4,842 research outputs found
Fusion of implementers for spinors on the circle
We consider the space of odd spinors on the circle, and a decomposition into
spinors supported on either the top or on the bottom half of the circle. If an
operator preserves this decomposition, and acts on the bottom half in the same
way as a second operator acts on the top half, then the fusion of both
operators is a third operator acting on the top half like the first, and on the
bottom half like the second. Fusion restricts to the Banach Lie group of
restricted orthogonal operators, which supports a central extension of
implementers on a Fock space. In this article, we construct a lift of fusion to
this central extension. Our construction uses Tomita-Takesaki theory for the
Clifford-von Neumann algebras of the decomposed space of spinors. Our
motivation is to obtain an operator-algebraic model for the basic central
extension of the loop group of the spin group, on which the fusion of
implementers induces a fusion product in the sense considered in the context of
transgression and string geometry. In upcoming work we will use this model to
construct a fusion product on a spinor bundle on the loop space of a string
manifold, completing a construction proposed by Stolz and Teichner.Comment: 49 page
Universal scaling dependence of QCD energy loss from data driven studies
In this paper we study the energy loss of jets in the QGP via the nuclear
modification factor for unidentified particles at high
() in and out of the reaction plane
of the collision. We argue that at such a high there are no
genuine flow effects and, assuming that the energy loss is only sensitive to
initial characteristics such as the density and geometry, find that
depends linearly on the (RMS) length extracted from Glauber
simulations. Furthermore we observe that for different centrality classes the
density dependence of the energy loss enters as the square root of the charged
particle multiplicity normalized to the initial overlap area. The energy loss
extracted for RHIC and LHC data from the is found to exhibit
a universal behavior.Comment: 15 pages, 5 figures, version to be published in Phys. Rev.
A two-scale Stefan problem arising in a model for tree sap exudation
The study of tree sap exudation, in which a (leafless) tree generates
elevated stem pressure in response to repeated daily freeze-thaw cycles, gives
rise to an interesting multi-scale problem involving heat and multiphase
liquid/gas transport. The pressure generation mechanism is a cellular-level
process that is governed by differential equations for sap transport through
porous cell membranes, phase change, heat transport, and generation of osmotic
pressure. By assuming a periodic cellular structure based on an appropriate
reference cell, we derive an homogenized heat equation governing the global
temperature on the scale of the tree stem, with all the remaining physics
relegated to equations defined on the reference cell. We derive a corresponding
strong formulation of the limit problem and use it to design an efficient
numerical solution algorithm. Numerical simulations are then performed to
validate the results and draw conclusions regarding the phenomenon of sap
exudation, which is of great importance in trees such as sugar maple and a few
other related species. The particular form of our homogenized temperature
equation is obtained using periodic homogenization techniques with two-scale
convergence, which we investigate theoretically in the context of a simpler
two-phase Stefan-type problem corresponding to a periodic array of melting
cylindrical ice bars with a constant thermal diffusion coefficient. For this
reduced model, we prove results on existence, uniqueness and convergence of the
two-scale limit solution in the weak form, clearly identifying the missing
pieces required to extend the proofs to the fully nonlinear sap exudation
model. Numerical simulations of the reduced equations are then compared with
results from the complete sap exudation model.Comment: 35 pages, 8 figures. arXiv admin note: text overlap with
arXiv:1411.303
Rohstoffspekulation und Nahrungsmittelmarkt
Es wird wissenschaftlich kontrovers diskutiert, ob kausal schlüssige und empirisch robuste Befunde für die Beeinflussung der "realen" Lebensmittelpreise durch Spekulanten vorliegen. Die korrelative Koinzidenz von ansteigender Terminmarktspekulation und einem steigenden Preisniveau lässt auf den ersten Blick einen kausalen Zusammenhang logisch erscheinen. Die Auswertung von wissenschaftlicher Literatur sowie eine eigens durchgeführte Analyse im vorliegenden Beitrag können die Gedankenkette der Spekulationsgegner jedoch nicht bestätigen. Nach aktuellem Stand der Forschung kann die Annahme nicht erhärtet werden, dass die erhöhte Terminmarktspekulation das Niveau und die Volatilität der Agrarrohstoffpreise hat signifikant ansteigen lassen.The existence of causal and empirical robust findings for the speculator's impact on food prices is an omnipresent issue in the academic discussion. The correlative coincidence of increasing speculative activity on the futures market and rising food prices make a causal relationship appear consistent. The review of academic literature and studies as well as a specific analysis in this paper cannot confirm this position. In fact, the findings cast considerable doubt on the belief that higher speculator's activity caused the rise in level and volatility of food prices
Deficits in high- (>60 Hz) gamma-band oscillations during visual processing in schizophrenia
Current theories of the pathophysiology of schizophrenia have focused on abnormal temporal coordination of neural activity. Oscillations in the gamma-band range (>25 Hz) are of particular interest as they establish synchronization with great precision in local cortical networks. However, the contribution of high gamma (>60 Hz) oscillations toward the pathophysiology is less established. To address this issue, we recorded magnetoencephalographic (MEG) data from 16 medicated patients with chronic schizophrenia and 16 controls during the perception of Mooney faces. MEG data were analysed in the 25–150 Hz frequency range. Patients showed elevated reaction times and reduced detection rates during the perception of upright Mooney faces while responses to inverted stimuli were intact. Impaired processing of Mooney faces in schizophrenia patients was accompanied by a pronounced reduction in spectral power between 60–120 Hz (effect size: d = 1.26) which was correlated with disorganized symptoms (r = −0.72). Our findings demonstrate that deficits in high gamma-band oscillations as measured by MEG are a sensitive marker for aberrant cortical functioning in schizophrenia, suggesting an important aspect of the pathophysiology of the disorder
- …