2,669 research outputs found
Suspicious Minds: Apportioning and Avoiding Blame for Distrustful Relationships and Deferring Medical Treatment in South Africa
Magnetic phase diagram of the Hubbard model
The competition between commensurate and incommensurate spin-density-wave
phases in the infinite-dimensional single-band Hubbard model is examined with
quantum Monte Carlo simulation and strong and weak coupling approximations.
Quantum fluctuations modify the weak-coupling phase diagram by factors of order
unity and produce remarkable agreement with the quantum Monte Carlo data, but
strong-coupling theories (that map onto effective Falicov-Kimball models)
display pathological behavior. The single-band model can be used to describe
much of the experimental data in Cr and its dilute alloys with V and Mn.Comment: 12 pages plus 3 uuencoded postscript figures, ReVTe
Structural Invariance of Sunspot Umbrae Over the Solar Cycle: 1993-2004
Measurements of maximum magnetic flux, minimum intensity, and size are
presented for 12 967 sunspot umbrae detected on the NASA/NSO
spectromagnetograms between 1993 and 2004 to study umbral structure and
strength during the solar cycle. The umbrae are selected using an automated
thresholding technique. Measured umbral intensities are first corrected for a
confirming observation of umbral limb-darkening. Log-normal fits to the
observed size distribution confirm that the size spectrum shape does not vary
with time. The intensity-magnetic flux relationship is found to be steady over
the solar cycle. The dependence of umbral size on the magnetic flux and minimum
intensity are also independent of cycle phase and give linear and quadratic
relations, respectively. While the large sample size does show a low amplitude
oscillation in the mean minimum intensity and maximum magnetic flux correlated
with the solar cycle, this can be explained in terms of variations in the mean
umbral size. These size variations, however, are small and do not substantiate
a meaningful change in the size spectrum of the umbrae generated by the Sun.
Thus, in contrast to previous reports, the observations suggest the equilibrium
structure, as testified by the invariant size-magnetic field relationship, as
well as the mean size (i.e. strength) of sunspot umbrae do not significantly
depend on solar cycle phase.Comment: 17 pages, 6 figures. Published in Solar Physic
Thermoelastic dissipation in inhomogeneous media: loss measurements and displacement noise in coated test masses for interferometric gravitational wave detectors
The displacement noise in the test mass mirrors of interferometric
gravitational wave detectors is proportional to their elastic dissipation at
the observation frequencies. In this paper, we analyze one fundamental source
of dissipation in thin coatings, thermoelastic damping associated with the
dissimilar thermal and elastic properties of the film and the substrate. We
obtain expressions for the thermoelastic dissipation factor necessary to
interpret resonant loss measurements, and for the spectral density of
displacement noise imposed on a Gaussian beam reflected from the face of a
coated mass. The predicted size of these effects is large enough to affect the
interpretation of loss measurements, and to influence design choices in
advanced gravitational wave detectors.Comment: 42 pages, 7 figures, uses REVTeX
Technical assistance, neo-colonialism or mutual trade? The experience of an Anglo/Ukrainian/Russian social work practice learning project
Since the collapse of the Soviet Union there has been a steady stream of Western consultants ready to work in Eastern Europe and Russia and share professional and academic expertise and experience. Social work, unknown as a discrete discipline or profession in the Soviet Union, has been a growth area with funding from a variety of sources to help promote East-West partnerships.Social work theory and practice emphasises critical appraisal of policy and embraces issues of power, discrimination and oppression. Social work educators should therefore be especially alert to the complex ethical questions which these kinds of collaborations raise, and adept at finding practical solutions or workable compromises. This article explores these ethical and political issues with reference to a project to develop social work practice learning in a Russian oblast' (region). The project was an ambitious partnership of British, Ukrainian and Russian educators, involving numerous Russian social work and related agencies, and four Russian universities and colleges in one oblast'. The authors use a series of vignettes to help the reader achieve insights into these East-West transactions. The article concludes with a discussion of different interpretations of these dealings, using three prisms: technical assistance, neo-colonialism and mutual trade
Phase diagrams of the 2D t-t'-U Hubbard model from an extended mean field method
It is well-known from unrestricted Hartree-Fock computations that the 2D
Hubbard model does not have homogeneous mean field states in significant
regions of parameter space away from half filling. This is incompatible with
standard mean field theory. We present a simple extension of the mean field
method that avoids this problem. As in standard mean field theory, we restrict
Hartree-Fock theory to simple translation invariant states describing
antiferromagnetism (AF), ferromagnetism (F) and paramagnetism (P), but we use
an improved method to implement the doping constraint allowing us to detect
when a phase separated state is energetically preferred, e.g. AF and F
coexisting at the same time. We find that such mixed phases occur in
significant parts of the phase diagrams, making them much richer than the ones
from standard mean field theory. Our results for the 2D t-t'-U Hubbard model
demonstrate the importance of band structure effects.Comment: 6 pages, 5 figure
Linear response within the projection-based renormalization method: Many-body corrections beyond the random phase approximation
The explicit evaluation of linear response coefficients for interacting
many-particle systems still poses a considerable challenge to theoreticians. In
this work we use a novel many-particle renormalization technique, the so-called
projector-based renormalization method, to show how such coefficients can
systematically be evaluated. To demonstrate the prospects and power of our
approach we consider the dynamical wave-vector dependent spin susceptibility of
the two-dimensional Hubbard model and also determine the subsequent magnetic
phase diagram close to half-filling. We show that the superior treatment of
(Coulomb) correlation and fluctuation effects within the projector-based
renormalization method significantly improves the standard random phase
approximation results.Comment: 17 pages, 7 figures, revised versio
The Wicked Machinery of Government: Malta and the Problems of Continuity under the New Model Administration
This is a study focused on the early years of British rule in Malta (1800-1813). It explores the application to the island of the “new model” of colonial government, one based on direct rule from London mediated by the continuation of existing laws and institutions. Systemic deficiencies are identified. These tended to undermine the effectiveness of direct British rule. This study also reveals, in the context of legal and constitutional continuity, unresolved tensions between modernity and tradition. The political stability of the island was damaged and the possibility of continued British possession was threatened
‘Sons of athelings given to the earth’: Infant Mortality within Anglo-Saxon Mortuary Geography
FOR 20 OR MORE YEARS early Anglo-Saxon archaeologists have believed children are underrepresented in the cemetery evidence. They conclude that excavation misses small bones, that previous attitudes to reporting overlook the very young, or that infants and children were buried elsewhere. This is all well and good, but we must be careful of oversimplifying compound social and cultural responses to childhood and infant mortality. Previous approaches have offered methodological quandaries in the face of this under-representation. However, proportionally more infants were placed in large cemeteries and sometimes in specific zones. This trend is statistically significant and is therefore unlikely to result entirely from preservation or excavation problems. Early medieval cemeteries were part of regional mortuary geographies and provided places to stage events that promoted social cohesion across kinship systems extending over tribal territories. This paper argues that patterns in early Anglo-Saxon infant burial were the result of female mobility. Many women probably travelled locally to marry in a union which reinforced existing social networks. For an expectant mother, however, the safest place to give birth was with experience women in her maternal home. Infant identities were affected by personal and legal association with their mother’s parental kindred, so when an infant died in childbirth or months and years later, it was their mother’s identity which dictated burial location. As a result, cemeteries central to tribal identities became places to bury the sons and daughters of a regional tribal aristocracy
Hole dynamics in noble metals
We present a detailed analysis of hole dynamics in noble metals (Cu and Au),
by means of first-principles many-body calculations. While holes in a
free-electron gas are known to live shorter than electrons with the same
excitation energy, our results indicate that d-holes in noble metals exhibit
longer inelastic lifetimes than excited sp-electrons, in agreement with
experiment. The density of states available for d-hole decay is larger than
that for the decay of excited electrons; however, the small overlap between d-
and sp-states below the Fermi level increases the d-hole lifetime. The impact
of d-hole dynamics on electron-hole correlation effects, which are of relevance
in the analysis of time-resolved two-photon photoemission experiments, is also
addressed.Comment: 4 pages, 2 figures, to appear in Phys. Rev. Let
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