Spatial p-q Resonant Orbits of the RTBP

The purpose of this paper is to extend the study of the so called p-q resonant orbits of the planar restricted three-body problem to the spatial case. The p-q resonant orbits are solutions of the restricted three-body problem which have consecutive close encounters with the smaller primary. If E, M and P denote the larger primary, the smaller one and the infinitesimal body, respectively, then p and q are the number of revolutions that P gives around M and M around E, respectively, between two consecutive close approaches. For fixed values of p and q and suitable initial conditions on a sphere of radius around the smaller primary, we will derive expressions for the final position and velocity on this sphere for the orbits under consideration.     

Effects of soil structure on soil behaviour: Illustrated with loess, glacially loaded clay and simulated flaser bedding examples

Soil structure is considered to be a systematic homogeneously repetitive heterogeneity of properties and conditions of soil. For upscaling and homogenisation of properties and conditions it is necessary to understand the ways in which soil structures occur, and to obtain understanding of the ways in which it influences soil behaviour. Using three case studies, different aspects of the effects of soil structure in soil mechanics are discussed. The very loose grain scale packing of loess deposits, held together by weak structural bonds between particles, results in dramatic propagating failure when the strength of the bonds is exceeded by deformations, as illustrated in the first case. Nonhorizontal stresses induced in the subsurface below moving continental ice sheets result in rotated stress fields within the affected soil. The rotated stress field is stored in the structure of the soil, as is shown in the second case, and influences present day properties and behaviour of these clays. It is shown in the third case that there is a large difference in the behaviour of clayey sand depending on whether the clay occurs in the form of the common clay flasers or whether the clay is homogeneously dispersed in the sand. The deformation and stress propagation in the case of sand with clay flasers results in local failures and shear planes due to the large contrast in the properties of the materials making up the sedimentary structure. The result is that many of the properties of sand with flasers are rather more like the clay of the flasers than the sand. Incorporation in the engineering practice of effects of common types of soil structure is made possible with the widespread availability of techniques such as numerical modelling. These techniques enable the development of appropriate tools for practical application.     

Do Planetary Motions Drive Solar Variability?

We examine the occasionally forwarded hypothesis that solar activity originates by planetary Newtonian attraction on the Sun. We do this by comparing three accelerations working on solar matter at the tachocline level: Those due to planetary tidal forces, to the motion of the Sun around the planetary system's centre of gravity, and the observed accelerations at that level. We find that the latter are by a factor of about 1000 larger than the former two and therefore cannot be caused by planetary attractions. We conclude that the cause of the dynamo is purely solar.     

Paleolimnological investigations of anthropogenic environmental change in Lake Tanganyika: II. Geochronologies and mass sedimentation rates based on <Superscript>14</Superscript>C and <Superscript>210</Superscript>Pb data

We established sediment geochronologies for cores from eight deltaic areas in Lake Tanganyika (the Lubulungu, Kabesi, Halembe, Malagarasi, Nyasanga/Kahama, Mwamgongo, Nyamusenyi, and Karonge/Kirasa River deltas), recording a range of watershed disturbance histories from the eastern margin of this African rift valley lake. Cores from currently disturbed sites on the central Tanzanian coast display remarkably uniform and low rates of sediment accumulation from the 18th century until the early 1960s, when a synchronous and dramatic rise in rates occurs. Through this same time interval sedimentation rates offshore from undisturbed Tanzanian watersheds either remain unchanged or decline. Further north, at disturbed sites along the northern Tanzania and Burundi coasts, the pattern of sedimentation rate increase is more complex. Although a mid-late 20th century increase is also evident in these sites, indications of earlier periods of increasing sediment erosion, dating from the mid-late 19th century, are also evident. Synchronous changes in sediment accumulation rates dating from the early 1960s may be the result of exceptionally wet years triggering an increase in the discharge of previously eroded and unconsolidated alluvium and stream/beach terrace deposits, previously accumulated in the deltas and stream valleys of impacted watersheds. Sedimentation rate impacts of deforestation on lake ecosystems are likely modulated by short-term climatic forcing events, which can impact the specific timing and location of sediment discharge to lakes.     

Radioheliograph observations of a pulsating structure associated with a moving type IV burst

Observations of a pulsating structure with the Mark II Nançay Radioheliograph are reported. These fluctuations are found to occur early in the development of a moving type IV burst. It is confirmed that the source of these fluctuations is of small extent and that it is embedded in the moving type IV continuum, plausibly at the top of an expanding arch.The observations suggest that the pulsating structure consists of recurrent enhanced pulses (mean recurrency time 1.7 s) followed by trains of periodic pulses (mean periodicity 0.37 s). The intensity of the enhanced pulses has a damping time of about 5 s. It is shown that previous interpretation of the pulsating structure by Rosenberg (1970) cannot account for the present observations.     

Impact of road building on gully erosion risk: a case study from the Northern Ethiopian Highlands

Although obvious in the field, the impact of road building on hydrology and gullying in Ethiopia has rarely been analysed. This study investigates how road building in the Ethiopian Highlands affects the gully erosion risk. The road between Makalle and Adwa in the highlands of Tigray (northern Ethiopia), built in 1993–1994, caused gullying at most of the culverts and other road drains. While damage by runoff to the road itself remains limited, off‐site effects are very important. Since the building of the road, nine new gullies were created immediately downslope of the studied road segment (6·5 km long) and seven other gullies at a distance between 100 and 500 m more downslope. The road induces a concentration of surface runoff, a diversion of concentrated runoff to other catchments, and an increase in catchment size, which are the main causes for gully development after road building. Topographic thresholds for gully formation are determined in terms of slope gradient of the soil surface at the gully head and catchment area. The influence of road building on both the variation of these thresholds and the modification of the drainage pattern is analysed. The slope gradient of the soil surface at the gully heads which were induced by the road varies between 0·06 and 0·42 m m^?1 (average 0·15 m m^?1), whereas gully heads without influence of the road have slope gradients between 0·09 and 0·52 m m^?1 (average 0·25 m m^?1). Road building disturbed the equilibrium in the study area but the lowering of topographic threshold values for gullying is not statistically significant. Increased gully erosion after road building has caused the loss of fertile soil and crop yield, a decrease of land holding size, and the creation of obstacles for tillage operations. Hence roads should be designed in a way that keeps runoff interception, concentration and deviation minimal. Techniques must be used to spread concentrated runoff in space and time and to increase its infiltration instead of directing it straight onto unprotected slopes. Copyright © 2002 John Wiley & Sons, Ltd.     

Time-dependency of runoff velocity and erosion the effect of the initial soil moisture profile

The paper reports on experiments carried out to evaluate the effect of the initial soil moisture profile on temporal variations in runoff erosion rate. The moisture profile was varied by applying infrared heating to the soil sample surface over various time periods, while runoff erosivity was varied by varying the slope of the flume. The experiment confirms that dry loamy soils are very erodible: on a slope length of only 4.3 m long sediment concentrations are near transporting capacity in case of a dry soil sample. It appears that temporal variations in sediment concentrations can be well simulated using a simple relationship between runoff erosion resistance and initial soil moisture content, thereby implicitly assuming that the effect of initial moisture content is persistent over the whole duration of the experiment. The implications of these findings with respect to the modelling of sediment output from larger catchments and the design of experiments on rill erodibility are discussed. The experiments also show that, under the present circumstances, mean velocities in the rills appear to be independent of slope. This finding may be of importance with respect to overland flow routing and deterministic erosion modelling.     

Origin of the northern Atlantic's Heinrich events

As first noted by Heinrich, 1988, glacial age sediments in the eastern part of the northern Atlantic contain layers with unusually high ratios of ice-rafted lithic fragments to foraminifera shells. He estimated that these layers are spaced at intervals of roughly 10 000 years. In this paper we present detailed information documenting the existence of the upper five of these layers in ODP core 609 from 50° N and 24° W. Their ages are respectively 15 000 radiocarbon years, 20 000 radiocarbon years, 27 000 radiocarbon years, about 40 000 years, and about 50 000 years. We also note that the high lithic fragment to foram ratio is the result of a near absence of shells in these layers. Although we are not of one mind regarding the origin of these layers, we lean toward an explanation that the Heinrich layers are debris released during the melting of massive influxes of icebergs into the northern Atlantic. These sudden inputs may be the result of surges along the eastern margin of the Laurentide ice sheet.Contribution to Clima Locarno — Past and Present Climate Dynamics; Conference September 1990, Swiss Academy of Sciences — National Climate Program     

Some dissenting remarks on ‘Deleterious effects of corexit 9527 on fertilization and development’

The following article discusses the relevance of laboratory toxicity studies of a chemical oil dispersant, in general, and the foregoing paper. While Lönning and Hagström use a sensitive means to determine the more subtle, sublethal effects of chemicals on marine life, two major aspects of their work should be clarified. First, a concentration of 1–10 ppm of chemical dispersant, wherein fertilization of the sea urchin egg was affected in their work, does not occur in the usual marine environment with proper use of the dispersant. Second, there is no evidence to support the conclusion that the specific chemical dispersants studied by Lönning and Hagström preferentially release ‘toxic substances’ from the crude oil.     

Sandy-gravelly mass-flow deposits in an ice-marginal lake (Saalian,Leuvenumsche Beek Valley,Veluwe, the Netherlands), with emphasis on plug-flow deposits

In three pits in the Leuvenumsche Beek Valley (near Ermelo and Elspeet), massive and diffusely banded clean gravelly sands, found in association with sandy sediments showing some similarities to the Bouma sequence, were interpreted as originating from sediment gravity flows. The flows, which came to rest on a ca. 6° paleoslope, probably originated from slumping of parts of the ice-pushed ridges at either side of an ice-marginal lake.Major characteristic features in the three sand pits studied are U-shaped channel forms with a maximum depth and width of 10 × 25 rmm. The fills consist of sand and gravels, locally containing giant sand-clasts. The sediments just below the base of these channel-forms are commonly distorted and folded. Especially the massive more sandy fills are surrounded by a finer-grained diffusely bedded and inversely graded zone.These sedimentary features suggest that “rigid” sediment plugs sheared downslope, generating a finer-grained shear zone around the plug scouring a slide scar till its present semi-cylindrical form and preserving the steep sides (exceeding the angle of repose) of the channel-form by “freezing”.The U-shaped channel forms (plugged troughs) are locally overlain by shallower gently sided trough structures, with mainly diffusely banded infillings. Very shallow and often smaller troughs are found again on top of these massive and diffusely banded infillings. The sediments in these troughs consist of repetitions of two types of microsequences: (1) thickly bedded sequences of normally graded massive sands, near-horizontal stratifications, plane beds and cross-bedded sets; and (2) thinly bedded sequences of relatively thick units T_A and thin units T_C and T_D of the Bouma sequence.The repetitions of the microsequences are interpreted as flow pulsations. Upwards thinning of the sequence, together with a finer grain size may point to waning flow conditions. Their association with plugged troughs is suggestive of retrogressive flow-slides.