1,124 research outputs found
Photoinjector-generation of a flat electron beam with transverse emittance ratio of 100
The generation of a flat electron beam directly from a photoinjector is an
attractive alternative to the electron damping ring as envisioned for linear
colliders. It also has potential applications to light sources such as the
generation of ultra-short x-ray pulses or Smith-Purcell free electron lasers.
In this Letter, we report on the experimental generation of a flat-beam with a
measured transverse emittance ratio of for a bunch charge of
nC; the smaller measured normalized root-mean-square emittance is
m and is limited by the resolution of our experimental setup.
The experimental data, obtained at the Fermilab/NICADD Photoinjector
Laboratory, are compared with numerical simulations and the expected scaling
laws.Comment: 5 pages, 3 figure
Treatment of calibration uncertainty in multi-baseline cross-correlation searches for gravitational waves
Uncertainty in the calibration of gravitational wave (GW) detector data leads to systematic errors, which must be accounted for in setting limits on the strength of GW signals. When cross-correlation measurements are made using data from a pair of instruments, as in searches for a stochastic GW background, the calibration uncertainties of the individual instruments can be combined into an uncertainty associated with the pair. With the advent of multi-baseline GW observation (e.g., networks consisting of multiple detectors such as the LIGO observatories and Virgo), a more sophisticated treatment is called for. We have described how the correlations between calibration factors associated with different pairs can be taken into account by marginalizing over the uncertainty associated with each instrument
Gravitational waves from Sco X-1: A comparison of search methods and prospects for detection with advanced detectors
The low-mass X-ray binary Scorpius X-1 (Sco X-1) is potentially the most
luminous source of continuous gravitational-wave radiation for interferometers
such as LIGO and Virgo. For low-mass X-ray binaries this radiation would be
sustained by active accretion of matter from its binary companion. With the
Advanced Detector Era fast approaching, work is underway to develop an array of
robust tools for maximizing the science and detection potential of Sco X-1. We
describe the plans and progress of a project designed to compare the numerous
independent search algorithms currently available. We employ a mock-data
challenge in which the search pipelines are tested for their relative
proficiencies in parameter estimation, computational efficiency, robust- ness,
and most importantly, search sensitivity. The mock-data challenge data contains
an ensemble of 50 Scorpius X-1 (Sco X-1) type signals, simulated within a
frequency band of 50-1500 Hz. Simulated detector noise was generated assuming
the expected best strain sensitivity of Advanced LIGO and Advanced VIRGO ( Hz). A distribution of signal amplitudes was then
chosen so as to allow a useful comparison of search methodologies. A factor of
2 in strain separates the quietest detected signal, at
strain, from the torque-balance limit at a spin frequency of 300 Hz, although
this limit could range from (25 Hz) to (750 Hz) depending on the unknown frequency of Sco X-1. With future
improvements to the search algorithms and using advanced detector data, our
expectations for probing below the theoretical torque-balance strain limit are
optimistic.Comment: 33 pages, 11 figure
Turbulent small-scale neutral and ion density fluctuations as measured during MAC/Epsilon
During the MAC/Epsilon campaign (Fall 1987, from Andoya, Northern Norway, 69 N, 16 E) a total of four altitude profiles of neutral gas number densities and six profiles of ion number densities were measured with high spatial resolution in the height range from 60 to 120 km. First results of these rocket-borne experiments are presented with emphasis on small scale turbulent density variations and related turbulent parameter as structure function constants and energy dissipation rates
Generation of angular-momentum-dominated electron beams from a photoinjector
Various projects under study require an angular-momentum-dominated electron
beam generated by a photoinjector. Some of the proposals directly use the
angular-momentum-dominated beams (e.g. electron cooling of heavy ions), while
others require the beam to be transformed into a flat beam (e.g. possible
electron injectors for light sources and linear colliders). In this paper, we
report our experimental study of an angular-momentum-dominated beam produced in
a photoinjector, addressing the dependencies of angular momentum on initial
conditions. We also briefly discuss the removal of angular momentum. The
results of the experiment, carried out at the Fermilab/NICADD Photoinjector
Laboratory, are found to be in good agreement with theoretical and numerical
models.Comment: 8 pages, 7 figures, submitted to Phys. Rev. ST Accel. Beam
Multi-messenger astronomy with a Southern-Hemisphere gravitational-wave observatory
Joint observations of gravitational waves and electromagnetic counterparts
will answer questions about cosmology, gamma-ray bursts, and the behaviour of
matter at supranuclear densities. The addition of a Southern-Hemisphere
gravitational-wave observatory to proposed global networks creates a longer
baseline, which is beneficial for sky localisation. We analyse how an
observatory in Australia can enhance the multi-messenger astronomy capabilities
of future networks. We estimate the number of binary neutron star mergers with
joint observations of gravitational waves and kilonova counterparts detectable
by the Vera C. Rubin Observatory. First, we consider a network of upgrades to
current observatories. Adding an Australian observatory to a three-observatory
network (comprising two observatories in the USA and one in Europe) boosts the
rate of joint observations from per year to
per year (a factor of two improvement). Then, we consider a
network of next-generation observatories. Adding a km Australian
observatory to a global network of a Cosmic Explorer km in the USA and an
Einstein Telescope in Europe only marginally increases the rate from
per year to per year (a factor of 1.1
improvement). The addition of an Australian observatory, however, ensures that
at least two observatories are online far more often. When the Cosmic Explorer
km is offline for a major upgrade, the Australian observatory increases
the joint observation rate from per year to
per year (a factor of 82 improvement). When the Einstein
Telescope is offline, the joint observation rate increases from
per year to per year (a factor of 113
improvement). We sketch out the broader science case for a Southern-Hemisphere
gravitational-wave observatory.Comment: v1, 13 pages, 7 figures. Submitted to PRD on August 24 202
Morphological Instabilities in a growing Yeast Colony: Experiment and Theory
We study the growth of colonies of the yeast Pichia membranaefaciens on
agarose film. The growth conditions are controlled in a setup where nutrients
are supplied through an agarose film suspended over a solution of nutrients. As
the thickness of the agarose film is varied, the morphology of the front of the
colony changes. The growth of the front is modeled by coupling it to a
diffusive field of inhibitory metabolites. Qualitative agreement with
experiments suggests that such a coupling is responsible for the observed
instability of the front.Comment: RevTex, 4 pages and 3 figure
Detectability of eccentric compact binary coalescences with advanced gravitational-wave detectors
Compact binary coalescences are a promising source of gravitational waves for second-generation interferometric gravitational-wave detectors such as advanced LIGO and advanced Virgo. While most binaries are expected to possess circular orbits, some may be eccentric, for example, if they are formed through dynamical capture. Eccentric orbits can create difficulty for matched filtering searches due to the challenges of creating effective template banks to detect these signals. In previous work, we showed how seedless clustering can be used to detect low-mass (M_total≤10M_⊙) compact binary coalescences for both spinning and eccentric systems, assuming a circular post-Newtonian expansion. Here, we describe a parametrization that is designed to maximize sensitivity to low-eccentricity (0≤ε≤0.6) systems, derived from the analytic equations. We show that this parametrization provides a robust and computationally efficient method for detecting eccentric low-mass compact binaries. Based on these results, we conclude that advanced detectors will have a chance of detecting eccentric binaries if optimistic models prove true. However, a null observation is unlikely to firmly rule out models of eccentric binary populations
Protostellar collapse: rotation and disk formation
We present some important conclusions from recent calculations pertaining to
the collapse of rotating molecular cloud cores with axial symmetry,
corresponding to evolution of young stellar objects through classes 0 and begin
of class I. Three main issues have been addressed: (1) The typical timescale
for building up a preplanetary disk - once more it turned out that it is of the
order of one free-fall time which is decisively shorter than the widely assumed
timescale related to the so-called 'inside-out collapse'; (2) Redistribution of
angular momentum and the accompanying dissipation of kinetic (rotational)
energy - together these processes govern the mechanical and thermal evolution
of the protostellar core to a large extent; (3) The origin of
calcium-aluminium-rich inclusions (CAIs) - due to the specific pattern of the
accretion flow, material that has undergone substantial chemical and
mineralogical modifications in the hot (exceeding 900 K) interior of the
protostellar core may have a good chance to be advectively transported outward
into the cooler remote parts (beyond 4 AU, say) of the growing disk and to
survive there until it is incorporated into a meteoritic body.Comment: 4 pages, 4 figure
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