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Mild spherocytosis and altered red cell ion transport in protein 4.2–null mice

Peters, Luanne L.; Jindel, Hitesh K.; Gwynn, Babette; Korsgren, Cathy; John, Kathryn M.; Lux, Samuel E.; Mohandas, Narla; Cohen, Carl M.; Cho, Michael R.; Golan, David E.; Brugnara, Carlo
Fonte: American Society for Clinical Investigation Publicador: American Society for Clinical Investigation
Tipo: Artigo de Revista Científica
Publicado em 01/06/1999 Português
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Protein 4.2 is a major component of the red blood cell (RBC) membrane skeleton. We used targeted mutagenesis in embryonic stem (ES) cells to elucidate protein 4.2 functions in vivo. Protein 4.2–null (4.2–/–) mice have mild hereditary spherocytosis (HS). Scanning electron microscopy and ektacytometry confirm loss of membrane surface in 4.2–/– RBCs. The membrane skeleton architecture is intact, and the spectrin and ankyrin content of 4.2–/– RBCs are normal. Band 3 and band 3–mediated anion transport are decreased. Protein 4.2–/– RBCs show altered cation content (increased K+/decreased Na+)resulting in dehydration. The passive Na+ permeability and the activities of the Na-K-2Cl and K-Cl cotransporters, the Na/H exchanger, and the Gardos channel in 4.2–/– RBCs are significantly increased. Protein 4.2–/– RBCs demonstrate an abnormal regulation of cation transport by cell volume. Cell shrinkage induces a greater activation of Na/H exchange and Na-K-2Cl cotransport in 4.2–/– RBCs compared with controls. The increased passive Na+ permeability of 4.2–/– RBCs is also dependent on cell shrinkage. We conclude that protein 4.2 is important in the maintenance of normal surface area in RBCs and for normal RBC cation transport.

Mapping of a palmitoylatable band 3-binding domain of human erythrocyte membrane protein 4.2.

Bhattacharyya, R; Das, A K; Moitra, P K; Pal, B; Mandal, I; Basu, J
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 01/06/1999 Português
Relevância na Pesquisa
56.693877%
Evidence accumulated over the years suggests that human erythrocyte membrane protein 4.2 is one of the proteins involved in strengthening the cytoskeleton-membrane interactions in the red blood cell. Deficiency of protein 4.2 is linked with a variety of hereditary haemolytic anaemia. However, the interactions of protein 4.2 with other proteins of the erythrocyte membrane remain poorly understood. The major membrane-binding site for protein 4.2 resides on the cytoplasmic domain of band 3 (CDB3). In order to carry out an initial characterization of its interaction with the CDB3, protein 4. 2 was subjected to proteolytic cleavage and gel renaturation assay, and the 23-kDa N-terminal domain was found to interact with band 3. This domain contained two putative palmitoylatable cysteine residues, of which cysteine 203 was identified as the palmitoylatable cysteine. Recombinant glutathione S-transferase-fusion peptides derived from this domain were characterized with respect to their ability to interact with the CDB3. Whereas these studies do not rule out the involvement of other subsites on protein 4.2 in interaction with the CDB3, the evidence suggests that the region encompassing amino acid residues 187-211 is one of the domains critical for the protein 4.2-CDB3 interaction. This is also the first demonstration that palmitoylation serves as a positive modulator of this interaction.

Mapping of a spectrin-binding domain of human erythrocyte membrane protein 4.2.

Mandal, Debabrata; Moitra, Prasun K; Basu, Joyoti
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/06/2002 Português
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Protein 4.2 is a major component of the red blood cell membrane skeleton. Deficiency of protein 4.2 is linked with a variety of hereditary haemolytic anaemias. However, the interactions of protein 4.2 with other proteins of the erythrocyte membrane remain poorly understood. The major membrane-binding site for protein 4.2 resides on the cytoplasmic domain of band 3. Protein 4.2 interacts directly with spectrin in solution, suggesting that it stabilizes interactions between the membrane skeleton and the erythrocyte membrane. A 30 kDa polypeptide, with its N-terminus corresponding to amino acid residue 269, derived by partial proteolysis of protein 4.2, was found to interact with biotinylated spectrin in gel renaturation assays. A series of overlapping glutathione S-transferase fusion peptides were constructed, and an alpha-helical domain encompassing residues 470-492 was found to be instrumental in mediating protein 4.2-spectrin interactions. Direct binding of a synthetic peptide, with the sequence corresponding to residues 470-492, to spectrin and the ability of the peptide to inhibit spectrin binding of protein 4.2 confirmed that these residues are crucial in mediating protein 4.2-spectrin interactions.

Identifying the Lipid-Protein Interface of the α4β2 Neuronal Nicotinic Acetylcholine Receptor: Hydrophobic Photolabeling Studies with [125I]TID †

Hamouda, Ayman K.; Sanghvi, Mitesh; Chiara, David C.; Cohen, Jonathan B.; Blanton, Michael P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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Using an acetylcholine-derivatized affinity column, we have purified human α4β2 neuronal nicotinic acetylcholine receptors (nAChR) from a stably transfected HEK-293 cell line. Both the quantity and the quality of the purified receptor are suitable for applying biochemical methods to directly study the structure of the α4β2 nAChR. In this first study, the lipid-protein interface of purified and lipid reconstituted α4β2 nAChRs was directly examined using photoaffinity labeling with the hydrophobic probe 3-trifluoromethyl-3-(m-[125I]iodophenyl) diazirine ([125I]TID). [125I]TID photoincorporated into both α4 and β2 subunits, and for each subunit the labeling was initially mapped to fragments containing the M4 and M1-M3 transmembrane segments. For both the α4 and β2 subunits, ~ 60% of the total labeling was localized within fragments that contain the M4 segment which suggests that the M4 segment has the greatest exposure to lipid. Within M4 segments, [125I]TID labeled homologous amino acids α4-Cys582/β2-Cys445 which are also homologous to the [125I]TID-labeled residues α1-Cys418 and β1-Cys447 in the lipid exposed face of Torpedo nAChR α1M4 and β1M4, respectively. Within the α4M1 segment, [125I]TID labeled residues Cys226 and Cys231 which correspond to the [125I]TID-labeled residues Cys222 and Phe227 at the lipid exposed face of the Torpedo α1M1 segment. In β2M1...

Photoaffinity Labeling the Agonist Binding Domain of α4β4 and α4β2 Neuronal Nicotinic Acetylcholine Receptors with [125I]Epibatidine and 5[125I]A-85380

Hamouda, Ayman K.; Jin, Xiaochun; Sanghvi, Mitesh; Srivastava, Shouryadeep; Pandhare, Akash; Duddempudi, Phaneendra K.; Steinbach, Joe Henry; Blanton, Michael P.
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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56.68536%
The development of nicotinic acetylcholine receptor (nAChR) agonists, particularly those that discriminate between neuronal nAChR subtypes, hold promise as potential therapeutic agents for many neurological diseases and disorders. To this end, we photoaffinity labeled human α4β2 and rat α4β4 nAChRs affinity-purified from stably transfected HEK-293 cells, with the agonists [125I]epibatidine and 5[125I]A-85380. Our results show that both agonists photoincorporated into the β4 subunit with little or no labeling of the β2 and α4 subunits respectively. [125I]epibatidine labeling in the β4 subunit was mapped to two overlapping proteolytic fragments that begin at β4V102 and contain Loop E (β4I109-P120) of the agonist binding site. We were unable to identify labeled amino acid(s) in Loop E by protein sequencing, but we were able to demonstrate that β4Q117 in Loop E is the principal site of [125I]epibatidine labeling. This was accomplished by substituting residues in the β2 subunit with the β4 homologs and finding [125I]epibatidine labeling in β4 and β2F119Q subunits with little, if any, labeling in α4, β2, or β2S113R subunits. Finally, functional studies established that the β2F119/β4Q117 position is an important determinant of the receptor subtype-selectivity of the agonist 5I-A-85380...

[3H]Epibatidine Photolabels Non-equivalent Amino Acids in the Agonist Binding Site of Torpedo and α4β2 Nicotinic Acetylcholine Receptors*

Srivastava, Shouryadeep; Hamouda, Ayman K.; Pandhare, Akash; Duddempudi, Phaneendra K.; Sanghvi, Mitesh; Cohen, Jonathan B.; Blanton, Michael P.
Fonte: American Society for Biochemistry and Molecular Biology Publicador: American Society for Biochemistry and Molecular Biology
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.58219%
Nicotinic acetylcholine receptor (nAChR) agonists, such as epibatidine and its molecular derivatives, are potential therapeutic agents for a variety of neurological disorders. In order to identify determinants for subtype-selective agonist binding, it is important to determine whether an agonist binds in a common orientation in different nAChR subtypes. To compare the mode of binding of epibatidine in a muscle and a neuronal nAChR, we photolabeled Torpedo α2βγδ and expressed human α4β2 nAChRs with [3H]epibatidine and identified by Edman degradation the photolabeled amino acids. Irradiation at 254 nm resulted in photolabeling of αTyr198 in agonist binding site Segment C of the principal (+) face in both α subunits and of γLeu109 and γTyr117 in Segment E of the complementary (−) face, with no labeling detected in the δ subunit. For affinity-purified α4β2 nAChRs, [3H]epibatidine photolabeled α4Tyr195 (equivalent to Torpedo αTyr190) in Segment C as well as β2Val111 and β2Ser113 in Segment E (equivalent to Torpedo γLeu109 and γTyr111, respectively). Consideration of the location of the photolabeled amino acids in homology models of the nAChRs based upon the acetylcholine-binding protein structure and the results of ligand docking simulations suggests that epibatidine binds in a single preferred orientation within the α-γ transmitter binding site...

Nicotinic α4β2 Receptor Imaging Agents. Part III. Synthesis and Biological Evaluation of 3-(2-(S)-Azetidinylmethoxy)-5-(3′-18F-Fluoropropyl)Pyridine (18F-Nifzetidine)

Pichika, Rama; Easwaramoorthy, Balu; Christian, Bradley T.; Shi, Bingzhi; Narayanan, Tanjore K.; Collins, Daphne; Mukherjee, Jogeshwar
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
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56.560254%
Thalamic and extrathalamic nicotinic α4β2 receptors found in the brain have been implicated in Alzheimer’s disease, Parkinson’s disease, substance abuse and other disorders. We report here the development of 3-(2-(S)-azetidinylmethoxy)-5-(3′-fluoropropyl)pyridine (nifzetidine) as a new putative high affinity antagonist for nicotinic α4β2 receptors. Nifzetidine in rat brain homogenate assays containing α4β2 sites labeled with 3H-cytisine exhibited a binding affinity, Ki = 0.67 nM. The fluorine-18 analog, 3-(2-(S)-azetidinylmethoxy)-5-(3′-18F-fluoropropyl)pyridine (18F-nifzetidine) was synthesized in 20–40% yield and apparent specific activity was estimated to be above 2 Ci/μmol. Rat brain slices indicated selective binding of 18F-nifzetidine to thalamus, subiculum, striata, cortex and other regions consistent with α4β2 receptor distribution. This selective binding was displaced >85% by 150 μM nicotine. PET imaging studies of 18F-nifzetidine in anesthetized rhesus monkey showed slow uptake in the various brain regions. Retention of 18F-nifzetidine was maximal in the thalamus and lateral geniculate followed by regions of the temporal and frontal cortex. Cerebellum showed the least uptake. Thalamus to cerebellum ratio was about 2.3 at 180 min post-injection and continued to rise. 18F-Nifzetidine shows promise as a new PET imaging agent for α4β2 nAChR. However...

Nicotinic α4β2 receptor imaging agents. Part IV. Synthesis and Biological Evaluation of 3-(2-(S)-3,4-dehydropyrrolinylmethoxy)-5-(3’-18F-Fluoropropyl)pyridine (18F-Nifrolene) using PET

Pichika, Rama; Kuruvilla, Sharon A.; Patel, Narmisha; Vu, Kenny; Sinha, Sangamitra; Easwaramoorthy, Balu; Narayanan, Tanjore K.; Shi, Bingzhi; Christian, Bradley; Mukherjee, Jogeshwar
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Português
Relevância na Pesquisa
56.5389%
Imaging agents for nicotinic α4β2 receptors in the brain have been underway for studying various CNS disorders. Previous studies from our laboratories have reported the successful development of agonist, 18F-nifene. In attempts to develop potential antagonists, 18F-nifrolidine and 18F-nifzetidine were previously reported. Further optimization of these fluoropropyl derivatives has now been carried out resulting in 3-(2-(S)-3,4-dehydropyrrolinylmethoxy)-5-(3′-Fluoropropyl)pyridine (nifrolene) as a new high affinity agent for nicotinic α4β2 receptors. Nifrolene in rat brain homogenate assays—labeled with 3H-cytisine—exhibited a binding affinity of 0.36 nM. The fluorine-18 analog, 18F-nifrolene, was synthesized in approximately 10–20% yield and specific activity was estimated to be >2000 Ci/mmol. Rat brain slices indicated selective binding to anterior thalamic nuclei, thalamus, subiculum, striata, cortex and other regions consistent with α4β2 receptor distribution. This selective binding was displaced >90% by 300 µM nicotine. Thalamus to cerebellum ratio (>10) was the highest for 18F-nifrolene with several other regions showing selective binding. In vivo rat PET studies exhibited rapid uptake of 18F-nifrolene in the brain with specific retention in the thalamus and other brain regions while clearing out from the cerebellum. Thalamus to cerebellum ratio value in the rat was >4. Administration of nicotine caused a rapid decline in the thalamic 18F-nifrolene suggesting reversible binding to nicotinic receptors. PET imaging studies of 18F-nifrolene in anesthetized rhesus monkey revealed highest binding in the thalamus followed by regions of the lateral cingulated and temporal cortex. Cerebellum showed the least binding. Thalamus to cerebellum ratio in the monkey brain was >3 at 120 min. These ratios of 18F-nifrolene are higher than measured for 18F-nifrolidine and 18F-nifzetidine. 18F-Nifrolene thus shows promise as a new PET imaging agent for α4β2 nAChR.

Allosteric inhibition of glycogen phosphorylase a by the potential antidiabetic drug 3-isopropyl 4-(2-chlorophenyl)-1,4-dihydro-1-ethyl-2-methyl-pyridine-3,5,6-tricarbo xylate.

Oikonomakos, N. G.; Tsitsanou, K. E.; Zographos, S. E.; Skamnaki, V. T.; Goldmann, S.; Bischoff, H.
Fonte: Cold Spring Harbor Laboratory Press Publicador: Cold Spring Harbor Laboratory Press
Tipo: Artigo de Revista Científica
Publicado em /10/1999 Português
Relevância na Pesquisa
56.625693%
The effect of the potential antidiabetic drug (-)(S)-3-isopropyl 4-(2-chlorophenyl)-1,4-dihydro-1-ethyl-2-methyl-pyridine-3,5,6-tricarbox ylate (W1807) on the catalytic and structural properties of glycogen phosphorylase a has been studied. Glycogen phosphorylase (GP) is an allosteric enzyme whose activity is primarily controlled by reversible phosphorylation of Ser14 of the dephosphorylated enzyme (GPb, less active, predominantly T-state) to form the phosphorylated enzyme (GPa, more active, predominantly R-state). Upon conversion of GPb to GPa, the N-terminal tail (residues 5-22), which carries the Ser14(P), changes its conformation into a distorted 3(10) helix and its contacts from intrasubunit to intersubunit. This alteration causes a series of tertiary and quaternary conformational changes that lead to activation of the enzyme through opening access to the catalytic site. As part of a screening process to identify compounds that might contribute to the regulation of glycogen metabolism in the noninsulin dependent diabetes diseased state, W1807 has been found as the most potent inhibitor of GPb (Ki = 1.6 nM) that binds at the allosteric site of T-state GPb and produces further conformational changes, characteristic of a T'-like state. Kinetics show W1807 is a potent competitive inhibitor of GPa (-AMP) (Ki = 10.8 nM) and of GPa (+1 mM AMP) (Ki = 19.4 microM) with respect to glucose 1-phosphate and acts in synergism with glucose. To elucidate the structural features that contribute to the binding...

Conversion of 1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl)methyl]cytosine to cidofovir by an intracellular cyclic CMP phosphodiesterase.

Mendel, D B; Cihlar, T; Moon, K; Chen, M S
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /03/1997 Português
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56.70243%
Cidofovir (HPMPC) [1-[(S)-3-hydroxy-2-(phosphonomethoxy)propyl]-cytosine] is an acyclic nucleotide analog with potent and selective activity against herpesviruses. The prodrug, cyclic HPMPC (cHPMPC) [1-[((S)-2-hydroxy-2-oxo-1,4,2-dioxaphosphorinan-5-yl) methyl]cytosine], has antiviral activity similar to that of the parent compound but exhibits reduced toxicity in animal models. cHPMPC is converted to cidofovir by a cellular cyclic CMP phosphodiesterase (EC 3.1.4.37) which hydrolyzes a variety of substrates, including adenosine 3',5'-cyclic monophosphate (cAMP) and cytidine 3',5'-cyclic monophosphate (cCMP). The K(m) and Vmax values for hydrolysis of cHPMPC by cCMP phosphodiesterase purified from human liver are 250 microM and 0.66 nmol.min-1.unit-1, respectively. These values are similar to the K(m) and Vmax values for cAMP (23 microM and 1.16 nmol.min-1.unit-1, respectively) and cCMP (75 microM and 2.32 nmol.min-1.unit of enzyme-1, respectively). The catalytic efficiency (Vmax/K(m) ratio) of this enzyme for the cHPMPC substrate is only 10- to 20-fold lower than those for the natural cyclic nucleotides, indicating that cHPMPC is a viable intracellular substrate for the human enzyme. Kinetic analysis indicates that cHPMPC, cAMP, and cCMP are competitive with respect to each other and that they are hydrolyzed by the same enzyme. cHPMPC is hydrolyzed to cidofovir in all primary human cell systems tested...

Potent and specific inhibition of human immunodeficiency virus type 1 replication by 4-(2,6-dichlorophenyl)-1,2,5-thiadiazol-3-Y1 N,N-dialkylcarbamate derivatives.

Ijichi, K; Fujiwara, M; Hanasaki, Y; Watanabe, H; Katsuura, K; Takayama, H; Shirakawa, S; Sakai, S; Shigeta, S; Konno, K
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /10/1995 Português
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56.68657%
4-(2,6-Dichlorophenyl)-1,2,5-thiadiazol-3-yl N,N-dialkylcarbamate (TDA) derivatives were found to be highly potent and specific inhibitors of human immunodeficiency virus type 1 (HIV-1) replication in a variety of cell cultures. The most potent congener of TDA derivatives, RD4-2024, inhibited HIV-1 replication by 50% at concentrations of 12.5 and 4.8 nM in MT-4 cells and peripheral blood mononuclear cells, respectively. These concentrations were more than 2,000- and 30,000-fold lower than its 50% cytotoxic concentrations, respectively. Although the TDA derivatives were active against 3'-azido-3'-deoxythymidine-resistant HIV-1, no antiviral activities were observed against HIV-2 and nonnucleoside reverse transcriptase inhibitor-resistant mutants of HIV-1. The TDA derivatives inhibited recombinant HIV-1 reverse transcriptase activity, depending on the template-primer used for the assay. However, they did not interact with HIV-2 reverse transcriptase. Thus, the TDA derivatives belong to the family of nonnucleoside reverse transcriptase inhibitors. Because of their potent anti-HIV-1 activities in vitro and their low levels of toxicity in mice, the TDA derivatives deserve further evaluation as candidate drugs for the treatment of patients with AIDS.

Microscopic Description of K^+ Scattering on 4^He, 16^O and 40^Ca Nuclei using Meson Exchange Theory

Hanna, K. M.; Sewailem, Sh. M.; Shalaby, A. G.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 02/09/2013 Português
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56.588223%
We have calculated the total cross section for k^+-4^He, 16^O, 40^Ca, intes at incident momenta of the kaon P_lab<1GeV . We derived the K^+-nucleon optical potential according to the exchange of 3- mesons (segma,roh,omega) and also for 4- (segma,roh,omega, segma_0) exchanged between the reactants. We showed both of the radial behavior of the real and the imaginary parts of the derived potential. Comparisons between the available experimental data, other theoretical work and the calculated total cross sections for the three studied nuclei which have shown a reasonable agreement. The extended four mesons exchanged optical potential gave better close results to the experimental data. Further, ratios of the total cross sections of the studied nuclei with respect to the total cross section with the deuteron nucleus for the two applied optical potentials were given. In addition, the ratio of the theoretical result of the total cross section for the interaction of the K^+ meson with the deuteron was compared with the corresponding experimental one to evaluate our theoretical results in a more clear manner.; Comment: 20 pages, 22 figures

The Conformal Group SO(4,2) and Robertson-Walker Spacetimes

Keane, Aidan J.; Barrett, Richard K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 01/07/1999 Português
Relevância na Pesquisa
56.609746%
The Robertson-Walker spacetimes are conformally flat and so are conformally invariant under the action of the Lie group SO(4,2), the conformal group of Minkowski spacetime. We find a local coordinate transformation allowing the Robertson-Walker metric to be written in a manifestly conformally flat form for all values of the curvature parameter k continuously and use this to obtain the conformal Killing vectors of the Robertson-Walker spacetimes directly from those of the Minkowski spacetime. The map between the Minkowski and Robertson-Walker spacetimes preserves the structure of the Lie algebra so(4,2). Thus the conformal Killing vector basis obtained does not depend upon k, but has the disadvantage that it does not contain explicitly a basis for the Killing vector subalgebra. We present an alternative set of bases that depend (continuously) on k and contain the Killing vector basis as a sub-basis (these are compared with a previously published basis). In particular, bases are presented which include the Killing vectors for all Robertson-Walker spacetimes with additional symmetry, including the Einstein static spacetimes and the de Sitter family of spacetimes, where the basis depends on the Ricci scalar R.; Comment: 23 pages, 3 figures...

Exclusive electroproduction of phi mesons at 4.2 GeV

CLAS Collaboration; Lukashin, K.; Smith, E. S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Português
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56.620405%
We studied the exclusive reaction e p --> e' p' phi using the phi --> K^+ K^- decay mode. The data were collected using a 4.2 GeV incident electron beam and the CLAS detector at Jefferson Lab. Our experiment covers the range in Q^2 from 0.7 to 2.2 GeV^2, and W from 2.0 to 2.6 GeV. Taken together with all previous data, we find a consistent picture of phi production on the proton. Our measurement shows the expected decrease of the t-slope with the vector meson formation time c Delta tau below 2 fm. At = 0.6 fm, we measure b_phi = 2.27 +- 0.42 GeV^-2. The cross section dependence on W as W^{0.2+-0.1} at Q^2 = 1.3 GeV^2 was determined by comparison with phi production at HERA after correcting for threshold effects. This is the same dependence as observed in photoproduction.; Comment: 13 pages, LaTeX, 16 eps figures, 3 tables, submitted to Phys Rev C; revised Fig 9 and Subsec "Differential Cross Section"

The Properties and Evolution of a K-band Selected Sample of Massive Galaxies at z~0.4 - 2 in the Palomar/DEEP2 Survey

Conselice, C. J.; Bundy, K.; Trujillo, I.; Coil, A.; Eisenhardt, P.; Ellis, R. S.; Georgakakis, A.; Huang, J.; Lotz, J.; Nandra, K.; Newman, J.; Papovich, C.; Weiner, B.; Willmer, C.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 07/08/2007 Português
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56.762124%
We present the results of a study on the properties and evolution of massive (M_* > 10^11 M_0) galaxies at z~0.4 - 2 utilising Keck spectroscopy, near-Infrared Palomar imaging, and Hubble, Chandra, and Spitzer data covering fields targeted by the DEEP2 galaxy spectroscopic survey. Our sample is K band selected based on wide-area NIR imaging from the Palomar Observatory Wide-Field Infrared Survey, which covers 1.53 deg^2 to K_s,vega~20.5. Our major findings include: (i) statistically the mass and number densities of M_* > 10^11 M_0 galaxies show little evolution between z = 0 - 1, and from z ~ 0 - 2 for M_* > 10^11.5 M_0 galaxies. (ii) Using Hubble ACS imaging, we find that M_* > 10^11 selected galaxies show a nearly constant elliptical fraction of ~70-90% at all redshifts. The remaining objects are peculiars possibly undergoing mergers at z > 0.8, while spirals dominate the remainder at lower redshifts. (iii) We find that only a fraction (~60%) of massive galaxies with M_* > 10^11 M_0 are on the red-sequence at z~1.4, while nearly 100% evolve onto it by z~0.4. (iv) By utilising Spitzer MIPS imaging and [OII] line fluxes we argue that M_* > 10^11.5 galaxies have a steeply declining star formation rate density ~(1+z)^6. By examining the contribution of star formation to the evolution of the mass function...

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
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76.62952%
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

Molecular ions in the O-rich evolved star OH231.8+4.2: HCO$^+$,H$^{13}$CO$^+$ and first detection of SO$^+$, N$_2$H$^+$, and H$_3$O$^+$

Contreras, C. Sánchez; Prieto, L. Velilla; Agúndez, M.; Cernicharo, J.; Quintana-Lacaci, G.; Bujarrabal, V.; Alcolea, J.; Goicoechea, J. R.; Herpin, F.; Menten, K. M.; Wyrowski, F.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/03/2015 Português
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56.552%
OH 231.8+4.2, a bipolar outflow around a Mira-type variable star, displays a unique molecular richness amongst circumstellar envelopes (CSEs) around O-rich AGB and post-AGB stars. We report line observations of the HCO+ and H13CO+ molecular ions and the first detection of SO+, N2H+, and (tentatively) H3O+ in this source. SO+ and H3O+ have not been detected before in CSEs around evolved stars. These data have been obtained as part of a full mm-wave and far-IR spectral line survey carried out with the IRAM 30 m radio telescope and with Herschel/HIFI. Except for H3O+, all the molecular ions detected in this work display emission lines with broad profiles (FWHM 50-90 km/s), which indicates that these ions are abundant in the fast bipolar outflow of OH 231.8. The narrow profile (FWHM 14 km/s) and high critical densities (>1e6cm-3 ) of the H3O+ transitions observed are consistent with this ion arising from denser, inner (and presumably warmer) layers of the fossil remnant of the slow AGB CSE at the core of the nebula. From rotational diagram analysis, we deduce excitation temperatures of Tex 10-20 K for all ions except for H3O+, which is most consistent with Tex 100 K. Although uncertain, the higher excitation temperature suspected for H3O+ is similar to that recently found for H2O and a few other molecules...

Thermoelectric properties of the Yb_9Mn_(4.2-x)Zn_xSb_9 solid solutions

Ohno, Saneyuki; Zevalkink, Alexandra; Takagiwa, Yoshiki; Bux, Sabah K.; Snyder, G. Jeffrey
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
Publicado em 28/05/2014 Português
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Yb_9Mn_(4.2)Sb_9 has been shown to have extremely low thermal conductivity and a high thermoelectric figure of merit attributed to its complex crystal structure and disordered interstitial sites. Motivated by previous work which shows that isoelectronic substitution of Mn by Zn leads to higher mobility by reducing spin disorder scattering, this study investigates the thermoelectric properties of the solid solution, Yb_9Mn_(4.2−x)Zn_xSb_9 (x = 0, 1, 2, 3 and 4.2). Measurements of the Hall mobility at high temperatures (up to 1000 K) show that the mobility can be increased by more than a factor of 3 by substituting Zn into Mn sites. This increase is explained by the reduction of the valence band effective mass with increasing Zn, leading to a slightly improved thermoelectric quality factor relative to Yb_9Mn_(4.2)Sb_9. However, increasing the Zn-content also increases the p-type carrier concentration, leading to metallic behavior with low Seebeck coefficients and high electrical conductivity. Varying the filling of the interstitial site in Yb_9Zn_(4+y)Sb_9 (y = 0.2, 0.3, 0.4 and 0.5) was attempted, but the carrier concentration (~10^(21) cm^(−3) at 300 K) and Seebeck coefficients remained constant, suggesting that the phase width of Yb_9Zn_(4+y)Sb_9 is quite narrow.

Glass-like lattice thermal conductivity and high thermoelectric efficiency in Yb_9Mn_(4.2)Sb_9

Bux, Sabah K.; Zevalkink, Alexandra; Janka, Oliver; Uhl, David; Kauzlarich, Susan; Snyder, Jeffrey G.; Fleurial, Jean-Pierre
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Article; PeerReviewed Formato: application/pdf; application/pdf
Publicado em //2014 Português
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Motivated by excellent thermoelectric performance in the well-known Yb-based Zintl compounds Yb_(14)MnSb_(11) and YbZn_(2−x)Mn_xSb_2, this study investigates the thermoelectric properties of Yb_9Mn_(4.2)Sb_9. Unlike most transition metal containing Zintl phases, Yb_9Mn_(4.2)Sb)9 contains a partially occupied Mn site and thus does not have a valence-precise stoichiometry. Samples were synthesized by direct ball milling of the elements, followed by hot pressing. Consistent with previous reports, X-ray diffraction and wavelength dispersive spectroscopy confirmed a narrow composition range near Yb_9Mn_(4.2)Sb_9. High temperature measurements of the electronic properties of Yb_9Mn_(4.2)Sb_9 indicate that it is a degenerate p-type semiconductor with a band gap sufficiently large for high temperature thermoelectric applications. Hall measurements reveal that Yb_9Mn_(4.2)Sb_9 has a high extrinsic carrier concentration (~10^(20) h^+ cm^(−3)), which is due to the deviation from the theoretical “Zintl composition” of Yb_9Mn_(4.5)Sb_9. The measured carrier concentration coincides with the optimum concentration predicted using a single parabolic band model. Measurements of the thermal diffusivity and heat capacity reveal an extremely low...

Dislocation mobility in pure copper at 4.2 °K

Jassby, K. M.; Vreeland, T., Jr.
Fonte: Instituto de Tecnologia da Califórnia Publicador: Instituto de Tecnologia da Califórnia
Tipo: Article; PeerReviewed Formato: application/pdf
Publicado em 15/10/1973 Português
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Torsional stress pulses of several microseconds duration were applied at 4.2 °K to cylindrical single crystals of copper containing freshly introduced dislocations. Dislocation displacements were measured by means of a double-etch technique, and subsequently the dislocation damping coefficient B was determined to be equal to 0.8 × 10-5 dyn sec/cm2. While B decreases monotonically with decreasing temperature, the value of B at 4.2 °K is greater than that predicted from theoretical calculations of the interaction between a moving dislocation and the conduction-electron gas in copper.