2,359 research outputs found
Non-collinearity in di-jet fragmentation in electron-positron scattering
We study fragmentation in electron-positron annihilation assuming a di-jet
situation, using variables defined independent of any frame. In a collinear
situation some of the variables are centered around zero with the small
deviations attributed to intrinsic transverse momenta and large deviations
attributed to additional hard subprocesses. Of course there is a gradual
transition. Our modest goal is to show that covariantly defined variables are
well suited to get a feeling for the magnitude of intrinsic transverse momenta.Comment: 10 pages, 12 figures, several minor correction
Reply to Comment on "Reevaluation of the parton distribution of strange quarks in the nucleon"
A Comment on the recently published reevaluation of the polarization-averaged
parton distribution of strange quarks in the nucleon using final data on the
multiplicities of charged kaons in semi-inclusive deep-inelastic scattering is
reviewed. Important features of the comparison of one-dimensional projections
of the multidimensional HERMES data are pointed out. A test of the
leading-order extraction of xS(x) using the difference between charged-kaon
multiplicities is repeated. The results are consistent with leading-order
predictions within the uncertainties in the input data, and do not invalidate
the earlier extraction of xS(x).Comment: Reply Comment to arXiv:1407.372
An AUC-based Permutation Variable Importance Measure for Random Forests
The random forest (RF) method is a commonly used tool for classification with high dimensional data as well as for ranking candidate predictors based on the so-called random forest variable importance measures (VIMs). However the classification performance of RF is known to be suboptimal in case of strongly unbalanced data, i.e. data where response class sizes differ considerably. Suggestions were made to obtain better classification performance based either on sampling procedures or on cost sensitivity analyses. However to our knowledge the performance of the VIMs has not yet been examined in the case of unbalanced response classes. In this paper we explore the performance of the permutation VIM for unbalanced data settings and introduce an alternative permutation VIM based on the area under the curve (AUC) that is expected to be more robust towards class imbalance. We investigated the performance of the standard permutation VIM and of our novel AUC-based permutation VIM for different class imbalance levels using simulated data and real data. The results suggest that the standard permutation VIM loses its ability to discriminate between associated predictors and predictors not associated with the response for increasing class imbalance. It is outperformed by our new AUC-based permutation VIM for unbalanced data settings, while the performance of both VIMs is very similar in the case of balanced classes. The new AUC-based VIM is implemented in the R package party for the unbiased RF variant based on conditional inference trees. The codes implementing our study are available from the companion website: http://www.ibe.med.uni-muenchen.de/organisation/mitarbeiter/070_drittmittel/janitza/index.html
Searching for Gravitational Waves from the Inspiral of Precessing Binary Systems: Astrophysical Expectations and Detection Efficiency of "Spiky'' Templates
Relativistic spin-orbit and spin-spin couplings has been shown to modify the
gravitational waveforms expected from inspiraling binaries with a black hole
and a neutron star. As a result inspiral signals may be missed due to
significant losses in signal-to-noise ratio, if precession effects are ignored
in gravitational-wave searches. We examine the sensitivity of the anticipated
loss of signal-to-noise ratio on two factors: the accuracy of the precessing
waveforms adopted as the true signals and the expected distributions of
spin-orbit tilt angles, given the current understanding of their physical
origin. We find that the results obtained using signals generated by
approximate techniques are in good agreement with the ones obtained by
integrating the 2PN equations. This shows that a complete account of all
high-order post-Newtonian effects is usually not necessary for the
determination of detection efficiencies. Based on our current astrophysical
expectations, large tilt angles are not favored and as a result the decrease in
detection rate varies rather slowly with respect to the black hole spin
magnitude and is within 20--30% of the maximum possible values.Comment: 7 fig., accepted by Phys. Rev. D Minor modification
Detectability of gravitational wave events by spherical resonant-mass antennas
We have calculated signal-to-noise ratios for eight spherical resonant-mass
antennas interacting with gravitational radiation from inspiralling and
coalescing binary neutron stars and from the dynamical and secular bar-mode
instability of a rapidly rotating star. We find that by using technology that
could be available in the next several years, spherical antennas can detect
neutron star inspiral and coalescence at a distance of 15 Mpc and the dynamical
bar-mode instability at a distance of 2 Mpc.Comment: 39 pages, 4 EPS Figures, some additional SNRs for secular
instabilities, some changes to LIGO SNRs, Appendix added on the asymptotic
expansion of energy sensitivity, corrected supernova rates. Results available
at http://www.physics.umd.edu/rgroups/gen_rel_exp/snr.html Submitted to Phys.
Rev.
Gravitational radiation from gamma-ray bursts as observational opportunities for LIGO and VIRGO
Gamma-ray bursts are believed to originate in core-collapse of massive stars.
This produces an active nucleus containing a rapidly rotating Kerr black hole
surrounded by a uniformly magnetized torus represented by two counter-oriented
current rings. We quantify black hole spin-interactions with the torus and
charged particles along open magnetic flux-tubes subtended by the event
horizon. A major output of Egw=4e53 erg is radiated in gravitational waves of
frequency fgw=500 Hz by a quadrupole mass-moment in the torus. Consistent with
GRB-SNe, we find (i) Ts=90s (tens of s, Kouveliotou et al. 1993), (ii)
aspherical SNe of kinetic energy Esn=2e51 erg (2e51 erg in SN1998bw, Hoeflich
et al. 1999) and (iii) GRB-energies Egamma=2e50 erg (3e50erg in Frail et al.
2001). GRB-SNe occur perhaps about once a year within D=100Mpc. Correlating
LIGO/Virgo detectors enables searches for nearby events and their spectral
closure density 6e-9 around 250Hz in the stochastic background radiation in
gravitational waves. At current sensitivity, LIGO-Hanford may place an upper
bound around 150MSolar in GRB030329. Detection of Egw thus provides a method
for identifying Kerr black holes by calorimetry.Comment: to appear in PRD, 49
Study of measured pulsar masses and their possible conclusions
We study the statistics of 61 measured masses of neutron stars (NSs) in
binary pulsar systems, including 18 double NS (DNS) systems, 26 radio pulsars
(10 in our Galaxy) with white dwarf (WD) companions, 3 NSs with main-sequence
companions, 13 NSs in X-ray binaries, and one undetermined system. We derive a
mean value of M = 1.46 +/- 0.30 solar masses. When the 46 NSs with measured
spin periods are divided into two groups at 20 milliseconds, i.e., the
millisecond pulsar (MSP) group and others, we find that their mass averages
are, respectively, M=1.57 +/- 0.35 solar masses and M=1.37+/- 0.23 solar
masses. In the framework of the pulsar recycling hypothesis, this suggests that
an accretion of approximately 0.2 solar mass is sufficient to spin up a neutron
star and place it in the millisecond pulsar group. An empirical relation
between the accreting mass and MSP spin period is \Delta M=0.43 (solar
mass)(P/1 ms)^{-2/3}. UNlike the standard recycling process, if a MSP is formed
by the accretion induced collapse (AIC) of a white dwarf with a mass less than
Chandrasekha limit, e.g. 1.35 solar mass, then the binary MSPs involved in AICs
is not be higher than 20%, which imposes a constraint on the AIC origin of
MSPs.Comment: 6 pages, 5 figures, in press, Astronomy and Astrophysics 2011, 527,
8
The Parkes multibeam pulsar survey: IV. Discovery of 180 pulsars and parameters for 281 previously known pulsars
The Parkes multibeam pulsar survey has led to the discovery of more than 700
pulsars. In this paper, we provide timing solutions, flux densities and pulse
profiles for 180 of these new discoveries. Two pulsars, PSRs J1736-2843 and
J1847-0130 have rotational periods P > 6s and are therefore among the slowest
rotating radio pulsars known. Conversely, with P = 1.8ms, PSR J1843-1113 has
the third shortest period of pulsars currently known. This pulsar and PSR
J1905+0400 (P = 3.8ms) are both solitary. We also provide orbital parameters
for a new binary system, PSR J1420-5625, which has P = 34ms, an orbital period
of 40 days and a minimum companion mass of 0.4 solar masses. The 10 degree-wide
strip along the Galactic plane that was surveyed is known to contain 264 radio
pulsars that were discovered prior to the multibeam pulsar survey. We have
redetected almost all of these pulsars and provide new dispersion measure
values and flux densities at 20cm for the redetected pulsars.Comment: 35 pages, accepted for publication in MNRAS, a high quality image of
the figure on page 32 is available from
http://www.atnf.csiro.au/research/pulsar/images/pmsurvey_fig.p
An -frequency dynamics algorithm for gravitational waves
Coalescence of low mass compact binaries of neutron stars and black holes are
primary burst sources for LIGO and VIRGO.Of importance in the early stages of
observations will be the classification of candidate detections by source-type.
The diversity in source parameters and serendipity in any new window of
observations suggest to consider model-independent detection algorithms. Here a
frequency dynamics algorithm is described which extracts a trajectory in the
-plane from the noisy signal. The algorithm is studied in simulated
binary coalescence. Robust results are obtained with experimental noise data.
Experiments show the method to be superior to matched filtering in the presence
of model imperfections.Comment: to appear in Rapid Commun, Phys Rev
Beam-helicity asymmetries for single-hadron production in semi-inclusive deep-inelastic scattering from unpolarized hydrogen and deuterium targets
A measurement of beam-helicity asymmetries for single-hadron production in
deep-inelastic scattering is presented. Data from the scattering of 27.6 GeV
electrons and positrons off gaseous hydrogen and deuterium targets were
collected by the HERMES experiment. The asymmetries are presented separately as
a function of the Bjorken scaling variable, the hadron transverse momentum, and
the fractional energy for charged pions and kaons as well as for protons and
anti-protons. These asymmetries are also presented as a function of the three
aforementioned kinematic variables simultaneously
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