Chaotic advection in blood flow

In this paper we argue that the effects of irregular chaotic motion of particles transported by blood can play a major role in the development of serious circulatory diseases. Vessel wall irregularities modify the flow field, changing in a nontrivial way the transport and activation of biochemically active particles. We argue that blood particle transport is often chaotic in realistic physiological conditions. We also argue that this chaotic behavior of the flow has crucial consequences for the dynamics of important processes in the blood, such as the activation of platelets which are involved in the thrombus formation.

Gravitational wave recoil in Robinson-Trautman spacetimes

We consider the gravitational recoil due to nonreflection-symmetric gravitational wave emission in the context of axisymmetric Robinson-Trautman spacetimes. We show that regular initial data evolve generically into a final configuration corresponding to a Schwarzschild black hole moving with constant speed. For the case of (reflection-)symmetric initial configurations, the mass of the remnant black hole and the total energy radiated away are completely determined by the initial data, allowing us to obtain analytical expressions for some recent numerical results that have appeared in the literature. Moreover, by using the Galerkin spectral method to analyze the nonlinear regime of the Robinson-Trautman equations, we show that the recoil velocity can be estimated with good accuracy from some asymmetry measures (namely the first odd moments) of the initial data. The extension for the nonaxisymmetric case and the implications of our results for realistic situations involving head-on collision of two black holes are also discussed.

Direct detection of Kaluza-Klein particles in neutrino telescopes

In theories with universal extra dimensions, all standard model fields propagate in the bulk and the lightest state of the first Kaluza-Klein (KK) level can be made stable by imposing a Z(2) parity. We consider a framework where the lightest KK particle (LKP) is a neutral, extremely weakly interacting particle such as the first KK excitation of the graviton, while the next-to-lightest KK particle (NLKP) is the first KK mode of a charged right-handed lepton. In such a scenario, due to its very small couplings to the LKP, the NLKP is long-lived. We investigate the production of these particles from the interaction of high energy neutrinos with nucleons in the Earth and determine the rate of NLKP events in neutrino telescopes. Using the Waxman-Bahcall limit for the neutrino flux, we find that the rate can be as large as a few hundreds of events a year for realistic values of the NLKP mass.

Structural and optical properties of rare earth-doped (Ba(0.77)Ca(0.23))(1-x)(Sm, Nd, Pr, Yb)(x)TiO(3)

The structural, dielectric, and vibrational properties of pure and rare earth (RE)-doped Ba(0.77) Ca(0.23)TiO(3) (BCT23; RE = Nd, Sm, Pr, Yb) ceramics obtained via solid-state reaction were investigated. The pure and RE-doped BCT23 ceramics sintered at 1450 degrees C in air for 4 h showed a dense microstructure in all ceramics. The use of RE ions as dopants introduced lattice-parameter changes that manifested in the reduction of the volume of the unit cell. RE-doped BCT23 samples exhibit a more homogenous microstructure due to the absence of a Ti-rich phase in the grain boundaries as demonstrated by scanning electron microscopy imaging. The incorporation of REs led to perturbations of the local symmetry of TiO(6) octahedra and the creation of a new Raman mode. The results of Raman scattering measurements indicated that the Curie temperature of the ferroelectric phase transition depends on the RE ion and ion content, with the Curie temperature shifting toward lower values as the RE content increases, with the exception of Yb(3+) doping, which did not affect the ferroelectric phase transition temperature. The phase transition behavior is explained using the standard soft mode model. Electronic paramagnetic resonance measurements showed the existence of Ti vacancies in the structure of RE-doped BCT23. Defects are created via charge compensation mechanisms due to the incorporation of elements with a different valence state relative to the ions of the pure BCT23 host. It is concluded that the Ti vacancies are responsible for the activation of the Raman mode at 840 cm(-1), which is in agreement with lattice dynamics calculations. (c) 2011 American Institute of Physics. [doi:10.1063/1.3594710]

Spin Hall effect due to intersubband-induced spin-orbit interaction in symmetric quantum wells

We investigate the intrinsic spin Hall effect in two-dimensional electron gases in quantum wells with two subbands, where a new intersubband-induced spin-orbit coupling is operative. The bulk spin Hall conductivity sigma(z)(xy) is calculated in the ballistic limit within the standard Kubo formalism in the presence of a magnetic field B and is found to remain finite in the B=0 limit, as long as only the lowest subband is occupied. Our calculated sigma(z)(xy) exhibits a nonmonotonic behavior and can change its sign as the Fermi energy (the carrier areal density n(2D)) is varied between the subband edges. We determine the magnitude of sigma(z)(xy) for realistic InSb quantum wells by performing a self-consistent calculation of the intersubband-induced spin-orbit coupling.

Three-dimensional fabrication of optically active microstructures containing an electroluminescent polymer

Microfabrication via two-photon absorption polymerization is a technique to design complex microstructures in a simple and fast way. The applications of such structures range from mechanics to photonics to biology, depending on the dopant material and its specific properties. In this paper, we use two-photon absorption polymerization to fabricate optically active microstructures containing the conductive and luminescent polymer poly(2-methoxy-5-(2'-ethylhexyloxy)-1,4-phenylenevinylene) (MEH-PPV). We verify that MEH-PPV retains its optical activity and is distributed throughout the microstructure after fabrication. The microstructures retain the emission characteristics of MEH-PPV and allow waveguiding of locally excited fluorescence when fabricated on top of low refractive index substrates. (C) 2009 American Institute of Physics. [doi: 10.1063/1.3232207]

Intersubband-induced spin-orbit interaction in quantum wells

Recently, we have found an additional spin-orbit (SO) interaction in quantum wells with two subbands [Bernardes , Phys. Rev. Lett. 99, 076603 (2007)]. This new SO term is nonzero even in symmetric geometries, as it arises from the intersubband coupling between confined states of distinct parities, and its strength is comparable to that of the ordinary Rashba. Starting from the 8x8 Kane model, here we present a detailed derivation of this new SO Hamiltonian and the corresponding SO coupling. In addition, within the self-consistent Hartree approximation, we calculate the strength of this new SO coupling for realistic symmetric modulation-doped wells with two subbands. We consider gated structures with either a constant areal electron density or a constant chemical potential. In the parameter range studied, both models give similar results. By considering the effects of an external applied bias, which breaks the structural inversion symmetry of the wells, we also calculate the strength of the resulting induced Rashba couplings within each subband. Interestingly, we find that for double wells the Rashba couplings for the first and second subbands interchange signs abruptly across the zero bias, while the intersubband SO coupling exhibits a resonant behavior near this symmetric configuration. For completeness we also determine the strength of the Dresselhaus couplings and find them essentially constant as function of the applied bias.

NMR analog of Bell's inequalities violation test

In this paper, we present an analog of Bell's inequalities violation test for N qubits to be performed in a nuclear magnetic resonance (NMR) quantum computer. This can be used to simulate or predict the results for different Bell's inequality tests, with distinct configurations and a larger number of qubits. To demonstrate our scheme, we implemented a simulation of the violation of the Clauser, Horne, Shimony and Holt (CHSH) inequality using a two-qubit NMR system and compared the results to those of a photon experiment. The experimental results are well described by the quantum mechanics theory and a local realistic hidden variables model (LRHVM) that was specifically developed for NMR. That is why we refer to this experiment as a simulation of Bell's inequality violation. Our result shows explicitly how the two theories can be compatible with each other due to the detection loophole. In the last part of this work, we discuss the possibility of testing some fundamental features of quantum mechanics using NMR with highly polarized spins, where a strong discrepancy between quantum mechanics and hidden variables models can be expected.

Antiferromagnetism with spin polarization of GaN-based diluted magnetic semiconductors

The diluted magnetic semiconductors are promising materials for spintronic applications. Usually one intents to find the ferromagnetic state but recently the antiferromagnetism (AFM) was proposed to have some advantages. In this work, we verify the possibility to obtain spin polarization with an AFM state. In particular, we studied GaN 5% double doped with two different transition metals atoms (Mn and Co or Cr and Ni), forming the Mn(x)Co(0.056-x)Ga(0.944)N and Cr(x)Ni(0.056-x)Ga(0.944)N quaternary alloys. In order to simulate these systems in a more realistic way, and take into account composition fluctuations, we adapted the generalized quasichemical approach to diluted alloys, which is used in combination with spin density-functional theory. We find that is possible to obtain an AFM ground state up to 70% spin polarization.

Multifractal regime transition in a modified minority game model

The search for more realistic modeling of financial time series reveals several stylized facts of real markets. In this work we focus on the multifractal properties found in price and index signals. Although the usual minority game (MG) models do not exhibit multifractality, we study here one of its variants that does. We show that the nonsynchronous MG models in the nonergodic phase is multifractal and in this sense, together with other stylized facts, constitute a better modeling tool. Using the structure function (SF) approach we detected the stationary and the scaling range of the time series generated by the MG model and, from the linear (non-linear) behavior of the SF we identified the fractal (multifractal) regimes. Finally, using the wavelet transform modulus maxima (WTMM) technique we obtained its multifractal spectrum width for different dynamical regimes. (C) 2009 Elsevier Ltd. All rights reserved.

Magnetostriction of polycrystalline Fe-Ge alloys

The longitudinal and transverse magnetostriction and microstructure of polycrystalline Fe(100-x)Ge(x) (x= 8, 12, 15, 20) alloys were investigated in order to correlate the magnetostriction with microstructure. In order to obtain different microstructures in the Fe(100-x)Ge(x) alloys, the samples were annealed at 600 degrees C during 2 h and at 1150 degrees C for half hour and then quenched in cold water. For Ge concentrations lower than 14 at.%, the longitudinal magnetostriction is positive and increases positively up to 22 ppm at 12 at.% Ge then decreases and vanishes at about 14 at.% Ge. For further Ge concentration increase the longitudinal magnetostriction is negative and reaches -30 ppm for Fe(80)Ge(20). This behavior, that is very similar to that reported for Fe-Si alloys, is explained by the structural changes caused by different thermal histories of the alloys. (C) 2008 Published by Elsevier B. V.

Morphological analysis of pitting corrosion in AISI 310S austenitic stainless steel after salt spray exposition

This paper aims to study evolution of increase, distribution and classification of pits in 310S austenitic stainless steels obtained in the state as-received and heat-treated under different exposure times in saline. This work applicability has been based on a technique development for morphologic characterization of localized corrosion associated with description aspects of shapes, size and population-specific parameters. Methodology has been consisted in the following steps: specimens preparation, corrosion tests via salt spray in different conditions, microstructural analysis, pits profiles analysis and images analysis, digital processing and image analysis in order to characterize the pits distribution, morphology and size. Results obtained in digital processing and profiles image analysis have been subjected to statistical analysis using median as parameter in the alloy as received and treated. The alloy as received displays the following morphology: hemispheric pits> transition region A> transition region B> irregular> conic. The pits amount in the treated alloy at each exposure time is: transition region B> hemispherical> transition region A> conic> irregular.

Microstructural characterization of rapidly solidified and heat-treated Ti(92)B(8) eutectic alloy

In this work, Ti(92)B(8) alloy was processed via rapid solidification (splat-cooling) and then heat-treated at 700 degrees C and 1000 degrees C. A careful microstructural characterization indicated that, after rapid solidification, a very fine two-phase microstructure was produced with no significant saturation of B in alpha/beta Ti. There was no indication of amorphous formation in the rapidly solidified splats. Both alpha Ti and TiB were observed in the microstructures of the splats after heat-treatment at 700 degrees C and 1000 degrees C, confirming the stability of the alpha Ti+TiB two-phase region in this temperature range. (C) 2008 Elsevier Inc. All rights reserved.

Superconducting current path and flux line shape in NbTiTa obtained by inter-diffusion process

This investigation presents a comprehensive characterization of magnetic and transport properties of an interesting superconducting wire, Nb-Ti -Ta, obtained through the solid-state diffusion between Nb-12 at.% Ta alloy and pure Ti. The physical properties obtained from magnetic and transport measurements related to the microstructure unambiguously confirmed a previous proposition that the superconducting currents flow in the center of the diffusion layer, which has a steep composition variation. The determination of the critical field also confirmed that the flux line core size is not constant, and in addition it was possible to determine that, in the center of the layer, the flux line core is smaller than at the borders. A possible core shape design is proposed. Among the wires studied, the one that presented the best critical current density was achieved for a diffusion layer with a composition of about Nb-32% Ti-10% Ta, obtained with a heat treatment at 700 degrees C during 120 h, in agreement with previous studies. It was determined that this wire has the higher upper critical field, indicating that the optimization of the superconducting behavior is related to an intrinsic property of the ternary alloy.

Mechanical properties of Y-TPZ ceramics obtained by liquid phase sintering using bioglass as additive

Yttria stabilized tetragonal zirconia (Y-TZP) ceramics were sintered by liquid phase sintering at low temperatures using bioglass as sintering additive. ZrO2-bioglass ceramics were prepared by mixing a ZrO2 stabilized with 3 Mol%Y2O3 and different amounts of bioglass based on 3CaO center dot P2O5-MgO-SiO2 system. Mixtures were compacted by uniaxial cold pressing and sintered in air, at 1200 and 1300 degrees C for 120 min. The influence of the bioglass content on the densification, tetragonal phase stability, bending strength, hardness and fracture toughness was investigated. The ceramics sintered at 1300 degrees C and prepared by addition of 3% of bioglass, exhibited the highest strength of 435 MPa, hardness of 1170 HV and fracture toughness of 6.3 MPa m(1/2). These results are related to the low monoclinic phase content, high relative density and the presence of the thermal residual stress generated between the ZrO2-matrix and bioglass grain boundary, contributing to the activation of the toughening mechanisms. (c) 2007 Elsevier B.V. All rights reserved.