Natural vs. Synthetic Phosphate as Efficient Heterogeneous Compounds for Synthesis of Quinoxalines

Natural phosphate (NP) and synthetic fluorapatite phosphate (SFAP) were proposed as stable, inexpensive, readily available and recyclable catalysts for the condensation of 1,2-diamines with 1,2-dicarbonyls in methanol to afford quinoxaline at room temperature. NP provided as high as 92–99% yield for quinoxalines in short reaction times (i.e., 1–45 min), while SFAP created quinoxalines with 87–97% yield in 60–120 min. From the chemical analyses, X-ray fluoresecency, X-ray diffraction, energy dispersive X-ray and Fourier-transform infrared spectroscopy methods, two main phases (CaO, P₂O₅) appeared in NP together with other low content phases (SiO₂, Fe₂O₃). Compared to other phases, apatite (CaO and P₂O₅ as Ca10(PO₄)₆) played a major role in the catalytic activity of NP. SFAP with similar Ca/P atomic ratio showed a relatively lower catalytic activity than NP for the condensation of 1,2-diamine with 1,2-dicarbonyl in methanol at ambient temperature. To investigate the recyclability of catalysts, the surface properties of NP and 6-recycled NP were investigated using scanning electron microscopy, energy dispersive X-ray and Brunauer–Emmett–Teller and Barrett–Joyner–Halenda methods. Some differences were observed in NP and 6-recycled NP’s particle size, surface area, the volume and size of pores, and the content of elements; nevertheless, the use–reuse process did not noticeably change the catalytic property of NP.     

Cost analysis of a two unit, three state standby redundant complex system with two types of repair facilities under waiting

This paper deals with the cost analysis of a two unit, three state standby redundant complex system, incorporating the concept of two types of repair facilities, viz. minor and major repair. The concept of waiting time for the major repair of the failed system has also been introduced. The system can suffer from two types of failures, namely catastrophic and partial. Failure and waiting times of units follow exponential time distribution, whereas repair of units follows general time distribution. Using the supplementary variable technique, Laplace transforms of probabilities of the complex system being in various states have been computed. In addition, using Abel's lemma, steady state behaviour has also been examined. Some important graphs have been sketched at the end to highlight the important results.     

Reconfigurable Printed Liquids

Liquids lack the spatial order required for advanced functionality. Interfacial assemblies of colloids, however, can be used to shape liquids into complex, 3D objects, simultaneously forming 2D layers with novel magnetic, plasmonic, or structural properties. Fully exploiting all‐liquid systems that are structured by their interfaces would create a new class of biomimetic, reconfigurable, and responsive materials. Here, printed constructs of water in oil are presented. Both form and function are given to the system by the assembly and jamming of nanoparticle surfactants, formed from the interfacial interaction of nanoparticles and amphiphilic polymers that bear complementary functional groups. These yield dissipative constructs that exhibit a compartmentalized response to chemical cues. Potential applications include biphasic reaction vessels, liquid electronics, novel media for the encapsulation of cells and active matter, and dynamic constructs that both alter, and are altered by, their external environment.     

Dielectric parameters and a.c. conductivity of pure and doped poly (methyl methacrylate) films at microwave frequencies

Dielectric properties of pure and doped poly (methyl methacrylate) (PMMA) films at microwave frequency, 8.92 GHz, have been studied at 35°C. Iodine, benzoic acid and FeCl₃ have been used as dopants. The losses in doped films are found to be larger than in pure PMMA films. The increased losses account for increased a.c. conductivity in doped films. The increase in conductivity is accounted due to creation of additional hopping sites for the charge carriers in doped samples. The dielectric data has also been used to evaluate optical constants, absorption index (K) and refractive index (n) of the films.     

Anomalous specific heat of the La-Ge system

The specific heat of the orthorhombically distorted -ThSi₂-type La-Ge intermetallic compound system has been measured in the temperature range 0.07 T 10 K. An anomalous behavior of the lattice part of the specific heat has been discovered. The specific heat data are analyzed and discussions are given, with particular attention to the superlattice structure observed in these compounds.     

Shelf life prediction software finds application with ethical drugs

Applications for approval of new ethical drugs require that stability studies be completed prior to submission to the FDA. If the company chooses packaging which is found (by conventional storage testing) to provide insufficient barrier protection, new packaging must be identified and storage tests re‐run. This iterative process must be repeated until packages are found which provide adequate protection. If the chosen package is over‐protective, stability studies show adequacy, but do not identify over‐protection. A third option is to employ a myriad of test packs which impacts negatively on facilities and personnel, and is expensive and time‐consuming. Package optimization requires additional testing and re‐submission of the New Drug Application (NDA). A combination of analysis and computer shelf life predictions can be utilized to develop optimal packaging without such repetitive testing. A study was initiated with Searle to apply analytical evaluations and shelf life simulations to identify appropriate packaging for new drugs prior to the initiation of conventional stability testing. The procedure used analytical evaluations of two ethical drugs (without package protection) to identify the susceptibilities of the product to storage‐induced changes. The analytical results were then plugged into a computer shelf life modelling program which identified barrier requirements which would provide the protection found to be required for the drug product. This then defined the packaging needs. The efficacy of this modelling approach was confirmed for one product by conducting conventional stability studies with packaging materials which satisfied the barrier requirements which had been specified by the computer simulations. Storage studies for the second product are in process, and performance to date supports the predicted values. Copyright © 1999 John Wiley & Sons, Ltd.     

Device linearity and intermodulation distortion comparison of dual material gate and conventional AlGaN/GaN high electron mobility transistor

In the work proposed, linearity performance of dual material gate (DMG) AlGaN/GaN HEMT has been analyzed and compared with the corresponding performance of Single Material Gate (SMG) AlGaN/GaN HEMT using ATLAS device simulation. Specifically, we investigate the linearity of DMG and conventional AlGaN/GaN HEMT based on the linearity metrics such as g_m, g_m2, g_m3, VIP₂, VIP₃, IIP₃, IMD₃ and 1-dB compression point. The impact of various device parameters on the device linearity such as the channel length, doping and thickness of the barrier and spacer layer, Al mole fraction and the work function difference of the two gate metals has also been investigated. It is observed that a suitably designed DMG AlGaN/GaN HEMT can considerably improve the linearity performance and minimize intermodulation distortion due to reduced drain induced barrier lowering and high-field effect; and a more uniform electric field for applications in 3-G mobile communication and low noise amplifiers.     

Gate dielectric engineering of quarter sub micron AlGaN/GaN MISHFET: A new device architecture for improved transconductance and high cut-off frequency

In this paper analytical modeling for a novel three region gate dielectric engineered AlGaN/GaN Metal Insulator Semiconductor heterostructure field effect transistor (MISHFET) device architecture is presented which shows high transconductance and enhanced cut-off frequency at quarter micron gate lengths. Using a three region analysis along the horizontal direction in the gate dielectric region the expressions for transconductance and cut-off frequency of the device are obtained. It has been observed that using these gate dielectric schemes, improvements on device performance are observed over conventional MISHFET structures. Relative comparison of T and Γ-gate shaped structures is done with uniform gate dielectric profile and enhancement in microwave performance is observed. The proposed model is capable of modeling electrical characteristics like drain current, output conductance and threshold voltage of various other existent structures like uniform gate dielectric MISHFETs, HFETs and T-gate HFETs. The present model is based on closed form expression and does not involve any fitting parameter. The results obtained are compared with experimental data and show excellent agreement, thereby proving the validity of the model.     

Miniaturization of EISCAP sensor for triglyceride detection

In this paper we discuss the fabrication and characterization of miniaturized triglyceride biosensors on crystalline silicon and porous silicon (PS) substrates. The sensors are miniaturized Electrolyte Insulator Semiconductor Capacitors (mini-EISCAPs), which primarily sense the pH variation of the electrolyte used. The lipase enzyme, which catalyses the hydrolysis of triglycerides, was immobilized on the sensor surface. Triglyceride solutions introduced into the enzyme immobilized sensor produced butyric acid which causes the change in pH of the electrolyte. Miniaturized EISCAP sensors were fabricated using bulk micromachining technique and have silicon nitride as the pH sensitive dielectric layer. The sensors are cubical pits of dimensions 1,500 microm x 1,500 microm x 100 microm which can hold an electrolyte volume of 0.1 microl. The pH changes in the solution can be sensed through the EISCAP sensors by monitoring the flatband voltage shift in the Capacitance-Voltage (C-V) characteristics taken during the course of the reaction. The reaction rate is found to be quite high in the miniature cells when compared to the sensors of bigger dimensions.