In the first part, the authors review a group of studies dealing with the identification of regional differences in Italian migratory patterns, especially using the concept of migration field. The second part is devoted to a study of the hierarchical clustering of Italian provinces using 1973 inter-provincial migratory flow data. (summary in ENG, FRE) 相似文献
Understanding and developing groundwater resources in arid regions such as El Salloum basin, along the northwestern coast of Egypt, remains a challenging issue. One-dimensional (1D) electrical sounding (ES), two-dimensional (2D) electrical resistivity imaging (ERI), and very low frequency electromagnetic (VLF-EM) measurements were used to investigate the hydrogeological framework of El Salloum basin with the aim of determining the potential for extraction of potable water. 1D resistivity sounding models were used to delineate geoelectric sections and water-bearing layers. 2D ERI highlighted decreases in resistivity with depth, attributed to clay-rich limestone combined with seawater intrusion towards the coast. A depth of investigation (DOI) index was used to constrain the information content of the images at depths up to 100 m. The VLF-EM survey identified likely faults/fractured zones across the study area. A combined analysis of the datasets of the 1D ES, 2D ERI, and VLF-EM methods identified potential zones of groundwater, the extent of seawater intrusion, and major hydrogeological structures (fracture zones) in El Salloum basin. The equivalent geologic layers suggest that the main aquifer in the basin is the fractured chalky limestone middle Miocene) south of the coastal plain of the study area. Sites likely to provide significant volumes of potable water were identified based on relatively high resistivity and thickness of laterally extensive layers. The most promising locations for drilling productive wells are in the south and southeastern parts of the region, where the potential for potable groundwater increases substantially.
In contrast to results for several other nations, hierarchical regionalizations based upon 1960 Philippine lifetime migration do not indicate that islands act as migration regions — groups of provinces, relatively self-contained with respect to migration flows. Inter-island links seem to be more important than intra-island ties. Northern Luzon, the Bicol Peninsula and the Southern Philippines are among the regions that appear. Manila and its suburban province of Rizal are exceptional both for the breadth and strength of their interprovincial migration ties. 相似文献
Forthcoming human planetary exploration will require increased scientific return (both in real time and post-mission), longer surface stays, greater geographical coverage, longer and more frequent EVAs, and more operational complexities than during the Apollo missions. As such, there is a need to shift the nature of astronauts’ scientific capabilities to something akin to an experienced terrestrial field scientist. To achieve this aim, the authors present a case that astronaut training should include an Apollo-style curriculum based on traditional field school experiences, as well as full immersion in field science programs. Herein we propose four Learning Design Principles (LDPs) focused on optimizing astronaut learning in field science settings. The LDPs are as follows:
(1)
LDP#1: Provide multiple experiences: varied field science activities will hone astronauts’ abilities to adapt to novel scientific opportunities
(2)
LDP#2: Focus on the learner: fostering intrinsic motivation will orient astronauts towards continuous informal learning and a quest for mastery
(3)
LDP#3: Provide a relevant experience—the field site: field sites that share features with future planetary missions will increase the likelihood that astronauts will successfully transfer learning
(4)
LDP#4: Provide a social learning experience—the field science team and their activities: ensuring the field team includes members of varying levels of experience engaged in opportunities for discourse and joint problem solving will facilitate astronauts’ abilities to think and perform like a field scientist.
The proposed training program focuses on the intellectual and technical aspects of field science, as well as the cognitive manner in which field scientists experience, observe and synthesize their environment. The goal of the latter is to help astronauts develop the thought patterns and mechanics of an effective field scientist, thereby providing a broader base of experience and expertise than could be achieved from field school alone. This will enhance their ability to execute, explore and adapt as in-field situations require. 相似文献
The production rate and isotopic composition of H2 derived from radiolytic reactions in H2O were measured to assess the importance of radiolytic H2 in subsurface environments and to determine whether its isotopic signature can be used as a diagnostic tool. Saline and pure, aerobic and anaerobic water samples with pH values of 4, 7, and 10 were irradiated in sealed vials at room temperature with an artificial γ source, and the H2 abundance in the headspace and its isotopic composition were measured. The H2 concentrations were observed to increase linearly with dosage at a rate of 0.40 ± 0.04 molecules (100 eV)−1 within the dosage range of 900 to 3500 Gray (Gy; Gy = 1 J Kg−1) with no indication of a maximum limit on H2 concentration. At ∼2000 Gy, the H2 concentration varied only by 16% across the experimental range of pH, salinity, and O2. Based upon this measured yield and H2 yields for α and β particles, a radiolytic H2 production rate of 10−9 to 10−4 nM s−1 was estimated for the range of radioactive element concentrations and porosities typical of crustal rocks. The δD of H2 was independent of the dosage, pH (except for pH 4), salinity, and O2 and yielded an αDH2O-H2 of 2.05 ± 0.07 (αDH2O-H2 = (D/H)H2O to (D/H)H2), slightly less than predicted radiolytic models. Although this radiolytic fractionation value is significantly heavier than that of equilibrium isotopic exchange between H2 and H2O, the isotopic exchange rate between H2 and H2O will erase the heavy δD of radiolytic H2 if the age of the groundwater is greater than ∼103 to 104 yr. The millimolar concentrations of H2 observed in the groundwater of several Precambrian Shields are consistent with radiolysis of water that has resided in the subsurface for a few million years. These concentrations are well above those required to support H2-utilizing microorganisms and to inhibit H2-producing, fermentative microorganisms. 相似文献
Redox hot spots occurring as metal-rich anoxic groundwater discharges through oxic wetland and river sediments commonly result in the formation of iron (Fe) oxide precipitates. These redox-sensitive precipitates influence the release of nutrients and metals to surface water and can act as ‘contaminant sponges’ by absorbing toxic compounds. We explore the feasibility of a non-invasive, high-resolution magnetic susceptibility (MS) technique to efficiently map the spatial variations of magnetic Fe oxide precipitates in the shallow bed of three rivers impacted by anoxic groundwater discharge. Laboratory analyses on Mashpee River (MA, USA) sediments demonstrate the sensitivity of MS to sediment Fe concentrations. Field surveys in the Mashpee and Quashnet rivers (MA, USA) reveal several discrete high MS zones, which are associated with likely anoxic groundwater discharge as evaluated by riverbed temperature, vertical head gradient, and groundwater chemistry measurements. In the East River (CO, USA), widespread cobbles/rocks exhibit high background MS from geological ferrimagnetic minerals, thereby obscuring the relatively small enhancement of MS from groundwater induced Fe oxide precipitates. Our study suggests that, in settings with low geological sources of magnetic minerals such as lowland rivers and wetlands, MS may serve as a complementary tool to temperature methods for efficiently mapping Fe oxide accumulation zones due to anoxic groundwater discharges that may function as biogeochemical hot spots and water quality control points in gaining systems. 相似文献