Network formation as a cluster-cluster diffusion-limited aggregation process, 2. Modelling the polyethylene crosslinking process using Monte Carlo and graph techniques

A Monte Carlo simulation of the network formation of polyethylene radicals has been carried out using the reaction modelling scheme and a graph exploration algorithm based on the breadth-first search technique. The results are obtained in a three dimensional cubic continuum space simulation with periodic boundary conditions. Results for three different polyethylene concentrations are reported. The structural evolution of the studied system was followed in terms of: number of reactions, molecular mass, aggregate dimension and fractal dimension analysis.     

Raman Spectroscopy for Intracellular Monitoring of Carotenoid in <Emphasis Type="Italic">Blakeslea trispora</Emphasis>

In the present study, we explore the feasibility of Raman spectroscopy for intracellular monitoring of carotenoid in filamentous fungi Blakeslea trispora. Although carotenoid production from this fungus has been extensively studied through various chromatographic methods and ultraviolet-visible spectroscopy, no intracellular monitoring has been demonstrated until now. The intensity of the Raman spectrum, and more conveniently that of the strongest ν ₁ carotenoid band at ∼1,519 cm⁻¹, exhibits a good linear correlation with the carotenoid content of the sample as determined by high-performance liquid chromatography (HPLC) and ultraviolet-visible (UV-Vis) spectroscopy. Our results suggest that Raman spectroscopy can serve as an alternative method for the study and quantification of carotenoid in batch-mated submerged cultivations of B. trispora and similar organisms. Although not as accurate as HPLC, it allows a rapid sampling and analysis, avoiding the prolonged and tedious classical isolation procedures required for carotenoid determination by HPLC and UV-Vis spectroscopy.     

Development and validation of an HPLC method for the determination of seven penicillin antibiotics in veterinary drugs and bovine blood plasma

Herein a quantitative method for the determination of seven penicillins in bovine plasma and veterinary drugs has been developed. Amoxicillin (AMO), ampicillin (AMP), penicillin G (PENG), penicillin V (PENV), oxacillin (OXA), cloxacillin (CLO) and dicloxacillin (DICLO) were separated on a Perfectsil ODS‐2 (250×4 mm, 5 μm) column, using gradient elution, with a mobile phase of 0.1% v/v TFA and ACN–methanol (90:10 v/v). PDA detection was used at 240 nm. Penicillins were isolated from bovine plasma by SPE on Lichrolut RP‐18 cartridges with mean recoveries from 85.7 to 113.5%. Colchicine (3 ng/μL) was used as an internal standard. The developed method was validated in terms of selectivity, linearity, accuracy, precision, stability and sensitivity. Repeatability (n = 5) and between‐day precision (n = 5) revealed RSD < 12%. The detection limits in the bovine plasma were estimated as 18 ng for AMO and AMP, 25 for PENG, PENV and OXA, 3 ng for CLO and 12 ng for DICLO. Spiked plasma samples were stable for 1 wk, except for AMP and CLO, which were stable for 3 wk and OXA for 4 wk. AMO, PENG and PENV were stable for two freeze–thaw cycles, OXA, CLO and DICLO for four, while AMP only for one.     

Magnetic resonance spectroscopy: a noninvasive diagnosis of gliomatosis cerebri

Gliomatosis cerebri (GC) is characterized by a diffuse infiltration of neoplastic glial cells with preservation of neuronal architecture. It can be very difficult to diagnose during life because the clinical manifestations are protean and tests are often nondiagnostic. The diagnosis of GC needs to be based on radiological, clinical and pathological criteria. We present a patient with GC, which initially presented as acute stroke attack. We discuss the usefulness of noninvasive methods, such a MR spectroscopy, in the diagnosis, grading and management of GC.     

A two-step back–forth algorithm for the solution of the unsteady adjoint equations

A new algorithm for the solution of the unsteady adjoint equations is proposed in this article, aiming at overcoming the excessive computational cost and memory requirements of the conventional adjoint approach for the optimisation of unsteady problems in computational mechanics. The total cost is equal to four times the cost of the unsteady state solution, which is twice the cost of the conventional backward-in-time adjoint calculation but the memory requirements are very small, equivalent to those of a steady-state problem, while stability is acceptable. The proposed algorithm is validated in the case of the 1D unsteady Burgers equation with non-smooth source terms.     

Legendre Pseudospectral Approximation of Boussinesq Systems and Applications to Wave Breaking

In this paper, we propose a spectral projection of a regularized Boussinesq system for wave propagation on the surface of a fluid. The spectral method is based on the use of Legendre polynomials, and is able to handle time-dependent Dirichlet boundary conditions with spectral accuracy.The algorithm is applied to the study of undular bores, and in particular to the onset of wave breaking connected with undular bores. As proposed in [2], an improved version of the breaking criterion recently introduced in [5] is used. This tightened breaking criterion together with a careful choice of the relaxation parameter yields rather accurate predictions of the onset of breaking in the leading wave of an undular bore.     

Imaging and manipulation of biological structures with the AFM

Many biologists have dreamt of physically touching and manipulating the biomolecules they were investigating. With the invention of the atomic force microscope (AFM), this dream has come true. Here, recent applications of the AFM to image and to manipulate biological systems at the nanometer scale are reviewed. Macromolecular biological assemblies as well as individual biomolecules can be subjected to controlled nanomanipulation. Examples of AFM application in imaging and nanomanipulation include the extraction of chromosomal DNA for genetic analysis, the disruption of antibody--antigen bonds, the dissection of biological membranes, the nanodissection of protein complexes, and the controlled modulation of protein conformations. Also reviewed is the novel combination of single molecule imaging and force spectroscopy which allows biomolecules to be imaged, and inter- and intramolecular forces to be measured. Future application of these nanotechniques will reveal new information on the structure, function and assembly of biomolecules.     

Stable-isotope dilution GC-MS method for ethanol in vapour ethanol and microdialysis systems based on carbonate-catalyzed extractive pentafluorobenzoylation

Common ethanol detection methods are not applicable to cell culture media and microdialysates due to interference with medium constituents including amino acids and pH indicators. We present a novel GC-MS method for the accurate and precise analysis of ethanol in cell cultures and microdialysates. The method is based on the carbonate-catalyzed extractive pentafluorobenzoylation of ethanol and deuterium-labelled ethanol serving as the internal standard and on their GC-MS analysis in the electron-capture negative-ion chemical ionization mode. The method was used to optimize experimental conditions in a custom-made ethanol vapour system utilized for studies examining ethanol influences on neuronal cell lines and in microdialysis.