Showing papers by "University of Amsterdam published in 1983"

Biodegradation behavior of various calcium-phosphate materials in bone tissue

Abstract: In order to study the biodegradation behavior of calcium phosphate materials, cylinders of standard size were implanted in the tibiae of rabbits. Material parameters were stoichiometry (hydroxyapatite with a Ca/P ratio of 1.67 versus tricalcium phosphate with a Ca/P ratio of 1.50), crystallographic structure (apatite versus beta-whitlockite), microporosity, and macroporosity. The extent of biodegradation was evaluated by radiography, light and fluorescence microscopy, microradiography, and porosity measurements. All calcium phosphate materials were biocompatible in bone tissue. Hydroxyapatite ceramics had a higher osteogenic potential than beta-whitlockite materials. Depending on their porosities, sintered tricalciumphosphate (beta-whitlockite) materials were more or less biodegradable, in contrast to sintered hydroxyapatite materials, which showed no detectable resorption over a period of 9 months of implantation.

Severe plasmalogen deficiency in tissues of infants without peroxisomes (Zellweger syndrome).

Abstract: The Zellweger syndrome is a lethal hereditary disease characterized by the absence of peroxisomes (microbodies) in liver and kidney, and variable abnormalities in mitochondria1–8. We show here that tissues from five infants that had died of this syndrome contain less than 10% of the normal levels of phosphatidylethanolamine plasmalogen (pPE), a major phospholipid component of cellular membranes. Heart and muscle, but not other tissues, also contain a substantial fraction of phosphatidylcholine plasmalogen (pPC), and this fraction is also strongly reduced in the Zellweger patients. No other abnormalities in cellular phospholipids were detected. Key enzymes of the biosynthesis of plasmalogens have previously been shown to be exclusively located in the peroxisomes of rodent liver and the microperoxisomes of rodent brain9,10. We infer that the corresponding enzymes are also located in peroxisomes in man and that the absence of peroxisomes in Zellweger patients leads to their inability to synthesize plasmalogens. Our results support the notion11 that the biosynthetic role of peroxisomes in mammals has thus far been underestimated. We suggest that the defect in plasmalogen synthesis and possibly as yet unknown peroxisomal reactions are responsible for the diverse abnormalities observed in Zellweger patients.

Binding energy and electronic structure of small copper particles

Abstract: The equilibrium geometry, binding energy, and electronic structure of small metal particles are investigated using self-consistent one-electron local-density theory. Results for ${\mathrm{Cu}}_{2}$, ${\mathrm{Cu}}_{4}$, and fcc ${\mathrm{Cu}}_{13}$ and ${\mathrm{Cu}}_{79}$ clusters show an increasing equilibrium bond length with cluster size, and a stiffening of the ${a}_{1}$ vibrational force constants. The calculated binding energies of 1.05 (${\mathrm{Cu}}_{2}$), 1.26 (${\mathrm{Cu}}_{4}$), 2.19 (${\mathrm{Cu}}_{13}$), and 3.03 (${\mathrm{Cu}}_{79}$) eV/atom compare well with the experimental values of 1.00 (${\mathrm{Cu}}_{2}$) and 3.50 (bulk) eV/atom. For ${\mathrm{Cu}}_{2}$ the theoretical bond length and vibrational frequency are found to be in good agreement with experiment. Densities of states and core-level shifts are analyzed to display cluster-size effects. Charge-density maps are used to display the buildup of metallic bonding charge with increasing particle size.

The Solid Angle of a Plane Triangle

Abstract: An analytical expression is presented for the solid angle subtended by a plane triangle at some arbitrary point in space. Using this expression, the time required for numerical computation is cut down to one third.

Discourse Analysis: Its Development and Application to the Structure of News

Abstract: Developments in the last decade within such areas as text linguistics and, more generally , within the growing interdisciplinary study of discourse, have potential applications for the systematic analysis of mass media messages. Discourse analysis can make more explicit the classical approaches to \"content analysis.\" It can also stimulate a research paradigm within mass communication that sees textual analysis not only as a method of research—for example, in the study of media effects—but also as an autonomous endeavor toward the construction of a sound theory of media discourse. Because the study of discourse has become a large field in the past ten years, my discussion here must be limited to those aspects of discourse analysis that seem most relevant for the study of media discourse. Thus, I will pay little attention to those properties of discourse that can be characterized in terms of linguistic grammar in the strict sense, such as the syntax and semantics of (isolated) sentences. Rather, I will be concerned with more specific textual structures that have been neglected in linguistics. Similarly, I cannot go into the details of stylistic and rhetorical analysis of media discourse, although much work in this área still needs to be done. Finally, I will also limit my application to news discourse in the press, thereby neglecting TV, film, and radio discourse, the role of images in audiovisual forms of discourse, and other types of newspaper discourse such as advertisements and commentaries.

Immunocompetent cells in psoriasis. In situ immunophenotyping by monoclonal antibodies.

Abstract: Immunocompetent cells in exacerbating untreated psoriasis vulgaris skin lesions were immunophenotypically studied by the application of a selection of monoclonal antibodies in a two-stage immunoperoxidase technique. Epidermal changes include: focal accumulation of immunoglobulins in the stratum corneum, as demonstrated by a mixture of monoclonal anti-kappa and anti-lambda antibodies; focal accumulation of OKM-1 positive but Mo-2 negative cells high in the epidermis, reflecting granulocytes in Munro's abscesses; a marked decrease in epidermal Langerhans cells with focal abnormal clumping and smaller dendrites, as demonstrated by monoclonal anti-HLA-DR and anti-T6 (OKT-6) antibodies; and, sporadic exocytosis of mainly T1 (Leu-1), T8 (Leu-2a) positive suppressor/cytotoxic T lymphocytes. The dermal infiltrates were found to consist mainly of partically activated T1 (Leu-1), T4 (Leu-3a) positive T-helper/inducer cells with a smaller compartment of T1 (Leu-1), T8 (Leu-2a) positive suppressor/cytotoxic lymphocytes. These cells were found in close apposition to T6 (OKT-6), HLA-DR positive Langerhans cells and further accompanied by a minor compartment of OKM-1, Mo-2 positive monocytes. No B-cells or plasma cells could be demonstrated in the dermis. Natural killer cells were observed only incidentally. These results fit best with the hypothesis that psoriasis is a chronic inflammatory condition as a result of persistent stimulation of T cells by immunogen(s) of epidermal origin.

Characterization of ferric reducing activity in roots of Fe-deficient Phaseolus vulgaris

Abstract: Iron-deficient bean plants (Phaseolus vulgaris L. cv. Prelude) exhibited a ferric reducing activity in the roots, with kinetics characteristic for matrix-bound enzymes: the reaction rate was proportional to substrate (Fe-EDTA) concentration until 100 μM, and at higher concentrations it leveled off to a maximum; the Lineweaver-Burk plot yielded a non-linear relationship between rate −1 and substrate −1. The Arrhenius plot yielded apparent activation energies which were dependent on substrate concentration. No evidence was obtained for the secretion by roots of a low molecular weight metabolite involved in the reduction of iron prior to its uptake. The results are interpreted to indicate that the ferric reducing activity in the roots of iron-deficient bean plants is located in an enzyme in the plasmalemma of the cortex or epidermis cells.

Growth of chromosome ends in multiplying trypanosomes

Abstract: Some of the genes for the variant surface glycoproteins of trypanosomes are located close to a discontinuity in the DNA, presumably a chromosome end We show here that DNA fragments containing these telomeres increase in length in multiplying trypanosomes at a rate of about 10 base pairs per division We argue that chromosome growth may not be restricted to trypanosomes and could explain the heterogeneity of telomeric DNA fragments observed in some other organisms

Relation between isometric force and stimulus rate in cat's hindlimb motor units of different twitch contraction time

Abstract: The relation between isometric force and rate (or pulse interval) of repetitive stimulation was studied for 77 motor units from m. peroneus longus of the cat. The units were activated by constant-frequency bursts of 1 s, and the stimulus interval needed for producing half the maximum tension was strongly correlated to twitch contraction time (twitch CT, non-potentiated values 13–42 ms). This remained true for comparisons within groups of fast and slow units respectively (fast/slow classification according to criteria of Burke et al. 1973). A mean contractile force of half maximum amplitude (0.5 Po) was produced by repetitive stimuli with a pulse interval of about 1.5 CT in fast and 2 CT in slow units. Among both kinds of unit, however, these stimulus rates corresponded to pulse intervals of about 1.4 times the half-relaxation time of the twitch. At half-maximum force, the rise of tension per Hz rise of stimulus frequency was about 2.5% Po for fast and 5.8% Po for slow units. Fast-twitch fatigue-sensitive (FF) and twitch fatigue-resistant (FR) units showed similar tension-frequency relations. Comparisons to results from m. gastrocnemius medialis showed that, for corresponding types of fast units (FF units), the twitch CT tended to be about 25% longer for gastrocnemius than for peroneus. The stimulus rate needed for a half-maximum contraction was, however, not lower for FF units from gastrocnemius than for those from the peroneus muscle.

Epidural analgesia and anticoagulant therapy. Experience with one thousand cases of continuous epidurals.

Abstract: One thousand lumbar epidural blocks in 950 patients undergoing vascular surgery are reported. All patients were receiving oral anticoagulants pre-operatively. Mean thrombotest (TT) was 19.3% (normal range 70-130%). During surgery intravascular heparin was administered. At the end of surgery, the kaolin cephalin clotting time (KCCT) was 68 (+/- 0.8) seconds (normal range 35-60 seconds), and partial thromboplastin time (PTT) was 536 (77.9%, normal control of 100%). Despite the anticoagulant therapy, no side effects were observed in any patient which could be related to haemorrhage or haematoma formation in the epidural space. It is concluded that, provided adequate precautions are taken, epidural analgesia can be safely used in patients receiving anticoagulant therapy.

Influence of muscle architecture on the length-force diagram of mammalian muscle

Abstract: The functions and geometrical characteristics of a pennate and a parallel-fibered muscle in rats are quantified and compared to each other. The pennate medial gastrocnemius and the more parallel fibered semimembranosus are investigated in fourteen male Wistar rats. The length force diagram, twitch time characteristics and muscle architecture are quantified. In the parallel fibered semimembranosus the length of the muscle fibres is about 70% of the muscle optimum length (the length at which the muscle performs maximal active force), while in the pennate fibered gastrocnemius the length of the muscle fibres is 36% of the muscle optimum length. The active length force diagrams normalized with respect to the muscle optimum length show considerable differences between semimembranosus and gastrocnemius: The normalized active length force diagram runs from about 71%-129% of the muscle optimum length for the semimembranosus and from about 82-118% for the gastrocnemius. The latter muscle also has a steeper normalized passive length force curve and produces more active tetanic force per gram muscle (877 g/g for gastrocnemius versus 379 g/g for semimembranosus). No differences between the semimembranosus and gastrocnemius are found with respect to the passive tension at twitch optimum length (38 g/cm2 versus 32 g/cm2), the maximal active tension (1.27 kg/cm2 versus 1.18 kg/cm2) and the twitch contraction time at twitch optimum length (43.8 ms versus 48.4 ms). It is concluded that several functional characteristics show a linear relationship with the index of architecture, a measure for the muscle architecture, while others (especially time and tension characteristics) are independent of muscle architecture.

Spheroids at the Cretaceous-Tertiary boundary are altered impact droplets of basaltic composition

Abstract: Sand-size spheroids of K-feldspar in the Cretaceous-Tertiary (C-T) boundary clay at Caravaca, southern Spain, were interpreted by Smit and Klaver as having solidified from a melt resulting from the impact of a large extraterrestrial body. Sand-size spheroids of K-feldspar, glauconite, and magnetite-quartz have been found in the C-T boundary clay in northern Italy, and spheroids of K-feldspar and pyrite were found in the boundary clay at Deep Sea Drilling Project Site 465A, in the central Pacific. These spheroids have textures similar to those of rapidly crystallized feldspar and mafic silicates. They are interpreted as diagenetically altered microcrystalline spherules of basaltic composition produced by the impact of a large asteroid in an ocean basin at the end of the Cretaceous. They are analogous to the glassy microtektites produced by impacts on more siliceous target rocks. 21 references, 4 figures.

Monoclonal antibodies against human platelet glycoprotein IIIa.

Abstract: Summary. Two murine monoclonal antibodies specific for human platelets were prepared and characterized by immunofluorescence, immunoprecipitation and by studying their effect on platelet function. Immunoprecipitation with lysates of normal platelets and platelets from a patient with Glanzmann's thrombasthenia revealed that the monoclonal antibodies were directed against glycoprotein GP IIIa. One of these anti-GP-IIIa antibodies (C17) inhibited both ADP- and collagen-induced platelet aggregation as well as ADP-induced fibrinogen binding to platelets. The other anti-GP-IIIa antibody (C15) also caused a complete inhibition of aggregation with collagen. However, a small, and fully reversible, ‘primary wave’ was observed if the platelets were stimulated with ADP when platelet-rich plasma was used. The ability to bind fibrinogen was unimpaired for platelets incubated with C15. These findings show that C15 and C17 probably recognize different determinants on GP IIIa. Neither of the monoclonal anti-GP-IIIa antibodies blocked the binding to Zwa-positive platelets of human polyclonal anti-Zwa antibodies. This implies that Zwa is different from the epitopes recognized by C15 and C17.

Time delays in the human baroreceptor reflex

Abstract: In 11 normotensive subjects with coronary artery disease, low intensity electrical stimulation of the carotid sinus nerves (CSN) was triggered by the R-wave in the electrocardiogram with an adjustable delay. The latent period was estimated between the start of CSN stimulation and the onset of the reflex-PP-interval prolongation and, during right atrial pacing, the onset of the reflex fall of diastolic arterial pressure and prolongation of the AV-interval. The latency to the reverse changes was determined after switching CSN stimulation off. The PP-interval changes started after a latency of 0.5-0.6 s. This latency was independent of the respiratory phase and it was independent of the directional change of the afferent activity. AV-interval changes started after about 1 s. When heart rate was fixed, arterial pressure changes started after 2-3 s. It is estimated that central processing of baroreceptor afferent activity may require 0.25 s in the human.

Uniform Consistency of Kernel Estimators of a Regression Function under Generalized Conditions

Abstract: In this article we prove uniform consistency of kernel estimators of a multivariate regression function under various assumptions on the distribution of the data. In addition to the usual assumptions that the data are iid and that the distribution of the regressors is absolutely continuous, we consider the cases that some regressors are discrete and the data are either stationary ϕ-mixing themselves or generated by a class of functions of one-sided infinite stationary ϕ-mixing sequences. Moreover, we demonstrate the performance of the kernel estimation method under these generalized conditions by a numerical example.

Disappearance and reappearance of high endothelial venules and immigrating lymphocytes in lymph nodes deprived of afferent lymphatic vessels: a possible regulatory role of macrophages in lymphocyte migration

Abstract: Interruption of the afferent lymphatic vessels of the popliteal lymph node resulted in the disappearance of high endothelial venules (HEV) and immigrating lymphocytes within 3 weeks HEV showed several characteristic morphological changes: the endothelial cells became flattened and less pyroninophilic, the chromatine became condensed and protein synthetizing and secretory cell organelles became scarce At the same time the number of macrophages in the lymph node was severely reduced Injection of sheep red blood cells into such lymph nodes, 6 weeks after operation, resulted in reappearance of HEV and immigrating lymphocytes, and development of many plasma cells and some germinal centres Injection of lipopolysaccharide into the operated lymph nodes resulted in the appearance of many plasma cells and a few poorly developed germinal centres; HEV and immigrating lymphocytes, however, remained almost absent The results show a relationship between the immigration of lymphocytes and the activity of the endothelial cells in the HEV The activation of the latter may occur by mediators released by antigen-stimulated macrophages and T cells Moreover, the morphological features of the HEV are independent of the presence of recirculating lymphocytes

The demise of the Old English impersonal construction

Abstract: Jespersen (1894) was the first to attempt to provide an account of the changes that the Old English (OE) impersonal construction was subject to over a period of time, finally ending in its disappearance from the language. The analysis that he proposed, and that he worked out in greater detail in Jespersen (1927), has essentially been taken over by other linguists writing on the subject since then, the only difference lying in the type of explanation they had to offer for the loss of the construction. It seems to have been generally taken for granted that Jespersen's choice of data on which to base the explanation for the disappearance of the construction is correct. As Tripp (1978: 177) puts it, ‘The discussion of the loss of impersonal constructions has reached a point where additional data seem unlikely to alter competing explanations of their disappearance.’ We have a radically different view of the matter in that we claim that all previous explanations of the loss of the impersonal construction (that we know of) are based on the same incorrect starting-point, i.e. a data base that is unduly limited and consequently an incorrect view of the changes involved in the loss of the construction, therefore inevitably leading to the wrong explanation. Rather than assuming, with Jespersen and others, that ‘impersonal’ verbs had one meaning in OE and another, the converse, meaning in New English (NE), we uphold that in OE both meanings existed side by side, systematically associable with different syntactic constructions.