Recent research and development has been incredibly successful at advancing the capabilities for vacuum electronic device (VED) sources of powerful terahertz (THz) and near-THz coherent radiation, both CW or average and pulsed. Currently, the VED source portfolio covers over 12 orders of magnitude in power (mW-to-GW) and two orders of magnitude in frequency (from ; 10 THz). Further advances are still possible and anticipated. They will be enabled by improved understanding of fundamental beam-wave interactions, electromagnetic mode competition and mode control, along with research and development of new materials, fabrication methods, cathodes, electron beam alignment and focusing, magnet technologies, THz metrology and advanced, broadband output radiation coupling techniques.

Vacuum Electronic High Power Terahertz Sources

Biodiesel production using heterogeneous catalysts.

Steep hikes of petroleum prices and rising demand of petroleum products compels the scientific society to think for the renewable alternative fuels like biodiesel. Biodiesel production is generally carried out through the process of transesterification reaction. The reaction is facilitated with a suitable catalyst either homogeneous or heterogeneous. The selection of appropriate catalyst depends on the amount of free fatty acids in the oil. Heterogeneous catalyst provides high activity, high selectivity, high water tolerance properties and these properties depend on the amount and strengths of active acid or basic sites. Basic catalyst can be subdivided based on the type of metal oxides and their derivatives. Similarly, acidic catalyst can be subdivided depending upon their active acidic sites. New varieties of mixed catalyst are also available in literatures. Catalyst generated from bio-waste and other biocatalysts which are heterogeneous in nature and extensively reported in literature are also reviewed. This review focused about the recent invention and use of the heterogeneous acid, base and biocatalysts for biodiesel production and their suitability for industrial application.

Modern heterogeneous catalysts for biodiesel production: A comprehensive review

Ultra-high temperature ceramics: Materials for extreme environments

Foundations For Microwave Engineering

Part 1: Coulomb's law Gauss' law in integral and differential (point) forms gradient of potential Poisson's and Laplace's equations Biot-Savert's law Ampere's law in integral and differential (point) forms magnetic vector potential Lorentz force continuity equation displacement current Faraday's law in integral and differential (point) forms Maxwell's equations wave equation skin depth and surface resistance boundary conditions Poynting vector and power flow. Part 2: Sheath and tape models of a helix field and equivalent circuit analyses dispersion relation characteristic and interaction impedances anisotropically and inhomogeneously loaded broad-band helical structures parallel-flow Pierce electron gun - Langmuir-Blodgett's law beam spread anode-aperture lens effects synthesis for gun dimensions conformal mapping of electrode shapes magnetic confinement of a linear electron beam Busch's theorem Brillouin conditions confined flow stability condition for a periodic permanent (PPM) structure growing-wave interaction - dispersion relation and Pierce's gain formula for a slow-wave TWT space-charge wave amplification in double-stream and beam-plasma amplifiers dispersion relation and Pierce-type gain formula for a fast-wave gyro-TWT.

Electromagnetic Theory and Applications in Beam-Wave Electronics

Investigating the enzyme-lignin binding with surfactants for improved saccharification of pilot scale pretreated wheat straw.

A model of a vane-loaded helical slow-wave structure (SWS), in which an infinite number of vanes (INV) of infinitesimal thickness is considered, is improved. The modified INV (MINV) model takes into account the effect of the finite number and angular thickness of the vanes. This is done by suitably modifying the radial vane dimension on the basis of the interpretation of the data on the penetration of the axial electric field beyond the tips of the vanes into the intervane region as a function of the SWS parameters, including the number and angular extent of vanes. The theoretical dispersion characteristics obtained from both the INV and MINV models are compared to theoretical and experimental results published elsewhere. The INV model is found to be suitable for a structure with a relatively larger number of vanes. The study shows the superiority of the MINV over INV model in practical situations, wherein relatively fewer vanes of finite angular thickness are used. Methods to estimate the characteristic as well as interaction impedance of the structure, under the INV model approximations, are indicated. >

Modeling of a vane-loaded helical slow-wave structure for broad-band traveling-wave tubes

The discrete longitudinal dielectric support bars for a TWT helical slow-wave structure of either of the circular and rectangular cross sections have been analyzed using the theoretical approach of smoothing out the supports azimuthally into a large number of dielectric tubes of their respective effective permittivity values. The number of such tubes is increased to a very large value in order to ensure converging results for better theoretical predictions. The method has been applied to study the dispersion characteristics of a helix in a metal envelope. The method has a special significance for better results for high-permittivity supports, large helix-to-envelope separation and high operating frequencies. The theoretical predictions are also compared with experimental values available elsewhere. The theoretical method suggested is general and is applicable to arbitrarily shaped support bars as well as to both glass/ceramic and metal envelopes.

Biswajit Basu

Papers

Electromagnetic Theory and Applications in Beam-Wave Electronics

Investigating the enzyme-lignin binding with surfactants for improved saccharification of pilot scale pretreated wheat straw.

Modeling of a vane-loaded helical slow-wave structure for broad-band traveling-wave tubes

The inhomogeneous loading effects of practical dielectric supports for the helical slow-wave structure of a TWT

Characterization of Indian origin oil shale using advanced analytical techniques