545 research outputs found
Geological evolution of the Pietersburg greenstonebelt, South Africa and associated gold mineralization
The polyphase history of gold mineralization seen in the Pietersburg greenstone belt is integrated with the geochemical and tectonic evolution of greenstone belts as a whole. The four distinct regional geological settings of gold mineralization are described
A universal constraint between charge and rotation rate for degenerate black holes surrounded by matter
We consider stationary, axially and equatorially symmetric systems consisting
of a central rotating and charged degenerate black hole and surrounding matter.
We show that always holds provided that a continuous sequence of
spacetimes can be identified, leading from the Kerr-Newman solution in
electrovacuum to the solution in question. The quantity is the black
hole's intrinsic angular momentum per unit mass, its electric charge and
the well known black hole mass parameter introduced by Christodoulou and
Ruffini.Comment: 19 pages, 2 figures, replaced with published versio
Towards the grain boundary phonon scattering problem: an evidence for a low-temperature crossover
The problem of phonon scattering by grain boundaries is studied within the
wedge disclination dipole (WDD) model. It is shown that a specific q-dependence
of the phonon mean free path for biaxial WDD results in a low-temperature
crossover of the thermal conductivity, . The obtained results allow to
explain the experimentally observed deviation of from a
dependence below in and .Comment: 4 pages, 2 figures, submitted to J.Phys.:Condens.Matte
OC-0160: Growth and oedema related shifts of brain metastasis treated with stereotactic radiosurgery
Phonons from neutron powder diffraction
The spherically averaged structure function \soq obtained from pulsed
neutron powder diffraction contains both elastic and inelastic scattering via
an integral over energy. The Fourier transformation of \soq to real space, as
is done in the pair density function (PDF) analysis, regularizes the data, i.e.
it accentuates the diffuse scattering. We present a technique which enables the
extraction of off-center phonon information from powder diffraction experiments
by comparing the experimental PDF with theoretical calculations based on
standard interatomic potentials and the crystal symmetry. This procedure
(dynamics from powder diffraction(DPD)) has been successfully implemented for
two systems, a simple metal, fcc Ni, and an ionic crystal, CaF. Although
computationally intensive, this data analysis allows for a phonon based
modeling of the PDF, and additionally provides off-center phonon information
from powder neutron diffraction
Reply to "Comment on 'Dynamic Peierls-Nabarro equations for elastically isotropic crystals' "
The Comment by Markenscoff that criticizes a recent dynamic extension of the
Peierls-Nabarro equation [Y.-P. Pellegrini, Phys. Rev. B 81, 024101 (2010)] is
refuted by means of simple examples that illustrate the interest of using an
approach based on generalized functions to compute dynamic stress fields.Comment: 4 pages, 1 figur
ICF-based Functional Components and Contextual Factors as Correlates of Perceived Quality of Life for Youth With Chronic Conditions
Purpose: To explore International Classification of Functioning, Disability and Health (ICF)-based functional components and contextual factors associated with perceived quality of life (QOL) for youth with chronic conditions from the perspective of youth and parents.
Method: Baseline data were obtained from a longitudinal study examining predictors of changes in perceived QOL for youth with chronic conditions. 439 youth aged 11–17 (and one of their parents) completed a questionnaire. Standardized tools were used to measure youth functioning, contextual factors and perceived QOL. Multivariate linear regression analyses, controlling for socio-demographic and health information, were conducted to explore correlations among youth functioning/contextual factors and youth and parent perceptions of youth QOL. Results: Significant (p0.05) negative correlates with both youth and parent perceptions of youth QOL included pain/other physical symptoms and emotional symptoms. Significant factors positively correlated with youth and parent perceptions of youth QOL included school productivity and spirituality. Other significant positive correlates of youth perspectives were family social support and school belongingness/safety. Family functioning was positively correlated, and youth social anxiety and environmental barriers were negatively correlated, with parent perceptions of youth QOL.
Conclusions: This study provides preliminary evidence of factors upon which services aimed at improving perceived QOL of youth with chronic conditions could be based
Breathing Current Domains in Globally Coupled Electrochemical Systems: A Comparison with a Semiconductor Model
Spatio-temporal bifurcations and complex dynamics in globally coupled
intrinsically bistable electrochemical systems with an S-shaped current-voltage
characteristic under galvanostatic control are studied theoretically on a
one-dimensional domain. The results are compared with the dynamics and the
bifurcation scenarios occurring in a closely related model which describes
pattern formation in semiconductors. Under galvanostatic control both systems
are unstable with respect to the formation of stationary large amplitude
current domains. The current domains as well as the homogeneous steady state
exhibit oscillatory instabilities for slow dynamics of the potential drop
across the double layer, or across the semiconductor device, respectively. The
interplay of the different instabilities leads to complex spatio-temporal
behavior. We find breathing current domains and chaotic spatio-temporal
dynamics in the electrochemical system. Comparing these findings with the
results obtained earlier for the semiconductor system, we outline bifurcation
scenarios leading to complex dynamics in globally coupled bistable systems with
subcritical spatial bifurcations.Comment: 13 pages, 11 figures, 70 references, RevTex4 accepted by PRE
http://pre.aps.or
Gross tumour volume delineation in anal cancer on T2-weighted and diffusion-weighted MRI - Reproducibility between radiologists and radiation oncologists and impact of reader experience level and DWI image quality
Abstract Purpose To assess how gross tumour volume (GTV) delineation in anal cancer is affected by interobserver variations between radiologists and radiation oncologists, expertise level, and use of T2-weighted MRI (T2W-MRI) vs. diffusion-weighted imaging (DWI), and to explore effects of DWI quality. Methods and materials We retrospectively analyzed the MRIs (T2W-MRI and b800-DWI) of 25 anal cancer patients. Four readers (Senior and Junior Radiologist; Senior and Junior Radiation Oncologist) independently delineated GTVs, first on T2W-MRI only and then on DWI (with reference to T2W-MRI). Maximum Tumour Diameter (MTD) was calculated from each GTV. Mean GTVs/MTDs were compared between readers and between T2W-MRI vs. DWI. Interobserver agreement was calculated as Intraclass Correlation Coefficient (ICC), Dice Similarity Coefficient (DSC) and Hausdorff Distance (HD). DWI image quality was assessed using a 5-point artefact scale. Results Interobserver agreement between radiologists vs. radiation oncologists and between junior vs. senior readers was good–excellent, with similar agreement for T2W-MRI and DWI (e.g. ICCs 0.72–0.94 for T2W-MRI and 0.68–0.89 for DWI). There was a trend towards smaller GTVs on DWI, but only for the radiologists (P = 0.03–0.07). Moderate-severe DWI-artefacts were observed in 11/25 (44%) cases. Agreement tended to be lower in these cases. Conclusion Overall interobserver agreement for anal cancer GTV delineation on MRI is good for both radiologists and radiation oncologists, regardless of experience level. Use of DWI did not improve agreement. DWI artefacts affecting GTV delineation occurred in almost half of the patients, which may severely limit the use of DWI for radiotherapy planning if no steps are undertaken to avoid them
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