216 research outputs found
Ga self-interstitials in GaN investigated by ab-initio calculations of the electronic g-tensor
No full textIn GaN, an exceptionally important role is played by Ga-interstitials being mobile at room temperature: Despite rather large formation energy, they have been observed in irradiated uurtzite-GaN: at least two similar, but clearly distict ODEPR-signals L5 and L6/L6* have been identified (via exceptionally large, nearly isotropic hyperfine splittings of about 4 GHz) as interstitial Ga-i(2+) in two diffent lattice configurations. However, judging from experimental data and total energy calculations alone, the exact microscopic configuration remains unclear. In this theoretical work, the situation is elucidated by ab-initio calculating the complete set of EPR parameters, hyperfine splittings as well as g-tensors, for the stable structural configurations of the Ga-interstitial using a gauge-including projector augmented plane wave (GI-PAW) approach. (c) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Uranium and thorium in soils, mineral sands, water and food samples in a tin mining area in Nigeria with elevated activity
No full textThe activity concentrations of uranium and thorium have been determined in soils and mineral sands from the Nigerian tin mining area of Bisichi, located in the Jos Plateau, and from two control areas in Nigeria (Jos City and Akure) using high-purity germanium detectors (HPGe). High resolution sector field inductively coupled plasma mass spectroscopy (HR-SF-ICP-MS) was used to determine uranium and thorium in liquids and foodstuffs consumed locally in the mining area. The activities of uranium and thorium measured in the soils and mineral sands from Bisichi ranged from 8.7 kBq kg−1 to 51 kBq kg−1 for 238U and from 16.8 kBq kg−1 to 98 kBq kg−1 for 232Th, respectively. These values were significantly higher than those in the control areas of Jos City and Akure and than the reference values reported in the literature. They even exceeded the concentrations reported for areas of high natural radioactive background. Radionuclide concentrations in samples of the local foodstuffs and in water samples collected in Bisichi were found to be higher than UNSCEAR reference values. The results reveal the pollution potential of the mining activities on the surrounding areas
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Campus sexual assault ::constitutional rights and fundamental fairness /
No full textSexual assault on college campuses has drawn tremendous public attention and colleges are under great pressure to respond. In many cases, the result has been a system of sexual assault tribunals that violates the rights of alleged assailants and assault survivors. Gerstmann shows how colleges are often punishing students as sex offenders without a fair hearing and are defining sexual offenses in an unconstitutionally broad manner. Using unbiased and accessible language, this book avoids easy answers and asks: how are colleges failing to assess accusations in a fair manner? Why are 'affirmative consent' laws unconstitutional? How can we do a better job preventing sexual assault? The author argues that colleges are too often making poor choices in terms of how they respond to allegations of sexual assault and, in doing so, they are depriving students of due process, while failing to protect victims of assault
Síndrome de gerstmann de desenvolvimento associada a neoplasia cerebelar: relato de um caso e revisão da literatura Developmental Gerstmann syndrome associated with cerebellar neoplasm: a case report with review of litterature
No full textÉ relatado um caso de síndrome de Gerstmann de Desenvolvimento, que apresentava acalculia, agrafía, confusão direita-esquerda, agnosia de dedos e apraxia construcional, em um menino de 7 anos. O tratamento inicial com metilfenidato determinou bons resultados no que concerne à hiperatividade, à atenção e à apraxia construcional. Durante o curso clínico, o paciente apresentou sintomatologia cerebelar, hipertensão intracraniana, tendo sido feita intervenção cirúrgica na fossa posterior, sendo excisado um meduloblastoma de cerebelo. O autor acredita que é esta a primeira descrição na literatura da concomitância da síndrome de Gerstmann de Desenvolvimento e neoplasia de fossa posterior. São feitos comentários focalizando cada um dos aspectos clínicos, fatores etiológicos e topográficos.A Developmental Gerstmann syndrome in a 7 years-old-boy with hyperactivity, short attention span, acalculia, agraphia, right-left confusion, finger agnosia and constructional apraxia is reported. An initial trial with methylphenidate was done with good improvement regarding hyperactivity, attention span and constructional apraxia. In the clinical course developed a cerebellar syndrome and intracranial hypertension. Surgical exploration of the cerebellum discovered a medulloblastoma. The author believes that this is the first described association of Developmental Gerstmann syndrome and cerebellar neoplasia. The clinical findings, the etiology and the topography of the Gerstmann syndrome are discussed
Inventory and geochemical host phases of natural radionuclides in tin mining materials from Nigeria
No full textOn the Nigerian Jos Plateau tin mining is extensively carried out in open pit style. Several types of materials occurring there (raw materials, waste, and soil) were analysed radiometrically. The geochemical host phases of the natural radionuclides were determined by a sequential extraction procedure according to the European BCR standard. It was found that especially easily mobilisable 228Ra must be taken into consideration as a radioactive contaminant for the mining are
Gerstmann-Sträussler-Scheinker Disease
No full textGerstmann-Sträussler-Scheinker disease (GSS) is a hereditary form of prion disease. GSS, in particular the form caused by the PRNP gene P102L mutation, is transmissible to primates and rodents. Thus, GSS is a unique disease that is both genetic and transmissible; however, the exact nature of the transmissible agent is not clear. The clinical picture of GSS comprises cerebellar ataxia, dementia and pyramidal and extrapyramidal signs and symptoms. However, the disease is heterogeneous and in different families and different mutations the clinical picture may vary. The neuropathological picture is characterized by the presence of amyloid plaques – mainly multicentric plaques. There are several models of GSS in transgenic mice and in Drosophila sp. In mice produced with an overexpressed transgene that carries the P101L mutation (corresponding to the P102L mutation in humans), “spontaneous” neurodegeneration is observed and this, in turn, is transmissible but to transgenic mice with a low copy number. In contrast, P101L transgenic mice produced by means of reciprocal recombination show no spontaneous neurodegeneration, but instead become more susceptible to transmission of human GSS following inoculation.Choroba Gerstmanna-Sträusslera-Scheinkera (GSS) jest genetycznie uwarunkowaną chorobą wywoływaną przez priony. Jest ona unikalna, ponieważ udało się przepasażować GSS na naczelne i gryzonie przynajmniej z mózgu obarczonego mutacją kodonu 102. Tym samym jest to jedyne schorzenie jednocześnie genetycznie uwarunkowane i zakaźne, aczkolwiek natura czynnika infekcyjnego (prionu) nadal stanowi przedmiot dyskusji. W obrazie klinicznym GSS dominuje postępująca ataksja móżdżkowa z towarzyszącym otępieniem i objawami piramidowo-pozapiramidowymi. Jest to jednak choroba heterogenna, o różnym obrazie klinicznym u nosicieli różnych mutacji, a nawet u nosicieli tej samej mutacji. Obraz neuropatologiczny obejmuje obecność PrPd – immunododatnich złogów amyloidu pod postacią blaszek, zwłaszcza tzw. blaszek wielordzeniowych. Istnieje kilka modeli GSS. U myszy transgenicznych z nadekspresją zmutowanego genu kodującego PrP obserwuje się spontaniczną chorobę zwyrodnieniową, pasażowalną na myszy transgeniczne o niskiej liczbie transgenu. U myszy transgenicznych uzyskanych drogą wzajemnej rekombinacji, a więc bez nadeskpresji, nie występuje choroba spontaniczna, niemniej stają się one wrażliwe na zakażenie GSS
Measurement techniques for tracer kinetic studies with stable isotopes of zirconium
No full textBiokinetic models are used in radiation protection to assess internal radiation doses. Experiments with stable isotopes as tracers can be performed to obtain characteristic parameters of these models. Two methods for the measurement of zirconium isotopes in human biological samples are presented - thermal ionisation mass spectrometry (TIMS) and proton nuclear activation analysis (PNA). Descriptions include sample preparation, operating conditions, relative uncertainties and method detection limits as well as important properties of both methods
Nitrogen donor aggregation in 4H-SiC: g-tensor calculations
No full textThe microscopic origin of the N-x EPR-lines observed in heavily nitrogen doped 4H-SiC and 6H-SiC is discussed with the help of EPR parameters calculated from first principles. Based on the symmetry of the g-tensors we propose a model with distant N-C donor pairs on inequivalent lattice sites which are coupled to S=1 centers but with nearly vanishing zero-field splittings, giving rise to an essentially S=1/2 like spectrum. The proposed aggregation in neutral donor pairs can contribute to the saturation of the free concentration observed in heavily nitrogen doped SiC
An insert mutation in the chromosome 20 amyloid precursor gene in a Gerstmann-Straussler-Scheinker family
No full textWe report the finding of an insert mutation in the chromosome 20 amyloid precursor gene in a family with neuropathologically-verified, experimentally-transmitted Gerstmann-Straussler-Scheinker syndrome (GSS). The insert consisted of 8 extra copies of a repeating octapeptide coding sequence in the region between codons 51 and 91; it was identified in the proband and a presently unaffected at-risk niece by full sequencing of the open reading frame, and was visualized electrophoretically in the proband and 6 of 12 at-risk relatives. Although affected members in this French-Breton family have shown a variety of clinical profiles, including durations of illness that ranged from 3 months to 13 years, all autopsied cases (including the patient with the shortest illness) have had the distinctive multicentric amyloid plaques that define GSS as a nosologic entity
New insight in scandium-mediated growth techniques: Sc-related defects in 4H-SiC and 6H-SiC
No full textScandium can be used to influence the stoichiometry of SiC during growth of the hexagonal polytypes. Using PL-EPR and total energy calculations in the framework of density functional theory, scandiurn is predicted to be built in predominantly at the Si-sublattice in form of Sc-Si acceptors with acceptor levels at 0.55 eV (6H-SiC) and 0.48 eV (4H-SiC). In addition, new PL-EPR spectra are found with a large anisotropy in the g-tensor suggesting defect pairs as an origin
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