High Intrinsic Mobility and Ultrafast Carrier Dynamics in Multilayer Metal Dichalcogenide MoS2

The ultimate limitations on carrier mobilities in metal dichalcogenides, and the dynamics associated with carrier relaxation, are unclear. We present measurements of the frequency-dependent conductivity of multilayer dichalcogenide MoS2 by optical-pump terahertz-probe spectroscopy. We find mobilities in this material approaching 4200 cm2/Vs at low temperatures. The temperature dependence of scattering indicates that the mobility, an order of magnitude larger than previously reported for MoS2, is intrinsically limited by acoustic phonon scattering at THz frequencies. Our measurements of carrier relaxation reveal picosecond cooling times followed by recombination lasting tens of nanoseconds and dominated by Auger scattering into defects. Our results provide a useful context in which to understand and evaluate the performance of MoS2-based electronic and optoelectronic devices.Comment: 13 pages, 8 figure

Effect of Proportion of Missing Data on Application of Data Imputation in Pavement Management Systems

Missing data are commonly found in pavement condition/performance databases. A common practice today is to apply statistical imputation methods to replace the missing data with imputed values. It is thus important for pavement management decision makers to know the uncertainty and errors involved in the use of datasets with imputed values in their analysis. An equally important information of practical significance is the maximum allowable proportion of missing data (i.e. level of data missingness in the pavement condition/performance records) that will still produce results with acceptable magnitude of error or risk when using imputed data. This paper proposes a procedure for determining such useful information. A numerical example analyzing pavement roughness data is presented to demonstrate the procedure through evaluating the error and reliability characteristics of imputed data. The roughness data of three road sections were obtained from the LTPP database. From these data records, datasets with different proportions of missing data were randomly generated to study the effect of level of data missingness. The analysis shows that the errors of imputed data increased with the level of data missingness, and their magnitudes are significantly affected by the effect of pavement rehabilitation. On the application of data imputation in PMS, the study suggests that at 95% confidence level, 25% of missing data appears to be a reasonable allowable maximum limit for analyzing pavement roughness time series data not involving rehabilitation within the analysis period. When pavement rehabilitation occurs within the analysis period, the maximum proportion of imputed data should be limited to 15%

An integrated computer-aided modular fixture design system for machining semi-circular parts

Productivity is one of the most important factors in manufacturing processes because of the high level of market competition. In this regard, modular fixtures (MFs) play an important role in practically improving productivity in flexible manufacturing systems (FMSs) due to this technology using highly productive computer numerical control (CNC) machines. MFs consist of devices called jigs and fixtures for accurately holding the workpiece during different machining operations. The design process is complex, and traditional methods of MF design were not sufficiently productive. Computer-aided design (CAD) software has rapidly improved as a result of the development of computer technology, and has provided huge opportunities for modular fixture designers to use its 3D modelling capabilities to develop more automated systems. Computer-aided fixture design (CAFD) systems have become automated by the use of artificial intelligence (AI) technology. This study will investigate the further improvement of automated CAFD systems by using AI tools. In this research, an integrated CAFD is developed by considering four main requirements: · a 3D model of the workpiece, · an expert system, · assembly automation of MFs, · an efficient feature library. The 3D model is an important factor that can provide the appropriate specification of the workpiece; SolidWorks is used the CAD environment for undertaking the 3D modelling in this study. The expert system is applied as a tool to make right decisions about the CAFD planning process, including locating and clamping methods and their related element selection. This helps achieve a feasible fixture design layout. SolidWorks API and Visual Basic programming language are employed for the automating and simulation of the assembly process of MFs. A feature library of modular fixture elements is constructed as a means to simplify the fixture design process

Recurrence Tracking Microscope

In order to probe nanostructures on a surface we present a microscope based on the quantum recurrence phenomena. A cloud of atoms bounces off an atomic mirror connected to a cantilever and exhibits quantum recurrences. The times at which the recurrences occur depend on the initial height of the bouncing atoms above the atomic mirror, and vary following the structures on the surface under investigation. The microscope has inherent advantages over existing techniques of scanning tunneling microscope and atomic force microscope. Presently available experimental technology makes it possible to develop the device in the laboratory

Keefektifan Pbl Dan Ibl Ditinjau Dari Prestasi Belajar, Kemampuan Representasi Matematis, Dan Motivasi Belajar

Penelitian ini bertujuan untuk mendeskripsikan keefektifan problem-based learning dan inquiry-based learning ditinjau dari prestasi belajar, kemampuan representasi matematis, dan motivasi belajar. Penelitian ini adalah penelitian eksperimen semu dengan pretest-posttest nonequivalent group design. Populasi dalam penelitian ini adalah seluruh siswa kelas VIII MTs sekecamatan Rasana'e Barat Kota Bima dan sampel dalam penelitian ini adalah siswa kelas VIII MTs Sartu Atap rasana'e Barat Kota Bima dan tiga kelas dipilih yaitu dua kelas eksperimen dan satu kelas kontrol. Data penelitian dianalisis dengan uji one sample t test, uji Bonferroni pada signifikansi 5% dan uji MANOVA. Hasil penelitian menunjukkan bahwa ditinjau dari prestasi belajar, kemampuan representasi matematis, dan motivasi belajar: (1) problem-based learning dan inquiry-based learning efektif, (sedangkan pembelajaran konvensional efektif ditinjau dari motivasi belajar siswa), (2) problem-based learning dan inquiry-based learning lebih efektif dibandingkan dengan pembelajaran konvensional, dan (3) problem-based learning lebih efektif dibandingkan dengan inquiry-based learning

Ultrafast Carrier Recombination and Generation Rates for Plasmon Emission and Absorption in Graphene

Electron-hole generation and recombination rates for plasmon emission and absorption in Graphene are presented. The recombination times of carriers due to plasmon emission have been found to be in the tens of femtoseconds to hundreds of picoseconds range. The recombination times depend sensitively on the carrier energy, carrier density, temperature, and the plasmon dispersion. Carriers near the Dirac point are found to have much longer lifetimes compared to carriers at higher energies. Plasmons in a Graphene layer on a polar substrate hybridize with the surface optical phonons and this hybridization modifies the plasmon dispersion. We also present generation and recombination rates of carriers due to plasmon emission and absorption in Graphene layers on polar substrates.Comment: 7 Pages, 11 Figures, To appear in Phys. Rev. B (2011

Improving Delay-Based Data Dissemination Protocol in VANETs with Network Coding

In vehicular ad hoc networks (VANETs), for a large number of applications, the destination of relevant information such as alerts, is the whole set of vehicles located inside a given area. Therefore dissemination with efficient broadcast is an essential communication primitive. One of the families of broadcast protocols suitable for such networks, is the family of delay-based broadcast protocols, where farthest receivers retransmit first and where transmissions also act as implicit acknowledgements. For lossless networks, such protocols may approach the optimum efficiency. However with realistic loss models of VANET wireless communication, their performance is noticeably degraded. This is because packet losses have a double effect: directly on the amount of successfully received packets and indirectly with implicit acknowledgement misses. In this article, in order to combat the effects of packet losses, we combine delay-based broadcast with network coding, through a new protocol: Delay-based Opportunistic Network Coding protocol (DONC). By design, DONC aims at cancelling the twofold effects of packet and implicit acknowledgement losses. We describe the details of the DONC protocol, and we study its behavior, with realistic models and simulations. Results illustrate the excellent performance of the protocol

Carrier Recombination and Generation Rates for Intravalley and Intervalley Phonon Scattering in Graphene

Electron-hole generation and recombination rates for intravalley and intervalley phonon scattering in Graphene are presented. The transverse and the longitudinal optical phonon modes ($E_{2g}$-modes) near the zone center ($\Gamma$-point) contribute to intravalley interband carrier scattering. At the zone edge ($K(K')$-point), only the transverse optical phonon mode ($A'_{1}$-mode) contributes significantly to intervalley interband scattering with recombination rates faster than those due to zone center phonons. The calculated recombination times range from less than a picosecond to more than hundreds of picoseconds and are strong functions of temperature and electron and hole densities. The theoretical calculations agree well with experimental measurements of the recombination rates of photoexcited carriers in graphene.Comment: 6 pages, 9 figure

A Study on Teacher’s Perception about Components of English Handwriting in Pakistan

Handwriting is an essential of school activities for the school going children. Good or legible handwriting remained a constant task for the teachers and students during the whole day. The teachers recognize the legible handwriting at a gland due to their routine work in the schools. The teacher’s criterion that lies behind their decision of good handwriting was a question to answer in this study. The purpose of this study was to identify the components of legibility from the teachers’ perspective. Referencing handwriting experts and a literature review, key variables were categorized and organized onto a 5-point Likert Scale questionnaire. Teachers’ responses to the various legibility criteria were then tallied with regards to primary school students. Mean, standard deviation, exploratory factor analysis and path diagram statistics were applied to the ordinal data. It was concluded that twelve components were important for the legibility of handwriting of primary school students. These include Readability, Margin, Similarity, Line, Space, Size, Shape, Roundness, Form, Slant, Alignment and Recognition