1,276 research outputs found
Chaos Synchronization and Spontaneous Symmetry Breaking in Symmetrically Delay Coupled Semiconductor Lasers
PACS: 05.45.Xt, 42.55.Px, 42.65.SfWe present experimental and numerical investigations of the dynamics of two device-identical, optically coupled semiconductor lasers exhibiting a delay in the coupling. Our results give evidence for subnanosecond coupling-induced synchronized chaotic dynamics in conjunction with a spontaneous symmetry-breaking: we find a well-defined time lag between the dynamics of the two lasers, and an asymmetric physical role of the subsystems. We demonstrate that the leading laser synchronizes its lagging counterpart, whereas the synchronized lagging laser drives the coupling-induced instabilities.Peer reviewe
Glueballs and k-strings in SU(N) gauge theories : calculations with improved operators
We test a variety of blocking and smearing algorithms for constructing
glueball and string wave-functionals, and find some with much improved overlaps
onto the lightest states. We use these algorithms to obtain improved results on
the tensions of k-strings in SU(4), SU(6), and SU(8) gauge theories. We
emphasise the major systematic errors that still need to be controlled in
calculations of heavier k-strings, and perform calculations in SU(4) on an
anisotropic lattice in a bid to minimise one of these. All these results point
to the k-string tensions lying part-way between the `MQCD' and `Casimir
Scaling' conjectures, with the power in 1/N of the leading correction lying in
[1,2]. We also obtain some evidence for the presence of quasi-stable strings in
calculations that do not use sources, and observe some near-degeneracies
between (excited) strings in different representations. We also calculate the
lightest glueball masses for N=2, ...,8, and extrapolate to N=infinity,
obtaining results compatible with earlier work. We show that the N=infinity
factorisation of the Euclidean correlators that are used in such mass
calculations does not make the masses any less calculable at large N.Comment: 49 pages, 15 figure
What's Decidable About Sequences?
We present a first-order theory of sequences with integer elements,
Presburger arithmetic, and regular constraints, which can model significant
properties of data structures such as arrays and lists. We give a decision
procedure for the quantifier-free fragment, based on an encoding into the
first-order theory of concatenation; the procedure has PSPACE complexity. The
quantifier-free fragment of the theory of sequences can express properties such
as sortedness and injectivity, as well as Boolean combinations of periodic and
arithmetic facts relating the elements of the sequence and their positions
(e.g., "for all even i's, the element at position i has value i+3 or 2i"). The
resulting expressive power is orthogonal to that of the most expressive
decidable logics for arrays. Some examples demonstrate that the fragment is
also suitable to reason about sequence-manipulating programs within the
standard framework of axiomatic semantics.Comment: Fixed a few lapses in the Mergesort exampl
Detuning effects in the one-photon mazer
The quantum theory of the mazer in the non-resonant case (a detuning between
the cavity mode and the atomic transition frequencies is present) is written.
The generalization from the resonant case is far from being direct. Interesting
effects of the mazer physics are pointed out. In particular, it is shown that
the cavity may slow down or speed up the atoms according to the sign of the
detuning and that the induced emission process may be completely blocked by use
of a positive detuning. It is also shown that the detuning adds a potential
step effect not present at resonance and that the use of positive detunings
defines a well-controlled cooling mechanism. In the special case of a mesa
cavity mode function, generalized expressions for the reflection and
transmission coefficients have been obtained. The general properties of the
induced emission probability are finally discussed in the hot, intermediate and
cold atom regimes. Comparison with the resonant case is given.Comment: 9 pages, 8 figure
The Prevalence of Thyroid Dysfunction in Elderly Cardiology Patients with Mild Excessive Iodine Intake in the Urban Area of São Paulo
OBJECTIVES: To evaluate the prevalence of thyroid dysfunction in elderly cardiac patients in an outpatient setting. SUBJECTS AND METHODS: A total of 399 consecutive patients (268 women, age range 60-92 years) who were followed at Heart Institute were evaluated for thyroid dysfunction with serum free T4, TSH, anti-Peroxidase antibodies, urinary iodine excretion measurements and thyroid ultrasound. RESULTS: Hyperthyroidism (overt and subclinical) was present in 29 patients (6.5%), whereas hypothyroidism (overt and subclinical) was found in 32 individuals (8.1%). Cysts were detected in 11 patients (2.8%), single nodules were detected in 102 (25.6%), and multinodular goiters were detected in 34 (8.5%). Hashimoto's thyroiditis was present in 16.8% patients, most of whom were women (83.6%). The serum TSH increased with age and was significantly higher (p= <0.01) in patients, compared to the normal control group. No significant differences in serum TSH and free T4 values were observed when patients with atrial fibrillation (AF) where compared with those without arrhythmia. The median urinary iodine levels were 210 µg/L (40-856 µg/L), and iodine levels were higher in men than in women (p<0.01). Excessive iodine intake (urinary iodine >300 µg/L) was observed in one-third of patients (30.8%). CONCLUSIONS: Elderly patients have a higher prevalence of both hypo- and hyperthyroidism as well as thyroid nodules when compared with the general population. About one-third of the older patients had elevated urinary secretion of iodine and a higher prevalence of chronic Hashimoto's thyroiditis. It is recommended that ultrasonographic studies, tests for thyroid function and autoimmunity should be evaluated in elderly patients
Transport Properties of the Quark-Gluon Plasma -- A Lattice QCD Perspective
Transport properties of a thermal medium determine how its conserved charge
densities (for instance the electric charge, energy or momentum) evolve as a
function of time and eventually relax back to their equilibrium values. Here
the transport properties of the quark-gluon plasma are reviewed from a
theoretical perspective. The latter play a key role in the description of
heavy-ion collisions, and are an important ingredient in constraining particle
production processes in the early universe. We place particular emphasis on
lattice QCD calculations of conserved current correlators. These Euclidean
correlators are related by an integral transform to spectral functions, whose
small-frequency form determines the transport properties via Kubo formulae. The
universal hydrodynamic predictions for the small-frequency pole structure of
spectral functions are summarized. The viability of a quasiparticle description
implies the presence of additional characteristic features in the spectral
functions. These features are in stark contrast with the functional form that
is found in strongly coupled plasmas via the gauge/gravity duality. A central
goal is therefore to determine which of these dynamical regimes the quark-gluon
plasma is qualitatively closer to as a function of temperature. We review the
analysis of lattice correlators in relation to transport properties, and
tentatively estimate what computational effort is required to make decisive
progress in this field.Comment: 54 pages, 37 figures, review written for EPJA and APPN; one parag.
added end of section 3.4, and one at the end of section 3.2.2; some Refs.
added, and some other minor change
Effective weakly supervised semantic frame induction using expression sharing in hierarchical hidden Markov models
We present a framework for the induction of semantic frames from utterances
in the context of an adaptive command-and-control interface. The system is
trained on an individual user's utterances and the corresponding semantic
frames representing controls. During training, no prior information on the
alignment between utterance segments and frame slots and values is available.
In addition, semantic frames in the training data can contain information that
is not expressed in the utterances. To tackle this weakly supervised
classification task, we propose a framework based on Hidden Markov Models
(HMMs). Structural modifications, resulting in a hierarchical HMM, and an
extension called expression sharing are introduced to minimize the amount of
training time and effort required for the user.
The dataset used for the present study is PATCOR, which contains commands
uttered in the context of a vocally guided card game, Patience. Experiments
were carried out on orthographic and phonetic transcriptions of commands,
segmented on different levels of n-gram granularity. The experimental results
show positive effects of all the studied system extensions, with some effect
differences between the different input representations. Moreover, evaluation
experiments on held-out data with the optimal system configuration show that
the extended system is able to achieve high accuracies with relatively small
amounts of training data
Sub-10ps Monolithic and Low-power Photodetector Readout
Recent advances in photon detectors have resulted in high-density imaging
arrays that offer many performance and cost advantages. In particular, the
excellent transit time spread of certain devices show promise to provide
tangible benefits in applications such as Positron Emission Tomography (PET).
Meanwhile, high-density, high-performance readout techniques have not kept on
pace for exploiting these developments. Photodetector readout for next
generation high event rate particle identification and time-resolved PET
requires a highly-integrated, low-power, and cost-effective readout technique.
We propose fast waveform sampling as a method that meets these criteria and
demonstrate that sub-10ps resolution can be obtained for an existing device.Comment: 12 pages, 20 figures, submitted to NIM
Quantum walk on distinguishable non-interacting many-particles and indistinguishable two-particle
We present an investigation of many-particle quantum walks in systems of
non-interacting distinguishable particles. Along with a redistribution of the
many-particle density profile we show that the collective evolution of the
many-particle system resembles the single-particle quantum walk evolution when
the number of steps is greater than the number of particles in the system. For
non-uniform initial states we show that the quantum walks can be effectively
used to separate the basis states of the particle in position space and
grouping like state together. We also discuss a two-particle quantum walk on a
two- dimensional lattice and demonstrate an evolution leading to the
localization of both particles at the center of the lattice. Finally we discuss
the outcome of a quantum walk of two indistinguishable particles interacting at
some point during the evolution.Comment: 8 pages, 7 figures, To appear in special issue: "quantum walks" to be
published in Quantum Information Processin
Hadron Structure on the Lattice
A few chosen nucleon properties are described from a lattice QCD perspective:
the nucleon sigma term and the scalar strangeness in the nucleon; the vector
form factors in the nucleon, including the vector strangeness contribution, as
well as parity breaking effects like the anapole and electric dipole moment;
and finally the axial and tensor charges of the nucleon. The status of the
lattice calculations is presented and their potential impact on phenomenology
is discussed.Comment: 17 pages, 9 figures; proceedings of the Conclusive Symposium of the
Collaborative Research Center 443 "Many-body structure of strongly
interacting systems", Mainz, February 23-25, 201
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