Two-dimensional pressure-driven nanorod-to-nanowire reactions in Langmuir monolayers at room temperature

Typical two-dimensional surface pressures prevalent within floating monolayer (Langmuir) films are on the order of a few dozen megapascals. One might expect, therefore, that some chemical reactions should be directly and strongly affected by this surface pressure, along with the well-known effect of pressure on the orientational order and the mere proximity of the molecules within the film. Here, we show that the two-dimensional surface pressure in Langmuir films provides a direct driving force, decreasing the activation energy of a cooperative oriented coalescence of ZnS nanorods into nanowires near room temperature. At low film surface pressure or low temperature, the nanorods do not react, while in solution, they react only above 140 degrees C, even though in all of these cases, the rods are organized in similar super-crystalline clusters. Electron microscopy and measurements of the reaction rates give a detailed picture of the order of the rods, their rearrangement, and their coalescence.     

A one-dimensional microscopic quantum mechanical theory of light enhanced desorption

A one-dimensional microscopic quantum mechanical model is used to inquire whether it is possible to enhance the desorption rate by employing a laser to induce vibrational excitation of the chemisorptive bond. For model parameters simulating CO/Cu it is found that the required laser intensity is very large, roughly 10⁴ times that of a conventional high power CO₂ laser (whose intensity we take to be $\text{5 × 10}{}^{10}\text{W}\text{cm}{}^2$). We suggest that surface roughness can be used to enhance substantially the effect of the laser and possibly to enable the observation of laser enhanced desorption.     

Simultaneous determination of ordering and amplifications of cascaded subsystems

Letn linear, time-invariant subsystems with transfer functionsT ₁(s),T ₂(s),...,T _n (s) be given. We are required to cascade these subsystems into a system with the transfer functionT(s)=kT ₁(s)T ₂(s) ...T _n (s), wherek>0, by determining the order of the subsystems and choosing for each subsystemi an amplification factork _i such thatk=k ₁ k ₂ ...k _n .We do this using the following optimality criterion: Given a setI, minimize the ratio of the maximum and the minimum of all the absolute values of all the intermediate outputs inI, for a flat input. This criterion is applicable in cases where the intermediate outputs should not be overdriven or underdriven. In particular, the method is applicable to the problem of determining an optimal ordering and intermediate amplifications of cascadedRC-active filters.The author is indebted to E. Lueder (Ref. 1) and J. Tow, who presented various criteria for optimal arrangements ofRC-active filters and motivated the formulation of this problem.     

Charge symmetry breaking interactions and coulomb energy differences

A detailed study of the possibility that the long standing discrepancies between theory and experiment in the values of Coulomb displacement energies have their origin in the charge asymmetry of the nuclear force is presented. A review of the present status of the theory of Coulomb displacement energies of mirror states is given. We have constructed a phenomenological charge asymmetric potential that can remove the Coulomb energy discrepancies for several mirror nuclei yet having only minimal effect on the ¹S₀ nucleon-nucleon scattering length. The form of this potential is however not compatible with the contributions due to charge asymmetric meson exchange processes that have been considered in the literature. We assume that these meson exchange effects can be reasonably described, up to strength factors, by a sum of one-pion, one-scalar-meson (σ) and one-vector-meson exchange potentials. The need for some additional type of charge asymmetric effect, e.g. three-body forces, is pointed out.     

The first general method for alpha-trifluoromethylation of carboxylic acids using BrF3

2-Carbomethoxy-1,1-bis(methylsulfide)-1-alkenes, easily made from carboxylic acids, CS(2) and MeI, were treated with BrF(3) producing eventually the desired alpha-trifluoromethyl carboxylate derivatives--RCH(CF(3))COOR'--in good yields.     

From alkyl halides to alkyltrifluoromethyls using bromine trifluoride

Under the right conditions, bromine trifluoride can be a useful tool for generating new types of reactions and compounds. Thus, tris(methylthio)alkyl derivatives, easily prepared from the corresponding alkyl bromides, were converted to the corresponding RCHBrCF2SMe or RCHBrCF3 compounds. The bromine atom, however, could be easily reduced forming eventually R'CF2SMe or R'CF3. If desired, the bromine atom can serve as an entry for constructing terminal difluoroolefins.     

Conducting Polymer Coated DNA

Gold electrode was modified with a 4-aminothiophenol layer (4-ATPh) to immobilize DNA. The immobilized DNA served as a template for the alignment of positively charged anilinium ions. The electrochemical oxidation of the anilinium ions resulted in wrapping of the DNA with polyaniline. This polyaniline coated DNA was characterized by cyclic voltammetry (CV), impedance spectroscopy and UV-VIS absorption spectroscopy.     

A note on conjugate gradient convergence – Part II

Summary. Continuing our previous analysis, we derive the exact number of conjugate gradient iterations needed (to achieve a given tolerance) for the one-dimensional discrete Poisson equation on a uniform grid, and a particularly smooth solution vector. Received July 29, 1998 / Published online March 16, 2000