1,686 research outputs found
Self-Employment among Immigrants: A Last Resort?
Based on unique register data of male immigrants in Denmark, we investigate whether self-employment is used as a last resort. To identify self-employment as a last resort, we define different types of immigrants as a function of transition probabilities between wage-employment, non-employment and self-employment. The transition probabilities are estimated using discrete competing risks models controlling for unobserved heterogeneity and duration dependence. We find that for certain groups of immigrants a large fraction can be characterized as using self-employment as a last resort.discrete competing risks; duration; random effects; self-employment
Self-employment among Immigrants:A last Resort?
Based on unique register data of male immigrants in Denmark, we investigate if immigrants use self-employment as a last resort to avoid non-employment. To identify self-employment as a last resort, we develop a general framework to identify types of indivuduals based on transitions probabilities among all states. The states here are wage-employment, non-employment and self-employment. The transition probabilities are estimated using discrete competing risks models controlling for unobserved heterogeneity and duration dependence. We find that for certain groups of immigrants, a large fraction can be characterized as using self-employment as a last resort. In many developed countries immigrants are more likely to be unemployed, outside the labour force (henceforth non-employed) or self-employed compared to natives. For example, in the empirical application of this paper, 47 % of the 30-50 years old male immigrants t
A generalized spherical version of the Blume-Emery-Griffits model with ferromagnetic and antiferromagnetic interactions
We have investigated analitycally the phase diagram of a generalized
spherical version of the Blume-Emery-Griffiths model that includes
ferromagnetic or antiferromagnetic spin interactions as well as quadrupole
interactions in zero and nonzero magnetic field. We show that in three
dimensions and zero magnetic field a regular paramagnetic-ferromagnetic (PM-FM)
or a paramagnetic-antiferromagnetic (PM-AFM) phase transition occurs whenever
the magnetic spin interactions dominate over the quadrupole interactions.
However, when spin and quadrupole interactions are important, there appears a
reentrant FM-PM or AFM-PM phase transition at low temperatures, in addition to
the regular PM-FM or PM-AFM phase transitions. On the other hand, in a nonzero
homogeneous external magnetic field , we find no evidence of a transition to
the state with spontaneous magnetization for FM interactions in three
dimensions. Nonethelesss, for AFM interactions we do get a scenario similar to
that described above for zero external magnetic field, except that the critical
temperatures are now functions of . We also find two critical field values,
, at which the reentrance phenomenon dissapears and
(), above which the PM-AFM transition temperature
vanishes.Comment: 21 pages, 6 figs. Title changed, abstract and introduction as well as
section IV were rewritten relaxing the emphasis on spin S=1 and Figs. 5 an 6
were improved in presentation. However, all the results remain valid.
Accepted for publication in Phys. Rev.
Structure of boson systems beyond the mean-field
We investigate systems of identical bosons with the focus on two-body
correlations. We use the hyperspherical adiabatic method and a decomposition of
the wave function in two-body amplitudes. An analytic parametrization is used
for the adiabatic effective radial potential. We discuss the structure of a
condensate for arbitrary scattering length. Stability and time scales for
various decay processes are estimated. The previously predicted Efimov-like
states are found to be very narrow. We discuss the validity conditions and
formal connections between the zero- and finite-range mean-field
approximations, Faddeev-Yakubovskii formulation, Jastrow ansatz, and the
present method. We compare numerical results from present work with mean-field
calculations and discuss qualitatively the connection with measurements.Comment: 26 pages, 6 figures, submitted to J. Phys. B. Ver. 2 is 28 pages with
modified figures and discussion
Correlated N-boson systems for arbitrary scattering length
We investigate systems of identical bosons with the focus on two-body
correlations and attractive finite-range potentials. We use a hyperspherical
adiabatic method and apply a Faddeev type of decomposition of the wave
function. We discuss the structure of a condensate as function of particle
number and scattering length. We establish universal scaling relations for the
critical effective radial potentials for distances where the average distance
between particle pairs is larger than the interaction range. The correlations
in the wave function restore the large distance mean-field behaviour with the
correct two-body interaction. We discuss various processes limiting the
stability of condensates. With correlations we confirm that macroscopic
tunneling dominates when the trap length is about half of the particle number
times the scattering length.Comment: 15 pages (RevTeX4), 11 figures (LaTeX), submitted to Phys. Rev. A.
Second version includes an explicit comparison to N=3, a restructured
manuscript, and updated figure
Two-body correlations in N-body boson systems
We formulate a method to study two-body correlations in a system of N
identical bosons interacting via central two-body potentials. We use the
adiabatic hyperspherical approach and assume a Faddeev-like decomposition of
the wave function. For a fixed hyperradius we derive variationally an optimal
integro-differential equation for hyperangular eigenvalue and wave function.
This equation reduces substantially by assuming the interaction range much
smaller than the size of the N-body system. At most one-dimensional integrals
then remain. We view a Bose-Einstein condensate pictorially as a structure in
the landscape of the potential given as a function of the one-dimensional
hyperradial coordinate. The quantum states of the condensate can be located in
one of the two potential minima. We derive and discuss properties of the
solutions and illustrate with numerical results. The correlations lower the
interaction energy substantially. The new multi-body Efimov states are
solutions independent of details of the two-body potential. We compare with
mean-field results and available experimental data.Comment: 19 pages (RevTeX4), 13 figures (latex). Journal-link:
http://pra.aps.org
Site-specific incorporation of phosphotyrosine using an expanded genetic code.
Access to phosphoproteins with stoichiometric and site-specific phosphorylation status is key to understanding the role of protein phosphorylation. Here we report an efficient method to generate pure, active phosphotyrosine-containing proteins by genetically encoding a stable phosphotyrosine analog that is convertible to native phosphotyrosine. We demonstrate its general compatibility with proteins of various sizes, phosphotyrosine sites and functions, and reveal a possible role of tyrosine phosphorylation in negative regulation of ubiquitination
Magnetic Structure of Heavy Fermion Ce2RhIn8
Magnetic structure of the heavy fermion antiferromagnet Ce2RhIn8 is
determined using neutron diffraction.Comment: 4 pages, 3 figures, 1 tabl
A one-dimensional lattice model for a quantum mechanical free particle
Two types of particles, A and B with their corresponding antiparticles, are
defined in a one dimensional cyclic lattice with an odd number of sites. In
each step of time evolution, each particle acts as a source for the
polarization field of the other type of particle with nonlocal action but with
an effect decreasing with the distance: A -->...\bar{B} B \bar{B} B \bar{B} ...
; B --> A \bar{A} A \bar{A} A ... . It is shown that the combined distribution
of these particles obeys the time evolution of a free particle as given by
quantum mechanics.Comment: 8 pages. Revte
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