1,265 research outputs found
Ionized gas and sources of its ionization in the Irr galaxy IC 10
IC 10 is the nearest starburst irregular galaxy remarkable for its
anomalously high number of WR stars. We report the results of an analysis of
the emission spectra of HII-regions ionized by star clusters and WR stars based
on observations made with the 6-m telescope of the Special Astrophysical
Observatory of the Russian Academy of Sciences using MPFS field spectrograph
and SCORPIO focal reducer operating in the slit spectrograph mode. We determine
the masses and ages of ionizing star clusters in the violent star-forming
region of the galaxy in terms of the new evolutionary models of emission-line
spectra of HII-regions developed by Martin-Manjon et al. (2010). We estimate
the amount of stars needed to ionize the gas in the brightest HII-region HL 111
and report new determinations of oxygen abundance in HII regions.Comment: To appear in the proceedings of the conference "A Universe of dwarf
galaxies" (Lyon, June 14-18, 2010
Spin-Polarized Electron Transport at Ferromagnet/Semiconductor Schottky Contacts
We theoretically investigate electron spin injection and spin-polarization
sensitive current detection at Schottky contacts between a ferromagnetic metal
and an n-type or p-type semiconductor. We use spin-dependent continuity
equations and transport equations at the drift-diffusion level of
approximation. Spin-polarized electron current and density in the semiconductor
are described for four scenarios corresponding to the injection or the
collection of spin polarized electrons at Schottky contacts to n-type or p-type
semiconductors. The transport properties of the interface are described by a
spin-dependent interface resistance, resulting from an interfacial tunneling
region. The spin-dependent interface resistance is crucial for achieving spin
injection or spin polarization sensitivity in these configurations. We find
that the depletion region resulting from Schottky barrier formation at a
metal/semiconductor interface is detrimental to both spin injection and spin
detection. However, the depletion region can be tailored using a doping density
profile to minimize these deleterious effects. For example, a heavily doped
region near the interface, such as a delta-doped layer, can be used to form a
sharp potential profile through which electrons tunnel to reduce the effective
Schottky energy barrier that determines the magnitude of the depletion region.
The model results indicate that efficient spin-injection and spin-polarization
detection can be achieved in properly designed structures and can serve as a
guide for the structure design.Comment: RevTex
Effective action approach and Carlson-Goldman mode in d-wave superconductors
We theoretically investigate the Carlson-Goldman (CG) mode in two-dimensional
clean d-wave superconductors using the effective ``phase only'' action
formalism. In conventional s-wave superconductors, it is known that the CG mode
is observed as a peak in the structure factor of the pair susceptibility
only just below the transition temperature T_c and only
in dirty systems. On the other hand, our analytical results support the
statement by Y.Ohashi and S.Takada, Phys.Rev.B {\bf 62}, 5971 (2000) that in
d-wave superconductors the CG mode can exist in clean systems down to the much
lower temperatures, . We also consider the manifestations of
the CG mode in the density-density and current-current correlators and discuss
the gauge independence of the obtained results.Comment: 23 pages, RevTeX4, 12 EPS figures; final version to appear in PR
Effects of Anomalous Magnetic Moment in the Quantum Motion of Neutral Particle in Magnetic and Electric Fields Produced by a Linear Source in a Conical Spacetime
In this paper we analyse the effect of the anomalous magnetic moment on the
non-relativistic quantum motion of a neutral particle in magnetic and electric
fields produced by linear sources of constant current and charge density,
respectively.Comment: 17 pages, no figur
Electrostatic self-energy and Bekenstein entropy bound in the massive Schwinger model
We obtain the electrostatic energy of two opposite charges near the horizon
of stationary black-holes in the massive Schwinger model. Besides the confining
aspects of the model, we discuss the Bekenstein entropy upper bound of a
charged object using the generalized second law. We show that despite the
massless case, in the massive Schwinger model the entropy of the black hole and
consequently the Bekenstein bound are altered by the vacuum polarization.Comment: 14 pages, accepted for publication in "Gen. Rel. Grav. (2005)
Soil-landscape and climatic relationships in the middle Miocene of the Madrid Basin
The Miocene alluvial-lacustrine sequences of the Madrid Basin, Spain, formed in highly varied landscapes. The presence of various types of palaeosols allows assessment of the effects of local and external factors onsedimentation, pedogenesis and geomorphological development. In the northern, more arid, tectonicallyactive arca, soils were weakly developed in aggrading alluvial fans, dominated by mass flows. reflecting high sedimentation rates. In more distal parts of the fans and in playa lakes calcretes and dolocretes developed: the former were associated with Mg-poor fan sediments whitc: the latter formed on Mg-rich lake clays exposed during minar lake lowstands. The nonh-east part of the basin had a less arid climate. Alluvial fans in this area were dominated by stream Aood deposits, sourced by carbonate terrains. Floodplain and freshwater lakc deposits formed in distal areas. The high local supply of calcium carbonate may have contributed to the preferential developmenl on calcretes on the fans. Both the fan and floodplain palaeosols exhibit pedofacies relationships and more mature soils developed in settings more distant from the sediment sources. Palaeosols also developed on pond and lake margin carbonates, and led to the formation of palustrine limestones. The spatial distributions and stratigraphies of palaeosols in the Madrid Basin alluvial fans suggest that soil formation was controlled by local factors. These palaeosols differ from those seen in Quatemary fans. Which are characterized by climatically induced periods of stability and instability
Vlasov-Maxwell, self-consistent electromagnetic wave emission simulations in the solar corona
1.5D Vlasov-Maxwell simulations are employed to model electromagnetic
emission generation in a fully self-consistent plasma kinetic model for the
first time in the solar physics context. The simulations mimic the plasma
emission mechanism and Larmor drift instability in a plasma thread that
connects the Sun to Earth with the spatial scales compressed appropriately. The
effects of spatial density gradients on the generation of electromagnetic
radiation are investigated. It is shown that 1.5D inhomogeneous plasma with a
uniform background magnetic field directed transverse to the density gradient
is aperiodically unstable to Larmor-drift instability. The latter results in a
novel effect of generation of electromagnetic emission at plasma frequency.
When density gradient is removed (i.e. when plasma becomes stable to
Larmor-drift instability) and a density, super-thermal, hot beam is
injected along the domain, in the direction perpendicular to the magnetic
field, plasma emission mechanism generates non-escaping Langmuir type
oscillations which in turn generate escaping electromagnetic radiation. It is
found that in the spatial location where the beam is injected, the standing
waves, oscillating at the plasma frequency, are excited. These can be used to
interpret the horizontal strips observed in some dynamical spectra. Quasilinear
theory predictions: (i) the electron free streaming and (ii) the beam long
relaxation time, in accord with the analytic expressions, are corroborated via
direct, fully-kinetic simulation. Finally, the interplay of Larmor-drift
instability and plasma emission mechanism is studied by considering
electron beam in the Larmor-drift unstable (inhomogeneous) plasma.
http://www.maths.qmul.ac.uk/~tsiklauri/movie1.mpg *
http://www.maths.qmul.ac.uk/~tsiklauri/movie2.mpg *
http://www.maths.qmul.ac.uk/~tsiklauri/movie3.mpgComment: Solar Physics (in press, the final, accepted version
Measurement of the Dalitz plot slope parameters for K- -> pi0 pi0 pi- decay using ISTRA+ detector
The Dalitz plot slope parameters g, h and k for the K- -> pi0 pi0 pi- decay
have been measured using in-flight decays detected with the ISTRA+ setup
operating in the 25 GeV negative secondary beam of the U-70 PS. About 252 K
events with four-momenta measured for the pi- and four involved photons were
used for the analysis. The values obtained g=0.627+/-0.004(stat)+/-0.010(syst),
h=0.046+/-0.004(stat)+/-0.012(syst), k=0.001+/-0.001(stat)+/-0.002(syst) are
consistent with the world averages dominated by K+ data, but have significantly
smaller errors.Comment: LaTeX, 10 pages, 8 eps-figures, update of IHEP 2002-1
Current correlators to all orders in the quark masses
The contributions to the coefficient functions of the quark and the mixed
quark-gluon condensate to mesonic correlators are calculated for the first time
to all orders in the quark masses, and to lowest order in the strong coupling
constant. Existing results on the coefficient functions of the unit operator
and the gluon condensate are reviewed. The proper factorization of short- and
long-distance contributions in the operator product expansion is discussed in
detail. It is found that to accomplish this task rigorously the operator
product expansion has to be performed in terms of non-normal-ordered
condensates. The resulting coefficient functions are improved with the help of
the renormalization group. The scale invariant combination of dimension 5
operators, including mixing with the mass operator, which is needed for the
renormalization group improvement, is calculated in the leading order.Comment: 24 pages, LateX file, TUM-T31-21/92, 1 postscript file include
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