5 resultados para Coexistences.
Resumo:
There is great interest in lead-free (Ba0.85Ca0.15)(Ti0.90Zr0.10)O-3 (15/10BCTZ) because of its exceptionally large piezoelectric response Liu and Ren, Phys. Rev. Lett. 103, 257602 (2009)]. In this paper, we have analyzed the nature of: (i) crystallographic phase coexistence at room temperature, (ii) temperature-and field-induced phase transformation to throw light on the atomistic mechanisms associated with the large piezoelectric response of this system. A detailed temperature-dependent dielectric and lattice thermal expansion study proved that the system exhibits a weak dielectric relaxation, characteristic of a relaxor ferroelectric material on the verge of exhibiting a normal ferroelectric-paraelectric transformation. Careful structural analysis revealed that a ferroelectric state at room temperature is composed of three phase coexistences, tetragonal (P4mm)+ orthorhombic (Amm2) + rhombohedral (R3m). We also demonstrate that the giant piezoresponse is associated with a significant fraction of the tetragonal phase transforming to rhombohedral. It is argued that the polar nanoregions associated with relaxor ferroelectricity amplify the piezoresponse by providing an additional degree of intrinsic structural inhomogeneity to the system.
Resumo:
植物功能生态学研究不仅提供了植物生理生态学与生态系统生态学的连接，还为植物种群生活史对策研究提供了材料。Westoby 等 (2002) 提出了利用植物功能性状变量的主导维度来确定和量化植物生活史的生态适应策略。在他们所提出四个主导维度中，叶大小－小枝大小是研究相对较少的一维；其内部各组分的关系、对环境的响应，以及与其它重要维度的关系，目前的理解非常有限。 本研究以贡嘎山不同海拔不同功能群物种为研究对象，采用种间比较和系统发生独立性比较等研究方法，系统研究了植物的功能特征及其相关性在不同生境及不同功能群间的差异，旨在分析不同功能群物种的叶大小－小枝大小的成本和收益。其研究结果将有助于我们理解植物生活史对策的进化，进而理解物种共存和维持物种多样性的机制。主要研究结果如下： 1. 叶大小－小枝大小关系 小枝茎横截面积与单叶面积和总叶面积均呈异速生长关系，即总叶面积和单叶面积的增加比茎横截面积的增加速度快。但是，总叶面积和叶片干重的增加却基本上与小枝茎干重的增加等速。系统发生独立性比较研究的结果与此相一致。表明，在某一给定的茎投入时，至少大叶大枝物种不比小叶小枝物种在支撑叶面积和叶片干重方面具有优势。同时，在某一给定的小枝茎投入时，常绿阔叶物种比落叶阔叶物种支撑更少的叶面积。在茎干重与总叶面积的关系中，落叶复叶物种比落叶单叶物种具有更高的y轴截距，表明复叶物种比单叶物种在展叶面积方面更有效。复叶物种与单叶物种相比，通常具有较大的叶大小和小枝大小。 2. 叶大小－叶数量关系 叶大小与数量间在不同的叶片习性、不同的叶片形态以及不同的生境类型的物种间均存在稳定的负的等速生长关系，且这种关系在系统发生独立性比较时依然成立。然而，在某一给定的出叶强度 (单位小枝的叶数量) 时，常绿阔叶物种比落叶物种具有更小的叶面积。而在给定体积基础上的出叶强度时，落叶复叶物种的叶面积显著大于落叶单叶物种，且复叶物种比单叶物种具有更大的叶大小和更小的出叶强度。但是，叶大小与数量间的关系在不同的海拔间并没有显著的差异。 3. 小枝大小－总叶面积关系 在不同的生活型或不同的生境下，小枝上总叶面积与茎干重和小枝干重均呈正的异速生长关系，且斜率显著小于1.0，表明小枝上总叶面积的增加都不能赶上小枝及茎大小的增加。这种“收益递减”表明随着小枝干重的增加，光截取的收益递减。此外，叶面积比 (总叶面积与小枝干重的比值) 与单叶干重呈显著负相关关系，系统发生独立性比较的结果与此相一致。根据以上结果，可以推测，大叶的物种在质量较好的生境中出现，而群落内部小枝茎的寿命较长的物种可以拥有较大的叶片。 4. 叶片色素浓度－LMA关系 随着海拔的升高，阔叶木本植物和草本植物的叶片色素浓度减少，叶绿素a/b和类胡萝卜素/叶绿素比值以及比叶重 (LMA) 增加。然而，在草本植物中的色素浓度、色素比值和LMA的变化比阔叶木本植物的更明显。同时，LMA与叶片色素浓度呈负相关关系，但是在落叶物种中的LMA对色素浓度的影响比常绿阔叶物种更强烈。总之，草本植物的叶片特征对海拔梯度的变化似乎比木本植物更敏感，LMA对叶片色素的保护作用在落叶物种中比在常绿阔叶物种显得更重要。这些结果表明不同生活型物种可能采取不同的保护机制来降低叶绿体器官的损伤和增加他们的碳获取能力。 Studies on plant functional ecology not only bridge plant eco-physiology and ecosystem functioning, but also enrich plant population biology. As pointed out by Westoby et al (2002), plant life history strategies can be identified and quantified by four leading dimensions of variations in plant functional traits, i.e., seed size/output, leaf mass per area and leaf life span, plant height, and leaf size-twig size. Compared to the other dimensions, the cost/benefit of the leaf size-twig size spectrum has scarcely been analyzed in relation to environmental gradients and life form types, and the adaptive significance of this spectrum is not fully understood. In the present study, the relationships between functional traits of plant twigs are determined for the species with different life forms along an altitudinal gradient of Gongga Mountain with both cross-species analysis and evolutionary divergence analysis. The primary objective of this study is to examine the cost/benefit of leaf size-twig size in plants. The study results are supposed to provide insights into the understanding of the mechanism of species coexistences. The results are shown in the following. 1. The relationship between leaf size and twig size Twig cross-sectional area allometrically scaled with both individual leaf area and total leaf area supported by the twigs. However, the increase in total lamina mass/area was generally proportional to the increase in stem mass. These correlations between trait variations were significant in both interspecies analysis and phylogenetically independent comparison (PIC) analysis, which indicated that thick-twigged/large-leaved species, at least, do not have an advantage in supporting leaf/lamina area and lamina mass for the same twig stem investment than thin-twigged/ small-leaved species. Meanwhile, the evergreen broad-leaved species supported a smaller leaf area for the same twig stem investment in terms of both cross-sectional area and stem mass than the deciduous species. The deciduous compound-leaved species have a higher y-intercept in the scaling relationship of twig stem mass versus total leaf area than the deciduous simple-leaved species, indicating that compound-leaved species were more efficient in displaying leaf area. The compound-leaved species were larger in both leaf size and twig size than their counterpart in the present study. 2. The relationship between leaf size and leaf number Significantly negative and isometric scaling relationships between leaf size and leafing intensity (leaf number per twig mass or volume) were found to be consistently conserved across species independent of leaf habit, leaf form and habitat type. The negative correlations between leaf size and leafing intensity were also observed across correlated evolutionary divergences. However, leaf area was smaller in the evergreen broad-leaved species at a given leafing intensity than in the deciduous species. The deciduous compound-leaved deciduous species were higher in leaf area than deciduous simple-laved species at a given volume-based leafing intensity. Moreover, the compound-leaved deciduous species were larger in leaf size but smaller in leafing intensity than their simple counterparts. No significant difference was found in the scaling relationships between altitudes. 3. The relationship between twig size and total leaf area Leaf area was found to scale positively and allometrically with both stem and twig mass (stem mass plus leaf mass) with slopes significantly smaller than 1.0, independent of life form and habitat type, indicating that the increase in total leaf area fails to keep pace with increasing twig size and stem size. This ‘diminishing returns’ suggests that the benefit of light intercept decreased with increasing twig mass. Moreover, the leaf area ratio (the ratio of total leaf area to stem or twig mass) correlated negatively with individual leaf mass. The results of PIC were consistent with the correlations. According to the results, it is speculated that large-leaved species may be favored when habitat is good and when stem longevity are long within community. 4. The relationship between leaf pigment concentrations and leaf mass per area With increasing altitude, the concentrations of pigments decreased, but the ratios of chlorophyll a/b and carotenoid/chlorophyll, and LMA increased, in both the broad-leaved woody species and herbaceous species groups. However, the changes in the pigment concentrations, ratios and LMA were more profound in the herbaceous species than in the woody species. In addition, pigment concentrations were negatively correlated with LMA in each life form type and in the pooled dataset. However, the LMA effect on leaf pigment concentrations was more profound in the deciduous species than in the evergreen braode-leaved species. In general, herbaceous species seemed more sensitive to the increasing altitude compared to woody species, and LMA seemed to be a more important mechanism for protecting leaf pigments in deciduous species than in evergreen broad-leaved species. These results suggested that the species with different life forms may employ different protective mechanisms to decrease the chloroplast apparatus damage and increase their carbon gain.
Resumo:
This research arose from the interest on the investigation about urban expansion from Caicó. Since its creation as a village and its ascent to the condition of city, but especially , the occurred expansion from the 70s, when the local cotton economy begins to present signs of exhaustion. The central theme of this work consists on the importance of the geographical events and its relations with the phenomenon of the urban expansion from Caicó that served us as empirical basis. In relation to the events, that appear as elements of analysis on the works from the Professor Milton Santos, especially on the book Nature of Space , they appear as a kind of urban extensors energizing the areas where are installed. Understood by us as a vehicle of one or more possibilities, according to Santos, (1999) we listed some events occurred in the caicoense urbs a nd we divided them into principal and derivative ones, such events implemented from their structures, forms and functions, through processes that resulted and still continue to result the enlargement of the caicoense urban perimeter , densifications enough important for this urban expansion. The technical periods of cattle raising , cotton, as well as the tertiary city and its connections with the role of fast men, as well as slow men is also important aspect in the body of this work. It is still pointed out the inequalities and the coexistences that are generated on the basis of these connections and finally we discussed the positive and negative consequences elapsed from the phenomenon of the urban expansion
Resumo:
The present study has the objective of analyzing how the ways of dwelling influences the uses and the functional and symbolic appropriations of the urban space in Fortaleza city center, through the perspective of the residents and their relation with the living place. Scenarios of development and degradation of its urban space have marked the city center of Fortaleza. The intensification of the commercial and services occupation promoted through the years, paradoxically, the valorization of the land price and the devalorization of the residential use. Thus, the residential occupation was consolidated in a discontinuous way, being concentrated mainly in the external limits of the historical core of the neighborhood. The research is structured over the delimitation of an area and the selection of multifamily residential buildings, built since the 1960s, close to the central core of the neighborhood. The spatial configuration analysis of the selected residential buildings, and their relations with the urban surroundings and the land uses, reveals different aspects related to the urban vitality, producing impacts over the ways of dwelling constituted by the daily life of the residents. The study of the ways of dwelling involves the comprehension that the dwelling is beyond the private residential boundaries and the functional occupation. The conceptual base of this research is developed over the perspective that the dwelling represents a fundamental aspect of the human condition, allowing the person to relate with the space in an essential way (HEIDEGGER, 2012). In this perspective of the dwelling, the space reunites the mental and the cultural, the social and the historical, being marked by simultaneous logics of the conceived, the perceived and the lived space (LEFEVBRE, 2006). The development of this study, over the point of view of the neighborhood residents, is inserted in the perspective of the lived space, related to the concept of place, understood as a qualitative phenomenon, giving essence and identity to the space. The place of dwelling, marked by coexistences, is one of the structural elements of the urban land use, and potential for the rehabilitation of the central areas in big cities. Therefore, the study starts from the hypothesis that the location, the nearby land uses and the spatial configuration of the residential buildings affect the ways of dwelling, in other words the residents dissolve the boundaries of the shelter and experience the urban space, from the dwelling place. The requalification of the dwelling is opposed to the residential space based in functionality, in hierarchy, in self sufficiency, in standardization and in the reproduction of the urban space, materialized in the dense contemporary residential buildings, that are unrelated to the city. The stages of the research involved the spatial configuration analysis of the selected residential buildings and their surrounding, the land use mapping and interviews with the residents. The collected data allowed verifying that the buildings are located in areas presenting heterogeneous land uses, with a great number of residents and users. However, these aspects are not sufficient to promote the vitality of the public spaces in the neighborhood, since the people movement in the streets is controlled by the opening hours of the predominant commercial use in the area. The word of the residents, collected in interviews, indicate that the conservation conditions of the public spaces and the insecurity influences their everyday relations with the place of dwelling, affecting fundamental aspects for the dwelling requalification in the central area of Fortaleza.
Resumo:
The present study has the objective of analyzing how the ways of dwelling influences the uses and the functional and symbolic appropriations of the urban space in Fortaleza city center, through the perspective of the residents and their relation with the living place. Scenarios of development and degradation of its urban space have marked the city center of Fortaleza. The intensification of the commercial and services occupation promoted through the years, paradoxically, the valorization of the land price and the devalorization of the residential use. Thus, the residential occupation was consolidated in a discontinuous way, being concentrated mainly in the external limits of the historical core of the neighborhood. The research is structured over the delimitation of an area and the selection of multifamily residential buildings, built since the 1960s, close to the central core of the neighborhood. The spatial configuration analysis of the selected residential buildings, and their relations with the urban surroundings and the land uses, reveals different aspects related to the urban vitality, producing impacts over the ways of dwelling constituted by the daily life of the residents. The study of the ways of dwelling involves the comprehension that the dwelling is beyond the private residential boundaries and the functional occupation. The conceptual base of this research is developed over the perspective that the dwelling represents a fundamental aspect of the human condition, allowing the person to relate with the space in an essential way (HEIDEGGER, 2012). In this perspective of the dwelling, the space reunites the mental and the cultural, the social and the historical, being marked by simultaneous logics of the conceived, the perceived and the lived space (LEFEVBRE, 2006). The development of this study, over the point of view of the neighborhood residents, is inserted in the perspective of the lived space, related to the concept of place, understood as a qualitative phenomenon, giving essence and identity to the space. The place of dwelling, marked by coexistences, is one of the structural elements of the urban land use, and potential for the rehabilitation of the central areas in big cities. Therefore, the study starts from the hypothesis that the location, the nearby land uses and the spatial configuration of the residential buildings affect the ways of dwelling, in other words the residents dissolve the boundaries of the shelter and experience the urban space, from the dwelling place. The requalification of the dwelling is opposed to the residential space based in functionality, in hierarchy, in self sufficiency, in standardization and in the reproduction of the urban space, materialized in the dense contemporary residential buildings, that are unrelated to the city. The stages of the research involved the spatial configuration analysis of the selected residential buildings and their surrounding, the land use mapping and interviews with the residents. The collected data allowed verifying that the buildings are located in areas presenting heterogeneous land uses, with a great number of residents and users. However, these aspects are not sufficient to promote the vitality of the public spaces in the neighborhood, since the people movement in the streets is controlled by the opening hours of the predominant commercial use in the area. The word of the residents, collected in interviews, indicate that the conservation conditions of the public spaces and the insecurity influences their everyday relations with the place of dwelling, affecting fundamental aspects for the dwelling requalification in the central area of Fortaleza.
