Showing papers by "University of Amsterdam published in 1974"

Experiments on simple magnetic model systems

Abstract: “…. For the truth of the conclusions of physical science, observation is the supreme Court of Appeal….” (Sir Arthur Eddington, The Philosophy of Physical Science.) In this paper we shall review the theoretical and experimental results obtained on simple magnetic model systems. We shall consider the Heisenberg, XY and Ising type of interaction (ferro and antiferromagnetic), on magnetic lattices of dimensionality 1, 2 and 3. Particular attention will be paid to the approximation of these model systems in real crystals, viz. how they can be realized or be expected to exist in nature. A large number of magnetic compounds which, according to the available experimental information, meet the requirements set by one or the other of the various models are considered and their properties discussed. Many examples will be given that demonstrate to what extent experiments on simple magnetic systems support theoretical descriptions of magnetic ordering phenomena and contribute to their understanding. It will a...

Interpretation of the polarization of Venus

Abstract: The linear polarization of sunlight reflected by Venus is analyzed by comparing observations with extensive multiple scattering computations. The analysis establishes that Venus is veiled by a cloud or haze layer of spherical particles. The refractive index of the particles is 1.44±0.015 at λ=0.55 μm with a normal dispersion, the refractive index decreasing from 1.46±0.015 at λ=0.365 μm to 1.43±0.015 at λ=0.99 μm. The cloud particles have a narrow size distribution with a mean radius of ∼1 μm; specifically, the effective radius of the size distribution is 1.05±0.10 μm and the effective variance is 0.07±0.02. The particles exist at a high level in the atmosphere, with the optical thickness unity occurring where the pressure is about 50 mb. The particle properties deduced from the polarization eliminate all but one of the cloud compositions which have been proposed for Venue. A concentrated solution of sulfuric acid (H2SO4-H2O) provides good agreement with the polarization data.

The Conducting Tissues in Congenitally Corrected Transposition

Abstract: The histopathological findings are reported in 11 cases of congenitally corrected transposition. For the purposes of this investigation, only hearts with a well-formed septum separating two ventricular sinuses were classed as corrected transposition. We did not, therefore, study any examples of single ventricle with inverted outlet chamber. Five of the cases formed the basis of a preliminary report, in which the distribution of conducting tissues in the anomaly was shown to differ from that reported in previous investigations. The six new cases confirmed this distribution. Thus, in all cases, the connecting atrioventricular node was anteriorly situated in the right atrium at the lateral junction of pulmonary and mitral valves. An anteriorly situated bundle descended into the morphologically left ventricle (right-sided) and encircled the anterolateral quadrant of the pulmonary outflow tract before descending on the anterior septum and bifurcating. The bundle branches were inverted. This distribution was ob...

A Combined Morphological and Electrophysiological Study of the Atrioventricular Node of the Rabbit Heart

Abstract: Thirteen rabbit atrioventricular nodes were studied both morphologically and electrophysiologically. Two of these nodes were subsequently reconstructed in three-dimensional fashion. From the morphological standpoint, it was shown that the atrioventricular node was divided into a smaller enclosed portion and a larger open portion by a fibrous collar derived from the central fibrous body. Three distinct nodal cell types were identified within these nodal segments. The open node was mostly occupied by transitional cells which merged proximally with the atrial myocardium. As they entered the enclosed node, some of these transitional cells merged into a knot of midnodal cells. Others passed circumferentially round this knot and together with the midnodal cells, joined with a tract of lower nodal cells. The latter cells were continuous with the His bundle anteriorly, but they also extended into the open node posteriorly. It was possible to correlate the activation sequence of the node accurately with the disposition of these cells. Using both reconstructions and techniques to mark cells from which action potentials had been recorded, it was shown that the transitional cells correlated with the AN zone of the node. Cells with N potentials were located in the environs of the midnodal cell knot. The anterior portion of the lower nodal cells correlated with the NH nodal zone. The posterior extension of the lower nodal cells and the overlay fibers of the anterior transitional cells both functioned as dead-end pathways. Histologically distinct tracts were not identified within the internodal atrial myocardium.

On the interdigitating cells in the thymus-dependent area of the rat spleen: a relation between the mononuclear phagocyte system and T-lymphocytes.

Abstract: Light- and electron microscopic studies reveal that the peri-arteriolar lymphocytic sheath of the rat spleen can be divided into two areas. The central area contains small lymphocytes, interdigitating cells (IDC, light staining cells with extensive cytoplasmic interdigitations) and some scattered reticulum cells. The peripheral area contains a mixed population of lymphocytes and circumferentially oriented reticulum cells. It is shown that only the central area of the peri-arteriolar lymphocytic sheath is thymus-dependent. In neonatally thymectomized rats, before interdigitating cells appear, monocytes and promonocytes reside in this area. It is suggested that the IDC are part of the mononuclear phagocyte system (Langevoort et al., 1970). They probably form the micro-environment necessary for the differentiation and proliferation of T-cells. The analogies between IDC, epithelioid cells and the macrophages in the migration inhibition test are discussed. The hypothesis is put forward that these cells are similar in ultrastructural and functional aspects because all three are macrophages under the influence of humoral factors from T-cells, such as migration inhibition factor.

Semipermeable membranes for improving the histochemical demonstration of enzyme activities in tissue sections

Abstract: Improved histochemical techniques for the demonstration of nonspecific esterase and β-glucuronidase activities in tissue sections are described. With these techniques a semipermeable membrane is interposed between the incubating solution and the tissue sections preventing diffusion of enzymes into the medium during incubation. Fixation of the tissue sections in order to minimize enzyme diffusion but which also causes partial inactivation of the enzymes is no longer necessary. In the histochemical systems the enzymes catalyze the hydrolyzes of 1-naphthol acetate and naphthol AS-BI β-D-glucuronide respectively. The localization of the enzymes is visualized by means of simultaneous coupling of the released naphthol with hexazotized pararosanilin. Problems involved in the histochemical demonstration of the enzymes are discussed.

Factors Influencing Prognosis of Bundle Branch Block Complicating Acute Antero-Septal Infarction

Abstract: Of 50 consecutive patients with bundle branch block (BBB) complicating acute antero-septal infarction, 37 died in hospital Patients with BBB of delayed onset or BBB of short duration had a significantly lower mortality His bundle recordings were made in 35 patients without pulmonary edema or shock at the time of appearance of BBB Thirteen of 16 patients with prolonged H-V intervals died compared to nine of 19 with normal H-V intervals (P<005) In patients with bifascicular block, 11 of 15 with prolonged H-V intervals developed complete A-V block compared to one of ten with normal H-V intervals (P < 0005)

Contributions to the Optimal Use of Human Blood

Abstract: . The influence of different variables on the yield of factor VIII in cryoprecipitate as prepared in the Central Laboratory of the Netherlands Red Cross Blood Transfusion Service, was studied. The following conclusions may be drawn: 1 In case blood should be stored, the use of the anticoagulant solution acid citrate dextrose (ACD) is preferable to citrate phosphate dextrose (CPD) or trisodium citrate (TSC). 2 The temperature of stored whole blood should not decrease below 8 °C because of a spontaneous precipitation of factor VIII from blood (and plasma) below this temperature. 3 Cryoprecipitate derived from rapidly frozen plasma (1 min) contains a decreased amount of proteins in comparison with cryoprecipitate prepared from slowly frozen plasma (45 min to 4 h). On the other hand, equal amounts of factor VIII activity were obtained in the precipitate after freezing of plasma at varying rates. 4 Rapid thawing of plasma results in both higher yields of factor VIII procoagulant activity and a higher specific activity of this factor in the resulting cryoprecipitate. 5 The sedimentation of cryoprecipitate is completed after 5 min centrifugation at 1,500 g. 6 At temperatures higher than 8 °C, cryoprecipitated factor VIII starts dissolving into the supernatant plasma or in buffer. 7 Factor VIII in lyophilized cryoprecipitate is stable at room temperature. At devated temperatures it rapidly looses its activity. 8 Evidence was obtained that the improvements which are introduced in the preparation of factor VIII do not lead to a product which is less stable in vitro as well as in vivo.

The pathology of pulmonary veno-occlusive disease

Abstract: The histopathology of the lungs is described in 13 patients with pulmonary veno-occlusive disease. The patients were mostly children or young adults and there was no sex preference as is seen in primary pulmonary hypertension.

Relations Between Gill Structure and Activity in Fish

Abstract: From well over 200 papers quantitative data concerning gill structure, oxygen consumption and activity in fish were compilated. These data were corrected, whenever necessary, for a body weight of 200 g and a surrounding temperature of 20° C, which enabled us to compare various species. The standard metabolism (expressed as the standard-oxygen-uptake) appeared to be a fairly good quantitative measure for the general activity of a fish species and was used as such. Comparing a series of species increasing in activity (in regard with behaviour), one finds that oxygen consumption does rise more slowly than the quotient of gill surface and membrane thickness. According to FICK'S law, this is due to the fact that under standard conditions in active fishes a considerably lower difference is maintained between the oxygen in the water and that in the blood than in slow-moving fishes. Partially this may be due to the greater resistance of the gills of active fishes, partially to the way of breathing of the very active species (ram-ventilation). In the hypothetical standard fish of 200 g, the gill surface and the thickness of the gill membrane appeared to be linear inversely proportional. Probably the gill membrane must have a minimum thickness in order to be equal to the defence against noxious particles, while the density of the secondary lamellae is limited by the membrane thickness. Data covering all of the examined parameters were known for only 9 species. The quantitative relations inferred from these were neither completely confirmed nor contradicted by comparing them with insufficiently documented species. If required, the quantitative relations may be expressed by the following formulas: in which: D = thickness ofgill membrane (μ) A 200 = gill surface of a standard fish (mm 2 /g) dP = difference in partial oxygen pressure over the gill membrane (atm) M 200 = oxygen consumption of a standard fish (mg/kg/hr) Applying our results to benthic species, it is conceivable that, while slowness of locomotion in an environment with a large supply of slow moving or even sessile food formed no hindrance, the sequence of causes and effects during gill evolution is as follows. Basic was a considerable thickness of the gill membrane, indispensable as defence against scouring particles. This room-consuming quality of the membrane limited the number of secondary lamellae, which put a limit to the disposable surface. And this limited surface, in its turn put a limit to the oxygen absorption and, thereby, to the activity of the fish.

Encapsulation of foreign materials experimentally introduced into the freshwater snail Lymnaea stagnalis. An electron microscopic and autoradiographic study.

Abstract: The encapsulation of experimentally introduced material was studied in Lymnaea stagnalis. Abiotic (yvelon sponge) and biotic materials (autografts, allografts and xenografts) were implanted into the cephalopedal blood sinus.

Recent advances in pyrolysis mass spectrometry of complex biological materials.

Abstract: Nonvolatile biological materials, such as biopolymers or even whole cells, can be made accessible to mass spectrometric analysis by pyrolysis techniques. In principle, this enables differentiation, classification and identification of these materials. Moreover, pyrolysis mass spectrometry can provide a general picture of the chemical composition and structure of the sample analysed. During the past few years we have investigated several pyrolysis techniques in combination with different mass spectrometric methods. These investigations included Curie point pyrolysis, infrared laser pyrolysis, low voltage electron impact ionization, field ionization1 and pyrolysis field desorption.1 Pyrolysis reactions were performed either at the gas inlet or directly at the ion source. The relative merits of these different experimental approaches are discussed. Additionally, examples of various applications, such as computer identification of bacteria and qualitative analyses of biopolymers, are given.

DNA‐DNA Hybridization on Nitrocellulose Filters

Abstract: 1. Comparison of DNA-DNA filter hybridization using either denaturated duplex DNA or artificial mixtures of the two complementary strands of T7 DNA shows that the competing renaturation reaction has two effects: (a) sequestering of 20–30% of the input DNA as duplex, unavailable for hybridization, and (b) hybridization of partially renatured DNA as a concatenane to the filter-bound DNA. 2. Experiments using artificial mixtures of 32P-labelled and 3H-labelled L and H strands of T7 show that 10–20% of the total hybrid bound results from concatenation. With a 1:1 input ratio of complementary strands in solution, 10% of the input bound to filter DNA of a single strand (e.g. L) is of the homologous strand (i.e. L). This effect is relatively unaffected by the concentration of DNA in solution. 3. Variation of the L:H ratio in solution shows that the strand in excess hybridizes and renatures more efficiently. This effect gives an underestimation of the amount of the minor strand present in solution. The numerical values obtained here are likely to be strongly dependent on the complexity of the DNA and the precise hybridization conditions. 4. The implication of the results for homology experiments and determination of strand specificity in transcription is discussed.