736 research outputs found
The Quiescent Spectrum of the AM CVn star CP Eri
We used the 6.5m MMT to obtain a spectrum of the AM CVn star CP Eri in
quiescence. The spectrum is dominated by He I emission lines, which are clearly
double peaked with a peak-to-peak separation of ~1900 km/s. The spectrum is
similar to that of the longer period AM CVn systems GP Com and CE 315, linking
the short and the long period AM CVn systems. In contrast with GP Com and CE
315, the spectrum of CP Eri does not show a central 'spike' in the line
profiles, but it does show lines of SiII in emission. The presence of these
lines indicates that the material being transferred is of higher metallicity
than in GP Com and CE 315, which, combined with the low proper motion of the
system, probably excludes a halo origin of the progenitor of CP Eri. We
constrain the primary mass to M_1>0.27 M_sun and the orbital inclination to 33
degr < i < 80 degr. The presence of the He I lines in emission opens up the
possibility for phase resolved spectroscopic studies which allows a
determination of the system parameters and a detailed study of helium accretion
disks under highly varying circumstances.Comment: 12 pages, 2 figures, accepted for publication in ApJ Letter
Persistence in Cluster--Cluster Aggregation
Persistence is considered in diffusion--limited cluster--cluster aggregation,
in one dimension and when the diffusion coefficient of a cluster depends on its
size as . The empty and filled site persistences are
defined as the probabilities, that a site has been either empty or covered by a
cluster all the time whereas the cluster persistence gives the probability of a
cluster to remain intact. The filled site one is nonuniversal. The empty site
and cluster persistences are found to be universal, as supported by analytical
arguments and simulations. The empty site case decays algebraically with the
exponent . The cluster persistence is related to the
small behavior of the cluster size distribution and behaves also
algebraically for while for the behavior is
stretched exponential. In the scaling limit and with fixed the distribution of intervals of size between
persistent regions scales as , where is the average interval size and . For finite the
scaling is poor for , due to the insufficient separation of the two
length scales: the distances between clusters, , and that between
persistent regions, . For the size distribution of persistent regions
the time and size dependences separate, the latter being independent of the
diffusion exponent but depending on the initial cluster size
distribution.Comment: 14 pages, 12 figures, RevTeX, submitted to Phys. Rev.
Martini: using literature keywords to compare gene sets
Life scientists are often interested to compare two gene sets to gain insight into differences between two distinct, but related, phenotypes or conditions. Several tools have been developed for comparing gene sets, most of which find Gene Ontology (GO) terms that are significantly over-represented in one gene set. However, such tools often return GO terms that are too generic or too few to be informative. Here, we present Martini, an easy-to-use tool for comparing gene sets. Martini is based, not on GO, but on keywords extracted from Medline abstracts; Martini also supports a much wider range of species than comparable tools. To evaluate Martini we created a benchmark based on the human cell cycle, and we tested several comparable tools (CoPub, FatiGO, Marmite and ProfCom). Martini had the best benchmark performance, delivering a more detailed and accurate description of function. Martini also gave best or equal performance with three other datasets (related to Arabidopsis, melanoma and ovarian cancer), suggesting that Martini represents an advance in the automated comparison of gene sets. In agreement with previous studies, our results further suggest that literature-derived keywords are a richer source of gene-function information than GO annotations. Martini is freely available at http://martini.embl.de
X-ray and optical observations of the unique binary system HD49798/RXJ0648.0-4418
We report the results of XMM-Newton observations of HD49798/RXJ0648.0-4418,
the only known X-ray binary consisting of a hot sub-dwarf and a white dwarf.
The white dwarf rotates very rapidly (P=13.2 s) and has a dynamically measured
mass of 1.28+/-0.05 M_sun. Its X-ray emission consists of a strongly pulsed,
soft component, well fit by a blackbody with kT~40 eV, accounting for most of
the luminosity, and a fainter hard power-law component (photon index ~1.6). A
luminosity of ~10^{32} erg/s is produced by accretion onto the white dwarf of
the helium-rich matter from the wind of the companion, which is one of the few
hot sub-dwarfs showing evidence of mass-loss. A search for optical pulsations
at the South African Astronomical Observatory 1.9-m telescope gave negative
results. X-rays were detected also during the white dwarf eclipse. This
emission, with luminosity 2x10^{30} erg/s, can be attributed to HD 49798 and
represents the first detection of a hot sub-dwarf star in the X-ray band.
HD49798/RXJ0648.0-4418 is a post-common envelope binary which most likely
originated from a pair of stars with masses ~8-10 M_sun. After the current
He-burning phase, HD 49798 will expand and reach the Roche-lobe, causing a
higher accretion rate onto the white dwarf which can reach the Chandrasekhar
limit. Considering the fast spin of the white dwarf, this could lead to the
formation of a millisecond pulsar. Alternatively, this system could be a Type
Ia supernova progenitor with the appealing characteristic of a short time
delay, being the descendent of relatively massive stars.Comment: Accepted for publication on The Astrophysical Journa
Survival Probability of a Ballistic Tracer Particle in the Presence of Diffusing Traps
We calculate the survival probability P_S(t) up to time t of a tracer
particle moving along a deterministic trajectory in a continuous d-dimensional
space in the presence of diffusing but mutually noninteracting traps. In
particular, for a tracer particle moving ballistically with a constant velocity
c, we obtain an exact expression for P_S(t), valid for all t, for d<2. For d
\geq 2, we obtain the leading asymptotic behavior of P_S(t) for large t. In all
cases, P_S(t) decays exponentially for large t, P_S(t) \sim \exp(-\theta t). We
provide an explicit exact expression for the exponent \theta in dimensions d
\leq 2, and for the physically relevant case, d=3, as a function of the system
parameters.Comment: RevTeX, 4 page
Cluster persistence in one-dimensional diffusion--limited cluster--cluster aggregation
The persistence probability, , of a cluster to remain unaggregated is
studied in cluster-cluster aggregation, when the diffusion coefficient of a
cluster depends on its size as . In the mean-field the
problem maps to the survival of three annihilating random walkers with
time-dependent noise correlations. For the motion of persistent
clusters becomes asymptotically irrelevant and the mean-field theory provides a
correct description. For the spatial fluctuations remain relevant
and the persistence probability is overestimated by the random walk theory. The
decay of persistence determines the small size tail of the cluster size
distribution. For the distribution is flat and, surprisingly,
independent of .Comment: 11 pages, 6 figures, RevTeX4, submitted to Phys. Rev.
Position-specific Performance Indicators that Discriminate between Successful and Unsuccessful Teams in Elite Women’s Indoor Field Hockey: Implications for Coaching
The aim of this investigation was to establish median performance profiles for the six playing positions in elite women’s indoor hockey and then identify whether these position-specific profiles could discriminate between qualifying (top four), mid-table and relegated teams in the 2011-12 England Hockey premier league. Successful passing in relegated teams was significantly lower (p<0.008) than in mid-table and qualifying teams in four of the five outfield positions. Furthermore, the right backs of qualifying teams demonstrated significantly fewer (p<0.008) unsuccessful passes (x̃=15.5 ±CLs 15.0 and 10.0 respectively) and interceptions (x̃=4.0 ±CLs 4.0 and 3.0 respectively) than relegated teams (x̃=19.5 ±CLs 21.0 and 17.0; x̃=7.5 ±CLs 8.0 and 6.0 respectively). Finally, the right forwards of relegated teams demonstrated significantly fewer (p<0.008) successful interceptions (x̃=4.0 ±CLs 5.0 and 4.0 respectively) than qualifying teams (x̃=5.0 ±CLs 6.0 and 3.0 respectively) and significantly more (p<0.008) unsuccessful interceptions (x̃=5.5 ±CLs 6.0 and 4.0 respectively) than mid-table teams (x̃=3.0 ±CLs 3.0 and 2.0 respectively). Based on these findings, coaches should adapt tactical strategies and personnel deployment accordingly to enhance the likelihood of preparing a qualifying team. Research should build from these data to examine dribbling, pressing and patterns of play when outletting
First Attempt at Spectroscopic Detection of Gravity Modes in a Long-Period Pulsating Subdwarf B Star -- PG 1627+017
In the first spectroscopic campaign for a PG 1716 variable (or long-period
pulsating subdwarf B star), we succeeded in detecting velocity variations due
to g-mode pulsations at a level of 1.0-1.5 km/s.The observations were obtained
during 40 nights on 2-m class telescopes in Arizona, South Africa,and
Australia. The target,PG1627+017, is one of the brightest and largest amplitude
stars in its class.It is also the visible component of a post-common envelope
binary.Our final radial velocity data set includes 84 hours of time-series
spectroscopy over a time baseline of 53 days. Our derived radial velocity
amplitude spectrum, after subtracting the orbital motion, shows three potential
pulsational modes 3-4 sigma above the mean noise level, at 7201.0s,7014.6s and
7037.3s.Only one of the features is statistically likely to be real,but all
three are tantalizingly close to, or a one day alias of, the three strongest
periodicities found in the concurrent photometric campaign. We further
attempted to detect pulsational variations in the Balmer line amplitudes. The
single detected periodicity of 7209 s, although weak, is consistent with
theoretical expectations as a function of wavelength.Furthermore, it allows us
to rule out a degree index of l= 3 or l= 5 for that mode. Given the extreme
weakness of g-mode pulsations in these stars,we conclude that anything beyond
simply detecting their presence will require larger telescopes,higher
efficiency spectral monitoring over longer time baselines,improved longitude
coverage, and increased radial velocity precision.Comment: 39 pages, 9 figures, 4 tables, ApJ accepted. See postscript for full
abtrac
Electrochemistry of nanozeolite-immobilized cytochrome c in aqueous and nonaqueous solutions
peer-reviewedThe electrochemical properties of cytochrome c (cyt c) immobilized on multilayer nanozeolite-modified electrodes have been examined in aqueous and nonaqueous solutions. Layers of Linde type-L zeolites were assembled on indium tin oxide (ITO) glass electrodes followed by the adsorption of cyt c, primarily via electrostatic interactions, onto modified ITO electrodes. The heme protein displayed a quasi-reversible response in aqueous solution with a redox potential of +324 mV (vs NHE), and the surface coverage (Gamma*) increased linearly for the first four layers and then gave a nearly constant value of 200 pmol cm(-2). On immersion of the modified electrodes in 95% (v/v) nonaqueous solutions, the redox potential decreased significantly, a decrease that originated from changes in both the enthalpy and entropy of reduction. On reimmersion of the modified electrode in buffer, the faradic response immediately returned to its original value. These results demonstrate that nanozeolites are potential stable supports for redox proteins and enzymes.ACCEPTEDpeer-reviewe
The Halo Black-Hole X-ray Transient XTE J1118+480
Optical spectra were obtained of the optical counterpart of the high latitude
soft X-ray transient XTE J1118+480 near its quiescent state with the new 6.5 m
MMT and the 4.2 m WHT. The spectrum exhibits broad, double-peaked, emission
lines of hydrogen from an accretion disk superposed with absorption lines of a
K7V-M0V secondary star. Cross-correlation of the 27 individual spectra with
late-type stellar template spectra reveals a sinusoidal variation in radial
velocity with amplitude K = 701 +/- 10 km/s and orbital period P = 0.169930 +/-
0.000004 d. The mass function, 6.1 +/- 0.3 solar masses, is a firm lower limit
on the mass of the compact object and strongly implies that it is a black hole.
Photometric observations (R-band) with the IAC 0.8 m telescope reveal
ellipsoidal light variations of full amplitude 0.2 mag. Modeling gives a large
mass ratio (M1/M2 ~ 20) and a high orbital inclination (i = 81 +/- 2 deg). Our
combined fits yield a mass of the black hole in the range M1 = 6.0-7.7 solar
masses (90% confidence) for plausible secondary star masses of M2 = 0.09-0.5
solar masses. The photometric period measured during the outburst is 0.5%
longer than our orbital period and probably reflects superhump modulations as
observed in some other soft X-ray transients. The estimated distance is d = 1.9
+/- 0.4 kpc corresponding to a height of 1.7 +/- 0.4 kpc above the Galactic
plane. The spectroscopic, photometric, and dynamical results indicate that XTE
J1118+480 is the first firmly identified black hole X-ray system in the
Galactic halo.Comment: 8 pages, 3 figures, AASTeX 5.0, To Appear in the Astrophysical
Journal, Part 1, Volume 556, July 20, 200
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