Nitrogen sulfide in quiescent dark clouds     

McGonagle D  Irvine WM  Ohishi M 《The Astrophysical journal》1994,422(2):621-625

We report the first detection of interstellar nitrogen sulfide (NS) in cold dark clouds. Several components of the 2 pi 1/2, J = 3/2 --> 1/2 and J = 5/2 --> 3/2 transitions were observed in TMC-1 and L134N. The inferred column density for TMC-1 is NNS approximately 8 x 10(12)cm-2 toward the NH3 peak in that cloud, and in L134N is NNS approximately 3 x 10(12)cm-2 toward the position of peak NH3 emission. These values correspond to fractional abundances relative to molecular hydrogen of fNS approximately 8 x 10(-10) for TMC-1, and fNS approximately 6 x 10(-10) for L134N. The NS emission is extended along the TMC-1 ridge and is also extended in L134N. The measured abundances are significantly higher than those predicted by some recent gas phase ion-molecule models.  相似文献   

WKB estimates for the onset of ideal MHD instabilities in solar coronal loops     

A. W. Hood  P. De Bruyne  R. A. M. Van Der Linden  M. Goossens 《Solar physics》1994,150(1-2):99-115

A WKB approach, based on the method of Connor, Hastie, and Taylor (1979), is used to obtain simple estimates of the critical conditions for the onset of ideal MHD instabilities in line-tied solar coronal loops. The method is illustrated for the constant twist, Gold-Hoyle (1960) field, and the critical conditions are compared with previous and new numerical results. For the force-free case, the WKB estimate for the critical loop length reduces to . For the sufficiently non-force-free case the critical length can be expressed in the forml ₀ +l ₁/m. The results confirm the findings of De Bruyne and Hood (1992) that for force-free fields them = 1 mode is the first mode to become unstable but for the sufficiently strong non-force-free case this reverses with them → ∞ mode being excited first.  相似文献   

Definition and measurement of salinity in salt lakes   总被引：4，自引：0，他引：4  

W. D. Williams  J. E. Sherwood 《International Journal of Salt Lake Research》1994,3(1):53-63

Salinity is the most important chemical attribute of athalassic salt lakes. Even so, some confusion persists of what salinity means and how to measure it. For sal lakes, salinity is best defined as the sum total of all ion concentrations, or total ion concentration. Ideally, it is recommended that salinities be expressed on a mass per mass basis and as ppt (parts per thousand). Direct measurements of salinity can only be derived from full ionic analyses. Indirect measurements can be derived by determinations of density, conductivity, freezing point depression and total dissolved solids or matter.  相似文献   

Mid-infrared imaging of ultracompact H II regions     

T. L. Hayward  J. W. Miles  J. R. Houck  T. K. Timberlake 《Experimental Astronomy》1994,3(1-4):159-160

We discuss preliminary results of an 11.7 m imaging survey of ultracompact H II regions from the Wood and Churchwell radio survey. We find that that the morphologies of ionized gas and warm dust are often significantly different, indicating that an H II region classification scheme should be based on more than radio data.  相似文献   

A verification of some methods to determine the fluxes of momentum,sensible heat,and water vapour using standard deviation and structure parameter of scalar meteorological quantities     

H. A. R. De Bruin  W. Kohsiek  B. J. J. M. Van Den Hurk 《Boundary-Layer Meteorology》1993,63(3):231-257

A set of micro-meteorological data collected over a horizontal, uniform terrain (the plain of La Crau, France) in June 1987 is analysed. Conditions were predominantly sunny and arid, while due to the Mistral the wind speed could exceed 10 m/s. Verification of several methods to evaluate surface fluxes of heat, momentum and water vapour from the standard deviation of temperature, wind and specific humidity is presented. Also, a similar approach using the structure parameter of temperature is considered. These methods are all based on Monin-Obukhov (M-O) similarity theory. It is found that the standard deviation of temperature, vertical and horizontal wind speed as well as the structure parameter for temperature behave according to M-O similarity. It is shown that the sensible heat flux and friction velocity can be determined from a fast response thermometer and a cup anemometer. Also, it appears that the analytic solution of the set of governing equations as derived by the first author yields good results. M-O theory does not appear to work for the standard deviation of specific humidity. This may be due to the relative importance of large eddies.  相似文献   

Deep-sea smokers: windows to a subsurface biosphere?   总被引：13，自引：0，他引：13  

Deming JW  Baross JA 《Geochimica et cosmochimica acta》1993,57(14):3219-3230

Since the discovery of hyperthermophilic microbial activity in hydrothermal fluids recovered from "smoker" vents on the East Pacific Rise, the widely accepted upper temperature limit for life (based on pure culture data) has risen from below the boiling point of water at atmospheric pressure to approximately 115 degrees C. Many microbiologists seem willing to speculate that the maximum may be closer to 150 degrees C. We have postulated not only higher temperatures than these (under deep-sea hydrostatic pressures), but also the existence of a biosphere subsurface to accessible seafloor vents. New geochemical information from the Endeavour Segment of the Juan de Fuca Ridge indicative of subsurface organic material caused us to re-examine both the literature on hyperthermophilic microorganisms cultured from deep-sea smoker environments and recent results of microbial sampling efforts at actively discharging smokers on the Endeavour Segment. Here we offer the case for a subsurface biosphere based on an interdisciplinary view of microbial and geochemical analyses of Endeavour smoker fluids, a case in keeping with rapidly evolving geophysical understanding of organic stability under deep-sea hydrothermal conditions.  相似文献   

Kinetics of peptide hydrolysis and amino acid decomposition at high temperature     

Qian Y  Engel MH  Macko SA  Carpenter S  Deming JW 《Geochimica et cosmochimica acta》1993,57(14):3281-3293

Dipeptide hydrolysis and amino acid decomposition appear to follow a first-order rate law. The hydrolysis rate increases exponentially with increasing temperature in aqueous solution at both 265 atm and water steam pressures over the temperature range of 100 to 220 degrees C. Dipeptide hydrolysis has a lower apparent activation energy at 265 atm (44.1 KJ/mol) than at water steam pressure (98.9 KJ/mol). At lower temperatures (<200-220 degrees C), the rate of peptide bond hydrolysis is faster at 265 atm than at water steam pressure. At higher temperatures (>200-220 degrees C), however, peptide bond hydrolysis is slower at 265 atm than at water steam pressure. In aqueous solution, amino acid decomposition rates also increase exponentially with increasing temperature. Amino acid decomposition rates are much higher at 265 atm than at water steam pressure over the entire temperature range investigated.  相似文献   

Molecular and bulk isotopic analyses of organic matter in marls of the Mulhouse Basin (Tertiary, Alsace, France)     

Hollander DJ  Sinninghe Damste JS  Hayes JM  de Leeuw JW  Huc AY 《Organic Geochemistry》1993,20(8):1253-1263

Contents of 13C in kerogens and carbonates in 21 samples from a core of the MAX borehole, Mulhouse Evaporite Basin, range from -27.3 to -23.5 and -3.7 to -1.8% vs PDB, respectively. Organic nitrogen in the same samples is enriched in 15N relative to atmospheric N2 by 12.2-15.7%. Hydrogen indices and delta values for kerogens vary systematically with facies, averaging 493 mg HC/g Corg and -25.7% in the most saline facies (dominated by inputs from aquatic sources) and 267 mg HC/g Corg and -23.7% in the least saline facies (50/50 aquatic/terrigenous). Values of delta were measured for individual aliphatic hydrocarbons from three samples representing three different organic facies. For all samples, terrigenous inputs were unusually rich in 13C, the estimated delta value for bulk terrigenous debris, apparently derived partly from CAM plants, being -22.5%. In the most saline facies, isotopic evidence indicates the mixing of 13C-depleted products of photosynthetic bacteria with 13C-enriched products of halotolerant eukaryotic algae. At lower salinities, a change in the producer community is marked by a decrease in the 13C content of algal lipids. The content of 13C in algal lipids increases in the least saline facies, due either to succession of different organisms or to decreased concentrations of dissolved CO2.  相似文献   

Abrupt climate change and transient climates during the Paleogene: a marine perspective     

Zachos JC  Lohmann KC  Walker JC  Wise SW 《The Journal of geology》1993,101(2):191-213

Detailed investigations of high latitude sequences recently collected by the Ocean Drilling Program (ODP) indicate that periods of rapid climate change often culminated in brief transient climates, with more extreme conditions than subsequent long term climates. Two examples of such events have been identified in the Paleogene; the first in latest Paleocene time in the middle of a warming trend that began several million years earlier: the second in earliest Oligocene time near the end of a Middle Eocene to Late Oligocene global cooling trend. Superimposed on the earlier event was a sudden and extreme warming of both high latitude sea surface and deep ocean waters. Imbedded in the latter transition was an abrupt decline in high latitude temperatures and the brief appearance of a full size continental ice-sheet on Antarctica. In both cases the climate extremes were not stable, lasting for less than a few hundred thousand years, indicating a temporary or transient climate state. Geochemical and sedimentological evidence suggest that both Paleogene climate events were accompanied by reorganizations in ocean circulation, and major perturbations in marine productivity and the global carbon cycle. The Paleocene-Eocene thermal maximum was marked by reduced oceanic turnover and decreases in global delta 13C and in marine productivity, while the Early Oligocene glacial maximum was accompanied by intensification of deep ocean circulation and elevated delta 13C and productivity. It has been suggested that sudden changes in climate and/or ocean circulation might occur as a result of gradual forcing as certain physical thresholds are exceeded. We investigate the possibility that sudden reorganizations in ocean and/or atmosphere circulation during these abrupt transitions generated short-term positive feedbacks that briefly sustained these transient climatic states.  相似文献   

Chemically Distinct Mafic Dike/Sill Sequences of Contrasting Age Ranges, Sawyers Bar Area, Central Klamath Mountains, Northern California     

ERNST  W. G. 《Journal of Petrology》1993,34(1):63-75

Mafic hypabyssal rocks in the western Triassic and Paleozoicbelt provide important clues to the nature of accretion andarc evolution along this sector of the North American margin.In the east-central part of the belt, near Sawyers Bar, somediabases have been metamorphosed before and accompanying emplacementof the mid-Jurassic English Peak and Russian Peak granitoidswithin the North Fork/Salmon River + Stuart Fork amalgamatedterrane. Certain other dikes/sills, chiefly mafic microdiorites,cut the calc-alkaline plutons but are themselves deutericallyaltered; at least two of these mafic microdiorites near theEnglish Peak body possess hornfelsic textures. Thus, althoughmost mafic microdioritic hypabyssals seem to have been injectedafter granitoid emplacement, a few must have preceded plutonicintrusion. Macroscopic appearances, phase assemblages, mineralcompositions, and textures of the mafic microdioritic and metadiabasicdikes/sills are sufficiently alike to preclude the ready fieldand petrographic distinction of the different magma series.Bulk-rock chemistries fall into two groups, however, with slightlymore porphyritic, altered, synplutonic mafic microdiorite samplesbeing distinctly richer in Si, K, P, Rb, Sr, Zr, and light rareearth elements (LREE) relative to the Mg + Cr + Ni-rich, preplutonicmetadiabases. Analyzed mafic microdiorites have bulk-rock chemicaland isotopic compositions similar to the more ferromagnesianportions of the mid-Jurassic English Peak and Russian Peak plutoniccomplexes, whereas the metadiabases are comparable with theearly Mesozoic Salmon River metabasalts. Although the two groupsof dikes/sills probably overlap in age of emplacement, the maficmicrodiorite group is predominantly younger and uniform in oxygenisotopic composition (bulk-rock ¹⁸O 11•37, 11•4 and11•46) compared with the older, more intensely metamorphosed,and variably metasomatized Salmon River metadiabases (bulk-rock5¹⁸ 9•4, 11•0, and 15•3). Both types of maficdike/sill locally intrude the more easterly Stuart Fork terrane.Therefore, suturing and regional metamorphism of the outboardNorth Fork/Salmon River oceanic-island arc and inboard StuartFork subduction complex must have occurred during terminal stagesof injection of the pregranitoid diabases into the North Fork(oceanic-island basalts)/Salmon River (island-arc tholeiites)arc + Stuart Fork terrane, but before invasion of the amalgamatedterrane assembly by the calc-alkaline plutons and most compositionallyrelated synplutonic mafic microdiorite dikes/sills. Becauseof their lateral continuation both north and south of the SawyersBar area, the North Fork/Salmon River igneous suite documentsthe construction of an oceanic arc of considerable lateral extentin the central Klamaths before terrane accretion. Suturing wasimmediately followed by the mid-Jurassic intrusion of calc-alkalineplutons + syngranitoid mafic microdioritic hypabyssals.  相似文献