71 research outputs found
Some Sociological Observations on the Response of Israeli Organizations to New Immigrants
Preliminary observation suggests that the contact between Israeli officials and newly arrived immigrants from traditional societies is considerably less bureaucratic than might have been predicted. For example, analysis of several cases of such bureaucrat-client relationships indicates that officials often add the role of teacher to their relatively specific roles as bureaucrats by teaching newcomers how to perform in the role. Moreover, the official often becomes not only a teacher but also a kind of informal leader. This indicates that under certain conditions, formal organizations may give birth to incipient social movements, a direction of organizational change wholly unanticipated in the theoretical literature. The case material is analyzed in terms of (1) a theory of role impingement in which bureaucratic roles are seen to become intertwined with roles that are bureaucratically irrelevant to the conduct of formal organization and (2) a theory of socialization where the official serves as socializing agent for his clients
Some Sociological Observations on the Response of Israeli Organizations to New Immigrants
Spin Dynamics of a J1-J2-K Model for the Paramagnetic Phase of Iron Pnictides
We study the finite-temperature spin dynamics of the paramagnetic phase of
iron pnictides within an antiferromagnetic J_1-J_2 Heisenberg model on a square
lattice with a biquadratic coupling between the
nearest-neighbor spins. Our focus is on the paramagnetic phase in the parameter
regime of this J_1-J_2-K model where the ground state is a (\pi,0) collinear
antiferromagnet. We treat the biquadratic interaction via a
Hubbard-Stratonovich decomposition, and study the resulting effective
quadratic-coupling model using both modified spin wave and Schwinger boson
mean-field theories; the results for the spin dynamics derived from the two
methods are very similar. We show that the spectral weight of dynamical
structure factor S(q,\omega) is peaked at ellipses in the momentum space at low
excitation energies. With increasing energy, the elliptic features expand
towards the zone boundary, and gradually split into two parts, forming a
pattern around (\pi,\pi). Finally, the spectral weight is anisotropic, being
larger along the major axis of the ellipse than along its minor axis. These
characteristics of the dynamical structure factor are consistent with the
recent measurements of the inelastic neutron scattering spectra on BaFe_2As_2
and SrFe_2As_2.Comment: 13 pages, 11 figures, to be published in Phys. Rev.
On the Spin Gap Phase of Strongly-Correlated Electrons
We discuss the possible existence of a spin-gap phase in the low-doping
regime of strongly-correlated two-dimensional electrons within the gauge field
description of the t-J model. The spin-gap phase was recently shown by Ubbens
and Lee to be destroyed by gauge field quantum fluctuations for a single-layer
2D system in the absence of disorder and for a full gap. We show that the same
conclusion applies both in the dirty limit and for the case of a gapless spinon
condensate.Comment: 7 pages, uuencoded Postscript, including 1 figur
Scaling theory of two-dimensional metal-insulator transitions
We discuss the recently discovered two-dimensional metal-insulator transition
in zero magnetic field in the light of the scaling theory of localization. We
demonstrate that the observed symmetry relating conductivity and resistivity
follows directly from the quantum critical behavior associated with such a
transition. In addition, we show that very general scaling considerations imply
that any disordered two dimensional metal is a perfect metal, but most likely
not a Fermi liquid.Comment: 4 pages, no figures, REVTEX. Minor corrections adde
Effective Lorentz Force due to Small-angle Impurity Scattering: Magnetotransport in High-Tc Superconductors
We show that a scattering rate which varies with angle around the Fermi
surface has the same effect as a periodic Lorentz force on magnetotransport
coefficients. This effect, together with the marginal Fermi liquid inelastic
scattering rate gives a quantitative explanation of the temperature dependence
and the magnitude of the observed Hall effect and magnetoresistance with just
the measured zero-field resistivity as input.Comment: 4 pages, latex, one epsf figure included in text. Several revisions
and corrections are included. Major conclusions are the sam
Frustrated kinetic energy, the optical sum rule, and the mechanism of superconductivity
The theory that the change of the electronic kinetic energy in a direction
perpendicular to the CuO-planes in high-temperature superconductors is a
substantial fraction of the condensation energy is examined. It is argued that
the consequences of this theory based on a rigorous -axis conductivity sum
rule are consistent with recent optical and penetration depth measurements.Comment: 4 pages (RevTeX) and 2 eps figure
Nearby quasar remnants and ultra-high energy cosmic rays
As recently suggested, nearby quasar remnants are plausible sites of
black-hole based compact dynamos that could be capable of accelerating
ultra-high energy cosmic rays (UHECRs). In such a model, UHECRs would originate
at the nuclei of nearby dead quasars, those in which the putative underlying
supermassive black holes are suitably spun-up. Based on galactic optical
luminosity, morphological type, and redshift, we have compiled a small sample
of nearby objects selected to be highly luminous, bulge-dominated galaxies,
likely quasar remnants. The sky coordinates of these galaxies were then
correlated with the arrival directions of cosmic rays detected at energies EeV. An apparently significant correlation appears in our data. This
correlation appears at closer angular scales than those expected when taking
into account the deflection caused by typically assumed IGM or galactic
magnetic fields over a charged particle trajectory. Possible scenarios
producing this effect are discussed, as is the astrophysics of the quasar
remnant candidates. We suggest that quasar remnants be also taken into account
in the forthcoming detailed search for correlations using data from the Auger
Observatory.Comment: 2 figures, 4 tables, 11 pages. Final version to appear in Physical
Review
Pairing fluctuations and pseudogaps in the attractive Hubbard model
The two-dimensional attractive Hubbard model is studied in the weak to
intermediate coupling regime by employing a non-perturbative approach. It is
first shown that this approach is in quantitative agreement with Monte Carlo
calculations for both single-particle and two-particle quantities. Both the
density of states and the single-particle spectral weight show a pseudogap at
the Fermi energy below some characteristic temperature T*, also in good
agreement with quantum Monte Carlo calculations. The pseudogap is caused by
critical pairing fluctuations in the low-temperature renormalized classical
regime of the two-dimensional system. With increasing temperature
the spectral weight fills in the pseudogap instead of closing it and the
pseudogap appears earlier in the density of states than in the spectral
function. Small temperature changes around T* can modify the spectral weight
over frequency scales much larger than temperature. Several qualitative results
for the s-wave case should remain true for d-wave superconductors.Comment: 20 pages, 12 figure
Conductance fluctuations at the fractional quantum Hall plateau transitions
We obtain a ``mean field'' scaling flow of the longitudinal and the Hall
conductivities in the fractional quantum Hall regime. Using the composite
fermion picture and assuming that the composite fermions follow the
Khmelnitskii-Pruisken scaling flow for the integer quantum Hall effect, the
unstable fixed points which govern the transitions between different fractional
quantum Hall states are identified. Distributions of the critical longitudinal
and Hall conductivities at the unstable fixed points are obtained and
implications of the results for the experiments on mesoscopic quantum Hall
systems are discussed.Comment: RevTex, 5 pages, 8 figures, 1 tabl
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