Generation of FDTD subcell equations by means of reduced order modeling

Adapted finite-difference time-domain (FDTD) update equations exist for a number of objects that are smaller than the grid step, such as wires and thin slots. We provide a technique that automatically generates new FDTD update equations for small objects. Our presentation focusses on 2D-FDTD. We start from the FDTD equations in a fine grid where the time derivative is not discretised. This yields a large state-space model that is drastically reduced with a reduced order modeling technique. The reduced state-space model is then translated into new FDTD update equations that can be used in an FDTD simulation in the same way as the existing update equations for wires and thin slots. This technique is applied to a number of numerical problems showing the accuracy and versatility of the proposed method.     

Distribution of salmonella strains in farrow-to-finish pig herds: a longitudinal study

The aims of this study were to investigate patterns of Salmonella shedding in finishing pigs and to study the role of the sow in the transmission of Salmonella to her offspring. In each of the three herds (A, B, and C), one cohort of sows (n = 34, n = 40, n = 32, respectively) together with three piglets of their offspring (n = 102, n = 120, n = 96, respectively) were selected. Individual fecal and blood samples were taken from the sows at different times during one production cycle and from the piglets from weaning until slaughter. At slaughter, contents from the jejunum, colon, and mesenteric lymph nodes were collected. Fecal samples, as well as the jejunum, colon, and mesenteric lymph node samples collected at slaughter, were submitted to a qualitative Salmonella analysis. Isolates were characterized by random amplified polymorphic DNA, and if necessary, further characterization was done by pulsed-field gel electrophoresis. In herds A and B, Salmonella shedding began in the nursery. A significant increase in the number of Salmonella shedders was seen after transferring pigs to the growing unit in herd B (P = 0.003) and to the finishing unit in herds A (P < 0.001) and B (P = 0.013). None of the fattening pigs in herd C were shedding Salmonella. This study reveals that transferring pigs is an important trigger to induce Salmonella shedding, leading to horizontal spread. Direct transmission of Salmonella from the sows to their piglets could not be demonstrated, but the similarities between the isolates found in the sows and those found during the nursery and finishing periods and at slaughter suggested indirect transmission.     

Out-of-plane scattering in photonic crystal slabs

Photonic crystal slabs combine a slab waveguide with an in-plane photonic crystal. Light is then confined in-plane by the photonic crystal and out-of-plane by the slab waveguide. The etched structures will cause light to scatter out of the waveguide plane. We studied the out-of-plane scattering losses using a two-dimensional approximation of this three-dimensional structure, with etched slots instead of holes. Our simulation techniques include mode expansion with perfectly matched layer absorbing boundary conditions. We show that the losses increase with higher index contrast, but that with very high-index contrasts light can be coupled into lossless Bloch modes     

Regularization of the moment matrix solution by a nonquadraticconjugate gradient method

Inspired by Tikhonov regularization, a nonlinear conjugate gradient method is proposed with the purpose of simultaneously regularizing and solving the moment matrix equation. The procedure is based on a nonquadratic conjugate gradient algorithm with exact line search, restart, and rescale. Applied to the problem of TM scattering by perfectly conducting rectangular cylinders, the method is shown to exhibit a fast convergence rate     

Occurrence and distribution of Arcobacter species in poultry processing

A total of 16 broiler flocks slaughtered in the morning in eight Belgian poultry slaughterhouses were examined for the presence of Campylobacteraceae. In samples collected before and after chilling, the prevalence of arcobacters was found to be higher than the prevalence of thermophilic campylobacters, with the slaughter procedure used having no clear effect. Two slaughterhouses were selected for a detailed investigation of the occurrence and distribution of arcobacters. Sampling carried out before slaughter revealed that both Arcobacter butzleri and Arcobacter cryaerophilus were commonly present on the slaughter equipment in both plants. These findings indicate inadequate decontamination of the slaughterhouse environment and suggest potential Arcobacter contamination of broiler carcasses through the slaughter equipment. Even before evisceration, contamination levels of hundreds to several thousands of arcobacters per gram of neck skin were detected. It appears unlikely that contamination through slaughter equipment alone explains the high contamination levels found for poultry products. Arcobacters were not isolated from the 30 intestinal tracts sampled for each broiler flock examined. A. cryaerophilus was the only Arcobacter species recovered from the transport crate samples collected before and after washing. Arcobacter contamination during slaughter, either direct (from chicken intestinal content or feces) or indirect (from equipment), was not confirmed. The origin and the precise routes of contamination remain to be determined.     

Campylobacter contamination during poultry slaughter in Belgium

The relation between internal carriage and surface contamination with thermophilic Campylobacter species in broilers was examined by molecular typing methods. Samples from 39 flocks were collected in three Belgian poultry slaughterhouses. From each flock, crop swabs before slaughter and intestines and neck skins during slaughter were collected. A total of 309 isolates were identified at species level and further characterized by flagellin gene A PCR/restriction fragment length polymorphism and pulsed-field gel electrophoresis. Isolates were identified as Campylobacter jejuni (90%), Campylobacter coli (8.7%), and Campylobacter lari (2.2%), and 27 genotypes could be distinguished by combining the two molecular methods. Seventy-two percent of the flocks arriving at the abattoir were colonized with campylobacters. After slaughter, 79% of the flocks had contaminated neck skins. In six flocks, genotypes isolated from the neck skins were also found in the alimentary tract from previously slaughtered flocks. Four of these flocks were initially free of Campylobacter. These four flocks might have had no contaminated carcasses after logistic slaughtering.     

Development of a new protocol for the isolation and quantification of Arcobacter species from poultry products.

None of the presently available selective supplements for the specific isolation of Arcobacter species allows the growth of Arcobacter butzleri, A. cryaerophilus and A. skirrowii and at the same time fully suppresses the accompanying flora present in poultry and poultry products. Furthermore, little is known about the contamination levels of poultry with Arcobacter species. In this study, a new selective supplement comprising amphotericin B (10 mg/l), cefoperazone (16 mg/l), 5-fluorouracil (100 mg/l), novobiocin (32 mg/l) and trimethoprim (64 mg/l) was developed. With a new isolation procedure, including enrichment in Arcobacter broth with the selective supplement, incubated for 24 to 48 h at 28 degrees C under microaerobic conditions, arcobacters were isolated from 100% (n = 34) of neck skin of laying hens and from 90% (n = 71) of similar samples from broilers. Of the broiler breast meat samples examined (n = 52), 65% were found to be contaminated with these bacteria. In 64% of the samples, A. butzleri was the only Arcobacter species isolated. In 9% of the samples, A. cryaerophilus was the only species present, while 11% of the samples were positive for both species simultaneously. Using direct isolation on the selective agar medium developed in this study, incubated for 24 to 48 h under microaerobic conditions at 28 degrees C. 32 out of 45 broiler carcasses and 6 out of 25 broiler breast meat samples carried a bacterial load of arcobacters of 10(2) to 10(3) cfu/g. The prevalence of Arcobacter in Belgian poultry was found higher than the prevalence of thermophilic Campylobacter species in each of the poultry categories examined. The enrichment procedure and the direct plating method were validated for the isolation of A. skirrowii. For this species, growth performance was less than the other two Arcobacter species and it was not isolated nor detected by m-PCR from the naturally contaminated poultry samples examined. This new protocol provides a fast and reliable method for the isolation of Arcobacter species from poultry and can contribute to more comprehensive epidemiological investigations.     

Circuit parameters for single and coupled microstrip lines by arigorous full-wave space-domain analysis

A rigorous full-wave analysis is applied to determine the dispersion characteristics and the impedance matrix of coplanar microstrip lines. It is shown that the impedance definition based on the propagating power and the longitudinal current is the most appropriate one. Examples are given for the single strip, for two coupled strips, either symmetric or asymmetric, and for a three-strip configuration. Some attention is also devoted to the current profiles associated with each eigenmode     

New fast and accurate line parameter calculation of generalmulticonductor transmission lines in multilayered media

An enhanced method to calculate the C, L, and R of a multiconductor bus in a multilayered medium is presented. Different board technologies, conductors of complicated shape, and conductors embedded in different layers can be handled without loss of accuracy or substantial increase in CPU time compared with existing simulation techniques. Correct determination of skin effect losses is shown to depend critically on surface charge modeling. Surface charge discontinuities are explicitly taken into account which results in reduced computation time. A further reduction of computation time is obtained by a particular treatment of the calculation of the Green's function