337 research outputs found
Kondo Temperature in Multilevel Quantum Dots
We develop a general method to evaluate the Kondo temperature in a multilevel
quantum dot that is weakly coupled to conducting leads. Our theory reveals that
the Kondo temperature is strongly enhanced when the intradot energy-level
spacing is comparable to or smaller than the charging energy. We propose an
experiment to test our result, which consists of measuring the size-dependence
of the Kondo temperature.Comment: 4 pages, 1 figure and supplementary material. Revised and improved
version, to appear in Phys. Rev. Let
Resonant Scattering and Recombination in CAL 87
The eclipsing supersoft X-ray binary CAL 87 has been observed with Chandra on
August 13/14, 2001 for nearly 100 ksec, covering two full orbital cycles and
three eclipses. The shape of the eclipse light curve derived from the
zeroth-order photons indicates that the size of the X-ray emission region is
about 1.5 solar radii. The ACIS/LETG spectrum is completely dominated by
emission lines without any noticeable continuum. The brightest emission lines
are significantly redshifted and double-peaked, suggestive of emanating in a
2000 km/s wind. We model the X-ray spectrum by a mixture of recombination and
resonant scattering. This allows us to deduce the temperature and luminosity of
the ionizing source to be kT = 50-100 eV and L_X = 5E37 erg/s.Comment: To appear in Proceedings of IAU Coll. 194 "Compact binaries in the
Galaxy and beyond" (Rev. Mex. A&A Conf. Series), eds. G. Tovmassian and E.
Sio
El yacimiento chatelperroniense al aire libre de Aranbaltza (Barrika, Euskadi)
Se presentan los materiales procedentes de un nuevo yacimiento al aire libre localizado en la costa de Bizkaia. Éste fue localizado como resultado de unas obras de saneamiento por lo que los materiales recuperados están desprovistos de un contexto arqueológico preciso. Aun así un análisis tecnológico y tipológico ha permitido valorar la unidad del conjunto proponiendo la adscripción del grueso del material al Chatelperroniense. Este hallazgo abre nuevas posibilidades para el conocimiento sobre este periodo en la región Cantábrica ya que supondría la primera evidencia de un hábitat al aire libre semejante a los excavados en torno a Bayona
Soliton Solutions with Real Poles in the Alekseev formulation of the Inverse-Scattering method
A new approach to the inverse-scattering technique of Alekseev is presented
which permits real-pole soliton solutions of the Ernst equations to be
considered. This is achieved by adopting distinct real poles in the scattering
matrix and its inverse. For the case in which the electromagnetic field
vanishes, some explicit solutions are given using a Minkowski seed metric. The
relation with the corresponding soliton solutions that can be constructed using
the Belinskii-Zakharov inverse-scattering technique is determined.Comment: 8 pages, LaTe
Development of thermally formed glass optics for astronomical hard x-ray telescopes
The next major observational advance in hard X-ray/soft gamma-ray astrophysics will come with the implementation of telescopes capable of focusing 10-200 keV radiation. Focusing allows high signal-to-noise imaging and spectroscopic observations of many sources in this band for the first time. The recent development of depth-graded multilayer coatings has made the design of telescopes for this bandpass practical, however the ability to manufacture inexpensive substrates with appropriate surface quality and figure to achieve sub-arcminute performance has remained an elusive goal. In this paper, we report on new, thermally-formed glass micro-sheet optics capable of meeting the requirements of the next-generation of astronomical hard X-ray telescopes
Interplay between Symmetric Exchange Anisotropy, Uniform Dzyaloshinskii-Moriya Interaction and Magnetic Fields in the Phase Diagram of Quantum Magnets and Superconductors
We theoretically study the joint influence of uniform Dzyaloshinskii-Moriya
(DM) interactions, symmetric exchange anisotropy (with its axis parallel to the
DM vector) and arbitrarily oriented magnetic fields on one-dimensional spin 1/2
antiferromagnets. We show that the zero-temperature phase diagram contains
three competing phases: (i) an antiferromagnet with Neel vector in the plane
spanned by the DM vector and the magnetic field, (ii) a {\em dimerized}
antiferromagnet with Neel vector perpendicular to both the DM vector and the
magnetic field, and (iii) a gapless Luttinger liquid. Phase (i) is destroyed by
a small magnetic field component along the DM vector and is furthermore
unstable beyond a critical value of easy-plane anisotropy, which we estimate
using Abelian and non-Abelian bosonization along with perturbative
renormalization group. We propose a mathematical equivalent of the spin model
in a one-dimensional Josephson junction (JJ) array located in proximity to a
bulk superconductor.
We discuss the analogues of the magnetic phases in the superconducting
context and comment on their experimental viability.Comment: 20 pages, 16 figures; submitted to Phys. Rev.
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