Showing papers by "University of Groningen published in 1983"
TL;DR: Comparison of the results indicates the range of values of the scattering and absorption parameters where the computationally fast diffusion approach is applicable.
Abstract: To allow the determination of scattering and absorption parameters of a turbid material from reflection measurements the relation of these parameters to the reflection has been described by two theoretical approaches. One approach is based on the diffusion theory which has been extended to include anisotropic scattering. This results in a reflection formula in which the scattering and absorption are described by one parameter each. As a second more general approach a Monte Carlo model is applied. Comparison of the results indicates the range of values of the scattering and absorption parameters where the computationally fast diffusion approach is applicable.
498 citations
TL;DR: In this article, the morphology and crystal growth of poly( l -lactic acid), PLLA have been studied from the melt as a function of undercooling and molecular weight using hot stage microscopy.
383 citations
TL;DR: A three-dimensional model of the p21 βαβ unit is presented which explains directly why glycine at position 12 cannot be replaced by another residue without altering the nucleotide-binding properties of p21.
Abstract: Recently, it has been demonstrated that a single point mutation is responsible for the acquisition of transforming properties by the EJ and T24 human bladder carcinoma gene1–3. The point mutation consists of the conversion of guanine into thymine, which results in the replacement of a glycine by a valine at position 12 of the p21 protein encoded by the EJ and T24 genes. Sequence data of retroviral analogues of the p21 protein1–5 also indicate the importance for a glycine residue at position 12 in normal p21. Comparison of the sequence of the 37 N-terminal residues of the normal human p21 protein with the sequence of the dinucleotide-binding βαβ unit in a group of structurally related enzymes, suggests that these residues of p21 fold into a very similar unit which is also involved in binding a nucleotide. We present here a three-dimensional model of the p21 βαβ unit which explains directly why glycine at position 12 cannot be replaced by another residue without altering the nucleotide-binding properties of p21.
347 citations
TL;DR: For Arabidopsis thaliana (L.) Heynh, 76 loci have now been assigned to five linkage groups, corresponding to the five chromosomes, and map lengths and centromere positions agree well with cytological observations of pre- recombination.
Abstract: For Arabidopsis thaliana (L.) Heynh. (2n = 10), 76 loci have now been assigned to five linkage groups, corresponding to the five chromosomes. From a large number of estimated recombination percentages Internally consistent linkage maps were con- structed, ranging in genetic length from 51 cM (chromosome 2) to 123 cM (chromosome 1). Map lengths and centromere positions agree well with cytological observations of pre-
347 citations
TL;DR: In this article, the authors discuss some general aspects of two estimation methods, which are designed for analysis of interrelationships between indirectly and directly observable variables, and summarize in broad terms what appears to be known about tthe asymptotic properties of maximum likelihood and partial least squares estimators.
298 citations
TL;DR: In this article, the first bifurcation point of a diffeomorphism is characterized, and a model for the local unfoldings of the periodic orbits of the diffeomorphic arcs is established.
Abstract: We consider one parameter families or arcs of diffeomorphisms. For families starting with Morse-Smale diffeomorphisms we characterize various types of (structural) stability at or near the first bifurcation point. We also give a complete description of the stable arcs of diffeomorphisms whose limit sets consist of finitely many orbits. Universal models for the local unfoldings of the bifurcating periodic orbits (especially saddle-nodes) are established, as well as several results on the global dynamical structure of the bifurcating diffeomorphisms. Moduli of stability related to saddle-connections are introduced.
296 citations
TL;DR: In this article, it was shown that both bound and scattering states of a certain class of potentials are related to the unitary representations of certain groups, such as the Morse and Poschl-Teller potentials.
285 citations
TL;DR: Renal biopsy specimens taken 7 months after transplantation showed almost complete resolution of the nephropathy and both patients remain free from proteinuria after a further 7 months, indicating that longstanding type 1 diabetes need not always contraindicate kidney donation.
275 citations
268 citations
TL;DR: The information on various aspects of the role of peroxisomes in the metabolism of one-carbon compounds in yeasts clearly shows that these unicellular organisms offer an almost ideal model system for the study of function, morphogenesis, and turnover of these intriguing organelles.
Abstract: Publisher Summary This chapter reviews the role of peroxisomes in the metabolism of methanol and methylated amines in yeasts. It provides information regarding their biogenesis and turnover. The studies on the physiology and biochemistry of methanol oxidation by methylotrophic yeasts exhibit that adaptation of these organisms to growth on methanol is associated with the proliferation of large microbodies in the cells. To evaluate the unique function and structure of the microbodies during methylotrophic growth in yeasts it is necessary to consider pertinent biochemical and physiological aspects of methanol metabolism in these organisms. Microbodies of methanol-grown yeasts show a number of characteristic properties.They appear in clusters in the cell and exist in close association with strands of endoplasmic reticulum. Evidence that the microbodies of methanol-grown yeasts contain alcohol oxidase and catalase is obtained via cell fractionation and cytochemical studies. The information on various aspects of the role of peroxisomes in the metabolism of one-carbon compounds in yeasts clearly shows that these unicellular organisms offer an almost ideal model system for the study of function, morphogenesis, and turnover of these intriguing organelles.
245 citations
TL;DR: Moment and work of the human calf muscles in level walking were determined by means of an EMG to force processor, based on a muscle analogue, and high power peaks can be delivered due to the 'catapult action'.
TL;DR: A new polymerization system for embedding soft tissues in glycol methacrylate is described, initiated by means of a barbituric acid derivative in combination with chloride ions and dibenzoyl peroxide, which contains no aromatic amines.
Abstract: The paper describes a new polymerization system for embedding soft tissues in glycol methacrylate (GMA). The polymerization of GMA is initiated by means of a barbituric acid derivative in combination with chloride ions and dibenzoyl peroxide. The catalyst system contains no aromatic amines which constitutes a toxicological advantage over the commonly employed system of peroxide/aromatic amine. Clear blocks are obtained from which 1-2 micrometers sections are easy to cut. In combination with an appropriate softener, polyethylene glycol 400, serial sectioning may be practiced.
TL;DR: The investigation shows that, in contrast to the previous report, the three-dimensional structure of porcine phospholipase A2 is very similar to that of bovine phosphate A2, including the active site, and an appreciable conformational difference is in the loop 59 to 70.
TL;DR: Experimental methods used in the study of membrane fusion are reviewed, primarily with respect to their capacity to monitor the kinetics of vesicle fusion, and the significance of these fusion rate constants to the duration of the fusion event is discussed.
TL;DR: Cell spreading and cell division rates of a transformed line of mouse lung fibroblasts were studied on various polymer surfaces in the presence of serum proteins, and cell spreading appeared independent of the dispersion surface free energy.
Abstract: Cell spreading and cell division rates of a transformed line of mouse lung fibroblasts were studied on various polymer surfaces in the presence of serum proteins. The bare polymer surfaces, as well as the protein-coated surfaces, were characterized by their polar (gamma ps) and dispersion (gamma ds) surface free energies. Cell spreading appeared to be dependent on the polar surface free energy. Cell spreading is low when the gamma ps of the bare surface is lower than 5 erg cm-2; marked spreading occurs when gamma ps is higher than 15 erg cm-2. A similar relationship was found between cell spreading and polarity of the protein-coated surfaces, although less pronounced than for the bare surfaces. Cell spreading appeared independent of the dispersion surface free energy. Cell division rate was the same on all surfaces tested.
TL;DR: In a theoretical eye with spherical and aspheric surfaces, the retinal illumination is calculated if a Ganzfeld luminance field is used and the resulting retinal light distribution is nearly homogeneous over the whole retina.
Abstract: In a theoretical eye with spherical and aspheric surfaces, the retinal illumination is calculated if a Ganzfeld luminance field is used. The resulting retinal light distribution is nearly homogeneous over the whole retina. The homogeneity is not much influenced by the size of the optical surfaces. The corresponding retinal area and the luminous flux entering the eye are calculated as functions of the size of the visual field. The values of the length of the light path through the crystalline lens and of the angle of incidence on the retina are described as functions of the angle in the visual field.
TL;DR: Inactivation of peroxisomal enzymes in the yeast Hansenula polymorpha was studied following transfer of cells into cultivation media in which their activity was no longer required for growth.
Abstract: Inactivation of peroxisomal enzymes in the yeast Hansenula polymorpha was studied following transfer of cells into cultivation media in which their activity was no longer required for growth. After transfer of methanol-grown cells into media containing glucose - a substrate that fully represses alcohol oxidase synthesis - the rapid inactivation of alcohol oxidase and catalase was paralleled by a disappearance of alcohol oxidase and catalase protein. The rate and extent of this inactivation was dependent upon conditions of cultivation of cells prior to their transfer. This carbon catabolite inactivation of alcohol oxidase was paralleled by degradation of peroxisomes which occurred by means of an autophagic process that was initiated by the formation of a number of electron-dense membranes around the organelles to be degraded. Sequestration was confined to peroxisomes; other cell-components such as ribosomes were absent in the sequestered cell compartment. Also, cytochemically, hydrolytic enzymes could not be demonstrated in these autophagosomes. The vacuole played a major role in the subsequent peroxisomal breakdown since it provided the enzymes required for proteolysis. Two basically similar mechanisms were observed with respect to the administration of vacuolar enzymes into the sequestered cell compartment. The first mechanism involved incorporation of a small vacuolar vesicle into the sequestered cell compartment. The delimiting membrane of this vacuolar vesicle subsequently disrupted, thereby exposing the contents of the sequestered cell compartment to vacuolar hydrolases which then degraded the peroxisomal proteins. The second mechanism, observed in cells which already contained one or more autophagic vacuoles, included fusion of the delimiting membranes of an autophagosome with the membrane surrounding an autophagic vacuole which led to migration of the peroxisome inside the latter organelle. Peroxisomes of methanol-grown H. polymorpha were degraded individually. In one cell 2 or 3 peroxisomes might be subject to degradation at the same time, but they were never observed together in one autophagosome. However, fusions of autophagic vacuoles in one cell were frequently observed. After inhibition of the cell's energy-metabolism by cyanide ions or during anaerobic incubations the formation of autophagosomes was prevented and degradation was not observed.
TL;DR: The Maudsley Marital Questionnaire (MMQ) as discussed by the authors is a short 20-item scale which was designed to assess degree of favourableness of attitude towards one's own marriage.
TL;DR: Quantitative data on the analysis of amniotic fluid samples collected from women in the 30th to 38th week are given together with a correlation study on their lecithin/sphingomyelin and their palmitic acid/stearic acid ratios.
TL;DR: The effect of steroid therapy on antibody levels was seen in all patient groups but was strongest in thymoma patients with early onset of disease, and the thymic pathology and age at onset seemed to act independently.
TL;DR: This chapter presents a discussion of spectrophotometric determination of hemoglobin and hemoglobin derivatives, which depends on the validity of the Lambert-Beer law.
Abstract: Publisher Summary This chapter presents a discussion of spectrophotometry of hemoglobin and hemoglobin derivatives. Many special photometers (hemoglobinometers, oximeters, etc.) presently available for the determination of hemoglobin and hemoglobin derivatives are mentioned only incidentally. Numerous (spectro) photometric methods are developed for the determination of oxyhemoglobin, either as oxyhemoglobin fraction or as oxygen saturation. Many conventional two-wavelength spectrophotometric methods are available, most of them involving the use of an isobestic point in the absorption spectra of Hb and HbO2—for example, a wavelength at which the absorptivity of the two components has the same value. This yields a single, linear relationship between the oxygen saturation and the ratio of the light absorbances of the sample at the two wavelengths used. All methods for the spectrophotometric determination of hemoglobin derivatives depend on the validity of the Lambert-Beer law. Many two-wavelength methods are also used in the determination of common dyshemoglobins in human blood (HbCO, Hi, SHb). In all of these methods, the samples undergo some kind of pretreatment so that, besides the dyshemoglobin species to be determined, only one other hemoglobin derivative is present.
TL;DR: In this article, both bound and scattering states of the P\"oschl-Teller potential are shown to be connected with unitary representations of certain groups, and the algebraic approach used for treating bound-state problems can be extended to scattering and band-structure problems.
Abstract: Both bound and scattering states of the P\"oschl-Teller potential are shown to be connected with unitary representations of certain groups. A family of periodic potentials, and their associated transfer matrices and band structure, can also be obtained from group theory and reduce to the above potential when the real period approaches infinity. These results suggest that the algebraic approach used for treating bound-state problems can be extended to scattering and band-structure problems.
TL;DR: In this article, the 18O fractionation between CO2 and H2O at 10 − 60°C was determined by measuring the ratio of 18O/16O ratio in water and CO2 equilibrated with this water.
TL;DR: The authors examined the evolution of the per capita income gap between developed and developing countries and concluded that the existing evidence supports the Landes-Kuznets position, and that Bairoch probably overstates the contemporary income gap and understates per-cap income growth in the developing world.
Abstract: This paper examines the evolution of the per capita income gap between developed and developing countries. Landes and Kuznets suggest that Western countries already had a big lead before their economic growth accelerated, but Bairoch has recently claimed that European living standards in the mid-eighteenth century were lower than in the rest of the world. I think the existing evidence supports the Landes-Kuznets position, and that Bairoch probably overstates the contemporary income gap and understates per capita income growth in the developing world. But there are contradictory elements in the evidence, on which further research is needed.
TL;DR: Tissue shrinkage caused by formalin fixation, and by dehydration, clearing and paraffin wax embedding did not differ significantly in the different directions and resulted in an average shrinkage of respectively 2.7% and 12.6% of the original dimensions.
Abstract: To evaluate the efficacy of cryocoagulation as a treatment for cervical intraepithelial neoplasia (C.I.N.), it is necessary to know the maximum depth of the glandular crypts, the maximum crypt involvement by C.I.N. and the extension of the cryolesion, obtained under standardized conditions. In a morphometric study on this subject, one has to take into account the shrinkage of the cervical tissue, caused by processing the tissue for histological examination. In the present study, tissue shrinkage of the cervix in different directions was measured in three separate steps. First shrinkage caused by formalin fixation was determined, second shrinkage caused by dehydration, clearing and paraffin wax embedding and finally that caused by section cutting and mounting. Shrinkage caused by formalin fixation, and by dehydration, clearing and paraffin wax embedding did not differ significantly in the different directions and resulted in an average shrinkage of respectively 2.7% and 12.6% of the original dimensions. The alterations of the dimensions by section cutting and mounting is not a process of shrinkage, but actually a deformation caused by pressure on the tissue during sectioning. Generally the dimension decreases in the cutting direction and increases in the direction perpendicular to it. In the calculation of the total shrinkage these alterations can be neglected, since the changes, although not consistent are small. It follows that in morphometric studies a total shrinkage of about 15% of the original dimensions has to be taken into consideration.
TL;DR: Findings suggested that the fact that retrospective data is being measured with the scales does not threaten the reliability and validity of gathered information due to faulty recall or falsified accounts.
Abstract: The EMBU, an instrument which was designed to assess one's memories of parental rearing behaviour, was psychometrically evaluated. Principal component factor analysis of data of a mixed sample of 841 non-institutionalized phobic individuals revealed four factors which were termed Rejection, Emotional warmth, Over-protection and Favouring subject, thereby contributing to the convergent (cross-national) reliability and validity of the structural model of perceived parental behaviour. Besides the utilization of data from aforementioned phobic sample, the scales' internal consistency was assessed in data of five additional samples, which consisted of 277 'normals', 40 agoraphobics, 29 social phobics, 21 height phobics and 38 obsessive-compulsive neurotics, and found to be very satisfactory. In the normal and mixed phobic sample, validity measures were shown to be acceptable and to be independent of the parent's sex. Furthermore, findings suggested that the fact that retrospective data is being measured with the scales does not threaten the reliability and validity of gathered information due to faulty recall or falsified accounts.
TL;DR: The results of a study on the magnitude and composition of the Ak~H~ of Streptococcus cremoris growing in continuous cultures at different rates and different pH values are presented.
Abstract: It is now generally accepted that the electrochemical proton gradient (Ak~H+) or proton-motive force (pmf) plays an important role in the metabolism of microorganisms. It is the main driving force for energy-requiring processes, such as ATP synthesis and secondary solute transport across the cytoplasmic membrane [1,2]. Recently, it was shown that the A/~H+ is also involved in other metabolic processes, such as nitrogen fixation [3], ppGpp breakdown [4] and DNA-uptake by genetic transformation [5]. Although there exists a considerable knowledge about the role of the A/~H~ in several specific metabolic events, surprisingly little is known about the A/~H+ in relation to the overall process of microbial growth. Besides ATP, which acts as a molecular currency of metabolic energy the A~ H ÷ is in many cases an obligate intermediate between energy-consuming and energy-producing processes. A complete description of the energetics of microbial growth will only be possible if during growth the A~H+ of microorganisms can be recorded. In this report we present the results of a study on the magnitude and composition of the Ak~H~ of Streptococcus cremoris growing in continuous cultures at different rates and different pH values.
TL;DR: The serial measurement of anti-AChR may be a valuable method of following the basic trend of the MG in severely affected patients after treatment with prednisone or immunosuppression and after thymectomy.
TL;DR: This paper describes the measuring system and indicates the area of application of the method, based on reflection measurements carried out on bulk material, which will be of great advantage in many applications.
Abstract: A new experimental method has been developed to determine the scattering and absorption characteristics of a turbid material. Existing methods usually require transmission and reflection measurements carried out on a thin slab of the material under study; this method is based on reflection measurements carried out on bulk material. This will be of great advantage in many applications. This paper describes the measuring system and indicates the area of application of the method. Calibration measurements have been carried out to substantiate the approach.