5,781 research outputs found
Rigorous Proof of Pseudospin Ferromagnetism in Two-Component Bosonic Systems with Component-Independent Interactions
For a two-component bosonic system, the components can be mapped onto a
pseudo-spin degree of freedom with spin quantum number S=1/2. We provide a
rigorous proof that for a wide-range of real Hamiltonians with component
independent mass and interaction, the ground state is a ferromagnetic state
with pseudospin fully polarized. The spin-wave excitations are studied and
found to have quadratic dispersion relations at long wave length.Comment: 4 pages, no figur
Long-term evolution of FU Orionis objects at infrared wavelengths
We investigate the brightness evolution of 7 FU Orionis systems in the 1-100
micrometer wavelength range using data from the Infrared Space Observatory
(ISO). The ISO measurements were supplemented with 2MASS and MSX observations
performed in the same years as the ISO mission (1995-98). The spectral energy
distributions (SEDs) based on these data points were compared with earlier ones
derived from the IRAS photometry as well as from ground-based observations
carried out around the epoch 1983. In 3 cases (Z CMa, Parsamian 21, V1331 Cyg)
no difference between the two epochs was seen within the measurement
uncertainties. V1057 Cyg, V1515 Cyg and V1735 Cyg have become fainter at
near-infrared wavelengths while V346 Nor has become slightly brighter. V1057
Cyg exhibits a similar flux change also in the mid-infrared. At lambda >= 60
micrometer most of the sources remained constant; only V346 Nor seems to fade.
Our data on the long-term evolution of V1057 Cyg agree with the model
predictions of Kenyon & Hartmann (1991) and Turner et al. (1997) at near- and
mid-infrared wavelengths, but disagree at lambda > 25 micrometer. We discuss if
this observational result at far-infrared wavelengths could be understood in
the framework of the existing models.Comment: 9 pages, 3 figures, to be published in Astronomy & Astrophysic
Continuous Damage Fiber Bundle Model for Strongly Disordered Materials
We present an extension of the continuous damage fiber bundle model to
describe the gradual degradation of highly heterogeneous materials under an
increasing external load. Breaking of a fiber in the model is preceded by a
sequence of partial failure events occurring at random threshold values. In
order to capture the subsequent propagation and arrest of cracks, furthermore,
the disorder of the number of degradation steps of material constituents, the
failure thresholds of single fibers are sorted into ascending order and their
total number is a Poissonian distributed random variable over the fibers.
Analytical and numerical calculations showed that the failure process of the
system is governed by extreme value statistics, which has a substantial effect
on the macroscopic constitutive behaviour and on the microscopic bursting
activity as well.Comment: 10 pages, 13 figure
Dense cores in the dark cloud complex LDN1188
We present a molecular line emission study of the LDN1188 dark cloud complex
located in Cepheus. In this work we focused on the densest parts of the cloud
and on the close neighbourhood of infrared point sources. We made ammonia
mapping with the Effelsberg 100-m radio telescope and identified 3 dense cores.
CS(1--0), CS(2--1) and HCO(1--0) measurements performed with the Onsala
20\,m telescope revealed the distribution of dense molecular material. The
molecular line measurements were supplemented by mapping the dust emission at
1.2\,mm in some selected directions using the IRAM 30\,m telescope. With these
data we could work out a likely evolutionary sequence in this dark clould
complex.Comment: YouResAstro2012 conference presentation; accepted to Astronomishen
Nachrichten (25-July-2013
Lattice structures of Larkin-Ovchinnikov-Fulde - Ferrell (LOFF) state
Starting from the Ginzburg-Landau free energy describing the normal state to
Larkin-Ovchinnikov-Fulde-Ferrell (LOFF) state transition, we evaluate the free
energy of seven most common lattice structures such as stripe, square,
triangular,Simple Cubic (SC), Face centered Cubic (FCC),Body centered Cubic
(BCC) and Quasi-crystal (QC). We find that the stripe phase which is the
original LO state, is the most stable phase. This result maybe relevant to the
detection of LOFF state in some heavy fermion compounds and the pairing lattice
structure of fermions with unequal populations in the BCS side of Feshbach
resonance in ultra-cold atoms.Comment: 8 pages, 10 figure
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