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.
We investigate asymptotic behaviour of solutions of the functional-differentialequation
where f and g arelocally Lipschitz functions, C is a continuous matrix and thesmooth lag function obeys 0 (t) t for t 0. We transformthe equation into a delay equation with an infinity of delaysand use a theorem of Söderlind to derive sufficient conditionsfor stability and for asymptotic stability in the case limt(t) = . The situation is qualitatively different when limt(t) = * < and we outline stability conditions for thatcase by employing direct techniques. 相似文献
Abstract An investigation of the effects of changing the nature of X, nitrogen base (B), and amino substituent (R2N) on the equilibrium 1?2 was carried out. The influence of the above structural changes on the time-averaged coupling constants JAP and JBP, determined at 300 MHz, were used to follow changes in Keq. With constant R2N, small effects from variation of X and B were found. A large range in Keq arose from changes in the steric size of R2N. These results will be related to the question of the ease of chair to twist interconversion of the phosphate ring essential to the biological activities of the naturally occurring diesters, cAMP and cGMP. 相似文献
Let F(n,r,k) denote the maximum possible number of distinctedge-colorings of a simple graph on n vertices with r colorswhich contain no monochromatic copy of Kk. It is shown thatfor every fixed k and all n>n0(k), and , where tk1(n)is the maximum possible number of edges of a graph on n verticeswith no Kk (determined by Turán's theorem). The caser=2 settles an old conjecture of Erds and Rothschild, whichwas also independently raised later by Yuster. On the otherhand, for every fixed r>3 and k>2, the function F(n,r,k)is exponentially bigger than . The proofs are based on Szemerédi's regularity lemmatogether with some additional tools in extremal graph theory,and provide one of the rare examples of a precise result provedby applying this lemma. 相似文献
A new experimental realisation of the travelling-wave amplified spontaneous emission (TWASE) is described utilising a prismatic arrangement to get the pulse front delay in the pump beam. Rhodamine dye solutions were pumped by the amplified 25 ps long 555 nm pulses of a distributed feedback dye laser. The pulse shortening in the TWASE resulted in 12 ps output pulses with 18% energy efficiency. The observed spectrum showed numerous lines, and it contained the amplified Raman line of the pump beam. Several spots were found in the far-field zone of the generated TWASE. 相似文献
The frequency dependence of the group delay of both a pulse stretcher and a stretcher–compressor system of a chirped pulse amplification laser is determined with a two-dimensional extension of a spectral interferometric method called the stationary phase point method. The 800-nm, 15-fs probe pulse from a Ti:S oscillator propagates through the stretcher or the stretcher–compressor system. The reference pulse is one of the subsequent oscillator pulses but passes the system and interferes with the probe pulse; hence, a Mach–Zehnder-type interferometer is formed. The shape of the spectrally resolved interference fringes is peculiar to the amount and sign of the relative dispersion properties of the pulses. Group-delay dispersion is obtained from the observation of the position of the stationary phase point in spectrally resolved interferograms at different time delays. This simple method allows for an almost complete and fast alignment of the stretcher–compressor system from scratch until the final adjustments. PACS 42.65.Re 相似文献
We prove Pach-Sharir type incidence theorems for a class of curves in Rn and surfaces in R3, which we call pseudoflats}. In particular, our results apply to a
wide class of generic irreducible real algebraic sets of bounded degree. 相似文献
A rate-equation model for describing the travelling-wave amplified spontaneous emission pulses (TWASE) in a transversally excited travelling wave arrangement is given. 6.35 ps long ASE pulses have been obtained by 12 ps long pump pulses. The effect of pump intensity, pump-pulse duration, molecular parameters of the dyes and pump-sweep velocity on the ASE pulses is studied. 相似文献