2,015,593 research outputs found
Symmetries and degrees of freedom in 2-dimensional dual models
The 2-dimensional version of the Schwarz and Sen duality model (Tseytlin
model) is analyzed at the classical and quantum levels. The solutions are
obtained after removing the gauge dependent sector using the Dirac method. The
Poincar\`e invariance is verified at both levels. An extension with global
supersymmetry is also proposed.Comment: 3 pages, revtex, minor correction
The excitation of near-infrared H2 emission in NGC 253
Because of its large angular size and proximity to the Milky Way, NGC 253, an
archetypal starburst galaxy, provides an excellent laboratory to study the
intricacies of this intense episode of star formation. We aim to characterize
the excitation mechanisms driving the emission in NGC 253. Specifically we aim
to distinguish between shock excitation and UV excitation as the dominant
driving mechanism, using Br\gamma, H_2 and [FeII] as diagnostic emission line
tracers. Using SINFONI observations, we create linemaps of Br\gamma,
[FeII]_{1.64}, and all detected H_2 transitions. By using symmetry arguments of
the gas and stellar gas velocity field, we find a kinematic center in agreement
with previous determinations. The ratio of the 2-1 S(1) to 1-0 S(1) H_2
transitions can be used as a diagnostic to discriminate between shock and
fluorescent excitation. Using the 1-0 S(1)/2-1 S(1) line ratio as well as
several other H_2 line ratios and the morphological comparison between H_2 and
Br\gamma and [FeII], we find that excitation from UV photons is the dominant
excitation mechanisms throughout NGC 253. We employ a diagnostic energy level
diagram to quantitatively differentiate between mechanisms. We compare the
observed energy level diagrams to PDR and shock models and find that in most
regions and over the galaxy as a whole, fluorescent excitation is the dominant
mechanism exciting the H_2 gas. We also place an upper limit of the percentage
of shock excited H_2 at 29%. We find that UV radiation is the dominant
excitation mechanism for the H_2 emission. The H_2 emission does not correlate
well with Br\gamma but closely traces the PAH emission, showing that not only
is H_2 fluorescently excited, but it is predominately excited by slightly lower
mass stars than O stars which excite Br\gamma, such as B stars
Critical dynamics of an interacting magnetic nanoparticle system
Effects of dipole-dipole interactions on the magnetic relaxation have been
investigated for three Fe-C nanoparticle samples with volume concentrations of
0.06, 5 and 17 vol%. While both the 5 and 17 vol% samples exhibit collective
behavior due to dipolar interactions, only the 17 vol% sample displays critical
behavior close to its transition temperature. The behaviour of the 5 vol%
sample can be attributed to a mixture of collective and single particle
dynamics.Comment: 19 pages, 8 figure
Numerical stress response functions of static granular layers
We investigate the stress response function of a layer of grains, i.e. the
stress profile in response to a localized overload. The shape of the profile is
very sensitive to the packing arrangement, and is thus a good signature of the
preparation procedure of the layer. This study has been done by the use of
molecular dynamics numerical simulations. Here, for a given rain-like
preparation, we present the scaling properties of the response function, and in
particular the influence of the thickness of the layer, and the importance of
the location of the overload and measurement points (at the boundaries, in the
bulk).Comment: 6 pages, 4 figures, to appear in the proceedings of the "Traffic and
Granular Flow 2003" conferenc
Wafering economies for industrialization from a wafer manufacturer's viewpoint
The key technical limitations which inhibit the lowering of value-added costs for state-of-the-art wafering techniques are assessed. From the best experimental results to date, a projection was made to identify those parts of each system which need to be developed in order to meet or improve upon the value-added cost reduction necessary for $0.70/Wp photovoltaics modules
Multipartite entangled states with two bosonic modes and qubits
We theoretically investigate the role of different phases of coupling
constants in the dynamics of atoms and two cavity modes, observing
deterministic generation of prototype or hybrid Bell, W, GHZ, and cluster
states. Commonly induced dipole-dipole interactions (far-off resonance) are
inhibited between particular pairs of qubits under suitable choice of those
phases. We evaluate the generation fidelities when imperfections such as
dissipative environments and time precision errors are considered. We show
violation of local realism for the generated cluster state under such
imperfections, even when approaching the weak coupling regime.Comment: 10 pages, 5 figures, REVTeX 4.1, BibTeX, final versio
- …