3,851 research outputs found
Spontaneous symmetry breaking: exact results for a biased random walk model of an exclusion process
It has been recently suggested that a totally asymmetric exclusion process
with two species on an open chain could exhibit spontaneous symmetry breaking
in some range of the parameters defining its dynamics. The symmetry breaking is
manifested by the existence of a phase in which the densities of the two
species are not equal. In order to provide a more rigorous basis to these
observations we consider the limit of the process when the rate at which
particles leave the system goes to zero. In this limit the process reduces to a
biased random walk in the positive quarter plane, with specific boundary
conditions. The stationary probability measure of the position of the walker in
the plane is shown to be concentrated around two symmetrically located points,
one on each axis, corresponding to the fact that the system is typically in one
of the two states of broken symmetry in the exclusion process. We compute the
average time for the walker to traverse the quarter plane from one axis to the
other, which corresponds to the average time separating two flips between
states of broken symmetry in the exclusion process. This time is shown to
diverge exponentially with the size of the chain.Comment: 42 page
Cultivated and wild varieties of the grasses in Iowa
Blue grass and the clovers do well in Iowa; but many of the cultivated grasses which are valued highly in moist climates, have not given satisfaction on account of occasional severe drouths and cold winters. As we believed that some of the wild western grasses might prove valuable under cultivation, the Iowa Agricultural Experiment Station collected the seeds of many native grasses in 1888, in Iowa, Minnesota, Dakota, Montana, Idaho and Colorado, which were planted in rows on our experiment grounds in the spring of 1889. We planted seeds of many of the cultivated grasses also alongside of them at the same time in rows and broadcast, so that it would be easy to determine differences of growth and adaptation to our soils and climate.
The common names of grasses will be given after their botanical names. We have concluded that it is best to give our notes on and the analyses of some of the best known cultivated grasses first
Analysis of conductor impedances accounting for skin effect and nonlinear permeability
It is often necessary to protect sensitive electrical equipment from pulsed electric and magnetic fields. To accomplish this electromagnetic shielding structures similar to Faraday Cages are often implemented. If the equipment is inside a facility that has been reinforced with rebar, the rebar can be used as part of a lighting protection system. Unfortunately, such shields are not perfect and allow electromagnetic fields to be created inside due to discontinuities in the structure, penetrations, and finite conductivity of the shield. In order to perform an analysis of such a structure it is important to first determine the effect of the finite impedance of the conductors used in the shield. In this paper we will discuss the impedances of different cylindrical conductors in the time domain. For a time varying pulse the currents created in the conductor will have different spectral components, which will affect the current density due to skin effects. Many construction materials use iron and different types of steels that have a nonlinear permeability. The nonlinear material can have an effect on the impedance of the conductor depending on the B-H curve. Although closed form solutions exist for the impedances of cylindrical conductors made of linear materials, computational techniques are needed for nonlinear materials. Simulations of such impedances are often technically challenging due to the need for a computational mesh to be able to resolve the skin depths for the different spectral components in the pulse. The results of such simulations in the time domain will be shown and used to determine the impedances of cylindrical conductors for lightning current pulses that have low frequency content
An off-shell I.R. regularization strategy in the analysis of collinear divergences
We present a method for the analysis of singularities of Feynman amplitudes
based on the Speer sector decomposition of the Schwinger parametric integrals
combined with the Mellin-Barnes transform. The sector decomposition method is
described in some details. We suggest the idea of applying the method to the
analysis of collinear singularities in inclusive QCD cross sections in the
mass-less limit regularizing the forward amplitudes by an off-shell choice of
the initial particle momenta. It is shown how the suggested strategy works in
the well known case of the one loop corrections to Deep Inelastic Scattering.Comment: 25 pages, 3 figure
Position Dependence of Charge Collection in Prototype Sensors for the CMS Pixel Detector
This paper reports on the sensor R&D activity for the CMS pixel detector.
Devices featuring several design and technology options have been irradiated up
to a proton fluencec of 1E15 n_eq/cm**2 at the CERN PS. Afterward they were
bump bonded to unirradiated readout chips and tested using high energy pions in
the H2 beam line of the CERN SPS. The readout chip allows a non zero suppressed
full analogue readout and therefore a good characterization of the sensors in
terms of noise and charge collection properties. The position dependence of
signal is presented and the differences between the two sensor options are
discussed.Comment: Contribution to the IEEE-NSS Oct. 2003, Portland, OR, USA, submitted
to IEEE-TNS 7 pages, 8 figures, 1 table. Revised, title change
Comparison of thromboelastometry (ROTEM®) with standard plasmatic coagulation testing in paediatric surgery
Background Thromboelastometry (ROTEM®) might be useful to detect intraoperative coagulation disorders early in major paediatric surgery. This observational trial compares this technique to standard coagulation tests. Methods Intraoperative blood sampling was obtained in children undergoing elective major surgery. At each time point, standard coagulation tests [activated partial thromboplastin time (aPTT), prothrombin time (PT), and fibrinogen level] and ROTEM® analyses (InTEM, ExTEM, and FibTEM) were performed simultaneously by trained hospital laboratory staff. Results A total of 288 blood samples from 50 subjects were analysed. While there was a poor correlation between PT and aPTT to ExTEM clotting time (CT) and InTEM CT, respectively, a good correlation was detected between PT and aPTT to clot formation time, and a very good correlation between fibrinogen level and FibTEM assay (r=0.882, P<0.001). Notably, 64% of PT and 94% of aPTT measurements were outside the reference range, while impaired CT was observed in 13% and 6.3%, respectively. Standard coagulation test results were available after a median of 53 min [inter-quartile range (IQR): 45-63 min], whereas 10 min values of ROTEM® results were available online after 23 min (IQR: 21-24 min). Conclusions PT and aPTT cannot be interchangeably used with ROTEM® CT. Based on the results of ROTEM®, recommended thresholds for PT and aPTT might overestimate the need for coagulation therapy. A good correlation was found between the fibrinogen level and the FibTEM assay. In addition, ROTEM® offered faster turnaround time
Extraction of electric field in heavily irradiated silicon pixel sensors
A new method for the extraction of the electric field in the bulk of heavily
irradiated silicon pixel sensors is presented. It is based on the measurement
of the Lorentz deflection and mobility of electrons as a function of depth. The
measurements were made at the CERN H2 beam line, with the beam at a shallow
angle with respect to the pixel sensor surface. The extracted electric field is
used to simulate the charge collection and the Lorentz deflection in the pixel
sensor. The simulated charge collection and the Lorentz deflection is in good
agreement with the measurements both for non-irradiated and irradiated up to
1E15 neq/cm2 sensors.Comment: 6 pages, 11 figures, presented at the 13th International Workshop on
Vertex Detectors for High Energy Physics, September 13-18, 2004,
Menaggio-Como, Italy. Submitted to Nucl. Instr. Meth.
Simulation of Heavily Irradiated Silicon Pixel Detectors
We show that doubly peaked electric fields are necessary to describe
grazing-angle charge collection measurements of irradiated silicon pixel
sensors. A model of irradiated silicon based upon two defect levels with
opposite charge states and the trapping of charge carriers can be tuned to
produce a good description of the measured charge collection profiles in the
fluence range from 0.5x10^{14} Neq/cm^2 to 5.9x10^{14} Neq/cm^2. The model
correctly predicts the variation in the profiles as the temperature is changed
from -10C to -25C. The measured charge collection profiles are inconsistent
with the linearly-varying electric fields predicted by the usual description
based upon a uniform effective doping density. This observation calls into
question the practice of using effective doping densities to characterize
irradiated silicon. The model is now being used to calibrate pixel hit
reconstruction algorithms for CMS.Comment: Invited talk at International Symposium on the Development of
Detectors for Particle, AstroParticle and Synchrtron Radiation Experiments,
Stanford Ca (SNIC06) 8 pages, LaTeX, 11 eps figure
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