DFT study of coinage metal-hydrogen associations as hydrogen storage materials stabilized by weakly coordinating anions

Density Functional Theory (DFT) calculations were employed to study a series of coinage metal-hydrogen associations formulated as [M(Η₂)_n][A] (M = Cu^I, Ag^I or Au^I, n = 1–5). The [M(Η₂)_n][A] salts utilize both their anions and cations for H₂ storage. The [M(Η₂)_n]⁺ cations could be stabilized in the solid state by voluminous counter-anions, i.e. the [(H₃B) (BH₂NH₂)₅(NH₂)]^-, [B(CNBH₃)₃]^- and [B₁₂H₁₂]^- anions. The estimated bond dissociation energies (BDEs) of the M···(η²-H₂) bonds are 5–17, 4–11 and 1–26 kcal/mol for the [Cu(Η₂)₄]⁺, [Ag (Η₂)₄]⁺ and [Au (Η₂)₄]⁺ cationic species respectively, while the fifth H₂ molecule is estimated to be very loosely associated to the metal center. Four H₂ molecules could be exploited from the [Cu(Η₂)_n][A] and [Ag (Η₂)_n][A] molecules in addition to the amount of H₂ stored in the anion [A]^-. Among the [M(Η₂)_n][A] salts optimal gravimetric, kinetic and thermodynamic properties and relatively low cost, are predicted for [Cu(Η₂)_n][(H₃B) (BH₂NH₂)₅(NH₂)].     

Mixed matrix proton exchange membranes for fuel cells: State of the art and perspectives

Proton-conducting mixed matrix membranes (PC-MMMs) have received considerable interest as promising materials that combine the properties of, and create synergism from interactions between, polymeric and inorganic components. The PC-MMM exhibit superior characteristics compared to individual ion-conducting polymeric membranes or free-standing electrolyte inorganic films. Recent advancements in material preparation have enhanced the ability to design PC-MMMs with specified properties. This critical review discusses the progress of the development of PC-MMMs, with special focus on PC-MMMs based on emerging materials, such as porous materials, metal organic frameworks (MOFs), carbon nanotubes (CNTs) and graphene oxides (GOs). Major challenges facing PC-MMMs and strategies taken to overcome those challenges and future perspectives are discussed.     

活性染料对海洋生物活性纤维染色性能的研究

本实验选取具有双活性基团的FN型、LS型、B型活性染料对其进行染色,通过测量残液吸光度来测定染料的上染率及固色率,确定选择上染率较高的B型活性染料上染海洋生物活性纤维。通过正交实验研究了盐量、碱剂及碱量对活性染料上染海洋生物活性纤维的上染速率的影响,最终得出B型活性染料染色的最佳工艺。     

Kinetics of dimethyl ether oxidation over Pt/ZSM-5 catalyst

A kinetic study of dimethyl ether (DME) combustion over Pt/ZSM-5 was performed below 423 K. Power law model and Langmuir-Hinshelwood model were established to predict the reaction rate. Reaction orders for DME and O₂ were 0.28 and 2.30, respectively. Activation energies for the two models were 99.35 and 109.30 kJ/mol. The reaction orders and adsorption constants suggested DME was more strongly adsorbed on Pt/ZSM-5 than O₂ at low temperatures. The reliability of the models was confirmed by the comparison between the predicted and experimental conversions of DME.     

Effect of the water content of padded cotton fabrics on reactive dye fixation in the pad-steam process

A series of padded cotton fabrics with various water contents were obtained through vacuum dehydration. The effects of the water content on the fabric temperature variation during steaming, the colour properties, and the dye fixation rate (%F) were investigated. Dye distribution in the dyed cotton fibres was assessed. The influences of steaming time and sodium carbonate concentration on K/S value and %F of the dyed fabrics with low water content were also evaluated. The results indicate that reducing the water content of the padded cotton fabric to around 25.0% prior to steaming was favoured for reactive dyeing. The temperature of the wet fabric rose rapidly, the K/S value and %F were enhanced, and in addition the dye penetration into the dyed cotton fibres was sufficient. However, for padded fabrics with extraordinarily low and high water contents (e.g. 1.4% and 70.9% respectively), both the K/S value and %F were decreased. Furthermore, a white core phenomenon was evident for the fibres of the dyed fabric with a water content of 1.4%. Variation in the L^* values was in line with the K/S values as the fabric water content varied. As expected, steaming time and sodium carbonate dosage can also affect reactive dye fixation greatly and should be determined accordingly for dyeing cotton fabric with low water content.     

具有震颤抑制的微创机器人主从控制系统设计

详述了一种用于抑制微创手术机器人震颤现象的主从控制系统，提出了针对人手生理震颤的新型零相位滤波方法及针对从操作臂关节“粘滑行为”的前馈补偿PD伺服算法。新型零相位滤波避免了传统低通滤波器容易造成延时和传统零相位滤波无法在线使用的缺点，前馈补偿PD伺服算法通过摩擦补偿克服了非线性摩擦对从操作臂运动造成的影响。最后，对系统进行仿真及实验，结果表明该方法能有效地抑制机器人手术工具末端的震颤现象。     

Bounded memory protocols

It is well-known that the Dolev–Yao adversary is a powerful adversary. Besides acting as the network, intercepting, decomposing, composing and sending messages, he can remember as much information as he needs. That is, his memory is unbounded. We recently proposed a weaker Dolev–Yao like adversary, which also acts as the network, but whose memory is bounded. We showed that this Bounded Memory Dolev–Yao adversary, when given enough memory, can carry out many existing protocol anomalies. In particular, the known anomalies arise for bounded memory protocols, where although the total number of sessions is unbounded, there are only a bounded number of concurrent sessions and the honest participants of the protocol cannot remember an unbounded number of facts or an unbounded number of nonces at a time. This led us to the question of whether it is possible to infer an upper-bound on the memory required by the Dolev–Yao adversary to carry out an anomaly from the memory restrictions of the bounded protocol. This paper answers this question negatively (Theorem 8).     

Structural evolution in graphitization of nanofibers and mats from electrospun polyimide–mesophase pitch blends

The evolution of structure in multi-step thermal treatment of polyimide–mesophase pitch (PI–pitch) blend nanofiber mats obtained by an electrospinning process is described. The mats were thermally treated at a series of stages up to 3000 °C. The structural transformation of the nanofiber mats consisted of three regimes. First regime corresponds to the removal of the majority of non-carbon elements and the formation of initial residual carbon. Second regime involves slow growth of the graphitic layers and slow improvement of their stacking order. Progressive graphitization occurs in regime three when the fibers become highly graphitic. The addition of pitch was found to give rise to overall enhanced graphitic order in the PI–pitch blend nanofibers as reflected in the smaller inter-layer spacing d₀₀₂ approaching that of the perfect graphite crystal, and the larger crystal sizes, L_c and L_a, confirmed by XRD analysis, as well as the higher ratio of graphitic structure revealed by Raman spectroscopy. Development of highly localized oriented domains in these nanofibers were observed by dark field TEM. The addition of pitch led to enhancement of both electrical and thermal conductivity.     

Developing lithium ion battery silicon/cobalt core-shell electrodes for enhanced electrochemical properties

In this work, core-shell Si/Co composite powders were produced using an electroless deposition process. The effect of different concentrations of CoSO₄ in the plating bath was studied to provide the Co deposition and to reveal the structure on the surface of silicon powders. The surface morphology and the composition of the produced Si/Co composite powders were characterized using scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS). X-ray diffraction (XRD) analysis was performed to investigate the structure of the Si/Co composite powders. The discharge capacities of Si/Co composite electrodes were determined with cyclically testing, and resistivity of the produced Si/Co composite electrodes were studied using electrochemical impedance spectroscopy (EIS). The silicon/cobalt composite electrode produced using 40 g/L CoSO₄ exhibited the most stable capacity retention, and a discharge capacity of approximately 220 mAh/g was obtained after 15 cycles for this electrode. This study demonstrated that the conductivity of the electrodes was improved and the capacity retention of the Si/Co composite electrodes was increased by increasing the shell structured cobalt content on the surface of silicon powders due to the buffering effect of cobalt against huge volume changes during the lithiation and delithiation process.