Estimation of a continuous spatio-temporal population model     

Javier Alvarez  Pascal Mossay 《Journal of Geographical Systems》2006,8(3):307-316

In this paper we propose a continuous spatio-temporal model that describes population change in a region in terms of population growth, migration drift towards regions with better economic or climate conditions, and population diffusion from more populated to less populated areas. Finite-differences are used to approximate the space and time derivatives. The model is estimated by using population data from the US census corresponding to the period 1790–1910. People tend to migrate from east to west, and to relocate towards regions with lower precipitation levels and more abundant coal and iron resources. Also population growth tends to be larger in zones with higher precipitation levels and higher temperatures.  相似文献   

Decay time of type III solar bursts observed at kilometric wavelengths     

Hector Alvarez  F. T. Haddock 《Solar physics》1973,30(1):175-182

Type III bursts were observed between 3.5 MHz and 50 kHz by the University of Michigan radio astronomy experiment aboard the OGO-5 satellite.Decay times were measured and then combined with published data ranging up to about 200 MHz. The observed decay times increase with decreasing frequency but at a rate considerably slower than that expected from electron-proton Coulomb collisions. At 50 kHz values differ by about a factor of 100. Using Hartle and Sturrock's solar wind model, Coulomb collisional frequencies were computed and compared with the apparent collisional frequencies deduced from the observations. It was found that the ratio of observed to computed values varies with heliocentric distance according to an inverse 0.71 power. This is similar to an ad hoc function used by Wolff, Brandt, and Southwick to increase the electron-proton collisional energy exchange and make the solar wind theory agree with the measurements of electron and proton temperature near the Earth. These results may provide a clue about the nature of the non-collisional plasma wave damping process responsible for the short duration of type III bursts.  相似文献   

Analytical and numerical solutions for carbonated waterflooding     

A. C. Alvarez  J. Bruining  W. J. Lambert  D. Marchesin 《Computational Geosciences》2018,22(2):505-526

We develop a Riemann solver for transport problems including geochemistry related to oil recovery. The example considered here concerns one-dimensional incompressible flow in porous media and the transport for several chemical components, namely H₂O, H⁺, OH^?, CO₂, \(\text {CO}_{3}^{2-}\), \(\text {HCO}_{3}^{-}\), and decane; they are in chemical equilibrium in the aqueous and oleic phases, leading to mass transfer of CO₂ between the oleic and aqueous phases. In our ionic model, we employ equations with zero diffusion coefficients. We do so because it is well known that for upscaled equations, the convection terms dominate the diffusion terms. The Riemann solution for this model can therefore be applied for upscaled transport processes in enhanced oil recovery involving geochemical aspects. In our example, we formulate the conservation equations of hydrogen, oxygen, hydrogen, and decane, in which we substitute regression expressions that are obtained by geochemical software. This can be readily done because Gibbs phase rule together with charge balance shows that all compositions can be rewritten in terms of a single composition, which we choose to be the hydrogen ion concentration (p H). In our example, we use the initial and boundary conditions for the carbonated aqueous phase injection in an oil reservoir containing connate water with some carbon dioxide. We compare the Riemann solution with a numerical solution, which includes capillary and diffusion effects. The significant new contribution is the effective Riemann solver we developed to obtain solutions for oil recovery problems including geochemistry and a variable total Darcy velocity, a situation in which fractional flow theory does not readily apply. We thus obtain an accurate solution for a carbonated waterflood, which elucidates some mechanisms of low salinity carbonated waterflooding.  相似文献   

New Sediment Cores Reveal Environmental Changes Driven by Tectonic Processes at Ancient Helike,Greece     

Max Engel  Kirstin Jacobson  Katrin Boldt  Peter Frenzel  Dora Katsonopoulou  Steven Soter  Carlos A. Alvarez Zarikian  Helmut Brückner 《Geoarchaeology》2016,31(2):140-155

According to various historical sources an earthquake and an associated tsunami wiped out the Greek city of Helike on the Gulf of Corinth in 373 B.C. This study combines stratigraphical data from a new series of sediment cores with archaeological findings of the Helike Project to better assess the fate of Helike. Abrupt lithological changes, for example, from coarse‐grained littoral facies at the base to fine‐grained lagoonal deposits, in three of the new cores suggest sudden formation of lagoonal or lacustrine conditions in the central delta during tectonic events of subsidence due to fault‐slip. These events date before c. 2550 B.C., before 348 cal. B.C.–64 cal. A.D. (probably 373 B.C.), and before 1437–1634 cal. A.D. (probably A.D. 1402). Vertically displaced isochronic surfaces between two neighboring cores may be related to active faulting of the fan‐delta north of the Western Helike Fault Zone in 373 B.C. and A.D. 1402. Although the Helike Project reported possible tsunami evidence in earlier cores and trenches, no unequivocal sedimentary traces of a tsunami were identified in the Classical horizons of the new cores.  相似文献   

Hydrographic and atmospheric analysis of an autumnal upwelling event in the Ria of Vigo (NW Iberian Peninsula)   总被引：2，自引：0，他引：2  

M. deCastro  A.W. Dale  M. Gmez-Gesteira  R. Prego  I. Alvarez 《Estuarine, Coastal and Shelf Science》2006,68(3-4):529

An autumnal upwelling event was observed in the Ria of Vigo (NW Iberian Peninsula) on 15th November 2001. This event was analyzed by means of thermohaline variables measured at CTD stations located in the study area, satellite sea surface temperature and wind data provided by QuikSCAT. Salinity and temperature distributions revealed that the upwelled water mass was Eastern North Atlantic Central Water (ENACW), typically observed during summer upwelling events. However, previous to the upwelling event, the characteristic autumnal body of water was recorded on 31st October 2001. Subsequent sea surface temperature and upwelling index corroborated the presence of an autumnal upwelling event of approximately 15 days duration. The probability of upwelling-favorable winds (from 1999 to 2004) was lower during autumn–winter than during spring–summer, although they may occur at any time of the year. Probabilities of 45% were calculated for February and November, with the highest probability (65%) corresponding to July.  相似文献   

Chicxulub impact ejecta from Albion Island, Belize     

Kevin O Pope  Adriana C Ocampo  Alfred G Fischer  Walter Alvarez  Bruce W Fouke  Clyde L Webster  Francisco J Vega  Jan Smit  A.Eugene Fritsche  Philippe Claeys 《Earth and Planetary Science Letters》1999,170(4):275-364

Impact ejecta from the Albion Formation are exposed in northern Belize. The ejecta come from the outer portion of the continuous ejecta blanket of the Chicxulub crater, which is located 360 km to the northwest. The basal unit of the Albion Formation is a 1-m-thick clay and dolomite spheroid bed composed of up to four discrete flows. The clay spheroids are altered impact glass, and the dolomite spheroids are accretionary lapilli. The upper unit is a 15-m-thick coarse diamictite bed containing altered glass, large accretionary blocks, striated, polished, and impacted cobbles, and rare shocked quartz. The abundance of accretionary clasts, evidence for atmospheric drag sorting, and the presence of multiple flows in the Albion Formation indicate that atmospheres play an important role in the formation of the outer portions of continuous ejecta blankets of large craters.  相似文献   

A winter upwelling event in the Northern Galician Rias: Frequency and oceanographic implications     

I. Alvarez  N. Ospina-Alvarez  Y. Pazos  M. deCastro  P. Bernardez  M.J. Campos  J.L. Gomez-Gesteira  M.T. Alvarez-Ossorio  M. Varela  M. Gomez-Gesteira  R. Prego   《Estuarine, Coastal and Shelf Science》2009,82(4):1362

A winter shelf-water upwelling evidence (February 2008) is described by first time in the Northern Galician Rias (NW Iberian Peninsula). On February 20, after 9 consecutive days of upwelling favorable conditions, inside the O Barqueiro Ria was observed the presence of seawater below 10 m depth which replaced the less saline water previously observed in January. This situation was in agreement with the analyzed Ekman transport close to the northern Galician coast. Salinity and temperature distribution revealed that the upwelled water inside the rias corresponds to shelf bottom seawater which is not associated with Eastern North Atlantic Central Water or the Iberian Poleward Current. In addition, TS diagram indicated a higher influence of upwelling eastward (Viveiro–Barqueiro–Ortigueira). Nutrient salts' concentrations also suggested the presence of seawater from subsurface origin with a small variation with regard to the winter mixing in this marine area. Plankton showed the existence of spring conditions related to solar radiation increase associated to upwelling favorable winds. Some species also corroborated the intrusion of shelf-water inside the ria. Results from the analysis of Ekman transport data from 1967 to 2007 revealed that this event cannot be considered an isolated episode. In fact, the number of days per month under upwelling favorable conditions in winter (January–March) was not negligible (8–10 days) showing that upwelling events along the northern Galician coast are also possible during winter.  相似文献   

Poleward intrusion in the northern Galician shelf     

I. Alvarez  N. Ospina-Alvarez  M. deCastro  M. Varela  M. Gomez-Gesteira  R. Prego 《Estuarine, Coastal and Shelf Science》2010

The evolution of a warm water mass related to the Iberian Poleward Current (IPC) was characterized along the northern Galician shelf in November 2008 by means of Sea Surface Temperature and wind data. It was observed that under upwelling favorable conditions water temperature decreased along the northern coast and a temperature break appeared between Cape Vilano and Cape Ortegal showing a relaxation of the poleward intrusion. The effect of the IPC was also analyzed inside the Northern Galician Rias taking into account the hydrographical and biogeochemical properties measured on November 18. Water driven by the IPC was observed close to the mouth of the rias, around Cape Estaca de Bares, causing a nutrient salts decrease. Inside the rias a slight biological activity was found near surface resulting from fluvial contributions.  相似文献   

Reionization: characteristic scales, topology and observability     

Ilian T. Iliev  Ue-Li Pen  Patrick McDonald  Paul R. Shapiro  Garrelt Mellema  Marcelo A. Alvarez 《Astrophysics and Space Science》2009,320(1-3):39-43

Recently the numerical simulations of the process of reionization of the universe at z>6 have made a qualitative leap forward, reaching sufficient sizes and dynamic range to determine the characteristic scales of this process. This allowed making the first realistic predictions for a variety of observational signatures. We discuss recent results from large-scale radiative transfer and structure formation simulations on the observability of high-redshift Ly-α sources. We also briefly discuss the dependence of the characteristic scales and topology of the ionized and neutral patches on the reionization parameters.  相似文献   

Observing the critical zone on a critical budget: The Peri Lake experimental catchment     

Pedro Luiz Borges Chaffe  Camyla Innocente dos Santos  Alondra Beatriz Alvarez Perez  João Henrique Macedo Sá  Tomas Carlotto  Leonardo Hoinaski 《水文研究》2021,35(3):e14087

The Peri Lake Experimental Catchment, in Southern Brazil, is a small coastal lake (5 km², 7 m depth) with a total catchment area of 20 km². The catchment is mainly covered by subtropical Atlantic Forest. Peri Lake is a recreational destination, an important ecosystem for biodiversity preservation, and a major water supply source. Even though there is a clear social and economic relevance, the information on this ecosystem is scarce, especially regarding the dynamics of water balance and water quality. We built this observatory using a low-cost, low-technology monitoring system to estimate the major components of the water budget on what we called a critical budget. We monitor meteorology, rainfall interception in two plots, overland flow and groundwater connectivity in a representative hillslope; and streamflow and velocity are measured in several small headwater rivers mostly starting during 2015. Geographic information on topography, land cover, geology, soil characteristics and the location of all the equipment installed in the field are also provided. The data set can be used to understand rainfall interception in Atlantic forests, catchment connectivity and streamflow permanence in coastal areas, spatial patterns of baseflow, and the modelling of complex processes in the critical zone involving the interaction between surface and groundwater, that are important in coastal lake ecosystems. Besides being used for research and education, we hope this observatory built on a shoestring budget will encourage fieldwork particularly in underrepresented and underfunded regions of the world.  相似文献