Laboratory Modeling of Standing Shocks and Radiatively Cooled Jets with Angular Momentum     

D. J. Ampleford  S. V. Lebedev  A. Ciardi  S. N. Bland  S. C. Bott  G. N. Hall  N. Naz  C. A. Jennings  M. Sherlock  J. P. Chittenden  A. Frank  E. Blackman 《Astrophysics and Space Science》2007,307(1-3):51-56

Collimated flows ejected from young stars are believed to play a vital role in the star formation process by extracting angular momentum from the accretion disk. We discuss the first experiments to simulate rotating radiatively cooled, hypersonic jets in the laboratory. A modification of the conical wire array $z$-pinch is used to introduce angular momentum into convergent flows of plasma, a jet-forming standing shock and into the jet itself. The rotation of the jet is evident in laser imaging through the presence of discrete filaments which trace the rotational history of the jet. The presence of angular momentum results in a hollow density profile in both the standing conical shock and the jet.  相似文献   

Structure and texture of a gravelly barrier island in the Fitzroy estuary,Western Australia,and the role of mangroves in the shore dynamics     

J.N. Jennings  R.J. Coventry 《Marine Geology》1973,15(3):145-167

In the stratification of the most coarse-textured barrier island of a system of sand and gravel barrier spits and islands on Point Torment peninsula, King Sound, W.A., foreslope beds due to swash-backwash on the beach face are unimportant. The main units are steeply-dipping backslope beds and topslope beds of gentle, chiefly landward inclination. Their bimodal sediments are poorly sorted for wave-built features. A very coarse mode usually at ?1.5 to ?2 ?i; belongs to a population of well-rounded but platy, impure limestone, of local but unlocated source, whereas the fine mode, almost invariably 1.00 to 1.25 ?i;, represents a population of quartz sand fed from low and sub-tidal estuarine shoals. The two populations are thought to derive from the surface creep and saltation cloud components of “traction carpets”. Swash of intermediate energy waves forms the topslope beds through percolation. Washover by waves of translation generated by occasional hurricanes erodes the top of the feature and deposits the backslope beds on the rear face in standing water at abnormally high levels through storm set-up. In both, unidirectional currents produce sediments with certain resemblances to fluvial “traction clog” deposits.Dated by underlying mangrove wood of 1200 B.P. in front and of 500 B.P. in the rear, this barrier probably retreated through mangrove swamp in the manner of some presently active members of the barrier system. The seaward mangrove swamps neither protect the embankments behind nor suffer seriously from the waves rolling the latter landward.  相似文献   

Electrical interferences observed in the Cassini CIRS spectrometer     

Cheong Chan  Shane Albright  Nicolas Gorius  John Brasunas  Don Jennings  F. Michael Flasar  Ronald Carlson  Ever Guandique  Conor Nixon 《Experimental Astronomy》2015,39(2):367-386

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Effects of acoustic alarms, designed to reduce small cetacean bycatch in gillnet fisheries, on the behaviour of North Sea fish species in a large tank     

Kastelein RA  van der Heul S  van der Veen J  Verboom WC  Jennings N  de Haan D  Reijnders PJ 《Marine environmental research》2007,64(2):160-180

World-wide many cetaceans drown incidentally in fishing nets. To reduce the unwanted bycatch in gillnets, pingers (acoustic alarms) have been developed that are attached to the nets. In the European Union, pingers will be made compulsory in some areas in 2005 and in others in 2007. However, pingers may effect non-target marine fauna such as fish. Therefore in this study, the effects of seven commercially-available pingers on the behaviour of five North Sea fish species in a large tank were quantified. The species tested were: sea bass (Dicentrarchus labrax), pout (Trisopterus luscus), thicklip mullet (Chelon labrosus), herring (Clupea harengus), and cod (Gadus morhua). The fish were housed as single-species schools of 9-13 individuals in a tank. The behaviour of fish in quiet periods was compared with their behaviour during periods with active pingers. The results varied both between pingers and between fish species. Sea bass decreased their speed in response to one pinger and swam closer to the surface in response to another. Thicklip mullet swam closer to the bottom in response to two pingers and increased their swimming speed in response to one pinger. Herring swam faster in response to one pinger, and pout and cod (close relatives) showed no behavioural responses to any of the pingers. Of the seven pingers tested, four elicited responses in at least one fish species, and three elicited no responses. Whether similar responses would be elicited in these fish species in the wild, and if so, whether such responses would influence the catch rate of fisheries, cannot be derived from the results of this study. However, the results indicate the need for field studies with pingers and fish. Based on the small number of fish species tested, the present study suggests that the higher the frequency of a pinger, the less likely it is to affect the behaviour of marine fish.  相似文献   

Highlights of fifty years of atmospheric aerosol research at Mace Head   总被引：1，自引：0，他引：1  

T.C. O'Connor  S.G. Jennings  C.D. O'Dowd   《Atmospheric Research》2008,90(2-4):338-ICNAA07

This paper summarises the development and principal results of fifty years of research on aerosols in the marine atmosphere at Mace Head Atmospheric Research Station on the west coast of Ireland. It concentrates on the sources, physico-chemical properties, number and mass concentrations, size range, volatility and chemical composition of aerosols in different air masses. It also examines optical properties of the aerosols and their long-range transport.  相似文献   

Perspectives on Quaternary outreach and aspirations for the future     

David E. Anderson  Eleanor J. Brown 《Proceedings of the Geologists' Association. Geologists' Association》2010,121(4):455-467

Outreach arising from the study of the British Quaternary offers many benefits for society, especially because of its relevance for understanding contemporary environmental issues and environmental change. Outreach is also important for the long-term health of the academic discipline and research agenda. Through engaging with the formal education system, institutions, policy makers, planners and with the public at large, Quaternary specialists can do much to advance interest in and appreciation of the British landscape and its Quaternary record. This opinion and review article considers the importance and benefits of outreach in its many forms, makes the case for practitioners to continue and increase their involvement, offers examples of good practice, and sets out aspirations for the future.  相似文献   

Holocene environmental evolution of the SE Greenland Shelf North and South of the Denmark Strait: Irminger and East Greenland current interactions     

A. Jennings  J. Andrews  L. Wilson 《Quaternary Science Reviews》2011,30(7-8):980-998

Holocene climatic and paleoceanographic development of the SE Greenland Shelf is studied from cores MD99-2317 and MD99-2322, at sites north and south of the Denmark Strait, respectively. Lithofacies, IRD counts, calcium carbonate percentages, benthic and planktic foraminiferal assemblages and oxygen isotope analyses, and summer SSTs reveal significant climate variations in the Holocene driven by declining solar insolation and its interaction with waning continental ice sheets, and changing atmospheric pressure patterns. Large changes in the East Greenland and Irminger Currents and the Greenland Ice Sheet are manifested as a 4-part division of the Holocene. An early Holocene cold interval dominated by melting of the Greenland Ice Sheet and Polar Front retreat extends from 11.8 to 9.5 cal kyr BP. A cold interval from 9.5 to 8.1 cal kyr BP involved episodic cooling of the Irminger Current resulting from the last phases of Laurentide Ice Sheet deglaciation and delayed the Holocene optimum off East Greenland by 3 kyr relative to peak summer solar insolation, which likely helped to limit the early Holocene melting of the Greenland Ice Sheet. The period 8.1–3.5 cal kyr BP represents a climatic optimum interval of maximum Greenland Ice Sheet retreat and strong Irminger Current inflow to the Denmark Strait. Between 6.8 and 3.5 cal kyr BP, the Irminger Current penetrated further North into the Nordic Seas than has been observed in recent decades. This signal is consistent with diminished northerly winds, a weaker Greenland High and contracted subpolar gyre. By 5 cal kyr BP, periods of increased Polar Water and decreasing salinity in the Irminger Current suggest a transition toward expansion of the subpolar gyre and increased Polar Water in the EGC. The Neoglacial interval from 3.5 to 0.2 cal kyr BP was cold and variable with increased freshwater forcing from the Arctic Ocean, advance of the Greenland Ice Sheet and southward advance of the Polar Front. Enhanced northerly winds and a strengthened Greenland High are consistent with thicker and more extensive Polar Water and greatly diminished northward advection of Irminger Current in the Denmark Strait.  相似文献   

Erratum to “Environmental correlates of large-scale spatial variation in the δC of marine animals” [Estuar. Coast. Shelf Sci. 81 (2009), 368–374]     

Carolyn Barnes  Simon Jennings  Jon. T. Barry 《Estuarine, Coastal and Shelf Science》2009,82(4):692

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Dynamic properties of planar,coupled shear walls     

Paul C. Jennings  Knut S. Skattum 《地震工程与结构动力学》1972,1(4):387-405

The paper is a study of the natural frequencies and mode shapes of planar, coupled shear walls, a common lateral resistive element in building construction. The equations of motion are derived for the general case, and the eigenvalue problem associated with free vibrations of equal, constant shear walls is solved, both with and without the inclusion of the inertia of vertical motion. Explicit solutions are presented for the characteristic equation and the mode shapes and the results are illustrated with figures, including an example calculation based on the shear walls of the Mt. McKinley Building, damaged by the Alaskan earthquake of 1964. The results affirm the necessity of including vertical displacement of the shear walls in the analysis of such systems, and suggest that the inertia of vertical motion also must be considered in the analysis for certain ranges of the parameters.  相似文献   

Climatic and geographic patterns of river runoff formation in Northern Eurasia     

Alexander Onuchin  Heiko Balzter  Helen Borisova  Eleanor Blyth 《Advances in water resources》2006

Siberian rivers are of global importance as they impact on the freshwater budget of the Arctic Ocean, which affects the Thermo-Haline circulation in the North Atlantic Ocean. Siberian rivers, in particular the tributaries to the larger rivers, are under-represented in the international river-regime databases. The runoff of three Russian rivers in the Central Siberian taiga (Kureyka, Karabula and Erba) is modelled to analyse the relative influence of climate. In addition three rivers (Rhine, Maas and Odra) in Western Europe are similarly assessed as a control. The results show that the role of precipitation and autocorrelation as factors in the formation of river runoff is stronger under oceanic climate conditions, increasing from the central regions of Northern Eurasia towards the Arctic Ocean in the North and the Atlantic in the West. At the same time the influence of summer temperatures is weakened. The formation of Northern Eurasian river runoff appears to be influenced by periodically thawing top horizons of permafrost soil. Time served as an indicator for land use change after inclusion of meteorological data in the models. Maas and Erba showed a significant influence of the time factor. For the Erba the onset of agricultural land use in the catchment coincides with a drop in runoff. A similar causal relationship is suggested for the Maas. Land use can change the formation of runoff, which in turn can be used as an environmental indicator for sustainable land use.  相似文献