Characterisation of indium phosphide using terahertz radiation

Specimens of undoped, n-type and p-type bulk InP have been investigated using THz radiation. Reflection spectroscopy permits the determination of the TO and LO phonon energies as well as the carrier concentration. Absorption spectroscopy reveals transitions between impurity states. We report the first absorption spectrum of an acceptor in InP. The transition energies agree well with electronic Raman scattering and photoluminescence data

Darcy-Reynolds forces during intrusion into granular-fluid beds

We experimentally study intrusion into fluid-saturated granular beds by a free-falling sphere, varying particle size and fluid viscosity. We test our results against Darcy-Reynolds theory, where the deceleration of the sphere is controlled by Reynolds dilatancy and the Darcy flow resistance. We find the observed intruder dynamics are consistent with Darcy-Reynolds theory for varied particle size. We also find that our experimental results for varied viscosity are consistent with Darcy Reynolds theory, but only for a limited range of the viscosity. For large viscosities, observed forces begin to decrease with increasing viscosity, in contrast with the theoretical prediction.Office of Naval ResearchOffice of Naval Research Global Visiting Scientist Program VSP 19-7-001N0001419WX0151

Viscous-like forces control the impact response of shear-thickening dense suspensions

We experimentally and theoretically study impacts into dense cornstarch and water suspensions. We vary impact speed as well as intruder size, shape, and mass, and we characterize the resulting dynamics using high-speed video and an onboard accelerometer. We numerically solve previously proposed models, most notably the added-mass model as well as a class of viscous-like models. In the viscous-like models, the intruder dynamics are dominated by large, viscous-like forces at the boundary of the jammed front where large shear rates and accompanying large viscosities are present. We find that our experimental data are consistent with this class of models and inconsistent with the added mass model. Our results strongly suggest that the added-mass model, which is the dominant model for understanding the dynamics of impact into shear-thickening dense suspensions, should be updated to include these viscous-like forces.Office of Naval ResearchOffice of Naval Research Global Visiting Scientist ProgramNo. N0001419WX01519VSP 19-7-00

Control of Neural Stem Cell Survival by Electroactive Polymer Substrates

Stem cell function is regulated by intrinsic as well as microenvironmental factors, including chemical and mechanical signals. Conducting polymer-based cell culture substrates provide a powerful tool to control both chemical and physical stimuli sensed by stem cells. Here we show that polypyrrole (PPy), a commonly used conducting polymer, can be tailored to modulate survival and maintenance of rat fetal neural stem cells (NSCs). NSCs cultured on PPy substrates containing different counter ions, dodecylbenzenesulfonate (DBS), tosylate (TsO), perchlorate (ClO4) and chloride (Cl), showed a distinct correlation between PPy counter ion and cell viability. Specifically, NSC viability was high on PPy(DBS) but low on PPy containing TsO, ClO4 and Cl. On PPy(DBS), NSC proliferation and differentiation was comparable to standard NSC culture on tissue culture polystyrene. Electrical reduction of PPy(DBS) created a switch for neural stem cell viability, with widespread cell death upon polymer reduction. Coating the PPy(DBS) films with a gel layer composed of a basement membrane matrix efficiently prevented loss of cell viability upon polymer reduction. Here we have defined conditions for the biocompatibility of PPy substrates with NSC culture, critical for the development of devices based on conducting polymers interfacing with NSCs

A bootstrap method for sum-of-poles approximations

A bootstrap method is presented for finding efficient sum-of-poles approximations of causal functions. The method is based on a recursive application of the nonlinear least squares optimization scheme developed in (Alpert et al. in SIAM J. Numer. Anal. 37:1138–1164, 2000), followed by the balanced truncation method for model reduction in computational control theory as a final optimization step. The method is expected to be useful for a fairly large class of causal functions encountered in engineering and applied physics. The performance of the method and its application to computational physics are illustrated via several numerical examples

Effects of antiplatelet therapy on stroke risk by brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases: subgroup analyses of the RESTART randomised, open-label trial

Background Findings from the RESTART trial suggest that starting antiplatelet therapy might reduce the risk of recurrent symptomatic intracerebral haemorrhage compared with avoiding antiplatelet therapy. Brain imaging features of intracerebral haemorrhage and cerebral small vessel diseases (such as cerebral microbleeds) are associated with greater risks of recurrent intracerebral haemorrhage. We did subgroup analyses of the RESTART trial to explore whether these brain imaging features modify the effects of antiplatelet therapy

Effects of fluoxetine on functional outcomes after acute stroke (FOCUS): a pragmatic, double-blind, randomised, controlled trial

Background Results of small trials indicate that fluoxetine might improve functional outcomes after stroke. The FOCUS trial aimed to provide a precise estimate of these effects. Methods FOCUS was a pragmatic, multicentre, parallel group, double-blind, randomised, placebo-controlled trial done at 103 hospitals in the UK. Patients were eligible if they were aged 18 years or older, had a clinical stroke diagnosis, were enrolled and randomly assigned between 2 days and 15 days after onset, and had focal neurological deficits. Patients were randomly allocated fluoxetine 20 mg or matching placebo orally once daily for 6 months via a web-based system by use of a minimisation algorithm. The primary outcome was functional status, measured with the modified Rankin Scale (mRS), at 6 months. Patients, carers, health-care staff, and the trial team were masked to treatment allocation. Functional status was assessed at 6 months and 12 months after randomisation. Patients were analysed according to their treatment allocation. This trial is registered with the ISRCTN registry, number ISRCTN83290762. Findings Between Sept 10, 2012, and March 31, 2017, 3127 patients were recruited. 1564 patients were allocated fluoxetine and 1563 allocated placebo. mRS data at 6 months were available for 1553 (99·3%) patients in each treatment group. The distribution across mRS categories at 6 months was similar in the fluoxetine and placebo groups (common odds ratio adjusted for minimisation variables 0·951 [95% CI 0·839–1·079]; p=0·439). Patients allocated fluoxetine were less likely than those allocated placebo to develop new depression by 6 months (210 [13·43%] patients vs 269 [17·21%]; difference 3·78% [95% CI 1·26–6·30]; p=0·0033), but they had more bone fractures (45 [2·88%] vs 23 [1·47%]; difference 1·41% [95% CI 0·38–2·43]; p=0·0070). There were no significant differences in any other event at 6 or 12 months. Interpretation Fluoxetine 20 mg given daily for 6 months after acute stroke does not seem to improve functional outcomes. Although the treatment reduced the occurrence of depression, it increased the frequency of bone fractures. These results do not support the routine use of fluoxetine either for the prevention of post-stroke depression or to promote recovery of function. Funding UK Stroke Association and NIHR Health Technology Assessment Programme

IMPACT RESPONSE OF FLUID-SATURATED GRANULAR BEDS AND DENSE SUSPENSIONS

Systems of sub-millimeter solid particles immersed in a simple fluid can exhibit a dramatic increase in flow resistance when they are rapidly sheared, often called discontinuous shear thickening (DST). A related process is impact-induced solidification, which occurs when an intruder is driven into a particle-fluid mixture. The resultant hardening is sufficient to dampen the movement of the intruder to essentially stop it in a distance much shorter than it would in other fluids. However, the fundamental physical processes that give rise to these behaviors are not well understood. An improved description would have several military applications, such as under-vehicle armor and pipe jacketing. It also could provide a better understanding of how mines interact with wet soils. This thesis presents a fundamental experimental and theoretical study of low-speed impacts into systems of glass beads of varying sizes mixed with water. Our results show that current models fail to capture many aspects of the behavior (e.g., how the peak stresses during impact depend on the initial impact speed and the particle diameter), suggesting that new theoretical descriptions are needed.Lieutenant, United States NavyApproved for public release. distribution is unlimite