24,026 research outputs found
Topological Aspects of Spin and Statistics in Nonlinear Sigma Models
We study the purely topological restrictions on allowed spin and statistics
of topological solitons in nonlinear sigma models. Taking as space the
connected -manifold , and considering nonlinear sigma models with the
connected manifold as target space, topological solitons are given by
elements of . Any topological soliton determines
a quotient \Stat_n(X,\alpha) of the group of framed braids on , such that
choices of allowed statistics for solitons of type are given by
unitary representations of \Stat_n(X,\alpha) when solitons are present.
In particular, when , as in the nonlinear sigma model with Hopf
term, and is a generator, we compute that
\Stat_n(\R^2,\alpha) = \Z, while \Stat_n(S^2,\alpha) = \Z_{2n}. It follows
that phase for interchanging two solitons of type on
must satisfy the constraint , , when such
solitons are present.Comment: 14 page
A comparison of soil moisture characteristics predicted by the Arya-Paris model with laboratory-measured data
Soil moisture characteristics predicted by the Arya-Paris model were compared with the laboratory measured data for 181 New Jersey soil horizons. For a number of soil horizons, the predicted and the measured moisture characteristic curves are almost coincident; for a large number of other horizons, despite some disparity, their shapes are strikingly similar. Uncertainties in the model input and laboratory measurement of the moisture characteristic are indicated, and recommendations for additional experimentation and testing are made
Phase--coherence Effects in Antidot Lattices: A Semiclassical Approach to Bulk Conductivity
We derive semiclassical expressions for the Kubo conductivity tensor. Within
our approach the oscillatory parts of the diagonal and Hall conductivity are
given as sums over contributions from classical periodic orbits in close
relation to Gutzwiller's trace formula for the density of states. Taking into
account the effects of weak disorder and temperature we reproduce recently
observed anomalous phase coherence oscillations in the conductivity of large
antidot arrays.Comment: 11 pages, 2 figures available under request, RevTe
Integrated control-system design via generalized LQG (GLQG) theory
Thirty years of control systems research has produced an enormous body of theoretical results in feedback synthesis. Yet such results see relatively little practical application, and there remains an unsettling gap between classical single-loop techniques (Nyquist, Bode, root locus, pole placement) and modern multivariable approaches (LQG and H infinity theory). Large scale, complex systems, such as high performance aircraft and flexible space structures, now demand efficient, reliable design of multivariable feedback controllers which optimally tradeoff performance against modeling accuracy, bandwidth, sensor noise, actuator power, and control law complexity. A methodology is described which encompasses numerous practical design constraints within a single unified formulation. The approach, which is based upon coupled systems or modified Riccati and Lyapunov equations, encompasses time-domain linear-quadratic-Gaussian theory and frequency-domain H theory, as well as classical objectives such as gain and phase margin via the Nyquist circle criterion. In addition, this approach encompasses the optimal projection approach to reduced-order controller design. The current status of the overall theory will be reviewed including both continuous-time and discrete-time (sampled-data) formulations
A compact 90 kilowatt electric heat source for heating inert gases to 1700 F
Design and fabrication of compact electric heat source for heating inert gase
Design and fabrication of a low-specific-weight parabolic dish solar concentrator
A segmented design and fabrication and assembly techniques were developed for a 1.8 m (6 ft) diameter parabolic concentrator for space application. This design and these techniques were adaptable to a low cost, mass-produced concentrator. Minimal machining was required. Concentrator segments of formed magnesium were used. The concentrator weighed only 1.6 kg sq m (0.32 lbm/sq ft)
Theoretical investigation into the possibility of very large moments in Fe16N2
We examine the mystery of the disputed high-magnetization \alpha"-Fe16N2
phase, employing the Heyd-Scuseria-Ernzerhof screened hybrid functional method,
perturbative many-body corrections through the GW approximation, and onsite
Coulomb correlations through the GGA+U method. We present a first-principles
computation of the effective on-site Coulomb interaction (Hubbard U) between
localized 3d electrons employing the constrained random-phase approximation
(cRPA), finding only somewhat stronger on-site correlations than in bcc Fe. We
find that the hybrid functional method, the GW approximation, and the GGA+U
method (using parameters computed from cRPA) yield an average spin moment of
2.9, 2.6 - 2.7, and 2.7 \mu_B per Fe, respectively.Comment: 8 pages, 3 figure
Spontaneous Raman scattering for simultaneous measurements of in-cylinder species
A technique for multi-species mole fraction measurement in internal combustion engines is described. The technique is based on the spontaneous Raman scattering. It can simultaneously provide the mole fractions of several species of N-2, O-2, H2O, CO2 and fuel. Using the system, simultaneous measurement of air/fuel ratio and burnt residual gas are carried out during the mixture process in a Controlled Auto Ignition (CAI) combustion engine. The accuracy and consistency of the measured results were confirmed by the measured air fuel ratio using an exhaust gas analyzer and independently calculated mole fraction values. Measurement of species mole fractions during combustion process has also been demonstrated. It shows that the SRS can provide valuable data on this process in a CAI combustion engine
Uncovering the (un-)occupied electronic structure of a buried hybrid interface
The energy level alignment at organic/inorganic (o/i) semiconductor
interfaces is crucial for any light-emitting or -harvesting functionality.
Essential is the access to both occupied and unoccupied electronic states
directly at the interface, which is often deeply buried underneath thick
organic films and challenging to characterize. We use several complementary
experimental techniques to determine the electronic structure of
p-quinquephenyl pyridine (5P-Py) adsorbed on ZnO(10-10). The parent anchoring
group, pyridine, significantly lowers the work function by up to 2.9 eV and
causes an occupied in-gap state (IGS) directly below the Fermi level
. Adsorption of upright-standing 5P-Py also leads to a strong work
function reduction of up to 2.1 eV and to a similar IGS. The latter is then
used as an initial state for the transient population of three normally
unoccupied molecular levels through optical excitation and, due to its
localization right at the o/i interface, provides interfacial sensitivity, even
for thick 5P-Py films. We observe two final states above the vacuum level and
one bound state at around 2 eV above , which we attribute to the
5P-Py LUMO. By the separate study of anchoring group and organic dye combined
with the exploitation of the occupied IGS for selective interfacial
photoexcitation this work provides a new pathway for characterizing the
electronic structure at buried o/i interfaces
First Experimental Evidence for Chaos-Assisted Tunneling in a Microwave Annular Billiard
We report on first experimental signatures for chaos-assisted tunneling in a
two-dimensional annular billiard. Measurements of microwave spectra from a
superconducting cavity with high frequency resolution are combined with
electromagnetic field distributions experimentally determined from a normal
conducting twin cavity with high spatial resolution to resolve eigenmodes with
properly identified quantum numbers. Distributions of so-called quasi-doublet
splittings serve as basic observables for the tunneling between whispering
gallery type modes localized to congruent, but distinct tori which are coupled
weakly to irregular eigenstates associated with the chaotic region in phase
space.Comment: 5 pages RevTex, 5 low-resolution figures (high-resolution figures:
http://linac.ikp.physik.tu-darmstadt.de/heiko/chaospub.html, to be published
in Phys. Rev. Let
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