Knuth-Bendix algorithm and the conjugacy problems in monoids

We present an algorithmic approach to the conjugacy problems in monoids, using rewriting systems. We extend the classical theory of rewriting developed by Knuth and Bendix to a rewriting that takes into account the cyclic conjugates.Comment: This is a new version of the paper 'The conjugacy problems in monoids and semigroups'. This version will appear in the journal 'Semigroup forum

Predicting risk among non-respondents in prospective studies

Potential non-response bias was investigated in a follow-up study of 2,011 chronically disabled patients. 82.5% and 73.3% of the study subjects responded to self-administered mail questionnaires respectively at 6-month and 1-year follow-up. Information on employment status, the outcome of interest, of approximately 90% of the non-respondents was obtained from indirect sources. Employment rate was lower among the non-respondents than the respondents. Non-response was associated with age, social class, previous employment record, and the type of disability; but none of these characteristics were associated with the outcome. Out of the five known independent risk factors for unemployment, only one (incompletion of rehabilitation course) was associated with non-response. The employment rate among the respondents was also assessed according to the delay in response, that is the number of reminders sent to achieve response. The outcome among- the late respondents was similar to that among the nonrespondents. These data suggest that (a) risk estimates may be biased even when the response rate is greater than 80%, (b) the prevalence of risk factors among non-respondents may not indicate the presence or the degree of non-response bias, but (c) reliable estimates can be obtained from extrapolations of the rates among the respondents according to the delay in response.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/42663/1/10654_2004_Article_BF00152716.pd

Mechanical Properties and Microstructural Characterization of Aged Nickel-based Alloy 625 Weld Metal

The aim of this work was to evaluate the different phases formed during solidification and after thermal aging of the as-welded 625 nickel-based alloy, as well as the influence of microstructural changes on the mechanical properties. The experiments addressed aging temperatures of 650 and 950 A degrees C for 10, 100, and 200 hours. The samples were analyzed by electron microscopy, microanalysis, and X-ray diffraction in order to identify the secondary phases. Mechanical tests such as hardness, microhardness, and Charpy-V impact test were performed. Nondestructive ultrasonic inspection was also conducted to correlate the acquired signals with mechanical and microstructural properties. The results show that the alloy under study experienced microstructural changes when aged at 650 A degrees C. The aging was responsible by the dissolution of the Laves phase formed during the solidification and the appearance of gamma aEuro(3) phase within interdendritic region and fine carbides along the solidification grain boundaries. However, when it was aged at 950 A degrees C, the Laves phase was continuously dissolved and the excess Nb caused the precipitation of the delta-phase (Ni3Nb), which was intensified at 10 hours of aging, with subsequent dissolution for longer periods such as 200 hours. Even when subjected to significant microstructural changes, the mechanical properties, especially toughness, were not sensitive to the dissolution and/or precipitation of the secondary phases

Multi-ancestry study of blood lipid levels identifies four loci interacting with physical activity

Many genetic loci affect circulating lipid levels, but it remains unknown whether lifestyle factors, such as physical activity, modify these genetic effects. To identify lipid loci interacting with physical activity, we performed genome-wide analyses of circulating HDL cholesterol, LDL cholesterol, and triglyceride levels in up to 120,979 individuals of European, African, Asian, Hispanic, and Brazilian ancestry, with follow-up of suggestive associations in an additional 131,012 individuals. We find four loci, in/near CLASP1, LHX1, SNTA1, and CNTNAP2, that are associated with circulating lipid levels through interaction with physical activity; higher levels of physical activity enhance the HDL cholesterol-increasing effects of the CLASP1, LHX1, and SNTA1 loci and attenuate the LDL cholesterol- increasing effect of the CNTNAP2 locus. The CLASP1, LHX1, and SNTA1 regions harbor genes linked to muscle function and lipid metabolism. Our results elucidate the role of physical activity interactions in the genetic contribution to blood lipid levels

High Power Thulium Fiber Lasers

Thulium fiber lasers at 2 μm are following a similar development path to ytterbium fiber lasers. We review recent progress exploiting the unique characteristics of these high power lasers in spectral and temporal domains. OCIS codes: (060.3510) Lasers, fiber ©2011 Optical Society of America

High Power Thulium Fiber Lasers

Thulium fiber lasers at 2 μm are following a similar development path to ytterbium fiber lasers. We review recent progress exploiting the unique characteristics of these high power lasers in spectral and temporal domains. OCIS codes: (060.3510) Lasers, fiber ©2011 Optical Society of America

Tunable High Power Thulium Fiber Lasers

Two thulium fiber laser configurations are described providing widely tunable and narrow linewidth output. We show that such systems can produce average powers greater than 100 W. ©2010 IEEE

Spectral Beam Combining Of 2 Μm Tm Fiber Laser Systems

We report spectral beam combining of three 2-μm Tm fiber lasers each locked to slightly different wavelengths, using a new spectral-limiting device, providing a path forward to beam-combining at the multi-kW level. © 2010 Optical Society of America

Atmospheric Propagation Testing With A High Power, Tunable Thulium Fiber Laser System

A tunable master oscillator power amplifier (MOPA) fiber laser system based on thulium doped silica fiber designed for investigation of multi-kilometer propagation through atmospheric transmission windows existing from ∼2030 nm to ∼2050 nm and from ∼2080 nm to beyond 2100 nm is demonstrated. The system includes a master oscillator tunable over \u3e200 nm of bandwidth from 1902 nm to beyond 2106 nm producing up to 10 W of linearly polarized, stable, narrow linewidth output power with near diffraction limited beam quality. Output from the seed laser is amplified in a power amplifier stage designed for operation at up to 200 W CW over a tuning range from 1927 - 2097 nm. Initial field tests of this system at the Innovative Science & Technology Experimental Facility (ISTEF) laser range on Cape Canaveral Air Force Station, Florida will be discussed. Results presented will include investigation of transmission versus wavelength both in and out of atmospheric windows, at a variety of distances. Investigations of beam quality degradation at ranges up to 1 km at a variety of wavelengths both in and out of atmospheric transmission windows will be also presented. Available theoretical models of atmospheric transmission are compared to the experimental results. © 2010 Copyright SPIE - The International Society for Optical Engineering

High-Power Widely Tunable Thulium Fiber Lasers

Applications requiring long-range atmospheric propagation are driving the development of high-power thulium fiber lasers. We report on the performance of two different laser configurations for high-power tunable thulium fiber lasers: one is a single oscillator utilizing a volume Bragg grating for wavelength stabilization; the other is a master oscillator power amplifier system with the oscillator stabilized and made tunable by a diffraction grating. Each configuration provides \u3e150 W of average power, \u3e50% slope efficiency, narrow output linewidth, and \u3e100 nm tunability in the wavelength range around 2 ,μm. © 2010 Optical Society of America