bluuebunny/crossref_metadata_2025 huggingface dataset:
Reproductive Patterns among Danish Women with Oral Clefts
Authors: Yttri Janne Elin , Christensen Kaare , Knudsen Lisbeth B. , Bille Camilla
Published: September 2010

Objective

The aim of this study was to compare reproduction patterns among Danish women born with isolated oral clefts versus the Danish background population.

Design and Setting

A nationwide population-based historic cohort study based on three registers: The Danish Facial Cleft Register, The Danish Civil Registration System, and the Fertility of Women and Couples Dataset.

Participants

Through linkages of the registers, the number of children and the exact age at childbirth of all Danish women born with an oral cleft from 1950 through 1988 (N = 1931) were obtained. These data were compared with similar data for the entire Danish female background population (N = 1,184,390).

Results and Conclusions

This study suggests that childlessness is higher among women born with an oral cleft (55%) than among women in the Danish background population (44%). Excluding women without children, women born with oral cleft had an average of 1.98 children per woman. This did not differ significantly from the background population (2.02 children/woman). Furthermore, the present study found that Danish women born with oral clefts on average were older (27.3 years of age) than the background population (24.7 years of age) when they had their first child (difference = 2.6 years, confidence interval = 2.41 to 2.80).

Conclusion

Danish women born with an oral cleft more often are childless or have their first child later, but if they have children, they tend to have as many children as other Danish women. Social, psychological, and biological reasons might be responsible for the reduced fertility.
Shape analysis of filamentous Precambrian microfossils and modern cyanobacteria
Authors: Boal David , Ng Ray
Published: September 2010

Variations in the orientation and cross-sectional shape of filamentous microfossils provide quantitative measures for characterizing them and probing their native mechanical structure. Here, we determine the tangent correlation length, which is the characteristic length scale for the variation in direction of a sinuous curve, for both a suite of Precambrian filamentous microfossils and six strains of modern filamentous cyanobacteria, all with diameters of a few microns. Among 1.9-2-Ga microfossils, Gunflintia grandis, Gunflintia minuta and Eomycetopsis filiformis possess, respectively, correlation lengths of 360 ± 40 μm, 670 ± 40 μm and 700 ±100 μm in two dimensions. Hundreds of times larger than the filament diameters, these values lie in the same range as the cyanobacteria Geitlerinema and Pseudanabaena, but are smaller than several strains of Oscillatoria. In contrast, the 2-Ga microfossil trichome Halythrix, is found to have a short correlation length of 29 ± 4 μm in two dimensions. Micron-wide pyritic replacement filaments observed in 3.23-Ga volcanogenic deposits also display a modest correlation length of 100 ± 15 μm in two dimensions. Sequences of species in two genera of our modern cyanobacteria possess tangent correlation lengths that rise as a power of the filament diameter D—D3.3 ± 1 for Oscillatoria and D5.1 ± 1 for Geitlerinema. These results can be compared with power-law scaling of D3 for hollow tubes and D4 for solid cylinders that is expected from continuum mechanics. Extrapolating the observed scaling behavior to smaller filament diameters, the measured correlation length of the pyrite filaments is consistent with modern Geitlerinema whereas that of Halythrix lies not far from modern Oscillatoria, suggesting that there may be structural similarities among these genera.
The living, the dead, and the expected dead: variation in life span yields little bias of proportional abundances in bivalve death assemblages
Authors: Kidwell Susan M. , Rothfus Thomas A.
Published: September 2010

All else being equal, species with short life spans are expected to be overrepresented in time-averaged death assemblages relative to their standing abundance in the living community, but the magnitude of the distortion of proportional abundance and assemblage evenness has received little attention. Here, information from 30 data sets on the living and dead abundances of marine bivalves in local habitats is combined with a global compilation of bivalve life spans to determine whether bias from mortality rate can explain observed differences in species proportional abundances. Although bivalve maximum life spans range from one to 75 years in these data sets, indicating annual mortality rates of 0.97 to 0.09, the “life span bias” (LB) of a species–the difference between its proportional abundance expected dead and that observed alive–is consistently small in magnitude (average change <2%, maximum about 20%) and random in sign relative to observed discordance (OD = difference between that species' proportional abundance observed dead and that observed alive). The aggregate result for 413 living species occurrences is a significantly positive but weak correlation of OD to LB, with only 10% of variation in OD explained. The model performs better among longer-lived species than among shorter-lived species, probably because longer-lived species conform better to the model assumption that species maintain a constant proportional abundance in the living assemblage over time. Among individual data sets, only seven exhibit significant positive correlations between OD and LB. The model also under-predicts the cases where a death assemblage is dominated by a species that is shorter lived than the dominant species in the living assemblage, indicating that some factor(s) other than or in addition to mortality rate is responsible for OD. We can find no evidence of preservational bias linked to life span, for example through body size. This negative outcome reflects a weak biological relationship between life span and living abundance among bivalves in local habitats, contrary to the terrestrial paradigm, and points toward a simpler model of time-averaged death assemblage formation where higher abundances reflect (under-sampled) past populations. Contrary to long-held expectations, variation in population turnover among species is not a major source of taphonomic bias in time-averaged death assemblages among bivalves and perhaps among other marine groups: bias must arise largely from other factors.
Governmentality of Youth: Managing Risky Subjects
Authors: Besley Tina (A.C.)
Published: September 2010

This article poses the question: How do understandings of governmentality play out in discourses of youth? In the twenty-first-century neoliberal contexts of consumer capitalist societies, discourses of youth need now to move beyond the valuable earlier understandings based on psychological and cultural/subcultural studies to harness Foucault's notion of governmentality. In terms of governmentality, if youth cannot or will not control their conduct, they cease to be ‘docile bodies' and ‘useful’ to the state. If their behavior becomes unacceptable and criminal, the state will intervene, administering its biopower in the form of the youth justice system – governmentality in action, which is probably the biggest risk of all for youth, especially in the disciplinary, punitive way it is formulated in much of the USA, where it totally ignores the theoretical findings of youth development that have been established in psychological discourses. The first section of the article briefly discusses the emergence of Foucault's notion of governmentality. The second section examines a dominant discourse of youth – youth ‘at risk’. It starts with definitions, and then covers therapeutic and economic aspects of risk management. These include technologies of the self via a range of voluntary and community-based socio-psy programs and interventions; and social security, risk assessment, risk management and insurance. The third section, ‘Beyond Cultural Studies’, analyzes the importance of changing economic conceptions of the self which demand something more than perspectives garnered solely from cultural studies. The author argues that a Foucauldian history of homo economicus, as in the last four lectures of The Birth of Bio-politics (2008), and a critical engagement with the economics of the self where the dominance of pure rationality models have given way to a consideration of a range of psychological attributes that influence our economic decision-making, are valuable additions to traditional cultural studies of youth.
Openness, Web 2.0 Technology, and Open Science
Authors: Peters Michael A.
Published: September 2010

This article begins by examining the dimensions of open science including the ethics of science and the peer review system before defining open science in terms of ‘wiki science’ or ‘science 2.0’. The article then briefly scrutinizes the future of open science, commenting upon the nature of open distributed knowledge systems and new models of production and innovation based on peer-to-peer systems.
National Level, City Level Auditor Industry Specialization and Cost of Debt
Authors: Li Chan , Xie Yuan , Zhou Jian
Published: September 2010

SYNOPSIS: We examine the relation between industry specialist auditors and cost-of-debt financing using a national and city level industry specialist framework. Consistent with the assumption that higher audit quality is associated with lower information risk, which benefits clients in raising debt capital, we find that firms audited by city level industry specialist auditors, either alone or jointly with national level industry specialist auditors, enjoy significantly lower cost-of-debt financing measured by both credit rating and bond spread. Our results suggest that, compared to clients of non-industry specialists, firms’ odds of worse credit ratings are 0.859 (0.664) times lower, and their bond spreads are 17 (16) basis points lower if they are clients of city-level-only (joint national and city level) industry specialists. In addition, our evidence shows that, for joint national and city level industry specialists, both information and insurance roles are significant to reduce cost-of-debt financing.
Deep penetration welding of nickel–aluminum–bronze
Authors: Leong Keng H. , Kirkham Peter A. , Meinert Kenneth C.
Published: September 2010

Recent advances in laser technology has enabled the achievement of high power and high quality beams by diode pumping of Nd:YAG slabs. TRW, under the Precision Laser Machining Program funded by DARPA, has produced a 3 kW diode pumped Nd:YAG slab laser. The effectiveness of this new laser was examined in recent welding tests on C95800 nickel–aluminum–bronze. The beam parameters were 1700 W at the workpiece, with a pulse repetition rate of 1000 Hz and a pulse width of 170 μs. Linear and serpentine welding patterns were used with welding speeds ranging from 2.11 to 127 mm/s. At the slowest speed, penetration depths exceeded 35 and 17 mm with the use of 360 and 517 mm focal length focusing lens, respectively. Details of the metallurgy and the effect of welding speed on weld quality are examined.
Effects of intrapulse structure on hole geometry in laser drilling
Authors: Cheng Jun , Kahlen Franz-Josef , Kar Aravinda
Published: September 2010

Lasers have been established as a commercial tool for drilling holes in a variety of materials. The beam quality and temporal shape of the laser pulse have been identified as critical parameters to create high quality (deeper holes, minimum taper angle, and minimum recast layer) holes. However, little attention has been directed toward an analytic investigation of the effect of different temporal pulse shapes on these product variables. In this study, a leading-edge, sharp-spiked, and a rectangular Nd:YAG laser pulse were used to drill holes in stainless steel 304 to examine the effects of these temporally different laser pulses on the drilling process. It is found that holes drilled with the sharp-spiked laser pulse are significantly deeper than for the case of rectangular pulses. Also an optimum processing regime is identified to drill holes with minimum taper angle and recast layer. A mathematical model describing the drilling process is presented in this article for different temporal profiles of the pulsed laser beams. The model assumes one-dimensional heat conduction in the material and it incorporates the Stefan conditions at the solid–liquid and liquid–vapor interfaces. The predicted drill depth and recast layer thickness are larger than the experimental data but follow the same trend.
Laser cutting stainless steel with dual focus lenses
Authors: Powell J. , Tan W. K. , Maclennan P. , Rudd D. , Wykes C. , Engstrom H.
Published: September 2010

In this article the performance of a new type of lens is compared with traditional meniscus lenses for CO2 laser cutting of medium (>5 mm) section stainless steel. Dual Focus™ lenses produce two focus spots, one above the other. This type of optic was found to be capable of higher cutting speeds and better quality cuts. A phenomenological model is presented which explains the superior performance of Dual Focus lenses. The model concentrates upon the fact that during high speed cutting of medium section metals, the laser does not irradiate the lower portion of the cut zone. This lower part of the cut is heated by the melt flowing over it, which has been previously heated by the laser. This melt preheating involves narrower kerfs and higher cut speeds if a dual focus lens is used.
Residual stresses in laser-deposited metal parts
Authors: Kahlen Franz-Josef , Kar Aravinda
Published: September 2010

Several laser-based techniques to fabricate parts by depositing metals, ceramic powders, or a combination thereof have been developed in recent years. These fabrication techniques are incomplete and not fully useful to an operator without any predictive capability to calculate the geometries of the fabricated parts or equations to calculate their expected yield and ultimate strengths. Data concerning the energy transfer from the processing laser beam to the material powder, such as the metal vapor–plasma plume temperature and plume absorption coefficient, the efficiency of laser energy transfer and mathematical analysis for the thermal and dimensional process characteristics are unavailable. Also, the characterization of the mechanical properties of such laser-fabricated parts has just begun. A one-dimensional model to calculate the thermal and dimensional process characteristics is developed. The model accounts for the transmission of the laser beam through the plume, energy transfer in the molten phase, and the Stefan conditions at the solid–liquid and liquid–vapor interfaces. The yield and ultimate strengths of laser-fabricated stainless steel (SS 304) parts have been measured. A mathematical model is developed accounting for directionally preferred solidification to calculate the residual stresses generated in the part during solidification.
A comparison of gas tungsten arc and CO2 laser beam welding of AA2024
Authors: Ion J. C. , Kokkonen J.
Published: September 2010

Mechanical fastening methods are used extensively to join aluminum alloys, particularly in the aerospace industries. Laser welding provides the possibility of a high productivity single-step process, with the added benefit of potential weight savings of about 10% in comparison with riveting. However, the weldability of many aluminum aerospace alloys is generally considered to be low, and little data are currently available. A procedure for CO2 laser welding of the alloy AA2024 is developed, with the use of 2319 filler wire. Weld property data are shown to achieve the requirements for the most stringent quality level of the current European workmanship standard for laser-welded joints in aluminum. Hardness and tensile strength properties are shown to be similar to those of gas tungsten arc (GTA) welds. The fatigue strength of GTA welds is superior to that of laser welds in the as-welded condition, but when the weld bead is machined flush with the plate surface the difference is reduced. The laser welds achieved the requirements of recommendations produced by the International Institute of Welding for single-sided welding of aluminum alloys. The quality of the weld toe is shown to have the greatest effect on fatigue strength.
Cutting of ceramic plates by optical fiber guided Nd:YAG laser
Authors: Quintero F. , Pou J. , Lusquiños F. , Larosi M. , Soto R. , Pérez-Amor M.
Published: September 2010

Advanced ceramics have excellent resistance to heat, wear, and corrosion and are used in many industrial applications were these properties are required. However, the high hardness and brittleness of ceramics make them difficult and expensive to machine by conventional manufacturing methods. In this article we present the results of the work carried out to analyze qualitatively the influence of some parameters such as the cutting speed and the assist gas pressure on the laser cutting of mullite-alumina plates. The experiments were performed with a 500 W pulsed Nd:YAG laser coupled to an optical fiber and a commercial cutting head. An inert gas (Ar) was used as assist gas, which was injected to the workpiece through a coaxial conical nozzle. Mullite-alumina plates having a thickness of 4 mm were cut at a maximum cutting speed of 5 mm/s. The results obtained demonstrate that the pulsed Nd:YAG laser connected to an optical fiber is a feasible and flexible tool for a successful cutting of components made of mullite alumina.
A procedure for multiple-pulse maximum permissible exposure determination under the Z136.1-2000 American National Standard for Safe Use of Lasers
Authors: Thomas Robert J. , Rockwell Benjamin A. , Marshall Wesley J. , Aldrich Robert C. , Zimmerman Sheldon A. , Rockwell R. James
Published: September 2010

The current national consensus standard for laser safety in the United States is the American National Standard for Safe Use of Lasers (ANSI Z136.1). Over the past few years, a comprehensive rewrite of this standard has been conducted. The updated version of the standard (Z136.1-2000) incorporates a wealth of new bioeffects data and establishes a number of new maximum permissible exposure (MPE) limits for laser safety. The updated standard also includes new procedures for the computation of MPE values, which must be understood by health physicists, laser safety officers, and others in the field of occupational safety. Here we present the first in a series of tutorial articles to clarify laser safety analysis procedures under this new standard. This article deals with the proper application of three rules for determining the appropriate MPE values for repetitively pulsed lasers or repeated exposures from laser beams.
Are you a laser product manufacturer?: Interpretation of the FDA regulations applicable to laser product manufacturers
Authors: Smith James F. , Rockwell R. James , Parkinson Jay , Dennis Jerome E.
Published: September 2010

Often, companies that manufacture, modify, or integrate laser products find themselves to be uncertain as to whether they are required to comply with the U.S. Federal Laser Product Performance Standard (FLPPS). The FLPPS is a regulation that applies to laser products manufactured on or after August 2, 1976 unless specifically exempted. Many companies make or alter (modify) specific laser products solely for in-house use for widespread applications, including industrial processes and process and product quality control systems. In-house applications may require several units to be built. Often a basic design may be altered for a different end-user within the company. The in-house system may consist of integrating a purchased laser system with handler and process control equipment, or modifying a complete purchased piece of equipment to suit the specific requirements of the in-house user. Other companies purchase existing certified laser products such as bar code reader, position sensor, or micrometer, etc. and incorporate these components into a machine which they manufacture and sell. In these scenarios, the question is often asked: “Am I a laser product “manufacturer” subject to the FLPPS?” The answer in many cases may at first be unclear. Occasionally there is also some confusion on other topics regarding laser product safety. Among them are: the applicability of the FLPPS vs the American National Standard Institute (ANSI) Z136.1 Standard for the safe use of lasers, the question of when has a product been modified; and what is a “manufacturer” in the context of applying the FLPPS. This paper addresses the fore mentioned topics, including history and various scenarios that will help to determine when “manufacturing” has taken place.
Laser welding of refractory metals
Authors: Leong Keng H.
Published: September 2010

Welding of thick section refractory metals is difficult with conventional arc processes but can be accommodated with high-intensity-beam sources such as the electron or laser beam. High-laser-beam irradiance is necessary to achieve deep penetration of refractory metals. Consequently, a focused beam of high power and beam quality is required. A 500 W diode pumped Nd:YAG was used to perform bead-on-plate tests on 2 mm sheets of rhenium and tungsten. The welds were sectioned and analyzed for profile and porosity. Results indicate the difficulty in using high-irradiance beams to weld rhenium and tungsten. Microhardness measurements indicate no significant decrease in hardness in the fusion zone. However, the presence of cracks tended to produce a slight decrease in the hardness measurements.
Effect of beam width on melt characteristics in large-area laser surface alloying
Authors: Liu Z. , Pirch N. , Gasser A. , Watkins K. G. , Hatherley P. G.
Published: September 2010

This article presents an investigation of the convection behavior of the melt pool for laser surface alloying with a wide beam. A line beam source with a dimension of 6 mm × 0.7 mm from a 3 kW cw Nd–YAG laser was used. The work concentrated on studies of the influence of various laser operating conditions, especially the melt width of the tracks and the substrate thermal properties, on the convection behavior during the laser surface alloying process. Three different substrates precoated with a Ni layer were selected on the basis of their different thermal properties. An investigation of the relationships between the laser beam dimension, the structure of melt flow, and concentration fields of the alloying elements was carried out. It was found that the beam width had a significant effect on the alloying patterns on solidification. It was also found that a wider beam width (varied with a mask aperture) produced a greater melt depth. A three-dimensional mathematical model was applied to numerically simulate the temperature field and convection flow of the melt pool. Some specific alloying patterns were found favorable for coinage applications.
Design characteristics and development of a nozzle for coaxial laser cladding
Authors: Lin J. , Steen W. M.
Published: September 2010

Laser cladding by blowing powder into a laser generated melt pool is finding greater use in industry particularly with the growing interest in direct build and repair techniques currently being investigated. The process is traditionally done with a side blown powder feed. This has the limitation of not being omnidirectional. To overcome this, a coaxial powder feed system has been developed. This article describes a particular system by both mathematical models and experiment. The system has so far achieved a catchment efficiency of up to 40% with a 1 kW CO2 laser beam. The parameters controlling this important commercial parameter are described. They include the flow structure of the powder in the beam. The control of this structure is discussed with reference to this particular coaxial flow system.
Laser cladding of cast aluminum–silicon alloys for improved dry sliding wear resistance
Authors: Kelly J. , Nagarathnam K. , Mazumder J.
Published: September 2010

AA333 specimens were hardfaced with mechanically mixed Mn–Al bronze powder by laser cladding to investigate its possible use in a boundary lubricated sliding application for better wear resistance. The coatings needed to be more seizure resistant than the AA333 currently in use. Like other cast aluminum alloys, AA333 possesses a hard, silicon rich secondary phase which helps impart good wear properties. However, in starved lubrication conditions, the relative softness and low melting point of the Al-rich matrix can result in its scuffing and even seizure. The laser used was a 6 kW cw CO2 laser, in an oscillating beam process. The experimental group of coatings consisted of a 3×3 matrix of three process parameters—laser power, traverse speed, and powder feed. The coatings were mechanically sound, relatively free of small cracks and porosities, with a strong, tough metallurgical bond. The coatings were 3 to 4 times harder than the AA333 substrate matrix which was about 90 Vhn. Many wear specimens were prepared from the coatings for comparison with AA333 properties, and for property versus process parameter correlations within the experimental matrix of coatings. The coating microstructure was primarily single phase, consisting of fcc columnar-type grains of varying size produced by rapid and directional solidification, with a homogeneous distribution of the alloying elements in solid solution (by wt %: 75 Cu, 12 Mn, 8 Al, 3 Fe, 2 Ni). Analysis of coating microstructures was carried out using optical and scanning electron microscopy, x-ray energy dispersive spectroscopy, and x-ray diffractometry. The interface microstructure was found to contain α-Al (fcc) in the remelt layer and θ-CuAl2 (tetragonal). Tribological tests showed that the seizure resistance of the coatings was superior to AA333 in dry sliding tribological tests, though the wear rates of the coatings show some dependence on the process parameters. The coatings exhibited up to 1/3 the wear rate of the AA333 substrate under the same dry wear test conditions of 4.5 kg normal load at 600 rpm, 30.3 mm radius of sliding, simulating actual component operation. However, the major benefit of the coating is increased resistance to an abrupt, work-stopping failure by seizure. Necessary repair and replacement of parts as a result of seizure can be very costly. The wear mechanisms of coatings and substrate are discussed, as are the coating properties versus process parameters.
Ophthalmoscopic and pathologic description of ocular damage induced by infrared laser radiation
Authors: Zuclich Joseph A. , Zwick Harry , Schuschereba Steven T. , Stuck Bruce E. , Cheney Frank E.
Published: September 2010

This study compares ocular damage effects induced by infrared (IR) lasers in the “eye-safe” wavelength range to those observed following visible wavlength laser exposures. In addition to routine fundus camera and slit-lamp observations, exposed subjects were examined via confocal scanning laser ophthalmoscopy. Histopathologic evaluation was conducted on eyes with both visible and IR laser induced focal lesions. IR laser exposure parameters which resulted in corneal, lenticular and/or retinal damage will be detailed. Unique aspects of the IR laser–tissue interaction will be discussed, including concurrent lesion formation in several tissues and secondary responses such as delayed inflammatory reactions. This latter effect may involve tissue not directly irradiated during the laser insult. Finally, implications for laser safety standards will be suggested.
Induced transmittance of eye-protective laser filters
Authors: Koschinski W. , Schirmacher A. , Sutter E.
Published: September 2010

Different kinds of eye-protective laser filters were investigated with short laser pulses with respect to their transmittance and stability in dependence on the irradiance. The irradiance was varied between 3×106 and 3×1013 W/m2. The investigations were performed at the wavelengths of 1064 and 532 nm using a Nd:YAG laser with a pulse duration of 15 ns and at a wavelength of 798 nm generated by a Ti:Sa laser with a pulse duration of about 250 fs. For filters based on semiconductor-doped glasses, an increase in the transmittance was observed with increasing irradiance at 532 nm. It extends over six orders of magnitude due to the saturation of the absorption. A similar dramatic effect was measured also on polycarbonate filters at 1064 nm. The dependence of the transmittance on the irradiance is discussed in a phenomenological model to show the importance of the relaxation time, the concentration of the absorption centers, and the absorption cross section for the nonlinear behavior. Taking into account two absorption processes, a complete fit of the measured irradiance-dependent transmittance is achieved. Thermal effects due to the absorbed energy can be neglected compared with the nonlinear optical behavior: Either no damage to the sample surface is observed at all or it is observed only after many pulses hit the surface. In the case of a surface damage, the regular transmittance will first decrease due to increased scattering of light and then increase due to removal of material. In the experiments with the fs Ti:Sa laser system, the destruction of the filter surface starts with the very first pulses in many cases. This becomes important for eye-protection filters using reflecting dielectric coatings.
Epithelial damage thresholds for sequences of 80 ns pulses of 10.6 μm laser radiation
Authors: McCally R. L. , Bargeron C. B.
Published: September 2010

Infrared radiation from a CO2 laser operating at 10.6 μm is almost totally absorbed by the tear film and corneal epithelium. Epithelial damage thresholds for single and multiple pulse exposures have been well characterized for exposures having pulse durations ⩾1 ms and a few damage thresholds have been reported for much shorter duration pulses. However until recently, no studies have been done to determine damage thresholds from sequences of very short pulses. The purpose of this study is to begin to fill this gap. New Zealand white rabbit corneas were exposed to sequences of 80 ns pulses from a CO2-TEA laser operating in the (TEM)00 mode (Gaussian beam profile). The damage threshold was defined as the energy density, EDth, that produced minimal superficial epithelial lesions. Thresholds have been determined for sequences of 2, 8, 32, 128, and 1024 pulses at a rate of 10 Hz. The damage data are shown to be correlated by empirical laws relating either the threshold energy density per pulse to the number of pulses, or the total threshold energy density to the duration of the pulse train. Research is underway to obtain data for pulse sequences at greater pulse rates and to examine the relative importance of thermal and acoustic damage mechanisms.
Bioeffects of near-infrared lasers
Authors: Lund David J. , Edsall Peter R. , Fuller Daniel R. , Hoxie Stephen W.
Published: September 2010

Retinal damage thresholds (ED50s) were determined in Rhesus monkey eyes for 100 ms exposures to collimated radiation from a tunable Ti:sapphire laser at several wavelengths from 690 to 900 nm. Prior research using 15 ns duration laser pulses showed a strong variability of ED50 with wavelength for retinal exposure in Rhesus monkeys to laser radiation in the near-infrared spectrum. Current studies with the Ti:sapphire laser show similar variability of ED50 with wavelength for 100 ms retinal exposures. Previously measured light transmission and absorption properties of ocular tissues do not provide a complete or obvious explanation for the significant variations of threshold with small changes in wavelength. Similar wavelength dependencies of ED50 for the two exposure durations in the wavelength range of 750–830 nm suggest that linear absorption is a cause of the variability. However, differences in the ED50 curves at other wavelengths show that nonlinear mechanisms also contribute.
Risk assessment of optically aided viewing
Authors: Sliney David H.
Published: September 2010

The definition and measurement of Class 1 and Class 3A accessible emission limits relates very much to one simple question: “How much energy will be collected by magnifying optics?” To simulate the increased risk of optically aided viewing by telescopes and binoculars, a 50 mm aperture (at one time 80 mm) has been used in ANSI, CDRH, and IEC standards. The current measurement criterion found in IEC 60825-1 was a compromise, and makes use of a 50 mm aperture at a distance of 100 mm to define a geometrical collection efficiency to simulate not only that of telescopes and binoculars, but also that of highly diverging laser and light emitting diode emission patterns as well. It was later recognized that this was a rather arbitrary mathematical construct designed to mimic both a high-power eye loupe at a very close distance (14 mm) and a 7×50 binocular at a much greater viewing distance. This approach is not followed in the U.S. standards, and the two types of sources are treated differently. While the IEC approach appears at a first glance to have the advantage of simplicity and requires little laboratory space for measurements, it fails to accurately describe the real hazard for both conditions of optically aided viewing. Hand-held magnifiers and eye loupes increase the retinal or corneal hazard by effectively collimating the divergent beam and directing more energy into the true limiting aperture: the eye’s pupil (simulated by the 7 mm aperture for dark-adapted viewing). By contrast, telescopes and binoculars which can produce a sharp image only at distances beyond at least 2 m, collect more radiant energy. A better simulation of risk is afforded by a 50 mm aperture at 2 m and a 7 mm aperture at about 10 cm.
Laser bending of high strength alloys
Authors: Magee J. , Watkins K. G. , Steen W. M. , Calder N. J. , Sidhu J. , Kirby J.
Published: September 2010

Laser bending has emerged as a candidate process for bending sheet metal. The dimensional accuracy of parts produced by bending processes is a topical issue. As the dimensions of a laser bent part depend on the temperature field induced in the workpiece, the correct laser processing parameters are essential. This work reports on an investigation into the factors influencing the dimensions of laser formed thin plates of an α-β titanium and an AlCuMg aluminum alloy. The influence of the energy input on the bend angle is examined empirically and compared with an analytical model. Results show that the plastic strain is critically dependent on the energy supplied to the workpiece surface. The decreasing bend rate with increasing irradiations over the same track is evident. This is attributed to an increase in the sample section modulus due to the thickening of the material along the bending edge. Edge effects are apparent in the samples. These effects can be minimized by varying the line energy supplied to the plate surface with the in plate location. The conclusions drawn are that the dimensions of the final part and the rate of bending can be controlled primarily from the temperature field. In addition, the increase in the section modulus and the edge effects influence the dimensional accuracy.
Welding characteristics with three Nd:YAG laser beams transmitted through single optical fiber
Authors: Fujinaga Shigeki , Miura Hiroshi , Narikiyo Toru , Katayama Seiji , Ohmori Akira
Published: September 2010

A YAG laser processing system in which three YAG laser beams were combined on the input end of a single optical fiber, and transmitted through the optical fiber, was developed. The effects of various oscillation wave forms on the penetration depth were examined by using this system. As a result, it was confirmed that the penetration depth with a rectangular modulated laser beam was deeper than that of a continuous laser beam, and the depth made with the rectangular modulated laser beam superimposed pulse laser beam was deeper than that of the former two type laser beams, though the average output powers of the three types of laser beams were equal to each other. The effective delay time of the pulse laser beam after rising of the rectangular modulated laser beam was 2 or 3 ms to obtain the deepest penetration. Moreover, the penetration depth increased with an increase in the pulse laser beam power to the total one.
Stochastic model of the deep penetration laser welding of metals
Authors: Kapadia Phiroze , Solana Pablo , Dowden John
Published: September 2010

Deep penetration laser welding of metals generates a keyhole surrounded by a molten region which forms the weld on freezing. Mathematical models of the process produce relationships between the process parameters to provide an effective simulation of the process and a guide to optimal operating conditions both for continuous wave (cw) and pulsed systems. It is usual when pursuing such an analysis to assume the existence of a suitably averaged keyhole structure. To assume a steady-state keyhole with suitably averaged properties, however, constitutes a considerable idealization. Actually, the keyhole manifests itself as a writhing, twisting entity. This characteristic arises from many different instabilities that can and do inevitably come into play. They represent the reaction of the material being welded to the laser beam. It is even more necessary to consider such reactions to the laser beam when pulsed lasers or cw lasers with pulsed modulation are considered. The details concerning the characteristics of specific instabilities are not considered here. Instead, a stochastic description of some aspects of the laser welding process is provided when the laser operates in the cw case. The applicability of current mathematical models is thus extended giving increased insight into the nature of the laser welding process.
Ray tracing of optical aids: Implications for ocular risk
Authors: Ritter Mark B. , Trewhella Jean M.
Published: September 2010

How do ocular aids impact retinal risk when viewing divergent sources? We present ray tracing calculations for ocular aids used in several common configurations and compare risk relative to an unaided eye. Retinal irradiance values for sources of different subtence and divergence were calculated for ocular aids of different magnifying power. The data show the stark difference between point sources, like lasers, and extended sources, such as light emitting diodes (LEDs) and lamps. Arguing from fundamental physiological phenomena we compare the relative ocular risks of various sources under a range of viewing conditions and compare these calculations with standards proposed to classify such different sources. We conclude that, if point sources are correctly classified, then extended sources, such as LEDs, are overclassified by the IEC 825-1/CENELEC.
New laser techniques for diagnosis and treatment of deep-seated brain lesions
Authors: Ward Helen Anne
Published: September 2010

The five year survival rate of deep-seated malignant brain tumors after surgery/radiotherapy is virtually 100% mortality. Special problems include: (1) lesions often present late; (2) position: lesion overlies vital structures, so complete surgical/radiotherapy lesion destruction can damage vital brain-stem functions; and (3) difficulty in differentiating normal brain from malignant lesions. This study aimed to use the unique properties of the laser: (a) to minimize damage during surgical removal of deep-seated brain lesions by operating via fine optic fibers; and (b) to employ the propensity of certain lasers for absorption of (nontoxic) dyes and absorption and induction of fluorescence in some brain substances, to differentiate borders of malignant and normal brain, for more complete tumor removal. A fine laser endoscopic technique was devised for removal of brain lesions, which minimized thermal damage and shock waves. A compatible endoscopic fluoroscopic laser technique was developed to differentiate brain tumor from normal brain.
Dynamics of keyhole and molten pool in laser welding
Authors: Matsunawa Akira , Kim Jong-Do , Seto Naoki , Mizutani Masami , Katayama Seiji
Published: September 2010

In laser and electron-beam welding, a deep cavity called a keyhole or beam hole is formed in the weld pool due to the intense recoil pressure of evaporation. The formation of the keyhole leads to a deep penetration weld with a high aspect ratio and this is the most advantageous feature of welding by high-energy-density beams. However, a hole drilled in a liquid is primarily unstable by its nature and the instability of the keyhole also causes the formation of porosity or cavities in the weld metal. In particular, the porosity formation is one of the serious problems in very high-power laser welding, but its mechanism has not been well understood. The authors have conducted systematic studies on observation of keyhole as well as weld pool dynamics and their related phenomena to reveal the mechanism of porosity formation and its suppression methods. The article will describe the real-time observation of keyhole and plume behaviors in the pulsed and continuous-wave laser welding by high-speed optical and x-ray transmission methods, the cavity formation process and its suppression measures.
Evolution of laser safety standards ANSI Z136.1s
Authors: Charschan Sidney S.
Published: September 2010

The story of a dynamic safety standard must start with the historical need, and lead up to the pressures of today. Originally laboratories, both military and civilian were dreaming of new weapons, medical breakthroughs, industrial applications, and the possibility of optical communication. Today’s dreams are the same. Tremendous progress has been made since the early 1960s, and the need for safety standards is still increasing. ANSI Z136.1 “for the Safe Use of Lasers” is finalizing its fifth revision, and has six Z136.X in various stages—from recent issue to new draft proposals.
Welding of die-casted magnesium alloys for production
Authors: Lehner C. , Reinhart G. , Schaller L.
Published: September 2010

The importance of light weight magnesium alloys, especially for the automotive industry, has grown significantly during the last years. To fully benefit from the whole designing potential of this material, joining processes have to be developed. Laser beam welding turns out to be very suitable to join magnesium parts. The results of welding magnesium alloys AZ91HP and AM50HP with a 3 kW Nd:YAG laser and a 6 kW CO2 laser with an industrial robot and a gantry robot system are shown from a production point of view. The determination of the process window by analyzing the influence of laser type, power, welding velocity, and shielding gas, as well as the influence of the base material, leads to conclusions about process stability and production tolerances. Further investigations concerning fixturing techniques as well as seam preparation and joint geometry show effects on the process flexibility and the effort to realize high quality seams under production conditions. The investigated process parameters are evaluated mainly with respect to their influence on the static strength of the welding seam.
Femtosecond ultraviolet laser micromachining of Al2O3–TiC ceramics
Authors: Mendes M. , Oliveira V. , Vilar R. , Beinhorn F. , Ihlemann J. , Conde O.
Published: September 2010

The micromachining of composite materials using excimer lasers has not yet been the subject of in depth investigations. In this work the authors studied the ablation behavior of Al2O3–34 wt % TiC composite ceramic using 500 fs laser pulses at 248 nm. It was found that the roughness does not change significantly with the number of pulses for constant laser fluences. The ablation rate decreases with increasing number of pulses reaching a stationary regime after 100 pulses. Characterization of the machined areas by scanning electron microscopy showed that a globular topography is responsible for the roughness of the samples. Increasing the laser fluence up to 12 J/cm2 increases the ablation rate for a constant number of pulses and decreases the surface roughness. At this fluence the measured roughness Ra was around 0.1 μm, when the original surface had a Ra≈0.05 μm. Chemical changes of the irradiated surface were investigated using Auger electron spectroscopy. Based on these results ablation mechanisms are suggested. Machining of submicron structures on the material is presented. Periodic line structures with line spacing below 520 nm were produced on the surface by multiple laser shot exposure. By using such structures one can identify different ablation thresholds for the constituents of the ceramic composite. Atomic force microscopy was used to characterize the surface topography.
Laser surface treatment of steels with CrB2 and Ni2B powders
Authors: Medres B. , Shepeleva L. , Ryk G. , Dehm G. , Bamberger M.
Published: September 2010

Results of laser surface alloying (LSA) of 1045 steel with CrB2 and Ni2B powders are presented. LSA was conducted with a 2.5 kW power cw CO2 laser. Laser treated zones were studied by optical and electron microscopy, energy dispersive spectroscopy, and by x-ray diffraction. Formation of complex borides within the treated zones resulted from the dissolution of the injected materials in the melt pool. Additionally, it was established that the dissolution extent determines the hardening mechanism provided by each type of injected material. Dissolution of injected material was found to depend mainly on their melting temperature. A study of the microstructure of treated zones showed that in the case of Ni2B the hardness increase was due to the formation of Fe2B and Fe3B. When CrB2 was used for LSA, an increase in hardness resulted from the dispersion of partially undissolved CrB2 particles, as well as iron borides (Fe2B and Fe3B) formation.
Production of nanosized zirconia particles by pulsed CO2 laser evaporation
Authors: Staupendahl G. , Michel G. , Eberhardt G. , Müller E. , Oestreich Ch. , Vogelsberger W. , Schlegel J.
Published: September 2010

In this article we report on the production of nanosized zirconia particles by CO2 laser evaporation. The radiation source was a transverse flow CO2 laser operating in the continuous or the pulsed mode. Pulses between 1 and 500 μs duration could be generated by two different Q-switching techniques. The evaporation rates as well as the diameter of the particles and their density distributions were investigated with regard to their dependence on the laser power, the pulse shape, and the properties of the carrier gas. By means of simple models the experimental results could be interpreted. Furthermore a kinetic rate equation has been derived for the formation and growth of small particles. Good agreement is found between the experiments and this theory.
Excimer laser ablation of glass fiber reinforced liquid crystal polymer
Authors: Yue T. M. , Mei S. M. , Chan K. C.
Published: September 2010

An analytical model has been developed to predict the ablation rate of fiber reinforced polymers as a function of the fiber volume fraction and the excimer laser incident fluence. An ablation experiment was carried out to determine the effective laser absorption coefficient and the threshold fluence of ablation for a liquid crystal polymer (LCP) and the reinforcement phase, i.e., glass fiber. Employing these results in the model, the ablation rate of the LCP composite for different incident fluences was obtained. The theoretical predictions on ablation rate compare extremely well with the experimental results. In addition, the experimental results show that accumulation of gases, debris fragments, etc. in front of the sample can significantly affect the ablation rate of the composite material, especially at high pulse frequencies (>40 pulses/s).
Temperature measurement inside and near the weld pool during laser welding
Authors: Lhospitalier S. , Bourges P. , Bert A. , Quesada J. , Lambertin M.
Published: September 2010

The work in this article deals with the measurement of temperature fields inside and near the weld pool during laser welding. The laser source used for this study is a 7.5 kW CO2 laser, and the welded material is a UNS N08904 austenitic stainless steel. The principle behind the actual experimentation is relatively simple: the welding operation is recorded with a charge coupled device camera equipped with infrared filters; after calibrating the camera sensor and image processing, the temperature distribution in the weld pool and near the melted zone is revealed.