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Showing papers by "Ghent University published in 1981"


Journal ArticleDOI
TL;DR: In this paper, a beam-propagation method for the calculation of the propagation of a light beam through an inhomogeneous medium is presented, and a set of conditions necessary for the accurate application of the method is derived.
Abstract: A method for the calculation of the propagation of a light beam through an inhomogeneous medium is presented. A theoretical analysis of this beam-propagation method is given, and a set of conditions necessary for the accurate application of the method is derived. The method is illustrated by the study of a number of integrated-optic structures, such as thin-film waveguides and gratings.

491 citations


Journal ArticleDOI
TL;DR: The introduction of some additional new techniques may possibly reduce the cost and broaden the range of plants that can be propagated economically in vitro and its adaptation to commercial practices.

310 citations


Journal ArticleDOI
TL;DR: In this paper, a new method for quantitative essential oil analysis, using combined steam distillation-extraction, was described, which allowed the quantitative analysis of total essential oil content and the percentage of the individual compounds in less than 4 hours.

282 citations


Journal ArticleDOI
TL;DR: A simple, inexpensive and reliable short-term routine test with Artemia larvae is proposed, based on the determination of the LC50-24 hr of instar II–III nauplii of a specific Artemia strain.

238 citations


Journal ArticleDOI
TL;DR: The following theorem is offered, which states that the conditional distribution of a given random variable X is the (normalized) product of the maximum entropy distribution and the initial distribution.
Abstract: It is well-known that maximum entropy distributions, subject to appropriate moment constraints, arise in physics and mathematics. In an attempt to find a physical reason for the appearance of maximum entropy distributions, the following theorem is offered. The conditional distribution of X_{l} given the empirical observation (1/n)\sum^{n}_{i}=_{l}h(X_{i})=\alpha , where X_{1},X_{2}, \cdots are independent identically distributed random variables with common density g converges to f_{\lambda}(x)=e^{\lambda^{t}h(X)}g(x) (Suitably normalized), where \lambda is chosen to satisfy \int f_{lambda}(x)h(x)dx= \alpha . Thus the conditional distribution of a given random variable X is the (normalized) product of the maximum entropy distribution and the initial distribution. This distribution is the maximum entropy distribution when g is uniform. The proof of this and related results relies heavily on the work of Zabell and Lanford.

230 citations


Journal ArticleDOI
TL;DR: In this article, a finite element program for the analysis of anisotropic optical waveguides is described and the appearance of spurious numerical modes, due to the fact that the functional is non-positive definite, is discussed and a possible solution to the problem is presented.
Abstract: A finite element program for the analysis of anisotropic optical waveguides is described. The appearance of spurious numerical modes, due to the fact that the functional is nonpositive definite is discussed and a possible solution to the problem is presented. For isotropic waveguides it is shown that both EH- and HE-type modes can be very accurately approximated by two different scalar finite element programs. Finally, a method for calculating the attenuation of leaky modes in a single material integrated optic waveguide using this scalar finite element method is proposed.

192 citations


Journal ArticleDOI
TL;DR: In this article, it was shown that open-circuit operation is a reversible process and leads to the Carnot efficiency, if one defines the efficiency in the way that is usual in the theory of thermodynamic engines.
Abstract: An infinite stack ofp—n junctions with smoothly varying bandgap from ∞ to 0 is considered. AnI —V characteristic is derived, which is more correct than the classical exponential characteristic. It is shown that open-circuit operation is a reversible process and leads to the Carnot efficiency, if one defines the efficiency in the way that is usual in the theory of thermodynamic engines. If instead one uses the definition of efficiency usual in photovoltaics, open-circuit mode gives rise to zero efficiency. Then operation at maximum efficiency equals operation at maximum power and is not reversible.

173 citations


Journal ArticleDOI
Joseph A. Thas1
TL;DR: In this article, it was shown that the polar space Q(2n, q) arising from a non-singular elliptic quadric has no ovoid, and the polar spaces H(n,q), q even, and H(q, q even) have no ovo.
Abstract: LetP be a finite classical polar space of rankr, r⩾2. An ovoidO ofP is a pointset ofP, which has exactly one point in common with every totally isotropic subspace of rankr. It is proved that the polar spaceW n (q) arising from a symplectic polarity ofPG(n, q), n odd andn > 3, that the polar spaceQ(2n, q) arising from a non-singular quadric inPG(2n, q), n > 2 andq even, that the polar space Q−(2n + 1,q) arising from a non-singular elliptic quadric inPG(2n + 1,q), n > 1, and that the polar spaceH(n,q 2) arising from a non-singular Hermitian variety inPG(n, q 2)n even andn > 2, have no ovoids. LetS be a generalized hexagon of ordern (⩾1). IfV is a pointset of order n3 + 1 ofS, such that every two points are at distance 6, thenV is called an ovoid ofS. IfH(q) is the classical generalized hexagon arising fromG 2 (q), then it is proved thatH(q) has an ovoid iffQ(6, q) has an ovoid. There follows thatQ(6, q), q=32h+1, has an ovoid, and thatH(q), q even, has no ovoid. A regular system of orderm onH(3,q 2) is a subsetK of the lineset ofH(3,q 2), such that through every point ofH(3,q 2) there arem (> 0) lines ofK. B. Segre shows that, ifK exists, thenm=q + 1 or (q + l)/2.If m=(q + l)/2,K is called a hemisystem. The last part of the paper gives a very short proof of Segre's result. Finally it is shown how to construct the 4-(11, 5, 1) design out of the hemisystem with 56 lines (q=3).

137 citations


Journal ArticleDOI
TL;DR: A self-tuning multistep predictor that predicts the output of a stochastic process with unknown, possibly slowly time-varying parameters over a range of several sampling periods in the future is presented.

116 citations


Journal ArticleDOI
TL;DR: In patients with rapidly changing renal function the new equation resulted in accurate predictions of CrCl within a few hours after the change, as opposed to several days with the other methods.
Abstract: An equation for predicting endogenous creatinine clearance (CrCl) in adults and children (with both stable and unstable renal function) from serum creatinine concentrations is presented. The predictions are compared with four other available estimating methods, based on values in 110 subjects with renal impairment of widely differing degrees. In patients with stable and with unstable renal function the correlation between measured and predicted CrCl was better with the new equation. In patients with rapidly changing renal function the new equation resulted in accurate predictions of CrCl within a few hours after the change, as opposed to several days with the other methods. The elimination rate constant of the aminoglycoside antibiotic amikacin correlated more precisely with CrCl values estimated from the new equation than with those measured during 24 hr or with the other prediction methods. Clinical Pharmacology and Therapeutics (1981) 30, 414–421; doi:10.1038/clpt.1981.181

109 citations


Journal ArticleDOI
TL;DR: In this article, the results from the duplicate impactor samples were normally in good agreement, indicating that the combined uncertainty of sampling and PIXE analysis was of the order of 20%.

Journal ArticleDOI
TL;DR: In this paper, the thermodynamics of various anaerobic digestion patterns of hexose to methane are compared and it appears that by directing the hexose-hydrolysis phase towards ethanol and lactic acid production, methanogenesis can be enhanced because the synthrophic bacteria are allocated more potentially available energy.
Abstract: The thermodynamics of the various anaerobic digestion patterns of hexose to methane are compared. It appears that by directing the hexose-hydrolysis phase towards ethanol and lactic acid production, methanogenesis can be enhanced because the synthrophic bacteria are allocated more potentially available energy. This hypothesis was confirmed in a series of laboratory tests runs. They revealed that lactic acid and ethanol as intermediates, in comparison to lower volatile fatty acids, give rise to a considerably high effluent quality and a slightly larger biogas production. 15 refs.

Journal ArticleDOI
TL;DR: The elemental composition of duplicate aerosol samples from north China, collected in particle size fractions by eight-stage cascade impactors on the Great Wall, near Beijing, is reported for 21 elements measured by particle induced X-ray emission analysis as discussed by the authors.

Journal ArticleDOI
TL;DR: The pathogenesis of this infection was similar to that of transmissible gastroenteritis (TGE), a known coronaviral infection of pigs, but where were some differences.

Journal ArticleDOI
01 Apr 1981-Catena
TL;DR: In this article, a comparison between the properties of permafrost and those of fragipans is made and it is concluded that only the permafure hypothesis can explain the complete set of properties of the fragipan.
Abstract: A comparison is made between the properties of permafrost and those of fragipans. The permafrost characteristics are summarized from published data on active permafrost and from personal observations on fossil permafrost. The study of the fragipans mainly concerns the silty sediments of Weichselian age which occur in Belgium and northern France. The distribution and the physical, macromorphological and micromorphological properties of fragipans can all satisfactorely be explained by the growth of segregated ice during permafrost aggradation. Particularly striking is the relationship of both permafrost and fragipans, to drainage conditions: the quantity of segregated ice is highest in moist or poorly drained soil and it is at such places that the best developed fragipans are observed. Certain arguments that can be stated against the hypothesis of fragipan genesis by permafrost are discussed: (1) the development of a platy structure by freeze-thaw or by wet-dry cycles, (2) the discontinuous distribution of the fragipan, (3) the development of the fragipan by pedogenetic weathering and migration processes. It is concluded that only the permafrost hypothesis can explain the complete set of properties of the fragipan.

Journal ArticleDOI
01 Feb 1981-Geoderma
TL;DR: In this article, the authors used Δ log K, which represents the difference between the logarithms of the absorption coefficients at 400 and 600 μm, to test the extractability of Al, Fe and C by those solutions.

Journal ArticleDOI
TL;DR: Porcine enteropathogenic coronavirus-like agent CVLA did not show cross reactivity with infectious bronchitis virus, transmissible gastroenteritis virus (TGEV), canine coronav virus (CCV), hemagglutinating encephalomyelitis viruses (HEV) or feline infectious peritonitisirus (FIPV).
Abstract: A possible antigenic relationship between the porcine enteropathogenic coronavirus-like agent (CVLA) and 6 known coronaviruses was examined by immunoelectron microscopy (IEM) and by immunofluorescence (IF). CVLA did not show cross reactivity with infectious bronchitis virus, transmissible gastroenteritis virus (TGEV), canine coronavirus (CCV) hemagglutinating encephalomyelitis virus (HEV), neonatal calf diarrhea coronavirus (NCDCV) or feline infectious peritonitis virus (FIPV). Antigenic relationship was detected by IEM between TGEV and CCV, NCDCV and HEV and by IF between TGEV and CCV, TGEV and FIPV, HEV and NCDCV.

Journal ArticleDOI
TL;DR: The hypothesis that monoclonal T cell antibodies may offer an important tool for the further evaluation of patients with rheumatoid arthritis and their individual response to treatment is supported.

Journal ArticleDOI
M. Verzele1, C. Dewaele1
TL;DR: In this paper, it is shown that metal traces in high-performance liquid chromatographic bonded-phase silica gel interfere with some separations, and a test for such activity, based on the chromatography of beer bitter acids, is described.

Journal ArticleDOI
TL;DR: In this paper, the relevant Maxwell's equations, boundary conditions, and constitutive equations for axes in linear sinusoidal motion are derived for reflections from a perfectly conducting plane in sinusoid vibration.
Abstract: The signal scattered by a moving object is traditionally evaluated by the quasistationary method. This method is not relativistically correct, although it yields satisfactory results in most practical cases. A correct approach implies solution of the problem in the accelerated reference system in which the object is at rest. The relevant Maxwell's equations, boundary conditions, and constitutive equations are derived for axes in linear sinusoidal motion. As a first application the reflections from a perfectly conducting plane in sinusoidal vibration are evaluated.

Journal ArticleDOI
01 May 1981-Lipids
TL;DR: The difference between goats and cows in the effectiveness with which these animals metabolize propionyl- CoA and methylmalonyl-CoA is discussed.
Abstract: Branched-chain fatty acids of the milk fat of goats were analyzed by high resolution gas chromatography-mass spectrometry. Iso- and anteiso-acids predominated, but a range of other monomethyl-branched components, mostly with methyl-substitution on carbons 4 and 6, was present. Analysis of the milk fat of cows revealed the presence of iso- and anteiso-fatty acid; other mono-methyl-substituted fatty acids, as found in the milk fat of the goat, were virtually absent. Only a trace amount of 6-methylhexadecanoate was detected. The difference between goats and cows in the effectiveness with which these animals metabolize propionyl-CoA and methylmalonyl-CoA is discussed.

Journal ArticleDOI
TL;DR: In this article, it was proved that any A-valued analytic function in an open subset of Rm can be extended to a monogenic function in a suitable open neighbourhood in Rm+1.
Abstract: It is proved that any A-valued analytic function in an open subset Ω of Rm may be extended to a monogenic function in a suitable open neighbourhood Ωof Ω in Rm+1. This result is applied to define a product between monogenic functions, which in its turn is used to determine a hypercomplex exponential function

Journal ArticleDOI
TL;DR: The known blocking effect of fentanyl at the vomiting center does not affect its gastric relaxing effect, and the results suggest that for gastric relaxation as well as for vomiting, apomorphine and morphine act on different receptors.

Journal ArticleDOI
Richard Ducatelle1, W. Coussement1, Maurice Pensaert1, P. Debouck1, J. Hoorens1 
TL;DR: The morphogenesis of a new porcine enteric coronavirus, CV777, in intestinal epithelial cells of experimentally infected newborn piglets is described and shows a morphogenetic pattern characteristic for members of the Coronaviridae family.
Abstract: The morphogenesis of a new porcine enteric coronavirus, CV777, in intestinal epithelial cells of experimentally infected newborn piglets is described. The virus shows a morphogenetic pattern characteristic for members of the Coronaviridae family. It is formed by budding through membranes of the endoplasmic reticulum. Some specific aspects of this morphogenesis are discussed.

Journal ArticleDOI
Etienne Muylle1, C. Vandenhende1, W. Oyaert1, H. Thoonen1, K. Vlaeminck1 
TL;DR: It is concluded that ingestion of monensin sodium by horses may cause either acute death or delayed cardiac circulatory failure as a result of specific cardiac myodegeneration.
Abstract: Thirty-two horses were examined with a history of poor performance and unthriftiness several months after the ingestion of feed containing monensin sodium. Cardiac abnormality was diagnosed in 8 cases and suspected in 4 others. Necropsy examinations were performed on 6 cases with marked clinical symptoms and evidence of circulatory failure was found. Marked cardiac myopathy and fibrosis was a consistent feature. It is concluded that ingestion of monensin sodium by horses may cause either acute death or delayed cardiac circulatory failure as a result of specific cardiac myodegeneration.

Journal ArticleDOI
TL;DR: Confrontation of cell aggregates and heart fragments in organotypic culture appeared to be a useful method to study directly the invasive properties of malignant transformants of neurogenic cells and might also permit prediction of tumorigenicity in the animal.
Abstract: Invasive properties of 15 continuous neurogenic rat cell lines were investigated in vitro and were compared to their tumorigenicity in inbred BD IX rats. The cell lines were obtained by treating animals with a single transplacental dose of the carcinogen N-ethyl-N-nitrosourea (ENU) and 1) subsequently transferring brain cells into cell culture shortly after treatment or 2) explanting the resultant tumors from the offspring to monolayer cultures. In addition, one continuous nonneoplastic rat fibroblast line and three samples of untreated fetal rat brain cells were investigated. Cells from monolayer cultures were suspended and allowed to form aggregates for 24 hours on a gyratory shaker. The cell aggregates were then brought into contact with and allowed to attach to fragments from 9-days embryonic chick heart and were cultured on a gyratory shaker. All tumorigenic cell lines invaded the heart fragments, as characterized by progressive replacement of heart cells by invading cells. The heart tissue degenerated irreversibly. Nontumorigenic cell lines did not show invasiveness in vitro. Confrontation of cell aggregates and heart fragments in organotypic culture appeared to be a useful method to study directly the invasive properties of malignant transformants of neurogenic cells. The method might also permit prediction of tumorigenicity in the animal.

Journal ArticleDOI
Dirk Aeyels1
TL;DR: In this article, it was shown that a dynamical system which is unobservable with respect to any sample program consisting of 1 n samples does not necessarily have a small perturbation of the dynamics and does not destroy the nonobservability.

Journal ArticleDOI
TL;DR: The minimal inhibitory concentrations of 11 growth promoting agents were determined by agar-dilution method against 113 strains of lactobacilli isolated from caeca of pigs, cattle and poultry.
Abstract: The minimal inhibitory concentrations of 11 growth promoting agents were determined by agar-dilution method against 113 strains of lactobacilli isolated from caeca of pigs, cattle and poultry. Only Lactobacillus acidophilus strains were susceptible to avoparcin and all strains were resistant to copper sulphate. Resistance was noted in cattle and poultry strains against bacitracin, in pig strains against virginiamycin, and in pig and poultry strains against nitrovin. Resistance against carbadox, flavomycin, lincomycin, oleandomycin, spiramycin and tylosin was noted in strains from all three host species.


Journal ArticleDOI
J. Janss, R. Minne1
TL;DR: In this article, a simple method for the design of steel columns in fire conditions is presented, which adopts the European buckling curves for axially loaded bare metal sections as the basic design curves for steel columns.