scispace - formally typeset
Search or ask a question

Showing papers by "University of Amsterdam published in 1984"


Journal ArticleDOI
TL;DR: The influence of contraction stresses, developed during the polymerization of composites, on adhesion to dentin treated with a dentin adhesive was studied for a chemically- and a light-activated microfilled composite, in both linear and 3-D models.
Abstract: The influence of contraction stresses, developed during the polymerization of composites, on adhesion to dentin treated with a dentin adhesive was studied for a chemically- and a light-activated microfilled composite. In both linear and 3-D models. The linear model consisted of an arrangement set up in a tensilometer in which the composites could be applied to a flat dentin surface fixed to the stationary cross-head at one end, and mechanically clamped to the cross-head connected to the load cell at the other end. The increase of the bond strength was measured at different time intervals from the start of mixing and was compared with the developing contraction stress. Throughout the complete polymerization process, the adhesion survived the contraction stress, which is explained by flow relaxation, which can occur sufficiently in this configuration. In the three-dimensional model, the composites are attached to more than two dentin walls. In this situation, flow is severely limited, and contraction stress values can exceed the bond strength, leading to separation. This was demonstrated in Class V cavities. The shape of the cavity is considered to be of great importance in conservation of the composite-dentin bond.

778 citations


Journal ArticleDOI
TL;DR: An arctangent model with three free parameters A(p) = Am(1/2 + tan-1 [p-p0)/p1)/pi explained over 99% of the variance in area with pressure for each aorta, and changes in compliance, characteristic impedance and propagation velocity are equally well described.

574 citations


Book ChapterDOI
01 Jan 1984

516 citations


Journal ArticleDOI
TL;DR: The hardening stresses in wall-to-wall bonded composites were measured and related to calculated values obtained from freely shrinking materials and the conclusion was drawn that the contraction was compensated for by flow instead of internal disruptions.
Abstract: The hardening stresses in wall-to-wall bonded composites were measured and related to calculated values obtained from freely shrinking materials. Since the ultimate tensile strength of the materials contracting under restricted conditions was not lower than that of composites which were not hindered during the polymerization shrinkage, the conclusion was drawn that the contraction was compensated for by flow instead of internal disruptions.

482 citations


Journal ArticleDOI
TL;DR: Both autospectra are equivalent for the considered heart rate data, but that, when relating the heart rate signal to other signals by means of cross spectra, the technique to be used depends on the characteristics of the second signal.
Abstract: Different methods for spectral analysis of the heart rate signal?considered as series of point events?are used in studies on heart rate variability. This paper compares these methods, focusing on the two principal ones: the interval spectrum, i.e., the spectrum of the interval series, and the spectrum of counts, which is related to the representation of the event series as a series of spikes (delta functions). Both autospectra are estimated for experimental heart rate data and are shown to produce similar results. This similarity is proven analytically, and it is shown that for small variations in interval length, the ratio of these spectra is PI(f)/PC(f) = [sin(?f?)/(?f?)]2, with PI and PC the interval spectrum and the spectrum of counts, respectively, f the frequency, and ?the mean interval length. It is concluded that both autospectra are equivalent for the considered heart rate data, but that, when relating the heart rate signal to other signals (e.g., respiration, blood pressure) by means of cross spectra, the technique to be used depends on the characteristics of the second signal.

352 citations


Journal ArticleDOI
TL;DR: The pathogenesis of parental strain T lymphocytes injected into adult F, mice respond to allogeneic MHC antigens and so induce the symptoms of systemic graft v. host disease (GVHD).

342 citations


Journal ArticleDOI
01 Mar 1984-Nature
TL;DR: Dynorphin and some benzomorphans potently and selectively inhibit the release of dopamine from slices of rat corpus striatum, by activating κ-opioid receptors.
Abstract: At least three different families of endogenous opioid peptides, the enkephalins, endorphins and dynorphins, are present in the mammalian central nervous system (CNS). Immuno-cytochemical studies have demonstrated their localization in neurones1–8, which supports the view that these peptides may have a role as neurotransmitters or neuromodulators. However, the target cells and cellular processes acted upon by the opioid peptides are still largely unknown. One possible function of neuropeptides, including the opioid peptides, may be presynaptic modulation of neurotransmission in certain neuronal pathways, for example, by inhibition or promotion of neurotransmitter release from the nerve terminals9–12. Here we report that dynorphin and some benzomorphans potently and selectively inhibit the release of (radiolabelled) dopamine from slices of rat corpus striatum, by activating κ-opioid receptors. In contrast, [Leu5]enkephalin and [D-Ala2, D-Leu5]enkephalin selectively inhibit acetylcholine release by activating δ-opioid receptors.

268 citations


Journal ArticleDOI
TL;DR: In this article, the lattice constants and the X-ray density of ternary tetragonal compounds of the composition R 2 Fe 14 B were determined for R = Y, La, Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Lu.

249 citations


Journal ArticleDOI
TL;DR: Dichloromethylene diphosphonate can be used for temporary elimination of macrophages in the spleen when administered after entrapment in liposomes.
Abstract: Dichloromethylene diphosphonate can be used for temporary elimination of macrophages in the spleen when administered after entrapment in liposomes No comparable effect on the macrophages of the spleen was observed with free dichloromethylene diphosphonate or in the case of empty liposomes Marginal metallophils on the boundary between white pulp and marginal zone as well as macrophages in the marginal zone and red pulp disappeared from the spleen within one day and remained largely absent for about a week After this time cells reappeared slowly, and at approximately four weeks after injection their presence in the spleen did not differ from that in control animals Marginal metallophils and macrophages in the spleen were demonstrated by use of enzyme-histochemical methods and by their capacity to ingest carbon particles

248 citations


Journal ArticleDOI
TL;DR: The maximal power (force times velocity) delivered by the constructed muscles is shown to be almost independent of the architecture of the muscles.
Abstract: A three-dimensional muscle model with complex geometry is described and tested against experimental data. Using this model, several muscles were constructed. These muscles have equal optimum length but differ in architecture. The force exerted by the constructed muscles, in relation to their actual length and velocity of shortening, is discussed. Generally speaking, the constructed muscles with considerable pennation have great fiber angles, a great physiological cross section, a narrow active and steep passive length-force relation, and a low maximal velocity of shortening. The maximal power (force times velocity) delivered by the constructed muscles is shown to be almost independent of the architecture of the muscles. The steepness of the passive length-force relation is determined mainly by the shortest fibers within the group of constructed muscles, wheras maximal velocity of shortening and the width of the active length-force relation are determined mainly by the longest fibers. The validity of the three-dimensional muscle model with respect to some morphological and functional characteristics is tested. Length-force relations of constructed muscles are compared with the actual length-force relations of mm. gastrocnemii mediales and mm. semimembranosi of male Wistar rats. Moreover, actual fiber angle, fiber length, and muscle thickness of three mm. gastrocnemii mediales are compared with values found for constructed muscles. It is concluded that the three-dimensional muscle model closely approximates the actual muscle form and function.

224 citations


Journal ArticleDOI
TL;DR: Initial reports concerning two of the newer agonist opioids, sufentanil and alfentAnil, suggest that they may prove to be suitable alternatives and perhaps provide advantages over morphine and fentanyl in patients with or without cardiovascular disease.
Abstract: In this article, an attempt has been made to review the use of receptor stimulating pure agonist opioids in anesthesia, especially in patients with cardiovascular disease. Particular emphasis has been placed on the use of opioids in high doses to produce anesthesia, techniques that recently have become popular in cardiovascular anesthesia. A major benefit of opioid anesthesia is the cardiovascular stability obtained during induction and throughout operation, even in patients with severely impaired cardiac function. There is a considerable body of evidence to support this claim when fentanyl is used. Anesthetic doses of morphine are associated with a higher incidence of cardiovascular disturbances and other problems, and, therefore, more attention to detail is required in order to achieve adequate anesthesia and hemodynamic stability. Although other opioids have been used as sole or principal agents in anesthesia for cardiovascular surgery, none have gained widespread acceptance. Meperidine, for example, which is widely used in lower (nonanesthetic) doses as a supplement to nitrous oxide in cardiac and noncardiac surgery, has proved unsuitable because of severe hemodynamic disturbances when high doses are given. However, initial reports concerning two of the newer agonist opioids, sufentanil and alfentanil, suggest that they may prove to be suitable alternatives and perhaps provide advantages over morphine and fentanyl in patients with or without cardiovascular disease. Although cardiovascular stability usually can be assured in the chronically sick cardiac patient with opioid anesthesia, this is not always so with the healthier patient, particularly those presenting for coronary artery surgery. A frequently occurring problem in these patients is hypertension during or after sternotomy, which can result in myocardial ischemia and infarction. The incidence of severe hypertension (increases in systolic blood pressure greater than 20% of control values) can be reduced drastically by increasing the dose of opioid, e.g., up to 140 micrograms/kg of fentanyl. However, despite such large doses, some patients will continue to need treatment with vasodilators, inhalation anesthetics, or other supplements at certain periods during cardiovascular operations. The use of very large doses of opioids also will prolong postoperative respiratory depression. High doses of opioids can reduce or prevent the hormonal and metabolic responses to the stress of surgery. However, even very large doses of fentanyl or its newer analogues do not prevent marked increases in plasma catecholamine concentrations in response to cardiopulmonary bypass.(ABSTRACT TRUNCATED AT 400 WORDS)

Journal ArticleDOI
TL;DR: The pharmacokinetics of sufentanil, a new thienyl analogue of fentanyl, were studied in 10 surgical patients and a biexponential equation was sufficient to describe the concentration-time data, yielding a distribution half-life of 4.7 min and an elimination half- life of 117 min.
Abstract: The pharmacokinetics of sufentanil, a new thienyl analogue of fentanyl, were studied in 10 surgical patients. Sufentanil, 5 micrograms/kg, was given intravenously as a bolus injection and plasma concentrations measured at intervals up to 8 h. Plasma sufentanil concentrations decreased rapidly after injection--98% of the administered dose having left the plasma within 30 min. In 9 of the 10 patients, a tri-exponential equation optimally described the sufentanil concentration decay curve, with average (+/-SEM) half-lives for the rapid (pi) and slow (alpha) distribution phases of 1.4 +/- 0.3 min and 17.7 +/- 2.6 min, respectively. The average terminal elimination (beta) half-life was 164 +/- 22 min. The average value for Vd beta was 2.9 +/- 0.2 1/kg, Vdss 1.7 +/- 0.2 1/kg and total plasma clearance 12.7 +/- 0.8 ml X kg-1 X min-1 (935 +/- 50 ml/min). In one patient, a bi-exponential equation was sufficient to describe the concentration-time data, yielding a distribution half-life of 4.7 min and an elimination half-life of 117 min.

Journal ArticleDOI
TL;DR: The influence of increasing molecular size and hydrophobicity on bioaccumulation kinetics in guppies (Poecilia reticulata) was investigated for a series of polychlorinated biphenyls (PCBs) in comparison with other halogenated aromatic compounds.
Abstract: The influence of increasing molecular size and hydrophobicity on bioaccumulation kinetics in guppies (Poecilia reticulata) was investigated for a series of polychlorinated biphenyls (PCBs) in comparison with other halogenated aromatic compounds Extremely low clearance rates were characteristic of the higher chlorinated biphenyls and resulted in a linear accumulation in fish For these compounds, in contrast to more soluble chemicals, direct uptake from water appeared to be less efficient than uptake from contaminated food Hexabromobenzene, octachlorodibenzo‐p‐dioxin and tetradecachloroterphenyl were not accumulated by living fish The importance of food‐chain accumulation (biomagnification) versus direct bio‐concentration is discussed in relation to molecular structure and physico‐chemical properties of organic chemicals

Journal ArticleDOI
TL;DR: The results of this study give rise to the question of whether the combination of carbamazepine, phenobarbitone, valproate, and/or phenytoin has teratogenic activity by accumulation of carbsepine‐10,11‐epoxide or other epoxide intermediates, and stress the need to take metabolic interactions into account when investigating the ter atogenic activity of antiepileptic drugs.
Abstract: Summary: A higher rate of congenital anomalies has been found after prenatal exposure to some combinations of antiepileptic drugs than to the separate drugs. In an earlier study a rate of 58% congenital anomalies was found among infants exposed to carbamazepine plus phenobarbitone plus valproate. In this study an attempt was made to determine whether this specific combination of drugs has teratogenic activity due to metabolic interaction. The epidemiological data were analyzed further. The high rate of congenital anomalies after prenatal exposure to this combination could not be explained by the effects of one or two of these drugs only, nor by additional exposure to phenytoin. Assuming that metabolic interaction in the arene oxide pathway resulting in accumulation of epoxide intermediates of antiepileptic drugs could be responsible for teratogenesis, the ratio of carbamazepine to carbamazepine-10,11-epoxide concentrations in serum was determined in adult patients with epilepsy who were treated with carbamazepine only and with different combinations of phenobarbitone, valproate, and/or phenytoin. For carbamazepine monotherapy the mean ratio was 8.19. For all combinations lower ratios were found, indicating accumulation of carbamazepine-10,11-epoxide. The combination of carbamazepine, phenobarbitone, valproate, and phenytoin showed the lowest ratio (1.94), followed by carbamazepine, valproate, and phenytoin and by carbamazepine, phenobarbitone, and valproate (2.81 and 3.18, respectively). These results give rise to the question of whether the combination of carbamazepine, phenobarbitone, valproate, and/or phenytoin has teratogenic activity by accumulation of carbamazepine-10,11-epoxide or other epoxide intermediates, and stress the need to take metabolic interactions into account when investigating the teratogenic activity of antiepileptic drugs. RESUMEN La exposicion prenatal a algunas combinaciones de drogas antiepilepticas ha producido un indice mas elevado de anomalias congenitas que si se administran separadamente. En un estudio previo se encontro un indice de un 58% de anomalias congenitas en ninos expuestos a carbamazepina + fenobarbital + valproate En este estudio se intenta determinar si esta combinacion especifica de medicaciones tiene actividad teratogenetica debida a interacciones metabolicas. La informacion epidemiologica se analiza con mas detalle. El elevado indice de anomalias congenitas tras la exposicion prenatal a esta combinacion no es posible explicaria por los efectos de una o dos drogas solamente, ni por la administracion adicional de fenitoina. Aceptando que la inter-accion metabolica en la via arene-oxido, de la que surje un acumulo de epoxidos intermediarios de las drogas antiepilepticas, podria ser responsable de la teratogenesis se ha determinado la relacion de concentraciones en suero de carbamazepina/carbamazepina-10, 11-epoxido. Esta determinacyon se realizo en epilepticos adultos que habian sido tratados con carbamazepina solo o combinada con fenobarbital, valproato y/o fenitoina. El cociente medio para la carbamazepina fue 8.19. Para todas las combinaciones se encontraron relaciones mas bajas, lo que indica un acumulo de carbamazepina-10, 11-epoxido. La combinacion carbamazepina + fenobarbital + valproato + fenitoina mostro la relacion mas baja (1.94), seguida de carbamazepina + valproato + fenitoina y carbamazepina + fenobarbital + valproato (2.81 y 3.18 respectivamente). Estos resultados plantean la posibilidad de si la combinacion carbamazepina + fenobarbital + valproato + fenitoina tiene actividad teratogenica por acumulo de carbamazepina-10, 11-epoxido o por otros intermediarios epoxidos. Tambien resalta la necesidad de tener presentes las interacciones metabolicas cuando se investiga la capacidad teratogea de las drogas antiepilecas. ZUSAMMENFASSUNG Nach pranataler Exposition gegenuber Kombinationen von Antiepileptika wird eine hohere Rate kongenitaler Anomalien gefunden als bei Exposition gegenuber einzelnen Medikamenten. In einer fruheren Untersuchung wurden 58% kongenitaler Anomalien bei Kindern gefunden, die einer Kombination von Carbamazepin, Phenobarbital und Valproat ausgesetzt waren. In dieser Untersuchung wird der Versuch gemacht, festzustellen, ob diese spezifische Kombination von Medikamenten eine teratogene Aktivitat aufgrund metabolischer Interaktionen besitzt. Die epidemiologischen Daten wurden weiter analysiert. Der hohe Prozentsatz kongenitaler Anomalien nach pranataler Einwirkung dieser Medikamentenkombination konnte nicht als Wirkung von einem oder von zwei dieser Medikamente Oder gar duch eine zusatzliche Exposition gegenuber Phenytoin erklart werden. In der Annahme, das metabolische Interaktionen bei der Oxydation zur Anhaufung von Epoxyd-Zwischenprodukten antiepileptischer Medikamente fuhrt, die teratogen wirken, wurde das Verhaltnis von Carbamazepin zu Carbamazepm-10, 11-Epoxyd im Serum von Erwachsenen mit Epilepsie untersucht, die mit Carbamazepin alleine und mit verschiedenen Kombinationen wie Phenobarbital, Valproat und/oder Phenytoin behandelt wurden. Fur die Carbamazepin-Monotherapie betrugt das mittlere Verhaltnis 8, 19. Fur alle Kombinationen wurden niedrigere Quotienten gefunden, die fur eine Akkumulation von Carbamazepin-10, 11-Epoxyd sprechen. Die Kombination von Carbamazepin, Phenobarbital, Valproat und Phenytoin zeigte den niedrigsten Quotienten (1,94); dann folgten Carbamazepin, Valproat und Phenytoin, schliesich Carbamazepin, Phenobarbital und Valproat (2,81, bzw. 3,18). Diese Ergebnisse lassen die Frage entstehen, ob die Kombination von Carbamazepin, Phenobarbital, Valproat und/oder Phenytoin durch Anhaufung von Carbamazepin-10, 11-Epoxyd oder andere Epoxyd-Intermediar-stoffe teratogen wirken. Sie betonten die Notwendigkeit, metabolische Interaktionen in Betracht zu Ziehen, wenn man die teratogene Aktivitat antiepileptischer Medikamente untersucht.

Journal ArticleDOI
TL;DR: An initially uniform Holcus lanatus-dominated sward came partly under hay-making and partly under sheep-grazing, giving rise to a macro-pattern of various plant communities and a micro-pattern developed in the grazed area, which was absent underHay-making.
Abstract: An initially uniform Holcus lanatus-dominated sward came partly under hay-making and partly under sheep-grazing. Preferential grazing by sheep resulted in grazing at different intensities giving rise to a macro-pattern of various plant communities. Besides this macro-pattern a micro-pattern developed in the grazed area, which was absent under hay-making. In the micro-pattern short, heavily grazed areas alternated with taller, lightly grazed patches, both having the same species composition. The heavily grazed area was characterized by equal amounts of monocots and dicots. The lightly grazed patches were dominated by Agrostis tenuis, and had a large amount of litter which probably causes the absence of mosses. The protein percentage of green material is higher in the heavily grazed areas than in the lightly grazed patches. Sequential charting indicated that the micro-pattern was more or less stable. An interaction between the vegetation micro-pattern and grazing patterns is suggested. Heavy grazing results in forage with a high protein content and hence attracts animals. Light grazing results in forage with a relatively low protein content, animals avoid the area and litter accumulates.

Journal ArticleDOI
TL;DR: In this paper, the influence of the factors Time Pressure (present or absent) and Focus of Attention (on information or on grammar) on the correct use of two Dutch word-order rules in the speech of 32 adult learners of that language was investigated.
Abstract: The first question of this study deals with the influence of the factors Time Pressure (present or absent) and Focus of Attention (on information or on grammar) on the correct use of two Dutch word-order rules in the speech of 32 adult learners of that language. In an experimental repeated measures design using a story retelling task. Attention had a significant effect, but Time did not. The second question deals with the relation between explicitness of rule knowledge, assessed in an interview, and rule application, elicited in the experiment. Although the learners without explicit knowledge of the two word-order rules made more errors in the story retelling task than learners with explicit knowledge, they were influenced by Time and Attention to the same extent as the learners with explicit knowledge. The results of this study are discussed in terms of Krashen's Monitor Theory and in terms of an information-processing approach that distinguishes executive control from metacognitive knowledge.

Journal ArticleDOI
TL;DR: The activity of peroxisomal enzymes was studied in human liver and cultured human skin fibroblasts in relation to the finding that morphologically distinct peroxISomes are not detectable in patients with the cerebro-hepato-renal (Zellweger) syndrome.

Journal ArticleDOI
TL;DR: The Zellweger syndrome constitutes the first inborn error of metabolism with a deficiency in an enzyme involved in phospholipid biosynthesis, and the findings suggest a method for prenatal diagnosis of this disease.

Journal ArticleDOI
TL;DR: This research presents a novel and scalable approach called “SmartCardiothoracic Cardiology,” which aims to provide real-time information about the dynamic response of the immune system to certain types of organ failure.
Abstract: 1 Department of Paediatrics, Cardiothoracic Institute, Brompton Hospital, London, England; 2 Department of Pathology, Wilhelmina Gasthuis, University of Amsterdam, The Netherlands; 3 Department of Cardiology, Hospital for Sick Children, Toronto, Canada; 4 Thoracic Unit, Hospital for Sick Children, London, England; 5 Department of Pediatric Cardiology, Centro Ramon y Cajal, Madrid, Spain; 6 Institute of Child Health, University of Liverpool, Royal Liverpool Children's Hospital, Liverpool, England; and 7 Department of Paediatrics, Guy's Hospital, London, England

Journal ArticleDOI
TL;DR: The human proerythroblastic leukemia cell-line K562 was induced to differentiate into megakaryocytic cells by 12-O-tetradecanoylphorbol-13-acetate (TPA), and monoclonal anti-platelet antibody appeared to react with K562 cells after induction, indicating that GP IIIa expressed on TPA-induced K562 differs structurally from that on normal platelets.

Journal ArticleDOI
TL;DR: In this paper, the symmetries of the staggered fermion formulation and the construction of local hadron fields on the lattice were investigated and the one-loop self-energy was calculated with a general non-degenerate mass matrix and the implications of the results were discussed.

Journal ArticleDOI
TL;DR: Cytoplasmic markers demonstrated that these small megakaryocyte precursors were themselves heterogenous by morphological criteria, and double‐fluorescent labelling demonstrated that the different platelet markers were coexpressed in a large majority of cells.
Abstract: Summary. Human megakaryocyte colonies were grown from the bone marrow in plasma clot or methyl cellulose cultures. Maturation of the megakaryocytic cells was sequentially studied from day 5 to day 16 of culture by fluorescent labelling with a panel of monoclonal and polyclonal antibodies against different platelet glycopro-teins (Gp), PI AI antigen, factor VIII RAg platelet factor 4 (PF 4), fibrinogen and platelet-derived growth factor (PDGF). Expression of Gp Ib was also studied by immunogold technique at electron microscopy. The first cells identifiable by these antibodies were found at day 5 of culture. They had the size of a lymphocyte. These small megakaryocyte precursors already expressed all the platelet antigens, HLA-DR and transferrin receptors and were devoid of erythroid or myeloid markers. Among the platelet antigens, Gp IIIa was the most sensitive marker for the identification of these precursors. However, double-fluorescent labelling demonstrated that the different platelet markers were coexpressed in a large majority of cells. Interestingly, cytoplasmic markers demonstrated that these small megakaryocyte precursors were themselves heterogenous by morphological criteria. During maturation, expression of Gps, particularly of Gp Ib, increased while the labelling pattern of anti factor VIII RAg and anti PF 4 antibodies switched from diffuse to granular staining. PDGF could also be detected in the megakaryocytes grown in culture.

Journal ArticleDOI
TL;DR: The results suggest that during the transition from low-to-high growth-irradiance levels chlorophyll a is diluted by cell division and is not actively degraded, similar to other planktonic diatom groups.
Abstract: The marine planktonic diatom Thalassiosira weisflogii was grown in turbidostat culture under both continuous and 12 hL: 12 hD illumination regimes in order to study the kinetics of adaptation to growth-irradiance levels. In both illumination regimes adaptation to a higher growth-irradiance level was accompanied by an increase in cell division rates and a decrease in chlorophyll a cell-1. The rates of adaptation for both processes, derived from first order kinetic analysis, equaled each other in each experiment. The results suggest that during the transition from low-to-high growth-irradiance levels chlorophyll a is diluted by cell division and is not actively degraded. Introduction of a light/dark cycle lowered the rate of adaptation. In transitions from high-to-low growth-irradiance levels there was a sharp drop in growth rates and a slow increase in chlorophyll a cell-1 under both continuous and intermittent illumination. In the 12 hL:12hD cycle there was a circadian rhythm in chlorophyll a cell-1, where cellular chlorophyll contents increased during the light cycle and decreased during the dark cycle. This circadian rhythm was distinctly different from light intensity adaptation. For kinetic analysis of light intensity adaptation in a 12 hL: 12 hD cycle, the circadian periodicity was separated from the light intensity response by subjecting the data to a Kaiser window optimization digital filter. Kinetic parameters for light-intensity adaptation were resolved from the filtered data. The kinetics of lightintensity adaptation of marine phytoplankton are discussed in relation to their spatial variations and time scales of mixing.

Journal ArticleDOI
01 Dec 1984-Geoderma
TL;DR: In this article, simple procedures for estimating soil aggregate stability by the water-drop method and ultrasonic dispersion are compared for a wide range of soils from Colombia, Kenya, Lesotho, Luxembeurg and Spain.

Journal ArticleDOI
TL;DR: Existing, qualitative notions with respect to the way in which enzyme properties control metabolism are discussed in the light of the control analysis developed by H. Kacser and J. A. Burns, and recent experimental data.
Abstract: Existing, qualitative notions with respect to the way in which enzyme properties control metabolism are discussed in the light of the control analysis developed by H. Kacser and J. A. Burns ((1973) in: Rate Control of Biological Processes, Davies DD, ed., Cambridge University Press, pp. 63–104) and R. Heinrich and T. A. Rapoport ((1974) Eur. 3. Biochem.42, 89–95), and recent experimental data. Points at which the existing notions should be adjusted are: (i) Metabolic control is shared by enzymes rather than confined to one rate-limiting enzyme per pathway. (if) Whether an enzyme exercises strong control on a flux cannot be deduced solely from its own properties, nor is it directly related to its distance from equilibrium. With respect to metabolic control, enzymes should be classified into four groups, rather than two (reversible versus irreversible). (iii) The distribution of control among the enzymes depends on the metabolic conditions. (iv) Control structures of metabolic pathways probably differ with the function of that pathway.

Journal ArticleDOI
TL;DR: Research findings do suggest that the degree of periodontal breakdown increases with age, that with increasing age inflammation of the periodontium tends to develop more rapidly and that in the process of aging theperiodontium shows a slower rate of wound healing, but these phenomena are overshadowed by the patients' susceptibility toperiodontal disease.
Abstract: It is generally known that the degree of periodontal breakdown increases with increasing age. The extent to which aging of periodontal tissues plays a part in this respect poses a question which is yet to be answered. Aging proves to be accompanied by a variety of periodontal changes. The periodontal tissues themselves show evidence of aging, there are indications that the composition of the plaque changes, and the reaction of the periodontium to the presence of plaque probably changes as well. There is as yet no sufficient evidence of a physiological apical migration of the epithelial attachment in human subjects. It seems plausible that periodontal breakdown can occur only in the presence of plaque with consequent inflammation of the periodontium, or as a result of trauma. Whether changes in plaque composition with age exert any influence on the course of periodontal breakdown is uncertain: the data available are not yet sufficient to warrant definite conclusions. The same applies to the influence which a changing reaction of the periodontium to the presence of plaque may have on the course of periodontal breakdown. Research findings do suggest that the degree of periodontal breakdown increases with age, that with increasing age inflammation of the periodontium tends to develop more rapidly and that in the process of aging the periodontium shows a slower rate of wound healing. However, these phenomena are overshadowed by the patients' susceptibility to periodontal disease. This implies that (1) the susceptibility to periodontal disease is more significant for the rate of periodontal destruction than the length of time plaque is present (the age effect) and (2) the greater the susceptibility to periodontal disease, the slower the rate of wound healing and the more rapidly inflammation of the periodontium tends to develop.

Journal ArticleDOI
TL;DR: Results indicate that NADPH is the electron donor for the high Fe(III) reduction activity found in iron-deficient roots, a process that is part of the Fe-uptake mechanism.
Abstract: Pyridine nucleotides were determined in lateral roots of iron-deficient and iron-sufficient Phaseolus vulgaris L. cv Prelude. In iron-deficient plants, total NADP per gram fresh weight and the NADPH/NADP + ratio were twice the values found in iron-sufficient plants. The NADPH/NADP + ratio in iron-deficient plants was considerably lowered after a 2 minute incubation in 1 millimolar ferricyanide. Total NAD was not influenced by growth conditions and was mainly present in oxidized form. These results indicate that NADPH is the electron donor for the high Fe III reduction activity found in iron-deficient roots, a process that is part of the Fe-uptake mechanism.

Journal ArticleDOI
TL;DR: The cardiovascular consequences of decreased systemic compliance in six closed chest anaesthetised dogs where ascending aortic flow transducers and left ventricular crystals had previously been implanted caused changes in the low frequency range of the input impedance: moduli increased and phase angles became more negative.
Abstract: Arterial compliance is part of the load faced by the heart. Decreased compliance increases this load. We have studied the cardiovascular consequences of decreased systemic compliance in six closed chest anaesthetised dogs where ascending aortic flow transducers and left ventricular crystals had previously been implanted. A stiff tube was put into the abdominal aorta from the left flank and moved to the ascending aorta. Inflation of a cuff on the proximal end of the tube forced the heart to eject into a non-compliant outflow conduit. The distal end of the tube was connected to the distal aorta and, via a pump, to a carotid artery where mean pressure was kept above 80 mmHg. We measured systemic pressures (catheter-tip manometer), cardiac output (electromagnetic flowmeter) and either left ventricular end-diastolic pressure (fluid filled catheter, Statham P23Db) or left ventricular diameter (ultrasound transit time method). From these variables we calculated systemic compliance and input impedance. A 35% decrease in compliance caused a 12% increase in systolic, and a 12% decrease in diastolic pressure while mean pressure and cardiac output did not change significantly. With a decrease in compliance of 63% systolic pressure increased by 18%, while diastolic pressure decreased by 24%. Mean pressure did not change significantly but cardiac output fell by 21%. In both groups of altered compliance peripheral resistance rose slightly but this was not significant. Decreased compliance mainly caused changes in the low frequency range of the input impedance: moduli increased and phase angles became more negative. We conclude that changes in arterial compliance alone cannot explain “isolated” systolic hypertension.

Journal ArticleDOI
TL;DR: A new, reliable and accurate three-dimensional measuring technique for quantitative evaluation of the wear resistance of posterior dental restorations was developed and promising wear values were obtained for the hybrid radioopaque composite resin, Miradapt.

Journal ArticleDOI
TL;DR: The review presented here covers metastatic local and systemic disease secondary to the accumulation of plaque or the formation of other pathogenic microbial depots in the mouth, to wit metastatic infection due to transient bacteremia, metastatic immunological injury, and metastatic toxic injury.
Abstract: The review presented here covers metastatic local and systemic disease secondary to the accumulation of plaque or the formation of other pathogenic microbial depots in the mouth. At least 3 pathways may link oral infection to secondary disease, to wit metastatic infection due to transient bacteremia, metastatic immunological injury, and metastatic toxic injury. The available evidence is presented and examples are provided. They concern among others such divergent diseases as acute bacterial myocarditis, infective endocarditis, brain abscess, uveitis and iridocyclitis, trigeminal and atypical facial neuralgia, unilateral facial paralysis, fever of "unknown' origin, and neutrophil dysfunction.