905 research outputs found
Steepest-Entropy-Ascent Quantum Thermodynamics Models in Materials Science
Steepest-entropy-ascent quantum thermodynamics, or SEAQT, is a unified
approach of quantum mechanics and thermodynamics that avoids many of the
inconsistencies that can arise between the two theories. Given a set of energy
levels, i.e., energy eigenstructure, accessible to a given physical system,
SEAQT predicts the unique kinetic path from any initial non-equilibrium state
to stable equilibrium by solving a master equation that directs the system
along the path of steepest entropy ascent. There are no intrinsic limitations
on the length and time scales the method can treat so it is well-suited for
calculations where the dynamics over multiple spacial scales need to be taken
into account within a single framework. In this paper, the theoretical
framework and its advantages are described, and several applications are
presented to illustrate the use of the SEAQT equation of motion and the
construction of a simplified, reduced-order, energy eigenstructure.Comment: 18 page
Predicting Polymer Brush Behavior in Solvents using the Steepest-Entropy-Ascent Quantum Thermodynamic Framework
The steepest-entropy-ascent quantum thermodynamic (SEAQT) framework is
utilized to study the effects of temperature on polymer brushes. The brushes
are represented by a discrete energy spectrum and energy degeneracies obtained
through the Replica-Exchange Wang-Landau algorithm. The SEAQT equation of
motion is applied to the energy landscape to establish a unique kinetic path
from an initial thermodynamic state to a stable equilibrium state. The kinetic
path describes the brush's evolution in state space as it interacts with a
thermal reservoir. The predicted occupation probabilities along the kinetic
path are used to determine expected thermodynamic and structural properties.
The brush density of a polystyrene brush in cyclohexane solvent is predicted
using the equation of motion and demonstrates qualitative agreement with
experimental density profiles. The Flory-Huggins parameter chosen to describe
brush-solvent interactions affects the solvent distribution in the brush but
has minimal impact on the brush density. Three types of non-equilibrium kinetic
paths are considered, i.e., a heating path, a cooling path, and a
heating-cooling path, differing in their entropy production, with properties
such as tortuosity, radius of gyration, brush density, solvent density, and
brush chain conformations calculated for each path
Locating the most energetic electrons in Cassiopeia A
We present deep (2.4 Ms) observations of the Cassiopeia A supernova
remnant with {\it NuSTAR}, which operates in the 3--79 keV bandpass and is the
first instrument capable of spatially resolving the remnant above 15 keV. We
find that the emission is not entirely dominated by the forward shock nor by a
smooth "bright ring" at the reverse shock. Instead we find that the 15 keV
emission is dominated by knots near the center of the remnant and dimmer
filaments near the remnant's outer rim. These regions are fit with unbroken
power-laws in the 15--50 keV bandpass, though the central knots have a steeper
() spectrum than the outer filaments ().
We argue this difference implies that the central knots are located in the 3-D
interior of the remnant rather than at the outer rim of the remnant and seen in
the center due to projection effects. The morphology of 15 keV emission does
not follow that of the radio emission nor that of the low energy (12 keV)
X-rays, leaving the origin of the 15 keV emission as an open mystery. Even
at the forward shock front we find less steepening of the spectrum than
expected from an exponentially cut off electron distribution with a single
cutoff energy. Finally, we find that the GeV emission is not associated with
the bright features in the {\it NuSTAR} band while the TeV emission may be,
suggesting that both hadronic and leptonic emission mechanisms may be at work.Comment: 12 pages, 11 figures, accepted for publication in Ap
Overproduction of Phospholipids by the Kennedy Pathway Leads to Hypervirulence in Candida albicans
Candida albicans is an opportunistic human fungal pathogen that causes life-threatening systemic infections, as well as oral mucosal infections. Phospholipids are crucial for pathogenesis in C. albicans, as disruption of phosphatidylserine (PS) and phosphatidylethanolamine (PE) biosynthesis within the cytidine diphosphate diacylglycerol (CDP-DAG) pathway causes avirulence in a mouse model of systemic infection. The synthesis of PE by this pathway plays a crucial role in virulence, but it was unknown if downstream conversion of PE to phosphatidylcholine (PC) is required for pathogenicity. Therefore, the enzymes responsible for methylating PE to PC, Pem1 and Pem2, were disrupted. The resulting pem1Δ/Δ pem2Δ/Δ mutant was not less virulent in mice, but rather hypervirulent. Since the pem1Δ/Δ pem2Δ/Δ mutant accumulated PE, this led to the hypothesis that increased PE synthesis increases virulence. To test this, the alternative Kennedy pathway for PE/PC synthesis was exploited. This pathway makes PE and PC from exogenous ethanolamine and choline, respectively, using three enzymatic steps. In contrast to Saccharomyces cerevisiae, C. albicans was found to use one enzyme, Ept1, for the final enzymatic step (ethanolamine/cholinephosphotransferase) that generates both PE and PC. EPT1 was overexpressed, which resulted in increases in both PE and PC synthesis. Moreover, the EPT1 overexpression strain is hypervirulent in mice and causes them to succumb to system infection more rapidly than wild-type. In contrast, disruption of EPT1 causes loss of PE and PC synthesis by the Kennedy pathway, and decreased kidney fungal burden during the mouse systemic infection model, indicating a mild loss of virulence. In addition, the ept1Δ/Δ mutant exhibits decreased cytotoxicity against oral epithelial cells in vitro, whereas the EPT1 overexpression strain exhibits increased cytotoxicity. Taken altogether, our data indicate that mutations that result in increased PE synthesis cause greater virulence and mutations that decrease PE synthesis attenuate virulence
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