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The Taylor–Melcher (TM) model is the standard model for describing the dynamics of poorly conducting leaky dielectric fluids under an electric field. The TM model treats the fluids as ohmic conductors, without modelling the underlying ion dynamics. On the other hand, electrodiffusion models, which have been successful in describing electrokinetic phenomena, incorporate ionic concentration dynamics. Mathematical reconciliation of the electrodiffusion picture and the TM model has been a major issue for electrohydrodynamic theory. Here, we derive the TM model from an electrodiffusion model in which we explicitly model the electrochemistry of ion dissociation. We introduce salt dissociation reaction terms in the bulk electrodiffusion equations and take the limit in which the salt dissociation is weak; the assumption of weak dissociation corresponds to the fact that the TM model describes poor conductors. Together with the assumption that the Debye length is small, we derive the TM model with or without the surface charge convection term depending upon the scaling of relevant dimensionless parameters. An important quantity that emerges is the Galvani potential (GP), the jump in voltage across the liquid–liquid interface between the two leaky dielectric media; the GP arises as a natural consequence of the interfacial boundary conditions for the ionic concentrations, and is absent under certain parametric conditions. When the GP is absent, we recover the TM model. Our analysis also reveals the structure of the Debye layer at the liquid–liquid interface, which suggests how interfacial singularities may arise under strong imposed electric fields. In the presence of a non-zero GP, our model predicts that the liquid droplet will drift under an imposed electric field, the velocity of which is computed explicitly to leading order.
It has not been well established whether dietary folate intake reduces the risk of diabetes development. We aimed to clarify the prospective association between dietary folate intake and type 2 diabetes (T2D) risk among 7333 Korean adults aged 40 years or older who were included in the Multi-Rural Communities Cohort. Dietary folate intake was estimated from all 106 food items listed on a FFQ, not including folate intake from supplements. Two different measurements of dietary folate intake were used: the baseline consumption and the average consumption from baseline until just before the end of follow-up. The association between folate intake and T2D risk was determined through a modified Poisson regression model with a robust error estimator controlling for potential confounders. For 29 745 person years, 319 cases of diabetes were ascertained. In multivariable analyses, dietary folate intake was inversely associated with risk of T2D for women, not for men. For women, the incidence rate ratio of diabetes in the third tertile compared with the first tertile was 0·57 (95 % CI 0·38–0·87, Pfor trend=0·0085) in the baseline consumption model and 0·64 (95 % CI 0·43–0·95, Pfor trend=0·0244) in the average consumption model. These inverse associations was found in both normal fasting blood glucose group and impaired fasting glucose group among women. Among non-users of multinutrients and vitamin supplements, the significant inverse association remained. Thus, higher dietary intake of folate is prospectively associated with lower risk of diabetes for women.
We have examined the global properties of 250 galaxies and galaxy pairs observed as part of the Five College Radio Astronomy Observatory (FCRAO) Extragalactic CO Survey with respect to bar type and arm type, and we have compared the results with the global properties of the same galaxies as a function of morphological type. The bar types of the galaxies were taken from RC2, and the arm types for 48% of the sample were taken from Elmegreen and Elmegreen (1987). We find the following:
1) There is little dependence of the star formation efficiency, as measured by the global FIR luminosity to molecular gas mass ratio, on bar type. Similarly, we find no obvious correlation between the global ratio of molecular to atomic gas mass and the bar type.
2) Variations of up to a factor of 6 are seen in the mean star formation efficiency with arm type, where flocculent galaxies appear to have slightly higher global star formation efficiencies than spirals with clearly delineated arms. Variations in the mean molecular to atomic gas mass ratio of a factor of 5 are seen as a function of arm type, but there is no apparent trend from flocculent to grand design spirals.
3) The decrease of a factor of 20 in the molecular to atomic gas mass ratio observed as a function of morphological type (Young and Knezek 1989) is more pronounced than the same ratio as a function of bar or arm type.
To assess iodine status among pregnant women in rural Zinder, Niger and to compare their status with the iodine status of school-aged children from the same households.
Seventy-three villages in the catchment area of sixteen health centres were randomly selected to participate in the cross-sectional survey.
Salt iodization is mandatory in Niger, requiring 20–60 ppm iodine at the retail level.
A spot urine sample was collected from randomly selected pregnant women (n 662) and one school-aged child from the same household (n 373). Urinary iodine concentration (UIC) was assessed as an indicator of iodine status in both groups. Dried blood spots (DBS) were collected from venous blood samples of pregnant women and thyroglobulin (Tg), thyroid-stimulating hormone and total thyroxine were measured. Iodine content of household salt samples (n 108) was assessed by titration.
Median iodine content of salt samples was 5·5 ppm (range 0–41 ppm), 98 % had an iodine content <20 ppm. Median (interquartile range) UIC of pregnant women and school-aged children was 69·0 (38·1–114·3) and 100·9 (61·2–163·2) µg/l, respectively. Although nearly all pregnant women were euthyroid, their median (interquartile range) DBS-Tg was 34·6 (23·9–49·7) µg/l and 38·4 % had DBS-Tg>40 µg/l.
In this region of Niger, most salt is inadequately iodized. UIC in pregnant women indicated iodine deficiency, whereas UIC of school-aged children indicated marginally adequate iodine status. Thus, estimating population iodine status based solely on monitoring of UIC among school-aged children may underestimate the risk of iodine deficiency in pregnant women.
This paper briefly describes the principle of operation and science goals of the AMANDA high energy neutrino telescope located at the South Pole, Antarctica. Results from an earlier phase of the telescope, called AMANDA-BIO, demonstrate both reliable operation and the broad astrophysical reach of this device, which includes searches for a variety of sources of ultrahigh energy neutrinos: generic point sources, Gamma-Ray Bursts and diffuse sources. The predicted sensitivity and angular resolution of the telescope were confirmed by studies of atmospheric muon and neutrino backgrounds. We also report on the status of the analysis from AMANDA-II, a larger version with far greater capabilities. At this stage of analysis, details of the ice properties and other systematic uncertainties of the AMANDA-II telescope are under study, but we have made progress toward critical science objectives. In particular, we present the first preliminary flux limits from AMANDA-II on the search for continuous emission from astrophysical point sources, and report on the search for correlated neutrino emission from Gamma Ray Bursts detected by BATSE before decommissioning in May 2000. During the next two years, we expect to exploit the full potential of AMANDA-II with the installation of a new data acquisition system that records full waveforms from the in-ice optical sensors.
The ‘holographic’ technique for accurately measuring the surface figure of large reflector antennas, described by Bennet et al, (1976) and Scott and Ryle (1977), has many advantages over older conventional survey methods. These include high speed, low cost, and the absence of any need for additional complex mechanical or optical survey devices. In essence, the technique consists of measuring the complex far-field response of the antenna at a single frequency using a terrestrial, satellite-borne or celestial radiation source of small angular diameter. This two-dimensional pattern is then Fourier-transformed to yield the complex illumination function across the antenna aperture. Antenna surface deviations are manifested as phase fluctuations in this function. In practice, a second antenna is needed to provide a phase reference.
The room temperature electronic characteristics of resonant tunneling diodes (RTDs) containing AlAs/InGaAs quantum wells are studied. Differences in the peak current and voltages, associated with device-to-device variations in the structure and width of the quantum well are analyzed. A method to use these differences between devices is introduced and shown to uniquely identify each of the individual devices under test. This investigation shows that quantum confinement in RTDs allows them to operate as physical unclonable functions.
In recent years, color-magnitude diagrams have revealed that nearby dwarf galaxies have a fascinating variety of star formation histories. The fact that the dwarfs have periods of star formation activity and inactivity raises several questions. How do the properties of the interstellar medium (ISM) in a galaxy affect its star formation rate? Are the interstellar media of dwarf galaxies similar to those in spirals? And what can we learn about dwarf galaxies’ evolution from their gas contents?
A numerical scheme based on the immersed interface method (IIM) is developed to simulate the dynamics of an axisymmetric viscous drop under an electric field. In this work, the IIM is used to solve both the fluid velocity field and the electric potential field. Detailed numerical studies on the numerical scheme show a second-order convergence. Moreover, our numerical scheme is validated by the good agreement with previous analytical models, and numerical results from the boundary integral simulations. Our method can be extended to Navier-Stokes fluid flow with nonlinear inertia effects.
The evolution of asymmetric leeward-side flow structures around a moving sphere in the viscous flow is investigated. Simulations are carried out to investigate the variations of vortex-ring system at the moderate Reynolds number. A parallel laboratory experiment is undertaken in this study. The sphere travels a certain distance at constant speed and then stops to collide with a wall. The motion of moving sphere in fluid is described by the hybrid Cartesian immersed boundary method. Drag forces behind the moving sphere are extremely substantial as the solid body falls through viscous fluid for comprehending the formation of wake flow. The dynamic behavior consists of growth and breakup of the vortices which depend on two specific moderate Reynolds numbers. The onset of physical instability in the wake is obviously affected at the Reynolds number of 800. The generated vortex-ring system rolls upward to compact the primary vortex ring and interact with the secondary vortex. An asymmetric generation of the pairs of vortices is developed since the physical instability effect leads to shed in the wake with the increasing Reynolds number. The results from numerical simulations are also conducted to exhibit good comparison with those from the laboratory experiment.
Understanding, predicting and eventually improving the resistance to fracture of silicate materials is of primary importance to design new glasses that would be tougher, while retaining their transparency. However, the atomic mechanism of the fracture in amorphous silicate materials is still a topic of debate. In particular, there is some controversy about the existence of ductility at the nano-scale during the crack propagation. Here, we present simulations of the fracture of three archetypical silicate glasses using molecular dynamics. We show that the methodology that is used provide realistic values of fracture energy and toughness. In addition, the simulations clearly suggest that silicate glasses can show different degrees of ductility, depending on their composition.
In this paper the dynamics of an inextensible capacitive elastic membrane under an electric field is investigated in the long-wave (lubrication) leaky dielectric framework, where a sixth-order nonlinear differential equation with an integral constraint is derived. Steady equilibrium profiles for a non-conducting membrane in a direct current (DC) field are found to depend only on the membrane excess area and the volume under the membrane. Linear stability analysis on a tensionless flat membrane in a DC field gives the growth rate in terms of membrane conductance and electric properties in the bulk. Numerical simulations of a capacitive conducting membrane under an alternating current (AC) field elucidate how variation of the membrane tension correlates with the nonlinear membrane dynamics. Different membrane dynamics, such as undulation and flip-flop, are found at different electric field strength and membrane area. In particular a travelling wave on the membrane is found as a response to a periodic AC field in the perpendicular direction.
We investigated the structural evolution of the Ni/Au contact on GaN(000l) during annealing in N2, using in-situ x-ray diffraction, anomalous x-ray scattering, and high resolution electron microscopy. GaN decomposition occurred mostly along GaN dislocations at temperature higher than 500°C. The decomposed Ga diffused into Au and Ni substitutional positions, and the decomposed nitrogen reacted with Ni, forming Ni4N. Interestingly, Ni4N was grown epitaxially. The epitaxial relationship of the Ni4N, Au, and Ni was identified as M(111)//GaN(0002) and M[1 −1 0]//GaN[1 1 −2 0] (M= Ni4N, Au, and Ni). At dislocation free regions, however, the atomically smooth interface remained intact up to 700 °C. Remarkable improvement of device reliability is expected in the contact on dislocation free regions compared with the contact on dislocations.
Certification initiatives are product-focused, rely on standards and use sustainability
metrics to inform end-users on the provenance of commodities. In the metals sector, the
phenomenon of formal certification programs has recently gained traction. Four initiatives
are reviewed to illustrate the status and prospects of metal certification. The prime case
is the Conflict Free Smelter Program operated by the global electronics industry. This
scheme has developed and applied standards on mineral chain-of-custody, including use of
third-parties to audit smelters and refineries all over the world. Additional programs
discussed are the Green Lead Project, Fair Trade and Fair Mined gold, and the Responsible
Jewellery Council. Collectively these initiatives address a variety of sustainability
criteria, including social, economic and environmental dimensions, but focus only on
precious and specialty metals (Au, platinum group, Pb, Sn, Ta and W). Metals
certifications programs are building capacity and infrastructure compared to mature
programs in agriculture and other commodity sectors. Opportunities and issues for growth
of metals certification are considered.