Preparation and examination of multilayer graphene nanosheets by exfoliation of graphite in high efficient attritor mill

Graphene multilayers have been prepared by mechanical method based on milling graphite in high efficient attritor mill. The results showed that the best dispersion media is ethanol, and 10 hours of intensive milling proved to be the most efficient way to separate the graphite layers as it was shown by scanning electron microscopy and X-ray diffraction measurements.      

Range Counting over Multidimensional Data Streams

We consider the problem of approximate range counting over a stream of d-dimensional points. In the data stream model the algorithm makes a single scan of the data, which is presented in an arbitrary order, and computes a compact summary data structure. The summary, whose size depends on the approximation parameter ε, can be used to count the number of points inside a query range within additive error εn, where n is the size of the stream seen so far. We present several results, deterministic and randomized, for both rectangle and halfspace ranges.     

Rapid methods for the determination of long-lived radionuclides in environmental samples by ICP-SFMS and radioanalytical techniques

Two improved sample preparation methods for the determination of americium and plutonium (Method 1) and plutonium (Method 2) from environmental samples by inductively coupled plasma sector field mass spectrometry (ICP-SFMS) and alpha spectrometry are presented. Both procedures involve a rapid CaF₂ co-precipitation step for pre-concentration and matrix removal followed by extraction chromatographic separations. The average recovery after sample preparation was better than 85 % for both americium and plutonium. The method developed also focused on the elimination of possible interferences in the mass spectrometric analysis caused by molecular ions (e.g. ²⁰⁸Pb¹⁶O ₂ ⁺ or ²³⁸U¹H⁺) by employing suitable matrix separation prior to ICP-SFMS analysis of the desolvated sample. Isotopes with alpha energies similar to the analytes that may cause interferences in alpha spectrometric analysis were also separated. For ²³⁹Pu, ²⁴⁰Pu, ²⁴¹Pu and ²⁴¹Am detection limits of 15, 9.2, 14 and 23 fg g⁻¹, respectively were achieved by ICP-SFMS, and 0.1 mBq obtained by alpha spectrometry. The methods developed are especially applicable for monitoring purposes of anthropogenic transuranium elements, as the analysis (sample preparation and ICP-SFMS measurement) can be carried out within 6 hours for one batch of samples.     

A study of a polysulfone membrane for use in an in-situ tunable microdialysis probe during monitoring of starch enzymatic hydrolysates

We report a study made on a 5 kDa molecular weight cut-off (MWCO) polysulfone membrane (SPS 4005) for use in microdialysis sampling of starch enzymatic hydrolysates on-line coupled to column liquid chromatography with integrated pulsed electrochemical detection. Membrane characteristics were evaluated by examining both the membrane and membrane support layer using a scanning electron microscope (SEM). This study was made so as to elucidate the mechanism or mode by which a membrane exposed to different bioprocess conditions is either fouled or destroyed. The correlation of extraction fraction data with SEM was a confirmatory test for the observed change in the membrane characteristics. Examinations were made after keeping the membrane in pure water for 5, 10 and 30 min at room temperature or after perfusing the membrane with pure water continuously at room temperature, 60 and 90°C for 24 h. Extraction fractions were evaluated at these temperatures to see applicability of the SPS 4005 membrane to high temperature bioprocesses. Scanning electron microscopy studies were also made on membranes used for sampling and sample clean-up during on-line monitoring of the hydrolysis of soluble starch (according to Zulkowsky) for 32 h, and the hydrolysis of wheat starch at room temperature, 60 and 90°C for 6 h. Non-specific/directed protein-membrane interactions were evaluated by sampling maltoheptaose with a microdialysis probe fitted with a 10 mm SPS 4005 membrane, before and after treatment with an enzyme solution of Termamyl (endo-1,4-- -glucan glucanohydrolase EC 3.2.1.78).     

MinimalG-functions. II

The concept of aG-function, introduced by Nowosad and Hoffman, gives an appropriate setting for many generalizations of the Gerschgorin Circle Theorem. In this paper, we extend our previous results for minimalG-functions to the partitioned matrix case.     

A note on the structure of pairwise balanced designs

We show that if a pairwise balanced design with λ = 1 has ν objects and block sizes between 2 and ν − 2, and it is not a symmetric balanced design, then each of its largest blocks has a nonempty intersection with at least ν other blocks