12,067 research outputs found
Differences in high p_t meson production between CERN SPS and RHIC heavy ion collisions
In this talk we present a perturbative QCD improved parton model calculation
for light meson production in high energy heavy ion collisions. In order to
describe the experimental data properly, one needs to augment the standard pQCD
model by the transverse momentum distribution of partons ("intrinsic k_T").
Proton-nucleus data indicate the presence of nuclear shadowing and
multiscattering effects. Further corrections are needed in nucleus-nucleus
collisions to explain the observed reduction of the cross section. We introduce
the idea of proton dissociation and compare our calculations with the SPS and
RHIC experimental data.Comment: Talk presented by G. Papp at Zakopane 2001 School, Zakopane, 2001
June; 10 pages with 3 EPS figure
Bimodal Distribution of Sulfuric Acid Aerosols in the Upper Haze of Venus
The upper haze (UH) of Venus is variable on the order of days and it is
populated by two particle modes. We use a 1D microphysics and vertical
transport model based on the Community Aerosol and Radiation Model for
Atmospheres to evaluate whether interaction of upwelled cloud particles and
sulfuric acid particles nucleated in situ on meteoric dust are able to generate
the two size modes and whether their observed variability are due to cloud top
vertical transient winds. Nucleation of photochemically produced sulfuric acid
onto polysulfur condensation nuclei generates mode 1 cloud droplets that then
diffuse upwards into the UH. Droplets generated in the UH from nucleation of
sulfuric acid onto meteoric dust coagulate with the upwelled cloud particles
and cannot reproduce the observed bimodal size distribution. The mass transport
enabled by cloud top transient winds are able to generate a bimodal size
distribution in a time scale consistent with observations. Sedimentation and
convection in the middle and lower clouds causes the formation of large mode 2
and mode 3 particles. Evaporation of these particles below the clouds creates a
local sulfuric acid vapor maximum that causes upwelling of sulfuric acid back
into the clouds. If the polysulfur condensation nuclei are small and their
production rate is high, coagulation of small droplets onto larger droplets in
the middle cloud may result in sulfuric acid "rain" below the clouds once every
few Earth months. Reduction of the polysulfur condensation nuclei production
rate destroys this oscillation and reduces the mode 1 particle abundance in the
middle cloud by two orders of magnitude, though it better reproduces the
sulfur-to-sulfuric-acid mass ratio in the cloud and haze droplets. In general
we find satisfactory agreement between our results and observations, though
improvements could be made by incorporating sulfur microphysics.Comment: 62 pages, 18 figures, 1 table. Accepted for publication in Icaru
1I/2017 U1 (`Oumuamua) is Hot: Imaging, Spectroscopy and Search of Meteor Activity
1I/2017 U1 (`Oumuamua), a recently discovered asteroid in a hyperbolic orbit,
is likely the first macroscopic object of extrasolar origin identified in the
solar system. Here, we present imaging and spectroscopic observations of
\textquoteleft Oumuamua using the Palomar Hale Telescope as well as a search of
meteor activity potentially linked to this object using the Canadian Meteor
Orbit Radar. We find that \textquoteleft Oumuamua exhibits a moderate spectral
gradient of , a value significantly lower
than that of outer solar system bodies, indicative of a formation and/or
previous residence in a warmer environment. Imaging observation and spectral
line analysis show no evidence that \textquoteleft Oumuamua is presently
active. Negative meteor observation is as expected, since ejection driven by
sublimation of commonly-known cometary species such as CO requires an extreme
ejection speed of m s at au in order to reach the
Earth. No obvious candidate stars are proposed as the point of origin for
\textquoteleft Oumuamua. Given a mean free path of ly in the solar
neighborhood, \textquoteleft Oumuamua has likely spent a very long time in the
interstellar space before encountering the solar system.Comment: ApJL in pres
Anyonic statistics with continuous variables
We describe a continuous-variable scheme for simulating the Kitaev lattice
model and for detecting statistics of abelian anyons. The corresponding quantum
optical implementation is solely based upon Gaussian resource states and
Gaussian operations, hence allowing for a highly efficient creation,
manipulation, and detection of anyons. This approach extends our understanding
of the control and application of anyons and it leads to the possibility for
experimental proof-of-principle demonstrations of anyonic statistics using
continuous-variable systems.Comment: 5 pages, 2 figures, appear in Phys. Rev.
Quantum cooling and squeezing of a levitating nanosphere via time-continuous measurements
With the purpose of controlling the steady state of a dielectric nanosphere
levitated within an optical cavity, we study its conditional dynamics under
simultaneous sideband cooling and additional time-continuous measurement of
either the output cavity mode or the nanosphere's position. We find that the
average phonon number, purity and quantum squeezing of the steady-states can
all be made more non-classical through the addition of time-continuous
measurement. We predict that the continuous monitoring of the system, together
with Markovian feedback, allows one to stabilize the dynamics for any value of
the laser frequency driving the cavity. By considering state-of-the-art values
of the experimental parameters, we prove that one can in principle obtain a
non-classical (squeezed) steady-state with an average phonon number .Comment: 10 pages, 9 figures; v2: close to published versio
Disability and Job Mismatches in the Australian Labour Market
We examine the relationship between disability, job mismatch, earnings and job satisfaction, using panel estimation on data from the Household, Income and Labour Dynamics in Australia (HILDA) Survey (2001-2008). While we do not find any relationship between work-limiting disability and over-skilling, it appears that there is a positive relationship between work-limiting disability and over-education, which is consistent with disability onset leading to downward occupational movement, at least in relative terms. We find a negative correlation between work-limiting disability and both earnings and job satisfaction. However, there is only evidence of a causal relationship in terms of the latter, where the impact of disability is found to be multifaceted.job mismatch, disability, earnings, job satisfaction
Gamma-ray Burst Afterglow with Continuous Energy Injection: Signature of a Highly-Magnetized Millisecond Pulsar
We investigate the consequences of a continuously injecting central engine on
the gamma-ray burst afterglow emission, focusing more specifically on a
highly-magnetized millisecond pulsar engine. For initial pulsar parameters
within a certain region of the parameter space, the afterglow lightcurves are
predicted to show a distinctive achromatic bump feature, the onset and duration
of which range from minutes to months, depending on the pulsar and the fireball
parameters. The detection of or upper limits on such features would provide
constraints on the burst progenitor and on magnetar-like central engine models.
An achromatic bump such as that in GRB 000301C afterglow may be caused by a
millisecond pulsar with P0=3.4 millisecond and Bp=2.7e14 Gauss.Comment: 5 pages, emulateapj style, to appear in ApJ Letters, updated with the
accepted version, a few corrections are mad
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