Mechanism for nucleic acid chaperone activity of HIV-1 nucleocapsid protein revealed by single molecule stretching

The nucleocapsid protein (NC) of HIV type 1 is a nucleic acid chaperone that facilitates the rearrangement of nucleic acids into conformations containing the maximum number of complementary base pairs. We use an optical tweezers instrument to stretch single DNA molecules from the helix to coil state at room temperature in the presence of NC and a mutant form (SSHS NC) that lacks the two zinc finger structures present in NC. Although both NC and SSHS NC facilitate annealing of complementary strands through electrostatic attraction, only NC destabilizes the helical form of DNA and reduces the cooperativity of the helix-coil transition. In particular, we find that the helix-coil transition free energy at room temperature is significantly reduced in the presence of NC. Thus, upon NC binding, it is likely that thermodynamic fluctuations cause continuous melting and reannealing of base pairs so that DNA strands are able to rapidly sample configurations to find the lowest energy state. The reduced cooperativity allows these fluctuations to occur in the middle of complex double-stranded structures. The reduced stability and cooperativity, coupled with the electrostatic attraction generated by the high charge density of NC, is responsible for the nucleic acid chaperone activity of this protein.

GÊNERO, RAÇA, DISCRIMINAÇÃO: O TOM DA COR NA DIREÇÃO DA ESCOLA PÚBLICA.

BRUNELLI, Conceição Aparecida Garcia: Gênero, raça, discriminação: o tom da cor na direção da escola pública. Mestrado em Educação. Universidade Metodista de São Paulo, São Bernardo do Campo - SP. 1 v. 244 p. 2007. Esse trabalho teve por objetivo investigar a trajetória das mulheres negras diretoras de escola pública e o processo de construção de sua identidade social, cultural, de gênero e raça. De fato, as mulheres negras em questão constroem suas identidades nadando entre águas profundas e revoltas: a das relações de gênero e a das relações raciais. A pesquisa permitiu-nos desvendar o processo seletivo pelo qual passam essas mulheres que conseguiram romper o duplo bloqueio formado pelas relações de gênero e de raça e atingiram a posição profissional de diretoras de escola pública. A questão central que norteia essa pesquisa diz respeito à trajetória de vida da mulher negra que optou pela carreira do magistério, as intercorrências encontradas ao longo de sua trajetória pessoal, de formação acadêmica e profissional, suas experiências, frustrações, expectativas, preconceitos e discriminações sofridos na caminhada até chegar ao exercício de sua atividade pública, sua ascensão social, o ingresso na carreira pública e as relações de poder que perpassam as questões de gênero e raça. Aborda ainda como essas intercorrências incidem sobre o processo de construção da identidade dessas mulheres negras e de suas relações com seus colegas brancos, homens e mulheres. A coleta de dados empíricos foi realizada através da história oral representada pela memória dessas mulheres, baseada nos depoimentos escritos e em entrevistas semi-estruturadas. Os depoimentos colhidos permitiram reunir material que foram interpretados segundo as relações de poder elaboradas por Foucault e que nos possibilitam a compreensão e uma reflexão do processo de construção das identidades individual e coletiva.

GÊNERO, RAÇA, DISCRIMINAÇÃO: O TOM DA COR NA DIREÇÃO DA ESCOLA PÚBLICA.

Esse trabalho teve por objetivo investigar a trajetória das mulheres negras diretoras de escola pública e o processo de construção de sua identidade social, cultural, de gênero e raça. De fato, as mulheres negras em questão constroem suas identidades nadando entre águas profundas e revoltas: a das relações de gênero e a das relações raciais. A pesquisa permitiu-nos desvendar o processo seletivo pelo qual passam essas mulheres que conseguiram romper o duplo bloqueio formado pelas relações de gênero e de raça e atingiram a posição profissional de diretoras de escola pública. A questão central que norteia essa pesquisa diz respeito à trajetória de vida da mulher negra que optou pela carreira do magistério, as intercorrências encontradas ao longo de sua trajetória pessoal, de formação acadêmica e profissional, suas experiências, frustrações, expectativas, preconceitos e discriminações sofridos na caminhada até chegar ao exercício de sua atividade pública, sua ascensão social, o ingresso na carreira pública e as relações de poder que perpassam as questões de gênero e raça. Aborda ainda como essas intercorrências incidem sobre o processo de construção da identidade dessas mulheres negras e de suas relações com seus colegas brancos, homens e mulheres. A coleta de dados empíricos foi realizada através da história oral representada pela memória dessas mulheres, baseada nos depoimentos escritos e em entrevistas semi-estruturadas. Os depoimentos colhidos permitiram reunir material que foram interpretados segundo as relações de poder elaboradas por Foucault e que nos possibilitam a compreensão e uma reflexão do processo de construção das identidades individual e coletiva.

Anomalous dephasing scattering rate of two-dimensional electrons in double quantum well structures

The results on the measurement of electrical conductivity and magnetoconductivity of a GaAs double quantum well between 0.5 and 1.1 K are reported. The zero magnetic-field conductivity is well described from the point of view of contributions made by both the weak localization and electron-electron interaction. At low field and low temperature, the magnetoconductivity is dominated by the weak localization effect only. Using the weak localization method, we have determined the electron dephasing times tau(phi) and tunneling times tau(t). Concerning tunneling, we concluded that tau(t) presents a minimum around the balance point; concerning dephasing, we observed an anomalous dependence on temperature and conductivity (or elastic mean free path) of tau(phi). This anomalous behavior cannot be explained in terms of the prevailing concepts for the electron-electron interaction in high-mobility two-dimensional electron systems.

Buckling strength of adhesively-bonded single and double-strap repairs on carbon-epoxy structures

This work reports on an experimental and finite element method (FEM) parametric study of adhesively-bonded single and double-strap repairs on carbon-epoxy structures under buckling unrestrained compression. The influence of the overlap length and patch thickness was evaluated. This loading gains a particular significance from the additional characteristic mechanisms of structures under compression, such as fibres microbuckling, for buckling restrained structures, or global buckling of the assembly, if no transverse restriction exists. The FEM analysis is based on the use of cohesive elements including mixed-mode criteria to simulate a cohesive fracture of the adhesive layer. Trapezoidal laws in pure modes I and II were used to account for the ductility of most structural adhesives. These laws were estimated for the adhesive used from double cantilever beam (DCB) and end-notched flexure (ENF) tests, respectively, using an inverse technique. The pure mode III cohesive law was equalled to the pure mode II one. Compression failure in the laminates was predicted using a stress-based criterion. The accurate FEM predictions open a good prospect for the reduction of the extensive experimentation in the design of carbon-epoxy repairs. Design principles were also established for these repairs under buckling.

Tensile behaviour of single and double-strap repairs on aluminium structures

In this work, an experimental study was performed on the influence of plug filling, loading rate and temperature on the tensile strength of single-strap (SS) and double-strap (DS) repairs on aluminium structures. The experimental programme includes repairs with different values of overlap length (LO=10, 20 and 30 mm), and with and without plug filling. The influence of the testing speed on the repairs strength is also addressed (considering 0.5, 5 and 25 mm/min). Accounting for the temperature effects, tests were carried out at room temperature, 50ºC and 80ºC. This will permit a comparative evaluation of the adhesive tested below and above the Glass Transition Temperature (Tg), established by the manufacturer at 67ºC. The global tendencies of the test results concerning the plug filling and overlap length analyses are interpreted from the fracture modes and typical stress distributions for bonded repairs. According to the results obtained from this work, design guidelines for repairing aluminium structures were recommended.

Model structures on the category of small double categories

In this paper we obtain several model structures on DblCat, the category of small double categories. Our model structures have three sources. We first transfer across a categorification-nerve adjunction. Secondly, we view double categories as internal categories in Cat and take as our weak equivalences various internal equivalences defined via Grothendieck topologies. Thirdly, DblCat inherits a model structure as a category of algebras over a 2-monad. Some of these model structures coincide and the different points of view give us further results about cofibrant replacements and cofi brant objects. As part of this program we give explicit descriptions and discuss properties of free double categories, quotient double categories, colimits of double categories, and several nerves and categorifications.

Two new mu-(1,3-azido)-bridged polymers: alternating single and double bridges in a 1D nickel(II) complex and uniform bridge in a 2D copper(II) complex: Syntheses, single-crystal structures and magnetic studies

Two polymeric azido bridged complexes [Ni2L2(N-3)(3)](n)(ClO4). (1) and [Cu(bpdS)(2)(N-3)],(ClO4),(H2O)(2.5n) (2) [L = Schiff base, obtained from the condensation of pyridine-2-aldehyde with N,N,2,2-tetramethyl-1,3-propanediamine; bpds = 4,4'-bipyridyl disulfide] have been synthesized and their crystal structures have been determined. Complex 1, C26H42ClN15Ni2O4, crystallizes in a triclinic system, space group P1 with a 8.089(13), b = 9.392(14), c = 12.267(18) angstrom, a = 107.28(l), b 95.95(1), gamma = 96.92(1)degrees and Z = 2; complex 2, C20H21ClCuN7O6.5S4, crystallizes in an orthorhombic system, space group Pnna with a = 10.839(14), b = 13.208(17), c = 19.75(2) angstrom and Z = 4. The crystal structure of I consists of 1D polymers of nickel(L) units, alternatively connected by single and double bridging mu-(1,3-N-3) ligand with isolated perchlorate anions. Variable temperature magnetic susceptibility data of the complex have been measured and the fitting,of magnetic data was carried out applying the Borris-Almenar formula for such types of alternating one-dimensional S = 1 systems, based on the Hamiltonian H = -J Sigma(S2iS2i-1 + aS(2i)S(2i+1)). The best-fit parameters obtained are J = -106.7 +/- 2 cm(-1); a = 0.82 +/- 0.02; g = 2.21 +/- 0.02. Complex 2 is a 2D network of 4,4 topology with the nodes occupied by the Cu-II ions, and the edges formed by single azide and double bpds connectors. The perchlorate anions are located between pairs of bpds. The magnetic data have been fitted considering the complex as a pseudo-one-dimensional system, with all copper((II)) atoms linked by [mu(1,3-azido) bridging ligands at axial positions (long Cu...N-3 distances) since the coupling through long bpds is almost nil. The best-fit parameters obtained with this model are J = -1.21 +/- 0.2 cm(-1), g 2.14 +/- 0.02. (c) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005).

Directing the structures of silver-antimony sulphides: a new topological variant of the [Ag5Sb3S8](2-) double layer

A new silver-antimony sulphide, [C6H20N4][Ag5Sb3S8], has been synthesised solvothermally in the presence of triethylenetetramine and characterised by single-crystal X-ray diffraction, thermogravimetry and elemental analysis. The compound crystallises in the space group P2(1)/m (a = 6.2778(7), b = 15.8175(16) and c = 12.4617(15) angstrom and beta = 104.561(5)degrees) and adopts a structure in which honeycomb-like sheets of fused six-membered silver-antimony-sulphide rings are linked through Ag-S bonds to form double layers. The idealised structure can be considered to be derived from that of antifluorite and represents a second structure type for the [Ag5Sb3S8](2-) double layer. (c) 2005 Elsevier Inc. All rights reserved.

Synthesis, crystal structures, magnetic properties and catecholase activity of double phenoxido-bridged penta-coordinated dinuclear nickel(II) complexes derived from reduced Schiff-base ligands: mechanistic inference of catecholase activity

Three double phenoxido-bridged dinuclear nickel(II) complexes, namely [Ni-2(L-1)(2)(NCS)(2)] (1), [Ni-2(L-2)(2)(NCS)(2)] (2), and [Ni-2(L-3)(2)(NCS)(2)] (3) have been synthesized using the reduced tridentate Schiff-base ligands 2-[1-(3-methylamino-propylamino)-ethyl]-phenol (HL1), 2-[1-(2-dimethylamino-ethylamino)-ethyl]-phenol (HL2), and 2-[1-(3-dimethylarnino-propylamino)-ethyl]-phenol (HL3), respectively. The coordination compounds have been characterized by X-ray structural analyses, magnetic-susceptibility measurements, and various spectroscopic methods. In all complexes, the nickel(II) ions are penta-coordinated in a square-pyramidal environment, which is severely distorted in the case of 1 (Addison parameter tau = 0.47) and 3 (tau = 0.29), while it is almost perfect for 2 (tau = 0.03). This arrangement leads to relatively strong antiferromagnetic interactions between the Ni(II) (S = 1) metal centers as mediated by double phenoxido bridges (with J values of -23.32 (1), -35.45 (2), and -34.02 (3) cm(3) K mol(-1), in the convention H = -2JS(1)S(2)). The catalytic activity of these Ni compounds has been investigated for the aerial oxidation of 3,5-di-tert-butylcatechol. Kinetic data analysis following Michaelis-Menten treatment reveals that the catecholase activity of the complexes is influenced by the flexibility of the ligand and also by the geometry around the metal ion. Electrospray ionization mass spectroscopy (ESI-MS) studies (in the positive mode) have been performed for all the coordination compounds in the presence of 3,5-DTBC to characterize potential complex-substrate intermediates. The mass-spectrometry data, corroborated by electron paramagnetic resonance (EPR) measurements, suggest that the metal centers are involved in the catecholase activity exhibited by the complexes.

THEORY OF ELECTRICAL CHARACTERISTICS OF A SCHOTTKY-BARRIER HAVING EXPONENTIALLY DISTRIBUTED IMPURITY STATES AND METAL-INSULATOR METAL STRUCTURES

The metal-insulator or metal-amorphous semiconductor blocking contact is still not well understood. Here, we discuss the steady state characteristics of a non-intimate metal-insulator Schottky barrier. We consider an exponential distribution (in energy) of impurity states in addition to impurity states at a single energy level within the depletion region. We present analytical expressions for the electrical potential, field, thickness of depletion region, capacitance, and charge accumulated in the depletion region. We also discuss ln I versus V(ap) data. Finally, we compare the characteristics in three cases: (i) impurity states at only a single energy level; (ii) uniform energy distribution of impurity states; and (iii) exponential energy distribution of impurity states.In general, the electrical characteristics of Schottky barriers and metal-insulator-metal structures with Schottky barriers depend strongly on the energy distribution of impurity states.

Theory of electrical characteristics for metal-oxide-insulator Schottky barrier and metal-insulator-metal structures

The metal-insulator or metal-amorphous semiconductor blocking contact is still not well understood. Here, the intimate metal-insulator and metal-oxide-insulator contact are discussed. Further, the steady-state characteristics of metal-oxide-insulator-metal structures are also discussed. Oxide is an insulator with wider energy band gap (about 50 Å thick). A uniform energetic distribution of impurities is considered in addition to impurities at a single energy level inside the surface charge region at the oxide-insulator interface. Analytical expressions are presented for electrical potential, field, thickness of the depletion region, capacitance, and charge accumulated in the surface charge region. The electrical characteristics are compared with reference to relative densities of two types of impurities. ln I is proportional to the square root of applied potential if energetically distributed impurities are relatively important. However, distribution of the electrical potential is quite complicated. In general energetically distributed impurities can considerably change the electrical characteristics of these structures.

Hydrodynamic stability theory of double ablation front structures in inertial confinement fusion.

The aim of inertial confinement fusion is the production of energy by the fusion of thermonuclear fuel (deuterium-tritium) enclosed in a spherical target due to its implosion. In the direct-drive approach, the energy needed to spark fusion reactions is delivered by the irradiation of laser beams that leads to the ablation of the outer shell of the target (the so-called ablator). As a reaction to this ablation process, the target is accelerated inwards, and, provided that this implosion is sufficiently strong a symmetric, the requirements of temperature and pressure in the center of the target are achieved leading to the ignition of the target (fusion). One of the obstacles capable to prevent appropriate target implosions takes place in the ablation region where any perturbation can grow even causing the ablator shell break, due to the ablative Rayleigh-Taylor instability. The ablative Rayleigh-Taylor instability has been extensively studied throughout the last 40 years in the case where the density/temperature profiles in the ablation region present a single front (the ablation front). Single ablation fronts appear when the ablator material has a low atomic number (deuterium/tritium ice, plastic). In this case, the main mechanism of energy transport from the laser energy absorption region (low density plasma) to the ablation region is the electron thermal conduction. However, recently, the use of materials with a moderate atomic number (silica, doped plastic) as ablators, with the aim of reducing the target pre-heating caused by suprathermal electrons generated by the laser-plasma interaction, has demonstrated an ablation region composed of two ablation fronts. This fact appears due to increasing importance of radiative effects in the energy transport. The linear theory describing the Rayleigh-Taylor instability for single ablation fronts cannot be applied for the stability analysis of double ablation front structures. Therefore, the aim of this thesis is to develop, for the first time, a linear stability theory for this type of hydrodynamic structures.

Investigation of AlInN barrier ISFET structures with GaN capping for pH detection

The pH response of GaN/AlInN/AlN/GaN ion-sensitive field effect transistor (ISFET) on Si substrates has been characterized. We analyzed the variation of the surface potential (ΔVsp/ΔpH) and current (ΔIds/ΔpH) with solution pH in devices with the same indium content (17%, in-plane lattice-matched to GaN) and different AlInN thickness (6 nm and 10 nm), and compared with the literature. The shrinkage of the barrier, that has the effect to increase the transconductance of the device, makes the 2-dimensional electron density (2DEG) at the interface very sensitive to changes in the surface. Although the surface potential sensitivity to pH is similar in the two devices, the current change with pH (ΔIds/ΔpH), when biasing the ISFET by a Ag/AgCl reference electrode, is almost 50% higher in the device with 6 nm AlInN barrier, compared to the device with 10 nm barrier. When measuring the current response (ΔIds/ΔpH) without reference electrode, the device with thinner AlInN layer has a larger response than the thicker one, of a factor of 140%, and that current response without reference electrode is only 22% lower than its maximum response obtained using reference electrode.

Structural and morphological studies on wet-etched InAlGaN barrier HEMT structures

The quaternary nitride-based high electron mobility transistor (HEMT) has been recently a focus of interest because of the possibility to grow lattice-matched barrier to GaN and tune the barrier bandgap at the same time.