21,201 research outputs found
A diode device combining lateral field-effect transport and vertical tunneling in a multi-quantum-well heterostructure
The authors discuss an electronic device with asymmetric contacts to a InGaAs-InP multilayer heterostructure. Current enters via an alloyed ohmic contact into the quantum wells (QWs) and flows laterally along capacitively coupled channels. It leaves via tunneling between the layers and through a forward-biased surface Schottky contact. A step-like I-V dependence is observed and interpreted by a model calculation
Investigation of Lunar Surface Chemical Contamination by LEM Descent Engine and Associated Equipment
Lunar surface and atmospheric contamination study caused by LEM rocket exhaust and inorganic, organic, and microbiological contaminant
Asynchronous response of coupled pacemaker neurons
We study a network model of two conductance-based pacemaker neurons of
differing natural frequency, coupled with either mutual excitation or
inhibition, and receiving shared random inhibitory synaptic input. The networks
may phase-lock spike-to-spike for strong mutual coupling. But the shared input
can desynchronize the locked spike-pairs by selectively eliminating the lagging
spike or modulating its timing with respect to the leading spike depending on
their separation time window. Such loss of synchrony is also found in a large
network of sparsely coupled heterogeneous spiking neurons receiving shared
input.Comment: 11 pages, 4 figures. To appear in Phys. Rev. Let
Optimization of Gutzwiller Wavefunctions in Quantum Monte Carlo
Gutzwiller functions are popular variational wavefunctions for correlated
electrons in Hubbard models. Following the variational principle, we are
interested in the Gutzwiller parameters that minimize e.g. the expectation
value of the energy. Rewriting the expectation value as a rational function in
the Gutzwiller parameters, we find a very efficient way for performing that
minimization. The method can be used to optimize general Gutzwiller-type
wavefunctions both, in variational and in fixed-node diffusion Monte Carlo.Comment: 9 pages RevTeX with 10 eps figure
Strangeness counting in high energy collisions
The estimates of overall strange quark production in high energy e+e-, pp and
ppbar collisions by using the statistical-thermal model of hadronisation are
presented and compared with previous works. The parametrization of strangeness
suppression within the model is discussed. Interesting regularities emerge in
the strange/non-strange produced quark ratio which turns out to be fairly
constant in elementary collisions while it is twice as large in SPS heavy ion
collision.Comment: talk given at Strangeness in Quark Matter 98, submitted to J. Phys.
Chemical Evolution in the Carina Dwarf Spheroidal
We present metallicities for 487 red giants in the Carina dwarf spheroidal
(dSph) galaxy that were obtained from FLAMES low-resolution Ca triplet (CaT)
spectroscopy. We find a mean [Fe/H] of -1.91 dex with an intrinsic dispersion
of 0.25 dex, whereas the full spread in metallicities is at least one dex. The
analysis of the radial distribution of metallicities reveals that an excess of
metal poor stars resides in a region of larger axis distances. These results
can constrain evolutionary models and are discussed in the context of chemical
evolution in the Carina dSph.Comment: 3 pages, 2 figures, to be published in the proceedings of the
ESO/Arcetri-workshop on "Chemical Abundances and Mixing in Stars", 13.-17.
Sep. 2004, Castiglione della Pescaia, Italy, L. Pasquini, S. Randich (eds.
Renormalization group improved black hole space-time in large extra dimensions
By taking into account a running of the gravitational coupling constant with
an ultra violet fixed point, an improvement of classical black hole space-times
in extra dimensions is studied. It is found that the thermodynamic properties
in this framework allow for an effective description of the black hole
evaporation process. Phenomenological consequences of this approach are
discussed and the LHC discovery potential is estimated.Comment: 13 pages, 6 figure
The Chemical and Dynamical Evolution of Isolated Dwarf Galaxies
Using a suite of simulations (Governato et al. 2010) which successfully
produce bulgeless (dwarf) disk galaxies, we provide an analysis of their
associated cold interstellar media (ISM) and stellar chemical abundance
patterns. A preliminary comparison with observations is undertaken, in order to
assess whether the properties of the cold gas and chemistry of the stellar
components are recovered successfully. To this end, we have extracted the
radial and vertical gas density profiles, neutral hydrogen velocity dispersion,
and the power spectrum of structure within the ISM. We complement this analysis
of the cold gas with a brief examination of the simulations' metallicity
distribution functions and the distribution of alpha-elements-to-iron.Comment: To appear in the proceedings of the JENAM 2010 Symposium "Dwarf
Galaxies: Keys to Galaxy Formation and Evolution" (Lisbon, 9-10 September
2010), P. Papaderos, S. Recchi, G. Hensler (eds.), Springer Verlag (2011), in
pres
- …