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Showing papers by "Dalhousie University published in 1973"


Journal ArticleDOI
K. H. Mann1
07 Dec 1973-Science
TL;DR: While the intertidal zone is inhabited primarily by the fucoids, or rockweeds, the sublittoral is dominated by fish, and the growth of seaweeds below lowtide level, in the sub littoral, is far richer than in the interTidal areas.
Abstract: [Fhe edge of the sea is one of the best habitats for plant growth in temperate latitudes. In favorable circumstances, net primary productivity may be as high as anywhere else on earthcomparable, for example, to a tropical rain forest. Seaweeds, which have successfully colonized this zone, are a unique form of life. They are attached to a hard substrate, not by a root system, but by a holdfast. Instead of relying on a rather localized supply of nuLtrients in the soil, they take their nutrients from the water that surrounds them. Because this water is kept in perpetual motion by tides and winds, the nutrient supply is virtually inexhauLstible. Even if the seaweeds aind plankton deplete the nutrients in surface waters, wind-induced or estuari ne mixing renews the supply by caus1ngQ upwelling of deeper water. TFhe -growth of seaweeds below lowtide level, in the sublittoral, is far richer than in the intertidal areas. Before the advent of underwater vehicles a,tnd scuiba g,ear, the al(ae of the intertidal zone were the focus Of attention .ind provided elegant examples of species zonatiotn in relation to gradients of environmenital factors, such as degree of exposure to air or anmount of wave ction (M). While the intertidal zone is inhabited primarily by the fucoids, or rockweeds, the sublittoral is dominated

726 citations


Journal ArticleDOI
TL;DR: The role of association between a stimulus and a reinforcer in producing a resemblance of the auto-shaped response to the consummatory response is demonstrated.
Abstract: The relation between the form of auto-shaped responses to the lighting of a key and the consummatory responses of pecking grain and drinking water was examined in pigeons. Responses on the key were analyzed by means of high-speed photography, recordings of the force of contact, and judges' ratings of response-form based on film and videotape recordings. The first experiment showed that food-deprived birds presented grain as a reinforcer responded on the key with a grain-pecking movement, while water-deprived birds presented water as a reinforcer responded with drinking-like movements. The second and third experiments showed that the resemblance between auto-shaped and consummatory responses does not require the dominance of the deprivational state appropriate to the reinforcer. Changing the dominant state of deprivation did not immediately change the form of the key response, and in subjects simultaneously deprived of food and water, the form of response depended on the reinforcer. In the fourth and fifth experiments, subjects simultaneously deprived of food and water received one stimulus signalling food and another signalling water in a random series. In most subjects, the response to each stimulus resembled the consummatory response to the particular reinforcer that was signalled by the stimulus. This result demonstrates the role of association between a stimulus and a reinforcer in producing a resemblance of the auto-shaped response to the consummatory response.

480 citations


Journal ArticleDOI
TL;DR: In this article, the International Biological Program (IBP) collected data from 43 lakes and 12 reservoirs, distributed from the tropics to the arctic, were subjected to statistical analysis to establish which factors are important in controlling production and how they are related.
Abstract: Data collected as part of the International Biological Program from 43 lakes and 12 reservoirs, distributed from the tropics to the arctic, were subjected to statistical analysis to establish which factors are important in controlling production and how they are related. In the whole body of data, variables related to solar energy input have a greater influence on production than variables related to nutrient concentration; in lakes within a narrow range of latitude, nutrient-related variables assume greater importance. Morphological factors have little influence on productivity per unit area in either case. Chlorophyll a concentration is a good indicator of nutrient conditions and when combined with an energyrelated variable constitutes a good estimator of primary production.

263 citations


Journal ArticleDOI
TL;DR: It is argued that the abnormal early visual experience of an astigmat induces matching neural alterations to occur within the visual system, which in turn result in the substantial differences in the ability to resolve contours of different orientations.

260 citations


Journal ArticleDOI
TL;DR: In this paper, four size classes of organic matter in seawater are investigated using carbon analyses, and it is suggested that this "subparticulate" class should be considered as colloidal organic matter.
Abstract: Using carbon analyses, four size classes of organic matter in seawater are investigated. An appreciable portion of the organic matter is smaller than the usually defined particulate class, but is most probably not truly dissolved. This portion can be segrcgatcd usinlg very fine membrane filters and using membranes for forced dialysis. It is suggested that this “subparticulate” class should be considered as colloidal organic matter. Membrane-mat filters have been used in oceanographic research since 1952 (Goldberg et al. 1952); both these and microporous sheet filters arc now widely used to separate “particulate” and “dissolved” matter. These classes, also referred to as suspended and soluble, have been arbitrarily delineated according to the nature of the filters used rather than by strict physical definitions. This is convenient for analytical purposes, but it is misleading to consider these classes as actually being particulate and dissolved. A dissolved organic molecule in an aqueous medium is one in which minimum free energy is attained by hydration of all potentially hydrophilic sites on the molecule. Any association of molecules allowing for loss of water of hydration and formation of a less hydrophilic species tends to remove the resulting molecular-associate from solution. A clear barrier between dissolved and particulate matter would be a difficult thing to describe, especially in a complex ionic solution like seawater. I-Iowever, organic matter in the colloidal size range should not be considered as dissolved. By definition, colloidal particles are those between about 1 pm and 1 nm in their smallest dimensions (Vold and Vold 1966). An attempt is made here to examine colloidal organic carbon in seawater as well as “particulate” and total organic carbon, This paper is based on a portion of a dissertation submitted to Dalhousie Uni’ Present address: Institute of Marine Resources, Scripps Institution of Oceanography, P. 0. Box 109, La Jolla, California 92037. versity. For aid and advice in this work, I am especially indebted to G. A. Riley and I?. J. Wangcrsky. I thank both of them, J. R. Beers, P. M. Williams, 0. HolmIIansen, and G. E. Dawson for helpful criticism of the manuscript.

188 citations


Journal ArticleDOI
24 Jan 1973-Nature
TL;DR: A depressant effect of Cholinesterase inhibition and of oxotremorine on evoked ACh release and the antagonism of this effect by atropine is reported.
Abstract: ACETYLCHOLINE (ACh) release from cholinergic terminals in the cerebral cortex can be measured after inhibiting Cholinesterase which otherwise would rapidly hydrolyse released ACh The lack of hydrolysis of released ACh, however, is likely to lead to an unphysiologically high extracellular ACh concentration which in itself might modify further release of ACh We have developed a method 1 by which ACh release resulting from electrical stimulation of rat cortical slices in vitro could be estimated in the absence of Cholinesterase inhibition We now report a depressant effect of Cholinesterase inhibition and of oxotremorine on evoked ACh release and the antagonism of this effect by atropine

185 citations


Journal ArticleDOI
16 Feb 1973-Nature
TL;DR: These two kittens reared in the dark except for a few hours each day spent in cylindrical chambers painted with black and white stripes at one orientation had no cortical neurones responding to the orientation perpendicular to the stripes that they saw when they were young.
Abstract: IN the primary visual cortex of a normal cat the neurones are almost all orientation detectors, which respond only if an edge or bar at the appropriate angle moves across the receptive field: all orientations are equally represented1. But early experience can grossly modify the visual cortex. Blakemore and Cooper2 reared two kittens in the dark except for a few hours each day spent in cylindrical chambers painted with black and white stripes at one orientation. These two animals, which experienced almost 300 h of exposure to stripes during their first 5 months of life, had no cortical neurones responding to the orientation perpendicular to the stripes that they saw when they were young. Almost all their cortical cells preferred orientations within 45 deg of the experienced angle. The phenomenon involves active modification of the receptive fields of the neurones, and not mere degeneration of unused cells, because there were no regions of silent cortex and no histological evidence of degeneration.

176 citations


Journal ArticleDOI
TL;DR: In this article, a method is described for the determination of organic carbon in liquid seawater samples by combustion at a high temperature, which has been successfully employed for a direct comparison to the standard method of persulfate oxidation.

172 citations


Journal ArticleDOI
TL;DR: Upon recovery these patients appear to function just about as well in ordinary situations as before the operation, except for some loss of short term memory.
Abstract: The operation is relatively simple in conception, if not in execution Both a frontal and a posterior opening are made in the top of the skull, followed by mid-line sectioning of the corpus callosum,2 the anterior and hippocampal commissures,3 and in some cases the massa intermedia as well Upon recovery these patients appear to function just about as well in ordinary situations as before the operation, except for some loss of short term memory However under testing conditions, where information is

137 citations


Journal ArticleDOI
TL;DR: Premature infant plasma degraded procaine hydrochloride and insecticide paraoxon more slowly than full‐term infants, while the rates of hydrolysis for these 2 groups were significantly lower than those detected for children older than 1 year or for adults.
Abstract: Erythrocyte acetylcholinesterase, plasma proteins, pseudocholinesterase, and arylesterase development was investigated in groups of premature infants of varying gestational ages, comparing the detected levels with those observed in groups of healthy older children and adults. A rapid increase in protein concentration was evident between 28 and 40 weeks gestation, followed by a slower rate of increase until 1 year of age. A rapid increase in plasma pseudocholinesterase and arylesterase activity occurred from 28 weeks gestation to 1 year of age, with no significant changes in activities from those of adults occurring after 1 year. In contrast, the erythrocyte acetylcholinesterase levels increased most markedly between 40 weeks gestation and 1 year of age. Premature infant plasma degraded procaine hydrochloride and insecticide paraoxon more slowly than full‐term infants, while the rates of hydrolysis for these 2 groups were significantly lower than those detected for children older than 1 year or for adults.

117 citations


Journal ArticleDOI
TL;DR: In this paper, the influence of a finite cavity backing a finite panel on the transmission of sound through the panel and on the vibration of the panel was investigated, and a graphical technique, first used in a one-dimensional study of this case, was applied in the three dimensional case to predict frequencies of interest.

Journal ArticleDOI
TL;DR: The electrophoretic patterns, optimum pH, substrate specificity, K m values, rates of substrate hydrolysis and sensitivity to inhibition by DFP, paraoxon and DDVP were compared for the plasma pseudocholinesterases of the horse, man, mouse, guinea pig, dog, cat, rat, rabbit, swine, goat and hamster.


Journal ArticleDOI
01 Jan 1973-Geology
TL;DR: Sediments originally deposited on the Alaskan Abyssal Plain have been depressed to form the eastern Aleutian Trench and a wedge of horizontally bedded sediments, about 1 km thick at its axis, has been deposited in the trench as mentioned in this paper.
Abstract: Sediments originally deposited on the Alaskan Abyssal Plain have been depressed to form the eastern Aleutian Trench. Simultaneously, a wedge of horizontally bedded sediments, about 1 km thick at its axis, has been deposited in the trench. The time-transgressive facies change between this wedge of sediment and the abyssal-plain sediment sequence shows up as a discontinuity on seismic records. Sediment is being deposited up to 10 times faster in the trench than on the abyssal plain. Ninety percent of the sediment in the trench arrived there by moving down the trench wall as slumps or in turbidity currents, and has been partly redistributed by turbidity currents flowing in a channel along the trench axis; 7 percent has come from the Surveyor Channel distribution system on the abyssal plain; and 3 percent is pelagic (mainly ice rafted). Sediments pass from a sandy facies near the trench wall to a silt-mud facies on the abyssal plain. If a similar trench were exposed on land, the stratigraphic sequence would consist of sandstone grading transitionally downward into shale, and then into an abyssal-plain sequence. Sediment fill in the Aleutian Trench is abnormally thick as a result of Pleistocene glaciation; Neogene trench-fill sediments would be less than 800 m thick.

Journal ArticleDOI
27 Apr 1973-Science
TL;DR: Cats reared during the first 5 months of life in environments that contain contours of a single orientation show a diminished ability to resolve gratings of the orthogonal orientation in later life, it is argued that these perceptual deficits result from changes in the organization of the visual cortex induced by the selected early visual input.
Abstract: Cats reared during the first 5 months of life in environments that contain contours of a single orientation show a diminished ability to resolve gratings of the orthogonal orientation in later life. It is argued that these perceptual deficits result from changes in the organization of the visual cortex induced by the selected early visual input.

Journal ArticleDOI
B. Horacek1
TL;DR: In this paper, a method for magnetocardiographic investigation is presented based on the development of integral equations for electric potential and magnetic field generated by current sources within an inhomogeneous volume conductor, and a numerical algorithm to solve these equations.
Abstract: A method for magnetocardiographic investigation is presented according to the following: 1) development of integral equations for electric potential and magnetic field generated by current sources within an inhomogeneous volume conductor, and 2) description of a numerical algorithm to solve these equations. This method was developed specifically for an inhomogeneous torso-shaped volume conductor containing an autonomic model which dynamically simulates the electrical activity of the heart; thus, numerical simulation of electrocardiograms and magnetocardiograms for different pathological heart conditions is possible.

Journal ArticleDOI
TL;DR: 7α-Hydroxysteroid dehydrogenase was examined in crude preparations of one strain of Escherichia coli B which was devoid of both 3α- and 12α-dehydrogenase activities, suggesting the presence of a single enzymatic entity for the oxidation of both conjugated and free 7α-hydroxy substrates.

Journal ArticleDOI
01 Apr 1973-Heredity
TL;DR: A knowledge of the genetics of these two systems may help in understanding why male sterility is present when self-incompatibility alone is sufficient to ensure crossing.
Abstract: Plantago lanceolata is self-incompatible and gynodioecious, and a knowledge of the genetics of these two systems may help in understanding why male sterility is present when self-incompatibility alone is sufficient to ensure crossing. This paper reports on the inheritance of self-incompatibility. Self-incompatibility is inherited through one gene with at least four alleles. Matings are incompatible if the pollen carries either of the two alleles present in the style. Control of the pollen incompatibility reaction is gametophytic, and there is individual action of the alleles present in the style.

Journal ArticleDOI
TL;DR: Fluorigenic labeling techniques have been used for several years in conjunction with thin-layer chromatography, and are now being used also to good advantage in high-speed liquid chromatography as mentioned in this paper.



Journal ArticleDOI
TL;DR: The authors raised the question of whether redistribution can be justified within the Paretian framework by appealing to considerations other than those depending on the assumption of a philanthropically-inclined rich.
Abstract: Although it has always been clearly recognized that economic methodology admits altruism as a possibility in explaining individual and social behaviour, economists have nevertheless traditionally been reluctant to rely too much on "heroic" conceptions of man in developing their theories, and the view of human motivations characteristically taken in economic theory has tended to be a fairly cynical one. Accordingly, it is of some interest to raise the question as to whether redistribution can be justified within the Paretian framework by appeal to considerations other than those depending on the assumption of a philanthropically-inclined rich.

Journal ArticleDOI
01 Jun 1973-Brain

Journal ArticleDOI
TL;DR: In this article, the structure and magnetic properties of some 15 austenitic stainless steels were examined after cyclic cooling treatments and low temperature deformation, and the structural instability was increased significantly after a sensitizing treatment in the weldable steels 304L, 321, and 347 leading to the formation of up to 11.2% a′ martensite.

Journal ArticleDOI
TL;DR: In this paper, the authors show that the pyroxene-tholeiites and plagioclase-tholesiites can be differentiated by crystal fractionation of the high-alumina plagioclase phenocrysts and more than 17% Al2O3.

Journal ArticleDOI
TL;DR: In the non-digitate complex of Laminaria in Nova Scotia two reported species, L. agardhii Kjell.
Abstract: In the non-digitate complex of Laminaria in Nova Scotia two reported species, L. agardhii Kjell. and L. longicruris de la Pyl. are difficult to distinguish using the diagnostic criteria of stipe length and stipe hollow occurrence. A study was made of these traits in relation to season, exposure, and depth. A marked seasonal variability in stipe morphology was found. When only mature plants were examined there was found to be a definite tendency for stipe length and hollow occurrence to increase with decreasing exposure. The differentiation of populations in relation to exposure was clinal with overlap in the variation patterns. When stipe morphology was examined in relation to depth, significant differentiation was found only in a population sampled in a sheltered locality. In exposed localities, no such differentiation occurred. In the sheltered site, the variation with depth was attributed to differing developmental class structures at various depths. The major taxonomic finding of the analyses...

Journal ArticleDOI
C.M. Boyd1
TL;DR: Aggregations of zooplankton were shown to occur within regions of high temperature gradients associated with thermal micro-structure in the upper 250 m of the high seas.

Journal ArticleDOI
TL;DR: In this article, a microprobe analysis of a glass is accepted as that of the liquid, its validity must be ascertained by alternative methods, such as alternative micro-probe analyses of glasses from experimental samples.

Journal ArticleDOI
TL;DR: Data are presented consistent with the notion that the 23s ribosomal ribonucleic acid (rRNA) of Anacystis nidulans undergoes specific endonucleolytic cleavage in vivo, to produce two fragments with molecular weights of 0.88 x 10(6) and 0.17 x 10 (6) daltons.
Abstract: Data are presented consistent with the notion that the 23 s ribosomal ribonucleic acid (rRNA) of Anacystis nidulans undergoes specific endonucleolytic cleavage in vivo, to produce two fragments with molecular weights of 0.88 × 10 6 and 0.17 × 10 6 daltons. Cleavage occurred at random after 23 s rRNA formation and was stimulated by light in this organism, an obligately photoautotrophic unicellular blue-green alga. The half-life of intact 23 s rRNA was about 5 h in illuminated cultures and 10 h in unilluminated cultures. 3-( p -Chlorophenyl)-1, 1-dimethylurea, an inhibitor of photosystem II, retarded 23 s rRNA cleavage in the light. The results are discussed in the context of recent reports of rRNA instability in a variety of eukaryotic and prokaryotic organisms.