Black Strings in Our World

The brane world scenario is a new approach to resolve the problem on how to compactify the higher dimensional spacetime to our 4-dimensional world. One of the remarkable features of this scenario is the higher dimensional effects in classical gravitational interactions at short distances. Due to this feature, there are black string solutions in our 4-dimensional world. In this paper, assuming the simplest model of complex minimally coupled scalar field with the local U(1) symmetry, we show a possibility of black-string formation by merging processes of type I long cosmic strings in our 4-dimensional world. No fine tuning for the parameters in the model might be necessary.Comment: 11pages, no figur

Axionic Mirage Mediation

Although the mirage mediation is one of the most plausible mediation mechanisms of supersymmetry breaking, it suffers from two crucial problems. One is the \mu-/B \mu-problem and the second is the cosmological one. The former stems from the fact that the B parameter tends to be comparable with the gravitino mass, which is two order of magnitude larger than the other soft masses. The latter problem is caused by the decay of the modulus whose branching ratio into the gravitino pair is sizable. In this paper, we propose a model of mirage mediation, in which Peccei-Quinn symmetry is incorporated. In this axionic mirage mediation, it is shown that the PQ symmetry breaking scale is dynamically determined around 10^{10-12} GeV due to the supersymmetry breaking effects, and the \mu-problem can be solved naturally. Furthermore, in our model, the lightest supersymmetric particle (LSP) is the axino, that is the superpartner of the axion. The overabundance of the LSPs due to decays of modulus/gravitino, which is the most serious cosmological difficulty in the mirage mediation, can be avoided if the axino is sufficiently light. The next-LSPs (NLSPs) produced by the gravitino decay eventually decay into the axino LSPs, yielding the dominant component of the axinos remaining today. It is shown that the axino with the mass of O(100) MeV is naturally realized, which can constitute the dark matter of the Universe, with the free-streaming length of the order of 0.1 Mpc. The saxion, the real scalar component of the axion supermultiplet, can also be cosmologically harmless due to the dilution of the modulus decay. The lifetime of NLSP is relatively long, but much shorter than 1 sec., when the big-bang nucleosynthesis commences. The decay of NLSP would provide intriguing collider signatures.Comment: reference added, typo correcte

Efficient synthesis of biazoles by aerobic oxidative homocoupling of azoles catalyzed by a copper(I)/2-pyridonate catalytic system.

A highly efficient and convenient CuCl/2-pyridonate catalytic system for oxidative homocoupling of azoles affording a biazole product has been developed. With this system, a variety of biazoles have been effectively synthesized in good to excellent yields in the presence of a very small amount of copper catalyst (1.0 mol%). It was feasible to employ air as a green oxidant

Analysis of velocity profiles of blood flow in microchannels using confocal micro-PIV and particle method

The combination of computational and experimental investigations provides an excellent approach to understand complex phenomena involved at a microscopic level. This paper emphasizes a new experimental technique capable to quantify the flow patterns inside microchannels with high spatial and temporal resolution. This technique, known as confocal micro-PIV, consists of a spinning disk confocal microscope, high speed camera and a diodepumped solid state (DPSS) laser. Velocity profiles of physiological fluids were measured within different microchannels. The measured results agree reasonably well with the predicted analytical values. This new PIV system is a very promising technique to confirm the validity of the data obtained by numerical simulations, such as the MPS particle method

Os métodos computacionais em hemodinâmica

Até à última década do século XX, a investigação realizada em hemodinâmica limitava-se, essencialmente, a estudos baseados em métodos experimentais e modelos matemáticos. No entanto, no final do século XX, os avanços tecnológicos na área da computação e o custo mais baixo de aquisição propiciaram uma nova forma de investigar os factores hemodinâmicos em termos fisiológicos e patológicos. Tal como tem acontecido em diversas áreas da ciência, os métodos computacionais constituem um complemento bastante promissor para investigar e analisar uma série de mecanismos fisiológicos e patológicos existentes nos vários órgãos do corpo humano. Este artigo trata, portanto, dos métodos computacionais em hemodinâmica e faz uma breve descrição do processo e da aplicação destes métodos no estudo do escoamento sanguíne

Velocity measurements of physiological flows in microchannels using a confocal micro-PIV system

The detail measurements of velocity profiles of in vitro blood flow in micorchannels are fundamental for a better understanding on the biomechanics of the microcirculation. Despite the high amount of research in microcirculation, there is not yet any detailed experimental information about flow velocity profiles, RBCs deformability and aggregation in microvessels (diameter in the order of 100μm or less). These lack of knowledge is mainly due to the absence of adequate techniques to measure and quantitatively evaluate fluid mechanical effects at a microscopic level [1, 2]. During the years the most research work in this area has focused in experimental studies using techniques such as laser Doppler anemometry (LDA) or conventional particle image velocimetry (PIV). However, due to limitations of those techniques to study effects at a micro-scale level, Meinhart and his colleagues [3] have proposed a measurement technique that combines the PIV system with an inverted epi-fluorescent microscope, which increases the resolution of the conventional PIV systems [3]. More recently, considerable progress in the development of confocal microscopy and consequent advantages of this microscope over the conventional microscopes [4, 5] have led to a new technique known as confocal micro-PIV. This technique combines the conventional PIV system with a spinning disk confocal microscope (SDCM). Due to its outstanding spatial filtering technique together with the multiple point light illumination system, this kind of microscope has the ability to obtain in-focus images with optical thickness less than 1 μm, task extremely difficult to be achieved by using a conventional microscope. As a result, by combining SDCM with the conventional PIV system it is possible to achieve a PIV system with not only extremely high spatial resolution but also with capability to generate 3D velocity profiles. The main purpose of the present study is to evaluate the performance of our confocal micro-PIV system in order to investigate its ability to study the behaviour of non-homogenous fluids such as physiological fluids

Confocal micro-PIV measurements of blood flow in microchannels

The detail measurements of velocity profiles of blood flow in microchannels are fundamental for a better understanding on the biomechanics of the microcirculation. It is therefore very important to obtain measurements with high accuracy and spatial resolution of the influence of the blood cells on the plasma flow behaviour. This paper presents and compares measurements of in vitro blood with different hematocrits within a square microchannel obtained by a confocal particle image velocimetry (PIV) system. This emerging technology by combining the conventional PIV system with a spinning confocal microscope has the ability to obtain not only high spatial resolution images but also three-dimensional (3D) optical sectioning velocity measurements. Velocity measurements of plasma seeded with 1 ~tm diameter fluorescent particles were performed at different locations along the depth of 100 ~tm square microchannel at a constant flow rate (0.15~tl/min) and Reynolds number (Re) of 0.025. By using our confocal micro-PIV system, it was possible to obtain time-series of instantaneous velocity profiles with high spatial resolution of 28.24 18.83 ~tm at time intervals of 5 ms between two images. The ensemble-averaged velocity results of blood flow with different hematocrits (up to 25%) have shown velocity profiles very close to a parabolic shape. However, by analysing the temporal variance of the instantaneous velocity profiles of different hematocrits, we have observed a substantial increase of the instantaneous velocity fluctuations by increasing the hematocrit within the plasma flow. Besides, some possible effects from the measurements accuracy and flow rate instabilities from the syringe pump, this observation also suggests that there is a direct correlation between the level of hematocrit and the temporal instantaneous velocity fluctuations

Confocal micro-PIV measurements of three-dimensional profiles of cell suspension flow in a square microchannel

A detailed measurement of the blood flow velocity profile in microchannels in vitro is fundamental to better understand the biomechanics of microcirculation. Therefore it is very important to determine the influence of suspended blood cells on the flow behaviour with high accuracy and spatial resolution. We measured the flow of blood cells suspended in a physiological fluid within a square microchannel using a confocal particle image velocimetry (PIV) system and compared it to pure water. This emerging technology combines a conventional PIV system with a spinning confocal microscope and has the ability to obtain high-resolution images and three-dimensional (3D) optical section velocity measurements. The good agreement obtained between the measured and estimated results suggests that macroscale flow theory can be used to predict the flow behaviour of a homogeneous fluid within a 100 μm square microchannel. Our results also demonstrated the potential of the confocal system for generating 3D profiles and consequently obtaining detailed information on microscale effects in microchannels using both homogeneous and non-homogeneous fluids, such as a suspension of blood cells. Furthermore, the results obtained from our confocal micro-PIV system show the ability of this system to measure velocities up to 0.52 mm s−1 in a blood cell suspension fluid