1,071 research outputs found
Looking ahead: subjective time perception and individual discounting
Time discounting is at the heart of economic decision-making. We disentangle hyperbolic discounting from subjective time perception using experimental data from incentive-compatible tests to measure time preferences, and a set of experimental tasks to measure time perception. The two behavioural parameters may be related to two factors that affect how we look ahead to future events. The first is that some component of time preferences reflect hyperbolic discounting. The second factor is that non-constant discounting may also be a reflection of subjective time perception: if people’s perception of time follows a near logarithmic process (as all other physiological perceptions such as heat, sound, and light do) then all existing estimates of individual discounting will be mis-measured and incorrectly suggest “hyperbolic” discounting, even if discounting over subjective time is constant. To test these hypotheses, we empirically estimate the two distinct behavioural parameters using data collected from 178 participants to an experiment conducted at the London School of Economics Behavioural Research Lab. The results support the hypothesis that apparent non-constant discounting is largely a reflection of subjective time perception
Evolutionary tracks for Betelgeuse
We have constructed a series of non-rotating quasi-hydrostatic evolutionary
models for the M2 Iab supergiant Betelgeuse (). Our models are
constrained by multiple observed values for the temperature, luminosity,
surface composition and mass loss for this star, along with the parallax
distance and high resolution imagery that determines its radius. We have then
applied our best-fit models to analyze the observed variations in surface
luminosity and the size of detected surface bright spots as the result of
up-flowing convective material from regions of high temperature in the surface
convective zone. We also attempt to explain the intermittently observed
periodic variability in a simple radial linear adiabatic pulsation model. Based
upon the best fit to all observed data, we suggest a best progenitor mass
estimate of and a current age from the start of the
zero-age main sequence of Myr based upon the observed ejected mass
while on the giant branch.Comment: 27 pages, 11 figures, Revised per referee suggestions, Accepted for
publication in the Astrophysical Journa
Polarised infrared emission from X-ray binary jets
Near-infrared (NIR) and optical polarimetric observations of a selection of
X-ray binaries are presented. The targets were observed using the Very Large
Telescope and the United Kingdom Infrared Telescope. We detect a significant
level (3 sigma) of linear polarisation in four sources. The polarisation is
found to be intrinsic (at the > 3 sigma level) in two sources; GRO J1655-40 (~
4-7% in H and Ks-bands during an outburst) and Sco X-1 (~ 0.1-0.9% in H and K),
which is stronger at lower frequencies. This is likely to be the signature of
optically thin synchrotron emission from the collimated jets in these systems,
whose presence indicates a partially-ordered magnetic field is present at the
inner regions of the jets. In Sco X-1 the intrinsic polarisation is variable
(and sometimes absent) in the H and K-bands. In the J-band (i.e. at higher
frequencies) the polarisation is not significantly variable and is consistent
with an interstellar origin. The optical light from GX 339-4 is also polarised,
but at a level and position angle consistent with scattering by interstellar
dust. The other polarised source is SS 433, which has a low level (0.5-0.8%) of
J-band polarisation, likely due to local scattering. The NIR counterparts of
GRO J0422+32, XTE J1118+480, 4U 0614+09 and Aql X-1 (which were all in or near
quiescence) have a linear polarisation level of < 16% (3 sigma upper limit,
some are < 6%). We discuss how such observations may be used to constrain the
ordering of the magnetic field close to the base of the jet in such systems.Comment: Accepted to be published in MNRAS; 13 pages, 6 figure
Extended phase space thermodynamics for charged and rotating black holes and Born-Infeld vacuum polarization
We investigate the critical behaviour of charged and rotating AdS black holes
in d spacetime dimensions, including effects from non-linear electrodynamics
via the Born-Infeld action, in an extended phase space in which the
cosmological constant is interpreted as thermodynamic pressure. For
Reissner-Nordstrom black holes we find that the analogy with the Van der Walls
liquid-gas system holds in any dimension greater than three, and that the
critical exponents coincide with those of the Van der Waals system. We find
that neutral slowly rotating black holes in four space-time dimensions also
have the same qualitative behaviour. However charged and rotating black holes
in three spacetime dimensions do not exhibit critical phenomena. For
Born-Infeld black holes we define a new thermodynamic quantity B conjugate to
the Born-Infeld parameter b that we call Born-Infeld vacuum polarization. We
demonstrate that this quantity is required for consistency of both the first
law of thermodynamics and the corresponding Smarr relation.Comment: 23 pages, 32 figures, v2: minor changes, upgraded reference
Threshold Corrections and Gauge Symmetry in Twisted Superstring Models
Threshold corrections to the running of gauge couplings are calculated for
superstring models with free complex world sheet fermions. For two N=1
models, the threshold corrections lead to a small increase
in the unification scale. Examples are given to illustrate how a given particle
spectrum can be described by models with different boundary conditions on the
internal fermions. We also discuss how complex twisted fermions can enhance the
symmetry group of an N=4 model to the gauge group
. It is then shown how a mixing angle analogous
to the Weinberg angle depends on the boundary conditions of the internal
fermions.Comment: easier to Tex version, figures to be sent separatel
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