The problem of habitat fragmentation is recently an important issue in ecological research as well as in the practical approach of nature conservation. According to the most popular approaches, habitats are considered...The problem of habitat fragmentation is recently an important issue in ecological research as well as in the practical approach of nature conservation. According to the most popular approaches, habitats are considered as the homogenous parts of the landscape. Also the metapopulation concept problem of the inert habitat heterogenity is considered quite seldom. These approaches have some weak points resulting from the assumption that the border between habitat patches and the metapopulation matrix is fairly sharp. This paper presents a resource-based concept of habitats, based on mathematical theory of point processes, which can be easily applied to analysing the problem of uneven distribution of resources. The basic assumption is that the random distribution of resources may be mathematically described as the realisation of a certain point process. According to our method, it is possible to calculate the expected quantities of available resources as well as the minimum area of habitat that includes the expected abundance of the resource. This approach may be very useful to understand some crucial phenomena in landscape ecology, such as the patch size effect and its connection to habitat loss and fragmentation.展开更多
Forest disturbances have been altering the ecological properties of ecosystems;meanwhile,disturbance events of varying sizes create different structures and functions for a forest landscape.Therefore,size and frequenc...Forest disturbances have been altering the ecological properties of ecosystems;meanwhile,disturbance events of varying sizes create different structures and functions for a forest landscape.Therefore,size and frequency are important attributes of disturbances,and their relationship should be studied.We present a hierarchical method through the modeling of the overall trend of the size–frequency distribution and the characterization of the non-constant variances of disturbance sizes at each frequency level.This method was demonstrated to accurately model the sizes as well as the corresponding frequencies;thus,the total disturbed area and number of disturbance patches were both accurately estimated.By applying the method to 13 provinces in China,consistent patterns were revealed by the modeling results and remote-sensing-based product,showing that between 2000 and 2005,forests in most provinces were dominated by moderate disturbances(10 ha<size<100 ha).Southeastern provinces contain the largest proportion of small disturbances(size<10 ha),whereas most of the very large disturbances(size>1000 ha)occurred in the northeastern and northwestern provinces.This study concludes that the proposed method can improve the representation of the size–frequency distribution of forest disturbances.展开更多
In this paper, the resonance and radiation characteristics of patch antennas fabricated with two different types of dielectric substrates have been investigated and compared at GSM 1800 MHz band. At first, the above-s...In this paper, the resonance and radiation characteristics of patch antennas fabricated with two different types of dielectric substrates have been investigated and compared at GSM 1800 MHz band. At first, the above-stated characteristics of a patch antenna loaded with conventional plastic substrate have been investigated. Later a high permittivity dielectric material (barium titanate) has been used as the antenna substrate. The main goal here is to reduce the antenna size with a high permittivity dielectric material and then to compare its resonance and radiation performance with the earlier low permittivity substrate loaded prototype. It is found that with the use of high permittivity substrate the antenna volume gets smaller (about 6% of the plastic substrate prototype) although the gain decreases by around 2.5 dB.展开更多
基金funded by Institute of Nature Conservation PASpartly by a Polish State Committee for Scientific Research/National Science Centre grant No.N N304 325836.
文摘The problem of habitat fragmentation is recently an important issue in ecological research as well as in the practical approach of nature conservation. According to the most popular approaches, habitats are considered as the homogenous parts of the landscape. Also the metapopulation concept problem of the inert habitat heterogenity is considered quite seldom. These approaches have some weak points resulting from the assumption that the border between habitat patches and the metapopulation matrix is fairly sharp. This paper presents a resource-based concept of habitats, based on mathematical theory of point processes, which can be easily applied to analysing the problem of uneven distribution of resources. The basic assumption is that the random distribution of resources may be mathematically described as the realisation of a certain point process. According to our method, it is possible to calculate the expected quantities of available resources as well as the minimum area of habitat that includes the expected abundance of the resource. This approach may be very useful to understand some crucial phenomena in landscape ecology, such as the patch size effect and its connection to habitat loss and fragmentation.
基金supported by the Natural Science Foundation of China[grant number 41901300]the Fundamental Research Funds for the Central Universities[grant number CCNU19TD002]the Scientific Research Project of Department of Natural Resources of Hubei Province[grant number ZRZY2020KJ01].
文摘Forest disturbances have been altering the ecological properties of ecosystems;meanwhile,disturbance events of varying sizes create different structures and functions for a forest landscape.Therefore,size and frequency are important attributes of disturbances,and their relationship should be studied.We present a hierarchical method through the modeling of the overall trend of the size–frequency distribution and the characterization of the non-constant variances of disturbance sizes at each frequency level.This method was demonstrated to accurately model the sizes as well as the corresponding frequencies;thus,the total disturbed area and number of disturbance patches were both accurately estimated.By applying the method to 13 provinces in China,consistent patterns were revealed by the modeling results and remote-sensing-based product,showing that between 2000 and 2005,forests in most provinces were dominated by moderate disturbances(10 ha<size<100 ha).Southeastern provinces contain the largest proportion of small disturbances(size<10 ha),whereas most of the very large disturbances(size>1000 ha)occurred in the northeastern and northwestern provinces.This study concludes that the proposed method can improve the representation of the size–frequency distribution of forest disturbances.
文摘In this paper, the resonance and radiation characteristics of patch antennas fabricated with two different types of dielectric substrates have been investigated and compared at GSM 1800 MHz band. At first, the above-stated characteristics of a patch antenna loaded with conventional plastic substrate have been investigated. Later a high permittivity dielectric material (barium titanate) has been used as the antenna substrate. The main goal here is to reduce the antenna size with a high permittivity dielectric material and then to compare its resonance and radiation performance with the earlier low permittivity substrate loaded prototype. It is found that with the use of high permittivity substrate the antenna volume gets smaller (about 6% of the plastic substrate prototype) although the gain decreases by around 2.5 dB.
