Bienzymatic Spectrophotometric Method for Uric Acid Estimation in Human Serum and Urine

Journal of Analytical Chemistry - In this study, a novel and efficient bienzymatic method for the quantification of uric acid in serum and urine samples was developed. This method is based on the...     

Size characterization by Sedimentation Field Flow Fractionation of silica particles used as food additives

Four types of SiO₂, available on the market as additives in food and personal care products, were size characterized using Sedimentation Field Flow Fractionation (SdFFF), SEM, TEM and Photon Correlation Spectroscopy (PCS). The synergic use of the different analytical techniques made it possible, for some samples, to confirm the presence of primary nanoparticles (10 nm) organized in clusters or aggregates of different dimension and, for others, to discover that the available information is incomplete, particularly that regarding the presence of small particles. A protocol to extract the silica particles from a simple food matrix was set up, enriching (0.25%, w w⁻¹) a nearly silica-free instant barley coffee powder with a known SiO₂ sample. The SdFFF technique, in conjunction with SEM observations, made it possible to identify the added SiO₂ particles and verify the new particle size distribution. The SiO₂ content of different powdered foodstuffs was determined by graphite furnace atomic absorption spectroscopy (GFAAS); the concentrations ranged between 0.006 and 0.35% (w w⁻¹). The protocol to isolate the silica particles was so applied to the most SiO₂-rich commercial products and the derived suspensions were separated by SdFFF; SEM and TEM observations supported the size analyses while GFAAS determinations on collected fractions permitted element identification.     

Minkowski Geometric Algebra of Complex Sets

A geometric algebra of point sets in the complex plane is proposed, based on two fundamental operations: Minkowski sums and products. Although the (vector) Minkowski sum is widely known, the Minkowski product of two-dimensional sets (induced by the multiplication rule for complex numbers) has not previously attracted much attention. Many interesting applications, interpretations, and connections arise from the geometric algebra based on these operations. Minkowski products with lines and circles are intimately related to problems of wavefront reflection or refraction in geometrical optics. The Minkowski algebra is also the natural extension, to complex numbers, of interval-arithmetic methods for monitoring propagation of errors or uncertainties in real-number computations. The Minkowski sums and products offer basic 'shape operators' for applications such as computer-aided design and mathematical morphology, and may also prove useful in other contexts where complex variables play a fundamental role – Fourier analysis, conformal mapping, stability of control systems, etc.     

Algorithms for Minkowski products and implicitly‐defined complex sets

Minkowski geometric algebra is concerned with the complex sets populated by the sums and products of all pairs of complex numbers selected from given complex‐set operands. Whereas Minkowski sums (under vector addition in Rⁿ have been extensively studied, from both the theoretical and computational perspective, Minkowski products in R² (induced by the multiplication of complex numbers) have remained relatively unexplored. The complex logarithm reveals a close relation between Minkowski sums and products, thereby allowing algorithms for the latter to be derived through natural adaptations of those for the former. A novel concept, the logarithmic Gauss maps of plane curves, plays a key role in this process, furnishing geometrical insights that parallel those associated with the “ordinary” Gauss map. As a natural generalization of Minkowski sums and products, the computation of “implicitly‐defined” complex sets (populated by general functions of values drawn from given sets) is also considered. By interpreting them as one‐parameter families of curves, whose envelopes contain the set boundaries, algorithms for evaluating such sets are sketched. This revised version was published online in June 2006 with corrections to the Cover Date.     

Kinematic Generation of Ruled Surfaces

This paper presents a method for kinematic generation of free-form ruled surfaces. The method is based on the kinematic displacement of lines. The ruled surfaces are represented as curves on a dual unit sphere. The curves are created by using the Lie Group structure of the dual space to generate dual displacement matrices for the lines. Free-form surfaces are created by repeated geodesic interpolation using the displacement matrices. An application for these surfaces is presented in five-axis cylindrical milling.     

Theoretische und experimentelle Untersuchungen über Reaktivitätsänderungen eines Reaktors,verursacht durch Xenonvergiftung

Summary Operation of a nuclear reactor leads to the formation of the poisoning fission product xenon. The time dependent equations for the concentration of this gas are well known for each point in the reactor.The calculation of the reactivity amount invested in the poison involves the formation of an average to be calculated for the whole reactor, depending on a space- and generally also a time-dependent flux distribution. We have tried to transform the relevant integrals into a form applicable for reactor operation. It is shown that the poisoning during the build-up of xenon can be expressed by an effective neutron flux. Contrary to this, the behavior of the reactivity after shut-down must be described by more than one effective parameter. Methods for the calculation of these parameters and their dependence on reactor geometry and power level are given. Finally numerical values for the research reactor DIORIT are evaluated and compared with the measured reactivity of the system. The agreement between experiment and theory is excellent, deviations being within the range of the experimental error. It is suggested to use the uniform xenon poison as a means to calibrate the total amount of reactivity of regulating devices.