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Measurements of oscillation frequencies of the Sun and stars can provide important independent constraints on their internal structure and dynamics. Seismic models of these oscillations are used to connect structure and rotation of the star to its resonant frequencies, which are then compared with observations, the goal being that of minimizing the difference between the two. Even in the case of the Sun, for which structure models are highly tuned, observed frequencies show systematic deviations from modeled frequencies, a phenomenon referred to as the “surface term.” The dominant source of this systematic effect is thought to be vigorous near-surface convection, which is not well accounted for in both stellar modeling and mode-oscillation physics. Here we bring to bear the method of homogenization, applicable in the asymptotic limit of large wavelengths (in comparison to the correlation scale of convection), to characterize the effect of small-scale surface convection on resonant-mode frequencies in the Sun. We show that the full oscillation equations, in the presence of temporally stationary 3D flows, can be reduced to an effective “quiet-Sun” wave equation with altered sound speed, Brünt–Väisäla frequency, and Lamb frequency. We derive the modified equation and relations for the appropriate averaging of 3D flows and thermal quantities to obtain the properties of this effective medium. Using flows obtained from 3D numerical simulations of near-surface convection, we quantify their effect on solar oscillation frequencies and find that they are shifted systematically and substantially. We argue therefore that consistent interpretations of resonant frequencies must include modifications to the wave equation that effectively capture the impact of vigorous hydrodynamic convection.
This study is a part of the surveillance study on childhood diarrhoea in the Andaman and Nicobar Islands; here we report the drug resistance pattern of recent isolates of Shigella spp. (2006–2011) obtained as part of that study and compare it with that of Shigella isolates obtained earlier during 2000–2005. During 2006–2011, stool samples from paediatric diarrhoea patients were collected and processed for isolation and identification of Shigella spp. Susceptibility to 22 antimicrobial drugs was tested and minimum inhibitory concentrations were determined for third-generation cephalosporins, quinolones, amoxicillin-clavulanic acid combinations and gentamicin. A wide spectrum of antibiotic resistance was observed in the Shigella strains obtained during 2006–2011. The proportions of resistant strains showed an increase from 2000–2005 to 2006–2011 in 20/22 antibiotics tested. The number of drug resistance patterns increased from 13 in 2000–2005 to 43 in 2006–2011. Resistance to newer generation fluoroquinolones, third-generation cephalosporins and augmentin, which was not observed during 2000–2005, appeared during 2006–2011. The frequency of resistance in Shigella isolates has increased substantially between 2000–2006 and 2006–2011, with a wide spectrum of resistance. At present, the option for antimicrobial therapy in shigellosis in Andaman is limited to a small number of drugs.
In this study, an in vitro blood-brain barrier model was developed using murine brain endothelioma cells (b.End3 cells). By comparing the permeability of FITC-Dextran at increasing exposure times in serum-free medium to such values in the literature, we confirm that the blood-brain barrier model was successfully established. After such confirmation, the permeability of five ferrofluid (FF) nanoparticle samples, GGB (ferrofluid synthesized using glycine, glutamic acid and BSA), GGC (glycine, glutamic acid and collagen), GGP (glycine, glutamic acid and PVA), BPC (BSA, PEG and collagen) and CPB (collagen, PVA and BSA), was determined using this model. In addition, all the five FF samples were characterized by zeta potential to determine their charge as well as TEM and dynamic light scattering for determining their hydrodynamic diameter. Results showed that FF coated with collagen had better permeability to the blood-brain barrier than FF coated with glycine and glutamic acid based on an increase of 4.5% in permeability. Through such experiments, magnetic nanomaterials, such as ferrofluids, that are less permeable to the blood brain barrier can be used to decrease neural tissue toxicity and magnetic nanomaterials with more permeable to the blood-brain barrier can be used for brain drug delivery.
Due to the high surface area and good bio-compatibility of nano structured ZnO, it finds good utility in biosensor applications. In this work we have fabricated highly dense ZnO nano bundles with the assistance of self assembled poly methylsilisesquoxane (PMSSQ) matrix which has been realized in a carpet like configuration with implanted ZnO nano-seeds. Such high aspect ratio structures (∼50) with carpet like layout have been realized for the first time using solution chemistry. Nanoparticles of PMMSQ are mixed with a nano-assembler Poly-propylene glycol (PPG) and Zinc Oxide nanoseeds (5-15 nm). The PPG acts by assembling the PMSSQ nanoparticles and evaporates from this film thus creating the highly porous nano-assembly of PMMSQ nanoparticles with implanted Zinc Oxide seeds. Nano-wire bundles with a high overall surface roughness are grown over this template by a daylong incubation of an aqueous solution of hexamethylene tetra amine and Zinc nitrate. Characterization of the fabricated structures has been extensively performed using FESEM, EDAX, and XRD. We envision these films to have potential of highly dense immobilization platforms for antibodies in immunosensors. The principle advantage in our case is a high aspect ratio of the nano-bundles and a high level of roughness in overall surface topology of the carpet outgrowing the zinc-oxide nanowire bundles. Antibody immobilization has been performed by modifying the surface with protein-G followed by Goat anti salmonella antibody. Antibody activity has been characterized by using 3D profiler, Bio-Rad Protein assay and UV-Visible spectrophotometer.
When women have a history of anorexia nervosa (AN), the advice given about becoming pregnant, and about the management of pregnancies, has usually been cautious. This study compared the pregnancy outcomes of women with and without a history of AN.
Women with a confirmed diagnosis of AN who had presented to psychiatric services in North East Scotland from 1965 to 2007 were identified. Those women with a pregnancy recorded in the Aberdeen Maternal and Neonatal Databank (AMND) were each matched by age, parity and year of delivery of their first baby with five women with no history of AN. Maternal and foetal outcomes were compared between these two groups of women. Comparisons were also made between the mothers with a history of AN and all other women in the AMND.
A total of 134 women with a history of AN delivered 230 babies and the 670 matched women delivered 1144 babies. Mothers with AN delivered lighter babies but this difference did not persist after adjusting for maternal body mass index (BMI) in early pregnancy. Standardized birthweight (SBW) scores suggested that the AN mothers were more likely to produce babies with intrauterine growth restriction (IUGR) [relative risk (RR) 1.54, 95% confidence interval (CI) 1.11–2.13]. AN mothers were more likely to experience antepartum haemorrhage (RR 1.70, 95% CI 1.09–2.65).
Mothers with a history of AN are at increased risk of adverse pregnancy outcomes. The magnitude of these risks is relatively small and should be appraised holistically by psychiatric and obstetric services.
We have successfully prepared La0.5Sr0.5MnO3nanowires using a novel hydrothermal synthesis process and studied their magnetic and magnetocaloric properties. The system exhibits an inverse magnetocaloric effect (IMCE) around 175 K indicating presence of significant AFM correlation. The MCE study reveals a clear paramagnetic (PM) to ferromagnetic (FM) transition near room temperature (T ~ 325K) which is followed by onset of AFM at lower temperatures. The development of the FM-like magnetic state at low temperature is attributed to the enhanced double exchange (DE) driven ferromagnetism in AFM state as predicted by recent theoretical studies.
The LaFeO3 and CaFeOX layers are grown using highly dense target prepared by Pechini method, with which accurate growth rate is achieved. Since the LaFeO3demonstrates the obvious RHEED oscillation until the end of growth, constant growth rate, and the step-terraces structure, the LFO is employed as a buffer and/or reference layer to determine the required pulses to deposit the thickness we desire in the superlattice. Superlattices show the clear satellite peaks and Laue oscillation in the XRD spectra as well as the oscillations caused by the film thickness with a flat surface and superstructure with a flat interface in the x-ray reflection spectrum. The streaky RHEED patterns and step-terraces surface are consistent with the results of spectra using x-ray.
Long wavelength photons in the red and near infrared region of the spectrum are poorly absorbed in thin film silicon cells, due to their long absorption lengths. Advanced light trapping methods are necessary to harvest these photons. The basic physical mechanisms underlying the enhanced light trapping in thin film solar cells using periodic back reflectors include strong diffraction coupled with light concentration. These will be contrasted with the scattering mechanisms involved in randomly textured back reflectors, which are commonly used for light trapping. A special class of conformal solar cells with plasmonic nano-pillar back reflectors will be described, that generates absorption beyond the classical 4n2 limit (the Lambertian limit) averaged over the entire wavelength range for nc-Si:H. The absorption beyond the classical limit exists for common 1 micron thick nc-Si:H cells, and is further enhanced for non-normal light. Predicted currents exceed 31 mA/cm2 for nc-Si:H. The nano-pillars are tapered into conical protrusions that enhance plasmonic effects. Such conformal nc-Si:H solar cells with the same device architecture were grown on periodic nano-hole, periodic nano-pillar substrates and compared with randomly textured substrates, formed by annealing Ag/ZnO or etched Ag/ZnO. The periodic back reflector solar cells with nano-pillars demonstrated higher quantum efficiency and higher photo-currents that were 1 mA/cm2higher than those for the randomly textured back reflectors. Losses within the experimental solar architectures are discussed.
Ba0.8Sr0.2TiO3 (BST) thin films and Ba0.8Sr0.2TiO3/ZrO2 heterostructured thin films have been successfully fabricated on Pt/Ti/SiO2/Si substrates by a sol-gel process. The dielectric properties of these films were measured as a function of temperature in the frequency range of 1 kHz to 1 MHz. It is clearly observed that the dielectric peaks exist and shift to high temperature with the increase of frequency indicating the presence of relaxor-type behavior in the films. Also it is seen that one dielectric peak is observed in single layer BST thin films whereas two dielectric peaks are observed in BST/ZrO2 heterostructured thin films due to the presence of two dielectric layers having different band gap energies. The variation of peak temperature Tm, corresponding to dielectric loss maximum, with frequency and fitting to Arrhenius law gives activation energy of 1.24 eV which is very close to the activation energy of oxygen vacancies in BaTiO3. Hence, oxygen vacancies are the active defects which are contributing to the relaxation process in these films.
In this paper, we report on the growth and fabrication of thin film Si photovoltaic devices on photonic structures which were fabricated on steel and PEN and Kapton substrates. Both amorphous Si and thin film nanocrystalline Si devices were fabricated. The 2 dimensional photonic reflector structures were designed using a scattering matrix theory and consisted of appropriately designed holes/pillars which were imprinted into a polymer layer coated onto PEN, Kapton and stainless steel substrates. The photonic structures were coated with a thin layer of Ag and ZnO. Both single junction and tandem junction (amorphous/amorphous and amorphous/nanocrystalline) cells were fabricated on the photonic layers. It was observed that the greatest increase in short circuit current and efficiency in these cells due to the use of photonic reflectors was in nanocrystalline Si cells, where an increase in current approaching 30% (compared to devices fabricated on flat substrates) was obtained for thin (∼ 1 micrometer thick i layers) films of nano Si deposited on steel structures. The photonic structures (which were nanoimprinted into a polymer) were shown to stand up to temperatures as large as 300 C, thereby making such structures practical when a steel (or glass) of kapton substrate is used. Detailed measurements and discussion of quantum efficiency and device performance for various photonic back reflector structures on steel, kapton and PEN substrates will be presented in the paper.
Acute diarrhoea remains a major public health challenge in developing countries. We examined the role of a probiotic in the prevention of acute diarrhoea to discover if there was an effect directed towards a specific aetiology. A double-blind, randomized, controlled field trial involving 3758 children aged 1–5 years was conducted in an urban slum community in Kolkata, India. Participants were given either a probiotic drink containing Lactobacillus casei strain Shirota or a nutrient drink daily for 12 weeks. They were followed up for another 12 weeks. The primary outcome of this study was the occurrence of first episodes of diarrhoea. We assessed this during 12 weeks of intake of study agent and also for 12 weeks of follow-up. There were 608 subjects with diarrhoea in the probiotic group and 674 subjects in the nutrient group during the study period of 24 weeks. The level of protective efficacy for the probiotic was 14% (95% confidence interval 4–23, P<0·01 in adjusted model). The reduced occurrence of acute diarrhoea in the probiotic group compared to nutrient group was not associated with any specific aetiology. No adverse event was observed in children of either probiotic or nutrient groups. The study suggests that daily intake of a probiotic drink can play a role in prevention of acute diarrhoea in young children in a community setting of a developing country.
The effect of anthanum substitution (0-20%) on phase formation, structural evolution and electrical properties of SrBi2Ta2O9 (SBT) ceramics were investigated. X-ray diffraction studies revealed that phase pure SBT bulk samples can be synthesized with lanthanum doping without any phase segregation. Raman spectroscopy was used to understand the lattice vibrational characteristics of La substituted SBT compound. The ferroelectric soft mode at 27 cm−1 was shifted towards the lower frequencies at room temperature with increase in La concentrations. The octahedral stretching mode (O-Ta-O) did not influenced by La substitution in SBT. The x-ray photoemission spectroscopy measurements showed the decrease of binding energy of Bi 4f core levels (5/2 and 7/2) upon La substitution in SBT. The dielectric constant was increased from 120 to 190 up to 10% La doping and decreased with further increase in La concentration.
This paper clarifies and extends previous work on the equivalence between monetary regimes and fiscal regimes involving social security systems. We show that monetary regimes of the type we study are equivalent to two alternative types of social security regimes. This result has an important implication. Notably, governments can finance a real expenditure by increasing the inflation rate, or finance the expenditure by increasing the tax rate on social security benefits. Such equivalence should help us better understand the role that monetary policy plays in these economies.This research was begun while Russell was visiting Iowa State University. We gratefully acknowledge helpful conversations with Scott Freeman and Peter Rangazas, and comments from participants at the Midwest Macroeconomics Meetings in Atlanta. The views expressed herein do not necessarily represent the views of the Board of Governors of the Federal Reserve System or the Federal Reserve Bank of Kansas City.
Lead strontium titanate (PbxSr1-xTiO3) (x=0.3–1.0) ceramic targets were prepared by the conventional powder-processing method. Thin films of these compositions were deposited on platinized silicon substrates by pulsed laser deposition technique. X-ray diffraction studies of the ceramic targets showed that the lattice structure changes from tetragonal to cubic phase with the increase of Sr content in PbTiO3. Raman spectroscopic studies of PbxSr1-xTiO3 (PST) ceramics and thin films showed that the soft mode decreases to lower frequency and finally disappear at around 60–70 at% Sr content, which confirms the tetragonal to cubic phase transition at room temperature. Dielectric constant measured for PST thin films was in the range of 900–1500 at 1 MHz, with maximum value obtained for PST30 thin film. The loss tangents at room temperature were in the range of 0.07–0.1 for PST thin films with different compositions.
The growth and structural characterization of UHV-compatible LPCVD grown strained-Si layer on linearly graded relaxed SiGe layer and the electrical properties of the high-k ultrathin ZrO2 films deposited on strained-Si layer using microwave-plasma CVD at low temperature (150°C) are reported. The strained-Si layer has been characterized using AFM, TEM and Raman spectroscopy. The C-V and G-V characteristics of ZrO2 films have been used to calculate the interface trap density, Dit, near the midgap energy, and the fixed oxide charge density, Qf/q. These are found to be 2.24 × 1012 cm−2 eV−1 and 1.45 × 1011 cm−2, respectively. Poole-Frenkel (PF) conduction mechanism is found to dominate the current conduction at room temperature.
In the present work micro-Raman spectroscopy has been used to understand the lattice dynamics of cation substituted SBT ceramics and thin films. Different concentrations of Ca and V were introduced into SBT lattices. Incorporation of Ca ion at Sr-site was confirmed by decrease in the lattice parameters calculated from x-ray diffraction data. The lowest Raman modes at 27 cm-1 and 58 cm-1 showed upward shift with increasing Ca concentration and was attributed to the lower mass and lower ionic radii of Ca. The temperature dependant Raman studies revealed the increase of the phase transition temperature with increased Ca content, and was attributed to the decrease in tolerance factor. Substitution of smaller cation at Sr site in SBT compound has increased lattice mismatch between SrO and TaO2 planes inside the stable perovskite unit of SrTa2O7 which has pronounced influence on ferroelectric properties of SBT. Substitution of vanadium at Ta-site of SBT did not influence the low frequency Raman modes of SBT. However, it showed a pronounced influence on the O-Ta-O stretching modes by splitting the mode frequency at 810 cm-1. The transition temperature of SBT was reduced with increasing vanadium contents.
We report ferroelectric properties and local hysteresis behavior of 2 mole percent Si added PbTiO3 thin films grown on Pt/TiO2/SiO2/Si substrate by using pulsed laser deposition technique. The ferroelectric hysteresis loop and scanning piezoresponce images obtained on these films by using AFM with conducting tip demonstrate excellent properties, which are equivalent to any other established ferroelectric material like PZT. Si segregating at the grain boundaries controls grain growth. The grain size and grain boundaries play a crucial role in determining ferroelectric hysteresis properties. The presence of Si in the matrix can be useful in tuning the properties.
The highest efficiency CuIn1-xGaxSe2 (CIGS) solar cells use thin-film polycrystalline CIGS absorber layers. We have applied variable angle spectroscopic ellipsometry (VASE) to characterize the dielectric functions of polycrystalline thin films of CIGS with Ga: (In + Ga) ratios ranging from 0.18 to 1.0. The Cu: (In + Ga) ratios in these films are approximately 0.90, which is the ratio that yields the highest efficiency CIGS devices. Spectra were measured over the energy range 0.7 to 5.0 eV at room temperatures. Models used to analyze the ellipsometry data include the full multi-layer structure of the sample, which enables us to report the actual dielectric function rather than the pseudo-dielectric function. We present data on how the critical points change with composition, and compare and contrast our results with measurements of single-crystal and bulk polycrystalline samples reported in the literature. Auger electron spectroscopy, atomic force microscopy, and X-ray diffraction have been used to verify the homogeneity, surface roughness, and phase purity, respectively.