478 research outputs found
Fermi Detection of the Pulsar Wind Nebula HESS J1640-465
We present observations of HESS J1640-465 with the Fermi-LAT. The source is
detected with high confidence as an emitter of high-energy gamma-rays. The
spectrum lacks any evidence for the characteristic cutoff associated with
emission from pulsars, indicating that the emission arises primarily from the
pulsar wind nebula. Broadband modeling implies an evolved nebula with a low
magnetic field resulting in a high gamma-ray to X-ray flux ratio. The Fermi
emission exceeds predictions of the broadband model, and has a steeper
spectrum, possibly resulting from a distinct excess of low energy electrons
similar to what is inferred for both the Vela X and Crab pulsar wind nebulae.Comment: 6 pages, 5 figures, accepted for publication in Ap
TDI noises transfer functions for LISA
The LISA mission is the future space-based gravitational wave (GW)observatory of the European Space Agency. It is formed by 3 spacecraftexchanging laser beams in order to form multiple real and virtualinterferometers. The data streams to be used in order to extract the largenumber and variety of GW sources are Time-Delay Interferometry (TDI) data. Oneimportant processing to produce these data is the TDI on-ground processingwhich recombines multiple interferometric on-board measurements to removecertain noise sources from the data such as laser frequency noise or spacecraftjitter. The LISA noise budget is therefore expressed at the TDI level in orderto account for the different TDI transfer functions applied for each noisesource and thus estimate their real weight on mission performance. In order toderive a usable form of these transfer functions, a model of the beams, themeasurements, and TDI have been developed, and several approximation have beenmade. A methodology for such a derivation has been established, as well asverification procedures. It results in a set of transfer functions, which arenow used by the LISA project, in particular in its performance model. Usingthese transfer functions, realistic noise curves for various instrumentalconfigurations are provided to data analysis algorithms and used for instrumentdesign.<br
A pilot study of behavioral, physiological, and subjective responses to varying mental effort requirements in attention-deficit/hyperactivity disorder
Background: Attention-deficit/hyperactivity disorder (ADHD) is presumed to involve mental effort application difficulties. To test this assumption, we manipulated task difficulty and measured behavioral, as well as subjective and psychophysiological indices of effort. Methods: Fifteen adolescent ADHD boys and 16 controls performed two tasks. First, subjective estimates and behavioral and pupillary measures of effort were recorded across five levels of N-back task difficulties. Second, effort discounting was assessed. In the latter, participants made repeated choices between performing a difficult N-back task for a high reward versus an easier N-back task for a smaller reward. Results: Increasing task difficulty led to similar deteriorations in performance for both groups - although ADHD participants performed more poorly at all difficulty levels than controls. While ADHD and control participants rated the tasks equally difficult and discounted effort similarly, those with ADHD displayed slightly different pupil dilation patterns with increasing task difficulty. Conclusion: The behavioral results did not provide evidence for mental effort problems in adolescent boys with ADHD. The subtle physiological effects, however, suggest that adolescents with ADHD may allocate effort in a different way than controls
Actin modulates shape and mechanics of tubular membranes
International audienceThe actin cytoskeleton shapes cells and also organizes internal membranous compartments. In particular, it interacts with membranes for intracellular transport of material in mammalian cells, yeast, or plant cells. Tubular membrane intermediates, pulled along microtubule tracks, are formed during this process and destabilize into vesicles. While the role of actin in tubule destabilization through scission is suggested, literature also provides examples of actin-mediated stabilization of membranous structures. To directly address this apparent contradiction, we mimic the geometry of tubular intermediates with preformed membrane tubes. The growth of an actin sleeve at the tube surface is monitored spatiotemporally. Depending on network cohesiveness, actin is able to entirely stabilize or locally maintain membrane tubes under pulling. On a single tube, thicker portions correlate with the presence of actin. These structures relax over several minutes and may provide enough time and curvature geometries for other proteins to act on tube stability
Study of Four Young TeV Pulsar Wind Nebulae with a Spectral Evolution Model
We study four young Pulsar Wind Nebulae (PWNe) detected in TeV gamma-rays,
G21.5-0.9, G54.1+0.3, Kes 75, and G0.9+0.1, using the spectral evolution model
developed and applied to the Crab Nebula in our previous work. We model the
evolution of magnetic field and particle distribution function inside a
uniformly expanding PWN considering a time-dependent injection from the pulsar
and radiative and adiabatic losses. Considering uncertainties in the
interstellar radiation field (ISRF) and their distance, we study two cases for
each PWN. Because TeV PWNe have a large TeV gamma-rays to X-rays flux ratio,
the magnetic energy of the PWNe accounts for only a small fraction of the total
energy injected (typically a few x 10^{-3}). The gamma-ray emission is
dominated by inverse Compton scattering off the infrared photons of the ISRF. A
broken power-law distribution function for the injected particles reproduces
the observed spectrum well, except for G0.9+0.1. For G0.9+0.1, we do not need a
low energy counterpart because adiabatic losses alone are enough to reproduce
the radio observations. High energy power-law indices at injection are similar
(2.5 -- 2.6), while low energy power-law indices range from 1.0 to 1.6. The
lower limit of the particle injection rate indicates that the pair multiplicity
is larger than 10^4. The corresponding upper limit of the bulk Lorentz factor
of the pulsar winds is close to the break energy of the broken power-law
injection, except for Kes 75.Comment: Accepted for publication in ApJ; 56pages, 15figure
The Infrared Detection of the Pulsar Wind Nebula in the Galactic Supernova Remnant 3C 58
We present infrared observations of 3C 58 with the Spitzer Space Telescope
and the Canada-France-Hawaii Telescope. Using the IRAC camera, we have imaged
the entire source resulting in clear detections of the nebula at 3.6 and 4.5
microns. The derived flux values are consistent with extrapolation of the X-ray
spectrum to the infrared band, demonstrating that any cooling break in the
synchrotron spectrum must occur near the soft X-ray band. We also detect the
torus surrounding PSR J0205+6449, the 65 ms pulsar that powers 3C 58. The torus
spectrum requires a break between the infrared and X-ray bands, and perhaps
multiple breaks. This complex spectrum, which is an imprint of the particles
injected into the nebula, has considerable consequences for the evolution of
the broadband spectrum of 3C 58. We illustrate these effects and discuss the
impact of these observations on the modeling of broadband spectra of pulsar
wind nebulae.Comment: 4 pages, 4 figures, accepted for publication in ApJ Letter
An Improved Search for the Neutron Electric Dipole Moment
A permanent electric dipole moment of fundamental spin-1/2 particles violates
both parity (P) and time re- versal (T) symmetry, and hence, also charge-parity
(CP) symmetry since there is no sign of CPT-violation. The search for a neutron
electric dipole moment (nEDM) probes CP violation within and beyond the Stan-
dard Model. The experiment, set up at the Paul Scherrer Institute (PSI), an
improved, upgraded version of the apparatus which provided the current best
experimental limit, dn < 2.9E-26 ecm (90% C.L.), by the RAL/Sussex/ILL
collaboration: Baker et al., Phys. Rev. Lett. 97, 131801 (2006). In the next
two years we aim to improve the sensitivity of the apparatus to sigma(dn) =
2.6E-27 ecm corresponding to an upper limit of dn < 5E-27 ecm (95% C.L.), in
case for a null result. In parallel the collaboration works on the design of a
new apparatus to further increase the sensitivity to sigma(dn) = 2.6E-28 ecm.Comment: APS Division for particles and fields, Conference Proceedings, Two
figure
Recommended from our members
Health-related quality of life in Huntingtonâs Disease patients: a comparison of proxy assessment and patient self-rating using the disease-specific Huntingtonâs Disease health-related quality of life questionnaire (HDQoL)
Huntingtonâs disease (HD) is a fatal, neurodegenerative disease for which there is no known cure. Proxy evaluation is relevant for HD as its manifestation might limit the ability of persons to report their health-related quality of life (HrQoL). This study explored patientâproxy ratings of HrQoL of persons at different stages of HD, and examined factors that may affect proxy ratings. A total of 105 patientâproxy pairs completed the Huntingtonâs disease health-related quality of life questionnaire (HDQoL) and other established HrQoL measures (EQ-5D and SF-12v2). Proxyâpatient agreement was assessed in terms of absolute level (mean ratings) and intraclass correlation. Proxiesâ ratings were at a similar level to patientsâ self-ratings on an overall Summary Score and on most of the six Specific Scales of the HDQoL. On the Specific Hopes and Worries Scale, proxies on average rated HrQoL as better than patientsâ self-ratings, while on both the Specific Cognitive Scale and Specific Physical and Functional Scale proxies tended to rate HrQoL more poorly than patients themselves. The patientâs disease stage and mental wellbeing (SF-12 Mental Component scale) were the two factors that primarily affected proxy assessment. Proxy scores were strongly correlated with patientsâ self-ratings of HrQoL, on the Summary Scale and all Specific Scales. The patientâproxy correlation was lower for patients at moderate stages of HD compared to patients at early and advanced stages. The proxy report version of the HDQoL is a useful complementary tool to self-assessment, and a promising alternative when individual patients with advanced HD are unable to self-report
A highly stable atomic vector magnetometer based on free spin precession
We present a magnetometer based on optically pumped Cs atoms that measures
the magnitude and direction of a 1 T magnetic field. Multiple circularly
polarized laser beams were used to probe the free spin precession of the Cs
atoms. The design was optimized for long-time stability and achieves a scalar
resolution better than 300 fT for integration times ranging from 80 ms to 1000
s. The best scalar resolution of less than 80 fT was reached with integration
times of 1.6 to 6 s. We were able to measure the magnetic field direction with
a resolution better than 10 rad for integration times from 10 s up to 2000
s
- âŠ