14,962 research outputs found
Pattern formation with trapped ions
Ion traps are a versatile tool to study nonequilibrium statistical physics,
due to the tunability of dissipation and nonlinearity. We propose an experiment
with a chain of trapped ions, where dissipation is provided by laser heating
and cooling, while nonlinearity is provided by trap anharmonicity and beam
shaping. The collective dynamics are governed by an equation similar to the
complex Ginzburg-Landau equation, except that the reactive nature of the
coupling leads to qualitatively different behavior. The system has the unusual
feature of being both oscillatory and excitable at the same time. We account
for noise from spontaneous emission and find that the patterns are observable
for realistic experimental parameters. Our scheme also allows controllable
experiments with noise and quenched disorder.Comment: 4 pages + appendi
A review and evaluation of the Langley Research Center's scientific and technical information program. Results of phase 1: Knowledge and attitudes survey, LaRC research personnel
The effectiveness of the Langley STI program was assessed using feedback obtained from Langley engineers and scientists. A survey research procedure was conducted in two stages. Personal interviews with 64 randomly selected Langley engineers and scientists were used to obtain information for questionnaire development. Data were then collected by means of the questionnaire which covered various aspects of the Langley STI program, utilized both open and closed ended questions and was pretested for finalization. The questions were organized around the six objectives for Phase 1. The completed questionnaires were analyzed. From the analysis of the data, recommendations were made for improving the Langley STI program
Domain Coarsening in Systems Far from Equilibrium
The growth of domains of stripes evolving from random initial conditions is
studied in numerical simulations of models of systems far from equilibrium such
as Rayleigh-Benard convection. The scaling of the size of the domains deduced
from the inverse width of the Fourier spectrum is studied for both potential
and nonpotential models. The morphology of the domains and the defect
structures are however quite different in the two cases, and evidence is
presented for a second length scale in the nonpotential case.Comment: 11 pages, RevTeX; 3 uufiles encoded postscript figures appende
Heat Transport in Mesoscopic Systems
Phonon heat transport in mesoscopic systems is investigated using methods
analogous to the Landauer description of electrical conductance. A "universal
heat conductance" expression that depends on the properties of the conducting
pathway only through the mode cutoff frequencies is derived. Corrections due to
reflections at the junction between the thermal body and the conducting bridge
are found to be small except at very low temperatures where only the lowest few
bridge modes are excited. Various non-equilibrium phonon distributions are
studied: a narrow band distribution leads to clear steps in the cooling curve,
analogous to the quantized resistance values in narrow wires, but a thermal
distribution is too broad to show such features.Comment: To be published in Superlattices and Microstructures, special issue
in honor of Rolf Landauer, March 198
Antiferromagnetic phase transition in a nonequilibrium lattice of Rydberg atoms
We study a driven-dissipative system of atoms in the presence of laser
excitation to a Rydberg state and spontaneous emission. The atoms interact via
the blockade effect, whereby an atom in the Rydberg state shifts the Rydberg
level of neighboring atoms. We use mean-field theory to study how the Rydberg
population varies in space. As the laser frequency changes, there is a
continuous transition between the uniform and antiferromagnetic phases. The
nonequilibrium nature also leads to a novel oscillatory phase and bistability
between the uniform and antiferromagnetic phases.Comment: 4 pages + appendi
Sources of Cardiovascular Health Information and Channels of Health Communication Among Urban Population in Nigeria
This study employed mixed methods to investigate the preferred sources of health information and later explored the views of community healthcare workers on the enablers, barriers and ways of overcoming barriers to health communication. The study found that majority of the participants preferred their source of CV (cardiovascular) health information from the healthcare workers including the medical doctors, nurses, and pharmacists. On the other hand, the least preferred source of health information was from friends, family members, and community leaders. Some of the identified enablers to community health communication include awareness programme via Non-Governmental Organisations (NGOs), community-based organisations such as faith-based organisations and healthcare facilities. Others are traditional media and social media. The identified barriers to community-based health communication include lack of knowledge and poverty, language barriers, and other miscellaneous issues including misuse of internet, lack of basic amenities and religious beliefs. The community-based healthcare providers articulated ways to overcome the identified barriers, including enlightenment programmes, using the language of the target audience, funding health awareness programmes, and monitoring of health education interventions. This study concludes that dissemination of health information using numerous channels is essential in ensuring population-wide primary prevention of diseases
Aging in the Relaxor Ferroelectric PMN/PT
The relaxor ferroelectric
(PbMnNbO)(PbTiO), ,
(PMN/PT(90/10)) is found to exhibit several regimes of complicated aging
behavior. Just below the susceptibility peak there is a regime exhibiting
rejuvenation but little memory. At lower temperature, there is a regime with
mainly cumulative aging, expected for simple domain-growth. At still lower
temperature, there is a regime with both rejuvenation and memory, reminiscent
of spin glasses. PMN/PT (88/12) is also found to exhibit some of these aging
regimes. This qualitative aging behavior is reminiscent of that seen in
reentrant ferromagnets, which exhibit a crossover from a domain-growth
ferromagnetic regime into a reentrant spin glass regime at lower temperatures.
These striking parallels suggest a picture of competition in PMN/PT (90/10)
between ferroelectric correlations formed in the domain-growth regime with
glassy correlations formed in the spin glass regime. PMN/PT (90/10) is also
found to exhibit frequency-aging time scaling of the time-dependent part of the
out-of-phase susceptibility for temperatures 260 K and below. The stability of
aging effects to thermal cycles and field perturbations is also reported.Comment: 8 pages RevTeX4, 11 figures; submitted to Phys. Rev.
Spatiotemporal dynamics of quantum jumps with Rydberg atoms
We study the nonequilibrium dynamics of quantum jumps in a one-dimensional
chain of atoms. Each atom is driven on a strong transition to a short-lived
state and on a weak transition to a metastable state. We choose the metastable
state to be a Rydberg state so that when an atom jumps to the Rydberg state, it
inhibits or enhances jumps in the neighboring atoms. This leads to rich
spatiotemporal dynamics that are visible in the fluorescence of the strong
transition.Comment: 10 page
Dividing the Ontology Alignment Task with Semantic Embeddings and Logic-based Modules
Large ontologies still pose serious challenges to state-of-the-art ontology alignment systems. In this paper we present an approach that combines a neural embedding model and logic-based modules to accurately divide an input ontology matching task into smaller and more tractable matching (sub)tasks. We have conducted a comprehensive evaluation using the datasets of the Ontology Alignment Evaluation Initiative. The results are encouraging and suggest that the proposed method is adequate in practice and can be integrated within the workflow of systems unable to cope with very large ontologies
- …