15,237 research outputs found
The Large Hadron Collider (LHC) project of CERN
The Large Hadron Collider (LHC) was approved by CERN's Council in December 1994 and a conceptual accelerator design published in October 1995. The LHC will provide proton-proton collisions of 7 TeV + 7 TeV with a luminosity of up to 10cms, at two collision points and lead-ion collisions with a total centre of mass energy of 1148 TeV and a luminosity up to 10cms. In this paper the status of the collider project will be described with emphasis on the latest developments. The experimental programme of the LHC is also in the process of being defined and is expected to include a dedicated heavy-ion detector, ALICE, and a specialised B-physics spectrometer, LHCb, as well as the already approved, high luminosity, general purpose detectors, ATLAS and CMS. A description of the experimental areas foreseen for these experiments will be given
The game transfer phenomena scale: an instrument for investigating the nonvolitional effects of video game playing
A variety of instruments have been developed to assess different dimensions of playing videogames and its effects on cognitions, affect, and behaviors. The present study examined the psychometric properties of the Game Transfer Phenomena Scale (GTPS) that assesses non-volitional phenomena experienced after playing videogames (i.e., altered perceptions, automatic mental processes, and involuntary behaviors). A total of 1,736 gamers participated in an online survey used as the basis for the analysis. Confirmatory factor analysis (CFA) was performed to confirm the factorial structure of the GTPS. The five-factor structure using the 20 indicators based on the analysis of gamers’ self-reports fitted the data well. Population cross-validity was also achieved and the positive associations between the session length and overall scores indicate the GTPS warranted criterion-related validity. Although the understanding of GTP is still in its infancy, the GTPS appears to be a valid and reliable instrument for assessing non-volitional gaming-related phenomena. The GTPS can be used for understanding the phenomenology of post-effects of playing videogames
Testing Theoretical Evolutionary Models with AB Dor C and the Initial Mass Function
We assess the constraints on the evolutionary models of young low-mass
objects that are provided by the measurements of the companion AB Dor C by
Close and coworkers and by a new comparison of model-derived IMFs of
star-forming regions to the well-calibrated IMF of the solar neighborhood.
After performing an independent analysis of Close's imaging and spectroscopic
data for AB Dor C, we find that AB Dor C is not detected at a significant level
(SN 1.2) in the SDI images when one narrow-band image is subtracted from
another, but that it does appear in the individual SDI frames as well as the
images at JHK. Using the age of 75-150 Myr for AB Dor from Luhman, Stauffer, &
Mamajek, the luminosity predicted by the models of Chabrier & Baraffe is
consistent with the value that we estimate. We measure a spectral type of
M6+/-1 from the K-band spectrum of AB Dor C, which is earlier than the value of
M8+/-1 from Close and is consistent with the model predictions when a dwarf
temperature scale is adopted. In a test of these models at much younger ages,
we show that the low-mass IMFs that they produce for star-forming regions are
similar to the IMF of the solar neighborhood. If the masses of the low-mass
stars and brown dwarfs in these IMFs of star-forming regions were
underestimated by a factor of two as suggested by Close, then the IMF
characterizing the current generation of Galactic star formation would have to
be radically different from the IMF of the solar neighborhood.Comment: 15 pages, accepted to the Astrophysical Journa
Simultaneous optical polarimetry and X-ray data of the near synchronous polar RX J2115-5840
We present simultaneous optical polarimetry and X-ray data of the near
synchronous polar RX J2115-5840. We model the polarisation data using the
Stokes imaging technique of Potter et al. We find that the data are best
modelled using a relatively high binary inclination and a small angle between
the magnetic and spin axes. We find that for all spin-orbit beat phases, a
significant proportion of the accretion flow is directed onto the lower
hemisphere of the white dwarf, producing negative circular polarisation. Only
for a small fraction of the beat cycle is a proportion of the flow directed
onto the upper hemisphere. However, the accretion flow never occurs near the
upper magnetic pole, whatever the orientation of the magnetic poles. This
indicates the presence of a non-dipole field with the field strength at the
upper pole significantly higher. We find that the brightest parts of the hard
X-ray emitting region and the cyclotron region are closely coincident.Comment: 9 pages, accepted for publication in MNRAS 2 March 200
The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables
The temperatures of electrons and ions in the post-shock accretion region of
a magnetic cataclysmic variable (mCV) will be equal at sufficiently high mass
flow rates or for sufficiently weak magnetic fields. At lower mass flow rates
or in stronger magnetic fields, efficient cyclotron cooling will cool the
electrons faster than the electrons can cool the ions and a two-temperature
flow will result. Here we investigate the differences in polarized radiation
expected from mCV post-shock accretion columns modeled with one- and
two-temperature hydrodynamics. In an mCV model with one accretion region, a
magnetic field >~30 MG and a specific mass flow rate of ~0.5 g/cm/cm/s, along
with a relatively generic geometric orientation of the system, we find that in
the ultraviolet either a single linear polarization pulse per binary orbit or
two pulses per binary orbit can be expected, depending on the accretion column
hydrodynamic structure (one- or two-temperature) modeled. Under conditions
where the physical flow is two-temperature, one pulse per orbit is predicted
from a single accretion region where a one-temperature model predicts two
pulses. The intensity light curves show similar pulse behavior but there is
very little difference between the circular polarization predictions of one-
and two-temperature models. Such discrepancies indicate that it is important to
model some aspect of two-temperature flow in indirect imaging procedures, like
Stokes imaging, especially at the edges of extended accretion regions, were the
specific mass flow is low, and especially for ultraviolet data.Comment: Accepted for publication in Astrophysics & Space Scienc
Evolution of the Radio Remnant of Supernova 1987A: Morphological Changes from Day 7000
We present radio imaging observations of supernova remnant 1987A at 9 GHz,
taken with the Australia Telescope Compact Array over 21 years from 1992 to
2013. By employing a Fourier modeling technique to fit the visibility data, we
show that the remnant structure has evolved significantly since day 7000
(mid-2006): the emission latitude has gradually decreased, such that the
overall geometry has become more similar to a ring structure. Around the same
time, we find a decreasing trend in the east-west asymmetry of the surface
emissivity. These results could reflect the increasing interaction of the
forward shock with material around the circumstellar ring, and the relative
weakening of the interaction with the lower-density material at higher
latitudes. The morphological evolution caused an apparent break in the remnant
expansion measured with a torus model, from a velocity of 4600+150-200 km/s
between day 4000 and 7000 to 2400+100-200 km/s after day 7000. However, we
emphasize that there is no conclusive evidence for a physical slowing of the
shock at any given latitude in the expanding remnant, and that a change of
radio morphology alone appears to dominate the evolution. This is supported by
our ring-only fits which show a constant expansion of 3890+/-50 km/s without
deceleration between days 4000 and 9000. We suggest that once the emission
latitude no longer decreases, the expansion velocity obtained from the torus
model should return to the same value as that measured with the ring model.Comment: 11 pages, 5 figures, accepted for publication in ApJ, Figure 1 has
been scaled dow
Thermal-radiation-induced nonequilibrium carriers in an intrinsic graphene
We examine an intrinsic graphene connected to the phonon thermostat at
temperature T under irradiation of thermal photons with temperature T_r, other
than T. The distribution of nonequilibrium electron-hole pairs was obtained for
the cases of low and high concentration of carriers. For the case when the
interparticle scattering is unessential, the distribution function is
determined by the interplay of intraband relaxation of energy due to acoustic
phonons and interband radiative transitions caused by the thermal radiation.
When the Coulomb scattering dominates, then the quasi-equilibrium distribution
with effective temperature and non-equilibrium concentration, determined
through balance equations, is realized. Due to the effect of thermal radiation
with temperature concentration and conductivity of carriers in
graphene modify essentially. It is demonstrated, that at the negative
interband absorption, caused by the inversion of carriers distribution, can
occur, i.e. graphene can be unstable under thermal irradiation.Comment: 5 pages, 4 figure
High-resolution radio observations of SNR 1987A at high frequencies
We present new imaging observations of the remnant of Supernova (SN) 1987A at
44 GHz, performed in 2011 with the Australia Telescope Compact Array (ATCA).
The 0\farcs35\times0\farcs23 resolution of the diffraction-limited image is
the highest achieved to date in high-dynamic range. We also present a new ATCA
image at 18 GHz derived from 2011 observations, which is super-resolved to
0\farcs25. The flux density is 402 mJy at 44 GHz and 816 mJy at 18
GHz. At both frequencies, the remnant exhibits a ring-like emission with two
prominent lobes, and an east-west brightness asymmetry that peaks on the
eastern lobe. A central feature of fainter emission appears at 44 GHz. A
comparison with previous ATCA observations at 18 and 36 GHz highlights higher
expansion velocities of the remnant eastern side. The 18-44 GHz spectral index
is (). The spectral index map
suggests slightly steeper values at the brightest sites on the eastern lobe,
whereas flatter values are associated with the inner regions. The remnant
morphology at 44 GHz generally matches the structure seen with contemporaneous
X-ray and H observations. Unlike the H emission, both the radio
and X-ray emission peaks on the eastern lobe. The regions of flatter spectral
index align and partially overlap with the optically-visible ejecta. Simple
free-free absorption models suggest that emission from a pulsar wind nebula or
a compact source inside the remnant may now be detectable at high frequencies,
or at low frequencies if there are holes in the ionised component of the
ejecta.Comment: References updated. High resolution version may be found at
http://ict.icrar.org/store/staff/gio/Papers/Zanardo_2013.pd
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