Terahertz graphene optics

The magnitude of the optical sheet conductance of single-layer graphene is universal, and equal to e ²/4? (where 2??? = h (the Planck constant)). As the optical frequency decreases, the conductivity decreases. However, at some frequency in the THz range, the conductivity increases again, eventually reaching the DC value, where the magnitude of the DC sheet conductance generally displays a sample- and doping-dependent value between ??e ²/h and 100 e ²/h. Thus, the THz range is predicted to be a non-trivial region of the spectrum for electron transport in graphene, and may have interesting technological applications. In this paper, we present the first frequency domain measurements of the absolute value of multilayer graphene (MLG) and single-layer graphene (SLG) sheet conductivity and transparency from DC to 1 THz, and establish a firm foundation for future THz applications of graphene.      

Ultrasonic machining of biomass using biodegradable slurry

Thrombi, e.g. blood clots, in circulatory system pose acute health risk, globally. This research investigated roles of biodegradable starch slurry in advancing biomass machining efficiency. Hard clots (fibrin-rich) prepared from rabbit blood were exposed in vitro concomitantly to ultrasound (1 MHz) and starch slurry. Starch slurry particles (diameter ∼250 nm) yielded a 200% increase in material removal (sonothrombolysis) efficiency. Mechanistic participation of starch, a non-Newtonian material, at the interface of biomass-ultrasonic radiation is discussed. Overall in subtractive biomanufacturing, the role of biodegradable slurry is critical for enhancing material removal efficiency.     

The present status of subsiding land vulnerable to roof collapse in the Jharia Coalfield,India, as obtained from shorter temporal baseline C-band DInSAR by smaller spatial subset unwrapped phase profiling

In this paper, we identified recently subsiding areas in Jharia Coalfield, Jharkhand, India from the shorter temporal baseline Radarsat-2 C-band interferometric synthetic aperture radar (InSAR) data pairs of 2012. Although shorter wavelength C-band differential InSAR (DInSAR) is more sensitive to slow deformation and better suited for higher precision land subsidence measurement, the dynamic and adverse land cover in mining areas and resulting temporal decorrelation problem poses a serious problem for DInSAR observation in mining areas. We used smaller temporal baseline data pairs and adopted InSAR coherence-guided incremental filtering with smaller moving windows to highlight the deformation fringes over temporal decorrelation noise. We identified the deformation fringes and validated them based on ground information to prepare the land subsidence map of the coalfield in 2012. Several new, previously unreported subsidence areas were detected in the present study with a total subsiding area of 6.9 km². The recent incidence of roof collapse on 15 November 2014 at Angar Patra village in Katras region of the coalfield where 45 houses collapsed and 10 people were injured is situated in a highly subsiding vulnerable area as obtained from the present study. Due to spatial discontinuities of InSAR coherence, DInSAR phase unwrapping for the entire study area in one go did not appear feasible. To avoid this problem, we performed DInSAR processing in smaller spatial subsets and unwrapping of the subset interferograms by a ‘minimum cost flow’ algorithm. Subsequently, we plotted unwrapped phase profiles across the deformation fringes and retrieved the maximum deformation phase with respect to background phase and translated them into radar line of sight (LOS) displacement rates. For obtaining the average subsidence rates, we adopted InSAR coherence-weighted LOS displacement rates taking into account the contribution of each data pair as a function of DInSAR phase quality of the fringe areas. Ground-based subsidence measurements by precision levelling were conducted in four test sites that had been undergoing active underground mining during the observation period. We compared space-borne DInSAR-based subsidence rates obtained by the adopted technique with precision levelling measurements. Overall, the results are found to agree well. In the four test sites with gentle to flat topography, land subsidence occurs at slow to moderate rates due to compression of in-filled material (resulting from sand stowing in underground mining), without any evidence of roof collapse. In such cases, the horizontal displacement component is less significant, and overall surface displacement occurs essentially in the vertical direction. However, we assessed the nature of subtle horizontal strain to infer relative shrinkage or dilation of the land surface which could be additive or subtractive to vertical displacement in DInSAR-based LOS displacement.     

Control design approach for improved voltage stability in microgrid energy storage system

Microsystem Technologies - Nowadays, microgrid energy storage system is in great demand in order to compensate the demand-generation mismatch. In this study a new control design strategy is...     

Correlated micro-photoluminescence and electron microscopy studies of the same individual heterostructured semiconductor nanowires

To correlate optical properties to structural characteristics, we developed a robust strategy for characterizing the same individual heterostructured semiconductor nanowires (NWs) by alternating low temperature micro-photoluminescence (μ-PL), low voltage scanning (transmission) electron microscopy and conventional transmission electron microscopy. The NWs used in this work were wurtzite GaAs core with zinc blende GaAsSb axial insert and AlGaAs radial shell grown by molecular beam epitaxy. The series of experiments demonstrated that high energy (200 kV) electrons are detrimental for the optical properties, whereas medium energy (5-30 kV) electrons do not affect the PL response. Thus, such medium energy electrons can be used to select NWs for correlated optical-structural studies prior to μ-PL or in NW device processing. The correlation between the three main μ-PL bands and crystal phases of different compositions, present in this heterostructure, is demonstrated for selected NWs. The positions where a NW fractures during specimen preparation can considerably affect the PL spectra of the NW. The effects of crystal-phase variations and lattice defects on the optical properties are discussed. The established strategy can be applied to other nanosized electro-optical materials, and other characterization tools can be incorporated into this routine.     

Application of a real-time predictive maintenance system to a production machine system

This paper develops earlier work that established the possibility of the classification of machine system parameters on the basis of motion current signature, using a neural network approach. A neural network requires a large amount of training data, which is impractical to generate using a production machine for real-time predictive maintenance system. Hence, a simulation model, which mapped the system parameters to the motion current signature, was developed. The accuracy of the system, to predict the changes in the value of the machine system parameter, is a direct function of the validity of the simulated data. Thus, the objective validation of the simulation model is important to ascertain that the simulation model is accurate with regards to its purpose.In this paper, the simulation model is validated against an on-line production machine. Various approaches to validate the simulation model are applied and a simulation model is developed.     

Emerging trends in information and communication technology in mine safety and disaster management

There is tremendous growth in the use of Geographic Information Systems (GIS), Global Positioning Systems (GPS), Remote Sensing, Satellite Communication, and Modeling &; Simulation techniques. These tools and techniques helps significantly in characterizing infrastructure, risk area and disaster zones, planning and implementation of hazards reduction measures etc. Communication satellites becomes vital for providing emergency communication and timely relief measures. Integration of space technology inputs into natural disaster monitoring and mitigation mechanisms is critical for hazard reduction. This paper mainly focused on all the issues described above. Major emphasis had been given to the recent developments in information &; communication technology enabled tools and their applications in mining industries for safe mining operations with increased productivity.     

Mine surface subsidence monitoring due to impacts of underground mining using persistent scatterer interferometry

The Singhbhum shear zone in India is well known for its historical underground copper mining activity. As a consequence, today some abandoned underground mines pose a serious risk to the local people and property. Thus it is essential for a long-term wide-range monitoring technique to map the surface subsidence over the mining areas. In this study, it has been tried to establish occurrence of ground subsidence with an advanced differential interferometric synthetic aperture radar technology called persistent scatterer interferometry, which is known for its capability of high-precision monitoring. The results clearly indicate trends of surface subsidence over abandoned mining regions.     

Stress Assessment in Precipitation Hardened IN718 Nickel-Base Superalloy Based on Hall Coefficient Measurements

The feasibility of residual stress assessment in precipitation hardened IN718 nickel-base superalloy based on Hall coefficient measurement is investigated through studying the influence of thermal hardening, cold work, and applied stress. Measurements in IN718 specimens of various hardness levels show that the Hall coefficient increases from 8 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in the fully annealed state of 14 HRC to 9.4 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in the fully hardened state of 45 HRC. Measurements in IN718 specimens of various cold work levels show that plastic deformation exerts negligible effect on the Hall coefficient of fully annealed IN718, while in fully hardened IN718 the Hall coefficient decreases more or less linearly with cold work from its peak value of 9.4 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in its intact state to 8.9 ± 0.1\(\,\times \,\)10\(^{-11}\) m\(^{3}\)/C in its most deformed state of 22% plastic strain. Measurements taken under applied stress show that elastic strain significantly increases the Hall coefficient of IN718 regardless of the state of hardening. The relative sensitivity of the Hall coefficient to elastic strain is called the galvanomagnetic gauge factor and defined as the ratio of the relative change of the Hall coefficient divided by the axial strain under applied uniaxial stress. The gauge factor of IN718 is in the range of 2.6–2.9 depending on the hardness level. Besides the fairly high value of the gauge factor, it is important that it is positive, which means that compressive stress in surface-treated components decreases the Hall coefficient in a similar way as plastic deformation does, therefore the unfortunate cancellation that occurs in fully hardened IN718 in the case of electric conductivity measurements does not happen in this case. In addition, the influence of thermal exposure up to 700 \({{}^{\circ }}\)C and the reversible temperature dependence of the Hall coefficient at room temperature are studied in IN718 at different hardness levels.     

On the energy consumption of Pure and Slotted Aloha based RFID anti-collision protocols

A recent development in wireless sensor networks (WSNs) research is to equip sensor nodes with an RFID reader so that they can be used to track animate or in-animate RFID tagged objects. A key problem in such networks, however, is the energy efficiency of current RFID anti-collision protocols. Specifically, the energy cost incurred by a RFID reader to read and monitor n tags.This paper, therefore, aims to identify the most energy efficient variant among 12 Pure and Slotted Aloha based RFID anti-collision protocols. We present an analytical methodology that evaluates the energy consumed in the following phases: (i) success, (ii) collision, and (iii) idle listening. We first calculate the delay of each phase and then use it to formulate the energy consumption, battery lifetime, and battery wastage of all variants. We found that the Pure Aloha with fast mode consumes the lowest energy and is suitable for tag identification. However, none of the protocols promises energy efficient monitoring of identified tags. In other words, the reader is required to re-read all tags every time to sense their presence; a process that consumes a significant amount of energy.