15,826 research outputs found
On worst-case investment with applications in finance and insurance mathematics
We review recent results on the new concept of worst-case portfolio optimization, i.e. we consider the determination of portfolio processes which yield the highest worst-case expected utility bound if the stock price may have uncertain (down) jumps. The optimal portfolios are derived as solutions of non-linear differential equations which itself are consequences of a Bellman principle for worst-case bounds. They are by construction non-constant ones and thus differ from the usual constant optimal portfolios in the classical examples of the Merton problem. A particular application of such strategies is to model crash possibilities where both the number and the height of the crash is uncertain but bounded. We further solve optimal investment problems in the presence of an additional risk process which is the typical situation of an insurer
Pulsars in FIRST Observations
We identified 16 pulsars from the Faint Images of the Radio Sky at Twenty-cm
(FIRST) at 1.4 GHz. Their positions and total flux densities are extracted from
the FIRST catalog. Comparing the source positions with those in the PSRcatalog,
we obtained better determined positions of PSRs J1022+1001, J1518+4904,
J1652+2651, and proper motion upper limits of another three pulsars PSRs
J0751+1807, J1012+5307, J1640+2224. Proper motions of the other 10 pulsars are
consistent with the values in the catalog.Comment: 6 pages, 2 figures, 3 tables, submited to CJA
Physical Structure of Planetary Nebulae. I. The Owl Nebula
The Owl Nebula is a triple-shell planetary nebula with the outermost shell
being a faint bow-shaped halo. We have obtained deep narrow-band images and
high-dispersion echelle spectra in the H-alpha, [O III], and [N II] emission
lines to determine the physical structure of each shell in the nebula. These
spatio-kinematic data allow us to rule out hydrodynamic models that can
reproduce only the nebular morphology. Our analysis shows that the inner shell
of the main nebula is slightly elongated with a bipolar cavity along its major
axis, the outer nebula is a filled envelope co-expanding with the inner shell
at 40 km/s, and the halo has been braked by the interstellar medium as the Owl
Nebula moves through it. To explain the morphology and kinematics of the Owl
Nebula, we suggest the following scenario for its formation and evolution. The
early mass loss at the TP-AGB phase forms the halo, and the superwind at the
end of the AGB phase forms the main nebula. The subsequent fast stellar wind
compressed the superwind to form the inner shell and excavated an elongated
cavity at the center, but has ceased in the past. At the current old age, the
inner shell is backfilling the central cavity.Comment: 10 pages, 6 figures, 1 table, to appear in the Astronomical Journa
Trends and Variation in End-of-Life Care for Medicare Beneficiaries With Severe Chronic Illness
Provides an updated analysis of regional and hospital variations in end-of-life care for Medicare beneficiaries with chronic illnesses, including percentage of hospital deaths, days in intensive care units, and physician labor per patient
Compositional redistribution during casting of Hg sub 0.8 Cd sub 0.2 Te alloys
A series of Hg(0.8)Cd(0.2)Te ingots was cast both vertically and horizontally under well-defined thermal conditions by using a two-zone furnace with isothermal heat-pipe liners. The main objective of the experiments was to establish correlations between casting parameters and compositional redistribution and to develop ground-based data for a proposed flight experiment of casting of Hg(1-x)Cd(x)Te alloys under reduced gravity conditions. The compositional variations along the axial and radial directions were determined by precision density measurements, infrared transmission spectra, and X-ray energy dispersion spectrometry. Comparison between the experimental results and a numerical simulation of the solidification process of Hg(0.8)Cd(0.2)Te is described
Heavy quark polarizations of in the general two Higgs doublet model
The polarizations of the heavy quark ( or ) in the process have been calculated in the general two Higgs doublet model.
The CP violating normal polarization of the top quark can reach 8%, and for the bottom quark, while it is zero in the standard model. The
longitudinal and transverse polarizations of the bottom quark can be
significantly different from those in SM and consequently could aslo be used as
the probe of the new physics.Comment: 12 pages, discussion on statistic significance added, version to
appear in PR
Magnetic influence on the frequency of the soft-phonon mode in the incipient ferroelectric EuTiO3
The dielectric constant of the incipient ferroelectric EuTiO exhibits a
sharp decrease at about 5.5K, at which temperature antiferromagnetic ordering
of the Eu spins simultaneously appears, indicating coupling between the
magnetism and dielectric properties. This may be attributed to the modification
of the soft-phonon mode, , which is the main contribution to the
large dielectric constant, by the Eu spins(7 per Eu). By adding the
coupling term between the magnetic and electrical subsystems as we show that the variation of the frequency of
soft-phonon mode depends on the spin correlation between the nearest neighbors
Eu spins and is substantially changed under a magnetic field.Comment: 13 pages, 4 figure
The Fading Radio Emission from SN 1961V: Evidence for a Type II Peculiar Supernova?
Using the Very Large Array (VLA), we have detected radio emission from the
site of SN 1961V in the Sc galaxy NGC 1058. With a peak flux density of 0.063
+/- 0.008 mJy/beam at 6 cm and 0.147 +/- 0.026 mJy/beam at 18 cm, the source is
non-thermal, with a spectral index of -0.79 +/- 0.23. Within errors, this
spectral index is the same value reported for previous VLA observations taken
in 1984 and 1986. The radio emission at both wavelengths has decayed since the
mid 1980's observations with power-law indices of beta(20cm) = -0.69 +/- 0.23
and beta(6cm) = -1.75 +/- 0.16. We discuss the radio properties of this source
and compare them with those of Type II radio supernovae and luminous blue
variables.Comment: 19 pages, 3 figures; To appear in the Astronomical Journa
Gravitational Corrections to the Energy-Levels of a Hydrogen Atom
The first order perturbations of the energy levels of a hydrogen atom in
central internal gravitational field are investigated. The internal
gravitational field is produced by the mass of the atomic nucleus. The energy
shifts are calculated for the relativistic 1S, 2S, 2P, 3S, 3P, 3D, 4S and 4P
levels with Schwarzschild metric. The calculated results show that the
gravitational corrections are sensitive to the total angular momentum quantum
number.Comment: 7 page
Nanopillar Arrays on Semiconductor Membranes as Electron Emission Amplifiers
A new transmission-type electron multiplier was fabricated from
silicon-on-insulator (SOI) material by integrating an array of one dimensional
(1D) silicon nanopillars onto a two dimensional (2D) silicon membrane. Primary
electrons are injected into the nanopillar-membrane system from the flat
surface of the membrane, while electron emission from the other side is probed
by an anode. The secondary electron yield (SEY) from nanopillars is found to be
about 1.8 times that of plane silicon membrane. This gain in electron number is
slightly enhanced by the electric field applied from the anode. Further
optimization of the dimensions of nanopillars and membrane and application of
field emission promise an even higher gain for detector applications and allow
for probing of electronic/mechanical excitations in nanopillar-membrane system
excited by incident particles or radiation.Comment: 4 figure
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