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Reactive surface area is one of the key parameters for studying the kinetics of mineral dissolution. The common practice in experimental kinetics is to normalize the dissolution rate to the surface area measured by the BET method. The relationship between BET surface area and the reactive surface area is not trivial in minerals such as smectites, which possess both internal and external surface areas, and in which the dissolution is controlled by the chemical attack on the edge surface. The present study examines two proxies for the reactive surface area of the Clay Mineral Society reference smectite SAz-1: BET surface area and the edge surface area measured using AFM.Since smectites are very microporous, their BET surface area is strongly influenced by the degassing procedure. It is demonstrated that outgassing the smectite powder at 135°C in a 15 mL min−1 N2 gas flow for at least 24 hours minimizes contribution from micropores to less than 11% of the BET surface area.Following dissolution experiments in solutions with a low electrolyte concentration, the BET surface area increased from 34 ± 2 m2 g−1 in raw SAz-1 to 127 ± 13 m2 g−1 in SAz-1 sample recovered from dissolution experiments. This increase in BET surface area is explained by a decrease in the average size of the smectite aggregates, and by an increase in microporosity due to the depletion in the major interlayer cation, i.e., Ca2+. As the BET surface area of the raw smectite sample includes considerably less microporosity compared to the BET surface area of the smectite recovered from dissolution experiments, the former is a better approximation of the external surface area of the dried sample powder.AFM measurements show that there is no correlation between the specific external surface area of the sample and its specific edge surface area. This observation is explained by the platy morphology of the smectite particle in which the specific external surface area depends linearly on the height reciprocal, whereas the specific edge surface area is independent of the particles height and depends linearly on the sum of the reciprocals of the length of the axes. Therefore, there is no reason to expect a correlation between the BET and the edge surface area. Our results show that the edge surface area (4.9 ± 0.7 m2 g−1) of the smectite particles cannot be predicted based on its external surface area (136 ± 20 m2 g−1). Therefore, the BET surface area cannot serve as a proxy for the reactive surface area. We suggest using AFM measurements of the specific edge surface area as an alternative proxy for the reactive surface area of smectite. 相似文献
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The aim of this study is to present an automatic approach for olive tree dendrometric parameter estimation from airborne laser scanning (ALS) data. The proposed method is based on a unique combination of the alpha-shape algorithm applied to normalized point cloud and principal component analysis. A key issue of the alpha-shape algorithm is to define the α parameter, as it directly affects the crown delineation results. We propose to adjust this parameter based on a group of representative trees in an orchard for which the classical field measurements were performed. The best value of the α parameter is one whose correlation coefficient of dendrometric parameters between field measurements and estimated values is the highest. We determined crown diameters as principal components of ALS points representing a delineated crown. The method was applied to a test area of an olive orchard in Spain. The tree dendrometric parameters estimated from ALS data were compared with field measurements to assess the quality of the developed approach. We found the method to be equally good or even superior to previously investigated semi-automatic methods. The average error is 19% for tree height, 53% for crown base height, and 13% and 9% for the length of the longer diameter and perpendicular diameter, respectively. 相似文献
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Winter synoptic-scale variability over the Mediterranean Basin under future climate conditions as simulated by the ECHAM5 总被引：3，自引：1，他引：2
Christoph Cornelius Raible Baruch Ziv Hadas Saaroni Martin Wild 《Climate Dynamics》2010,35(2-3):473-488
Changes of the winter climate in the Mediterranean Basin (MB) for future A2 conditions are investigated for the period 2071–2100 and compared with the control period 1961–1990. The analysis is based on time-slice simulations of the latest version of the ECHAM model. First, the control simulation is evaluated with reanalysis data. The emphasis is given to synoptic and large-scale features and their variability in the MB. The model is found to be capable of reproducing the main features of the MB and southern Europe in the winter season. Second, the A2 simulation is compared with the control simulation, revealing considerable changes of the synoptic variability. Focusing on the synoptic spatio-temporal scale aims to unfold the dynamic background of the climatic changes. The Mediterranean cyclones, which are individually detected and tracked, decrease by 10% in the Western Mediterranean (WM) whereas no significant change is found in the Eastern Mediterranean. The cyclone intensity is slightly reduced in the entire region. To understand these changes, the underlying dynamical background is analyzed. It is found that changes in baroclinicity, static stability, transformation from eddy kinetic energy to kinetic energy of the mean flow and stationary wave activity are significant in particular in the WM and the coastline of North Africa. The reduction of cyclonic activity severely impacts the precipitation mainly in the southern part of the WM. 相似文献
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The rainfall distribution within the rainy season has crucial implications on a variety of disciplines. According to one approach of analyzing the intraseasonal rainfall distribution, it is essential to examine the date of different accumulated percentage (DAP hereafter), as presented in Paz and Kutiel (Isr J Earth Sci 52:47–63, 2003). The present study identifies various intraseasonal temporal distributions of rainfall, in 41 stations within the Mediterranean basin. Furthermore, classifications of these distributions according to their time, yield, and length are presented. The accumulated percentage was calculated for each Julian day for every available year in all stations. A correlation matrix between every possible pair of years, in each station, was calculated, and a cluster analysis (average linkage method) was performed. Finally, the averages of the entire dataset and the average of every cluster were compared in order to classify the clusters by using three parameters: timing represented by DAP(25%, 50%, 75%) annual rainfall total and the rainy season length (RSL). Between 2 and 5 different types of clusters, with various probabilities, were defined for every station. Out of 132 overall clusters, which were found in 41 stations, the most frequent type (cluster 1) was the median in all three parameters. There were 16 clusters identified as short in their RSL, and 18 were identified as having a long classification. There were 19 dry clusters, and only eight were identified as wet. As for the parameter of timing, 39 clusters were classified as early and 38 as late. One conclusion of this study was that the probability of a dry year is higher than a wet one, and likewise, the probability of a long year is higher than of a short one. 相似文献
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The study examines the synoptic situations and weather conditions under which occurred Israel's largest forest fires between
the years 1987–1995. Annual rainfall and maximum temperature were found to have a positive correlation with both the size
of the burnt area and the frequency of fires. A negative correlation was found for the relative humidity at 12 UTC for the
same parameters. The fire season in Israel starts in May and ends in November, the peak months being May, June and July. No
large fires were observed during the rainy season, December–February, despite the relatively low precipitation characterizing
the region. Atmospheric disturbances as well as quasi-stationary systems were found to be favorable for the development of
forest fires in Israel: the North African (‘Sharav’) cyclone and the Red Sea trough, which are common during spring and autumn.
These systems carry hot, dry air from the deserts and are responsible for 55% of the burnt area from major forest fires in
Israel and up to 33% of the major forest fires. Sixty-five percent of the forest fires occurred during the summer all of them
under the quasi-stationary system of the Persian Gulf trough. These fires did not spread as widely as those that occurred
under the North African cyclone and the Red Sea trough systems. The role of weather in the propagation of fire is exemplified
in the case study of the ‘Sha'ar ha Gai’ fire of July 1995 — the biggest forest fire in the history of Israel (1300 ha).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
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This study deals with potential changes in the relative humidity associated with global warming and their implications on
heat stress along the coastal region of the Mediterranean in the summer season. It is based on the assumption that the regional
warming will enhance the lower-level stability due to the thermal inertia of the sea with respect to its overlying air. The
enhanced stability implies more effective trapping of the near surface moisture, and as a result—further increase of the relative
humidity. The marine boundary layer over the Mediterranean is modeled. The central feature of the model is the marine inversion
capping the marine moist air, which intensity is positively correlated with the stability. Simple calculations indicate that
if the temperature increases, while the stability remains unchanged, the near-surface relative humidity would not be affected.
But, an increase in the stability would result in an increase in the near-surface relative humidity. This prediction is validated
through observed trends of the respective fields, using the NCEP/NCAR reanalysis data and soundings from the eastern Mediterranean.
The results are consistent in indicating an increase in the near-surface temperature, the lower-level stability and the relative
humidity over the eastern part of the Mediterranean, but not in its western part. The results for the eastern Mediterranean
support the expectation for an aggravation of heat stress beyond that imparted by the temperature rise. 相似文献
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A. Hadas 《Theoretical and Applied Climatology》1965,14(2):224-262
Zusammenfassung Eine endliche Reihe (Sequenz) wird als eine der möglichen Permutationen ihrer Glieder aufgefaßt. Es wird gezeigt, daß die Summe der absoluten Differenzen der aufeinanderfolgenden Glieder gleich ist
, wo die natürliche Zahlen sind und nur von der Rangordnung der Glieder der Reihe (von der Permutation) abhängen; die j sind von der Reihenfolge unabhängig und werden durch die Dispersion der Reihenglieder bestimmt. Die j und die j werden separat untersucht; der Erwartungswert der erwähnten Differenzsumme wird abgeleitet. Verschiedene bereits bekannte und auch erstmalig hier vorgeschlagene Maßzahlen werden geprüft. An Reihen jährlicher Regenmengen wird die Rolle der j und der j und das Verhalten der besprochenen Maßzahlen veranschaulicht.
Summary A series ofn members can be considered as one of the possible permutations of its members. It is shown that the sum of the linear successive differences is equal to the expression , where the j are positive integers, dependent only upon the rank-order (the permutation) of the members, while the j are independent of the order of the succession and are determined by the dispersion of the members of the series. The factors j and j are separately investigated; the expected value of the sum of the linear successive differences is established. Various related statistical measures, already in usage and new ones suggested here, are discussed. Series of yearly rainfall amounts are used to show the effects of the j and j and to discuss the behaviour of the various measures.
Résumé Une série, constituée parn valeurs, est regardée comme une des possibles permutations de ces valeurs. L'auteur montre que la somme des différences absolues, qui se présentent entre les valeurs consécutives de la série, est égale à l'expression . Les j sont des nombres entiers positifs et ne dépendent que de l'ordre des membres de la série, tandis que les j, indépendants de l'ordre, sont déterminés par la dispersion des membres. Les facteurs j et j sont étudiés séparément; l'espérance mathématique de la somme mentionnée est dérivée. Des paramètres statistiques déjà connus ou proposés ici pour la première fois, sont discutés. Le rôle des j et des j et le comportement des divers paramètres sont montrés à l'aide de séries de totaux annuels de pluies.相似文献
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Banville Simon Sieradzki Rafal Hoque Mainul Wezka Kinga Hadas Tomasz 《GPS Solutions》2017,21(4):1817-1828
GPS Solutions - Higher-order ionospheric effects, if not properly accounted for, can propagate into geodetic parameter estimates. For this reason, several investigations have led to the development... 相似文献