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31.
A greenhouse experiment was conducted to examine the effects of salinity, nitrogen, and aeration on the growth of Spartina alterniflora Loisel. The experiment was conducted in a factorial arrangement of treatments with salt marsh substrate at three salinity levels (15, 30, 45‰), at two nitrogen levels (0 and 168 kg/ha) and at two aeration levels (zero and oxygen saturation). The maximum biomass was found in the low salinity, nitrogen enhanced, aerated treatment which had 11 times more biomass than the highest (45‰) salinity, nitrogen poor, unaerated treatment. the average effect of nitrogen over the three salinity levels was a 2.01, 1.47, 1.25, and 1.52 times increase in aerial biomass, density, height, and belowground biomass of the plants, respectively. The main effect of aeration was a 2.49, 2.01, 1.57, and 1.85 times increase in the same variables. The combination effect of aeration and nitrogen additions enhanced biomass by 453%. An increase in salinity from 15‰ to 45‰ decreased biomass, density, height and belowground biomass of S. alterniflora by 66, 53, 38, and 61%, respectively. The effect of salinity was more pronounced between 30 and 45‰ than it was between 15 and 30‰. N, P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, and S concentrations in the aerial living biomass were also examined. There was no evidence to suggest that elemental concentrations (on a per gram basis) were consistently correlated with increased or decreased growth. In relation to salinity, correlations between growth and elemental concentrations were negative while for nitrogen enhanced and/or aerated systems, the correlations were positive. 相似文献
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34.
Fourteen whole-rock samples from three traverses through the contact aureole of the Stillwater Complex were analyzed for Rb, Sr and87Sr/86Sr. Twelve of these samples yielded an age of 2750 ± 45m.y.; (87Sr/86Sr)0 = 0.705 ± 0.003 (2σ). In addition one whole rock and a biotite separate derived from it gave an age of 2544 m.y.; (87Sr/86Sr)0 = 0.714. These data support a minimum age of 2750 m.y. for the intrusion of the complex. 相似文献
35.
Very Long Baseline Interferometry (VLBI) is one of the new techniques which will probably dominate geodesy and geophysics
in the near future. Its main advantage lies in the fact that it brings the accuracy of direction measurements to a level previously
possible only for range measurements. This closes the gap between powerful range determination techniques such as laser ranging
and the much less accurate determination of directions through photographic tracking of artificial earth satellites.
The technique is geometric in the sense that the relevant observations are independent of the gravity field of the earth.
However, the “orbits” of the observed extragalactic radio sources with respect to an earth-fixed system are dominated and
perturbed by the rotation of the earth with respect to inertial frame. This allows the determination of polar motion, precession-nutation
and length-of-the-day variations, and the technique becomes also “dynamic” in this respect.
The capability of determining the geometry of a network of stations within a short time interval and with a centimeter level
accuracy also allows the study of the variation of network geometry with time caused by earth tides and other periodic or
secular station drifts.
The main objective of the present work is the exploration of the capabilities of VLBI for the recovery of earth rotation and
network geometry parameters. For this purpose, a number of characteristic experimental designs based on present and candidate
for the near future station locations is chosen. The results from the analysis of simulated observations for each particular
design are presented in the paper.
Presented at IAG International Symposium on “Optimization of Design and Computation of Control Networks”, Sopron, Hungary,
4–10 July 1977. 相似文献
36.
The spaceborne laser ranging (or lasering) system provides a method of precise positioning of a large number of points on
the earth's surface in a short period of time. That is, a measure of the relative location of geodetic markers from a space
platform can maintain horizontal and vertical control to 2 to 5 cm. At this level of control, small earth surface crustal
motions should be detectable. Development of a model for the strain field can be constructed. Furthermore, the spaceborne
lasering system can survey an area in a very short period of time (one to two weeks) and resurvey the area as required.
System design parameters are now being established by NASA for a possible test flight aboard the Shuttle in 1982. These include
design specifications of economical corner cubes for ground retroreflectors coupled with the evolution of engineering model
to flight model development. If the experiment of the Shuttle proves to be successful, it is hoped to put the laser in a free
flight satellite. This paper presents the results of a simulated analysis for this latter case.
The system is conceived as an orbiting ranging device with a ground base grid of reflectors or transponders (spacing 10 to
30 km), which are projected to be of low cost (maintenance-free and unattended) and which will permit the saturation of a
local area to obtain data useful to monitor crustal movements. The test network includes 75 stations with roughly half of
them on either side of the San Andreas fault zone. Critical study comparatively evaluates various observational schemes and
statistically analyzed crustal motion recovery.
The study considers laser radar as the main ranging system pending final selection from many possible candidates. The satellite
orbit is inclined at 110° and slightly eccentric (e=0.04) with orbital altitudes varying from 370 km to 930 km.
The results indicate that the geometric mode (simultaneous ranging) with a minimum of five grid and three distant (fundamental)
stations and mixed ranging to satellite and airplane seems to be most promising. The fundamental stations are distinguished
from the grid station in their location and this location should be “distant” enough from the area of crustal movement so
that they can be considered stationary over the time span of the motion involved.
Presented at the 1977 I.A.G. International Symposia on Satellite Geodesy, Budapest, Hungary, June 28–July 1, and on Recent
Crustal Movements, Palo Alto, California, USA, July 25–30. 相似文献
37.
The latest measurements from the two encounters of the MESSENGER spacecraft in year 2008 have discovered several interesting features of the magnetosphere of Mercury. We have performed high-resolution 3D hybrid model calculations to simulate the solar wind interaction with the Hermean magnetosphere during the first two Mercury encounters of the MESSENGER spacecraft in 2008. It is found that the global structure of the Hermean magnetosphere is significantly controlled by the direction of the interplanetary magnetic field. The bow shock size and shape and the magnetotail configuration have very large differences in these two encounters with northward-pointing and southward-pointing interplanetary magnetic field, respectively. Comparisons are also given with the observed magnetic field profiles and the computational results. In general, good agreement can be found including the interesting feature of the relatively thick magnetopause current layer at outbound measurements. Our work shows that 3D hybrid simulation is a promising method to study in detail the Hermean magnetosphere in parallel with the post-MOI observations of the MESSENGER spacecraft and the Bepi-Colombo mission in future. 相似文献
38.
Paul A. Mueller Joseph L. Wooden David W. Mogk Darrell J. Henry Donald R. Bowes 《Precambrian Research》2010
The voluminous Meso- to Neoarchean rocks exposed in the Beartooth Mountains of the northern Wyoming Province of western North America comprise the Long Lake Magmatic Complex (LLMC), a variably metamorphosed and deformed association of igneous and meta-igneous plutonic rocks with SiO2 ranging from at least 52 to 78 wt%. Within this compositional range, rock types include lineated amphibolites to hornblende-bearing gneisses of intermediate composition and multiple generations of foliated to unfoliated granitoids. Emplacement ages range between approximately 2.79 and 2.83 Ga, based on U–Pb zircon geochronology (SHRIMP). Field relations, elemental compositions, and geochronology indicate that these rocks do not represent a single fractional crystallization sequence, but rather, the LLMC was constructed by injection of numerous, discrete magmas as sill-like bodies over an ∼40 Ma period. Although there is a continuum of compositions in the LLMC, trace element abundances can be used to distinguish distinct sources and petrogenetic processes that can be broadly extrapolated to at least 3 compositional groupings: (1) trondhjemitic to granitic intrusive rocks with SiO2 >70 wt%, (2) variably metamorphosed granodioritic orthogneisses with SiO2 between 63 and 70 wt%, and (3) amphibole-bearing mafic to intermediate gneisses with SiO2 between 52 and 63 wt%. Despite the range of SiO2 contents, maximum LREE abundances are similar across the compositional range and, consequently, exhibit a wide range of (La/Yb)n ratios (∼20–130). All LLMC rocks share a relative depletion in HFSE abundances similar to modern convergent margin magmas. Initial Sr and Nd isotopic compositions across the compositional range are consistently offset from typical bulk silicate earth (BSE) values and preclude unaltered derivation from primitive or depleted mantle. Common Pb isotopic data define a single array that lies above model crustal growth curves and, along with the Nd and Sr data, suggest relatively uniform interaction with, or derivation from, older lithosphere. The combined isotopic and elemental data suggest the LLMC resulted from simultaneous, rapid, and voluminous production of diverse magmas that represent melting of isotopically similar, but compositionally distinct, crustal and mantle sources. Dynamically, Meso- to Neo-archean crustal growth in the northern Wyoming Province appears to require an environment similar to a modern ocean–continent convergent margin with a comparable rate of crustal production and diversity of magma series. The resultant crust and associated mantle lithosphere (keel) appear to have suffered little-to-no modification prior to Laramide (Cretaceous) uplift and exposure. 相似文献
39.
We calculate the direction of the rotational angular momentum vector,M, of comet 19P/Borrelly based on rotational lightcurve data from 2000, groundbased imaging of the coma during the Deep Space
1encounter, and the basic near-nucleus coma morphology as revealed by the Deep Space 1 spacecraft. For the most likely direction,
we derivea family of solutions (with center at RA = 221°, Dec = -7°) if the direction of M is towards the sunward hemisphere during the Deep Space 1 encounter, whereas if the rotation is of opposite sense, the diametrically
opposite family of solutions (with center at RA = 41°, Dec = 7°) would result. We argue that the coma morphology in September
2001 is consistent with the nucleus being a principal axis rotator or one observationally indistinguishable from it. Therefore,
for all practical purposes, the direction of the rotational angular momentum vector coincides with the spin axis. We also
discuss why the determination of the spin axis direction based on observations from the last apparition is in disagreement
with the current result. 相似文献
40.