Umbral oscillations and penumbral waves in Hα     

R. L. Moore  Frances Tang 《Solar physics》1975,41(1):81-88

We present examples of umbral oscillations observed on Big Bear H filtergram movies and investigate the relation between umbral oscillations and running penumbral waves occurring in the same sunspot. Umbral oscillations near the center of the umbra are probably physically independent of the penumbral waves because the period of these umbral oscillations (150 s) is shorter than the penumbral wave period (270 s) but not a harmonic. We also report dark puffs which emerge from the edge of the umbra and move outward across the penumbra, and which have the same period as the running penumbral waves. We interpret these dark puffs to be the extension of chromospheric umbral oscillations at the edge of the umbra. It is suggested that the dark puffs and the running penumbral waves have a common source: photospheric oscillations just inside the umbra.  相似文献   

Markets, ethnicity and environment in a vulnerable landscape: the case of small-scale vegetable production on the Jos Plateau, Nigeria, 1991–2001     

Gina Porter  Frances Harris†  Fergus Lyon‡  Jasper Dung§  A A Adepetu§ 《The Geographical journal》2003,169(4):370-381

This paper explores changing socio-environmental interactions in the vegetable producing areas of the Jos Plateau over the decade 1991–2001. It considers the pressures of market forces and ethnic competition and the tensions which arise as interactions between the two are played out in a fragile physical, social and institutional environment. The region has seen a remarkable expansion in irrigated vegetable production, as dry season surveys in 1991 and 2001 attest. Local farmers appear extremely positive in their perceptions of change, pointing not only to expanded production, but also to other improvements, like growing percentages of children in school and improved transport. But behind this rosy view of change there are tensions and a series of unresolved questions which may soon have to be addressed. We examine the changing nature of socio-environmental interactions over the decade and ask whether and how current levels of production can be sustained in the context of a currently largely unregulated production system and growing competition for land. Given the important role of the Plateau as a source of temperate fruit and vegetables in West Africa, these questions have significance far beyond the Plateau region itself.  相似文献   

Feature     

Frances Wall 《Geology Today》2003,19(6):206-211

Numerous world class mineral deposits make the Kola Peninsula a 'Mecca' for mineralogists, and key economic deposits make it one of Russia's most important industrial areas. For geologists there is the challenge of explaining how this situation has come about.  相似文献   

Late Holocene δC and pollen records of paleosalinity from tidal marshes in the San Francisco Bay estuary, California     

Frances Malamud-Roam  B. Lynn Ingram 《Quaternary Research》2004,62(2):134-145

Records of stable carbon isotopes (δ¹³C) are presented from cores collected from four San Francisco Bay marshes and used as a proxy for changes in estuary salinity. The δ¹³C value of organic marsh sediments are a reflection of the relative proportion of C₃ vs. C₄ plants occupying the surface, and can thus be used as a proxy for vegetation change on the marsh surface. The four marshes included in this study are located along a natural salinity gradient that exists in the San Francisco Bay, and records of vegetation change at all four sites can be used to infer changes in overall estuary paleosalinity. The δ¹³C values complement pollen data from the same marsh sites producing a paleoclimate record for the late Holocene period in the San Francisco Bay estuary. The data indicate that there have been periods of higher-than-average salinity in the Bay estuary (reduced fresh water inflow), including 1600-1300 cal yr B.P., 1000-800 cal yr B.P., 300-200 cal yr B.P., and ca. A.D. 1950 to the present. Periods of lower-than-average salinity (increased fresh water inflow) occurred before 2000 cal yr B.P., from 1300 to 1200 cal yr B.P. and ca. 150 cal yr B.P. to A.D. 1950. A comparison of the timing of these events with records from the California coast, watershed, and beyond the larger drainage of the Bay reveals that the paleosalinity variations reflected regional precipitation.  相似文献   

Low Food Availability Narrows the Tolerance of the Copepod Eurytemora affinis to Salinity,but Not to Temperature     

Bruce G. Hammock  Sarah Lesmeister  Ida Flores  Gideon S. Bradburd  Frances H. Hammock  Swee J. Teh 《Estuaries and Coasts》2016,39(1):189-200

  相似文献   

A suggested origin of MARID xenoliths in kimberlites by high pressure crystallization of an ultrapotassic rock such as lamproite   总被引：1，自引：0，他引：1  

Frances G. Waters 《Contributions to Mineralogy and Petrology》1987,95(4):523-533

Chemical, mineralogical and isotopic studies have been made on nodules of the MARID (Mica-Amphibole-Rutile-Ilmenite-Diopside) xenolith suite in southern African kimberlites. All are ultramafic and ultrapotassic (MgO= 20–25%, K₂O=4–9%), with bulk compositions reflecting the wide variation in relative proportions of the five minerals amongst the nodules. They are comparable in major element compositions to magnesian lamproites, in particular the ultrabasic olivine-lamproites of Western Australia. In a number of high pressure experimental studies on ultra-potassic rocks, the phases produced between 25–30 kbar from compositions comparable to those of MARID rocks (in the presence of additional water), were predominantly phlogopite and diopside (±K-richterite, ±ilmenite, ±rutile). Furthermore the compositions of experimental minerals produced in the synthetic-biotite-mafurite-H₂O system by Edgar et al. (1976) are similar to those in MARID rocks.It is suggested on the basis of these observations and the textural appearance of MARID rocks that they are magmatic compositional equivalents of MgO-rich lamproites that crystallized at high pressures. While lamproites have higher average concentrations of incompatible elements, (including REE), some MARID rocks have comparable abundances. It is suggested that late stage vapour-rich melts carrying substantial REE and other incompatible elements escaped from crystallizing MARID magmas into surrounding subcontinental lithosphere, thus resulting in lower levels of these elements in most MARID rocks. In contrast faster crystallization of lamproitic rocks under volcanic/ hypabyssal conditions would prevent similar losses.The MARID proto-magmas are thought to be either partial melts of metasomatised phlogopite peridotite, or small volume asthenospheric melts which are modified and further enriched by incorporation of small partial melts of enriched subcontinental lithosphere during magma ascent.  相似文献   

Laboratory tests as a basis for the control of sewage sludge dumping at sea     

Frances L Franklin 《Marine pollution bulletin》1983,14(6):217-223

Toxicity and bioaccumulation studies were carried out on a number of UK sewage sludges to determine whether laboratory experiments could be used to regulate sludge dumping at sea. Whilst the acute toxicity of sewage sludges to adult marine organisms was generally low, shrimp larvae were found to be up to 500 times more sensitive than adults of the same species. No significant bioaccumulation of mercury or cadmium could be detected following up to 60 days exposure of fish, shrimps and mussels to the most heavily contaminated sludges available, although there was some uptake of lead, zinc and copper.  相似文献   

Fish assemblage structure in relation to environmental variation in a Texas Gulf coastal wetland     

Frances P. Gelwick  Senol Akin  D. Albrey Arrington  Kirk O. Winemiller 《Estuaries and Coasts》2001,24(2):285-296

We described seasonal fish-assemblages in an estuarine marsh fringing Matagorda Bay, Gulf of Mexico. Habitat zones were identified by patterns of fish species abundance and indicator species optima along gradients in salinity, dissolved oxygen (DO), and depth in our samples. Indicators of the lower brackish zone (lower lake and tidal bayou closest to the bay) were gulf menhaden (Brevoortia patronus), bay anchovy (Anchoa mitchilli), silver perch (Bairdiella chrysoura), and spotted seatrout (Cynoscion nebulosus) at salinity >15‰, DO 7–10 mg l⁻¹, and depth <0.5 m. Indicators of the upper brackish zone (lake and fringing salt marsh) were pinfish (Lagodon rhomboides) and spot (Leiostomus xanthurus) at salinity 10–20‰, DO >10 mg l⁻¹, and depth <0.5 m. In the freshwater wetland zone (diked wetland, ephemeral pool, and perennial scour pool), indicators were sheepshed minnow (Cyprinod on variegatus), rainwater killifish (Lucania parva), mosquitofish (Gambusia affinis), and sailfin molly (Poecilia latipinna) at salinity <5‰, DO <5 mg l⁻¹, and depth ≥1 m. In the freshwater channelized zone (slough and irrigation canal), indicators were three sunfish species (Lepomis), white crappie (Pomoxis annularis), and gizzard shad (Dorosoma cepedianum) at salinity <5‰, DO <5 mg l⁻¹, and depth >1.5 m. In brackish zones, seasonal variation in species diversity among sites was positively correlated with temperature, but assemblage structure also was influenced by depth and DO. In the freshwater zones, seasonal variation in species diversity among sites was positively correlated with depth, DO, and salinity, but assemblage structure was weakly associated with temperature. Species diversity and assemblage structure were strongly affected by the connectivity between freshwater wetland and brackish zones. Uncommon species in diked wetlands, such as tarpon (Megalops atlanticus) and fat sleeper (Dormitator maculatus), indicated movement of fishes from the brackish zone as the water level rose during natural flooding and scheduled (July) releases from the diked wetland. From September to July, diversity in the freshwater wetland zone decreased as receding waters left small isolated pools, and fish movement became blocked by a water-control structure. Subsequently, diversity was reduced to a few species with opportunistic life histories and tolerance to anoxic conditions that developed as flooded vegetation decayed.  相似文献   

Calcio-carbonatite melts and metasomatism in the mantle beneath Mt. Vulture (Southern Italy)     

Gianluigi Rosatelli  Frances Wall  Francesco Stoppa 《Lithos》2007,99(3-4):229-248

At Mt. Vulture volcano (Basilicata, Italy) calcite globules (5–150 μm) are hosted by silicate glass pools or veins cross-cutting amphibole-bearing, or more common spinel-bearing mantle xenoliths and xenocrysts. The carbonate globules are rounded or elongated and are composed of a mosaic of 2–20 μm crystals, with varying optical orientation. These features are consistent with formation from a quenched calciocarbonatite melt. Where in contact with carbonate amphibole has reacted to form fassaitic pyroxene. Some of these globules contain liquid/gaseous CO₂ bubbles and sulphide inclusions, and are pierced by quench microphenocrysts of silicate phases. The carbonate composition varies from calcite to Mg-calcite (3.8–5.0 wt.% MgO) both within the carbonate globules and from globule to globule. Trace element contents of the carbonate, determined by LAICPMS, are similar to those of carbonatites worldwide including ΣREE up to 123 ppm. The Sr–Nd isotope ratios of the xenolith carbonate are similar to the extrusive carbonatite and silicate rocks of Mt. Vulture testifying to derivation from the same mantle source. Formation of immiscibile silicate–carbonatite liquids within mantle xenoliths occurred via disequilibrium immiscibility during their exhumation.  相似文献   

Sea level,climate change and coastal evolution in Morar,northwest Scotland     

Shennan  Ian  Tooley  Michael  Green  Frances  Innes  Jim  Kennington  Kevin  Lloyd  Jeremy  Rutherford  Mairead 《Geologie en Mijnbouw》1998,77(3-4):247-262

Analyses of geomorphologically contrasting sites in Morar, NW Scotland, describe the forcing mechanisms of coastal change. Isolation basins (i.e. basins behind rock sills and now isolated from the sea following isostatic uplift) accumulated continuous marine and freshwater sediments from c.12 to 2 ka BP. Raised dune, marsh and wetland sites register breaching, migration and stability of dunes from c. 9 to 2 ka BP. High-resolution methods designed to address issues of macroscale and microscale sea-level changes and patterns of storminess include 1-mm sampling for pollen, dinocyst and diatom analyses, infra-red photography, X-ray photography and thin-section analysis. The data enhance the record of relative sea-level change for the area. Major phases of landward migration of the coast occurred during the period of low sea-level rise in the mid-Holocene as the rate of rise decreased from c. 3 to < 1 mm/year. Relative sea-level change controls the broad pattern of coastal evolution at each site; local site-specific factors contribute to short-term process change. There is no record of extreme events such as tsunami. Within a system of dynamic metastable equilibrium, the Holocene records show that site-specific factors determine the exact timing of system breakdown, e.g. dune breaching, superimposed on regional sea-level rise. The global average sea-level rise of 3 to 6 mm/yr by AD 2050 predicted by IPCC would only partly be offset in the Morar area by isostatic uplift of about 1 mm/yr. A change from relative sea-level fall to sea-level rise, in areas where the regional rate of uplift no longer offsets global processes, is a critical factor in the management of coastal resources.  相似文献