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Distribution of human immunodeficiency virus type 1 subtypes in the State of Amazonas, Brazil, and subtype C identification

Cunha, L. K. H.; Kashima, S.; Amarante, M. F. C.; Haddad, R.; Rodrigues, E. S.; Silva, K. L. T.; Lima, T. A.; Castro, D. B.; Brito, F. C.; Almeida, E. G.; Covas, D. T.; Malheiro, A.
Fonte: ASSOC BRAS DIVULG CIENTIFICA; SAO PAULO Publicador: ASSOC BRAS DIVULG CIENTIFICA; SAO PAULO
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.502007%
Few studies have reported the molecular epidemiological characterization of HIV-1 in the Northern region of Brazil. The present study reports the molecular and epidemiological characterization of 31 HIV-1 isolates from blood donors from the State of Amazonas who donated blood between April 2006 and March 2007. Serum/plasma samples from all donors were screened for HIV antibodies by ELISA and the results confirmed by Western blot analysis. Genomic DNA was extracted from the buffy coat using the Super Quik-Gene-DNA Isolation kit. Nested PCR was performed on the env, gag, and pol regions of HIV-1 using the Gene Amp PCR System 9700. Sequencing reactions were performed using the inner PCR primers and the DYEnamic (TM) ET Dye Terminator Kit, and phylogenetic analysis was performed using the gag, pol, and env gene sequences. We collected samples from 31 blood donors who tested positive for HIV-1 in confirmatory experiments. The male: female ratio of blood donors was 3.4:1, and the mean age was 32.4 years (range: 19 to 61 years). Phylogenetic analysis showed that subtype B is the most prevalent among Northern Brazilian HIV-1-seropositive blood donors. One HIV-1 subtype C and one circulating recombinant form (CRF_BF) of HIV-1 were identified in the State of Amazonas. This is the first study showing the occurrence of a possible "homogenous" subtype C in this region of Brazil. This finding could contribute to a better characterization of the HIV-1 strains that circulate in the country.; CNPq; CNPq; Fundacao de Amparo a Pesquisa do Estado do Amazonas; Fundacao de Amparo a Pesquisa do Estado do Amazonas; Center for Cell-Therapy (CTC)/Fundacao Hemocentro de Ribeirao Preto; Center for CellTherapy (CTC)/Fundacao Hemocentro de Ribeirao Preto; FAPESP; FAPESP

Distribution of human immunodeficiency virus type 1 subtypes in the state of Amazonas, Brazil, and subtype C identification

Cunha, L.K.H.; Kashima, S.; Amarante, M.F.C.; Haddad, R.; Rodrigues, E.S.; Silva, K.L.T.; Lima, T.A.; Castro, D.B.; Brito, F.C.; Almeida, E.G.; Covas, D.T.; Malheiro, A.
Fonte: Associação Brasileira de Divulgação Científica Publicador: Associação Brasileira de Divulgação Científica
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.49784%
Few studies have reported the molecular epidemiological characterization of HIV-1 in the Northern region of Brazil. The present study reports the molecular and epidemiological characterization of 31 HIV-1 isolates from blood donors from the State of Amazonas who donated blood between April 2006 and March 2007. Serum/plasma samples from all donors were screened for HIV antibodies by ELISA and the results confirmed by Western blot analysis. Genomic DNA was extracted from the buffy coat using the Super Quik-Gene-DNA Isolation kit. Nested PCR was performed on the env, gag, and pol regions of HIV-1 using the Gene Amp PCR System 9700. Sequencing reactions were performed using the inner PCR primers and the DYEnamic™ ET Dye Terminator Kit, and phylogenetic analysis was performed using the gag, pol, and env gene sequences. We collected samples from 31 blood donors who tested positive for HIV-1 in confirmatory experiments. The male:female ratio of blood donors was 3.4:1, and the mean age was 32.4 years (range: 19 to 61 years). Phylogenetic analysis showed that subtype B is the most prevalent among Northern Brazilian HIV-1-seropositive blood donors. One HIV-1 subtype C and one circulating recombinant form (CRF_BF) of HIV-1 were identified in the State of Amazonas. This is the first study showing the occurrence of a possible "homogenous" subtype C in this region of Brazil. This finding could contribute to a better characterization of the HIV-1 strains that circulate in the country.

Ontogenia das proteínas aquaporina-4 e Kir 4.1 e o efeito de inibidores dessas proteínas sobre a secreção de S100B em fatias hipocampais de rato

Zanotto, Caroline
Fonte: Universidade Federal do Rio Grande do Sul Publicador: Universidade Federal do Rio Grande do Sul
Tipo: Dissertação Formato: application/pdf
Português
Relevância na Pesquisa
57.014683%
A aquaporina-4 (AQP-4) é o principal canal de água localizado no sistema nervoso central (SNC). Durante o aumento do potássio (K+) extracelular, a captação de K+ pelos astrócitos está provavelmente associada com o co-transporte de água. Neste caso, a AQP-4 poderia servir como uma rota de saída para a água, e isto seria vantajoso para a liberação de K+ se a permeabilidade à água da AQP-4 fosse aumentada pela alta concentração de K+ extracelular. Diversos estudos demonstraram a sobreposição da expressão ontogenética de AQP-4 e do canal retificador interno de K+ Kir 4.1, sugerindo uma associação molecular da AQP-4 e Kir 4.1 no tamponamento espacial do K+, o que facilitaria o movimento de água através da membrana plasmática. A S100B é uma proteína expressa e secretada no SNC principalmente por astrócitos, que possui efeitos neurotróficos quando expressa em concentrações nanomolar (nM) e efeitos neurotóxicos quando presente em concentrações micromolar (μM). Foi demonstrado um aumento compensatório na AQP-4 em resposta a superexpressão de S100B, no entanto ainda não foi demonstrado se a AQP-4 ou os canais Kir 4.1 podem modular a secreção de S100B. Além disso, há poucos relatos sobre as alterações da expressão de AQP-4 e Kir 4.1 ao longo do desenvolvimento cerebral. Nós investigamos se a secreção de S100B é alterada em fatias hipocampais de ratos com diferentes idades (15...

Distribution of human immunodeficiency virus type 1 subtypes in the state of Amazonas, Brazil, and subtype C identification

Cunha,L.K.H.; Kashima,S.; Amarante,M.F.C.; Haddad,R.; Rodrigues,E.S.; Silva,K.L.T.; Lima,T.A.; Castro,D.B.; Brito,F.C.; Almeida,E.G.; Covas,D.T.; Malheiro,A.
Fonte: Associação Brasileira de Divulgação Científica Publicador: Associação Brasileira de Divulgação Científica
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/02/2012 Português
Relevância na Pesquisa
56.49784%
Few studies have reported the molecular epidemiological characterization of HIV-1 in the Northern region of Brazil. The present study reports the molecular and epidemiological characterization of 31 HIV-1 isolates from blood donors from the State of Amazonas who donated blood between April 2006 and March 2007. Serum/plasma samples from all donors were screened for HIV antibodies by ELISA and the results confirmed by Western blot analysis. Genomic DNA was extracted from the buffy coat using the Super Quik-Gene-DNA Isolation kit. Nested PCR was performed on the env, gag, and pol regions of HIV-1 using the Gene Amp PCR System 9700. Sequencing reactions were performed using the inner PCR primers and the DYEnamic™ ET Dye Terminator Kit, and phylogenetic analysis was performed using the gag, pol, and env gene sequences. We collected samples from 31 blood donors who tested positive for HIV-1 in confirmatory experiments. The male:female ratio of blood donors was 3.4:1, and the mean age was 32.4 years (range: 19 to 61 years). Phylogenetic analysis showed that subtype B is the most prevalent among Northern Brazilian HIV-1-seropositive blood donors. One HIV-1 subtype C and one circulating recombinant form (CRF_BF) of HIV-1 were identified in the State of Amazonas. This is the first study showing the occurrence of a possible "homogenous" subtype C in this region of Brazil. This finding could contribute to a better characterization of the HIV-1 strains that circulate in the country.

Differentiation-associated switches in protein 4.1 expression. Synthesis of multiple structural isoforms during normal human erythropoiesis.

Chasis, J A; Coulombel, L; Conboy, J; McGee, S; Andrews, K; Kan, Y W; Mohandas, N
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1993 Português
Relevância na Pesquisa
56.54505%
Erythroid differentiation is accompanied by dramatic alterations in morphology and membrane mechanical properties resulting, in large part, from reorganization of the membrane skeletal protein network. The 80-kD protein 4.1 is an important organizational component of this membrane skeleton. Recently, it has been recognized that multiple structural isoforms of 4.1 are encoded by a single gene via alternative pre-mRNA splicing, and that an upstream ATG can be spliced in and used for translation of high molecular weight 4.1. We are exploring the hypothesis that differentiation-associated switches in protein 4.1 structure play an important role in membrane reorganization. To study changes in 4.1 gene expression during normal human differentiation, we analyzed 4.1 protein and mRNA structure at various developmental stages. Using immunofluorescence microscopy, we observed high molecular weight 4.1 isoforms in preproerythroblasts producing punctate, predominantly cytoplasmic staining with a perinuclear area of intense fluorescence, while mature red cells expressed very little high molecular weight 4.1. Isoforms containing an alternatively expressed 102-nucleotide exon near the COOH terminus were abundant in both preproerythroblasts and mature cells but produced a punctate distribution of fluorescence over the entire preproerythroblast and intense membrane-associated fluorescence in the erythrocyte. Characterization of RNA by polymerase chain reaction and nuclease protection assays revealed a differentiation-associated switch in pre-mRNA splicing in the spectrin-actin binding domain. Since this domain plays a critical role in regulating membrane material properties...

Protein 4.1: its association with the human erythrocyte membrane.

Shiffer, K A; Goodman, S R
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1984 Português
Relevância na Pesquisa
56.54402%
125I-labeled protein 4.1a and 4.1b have equal ability to reassociate with inside-out erythrocyte vesicles that were depleted of protein 4.1 in addition to other peripheral membrane proteins. The reassociation of 125I-labeled protein 4.1 to protein 4.1-depleted vesicles at 4 degrees C is salt dependent, pH dependent, and saturable with a Kd of 42-50 nM and an extrapolated maximal binding capacity of 120-140 micrograms of protein 4.1 bound per mg of vesicle protein or 60-70 micrograms of protein 4.1 bound per mg of ghost protein, correlating with the protein 4.1 content in the erythrocyte membrane (6-7% of the total membrane protein). Selective proteolytic cleavage of these vesicles with papain (5 micrograms/ml at 4 degrees C) eliminates greater than 60% of the high-affinity binding sites; therefore, we conclude that the interaction of protein 4.1 with the cytoplasmic membrane surface is through a specific high-affinity protein-protein association.

Integrin α4β1 Promotes Focal Adhesion Kinase-Independent Cell Motility via α4 Cytoplasmic Domain-Specific Activation of c-Src‡

Hsia, Datsun A.; Lim, Ssang-Taek; Bernard-Trifilo, Joie A.; Mitra, Satyajit K.; Tanaka, Sakae; den Hertog, Jeroen; Streblow, Daniel N.; Ilic, Dusko; Ginsberg, Mark H.; Schlaepfer, David D.
Fonte: American Society for Microbiology Publicador: American Society for Microbiology
Tipo: Artigo de Revista Científica
Publicado em /11/2005 Português
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56.570747%
The fibronectin binding integrins α5β1 and α4β1 generate signals pivotal for cell migration through distinct yet undefined mechanisms. For α5β1, β1-mediated activation of focal adhesion kinase (FAK) promotes c-Src recruitment to FAK and the formation of a FAK-Src signaling complex. Herein, we show that FAK expression is essential for α5β1-stimulated cell motility and that exogenous expression of human α4 in FAK-null fibroblasts forms a functional α4β1 receptor that promotes robust cell motility equal to the α5β1 stimulation of wild-type and FAK-reconstituted fibroblasts. α4β1-stimulated FAK-null cell spreading and motility were dependent on the integrity of the α4 cytoplasmic domain, independent of direct paxillin binding to α4, and were not affected by PRNK expression, a dominant-negative inhibitor of Pyk2. α4 cytoplasmic domain-initiated signaling led to a ∼4-fold activation of c-Src which did not require paxillin binding to α4. Notably, α4-stimulated cell motility was inhibited by catalytically inactive receptor protein-tyrosine phosphatase α overexpression and blocked by the p50Csk phosphorylation of c-Src at Tyr-529. α4β1-stimulated cell motility of triple-null Src−/−, c-Yes−/−, and Fyn−/− fibroblasts was dependent on c-Src reexpression that resulted in p130Cas tyrosine phosphorylation and Rac GTPase loading. As p130Cas phosphorylation and Rac activation are common downstream targets for α5β1-stimulated FAK activation...

Q-Band EPR of the S2 State of Photosystem II Confirms an S = 5/2 Origin of the X-Band g = 4.1 Signal

Haddy, Alice; Lakshmi, K. V.; Brudvig, Gary W.; Frank, Harry A.
Fonte: Biophysical Society Publicador: Biophysical Society
Tipo: Artigo de Revista Científica
Publicado em /10/2004 Português
Relevância na Pesquisa
56.488135%
Disagreement has remained about the spin state origin of the g = 4.1 EPR signal observed at X-band (9 GHz) from the S2 oxidation state of the Mn cluster of Photosystem II. In this study, the S2 state of PSII-enriched membrane fragments was examined at Q-band (34 GHz), with special interest in low-field signals. Light-induced signals at g = 3.1 and g = 4.6 were observed. The intensity of the signal at g = 3.1 was enhanced by the presence of F− and suppressed by the presence of 5% ethanol, indicating that it was from the same spin system as the X-band signal at g = 4.1. The Q-band signal at g = 4.6 was also enhanced by F−, but not suppressed by 5% ethanol, making its identity less clear. Although it can be accounted for by the same spin system, other sources for the signal are considered. The observation of the signal at g = 3.1 agrees well with a previous study at 15.5 GHz, in which the X-band g = 4.1 signal was proposed to arise from the middle Kramers doublet of a near rhombic S = 5/2 system. Zero-field splitting values of D = 0.455 cm−1 and E/D = 0.25 are used to simulate the spectra.

Expression of endogenous retroviruses, ERV3 and lambda 4-1, in synovial tissues from patients with rheumatoid arthritis.

Takeuchi, K; Katsumata, K; Ikeda, H; Minami, M; Wakisaka, A; Yoshiki, T
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1995 Português
Relevância na Pesquisa
56.613384%
We addressed the question of whether or not expression of human endogenous retroviruses (ERV), ERV3 and lambda 4-1, is related to the pathogenesis of rheumatoid arthritis (RA). In genomic Southern hybridization, there were no significant differences between RA patients and healthy volunteers with regard to frequencies of restriction fragment length polymorphism (RFLP) patterns, for either ERV3 or lambda 4-1. By Northern blot analysis using fresh synovial tissues, cultured synovial cells, and peripheral blood mononuclear cells (PBMC) from patients with RA, we noted two molecular species of ERV3 mRNAs of 3.5 kb and 9.0 kb sizes, and one single molecular species of lambda 4-1 mRNAs of 4.2 kb size. The expression was detected not only in RA patients but also in synovial cells from osteoarthritis (OA) as a non-RA control and PBMC from healthy volunteers, and was not related to RA activities or treatments. Although ERV3 and lambda 4-1 expression may not be directly associated with the pathogenic pathway of RA, the possibility exists that human ERV may have a causative role in autoimmune diseases, including RA. We also examined the effect of cytokines on the transcriptional regulation of ERV3. Although the level of ERV3 expression in cultured synovial cells did not change with IL-1 beta treatment...

Proteolytic Shedding of ST6Gal-I by BACE1 Regulates the Glycosylation and Function of α4β1 Integrins*

Woodard-Grice, Alencia V.; McBrayer, Alexis C.; Wakefield, John K.; Zhuo, Ya; Bellis, Susan L.
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Publicado em 26/09/2008 Português
Relevância na Pesquisa
56.51378%
Differentiation of monocytes into macrophages is accompanied by increased cell adhesiveness, due in part to the activation of α4β1 integrins. Here we report that the sustained α4β1 activation associated with macrophage differentiation results from expression of β1 integrin subunits that lack α2–6-linked sialic acids, a carbohydrate modification added by the ST6Gal-I sialyltransferase. During differentiation of U937 monocytic cells and primary human CD14+ monocytes, ST6Gal-I is down-regulated, leading to β1 hyposialylation and enhanced α4β1-dependent VCAM-1 binding. Importantly, ST6Gal-I down-regulation results from cleavage by the BACE1 secretase, which we show is dramatically up-regulated during macrophage differentiation. BACE1 up-regulation, ST6Gal-I shedding, β1 hyposialylation, and α4β1-dependent VCAM-1 binding are all temporally correlated and share the same signaling mechanism (protein kinase C/Ras/ERK). Preventing ST6Gal-I down-regulation (and therefore integrin hyposialylation), through BACE1 inhibition or ST6Gal-I constitutive overexpression, eliminates VCAM-1 binding. Similarly, preventing integrin hyposialylation inhibits a differentiation-induced increase in the expression of an activation-dependent conformational epitope on the β1 subunit. Collectively...

Distinct FAK-Src activation events promote α5β1 and α4β1 integrin-stimulated neuroblastoma cell motility

Wu, Lihua; Bernard-Trifilo, Joie A.; Lim, Yangmi; Lim, Ssang-Taek; Mitra, Satyajit K.; Uryu, Sean; Chen, Min; Pallen, Catherine J.; Cheung, Nai-Kong V.; Mikolon, David; Mielgo, Ainhoa; Stupack, Dwayne G.; Schlaepfer, David D.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.556426%
Signals from fibronectin-binding integrins promote neural crest cell motility during development in part through protein-tyrosine kinase (PTK) activation. Neuroblastoma (NB) is a neural crest malignancy with high metastatic potential. We find that α4 and α5 integrins are present in late-stage NB tumors and cell lines derived thereof. To determine the signaling connections promoting either α4β1- or α5β1-initiated NB cell motility, pharmacological, dominant-negative, and short-hairpin RNA (shRNA) inhibitory approaches were undertaken. shRNA knockdown revealed that α5β1-stimulated NB motility is dependent upon focal adhesion kinase (FAK) PTK, Src PTK, and p130Cas adaptor protein expression. Cell reconstitution showed that FAK catalytic activity is required for α5β1-stimulated Src activation in part through direct FAK phosphorylation of Src at Tyr-418. Alternatively, α4β1-stimulated NB cell motility is dependent upon Src and p130Cas but FAK is not essential. Catalytically-inactive receptor protein-tyrosine phosphatase α over-expression inhibited α4β1-stimulated NB motility and Src activation consistent with α4-regulated Src activity occurring through Src Tyr-529 dephosphorylation. In α4 shRNA-expressing NB cells, α4β1-stimulated Src activation and NB cell motility were rescued by wild type but not cytoplasmic domain truncated α4 re-expression. These studies...

Heparin II domain of fibronectin mediates contractility through an α4β1 co-signaling pathway

Schwinn, Marie K.; Gonzalez, Jose M.; Gabelt, B’Ann T.; Sheibani, Nader; Kaufman, Paul L.; Peters, Donna M.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.50313%
In the trabecular meshwork (TM) of the eye, regulation of tissue contractility by the PPRARI sequence within the Heparin II (HepII) domain of fibronectin is believed to control the movement of aqueous humor and dictate the level of intraocular pressure. This study shows that the HepII domain utilizes activated α4β1 integrin and collagen to mediate a co-signaling pathway that down-regulates contractility in TM cells. siRNA silencing of α4β1 integrin blocked the actin disrupting effects of both PPRARI and the HepII domain. The down-regulation of the actin cytoskeleton and contractility did not involve syndecan-4 or other heparan sulfate proteoglycans (HSPGs) since siRNA silencing of syndecan-4 expression or heparitinase removal of cell surface HSPGs did not prevent the HepII-mediated disruption of the actin cytoskeleton. HepII-mediated disruption of the cytoskeleton depended upon the presence of collagen in the extracellular matrix, and cell binding studies indicated that HepII signaling involved cross-talk between α41β1 and α1/α2β1 integrins. This is the first time that the PPRARI sequence in the HepII domain has been shown to serve as a physiological α4β1 ligand, suggesting that α4β1 integrin may be a key regulator of tissue contractility.

Surface expression of GluR-D AMPA receptor is dependent upon an interaction between its C-terminal domain and a 4.1 protein

Coleman, S.; Cai, C.; Mottershead, D.; Haapalahti, J.P.; Keinanen, K.
Fonte: Soc Neuroscience Publicador: Soc Neuroscience
Tipo: Artigo de Revista Científica
Publicado em //2003 Português
Relevância na Pesquisa
76.639727%
Dynamic regulation of the number and activity of AMPA receptors is believed to underlie many forms of synaptic plasticity and is presumably mediated by specific protein-protein interactions involving the C-terminal domain of the receptor. Several proteins interacting with the C-terminal tails of the glutamate receptor (GluR)-A and GluR-B subunits have been identified and implicated in the regulation of endocytosis and exocytosis, clustering, and anchoring of AMPA receptors to the cytoskeleton. In contrast, little is known of the molecular interactions of the GluR-D subunit, or of the mechanisms regulating the traffic of GluR-D-containing AMPA receptors. We analyzed the subcellular localization of homomeric GluR-D receptors carrying C-terminal deletions in transfected human embryonic kidney (HEK) 293 cells and in primary neurons by immunofluorescence microscopy and ELISA. A minimal requirement for a 14-residue cytoplasmic segment for the surface expression of homomeric GluR-D receptors was identified. Previously, a similar region in the GluR-A subunit was implicated in an interaction with 4.1 family proteins. Coimmunoprecipitation demonstrated that GluR-D associated with 4.1 protein(s) in both HEK293 cells and rat brain. Moreover, glutathione S-transferase pull-down experiments showed that the same 14-residue segment is critical for 4.1 binding to GluR-A and GluR-D. Point mutations within this segment dramatically decreased the surface expression of GluR-D in HEK293 cells...

Domain-wall fermions with U(1) dynamical gauge fields in (4+1)-dimensions

Aoki, S.; Nagai, K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/09/1996 Português
Relevância na Pesquisa
56.48978%
We carry out a numerical simulation of a domain-wall model in (4+1) dimensions, in the presence of a quenched U(1) dynamical gauge field only in an extra dimension, corresponding to the weak coupling limit of a (4-dimensional) physical gauge coupling. Our numerical data suggest that the zero mode seems absent in the symmetric phase, so that it is difficult to construct a lattice chiral gauge theory in the continuum limit.; Comment: 3 pages, latex, 5 figures, Talk presented at LATTICE96(chiral gauge) by K. Nagai

Koszulity of cohomology = $K(\pi,1)$-ness + quasi-formality

Positselski, Leonid
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.525986%
This paper is a greatly expanded version of Section 9.11 in arXiv:1006.4343. A series of definitions and results illustrating the thesis in the title (where quasi-formality means vanishing of a certain kind of Massey multiplications in the cohomology) is presented. In particular, we include a categorical interpretation of the "Koszulity implies $K(\pi,1)$" claim, discuss the differences between two versions of Massey operations, and apply the derived nonhomogeneous Koszul duality theory in order to deduce the main theorem. In the end we demonstrate a counterexample providing a negative answer to a question of Hopkins and Wickelgren about formality of the cochain DG-algebras of absolute Galois groups, thus showing that quasi-formality cannot be strengthened to formality in the title assertion.; Comment: LaTeX 2e, 31 pages; v.2: additions in the introduction and sections 2 and 4, proposition inserted in section 3, small corrections and improvements in section 5, several references added; v.3: section 4 expanded; v.4: several misprints corrected in section 5; v.5: mistake in example 5.4 corrected, example 5.5 inserted, two misprints corrected and a reference added in section 2

Choice number of complete multipartite graphs $K_{3*3,2*(k-5),1*2}$ and $K_{4,3*2,2*(k-6),1*3}$

He, Wenjie; Zhang, Lingmin; Cranston, Daniel W.; Shen, Yufa; Zheng, Guoping
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 14/08/2013 Português
Relevância na Pesquisa
56.911104%
A graph $G$ is called \emph{chromatic-choosable} if its choice number is equal to its chromatic number, namely $Ch(G)=\chi(G)$. Ohba has conjectured that every graph $G$ satisfying $|V(G)|\leq 2\chi(G)+1$ is chromatic-choosable. Since each $k$-chromatic graph is a subgraph of a complete $k$-partite graph, we see that Ohba's conjecture is true if and only if it is true for every complete multipartite graph. However, the only complete multipartite graphs for which Ohba's conjecture has been verified are: $K_{3*2,2*(k-3),1}$, $K_{3,2*(k-1)}$, $K_{s+3,2*(k-s-1),1*s}$, $K_{4,3,2*(k-4),1*2}$, and $K_{5,3,2*(k-5),1*3}$. In this paper, we show that Ohba's conjecture is true for two new classes of complete multipartite graphs: graphs with three parts of size 3 and graphs with one part of size 4 and two parts of size 3. Namely, we prove that $Ch(K_{3*3,2*(k-5),1*2})=k$ and $Ch(K_{4,3*2,2*(k-6),1*3})=k$ (for $k\geq 5$ and $k\geq 6$, respectively).; Comment: 10 pages; this paper proves 2 special cases of Ohba's Conjecture, which has now been proved completely: http://arxiv.org/abs/1211.1999

Lyman break galaxies, Lya emitters and a radio galaxy in a protocluster at z=4.1

Overzier, Roderik A.; Bouwens, R. J.; Cross, N. J. G.; Venemans, B.; Miley, G. K.; Zirm, A. W.; Benitez, N.; Blakeslee, J. P.; Coe, D.; Demarco, R.; Ford, H.; Homeier, N.; Illingworth, G. D.; Kurk, J. D.; Martel, A.; Mei, S.; Oliveira, I.; Rottgering, H.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.499634%
We present deep HST/ACS observations in g,r,i,z towards the z=4.1 radio galaxy TN J1338-1942 and its overdensity of >30 spectroscopically confirmed Lya emitters (LAEs). We select 66 g-band dropouts to z=27, 6 of which are also a LAE. Although our color-color selection results in a relatively broad redshift range centered on z=4.1, the field of TN J1338-1942 is richer than the average field at the >5 sigma significance, based on a comparison with GOODS. The angular distribution is filamentary with about half of the objects clustered near the radio galaxy, and a small, excess signal (2 sigma) in the projected pair counts at separations of <10" is interpreted as being due to physical pairs. The LAEs are young (a few x 10^7 yr), small ( = 0.13") galaxies, and we derive a mean stellar mass of ~10^8-9 Msun based on a stacked K-band image. We determine star formation rates, sizes, morphologies, and color-magnitude relations of the g-dropouts and find no evidence for a difference between galaxies near TN J1338-1942 and in the field. We conclude that environmental trends as observed in clusters at much lower redshift are either not yet present, or are washed out by the relatively broad selection in redshift. The large galaxy overdensity...

Unsatisfiable (k,(4*2^k/k))-CNF formulas

Gebauer, Heidi
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 10/10/2008 Português
Relevância na Pesquisa
56.552124%
A boolean formula in a conjuctive normal form is called a (k,s)-formula if every clause contains exactly k variables and every variable occurs in at most s clauses. We prove the existence of a (k, 4 * (2^k/k))-CNF formula which is unsatisfiable.; Comment: 3 pages, 1 figure

Dominant g(9/2)^2 neutron configuration in the 4+1 state of 68Zn based on new g factor measurements

Leske, J.; Speidel, K. -H.; Schielke, S.; Gerber, J.; Maier-Komor, P.; Engeland, T.; Hjorth-Jensen, M.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 05/06/2005 Português
Relevância na Pesquisa
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The $g$ factor of the $4_1^+$ state in $^{68}$Zn has been remeasured with improved energy resolution of the detectors used. The value obtained is consistent with the previous result of a negative $g$ factor thus confirming the dominant $0g_{9/2}$ neutron nature of the $4_1^+$ state. In addition, the accuracy of the $g$ factors of the $2_1^+$, $2_2^+$ and $3_1^-$ states has been improved an d their lifetimes were well reproduced. New large-scale shell model calculations based on a $^{56}$Ni core and an $0f_{5/2}1pg_{9/2}$ model space yield a theoretical value, $g(4_1^+) = +0.008$. Although the calculated value is small, it cannot fully explain the experimental value, $g(4_1^+) = -0.37(17)$. The magnitude of the deduced B(E2) of the $4_1^+$ and $2_1^+$ transition is, however, rather well described. These results demonstrate again the importance of $g$ factor measurements for nuclear structure determination s due to their specific sensitivity to detailed proton and neutron components in the nuclear wave functions.; Comment: 7 pages, 3 figs, submitted to PLB

New results on e+e- -> hadrons exclusive cross sections from experiments with SND detector at VEPP-2M e+e- collider in the energy range sqrt(s)=0.4-1.4 GeV

Serednyakov, S. I.; Achasov, M. N.; Beloborodov, K. I.; Bogdanchikov, A. G.; Bozhenok, A. V.; Bukin, A. D.; Bukin, D. A.; Dimova, T. V.; Druzhinin, V. P.; Golubev, V. B.; Korol, A. A.; Koshuba, S. V.; Pakhtusova, E. V.; Shatunov, Yu. M.; Sidorov, V. A.; S
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 12/12/2005 Português
Relevância na Pesquisa
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New results of the e+e- -> pi+pi-, K+K-, K_SK_L, pi0/gamma, eta0/gamma processes cross section measurements are presented. The results are based on the 30 pb^-1 data, accumulated by SND detector at VEPP-2M e+e- collider in the energy range sqrt(s)=0.4-1.4 GeV during 1995-2000 years. The comparison with existing experimental data shows that the measurement accuracy is close to or better than the world average. For the e+e- -> pi+pi- process the accuracy is about 0.01. This is important for calculation of hadronic contribution into the muon anomalous magnetic moment.; Comment: 4 pages, 7 figures, contribution to the proceedings of International Europhysics Conference on High Energy physics, 2005, Lisbon, Portugal