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.
Chromatographia - The gas chromatographic retention indices of some typicaltrans-diazenes were determined on a methyl silicone capillary column. Thetrans-diazenes are less strongly retained than... 相似文献
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
The transition states of intramolecular 1,4 and 1,5 H-atom transfers, from/to primary (p), secondary (s) or tertiary alkyl (t) and primary (pa), secondary (sa) or tertiary (ta) allyl carbon atoms, have been studied at the level of the semiempirical quantum-chemical method AM1 with the UHF approximation. The activation and reaction enthalpies were calculated and compared with experimental data available in the literature and the calculated data obtained for analogous reactions in alkyl radicals. Correlations were found between the activation enthalpies and the dissociation enthalpies of the bonds broken and formed. 相似文献
The energy of activation of CH
3.
radical rupture from the radical (CH3)2juvyCCH(CH3)2 is 142.2 kJ mol–1; the selfcombination rate constant is kc {(CH3)2juvyCCH(CH3)2}=107.3 dm3 mol–1 s–1.
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
We present a complete systematics (excitation functions and system-size dependences) of global stopping and side flow for heavy ion reactions in the energy range between 0.09A and 1.93A GeV. For the heaviest system, Au+Au, we observe a plateau of maximal stopping extending from about 0.2A to 0.8A GeV with a fast drop on both sides. The degree of stopping, which is shown to remain significantly below the expectations of a full stopping scenario, is found to be highly correlated to the amount of side flow. 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
Experimental results on the pulse compression of 1-nJ, 150-fs pulses from a tunable, 76-MHz Ti:sapphire laser oscillator operating
at around 750 nm are reported. The length of the pulses can be compressed to nearly one tenth by applying a high-delta, single-mode
microstructured optical fiber exhibiting zero group-delay dispersion at 767 nm, and by a prism-pair/chirped-mirror compressor.
The experimental results are verified by theoretical investigations modeling the pulse propagation taking into account non-linear
self-phase modulation and fiber dispersion.
Received: 10 June 2002 / Revised version: 15 November 2002 / Published online: 12 February 2003
RID="*"
ID="*"Corresponding author. Fax: +36-1/375-4553, E-mail: szipoecs@sunserv.kfki.hu 相似文献