Thermal field emission as a mechanism for infrared laser light detection in metal whisker diode

The non-linear current-voltage characteristic of thermally enhanced field emission is proposed to explain the operation of a metal-metal point contact diode used for laser harmonic frequency generation and frequency mixing in the infrared region. This mechanism can explain several experimental observations which appear inconsistent with the previous analysis based on a planar metal-oxide-metal tunneling geometry.     

Generalized gauge independence and the physical limitations on the von Neumann measurement postulate

An analysis is presented of the significance and consequent limitations on the applicability of the von Neumann measurement postulate in quantum mechanics. Directly observable quantities, such as the expectation value of the velocity operator, are distinguished from mathematical constructs, such as the expectation value of the canonical momentum, which are not directly observable. A simple criterion to distinguish between the two types of operators is derived. The non-observability of the electromagnetic four-potentials is shown to imply the non-measurability of the canonical momentum. The concept of a mechanical gauge is introduced and discussed. Classically the Lagrangian is nonunique within a total time derivative. This may be interpreted as the freedom of choosing a mechanical (M) gauge function. In quantum mechanics it is often implicitly assumed that the M-gauge vanishes. However, the requirement that directly observable quantities be independent of the arbitrary mechanical gauge is shown to lead to results analogous to those derived from the requirement of electromagnetic gauge independence of observables. The significance of the above to the observability of transition amplitudes between field-free energy eigenstates in the presence (and absence) of electromagnetic fields is discussed. E- and M-gauge independent transition amplitudes between field-free energy eigenstates in the absence of electromagnetic fields are defined. It is shown that, in general, such measurable amplitudes cannot be defined in the presence of externally applied time-dependent fields. Transition amplitudes in the presence of time-independent fields are discussed. The path dependence of previous derivations of E-gauge independent Hamiltonians and/or transition amplitudes in the presence of electromagnetic fields are related to the inherent M-gauge dependence of these quantities in the presence of such fields.     

An affinity probe for isolation of abscisic acid-binding proteins

An affinity probe has been developed for isolation of receptor proteins that bind the plant hormone abscisic acid (ABA). The structural features required for biological activity have been preserved, and the probe has been demonstrated to bind to known ABA-binding proteins.     

Threefold bonding of tellurium in liquid semiconductor alloys

Bond orbital considerations show that a third covalent band in tellurium is unstable unless the concentration of threefold bonded (3F) tellurium atoms is smaller than the concentration of dangling bonds. At low hole concentrations, the formation of 3F atoms is inhibited further because of non-linear screening of their positive charge, which results in a large electrostatic energy. Consequently 3F bonding becomes important only in liquids whose electrical conductivity is higher than an estimated value $\text{≈1500 Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$.     

Extremal Graphs for Homomorphisms II

Extremal problems for graph homomorphisms have recently become a topic of much research. Let denote the number of homomorphisms from G to H. A natural set of problems arises when we fix an image graph H and determine which graph(s) G on n vertices and m edges maximize . We prove that if H is loop‐threshold, then, for every n and m, there is a threshold graph G with n vertices and m edges that maximizes . Similarly, we show that loop‐quasi‐threshold image graphs have quasi‐threshold extremal graphs. In the case , the path on three vertices in which every vertex in looped, the authors [5] determined a set of five graphs, one of which must be extremal for . Also in this article, using similar techniques, we determine a set of extremal graphs for “the fox,” a graph formed by deleting the loop on one of the end‐vertices of . The fox is the unique connected loop‐threshold image graph on at most three vertices for which the extremal problem was not previously solved.     

Nanopod formation through gold nanoparticle templated and catalyzed cross-linking of polymers bearing pendant propargyl ethers

A novel method for synthesizing polymer nanopods from a linear polymer bearing pendant propargyl ether groups, using gold nanoparticles as both the template and the catalyst for the cross-linking reaction, is reported. The transformations involved in the cross-linking process are unprecedented on the surface of a gold particle. A tentative cross-linking mechanism is proposed.     

Minimizing the number of independent sets in triangle-free regular graphs

Recently, Davies, Jenssen, Perkins, and Roberts gave a very nice proof of the result (due, in various parts, to Kahn, Galvin–Tetali, and Zhao) that the independence polynomial of a $d$-regular graph is maximized by disjoint copies of $K_{d,d}$. Their proof uses linear programming bounds on the distribution of a cleverly chosen random variable. In this paper, we use this method to give lower bounds on the independence polynomial of regular graphs. We also give a new bound on the number of independent sets in triangle-free cubic graphs.     

Effect of minor alloying additions on the solidification of single-crystal Ni-base superalloys

Grain boundary elements, such as carbon and boron, were initially removed from single-crystal alloys, but more recently they have been added back into single-crystal alloys for increased castability and defect tolerance. The mechanism(s) for the increased castability is not completely understood. In this study, carbon was added to the second generation, single crystal, Ni-base superalloy and CMSX-4, to form MC-type carbides. Then either nitrogen or boron was added to the carbon-containing alloy to alter the carbide morphology and the castability of the alloy. The segregation coefficients of the alloying elements in CMSX-4 were measured with varying techniques, but no changes in partitioning were observed. The addition of carbon to CMSX-4 did reduce the number of solidification defects observed in the samples. The addition of carbon and boron to CMSX-4 did not significantly change the number of solidification defects compared to the carbon-only alloy. However, the addition of nitrogen and carbon resulted in an increase in the number of solidification defects in the CMSX-4 samples compared to the baseline CMSX-4 and carbon-containing CMSX-4 samples. The effects of these alloy additions on the carbide morphology and solidification defects are discussed.