6,776 research outputs found
There is no variational characterization of the cycles in the method of periodic projections
The method of periodic projections consists in iterating projections onto
closed convex subsets of a Hilbert space according to a periodic sweeping
strategy. In the presence of sets, a long-standing question going
back to the 1960s is whether the limit cycles obtained by such a process can be
characterized as the minimizers of a certain functional. In this paper we
answer this question in the negative. Projection algorithms that minimize
smooth convex functions over a product of convex sets are also discussed
Microlensing Surveys of M31 in the Wide Field Imaging Era
The Andromeda Galaxy (M31) is the closest large galaxy to the Milky Way, thus
it is an important laboratory for studying massive dark objects in galactic
halos (MACHOs) by gravitational microlensing. Such studies strongly complement
the studies of the Milky Way halo using the the Large and Small Magellanic
Clouds. We consider the possibilities for microlensing surveys of M31 using the
next generation of wide field imaging telescopes with fields of view in the
square degree range. We consider proposals for such imagers both on the ground
and in space. For concreteness, we specialize to the SNAP proposal for a space
telescope and the LSST proposal for a ground based telescope. We find that a
modest space-based survey of 50 visits of one hour each is considerably better
than current ground based surveys covering 5 years. Crucially, systematic
effects can be considerably better controlled with a space telescope because of
both the infrared sensitivity and the angular resolution. To be competitive, 8
meter class wide-field ground based imagers must take exposures of several
hundred seconds with several day cadence.Comment: 10 pages, 4 figures, 2 table
Optimal Microlensing Observations
One of the major limitations of microlensing observations toward the Large
Magellanic Cloud (LMC) is the low rate of event detection. What can be done to
improve this rate? Is it better to invest telescope time in more frequent
observations of the inner high surface-brightness fields, or in covering new,
less populated outer fields? How would a factor 2 improvement in CCD
sensitivity affect the detection efficiency? Would a series of major (factor
2--4) upgrades in telescope aperture, seeing, sky brightness, camera size, and
detector efficiency increase the event rate by a huge factor, or only
marginally? I develop a simplified framework to address these questions. With
observational resources fixed at the level of the MACHO and EROS experiments,
the biggest improvement (factor ~2) would come by reducing the time spent on
the inner ~25 deg^2 and applying it to the outer ~100 deg^2. By combining this
change with the characteristics of a good medium-size telescope (2.5 m mirror,
1" point spread function, thinned CCD chips, 1 deg^2 camera, and dark sky), it
should be possible to increase the detection of LMC events to more than 100 per
year (assuming current estimates of the optical depth apply to the entire LMC).Comment: Submitted to ApJ, 13 pages plus 3 figure
Asymptotic behavior of compositions of under-relaxed nonexpansive operators
In general there exists no relationship between the fixed point sets of the
composition and of the average of a family of nonexpansive operators in Hilbert
spaces. In this paper, we establish an asymptotic principle connecting the
cycles generated by under-relaxed compositions of nonexpansive operators to the
fixed points of the average of these operators. In the special case when the
operators are projectors onto closed convex sets, we prove a conjecture by De
Pierro which has so far been established only for projections onto affine
subspaces
Group decision rules and group rationality under risk
This paper investigates the rationality of group decisions versus individual decisions under risk. We study two group decision rules, majority and unanimity, in stochastic dominance and Allais paradox tasks. We distinguish communication effects (the effects of group discussions and interactions) from aggregation effects (mere impact of the voting procedure), which makes it possible to better understand the complex dynamics of group decision making. In an experiment, both effects occurred for intellective tasks whereas there were only aggregation effects in judgmental tasks. Communication effects always led to more rational choices; aggregation effects did so sometimes but not always. Groups violated stochastic dominance less often than individuals did, which was due to both aggregation and communication effects. In the Allais paradox tasks, there were almost no communication effects, and aggregation effects made groups deviate more from expected utility than individuals
The Anomaly in the Candidate Microlensing Event PA-99-N2
The lightcurve of PA-99-N2, one of the recently announced microlensing
candidates towards M31, shows small deviations from the standard Paczynski
form. We explore a number of possible explanations, including correlations with
the seeing, the parallax effect and a binary lens. We find that the
observations are consistent with an unresolved RGB or AGB star in M31 being
microlensed by a binary lens. We find that the best fit binary lens mass ratio
is about one hundredth, which is one of most extreme values found for a binary
lens so far. If both the source and lens lie in the M31 disk, then the standard
M31 model predicts the probable mass range of the system to be 0.02-3.6 solar
masses (95 % confidence limit). In this scenario, the mass of the secondary
component is therefore likely to be below the hydrogen-burning limit. On the
other hand, if a compact halo object in M31 is lensing a disk or spheroid
source, then the total lens mass is likely to lie between 0.09-32 solar masses,
which is consistent with the primary being a stellar remnant and the secondary
a low mass star or brown dwarf. The optical depth (or alternatively the
differential rate) along the line of sight toward the event indicates that a
halo lens is more likely than a stellar lens provided that dark compact objects
comprise no less than 15 per cent (or 5 per cent) of haloes.Comment: Latex, 23 pages, 9 figures, in press at The Astrophysical Journa
AGAPE, an experiment to detect MACHO's in the direction of the Andromeda galaxy
The status of the Agape experiment to detect Machos in the direction of the
andromeda galaxy is presented.Comment: 4 pages, 1 figure in a separate compressed, tarred, uuencoded uufile.
In case ofproblem contact [email protected]
First measurement of the cross section for top-quark pair production in protonâproton collisions at âs = 7 TeV
20 pĂĄginas, 3 figuras, 1 tabla.-- This article is published Open Access at sciencedirect.com. It
is distributed under the terms of the Creative Commons Attribution
License 3.0.-- CMS Collaboration: et al.The first measurement of the cross section for top-quark pair production in pp collisions at the
Large Hadron Collider at center-of-mass energy âs = 7 TeV has been performed using a data sample
corresponding to an integrated luminosity of 3.1 ± 0.3 pbâ1 recorded by the CMS detector. This result
utilizes the final state with two isolated, highly energetic charged leptons, large missing transverse
energy, and two or more jets. Backgrounds from DrellâYan and non-W/Z boson production are estimated
from data. Eleven events are observed in the data with 2.1 ± 1.0 events expected from background. The
measured cross section is 194±72(stat.)±24(syst.)±21(lumi.) pb, consistent with next-to-leading order
predictions.Acknowledge support from: FMSR (Austria);
FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ, and FAPESP
(Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC (China);
COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus); Academy
of Sciences and NICPB (Estonia); Academy of Finland, ME, and
HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG, and HGF
(Germany); GSRT (Greece); OTKA and NKTH (Hungary); DAE and
DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF and WCU
(Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and UASLPFAI
(Mexico); PAEC (Pakistan); SCSR (Poland); FCT (Portugal); JINR
(Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST and MAE
(Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss Funding
Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK (Turkey);
STFC (United Kingdom); DOE and NSF (USA).Peer reviewe
Search for supersymmetry in pp collisions at 7 TeV in events with jets and missing transverse energy
Acknowledge support from:
FMSR (Austria); FNRS and FWO (Belgium); CNPq, CAPES, FAPERJ,
and FAPESP (Brazil); MES (Bulgaria); CERN; CAS, MoST, and NSFC
(China); COLCIENCIAS (Colombia); MSES (Croatia); RPF (Cyprus);
Academy of Sciences and NICPB (Estonia); Academy of Finland,
ME, and HIP (Finland); CEA and CNRS/IN2P3 (France); BMBF, DFG,
and HGF (Germany); GSRT (Greece); OTKA and NKTH (Hungary);
DAE and DST (India); IPM (Iran); SFI (Ireland); INFN (Italy); NRF
and WCU (Korea); LAS (Lithuania); CINVESTAV, CONACYT, SEP, and
UASLP-FAI (Mexico); PAEC (Pakistan); SCSR (Poland); FCT (Portugal);
JINR (Armenia, Belarus, Georgia, Ukraine, Uzbekistan); MST
and MAE (Russia); MSTD (Serbia); MICINN and CPAN (Spain); Swiss
Funding Agencies (Switzerland); NSC (Taipei); TUBITAK and TAEK
(Turkey); STFC (United Kingdom); DOE and NSF (USA).A search for supersymmetry with R-parity conservation in protonâproton collisions at a centre-of-mass
energy of 7 TeV is presented. The data correspond to an integrated luminosity of 35 pbâ1 collected by
the CMS experiment at the LHC. The search is performed in events with jets and significant missing
transverse energy, characteristic of the decays of heavy, pair-produced squarks and gluinos. The primary
background, from standard model multijet production, is reduced by several orders of magnitude to a
negligible level by the application of a set of robust kinematic requirements. With this selection, the
data are consistent with the standard model backgrounds, namely tÂŻt, W + jet and Z + jet production,
which are estimated from data control samples. Limits are set on the parameters of the constrained
minimal supersymmetric extension of the standard model. These limits extend those set previously by
experiments at the Tevatron and LEP colliders.23 pĂĄginas, 5 figuras, 2 tablas.-- Open access:
This article is distributed under the terms of the Creative Commons Attribution
License 3.0.-- CMS Collaboration: et al.Peer reviewe
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