81 research outputs found
Disparities in Health-Related Quality of Life among Adolescent and Young Adult (AYA) Cancer Survivors
https://openworks.mdanderson.org/sumexp22/1067/thumbnail.jp
Upper limits on stray force noise for LISA
We have developed a torsion pendulum facility for LISA gravitational
reference sensor ground testing that allows us to put significant upper limits
on residual stray forces exerted by LISA-like position sensors on a
representative test mass and to characterize specific sources of disturbances
for LISA. We present here the details of the facility, the experimental
procedures used to maximize its sensitivity, and the techniques used to
characterize the pendulum itself that allowed us to reach a torque sensitivity
below 20 fNm /sqrt{Hz} from 0.3 to 10 mHz. We also discuss the implications of
the obtained results for LISA.Comment: To be published in Classical and Quantum Gravity, special issue on
Amaldi5 2003 conference proceedings (10 pages, 6 figures
Identification of cardiovascular disparities among Black and Hispanic survivors of adolescent and young adult (AYA) lymphoma
https://openworks.mdanderson.org/sumexp22/1055/thumbnail.jp
Quantum fluctuations for drag free geodesic motion
The drag free technique is used to force a proof mass to follow a geodesic
motion. The mass is protected from perturbations by a cage, and the motion of
the latter is actively controlled to follow the motion of the proof mass. We
present a theoretical analysis of the effects of quantum fluctuations for this
technique. We show that a perfect drag free operation is in principle possible
at the quantum level, in spite of the back action exerted on the mass by the
position sensor.Comment: 4 pages, 1 figure, RevTeX, minor change
STEP: Satellite Test of the Equivalence Principle. Report on the phase A study
During Phase A, the STEP Study Team identified three types of experiments that can be accommodated on the STEP satellite within the mission constraints and whose performance is orders of magnitude better than any present or planned future experiment of the same kind on the ground. The scientific objectives of the STEP mission are to: test the Equivalence Principle to one part in 10(exp 17), six orders of magnitude better than has been achieved on the ground; search for a new interaction between quantum-mechanical spin and ordinary matter with a sensitivity of the mass-spin coupling constant g(sub p)g(sub s) = 6 x 10(exp -34) at a range of 1 mm, which represents a seven order-of-magnitude improvement over comparable ground-based measurements; and determine the constant of gravity G with a precision of one part in 10(exp 6) and to test the validity of the inverse square law with the same precision, both two orders of magnitude better than has been achieved on the ground
Acceleration disturbances and requirements for ASTROD I
ASTRODynamical Space Test of Relativity using Optical Devices I (ASTROD I)
mainly aims at testing relativistic gravity and measuring the solar-system
parameters with high precision, by carrying out laser ranging between a
spacecraft in a solar orbit and ground stations. In order to achieve these
goals, the magnitude of the total acceleration disturbance of the proof mass
has to be less than 10−13 m s−2 Hz−1/2 at 0.1 m Hz. In this
paper, we give a preliminary overview of the sources and magnitude of
acceleration disturbances that could arise in the ASTROD I proof mass. Based on
the estimates of the acceleration disturbances and by assuming a simple
controlloop model, we infer requirements for ASTROD I. Our estimates show that
most of the requirements for ASTROD I can be relaxed in comparison with Laser
Interferometer Space Antenna (LISA).Comment: 19 pages, two figures, accepted for publication by Class. Quantum
Grav. (at press
Detecting very-high-frequency relic gravitational waves by electromagnetic wave polarizations in a waveguide
The polarization vector (PV) of an electromagnetic wave (EW) will experience
a rotation in a region of spacetime perturbed by gravitational waves (GWs).
Based on this idea, Cruise's group has built an annular waveguide to detect
GWs. We give detailed calculations of the rotations of the polarization vector
of an EW caused by incident GWs from various directions and in various
polarization states, and then analyze the accumulative effects on the
polarization vector when the EW passes n cycles along the annular waveguide. We
reexamine the feasibility and limitation of this method to detect GWs of high
frequency around 100 MHz, in particular, the relic gravitational waves (RGWs).
By comparing the spectrum of RGWs in the accelerating universe with the
detector sensitivity of the current waveguide, it is found that the amplitude
of the RGWs is too low to be detected by the waveguide detectors currently
running. Possible ways of improvements on detection are discussed also.Comment: 18pages, 10 figures, accepted by ChJA
Collective firm bankruptcies and phase transition in rating dynamics
We present a simple model of firm rating evolution. We consider two sources
of defaults: individual dynamics of economic development and Potts-like
interactions between firms. We show that such a defined model leads to phase
transition, which results in collective defaults. The existence of the
collective phase depends on the mean interaction strength. For small
interaction strength parameters, there are many independent bankruptcies of
individual companies. For large parameters, there are giant collective defaults
of firm clusters. In the case when the individual firm dynamics favors dumping
of rating changes, there is an optimal strength of the firm's interactions from
the systemic risk point of view
Sensitivity of wide band detectors to quintessential gravitons
There are no reasons why the energy spectra of the relic gravitons, amplified
by the pumping action of the background geometry, should not increase at high
frequencies. A typical example of this behavior are quintessential inflationary
models where the slopes of the energy spectra can be either blue or mildly
violet. In comparing the predictions of scenarios leading to blue and violet
graviton spectra we face the problem of correctly deriving the sensitivities of
the interferometric detectors. Indeed, the expression of the signal-to-noise
ratio not only depends upon the noise power spectra of the detectors but also
upon the spectral form of the signal and, therefore, one can reasonably expect
that models with different spectral behaviors will produce different
signal-to-noise ratios. By assuming monotonic (blue) spectra of relic gravitons
we will give general expressions for the signal-to-noise ratio in this class of
models. As an example we studied the case of quintessential gravitons. The
minimum achievable sensitivity to of different pairs of
detectors is computed, and compared with the theoretical expectations.Comment: 10 pages in Revtex style, 3 figure
Scope for Credit Risk Diversification
This paper considers a simple model of credit risk and derives the limit distribution of losses under different assumptions regarding the structure of systematic risk and the nature of exposure or firm heterogeneity. We derive fat-tailed correlated loss distributions arising from Gaussian risk factors and explore the potential for risk diversification. Where possible the results are generalised to non-Gaussian distributions. The theoretical results indicate that if the firm parameters are heterogeneous but come from a common distribution, for sufficiently large portfolios there is no scope for further risk reduction through active portfolio management. However, if the firm parameters come from different distributions, then further risk reduction is possible by changing the portfolio weights. In either case, neglecting parameter heterogeneity can lead to underestimation of expected losses. But, once expected losses are controlled for, neglecting parameter heterogeneity can lead to overestimation of risk, whether measured by unexpected loss or value-at-risk
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