Calculation of residual thermal stress in GaN epitaxial layers grown on technologically important substrates

A detailed investigation of residual thermal stress and misfit strain in GaN epitaxial layers grown on technologically important substrates is performed. The thermal stress is low when GaN is grown on AlN, SiC and Si, and relatively higher when Al₂O₃ substrate is used. The stress is compressive for AlN and Al₂O₃ and tensile for Si and SiC substrates. Residual thermal stress analysis was also performed for three layer heterostructures of GaN/AlN/6H-SiC and GaN/AlN/Al₂O₃. The stress remains the same when a sapphire substrate is used with or without an AlN buffer layer but reduces by an order of magnitude when a 6H-SiC substrate is used with an AlN buffer layer.     

Development of a Broadband NbTiN Traveling Wave Parametric Amplifier for MKID Readout

The sensitivity of microwave kinetic inductance detectors (MKIDs) using dissipation readout is limited by the noise temperature of the cryogenic amplifier, usually a HEMT with \(T_n \sim \) 5 K. A lower noise amplifier is required to improve NEP and reach the photon noise limit at millimeter wavelengths. Eom et al. have proposed a kinetic inductance traveling wave (KIT) parametric amplifier (also called the dispersion-engineered travelling wave kinetic inductance parametric amplifier) that utilizes the nonlinearity with very low dissipation of NbTiN. This amplifier has the promise to achieve quantum limited noise, broad bandwidth, and high dynamic range, all of which are required for ideal MKID dissipation readout. We have designed a KIT amplifier which consists of a 2.2 m long coplanar waveguide transmission line fabricated in a double spiral format, with periodic loadings and impedance transformers at the input/output ports on a 2 by 2 cm Si chip. The design was fabricated with 20 nm NbTiN films. The device has shown over 10 dB of gain from 4 to 11 GHz. We have found the maximum gain is limited by abrupt breakdown at defects in the transmission line in the devices. By cascading two devices, more than 20 dB of gain was achieved from 4.5 to 12.5 GHz, with a peak of \(\sim \) 27 dB.     

Two‐echelon manufacturer–retailer supply chain strategies with price,quality, and promotional effort sensitive demand

This study deals with the two‐layer supply chain model of one manufacturer and one retailer for a single commodity where market demand is assumed to be dependent on selling price, quality of the products, and promotional effort of the retailer. We investigate the behavior of the supply chain under centralized, manufacturer Stackelberg, conditional manufacturer Stackelberg, retailer Stackelberg, conditional retailer Stackelberg, and vertical Nash model structure. The nature of the above models provides great insights to a firm's manager for achieving optimal strategy in a competitive marketing system. Quite often, not all items produced in a firm are of perfect quality; some are perfect (conforming) quality and others are imperfect (nonconforming) quality. The nonconforming products are sold in a secondary shop or by other retailers. The procurement cost of finished products depends on the quality of the products due to more investment in advanced technology, better raw materials, and skilled labor, etc. The warranty policy for the products is also imposed to attract the customers to buy more. Here, both members (manufacturer and retailer) jointly share the cost of the warranty policy. The objective of this paper is to determine the optimal selling price and promotional effort of the retailer, while the optimal wholesale price and quality of the products are determined by the manufacturer so that the above strategies are maximized. Finally, numerical examples with sensitivity analysis of the key parameters are illustrated to investigate the proposed model.     

High dielectric permittivity and percolative behavior of polyvinyl alcohol/potassium dihydrogen phosphate composites

A new kind of anhydrous, transparent, and flexible potassium dihydrogen phosphate (KH₂PO₄ or KDP)/polyvinyl alcohol (PVA) composite in the form of film (0.10 mm) has been prepared by solution casting technique. KDP is well dispersed in the polymer matrix as observed from the microstructural studies. Frequency and temperature dependent dielectric properties of the composites have been studied with varying KDP concentrations. The PVA/KDP composite films exhibited extraordinarily high relative permittivity ε′ ∼ 430 (80 times higher compared with pure PVA and even higher than KDP) near the percolation threshold (ϕ_C = 2.5 wt % KDP) with low dielectric losses (∼ 0.15) at 1 kHz and room temperature. Such flexible, low loss and high dielectric permittivity material has enormous importance for application in devices. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012     

Destruction of percolative network using green synthesized gold nanoparticles: Formation of high dielectric material

Gold nanoparticles (AuNPs) of about 5 nm in diameter were biosynthesized at room temperature (300 K). The PVA/2.5 wt% KH₂PO₄ or KDP composite film and PVA/2.5 wt% KDP/AuNPs nanocomposite films with different concentrations of AuNPs were prepared. Interestingly, addition of 0.05 wt% of AuNPs to the PVA/2.5 wt% KDP percolative composite film destroys percolative behavior of this composite film. Furthermore, the PVA/2.5 wt% KDP/0.05 wt% AuNPs nanocomposite film exhibited high room temperature dielectric permittivity (ε′ ∼ 590 at 1 kHz). The behavior of AC conductivity (σ_ac) of the nanocomposite films indicated correlated barrier hopping type of conduction mechanism. The Cole–Davidson dielectric response becomes evident as the interfacial polarization process acquires a more symmetric form, tending to Debye relaxation. High value of ε′ promises direct application in capacitors. Moreover, the novel feature of destroying the percolative behavior by AuNPs may be applied even in other systems.     

Validity of modified Gompertz and Logistic models in predicting cell growth of Pediococcus acidilactici H during the production of bacteriocin pediocin AcH

Data for the cell growth of Pediococcus acidilactici H during the fermentative production of bacteriocin, pediocin AcH (taken from a previous study) was modeled by two sigmoidal functions, modified Gompertz and Logistic. Results showed that the models could adequately account for the cell growth up to the growth phase, but failed to account for the stationary and death phase.     

Ratiometric Interactions of Anionic Surfactants with Calf Thymus DNA Bound Cationic Surfactants: Study II

Cationic surfactant cetyltrimethylammonium bromide (CTAB) and cetylpyridinium bromide (CPB) bind to the calf thymus DNA (ct‐DNA) like anionic biopolymers electrostatically, and establish equilibrium in aqueous medium at pH 7. At low concentration, ct‐DNA does not interact with anionic surfactants, sodium dodecylsulfate (SDS) and sodium dodecylbenzylsulfonate (SDBS). However, in the ground state, anionic surfactant is found to clearly establish equilibrium with ct‐DNA‐bound cationic surfactant whereby the same surfactant–DNA isosbestic point reappears. We herein report a detail ratiometric binding of CPB with ct‐DNA, and interaction of anionic SDBS with DNA‐bound CPB in comparison with the combined ct‐DNA–CTAB–SDS system. Compaction of ct‐DNA in presence of CPB and its decompaction using anionic SDBS is also studied in comparison with CTAB–SDS combination. The techniques used are tensiometry, spectrophotometry, viscometry, cyclic voltammetry, circular dichroism, isothermal titration calorimetry, and density functional theory (DFT)‐based computational calculations. The size and surface charge density of the surfactant headgroups and the phosphate group in DNA have a contributing role in the DNA compaction–decompaction phenomenon.     

Bandwidth Enhancement of a Wide Slot Antenna Using Fractal Geometry for UWB Application with Multiple Notched Bands

Wireless Personal Communications - In this paper a combination of rectangular and elliptical fractal geometry is applied on a regular hexagonal wide slot antenna fabricated using a FR4 substrate to...     

Microstructural study of the titanium alloy Ti-15Mo-2.7Nb-3Al-0.2Si (TIMETAL 21S)

A relatively new titanium alloy, TIMETAL 21S (Ti-15Mo-2.7Nb-3Al-0.2Si-0.15O (in wt pct)), is a potential matrix material for advanced titanium matrix composites for elevated temperature use. In order to develop a perspective on the microstructural stability of this alloy, the influence of several commonly used heat treatments on the microstructure of TIMETAL 21S was studied using optical and transmission electron microscopy (TEM). Depending on the specific thermal treatment, a number of phases, includingα,ω- type, and silicide, can form in this alloy. It was found that both recrystallized and nonrecrystallized areas could be present in the microstructure of an annealed bulk alloy, but the microstructure of annealed sheet alloy was fully recrystallized. The mixed structure of the bulk alloy, developed as a result of inhomogeneous deformation, could not be removed by heat treatment alone at 900 °C. Athermalω-type phase formed in this alloy upon quenching from the solution treatment temperature (900 °C). Silicide precipitates were also found in the quenched sample. Thermal analysis was used to determine theβ transus and silicide solvus as close to 815 °C and 1025 °C, respectively. In solution-treated and quenched samples, a high-temperature aging at 600 °C resulted in the precipitation ofα phase. The precipitation reaction was slower in the recrystallized regions compared to the nonrecrystallized regions. During low-temperature aging (350 °C), the ellipsoidalω-type phase persisted in the recrystallized areas even after 100 hours, whereas a high density ofα precipitates developed in the nonrecrystallized areas within only 3 hours. The observed behavior in precipitation may be related to the influence of substructure in the nonrecrystallized areas, providing for an enhanced kinetics during aging. Theα precipitates (formed during continuous cooling from the solution treatment temperature, low-temperature aging, and high-temperature aging) always obeyed the Burgers orientation relationship. With respect to the microstructure, TIMETAL 21S is similar to other solute-lean, metastableβ titanium alloys.     

Avalanching flow of cohesive powders

The flow dynamics of cohesive powders is investigated in rotating cylinders with an L : R ratio of 3 : 1 using experiments and DEM simulations. Flow onset and steady-state behavior are compared for free-flowing (cohesionless) dry glass beads, wet glass beads, and “dry” cohesive powders (lactose, microcrystalline cellulose). The avalanching dynamics of powders is substantially different from those observed for free-flowing or wet-cohesive glass beads. Dry cohesive powders exhibit history-dependent flow dynamics, significant dilation, aperiodic avalanche frequencies, and variable avalanche size. These behaviors also provide a route for effective characterization of cohesive forces under dilated conditions characteristic of unconfined flows.