纳米晶枝CuAu合金催化剂对二氧化碳电催化还原性能的研究

利用可再生清洁能源将CO2转化为CO和其他小分子是合成含碳燃料的可观方法之一.间歇性可再生能源存储的重要策略之一是将二氧化碳进行电化学还原.选择具有高活性和稳定性的电催化剂对于电化学还原CO2至关重要.在这项研究中,我们使用简单的电沉积方法合成了具有纳米晶枝状结构的CuAu合金电极.各项表征显示原子比约为1∶1的CuA...     

Determination of boric acid in high nickel content solutions by neutron absorption method

Determination of boric acid in high nickel content solutions during nickel cathode production was made by measuring the transmission loss of thermal neutrons. According to industrial requirements, adequate accuracy and reproducibility were obtained.     

Using biased randomization for solving the two-dimensional loading vehicle routing problem with heterogeneous fleet

This paper discusses the two-dimensional loading capacitated vehicle routing problem (2L-CVRP) with heterogeneous fleet (2L-HFVRP). The 2L-CVRP can be found in many real-life situations related to the transportation of voluminous items where two-dimensional packing restrictions have to be considered, e.g.: transportation of heavy machinery, forklifts, professional cleaning equipment, etc. Here, we also consider a heterogeneous fleet of vehicles, comprising units of different capacities, sizes and fixed/variable costs. Despite the fact that heterogeneous fleets are quite ubiquitous in real-life scenarios, there is a lack of publications in the literature discussing the 2L-HFVRP. In particular, to the best of our knowledge no previous work discusses the non-oriented 2L-HFVRP, in which items are allowed to be rotated during the truck-loading process. After describing and motivating the problem, a literature review on related work is performed. Then, a multi-start algorithm based on biased randomization of routing and packing heuristics is proposed. A set of computational experiments contribute to illustrate the scope of our approach, as well as to show its efficiency.     

Development and optimization of a solid composite tyrosinase biosensor for phenol detection in flow injection systems

Bulk-modified epoxy-graphite tyrosinase biosensors were fabricated by four different procedures. The influence of these fabrication procedures on the analytical performance of the enzyme electrode in an amperometric wall-jet flow cell has been studied. The bioprobe performance is assessed by cyclic voltammetry. Higher current densities and narrower peaks were obtained when the enzyme was introduced in the dry state into the epoxy-graphite material, instead of introducing it previously dissolved in the buffer. In the F1 system responses of 11.79 μA cm⁻² and 1.43 μA cm⁻² are then obtained for catechol and phenol respectively for 50 μL injections of 20 μM solutions. Moreover, if gold/palladium is introduced into the epoxy-graphite, a further increase in current is achieved resulting in 27.70μA cm⁻² and 4.90μA cm⁻²for catechol and phenol, respectively. This biosensor can operate in aqueous as well as in mixed aqueous-organic environments.     

The Rhodium(II) Carbenoid Cyclization-Cycloaddition Cascade of alpha-Diazo Dihydroindolinones for the Synthesis of Novel Azapolycyclic Ring Systems

Tandem carbonyl ylide formation-1,3-dipolar cycloaddition of α-diazo N-acetyl-tetrahydro-β-carbolin-1-one derivatives occur efficiently in the presence of a dirhodium catalyst to afford bimolecular cycloadducts in high yield. The Rh(II)-catalyzed reaction also takes place intramolecularly to give products derived from trapping of the carbonyl ylide dipole with a tethered alkene. The power of the intramolecular cascade sequence is that it rapidly assembles a pentacyclic ring system containing three new stereocenters and two adjacent quaternary centers stereospecifically in a single step and in high yield.     

Homogeneous pyrolysis kinetics of ethyl 3-hydroxy-3-methylbutanoate in the gas phase

The pyrolysis kinetics of ethyl 3-hydroxy-3-methylbutanoate have been examined over the temperature range of 286–330°C and pressure range of 29–108 Torr. In a seasoned vessel and in the presence of the free radical inhibitor cyclohexene or toluene the reaction is homogeneous, unimolecular and obeys a first-order rate law. The elimination products are mainly acetone and ethyl acetate, and very small amounts of ethyl 3-butenoate, acetic acid, ethylene and H₂O. The rate coefficient is expressed by the following equation: log k₁(s^–1)=(12.39±0.46)–(174.5±5.2) kJ mol^–1 (2.303RT)^–1. The mechanism appears to proceed via a six-membered cyclic transition state, where polarization of the (CH₃)C(OH)^+...-CH₂COOCH₂CH₃ bond is rate determining.     

A planar subharmonically-pumped 71 GHz receiver with integral feed antenna

A planar, subharmonically-pumped, hybrid millimeter-wave receiver with integral antenna is described. Coplanar waveguide filters are used to isolate the ports and provide image enhancement. The integral planar antenna has 12 dB gain and is suited for use as a feed. The main lobe is normal to the substrate surface. The receiver is designed for an instantaneous bandwidth of 10 GHz. Experiments at 71 GHz indicate single-sideband mixer conversion loss of 6.5 dB. We believe that this represents the highest level of integration yet demonstrated in this frequency range.     

The mechanism of the elimination kinetics of 2-bromo-2-butene in the gas phase

The kinetics of the gas phase elimination of 2-bromo-2-butene were determined in a static system over the temperature range of 340–380°C and pressure range of 37–134 torr. The reaction in seasoned vessels, even in the presence of a free radical inhibitor, is catalyzed by hydrogen bromide. Under maximum catalysis of HBr, the kinetics were found to be of order 1.0. The reaction, when maximally catalyzed with HBr, appears to undergo a molecular elimination of HBr which follows first-order kinetics. The products are 1,2-butadiene and hydrogen bromide. The rate coefficients. under maximum catalysis, are given by the Arrhenius equation log ??₁(s^?1) = (13.57 ± 0.56) ? (200.4 ± 6.8) kJ mol^?1 (2.303RT)^?1. The catalyzed pyrolysis of 2-bromo-2-butene appears to proceed through a six-membered cyclic transition-state type of mechanism.