Optically controlled current-voltage characteristics of ion-implanted MESFETs

Optically controlled MESFETs are useful as optical devices for optical communications, and as photodetectors. In this paper, a theoretical model for the I–V characteristics of these MESFETs is presented. The model considers the nonuniform Gaussian doping for ion-implanted channels. It takes both the photogenerated carriers as well as the doping generated residual carriers into account. It is noted that the density of photogenerated carriers in the channel due to diffusion is much less than that due to drift. Treatment both under gradual channel approximation and saturation velocity approximation has been presented. The gradual channel and the velocity saturation approximations are applied to study the I–V characteristics of long-channel and short-channel MESFETs, respectively. Results for both long-channel and short-channel MESFETs indicate that drain saturation current and transconductance can be improved by properly fixing the optical flux, and the absorption coefficient of the material.     

A comprehensive study on the kinetics of aqueous free-radical homo- and copolymerization of acrylamide and diallyldimethylammonium chloride by online 1H-NMR spectroscopy

Free-radical homo- and copolymerization of acrylamide (AAm) and diallyldimethylammonium chloride (DADMAC) initiated with potassium persulfate (KPS) were performed in the presence of 0.1 M NaCl solution in D₂O at 50 °C. Online ¹H-NMR kinetic experiments were used to study polymerization kinetics via determination of the individual and overall conversion of the comonomers and compositions of the comonomer mixture and produced copolymer as a function of the reaction time. Reactivity ratios of the AAm and DADMAC were calculated by Mao-Huglin (MH) and extended Kelen-Tudos (KT) methods to be 7.0855?±?1.3963, 0.1216?±?0.0301 and 6.9458?±?2.0113, 0.1201?±?0.0437 respectively. “Lumped” kinetic parameter (k _p k _t ^??0.5 ) was estimated from experimental data. Results showed that k _p k _t ^??0.5 value increases by increasing mole fraction of the AAm in the initial reaction mixture. Drift in the comonomer mixture and copolymer compositions with reaction progress was evaluated experimentally and theoretically. Theoretical values were calculated from Meyer-Lowry equation by using reactivity ratios obtained from MH method. A good fitting between the experimental and theoretical values was observed, indicating accuracy of the reactivity ratios estimated in the present work. It was found from following changes in the copolymer composition with the comonomer conversion that produced copolymer has a statistical structure.     

Statistical Thermodynamic Study of Gas Adsorption with Different Adsorption Geometries on Homogeneous Solid Surface

In the present study, the non-dissociative gas adsorption with different chemisorption geometries on homogeneous solid surface has been studied. By considering the different chemisorption geometries for an adsorbate, an isotherm has been derived by statistical thermodynamics. Statistical thermodynamics study of adsorption leads to the concept of a constant parameter, α, which shows the ratio of the number of occupied sites to the number of adsorbed molecules. The isotherm has been analyzed by some of the experimental data of adsorption at solid/gas interface. Comparisons between the obtained isotherm and some famous isotherms like Langmuir, Freundlich, Langmuir–Freundlich, Toth, Temkin, and Frumkin have been provided. The results showed the new equation has a good conformity with experimental data.     

Microwave ferrites, part 2: passive components and electrical tuning

Low-loss ferrimagnets are the basis for passive microwave components operating in a wide range of frequencies. The magnetic resonances of passive components can be tuned using static magnetic fields over a wide frequency range, where higher operation frequencies require higher magnetic bias unless hexaferrites with large crystalline anisotropy are used. However, electrical tuning of the operation frequency, which can be achieved if the magnetic property of the material is sensitive to the field through magnetoelectric (ME) coupling, is more attractive than magnetic tuning. In the so-called multiferroic materials such as TbMnO₃, TbMn₂O₅, BiFeO₃, Cr₂O₃, and BiMnO₃, which possess simultaneously both the ferroelectric and ferromagnetic properties, ME coupling is very small to be practical. The ME effect, however, can be significantly enhanced in the case of bilayer/multilayer structures with one constituent highly piezoelectric, such as Pb(Zr_1 ? x Ti _x )O₃ (PZT) and 0.7Pb(Mg_1/3Nb_2/3)O₃-0.3PbTiO₃ (PMN-PT), and the other highly ferromagnetic, opening up the possibility for a whole host of tunable microwave passive components. In such structures, the strain induced by the electric field applied across the piezoelectric material is transferred mechanically to the magnetic material, which then experiences a change in its magnetic permeability through magnetostriction. Additionally, electrical tuning coupled with high dielectric permittivity and magnetic susceptibility could lead to miniature microwave components and/or make operation at very high frequencies possible without the need for increased size and weight common in conventional approaches. In Part 1 of this review, fundamentals of ferrite materials, interconnecting chemical, structural, and magnetic properties with the treatment of various types of ferrites used in microwave systems are discussed. Part 2 discusses the basis for coupling between electrical and magnetic properties for highly attractive electrical tuning of passive components by combining piezoelectric materials with ferrites and various device applications of ferrites.     

Substrate dependence of InP m.e.s.f.e.t. performance

There is evidence to suggest that Fe outdiffuses, during the growth, into the epitaxial films prepared by vapour-phase epitaxy at 650°C. Field-effect transistors on Fe-doped material show substantial looping that was absent on Cr-doped material and exhibit about 2 dB worse noise figure at about 7 GHz. Experiments with low 1015 S-doped InP grown on Sn-, Cr- and Fe-doped substates indicate that such outdiffusion is typically about 5 ?m. Saturation velocity levels in the m.e.s.f.e.t. channel are about 1.7 × 107 cm/s and 1.3 × 107 cm/s, associated with Cr and Fe doped substrates, respectively.     

Protein detection through different platforms of immuno-loop-mediated isothermal amplification

Different immunoassay-based methods have been devised to detect protein targets. These methods have some challenges that make them inefficient for assaying ultra-low-amounted proteins. ELISA, iPCR, iRCA, and iNASBA are the common immunoassay-based methods of protein detection, each of which has specific and common technical challenges making it necessary to introduce a novel method in order to avoid their problems for detection of target proteins. Here we propose a new method nominated as ‘immuno-loop-mediated isothermal amplification’ or ‘iLAMP’. This new method is free from the problems of the previous methods and has significant advantages over them. In this paper we also offer various configurations in order to improve the applicability of this method in real-world sample analyses. Important potential applications of this method are stated as well.     

An innovative approach to fabricate a thermosensitive melatonin-loaded conductive pluronic/chitosan hydrogel for myocardial tissue engineering

This study aimed at designing and fabrication of a novel injectable and thermosensitive melatonin-loaded pluronic/chitosan hydrogel containing gold nanoparticles (GNPs) and poly glycerol sebacate (PGS) for myocardial tissue engineering. The PGS nanoparticles were used as the melatonin (drug model) carrier. The gelation time, syringeability, stability, and swelling of the hydrogel were scrutinized. Rheological properties, chemical composition, and morphology of the samples were also investigated. The effect of GNPs addition on the electrical conductivity of hydrogel was assessed. The cytotoxicity of hydrogels was assessed through MTT assay in the exposure of H9C2 cells up to 7 days. Scanning electron microscopy was applied to evaluate the morphology of seeded cells. The synthesis parameters of PGS nanoparticles were optimized through which 2.5%w/v of PGS and 1:10 organic phase to aqueous phase (O/A) ratio were found desirable. The optimum hydrogel illustrated 2 min gelation time and was stable up to 20 days with 5% swelling in the first 12 h into phosphate buffered saline. The GNPs with a uniform distribution rendered the hydrogel electrically conductive (1500 μS/cm). According to the MTT assay results, 3.125 μM melatonin was considered as the suitable concentration by which a significant increase in the cell viability was observed. The results exhibited that the prepared hydrogel composed of pluronic/chitosan/GNPs, and 3.125 μM melatonin-loaded PGS nanoparticles could be applied as a promising scaffold for myocardial tissue engineering.     

Microwave ferrites, part 1: fundamental properties

Ferrimagnets having low RF loss are used in passive microwave components such as isolators, circulators, phase shifters, and miniature antennas operating in a wide range of frequencies (1–100 GHz) and as magnetic recording media owing to their novel physical properties. Frequency tuning of these components has so far been obtained by external magnetic fields provided by a permanent magnet or by passing current through coils. However, for high frequency operation the permanent part of magnetic bias should be as high as possible, which requires large permanent magnets resulting in relatively large size and high cost microwave passive components. A promising approach to circumvent this problem is to use hexaferrites, such as BaFe₁₂O₁₉ and SrFe₁₂O₁₉, which have high effective internal magnetic anisotropy that also contributes to the permanent bias. Such a self-biased material remains magnetized even after removing the external applied magnetic field, and thus, may not even require an external permanent magnet. In garnet and spinel ferrites, such as Y₃Fe₅O₁₂ (YIG) and MgFe₂O₄, however, the uniaxial anisotropy is much smaller, and one would need to apply huge magnetic fields to achieve such high frequencies. In Part 1 of this review of microwave ferrites a brief discussion of fundamentals of magnetism, particularly ferrimagnetism, and chemical, structural, and magnetic properties of ferrites of interest as they pertain to net magnetization, especially to self biasing, are presented. Operational principles of microwave passive components and electrical tuning of magnetization using magnetoelectric coupling are discussed in Part 2.     

The effects of psyllium supplementation on body weight,body mass index and waist circumference in adults: A systematic review and dose-response meta-analysis of randomized controlled trials

Abstract

Background: Previous studies reported inconsistent findings regarding the effects of psyllium supplementation on obesity measures. This systematic review and meta-analysis was performed to summarize data from available randomized clinical trials (RCTs) on the effect of psyllium supplementation on body weight, body mass index (BMI), and waist circumference (WC) in adults.

Methods: PubMed, SCOPUS, Cochrane Library, and Google Scholar were searched to identify relevant articles up to August 2018. The effect sizes were presented as weighted mean difference (WMD) and 95% confidence intervals (CI) by using random effects model. To detect dose-response relationships, we used fractional polynomial modeling.

Results: A total of 22 RCTs were included. Meta-analysis did not find any significant effect of psyllium supplementation on body weight (MD: ?0.28?kg, 95% CI: ?0.78, 0.21, p?=?0.268), BMI (MD: ?0.19?kg/m², 95% CI: ?0.55, 0.15, p?=?0.27) and WC (MD: ?1.2?cm, 95% CI: ?2.6, 0.2, p?=?0.09). Subgroup analysis showed that psyllium dosage, kind of psyllium administration, duration of trial, study design, sample size, and gender were potential sources of heterogeneity. Moreover, there was nonlinear association between duration of psyllium consumption, BMI and WC.

Conclusion: Psyllium supplementation does not reduce body weight, BMI, and WC significantly.