On the entropy operator for the general SU(1,1) TFD formulation

In this Letter, an entropy operator for the general unitary SU(1, 1) TFD formulation is proposed and used to lead a bosonic system from zero to finite temperature. Namely, considering the closed bosonic string as the target system, the entropy operator is used to construct the thermal vacuum. The behaviour of such a state under the breve conjugation rules is analyzed and it was shown that the breve conjugation does not affect the thermal effects. From this thermal vacuum the thermal energy, the entropy and the free energy of the closed bosonic string are calculated and the appropriated thermal distribution for the system is found after the free energy minimization. (C) 2004 Elsevier B.V. All rights reserved.

Can one cure the nommitarity of three-dimensional quadratic gravity using a topological Chern-Simons term?

Quadratic gravity in (2+1)D is nonunitarity at the tree level. When a topological Chern-Simons term is added to this theory, the harmless massive scalar mode of the former gives rise to a troublesome massive spin-0 ghost, while the massive spin-2 ghost is replaced by two massive physical particles both of spin-2. Therefore, unlike what it is claimed in the literature, quadratic Chern-Simons gravity in (2+1)D is nonunitary at the tree level.

Superstring in a pp-wave background at finite temperature. TFD approach

A thermodynamical analysis for the type IIB superstring in a pp-wave background is considered. The thermal Fock space is built and the temperature SUSY breaking appears naturally by analyzing the thermal vacuum. All the thermodynamical quantities are derived by evaluating matrix elements of operators in the thermal Fock space. This approach seems to be suitable to study thermal effects in the BMN correspondence context. (C) 2004 Elsevier B.V. All rights reserved.

A QCD sum rule study of Theta(+) in nuclear matter

We consider a [ud](2)(s) over bar current, in the finite-density QCD sum rule approach, to investigate the scalar and vector self-energies of the recently observed pentaquark state Theta(+)(1540), propagating in nuclear matter. We find that, opposite to what was obtained for the nucleon, the vector self-energy is negative, and the scalar self-energy is positive. There is a substantial cancellation between them resulting in an attractive net self-energy of the same order as in the nucleon case. (C) 2004 Elsevier B.V. All rights reserved.

Semiclassical particle spectrum of double sine-Gordon model

We present new theoretical results on the spectrum of the quantum field theory of the double sine-Gordon model. This non-integrable model displays different varieties of kink excitations and bound states thereof. Their mass can be obtained by using a semiclassical expression of the matrix elements of the local fields. In certain regions of the coupling-constants space the semiclassical method provides a picture which is complementary to the one of the form factor perturbation theory, since the two techniques give information about the mass of different types of excitations. In other regions the two methods are comparable, since they describe the same kind of particles. Furthermore, the semiclassical picture is particularly suited to describe the phenomenon of false vacuum decay, and it also accounts in a natural way the presence of resonance states and the occurrence of a phase transition. (C) 2004 Elsevier B.V. All rights reserved.

Some comments on the numerical simulation of self-synchronization of four non-ideal exciters

In this paper, self-synchronization of four non-ideal exciters is examined via numerical simulation. The mathematical model consists of four unbalanced direct Current motors with limited power supply mounted on a flexible Structural frame support. (c) 2004 Elsevier B.V. All rights reserved.

Kinetics of Ag-rich precipitates formation in Cu-Al-Ag alloys

The kinetics of Ag-rich precipitates formation in the Cu-2 wt.% Al alloy with additions of 2, 4, 6, 8, 10 and 12 wt.% Ag was studied using microhardness changes with temperature and time, differential scanning calorimetry (DSC), differential thermal analysis (DTA), scanning electron microscopy (SEM), optical microscopy (OM), energy dispersive X-ray analysis (EDX) and X-ray diffractometry (XRD). The results indicated that an increase in the Ag content decreases the activation energy for Ag-rich precipitates formation, and that it is possible to estimate the values of the diffusion and nucleation activation energies for the Ag precipitates. (C) 2004 Elsevier B.V. All rights reserved.

Characterization of lanthanum-doped bismuth titanate thin films prepared by polymeric precursor method

Lanthanum-modified bismuth titanate, Bi4-xLaxTi3O12 (BLT), with x ranging from 0 to 0.75 was grown on Pt/Ti/SiO2/Si substrates using a polymeric precursor solution and spin-coating method. The dielectric constant of highly doped bismuth titanate was equal to 148 while dielectric losses remained low (tan delta = 0.0018), and the films showed well-saturated polarization-electric field curves (2P(r) = 40.6 muC/cm(2) and V-c = 0.99 V). The leakage current densities improve for the lanthanum-doped system. For five-layered BLT films with x = 0.75, a charge storage density of 35 fC/mum(2) and a thickness of 320 nm were found. (C) 2004 Elsevier B.V. All rights reserved.

Influência da secagem, armazenamento e embalagem nos resultados da análise química de terra para fins de fertilidade

Amostras de terra provenientes de uma Terra Roxa Estruturada e um Latossol Vermelho Escuro textura média foram analisados quimicamente para se verificar a influência de embalagem (caixa de papelão saco de polietileno), tempo de armazenamento (1-32 dias) e processo de secagem (ao ar ou estufa a 60°C). A secagem foi o fator que mais influenciou a análise determinando variações nos resultados analíticos principalmente para pH e fósforo. O armazenamento apresentou influência apenas para fósforo trocável enquanto que a embalagem não influiu nos resultados. As variações dos resultados analíticos para pH, em função da secagem, e fósforo, em função da secagem e tempo de armazenamento, foram de ordem a alterar a interpretação da fertilidade quanto aos limites de classes.

Efeitos das respostas de observação diferenciais sobre a aprendizagem de relações condicionais com estímulos complexos

Este estudo avaliou se relações entre os componentes do estímulo modelo complexo exerceriam controle condicional em tarefas de matching-to-sample simultâneo. Na Fase 1, 3 crianças com necessidades especiais de ensino foram expostas ao treino das relações A1B1 e A2B2 e ao teste das respectivas relações simétricas. em seguida, as contingências de treino exigiram respostas de observação diferenciais que consistiram no estabelecimento de relações condicionais de identidade entre estímulos complexos (relações AB-AB) precedendo o acesso ao treino das relações condicionais ABX. Neste treino, diante de estímulos modelos complexos cujos componentes sustentavam condicionalidade treinada (A1B1 e A2B2), X1 foi o estímulo de escolha correto; X2 exerceu esta função quando os componentes do estímulo modelo não sustentavam tal relação (A1B2 e A2B1). Na Fase 2, ocorreria o treino PQ, testes QP e PQX que avaliariam a extensão do controle condicional definido pelas relações entre os estímulos P e Q. As três crianças registraram a aprendizagem das relações AB, a emergência das relações simétricas e índices elevados de acerto nas respostas de observação diferenciais, ou seja, no estabelecimento das relações condicionais de identidade com estímulos complexos. Contudo, as três demonstraram relações de controle distintas das previstas no treino ABX, sendo, portanto, o experimento finalizado na Fase 1. Tais resultados sugerem uma independência funcional entre as habilidades discriminativas exigidas nas duas contingências de ensino de relações condicionais com estímulos modelo complexos.

Formação de classes ordinais após a aprendizagem de seqüências independentes

A aquisição de relações ordinais entre estímulos arbitrários é uma importante habilidade comportamental, requisito para a aprendizagem de comportamentos acadêmicos, especialmente a alfabetização. O propósito deste estudo foi investigar o efeito do ensino de seqüências de dois termos com sobreposição na emergência de relações ordinais com mais de dois estímulos. A sobreposição ocorre quando o último estímulo em uma seqüência de dois estímulos é o primeiro de outra seqüência (e.g., S1 -> S2 e S2 ->S3, onde S2 é o estímulo sobreposto). Nas Etapas 1 e 2 de um experimento conduzido com cinco estudantes do ensino fundamental foram ensinadas seqüências de dois termos com os cinco estímulos de um conjunto A (A1 -> A2, A2 -> A3, A3 -> A4, A4 ->A5) e os cinco de um conjunto B (B1 -> B2, B2 ->B3, B3 -> B4, B4 -> B5). Estabelecida essa linha de base, foram conduzidos testes da emergência de relações ordinais com três, quatro e cinco termos dos conjuntos A e B, separadamente. A Etapa 3 avaliou se estímulos das seqüências ensinadas eram mutuamente substituíveis, com base na mesma função ordinal (primeiro, secundo, etc.). Os estudantes compuseram as relações ordinais ensinadas e apresentaram relações ordinais emergentes com estímulos dos conjuntos A e B, separadamente. Três estudantes também realizaram a substituição mútua entre estímulos dos conjuntos A e B na Etapa 3. Esses resultados sugerem a formação de cinco classes de estímulos (A1B1, A2B2, etc.), cada uma consistindo de estímulos que ocuparam a mesma função ordinal em diferentes seqüências. Os resultados têm implicações para a análise de comportamento simbólico complexo. Merecem consideração, também, aspectos metodológicos que favoreceram a aprendizagem relacional e a emergência de comportamento novo.

GCHF basis sets and their application in the electronic structure study of PrMnO3

The approach called generator coordinate Hartree-Fock (GCHF) method is used in the selection of Gaussian basis set [25s18p for O ((3)p), 31s21p14d for Mn (S-6), and 33s22p16d9f for Pr ((4)J)] for atoms. The role of the weight functions in the assessment of the numerical integration range of the GCHF equations is shown. These basis sets are contracted to (25s18p/9s5p), (31s21p14d/9s6p4d), and (33s22pl6d9f118sl2p5d3f) by segmented contraction scheme of Dunning and they are utilized in calculations of Restricted-Open-HF (ROHF) Total and Orbital energies of the (MnO+1)-Mn-3 and (PrO+1)-Pr-1 fragments, to evaluate their quality in molecular studies. The addition of one d polarization function in the contracted (9s5p) basis set for O(P-3) atom and their application with the contracted (9s6p4d), (18s21p5d3f) basis sets for Mn (S-6) and Pr-Pr ((4)j) atoms lead to the electronic structure study of PrMnO3. The dipole moment, the total energy, and total atomic charges properties were calculated and were carried out at ROHF level with the [PrMnO3](2) fragment. The calculated values show that PrMnO3 does not present piezoelectric properties. (C) 2004 Elsevier B.V. All rights reserved.

A DFT rationalization of the room temperature photoluminescence of Li2TiSiO5

Li2TiSiO5 powders were synthesized by the polymeric precursor method. The calcination temperatures were progressively increased until the complete crystallization of the phase occurring at 870 degreesC. For the first time, a strong photoluminescence was measured at room temperature with a 488 nm excitation wavelength for the non-crystalline samples. This photoluminescence in disordered phases has been interpreted by means of high-level quantum mechanical calculations based on density functional theory. Two periodic models have been used to represent the crystalline and disordered powders. They allowed to calculate electronic properties consistent with experimental data and to explain the relations between photoluminescence and structural disorder. (C) 2004 Elsevier B.V. All rights reserved.

Photo-induced transformations in chalcogenide nanocomposite layers

Investigations of photo-induced structural transformations (PST) and related changes of optical parameters in amorphous chalcogenide layers were further developed towards the establishment of their dependence on the compositional modulation of the material at nanoscale-dimensions (similar to3-10 nm) and possible improvement of optical recording parameters as well. Besides the known amorphous-amorphous PST, photo-stimulated interdiffusion and crystallization in multilayer structures were found as a useful method for amplitude-phase optical relief formation. The last two types of PST were influenced by size restrictions and efficiently operated by the composition and by the modulation period of the layered nanocomposite. Experimental evidences were obtained in Se-, AsSe-, Se0.4Te0.6-containing layered or quasi zero-dimensional structures based on As2S3 or SiOx and MgF2 matrix. Comparison was made with As2S3- and GeS2-based multicomponent layers, containing Se, Te and Ga. (C) 2004 Elsevier B.V. All rights reserved.

Variations in tree community composition and structure in a fragment of tropical semideciduous forest in southeastern Brazil related to different human disturbance histories

In an area of tropical seasonal semideciduous forest, the soil characteristics, floristic composition, physiognomic structure, and the distribution of three regeneration and three dispersal guilds were studied for four stands within the forest that had documented histories of varying degrees of human disturbance. The aim was to study forest regeneration in areas of preserved forest and secondary forest, with parts of both types of forest experiencing either 'intensive' or 'occasional' cattle trampling. The study was carried out in the Sebastiao Aleixo da Silva Ecological Station, Bauru, São Paulo State, Brazil. Two stands were called 'secondary' because they corresponded to forest tracts that were felled and occupied by crops and pastures in the past and then abandoned to forest regeneration ca. 40 years before this study. The other two stands, called 'preserved', corresponded to areas of the fragment where the forest has been maintained with only minor human impacts. The arboreal component of the tree community (diameter at breast height or dbh greater than or equal to 5 cm) was sampled in 20 plots of 40 m x 40 m, and the subarboreal component (diameter at the base of the stem or dbs < 5 cm and height greater than or equal to 0.5 m) in subplots of 40 m x 2 m. Physiognomic features, such as canopy height and density of climbing plants, were registered all over a 5 m x 5 m gridline laid on the sample plots. Soil bulk samples were collected for chemical and textural analyses. Most detected differences contrasted the secondary to the preserved forest stands. The soils of the secondary stands showed higher proportions of sand and lower levels of mineral nutrients and organic matter than those of the preserved stands, probably due to higher losses by leaching and erosion. Compared to the secondary stands, the preserved ones had higher proportions of tall trees, higher mean canopy height, lower species diversity, higher abundance of autochorous and shade-tolerant climax species, and lower abundance of pioneer and light-demanding climax species. Despite the high proportion of species shared by the preserved and secondary stands (108 out of 139), they differed consistently in terms of density of the most abundant species. on the other hand, the secondary and preserved stands held similar values for tree density and basal area, suggesting that 40 years were enough to restore these features. Effects of cattle trampling on the vegetation were detected for the frequency of trees of anemochorous and zoochorous species, which were higher in the stands under occasional and intensive cattle trampling, respectively. The density of thin climbers was lower in the stands with intensive trampling. (C) 2004 Elsevier B.V. All rights reserved.