629 research outputs found
Measurements of neutron-induced reactions in inverse kinematics and applications to nuclear astrophysics
Neutron capture cross sections of unstable isotopes are important for
neutron-induced nucleosynthesis as well as for technological applications. A
combination of a radioactive beam facility, an ion storage ring and a high flux
reactor would allow a direct measurement of neutron induced reactions over a
wide energy range on isotopes with half lives down to minutes. The idea is to
measure neutron-induced reactions on radioactive ions in inverse kinematics.
This means, the radioactive ions will pass through a neutron target. In order
to efficiently use the rare nuclides as well as to enhance the luminosity, the
exotic nuclides can be stored in an ion storage ring. The neutron target can be
the core of a research reactor, where one of the central fuel elements is
replaced by the evacuated beam pipe of the storage ring. Using particle
detectors and Schottky spectroscopy, most of the important neutron-induced
reactions, such as (n,), (n,p), (n,), (n,2n), or (n,f), could
be investigated.Comment: 5 pages, 7 figures, Invited Talk given at the Fifteenth International
Symposium on Capture Gamma-Ray Spectroscopy and Related Topics (CGS15),
Dresden, Germany, 201
Billiards and Brains: Cognitive Ability and Behavior in a p-Beauty Contest
"Beauty contests" are well-studied, dominance-solvable games that generate two interesting results. First, most behavior does not conform to the unique Nash equilibrium. Second, there is considerable unexplained heterogeneity in behavior. In this work, we evaluate the relationship between beauty contest behavior and cognitive ability. We find that subjects with high cognitive ability exhibit behavior that is closer to the Nash equlibrium. We examine this finding through the prism of economic and biological theory.beauty contest; rationality; cognitive ability; Nash equlibrium
Rational Cooperation In One-Shot Simultaneous Pd-Situations
The paper shows that being able to forecast another player's actual cooperation better than pure chance can change players' strategic incentives in a one-shot simultaneous PD-situation. In particular, it is shown that if both players have such ability (to forecast each others' actual choices better than pure chance), then "conditionally cooperative" Nash equilibria may exist in addition to the "always defect" equilibrium. By "conditionally cooperative" we mean that players do not cooperate because of a behavioral "disposition" to act cooperatively, but cooperate rather selectively contingent on their forecasting of the opponent's cooperation (cooperate if and only if each other is forecasted to cooperate). -- Der Beitrag zeigt, daß Spieler, die in der Lage sind, die Aktionen ihrer Gegenspieler eher richtig als falsch zu prognostizieren, in einer prototypischen Gefangenendilemmasituation einen Anreiz haben, sich kooperativ zu verhalten. Insbesondere wird nachgewiesen, daß es neben dem aus der tradtitionellen Analyse bekannten Ergebnis der allseitigen Defektion auch zu sogenannten "bedingt kooperativen" Nash-Gleichgewichten kommen kann, falls beide Spieler diese Prognosefähigkeit besitzen. Die Spieler kooperieren dabei nicht aufgrund einer Disposition für kooperatives Verhalten, sondern vielmehr selektiv und bedingt auf ihre Vorhersagefähigkeit.prisoner's dilemma,reliability condition,forecasting ability,trust
Formation and Evolution of Planetary Systems (FEPS): Properties of Debris Dust around Solar-type Stars
We present Spitzer photometric (IRAC and MIPS) and spectroscopic (IRS low
resolution) observations for 314 stars in the Formation and Evolution of
Planetary Systems (FEPS) Legacy program. These data are used to investigate the
properties and evolution of circumstellar dust around solar-type stars spanning
ages from approximately 3 Myr to 3 Gyr. We identify 46 sources that exhibit
excess infrared emission above the stellar photosphere at 24um, and 21 sources
with excesses at 70um. Five sources with an infrared excess have
characteristics of optically thick primordial disks, while the remaining
sources have properties akin to debris systems. The fraction of systems
exhibiting a 24um excess greater than 10.2% above the photosphere is 15% for
ages < 300 Myr and declines to 2.7% for older ages. The upper envelope to the
70um fractional luminosity appears to decline over a similar age range. The
characteristic temperature of the debris inferred from the IRS spectra range
between 60 and 180 K, with evidence for the presence of cooler dust to account
for the strength of the 70um excess emission. No strong correlation is found
between dust temperature and stellar age. Comparison of the observational data
with disk models containing a power-law distribution of silicate grains suggest
that the typical inner disk radius is > 10 AU. Although the interpretation is
not unique, the lack of excess emission shortwards of 16um and the relatively
flat distribution of the 24um excess for ages <300~Myr is consistent with
steady-state collisional models.Comment: 85 pages, 18 figures, 4 tables; accepted for publication in ApJ
A dynamic theory of fidelity networks with an application to the spread of HIV/AIDS
We study the dynamic stability of fidelity networks, which are networks that form in a mating economy of agents of two types (say men and women), where each agent desires direct links with opposite type agents, while engaging in multiple partnerships is considered an act of infidelity. Infidelity is punished more severely for women than for men. We consider two stochastic processes in which agents form and sever links over time based on the reward from doing so, but may also take non-beneficial actions with small probability. In the first process, an agent who invests more time in a relationship makes it stronger and harder to break by his/her partner; in the second, such an agent is perceived as weak. Under the first process, only egalitarian pairwise stable networks (in which all agents have the same number of partners) are visited in the long run, while under the second, only anti-egalitarian pairwise stable networks (in which all women are matched to a small number of men) are. Next, we apply these results to find that under the first process, HIV/AIDS is equally prevalent among men and women, while under the second, women bear a greater burden. The key message is that anti-female discrimination does not necessarily lead to higher HIV/AIDS prevalence among women in the short run, but it does in the long run.fidelity networks; anti-female discrimination; stochastic stability; HIV/AIDS; union formation models
Extrasolar Asteroid Mining as Forensic Evidence for Extraterrestrial Intelligence
The development of civilisations like ours into spacefaring, multi-planet
entities requires significant raw materials to construct vehicles and habitats.
Interplanetary debris, including asteroids and comets, may provide such a
source of raw materials. In this article we present the hypothesis that
extraterrestrial intelligences (ETIs) engaged in asteroid mining may be
detectable from Earth. Considering the detected disc of debris around Vega as a
template, we explore the observational signatures of targeted asteroid mining
(TAM), such as unexplained deficits in chemical species, changes in the size
distribution of debris and other thermal signatures which may be detectable in
the spectral energy distribution (SED) of a debris disc. We find that
individual observational signatures of asteroid mining can be explained by
natural phenomena, and as such they cannot provide conclusive detections of
ETIs. But, it may be the case that several signatures appearing in the same
system will prove harder to model without extraterrestrial involvement.
Therefore signatures of TAM are not detections of ETI in their own right, but
as part of "piggy-back" studies carried out in tandem with conventional debris
disc research, they could provide a means of identifying unusual candidate
systems for further study using other SETI techniques.Comment: 15 pages, 2 figures, accepted for publication in the International
Journal of Astrobiolog
A Resolved Molecular Gas Disk around the Nearby A Star 49 Ceti
The A star 49 Ceti, at a distance of 61 pc, is unusual in retaining a
substantial quantity of molecular gas while exhibiting dust properties similar
to those of a debris disk. We present resolved observations of the disk around
49 Ceti from the Submillimeter Array in the J=2-1 rotational transition of CO
with a resolution of 1.0x1.2 arcsec. The observed emission reveals an extended
rotating structure viewed approximately edge-on and clear of detectable CO
emission out to a distance of ~90 AU from the star. No 1.3 millimeter continuum
emission is detected at a 3-sigma sensitivity of 2.1 mJy/beam. Models of disk
structure and chemistry indicate that the inner disk is devoid of molecular
gas, while the outer gas disk between 40 and 200 AU from the star is dominated
by photochemistry from stellar and interstellar radiation. We determine
parameters for a model that reproduces the basic features of the spatially
resolved CO J=2-1 emission, the spectral energy distribution, and the
unresolved CO J=3-2 spectrum. We investigate variations in disk chemistry and
observable properties for a range of structural parameters. 49 Ceti appears to
be a rare example of a system in a late stage of transition between a gas-rich
protoplanetary disk and a tenuous, virtually gas-free debris disk.Comment: 11 pages, 6 figures, accepted for publication in Ap
- …