Field-induced length changes in the spin-liquid candidate κ-(BEDT-TTF) 2Cu 2(CN) 3

Measurements of the coefficient of thermal expansion on the spin-liquid candidate κ-(BEDT-TTF) 2Cu 2(CN) 3 have revealed distinct and strongly anisotropic lattice effects around 6 K - a possible spin liquid instability. In order to study the effects of a magnetic field on the low-temperature spin-liquid state, dilatometric measurements have been conducted both as a function of temperature at B = const. and as a function of field at T = const. While the 6 K anomaly is found to be insensitive to magnetic fields B ≤ 10 T, the maximum field applied, surprisingly strong B -induced effects are observed for magnetic fields applied along the in-plane b-axis. Above a threshold field of 0.5 T < B c ≤ 1 T, a jump-like anomaly is observed in the b-axis lattice parameter. This anomaly, which is located at 8.7 K at B = 1 T, grows in size and shifts to lower temperatures with increasing the magnetic field. Although the anomaly bears resemblance to a first-order phase transition, the lack of hysteresis suggests otherwise. © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

Simulação numérica do comportamento da madeira de Eucalytus citrodora ao cisalhamento através do ensaio de tração Off-Axis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

U-Pb SHRIMP and 40Ar/39Ar constraints on the timing of mineralization in the Paleoproterozoic Caxias orogenic gold deposit, São Luís cratonic fragment, Brazil

Caxias é um depósito de ouro orogênico do fragmento cratônico São Luís, que é correlacionável aos terrenos Riacianos do Cráton Oeste-Africano. O depósito se formou após o metamorfismo regional (estimado em 2100 ± 15 Ma) e está hospedado em zona de cisalhamento que secciona xistos do Grupo Aurizona (2240 ± 5 Ma) e o Microtonalito Caxias. O microtonalito foi aqui datado em 2009 ± 11 Ma, e representa um estágio magmático tardio na evolução do fragmento cratônico São Luís. Cristais de zircão com idades de 2139 ± 10 Ma foram herdados da fonte magmática ou são produto de contaminação durante a intrusão. A composição dos isótopos de chumbo sugere que granitoides de arco de ilhas de ca. 2160 Ma são a fonte provável para o Pb incorporado na pirita relacionada com o minério. Sericita hidrotermal mostra idade ⁴⁰Ar/³⁹Ar de 1990 ± 30 Ma, que, combinada com a idade de posicionamento do microtonalito hospedeiro, limita o evento mineralizador ao intervalo 2020-1960 Ma.

Lattice effects in the quasi-two-dimensional valence-bond-solid Mott insulator EtMe3P[Pd(dmit)(2)](2)

The organic charge-transfer salt EtMe3P[Pd(dmit)(2)](2) is a quasi-two-dimensional Mott insulator with localized spins S = 1/2 residing on a distorted triangular lattice. Here we report measurements of the uniaxial thermal expansion coefficients alpha(i) along the in-plane i = a and c axis as well as along the out-of-plane b axis for temperatures 1.4 K <= T <= 200 K. Particular attention is paid to the lattice effects around the phase transition at T-VBS = 25 K into a low-temperature valence-bond-solid phase and the paramagnetic regime above where effects of short-range antiferromagnetic correlations can be expected. The salient results of our study include (i) the observation of strongly anisotropic lattice distortions accompanying the formation of the valence-bond-solid phase, and (ii) a distinct anomaly in the thermal expansion coefficients in the paramagnetic regime around 40 K. Our results demonstrate that upon cooling through T-VBS the in-plane c axis, along which the valence bonds form, contracts while the second in-plane a axis elongates by the same relative amount. Surprisingly, the dominant effect is observed for the out-of-plane b axis which shrinks significantly upon cooling through T-VBS. The pronounced anomaly in alpha(i) around 40 K is attributed to short-range magnetic correlations. It is argued that the position of this maximum, relative to that in the magnetic susceptibility around 70 K, speaks in favor of a more anisotropic triangular-lattice scenario for this compound than previously thought.

The influence of self-weight of elastic 2D structures in topology optimization via numerical technique Smooth Evolutionary Structural Optimization (SESO)

This paper deals with topology optimization in plane elastic-linear problems considering the influence of the self weight in efforts in structural elements. For this purpose it is used a numerical technique called SESO (Smooth ESO), which is based on the procedure for progressive decrease of the inefficient stiffness element contribution at lower stresses until he has no more influence. The SESO is applied with the finite element method and is utilized a triangular finite element and high order. This paper extends the technique SESO for application its self weight where the program, in computing the volume and specific weight, automatically generates a concentrated equivalent force to each node of the element. The evaluation is finalized with the definition of a model of strut-and-tie resulting in regions of stress concentration. Examples are presented with optimum topology structures obtaining optimal settings. (C) 2012 CIMNE (Universitat Politecnica de Catalunya). Published by Elsevier Espana, S.L.U. All rights reserved.

Verification of applicability of the polyurethane adhesive based on castor oil in the manufacture of glued laminated bamboo

The current concern with the environment promotes the development of new technologies for production with use of alternative materials, from renewable resources, and changes in production processes, having as main objective the reduction of environmental impact. One of the alternatives for cleaner production is the use of castor oil derivatives instead of non-renewable sources, such as adhesives based on PVA (polyvinyl acetate), applied in the manufacturing process of glued laminated bamboo. Based on the versatility of the bamboo laminate and the castor oil, and from the perspective of sustainability, this study aims to contribute to the application of new materials and processes, used in the manufacturing industry, by proposing the use of the polyurethane adhesive based on castor oil for glued laminated bamboo manufacturing, which can later be used in the manufacture of several products. To verify the applicability of the polyurethane adhesive based on castor oil in the glued laminated bamboo manufacture, mechanical tests of traction and shearing of the glue sheet were performed in specimens of the said material, and the results were compared with the Cascorez 2590 and Waterbond adhesives. The results showed that the polyurethane adhesive based on castor oil, in the traction test, has superior performance than the Waterbond adhesive and slightly below than the Cascorez 2590 adhesive, but in the shear test, the polyurethane adhesive based on castor oil presented a slightly inferior performance than the other two adhesives used in the comparison.

Anisotropic Brownian motion in ordered phases of DNA fragments

Using Fluorescence Recovery After Photobleaching, we investigate the Brownian motion of DNA rod-like fragments in two distinct anisotropic phases with a local nematic symmetry. The height of the measurement volume ensures the averaging of the anisotropy of the in-plane diffusive motion parallel or perpendicular to the local nematic director in aligned domains. Still, as shown in using a model specifically designed to handle such a situation and predicting a non-Gaussian shape for the bleached spot as fluorescence recovery proceeds, the two distinct diffusion coefficients of the DNA particles can be retrieved from data analysis. In the first system investigated (a ternary DNA-lipid lamellar complex), the magnitude and anisotropy of the diffusion coefficient of the DNA fragments confined by the lipid bilayers are obtained for the first time. In the second, binary DNA-solvent system, the magnitude of the diffusion coefficient is found to decrease markedly as DNA concentration is increased from isotropic to cholesteric phase. In addition, the diffusion coefficient anisotropy measured within cholesteric domains in the phase coexistence region increases with concentration, and eventually reaches a high value in the cholesteric phase.

Kinematic interaction factors of deep foundations with inclined piles.

[EN]The beneficial or detrimental role of battered piles on the dynamic response of piled foundations has not been yet fully elucidated. In order to shed more light on this aspect, kinematic interaction factors of deep foundations with inclined piles, are provided for single battered piles, as well as for 2X2 and 3X3 groups of piles subjected to vertically incident plane shear S waves.

Metodi avanzati di indagine di ammassi rocciosi a blocchi in matrice (bimrock).

The research focuses on the implementation and validation of advanced direct and indirect methods of investigation for the structural and mechanical characterisation of bimrocks. In particular, a non conventional in situ shear test has been develop in order to evaluate the strength parameters of bimrocks by properly taking into account the influence of blocks. Also, a geostatistical approach has been introduced for the investigation of block morphological and spatial properties from digital images, by means of a variographic analysis of the block Indicator Variable.

Point defects in carbon nanostructures studied by in-situ electron microscopy

In the present work, the formation and migration of point defects induced by electron irradiation in carbon nanostructures, including carbon onions, nanotubes and graphene layers, were investigated by in-situ TEM. The mobility of carbon atoms normal to the layers in graphitic nanoparticles, the mobility of carbon interstitials inside SWCNTs, and the migration of foreign atoms in graphene layers or in layers of carbon nanotubes were studied. The diffusion of carbon atoms in carbon onions was investigated by annealing carbon onions and observing the relaxation of the compressed clusters in the temperature range of 1200 – 2000oC. An activation energy of 5.0±0.3 eV was obtained. This rather high activation energy for atom exchange between the layers not only prevents the exchange of carbon atoms between the layers at lower temperature but also explains the high morphological and mechanical stability of graphite nanostructures. The migration of carbon atoms in SWCNTs was investigated quantitatively by cutting SWCNT bundles repeatedly with a focused electron beam at different temperatures. A migration barrier of about 0.25 eV was obtained for the diffusion of carbon atoms inside SWCNTs. This is an experimental confirmation of the high mobility of interstitial atoms inside carbon nanotubes, which corroborates previously developed theoretical models of interstitial diffusivity. Individual Au and Pt atoms in one- or two-layered graphene planes and MWCNTs were monitored in real time at high temperatures by high-resolution TEM. The direct observation of the behavior of Au and Pt atoms in graphenic structures in a temperature range of 600 – 700°C allows us to determine the sites occupied by the metal atoms in the graphene layer and the diffusivities of the metal atoms. It was found that metal atoms were located in single or multiple carbon vacancies, not in off-plane positions, and diffused by site exchange with carbon atoms. Metal atoms showed a tendency to form clusters those were stable for a few seconds. An activation energy of around 2.5 eV was obtained for the in-plane migration of both Au and Pt atoms in graphene (two-dimensional diffusion). The rather high activation energy indicates covalent bonding between metal and carbon atoms. Metal atoms were also observed to diffuse along the open edge of graphene layers (one-dimensional diffusion) with a slightly lower activation energy of about 2.3 eV. It is also found that the diffusion of metal atoms in curved graphenic layers of MWCNTs is slightly faster than in planar graphene.

Effective Length K-Factors For Flexural Buckling Strengths Of Web Members In Open Web Steel Joists

Open web steel joists are designed in the United States following the governing specification published by the Steel Joist Institute. For compression members in joists, this specification employs an effective length factor, or K-factor, in confirming their adequacy. In most cases, these K-factors have been conservatively assumed equal to 1.0 for compression web members, regardless of the fact that intuition and limited experimental work indicate that smaller values could be justified. Given that smaller K-factors could result in more economical designs without a loss in safety, the research presented in this thesis aims to suggest procedures for obtaining more rational values. Three different methods for computing in-plane and out-of-plane K-factors are investigated, including (1) a hand calculation method based on the use of alignment charts, (2) computational critical load (eigenvalue) analyses using uniformly distributed loads, and (3) computational analyses using a compressive strain approach. The latter method is novel and allows for computing the individual buckling load of a specific member within a system, such as a joist. Four different joist configurations are investigated, including an 18K3, 28K10, and two variations of a 32LH06. Based on these methods and the very limited number of joists studied, it appears promising that in-plane and out-of-plane K-factors of 0.75 and 0.85, respectively, could be used in computing the flexural buckling strength of web members in routine steel joist design. Recommendations for future work, which include systematically investigating a wider range of joist configurations and connection restraint, are provided.

Thrombospondin-1 mediates platelet adhesion at high shear via glycoprotein Ib (GPIb): an alternative/backup mechanism to von Willebrand factor

Acute thrombotic arterial occlusion is the leading cause of morbidity and mortality in the Western world. Von Willebrand factor is thought to be the only indispensable adhesive substrate to promote thrombus formation in high shear environments. We found that thrombospondin-1, a glycoprotein enriched in arteriosclerotic plaques, might function as an alternative substrate for thrombus formation. Platelets adhered to thrombospondin-1 in a shear dependent manner with an optimum shear as found in stenosed arteries. Adhesion is extremely firm, with no detachment of platelets up to a shear rate of 4000 s(-1). Experiments using platelets from a patient completely lacking von Willebrand factor showed that von Willebrand factor is not involved in platelet binding to thrombospondin-1. Platelet adhesion to thrombospondin-1 is not mediated via beta3-integrins or GPIa. CD36 partially mediates the adhesion of pre-activated platelets. We identified GPIb as high shear adhesion-receptor for thrombospondin-1. Soluble GPIb, as well as antibodies against the GPIb, blocked platelet adhesion almost completely. The new discovered thrombospondin-1-GPIb adhesion axis under arterial shear conditions might be important, not only during thrombus formation but also for pathological processes where other cells bind to the endothelium or subendothelium, including arteriosclerosis, inflammation and tumor metastasis, and a promising therapeutic target.

Effect of zirconia surface treatments on the shear strength of zirconia/veneering ceramic composites

Aim of the investigation was to assess the effect of different surface treatments on the bond strength of veneering ceramics to zirconia. In a shear test, the influences of polishing, sandblasting, and silica-coating of the zirconia surface on bonding were assessed with five different veneering ceramics. In addition the effect of liner application was examined. With one veneering ceramic, the impact of regeneration firing of zirconia was also evaluated. Statistical analysis was performed with one-way ANOVA and post hoc Scheffé's test. Failure in every case occurred in the veneering ceramic adjacent to the interface with a thin layer of ceramic remaining on the zirconia surface, indicating that bond strength was higher than the cohesive strength of the veneering ceramic. Shear strength ranged from 23.5 +/- 3.4 MPa to 33.0 +/- 6.8 MPa without explicit correlation to the respective surface treatment. Regeneration firing significantly decreased the shear strength of both polished and sandblasted surfaces. Findings of this study revealed that bonding between veneering ceramics and zirconia might be based on chemical bonds. On this note, sandblasting was not a necessary surface pretreatment to enhance bond strength and that regeneration firing was not recommended.

Successful lower extremity angioplasty improves brachial artery flow-mediated dilation in patients with peripheral arterial disease

INTRODUCTION: Peripheral arterial disease (PAD) is associated with systemic impaired flow-mediated dilation (FMD) and increased risk for cardiovascular events. Decreased FMD may be caused by a decrease in arterial shear stress due to claudication and inflammation due to muscle ischemia and reperfusion. We assumed that endovascular revascularization of lower limb arterial obstructions ameliorates FMD and lowers inflammation through improvement of peripheral perfusion. METHODS: The study was a prospective, open, randomized, controlled, single-center follow-up evaluation assessing the effect of endovascular revascularization on brachial artery reactivity (FMD) measured by ultrasound, white blood cell (WBC) count, high-sensitive C-reactive protein (hs-CRP), and fibrinogen. We investigated 33 patients (23 men) with chronic and stable PAD (Rutherford 2 to 3) due to femoropopliteal obstruction. Variables were assessed at baseline and after 4 weeks in 17 patients (group A) who underwent endovascular revascularization and best medical treatment, and in 16 patients (group B) who received best medical treatment only. RESULTS: FMD did not differ between group A and B (4.96% +/- 1.86% vs 4.60% +/- 2.95%; P = .87) at baseline. It significantly improved after revascularization in group A (6.44% +/- 2.88%; P = .02) compared with group B at 4 weeks of follow-up (4.53% +/- 3.17%; P = .92), where it remained unchanged. The baseline ankle-brachial index (ABI) was similar for group A and B (0.63 +/- 0.15 vs 0.66 +/- 0.10; P = .36). At 4 weeks of follow-up, ABI was significantly increased in group A (1.05 +/- 0.15; P = .0004) but remained unchanged in group B (0.62 +/- 0.1). WBC counts of the two groups were comparable at baseline (group A: 7.6 +/- 2.26 x 10(6)/mL and group B: 7.8 +/- 2.02 x 10(6)/mL, P = .81). In group A, the leukocyte count significantly decreased after angioplasty from 7.6 +/- 2.26 to 6.89 +/- 1.35 x 10(6)/mL (P = .03). For group B, WBC count did not differ significantly compared with baseline (7.76 +/- 2.64 x 10(6)/mL; P = .94). No effects were observed on hs-CRP or fibrinogen from endovascular therapy. CONCLUSION: Endovascular revascularization with reestablishment of peripheral arterial perfusion improves FMD and reduces WBC count in patients with claudication. Revascularization may therefore have clinical implications beyond relief of symptoms, for example, reducing oxidative stress caused by repeated muscle ischemia or increased shear stress due to improved ambulatory activity.

Long-term reaction to bone cement in osteoporotic bone: new bone formation in vertebral bodies after vertebroplasty

Elderly patients frequently suffer from osteoporotic vertebral fractures resulting in the need of vertebroplasty or kyphoplasty. Nevertheless, no data are available about the long-term consequences of cement injection into osteoporotic bone. Therefore, the aim of the present study was to evaluate the long-term tissue reaction on bone cement injected to osteoporotic bone during vertebroplasty. The thoracic spine of an 80-year-old female was explanted 3.5 years after vertebroplasty with polymethylmethacrylate. The treatment had been performed due to painful osteoporotic compression fractures. Individual vertebral bodies were cut in axial or sagittal sections after embedding. The sections were analysed using contact radiography and staining with toluidine blue. Furthermore, selected samples were evaluated with scanning electron microscopy and micro-compted tomography (in-plane resolution 6 microm). Large amounts of newly formed callus surrounding the injected polymethylmethacrylate were detected with all imaging techniques. The callus formation almost completely filled the spaces between the vertebral endplate, the cancellous bone, and the injected polymethylmethacrylate. In trabecular bone microfractures and osteoclast lacuna were bridged or filled with newly formed bone. Nevertheless, the majority of the callus formation was found in the immediate vicinity of the polymethylmethacrylate without any obvious relationship to trabecular fractures. The results indicate for the first time that, contrary to established knowledge, even in osteoporosis the formation of large amounts of new bone is possible.