5,671 research outputs found
Position-sensitive detector for the 6-meter optical telescope
The Position-Sensitive Detector (PSD) for photometrical and spectral
observation on the 6-meter optical telescope of the Special Astrophysical
Observatory (Russia) is described. The PSD consists of a position-sensitive
tube, amplifiers of output signals, analog-to-digital converters (ADC) and a
digital logic plate, which produces a signal for ADC start and an external
strob pulse for reading information by registration system. If necessary, the
thermoelectric cooler can be used. The position-sensitive tube has the
following main elements: a photocathode, electrodes of inverting optics, a
block of microchannel plates (MCP) and a position-sensitive collector of
quadrant type. The main parameters of the PSD are the diameter of the sensitive
surface is 25 mm, the spatial resolution is better than 100 (\mu)m in the
centre and a little worse on the periphery; the dead time is near 0.5 (\mu)s;
the detection quantum efficiency is defined by the photocathode and it is not
less than 0.1, as a rule; dark current is about hundreds of cps, or less, when
cooling. PSD spectral sensitivity depends on the type of photocathode and input
window material. We use a multialkali photocathode and a fiber or UV-glass,
which gives the short- wave cut of 360 nm or 250 nm, respectively.Comment: 4 pages, 7 figures, to be published in Nuclear Instruments & Methods
in Physics Researc
Phase and Intensity Distributions of Individual Pulses of PSR B0950+08
The distribution of the intensities of individual pulses of PSR B0950+08 as a
function of the longitudes at which they appear is analyzed. The flux density
of the pulsar at 111 MHz varies strongly from day to day (by up to a factor of
13) due to the passage of the radiation through the interstellar plasma
(interstellar scintillation). The intensities of individual pulses can exceed
the amplitude of the mean pulse profile, obtained by accumulating 770 pulses,
by more than an order of magnitude. The intensity distribution along the mean
profile is very different for weak and strong pulses. The differential
distribution function for the intensities is a power law with index n = -1.1 +-
0.06 up to peak flux densities for individual pulses of the order of 160 Jy
Scattering and Diffraction in Magnetospheres of Fast Pulsars
We apply a theory of wave propagation through a turbulent medium to the
scattering of radio waves in pulsar magnetospheres. We find that under
conditions of strong density modulation the effects of magnetospheric
scintillations in diffractive and refractive regimes may be observable. The
most distinctive feature of the magnetospheric scintillations is their
independence on frequency.
Results based on diffractive scattering due to small scale inhomogeneities
give a scattering angle that may be as large as 0.1 radians, and a typical
decorrelation time of seconds.
Refractive scattering due to large scale inhomogeneities is also possible,
with a typical angle of radians and a correlation time of the order
of seconds. Temporal variation in the plasma density may also result
in a delay time of the order of seconds. The different scaling of the
above quantities with frequency may allow one to distinguish the effects of
propagation through a pulsar magnetosphere from the interstellar medium. In
particular, we expect that the magnetospheric scintillations are relatively
more important for nearby pulsars when observed at high frequencies.Comment: 19 pages, 1 Figur
CEP-stable Tunable THz-Emission Originating from Laser-Waveform-Controlled Sub-Cycle Plasma-Electron Bursts
We study THz-emission from a plasma driven by an incommensurate-frequency
two-colour laser field. A semi-classical transient electron current model is
derived from a fully quantum-mechanical description of the emission process in
terms of sub-cycle field-ionization followed by continuum-continuum electron
transitions. For the experiment, a CEP-locked laser and a near-degenerate
optical parametric amplifier are used to produce two-colour pulses that consist
of the fundamental and its near-half frequency. By choosing two incommensurate
frequencies, the frequency of the CEP-stable THz-emission can be continuously
tuned into the mid-IR range. This measured frequency dependence of the
THz-emission is found to be consistent with the semi-classical transient
electron current model, similar to the Brunel mechanism of harmonic generation
Hadronization corrections to helicity components of the fragmentation function
In the hadronic decays of Z, gluon emission leads to the appearance of the
longitudinal component of the fragmentation function, F_L. Measurement of F_L
and the transverse component, F_T, could thus provide an insight into the gluon
fragmentation function. However, hadronization corrections at low x can be
significant. Here we present a method of accounting for such corrections, using
the JETSET event generator as illustration.Comment: 11 pages, 5 figure
Atlas Data-Challenge 1 on NorduGrid
The first LHC application ever to be executed in a computational Grid
environment is the so-called ATLAS Data-Challenge 1, more specifically, the
part assigned to the Scandinavian members of the ATLAS Collaboration. Taking
advantage of the NorduGrid testbed and tools, physicists from Denmark, Norway
and Sweden were able to participate in the overall exercise starting in July
2002 and continuing through the rest of 2002 and the first part of 2003 using
solely the NorduGrid environment. This allowed to distribute input data over a
wide area, and rely on the NorduGrid resource discovery mechanism to find an
optimal cluster for job submission. During the whole Data-Challenge 1, more
than 2 TB of input data was processed and more than 2.5 TB of output data was
produced by more than 4750 Grid jobs.Comment: Talk from the 2003 Computing in High Energy Physics and Nuclear
Physics (CHEP03), La Jolla, Ca, USA, March 2003, 7 pages, 3 ps figure
The NorduGrid architecture and tools
The NorduGrid project designed a Grid architecture with the primary goal to
meet the requirements of production tasks of the LHC experiments. While it is
meant to be a rather generic Grid system, it puts emphasis on batch processing
suitable for problems encountered in High Energy Physics. The NorduGrid
architecture implementation uses the \globus{} as the foundation for various
components, developed by the project. While introducing new services, the
NorduGrid does not modify the Globus tools, such that the two can eventually
co-exist. The NorduGrid topology is decentralized, avoiding a single point of
failure. The NorduGrid architecture is thus a light-weight, non-invasive and
dynamic one, while robust and scalable, capable of meeting most challenging
tasks of High Energy Physics.Comment: Talk from the 2003 Computing in High Energy Physics and Nuclear
Physics (CHEP03), La Jolla, Ca, USA, March 2003, 9 pages,LaTeX, 4 figures.
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