Comparison of the Spherical Averaged Pseudopotential Model with the Stabilized Jellium Model

We compare Kohn-Sham results (density, cohesive energy, size and effect of charging) of the Spherical Averaged Pseudopotential Model with the Stabilized Jellium Model for clusters of sodium and aluminum with less than 20 atoms. We find that the Stabilized Jellium Model, although conceptually and practically more simple, gives better results for the cohesive energy and the elastic stiffness. We use the Local Density Approximation as well as the Generalized Gradient Approximation to the exchange and correlation energies.Comment: 13 pages, latex, 8 figures, compressed postscript version available at http://www.fis.uc.pt/~vieir

Basal lamina heparan sulphate proteoglycan is involved in otic placode invagination in chick embryos

Producción CientíficaInvagination of other cup-shaped organ primordia. It is known that the cellular cytoskele- ton plays a Abstract Formation of the otocyst from the otic placode appears to differ from limited role in otic placode invagination, whilst the extracellular matrix underlying the otic pri- mordium intervenes in the folding process. In this study we have analysed the role of the basal lamina heparan sulphate proteoglycan in otic primordium invagination. At 10 H.H. stage, heparan sulphate proteoglycan im- the otic epithelium. Our findings support the theory that otic primordium invagination may be regulated, at least in part, by the basal lamina components, which might contribute towards anchoring the otic epithelium to adja- cent structures. Key words Otic development • Heparinase • Microinjection • Epithelial folding • Extracellular matrix munomarking begins to appear on the otic placode basal lamina, increasing noticeably at 13 H.H. stage, coincid- ing with maximum folding of the otic epithelium, and is still present at later stages. Enzyme degradation of hepa- ran sulphate proteoglycan in the otic primordium basal lamina, by means of microinjection with heparinase III prior to folding, significantly disrupts invagination of the otic placode, which remains practically flat, with a sig- nificant reduction in the depth of the otic pit and an in- crease in the diameter of the otic opening. The immuno- cytochemistry analysis revealed a notable depletion of basal lamina heparan sulphate proteoglycan in the otic primordia microinjected with heparinase, with no statis- tically significant differences observed in the volume or rate of cell proliferation in the otic epithelium relative to the control, which suggests that heparan sulphate prot- eoglycan disruption does not interfere with the epithelial growth. In addition, a study of apoptosis distribution by the TUNEL method confirmed that treatment with hepa- rinase does not cause interference with cell survival i

Evaluation of Exchange-Correlation Energy, Potential, and Stress

We describe a method for calculating the exchange and correlation (XC) contributions to the total energy, effective potential, and stress tensor in the generalized gradient approximation. We avoid using the analytical expressions for the functional derivatives of E_xc*rho, which depend on discontinuous second-order derivatives of the electron density rho. Instead, we first approximate E_xc by its integral in a real space grid, and then we evaluate its partial derivatives with respect to the density at the grid points. This ensures the exact consistency between the calculated total energy, potential, and stress, and it avoids the need of second-order derivatives. We show a few applications of the method, which requires only the value of the (spin) electron density in a grid (possibly nonuniform) and returns a conventional (local) XC potential.Comment: 7 pages, 3 figure

All electron and pseudopotential study of the spin polarization of the V (001) surface: LDA versus GGA

The spin-polarization at the V(001) surface has been studied by using different local (LSDA) and semilocal (GGA) approximations to the exchange-correlation potential of DFT within two ab initio methods: the all-electron TB-LMTO-ASA and the pseudopotential LCAO code SIESTA (Spanish Initiative for Electronic Simulations with Thousands of Atoms). A comparative analysis is performed first for the bulk and then for a N-layer V(001) film (7 < N < 15). The LSDA approximation leads to a non magnetic V(001) surface with both theoretical models in agreement (disagreement) with magneto-optical Kerr (electron-capture spectroscopy) experiments. The GGA within the pseudopotential method needs thicker slabs than the LSDA to yield zero moment at the central layer, giving a high surface magnetization (1.70 Bohr magnetons), in contrast with the non magnetic solution obtained by means of the all-electron code.Comment: 12 pages, 1 figure. Latex gzipped tar fil

FGF2 plays a key role in embryonic cerebrospinal fluid trophic properties over chick embryo neuroepithelial stem cells

Producción CientíficaDuring early stages of brain development, neuroepithelial stem cells undergo intense proliferation as neurogenesis begins. Fibroblast growth factor 2 (FGF2) has been involved in the regulation of these processes, and although it has been suggested that they work in an autocrine–paracrine mode, there is no general agreement on this because the behavior of neuroepithelial cells is not self-sufficient in explants cultured in vitro. In this work, we show that during early stages of development in chick embryos there is another source of FGF2, besides that of the neuroepithelium, which affects the brain primordium, since the cerebrospinal fluid (E-CSF) contains several isoforms of this factor. We also demonstrate, both in vitro and in vivo, that the FGF2 from the E-CSF has an effect on the regulation of neuroepithelial cell behavior, including cell proliferation and neurogenesis. In order to clarify putative sources of FGF2 in embryonic tissues, we detected by in situ hybridization high levels of mRNA expression in notochord, mesonephros and hepatic primordia, and low levels in brain neuroectoderm, corroborated by semiquantitative PCR analysis. Furthermore, we show that the notochord segregates several FGF2 isoforms which modify the behavior of the neuroepithelial cells in vitro. In addition, we show that the FGF2 ligand is present in the embryonic serum; and, by means of labeled FGF2, we prove that this factor passes via the neuroepithelium from the embryonic serum to the E-CSF in vivo. Considering all these results, we propose that, in chick embryos, the behavior of brain neuroepithelial stem cells at the earliest stages of development is influenced by the action of the FGF2 contained within the E-CSF which could have an extraneural origin, thus suggesting a new and complementary way of regulating brain development. © 2006 Elsevier Inc. All rights reserved

Market consistent valuations with financial imperfection

In this paper, we study market consistent valuations in imperfect markets. In the first part of the paper, we observe that in an imperfect market one needs to distinguish two type of market consistencies, namely types I and II. We show that while market consistency of type I holds without very strong conditions, market consistency of type II (which in the literature is known as the usual definition of market consistency) is only well defined in perfect markets. This is important since the existing literature on market consistency considers perfect markets where the two market consistencies are equivalent. In the second part of the paper, by introducing a best estimator we find strong connections between hedging and market consistency of either type. We show under very general conditions, the type I and the type II market consistent evaluators are best estimators, and establish a two-step representation for the market consistent risk evaluators. In the third part of the paper, we present several families of market consistent evaluators in imperfect markets

Radiative Cooling in MHD Models of the Quiet Sun Convection Zone and Corona

We present a series of numerical simulations of the quiet Sun plasma threaded by magnetic fields that extend from the upper convection zone into the low corona. We discuss an efficient, simplified approximation to the physics of optically thick radiative transport through the surface layers, and investigate the effects of convective turbulence on the magnetic structure of the Sun's atmosphere in an initially unipolar (open field) region. We find that the net Poynting flux below the surface is on average directed toward the interior, while in the photosphere and chromosphere the net flow of electromagnetic energy is outward into the solar corona. Overturning convective motions between these layers driven by rapid radiative cooling appears to be the source of energy for the oppositely directed fluxes of electromagnetic energy.Comment: 20 pages, 5 figures, Solar Physics, in pres

Metabolic Deficiences Revealed in the Biotechnologically Important Model Bacterium Escherichia coli BL21(DE3)

The Escherichia coli B strain BL21(DE3) has had a profound impact on biotechnology through its use in the production of recombinant proteins. Little is understood, however, regarding the physiology of this important E. coli strain. We show here that BL21(DE3) totally lacks activity of the four [NiFe]-hydrogenases, the three molybdenum- and selenium-containing formate dehydrogenases and molybdenum-dependent nitrate reductase. Nevertheless, all of the structural genes necessary for the synthesis of the respective anaerobic metalloenzymes are present in the genome. However, the genes encoding the high-affinity molybdate transport system and the molybdenum-responsive transcriptional regulator ModE are absent from the genome. Moreover, BL21(DE3) has a nonsense mutation in the gene encoding the global oxygen-responsive transcriptional regulator FNR. The activities of the two hydrogen-oxidizing hydrogenases, therefore, could be restored to BL21(DE3) by supplementing the growth medium with high concentrations of Ni2+ (Ni2+-transport is FNR-dependent) or by introducing a wild-type copy of the fnr gene. Only combined addition of plasmid-encoded fnr and high concentrations of MoO42− ions could restore hydrogen production to BL21(DE3); however, to only 25–30% of a K-12 wildtype. We could show that limited hydrogen production from the enzyme complex responsible for formate-dependent hydrogen evolution was due solely to reduced activity of the formate dehydrogenase (FDH-H), not the hydrogenase component. The activity of the FNR-dependent formate dehydrogenase, FDH-N, could not be restored, even when the fnr gene and MoO42− were supplied; however, nitrate reductase activity could be recovered by combined addition of MoO42− and the fnr gene. This suggested that a further component specific for biosynthesis or activity of formate dehydrogenases H and N was missing. Re-introduction of the gene encoding ModE could only partially restore the activities of both enzymes. Taken together these results demonstrate that BL21(DE3) has major defects in anaerobic metabolism, metal ion transport and metalloprotein biosynthesis

Application of the bacteriophage Mu-driven system for the integration/amplification of target genes in the chromosomes of engineered Gram-negative bacteria—mini review

The advantages of phage Mu transposition-based systems for the chromosomal editing of plasmid-less strains are reviewed. The cis and trans requirements for Mu phage-mediated transposition, which include the L/R ends of the Mu DNA, the transposition factors MuA and MuB, and the cis/trans functioning of the E element as an enhancer, are presented. Mini-Mu(LR)/(LER) units are Mu derivatives that lack most of the Mu genes but contain the L/R ends or a properly arranged E element in cis to the L/R ends. The dual-component system, which consists of an integrative plasmid with a mini-Mu and an easily eliminated helper plasmid encoding inducible transposition factors, is described in detail as a tool for the integration/amplification of recombinant DNAs. This chromosomal editing method is based on replicative transposition through the formation of a cointegrate that can be resolved in a recombination-dependent manner. (E-plus)- or (E-minus)-helpers that differ in the presence of the trans-acting E element are used to achieve the proper mini-Mu transposition intensity. The systems that have been developed for the construction of stably maintained mini-Mu multi-integrant strains of Escherichia coli and Methylophilus methylotrophus are described. A novel integration/amplification/fixation strategy is proposed for consecutive independent replicative transpositions of different mini-Mu(LER) units with “excisable” E elements in methylotrophic cells