143 research outputs found
Channeling Effects in Direct Dark Matter Detectors
The channeling of the ion recoiling after a collision with a WIMP changes the
ionization signal in direct detection experiments, producing a larger signal
than otherwise expected. We give estimates of the fraction of channeled
recoiling ions in NaI (Tl), Si and Ge crystals using analytic models produced
since the 1960's and 70's to describe channeling and blocking effects. We find
that the channeling fraction of recoiling lattice nuclei is smaller than that
of ions that are injected into the crystal and that it is strongly temperature
dependent.Comment: 8 pages, 12 figures, To appear in the Proceedings of the sixth
International Workshop on the Dark Side of the Universe (DSU2010) Leon,
Guanajuato, Mexico 1-6 June 201
Transient thermal effects in solid noble gases as materials for the detection of Dark Matter
The transient phenomena produced in solid noble gases by the stopping of the
recoils resulting from the elastic scattering processes of WIMPs from the
galactic halo were modelled, as dependencies of the temperatures of lattice and
electronic subsystems on the distance to the recoil's trajectory, and time from
its passage. The peculiarities of these thermal transients produced in Ar, Kr
and Xe were analysed for different initial temperatures and WIMP energies, and
were correlated with the characteristics of the targets and with the energy
loss of the recoils. The results were compared with the thermal spikes produced
by the same WIMPs in Si and Ge. In the range of the energy of interest, up to
tens of keV for the self-recoil, local phase transitions solid - liquid and
even liquid - gas were found possible, and the threshold parameters were
established.Comment: Minor corrections and updated references; accepted to JCA
Verifications of primal energy identities for variational problems with obstacles
We discuss error identities for two classes of free boundary problems
generated by obstacles. The identities suggest true forms of the respective
error measures which consist of two parts: standard energy norm and a certain
nonlinear measure. The latter measure controls (in a weak sense) approximation
of free boundaries. Numerical tests confirm sharpness of error identities and
show that in different examples one or another part of the error measure may be
dominant.Comment: 8 pages, 2 figures, conference paper: LSSC (Large-Scale scientific
computing), Sozopol, Bulgaria, 2017. The final version will be published at
Springe
A space-time pseudospectral discretization method for solving diffusion optimal control problems with two-sided fractional derivatives
We propose a direct numerical method for the solution of an optimal control
problem governed by a two-side space-fractional diffusion equation. The
presented method contains two main steps. In the first step, the space variable
is discretized by using the Jacobi-Gauss pseudospectral discretization and, in
this way, the original problem is transformed into a classical integer-order
optimal control problem. The main challenge, which we faced in this step, is to
derive the left and right fractional differentiation matrices. In this respect,
novel techniques for derivation of these matrices are presented. In the second
step, the Legendre-Gauss-Radau pseudospectral method is employed. With these
two steps, the original problem is converted into a convex quadratic
optimization problem, which can be solved efficiently by available methods. Our
approach can be easily implemented and extended to cover fractional optimal
control problems with state constraints. Five test examples are provided to
demonstrate the efficiency and validity of the presented method. The results
show that our method reaches the solutions with good accuracy and a low CPU
time.Comment: This is a preprint of a paper whose final and definite form is with
'Journal of Vibration and Control', available from
[http://journals.sagepub.com/home/jvc]. Submitted 02-June-2018; Revised
03-Sept-2018; Accepted 12-Oct-201
Recoiling Ion-Channeling in Direct Dark Matter Detectors
The channeling of the recoiling nucleus in crystalline detectors after a WIMP
collision would produce a larger scintillation or ionization signal in direct
detection experiments than otherwise expected. I present estimates of
channeling fractions obtained using analytic models developed from the 1960's
onwards to describe channeling and blocking effects. We find the fractions to
be too small to affect the fits to potential WIMP candidates. I also examine
the possibility of detecting a daily modulation of the dark matter signal due
to channeling.Comment: Talk presented at the DSU 2011 Conference, KITPC, Beijing, China,
Sept 26-30, 2011. 8 pages, 14 figures, jpconf.cls and jpconf11.clo necessary
to typese
Relevance of Ion-Channeling for Direct DM Detection
The channeling of the recoiling nucleus in crystalline detectors after a WIMP
collision would produce a larger scintillation or ionization signal in direct
detection experiments than otherwise expected. I present estimates of the
importance of this effect for the total direct detection rate and the daily
modulation of the signal using analytic models produced in the 1960's and 70's
to describe the effects of channeling and blocking in crystals.Comment: Talk given at the TAUP 2009 conference, Rome, Italy, July 1-5 2009. 3
pages, 4 figures. jpconf.cls and jpconf11.clo files need to typeset the tex
fil
Quality of Life Among Veterans With Chronic Spinal Cord Injury and Related Variables
Background: In recent decades, the incidence of spinal cord injuries has increased. In a systemic review on epidemiology of traumatic spinal cord injury in developing countries reported 25.5/million cases per year.
Objectives: To assess the quality of life (QOL) of the veterans among Iran-Iraq war with chronic spinal cord injuries (SCI) and to evaluate long-term impressions of SCI on their quality of life.
Patients and Methods: Fifty-two veterans, all male, with chronic spinal cord injury from Iran-Iraq war (1980-1988) were interviewed and examined. The mean age of veterans at the time of interview was 49.3 years (38 to 80 years). Veterans were assessed by using a 36-item short-form (SF-36), hospital anxiety and depression scale (HADS) and the Barthel index. The presence or absence of pressure sores and spasticity were documented as well.
Results: The mean age of veterans at the time of study was 49.3 years. Pearson's correlation test showed that depression and anxiety have a reverse association with mental component summary (MCS) scale and physical component summary (PCS) scale scores, respectively. Regression analysis showed a negative effect of depression and pressure sore on PCS. Moreover, no association was found between the duration of injury and age with quality of life.
Conclusions: Lower QOL was found among veterans with chronic SCI. More researches on health-related quality of life (HRQOL) are needed to give us a better understanding of changes in life of patients with SCI and the ways to improve them
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