14,584 research outputs found
Hydrodynamic interactions in active colloidal crystal microrheology
In dense colloids it is commonly assumed that hydrodynamic interactions do
not play a role. However, a found theoretical quantification is often missing.
We present computer simulations that are motivated by experiments where a large
colloidal particle is dragged through a colloidal crystal. To qualify the
influence of long-ranged hydrodynamics, we model the setup by conventional
Langevin dynamics simulations and by an improved scheme with limited
hydrodynamic interactions. This scheme significantly improves our results and
allows to show that hydrodynamics strongly impacts on the development of
defects, the crystal regeneration as well as on the jamming behavior.Comment: 5 pages, 4 figure
Equilibrium topology of the intermediate state in type-I superconductors of different shapes
High-resolution magneto-optical technique was used to analyze flux patterns
in the intermediate state of bulk Pb samples of various shapes - cones,
hemispheres and discs. Combined with the measurements of macroscopic
magnetization these results allowed studying the effect of bulk pinning and
geometric barrier on the equilibrium structure of the intermediate state.
Zero-bulk pinning discs and slabs show hysteretic behavior due to geometric
barrier that results in a topological hysteresis -- flux tubes on penetration
and lamellae on flux exit. (Hemi)spheres and cones do not have geometric
barrier and show no hysteresis with flux tubes dominating the intermediate
field region. It is concluded that flux tubes represent the equilibrium
topology of the intermediate state in reversible samples, whereas laminar
structure appears in samples with magnetic hysteresis (either bulk or
geometric). Real-time video is available in
http://www.cmpgroup.ameslab.gov/supermaglab/video/Pb.html
NOTE: the submitted images were severely downsampled due to Arxiv's
limitations of 1 Mb total size
Quasi-matter bounce and inflation in the light of the CSL model
The Continuous Spontaneous Localization (CSL) model has been proposed as a
possible solution to the quantum measurement problem by modifying the
Schr\"{o}dinger equation. In this work, we apply the CSL model to two
cosmological models of the early Universe: the matter bounce scenario and slow
roll inflation. In particular, we focus on the generation of the classical
primordial inhomogeneities and anisotropies that arise from the dynamical
evolution, provided by the CSL mechanism, of the quantum state associated to
the quantum fields. In each case, we obtained a prediction for the shape and
the parameters characterizing the primordial spectra (scalar and tensor), i.e.
the amplitude, the spectral index and the tensor-to-scalar ratio. We found that
there exist CSL parameter values, allowed by other non-cosmological
experiments, for which our predictions for the angular power spectrum of the
CMB temperature anisotropy are consistent with the best fit canonical model to
the latest data released by the Planck Collaboration.Comment: 27 pages, including 6 figures, 2 tables and one Appendix. Final
version. Accepted in EPJ
Stability of the vortex lattice in a rotating superfluid
We analyze the stability of the vortex lattice in a rotating superfluid
against thermal fluctuations associated with the long-wavelength Tkachenko
modes of the lattice. Inclusion of only the two-dimensional modes leads
formally to instability in infinite lattices; however, when the full
three-dimensional spectrum of modes is taken into account, the
thermally-induced lattice displacements are indeed finite.Comment: 16 page
Simulation of Cosmic Ray neutrinos Interactions in Water
The program CORSIKA, usually used to simulate extensive cosmic ray air
showers, has been adapted to a water medium in order to study the acoustic
detection of ultra high energy neutrinos. Showers in water from incident
protons and from neutrinos have been generated and their properties are
described. The results obtained from CORSIKA are compared to those from other
available simulation programs such as Geant4.Comment: Talk presented on behalf of the ACoRNE Collaboration at the ARENA
Workshop 200
Snell's Law from an Elementary Particle Viewpoint
Snell's law of light deflection between media with different indices of
refraction is usually discussed in terms of the Maxwell electromagnetic wave
theory. Snell's law may also be derived from a photon beam theory of light
rays. This latter particle physics view is by far the most simple one for
understanding the laws of refraction.Comment: ReVTeX Format 2 *.eps figure
Renormalization group approach to Fermi Liquid Theory
We show that the renormalization group (RG) approach to interacting fermions
at one-loop order recovers Fermi liquid theory results when the forward
scattering zero sound (ZS) and exchange (ZS) channels are both taken into
account. The Landau parameters are related to the fixed point value of the
``unphysical'' limit of the forward scattering vertex. We specify the
conditions under which the results obtained at one-loop order hold at all order
in a loop expansion. We also emphasize the similarities between our RG approach
and the diagrammatic derivation of Fermi liquid theory.Comment: 4 pages (RevTex) + 1 postcript file, everything in a uuencoded file,
uses epsf (problem with the figure in the first version
Technology as an economic catalyst in rural and depressed places in Massachusetts
This paper uses case studies, including two cities (Lynn and New Bedford), a sub-city district (Roxbury) and two towns in rural Franklin County (Greenfield and Orange), to examine the role of technology as a potential economic catalyst in rural and depressed places in Massachusetts. Though the five target areas vary in size, density, geographic area, demographic characteristics and economic resources, each exhibits chronic patterns of economic distress related to the decline of manufacturing, construction and other key industries
The application of the global isomorphism to the study of liquid-vapor equilibrium in two and three dimensional Lenard-Jones fluids
We analyze the interrelation between the coexistence curve of the
Lennard-Jones fluid and the Ising model in two and three dimensions within the
global isomorphism approach proposed earlier [V. L. Kulinskii, J. Phys. Chem. B
\textbf{114} 2852 (2010)]. In case of two dimensions we use the exact Onsager
result to construct the binodal of the corresponding Lennard-Jones fluid and
compare it with the results of the simulations. In the three dimensional case
we use available numerical results for the Ising model for the corresponding
mapping. The possibility to observe the singularity of the binodal diameter is
discussed.Comment: 9 pages, 2 figure
Stationary and non-stationary fluid flow of a Bose-Einstein condensate through a penetrable barrier
We experimentally study the fluid flow induced by a broad, penetrable barrier
moving through an elongated dilute gaseous Bose-Einstein condensate. The
barrier is created by a laser beam swept through the condensate, and the
resulting dipole potential can be either attractive or repulsive. We examine
both cases and find regimes of stable and unstable fluid flow: At slow speeds
of the barrier, the fluid flow is stationary due to the superfluidity of the
condensate. At intermediate speeds, we observe a non-stationary regime in which
the condensate gets filled with dark solitons. At faster speeds, soliton
formation completely ceases and a remarkable absence of excitation in the
condensate is seen again.Comment: 4 pages, 4 figure
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