Electron Paramagnetic Resonance and Photoluminescence Studies of LaMgAl11O19:Mn2+ Green Phosphors

Manganese-doped LaMgAl₁₁O₁₉ powder has been prepared by an easy combustion method. Powder x-ray diffraction and scanning electron microscopy have been used to characterize the as-prepared phosphor. The electron paramagnetic resonance (EPR) spectrum of LaMgAl₁₁O₁₉:Mn²⁺ phosphor exhibits six-line hyperfine structure centered at g ≈ 1.973. The number of spins participating in resonance (N) and the paramagnetic susceptibility (χ) for the resonance signal at g ≈ 1.973 have been calculated as a function of temperature. The photoluminescence spectrum exhibits green emission at 516 nm, which is attributed to ⁴T₁ → ⁶A₁ transition of Mn²⁺ ions. From EPR and luminescence studies, it is observed that Mn²⁺ ions occupy Mg²⁺ sites and Mn²⁺ ions are located at tetrahedral sites in the prepared phosphors.     

Synthesis of initializable asynchronous circuits

We show that existing synthesis techniques may produce asynchronous circuits that are not initializable by gate level analysis tools even when the design is functionally initializable. Due to the absence of any initialization sequence, a fault simulator or test generator that assumes an unknown starting state will be completely ineffective for these circuits. In this paper, we show that proper consideration of initializability during the asynchronous circuit synthesis procedure can guarantee initializable implementations. We show that the assignment of don't cares during the synthesis procedure affects the initializability of the final implementation. We present a novel implicit enumeration procedure that selectively assigns don't cares to obtain an initializable implementation. Initialization sequences are obtained as a by-product of our synthesis procedure     

Initialization issues in asynchronous circuit synthesis

A design specification is said to be functionally uninitializable if an initializable implementation cannot be obtained. Due to the absence of any initialization sequence, a fault simulator or test generator that assumes an unknown starting state will be completely ineffective for uninitializable circuits. We present a novel procedure for synthesizing initializable asynchronous circuits from functionally uninitializable Signal Transition Graphs (STG). After characterizing the necessary conditions for functional uninitializability, we propose a technique that transforms the original STG into an equivalent, functionally initializable STG. We show that the presence of concurrency provides the designer with an extra degree of flexibility when implementing the circuit. It is shown that initializability can be achieved by sacrificing minimal concurrency and without violating the syntactic properties of the STG required for a hazard-free implementation. The synthesis of a trigger module illustrates this procedure.A preliminary version was presented at the International Conference on Computer Design, October 1994.     

Investigations on green-emitting,Mn<Superscript>2+</Superscript>: BaAl<Subscript>12</Subscript>O<Subscript>19</Subscript> phosphors obtained by solution combustion process

Manganese-doped BaAl₁₂O₁₉ green phosphor was prepared using a self-propagating (combustion) synthesis. Powder X-ray diffraction and scanning electron microscopy were used to characterize the as-prepared combustion product. A room temperature photoluminescence study shows an emission line at 513 nm corresponding to a transition from the upper ⁴T₁ → ⁶A₁ ground state of Mn²⁺ ions. The electron paramagnetic resonance (EPR) spectrum exhibits six line hyperfine structure at g = 1.981. From the EPR spectrum, the spin-Hamiltonian parameters have been evaluated. The g value indicates that the site symmetry around Mn²⁺ ions is distorted tetrahedral. The number of spins (N) participating in the resonance for g = 1.981 is measured as a function of temperature. The paramagnetic susceptibility (χ) is calculated from the EPR data at various temperatures. From the plot 1/χ versus T, the Curie constant (C) and Curie paramagnetic temperature (θ_p) have been evaluated and discussed.     

Machinability studies on 17-4 PH stainless steel under cryogenic cooling environment

Under higher cutting conditions, machining of 17-4 precipitation hardenable stainless steel (PH SS) is a difficult task due to the high cutting temperatures as well as accumulation of chips at the machining zone, which causes tool damage and impairment of machined surface finish. Cryogenic machining is an efficient, eco-friendly manufacturing process. In the current work, cutting temperature, tool wear (flank wear (V_b) and rake wear), chip morphology, and surface integrity (surface topography, surface finish (R_a), white layer thickness (WLT)) were considered as investigative machinability characteristics under the cryogenic (liquid nitrogen), minimum quantity lubrication (MQL), wet and dry environments at varying cutting velocities while machining 17-4 PH SS. The results show that the maximum cutting temperature drop found in cryogenic machining was 72%, 62%, and 61%, respectively, in contrast to dry, wet, and MQL machining conditions. Similarly, the maximum tool wear reduction was found to be 60%, 55%, and 50% in cryogenic machining over the dry, wet, and MQL machining conditions, respectively. Among all the machining environments, better surface integrity was obtained by cryogenic machining, which could produce the functionally superior products.     

An intelligent system for monitoring students' engagement in large classroom teaching through facial expression recognition

Students' disengagement problem has become critical in the modern scenario due to various distractions and lack of student-teacher interactions. This problem is exacerbated with large offline classrooms, where it becomes challenging for teachers to monitor students' engagement and maintain the right-level of interactions. Traditional ways of monitoring students' engagement rely on self-reporting or using physical devices, which have limitations for offline classroom use. Student's academic affective states (e.g., moods and emotions) analysis has potential for creating intelligent classrooms, which can autonomously monitor and analyse students' engagement and behaviours in real-time. In recent literature, a few computer vision based methods have been proposed, but they either work only in the e-learning domain or have limitations in real-time processing and scalability for large offline classes. This paper presents a real-time system for student group engagement monitoring by analysing their facial expressions and recognizing academic affective states: ‘boredom,’ ‘confuse,’ ‘focus,’ ‘frustrated,’ ‘yawning,’ and ‘sleepy,’ which are pertinent in the learning environment. The methodology includes certain pre-processing steps like face detection, a convolutional neural network (CNN) based facial expression recognition model, and post-processing steps like frame-wise group engagement estimation. For training the CNN model, we created a dataset of the aforementioned facial expressions from classroom lecture videos and added related samples from three publicly available datasets, BAUM-1, DAiSEE, and YawDD, to generalize the model predictions. The trained model has achieved train and test accuracy of 78.70% and 76.90%, respectively. The proposed methodology gave promising results when compared with self-reported engagement levels by students.     

Scheduling concurrent applications on a cluster of CPU–GPU nodes

Heterogeneous architectures comprising a multi-core CPU and many-core GPU(s) are increasingly being used within cluster and cloud environments. In this paper, we study the problem of optimizing the overall throughput of a set of applications deployed on a cluster of such heterogeneous nodes. We consider two different scheduling formulations. In the first formulation, we consider jobs that can be executed on either the GPU or the CPU of a single node. In the second formulation, we consider jobs that can be executed on the CPU, GPU, or both, of any number of nodes in the system. We have developed scheduling schemes addressing both of the problems. In our evaluation, we first show that the schemes proposed for first formulation outperform a blind round-robin scheduler and approximate the performances of an ideal scheduler that involves an impractical exhaustive exploration of all possible schedules. Next, we show that the scheme proposed for the second formulation outperforms the best of existing schemes for heterogeneous clusters, TORQUE and MCT, by up to 42%. Additionally, we evaluate the robustness of our proposed scheduling policies under inaccurate inputs to account for real execution scenarios. We show that, with up to 20% of inaccuracy in the input, the degradation in performance is marginal (less than 7%) on the average.     

Magnetoresistance studies on barium doped nanocrystalline manganite

An energetically attractive, simple, fast and a novel low temperature (300 °C) solution combustion route for the synthesis of crystalline and homogeneous nanoparticles of lanthanum barium manganese oxide La_0.9Ba_0.1MnO_3+δ (LBMO) is reported. Formation and homogeneity of the solid solutions have been confirmed by powder X-ray diffraction (PXRD) and energy dispersive X-ray analysis (EDS) respectively. The Rietveld analysis shows both as-formed as well as calcined samples are in cubic phase with space group pm3m. The microstructure and agglomerated particle size of the compounds are examined by scanning electron microscope. Infrared spectroscopy revealed that both MnOMn bending mode and MnO stretching mode are influenced by calcination temperature. The magnetoresistance measurement on sintered LBMO pellet exhibits a broad metal–insulator transition (T_M-I) at around 228 K. At 1 T applied magnetic field, LBMO shows magnetoresistance (MR) of 10%, whereas for 4 and 7 T, the negative magnetoresistance values are in the range 51 and 59% respectively at T_M-I. The experimental resistivity data of the present investigation are fitted to a simple empirical equation in order to understand conduction mechanism in this compound.     

Estimation of thermal breakdown voltage of HVDC cables - A theoretical framework

The insulation in a DC cable is subjected to both thermal and electric stress at the same time. While the electric stress is generic to the cable, the temperature rise in the insulation is, by and large, due to the ohmic losses in the conductor. The consequence of this synergic effect is to reduce the maximum operating voltage and causes a premature failure of the cable. The authors examine this subject in some detail and propose a comprehensive theoretical formulation relating the maximum thermal voltage (MTV) to the physical and geometrical parameters of the insulation. The heat flow patterns and boundary conditions considered by the authors here and those found in earlier literature are provided. The MTV of a DC cable is shown to be a function of the load current apart from the resistance of the insulation. The results obtained using the expressions, developed by the authors, are compared with relevant results published in the literature and found to be in close conformity     

Optical,structural and morphological studies of nanostructures fabricated on silicon surface by femtosecond laser irradiation

Journal of Materials Science - We report here a detailed analysis of the ultrashort laser pulse irradiation effects on a single crystalline silicon surface. A systematic study has been performed to...