202 research outputs found
The Value of Monitoring Risk Averse Agents in Teams.
Vander Veen (1995) has argued that a principal has an incentive to monitor risk averse agents engaging in team production. We show that this result rests on specific informational assumptions that are not essential to team production. Moreover, under typical team environments and contract conditions there is no benefit from monitoring of individual agents, leaving only costs for the principal. We identify an additional mechanism design problem that arises in certain team settings-the principal must determine when to make information about each agent's reported ability public to the other team members.RISK ; MICROECONOMICS
ep â ep Ïâ° Reaction Studied in the Î(1232) Mass Region Using Polarization Asymmetries
Measurements of the angular distributions of target and double-spin asymmetries for the Î+(1232) in the exclusive channel â p(âe,e\u27p)Ï0 obtained at the Jefferson Lab in the Q2 range from 0.5 to 1.5 GeV2/c2 are presented. Results of the asymmetries are compared with the unitary isobar model [D. Drechsel , Nucl. Phys. A645, 145 (1999)], dynamical models [T. Sato and T. S. Lee, Phys. Rev. C 54, 2660 (1996); S. S. Kamalov , Phys. Lett. B 27, 522 (2001)], and the effective Lagrangian theory [R. M. Davidson , Phys. Rev. D 43, 71 (1991)]. Sensitivity to the different models was observed, particularly in relation to the description of background terms on which the target asymmetry depends significantly
Electron Scattering from High-Momentum Neutrons in Deuterium
We report results from an experiment measuring the semiinclusive reaction 2H(e,eâČps) in which the proton ps is moving at a large angle relative to the momentum transfer. If we assume that the proton was a spectator to the reaction taking place on the neutron in deuterium, the initial state of that neutron can be inferred. This method, known as spectator tagging, can be used to study electron scattering from high-momentum (off-shell) neutrons in deuterium. The data were taken with a 5.765 GeV electron beam on a deuterium target in Jefferson Laboratory\u27s Hall B, using the CEBAF large acceptance spectrometer. A reduced cross section was extracted for different values of final state missing mass Wâ, backward proton momentum âps, and momentum transfer Q2. The data are compared to a simple plane wave impulse approximation (PWIA) spectator model. A strong enhancement in the data observed at transverse kinematics is not reproduced by the PWIA model. This enhancement can likely be associated with the contribution of final state interactions (FSI) that were not incorporated into the model. Within the framework of the simple spectator model, a âbound neutron structure functionâ Feff2n was extracted as a function of Wâ and the scaling variable xâ at extreme backward kinematics, where the effects of FSI appear to be smaller. For ps \u3e 0.4 GeV/c, where the neutron is far off-shell, the model overestimates the value of Feff2n in the region of xâ between 0.25 and 0.6. A dependence of the bound neutron structure function on the neutron\u27s âoff-shell-nessâ is one possible effect that can cause the observed deviation
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Psychiatric intensive care units: A literature review
Background: Psychiatric Intensive Care Units (PICU) have been part of most inpatient psychiatric services for some time, however information about their functioning and outcome has not previously been collated.
Aim: To conduct a systematic literature review to assess the current state of knowledge about such services.
Method: A search of electronic databases was undertaken, followed by obtaining additional references from items obtained.
Results: Over 50 papers in English containing some empirical data were identified. Most studies were retrospective. Typical PICU patients are: male; younger; single; unemployed; suffering from schizophrenia or mania; from a black Caribbean or African background; legally detained; with a forensic history. The most common reason for admission is for aggression management, and most patients stay a week or less. Evidence of the efficacy of PICU care is very poor.
Conclusions: Most research so far has been small scale, and more substantial work using better methodologies is clearly required
Factorizing the hard and soft spectator scattering contributions for the nucleon form factor F_1 at large Q^2
We investigate the soft spectator scattering contribution for the FF .
We focus our attention on factorization of the hard-collinear scale corresponding to transition from SCET-I to SCET-II. We compute the
leading order jet functions and find that the convolution integrals over the
soft fractions are logarithmically divergent. This divergency is the
consequence of the boost invariance and does not depend on the model of the
soft correlation function describing the soft spectator quarks. Using as
example a two-loop diagram we demonstrated that such a divergency corresponds
to the overlap of the soft and collinear regions. As a result one obtains large
rapidity logarithm which must be included in the correct factorization
formalism. We conclude that a consistent description of the factorization for
implies the end-point collinear divergencies in the hard and soft
spectator contributions, i.e. convolution integrals with respect to collinear
fractions are not well-defined. Such scenario can only be realized when the
twist-3 nucleon distribution amplitude has specific end-point behavior which
differs from one expected from the evolution of the nucleon distribution
amplitude. Such behavior leads to the violation of the collinear factorization
for the hard spectator scattering contribution. We suggest that the soft
spectator scattering and chiral symmetry breaking provide the mechanism
responsible for the violation of collinear factorization in case of form factor
.Comment: 25 pages, 6 figures, text is improved, few typos corrected, one
figure added, statement about end-point behavior of the nucleon DA is
formulated more accuratel
Real and Virtual Compton Scattering: the nucleon polarisabilities
We give an overview of low-energy Compton scattering (gamma^(*) p --> gamma
p) with a real or virtual incoming photon. These processes allow the
investigation of one of the fundamental properties of the nucleon, i.e. how its
internal structure deforms under an applied static electromagnetic field. Our
knowledge of nucleon polarisabilities and their generalization to non-zero
four-momentum transfer will be reviewed, including the presently ongoing
experiments and future perspectives.Comment: 20 pages, 12 figures. Minireview/Proceedings of "Many-Body Structure
of Strongly Interacting Systems", Mainz, Germany, Feb. 23-25 2011 . V2: typos
corrected. version to appear in EPJ Special Topic
A new measurement of the structure functions and in virtual Compton scattering at 0.33 (GeV/c)
The cross section of the reaction has been measured at
(GeV/c). The experiment was performed using the electron beam
of the MAMI accelerator and the standard detector setup of the A1
Collaboration. The cross section is analyzed using the low-energy theorem for
virtual Compton scattering, yielding a new determination of the two structure
functions P_LL}-P_{TT}/epsilon and which are linear combinations of
the generalized polarizabilities of the proton. We find somewhat larger values
than in the previous investigation at the same . This difference, however,
is purely due to our more refined analysis of the data. The results tend to
confirm the non-trivial -evolution of the generalized polarizabilities and
call for more measurements in the low- region ( 1 (GeV/c)).Comment: 9 pages, 10 figures. EPJA version. slight revisions in the text and
figure
Scaling Tests of the Cross Section for Deeply Virtual Compton Scattering
We present the first measurements of the \vec{e}p->epg cross section in the
deeply virtual Compton scattering (DVCS) regime and the valence quark region.
The Q^2 dependence (from 1.5 to 2.3 GeV^2) of the helicity-dependent cross
section indicates the twist-2 dominance of DVCS, proving that generalized
parton distributions (GPDs) are accessible to experiment at moderate Q^2. The
helicity-independent cross section is also measured at Q^2=2.3 GeV^2. We
present the first model-independent measurement of linear combinations of GPDs
and GPD integrals up to the twist-3 approximation.Comment: 5 pages, 4 figures, 2 tables. Text shortened for publication.
References added. One figure remove
Tensor Correlations Measured in 3He(e,e'pp)n
We have measured the 3He(e,e'pp)n reaction at an incident energy of 4.7 GeV
over a wide kinematic range. We identified spectator correlated pp and pn
nucleon pairs using kinematic cuts and measured their relative and total
momentum distributions. This is the first measurement of the ratio of pp to pn
pairs as a function of pair total momentum, . For pair relative
momenta between 0.3 and 0.5 GeV/c, the ratio is very small at low and
rises to approximately 0.5 at large . This shows the dominance of
tensor over central correlations at this relative momentum.Comment: 4 pages, 4 figures, submitted to PR
Nucleon electromagnetic form factors in a quark-gluon core model
We study the nucleon electromagnetic form factors in a quark-gluon core model
framework, which can be viewed as an extension of the Isgur-Karl model of
baryons. Using this picture we derive nucleon electromagnetic dipole form
factors at low Q^2 and the deviation from the dipole form at high Q^2, that are
consistent with the existing experimental data.Comment: 5 pages, 3 figure
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