Robustness of a local Fermi Liquid against Ferromagnetism and Phase Separation

We study the properties of Fermi Liquids with the microscopic constraint of a local self-energy. In this case the forward scattering sum-rule imposes strong limitations on the Fermi-Liquid parameters, which rule out any Pomeranchek instabilities. For both attractive and repulsive interactions, ferromagnetism and phase separation are suppressed. Superconductivity is possible in an s-wave channel only. We also study the approach to the metal-insulator transition, and find a Wilson ratio approaching 2. This ratio and other properties of Sr_{1-x}La_xTiO_3 are all consistent with the local Fermi Liquid scenario.Comment: 4 pages (twocolumn format), can compile with or without epsf.sty latex style file -- Postscript files: fig1.ps and fig2.p

The effects of next to nearest neighbor hopping on Bose-Einstein condensation in cubic lattices

In this paper, we present results of our calculations on the effects of next to nearest neighbor boson hopping ($t^{\prime}$) energy on Bose-Einstein condensation in cubic lattices. We consider both non-interacting and repulsively interacting bosons moving in the lowest Bloch band. The interacting bosons are studied making use of the Bogoliubov method. We find that the bose condensation temperature is enhanced with increasing $t^{\prime}$ for bosons in a simple cubic (sc) lattice and decreases for bosons in body-centered cubic (bcc) and face-centered cubic (fcc) lattices. We also find that interaction induced depletion of the condensate is reduced for bosons in a sc lattice while is enhanced for bosons in bcc and fcc lattices.Comment: revised version, 10 pages with figures, intro and conclusions modified, more results added, references adde

Small Polarons in Transition Metal Oxides

The formation of polarons is a pervasive phenomenon in transition metal oxide compounds, with a strong impact on the physical properties and functionalities of the hosting materials. In its original formulation the polaron problem considers a single charge carrier in a polar crystal interacting with its surrounding lattice. Depending on the spatial extension of the polaron quasiparticle, originating from the coupling between the excess charge and the phonon field, one speaks of small or large polarons. This chapter discusses the modeling of small polarons in real materials, with a particular focus on the archetypal polaron material TiO2. After an introductory part, surveying the fundamental theoretical and experimental aspects of the physics of polarons, the chapter examines how to model small polarons using first principles schemes in order to predict, understand and interpret a variety of polaron properties in bulk phases and surfaces. Following the spirit of this handbook, different types of computational procedures and prescriptions are presented with specific instructions on the setup required to model polaron effects.Comment: 36 pages, 12 figure

MicroRNA let-7c Is Downregulated in Prostate Cancer and Suppresses Prostate Cancer Growth

Prostate cancer (PCa) is characterized by deregulated expression of several tumor suppressor or oncogenic miRNAs. The objective of this study was the identification and characterization of miR-let-7c as a potential tumor suppressor in PCa.Levels of expression of miR-let-7c were examined in human PCa cell lines and tissues using qRT-PCR and in situ hybridization. Let-7c was overexpressed or suppressed to assess the effects on the growth of human PCa cell lines. Lentiviral-mediated re-expression of let-7c was utilized to assess the effects on human PCa xenografts.We identified miR-let-7c as a potential tumor suppressor in PCa. Expression of let-7c is downregulated in castration-resistant prostate cancer (CRPC) cells. Overexpression of let-7c decreased while downregulation of let-7c increased cell proliferation, clonogenicity and anchorage-independent growth of PCa cells in vitro. Suppression of let-7c expression enhanced the ability of androgen-sensitive PCa cells to grow in androgen-deprived conditions in vitro. Reconstitution of Let-7c by lentiviral-mediated intratumoral delivery significantly reduced tumor burden in xenografts of human PCa cells. Furthermore, let-7c expression is downregulated in clinical PCa specimens compared to their matched benign tissues, while the expression of Lin28, a master regulator of let-7 miRNA processing, is upregulated in clinical PCa specimens.These results demonstrate that microRNA let-7c is downregulated in PCa and functions as a tumor suppressor, and is a potential therapeutic target for PCa

Peptide design using α,β-dehydro amino acids: from β-turns to helical hairpins

Incorporation of &#945;,&#946;-dehydrophenylalanine (&#916;Phe) residue in peptides induces folded conformations: &#946;-turns in short peptides and 3<SUB>10</SUB>-helices in larger ones. A few exceptions-namely, &#945;-helix or flat &#946;-bend ribbon structures-have also been reported in a few cases. The most favorable conformation of &#916;Phe residues are (&#934;,&#968;) ~ (&#8722;60&#176;, &#8722;30&#176;), (&#8722;60&#176;, 150&#176;), (80&#176;, 0&#176;) or their enantiomers. &#916;Phe is an achiral and planar residue. These features have been exploited in designing &#916;Phe zippers and helix-turn-helix motifs. &#916;Phe can be incorporated in both right and left-handed helices. In fact, consecutive occurrence of three or more &#916;Phe amino acids induce left-handed screw sense in peptides containing L-amino acids. Weak interactions involving the &#916;Phe residue play an important role in molecular association. The C-H<SUP>...</SUP>O=C hydrogen bond between the &#916;Phe side-chain and backbone carboxyl moiety, &#960;-&#960; stacking interactions between &#916;Phe side chains belonging to enantiomeric helices have shown to stabilize folding. The unusual capability of a &#916;Phe ring to form the hub of multicentered interactions namely, a donor in aromatic C-H<SUP>...</SUP>&#960; and C-H<SUP>...</SUP>O=C and an acceptor in a CH<SUB>3</SUB><SUP>...</SUP>&#960; interaction suggests its exploitation in introducing long-range interactions in the folding of supersecondary structures

Crystallization and preliminary X-ray study of a family 10 alkali-thermostable xylanase from alkalophilic Bacillus sp. strain NG-27

A family 10 alkali-thermostable xylanase from Bacillus sp. NG-27 has been crystallized. A diffraction data set has been collected to 2.2 Å resolution

Helix termination and chain reversal: crystal and molecular structure of the alpha, beta-dehydrooctapeptide Boc-Val-DeltaPhe-Phe-Ala-Leu-Ala-DeltaPhe-Leu-OH

The crystal structure of the dehydro octapeptide Boc-Val-DeltaPhe-Phe-Ala-Leu-Ala-DeltaPhe-Leu-OH has been determined to atomic resolution by X-ray crystallographic methods. The crystals grown by slow evaporation of peptide solution in methanol/water are orthorhombic, space group P2(1)2(1)2(1). The unit cell parameters are a= 8.404(3), b= 25.598(2) and c= 27.946(3) Angstrom, Z=4. The agreement factor is R = 7.58% for 3636 reflections having (vertical bar Fo vertical bar) > or = 3sigma (vertical bar Fo vertical bar). The peptide molecule is characterised by a 3(10)-helix at the N-terminus and a pi-turn at the C-terminus. This conformation is exactly similar to the helix termination features observed in proteins. The pi-turn conformation observed in the octapeptide is in good agreement with the conformational features of pi-turns seen in some proteins. The alphaL-position in the pi-turn of the octapeptide is occupied by DeltaPhe7, which shows that even bulky residues can be accommodated in this position of the pi-turns. In proteins, it is generally seen that alphaL-position is occupied by glycine residue. No intermolecular head-to-tail hydrogen bonds are observed in solid state structure of the octapeptide. A water molecule located in the unit cell of the peptide molecule is mainly used to hold the peptide molecule together in the crystal. The conformation observed for the octapeptide might be useful to understand the helix termination and chain reversal in proteins and to construct helix terminators for denovo protein design

Crystal structure of Boc-LAla-ΔPhe-ΔPhe-ΔPhe-ΔPhe-NHMe: a left-handed helical peptide

&#945;&#946;-Dehydrophenylalanine residues constrain the peptide backbone to &#946;-bend conformation. A pentapeptide containing four consecutive (APhe) residues has been synthesised and crystallised. The peptide Boc-LAla-&#916;Phe-&#916;Phe-&#916;Phe-&#916;Phe-NHMe (C45H46N6O7, MW = 782.86) was crystallised from an acetonitrile/ methanol mixture. The crystal belongs to the orthorhombic space group P212121 with a = 19.455(6), b = 20.912(9), c = 11.455(4) &#197; and Z = 4. The X-ray (MoK &#945; , lD = 0.7107 &#197;) intensity data were collected using the Rigaku-AFC7 diffractrometer. The crystal structure was determined by direct methods and refined using the least-squares technique, R = 8.41% for 1827 reflections with ||F0|| &gt; 4&#963;||Fo||. The molecule contains the largest stretch of consecutive dehydrophenylalanine residues whose crystal structure has been determined so far. The peptide adopts left-handed 310-helical conformation despite the presence of LAla at the N-terminus. The mean &#8709;, &#968; values, averaged across the last four residues are 56.8&#176; and 17.5&#176;, respectively. There are four 41 intramolecular hydrogen bonds, characteristic of the 310-helix. In the crystal each molecule interacts with four crystallographically symmetric molecules with one hydrogen bond each