5,307 research outputs found
The influence of particle surface friction on the behavior of gas-fluidized beds: Development of a two fluid model
The influence of physically realistic collisional properties on the hydrodynamics in a bubbling dense gas-solid fluidized bed is investigated using both a Discrete Particle Model (DPM) and a Two Fluid Model (TFM) incorporating a kinetic theory of granular flow (KTGF) for rough spheres by Lei et al. (1). The validated KTGF accounts for particle rotation and particle surface friction expilicitly. Comparisons between the two models are carried out to investigate the influence of particle friction on axial particle velocity, solids circulation pattern, and bubble behavior. The simulated results from both models reveal that the friction coefficient plays an important role in the formation of heterogeneous structures in a bubbling bed. When the friction coefficient is increased, larger bubbles appear and the fluidization in the bed is more vigorous. In addition, the time-averaged gas-solid flow field and time-averaged solids volume fraction vary significantly with different friction coefficient. Less dense zones are found in the bed for larger values of the friction coefficient.
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Holonomy Transformation in the FRW Metric
In this work we investigate loop variables in Friedman-Robertson-Walker
spacetime. We analyze the parallel transport of vectors and spinors in several
paths in this spacetime in order to classify its global properties. The band
holonomy invariance is analysed in this background.Comment: 8 page
Performance of commercial tests for molecular detection of Shiga toxin-producing Escherichia coli (STEC): A systematic review and meta-analysis protocol
Magnetic field and pressure effects on charge density wave, superconducting, and magnetic states in LuIrSi and ErIrSi
We have studied the charge-density-wave (CDW) state for the superconducting
LuIrSi and the antiferromagnetic ErIrSi as
variables of temperature, magnetic field, and hydrostatic pressure. For
LuIrSi, the application of pressure strongly suppresses the CDW
phase but weakly enhances the superconducting phase. For ErIrSi,
the incommensurate CDW state is pressure independent and the commensurate CDW
state strongly depends on the pressure, whereas the antiferromagnetic ordering
is slightly depressed by applying pressure. In addition, ErIrSi
shows negative magnetoresistance at low temperatures, compared with the
positive magnetoresistance of LuIrSi.Comment: 12 pages, including 6 figure
Chesapeake Bay Nitrogen Fluxes Derived From a Land-Estuarine Ocean Biogeochemical Modeling System: Model Description, Evaluation, and Nitrogen Bonds
The Chesapeake Bay plays an important role in transforming riverine nutrients before they are exported to the adjacent continental shelf. Although the mean nitrogen budget of the Chesapeake Bay has been previously estimated from observations, uncertainties associated with interannually varying hydrological conditions remain. In this study, a land-estuarine-ocean biogeochemical modeling system is developed to quantify Chesapeake riverine nitrogen inputs, within-estuary nitrogen transformation processes and the ultimate export of nitrogen to the coastal ocean. Model skill was evaluated using extensive in situ and satellite-derived data, and a simulation using environmental conditions for 2001-2005 was conducted to quantify the Chesapeake Bay nitrogen budget. The 5 year simulation was characterized by large riverine inputs of nitrogen (154 x 109 g N yr-1) split roughly 60: 40 between inorganic: organic components. Much of this was denitrified (34 x 109 g N yr-1) and buried (46 x 109 g N yr-1) within the estuarine system. A positive net annual ecosystem production for the bay further contributed to a large advective export of organic nitrogen to the shelf (91 x 109 g N yr-1) and negligible inorganic nitrogen export. Interannual variability was strong, particularly for the riverine nitrogen fluxes. In years with higher than average riverine nitrogen inputs, most of this excess nitrogen (50-60%) was exported from the bay as organic nitrogen, with the remaining split between burial, denitrification, and inorganic export to the coastal ocean. In comparison to previous simulations using generic shelf biogeochemical model formulations inside the estuary, the estuarine biogeochemical model described here produced more realistic and significantly greater exports of organic nitrogen and lower exports of inorganic nitrogen to the shelf
Using Optical Coherence Tomography to Characterize the Crack Morphology of Ceramic Glaze and Jade
Neoplastic transformation of mouse C3H 10T1/2 and Syrian hamster embryo cells by heavy ions
C3H 10T1/2 mouse-embryo fibroblasts were used for transformation experiments to study the effectiveness of various heavy ions with energies up to 20 MeV/u and LET values from 170 to 16.000 keV/μm. The transformation frequency per unit absorbed dose decreased with increasing ionization density; at the highest values of LET we found a decrease even of the transformation efficiency per unit fluence. Uranium ions at energies of 5, 9, and 16.3 MeV/u did not induced any transformation.
In additional studies piimary Syrian hamster embryo cells (SHE) were exposed to heavy ions in order to characterize cytological and molecular changes which may be correlated with neoplastic transformation. Growth behaviour, chromosomal status, tumorigenicity in nude mice, and expression of oncogenes of transformed cell lines were examined
Anisotropic Transport of Quantum Hall Meron-Pair Excitations
Double-layer quantum Hall systems at total filling factor can
exhibit a commensurate-incommensurate phase transition driven by a magnetic
field oriented parallel to the layers. Within the commensurate
phase, the lowest charge excitations are believed to be linearly-confined Meron
pairs, which are energetically favored to align with . In order
to investigate this interesting object, we propose a gated double-layer Hall
bar experiment in which can be rotated with respect to the
direction of a constriction. We demonstrate the strong angle-dependent
transport due to the anisotropic nature of linearly-confined Meron pairs and
discuss how it would be manifested in experiment.Comment: 4 pages, RevTex, 3 postscript figure
Constraints on ultracompact minihalos from extragalactic {\gamma}-ray background
It has been proposed that ultracompact minihalos (UCMHs) might be formed in
earlier epoch. If dark matter consists of Weakly Interacting Massive Particles
(WIMPs), UCMHs can be treated as the {\gamma}-ray sources due to dark matter
annihilation within them. In this paper, we investigate the contributions of
UCMHs formed during three phase transi- tions (i.e., electroweak symmetry
breaking, QCD confinement and e+ e- annihilation) to the extragalactic
{\gamma}-ray background. Moreover, we use the Fermi-LAT observation data of the
extragalactic {\gamma}-ray background to get the constraints on the current
abundance of UCMHs produced during these phase transitions. We also compare
these results with those obtained from Cosmic Microwave Background (CMB)
observations and find that the constraints from the Fermi-LAT are more
stringent than those from CMBComment: 13 pages, 4 figures, 1 tabl
Description of surfaces associated with sigma models on Minkowski space
The objective of this paper is to construct and investigate smooth orientable
surfaces in by analytical methods. The structural equations of
surfaces in connection with sigma models on Minkowski space are
studied in detail. This is carried out using moving frames adapted to surfaces
immersed in the algebra. The first and second fundamental forms of this
surface as well as the relations between them as expressed in the
Gauss-Weingarten and Gauss-Codazzi-Ricci equations are found. The Gaussian
curvature, the mean curvature vector and the Willmore functional expressed in
terms of a solution of sigma model are obtained. An example of a
surface associated with the model is included as an illustration of the
theoretical results.Comment: 19 pages, 1 figure; shorter version, some typos and minor mistakes
correcte
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