Effect of Ti pretreatment on photoelectric properties of TiO2 layers prepared by plasma-anodic oxidation

Photoactive TiO₂ layers were formed by anodic oxidation of Ti in O₂ RF plasma under various conditions and Ti surface pretreatment. The photocurrent spectrum in 1M NaOH was used to calculate the quantum efficiency of the photocurrent production and the band-gap energy for indirect transitions. Photoelectrochemical properties of TiO₂ layers were studied on the decomposition of p-cresol water solution. The method of Ti surface pretreatment (mechanical polishing or chemical etching) has a decisive influence on the photoelectrochemical properties and the structure of the polycrystalline oxide, rutile, anatase or amorphous phase content.This study was supported by the Grant Agency for Sciences of Slovakia.     

A fast algorithm for repeated computation of linear recurrence relations

Let the calculation of thenth term of a general recurrence relation requireO(q(n)) arithmetical operations. The derivation is given of a new algorithm that performsm repetitions of this calculation with different initial conditions requiring onlyO(q(n)) +O(m) operations. The application of this algorithm to accelerate the calculation of continued fractions and the solution of three- and five-diagonal systems of linear equations, is also described.     

Effect of immobilizing adsorption on mass transport through polymer films

The Freundlich isotherm used in place of the Langmuir isotherm to describe the adsorption mode in the dual sorption theory of glassy polymer—gas systems. Time-lag expressions have been derived and compared with the available corresponding results for the Langmuir case. In the case of large and moderate values of the upstream boundary activity a₀, the value of the time-lag function L^a)(l) calculated with the proposed model is close to that calculated by Paul for the Langmuir isotherm. In the case of small values of a₀, the L^a(l) values predicted by Paul and the proposed model are different and the difference increases when the value of a₀ decreases. The ability of the present model to represent systems exhibiting positive deviations from Henry's law is also described.     

Einsatz von rechenanlagen in der emissions-spektrochemie : II Teil. Aufstellung,Bewertung und Linearisierung der analytischen Eichgeraden

The Use of Computers in Emission Spectroscopy. Part 2. Establishment, Evaluation and Linearization of Analytical Calibration CurvesThe problems of establishing optimum linear calibration plots for atomic emission spectrometry are described, particularly when photographic recording techniques are employed. The calculation procedure, based on the least-squares method, generates additional statistical values which permit linearity to be checked. As the desired linearity is not always achieved at the first attempt, the process is repeated after exclusion of unreliable input data.     

Infinite families of crossing-critical graphs with a given crossing number

A graph is crossing-critical if deleting any edge decreases its crossing number on the plane. It is proved that, for any n ? 3, there is an infinite family of 3-connected crossing-critical graphs with crossing number n.     

Triangle group representations and constructions of regular maps

A regular map of type {m,n} is a 2-cell embedding of a graphin an orientable surface, with the property that for any twodirected edges e and e' there exists an orientation-preservingautomorphism of the embedding that takes e onto e', and in whichthe face length and the vertex valence are m and n, respectively.Such maps are known to be in a one-to-one correspondence withtorsion-free normal subgroups of the triangle groups T(2,m,n).We first show that some of the known existence results aboutregular maps follow from residual finiteness of triangle groups.With the help of representations of triangle groups in speciallinear groups over algebraic extensions of Z we then constructivelydescribe homomorphisms from T(2,m,n)=y,z|y^m=zⁿ=(yz)²=1 intofinite groups of order at most c^r where c=c(m,n), such thatno non-identity word of length at most r in x,y is mapped ontothe identity. As an application, for any hyperbolic pair {m,n}and any r we construct a finite regular map of type {m,n} ofsize at most C^r, such that every non-contractible closed curveon the supporting surface of the map intersects the embeddedgraph in more than r points. We also show that this result isthe best possible up to determining C=C(m,n). For r>m thegraphs of the above regular maps are arc-transitive, of valencen, and of girth m; moreover, if each prime divisor of m is largerthan 2n then these graphs are non-Cayley. 2000 Mathematics SubjectClassification: 05C10, 05C25, 20F99, 20H25.     

Liquid chromatographic determination of tylosin in mastitic cow's milk following therapy

Liquid chromatographic analysis of milk samples from 6 cows treated with tylosin in a veterinary practice indicated that tylosin persisted in milk for more than 3 days after the final treatment. The concentration of tylosin was not below the stated maximum residue limit (0.05 mg/kg). The milk from 3 cows being treated for mastitis catarrhalis chronica contained tylosin residues for 3.5 days after the last withdrawal time (72 h). No residue was detected in the milk of any animal 6 days after cessation of therapy.