J. De Geest

Adaptive CAD-model building algorithm for general planar microwave structures

A new adaptive technique is presented for building multidimensional parameterized analytical models for general planar microwave structures with a predefined accuracy and based on full-wave electromagnetic (EM) simulations. The models can be incorporated in a circuit simulator and the time required to calculate the circuit representation of a practical network is reduced by several orders of magnitude compared to full EM simulations. Furthermore, the accuracy of the results is significantly better compared to the circuit models used in state-of-the-art computer-aided design tools.

Modeling differential via holes

In this paper, we present a method to characterize differential via holes in printed circuit boards in a both fast and accurate way. The via hole is modeled as a cascade of capacitances and inductances. We use FASTCAP to compute the values of the capacitances, and a closed form formula to obtain the inductance values. The numerical predictions are compared with experimental data.

Modelling complex via hole structures

Derives a physics-based circuit model for complex via hole structures in printed circuit boards. The via hole is modeled as a cascade of capacitance and inductance matrices. Capacitance values are computed using a three-dimensional electrostatic solver and inductance values are computed from a two-dimensional quasi-TEM solver. This model is valid at frequencies up to a few gigahertz for typical via hole geometries, where the return current follows a well defined path.

Development of the retina in the porcine fetus. A light microscopic study.

Morphogenesis of the porcine retina was studied using light microscopy from 4 weeks of gestation until birth (18 to 310mm crown‐rump length), and compared with the adult stage (6 months). Tissue samples were examined from the posterior and peripheral parts of the retina. At 18mm the retina consists of an inner marginal layer and an outer layer of neuroblastic cells. At 18–40mm the latter layer is divided into an inner and an outer neuroblastic layer by the transient layer of Chievitz. Subsequently, the development of the different retinal layers begins at the inner retinal border and moves progressively outwards; it also spreads from the posterior to the peripheral part of the neural retina. Many cells of the inner neuroblastic layer are prospective ganglionic cells which migrate inwards, thus forming the ganglion cell layer and the inner plexiform layer at 90mm. At 120mm, primitive horizontal cells appear within the outer neuroblastic layer. Separation of this layer into the inner nuclear, outer plexiform and outer nuclear layers is first evident at 180mm. At this stage all retinal layers are present, except the layer of the photoreceptor cells which is not widespread until at 220mm. The inner and outer segments of the photoreceptor cells lengthen considerably during the last month of gestation. During the late fetal stage the nerve fiber layer, the inner and outer plexiform layers and the layer of rods and cones all continue to increase in thickness. Concurrently, the ganglion cell layer and the inner and outer nuclear layers have reached their maximal thickness and become thinner. After the total thickness of the neural retina amounts to approximately 180μm at two to three weeks before birth, it then thins to approximately 160μm in the adult stage.

Modelling differential via holes

With the ever-increasing frequencies of printed circuit board (PCB) interconnections, the role played by via holes is no longer negligible. Thoughtless design of via holes on a board may seriously degrade signal integrity due to reflections, ground bounce, etc. However, the characterisation of via holes has not drawn much attention until now. This paper presents a method for the characterisation of differential via holes as a cascade of capacitances and inductances. Capacitances are computed using FASTCAP and inductances using simple analytical models.

Recovering lossy multiconductor transmission line parameters from impedance or scattering representations

In this paper, we present a generalization of the simultaneous diagonalization technique by means of congruence transformations to the general reciprocal lossy multiconductor transmission line case. The method paves the way to solving the inverse problem, i.e., given a lossy multiconductor transmission line system of a given length, recover the transmission line parameters from the impedance or scattering descriptions.

Recent trends in the integration of circuit optimization and full-wave electromagnetic analysis

In this paper, we provide an overview of some recent trends for the general electromagnetic (EM) circuit co-optimization approach based on an electromagnetic database (EMDB). This study is the result of long-standing efforts toward the development of an efficient planar EM simulator and its seamless integration in and combination with a circuit design environment. Two complementary techniques are put forward to build an EMDB model. Flexibility, accuracy, and computational efficiency of both techniques are validated by several examples.

EM-based multidimensional parameterized modeling of general passive planar components

A new adaptive algorithm is presented for building multidimensional parameterized analytical models for general passive planar components. The component models are based on multiple full-wave electromagnetic (EM) simulations. The modeling accuracy level is chosen by the user. Models can be generated for arbitrary geometries and substrates, and they can be easily implemented and used in commercial circuit simulators. The adaptive model generation process is an up-front time investment and requires multiple EM simulations. The model extraction provides EM-accuracy and generality at traditional circuit simulation speed.

The hyaloid vascular system of the pig

SummaryThe hyaloid vascular system of the pig was studied from 4 weeks of gestation until 2 weeks after birth by means of semithin sections and vascular corrosion casts. The vascular tunic of the lens is supplied by the posterior lens branches of the hyaloid artery (at the posterior lens pole), by the intermediate lens branches of the proper hyaloid arteries (at the lens equator) and by the anterior lens branches of the radial iridial arteries (at the anterior lens pole). Venous drainage takes place via the venous lens branches which leave the lens anteriorly and drain into the radial iridial veins. Regression of the vascular tunic of the lens occurs during the second half of fetal life and is nearly completed in the first postnatal days. The involution first affects the proper hyaloid arteries and their intermediate lens branches. Subsequently, the posterior lens branches regress, whereas the anterior lens branches in the pupillary membrane disappear in the perinatal period only.

Effect of intratesticular inoculation with Aujeszky's disease virus on genital organs of boars

Ten 8-10-month-old Belgian Landrace boars were intratesticularly inoculated with 500 TCID50 of a virulent Belgian Aujeszkys disease virus (ADV) isolate (75V19) in 0.1 ml volume. One control boar was similarly inoculated with phosphate-buffered saline solution. The genital organs of six inoculated boars were examined by virus isolation and immunofluorescence. In spite of high virus titers, the fluorescence in the testicles remained limited to a few small foci in the interstitial connective tissue and tunica albuginea at or close to the inoculation site. Neither virus replication, necrosis nor inflammatory lesions could be demonstrated in the epithelium of the seminiferous tubules. However, virus replication was regularly demonstrated in the serosa covering testicles, plexus pampiniformis, ductus deferens and tunica vaginalis. Virus was also isolated from the scrotal fluid. It is suggested that the serosa is the primary target tissue for ADV. The other four boars were inoculated to study the effect of ADV on semen. Severe morphologic alteration and lowered sperm cell concentrations were observed during several weeks after inoculation or until slaughter at 47, 53 and 58 days post inoculation. Virus was isolated from semen of only two out of four boars examined at 9 and 10 days post inoculation.