8,388 research outputs found
Ising-like dynamics and frozen states in systems of ultrafine magnetic particles
We use Monte-Carlo simulations to study aging phenomena and the occurence of
spinglass phases in systems of single-domain ferromagnetic nanoparticles under
the combined influence of dipolar interaction and anisotropy energy, for
different combinations of positional and orientational disorder. We find that
the magnetic moments oriente themselves preferably parallel to their anisotropy
axes and changes of the total magnetization are solely achieved by 180 degree
flips of the magnetic moments, as in Ising systems. Since the dipolar
interaction favorizes the formation of antiparallel chain-like structures,
antiparallel chain-like patterns are frozen in at low temperatures, leading to
aging phenomena characteristic for spin-glasses. Contrary to the intuition,
these aging effects are more pronounced in ordered than in disordered
structures.Comment: 5 pages, 6 figures. to appear in Phys. Rev.
Frozen metastable states in ordered systems of ultrafine magnetic particles
For studying the interplay of dipolar interaction and anisotropy energy in
systems of ultrafine magnetic particles we consider simple cubic systems of
magnetic dipoles with anisotropy axes pointing into the -direction. Using
Monte Carlo simulations we study the magnetic relaxation from several initial
states. We show explicitely that, due to the combined influence of anisotropy
energy and dipole interaction, magnetic chains are formed along the
-direction that organize themselves in frozen metastable domains of columnar
antiferromagnetic order. We show that the domains depend explicitely on the
history and relax only at extremely large time scales towards the ordered
state. We consider this as an indication for the appearence of frozen
metastable states also in real sytems, where the dipoles are located in a
liquid-like fashion and the anisotropy axes point into random directions
A full field, 3-D velocimeter for microgravity crystallization experiments
The programming and algorithms needed for implementing a full-field, 3-D velocimeter for laminar flow systems and the appropriate hardware to fully implement this ultimate system are discussed. It appears that imaging using a synched pair of video cameras and digitizer boards with synched rails for camera motion will provide a viable solution to the laminar tracking problem. The algorithms given here are simple, which should speed processing. On a heavily loaded VAXstation 3100 the particle identification can take 15 to 30 seconds, with the tracking taking less than one second. It seeems reasonable to assume that four image pairs can thus be acquired and analyzed in under one minute
Electron muon identification by atmospheric shower and electron beam in a new concept of an EAS detector
We present results demonstrating the time resolution and /e separation
capabilities with a new concept of an EAS detector capable for measurements of
cosmic rays arriving with large zenith angles. This kind of detector has been
designed to be a part of a large area (several square kilometers) surface array
designed to measure Ultra High Energy (10-200 PeV) neutrinos using the
Earth-skimming technique. A criteria to identify electron-gammas is also shown
and the particle identification capability is tested by measurements in
coincidence with the KASKADE-GRANDE experiment in Karlsruhe, Germany.Comment: accepted by Astrophysical Journal on January 12 2015, 16 pages 3
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Scaling of the localization length in linear electronic and vibrational systems with long-range correlated disorder
The localization lengths of long-range correlated disordered chains are
studied for electronic wavefunctions in the Anderson model and for vibrational
states. A scaling theory close to the band edge is developed in the Anderson
model and supported by numerical simulations. This scaling theory is mapped
onto the vibrational case at small frequencies. It is shown that for small
frequencies, unexpectateley the localization length is smaller for correlated
than for uncorrelated chains.Comment: to be published in PRB, 4 pages, 2 Figure
Recent Results from SELEX
The SELEX experiment (E781) is 3-stage magnetic spectrometer for the study of
charm hadroproduction at large xF using 600 Gev Sigma-, pi- and p beams. New
precise measurements of the Lambda_c, D0, and Ds lifetimes are presented. We
also report results on Lambda_c and Ds production by Sigma-, pi- and p beams at
xF>0.2. The data agree with expectations from color-drag models to explain
charm particle/antiparticle production asymmetries.Comment: 3 pages, 1 figure. Talk given by J.Russ at the XXXth International
Conference on High Energy Physics July 27 - August 2, 2000, Osaka, Japan.
Proceedings to be published by World Scientifi
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