Arnold, D. M.; Steele, I. A.; Guidorzi, C.; Dichiara, S.; Kobayashi, S.; Gomboc, A.; Harrison, R. M.; Lamb, G. P.; Melandri, A.; Smith, R. J.; Virgili, F. J.; Castro-Tirado, A. J.; Gorosabel, J.; Järvinen, A.; Sánchez-Ramírez, R.; Oates, S. R.; Jelínek, M.

2015-11-01

Gamma-ray burst GRB 140430A was detected by the Swift satellite and observed promptly with the imaging polarimeter RINGO3 mounted on the Liverpool Telescope, with observations beginning while the prompt γ-ray emission was still ongoing. In this paper, we present densely sampled (10-s temporal resolution) early optical light curves (LCs) in 3 optical bands and limits to the degree of optical polarization. We compare optical, X-ray, and gamma-ray properties and present an analysis of the optical emission during a period of high-energy flaring. The complex optical LC cannot be explained merely with a combination of forward and reverse shock emission from a standard external shock, implying additional contribution of emission from internal shock dissipation. We estimate an upper limit for time averaged optical polarization during the prompt phase to be as low as P < 12% (1σ). This suggests that the optical flares and early afterglow emission in this GRB are not highly polarized. Alternatively, time averaging could mask the presence of otherwise polarized components of distinct origin at different polarization position angles.

Variational optical flow estimation for images with spectral and photometric sensor diversity

NASA Astrophysics Data System (ADS)

Bengtsson, Tomas; McKelvey, Tomas; Lindström, Konstantin

2015-03-01

Motion estimation of objects in image sequences is an essential computer vision task. To this end, optical flow methods compute pixel-level motion, with the purpose of providing low-level input to higher-level algorithms and applications. Robust flow estimation is crucial for the success of applications, which in turn depends on the quality of the captured image data. This work explores the use of sensor diversity in the image data within a framework for variational optical flow. In particular, a custom image sensor setup intended for vehicle applications is tested. Experimental results demonstrate the improved flow estimation performance when IR sensitivity or flash illumination is added to the system.

Estimation of Energy Expenditure during Treadmill Exercise via Thermal Imaging.

PubMed

Jensen, Martin Møller; Poulsen, Mathias Krogh; Alldieck, Thiemo; Larsen, Ryan Godsk; Gade, Rikke; Moeslund, Thomas Baltzer; Franch, Jesper

2016-12-01

Noninvasive imaging of oxygen uptake may provide a useful tool for the quantification of energy expenditure during human locomotion. A novel thermal imaging method (optical flow) was validated against indirect calorimetry for the estimation of energy expenditure during human walking and running. Fourteen endurance-trained subjects completed a discontinuous incremental exercise test on a treadmill. Subjects performed 4-min intervals at 3, 5, and 7 km·h (walking) and at 8, 10, 12, 14, 16, and 18 km·h (running) with 30 s of rest between intervals. Heart rate, gas exchange, and mean accelerations of ankle, thigh, wrist, and hip were measured throughout the exercise test. A thermal camera (30 frames per second) was used to quantify optical flow, calculated as the movements of the limbs relative to the trunk (internal mechanical work) and vertical movement of the trunk (external vertical mechanical work). Heart rate, gross oxygen uptake (mL·kg·min) together with gross and net energy expenditure (J·kg·min) rose with increasing treadmill velocities, as did optical flow measurements and mean accelerations (g) of ankle, thigh, wrist, and hip. Oxygen uptake was linearly correlated with optical flow across all exercise intensities (R = 0.96, P < 0.0001; V˙O2 [mL·kg·min] = 7.35 + 9.85 × optical flow [arbitrary units]). Only 3-4 s of camera recording was required to estimate an optical flow value at each velocity. Optical flow measurements provide an accurate estimation of energy expenditure during horizontal walking and running. The technique offers a novel experimental method of estimating energy expenditure during human locomotion, without use of interfering equipment attached to the subject.

Microfluidic flow rate detection based on integrated optical fiber cantilever.

PubMed

Lien, Victor; Vollmer, Frank

2007-10-01

We demonstrate an integrated microfluidic flow sensor with ultra-wide dynamic range, suitable for high throughput applications such as flow cytometry and particle sorting/counting. A fiber-tip cantilever transduces flow rates to optical signal readout, and we demonstrate a dynamic range from 0 to 1500 microL min(-1) for operation in water. Fiber-optic sensor alignment is guided by preformed microfluidic channels, and the dynamic range can be adjusted in a one-step chemical etch. An overall non-linear response is attributed to the far-field angular distribution of single-mode fiber output.

Dense, gravity-driven granular-liquid flows down steep channels

NASA Astrophysics Data System (ADS)

Armanini, A.; Larcher, M.; Nucci, E.

2011-12-01

Debris flows are complex natural phenomena, characterized by a mixture of poorly sorted sediments and water driven by gravity. Depending on the size distribution, on the volume concentration of sediments and on the geometry and topography of the channel, flow conditions may be very different, ranging from very fast flows, dominated by granular collisions and by the turbulence on the liquid phase, to very slow and dense flows, dominated by the frictional contacts among the grains. To investigate the basic physics of debris flows, it is very useful to analyze the flow of a mixture of identical spherical particles saturated by water and driven by gravity down a steep channel in steady flow condition (Armanini et al. 2005). The flow presents three regions: an external one, near to the free surface, dominated by nearly instantaneous contacts among the particles (collisional regime), an internal region dominated by prolonged contacts among the particles (frictional regime) and a static bed in which the particles are immobile. The detailed vertical structure of this kind of flows was obtained by means of experiments carried out by Armanini et al. (2005) and Larcher et al. (2007). Armanini et al. (2009) analysed the stratification of rheological mechanisms inside the flow, focusing on the coexistence of frictional and collisional regimes, on the stress transmission inside the flow and on particles kinematics. In particular, it was observed that debris flows may show locally a typical intermittence of the flow regime, switching alternatively from frictional to collisional. While the rheology of the collisional layers is well described by the dense gas analogy (kinetic theory), a persuasive theoretical description of the frictional regime does not yet exist. A Coulombian scheme is often assumed, but this hypothesis is rather limitative because it requires a constant concentration or a distribution of particles concentration known a priori. An interesting scheme of this kind was recently proposed by GDR-Midi (2004), but this model does not contain a suitable formulation for the granular pressure (equation of state of the mixture). Following Armanini (2010), we propose a reinterpretation of the model, as weighted average of a pure Coulombian stress (dependent on the static friction angle at the static bed level) and of a dynamic stress, represented by a dynamic friction angle. Besides, a state relation is introduced for the granular pressure and the dynamic friction angle is derived from the kinetic theory. The proposed relations are finally successfully compared with the experimental data introduced above. REFERENCES A. Armanini, H. Capart, L. Fraccarollo, M. Larcher, 2005, J.F.M., 532, 269-319. A. Armanini, M. Larcher, L. Fraccarollo, Ph. Rev. E, 2009, 79, 051306. A. Armanini, 2010, Palermo, Proc. XXXII Conv. Naz. di Idr. e C.I. (in Italian) GDR MiDi, 2004. Eur. Phys. J. E, 14, 341-365 M. Larcher, L. Fraccarollo, A. Armanini, H. Capart, 2007, Journal Hydr. Res., 45, 59-71.

Carbonate-periplatform sedimentation by density flows: A mechanism for rapid off-bank and vertical transport of shallow-water fines

USGS Publications Warehouse

Wilson, P.A.; Roberts, Harry H.

1993-01-01

Existing theories of off-bank sediment transport cannot account for rapid rates of sedimentation observed in Bahama bank and Florida shelf periplatform environments. Analysis of the physical processes operating during winter cold fronts suggests that accelerated off-bank transport of shallow-water mud may be achieved by sinking off-bank flows of sediment-charged hyperpycnal (super-dense) platform waters.

Characterizing relationship between optical microangiography signals and capillary flow using microfluidic channels

PubMed Central

Choi, Woo June; Qin, Wan; Chen, Chieh-Li; Wang, Jingang; Zhang, Qinqin; Yang, Xiaoqi; Gao, Bruce Z.; Wang, Ruikang K.

2016-01-01

Optical microangiography (OMAG) is a powerful optical angio-graphic tool to visualize micro-vascular flow in vivo. Despite numerous demonstrations for the past several years of the qualitative relationship between OMAG and flow, no convincing quantitative relationship has been proven. In this paper, we attempt to quantitatively correlate the OMAG signal with flow. Specifically, we develop a simplified analytical model of the complex OMAG, suggesting that the OMAG signal is a product of the number of particles in an imaging voxel and the decorrelation of OCT (optical coherence tomography) signal, determined by flow velocity, inter-frame time interval, and wavelength of the light source. Numerical simulation with the proposed model reveals that if the OCT amplitudes are correlated, the OMAG signal is related to a total number of particles across the imaging voxel cross-section per unit time (flux); otherwise it would be saturated but its strength is proportional to the number of particles in the imaging voxel (concentration). The relationship is validated using microfluidic flow phantoms with various preset flow metrics. This work suggests OMAG is a promising quantitative tool for the assessment of vascular flow. PMID:27446700

Modeling heading and path perception from optic flow in the case of independently moving objects

PubMed Central

Raudies, Florian; Neumann, Heiko

2013-01-01

Humans are usually accurate when estimating heading or path from optic flow, even in the presence of independently moving objects (IMOs) in an otherwise rigid scene. To invoke significant biases in perceived heading, IMOs have to be large and obscure the focus of expansion (FOE) in the image plane, which is the point of approach. For the estimation of path during curvilinear self-motion no significant biases were found in the presence of IMOs. What makes humans robust in their estimation of heading or path using optic flow? We derive analytical models of optic flow for linear and curvilinear self-motion using geometric scene models. Heading biases of a linear least squares method, which builds upon these analytical models, are large, larger than those reported for humans. This motivated us to study segmentation cues that are available from optic flow. We derive models of accretion/deletion, expansion/contraction, acceleration/deceleration, local spatial curvature, and local temporal curvature, to be used as cues to segment an IMO from the background. Integrating these segmentation cues into our method of estimating heading or path now explains human psychophysical data and extends, as well as unifies, previous investigations. Our analysis suggests that various cues available from optic flow help to segment IMOs and, thus, make humans' heading and path perception robust in the presence of such IMOs. PMID:23554589

Modulation analysis of nonlinear beam refraction at an interface in liquid crystals

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

Assanto, Gaetano; Smyth, Noel F.; Xia Wenjun

2011-09-15

A theoretical investigation of solitary wave refraction in nematic liquid crystals is undertaken. A modulation theory based on a Lagrangian formulation of the governing optical solitary wave equations is developed. The resulting low-dimensional equations are found to give solutions in excellent agreement with full numerical solutions of the governing equations, as well as with previous experimental studies. The analysis deals with a number of types of refraction from a more to a less optically dense medium, the most famous being the Goos-Haenchen shift upon total internal reflection.

First demonstration and field trial on multi-user UDWDM-PON full duplex PSK-PSK with single monolithic integrated dual-output-DFB-SOA based ONUs.

PubMed

Chu, GuangYong; Maho, Anaëlle; Cano, Iván; Polo, Victor; Brenot, Romain; Debrégeas, Hélène; Prat, Josep

2016-10-15

We demonstrate a monolithically integrated dual-output DFB-SOA, and conduct the field trial on a multi-user bidirectional coherent ultradense wavelength division multiplexing-passive optical network (UDWDM-PON). To the best of our knowledge, this is the first achievement of simplified single integrated laser-based neighboring coherent optical network units (ONUs) with a 12.5 GHz channel spaced ultra-dense access network, including both downstream and upstream, taking the benefits of low footprint and low-temperature dependence.

Analytical expressions for the nonlinear interference in dispersion managed transmission coherent optical systems

NASA Astrophysics Data System (ADS)

Qiao, Yaojun; Li, Ming; Yang, Qiuhong; Xu, Yanfei; Ji, Yuefeng

2015-01-01

Closed-form expressions of nonlinear interference of dense wavelength-division-multiplexed (WDM) systems with dispersion managed transmission (DMT) are derived. We carry out a simulative validation by addressing an ample and significant set of the Nyquist-WDM systems based on polarization multiplexed quadrature phase-shift keying (PM-QPSK) subcarriers at a baud rate of 32 Gbaud per channel. Simulation results show the simple closed-form analytical expressions can provide an effective tool for the quick and accurate prediction of system performance in DMT coherent optical systems.

Black GE based on crystalline/amorphous core/shell nanoneedle arrays

DOEpatents

Javey, Ali; Chueh, Yu-Lun; Fan, Zhiyong

2014-03-04

Direct growth of black Ge on low-temperature substrates, including plastics and rubber is reported. The material is based on highly dense, crystalline/amorphous core/shell Ge nanoneedle arrays with ultrasharp tips (.about.4 nm) enabled by the Ni catalyzed vapor-solid-solid growth process. Ge nanoneedle arrays exhibit remarkable optical properties. Specifically, minimal optical reflectance (<1%) is observed, even for high angles of incidence (.about.75.degree.) and for relatively short nanoneedle lengths (.about.1 .mu.m). Furthermore, the material exhibits high optical absorption efficiency with an effective band gap of .about.1 eV. The reported black Ge can have important practical implications for efficient photovoltaic and photodetector applications on nonconventional substrates.

Aerogel mass production for the CLAS12 RICH: Novel characterization methods and optical performance

NASA Astrophysics Data System (ADS)

Contalbrigo, M.; Balossino, I.; Barion, L.; Barnyakov, A. Yu.; Battaglia, G.; Danilyuk, A. F.; Katcin, A. A.; Kravchenko, E. A.; Mirazita, M.; Movsisyan, A.; Orecchini, D.; Pappalardo, L. L.; Squerzanti, S.; Tomassini, S.; Turisini, M.

2017-12-01

A large area ring-imaging Cherenkov detector has been designed to provide clean hadron identification capabilities in the momentum range from 3 GeV/c to 8 GeV/c for the CLAS12 experiments at the Jefferson Lab upgraded 12 GeV continuous electron beam accelerator facility. The adopted solution foresees a novel hybrid optics design based on an aerogel radiator, composite mirrors and densely-packed and highly-segmented photon detectors. Cherenkov light will either be imaged directly (forward tracks) or after two mirror reflections (large angle tracks). The status of the aerogel mass-production and the assessment studies of the aerogel optical performance are here reported.

Fantastic Striations and Where to Find Them: The Origin of Magnetically Aligned Striations in Interstellar Clouds

NASA Astrophysics Data System (ADS)

Chen, Che-Yu; Li, Zhi-Yun; King, Patrick K.; Fissel, Laura M.

2017-10-01

Thin, magnetically aligned striations of relatively moderate contrast with the background are commonly observed in both atomic and molecular clouds. They are also prominent in MHD simulations with turbulent converging shocks. The simulated striations develop within a dense, stagnated sheet in the midplane of the post-shock region where magnetically induced converging flows collide. We show analytically that the secondary flows are an inevitable consequence of the jump conditions of oblique MHD shocks. They produce the stagnated, sheet-like sub-layer through a secondary shock when, roughly speaking, the Alfvénic speed in the primary converging flows is supersonic, a condition that is relatively easy to satisfy in interstellar clouds. The dense sub-layer is naturally threaded by a strong magnetic field that lies close to the plane of the sub-layer. The substantial magnetic field makes the sheet highly anisotropic, which is the key to the striation formation. Specifically, perturbations of the primary inflow that vary spatially perpendicular to the magnetic field can easily roll up the sheet around the field lines without bending them, creating corrugations that appear as magnetically aligned striations in column density maps. On the other hand, perturbations that vary spatially along the field lines curve the sub-layer and alter its orientation relative to the magnetic field locally, seeding special locations that become slanted overdense filaments and prestellar cores through enhanced mass accumulation along field lines. In our scenario, the dense sub-layer, which is unique to magnetized oblique shocks, is the birthplace for both magnetically aligned diffuse striations and massive star-forming structures.

Eye morphogenesis driven by epithelial flow into the optic cup facilitated by modulation of bone morphogenetic protein

PubMed Central

Heermann, Stephan; Schütz, Lucas; Lemke, Steffen; Krieglstein, Kerstin; Wittbrodt, Joachim

2015-01-01

The hemispheric, bi-layered optic cup forms from an oval optic vesicle during early vertebrate eye development through major morphological transformations. The overall basal surface, facing the developing lens, is increasing, while, at the same time, the space basally occupied by individual cells is decreasing. This cannot be explained by the classical view of eye development. Using zebrafish (Danio rerio) as a model, we show that the lens-averted epithelium functions as a reservoir that contributes to the growing neuroretina through epithelial flow around the distal rims of the optic cup. We propose that this flow couples morphogenesis and retinal determination. Our 4D data indicate that future stem cells flow from their origin in the lens-averted domain of the optic vesicle to their destination in the ciliary marginal zone. BMP-mediated inhibition of the flow results in ectopic neuroretina in the RPE domain. Ultimately the ventral fissure fails to close resulting in coloboma. DOI: http://dx.doi.org/10.7554/eLife.05216.001 PMID:25719386

A highly accurate symmetric optical flow based high-dimensional nonlinear spatial normalization of brain images.

PubMed

Wen, Ying; Hou, Lili; He, Lianghua; Peterson, Bradley S; Xu, Dongrong

2015-05-01

Spatial normalization plays a key role in voxel-based analyses of brain images. We propose a highly accurate algorithm for high-dimensional spatial normalization of brain images based on the technique of symmetric optical flow. We first construct a three dimension optical model with the consistency assumption of intensity and consistency of the gradient of intensity under a constraint of discontinuity-preserving spatio-temporal smoothness. Then, an efficient inverse consistency optical flow is proposed with aims of higher registration accuracy, where the flow is naturally symmetric. By employing a hierarchical strategy ranging from coarse to fine scales of resolution and a method of Euler-Lagrange numerical analysis, our algorithm is capable of registering brain images data. Experiments using both simulated and real datasets demonstrated that the accuracy of our algorithm is not only better than that of those traditional optical flow algorithms, but also comparable to other registration methods used extensively in the medical imaging community. Moreover, our registration algorithm is fully automated, requiring a very limited number of parameters and no manual intervention. Copyright © 2015 Elsevier Inc. All rights reserved.

An Optical Flow-Based Full Reference Video Quality Assessment Algorithm.

PubMed

K, Manasa; Channappayya, Sumohana S

2016-06-01

We present a simple yet effective optical flow-based full-reference video quality assessment (FR-VQA) algorithm for assessing the perceptual quality of natural videos. Our algorithm is based on the premise that local optical flow statistics are affected by distortions and the deviation from pristine flow statistics is proportional to the amount of distortion. We characterize the local flow statistics using the mean, the standard deviation, the coefficient of variation (CV), and the minimum eigenvalue ( λ min ) of the local flow patches. Temporal distortion is estimated as the change in the CV of the distorted flow with respect to the reference flow, and the correlation between λ min of the reference and of the distorted patches. We rely on the robust multi-scale structural similarity index for spatial quality estimation. The computed temporal and spatial distortions, thus, are then pooled using a perceptually motivated heuristic to generate a spatio-temporal quality score. The proposed method is shown to be competitive with the state-of-the-art when evaluated on the LIVE SD database, the EPFL Polimi SD database, and the LIVE Mobile HD database. The distortions considered in these databases include those due to compression, packet-loss, wireless channel errors, and rate-adaptation. Our algorithm is flexible enough to allow for any robust FR spatial distortion metric for spatial distortion estimation. In addition, the proposed method is not only parameter-free but also independent of the choice of the optical flow algorithm. Finally, we show that the replacement of the optical flow vectors in our proposed method with the much coarser block motion vectors also results in an acceptable FR-VQA algorithm. Our algorithm is called the flow similarity index.

Velocity fields and optical turbulence near the boundary in a strongly convective laboratory flow

NASA Astrophysics Data System (ADS)

Matt, Silvia; Hou, Weilin; Goode, Wesley; Hellman, Samuel

2016-05-01

Boundary layers around moving underwater vehicles or other platforms can be a limiting factor for optical communication. Turbulence in the boundary layer of a body moving through a stratified medium can lead to small variations in the index of refraction, which impede optical signals. As a first step towards investigating this boundary layer effect on underwater optics, we study the flow near the boundary in the Rayleigh-Bénard laboratory tank at the Naval Research Laboratory Stennis Space Center. The tank is set up to generate temperature-driven, i.e., convective turbulence, and allows control of the turbulence intensity. This controlled turbulence environment is complemented by computational fluid dynamics simulations to visualize and quantify multi-scale flow patterns. The boundary layer dynamics in the laboratory tank are quantified using a state-of-the-art Particle Image Velocimetry (PIV) system to examine the boundary layer velocities and turbulence parameters. The velocity fields and flow dynamics from the PIV are compared to the numerical model and show the model to accurately reproduce the velocity range and flow dynamics. The temperature variations and thus optical turbulence effects can then be inferred from the model temperature data. Optical turbulence is also visible in the raw data from the PIV system. The newly collected data are consistent with previously reported measurements from high-resolution Acoustic Doppler Velocimeter profilers (Nortek Vectrino), as well as fast thermistor probes and novel next-generation fiber-optics temperature sensors. This multi-level approach to studying optical turbulence near a boundary, combining in-situ measurements, optical techniques, and numerical simulations, can provide new insight and aid in mitigating turbulence impacts on underwater optical signal transmission.

DLP technolgy: applications in optical networking

NASA Astrophysics Data System (ADS)

Yoder, Lars A.; Duncan, Walter M.; Koontz, Elisabeth M.; So, John; Bartlett, Terry A.; Lee, Benjamin L.; Sawyers, Bryce D.; Powell, Donald; Rancuret, Paul

2001-11-01

For the past five years, Digital Light Processing (DLP) technology from Texas Instruments has made significant inroads in the projection display market. With products encompassing the world's smallest data & video projectors, HDTVs, and digital cinema, DLP is an extremely flexible technology. At the heart of these display solutions is Texas Instruments Digital Micromirror Device (DMD), a semiconductor-based light switch array of thousands of individually addressable, tiltable, mirror-pixels. With success of the DMD as a spatial light modulator in the visible regime, the use of DLP technology under the constraints of coherent, infrared light for optical networking applications is being explored. As a coherent light modulator, the DMD device can be used in Dense Wavelength Division Multiplexed (DWDM) optical networks to dynamically manipulate and shape optical signals. This paper will present the fundamentals of using DLP with coherent wavefronts, discuss inherent advantages of the technology, and present several applications for DLP in dynamic optical networks.

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

Andorf, M. B.; Lebedev, V. A.; Piot, P.

Optical stochastic cooling (OSC) is expected to enable fast cooling of dense particle beams. Transition from microwave to optical frequencies enables an achievement of stochastic cooling rates which are orders of magnitude higher than ones achievable with the classical microwave based stochastic cooling systems. A subsystemcritical to the OSC scheme is the focusing optics used to image radiation from the upstream “pickup” undulator to the downstream “kicker” undulator. In this paper, we present simulation results using wave-optics calculation carried out with the Synchrotron Radiation Workshop (SRW). Our simulations are performed in support to a proof-of-principle experiment planned at the Integrablemore » Optics Test Accelerator (IOTA) at Fermilab. The calculations provide an estimate of the energy kick received by a 100-MeV electron as it propagates in the kicker undulator and interacts with the electromagnetic pulse it radiated at an earlier time while traveling through the pickup undulator.« less

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

Khan, Shiraj; Ganguly, Auroop R; Bandyopadhyay, Sharba

Cross-spectrum analysis based on linear correlations in the time domain suggested a coupling between large river flows and the El Nino-Southern Oscillation (ENSO) cycle. A nonlinear measure based on mutual information (MI) reveals extrabasinal connections between ENSO and river flows in the tropics and subtropics, that are 20-70% higher than those suggested so far by linear correlations. The enhanced dependence observed for the Nile, Amazon, Congo, Paran{acute a}, and Ganges rivers, which affect large, densely populated regions of the world, has significant impacts on inter-annual river flow predictabilities and, hence, on water resources and agricultural planning.