High power single-frequency continuous-wave Nd:YVO4 master-oscillator power amplifier

We report a highly-efficient, high-power, single-frequency Nd:YVO₄ master-oscillator power-amplifier with near-diffraction-limited output beam quality. A diode-pumped Nd:YVO₄ ring laser incorporating a passive method for suppressing axial-mode-hopping was employed as the master-oscillator, and was amplified by a three-stage diode-end-pumped Nd:YVO₄ amplifier, yielding 79 W of output with an extraction efficiency of 29%. The overall power gain was 15 dB for an input power from the master-oscillator of 2.4 W, and the M² parameter was less than 1.5 at the maximum power. The prospects for a further increase of power and brightness via this approach are considered. PACS 42.55.Xi; 42.60.Da; 42.60.Jf     

Using integer programming techniques for the solution of an experimental design problem

Latin hypercube sampling is often used to estimate the distribution function of a complicated function of many random variables. In so doing, it is typically necessary to choose a permutation matrix which minimizes the correlation among the cells in the hypercube layout. This problem can be formulated as a generalized, multi-dimensional assignment problem. For the two-dimensional case, we provide a polynomial algorithm. For higher dimensions, we offer effective heuristic and bounding procedures.Supported in part by a grant from the National Institute of Standards and Technology (60NANB9D-0974).Supported in part by grants from the Office of Naval Research (N00014-90-J-1324) and the Air Force Office of Scientific Research (F49 620-90-C-0022).Research partially performed while visiting the Department of Mathematics, Brunel University, Uxbridge, England.     

Catalyst,additive and counterion effects on the efficiency and enantioselectivity of copper-catalysed C–H insertion reactions of α-diazosulfones

Asymmetric copper-catalysed intramolecular C–H insertion reactions of α-diazosulfones in the presence of various group I salts are reported leading to substantial variation in reaction efficiencies and enantioselectivities. The borate additives NaBARF and KBARF were found to be the most effective additives for permitting highly enantioselective syntheses with short reactions times and high efficiency. Significantly, direct evidence of the critical role of the additive in enantioselective carbenoid reactions has been secured.     

An iterative solver for a coupled system of Helmholtz equations

An iterative solver for a pair of coupled partial differential equations that are related to the Maxwell equations is discussed. The convergence of the scheme depends on the choice of two parameters. When the first parameter is fixed, the scheme is seen to be a successive under-relaxation scheme in the other parameter. A theory for convergence of the scheme is discussed for a special case of the equations, and several numerical examples are presented. © 1996 John Wiley & Sons, Inc.     

High power, long pulse duration, single-frequency Nd:YVO4 master-oscillator power-amplifier

An efficient single-frequency Nd:YVO₄ master-oscillator power-amplifier is described. Gated pulses from a CW diode-pumped ring laser were amplified by three Nd:YVO₄ amplifiers. Pulses of 1mJ energy; 2 kW peak power and 1 μs duration were obtained at a repetition frequency of 10 kHz. Analogue shaping of the input pulses was used to control the output pulse shape and thus extend the useful range of pulse widths from the 100 ns to the μs regime. A simple mathematical expression was used to model the results which provided reasonable agreement with the experimental work. This system offers a promising pump source for a quasi-CW singly-resonant optical parametric oscillators.     

Screening for cell migration inhibitors via automated microscopy reveals a Rho-kinase inhibitor

Small-molecule kinase inhibitors are predominantly discovered in pure protein assays. We have discovered an inhibitor of Rho-kinase (ROCK) through an image-based, high-throughput screen of cell monolayer wound healing. Using automated microscopy, we screened a library of approximately 16,000 compounds finding many that affected cell migration or cell morphology as well as compounds that blocked mitotic progression. We tested approximately 200 compounds in a series of subassays and chose one, 3-(4-pyridyl)indole (Rockout), for more detailed characterization. Rockout inhibits blebbing and causes dissolution of actin stress fibers, phenocopying Rho-kinase inhibitors. Testing Rho-kinase activity in vitro, Rockout inhibits with an IC50 of 25 microM ( approximately 5-fold less potent than Y-27632) but has a similar specificity profile. We also profile the wound healing assay with a library of compounds with known bioactivities, revealing multiple pathways involved in the biology.     

The Two-Period Travelling Salesman Problem Applied to Milk Collection in Ireland

We describe a new extension to the Symmetric Travelling Salesman Problem (STSP) in which some nodes are visited inboth of 2 periods and the remaining nodes are visited in either 1 ofthe periods. A number of possible Integer Programming Formulationsare given. Valid cutting plane inequalities are defined for thisproblem which result in an, otherwise prohibitively difficult, modelof 42 nodes becoming easily solvable by a combination of cuts andBranch-and-Bound. Some of the cuts are entered in a pool andonly used when it is automatically verified that they are violated.Other constraints which are generalisations of the subtour and combinequalities for the single period STSP, are identified manuallywhen needed. Full computational details of solution process aregiven.     

Condensation in preferential attachment models with location‐based choice

We introduce a model of a preferential attachment based random graph which extends the family of models in which condensation phenomena can occur. Each vertex has an associated uniform random variable which we call its location. Our model evolves in discrete time by selecting r vertices from the graph with replacement, with probabilities proportional to their degrees plus a constant α. A new vertex joins the network and attaches to one of these vertices according to a given probability associated to the ranking of their locations. We give conditions for the occurrence of condensation, showing the existence of phase transitions in α below which condensation occurs. The condensation in our model differs from that in preferential attachment models with fitness in that the condensation can occur at a random location, that it can be due to a persistent hub, and that there can be more than one point of condensation.