1,024 research outputs found
Some remarks about simulation of cosmic ray phenomena with use of nuclear interaction models based on the current SPS proton-antiproton data
The x-y controversy is studied by introducing models with as many features (except for x and y distributions) in common, as possible, to avoid an extrapolation problem, only primary energies of 500 TeV are considered. To prove the point, Monte Carlo simulations are performed of EAS generated by 500 TeV vertical primary protons. Four different nuclear interaction models were used. Two of them are described elsewhere. Two are: (1) Model M-Y00 - with inclusive x and y distributions behaving in a scaling way; and (2) Model M-F00 - at and below ISR energies (1 TeV in Lab) exactly equivalent to the above, then gradually changing to provide the distributions in rapidity at 155 TeV as given by SPS proton-antiproton. This was achieved by gradual decrease in the scale unit in x distributions of produced secondaries, as interaction energy increases. Other modifications to the M-Y00 model were made
Electrons, muons and hadrons in extensive air showers and how do they depend on nuclear interaction model, part 2
Some of the results of Monte Carlo simulations of extensive air showers for nuclear interactions models are presented. The most significant part of scaling violation effect is generated by the inclusion of rising cross-section. Among the models considered the lowest value for Eo/N(max) is obtained when rapidly rising cross-section and charge exchange are both included (model R-F01). The value is still 1.38 GeV/electron. Except at the highest energies, the sensitivity to atomic mass of the primary is greater than to specific assumptions about multiple production
Measurement of long-range steric repulsions between microspheres due to an adsorbed polymer
We have measured the interparticle potential between pairs of micron-sized silica spheres induced by adsorbed polyethylene oxide polymer using a line-scanned optical tweezer. We found this long-range steric repulsion to be exponential over the range of energies (0.1kBT–5kBT) and polymer molecular weights (452 000–1 580 000) studied, and that the potential scaled with the polymer’s radius of gyration RG. The potential’s exponential decay length was about 0.6RG and its range was about 4RG, although both parameters varied significantly from one pair of spheres to another. The potential’s exponential prefactor was greater than mean-field predictions
Effects of Particle Shape on Growth Dynamics at Edges of Evaporating Colloidal Drops
We study the influence of particle shape on growth processes at the edges of
evaporating drops. Aqueous suspensions of colloidal particles evaporate on
glass slides, and convective flows during evaporation carry particles from drop
center to drop edge, where they accumulate. The resulting particle deposits
grow inhomogeneously from the edge in two-dimensions, and the deposition front,
or growth line, varies spatio-temporally. Measurements of the fluctuations of
the deposition front during evaporation enable us to identify distinct growth
processes that depend strongly on particle shape. Sphere deposition exhibits a
classic Poisson like growth process; deposition of slightly anisotropic
particles, however, belongs to the Kardar-Parisi-Zhang (KPZ) universality
class, and deposition of highly anisotropic ellipsoids appears to belong to a
third universality class, characterized by KPZ fluctuations in the presence of
quenched disorder
Helical Packings and Phase Transformations of Soft Spheres in Cylinders
The phase behavior of helical packings of thermoresponsive microspheres
inside glass capillaries is studied as a function of volume fraction. Stable
packings with long-range orientational order appear to evolve abruptly to
disordered states as particle volume fraction is reduced, consistent with
recent hard sphere simulations. We quantify this transition using correlations
and susceptibilities of the orientational order parameter psi_6. The emergence
of coexisting metastable packings, as well as coexisting ordered and disordered
states, is also observed. These findings support the notion of phase
transition-like behavior in quasi-1D systems.Comment: 5 pages, with additional 4 pages of supplemental material, accepted
to Physical Review E: Rapid Communication
Brownian Dynamics Of Particles “Dressed” By Chiral Director Configurations In Lyotropic Chromonic Liquid Crystals
We study Brownian dynamics of colloidal spheres, with planar anchoring conditions, suspended in the nematic phase of the lyotropic chromonic liquid crystal disodium chromoglycate (DSCG). Unlike typical liquid crystals, the unusually small twist elastic modulus of DSCG permits two energetically distinct helical distortions (twisted tails) of the nematic director to “dress” the suspended spheres. Video microscopy is used to characterize the helical distortions versus particle size and to measure particle mean-square displacements. Diffusion coefficients parallel and perpendicular to the far-field director, and their anisotropy ratio, are different for the two twisted tail configurations. Moreover, the crossover from subdiffusive to diffusive behavior is anomalously slow for motion perpendicular to the director (\u3e100 s). Simple arguments using Miesowicz viscosities and ideas about twist relaxation are suggested to understand the mean-square displacement observations
Measurement of correlations between low-frequency vibrational modes and particle rearrangements in quasi-two-dimensional colloidal glasses
We investigate correlations between low-frequency vibrational modes and
rearrangements in two-dimensional colloidal glasses composed of thermosensitive
microgel particles which readily permit variation of sample packing fraction.
At each packing fraction, the particle displacement covariance matrix is
measured and used to extract the vibrational spectrum of the "shadow" colloidal
glass (i.e., the particle network with the same geometry and interactions as
the sample colloid but absent damping). Rearrangements are induced by
successive, small reductions in packing fraction. The experimental results
suggest that low-frequency quasi-localized phonon modes in colloidal glasses,
i.e., modes that present low energy barriers for system rearrangements, are
spatially correlated with rearrangements in this thermal system
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