9,453 research outputs found
From Labor Law to Employment Law: What Next?
[Excerpt] If bargaining is broad-based (in nonfragmented units) and if the parties have full resort to a reasonable panoply of economic weapons, the stakes usually will be too high for either side to press for impasse. But in the event of a breakdown in negotiations, the parties should be allowed to engage in a fair fight
The dual parameterization of the proton generalized parton distribution functions H and E and description of the DVCS cross sections and asymmetries
We develop the minimal model of a new leading order parameterization of GPDs
introduced by Shuvaev and Polyakov. The model for GPDs H and E is formulated in
terms of the forward quark distributions, the Gegenbauer moments of the D-term
and the forward limit of the GPD E. The model is designed primarely for small
and medium-size values of x_B, x_B \leq 0.2.
We examined two different models of the t-dependence of the GPDs: The
factorized exponential model and the non-factorized Regge-motivated model.
Using our model, we successfully described the DVCS cross section measured by
H1 and ZEUS, the moments of the beam-spin A_{LU}^{\sin \phi}, beam-charge
A_{C}^{\cos \phi} and transversely-polarized target A_{UT}^{\sin \phi \cos
\phi} DVCS asymmetries measured by HERMES and A_{LU}^{\sin \phi} measured by
CLAS. The data on A_{C}^{\cos \phi} prefers the Regge-motivated model of the
t-dependence of the GPDs. The data on A_{UT}^{\sin \phi \cos \phi} indicates
that the u and d quarks carry only a small fraction of the proton total angular
momentum.Comment: 33 pages, 11 figure
Is Task-Irrelevant Learning Really Task-Irrelevant?
In the present study we address the question of whether the learning of task-irrelevant stimuli found in the paradigm of task-irrelevant learning (TIPL) [1]–[9] is truly task irrelevant. To test the hypothesis that associations that are beneficial to task-performance may develop between the task-relevant and task-irrelevant stimuli, or the task-responses and the task-irrelevant stimuli, we designed a new procedure in which correlations between the presentation of task-irrelevant motion stimuli and the identity of task-targets or task-responses were manipulated. We found no evidence for associations developing between the learned (task-irrelevant) motion stimuli and the targets or responses to the letter identification task used during training. Furthermore, the conditions that had the greatest correlations between stimulus and response showed the least amount of TIPL. On the other hand, TIPL was found in conditions of greatest response uncertainty and with the greatest processing requirements for the task-relevant stimuli. This is in line with our previously published model that suggests that task-irrelevant stimuli benefit from the spill-over of learning signals that are released due to processing of task-relevant stimuli
Is Task-Irrelevant Learning Really Task-Irrelevant?
In the present study we address the question of whether the learning of task-irrelevant stimuli found in the paradigm of task-irrelevant learning (TIPL) [1]–[9] is truly task irrelevant. To test the hypothesis that associations that are beneficial to task-performance may develop between the task-relevant and task-irrelevant stimuli, or the task-responses and the task-irrelevant stimuli, we designed a new procedure in which correlations between the presentation of task-irrelevant motion stimuli and the identity of task-targets or task-responses were manipulated. We found no evidence for associations developing between the learned (task-irrelevant) motion stimuli and the targets or responses to the letter identification task used during training. Furthermore, the conditions that had the greatest correlations between stimulus and response showed the least amount of TIPL. On the other hand, TIPL was found in conditions of greatest response uncertainty and with the greatest processing requirements for the task-relevant stimuli. This is in line with our previously published model that suggests that task-irrelevant stimuli benefit from the spill-over of learning signals that are released due to processing of task-relevant stimuli
HST/ACS weak lensing analysis of the galaxy cluster RDCS 1252.9-2927 at z=1.24
We present a weak lensing analysis of one of the most distant massive galaxy
cluster known, RDCS 1252.9-2927 at z=1.24, using deep images from the Advanced
Camera for Survey (ACS) on board the Hubble Space Telescope (HST). By taking
advantage of the depth and of the angular resolution of the ACS images, we
detect for the first time at z>1 a clear weak lensing signal in both the i
(F775W) and z (F850LP) filters. We measure a 5-\sigma signal in the i band and
a 3-\sigma signal in the shallower z band image. The two radial mass profiles
are found to be in very good agreement with each other, and provide a
measurement of the total mass of the cluster inside a 1Mpc radius of M(<1Mpc) =
(8.0 +/- 1.3) x 10^14 M_\odot in the current cosmological concordance model h
=0.70, \Omega_m=0.3, \Omega_\Lambda=0.7, assuming a redshift distribution of
background galaxies as inferred from the Hubble Deep Fields surveys. A weak
lensing signal is detected out to the boundary of our field (3' radius,
corresponding to 1.5Mpc at the cluster redshift). We detect a small offset
between the centroid of the weak lensing mass map and the brightest cluster
galaxy, and we discuss the possible origin of this discrepancy. The cumulative
weak lensing radial mass profile is found to be in good agreement with the
X-ray mass estimate based on Chandr and XMM-Newton observations, at least out
to R_500=0.5Mpc.Comment: 38 pages, ApJ in press. Full resolution images available at
http://www.eso.org/~prosati/RDCS1252/Lombardi_etal_accepted.pd
Critical behaviour of combinatorial search algorithms, and the unitary-propagation universality class
The probability P(alpha, N) that search algorithms for random Satisfiability
problems successfully find a solution is studied as a function of the ratio
alpha of constraints per variable and the number N of variables. P is shown to
be finite if alpha lies below an algorithm--dependent threshold alpha\_A, and
exponentially small in N above. The critical behaviour is universal for all
algorithms based on the widely-used unitary propagation rule: P[ (1 + epsilon)
alpha\_A, N] ~ exp[-N^(1/6) Phi(epsilon N^(1/3)) ]. Exponents are related to
the critical behaviour of random graphs, and the scaling function Phi is
exactly calculated through a mapping onto a diffusion-and-death problem.Comment: 7 pages; 3 figure
An optical study of the GRB 970111 field beginning 19 hours after the Gamma-Ray Burst
We present the results of the monitoring of the GRB 970111 field that started
19 hours after the event. This observation represents the fastest ground-based
follow-up performed for GRB 970111 in all wavelengths. As soon as the detection
of the possible GRB 970111 X-ray afterglow was reported by Feroci et al. (1998)
we reanalyzed the optical data collected for the GRB 970111 field. Although we
detect small magnitude variability in some objects, no convincing optical
counterpart is found inside the WFC error box. Any change in brightness 19
hours after the GRB is less than 0.2 mag for objects with B < 21 and R < 20.8.
The bluest object found in the field is coincident with 1SAXJ1528.8+1937.
Spectroscopic observations revealed that this object is a Seyfert-1 galaxy with
redshift z=0.657, which we propose as the optical counterpart of the X-ray
source.
Further observations allowed to perform multicolour photometry for objects in
the GRB 970111 error box. The colour-colour diagrams do not show any object
with unusual colours. We applied a photometric classification method to the
objects inside the GRB error box, that can distinguish stars from galaxies and
estimate redshifts. We were able to estimate photometric redshifts in the range
0.2 < z < 1.4 for several galaxies in this field and we did not find any
conspicuous unusual object.
We note that GRB 970111 and GRB 980329 could belong to the same class of
GRBs, which may be related to nearby sources (z ~1) in which high intrinsic
absorption leads to faint optical afterglows.Comment: 10 pages with 11 encapsulated PostScript figures included. Uses
Astronomy & Astrophysics LaTeX macros. Accepted for publication in Astronomy
& Astrophysic
Microlensing toward crowded fields: Theory and applications to M31
We present a comprehensive treatment of the pixel-lensing theory and apply it
to lensing experiments and their results toward M31. Using distribution
functions for the distances, velocities, masses, and luminosities of stars, we
derive lensing event rates as a function of the event observables. In contrast
to the microlensing regime, in the pixel-lensing regime (crowded or unresolved
sources) the observables are the maximum excess flux of the source above a
background and the full width at half-maximum (FWHM) time of the event. To
calculate lensing event distribution functions depending on these observables
for the specific case of M31, we use data from the literature to construct a
model of M31, reproducing consistently photometry, kinematics and stellar
population. We predict the halo- and self-lensing event rates for bulge and
disk stars in M31 and treat events with and without finite source signatures
separately. We use the M31 photon noise profile and obtain the event rates as a
function of position, field of view, and S/N threshold at maximum
magnification. We calculate the expected rates for WeCAPP and for a potential
Advanced Camera for Surveys (ACS) lensing campaign. The detection of two events
with a peak signal-to-noise ratio larger than 10 and a timescale larger than 1
day in the WeCAPP 2000/2001 data is in good agreement with our theoretical
calculations. We investigate the luminosity function of lensed stars for noise
characteristics of WeCAPP and ACS. For the pixel-lensing regime, we derive the
probability distribution for the lens masses in M31 as a function of the FWHM
timescale, flux excess and color, including the errors of these observables.Comment: 45 pages, 27 figures LaTeX; corrected typos; published in the
Astrophysical Journal Supplemen
The star formation rate history in the FORS Deep and GOODS South Fields
We measure the star formation rate (SFR) as a function of redshift z up to z
\~4.5, based on B, I and (I+B) selected galaxy catalogues from the FORS Deep
Field (FDF) and the K-selected catalogue from the GOODS-South field. Distances
are computed from spectroscopically calibrated photometric redshifts accurate
to (Delta_z / (z_spec+1)) ~0.03 for the FDF and ~0.056 for the GOODS-South
field. The SFRs are derived from the luminosities at 1500 Angstroem. We find
that the total SFR estimates derived from B, I and I+B catalogues agree very
well (\lsim 0.1 dex) while the SFR from the K catalogue is lower by ~0.2 dex.
We show that the latter is solely due to the lower star-forming activity of
K-selected intermediate and low luminosity (L<L_*) galaxies. The SFR of bright
(L>L_*) galaxies is independent of the selection band, i.e. the same for B, I,
(I+B), and K-selected galaxy samples. At all redshifts, luminous galaxies
(L>L_*) contribute only ~1/3 to the total SFR. There is no evidence for
significant cosmic variance between the SFRs in the FDF and GOODs-South field,
~0.1 dex, consistent with theoretical expectations. The SFRs derived here are
in excellent agreement with previous measurements provided we assume the same
faint-end slope of the luminosity function as previous works (alpha ~ -1.6).
However, our deep FDF data indicate a shallower slope of alpha=-1.07, implying
a SFR lower by ~0.3 dex. We find the SFR to be roughly constant up to z ~4 and
then to decline slowly beyond, if dust extinctions are assumed to be constant
with redshift.Comment: 6 pages, 2 figures, Accepted for publication in ApJ
- …