8,068 research outputs found
A Categorical Approach to Groupoid Frobenius Algebras
In this paper, we show that \C{G}-Frobenius algebras (for \C{G} a finite
groupoid) correspond to a particular class of Frobenius objects in the
representation category of D(k[\C{G}]), where D(k[\C{G}]) is the Drinfeld
double of the quantum groupoid k[\C{G}].Comment: final version; to appear in Applied Categorical Structure
Wearable Quarter-Wave Folded Microstrip Antenna for Passive UHF RFID Applications
A wearable low-profile inset-fed quarter-wave folded microstrip patch antenna for noninvasive activity monitoring of elderly is presented. The proposed antenna is embedded with a sensor-enabled passive radio-frequency identification (RFID) tag operating in the ultra-high frequency (UHF) industrial-scientific-medical (ISM) band around 900 MHz. The device exhibits a low and narrow profile based on a planar folded quarter-wave length patch structure and is integrated on a flexible substrate to maximise comfort to the wearer. An extended ground plane made from silver fabric successfully minimises the impact of the human body on the antenna performance. Measurements on a prototype demonstrate a reflection coefficient (S₁₁) of −30 dB at resonance and a −10 dB bandwidth from 920 MHz to 926 MHz. Simulation results predict a maximum gain of 2.8 dBi. This is confirmed by tag measurements where a 4-meter read range is achieved using a transmit power of 30 dBm, for the case where the passive wearable tag antenna is mounted on a body in a practical setting. This represents an almost 40% increase in read range over an existing dipole antenna placed over a 10 mm isolator layer on a human subject.Thomas Kaufmann, Damith C. Ranasinghe, Ming Zhou, and Christophe Fumeau
Implications of surface noise for the motional coherence of trapped ions
Electric noise from metallic surfaces is a major obstacle towards quantum
applications with trapped ions due to motional heating of the ions. Here, we
discuss how the same noise source can also lead to pure dephasing of motional
quantum states. The mechanism is particularly relevant at small ion-surface
distances, thus imposing a new constraint on trap miniaturization. By means of
a free induction decay experiment, we measure the dephasing time of the motion
of a single ion trapped 50~m above a Cu-Al surface. From the dephasing
times we extract the integrated noise below the secular frequency of the ion.
We find that none of the most commonly discussed surface noise models for ion
traps describes both, the observed heating as well as the measured dephasing,
satisfactorily. Thus, our measurements provide a benchmark for future models
for the electric noise emitted by metallic surfaces.Comment: (5 pages, 4 figures
A Proof Strategy Language and Proof Script Generation for Isabelle/HOL
We introduce a language, PSL, designed to capture high level proof strategies
in Isabelle/HOL. Given a strategy and a proof obligation, PSL's runtime system
generates and combines various tactics to explore a large search space with low
memory usage. Upon success, PSL generates an efficient proof script, which
bypasses a large part of the proof search. We also present PSL's monadic
interpreter to show that the underlying idea of PSL is transferable to other
ITPs.Comment: This paper has been submitted to CADE2
Relationship between hippocampal structure and memory function in elderly humans
With progressing age, the ability to recollect personal events declines, whereas familiarity-based memory remains relatively intact. It has been hypothesized that age-related hippocampal atrophy may contribute to this pattern because of its critical role for recollection in younger humans and after acute injury. Here, we show that hippocampal volume loss in healthy older persons correlates with gray matter loss (estimated with voxel-based morphometry) of the entire limbic system and shows no correlation with an electrophysiological (event-related potential [ERP]) index of recollection. Instead, it covaries with more substantial and less specific electrophysiological changes of stimulus processing. Age-related changes in another complementary structural measure, hippocampal diffusion, on the other hand, seemed to be more regionally selective and showed the expected correlation with the ERP index of recollection. Thus, hippocampal atrophy in older persons accompanies limbic atrophy, and its functional impact on memory is more fundamental than merely affecting recollection
Formality of the chain operad of framed little disks
We extend Tamarkin's formality of the little disk operad to the framed little
disk operad.Comment: 5 page
A burst with double radio spectrum observed up to 212 GHz
We study a solar flare that occurred on September 10, 2002, in active region
NOAA 10105 starting around 14:52 UT and lasting approximately 5 minutes in the
radio range. The event was classified as M2.9 in X-rays and 1N in H\alpha.
Solar Submillimeter Telescope observations, in addition to microwave data give
us a good spectral coverage between 1.415 and 212 GHz. We combine these data
with ultraviolet images, hard and soft X-rays observations and full-disk
magnetograms. Images obtained from Ramaty High Energy Solar Spectroscopic
Imaging data are used to identify the locations of X-ray sources at different
energies and to determine the X-ray spectrum, while ultra violet images allow
us to characterize the coronal flaring region. The magnetic field evolution of
the active region is analyzed using Michelson Doppler Imager magnetograms. The
burst is detected at all available radio-frequencies. X-ray images (between 12
keV and 300 keV) reveal two compact sources and 212 GHz data, used to estimate
the radio source position, show a single compact source displaced by 25" from
one of the hard X-ray footpoints. We model the radio spectra using two
homogeneous sources, and combine this analysis with that of hard X-rays to
understand the dynamics of the particles. Relativistic particles, observed at
radio wavelengths above 50 GHz, have an electron index evolving with the
typical soft-hard-soft behaviour.Comment: Submitted to Solar Physics, 20 pages, 8 fugure
Simulating changes in shape of thermionic cathodes during operation of high-pressure arc discharges
A numerical model of current transfer to thermionic cathodes of high-pressure arc discharges
is developed with account of deviations from local thermodynamic equilibrium occurring
near the cathode surface, in particular, of the near-cathode space-charge sheath, melting of the
cathode, and motion of the molten metal under the effect of the plasma pressure, the Lorentz
force, gravity, and surface tension. Modelling results are reported for a tungsten cathode of
an atmospheric-pressure argon arc and the computed changes in the shape of the cathode
closely resemble those observed in the experiment. The modelling has shown that the time
scale of change of the cathode shape during arc operation is very sensitive to the temperature
attained by the cathode. The fact that the computed time scales conform to those observed
in the experiment indicate that the model of non-equilibrium near-cathode layers in high pressure arc discharges, employed in this work, predicts the cathode temperature for a given
arc current with adequate accuracy. In contrast, modelling based on the assumption of local
thermodynamic equilibrium in the whole arc plasma computation domain up to the cathode
surface could hardly produce a similar agreement.info:eu-repo/semantics/publishedVersio
Parkinson's Law Quantified: Three Investigations on Bureaucratic Inefficiency
We formulate three famous, descriptive essays of C.N. Parkinson on
bureaucratic inefficiency in a quantifiable and dynamical socio-physical
framework. In the first model we show how the use of recent opinion formation
models for small groups can be used to understand Parkinson's observation that
decision making bodies such as cabinets or boards become highly inefficient
once their size exceeds a critical 'Coefficient of Inefficiency', typically
around 20. A second observation of Parkinson - which is sometimes referred to
as Parkinson's Law - is that the growth of bureaucratic or administrative
bodies usually goes hand in hand with a drastic decrease of its overall
efficiency. In our second model we view a bureaucratic body as a system of a
flow of workers, which enter, become promoted to various internal levels within
the system over time, and leave the system after having served for a certain
time. Promotion usually is associated with an increase of subordinates. Within
the proposed model it becomes possible to work out the phase diagram under
which conditions bureaucratic growth can be confined. In our last model we
assign individual efficiency curves to workers throughout their life in
administration, and compute the optimum time to send them to old age pension,
in order to ensure a maximum of efficiency within the body - in Parkinson's
words we compute the 'Pension Point'.Comment: 15 pages, 5 figure
Исследование условий генерации когерентного излучения в плазме продольного разряда
Создание генератора накачки для азотного лазера с поперечным разрядом. Импульсный генератор основан на высоковольтном источнике питания, тиратроне, магнитной компрессии и разрядном промежутке. Источник питания основан на резонансном инверторе с последовательным колебательным контуром. для уменьшения длительности импульса используются ячейки магнитной компрессии, которые сократили длительность импульса в десять раз.Create a generator for pumping nitrogen laser with transverse discharge. The pulse generator is based on the high-voltage power supply, thyratron, magnetic compression, and discharge gap. The power supply is based on a resonant inverter with series resonant circuit. to reduce the pulse width of the cell using magnetic compression which reduced the pulse width of ten
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