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Atmospheric nitrogen deposition from a remote source enriches macroalgae in coral reef ecosystems near Green Turtle Cay, Abacos, Bahamas 总被引：1，自引：0，他引：1
Over the past several decades, the fixation of "new" nitrogen to the biosphere has doubled. For the early 21st century, the most significant rate increases in atmospheric nitrogen deposition are predicted for developing nations. Wet nitrogen deposition was assessed on the remote island of Green Turtle Cay, Bahamas in a dry and wet season from January to July 2000. Episodic deposition of nitrate (approximately 1-137 microM) and ammonia (approximately 2-122 microM) represented a mean deposition rate of approximately 0.2 mgDIN m(-2) yr(-1). Wet deposition of nitrogen to the climatologically-linked east coast of Florida is approximately 4 times greater than the estimated annual wet nitrogen deposition value at Green Turtle Cay, suggesting the continental US as a principal airshed for this loading source. Short-term bioassays of macroalgal productivity with a 5% rainfall solution caused depressed net productivity and increased dark respiration, well known "transient metabolic" responses by nutrient-limited tropical macroalgae. Wet deposition of inorganic nitrogen from episodic rainfall events may provide up to 20% of the "new" nitrogen necessary to meet growth demands of macroalgae on coral reefs near Green Turtle Cay. 相似文献
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基于2014—2019年四川气象监测的雷电大气静电场资料,研究了同期四川MS≥5.0地震前的异常信息。结果显示,50%的MS≥5.0地震前,大气静电场日均值有异常变化,主要表现为低值突跳,异常形态呈多样性,较突出的有不规则“W”“V”“U”型等。日均值低值异常出现后114天r=eM空间范围内发生MS≥5.0地震的可能性较大,其中,第10—19天,发震概率为33%;第2—9天,发震概率为17%。基于气象雷电监测的大气静电场观测资料,在排除雷电等干扰的情况下,可用于地震监测预报。 相似文献
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Summary The basic concept of synoptic statistical methods for construction of prognostic charts was outlined by the author in a previous paper. As a result of these investigations it was found that a high correlation exists between time and space means of contourheights of an isobaric surface (850 mb surface). As it has been shown later byPichler this result may be interpreted by assuming that the geopotential fields obeys a numerical solution of the second order homogenous differential equation for wave propagation (hyperbolic equation) provided the phase velocity is given by
. SinceReuter has used for s=666 km and for t=24 hours the conclusion may be drawn that the phase velocity of the wave propagation has an order of magnitude of 5 m/sec. Actually for long waves in the westerlies such a value can be found on an average. The same method can be used for extended forecast procedures if the wave equation is set down for 5 days mean values. Theoretical considerations lead then to a prognostic formula for a 5 days mean chart (8a). This formula can be applied for a sufficient number of grid points in order to construct prognostic charts. The underlying assumption, namely that the mean geopotential field satisfies also a solution of the wave equation turns out to be quite accurate even if only average values of the phase velocity were used for the computation. The usefullness of the method is illustrated for two cases.
Vortrag gehalten am 7. April 1961 auf der 9. Allgemeinversammlung der «Società Italiana di Geofisica e Meteorologia» (Genova, 6.8. April 1961). 相似文献
Vortrag gehalten am 7. April 1961 auf der 9. Allgemeinversammlung der «Società Italiana di Geofisica e Meteorologia» (Genova, 6.8. April 1961). 相似文献
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Quantitative microbial risk assessment: uncertainty and measures of central tendency for skewed distributions 总被引：1，自引：1，他引：0
K. K. Benke A. J. Hamilton 《Stochastic Environmental Research and Risk Assessment (SERRA)》2008,22(4):533-539
In the past, arithmetic and geometric means have both been used to characterise pathogen densities in samples used for microbial
risk assessment models. The calculation of total (annual) risk is based on cumulative independent (daily) exposures and the
use of an exponential dose–response model, such as that used for exposure to Giardia or Cryptosporidium. Mathematical analysis suggests that the arithmetic mean is the appropriate measure of central tendency for microbial concentration
with respect to repeated samples of daily exposure in risk assessment. This is despite frequent characterisation of microbial
density by the geometric mean, since the microbial distributions may be Log normal or skewed in nature. Mathematical derivation
supporting the use of the arithmetic mean has been based on deterministic analysis, prior assumptions and definitions, the
use of point-estimates of probability, and has not included from the outset the influence of an actual distribution for microbial
densities. We address these issues by experiments using two real-world pathogen datasets, together with Monte Carlo simulation,
and it is revealed that the arithmetic mean also holds in the case of a daily dose with a finite distribution in microbial
density, even when the distribution is very highly-skewed, as often occurs in environmental samples. Further, for simplicity,
in many risk assessment models, the daily infection risk is assumed to be the same for each day of the year and is represented
by a single value,
which is then used in the calculation of p
Σ, which is a numerical estimate of annual risk, P
Σ, and we highlight the fact that is simply a function of the geometric mean of the daily complementary risk probabilities (although it is sometimes approximated
by the arithmetic mean of daily risk in the low dose case). Finally, the risk estimate is an imprecise probability with no
indication of error and we investigate and clarify the distinction between risk and uncertainty assessment with respect to
the predictive model used for total risk assessment. 相似文献
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"桑拿天"是发生在夏季高温、高湿环境之下的重要天气现象.而过去单靠温度这一变量来诊断预报"桑拿天",有较大难度.而且从已有的研究中,"桑拿天"多发生在下沉运动或相对稳定的环流背景下.因此,寻找一个简单有效、且使用方便的物理变量来揭示"桑拿天"高湿、高湿的综合特征,显得特别重要.本文在前人研究的基础上,将以往暴雨研究中的IM (Ingredients-based Methodology)理论方法拓展至"桑拿天"的研究,将过去表征桑拿天高温、高湿、下沉运动环流特点的这些单个物理量综合进IM方法,尝试性地引入热力螺旋度(TH)、水汽螺旋度(MH)、以及湿热力螺旋度(MTH)等,对发生在2002年7月30日-8月4日和2009年7月7-9日的两次华北地区高温高湿的强"桑拿天"过程进行动力识别和诊断,并与广义湿位涡(GMPV)进行对比分析.分析结果表明,MH的异常大值区相对集中在北京及其周边的华北地区的对流层低层,并维持.而TH的异常大值区涵盖的范围远大于我们要研究的华北地区"桑拿天"的爆发范围.即使结合了温、湿效应的MTH和GMPV的异常大值区,其涵盖的范围亦逊于MH对"桑拿天"的动力识别.可见,在夏季普遍高温的大环境下,湿度是华北闷热的"桑拿天"爆发的一个决定性因素.结合了环流特征与湿度效应的MH,是对"桑拿天"进行动力识别的一个优化因子,具有较大的实际应用价值. 相似文献
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随机子空间识别方法计算效率的改进 总被引：4，自引：0，他引：4
参数识别是结构健康监测领域研究中的重点。随机子空间法是近年来发展起来的一种线性系统辩识方法,可以有效地从环境激励的结构响应中获取模态参数。该方法的基本原理是将“将来”数据向“过去”数据进行垂直投影,进而根据该投影计算出可观测矩阵和一个Kalman滤波状态序列。而Kalman滤波序列是“过去”输出信号的线性组合,即“过去”输出和“将来”状态估计建立了关系。而从Hankel矩阵的组成来看,由于要使得该矩阵具有单无限的条件,所需的计算时间也比较长。据此对随机子空间方法进行了改进。改进的基本思想是采用一个测点的信号作为“过去”作为输出信号代替全部测点的信号。这样就减少了计算量。最后用一数值模拟算例进行了验证,结果良好。 相似文献
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Under constant hydrodynamic conditions and assuming horizontal homogeneity, negatively buoyant particles released at the surface of the water column have a mean residence time in the surface mixed layer of h/w, where h is the thickness of the latter and w ( > 0) is the sinking velocity Deleersnijder (Environ Fluid Mech 6(6):541–547, 2006a). The residence time does not depend on the diffusivity and equals the settling timescale. We show that this behavior is a result of the particular boundary conditions of the problem and that it is related to a similar property of the exposure time in a one-dimensional infinite domain. In 1-D advection–diffusion problem with a constant and uniform velocity, the exposure time—which is a generalization of the residence time measuring the total time spent by a particle in a control domain allowing the particle to leave and reenter the control domain—is also equal to the advection timescale at the upstream boundary of the control domain. To explain this result, the concept of point exposure is introduced; the point exposure is the time integral of the concentration at a given location. It measures the integrated influence of a point release at a given location and is related to the concept of number of visits of the theory of random walks. We show that the point exposure takes a constant value downstream the point of release, even when the diffusivity varies in space. The analysis of this result reveals also that the integrated downstream transport of a passive tracer is only effected by advection. While the diffusion flux differs from zero at all times, its integrated value is strictly zero.
相似文献10.
Discussion of Mean Gravity Along the Plumbline 总被引：2，自引：1，他引：1
According to the definition of the orthometric height, the mean value of gravity along the plumbline between the Earth's surface and the geoid is defined in an integral sense. In Helmert's (1890) definition of the orthometric height, a linear change of the gravity with depth is assumed. The mean gravity is determined so that the observed gravity at the Earth's surface is reduced to the approximate mid-point of the plumbline using Poincaré-Prey's gravity gradient. Niethammer (1932) and later Mader (1954) took into account the mean value of the gravimetric terrain correction within the topography considering the constant topographical density distribution along the plumbline (for more details see Heiskanen and Moritz, 1967). Vaníek et al. (1995) included the effect of the lateral variation of the topographical density into the definition of Helmert's orthometric height. Recently, Hwang and Hsiao (2003) discussed the influence of the vertical gradient of disturbing gravity on the orthometric heights. In this paper, the mean integral value of gravity along the plumbline within the topography is defined so that the actual topographical density distribution and the change of the disturbing gravity with depth are taken into account. Based on the definition of the mean gravity, the relation between the orthometric and normal heights is discussed. 相似文献
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Y. Ohsaki 《地震工程与结构动力学》1979,7(5):427-439
A number of problems relating to characteristics of harmonic phase angles contained in earthquake ground motions are discussed, which have been mostly overlooked in the past in contrast with the importance placed on harmonic amplitudes. Particularly, the significance of the concept of phase differences in certain properties of earthquake ground motions is emphasized. A few applications of this new concept to earthquake engineering problems are illustrated as well. 相似文献
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Jörg Overmann Gerhard Sandmann Ken J. Hall Tom G. Northcote 《Aquatic Sciences - Research Across Boundaries》1993,55(1):31-39
Vertical distribution of fossil carotenoids in a sediment core from meromictic Mahoney Lake was studied. Besides okenone and demethylated okenone, lutein and zeaxanthin and-carotene isomers were identified. No carotenoids typical for purple nonsulfur or green sulfur bacteria were detected. The ratio of zeaxanthin to lutein (above 1:1 in all samples) indicates a dominance of cyanobacteria over green algae in the phytoplankton assemblages of the past. Okenone, which is found exclusively in Chromatiaceae, was the dominating carotenoid in all sediment zones.The oldest sediment layers containing okenone were deposited 11 000 years ago. Between 9000 and 7000 and since 3000 years b.p., Chromatiaceae reached a considerable biomass in the lake. Vertical changes in okenone concentration were not related to changes of paleotemperatures. In contrast, okenone concentrations decreased during periods of volcanic ash input. During most of the lake history, however, mean okenone concentrations were positively correlated with sedimentation rates. This indicates that vertical changes of okenone concentration in the sediment reflect past changes of purple sulfur bacterial biomass in the lake.According to these results, the past limnology of Mahoney Lake resembled that of the present with a sulfide-containing monimolimnion and a well-developed population of okenone-bearing purple sulfur bacteria. 相似文献
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E.A. Stirling 《Marine pollution bulletin》1975,6(8):122-124
Prediction of safe levels of effluent discharge have in the past been largely based on the results of short term acute toxicity tests (LC5 0s). Such tests are usually carried out in unnatural experimental conditions, and in consequence the results are of only limited value. There is a need to enlarge the concept of the routine bioassay test to include quantitative measurement of the effects of pollutants on behaviour, physiology and metabolism. This paper describes a simple rapid bioassay test in which the effect of pollutants on the burrowing of the bivalve Tellina tenuis has been used as a quantitative measure of pollutant effect. 相似文献
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Predicting unit plot soil loss in Sicily,south Italy 总被引：2，自引：0，他引：2
Predicting soil loss is necessary to establish soil conservation measures. Variability of soil and hydrological parameters complicates mathematical simulation of soil erosion processes. Methods for predicting unit plot soil loss in Sicily were developed by using 5 years of data from replicated plots. At first, the variability of the soil water content, runoff, and unit plot soil loss values collected at fixed dates or after an erosive event was investigated. The applicability of the Universal Soil Loss Equation (USLE) was then tested. Finally, a method to predict event soil loss was developed. Measurement variability decreased as the mean increased above a threshold value but it was low also for low values of the measured variable. The mean soil loss predicted by the USLE was lower than the measured value by 48%. The annual values of the soil erodibility factor varied by seven times whereas the mean monthly values varied between 1% and 244% of the mean annual value. The event unit plot soil loss was directly proportional to an erosivity index equal to , being QRRe the runoff ratio times the single storm erosion index. It was concluded that a relatively low number of replicates of the variable of interest may be collected to estimate the mean for both high and particularly low values of the variable. The USLE with the mean annual soil erodibility factor may be applied to estimate the order of magnitude of the mean soil loss but it is not usable to estimate soil loss at shorter temporal scales. The relationship for estimating the event soil loss is a modified version of the USLE‐M, given that it includes an exponent for the QRRe term. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
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Summary As regards the concept of complete weight p with which an observed quantity (e.g., the direction of theA–G net) should enter the net adjustment, according to Eq.(1), apart from the fundamental weight p
0
), determined by the number of repetitions, it should also contain the time parameter pt according to Eq.(11), where c>1 is a constant, and t is the number of days of observation, and also the refraction factor pr according to Eqs(17, 18), where q is the structural weight of the direction. The condition for being able to determine pr with the directions is observation by means of the three-directional vertex method[2], because it is not possible to localize lateral refraction by angular methods. The theory of complete weight is in favour of observations with a high fundamental weight p
0
which automatically yield higher values of t, and also of pt. The introduction of the complete weight into the experimental directional net in Fig. 2 caused the mean value of the uneliminated refraction error to decrease from 0.24 to 0.12, the mean square error of the adjusted direction being 0.17. The value of the constant c was investigated and the method of determining the parameter pr was derived also for lengths measured electro-optically. Mention is made of the effect of complete weights on the length adjustment of a net in[6]. 相似文献
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A nonlinear mean field dynamo in turbulent disks and spherical shells is discussed. We use a nonlinearity in the dynamo which includes the effect of delayed back-reaction of the mean magnetic field on the magnetic part of the — effect. This effect is determined by an evolutionary equation. The axisymmetric case is considered. An analytical expression (in a single-mode approximation) is derived which gives the magnitude of the mean magnetic field as a function of rotation and the parameters for turbulent disks. The value obtained for the mean magnetic field is in agreement with observations for galaxies. 相似文献
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Bryan Johns 《Pure and Applied Geophysics》1965,60(1):107-116
Summary A perturbation method is used to calculate steady non-linear effects in rotatory tidal currents. The inclusion of the Coriolis acceleration leads to a uniquely determined second order current system in the tidal stream. This is shown to be absent in high frequency gravity waves. It is found that particle drift, or mass transport, is critically dependent on this mean current, and consequently on the value off/,f being the Coriolis parameter, and the angular frequency of the oscillation. 相似文献
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2021年第6号台风“烟花”是2021年度对江苏地区影响最强烈的台风。地震台站台基噪声是影响观测质量的关键因素,为了探究台风“烟花”对江苏地区地震台站台基噪声的影响,利用江苏地震台网2021年7月1日至8月3日记录的连续波形数据,通过计算波形自相关函数卓越周期与台基噪声水平的速度均方根有效振幅（RMS）,研究其与台风参数之间的关系。结果表明：①在台风“烟花”初始发育阶段,卓越周期由平时的2—4 s逐步上升到4—7 s,随着台风影响范围逐渐向陆地转移,卓越周期缓慢降低,随着台风完全登陆并不断减弱,卓越周期又恢复到正常水平;②在台风“烟花”的整个进程中,绝大多数台站的RMS值变化幅度不超过正常值的15%,各台站RMS值变化幅度在正常波动范围内。 相似文献
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D. D. Sokoloff 《Izvestiya Physics of the Solid Earth》2017,53(6):855-859
The behavior of the dipole magnetic moment of the geomagnetic field during the reversals is considered. By analogy with the reversals of the magnetic field of the Sun, the scenario is suggested in which during the reversal the mean dipole moment becomes zero, whereas the instantaneous value of the dipole magnetic moment remains nonzero and the corresponding vector rotates from the vicinity of one geographical pole to the other. A thorough discussion concerning the definition of the mean magnetic moment, which is used in this concept, is presented. Since the behavior of the geomagnetic field during the reversal is far from stationary, the ensemble average instead of the time average has to be considered. 相似文献