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221.
The second Arctic Gas and Aerosol Sampling Program (AGASP-II) was conducted across the non-Soviet Arctic in March and April 1986, to study the aerosol, gaseous, chemical, and optical properties of Arctic haze. One component of the program was supported with an instrumented NOAA WP-3D atmospheric research aircraft. Measurements of wind, temperature, ozone, water vapor, condensation nucleus concentration, and aerosol scattering extinction coefficient were used to determine the locations and properties of haze layers. The first three NOAA WP-3D research flights were conducted north of Barrow, Alaska, and over the Beaufort Sea northeast of Barter Island, Alaska. The next three sampled conditions in the high Arctic near Alert, Northwest Territories, Canada. All basic meteorological, gas, and aerosol systems are described. The WP-3D flight tracks and operations are presented. 相似文献
222.
为了定量地分析航摄底片的信息容量,本文在影象数字化的基础上,从理论上分析信息容量的估算公式,监重点研究用“比特分割”的方法确定其有效的比特数。 相似文献
223.
Immature Torbanite and the resistant biopolymer (PRB A) isolated from extant B. braunii were previously compared using bulk spectroscopic methods. In the present work, analysis of 400°C pyrolysis products and pyrolysis residues provided further information on their structure and possible relationships. It appears that such polymers are based upon unbranched, saturated, cross-linked hydrocarbon chains up to C31. In addition to these bridging structures, a substantial part of the alkyl chains is singly bound, as esters of unbranched, saturated or cis unsaturated, even fatty acids. These esters are sterically protected, against chemical degradations, by the network of the bioand geopolymer.Quantitative and qualitative observations derived from 400°C pyrolysis confirm that the chemical structure of PRB A and immature Torbanite are closely related. The pyrolysis residues show a similar evolution and numerous common features are noted, with respect to the nature and the distribution of the major constituents of the pyrolysates (hydrocarbons and fatty acids). Accordingly, Botryococcus provides what seems to be the first example of a close structural relationship between a biopolymer produced in large amounts by an extant alga and the geopolymer of an immature kerogen. The essential role of PRB A in Torbanite formation is ascertained. Moreover, it is found that the resistant biopolymer does not undergo important structural changes during the first stages of diagenesis. Thus, owing to steric protection, the esters of immature Torbanite show a distribution quite close to the one of PRB A esters, with exclusively even constituents and a large contribution of unsaturated acids.Recent observations pointed to the possible genesis of some algal kerogens principally by selective preservation of resistant macromolecules. Such a type of formation is clearly predominant in Torbanite, where the bulk of the fossil organic matter corresponds to a selectively preserved and weakly altered, resistant biopolymer, while incorporation of lipids into the kerogen structure during diagenesis seems to play a minor role. 相似文献
224.
Stefan Keller 《Surveys in Geophysics》1995,16(5-6):661-670
Laboratory simulation of powder snow avalanches serves for the validation of numerical models and as a tool in its own right for consulting and research purposes. Two-phase gravity currents are simulated in water with quartz powder or glass spheres as the particle phase. Particle-phase velocity profiles and particle-phase volume fraction profiles are measured with an ultrasonic device. The experimental setup and the current state of the measurement technique are described and preliminary results are presented. 相似文献
225.
Although several researchers have pointed out some advantages and disadvantages of various soil sampling designs in the presence of spatial autocorrelation, a more detailed study is presented herein which examines the geometrical relationship of three sampling designs, namely the square, the equilateral triangle, and the regular hexagon. Both advantages and disadvantages exist in the use of these designs with respect to estimation of the semivariogram and their effect on the mean square error or variance of error. This research could be used to design optimal sampling strategies; it is based on the theory of regionalized variables, in which the intrinsic hypothesis is satisfied. Among alternative designs, an equilateral triangle design gives the most reliable estimate of the semivariogram. It also gives the minimum maximum mean square error of point estimation of the concentration over the other two designs for the same number of measurements when the nugget effect is small relative to the variance. If the nugget effect is large (.90
2
or more), and the linear sampling density is >0.85r where r is the range, the hexagonal design is best. This study computes and compares the maximum mean square error for each of these designs. 相似文献
226.
In order to study the relationship between water composition and stream flow rate, it is desirable to sample at a frequency related to flow rate, especially during storm events. In a rural catchment of 18 ha near Oxford, the rate of rainfall was found to be linearly related to discharge on the rising limb of the stream hydrograph. A sampling system was therefore designed in which electrical pulses from a tipping-bucket raingauge were used to initiate and control the action of an automatic water sampler. A threshold rainfall intensity is set above which sampling commences. Sampling then continues at regular increments of rainfall until the intensity drops below the threshold, after which sampling occurs at regular intervals during the period that the stream flow reverts to normal. The CMOS electrical circuits which control the sampling also operate a cassette tape recorder which records the time of each tip of the raingauge and operation of the sampler. Since the sytem is designed to impose very little additional load on the battery which powers the water sampler, and can operate unattended for at least a fortnight, it is ideal for use in small, remote catchments. The system has been extended to include measurements of water temperature and could provide other measurements as well. 相似文献
227.
228.
M. D. Sharma 《Journal of Earth System Science》2007,116(4):357-367
Anisotropic wave propagation is studied in a fluid-saturated porous medium, using two different approaches. One is the dynamic
approach of Biot’s theories. The other approach known as homogenisation theory, is based on the averaging process to derive
macroscopic equations from the microscopic equations of motion. The medium considered is a general anisotropic poroelastic
(APE) solid with a viscous fluid saturating its pores of anisotropic permeability. The wave propagation phenomenon in a saturated
porous medium is explained through two relations. One defines modified Christoffel equations for the propagation of plane
harmonic waves in the medium. The other defines a matrix to relate the relative displacement of fluid particles to the displacement
of solid particles. The modified Christoffel equations are solved further to get a quartic equation whose roots represent
complex velocities of the four attenuating quasi-waves in the medium. These complex velocities define the phase velocities
of propagation and quality factors for attenuation of all the quasi-waves propagating along a given phase direction in three-dimensional
space. The derivations in the mathematical models from different theories are compared in order to work out the equivalence
between them. The variations of phase velocities and attenuation factors with the direction of phase propagation are computed,
for a realistic numerical model. Differences between the velocities and attenuations of quasi-waves from the two approaches
are exhibited numerically. 相似文献
229.
方法,相干目标分析是利用时间序列多景影像获取地表稳定反射体——高相干点目标的新方法.实验区选择上海市主城区约100 km2 区域,InSAR的实验数据采用覆盖1992~2000年间的25景ERS-1/2的单视复影像.在无先验沉降场模型的情况下,实验结果显示该实验区的地面沉降场在时间范围上跨越8年,平均观测时间采样率约为4个月,垂直形变精度优于5 mm,满足我国对城市地面沉降形变观测的要求.研究结果表明该方法可以用于今后大时间/空间尺度上的高精度地表形变观测. 相似文献
230.
This study investigates the dynamic behavior of suspended sediment load transport at different temporal scales in the Mississippi River basin. Data corresponding to five successively doubled temporal scales (i.e. daily, two‐day, four‐day, eight‐day and 16‐day) from the St. Louis gaging station in Missouri are analyzed. The investigation is focused on identifying possible low‐dimensional deterministic behavior in the suspended sediment load transport dynamics, with an aim towards reduction in model complexity. The correlation dimension method is used to identify low‐dimensional determinism. The suspended sediment load dynamics are represented through phase‐space reconstruction, and the variability is estimated using the (proximity of) reconstructed vectors in the phase space. The results indicate the presence of low‐dimensional determinism in the suspended sediment load series at each of the five temporal scales, with the variables dominantly governing the dynamics in the order of three or four. These results not only suggest the appropriateness of relatively simpler models but also hint at possible scale invariance in the suspended sediment load transport dynamics. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献