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Showing papers by "Australian National University published in 1987"


Journal ArticleDOI
TL;DR: A-type granites as mentioned in this paper were found to have high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr.
Abstract: New analyses of 131 samples of A-type (alkaline or anorogenic) granites substantiate previously recognized chemical features, namely high SiO2, Na2O+K2O, Fe/Mg, Ga/Al, Zr, Nb, Ga, Y and Ce, and low CaO and Sr. Good discrimination can be obtained between A-type granites and most orogenic granites (M-, I and S-types) on plots employing Ga/Al, various major element ratios and Y, Ce, Nb and Zr. These discrimination diagrams are thought to be relatively insensitive to moderate degrees of alteration. A-type granites generally do not exhibit evidence of being strongly differentiated, and within individual suites can show a transition from strongly alkaline varieties toward subalkaline compositions. Highly fractionated, felsic I- and S-type granites can have Ga/Al ratios and some major and trace element values which overlap those of typical A-type granites. A-type granites probably result mainly from partial melting of F and/or Cl enriched dry, granulitic residue remaining in the lower crust after extraction of an orogenic granite. Such melts are only moderately and locally modified by metasomatism or crystal fractionation. A-type melts occurred world-wide throughout geological time in a variety of tectonic settings and do not necessarily indicate an anorogenic or rifting environment.

4,216 citations


Journal ArticleDOI
TL;DR: Dementia prevalence rates were found to vary as a function of methodological differences between studies, however, despite these differences, the relationship between prevalence and age was found to be consistent across studies, with rates doubling every 5.1 years.
Abstract: — Data from studies of dementia prevalence between 1945 to 1985 were analyzed statistically. Prevalence rates were found to vary as a function of methodological differences between studies. However, despite these differences, the relationship between prevalence and age was found to be consistent across studies, with rates doubling every 5.1 years. Across studies, Alzheimer's disease (AD) was found to be more common in women, with a tendency for multi-infarct dementia (MID) to be more common in men. There were also national differences in the relative prevalence of AD and MID, with MID being more commmon in Japanese and Russian studies, no difference in Finnish and American studies, and an excess of AD in other Western European countries.

1,207 citations




Journal ArticleDOI
TL;DR: In all three viruses, which represent the three major serological subgroups of the mosquito-borne flaviviruses, the 3'-proximal conserved sequence element, which is found immediately adjacent to the potential 3'-terminal hairpin, is complementary to another conserved domain near the 5' end of the viral RNAs, suggesting that flavivirus RNAs can cyclize.

349 citations


Journal ArticleDOI
TL;DR: Phacl ofen may be useful in determining the physiological significance of central and peripheral bicuculline-insensitive receptors with which GABA and (-)-baclofen interact.

340 citations


Journal ArticleDOI
TL;DR: Human EDF represents a distinct hemopoietic growth factor that could play a central role in the regulation of eosinophilia and shows strong homology with that of murine EDF.
Abstract: The human eosinophil differentiation factor (EDF) gene was cloned from a genomic library in lambda phage EMBL3A by using a murine EDF cDNA clone as a probe. The DNA sequence of a 3.2-kilobase BamHI fragment spanning the gene was determined. The gene contains three introns. The predicted amino acid sequence of 134 amino acids is identical with that recently reported for human interleukin 5 but shows no significant homology with other known hemopoietic growth regulators. The amino acid sequence shows strong homology (approximately 70% identity) with that of murine EDF. Recombinant human EDF, expressed from the human EDF gene after transfection into monkey COS cells, stimulated the production of eosinophils and eosinophil colonies from normal human bone marrow but had no effect on the production of neutrophils or mononuclear cells (monocytes and lymphoid cells). The apparent specificity of human EDF for the eosinophil lineage in myeloid hemopoiesis contrasts with the properties of human interleukin 3 and granulocyte/macrophage and granulocyte colony-stimulating factors but is directly analogous to the biological properties of murine EDF. Human EDF therefore represents a distinct hemopoietic growth factor that could play a central role in the regulation of eosinophilia.

316 citations


Journal ArticleDOI
TL;DR: In this article, a gem quality crystal of Durango fluorapatite was found to have a 4He content consistent with complete retention of radiogenic helium since its formation at about 31 Ma.

307 citations


Journal ArticleDOI
TL;DR: Some nonstandard finite element spaces are introduced, which, though based on the usual square bilinear elements, permit local mesh refinement and an “equivalent estimator” for the H 1 finite element error is developed.
Abstract: This paper is the first in a series of two in which we discuss some theoretical and practical aspects of a feedback finite element method for solving systems of linear second-order elliptic partial differential equations (with particular interest in classical linear elasticity). In this first part we introduce some nonstandard finite element spaces, which, though based on the usual square bilinear elements, permit local mesh refinement. The algebraic structure of these spaces and their approximation properties are analyzed. An “equivalent estimator” for the H 1 finite element error is developed. In the second paper we shall discuss the asymptotic properties of the estimator and computational experience.

280 citations


Journal ArticleDOI
TL;DR: In this article, the pyroxene-garnet transformation in a model pyrolite composition has been investigated over the pressure interval 4.0 to 17.5 GPa at temperatures of 1200-1400°C.

266 citations


Journal ArticleDOI
TL;DR: It is proposed that these phenolic compounds secreted from the roots of white clover plants act at the bacterial membrane or that an active uptake system is involved.
Abstract: Rhizobium trifolii mutants containing Escherichia coli lac gene fusions to specific nodulation (nod) genes were used to characterise phenolic compounds secreted from the roots of white clover (Trifolium repens) plants. These compounds either had stimulatory or inhibitory effects upon the induction of the nod genes. The stimulatory compounds were hydroxylated flavones and the most active compound was 7,4'-dihydroxyflavone. The inhibitory compounds present in white clover root exudates were umbelliferone (a coumarin) and formononetin (an isoflavone). Transcriptional activation of nod gene promoters in response to short exposures (3 h) of 7,4'-dihydroxyflavone was growth phase dependent; cells in early log phase were highly responsive to flavone additions in vitro and nod gene induction could be detected within 20 min of exposure at 5 x 10 M. Cells in other growth phases were generally unresponsive. A 10-fold molar excess of umbelliferone to 7,4'-dihydroxyflavone resulted in complete inhibition of nod gene induction. Some commercially-obtained flavones were found to have weak stimulatory activity but could also inhibit nod gene induction by more effective stimulatory compounds. Strong stimulatory and inhibitory compounds all possessed a 7-hydroxy moiety and showed other structural similarities. This suggested that there was one binding site for these compounds. Because the response to these compounds was rapid, we propose that these phenolics act at the bacterial membrane or that an active uptake system is involved.

Journal ArticleDOI
TL;DR: In this paper, kernel density estimators are used for the estimation of integrals of various squared derivatives of a probability density, and rates of convergence in mean squared error are calculated, which show that appropriate values of the smoothing parameter are much smaller than those for ordinary density estimation.

Journal ArticleDOI
01 Feb 1987
TL;DR: In this article, two curved surfaces of molecularly smooth mica are brought into contact under a controlled load, and their deformed shape is measured using optical interference fringes of equal chromatic order.
Abstract: Two curved surfaces of molecularly smooth mica are brought into contact under a controlled load, and their deformed shape is measured using optical interference fringes of equal chromatic order. This technique allows exceptionally accurate measurements of surface profiles at separations down to a molecular scale. Contact between the surfaces can be made either adhesive or nonadhesive by suitable choice of the medium between them. Results have been obtained in both cases and compared with the theories of Hertz (nonadhesive contact) and Johnson, Kendall, and Roberts (adhesive contact).

Journal ArticleDOI
TL;DR: In this article, the authors describe the larger scale aspects of the weathering of several southeastern Australian basalts on samples taken from the fresh, rounded, core-stone out to the edge of the surrounding coherent weathering rinds and discuss the changes in bulk-rock chemistry and mineralogy that accompanied this early weathering.
Abstract: The weathering of eastern Australian basalts, sampled from the rounded, hard, core-stone to the rind of softer weathered material, has been examined by bulk chemical analyses, thin section pe- trography, electron microprobe, and X-ray powder diffraction analyses. Using density as a measure of weathering intensity, data from four core-stones show that at a stage of weathering in which the total loss due to dissolution is I/3 (i.e., at the core-stone rim), the percentages lost of the following major elements are: Ca, 85; Mg, 80; Na, 70; K, 50-80; P, 55; Si, 45; Mn, 40; A1, 5; Fe, 0; and Ti, 0. With more intense weathering, deposition of some elements, particularly rare earths and Ba, and mobilization and deposition of A1 and Fe make quantification impossible. The rate of weathering of individual minerals is consistent with the well-known susceptibility series: glass ~ olivine > plagioclase > pyroxene > opaque minerals. Clay minerals in the core-stones are dominated by smectites, whereas those in the surrounding more intensely weathered rinds are dominated by halloysite and goethite. The investigations described in this and succeeding papers of this series were conducted to understand the mechanism of basalt weathering by examining the pro- cess at the maximum available resolution. Optical mi- croscopic, X-ray powder diffraction, transmission and scanning electron microscopic, bulk chemical, energy- dispersive X-ray, electron microprobe, and various other analytical techniques were used to trace mineral alterations and to evaluate these alterations within a broader framework of the bulk changes occurring in the whole rock during the weathering process. The present paper describes the larger scale aspects of the weathering of several southeastern Australian basalts on samples taken from the fresh, rounded, core- stone out to the edge of the surrounding coherent weathering rinds and discusses the changes in bulk- rock chemistry and mineralogy that accompanied this early weathering. Later papers will present detailed ex- aminations of the alteration of individual minerals, including the weathering of olivine to iddingsite and bowlingite and the weathering of plagioclase, pyroxene, and opaque oxides. BACKGROUND

Journal ArticleDOI
TL;DR: In this article, the authors examined the mathematical requirements for obtaining satisfactory solutions for the sea-level equation rather than emphasizing results for the Earth's response to the surface loads and concluded that careful consideration needs to be given to both the definition of the ice load and the geometry of the redistributed water load if geophysically significant Earth-response parameters are to be deduced from observations of relative sea level.
Abstract: Summary. Late Pleistocene and Holocene changes in sea-level at technically stable shorelines contain information on the melting history of the ice sheets and on the response of the Earth to changes in surface loads on time scales of 104yr. Some separation of parameters defining the ice loads and the Earth's response can be achieved by examining sea-level change at different sites around the world and at different epochs. This paper examines the mathematical requirements for obtaining satisfactory solutions for the sea-level equation rather than emphasizing results for the Earth's response to the surface loads. an examination of the equation expressing the sea-level variation on a viscoelastic earth indicates that careful consideration needs to be given to both the definition of the ice load and the geometry of the redistributed water load if geophysically significant Earth-response parameters are to be deduced from observations of relative sea-level. the spectrum of the 5°x 5° area-mean description of the ice load, widely used in glacial rebound studies, contains significant power at high degrees (n > 30) and can result in substantial spatial variations in sea-level unless a thick lithosphere is introduced in the Earth's response function. A smoothed 1°× 1° description of the ice model avoids these high-degree oscillations in relative sea-level and produces satisfactory sea-level results without requiring a thick lithosphere. At far field sites, the Holocene sea-levels are sensitive to the Earth's response to the meltwater loading in the vicinity of the site and a high-degree spatial resolution of coastline geometry is required to model the mantle flow driven by the differential loading about the site. At some sites convergence of the solution to the sea-level equation is not obtained, even when the solution is expanded to degree 180. Convergent solutions at lower degrees can be achieved by introducing earth models with a moderately thick lithosphere. If high-resolution ice and meltwater load models are not used then the tendency will be to overestimate the effective elastic thickness of the lithosphere. Estimates of mantle viscosity are also of questionable value if these high resolution models are not used. A preliminary examination of sea-levels at sites in both the near- and far-field places an upper limit of about 50–80 km on the effective lithospheric thickness. These sea-level observations are also consistent with an upper mantle viscosity of about 1021 Pas with a lower mantle viscosity in the range of 1021-1023Pa s.

Journal Article
TL;DR: Observations are consistent with the concept that T cell-dependent, macrophage-derived mediators are central to the type of malarial immunity that kills parasites inside circulating red cells, and suggest that both TNF and reactive oxygen species are involved, and that the role of TNF may be more indirect, although no less important, than that of reactive forms of oxygen.
Abstract: Cell-mediated immunity to malaria may involve macrophages, the monokines that mediate endotoxicity, and reactive oxygen species. Since interferon-gamma activates macrophages to release reactive oxygen species, and tumor necrosis factor-alpha (TNF-alpha) helps both to mediate endotoxicity and to induce leukocytes to secrete reactive oxygen, we monitored the effects of administering recombinant forms of these cytokines on Plasmodium chabaudi adami infections in mice. We also fed infected mice a diet containing 0.75% butylated hydroxyanisole, a scavenger of free radicals. Infections were suppressed by daily i.p. injections of 5 x 10(4) U of recombinant mouse interferon-gamma from day -1 or by recombinant human TNF released from i.p. osmotic pumps at the rate of 6 x 10(3) U/hr. Degenerate intraerythrocytic parasites (crisis forms) were evident much sooner in the course of the suppressed infections, and parasitemias fell correspondingly earlier. The butylated hydroxyanisole diet, in contrast, enhanced the infections. In these mice crisis forms were seen later, and at higher parasitemias, than they normally occur. These observations are consistent with the concept that T cell-dependent, macrophage-derived mediators are central to the type of malarial immunity that kills parasites inside circulating red cells. They also suggest, but do not prove, that both TNF and reactive oxygen species are involved, and that the role of TNF may be more indirect, although no less important, than that of reactive forms of oxygen.

Journal ArticleDOI
TL;DR: In this paper, the mineral proportions and density profiles in the subducting oceanic lithosphere, modelled by a combination of 80% harzburgite + 20% primitive MORB compositions are calculated as a function of depth under conditions isothermal with surrounding pyrolite mantle, and also for a temperature distribution in which the slab is substantially cooler than surrounding mantle to below 700 km.

Book
01 Jun 1987
TL;DR: Kim Anderson, Yujiro Hayami, Aurelia George, Masayoshi Honma, Keijiro Otsuka, Eric Saxon, Shun-yi Shei, Rodney Tyres
Abstract: Kim Anderson, Yujiro Hayami, Aurelia George, Masayoshi Honma, Keijiro Otsuka, Eric Saxon, Shun-yi Shei, Rodney Tyres

Journal ArticleDOI
TL;DR: The relative numbers and locations of neurons projecting to the “fore‐limb” region of the precentral motor cortex were studied in three monkeys by using the retrograde transport of horseradish peroxidase.
Abstract: The relative numbers and locations of neurons projecting to the "forelimb" region of the precentral motor cortex were studied in three monkeys by using the retrograde transport of horseradish peroxidase. Within the forelimb area of the motor cortex itself, there are extensive and profuse interconnections. However, regions within this area receive afferents from very few neurons in other parts of the motor cortex representing hindlimb or head movements. Most of the motor cortical representation of the forelimb in the anterior bank of the central sulcus is devoid of callosal connections. In both the ipsilateral and contralateral hemispheres, the premotor (lateral area 6) and supplementary motor (medial area 6) areas dominate quantitatively the inputs to the motor cortical representation of the forelimb. The afferents from the premotor area are restricted and come from a region immediately behind the arcuate spur and adjacent parts of the superior and inferior limbs of the arcuate sulcus in the floor, caudal bank, and caudal lip of that sulcus. From the supplementary motor area (SMA), afferents originate from its whole rostrocaudal extent. Thalamic nuclear regions projecting to a restricted zone in the anterior bank of the central sulcus are recipients of cerebellar and somatosensory outputs. Involvement of more anterior parts of the motor cortex by the tracer labels thalamocortical cells, which are targets of pallidal output also. Within the first somatosensory cortex, cytoarchitectonic areas 1, 2, and 3a project to area 4. The projection from area 3a may provide one pathway by which short-latency peripheral inputs, especially from muscles, reach the motor cortex.

Journal ArticleDOI
01 Feb 1987-Nature
TL;DR: In this article, maps of the magnetic field at the core-mantle boundary for 1715-1980 reveal static features in the field and an absence of westward drift from much of the core mantle boundary.
Abstract: Maps of the magnetic field at the core–mantle boundary for 1715–1980 reveal static features in the field and an absence of westward drift from much of the core–mantle boundary. The static features suggest that flow in the core is coupled to the mantle. We examine different coupling mechanisms and predict lateral inhomogeneity at the core–mantle boundary. Comparison with models of the lower mantle and core–mantle boundary derived seismically and from the geoid is encouraging, though their resolution is currently inadequate for a full comparison to be made with the much better-resolved magnetic field.

Journal ArticleDOI
TL;DR: In this paper, two natural classes of kernel density estimators for use with spherical data are studied, and explicit formulae are given for bias, variance and loss, and large-sample properties of these quantities are described.
Abstract: SUMMARY We study two natural classes of kernel density estimators for use with spherical data. Members of both classes have already been used in practice. The classes have an element in common, but for the most part they are disjoint. However, all members of the first class are asymptotically equivalent to one another, and to a single element of the second class. In this sense the second class 'contains' the first. It includes some estimators which out-perform all those in the first class, if loss is measured in either squared-error or Kullback-Leibler senses. Explicit formulae are given for bias, variance and loss, and large-sample properties of these quantities are described. Numerical illustrations are presented.

Journal ArticleDOI
08 Oct 1987-Nature
TL;DR: A recombinant vaccinia virus expressing murine interleukin-2 (IL-2) is described and it is shown that athymic nude mice infected with the recombinant virus resolve the virus infection rapidly whereas miceinfected with control virus develop a progressive vaccinal disease.
Abstract: Vaccinia virus recombinants that express cloned genes encoding antigens of unrelated infectious agents, such as hepatitis B virus1 and human immunodeficiency virus (HIV)2,3, provide a new approach to the development of live vaccines. Although there is evidence that genetically engineered vaccinia viruses have reduced pathogenicity4 a major obstacle to their use as vaccines is that severe complications can occur after vaccination, especially in immunodeficient individuals5,6. We describe here a recombinant vaccinia virus expressing murine interleukin-2 (IL-2) and show that athymic nude mice infected with the recombinant virus resolve the virus infection rapidly whereas mice infected with control virus develop a progressive vaccinal disease. By incorporating the gene for IL-2 in live virus vaccines it may be possible to prevent the severe complications that arise in recipients with an impaired immune system.

Journal ArticleDOI
TL;DR: Results directly show a central release of SPiR with excitation of nociceptors by heat in barbiturate anaesthetized spinal cats.

Journal Article
TL;DR: The outcome of injecting recombinant human TNF/cachectin into normal mice and others with low parasitemias of Plasmodium vinckei showed how precisely the pathologic features of the terminal stages of this infection could be produced.
Abstract: The authors have earlier proposed that tumor necrosis factor (TNF) might contribute to the pathology of malaria. Here they report the outcome of injecting recombinant human TNF/cachectin into normal mice and others with low parasitemias (6-35%) of Plasmodium vinckei. The object was to see how precisely the pathologic features of the terminal stages of this infection could be produced, when parasitemias are 70-80%. Hypoglycemia, mid-zonal liver damage, and pulmonary accumulation of neutrophils in the pulmonary vasculature, all of which are seen in severe P vinckei infection, occurred within 4-12 hours after the mildly infected mice received TNF/cachectin. Uninfected mice were much less susceptible. TNF/cachectin also increases plasma lactate, a change seen in both the human and rodent diseases. From these findings and the recent literature on TNF/cachectin, including its detection in serum from malarial patients, it seems likely that excessive release of this monokine could account for certain of the unexplained pathologic features of human malaria.

Journal ArticleDOI
01 Feb 1987-Geology
TL;DR: In this paper, the authors proposed that many intermediate and high-pressure granulites form in the lower parts of thickened crust and therefore require a two-stage cycle of tectonism to be uplifted and exposed at the earth9s surface.
Abstract: Rocks buried in the upper part of a doubly thickened crust during orogeny can show prograde reactions with transitional features from lower grade rocks up to granulite facies. They can be exposed at the earth9s surface within this one erogenic cycle. For example, the granulites exposed in British Columbia have concordant U/Pb zircon ages of 65–85 Ma. In contrast, rocks buried in the lower part of a thickened crust will crystallize granulites that typically show only retrograde relations with younger, lower grade rocks. At the cessation of orogeny, such rocks will undergo near-isobaric cooling from the peak metamorphism and can have very long residence times at the base of a crust of normal thickness. These granulites require a second orogeny to uplift and expose them at the surface. As an example, the Archean granulites of Enderby Land, Antarctica, were metamorphosed at 3070 Ma at 1000 °C at 8–10-kbar pressure. They then followed at least a 400 °C isobaric cooling path. They also had a prolonged residence time of 2000 m.y. near the base of the crust before uplift. No doubt a continuum exists between these extremes, but it is proposed that many intermediate- and high-pressure granulites form in the lower parts of thickened crust and therefore require a two-stage cycle of tectonism to be uplifted and exposed at the earth9s surface. Although most granulites probably form in thickened crust at active plate margins, underplating of normal (30–40-km thickness) crust by mantle melts during extension can also produce granulites. These granulites would also undergo isobaric cooling and require a later orogeny to expose them. An example is the Paleozoic Lachlan Fold Belt of eastern Australia, which has undergone only minor uplift since the major ultrametamorphism at about 400 Ma. However, isotopic, petrologic, and geochemical differences are to be expected between these extremes of granulite formation.

Journal ArticleDOI
TL;DR: In this article, the authors compare different data-driven approaches to the determination of window size, and show that the observable window ĥ� c>>\s performs as well as the so-called "optimal" but unattainable window h>>\s to both first and second order.
Abstract: Let h o, ĥ o and ĥ c be the windows which minimise mean integrated square error, integrated square error and the least-squares cross-validatory criterion, respectively, for kernel density estimates. It is argued that ĥ o, not h o, should be the benchmark for comparing different data-driven approaches to the determination of window size. Asymptotic properties of h o-ĥ o and ĥ c -ĥ o, and of differences between integrated square errors evaluated at these windows, are derived. It is shown that in comparison to the benchmark ĥ o, the observable window ĥ c performs as well as the so-called “optimal” but unattainable window h o, to both first and second order.

Journal ArticleDOI
TL;DR: In this paper, a simpie structural backscatter model for a forest stand, suitable for use with L-band HH polarized radar imagery, was used to explain the increased level of backscattering observed from flooded forests.
Abstract: A simpie structural backscatter model for a forest stand, suitable for use with L-band HH polarized radar imagery, is used to explain the increased level of backscattering observed from flooded forests. Measurements made of relative levels of backscatter from SIR-B image data of a flooded Australian forest are consistent with an interpretation based upon scattering mechanisms involving both the tree components and the understorey or forest floor. The change in Fresnel power reflection coefficient of the ground with flooding is advanced as the cause of the enhancement in backscattered power levels.

Journal ArticleDOI
TL;DR: In low- to medium-grade metamorphic environments, the mobilization of species is closely associated with the operation of solution-precipitation creep processes during foliation development as mentioned in this paper.

Journal ArticleDOI
TL;DR: In this article, the physical processes of raindrop impact and water flow on the leaves and branches of selected tropical tree species were examined under laboratory conditions using simulated rainfall, and inclined branches were found to be particularly efficient in detaining impacting water droplets.
Abstract: The physical processes of raindrop impact and water flow on the leaves and branches of selected tropical tree species were examined under laboratory conditions using simulated rainfall. Inclined branches were found to be particularly efficient in detaining impacting water droplets. This efficiency in raindrop detention increases linearly as a function of branch inclination on branches that are initially dry. On branches that have been thoroughly wetted, this increase in raindrop detention with branch inclination is best expressed as a logarithmic function. At branch inclinations of 60" above the horizontal, the quantity of branchflow was found to be > 80 per cent of the total quantity of impacting rainfall, indicating that < 20 per cent was lost to rainsplash. The strong positive relationship between branchflow and branch inclination explains why trees with large projected areas of steeply inclined upthrust branches have significant quantities of intercepted water draining from their branches and trunks under heavy rainfall conditions. This drainage from the woody frame of trees influences surficial processes by generating both stemflow and large throughfall droplets.

Journal ArticleDOI
TL;DR: A quantitative synthesis of published research showed that the sex difference in depression is age specific, and the age-specific nature of these sex differences may be explainable in terms of differences in social roles at various ages.
Abstract: It is commonly believed that depression is more common in females than in males. A quantitative synthesis of published research showed, however, that the sex difference is age specific. There is little sex difference in either childhood or advanced old age, but a notable sex difference in middle life. This sex difference appears because rates for females rise sharply from childhood to adulthood and then decline somewhat in old age. By contrast, rates for males show a small rise in early adulthood but are otherwise fairly stable throughout life. The age-specific nature of these sex differences may be explainable in terms of differences in social roles at various ages.