Effect of SiC/Al2O3 particle size reinforcement in recycled LDPE matrix on mechanical properties of FDM feed stock filament

In this research work, an effort has been made to develop fused deposition modelling (FDM), feed stock filament wire from recycled low-density polyethylene (LDPE) with different particle sizes (i.e. single particle size (SPS), double particle size (DPS) and triple particle size (TPS) in different proportions) of SiC/Al₂O₃ as reinforcement. After evaluation of melt flow index (MFI), the best combinations were selected and used for filament wire preparation on twin screw extruder. The results of the study highlight that Al₂O₃-based DPS reinforcement resulted in better mechanical properties of the feed stock filament. Finally, the non-functional prototypes have been printed with feed stock filament prepared on open-source FDM. The Al₂O₃-based DPS reinforcement in LDPE resulted in better dimensional stability with improved surface hardness. The results have been supported by SEM-based photomicrographs and differential scanning calorimetry (DSC).     

Building bulk-resist model for image formation in chemically amplified resists at EUV

With the shrinkage of feature sizes, there is a need for bulk-resist models to evaluate resist performance in process simulators. This study investigates the sources of blur during image formation in chemically amplified resist (CAR) for extreme ultraviolet (EUV) exposure. It evaluates the acid generation blur due to photo acid generator (PAG) activation before post exposure bake (PEB) and the de-protection blur during PEB due to diffusion–reaction coupling of generated acids in the resist. The acid generation bulk-resist model is derived from the molecular formulation of resists [T. Kozawa, A. Saeki, S. Tagawa, Appl. Phys. Exp. 1 (2008) 027001]. While, the PEB de-protection blur is obtained from a chemical kinetics model [F.A. Houle, et. al. J. Vac. Sci. Technol. B19 (2000) 1874]. These derived bulk-resist models depend largely on the experimental data for obtaining resist-blur (kernel) parameters. In order to present the complete image formation in resist, an optimization model is proposed to build the kernel functionality and extract the kernel parameters using EUV critical dimension (CD) data on the test pattern.     

Dielectric and Impedance Spectroscopy of Barium Orthoniobate Ceramic

Barium orthoniobate (Ba₃Nb₂O₈), a derivative of the perovskite family, was prepared using a high-temperature solid-state reaction technique (calcination temperature = 1425°C and sintering temperature = 1450°C for 4 h). Preliminary x-ray structural analysis with room-temperature x-ray diffraction data confirmed the formation of a single-phase compound with hexagonal crystal structure. Study of the microstructure of a gold-coated pellet by scanning electron microscopy (SEM) showed that the sample has well-defined grains that are distributed uniformly throughout the surface of the sample. Detailed studies showed that the dielectric parameters (ε _r and tan δ) of the compound at three different frequencies (10 kHz, 100 kHz, and 1000 kHz) are almost constant in the low-temperature region (from room temperature to about 200°C). An anomaly in the relative permittivity (ε _r) (～357°C) suggests the possible existence of a ferroelectric–paraelectric phase transition of diffuse type in the material. Detailed studies of impedance and related parameters show that the electrical properties of the material are strongly dependent on temperature, showing good correlation with its microstructure. The bulk resistance (evaluated from impedance studies) is found to decrease with increasing temperature. This shows that the material has negative temperature coefficient of resistance (NTCR), similar to that of semiconductors. Studies of electric modulus indicate the presence of a hopping conduction mechanism in the system with nonexponential-type conductivity relaxation. The nature of the variation of the direct-current (dc) conductivity with temperature confirms the Arrhenius and NTCR behavior in the material. The alternating-current (ac) conductivity spectra show a typical signature of an ionic conducting system and are found to obey Jonscher’s universal power law.     

Dielectric and Pyroelectric Properties of La- and Pr-Modified Tungsten-Bronze Ferroelectrics

The polycrystalline materials Li₂Pb₂R₂W₂Ti₄Nb₄O₃₀ (R = La, Pr) of the tungsten-bronze structural family have been synthesized using a high-temperature mixed-oxide method. Room-temperature x-ray diffraction (XRD) analysis confirms the formation of single-phase compounds. Room-temperature scanning electron micrography of the pellet samples shows a uniform distribution of well-defined different sizes of grains on the surface of the samples, confirming the formation of single-phase compounds. Study of the frequency and temperature dependence of the dielectric constant and loss tangent suggests the existence of dielectric dispersion in the materials. The ferroelectric phase transition in the samples has been studied based on the variation of fitting parameters (calculated from a theoretical model) with temperature. Studies of pyroelectric properties [figure of merit (FOM) and coefficient] show that the materials have reasonably high FOM useful for pyroelectric detectors. The variation of alternating-current (AC) and direct-current (DC) conductivity with inverse absolute temperature (obtained from dielectric data) follows a typical Arrhenius relation. The low leakage current and negative temperature coefficient of resistance behavior of the samples have been verified from J–E plots.     

Electrical Characteristics of Al/Poly(methyl methacrylate)/p-Si Schottky Device

Al/Poly(methyl methacrylate)(PMMA)/p-Si organic Schottky devices were fabricated on a p-Si semiconductor wafer by spin coating of PMMA solution. The capacitance–voltage (C–V) and conductance–voltage (G–V) characteristics of Al/PMMA/p-Si structures have been investigated in the frequency range of 1 kHz–10 MHz at room temperature. The diode parameters such as ideality factor, series resistance and barrier height were calculated from the forward bias current–voltage (I–V) characteristics. In order to explain the electrical characteristics of metal–polymer–semiconductor (MPS) with a PMMA interface, the investigation of interface states density and series resistance from C–V and G–V characteristics in the MPS structures with thin interfacial insulator layer have been reported. The measurements of capacitance (C) and conductance (G) were found to be strongly dependent on bias voltage and frequency for Al/PMMA/p-Si structures. The values of interface state density (D _it) were calculated. These values of D _it and series resistance (R _s) were responsible for the non-ideal behavior of I–V and C–V characteristics.     

Optimizing the Energy Consumed by Secure Wireless Sessions – Wireless Transport Layer Security Case Study

In this paper we identified the various sources of energy consumption during the setup, operation and tear down of a secure wireless session by considering the wireless transport layer security protocol. Our analysis showed that data transfers during a secure wireless transaction, number and size of messages exchanged during secure session establishment and cryptographic computations used for data authentication and privacy during secure data transactions in that order are the main sources of energy consumption during a secure wireless session. We developed techniques based on information compression, session negotiation protocol optimization and hardware acceleration of crypto-mechanisms to reduce the energy consumed by a secure session. A mobile test bed was developed to verify our energy management schemes and to study the energy consumption versus security tradeoffs. Using our proposed schemes we were able to reduce the session establishment energy by more than 6.5× and the secure data transaction energy by more than 1.5× during data transmission and by more than 2.5× during data reception.     

Design of a hard real-time multi-core testbed for energy measurement

This paper presents a systematic methodology for designing a hard real-time multi-core testbed to validate and benchmark various rate monotonic scheduling (RMS)-based task allocation and scheduling schemes in energy consumption. The hard real-time multi-core testbed comprises Intel Core Duo T2500 processor with dynamic voltage scaling (DVS) capability and runs the Linux Fedora 8 operating system supporting soft real-time scheduling. POSIX threads API and Linux FIFO scheduling policy are utilized to facilitate the design and Dhrystone-based tasks are generated to verify the design. A LabView-based DAQ system is designed to measure the energy consumption of CPU and system board of the testbed. A case study of task allocation and scheduling algorithms is also presented that aim to optimize the schedule feasibility and energy consumed by the processor and memory module in the multi-core platform. The experience from the implementation is summarized to serve as potential guidelines for other researchers and practitioners.     

Microwave assisted enzyme catalysis for synthesis of <Emphasis Type="Italic">n-</Emphasis>butyl dipheyl methyl mercapto acetate in non-aqueous media

n-Butyl dipheyl methyl mercapto acetate is an important pharmaceutical intermediate, having applications in the synthesis of Modafinil, a CNS stimulant drug. The current process is highly polluting and requires alternate green processes. Synthesis of it was carried out via lipase in the presence of microwave irradiation. Optimization of reaction conditions, such as catalyst loading, mole ratio of reactants, reaction temperature, water concentration and reusability of catalysts under the microwave irradiation was done. Among all, the commercially available lipases Novozym 435 was found best and gives the conversion 34% in 24 h at 60°C. A ping–pong bi–bi model with substrate n-butanol inhibition at higher concentration was found to be suitable for kinetics of the reaction.     

Synthesis and characterization of Na2Pb2Pr2W2Ti4Ta4O30

A new complex oxide (Na₂Pb₂Pr₂W₂Ti₄Ta₄O₃₀) of tungsten bronze structural family has been synthesized by a high-temperature solid-state reaction (mixed-oxide) route at 1,050 °C. Room temperature structural analysis shows the formation of a single phase new compound. Study of microstructure of the pellet sample, recorded by scanning electron microscope, exhibits the uniform distribution of different size and shape of grains (with a few small voids) on the surface of the sample. Detailed studies of dielectric properties as a function of frequency and temperature show a dielectric anomaly above room temperature suggesting the existence of a ferroelectric phase transition in the material. Impedance spectroscopic analysis and electrical conductivity of the material exhibit a strong correlation between microstructure and electrical parameters. The temperature dependence of dc conductivity of the compound follows Arrhenius equation. The frequency and temperature dependence of ac conductivity (with fittings) shows the signature of Jonscher’s universal power law. The existence of non-exponential-type of conductivity relaxation in the compound was confirmed.     

On the interaction of Class C fly ash with Portland cement–calcium sulfoaluminate cement binder

Shrinkage cracking in concrete is a widespread problem, especially in concrete structures with high surface-to-volume ratio such as bridge decks. Expansive cements based on calcium sulfoaluminate phase were developed to mitigate the shrinkage cracking of concrete. The compressive stress induced due to restrained expansion of concrete has been shown to counteract the tensile stress generated during drying shrinkage. This research attempts to address the differential behavior of fly ash type (i.e., Class C vs. Class F) on early-age expansion and hydration characteristics of ordinary Portland cement (OPC)–calcium sulfoaluminate (CSA) cement blend. It was observed earlier that the presence of Class C fly ash (CFA), unlike Class F fly ash, shortened the expansion duration of OPC–CSA cement blend, which was hypothesized to be correlated to early depletion of gypsum. This paper presents a detailed verification of the hypothesis. Addition of external gypsum to OPC–CSA–CFA blend led to simultaneous increase in expansion and disappearance of a shoulder peak in the calorimetric curve. Thermodynamic calculations using a geochemical modeling program (GEMS-PSI) revealed higher saturation levels of ettringite in presence of external gypsum, which led to higher crystallization stress, and thereby increased expansion.