2,690 research outputs found
Comparação de métodos de extração de DNA para caracterização molecular de Bacillus thuringiensis.
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Tuning in magnetic modes in Tb(Co_{x}Ni_{1-x})_{2}B_{2}C: from longitudinal spin-density waves to simple ferromagnetism
Neutron diffraction and thermodynamics techniques were used to probe the
evolution of the magnetic properties of Tb(Co_{x}Ni_{1-x})_{2}B_{2}C. A
succession of magnetic modes was observed as x is varied: the longitudinal
modulated k=(0.55,0,0) state at x=0 is transformed into a collinear
k=([nicefrac]\nicefrac{1}{2},0,[nicefrac]\nicefrac{1}{2})
antiferromagnetic state at x= 0.2, 0.4; then into a transverse c-axis modulated
k=(0,0,[nicefrac]\nicefrac{1}{3}) mode at x= 0.6, and finally
into a simple ferromagnetic structure at x= 0.8 and 1. Concomitantly, the
low-temperature orthorhombic distortion of the tetragonal unit cell at x=0 is
reduced smoothly such that for x >= 0.4 only a tetragonal unit cell is
manifested. Though predicted theoretically earlier, this is the first
observation of the k=(0,0,[nicefrac]\nicefrac{1}{3}) mode in
borocarbides; our findings of a succession of magnetic modes upon increasing x
also find support from a recently proposed theoretical model. The implication
of these findings and their interpretation on the magnetic structure of the
RM_{2}B_{2}C series are also discussed
Disordered two-dimensional superconductors: roles of temperature and interaction strength
We have considered the half-filled disordered attractive Hubbard model on a
square lattice, in which the on-site attraction is switched off on a fraction
of sites, while keeping a finite on the remaining ones. Through Quantum
Monte Carlo (QMC) simulations for several values of and , and for system
sizes ranging from to , we have calculated the
configurational averages of the equal-time pair structure factor , and,
for a more restricted set of variables, the helicity modulus, , as
functions of temperature. Two finite-size scaling {\it ansatze} for have
been used, one for zero-temperature and the other for finite temperatures. We
have found that the system sustains superconductivity in the ground state up to
a critical impurity concentration, , which increases with , at least up
to U=4 (in units of the hopping energy). Also, the normalized zero-temperature
gap as a function of shows a maximum near , for . Analyses of the helicity modulus and of the pair structure factor
led to the determination of the critical temperature as a function of , for
4 and 6: they also show maxima near , with the highest
increasing with in this range. We argue that, overall, the observed
behavior results from both the breakdown of CDW-superconductivity degeneracy
and the fact that free sites tend to "push" electrons towards attractive sites,
the latter effect being more drastic at weak couplings.Comment: 9 two-column pages, 14 figures, RevTe
Materials for solar hydrogen production with simultaneous mineralization of ethanol
The photo-catalytic production of hydrogen by means of irradiation of a suspension of semiconductor oxides presents attractive features over other methods with higher cost such as water electrolysis. In this work, photocatalytic hydrogen production from water is studied, using ethanol as sacrificial agent. New nanostructured multifunctionalised semiconductor materials based on titanium dioxide, with effective photo-catalytic properties under UV illumination were synthesized using sol-gel technology and characterised by X-Ray diffraction and scanning electron microscopy. Aqueous suspensions of the semiconductor powders were used and the effect of solution pH and temperature (20-70ºC) as well as the effect of concentration of ethanol on hydrogen production were studied, for fixed concentrations of the catalyst. Comparison is made with doped Degussa-P25 TiO2 titanium dioxide. The need to decrease the electron-hole recombination rate was accounted for by metal doping [1] with the ethanol molecule acting as a hole trap. An increase in the hydrogen production rate was found as a result of the percentage of metal on doped titania and optimisation of experimental conditions with rate values being superior to recently published literature data [2]. Particle size, reactive surface area, structure and crystallinity of the semiconductor were found to be determinant in the production of highly photoactive titanium dioxide. Research in progress includes development of catalyst that allows effective utilization of visible light and design of an experimental reacto
Produção de hidrogénio solar com simultânea mineralização de poluentes orgânicos
A produção foto-catalítica de hidrogénio por iluminação de uma suspensão de nanopartículas de óxidos semicondutores apresenta vantagens atractivas sobre outros métodos de elevado custo, como a electrólise. Como barreira tecnológica à aplicação comercial daquela tecnologia salienta-se a sua baixa eficiência. Neste trabalho demonstra-se o aumento na eficiência da produção foto-catalítica de hidrogénio a partir de água, utilizando poluentes orgânicos como agentes sacrificiais. Os catalisadores desenvolvidos permitem também estender a aplicação do processo à utilização de luz solar directa ou luz artificial, fundamental para o avanço e implementação da tecnologi
Transient thermal behavior of simple structures in a simulated space environment by model testing
Modeling criteria for transient thermal test of spacecraft structures in space environment simulatio
Accelerated age-related olfactory decline among type 1 Usher patients
Usher Syndrome (USH) is a rare disease with hearing loss, retinitis pigmentosa and, sometimes, vestibular dysfunction. A phenotype heterogeneity is reported. Recent evidence indicates that USH is likely to belong to an emerging class of sensory ciliopathies. Olfaction has recently been implicated in ciliopathies, but the scarce literature about olfaction in USH show conflicting results. We aim to evaluate olfactory impairment as a possible clinical manifestation of USH. Prospective clinical study that included 65 patients with USH and 65 normal age-gender-smoking-habits pair matched subjects. A cross culturally validated version of the Sniffin' Sticks olfaction test was used. Young patients with USH have significantly better olfactory scores than healthy controls. We observe that USH type 1 have a faster ageing olfactory decrease than what happens in healthy subjects, leading to significantly lower olfactory scores in older USH1 patients. Moreover, USH type 1 patients showed significantly higher olfactory scores than USH type 2, what can help distinguishing them. Olfaction represents an attractive tool for USH type classification and pre diagnostic screening due to the low cost and non-invasive nature of the testing. Olfactory dysfunction should be considered among the spectrum of clinical manifestations of Usher syndrome
Perfil de sensibiblidade de helmintos gastrointestinais de ovinos a diferentes grupos de anti-helmínticos em duas propriedades na região Leste de São Paulo.
Caracterização molecular de cepas de Bacillus thuringiensis berliner para o biocontrole da lagarta-do-cartucho do milho.
Identificação de polimorfimos de base única (SNPs) em genes relacionados à taxa de ovulação em ovinos.
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