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Interaction of 10-(octyloxy) decyl-2-(trimethylammonium) ethyl phosphate with mimetic membranes and cytotoxic effect on leukemic cells

SANTOS, G. A. dos; THOME, C. H.; FERREIRA, G. A.; YONEDA, J. S.; NOBRE, T. M.; DAGHASTANLI, K. R. P.; SCHEUCHER, P. S.; GIMENES-TEIXEIRA, H. L.; CONSTANTINO, M. G.; OLIVEIRA, K. T. de; FACA, V. M.; FALCAO, R. P.; GREENE, L. J.; REGO, E. M.; CIANCAGLINI, P
Fonte: ELSEVIER SCIENCE BV Publicador: ELSEVIER SCIENCE BV
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.72%
10-(Octyloxy) decyl-2-(trimethylammonium) ethyl phosphate (ODPC) is an alkylphospholipid that can interact with cell membranes because of its amphiphilic character. We describe here the interaction of ODPC with liposomes and its toxicity to leukemic cells with an ED-50 of 5.4, 5.6 and 2.9 pM for 72 h of treatment for inhibition of proliferation of NB4, U937 and K562 cell lines, respectively, and lack of toxicity to normal hematopoietic progenitor cells at concentrations up to 25 pM. The ED-50 for the non-malignant HEK-293 and primary human umbilical vein endothelial cells (HUVEC) was 63.4 and 60.7 mu M, respectively. The critical micellar concentration (CMC) of ODPC was 200 mu M. Dynamic light scattering indicated that dipalmitoylphosphatidylcholine (DPPC) liposome size was affected only above the CMC of ODPC. Differential calorimetric scanning (DCS) of liposomes indicated a critical transition temperature (T(c)) of 41.5 degrees C and an enthalpy (Delta H) variation of 7.3 kcal mol(-1). The presence of 25 mu M ODPC decreased T(c) and Delta H to 393 degrees C and 4.7 kcal mol(-1), respectively. ODPC at 250 mu M destabilized the liposomes (36.3 degrees C. 0.46 kcal mol(-1)). Kinetics of 5(6)-carboxyfluorescein (CF) leakage from different liposome systems indicated that the rate and extent of CF release depended on liposome composition and ODPC concentration and that above the CMC it was instantaneous. Overall...

Triple Structural Transition below Room Temperature in the Antifilarial Drug Diethylcarbamazine Citrate

SILVA, Cecilia C. P. da; MARTINS, Felipe T.; HONORATO, Sara B.; BOECHAT, Nubia; AYALA, Alejandro P.; ELLENA, Javier
Fonte: AMER CHEMICAL SOC Publicador: AMER CHEMICAL SOC
Tipo: Artigo de Revista Científica
ENG
Relevância na Pesquisa
35.82%
A very unusual triple structural transition pattern below room temperature was observed for the antifilarial drug diethylcarbamazine citrate. Besides the first thermal, crystallographic, and vibrational investigations of this first-line drug used in clinical treatment for lymphatic filariasis, a noteworthy behavior with three structural transformations as a function of temperature was demonstrated by differential scanning calorimetry, Raman spectroscopy, and single-crystal X-ray diffractometry. Our X-ray data on single crystals allow for a complete featuring and understanding of all transitions, since the four structures associated with the three solid-solid phase transformations were accurately determined. Two of three structural transitions show an order-disorder mechanism and temperature hysteresis with exothermic peaks at 224 K (T(1)`) and 213 K (T(2)`) upon cooling and endothermic ones at 248 K (T(1)) and 226 K (T(2)) upon heating. The other transition occurs at 108 K (T(3)) and it is temperature-rate sensitive. Molecular displacements onto the (010) plane and conformational changes of the diethylcarbamazine backbone as a consequence of the C-H center dot center dot center dot N hydrogen bonding formation/cleavage between drug molecules explain the mechanism of the transitions at T(1)`/T(2). However...

Partial molar volume of mefenamic acid in alcohol at temperatures between T=293.15 and T=313.15 K

Iqbal,Muhammad J.; Siddiquah,Mahrukh
Fonte: Sociedade Brasileira de Química Publicador: Sociedade Brasileira de Química
Tipo: Artigo de Revista Científica Formato: text/html
Publicado em 01/10/2006 EN
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35.81%
Apparent molar volume (Vphi), partial molar volume (V), solute-solute interaction parameter (Sv), partial molar expansivity (E(0)2) and isobaric thermal expansion coefficient (alpha2) of mefenamic acid in six different organic solvents namely, methanol, ethanol, 1-propanol, 2-propanol, 1-butanol, and 2-butanol, have been calculated from the measured solution densities over a temperature range of T=293.15 and T=313.15±0.1K. The solution densities were measured by an automated vibrating tube densitymeter (Anton Paar DMA-48). The molality range investigated was between 6×10-3 and 3.25 ×10-2 mol kg -1. The effect of temperature on apparent molar volume and partial molar volume was also determined. Decrease in solute-solvent interactions with an increase in temperature has been noted. Partial molar volume of mefenamic acid changes with the change in solvent polarity.

Molecular cloning and functional expression of the bumetanide-sensitive Na-K-Cl cotransporter.

Xu, J C; Lytle, C; Zhu, T T; Payne, J A; Benz, E; Forbush, B
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/03/1994 EN
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35.73%
By mediating the coupled movement of Na, K, and Cl ions across the plasma membrane of most animal cells, the bumetanide-sensitive Na-K-Cl cotransporter (NKCC) plays a vital role in the regulation of ionic balance and cell volume. The transporter is a central element in the process of vectorial salt transport in secretory and absorptive epithelia. A cDNA encoding a Na-K-Cl cotransport protein was isolated from a shark rectal gland library by screening with monoclonal antibodies to the native shark cotransporter. The 1191-residue protein predicted from the cDNA sequence has 12 putative transmembrane domains flanked by large cytoplasmic N and C termini. Regulatory phosphoacceptor residues in isolated peptides are identified as Thr-189 and Thr-1114 in the predicted sequence. Northern blot analysis identified a 7.4-kb mRNA in rectal gland and most other shark tissues; a 5.2-kb mRNA was restricted to shark kidney. Homology with an uncharacterized gene from Caenorhabditis elegans and with the thiazide-sensitive Na-Cl cotransporter of flounder urinary bladder was found over most of the coding region; shorter stretches of homology were found with a C. elegans cDNA and with an uncharacterized gene of cyanobacterium. Human HEK-293 cells have been stably transfected with the shark cDNA and shown to express Na-K-Cl cotransport activity with the bumetanide sensitivity of the shark protein. The expressed transporter is functionally quiescent in the host cells and can be activated by depleting the cells of chloride.

Analysis of a YAC with human telomeres and oriP from epstein-barr virus in yeast and 293 cells.

Tolmachova, T; Simpson, K; Huxley, C
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 15/09/1999 EN
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35.79%
One approach to the construction and propagation of a mammalian artificial chromosome is to build it up in Saccharomyces cerevisiae, using a yeast artificial chromosome (YAC) base. We have demonstrated that circular YACs carrying the Epstein-Barr virus origin of plasmid replication ( oriP ) are maintained as stable, episomal elements in human cells. We wished to determine whether this technology could be extended, to generate linear extrachromosomal elements. Here, we describe the generation of retrofitting constructs, which permit the addition of human telomeres and the oriP domain to YACs. The constructs contain 0.8 kb of human telomere sequence separated by a unique Not I site from 0.7 kb of Tetrahymena telomere sequence. These constructs seed telomere formation with approximately 40-60% efficiency in human 293-EBNA and HT1080 cells whether or not the Tetrahymena sequence is removed by Not I digestion. A detailed analysis demonstrates that YACs carrying the human telomere cassettes on both arms show instability of the telomere sequences in S.cerevisiae at a frequency of approximately 50%. Introduction of correctly retrofitted, linear oriP YACs into human 293-EBNA cells by lipofection resulted in the generation of circular extrachromosomal elements varying in size from 8 to 300 kb. However...

Topoisomerase activity is associated with purified SV40 T antigen.

Mann, K
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em 25/04/1993 EN
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35.84%
Purified SV40 T antigen has been assayed for topoisomerase activity. The ability to relax negatively-supercoiled SV40 DNA was found in preparations of T antigen purified either from human 293 cells infected with Ad5-SVR111 virus or from insect Sf9 cells infected with recombinant baculovirus 941T. The T antigen-associated relaxing activity was stimulated by MgCl2 and was not dependent on ATP, suggesting that it is not due to cellular topoisomerase II. The topoisomerase activity was immunoprecipitated by a monoclonal antibody specific for T antigen, but not by a control monoclonal antibody. In addition, immunoblotting of purified T antigen from human 293 cells with antihuman topoisomerase I and anti-human topoisomerase II antibodies failed to detect cellular topoisomerases I or II. Sedimentation analysis of purified T antigen revealed that the topoisomerase activity co-sedimented with the hexameric form of T antigen at 23S. The topoisomerase activity is, therefore, either inherent to T antigen or due to a cellular topoisomerase I tightly bound to, and co-purifying with, T antigen.

Properties of HERG channels stably expressed in HEK 293 cells studied at physiological temperature.

Zhou, Z; Gong, Q; Ye, B; Fan, Z; Makielski, J C; Robertson, G A; January, C T
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /01/1998 EN
Relevância na Pesquisa
35.77%
We have established stably transfected HEK 293 cell lines expressing high levels of functional human ether-a go-go-related gene (HERG) channels. We used these cells to study biochemical characteristics of HERG protein, and to study electrophysiological and pharmacological properties of HERG channel current at 35 degrees C. HERG-transfected cells expressed an mRNA band at 4.0 kb. Western blot analysis showed two protein bands (155 and 135 kDa) slightly larger than the predicted molecular mass (127 kDa). Treatment with N-glycosidase F converted both bands to smaller molecular mass, suggesting that both are glycosylated, but at different levels. HERG current activated at voltages positive to -50 mV, maximum current was reached with depolarizing steps to -10 mV, and the current amplitude declined at more positive voltages, similar to HERG channel current expressed in other heterologous systems. Current density at 35 degrees C, compared with 23 degrees C, was increased by more than twofold to a maximum of 53.4 +/- 6.5 pA/pF. Activation, inactivation, recovery from inactivation, and deactivation kinetics were rapid at 35 degrees C, and more closely resemble values reported for the rapidly activating delayed rectifier K+ current (I(Kr)) at physiological temperatures. HERG channels were highly selective for K+. When we used an action potential clamp technique...

Properties of WT and mutant hERG K+ channels expressed in neonatal mouse cardiomyocytes

Lin, Eric C.; Holzem, Katherine M.; Anson, Blake D.; Moungey, Brooke M.; Balijepalli, Sadguna Y.; Tester, David J.; Ackerman, Michael J.; Delisle, Brian P.; Balijepalli, Ravi C.; January, Craig T.
Fonte: American Physiological Society Publicador: American Physiological Society
Tipo: Artigo de Revista Científica
EN
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35.77%
Mutations in human ether-a-go-go-related gene 1 (hERG) are linked to long QT syndrome type 2 (LQT2). hERG encodes the pore-forming α-subunits that coassemble to form rapidly activating delayed rectifier K+ current in the heart. LQT2-linked missense mutations have been extensively studied in noncardiac heterologous expression systems, where biogenic (protein trafficking) and biophysical (gating and permeation) abnormalities have been postulated to underlie the loss-of-function phenotype associated with LQT2 channels. Little is known about the properties of LQT2-linked hERG channel proteins in native cardiomyocyte systems. In this study, we expressed wild-type (WT) hERG and three LQT2-linked mutations in neonatal mouse cardiomyocytes and studied their electrophysiological and biochemical properties. Compared with WT hERG channels, the LQT2 missense mutations G601S and N470D hERG exhibited altered protein trafficking and underwent pharmacological correction, and N470D hERG channels gated at more negative voltages. The ΔY475 hERG deletion mutation trafficked similar to WT hERG channels, gated at more negative voltages, and had rapid deactivation kinetics, and these properties were confirmed in both neonatal mouse cardiomyocyte and human embryonic kidney (HEK)-293 cell expression systems. Differences between the cardiomyocytes and HEK-293 cell expression systems were that hERG current densities were reduced 10-fold and deactivation kinetics were accelerated 1.5- to 2-fold in neonatal mouse cardiomyocytes. An important finding of this work is that pharmacological correction of trafficking-deficient LQT2 mutations...

Temperature-Dependent Asymmetry of Anisotropic Magnetoresistance in Silicon p-n Junctions

Yang, D. Z.; Wang, T.; Sui, W. B.; Si, M. S.; Guo, D. W.; Shi, Z.; Wang, F. C.; Xue, D. S.
Fonte: Nature Publishing Group Publicador: Nature Publishing Group
Tipo: Artigo de Revista Científica
Publicado em 01/09/2015 EN
Relevância na Pesquisa
35.86%
We report a large but asymmetric magnetoresistance in silicon p-n junctions, which contrasts with the fact of magnetoresistance being symmetric in magnetic metals and semiconductors. With temperature decreasing from 293 K to 100 K, the magnetoresistance sharply increases from 50% to 150% under a magnetic field of 2 T. At the same time, an asymmetric magnetoresistance, which manifests itself as a magnetoresistance voltage offset with respect to the sign of magnetic field, occurs and linearly increases with magnetoresistance. More interestingly, in contrast with other materials, the lineshape of anisotropic magnetoresistance in silicon p-n junctions significantly depends on temperature. As temperature decreases from 293 K to 100 K, the width of peak shrinks from 90° to 70°. We ascribe these novel magnetoresistance to the asymmetric geometry of the space charge region in p-n junction induced by the magnetic field. In the vicinity of the space charge region the current paths are deflected, contributing the Hall field to the asymmetric magnetoresistance. Therefore, the observed temperature-dependent asymmetry of magnetoresistance is proved to be a direct consequence of the spatial configuration evolution of space charge region with temperature.

Coarse-grained simulations of the solution-phase self-assembly of poly(3-hexylthiophene) nanostructures

Schwarz, K.; Kee, T.; Huang, D.
Fonte: Royal Society of Chemistry Publicador: Royal Society of Chemistry
Tipo: Artigo de Revista Científica
Publicado em //2013 EN
Relevância na Pesquisa
35.94%
Under certain conditions the conjugated polymer poly(3-hexylthiophene) (P3HT) self-assembles into high-aspect-ratio nanostructures (known as nanofibres, nanowires, or nanoribbons) when cooled below its solubility limit in a marginal solvent such as anisole. Such nanostructures are potentially beneficial for organic photovoltaic device performance. In this work, Langevin dynamics simulations of a coarse-grained model of P3HT in implicit anisole solvent are used to study the self-assembly of P3HT nanostructures for polymer chain lengths and concentrations used experimentally to prepare P3HT nanofibres. The coarse-grained model is parametrised to match the local structure and dynamics of an atomistic model with explicit solvent. Nanofibres are also prepared experimentally and characterised by atomic force microscopy and UV-vis spectroscopy. The simulations match the experimental phase behaviour of P3HT in anisole, showing aggregation of P3HT at 293 and 308 K but not at 323 or 353 K. Single-chain simulations at 293 K reveal two distinct nano-scale aggregate morphologies: hairpins and helices. Hairpin aggregates, which are the precursors of nanofibres, are slightly favoured energetically at 293 K for nuclei of the critical size of ≈80 monomers for aggregation. Consequently...

Comparison of the alpha-decay half-life of 210Po implanted in a copper matrix at 4.2 and 293 K

POEML PHILIPP; BELLONI F.; D'AGATA Elio; COLINEAU Eric; MORGENSTERN Alfred; GRIVEAU Jean-Christophe; RONDINELLA Vincenzo; REPNOW R; NASSISI V.; BENNEKER P; LAPETITE Jean-Marc; HIMBERT Jerome
Fonte: AMER PHYSICAL SOC Publicador: AMER PHYSICAL SOC
Tipo: Articles in Journals Formato: Printed
ENG
Relevância na Pesquisa
45.64%
In light of recent speculations on a potentially increased speed of the radioactive decay of alpha-emitters embedded in a metallic matrix at very low temperature, four high-purity Cu discs deep- implanted with 209Bi were prepared. The discs were irradiated in a high-flux reactor and the 209Bi transmuted into 210Po. After the irradiation the 210Po-activity was measured for all four discs. While two of the discs were stored at room temperature, the two other discs were stored in a sealed container submerged in liquid helium (T = 4.2 K) for approximately 200 days. After the storage time the 210Po-activity measurements were repeated and the 210Po-half-life calculated for each sample. No difference between the half-lives for the four samples could be detected within the uncertainties of the measurements. In other words, the results of this study show no evidence for an increase of activity for a-emitters embedded in a metallic matrix at very low temperature.; JRC.E.2-Safety of Irradiated Nuclear Materials

Functional coupling of a recombinant Human 5-HT5A receptor to G-proteins in HEK-293 cells

Hurley, P T; McMahon, R A; Fanning, P; O'Boyle, K M; Rogers, M; Martin, F
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /07/1998 EN
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35.79%
We have cloned, expressed and pharmacologically characterized the Human 5-HT5A receptor.We have shown that ligand activation of the Human 5-HT5A receptor results in functional coupling to G-proteins in HEK-293 cells.Stimulation of the receptor with 5-CT (5-carboxamidotryptamine) resulted in a dose-dependent increase in the % [35S]-GTPγS binding over the basal level. This is the first study to describe such G-protein activation for the Human 5-HT5A receptor in any cell.A dose-dependent inhibition of cyclic AMP accumulation was observed in the recombinant Human 5-HT5A receptor cell line, suggesting a functional coupling to a Gαi, G-protein in the HEK-293 cell line.A ligand-stimulated reduction in the detectable level of the catalytic domain of protein kinase A (PKA) in nuclear extracts isolated from Human 5-HT5A expressing cells was observed. This observation was consistent with the reduction in the level of cyclic AMP accumulation, in response to receptor activation.

Calcium-mediated DNA adsorption to yeast cells and kinetics of cell transformation by electroporation.

Neumann, E; Kakorin, S; Tsoneva, I; Nikolova, B; Tomov, T
Fonte: PubMed Publicador: PubMed
Tipo: Artigo de Revista Científica
Publicado em /08/1996 EN
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35.82%
Detailed kinetic data suggest that the direct transfer of plasmid DNA (YEp 351, 5.6 kbp, supercoiled, Mr approximately 3.5 x 10(6)) by membrane electroporation of yeast cells (Saccharomyces cerevisiae, strain AH 215) is mainly due to electrodiffusive processes. The rate-limiting step for the cell transformation, however, is a bimolecular DNA-binding interaction in the cell interior. Both the adsorption of DNA, directly measured with [32P]dCTP DNA, and the number of transformants are collinearly enhanced with increasing total concentrations [Dt] and [Cat] of DNA and of calcium, respectively. At [Cat] = 1 mM, the half-saturation or equilibrium constant is KD = 15 +/- 1 nM at 293 K (20 degrees C). The optimal transformation frequency is TFopt = 4.1 +/- 0.4 X 10(-5) if a single exponential pulse of initial field strength E0 = 4 kV cm-1 and decay time constant tauE = 45 ms is applied at [Dt] = 2.7 nM and 10(8) cells in 0.1 ml. The dependence of TF on [Cat] yields the equilibrium constants KCazero = 1.8 +/- 0.2 mM (in the absence of DNA) and K'Ca (at 2.7 nM DNA), comparable with and derived from electrophoresis data. In yeast cells, too, the appearance of a DNA molecule in its whole length in the cell interior is clearly an after-field event. At Eo = 4.0 kV cm-1 and T = 293 K...

Relativistic mean field study of the properties of Z=117 nucleus and the decay chains of $^{293,294}$117 isotopes

Bhuyan, M.; Gupta, S. K. Patra Raj K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 25/10/2010
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35.77%
We have calculated the binding energy, root-mean-square radius and quadrupole deformation parameter for the recently synthesized superheavy element Z=117, using the axially deformed relativistic mean field (RMF) model. The calculation is extended to various isotopes of Z=117 element, strarting from A=286 till A=310. We predict almost spherical structures in the ground state for almost all the isotopes. A shape transition appears at about A=292 from prolate to a oblate shape structures of Z=117 nucleus in our mean field approach. The most stable isotope (largest binding energy per nucleon) is found to be the $^{288}$117 nucleus. Also, the Q-value of $\alpha$-decay $Q_\alpha$ and the half-lives $T_{\alpha}$ are calculated for the $\alpha$-decay chains of $^{293}$117 and $^{294}$117, supporting the magic numbers at N=172 and/ or 184.; Comment: 6 Pages and 8 Figures

Cross Section Limits for the $^{208}$Pb($^{86}$Kr,n)$^{293}$118 Reaction

Gregorich, K. E.; Ginter, T. N.; Loveland, W.; Peterson, D.; Patin, J. B.; Folden III, C. M.; Hoffman, D. C.; Lee, D. M.; Nitsche, H.; Omtvedt, J. P.; Omtvedt, L. A.; Stavsetra, L.; Sudowe, R.; Wilk, P. A.; Zielinski, P. M.; Aleklett, K.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 04/09/2002
Relevância na Pesquisa
35.84%
In April-May, 2001, the previously reported experiment to synthesize element 118 using the $^{208}$Pb($^{86}$Kr,n)$^{293}$118 reaction was repeated. No events corresponding to the synthesis of element 118 were observed with a total beam dose of 2.6 x 10$^{18}$ ions. The simple upper limit cross sections (1 event) were 0.9 and 0.6 pb for evaporation residue magnetic rigidities of 2.00 $T m$ and 2.12 $T m$, respectively. A more detailed cross section calculation, accounting for an assumed narrow excitation function, the energy loss of the beam in traversing the target and the uncertainty in the magnetic rigidity of the Z=118 recoils is also presented. Re-analysis of the primary data files from the 1999 experiment showed the reported element 118 events are not in the original data. The current results put constraints on the production cross section for synthesis of very heavy nuclei in cold fusion reactions.; Comment: 7 pages, 2 figures. Submitted to EPJA

Metallicity of M dwarfs IV. A high-precision [Fe/H] and Teff technique from high-resolution optical spectra for M dwarfs

Neves, V.; Bonfils, X.; Santos, N. C.; Delfosse, X.; Forveille, T.; Allard, F.; Udry, S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.75%
Aims. In this work we develop a technique to obtain high precision determinations of both metallicity and effective temperature of M dwarfs in the optical. Methods. A new method is presented that makes use of the information of 4104 lines in the 530-690 nm spectral region. It consists in the measurement of pseudo equivalent widths and their correlation with established scales of [Fe/H] and $T_{eff}$. Results. Our technique achieves a $rms$ of 0.08$\pm$0.01 for [Fe/H], 91$\pm$13 K for $T_{eff}$, and is valid in the (-0.85, 0.26 dex), (2800, 4100 K), and (M0.0, M5.0) intervals for [Fe/H], $T_{eff}$ and spectral type respectively. We also calculated the RMSE$_{V}$ which estimates uncertainties of the order of 0.12 dex for the metallicity and of 293 K for the effective temperature. The technique has an activity limit and should only be used for stars with $\log{L_{H_{\alpha}}/L_{bol}} < -4.0$. Our method is available online at \url{http://www.astro.up.pt/resources/mcal}.; Comment: Accepted in Astronomy and Astrophysics. Updated one important reference in the introduction. Some typos corrected

Impact of lithium composition on the thermoelectric properties of the layered cobalt oxide system LixCoO2

Motohashi, T.; Sugimoto, Y.; Masubuchi, Y.; Sasagawa, T.; Koshibae, W.; Tohyama, T.; Yamauchi, H.; Kikkawa, S.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Relevância na Pesquisa
35.76%
Thermoelectric properties of the layered cobalt oxide system LixCoO2 were investigated in a wide range of Li composition, 0.98 >= x >= 0.35. Single-phase bulk samples of LixCoO2 were successfully obtained through electrochemical deintercalation of Li from the pristine LiCoO2 phase. While LixCoO2 with x >= 0.94 is semiconductive, the highly Li-deficient phase (0.75 >= x >= 0.35) exhibits metallic conductivity. The magnitude of Seebeck coefficient at 293 K (S293K) significantly depends on the Li content (x). The S293K value is as large as +70 ~ +100 uV/K for x >= 0.94, and it rapidly decreases from +90 uV/K to +10 uV/K as x is lowered within a Li composition range of 0.75 >= x >= 0.50. This behavior is in sharp contrast to the results of x <= 0.40 for which the S293K value is small and independent of x (+10 uV/K), indicating that a discontinuous change in the thermoelectric characteristics takes place at x = 0.40 ~ 0.50. The unusually large Seebeck coefficient and metallic conductivity are found to coexist in a narrow range of Li composition at about x = 0.75. The coexistence, which leads to an enhanced thermoelectric power factor, may be attributed to unusual electronic structure of the two-dimensional CoO2 block.; Comment: 29 pages...

The Central Parsecs of the Bright Quasar PKS 1921 - 293

Shen, Z. -Q.; Moran, J. M.; Kellermann, K. I.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/09/2002
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35.79%
We report on a VLBA imaging study of the nearby bright southern blazar PKS 1921 - 293 (OV - 236). High resolution VLBA observations, made at four frequencies (5, 12, 15, and 43 GHz) over the period 1994 - 2000, have revealed a strongly curved jet extending out to about 50 parsecs from the presumed central engine. Two epoch VLBA observations, each simultaneously carried out at both 5 and 43 GHz, show a large position angle difference of 51 - 67 degrees between the jet emission at 5 and 43 GHz. Although the core of PKS 1921 - 293 has one of the highest brightness temperatures measured in any compact radio source, unlike other bright blazars it is not a source of gamma-ray emission. However, there is evidence in these images for superluminal motion within the central region (a few parsecs from the core) and within the north-east diffuse emission region. In all six-epoch 43 GHz images, two equally compact bright components within the central parsec are seen.; Comment: 2 pages including 2 ps figures, to appear in the proceedings of IAU 8th Asian-Pacific Regional Meeting (July 2 - 5, 2002, Tokyo, Japan), eds: S. Ikeuchi, J. Hearnshaw and T. Hanawa

Calculations of the cross sections for synthesis of new {293-296}118 isotopes in {249-252}Cf(48Ca,xn) reactions

Cap, T.; Siwek-Wilczynska, K.; Kowal, M.; Wilczynski, J.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 19/08/2013
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45.73%
A project of using a target consisting of the mixture of (249-252)Cf isotopes to be bombarded with the 48Ca beam, aimed to synthesize new isotopes of the heaviest known element Z = 118, is under way at the FLNR in Dubna. In the present work excitation functions for all the reactions: 249Cf(48Ca,xn)(297-x)118, 250Cf(48Ca,xn)(298-x)118, 251Cf(48Ca,xn)(299-x)118 and 252Cf(48Ca,xn)(300-x)118 have been calculated in the framework of the fusion-by-diffusion model, assuming fission barriers, ground-state masses and shell effects of the superheavy nuclei predicted by Kowal et al. Energy dependence of the effective cross sections for the synthesis of selected new isotopes: (293)118, (294)118, (295)118 and (296)118 is predicted for the particular isotopic composition of the Cf target prepared for the Dubna experiment.; Comment: 5 pages, 2 figures

High Precision CTE-Measurement of SiC-100 for Cryogenic Space-Telescopes

Enya, K.; Yamada, N.; Onaka, T.; Nakagawa, T.; Kaneda, H.; Hirabayashi, M.; Toulemont, Y.; Castel, D.; Kanai, Y.; Fujishiro, N.
Fonte: Universidade Cornell Publicador: Universidade Cornell
Tipo: Artigo de Revista Científica
Publicado em 11/04/2007
Relevância na Pesquisa
35.73%
We present the results of high precision measurements of the thermal expansion of the sintered SiC, SiC-100, intended for use in cryogenic space-telescopes, in which minimization of thermal deformation of the mirror is critical and precise information of the thermal expansion is needed for the telescope design. The temperature range of the measurements extends from room temperature down to $\sim$ 10 K. Three samples, #1, #2, and #3 were manufactured from blocks of SiC produced in different lots. The thermal expansion of the samples was measured with a cryogenic dilatometer, consisting of a laser interferometer, a cryostat, and a mechanical cooler. The typical thermal expansion curve is presented using the 8th order polynomial of the temperature. For the three samples, the coefficients of thermal expansion (CTE), $\bar{\alpha}_{#1}$, $\bar{\alpha}_{#2}$, and $\bar{\alpha}_{#3}$ were derived for temperatures between 293 K and 10 K. The average and the dispersion (1 $\sigma$ rms) of these three CTEs are 0.816 and 0.002 ($\times 10^{-6}$/K), respectively. No significant difference was detected in the CTE of the three samples from the different lots. Neither inhomogeneity nor anisotropy of the CTE was observed. Based on the obtained CTE dispersion...