A repetitively pulsed sealed-TE CO2 laser using an oxygen tolerant discharge scheme

A repetitively pulsed (40 Hz) TE CO₂ laser using an oxygen tolerant discharge scheme is described. Long lived (>10⁵ shots) stable discharges at high pump energy density (200 J.l^–1 atm^–1) have been achieved both with and without the use of additive gases.     

The mathematics of scattering by unbounded,rough, inhomogeneous layers

In this paper we study, via variational methods, a boundary value problem for the Helmholtz equation modelling scattering of time harmonic waves by a layer of spatially varying refractive index above an unbounded rough surface on which the field vanishes. In particular, in the 2D case with TE polarization, the boundary value problem models the scattering of time harmonic electromagnetic waves by an inhomogeneous conducting or dielectric layer above a perfectly conducting unbounded rough surface, with the magnetic permeability a fixed positive constant in the medium. Via analysis of an equivalent variational formulation, we show that this problem is well-posed in two important cases: when the frequency is small enough; and when the medium in the layer has some energy absorption. In this latter case we also establish exponential decay of the solution with depth in the layer. An attractive feature is that all constants in our estimates are bounded by explicit functions of the index of refraction and the geometry of the scatterer.     

Screening of rationally designed oligopeptides for Listeria monocytogenes detection by means of a high density colorimetric microarray

The aim of this work was to optimize, by means of molecular modeling software, biomimetic-based traps for pathogen detection suitable for analytical applications like screening or pre-analytical methods. The pathogen prototype system chosen was Listeria monocytogenes because of the large number of X ray and NMR structures available. 298 oligopeptides were computationally designed mimicking the binding pocket of the mammalian protein E-cadherin, the target of Listeria monocytogenes adhesion, internalin A. The contribution of individual peptides to bind was investigated using FRED, a protein-ligand docking program. Ten peptides were selected for experimental analysis taking as selection parameters the length, the position in the docking pocket and the score of simulated binding energy. A series of competition assays were carried out using high density colorimetric microarray using various bacteria species (Listeria monocytogenes, Listeria monocytogenes genetically modified without internalin A, Listeria innocua and Lactococcus lactis) in solution with computationally selected peptides. The data demonstrated that peptides could be able to distinguish Listeria monocytogenes with an EC₅₀ up to 10⁷cfu × mL^?1. In particular the peptide with the best calculated binding score gave the highest statistically unambiguous response toward Listeria monocytogenes compared to other bacteria, demonstrating that rationally simulated approach can be useful as preliminary screening in the choice of biomimetic ligands.     

A New Algorithm in Electromagnetic Inverse Scattering Theory with an Application to Medical Imaging

We consider the electromagnetic inverse scattering problem of determining the index of refraction of an isotropic inhomogeneous medium from a knowledge of the total electric near field data. We consider both the case of scattering by an infinite inhomogeneous cylinder and a bounded inhomogeneous region in space. We conclude by giving an application of our method to the problem of imaging leukemia in the upper leg by means of microwaves. © 1997 by B. G. Teubner Stuttgart–John Wiley & Sons Ltd.     

Gauss point mass lumping schemes for Maxwell's equations

Finite element and finite difference methods for approximating the Maxwell system propagate numerical waves with slightly incorrect velocities, and this results in phase error in the computed solution. Indeed this error limits the type of problem that can be solved, because phase error accumulates during the computation and eventually destroys the solution. Here we propose a family of mass-lumped finite element schemes using edge elements. We emphasize in particular linear elements that are equivalent to the standard Yee FDTD scheme, and cubic elements that have superior phase accuracy. We prove theorems that allow us to perform a dispersion analysis of the two common families of edge elements on rectilinear grids. A result of this analysis is to provide some justification for the choice of the particular family we use. We also provide a limited selection of numerical results that show the efficiency of our scheme. © 1998 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 14: 63–88, 1998     

Determination of beryllium by means of hexamminecobalt(III) carbonatoberyllate—I Composition of the precipitate and its suitability as a weighing form for beryllium

The precipitate obtained when hexamminecobalt(III) chloride is added to a solution of beryllium in excess ammonium carbonate has been analysed and its behaviour under different humidity conditions examined. The composition is that of hexamminecobalt(III) hexacarbonato-oxo-tetraberyllate [Co(NH₃)₆]₂[Be₄O(CO₃)₆]·xH₂O, as suggested by Sen Gupta, rather than that of Pirtea [Co(NH₃)₆][(H₂O)₂ Be₂(CO₃)₂(OH)₃]·3H₂O.x depends on the humidity of conditioning, varying between 10.8 and 11.1 at relative humidities between 32 and 80%. Drying the precipitate in vacuo over anhydrous magnesium perchlorate or phosphorus pentoxide results in 3 molecules of water being retained. The compound as normally precipitated may be a mixture of the deca- and dodecahydrates that Sen Gupta prepared. After conditioning at a definite humidity and if an empirical factor is used, the precipitate may be suitable as a gravimetric form for determining beryllium where precision requirements are not too exacting.     

The generation of Bessel beams at millimetre-wave frequencies by use of an axicon

An axicon is used to generate a Bessel beam at 90 GHz in the millimetre-wave region of the spectrum. The Bessel beam has a central intensity maximum of approximately 4 mm in diameter that is maintained over a propagation distance greater than 60 mm.