Investigation of the resilient behavior of granular base materials with simple test apparatus

In many developing countries, where resources are at premium, thin asphalt layers or chip seals are widely used to provide a durable all weather pavement surfacing. In such pavements the role of granular layers is very important in the general performance of the structure. Pavement designs in these countries are empirical in nature and rely on simple input parameters like California Bearing Ratio (CBR) values. Although widely applicable the traditional CBR test does not provide the mechanical properties such as resilient and permanent deformation characteristics of granular road materials. This paper documents the characterization technique developed to determine the mechanical behavior of granular (sub-) base materials based on CBR test using repeated load cycles. The confining pressure developed in the complex CBR stress state is estimated using strain gauges. Finite Element analysis has been attempted to model the repeated load CBR (RL-CBR) and derive an equivalent resilient modulus. Furthermore, a large scale cyclic load triaxial test was carried out on coarse unbound granular materials (UGMs) to validate the result of the RL-CBR. The RL-CBR test reasonably estimates the resilient modulus of UGMs which can be used as an input in mechanistic pavement design analysis in the absence of triaxial testing facilities.     

Empirical correlations for the solubility of pressurant gases in cryogenic propellants

We have analyzed data published by others reporting the solubility of helium in liquid hydrogen, oxygen, and methane, and of nitrogen in liquid oxygen, to develop empirical correlations for the mole fraction of these pressurant gases in the liquid phase as a function of temperature and pressure. The data, compiled and provided by NIST, are from a variety of sources and covers a large range of liquid temperatures and pressures. The correlations were developed to yield accurate estimates of the mole fraction of the pressurant gas in the cryogenic liquid at temperature and pressures of interest to the propulsion community, yet the correlations developed are applicable over a much wider range. The mole fraction solubility of helium in all these liquids is less than 0.3% at the temperatures and pressures used in propulsion systems. When nitrogen is used as a pressurant for liquid oxygen, substantial contamination can result, though the diffusion into the liquid is slow.     

High-speed video recording of basal shear layers in snow chute flows

Run-out distances and flow velocities of snow avalanches are mainly determined by frictional processes originating from the interaction with the ground. At the SLF snow chute at the Weissfluhjoch near Davos, a setup was developed which allowed us to record high-speed movies of the basal shear layer of small-scale avalanches with a frame rate of 1000 frames per second. Shear processes could be observed in high-resolution slow motion. Downstream velocity profiles were extracted by a pattern matching algorithm. The comparison of computed profiles with velocity profiles obtained from optical sensors showed good agreement. However, the temporal and spatial resolutions are much higher for the high-speed video data. Because the optical velocity sensors are one-dimensional, we found that they overestimate the velocities when a flow-normal velocity component exists as well. All measured velocity profiles exhibited very high shear rates near the ground. The maximum shear rates were up to 600/s for dry snow and 200/s for wet snow avalanches. The observations of the video images suggested a turbulent motion of the snow in the basal shear layer.     

Studies on the structure and gas sensing properties of nickel–cobalt ferrite thin films prepared by spin coating

The influence of Co²⁺ ions content on structure and sensing properties of Ni_1−xCo_xFe₂O₄ (x = 0.25, 0.5, 0.75) thin films deposited on glass substrates by spin coating is presented. Structural characterization evidenced thin films with cubic spinel structures and morphologies dependent on cobalt content. Repartition of cations in spinel tetrahedral and octahedral sites was determined and was found that the presence of Co²⁺ ions in octahedral sites favor the formation of Fe²⁺ species. The sensitivity to some reducing vapor gases (acetone, liquefied petroleum gas LPG, ethyl alcohol and methyl alcohol) was investigated and was found that thin films with x = 0.75 exhibit high sensitivity to ethyl alcohol and thin films with x = 0.25 have high sensitivity to acetone. This sensitivity largely depends on the temperature and test gas concentration and was related to the Fe²⁺ species formed in octahedral sites.     

Multi-height phase recovery combined with Fast Iterative Shrinkage-Thresholding Algorithm to handle phase microspheres from complex diffracted field in inline holography

ABSTRACT

We describe in this work an approach that individually combines constant initialization, free-space backpropagation, transport of intensity equation (TIE) and multi-height phase recovery with Fast Iterative Shrinkage-Thresholding Algorithm (FISTA) to predict reconstruction of the phase microspheres from diffracted field measurements. We incorporate appropriate initialization and regularization to reconstruct unknown phase microspheres (transparent objects).     

Electrical Detection of Spin Precession in Freely Suspended Graphene Spin Valves on Cross‐Linked Poly(methyl methacrylate)

Spin injection and detection is achieved in freely suspended graphene using cobalt electrodes and a nonlocal spin‐valve geometry. The devices are fabricated with a single electron‐beam‐resist poly(methyl methacrylate) process that minimizes both the fabrication steps and the number of (aggressive) chemicals used, greatly reducing contamination and increasing the yield of high‐quality, mechanically stable devices. As‐grown devices can present mobilities exceeding 10⁴ cm² V^?1 s^?1 at room temperature and, because the contacts deposited on graphene are only exposed to acetone and isopropanol, the method is compatible with almost any contacting material. Spin accumulation and spin precession are studied in these nonlocal spin valves. Fitting of Hanle spin precession data in bilayer and multilayer graphene yields a spin relaxation time of ～125‐250 ps and a spin diffusion length of 1.7‐1.9 μm at room temperature.     

Superparamagnetic Unusual Behavior of Micrometric Magnetite Monodisperse Monocrystals Synthesized by Fe-EDTA Thermal Decomposition

We developed a new procedure for synthesizing micrometric magnetite by hydrothermal decomposition of the Fe-EDTA complex in the presence of urea, starting from Fe(III)-ferric ammonium sulfate and Na₄EDTA as main precursors. Microcrystals with superparamagnetic behavior with 25–45 μm in size were obtained (5 emu/g at 3.8 kOe magnetic field).