388 research outputs found
Experiments with metallic and ceramic porous media
Work in the area of mechano-caloric phenomena was initiated during 1988 with startup in the Summer 1988 period. The ideal system utilizing He-II super-phenomena is modeled readily, within the frame of thermodynamics energetics, using the concept of an ideal superleak. The real system however uses porous media of non-ideal pore-grain ingredients. The early phase of experimental and related modeling studies is outlined for the time period from Summer 1988 to the end of 1988
g-natural metrics: new horizons in the geometry of tangent bundles of Riemannian manifolds
Traditionally, the Riemannian geometry of tangent and unit tangent bundles was related to the Sasaki metric. The study of the relationship between the geometry of a manifold (M,g) and that of its tangent bundle TM equipped with the Sasaki metric gs had shown some kinds of rigidity. The concept of naturality allowed O.Kowalski and M.Sekizawa to introduce a wide class of metrics on TM naturally constructed from some classical and non-classical lifts of g. This class contains the Sasaki metric as well as the well known Cheeger-Gromoll metric and the metrics of Oproiu-type.
We review some of the most interesting results, obtained recently, concerning the geometry of the tangent and the unit tangent bundles equipped with an arbitrary Riemannian g-natural metric
Thermomechanical force application
The present work conducted in Summer 1987 continues investigations on Thermal Components for 1.8 K Space Cryogenics (Grant NAG 1-412 of 1986). The topics addressed are plug characterization efforts in a small pore size regime of sintered metal plugs, characterization in the nonlinear regime, temperature profiles in a heat supply unit for a fountain effect pump and modeling efforts
Utilization of FEP energetics
The research and development work on Fountain Effect Pump Systems (FEP systems) has been of interest in the competition between mechanical pumps for He II and FEP units. The latter do not have moving parts. In the course of the work, the energetics have been addressed using one part of a simple four-changes-of-state cycle. One option is the FEP ideal change of state at constant chemical potential (mu). The other option is the two-state sequence mu-P with a d mu=0 state change followed by an isobar. Questions of pump behavior, of flow rate response to temperature difference at the hot end, and related questions of thermodynamic cycle completion and heat transfer have been addressed. Porous media data obtained elucidate differences between vapor-liquid phase separation (VLPS) and Zero Net Mass Transfer (ZNMF)
An Accurate Method for Extracting the Critical Field in Short Channel NMOS Devices
In this letter, an accurate method for extracting the critical field Ec in short channel
MOSFET's is presented. The principle of this method is based on the comparison
between two models which give drain saturation voltage evolution against gate
voltage Vdsat(Vg) continuously. The results obtained by this technique have shown
better agreement with measurements data and have allow in the same time to
determine the validity domain of Sodini's law [1]
Vertically Self-Gravitating ADAFs in the Presence of Toroidal Magnetic Field
Force due to the self-gravity of the disc in the vertical direction is
considered to study its possible effects on the structure of a magnetized
advection-dominated accretion disc. We present steady-sate self similar
solutions for the dynamical structure of such a type of the accretion flows.
Our solutions imply reduced thickness of the disc because of the self-gravity.
It also imply that the thickness of the disc will increase by adding the
magnetic field strength.Comment: Accepted for publication in Astrophysics and Space Science
Testing Unimodular Gravity
We consider models of gravitation that are based on unimodular general
coordinate transformations (GCT). These transformations include only those
which do not change the determinant of the metric. We treat the determinant as
a separate field which transforms as a scalar under unimodular GCT. We consider
a class of such theories. In general, these theories do not transform
covariantly under the full GCT. We characterize the violation of general
coordinate invariance by introducing a new parameter. We show that the theory
is consistent with observations for a wide range of this parameter. This
parameter may serve as a test for possible violations of general coordinate
invariance. We also consider the cosmic evolution within the framework of these
models. We show that in general we do not obtain consistent cosmological
solutions if we assume the standard cosmological constant or the standard form
of non-relativistic matter. We propose a suitable generalization which is
consistent with cosmology. We fit the resulting model to the high redshift
supernova data. We find that we can obtain a good fit to this data even if
include only a single component, either cosmological constant or
non-relativistic matter.Comment: 14 pages one figure, significantly revised with several new results
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Paleoearthquakes and slip rates of the North Tabriz Fault, NW Iran: preliminary results
The North Tabriz Fault is a major seismogenic fault in NW Iran. The last damaging earthquakes on this fault
occurred in 1721, rupturing the southeastern fault segment, and in 1780, rupturing the northwestern one. The
understanding of the seismic behavior of this fault is critical for assessing the hazard in Tabriz, one of the major
cities of Iran; the city suffered major damage in both the 1721 and 1780 events. Our study area is located on the
northwestern fault segment, west of the city of Tabriz. We performed geomorphic and trenching investigations,
which allowed us to recognize evidence for repeated faulting events since the Late Pleistocene. From the trenches,
we found evidence for at least four events during the past 3.6 ka, the most recent one being the 1780 earthquake.
On the basis of different approaches, horizontal slip per event and slip rates are found in the ranges of 4 ± 0.5 m
and 3.1-6.4 mm/yr, respectively. We also attempted an estimate of the average recurrence intervals which appears
to be in the range 350-1430 years, with a mean recurrence interval of 821 ± 176 years. On the basis of these results,
the northwestern segment of the North Tabriz Fault does not appear to present a major seismic potential for
the near future, however, not enough is known about the southeastern segment of the fault to make a comparable
conclusion
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