777 research outputs found
Long range correlations in the non-equilibrium quantum relaxation of a spin chain
We consider the non-stationary quantum relaxation of the Ising spin chain in
a transverse field of strength h. Starting from a homogeneously magnetized
initial state the system approaches a stationary state by a process possessing
quasi long range correlations in time and space, independent of the value of
. In particular the system exhibits aging (or lack of time translational
invariance on intermediate time scales) although no indications of coarsening
are present.Comment: 4 pages RevTeX, 2 eps-figures include
Criteria for the diagnosis of corticobasal degeneration
Current criteria for the clinical diagnosis of pathologically confirmed corticobasal degeneration (CBD) no longer reflect the expanding understanding of this disease and its clinicopathologic correlations. An international consortium of behavioral neurology, neuropsychology, and movement disorders specialists developed new criteria based on consensus and a systematic literature review. Clinical diagnoses (early or late) were identified for 267 nonoverlapping pathologically confirmed CBD cases from published reports and brain banks. Combined with consensus, 4 CBD phenotypes emerged: corticobasal syndrome (CBS), frontal behavioral-spatial syndrome (FBS), nonfluent/agrammatic variant of primary progressive aphasia (naPPA), and progressive supranuclear palsy syndrome (PSPS). Clinical features of CBD cases were extracted from descriptions of 209 brain bank and published patients, providing a comprehensive description of CBD and correcting common misconceptions. Clinical CBD phenotypes and features were combined to create 2 sets of criteria: more specific clinical research criteria for probable CBD and broader criteria for possible CBD that are more inclusive but have a higher chance to detect other tau-based pathologies. Probable CBD criteria require insidious onset and gradual progression for at least 1 year, age at onset ≥50 years, no similar family history or known tau mutations, and a clinical phenotype of probable CBS or either FBS or naPPA with at least 1 CBS feature. The possible CBD category uses similar criteria but has no restrictions on age or family history, allows tau mutations, permits less rigorous phenotype fulfillment, and includes a PSPS phenotype. Future validation and refinement of the proposed criteria are needed
The quantum phase transition of itinerant helimagnets
We investigate the quantum phase transition of itinerant electrons from a
paramagnet to a state which displays long-period helical structures due to a
Dzyaloshinskii instability of the ferromagnetic state. In particular, we study
how the self-generated effective long-range interaction recently identified in
itinerant quantum ferromagnets is cut-off by the helical ordering. We find that
for a sufficiently strong Dzyaloshinskii instability the helimagnetic quantum
phase transition is of second order with mean-field exponents. In contrast, for
a weak Dzyaloshinskii instability the transition is analogous to that in
itinerant quantum ferromagnets, i.e. it is of first order, as has been observed
in MnSi.Comment: 5 pages RevTe
Non-Extremal D-instantons and the AdS/CFT Correspondence
We investigate non-extremal D-instantons in an asymptotically background and the role they play in the correspondence.
We find that the holographic dual operators of non-extremal D-instanton
configurations do not correspond to self-dual Yang-Mills instantons, and we
compute explicitly the deviation from self-duality. Furthermore, a class of
non-extremal D-instantons yield Euclidean axionic wormhole solutions with two
asymptotic boundaries. After Wick rotating, this provides a playground for
investigating holography in the presence of cosmological singularities in a
closed universe.Comment: 30 pages, 3 figure
Bilingualism, social cognition and executive functions:A tale of chickens and eggs
AbstractThe influence of bilingualism on cognitive functioning is currently a topic of intense scientific debate. The strongest evidence for a cognitive benefit of bilingualism has been demonstrated in executive functions. However, the causal direction of the relationship remains unclear: does learning other languages improve executive functions or are people with better executive abilities more likely to become bilingual?To address this, we examined 90 male participants of the Lothian Birth Cohort 1936; 26 were bilingual, 64 monolingual. All participants underwent an intelligence test at age 11 years and were assessed on a wide range of executive and social cognition tasks at age 74. The only notable differences between both groups were found for the Simon Effect (which indexes stimulus-response conflict resolution; β=−.518, p=0.025) and a trend effect for the Faux Pas task (a measure of complex theory of mind; ToM, β=0.432, p=0.060). Controlling for the influence of childhood intelligence, parental and own social class significantly attenuated the bilingual advantage on the Faux Pas test (β=0.058, p=0.816), whereas the Simon task advantage remained (β=−.589, p=0.049).We find some weak evidence that the relationship between bilingualism and cognitive functions may be selective and bi-directional. Pre-existing cognitive and social class differences from childhood may influence both ToM ability in older age and the likelihood of learning another language; yet, bilingualism does not appear to independently contribute to Faux Pas score. Conversely, learning a second language is related to better conflict processing, irrespective of initial childhood ability or social class
Review of AdS/CFT Integrability, Chapter IV.3: N=6 Chern-Simons and Strings on AdS4xCP3
We review the duality and integrability of N=6 superconformal Chern-Simons
theory in three dimensions and IIA superstring theory on the background
AdS4xCP3. We introduce both of these models and describe how their degrees of
freedom are mapped to excitations of a long-range integrable spin-chain.
Finally, we discuss the properties of the Bethe equations, the S-matrix and the
algebraic curve that are special to this correspondence and differ from the
case of N=4 SYM theory and strings on AdS5xS5.Comment: 22 pages, see also overview article arXiv:1012.3982, v2: references
to other chapters updated, v3: references added, v4: brief discussion of
giant magnons added, further minor changes, published version, v5: union of
v3 and v4 because changes made in v3 were accidentally lost in v
Metamorphosis of plasma turbulence-shear flow dynamics through a transcritical bifurcation
The structural properties of an economical model for a confined plasma
turbulence governor are investigated through bifurcation and stability
analyses. A close relationship is demonstrated between the underlying
bifurcation framework of the model and typical behavior associated with low- to
high-confinement transitions such as shear flow stabilization of turbulence and
oscillatory collective action. In particular, the analysis evinces two types of
discontinuous transition that are qualitatively distinct. One involves
classical hysteresis, governed by viscous dissipation. The other is
intrinsically oscillatory and non-hysteretic, and thus provides a model for the
so-called dithering transitions that are frequently observed. This
metamorphosis, or transformation, of the system dynamics is an important late
side-effect of symmetry-breaking, which manifests as an unusual non-symmetric
transcritical bifurcation induced by a significant shear flow drive.Comment: 17 pages, revtex text, 9 figures comprised of 16 postscript files.
Submitted to Phys. Rev.
A limiting velocity for quarkonium propagation in a strongly coupled plasma via AdS/CFT
We study the dispersion relations of mesons in a particular hot strongly
coupled supersymmetric gauge theory plasma. We find that at large momentum k
the dispersion relations become omega = v_0 k + a + b/k + ..., where the
limiting velocity v_0 is the same for mesons with any quantum numbers and
depends only on the ratio of the temperature to the quark mass T/m_q. We
compute a and b in terms of the meson quantum numbers and T/m_q. The limiting
meson velocity v_0 becomes much smaller than the speed of light at temperatures
below but close to T_diss, the temperature above which no meson bound states at
rest in the plasma are found. From our result for v_0, we find that the
temperature above which no meson bound states with velocity v exist is
T_diss(v) \simeq (1-v^2)^(1/4) T_diss, up to few percent corrections.We thus
confirm by direct calculation of meson dispersion relations a result inferred
indirectly in previous work via analysis of the screening length between a
static quark and antiquark in a moving plasma. Although we do not do our
calculations in QCD, we argue that the qualitative features of the dispersion
relation we compute, including in particular the relation between dissociation
temperature and meson velocity, may apply to bottomonium and charmonium mesons
propagating in the strongly coupled plasma of QCD. We discuss how our results
can contribute to understanding quarkonium physics in heavy ion collisions.Comment: 57 pages, 12 figures; references adde
Spectral evolution in (Ca,Sr)RuO_3 near the Mott-Hubbard transition
We investigated the optical properties of (Ca,Sr)RuO_3 films on the
borderline of a metal-insulator (M-I) transition. Our results show all of the
predicted characteristics for a metallic Mott-Hubbard system, including (i) a
mass enhancement in dc-limit, (ii) an U/2 excitation, and (iii) an U
excitation. Also, a self-consistency is found within the
Gutzwiller-Brinkman-Rice picture for the Mott transition. Our finding displays
that electron correlation should be important even in 4d materials.Comment: REVTEX 4 pages, 5 EPS figures, submitted to Phys. Rev. Let
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