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91.
Forest density expressing the stocking status constitutes the major stand physiognomic parameter of Indian forest. Density
and age are often taken as surrogate to structural and compositional changes that occur with the forest succession. Satellite
remote sensing spectral response is reported to provide information on structure and composition of forest stands. The various
vegetation indices are also correlated with forest canopy closure. The paper presents a three way crown density model utilizing
the vegetation indices viz., advanced vegetation index, bare soil index and canopy shadow index for classification of forest
crown density. The crop and water classes which could not be delineated by the model were finally masked from normalized difference
vegetation index and TM band 7 respectively. The rule based approach has been implemented for land use and forest density
classification. The broad land cover classification accuracy has been found to be 91.5%. In the higher forest density classes
the classification accuracy ranged between 93 and 95%, whereas in the lower density classes it was found to be between 82
and 85%. 相似文献
92.
The MC dynamics of an off-lattice all-atom protein backbone model with rigid amide planes are studied. The only degrees of freedom are the dihedral angle pairs of the C-atoms. Conformational changes are generated by Monte Carlo (MC) moves. The MC moves considered are single rotations (simple moves, SM's) giving rise to global conformational changes or, alternatively, cooperative rotations in a window of amide planes (window moves, WM's) generating local conformational changes in the window. Outside the window the protein conformation is kept invariant by constraints. These constraints produce a bias in the distribution of dihedral angles. The WM's are corrected for this bias by suitable Jacobians. The energy function used is derived from the CHARMM force field. In a first application to polyalanine it is demonstrated that WM's sample the conformational space more efficiently than SM's.Abbreviations CPU
Central Processing Unit
- MC
Monte Carlo
- MCD
Monte Carlo Dynamics
- MD
Molecular Dynamics
- RMS
Root-Mean-Square
- RMSD
Root-Mean-Square-Deviation
- SM
Simple Move
- WM
Window Move 相似文献
93.
The time dependence of the human
1-antitrypsin polymerization process was studied by means of the intrinsic fluorescence stopped-flow technique as well as the fluorescence-quenching-resolved spectra (FQRS) method and native PAGE. The polymerization was induced by mild denaturing conditions (1 M GuHCl) and temperature. The data show that the dimer formation reaction under mild conditions was followed by an increase of fluorescence intensity. This phenomenon is highly temperature sensitive. The structure of
1-antitrypsin dimer resembles the conformation of antithrombin III dimer. In the presence of the denaturant the polymerization process is mainly limited to the dimer state. The
1-antitrypsin activity measurements confirm monomer-to-dimer transition under these conditions. These results are in contrast to the polymerization process induced by temperature, where the dimer state is an intermediate step leading to long-chain polymers. On the basis of stopped-flow and electrophoretic data it is suggested that both C-sheet as well as A-sheet mechanisms contribute to the polymerization process under mild conditions.Abbreviations GuHCL
guanidinium hydrochloride
- RSL
reactive site loop
- PAI-1
plasminogen activator inhibitor type 1
- AT III
antithrombin III
- FQRS
fluorescence quenching resolved spectra 相似文献
94.
A. Cavallini L. Natali T. Giordani M. Durante P. G. Cionini 《TAG. Theoretical and applied genetics. Theoretische und angewandte Genetik》1996,92(3-4):285-291
Complex alterations in the redundancy and methylation of repeated DNA sequences were shown to differentiate the nuclear genome of individuals belonging to single progenies of homozygous plants of the sunflower. DNA was extracted from seedlings obtained from seeds collected at the periphery of flowering heads (P DNA) or from seedlings obtained from seeds collected in their middle (M DNA). Three fractions of repeated sequences were isolated from genomic DNA: a highly repetitive fraction (HR), which reassociates within an equivalent Cot of about 2 × 10-1, and two medium repetitive fractions (MR1 and MR2) having Cot ranges of about 2 × 10-1-2 and 2-102, respectively. Denaturation kinetics allowed different sequence families to be recognized within each fraction of repetitive DNA, and showed significant differences in sequence redundancy to occur between P and M DNA, particularly as far as the MR2 fraction is concerned. Most DNA sequence families are more represented in P DNA than in M DNA. However, the redundancy of certain sequences is greater in the latter than in the former. Each repetitive DNA fraction was hybridized to Southern blots of genomic P or M DNA which was digested to completion by three pairs of isoschizomeric restriction endonucleases which are either insensitive or sensitive to the methylation of a cytosine in the recognition site. The results obtained showed that the repetitive DNA of H. annuus is highly methylated. Clear-cut differences in the degree of methylation of P and M DNA were found, and these differences were particularly apparent in the MR2 fraction. It is suggested that alterations in the redundancy of given DNA sequences and changes in their methylation patterns are complementary ways to produce continuous genotypic variability within the species which can be exploited in environmental adaptation.Research supported by National Research Council of Italy, Special Project RAISA, Sub-project No. 2 相似文献
95.
REYNALDO LUIZ VICTORIA FERNANDO FERNANDES† LUIZ ANTONIO MARTINELLI MARISA DE CÁSSIA PICCOLO PLINIO BARBOSA DE CAMARGO SUSAN TRUMBORE‡ 《Global Change Biology》1995,1(3):165-171
Measurements of the organic carbon inventory, its stable isotopic composition and radiocarbon content were used to deduce vegetation history from two soil profiles in arboreal and grassy savanna ecotones in the Brazilian Pantanal. The Pantanal is a large floodplain area with grass-dominated lowlands subject to seasonal flooding, and arboreal savanna uplands which are only rarely flooded. Organic carbon inventories were lower in the grassy savanna site than in the upland arboreal savanna site, with carbon decreasing exponentially with depth from the surface in both profiles. Changes in 13C of soil organic matter (SOM) with depth differed markedly between the two sites. Differences in surface SOM 13C values reflect the change from C3 to C4 plants between the sites, as confirmed by measurements of 13C of vegetation and the soil surface along a transect between the upland closed-canopy forest and lowland grassy savanna. Changes of 13C in SOM with depth at both sites are larger than the 3–4 per mil increases expected from fractionation associated with organic matter decomposition. We interpret these as recording past changes in the relative abundance of C3 and C4 plants at these sites. Mass balances with 14C and 13C suggest that past vegetational changes from C3 to C4 plants in the grassy savanna, and in the deeper part of the arboreal savanna, occurred between 4600 and 11 400 BP, when major climatic changes were also observed in several places of the South American Continent. The change from C4 to C3, observed only in the upper part of the arboreal savanna, was much more recent (1400 BP), and was probably caused by a local change in the flooding regime. 相似文献
96.
Population-based data have not been readily available on relatively short-term changes in weight. Therefore, we sought to determine the nature of self-reported substantial (> 10%) weight change over one year in a representative sample of the US population which participated in the 1989 National Health Interview Survey (NHIS). Across all ages, a larger proportion of women than men reported both weight loss as well as weight gain of any amount (18.9% vs. 16.1% for weight loss and 20.0% vs. 16.1% for weight gain). In sex-specific logistic regression analyses, significant risk factors common to both sexes for substantial weight loss included divorced/separated marital status, smoking, increased number of blood pressure checks, increased BMI (body mass index) and increased number of bed days. Black race reduced the risk of weight loss for both men and women. Sex-specific risk factors for weight loss in men only were widowhood or never married marital status, while increasing age was a protective factor in women only. Concerning weight gain > 10% over the past year, increased number of blood pressure checks and having one or more diabetic parents were significant risk factors among both men and women; while never being married, increased age, BMI, and education exerted a protective effect in both sexes. For women only, risk factors for weight gain included black race, increased number of contacts with a health professional, and being unemployed. Intention to lose weight was associated with both weight gain and weight loss in both sexes, although it did not serve as a confounder in any of these relationships. A greater likelihood of substantial weight loss among women relative to men was diminished for persons with higher BMI, higher number of blood pressure checks, being widowed, divorced or separated, and intention to lose weight. A greater likelihood of substantial weight gain among women relative to men was diminished for persons with low BMI. The results of this cross-sectional study of weight change, involving a one-year follow-up period, generally correspond with the results obtained by longitudinal studies involving a longer follow-up. 相似文献
97.
武汉东湖水生植被及其恢复途径探讨 总被引:4,自引:0,他引:4
1992~1993年对武汉东湖三个主要湖区(郭郑湖、汤林湖和牛巢湖)水生植被的调查表明,该湖区共有水生植物32种,优势种为大茨藻、狐尾藻、苦草和菱。金鱼藻呈不断扩大的趋势。植被类型可分为11个群丛,植被面积约为0.65km ̄2,总生物量为1236.39t(湿重),植被带状分布仅见于汤林湖北部和其他部分湖汊。汤林湖和牛巢湖水生植被正处于自然恢复演替阶段。 相似文献
98.
99.
Consequences of a tidal reduction for the salt-marsh vegetation in the Oosterschelde estuary (The Netherlands) 总被引:4,自引:4,他引:0
A storm-surge barrier was constructed in the mouth of the Oosterschelde, a euhaline mesotidal estuary in the SW Netherlands (mean tidal range 3.6 m). As a consequence, the tidal range and the Mean High Water in the estuary have been reduced to about 88% of their original values.During the final construction stage of this barrier (1986–87) both were reduced to a maximum of 65% for more than 18 months. During this period, large-scale die-back of the vegetation occurred in vast areas on the salt marshes; locally, a complete die-back of the vegetation took place. Glycophytes and disturbance indicating species appeared on a large scale and grew abundantly. After the new tidal regime had been established, the vegetation recovered. The species characteristic of disturbance, are gradually being replaced by perennial salt marsh species. In addition, most species are shifting into zones of lower elevation, which correspond (in 1990/1991) more or less with the original flooding frequencies. Moreover, in many basins the levee-species Halimione portulacoides and Elymus pycnanthus are far more prominent than before, probably as a result of the strong ripening of the soil that has occurred in these basins during the extra tidal reduction. In 1991, four years after the establishment of the new tidal regime, the salt marsh vegetation had still not been stabilized. 相似文献
100.
The influence of riparian vegetation on macroinvertebrate community structure and functional organization in six new Guinea streams 总被引:2,自引:1,他引:1
David Dudgeon 《Hydrobiologia》1994,294(1):65-85
Information on the ecology of New Guinea streams is meagre, and data are needed on the trophic basis of aquatic production in rivers such as the Sepik in Papua New Guinea which have low fish yields. This study investigates the relationship between riparian shading (from savanna grassland to primary rainforest), algal and detrital food, and macroinvertebrate abundance and community structure in 6 Sepik River tributary streams. A particular aim was to elucidate macroinvertebrate community responses to changes in riparian conditions. All streams supported diverse benthic communities, but morphospecies richness (overall total 64) was less than in streams on the tropical Asian mainland; population densities of benthic invertebrates, by contrast, were similar to those recorded elsewhere. Low diversity could reflect limited taxonomic penetration, but may result from the absence of major groups (Plecoptera, Heptageniidae, Ephemerellidae, Psephenidae, Megaloptera, etc.) which occur on the Asian mainland. Population densities of all 19 of the most abundant macroinvertebrate taxa varied significantly among the 6 study streams, but community composition in each was broadly similar with dominance by Baetidae and (in order of decreasing importance), Leptophlebiidae, Orthocladiinae, Elmidae and Hydropsychidae. Principal components analysis (PCA) undertaken on counts of abundant macroinvertebrate taxa clearly separated samples taken in two streams from the rest. Both streams contained high detrital standing stocks and one was completely shaded by rainforest. Stepwise multiple-regression analysis indicated that population densities of the majority of abundant taxa (11 out of 19) across streams (10 samples per stream; n = 60) were influenced by algae and/or detritus, although standing stocks of these variables were not clearly related to riparian conditions. When regression analysis was repeated on mean counts of taxa per stream (dependent variables) versus features of each stream as a whole (thus n = 6), % shading and detritus were the independent variables yielding significant regression models most frequently, but pH, total-nitrogen loads and algae were also significant predictors of faunal abundance. Further regression analysis, undertaken separately on samples (n = 10) from each stream, confirmed the ability of algae and detritus to account for significant portions of the variance in macroinvertebrate abundance, but the significance of these variables varied among streams with the consequence that responses of individual taxa to algae or detritus was site-specific.Community functional organization — revealed by investigation of macroinvertebrate functional feeding groups (FFGs) — was rather conservative, and streams were codominated by collector-gatherers (mean across 6 streams = 43%) and grazers (36%), followed by filter-feeders (15%) and predators (7%). The shredder FFG was species-poor and comprised only 0.4% of total macroinvertebrate populations; shredders did not exceed 2% of benthic populations in any stream. PCA of FFG abundance data was characterized by poor separation among streams, although there was some evidence of clustering of samples from unshaded sites. The first 2 PCA axes accounted for 84% of the variation in the data suggesting that the poor separation resulted from the general similarity of FFG representation among streams. Although stepwise multiple-regression analysis indicated that algae and detritus accounted for significant proportions of the variations in population density and relative abundance of some FFGs, the response of community functional organization to changes in riparian conditions and algal and detrital food base was weak — unlike the deterministic responses that may be typical of north-temperate streams. 相似文献