Structural distortion,charge modulation and local anisotropies in magnetite below the Verwey transition using resonant X‐ray scattering

The pattern of charge modulations and local anisotropies below the Verwey transition has been determined and quantified in high‐quality Fe₃O₄ single crystals and thin films grown on MgO by using resonant X‐ray scattering at the Fe K‐edge. The energy, polarization and azimuthal angle dependencies of an extensive set of reflections with potential sensitivity to charge or local anisotropy orderings have been analyzed to explore their origins. A charge disproportion on octahedral B sites of 0.20 ± 0.05 e^? with [0 0 1] and cubic periodicities has been confirmed, while no significant charge disproportion has been obtained with [0 0 1/2] cubic periodicity. Additional charge modulations in the monoclinic a–b plane are also present. In addition, the occurrence of new forbidden (1, 1, 0) and (0, 0, 2n + 1/2) cubic reflections that arise from the anisotropy of the local structure around different tetrahedral and octahedral Fe atoms is shown. This complex pattern of weak charge modulations and local anisotropies is fully compatible with the low‐temperature crystal structure refined in the non‐polar C2/c space group and disproves any bimodal charge disproportion of the octahedral Fe atoms.     

Growth of Sr2CrReO6 epitaxial thin films by pulsed laser deposition

We report the growth, structural, magnetic, and electrical transport properties of epitaxial Sr₂CrReO₆ thin films. We have succeeded in depositing films with a high crystallinity and a relatively large cationic order in a narrow window of growth parameters. The epitaxy relationship is Sr₂CrReO₆ (SCRO) (0 0 1) [1 0 0]∥SrTiO₃ (STO) (0 0 1) [1 1 0] as determined by high-resolution X-ray diffraction and scanning transmission electron microscopy (STEM). Typical values of saturation magnetization of M_S (300 K)=1 μ_B/f.u. and ρ (300 K)=2.8 mΩ cm have been obtained in good agreement with previous published results in sputtered epitaxial thin films. We estimate that the antisite defects concentration in our thin films is of the order of 14%, and the measured Curie temperature is T_C=481(2) K. We believe these materials be of interest as electrodes in spintronic devices.     

Accreditation of sampling activities

Since the introduction of ISO/IEC 17025 it is a requirement for all accredited laboratories to include sampling in their quality statements. It is well understood that sampling and handling of the sample are key factors in the validity of a result. The fact that many laboratories worldwide are not involved in sampling poses a challenge to accreditors liability. This article describes the Israel Laboratory Accreditation Authoritys (ISRAC) and other accreditors approaches to sampling.Presented at the Second International Conference on Metrology—Trends and Applications in Calibration and Testing Laboratories, 4–6 November 2003, Eilat, Israel.     

Proficiency testing as a tool for assessing the medical and economic impact of laboratory results: The blood coagulation case

An international commercial proficiency testing scheme was used to evaluate the impact of laboratory results on clinical decisions. The affect on atrial fibrillation was chosen as a model with 16 Israeli laboratories participating in an international study. A Markov model was constructed to evaluate the impact of any inaccurate results on the clinical outcomes. From the proficiency test study and the Markov model, 13–21% of the results were inaccurate and would have yielded erroneous medical decisions.     

A method for quick, low-cost automated confluency measurements

A culture's confluency is a fundamental measure in the field of biology, and routine quantification of confluence in cell culture protocols, biological assays and tissue engineering work is important. However, current techniques for obtaining confluency are either subjective, destructive, not simple enough, or time-consuming. We developed an image processing method for automated confluency measurement from a single microscope image without any chemical staining. To demonstrate utility we monitored the confluency of three cell types: NIH3T3 fibroblasts, C2C12 myoblasts, and 3T3L1 pre-adipocytes for 5 days, twice a day. The captured micrographs had different and uneven illumination, the cell types varied in cell-to-background contrast, and the confluency ranged between 10% and 100%. Despite these variable conditions, our method was shown to be practical, economic, and easy to implement, providing quantitative confluency measurements over time in each culture case. The method is hence suitable for routine automatic determination of confluency to standardize handling of cells, achieve reproducibility across trials, and improve accuracy in experimental outcome measures.     

Gaussian Closure of One-Dimensional Unsaturated Flow in Randomly Heterogeneous Soils

We propose a new method for the solution of stochastic unsaturated flow problems in randomly heterogeneous soils which avoids linearizing the governing flow equations or the soil constitutive relations, and places no theoretical limit on the variance of constitutive parameters. The proposed method applies to a broad class of soils with flow properties that scale according to a linearly separable model provided the dimensionless pressure head has a near-Gaussian distribution. Upon treating as a multivariate Gaussian function, we obtain a closed system of coupled nonlinear differential equations for the first and second moments of pressure head. We apply this Gaussian closure to steady-state unsaturated flow through a randomly stratified soil with hydraulic conductivity that varies exponentially with where =(1/) is dimensional pressure head and is a random field with given statistical properties. In one-dimensional media, we obtain good agreement between Gaussian closure and Monte Carlo results for the mean and variance of over a wide range of parameters provided that the spatial variability of is small. We then provide an outline of how the technique can be extended to two- and three-dimensional flow domains. Our solution provides considerable insight into the analytical behavior of the stochastic flow problem.     

Development of an immunoassay and a sol-gel-based immunoaffinity cleanup method for coplanar polychlorinated biphenyls from soil and sediment samples

Two polychlorinated biphenyls (PCB) enzyme linked immunosorbent assays (ELISAs) were developed using goat PCB purified immunoglobulin (IgG) antibodies (Abs). The IgGs exhibited the highest affinity toward PCB-77 (24 ng mL⁻¹) with sensitivities in the range of 6-11 ng mL⁻¹. The Abs cross-reacted with PCB-126 and the heptachlorodibenzofuran 1,2,3,4,6,7,8-HpCDF but not with PCB-169, PCB-118, Aroclor 1232, 1248, 1260 or the hexachlorodibenzofuran 2,3,4,6,7,8-HxCDF. The IgGs were also used to develop a sol-gel-based immunoaffinity purification (IAP) method for cleanup of PCB-126. Recovery efficiencies depended on the sol-gel formats; a 1:12 format resulted in the highest binding capacity. Net binding capacity ranged from 112 to 257 ng, and 90% of the analyte could be eluted with only 2 mL of ethanol. The method was also very efficient in purifying PCB-126 from spiked soil and sediment samples from contaminated sites; and eliminating matrix interferences to a degree that enabled analysis of the purified samples by ELISA. The approaches developed in the course of the study form a basis for the development of additional IAP methods for other PCBs, and their implementation in high-throughput screening programs for PCB in food, soil, and other environmental and biological samples.     

Influence of buffer quality on pH measurement uncertainty: prediction and experimental evaluation

Dependence of the uncertainty of a pH measurement result on the quality of buffers (i.e. the uncertainty of their certified pH values) at different levels of instrumental uncertainty (pH-meter, etc.) was simulated using the Monte Carlo method and regression analysis. The contribution of the instrumental standard uncertainty (in the studied range from 0.1 to 1 mV) to the uncertainty of the pH measurement result is negligible, if the standard uncertainties of the pH buffers exceed 0.04 pH (e. g. for in-house buffers). It is shown how the choice of pH-meter and buffers should be correlated in order to meet the required uncertainty of a pH measurement result in a sample under analysis. The results of the simulation were compared with experimental data obtained from calibrations of a pH/ion-meter with a hydrogen working electrode (Radiometer PHM-240) and with a glass electrode (Metrohm 744). Buffers of different quality (National Institute for Standards and Technology standard reference materials, certified Radiometer buffers and Merck CertiPUR buffers) were used for the calibrations. The uncertainties of the experimental results are close to the predicted ones obtained by the simulation. Received: 16 June 2002 Accepted: 19 July 2002 Presented at the 14^th International Conference of the Israel Society for Quality, 18–21 November 2002, Jerusalem, Israel Correspondence to I. Kuselman     

Current best practice for traceability in testing laboratories,when certified reference materials are unavailable

Since the implementation of ISO/IEC 17025 in 2002, all accredited laboratories (at the least) need to establish traceability in all their tests and calibration methods. Traceabilty, though well understood in the calibration field (through an unbroken chain of comparisons to the International System of Units —SI), is less straight forward and not so well understood in the testing laboratories. Traceability in analytical and biological testing is found through the use of reference materials, and the validated steps of a test method. This article describes the possibilities to comply with the traceability requirement of ISO/IEC 17025 in testing laboratories , when certified reference materials are unavailable.Presented at the Second International Conference on Metrology—Trends and Applications in Calibration and Testing Laboratories, 4–6 November, 2003, Eilat, Israel     

Gaussian Closure of Transient Unsaturated Flow in Random Soils

The Gaussian closure approximation, previously used by the authors to solve steady state stochastic unsaturated flow problems in randomly heterogeneous soils, is extended here to transient flow. The method avoids linearizing the governing flow equations or the soil constitutive relations. It places no theoretical limit on the variance of constitutive parameters and applies to a broad class of soils with flow properties that scale according to a linearly separable model. Closure is obtained by treating the dimensionless pressure head as a multivariate Gaussian function. It yields a system of coupled nonlinear differential equations for the first and second moments of . We apply the Gaussian closure technique to the problem of transient infiltration into a randomly stratified soil. In each layer, hydraulic conductivity and water content vary exponentially with . Elsewhere we show that application of the technique to other constitutive relations is straightforward. Our solution for the mean and variance of in a one-dimensional layer with random conductivity compares well with Monte Carlo results over a wide range of parameters, provided that the spatial variability of the constitutive exponent is small. The solution provides considerable insight into the behavior of the transient unsaturated stochastic flow problem.