1,409 research outputs found
U(1) Gauge Theory as Quantum Hydrodynamics
It is shown that gauge theories are most naturally studied via a polar
decomposition of the field variable. Gauge transformations may be viewed as
those that leave the density invariant but change the phase variable by
additive amounts. The path integral approach is used to compute the partition
function. When gauge fields are included, the constraint brought about by gauge
invariance simply means an appropriate linear combination of the gradients of
the phase variable and the gauge field is invariant. No gauge fixing is needed
in this approach that is closest to the spirit of the gauge principle.
We derive an exact formula for the condensate fraction and in case it is
zero, an exact formula for the anomalous exponent. We also derive a formula for
the vortex strength which involves computing radiation corrections.Comment: 15 pages, Plain LaTeX, final published versio
Single vibronic level emission spectroscopic studies of the ground state energy levels and molecular structures of jet-cooled HGeBr, DGeBr, HGeI, and DGeI
Single vibronic level dispersed fluorescence spectra of jet-cooled HGeBr, DGeBr, HGeI, and DGeI have been obtained by laser excitation of selected bands of the à A″1-X̃ A′1 electronic transition. The measured ground state vibrational intervals were assigned and fitted to anharmonicity expressions, which allowed the harmonic frequencies to be determined for both isotopomers. In some cases, lack of a suitable range of emission data necessitated that some of the anharmonicity constants and vibrational frequencies be estimated from those of HGeCl∕DGeCl and the corresponding silylenes (HSiX). Harmonic force fields were obtained for both molecules, although only four of the six force constants could be determined. The ground state effective rotational constants and force field data were combined to calculate average (rz) and approximate equilibrium (rze) structures. For HGeBr rze(GeH)=1.593(9)Å, rze(GeBr)=2.325(21)Å, and the bond angle was fixed at our CCSD(T)/aug-cc-pVTZ ab initio value of 93.6°. For HGeI we obtained rze(GeH)=1.589(1)Å, rze(GeI)=2.525(5)Å, and bond angle=93.2°. Franck-Condon simulations of the emission spectra using ab initio Cartesian displacement coordinates reproduce the observed intensity distributions satisfactorily. The trends in structural parameters in the halogermylenes and halosilylenes can be readily understood based on the electronegativity of the halogen substituent. ACKNOWLEDGMENT
Incorporating interactive 3-dimensional graphics in astronomy research papers
Most research data collections created or used by astronomers are
intrinsically multi-dimensional. In contrast, all visual representations of
data presented within research papers are exclusively 2-dimensional. We present
a resolution of this dichotomy that uses a novel technique for embedding
3-dimensional (3-d) visualisations of astronomy data sets in electronic-format
research papers. Our technique uses the latest Adobe Portable Document Format
extensions together with a new version of the S2PLOT programming library. The
3-d models can be easily rotated and explored by the reader and, in some cases,
modified. We demonstrate example applications of this technique including: 3-d
figures exhibiting subtle structure in redshift catalogues, colour-magnitude
diagrams and halo merger trees; 3-d isosurface and volume renderings of
cosmological simulations; and 3-d models of instructional diagrams and
instrument designs.Comment: 18 pages, 7 figures, submitted to New Astronomy. For paper with
3-dimensional embedded figures, see http://astronomy.swin.edu.au/s2plot/3dpd
From Capillary Condensation to Interface Localization Transitions in Colloid Polymer Mixtures Confined in Thin Film Geometry
Monte Carlo simulations of the Asakura-Oosawa (AO) model for colloid-polymer
mixtures confined between two parallel repulsive structureless walls are
presented and analyzed in the light of current theories on capillary
condensation and interface localization transitions. Choosing a polymer to
colloid size ratio of q=0.8 and studying ultrathin films in the range of D=3 to
D=10 colloid diameters thickness, grand canonical Monte Carlo methods are used;
phase transitions are analyzed via finite size scaling, as in previous work on
bulk systems and under confinement between identical types of walls. Unlike the
latter work, inequivalent walls are used here: while the left wall has a
hard-core repulsion for both polymers and colloids, at the right wall an
additional square-well repulsion of variable strength acting only on the
colloids is present. We study how the phase separation into colloid-rich and
colloid-poor phases occurring already in the bulk is modified by such a
confinement. When the asymmetry of the wall-colloid interaction increases, the
character of the transition smoothly changes from capillary condensation-type
to interface localization-type. The critical behavior of these transitions is
discussed, as well as the colloid and polymer density profiles across the film
in the various phases, and the correlation of interfacial fluctuations in the
direction parallel to the confining walls. The experimental observability of
these phenomena also is briefly discussed.Comment: 36 pages, 15 figure
Structure and Instability of High-Density Equations for Traffic Flow
Similar to the treatment of dense gases, fluid-dynamic equations for the
dynamics of congested vehicular traffic are derived from Enskog-like kinetic
equations. These contain additional terms due to the anisotropic vehicle
interactions. The calculations are carried out up to Navier-Stokes order. A
linear instability analysis indicates an additional kind of instability
compared to previous macroscopic traffic models. The relevance for describing
granular flows is outlined.Comment: For related work see
http://www.theo2.physik.uni-stuttgart.de/helbing.htm
Lithic artifact assemblage transport and micro-wear modification in a fluvial setting: a radio frequency identification tag experiment
River processes are widely assumed to have impacted the integrity of lithic assemblages when artifacts are found in fluvial sediments, but the specifics of these influences remain largely unknown. We conducted a real-world experiment to determine how the initial stages of fluvial entrainment affected lithic artifact assemblages. We inserted replica artifacts with Radio Frequency Identification (RFID) tags into a gravel-bedded river in Wales (UK) for seven months and related their transport distances to their morphology and the recorded streamflow. Additionally, nine artifacts were recovered at the end of the experiment and analyzed for micro-wear traces. In sum, our results show that in a gravel bedded river with a mean discharge of 5.1 m3s-1, artifact length and width were the main variables influencing artifact transport distances. The experiment also resulted in characteristic micro-wear traces developing on the artifacts over distances of 485 m or less. These results emphasize the multifaceted nature of alluvial site formation processes in a repeatable experiment and highlight new ways to identify the transport of replica Paleolithic material
When Models Interact with their Subjects: The Dynamics of Model Aware Systems
A scientific model need not be a passive and static descriptor of its
subject. If the subject is affected by the model, the model must be updated to
explain its affected subject. In this study, two models regarding the dynamics
of model aware systems are presented. The first explores the behavior of
"prediction seeking" (PSP) and "prediction avoiding" (PAP) populations under
the influence of a model that describes them. The second explores the
publishing behavior of a group of experimentalists coupled to a model by means
of confirmation bias. It is found that model aware systems can exhibit
convergent random or oscillatory behavior and display universal 1/f noise. A
numerical simulation of the physical experimentalists is compared with actual
publications of neutron life time and {\Lambda} mass measurements and is in
good quantitative agreement.Comment: Accepted for publication in PLoS-ON
Geometric frustration and magnetization plateaus in quantum spin and Bose-Hubbard models on tubes
We study XXZ Heisenberg models on frustrated triangular lattices wrapped
around a cylinder. In addition to having interesting magnetic phases, these
models are equivalent to Bose-Hubbard models that describe the physical problem
of adsorption of noble gases on the surface of carbon nanotubes. We find
analytical results for the possible magnetization plateau values as a function
of the wrapping vectors of the cylinder, which in general introduce extra
geometric frustration besides the one due to the underlying triangular lattice.
We show that for particular wrapping vectors , which correspond to the
zig-zag nanotubes, there is a macroscopically degenerate ground state in the
classical Ising limit. The Hilbert space for the degenerate states can be
enumerated by a mapping first into a path in a square lattice wrapped around a
cylinder (a Bratteli diagram), and then to free fermions interacting with a
single degree of freedom. From this model we obtain the spectrum in
the anisotropic Heisenberg limit, showing that it is gapless. The continuum
limit is a conformal field theory with compactification radius set
by the physical tube radius. We show that the compactification radius
quantization is exact in the projective limit, and that
higher order corrections reduce the value of . The particular case of a
tube, which corresponds to a 2-leg ladder with cross links, is
studied separately and shown to be gapped because the fermion mapped problem
contains superconducting pairing terms.Comment: 10 pages, 11 figure
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