2,156 research outputs found
Approximation bias in estimating risk aversion
The asymmetric approximation originally employed by Pratt (1964) to construct reduced-form measures of risk aversion s a downward bias when used for empirical estimation. Calculations based on recent survey data indicate that estimates from a symmetric approximation are generally three times larger than their asymmetric counterparts, a finding that may help to explain the equity premium puzzle.
Measuring Aversion to Health Risks
Researchers have commonly used financial gambles to assess risk preferences, though attitudes regarding monetary gambles may differ from those concerning health risks. Moreover, the conventional measure of risk preference—the Pratt-Arrow coefficient of relative risk aversion—is a point-elasticity suitable only for trivial risks, whereas the risks pertaining to medical treatment—often involving life-ordeath decisions—are quite substantial. Our objective is to examine attitudes toward health risks and the variables that influence those attitudes. In addition to the conventional metric, we employ an alternative measure of risk aversion designed for large-scale risks; the latter is calculated as an arc-elasticity of marginal utility. Both measures are applied to responses from a health preference survey, which incorporates a standard gamble over longevity. Measured risk aversion is then related to health and demographic variables using multiple linear regressions. Our research suggests that tolerance of health risks may be influenced by an endowment effect reflecting the asymmetry of medical information between patients and providers. We also find that the arc-elasticity measure captures more of the significant differences and has a stronger correlation to demographic and socio-economic variables than does the more traditional point-elasticity measure, indicating that the conventional measures of risk aversion are indeed ill suited to large-scale risks such as those involving health. In addition, our results suggest that health-related risk preferences may differ from financial risk attitudes. Although our sample is relatively small and largely homogeneous, these results collectively provide a basis for replication and a justification for additional study on the measurement of risk aversion with regard to health
Performance of astrometric detection of a hotspot orbiting on the innermost stable circular orbit of the galactic centre black hole
The galactic central black hole Sgr A* exhibits outbursts of radiation in the
near infrared (so-called IR flares). One model of these events consists in a
hotspot orbiting on the innermost stable circular orbit (ISCO) of the hole.
These outbursts can be used as a probe of the central gravitational potential.
One main scientific goal of the second generation VLTI instrument GRAVITY is to
observe these flares astrometrically. Here, the astrometric precision of
GRAVITY is investigated in imaging mode, which consists in analysing the image
computed from the interferometric data. The capability of the instrument to put
in light the motion of a hotspot orbiting on the ISCO of our central black hole
is then discussed.
We find that GRAVITY's astrometric precision for a single star in imaging
mode is smaller than the Schwarzschild radius of Sgr A*. The instrument can
also demonstrate that a body orbiting on the last stable orbit of the black
hole is indeed moving. It yields a typical size of the orbit, if the source is
as bright as m_K=14.
These results show that GRAVITY allows one to study the close environment of
Sgr A*. Having access to the ISCO of the central massive black hole probably
allows constraining general relativity in its strong regime. Moreover, if the
hotspot model is appropriate, the black hole spin can be constrained.Comment: 13 pages, 11 figures ; accepted by MNRA
Kalman-filter control schemes for fringe tracking. Development and application to VLTI/GRAVITY
The implementation of fringe tracking for optical interferometers is
inevitable when optimal exploitation of the instrumental capacities is desired.
Fringe tracking allows continuous fringe observation, considerably increasing
the sensitivity of the interferometric system. In addition to the correction of
atmospheric path-length differences, a decent control algorithm should correct
for disturbances introduced by instrumental vibrations, and deal with other
errors propagating in the optical trains. We attempt to construct control
schemes based on Kalman filters. Kalman filtering is an optimal data processing
algorithm for tracking and correcting a system on which observations are
performed. As a direct application, control schemes are designed for GRAVITY, a
future four-telescope near-infrared beam combiner for the Very Large Telescope
Interferometer (VLTI). We base our study on recent work in adaptive-optics
control. The technique is to describe perturbations of fringe phases in terms
of an a priori model. The model allows us to optimize the tracking of fringes,
in that it is adapted to the prevailing perturbations. Since the model is of a
parametric nature, a parameter identification needs to be included. Different
possibilities exist to generalize to the four-telescope fringe tracking that is
useful for GRAVITY. On the basis of a two-telescope Kalman-filtering control
algorithm, a set of two properly working control algorithms for four-telescope
fringe tracking is constructed. The control schemes are designed to take into
account flux problems and low-signal baselines. First simulations of the
fringe-tracking process indicate that the defined schemes meet the requirements
for GRAVITY and allow us to distinguish in performance. In a future paper, we
will compare the performances of classical fringe tracking to our Kalman-filter
control.Comment: 17 pages, 8 figures, accepted for publication in A&
GCIRS16SW: a massive eclipsing binary in the Galactic Center
We report on the spectroscopic monitoring of GCIRS16SW, an Ofpe/WN9 star and
LBV candidate in the central parsec of the Galaxy. SINFONI observations show
strong daily spectroscopic changes in the K band. Radial velocities are derived
from the HeI 2.112 um line complex and vary regularly with a period of 19.45
days, indicating that the star is most likely an eclipsing binary. Under
various assumptions, we are able to derive a mass of ~ 50 Msun for each
component.Comment: 4 pages, 4 figures, ApJ Letters accepte
Distinguishing an ejected blob from alternative flare models at the Galactic centre with GRAVITY
The black hole at the Galactic centre exhibits regularly flares of radiation,
the origin of which is still not understood. In this article, we study the
ability of the near-future GRAVITY infrared instrument to constrain the nature
of these events. We develop realistic simulations of GRAVITY astrometric data
sets for various flare models. We show that the instrument will be able to
distinguish an ejected blob from alternative flare models, provided the blob
inclination is >= 45deg, the flare brightest magnitude is 14 <= mK <= 15 and
the flare duration is >= 1h30.Comment: 11 pages, 9 figures, accepted by MNRA
GRAVITY: The AO-Assisted, Two-Object Beam-Combiner Instrument
We present the proposal for the infrared adaptive optics (AO) assisted,
two-object, high-throughput, multiple-beam-combiner GRAVITY for the VLTI. This
instrument will be optimized for phase-referenced interferometric imaging and
narrow-angle astrometry of faint, red objects. Following the scientific
drivers, we analyze the VLTI infrastructure, and subsequently derive the
requirements and concept for the optimum instrument. The analysis can be
summarized with the need for highest sensitivity, phase referenced imaging and
astrometry of two objects in the VLTI beam, and infrared wavefront-sensing.
Consequently our proposed instrument allows the observations of faint, red
objects with its internal infrared wavefront sensor, pushes the optical
throughput by restricting observations to K-band at low and medium spectral
resolution, and is fully enclosed in a cryostat for optimum background
suppression and stability. Our instrument will thus increase the sensitivity of
the VLTI significantly beyond the present capabilities. With its two fibers per
telescope beam, GRAVITY will not only allow the simultaneous observations of
two objects, but will also push the astrometric accuracy for UTs to 10
micro-arcsec, and provide simultaneous astrometry for up to six baselines.Comment: 12 pages, to be published in the Proceedings of the ESO Workshop on
"The Power of Optical/IR Interferometry: Recent Scientific Results and 2nd
Generation VLTI Instrumentation", eds. F. Paresce, A. Richichi, A. Chelli and
F. Delplancke, held in Garching, Germany, 4-8 April 200
Improved Light Management in Crystalline Silicon Thin Film Solar Cells by Advanced Nano Texture Fabrication
We present a texturing method for liquid phase crystallized silicon thin film solar cells enabling a maximum achievable short circuit current density of 36.5mA cm 2 due to optimized light management compared to current textured device
Tailoring nano textures for optimized light in coupling in liquid phase crystallized silicon thin film solar cells
Thin film solar cells based on liquid phase crystallized silicon LPC Si with 8 20 m thick absorber layers demand for advanced light management to achieve high photocurrent densities. Open circuit voltages Voc gt;600 mV underline the high silicon material quality of LPC silicon thin films on nano textured glass superstrates. We present a 500 nm pitched sinusoidal nano texture which outperforms larger pitched gratings with respect to light in coupling at the buried glass silicon interface. In the wavelength range of interest reflection of incident light is minimized to values close to 4 , which is the reflection at the sun facing air glass interface. Further, the electronic material quality of sinusoidally textured devices is analyzed on basis of a comparison of maximum achieved open circuit voltages on different texture types. The Voc on sinusoidally textured glass superstrates could be raised to 630 mV by changing the interlayer deposition method from a PVD to a PECVD process. Thus, we are able to unify high optical and electronic properties of silicon absorber layers on sinusoidal textured glass substrates. These results constitute a crucial step towards fully exploiting the optical potential of LPC silicon thin film solar cell
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