Time-of-Flight Measurements of Vortices Emitted from Quantum Turbulence in Superfluid 4He

An oscillating obstacle generates quantum turbulence in superfluids, when vortices remained attached to obstacle surfaces or vortex rings collided with it during oscillation. Turbulence provides a source of vortices; however, the characteristics of these vortices are not clear. In the present work, we report the flight of vortices emitted from quantum turbulence in superfluid ⁴He at low temperatures, using vibrating wires as a generator and a detector of vortices. A vortex-free vibrating wire can detect only the first colliding vortex ring, though it will be refreshed after low vibration and be able to detect a vortex ring again. By measuring a period from the start of turbulence generation to the vortex detection repeatedly, we find an exponential distribution of time-of-flights with a non-detection period t ₀ and a mean detection period t ₁, suggesting a Poisson process. Both periods t ₀ and t ₁ increase with increasing distance between a generator and a detector. A vortex flight velocity estimated from period t ₀ suggests that the sizes of the emitted vortex rings distribute to a range smaller than a generator thickness or a generator vibration amplitude. Vortices are emitted radially from a turbulence region, at least in the direction of oscillator vibration.     

Wettability Improvement by Plasma Irradiation and Its Applications to Phase-Change Phenomena

Plasma irradiation is one of the techniques to improve surface wettability. This technique can be used to enhance heat transfer of liquid–vapor phase change. For instance, evaporation of a water droplet can be enhanced by plasma irradiation. The relation between plasma irradiation time and contact angle was examined first for three metals and then the lifetime of a water drop on a hot surface was measured changing the surface wettability by plasma irradiation. The lifetime of the water drop decreased and the wetting limit temperature increased with the increasing irradiation time of plasma. Hydrophilicity by plasma irradiation is not a permanent effect but it will be useful for enhancement of cooling of hot metal.     

NUMERICAL SIMULATION OF NATURAL CONVECTION WITH DENSITY INVERSION IN A SQUARE CAVITY

Water has its density maximum at 4^oC, and natural convection around the temperature is complicated. In this study, natural convection with density inversion in a two-dimensional vertical square cavity is investigated numerically. To express the average Nusselt number nondimensionally, some parameters are chosen by observing the calculated flow-temperature fields. Then a simple expression of heat transfer correlation as a function of Galilei number, wall temperature ratio, and density function is proposed. The present correlation has a deviation of about 10%.     

Development of a Particle Interaction Kernel for Convection-Diffusion Scalar Transport Equation

In this study we derive a mathematically rigorous kernel function, which accounts for the interaction among particles, within the framework of the particle method, to predict a computationally more accurate solution for the convection-diffusion equation investigated at low as well as high Peclet numbers. Determination of the functional dependence of the kernel function on the distance vector between the particles is therefore a key to the success of the interaction model. The smoothed quantity for a scalar or for a vector at a particle location is mathematically identical to its collocated value provided that the kernel function is chosen as the delta function. Such a kernel is unfortunately not computable in a discrete context. Our guideline for developing the modified kernel function is therefore to make it closer to the delta function as much as possible in cases when diffusion dominates convection. To achieve this goal, we enforce five constraint conditions in a derivation of the kernel function for the pure diffusion equation. In addition, this kernel function has no effect on the particles outside of the disk, which has the user's specified radius r _e . To mimic the delta function we demand that the developed kernel function at r = r _e should smoothly approach zero. It is also desired to acquire the largest possible value for the kernel function near r = 0. As flow convection prevailingly dominates its diffusion counterpart, particle interaction at the upstream side should be more favorably taken into account to avoid numerical oscillations due to convective instability. We present in this study a two-dimensional upwind kernel function to enhance numerical stability along the flow direction. The proposed upwind kernel function can render an exact solution for the investigated convection-diffusion equation in the limiting one-dimensional case. The proposed particle interaction model featuring the newly developed kernel function is validated through several problems that are amenable to analytical solutions or have available benchmark solutions. Analysis of the stability condition and spatial accuracy order of the proposed particle interaction model are also provided in details.     

Development of ocean dispersion concentration maps of the contaminated water released from the Fukushima Dai-ichi Nuclear Power Plant

Ocean dispersion concentration maps were developed to gain an understanding of the migration behavior of contaminated water leaking from the Fukushima Dai-ichi Nuclear Power Plant. We used ensemble mean values to define the semi-climatological seasonal field in our calculations of the trajectories of the contaminated water. The maps were validated by conducting actual release events in two different seasons. The results showed that despite their simplicity, the proposed methods yield relatively good results.     

Extended cross-section adjustment method to improve the prediction accuracy of core parameters

An extended cross-section adjustment method has been developed to improve the prediction accuracy of target core parameters. The present method is on the basis of a cross-section adjustment method which minimizes the uncertainties of target core parameters under the conditions that integral experimental data are given. The present method enables us to enhance the prediction accuracy better than the conventional cross-section adjustment method by taking into account the target core parameters, as well as the extended bias factor method. In addition, it is proved that the present method is equivalent to the extended bias factor method when only one target core parameter is taken into account. The present method is implemented in an existing cross-section adjustment solver. Numerical calculations verify the derived formulation and demonstrate an applicability of an adjusted cross-section set which is specialized for the target core parameters.     

Antihypertensive Activities of Peptides Derived from Porcine Skeletal Muscle Myosin in Spontaneously Hypertensive Rats

ABSTRACT: Antihypertensive activities derived from porcine skeletal muscle proteins were investigated. Thermolysin hydrolysates of porcine muscle water-insoluble proteins demonstrated antihypertensive activities in spontaneously hypertensive rats when administrated in single oral doses. Hydrolysates of porcine myosin and peptides (Met-Asn-Pro-Pro-Lys, Ile-Thr-Thr-Asn-Pro, Met-Asn-Pro, Pro-Pro-Lys) with parts of the sequence of myosin showed antihypertensive activities. This is the first report of antihypertensive activities of peptides derived from muscle proteins of domestic animals. The hydrolysates of porcine muscle protein and their corresponding bioactive peptides might be utilized for physiologically functional foods.     

Alignment of 3-D optical coherence tomography scans to correct eye movement using a particle filtering

Eye movement artifacts occurring during 3-D optical coherence tomography (OCT) scanning is a well-recognized problem that may adversely affect image analysis and interpretation. A particle filtering algorithm is presented in this paper to correct motion in a 3-D dataset by considering eye movement as a target tracking problem in a dynamic system. The proposed particle filtering algorithm is an independent 3-D alignment approach, which does not rely on any reference image. 3-D OCT data is considered as a dynamic system, while the location of each A-scan is represented by the state space. A particle set is used to approximate the probability density of the state in the dynamic system. The state of the system is updated frame by frame to detect A-scan movement. The proposed method was applied on both simulated data for objective evaluation and experimental data for subjective evaluation. The sensitivity and specificity of the x-movement detection were 98.85% and 99.43%, respectively, in the simulated data. For the experimental data (74 3-D OCT images), all the images were improved after z-alignment, while 81.1% images were improved after x-alignment. The proposed algorithm is an efficient way to align 3-D OCT volume data and correct the eye movement without using references.     

Effect of stress transfer between fiber and matrix on toughness of polymer composite

Thanks to their lightweight properties, formability and low cost, polymers have become an essential material for manufactured products. To improve the mechanical properties, almost all polymers are blended with some kind of fiber made from glass, carbon, organic or natural material. The importance of interfacial strength between matrix and fiber is a well known requirement for effective mechanical properties and some experimental results indicate that low interfacial strength helps increase the toughness of composites. In this paper, models of composite reinforced by fiber aligned with maximum principal stress under uni‐tensile loading are simulated. Based on the simulation result, we discuss the effect of interfacial strength, aspect ratio of fiber and friction force between matrix and fiber on stable deformation and provide the guidelines for establishing composites with high modulus and toughness. POLYM. COMPOS. 2011. © 2011 Society of Plastics Engineers