Development of a novel approach for the production of dried genomic DNA for use as standards for qualitative PCR testing of food-borne pathogens

As part of a multi-centre European project, FOOD-PCR, the feasibility of a novel approach for production of dried bacterial DNA that could be used as certified reference materials (CRM) was assessed. Selected strains of Salmonella typhimurium, Listeria monocytogenes, Escherichia coli O157, Campylobacter jejuni and Yersinia enterocolitica were used to produce genomic DNA (gDNA). These preparations gave support to method development for qualitative polymerase chain reaction (PCR) detection methods for food-borne pathogens. Purified gDNA was transformed into stable and dry gDNA by using polypropylene vials as carrier and applying a vacuum-drying technique. The gDNA preparations were shown to be sufficiently stable under ambient transport conditions without cooling and proved to have long-term stability at 5°C of at least 22 months. The dried DNA was easily reconstituted by addition of distilled water then gentle shaking. These studies have shown that production of stable and dry bacterial gDNA material is feasible and could help satisfy the increasing need for certified reference DNA positive control samples in the field of PCR testing for detection and verification of food-borne microbial pathogens.     

A class of scaled direct methods for linear systems

A generalization of the class of direct methods for linear systems recently introduced by Abaffy, Broyden and Spedicato is obtained by applying these algorithms to a scaled system. The resulting class contains an essentially free parameter at each step, giving a unified approach to finitely terminating methods for linear systems. Various properties of the generalized class are presented. Particular attention is paid to the subclasses that contain the classic Hestenes-Stiefel method and the Hegedus-Bodocs biorthogonalization methods.This work was partially supported by CNR under contract 85.02648.01.     

On a possibility of analysing the temporal characteristics of short light pulses

The problem of noncollinear second harmonic generation (NSHG) of short, spatially limited light pulses in uni-axial nonlinear crystals has been solved. Based on an analysis of the obtained solution concrete experimental procedures to determine the duration of ultra-short laser pulses are suggested. Expressions for the evaluation of experimental results are given.     

On the Uniform Distribution of Inverses modulo n

In this expository note we use uniform distribution to clarify a result on the difference of an element and its inverse in (Z/nZ)*. We then explain why our remarks apply to some other settings. In doing so we state and prove a couple of folklore theorems on uniform distribution. This revised version was published online in June 2006 with corrections to the Cover Date.     

Tilted-pulse second-harmonic beam analysis for femtosecond to subnanosecond laser pulse-duration measurements

The possibility of extending the second-harmonic beam (SHB) method proposed originally for picosecond and subpicosecond pulse-duration measurements to the femtosecond region is pointed out. This can be achieved by introducing a differential time delay of the pulse wave front corresponding to a tilting of the pulse in the direction other than that applied by Wyatt and Marinero, and also by Saltiel et al., who achieved extensions towards the subnanosecond region. The solution of the wave equations for noncollinear second-harmonic generation in the case of arbitrarily tilted pulses has been carried out. Simple formulae valid from the subnanosecond to the femtosecond region are presented.     

Phase transitions in mesophase macromolecules. I. Novel behavior in the vitrification of poly(ethylene terephthalate-co-p-oxybenzoate)

A 40:60 mole ratio poly(ethylene terephthalate-co-p-oxybenzoate) was studied by dynamic scanning calorimetry. Vitrification occurred in two steps, which could be linked by optical microscopy to a two-phase structure. For the lower glass transition, hysteresis was absent on heating and cooling through the transition temperature. Since all prior studied glasses show such hysteresis, this may be linked to the mesophase structure and raises the question whether mesophases always display such glass-transition behavior.     

On the Number of Sums and Products

A new lower bound on max{|A + A|, |A · A|} is given,where A is a finite set of complex numbers. 2000 MathematicsSubject Classification 11B75 (primary), 52C10 (secondary).     

Sum frequency beam analysis for the determination of the temporal characteristics of ultrashort light pulses

An extension of the single-shot second harmonic beam method proposed earlier for picosecond pulse duration measurements is presented for the case of two incident pulses of differing frequencies, durations and transverse sizes. The solution of the wave equation for noncollinear sum frequency generation in a nonlinear crystal by two Gaussian, spatially limited ultrashort pulses is given. It is shown that the width ( ₁ ² + ₂ ² )^1/2 of the temporal cross-correlation function of the two pulses can be deduced from the spatial energy distribution of the sum frequency beam. The method can be used e.g. in the case of a relatively weak secondary pulse obtained in some nonlinear processes. Preliminary experimental results demonstrating the possibilities offered by the method are presented.     

On the spectrum of the F-centres in the neighbourhood of charged dislocations

Upon deformation of alkali halide crystals an electrical voltage can be observed between suitably placed electrodes due to the movement of charged dislocations. When the specimen is coloured, light induces electrical relaxation, the dislocation photoconduction. We analysed the spectrum of dislocation photoconduction as a spectrum of F-centres situated in the neigh-bourhood of charged dislocations. It is difficult to segregate the two competing effects on the F-spectrum, namely the electric and the strain field of the dislocation, so when we discussed our experimental data we had to assume that the change was caused by either the strain or the electric field. In this paper we discuss this problem theoretically by means of the method of moments. Comparing the expressions of the changes of the first and second moments for the strain field with the analogous ones for the Coulomb field of a charged dislocation jog we see that for every reasonable distance between the dislocation and the F-centre the effect of the strain field is the dominant one. The change of moments can be fitted to experimental data.The authors express their gratitude to I.Tarján and R.Voszka for their interest in this work and I.Gaál for his constructive criticism, he also directed our attention to the dislocation quadrupole field as to a possible third effect.     

Pulsed EPR and DFT characterization of radicals produced by photo-oxidation of zeaxanthin and violaxanthin on silica-alumina

Pulsed electron nuclear double resonance (ENDOR) and two-dimensional (2D)-hyperfine sublevel correlation spectroscopy (HYSCORE) studies in combination with density functional theory (DFT) calculations revealed that photo-oxidation of natural zeaxanthin (ex Lycium halimifolium) and violaxanthin (ex Viola tricolor) on silica-alumina produces the carotenoid radical cations (Car*+) and also the neutral carotenoid radicals (#Car*) as a result of proton loss (indicated by #) from the C4(4') methylene position or one of the methyl groups at position C5(5'), C9(9'), or C13(13'), except for violaxanthin where the epoxide at positions C5(5')-C6(6') raises the energy barrier for proton loss, and the neutral radicals #Car*(4) and #Car*(5) are not observed. DFT calculations predict the largest isotropic beta-methyl proton hyperfine couplings to be 8 to 10 MHz for Car*+, in agreement with previously reported hyperfine couplings for carotenoid pi-conjugated radicals with unpaired spin density delocalized over the whole molecule. Anisotropic alpha-proton hyperfine coupling tensors determined from the HYSCORE analysis were assigned on the basis of DFT calculations with the B3LYP exchange-correlation functional and found to arise not only from the carotenoid radical cation but also from carotenoid neutral radicals, in agreement with the analysis of the pulsed ENDOR data. The formation of the neutral radical of zeaxanthin should provide another effective nonphotochemical quencher of the excited state of chlorophyll for photoprotection in the presence of excess light.