Multi-gigabit WDM optical networking for next generation avionics system communications

It is envisaged that photonic networking will play a significant role in improving performance and reliability in both civil and military avionics systems. Of all the available photonic multiplexing technologies, wavelength-division multiplexing (WDM) has been the primary focus of attention within mainstream telecommunications offering increased throughput at a reasonable cost, with scope for enhanced routing flexibility, connectivity and network survivability. A direct mapping of techniques and devices from the maturing telecommunications sector is, however, not possible because of the stringent requirements of systems operating in the hostile aerospace environment. This paper gives an outline of these requirements and discusses, in detail, the design and development of a multi-gigabit, broadband optical WDM network architecture, specifically for use on aerospace platforms. The paper will also discuss a key element in the system, the arrayed-waveguide grating (AWG) wavelength multiplexing component, which has been designed to allow operation over the full military temperature specification without environmental conditioning.     

Combinatorial Isols and the Arithmetic of Dekker Semirings

In his long and illuminating paper [1] Joe Barback defined and showed to be non‐vacuous a class of infinite regressive isols he has termed “complete y torre” (CT) isols. These particular isols a enjoy a property that Barback has since labelled combinatoriality. In [2], he provides a list of properties characterizing the combinatoria isols. In Section 2 of our paper, we extend this list of characterizations to include the fact that an infinite regressive isol X is combinatorial if and only if its associated Dekker semiring D (X) satisfies all those Π₂ sentences of the anguage L_N for isol theory that are true in the set ω of natural numbers. (Moreover, with X combinatorial, the interpretations in D(X)of the various function and relation symbols of L_N via the “lifting ” to D(X) of their Σ₁ definitions in ω coincide with their interpretations via isolic extension.) We also note in Section 2 that Π₂(L)‐correctness, for semirings D(X), cannot be improved to Π ₃(L)‐correctness, no matter how many additional properties we succeed in attaching to a combinatoria isol; there is a fixed (L) sentence that blocks such extension. (Here L is the usual basic first‐order language for arithmetic.) In Section 3, we provide a proof of the existence of combinatorial isols that does not involve verification of the extremely strong properties that characterize Barback's CT isols.     

Existence and uniqueness results for the non-autonomous coagulation and multiple-fragmentation equation

An initial-value problem modelling coagulation and fragmentation processes is studied. The results of earlier papers are extended to models where either one or both of the rates of coagulation and fragmentation depend on time. An abstract integral equation, involving the solution operator to the linear fragmentation part, is investigated via the contraction mapping principle. A unique global, non-negative, mass-conserving solution to this abstract equation is shown to exist. The latter solution is used to generate a global, non-negative, mass-conserving solution to the original non-autonomous coagulation and multiple-fragmentation equation. © 1998 B. G. Teubner Stuttgart–John Wiley & Sons Ltd.     

Movement of drops on a solid surface due to a contact angle gradient

Experimental results on the motion of liquid drops on horizontal surfaces resulting from a contact angle gradient are presented. Silicon surfaces were modified using dodecyltrichlorosilane to generate the gradient. Water drops with initial diameters of 0.31 ‐ 0.5 mm (15 ‐ 65 nl) were placed on the surface, their movement videotaped, and subsequently analyzed. To characterize the gradient surface the static contact angle was measured along the surface.     

Chemical tuning of positive and negative magnetoresistances, and superconductivity in 1222-type ruthenocuprates

A remarkable variety of conducting states has been found in RuSr2(R2-xCex)Cu2O10-delta ruthenocuprates by tuning the properties of the magnetic CuO2 and RuO2 layers through small changes in the chemistry of the (R,Ce)2O2-delta slab. Both the R3+ cation size and the charge transfer determined by the R/Ce ratio and the oxygen deficiency delta are important controlling parameters that tune ground-state properties from positive magnetoresistive to negative magnetoresistive to superconducting.     

Experiments on the motion of drops on a horizontal solid surface due to a wettability gradient

Results from experiments performed on the motion of drops of tetraethylene glycol in a wettability gradient present on a silicon surface are reported and compared with predictions from a recently developed theoretical model. The gradient in wettability was formed by exposing strips cut from a silicon wafer to dodecyltrichlorosilane vapors. Video images of the drops captured during the experiments were subsequently analyzed for drop size and velocity as functions of position along the gradient. In separate experiments on the same strips, the static contact angle formed by small drops was measured and used to obtain the local wettability gradient to which a drop is subjected. The velocity of the drops was found to be a strong function of position along the gradient. A quasi-steady theoretical model that balances the local hydrodynamic resistance with the local driving force generally describes the observations; possible reasons for the remaining discrepancies are discussed. It is shown that a model in which the driving force is reduced to accommodate the hysteresis effect inferred from the data is able to remove most of the discrepancy between the observed and predicted velocities.     

Removal of a single minor-groove functional group eliminates A-tract curvature

Much of the work in studying the phenomenon of A-tract curvature has involved the insertion of modified residues into the A-tract sequence and then cross-correlation of the structural differences with the resulting curvature effects. In the A-tract sequence d(A-T)5, removal of a single functional group (the O2-carbonyl of the central dT residue) by its replacement with hydrogen completely eliminates the curvature properties. This atom-specific change was accomplished by using the C-nucleoside dm32P in which the O2-carbonyl is replaced with -H but normal Watson-Crick hydrogen bonding is maintained. Similar derivatives with -F (dF62P) or -CH3 (dm62P) when present for the central dT residue also eliminate curvature. Finally, we have shown that the extent of curvature for sequences containing this carbonyl are sensitive to the [Mg2+], while those lacking the carbonyl show little to no Mg2+ dependence, strongly suggesting, we believe, a role for Na+/Mg2+ cooperative interactions in the minor groove to explain the curvature phenomenon.     

Regioselective bond cleavage in the dissociative electron transfer to benzyl thiocyanates: the role of radical/ion pair formation

Important aspects of the electrochemical reduction of a series of substituted benzyl thiocyanates were investigated. A striking change in the reductive cleavage mechanism as a function of the substituent on the aryl ring of the benzyl thiocyanate was observed, and more importantly, a regioselective bond cleavage was encountered. A reductive alpha-cleavage (CH(2)-S bond) was seen for cyano and nitro-substituted benzyl thiocyanates leading to the formation of the corresponding nitro-substituted dibenzyls. With other substituents (CH(3)O, CH(3), H, Cl, and F), both the alpha (CH(2)-S) and the beta (S-CN) bonds could be cleaved as a result of an electrochemical reduction leading to the formation of the corresponding substituted monosulfides, disulfides, and toluenes. These final products are generated through either a protonation or a nucleophilic reaction of the two-electron reduction-produced anion on the parent molecule. The dissociative electron transfer theory and its extension to the formation/dissociation of radical anions, as well as its extension to the case of strong in-cage interactions between the produced fragments ("sticky" dissociative electron transfer (ET)), along with the theoretical calculation results helped rationalize (i) the observed change in the ET mechanism, (ii) the dissociation of the radical anion intermediates formed during the electrochemical reduction of the nitro-substituted benzyl thiocyanates, and more importantly (iii) the regioselective reductive bond cleavage.     

Synthesis of a naphthyridone p38 MAP kinase inhibitor

Compound 1 is a p38 MAP kinase inhibitor potentially useful for the treatment of rheumatoid arthritis and psoriasis. A novel six-step synthesis suitable for large-scale preparation was developed in support of a drug development program at Merck Research Laboratories. The key steps include a tandem Heck-lactamization, N-oxidation, and a highly chemoselective Grignard addition of 4-(N-tert-butylpiperidinyl)magnesium chloride to a naphthyridone N-oxide. The N-oxide exerted complete chemoselectivity via chelation in directing the Grignard addition to the alpha position as opposed to 1,4-addition on the ene-lactam. The dihydropyridyl adduct was in situ aromatized with isobutylchloroformate followed by heating in pyridine. Syntheses of Grignard precursor, N-tert-butyl-4-chloro-piperidine, were accomplished via transamination with a quaternary ammonium piperidone or via addition of methylmagnesium chloride to an iminium ion. Utilizing this chemistry, multi-kilogram preparation of compound 1 was successfully demonstrated.