787 research outputs found
The Dirichlet Super-p-Branes in Ten-Dimensional Type IIA and IIB Supergravity
We give the full supersymmetric and kappa-symmetric actions for the Dirichlet
p-branes, including their coupling to background superfields of ten-dimensional
type IIA and IIB supergravity.Comment: 24 pages, plain TeX. Replacement corrects text positioning in
automatically generated postscript fil
Synthetic magnetism for photon fluids
We develop a theory of artificial gauge fields in photon fluids for the cases
of both second-order and third-order optical nonlinearities. This applies to
weak excitations in the presence of pump fields carrying orbital angular
momentum, and is thus a type of Bogoliubov theory. The resulting artificial
gauge fields experienced by the weak excitations are an interesting
generalization of previous cases and reflect the PT-symmetry properties of the
underlying non-Hermitian Hamiltonian. We illustrate the observable consequences
of the resulting synthetic magnetic fields for examples involving both
second-order and third-order nonlinearities
Low-Temperature Scaling Regime of Random Ferromagnetic-Antiferromagnetic Spin Chains
Using the Continuous Time Quantum Monte Carlo Loop algorithm, we calculate
the temperature dependence of the uniform susceptibility, and the specific heat
of a spin-1/2 chain with random antiferromagnetic and ferromagnetic couplings,
down to very low temperatures. Our data show a consistent scaling behavior in
both quantities and support strongly the conjecture drawn from the
approximative real-space renormalization group treatment. A statistical
analysis scheme is developed which will be useful for the search scaling
behavior in numerical and experimental data of random spin chains.Comment: 4 pages and 3 figure
Monte Carlo Study of the Separation of Energy Scales in Quantum Spin 1/2 Chains with Bond Disorder
One-dimensional Heisenberg spin 1/2 chains with random ferro- and
antiferromagnetic bonds are realized in systems such as . We have investigated numerically the thermodynamic properties of a
generic random bond model and of a realistic model of by the quantum Monte Carlo loop algorithm. For the first time we
demonstrate the separation into three different temperature regimes for the
original Hamiltonian based on an exact treatment, especially we show that the
intermediate temperature regime is well-defined and observable in both the
specific heat and the magnetic susceptibility. The crossover between the
regimes is indicated by peaks in the specific heat. The uniform magnetic
susceptibility shows Curie-like behavior in the high-, intermediate- and
low-temperature regime, with different values of the Curie constant in each
regime. We show that these regimes are overlapping in the realistic model and
give numerical data for the analysis of experimental tests.Comment: 7 pages, 5 eps-figures included, typeset using JPSJ.sty, accepted for
publication in J. Phys. Soc. Jpn. 68, Vol. 3. (1999
Phase-Insensitive Scattering of Terahertz Radiation
The nonlinear interaction between Near-Infrared (NIR) and Terahertz pulses is
principally investigated as a means for the detection of radiation in the
hardly accessible THz spectral region. Most studies have targeted second-order
nonlinear processes, given their higher efficiencies, and only a limited number
have addressed third-order nonlinear interactions, mainly investigating
four-wave mixing in air for broadband THz detection. We have studied the
nonlinear interaction between THz and NIR pulses in solid-state media
(specifically diamond), and we show how the former can be frequency-shifted up
to UV frequencies by the scattering from the nonlinear polarisation induced by
the latter. Such UV emission differs from the well-known electric-field-induced
second harmonic (EFISH) one, as it is generated via a phase-insensitive
scattering, rather than a sum- or difference-frequency four-wave-mixing
process
Aperiodic quantum XXZ chains: Renormalization-group results
We report a comprehensive investigation of the low-energy properties of
antiferromagnetic quantum XXZ spin chains with aperiodic couplings. We use an
adaptation of the Ma-Dasgupta-Hu renormalization-group method to obtain
analytical and numerical results for the low-temperature thermodynamics and the
ground-state correlations of chains with couplings following several two-letter
aperiodic sequences, including the quasiperiodic Fibonacci and other
precious-mean sequences, as well as sequences inducing strong geometrical
fluctuations. For a given aperiodic sequence, we argue that in the easy-plane
anisotropy regime, intermediate between the XX and Heisenberg limits, the
general scaling form of the thermodynamic properties is essentially given by
the exactly-known XX behavior, providing a classification of the effects of
aperiodicity on XXZ chains. We also discuss the nature of the ground-state
structures, and their comparison with the random-singlet phase, characteristic
of random-bond chains.Comment: Minor corrections; published versio
An auditory, acoustic, articulatory and sociophonetic study of Swedish Viby-i
The study investigates the acoustic, articulatory and sociophonetic properties of the Swedish /iː/ variant known as 'Viby-i' in 13 speakers of Central Swedish from Stockholm, Gothenburg, Varberg, Jönköping and Katrineholm. The vowel is described in terms of its auditory quality, its acoustic F1 and F2 values, and its tongue configuration. A brief, qualitative description of lip position is also included. Variation in /iː/ production is mapped against five sociolinguistic factors: city, dialectal region, metropolitan vs. urban location, sex and socioeconomic rating. Articulatory data is collected using ultrasound tongue imaging (UTI), for which the study proposes and evaluates a methodology.
The study shows that Viby-i varies in auditory strength between speakers, and that strong instances of the vowel are associated with a high F1 and low F2, a trend which becomes more pronounced as the strength of Viby-i increases. The articulation of Viby-i is characterised by a lowered and backed tongue body, sometimes accompanied by a double-bunched tongue shape. The relationship between tongue position and acoustic results appears to be non-linear, suggesting either a measurement error or the influence of additional articulatory factors. Preliminary images of the lips show that Viby-i is produced with a spread but lax lip posture. The lip data also reveals parts of the tongue, which in many speakers appears to be extremely fronted and braced against the lower teeth, or sometimes protruded, when producing Viby-i. No sociophonetic difference is found between speakers from different cities or dialect regions. Metropolitan speakers are found to have an auditorily and acoustically stronger Viby-i than urban speakers, but this pattern is not matched in tongue backing or lowering. Overall the data shows a weak trend towards higher-class females having stronger Viby-i, but these results are tentative due to the limited size and stratification of the sample. Further research is needed to fully explore the sociophonetic properties of Viby-i
Spin Waves in Random Spin Chains
We study quantum spin-1/2 Heisenberg ferromagnetic chains with dilute, random
antiferromagnetic impurity bonds with modified spin-wave theory. By describing
thermal excitations in the language of spin waves, we successfully observe a
low-temperature Curie susceptibility due to formation of large spin clusters
first predicted by the real-space renormalization-group approach, as well as a
crossover to a pure ferromagnetic spin chain behavior at intermediate and high
temperatures. We compare our results of the modified spin-wave theory to
quantum Monte Carlo simulations.Comment: 3 pages, 3 eps figures, submitted to the 47th Conference on Magnetism
and Magnetic Material
Kaon Condensation in the Bound-State Approach to the Skyrme Model
We explore kaon condensation using the bound-state approach to the Skyrme
model on a 3-sphere. The condensation occurs when the energy required to
produce a falls below the electron fermi level. This happens at the
baryon number density on the order of 3--4 times nuclear density.Comment: LaTeX format, 15 pages. 3 Postscript figures, compressed and
uuencode
- …