6,468 research outputs found
The Tea4-PP1 landmark promotes local growth by dual Cdc42 GEF recruitment and GAP exclusion.
Cell polarization relies on small GTPases, such as Cdc42, which can break symmetry through self-organizing principles, and landmarks that define the axis of polarity. In fission yeast, microtubules deliver the Tea1-Tea4 complex to mark cell poles for growth, but how this complex activates Cdc42 is unknown. Here, we show that ectopic targeting of Tea4 to cell sides promotes the local activation of Cdc42 and cell growth. This activity requires that Tea4 binds the type I phosphatase (PP1) catalytic subunit Dis2 or Sds21, and ectopic targeting of either catalytic subunit is similarly instructive for growth. The Cdc42 guanine-nucleotide-exchange factor Gef1 and the GTPase-activating protein Rga4 are required for Tea4-PP1-dependent ectopic growth. Gef1 is recruited to ectopic Tea4 and Dis2 locations to promote Cdc42 activation. By contrast, Rga4 is locally excluded by Tea4, and its forced colocalization with Tea4 blocks ectopic growth, indicating that Rga4 must be present, but at sites distinct from Tea4. Thus, a Tea4-PP1 landmark promotes local Cdc42 activation and growth both through Cdc42 GEF recruitment and by creating a local trough in a Cdc42 GAP
Multiple relativistic outbursts of GRS 1915+105: radio emission and internal shocks
We present 5-GHz MERLIN radio images of the microquasar GRS 1915+105 during
two separate outbursts in 2001 March and 2001 July, following the evolution of
the jet components as they move outwards from the core of the system. Proper
motions constrain the intrinsic jet speed to be >0.57c, but the uncertainty in
the source distance prevents an accurate determination of the jet speed. No
deceleration is observed in the jet components out to an angular separation of
about 300mas. Linear polarisation is observed in the approaching jet component,
with a gradual rotation in position angle and a decreasing fractional
polarisation with time. Our data lend support to the internal shock model
whereby the jet velocity increases leading to internal shocks in the
pre-existing outflow before the jet switches off. The compact nuclear jet is
seen to re-establish itself within two days, and is visible as core emission at
all epochs. The energetics of the source are calculated for the possible range
of distances; a minimum power of 1-10 per cent of the Eddington luminosity is
required to launch the jet.Comment: 18 pages, 14 figures, accepted for publication in MNRAS. For
higher-resolution versions of Figures 3, 5, and 12, see
http://remote.science.uva.nl/~jmiller/grs1915/figures.htm
The Flexible Plasma Trap (FPT) for the production of overdense plasmas
Electron Cyclotron Resonance Ion Sources are currently the most efficient ionsources among those used in facilities dedicated to nuclear physics. The needfor a more flexible magnetic field and RF injection system suggested to designand develop a different type of plasma trap, named Flexible Plasma Trap (FPT).The magnetic field of FPT is generated by means of three coils while microwavesin the range 4-7 GHz can be injected by three different inputs, one placedalong the axis and two placed radially. FPT can work in different plasmaheating schemes so it will be an ideal tool for studies of plasma andmultidisciplinary physics. Moreover, a microwave launcher has been designed andinstalled to the FPT for launching microwaves with a variable tilt angle withrespect to the magnetic field. This paper describes the characteristics of theFPT along with the preliminary results of plasma diagnostics
Global optical/infrared - X-ray correlations in X-ray binaries: quantifying disc and jet contributions
The optical/near-infrared (OIR) region of the spectra of low-mass X-ray
binaries appears to lie at the intersection of a variety of different emission
processes. In this paper we present quasi-simultaneous OIR - X-ray observations
of 33 XBs in an attempt to estimate the contributions of various emission
processes in these sources, as a function of X-ray state and luminosity. A
global correlation is found between OIR and X-ray luminosity for low-mass black
hole candidate XBs (BHXBs) in the hard X-ray state, of the form L_OIR is
proportional to Lx^0.6. This correlation holds over 8 orders of magnitude in Lx
and includes data from BHXBs in quiescence and at large distances (LMC and
M31). A similar correlation is found in low-mass neutron star XBs (NSXBs) in
the hard state. For BHXBs in the soft state, all the near-infrared (NIR) and
some of the optical emission is suppressed below the correlation, a behaviour
indicative of the jet switching off/on in transition to/from the soft state. We
compare these relations to theoretical models of a number of emission
processes. We find that X-ray reprocessing in the disc and emission from the
jets both predict a slope close to 0.6 for BHXBs, and both contribute to the
OIR in BHXBs in the hard state, the jets producing ~90 percent of the NIR
emission at high luminosities. X-ray reprocessing dominates the OIR in NSXBs in
the hard state, with possible contributions from the jets (only at high
luminosity) and the viscously heated disc. We also show that the optically
thick jet spectrum of BHXBs extends to near the K-band. (abridged)Comment: Accepted for publication in MNRAS; 19 pages, 7 figure
BlackCAT: A catalogue of stellar-mass black holes in X-ray transients
During the last ~50 years, the population of black hole candidates in X-ray
binaries has increased considerably with 59 Galactic objects detected in
transient low-mass X-ray binaries, plus a few in persistent systems (including
~5 extragalactic binaries). We collect near-infrared, optical and X-ray
information spread over hundreds of references in order to study the population
of black holes in X-ray transients as a whole. We present the most updated
catalogue of black hole transients, which contains X-ray, optical and
near-infrared observations together with their astrometric and dynamical
properties. It provides new useful information in both statistical and
observational parameters providing a thorough and complete overview of the
black hole population in the Milky Way. Analysing the distances and spatial
distribution of the observed systems, we estimate a total population of ~1300
Galactic black hole transients. This means that we have already discovered less
than ~5% of the total Galactic distribution. The complete version of this
catalogue will be continuously updated online and in the Virtual Observatory,
including finding charts and data in other wavelengths.Comment: http://www.astro.puc.cl/BlackCAT - Accepted for publication in
Astronomy & Astrophysics. 20 pages, 8 figures, 5 Table
Azimuthal asymmetry in the risetime of the surface detector signals of the Pierre Auger Observatory
The azimuthal asymmetry in the risetime of signals in Auger surface detector
stations is a source of information on shower development. The azimuthal
asymmetry is due to a combination of the longitudinal evolution of the shower
and geometrical effects related to the angles of incidence of the particles
into the detectors. The magnitude of the effect depends upon the zenith angle
and state of development of the shower and thus provides a novel observable,
, sensitive to the mass composition of cosmic rays
above eV. By comparing measurements with predictions from
shower simulations, we find for both of our adopted models of hadronic physics
(QGSJETII-04 and EPOS-LHC) an indication that the mean cosmic-ray mass
increases slowly with energy, as has been inferred from other studies. However,
the mass estimates are dependent on the shower model and on the range of
distance from the shower core selected. Thus the method has uncovered further
deficiencies in our understanding of shower modelling that must be resolved
before the mass composition can be inferred from .Comment: Replaced with published version. Added journal reference and DO
Measurements of branching fraction ratios and CP-asymmetries in suppressed B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^- decays
We report the first reconstruction in hadron collisions of the suppressed
decays B^- -> D(-> K^+ pi^-)K^- and B^- -> D(-> K^+ pi^-)pi^-, sensitive to the
CKM phase gamma, using data from 7 fb^-1 of integrated luminosity collected by
the CDF II detector at the Tevatron collider. We reconstruct a signal for the
B^- -> D(-> K^+ pi^-)K^- suppressed mode with a significance of 3.2 standard
deviations, and measure the ratios of the suppressed to favored branching
fractions R(K) = [22.0 \pm 8.6(stat)\pm 2.6(syst)]\times 10^-3, R^+(K) =
[42.6\pm 13.7(stat)\pm 2.8(syst)]\times 10^-3, R^-(K)= [3.8\pm 10.3(stat)\pm
2.7(syst]\times 10^-3, as well as the direct CP-violating asymmetry A(K) =
-0.82\pm 0.44(stat)\pm 0.09(syst) of this mode. Corresponding quantities for
B^- -> D(-> K^+ pi^-)pi^- decay are also reported.Comment: 8 pages, 1 figure, accepted by Phys.Rev.D Rapid Communications for
Publicatio
Search for New Physics with Jets and Missing Transverse Momentum in pp collisions at sqrt(s) = 7 TeV
A search for new physics is presented based on an event signature of at least
three jets accompanied by large missing transverse momentum, using a data
sample corresponding to an integrated luminosity of 36 inverse picobarns
collected in proton--proton collisions at sqrt(s)=7 TeV with the CMS detector
at the LHC. No excess of events is observed above the expected standard model
backgrounds, which are all estimated from the data. Exclusion limits are
presented for the constrained minimal supersymmetric extension of the standard
model. Cross section limits are also presented using simplified models with new
particles decaying to an undetected particle and one or two jets
Search for the standard model Higgs boson in the H to ZZ to 2l 2nu channel in pp collisions at sqrt(s) = 7 TeV
A search for the standard model Higgs boson in the H to ZZ to 2l 2nu decay
channel, where l = e or mu, in pp collisions at a center-of-mass energy of 7
TeV is presented. The data were collected at the LHC, with the CMS detector,
and correspond to an integrated luminosity of 4.6 inverse femtobarns. No
significant excess is observed above the background expectation, and upper
limits are set on the Higgs boson production cross section. The presence of the
standard model Higgs boson with a mass in the 270-440 GeV range is excluded at
95% confidence level.Comment: Submitted to JHE
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