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Efficiency of partial treatment of cattle infested with horn fly using 40% diazinon

Almeida, Fabiana Alves de; Alari, Fernando de Oliveira; Seno, Maria Conceicao Zocoller; Lima, Marco Monteiro de; Nascimento, Sheila Tavares; Chiquitelli Neto, Marcos
Fonte: Colégio Brasileiro de Parasitologia Veterinária Publicador: Colégio Brasileiro de Parasitologia Veterinária
Tipo: Artigo de Revista Científica Formato: 554-558
Português
Relevância na Pesquisa
18.26%
Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP); The aim of this investigation was to evaluate the efficiency of partial treatment of animals infested with horn flies. Forty-five Guzerat cows between 4 and 7 years of age were divided into three groups (15 cows per group). The treatments were as follows: in groups G33 and G100, 33.3 and 100% of the cows were treated with one insecticide-impregnated ear tag/animal (40% diazinon), respectively, while in the group GC, the cows were not treated (control). The flies on the cervico-dorsal-lumbar region of the cows, in all three groups, were counted every 14 days. The experiment lasted from September 2006 to September 2009. Over this period, six four-month ear tag treatments, with intervals of one to two months, were conducted on both treated groups. The animals of group G33 had a higher infection than those of group G100, and the number of flies ranged from 12 to 27 (group G33) and from 3 to 11 (group G100). However, groups G33 and G100 had lower infection levels than group GC, which presented from 45 to 87 flies. Partial treatment of cattle infested with horn flies using 40% diazinon insecticide is an efficient alternative for controlling this ectoparasite.; Com objetivo de avaliar a eficiência do tratamento parcial de animais infestados por mosca-dos-chifres...

Electromechanical properties of textured K0.5Na0.5NbO3 ceramics; Propriedades electromecânicas de cerâmicos de K0.5Na0.5NbO3 texturizado

Pinho, Rui Manuel de Oliveira
Fonte: Universidade de Aveiro Publicador: Universidade de Aveiro
Tipo: Dissertação de Mestrado
Português
Relevância na Pesquisa
17.31%
This work is about lead-free ceramic materials intended for electromechanical applications and candidates to replace lead-based electroceramics. One of the most widely used piezoelectric ceramics is lead zirconate titanate (PZT). However, it contains more than 60% of lead and it is toxic for humans and environment. In 2003, a directive from European Union has prohibited the use of potentially hazardous elements as lead. Due to the lack of competitive materials for PZT replacement an exception was created until a competitive alternative be found. Potassium and sodium niobate due to its high Curie temperature and moderate piezoelectric properties is currently one of the most promising lead-free materials for PZT substitution. However, its effective industrial adoption requires, among others, optimization of its properties. In this context, in this work we initially studied the effect of dopants, texturing and sintering temperature of KNN ceramics. For this purpose KNN ceramics doped with i) 1.5 mol% CuO + 2.0 mol% Li2O, ii) 1.5 mol% CuO + 4.0 mol% Li2O and iii) 1.5 mol% CuO + 0.5 mol% MnO using different sintering temperatures (1050, 1065 and 1080 °C) were prepared. In addition in order to maximize the preferential crystallographic orientation of the ceramic KNN (texturing)...

Why standard risk models failed in the subprime crisis? An approach based on Extreme Value Theory as a measure to quantify market risk of equity securities and portfolios

Marques, Áurea Ponte
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2010 Português
Relevância na Pesquisa
16.68%
Mestrado em Finanças / JEL classification: G01, G21, G24, G28, G32, G33; The assessment of risk is an important and complex task with which market regulators and financial institutions are faced, especially after the last subprime crisis. It is argued that since market data is endogenous to market behaviour, statistical analysis made in times of stability does not provide much guidance in times of crisis. It is well known that the use of Gaussian models to assess financial risk leads to an underestimation of risk. The reason is because these models are unable to capture some important facts such as heavy tails which indicate the presence of large fluctuations in returns. This thesis provides an overview of the role of extreme value theory in risk management, as a method for modelling and measuring extreme risks. In this empirical study, the performance of different models in estimating value at risk and expected tail loss, using historical data, are compared. Daily returns of nine popular indices (PSI20, CAC40, DAX, Nikkei225, FTSE100, S&P500, Nasdaq, Dow Jones and Sensex) and seven stock market firms (Apple, Microsoft, Lehman Brothers, BES, BCP, General Electric and Goldman Sachs), during the period from 1999 to 2009...

Turnaround em Portugal

Ó, Rogério Ferreira do
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2010 Português
Relevância na Pesquisa
16.68%
Projecto de Mestrado em Gestão/ JEL - M10, JEL - M19,JEL - G34, JEL - G33; O presente estudo aborda o fenómeno de recuperação de empresas (Turnaround) em Portugal. Através de inquéritos e entrevistas a gestores e outros protagonistas de casos bem sucedidos de Turnaround em Portugal, este estudo procura identificar se há um conjunto de factores característicos dos Turnaround em Portugal e, confirmada essa hipótese, se desses factores é possível extrair conhecimentos potencialmente úteis para a gestão de empresas em situação de declínio. Na primeira parte enunciam-se os objectivos do estudo e a revisão da literatura sobre Turnaround. A segunda parte apresenta a metodologia utilizada e procede à análise e discussão dos resultados, enquadrando-os no âmbito da literatura consultada. Por último, expõem-se as conclusões de que há uma matriz comum aos processos de Turnaround bem sucedidos em Portugal e sobre a mesma, extraem-se perspectivas sobre a gestão de empresas em dificuldades.; This paper studies the Turnaround in Portugal. Through inquiries and interviews to managers and other experienced players, this study seeks to confirm the existence of a framework of common factors to the Portuguese successful Turnaround processes...

Idiossincracias sectoriais no risco de crédito

Marques, Marina Isabel Vicente
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2012 Português
Relevância na Pesquisa
16.68%
Mestrado em Gestão/ Classificação JEL: G32; G33; O risco de crédito é um conceito que tem vindo a ganhar popularidade ao longo das últimas décadas e, muito especialmente, nos últimos anos, em consequência da crise do crédito hipotecário nos EUA em 2007 e que se propagou a nível mundial. Uma vez que se torna cada vez mais imperativo a gestão eficaz deste tipo de risco, sobretudo para as instituições financeiras, este estudo surge com o objectivo de compreender em que medida a informação qualitativa, especialmente o sector de actividade em que se insere uma média empresa portuguesa, pode contribuir para melhorar a capacidade preditiva dos actuais modelos de avaliação de risco de crédito. Procurou-se primeiramente efectuar um enquadramento da evolução histórica dos modelos de previsão de incumprimento, tendo-se verificado que, enquanto no desenvolvimento dos primeiros modelos eram apenas considerados rácios financeiros, mais recentemente alguns autores têm sugerido que a inclusão de informação qualitativa nestes modelos aumenta a sua capacidade preditiva. Neste sentido, ao utilizar uma base de dados de mais de 10.000 médias empresas clientes de uma Instituição Financeira portuguesa durante o período 2005-2011...

Determinantes da estrutura de capital das PME portuguesas

Oliveira, Inês Gonçalves de
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2012 Português
Relevância na Pesquisa
16.68%
Tese de Mestrado em Finanças / Classificação JEL: C23, G32, G33; Desde o clássico e pioneiro artigo de Modigliani e Miller (1958), a estrutura de capital tem sido um dos temas mais estudados em finanças empresariais. A heterogeneidade das conclusões e dos resultados encontrados não permitiu ainda chegar a uma posição concreta e universalmente aceite. A presente dissertação tem como objectivo investigar se as práticas empresariais seguidas pelas pequenas e médias empresas portuguesas (PME), no que se refere às decisões financeiras, permitem validar os argumentos propostos pelas teorias explicativas da estrutura de capital. Tendo como base uma amostra de dados em painel, com 3,748 observações relativas a 1,743 PME portuguesas referente ao período entre 2007 e 2010, os resultados empíricos não evidenciam uma tendência clara de que estas empresas sigam uma abordagem concreta na definição da sua estrutura de capital. Ao invés, as decisões sobre a estrutura de capital parecem obedecer à observação de um conjunto de atributos resultantes da sobreposição de várias abordagens teóricas referidas pela literatura. Os atributos cujos coeficientes estimados reúnem maior significância estatística ao nível dos sectores de actividade analisados...

Modelos de risco de crédito: análise de telecoms europeias e bancos americanos

Santana, Carolina Albardeiro
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2014 Português
Relevância na Pesquisa
16.68%
Mestrado em Finanças/ G24, G33; Este trabalho tem como objetivo apresentar e testar modelos quantitativos de risco de crédito para instituições financeiras e não financeiras cotadas em bolsa de valores. Estes modelos consistem no cálculo da probabilidade de default, ou seja, a incapacidade da instituição em pagar as suas responsabilidades financeiras nas respetivas maturidades. A forma mais simples de avaliar a probabilidade de default de instituições financeiras e não financeiras assenta na utilização de modelos de scoring de risco de crédito através da análise de rácios financeiros. Os modelos estruturais têm como base as teorias desenvolvidas por Merton (1973, 1974) e Black & Scholes (1973) conhecidas como a análise de contingent claims. Estas teorias derivaram em diversas extensões originando modelos de elevada notoriedade, tais como, o modelo KMV e o modelo CreditGrades. A vertente teórica do trabalho baseia-se em descrever os modelos e explicar as várias técnicas utilizadas para quantificar o risco de default de instituições financeiras e não financeiras. A vertente prática consiste na implementação dos diferentes modelos para testar e confrontar os resultados obtidos.; The objective of this thesis is to present and test credit risk models for financial and non-financial institutions listed on stock markets. These models provide a default probability calculation...

Turnaround empresarial: fatores determinantes para o sucesso: estudo de casos

Osório, Fernanda Maria Ferreira
Fonte: Instituto Universitário de Lisboa Publicador: Instituto Universitário de Lisboa
Tipo: Dissertação de Mestrado
Publicado em //2014 Português
Relevância na Pesquisa
16.68%
Dissertação de mestrado em Gestão / Classificação JEL: G00, G33; Os processos de turnaround empresarial são situações que envolvem emoções intensas devido às mudanças que são necessárias implementar no seio das empresas, exigindo um conjunto de ações para perceber por um lado, as causas do declínio e, por outro, formular estratégias adequadas para transformar as empresas e dar-lhes um novo “sopro de vida”, pelo que dependendo da situação e da organização, diferentes estratégias podem ser adotadas e diferentes resultados podem ser conseguidos. O objetivo deste trabalho é dar uma visão prática sobre os principais determinantes que devem estar presentes num processo de turnaround empresarial, em particular para empresas industriais, que garantam um maior potencial de sucesso, partindo de um conjunto de hipóteses que foram elaboradas tendo em consideração o referencial teórico associado ao tema. O conjunto de hipóteses foram validadas junto de quatro empresas, especialmente selecionadas para o efeito, utilizando uma abordagem mista, combinando o método quantitativo com o qualitativo, o que permitiu concluir que a velocidade com que se iniciam e ativam respostas e ações globais para promover a recuperação dependem da gravidade do declínio. Confirmou-se...

Efficiency of partial treatment of cattle infested with horn fly using 40% diazinon

Almeida,Fabiana Alves de; Alari,Fernando de Oliveira; Seno,Maria Conceicao Zocoller; Lima,Marco Monteiro de; Nascimento,Sheila Tavares; Chiquitelli Neto,Marcos
Fonte: Colégio Brasileiro de Parasitologia Veterinária Publicador: Colégio Brasileiro de Parasitologia Veterinária
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/12/2013 Português
Relevância na Pesquisa
17.84%
The aim of this investigation was to evaluate the efficiency of partial treatment of animals infested with horn flies. Forty-five Guzerat cows between 4 and 7 years of age were divided into three groups (15 cows per group). The treatments were as follows: in groups G33 and G100, 33.3 and 100% of the cows were treated with one insecticide-impregnated ear tag/animal (40% diazinon), respectively, while in the group GC, the cows were not treated (control). The flies on the cervico-dorsal-lumbar region of the cows, in all three groups, were counted every 14 days. The experiment lasted from September 2006 to September 2009. Over this period, six four-month ear tag treatments, with intervals of one to two months, were conducted on both treated groups. The animals of group G33 had a higher infection than those of group G100, and the number of flies ranged from 12 to 27 (group G33) and from 3 to 11 (group G100). However, groups G33 and G100 had lower infection levels than group GC, which presented from 45 to 87 flies. Partial treatment of cattle infested with horn flies using 40% diazinon insecticide is an efficient alternative for controlling this ectoparasite.

An Active Site Guanine Participates in glmS Ribozyme Catalysis in its Protonated State

Viladoms, Júlia; Scott, Lincoln G.; Fedor, Martha J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
17.84%
Active site guanines that occupy similar positions have been proposed to serve as general base catalysts in hammerhead, hairpin, and glmS ribozymes, but no specific roles for these guanines have been demonstrated conclusively. Structural studies place G33(N1) of the glmS ribozyme of Bacillus anthracis within hydrogen-bonding distance of the 2′-OH nucleophile. Apparent pKa values determined from the pH dependence of cleavage kinetics for wild-type and mutant glmS ribozymes do not support a role for G33, or any other active site guanine, in general base catalysis. Furthermore, discrepancies between apparent pKa values obtained from functional assays and microscopic pKa values obtained from pH-fluorescence profiles with ribozymes containing a fluorescent guanosine analog, 8-azaguanosine, at position 33 suggest that the pH-dependent step in catalysis does not involve G33 deprotonation. These results point to an alternative model in which G33(N1) in its neutral, protonated form, donates a hydrogen bond to stabilize the transition state.

Conserved Glycine 33 Residue in Flexible Domain I of Hepatitis C Virus Core Protein Is Critical for Virus Infectivity

Angus, Allan G. N.; Loquet, Antoine; Stack, Séamus J.; Dalrymple, David; Gatherer, Derek; Penin, François; Patel, Arvind H.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /01/2012 Português
Relevância na Pesquisa
17.31%
Hepatitis C virus core protein forms the viral nucleocapsid and plays a critical role in the formation of infectious particles. In this study, we demonstrate that the highly conserved residue G33, located within domain 1 of the core protein, is important for the production of cell culture-infectious virus (HCVcc). Alanine substitution at this position in the JFH1 genome did not alter viral RNA replication but reduced infectivity by ∼2 logs. Virus production by this core mutant could be rescued by compensatory mutations located immediately upstream and downstream of the original G33A mutation. The examination of the helix-loop-helix motif observed in the core protein structure (residues 15 to 41; Protein Data Bank entry 1CWX) indicated that the residues G33 and F24 are in close contact with each other, and that the G33A mutation induces a steric clash with F24. Molecular simulations revealed that the compensatory mutations increase the helix-loop-helix flexibility, allowing rescue of the core active conformation required for efficient virus production. Taken together, these data highlight the plasticity of core domain 1 conformation and illustrate the relationship between its structural tolerance to mutations and virus infectivity.

Diversidade fenotípica e molecular, correlações entre caracteres , adaptabilidade e estabilidade de genótipos de soja; Molecular and phenotypic diversity, correlations among traits, adaptability and stability of soybean genotypes

Sousa, Larissa Barbosa de
Fonte: Universidade Federal de Uberlândia Publicador: Universidade Federal de Uberlândia
Tipo: Tese de Doutorado
Português
Relevância na Pesquisa
17.31%
Este trabalho teve como objetivos: a) avaliar a diversidade genética entre genótipos de soja, utilizando-se caracteres agronômicos e marcadores moleculares microssatélites; b) avaliar as correlações fenotípicas e genotípicas entre caracteres agronômicos de linhagens de soja oriundas de diferentes cruzamentos, c) estudar a interação genótipos por ambientes para o caráter produtividade de grãos e d) avaliar a adaptabilidade e estabilidade de genótipos de soja de ciclo precoce e tardio pelos métodos AMMI, GGE Biplot e análise de fatores. Para o estudo de divergência genética, conduziu-se um experimento de campo na Fazenda Capim Branco (análise fenotípica) e as análises moleculares foram realizadas no Laboratório de Genética do Instituto de Genética e Bioquímica, ambos pertencentes à Universidade Federal de Uberlândia. Avaliaram-se 35 genótipos de soja por meio de sete caracteres agronômicos e nove marcadores microssatélites. Realizou-se o agrupamento dos genótipos pelos métodos UPGMA e Tocher, para ambas as análises e concluiu-se que o uso de caracteres agronômicos e os marcadores moleculares microssatélites concomitante permitiram detectar genitores potenciais para o programa de melhoramento de soja e que hibridações entre os genótipos G11...

Rat gene 33: analysis of its structure, messenger RNA and basal promoter activity.

Chrapkiewicz, N B; Davis, C M; Chu, D T; Caldwell, C M; Granner, D K
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 25/08/1989 Português
Relevância na Pesquisa
17.31%
Several overlapping cDNA and genomic DNA clones corresponding to mRNA g33 and gene 33, respectively, were isolated and characterized. The mRNA g33 molecule is 2971 nt in length, exclusive of a poly(A+) tail, and encodes a putative 459 amino acid protein (49,946 daltons). The 13.2 kbp gene consists of four exons, three introns, and has two initiation sites located 27 and 30 bp downstream from a TATA box. Transfection of H4IIE cells with a fusion gene 33 (-1900 to +32)/luciferase construct (pSL330A) gave rise to readily detectable luciferase activity. In addition, primer extension analysis of the gene 33/luciferase mRNA transcribed in these experiments showed that transcription initiates in the gene 33 DNA at two sites consistent with those found in vivo. Analysis of the effect of 5' deletions on basal promoter activity showed that, in relation to the promoter activity of pSL330A, approximately 40% of the activity is lost between -1643 and -1050, another approximately 40% between -550 and -475, and deletion to -55 causes a total loss of detectable luciferase activity.

GxxxG motifs within the amyloid precursor protein transmembrane sequence are critical for the etiology of Aβ42

Munter, Lisa-Marie; Voigt, Philipp; Harmeier, Anja; Kaden, Daniela; Gottschalk, Kay E; Weise, Christoph; Pipkorn, Rüdiger; Schaefer, Michael; Langosch, Dieter; Multhaup, Gerd
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
17.31%
Processing of the amyloid precursor protein (APP) by β- and γ-secretases leads to the generation of amyloid-β (Aβ) peptides with varying lengths. Particularly Aβ42 contributes to cytotoxicity and amyloid accumulation in Alzheimer's disease (AD). However, the precise molecular mechanism of Aβ42 generation has remained unclear. Here, we show that an amino-acid motif GxxxG within the APP transmembrane sequence (TMS) has regulatory impact on the Aβ species produced. In a neuronal cell system, mutations of glycine residues G29 and G33 of the GxxxG motif gradually attenuate the TMS dimerization strength, specifically reduce the formation of Aβ42, leave the level of Aβ40 unaffected, but increase Aβ38 and shorter Aβ species. We show that glycine residues G29 and G33 are part of a dimerization site within the TMS, but do not impair oligomerization of the APP ectodomain. We conclude that γ-secretase cleavages of APP are intimately linked to the dimerization strength of the substrate TMS. The results demonstrate that dimerization of APP TMS is a risk factor for AD due to facilitating Aβ42 production.

Les déterminants des faillites bancaires dans les pays en développement: le cas des pays de l'Union économique et monétaire Ouest-africaine (UEMOA)

POWO FOSSO, Bruno
Fonte: Université de Montréal Publicador: Université de Montréal
Tipo: Artigo de Revista Científica Formato: 175606 bytes; application/pdf
Português
Relevância na Pesquisa
17.31%
L’objectif de ce papier est de déterminer les facteurs susceptibles d’expliquer les faillites bancaires au sein de l’Union économique et monétaire ouest-africaine (UEMOA) entre 1980 et 1995. Utilisant le modèle logit conditionnel sur des données en panel, nos résultats montrent que les variables qui affectent positivement la probabilité de faire faillite des banques sont : i) le niveau d’endettement auprès de la banque centrale; ii) un faible niveau de comptes disponibles et à vue; iii) les portefeuilles d’effets commerciaux par rapport au total des crédits; iv) le faible montant des dépôts à terme de plus de 2 ans à 10 ans par rapport aux actifs totaux; et v) le ratio actifs liquides sur actifs totaux. En revanche, les variables qui contribuent positivement sur la vraisemblance de survie des banques sont les suivantes : i) le ratio capital sur actifs totaux; ii) les bénéfices nets par rapport aux actifs totaux; iii) le ratio crédit total sur actifs totaux; iv) les dépôts à terme à 2 ans par rapport aux actifs totaux; et v) le niveau des engagements sous forme de cautions et avals par rapport aux actifs totaux. Les ratios portefeuilles d’effets commerciaux et actifs liquides par rapport aux actifs totaux sont les variables qui expliquent la faillite des banques commerciales...

RR Lyrae Variables in the Globular Clusters of M31: a First Detection of Likely Candidates

Clementini, G.; Federici, L.; Corsi, C. E.; Cacciari, C.; Bellazzini, M.; Smith, H. A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
17.64%
The purpose of this paper is to show that RR Lyrae variables exist and can be detected in M31 globular clusters. We report on the first tentative identification of RR Lyrae candidates in four globular clusters of the Andromeda galaxy, i.e. G11, G33, G64 and G322. Based on HST-WFPC2 archive observations in the F555W and F814W filters spanning a total interval of about 5 consecutive hours we find evidence for 2, 4, 11 and 8 RR Lyrae variables of both ab and c Bailey types in G11, G33, G64 and G322, respectively. Several more candidates can be found by relaxing slightly the selection criteria. These numbers are quite consistent with the horizontal branch morphology exhibited by the four clusters, starting from the very blue HB in G11, and progressively moving to redder HBs in G64, G33 and G322.; Comment: 4 pages, 3 included figures, accepted for publication by ApJ Letters

Bursting Activity in a High-Mass Star-Forming Region G33.64-0.21 Observed with the 6.7 GHz Methanol Maser

Fujisawa, Kenta; Sugiyama, Koichiro; Aoki, Nozomu; Hirota, Tomoya; Mochizuki, Nanako; Doi, Akihiro; Honma, Mareki; Kobayashi, Hideyuki; Kawaguchi, Noriyuki; Ogawa, Hideo; Omodaka, Toshihiro; Yonekura, Yoshinori
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/09/2011 Português
Relevância na Pesquisa
27.31%
We report the detection of bursts of 6.7 GHz methanol maser emission in a high-mass star-forming region, G33.64-0.21. One of the spectral components of the maser in this source changed its flux density by 7 times that of the previous day, and it decayed with a timescale of 5 days. The burst occurred repeatedly in the spectral component, and no other components showed such variability. A VLBI observation with the Japanese VLBI Network (JVN) showed that the burst location was at the southwest edge of a spatial distribution, and the bursting phenomenon occurred in a region much smaller than 70 AU. We suggest an impulsive energy release like a stellar flare as a possible mechanism for the burst. These results imply that 6.7 GHz methanol masers could be a useful new probe for studying bursting activity in the process of star formation of high-mass YSOs with a high-resolution of AU scale.; Comment: 6 pages, 4 figures, accepted for publication in PASJ

Fragmentation and OB Star Formation in High-Mass Molecular Hub-Filament System

Liu, Hauyu Baobab; Jiménez-Serra, Izaskun; Ho, Paul T. -P.; Chen, Huei-Ru; Zhang, Qizhou; Li, Zhi-Yun
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 09/06/2012 Português
Relevância na Pesquisa
17.31%
Filamentary structures are ubiquitously seen in the interstellar medium. The concentrated molecular mass in the filaments allows fragmentation to occur in a shorter timescale than the timescale of the global collapse. Such hierarchical fragmentation may further assist the dissipation of excessive angular momentum. It is crucial to resolve the morphology and the internal velocity structures of the molecular filaments observationally. We perform 0".5-2".5 angular resolution interferometric observations toward the nearly face-on OB cluster forming region G33.92+0.11. Observations of various spectral lines as well as the millimeter dust continuum emission, consistently trace several $\sim$1 pc scale, clumpy molecular arms. Some of the molecular arms geometrically merge to an inner 3.0$^{{\scriptsize{+2.8}}}_{{-\scriptsize{1.4}}}\cdot10^{3}$\,$M_{\odot}$, 0.6 pc scale central molecular clump, and may directly channel the molecular gas to the warm ($\sim$50 K) molecular gas immediately surrounding the centrally embedded OB stars. The NH$_{3}$ spectra suggest a medium turbulence line width of FWHM$\lesssim$2\,km\,s$^{-1}$ in the central molecular clump, implying a $\gtrsim$10 times larger molecular mass than the virial mass. Feedbacks from shocks and the centrally embedded OB stars and localized (proto)stellar clusters...

ALMA resolves the spiraling accretion flow in the luminous OB cluster forming region G33.92+0.11

Liu, Hauyu Baobab; Galván-Madrid, Roberto; Jiménez-Serra, Izaskun; Román-Zúñiga, Carlos; Zhang, Qizhou; Li, Zhiyun; Chen, Huei-Ru
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 16/05/2015 Português
Relevância na Pesquisa
27.84%
How rapidly collapsing parsec-scale massive molecular clumps feed high-mass stars, and how they fragment to form OB clusters, have been outstanding questions in the field of star-formation. In this work, we report the resolved structures and kinematics of the approximately face-on, rotating massive molecular clump, G33.92+0.11. Our high resolution Atacama Large Millimeter/submillimeter Array (ALMA) images show that the spiral arm-like gas overdensities form in the eccentric gas accretion streams. First, we resolved that the dominant part of the $\sim$0.6 pc scale massive molecular clump (3.0$^{+2.8}_{-1.4}$$\cdot$10$^{3}$ $M_{\odot}$) G33.92+0.11 A is tangled with several 0.5-1 pc size molecular arms spiraling around it, which may be connected further to exterior gas accretion streams. Within G33.92+0.11 A, we resolved the $\sim$0.1 pc width gas mini-arms connecting with the two central massive (100-300 $M_{\odot}$) molecular cores. The kinematics of arms and cores elucidate a coherent accretion flow continuing from large to small scales. We demonstrate that the large molecular arms are indeed the cradles of dense cores, which are likely current or future sites of high-mass star formation. Since these deeply embedded massive molecular clumps preferentially form the highest mass stars in the clusters...

Observations of the Bursting Activity of the 6.7GHz Methanol Maser in G33.641-0.228

Fujisawa, Kenta; Aoki, Nozomu; Nagadomi, Yoshito; Kimura, Saki; Shimomura, Tadashi; Takase, Genta; Sugiyama, Koichiro; Motogi, Kazuhito; Niinuma, Kotaro; Hirota, Tomoya; Yonekura, Yoshinori
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 15/08/2014 Português
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We have observed bursting variability of the 6.7 GHz methanol maser of G33.641-0.228. Five bursts were detected in the observation period of 294 days from 2009 to 2012. The typical burst is a large flux density rise in about one day followed by a slow fall. A non-typical burst observed in 2010 showed a large and rapid flux density enhancement from the stable state, but the rise and fall of the flux density were temporally symmetric and a fast fluctuation continued 12 days. On average, the bursts occurred once every 59 days, although bursting was not periodic. Since the average power required for causing the burst of order of 10^21 Js^-1 is far smaller than the luminosity of G33.641-0.228, a very small fraction of the source's power would be sufficient to cause the burst occasionally. The burst can be explained as a solar-flare like event in which the energy is accumulated in the magnetic field of the circumstellar disk, and is released for a short time. However, the mechanism of the energy release and the dust heating process are still unknown.; Comment: 11 pages, 4 figures, accepted to PASJ