2,859 research outputs found
Use of dialkyldithiocarbamato complexes of bismuth(III) for the preparation of nano- and microsized Bi2S3 particles and the X-ray crystal structures of [Bi{S2CN(CH3)(C6H13)}(3)] and [Bi{S2CN(CH3)(C6H13)}(3)(C12H8N2)]
A range of bismuth(III) dithiocarbamato complexes were prepared and characterized. The
X-ray crystal structures of the compounds [Bi{S2CN(CH3)(C6H13)}3] (1) and [Bi{S2CN(CH3)-
(C6H13)}3(C12H8N2)] (2) are reported. The preparation of Bi2S3 particulates using a wet
chemical method and involving the thermalysis of Bi(III) dialkyldithiocarbamato complexes
is described. The influence of several experimental parameters on the optical and
morphological properties of the Bi2S3 powders was investigated. Nanosized Bi2S3 colloids
were obtained having long-term stability and showing a blue shift on the optical band edge;
the presence of particles exhibiting quantum size effects is discussed. Morphological welldefined Bi2S3 particles were obtained in which the fiber-type morphology is prevalent.FCT - POCTI/1999/CTM/ 3545
Spin and Charge Josephson effects between non-uniform superconductors with coexisting helimagnetic order
We consider the spin and charge Josephson current between two non-uniform
Fulde-Ferrel-Larkin-Ovchinnikov superconductors with helimagnetic order. We
demonstrate that the presence of the helimagnetic phase generates a spin
Josephson effect and leads to additional contributions to both single-particle
and Josephson charge current. It is shown that for such systems the AC effect
differs more radically from the DC effect than in the case of a BCS
superconductor with helimagnetic order considered earlier in the literature [M.
L. Kuli\'c and I. M. Kuli\'c, Phys. Rev. B {\bf 63}, 104503 (2001)] where a
spin Josephson current has also been found. In our system the most interesting
effect occurs in the presence of an external magnetic field and in absence of
voltage, where we show that the charge Josephson current can be tuned to zero
while the spin Josephson current is non-vanishing. This provides a well
controlled mechanism to generate a spin supercurrent in absence of charge
currents.Comment: final versio
The superconducting phase transition and gauge dependence
The gauge dependence of the renormalization group functions of the
Ginzburg-Landau model is investigated. The analysis is done by means of the
Ward-Takahashi identities. After defining the local superconducting order
parameter, it is shown that its exponent is in fact gauge independent.
This happens because in the Landau gauge is the only gauge having a
physical meaning, a property not shared by the four-dimensional model where any
gauge choice is possible. The analysis is done in both the context of the
-expansion and in the fixed dimension approach. It is pointed out the
differences that arise in both of these approaches concerning the gauge
dependence.Comment: RevTex, 3 pages, no figures; accepted for publication in PRB; this
paper is a short version of cond-mat/990527
Deconfined quantum criticality driven by Dirac fermions in SU(2) antiferromagnets
Quantum electrodynamics in 2+1 dimensions is an effective gauge theory for
the so called algebraic quantum liquids. A new type of such a liquid, the
algebraic charge liquid, has been proposed recently in the context of
deconfined quantum critical points [R. K. Kaul {\it et al.}, Nature Physics
{\bf 4}, 28 (2008)]. In this context, we show by using the renormalization
group in spacetime dimensions, that a deconfined quantum
critical point occurs in a SU(2) system provided the number of Dirac fermion
species . The calculations are done in a representation where the
Dirac fermions are given by four-component spinors. The critical exponents are
calculated for several values of . In particular, for and
() the anomalous dimension of the N\'eel field is given by
, with a correlation length exponent . These values change
considerably for . For instance, for we find and . We also investigate the effect of chiral
symmetry breaking and analyze the scaling behavior of the chiral holon
susceptibility, .Comment: 13 pages, 3 figures; published versio
Portuguese Adaptation of Students Engagement in Schools International Scale (SESIS)
The importance of student’s engagement has been recently pointed out in research. However, there has been a lack of engagement assessment instrument, pertaining psychometric qualities. Objective: This paper presents the Portuguese adaptation of the “Student’s Engagement in School International Scale” (SESIS), drawn up from a12 countries international study (Lam et al., 2012; Lam et al., in press). Method: Psychometric properties of this scale were examined with data from 685 students from different grades (6th, 7th, 9th and 10th), from both sexes, and different regions of the country. Results: Factorial analysis of the results, with varimax rotation, lead to three different factors which explain 50.88% of the variance. The scale integrates the original 33 items, and cognitive, affective and behavioural dimensions. For the external validity study, the relationship between student’s engagement in school results and other school variables — academic performance, self-concept — was considered, and significant relations were observed, as expected. Conclusion: The data presented highlights the qualities of SESIS, as well as its usefulness for research purposes. Suggestion: It is suggested the investigation of the extension of SESIS’s three-dimensionality, in future studiesKeywords: Innovation, technology, research projects, etc. [Arial 10-point, justified alignment]
Carbamazepine polymorphism: a re-visitation using Raman imaging
Raman imaging methods have appeared in the last years as a powerful approach to monitoring the quality of pharmaceutical compounds. Because polymorphism occurs in many crystalline pharmaceutical compounds, it is essential to monitor polymorphic transformations induced by different external stimulus, such as temperature changes, to which those compounds may be submitted. Raman imaging with k-means cluster analysis (CA) is used here as an essential technique to investigate structural and chemical transformations occurring in carbamazepine p-monoclinic (CBZ III) into carbamazepine triclinic (CBZ I) when submitted to temperatures near the melting point of CBZ III (178 °C) and CBZ I (193 °C). CBZ III commercial powder and laboratorial prepared CBZ I were analyzed by differential scanning calorimetry, powder X-ray diffraction and Raman spectroscopy with variable temperature. After thermal treatment, the resultant CBZ powder was evaluated by Raman imaging, in which all imaging data was analyzed using CA. Raman imaging allowed the identification of different polymorphs of CBZ (CBZ III and CBZ I) and iminostilbene (IMS), a degradation product of CBZ, in the treated samples, depending on the heating treatment method.publishe
Gauge dependenceof the order parameter anomalous dimension in the Ginzburg-Landau model and the critical fluctuations in superconductors
The critical fluctuations of superconductors are discussed in a fixed
dimension scaling suited to describe the type II regime. The gauge dependence
of the anomalous dimension of the scalar field is stablished exactly from the
Ward-Takahashi identities. Its fixed point value gives the critical
exponent and it is shown that is gauge independent, as expected on
physical grounds. In the scaling considered, is found to be zero at
1-loop order, while . This result is just the 1-loop values
for the XY model obtained in the fixed dimension renormalization group
approach. It is shown that this XY behavior holds at all orders. The result
should be contrasted with the negative values frequently
reported in the literature.Comment: EuroLaTex, 7 pages, 2 figures, reference updated; version to be
published in Europhysics Letter
Wall material selection for microencapsulating glicine max and punica granatum oils by spray drying.
Pomegranate seed oil, even though highly sensitive to oxidation, has been extensively studied due to its anti-inflammatory potential. Microencapsulation by spray drying can protect the oil and increase its shelf life. Modified starch, maltodextrin and gum arabic are evaluated by a mixture design to get the better wall material composition. The better response for drying process yield (41%) and oxidative stability (42%) were achieved using modified starch and gum arabic at the same proportion as wall material
Blending of pressed vegetable oils from pomegranate seeds and soybean to increase functional lipids consume.
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