Shock Compression, Release Wave Speed, and Window Correction in z-Cut Quartz
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36 MATERIALS SCIENCE↗
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Optical Response of Soda-Lime Glass Shocked to 14 GPa
To investigate the potential use of soda-lime glass (SLG) as an optical window in shock wave experiments, laser interferometry (VISAR) was used to determine the window correction and the refractive index in SLG samples subjected to plane shock wave compression. Symmetric plate impact experiments were conducted at peak stresses varying between 4 and 14 GPa and laser interferometry ($λ_0$ = 532$\textit {nm}$ wavelength) measurements were used to monitor the particle velocity histories at the impact surface. The higher stress experiments displayed a constant state prior to stress unloading. In contrast, the lower stress experiments (4.3 and 7.8 GPa) displayed an initial constant state followed by weakly time-dependent response prior to stress unloading. Because the actual particle velocities were independently known from the projectile velocity measurements, the window correction factor and the refractive index changes were determined over the stress range examined. Above 7.5 GPa, our window correction and refractive index results show significant differences with previously published data for the same material. Potential reasons for these differences are indicated.
36 MATERIALS SCIENCE↗
Window aberration correction in laser velocimetry using multifaceted holographic optical elements
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Schock, H. J.↗
Shock compression of diamond single crystals to 120 GPa: Refractive index and nonlinear photoelasticity
The optical response of transparent solids at extreme conditions is important for both fundamental science and many applications. Strong transparent solids are of particular interest for use as optical windows in dynamic compression experiments. Due to diamond’s exceptional strength and optical properties, laser-driven shock experiments and plate impact experiments were carried out to examine the diamond optical response for shock wave compression along two different crystal orientations. Using laser interferometry at 532 nm and 1550 nm wavelengths, optical transparency was observed and refractive indices were determined for [100] diamond at stresses up to 119 GPa and for [111] diamond at stresses up to 87 GPa. From these results, the nonlinear photoelastic response for [100] and [111] diamond was determined, revealing significant dependence on both crystal orientation and laser wavelength. To enable [100] diamond as an interferometry window in dynamic compression experiments, the requisite window corrections were determined for 532 nm and 1550 nm wavelengths. Because of diamond’s excellent x-ray transparency, the present findings will be particularly useful for incorporating [100] diamonds as windows in dynamic compression experiments involving x-ray diffraction or other x-ray diagnostics.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Non-uniform window phenomena and correction options for PDV [Slides]
Abstract not provided.
97 MATHEMATICS AND COMPUTING↗
Laser anemometer measurements and computations in an annular cascade of high turning core turbine vanes
An advanced laser anemometer (LA) was used to measure the axial and tangential velocity components in an annular cascade of turbine stator vanes designed for a high bypass ratio engine. These vanes were based on a redesign of the first-stage stator, of a two-stage turbine, that produced 75 degrees of flow turning. Tests were conducted on a 0.771 scale model of the engine size stator. The advanced LA fringe system was designed to employ thinner than usual laser beams resulting in a 50-micron-diameter probe volume. Window correction optics were used to ensure that the laser beams did not uncross in passing through the curved optical access port. Experimental LA measurements of velocity and turbulence were obtained both upstream, within, and downstream of the stator vane row at the design exit critical velocity ratio of 0.896 at the hub. Static pressures were also measured on the vane surface. The measurements are compared, where possible with calculations from a 3-D inviscid flow analysis. The data are presented in both graphic and tabulated form so that they may be readily used to compare against other turbomachinery computations.
Goldman, Louis J.↗
Laser anemometer measurements and computations for transonic flow conditions in an annular cascade of high turning core turbine vanes
An advanced laser anemometer (LA) was used to measure the axial and tangential velocity components in an annular cascade of turbine stator vanes operating at transonic flow conditions. The vanes tested were based on a previous redesign of the first-stage stator in a two-stage turbine for a high-bypass-ratio engine. The vanes produced 75 deg of flow turning. Tests were conducted on a 0.771-scale model of the engine-sized stator. The advanced LA fringe system employed an extremely small 50-micron diameter probe volume. Window correction optics were used to ensure that the laser beams did not uncross in passing through the curved optical access port. Experimental LA measurements of velocity and turbulence were obtained at the mean radius upstream of, within, and downstream of the stator vane row at an exit critical velocity ratio of 1.050 at the hub. Static pressures were also measured on the vane surface. The measurements are compared, where possible, with calculations from a three-dimensional inviscid flow analysis. Comparisons were also made with the results obtained previously when these same vanes were tested at the design exit critical velocity ratio of 0.896 at the hub. The data are presented in both graphical and tabulated form so that they can be readily compared against other turbomachinery computations.
Goldman, Louis J.↗
Laser Radar Through the Window (LRTW) Coordinate Correction Method
A method for corrections of measurements of points of interests measured by beams of radiation propagating through stratified media including performance of ray-tracing of at least one ray lunched from a metrology instrument in a direction of an apparent point of interest, calculation a path length of the ray through stratified medium, and determination of coordinates of true position of the point interest using the at least one path length and the direction of propagation of the ray.
Hayden, Joseph Ethan↗
A full-ring variable-aperture cadmium zinc telluride system for whole-body single photon emission computed tomography: realistic simulations with phantoms
Single photon emission computed tomography (SPECT) is an imaging modality that has demonstrated its utility in a number of clinical indications. Despite this progress, a high sensitivity, high spatial resolution, multi-tracer SPECT with a large field of view suitable for whole-body imaging of a broad range of radiotracers for theranostics is not available. Purpose We have designed a cadmium zinc telluride (CZT) variable-aperture full-ring SPECT scanner instrumented with a broad-energy tungsten collimator intended to fill this technological gap. The final purpose is to provide a multi-tracer solution for brain and whole-body imaging. Our static SPECT scanner breaks the paradigm of the standard dual- and triple-head rotational SPECT systems, utilizing a larger detector area in each scan increasing the sensitivity. We provide a demonstration of the performance of our design using a realistic model of our detector with simulated body-sized 99mTc phantoms. Methods We developed a realistic model of our detector by using a combination of a Geant4 Monte Carlo simulation and a CZT detector response model based on a finite element model. Our approach models the characteristic low-energy tail effect in CZT that noticeably affects the sensitivity and the quality of the scatter correction in CZT detectors. We implement a modified dual energy window scatter correction adapted to include the CZT low-energy tail effect. A dedicated correction is also developed to eliminate the undesirable truncation observed in images given the presence of detector edges and gaps between detectors, due to the non-rotational nature of our device. Corrections for the attenuation, detector response and the presence of collimators are also included. The images are reconstructed using the maximum-likelihood expectation-maximization algorithm implemented in the reconstruction open software STIR. Detector and reconstruction performance are characterized with a Derenzo phantom and a body-sized National Electrical Manufacturers Association (NEMA) Image Quality (IQ) phantom containing 99mTc. Results Our SPECT design can resolve 6.4mm rods in a Derenzo phantom and obtain a good image contrast with the IQ phantom. Explicit testing of the gap and edge correction is provided, showing an excellent performance in eliminating the image truncation artifacts. Our modified scatter correction shows no overestimation of the contrast-recovery ratio for our realistic CZT detector model, as opposed to the cases without correction and with a standard dual-energy window scatter correction. Conclusions In this paper, we further demonstrate the performance of our design for whole-body imaging purposes. This adds to our previous demonstration of improved qualitative and quantitative 99mTc imaging for brain perfusion and 123I imaging for dopamine transport with respect to state-of-the-art NaI dual-head cameras. We show that our design performs similarly to the VERITON SPECT from Spectrum Dynamics, a commercial full-ring CZT SPECT camera, with the potential advantage of the broader energy range of application given by our custom-design tungsten collimators. Here, our device combines high sensitivity and image resolution with a broad-energy imaging application for the purpose of clinical imaging and theranostics of emerging radionuclides.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
Launch window expansion and trajectory correction strategies prior to the first lunar swingby
Double lunar swing-by (DLSB) orbits will be employed by 'Geotail' and other spacecraft in the International Solar Terrestrial Physics program in order to conduct observations in the geomagnetic tail and front field regions of the earth begining in 1992. For these missions, first swing-by dates are virtually fixed due to the dependency of the inertial frame apsis direction on them; in addition, the relative velocity magnitude to the moon is defined so that the DLSB condition will hold rigorously. These two conditions entail that the spacecraft intercept the moon on the prescribed dates. Several revolutions in intermediate transfer orbits are required prior to the first swing-by, in order to adjust flight time while maintaining the requisite lunar swing-by date.
Engel, Cheryl↗
Observations of the Earth in polarized light from the US Space Shuttle
During the four American Space Shuttle missions of year 1985, the crewmembers took pictures of the Earth in polarized light. Different problems were encountered in the quantitative use of the data: induced polarization by the shuttle window, lack of calibration correction of the window polarization and enveloped in flight calibration methods. The analysis of the selected data first confirmed the previous observation over snow and sand. A low polarization on these surfaces was observed. On the other hand, the measurements show the potentiability of the polarization for agricultural inventory. Contamination of the atmosphere is well characterized.
Roger, Jean-Claude↗
Pressurized Rover Lunar Surface Windows Thermal Trade Study
The pressurized rover (PR) is a habitable lunar vehicle that supports up to two crew members and EVAs. The PR is expected to operate with a crew at the lunar south pole for up to 30 consecutive days. Lunar surface missions represent a significant thermal challenge due in part to the extreme changes in temperature environment. Minimizing heat leaks is essential to be able to survive cold phases of lunar surface missions. Windows in particular can be a significant source of heat leak when designed without thermal performance in mind. In addition, correctly modeling windows, and transparent materials in general, represents a significant thermal challenge. It can also be challenging to obtain accurate radiative properties for modern window materials. This study focuses on the modeling approach, results, and possible window heat leak mitigation techniques for pressurized rover. Mitigation techniques explored in this study include low emissivity coatings and removable internal or external covers. Window layup, geometry, and size are also assessed in this study for their impact to heat leak.
Sydney June Taylor↗
Towards a self-consistent analysis of the anisotropic galaxy two- and three-point correlation functions on large scales: application to mock galaxy catalogues
We establish a practical method for the joint analysis of anisotropic galaxy two- and three-point correlation functions (2PCF and 3PCF, respectively) on the basis of the decomposition formalism of the 3PCF using tripolar spherical harmonics. We perform such an analysis with MultiDark-Patchy mock catalogues to demonstrate and understand the benefit of the anisotropic 3PCF. We focus on scales above $80\, h^{-1}\, {\rm Mpc}$, and use information from the shape and the baryon acoustic oscillation (BAO) signals of the 2PCF and 3PCF. We also apply density field reconstruction to increase the signal-to-noise ratio of BAO in the 2PCF measurement, but not in the 3PCF measurement. In particular, we study in detail the constraints on the angular diameter distance and the Hubble parameter. We build a model of the bispectrum or 3PCF that includes the non-linear damping of the BAO signal in redshift space. We carefully account for various uncertainties in our analysis including theoretical models of the 3PCF, window function corrections, biases in estimated parameters from the fiducial values, the number of mock realizations to estimate the covariance matrix, and bin size. The joint analysis of the 2PCF and 3PCF monopole and quadrupole components shows a $30{{\ \rm per\ cent}}$ and $20{{\ \rm per\ cent}}$ improvement in Hubble parameter constraints before and after reconstruction of the 2PCF measurements, respectively, compared to the 2PCF analysis alone. Furthermore, this study clearly shows that the anisotropic 3PCF increases cosmological information from galaxy surveys and encourages further development of the modelling of the 3PCF on smaller scales than we consider.
79 ASTRONOMY AND ASTROPHYSICS↗
New constraints on cosmological modified gravity theories from anisotropic three-point correlation functions of BOSS DR12 galaxies
Here we report a new test of modified gravity theories using the large-scale structure of the Universe. This paper is the first attempt to (1) apply a joint analysis of the anisotropic components of galaxy two- and three-point correlation functions (2 and 3PCFs) to actual galaxy data and (2) constrain the non-linear effects of degenerate higher-order scalar-tensor (DHOST) theories on cosmological scales. Applying this analysis to the Baryon Oscillation Spectroscopic Survey (BOSS) data release 12, we obtain the lower bounds of –1.655 < ξ t and –0.504 < ξ s at the $95{{\ \rm per\ cent}}$ confidence level on the parameters characterizing the time evolution of the tidal and shift terms of the second-order velocity field. These constraints are consistent with GR predictions of ξ t = 15/1144 and ξs = 0. Moreover, they represent a 35-fold and 20-fold improvement, respectively, over the joint analysis with only the isotropic 3PCF. We ensure the validity of our results by investigating various quantities, including theoretical models of the 3PCF, window function corrections, cumulative S/N, Fisher matrices, and statistical scattering effects of mock simulation data. We also find statistically significant discrepancies between the BOSS data and the Patchy mocks for the 3PCF measurement. Finally, we package all of our 3PCF analysis codes under the name hitomi and make them publicly available so that readers can reproduce all the results of this paper and easily apply them to ongoing future galaxy surveys.
79 ASTRONOMY AND ASTROPHYSICS↗
Zoom lens compensator for a cylindrical window in laser anemometer uses
In laser anemometer systems, the flow fields under study are typically enclosed by a window. Aberration of a flat window can be corrected by a shift of the object distance. A zooming correction lens elimates the astigmatism caused by a thick cylindrical window and yields diffraction-limited performance for a monochromatic laser anemometer system. The effects of residual anamorphic distortion are discussed, and procedures for correcting these effects are presented.
Wernet, Mark P.↗
Vision-based Velocimetry over Unknown Terrain with a Low-Noise IMU
This paper presents a novel approach to terrain-relative navigation with a visual camera and Inertial Measurement Unit (IMU). The proposed algorithm uses an Extended Kalman Filter (EKF) to combine an IMU propagated state estimate with batch correction estimates computed over a sliding window of measurements. The batch correction algorithm follows the Maximum Likelihood Estimation (MLE) approach used in other Bundle Adjustment systems. Unlike other systems, the proposed system parameterizes the state over the entire window in terms of the state at a single epoch. By ignoring IMU error over the window duration, we obtain a state epoch MLE that jointly estimates the epoch state and terrain parameters with drastically reduced computationally cost. This paper presents the general architecture which can be adapted for various state parameterizations and measurement inputs. For space applications with high-accuracy IMUs, the reduction in computational cost comes with only a modest increase in estimation errors. The increase in error is quantified via a linear covariance analysis presented in this paper. Furthermore, we present simulation results which show the applicability of this algorithm to planetary landing problems.
San Martin, A. Miguel↗
Resource sharing on CSMA/CD networks in the presence of noise
Resource sharing on carrier sense multiple access with collision detection (CSMA/CD) networks can be accomplished by using window-control algorithms for bus contention. The window-control algorithms are designed to grant permission to transmit to the station with the minimum contention parameter. Proper operation of the window-control algorithm requires that all stations sense the same state of the newtork in each contention slot. Noise causes the state of the network to appear as a collision. False collisions can cause the window-control algorithm to terminate without isolating any stations. A two-phase window-control protocol and approximate recurrence equation with noise as a parameter to improve the performance of the window-control algorithms in the presence of noise are developed. The results are compared through simulation, with the approximate recurrence equation yielding the best overall performance. Noise is even a bigger problem when it is not detected by all stations. In such cases it is possible for the window boundaries of the contending stations to become out of phase. Consequently, it is possible to isolate a station other than the one with the minimum contention parameter. To guarantee proper isolation of the minimum, a broadcast phase must be added after the termination of the algorithm. The protocol required to correct the window-control algorithm when noise is not detected by all stations is discussed.
Dinschel, Duane Edward↗
Refractive index of lithium fluoride at high dynamic stresses
Alkali halides are prototypical ionic solids whose refractive index is a fundamental property related to their lattice structure and ionic polarizability. In particular, lithium fluoride (LiF) has the largest band gap of any known transparent material and maintains transparency at high pressures, making it well suited for use as an optical window in dynamic compression experiments. While empirical fits to the measured density dependence of the refractive index have been provided, a model that is valid over the entire pressure range of experiments and based on a polarization-based theoretical description is lacking. We present a refractive index model for dynamically compressed LiF based on the Lorentz-Lorenz equation, where the molecular polarizability is determined using a single oscillator model with a strain polarizability parameter Λ=0.73. Here, we show that our modeling approach provides an excellent match to the LiF refractive index data for both shock and ramp compression experiments to 900 GPa (density compression greater than threefold). Additionally, updated fits are provided to determine the refractive index correction for LiF windows used in dynamic compression experiments.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗