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1.
Vladimir Garrido Ortega Gladys Lopes Vieira J.A. de Freitas Pacheco 《Astrophysics and Space Science》1998,262(3):271-295
On the basis of Jeans equations we study some dynamical properties of a sample of E galaxies considered as oblate and prolate spheroids. Although the results emphasize the anisotropy as the dominant dynamical factor both for oblate and prolate configurations, the sample contains some oblate galaxies apparently isotropic consistent with full rotational support. Comparisons of the mass-to-luminosity ratios obtained from our models with ratios derived from recent evolutionary synthesis models do not seem to leave room for nonluminous matter within the ranges (of the order of one de Vaucouleurs' radius) of the kinematical observations. Such comparisons suggest that a flatter than the classical Salpeter IMF would lead to better agreement with the dynamical results obtained within the framework of our models. 相似文献
2.
Climate change adaptation of coffee production in space and time 总被引:1,自引:0,他引:1
Peter Läderach Julian Ramirez–Villegas Carlos Navarro-Racines Carlos Zelaya Armando Martinez–Valle Andy Jarvis 《Climatic change》2017,140(1):47-61
Savannas constitute the most fire-prone vegetation type on earth and are a significant source of greenhouse gas emissions. Most savanna fires are lit by people for a variety of livelihood applications. ‘Savanna burning’ is an accountable activity under the Kyoto Protocol, but only Australia, as a developed economy, accounts for emissions from this source in its national accounts. Over the past decade considerable effort has been given to developing savanna burning projects in northern Australia, combining customary indigenous (Aboriginal) approaches to landscape-scale fire management with development of scientifically robust emissions accounting methodologies. Formal acceptance by the Australian Government of that methodology, and its inclusion in Australia’s developing emissions trading scheme, paves the way for Aboriginal people to commercially benefit from savanna burning projects. The paper first describes this Australian experience, and then explores options for implementing community-based savanna burning emissions reduction projects in other continental savanna settings, specifically in Namibia and Venezuela. These latter examples illustrate that savanna fire management approaches potentially have broader application for contributing to livelihood opportunities in other fire-prone savanna regions. 相似文献
3.
Jorge Villegas Corene Matyas Sivaramakrishnan Srinivasan Ignatius Cahyanto Brijesh Thapa Lori Pennington-Gray 《Natural Hazards》2013,66(1):97-116
Tourists are particularly vulnerable to natural disasters such as hurricanes since they might be less informed and prepared than residents of disaster-prone areas. Thus, understanding how the traits of a tropical cyclone as well as specific characteristics of tourists influence affective and cognitive responses to a hurricane warning message is a critical component in disaster planning. Using scenarios that presented tropical cyclones with different relevant characteristics (such as category at landfall), tourists’ knowledge, experience with hurricanes, trip traits, and the location of the survey (coastal or inland), this study contributes to the literature on sociological issues related to natural disasters. The findings suggest that risk perceptions and fear are influenced differently by the traits of the hurricanes and tourists’ knowledge and experience. Risk is strongly influenced by the projected category of the hurricane at landfall, while fear is not as sensitive to this extremely relevant trait of cyclones. The results also suggest that the influence of risk and fear on evacuation likelihood is strong and positive. This study shows the value of studying cognitive and affective responses to uncertain events. 相似文献
4.
Precipitation is the most fundamental input of water for terrestrial ecosystems. Most precipitation inputs are vertical, via rain, but can be horizontal, via wind‐driven rain and snow, or, in some ecosystems such as tropical montane cloud forests (TMCFs), via fog interception. Fog interception can be particularly important in ecosystems where fog is frequently present and there are seasonal periods of lower rainfall. Epiphytes in trees are a major ecological component of TMCFs and are particularly dependent on fog interception during periods of lower rainfall because they lack access to soil water. But assessing fog interception by epiphytes remains problematic because: (i) a variety of field or laboratory methods have been used, yet comparisons of interception by epiphytes versus interception by various types of fog gauge are lacking; (ii) previous studies have not accounted for potential interactions between meteorological factors. We compared fog interception by epiphytes with two kinds of commonly used fog gauges and developed relations between fog interception and meteorological variables by conducting laboratory experiments that manipulated key fog characteristics and from field measurements of fog interception by epiphytes. Fog interception measured on epiphytes was correlated with that measured from fog gauges but was more than an order of magnitude smaller than the actual measurements from fog gauges, highlighting a key measurement issue. Our laboratory measurements spanned a broad range of liquid water content (LWC) values for fog and indicate how fog interception is sensitive to an interaction between wind speed and LWC. Based on our results, considered in concert with those from other studies, we hypothesize that fog interception is constrained when LWC is low or high, and that fog interception increases with wind speed for intermediate values of LWC—a net result of deposition, impaction, and evaporation processes—until interception begins to decrease with further increases in wind speed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
5.
Juan Argüelles Ricardo Tafur Anatolio Taipe Piero Villegas Friedeman Keyl Noel Dominguez Martín Salazar 《Progress in Oceanography》2008,79(2-4):308
Changes in population structure of the jumbo flying squid Dosidicus gigas in Peruvian waters were studied based on size-at-maturity from 1989 to 2004. From 1989 to 1999, mature squid belonging to the medium-sized group prevailed, but from 2001 on, mature squids were larger. This change is not related to the changes in sea surface temperature and we hypothesized that it was caused by the population increase of mesopelagic fishes as prey. 相似文献
6.
Gladys V. Melián Inés Galindo Nemesio M. Pérez Pedro A. Hernández Mario Fernández Carlos Ramírez Raúl Mora Guillermo E. Alvarado 《Pure and Applied Geophysics》2007,164(12):2465-2487
We report the results of four soil H2 surveys carried out in 2000–2003 at Poás volcano, Costa Rica, to investigate the soil H2 distribution and evaluate the diffuse H2 emission as a potential surveillance tool for Poás volcano. Soil gas H2 contents showed a wide range of concentration from 0.2 to 7,059 ppmV during the four surveys. Maps of soil gas H2 based on Sequential Gaussian Simulation showed low H2 concentration values in the soil atmosphere (<0.7 ppmV) for most of the study area, whereas high soil gas H2 values were observed inside the active crater of Poás. A significant increase in soil gas H2 concentration was observed inside the active crater during 2001 and 2002 with respect to year 2000, followed by a decrease
in 2003. The observed spatial and temporal variations of soil H2 concentration have been well correlated with seismicity, microgravimetry and fumarolic chemistry changes which occurred during
this study. These observations evidence changes in the shallow magmatic-hydrothermal system of Poás, and it might be related
to a potential magmatic intrusion during the period 1998–2004. Therefore, monitoring diffuse H2 emission of Poás has become an important geochemical tool for the monitoring of its volcanic activity. 相似文献
7.
Henry Villegas 《国际地球制图》2013,28(1):67-74
Abstract On November the 13th of 1985, the City of Armero (Colombia) was destroyed by debris flows generated by a reactivation of the Nevado del Ruiz Volcano. The flows ocurred in at least three principal pulses, as was observed by the disater's survivors. Landsat TM 5 data processing was carried out in subscenes taken before and after the lahar sedimentation. False color composites were generated and combined with the geological information available in order to visualize the magnitude of the catastrophe and the flow characteristics. Taking advantage of Landsat TM 5 images with high spectral resolution, a detailed photogeological mapping of the three principal pulses of the debris flows was carried out. Landsat TM 5 proved to be a powerful complementary source of information for hazard assesment of these catastrophic debris flows. The images were used in addition to ground‐based information, and were an easy way to help ordinary people and decision makers understand such hazardous volcanic situations. 相似文献
8.
Eleazar Padrón Gladys Melián Rayco Marrero Dácil Nolasco José Barrancos Germán Padilla Pedro A. Hernández Nemesio M. Pérez 《Pure and Applied Geophysics》2008,165(1):95-114
Significant changes in the diffuse emission of carbon dioxide were recorded in a geochemical station located at El Hierro,
Canary Islands, before the occurrence of several seismic events during 2004. Two precursory CO2 efflux increases started thirteen and nine days before two seismic events of magnitude 2.3 and 1.7, which took place near
El Hierro Island, Canary Islands, on March 23 and April 15, reaching a maximun value of 51.1 and 46.2 g m−2 d−1, respectively, five and eight days before the two seismic events. Other similar increases started thirteen and five days
before the occurrence of two seismic events of magnitude 1.3 and 1.5 which took place on October 15 and 21 respectively, reaching
the maximum values four and one day before the earthquakes. These changes were not related to variations in atmospheric or
soil parameters. The Material Failure Forecast Method (FFM), which analyzes the rate of precursory phenomena, was successfully
applied to forecast the first seismic event that took place in El Hierro Island in 2004. 相似文献
9.
Gladys Villegas Wenzhi Liao Ronald Criollo Wilfried Philips Daniel Ochoa 《地球空间信息科学学报》2017,20(4):325-332
AbstractClose-range hyperspectral images are a promising source of information in plant biology, in particular, for in vivo study of physiological changes. In this study, we investigate how data fusion can improve the detection of leaf elements by combining pixel reflectance and morphological information. The detection of image regions associated to the leaf structures is the first step toward quantitative analysis on the physical effects that genetic manipulation, disease infections, and environmental conditions have in plants. We tested our fusion approach on Musa acuminata (banana) leaf images and compared its discriminant capability to similar techniques used in remote sensing. Experimental results demonstrate the efficiency of our fusion approach, with significant improvements over some conventional methods. 相似文献