25,900 research outputs found
Random Aharonov-Bohm vortices and some funny families of integrals
A review of the random magnetic impurity model, introduced in the context of
the integer Quantum Hall effect, is presented. It models an electron moving in
a plane and coupled to random Aharonov-Bohm vortices carrying a fraction of the
quantum of flux. Recent results on its perturbative expansion are given. In
particular, some funny families of integrals show up to be related to the
Riemann and .Comment: 10 page
Phase transitions and the internal noise structure of nonlinear Schr\"odi nger equation solitons
We predict phase-transitions in the quantum noise characteristics of systems
described by the quantum nonlinear Schr\"odinger equation, showing them to be
related to the solitonic field transition at half the fundamental soliton
amplitude. These phase-transitions are robust with respect to Raman noise and
scattering losses. We also describe the rich internal quantum noise structure
of the solitonic fields in the vicinity of the phase-transition. For optical
coherent quantum solitons, this leads to the prediction that eliminating the
peak side-band noise due to the electronic nonlinearity of silica fiber by
spectral filtering leads to the optimal photon-number noise reduction of a
fundamental soliton.Comment: 10 pages, 5 figure
High-magnetic field phase diagram and failure of magnetic Gr\"uneisen scaling in LiFePO
We report the magnetic phase diagram of single-crystalline LiFePO in
magnetic fields up to 58~T and present a detailed study of magneto-elastic
coupling by means of high-resolution capacitance dilatometry. Large anomalies
at \tn\ in the thermal expansion coefficient imply pronounced
magneto-elastic coupling. Quantitative analysis yields the magnetic Gr\"uneisen
parameter ~mol/J. The positive
hydrostatic pressure dependence ~K/GPa is dominated
by uniaxial effects along the -axis. Failure of Gr\"uneisen scaling below
~K, i.e., below the peak temperature in the magneto-electric
coupling coefficient [\onlinecite{toft2015anomalous}], implies several
competing degrees of freedom and indicates relevance of recently observed
hybrid excitations~[\onlinecite{yiu2017hybrid}]. A broad and strongly
magnetic-field-dependent anomaly in in this temperature regime
highlight the relevance of structure changes. Upon application of magnetic
fields -axis, a pronounced jump in the magnetisation implies
spin-reorientation at ~T as well as a precursing phase at 29~T
and ~K. In a two-sublattice mean-field model, the saturation field
~T enables the determination of the effective
antiferromagnetic exchange interaction ~meV as well as
the anisotropies ~meV and ~meV
The X-ray coronae of the two brightest galaxies in the Coma cluster
We use deep Chandra X-ray Observatory observations to examine the coronae of
the two brightest cluster galaxies in the Coma cluster of galaxies, NGC 4874
and NGC 4889. We find that NGC 4889 hosts a central depression in X-ray surface
brightness consistent with a cavity or pair of cavities of radius 0.6 kpc. If
the central cavity is associated with an AGN outburst and contains relativistic
material, its enthalpy should be around 5x10^55 erg. The implied heating power
of this cavity would be around an order of magnitude larger than the energy
lost by X-ray emission. It would be the smallest and youngest known cavity in a
brightest cluster galaxy and the lack of over pressuring implies heating is
still gentle. In contrast, NGC 4874 does not show any evidence for cavities,
although it hosts a well-known wide-angle-tail radio source which is visible
outside the region occupied by the X-ray corona. These two galaxies show that
AGN feedback can behave in varied ways in the same cluster environment.Comment: 11 pages, 11 figures, accepted by MNRA
Capacity of different cell types to stimulate cytotoxic T lymphocyte precursor cells in the presence of interleukin 2
Plastic-adherent cells enriched for dendritic cells (AC) were found to be among the most potent stimulator cells for the activation of cytotoxic T lymphocytes (CTL) in vitro in the presence of interleukin 2 (IL 2) and a constant second set of allogeneic stimulator cells. Concanavalin A-activated nylon wool-nonadherent spleen cells ( CNWT ), concanavalin A-activated unfractionated spleen cells ( Cspl ), and some variants of the ESb T lymphoma line were equally effective as stimulator cells, however, and provoked a substantial cytotoxic response at concentrations of 10(4) cells per culture or less. In contrast, nonactivated nylon wool-nonadherent spleen cells ( NWT ) or unfractionated spleen cells (Spl) and cells of the P815 mastocytoma, the Meth A fibrosarcoma, and the T cell lymphomas Ly 5178 Eb and ESb did not stimulate cytotoxic responses at these cell concentrations. The strong stimulatory potential of the Cspl preparation was reduced by treatment with anti-Thy-1 antibody plus complement, whereas the stimulatory activity of the AC preparation was resistant to this treatment. All cell types tested expressed class I major histocompatibility antigens. Nonactivated NWT cells, in contrast to the CNWT preparation, showed no detectable staining with anti-I-E or anti-I-A antibodies and also a slightly weaker staining with class I antisera. Experiments with the tumor cell lines revealed, however, that there was no strict correlation between stimulatory potential and density of class I alloantigens or the expression of I-E determinants. Experiments on primary cytotoxic responses in vivo gave similar results. Experiments in cultures with a single set of stimulator cells and I region-compatible responder cells indicated that AC and Cspl or CNWT also have a markedly stronger capacity than NWT to induce IL 2-dependent DNA synthesis
Better Bell Inequality Violation by Collective Measurements
The standard Bell inequality experiments test for violation of local realism
by repeatedly making local measurements on individual copies of an entangled
quantum state. Here we investigate the possibility of increasing the violation
of a Bell inequality by making collective measurements. We show that
nonlocality of bipartite pure entangled states, quantified by their maximal
violation of the Bell-Clauser-Horne inequality, can always be enhanced by
collective measurements, even without communication between the parties. For
mixed states we also show that collective measurements can increase the
violation of Bell inequalities, although numerical evidence suggests that the
phenomenon is not common as it is for pure states.Comment: 7 pages, 4 figures and 1 table; references update
Diffuse Extragalactic Background Radiation
Attenuation of high--energy gamma rays by pair--production with UV, optical
and IR background photons provides a link between the history of galaxy
formation and high--energy astrophysics. We present results from our latest
semi-analytic models (SAMs), based upon a CDM hierarchical structural
formation scenario and employing all ingredients thought to be important to
galaxy formation and evolution, as well as reprocessing of starlight by dust to
mid- and far-IR wavelengths. Our models also use results from recent
hydrodynamic galaxy merger simulations. These latest SAMs are successful in
reproducing a large variety of observational constraints such as number counts,
luminosity and mass functions, and color bimodality. We have created 2 models
that bracket the likely ranges of galaxy emissivities, and for each of these we
show how the optical depth from pair--production is affected by redshift and
gamma-ray energy. We conclude with a discussion of the implications of our
work, and how the burgeoning science of gamma-ray astronomy will continue to
help constrain cosmology.Comment: 12 pages, 8 figures, to be published in the Proceedings of the 4th
Heidelberg International Symposium on High Energy Gamma-Ray Astronomy, held
July 2008 in Heidelberg, German
Norm Optimal Iterative Learning Control with Application to Problems in Accelerator based Free Electron Lasers and Rehabilitation Robotics
This paper gives an overview of the theoretical basis of the norm optimal approach to iterative learning control followed by results that describe more recent work which has experimentally benchmarking the performance that can be achieved. The remainder of then paper then describes its actual application to a physical process and a very novel application in stroke rehabilitation
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