9,863 research outputs found
A frictional Cosserat model for the flow of granular materials through a vertical channel
A rigid-plastic Cosserat model has been used to study dense, fully developed
flow of granular materials through a vertical channel. Frictional models based
on the classical continuum do not predict the occurrence of shear layers, at
variance with experimental observations. This feature has been attributed to
the absence of a material length scale in their constitutive equations. The
present model incorporates such a material length scale by treating the
granular material as a Cosserat continuum. Thus localised couple stresses exist
and the stress tensor is asymmetric. The velocity profiles predicted by the
model are in close agreement with available experimental data. The predicted
dependence of the shear layer thickness on the width of the channel is in
reasonable agreement with data. In the limit of the ratio of the particle
diameter to the half-width of the channel being small, the model predicts that
the shear layer thickness scaled by the particle diameter grows.Comment: 17 pages, 12 PostScript figures, uses AmsLaTeX, psfrag and natbib.
Accepted for publication in Acta Mechanic
Exploration of The Duality Between Generalized Geometry and Extraordinary Magnetoresistance
We outline the duality between the extraordinary magnetoresistance (EMR),
observed in semiconductor-metal hybrids, and non-symmetric gravity coupled to a
diffusive gauge field. The corresponding gravity theory may be
interpreted as the generalized complex geometry of the semi-direct product of
the symmetric metric and the antisymmetric Kalb-Ramond field:
(). We construct the four dimensional covariant
field theory and compute the resulting equations of motion. The equations
encode the most general form of EMR within a well defined variational
principle, for specific lower dimensional embedded geometric scenarios. Our
formalism also reveals the emergence of additional diffusive pseudo currents
for a completely dynamic field theory of EMR. The proposed equations of motion
now include terms that induce geometrical deformations in the device geometry
in order to optimize the EMR. This bottom-up dual description between EMR and
generalized geometry/gravity lends itself to a deeper insight into the EMR
effect with the promise of potentially new physical phenomena and properties.Comment: 13 pages and 6 figures. Revised/edited for clarity and purpose.
Several references added. Updated title based on suggestions and comments
received. Version accepted for publication in Phys.Rev.
Radio Recombination Lines from Starbursts: NGC 3256, NGC 4945 and the Circinus Galaxy
A renewed attempt to detect radio recombination lines from external galaxies
has resulted in the measurement of lines from several bright starburst
galaxies. The lines are produced by hydrogen ionized by young, high-mass stars
and are diagnostic of the conditions and gas dynamics in the starburst regions
without problems of dust obscuration. We present here detections of the lines
H91alpha and H92alpha near 8.6 GHz from the starburst nuclei in NGC 3256, NGC
4945, and the Circinus galaxy using the ATCA and VLA. Modelling the line
emitting region as a collection of H II regions, we derive the required number
of H II regions, their temperature, density, and distribution.Comment: 6 pages, to appear in "Proc 331. Heraeus Seminar: The Evolution of
Starbursts", Bad Honnef, Germany, Aug 16 - 20, 2004, Eds: S. Huettemeister,
S. Aalto, D.J. Bomans, and E. Manthe
Temporally and spatially resolved flow in a two-stage axial compressor. Part 2: Computational assessment
Fluid dynamics of turbomachines are complicated due to aerodynamic interactions between rotors and stators. It is necessary to understand the aerodynamics associated with these interactions in order to design turbomachines that are both light and compact as well as reliable and efficient. The current study uses an unsteady, thin-layer Navier-Stokes zonal approach to investigate the unsteady aerodynamics of a multi-stage compressor. Relative motion between rotors and stators is made possible by use of systems of patched and overlaid grids. Results have been computed for a 2 1/2-stage compressor configuration. The numerical data compares well with experimental data for surface pressures and wake data. In addition, the effect of grid refinement on the solution is studied
AYURVEDIC MANAGEMENT IN THREATENED ABORTION AND FOETAL ANOMALY – A CASE REPORT
Congenital anomalies amount to 50% of causative factor to first trimester abortions. Ayurvedic Ante Natal Care is highly effective in maintaining a healthy pregnancy and delivering a healthy progeny. A 28 year old female with bleeding per vaginum which started at 5 weeks of pregnancy, was advised for Medical Termination of Pregnancy. But she wanted to try Ayurvedic management and was treated with Ayurvedic medicines. The bleeding stopped in 11 days and fetal pole was visualized. She had occasional spotting in between and was detected with long bone growth lower than the normal limit in her anomaly scan at 20 weeks of gestation. She was advised termination owing to the risk of fetal anomalies but she was unwilling and wanted to continue Ayurvedic treatment. She was explained regarding all the possible consequences of continuing the pregnancy and with the consent of the patient and her family Ayurvedic treatment was continued. She delivered a healthy male baby of birth weight 2.57kg through Lower Segment Caesarean Section at term with an APGAR score of 9 at 1 minute. The baby had no gross or obvious anomalies at birth. The present case demonstrates the effectiveness of Ayurvedic Ante Natal Care in positive prognosis of threatened abortion
The Old is Made New
This panel will consider old and new technologies, materials and processes of iron casting, mold making and foundry practice in the light of contemporary attitudes on environmental impacts. Are some of the old methods and practices of iron casting more environmentally “green” than contemporary practice
Lateral transition metal dichalcogenide heterostructures for high efficiency thermoelectric devices
Increasing demands for renewable sources of energy has been a major driving
force for developing efficient thermoelectric materials. Two-dimensional (2D)
transition-metal dichalcogenides (TMDC) have emerged as promising candidates
for thermoelectric applications due to their large effective mass and low
thermal conductivity. In this article, we study the thermoelectric performance
of lateral TMDC heterostructures within a multiscale quantum transport
framework. Both -type and -type lateral heterostructures are considered
for all possible combinations of semiconducting TMDCs: MoS, MoSe,
WS, and WSe. The band alignment between these materials is found to
play a crucial in enhancing the thermoelectric figure-of-merit () and power
factor far beyond those of pristine TMDCs. In particular, we show that the
room-temperature value of -type WS with WSe triangular
inclusions, is five times larger than the pristine WS monolayer. -type
MoSe with WSe inclusions is also shown to have a room-temperature
value about two times larger than the pristine MoSe monolayer. The peak
power factor values calculated here, are the highest reported amongst gapped 2D
monolayers at room temperature. Hence, 2D lateral TMDC heterostructures open
new avenues to develop ultra-efficient, planar thermoelectric devices
A frictional Cosserat model for the slow shearing of granular materials
A rigid-plastic Cosserat model for slow frictional flow of granular materials, proposed by us in an earlier paper, has been used to analyse plane and cylindrical Couette flow. In this model, the hydrodynamic fields of a classical continuum are supplemented by the couple stress and the intrinsic angular velocity fields. The balance of angular momentum, which is satisfied implicitly in a classical continuum, must be enforced in a Cosserat continuum. As a result, the stress tensor could be asymmetric, and the angular velocity of a material point may differ from half the local vorticity. An important consequence of treating the granular medium as a Cosserat continuum is that it incorporates a material length scale in the model, which is absent in frictional models based on a classical continuum. Further, the Cosserat model allows determination of the velocity fields uniquely in viscometric flows, in contrast to classical frictional models. Experiments on viscometric flows of dense, slowly deforming granular materials indicate that shear is confined to a narrow region, usually a few grain diameters thick, while the remaining material is largely undeformed. This feature is captured by the present model, and the velocity profile predicted for cylindrical Couette flow is in good agreement with reported data. When the walls of the Couette cell are smoother than the granular material, the model predicts that the shear layer thickness is independent of the Couette gap H when the latter is large compared to the grain diameter dp. When the walls are of the same roughness as the granular material, the model predicts that the shear layer thickness varies as (H/dp)1/3 (in the limit H/dp [dbl greater-than sign] 1) for plane shear under gravity and cylindrical Couette flow
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