Second- and third-order harmonic distortion in DFB lasers

The second- and third-order harmonic distortion in distributed feedback (DFB) lasers is simulated using a time domain large signal dynamic model. The effects of the longitudinal spatial hole burning, nonlinear gain, spontaneous emission, and current leakage are included in the model. Composite second-order (CSO) and composite triple beat (CTB) are calculated for an 80 channel 60-540 MHz system with 3% modulation depth in each channel. The simulation results are compared with the experimental harmonic distortion measurements     

The role of axially nonuniform carrier density in altering theTE-TE gain margin in InGaAsP-InP DFB lasers

Axial nonuniformities in the carrier density profile of 1.55 μm capped-mesa-buried-heterostructure distributed-feedback (CMBH-DFB) InGaAsP-InP diode lasers are discussed. This is accomplished by directly measuring the spontaneous emission at various locations in the laser optical cavity. The authors observe that the highly asymmetric optical field, inherent in DFB lasers, produces a strong longitudinal nonuniformity in the carrier density. This promotes degradation of the lasing gain margin between the dominant TE Bragg modes, which is verified through measurements of the relative shift of the lasing mode in the stopband. The reduction of gain margin is shown to cause multimode operation in devices with large optical field asymmetries. In devices with modest optical field asymmetries, the reduction of the gain margin saturates, and single mode behavior is maintained. Measurements are consistent in many respects with the predicted consequences of spatial hole burning     

Characterization of functionalized nanoporous supports for protein confinement

Here we characterize a highly efficient approach for protein confinement and enzyme immobilization in NH(2)-?or HOOC-?functionalized mesoporous silica (FMS) with pore sizes as large as tens of nanometres. We observed a dramatic increase of enzyme loading in both enzyme activity and protein amount when using appropriate FMS in comparison with unfunctionalized mesoporous silica and normal porous silica. With different protein loading density in NH(2)-FMS, the negatively charged glucose oxidase (GOX) displayed an immobilization efficiency (I(e), the ratio of the specific activity of the immobilized enzyme to the specific activity of the free enzyme in stock solution) in a range from 30% to 160%, while the same charged glucose isomerase (GI) showed an I(e) of 100% to 120%, and the positively charged organophosphorus hydrolase (OPH) exhibited I(e) of more than 200% in HOOC-FMS. The enzyme-FMS composite was stained with the charged gold nanoparticles and imaged by transmission electron microscopy (TEM). Fourier transform infrared (FTIR) spectroscopy showed no major secondary structural change for the enzymes entrapped in FMS. Thanks to the large, rigid, open pore structure of FMS, the reaction rate and K(m) of the entrapped enzymes in FMS were comparable to those of the free enzymes in solution. In principle, the general approach described here should be applicable to many enzymes, proteins, and protein complexes since both pore sizes and functional groups of FMS are controllable.     

Cost-effectiveness of a targeted disinfection program in household kitchens to prevent foodborne illnesses in the United States, Canada, and the United Kingdom

Foodborne illnesses impose a substantial economic and quality-of-life burden on society by way of acute morbidity and chronic sequelae. We developed an economic model to evaluate the potential cost-effectiveness of a disinfection program that targets high-risk food preparation activities in household kitchens. For the United States, Canada, and the United Kingdom, we used published literature and expert opinion to estimate the cost of the program (excluding the educational component); the number of cases of Salmonella, Campylobacter, and Escherichia coli O157:H7 infections prevented; and the economic and quality-of-life outcomes. In our primary analysis, the model estimated that approximately 80,000 infections could be prevented annually in U.S. households, resulting in 138 million dollars in direct medical cost savings (e.g., physician office visits and hospitalizations avoided), 15,845 quality-adjusted life-years (QALYs) gained, 788 million dollars in program costs, and a favorable cost-effectiveness ratio of 41,021 dollars/QALY gained. Results were similar for households in Canada and the United Kingdom (21,950 dollars Can/QALY gained and 86,341 pounds sterling/QALY gained, respectively). When we evaluated implementing the program only in U.S. households with high-risk members (those less than 5 years of age, greater than 65 years of age, or immunocompromised), the cost-effectiveness ratio was more favorable (10,163 dollars/QALY gained). Results were similar for high-risk households in Canada and the United Kingdom (1,915 dollars Can/QALY gained and 28,158 pounds sterling/QALY gained, respectively). Implementing a targeted disinfection program in household kitchens in the United States, Canada, and the United Kingdom appears to be a cost-effective strategy, falling within the range generally considered to warrant adoption and diffusion (<100,000 dollars/QALY gained).     

From technology push,to industrial pull: superplastic forming and diffusion bonding using lasers

The process of Superplastic Forming (SPF) has produced a vast number of components, from simple shapes to those with complex geometric features, all to a dimensional accuracy difficult to obtain by traditional sheet metal methods. When used in conjunction with Diffusion Bonding (DB), extraordinarily lightweight, stiff, strong and fatigue enduring components and structures can be manufactured that are virtually impossible to produce by any other means. However, SPF/DB is often criticised as too complicated, expensive, slow and unstable, a reputation that has contributed to its use being largely confined to manufacturing when no other means of production can be found. Perhaps, the fundamental cause of this negative perception of SPF/DB is the fact that derivatives of mid 18^th century hydraulic presses are used, virtually universally, that provide only a single temperature to the work piece, which is heated primarily through conduction, a form of heating which is slow and expensive. By comparison, modern, electrically efficient, lasers, if used to directly heat the work piece, could transform SPF/DB into a mainstream process and the first choice of designers. This paper compares, and contrasts, the two systems.     

Assessment and modeling of aging in electro-absorption distributedBragg reflector lasers

We describe a protocol for assessing aging in the tuning section of a multisection distributed Bragg reflector laser integrated with amplifier, tap coupler, and electro-absorption modulator. Under accelerated aging, we observe a transient change of nonradiative recombination followed by saturation. A simple model of aging of the Bragg section of the tunable lasers enables prediction of changes in each wavelength channel using information obtained from a single channel only     

The risks and rewards of online editing

The advantages and disadvantages of online editing by an editor of author-submitted materials are examined. It is concluded that online editing makes it possible to provide editing services for some documents that otherwise might not get edited at all because of schedule pressures. In shops where trespassing could be a major problem, the use of this tool helps eliminate any serious concerns. Because it is instantly available, online editing expedites author review, up to and including the very last change before a document is published     

Repeated measures analysis of means in clinical research.

Discusses assumptions for analyzing treatment means in repeated measures designs and suggests that the traditional F test has been shown to have limitations, given violations of the assumption of sphericity. This assumption is probably infrequently satisfied in clinical applications. Analytic alternatives based on a 3-step approach by S. Geisser and S. Greenhouse (1958) are discussed. (12 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)