30,577 research outputs found
Spectral reflectivity of solid surfaces at low temperatures
Spectral reflectivity of solid surfaces at low temperature
The analysis of user behaviour of a network management training tool using a neural network
A novel method for the analysis and interpretation of data that describes the interaction between trainee network managers and a network management training tool is presented. A simulation based approach is currently being used to train network managers, through the use of a simulated network. The motivation is to provide a tool for exposing trainees to a life like situation without disrupting a live network. The data logged by this system describes the detailed interaction between trainee network manager and simulated network. The work presented here provides an analysis of this interaction data that enables an assessment of the capabilities of the trainee network manager as well as an understanding of how the network management tasks are being approached. A neural network architecture is implemented in order to perform an exploratory data analysis of the interaction data. The neural network employs a novel form of continuous self-organisation to discover key features in the data and thus provide new insights into the learning and teaching strategies employed
A General Expression for Symmetry Factors of Feynman Diagrams
The calculation of the symmetry factor corresponding to a given Feynman
diagram is well known to be a tedious problem. We have derived a simple formula
for these symmetry factors. Our formula works for any diagram in scalar theory
( and interactions), spinor QED, scalar QED, or QCD.Comment: RevTex 11 pages with 10 figure
Changing quantum reference frames
We consider the process of changing reference frames in the case where the
reference frames are quantum systems. We find that, as part of this process,
decoherence is necessarily induced on any quantum system described relative to
these frames. We explore this process with examples involving reference frames
for phase and orientation. Quantifying the effect of changing quantum reference
frames serves as a first step in developing a relativity principle for theories
in which all objects including reference frames are necessarily quantum.Comment: 21 pages, 6 figures, comments welcome; v2 added some references; v3
published versio
MONTE CARLO SIMULATIONS OF MUON PRODUCTION
Muon production requirements for a muon collider are presented. Production of
muons from pion decay is studied. Lithium lenses and solenoids are considered
for focussing pions from a target, and for matching the pions into a decay
channel. Pion decay channels of alternating quadrupoles and long solenoids are
compared. Monte Carlo simulations are presented for production of by protons over a wide energy range, and criteria for
choosing the best proton energy are discussed.Comment: Latex uses mu95.sty, 19 pages, 5 postscript figures. A postscript
file can be seen at URL http://www.cap.bnl.gov/~cap/mumu/important.html
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Foot and Mouth Epidemic Reduces Cases of Human Cryptosporidiosis in Scotland.
In Scotland, rates of cryptosporidiosis infection in humans peak during the spring, a peak that is coincident with the peak in rates of infection in farm animals (during lambing and calving time). Here we show that, during the outbreak of foot and mouth disease (FMD) in 2001, there was a significant reduction in human cases of cryptosporidiosis infection in southern Scotland, where FMD was present, whereas, in the rest of Scotland, there was a reduction in cases that was not significant. We associate the reduction in human cases of cryptosporidiosis infection with the reduction in the number of young farm animals, together with restrictions on movement of both farm animals and humans, during the outbreak of FMD in 2001. We further show that, during 2002, there was recovery in the rate of cryptosporidiosis infection in humans throughout Scotland, particularly in the FMD-infected area, but that rates of infection remained lower, though not significantly, than pre-2001 levels
Response of pteropods and foraminifera to changing pCO2 and pH: Examples from the Mediterranean Sea
Amplified Dispersive Fourier-Transform Imaging for Ultrafast Displacement Sensing and Barcode Reading
Dispersive Fourier transformation is a powerful technique in which the
spectrum of an optical pulse is mapped into a time-domain waveform using
chromatic dispersion. It replaces a diffraction grating and detector array with
a dispersive fiber and single photodetector. This simplifies the system and,
more importantly, enables fast real-time measurements. Here we describe a novel
ultrafast barcode reader and displacement sensor that employs
internally-amplified dispersive Fourier transformation. This technique
amplifies and simultaneously maps the spectrally encoded barcode into a
temporal waveform. It achieves a record acquisition speed of 25 MHz -- four
orders of magnitude faster than the current state-of-the-art.Comment: Submitted to a journa
A Burst and Simultaneous Short-Term Pulsed Flux Enhancement from the Magnetar Candidate 1E 1048.1-5937
We report on the 2004 June 29 burst detected from the direction of the
Anomalous X-ray Pulsar (AXP) 1E 1048.1-5937 using the Rossi X-ray Timing
Explorer (RXTE). We find a simultaneous increase of ~3.5 times the quiescent
value in the 2-10 keV pulsed flux of 1E 1048.1-5937 during the tail of the
burst which identifies the AXP as the burst's origin. The burst was overall
very similar to the two others reported from the direction of this source in
2001. The unambiguous identification of 1E 1048.1-5937 as the burster here
confirms it was the origin of the 2001 bursts as well. The epoch of the burst
peak was very close to the arrival time of 1E 1048.1-5937's pulse peak. The
burst exhibited significant spectral evolution with the trend going from hard
to soft. During the 11 days following the burst, the AXP was observed further
with RXTE, XMM-Newton and Chandra. Pre- and post-burst observations revealed no
change in the total flux or spectrum of the quiescent emission. Comparing all
three bursts detected thus far from this source we find that this event was the
most fluent (>3.3x10^-8 erg/cm^2 in the 2-20 keV band), had the highest peak
flux (59+/-9x10^-10 erg/s/cm^2 in the 2-20 keV band), and the longest duration
(>699 s). The long duration of the burst differentiates it from Soft Gamma
Repeater (SGR) bursts which have typical durations of ~0.1 s. Bursts that occur
preferentially at pulse maximum, have fast-rises and long X-tails containing
the majority of the total burst energy have been seen uniquely from AXPs. The
marked differences between AXP and SGRs bursts may provide new clues to help
understand the physical differences between these objects.Comment: 24 pages, 4 figures, submitted to the Astrophysical Journa
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