On estimating pressure build-up in severely accelerated,shocked flow

A new approach to the calculation of the high pressures characterizing the flow field in front of a piston undergoing severe acceleration over the short term is presented. In contrast with previous approaches where the computational domain is altered but which stop short of transforming velocities, here the problem is solved in an accelerating non-Euclidean co-ordinate system where the piston is stationary. The method is applied to a study of the problem of premature sabot separation. Through use of Harten's second-order-accurate TVD scheme, flow simulations are performed for both 1D and 3D axisymmetric geometries. The simple 1D model gives pressure profiles surprisingly close to those of the more physical 3D model.     

Design,Synthesis, and Biochemical Evaluation of Alpha-Amanitin Derivatives Containing Analogs of the trans-Hydroxyproline Residue for Potential Use in Antibody-Drug Conjugates

Alpha-amanitin, an extremely toxic bicyclic octapeptide extracted from the death-cap mushroom, Amanita phalloides, is a highly selective allosteric inhibitor of RNA polymerase II. Following on growing interest in using this toxin as a payload in antibody-drug conjugates, herein we report the synthesis and biochemical evaluation of several new derivatives of this toxin to probe the role of the trans-hydroxyproline (Hyp), which is known to be critical for toxicity. This structure activity relationship (SAR) study represents the first of its kind to use various Hyp-analogs to alter the conformational and H-bonding properties of Hyp in amanitin.     

Reynolds number effects on flow/acoustic mechanisms in spherical windscreens

There is a practical need to fully understand the mechanisms involved in the flow/pressure fluctuations around a screened microphone. A stream of uniform flow with low-frequency turbulence encountering a rigid, impermeable spherical windscreen is considered in this study. Pressure distributions on the surface of the sphere are determined by the flow structure. Pressure fluctuations at the center of the sphere are then calculated based on the integration of surface pressure distributions. Because of the low-frequency assumption, results from steady-state laminar flows can be used to investigate the Reynolds number effects on wind noise reduction. Three types of flow have been studied in this paper: an inviscid case, a low-Reynolds-number Stokes flow, and intermediate- and high-Reynolds-number flows. A Reynolds-number/wind-noise-reduction correlation shows that the wind noise reduction increases with decreasing Reynolds number.     

High-resolution optical correlation imaging in a scattering medium

An optical correlation setup is used to image transparent objects through scattering media, and 10-mum longitudinal and 2.5-mum transverse resolution are achieved. Spectral-bandwidth sampling of the light source is made possible by a tunable dye laser and leads to signal enhancement as a result of sampling interferogram filtering. An optical system allows observation of sample slices without the need for a translation stage.     

Dilatational-wave-induced pore-water pressure in soil

This paper examines peak and residual pore-water pressures in water-saturated soil induced by a dilatational stress wave. Our new laboratory testing device applies submillisecond, high pressure dilatational stress-wave loadings to water-saturated soil. The soil's initial effective stress, density, back pressure and saturation can be controlled with our device. Experimental results show that it is possible to induced residual excess pore-water pressure and liquefaction in water-saturated Monterey No. 0/30 sand. Liquefaction is induced with compressive strains exceeding 0.1 percent for loose samples consolidated at 172 kPa and 1 percent for dense samples consolidated at 690 kPa. Below a threshold compressive strain of about 0.005 percent, no significant residual excess pore-water pressures are developed.     

Imaging through scattering medium by recording 3D “spatial-frequential” interferograms

Speed acquisition for image formation process through scattering medium is a challenge in optical coherence tomography (OCT) approach. Besides time domain (TD), spectral Fourier domain (FD) is now widely studied. By using a swept laser source, we demonstrate that a particular time domain OCT method (optical SISAM correlator) can be simultaneously implemented in a single set-up with the corresponding Fourier domain OCT approach (spectral interferometry). Then, FD-OCT and TD-OCT signals are obtained by processing a 3D “spatial-frequential” interferences pattern. We show that these two numerical approaches can be complementary when imaging in scattering medium is achieved.