291 research outputs found
Exponential distributions of collective flow-event properties in viscous liquid dynamics
We study the statistics of flow events in the inherent dynamics in
supercooled two- and three-dimensional binary Lennard-Jones liquids.
Distributions of changes of the collective quantities energy, pressure and
shear stress become exponential at low temperatures, as does that of the event
"size" . We show how the -distribution controls the
others, while itself following from exponential tails in the distributions of
(1) single particle displacements , involving a Lindemann-like length
and (2) the number of active particles (with ).Comment: Accepter version (PRL
Effect of bioactive coating of the tibial component on migration pattern in uncemented total knee arthroplasty: a randomized RSA study of 14 knees presented according to new RSA-guidelines
The Distance to NGC 4993: The Host Galaxy of the Gravitational-wave Event GW170817
The historic detection of gravitational waves from a binary neutron star
merger (GW170817) and its electromagnetic counterpart led to the first accurate
(sub-arcsecond) localization of a gravitational-wave event. The transient was
found to be 10" from the nucleus of the S0 galaxy NGC 4993. We report
here the luminosity distance to this galaxy using two independent methods. (1)
Based on our MUSE/VLT measurement of the heliocentric redshift () we infer the systemic recession velocity of the
NGC 4993 group of galaxies in the cosmic microwave background (CMB) frame to be
km s. Using constrained cosmological
simulations we estimate the line-of-sight peculiar velocity to be km s, resulting in a cosmic velocity of km s () and a
distance of Mpc assuming a local Hubble constant of
km s Mpc. (2) Using Hubble Space Telescope
measurements of the effective radius (15.5" 1.5") and contained intensity
and MUSE/VLT measurements of the velocity dispersion, we place NGC 4993 on the
Fundamental Plane (FP) of E and S0 galaxies. Comparing to a frame of 10
clusters containing 226 galaxies, this yields a distance estimate of Mpc. The combined redshift and FP distance is Mpc. This 'electromagnetic' distance estimate is consistent
with the independent measurement of the distance to GW170817 as obtained from
the gravitational-wave signal ( Mpc) and
confirms that GW170817 occurred in NGC 4993.Comment: 9 pages, 5 figure
Isomorphs in model molecular liquids
Isomorphs are curves in the phase diagram along which a number of static and
dynamic quantities are invariant in reduced units. A liquid has good isomorphs
if and only if it is strongly correlating, i.e., the equilibrium
virial/potential energy fluctuations are more than 90% correlated in the NVT
ensemble. This paper generalizes isomorphs to liquids composed of rigid
molecules and study the isomorphs of two systems of small rigid molecules, the
asymmetric dumbbell model and the Lewis-Wahnstrom OTP model. In particular, for
both systems we find that the isochoric heat capacity, the excess entropy, the
reduced molecular center-of-mass self part of the intermediate scattering
function, the reduced molecular center-of-mass radial distribution function to
a good approximation are invariant along an isomorph. In agreement with theory,
we also find that an instantaneous change of temperature and density from an
equilibrated state point to another isomorphic state point leads to no
relaxation. The isomorphs of the Lewis-Wahnstrom OTP model were found to be
more approximative than those of the asymmetric dumbbell model, which is
consistent with the OTP model being less strongly correlating. For both models
we find "master isomorphs", i.e., isomorphs have identical shape in the
virial/potential energy phase diagram.Comment: 20 page
Ac hopping conduction at extreme disorder takes place on the percolating cluster
Simulations of the random barrier model show that ac currents at extreme
disorder are carried almost entirely by the percolating cluster slightly above
threshold; thus contradicting traditional theories contributions from isolated
low-activation-energy clusters are negligible. The effective medium
approximation in conjunction with the Alexander-Orbach conjecture leads to an
excellent analytical fit to the universal ac conductivity with no nontrivial
fitting parameters
Diffusion and jump-length distribution in liquid and amorphous CuZr
Using molecular dynamics simulation, we calculate the distribution of atomic
jum ps in CuZr in the liquid and glassy states. In both states
the distribution of jump lengths can be described by a temperature independent
exponential of the length and an effective activation energy plus a
contribution of elastic displacements at short distances. Upon cooling the
contribution of shorter jumps dominates. No indication of an enhanced
probability to jump over a nearest neighbor distance was found. We find a
smooth transition from flow in the liquid to jumps in the g lass. The
correlation factor of the diffusion constant decreases with decreasing
temperature, causing a drop of diffusion below the Arrhenius value, despite an
apparent Arrhenius law for the jump probability
Dynamics of Baltic ecosystems and causes of their variability
Dynamics of Baltic ecosystems and causes of their variability are discussed and special attention is paid to the use of ecological models as a tool for research and management. - The causes of the observed changes in salinity, temperature, and oxygen of the deep water of the Baltic Sea are reviewed and discussed. - The work has led to the formulation of a hypothesis by which it appears possible to explain the oxygen development and the long-term development of other hydrographic components. The analyses indicate that the change of the level of the interface from - 80 m at the beginning of the century to about - 60 m today has increased the quantity of dead organic matter sinking down through the halocline as a consequence of the increased area of contact between the surface water and the deep water. The increased contact area has led to a corresponding increase in all fluxes through the halocline driven by turbulent gradient diffusion including an increase in the upward flux of nutrients. This has led to a fertilization of the surface water which has increased organic production in the surface zone. This in turn increases the amount of dead organic matter supplied to the deep water. At the same time the temperature increase has increased the rate of oxygen consumption. The net result is that oxygen in the deep water is being consumed at a much higher rate today than previously. lt is estimated that the rate of consumption has increased about 110% since the end of the last century. This implies an increase in the primary production of about 40%. - The supply of oxygen to the deep water has increased primarily as a consequence of the increase in the area of contact between the surface water and the deep water, and secondly as a consequence of an increase in the vertical oxygen concentration gradient. However, the rate of increase of supply has been smaller than the rate of increase of the consumption. The relative difference between the consumption and the supply has increased from 0 at equilibrium conditions at the end of the last century to about 10% today. Although this change in the balance between supply and consumption appears to be marginal, it is nevertheless sufficient to bring about the dramatic decrease of the oxygen concentration in the deep water from about 3 ml/l at the end of the last century to close to O ml/l today. - The model introduced represents a preliminary step towards a Baltic model, which necessarily must take the changing position of the halocline and related effects into account
NVU dynamics. II. Comparing to four other dynamics
In the companion paper [Ingebrigtsen et al., arXiv:1012.3447] an algorithm
was developed for tracing out a geodesic curve on the constant-potential-energy
hypersurface. Here simulations of this NVU dynamics are compared to results for
four other dynamics, both deterministic and stochastic. First, NVU dynamics is
compared to the standard energy-conserving Newtonian NVE dynamics by
simulations of the Kob-Andersen binary Lennard-Jones liquid, its WCA version
(i.e., with cut-off's at the pair potential minima), and the Gaussian
Lennard-Jones liquid. We find identical results for all quantities probed:
radial distribution functions, incoherent intermediate scattering functions,
and mean-square displacement as function of time. Arguments are then presented
for the equivalence of NVU and NVE dynamics in the thermodynamic limit; in
particular to leading order in 1/N these two dynamics give identical
time-autocorrelation functions. In the final section NVU dynamics is compared
to Monte Carlo dynamics, to a diffusive dynamics of small-step random walks on
the constant-potential-energy hypersurface, and to Nose-Hoover NVT dynamics. If
time is scaled for the two stochastic dynamics to make their single-particle
diffusion constants identical to those of NVE dynamics, the simulations show
that all five dynamics are equivalent at low temperatures except at short
times
Observation of Single Transits in Supercooled Monatomic Liquids
A transit is the motion of a system from one many-particle potential energy
valley to another. We report the observation of transits in molecular dynamics
(MD) calculations of supercooled liquid argon and sodium. Each transit is a
correlated simultaneous shift in the equilibrium positions of a small local
group of particles, as revealed in the fluctuating graphs of the particle
coordinates versus time. This is the first reported direct observation of
transit motion in a monatomic liquid in thermal equilibrium. We found transits
involving 2 to 11 particles, having mean shift in equilibrium position on the
order of 0.4 R_1 in argon and 0.25 R_1 in sodium, where R_1 is the nearest
neighbor distance. The time it takes for a transit to occur is approximately
one mean vibrational period, confirming that transits are fast.Comment: 19 pages, 8 figure
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