Study of parameters associated with the determination of cadmium in lake sediments by slurry sampling electrothermal atomic absorption spectrometry

Cadmium concentration in lake sediments is determined by suspending the solid samples in a solution containing 5% (v/v) concentrated nitric acid and 0.1% (v/v) Triton X-100. Three modifiers were tested for the direct determination. The furnace temperature programmes and appropriate amount for each modifier were optimised to get the highest signal and the best separation between the atomic and background signals. The drying stage is performed by programming a 400 °C temperature, a ramp time of 25 s and hold time of 10 s on the power supply of the atomiser. No ashing step is used and platform atomisation is carried out at 2200 °C. W–Rh permanent modifier combined with conventional modifier by delivering 10 μl of 0.50% (w/v) NH₄H₂PO₄ solution was the best chemical modifier for cadmium determination. This modifier also acts as a liquid medium for the slurry, thus simplifying the procedure. Calibration is performed using aqueous standards in the 1–5 μg l⁻¹ range. The optimised method gave a limit of detection of 0.56 ng ml⁻¹, characteristic mass of 10.1±0.8 pg for aqueous standard, 9.6±0.7 pg for slurry samples containing different Cd concentrations and good precision (7.6–5.2%). The method was validated by analysing four certified reference lake sediment materials: LKSD-1, LKSD-2, LKSD-3 and LKSD-4; satisfactory recoveries were obtained (90.0–96.3%) and no statistical differences were observed between the experimental and the certified cadmium concentration. The developed methodology was used to determine cadmium in three ‘real’ sediment samples from lakes in the area of Wielkopolski National Park, Poland.     

The raised-cosine wavelets in computerized tomography

In Computerized Tomography (CT), an image must be recovered from its sampled projections in the form of values of the Radon transform. In this work a method of recovering the image is based on the properties of the raised-cosine wavelet. This wavelet has a closed form which allows for certain precomputations and avoids convolution. The rate of convergence of the resulting algorithm to the image density function is found under suitable hypotheses. This algorithm is then tested on the standard Shepp–Logan     

Noether's Theorem on Surfaces

In this article we prove a version of Noether's Theorem (of Calculus of Variations) which is valid for a general regular (compact) surface. As a special feature, the Lie group of transformations is allowed to act on the Cartesian product of the surface and the functional space. Additionally, we apply the Theorem to a problem in Classical Differential Geometry of surfaces. The given application is actually an example showing how Noether's Theorem can be used to construct invariant properties of the solutions to variational problems defined on surfaces, or equivalently, of the solutions to the associated Euler-Lagrange equations resulting from them.     

The U.S. Department of Energy (DOE) Sampling and Analytical Chemistry Guide: Doe Methods for Evaluating Environmental and Waste Management Samples

Abstract

DOE Methods for Evaluating Environmental and Waste Management Samples (DOE Methods) is a guidance/methods document to support sampling and analysis activities at DOE sites. DOE Methods is intended to supplement existing guidance documents (e.g., EPA's Test Methods for Evaluating Solid Waste, SW-846), which generally apply to low-level or nonradioactive samples. DOE Methods targets the complexities of DOE radioactive mixed waste and environmental samples. The document contains quality assurance (QA), quality control (QC), safety, sampling, organic analysis, inorganic analysis, and radioanalytical guidance as well as sampling and analytical methods. An addendum is distributed every six months (April and October) with updated guidance and additional methods.

DOE Methods provides a vehicle for technology transfer within the environmental restoration (ER) and waste management (WM) (collectively known as EM) community. As DOE Methods evolves, its usefulness and applicability are anticipated to grow to meet the demands of the DOE/EM mission. At the present time, DOE Methods contains methods and guidance information supplied by DOE sites. Because the EM activities in DOE are not unique to the United States, the international environmental community could benefit from the information gathered for the DOE program. This information could provide additional resources for their EM activities.     

Unscaled spatial branging process with interaction: macrospic equation and local equilibrium

For some spatial branching processes with interaction considered as measure–valued processes, convergence to solutions of non–linear macroscopic equation and local equilibrium are proved, without scaling but providing each particle with a small mass ε and assuming convergence of the initial distribution when ε goes to 0     

Pressure dependent study of semiconductors using semiempirical equations of state

Abstract

Variation of bulk modulus of Si, Ge and GaAs with pressure is studied using four semiempirical equations of state, two of which being proposed very recently. Hence an expression for bulk modulus for arbitrary pressure for the semiconductors similar to Cohen's formula for zero pressure is arrived at. The applicability of these equations of state for the high pressure phases of Si and Ge is tested using the recent experimental and theoretical pressure-volume data of these phases.     

Variational Operators,Symplectic Operators,and the Cohomology of Scalar Evolution Equations

For a scalar evolution equation u_t = K(t, x, u, u_x, . . . , u_2m+1) with m ≥ 1, the cohomology space H^1,2() is shown to be isomorphic to the space of variational operators and an explicit isomorphism is given. The space of symplectic operators for u_t = K for which the equation is Hamiltonian is also shown to be isomorphic to the space H^1,2() and subsequently can be naturally identified with the space of variational operators. Third order scalar evolution equations admitting a first order symplectic (or variational) operator are characterized. The variational operator (or symplectic) nature of the potential form of a bi-Hamiltonian evolution equation is also presented in order to generate examples of interest.     

Dew Points of Binary Methane + Water: Measurement and Correlation

Experimental measurements of dew points for four methane + water mixtures between 2.6 2 10 5 Pa and 100.4 2 10 5 Pa and the temperature range from 225.5 K to 272.7 K were carried out. The experimental results were analysed in terms of both an equation of state model and an excess function-equation of state method, which reproduced the experimental data within AAD from 1.8 to 3.1 K and from 0.9 to 1.8 K, respectively.