2,336 research outputs found
Silicon surface with giant spin-splitting
We demonstrate the induction of a giant Rashba-type spin-splitting on a
semiconducting substrate by means of a Bi trimer adlayer on a Si(111) wafer.
The in-plane inversion symmetry is broken so that the in-plane potential
gradient induces a giant spin-splitting with a Rashba energy of about 140 meV,
which is more than an order of magnitude larger than what has previously been
reported for any semiconductor heterostructure. The separation of the
electronic states is larger than their lifetime broadening, which has been
directly observed with angular resolved photoemission spectroscopy. The
experimental results are confirmed by relativistic first-principles
calculations. We envision important implications for basic phenomena as well as
for the semiconductor based technology
Micromechanical High-doses Radiation Sensor with Bossed Membrane and Interferometry Optical Read-out
AbstractThe silicon-glass MEMS high-doses radiation sensor with in situ detection, so far not possible in the field of detection of doses above 10 kGy, has been presented. The sensor consists of a chamber filled with the high density polyethylene (HDPE) and a silicon bossed membrane. The radiolysis product of HDPE increases the pressure inside the chamber causing the deflection of the membrane, which is proportional to the pressure, thus to radiation dose. The sensor has been irradiated with high energy electron beam and shows good detectability for 10-40 kGy. The deflection of the membrane has been detected by optical interferometer
Hamiltonian Noether theorem for gauge systems and two time physics
The Noether theorem for Hamiltonian constrained systems is revisited. In
particular, our review presents a novel method to show that the gauge
transformations are generated by the conserved quantities associated with the
first class constraints. We apply our results to the relativistic point
particle, to the Friedberg et al. model and, with special emphasis, to two time
physics.Comment: 20 pages, Latex, references added, the "massless" sense of (87) is
clarifie
Electromagnetic waves in NUT space: Solutions to the Maxwell equations
In this paper, using the Newman-Penrose formalism, we find the Maxwell
equations in NUT space and after separation into angular and radial components
solve them analytically. All the angular equations are solved in terms of
Jaccobi polynomials. The radial equations are transformed into Hypergeometric
and Heun's equations with the right hand sides including terms of different
order in the frequency of the perturbation which allow solutions in the
expansion of this parameter.Comment: 19 pages, Revtex format, Minor changes including an extention of the
discussion and typos correction, (Extended version of the article presented
to the GR16 conference, July 15-21 2001, Durban, South Africa
Quantum States of Topologically Massive Electrodynamics and Gravity
The free quantum states of topologically massive electrodynamics and gravity
in 2+1 dimensions, are explicitly found. It is shown that in both theories the
states are described by infrared-regular polarization tensors containing a
regularization phase which depends on the spin. This is done by explicitly
realizing the quantum algebra on a functional Hilbert space and by finding the
Wightman function to define the scalar product on such a Hilbert space. The
physical properties of the states are analyzed defining creation and
annihilation operators.
For both theories, a canonical and covariant quantization procedure is
developed. The higher order derivatives in the gravitational lagrangian are
treated by means of a preliminary Dirac procedure.
The closure of the Poincar\'e algebra is guaranteed by the
infrared-finiteness of the states which is related to the spin of the
excitations through the regularization phase. Such a phase may have interesting
physical consequences.Comment: 21 page, latex, no figure
Atom laser dynamics in a tight-waveguide
We study the transient dynamics that arise during the formation of an atom
laser beam in a tight waveguide. During the time evolution the density profile
develops a series of wiggles which are related to the diffraction in time
phenomenon. The apodization of matter waves, which relies on the use of smooth
aperture functions, allows to suppress such oscillations in a time interval,
after which there is a revival of the diffraction in time. The revival time
scale is directly related to the inverse of the harmonic trap frequency for the
atom reservoir.Comment: 6 pages, 5 figures, to be published in the Proceedings of the 395th
WE-Heraeus Seminar on "Time Dependent Phenomena in Quantum Mechanics ",
organized by T. Kramer and M. Kleber (Blaubeuren, Germany, September 2007
El yacimiento de Mas Castellar de Pontós y el comercio del cereal ibérico en la zona de Emporion y Rhode (SS.IV-II a.C.)
This paper deals with somne recents findings which suggest that in the last phase (siglos IV-II a. C.) the site of Mas Castella (PontĂłs) was a sanctuary dedicated to DemĂ©ter and Kore which was surrounder by a field of silos. The findings of a cultual structure with an Hellenistic altar made of Penthelic marble and of a big votive deposit within a silo point to this possibility. This deposit allowed us to understand the ritual meaning of some other tindings within si los which were made in former excavations.Se presentan nuevos hallazgos en el yacimiento que permiten identificar en su Ăşltima fase (siglos IV-II a. C.) un posible santuario de DemĂ©ter y Core rodeado de un campo de silos. Apuntan en este sentido el hallazgo de una estructura de culto incluyendo un altar helenĂstico en mármol pentĂ©lico y un gran depĂłsito votivo localizado en el interior de un silo. Este depĂłsito permite identificar el significado ritual de otros hallazgos anteriores en el interior de silos
The giant planet orbiting the cataclysmic binary DP Leonis
Planets orbiting post-common envelope binaries provide fundamental
information on planet formation and evolution, especially for the yet nearly
unexplored class of circumbinary planets. We searched for such planets in \odp,
an eclipsing short-period binary, which shows long-term eclipse-time
variations. Using published, reanalysed, and new mid-eclipse times of the white
dwarf in DP\,Leo, obtained between 1979 and 2010, we find agreement with the
light-travel-time effect produced by a third body in an elliptical orbit. In
particular, the measured binary period in 2009/2010 and the implied radial
velocity coincide with the values predicted for the motion of the binary and
the third body around the common center of mass. The orbital period, semi-major
axis, and eccentricity of the third body are P_c = 28.0 +/- 2.0 yrs, a_c = 8.2
+/- 0.4 AU, and e_c = 0.39 +/- 0.13. Its mass of M_c sin(i_c) = 6.1 +/- 0.5 M_J
qualifies it as a giant planet. It formed either as a first generation object
in a protoplanetary disk around the original binary or as a second generation
object in a disk formed in the common envelope shed by the progenitor of the
white dwarf. Even a third generation origin in matter lost from the present
accreting binary can not be entirely excluded. We searched for, but found no
evidence for a fourth body.Comment: Accepted by A&
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