2,072 research outputs found
A new method to calibrate ionospheric pulse dispersion for UHE cosmic ray and neutrino detection using the Lunar Cherenkov technique
UHE particle detection using the lunar Cherenkov technique aims to detect
nanosecond pulses of Cherenkov emission which are produced during UHE cosmic
ray and neutrino interactions in the Moon's regolith. These pulses will reach
Earth-based telescopes dispersed, and therefore reduced in amplitude, due to
their propagation through the Earth's ionosphere. To maximise the received
signal to noise ratio and subsequent chances of pulse detection, ionospheric
dispersion must therefore be corrected, and since the high time resolution
would require excessive data storage this correction must be made in real time.
This requires an accurate knowledge of the dispersion characteristic which is
parameterised by the instantaneous Total Electron Content (TEC) of the
ionosphere. A new method to calibrate the dispersive effect of the ionosphere
on lunar Cherenkov pulses has been developed for the LUNASKA lunar Cherenkov
experiments. This method exploits radial symmetries in the distribution of the
Moon's polarised emission to make Faraday rotation measurements in the
visibility domain of synthesis array data (i. e. instantaneously). Faraday
rotation measurements are then combined with geomagnetic field models to
estimate the ionospheric TEC. This method of ionospheric calibration is
particularly attractive for the lunar Cherenkov technique as it may be used in
real time to estimate the ionospheric TEC along a line-of-sight to the Moon and
using the same radio telescope.Comment: 4 pages, 2 figures, Proceedings of ARENA 2010, Nantes, France;
doi:10.1016/j.nima.2010.10.12
Peptide redesign for inhibition of the complement system: Targeting age-related macular degeneration.
PurposeTo redesign a complement-inhibiting peptide with the potential to become a therapeutic for dry and wet age-related macular degeneration (AMD).MethodsWe present a new potent peptide (Peptide 2) of the compstatin family. The peptide is developed by rational design, based on a mechanistic binding hypothesis, and structural and physicochemical properties derived from molecular dynamics (MD) simulation. The inhibitory activity, efficacy, and solubility of Peptide 2 are evaluated using a hemolytic assay, a human RPE cell-based assay, and ultraviolet (UV) absorption properties, respectively, and compared to the respective properties of its parent peptide (Peptide 1).ResultsThe sequence of Peptide 2 contains an arginine-serine N-terminal extension (a characteristic of parent Peptide 1) and a novel 8-polyethylene glycol (PEG) block C-terminal extension. Peptide 2 has significantly improved aqueous solubility compared to Peptide 1 and comparable complement inhibitory activity. In addition, Peptide 2 is more efficacious in inhibiting complement activation in a cell-based model that mimics the pathobiology of dry AMD.ConclusionsWe have designed a new peptide analog of compstatin that combines N-terminal polar amino acid extensions and C-terminal PEGylation extensions. This peptide demonstrates significantly improved aqueous solubility and complement inhibitory efficacy, compared to the parent peptide. The new peptide overcomes the aggregation limitation for clinical translation of previous compstatin analogs and is a candidate to become a therapeutic for the treatment of AMD
VLA Observations of Candidate Supernova Remnants from the Clark Lake 30.9 MHz Galactic Plane Survey
We report the results of 1464 MHz continuum VLA observations of eight fields containing unidentified
small-diameter objects associated with candidate supernova remnants from the Clark Lake 30.9 MHz
galactic plane survey. The observations were made in the C configuration, giving a resolution of
-12-20 arcsec, and a sensitivity of typically <0.5 mJy per beam. Polarization measurements were
made as well. One of the 30.9 MHz candidates, G41.4+ 1.2, appears to be confirmed as a supernova
remnant by our observations. Of the remaining seven fields observed, three were found to contain
small-diameter objects which met some of the criteria for nonthermal origin, but will require further
study to evaluate whether they are associated with the candidate supernova remnants. Two of the fields
were found to contain groups of unresolved objects consistent with expectations for extragalactic
background sources. In these cases the 30.9 MHz observations, which could not resolve the individual
sources but would view them as a single extended source, may have mistakenly identified them as
possible supernova remnants. Finally, two fields contained bright H II region
The ExaVolt Antenna: Concept and Development Updates
A flux of ultrahigh energy neutrinos is expected both directly from sources and from interactions between ultrahigh energy cosmic rays and the cosmic microwave background. Using the cost-effective radio Cherenkov technique to search for these neutrinos, the ExaVolt Antenna (EVA) is a mission concept that aims to build on the capabilities of earlier radio-based balloon-borne neutrino detectors and increase the sensitivity to lower energies and fluxes. The novel EVA design exploits the surface of the balloon to provide a focusing reflector that aims to provide a signal gain of ~ 30 dBi (compared to 10 dBi on ANITA). This increase in gain when combined with a large instantaneous viewing angle will yield a 10-fold increase in sensitivity and will allow this balloon-borne experiment to probe the expected low neutrino fluxes even at energies greater than 1019 eV. This contribution will present an overview of the mission concept, recent technology developments, and the results of a hang test of a 1:20-scale model which demonstrates the effectiveness of the design
Experimental Limit on the Cosmic Diffuse Ultra-high Energy Neutrino Flux
We report results from 120 hours of livetime with the Goldstone Lunar
Ultra-high energy neutrino Experiment (GLUE). The experiment searches for <10
ns microwave pulses from the lunar regolith, appearing in coincidence at two
large radio telescopes separated by 22 km and linked by optical fiber. Such
pulses would arise from subsurface electromagnetic cascades induced by
interactions of >= 100 EeV neutrinos in the lunar regolith. No candidates are
yet seen, and the implied limits constrain several current models for
ultra-high energy neutrino fluxes.Comment: 4 pages, 4 figures, revtex4 style. New intro section, Fig. 2, Fig 4;
in final PRL revie
Verbal ability, previous practice and load on short-term memory as determiners of differences in a complex learning task: an experimental study
Traditional psychometric theory and practice classify
people according to broad ability dimensions but do not examine
how these mental processes occur. Hunt and Lansman
(1975) proposed a 'distributed memory' model of cognitive
processes with emphasis on how to describe individual differences
based on the assumption that each individual possesses
the same components. It is in the quality of these components
~hat individual differences arise. Carroll (1974) expands
Hunt's model to include a production system (after Newell and
Simon, 1973) and a response system. He developed a framework
of factor analytic (FA) factors for : the purpose of describing
how individual differences may arise from them. This
scheme is to be used in the analysis of psychometric tes ts .
Recent advances in the field of information processing
are examined and include. 1) Hunt's development of differences
between subjects designated as high or low verbal ,
2) Miller's pursuit of the magic number seven, plus or minus
two, 3) Ferguson's examination of transfer and abilities and,
4) Brown's discoveries concerning strategy teaching and
retardates .
In order to examine possible sources of individual
differences arising from cognitive tasks, traditional psychometric
tests were searched for a suitable perceptual task
which could be varied slightly and administered to gauge
learning effects produced by controlling independent variables.
It also had to be suitable for analysis using Carroll's
f ramework . The Coding Task (a symbol substitution test) found
i n the Performance Scale of the WISe was chosen.
Two experiments were devised to test the following
hypotheses. 1) High verbals should be able to complete significantly
more items on the Symbol Substitution Task than
low verbals (Hunt, Lansman, 1975). 2) Having previous practice
on a task, where strategies involved in the task may be
identified, increases the amount of output on a similar task
(Carroll, 1974). J) There should be a sUbstantial decrease
in the amount of output as the load on STM is increased
(Miller, 1956) . 4) Repeated measures should produce an increase
in output over trials and where individual differences
in previously acquired abilities are involved, these should
differentiate individuals over trials (Ferguson, 1956).
S) Teaching slow learners a rehearsal strategy would improve
their learning such that their learning would resemble that
of normals on the ,:same task. (Brown, 1974).
In the first experiment 60 subjects were d.ivided·into
high and low verbal, further divided randomly into a practice
group and nonpractice group. Five subjects in each group
were assigned randomly to work on a five, seven and nine
digit code throughout the experiment. The practice group
was given three trials of two minutes each on the practice
code (designed to eliminate transfer effects due to symbol
similarity) and then three trials of two minutes each on
the actual SST task . The nonpractice group was given three
trials of two minutes each on the same actual SST task .
Results were analyzed using a four-way analysis of variance .
In the second experiment 18 slow learners were divided
randomly into two groups. one group receiving a planned
strategy practioe, the other receiving random practice. Both
groups worked on the actual code to be used later in the
actual task. Within each group subjects were randomly assigned
to work on a five, seven or nine digit code throughout. Both
practice and actual tests consisted on three trials of two
minutes each. Results were analyzed using a three-way
analysis of variance .
It was found in t he first experiment that 1) high or
low verbal ability by itself did not produce significantly
different results. However, when in interaction with the
other independent variables, a difference in performance
was noted . 2) The previous practice variable was significant
over all segments of the experiment. Those who received
previo.us practice were able to score significantly higher
than those without it. J) Increasing the size of the load
on STM severely restricts performance. 4) The effect of
repeated trials proved to be beneficial. Generally, gains
were made on each successive trial within each group.
S) In the second experiment, slow learners who were allowed
to practice randomly performed better on the actual task
than subjeots who were taught the code by means of a planned
strategy.
Upon analysis using the Carroll scheme, individual
differences were noted in the ability to develop strategies
of storing, searching and retrieving items from STM, and
in adopting necessary rehearsals for retention in STM. While
these strategies may benef it some it was found that for
others they may be harmful . Temporal aspects and perceptual
speed were also found to be sources of variance within
individuals .
Generally it was found that the largest single factor
i nfluencing learning on this task was the repeated measures .
What e~ables gains to be made, varies with individuals .
There are environmental factors, specific abilities, strategy
development, previous learning, amount of load on STM ,
perceptual and temporal parameters which influence learning
and these have serious implications for educational programs
Observation of the Askaryan Effect: Coherent Microwave Cherenkov Emission from Charge Asymmetry in High Energy Particle Cascades
We present the first direct experimental evidence for the charge excess in
high energy particle showers predicted nearly 40 years ago by Askaryan. We
directed bremsstrahlung photons from picosecond pulses of 28.5 GeV electrons at
the SLAC Final Focus Test Beam facility into a 3.5 ton silica sand target,
producing electromagnetic showers several meters long. A series of antennas
spanning 0.3 to 6 GHz were used to detect strong, sub-nanosecond radio
frequency pulses produced whenever a shower was present. The measured electric
field strengths are consistent with a completely coherent radiation process.
The pulses show 100% linear polarization, consistent with the expectations of
Cherenkov radiation. The field strength versus depth closely follows the
expected particle number density profile of the cascade, consistent with
emission from excess charge distributed along the shower. These measurements
therefore provide strong support for experiments designed to detect high energy
cosmic rays and neutrinos via coherent radio emission from their cascades.Comment: 10 pages, 4 figures. Submitted to Phys. Rev. Let
Optimal Radio Window for the Detection of Ultra-High-Energy Cosmic Rays and Neutrinos off the Moon
When high-energy cosmic rays impinge on a dense dielectric medium, radio
waves are produced through the Askaryan effect. We show that at wavelengths
comparable to the length of the shower produced by an Ultra-High Energy cosmic
ray or neutrino, radio signals are an extremely efficient way to detect these
particles. Through an example it is shown that this new approach offers, for
the first time, the realistic possibility of measuring UHE neutrino fluxes
below the Waxman-Bahcall limit. It is shown that in only one month of observing
with the upcoming LOFAR radio telescope, cosmic-ray events can be measured
beyond the GZK-limit, at a sensitivity level of two orders of magnitude below
the extrapolated values.Comment: Submitted to Astroparticle Physic
Time-Domain Measurement of Broadband Coherent Cherenkov Radiation
We report on further analysis of coherent microwave Cherenkov impulses
emitted via the Askaryan mechanism from high-energy electromagnetic showers
produced at the Stanford Linear Accelerator Center (SLAC). In this report, the
time-domain based analysis of the measurements made with a broadband (nominally
1-18 GHz) log periodic dipole array antenna is described. The theory of a
transmit-receive antenna system based on time-dependent effective height
operator is summarized and applied to fully characterize the measurement
antenna system and to reconstruct the electric field induced via the Askaryan
process. The observed radiation intensity and phase as functions of frequency
were found to agree with expectations from 0.75-11.5 GHz within experimental
errors on the normalized electric field magnitude and the relative phase; 0.039
microV/MHz/TeV and 17 deg, respectively. This is the first time this agreement
has been observed over such a broad bandwidth, and the first measurement of the
relative phase variation of an Askaryan pulse. The importance of validation of
the Askaryan mechanism is significant since it is viewed as the most promising
way to detect cosmogenic neutrino fluxes at E > 10^15 eV.Comment: 10 pages, 9 figures, accepted by Phys. Rev.
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