Static and stationary solutions of the Einstein-Maxwell equations

The Weyl axially symmetric electrovac formalism for coincident gravitational and electrostatic equipotential surfaces is used to generate charged versions of some axially symmetric vacuum fields. The metric for two separated charged Curzon particles held in equilibrium by a strut is found and the condition for the removal of the strut is discussed. Kinnersley transformations applied to the two-particle metric yield spin but line singularities invariably appear along the symmetry axis and the metric is asymptotically NUT-like. It is shown that any Kinnersley transformation applied to a static axially symmetric asymptotically flat vacuum metric generates another asymptotically flat metric only if the latter is static. Moreover, the transformed metric is always undercharged (q ²<m ²) if it is asymptotically flat. A necessary and sufficient condition for asymptotic flatness in terms of the relevant parameters is found. A generalization of the Kinnersley transformation scheme is presented and illustrated by an example.     

Existence,uniqueness and continuous dependence for hereditary systems

Summary An hereditary system is a system whose present state is determined in some way by its past history. We formulate a class of such systems which includes functional differential equations of retarded type and many equations of neulral type as well as Volterra integral equations. Theorems of existence, uniqueness, continuation and continuous dependence are proved. Preparation of this paper was sponsored in part by the Office of Naval Research under Contract NONR 233(76). Reproduction in whole or in part is permitted for any purpose of the United States Government. Entrata in Redazione il 22 gennaio 1969.     

ChemMatrix, a poly(ethylene glycol)-based support for the solid-phase synthesis of complex peptides

CM (ChemMatrix) resin is a new, totally poly(ethylene glycol) (PEG)-based resin, made exclusively from primary ether bonds and, therefore, highly chemically stable. It exhibits good loading and is user-friendly because of its free-flowing form upon drying. It performs excellently for the preparation of hydrophobic, highly structured, and poly-Arg peptides, as compared to polystyrene (PS) resins. In the most striking example, stepwise solid-phase assembly of the highly complex beta-amyloid (1-42) peptide resulted in a crude material of 91% purity. In contrast, literature procedures using PS or PEG-PS-based resins for this peptide required convergent approaches, additional time-consuming steps, or both. In addition to the difficulties of its synthesis, characterization of the beta-amyloid (1-42) peptide as a monomer is also a challenge, and methods for characterization by HPLC and MALDI-TOF have also been developed.     

Density excitations of a harmonically trapped ideal gas

The dynamic structure factor S(q, ω) of a harmonically trapped Bose gas has been calculated well above the Bose-Einstein condensation temperature by treating the gas cloud as a canonical ensemble of non-interacting classical particles. The static structure factor is found to vanish s8 q ² in the long-wavelength limit. We also incorporate a relaxation mechanism phenomenologically by including a stochastic friction force to study S(q, ω). A significant temperature dependence of the density fluctuation spectra is found. The Debye-Waller factor has been calculated for the trapped thermal cloud as a function of q and the number N of atoms. A substantial difference is found for small- and large-N clouds.     

Features of formation of channels during laser treatment of AlN ceramics

Using electron microscopy and X-ray microanalysis, the formation of tracks by laser processing of AlN:Y₂O₃ ceramic surfaces was investigated. The main process of channel formation is the decomposition of aluminum nitride (AlN). Due to aluminothermic reduction of Y₂O₃, the metallization of channel surfaces occurs. The main products of ablation are Al₂O₃, AlN, and AlON.     

Coherence freeze in an optical lattice investigated via pump-probe spectroscopy

Motivated by our observation of fast echo decay and a surprising coherence freeze, we have developed a pump-probe spectroscopy technique for vibrational states of 85Rb atoms in an optical lattice to gain information about the memory dynamics of the system. We monitor the time-dependent changes of frequencies experienced by atoms and characterize the probability distribution of these frequency trajectories. We show that the inferred distribution, unlike a naive microscopic model of the lattice, correctly predicts the main features of the observed echo decay.     

Multi-objective performance improvements of general finite single-server queueing networks

Optimizing the performance of general finite single-server acyclic queueing networks is a challenging problem and has been the subject of many studies. The version of the optimization problem treated here considers the minimization of the buffer areas and the service rates simultaneously with the maximization of the throughput. These are conflicting objectives, and the most appropriate methodology appears to be a multi-objective methodology. In fact, algorithms have previously been proposed, and the aim here is to show that the use of a mixed methodology can occasionally improve solutions without a significant increase in the computational costs. This paper shows that improvements in throughput can be achieved through a solution of a type of stochastic knapsack problem, which consists of redistributing the buffer spaces between the lines while preserving the overall capacity using a simulated annealing algorithm; that is, one objective is improved (the throughput) without worsening the other (the overall allocated capacity). A set of computational experiments are presented to demonstrate the effectiveness of the proposed approach. Additionally, some of the insights presented here may help scientists and practitioners in finite single-server queueing network planning.     

Macrocyclic chiral receptors toward enantioselective recognition of naproxen

[structure: see text] A macrocyclic receptor based on a bischromenylurea and an alpha,alpha'-(o,o'-dialkyl)diphenyl-p-xylylenediamine spacer provides a C(2) chiral cavity to associate carboxylates by H-bonds. The extent of the selectivity obtained for the racemic receptor 2 and enantiomerically pure (S)-naproxen is 7.2:1. Steric repulsions close to the cavity are decisive for the chiral selectivity.     

A residual method for solving nonlinear operator equations and their application to nonlinear integral equations using symbolic computation

A derivative-free residual method for solving nonlinear operator equations in real Hilbert spaces is discussed. This method uses in a systematic way the residual as search direction, but it does not use first order information. Furthermore a convergence analysis and numerical results of the new method applied to nonlinear integral equations using symbolic computation are presented.     

Electronic stopping power: Bragg's rule and Firsov's theory

It is shown that a modified version of Firsov's theory of the electronic stopping power, dE/dx, is a convenient formalism for studying departures from Bragg's Rule for composite targets. Within the procedures of this theory molecular hydrogen targets are compared with atomic hydrogen targets, and it is shown that Bragg's rule overestimates dE/dx for protons incident on molecular hydrogen by 11% at low proton velocities. A geometrical interpretation is given to the predicted chemical effects on dE/dx.