753,828 research outputs found
Shear Stress Correlations in Hard and Soft Sphere Fluids
The shear stress autocorrelation function has been studied recently by
molecular dynamics simulation using the 1/q^n potential for very large n. The
results are analyzed and interpreted here by comparing them to the shear stress
response function for hard spheres. It is shown that the hard sphere response
function has a singular contribution and that this is reproduced accurately by
the simulations for large n. A simple model for the stress autocorrelation
function at finite n is proposed, based on the required hard sphere limiting
form.Comment: 14 pages, 2 figures; submitted for special issue of Molecular Physic
Elastocaloric response of PbTiO3 predicted from a first-principles effective Hamiltonian
A first-principles based effective Hamiltonian is used within a molecular
dynamics simulation to study the elastocaloric effect in PbTiO3. It is found
that the transition temperature is a linear function of uniaxial tensile
stress. Negative temperature change is calculated, when the uniaxial tensile
stress is switched off, as a function of initial temperature
Delta-T(T_initial). It is predicted that the formation of domain structures
under uniaxial tensile stress degrades the effectiveness of the elastocaloric
effect.Comment: 6 pages, 7 figures, published in JPS
Rheology of a Supercooled Polymer Melt
Molecular dynamics simulations are performed for a polymer melt composed of
short chains in quiescent and sheared conditions. The stress relaxation
function exhibits a stretched exponential form in a relatively early
stage and ultimately follows the Rouse function in quiescent supercooled state.
Transient stress evolution after application of shear obeys the linear growth
for strain less than 0.1 and then saturates into a
non-Newtonian viscosity. In steady states, strong shear-thinning and elongation
of chains into ellipsoidal shapes are found at extremely small shear. A glassy
component of the stress is much enhanced in these examples.Comment: 4 pages, 5 figure
From network to phenotype : the dynamic wiring of an Arabidopsis transcriptional network induced by osmotic stress
Plants have established different mechanisms to cope with environmental fluctuations and accordingly fine-tune their growth and development through the regulation of complex molecular networks. It is largely unknown how the network architectures change and what the key regulators in stress responses and plant growth are. Here, we investigated a complex, highly interconnected network of 20 Arabidopsis transcription factors (TFs) at the basis of leaf growth inhibition upon mild osmotic stress. We tracked the dynamic behavior of the stress-responsive TFs over time, showing the rapid induction following stress treatment, specifically in growing leaves. The connections between the TFs were uncovered using inducible overexpression lines and were validated with transient expression assays. This study resulted in the identification of a core network, composed of ERF6, ERF8, ERF9, ERF59, and ERF98, which is responsible for most transcriptional connections. The analyses highlight the biological function of this core network in environmental adaptation and its redundancy. Finally, a phenotypic analysis of loss-of-function and gain-of-function lines of the transcription factors established multiple connections between the stress-responsive network and leaf growth
DJ-1 interacts with and regulates paraoxonase-2, an enzyme critical for neuronal survival in response to oxidative stress.
Loss-of-function mutations in DJ-1 (PARK7) gene account for about 1% of all familial Parkinson's disease (PD). While its physiological function(s) are not completely clear, DJ-1 protects neurons against oxidative stress in both in vitro and in vivo models of PD. The molecular mechanism(s) through which DJ-1 alleviates oxidative stress-mediated damage remains elusive. In this study, we identified Paraoxonase-2 (PON2) as an interacting target of DJ-1. PON2 activity is elevated in response to oxidative stress and DJ-1 is crucial for this response. Importantly, we showed that PON2 deficiency hypersensitizes neurons to oxidative stress induced by MPP+ (1-methyl-4-phenylpyridinium). Conversely, over-expression of PON2 protects neurons in this death paradigm. Interestingly, PON2 effectively rescues DJ-1 deficiency-mediated hypersensitivity to oxidative stress. Taken together, our data suggest a model by which DJ-1 exerts its antioxidant activities, at least partly through regulation of PON2
Bent surface free energy differences from simulation
We present a calculation of the change of free energy of a solid surface upon
bending of the solid. It is based on extracting the surface stress through a
molecular dynamics simulation of a bent slab by using a generalized stress
theorem formula, and subsequent integration of the stress with respect to
strain as a function of bending curvature. The method is exemplified by
obtaining and comparing free energy changes with curvature of various
reconstructed Au(001) surfaces.Comment: 14 pages, 2 figures, accepted for publication in Surface Science
(ECOSS-19
New model for surface fracture induced by dynamical stress
We introduce a model where an isotropic, dynamically-imposed stress induces
fracture in a thin film. Using molecular dynamics simulations, we study how the
integrated fragment distribution function depends on the rate of change and
magnitude of the imposed stress, as well as on temperature. A mean-field
argument shows that the system becomes unstable for a critical value of the
stress. We find a striking invariance of the distribution of fragments for
fixed ratio of temperature and rate of change of the stress; the interval over
which this invariance holds is determined by the force fluctuations at the
critical value of the stress.Comment: Revtex, 4 pages, 4 figures available upon reques
Activated dynamics and effective temperature in a steady state sheared glass
We conduct nonequilibrium molecular dynamics simulations to measure the shear
stress, the average inherent structure energy, and the effective temperature
of a sheared model glass as a function of bath temperature and
shear strain rate. For above the glass transition temperature , the
rheology approaches a Newtonian limit and approaches as the
strain rate approaches zero, while for , the shear stress approaches a
yield stress and approaches a limiting value near . In the
shear-dominated regime at high , high strain rate or at low , we find
that the shear stress and the average inherent structure energy each collapse
onto a single curve as a function of . This indicates that
is controlling behavior in this regime.Comment: 4 pages, 2 figures. Revised to include additional data. Inherent
structure energy results were included, and much of the shear transformation
zone discussion was remove
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