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The aging analysis of nuclear power plant components and materials is crucial for the power plant's safety, and for its upgradation and life extension. The health monitoring of power plant materials, such as steel, is mostly done by employing conventional non-destructive evaluation (NDE) techniques. Considering the limitations associated with conventional NDE techniques, thermoelectric power based NDE (TNDE) is being explored. This paper presents the first ever development and successful demonstration of TNDE in Pakistan. Moreover, the aging analysis of carbon steel grade SA 106B is also being presented for the first time. The extractionsteam pipe samples (new and aged) of SA 106B, from a 46-years-old operating nuclear power plant, are being analyzed and the sensitivity of TNDE to aging induced changes in microstructure is demonstrated. Further, the aged SA 106B is simulated via heat treatment and the equipment is calibrated for its utilization in the nuclear power plant. The correlation between thermoelectric power (TEP) and Vicker hardness (HV) [TEP (µV/oC) = ~2x10-5 Hardness (HV) + 0.008] has been analyzed. It is revealed that the technique has the potential to analyze mechanical properties of aged extraction steam piping without cutting and taking the samples to the laboratory. [ABSTRACT FROM AUTHOR]

Large area ratio nozzles that are employed for space propulsion applications are not meant to be tested at the ground- level conditions because of the flow conditions that occurs in their divergent section due to their low exhaust pressures. Therefore, it is desired to perform the experimental evaluation at high-altitude to evaluate the performance of the said nozzles. Generally, a high-altitude test facility, consisting of a supersonic exhaust diffuser, is generally employed. In this paper, a second-throat exhaust diffuser has been numerically investigated to predict its minimum starting pressure, and to understand the flow physics in the diffuser using Computational Fluid Dynamics (CFD). Numerical computation of the flow field in the diffuser system is done for the two cases: 1) when the nozzle and the diffuser system are initially evacuated to a low pressure, and 2) when the nozzle and the diffuser system are initially at ambient pressure (1 bar). Simulations have been carried out for cold flow situation (Û=1.4) over a range of nozzle inlet stagnation pressures. Numerical results compare favorably with the theoretical and experimental results and provide adequate insight to the flow physics and internal shock structures formed in the diffuser in addition to minimum starting pressure, diffuser wall pressure and vacuum thrust. [ABSTRACT FROM AUTHOR]

Various organizations have plunged towards cloud computing solutions because of high cost, storage space and maintenance issues from big data. Big data is utilized by institutions in decision making process to achieve valuable insights in real time. Nevertheless big data has indeed helped organizations, and even small to medium-sized businesses, but it characteristics has posed great challenges at same time. The cloud platform has facilitated in handling computational, networking and storage capacity related issues but still these mechanisms are inadequate to deal with the rapid data explosion. Moreover data is not secure in Cloud Environment as the servers are governed by third party. In recent years fusion of big data and blockchain technology has pushed big data beyond imagination and imparted great prospective in better-quality big data services and applications. Organizations certainly will adopt these two emerging technologies to transform their business needs. In this paper we present an overview of security related issue of big sensitive data on cloud platform along with motivation behind paradigm shift i.e. Integration of big data and blockchain technology. [ABSTRACT FROM AUTHOR]

A 3-D finite-difference time-domain analysis of a photoconductive-semiconductor-switch-based terahertz (THz) source, integrated with a standard dipole and a large-aperture radiator, is presented. The simulation analysis is based on the coupling of semiconductor equations for charge transport with Maxwell electromagnetic equations. The simulation provides the transient field redistribution, carrier generation characteristics, and the field acceleration as a result of the bias voltage on the device, contributing to the nonlinear behavior of THz-pulse generation. A comparison of the radiation characteristics of the two antenna types shows that the large-aperture antenna produces approximately three times higher radiation amplitude and broader power spectrum than those produced by the dipole antenna. Index Terms--Finite-difference time-domain (FDTD) method, high-power photoconductive antenna, terahertz (THz)-pulse generation.

Experiment and electromagnetic-topology (EMT)-based simulation are performed to study the effects of wideband EM pulses on large electrical systems. The EMT simulation relies on the topological modular junction concept with the simultaneous use of a number of analytical and computational methods, including the transmission-line-matrix compaction method, the finite-difference time-domain method, and the reciprocity theorem, to come up with a final result. The EMT simulation approach that uses the topological modular concept is an effective way to perform tradeoff analysis of different wideband pulse excitations without having to repeat the simulations of the entire system. As part of validating the EMT simulation approach, we performed the experiment to measure the current induced by a wideband EM pulse on a cable behind a slot aperture. The simulated current and the measured current resulted in good agreement with each other, thus demonstrating the validity of the proposed simulation scheme. Index Terms--Aperture-cable coupling, electromagnetic topology (EMT), wideband pulse interaction.

The ON-state characteristics of a 6-H silicon carbide (SIC) photoconductive switch with vertical geometry, transverse illumination, and linear-mode operation are presented. The switch is triggered by an optical source with a photon energy that is less than the bandgap energy of SiC. Following low-power matching characteristics, the analysis of a design incorporating [n.sup.+] and [p.sup.+] layers next to the cathode shows higher hold-off voltage with an improved ON-state response mechanism. The p-layered photoconductive semiconductor switch (PCSS) can be operated at a maximum field of 875 kV/cm, whereas the n-layered PCSS, which is operating at a slightly lower field, shows higher current carrying capabilities. Higher current for the n-layer PCSS can be attributed to the nature of the region adjacent to the cathode. In the p-layered PCSS, this region inhibits an initial hole collection, thus decreasing the collected charge. In addition, a kink during the initial collection for the p-layered PCSS could influence the rise time when operating beyond 35-kV bias. Index Terms--High-power microwaves, photoconductive semiconductor switches (PCSSs), silicon carbide (SIC).

In this paper, the response of a semi-insulating gallium arsenide photoconductive switch used in high-power microwave generation has been analyzed through experiment and simulation. The switch characteristics as a result of trapping and detrapping phenomena during a transient are studied. Analysis show that field-enhanced capture at high field locations during the onstate creates a temporary reservoir of trapped charge at different pockets in the device. Release of trapped charge and the subsequent injection of carriers from the contacts to maintain charge neutrality helps maintain conduction, which persists even after the laser pulse until all charges are transferred across the device. A model has been presented which can explain such phenomena as lock-on effect, persistent conductivity, and low-power requirement during transients. This phenomenon is unique to semi-insulating gallium arsenide and is primarily due to field-enhanced trapping and could be applicable to other materials that have similar characteristics. Index Terms--Gallium arsenide, lock-on, nonlinear photoconductive switch, semi-insulating.

The response of a nonlinear opposed contact GaAs photoconductive switch, which is used in high-power microwave generation, was studied for high-power radio-frequency heating effects and compared with a linear-mode SiC switch. Current-controlled negative resistivity behavior was observed at elevated temperature in both cases. Better thermal conductivity and the absence of a heat sink result in a faster temperature increase and in local thermal carrier generation in SiC. Negative resistivity characteristics leading to unstable filamentation and thermal runaway are therefore more severe and occur at a lower bias in SiC as compared with a GaAs switch. To counter such effects, mechanisms to remove excess heat in switches in high-power application must be devised. Index Terms--High-power microwaves (HPMs), photoconductive semiconductor switches (PCSSs), radio-frequency (RF) heating effects.

Photoconductive semiconductor switches (PCSSs) made from semi-insulating (SI) GaAs are the primary switching component of one class of high-power, ultra-wideband (UWB) microwave sources. The high resistivity of the GaAs can be achieved through different processing techniques. The resultant device characteristics of the PCSS such as breakdown voltage, rise time, and turn-on delay will depend on the actual processing technique that was used for the material. Simulation studies comparing an intrinsic material and a high resistivity SI GaAs PCSS grown through the liquid-encapsulated Czochralski (LEC) process with a deep donor and shallow acceptor compensation mechanism highlight these differences. Simulations also elucidate the role of an [n.sup.+] -doped layer placed next to the cathode, which increases the breakdown voltage of the device. Extending the [n.sup.+] layer length beyond the cathode does not yield further improvement but leads to current confinement along a narrow strip that can initiate local heating or burnout. The doping profile of the [n.sup.+] layer also affects hold-off characteristics, a faster gradient ensuring better protection of the cathode against the substrate field, and electron injection. Doping the [n.sup.+] region with a higher concentration of carbon impurities does not produce the same effect as doping the [n.sup.+] -SI interface. These material-related issues are critical to further extending the performance characteristics of PCSSs. Index Terms--Fast semiconductor switching, photoconductive semidconductor switches (PCSS), ultra-wideband microwave sources (UWB).