Multi-Scale joints roughness characterization using wavelet and shear modeling

Mechanical behavior prediction of rock joints is very important in the rock mechanics. Many models have been proposed to predict the mechanical behavior of joints at which lack of correct evaluation of effective roughness coefficient has been the most important shortage. In this research, each of the upper and lower profiles of joint surfaces is considered as a 2-dimensional wave. Then, multi-scale decomposition based on wavelet theory has been applied studying on asperities. Upper and lower profiles have been combined to produce a composite surface having asperities characteristics of both joint surfaces. Each of the composed wave components (roughness and undulation) has been characterized with statistical quantity of arithmetic mean deviation (Ra). This procedure of characterizing for 2-dimensional waves has been easily extended to 3-dimensional joint surfaces. Conformity in the results of shear and dilation modeling and laboratory tests satisfactorily verifies success of the proposed procedure

Diode-pumped ultrafast Yb:KGW laser with 56 fs pulses and multi-100 kW peak power based on SESAM and Kerr-lens mode locking

A high-power sub-60 fs mode-locked diode-pumped Yb:KGW laser based on hybrid action of an InGaAs quantum-dot saturable absorber mirror and Kerr-lens mode locking was demonstrated. The laser delivered 56 fs pulses with 1.95 W of average power corresponding to 450 kW of peak power. The width of the generated laser spectrum was 20.5 nm, which was near the gain bandwidth limit of the Yb:KGW crystal. To the best of our knowledge, these are the shortest pulses generated from the monoclinic double tungstate crystals (and Yb:KGW laser crystal in particular) and the most powerful in the sub-60 fs regime. At the same time, they are also the shortest pulses produced to date with the help of a quantum-dot-based saturable absorber. High-power operation with a pulse duration of 90 fs and 2.85 W of average output power was also demonstrated

Teachers’ technology-related self-images and roles: Exploring CALL teachers’ professional identity

Despite the surge of interest in language teachers’ professional identity (TPI) as an integral component of their professional growth (Barkhuizen, 2017; Clarke, 2018) and the increasing interest in the field of computer assisted language learning (CALL) (Nami et al., 2015), there is still a paucity of research on the professional identity of language teachers who integrate technology with language instruction (CALL teachers). To bridge this gap, the present study explored the components that construct CALL teachers’ professional identity (CALLTPI). The data were collected from a set of in-depth, semi-structured interviews investigating perceptions of 24 CALL informants (educators, experts, professors, and teachers) from different contexts and countries about CALL teachers’ roles in technology integration in English language teaching (ELT). Fifteen sub-components were inferred from the thematic analysis of the interview transcripts as compared against the available literature on CALL teacher education and language teachers’ professional identity. These sub-components corresponded to three major components, namely, CALL teachers’ individual identity, classroom-based identity, and agentive identity. The results can provide CALL teacher educators with implications for designing professional development programs with the aim of developing teachers’ professional identity and enhancing the effectiveness of technology integration in ELT

Engine displacement modularity for enhancing automotive s.i. engines efficiency at part load

Cylinder deactivation is a well-known and effective technology to improve spark ignition engines’ efficiency at part load, thanks to its capability of significantly reducing pumping losses, by switching off a fraction of the cylinders at part load, while operating the active cylinders at higher loads and therefore with higher efficiencies. This technology can be utilized as an alternative to, or in combination with, other efficiency improving measures such as engine downsizing and Variable Valve Actuation (VVA). It is worth mentioning however that the implementation of a cylinder deactivation strategy generally requires intake and exhaust valve deactivation in deactivated cylinders, so to minimize pumping losses thanks to the “gas spring” behavior of the trapped charge. In this paper the effects and possible benefits of cylinder deactivation on a four cylinder turbocharged downsized gasoline engine equipped with MultiAir VVA system were experimentally investigated, aiming to obtain further reductions of pumping losses beyond those achievable through normally adopted Early Intake Valve Closure (EIVC) strategies. Moreover, since the MultiAir VVA system does not allow exhaust valve deactivation, an innovative strategy was developed, exploiting internal Exhaust Gas Recirculation (iEGR) in the inactive cylinders in order to minimize their pumping losses. This innovative cylinder deactivation technique was demonstrated to be effective in the low speed and low load operating region of the engine map, leading to an impressive 30% reduction of pumping losses compared to the EIVC unthrottled load control

Effect of activated carbon xerogel pore size on the capacitance performance of ionic liquid electrolytes

The use of ionic liquid (IL) electrolytes promises to improve the energy density of electrochemical capacitors (ECs) by allowing for operation at higher voltages. Several studies have also shown that the pore size distribution of materials used to produce electrodes is an important factor in determining EC performance. In this research the capacitative, energy and power performance of ILs 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF(4)), 1-ethyl-3-methylimidazolium dicyanamide (EMImN(CN)(2)), 1,2-dimethyl-3-propylimidazolium bis(trifluoromethylsulfonyl)imide (DMPImTFSI), and 1-butyl-3-methylpyrrolidinium tris(pentafluoroethyl)trifluorophosphate (BMPyT(F5Et)PF3) were studied and compared with the commercially utilised organic electrolyte 1M tetraethylammonium tetrafluoroborate solution in anhydrous propylene carbonate (Et4NBF4-PC 1 M). To assess the effect of pore size on IL performance, controlled porosity carbons were produced from phenolic resins activated in CO2. The carbon samples were characterised by nitrogen adsorption-desorption at 77 K and the relevant electrochemical behaviour was characterised by cyclic voltammetry, galvanostatic charge-discharge and electrochemical impedance spectroscopy. The best capacitance performance was obtained for the activated carbon xerogel with average pore diameter 3.5 nm, whereas the optimum rate performance was obtained for the activated carbon xerogel with average pore diameter 6 nm. When combined in an EC with IL electrolyte EMImBF(4) a specific capacitance of 210 F g(-1) was obtained for activated carbon sample with average pore diameter 3.5 nm at an operating voltage of 3 V. The activated carbon sample with average pore diameter 6 nm allowed for maximum capacitance retention of approximately 70% at 64 mA cm(-2)

Experimental Investigation on Early and Late Intake Valve Closures for Knock Mitigation Through Miller Cycle in a Downsized Turbocharged Engine

The application of Miller cycle through Late Intake Valve Closure (LIVC) or Early Intake Valve Closure (EIVC) for knock mitigation at high load on a turbocharged downsized spark ignition engine was experimentally investigated. By reducing the effective compression ratio due to a shorter compression stroke and hence achieving lower charge temperatures inside the cylinder, significant mitigation of knock tendency could be obtained. As a consequence, the spark advance retard could be substantially decreased and the enrichment of the mixture could significantly be reduced, thus obtaining impressive efficiency improvements. In this research, both EIVC and LIVC strategies have been examined aiming to achieve possible improvements for knock mitigation and after some preliminary investigations confirmed LIVC being more effective than EIVC for this goal, the latter was discarded and the research activities were focused on LIVC only. Significant reductions in fuel consumption for high load engine operating points were achieved, especially at moderately high engine speeds, above 2500 RPM, where the turbocharger group was capable to compensate for the reduction of volumetric efficiency caused by the LIVC by means of an increased boost pressure. However, at lower engine speeds, despite these operating conditions being generally the most critical for knock occurrence, only minor positive effects were observed, since the lack of an adequate boost pressure did not allow further delays of the IVC, thus preventing the full exploitation of the Miller cycle. The highest gains were registered at 3000 RPM, at 18 bar and 20 bar BMEP, where the engine indicated fuel conversion efficiency was improved by about 11 and 20 percent, respectively. It is worth mentioning that, thanks to the Miller cycle exploitation, the engine could be operated under stoichiometric conditions in this region of its operating map, while normally adopted IVC timings typically require significant mixture enrichments

Analysis and Design of a Permanent-Magnet Outer-Rotor Synchronous Generator for a Direct-Drive Vertical-Axis Wind Turbine

In Permanent-Magnet Synchronous Generators (PMSGs) the reduction of cogging torque is one of the most important problems in their performance and evaluation. In this paper, at first, a direct-drive vertical-axis wind turbine is chosen. According to its nominal value operational point, necessary parameters for the generator is extracted. Due to an analytical method, four generators with different pole-slot combinations are designed. Average torque, torque ripple and cogging torque are evaluated based on finite element method. The combination with best performance is chosen and with the analysis of variation of effective parameters on cogging torque, and introducing a useful method, an improved design of the PMSG with lowest cogging torque and maximum average torque is obtained. The results show a proper performance and a correctness of the proposed method