7,556 research outputs found
Line adapter provides quick disconnect under moderate side loading
Line adapter acts as quick and simple disconnect system. It quickly separates upon the application of a side load of 15 pounds with standing line pressure at 100 psig
Thermal conductivity in large- two-dimensional antiferromagnets: Role of phonon scattering
Motivated by the recent heat transport experiments in 2D antiferromagnets,
such as LaCuO, where the exchange coupling is larger than the Debye
energy , we discuss different types of relaxation processes for
magnon heat current with a particular focus on coupling to 3D phonons. We study
thermal conductivity by these in-plane magnetic excitations using two distinct
techniques, Boltzmann formalism within the relaxation-time approximation and
memory-function approach. Within these approaches, a close consideration is
given to the scattering of magnons by both acoustic and optical branches of
phonons. A remarkable accord between the two methods with regards to the
asymptotic behavior of the effective relaxation rates is demonstrated.
Additional scattering mechanisms, due to grain boundaries, impurities, and
finite correlation length in the paramagnetic phase, are discussed and included
in the calculations of the thermal conductivity . Again, we
demonstrate a close similarity of the results from the two techniques of
calculating . Our complementary approach strongly suggests that
scattering from optical or zone-boundary phonons is important for magnon heat
current relaxation in a high temperature window of .Comment: 21+ pages, 16 figure
Effective Kbar N interaction based on chiral SU(3) dynamics
The effective Kbar N interaction based on chiral SU(3) coupled-channel
dynamics is derived and its extrapolation below the Kbar N threshold is studied
in detail. Starting from the coupled-channel scattering equations, we eliminate
the channels other than Kbar N and obtain an effective interaction in the
single Kbar N channel. An equivalent local potential in coordinate space is
constructed such as to reproduce the full scattering amplitude of the chiral
SU(3) coupled-channel framework. We discuss several realistic chiral
SU(3)-based models in comparison to reach conclusions about the uncertainties
involved. It turns out that, in the region relevant to the discussion of deeply
bound Kbar-nuclear few-body systems, the resulting energy-dependent, equivalent
local potential is substantially less attractive than the one suggested in
previous purely phenomenological treatments.Comment: RevTeX4, 16 pages, 15 figures, 5 tables, effect of higher order terms
is discussed, final version to appear in Phys. Rev.
How bacterial cells and colonies move on solid substrates
Many bacteria rely on active cell appendages, such as type IV pili, to move
over substrates and interact with neighboring cells. Here, we study the motion
of individual cells and bacterial colonies, mediated by the collective
interactions of multiple pili. It was shown experimentally that the substrate
motility of Neisseria gonorrhoeae cells can be described as a persistent random
walk with a persistence length that exceeds the mean pili length. Moreover, the
persistence length increases for a higher number of pili per cell. With the
help of a simple, tractable stochastic model, we test whether a tug-of-war
without directional memory can explain the persistent motion of single
Neisseria gonorrhoeae cells. While the persistent motion of single cells indeed
emerges naturally in the model, a tug-of-war alone is not capable of explaining
the motility of microcolonies, which becomes weaker with increasing colony
size. We suggest sliding friction between the microcolonies and the substrate
as the missing ingredient. While such friction almost does not affect the
general mechanism of single cell motility, it has a strong effect on colony
motility. We validate the theoretical predictions by using a three-dimensional
computational model that includes explicit details of the pili dynamics, force
generation and geometry of cells.Comment: 25 pages, 17 figure
On a price formation free boundary model by Lasry & Lions: The Neumann problem
We discuss local and global existence and uniqueness for the price formation
free boundary model with homogeneous Neumann boundary conditions introduced by
Lasry & Lions in 2007. The results are based on a transformation of the problem
to the heat equation with nonstandard boundary conditions. The free boundary
becomes the zero level set of the solution of the heat equation. The
transformation allows us to construct an explicit solution and discuss the
behavior of the free boundary. Global existence can be verified under certain
conditions on the free boundary and examples of non-existence are given
Parabolic free boundary price formation models under market size fluctuations
In this paper we propose an extension of the Lasry-Lions price formation
model which includes fluctuations of the numbers of buyers and vendors. We
analyze the model in the case of deterministic and stochastic market size
fluctuations and present results on the long time asymptotic behavior and
numerical evidence and conjectures on periodic, almost periodic and stochastic
fluctuations. The numerical simulations extend the theoretical statements and
give further insights into price formation dynamics
On computational irreducibility and the predictability of complex physical systems
Using elementary cellular automata (CA) as an example, we show how to
coarse-grain CA in all classes of Wolfram's classification. We find that
computationally irreducible (CIR) physical processes can be predictable and
even computationally reducible at a coarse-grained level of description. The
resulting coarse-grained CA which we construct emulate the large-scale behavior
of the original systems without accounting for small-scale details. At least
one of the CA that can be coarse-grained is irreducible and known to be a
universal Turing machine.Comment: 4 pages, 2 figures, to be published in PR
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