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On the noncommutative hypergeometric equation

Conflitti, Alessandro; Schlosser, Michael J.
Fonte: Centro de Matemática da Universidade de Coimbra Publicador: Centro de Matemática da Universidade de Coimbra
Tipo: Pré-impressão
Português
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17.13%
Recently, J. A. Tirao [Proc. Nat. Acad. Sci. 100 (14) (2003), 8138–8141] considered a matrix-valued analogue of the 2F1 Gauß hypergeometric function and showed that it is the unique solution of a matrix-valued hypergeometric equation analytic at z = 0 with value I, the identity matrix, at z = 0. We give an independent proof of Tirao’s result, extended to the slightly more general setting of hypergeometric functions over an abstract unital Banach algebra. We provide a similar (but more complicated-looking) result for a second type of noncommutative 2F1 Gauß hypergeometric function.; CMUC; FWF Austrian Science Fund grant P17563–N13; FWF Austrian Science Fund grant P17563–N13; FWF, S9607

Produção de celulases fúngicas por fermentação em estado sólido e submersa utilizando biomassa lignocelulósica

Zanchetta, Ariane
Fonte: Universidade Estadual Paulista (UNESP) Publicador: Universidade Estadual Paulista (UNESP)
Tipo: Dissertação de Mestrado Formato: 88 f. : il.
Português
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Pós-graduação em Microbiologia - IBILCE; O aumento no consumo de combustíveis fósseis e a crescente preocupação ambiental multiplicaram o interesse por tecnologias limpas e de baixo custo, para a obtenção de produtos de valor agregado para as indústrias química, energética e de alimentos. Neste contexto, as enzimas tem sido importantes ferramentas em diversos processos, principalmente no que diz respeito à produção de etanol a partir de materiais lignocelulósicos. Neste trabalho foi avaliado o perfil de produção enzimática dos fungos termofílicos Chaetomium sp. N13, Humicola grisea var. thermoidea e Thermomucor indicae-seudaticae N31 por fermentação em estado sólido (FES) e fermentação submersa (FSm) em bagaço de cana e farelo de trigo (1:1, 1:9 ou 9:1), palha de milho e farelo de trigo (9:1), palha de milho e cevada (9:1), cevada e farelo de trigo (9:1) e, somente farelo de trigo como substratos. No processo de fermentação em estado sólido, a maior produção de xilanase (1569,4 U/g ou 78,5 U/mL) foi obtida por Chaetomium sp. N13 em 240h de cultivo em bagaço de cana e farelo de trigo (1:1). O fungo Humicola grisea var. thermoidea foi o melhor produtor de CMCase (232,8 U/g ou 11,6 U/mL), avicelase (18...

Estudo das propriedades magnéticas de novos compostos intermetálicos de terras raras; Magnetic properties of a new series of rare-earth based intermetallic

Eduardo Matzenbacher Bittar
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Dissertação de Mestrado Formato: application/pdf
Publicado em 28/03/2006 Português
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Primeiramente sintetizados por Remeika et al., para M = Rh, em 1980, os compostos intermetálicos ternários do tipo R3M4S n13, onde R = íon de terra rara e M = metal de transição (por exemplo, Rh, Ir e Co), cristalizam-se em uma estrutura cúbica. Apesar de possuírem uma estrutura cristalina relativamente simples, esses sistemas apresentam uma série de propriedades físicas interessantes que resultam da combinação de interações microscópicas fundamentais tais como: interaçãoes magnéticas tipo RKKY (Ruderman-Kittel-Kasuya-Yosida), efeitos de campo cristalino, acoplamento elétron-fónon e efeito Kondo. Dentro dessas séries, podemos encontrar, por exemplo, materiais supercondutores, férmions pesados, metais com ordenamentos magnéticos e paramagnéticos. Neste trabalho descrevemos o processo de síntese e as propriedades físicas para a série inédita com M = Co, que apesar de possuir suas estruturas catalogadas, jamais teve suas propriedades físicas reportadas (ao menos que tenhamos conhecimento). Monocristais de R3Co4Sn13, onde R = La, Ce, Pr, Nd e Gd, foram crescidos pela técnica de fluxo metálico. A estrutura cristalina desses compostos intermetálicos foi determinada por difração de raios X. Eles se cristalizam em uma estrutura cúbica tipo Yb3Rh4Sn13...

Estudos das lesões de vias medulares através dos potenciais evocados somatossensitivos (PESS) e motores (PEM) em pacientes com mucopolissacaridoses (MPS)

Silva, Daniel de Souza e
Fonte: Instituto Fernandes Figueira Publicador: Instituto Fernandes Figueira
Tipo: Dissertação
Português
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17.13%
As mucopolisacaridoses (MPS) são doenças geneticamente determinadas, causadas pela deficiência de enzimas lisossômicas, o que leva ao acúmulo de glicosaminoglicanos (GAGs) universalmente. As mielopatias cervicais ao nível da junção craniocervical são uma complicação frequente, grave e multifatorial das MPS. Este trabalho teve como principal objetivo o estudo das vias sensitivas e motoras centrais (cordão posterior e trato córtico-espinhal) em topografia medular cervical nos pacientes com mucopolissacaridoses (MPS), utilizando os potenciais evocados somatossensitivos e motores. Como objetivos específicos, a avaliação dos pacientes com MPS em fases distintas da doença, a demonstração da existência de comprometimento da condução nervosa nos trajetos das vias medulares na topografia já mencionada e o destaque do papel dos testes neurofisiológicos (funcionais) no diagnóstico, acompanhamento e na tomada de decisões terapêuticas nos pacientes com MPS. Foi realizado um estudo transversal, de uma série de casos, tendo como metodologia a revisão de prontuários, no Instituto Nacional de Saúde da Mulher, da Criança e do Adolescente Fernandes Figueira. Foram incluídos os pacientes com o diagnóstico de MPS, sem restrições quanto à idade...

Median nerve somatosensory evoked potentials studies on latency variability as a function of subject height, limb length and nerve conduction velocity: estudos de variabilidade das latências em função da altura, comprimento do membro superior e velocidade de condução nervosa.

Brasil-Neto,Joaquim P.
Fonte: Academia Brasileira de Neurologia - ABNEURO Publicador: Academia Brasileira de Neurologia - ABNEURO
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/06/1991 Português
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Report on the results of regression analysis studies concerning median nerve somatosensory evoked potentials (SEPs) latencies, as dependent variables, and subject height, limb length and nerve conduction velocity (NCV), as independent variables. The tests were performed on 23 normal volunteers. Absolute SEP latencies could be predicted by a linear regression model when the independent variable was arm length; when it was subject height, however, both exponential and polynomial models proved better, the Latter showing the best coefficients of determination, R 2. Multiple linear regression with two independent variables (arm length and NCV) was found to be better than simple linear regression for predicting P/N13 latency. The regression line for EP-P/N13 latency on height was found to be a polynomial curve; although the regression was found to be significant by the «F» test (alpha= 1%), the model had a low R2 value (0.41). The same applies to the P/N13-N19 interpeak latency regression curve, but the regression was significant for alpha =5% in that case. Although interwave latencies are the most useful parameters for clinical interpretation of median SEPs, absolute latencies may occasionally be important, and should be corrected for body size; in unusually tall subjects...

Role of the nhaC-encoded Na+/H+ antiporter of alkaliphilic Bacillus firmus OF4.

Ito, M; Guffanti, A A; Zemsky, J; Ivey, D M; Krulwich, T A
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /06/1997 Português
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Application of protoplast transformation and single- and double-crossover mutagenesis protocols to alkaliphilic Bacillus firmus OF4811M (an auxotrophic strain of B. firmus OF4) facilitated the extension of the sequence of the previously cloned nhaC gene, which encodes an Na+/H+ antiporter, and the surrounding region. The nhaC gene is part of a likely 2-gene operon encompassing nhaC and a small gene that was designated nhaS; the operon is preceded by novel direct repeats. The predicted alkaliphile NhaC, based on the extended sequence analysis, would be a membrane protein with 462 amino acid residues and 12 transmembrane segments that is highly homologous to the deduced products of homologous genes of unknown function from Bacillus subtilis and Haemophilus influenzae. The full-length version of nhaC complemented the Na+-sensitive phenotype of an antiporter-deficient mutant strain of Escherichia coli but not the alkali-sensitive growth phenotypes of Na+/H+-deficient mutants of either alkaliphilic B. firmus OF4811M or B. subtilis. Indeed, NhaC has no required role in alkaliphily, inasmuch as the nhaC deletion strain of B. firmus OF4811M, N13, grew well at pH 10.5 at Na+ concentrations equal to or greater than 10 mM. Even at lower Na+ concentrations...

Gene structure and expression of the Corynebacterium flavum N13 ask-asd operon.

Follettie, M T; Peoples, O P; Agoropoulou, C; Sinskey, A J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1993 Português
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Two promoters required for expression of the ask-asd genes, encoding aspartokinase (AK) and aspartate-semialdehyde dehydrogenase (ASD), in Corynebacterium flavum N13, askP1 and askP2, have been identified by deletion analysis and S1 nuclease mapping. Transcription from askP1 initiates 35 and 38 bp upstream of the ask structural gene. A second promoter, askP2, lies within the ask coding region, upstream of the translation start site of the AK beta subunit and can direct the expression of AK beta and ASD. Western immunoblot analysis and heterologous expression in Escherichia coli demonstrate that two separate polypeptides, a 44.8-kDa alpha subunit and an 18.5-kDa beta subunit, are expressed from the C. flavum N13 ask gene from distinct, in-frame translation initiation sites. A second AK mutation, G345D, which reduces the sensitivity of AK to concerted feedback inhibition by threonine plus lysine, was identified.

Investigations on the nervous mechanisms underlying the somatosensory cervical response in man.

Favale, E; Ratto, S; Leandri, M; Abbruzzese, M
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /09/1982 Português
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The main features (amplitude, latency and shape) of the cervical activity evoked by stimulation of the median nerve, recorded throughout the cervical spine, have been concurrently investigated by monopolar, bipolar longitudinal and bipolar transverse recordings. In some subjects the derivation C7-Sn (suprasternal notch) has been employed as well. A comparative evaluation of the refractory period of each component of the cervical responses under investigation has been performed to differentiate presynaptic from postsynaptic events. Additional information has been obtained by cervical activity recorded by longitudinal and transverse bipolar derivations upon stimulation of the lower limb. It was thus demonstrated that both presynaptic and postsynaptic events were responsible for the cervical sensory evoked potential, as appearing when recorded against a cranial reference (that is the upper midfrontal region). The structures involved were the brachial plexus (N9), the cervical roots (P10 and a minor part of N11a), the dorsal columns both at caudal (N11a) and rostral (N11b) cervical levels, and the dorsal column nuclei (N13). However a contribution of the spinal segmental activity to the postsynaptic portion of the cervical response, more specifically to N13...

Short latency evoked potentials: new criteria for brain death?

Facco, E; Casartelli Liviero, M; Munari, M; Toffoletto, F; Baratto, F; Giron, G P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /04/1990 Português
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The aim of this study was to evaluate whether the auditory brain stem responses (ABR) and short latency somatosensory potentials (SEP) from median nerve stimulation are effective tools in the confirmation of brain death. Thirty six brain dead patients were submitted to ABR and 24 to SEP in the same session. All waves of the ABR were absent in 28 (77.8 per cent) patients, while only wave I was present in the others (22.2 per cent). In SEP recordings the components later than P13 were absent in 17 (70.8 per cent) of cases; in the remaining seven patients (29.2 per cent) a N13/P13 dissociation (namely, retention of the cervical N13 and absence of the far-field P13) was found. The results suggest that SEP and ABR are reliable tools in the diagnosis of brain death and should be included in the criteria: they enable the functional status of two pathways in the brainstem to be checked, which cannot be explored by the clinical examination.

Subcomponents of the cervical evoked response in patients with intracerebral circulatory arrest.

Ganes, T; Nakstad, P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1984 Português
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The subcomponents of the cervical evoked response, N11, N13, N14, and the following positivity, were studied in 13 patients with full arrest of the intracerebral circulation, isoelectric EEGs and abolished cortical somatosensory evoked responses. The peak negativity (N13) and the following positive wave were present in all patients. Also N11 and N14 could be identified in most patients either at standard stimulation frequency (2 Hz) or by increasing the stimulation rate. The results point to a spinal origin of these sub-components in the human cervical evoked response.

Somatosensory evoked potentials following nerve and segmental stimulation do not confirm cervical radiculopathy with sensory deficit.

Schmid, U D; Hess, C W; Ludin, H P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /02/1988 Português
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Twenty eight patients with unilateral cervical radiculopathy were studied by somatosensory evoked potentials (SEPs) from nerve stimulation at the wrist and from skin stimulation at the first, third or fifth finger depending on the root involved. In order to evaluate the reliability of various "radicular SEP patterns" as described in the literature, absolute latencies and side-to-side differences of the brachial plexus component from the supraclavicular fossa (N9), the medullary component (N13) from the cervical vertebra Cv7, and the primary cortical component (N20, P25) were assessed. Side-to-side differences of the amplitudes of N20/P25 and of the conduction times across the intervertebral fossa (interval N9-N13) were analysed. After nerve stimulation, 68% of the patients had false negative findings on the symptomatic, while 36% had positive findings on the asymptomatic side. After segmental stimulation, 72% of the patients had false negative findings on the symptomatic, while 22% had positive findings on the asymptomatic side. It is concluded that SEPs following nerve and segmental stimulation do not reliably confirm clear-cut already established diagnoses of unilateral radiculopathy with sensory and motor deficit. Therefore, they will not be helpful in the electrophysiological investigation of cervicobrachialgias of unknown origin.

Use of the COOH Portion of the Nucleocapsid Protein in an Antigen-Capturing Enzyme-Linked Immunosorbent Assay for Specific and Sensitive Detection of Severe Acute Respiratory Syndrome Coronavirus

Qiu, Maofeng; Wang, Jin; Wang, Hongxia; Chen, Zeliang; Dai, Erhei; Guo, Zhaobiao; Wang, Xiaoyi; Pang, Xin; Fan, Baoxing; Wen, Jie; Wang, Jian; Yang, Ruifu
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /03/2005 Português
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Antibody detection with a recombinant COOH portion of the severe acute respiratory syndrome (SARS) coronavirus nucleocapsid (N) protein, N13 (amino acids 221 to 422), was demonstrated to be more specific and sensitive than that with the full-length N protein, and an N13-based antigen-capturing enzyme-linked immunosorbent assay providing a convenient and specific test for serodiagnosis and epidemiological study of SARS was developed.

Somatosensory evoked potentials after multisegmental upper limb stimulation in diagnosis of cervical spondylotic myelopathy.

Restuccia, D; Valeriani, M; Di Lazzaro, V; Tonali, P; Mauguière, F
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1994 Português
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Radial, median, and ulnar nerve somatosensory evoked potentials (SEPs) were recorded, with non-cephalic reference montage, in 38 patients with clinical signs of cervical myelopathy and MRI evidence of spondylotic compression of the cervical cord. Upper limb SEPs are useful in spondylotic myelopathy because SEPs were abnormal in all patients for at least one of the stimulated nerves and SEP abnormalities were bilateral in all patients but one. Reduction of the amplitude of the N13 potential indicating a segmental dysfunction of the cervical cord was the most frequent abnormality; it occurred in 93.4%, 84.2%, and 64.5% of radial, median, and ulnar nerve SEPs respectively. A second finding was that the P14 far-field potential was more sensitive than the cortical N20 potential to slowing of conduction in the dorsal column fibres. The high percentage of N13 abnormalities in the radial and median rather than in the ulnar nerve SEPs correlated well with the radiological compression level, mainly involving the C5-C6 vertebral segments. Therefore the recording of the N13 response is a reliable diagnostic tool in patients with cervical spondylotic myelopathy and P14 abnormalities, though less frequent, can be useful in assessing subclinical dorsal column dysfunction.

Distinct Transport and Intracellular Activities of Two GlcAT-P Isoforms*S⃞

Kizuka, Yasuhiko; Tonoyama, Yasuhiro; Oka, Shogo
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Publicado em 03/04/2009 Português
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17.62%
A neural glycotope, human natural killer-1 carbohydrate, is involved in synaptic plasticity. The key biosynthetic enzyme is a glucuronyltransferase, GlcAT-P, a type II membrane protein comprising an N-terminal cytoplasmic tail, transmembrane domain, stem region, and C-terminal catalytic domain. Previously, we reported that GlcAT-P has two isoforms differing in only the presence or absence of the N-terminal 13 amino acids (P-N13) in the cytoplasmic tail, but the functional distinction of these two isoforms has not been reported. Herein, we show that when expressed in Neuro2A cells, short form GlcAT-P (sGlcAT-P) exhibited significantly higher glucuronylation activity than the longer form (lGlcAT-P), despite their comparable specific activities in vitro. In addition, sGlcAT-P was strictly localized in Golgi apparatus, whereas lGlcAT-P was mainly localized in Golgi but partly in the endoplasmic reticulum. We demonstrated that the small GTPase, Sar1, recognized a dibasic motif in the cytoplasmic tail near P-N13 that was important for exiting the endoplasmic reticulum, and Sar1 interacted with sGlcAT-P more strongly than lGlcAT-P. Finally, the attachment of P-N13 to another glycosyltransferase, polysialyltransferase-I (ST8Sia-IV)...

Substrate Specificity, Membrane Topology, and Activity Regulation of Human Alkaline Ceramidase 2 (ACER2)*

Sun, Wei; Jin, Junfei; Xu, Ruijuan; Hu, Wei; Szulc, Zdzislaw M.; Bielawski, Jacek; Obeid, Lina M.; Mao, Cungui
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Português
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17.43%
Human alkaline ceramidase 2 (ACER2) plays an important role in cellular responses by regulating the hydrolysis of ceramides in cells. Here we report its biochemical characterization, membrane topology, and activity regulation. Recombinant ACER2 was expressed in yeast mutant cells (Δypc1Δydc1) that lack endogenous ceramidase activity, and microsomes from ACER2-expressiong yeast cells were used to biochemically characterize ACER2. ACER2 catalyzed the hydrolysis of various ceramides and followed Michaelis-Menten kinetics. ACER2 required Ca2+ for both its in vitro and cellular activities. ACER2 has 7 putative transmembrane domains, and its amino (N) and carboxyl (C) termini were found to be oriented in the lumen of the Golgi complex and cytosol, respectively. ACER2 mutant (ACER2ΔN36) lacking the N-terminal tail (the first 36 amino acid residues) exhibited undetectable activity and was mislocalized to the endoplasmic reticulum, suggesting that the N-terminal tail is necessary for both ACER2 activity and Golgi localization. ACER2 mutant (ACER2ΔN13) lacking the first 13 residues was also mislocalized to the endoplasmic reticulum although it retained ceramidase activity. Overexpression of ACER2, ACER2ΔN13, but not ACER2ΔN36 increased the release of sphingosine 1-phosphate from cells...

Near-IR Resonance Raman Spectroscopy of Archaerhodopsin 3: Effects of Transmembrane Potential

Saint Clair, Erica C.; Ogren, John I.; Mamaev, Sergey; Russano, Daniel; Kralj, Joel M.; Rothschild, Kenneth J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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17.43%
Archaerhodopsin 3 (AR3) is a light driven proton pump from Halorubrum sodomense that has been used as a genetically targetable neuronal silencer and an effective fluorescent sensor of transmembrane potential. Unlike the more extensively studied bacteriorhodopsin (BR) from Halobacterium salinarum, AR3 readily incorporates into the plasma membrane of both E. coli and mammalian cells. Here, we used near-IR resonance Raman confocal microscopy to study the effects of pH and membrane potential on the AR3 retinal chromophore structure. Measurements were performed both on AR3 reconstituted into E. coli polar lipids and in vivo in E. coli expressing AR3 in the absence and presence of a negative transmembrane potential. The retinal chromophore structure of AR3 is in an all-trans configuration almost identical to BR over the entire pH range from 3–11. Small changes are detected in the retinal ethylenic stretching frequency and Schiff Base (SB) hydrogen bonding strength relative to BR which may be related to a different water structure near the SB. In the case of the AR3 mutant D95N, at neutral pH an all-trans retinal O-like species (Oall-trans) is found. At higher pH a second 13-cis retinal N-like species (N13-cis) is detected which is attributed to a slowly decaying intermediate in the red-light photocycle of D95N. However...

An investigation of the level structure of nitrogen-14 by the bombardment of carbon-13 with protons

Belote, Thomas A.
Fonte: Universidade Rice Publicador: Universidade Rice
Português
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17.43%
States in N14 in the region of excitation energy between 10.6 and 12.2 Mev have been studied by means of the C 13(p,n)N13, C13(p,d)C12, and C13(p,p1)C13* reactions. The C13(p,n)N13 total cross section has been measured from threshold, Eplab = 3.236, to 5.2 Mev in 30-kev steps by measuring the activation of the N13(half life = 10.1 min). The differential cross sections for the C13(p,d)C 12 and C13(p,p1)C13* reactions have been taken at center of mass angles near thetacm = 90° and 160°. This data along with that of Kashy et al., of the elastically scattered protons from C13 have been analyzed. Reaction-particle widths for the 11.05 (1+), 11.240 (3 -), 11.30 (2-), 11.39 (1+), and 11.503 (3+) states assigned from the elastic scattering data have been determined. Resonances at Eplab = 4.50 Mev (Gamma = 140 kev) 4.58 (Gamma = 60), 4.76 (Gamma = 320) and 5.04 (Gamma = 320) corresponding to levels at 11.72, 11.80, 11.96 and 12.22 Mev with assignments of 1-, 2+, 2 -, and 3- have also been investigated. Reaction particle-widths for these states have also been determined.

An organizational analysis of the Military (Navy) Personnel Plans and Policy Division (N13)

Bruner, Bradley D.
Fonte: Monterey, California. Naval Postgraduate School Publicador: Monterey, California. Naval Postgraduate School
Tipo: Tese de Doutorado
Português
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27.84%
This thesis is a descriptive organization analysis of N13, the Military (Navy) Personnel Plans and Policy Division. The purpose of the study was to describe the strategy, structure, processes, tasks, people, and culture of Nl3 using three models: the Systems model; the Configuration model, and, the Mintzberg model. Based on model comparisons, document reviews, semi-structured interviews and questionnaire responses of N13 leaders and managers, conclusions indicate that N13 is severely stressed due to personnel reductions and a partial relocation of BUPERS to Millington, Tennessee. N13 is struggling to cope with fast-changing 199Os problems using a post Cold War, Political-Reactive configuration. Recommendations are offered to assist leaders and managers in making systematic change to improve the efficiency and effectiveness of N13 as well as the manpower and personnel system. Specific recommendations include; realignment to a team-based community approach vice the current fragmented and duplicative approach; divestiture of non-core areas; and creation of a realistic training program tailored to rapidly enhance individual knowledge and skill sets.

Establishment of ANSI N13.11 X-ray radiation fields for personal dosimetry performance test by computation and experiment.

Kim, J L; Kim, B H; Chang, S Y; Lee, J K
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /12/1997 Português
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This paper describes establishment by computational and experimental methods of the American National Standard Institute (ANSI) N13.11 X-ray radiation fields by the Korea Atomic Energy Research Institute (KAERI). These fields were used in the standard irradiations of various personal dosimeters for the personal dosimetry performance test program performed by the Ministry of Science and Technology of Korea in the autumn of 1995. Theoretical X-ray spectra produced from two KAERI X-ray generators were estimated using a modified Kramers' theory with target attenuation and backscatter correction and their spectral distributions experimentally measured by a high-purity germanium semiconductor detector through proper corrections for measured pulse height distributions with photopeak efficiency, Compton fraction, and K-escape fraction. The average energies and conversion coefficients obtained from the computation and experimental methods, when compared with ANSI N13.11 and the recently published National Institute of Standards and Technology X-ray beams, appeared to be in good agreement--(+/-)3% between corresponding values--and thus, could be satisfactorily applied in the performance test of personal dosimeters.

The cross section for the radiative capture of protons by C12 near 100 Kev

Hall, Robert Noel; Fowler, William Alfred
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 15/01/1950 Português
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A low voltage accelerator and high current ion source has been used to determine the cross section of the reaction C12(pγ)N13 over the energy range from 88 to 128 kev. A counter arrangement is described which detects 26 percent of all the positrons from the decay of the N13 produced in the reaction and which has a low background rate of 5.5 counts per minute. With this accelerator and detector, yields of the order of 10^-16 positron per proton and cross sections as low as 10^-10 barn or 10^-34 cm^2 can be measured with errors of the order of ±20 percent. The cross section for the C12(pγ)N13 reaction has been found to fit the semi-empirical expression σ=0.0024E^-1exp[-6E^-1/2] barn with E in Mev over the energy range measured. This is in satisfactory agreement with the Breit-Wigner one-level dispersion formula using constants determined at the 456-kev resonance. The astrophysical implications of these results in connection with the carbon-nitrogen cycle of nuclear reactions in stellar interiors are discussed.