Improved coupled mode analysis of corrugated waveguides and lasers

Corrugated waveguides and lasers in resonant and non-resonant situations are analyzed by an improved coupled mode theory based on a set of the coupled mode equations for guided modes and radiation continuum. The distributed feedback (DFB) coefficient and the radiation loss coefficient are given in closed forms. The formulation can be applicable to arbitrarily shaped gratings and multilayer waveguide structures. The accuracy of the theory is examined by comparing it with Tamir's exact calculation for a nonresonant situation and also with Streifer's one for a DFB structure. Reasonable accuracy is obtained by the proper choice of the unperturbed waveguide parameter. The dependence of the two coefficients on the grating depth, the grating period, the guide layer thickness, and the refractive index difference between core and cladding layers is obtained for all Bragg orders up to the fourth, and for four typical grating shapes, namely, for rectangular, sinusoidal, symmetric triangular, and sawtooth gratings. Both the threshold gain of DFB lasers utilizing higher order Bragg reflection and the output coupling efficiency of grating beam couplers are also calculated for these parameters. A new multilayer structure for controlling the radiation loss is proposed and analyzed. This structure is suitable for the suppression of the radiation loss in DBR reflectors as well as for the improvement of the output coupling efficiency in grating beam couplers.     

BEM and FEM combination parallel analysis using conjugate gradient and condensation

Boundary element and finite element combination analysis on parallel schemes are improved in this paper. The conjugate gradient method (CG method) is introduced for renewal of unknowns on the combination boundary in place of the Schwarz method previously used, which makes it possible to determine a parameter required in the renewal iteration automatically. Further, the condense method is employed for higher efficiency of solution by reducing the number of degree of freedoms in both equations for the finite element and boundary element domains. Comparison of the present algorithm with the previous one in some numerical examples shows marked improvement in computational efficiency.     

Preparation and characteristics of dextran-methyl methacrylate graft copolymer

A graft polymer of dextran-methyl methacrylate (MMA) has been prepared using ceric nitrate. The solubility, infra-red absorption spectrum and thermal behaviour of the graft copolymer together with those of dextran and PMMA have been studied. It was found that a hot-pressed film of the copolymer not only shows better water wettability and water absorbing power than PMMA but also thrombo-resistance, and can be shaped into a transparent contact lens having an affinity for tears and blood. High resolution electron scanning microscopy shows that the surface of the contact lens has a micro-heterogeneous structure, consisting of phase separated grains of about 0.2 μm in size which are distributed uniformly.     

Effect of phenolic compounds on liquefaction of coal in the presence of hydrogen-donor solvent

Phenolic compounds have a remarkable positive effect on coal liquefaction in the presence of tetralin, depending strongly on the character of the coal and on the concentrations of phenols. The solvent-refined coal obtained in the presence of phenol was low in hydrogen content and high in the fraction of aromatic hydrogen; these results corresponded well to the fact that coal conversion increases without increase of hydrogen consumption in the presence of phenols. The effect of phenols on coal liquefaction may be caused mainly by accelerated scission of ether linkages, since the decomposition of 2,2′-dinaphthyl ether was considerably enhanced by the addition of phenols.     

Nocardicin A, a new monocyclic beta-lactam antibiotic II. Structure determination of nocardicins A and B

The structures of nocardicins A and B, novel monocyclic beta-lactam antibiotics produced by a strain of Nocardia, have been established as 1 and 2, respectively, on the basis of spectroscopic and chemical evidence. They are the first examples of monocyclic beta-lactam antibiotics possessing relatively high antimicrobial activity, and are stereochemically and biologically related to penicillins and cephalosporins.     

Effects of Unphysiological Factors on Cardiac Output Regulation During Artificial Heart Pumping

Several Factors affecting artificial heart output were studied employing two mathematical models of prosthetic hearts, i.e., sac and diaphragm heart models. The stroke volume sensitivity to changes in venous pressure was analyzed by numerical computations. Increased inflow valve resistance, increased pump vacuum pressure, decreased elasticity of the ventricular sac or diaphragm and decreased size of the ventricle were shown to depress artificial heart function. In total prosthetic heart replacement experiments in calves, the resistance at the junction of the right heart to the natural atrium was measured by varying the pump vacuum pressure. When the vacuum pressure exceeded ?20 mmHg, the orifice resistance to flow increased approximately 4 times. Optimizing the above factors, a prosthetic heart should be designed that provides sufficient flow with a pump vacuum pressure not greater than ?20 mmHg.     

Double switch operation in cardiac anomalies with atrioventricular and ventriculoarterial discordance

Since June 1987, 10 of 19 consecutive patients with atrioventricular and ventriculoarterial discordance (average age 4 +/- 2 years) had undergone a double switch operation with the morphologically left ventricle used as a systemic ventricle. There were two combinations of procedures. Atrial switch combined with arterial switch was used in two patients who had a normal pulmonary valve. Atrial switch combined with ventriculoarterial switch by Rastelli's procedure was used in eight patients with pulmonary stenosis or atresia and a large ventricular septal defect. One early death and two late deaths have occurred in a postoperative follow-up period of up to 4 years. Subsequent problems were mainly related to the results of atrial switch procedures in patients who had a small atrium because of low pulmonary flow, especially in patients with apicocaval juxtaposition. Our experience suggested that the double switch operation would open a new era of definitive surgical treatment in half of the patients with atrioventricular and ventriculoarterial discordance.