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Search Results: 1 - 10 of 593204 matches for " A. L. Finkelstein "
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Persistent Orbital Degeneracy in Carbon Nanotubes
A. Makarovski,L. An,J. Liu,G. Finkelstein
Physics , 2005, DOI: 10.1103/PhysRevB.74.155431
Abstract: The quantum-mechanical orbitals in carbon nanotubes are doubly degenerate over a large number of states in the Coulomb blockade regime. We argue that this experimental observation indicates that electrons are reflected without mode mixing at the nanotube-metal contacts. Two electrons occupying a pair of degenerate orbitals (a ``shell'') are found to form a triplet state starting from zero magnetic field. Finally, we observe unexpected low-energy excitations at complete filling of a four-electron shell.
Novel Technology for Chlorination of Niobium and Tantalum Oxides and Their Low-Grade Ore Concentrates  [PDF]
B. A. Shainyan, Yu. S. Danilevich, Yu. L. Garmazov, A. L. Finkelstein, T. S. Aisueva, V. K. Turchaninov
Journal of Minerals and Materials Characterization and Engineering (JMMCE) , 2008, DOI: 10.4236/jmmce.2008.72013
Abstract: A novel energy-economic and environmentally benign technological procedure for chlorination of niobium and tantalum oxides as well as their low-grade ore concentrates was elaborated. The process is based on using carbon tetrachloride or silicon tetrachloride as a chlorinating agent under pressure. It proceeds at moderate temperatures and is free from the shortcomings of conventional carbochlorination processes such as the use of chlorine gas at very high temperatures and formation of toxic products and ozone depleting agents (phosgene, carbon monoxide, chlorohydrocarbons).
Nature of the electronic states involved in the chemical bonding and superconductivity at high pressure in SnO
J. A. McLeod,A. V. Lukoyanov,E. Z. Kurmaev,L. D. Finkelstein,A. Moewes
Physics , 2011, DOI: 10.1134/S0021364011140098
Abstract: We have investigated the electronic structure and the Fermi surface of SnO using density functional theory (DFT) calculations within recently proposed exchange-correlation potential (PBE+mBJ) at ambient conditions and high pressures up to 19.3 GPa where superconductivity was observed. It was found that the Sn valence states 5s, 5p, and 5d are strongly hybridized with the O 2p-states, and that our DFT-calculations are in good agreement with O K-edge X-ray spectroscopy measurements for both occupied and empty states. It was demonstrated that the metallic states appearing under pressure in the semiconducting gap stem due to the transformation of the weakly hybridized O 2p-Sn 5sp subband corresponding to the lowest valence state of Sn in SnO. We discuss the nature of the electronic states involved in chemical bonding and formation of the hole and electron pockets with nesting as a possible way to superconductivity.
Efficacy of a diarylheptanoid derivative against Leishmania amazonensis
Alves, Luciana Vignólio;Temporal, Rosane Maria;Cysne-Finkelstein, Léa;Leon, Leonor Laura;
Memórias do Instituto Oswaldo Cruz , 2003, DOI: 10.1590/S0074-02762003000400024
Abstract: the activity of several diarylheptanoid derivatives (curcuminoids) was previously evaluated against leishmania amazonensis promastigotes and among them the most active compound was the [1-(4-methoxy-phenyl)-7-(3,4-methoxy-4-hydroxy-phenyl)-1,6-heptadien-3, 5-dione]. this derivative was chosen to be assayed in vivo in a treatment trial. for these experiments, the curcuminoid compound was used in a concentration equivalent to the ic50/24 h, obtained from the previous study. balb/c mice were inoculated subcutaneously in the footpad with l. amazonensis infective promastigotes and 4 weeks after the inoculation, the animals were treated with different schemes, varying from 1 to 3 doses. in all the experiments, pentamidine isethionate was used as reference drug under the same experimental conditions. the results showed that one dose was not enough to heal the lesion, however, with 2 and 3 doses the efficiency of the assayed compound was clear. on the other hand, treatment with pentamidine isethionate using the three different schemes was not satisfactory when compared to the curcuminoid derivative.
Efficacy of a diarylheptanoid derivative against Leishmania amazonensis
Alves Luciana Vignólio,Temporal Rosane Maria,Cysne-Finkelstein Léa,Leon Leonor Laura
Memórias do Instituto Oswaldo Cruz , 2003,
Abstract: The activity of several diarylheptanoid derivatives (curcuminoids) was previously evaluated against Leishmania amazonensis promastigotes and among them the most active compound was the [1-(4-methoxy-phenyl)-7-(3,4-methoxy-4-hydroxy-phenyl)-1,6-heptadien-3, 5-dione]. This derivative was chosen to be assayed in vivo in a treatment trial. For these experiments, the curcuminoid compound was used in a concentration equivalent to the IC50/24 h, obtained from the previous study. Balb/c mice were inoculated subcutaneously in the footpad with L. amazonensis infective promastigotes and 4 weeks after the inoculation, the animals were treated with different schemes, varying from 1 to 3 doses. In all the experiments, Pentamidine Isethionate was used as reference drug under the same experimental conditions. The results showed that one dose was not enough to heal the lesion, however, with 2 and 3 doses the efficiency of the assayed compound was clear. On the other hand, treatment with Pentamidine Isethionate using the three different schemes was not satisfactory when compared to the curcuminoid derivative.
Probing the Star Formation History and Initial Mass Function of the z~2.5 Lensed Galaxy SMM J163554.2+661225 with Herschel
Keely D. Finkelstein,Casey Papovich,Steven L. Finkelstein,Christopher N. A. Willmer,Jane R. Rigby,Gregory Rudnick,Eiichi Egami,Marcia Rieke,J. -D. T. Smith
Physics , 2011, DOI: 10.1088/0004-637X/742/2/108
Abstract: We present the analysis of Herschel SPIRE far-infrared (FIR) observations of the z = 2.515 lensed galaxy SMM J163554.2+661225. Combining new 250, 350, and 500 micron observations with existing data, we make an improved fit to the FIR spectral energy distribution (SED) of this galaxy. We find a total infrared (IR) luminosity of L(8--1000 micron) = 6.9 +/- 0.6x10^11 Lsol; a factor of 3 more precise over previous L_IR estimates for this galaxy, and one of the most accurate measurements for any galaxy at these redshifts. This FIR luminosity implies an unlensed star formation rate (SFR) for this galaxy of 119 +/- 10 Msol per yr, which is a factor of 1.9 +/- 0.35 lower than the SFR derived from the nebular Pa-alpha emission line (a 2.5-sigma discrepancy). Both SFR indicators assume identical Salpeter initial mass functions (IMF) with slope Gamma=2.35 over a mass range of 0.1 - 100 Msol, thus this discrepancy suggests that more ionizing photons may be necessary to account for the higher Pa-alpha-derived SFR. We examine a number of scenarios and find that the observations can be explained with a varying star formation history (SFH) due to an increasing star formation rate (SFR), paired with a slight flattening of the IMF. If the SFR is constant in time, then larger changes need to be made to the IMF by either increasing the upper-mass cutoff to ~ 200 Msol, or a flattening of the IMF slope to 1.9 +/- 0.15, or a combination of the two. These scenarios result in up to double the number of stars with masses above 20 Msol, which produce the requisite increase in ionizing photons over a Salpeter IMF with a constant SFH.
Searching for the First Galaxies
Steven L. Finkelstein
Physics , 2010,
Abstract: As some of the first known objects to exist in the Universe, Lyman alpha emitting galaxies (LAEs) naturally draw a lot of interest. First discovered over a decade ago, they have allowed us to probe the early Universe, as their strong emission line compensates for their faint continuum light. While initially thought to be indicative of the first galaxies forming in the Universe, recent studies have shown them to be increasingly complex, as some fraction appear evolved, and many LAEs appear to be dusty, which one would not expect from primordial galaxies. Presently, much interest resides in discovering not only the highest redshift galaxies to constrain theories of reionization, but also pushing closer to home, as previous ground-based studies have only found LAEs at z > 3 due to observational limitations. In this review talk I will cover everything from the first theoretical predictions of LAEs, to their future prospects for study, including the HETDEX survey here in Texas.
Probing Stellar Populations at z ~ 7 - 8
Steven L. Finkelstein
Physics , 2010, DOI: 10.1063/1.3518856
Abstract: In this proceeding we present the results from a study of very high-redshift galaxies with the newly commissioned Wide Field Camera 3 on the Hubble Space Telescope. With the deepest near-infrared data ever taken, we discovered 31 galaxies at 6.3 < z < 8.6. The rest-frame ultraviolet (UV) colors of these galaxies are extremely blue, showing significant (> 4 sigma) evolution from z ~ 3, over only 1 Gyr of cosmic time. While we cannot yet diagnose the exact cause of the bluer colors, it appears a low dust content is the primary factor. The stellar masses of these galaxies are less than comparably selected galaxies at 3 < z < 6, highlighting evolution in the stellar mass of characteristic (L*) galaxies with redshift. Lastly, the measured rest-UV luminosity density of galaxies in our sample seems sufficient to sustain reionization at z ~ 7 when we account for the likely contribution from galaxies below our magnitude limit.
Observational Searches for Galaxies at z > 6
Steven L. Finkelstein
Physics , 2015,
Abstract: Although the universe at redshifts greater than six represents only the first one billion years (<10%) of cosmic time, the dense nature of the early universe led to vigorous galaxy formation and evolution activity which we are only now starting to piece together. Technological improvements have, over only the past decade, allowed large samples of galaxies at such high redshifts to be collected, providing a glimpse into the epoch of formation of the first stars and galaxies. A wide variety of observational techniques have led to the discovery of thousands of galaxy candidates at z > 6, with spectroscopically confirmed galaxies out to nearly z = 9. Using these large samples, we have begun to gain a physical insight into the processes inherent in galaxy evolution at early times. In this review, I will discuss i) the selection techniques for finding distant galaxies, including a summary of previous and ongoing ground and space-based searches, and spectroscopic followup efforts, ii) insights into galaxy evolution gleaned from measures such as the rest-frame ultraviolet luminosity function, the stellar mass function, and galaxy star-formation rates, and iii) the effect of galaxies on their surrounding environment, including the chemical enrichment of the universe, and the reionization of the intergalactic medium. Finally, I conclude with prospects for future observational study of the distant universe, using a bevy of new state-of-the-art facilities coming online over the next decade and beyond.
A Selective Macro-learning Algorithm and its Application to the NxN Sliding-Tile Puzzle
L. Finkelstein,S. Markovitch
Computer Science , 1998,
Abstract: One of the most common mechanisms used for speeding up problem solvers is macro-learning. Macros are sequences of basic operators acquired during problem solving. Macros are used by the problem solver as if they were basic operators. The major problem that macro-learning presents is the vast number of macros that are available for acquisition. Macros increase the branching factor of the search space and can severely degrade problem-solving efficiency. To make macro learning useful, a program must be selective in acquiring and utilizing macros. This paper describes a general method for selective acquisition of macros. Solvable training problems are generated in increasing order of difficulty. The only macros acquired are those that take the problem solver out of a local minimum to a better state. The utility of the method is demonstrated in several domains, including the domain of NxN sliding-tile puzzles. After learning on small puzzles, the system is able to efficiently solve puzzles of any size.
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