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We use particle-resolved direct numerical simulation (PR-DNS) as a model-free physics-based numerical approach to validate particle acceleration modelling in gas-solid suspensions. To isolate the effect of the particle acceleration model, we focus on point-particle direct numerical simulation (PP-DNS) of a collision-free dilute suspension with solid-phase volume fraction
in a decaying isotropic turbulent particle-laden flow. The particle diameter
in the suspension is chosen to be the same as the initial Kolmogorov length scale
) in order to overlap with the regime where PP-DNS is valid. We assess the point-particle acceleration model for two different particle Stokes numbers,
and 100. For the high Stokes number case, the Stokes drag model for particle acceleration under-predicts the true particle acceleration. In addition, second moment quantities which play key roles in the physical evolution of the gas–solid suspension are not correctly captured. Considering finite Reynolds number corrections to the acceleration model improves the prediction of the particle acceleration probability density function and second moment statistics of the point-particle model compared with the particle-resolved simulation. We also find that accounting for the undisturbed fluid velocity in the acceleration model can be of greater importance than using the most appropriate acceleration model for a given physical problem.
The linear stability of three-dimensional vortices in rotating, stratified flows has been studied by analysing the non-hydrostatic inviscid Boussinesq equations. We have focused on a widely used model of geophysical and astrophysical vortices, which assumes an axisymmetric Gaussian structure for pressure anomalies in the horizontal and vertical directions. For a range of Rossby numbers (
) and Burger numbers (
) relevant to observed long-lived vortices, the growth rate and spatial structure of the most unstable eigenmodes have been numerically calculated and presented as a function of
. We have found neutrally stable vortices only over a small region of the
parameter space: cyclones with
. However, we have also found that anticyclones in general have slower growth rates compared to cyclones. In particular, the growth rate of the most unstable eigenmode for anticyclones in a large region of the parameter space (e.g.
$0.5\lesssim Bu\lesssim 1.3$
) is slower than 50 turnaround times of the vortex (which often corresponds to several years for ocean eddies). For cyclones, the region with such slow growth rates is confined to
$0.5\lesssim Bu\lesssim 1.3$
. While most calculations have been done for
are the Coriolis and background Brunt–Väisälä frequencies), we have numerically verified and explained analytically, using non-dimensionalized equations, the insensitivity of the results to reducing
to the more ocean-relevant value of 0.01. The results of our stability analysis of Gaussian vortices both support and contradict the findings of earlier studies with QG or multilayer models or with other families of vortices. The results of this paper provide a stepping stone to study the more complicated problems of the stability of geophysical (e.g. those in the atmospheres of giant planets) and astrophysical vortices (in accretion disks).
Bats are known to be reservoirs of several medically important viruses including lyssaviruses. However, no systematic surveillance for bat rabies has been carried out in India, a canine rabies endemic country with a high burden of human rabies. Surveillance for rabies virus (RABV) infection in bats was therefore carried out in Nagaland, a north-eastern state in India at sites with intense human–bat interfaces during traditional bat harvests. Brain tissues and sera from bats were tested for evidence of infection due to RABV. Brain tissues were subjected to the fluorescent antibody test for detection of viral antigen and real-time reverse transcriptase PCR for presence of viral RNA. Bat sera were tested for the presence of rabies neutralizing antibodies by the rapid fluorescent focus inhibition test. None of the bat brains tested (n = 164) were positive for viral antigen or viral RNA. However, rabies neutralizing antibodies were detected in 4/78 (5·1%) bat sera tested, suggesting prior exposure to RABV or related lyssaviruses. The serological evidence of lyssaviral infection in Indian bats may have important implications in disease transmission and rabies control measures, and warrant extensive bat surveillance to better define the prevalence of lyssaviral infection in bats.
Routine high-dose Fe supplementation in non-anaemic pregnant women may induce oxidative stress and eventually affect birth outcomes. The aim of the present study was to measure oxidative stress markers in pregnant women with low/normal and high Hb values in trimester 1 (Hb1) and to relate these to birth weight.
A cross-sectional study where selected oxidative stress markers were analysed in both maternal (trimester 1; T1) and cord blood samples and correlated with birth weight.
A tertiary hospital in urban South India.
One hundred women were chosen based on their Hb1 values (forty women with low/normal Hb1 (<110 g/l) and sixty women with high Hb1 (≥120 g/l)).
In T1, women with high Hb1 values were found to have lower paraoxonase-1 (PON-1) activity (424·7 (sd 163·7) v. 532·9 (sd 144·7) pmol p-nitrophenol formed/min per ml plasma, P=0·002) and higher lipid peroxides compared with women with low/normal Hb1. Routine supplementation of Fe to these women resulted in persistent lower PON-1 activity in cord blood (P=0·02) and directionally lower (P=0·142) birth weights. Furthermore, women with high Hb1 who delivered low-birth-weight babies were observed to have lowest PON-1 activity in T1. No changes were observed in other markers (myeloperoxidase activity and total antioxidant levels).
Routine Fe supplementation in pregnant women with high Hb1 associated with increased oxidative stress, as reflected by low PON-1 activity in T1, could potentially lead to deleterious effects on birth weight.
Surgery is currently the only curative treatment for medullary thyroid cancer. Unfortunately, the surgical strategy that will offer patients at each disease stage the best chance of a biochemical cure remains unclear. The American Thyroid Association and British Thyroid Association guidelines offer different strategies.
A retrospective analysis of the surgical management of 47 patients with medullary thyroid cancer diagnosed between 1994 and 2013 was performed. Surgical management was compared with current American Thyroid Association and British Thyroid Association guidelines. Outcome was defined as the first post-operative calcitonin measurement.
All patients with stage I–III disease achieved a post-operative biochemical cure regardless of the guidelines followed. The overall biochemical cure rate for patients with stage IVa disease was significantly reduced to 10 per cent (p < 0.01), but the biochemical cure rate for stage IVa disease patients who underwent bilateral lateral lymph node dissection was 33.3 per cent.
The conservative, surveillance-driven approach recommended by the American Thyroid Association is appropriate for stage I–III disease. However, the more aggressive approach advocated by the British Thyroid Association might provide stage IVa disease patients a greater chance of achieving a biochemical cure.
Fe-50 wt% Co alloy powders with average particle size of 10 μm were compacted by spark plasma sintering (SPS) at 700, 800, 900 and 950oC by applying 40, 80, 100 MPa uniaxial pressures for 2, 5, 10 minutes. The densities of the samples were found to increase with temperature from 700 to 900oC for constant sintering pressure and time and to decrease for the material sintered at 950oC. The effects of sintering time on density were more significant in samples sintered at 700oC and 800oC than those densified at 900oC. The consequences of small increases in mechanical pressure during sintering on density values were significant for samples sintered at 700oC. The coercivity (Hc) of the compacts decreased significantly with increasing sintering temperature, and with increasing dwell time at sintering temperatures lower than 700oC. The sample sintered at 950oC, which contains the largest grains among the prepared samples and porous microstructure, exhibited the minimum coercivity. Unlike Hc, the remanence (Br) and saturation induction (Bsat) values were more strongly affected by the specimen density than by grain size. Br and Bsat values were found to vary linearly with sintering temperature and pressure owing to increasing density. An increase in soaking time at 800 and 900 oC, although enabling higher density, exhibited contradicting effects on Bsat values. The SPS parameters to obtain maximum density and optimum magnetic properties for Fe-50% Co alloy were found to be 900oC, 80 MPa and 2-5 minutes.
We investigated the plasmon characteristics on luminescent porous silicon using electron energy loss spectroscopy. The samples were prepared from p-type crystalline silicon, (100) face, using the conventional electrochemical etching technique with the usual solution of HF, ethanol and water, followed by a critical point drying process. The energy of the bulk plasmon was measured both before and after sputter cleaning the sample with argon-ion bombardment. We found that initially the plasmon energy was slightly higher, ∼18 eV, than the plasmon energy of crystalline silicon. After sputter cleaning the sample with 5 keV Ar+ ions, the plasmon energy increased to ∼20 eV. Exposure to the electron beam used for the measurements caused a slow upward shift of the plasmon energy as a function of time, toward a saturation energy of 22-23 eV, an energy close to the plasmon energy of SiC. Auger spectroscopy performed in parallel showed an increasing carbon coverage. We prepared also samples without ethanol in the etching solution and/or with no critical point drying. Samples that did not undergo the critical point drying process showed consistently a practically constant plasmon energy, with almost no change upon sputtering and/or exposure to the electron beam. On the other hand, samples that were prepared with or without ethanol but using the critical point drying process, showed an appreciable increase in the plasmon energy upon exposure to the electron beam.
We conclude that traces of CO2, used in the critical point drying process, are stored in the pores of the porous silicon surface and serve as a source of carbon. Apparently, upon activation by argon bombardment or by the electron beam, the carbon interacts with the porous Si surface forming a carbon-silicon compound, most probably SiC.
The present cross-sectional study was conducted to determine the vitamin D status of pregnant Indian women and their breast-fed infants. Subjects were recruited from the Department of Obstetrics, Armed Forces Clinic and Army Hospital (Research and Referral), Delhi. A total of 541 apparently healthy women with uncomplicated, single, intra-uterine gestation reporting in any trimester were consecutively recruited. Of these 541 women, 299 (first trimester, ninety-seven; second trimester, 125; third trimester, seventy-seven) were recruited in summer (April–October) and 242 (first trimester, fifty-nine, second trimester, ninety-three; third trimester, ninety) were recruited in winter (November–March) to study seasonal variations in vitamin D status. Clinical, dietary, biochemical and hormonal evaluations for the Ca–vitamin D–parathormone axis were performed. A subset of 342 mother–infant pairs was re-evaluated 6 weeks postpartum. Mean serum 25-hydroxyvitamin D (25(OH)D) of pregnant women was 23·2 (sd 12·2) nmol/l. Hypovitaminosis D (25(OH)D < 50 nmol/l) was observed in 96·3 % of the subjects. Serum 25(OH)D levels were significantly lower in winter in the second and third trimesters, while serum intact parathormone (iPTH) and alkaline phosphatase levels were significantly higher in winter in all three trimesters. A significant negative correlation was found between serum 25(OH)D and iPTH in mothers (r − 0·367, P = 0·0001) and infants (r − 0·56, P = 0·0001). A strong positive correlation was observed between 25(OH)D levels of mother–infant pairs (r 0·779, P = 0·0001). A high prevalence of hypovitaminosis D was observed in pregnancy, lactation and infancy with no significant inter-trimester differences in serum 25(OH)D levels.
The VO2 phase of vanadium oxide is known to exhibit large changes in the electrical and optical properties in the vicinity of the structural phase transition at 68C. Here, we report on the fabrication and study of thin film vanadium oxide (VO2) devices deposited on R-plane sapphire. Thin films prepared by electron beam evaporation have been processed by photolithography into two-terminal strips for electrical measurements. Measurements on such specimens exhibit reproducibility across a chip, in addition to hysteretic transport, and a one-to-two orders of magnitude change in the resistance in the vicinity of the structural transition. In sum, these experiments show that e-beam evaporation of VO2 constitutes a simple and useful approach to realizing devices from this technologically important material.
Pulse measurements on the porous-Si/electrolyte system are employed to determine the surface effective area and the surface-state density at various stages of the anodization process used to produce the porous material. Such measurements were combined with studies of the luminescence spectra and scanning tunneling microscopy (STM). Both the effective area and the luminescence intensity are found to increase with anodization time, reaching maximum values for the same anodization time (1–2 minutes). In most cases, they decrease monotonically with further anodization. The surface state density, on the other hand, decreases with anodization time from the initial value of ∼1012 cm−2 for the virgin surface, down to ∼1011 cm−2 at the common anodization time for which both the effective area and the luminescence intensity are peaked. The surface-state density increases upon further anodization, reaching a value of at least 1013 cm−2 after ∼10 minutes of anodization. Apart from its intensity, the luminescence spectrum is essentially independent of anodization time. The common peak of the spectra is at about 700 nm. The STM measurements reveal a pronounced surface roughness. Preliminary results indicate that for 1 - 2 minute anodization (maximum effective area), the roughness scale is of the order of 1 -2 nm. After 10-minutes anodization, on the other hand, the roughness microstructure becomes finer (roughness scale of only 0.5 - 0.7 nm). These findings indicate that the various characteristics studied are closely interrelated. Such information may help in understanding the luminescence mechanism, but further work is required in order to interpret more fully the results presented.
Pulse measurements on the porous-Si/electrolyte system are employed to determine the surface effective area and the surface-state density at various stages of the anodization process used to produce the porous material. Such measurements were combined with studies of the photoluminescence spectra. These spectra were found to shift progressively to the blue as a function of anodization time. The luminescence intensity increases initially with anodization time, reaches a maximum and then decreases with further anodization. The surface state density, on the other hand, increases with anodization time from an initial value of ∼2×1012 cm−2 for the virgin surface to ∼1013 cm−2 for the anodized surface. This value is attained already after ∼2 min anodization and upon further anodization remains fairly constant. In parallel, the effective surface area increases by a factor of 10–30. This behavior is markedly different from the one observed previously for n-type porous Si.
The progress that has been made in SiC diodes and GTOs is reviewed. A 100 A/1000 V SiC pi- n diode package, the highest current rating reported for any SiC device, a 69 A conduction/ 11 A turn-off of a SiC GTO and MTOTM, as well as the first all-SiC, 3 phase Pulse Width Modulated (PWM) inverter are reported, herein, for the first time. The inverter achieves voltage controlled turn off with a high temperature capable, hybrid SiC JFET. Material and process technology issues that will need to be addressed before device commercialization can be realized are discussed.
Two major problems associated with Si-based MEMS devices are stiction and wear. Surface modifications are needed to reduce both adhesion and friction in micromechanical structures to solve these problems. In this paper, we will present a process used to selectively coat MEMS devices with tungsten using a CVD (Chemical Vapor Deposition) process. The selective W deposition process results in a very conformal coating and can potentially solve both stiction and wear problems confronting MEMS processing. The selective deposition of tungsten is accomplished through silicon reduction of WF6, which results in a self-limiting reaction. The selective deposition of W only on polysilicon surfaces prevents electrical shorts. Further, the self-limiting nature of this selective W deposition process ensures the consistency necessary for process control. Selective tungsten is deposited after the removal of the sacrificial oxides to minimize process integration problems. This tungsten coating adheres well and is hard and conducting, requirements for device performance. Furthermore, since the deposited tungsten infiltrates under adhered silicon parts and the volume of W deposited is less than the amount of Si consumed, it appears to be possible to release stuck parts that are contacted over small areas such as dimples. Results from tungsten deposition on MEMS structures with dimples will be presented. The effect of wet and vapor phase cleans prior to the deposition will be discussed along with other process details. The W coating improved wear by orders of magnitude compared to uncoated parts. Tungsten CVD is used in the integrated-circuit industry, which makes this approach manufacturable.
Two major problems associated with Si-based MEMS (MicroElectroMechanical Systems) devices are stiction and wear. Surface modifications are needed to reduce both adhesion and friction in micromechanical structures to solve these problems. In this paper, we will present a CVD (Chemical Vapor Deposition) process that selectively coats MEMS devices with tungsten and significantly enhances device durability. Tungsten CVD is used in the integrated-circuit industry, which makes this approach manufacturable. This selective deposition process results in a very conformal coating and can potentially address both stiction and wear problems confronting MEMS processing. The selective deposition of tungsten is accomplished through the silicon reduction of WF6. The self-limiting nature of this selective W deposition process ensures the consistency necessary for process control. The tungsten is deposited after the removal of the sacrificial oxides to minimize stress and process integration problems. Tungsten coating adheres well and is hard and conducting, requirements for device performance. Furthermore, since the deposited tungsten infiltrates under adhered silicon parts and the volume of W deposited is less than the amount of Si consumed, it appears to be possible to release stuck parts that are contacted over small areas such as dimples. The wear resistance of selectively coated W parts has been shown to be significantly improved on microengine test structures.
Silicon Carbide (SiC) is an emerging semiconductor material which has been widely predicted to be superior to both Si and GaAs in the area of power electronic switching devices . This paper presents an overview of SiC power devices and concludes that MOS Turn-Off Thyristor (MTOTM) is one of the most promising near term SiC switching device given its high power potential, ease of turn-off, 500°C operation and resulting reduction in cooling requirements. It is further concluded that in order to take advantage of SiC power devices, high temperature packages and components with double sided attachment need to be developed along with the SiC power devices.
Effects of convective mixing on the concentration homogeneity of the crystal has been demonstrated. Insitu observations of the solid liquid interface shape during crystal growth are presented which can be used to optimize the dopant distribution. Observations of the interface during growth are discussed varying the parameters in a controlled manner to minimize the thermosolutal effects. It has been observed that beyond a critical velocity for the particular dopant level, the interface shape changes. The change in the interface shape can be related to the fluid flow in the melt. Two different instability regions, namely convective and morphological are addressed. Experimentally observed result are compared with the existing convecto-diffusive theories.
—Bioassays were conducted with Bacillus sphaericus (Neide) 1593M (Bsph) and a neem based biopesticide formulation, Neemtox® (0.03% azadirachtin), independently and in different combinations, to evaluate any synergistic effects on Culex quinquefasciatus Say (Diptera: Culicidae) larvae susceptible to Bsph. The results indicated that the two biopesticides have no synergistic interaction on the larvae. These results are discussed in light of earlier experiments with resistant C. quinquefasciatus, in which Bspfc-Neemtox synergism was seen.