Valley Coherent Hot Carriers and Thermal Relaxation in Monolayer Transition Metal Dichalcogenides

We show room temperature valley coherence with in MoS2, MoSe2, WS2 and WSe2 monolayers using linear polarization resolved hot photoluminescence (PL), at energies close to the excitation - demonstrating preservation of valley coherence before sufficient scattering events. The features of the co-polarized hot luminescence allow us to extract the lower bound of the binding energy of the A exciton in monolayer MoS2 as 0.42 (+/- 0.02) eV. The broadening of the PL peak is found to be dominated by Boltzmann-type hot luminescence tail, and using the slope of the exponential decay, the carrier temperature is extracted in-situ at different stages of energy relaxation. The temperature of the emitted optical phonons during the relaxation process are probed by exploiting the corresponding broadening of the Raman peaks due to temperature induced anharmonic effects. The findings provide a physical picture of photo-generation of valley coherent hot carriers, and their subsequent energy relaxation path ways

Review of Environment Perception for Intelligent Vehicles

Overview of environment perception for intelligent vehicles supposes to the state-of-the-art algorithms and modeling methods are given, with a summary of their pros and cons. A special attention is paid to methods for lane and road detection, traffic sign recognition, vehicle tracking, behavior analysis, and scene understanding. Integrated lane and vehicle tracking for driver assistance system that improves on the performance of both lane tracking and vehicle tracking modules. Without specific hardware and software optimizations, the fully implemented system runs at near-real-time speeds of 11 frames per second. On-road vision-based vehicle detection, tracking, and behavior understanding. Vision based vehicle detection in the context of sensor-based on-road surround analysis. We detail advances in vehicle detection, discussing monocular, stereo vision, and active sensor–vision fusion for on-road vehicle detection. The traffic sign detection detailing detection systems for traffic sign recognition (TSR) for driver assistance. Inherently in traffic sign detection to the various stages: segmentation, feature extraction, and final sign detection

DEVELOPMENT AND VALIDATION OF RP-HPLC METHOD FOR SIMULTANEOUS ESTIMATION OF LAMIVUDINE AND ZIDOVUDINE IN BULK

Objective: The scope of the present work is to expand and optimization of the chromatographic conditions and to develop RP-HPLC method. Methods: The method was performed with various columns like C18 column, kromasil column, Hypersil BDS column. Among them, Symmetry C18 (250x4.6 mm, 5um) was found to be ideal as it gave good peak shape at 0.8 ml/min flow and validated for various parameters such as linearity, precision, accuracy, System suitability, Specificity, % Assay, Robustness, etc. Results: The system suitability parameters were evaluated from standard chromatograms by calculating the % RSD from five replicate injections for Lamivudine and Zidovudine retention times and peak areas. The % RSD for the retention times of principal peak from 5 replicate injections of each standard solution were less than 2.0 %. The Linearity and correlation coefficient of Lamivudine and zidovudine was found to be 0.999. Precision was performed and % RSD for Lamivudine and Zidovudine were found to be less than 2.0. The % Recovery for each level was found to be the range of 98.0 to 102%. In Robustness, the % RSD of the peak area of all peaks for five replicate injections should be not more than 2.0. Conclusion: Hence, the chromatographic method developed for Lamivudine and Zidovudine is said to be rapid, simple, specific, sensitive, precise, accurate and reliable that can be effectively applied for routine analysis in research institutions, quality control department in industries, approved testing laboratories, bio-pharmaceutics and bio-equivalence studies and in clinical pharmacokinetic studies

Photoresponse of atomically thin MoS2 layers and their planar heterojunctions

MoS2 monolayers exhibit excellent light absorption and large thermoelectric power, which are, however, accompanied with very strong exciton binding energy - resulting in complex photoresponse characteristics. We study the electrical response to scanning photo-excitation on MoS2 monolayer (1L) and bilayer (2L) devices, and also on monolayer/bilayer (1L/2L) planar heterojunction and monolayer/few-layer/multi-layer (1L/FL/ML) planar double heterojunction devices to unveil the intrinsic mechanisms responsible for photocurrent generation in these materials and junctions. Strong photoresponse modulation is obtained by scanning the position of the laser spot, as a consequence of controlling the relative dominance of a number of layer dependent properties, including (i) photoelectric effect (PE), (ii) photothermoelectric effect (PTE), (iii) excitonic effect, (iv) hot photo-electron injection from metal, and (v) carrier recombination. The monolayer and bilayer devices show peak photoresponse when the laser is focused at the source junction, while the peak position shifts to the monolayer/multi-layer junction in the heterostructure devices. The photoresponse is found to be dependent on the incoming light polarization when the source junction is illuminated, although the polarization sensitivity drastically reduces at the monolayer/multi-layer heterojunction. Finally, we investigate laser position dependent transient response of photocurrent to reveal trapping of carriers in SiO2 at the source junction is the critical factor to determine the transient response in 2D photodetectors, and also show that, by systematic device design, such trapping can be avoided in the heterojunction devices, resulting in fast transient response. The insights obtained will play an important role in designing fast 2D TMDs based photodetector and related optoelectronic and thermoelectric devices.Comment: Nanoscale, 201

Parameter Uniform Numerical Methods for Singularly Perturbed Parabolic Partial Differential Equations

This thesis deals with some efficient and higher order numerical methods for solving singularly perturbed parabolic partial differential equations (SPPDEs) in one and two dimensions. The model problems includes one dimensional SPPDEs, time delay SPPDEs, two dimensional SPPDEs and mixed type of parabolic-elliptic problems. In general, these problems are described by partial differential equations in which the highest order derivative is multiplied by a small parameter ε, known as the “singular perturbation parameter” (0 < ε ≪ 1). If the parameter ε tends to 0, the problem has a limiting solution, which is called the solution of the reduced problem. The regions of nonuniform convergence lie near the boundary of the domain, which are known as boundary/interior layers. Due to this layer phenomena, it is a very difficult and challenging task to provide parameter uniform numerical methods for solving SPPDEs. The term “parameter uniform” is meant to identify those numerical methods, in which the approximate solution converges (measured in the supremum norm) independently with respect to the perturbation parameter. The purpose of the thesis is to analyze, develop and optimize the parameter uniform fitted mesh methods for solving SPPDEs on Shishkin-type meshes like the standard Shishkin mesh (S-mesh), the Bakhvalov-Shishkin mesh (B-S mesh), and the modified Bakhvalov-Shishkin mesh (M-B-S mesh) in the spacial direction. This thesis contains eight chapters. It begins with introduction along with the objective and the motivation for solving SPPDEs. Next, Chapter 2 contains a time delay SPPDE which is solved using a hybrid scheme (combination of the midpoint upwind scheme and the central difference scheme) on S-mesh and B-S mesh in space direction and the implicit trapezoidal scheme on uniform mesh in time direction. We have obtained an optimal global second order accuracy with respect to space and time. In Chapter 3, a monotone hybrid scheme for discretization in space and the implicit Euler, then the implicit trapezoidal scheme for discretization in time are used to solve a SPPDE. A monotone hybrid scheme is different from the usual hybrid scheme, which is a combination of the midpoint and the central difference scheme with variable weights. Here, an optimal second order accuracy is obtained in space and time. Again, the same monotone hybrid scheme in spatial direction and the Euler scheme in time direction are used in Chapter 4 for solving the model problem considered in Chapter 2. Chapter 5 contains a singularly perturbed time delay reaction-diffusion problem and it is solved by using the central difference scheme on S-mesh and B-S mesh in space direction and the implicit Euler, the implicit trapezoidal scheme in time direction to get a second order accuracy. Then, the post-processing technique (Richardson extrapolation) is used to improve the accuracy from second order to fourth order. Chapter 6 presents the hybrid scheme on Shishkin-type meshes in spatial direction and the implicit Euler, the Crack-Nicolson schemes in time direction for solving the singularly perturbed mixed type of parabolic-elliptic problem. Next, we extend from 1D problem to 2D problem SPPDE in Chapter 7, in which a 2D SPPDE is solved by using the central difference scheme on Shishkin-type meshes in space direction and the Peaceman-Rachford scheme in time direction. Here, we have achieved an optimal second order accuracy in both spatial and temporal direction. In all cases, Thomas algorithm is used throughout this thesis to reduce the computational time over the usual matrix inverse method. Finally, Chapter 8 summarizes the results made by this thesis. Extensive numerical results are presented in support of the theoretical findings and also to demonstrate the accuracy of the proposed methods. The corresponding numerical results are presented in the numerical section of each chapter of the thesis in shape of tables and figures. Some comparison results are also provided which confirms the efficiency of the proposed methods made in this thesis over the existing methods in literature