1,515 research outputs found
Indenture as a Commitment Device in Self-Enforced Contracts: An Experimental Test
How can a principal (an agent) ensure that an agent (a principal) will work (pay up), if payment (work) precedes work (payment)? When a banknote is torn in two, each part is by itself worthless. A principal can pre-commit to payment-on-delivery, by tearing a banknote and giving the agent the first half as "prepayment"; the agent receives the completing half upon delivery of the service. This contract design is known as "indenture". It is selfenforcing and incentive-compatible. This paper experimentally tests the efficacy of the "indenture game" and its implications for cooperation in one-shot environments. We find that cooperation rates are high and stable over time. Its efficacy is moderated by expected losses due to the existence of uncooperative types.Cooperation, Experiment, Contracts, Indenture, Reciprocity
Indenture as a Self-Enforced Contract Device: An Experimental Test
We experimentally test the efficacy of indenture as a self-enforced contract device. In an indenture game, the principal signals the intention of payment-on-delivery, by tearing a banknote and giving the agent half of it as "prepayment"; the agent receives the completing half after delivering the service. By forward induction, cooperation is incentive-compatibly self-enforcing. The indenture performs very well, inducing a significantly higher level of cooperation than that in a three-stage centipede game, which we use to benchmark the natural rate of cooperation. The difference between cooperation rates in both games increases over time.Cooperation, experiment, contracts, indenture, reciprocity
Compiler Optimization Effects on Register Collisions
We often want a compiler to generate executable code that runs as fast as possible. One consideration toward this goal is to keep values in fast registers to limit the number of slower memory accesses that occur. When there are not enough physical registers available for use, values are ``spilled\u27\u27 to the runtime stack. The need for spills is discovered during register allocation wherein values in use are mapped to physical registers. One factor in the efficacy of register allocation is the number of values in use at one time (register collisions). Register collision is affected by compiler optimizations that take place before register allocation. Though the main purpose of compiler optimizations is to make the overall code better and faster, some optimizations can actually increase register collisions. This may force the register allocation process to spill. This thesis studies the effects of different compiler optimizations on register collisions
The Economics of Solidarity: A Conceptual Framework
For many people "solidarity" has become a meaningless word used in slogans - too often used without leading to any economic consequences. We show in this paper conditions under which solidarity can be a powerful instrument. In a solidary action, an individual in a group contributes to a series of actions that aims for a reallocation of scarce resources. The willingness to contribute is mainly influenced by the efficiency of the objective of the solidary action, and is enhanced by feelings of mutual exchange (solidarity) within a group. --solidarity,altruism,dynamic,mutual
The Becklin-Neugebauer Object as a Runaway B Star, Ejected 4000 years ago from the theta^1C system
We attempt to explain the properties of the Becklin-Neugebauer (BN) object as
a runaway B star, as originally proposed by Plambeck et al. (1995). This is one
of the best-studied bright infrared sources, located in the Orion Nebula
Cluster -- an important testing ground for massive star formation theories.
From radio observations of BN's proper motion, we trace its trajectory back
to Trapezium star theta^1C, the most massive (45 Msun) in the cluster and a
relatively tight (17 AU) visual binary with a B star secondary. This origin
would be the most recent known runaway B star ejection event, occurring only
\~4000 yr ago and providing a unique test of models of ejection from multiple
systems of massive stars. Although highly obscured, we can constrain BN's mass
(~7 Msun) from both its bolometric luminosity and the recoil of theta^1C.
Interaction of a runaway B star with dense ambient gas should produce a compact
wind bow shock. We suggest that X-ray emission from this shocked gas may have
been seen by Chandra: the offset from the radio position is ~300 AU in the
direction of BN's motion. Given this model, we constrain the ambient density,
wind mass-loss rate and wind velocity. BN made closest approach to the massive
protostar, source ``I'', 500 yr ago. This may have triggered enhanced accretion
and thus outflow, consistent with previous interpretations of the outflow being
a recent (~10^3 yr) "explosive" event.Comment: 6 pages, accepted to ApJ Letter
A Census of Outflow to Magnetic Field Orientations in Nearby Molecular Clouds
We define a sample of 200 protostellar outflows showing blue and redshifted
CO emission in the nearby molecular clouds Ophiuchus, Taurus, Perseus and Orion
to investigate the correlation between outflow orientations and local, but
relatively large-scale, magnetic field directions traced by Planck 353 GHz dust
polarization. At high significance (p~1e-4), we exclude a random distribution
of relative orientations and find that there is a preference for alignment of
projected plane of sky outflow axes with magnetic field directions. The
distribution of relative position angles peaks at ~30deg and exhibits a broad
dispersion of ~50deg. These results indicate that magnetic fields have
dynamical influence in regulating the launching and/or propagation directions
of outflows. However, the significant dispersion around perfect alignment
orientation implies that there are large measurement uncertainties and/or a
high degree of intrinsic variation caused by other physical processes, such as
turbulence or strong stellar dynamical interactions. Outflow to magnetic field
alignment is expected to lead to a correlation in the directions of nearby
outflow pairs, depending on the degree of order of the field. Analyzing this
effect we find limited correlation, except on relatively small scales < 0.5 pc.
Furthermore, we train a convolutional neural network to infer the inclination
angle of outflows with respect to the line of sight and apply it to our outflow
sample to estimate their full 3D orientations. We find that the angles between
outflow pairs in 3D space also show evidence of small-scale alignment.Comment: ApJ Accepte
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Plxnd1 Expression in Thymocytes Regulates Their Intrathymic Migration While That in Thymic Endothelium Impacts Medullary Topology
An important role for plexinD1 in thymic development is inferred from studies of germline Plxnd1 knockout (KO) mice where mislocalized CD69+ thymocytes as well as ectopic thymic subcapsular medullary structures were observed. Given embryonic lethality of the Plxnd1â/â genotype, fetal liver transplantation was employed in these prior analyses. Such embryonic hematopoietic reconstitution may have transferred Plxnd1 KO endothelial and/or epithelial stem cells in addition to Plxnd1 KO lymphoid progenitors, thereby contributing to that phenotype. Here we use Plxnd1flox/flox mice crossed to pLck-Cre, pKeratin14-Cre, or pTek-Cre transgenic animals to create cell-type specific conditional knockout (CKO) lines involving thymocytes (D1ThyCKO), thymic epithelium (D1EpCKO), and thymic endothelium (D1EnCKO), respectively. These CKOs allowed us to directly assess the role of plexinD1 in each lineage. Loss of plexinD1 expression on double positive (DP) thymocytes leads to their aberrant migration and cortical retention after TCR-mediated positive selection. In contrast, ectopic medulla formation is a consequence of loss of plexinD1 expression on endothelial cells, in turn linked to dysregulation of thymic angiogenesis. D1EpCKO thymi manifest neither abnormality. Collectively, our findings underscore the non-redundant roles for plexinD1 on thymocytes and endothelium, including the dynamic nature of medulla formation resulting from crosstalk between these thymic cellular components
IN-SYNC. V. Stellar kinematics and dynamics in the Orion A Molecular Cloud
The kinematics and dynamics of young stellar populations enable us to test
theories of star formation. With this aim, we continue our analysis of the
SDSS-III/APOGEE IN-SYNC survey, a high resolution near infrared spectroscopic
survey of young clusters. We focus on the Orion A star-forming region, for
which IN-SYNC obtained spectra of stars. In Paper IV we used these
data to study the young stellar population. Here we study the kinematic
properties through radial velocities (). The young stellar population
remains kinematically associated with the molecular gas, following a
gradient along filament. However, near the center
of the region, the distribution is slightly blueshifted and asymmetric;
we suggest that this population, which is older, is slightly in foreground. We
find evidence for kinematic subclustering, detecting statistically significant
groupings of co-located stars with coherent motions. These are mostly in the
lower-density regions of the cloud, while the ONC radial velocities are
smoothly distributed, consistent with it being an older, more dynamically
evolved cluster. The velocity dispersion varies along the filament.
The ONC appears virialized, or just slightly supervirial, consistent with an
old dynamical age. Here there is also some evidence for on-going expansion,
from a --extinction correlation. In the southern filament, is
-- times larger than virial in the L1641N region, where we infer a
superposition along the line of sight of stellar sub-populations, detached from
the gas. On the contrary, decreases towards L1641S, where the
population is again in agreement with a virial state.Comment: 14 pages, 13 figures, ApJ accepte
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