184,828 research outputs found
Dynamic simulation of coronal mass ejections
A model is developed for the formation and propagation through the lower corona of the loop-like coronal transients in which mass is ejected from near the solar surface to the outer corona. It is assumed that the initial state for the transient is a coronal streamer. The initial state for the streamer is a polytropic, hydrodynamic solution to the steady-state radial equation of motion coupled with a force-free dipole magnetic field. The numerical solution of the complete time-dependent equations then gradually approaches a stationary coronal streamer configuration. The streamer configuration becomes the initial state for the coronal transient. The streamer and transient simulations are performed completely independent of each other. The transient is created by a sudden increase in the pressure at the base of the closed-field region in the streamer configuration. Both coronal streamers and coronal transients are calculated for values of the plasma beta (the ratio of thermal to magnetic pressure) varying from 0.1 to 100
Pressure study of nematicity and quantum criticality in SrRuO for an in-plane field
We study the relationship between the nematic phases of SrRuO and
quantum criticality. At ambient pressure, one nematic phase is associated with
a metamagnetic quantum critical end point (QCEP) when the applied magnetic
field is near the \textit{c}-axis. We show, however, that this metamagnetic
transition does not produce the same nematic signatures when the QCEP is
reached by hydrostatic pressure with the field applied in the
\textit{ab}-plane. Moreover, a second nematic phase, that is seen for field
applied in the \textit{ab}-plane close to, but not right at, a second
metamagnetic anomaly, persists with minimal change to the highest applied
pressure, 16.55 kbar. Taken together our results suggest that metamagnetic
quantum criticality may not be necessary for the formation of a nematic phase
in SrRuO
Deriving a geocentric reference frame for satellite positioning and navigation
With the advent of Earth-orbiting geodetic satellites, nongeocentric datums or reference frames have become things of the past. Accurate geocentric three-dimensional positioning is now possible and is of great importance for various geodetic and oceanographic applications. While relative positioning accuracy of a few centimeters has become a reality using very long baseline interferometry (VLBI), the uncertainty in the offset of the adopted coordinate system origin from the geocenter is still believed to be on the order of 1 meter. Satellite laser ranging (SLR), however, is capable of determining this offset to better than 10 cm, but this is possible only after years of measurements. Global Positioning System (GPS) measurements provide a powerful tool for an accurate determination of this origin offset. Two strategies are discussed. The first strategy utilizes the precise relative positions that were predetermined by VLBI to fix the frame orientation and the absolute scaling, while the offset from the geocenter is determined from GPS measurements. Three different cases are presented under this strategy. The reference frame thus adopted will be consistent with the VLBI coordinate system. The second strategy establishes a reference frame by holding only the longitude of one of the tracking sites fixed. The absolute scaling is determined by the adopted gravitational constant (GM) of the Earth; and the latitude is inferred from the time signature of the Earth rotation in the GPS measurements. The coordinate system thus defined will be a geocentric Earth-fixed coordinate system
Anomalies, Horizons and Hawking radiation
Hawking radiation is obtained from the Reissner-Nordstr\"{o}m blackhole with
a global monopole and the Garfinkle-Horowitz-Strominger blackhole falling in
the class of the most general spherically symmetric blackholes
, using only chiral anomaly near the event horizon and
covariant boundary condition at the event horizon. The approach differs from
the anomaly cancellation approach since apart from the covariant boundary
condition, the chiral anomaly near the horizon is the only input to derive the
Hawking flux.Comment: minor corrections made, To appear in Euro. Phys. Letter
Review study and evaluation of possible flight experiments relating to cloud physics experiments in space
The general objectives of the Zero-Gravity Atmospheric Cloud Physics Laboratory Program are to improve the level of knowledge in atmospheric cloud research by placing at the disposal of the terrestrial-bound atmospheric cloud physicist a laboratory that can be operated in the environment of zero-gravity or near zero-gravity. This laboratory will allow studies to be performed without mechanical, aerodynamic, electrical, or other techniques to support the object under study. The inhouse analysis of the Skylab 3 and 4 experiments in dynamics of oscillations, rotations, collisions and coalescence of water droplets under low gravity-environment is presented
The first geocenter estimation results using GPS measurements
The center of mass of the Earth is the natural and unambiguous origin of a geocentric satellite dynamical system. A geocentric reference frame assumes that the origin of its coordinate axes is at the geocenter, in which all relevant observations and results can be referred and in which geodynamic theories or models for the dynamic behavior of Earth can be formulated. In practice, however, a kinematically obtained terrestrial reference frame may assume an origin other than the geocenter. A fast and accurate method of determining origin offset from the geocenter is highly desirable. Global Positioning System (GPS) measurements, because of their abundance and broad distribution, provide a powerful tool to obtain this origin offset in a short period of time. Two effective strategies have been devised. Data from the first Central and South America (Casa Uno) global GPS experiment were studied to demonstrate the ability of recovering the geocenter location with present-day GPS satellites and receivers
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