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1.
Donald H. Eckhardt 《Celestial Mechanics and Dynamical Astronomy》1993,57(1-2):307-324
The acceleration of the mean lunar longitude has a small effect on the periods of most terms in a Fourier expansion of the longitude. There are several planetary perturbation terms that have small amplitudes, but whose periods are close to the resonant period of the lunar libration in longitude. Some of these terms are moving toward resonance, some are moving away from resonance, and the periods of those terms that do not include the Delaunay variables in their arguments are not moving. Because of its acceleration of longitude, the Moon is receding from the Earth, so the magnitude of the restoring torque that the Earth exerts on the rotating Moon is gradually attenuating; thus resonance itself is moving, but at a much slower rate than the periods of the accelerating planetary perturbations. There are five planetary perturbation terms from the ELP-2000 Ephemeris (with amplitudes of 0.00001 or greater) that have passed through resonance in the past two million years. One of them is of special interest because it appears to be the excitation source of a supposed free libration in longitude that has been detected by the lunar laser ranging experiment. The amplitude of the term is only 0.00021 but it could be the source of the 1 amplitude free libration term if the viscoelastic properties of the Moon are similar to those of the Earth. 相似文献
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Lunar physical librations and laser ranging 总被引：1，自引：0，他引：1
The analysis of lunar laser ranging data requires very accurate calculations of the lunar physical librations. Libration terms are given which arise from the additive and planetary terms in the lunar theory. The large size of the recently discovered terms due to third degree gravitational harmonics will allow some of these harmonics to be measured, in addition to and, by laser ranging to the Moon. Combining the laser ranging determinations of = 630.6 ± 0.5 × 10–6 and = 226.4 ± 3.0 × 10–6 with lunar orbiter measurements ofC
20 andC
22 givesC/MR
2=0.395
-0.010
+0.006
. Numerical integration promises to be an effective method of calculating librations. Comparison of numerical integrations with analytic series indicates that the calculation of the series due to third and fourth degree harmonics is not yet as accurate as the more extensively developed second degree terms.Communication presented at the Conference on Lunar Dynamics and Observational Coordinate Systems, held January 15–17, 1973, at the Lunar Science Institute, Houston, Tex., U.S.A. 相似文献
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Anestis J. Romaides Christopher Jekeli Donald H. Eckhardt Charles L. Taylor 《Journal of Geodesy》1991,65(4):230-242
An experiment was conducted in 1987 in search for a possible non-Newtonian component to gravity. The test compared accurately measured gravity values on a 600 m tower with upward continued surface gravity. The results indicated a dominant attractive non-Newtonian force that asymptotically approached -540 µGal at the top of the tower. An exhaustive search of possible error sources led to the discovery that our surface data did not accurately represent some of the local topographic features. The surface survey was supplemented by gravity data to remove some of the biases that were caused by the misrepresentation. In addition, a rigorous terrain correction was applied to the surface data resulting in terrain-corrected Bouguer anomalies. These anomalies were then upward continued using two independent techniques. The terrain effect was added back to the predicted values at altitude. With this procedure almost the entire non-Newtonian effect was explained. Currently we find no conclusive evidence for a non-Newtonian force over the range of several hundred meters. 相似文献
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癌细胞与正常的人体细胞不同。根据体细胞突变理论（SMT）,癌细胞是基因突变的结果。该理论还采用达尔文主义的基本原理,假设癌细胞生长是自然选择下“适者生存”的结果。与此相反,我们采用Margulis的演化理论来解释癌症的起源,并提出癌细胞由遗传而来：癌基因组起源于寄生在原核生物宿主中的细菌;在大约20亿年前的“氧气革命”期间,癌基因组与原核生物基因组因内共生作用而融合;后来宿主演化成为真核生物（原生生物、真菌、植物和动物）,每种真核生物都具有其独特的基因组;经过同样的时间间隔,原寄生细菌基因组则演化成为真核生物内的癌干细胞基因组。当前SMT假设人类基因组的突变导致癌症,但该理论无法识别编码肿瘤生长的基因组序列,也无法解释：突变为何会造成癌细胞失控性生长及复制？癌症为何是一种代谢性疾病？癌症死亡率为何与亚硝酸盐污染有关？中国用不含亚硝酸盐的公共供水源的试验为何竟可以拯救许多癌症患者的生命？SMT没能充分回答许多“神秘”的癌症问题。相反,我们提出的生物演化理论可以回答这些相关事实,包括那些SMT不能充分解释的问题。我们的理论根据是：癌基因组图谱（TCGA）的科学家未能在正常的人类基因组序列中发现突变或未突变的癌基因组。是癌基因组编码了癌细胞的生长及复制和一种不同的代谢模式。我们的理论假设,癌症起源于“休眠中”的癌干细胞因为受亚硝酸盐的影响而被激活,其中一个癌基因组编码了厌氧或缺氧的代谢模式,为癌细胞的生长及复制提供能量和生物量,其他基因组则编码了癌细胞的失控性生长及复制和其他癌症特征。亚硝酸盐以10-9 级别的浓度干扰人体正常的代谢和复制等机能。事实说明,亚硝酸盐可被定义为一种毒药。识别慢性中毒的困难可以用孟加拉国公共供水造成的砷中毒作为例证。癌症应被视为由亚硝酸盐中毒引起的疾病来进行治疗是一个假说,它可以解释为什么当中国部分地区的正常公共供水改用标准化深井水（SDWW）时,癌症死亡率可以减半。这个假说需要另一个假设来解释亚硝酸盐中毒并不影响所有饮用公共供水的人,而只影响其中一部分人。我们必须假设癌症的产生是由于干细胞,其中包括一个癌干细胞,被召唤去以修复细胞的损伤。将这些打破常规的假说放在一起,很多专家认为我们的生物演化理论是天方夜谭而不予理会。实际上,这个假说已由中国过去的SDWW实验所证实。一些医院的试验也证实,若癌症晚期患者每天饮用不含亚硝酸盐的水,癌症可以被治愈。我们对癌症晚期不可治愈这一论断提出质疑,并假定癌症是慢性亚硝酸盐中毒所致。我们呼吁其他科学家进行实验和临床试验来验证这一假说,使至少一半的晚期癌症患者,当他们的饮用水供应源不含亚硝酸盐时,可以被治愈。与此同时,我们应该将过去半个世纪以来献身医学的科学家们的成果,整合为一个“新的体系”。 相似文献
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Donald H. Eckhardt 《Journal of Geodesy》1983,57(1-4):394-409
Meissl has derived weighting functions for converting point gravity anomaly degree variances into mean anomaly variances over a circular cap on a sphere. If the cap is sufficiently small so that the cap on a sphere degenerates into a circle on a plane, the problem may be considered that of the gain of a circular filter for a surface wave whose wave number depends on the spherical harmonic degree. The Meissl weights then become replaced by diffraction integrals of optical physics. The expected gain for a square filter for waves coming from random directions is derived and shown to be close to the gain of a circular filter with the same area. The expected gains and cross-gains for rectangular filters are also derived. When weighted by an anomaly degree variance model, these gains and cross-gains can be used to determine rectangular anomaly variances and covariances for arbitrary bandwidths. Using the Tscherning-Rapp model, analytic gravity anomaly variances and covariances are calculated for 1°×1° blocks. 相似文献
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Impact of Climate on Tourist Demand 总被引：2，自引：2，他引：2
Tourism, being volatile and situation-specific, is responsive to climate change. A cross-section analysis is conducted on destinations of OECD tourists and a factor and regression analysis on holiday activities of Dutch tourists, to find optimal temperatures at travel destination for different tourists and different tourist activities. Globally, OECD tourists prefer a temperature of 21 °C (average of the hottest month of the year) at theirchoice of holiday destination. This indicates that, under a scenario of gradual warming, tourists would spend their holidays in different places than they currently do. The factor and regression analysis suggests that preferences for climates at tourist destinations differ among age and income groups. 相似文献
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Donald H. Eckhardt 《Earth, Moon, and Planets》1970,1(2):264-275
The selenographic direction cosines of the Earth and of the pole of the ecliptic are developed in trigonometric series; the time dependence of each term enters through the Delaunay arguments. These and other series are tabulated for different libration parameters to provide means for calculating at any epoch the lunar librations and their partial derivatives with respect to the parameters. 相似文献
10.
Wietze Eckhardt 《Geophysical Prospecting》1994,42(8):975-986
For successful prestack depth migration an accurate velocity model is needed. One method for model updating is based on image gather analysis. In an image gather all reflectors line up horizontally if the correct velocities are used for the depth migration. This is also true for dipping reflectors, as all traces of an image gather belong to the same surface coordinate. The images of the reflector in an image gather curve upwards if the velocity used for the migration is too low, or downwards if the velocity is too high. This deviation can be used for model updating. Curves which depend on depth, offset and a parameter which relates the estimated to the true model are fitted to the image. By calculating the coherence along the deviation curves, this parameter can be estimated and hence an update can be calculated. Formulae are derived for the deviation curves and the update of the velocity depth model for a multilayered model for both shot and common-offset migrated data, with and without gradients. The method is tested on synthetic data with satisfactory results. 相似文献