The effect of recreational impacts on soil and vegetation of stabilised Coastal Dunes in the Sharon Park, Israel

Coastal sand dunes are considered among the most susceptible habitats to recreational use. The aim of this study was to monitor the impact of visitor use on soil and annual plants on long-established trails in the stabilised coastal dunes of the Sharon Park, Israel. The results indicate that:

1. The vegetation cover, height and species richness and diversity, as well as soil organic matter content were lower on trails subjected to high visitor use than that on trails under low use. However, soil compaction and moisture on high-use trails were higher than that on low use.

2. The rate of change in each of the vegetation properties moving outwards from the centre of the trail towards the undamaged area on its margins and beyond, was higher on trails under high visitor use than on low-use trails.

3. The impact of high visitor use is localised and limited to the trail boundaries and their immediate surroundings (6 m axis perpendicular to the trails), while the effect on low-use trails is dispersed over a larger area, apparently because the trail borders are less visually defined to the visitor.

The conclusion derived from this study is that the spatial damage caused to the park by the numerous low-use trails is higher than that caused by the trails under high visitor use. Thus, there is an immediate need to reduce the number of this type of trails and to rehabilitate them.     

Oxygen and nutrient fluxes through the Straits of the Cretan Arc (March 1994–January 1995)

The Straits of the Cretan Arc are the gateways through which water exchanges between the Cretan Sea and the SE Ionian and NW Levantine Seas. Dissolved oxygen and nutrient fluxes have been quantified for the major straits — Antikithira, Kassos and Karpathos — by combining chemical bottle-sample data and current measurements obtained during the PELAGOS Project during 1994–1995. Two water masses, Cretan Deep Water (CDW) and Transitional Mediterranean Water (TMW) dominate the circulation through the straits and lead to a vertical redistribution of nutrients in the Eastern Mediterranean Sea.The transport of chemicals through the major straits of the Cretan Arc appears to be highly variable. In the Antikithira and Kassos Straits, a net export of oxygen and nutrients from the Cretan Sea towards the open waters of the Eastern Mediterranean was observed throughout the entire study period. In contrast, a net inflow of oxygen and nutrients of Levantine origin was taking place through the Karpathos Strait. It is concluded that the export of nutrients through the Antikithira and Kassos Straits are almost completely balanced by the net import through the Karpathos Strait.     

The age and thermal history of Cerro Rico de Potosi, Bolivia

 Cerro Rico de Potosi, Bolivia, is the world’s largest silver deposit and has been mined since the sixteenth century for silver, and for tin and zinc during the twentieth century, together with by-product copper and lead. The deposit consists primarily of veins that cut an altered igneous body that we interpret to be a dacitic volcanic dome and its underlying tuff ring and explosion breccia. The deposit is compositionally and thermally zoned, having a core of cassiterite, wolframite, bismuthinite, and arsenopyrite surrounded by a peripheral, lower-temperature mineral assemblage consisting principally of sphalerite, galena, lead sulfosalt, and silver minerals. The low-temperature assemblage also was superimposed on the high-temperature assemblage in response to cooling of the main hydrothermal system. Both the dacite dome and the ore fluids were derived from a larger magmatic/hydrothermal source at depth. The dome was repeatedly fractured by recurrent movement on the fault system that guided its initial emplacement. The dome was extruded at 13.8±0.2 Ma (2σ), based on U-Th-Pb dating of zircon. Mineralization and alteration occurred within about 0.3 my of dome emplacement, as indicated by a ⁴⁰Ar/³⁹Ar date of 13.76±0.10 Ma (1σ) for sericite from the pervasive quartz-sericite-pyrite alteration associated with the main-stage, high-temperature, mineralization. The last thermal event able to reset zircon fission tracks occurred no later than 12.5±1.1 Ma (1σ), as indicated by fission-tract dating. Minor sericite, and magmatic-steam alunite veins, were episodically formed around 11 Ma and between 8.3 and 5.7 Ma; the younger episodes occurring at the time of extensional fracturing at Cerro Rico and widespread volcanism in the adjacent Los Frailes volcanic field. None of these younger events appear to be significant thermal/mineralizing events; the exceptionally flat thermal release pattern of ³⁹Ar from sericite and the results of the fission-tract dating of zircon show that none of the younger events was hot enough, and lasted long enough, to cause significant loss of Ar or annealing of zircon fission tracks. U-Th-Pb dating of zircon cores indicates a Precambrian progenitor for some zircons, and REE analyses of dated samples of hydrothermally altered dacite show the presence of a prominent positive Eu anomaly, which constrains interpretations of the origin and evolution of the magmatic/hydrothermal system. Received: 14 October 1995/Accepted: 29 January 1996     

Using large radio telescopes at decametre wavelengths

With the aim of evaluating the actual possibilities of doing, from the ground, sensitive radio astronomy at decametre wavelengths (particularly below ), an extensive program of radio observations was carried out, in 1999–2002, by using digital spectral and waveform analysers (DSP) of new generation, connected to several of the largest, decametre radio telescopes in the world (i.e., the UTR-2 and URANs arrays in Ukraine, and the Nançay Decametre Array in France).

We report and briefly discuss some new findings, dealing with decametre radiation from Jupiter and the Solar Corona: namely the discovery of new kinds of hyper fine structures in spectrograms of the active Sun, and a new characterisation of Jupiter's “millisecond” radiation, whose waveform samples, with time resolution down to 40 ns, and correlated measurements, by using far distant antennas (3000 km), have been obtained. In addition, scattering effects, caused by the terrestrial ionosphere and the interplanetary medium, could be disentangled through high time resolution and wide-band analyses of solar, planetary and strong galactic radio sources. Consequences for decametre wavelength imaging at high spatial resolution (VLBI) are outlined. Furthermore, in spite of the very unfavourable electromagnetic environment in this frequency range, a substantial increase in the quality of the observations was shown to be provided by using new generation spectrometers, based on sophisticated digital techniques. Indeed, the available, high dynamic range of such devices greatly decreases the effects of artificial and natural radio interference. We give several examples of successful signal detection in the case of much weaker radio sources than Solar System ones, down to the intensity level.

In summary, we conclude that searching for sensitivity improvement at the decametre wavelength is scientifically quite justified, and is now technically feasible, in particular by building giant, phased antenna arrays of much larger collecting area (as in the LOFAR project). In this task, one must be careful of some specifics of this wavelength range—somewhat unusual in “classical” radio astronomy—i.e., very high level and density of radio interference (telecommunications) and the variable terrestrial ionosphere.     

Investigation of Barred Galaxies. VII. Comparative Statistics of SB and SA Galaxies. Near and Mid-IR Regions

The near and mid-IR properties of barred and unbarred spiral galaxies are discussed on the basis of complete samples that were compiled earlier. The two types of spirals are shown not to differ from one another in emission power in the near and mid-IR ranges. Multiple regression and principal component analysis have been applied to investigate near and mid-IR properties of SB and SA galaxies, particularly their relation to X-ray and radio continuum emissions. There are definite differences between SB and SA spirals in the near and mid-IR. In the case of SB galaxies, the compactness of 10 m emission is closely related to the J - H color index, and the redder J - H color corresponds to relatively more extended emission at 10 m. It is assumed that these are caused by the bar itself, which stimulates enhanced star formation in a barred galaxy with respect to unbarred spiral.     

Excitation of whistler waves by reflected auroral electrons

Excitation of electron cyclotron waves and whistlers by reflected auroral electrons which possess a loss-cone distribution is investigated. Based on a given magnetic field and density model, the instability problem is studied over a broad region along the auroral field lines. This region covers altitudes ranging from one quarter of an Earth radius to five Earth radii. It is found that the growth rate is significant only in the region of low altitude, say below the source region of the auroral kilometric radiation. In the high altitude region the instability is insignificant either because of low refractive indices or because of small loss cone angles.     

The Aristarchus-Harbinger region of the moon: Surface geology and history from recent remote-sensing observations

The region including the Aristarchus Plateau and Montes Harbinger is probably the most diverse, geologically, of any area of comparble size on the Moon. This part of the northwest quadrant of the lunar near side includes unique dark mantling material; both the densest concentration and the largest of the sinuous rilles; apparent volcanic vents, sinks, and domes; mare materials of various ages and colors; one of the freshest large craters (Aristarchus) with ejecta having unique colors and albedos; and three other large craters in different states of flooding and degradation (krieger, Herodotus, and Prinz). The three best-authenticated lunar transient phenomena were also observed here.This study is based principally on photographic and remote sensing observations made from Earth and Apollo orbiting space craft. Results include (1) delineation of geologic map units and their stratigraphic relationships; (2) discussion of the complex interrelationships between materials of volcanic and impact origin, including the effects of excavation, redistribution and mixing of previously deposited materials by younger impact craters; (3) deduction of physical and chemical properties of certain of the geologic units, based on both the remote-sensing information and on extrapolation of Apollo data to this area; and (4) development of a detailed geologic history of the region, outlining the probable sequence of events that resulted in its present appearance.A primary concern of the investigation has been anomalous red dark mantle on the Plateau. Based on an integration of Earth- and lunar orbit-based data, this layer seems to consist of fine-grained, block-free material containing a relatively large fraction of orange glass. It is probably of pyroclastic origin, laid down at some time during the Imbrian period of mare flooding.     

A polarimetric investigation of the eclipsing binary XY ursae majoris

On three nights in February 1976 we carried out polarimetric measurements, in V, of the short periodic eclipsing binary XY UMa, covering a complete cycle. The results are as follows:

1. Within all phase intervals the linear polarization does not exceed 0.1%.
2. In the phase range 0 ^p .95–1 ^p .35 the scatter of the Stokes parametersQ andU is about twice that within the phase interval 0 ^p .35–0 ^p .95.
3. A periodogram analysis of these data revealed a period of 21000 s, which is equal to half the orbital periodP _o=0^d.47899 within 1.5%.

From these we derive the conclusions that no circumstellar envelope can be made responsible for the observed long-term changes of the light curve and system brightness, supporting the earlier spectroscopic finding. The different scatter of the Stokes parameters at different phase intervals and theP _o/2 periodicity are in favor of the star spot model for XY UMa proposed by one of the authors (E. G.).