5,529 research outputs found
Cooperative surmounting of bottlenecks
The physics of activated escape of objects out of a metastable state plays a
key role in diverse scientific areas involving chemical kinetics, diffusion and
dislocation motion in solids, nucleation, electrical transport, motion of flux
lines superconductors, charge density waves, and transport processes of
macromolecules, to name but a few. The underlying activated processes present
the multidimensional extension of the Kramers problem of a single Brownian
particle. In comparison to the latter case, however, the dynamics ensuing from
the interactions of many coupled units can lead to intriguing novel phenomena
that are not present when only a single degree of freedom is involved. In this
review we report on a variety of such phenomena that are exhibited by systems
consisting of chains of interacting units in the presence of potential
barriers.
In the first part we consider recent developments in the case of a
deterministic dynamics driving cooperative escape processes of coupled
nonlinear units out of metastable states. The ability of chains of coupled
units to undergo spontaneous conformational transitions can lead to a
self-organised escape. The mechanism at work is that the energies of the units
become re-arranged, while keeping the total energy conserved, in forming
localised energy modes that in turn trigger the cooperative escape. We present
scenarios of significantly enhanced noise-free escape rates if compared to the
noise-assisted case.
The second part deals with the collective directed transport of systems of
interacting particles overcoming energetic barriers in periodic potential
landscapes. Escape processes in both time-homogeneous and time-dependent driven
systems are considered for the emergence of directed motion. It is shown that
ballistic channels immersed in the associated high-dimensional phase space are
the source for the directed long-range transport
A method to correct differential nonlinearities in subranging analog-to-digital converters used for digital gamma-ray spectroscopy
The influence on -ray spectra of differential nonlinearities (DNL) in
subranging, pipelined analog-to-digital converts (ADCs) used for digital
-ray spectroscopy was investigated. The influence of the DNL error on
the -ray spectra, depending on the input count-rate and the dynamic
range has been investigated systematically. It turned out, that the DNL becomes
more significant in -ray spectra with larger dynamic range of the
spectroscopy system. An event-by-event offline correction algorithm was
developed and tested extensively. This correction algorithm works especially
well for high dynamic ranges
Influence of mirtazapine on salivary cortisol in depressed patients
Unlike other antidepressants, mirtazapine does not inhibit the reuptake of norepinephrine or serotonin but acts as an antagonist at presynaptic alpha(2)-receptors, at postsynaptic 5-HT2 and 5-HT3 receptors, and at histaminergic H1 receptors. Furthermore, mirtazapine has been shown to acutely inhibit cortisol secretion in healthy subjects. In the present study, the impact of mirtazapine treatment on salivary cortisol secretion was investigated in 12 patients (4 men, 8 women) suffering from major depression according to DSM-IV criteria. Patients were treated with mirtazapine for 3 weeks, receiving 15 mg mirtazapine on day 0, 30 mg on day 1 and 45 mg per day from day 2 up to the end of the study (day 21). Response to mirtazapine treatment was defined by a reduction of at least 50% in the Hamilton Rating Scale for Depression after 3 weeks of therapy. Salivary cortisol concentrations were measured before treatment (day -1), at the beginning of treatment (day 0), after 1 week (day 7) and after 3 weeks (day 21) of treatment with mirtazapine. Saliva samples were collected hourly from 08.00 until 20.00 h. The area under the curve values served as parameter for the salivary cortisol secretion. Following analysis of variance with a repeated measures design, tests with contrasts revealed a significant reduction of cortisol concentrations already after 1 day of mirtazapine treatment that was comparable in responders and nonresponders. In addition to new pharmacological approaches such as CRH1 receptor antagonists, mirtazapine therefore appears to be an effective strategy to decrease hypercortisolism and restore HPA system dysregulation in depression. However, the importance of the acute inhibitory effects of mirtazapine on cortisol secretion for its antidepressant efficacy has to be further clarified. Copyright (C) 2003 S. Karger AG, Basel
Trust as a Determinant of Consumer Behaviour in Food Safety Crises
Based on an enhancement of Ajzen's Theory of Planned Behaviour, this article investigates German consumers' trust in different sources of information. Moreover, it discusses the settings and the extent to which consumers' trust influences consumers' behaviour both in the case of a standard purchasing situation and in the environment of a hypothetical food safety incidence such as bird flu . Results indicate that both the consumers' attitude and their trust in suppliers of information is a crucial factor determining their behaviour under uncertainty.consumer behaviour, uncertainty, trust, food safety, Food Consumption/Nutrition/Food Safety,
Negative refraction with tunable absorption in an active dense gas of atoms
Applications of negative index materials (NIM) presently are severely limited
by absorption. Next to improvements of metamaterial designs, it has been
suggested that dense gases of atoms could form a NIM with negligible losses. In
such gases, the low absorption is facilitated by quantum interference. Here, we
show that additional gain mechanisms can be used to tune and effectively remove
absorption in a dense gas NIM. In our setup, the atoms are coherently prepared
by control laser fields, and further driven by a weak incoherent pump field to
induce gain. We employ nonlinear optical Bloch equations to analyze the optical
response. Metastable Neon is identified as a suitable experimental candidate at
infrared frequencies to implement a lossless active negative index material.Comment: 10 pages, 9 figure
Nonlinear response of a linear chain to weak driving
We study the escape of a chain of coupled units over the barrier of a
metastable potential. It is demonstrated that a very weak external driving
field with suitably chosen frequency suffices to accomplish speedy escape. The
latter requires the passage through a transition state the formation of which
is triggered by permanent feeding of energy from a phonon background into humps
of localised energy and elastic interaction of the arising breather solutions.
In fact, cooperativity between the units of the chain entailing coordinated
energy transfer is shown to be crucial for enhancing the rate of escape in an
extremely effective and low-energy cost way where the effect of entropic
localisation and breather coalescence conspire
Probabilistic Linear Solvers: A Unifying View
Several recent works have developed a new, probabilistic interpretation for
numerical algorithms solving linear systems in which the solution is inferred
in a Bayesian framework, either directly or by inferring the unknown action of
the matrix inverse. These approaches have typically focused on replicating the
behavior of the conjugate gradient method as a prototypical iterative method.
In this work surprisingly general conditions for equivalence of these disparate
methods are presented. We also describe connections between probabilistic
linear solvers and projection methods for linear systems, providing a
probabilistic interpretation of a far more general class of iterative methods.
In particular, this provides such an interpretation of the generalised minimum
residual method. A probabilistic view of preconditioning is also introduced.
These developments unify the literature on probabilistic linear solvers, and
provide foundational connections to the literature on iterative solvers for
linear systems
Global Phase Space of Coherence and Entanglement in a double-well BEC
Ultracold atoms provide an ideal system for the realization of quantum
technologies, but also for the study of fundamental physical questions such as
the emergence of decoherence and classicality in quantum many-body systems.
Here, we study the global structure of the quantum dynamics of bosonic atoms in
a double-well trap and analyze the conditions for the generation of
many-particle entanglement and spin squeezing which have important applications
in quantum metrology. We show how the quantum dynamics is determined by the
phase space structure of the associated mean-field system and where true
quantum features arise beyond this `classical' approximation
Milk Handling in the Supply Chains: The Case of Smallholder Retail Outlets In Nakuru, Kenya
This paper characterises smallholder milk outlets in Nakuru district one of the major milk producing Districts in Kenya, and also analyses factors that influence their current operating and handling capacities. Data comes from four divisions of the district. A sample of 137 smallholder milk retail outlets was made using systematic random sampling methodology. Both descriptive and ordinary regression methods were used in the analysis. A characterisation of the retail outlets is brought out and the factors that affect their current operating capacities presented. Results show that a unit change in education, experience and selling prices leads to 0.29, 0.18 and 0.23 significant changes in milk handling capacities by the retail outlets respectively. These imply that there is an efficiency gain from education and better prices through higher consumer incomes in the industry. Enhancement of milk retailers' value addition through provision of physical facilities such as cooling equipment and stability in prices should be encouraged through policy intervention to promote informal sector investments in the sub-sector.milk supply chain, smallholder retail outlets, Kenya, Industrial Organization, Marketing,
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