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1.
Andreja Rajkovic Nada Smigic Mieke Uyttendaele Helga Medic Lieven de Zutter Frank Devlieghere 《Food microbiology》2009,26(8):889-895
While maintaining nutritional and sensorial attributes of fresh foods mild processing technologies generally deliver microbiologically perishable food products. Currently little information exists on possible increase in the resistance of pathogens after repetitive exposure to mild (sub-lethal) treatments. Multiple strain-cocktails of Listeria monocytogenes, Escherichia coli O157:H7 and Campylobacter jejuni were exposed to 20 consecutive cycles of sub-lethal inactivation by three different techniques. Used techniques comprised inactivation with lactic acid (LA), chlorine dioxide (ClO2) and intense light pulses (ILP). Results showed that the selection of resistant cells was both species and technique dependent. While repetitive cycles of ClO2 treatment did not result in increased resistance, repetitive inactivation with LA yielded L. monocytogenes culture of higher resistance in comparison to the parental culture. The increased resistance, expressed as decreased level of reduction in bacterial counts in subsequent inactivation cycles, was also observed with ILP for both L. monocytogenes and E. coli O157:H7 strains. Visual trend observations were confirmed through statistical linear regression analysis. No such effects were noted for C. jejuni which became undetectable after first 2–5 cycles. Current findings indicate the ability of foodborne pathogens to adapt to mild bactericidal treatments creating new challenges in risk assessment and more specifically in hazard analysis. 相似文献
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Rijpens N Herman L Vereecken F Jannes G De Smedt J De Zutter L 《International journal of food microbiology》1999,46(1):37-44
The rapid detection of an average of 5.9 stressed Salmonella cells in 25 g of food product using immunomagnetic separation (IMS) and PCR is described. For pasteurised egg yolk, egg yolk powder, ice-cream, whole egg, egg white and cheeses made from pasteurised milk PCR was applied after 16 h of preenrichment in buffered peptone water (BPW) using IMS and alkaline lysis as sample preparation method. For whole egg and egg white the BPW was supplemented with iron. For milk powder, and raw milk cheeses, the 16-h preenrichment in BPW was followed by IMS and a 4-h enrichment in Rappaport-Vassiliadis broth. In the latter case, PCR was applied on the enrichment medium after centrifugation and alkaline lysis. For PCR the primers ST11 and ST15 (Aabo et al., 1993) producing a fragment of 429 bp were used. An internal PCR control, designed to be co-amplified with the target DNA using the same primers but producing a smaller fragment of 240 bp, was used. 相似文献
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Luc Knockaert Hendrik Rogier Daniël De Zutter 《AEUE-International Journal of Electronics and Communications》2005,59(4):1802
We propose to find the propagation constants of modes in layered media by means of signal identification methods. To this effect we employ Cauchy's theorem, conformal mapping and Fast Fourier Transform (FFT) techniques to generate relevant Hankel moments, afterwards to be processed with selected signal identification algorithms. The method, terminated by a few Newton steps, provides a batch of highly accurate roots in appropriate disks or half-disks. 相似文献
6.
Sara Van den Bulcke Ann Franchois Daniel De Zutter 《Journal of Infrared, Millimeter and Terahertz Waves》2010,31(12):1478-1490
In this contribution, the authors provide a proof of principle for quantitative imaging of concealed objects on the human body using millimeter waves. A two-and-a-half-dimensional (2.5D) quantitative millimeter
wave imaging algorithm is applied to reconstruct a hidden dielectric object on a clothed simplified human body model. At millimeter
wave frequencies, the incident field is typically a fully three-dimensional (3D) Gaussian beam, illuminating only a limited
spot on the body. Due to the large dimensions of the human body in terms of wavelengths, a 3D discretization is hardly feasible.
Therefore, it is assumed that the electromagnetic properties of the body do not significantly change within the illuminated
spot, along the longitudinal direction of a person. Hence, only the cross-section of a human body model is discretized. This
2.5D assumption however is still not sufficient to reduce the forward problem to a feasible size. Therefore, a priori knowledge
on the illumination and on the scattering properties of the clothed human body is used to deduce a simplified model to describe
the cross-section of the clothed human abdomen. The complex permittivity profile of a small dielectric object, hidden underneath
clothing and representing some type of explosive, is reconstructed. The complex permittivity profiles of all other scatterers
are assumed to be known. The presented quantitative inverse scattering algorithm is based on a Newton-type optimization, combined
with an approximate line search and regularized by applying Stepwise Relaxed Value Picking regularization. The input data
of the quantitative inverse scattering problem are synthetic scattering data since the authors are not aware of any amplitude
and phase measurement data for concealed weapon detection yet made available to the inversion community at these high frequencies. 相似文献
7.
The scattering of a time-harmonicE -wave by a dielectric cylinder is solved by a single integral equation. Two alternatives are investigated to derive such a single integral equation. Interest is focused on the fields inside the dielectric. In this case the integral equation has only the incident electric field as its source term. 相似文献
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The frequency-dependent propagation characteristics of lossless and lossy open coupled polygonal conductor transmission lines in a multilayered medium are determined based on a rigorous full-wave analysis. A boundary integral equation technique is used in conjunction with the method of moments. Losses in conductors and layers are included in an exact way without making use of a perturbation approach. Dispersion curves for the complex propagation constants and impedances are presented for a number of relevant examples and, where possible, compared with published data 相似文献
10.
This paper combines a multilevel moments method (MMM) scheme with a modified diakoptics (MD) technique and a block Gauss-Seidel (BGS) iterative technique to reduce the solution time of large planar microwave structures. The proposed MMM scheme has two levels. On the lower level, the planar circuit is divided into several subcircuits using two types of artificial ports. At the higher level, general basis functions defined over the complete circuit are generated in an iterative way. The validity and the efficiency of the new technique are validated by several examples, including a large low-pass filter 相似文献