Influence of Sinusoidal Drive Speed Modulation on Rotor with Continuous Stator Contact

Torsional vibrations experienced by drill strings can be detrimental to drilling operations. With a goal of understanding torsional vibrations experienced by drill strings and determining means to attenuate undesired vibrations, the authors have studied the effect of adding a sinusoidal modulation to a constant rotation speed of a drill string. A combination of modeling, analysis, and experiments is used to explore the influence of this rotation input modulation on the system response. The drill string is modeled as a modified Jeffcott rotor, which is described by a system with three degrees of freedom. Considering the case of forward whirling of a rotor in continuous contact with a stator, the equations of motion are reduced to a single degree-of-freedom nonlinear oscillator describing the torsional motions. In order to understand the fast time scale and slow time scale components of the motion, the method of direct partitions of motions is used to determine an approximate response to the nonlinear oscillator. The obtained results of the analysis illustrate that with the sinusoidal modulation of the rotor drive speed, the equivalent torsion stiffness can be enhanced and the character of the friction force at the contact can be made smooth. The analyses helps bring forth the stabilizing influence of the added sinusoidal input to the rotor drive speed. Over the considered parameter ranges, the numerical results obtained with the full three degree-of-freedom model and the reduced single degree-of-freedom model are found to be in agreement with each other. Furthermore, the results from these models are found to compare well with those obtained by using the method of direct partition of motions. Experiments with a laboratory scale drill-string arrangement are to be carried out to validate the analytical and numerical findings and further explore the effectiveness of the drive speed modulation on the rotor dynamics.qscienc

Synthesis and Characterization of Soluble Thiophene-Selenophene- and Tellurophene-Vinylene Copolymers

Organic electronic devices based on polymers received significant attention in the last decade, especially for organic photovoltaics (OPVs) and field-effect transistors (OFETs) despite their performances and stability clearly falling short of today's state-of-the-art crystalline silicon or copper indium germanium selenide (CIGS)-based devices. Flexibility in the manufacturing, light weight, lower fabrication cost, ease of integration into various devices, and large area coating are some of the major potential advantages of polymers over inorganic devices. 1 Among organic polymers, conjugated polymers attracted widespread attention for a wide range of applications. Thiophene-containing conjugated polymers, especially, poly(3-alkylthiophne) (P3AT) has been subjected to intensive research over last decade due to their excellent optical and electronic properties. 2 Moreover, poly(thienylenevinylene) (PTV) class of polymers displays high charge carrier mobilities in OFETs and promising performances in OPVs. 3 When a single solubilizing alkyl chain is included onto the PTV backbone, the resulting copolymer can be solution processed for optical devices. One simple strategy to manipulate the copolymer property is by changing the heteroatom of the thiophene from sulfur to other chalcogens, selenium or tellurium. 4 Theoretical calculations indicated that substitution with selenium or tellurium may reduce the optical band gap of the resulting polymer in comparison to their sulfur-containing analogues. Inclusion of larger and more polarizable selenium or tellurium also expected to have a strong influence on the charge transport properties. Notably, Heeney and co-workers showed that the band gap of P3AT can be reduced by as much as 0.3 eV by only substituting sulfur with selenium in the polymer backbone. 5 The reduction of band gap resulted from larger and more polarizable selenium facilitate better π orbital overlap with the polymer backbone and thus stabilize the polymer LUMO (lowest unoccupied molecular orbital). Low-lying LUMO levels are believe to facilitate both electron injection and transport. Recently, PBDTT-SeDPP polymer showed a high Jsc of 16.8 mA/cm2, a Voc of 0.69 V, and a FF of 62%, enabling the best PCE of 7.2%. 6 However, despite fascinating properties of selenium substituted polymers, tellurium containing polymers are less explored, may be due to challenging tellurium chemistry. Jahnke and co-workers recently reported first soluble tellurophene polymer, poly(3-alkyltellurophene) (P3ATe), prepared by both electrochemical and Kumuda coupling polymerization method. 7 Even though, preliminary PCE (1.1%) was modest, tellurium substitution resulted in red-shifted film absorption. In this contribution, we report the synthesis and characterization of vinylene copolymers containing 3-alkylthiophene, selenophene or tellurophene. This allows us systematically investigate the role of selenium or tellurium on the polymer properties. Here, we report the first synthesis of novel 2,5-dibrominated 3-alkyltellurophene monomer and its Pd[0]-catalyzed copolymerization with (E)1,2-bis(tributylstannyl)ethylene to afford poly(3-alkyltellurophenylenevinylene) (P3ATeV). 8 We compare the optoelectronic properties of P3ATeV with analogous sulfur (P3ATV) and selenium (P3ASV) containing polymers. Preliminary OFET data will also be incorporated. Scheme 1. Structures of P3AX, P3AXV copolymers.Qscienc

Tailoring the deposition of MoSe2 on TiO2 nanorods arrays via radiofrequency magnetron sputtering for enhanced photoelectrochemical water splitting

MoSe2/1 D TiO2 nanorods (NRs) heterojunction assembly was systematically fabricated, and its photoelectrocatalytic properties were investigated. The fabrication process involves the growth of 1D TiO2 NRs arrays on FTO substrates using hydrothermal synthesis followed by the deposition of MoSe2 nanosheets on the TiO2 NRs using radiofrequency magnetron sputtering (RF magnetron sputtering). The photoelectrochemical properties of the heterojunction were explored and optimized as a function of the thickness of the MoSe2 layer, which was controlled by the sputtering time. The MoSe2 grows perpendicularly on TiO2 NRs in a 2D layered structure, maximizing the exposed active edges, an essential aspect that permits maximum exploitation of deposited MoSe2. Compared to pure TiO2 NRs, the heterojunction nanostructured assembly displayed excellent spectral and photoelectrochemical properties, including more surface oxygen vacancies, enhanced visible-light absorption, higher photocurrent response, and decreased charge transfer resistance. In particular, the sample synthesized by sputtering of MoSe2 for 90 s, i.e., MoSe2@TiO2-90 s, depicted the highest current density (1.86 mA cm−2 at 0.5 V vs. Ag/AgCl) compared to other samples. The excellent photoelectrochemical activity of the heterojunction stemmed from the synergy between tailored loading of MoSe2 nanosheets and the 1D structure of TiO2 NRs, which afford a high surface/volume ratio, effective charge separation, fast electron transfer, and easy accessibility to the MoSe2 active edges. These factors boost the catalytic activity.This work was made possible by NPRP Grant no. NPRP 12S-0304-190218 from the Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors. Open Access funding provided by the Qatar National Library.Scopu

Microwave-Assisted Solvothermal Synthesis of Mo-Doped TiO2 with Exceptional Textural Properties and Superior Adsorption Kinetics

Assigned to their outstanding physicochemical properties, TiO2-based materials have been studied in various applications. Herein, TiO2 doped with different Mo contents (Mo-TiO2) was synthesized via a microwave-assisted solvothermal approach. This was achieved using titanium (IV) butoxide and molybdenum (III) chloride as a precursor and dodecylamine as a surface directing agent. The uniform effective heating delivered by microwave heating reduced the reaction time to less than 30 min, representing several orders of magnitude lower than conventional heating methods. The average particle size ranged between 9.7 and 27.5 nm and it decreased with increasing the Mo content. Furthermore, Mo-TiO2 revealed mesoporous architectures with a high surface area ranging between 170 and 260 m2 g−1, which is superior compared to previously reported Mo-doped TiO2. The performance of Mo-TiO2 was evaluated towards the adsorption of Rhodamine B (RhB). In contrast to TiO2, which revealed negligible adsorption for RhB, Mo-doped samples depicted rapid adsorption for RhB, with a rate that increased with the increase in Mo content. Additionally, Mo-TiO2 expressed enhanced adsorption kinetics for RhB compared to state-of-the-art adsorbents. The introduced synthesis procedure holds a grand promise for the versatile synthesis of metal-doped TiO2 nanostructures with outstanding physicochemical properties.NPRP Grant no. NPRP 12S-0304-190218 from the Qatar National Research Fund (a member of the Qatar Foundation). The statements made herein are solely the responsibility of the authors

Russia and the Arab Spring: supporting the counter-revolution

Russia’s response to the Arab Spring ranged from apprehension to deep anxiety and diverged significantly from the US and the EU responses. While initially welcoming the popular demands for political reform in North Africa, the Russian reaction rapidly became more critical as a result of Western military intervention into Libya and the threat of the spread of Islamist extremism. It was these twin fears which prompted the Russian leadership to adopt an uncompromizing stance towards Syria. While geopolitical factors certainly played a role in driving Russian strategy, domestic political factors were also more significant. As the Russian leadership felt internally threatened by the growing opposition within the country, conflict in the Middle East highlighted the perceived flaws of the imposition of Western liberal democracy and the virtues of Russia’s own model of state-managed political order. There was, as such, a significant ideational and ideological dimension to the Russian response to the Arab Spring

The double [3+2] photocycloaddition reaction

One of a synthetic organic chemists‟ greatest challenges is to create step-efficient routes toward compounds with high molecular complexity. Therefore, reactions such as the meta photocycloaddition of an olefin to a benzene derivative, which provide more than one bond in a single step are of significant importance. It this remarkable reaction three new σ bonds, three new rings and up to six new stereocenters are formed simultaneously. Additional complexity can be added by tethering the two reacting partners together and this form of the reaction has found many uses in natural product synthesis. In this work a remarkable double [3+2] photocycloaddition reaction is reported that results in the formation of a complex cis, cis, cis, trans-[5, 5, 5, 5] fenestrane derivative from a simple flat aromatic acetal with two branching alkenes. During this dramatic transformation four carboncarbon bonds, five new rings and seven new stereocenters are created in a single one-pot process using only UV light. The reaction occurs in a sequential manner from the linear meta photocycloadduct, via a secondary [3+2] addition of the alkene across the cyclopropane of the adduct. In addition, an angular meta photocycloadduct also produced in the initial addition step, undergoes an alternative fragmentation-translocation photoreaction to afford a silphinene-like angular tricyclic compound. In this work the investigation of this newly discovered process is discussed via the synthesis and subsequent irradiation of a series of photosubstrates containing different functional groups in the arene-alkene tether. In addition, attempts toward the synthesis of alternative structures using the same double [3+2] photocycloaddition are reported