Torsional buckling of a DWCNT embedded on winkler and pasternak foundations using nonlocal theory

The small-scale effect on the torsional buckling of a double-walled carbon nanotube (DWCNT) embedded on Winkler and Pasternak foundations is investigated in this study using the theory of nonlocal elasticity. The effects of the surrounding elastic medium, such as the spring constant of the Winkler type and the shear constant of the Pasternak type, as well as the van der Waals (vdW) forces between the inner and the outer nanotubes are taken into account. Finally, based on the theory of nonlocal elasticity and by employing the continuum models, an elastic double-shell model is presented for the nonlocal torsional buckling load of a DWCNT. It is seen from the results that the shear constant of the Pasternak type increases the nonlocal critical torsional buckling load, while the difference between the presence and the absence of the shear constant of the Pasternak type becomes large. It is shown that the nonlocal critical buckling load is lower than the local critical buckling load. Moreover, a simplified analysis is carried out to estimate the nonlocal critical torque for the torsional buckling of a DWCNT.     

Organic field-effect transistors as new paradigm for large-area molecular junctions

Self-Assembly Monolayers (SAMs) are considered a promising route for solving technological hindrances (such as bias-stress, contact resistance, charge trapping) affecting the electrical performances of the Organic Field-Effect Transistors (OFETs). Here we use an OFET based on pentacene thin film to investigate the charge transport across conjugated SAMs at the Au/pentacene interface. We synthesized a homolog series of π-conjugated molecules, termed Tn-C8-SH, consisting of a n-unit oligothienyl Tn (n = 1…4) bound to an octane-1-thiol (C8-SH) chain that self-assembles on the Au electrodes. The multi-parametric response of such devices yields an exponential behavior of the field-effect mobility (μ), current density (J), and total resistivity (R), due to the SAM at the charge injection interface (i.e. Au-SAM-pentacene). The surface treatment of the OFETs induces a clear stabilization of different parameters, like sub-threshold slope and threshold voltage, thanks to standardized steps in the fabrication process.     

OPTIMAL KINETIC PARAMETERS AND BATCH MODELING FOR PECTIN HYDROLYSIS TO GALACTURONIC ACID WITH PECTINEX ULTRA SP-L ENZYME

Galacturonic acid is a monosaccharide obtained by pectin hydrolysis and a suitable substrate to produce bioethanol by fermentation. This article focuses on quantification of citrus pectin hydrolysis to galacturonic acid and provides new, reliable kinetic parameters for the Michaelis-Menten equation when the well-known commercial Pectinex Ultra SP-L is employed as enzyme. They are: r _max  = 1.10 g/(L min), K _m  = 10.42 g/L, and K _IGA  = 10.05 g/L, as obtained with a great accuracy by a nonlinear regression method and confirmed by the three classical linearization procedures (Lineweaver-Burk, Langmuir, and Eadie-Hofstee). The quantification of product inhibition has been achieved, with its inclusion in the rate equation. A batch reactor model yields perfect agreement between predictions and experiments, even under conditions different from those on which the parameters had been determined by regression.     

PHEV powertrain co-design with vehicle performance considerations using MDSDO

Structural and Multidisciplinary Optimization - The complexity of plug-in hybrid-electric vehicles (PHEVs) motivates the simultaneous integration of component design and supervisory control...     

Dynamic modeling and base inertial parameters determination of a 2-DOF spherical parallel mechanism

This paper deals with the dynamic modeling and base inertial parameter determination of a general 5R 2-degree-of-freedom spherical parallel manipulator. By using a new geometric approach, inverse and forward kinematic problem are transformed to the problem of determining the intersection of two cones with common vertex. Compared to other proposed methods, this approach yields more compact and closed-form solutions. The instantaneous kinematic and acceleration problem is solved via employing the screw theory. The dynamic model is formulated by means of the principle of virtual work and the concept of link Jacobian matrices. In order to verify the proposed methods and equations, a case study is performed, in which an orthogonal 2-DOF spherical parallel manipulator, named TezGoz, is considered. Performed simulations and comparisons with a SimMechanics model show the correctness of the derived equations. Furthermore, a reduced dynamic model is obtained by determining the base inertial parameters. To do so, first the dynamic model is rewritten in a linear matrix form with respect to the inertial parameters of the mechanism, then parameters are grouped to obtain a set of independent base parameters, reducing the number of inertial parameters from 40 to 19. As a result, while maintaining the accuracy, the computational time is reduced to 63% of that of the original dynamic model. Finally, to calibrate the dynamic model, an experimental dynamic identification is performed.     

Power‐efficient burst‐mode RF transmitter based on reference‐adaptive multilevel pulse‐width modulation

Burst‐mode operation of power amplifier (PA) based on multilevel pulse‐width modulation (MPWM) has been frequently discussed as a potential solution to achieve higher efficiency in radio frequency (RF) transmitters. In this paper, a novel multilevel PWM modulator is proposed that utilizes adaptive triangular reference waveforms. As compared with conventional MPWM modulators, the proposed architecture provides significant wider design space such that the efficiency of system can be effectively optimized. A general transmitter architecture based on the proposed concept is analyzed in terms of power efficiency. Efficiency optimization procedures are presented according to input magnitude statistics. Based on the proposed modulator, an optimized 2.4‐GHz RF transmitter is designed in a 0.18‐μm complementary metal‐oxide‐semiconductor (CMOS) process. The circuit‐level simulations show that it delivers 25.8‐dBm peak output power with 46.1% peak efficiency. For a 20‐MHz worldwide interoperability for microwave access (WiMAX) signal with 8.5‐dB peak‐to‐average‐power ratio (PAPR), this transmitter achieves 28.8% (average) efficiency at 17.3‐dBm (average) output power with an error vector magnitude (EVM) of 2.97% rms.     

Reactivity of generated oxygen species from nitrous oxide over [Fe,Al]MFI catalysts for the direct oxidation of benzene to phenol

The catalytic performance of various steam-activated [Fe,Al]MFI catalysts in the direct oxidation of benzene to phenol using N₂O as oxidant is described. All [Fe,Al]MFI catalysts contain ca. 90% of iron in the high-spin Fe²⁺ state, independent of the iron concentration (0.075–0.6 wt.% iron). In the presence of N₂O at 623 K, most Fe²⁺ ions (>90%) were oxidized to Fe³⁺ ions as deduced from Mössbauer spectroscopy. In the presence of benzene, subsequent reduction of Fe³⁺ to Fe²⁺ takes place. However, not all of the oxidized Fe²⁺ to Fe³⁺ ions were able to selectively oxidize benzene to phenol. This indicates that only a fraction of iron is catalytically active. For [Fe,Al]MFI catalysts with relatively high iron concentration, most of the extra-framework iron species formed are inactive in the direct oxidation of benzene to phenol. Finally, a more detailed in situ Mössbauer study for one sample, i.e. [Fe,Al]MFI (1:8) catalyst, was performed to illustrate the reduction/oxidation properties of the different iron species formed after steam-treatment.     

Controllable synthesis of a hollow Cr2O3 electrocatalyst for enhanced nitrogen reduction toward ammonia synthesis

As a fascinating alternative to the energy-intensive Haber-Bosch process,the electrochemically-driven N2 reduction reaction (NRR) utilizing the N2 and H2O for the production of NH3 has received enormous attention.The development and preparation of promising electrocatalysts are requisite to realize an effi-cient N2 conversion for NH3 production.In this research,we propose a template-assisted strategy to con-struct the hollow electrocatalyst with controllable morphology.As a paradigm,the hollow Cr2O3 nanocatalyst with a uniform size (～170 nm),small cavity and ultrathin shell (～15 nm) is successfully fabricated with this strategy.This promising hollow structure is favourable to trap N2 into the cavity,pro-vides abundant active sites to accelerate the three-phase interactions,and facilitates the reactant transfer across the shell.Attributed to these synergetic effects,the designed catalyst displays an outstanding behaviour in N2 fixation for NH3 production in ambient condition.In the neutral electrolyte of 0.1 mol·L-1 Na2SO4,an impressive electrocatalytic performance with the NH3 generation rate of 2.72 μg·h-1·cm 2 and a high FE of 5.31％ is acquired respectively at-0.85 V with the hollow Cr2O3 cat-alyst.Inspired by this work,it is highly expected that this approach could be applied as a universal strat-egy and extended to fabricating other promising electrocatalysts for realizing highly efficient nitrogen reduction reaction (NRR).