bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of Withdrawals on Tests Involving Censored Data in Toxicology Experiments
Authors: Groggel D , Schaefer R , Skillings J
Published: February 2009

Censoring can occur with some response variables that are frequently of interest in toxicology studies (for example, time to maturation or lifetime). This censoring can be in the form of fixed right censoring or a withdrawal, and its presence can have a major impact on the analysis of the data. In this paper we consider the effect of censoring on statistical procedures that are commonly used in toxicology experiments. The tests examined in this study are the Gehan and log rank tests which are available on the major statistical packages (SAS, SPSSX, and BMDP). The application of these tests for k ⩾ 2 samples and for multiple comparisons is considered. The effect of withdrawals on the performance of these tests is found to be quite different than the effect of fixed right censored observations. Our study results indicate that these tests can lead to incorrect or misleading inferences when there is a high percentage of withdrawals. The tests may have very poor sensitivity to treatment differences, and the actual significance levels may be quite different from what the user specifies.
Sensitivity and Uncertainty Analyses for Use with Chemical Fate and Transport Models
Authors: Staples CA , Sebaugh JL
Published: February 2009

A method for evaluating sensitivity and uncertainty analyses is presented here for use with chemical environmental exposure models. Sensitivity analysis allows one to assess the relationship between a set of potentially important model input variables and the model output. Uncertainty analysis allows one to assess the set of output values obtained and estimate various statistical properties such as the mean, median, standard deviation, and range. Absence of the ability to quantify parameter value uncertainty and model output uncertainty limits the validity of predictive model use. Use of the methods presented in this paper can increase the confidence in predictive environmental chemical fate model use.

The present investigation employed the Latin hypercube sampling method developed by Iman and Shortencarier at Sandia National Laboratories, Albuquerque, NM. It requires that a set of input variables be identified, and the probability distribution of each be specified. The range of each input variable is divided into intervals having equal probabilities, and one value is randomly selected from each interval. Sets of model input variables are then generated which cover the range of each variable. Some model inputs may then be calculated as functions of these key input variables. The computer model is run for each set of input variables and the model output is obtained.

Regression techniques can then be employed to examine the differential sensitivity of the model to the various input variables and functions thereof, for example, cross products of input variables. Since the model input values are chosen based on probabilities, the set of model outputs can also be interpreted on a probabilistic basis.

The techniques discussed in this paper respond to the growing need by chemical exposure model users for better defined sensitivity analysis procedures which can aid in explaining and interpreting results. An example problem data set is presented which highlights the methodological techniques and their utility.
Results of Interlaboratory Testing of the Standardized Aquatic Microcosm Protocol
Authors: Taub FB , Kindig AC , Conquest LL , Meador JP
Published: February 2009

The “standardized aquatic microcosm” (SAM) protocol was performed by four laboratories, including the authors' laboratory, and the results of seven experiments are presented. Each laboratory tested the toxicant copper at three concentrations (500, 1000, and 2000 ppb) plus a control.

Nitrate depletion and an early algal bloom which was terminated by an increase in grazers (mainly Daphnia) were consistently observed in the control microcosm. In comparison with controls, the copper-treated microcosms were associated with reductions in Daphnia and in sensitive algal populations. In all toxicant treatments, copper eliminated the Daphnia and inhibited primary production; the duration of inhibition was prolonged at the higher copper concentrations. At the lowest concentration, recovery was characterized by an algal bloom of copper-resistant green algae, which was followed by a Daphnia bloom. Recovery occurred in most of the 1000-ppb copper-treated microcosms but was usually absent at the 2000-ppb concentration until late in the experiment.

All experiments exhibited the same sequence of events, but the timing of these events varied among experiments. Experiments provided similar statistical differences between control and treatment microcosms within the same experiment and gave the same rank order of the day-weighted-by-variable” (DWV) statistic, denned in the text. Comparison of the variable means on a day-by-day analysis of variance did show the experiments to be statistically different because of differences in the timing of events.
Prediction of Daphnia magna EC50 Values from Rat Oral LD50 and Structural Parameters
Authors: Enslein K , Tuzzeo TM , Blake BW , Hart JB , Landis WG
Published: February 2009

We describe a structure-activity model of Daphnia magna median effective concentration (EC50) based on rat oral median lethal concentration (LD50) and structural parameters. Based on 182 compounds for which both biological end points were available, a regression equation explaining 84% of the variation in D. magna EC50 was developed. The independent parameters used in the equation consist of substructural keys and molecular connectivity indexes (MCI). Alternate models based on octanol/water partition coefficients did not perform as well as those based on MCIs and keys. An equation for twelve cholinesterase-inhibiting compounds explained 80% of the EC50 variation in those compounds, based on one MCI, the molecular weight, and rat oral LD50.
Structure-Toxicity Relationships of Para-Position Alkyl- and Halogen-Substituted Monoaromatic Compounds
Authors: Schultz TW , Cajina-Quezada M , Chang M , Lin DT , Jain R
Published: February 2009

The relative toxicity of 46 para-position alkyl- and halogen-substituted pyridines, cyanobenzenes, nitrobenzenes, phenols, benzyl alcohols, and benzaldehydes was determined by measuring the population growth impairment (log BR) of the ciliate Tetrahymena pyriformis. The 1-octanol/water partition coefficient (log KOW)-dependent quantitative structure-activity relationship (QSAR) for the pyridines, cyanobenzenes, and nitrobenzenes is log BR = 0.8222 (log KOW) - 1.7889; n = 19, r2 = 0.937, and s = 0.155. A similar QSAR for the phenols, benzyl alcohols, and benzaldehydes is log BR = 0.6360 (log KOW) - 1.2012; n = 27, r2 = 0.726, and s = 0.284 (where n = the number of data points; r2 = the coefficient of determination; and s = root mean square.) The predictability of the latter QSAR is improved by the addition of the orthogonal field electronic parameter F. The resulting QSAR is log BR = 0.7891 (log KOW) + 0.6793 (F) - 1.7457; n = 27, r2= 0.925, and s = 0.163.
Predictability of Unusually High Acute Toxicity to Photobacterium phosphoreum of 1,4-Di-Substituted Benzene Derivatives
Authors: Kaiser KLE , Gough KM
Published: February 2009

The authors report here on the relationships of the acute toxicities to Photobacterium phosphoreum of 1,4-di-substituted benzenes with their pctanol/water partition coefficients and with the toxicities of the corresponding mono-substituted benzene derivatives and also identify the types of derivatives for which such toxicities can or cannot safely be predicted. "Outliers" to the previously established quantitative structure-activity relationships (QSARs) are identified, and reasons for their aberrant behavior are discussed in terms of specific substituent groups and their electronic effects on the basic molecule and on the other substituents present, as measured by the substituent-induced chemical shifts of carbon-13 (13C) nuclear magnetic resonance data of the substituent-bearing carbon atoms of the benzene ring. With the combination of these parameters, the toxicity of highly toxic compounds can be predicted within an error of approximately 0.35 logarithmic toxicity units over more than four orders of magnitude. Nitrobenzene derivatives require the use of a parameter for the charge buildup on the oxygen atoms of the nitro group.
Use of Aquatic Lethality Tests to Estimate Safe Toxicant Concentrations for Initial Ecological Risk Assessments
Authors: Holcombe GW , Phipps GL , Veith GD
Published: February 2009

This article presents an approach which allows the body of comparative toxicity data to be used in initial ecological risk assessments to extrapolate from an acute test with an indicator species to an estimate of the no-effect concentration in the environment. The fathead minnow (Pimephales promelas) acute value was selected as the reference value since this ecotoxicity endpoint has the largest data base for comparative toxicity comparisons. Comparative toxicity endpoints for fish and invertebrates were collected from various sources. When data for all ecotoxicity endpoints are plotted for all chemicals, this plot can be analyzed statistically using regression analysis to calculate an equation defining the upper 95 percentile prediction limit. The upper 95% prediction limit uses the reference test (fathead 96-h acute value) to calculate a concentration that would be safe for 95% of the species and chemicals, assuming that enough comparative toxicological data (especially chronic endpoints) are included in the data set.
An Approach for Development of Structure-Biodegradation Relationships of Organic Chemicals
Authors: Niemi GJ , Veith GD
Published: February 2009

Success in the development of predictive methods for relating biodegradation rates in water to chemical structure has been elusive. We present a strategy for evaluation of biodegradability of chemicals that involves a combination of structure-biodegradation relationships (SBR) and laboratory testing arranged in a four-tier heirarchy. The first tier involves a search of a data base on biodegradation information. Each subsequent tier consists of a query of potential SBR for the chemical or an experimental laboratory test of the chemical using a tier-specific procedure. The tiered hierarchy proceeds from a data base search, the simplest and cheapest level, to a river die-away test, the most complex and expensive level.

The main purpose of the first three tiers in this strategy is to discriminate readily biodegradable from persistent chemicals. The fourth tier involves the measurement of a biodegradation rate constant under experimental conditions. If a chemical is determined to be degradable, then metabolites of the chemical are also evaluated to identify possible recalcitrant by-products. The approach (a) satisfies the critical need to develop a systematic reference data base on biodegradation endpoints for existing and new chemicals, (b) incorporates the metabolites of biodegradation into the process, and (c) provides an economical means to evaluate chemical biodegradation.
A Quantitative Structure-Activity Relationship Study of Overton's Data on the Narcosis and Toxicity of Organic Compounds to the Tadpole, Rana temporaria
Authors: Lipnick RL
Published: February 2009

A quantitative structure-activity relationship (QSAR) study has been performed on the toxicity of organic compounds to the tadpole, Rana temporaria. The biological test data were taken from Charles Ernest Overton's classic monograph Studien über die Narkose, which has been widely cited by researchers studying the correlation of biological activity with partition coefficient and the mechanism of anesthesia. A baseline narcosis QSAR model, log (1/C = 0.909 log P + 0.727, was derived using data on 18 alcohols, ketones, and hydrocarbons, where C is the lowest narcosis-inducing concentration in moles per litre, and P is the n-octanol/water partition coefficient. The corresponding lowest tadpole test concentration producing narcosis or other toxic effects for the remaining 100 compounds was compared with that predicted by the above QSAR equation. In general, very good agreement was obtained between the predicted and measured values for those nonelectrolytes producing solely a narcosis physiological response. In contrast, acetamide, succinimide, urea, and ethylene glycol produced lethality without narcosis at considerably lower concentrations than predicted. These compounds, which have low lipoid solubility and undergo little or no membrane transport, produce osmotic effects. The observed and predicted narcotic concentrations for the two hypnotic agents, sulfonal and trional, are in general agreement, based upon log P values calculated from the water solubility and melting point. The lack of observed effect for cetyl alcohol, anthracene, anthraquinone, parachloralose, and terpin hydrate, even in tadpole tests of long duration, can be attributed to a water solubility limitation, or cutoff, that is due to a high log P, a high melting point, or a combination of these factors. Although coumarin is 17 times more toxic than predicted, it produces reversible narcosis effects only. This behavior may reflect a reversible Michael-type addition by nucleophilic moieties present in mole cules comprising the membrane lipoid site of action. Alkaloids and strongly basic amines are all more toxic than predicted.
Interspecific and Geographical Variation of the Chromium Sensitivity of Algae
Authors: Riedel GF
Published: February 2009

The toxic effect of hexavalent chromium on the growth rate of ten species of estuarine phytoplankton was examined in a defined growth medium. The concentration causing 50% inhibition of growth rate varied by a factor of more than 50 among the species. Three possible causes of interspecific variation in the sensitivity were examined: detoxification by extracellular reduction, interspecific differences in growth rate, and interspecific differences in chromium (VI) uptake. Results indicate that none of these hypotheses explains the interspecific variation in chromium sensitivity.

The chromium (VI) sensitivity of each algal species was also tested at two different sulfate concentrations. In every case, the toxicity of chromium (VI) was greater in the medium with lower sulfate concentrations. This confirms and extends previous results showing that chromate sensitivity in algae is closely correlated to the sulfate concentration of the growth medium.
An In Vitro Submitochondrial Bioassay for Predicting Acute Toxicity in Fish
Authors: Blondin GA , Knobeloch LM , Read HW , Harkin JM
Published: February 2009

A new, rapid, and reliable bioassay for monitoring the acute toxicity of aquatic samples has been developed. The method is based on metabolic changes in preparations made from isolated animal mitochondria which affect the ratio of reduced to oxidized nicotinamide adenine dinucleotide (NADH/NAD) as measured in a spectrophotometer. Stable submitochondrial electron-transfer particles (SMP), made by sonic disruption of the cristae membranes of bovine heart mitochondria, afford the most practical biological test material because these vesicles can be stored indefinitely prior to use as frozen or freeze-dried preparations with full retention of biological activity. Under appropriate conditions, SMP can be programed to reduce exogenous NAD + by coupled reverse electron transfer (RET) or to oxidize NADH by the conventional electron transfer pathway (ETR). Exposure to toxicants inhibits one or both redox activities by an amount proportional to the toxicant concentration. Hence, bioassay procedures can be based on RET and ETR tests which are often complementary. Reliable data can be obtained in 2 to 18 min without interference caused by “hard water” conditions. The toxicities of 64 industrial chemicals, inorganics, and pesticides to SMP correlate closely with the results from tests with the fathead minnow ( r 2 = 83%). The correlation was substantially poorer between fish toxicity and available data for the same toxicants from another short-term bioassay utilizing the Microtox procedure. In the new bioassay, the biological materials of the SMP test are handled like a chemical reagent. The test requires only small sample volumes, has good reproducibility, and promises to be relatively inexpensive, rapid, and simple. Bioassay variants and potential enhancements of the SMP test system are discussed.
The In-Situ Measurement of the Undrained Shear Strength of Clays Using the Field Vane
Authors: Chandler RJ
Published: February 2009

A brief review of the standard dimensions, insertion procedures, and rates of rotation of the field vane is followed by consideration of those factors that influence the undrained shear strength measured by the field vane. These factors include the disturbance effects of vane insertion, the consequences of a “rest” period before shear, strain-rate effects, the rotation rate necessary to ensure undrained conditions during shear, and the method of calculation of cu. Following a discussion of the relative magnitude of cu, measured by the field vane, it is concluded that there is a consistent relationship with other measures of cu, depending on the plasticity index, provided the other strength measurements are made on specimens reconsolidated to the in-situ stresses. After consideration of a number of case records reported in the literature, it is suggested that for “standard” clays the approximate expression, cuσv = S1 (OCR)0.95, may be useful as a check on the measured field vane strength, or as an estimate of OCR. In this equation the strength ratio S1 = (cu/σv) is that given by Bjerrum for “Young” clays, for which OCR ≅ 1.0.
In-Situ Vane Shear Testing at Sea
Authors: Young AG , McClelland B , Quiros GW
Published: February 2009

In-situ vane shear testing to measure undrained shear strength in the offshore environment has experienced increased use and significant equipment improvements over the last decade. These changes arose from (1) the offshore petroleum industry's need to improve the quality of foundation site investigations for their structures, (2) technological advancements in mechanical and electrical systems, and (3) recognition by the geotechnical profession of the benefits of acquiring vane shear testing data for better interpretation of cohesive soil strength properties. This paper provides insight into the current international practice of in-situ vane shear testing by presenting results of a questionnaire to international experts. The paper also describes the historical developments that led to the current state of practice. A review of field vane deployment and important operational details is presented along with an appraisal of the applications of vane shear testing for foundation design purposes. The paper also presents various case studies demonstrating how vane shear testing data proved beneficial for offshore foundation design. Finally, the paper summarizes the author's opinions relative to the current state of the art of offshore vane shear testing and includes comments on possible future developments and applications.
Errors Caused by Friction in Field Vane Tests
Authors: Ortigão JAR , Collet HB
Published: February 2009

Field vane tests have been traditionally employed with reported success in design on soft soils. In Brazil, most of the available vane test equipment requires preboring. With these devices soil-rod friction influences the data and should be accounted for through calibration tests. An investigation was carried out on Rio de Janeiro clay, and the results showed that soil-rod friction tests can provide unreliable results. Therefore, friction should be eliminated through a better mechanical design, as accomplished in the vaneborer apparatus, with which field vane (FV) tests have shown less data scatter. The FV strength profile was evaluated in a stability analysis of an embankment failure on Rio de Janeiro clay, and a factor of safety close to one was obtained in this highly plastic clay. This led to the conclusion that recommended FV correction factors are too conservative for the Rio de Janeiro clay.
Progressive Failure in the Vane Test
Authors: DeAlencar JA , Chan DH , Morgenstern NR
Published: February 2009

A finite-element analysis of the undrained vane test has been performed using an elasto-plastic constitutive relation with strain-softening behavior. A hyperbolic strain softening model has been developed to model the post peak behavior of the soil. This constitutive relationship assumes an elastic behavior up to peak strength, and the material subsequently softens according to a hyperbolic relationship. As a result one can model different rates of post peak softening in a compact manner while maintaining the same peak and residual strength. The results of the analysis show that the peak torque measured in a vane test depends not only on the peak strength and the residual strength of the material, but also that the rate of post peak softening has a dramatic effect on the peak torque and the torque-rotation relationship of the test. If the material possesses moderate rates of softening behavior, the maximum torque is close to the value calculated based on peak strength. In other words, the results of the vane test can be used to deduce the peak strength of the material. At high rates of softening, the progressive development of the failure zone results from stress concentration effects at the blades of the vane, and the strength is mobilized in a nonuniform manner around the vane at maximum torque. Therefore the distribution of stresses around the perimeter of the vane is not known and the assumption of uniform mobilization of shear strength will lead to an incorrect evaluation of the peak strength of the material. This effect is especially pronounced in very strain sensitive soils. The finite-element results also reveal a localized failure zone around the vane when the maximum torque is reached. Comparisons between the finite-element results and existing experimental studies of soil behavior around a vane are in agreement for the failure mechanism developed during a vane test.
Measurement of Residual/Remolded Vane Shear Strength of Marine Sediments
Authors: Chaney RC , Richardson GN
Published: February 2009

The measurement of both residual and remolded shear strength using the vane shear apparatus is discussed. Residual shear strength is defined to be measured after 90° of vane rotation. In contrast, remolded shear strength is dependent on whether it is measured by vane remolding or hand remolding. To accomplish vane remolding, a minimum of three vane revolutions are required. The relative strengths of the various remolding methods show that (1) field vane remolding gives highest strength, (2) followed by either laboratory vane remolding or hand remolding. Order of the last two appears to depend on soils plasticity. Vane remolding is shown to be influenced by a soils anisotropy while hand remolding is not. Case studies are presented for a DSDP site in the North Pacific and the Mississippi Fan in the Gulf of Mexico. Standardization and measurement procedures to obtain repeatable and comparable results are presented.
Micromorphological Aspects of the Vane Shear Test
Authors: Veneman PLM , Edil TB
Published: February 2009

Micromorphological studies of the mode of failure using thin sections of soil obtained during laboratory vane shear testing indicate that the actual failure surface is not a sharply defined cylindrical surface, but rather a shear zone. The diameter of the failure surface at large angles of vane rotation in a soft and a very soft silty clay appeared to be equal to the diameter of the vane device. The shear structures that develop as the vane rotates may or may not fully develop to a continuous circular surface when the maximum torque is reached depending on the consistency of the soil. The results indicate that undrained shear strength calculations based on the assumption of a fully developed cylindrical surface may somewhat underestimate the actual soil strength, but that the magnitude of this deviation is soil type dependent.
Low-Strain Shear Measurement Using a Triaxial Vane Device
Authors: Pamukcu S , Suhayda J
Published: February 2009

Laboratory determination of low strain shear behavior or shear modulus of soft saturated clays can be complicated if high-frequency dynamic testing methods are utilized. Cyclic loading can promote fast degradation of moduli for these soils. A monotonic torsional shear device, namely, a triaxial vane device, was equipped with a computer aided data acquisition system to detect low strain shear deformations under quasi-static loading conditions. The average range of electronically measured strain was 10-4 to 1%, which was compatible with that of a high-frequency low-strain dynamic testing method, namely, resonant column. Comparison of the dynamic and static moduli reduction curves of artificially prepared soft kaolinite specimens demonstrated the cyclic degradation effects on strain dependent dynamic moduli. For normally consolidated specimens under confining pressure of 100 kPa, the ratio of maximum static shear modulus to maximum dynamic shear modulus was estimated to be around 0.85. This value and the observed trend of dynamic and static moduli reduction curves at low strains are in agreement with the findings of other investigators. The relatively continuous, high-resolution low-strain static data indicated further gain in understanding of low-strain nonlinearity and yielding behavior of soft marine clays.
Miniature Vane and Cone Penetration Tests During Centrifuge Flight
Authors: Almeida MSS , Parry RHG
Published: February 2009

Correct assessment of soil properties in centrifuge tests require these to be measured during flight, and small vane and penetrometer devices have been developed with this purpose. The vane is fixed in position, but the penetrometer can traverse the length of the model, allowing tests to be made at different positions. A program of tests has been conducted in the centrifuge at 100g investigating the use of these methods in consolidated beds of clay. Clay beds consist of an overconsolidated layer with a top stiffer layer overlaying a normally consolidated layer. Curves of point resistance with depth are similar in shape to curves of vane strength with depth, and the stiffer layer obtained as a result of the stress history is indicated in both tests. However measured point resistances are lower than expected, which is attributed to water pressure effects around the cone tip.
Experience with Field Vane Testing at Sepetiba Test Fills
Authors: Garga VK
Published: February 2009

The design of new port of Sepetiba, near Rio de Janeiro, required a detailed evaluation of in-situ behavior of the sub-soil. The subsoil at this large site consists essentially of soft clays, but with extreme variability in sand and silt content and organic matter. The construction of two large instrumented test fills provided a good opportunity to monitor the increase in undrained strength Su with increase in effective stress. Investigations were also carried out to measure strength anisotropy using vane tests at a site nearby the test fills. The investigations suggest the following conclusions: (1) the vane strengths are very similar to those for unconfined compression and unconsolidated undrained laboratory triaxial tests, (2) the increase in vane strengths did not accompany the increase in effective stress underneath the test fills, (3) the stress ratio Su/σv after consolidation in the foundation was lower than before construction, and (4) tests with vanes of different height to diameter ratios were not successful in determining the strength anisotropy at this site.
Evaluation of Offshore In-Situ Vane Test Results
Authors: Kolk HJ , Hoope Jt , Ims BW
Published: February 2009

An evaluation is presented of results from about 450 tests obtained with an offshore in-situ vane during geotechnical investigations in the North Sea and off the west coast of India. The soils tested are normally consolidated and included silts and clays with differing carbonate contents. The strength values of the in-situ vane are compared with strength results from triaxial tests, laboratory vane, and Torvane tests. These data are also correlated with in-situ test results obtained with the piezocone penetrometer. The in-situ vane shear strength data show a small scatter, and good agreement was found with unconsolidated undrained (UU) triaxial test results. The rate of post peak reduction in soil strength, measured on the vane shear strength-rotation curve, appears to depend on plasticity. Based on this study it is recommended that the vane be rotated to a minimum of 40° for very plastic clays to approximately 150° for clays with low plasticity, to determine post-peak strength behavior with great accuracy. It is suggested that the undrained shear strength values determined with the in-situ vane may be of greater value than other undrained shear strength measurements for axial pile design purposes. This study also yielded encouraging estimates of the coefficient of lateral stress at rest K0 based on in-situ vane and triaxial test data.
Approximate Analysis for Optimizing Prestress Treatments
Authors: Fuchs HO
Published: February 2009

A method of analysis for finding optimum shot peening specifications for given parts and loading conditions is explained. The method is applied to a part with fillets loaded in rotating bending. The computed optimum intensity is 9 C. Fatigue tests are reported which compare this intensity to the conventionally specified 7A. The higher intensity proved clearly superior.
Stress Intensity Factors Caused by Residual Stress Fields in Autofrettaged Tubing
Authors: Stacey A , Webster GA
Published: February 2009

The influence of residual stress distributions on the stress intensity factors developed in thick-walled cylinders containing line cracks is quantified. A stress intensity factor caused by the residual stress field, Kres, is evaluated using the superposition principle. This can then be superposed on the stress intensity factor associated with the applied loading to give an effective stress intensity factor controlling crack growth.

Boundary integral equation and weight function methods are applied to determine Kres as a function of crack depth for internally and externally flawed as-received and autofrettaged cylinders with a diameter ratio of 2.07. Good agreement is obtained between the two approaches over the range of normalized crack depth 0 ≤ a/W ≤ 0.7 (a = crack length, W = specimen width). Actual measured residual stress distributions, as well as analytical residual stress fields for autofrettaged tubing obtained assuming elastic-perfectly plastic behavior and the von Mises and Tresca yield criteria, are investigated. The Kres caused by autofrettage residual hoop stresses is essentially negative for internal cracks and positive for external cracks. The Kres solutions for the experimentally measured and von Mises distributions compare very favorably. The results for the Tresca distribution are approximately twice as large and are considered to be too conservative.
Increased Pressure Vessel Fatigue Life Caused by Decreased Autofrettage
Authors: Brown BB
Published: February 2009

Pressure vessels, while gaining fatigue life at interior surfaces caused by autofrettage residual stresses, suffer a decreased life when fatigue cracking initiates at the exterior. This situation may result in a less than optimum vessel life if maximum autofrettage is applied. A series of controlled experiments have been performed along with analyses to maximize the life of a pressure vessel by optimizing the level of autofrettage.

The experiments used specimens with an outer diameter of 284 mm, a 64-mm wall thickness, and an exterior groove. Autofrettage overstrain levels were varied incrementally from 100 to 50% with fatigue life increases over 100%. Normally, pressure vessels would experience a decrease in fatigue lives with decreasing overstrains of this range. In this experiment, because of the exterior stress concentration of the groove, fatigue lives increased with the reduced overstrains. The work has been subsequently applied to operating pressure vessels with fatigue test data taken on these vessels.
Influence of Residual Stress on Fatigue Crack Growth in Thick-Walled Cylinders
Authors: Stacey A , Webster GA
Published: February 2009

An investigation was conducted into fatigue crack growth in samples of as-received and autofrettaged, high-strength, low-alloy steel tubing containing residual stresses. Compact tension and C-shaped and ring specimens were used to measure properties in the axial and radial directions. Internally and externally flawed ring specimens were employed to propagate cracks through the original residual stress field. Experiments were performed for load ratios ranging between -0.5 and 0.8. Fatigue crack growth rates were substantially reduced by compressive residual stresses. The data were corrected for residual stress effects using the superposition principle. An effective stress intensity factor range, ΔKeff, was defined that incorporates the residual stress intensity factor, Kres, and the applied ΔK range. Using this approach, the correlation with the characteristics for no residual stress was very good. In addition, it was shown that fatigue crack growth rate characteristics measured with C-specimens can significantly misrepresent the actual behavior of the material and tubing under investigation if the remaining residual stress field is not taken into consideration.
Development of Silicophosphate Glass HAP-3
Authors: Izumitani T , Matsukawa M , Hata C , Tanaka K , Toratani H
Published: February 2009

Silicophosphate glass HAP with high thermal shock resistance was developed. As the thermal conductivity of glass can not be increased, thermal expansion coefficient was tried to make smaller and mechanical strength to make higher. P2O5-SiO2-Li2O system was investigated. In P2O5-SiO2-Li2O system, thermal expansion coefficient decreases and mechanical strength increases with SiO2 content, but chemical durability becomes worse. The weak chemical durability was improved by introducing Al2O3 in the system. HAP-3 selected from P2O5-SiO2-Li2O has higher thermal shock resistance, as 2.7 times as LHG-8, as 1.6 times high as LHG-5, low content of water and low concentration quenching.
LIMA in Damage Diagnostics
Authors: Laidler I , Edge GJ , Emmony DC , Temple PA
Published: February 2009

LIMA (laser induced mass analysis) has been used as a damage testing facility incorporating damage detection and analysis of all ionic species generated by breakdown and plasma formation on a surface.

The laser radiation is frequency quadrupled Nd-YAG at 266 nm, enabling studies in the UV near to the most important KrF emission.

Preliminary qualitative results give an insight into damage mechanisms and coating weaknesses.

Two prototype coatings, an A.R. and an H.R., have been studied above and below the 50% damage fluence. The state of coating cleanliness is immediately obvious and it is possible to conclude the sources of sub-threshold damage and the extent of coating disruption. The ready availability of this information should led to forthcoming improvements from coating manufacturers.
Laser-Induced Damage to Titanium-Doped Sapphire Using 532 nm Wavelength Pulses of 10 ns Duration
Authors: Seitel SC , DeShazer LG
Published: February 2009

Preliminary laser exposure tests of uncoated, polished titanium-doped sapphire from Union Carbide Corporation are reported. The measured surface damage thresholds varied from ∼3 to ∼14 J/cm2, depending on surface finish and sample orientation. The dependence on orientation is not correlated with crystallographic direction. A strong dependence on doping level was not observed. Well polished samples failed by pitting of the surface. On one sample, internal damage was also observed at fluences as low as 7 J/cm2.
Performance Characteristics of a Beam Profiling System Consisting of Various Solid State Imaging Devices and an 8-Bit Image Processor
Authors: O'Connell RM , Stewart AF
Published: February 2009

A beam profiling system that interfaces an 8-bit image processor to either of two self-scanned solid state area array cameras is described. Results of measurements to characterize the performance of the camera sensors, a frame transfer charge coupled device (CCD) and a charge injection device (CID), are presented and discussed. The CCD camera is shown to have the advantages of simpler interfacing requirements, greater access to the image processor software, better dark current pattern noise, and wider spatial frequency bandwidth. The CID camera may have wider dynamic range and better photosensitivity pattern noise, but further measurements of these properties are warranted.
Laser-Induced Damage Detection and Assessment by Enhanced Surface Scattering
Authors: Seitel SC , Babb MT
Published: February 2009

A photoelectric damage detection and assessment system based on laser-induced changes in surface scattering is reported. The system is similar to one reported by Franck, et. al., with improved operating flexibility. It is integrated with a 1064/532 nm damage test facility used for routine testing of production optics. For some types of coated samples, a plot of scatter change vs. applied fluence can be extrapolated to the threshold fluence for surface pitting, eliminating the need for tedious microscopic assessment of near-threshold test sites. The system permits quantitative assessment of surface quality (by forward scatter) at a test site just prior to exposure by the damaging beam. thus, correlations between surface scatter and damage susceptibility may be investigated directly.
Thermal Properties of Optical Materials
Authors: Decker DL
Published: February 2009

A knowledge of the thermal properties of optical materials is essential to an understanding of laser-induced damage for long-pulse or continuous-wave irradiation. This area has been long neglected partly because of the difficulty of reliable measurement. An extension of the thin film measurement technique described at the Boulder Laser Damage Conference in 1984 for the measurement of thermal conductivity is presented in this paper. Data are given for bulk Si, SiC, Si/SiC, and SiO2. These results are interpreted using simple theories of inhomogeneous or locally disordered materials. Also indicated are the relationships between local material stress and thermal conductivity, and the temperature dependence of the thermal conductivity for several models of local disorder. Recommendations for further work are also indicated.
Beam-Induced Spherical Aberration in Cooled CW Laser Light Transmitting Components
Authors: Klein CA
Published: February 2009

Thermally induced optical distortions severely degrade the quality of a laser beam thus reducing the irradiance on target. The objective of this paper is to formulate procedures for evaluating the impact of spherical aberrations generated by optically transparent cylindrical components subjected to CW laser radiation; specifically, the paper concerns edge- and face-cooled optical elements and assesses how beam shape and cooling strength affect the performance. The author first reviews the physics of thermal lensing and discusses how optical distortion coefficients relate the spatial temperature distribution to the wavefront error functions δϕ+ and δϕ-. For semiconductors with positive thermo-optic coefficients, the analysis can be carried out on a scalar diffraction basis, which implies that the degradation in focal irradiance associated with primary spherical aberrations originates from a single quartic term, δϕ4ρ4. On assuming that it is a good approximation to describe the beam-induced temperature rise by means of a fourth-order even polynomial, it is shown that the amplitude-weighted variance of δϕ4ρ4 provides a suitable measure of the degradation, which leads to the concept of a spherical aberration factor S = δT4√var[ρ4].The heat-flow equations for both edge- and face-cooled cylindrical components can be formulated non-dimensionally and solved exactly thus demonstrating that (a) temperature variations causing optical distortion scale with βP/K, i.e., the total power deposited per unit length and the inverse thermal conductivity of the medium; (b) with the possible exception of high-truncation-parameter Gaussians, fourth-order polynomials yield reasonably accurate temperature profiles; and (c) apodization can be very useful in mitigating the deleterious effects of thermal lensing. For edge-cooled optical elements, the heat-transfer coefficient has no influence on the temperature profile, and the aperture diameter does not affect the performance. An appropriate materials figure of merit is K/(χβV),which includes the thermal conductivity K, the distortion coefficient χ, and the absorption coefficient βV. The treatment of face cooling requires a more elaborate analysis and involves the Nusselt number Nu = hLC/K, the sympol LC referring to the characteristic length (D/2)2/L. For weak cooling (Nu.⩽ 1), the spherical aberration factors are similar to those of edge cooling, but Nusselt numbers Nu ≳ 10 result in a significant reduction of the distortion, which has important implications for selecting proper operating conditions.
The Effect of Impurities on U.V. Damage in CaF2
Authors: Laidler I , Emmony DC
Published: February 2009

The paper discusses the role of impurities in bulk laser breakdown. Crystals of CaF2 have been grown with different impurity content. The introduced impurities are mainly rare earths, these being the most common contaminent species found in CaF2. Crystals selectively doped with Ce as well as very pure, strain annealed specimens were also grown. The generation of defect centres as a function of incident 248 nm laser fluence was monitored by transient absorption measurements. Bulk damage measurements indicated that the Ce doped crystals had the lowest thresholds followed by the pure strain annealed crystals, despite a complete absence of excited state absorbing centres produced during laser irradiation. Those crystals which showed a significant production of transient defects and fluorescent levels had very high damage thresholds.
Comparison of Frequency Response Characteristics of an Optical Scatterometer and a Mechanical Profilometer
Authors: Wilson SR , Al-Jumaily GA , McNeil JR
Published: February 2009

The frequency response characteristics of an angle-resolved optical scatterometer and a mechanical profilometer are examined. The transfer function for the scatterometer is found to be constant within the spatial frequency bandwidth of the system. The mechanical profilometer is found to have a nonlinear, lowpass-like response. A computational model is used to examine the effects of the nonlinear stylus response on realistic surfaces.
Ultrasmooth Sapphire Produced by Noncontact Polishing
Authors: Shaffer JJ , Bennett JM
Published: February 2009

The history and theory of noncontact polishing is discussed, along with a simple machine that will perform noncontact polishing including lap speeds and polishing pressure. Research using this machine is described. An extended polishing experiment produced the smoothest surface ever measured at the Naval Weapons Center.
Optical Damage in Epoxy Polymers by Millisecond Light Pulses
Authors: Wolfe CR , Campbell JH , Lyon RE , Pitts JH , Powell HT
Published: February 2009

We have studied optical damage in epoxy based polymers used to attach absorbing cladding onto the edge of laser disks of the Nova laser. Damage was produced by exposing the polymers to a 20-40 J/cm2 fluence of broad band Xe-flashlamp light having a pulselength of approximately 0.5 ms. This simulates the pump environment of Nd:glass laser amplifiers. The predominant damage mechanisms appear to be pyrolysis, associated with absorbing Inclusions and photolysis, associated with Intrinsic absorption of the polymer. The amount of damage can be minimized by: (1) careful filtering of the polymer to reduce the presence of foreign material, (2) minimizing the near UV absorption of the polymer and (3) reducing the UV emission of the flashlamps.
Variations with Laser Pulse Duration of the Thresholds at 350-nm and 1064-nm for Bulk Damage in Crystals of KDP
Authors: Gonzales RP , Staggs MC , Singleton MF , George D , Weinzapfel CL , Weinzapfel S
Published: February 2009

Five separate laser facilities were used to measure 350-nm and 1064-nm thresholds for bulk damage in crystals of KDP. At 1064-nm, tests were made with single laser pulses having durations of 1, 9 and 25 ns and with 9-ns pulses incident at 10 Hz. At 350-nm test were made with single pulses having durations of 0.6, 5.0 and 25 ns and with 25-nm pulses incident at rates up to 50 Hz. Over the range from 0.6 to 25 ns, 350-nm thresholds increased by a factor of approximately 2, and 350-nm thresholds were almost independent of laser repetition rate. The 1064-nm thresholds increased by a factor > 3 as pulse duration increased from 1 to 25 ns. Laser hardening of thresholds was observed at both 350-nm and 1064-nm.
Temperature Effects on Laser Induced Damage and Accumulation in Silicon
Authors: Platenak JR , Walser RM , Becker MF
Published: February 2009

In this paper we describe an investigation of the accumulation effect in N-on-1 laser damage to silicon at 1.06 microns. Experiments were conducted on thermally annealed samples and on samples at elevated temperatures at various pulse repetition rates. Experiments on thermally annealed samples suggest accumulation is not due to any extrinsic structural defect that could be annealed at 1000°C. Experiments involving accumulation at elevated temperatures as a function fo pulse repetition rate indicate that any defect responsible for accumulation must have a lifetime of at least 1 second at 500°C. This suggests that an extended structural defect may be involved in accumulation. Results of these experiments also support a thermal melting model for laser damage to silicon at 1.06 microns.
Scatter Intensity Mapping of Laser-Illuminated Coating Defects
Authors: Moran MB , Kuo RH , Marrs CD
Published: February 2009

The ability to detect and locate defects nondestructively in multilayer optical coatings has been demonstrated using a video microscopy system. The system uses laser-excited scattering to illuminate defects responsible for laser-induced damage in multi-layer dielectric mirrors. So far, attempts to predict the particular defect that will initiate damage have been unsuccessful. Presently, intensity maps and contours can be generated by digitizing the video images of scattering from individual defects. These can reveal characteristic defect scatter features possibly related to damage probability, and they offer a means to follow the development of these features from incipient to catastrophic damage. Examples of defect scatter maps and intensity contours for a dielectric mirror will be presented and discussed.
Spectral Emission Studies of Optical Coating Defects
Authors: Marrs CD , Walker SJ , Moran MB , Porteus JO
Published: February 2009

Video monitoring of pulsed visible-wavelength mirror damage led to the previously reported observation of illuminated coating defects as precursors to microscopic damage. Typically, many defects are observed in the laser interaction area, but only a few act as damage initiators. The present study seeks to identify the latter defects via any special characteristic of their laser-excited emission spectra that may serve as a recognizable signature. The ability to make such recognition nondestructively is crucial to producing optical coatings that perform at intrinsic damage levels. The video microscopy apparatus and methodology for measuring emission spectra of individual defects will be described. Results from various dielectric mirrors will be presented, including conclusive evidence that defect illumination is primarily the result of defect scattering. The dependence of defect image intensity on laser wavelength is examined more closely.