Showing papers by "Dalhousie University published in 1975"
TL;DR: The results imply that the efficiency of synaptic transmission in the perforant path-granule cell synapse can be modified.
514 citations
TL;DR: Prestige strategies may emphasize attaining prestige through being part of a prestigious group or may be more individualistically oriented as discussed by the authors, and they may also stress receipt of the approbation of internal representations of absent or imaginary others or emphasize the respect of those physically present.
Abstract: Examination of human prestige-striving in phylogenetic perspective suggests it to be essentially homologous with primate social dominance. In our own species, however, selection for "cultural capacity" has transformed striving for social dominance into striving to evaluate the self as being higher in rank than others or, in other words, into striving for self-esteem. We maintain self-esteem through symbolic means, usually referred to as seeking "prestige." We also utilize various distortions of perception and cognition to this end, including rationalization, identification, and change of reference group. Prestige strategies may emphasize attaining prestige through being part of a prestigious group or may be more individualistically oriented. They may also stress receipt of the approbation of internal representations of absent or imaginary others or emphasize the respect of those physically present. Traditional societies provide culturally patterned strategies which tend to perpetuate these societies. Thus...
287 citations
TL;DR: In this article, the C : N ratio of incubated detritus decreased from over 20 : 1 to as low as 11 : 1, indicating an increase in its potential food value.
Abstract: In laboratory decomposition experiments dead eelgrass leaves lost a maximum of 35% of the original dry weight in 100 days at 20°C. Whole leaves lost 0.5% of their organic content per day whereas particles smaller than 1 mm lost 1% per day. Sterilization of leaves by dry heat or potassium cyanide showed that leaching accounted for 82% of the total loss of organic matter from predried material and 65% of the loss from undried material. Bacteria acting alone increased the nitrogen content of the detritus but only slowly degraded the leaf material. When protozoa were introduced, they grazed on the bacteria, maintained the bacterial population in an active metabolic state, and hastened the rate of decay. The C : N ratio of incubated detritus decreased from over 20 : 1 to as low as 11 : 1, indicating an increase in its potential food value. The overall slow rate of decomposition could enable the eelgrass detritus system to continue functioning during periodic short term fluctuations in eelgrass primary production by ensuring that a reservoir of slowly decomposing material is always present.
242 citations
TL;DR: Results support histochemical and anatomical data which indicates that there is a cholinergic pathway from the MS to the hippocampus and that the bulk of the fibers travel in the fimbria.
178 citations
TL;DR: In this article, a new procedure described here provides a limit (r) to the number of significant contrasts which can be asserted when Fm in anova is significant, and a table is provided of new critical F values which set this expectation at a constant (0.05 or 0.01).
Abstract: When Fm in anova is significant, Scheffe's procedure provides no limit to the number of contrasts which can be declared significant. The new procedure described here provides a limit (r) to the number of significant contrasts which can be asserted. If assertions are made for v1 contrasts, which include r declarations of significance, the expectation of r/v1 will be a linearly decreasing function of v1 if traditional critical F values are used. A table is provided of new critical F values which set this expectation at a constant (0.05 or 0.01). The new critical F values are recommended for use whenever contrasts are sought, post hoc, for significance.
140 citations
TL;DR: Small or negligible differences in growth rates, average cell size, yields in cell numbers and total cell volumes were found in cultures of Thalassiosira fluviatilis inriched with nitrate, ammonium, or urea, but urea was not accumlated internally.
Abstract: Small or negligible differences in growth rates, average cell size, yields in cell numbers and total cell volumes were found in cultures of Thalassiosira fluviatilis inriched with nitrate, ammonium, or urea. Intracellular pools of unassimilated nitrate, nitrate, and ammonium were found in nutrient-rich conditions, but urea was not accumlated internally. Nitrogen assimilation into organic combination rather than nitrogen nutrient uptake was a critical rate-limiting step in nitrogen utilization. The free amino acid pool, protein, lipid-associated nitrogen, pigments, and total cell nitrogen were all highest in young or mature phase cells and decreased with age in senescent cells, whereas chitan, lipid, carbohydrate, and total cellular carbon all continued to increase during senescence. Dissolved organic nitrogen compounds accumulated in the medium only during senescence. C:N and lipid:protein were sensitive indicators of nitrogen depletion and age in T. fluviatilis.
112 citations
TL;DR: In this article, the hyperfine field at a given site is strongly dependent in magnitude and sign on the magnetic character of the local screening charge, and the effect of local screening on the Hyperfine Field Systematics at non-magnetic sites in Heusler alloys was established.
Abstract: The present study establishes hyperfine field systematics at the non-magnetic sites in Heusler alloys and emphasizes the effect of local screening on the hyperfine field value. A range of Heusler alloy hosts were doped with 1 at.% of the isotope 119Sn for examination using the Mossbauer effect. The results reported indicate that the hyperfine field at a given site is strongly dependent in magnitude and sign on the magnetic character of the local screening charge. The fields at Sb sites in several alloys have been measured using the Mossbauer isotope 121Sb and at a Cd impurity site in Ni2MnIn using the method of time-differential perturbed angular correlations. The Sn site fields have been measured in the Co based alloys Co2TiSn, Co2ZrSn and Co2HfSn. The similarity of the values obtained is interpreted in terms of the similar outer electron structure of these alloys.
96 citations
TL;DR: It is shown that chromosome recombination between non-homologues most often in situations associated with an increased frequency of chromosome breakage and reunion is identified.
Abstract: SOMATIC cells dividing in vitro occasionally show chromosome recombination between non-homologues most often in situations associated with an increased frequency of chromosome breakage and reunion1,2 their occurrence being recognised by the observation of exchange figures. With the advent of new techniques for chromosome identification3 it is now possible to identify the chromosomes involved in these rearrangements and to recognise some translocations which might otherwise be missed.
93 citations
TL;DR: In this paper, the equation of state of a mixture of hard spheres with non-additive diameters has been found by molecular dynamical simulation and the mixture undergoes a fluid-fluid phase transition at high densities.
Abstract: The equation of state of a mixture of hard spheres with non-additive diameters has been found by molecular dynamical simulation. The mixture undergoes a fluid-fluid phase transition at high densities. A perturbation equation of state using a multicomponent reference fluid was found to give good agreement with the simulation results.
87 citations
TL;DR: In this article, the first-order spin-rotation coupling constant (γ) and the second-order centrifugal spin-orbit constant (A D = 2 A J ) in 2 Π states of OD were analyzed by the direct two-state fit approach.
80 citations
TL;DR: The histology of the skeletal tissues of the Ordovician agnatha is reviewed with the conclusion that the skeletal tissue of the first vertebrates were as diverse and as specialized as are those of present-day vertebrates.
Abstract: Some aspects of the differentiation, growth, and morphogenesis of the tissues within the skeleton are discussed and related to the evolution of the vertebrate skeleton. The tissues considered are bone, cartilage, dentine, and enamel.
The histology of the skeletal tissues of the Ordovician agnatha is reviewed with the conclusion that the skeletal tissues of the first vertebrates were as diverse and as specialized as are those of present-day vertebrates. Phylogenies of skeletal tissues cannot be established. The trend during evolution appears to have been toward reduction in amount of skeletal tissue and in the number of types of tissues present.
The factors which determine when and where a skeletal element develops ontogenetically are reviewed and used to discuss the origin and evolution of jaws, the evolution of membrane bones and the origin of such structures as sesamoid bones. Special importance is attached to epithelial-mesenchymal interactions.
The factors which determine what particular skeletal tissue will form at a particular site within the body are reviewed with especial reference to modulation, germ layer derivation, and the role of epigenetic factors.
The factors which determine size and shape of the skeleton, both ontogenetically and phylogenetically, are reviewed and the directive role of adjacent tissues emphasized.
TL;DR: Stereoblind humans, who show no transfer whatsoever may, like cats and monkeys deprived of concordant binocular visual input early in life, suffer from a lack of binocular neurons.
Abstract: The extent of interocular transfer of the motion after-effect was measured in 4 stereoblind subjects and in 19 subjects having varying degrees of stereopsis. Stereoblind individuals failed completely to show any interocular transfer of this after-effect, while subjects with good stereopsis exhibited between 55 and 82% transfer (mean 73%). Furthermore, normal subjects who manifested a clear eye dominance tended to show greater transfer from the dominant to the nondominant eye than vice versa. Individuals who either had a history of a strabismus or possessed some other early impediment to clear binocular vision tended to show less transfer. Overall there was a significant positive correlation of 0.75 between the extent of interocular transfer and the subject's stereoacuity.
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TL;DR: In this article, the authors interpreted the tidal response of a gulf as a three-stage process: (i) direct forcing produces separate responses in the gulf and ocean, treating the mouth of the gulf as closed, (ii) the difference in elevations VG and VO at the mouth causes a mass flux = (VO − VG) (ZO + ZG)−1 through the entrance, where ZO, ZG are impedances, and (iii) this mass flux produces a response in both gulf and oceans.
TL;DR: One parameter of the single fiber's response, the temporal arrangement of impulses, provides sufficient information during steady temperatures to account for published data on thermoregulatory responses, and the organization of the impulse pattern in cold fibers may constitute an additional code capable of conveying information about steady skin temperature centrally.
TL;DR: Three shell-shape parameters of Littorina saxatilis were measured and found to vary in a regular pattern with distance up an estuary, consistent with the theory that a trait under selection will show little additive genetic variance.
Abstract: Three shell-shape parameters of Littorina saxatilis were measured and found to vary in a regular pattern with distance up an estuary. The translation rate of the shell increased, the rate of whorl expansion decreased and the circularity of the aperture decreased proceeding from the exposed shore to the protected shore. The genetic variance of these traits was estimated from the full-sib covariance and the motheroffspring covariance. The genetic variance of the translation rate and the circularity of the aperture was low in all populations, but the genetic variance of the rate of whorl expansion was high on the exposed shore and low on the protected shore. It is argued that the change in mean phenotype of these traits is the result of natural selection produced by varying degrees of wave action and desiccation. The observed genetic variance is consistent with the theory that a trait under selection will show little additive genetic variance.
TL;DR: In this paper, the first gradient corrections to the exchange and correlation energy of an inhomogeneous electron gas were derived, based on the random-phase approximation and is exact at high density.
Abstract: An exact result is derived for the coefficient ${B}_{\mathrm{xc}}$ which determines the first gradient corrections to the exchange and correlation energy of an inhomogeneous electron gas. A method of approximation, which is based on the random-phase approximation and is exact at high density, is given for the explicit evaluation of ${B}_{\mathrm{xc}}$. Numerical results are also given for the metallic density range and applications are discussed.
TL;DR: A linear operator A is called reflexive if the only operators that leave invariant the invariant subspaces of A are the operators in the weak closure of the algebra of polynomials in A.
TL;DR: The NADP-dependent dehydrogenase was unstable and rapidly lost activity after polyacylamide disc-gel electrophoresis, ultracentrifugation, freezing on refrigeration at 4 degrees C, and a fairly sharp optimal activity range of 9.5--10.0 for the NAD-dependent enzyme.
TL;DR: An ultrastructural investigation of the calyx region of the ichneumonid endoparasitoid Campoletis sonorensis appears that synthesis of electrondense secretory particles occurs within nuclei of calyx cells.
Abstract: The present study is an ultrastructural investigation of the calyx region of the ichneumonid endoparasitoid Campoletis sonorensis. It appears that synthesis of electrondense secretory particles occurs within nuclei of calyx cells. The particles consist of an ovocylindrical electron-dense inner core and a surrounding unit membrane. After their formation the particles pass from the nucleus by budding through both membranes of the nuclear envelope. The particles, along with fully developed parasitoid eggs concentrate within the lateral oviduct lumen. Feulgen histochemical studies suggest the presence of DNA within the calyx fluid. The possible function of the particles is discussed.
TL;DR: Both response-independent and response-dependent social stimulation were effective in producing increased rates of vocalizations, but only when each of four infants could see the eyes of the adult who delivered the social stimulus.
TL;DR: Cats were reared in a visual environment in which irregularly-shaped patches of luminescent paint moved constantly leftward, and although no anisotropy of orientation was present in the rearing environment, most cortical neurons responded optimally to stimuli oriented at or near vertical.
Abstract: Cats were reared in a visual environment in which irregularly-shaped patches of luminescent paint moved constantly leftward. The distribution of preferred directions and orientations of cortical neurons in these cats was examined. Most cortical neurons encountered had leftward components in their preferred directions, and although no anisotropy of orientation was present in the rearing environment, most cortical neurons responded optimally to stimuli oriented at or near vertical. Variations in the strength of the induced bias of direction and orientation were noted among the different subclasses of cortical neurons. Preferred velocities of cortical neurons did not appear matched to the velocity of stimuli in the rearing environment. The ocular dominance distribution among cortical neurons in the unidirectional cats was skewed toward the contralateral eye relative to normal cats. The distribution of preferred directions in collicular neurons was largely unaltered by the rearing procedures employed. As in normal cats, units in the left colliculus more frequently responded best to rightward stimulus movement while those in the right colliculus preferred leftward movement. The ocular dominance distribution among collicular units was somewhat skewed toward the contralateral eye.
TL;DR: A brief review evaluates some of the recent experimental approaches used in the study of the osteoclast, especially whether they form from intra‐ or extra‐skeletal progenitor cells, whether from the same osteoprogenitor cell as the osteoblast, and whether, once formed, they may modulate to osteoblasts.
Abstract: Despite intensive and ingenious investigation, the origins and ultimate fate of the osteoclast remain shrouded in mystery. This brief review evaluates some of the recent experimental approaches used in the study of the osteoclast, especially whether they form from intra- or extra-skeletal progenitor cells, whether from the same osteoprogenitor cell as the osteoblast, and whether, once formed, they may modulate to osteoblasts. That osteoprogenitor cells can, and do, become osteoclasts is well founded, as is the conclusion that such progenitor cells originate as blood-borne, extra-skeletal cells. Evidence that sessile, intra-skeletal, progenitor cells can form osteoclasts is less direct. There is good evidence that osteoclasts both shed and take-up nuclei, but no direct evidence that nuclear shedding is accompanied by death of the osteoclast, and no direct evidence for the fate of the shed nuclei. Whether the same osteoprogenitor cell can produce either an osteoblast or an osteoclast also remains an open question.
TL;DR: The similarities of form and context of facial expressions used by the two species suggest common causation, but a greater number of those of A. forsteri is considered communicative, in agreement with known ecological and social characteristics of the twospecies.
Abstract: Fur seals Arctocephalus forsteri and walruses Odobenus rosmarus show similar facial expressions in a variety of social and non-social contexts. In non-social settings, both species modify the facial appearance by erecting the mystacial vibrissae while grooming the forequarters, while yawning, and during olfactory/tactile investigation of objects. During naso-nasal greetings, vibrissae are often erected in fur seals, and are erected and moved against the interactant's mystacial pads in walruses. Highly submissive animals show: for A. forsteri, erection of the vibrissae, wide gape, relaxed lips, posterior retraction of the corners of the mouth, wide-eyed stare; for walruses, dorsomedial drawing up of the mystacial pads and erection of the vibrissae, imparting a 'pig snout' appearance. In high intensity threat, both species show facial expressions involving: for A. forsteri, slight lateral expansion of the mystacial pads, slight to moderate opening of the mouth, direct or oblique visual orientation from a head-up posture; for O. rosinarus, lateral and dorsoventral expansion of the mystacial pads, attendant exposure and stretching of the skin of the upper lip, especially around the bases of the tusks, and inflation of the rostrum posterolateral to the nostrils. The similarities of form and context of facial expressions used by the two species suggest common causation, but a greater number of those of A. forsteri is considered communicative, in agreement with known ecological and social characteristics of the two species.
TL;DR: Three-dimensional X-ray diffraction data were used to determine the crystal structure of alpha-D-glucuronate CaBr times 3H20, a model system for investigating the factors involved in the binding of calcium ions to D-glUCuronate residues of oligo-and poly-saccharides.
TL;DR: Ca2+ may also play a role in the uptake of noradrenaline by presynaptic nerve‐endings in the CNS, and the kinetics of uptake were examined, it was found that removing both Ca2+ and Mg2+ from the medium resulted in a reduction of the Vmax for nor adrenaline uptake.
Abstract: –The effects of divalent cations on the initial rates of noradrenaline uptake by synaptosomes were determined using Millipore filtration to terminate the reaction. The removal of either Ca2+ or Mg2+ from the incubation medium had no effect on uptake, but when both Ca2+ and Mg2+ were removed, uptake was reduced. Uptake was also diminished when Ca2+ was absent and 1 mm-EGTA added to the medium. It appeared that Ca2+ was required for optimal uptake but that Mg2+ could partially substitute for Ca2+ in this regard. The reduction in the rate of uptake when both Ca2+0 and Mg2+ were absent could be rapidly and completely reversed by restoring Ca2+, Mg2+, or both Ca2+ and Mg2+ to the incubation medium. Of the divalent cations tested, Ca2+ and Mg2+, but not Mn2+, supported noradrenaline uptake. When the kinetics of uptake were examined, it was found that removing both Ca2+ and Mg2+ from the medium resulted in a reduction of the Vmax for noradrenaline uptake. It is apparent from these results that, in addition to facilitating the release of noradrenaline from noradrenergic terminals, Ca2+ may also play a role in the uptake of noradrenaline by presynaptic nerve-endings in the CNS.
TL;DR: Spring diatom flowerings in Bedford Basin, Nova Scotia, almost exhausted the available nitrogen supplies, and the supply of nitrate appeared to regulate the magnitude of the bloom, which could be interpreted in terms of nitrogen limitation.
Abstract: Spring diatom flowerings in Bedford Basin, Nova Scotia, almost exhausted the available nitrogen supplies. The supply of nitrate appeared to regulate the magnitude of the bloom. Other nutrient supplies may also have been limiting. Certain alterations in quantities of major metabolites could be interpreted in terms of nitrogen limitation. Nitrate, (nitrite), and ammonium were generally utilized simultaneously by Thalassiosira nordenskioldii, the dominant bloom organism. This species did not effectively utilize urea in either laboratory culture or in the natural environment. T. fluviatilis simultaneously utilized all nitrogen sources provided in laboratory experiments simulating natural nutrient conditions.
TL;DR: For those enzymes closely associated with the hepatic endoplasmic reticulum, enhanced induction of activity was observed with agents having chlorine atoms substituted at the 4- and 4′-positions, irrespective of chlorination at other positions, while for those enzymes less discretely localized in the hepatocyte, the position of the chlorine atoms appeared to be less important.
TL;DR: Heterologous anti-melanoma sera produced against any one patient's tumour cross-react, to varying degrees, with both the cytoplasmic and surface antigens of melanoma cells from other patients.
TL;DR: In this paper, the authors investigated the formation and fate of such films and found that most of the organic material in seawater is nonliving and capable of passing a filter with a pore size of somewhat less than 1 p.
Abstract: Films that accumulate from lake water, coastal seawater, and Sargasso Sea water with low concentrations of added protein can collapse when subjected to increased surface pressure. Collapse is accompanied by the transformation of some film organic material to particulate material that cannot spread at the interface; these particles are formed from filterpassing organic material previously in the bulk liquid. Film collapse and accompanying particle formation in nature may be a part of a process that, in some arcas, removes filterpassing surface-active material from water and precipitates it as particles back into the water column. Such particles tend to sink and could provide particulate food to organisms in the surface waters and perhaps at greater depths. Most of the organic material in seawater is nonliving and capable of passing a filter with a pore size of somewhat less than 1 p. This material has been termed “dissolved organic matter,” but probably includes a spectrum of sizes and states ranging from molecules in solution through small particles ( Sharp 1973). Organic materials are released by living, as well as dead plants and animals. Although most of this material has not been characterized, it undoubtedly reflects the biochemical composition of organisms and may be a source of nutriment either dissolved or after transformation to the particulate state (Baylor and Sutcliffe 1963; Wangersky 1965); indeed, its mass in surface waters is so great when compared with the mass of phytoplankton that this nonliving material may be an appreciable source oE nutriment at least at some trophic levels (Riley 1963, 1970). Many dissolved organic substances are surface-active and tend to accumulate at a water-air interface to form a surface film (Jarvis lQ67; Garrett 1967). Natural films are believed to influence the distributions of near-surface cations (Piotrowicz et al. 1972), to affect bursting bubbles and thus the sea to air transfer of particulate material ( Blanchard and Syzdek 1972)) and to influence rates of gas transfer between water and air, Aspects of the formation and fate of such films are the subject of this report. l Present address: University of Georgia Marine Institute, Sapelo Island 31327. Most of this work was submitted as part of a doctoral thesis to the Dalhousie University Institute of Oceanography. Some of the work was done while I was a postdoctoral fellow at the Marine Ecology Laboratory, Fisheries Rcscarch Board of Canada. I thank G. A. Riley and P. J. Wangersky for their advice and criticism during the course of the research, and for critically reading the manuscript. I thank L. M. Dickie for providing laboratory space at the Bedford Institute of Oceanography.