Changes in surface chemistry of an Ir---W mixed metal coated cathode during activation

A comparative study has been made between a mixed metal (60% Ir-40%W) coated cathode and a “B” cathode during activation and also in their respective steady states. The rate limiting factor in the activation of the coated cathode is the oxidation of the initial Ba type surface to a BaO type surface. Since on the “B” cathode Ba and O emerge together, its activation is faster than the coated cathode. In the steady state of operation, both cathodes exhibit a surface near BaO stoichiometry which is the optimum composition for the minimum work function. This work function is about 0.2 eV lower on the coated cathode than on the “B” cathode. An accelerated life test at 1575 K indicated a gradual decrease of the Ir concentration in the coating.     

The Preparation of Heptacyclo[6.6.0.0.2,60.3,130.4,11 0.5,90.10,14]Tetradecane Derivatives and the Analysis of Their NMR Spectra

The title compound is functionalized by a series of reactions to yield derivatives in the forms of hydroxides, ketones, ketals, lactones, etc. Their structures are analyzed by NMR spectroscopy.     

On the dynamics of a tethered satellite system

The Hamiltonian structure for a fundamental model of a tethered satellite system is constructed. The model is composed of two point masses connected by a string with no restrictions on the motions of the two masses. A certain symmetry with respect to the special orthogonal group SO(3) for such a system is observed. The classical station-keeping mode for the tethered system is found to be nothing more than the relative equilibrium corresponding to the reduction of the system by the symmetry. The microgravity forces on the two point masses are responsible for the possible configurations of the string at the so-called radial relative equilibrium. A stability analysis is performed on the basis of the reduced energy-momentum method. Criteria for stability are derived, which could find potential applications in space technology.     

Generalized quasi-variational inequalities in locally convex topological vector spaces

Let E be a Hausdorff topological vector space and X ? E an arbitrary nonempty set. Denote by E′ the dual space of E and the pairing between E′ and E by 〈w, x〉 for w?E′ and x?E. Given a point-to-set map S: X → 2^X and a point-to-set map T: X → 2^E′, the generalized quasi-variational inequality problem (GQVI) is to find a point $\text{y}\text{?}\text{? S(}\text{y}\text{?}\text{)}$ and a point $\text{u}\text{?}\text{? T(}\text{y}\text{?}\text{)}$ such that $\text{Re}\text{〈}\text{u}\text{?}\text{,}\text{y}\text{?}\text{? x〉 ? 0}$ for all $\text{x ? S(}\text{y}\text{?}\text{)}$. By using the Ky Fan minimax principle or its generalized version as a tool, some general theorems on solutions of the GQVI in locally convex Hausdorff topological vector spaces are obtained which include a fixed point theorem due to Ky Fan and I. L. Glicksberg, and two different multivalued versions of the Hartman-Stampacchia variational inequality.     

Co-ordinated movements to avoid collisions of a twin-robot system

A method of modelling collision avoidance between separate coordinated arms in the process of changing hands is presented. The shortest distance between two forearms is chosen as the criterion for kinematic modelling. Trajectories of various geometries are classified with respect to different collision situations. Parameters to be adjusted to avoid collisions are also discussed. To illustrate the modelling technique, two redundant anthropomorphic robots are considered to cooperate in rotating a wheel.     

Enhancing control of grid distribution in algebraic grid generation

Three techniques are presented to enhance the control of grid-point distribution for a class of algebraic grid generation methods known as the two-, four- and six-boundary methods. First, multidimensional stretching functions are presented, and a technique is devised to construct them based on the desired distribution of grid points along certain boundaries. Second, a normalization procedure is proposed which allows more effective control over orthogonality of grid lines at boundaries and curvature of grid lines near boundaries. And third, interpolating functions based on tension splines are introduced to control curvature of grid lines in the interior of the spatial domain. In addition to these three techniques, consistency conditions are derived which must be satisfied by all user-specified data employed in the grid generation process to control grid-point distribution. The usefulness of the techniques developed in this study was demonstrated by using them in conjunction with the two- and four-boundary methods to generate several grid systems, including a three-dimensional grid system in the coolant passage of a radial turbine blade with serpentine channels and pin fins.     

二异丁基锌控制高密度聚乙烯分子量的研究

本文报告了TiCl_4-MgCl_2-AlCl_3/Al(i-Bu)_3-Zn(i-Bu)_2催化体系的乙烯聚合反应中,二异丁基锌对产物分子量和聚合活性的影响。结果表明:在适宜的聚合条件下,二异丁基锌可以有效地控制产物的分子量。     

PPC-based Reactive Hot Melt Polyurethane Adhesive(RHMPA)——Efficient Glues for Multiple Types of Substrates

Tens of billion metric tons of anthropogenic CO_2 discharged from the burning of fossil fuels lead to an enormous environmental and resource burden. It is charming to transform CO_2 to desirable, economical chemicals and materials. Poly(propylene carbonate)(PPC) is an emerging CO_2-based material. Herein, we report the design, synthesis and characterization of the reactive hot melt polyurethane adhesive(RHMPA) based on PPC polyol. The resultant RHMPAs exhibit good adhesion properties to multiple substrates including plastics(PC, PMMA, ABS) and metals(aluminium, steel), which is comparable to or even better than conventional RHMPAs prepared from petro-based polyol. Furthermore, the PPC-based RHMPAs have tunable mechanical properties, and are thermally stable in the typical working range of bonding process(up to 270 °C). The study is expected to expand the applications of PPC and provide a new type of CO_2-based renewable and eco-friendly materials.     

Selective Nascent Polymer Catch‐and‐Release Enables Scalable Isolation of Multi‐Kilobase Single‐Stranded DNA

Scalable methods currently are lacking for isolation of long ssDNA, an important material for numerous biotechnological applications. Conventional biomolecule purification strategies achieve target capture using solid supports, which are limited in scale and susceptible to contamination owing to nonspecific adsorption and desorption on the substrate surface. We herein disclose selective nascent polymer catch and release (SNAPCAR), a method that utilizes the reactivity of growing poly(acrylamide‐co‐acrylate) chains to capture acrylamide‐labeled molecules in free solution. The copolymer acts as a stimuli‐responsive anchor that can be precipitated on demand to pull down the target from solution. SNAPCAR enabled scalable isolation of multi‐kilobase ssDNA with high purity and 50–70 % yield. The ssDNA products were used to fold various DNA origami. SNAPCAR‐produced ssDNA will expand the scope of applications in nanotechnology, gene editing, and DNA library construction.     

Synthesis of N,N2-Disubstituted DL-β-Asparagines as Potential Hypocholesteremics

By the addition of equivalent amount of appropriate amine on the carbon-carbon double bond of N-substituted maleamic acids under the influence of pyridine, a number of potential hypocholesteremics, N,N²-disubstituted DL-β-asparagines was prepared. For all N-alkyl- and N-arylmaleamic acids, the addition proceeded smoothly and resulted in satisfactory yields, but in the cases of N-heterocyclic analogs, transamidation was observed to occur simultaneously with the addition reactions.