13,656 research outputs found
Bose-Einstein or HBT correlations and the anomalous dimension of QCD
Bose-Einstein (or HBT) correlation functions are evaluated for the fractal
structure of QCD jets. These correlation functions have a stretched exponential
(or Levy-stable) form. The anomalous dimension of QCD determines the Levy index
of stability, thus the running coupling constant of QCD becomes measurable with
the help of two-particle Bose-Einstein correlation functions. These
considerations are tested on NA22 and UA1 two-pion correlation data.Comment: 8 pages, 5 figures, presented by T. Csorgo at the XXXIV International
Symposium on Multiparticle Dynamics, Sonoma County, California, USA, July
2004, to appear in Acta Physica Polonica
Bose-Einstein or HBT correlation signature of a second order QCD phase transition
For particles emerging from a second order QCD phase transition, we show that
a recently introduced shape parameter of the Bose-Einstein correlation
function, the Levy index of stability equals to the correlation exponent - one
of the critical exponents that characterize the behavior of the matter in the
vicinity of the second order phase transition point. Hence the shape of the
Bose-Einstein / HBT correlation functions, when measured as a function of
bombarding energy and centrality in various heavy ion reactions, can be
utilized to locate experimentally the second order phase transition and the
critical end point of the first order phase transition line in QCD.Comment: 8 pages, talk given by T. Csorgo at the Workshop on Particle
Correlations and Femtoscopy 2005, Kromeriz, Czech Republic, August 200
Influence of the particle shape on the equilibrium morphologies of supracolloidal magnetic filaments
We investigate the equilibrium morphologies of linear and ring-shaped
magnetic filaments made from crosslinked ferromagnetic spherical or ellipsoidal
colloidal particles. Using Langevin dynamics simulations, we calculate the
radius of gyration and total magnetic moment of a single filament at zero field
and different temperatures, analyzing the influence of the particles shape, the
strength of their magnetic moment and the filament length. Our results show
that, among such parameters, the shape of the particles has the strongest
qualitative impact on the equilibrium behavior of the filaments
Suspensions of supracolloidal magnetic polymers: self-assembly properties from computer simulations
We study self-assembly in suspensions of supracolloidal polymer-like
structures made of crosslinked magnetic particles. Inspired by self-assembly
motifs observed for dipolar hard spheres, we focus on four different topologies
of the polymer-like structures: linear chains, rings, Y-shaped and X-shaped
polymers. We show how the presence of the crosslinkers, the number of beads in
the polymer and the magnetic interparticle interaction affect the structure of
the suspension. It turns out that for the same set of parameters, the rings are
the least active in assembling larger structures, whereas the system of Y- and
especially X-like magnetic polymers tend to form very large loose aggregates
Magnetization dynamics in the single-molecule magnet Fe8 under pulsed microwave irradiation
We present measurements on the single molecule magnet Fe8 in the presence of
pulsed microwave radiation at 118 GHz. The spin dynamics is studied via time
resolved magnetization experiments using a Hall probe magnetometer. We
investigate the relaxation behavior of magnetization after the microwave pulse.
The analysis of the experimental data is performed in terms of different
contributions to the magnetization after-pulse relaxation. We find that the
phonon bottleneck with a characteristic relaxation time of 10 to 100 ms
strongly affects the magnetization dynamics. In addition, the spatial effect of
spin diffusion is evidenced by using samples of different sizes and different
ways of the sample's irradiation with microwaves.Comment: 14 pages, 12 figure
Time relaxation of interacting single--molecule magnets
We study the relaxation of interacting single--molecule magnets (SMMs) in
both spatially ordered and disordered systems. The tunneling window is assumed
to be, as in Fe8, much narrower than the dipolar field spread. We show that
relaxation in disordered systems differs qualitatively from relaxation in fully
occupied cubic and Fe_8 lattices. We also study how line shapes that develop in
''hole--digging'' experiments evolve with time t in these fully occupied
lattices. We show (1) that the dipolar field h scales as t^p in these hole line
shapes and show (2) how p varies with lattice structure. Line shapes are not,
in general, Lorentzian. More specifically, in the lower portion of the hole,
they behave as (h/t^p)^{(1/p)-1} if h is outside the tunnel window. This is in
agreement with experiment and with our own Monte Carlo results.Comment: 21 LaTeX pages, 6 eps figures. Submitted to PRB on 15 June 2005.
Accepted on 13 August 200
Radius Dependent Luminosity Evolution of Blue Galaxies in GOODS-N
We examine the radius-luminosity (R-L) relation for blue galaxies in the Team
Keck Redshift Survey (TKRS) of GOODS-N. We compare with a volume-limited, Sloan
Digital Sky Survey sample and find that the R-L relation has evolved to lower
surface brightness since z=1. Based on the detection limits of GOODS this can
not be explained by incompleteness in low surface-brightness galaxies. Number
density arguments rule out a pure radius evolution. It can be explained by a
radius dependent decline in B-band luminosity with time. Assuming a linear
shift in M_B with z, we use a maximum likelihood method to quantify the
evolution. Under these assumptions, large (R_{1/2} > 5 kpc), and intermediate
sized (3 < R_{1/2} < 5 kpc) galaxies, have experienced Delta M_B =1.53
(-0.10,+0.13) and 1.65 (-0.18, +0.08) magnitudes of dimming since z=1. A simple
exponential decline in star formation with an e-folding time of 3 Gyr can
result in this amount of dimming. Meanwhile, small galaxies, or some subset
thereof, have experienced more evolution, 2.55 (+/- 0.38) magnitudes. This
factor of ten decline in luminosity can be explained by sub-samples of
starbursting dwarf systems that fade rapidly, coupled with a decline in burst
strength or frequency. Samples of bursting, luminous, blue, compact galaxies at
intermediate redshifts have been identified by various previous studies. If
there has been some growth in galaxy size with time, these measurements are
upper limits on luminosity fading.Comment: 34 Total pages, 15 Written pages, 19 pages of Data Table, 13 Figures,
accepted for publication in Ap
Crystal structures and proton dynamics in potassium and cesium hydrogen bistrifluoroacetate salts with strong symmetric hydrogen bonds
The crystal structures of potassium and cesium bistrifluoroacetates were
determined at room temperature and at 20 K and 14 K, respectively, with the
single crystal neutron diffraction technique. The crystals belong to the I2/a
and A2/a monoclinic space groups, respectively, and there is no visible phase
transition. For both crystals, the trifluoroacetate entities form dimers linked
by very short hydrogen bonds lying across a centre of inversion. Any proton
disorder or double minimum potential can be rejected. The inelastic neutron
scattering spectral profiles in the OH stretching region between 500 and 1000
cm^{-1} previously published [Fillaux and Tomkinson, Chem. Phys. 158 (1991)
113] are reanalyzed. The best fitting potential has the major characteristics
already reported for potassium hydrogen maleate [Fillaux et al. Chem. Phys. 244
(1999) 387]. It is composed of a narrow well containing the ground state and a
shallow upper part corresponding to dissociation of the hydrogen bond.Comment: 31 pages, 7 figure
Temperature dependence of the coercive field in single-domain particle systems
The magnetic properties of Cu97Co3 and Cu90Co10 granular alloys were measured
over a wide temperature range (2 to 300K). The measurements show an unusual
temperature dependence of the coercive field. A generalized model is proposed
and explains well the experimental behavior over a wide temperature range. The
coexistence of blocked and unblocked particles for a given temperature rises
difficulties that are solved here by introducing a temperature dependent
blocking temperature. An empirical factor gamma arise from the model and is
directly related to the particle interactions. The proposed generalized model
describes well the experimental results and can be applied to other
single-domain particle system.Comment: 7 pages, 8 figures, revised version, accepted to Physical Review B on
29/04/200
The structure of clusters formed by Stockmayer supracolloidal magnetic polymers
Abstract.: Unlike Stockmayer fluids, that prove to undergo gas-liquid transition on cooling, the system of dipolar hard or soft spheres without any additional central attraction so far has not been shown to have a critical point. Instead, in the latter, one observes diverse self-assembly scenarios. Crosslinking dipolar soft spheres into supracolloidal magnetic polymer-like structures (SMPs) changes the self-assembly behaviour. Moreover, aggregation in systems of SMPs strongly depends on the constituent topology. For Y- and X-shaped SMPs, under the same conditions in which dipolar hard spheres would form chains, the formation of very large loose gel-like clusters was observed (E. Novak et al., J. Mol. Liq. 271, 631 (2018)). In this work, using molecular dynamics simulations, we investigate the self-assembly in suspensions of four topologically different SMPs --chains, rings, X and Y-- whose monomers interact via Stockmayer potential. As expected, compact drop-like clusters are formed by SMPs in all cases if the central isotropic attraction is introduced, however, their shape and internal structure turn out to depend on the SMPs topology. Graphical abstract: [Figure not available: see fulltext.]. © 2019, The Author(s)
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