Quantifying potential propagule pressure of aquatic invasive species from the commercial shipping industry in Canada

We quantify and compare different measures of potential propagule pressure (PPP) of aquatic invasive species (AIS) from commercial vessels in Canada. We used ship arrivals and ballast water discharge volumes as proxies for PPP from ballast water organisms, and wetted surface area (WSA) as a proxy for hull fouling PPP, to determine their relative contributions to total PPP. For three regions studied, PPP proxies correlated significantly across ports and some vessel categories. Relative contributions of ship arrivals, ballast discharge, and WSAs to PPP, evidenced by non-significant correlations across these measures, varied across regions, ports, vessel types, and seasons. Flow-through (dominant on east and west coasts) and empty-refill (in Great Lakes-St. Lawrence region) were the major ballast water exchange methods employed by the vessels surveyed. These methods have different biological efficacy for AIS removal, influencing PPP. Our study illustrates benefits and limitations of using different PPP proxies to estimate invasion risk.     

Fine structure of a very bright active region at a wavelength of 2.8 cm

The radio structure of the active region McMath 11976 has been investigated with an east-west resolution of 16″ at a wavelength of 2.8 cm. Six bright components were found with angular sizes of the order of 20″. From the position measure of these components in two following days the heights above the solar photosphere are determined. Their positions are compared with the Hα and magnetic structure of the active region. The derived brightness temperatures reach unusual values, up to 6 × 10⁶K for the brightest component.     

Sinkhole hazards along the eastern Dead Sea shoreline area, Jordan: a geological and geotechnical consideration

For the last four decades, the level of the Dead Sea has been subjected to continual variation which, among other important factors, has led to the occurrence of much subsidence and many sinkholes in the southern Dead Sea area. Sinkhole activities occurred repetitively and were observed in open farms, across roads, near dwellings and near an existing factory, thus causing a serious threat to the locals and farmers of the area and their properties. This paper presents the main results from detailed geological and geotechnical studies of this area. Aerial photo interpretation and borehole drilling aided these studies. Parallel geophysical investigations (vertical electrical sounding and seismic refraction) and hydrological and hydrogeological studies were made by others in the same area to also investigate this phenomenon. It was found that sinkholes are aligned to and follow old water channels and are concentrated parallel to the recent shoreline of the Dead Sea. The development of subsurface cavities is associated mainly with the variation in the level of the Dead Sea over the four past decades, the presence of regional salt intrusion under the surface of salt beds, the fluctuation of the water table and continuous dissolution and the active tectonism of the area. Moreover, this work showed that the area is still under active sinkhole hazards and other parts of the area will be inevitably affected by sinkholes in the future.No practical engineering solution to this problem is feasible. Received: 1 July 1999 / Accepted: 11 October 1999     

Recent Results from Studies of Electric Discharges in the Mesosphere

The paper reviews recent advances in studies of electric discharges in the stratosphere and mesosphere above thunderstorms, and their effects on the atmosphere. The primary focus is on the sprite discharge occurring in the mesosphere, which is the most commonly observed high altitude discharge by imaging cameras from the ground, but effects on the upper atmosphere by electromagnetic radiation from lightning are also considered. During the past few years, co-ordinated observations over Southern Europe have been made of a wide range of parameters related to sprites and their causative thunderstorms. Observations have been complemented by the modelling of processes ranging from the electric discharge to perturbations of trace gas concentrations in the upper atmosphere. Observations point to significant energy deposition by sprites in the neutral atmosphere as observed by infrasound waves detected at up to 1000 km distance, whereas elves and lightning have been shown significantly to affect ionization and heating of the lower ionosphere/mesosphere. Studies of the thunderstorm systems powering high altitude discharges show the important role of intracloud (IC) lightning in sprite generation as seen by the first simultaneous observations of IC activity, sprite activity and broadband, electromagnetic radiation in the VLF range. Simulations of sprite ignition suggest that, under certain conditions, energetic electrons in the runaway regime are generated in streamer discharges. Such electrons may be the source of X- and Gamma-rays observed in lightning, thunderstorms and the so-called Terrestrial Gamma-ray Flashes (TGFs) observed from space over thunderstorm regions. Model estimates of sprite perturbations to the global atmospheric electric circuit, trace gas concentrations and atmospheric dynamics suggest significant local perturbations, and possibly significant meso-scale effects, but negligible global effects.     

FURTHER DEVELOPMENT OF A HIGH-FREQUENCY SEISMIC SOURCE FOR USE IN BOREHOLES1

A borehole sparker seismic source enclosed in a semi-flexible tube has been developed to produce a short compressional seismic pulse with a frequency content in the range 250 Hz to 3.5 kHz with a peak power at 570 Hz. The pulse shape and frequency content are shown to be a function of the input power, the diameter of the spark chamber, the salinity of the electrolyte, the material of the spark chamber and the electrode configuration. When in a borehole, the source produces a vertically polarized shear wave but, being similar to a small explosive charge does not allow phase reversal as a means of identifying the shear wave in the received pulse train. The source is shown to be ideal for tomographic imaging surveys because of its repetitive nature, high frequency content and reliability. Very high resolution seismic reflection surveys are also shown to be possible under favourable circumstances.     

The afterglow of a dense molecular cloud after the passage of a cosmological gamma-ray burst

Bolometric light curves for the afterglow resulting from the passage of a gamma-ray burst through a molecular cloud are computed. The profile and duration of the afterglow light curve depend strongly on the distribution of matter in the cloud, the degree of collimation of the gamma-ray radiation, and the observing conditions. The peak can be reached as soon as seven days (the gamma-ray burst is located at some distance from the center of a molecular cloud with small-scale density enhancements), or as long as one to three years (the gamma-ray burst is located at the center of a uniform molecular cloud) after the burst. The bolometric luminosity of the re-radiated signal can reach 6.5 × 10⁴² erg/s.     

An early estimate for the size of cycle 23

Two features are found in the modern era sunspot record (cycles 10–22: ca. 1850-present) that may prove useful for gauging the size of cycle 23, the next sunspot cycle, several years ahead of its actual onset. These features include an inferred long-term increase against time of maximum amplitude (RM, the maximum value of smoothed sunspot number for a cycle) and the apparently inherent differing natures of even- and odd-numbered sunspot cycles, especially when grouped consecutively as even-odd cycle pairs. Concerning the first feature, one finds that 6 out of the last 6 sunspot cycles have had RM 110.6 (the median value for the modern era record) and that 4 out of 6 have had RM > 150. Presuming this trend to continue, one anticipates that cycle 23 will likewise have RM 110.6 and, perhaps, RM > 150. Concerning the second feature, one finds that, when one groups sunspot cycles into consecutively paired even-odd cycles, the odd-following cycle has always been the larger cycle, 6 out of 6 times. Because cycle 22 had RM = 158.5, one anticipates that cycle 23 will have RM > 158.5. Additionally, because the average difference between RM(odd) and RM(even) for consecutively paired even-odd cycles is 40.3 units (sd = 14.2), one expects cycle 23 to have RM 162.3 (RM = 198.8 ± 36.5 at the 95% level of confidence). Further, because of the rather strong linear correlation (r = 0,959, se = 13.5) found between RM(odd) and RM(even) for consecutively paired even-odd cycles, one infers that cycle 23 should have RM 176.4 (RM = 213.9 ± 37.5 at the 95% level of confidence). Since large values of RM tend to be associated with fast rising cycles of short ascent duration and high levels of 10.7-cm solar radio flux, cycle 23 is envisioned to be potentially one of the greatest cycles of the modern era, if not the greatest.     

长江上游国土资源,生态环境与灾害防治

长江上游干流流经青、藏、川、滇、鄂、渝6省市,支流涉及甘肃、陕西、贵州3省,流域面积为105.4×10⁴km²,人口1.55亿,占全国国土面积的11.1%。
长江上游地区经济发展相对落后,人均国民收入低,少数民族众多,与中下游经济发达地区差距很大。但上游地区蕴藏着巨大的经济开发潜能,丰富的水力和矿产等自然资源,以及农、林、牧等物产,对中下游地区经济发展有着巨大的支援作用。同时,由于自然地理上的相关性,又使上游地区的开发治理,对中下游地区的生态环境和可持续发展有着至关重要的作用。
目前,长江上游森林植被大量减少,水源涵养能力下降,水土流失加剧:泥石流、滑坡、崩塌等地质灾害严重,旱、洪灾害频发;沿江大量排放废气、废水、污水,使大气和水体严重污染。随着上游地区生态环境的日益恶化,给中下游地区带来严重危害,河道、湖泊、水库淤积加速,洪涝灾害频繁发生,造成中下游地区经济建设和人民生命财产的重大损失。因此,必须尽快对长江上游地区进行全面综合治理,尽快开展新一轮国土资源大调查,制定各种自然资源的合理开发利用和保护方案;控制沿江污染源的排放,建立大气和水体污染监测系统;运用高新技术,建立上游重点地带地壳形变的动态监测和预警系统,防治地质灾害;充分利用上游地区丰富的水力资源,兴建多级水利设施,对地表水实施人工的时空控制,消除旱、洪灾害。     

A mixed finite element method for Hele-Shaw cell equations

A new numerical method to solve the system of equations describing two phase flow in a Hele-Shaw cell is presented. It combines a mixed finite element method, the method of subtraction of the singularity and a front tracking grid in a single computational strategy. This choice of discretization techniques is well motivated by the difficulties present in the system of equations and the physics of the problem. The new method was tested against analytical solutions and also by solving the Saffman–Taylor viscous fingering problem for finite and infinite mobility ratios. In both cases convergence under mesh refinement is achieved for the fingers developed from an initial sinusoidal interface. Finger splitting is observed for low values of the surface tension and high mobility ratio. Different explanations, based in our results, are provided for this phenomenon. This revised version was published online in July 2006 with corrections to the Cover Date.