19,872 research outputs found
The magnetic field in the NGC 2024 FIR 5 dense core
We used the Submillimeter Array (SMA) to observe the thermal polarized dust
emission from the protostellar source NGC 2024 FIR 5. The polarized emission
outlines a partial hourglass morphology for the plane-of-sky component of the
core magnetic field. Our data are consistent with previous BIMA maps, and the
overall magnetic field geometries obtained with both instruments are similar.
We resolve the main core into two components, FIR 5A and FIR 5B. A possible
explanation for the asymmetrical field lies in depolarization effects due to
the lack of internal heating from FIR 5B source, which may be in a prestellar
evolutionary state. The field strength was estimated to be 2.2 mG, in agreement
with previous BIMA data. We discuss the influence of a nearby H{\sc ii} region
over the field lines at scales of pc. Although the hot component is
probably compressing the molecular gas where the dust core is embedded, it is
unlikely that the radiation pressure exceeds the magnetic tension. Finally, a
complex outflow morphology is observed in CO (3 2) maps. Unlike
previous maps, several features associated with dust condensations other than
FIR 5 are detected.Comment: 48 pages, 12 figures, accepted for publication in The Astrophysical
Journa
Two Purified Domains of Telomerase Reverse Transcriptase Reconstitute Sequence-Specific Interactions with RNA
Telomerase reverse transcriptase (TERT) and telomerase RNA (TER) function together to create a uniquely specialized polymerase. Here we have described for the first time domains of bacterially expressed Tetrahymena TERT that interacted directly with TER in the absence of assembly chaperones. We used quantitative binding assays to define TER sequence requirements for recognition by the high affinity RNA binding domain and an independent N-terminal RNA interaction domain. The TERT RNA binding domain and N-terminal RNA interaction domain had distinct, nonoverlapping requirements for TER sequence and structure that together accounted for all of the sites of TER contact inferred for full-length TERT. The TER residues important for TERT binding are only a subset of the residues required for catalytic activity. Our findings demonstrate telomerase functional specialization by an elaborate ribonucleoprotein architecture physically separable from the active site
Parity Violation in Neutrino Transport and the Origin of Pulsar Kicks
In proto-neutron stars with strong magnetic fields, the neutrino-nucleon
scattering/absorption cross sections depend on the direction of neutrino
momentum with respect to the magnetic field axis, a manifestation of parity
violation in weak interactions. We study the deleptonization and thermal
cooling (via neutrino emission) of proto-neutron stars in the presence of such
asymmetric neutrino opacities. Significant asymmetry in neutrino emission is
obtained due to multiple neutrino-nucleon scatterings. For an ordered magnetic
field threading the neutron star interior, the fractional asymmetry in neutrino
emission is about , corresponding to a pulsar kick velocity
of about km/s for a total radiated neutrino energy of
erg.Comment: AASTeX, 10 pages including 2 ps figures; ApJ Letter in press (March
10, 1998). Shortened to agree with the published versio
Transition to manual: Driver behaviour when resuming control from a highly automated vehicle
A driving simulator study was designed to investigate drivers’ ability to resume control from a highly automated vehicle in two conditions: (i) when automation was switched off and manual control was required at a system-based, regular interval and (ii) when transition to manual was based on the length of time drivers were looking away from the road ahead. In addition to studying the time it took drivers to successfully resume control from the automated system, eye tracking data were used to observe visual attention to the surrounding environment and the pattern of drivers’ eye fixations as manual control was resumed in the two conditions. Results showed that drivers’ pattern of eye movement fixations remained variable for some time after automation was switched off, if disengagement was actually based on drivers’ distractions away from the road ahead. When disengagement was more predictable and system-based, drivers’ attention towards the road centre was higher and more stable. Following a lag of around 10 s, drivers’ lateral control of driving and steering corrections (as measured by SDLP and high frequency component of steering, respectively) were more stable when transition to manual control was predictable and based on a fixed time. Whether automation transition to manual was based on a fixed or variable interval, it took drivers around 35–40 s to stabilise their lateral control of the vehicle. The results of this study indicate that if drivers are out of the loop due to control of the vehicle in a limited self-driving situation (Level 3 automation), their ability to regain control of the vehicle is better if they are expecting automation to be switched off. As regular disengagement of automation is not a particularly practical method for keeping drivers in the loop, future research should consider how to best inform drivers of their obligation to resume control of driving from an automated system
Adaptive online deployment for resource constrained mobile smart clients
Nowadays mobile devices are more and more used as a platform for applications. Contrary to prior generation handheld devices configured with a predefined set of applications, today leading edge devices provide a platform for flexible and customized application deployment. However, these applications have to deal with the limitations (e.g. CPU speed, memory) of these mobile devices and thus cannot handle complex tasks. In order to cope with the handheld limitations and the ever changing device context (e.g. network connections, remaining battery time, etc.) we present a middleware solution that dynamically offloads parts of the software to the most appropriate server. Without a priori knowledge of the application, the optimal deployment is calculated, that lowers the cpu usage at the mobile client, whilst keeping the used bandwidth minimal. The information needed to calculate this optimum is gathered on the fly from runtime information. Experimental results show that the proposed solution enables effective execution of complex applications in a constrained environment. Moreover, we demonstrate that the overhead from the middleware components is below 2%
Current-oscillator correlation and Fano factor spectrum of quantum shuttle with finite bias voltage and temperature
A general master equation is derived to describe an electromechanical
single-dot transistor in the Coulomb blockade regime. In the equation, Fermi
distribution functions in the two leads are taken into account, which allows
one to study the system as a function of bias voltage and temperature of the
leads. Furthermore, we treat the coherent interaction mechanism between
electron tunneling events and the dynamics of excited vibrational modes.
Stationary solutions of the equation are numerically calculated. We show
current through the oscillating island at low temperature appears step like
characteristics as a function of the bias voltage and the steps depend on mean
phonon number of the oscillator. At higher temperatures the current steps would
disappear and this event is accompanied by the emergence of thermal noise of
the charge transfer. When the system is mainly in the ground state, zero
frequency Fano factor of current manifests sub-Poissonian noise and when the
system is partially driven into its excited states it exhibits super-Poissonian
noise. The difference in the current noise would almost be removed for the
situation in which the dissipation rate of the oscillator is much larger than
the bare tunneling rates of electrons.Comment: 14 pages, 8 figure
Exploring the Structure of Distant Galaxies with Adaptive Optics on the Keck-II Telescope
We report on the first observation of cosmologically distant field galaxies
with an high order Adaptive Optics (AO) system on an 8-10 meter class
telescope. Two galaxies were observed at 1.6 microns at an angular resolution
as high as 50 milliarcsec using the AO system on the Keck-II telescope. Radial
profiles of both objects are consistent with those of local spiral galaxies and
are decomposed into a classic exponential disk and a central bulge. A
star-forming cluster or companion galaxy as well as a compact core are detected
in one of the galaxies at a redshift of 0.37+/-0.05. We discuss possible
explanations for the core including a small bulge, a nuclear starburst, or an
active nucleus. The same galaxy shows a peak disk surface brightness that is
brighter than local disks of comparable size. These observations demonstrate
the power of AO to reveal details of the morphology of distant faint galaxies
and to explore galaxy evolution.Comment: 5 pages, Latex, 3 figures. Accepted for publication in P.A.S.
Gastroparesis: New insights into an old disease
Gastroparesis (Gp) is a chronic disease characterized by a delayed gastric emptying in the absence of mechanical obstruction. Although this condition has been reported in the literature since the mid-1900s, only recently has there been renewed clinical and scientific interest in this disease, which has a potentially great impact on the quality of life. The aim of this review is to explore the pathophysiological, diagnostic and therapeutical aspects of Gp according to the most recent evidence. A comprehensive online search for Gp was carried out using MEDLINE and EMBASE. Gp is the result of neuromuscular abnormalities of the gastric motor function. There is evidence that patients with idiopathic and diabetic Gp may display a reduction in nitrergic inhibitory neurons and in interstitial cells of Cajal and/or telocytes. As regards diagnostic approach, 99-Technetium scintigraphy is currently considered to be the gold standard for Gp. Its limits are a lack of standardization and a mild risk of radiation exposure. The C13 breath testing is a valid and safe alternative method. 13C acid octanoic and the 13C Spirulina platensis recently approved by the Food and Drug Administration are the most commonly used diagnostic kits. The wireless motility capsule is a promising technique, but its use is limited by costs and scarce availability in many countries. Finally, therapeutic strategies are related to the clinical severity of Gp. In mild and moderate Gp, dietary modification and prokinetic agents are generally sufficient. Metoclopramide is the only drug approved by the Food and Drug Administration for Gp. However, other older and new prokinetics and antiemetics can be considered. As a second-line therapy, tricyclic antidepressants and cannabinoids have been proposed. In severe cases the normal nutritional approach can be compromised and artificial nutrition may be needed. In drug-unresponsive Gp patients some alternative strategies (endoscopic, electric stimulation or surgery) are available
- …