Emigration,return, immigration: a review and evaluation of Greece's postwar experience of international migration

"This paper offers a review and evaluation of the Greek experience of international migration.... The analysis is based partly on available published data, and partly on qualitative appraisals. Three major international migration phases are analysed--emigration, return migration and immigration--and the main socio-economic and cultural effects of these migration trends are discussed. The paper pays particular attention to the recent mass immigration movements, noting their heterogeneity...and describing their impact on the Greek labour market. The article concludes with some comments on the difficulties of formulating a Greek migration policy in the light of the country's location, open borders and internationalized economy."     

Imaging coronal emission lines under high sky-background conditions

We have obtained images in solar coronal emission lines under high sky-background conditions by making precise differential measurements between the coronal emission line and the near-by continuum, which is primarily due to scattered light from the solar disk. Chopping between the two wavelengths was performed at 100 kHz to avoid artifacts from fast-flying dust particles and other aerosols, and also from seeing effects. The differential signal was detected with a novel CCD camera that demodulates signals up to 100 kHz. These preliminary observations show coronal emission at the 0.2% level of the scattered-light background and pave the way to efficient and precise imaging of coronal emission features under less than ideal coronal-sky conditions.Operated by the Association of Universities for Research in Astronomy, Inc. (AURA) under cooperative agreement with the National Science Foundation.     

The effects of solar and ionospheric parameters on seasonal variation of 6300 Å line emission at Calcutta

The purpose of this paper is to find correlation between OI 6300 Å line intensity with solar and ionospheric parameters. A critical study have been made and the following important results are obtained:

Sediment oxygen profiles in a super-oxygenated antarctic lake

Perennially ice-covered lakes are found in the McMurdo Dry Valleys of southern Victoria Land, Antarctica. In contrast to temperate lakes that have diurnal photic periods, antarctic (and arctic) lakes have a yearly photic period. An unusual feature of the antarctic lakes is the occurrence of O2 at supersaturated levels in certain portions of the water column. Here we report the first sediment O2 profiles obtained using a microelectrode from a perennially ice-covered antarctic lake. Sediment cores collected in January and October 1987 from Lake Hoare in Taylor Valley show oxygenation down to 15, and in some cases, 25 cm. The oxygenation of sediments several centimeters below the sediment-water interface is atypical for lake sediments and may be characteristic of perennially ice-covered lakes. There is a significant difference between the observed January and October sediment O2 profiles. Several explanations may account for the difference, including seasonality. A time-dependent model is presented which tests the feasibility of a seasonal cycle resulting from the long photoperiod and benthic primary production in sediments overlain by a highly oxygenated water column.     

Dynamics of the plasmasphere in the dusk sector as observed in the outer ionosphere

Summary Direct measurements of the thermal plasma parameters in the topside ionosphere reveal variations of the plasmasphere boundary in the dusk sector. The ACTIVE satellite's near-polar orbits at altitudes of 500 – 1800 km around winter solstice 1989 were used to study the bulge region of the plasmasphere during intervals with different levels of geomagnetic agitation. The narrow, sharply defined trough in electron concentration corresponding to the plasmapause under quiet conditions situated at L = 6 – 7 moved to lower L-values with increasing geomagnetic activity. This narrow trough can be found in all main ion constituents. During periods of moderate geomagnetic activity, following the onset of a weak magnetic storm, a portion of the plasmaspheric bulge region was separated from the main plasmaspheric body. This can be seen in the outer ionosphere as an inner narrow trough at lower L-value. Troughs in light ions need no longer coincide with this in electron concentration. He⁺ is the most sensitive constituent reflecting the dusk sector plasmaspheric situation at this altitude.Dedicated to the Memory of Professor Karel P     

Paleogeothermal gradient in the boskovice furrow

Summary A coalification data set from the first seam of the Rosice-Oslavany coal district in the Boskovice furrow was used to estimate the temperature gradient prevailing within the furrow during Autunian sedimentation. An appreciable scatter of the data reflects the complicated history of the sedimentary region. The northern part of the district displays a higher degree of coalification. The results of the evaluation suggest that the region ceased to subside in the upper Autunian, and that the extent of the post-Autunian erosion does not exceed 500 metres. This version of the burial history, which is consistent with geological data, yields a temperature paleogradient of 76 mK/m for the northern part and of 72 mK/m for the southern part of the district. The gradients estimated are higher than those prevailing during the Carboniferous sedimentation in the Central Bohemian Basin (45 – 53 mK/m), lower than values found for the Ostrava Formation in the Upper Silesian Basin during its Namurian A sedimentation (about 95 mK/m), but comparable with values evaluated for the Karviná Formation of the same basin deposited during the Namurian B - C and Westphalian A (60 – 77 mK/m).Dedicated to the Memory of Professor Karel P     

A rural “eye” in the Capital: Tuti Island,Khartoum, Sudan

Islands at strategic points have often become the core of a modern city, or have been developed as historic heritage sites. This has been especially true when the settlers have been strangers in the land. This paper examines why such a situation has not occurred with Tuti Island at the confluence of the White and Blue Niles in the centre of Sudan's Three Towns capital, even though the first permanent inhabitants at the confluence were strangers and chose Tuti Island for their first settlement. The paper questions whether Tuti can survive as a green eye in its present form with the increasing pressures from the urban areas surrounding it.     

Behavioural-geographical aspects of environmental quality

The behavioural approach in human geography accentuates the view of quality of the environment through man and his value orientations. The quality of environment from the point of view of human experience raises behavioural-geographical questions that are the core of the presented topic. Aspects of environmental imaginations and sensations as well as human value system are presented as variables affecting the structure of the perceived environment and human spatial behaviour. In this context, the authors present results of two behavioural studies that correspond to new models of man and environment from the viewpoint of a behavioural approach. The suggested humanistic approach in behavioural geography emphasizes above all the emotional aspect of the relationship between man and environment, which through environmental values, spatial sensations, and meanings, leads to human spatial behaviour.     

Seismic hazard of Egypt

Earthquake hazard parameters such as maximum expected magnitude,M _max, annual activity rate,, andb value of the Gutenberg-Richter relation have been evaluated for two regions of Egypt. The applied maximum likelihood method permits the combination of both historical and instrumental data. The catalogue used covers earthquakes with magnitude 3 from the time interval 320–1987. The uncertainties in magnitude estimates and threshold of completeness were taken into account. The hazard parameter determination is performed for two study areas. The first area, Gulf of Suez, has higher seismicity level than the second, all other active zones in Egypt.b-values of 1.2 ± 0.1 and 1.0 ± 0.1 are obtained for the two areas, respectively. The number of annually expected earthquakes with magnitude 3 is much larger in the Gulf of Suez, 39 ± 2 than in the other areas, 6.1 ± 0.5. The maximum expected magnitude is calculated to be 6.5 ± 0.4 for a time span of 209 years for the Gulf of Suez and 6.1 ± 0.3 for a time span of 1667 years for the remaining active areas in Egypt. Respective periods of 10 and 20 years were reported for earthquakes of magnitude 5.0 for the two subareas.     

Blind prediction of the site effects at Ashigara Valley,Japan, and its comparison with reality

Weak and strong ground motions were numerically predicted for three stations of the Ashigara Valley test site. The prediction was based on the records from a rock-outcrop station, one weak-motion record from a surface-sediments station, and the standard geotechnical model. The data were provided by the Japanese Working Group on the Effects of Surface Geology as a part of an international experiment. The finite-difference method for SH waves in a 2-D linear viscoelastic medium (a causalQ model) was employed.Comparison with the real records shows that at two stations the predictions fit better than at the third one. Strangely, the two better predictions were for stations situated at larger distances from the reference rock station (one station was on the surface, the other in a borehole). The strong ground motion (the peak acceleration of about 200 cm s^–2) was not predicted qualitatively worse than the weak motion (8 cm s^–2). A less sophisticated second prediction (not submitted during the experiment), in which we did not attempt to fit the available weak-motion record at the sedimentary station, agrees with the reality significantly better.