Showing papers by "Aarhus University published in 1974"

Intrinsic rate of natural increase: The relationship with body size

Abstract: The relationship between previously published values of "the intrinsic rate of natural increase" (r m ) and body weight is studied. When organisms covering a wide range of body weights are compared, a correlation is found which can be described by the equation r m =aW n where r m is the intrinsic rate of natural increase per day and W is the average body weight in grams; a is a constant which takes three different values for unicellular organisms and heterotherm and homoiotherm animals respectively. The constant n has a value of about-0.275 for all three groups. This result is compared to the previously found relationship between the metabolic rate per unit weight and body size. It is shown that r m can be inter-preted as the productivity of an exponentially growing population and thus must correlate with metabolic rate. The values of the constants a and n, however, show that for each of the three groups, unicellular organisms, heterotherms and homoiotherms the ratio of energy used for maintenance to that used for production increases with increasing body size and that the evolution from protozoa to metazoa and the evolution from heterotherm to homoiotherm animals in both cases resulted in not only an increased metabolic rate, as shown previously, but also in a decreased population growth efficiency. It is shown that the increase in reproductive potential of homoiotherms relative to that of heterotherms is due to a shorter prereproductive period in the former group.Previous estimates of r m for different species and comparisons between these values in relation to their ecology are discussed in context with the found "r m -body weight" relationship. Attempts to show that such comparisons will be more meaningful when body size is included in the considerations are made. It is suggested that the found relationship may represent the maximum values r m can take rather than average values for all species, since it is likely that the species used for laboratory population-studies are biased in favor of species with high reproductive potentials.

The sulfur cycle of a marine sediment model system

Abstract: In a laboratory sediment model consisting of sand and chopped Zostera marina leaves, the sulfur cycle and the succession and zonation patterns of sulfur bacteria were studied for a period of 7 months. The pool size of different forms of sulfur was quantified, and the rate of sulfate reduction was measured with an in situ radio-tracer technique at regular intervals. From these data, transfer rates of the sulfur cycle in the system could be calculated for different periods. The rate of sulfate reduction was initially 80 nMS·cm3·day-1; this decreased to 25 nMS·cm3·day-1 towards the end of the experiment as the system started to become oxidized. There was a transient accumulation of elemental sulfur in the bacterial plate at the sediment surface. More than 50% of the total mineralization of the organic material was due to sulfate reduction. Comparison with the net oxygen uptake showed that, during the first 2 to 3 months (when the sediment closely resembled a natural, reduced shallow water sediment), SO4- was equally as important as O2 for transporting oxidacion equivalents from the water to the sediment.

The (Na++K+) activated enzyme system and its relationship to transport of sodium and potassium.

Abstract: It seems to be the membrane bound (Na++K +)-activated enzyme system which transforms the energy from a hydrolysis of ATP into a vectorial movement of sodium out and potassium into the cell against electrochemical gradients, i.e. this systems seems to be the transport system for sodium and potassium (see, for example, review by Skou, 1972; Hokin & Dahl, 1972).

Nonlinear effects in heavy-ion sputtering

Abstract: To test the suggestion that an enhancement of sputtering occurs in very dense collision cascades, the sputtering yield per atom was compared for atomic and molecular ions. In all cases tested, the yield per atom was higher for the molecular ions. This effect is the more pronounced the heavier the projectile and the target. In the molecular cases the overlapping cascades have higher energy densities than those initiated by the atomic ions; our results, therefore, support the suggestion of a sputtering enhancement in dense cascades.

Isolation and characterization of the components of the sodium pump

Abstract: A satisfactory understanding of the functions of the sodium pump, the system responsible for the active transport of sodium and potassium, require the isolation and characterization of its protein and lipid components which are integrated in the structure of the cell membrane The enzyme system (Na+ + K+)-ATPase, is located in membrane fragments and behaves in the test tube like the transport system in the intact cell membrane (Skou,1957) Purified preparations of this enzyme will contain some, if not all, of the components of the sodium pump

The rotational and rotation‐vibrational Raman spectra of 14N2, 14N15N and 15N2

Abstract: The pure rotational and rotation-vibrational Raman spectra of 14N2, 14N15N and 15N2 have been photographed using a previously described instrument. The analyses of the bands yield for each molecule v0, B0, B1-B0 and D. From the values of B0 and B0-B1 the internuclear distances re are calculated independently for each species. Within the experimental accuracy the distances are identical as required by the Born-Oppenheimer approximation. The mean value for re is 1.097701 ± ± 0.000004 A.

A comparison of nasal and tracheobronchial clearance.

Abstract: Tracheobronchial clearance and nasal clearance were compared in 13 pairs of monozygotic twins and 11 nontwins. Tracheobronchial clearance was studied by having the subjects inhale, by mouth, a test aerosol of 6μmol particles tagged with technetium Tc 99m (99mTc) and making external measurements of the radioactivity. Nasal clearance was studied with two methods: (1) a 0.6-mm anion resin particle tagged with 99mTc was externally followed at five different points along the nasal passage and (2) a saccharine particle was placed on the mucociliary mucosa anteriorly in the nose and the time was registered until the subject noted a sweet taste. A weak positive association existed between tracheobronchial clearance and nasal clearance as studied with the saccharine particle method, but no association was found between tracheobronchial clearance and nasal clearance as tested by the tagged resin particle method.

A simple method for R banding of human chromosomes, showing a pH-dependent connection between R and G bands.

Abstract: Incubation in an unbuffered solution of 1 M NaH2PO4 at 88°C (pH 4.0–4.5) causes R banding to appear on human chromosomes after subsequent staining in Giemsa dissolved in distilled water. G banding, results when the pH of the incubation medium is adjusted towards neutral.

HL-A in psoriasis vulgaris and in pustular psoriasis--population and family studies.

Abstract: SUMMARY A collaborative study of HL-A typing was done on 156 unrelated patients with psoriasis vulgaris and thirty-one patients with pustular psoriasis. Highly significant increases of HL-A13 and HL-A17 were found in psoriasis vulgaris: about half of the patients carried either of these antigens as compared to about 12% of the controls. The effect of HL-A13 and 17 is confined almost exclusively to psoriasis with onset before the age of 35 years. In contrast, none of these antigens was increased in pustular psoriasis, indicating that pustular and common psoriasis are different aetiological entities. Family studies in psoriasis vulgaris showed that psoriasis can develop in relatives lacking the HL-A haplotype following psoriasis in the other family members. Hence, it seems most likely that HL-A represents only part of the genetic basis of psoriasis vulgaris. This disease is probably of a polygenic threshold character, and HL-A13 and 17 decreases the threshold making the expression of psoriasis more likely in individuals carrying these determinants in addition to other probably non-HL-A linked psoriasis determinants. This concept is supported by the observation of a higher incidence of a positive family history in HL-A13 and/or 17 positive patients than in patients lacking these antigens. Studies of antistreptolysin O and antistreptococcal hyaluronidase titres and of triggering streptococcal infections yielded no clue as to the pathogenetic effect of HL-A. The frequencies of HL-A13 and 17 were not significantly increased in twenty-one patients with psoriatic arthritis, but HL-A27 may be increased in these patients. This study shows the importance of HL-A in the subdivision of diseases and stresses the importance of family studies for clarifying the associations between HL-A and disease.

Evidence for continental crust beneath the Faeroe Islands

Abstract: Recent crustal seismic refraction experiments in the North Atlantic indicate that the Faeroe Islands are underlain by continental crust. This suggests that the whole Rockall-Faeroe Plateau may be a microcontinent which formed during the early evolution of the North Atlantic.

Peripheral blood flow and metabolic control in juvenile diabetes.

Abstract: Peripheral blood flow was measured during periods of good and poor metabolic control in juvenile diabetics with less than five years duration of the disease. Previously insulin treated patients, in whom the insulin was withdrawn for a few days, showed elevated blood flow in muscular, adipose and cutaneous tissue, whereas a group of newly diagnosed diabetics before treatment showed elevated blood flow in adipose and cutaneous tissue only. In good metabolic control the diabetics had normal values of both muscular, adipose and cutaneous tissue blood flow. In poorly controlled diabetics blood pressure, pulse rate and body temperature were elevated. These parameters are also normalized when the metabolism is brought under control. It is suggested, that the increased peripheral blood flow seen in diabetics in poor control is the effect of a generally increased turn-over of energy in combination with local factors, different from tissue to tissue.

Human response to 78-hour exposure to dry air

Abstract: We studied the effects of dry air on nasal mucus flow rate, nasal resistance, forced vital capacity, skin resistance, and discomfort in eight young healthy men exposed to clean air at 23 C in a climate chamber. After 27 hours at 50% relative humidity (RH) they lived for 78 hours at 9% RH and then returned to the initial level of 50% RH for 20 hours. No significant changes were observed in the nasal mucus flow rate throughout the experiment. Nor did a tenfold increase in nasal respiration during 20-minute periods of exercise in the dry air cause any change in mucus flow rate. No changes were observed in nasal or tracheobronchial resistance except for a 58% increase in calculated cross-sectional nasal area during exercise. The humidity voting for the subjects varied widely and related poorly to the humidity conditions; the average votings always were in the comfort range. No discomfort was reported from the body surfaces, and skin resistance did not change. The study indicates that there is no physiological...

A Variable Projection Method for Solving Separable Nonlinear Least Squares Problems

Abstract: Consider the separable nonlinear least squares problem of finding ~a in R^n and ~alpha in R^k which, for given data (y_i, t_i) i=1,...,m and functions varphi_j(~alpha,t) j=1,2,...n (m>n), minimize the functional r(~a,~alpha) = ||~y - Phi(~alpha)~a||_(2)^(2) where Phi(~alpha)_(i,j) = varphi_(j)(~alpha,t_j). This problem can be reduced to a nonlinear least squares problem involving $\mathovd{\mathop{\alpha}\limits_{\textstyle\tilde{}}}$ only and a linear least squares problem involving ~a only. the reduction is based on the results of Colub and Pereyra, SIAM J. Numerical Analysis , April 1973, and on the trapezoidal decomposition of Phi, in which an orthogonal matrix Q and a permutation matrix P are found such that \begin{displaymath} Q Phi R = R & S 0 & 0 \end{array}\right) \begin{array}{l} \rbrace\, r \\ \mbox{} \end{array} \end{displaymath} where R is nonsingular and upper trianular. To develop an algorithm to solve the nonlinear least squares probelm a formula is proposed for the Frechet derivation D(Phi_(2) (~alpha)) where Q i partioned into

Distribution of heavy metals in the hippocampal region of the guinea pig. A light microscope study with Timm's sulfide silver method.

Abstract: With the present modification of Timm's sulfide silver method all parts of the hippocampal region show a distinctly stratified staining pattern, suggesting large regional differences in the content of heavy metals. The stain is largely confined to distinct grains, partly associated with neuronal somata and partly dispersed in the neuropil. Work in progress supports the idea that the grains in the neuropil are synaptic boutons, as has been shown previously for the mossy fibre layer. The staining pattern has been compared in detail with the fields and layers of the hippocampal region as delineated by cyto- and fibroarchitectonics. Previous concepts of the subdivision of this cortical region are confirmed and supplemented. The sulfide silver pattern of the guinea pig hippocampal region is fundamentally similar to that of the rat. However, the entorhinal area, the regio inferior hippocampi, and the dentate area show notable differences in the staining pattern between the two species.

Geographical Patterns of Four Polymorphisms in ZOARCES VIVIPARUS as Evidence of Selection

Abstract: Two unlinked polymorphisms of a marine teleost, one in hemoglobin and one in esterase, show parallel clines through Danish waters, while two unlinked phosphoglucosemutase polymorphisms maintain constant gene frequencies. It is argued that the clinal and the constant polymorphisms cannot be accounted for simultaneously by random genetic drift of selectively neutral genes. It is therefore concluded that selection is responsible for at least one of the two classes of geographical patterns, be it the clinal, the constant, or both.