35,592 research outputs found
Measurements and Monte-Carlo simulations of the particle self-shielding effect of B4C grains in neutron shielding concrete
A combined measurement and Monte-Carlo simulation study was carried out in
order to characterize the particle self-shielding effect of B4C grains in
neutron shielding concrete. Several batches of a specialized neutron shielding
concrete, with varying B4C grain sizes, were exposed to a 2 {\AA} neutron beam
at the R2D2 test beamline at the Institute for Energy Technology located in
Kjeller, Norway. The direct and scattered neutrons were detected with a neutron
detector placed behind the concrete blocks and the results were compared to
Geant4 simulations. The particle self-shielding effect was included in the
Geant4 simulations by calculating effective neutron cross-sections during the
Monte-Carlo simulation process. It is shown that this method well reproduces
the measured results. Our results show that shielding calculations for
low-energy neutrons using such materials would lead to an underestimate of the
shielding required for a certain design scenario if the particle self-shielding
effect is not included in the calculations.Comment: This manuscript version is made available under the CC-BY-NC-ND 4.0
license http://creativecommons.org/licenses/by-nc-nd/4.0
Inertial sensor-based knee flexion/extension angle estimation
A new method for estimating knee joint flexion/extension angles from segment acceleration and angular velocity data is described. The approach uses a combination of Kalman filters and biomechanical constraints based on anatomical knowledge. In contrast to many recently published methods, the proposed approach does not make use of the earth’s magnetic field and hence is insensitive to the complex field distortions commonly found in modern buildings. The method was validated experimentally by calculating knee angle from measurements taken from two IMUs placed on adjacent body segments. In contrast to many previous studies which have validated their approach during relatively slow activities or over short durations, the performance of the algorithm was evaluated during both walking and running over 5 minute periods. Seven healthy subjects were tested at various speeds from 1 to 5 miles/hour. Errors were estimated by comparing the results against data obtained simultaneously from a 10 camera motion tracking system (Qualysis). The average measurement error ranged from 0.7 degrees for slow walking (1 mph) to 3.4 degrees for running (5mph). The joint constraint used in the IMU analysis was derived from the Qualysis data. Limitations of the method, its clinical application and its possible extension are discussed
The AdHOC study of older adults’ adherence to medication in 11 countries
BACKGROUND: Compared with the resources expended developing, evaluating
and making clinical decisions about prescribing medication, we know little about
what determines whether people take it. Older adults are prescribed more
medication than any other group. Poor adherence is a common reason for nonresponse
to medication.
OBJECTIVES: To investigate cross-nationally the impact of demographic,
psychiatric (including cognitive), physical health, behavioural and medication factors
on adherence to medication in older adults.
METHODS: Researchers interviewed 3881 people over 65 who receive home
care services using a structured interview at participants’ places of residence in
eleven countries. The main outcome measure was the percentage participants not
adherent to medication.
RESULTS: 12.5% (n= 456) of people reported they were not fully adherent to
medication. Non-adherence was predicted by problem drinking (OR=3.6), not having
a doctor review medication (OR=3.3), dementia (OR=1.4 for every one point
increase in impairment), good physical health (OR=1.2), resisting care (OR=2.1)
being married (OR=2.3) and living in the Czech Republic (OR=4.7) or Germany
(OR=1.4).
CONCLUSION: People, who screen positive for problem drinking and with
dementia, often undiagnosed are less likely to adhere to medication. Therefore
doctors should consider dementia and problem drinking when prescribing for older
adults. Interventions to improve adherence in older adults might be more effective if
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targeted at these groups. It is possible that medication review enhances adherence,
by improving the patient-doctor relationship, or by emphasising the relevance of
medications
Nuclear magnetic resonance probes for the Kondo scenario for the 0.7 feature in semiconductor quantum point contact devices
We propose a probe based on nuclear relaxation and Knight shift measurements
for the Kondo scenario for the "0.7 feature" in semiconductor quantum point
contact (QPC) devices. We show that the presence of a bound electron in the QPC
would lead to a much higher rate of nuclear relaxation compared to nuclear
relaxation through exchange of spin with conduction electrons. Furthermore, we
show that the temperature dependence of this nuclear relaxation is very
non-monotonic as opposed to the linear-T relaxation from coupling with
conduction electrons. We present a qualitative analysis for the additional
relaxation due to nuclear spin diffusion (NSD) and study the extent to which
NSD affects the range of validity of our method. The conclusion is that nuclear
relaxation, in combination with Knight shift measurements, can be used to
verify whether the 0.7 feature is indeed due to the presence of a bound
electron in the QPC.Comment: Published version. Appears in a Special Section on the 0.7 Feature
and Interactions in One-Dimensional Systems. 16 page
Field pea agronomy.
Field peas sowing rates, 87A31. Field peas time of sowing, 87A32. Field peas factional agronomy, 87A33. Field pea sowing rates, 87N092. Field peas time of sowing, 87N093. field peas - factorial agronomy, 87N094
IMAGING GENOMICS
Imaging genomics is an emerging research field, where integrative analysis of imaging and omics data is performed to provide new insights into the phenotypic characteristics and genetic mechanisms of normal and/or disordered biological structures and functions, and to impact the development of new diagnostic, therapeutic and preventive approaches. The Imaging Genomics Session at PSB 2017 aims to encourage discussion on fundamental concepts, new methods and innovative applications in this young and rapidly evolving field
Perturbative nonequilibrium dynamics of phase transitions in an expanding universe
A complete set of Feynman rules is derived, which permits a perturbative
description of the nonequilibrium dynamics of a symmetry-breaking phase
transition in theory in an expanding universe. In contrast to a
naive expansion in powers of the coupling constant, this approximation scheme
provides for (a) a description of the nonequilibrium state in terms of its own
finite-width quasiparticle excitations, thus correctly incorporating
dissipative effects in low-order calculations, and (b) the emergence from a
symmetric initial state of a final state exhibiting the properties of
spontaneous symmetry breaking, while maintaining the constraint . Earlier work on dissipative perturbation theory and spontaneous symmetry
breaking in Minkowski spacetime is reviewed. The central problem addressed is
the construction of a perturbative approximation scheme which treats the
initial symmetric state in terms of the field , while the state that
emerges at later times is treated in terms of a field , linearly related
to . The connection between early and late times involves an infinite
sequence of composite propagators. Explicit one-loop calculations are given of
the gap equations that determine quasiparticle masses and of the equation of
motion for and the renormalization of these equations is
described. The perturbation series needed to describe the symmetric and
broken-symmetry states are not equivalent, and this leads to ambiguities
intrinsic to any perturbative approach. These ambiguities are discussed in
detail and a systematic procedure for matching the two approximations is
described.Comment: 22 pages, using RevTeX. 6 figures. Submitted to Physical Review
Analytic and Numerical Study of Preheating Dynamics
We analyze the phenomenon of preheating,i.e. explosive particle production
due to parametric amplification of quantum fluctuations in the unbroken case,
or spinodal instabilities in the broken phase, using the Minkowski space
vector model in the large limit to study the non-perturbative issues
involved. We give analytic results for weak couplings and times short compared
to the time at which the fluctuations become of the same order as the tree
level,as well as numerical results including the full backreaction.In the case
where the symmetry is unbroken, the analytic results agree spectacularly well
with the numerical ones in their common domain of validity. In the broken
symmetry case, slow roll initial conditions from the unstable minimum at the
origin, give rise to a new and unexpected phenomenon: the dynamical relaxation
of the vacuum energy.That is, particles are abundantly produced at the expense
of the quantum vacuum energy while the zero mode comes back to almost its
initial value.In both cases we obtain analytically and numerically the equation
of state which turns to be written in terms of an effective polytropic index
that interpolates between vacuum and radiation-like domination. We find that
simplified analysis based on harmonic behavior of the zero mode, giving rise to
a Mathieu equation forthe non-zero modes miss important physics. Furthermore,
analysis that do not include the full backreaction do not conserve energy,
resulting in unbound particle production. Our results do not support the recent
claim of symmetry restoration by non-equilibrium fluctuations.Finally estimates
of the reheating temperature are given,as well as a discussion of the
inconsistency of a kinetic approach to thermalization when a non-perturbatively
large number of particles is created.Comment: Latex file, 52 pages and 24 figures in .ps files. Minor changes. To
appear in Physical Review D, 15 December 199
Dual Response Models for the Fractional Quantum Hall Effect
It is shown that the Jain mapping between states of integer and fractional
quantum Hall systems can be described dynamically as a perturbative
renormalization of an effective Chern-Simons field theory. The effects of
mirror duality symmetries of toroidally compactified string theory on this
system are studied and it is shown that, when the gauge group is compact, the
mirror map has the same effect as the Jain map. The extrinsic ingredients of
the Jain construction appear naturally as topologically non-trivial field
configurations of the compact gauge theory giving a dynamical origin for the
Jain hierarchy of fractional quantum Hall states.Comment: 8 pages LaTe
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