Polymerization mechanisms and molecular weight distribution. I. Mathematical treatment

A novel method for determining the polymerization mechanism and the kinetic rate constants from the molecular weight distribution is proposed. The particular criterion function used as basis for parameter adjustment is where θ is the vector of dependent variables, y(r, θ) is the theoretical molecular weight distribution for the assumed polymerization mechanism, and y_E(r) is the experimental molecular weight distribution which is a function of the chain length r. A form of the gradient method of optimization was used to solve the criterion function. The proposed method is particularly powerful since the whole molecular weight distribution is utilized.     

Evaluating the impact of extraction and cleanup parameters on the yield of total petroleum hydrocarbons in soil

Interlaboratory comparisons for the analysis of mineral oil in polluted soil using the GC–FID method indicate that extraction and cleanup conditions have significant effects on the analytical results. In this investigation a ruggedness test was performed on the extraction and cleanup method for the determination of total petroleum hydrocarbons in soil. A two-level Plackett–Burman design was utilized to study the effect of 11 different method parameters on the extraction recovery of total petroleum hydrocarbons (TPH) in soil. Both qualitative and quantitative factors were investigated. The results indicate that total petroleum hydrocarbons can be relatively reliably monitored through strict implementation of the ISO and CEN draft standards. However, variation in certain method parameters readily affects the validity of the results. The most critical factors affecting TPH recovery were the solvent and co-solvent used for extraction, the extraction time, adsorbent and its weight and sample TPH concentration. Because adaptation of the draft standards especially with respect to these factors easily leads to TPH recoveries higher than 200% or lower than 70%, the validity of the adapted method should always be verified. A proper estimate of the expanded uncertainty should also be appended to TPH results, because only then can the reliability of the results be guaranteed and further justification is gained to support the end-use of the data. This also supports the credibility of the analytical services and prevents the data end-users from drawing misleading conclusions concerning the environmental risks and potential remediation requirements.     

Lower bounds for the largest eigenvalue of the gcd matrix on {1, 2,..., n}

Consider the n×n matrix with (i, j)’th entry gcd (i, j). Its largest eigenvalue λ_n and sum of entries s_n satisfy λ_n > s_n/n. Because s_n cannot be expressed algebraically as a function of n, we underestimate it in several ways. In examples, we compare the bounds so obtained with one another and with a bound from S.Hong, R.Loewy (2004). We also conjecture that λ_n > 6π^?2nlogn for all n. If n is large enough, this follows from F.Balatoni (1969).     

Structure of anionic phospholipid coatings on silica by dissipative quartz crystal microbalance

The adsorption of anionic phospholipids on silica was investigated by the dissipative quartz crystal microbalance (QCM) technique. Liposomes composed of 1 mM 80:20 mol % of 1-palmitoyl-2-oleyl-sn-glycero-3-phosphatidylcholine (POPC)/phosphatidic acid, POPC/phosphatidylglycerol, or POPC/phosphatidylserine in N-(2-hydroxyethyl)piperazine-N'-(2-ethanesulfonic acid) buffer at pH 7.4 (with or without 3 mM of CaCl2) were examined. We have previously demonstrated that similar phospholipid coatings can be used in capillary electrochromatography as a stationary phase for the separation of analytes. In this work, we focus on the formation of the coatings and on the type of lipid structure formed on silica. The QCM investigation comprised qualitative results based on changes in frequency and resistance, and quantitative modeling of the obtained results. The latter was performed using the dissipative QCM, which measures the quartz crystal impedance, combined with equivalent circuit analysis. A previously developed coating and cleaning procedure for phospholipid-coated fused silica capillaries was adopted in this study, and the same silica-coated crystal was used throughout the QCM study. We will demonstrate in this work that the type of lipid structure formed on silica, that is, a rather rigid supported lipid bilayer or a viscoelastic supported vesicle layer (SVL), is highly dependent on the lipid and solvent composition. We also show for the first time that the modeling of the dissipative QCM data can be used to extract a more quantitative picture of an adsorbed SVL, because, so far, published studies have merely used the QCM data in a qualitative sense.     

Determination of selenium in small volumes of blood plasma and serum by electrothermal atomic absorption spectrometry

A graphite-furnace atomic absorption spectrometric method is described for the determination of selenium in blood plasma and serum. Samples are diluted (1 + 9) with a solution containing nickel and nitric acid and measured by a standard additions method. Repeatability for a serum sample containing 87 μg Se l^-1 was 4.4%. The mean recovery of selenium(IV) from a human protein solution was 97.5%. The method was further tested in an interlaboratory comparison study. The standard additions procedure requires a sample volume of 200 μl and a total time of about 7.5 min. A secondary calibration graph can be used, however, resulting in increased throughput up to 13 samples per hour, and a decrease in the sample volume needed to 100 μl.     

Dual-capillary electroencapsulation of mesoporous silicon drug carrier particles for controlled oral drug delivery

The feasibility of electroencapsulation of mesoporous silicon (PSi) micro- and nanoparticles as a method to seal the PSi particles in mechanically processable solid units, and to facilitate time and site specific drug release from the pores of PSi particles, is of interest in the present work. Suitable microcapsules and micromatrix particles were produced in a single-step process using a setup with two electrospraying nozzles kept at high electric potentials of opposite polarities. The structures of the produced particles were analyzed by microscope and X-ray micro- and nanotomography imaging, and optimization of the electroencapsulation process production efficiency is discussed.     

Two inequalities for the sum of elements of a matrix

The inequalities su A^t su A^m ≥ su A^p su A^q and A^t+ su A^m≥ su A^p+ su A^q are studied and generalized. Here su A denotes the sum of elements of the square matrix A.     

Uncle-attributed grammars

Evaluation of inherited attributes is a problem in conjunction with LR parsing, because the derivation tree is incomplete during parsing. An evaluation scheme for inherited attributes is presented based on a restricted grammar class, uncle-attributed grammars. A transformation to the uncle-attributed form is described for L-attributed grammars.     

Preparation, thermal stability and luminescence properties of selected rare earth oxycarbonates

A comparative TG and DTG study of the preparation and thermal stability of selected rare earth oxycarbonates, (REO)₂CO₃ (RE = La and Gd), shows that the ease of formation as well as the stability of these compounds decreases strongly with increasing atomic number of the host cation. According to X-ray powder diffraction analyses, the RE oxycarbonates obtained as decomposition products of acetate and carbonate hydrates belong to the tetragonal IA-type. UV- and dye laser-excited luminescence studies of Eu³⁺-doped (LaO)₂CO₃ and (GdO)₂CO₃ reveal the presence of two different sites for the host cation. One of the sites resembles closely that prevailing in the tetragonal RE oxysalts, i.e. oxyhalides, oxysulphates, oxymolybdates and oxynitrates. A crystal field analysis carried out on the ⁷F₁ and ⁷F₂ level schemes according to a C_2v site symmetry confirms this hypothesis.