15,614 research outputs found
A numerical study of a method for measuring the effective in situ sound absorption coefficient
The accuracy of a method [Wijnant et al., “Development and applica-
tion of a new method for the in-situ measurement of sound absorption”, ISMA 31,
Leuven, Belgium (2010).], for measurement of the effective area-averaged in situ
sound absorption coefficient is investigated. Based on a local plane wave assump-
tion, this method can be applied to sound fields for which a model is not available.
Investigations were carried out by means of finite element simulations for a typical
case. The results show that the method is a promising method for determining the
effective area-averaged in situ sound absorption coefficient in complex sound fields
Organic Single-Crystal Field-Effect Transistors
We present an overview of recent studies of the charge transport in the field
effect transistors on the surface of single crystals of organic
low-molecular-weight materials. We first discuss in detail the technological
progress that has made these investigations possible. Particular attention is
devoted to the growth and characterization of single crystals of organic
materials and to different techniques that have been developed for device
fabrication. We then concentrate on the measurements of the electrical
characteristics. In most cases, these characteristics are highly reproducible
and demonstrate the quality of the single crystal transistors. Particularly
noticeable are the small sub-threshold slope, the non-monotonic temperature
dependence of the mobility, and its weak dependence on the gate voltage. In the
best rubrene transistors, room-temperature values of as high as 15
cm/Vs have been observed. This represents an order-of-magnitude increase
with respect to the highest mobility previously reported for organic thin film
transistors. In addition, the highest-quality single-crystal devices exhibit a
significant anisotropy of the conduction properties with respect to the
crystallographic direction. These observations indicate that the field effect
transistors fabricated on single crystals are suitable for the study of the
\textit{intrinsic} electronic properties of organic molecular semiconductors.
We conclude by indicating some directions in which near-future work should
focus to progress further in this rapidly evolving area of research.Comment: Review article, to appear in special issue of Phys. Stat. Sol. on
organic semiconductor
Basilar-membrane responses to multicomponent (Schroeder-phase) signals: Understanding intensity effects
Monitoring the Variable Interstellar Absorption toward HD 219188 with HST/STIS
We discuss the results of continued spectroscopic monitoring of the variable
intermediate-velocity (IV) absorption at v = -38 km/s toward HD 219188. After
reaching maxima in mid-2000, the column densities of both Na I and Ca II in
that IV component declined by factors >= 2 by the end of 2006. Comparisons
between HST/STIS echelle spectra obtained in 2001, 2003, and 2004 and HST/GHRS
echelle spectra obtained in 1994--1995 indicate the following: (1) The
absorption from the dominant species S II, O I, Si II, and Fe II is roughly
constant in all four sets of spectra -- suggesting that the total N(H) and the
(mild) depletions have not changed significantly over a period of nearly ten
years. (2) The column densities of the trace species C I (both ground and
excited fine-structure states) and of the excited state C II* all increased by
factors of 2--5 between 1995 and 2001 -- implying increases in the hydrogen
density n_H (from about 20 cm^{-3} to about 45 cm^{-3}) and in the electron
density n_e (by a factor >= 3) over that 6-year period. (3) The column
densities of C I and C II* -- and the corresponding inferred n_H and n_e --
then decreased slightly between 2001 and 2004. (4) The changes in C I and C II*
are very similar to those seen for Na I and Ca II. The relatively low total
N(H) and the modest n_H suggest that the -38 km/s cloud toward HD 219188 is not
a very dense knot or filament. Partial ionization of hydrogen appears to be
responsible for the enhanced abundances of Na I, C I, Ca II, and C II*. In this
case, the variations in those species appear to reflect differences in density
and ionization [and not N(H)] over scales of tens of AU.Comment: 33 pages, 6 figures, aastex, accepted to Ap
Design Actions for Shifting Conditions
Considering the growing importance that the urban environments assume within contemporary territorial transformations yet little room is offered within market-driven societies to critically reflect the spatial impact that cities face vis-à-vis the urgencies for environmental rebalancing. It embraces a wide range of phenomena we all live and experience nowadays, not only incidentally but more in a structural
way, forcing us to rethink our present state and explore futures. Transitions embody the fluctuating form of late capitalism with its raisings and disruptions. Regarding the environmental conditions, they are affecting the world regions’ habitability, the phenomenon of progressive urbanization versus agricultural land abandonment (UN 2018). With these premises, transitions seem to be a proper reference for an interdisciplinary and conceptual frame addressing the transformation of urban and metropolitan contexts, which will be the leading players for the coming decades
Supersymmetry and LHC
The motivation for introduction of supersymmetry in high energy physics as
well as a possibility for supersymmetry discovery at LHC (Large Hadronic
Collider) are discussed. The main notions of the Minimal Supersymmetric
Standard Model (MSSM) are introduced. Different regions of parameter space are
analyzed and their phenomenological properties are compared. Discovery
potential of LHC for the planned luminosity is shown for different channels.
The properties of SUSY Higgs bosons are studied and perspectives of their
observation at LHC are briefly outlined.Comment: Lectures given at the 9th Moscow International School of Physics
(XXXIV ITEP Winter School of Physics
Droplet minimizers for the Gates-Lebowitz-Penrose free energy functional
We study the structure of the constrained minimizers of the
Gates-Lebowitz-Penrose free-energy functional ,
non-local functional of a density field , , a
-dimensional torus of side length . At low temperatures, is not convex, and has two distinct global minimizers,
corresponding to two equilibrium states. Here we constrain the average density
L^{-d}\int_{{\cal T}_L}m(x)\dd x to be a fixed value between the
densities in the two equilibrium states, but close to the low density
equilibrium value. In this case, a "droplet" of the high density phase may or
may not form in a background of the low density phase, depending on the values
and . We determine the critical density for droplet formation, and the
nature of the droplet, as a function of and . The relation between the
free energy and the large deviations functional for a particle model with
long-range Kac potentials, proven in some cases, and expected to be true in
general, then provides information on the structure of typical microscopic
configurations of the Gibbs measure when the range of the Kac potential is
large enough
AdS Duals of Matrix Strings
We review recent work on the holographic duals of type II and heterotic
matrix string theories described by warped AdS_3 supergravities. In particular,
we compute the spectra of Kaluza-Klein primaries for type I, II supergravities
on warped AdS_3xS^7 and match them with the primary operators in the dual
two-dimensional gauge theories. The presence of non-trivial warp factors and
dilaton profiles requires a modification of the familiar dictionary between
masses and ``scaling'' dimensions of fields and operators. We present these
modifications for the general case of domain wall/QFT correspondences between
supergravities on warped AdS_{d+1}xS^q geometries and super Yang-Mills theories
with 16 supercharges.Comment: 7 pages, Proceedings of the RTN workshop ``The quantum structure of
spacetime and the geometric nature of fundamental interactions'', Leuven,
September 200
Lattice Models with N=2 Supersymmetry
We introduce lattice models with explicit N=2 supersymmetry. In these
interacting models, the supersymmetry generators Q^+ and Q^- yield the
Hamiltonian H={Q^+,Q^-} on any graph. The degrees of freedom can be described
as either fermions with hard cores, or as quantum dimers. The Hamiltonian of
our simplest model contains a hopping term and a repulsive potential, as well
as the hard-core repulsion. We discuss these models from a variety of
perspectives: using a fundamental relation with conformal field theory, via the
Bethe ansatz, and using cohomology methods. The simplest model provides a
manifestly-supersymmetric lattice regulator for the supersymmetric point of the
massless 1+1-dimensional Thirring (Luttinger) model. We discuss the
ground-state structure of this same model on more complicated graphs, including
a 2-leg ladder, and discuss some generalizations.Comment: 4 page
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