4,010 research outputs found
On the Clustering of GRBs on the Sky
The two-point correlation of the 4th (current) BATSE catalog (2494 objects)
is calculated. It is shown to be consistent with zero at nearly all angular
scales of interest. Assuming that GRBs trace the large scale structure in the
universe we calculate the angular correlation function for the standard CDM
(sCDM) model. It is shown to be at if the
BATSE catalog is assumed to be a volume-limited sample up to .
Combined with the error analysis on the BATSE catalog this suggests that nearly
GRBs will be needed to make a positive detection of the two-point
angular correlation function at this angular scale.Comment: 5 pages, Latex with aipproc.sty, incl. 1 ps-Fig., Proc. of the 5th
Huntsville Gamma Ray Burst Symposium, Oct. 1999, ed. R.M. Kippen, AI
On the phase structure and thermodynamics of QCD
We discuss the phase structure and thermodynamics of QCD by means of
dynamical chiral effective models. Quark and meson fluctuations are included
via the functional renormalization group. We study the influence of confinement
in addition to the impact of fluctuations by comparing the results of the
chiral models to their Polyakov-loop extended versions. Furthermore, we discuss
the mass sensitivity of the phase structure and thermodynamics and find
interesting modifications close to the chiral limit.Comment: 13 pages, 11 figures; Appendix added; published versio
Coupling of Active Motion and Advection Shapes Intracellular Cargo Transport
Intracellular cargo transport can arise from passive diffusion, active
motor-driven transport along cytoskeletal filament networks, and passive
advection by fluid flows entrained by such motor/cargo motion. Active and
advective transport are thus intrinsically coupled as related, yet different
representations of the same underlying network structure. A
reaction-advection-diffusion system is used here to show that this coupling
affects the transport and localization of a passive tracer in a confined
geometry. For sufficiently low diffusion, cargo localization to a target zone
is optimized either by low reaction kinetics and decoupling of bound and
unbound states, or by a mostly disordered cytoskeletal network with only weak
directional bias. These generic results may help to rationalize subtle features
of cytoskeletal networks, for example as observed for microtubules in fly
oocytes.Comment: revtex, 5 pages, 5 figures, to appear in PRL (http://prl.aps.org/
Differing preferences of Antarctic soil nematodes for microbial prey
We tested the preferences of three nematode taxa, Geomonhystera villosa, Plectus spp. and Teratocephalus spp., extracted from moss at Signy Island in the Maritime Antarctic, for two microalgae, three microfungi and six heterotrophic bacteria, each also from soils at Signy Island. Choice test experiments on water agar medium, in which nematodes were enumerated in wells containing microbes at 24 and 48 h, indicated that there were differing preferences between nematodes for distinct prey. G. villosa was significantly attracted to the alga Chlorella cf. minutissima and the fungus Mortierella hyalina, and was more attracted to all algae and fungi than either of the other two nematodes. Both G. villosa and Teratocephalus spp. were attracted to an actinobacterium. Plectus spp. were significantly attracted to the alga Stichococcus bacillaris and bacteria with close taxonomic affinities to Arthrobacter, Pseudomonas and Polaromonas. Experiments using 0.5 μm diameter fluorescent beads indicated significantly increased ingestion by nematodes in the presence of each of these microbes compared with controls, except by Plectus spp. in the presence of S. bacillaris. We conclude that complex trophic interactions may occur in apparently simple Antarctic soil food webs
Looking for black-holes in X-ray binaries with XMM-Newton: XTE J1817-330 and XTE J1856+053
The X-ray binary XTE J1817-330 was discovered in outburst on 26 January 2006
with RXTE/ASM. One year later, another X-ray transient discovered in 1996, XTE
J1856+053, was detected by RXTE during a new outburst on 28 February 2007. We
triggered XMM-Newton target of opportunity observations on these two objects to
constrain their parameters and search for a stellar black holes. We summarize
the properties of these two X-ray transients and show that the soft X-ray
spectra indicate indeed the presence of an accreting stellar black hole in each
of the two systems.Comment: to appear in the proceedings of the Second Kolkata Conference on
Observational Evidence for Black Holes in the Universe, Feb. 2008, Editor
Sandip Chakrabarti, AI
Fiscal Effects of Minimum Wages – An Analysis for Germany
Against the background of the current discussion on the introduction of statutory minimum wages in Germany, this paper analyzes the potential employment and fiscal effects of such a policy. Based on estimated labor demand elasticities obtained from a structural labor demand model, the empirical results imply that the introduction of minimum wages in Germany will be associated with significant employment losses that are concentrated among marginal and low- and semi-skilled full-time workers. Even though minimum wages will lead to increased public revenues from income taxes and social security benefits, they will result in a significant fiscal burden, due to increased expenditures for unemployment benefits and decreased revenues from corporate taxes.Minimum wages, employment, public budget, fiscal effects
Exploring the Phase Structure and Thermodynamics of QCD
We put forward a Polyakov-loop extended quark meson model, where matter as
well as glue fluctuations are taken into account, cf. [1]. The latter are
included via a Polyakov-loop potential. Usually such a glue potential is based
on Yang-Mills lattice data only. We show that a parametrisation of unquenching
effects as proposed in [2], together with the inclusion of fluctuations via the
functional renormalisation group [3,4], accounts for the relevant dynamics.
This is demonstrated by a comparison of order parameters and thermodynamic
observables to recent lattice results at vanishing chemical potential, where we
find very good agreement.Comment: 11 pages, 2 figures, contribution to "QCD-TNT-III: From quarks and
gluons to hadronic matter: A bridge too far?", ECT*, Trento (Italy),
September 2-6, 201
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Existence and uniqueness for four-dimensional variational data assimilation in discrete time
Variational techniques for data assimilation, i.e., estimating orbits of dynamical models from observations, are revisited. It is shown that under mild hypotheses a solution to this variational problem exists. Using ideas from optimal control theory, the problem of uniqueness is investigated and a number of results (well known from optimal control) are established in the present context. The value function is introduced as the minimal cost over all feasible trajectories starting from a given initial condition. By combining the necessary conditions with an envelope theorem, it is shown that the solution is unique if and only if the value function has a derivative at the given initial condition. Further, the value function is Lipschitz and hence has a derivative for almost all (with respect to the Lebesgue measure) initial conditions. Several examples are studied which demonstrate that points of nondifferentiability of the value function (and hence nonuniqueness of solutions) are nevertheless to be expected in practice
An all-optical buffer based on temporal cavity solitons operating at 10 Gb/s
We demonstrate the operation of an all-optical buffer based on temporal
cavity solitons stored in a nonlinear passive fiber ring resonator. Unwanted
acoustic interactions between neighboring solitons are suppressed by modulating
the phase of the external laser driving the cavity. A new locking scheme is
presented that allows the buffer to operate with an arbitrarily large number of
cavity solitons in the loop. Experimentally, we are able to demonstrate the
storage of 4536 bits of data, written all-optically into the fiber ring at 10
Gb/s, for 1 minute.Comment: 5 pages, 4 figure
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