816 research outputs found
Gauge Theory of Gravity Requires Massive Torsion Field
One of the greatest unsolved issues of the physics of this century is to find
a quantum field theory of gravity. According to a vast amount of literature
unification of quantum field theory and gravitation requires a gauge theory of
gravity which includes torsion and an associated spin field. Various models
including either massive or massless torsion fields have been suggested. We
present arguments for a massive torsion field, where the probable rest mass of
the corresponding spin three gauge boson is the Planck mass.Comment: 3 pages, Revte
Effects of message repetition and negativity on credibility judgments and political attitudes
Mamíferos del Wealdiense de Uña, cerca de Cuenca
En esta nota preliminar se dan a conocer los hallazgos realizados en el Wealdiense de Uña, en la provincia de Cuenca corresponidientes a diversos mamíferos niesozoicos que se integran dentro de los grupos de los Pantoterios y los Multituberculados. Este es el segundo yacimiento de España de mamíferos secutidarios, siendo el primero el de Galve, en la provincia de Teruel. La descripción definitiva de los materiales será realizada por cada cada uno de los dos firmantes; por el primero, el de Uña y por el segundo, el de Galve
Zuchtwertschätzung von vatertieren unter exakter gewichtung der nachkommendurchschnitte je mutter
International audienc
Time-Varying Fine-Structure Constant Requires Cosmological Constant
Webb et al. presented preliminary evidence for a time-varying fine-structure
constant. We show Teller's formula for this variation to be ruled out within
the Einstein-de Sitter universe, however, it is compatible with cosmologies
which require a large cosmological constant.Comment: 3 pages, no figures, revtex, to be published in Mod. Phys. Lett.
Quantum critical dynamics of a S = 1/2 antiferromagnetic Heisenberg chain studied by 13C-NMR spectroscopy
We present a 13C-NMR study of the magnetic field driven transition to
complete polarization of the S=1/2 antiferromagnetic Heisenberg chain system
copper pyrazine dinitrate Cu(C_4H_4N_2)(NO_3)_2 (CuPzN). The static local
magnetization as well as the low-frequency spin dynamics, probed via the
nuclear spin-lattice relaxation rate 1/T_1, were explored from the low to the
high field limit and at temperatures from the quantum regime (k_B T << J) up to
the classical regime (k_B T >> J). The experimental data show very good
agreement with quantum Monte Carlo calculations over the complete range of
parameters investigated. Close to the critical field, as derived from static
experiments, a pronounced maximum in 1/T_1 is found which we interpret as the
finite-temperature manifestation of a diverging density of zero-energy magnetic
excitations at the field-driven quantum critical point.Comment: 5 pages, 4 figure
Phase Transitions in Two-Dimensional Traffic Flow Models
We introduce two simple two-dimensional lattice models to study traffic flow
in cities. We have found that a few basic elements give rise to the
characteristic phase diagram of a first-order phase transition from a freely
moving phase to a jammed state, with a critical point. The jammed phase
presents new transitions corresponding to structural transformations of the
jam. We discuss their relevance in the infinite size limit.Comment: RevTeX 3.0 file. Figures available upon request to e-address
[email protected] (or 'dopico' or 'molera' or 'anxo', same node
Modeling and Simulation of Multi-Lane Traffic Flow
A most important aspect in the field of traffic modeling is the simulation of
bottleneck situations. For their realistic description a macroscopic multi-lane
model for uni-directional freeways including acceleration, deceleration,
velocity fluctuations, overtaking and lane-changing maneuvers is systematically
deduced from a gas-kinetic (Boltzmann-like) approach. The resulting equations
contain corrections with respect to previous models. For efficient computer
simulations, a reduced model delineating the coarse-grained temporal behavior
is derived and applied to bottleneck situations.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
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