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Efeito da adição do óleo de soja, óleo de linhaça, óleo de coco babaçu e sebo bovino nos parâmetros produtivos e reprodutivos de fêmeas suínas em lactação; Reproductive and productive performance of lactating sows fed diets supplemented with vegetable oil or tallow

Muniz, Adriana
Fonte: Biblioteca Digitais de Teses e Dissertações da USP Publicador: Biblioteca Digitais de Teses e Dissertações da USP
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 04/08/2004 Português
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O objetivo do experimento foi verificar o efeito da adição do óleo de soja, óleo de linhaça, óleo de coco babaçu e sebo bovino na ração de fêmeas suínas lactantes. As dietas eram energeticamente altas, sendo uma dieta basal acrescida em 8% por diferentes fontes de energia, (1) óleo de soja, (2) óleo de linhaça, (3) óleo de coco e (4) gordura animal, tratamentos 1, 2, 3 e 4 respectivamente. O experimento foi realizado na Fazenda Santa Rosa, Leme, SP. As variáveis avaliadas foram peso inicial, aos 100 dias de gestação (PI), peso à desmama (PD), espessura de toucinho aos 100 dias de gestação (ETI), espessura de toucinho à desmama (ETD), mudanças corporais no período lactacional como perda de peso (PP), perda de espessura de toucinho (PET), produção de leite (PL) e peso dos leitões (Ple) nos dias 7, 14 e 21 da lactação, intervalo desmama estro (IDE), duração do estro (DE) e concentrações de estrógeno (Es) à desmama, 48 horas após a desmama e no estro. A espessura de toucinho foi medida no P2. A técnica de PL foi realizada pela técnica de peso dos leitões antes e depois das mamadas. O manejo para diagnóstico do estro foi realizado duas vezes ao dia. As coletas de sangue foram realizadas em 3 ocasiões à desmama (Dia 1)...

A produção científica sobre imagens técnicas na Ciência da Informação

Costa, Juliana Peres da
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Trabalho de Conclusão de Curso Formato: application/pdf
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Busca levantar o estado da arte da produção científica sobre o tema imagens técnicas na área de Ciência da Informação (CI). Contextualiza: imagens técnicas, baseado em Arlindo Machado, Vilém Flusser, Philippe Dubois, André Parente; e produção científica, baseado em Le Coadic, Tefko Saracevic, Leilah Bufrem. Compreende os seguintes objetivos específicos: identificar os autores que publicam sobre o tema e as instituições às quais estão vinculados; diferenciar os níveis de formação dos referidos autores e suas áreas de formação; relacionar os periódicos científicos que publicam sobre o tema; discernir cronologicamente a produção bibliográfica; verificar quais os enfoques dados nas publicações sobre o tema. Utiliza uma metodologia mista – que inclui o estudo bibliométrico e a técnica de análise de conteúdo, criando-se categorias a posteriori – cujo contexto é a Base Referencial de Artigos de Periódicos em Ciência da Informação (BRAPCI), que indexa 24 revistas vigentes e 11 históricas. Examina os títulos, os resumos e as palavras-chaves dos artigos, utilizando-se de planilha gerada a partir dos resultados obtidos na busca, conforme os objetivos específicos do trabalho. Os dados são processados com a utilização de gráficos e tabelas e os resultados são analisados conforme cada um dos objetivos específicos. Conclui que: a produção científica sobre imagens técnicas na CI soma um total de 169 artigos...

Estudos de comparação estrutural e funcional de duas PLA2s isoladas do veneno total de Bothriopsis bilineata e Bothriopsis taeniata; Comparison studies between structure/function of two isolated PLA2s from the whole venom Botriopsis bilineata and Bothriopsis taeniata

Victor Corasolla Carregari
Fonte: Biblioteca Digital da Unicamp Publicador: Biblioteca Digital da Unicamp
Tipo: Tese de Doutorado Formato: application/pdf
Publicado em 02/03/2015 Português
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Os venenos de serpentes são uma mistura complexa de moléculas funcionais sendo em sua maior parte proteínas. Para a perpetuação da espécie, e sendo selecionadas a partir do processo de seleção natural, as serpentes apresentam uma alta variabilidade de mutações gênicas responsáveis por expressar proteínas e componentes dos venenos ocorrendo um processo denominado de microevolução, com isso criou diversas toxinas com uma alta complexidade funcional e uma alta similaridade estrutural. Essas toxinas são responsáveis por uma grande variedade de efeitos farmacológicos que geram alterações fisiológicas e com isso imobilizando a presa (neurotoxicidade e miotoxicidade) impedindo a fuga do local de ataque, tendo componentes nos venenos que também iniciam a digestão da presa facilitando a alimentação da serpente. Estas toxinas têm sido utilizadas como ferramentas moleculares para uma melhor compreensão de processos fisiológicos. Através da identificação de modificações químicas em aminoácidos específicos e sequenciamento de "de novo" através de espectrometria de massas de PLA2s isoladas a partir do veneno de serpentes, foi possível correlacionar estrutura e função destas enzimas e elucidar certos mecanismos de ações farmacológicas específicas. As modificações químicas através dos reagentes p-BPB e AA da Bbil-TX foram identificadas e confirmadas por espectrometria de massas...

Sensitive and Specific Detection of Staphylococcal Epidermolysins A and B in Broth Cultures by Flow Cytometry-Assisted Multiplex Immunoassay

Joubert, Olivier; Keller, Daniel; Pinck, Anne; Monteil, Henri; Prévost, Gilles
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /03/2005 Português
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Two of the most common bacterial skin infections of young infants and children are bullous impetigo due to Staphylococcus aureus and its more acute form, staphylococcal scalded skin syndrome. Epidermolysin A (ETA), ETB and, possibly, ETD are responsible for these diseases, which may appear as epidemics in pediatric patients. We tested the reliability of a flow cytometry-assisted multiplex immunoassay (Bio-Plex system) for the detection of ETA and ETB. The Bio-Plex system was found to be highly specific and highly sensitive for toxin concentrations of between 2 and 80,000 pg/ml. The results of this assay were 100% identical to the results of a PCR-based method. We demonstrated that this test did not generate any cross-reactions with ETD-producing isolates. The level of detection of ETB by this test differed according to culture conditions and from isolate to isolate; these results must be taken into account for diagnostic purposes.

Parallel Ion Parking: Improving Conversion of Parents to First-Generation Products in Electron Transfer Dissociation

Chrisman, Paul A.; Pitteri, Sharon J.; McLuckey, Scott A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/05/2005 Português
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Electron-transfer dissociation (ETD) in a tandem mass spectrometer is an analytically useful ion/ion reaction technique for deriving polypeptide sequence information, but its utility can be limited by sequential reactions of the products. Sequential reactions lead to neutralization of some products, as well as to signals from products derived from multiple cleavages that can be difficult to interpret. A method of inhibiting sequential ETD fragmentation in a quadrupole ion trap is demonstrated here for the reaction of a triply protonated peptide with nitrobenzene anions. A tailored waveform (in this case, a filtered noise field) is applied during the ion/ion reaction time to accelerate simultaneously first-generation product ions and thereby inhibit their further reaction. This results in a ~50% gain in the relative yield of first-generation products and allows for the conversion of more than 90% of the original parent ions into first-generation products. Gains are expected to be even larger when higher charge-state cations are used, as the rates of sequential reaction become closer to the initial reaction rate.

Complementary Structural Information from a Tryptic N-Linked Glycopeptide via Electron Transfer Ion/Ion Reactions and Collision-Induced Dissociation

Hogan, Jason M.; Pitteri, Sharon J.; Chrisman, Paul A.; McLuckey, Scott A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2005 Português
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Glycosylation is an important post-translational modification. Analysis of glycopeptides is difficult using collision-induced dissociation, as it typically yields only information about the glycan structure, without any peptide sequence information. We demonstrate here how a 3D-quadrupole ion trap, using the complementary techniques of collision induced dissociation (CID) and electron-transfer dissociation (ETD), can be used to elucidate the glycan structure and peptide sequence of the N-glycosylated peptide from a fractionated tryptic digest of the lectin from the coral tree, Erythina cristagalli. CID experiments on the multiply protonated glycopeptide ions yield, almost exclusively, cleavage at glycosidic bonds, with little peptide backbone fragmentation. ETD reactions of the triply charged glycopeptide cations with either sulfur dioxide or nitrobenzene anions yield cleavage of the peptide backbone with no loss of the glycan structure. These results show that a 3D-quadrupole ion trap can be used to provide glycopeptide amino acid sequence information as well as information about the glycan structure.

Selective fluorescent imaging of superoxide in vivo using ethidium-based probes

Robinson, Kristine M.; Janes, Michael S.; Pehar, Mariana; Monette, Jeffrey S.; Ross, Meredith F.; Hagen, Tory M.; Murphy, Michael P.; Beckman, Joseph S.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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The putative oxidation of hydroethidine (HE) has become a widely used fluorescent assay for the detection of superoxide in cultured cells. By covalently joining HE to a hexyl triphenylphosphonium cation (Mito-HE), the HE moiety can be targeted to mitochondria. However, the specificity of HE and Mito-HE for superoxide in vivo is limited by autooxidation as well as by nonsuperoxide-dependent cellular processes that can oxidize HE probes to ethidium (Etd). Recently, superoxide was shown to react with HE to generate 2-hydroxyethidium [Zhao, H., Kalivendi, S., Zhang, H., Joseph, J., Nithipatikom, K., Vasquez-Vivar, J. & Kalyanaraman, B. (2003) Free Radic. Biol. Med. 34, 1359–1368]. However, 2-hydroxyethidium is difficult to distinguish from Etd by conventional fluorescence techniques exciting at 510 nm. While investigating the oxidation of Mito-HE by superoxide, we found that the superoxide product of both HE and Mito-HE could be selectively excited at 396 nm with minimal interference from other nonspecific oxidation products. The oxidation of Mito-HE monitored at 396 nm by antimycin-stimulated mitochondria was 30% slower than at 510 nm, indicating that superoxide production may be overestimated at 510 nm by even a traditional superoxide-stimulating mitochondrial inhibitor. The rate-limiting step for oxidation by superoxide was 4 × 106 M−1·s−1...

Early death during chemotherapy in patients with small-cell lung cancer: derivation of a prognostic index for toxic death and progression

Lassen, U N; Østerlind, K; Hirsch, F R; Bergman, B; Dombernowsky, P; Hansen, H H
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em /02/1999 Português
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Based on an increased frequency of early death (death within the first treatment cycle) in our two latest randomized trials of combination chemotherapy in small-cell lung cancer (SCLC), we wanted to identify patients at risk of early non-toxic death (ENTD) and early toxic death (ETD). Data were stored in a database and logistic regression analyses were performed to identify predictive factors for early death. During the first cycle, 118 out of 937 patients (12.6%) died. In 38 patients (4%), the cause of death was sepsis. Significant risk factors were age, performance status (PS), lactate dehydrogenase (LDH) and treatment with epipodophyllotoxins and platinum in the first cycle (EP). Risk factors for ENTD were age, PS and LDH. Extensive stage had a hazard ratio of 1.9 (P = 0.07). Risk factors for ETD were EP, PS and LDH, whereas age and stage were not. For EP, the hazard ratio was as high as 6.7 (P = 0.0001). We introduced a simple prognostic algorithm including performance status, LDH and age. Using a prognostic algorithm to exclude poor-risk patients from trials, we could minimize early death, improve long-term survival and increase the survival differences between different regimens. We suggest that other groups evaluate our algorithm and exclude poor prognosis patients from trials of dose intensification. © 1999 Cancer Research Campaign

Human embryonic stem cell phosphoproteome revealed by electron transfer dissociation tandem mass spectrometry

Swaney, Danielle L.; Wenger, Craig D.; Thomson, James A.; Coon, Joshua J.
Fonte: National Academy of Sciences Publicador: National Academy of Sciences
Tipo: Artigo de Revista Científica
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Protein phosphorylation is central to the understanding of cellular signaling, and cellular signaling is suggested to play a major role in the regulation of human embryonic stem (ES) cell pluripotency. Here, we describe the use of conventional tandem mass spectrometry-based sequencing technology—collision-activated dissociation (CAD)—and the more recently developed method electron transfer dissociation (ETD) to characterize the human ES cell phosphoproteome. In total, these experiments resulted in the identification of 11,995 unique phosphopeptides, corresponding to 10,844 nonredundant phosphorylation sites, at a 1% false discovery rate (FDR). Among these phosphorylation sites are 5 localized to 2 pluripotency critical transcription factors—OCT4 and SOX2. From these experiments, we conclude that ETD identifies a larger number of unique phosphopeptides than CAD (8,087 to 3,868), more frequently localizes the phosphorylation site to a specific residue (49.8% compared with 29.6%), and sequences whole classes of phosphopeptides previously unobserved.

Valence Parity Renders z•-Type Ions Chemically Distinct

Hubler, Shane L.; Jue, April; Keith, Jason; McAlister, Graeme C.; Craciun, Gheorghe; Coon, Joshua J.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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Here we report that the odd electron z•-type ions formed by the electron-based peptide dissociation methods (electron capture or transfer, ECD or ETD) have distinctive chemical compositions from other common product ion types. Specifically, b-, c-, and y-type ions have an odd number of atoms with an odd valence (e.g., N and H), while z•-type ions contain an even number of atoms with an odd valence. This tenet, referred to as the valence parity rule, mandates that no c-type ion shall have the same chemical composition, and by extension mass, as a z•-type ion. By experiment we demonstrate that nearly half of all observed c- and z•-type product ions resulting from 226 ETD product ion spectra can be assigned to a single, correct, chemical composition and ion type by simple inspection of the m/z peaks. The assignments provide (1) a platform to directly determine amino acid composition, (2) an input for database search algorithms, or (3) a basis for de novo sequence analysis.

Electron Transfer Dissociation of Oligonucleotide Cations

Smith, Suncerae I.; Brodbelt, Jennifer S.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/06/2009 Português
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Electron transfer dissociation (ETD) of multi-protonated 6 - 20-mer oligonucleotides and 12- and 14-mer duplexes is compared to collision activated dissociation (CAD). ETD causes efficient charge reduction of the multi-protonated oligonucleotides in addition to limited backbone cleavages to yield sequence ions of low abundance. Subsequent CAD of the charge-reduced oligonucleotides formed upon electron transfer, in a net process termed electron transfer collision activated dissociation (ETcaD), results in rich fragmentation in terms of w, a, z, and d products, with a marked decrease in the abundance of base loss ions and internal fragments. Complete sequencing was possible for nearly all oligonucleotides studied. ETcaD of an oligonucleotide duplex resulted in specific backbone cleavages, with conservation of weaker non-covalent bonds.

Electron Transfer Dissociation of Doubly Sodiated Glycerophosphocholine Lipids

Liang, Xiaorong; Liu, Jian; LeBlanc, Yves; Covey, Tom; Ptak, A. Celeste; Brenna, J. Thomas; McLuckey, Scott A.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
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The ability to generate gaseous doubly charged cations of glycerophosphocholine (GPC) lipids via electrospray ionization has made possible the evaluation of electron transfer dissociation (ETD) for their structural characterization. Doubly sodiated GPC cations have been reacted with azobenzene radical anions in a linear ion trap mass spectrometer. The ion/ion reactions proceed through sodium transfer, electron transfer, and complex formation. Electron transfer reactions are shown to give rise to cleavage at each ester linkage with the subsequent loss of a neutral quaternary nitrogen moiety. Electron transfer without dissociation produces [M+2Na]+• radical cations, which undergo collision-induced dissociation (CID) to give products that arise from bond cleavage of each fatty acid chain. The CID of the complex ions yields products similar to those produced directly from the electron transfer reactions of doubly sodiated GPC, although with different relative abundances. These findings indicate that the analysis of GPC lipids by ETD in conjunction with CID can provide some structural information, such as the number of carbons, degree of unsaturation for each fatty acid substituent, and the positions of the fatty acid substituents; some information about the location of the double bonds may be present in low intensity CID product ions.

Combined Pulsed-Q dissociation and electron transfer dissociation for identification and quantification of iTRAQ–labeled phosphopeptides

Yang, Feng; Wu, Si; Stenoien, David L.; Zhao, Rui; Monroe, Matthew E.; Gristenko, Marina A.; Purvine, Samuel O.; Polpitiya, Ashoka D.; Tolić, Nikola; Zhang, Qibin; Norbeck, Angela D.; Orton, Daniel J.; Moore, Ronald J.; Tang, Keqi; Anderson, Gordon A.; P
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/05/2009 Português
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Here, we report a new approach that integrates pulsed Q dissociation (PQD) and electron transfer dissociation (ETD) techniques for confident and quantitative identification of iTRAQ-labeled phosphopeptides. The use of isobaric tags for relative and absolute quantification enables a high-throughput quantification of peptides via reporter ion signals in the low m/z range of tandem mass spectra. PQD, a form of ion trap collision activated dissociation allows for detection of low mass-to-charge fragment ions and electron transfer dissociation is especially useful for sequencing peptides that contain post-translational modifications. Analysis of the phosphoproteome of human fibroblast cells using a sensitive linear ion trap mass spectrometer demonstrated that this hybrid approach improves both identification and quantification of phosphopeptides. ETD improved phosphopeptide identification, while PQD provides improved quantification of iTRAQ-labeled phosphopeptides.

Entrapment of Ketorolac Tromethamine in Polymeric Vehicle for Controlled Drug Delivery

Paliwal, S. K.; Chauhan, Rajani; Sharma, Veena; Majumdar, D. K.; Paliwal, S.
Fonte: Medknow Publications Publicador: Medknow Publications
Tipo: Artigo de Revista Científica
Publicado em //2009 Português
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The most common method for applying a drug in to the eye is to formulate the drug in the form of an eye drop, but this method is not considered ideal for ocular delivery of drug because of poor bioavailability arising from precorneal loss processes, this loss of drug from the precorneal area is a net effect of drainage, tear secretion and noncorneal absorption. Following the above lead we tried to improve the ocular bioavailability by increasing the corneal contact time and the feasible way was to formulate a drug with mucoadhesive/viscosity imparting agents. The adhesive strength of various polymers on corneal surface was studied with the help of self modified Franz diffusion cell and freshly excised goat/bovine cornea. The polymers hydroxypropylmethylcellulose, carboxymethylcellulose sodium, Eudragit type E/RL/RS, Carbopol ETD 2020 and Carbopol 934 National Formulary were formulated with drug, ketorolac tromethamine. The adhesive strength of polymers on corneal surface and permeation characteristics of drug through cornea were investigated by using above said formulations. Eudragit type E/RL/RS did not show any improvement in mucoadhesion, but the formulations containing Carbopol ETD 2020 and Carbopol 934 national formulary showed good mucoadhesion on corneal surface in the concentration as low as 0.75%. The mucoadhesive strength was also evaluated using the combination of Carbopol acrylates/C 10-30 alkylacrylate with allylpentaerithrital and preservative benzalkonium chloride...

Gas-phase rearrangements do not affect site localization reliability in phosphoproteomics data sets

Aguiar, Mike; Haas, Wilhelm; Beausoleil, Sean A.; Rush, John; Gygi, Steven P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 04/06/2010 Português
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Intramolecular transfer of phosphate during collision-induced dissociation (CID) in ion trap mass spectrometers has recently been described. Because phosphorylation events are assigned to discrete serine, threonine, and tyrosine residues based on the presence of site-determining ions in MS/MS spectra, phosphate transfer may invalidate or confound site localization in published large-scale phosphorylation data sets. Here, we present evidence for the occurrence of this phenomenon using synthetic phosphopeptide libraries, specifically for doubly-charged species. We found, however, that the extent of the transfer reaction was insufficient to cause localization of phosphorylation sites to incorrect residues. We further compared CID to electron-transfer dissociation (ETD) for site localization using synthetic libraries and a large-scale yeast phosphoproteome experiment. The agreement in site localization was >99.5 and 93%, respectively, suggesting that ETD-based site localization is no more reliable than CID. We conclude that intramolecular phosphate transfer does not affect the reliability of current or past phosphorylation data sets.

Mass spectrometric analysis, automated identification and complete annotation of O-linked glycopeptides

Darula, Z.; Chalkley, R.J.; Baker, P.; Burlingame, A.L.; Medzihradszky, K.F.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em //2010 Português
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Complex mixtures containing O-linked glycopeptides bearing SA1-0GalGalNAc structures, or single GalNAc units were subjected to CID and ETD analysis on a linear ion trap – Orbitrap mass spectrometer and the resulting data was analyzed using the Protein Prospector software. An overview of the structural information provided by the different fragmentation techniques, as well as their limitations is presented. We illustrate the importance of the complementary information in the MS survey scans as well as the different MS/MS techniques. We also present some unique features offered by Protein Prospector that are advantageous in glycopeptide analysis: i) considering a modification that will produce a neutral loss, without “labeling” the original modification site; ii) merging CID and ETD search results; iii) permitting the comparison of different modification site-assignments. Although these data were obtained from secreted glycopeptides, the observations and conclusions are also valid for the intracellular regulatory O-GlcNAc modification.

Scutellarin Reduces Endothelium Dysfunction through the PKG-I Pathway

Du, Xiaohua; Chen, Chen; Zhang, Min; Cai, Donghua; Sun, Jiaqi; Yang, Jian; Hu, Na; Ma, Congji; Zhang, Liyan; Zhang, Jun; Yang, Weimin
Fonte: Hindawi Publishing Corporation Publicador: Hindawi Publishing Corporation
Tipo: Artigo de Revista Científica
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Purpose. In this report, we investigated the protective mechanism of scutellarin (SCU) in vitro and in vivo which could be involved in endothelial cGMP-dependent protein kinase (PKG), vasodilator stimulated phosphoprotein (VASP) pathway, and vascular endothelium dysfunction (EtD). Method. Human brain microvascular endothelial cells (HBMECs) with hypoxia reoxygenation (HR) treatment and rats with cerebral ischemia reperfusion (CIR) treatment were applied. Protein and mRNA expression of PKG, VASP, and p-VASP were evaluated by Western blot and RT-PCR methods. Vascular EtD was assessed by using wire myography to determine endothelium-dependent vasorelaxation in isolated rat basilar artery (BA). Result. In cultured HBMECs, SCU (0.1, 1, and 10 μM) increased cell viability, mRNA, protein level, and phosphorylative activity of PKG and VASP against HR injury. In HR model of BA, SCU increased protein level of P-VASP. In rat CIR model, wire myography demonstrated that SCU (45 and 90 mg/kg, i.v.) significantly reduced ischemic size by partially restoring the endothelium dependent vasodilation of BA; PKG inhibitor Rp-8-Br-cGMPS (50 μg/kg, i.v.) reversed this protection of SCU in CIR rats. Conclusion. SCU protects against cerebral vascular EtD through endothelial PKG pathway activation.

The molecular circumnuclear disk (CND) in Centaurus A: A multi-transition CO and [CI] survey with Herschel, APEX, JCMT, and SEST

Israel, F. P.; Guesten, R.; Meijerink, R.; Loenen, A. F.; Requena-Torres, M. A.; Stutzki, J.; van der Werf, P.; Harris, A.; Kramer, C.; Martin-Pintado, J.; Weiss, A.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/02/2014 Português
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We present new CO and C^o line measurements of the compact circumnuclear disk in the center of NGC 128 (Centaurus~A) obtained with the Herschel Space Observatory, as well as SEST, JCMT, and APEX. The Cen A center CO ladder is quite different from those of either star-burst galaxies or AGNs. In addition, the relative intensity of the central Cen A [CI] emission lines is much greate than that in any other galaxy. The CO surface brightness of the compact circumnuclear disk (CND) is significantly higher than that of the much more extended thin disk (ETD) in the same line of sight. Our LVG and PDR/XDR models suggest that much of the CND gas is relatively cool (25 - 80 K) and not very dense (~ 300 cm^{-3}) if the heating is by UV photons, although there is some gas in both the CND and the ETD with a much higher density of ~30 000 cm^{-3}. Finally, there is also high-excitation, high-density phase in the CND (but not in the ETD), either in the form of an extreme PDR but more likely in the form of an XDR. The total gas mass of the Cen A CND is 8.4 x 10^{7} M(sun), uncertain by a factor of two. The CO-H2 conversion factor is 4 x 10^{20} K km/s, also within a factor of two.; Comment: 14 pages, 5 figures; A&A in press

A Class of Exponential Integrators Based on Spectral Deferred Correction

Buvoli, Tommaso
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 21/04/2015 Português
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We introduce a new class of arbitrary-order exponential time differencing methods based on spectral deferred correction (ETDSDC) and describe a simple procedure for initializing the requisite matrix functions. We compare the stability and accuracy properties of our ETDSDC meth- ods to those of an existing implicit-explicit spectral deferred correction scheme (IMEXSDC). We find that ETDSDC methods have larger accuracy regions and comparable stability regions. We conduct numerical experiments to compare ETD and IMEX spectral deferred correction schemes against a competing fourth-order ETD Runge-Kutta scheme. We find that high-order ETDSDC schemes are the most efficient in terms of function evaluations and overall speed when solving partial differential equations to high accuracy. Our results suggest that high-order ETDSDC schemes are well-suited to work in conjunction with spectral spatial methods or other high-order spatial discritizations. Addi- tionally, ETDSDC schemes appear to be immune to severe order reduction, a problem which affects other ETD and IMEX schemes, including IMEXSDC.; Comment: 23 pages, 4 figures

Emphatic TD Bellman Operator is a Contraction

Hallak, Assaf; Tamar, Aviv; Mannor, Shie
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
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Recently, \citet{SuttonMW15} introduced the emphatic temporal differences (ETD) algorithm for off-policy evaluation in Markov decision processes. In this short note, we show that the projected fixed-point equation that underlies ETD involves a contraction operator, with a $\sqrt{\gamma}$-contraction modulus (where $\gamma$ is the discount factor). This allows us to provide error bounds on the approximation error of ETD. To our knowledge, these are the first error bounds for an off-policy evaluation algorithm under general target and behavior policies.