1,019 research outputs found
Alpha Backgrounds for HPGe Detectors in Neutrinoless Double-Beta Decay Experiments
The Majorana Experiment will use arrays of enriched HPGe detectors to search
for the neutrinoless double-beta decay of 76Ge. Such a decay, if found, would
show lepton-number violation and confirm the Majorana nature of the neutrino.
Searches for such rare events are hindered by obscuring backgrounds which must
be understood and mitigated as much as possible. A potentially important
background contribution to this and other double-beta decay experiments could
come from decays of alpha-emitting isotopes in the 232Th and 238U decay chains
on or near the surfaces of the detectors. An alpha particle emitted external to
an HPGe crystal can lose energy before entering the active region of the
detector, either in some external-bulk material or within the dead region of
the crystal. The measured energy of the event will only correspond to a partial
amount of the total kinetic energy of the alpha and might obscure the signal
from neutrinoless double-beta decay. A test stand was built and measurements
were performed to quantitatively assess this background. We present results
from these measurements and compare them to simulations using Geant4. These
results are then used to measure the alpha backgrounds in an underground
detector in situ. We also make estimates of surface contamination tolerances
for double-beta decay experiments using solid-state detectors.Comment: 10 pages, 11 figures, submitted to NIM
Self-consistent cluster CPA methods and the nested CPA theory
The coherent potential approximation, CPA, is a useful tool to treat systems
with disorder. Cluster theories have been proposed to go beyond the translation
invariant single-site CPA approximation and include some short range
correlations. In this framework one can also treat simultaneously diagonal
disorder (in the site-diagonal elements of the Hamiltonian) and non-diagonal
disorder (in the bond energies). It proves difficult to obtain reasonable
results, free of non-analyticities, for lattices of dimension higher than one
(D>1). We show electronic structure results obtained for a Hubbard model,
treated in mean field approximation, on a square lattice and a simple cubic
lattice, with the simultaneous inclusion of diagonal and non-diagonal disorder.
We compare the results obtained using three different methods to treat the
problem: a self-consistent 2-site cluster CPA method, the
Blackman-Esterling-Berk single-site like extension of the CPA and a nested CPA
approach.Comment: 5 pages + 2 figures, to appear in Physica B. Presented at the SCES'99
conference, Nagano, Japan (Aug.'99
Leadership legitimacy and the mobilization of capital(s): Disrupting politics and reproducing heteronormativity
The rise of populist leaders in the political sphere mounts a challenge to normative understandings of leadership. To better understand this challenge, we examine how political leaders mobilize different forms of social capital in pursuit of leadership legitimacy, providing insight into the dynamics of how leadership norms are maintained. While research has tended to focus on specific forms of capital, this article considers capital as multidimensional and strategically mobilized. The article applies a multimodal analysis to examine interactions between Donald Trump and Hillary Clinton during peak âTwitter Momentsâ of the three 2016 presidential election debates. We theorize the paradoxical dynamics of the mobilization of multiple capitals and their intersection as a simultaneously disruptive and reproductive resource. While the mobilization of multiple capitals operates to disrupt traditional notions of who can claim legitimacy as a leader in the political field, their disruptive mobilization serves to reproduce implicit heteronormative leadership values. Hence, our theorization illuminates the resilience of implicit leadership values, and their intimate connection with heteronormativity, calling for the need to interrogate leadership legitimacy claims that promise ânewâ approaches
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Non-stoichiometric oxide and metal interfaces and reactions
We have employed a combination of experimental surface science techniques and density functional calculations to study the reduction of TiO2(110) surfaces through the doping with submonolayer transition metals. We concentrate on the role of Ti adatoms in self doping of rutile and contrast the behaviour to that of Cr. DFT+U calculations enable identification of probable adsorption structures and their spectroscopic characteristics. Adsorption of both metals leads to a broken symmetry and an asymmetric charge transfer localised around the defect site of a mixed localised/delocalised character. Charge transfer creates defect states with Ti 3d character in the band gap at similar to 1-eV binding energy. Cr adsorption, however, leads to a very large shift in the valence-band edge to higher binding energy and the creation of Cr 3d states at 2.8-eV binding energy. Low-temperature oxidation lifts the Ti-derived band-gap states and modifies the intensity of the Cr features, indicative of a change of oxidation state from Cr3+ to Cr4+. Higher temperature processing leads to a loss of Cr from the surface region, indicative of its substitution into the bulk
Defect-induced condensation and central peak at elastic phase transitions
Static and dynamical properties of elastic phase transitions under the
influence of short--range defects, which locally increase the transition
temperature, are investigated. Our approach is based on a Ginzburg--Landau
theory for three--dimensional crystals with one--, two-- or three--dimensional
soft sectors, respectively. Systems with a finite concentration of
quenched, randomly placed defects display a phase transition at a temperature
, which can be considerably above the transition temperature
of the pure system. The phonon correlation function is calculated in
single--site approximation. For a dynamical central peak
appears; upon approaching , its height diverges and its width
vanishes. Using an appropriate self--consistent method, we calculate the
spatially inhomogeneous order parameter, the free energy and the specific heat,
as well as the dynamical correlation function in the ordered phase. The
dynamical central peak disappears again as the temperatur is lowered below
. The inhomogeneous order parameter causes a static central
peak in the scattering cross section, with a finite width depending on the
orientation of the external wave vector relative to the soft sector.
The jump in the specific heat at the transition temperatur of the pure system
is smeared out by the influence of the defects, leading to a distinct maximum
instead. In addition, there emerges a tiny discontinuity of the specific heat
at . We also discuss the range of validity of the mean--field
approach, and provide a more realistic estimate for the transition temperature.Comment: 11 pages, 11 ps-figures, to appear in PR
Impact of CP phases on neutrinoless double beta decay
We highlight in a model independent way the dependence of the effective
Majorana mass parameter, relevant for neutrinoless double beta decay, on the CP
phases of the PMNS matrix, using the most recent neutrino data including the
cosmological WMAP measurement. We perform our analysis with three active
neutrino flavours in the context of three kinds of mass spectra:
quasi-degenerate, normal hierarchical and inverted hierarchical. If a
neutrinoless double beta decay experiment records a positive signal, then
assuming that Majorana masses of light neutrinos are responsible for it, we
show how it might be possible to discriminate between the three kinds of
spectra.Comment: 10 pages, latex, 9 eps figs, version to appear in Phys Rev
Effectiveness of recovered magnesium phosphates as fertilizers in neutral and slightly alkaline soils
Magnesium phosphates such as struvite (MgNH4PO4 · 6H2O) can be recovered from municipal, industrial, and agricultural
wastewaters. However, limited information is available on the beneficial reuse of these recovered products; research has focused
on low pH soils. Th is study determined whether recovered struvite and dittmarite (MgNH4PO4 · H2O) were effective P fertilizers
in neutral to slightly alkaline soils. In addition to commercially available triple superphosphate (TSP) and certified organic
rock phosphate (RP), recovered struvite, dittmarite, and a heterogeneous recovered phosphate were evaluated in a laboratory
dissolution study and as fertilizers for spring wheat (Triticum aestivum L.) in a greenhouse study. Struvite and dittmarite were
much more soluble than RP, but less soluble than TSP. Laboratory dissolution kinetics were fast, with most materials nearing
equilibrium within 7 to 14 d. At a soil pH of 6.5, both dittmarite and struvite increased the average plant P concentration over the
control. Struvite and dittmarite performance was similar to TSP. There were no significant differences in plant dry matter (DM)
production or total P uptake at pH 6.5. In the limed soil (pH 7.6), many treatments had plant P concentrations significantly lower
than the control, but most fertilizers increased DM production over the control; all fertilizers generally performed similarly to
one another. These findings support previous work showing recovered Mg phosphates to be effective in acidic soils, and provide
evidence that they are also effective in slightly alkaline soils. Recovered Mg phosphates could become a useful alternative for P
fertilization in arid and semiarid environments
Female sex is a risk factor for painful diabetic peripheral neuropathy: the EURODIAB prospective diabetes complications study
Aims/hypothesis
While the risk factors for diabetic peripheral neuropathy (DPN) are now well recognised, the risk factors for painful DPN remain unknown. We performed analysis of the EURODIAB Prospective Complications Study data to elucidate the incidence and risk factors of painful DPN.
Methods
The EURODIAB Prospective Complications Study recruited 3250 participants with type 1 diabetes who were followed up for 7.3±0.6 (mean ± SD) years. To evaluate DPN, a standardised protocol was used, including clinical assessment, quantitative sensory testing and autonomic function tests. Painful DPN (defined as painful neuropathic symptoms in the legs in participants with confirmed DPN) was assessed at baseline and follow-up.
Results
At baseline, 234 (25.2%) out of 927 participants with DPN had painful DPN. At follow-up, incident DPN developed in 276 (23.5%) of 1172 participants. Of these, 41 (14.9%) had incident painful DPN. Most of the participants who developed incident painful DPN were female (73% vs 48% painless DPN p=0.003) and this remained significant after adjustment for duration of diabetes and HbA1c (OR 2.69 [95% CI 1.41, 6.23], p=0.004). The proportion of participants with macro- or microalbuminuria was lower in those with painful DPN compared with painless DPN (15% vs 34%, p=0.02), and this association remained after adjusting for HbA1c, diabetes duration and sex (p=0.03).
Conclusions/interpretation
In this first prospective study to investigate the risk factors for painful DPN, we definitively demonstrate that female sex is a risk factor for painful DPN. Additionally, there is less evidence of diabetic nephropathy in incident painful, compared with painless, DPN. Thus, painful DPN is not driven by cardiometabolic factors traditionally associated with microvascular disease. Sex differences may therefore play an important role in the pathophysiology of neuropathic pain in diabetes. Future studies need to look at psychosocial, genetic and other factors in the development of painful DPN
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