9,584 research outputs found
On spontaneous scalarization
We study in the physical frame the phenomenon of spontaneous scalarization
that occurs in scalar-tensor theories of gravity for compact objects. We
discuss the fact that the phenomenon occurs exactly in the regime where the
Newtonian analysis indicates it should not. Finally we discuss the way the
phenomenon depends on the equation of state used to describe the nuclear
matter.Comment: 41 pages, RevTex, 10 ps figures, submitted to Phys. Rev.
Spin-dependent phenomena and device concepts explored in (Ga,Mn)As
Over the past two decades, the research of (Ga,Mn)As has led to a deeper
understanding of relativistic spin-dependent phenomena in magnetic systems. It
has also led to discoveries of new effects and demonstrations of unprecedented
functionalities of experimental spintronic devices with general applicability
to a wide range of materials. In this article we review the basic material
properties that make (Ga,Mn)As a favorable test-bed system for spintronics
research and discuss contributions of (Ga,Mn)As studies in the general context
of the spin-dependent phenomena and device concepts. Special focus is on the
spin-orbit coupling induced effects and the reviewed topics include the
interaction of spin with electrical current, light, and heat.Comment: 47 pages, 41 figure
Rotating star initial data for a constrained scheme in numerical relativity
A new numerical code for computing stationary axisymmetric rapidly rotating
stars in general relativity is presented. The formulation is based on a fully
constrained-evolution scheme for 3+1 numerical relativity using the Dirac gauge
and maximal slicing. We use both the polytropic and MIT bag model equations of
state to demonstrate that the code can construct rapidly rotating neutron star
and strange star models. We compare numerical models obtained by our code and a
well-established code, which uses a different gauge condition, and show that
the two codes agree to high accuracy.Comment: Minor changes and one figure added. Version accepted for publication
in Class. Quant. Gra
Testing Magnetic Field Models for the Class 0 Protostar L1527
For the Class 0 protostar, L1527, we compare 131 polarization vectors from
SCUPOL/JCMT, SHARP/CSO and TADPOL/CARMA observations with the corresponding
model polarization vectors of four ideal-MHD, non-turbulent, cloud core
collapse models. These four models differ by their initial magnetic fields
before collapse; two initially have aligned fields (strong and weak) and two
initially have orthogonal fields (strong and weak) with respect to the rotation
axis of the L1527 core. Only the initial weak orthogonal field model produces
the observed circumstellar disk within L1527. This is a characteristic of
nearly all ideal-MHD, non-turbulent, core collapse models. In this paper we
test whether this weak orthogonal model also has the best agreement between its
magnetic field structure and that inferred from the polarimetry observations of
L1527. We found that this is not the case; based on the polarimetry
observations the most favored model of the four is the weak aligned model.
However, this model does not produce a circumstellar disk, so our result
implies that a non-turbulent, ideal-MHD global collapse model probably does not
represent the core collapse that has occurred in L1527. Our study also
illustrates the importance of using polarization vectors covering a large area
of a cloud core to determine the initial magnetic field orientation before
collapse; the inner core magnetic field structure can be highly altered by a
collapse and so measurements from this region alone can give unreliable
estimates of the initial field configuration before collapse.Comment: 43 pages, 9 figures, 4 tables. Accepted by the Astrophysical Journa
Far-infrared polarimetry from the Stratospheric Observatory for Infrared Astronomy
Multi-wavelength imaging polarimetry at far-infrared wavelengths has proven
to be an excellent tool for studying the physical properties of dust, molecular
clouds, and magnetic fields in the interstellar medium. Although these
wavelengths are only observable from airborne or space-based platforms, no
first-generation instrument for the Stratospheric Observatory for Infrared
Astronomy (SOFIA) is presently designed with polarimetric capabilities. We
study several options for upgrading the High-resolution Airborne Wideband
Camera (HAWC) to a sensitive FIR polarimeter. HAWC is a 12 x 32 pixel bolometer
camera designed to cover the 53 - 215 micron spectral range in 4 colors, all at
diffraction-limited resolution (5 - 21 arcsec). Upgrade options include: (1) an
external set of optics which modulates the polarization state of the incoming
radiation before entering the cryostat window; (2) internal polarizing optics;
and (3) a replacement of the current detector array with two state-of-the-art
superconducting bolometer arrays, an upgrade of the HAWC camera as well as
polarimeter. We discuss a range of science studies which will be possible with
these upgrades including magnetic fields in star-forming regions and galaxies
and the wavelength-dependence of polarization.Comment: 12 pages, 5 figure
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