3,099 research outputs found
Searching for hexagonal analogues of the half-metallic half-Heusler XYZ compounds
The XYZ half-Heusler crystal structure can conveniently be described as a
tetrahedral zinc blende YZ structure which is stuffed by a slightly ionic X
species. This description is well suited to understand the electronic structure
of semiconducting 8-electron compounds such as LiAlSi (formulated
Li[AlSi]) or semiconducting 18-electron compounds such as TiCoSb
(formulated Ti[CoSb]). The basis for this is that [AlSi]
(with the same electron count as Si) and [CoSb] (the same electron
count as GaSb), are both structurally and electronically, zinc-blende
semiconductors. The electronic structure of half-metallic ferromagnets in this
structure type can then be described as semiconductors with stuffing magnetic
ions which have a local moment: For example, 22 electron MnNiSb can be written
Mn[NiSb]. The tendency in the 18 electron compound for a
semiconducting gap -- believed to arise from strong covalency -- is carried
over in MnNiSb to a tendency for a gap in one spin direction. Here we similarly
propose the systematic examination of 18-electron hexagonal compounds for
semiconducting gaps; these would be the "stuffed wurtzite" analogues of the
"stuffed zinc blende" half-Heusler compounds. These semiconductors could then
serve as the basis for possibly new families of half-metallic compounds,
attained through appropriate replacement of non-magnetic ions by magnetic ones.
These semiconductors and semimetals with tunable charge carrier concentrations
could also be interesting in the context of magnetoresistive and thermoelectric
materials.Comment: 11 pages, 6 figures, of which 4 are colou
Systematical, experimental investigations on LiMgZ (Z= P, As, Sb) wide band gap semiconductors
This work reports on the experimental investigation of the wide band gap
compounds LiMgZ (Z = P, As, Sb), which are promising candidates for
opto-electronics and anode materials for Lithium batteries. The compounds
crystallize in the cubic (C1_b) MgAgAs structure (space group F-43m). The
polycrystalline samples were synthesized by solid state reaction methods. X-ray
and neutron diffraction measurements show a homogeneous, single-phased samples.
The electronic properties were studied using the direct current (DC) method.
Additionally UV-VIS diffuse reflectance spectra were recorded in order to
investigate the band gap nature. The measurements show that all compounds
exhibit semiconducting behavior with direct band gaps of 1.0 eV to 2.3 eV
depending on the Z element. A decrease of the peak widths in the static 7Li
nuclear magnetic resonance (NMR) spectra with increasing temperature was
observed, which can directly be related to an increase of Li ion mobility.Comment: 8 page
Increased Hepato-Splanchnic Vasoconstriction in Diabetics during Regular Hemodialysis
BACKGROUND AND OBJECTIVES:Ultrafiltration (UF) of excess fluid activates numerous compensatory mechanisms during hemodialysis (HD). The increase of both total peripheral and splanchnic vascular resistance is considered essential in maintaining hemodynamic stability. The aim of this study was to evaluate the extent of UF-induced changes in hepato-splanchnic blood flow and resistance in a group of maintenance HD patients during regular dialysis. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS:Hepato-splanchnic flow resistance index (RI) and hepato-splanchnic perfusion index (QI) were measured in 12 chronic HD patients using a modified, non-invasive Indocyaningreen (ICG) dilution method. During a midweek dialysis session we determined RI, QI, ICG disappearance rate (kICG), plasma volume (Vp), hematocrit (Hct), mean arterial blood pressure (MAP) and heart rate (HR) at four times in hourly intervals (t1 to t4). Dialysis settings were standardized and all patient studies were done in duplicate. RESULTS:In the whole study group mean UF volume was 1.86 ± 0.46 L, Vp dropped from 3.65 ± 0.77L at t1 to 3.40 ± 0.78L at t4, and all patients remained hemodynamically stable. In all patients RI significantly increased from 12.40 ± 4.21 mmHg∙s∙m2/mL at t1 to 14.94 ± 6.36 mmHg∙s∙m2/mL at t4 while QI significantly decreased from 0.61 ± 0.22 at t1 to 0.52 ± 0.20 L/min/m2 at t4, indicating active vasoconstriction. In diabetic subjects, however, RI was significantly larger than in non-diabetics at all time points. QI was lower in diabetic subjects. CONCLUSIONS:In chronic HD-patients hepato-splanchnic blood flow substantially decreases during moderate UF as a result of an active splanchnic vasoconstriction. Our data indicate that diabetic HD-patients are particularly prone to splanchnic ischemia and might therefore have an increased risk for bacterial translocation, endotoxemia and systemic inflammation
Measuring Atmospheric Neutrino Oscillations with Neutrino Telescopes
Neutrino telescopes with large detection volumes can demonstrate that the
current indications of neutrino oscillation are correct or if a better
description can be achieved with non-standard alternatives. Observations of
contained muons produced by atmospheric neutrinos can better constrain the
allowed region for oscillations or determine the relevant parameters of
non-standard models. We analyze the possibility of neutrino telescopes
measuring atmospheric neutrino oscillations. We suggest adjustments to improve
this potential. An addition of four densely-instrumented strings to the AMANDA
II detector makes observations feasible. Such a configuration is competitive
with current and proposed experiments.Comment: 36 pages, 21 figures, revte
Lepton Flavor Violation at the LHC
Recent results from Super Kamiokande suggest mixing and
hence lepton flavor violation. In supersymmetric models, this flavor violation
may have implications for the pattern of slepton masses and mixings. Possible
signals for this mixing in the decays of sleptons produced at the LHC are
discussed. The sensitivity expected is compared to that of rare decays such as
.Comment: 14 pages, 9 figure
RNA from stabilized whole blood enables more comprehensive immune gene expression profiling compared to RNA from peripheral blood mononuclear cells
Monitoring changes in the immune profile in blood samples can help identifying changes in
tumor biology and therapy responsiveness over time. Immune-related gene expression profiles offer a highly reproducible method to monitor changes of the immune system. However,
measuring gene expression profiles in whole blood samples can be complicated because of
the high protein and enzyme abundancy that affect the stability and quality of the RNA.
Peripheral blood mononuclear cells (PBMCs) are one the most commonly used source for
immune cell RNA extraction, though, this method does not reflect all components of the
peripheral blood. The aim of this study was to determine the differences in immune-related
gene expression between RNA isolated from stabilized whole blood and RNA isolated from
PBMCs. Whole blood samples from 12 pancreatic cancer patients were collected before
and after chemotherapy (n = 24). Blood samples were collected in both EDTA tubes, and
Tempus tubes containing an RNA stabilizer (total n = 48). PBMCs were isolated from EDTA
samples using Ficoll and were snap frozen. Subsequently, immune-related gene expression
was profiled using the PanCancer Immune Profiling Panel of NanoString technology. Gene
expression profiles of PBMCs were compared to that of Tempus tubes using the Advanced
Analysis module of nSolver software. Both types of samples provided good quality RNA and
gene expression measurements. However, RNA isolated from Tempus tubes resulted in
significantly higher gene counts than PBMCs; 107/730 genes were exclusively detected in
Tempus samples, while under the detection limit in PBMCs. In addition, 192/730 genes
showed significantly higher gene counts in Tempus samples, 157/730 genes showed higher
gene counts in PBMCs. Thus, RNA isolated from whole blood stabilizing blood tubes, such
as Tempus tubes, enable higher gene counts and more comprehensive measurements of
gene expression profiles compared to RNA isolated from PBMCs
Solutions of the atmospheric, solar and LSND neutrino anomalies from TeV scale quark-lepton unification
There is a unique gauge model which
allows quarks and leptons to be unified at the TeV scale. It is already known
that the neutrino masses arise radiatively in the model and are naturally
light. We study the atmospheric, solar and LSND neutrino anomalies within the
framework of this model.Comment: Minor changes, 31 page
Positivity constraints for lepton polarization in neutrino deep inelastic scattering
We consider the spin polarization of leptons produced in neutrino and
antineutrino nucleon deep inelastic scattering, via charged currents, and we
study the positivity constraints on the spin components in a model independent
way. These results are very important, in particular in the case of
leptons, because the polarization information is crucial in all
future neutrino oscillation experiments.Comment: 14 pages, 4 figure
Testing maximal electron and muon neutrino oscillations with sub-GeV SuperKamiokande atmospheric neutrino data
Motivated by the Exact Parity Model and other theories, the hypothesis that
each of the known neutrinos oscillates maximally with a sterile partner has
been put forward as an explanation of the atmospheric and solar neutrino
anomalies. We provide detailed predictions for muon and electron flux ratios
induced in the Kamiokande and SuperKamiokande detectors by sub-GeV atmospheric
neutrinos. Several different, carefully chosen cuts on momentum and zenith
angle are proposed, emphasizing the role of up-down flux asymmetries.Comment: LaTeX, 8 figures, 17 pages, version to appear in Phys. Rev. D Rapid
Communication
Investigation into cardiac sympathetic innervation during the commencement of haemodialysis in patients with chronic kidney disease
Background: Patients with chronic kidney disease (CKD) who undergo chronic haemodialysis (HD) show altered sympathetic tone, which is related to a higher cardiovascular mortality. The purpose of this study was to investigate the effect of transition from pre-HD to HD on cardiac sympathetic innervation. Methods: Eighteen patients aged 58 ± 18 years (mean ± standard deviation [SD]), 13 males and five females, with stage 5 CKD and nine healthy control subjects aged 52 ± 17 (mean ± SD), three males and six females, were included in this prospective study between May 2010 and December 2013. All patients underwent 123I-labelled meta-iodobenzylguanidine (123I-MIBG) scintigraphy for cardiac sympathetic innervation and electrocardiographically gated adenosine stress and rest 99mTc-labelled tetrofosmin single-photon emission computed tomography for myocardial perfusion imaging prior to (pre-HD) and 6 months after the start of HD. Results of 123I-MIBG scans in patients were compared to controls. Impaired cardiac sympathetic innervation was defined as late heart-to-mediastinum ratio (HMR) < 2.0. Results: Mean late HMR was lower in patients during HD (2.3) than in controls (2.9) (p = 0.035); however, in patients it did not differ between pre-HD and after the start of HD. During HD, two patients showed new sympathetic innervation abnormalities, and in three patients innervation abnormalities seemed to coincide with myocardial perfusion abnormalities. Conclusions: CKD patients show cardiac sympathetic innervation abnormalities, which do not seem to progress during the maintenance HD. The relationship between sympathetic innervation abnormalities and myocardial perfusion abnormalities in HD patients needs further exploration
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