106 research outputs found
Conformal anomaly as a source of soft photons in heavy ion collisions
We introduce a novel photon production mechanism stemming from the conformal
anomaly of QCDxQED and the existence of strong (electro)magnetic fields in
heavy ion collisions. Using the hydrodynamical description of the bulk modes of
QCD plasma, we show that this mechanism leads to the photon production yield
that is comparable to the yield from conventional sources. This mechanism also
provides a significant positive contribution to the azimuthal anisotropy of
photons, , as well as to the radial "flow". We compare our results to the
data from the PHENIX Collaboration.Comment: 5 pages, 3 figures; version accepted to Phys. Rev. Let
A Gauge-Gravity Relation in the One-loop Effective Action
We identify an unusual new gauge-gravity relation: the one-loop effective
action for a massive spinor in 2n dimensional AdS space is expressed in terms
of precisely the same function [a certain multiple gamma function] as the
one-loop effective action for a massive charged scalar in 4n dimensions in a
maximally symmetric background electromagnetic field [one for which the
eigenvalues of F_{\mu\nu} are maximally degenerate, corresponding in 4
dimensions to a self-dual field, equivalently to a field of definite helicity],
subject to the identification F^2 \Lambda, where \Lambda is the
gravitational curvature. Since these effective actions generate the low energy
limit of all one-loop multi-leg graviton or gauge amplitudes, this implies a
nontrivial gauge-gravity relation at the non-perturbative level and at the
amplitude level.Comment: 6 page
Inhomogeneous Condensates in the Thermodynamics of the Chiral NJL_2 model
We analyze the thermodynamical properties, at finite density and nonzero
temperature, of the (1+1)-dimensional chiral Gross-Neveu model (the NJL_2
model), using the exact inhomogeneous (crystalline) condensate solutions to the
gap equation. The continuous chiral symmetry of the model plays a crucial role,
and the thermodynamics leads to a broken phase with a periodic spiral
condensate, the "chiral spiral", as a thermodynamically preferred limit of the
more general "twisted kink crystal" solution of the gap equation. This
situation should be contrasted with the Gross-Neveu model, which has a discrete
chiral symmetry, and for which the phase diagram has a crystalline phase with a
periodic kink crystal. We use a combination of analytic, numerical and
Ginzburg-Landau techniques to study various parts of the phase diagram.Comment: 28 pages, 13 figure
Self-consistent crystalline condensate in chiral Gross-Neveu and Bogoliubov-de Gennes systems
We derive a new exact self-consistent crystalline condensate in the 1+1
dimensional chiral Gross-Neveu model. This also yields a new exact crystalline
solution for the one dimensional Bogoliubov-de Gennes equations and the
Eilenberger equation of semiclassical superconductivity. We show that the
functional gap equation can be reduced to a solvable nonlinear equation, and
discuss implications for the temperature-chemical potential phase diagram.Comment: 5 pages, 5 figures; v2 minor corrections, version for PR
Gross-Neveu Models, Nonlinear Dirac Equations, Surfaces and Strings
Recent studies of the thermodynamic phase diagrams of the Gross-Neveu model
(GN2), and its chiral cousin, the NJL2 model, have shown that there are phases
with inhomogeneous crystalline condensates. These (static) condensates can be
found analytically because the relevant Hartree-Fock and gap equations can be
reduced to the nonlinear Schr\"odinger equation, whose deformations are
governed by the mKdV and AKNS integrable hierarchies, respectively. Recently,
Thies et al have shown that time-dependent Hartree-Fock solutions describing
baryon scattering in the massless GN2 model satisfy the Sinh-Gordon equation,
and can be mapped directly to classical string solutions in AdS3. Here we
propose a geometric perspective for this result, based on the generalized
Weierstrass spinor representation for the embedding of 2d surfaces into 3d
spaces, which explains why these well-known integrable systems underlie these
various Gross-Neveu gap equations, and why there should be a connection to
classical string theory solutions. This geometric viewpoint may be useful for
higher dimensional models, where the relevant integrable hierarchies include
the Davey-Stewartson and Novikov-Veselov systems.Comment: 27 pages, 1 figur
A Twisted Kink Crystal in the Chiral Gross-Neveu model
We present the detailed properties of a self-consistent crystalline chiral
condensate in the massless chiral Gross-Neveu model. We show that a suitable
ansatz for the Gorkov resolvent reduces the functional gap equation, for the
inhomogeneous condensate, to a nonlinear Schr\"odinger equation, which is
exactly soluble. The general crystalline solution includes as special cases all
previously known real and complex condensate solutions to the gap equation.
Furthermore, the associated Bogoliubov-de Gennes equation is also soluble with
this inhomogeneous chiral condensate, and the exact spectral properties are
derived. We find an all-orders expansion of the Ginzburg-Landau effective
Lagrangian and show how the gap equation is solved order-by-order.Comment: 28 pages, 13 figs; v2: new appendix on Eilenberger eq and refs;
version in PR
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Effect of powder metallurgy synthesis parameters for pure aluminium on resultant mechanical properties
In this work, pure aluminium powders of different average particle size were compacted, sintered into discs and tested for mechanical strength at different strain rates. The effects of average particle size (15, 19, and 35 μm), sintering rate (5 and 20 °C/min) and sample indentation test speed (0.5, 0.7, and 1.0 mm/min) were examined. A compaction pressure of 332 MPa with a holding time of six minutes was used to produce the green compacted discs. The consolidated green specimens were sintered with a holding time of 4 h, a temperature of 600 °C in an argon atmosphere. The resulting sintered samples contained higher than 85% density. The mechanical properties and microstructure were characterized using indentation strength measurement tests and SEM analysis respectively. After sintering, the aluminium grain structure was observed to be of uniform size within the fractured samples. The indentation test measurements showed that for the same sintering rate, the 35 μm powder particle size provided the highest radial and tangential strength while the 15 μm powder provided the lowest strengths. Another important finding from this work was the increase in sintered sample strength which was achieved using the lower sinter heating rate, 5 °C/min. This resulted in a tangential stress value of 365 MPa which was significantly higher than achieved, 244 MPa, using the faster sintering heating rate, 20 °C/min
Dermacentor reticulatus: a vector on the rise
Dermacentor reticulatus is a hard tick species with extraordinary biological features. It has a high reproduction rate, a rapid developmental cycle, and is also able to overcome years of unfavourable conditions. Dermacentor reticulatus can survive under water for several months and is cold-hardy even compared to other tick species. It has a wide host range: over 60 different wild and domesticated hosts are known for the three active developmental stages. Its high adaptiveness gives an edge to this tick species as shown by new data on the emergence and establishment of D. reticulatus populations throughout Europe. The tick has been the research focus of a growing number of scientists, physicians and veterinarians. Within the Web of Science database, more than a fifth of the over 700 items published on this species between 1897 and 2015 appeared in the last three years (2013–2015). Here we attempt to synthesize current knowledge on the systematics, ecology, geographical distribution and recent spread of the species and to highlight the great spectrum of possible veterinary and public health threats it poses. Canine babesiosis caused by Babesia canis is a severe leading canine vector-borne disease in many endemic areas. Although less frequently than Ixodes ricinus, D. reticulatus adults bite humans and transmit several Rickettsia spp., Omsk haemorrhagic fever virus or Tick-borne encephalitis virus. We have not solely collected and reviewed the latest and fundamental scientific papers available in primary databases but also widened our scope to books, theses, conference papers and specialists colleagues’ experience where needed. Besides the dominant literature available in English, we also tried to access scientific literature in German, Russian and eastern European languages as well. We hope to inspire future research projects that are necessary to understand the basic life-cycle and ecology of this vector in order to understand and prevent disease threats. We conclude that although great strides have been made in our knowledge of the eco-epidemiology of this species, several gaps still need to be filled with basic research, targeting possible reservoir and vector roles and the key factors resulting in the observed geographical spread of D. reticulatus. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (doi:10.1186/s13071-016-1599-x) contains supplementary material, which is available to authorized users
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