Limitations on the uses of multimedia exposure measurements for multipathway exposure assessment--Part I: Handling observations below detection limits.

Multimedia data from two probability-based exposure studies were investigated in terms of how censoring of nondetects affected estimation of population parameters and associations. Appropriate methods for handling censored below-detection-limit(BDL)values in this context were unclear since sampling weights were involved and since bivariate associations/measures were of interest. Both simple substitution(e.g., using 1/2 or 2/3 of the detection limit(DL)for BDL values)and truncation-based strategies were investigated by creating some artificial DLs and comparing resultant estimates with the original studies'uncensored results. The substitution methods generally outperformed the truncation methods, with the(2/3)DL substitution generally performing best.     

The Italian national survey of aircrew exposure: II. On-board measurements and results

The Italian survey of aircrew exposure has been carried out with different advanced dosimetric systems, as described in part I of this paper. The key strategy of the survey was to obtain on-board comparison of measurements for both passive and real-time detectors flown together with passengers. The survey has been carried out in the period of solar minimum (1995-1997), in which the exposure to galactic cosmic rays reaches its maximum value. Even though carrying out the survey in the period of solar minimum was entirely coincidental, this circumstance has been used to good advantage to obtain a comprehensive set of data of the galactic cosmic radiation with little or no disturbance by the solar activity modulation. This comprehensive set of data covers flight routes between -20 degrees and 75 degrees geographic latitude at different civil aviation altitudes. The survey obtained with different advanced dosimetric systems has been supplemented by a large variety of data gathered with passive stacks on different short-range and long-range flights at supersonic and subsonic altitudes. Some of the most important conclusions which can be drawn from the survey are: (i) aircrew of civil aviation receive annual doses within the range of 1 mSv to 6 mSv; (ii) data from different periods of solar minimum agree well, since the discrepancies encountered seem mainly due to the different dosimetric systems used; (iii) repeated measurements on the same route are highly consistent.     

Effect of the exposure time on hardness measurements on the HRC scale

Summary The time of exposure under full load must not be less than 10±1 sec for reference and standard tests, 5±1 sec for calibrations, and 3±1 sec for commercial instruments.The instruments should be adjusted and used at the same exposure time.The automation of measurements will provide a greater accuracy and reliability.     

Quality and exposure control in semiconductor manufacturing. Part II: Evaluation

The purpose of this article is to test the performance of a heuristic algorithm that computes a quality control plan. The objective of the tests reported in this paper is twofold: (1) to compare the proposed heuristic algorithm (HA) to an optimal allocation (OA) method; and (2) to analyse the behaviour and limitations of the proposed HA on a scale-1 test with a before/after test. The method employed to evaluate this algorithm is based on comparisons: 1. The first test illustrates the method and its sensitivity to internal parameters. It is based on a simplified case study of a product from the semiconductor industry. The product is made up of 1000, 800 and 1200 wafers incorporating three different technologies. The production duration is 1 week, and three tools were involved in this test. The behaviour of the proposed algorithm is checked throughout the evolution of the model parameters: risk exposure limit (R_L ) and measurement capacity (P). The quality control plan for each tool and product are analysed and compared to those from a one stage allocation process (named C ⁰) that does not take into account risk exposure considerations. A comparison is also performed with OA.

2. The second scale-1 test is based on three scenarios of several months of regular semiconductor production. Data were obtained from 23 etching and 12 photolithographical tools. The outputs provided by the HA are used in the sampling scheduler implemented at this plant. The resulting samples are compared against three indicators.

The results of these comparisons show that, for small instances, OA is more relevant than the HA method. The HA provides realistic limits that are suitable for daily operations. Even though the HA may provide far from optimal results, it demonstrates major MAR improvement. In terms of the maximum inhibit limit, the HA achieves better performances than C ⁰, and they are strongly correlated to R_L and to the control capacity. The article concludes that the proposed algorithm can be used to plan controls and to guide their scheduling. It can also improve the insurance design for several levels of acceptance of risk.     

输入数据缺失情况下的OE模型辨识算法研究

针对辨识技术应用过程中出现的一类输入数据随机缺失时的辨识问题进行了研究。针对输出误差(OE)模型描述的一类系统,提出了一种模型辨识和缺失数据预测交互迭代的辨识算法。在模型辨识中采用了递推的辨识算法便于形成实时更新的在线辨识策略;而在缺失数据的预测过程中,利用小波降噪技术对预测数据进行适应性的滤波。仿真和分析表明,所提出的辨识算法对连续性输入数据缺失具有很强的鲁棒性;与没有小波技术参与的辨识算法相比,该算法具有较高的模型辨识精度和对缺失数据较好的预测能力。     

A multimedia, multiple pathway exposure assessment of atrazine: fate, transport and uncertainty analysis

The potential danger posed to human health from pesticides and herbicides has been a growing national concern due to the increased frequency of agrochemical residues found in food and water. It is becoming critical to determine the concentration in all environmental media for a complete picture of potential human exposure. A multimedia transport model is used to determine the concentration of atrazine in surface water, ground water, surface soil, root zone soil, plants, and air at a typical mid-western location. A range of values is used for each model input, resulting in a distribution of possible concentrations in each medium. A sensitivity analysis determines the influence each parameter has on the outcome variance for each environmental media concentration. The concentrations determined for ground and surface water are then compared to measured concentrations in the region to validate the model. The concentrations are then compared to measured concentrations in the region to validate the model. A companion paper utilizes these concentrations and translates them into human exposure and risk.     

High-efficiency aerosol scatterometer that uses an integrating sphere for the calibration of multiwavelength lidar data

For the purpose of calibrating multiwavelength lidar data, we developed a scatterometer to measure the aerosol scattering coefficient at the ground level. The system is based on an integrating sphere, cw lasers (532 and 633 nm), and a controlled flow of the ambient air, including aerosol particles. The simulation study and experimental results indicate that the detection efficiency of this instrument is approximately 10%-40% better than that of an integrating nephelometer, because of the wider acceptance angle of the scattered light. The scattering coefficients measured at the two wavelengths, as well as the resulting value of the angstrom exponent, show good correlation with the results simultaneously measured with an integrating nephelometer and an optical particle counter.     

Effects of the cavity walls on perturbation measurements

Perturbation methods in microwave measurements are addressed. The perturbation formulas will not remain correct when the perturbation object approaches the wall of the resonant cavity. This is a consequence of the effect of the induced charges on the cavity wall when the object approaches it. The author takes this effect into account, and gives modified perturbation formulas which were verified by experimental results. These modified perturbation formulas can be widely used in the measurement of the electromagnetic fields in linear accelerators and other microwave devices. In deriving the formulas, metallic and dielectric spheres are used in perturbing objects     

Tissue characterization using the continuous wavelet transform. Part II: Application on breast RF data

For pt.I see ibid., vol.48, no.2, p.356-63 (2001). In the first part of this work (Georgiou and Cohen 2000), a wavelet-based decomposition algorithm of the RF echo into its coherent and diffuse components was introduced. In this paper, the proposed algorithm is used to estimate structural parameters of the breast tissue such as the number and energy of coherent scatterers, the energy of the diffuse scatterers, and the correlation between them. Based on these individual parameters, breast tissue characterization is performed. The database used consists of 155 breast scans from 42 patients. The results are presented in terms of empirical receiver operating characteristics (ROC) curves. The results of this study are discussed in relation to the tissue microstructure. Individual estimated parameters are able to differentiate reliably between normal and fibroadenoma or fibrocystic or cancerous tissue (area under the ROC A_z>0.93). Also, the differentiation between malignant and benign (normal, fibrocystic, and fibroadenoma) tissue was possible (A_z>0.89)     

Individual monitoring for internal exposure in Europe and the integration of dosimetric data

The European Radiation Dosimetry Group, EURADOS, established a working group consisting of experts whose aim is to assist in the process of harmonisation of individual monitoring as part of the protection of occupationally exposed workers. A catalogue of facilities and internal dosimetric techniques related to individual monitoring in Europe has been completed as a result of this EURADOS study. A questionnaire was sent in 2002 to services requesting information on various topics including type of exposures, techniques used for direct and indirect measurements including calibration and sensitivity data and the methods employed for the assessment of internal doses. Information relating to Quality Control procedures for direct and indirect measurements, Quality Assurance Programmes in the facilities and legal requirements for "approved dosimetric services" were also considered. A total of 71 completed questionnaires were returned by internal dosimetry facilities in 26 countries. This results in an overview of the actual status of the processes used in internal exposure estimation in Europe. In many ways harmonisation is a reality in internal dose assessments, especially when taking into account the measurements of the activity retained or excreted from the body. However, a future study detailing the estimation of minimum detectable activity in the laboratories is highly recommended. Points to focus on in future harmonisation activities are as follows: the process of calculation of doses from measured activity, establishment of guidelines, similar dosimetric tools and application of the same ICRP recommendations. This would lead to a better and more harmonised approach to the estimation of internal exposures in all European facilities.     

A model of the effects of hydrophone and amplifier frequency response on ultrasound exposure measurements

To examine how less-than-ideal hydrophones and amplifiers could affect the measurement of pulse parameters, a simulated distorted pressure pulse is analyzed before and after being filtered by hydrophone and amplifier response models. The hydrophone model used is similar to the response of piezopolymer membrane hydrophones. The amplifier model is taken from typical responses of integrated circuit operational amplifier-based designs. The pressure pulse, hydrophone, and amplifier are characterized respectively by the pulse center frequency, f (c), the hydrophone resonance frequency, f(h), and the amplifier low-pass corner frequency, f(a).     

Direct numerical inversion method for kinetic ellipsometric data. II. Implementation and experimental verification

A direct numerical inversion method is applied to the monitoring of thin-film growth. Several improvements of the method, including a correction for weakly absorbing materials, are presented. The method has been successfully applied to the inversion of the growth of constant-refractive-index layers andused for the process calibration of plasma-enhanced chemical vapor deposition of silicon oxynitrides. The validity of this calibration has been successfully tested on a linear index gradient and quintic matching layer between a polycarbonate substrate and a scratch-resistant coating.     

Limitations of data compiled from police reports on pediatric pedestrian and bicycle motor vehicle events

Police reports were compared to the information provided by a hospital monitoring system for children under 15 years old injured as pedestrians and bicyclists by moving motor vehicles in Orange County, California. The analysis was limited to identifying caveats in the police report database. Underreporting by police was conservatively estimated at 20% for pedestrians and 10% for bicyclists. Comparison of the pedestrian databases suggested underreporting by police of incidents involving 0-4-year-olds, nontraffic incidents, incidents in which the vehicle was backing up, and cases not involving a child crossing a street. Comparison of the bicyclist databases indicated an underreporting by police of nontraffic cases. These caveats, in part, are related to police agency reporting requirements. The police injury severity scale was found to correlate poorly with a scale based on medical diagnoses, and substantial underreporting by police of serious injuries was demonstrated. We suggest that utilization of police injury severity scales be limited to categories of fatal, injured, and not injured (when available).     

Polarized radiance distribution measurement of skylight. II. Experiment and data

Measurements of the skylight polarized radiance distribution were performed at different measurement sites, atmospheric conditions, and three wavelengths with our newly developed Polarization Radiance Distribution Camera System (RADS-IIP), an analyzer-type Stokes polarimeter. Three Stokes parameters of skylight (I, Q, U), the degree of polarization, and the plane of polarization are presented in image format. The Arago point and neutral lines have been observed with RADS-IIP. Qualitatively, the dependence of the intensity and polarization data on wavelength, solar zenith angle, and surface albedo is in agreement with the results from computations based on a plane-parallel Rayleigh atmospheric model.     

Rayleigh-Mie Doppler wind lidar for atmospheric measurements. II. Mie scattering effect, theory, and calibration

A theoretical and experimental study is conducted for the direct-detection Doppler Lidar developed by the Service d'Aéronomie du Centre National de la Recherche Scientifique. Thanks to a specific design, the double-edge technique that applies primarily to Rayleigh scattering can also be employed in presence of aerosols backscatter. We focus on a careful estimate of the particle-induced error on the wind measurements. With a theoretical model for the Fabry-Perot interferometer and two sets of calibration measurements, the true spectral properties of the interferometer and the calibration curves are recovered. Furthermore, the particle-induced error is estimated for varying values of the scattering ratio at 532 nm. When applied to real atmospheric signals, this error is shown to be negligible. A comparison between ancillary data and the wind and backscatter ratio as retrieved from the Doppler lidar signals confirms our estimate.