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An analytical study of the small amplitude electron acoustic double layers in a magnetized plasma consisting of superthermal electrons and ions along with cold fluid electrons is discussed. The dispersion relation allows electron acoustic waves with the frequency within electron and ion gyro-frequency in the modelled plasma. In the process of study of the nonlinear structures, the Sagdeev pseudo-potential method for small amplitude regions is employed. The existence domains for the double layers are investigated in terms of the Mach numbers of the structures and the temperature ratios of the species for different ratios of their concentration. The effects of the compositional parameters on the nature and size of the double layers are also explored and it is observed that the plasma can support both compressive and rarefactive double layers depending on the values of those parameters and the Mach numbers.
Spiking Neural Networks propose to mimic nature’s way of recognizing patterns and making decisions in a fuzzy manner. To develop such networks in hardware, a highly manufacturable technology is required. We have proposed a silicon-based leaky integrate and fire (LIF) neuron, on a sufficiently matured 32 nm CMOS silicon-on-insulator (SOI) technology. The floating body effect of the partially depleted (PD) SOI transistor is used to store “holes” generated by impact ionization in the floating body, which performs the “integrate” function. Recombination or equivalent hole loss mimics the “leak” functions. The “hole” storage reduces the source barrier to increase the transistor current. Upon reaching a threshold current level, an external circuit records a “firing” event and resets the SOI MOSFET by draining all the stored holes. In terms of application, the neuron is able to show classification problems with reasonable accuracy. We looked at the effect of scaling experimentally. Channel length scaling reduces voltage for impact ionization and enables sharper impact ionization producing significant designability of the neuron. A circuit equivalence is also demonstrated to understand the dynamics qualitatively. Three distinct regimes are observed during integration based on different hole leakage mechanism.
A total of 45 strains of Vibrio cholerae O1 isolated from 10 different places in India where they were associated with cases of cholera between the years 2007 and 2008 were examined by molecular methods. With the help of phenotypic and genotypic tests the strains were confirmed to be O1 El Tor biotype strains with classical ctxB gene. Polymerase chain reaction (PCR) analysis by double – mismatch amplification mutation assay PCR showed 16 of these strains carried the ctxB-7 allele reported in Haitian strains. Sequencing of the ctxB gene in all the 45 strains revealed that in 16 strains the histidine at the 20th amino acid position had been replaced by asparagine and this single nucleotide polymorphism did not affect cholera toxin production as revealed by beads enzyme-linked immunosorbent assay. This study shows that the new ctxB gene sequence was circulating in different places in India. Seven representatives of these 45 strains analysed by pulsed – field gel electrophoresis showed four distinct Not I digested profiles showing that multiple clones were causing cholera in 2007 and 2008.
There is a genetic contribution to the risk of suicide, but sparse prior research on the genetics of suicidal ideation.
Active and passive suicidal ideation were assessed in a Sri Lankan population-based twin registry (n = 3906 twins) and a matched non-twin sample (n = 2016). Logistic regression models were used to examine associations with socio-demographic factors, environmental exposures and psychiatric symptoms. The heritability of suicidal ideation was assessed using structural equation modelling.
The lifetime prevalence of any suicidal ideation was 13.0% (11.7–14.3%) for men; 21.8% (20.3–23.2%) for women, with no significant difference between twins and non-twins. Factors that predicted suicidal ideation included female gender, termination of marital relationship, low education level, urban residence, losing a parent whilst young, low standard of living and stressful life events in the preceding 12 months. Suicidal ideation was strongly associated with depression, but also with abnormal fatigue and alcohol and tobacco use. The best fitting structural equation model indicated a substantial contribution from genetic factors (57%; CI 47–66) and from non-shared environmental factors (43%; CI 34–53) in both men and women. In women this genetic component was largely mediated through depression, but in men there was a significant heritable component to suicidal ideation that was independent of depression.
These are the first results to show a genetic contribution to suicidal ideation that is independent of depression outside of a high-income country. These phenomena may be generalizable, because previous research highlights similarities between the aetiology of mental disorders in Sri Lanka and higher-income countries.
Spectrum tuning in phosphor converted white light emitting diodes (pc-WLED) is done by mixing powders of phosphor compounds (with different emission wavelengths) in different weight ratios. In this paper, a new methodology for designing unique full spectrum phosphor mixtures (with fixed weight ratios of different emission phosphor) has been presented that could provide a wide range of pc-WLED spectrum. This is done by optimizing the excitation and emission spectra of the phosphor compounds used in the mixture. A unique phosphor mixture comprising of Eu2+ and Ce3+-Na1+ activated compounds of SrGa2S4, CaGa2S4, SrS, CaS and CaF2 was used to produce full spectrum warm, neutral and cool white LEDs with color temperatures between 2500 K and 7500 K and with color rendering index exceeding 95.
We calculate the temperature fluctuations in the microwave background in open primeval isocurvature baryon models (Peebles, 1987) with cosmological densities in the range 0.05 ≤ ω ≤ 0.2 We assume that the power spectrum of fluctuations is a power law with the index varying between – 1 ≤ n ≤ 0, as indicated by observations of large scale structure in the Universe. The Universe is assumed to be always fully ionized. The South Pole 13 field point experiment (Schuster et al., 1993) is compared to our theoretical predictions, and we find that the models predict larger temperature fluctuations than are observed. The observed temperature fluctuations on intermediate scales of ≲ 1° thus seem difficult to reconcile with the isocurvature baryon model.
We address two aspects of finitely generated modules of finite projective dimension over local rings and their connection in between: embeddability and grade of order ideals of minimal generators of syzygies. We provide a solution of the embeddability problem and prove important reductions and special cases of the order ideal conjecture. In particular, we derive that, in any local ring R of mixed characteristic p > 0, where p is a nonzero divisor, if I is an ideal of finite projective dimension over R and p 𝜖 I or p is a nonzero divisor on R/I, then every minimal generator of I is a nonzero divisor. Hence, if P is a prime ideal of finite projective dimension in a local ring R, then every minimal generator of P is a nonzero divisor in R.
Surfactant-free SnS nanoparticles were synthesized using continuous spray pyrolysis (CoSP) technique and used as sensitizers on electro-deposited ZnO nanowire arrays for fabrication of extremely thin absorbing (ETA) layers. The high-surface-area nanowire layer on ITO substrate was directly over-coated by SnS nanoparticles. The morphology of the ZnO/SnS nanostructures showed the coverage of orthorhombic SnS nanocrystals on hexagonal ZnO prismatic nanowires. The crystalline phase of the ZnO/SnS nanostructures was studied using X-ray diffraction. Conducting AFM showed a nonlinear characteristics confirming the junction formation.
We develop a framework for analysing the outcome of resource competition based on
bifurcation theory. We elaborate our methodology by readdressing the problem of
competition of two species for two resources in a chemostat environment. In the case of
perfect-essential resources it has been extensively discussed using Tilman’s
representation of resource quarter plane plots. Our mathematically rigorous analysis
yields bifurcation diagrams with a striking similarity to Tilman’s method including the
interpretation of the consumption vector and the resource supply vector. However, our
approach is not restricted to a particular class of models but also works with other
trophic interaction formulations. This is illustrated by the analysis of a model
considering interactively-essential or complementary resources instead of
prefect-essential resources. Additionally, our approach can also be used for other
ecosystem compositions: multiple resources–multiple species communities with equilibrium
or oscillatory dynamics. Hence, it gives not only a new interpretation of Tilman’s
graphical approach, but it constitutes an extension of competition analyses to communities
with many species as well as non-equilibrium dynamics.
A temporal relationship of Japanese encephalitis virus (JEV) transmission in pigs, mosquitoes and humans revealed that sentinel pig seroconversions were significantly associated with human cases 4 weeks before (P = 0·04) their occurrence, highly correlated during the same time and 2 weeks before case occurrence (P < 0·001), and remained significantly correlated up to 2 weeks after human case occurrence (P < 0·01). JEV was detected in the same month in pigs and mosquitoes, and peaks of pig seroconversion were preceded by 1–2 months of peaks of infection in vectors. Kaplan–Meier analysis indicated that detection of JEV-positive mosquitoes was significantly associated with the median time to occurrence of seroconversion in pigs (P < 0·05). This study will not only help in predicting JEV activity but also accelerate timely vector control measures and vaccination programmes for pigs and humans to reduce the Japanese encephalitis risk in endemic areas.
We present an extremely rare case of isolated angiokeratoma of the tongue.
Case report and review of related literature.
An 18-year-old, male adolescent presented with a fleshy, intermittently bleeding mass in the posterior third and base of the tongue. The lesion was initially suspected to be a lingual thyroid or haemangioma, but histopathological features were consistent with angiokeratoma. Magnetic resonance imaging revealed that the lesion extended up to the vallecula and involved the lamina propria and superficial tongue musculature. No similar lesions were found elsewhere in the body. No metabolic derangements were identified in the patient or his family. The 2.6 × 1.5 × 0.5 cm mass was excised under general anaesthesia.
We present the 1st case of isolated lingual angiokeratoma in a male, the 4th such case overally, the largest ever documented. The lesion was situated in the posterior third and base of the tongue, a position not previously described.
Four series of samples, prepared at 250° C by decomposition of a mixture of silane and argon in a radio frequency powered deposition systems (rf-PECVD), have been studied. The dilution rates were 1 %, 1.5 %, 5 % and 10 % of silane in argon and the total pressure was 0.5 Torr for the first series and 0.2 Torr for the others. Structural and transport properties of the materials have been studied as function of power density. Structural studies show the transition from purely amorphous material towards microcrystalline material with increasing rf power density. The transport parameters were measured in the as-deposited, light-soaked and annealed states and compared to those obtained on state of the art material. The best material obtained is clearly device grade material. This study shows that argon dilution allows to tailor the material for a given application.
Recent developments in our laboratory related to polymer-based light sensors are reviewed. The inherent processibility of the active polymer medium is utilized in the implementation of different designs for the opto-electronic applications. The utility of these devices as sensitive photodetectors, image sensors and position sensitive detectors is demonstrated. The schottky-type layer formation at interfaces of polymers such as polyalkylthiophenes and aluminum accompanied by the enhanced photo-induced charge separation due to high local electric field is tapped for some of these device structures. The sensitivity of polymer-based field effect transistors to light also provides a convenient lateral geometry for efficient optical-coupling and control of the transistor state. The range of these polymer-detectors available with the option of operating in the diode and transistor modes should be an attractive feature for many potential applications.
The multilayers of ferroelectric (FE) Pb(Zr, Ti)O3 (PZT) and ferromagnetic (FM) CoFe2O4 (CFO) thin films with 3, 5, and 9 layers having configurations PZT/CFO (PC) and CFO/PZT (CP) were fabricated by pulsed laser deposition technique. We have investigated the effect of inter-diffusion at the interface of multilayers (MLs) and reversing the order of FE and FM layers in the multilayers configuration on the electrical/magnetic properties. The TEM of the films showed that the layer structure was not maintained and the inter-diffusion of the CFO into PZT and vice verse were observed at the interface of MLs. Both the PC and CP configurations of multilayer films exhibited pseudo FE hysteresis loop and proper FM hysteresis loops at room temperature. Reversing the multilayer configuration from CP to PC resulted in increasing the pseudo remanent polarization, however this behavior was not observed in magnetic properties. The frequency and temperature dependences of the impedance and modulus spectroscopy of the multilayer PC and CP films were studied in the ranges of 102 to 106 Hz and 200 to 650 K respectively. The electrical response of all multilayer films investigated could be resolved into two contributions. We attributed these to the grain and grain boundary effects in impedance and modulus formalism. We found that the difference between the grain and grain boundary capacitive effect decreased due to increase of the number of layers.
The fabrication and performance characteristics of an integrated distributed feedback (DFB) laser and optical amplifier structure are described. The structure utilizes semi-insulating Fe doped InP layers for current confinement to the active region, electrical isolation between the two sections and for lateral index guiding. The amplified output has a slope of 1 mW/mA of laser current with the amplifier biased at 150 mA which is a factor of 5 larger than that for a typical laser. The laser emits near 1.55 μm and the spectral width under modulation of the amplified output is considerably smaller than that for a DFB laser for the same on/off ratio.
Microelectronic solder joints are exposed to aggressive thermo-mechanical cycling (TMC) during service, resulting in strain localization near solder / bond-pad interfaces, which eventually leads to low-cycle fatigue (LCF) failure of the joint. In order to mitigate these strain concentrations and thereby improve LCF life, a ‘smart solder’ reinforced with a martensitic NiTi based shape memory alloy (SMA) is being developed. This paper presents an overview of processing, characterization and modeling of these composite solders, and articulates the role of NiTi particles on strain evolution in composite solders. Based on finite element modeling and experiments on model single fiber composites, it is shown that NiTi pariculate reinforcements can reduce inelastic strain levels in the solder via shape recovery associated with the B19′→B2 transformation. In situ TMC studies in the SEM, in conjunction with strain analysis via digital image correlation, show evidence of reverse deformation in the solder commensurate with the NiTi phase transformation, demonstrating the conceptual viability of the smart solder approach. Details of processing and joint formation, and the resultant microstructures of smart solder are discussed. Finally, results of TMC experiments on monolithic solder and NiTi/solder composite joints are reported, highlighting the beneficial effect of shape-memory transformation in reducing inelastic strain range, and hence enhancing the LCF life, of solders.
Fabrication strategies based on mechanisms of self-assembly are now widely being recognized as inevitable tools in nanotechnology. Self-organized construction of advanced materials and devices may be done starting with tailor made nanoparticles as building blocks. Multilayer thin films of gold, zinc sulphide and manganese doped zinc Sulfide nanoparticles were fabricated by a modified polyelectrolyte deposition process. A prerequisite to utilization of colloids for the fabrication of uniform layers is that they remain in suspension and resist unwanted agglomeration. The stability of colloids is generally achieved either by electrostatic stabilization, involving the creation of an electrical double layers arising from ions intentionally adsorbed on the surface of the particle and associated counter ions that surround the particle, or by steric hindrance that is achieved by the adsorption of macromolecules on the surface of the particles. The inherent necessity to introduce electrostatic or steric hindrance to avoid colloidal agglomeration was utilized to induce self-assembly of multilayers applying similar concept used for the layering of polyelectrolytes. Polyacrylic acid was used as the polyanion and chitosan as the polycation for the deposition process. Upto 100 layers of nanoparticles were constructed and films that were found to be stable and uniform over the substrate. The layer-by-layer deposition of multilayers of several different structures was prepared and devices showing resistive and capacitive electrical characteristics have been fabricated. The onset of electrical conduction in the resistive devices could be varied by introducing a dielectric interlayer between gold nanoparticles and by introducing a gold overlayer on the zinc sulphide nanoparticle devices.
This study evaluates variations in SiCl4 reactive ion etching (RIE) process parameters in order to optimize the fabrication of lateral quantum well arrays (QWA) used in III–V semiconductor laser and detector designs. Since fabrication involves MBE regrowth on SiCl4 etched surfaces, material quality of both the etched surface and GaAs regrowth are evaluated. The variation of RIE parameters involved power levels, DC bias and etch times (10 Watts, -30V, 8 min.; 25 Watts, -100V, 5 min.; 95 Watts,-340V, 2 min.) while material removal was held constant (400nm). Evaluation of the etched surfaces revealed that the lattice damage depth exceeded lOOnm for all power levels. The extent of disorder beneath the etched surface was less for the low power long etch time. Etching at higher power levels for shorter time periods resulted in smoother surfaces and enhanced electrical characteristics, which in turn yielded a higher quality GaAs regrowth region. For the RIE parameters examined in this study, the variation in defect densities seemed to have a lesser effect on device performance as compared to the extreme differences in surface morphologies. Thus, for the parameters evaluated in this work, we suggest that QWA fabrication is optimized via SiClif RIE at the high power level for a short time period.
Chromophoric multilayer thin films exhibiting efficient second harmonic generation have been constructed on inorganic substrates via a stepwise layer-by-layer process using molecular self-assembly techniques. In each step, chemical species bearing appropriate functional groups form covalent bonds with functional groups deposited in the previous step. Bulk acentricity is achieved by the orientation of chromophore-containing layers outward from the substrate surface. A new chromophore having comparable hyperpolarizability but different steric and transparency characteristics than the stilbazolium chromophore used previously has been incorporated into self-assembled films. The large effects of octachlorotrisiloxane capping on the structure of these films have been investigated by second harmonic generation and X-ray reflectivity measurements. Novel in situ measurements of second harmonic generation efficiency as a function of chromophore layer growth are described and provide information useful for optimizing deposition conditions and understanding the film growth process.