Nonlinear Dynamics and Dissipation of a Curvilinear Vortex Driven by a Strong Time-Dependent Meissner Current

We report numerical simulations of large-amplitude oscillations of a trapped vortex line under a strong ac magnetic field H(t)=H sinωt parallel to the surface. The power dissipated by an oscillating vortex segment driven by the surface ac Meissner currents was calculated by taking into account the nonlinear vortex line tension, vortex mass, and a nonlinear Larkin-Ovchinnikov (LO) viscous drag coefficient η(v). We show that the LO decrease of η(v) with the vortex velocity v can radically change the field dependence of the surface resistance Ri(H) caused by trapped vortices. At low frequencies, Ri(H) exhibits a conventional increase with H, but as ω increases, the surface resistance becomes a nonmonotonic function of H which decreases with H at higher fields. The effects of frequency, pin spacing, and the mean-free path li on the field dependence of Ri(H) were calculated. It is shown that, as the surface gets dirtier and li decreases, the anomalous drop of Ri(H) with H shifts to lower fields which can be much smaller than the lower critical magnetic field. Our numerical simulations also show that the LO decrease of η(v) with v can cause a vortex bending instability at high field amplitudes and frequencies, giving rise to the formation of dynamic kinks along the vortex. Measurements of Ri(H) caused by sparse vortices trapped perpendicular to the surface can offer opportunities to investigate an extreme nonlinear dynamics of vortices driven by strong current densities up to the depairing limit at low temperatures. The behavior of Ri(H), which can be tuned by varying the rf frequency or concentration of nonmagnetic impurities, is not masked by strong heating effects characteristic of dc or pulse transport measurements

Estimating rainfall distributions at high temporal resolutions using a multifractal model

International audienceRainfall data from 18 stations in the vicinity of Tokyo city, measured to a precision of 1 mm, were analysed for multifractal properties. A multifractal model based on the scaling properties of temporal distribution of rainfall intensities was formulated to investigate the intensity distribution relationships in the available scaling regime. Although conventional analysis did not provide encouraging results with these measurements, an alternative approach that could be applied to rainfall data of widely variable quality and duration was used to establish a scaling relationship between daily and hourly rainfall intensities. Using a discrete cascade algorithm based on the log-Lèvy generator, synthetic hourly rainfall series were generated from the multifractal statistics of daily-accumulated rainfall. Several properties of rainfall time series that are relevant to the use of rainfall data in surface hydrological studies were used to determine, statistically, the degree of agreement between the synthetic hourly series and observed hourly rainfall. Keywords: rainfall modelling, cascades, multifractal, downscalin

Development of a low cost method for breeding paracheirodon innesi (Neon Tetra) in captivity.

The Tetras are one of the most popular groups of fishes that are kept in modern aquaria. The neon tetra, Paracheirodon innesi, is one of the most popular tetras in the world and they are the second highest fish imported to the U.S both in numbers of individuals and total value, second only to the Guppy, Poecillia reticulate. The production of neon tetra in Sri Lanka is inadequate to fulfill the demand in export market since efforts of aquarists in breeding them has failed in most instances. Commercial breeding is done successfully in other countries but breeding in small scale has also reported not successful. Water pH is recognized as the main factor affecting on neon tetra breeding and artificially acidified fresh water is recommended. Pairs of brood fish have routinely spawned in acidified, soft water at 25 0 C (pH, 5.5—6.5, adjusted with phosphoric acid; total alkalinity, 3.2 mg 1-1 and total hardness, 6.0 mg I-I , as CaC03). Water was also conditioned with humic acids (0.04%). Water acidification is not a cost effective method for Sri Lanka and this study attempted to find an alternative low cost method to breed neon tetra in captivity. Twenty one glass aquarium tanks were settled inside the hatchery and rain water, river water and well water were used separately for the experiment. Temperature and the pH of water in each tank were recorded daily using a pH meter (EcoScan pH 5). Four sides of the tanks were covered with black polythene papers to control the light further. Brooders were introduced to the tanks (pair per tank) and after 24 hours the tanks were observed for the eggs. Brooders were removed from the tanks and 2 ppm methylene blue was added. Fry were started to feed with paramecium culture and fry were transferred to cement tanks after 10 days. Collected data were analyzed with Pearson Chi-Squire Test using Minitab 14 statistical package. The pH of rain water, river water and well water during the period of study were 6.2± 0.05, 8.0±0.04 and 7.5±0.05 respectively. Spawning and hatching were only observed in tanks filled with rain water. After the tetras were transferred to the cement tank, there was a 5% of reduction of the population. The results of the study has shown that the rain water has a significant effect (P<0.05) on the breeding of neon tetra. The reported rearing pH of the neon tetra is 6.9 — 7.4 and the breeding pH of the neon tetra is 5.5 — 6.5. The tropical rain forests in South American countries where neon tetra originated also have low pH level, low light condition and moderate temperature. These findings are directly compatible with the recent findings about the neon tetra breeding. Breeding of neon tetra with rain water is possible in aquarium condition. Use of rain water is a low cost method to breed neon tetra rather than using expensive chemicals

Depression, anxiety and risk of hypertension in mid-aged women::a prospective longitudinal study

The evidence for an association between depression and anxiety and increased hypertension risk is inconsistent. We aimed to investigate the association between each of depression and anxiety and incident hypertension

Superheating Field in Superconductors with Nanostructured Surfaces

We report calculations of a dc superheating field Hsh in superconductors with nanostructured surfaces. Numerical simulations of the Ginzburg-Landau (GL) equations were performed for a superconductor with an inhomogeneous impurity concentration, a thin superconducting layer on top of another superconductor, and superconductor-insulator-superconductor (S-I-S) multilayers.The superheating field was calculated taking into account the instability of the Meissner state with a nonzero wavelength along the surface, which is essential for realistic values of the GL parameter κ. Simulations were done for the materials parameters of Nb and Nb3Sn at different values of κ and the mean free paths. We show that the impurity concentration profile at the surface and thicknesses of S-I-S multilayers can be optimized to enhance Hsh above the bulk superheating fields of both Nb and Nb3Sn. For example, a S-I-S structure with 90 nm thick Nb3Sn layer on Nb can boost the superheating field up to ≈ 500 mT, while protecting the SRF cavity from dendritic thermomagnetic avalanches caused by local penetration of vortices

Staged cost optimization of urban storm drainage systems based on hydraulic performance in a changing environment

International audienceUrban flooding causes large economic losses, property damage and loss of lives. The impact of environmental changes mainly, the urbanization and the climatic change leads to increased runoff and increased peak flows which the drainage system must be able to cope with to overcome possible damage and inconveniences caused by the induced flooding. Allowing for detention storage to compliment the capacity of the drainage system network is one of the approaches to reduce urban floods. The traditional practice was to design systems against stationary environmental forcings ? including design rainfall, landuse, etc. Due to the rapid change in climate-environment, this approach is no longer economically viable and safe, and explicit consideration of changes that gradually take place during the life-time of the drainage system is warranted. In this paper, a staged cost optimization tool based on the hydraulic performance of the drainage system is presented. A one dimensional hydraulic model is used for hydraulic evaluation of the network together with a genetic algorithm based optimization tool to determine optimal intervention timings and amounts throughout the lifespan of the drainage network. The model was applied in a case study area in the city of Porto Alegre, Brazil. It was concluded that considerable financial savings and/or additional level of flood-safety can be achieved by approaching the design problem as a staged plan rather than one-off scheme

Nonlinear Dynamics and Dissipation of a Curvilinear Vortex Driven by a Strong Time-Dependent Meissner Current

We report numerical simulations of large-amplitude oscillations of a trapped vortex line under a strong ac magnetic field $H(t)=H\sin\omega t$ parallel to the surface. The power dissipated by an oscillating vortex segment driven by the surface ac Meissner currents was calculated by taking into account the nonlinear vortex line tension, vortex mass and a nonlinear Larkin-Ovchinnikov (LO) viscous drag coefficient $\eta(v)$. We show that the LO decrease of $\eta(v)$ with the vortex velocity $v$ can radically change the field dependence of the surface resistance $R_i(H)$ caused by trapped vortices. At low frequencies $R_i(H)$ exhibits a conventional increases with $H$, but as $\omega$ increases, the surface resistance becomes a nonmonotonic function of $H$ which decreases with $H$ at higher fields. The effects of frequency, pin spacing and the mean free path $l_i$ on the field dependence of $R_{i}(H)$ were calculated. It is shown that, as the surface gets dirtier and $l_i$ decreases, the anomalous drop of $R_{i}(H)$ with $H$ shifts to lower fields which can be much smaller than the lower critical magnetic field. Our numerical simulations also show that the LO decrease of $\eta(v)$ with $v$ can cause a vortex bending instability at high field amplitudes and frequencies, giving rise to the formation of dynamic kinks along the vortex. Measurements of $R_i(H)$ caused by sparse vortices trapped perpendicular to the surface can offer opportunities to investigate an extreme nonlinear dynamics of vortices driven by strong current densities up to the depairing limit at low temperatures. The behavior of $R_i(H)$ which can be tuned by varying the rf frequency or concentration of nonmagnetic impurities is not masked by strong heating effects characteristic of dc or pulse transport measurements

Chip-on-board assembly of 800V Si LIGBTs for high performance ultra-compact LED drivers

This paper presents a novel chip on board assembly design for an integrated power switch, based on high power density 800V silicon lateral insulated gate bipolar transistor (Si LIGBT) technology. LIGBTs offer much higher current densities (5-10X), significantly lower leakage currents, lower parasitic device capacitances and gate charge compared to conventional vertical MOSFETs commonly used in LED drivers. The higher voltage ratings offered (up to 1kV), the development of high voltage interconnection between parallel IGBTs, self-isolated nature and absence of termination region unlike in a vertical MOSFET makes these devices ideal for ultra-compact, low bill of materials (BOM) count LED drives. Chip on board LIGBTs also offer significant advantages over MOSFETs due to high temperatures seen on most of the LED lamp enclosures as the LIGBT's on-state losses increase only marginally with temperature. the design is based on a built-in reliability approach which focuses on a compact LED driver as a case study of a cost sensitive large volume production item