90 research outputs found
When lack of control enhances closeness to others : the case of unemployment and economic threat
When personal control is threatened, people often turn to their own group
and show negativity towards others. In three studies, we tested an alternative prediction that the salient lack of personal control (vs. control) experienced in the context of unemployment can lead to connectedness and
more positive perception of similar others (e.g., members of groups affected
by unemployment or the economic crisis). In two European countries, we
found experimental (Study 1: Poland) and correlational (Study 2: Spain)
evidence that a lowered sense of control of unemployed people was related
to more favorable intergroup evaluations. Furthermore, when lack of control related to unemployment threat was experimentally induced, participants perceived a Greek outgroup more positively, and this effect was
mediated by identification with and similarity to this group (Study 3). We
discuss the role of the shared experience of collective uncontrollability in
promoting positive intergroup relation
Constraining compactness and magnetic field geometry of X-ray pulsars from the statistics of their pulse profiles
The light curves observed from X-ray pulsars and magnetars reflect the
radiation emission pattern, the geometry of the magnetic field, and the neutron
star compactness. We study the statistics of X-ray pulse profiles in order to
constrain the neutron star compactness and the magnetic field geometry. We
collect the data for 124 X-ray pulsars, which are mainly in high-mass X-ray
binary systems, and classify their pulse profiles according to the number of
observed peaks seen during one spin period, dividing them into two classes,
single- and double-peaked. We find that the pulsars are distributed about
equally between both groups. We also compute the probabilities predicted by the
theoretical models of two antipodal point-like spots that emit radiation
according to the pencil-like emission patterns. These are then compared to the
observed fraction of pulsars in the two classes. Assuming a blackbody emission
pattern, it is possible to constrain the neutron star compactness if the
magnetic dipole has arbitrary inclinations to the pulsar rotational axis. More
realistic pencil-beam patterns predict that 79% of the pulsars are
double-peaked independently of their compactness. The theoretical predictions
can be made consistent with the data if the magnetic dipole inclination to the
rotational axis has an upper limit of 40+/-4 deg. We also discuss the effect of
limited sensitivity of the X-ray instruments to detect weak pulses, which
lowers the number of detected double-peaked profiles and makes the theoretical
predictions to be consistent with the data even if the magnetic dipole does
have random inclinations. This shows that the statistics of pulse profiles does
not allow us to constrain the neutron star compactness. In contrast to the
previous claims by Bulik et al. (2003), the data also do not require the
magnetic inclination to be confined in a narrow interval.Comment: 14 pages, 10 figures, Astronomy and Astrophysics, in pres
Clustering-based approaches to SAGE data mining
Serial analysis of gene expression (SAGE) is one of the most powerful tools for global gene expression profiling. It has led to several biological discoveries and biomedical applications, such as the prediction of new gene functions and the identification of biomarkers in human cancer research. Clustering techniques have become fundamental approaches in these applications. This paper reviews relevant clustering techniques specifically designed for this type of data. It places an emphasis on current limitations and opportunities in this area for supporting biologically-meaningful data mining and visualisation
A Puzzling Paucity of Double Peaked X-ray Pulsars
Accretion powered pulsars exhibit a variety of lightcurves. In this paper we
propose to classify the observed lightcurves as single or double pulsed.We
analyze the lightcurves of 86 accretion powered pulsars and assign them to
these classes. We present three datasets: first in which the classification can
be easily done, second for which the classification is more difficult and not
certain, and third for which we were unable to classify the pulsar because of
lack of published data. We analyze a simple model in which the angles between
the magnetic and rotation axis , and between the rotation axis and the
line of sight are random, and show that it is inconsistent with the
data. We also present a model in whichthe angle between the magnetic axis and
rotation axis is restricted and compare it with the data. This leads to an
upper limit on the angle . We conclude that there must be a
mechanism that leads to alignment of the magnetic and spin axis in X-ray
pulsars.Comment: submitted to A&
Observations of Accreting Pulsars
We summarize five years of continuous monitoring of accretion-powered pulsars
with the Burst and Transient Source Experiment (BATSE) on the Compton Gamma Ray
Observatory. Our 20-70 keV observations have determined or refined the orbital
parameters of 13 binaries, discovered 5 new transient accreting pulsars,
measured the pulsed flux history during outbursts of 12 transients (GRO
J1744-28, 4U 0115+634, GRO J1750-27, GS 0834-430, 2S 1417-624, GRO J1948+32,
EXO 2030+375, GRO J1008-57, A 0535+26, GRO J2058+42, 4U 1145-619 and A
1118-616), and also measured the accretion torque history of during outbursts
of 6 of those transients whose orbital parameters were also known. We have also
continuously measured the pulsed flux and spin frequency for eight persistently
accreting pulsars (Her X-1, Cen X-3, Vela X-1, OAO 1657-415, GX 301-2, 4U
1626-67, 4U 1538-52, and GX 1+4). Because of their continuity and uniformity
over a long baseline, BATSE observations have provided new insights into the
long-term behavior of accreting magnetic stars. We have found that all
accreting pulsars show stochastic variations in their spin frequencies and
luminosities, including those displaying secular spin-up or spin-down on long
time scales, blurring the conventional distinction between disk-fed and
wind-fed binaries. Pulsed flux and accretion torque are strongly correlated in
outbursts of transient accreting pulsars, but uncorrelated, or even
anticorrelated, in persistent sources.Comment: LaTeX, psfig, 90 pages, 42 figures. To appear in Dec. 1997 ApJS, Vol
113, #
Development of the self-modulation instability of a relativistic proton bunch in plasma
Self-modulation is a beam–plasma instability that is useful to drive large-amplitude wakefields with bunches much longer than the plasma skin depth. We present experimental results showing that, when increasing the ratio between the initial transverse size of the bunch and the plasma skin depth, the instability occurs later along the bunch, or not at all, over a fixed plasma length because the amplitude of the initial wakefields decreases. We show cases for which self-modulation does not develop, and we introduce a simple model discussing the conditions for which it would not occur after any plasma length. Changing bunch size and plasma electron density also changes the growth rate of the instability. We discuss the impact of these results on the design of a particle accelerator based on the self-modulation instability seeded by a relativistic ionization front, such as the future upgrade of the Advanced WAKefield Experiment
Simulation and experimental study of proton bunch self-modulation in plasma with linear density gradients
We present numerical simulations and experimental results of the self-modulation of a long proton bunch in a plasma with linear density gradients along the beam path. Simulation results agree with the experimental results reported [F. Braunmller, T. Nechaeva et al. (AWAKE Collaboration), Phys. Rev. Lett. 125, 264801 (2020)PRLTAO0031-900710.1103/PhysRevLett.125.264801]: with negative gradients, the charge of the modulated bunch is lower than with positive gradients. In addition, the bunch modulation frequency varies with gradient. Simulation results show that dephasing of the wakefields with respect to the relativistic protons along the plasma is the main cause for the loss of charge. The study of the modulation frequency reveals details about the evolution of the self-modulation process along the plasma. In particular for negative gradients, the modulation frequency across time-resolved images of the bunch indicates the position along the plasma where protons leave the wakefields. Simulations and experimental results are in excellent agreement
Hard Spectra of X-Ray Pulsars from INTEGRAL Data
We present spectra for 34 accretion-powered X-ray and one millisecond pulsars
that were within the field of view of the INTEGRAL observatory over two years
(December 2002 - January 2005) of its in-orbit operation and that were detected
by its instruments at a statistically significant level (> 8 sigma in the
energy range 18--60 keV). There are seven recently discovered objects of this
class among the pulsars studied: 2RXP J130159.6-635806, IGR/AX J16320-4751, IGR
J16358-4726, AX J163904-4642, IGR J16465-4507, SAX/IGR J18027-2017 and AX
J1841.0-0535. We have also obtained hard X-ray (> 20 keV) spectra for the
accretion-powered pulsars A 0114+650, RX J0146.9+6121, AX J1820.5-1434, AX
J1841.0-0535 and the millisecond pulsar XTE J1807-294 for the first time. We
analyze the evolution of spectral parameters as a function of the intensity of
the sources and compare these with the results of previous studies.Comment: 33 pages, 2 figures Astronomy Letters, 31, pp. 729 (2005
SDSS-III: Massive Spectroscopic Surveys of the Distant Universe, the Milky Way Galaxy, and Extra-Solar Planetary Systems
Building on the legacy of the Sloan Digital Sky Survey (SDSS-I and II),
SDSS-III is a program of four spectroscopic surveys on three scientific themes:
dark energy and cosmological parameters, the history and structure of the Milky
Way, and the population of giant planets around other stars. In keeping with
SDSS tradition, SDSS-III will provide regular public releases of all its data,
beginning with SDSS DR8 (which occurred in Jan 2011). This paper presents an
overview of the four SDSS-III surveys. BOSS will measure redshifts of 1.5
million massive galaxies and Lya forest spectra of 150,000 quasars, using the
BAO feature of large scale structure to obtain percent-level determinations of
the distance scale and Hubble expansion rate at z<0.7 and at z~2.5. SEGUE-2,
which is now completed, measured medium-resolution (R=1800) optical spectra of
118,000 stars in a variety of target categories, probing chemical evolution,
stellar kinematics and substructure, and the mass profile of the dark matter
halo from the solar neighborhood to distances of 100 kpc. APOGEE will obtain
high-resolution (R~30,000), high signal-to-noise (S/N>100 per resolution
element), H-band (1.51-1.70 micron) spectra of 10^5 evolved, late-type stars,
measuring separate abundances for ~15 elements per star and creating the first
high-precision spectroscopic survey of all Galactic stellar populations (bulge,
bar, disks, halo) with a uniform set of stellar tracers and spectral
diagnostics. MARVELS will monitor radial velocities of more than 8000 FGK stars
with the sensitivity and cadence (10-40 m/s, ~24 visits per star) needed to
detect giant planets with periods up to two years, providing an unprecedented
data set for understanding the formation and dynamical evolution of giant
planet systems. (Abridged)Comment: Revised to version published in The Astronomical Journa
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