1,295 research outputs found
Conduction in jammed systems of tetrahedra
Control of transport processes in composite microstructures is critical to
the development of high performance functional materials for a variety of
energy storage applications. The fundamental process of conduction and its
control through the manipulation of granular composite attributes (e.g., grain
shape) are the subject of this work. We show that athermally jammed packings of
tetrahedra with ultra-short range order exhibit fundamentally different
pathways for conduction than those in dense sphere packings. Highly resistive
granular constrictions and few face-face contacts between grains result in
short-range distortions from the mean temperature field. As a consequence,
'granular' or differential effective medium theory predicts the conductivity of
this media within 10% at the jamming point; in contrast, strong enhancement of
transport near interparticle contacts in packed-sphere composites results in
conductivity divergence at the jamming onset. The results are expected to be
particularly relevant to the development of nanomaterials, where nanoparticle
building blocks can exhibit a variety of faceted shapes.Comment: 9 pages, 10 figure
HIV-1 reverse transcriptase mutations that confer decreased in vitro susceptibility to anti-RT DNA aptamer RT1t49 confer cross resistance to other anti-RT aptamers but not to standard RT inhibitors
RNA and DNA aptamers specific for HIV-1 reverse transcriptase (RT) can inhibit reverse transcription in vitro. RNA aptamers have been shown to potently block HIV-1 replication in culture. We previously reported mutants of HIV-1 RT with substitutions N255D or N265D that display resistance to the DNA aptamer RT1t49. Variant viruses bearing these mutations singly or in combination were compromised for replication. In order to address the wider applicability of such aptamers, HIV-1 RT variants containing the N255D, N265D or both (Dbl) were tested for the extent of their cross-resistance to other DNA/RNA aptamers as well as to other RT inhibitors. Both N265D and Dbl RTs were resistant to most aptamers tested. N255D mutant displayed mild resistance to two of the DNA aptamers, little change in sensitivity to three and hypersensitivity to one. Although all mutants displayed wild type-like ribonuclease H activity, their activity was compromised under conditions that prevent re-binding. This suggests that the processivity defect caused by these mutations can also affect RNase H function thus contributing further to the replication defect in mutant viruses. These results indicate that mutants conferring resistance to anti-RT aptamers significantly affect many HIV-1 RT enzymatic activities, which could contribute to preventing the development of resistance in vivo. If such mutations were to arise in vivo, our results suggest that variant viruses should remain susceptible to many existing anti-RT inhibitors. This result was tempered by the observation that NRTI-resistance mutations such as K65R can confer resistance to some anti-RT aptamers
Variable-cell method for stress-controlled jamming of athermal, frictionless grains
A new method is introduced to simulate jamming of polyhedral grains under
controlled stress that incorporates global degrees of freedom through the
metric tensor of a periodic cell containing grains. Jamming under
hydrostatic/isotropic stress and athermal conditions leads to a precise
definition of the ideal jamming point at zero shear stress. The structures of
tetrahedra jammed hydrostatically exhibit less translational order and lower
jamming-point density than previously described `maximally random jammed' hard
tetrahedra. Under the same conditions, cubes jam with negligible nematic order.
Grains with octahedral symmetry jam in the large-system limit with an abundance
of face-face contacts in the absence of nematic order. For sufficiently large
face-face contact number, percolating clusters form that span the entire
simulation box. The response of hydrostatically jammed tetrahedra and cubes to
shear-stress perturbation is also demonstrated with the variable-cell method.Comment: 10 pages, 8 figure
Thin Electrical Double Layer Simulation of Micro-electrochemical Supercapacitors
The deteriorating state of the environment has drawn many people to hybrid electric vehicles. Electrochemical micro-supercapacitors are of interest in this field because of their high power density relative to other micro-power sources. However, little is known about how the properties of the electrolyte used affect the performance of such devices. The first step of this investigation was to use thermoreflectance microscopy to measure the temperature change of the electrodes while charging and discharging supercapacitor samples. The components of these samples were graphitic petal electrodes with a Ti/Au covering (for enhanced light reflectance) on a SiO2 base, with a PVA and H2SO4 polymer gel electrolyte. These experiments showed cooling of over 10°C. In order to better understand these results and the underlying mechanism of supercapacitors, a model to predict their behavior was needed. Therefore, a description of the dynamic and equilibrium behavior of ions in thin electrical double layers was constructed. The most accurate model was found to be the Poisson-Boltzmann equation modified to account for steric effects. MATLAB code was written and tested against previous theoretical research and will be published on nanoHUB. This will later be expanded to account for other supercapacitor features such as pseudocapacitance and high surface area of activated carbon electrodes
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