Migration in a transitional economy: Beyond the planned and spontaneous dichotomy in Vietnam     

Heather Xiaoquan Zhang  P. Mick Kelly  Catherine Locke  Alexandra Winkels  W. Neil Adger 《Geoforum》2006,37(6):1066-1081

Migration is frequently portrayed as a negative force in its relationship with economic and social development. This negative perception is exhibited through describing population movements as either ‘forced’ (e.g. political and environmental refugees) or ‘voluntary’ movements (e.g. economic and uninhibited relocation). This paper examines the limitations of this conceptual dualism. It points out that the dualistic approach, widely used in the context of developing countries, simplifies a highly complex phenomenon by ignoring its essential heterogeneity and spatial and temporal dynamics. As such, it is limited in explaining and understanding the globally diversified, historically and politically contextualised situations. Focusing on the migratory experiences of contemporary Vietnam, the study identifies major patterns and trends of population mobility in the country in the past fifty years. It shows that despite the state’s continued attempts to reshape the spatial distribution of population over recent historical periods, the policy outcomes with respect to population mobility have been swayed as much by individuals and their families in pursuit of their own aspirations and livelihoods as by state plans. The Vietnam case has provided evidence of a much more complicated relationship between migration and livelihoods than the conceptual dichotomy assumes, and the opportunity for a richer set of policy options. We argue that the evidence from Vietnam, and elsewhere, warrants an integrated approach to studying migration, combining analysis at the macro- and micro-levels with the nexus lying at the critical decision-making point of the individual or household.  相似文献   

The psychology of beach users: importance of confirmation bias,action, and intention to improving rip current safety     

Ménard  A. Dana  Houser  Chris  Brander  Robert W.  Trimble  Sarah  Scaman  Alexandra 《Natural Hazards》2018,94(2):953-973

Natural Hazards - The rip current hazard on beaches is a global public health issue. While physical controls on rip current formation and flow behavior are relatively well understood, there has...  相似文献   

Nanogeochemistry of hydrothermal magnetite     

Artur?P.?DeditiusEmail author  Martin?Reich  Adam?C.?Simon  Alexandra?Suvorova  Jaayke?Knipping  Malcolm?P.?Roberts  Sergey?Rubanov  Aaron?Dodd  Martin?Saunders 《Contributions to Mineralogy and Petrology》2018,173(6):46

Magnetite from hydrothermal ore deposits can contain up to tens of thousands of parts per million (ppm) of elements such as Ti, Si, V, Al, Ca, Mg, Na, which tend to either structurally incorporate into growth and sector zones or form mineral micro- to nano-sized particles. Here, we report micro- to nano-structural and chemical data of hydrothermal magnetite from the Los Colorados iron oxide–apatite deposit in Chile, where magnetite displays both types of trace element incorporation. Three generations of magnetites (X–Z) were identified with concentrations of minor and trace elements that vary significantly: SiO₂, from below detection limit (bdl) to 3.1 wt%; Al₂O₃, 0.3–2.3 wt%; CaO, bdl–0.9 wt%; MgO, 0.02–2.5 wt%; TiO₂, 0.1–0.4 wt%; MnO, 0.04–0.2 wt%; Na₂O, bdl–0.4 wt%; and K₂O, bdl–0.4 wt%. An exception is V₂O₃, which is remarkably constant, ranging from 0.3 to 0.4 wt%. Six types of crystalline nanoparticles (NPs) were identified by means of transmission electron microscopy in the trace element-rich zones, which are each a few micrometres wide: (1) diopside, (2) clinoenstatite; (3) amphibole, (4) mica, (5) ulvöspinel, and (6) Ti-rich magnetite. In addition, Al-rich nanodomains, which contain 2–3 wt% of Al, occur within a single crystal of magnetite. The accumulation of NPs in the trace element-rich zones suggest that they form owing to supersaturation from a hydrothermal fluid, followed by entrapment during continuous growth of the magnetite surface. It is also concluded that mineral NPs promote exsolution of new phases from the mineral host, otherwise preserved as structurally bound trace elements. The presence of abundant mineral NPs in magnetite points to a complex incorporation of trace elements during growth, and provides a cautionary note on the interpretation of micron-scale chemical data of magnetite.  相似文献   

Accurate Ocean Bottom Seismometer Positioning Method Inspired by Multilateration Technique     

Omar Benazzouz  Luis M. Pinheiro  Luis M. A. Matias  Alexandra Afilhado  Daniel Herold  Seth S. Haines 《Mathematical Geosciences》2018,50(5):569-584

The positioning of ocean bottom seismometers (OBS) is a key step in the processing flow of OBS data, especially in the case of self popup types of OBS instruments. The use of first arrivals from airgun shots, rather than relying on the acoustic transponders mounted in the OBS, is becoming a trend and generally leads to more accurate positioning due to the statistics from a large number of shots. In this paper, a linearization of the OBS positioning problem via the multilateration technique is discussed. The discussed linear solution solves jointly for the average water layer velocity and the OBS position using only shot locations and first arrival times as input data.  相似文献   

Evolution of silicic magmas in the Kos-Nisyros volcanic center,Greece: a petrological cycle associated with caldera collapse   总被引：2，自引：1，他引：1  

Olivier?BachmannEmail author  Chad?D.?Deering  Janina?S.?Ruprecht  Christian?Huber  Alexandra?Skopelitis  Cedric?Schnyder 《Contributions to Mineralogy and Petrology》2012,163(1):151-166

Multiple eruptions of silicic magma (dacite and rhyolites) occurred over the last ~3 My in the Kos-Nisyros volcanic center (eastern Aegean sea). During this period, magmas have changed from hornblende-biotite-rich units with low eruption temperatures (≤750–800°C; Kefalos and Kos dacites and rhyolites) to hotter, pyroxene-bearing units (>800–850°C; Nisyros rhyodacites) and are transitioning back to cooler magmas (Yali rhyolites). New whole-rock compositions, mineral chemistry, and zircon Hf isotopes show that these three types of silicic magmas followed the same differentiation trend: they all evolved by crystal fractionation and minor crustal assimilation (AFC) from parents with intermediate compositions characterized by high Sr/Y and low Nb content, following a wet, high oxygen fugacity liquid line of descent typical of subduction zones. As the transition between the Kos-Kefalos and Nisyros-type magmas occurred immediately and abruptly after the major caldera collapse in the area (the 161 ka Kos Plateau Tuff; KPT), we suggest that the efficient emptying of the magma chamber during the KPT drew out most of the eruptible, volatile-charged magma and partly solidified the unerupted mush zone in the upper crust due to rapid unloading, decompression, and coincident crystallization. Subsequently, the system reestablished a shallow silicic production zone from more mafic parents, recharged from the mid to lower crust. The first silicic eruptions evolving from these parents after the caldera collapse (Nisyros units) were hotter (up to >100°C) than the caldera-forming event and erupted from reservoirs characterized by different mineral proportions (more plagioclase and less amphibole). We interpret such a change as a reflection of slightly drier conditions in the magmatic column after the caldera collapse due to the decompression event. With time, the upper crustal intermediate mush progressively transitioned into the cold-wet state that prevailed during the Kefalos-Kos stage. The recent eruptions of the high-SiO₂ rhyolite on Yali Island, which are low temperature and hydrous phases (sanidine, quartz, biotite), suggest that another large, potentially explosive magma chamber is presently building under the Kos-Nisyros volcanic center.  相似文献   

Evaluating the anthropogenic impacts on groundwaters; a methodology based on the determination of natural background levels and threshold values   总被引：1，自引：0，他引：1  

Alexandra Gemitzi 《Environmental Earth Sciences》2012,67(8):2223-2237

The present work investigates the long-term effects of human intervention on groundwaters based on the determination of natural background levels (NBLs) and threshold values (TVs) for groundwater electrical conductivity, chloride, ammonium, sulphates and nitrates. The methodology adopted is the one proposed in the 6th Framework European Project ??BRIDGE??, which was applied with some adjustments in Rhodope area (Northern Greece). The study area was especially selected because it incorporates two distinct subareas: the northern one which can be safely considered as a pristine area, where NBLs for groundwaters were assessed from; the southern part which forms a typical Mediterranean region, intensively cultivated for the last 40?years. Groundwater TVs were determined considering two types of groundwater receptors: (a) groundwater ??itself?? and (b) groundwater dependent lagoons in the coastal part of the study area. Results showed that groundwater quality is altered seriously from its natural background composition indicating how human activities have affected groundwater quality and showed that chemical status of groundwater has been seriously aggravated. The number and the spatial distribution of monitoring locations exceeding TVs revealed that chloride and nitrates are the most serious threats for groundwater in the study area.  相似文献   

Sea surface temperatures at tide gauges: Case study of San Francisco,California, from 1855 to 1993     

Alexandra Carvalho  George A. Maul 《Marine Geodesy》2013,36(4):317-324

Tide gauge observations usually include temperature and density measurements. As an example of such data, a time series of sea surface temperature (SST) from 1855 to 1877 and from 1921 to 1993 at Fort Point, San Francisco, California (the longest U.S. record), and mean air temperature at Mission Dolores (San Francisco), California, from 1936 to 1990, were analyzed. Annual mean Fort Point SST increased at a rate of 0.3°C per century, but the coefficient of determination (r²) was below 0.06; for air temperature the results were 1.6°C per century and r² = 0.16 respectively. Evidence of El Niño were found in the periodogram of the mean annual SST but not in the air temperature. The annual and semiannual peaks in the monthly time‐series analysis of SST and air temperature dominate their periodograms, and the cross‐correlation between them has r² = 0.47. Of the 1.3 mmlyr sea level rise over the same time period. 0.003°C/yr accounts for 0.04 mmlyr in thermal expansion if the upper 100 m of the water column were uniformly warmed.  相似文献   

The use of bioluminescent dinoflagellates as an environmental risk assessment tool     

Lapota D  Osorio AR  Liao C  Bjorndal B 《Marine pollution bulletin》2007,54(12):1857-1867

A novel toxicity method to determine sublethal and lethal effects of manmade contaminants on the bioluminescence output from marine dinoflagellates has been developed and tested over the course of 16 years. The toxicity system, QwikLite™, was developed for the sole purpose of evaluating the potential toxicity of various materials used in bay sediments, storm water discharges, industrial discharges from Naval facilities, and antifoulant paints. Bioluminescence inhibition was observed in the following dinoflagellates: Lingulodinium polyedrum (formerly known as Gonyaulax polyedra), Ceratocorys horrida, Pyrocystis noctiluca, Pyrocystis lunula, Pyrocystis fusiformis, and Pyrophacus steinii. Cultured cells were exposed to various concentrations of contaminants from hours through 10 days. Further application with bioluminescent dinoflagellates in a variety of toxicity testing schemes have shown that these species can be used as a screening assay organism in lieu of the more costly, labor intensive bioassays presently in use.  相似文献