13,229 research outputs found
In-Beam Background Suppression Shield
The long (3ms) proton pulse of the European Spallation Source (ESS) gives
rise to unique and potentially high backgrounds for the instrument suite. In
such a source an instrument capabilities will be limited by it's Signal to
Noise (S/N) ratio. The instruments with a direct view of the moderator, which
do not use a bender to help mitigate the fast neutron background, are the most
challenging. For these beam lines we propose the innovative shielding of
placing blocks of material directly into the guide system, which allow a
minimum attenuation of the cold and thermal fluxes relative to the background
suppression. This shielding configuration has been worked into a beam line
model using Geant4. We study particularly the advantages of single crystal
sapphire and silicon blocks .Comment: 12 pages, 8 figures, proceeding of NDS 2015, 4th International
Workshop on Neutron Delivery Systems, 28 -30 September 2015, ILL Grenoble,
Franc
Widths of crossings in Poisson Boolean percolation
We answer the following question: if the occupied (or vacant) set of a planar
Poisson Boolean percolation model does contain a crossing of an
square, how wide is this crossing? The answer depends on the whether we
consider the critical, sub- or super-critical regime, and is different for the
occupied and vacant sets
SiC(0001): a surface Mott-Hubbard insulator
We present ab-initio electronic structure calculations for the Si-terminated
SiC(0001) surface. While local density approximation
(LDA) calculations predict a metallic ground state with a half-filled narrow
band, Coulomb effects, included by the spin-polarized LDA+U method, result in a
magnetic (Mott-Hubbard) insulator with a gap of 1.5 eV, comparable with the
experimental value of 2.0 eV. The calculated value of the inter-site exchange
parameter, J=30K, leads to the prediction of a paramagnetic Mott state, except
at very low temperatures. The observed Si 2p surface core level doublet can
naturally be explained as an on-site exchange splitting.Comment: RevTex, 4 pages, 4 eps-figure
Retroperitoneal fibrosis: a case of a patient (63y/o) treated with low-dose methotrexate (MTX) and 6-methylprednisolone (6-MP)
Retroperitoneal fibrosis (RPF), is a rare fibroinflammatory disease. The pathogenesis of RPF is still unclear and numerous theories have
been reported such as environmental factors, immunologic process, genetic component, local inflammation and advanced atherosclerosis.
RPF is characterized by the presence of a particular retroperitoneal fibrotic tissue which is white, woody and involving retroperitoneal
structures such as the great vessels, ureters and psoas muscle. The main complication of RPF is the obstruction of local structures such as
the ureters due to the fibrosis and the treatment of this aspect represents the main challenge for this pathology.
RPF medical treatment consists of corticosteroids or/and immunosuppressive therapy. We report a case of a patient (63y/o) affected by
idiopathic RPF treated with low-dose methotrexate (MTX) and 6-methylprednisolone (6-MP) for two years, describing and confirming the
effectiveness and safety of a long-term low-dose MTX and 6-MP treatment
Research in dynamic transitional processes of functioning of combine harvester hydraulic drives
An analysis of perspective methods is made for diagnosing hydraulic drives, based on the on-board automated tools. Prospects are substantiated for the development of technical diagnostics of agricultural machinery on the basis of on-board electronic means. Special attention is paid to the need for significant research in the direction of creating new diagnostic parameters, adapted to these means, and methods of their measurement. The parameters of the characteristics of changes in the pressure of the working fluid in the hydraulic aggregates in transitional modes of operation of the hydraulic drives are advisable to be used as diagnostic, since the veracity (accuracy) of the parameters, based on them, is not less than 95%. As an example, a method of diagnosing on dynamic transitional modes of operation of the hydraulic drives is given, which is the basis for the development and use of built-in and portable electronic means for conducting CIP diagnostics, which will provide 2-3 times decrease in the labour intensity and the cost of work with at least 85% veracity of diagnosis and the permissible error measurements no more than ± 4%. The novelty of this work lies in the method we have developed for diagnosing the dynamic transient modes of operation of hydraulic drives
Random Flows of Covariance Operators and their Statistical Inference
We develop a statistical framework for conducting inference on collections of
time-varying covariance operators (covariance flows) over a general, possibly
infinite dimensional, Hilbert space. We model the intrinsically non-linear
structure of covariances by means of the Bures-Wasserstein metric geometry. We
make use of the Riemmanian-like structure induced by this metric to define a
notion of mean and covariance of a random flow, and develop an associated
Karhunen-Lo\`eve expansion. We then treat the problem of estimation and
construction of functional principal components from a finite collection of
covariance flows. Our theoretical results are motivated by modern problems in
functional data analysis, where one observes operator-valued random processes
-- for instance when analysing dynamic functional connectivity and fMRI data,
or when analysing multiple functional time series in the frequency domain.
{Nevertheless, our framework is also novel in the finite-dimensions (matrix
case), and we demonstrate what simplifications can be afforded then}. We
illustrate our methodology by means of simulations and a data analyses
Population status of the Oblong turtle in Armadale’s wetlands
The Oblong turtle (Chelodina oblonga) is becoming a flagship species for Perth wetlands. As an apex predator the species plays an essential role in wetland ecosystem health. However, urban populations appear to be in decline due to numerous threats including habitat modification and destruction, wildlife-vehicle mortality, and predation. Three wetlands within City of Armadale were identified by the Armadale Gosnells Landcare Group as potentially significant sites for populations of the Oblong turtle. No baseline information on the presence and/or population status of C. oblonga within these wetlands currently exists. Modified funnel traps and fyke nets were deployed for an overnight trapping period in each wetland during October 2020. In total, thirty-four turtles were captured and released from the wetlands. The turtles captured were mainly adults and the few juveniles captured were >100 mm. Sex ratio varied from heavily male-dominated to slightly female-dominated. The results suggest that these populations have been experiencing low recruitment, and sex biased mortality at the heavily male dominated population. Continued monitoring of these populations as well as expansion of surveys to additional wetlands will enable a deeper understanding of C. oblonga population dynamics within the City of Armadale, as well as wetland-specific management recommendations
Speeding up critical system dynamics through optimized evolution
The number of defects which are generated on crossing a quantum phase
transition can be minimized by choosing properly designed time-dependent
pulses. In this work we determine what are the ultimate limits of this
optimization. We discuss under which conditions the production of defects
across the phase transition is vanishing small. Furthermore we show that the
minimum time required to enter this regime is , where
is the minimum spectral gap, unveiling an intimate connection between
an optimized unitary dynamics and the intrinsic measure of the Hilbert space
for pure states. Surprisingly, the dynamics is non-adiabatic, this result can
be understood by assuming a simple two-level dynamics for the many-body system.
Finally we classify the possible dynamical regimes in terms of the action
.Comment: 6 pages, 6 figure
Uniquely colourable m-dichromatic oriented graphs
AbstractThe dichromatic number dk(D) of a diagraph D is the minimum number of colours needed to colour V(D) in such a way that no monochromatic directed cycle is obtained. A digraph D is called uniquely colourable if any acyclic dk(D)-colouring of V(D) induces the same partition of V(D). In this paper we construct an infinite family of uniquely colourable m-dichromatic oriented graphs for all m ⩾ 2
Exactly quantized dynamics of classical incommensurate sliders
We report peculiar velocity quantization phenomena in the classical motion of
an idealized 1D solid lubricant, consisting of a harmonic chain interposed
between two periodic sliders. The ratio v_cm/v_ext of the chain center-of-mass
velocity to the externally imposed relative velocity of the sliders stays
pinned to exact "plateau" values for wide ranges of parameters, such as sliders
corrugation amplitudes, external velocity, chain stiffness and dissipation, and
is strictly determined by the commensurability ratios alone. The phenomenon is
explained by one slider rigidly dragging the kinks that the chain forms with
the other slider. Possible consequences of these results for some real systems
are discussed.Comment: 5 pags 4 fig
- …