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The reduction of lean NOx using ethanol in simulated diesel engine exhaust was carried out over Ag/Al2O3catalysts in the presence of H2O and SO2. The Ag/Al2O3catalysts are highly active for the reduction of lean NOx by ethanol but the reaction is accompanied by side reactions to form CH3CHO, CO along with small amounts of hydrocarbons (C3H6, C2H4, C2H2and CH4) and nitrogen compounds such as NH3and N2O. The presence of H2O enhances the NOx reduction while SO2suppresses the reduction. The presence of SO2along with H2O suppresses the formation of acetaldehyde and NH3. By infrared spectroscopy, it was revealed that the reactivity of NCO species formed in the course of the reaction was greatly enhanced in the presence of H2O. The NCO species readily reacts with NO in the presence of O2and H2O at room temperature, being converted to N2and CO2(CO). Addition of SO2suppresses the formation of NCO species and lowers the reactivity of the NCO species. However, the reduction of NOx is still kept at high conversion levels in the presence of H2O and SO2over the present catalysts. About 80% of NOx in the simulated diesel engine exhaust was removed at 743 K.

A soil cleanup method using a disposable microcolumn and a modified capillary gas chromatographic method is described for the analysis of hexazinone (3-cyclohexyl-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione) and two primary metabolites, 3-(4-hydroxycyclohexyl)-6-(dimethylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione (metabolite A) and 3-cyclohexyl-6-(methylamino)-1-methyl-1,3,5-triazine-2,4(1H,3H)-dione (metabolite B). The limits of detection (LOD) were 7, 18, and 36 ng g−1for hexazinone, metabolite B, and metabolite A, respectively; limits of quantitation (LOQ) were 22, 52, and 99 ng g−1, respectively. The mean recoveries were 94 ± 3% and 94 ± 5% for hexazinone and the phytotoxic metabolite B fortified above LOQ and ranging from 0.03 to 6.25 and 0.06 to 12.5 μg g−1, respectively. The recoveries from the non-phytotoxic metabolite A above LOQ increased with concentrations from 0.125 to 25 μg g−1, but were consistent at each level. The final product of cleanup was stable for at least 6 months, and no derivatization was needed before gas chromatography. The use of toluene as the final solvent and the modification of the injection system of the gas chromatograph improved the stability of peak responses. The method is three times more efficient than conventional methods. The cleanup method for soils was modified for the analysis of vegetation samples. Efficient removal of chlorophyll enabled quantitation of hexazinone by gas chromatography. Recoveries of hexazinone ranged from 73 to 96% for forest litter and four different plant species.

Does the abandonment of hypothermic perfusion during cardiopulmonary bypass compromise cerebral protection and thus lead to a higher incidence of stroke? From 1987 to June 1993, 2,585 consecutive patients underwent myocardial revascularization using warm-body (perfusion at 37°C), cold-heart (cold cardioplegic arrest) surgical technique and were followed for new overt neurologic deficits. Perfusion pressure was maintained between 50 and 70 mm Hg, and hematocrit was kept around 20%. There were 25 operative deaths (1%) in this normothermic group, and new neurologic deficits developed after operation in 25 patients (1%). These results were compared retrospectively with those in 1,605 patients who underwent myocardial revascularization between 1980 and 1986 with moderate hypothermic (25° to 30°C) perfusion ame surgical team, and similar operative techniques. The normothermic group included more elderly patients, more patients with left ventricular dysfunction and unstable angina, and more frequent use of an internal mammary artery conduit. Neurologic complication rates were 1% and 1.3% for the normothermic and hypothermic perfusion groups, respectively. Risk factors for stroke that were identified included age greater than 70 years, severity of aortic arch atherosclerosis, and severe hypotension in the perioperative period. Thus, in a large clinical series, the incidence of overt neurologic injuries was found to be no higher with normothermic perfusion than with hypothermic perfusion.

Between February and June, 1983, four cases of Citrobacter diversusneonatal meningitis were identified at a suburban Baltimore hospital. One of the 4 infants died at age 13 months, 2 (both of whom had brain abscesses) have evidence of developmental delay and 1 appears to be normal after 33 months of follow-up. A review of microbiology records revealed that C. diversushad been present in the hospital nursery prior to identification of the first infant with meningitis, with isolation from infants born 7 months, 4 months and 4 days, respectively, before the first meningitis case. C. diversuswas isolated from 21 infants born during the outbreak period and from hand or rectal cultures of 5 nursing personnel. All isolates were biotype E, with two distinct clusters of cases identified on the basis of plasmid profile and serotype. In a case-control study isolation of C. diversuswas significantly associated with male sex, low birth weight and care by house pediatricians. The outbreak was controlled by stringent infection control measures and exclusion of personnel carriers. During the 24 months following the outbreak 3431 babies discharged from the nursery were cultured for C. diversus; 3 were colonized with the organism.

Global bifurcations of a fourth-order Hamiltonian system with Z2 l⊕Z2 symmetry are studied. The system represents normal-form equations that arise in a variety of problems which have one-one internal resonance and which are forced sinusoidally at the natural frequencies. Four qualitatively different types of global behaviours are shown to occur. Using a generalization of the Melnikov method, three different heteroclinic cycles are shown to break, generating Smale horseshoes and resulting in chaotic phenomena. The theoretical results are verified by numerical simulations. The main conclusion of the analysis is that chaotic phenomena are very common in this class of system

We study the dynamics of a simple mechanical system containing a mass and a bar made of shape memory alloys. Our objective is to understand the effect of stress induced phase transtormation on the system dynamics. Specifically, the effectiveness of an idealized vibration isolator made of shape memory alloys is examined both numerically and experimentally. We find that the stress induced phase transformation within the material has two effects: the resonance frequency of the system is lower and the peak response near the resonance is heavily suppressed. Furthermore, both of these effects depend on the forcing amplitude and they are more pronounced at large forcing amplitudes. We also find that nonlinearity associated with the phase transformation gives rise to complicated dynamics. In particular, period-three responses are found for some forcing parameters. It the case of a biased load, period-doubling cascade and chaotic motion can occur. However, this complicated dynamics disappears at large forcing amplitudes, making the shape memory alloy vibration isolator an effective device at large forcing amplitudes.

To determine the contemporary antibiotic susceptibility profile of vertically acquired group B streptococcal isolates.

The crystallization characteristics of an amorphous NiZr2 alloy have been studied by transmission electron microscopy. Striations in NiZr2 crystallites were found to be narrow twin bands, sometimes only a few layers thick, with 〈110〉 as the twin axes and a rotation of ±120°. High-resolution lattice images prove the composition plane to be the {110} planes perpendicular to the 〈110〉 twin axes. This twin relationship can be accounted for by the existence of a hexagonal cluster of Ni and Zr atoms parallel to {110} within the body-centred tetragonal unit cell of NiZr2.

By examining the modal interaction between two non-resonant shape oscillation modes of a charged liquid drop, we have identified a new route to instability via nonlinear coupling. We present numerical simulation results to show that when shape perturbation of a high-mode number Legendre mode is applied to the drop, the prolate–oblate mode of the drop may grow unbounded. Using multiple-scale analysis, we derive amplitude equations for the high-mode-number shape mode and the prolate–oblate mode to show the nonlinear coupling between the two modes.

The finite element method was used to analyze the stresses in a rock bit cutter tooth under applied loads. Detailed finite element models were constructed to allow accurate descriptions of the structural material properties of a tooth design which includes carburization and hardmetal application. Numerical solutions were obtained for investigating stress concentrations and plastic region growths in a cutter tooth when loaded beyond its yield point. It was found that the finite element method can be a powerful tool for improving the performance of a cutter tooth. Design objectives can be achieved through parameteric studies of stress level variations against geometry and material property changes on a computer system.

Numerical simulation of the dynamics of acoustically levitated drops is accomplished by solving the Helmholtz equation governing the acoustic scattering problem and the Laplace equation governing the motion of an inviscid and incompressible drop. The boundary element method with quadratic elements is used to solve the surface integral forms of both the Helmholtz equation and the Laplace equation simultaneously. Boundary conditions on the drop surface render a system of first‐order differential equations which is integrated with respect to time by the use of fourth‐order Runge‐Kutta integration to study the drop translational frequency, shape oscillation frequency, and the static equilibrium shape. A spherical shape approximation method is used to obtain an analytic estimate of the minimum trapping pressure (MTP) and the translational frequency of the drop. In particular, the translational frequency is shown to agree with the analytic result obtained from the spherical shape approximation for a small acoustic number or a small wave number. The shape oscillation frequencies are found to increase initially with the increasing acoustic number, D [D=(a0Prms2)/(ρoc2σ), Prms is the root‐mean‐squared sound intensity, a0 is the equivalent radius of drop, ρo is the density of host medium, c is the sound speed in host medium, σ is the surface tension of the drop liquid] up to a critical value and then decreases with the increasing acoustic number due to the nonlinear nature of the acoustic radiation pressure. The equilibrium shape of the drop is computed by incorporating the normal viscous stress terms into the dynamical system intentionally to get rid of the transients. The equilibrium shapes are found to agree with the existing result for small acoustic numbers but differ for large acoustic numbers. © 1996 Acoustical Society of America.

Vaccines have given health care providers control over a substantial portion of the morbidity and mortality in the developing world. Global efforts have immunized two-thirds of the world’s children with DTP and polio vaccines; 72% have received BCG and 59% measles vaccine; but only 29% of pregnant women have received two doses of tetanus toxoid. In addition, vaccines against yellow fever, Japanese encephalitis, hepatitis B, rubella, and mumps and meningococcal polysaccharide vaccine are being used in specific regions of the world. New vaccine candidates will enhance the vaccine armamentarium over the next decade to include the causes of pneumonia, diarrhea, and meningitis: Haemophilus influenzaetype b, pneumococcal and meningococcal protein conjugate vaccines, typhoid and rotavirus vaccine. Genetically engineered vaccine vehicles, genetic reassortants, and genetic deletions are being investigated as new vaccine candidates.

A general procedure has been developed for the analysis of 8 different insect growth regulators (IGRs) by using reversed-phase high-performance liquid chromatography with gradient solvent systems. The method has been used to identify and separate 8 insect growth regulators from a mixture of the standards. The method has been evaluated with different column conditions and under different solvent systems. Best resolution was obtained by using a double column and methanol/water gradient system.

Vapor−liquid equiliibria were measured at 101.3 kPa for three binary mixtures of 2-butanol + butyl acetate, hexane + butyl acetate, and cyclohexane + 2-butanol. The isobaric T−x−y data were reported, including an azeotropic point for the binary mixture of cyclohexane + 2-butanol. Calculations of the nonideality of the vapor phase were made with the second virial coefficients determined by the Tsonopoulos correlation equation. Various activity coefficient models were used to correlate the experimental data. Satisfactory results were obtained, and optimally fitted binary parameters are presented.

The commensurate and incommensurate phases in a rapidly solidified V40 Co43Si17 alloy are studied with analytical and high-resolution electron microscopy. The 'commensurate' phases are observed to contain many domain-like substructures and actually are incommensurate. A series of incommensurate phases is observed to exist with the character parameter ε running from about 0·06 down to close to zero in this alloy. The true commensurate phase with ε=O (the γ-phase) exists only in regions within a domain, The domain boundaries are suggested to be responsible for the incommensurability of the incommensurate phase, and are found to have the effect of accumulating V and Si, and to expand the unit cell of the commensurate γ-phase in this alloy.

Background.Prosthetic valve replacement in a small aortic root without annulus enlargement raises concern about its long-term benefits.

Four isolates of rickettsiae from sick dogs on Cape Cod, Mass., were serologically identical to isolates of Rickettsia rickettsii from human patients with Rocky Mountain spotted fever. The antigenic analysis used the indirect fluorescent-antibody test and antisera prepared in mice to each of the isolates and to reference strains of R. rickettsii and Rickettsia montana. Serological responses of infected dogs were specific for R. rickettsii, although antibodies to R. montana were also detected in the sera of most of the canines.

We study the symmetries admitted by the amplitude equations governing the nonlinear nonplanar parametric responses of an inextensional beam (Nayfeh and Pai, 1989). As a result of these symmetries, the differential equations can be integrated in two limiting cases.

Twin-related crystalline surface layer structures on Al-Li-Cu, Al-Cu-Fe icosahedral quasicrystals and rapidly solidified Al-Cu-Co decagonal quasicrystals have been studied, for the first time, by transmission electron microscopy. The structure of the surface layer is cubic with a lattice parameter of a = 0.29 nm and with a b.c.c. lattice in Al-Li-Cu and Al-Cu-Fe but a B2 structure in Al-Cu-Co. Interfacial misfit dislocations between the bulk quasicrystal and the surface layer have also been observed.

Examination of those plant extracts which were previously found (Feng and others, 1962) to have transient depressor activity has led to the isolation of γ-aminobutyric acid, from the leaves of Artocarpus incisaL. and of Piper amalagoL. and to the demonstration by paper chromatography of its presence in several extracts. Extracts showing pressor activity were also examined and tyramine has been isolated from Phoradendron wattiiKr. and Urb. and dopamine has been shown by paper chromatography to be present in Piper amalagoL. and Stachytarpheta jamaicensisVahl.

A systematic pharmacological examination has been made of 55 Jamaican plants, most of which have a local reputation as medicinals. A number of interesting, but no outstanding, activities were observed. The results are tabulated.

Thispaper presents a study of simulation of structural systems and heat flow problems by use of oriented flow graphs. Linear elastic structural systems are transformed into graph representation using two kinds of parametric analyses.In one case, flexibility parametersof structural components are used as branch transmittances of the or iented graphs, and geometric displacements are the ex ternal sources or inputs to the graph. In the other ap proach, stiffness coefficients as graph transmittances and unbalanced residual loads as source inputs lead to relax ation operations which can be represented by feedback analysis. Each of these approaches is the dual of the other in a topological sense.Two-dimensional problems governed by the Laplacian partial differential equation are solved by using first-order central difference analysis to transform the governing equation into an oriented graph. The graph networks of physical systems of this type can be constructed by in spection of the mesh network without recourse to the difference equations. Initial boundary values are treated as independent source inputs to the graph. A solution of the steady-state heat flow in a thin plate is presented.The simulation of physical systems by oriented flow graphs treats the system as an entity in which the physical characteristics are transformed topologically into graph representations. Oriented graphs are essentially analog setups from which numerical results can be obtained by analog computers. If use is made of the loop-rule equa tions of graph theory, efficient use of the digital computer is indicated. The nature of design of structural systems is complex because of the range of parameters to be con sidered and because of required accuracy. Flow graph simulation can give information on the effect of variation of parameters by way of sensitivity analysis and can be an aid in the study of design.

A photoelastic solution of the distribution of stresses around a centrally located elliptical hole in a plate of finite width subjected to uniform axial loading is presented in this paper. Stress distributions at the boundaries are given for a wide range of the parameters, and stress-concentration factors have been computed for the points of maximum tensile and of maximum compressive stress. Comparisons are made with available theoretical solutions. Some appreciable discrepancies are pointed out.

The general problem of the two-dimensional state of stress in a strip of elastic material under normal loading is considered. A series expansion of displacement functions generated along lines suggested by Mindlin and Medick [1] for dynamical questions arising in plate theory is employed in the solution. The variational procedure generates a set of variational equations of motion. In order to obtain useful results the series is truncated in such a way that the analysis gives an approximate solution valid for ratios of loaded length to plate thickness greater than unity.

The bonding of immiscible system Mg/steel was facilitated by adding an Al interlayer using laser welding. The influence of the added interlayer thickness on the microstructure and mechanical properties of the dissimilar joints were investigated. The Al interlayer was dissolved into the Mg fusion zone and mutual diffusion with steel, causing metallurgical bonding of Mg and steel at the interface. Fe-Al reaction layers with different thicknesses were produced along the fusion zone-steel interface. Two different reaction layers divided by the thickness of the reaction layer (2 μm) were thereafter identified by TEM analysis. The phases formed adjacent to the steel substrate were Fe(Al) solid solution and Al8(Mn, Fe)5 phase on the Fe(Al) surface, while the Al6Fe phase formed when the reaction layer was more than 2 μm. Three different fracture modes were distinguished from all the joints, which was closely associated with the interfacial reaction. Insufficient atomic diffusion caused interfacial failure. Fracture occurred in the fusion zone when the thickness of the Al interlayer was 0.2–0.5 mm. The maximum value of the tensile-shear fracture load reached 133 N/mm, which represented 40.3% joint efficiency with respect to the steel base metal. However, the excessive interfacial reaction resulted in cracking at the interface and a greater amount of brittle Mg-Al compounds, giving rise to decreased mechanical properties. [ABSTRACT FROM AUTHOR]

The use of laparoscopic techniques in the construction of an antegrade continence enema (ACE) channel is evolving as a minimally invasive procedure that attempts to address issues of morbidity commonly associated with the technique as originally described. Because of our experience with “open” ACE construction, we maintain that true fecal continence of the ACE channel requires more than dependence on the appendicocecal sphincteric mechanism. Therefore, we have implemented intracorporeal or extracorporeal suturing to create a reliable continence mechanism.

Clean intermittent self-catheterization has been shown to be an effective method for the prevention of upper tract urinary disease in patients who are unable to void efficiently. When the urethra is not available for catheterization surgeons can construct a catheterizable channel from the appendix or retubularized bowel. However, for patients without an appendix and limited bowel segments we have reimplanted the ureter to prevent reflux and tunneled the distal portion of the sameureter to construct a catheterizable stoma, the “double tunnel.”

Vacuum brazing of TiAl based alloy to 40Cr steel has been carried out at 1173 K for 0·5–40 min using Ag–Cu–Ti filler metal. The microstructural analyses indicate that three reaction products, Ti (Cu,Al)2, an Ag based solid solution (Ag(s.s.)), and TiC, are present in the brazing seam, and the interfacial structure of the brazed joint is TiAl/Ti(Cu,Al)2+ Ag(s.s.)/Ag(s.s.) + Ti(Cu,Al)2/TiC/40Cr. The experimental results show that the shear strength of the brazed TiAl/40Cr joints decreases as the brazing time increases, and it is up to 175 MPa when the joint is brazed at 1173 K for less than 2 min.

A novel realtime induction heating-assisted underwater wet welding process was investigated. The addition of induction heating could reduce the cooling rate of the joint in underwater wet welding. The macroand microstructures, mechanical properties such as tensile, impact, and bending properties, and Yslit restraint testing were studied. The results showed the content of martensite (M) and upper bainite (BU) phases decreased, while the proeutectoid ferrite (PF) and acicular ferrite (AF) phases increased as the induction heating voltage increased. Mechanical properties of the joint were improved through addition of induction heating and fracture morphology with characteristic uniform dimples belonging to ductile fracture. The cracking ratio of Yslit restraint testing was also decreased. Therefore, the susceptibility to cold cracking of the wet welding joint was improved. [ABSTRACT FROM AUTHOR]