Calculate Correlation Factors Research Articles

Evaluating the Theoretical Background of STOFFENMANAGER® and the Advanced REACH Tool.

STOFFENMANAGER® and the Advanced REACH Tool (ART) are recommended tools by the European Chemical Agency for regulatory chemical safety assessment. The models are widely used and accepted within the scientific community. STOFFENMANAGER® alone has more than 37 000 users globally and more than 310 000 risk assessment have been carried out by 2020. Regardless of their widespread use, this is the first study evaluating the theoretical backgrounds of each model. STOFFENMANAGER® and ART are based on a modified multiplicative model where an exposure base level (mg m−3) is replaced with a dimensionless intrinsic emission score and the exposure modifying factors are replaced with multipliers that are mainly based on subjective categories that are selected by using exposure taxonomy. The intrinsic emission is a unit of concentration to the substance emission potential that represents the concentration generated in a standardized task without local ventilation. Further information or scientific justification for this selection is not provided. The multipliers have mainly discrete values given in natural logarithm steps (…, 0.3, 1, 3, …) that are allocated by expert judgements. The multipliers scientific reasoning or link to physical quantities is not reported. The models calculate a subjective exposure score, which is then translated to an exposure level (mg m−3) by using a calibration factor. The calibration factor is assigned by comparing the measured personal exposure levels with the exposure score that is calculated for the respective exposure scenarios. A mixed effect regression model was used to calculate correlation factors for four exposure group [e.g. dusts, vapors, mists (low-volatiles), and solid object/abrasion] by using ~1000 measurements for STOFFENMANAGER® and 3000 measurements for ART. The measurement data for calibration are collected from different exposure groups. For example, for dusts the calibration data were pooled from exposure measurements sampled from pharmacies, bakeries, construction industry, and so on, which violates the empirical model basic principles. The calibration databases are not publicly available and thus their quality or subjective selections cannot be evaluated. STOFFENMANAGER® and ART can be classified as subjective categorization tools providing qualitative values as their outputs. By definition, STOFFENMANAGER® and ART cannot be classified as mechanistic models or empirical models. This modeling algorithm does not reflect the physical concept originally presented for the STOFFENMANAGER® and ART. A literature review showed that the models have been validated only at the ‘operational analysis’ level that describes the model usability. This review revealed that the accuracy of STOFFENMANAGER® is in the range of 100 000 and for ART 100. Calibration and validation studies have shown that typical log-transformed predicted exposure concentration and measured exposure levels often exhibit weak Pearson’s correlations (r is <0.6) for both STOFFENMANAGER® and ART. Based on these limitations and performance departure from regulatory criteria for risk assessment models, it is recommended that STOFFENMANAGER® and ART regulatory acceptance for chemical safety decision making should be explicitly qualified as to their current deficiencies.

Meteorological parameters as an important factor on the energy recovery of landfill gas in landfills

The effect of meteorological factors on the composition and the energy recovery of the landfill gas (LFG) were evaluated in this study. Landfill gas data consisting of methane, carbon dioxide, and oxygen content as well as LFG temperature were collected from April 2009 to March 2010 along with meteorological data. The data set were, first, used to visualize the similarity by using self-organizing maps and to calculate correlation factors. Then, the data was used with ANN to further analyze the impacts of meteorological factors. In both analysis, it is seen that the most important meteorological parameter effective on LFG energy content is soil temperatures. Furthermore, ANN was found to be successful in explaining variations of methane content and temperature of LFG with correlation coefficients of 0.706 and 0.984, respectively. ANN was proved itself to be a useful tool for estimating energy recovery of the landfill gas.

Motor Consciousness during Intention-Based and Stimulus-Based Actions: Modulating Attention Resources through Mindfulness Meditation

Mindfulness-Based Stress Reduction meditation (MBSR) may offer optimal performance through heightened attention for increased body consciousness. To test this hypothesis, MBSR effects were assessed on the simple task of lifting an object. A dual task paradigm was included to assess the opposite effect of a limited amount of attention on motor consciousness. In a stimulus-based condition, the subjects’ task was to lift an object that was hefted with weights. In an intentional-based condition, subjects were required to lift a light object while imagining that the object was virtually heavier and thus, adjust their grip voluntarily. The degree of motor consciousness was evaluated by calculating correlation factors for each participant between the grip force level used during the lift trial (“lift the object”) and that used during its associated reproduce trial (“without lifting, indicate the force you think you used in the previous trial”). Under dual task condition, motor consciousness decreased for intention- and stimulus-based actions, revealing the importance of top-down attention for building the motor representation that guides action planning. For MBSR-experts, heightened attention provided stronger levels of motor consciousness; this was true for both intention and stimulus-based actions. For controls, heightened attention decreased the capacity to reproduce force levels, suggesting that voluntary top-down attention interfered with the automatic bottom-up emergence of body sensations. Our results provide strong arguments for involvement of two types of attention for the emergence of motor consciousness. Bottom-up attention would serve as an amplifier of motor-sensory afferences; top-down attention would help transfer the motor-sensory content from a preconscious to a conscious state of processing. MBSR would be a specific state for which both types of attention are optimally combined to provide experts with total experiences of their body in movement.

Simulation of earthquake ground motions by a deterministic approach

A numerical method is presented for the computation of artificial earthquake records consistent with any arbitrarily specified target response spectra or power spectral density requirements. The proposed algorithm does not create new time histories but rather modifies, on the basis of an iterative deterministic approach, existing records to fit specific design requirements. The efficiency of the algorithm and the accuracy of the fitting process are substantially improved on the basis of a predictor–corrector type approach. The associated integrated computer code can, among its many other features, produce artificial earthquake records consistent with a number of compatible target response spectra at various damping levels, perform quadratic baseline correction, and calculate correlation factors for up to three earthquake records.

Conductivity and ordering on the planar honeycomb lattice: A Monte Carlo study of transport and order parameters in β″ aluminas

The effects of ordering on the conductivity of carriers on a planar honeycomb lattice is studied using a modified Monte Carlo technique. The hopping model includes repulsion between carriers on nearest-neighbor sites. In agreement with previous work, we find an ordered region on the phase diagram for ion density ρ in the range 0.41≤ρ≤0.59 for sufficiently low temperatures. Within this composition range of the phase diagram, ordering effects on the conductivity and on its temperature dependence are very substantial; previous results which did not correctly include the ordering effects yield quite different conductivities. We also calculate correlation factors, diffusion coefficients, and several different kinds of order parameters. Experiments on systems such as Ba++ β″-alumina and AgCrSe2 should be able to probe these ordered regions, and our results predict the influence of structure on the transport of the mobile ionic species in such compounds.

Transmission characteristics of a single-mode fiber in the 1.3-µm wavelength region

Transmission characteristics of 1.3-μm-band single-mode optical fibers were studied experimentally and theoretically. OH-ion content dependence of optical loss in the 1.3-μm region was investigated on single-mode fibers fabricated by the VAD method. The optical loss was evaluated for OH-ion content by calculating correlation factors between the optical loss and 1.39-μm OH-peak absorption loss. It was clarified that the optical loss calculated by correlation factors agreed approximately with the loss given by Lorentzian absorption in case of 0.0253-μm absorption half width, Next, the relationship between chromatic dispersion and fiber parameters was studied for step-index single-mode fibers. It was found that the zero-dispersion wavelength and the incline at the wavelength was expressed as simple functions of effective cutoff wavelength and relative index difference. Experimentally obtained zero-dispersion wavelengths on single-mode fibers fabricated by the VAD method were found to be in excellent agreement with the calculated values.

Integral methods in the calculation of correlation factors for impurity diffusion

Abstract A new method of calculating correlation factors in impurity diffusion is developed. The method, which is based on the theory of random walks on an imperfect lattice, yields a rigorous result within the framework of the adopted model. The expressions for the correlation factors in the five- (or four-) vacancy jump frequency model are given for the b.c.c., f.c.c. and diamond-structure lattices.

On diffusion kinetics in ordered binary alloys

Abstract It is shown that for self–diffusion by means of vacancies, in an ordered binary alloy with the B2 (CsCl) structure the diffusion coefficients can be decomposed into three relevant factors : the average correlation factor, the average vacancy–availability factor and the average atom–vacancy exchange rate. Within a model of only nearest–neighbour interaction the full procedure to obtain reasonably reliable estimates of all these factors is described. In this treatment Monte Carlo computer simulation serves as a criterion. The pair approximation of Kikuchi and Sato (1969, 1972} is found to give good results for vacancy availability and exchange frequency. An interpretation is given of the theory of Manning (1967, 1971) for the random alloy and it is demonstrated how a modification can be applied to calculate correlation factors for diffusion in ordered structures. The results always turn out to be better than the values obtained by Kikuchi and Sato's path–probability calculations. In a large majority of cases the agreement with the results of computer simulation is satisfactory. Only under the condition of extreme ratios of exchange frequencies of both species, do discrepancies occur. However, those situations are traceable.

Correlation Effects and Activation Energies for Diffusion in Alloys

Abstract The problems involved in calculating correlation factors for diffusion in dilute alloys can be contrasted to those arising in concentrated solid solutions. As one moves from the pure element to the dilute alloy to the concentrated alloy, the calculation becomes progressively more difficult. Because of the complex atom configurations which can occur in concentrated alloys, it usually is not possible to calculate correlation factors in these alloys exactly. Several important simplifications are available in non-dilute random alloys. A large reduction in complexity can be secured by using a random alloy model where each atom is treated as diffusing in a uniform matrix, with the matrix properties being determined by the composition and jump frequencies in the alloy. Resulting equations in this random alloy model can be expressed directly in terms of the experimentally measurable tracer diffusion coefficients with no unknown vacancy jump frequencies appearing. Also these equations have the advantage of being in simple analytic form and not requiring numerical methods to evaluate the correlation factors. These two features make possible the direct expression of the temperature dependence of the correlation factor in terms of the experimental activation energies. Equations are found for ΔH/ΔQ in random binary cubic alloys, where AH is the difference between the activation enthalpies for diffusion of the two species and ΔQ is the difference between the experimentally measured activation energies of the two species. This ratio is never less than unity and can be much larger than unity. Values are plotted for diamond, body-centered cubic and face-centered cubic structures. From the magnitude and composition dependence of ΔH/ΔQ, it is concluded that the temperature dependence of the correlation factor cannot by itself explain the difference between the activation energies measured from tracer diffusion and from internal friction in the non-dilute range

Diffusivity and Isotope-Effect Measurements in Equiatomic Fe-Co

Several radioactive isotopes of Fe and Co were simultaneously diffused into an equiatomic FeCo alloy which exhibits fcc, bcc, and CsCl-type ordered phases with decreasing temperature. Penetration profiles were obtained by standard lathe sectioning and a grinding-sectioning technique described in this paper. From In D-versus-$\frac{1}{T}$ plots, activation energies of 68.5 and 55 kcal and frequency factors of 1.26 and 0.25 ${\mathrm{cm}}^{2}$/sec were obtained for diffusion of ${\mathrm{Fe}}^{59}$ in the fcc and bcc phases, respectively. From similar plots, activation energies of 69.4 and 60.0 kcal and frequency factors of 1.33 and 2.00 ${\mathrm{cm}}^{2}$/sec were obtained for diffusion of ${\mathrm{Co}}^{57}$ in the fcc and bcc phases of the FeCo alloy. The average isotope-effect parameters were 0.66 in the fcc phase and 0.52 in the bcc phase. Manning's theory for concentrated alloys was used to calculate correlation factors for the FeCo alloy. From these calculated values and experimentally measured isotope-effect parameters, $\ensuremath{\Delta}K$ was determined to be slightly larger in the fcc and bcc phases of the FeCo alloy than has been reported in pure Fe. The observed decrease in the isotope-effect parameter with increasing degree of order during the bcc-to-CsCl-type ordering transformation is explained in terms of an increase in atom-jump correlation with the onset of long-range order.

Correlation Factors for Impurity Diffusion. bcc, Diamond, and fcc Structures

A general equation for the impurity correlation factor is derived in terms of effective escape frequencies. This equation applies even when the vacancy-jump frequency for association of a vacancy-impurity complex differs from the frequency far from an impurity. Parameters in this equation are calculated for body-centered cubic, diamond, and face-centered cubic structures. In these calculations, it is assumed that vacancy jumps which do not involve a nearest neighbor of the impurity are unaffected by the impurity but that association and dissociation jumps, which do involve nearest neighbors of the impurity, are affected. Analytical expressions for the correlation factor in terms of vacancy-jump-frequency ratios are obtained. In the bcc and fcc structures, results are given for two cases: (A) where all dissociative jumps are equally likely, and (B) where a vacancy which makes a dissociative jump to a second-nearest-neighbor site is still partially bound to the impurity, but vacancies which make dissociative jumps to other sites are not. In the diamond structure, case A cannot be distinguished from case B. Results for the diamond structure and for case A in the fcc structure differ only slightly from previous more approximate results. A comparison is made between the present random-walk method of calculating correlation factors and the pair-association method.

New Technique for Calculating Correlations for Vacancy Diffusion

A method is described for calculating correlation factors for diffusion of vacancy-impurity pairs. The calculation is shown for the case in which the correlation is neglected unless the vacancy and impurity are nearest neighbors, but the correlations may have much longer ranges. The case of graphite-type structure is considered as an example. The method is applicable to both isotropic and anisotropic diffusion. (T.F.H.)