Topographic Shear and the Relation of Ocular Dominance Columns to Orientation Columns in Prime and Cat Visual Cortex

Shear has been known to exist for many years in the topographic structure of prirnary visual cortex, but has received little attention in the modeling literature. Although the topographic map of V1 is largely conformal (i.e. zero shear), several groups have observed topographic shear in the region of the V1/V2 border. Furthennore, shear has also been revealed by anisotropy of cortical magnification factor within a single ocular dominance colunm. In the present paper, we make a functional hypothesis: the major axis of the topographic shear tensor provides cortical neurons with a preferred direction of orientation tuning. We demonstrate that isotropic neuronal summation of a sheared topographic map, in the presence of additional random shear can provide the major features of corlical functional architecture with the ocular dominance column system acting as the principal source of the shear tensor. The major principal axis of the shear tensor determines the direction and its eigenvalues the relative strength of cortical orientation preference. This hypothesis is then shown to be qualitatively consistent with a variety of experimental results on cat and monkey orientation column properties obtained from optical recording and from other anatomical and physiological techniques. In addition, we show that a recent result of (Das and Gilbert, 1997) is consistent with an infinite set of parameterized solutions for the cortical map. We exploit this freedom to choose a particular instance of the Das-Gilbert solution set which is consistent with the full range of local spatial structure in V1. These results suggest that further relationships between ocular dominance columns, orientation columns, and local topography may be revealed by experimental testing

The Solar X-ray Limb

We describe a new technique to measure the height of the X-ray limb with observations from occulted X-ray flare sources as observed by the RHESSI (the Reuven Ramaty High-Energy Spectroscopic Imager) satellite. This method has model dependencies different from those present in traditional observations at optical wavelengths, which depend upon detailed modeling involving radiative transfer in a medium with complicated geometry and flows. It thus provides an independent and more rigorous measurement of the "true" solar radius, meaning that of the mass distribution. RHESSI's measurement makes use of the flare X-ray source's spatial Fourier components (the visibilities), which are sensitive to the presence of the sharp edge at the lower boundary of the occulted source. We have found a suitable flare event for analysis, SOL2011-10-20T03:25 (M1.7), and report a first result from this novel technique here. Using a 4-minute integration over the 3-25 keV photon energy range, we find $R_{\mathrm{X-ray}} = 960.11\ \pm\ 0.15 \pm 0.29$ arcsec, at 1 AU, where the uncertainties include statistical uncertainties from the method and a systematic error. The standard VAL-C model predicts a value of 959.94 arcsec, about 1$\sigma$ below our value.Comment: 12 pages, 5 figures, accepted for publication in Ap

Virtual Diagnostic Interface: Aerospace Experimentation in the Synthetic Environment

The Virtual Diagnostics Interface (ViDI) methodology combines two-dimensional image processing and three-dimensional computer modeling to provide comprehensive in-situ visualizations commonly utilized for in-depth planning of wind tunnel and flight testing, real time data visualization of experimental data, and unique merging of experimental and computational data sets in both real-time and post-test analysis. The preparation of such visualizations encompasses the realm of interactive three-dimensional environments, traditional and state of the art image processing techniques, database management and development of toolsets with user friendly graphical user interfaces. ViDI has been under development at the NASA Langley Research Center for over 15 years, and has a long track record of providing unique and insightful solutions to a wide variety of experimental testing techniques and validation of computational simulations. This report will address the various aspects of ViDI and how it has been applied to test programs as varied as NASCAR race car testing in NASA wind tunnels to real-time operations concerning Space Shuttle aerodynamic flight testing. In addition, future trends and applications will be outlined in the paper

Design and Fabrication of a Self-Calibrating Germanium Photodiode for Radiometric Applications

This work is concerned with the design and fabrication of an absolute radiometric detector operated over the 0.7 to 1.5 μm wavelength range. This application requires a semiconductor photodiode with high internal quantum efficiency and long term stability. Of many possible materials, germanium is chosen because high quality material is available, the fabrication processes are relatively straight forward, and a high quantum efficiency is achievable. The fabrication procedures for a germanium cell were developed. Two types of germanium photodiodes were fabricated and tested. In both photodiodes, a channel stop has been employed to reduce the lateral current due to surface inversion. Ion implantation is used to form the n+-p junction, the channel stop and the back surface field. To reduce the surface recombination, CVD Si02 was deposited for surface passivation. A Ti/Pd/Ag metal layer was then sputtered to make the interconnections. With this process, dark current as low as 0.35 mA/cm2 has been observed on a 2 Ω -cm substrate. The n+pp+ photodiodes had a considerably low quantum efficiency than the induced junction photodiodes. It is shown by computer simulation that the internal quantum efficiency, η, of an n+pp+ diode is strongly affected by the carrier lifetime, r, in the emitter and the surface recombination velocity, S, at the SiO2-Ge surface. The high quantum efficiency in the induced junction diodes can be attributed to the absence of implantation induced damage in the emitter, and an electric field near the surface, induced by the fixed charges of the SiO2 layer. With the induced junction structure, we have observed an internal quantum efficiency of 98.8% at 0.7 μm and of 97% at 1.5 μm

Virtual Diagnostic Interface: Aerospace Experimentation in the Synthetic Environment

The Virtual Diagnostics Interface (ViDI) methodology combines two-dimensional image processing and three-dimensional computer modeling to provide comprehensive in-situ visualizations commonly utilized for in-depth planning of wind tunnel and flight testing, real time data visualization of experimental data, and unique merging of experimental and computational data sets in both real-time and post-test analysis. The preparation of such visualizations encompasses the realm of interactive three-dimensional environments, traditional and state of the art image processing techniques, database management and development of toolsets with user friendly graphical user interfaces. ViDI has been under development at the NASA Langley Research Center for over 15 years, and has a long track record of providing unique and insightful solutions to a wide variety of experimental testing techniques and validation of computational simulations. This report will address the various aspects of ViDI and how it has been applied to test programs as varied as NASCAR race car testing in NASA wind tunnels to real-time operations concerning Space Shuttle aerodynamic flight testing. In addition, future trends and applications will be outlined in the paper

LiveView3D: Real Time Data Visualization for the Aerospace Testing Environment

This paper addresses LiveView3D, a software package and associated data visualization system for use in the aerospace testing environment. The LiveView3D system allows researchers to graphically view data from numerous wind tunnel instruments in real time in an interactive virtual environment. The graphical nature of the LiveView3D display provides researchers with an intuitive view of the measurement data, making it easier to interpret the aerodynamic phenomenon under investigation. LiveView3D has been developed at the NASA Langley Research Center and has been applied in the Langley Unitary Plan Wind Tunnel (UPWT). This paper discusses the capabilities of the LiveView3D system, provides example results from its application in the UPWT, and outlines features planned for future implementation

Advanced Visualization of Experimental Data in Real Time Using LiveView3D

LiveView3D is a software application that imports and displays a variety of wind tunnel derived data in an interactive virtual environment in real time. LiveView3D combines the use of streaming video fed into a three-dimensional virtual representation of the test configuration with networked communications to the test facility Data Acquisition System (DAS). This unified approach to real time data visualization provides a unique opportunity to comprehend very large sets of diverse forms of data in a real time situation, as well as in post-test analysis. This paper describes how LiveView3D has been implemented to visualize diverse forms of aerodynamic data gathered during wind tunnel experiments, most notably at the NASA Langley Research Center Unitary Plan Wind Tunnel (UPWT). Planned future developments of the LiveView3D system are also addressed

Real-Time Aerodynamic Flow and Data Visualization in an Interactive Virtual Environment

Significant advances have been made to non-intrusive flow field diagnostics in the past decade. Camera based techniques are now capable of determining physical qualities such as surface deformation, surface pressure and temperature, flow velocities, and molecular species concentration. In each case, extracting the pertinent information from the large volume of acquired data requires powerful and efficient data visualization tools. The additional requirement for real time visualization is fueled by an increased emphasis on minimizing test time in expensive facilities. This paper will address a capability titled LiveView3D, which is the first step in the development phase of an in depth, real time data visualization and analysis tool for use in aerospace testing facilities

Computer Modeling of Electronic Properties in Thin Film Silicon Hydrogen-Alloy and Its Application to Solar Cells

A self-consistent numerical model for hydrogenated amorphous silicon(a-Si:H) has been developed to aid in the understanding of the details of the electronic behavior of silicon-hydrogen alloy material and the characteristic features of devices made from it. A gap state model incorporating exponential tail state s and Gaussian distributed dangling bond states and doping states based on the experimental results and theoretical background is proposed. Detailed transport equations including charge trapping and recombination processes are formulated, and solved numerically in one-dimension. Since a large number of material and geometrical parameters are involved, it is possible to fit experimental data with more than one parameter set. Therefore the consistency pf the proposed model was tested by fitting diverse experiments with the same material parameters. The detailed model calculations are compared with published experimental results for the dependence of dark conductivity on doping and temperature, and dependence of sweep-out charge on doping. It is also used to evaluate a one-to-one relationship between four-fold coordinated doping atoms and dangling bonds, as well as the dangling bond energy levels and distribution. The dependence of the photoconductivity on light-intensity, temperature, and spin density was investigated to understand the recombination processes and transport mechanism in a-Si:H material. The capture cross-sections for tail states and dangling bonds are determined by comparing the model calculated photoconductivity results with corresponding experimental results. An example of the use of the program TFSSP (Thin Film Semiconductor Simulation Program) for the analysis of solar cell parameters, (open-circuit voltage, short-circuit current, fill factor, collection efficiency, and conversion efficiency) as function of cell thicknesses for an a-SiC:H p-/a-Si:H i-n structure is presented and compared with corresponding experimental results. The model program is also implemented to design optimum solar cells. In conclusion, a self-consistent numerical model for thin film silicon hydrogen alloy materials and devices has been developed which includes the one-to-one relationship between doping and dangling bonds. The model turns out to be an excellent tool for the analysis of dark conductivity, photoconductivity, and the characteristics of a-SiC:11 p-/a-Si:ll i-n solar cells, and for cell design as well