3,425 research outputs found
A proposal for a new type of thin-film field-emission display by edge breakdown of MIS structure
A new type of field emission display(FED) based on an edge-enhance electron
emission from metal-insulator-semiconductor (MIS) thin film structure is
proposed. The electrons produced by an avalanche breakdown in the semiconductor
near the edge of a top metal electrode are initially injected to the thin film
of an insulator with a negative electron affinity (NEA), and then are injected
into vacuum in proximity to the top electrode edge. The condition for the
deep-depletition breakdown near the edge of the top metal electrode is
analytically found in terms of ratio of the insulator thickness to the maximum
(breakdown) width of the semiconductor depletition region: this ratio should be
less than 2/(3 \pi - 2) = 0.27. The influence of a neighboring metal electrode
and an electrode thickness on this condition are analyzed. Different practical
schemes of the proposed display with a special reference to M/CaF_2/Si
structure are considered.Comment: 11 pages, 5 figure
The Megasecond Chandra X-Ray Visionary Project Observation of NGC 3115 (III): luminosity functions of LMXBs and dependence on stellar environments
We have studied the X-ray luminosity function (XLF) of low-mass X-ray
binaries (LMXBs) in the nearby lenticular galaxy NGC 3115, using the Megasecond
Chandra X-Ray Visionary Project Observation. With a total exposure time of ~1.1
Ms, we constructed the XLF down to a limiting luminosity of ~10^36 erg/s, much
deeper than typically reached for other early-type galaxies. We found
significant flattening of the overall LMXB XLF from dN/dL \propto
L^{-2.2\pm0.4} above 5.5x10^37 erg/s to dN/dL \propto L^{-1.0\pm0.1} below it,
though we could not rule out a fit with a higher break at ~1.6x10^38 erg/s. We
also found evidence that the XLF of LMXBs in globular clusters (GCs) is overall
flatter than that of field LMXBs. Thus our results for this galaxy do not
support the idea that all LMXBs are formed in GCs. The XLF of field LMXBs seems
to show spatial variation, with the XLF in the inner region of the galaxy being
flatter than that in the outer region, probably due to contamination of LMXBs
from undetected and/or disrupted GCs in the inner region. The XLF in the outer
region is probably the XLF of primordial field LMXBs, exhibiting dN/dL \propto
L^{-1.2\pm0.1} up to a break close to the Eddington limit of neutron star LMXBs
(~1.7x10^38 erg/s). The break of the GC LMXB XLF is lower, at ~1.1x10^37 erg/s.
We also confirm previous findings that the metal-rich/red GCs are more likely
to host LMXBs than the metal-poor/blue GCs, which is more significant for more
luminous LMXBs, and that more massive GCs are more likely to host LMXBs.Comment: 12 pages, 8 figures, accepted for publication in Ap
The Megasecond Chandra X-Ray Visionary Project Observation of NGC 3115 (II): properties of point sources
We have carried out an in-depth study of low-mass X-ray binaries (LMXBs)
detected in the nearby lenticular galaxy NGC 3115, using the Megasecond Chandra
X-Ray Visionary Project observation (total exposure time 1.1 Ms). In total we
found 136 candidate LMXBs in the field and 49 in globular clusters (GCs) above
2\sigma\ detection, with 0.3--8 keV luminosity L_X ~10^36-10^39 erg/s. Other
than 13 transient candidates, the sources overall have less long-term
variability at higher luminosity, at least at L_X > 2x10^37 erg/s. In order to
identify the nature and spectral state of our sources, we compared their
collective spectral properties based on single-component models (a simple power
law or a multicolor disk) with the spectral evolution seen in representative
Galactic LMXBs. We found that in the L_X versus photon index \Gamma_PL and L_X
versus disk temperature kT_MCD plots, most of our sources fall on a narrow
track in which the spectral shape hardens with increasing luminosity below
L_X~7x10^37 erg/s but is relatively constant (\Gamma_PL~1.5 or kT_MCD~1.5 keV)
above this luminosity, similar to the spectral evolution of Galactic neutron
star (NS) LMXBs in the soft state in the Chandra bandpass. Therefore we
identified the track as the NS LMXB soft-state track and suggested sources with
L_X7x10^37 erg/s
as Z sources. Ten other sources (five are transients) displayed significantly
softer spectra and are probably black hole X-ray binaries in the thermal state.
One of them (persistent) is in a metal-poor GC.Comment: 26 pages, 9 figures, four online tables, accepted for publication in
Ap
Revisiting the Globular Cluster System of the Merger Remnant Elliptical NGC 3610
We have obtained Keck spectra of six candidate globular clusters (GCs) in the
dynamically young elliptical galaxy NGC 3610, supplementing our previous Keck
spectra of eight confirmed GCs (Strader et al. 2003). Five of our new
candidates are confirmed to be GCs. Of the thirteen GCs, eleven are located
within the K band effective radius of 7 kpc. Two of these thirteen clusters are
found to be young (~ 2 Gyr) and very metal-rich ([Z/H] ~ +0.5), three are old
and metal-poor, and the remaining eight clusters are old and metal-rich. The
ages of the young clusters are consistent with a recent spectroscopic age
estimate of 1.6+/-0.5 Gyr for the galaxy itself (Denicolo et al. 2003) and
suggest that these clusters formed in the disk-disk merger which likely created
NGC 3610. Intriguingly, both young GCs have [alpha/Fe] ~ +0.3, while the
majority of the old clusters are not alpha-enhanced, in contrast to Galactic
and M31 GCs, and contrary to predictions of nucleosynthetic calculations. The
two old subpopulations of GCs can be attributed to the merger progenitors. The
relative numbers of old and new metal-rich GCs are poorly constrained because
of the expected differences in radial distributions of the two subpopulations.
However, based on our spectroscopic results and a comparison of the Hubble
Space Telescope color magnitude diagram (Whitmore et al. 2002) with stellar
population models, we argue that more than half of the metal-rich GCs are
likely to be old.Comment: 21 pages, 6 figures, accepted for Jan 2004 A
Dissipative quantum mechanics and Kondo-like impurities on noncommutative two-tori
In a recent paper, by exploiting the notion of Morita equivalence for field
theories on noncommutative tori and choosing rational values of the
noncommutativity parameter (in appropriate units), a general
one-to-one correspondence between the -reduced conformal field theory (CFT)
describing a quantum Hall fluid (QHF) at paired states fillings and an Abelian noncommutative field theory (NCFT) has been
established . That allowed us to add new evidence to the relationship between
noncommutativity and quantum Hall fluids\cite% {ncmanybody}. On the other hand,
the -reduced CFT is equivalent to a system of two massless scalar bosons
with a magnetic boundary interaction as introduced by Callan et al., at the so
called ``magic''\ points. We are then able to describe, within such a
framework, the dissipative quantum mechanics of a particle confined to a plane
and subject to an external magnetic field normal to it. Here we develop such a
point of view by focusing on the case which corresponds to a quantum Hall
bilayer. The key role of a localized impurity which couples the two layers is
emphasized and the effect of noncommutativity in terms of generalized magnetic
translations (GMT) is fully exploited. As a result, general GMT operators are
introduced, in the form of a tensor product, which act on the QHF and defect
space respectively, and a comprehensive study of their rich structure is
performed.Comment: 18 pages, 1 figure, accepted for publication in International Journal
of Modern Physics
Three-point Green function of the stress-energy tensor in the AdS/CFT correspondence
We compute the 3-point function of the stress-energy tensor in the
d-dimensional CFT from the AdS_{d+1} gravity. For d=4 the coefficients of the
three linearly independent conformally covariant forms entering the 3-point
function are exactly the same as given by the free field computations in the
SYM just as expected from the known renormalization theorems. For
d=3 and d=6 our results give the value of the corresponding 3-point function in
the theories of strongly coupled superconformal scalar and (2,0)
tensor multiplets respectively.Comment: Latex, 13 pages, eq. (2.10) is correcte
Some Cubic Couplings in Type IIB Supergravity on and Three-point Functions in SYM_4 at Large N
All cubic couplings in type IIB supergravity on that
involve two scalar fields that are mixtures of the five form field
strength on and the trace of the graviton on are derived by using
the covariant equations of motion and the quadratic action for type IIB
supergravity on . All corresponding three-point functions in
SYM are calculated in the supergravity approximation. It is pointed out
that the scalars correspond not to the chiral primary operators in the
SYM but rather to a proper extension of the operators.Comment: Latex, 24p, misprints are correcte
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