Compact thermal ion detector for space and laboratory applications

Segmentation versus integration in visual motion processing.

Scanning acoustic microscopy investigation of weld lines in injection-molded parts manufactured from industrial thermoplastic polymer

The metamorphism of snow in the absence of a significant temperature gradient was investigated. The first part of the study involved analytical modeling of the exchange of mass between grains of differing surface curvature and the process of intergranular sintering. Physical models were developed to evaluate these two processes. For the first process, it was assumed that mass exchange took place primarily by vapor transport between neighboring grains. The principles of mass balance, momentum balance and energy balance were utilized to evaluate time and spatial variations in temperature, vapor velocity, vapor pressure and mass exchange between the two grains. For the second process, mass exchange was also assumed to be dominated by vapor flow from the grain surface to the neck surface. The same variables were solved for in this second process. Results obtained show that, as expected, the exchange rates between grains of different surface curvature depend upon the radii of curvature, pore size and temperature. The rate of sintering, as determined by the rate of vapor deposition on the neck is determined by temperature, grain curvature, and neck curvature. In addition to the physical modeling, an experimental program was undertaken to measure rates of metamorphism in specially prepared snow consisting of fine-grained spherical particles. This snow was made using specialized instrumentation developed in Japan. The mean grain size was 20 μm, which, while very small, allowed the observation of measurable changes in snow microstructure over short time spans. Test results showed that the grain size increased markedly with time and that the small grains were sacrificed as the large grains acquired mass from the smaller grains.

Fracturing process of granite inferred from measurements of spatial and temporal variations in velocity during triaxial deformations : Yukutake, H J Geophys ResV94, NB11, Nov 1989, P15639–15651

Pelagic copepods are subject to predation throughout much of their planktonic life. As a result, predator detection and avoidance are crucial to the survival of individuals. By using a quantifiable fluid mechanical disturbance we determine the fluid characteristics needed to elicit an escape reaction in Pleuromamma xiphias (Calanoida: Metridinidae). Four different siphon configurations were used to spatially separate regions of maximum flow speed and acceleration from regions with maximum shear surrounding the siphons. The patterns of escapes indicate that the spatial variation in fluid velocity is the proximate cue which elicits the escape reaction in P. xiphias. An average threshold shear value of 15 /s was needed to elicit the escape reaction. These results suggest that small scale fluid motion, such as those caused by a predator’s feeding current, with shear values greater than the 15 /s are more likely to initiate an escape reaction in P. xiphias.

Perennial water storage in firn aquifers has been observed within the lower percolation zone of the southeast Greenland ice sheet. Spatially distributed seismic and radar observations, made ~50 km upstream of the Helheim Glacier terminus, reveal spatial variations of seismic velocity within a firn aquifer. From 1.65 to 1.8 km elevation, shear‐wave velocity (Vs) is 1,290 ± 180 m/s in the unsaturated firn, decreasing below the water table (~15 m depth) to 1,130 ± 250 m/s. Below 1.65 km elevation, Vs in the saturated firn is 1,270 ± 220 m/s. The compressional‐to‐shear velocity ratio decreases in the downstream saturated zone, from 2.30 ± 0.54 to 2.01 ± 0.46, closer to its value for pure ice (2.00). Consistent with colocated firn cores, these results imply an increasing concentration of ice in the downstream sites, reducing the porosity and storage potential of the firn likely caused by episodic melt and freeze during the evolution of the aquifer.

In-place filter testing is a widely accepted practice for assuring performance of high-efficiency particulate air (HEPA) filter systems. American Society of Mechanical Engineers (ASME) standards address aspects of uncertainty in in-place filter test results through limits on spatial variation of test aerosol concentration and flow velocity. This article augments the standards by developing an approximate expression for test result uncertainty. The expression uses concentration, flow velocity, and penetration heterogeneities as indices of spatial variation. The uncertainty expression is used to evaluate testing of a hypothetical HEPA filter system meeting requirements of the standards and of an operating field HEPA filter system. At a performance acceptance limit of 5×10−4 penetration, uncertainty in tests on the standard system is just over the inferred ASME system acceptance limit of 6.7%. Uncertainty for field system tests is more than twice the limit. The uncertainty expression is used to determine lim...

Colloid transport studies were conducted in water-saturated physically heterogeneous systems to gain insight into the processes controlling transport in natural aquifer and vadose zone (variably saturated) systems. Stable monodispersed colloids (carboxyl latex microspheres) and porous media (Ottawa quartz sands) that are negatively charged were employed in these studies. The physically heterogeneous systems consisted of various combinations of a cylindrical sand lens embedded in the center of a larger cylinder of matrix sand. Colloid migration was found to strongly depend on colloid size and physical heterogeneity. A decrease in the peak effluent concentration and an increase in the colloid mass removal in the sand near the column inlet occurred when the median grain size of the matrix sand decreased or the size of the colloid increased. These observations and numerical modeling of the transport data indicated that straining was sometimes an important mechanism of colloid retention. Experimental and simulation results suggest that attachment was more important when the colloid size was small relative to the sand pore size. Transport differences between conservative tracers and colloids were attributed to flow bypassing of finer-textured sands, colloid retention at interfaces of soil textural contrasts, and exclusion of colloids from smaller pore spaces. Colloid retention in the heterogeneous systems was also influenced by spatial variations in the pore water velocity. Parameters in straining and attachment models were successfully optimized to the colloid transport data. The straining model typically provided a better description of the effluent and retention data than the attachment model, especially for larger colloids and finer-textured sands. Consistent with previously reported findings, straining occurred when the ratio of the colloid and median grain diameters was >0.5%.

Colloid transport studies were conducted in water‐saturated physically heterogeneous systems to gain insight into the processes controlling transport in natural aquifer and vadose zone (variably saturated) systems. Stable monodispersed colloids (carboxyl latex microspheres) and porous media (Ottawa quartz sands) that are negatively charged were employed in these studies. The physically heterogeneous systems consisted of various combinations of a cylindrical sand lens embedded in the center of a larger cylinder of matrix sand. Colloid migration was found to strongly depend on colloid size and physical heterogeneity. A decrease in the peak effluent concentration and an increase in the colloid mass removal in the sand near the column inlet occurred when the median grain size of the matrix sand decreased or the size of the colloid increased. These observations and numerical modeling of the transport data indicated that straining was sometimes an important mechanism of colloid retention. Experimental and simulation results suggest that attachment was more important when the colloid size was small relative to the sand pore size. Transport differences between conservative tracers and colloids were attributed to flow bypassing of finer‐textured sands, colloid retention at interfaces of soil textural contrasts, and exclusion of colloids from smaller pore spaces. Colloid retention in the heterogeneous systems was also influenced by spatial variations in the pore water velocity. Parameters in straining and attachment models were successfully optimized to the colloid transport data. The straining model typically provided a better description of the effluent and retention data than the attachment model, especially for larger colloids and finer‐textured sands. Consistent with previously reported findings, straining occurred when the ratio of the colloid and median grain diameters was >0.5%.

It is desirable to perform nondestructive evaluation to assess material properties and part homogeneity because manufacturing of carbon/carbon (C/C) composites requires complicated and costly processes. In this work several ultrasonic techniques were applied to carbon/carbon composites for the evaluation of spatial variations in material properties that are attributable to the manufacturing process. In a large carbon/carbon composite manufactured by chemical vapor infiltration (CVI) method, the spatial variation of ultrasonic velocity was measured and found to be consistent with the densification behavior in CVI process in order to increase the density of C/C composites. Ultrasonic velocity and attenuation depend on a density variation of materials. Low frequency through-transmission scans based on both amplitude and time-of-flight of the ultrasonic pulse were used for mapping out the material property inhomogeneity. These results were compared with that obtained by dry-coupling ultrasonics. Pulse-echo C-scans was used to image near-surface material property anomalies such as the placement of spacers between disks during CVI. Also, optical micrograph had been examined on the surface of C/C composites using a destructive way.

Ultra-high-resolution synthetic aperture radar (SAR) has important applications in military and civilian fields. However, the acquisition of high-resolution SAR imagery poses considerable processing challenges, including limitations in traditional slant range model precision, the spatial variation in equivalent velocity, spectral aliasing, and non-negligible error introduced by stop-and-go assumption. To this end, this paper proposes an improved extended wavenumber domain imaging algorithm for ultra-high-resolution SAR to systematically address the imaging quality degradation caused by these challenges. In the proposed algorithm, the one-step motion compensation method is employed to compensate for the errors caused by orbital curvature through range-dependent envelope shift interpolation and phase function correction. Then, the interpolation based on modified Stolt mapping is performed, thereby facilitating effective separation of the range and azimuth focusing. Finally, the residual range cell migration correction is applied to eliminate range position errors, followed by azimuth compression to achieve high-precision focusing. Both simulation and spaceborne data experiments are performed to verify the effectiveness of the proposed algorithm.

We have obtained spectra of the four components of the system B1422+231 with HST's Faint Object Spectrograph in order to study spatial inhomogeneities and velocity variations in the absorbers which are pierced by the four lines of sight. The four images are well resolved, and the spectra clearly show the system is a lensed quasar; a new redshift based on the Lyα and N V emission lines is measured to be 3.6261. The following are results from the analysis of the four individual lines of sight that probe redshifts 2.9 ≤ z ≤ 3.5 and transverse dimensions 0-0.14 h -->−1100 kpc: (1) In the region between Lyβ and Lyα (less 6000 km s-1 to allow for the proximity effect: 4745-5511 A), the limiting rest equivalent width (1σlim) is measured to be 0.059, 0.052, 0.034, and 0.22 A for components A, B, C, and D, respectively. (2) The total number of 5σW lines found in this region are 83, 85, 102, and 44 for A-D, respectively; for A-C 11, 9, and 13 are identified with metal line systems and the remaining 72, 76, and 89 are assumed to be Lyα lines. Between paired lines of sight A and B to C, and A paired to B, there are 62, 68, and 62 coincidences and 3, 1, and 1, anticoincidences for the Lyα lines. For the metal lines there are 8, 9, and 8 coincidences for AC, BC, and AB, respectively, and each has one anticoincidence. (3) Scatter plots of the equivalent widths for the coincident lines for both Lyα and metals are highly correlated and all pairs match within 100 and 75 km s-1, respectively. (4) Maximum-likelihood analysis limits spatial inhomogeneity for Lyα absorbers in components A, B, and C to no more than ~15% of the equivalent width of an average (W = 2 A) line. This corresponds to a limit on the mean variation in column density, assuming unsaturated lines, of log (ΔNH) = 13.1 cm-2. (5) A method of detecting spatial inhomogeneities independent of continuum-fitting and line-profile measurement is developed yielding an upper limit on the column density difference for unsaturated lines of log (ΔNH) = 12.8. This is approximately a factor of 2 smaller than the limits obtained from the line pairs. (6) The distribution of the velocity differences for AC, BC, and AB for the Lyα lines and the metal line pairs have a mean close to zero and rms ~40 km s-1. Maximum-likelihood analysis gives an upper limit on the variations in velocity of ~40 km s-1 for Lyα absorbers in paired lines of sight. The overall result of this work is a set of stringent limits on the inhomogeneity of low column density hydrogen absorbers on subkiloparsec scales at high redshift.

<p>We characterize the spatiotemporal variations surface velocity of glaciers on the Kenai Peninsula, Alaska, using intensity offset tracking on a set of repeat-pass Sentinel-1 data and TerraSAR-X data. We derived 92 velocity fields and generated time-averaged annual and seasonal surface velocity maps for the period October 2014 to December 2019, as well as time series surface velocity profiles along centerlines for individual glaciers. We find considerable spatial and seasonal variations in surface velocity in the study area, especially a pronounced average spring speedup of 50% averagely compared to annual mean velocity. Ice velocities varied systematically between glaciers with different terminus types. Generally, the pixel-averaged velocity of tidewater and lake-terminating glaciers are up to 2 and 1.5 times greater than those of the land-terminating glaciers, respectively. For Bear glacier, with the analysis of surface velocity profile and the terminus change, we state this glacier retreat and accelerate. While the time-series result shows the velocity speed-up of the Bear glacier synchronizes well with the ice-damaged lake outburst flood (GLOF) events.</p>

Reaction and sound propagation are coupled in ideal gas phase reactions which have a difference in the sums of stoichiometric coefficients of reactants and products, or which have a pressure-dependent rate coefficient. Numerical and approximate analytical (WKB-type) solutions are obtained for the hydro-dynamic equations which take into account this coupling and which describe the spatial and temporal variations in density, velocity and concentration for an isothermal system far from equilibrium. Specific results are given for a unimolecular reaction of the type A → B+C, where sound is shown to be amplified in both high and low pressure regions, with an accompanying change in frequency; the system is unstable to small perturbations. Possible applications include a new method for the determination of rate coefficients by acoustic means.

Understanding the physics of fluid displacement through the pore spaces in multiphase environments are essential for improving the safety and optimizing the performance of diverse complex subsurface engineering applications. We conduct high-fidelity two phase flow simulations at the pore-scale using direct numerical simulations on six porous media that have different permeability. We consider nine viscosity ratios and ten contact angles, resulting in a total of 540 simulations. The open-source dataset available on Zenodo includes specifics related to the flow patterns, as well as the spatial and temporal variations of pressure and velocity within the pore spaces. This comprehensive dataset can support (i). the training of machine learning algorithms and (ii). serve as a benchmark for flows predicted by computationally efficient tools including machine learning algorithms and pore network models.