3,822 research outputs found
The partially asymmetric zero range process with quenched disorder
We consider the one-dimensional partially asymmetric zero range process where
the hopping rates as well as the easy direction of hopping are random
variables. For this type of disorder there is a condensation phenomena in the
thermodynamic limit: the particles typically occupy one single site and the
fraction of particles outside the condensate is vanishing. We use extreme value
statistics and an asymptotically exact strong disorder renormalization group
method to explore the properties of the steady state. In a finite system of
sites the current vanishes as , where the dynamical exponent,
, is exactly calculated. For the transport is realized by active particles, which move with a constant velocity, whereas for
the transport is due to the anomalous diffusion of a single Brownian
particle. Inactive particles are localized at a second special site and their
number in rare realizations is macroscopic. The average density profile of
inactive particles has a width of, , in terms of the
asymmetry parameter, . In addition to this, we have investigated the
approach to the steady state of the system through a coarsening process and
found that the size of the condensate grows as for large
times. For the unbiased model is formally infinite and the coarsening is
logarithmically slow.Comment: 12 pages, 9 figure
Sudden Collapse of a Granular Cluster
Single clusters in a vibro-fluidized granular gas in N connected compartments
become unstable at strong shaking. They are experimentally shown to collapse
very abruptly. The observed cluster lifetime (as a function of the driving
intensity) is analytically calculated within a flux model, making use of the
self-similarity of the process. After collapse, the cluster diffuses out into
the uniform distribution in a self-similar way, with an anomalous diffusion
exponent 1/3.Comment: 4 pages, 4 figures. Figure quality has been reduced in order to
decrease file-siz
Mapping of Hydrothermal Alteration in Mount Berecha Area of Main Ethiopian Rift using Hyperspectral Data
Airborne Imaging Spectroradiometer for Applications (AISA) Hawk data was used to identify and map hydrothermal alteration mineralogy in Mount Berecha area of Main Ethiopian Rift valley. The Airborne image mapping was coupled with laboratory analysis involving reflectance spectroscopic measurements with the use of ASD FieldSpec for mineral and rock samples. The study was based in the shortwave infrared wavelength (SWIR) region. Laboratory spectra acquired from field data analysis served as guide in selecting image endmembers which were used as input in Spectral Angle Mapper (SAM) classification for mineral mapping. SWIR spectroscopy was able to detect the main very fine grained mineral assemblages which occur in the study area, including kaolinite, halloysite, opal, montmorillonite, nontronite, calcite, K-alunite, palygorskite, MgChlorite, zoisite, illite and mixtures of these minerals. SAM classification algorithm gives the overall classification of the alteration minerals of Berecha area and was used to generate the surficial mineral map of the study area. Berecha alteration is related to low sulfidation system and the most widespread alteration effects are represented essentially in advanced argillic alteration assemblage consisting mainly of kaolinite + opal + smectite + alunite which is likely of steam heated origin. Keywords: Hyperspectral, Imaging Spectrometry, AISA Hawk, Berecha, ASD FieldSpec, Spectral Angle Mappe
Zero-range processes with saturated condensation: the steady state and dynamics
We study a class of zero-range processes in which the real-space condensation
phenomenon does not occur and is replaced by a saturated condensation: that is,
an extensive number of finite-size "condensates" in the steady state. We
determine the conditions under which this occurs, and investigate the dynamics
of relaxation to the steady state. We identify two stages: a rapid initial
growth of condensates followed by a slow process of activated evaporation and
condensation. We analyze these nonequilibrium dynamics with a combination of
meanfield approximations, first-passage time calculations and a
fluctuation-dissipation type approach.Comment: 21 pages, 12 figure
Transverse confinement in stochastic cooling of trapped atoms
Stochastic cooling of trapped atoms is considered for a laser-beam
configuration with beam waists equal or smaller than the extent of the atomic
cloud. It is shown, that various effects appear due to this transverse
confinement, among them heating of transverse kinetic energy. Analytical
results of the cooling in dependence on size and location of the laser beam are
presented for the case of a non-degenerate vapour.Comment: 14 pages, 5 figures, accepted for publication in Journal of Optics
Microfluidic Technology in Vascular Research
Vascular cell biology is an area of research with great biomedical relevance. Vascular dysfunction is involved in major diseases such as atherosclerosis, diabetes, and cancer. However, when studying vascular cell biology in the laboratory, it is difficult to mimic the dynamic, three-dimensional microenvironment that is found in vivo. Microfluidic technology offers unique possibilities to overcome this difficulty. In this review, an overview of the recent applications of microfluidic technology in the field of vascular biological research will be given. Examples of how microfluidics can be used to generate shear stresses, growth factor gradients, cocultures, and migration assays will be provided. The use of microfluidic devices in studying three-dimensional models of vascular tissue will be discussed. It is concluded that microfluidic technology offers great possibilities to systematically study vascular cell biology with setups that more closely mimic the in vivo situation than those that are generated with conventional methods
On the Microscopic Origin of Cholesteric Pitch
We present a microscopic analysis of the instability of the nematic phase to
chirality when molecular chirality is introduced perturbatively. We show that
previously neglected short-range biaxial correlations play a crucial role in
determining the cholesteric pitch. We propose an order parameter which
quantifies the chirality of a molecule.Comment: RevTeX 3.0, 4 pages, one included eps figure. Published versio
Tryptophan depletion in chronic fatigue syndrome, a pilot cross-over study
Background: Chronic fatigue syndrome (CFS) is still an enigmatic disorder. CFS can be regarded as a complex disorder with tremendous impact on lives of CFS-patients. Full recovery without treatment is rare. A somatic explanation for the fatigue is lacking. There is clinical and experimental evidence implicating enhanced serotonergic neurotransmission in CFS. Genetic studies and imaging studies support the hypothesis of upregulated serotonin system in CFS. In line with the hypothesis of an increased serotonergic state in CFS, we performed a randomised clinical trial investigated the effect of 5-HT3 receptor antagonism in CFS. No benefit was found of the 5-HT3 receptor antagonist ondansetron compared to placebo. To further investigate the involvement of serotonin in CFS we performed a placebo controlled cross over pilot study investigating the effect of Acute Tryptophan Depletion. Findings: Five female CFS-patients who met the US Center for Disease Control and Prevention criteria for CFS were recruited. There were two test days, one week apart. Each participant received placebo and ATD. To evaluate the efficacy of the ATD procedure tryptophan and the large neutral amino acids were measured. The outcome measures were fatigue severity, concentration and mood states. ATD resulted in a significant plasma tryptophan to large neutral amino acid ratio reduction of 96%. There were no significant differences in fatigue-, depression and concentration between the placebo- and ATD condition. Conclusions: These first five CFS-patients did not respond to the ATD procedure. However, a much larger sample size is needed to draw final conclusions on the hypothesis of an increased serotonergic state in the pathophysiology of CFS. Trial registration: ISRCTN0751814
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