1,585 research outputs found
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
The first version Buffered Large Analog Bandwidth (BLAB1) ASIC for high luminosity collider and extensive radio neutrino detectors
Future detectors for high luminosity particle identification and ultra high
energy neutrino observation would benefit from a digitizer capable of recording
sensor elements with high analog bandwidth and large record depth, in a
cost-effective, compact and low-power way. A first version of the Buffered
Large Analog Bandwidth (BLAB1) ASIC has been designed based upon the lessons
learned from the development of the Large Analog Bandwidth Recorder and
Digitizer with Ordered Readout (LABRADOR) ASIC. While this LABRADOR ASIC has
been very successful and forms the basis of a generation of new, large-scale
radio neutrino detectors, its limited sampling depth is a major drawback. A
prototype has been designed and fabricated with 65k deep sampling at
multi-GSa/s operation. We present test results and directions for future
evolution of this sampling technique.Comment: 15 pages, 26 figures; revised, accepted for publication in NIM
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
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
Picosecond timing of Microwave Cherenkov Impulses from High-Energy Particle Showers Using Dielectric-loaded Waveguides
We report on the first measurements of coherent microwave impulses from
high-energy particle-induced electromagnetic showers generated via the Askaryan
effect in a dielectric-loaded waveguide. Bunches of 12.16 GeV electrons with
total bunch energy of GeV were pre-showered in tungsten, and
then measured with WR-51 rectangular (12.6 mm by 6.3 mm) waveguide elements
loaded with solid alumina () bars. In the 5-8 GHz
single-mode band determined by the presence of the dielectric in the waveguide,
we observed band-limited microwave impulses with amplitude proportional to
bunch energy. Signals in different waveguide elements measuring the same shower
were used to estimate relative time differences with 2.3 picosecond precision.
These measurements establish a basis for using arrays of alumina-loaded
waveguide elements, with exceptional radiation hardness, as very high precision
timing planes for high-energy physics detectors.Comment: 16 pages, 15 figure
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.
Correlation between microstructure and magnetotransport in organic semiconductor spin valve structures
We have studied magnetotransport in organic-inorganic hybrid multilayer
junctions. In these devices, the organic semiconductor (OSC) Alq
(tris(8-hydroxyquinoline) aluminum) formed a spacer layer between ferromagnetic
(FM) Co and Fe layers. The thickness of the Alq layer was in the range of
50-150 nm. Positive magnetoresistance (MR) was observed at 4.2 K in a current
perpendicular to plane geometry, and these effects persisted up to room
temperature. The devices' microstructure was studied by X-ray reflectometry,
Auger electron spectroscopy and polarized neutron reflectometry (PNR). The
films show well-defined layers with modest average chemical roughness (3-5 nm)
at the interface between the Alq and the surrounding FM layers.
Reflectometry shows that larger MR effects are associated with smaller
FM/Alq interface width (both chemical and magnetic) and a magnetically dead
layer at the Alq/Fe interface. The PNR data also show that the Co layer,
which was deposited on top of the Alq, adopts a multi-domain magnetic
structure at low field and a perfect anti-parallel state is not obtained. The
origins of the observed MR are discussed and attributed to spin coherent
transport. A lower bound for the spin diffusion length in Alq was estimated
as nm at 80 K. However, the subtle correlations between
microstructure and magnetotransport indicate the importance of interfacial
effects in these systems.Comment: 21 pages, 11 figures and 2 table
IceCube-Plus: An Ultra-High Energy Neutrino Telescope
While the first kilometer-scale neutrino telescope, IceCube, is under
construction, alternative plans exist to build even larger detectors that will,
however, b e limited by a much higher neutrino energy threshold of 10 PeV or
higher rather than 10 to 100 GeV. These future projects detect radio and
acoustic pulses as w ell as air showers initiated by ultra-high energy
neutrinos. As an alternative, we here propose an expansion of IceCube, using
the same strings, placed on a gri d with a spacing of order 500 m. Unlike other
proposals, the expanded detector uses methods that are understood and
calibrated on atmospheric neutrinos. Atmosp heric neutrinos represent the only
background at the energies under consideratio n and is totally negligible.
Also, the cost of such a detector is understood. We conclude that supplementing
the 81 IceCube strings with a modest number of addi tional strings spaced at
large distances can almost double the effective volume of the detector.
Doubling the number of strings on a 800 m grid can deliver a d etector that
this a factor of 5 larger for horizontal muons at modest cost.Comment: Version to be published in JCA
Stable Gene Targeting in Human Cells Using Single-Strand Oligonucleotides with Modified Bases
Recent advances allow multiplexed genome engineering in E. coli, employing easily designed oligonucleotides to edit multiple loci simultaneously. A similar technology in human cells would greatly expedite functional genomics, both by enhancing our ability to test how individual variants such as single nucleotide polymorphisms (SNPs) are related to specific phenotypes, and potentially allowing simultaneous mutation of multiple loci. However, oligo-mediated targeting of human cells is currently limited by low targeting efficiencies and low survival of modified cells. Using a HeLa-based EGFP-rescue reporter system we show that use of modified base analogs can increase targeting efficiency, in part by avoiding the mismatch repair machinery. We investigate the effects of oligonucleotide toxicity and find a strong correlation between the number of phosphorothioate bonds and toxicity. Stably EGFP-corrected cells were generated at a frequency of 0.05% with an optimized oligonucleotide design combining modified bases and reduced number of phosphorothioate bonds. We provide evidence from comparative RNA-seq analysis suggesting cellular immunity induced by the oligonucleotides might contribute to the low viability of oligo-corrected cells. Further optimization of this method should allow rapid and scalable genome engineering in human cells
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