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141.
142.
We discuss Arp's hypothesis that the HII regions are more numerous and more conspicuous on the side of a galaxy facing its companion. Arp's hypothesis seems not to be true if we add to Hodge's sets of galaxies only the most probably tidally-interacting cases. 相似文献
143.
144.
J. A. Adam 《Astrophysics and Space Science》1977,47(1):L5-L7
Simple bounds on the growth rates of magneto-atmospheric instabilities are derived, both for perturbations along and perpendicular to a horizontal magnetic field. The physical significance of a singular level for stable modes is briefly discussed. 相似文献
145.
It is shown that the non-keplerian character of the rotation of the ring of gas particles in a close binary system gives too large an amplitude of the radial velocity curve if this amplitude is determined from the positions of the emission lines of the ring. 相似文献
146.
147.
Sokołowski A Wołowicz M Hummel H Smolarz-Górska K Fichet D Radenac G Thiriot-Quiévreux C Namieśnik J 《Marine pollution bulletin》2004,49(1-2):17-22
Recent studies of the Baltic clam Macoma balthica (L.) from the southern Baltic (the Gulf of Gdansk) have revealed striking morphological, histological and cytogenetic features. Strong deformation of the shell, including elongation of the posterior end and the appearance of an easily visible flexure in this part, has been recorded. The population contribution of the deformed blunt shelled ("irregular") clams ranged from 0% to 65% and tended to increase with depth. The morphologically "irregular" clams had higher accumulated tissue concentrations of trace metals (As, Ag, Cd, Pb, Cu and Zn), indicating a different metal handling ability. Adverse conditions in deeper water regions of the Gulf (e.g. hypoxia, hydrogen sulphide, elevated bioavailability of contaminants) have been suggested as inducers of the phenotypical changes (morphological deformation) in part of the population and, in parallel, of the specific physiological adaptations that result in higher metal accumulation in the "irregular" clams. Cytogenetic and histological analyses showed the presence of tumours in gill cells and digestive system of the affected clams, the prevalence of disseminated neoplasia ranging from 0% to 94% depending on the site. The disease was manifested by a modified karyotype (i.e. an abnormal number and morphology of chromosomes), a higher activity of nucleolar organizer regions (AgNORs), and tissue lesions (enlarged cells, actively proliferative with pleomorphic nuclei). Bottom sediments showed acute toxicity and have been proposed as a source of an initialising carcinogenic factor. However, none of the ecotoxicological studies provided was successful in the clear demonstration of a single (or multifactorial) agent that can account for the disseminated neoplasia. 相似文献
148.
William J. Green Brian R. Stage Bonnie Jo Bratina Shannon Wagers Adam Preston Kevin O’bryan Joseph Shacat Silvia Newell 《Aquatic Geochemistry》2004,10(3-4):303-323
Lake Vanda is a closed-basin, permanently ice-covered lake located in the Wright Valley of Antarctica. The lakes more important geochemical features include the fact that it is fed by a single glacial melt water stream for only 6–8weeks out of the year; that it has remained stratified for more than a millennium; and that, like other lakes in the region, it is remote from anthropogenic influence. These, together with the fact that it is among the least biologically productive lakes in the world, make it an ideal system for examining the transport, cycling and fate of trace metals in the aquatic environment. Like others before us, we view this lake as a natural geochemical laboratory, a flask in the desert. This paper presents the first set of closely spaced, vertical, profiles for dissolved and particulate Mn, Fe, Ni, Cu, Zn and Cd in the water column. Despite the absence of an outflow, metals in the fresh upper waters of the lake have extremely low concentrations, in the pico-molar to nano-molar range, and are partitioned largely into dissolved rather than particulate phases. Efficient metal scavenging by particles from these oxygen-rich waters is indicated. Significant increases in metal concentrations begin to appear at depth, between 57 and 60m, and these increases coincide with the onset of manganese oxide dissolution in oxic, but lower pH waters. Vertical profiles suggest that the entire suite of trace metals (Ni, Cu, Zn, and Cd) is being released from manganese oxide carrier phases. Thermodynamic analysis indicates that Mn3 O4 (i.e., the mineral hausmannite) may be important in metal sequestration and recycling in the deeper waters of Lake Vanda. Manganese-reducing organisms reported by Bratina etal. (1998) are active in the zone of metal release and these could also contribute to the observed cycling. 相似文献
149.
Adam C. Simon Thomas Pettke Philip M. Piccoli 《Geochimica et cosmochimica acta》2006,70(22):5583-5600
The effect of sulfur on the partitioning of Cu in a melt-vapor-brine ± magnetite ± pyrrhotite assemblage has been quantified at 800 °C, 140 MPa, fO2 = nickel-nickel oxide (NNO), logfS2=-3.0 (i.e., on the magnetite-pyrrhotite curve at NNO), logfH2S=-1.3 and logfSO2=-1. All experiments were vapor + brine saturated. Vapor and brine fluid inclusions were trapped in silicate glass and self-healed quartz fractures. Vapor and brine are dominated by NaCl, KCl and HCl in the S-free runs and NaCl, KCl and FeCl2 in S-bearing runs. Pyrrhotite served as the source of sulfur in S-bearing experiments. The composition of fluid inclusions, glass and crystals were quantified by laser-ablation inductively coupled plasma mass spectrometry. Major element, chlorine and sulfur concentrations in glass were quantified by using electron probe microanalysis. Calculated Nernst-type partition coefficients (±2σ) for Cu between melt-vapor, melt-brine and vapor-brine are , , and , respectively, in the S-free system. The partition coefficients (±2σ) for Cu between melt-vapor, melt-brine and vapor-brine are , , and , respectively, in the S-bearing system. Apparent equilibrium constants (±1σ) describing Cu and Na exchange between vapor and melt and brine and melt were also calculated. The values of are 34 ± 21 and 128 ± 29 in the S-free and S-bearing runs, respectively. The values of are 33 ± 22 and60 ± 5 in the S-free and S-bearing runs, respectively. The data presented here indicate that the presence of sulfur increases the mass transfer of Cu into vapor from silicate melt. Further, the nearly threefold increase in suggests that Cu may be transported as both a chloride and sulfide complex in magmatic vapor, in agreement with hypotheses based on data from natural systems. Most significantly, the data demonstrate that the presence of sulfur enhances the partitioning of Cu from melt into magmatic volatile phases. 相似文献
150.
Francine McCarthy Sarah Tiffin Adam Sarvis John McAndrews Stephan Blasco 《Journal of Paleolimnology》2012,47(3):429-445
Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods)
record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has
been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the
end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these
are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven
far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions
that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for
hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones
2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated
fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated
with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800–7,200 (9,900–8,050 cal)
BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians:
predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people
around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations
in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate
change and resource management in the Great Lakes, one of the world’s largest freshwater resources. 相似文献