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1.
We combine information about the evolutionary history and distributional patterns of the genus Saintpaulia H. Wendl. (Gesneriaceae; ‘African violets’) to elucidate the factors and processes behind the accumulation of species in tropical montane areas of high biodiversity concentration. We find that high levels of biodiversity in the Eastern Arc Mountains are the result of pre-Quaternary speciation processes and environmental stability. Our results support the hypothesis that climatically stable mountaintops may have acted as climatic refugia for lowland lineages during the Pleistocene by preventing extinctions. In addition, we found evidence for the existence of lowland micro-refugia during the Pleistocene, which may explain the high species diversity of East African coastal forests. We discuss the conservation implications of the results in the context of future climate change. 相似文献
2.
For the first time the expression of C3 and CAM in the leaves of different age of Marrubium frivaldszkyanum Boiss, is reported. With increasing leaf age a typical C3 photosynthesis pattern and high transpiration rate were found. In older leaves a shift to CAM occurred and the 24-h transpiration water loss decreased. A correlation was established between leaf area and accumulation of malate. Water loss at early stages of leaf expansion may be connected with the shift to CAM and the water economy of the whole plant. 相似文献
3.
Sam Mavandadi Steve Feng Frank Yu Stoyan Dimitrov Karin Nielsen-Saines William R. Prescott Aydogan Ozcan 《PloS one》2012,7(10)
We propose a methodology for digitally fusing diagnostic decisions made by multiple medical experts in order to improve accuracy of diagnosis. Toward this goal, we report an experimental study involving nine experts, where each one was given more than 8,000 digital microscopic images of individual human red blood cells and asked to identify malaria infected cells. The results of this experiment reveal that even highly trained medical experts are not always self-consistent in their diagnostic decisions and that there exists a fair level of disagreement among experts, even for binary decisions (i.e., infected vs. uninfected). To tackle this general medical diagnosis problem, we propose a probabilistic algorithm to fuse the decisions made by trained medical experts to robustly achieve higher levels of accuracy when compared to individual experts making such decisions. By modelling the decisions of experts as a three component mixture model and solving for the underlying parameters using the Expectation Maximisation algorithm, we demonstrate the efficacy of our approach which significantly improves the overall diagnostic accuracy of malaria infected cells. Additionally, we present a mathematical framework for performing ‘slide-level’ diagnosis by using individual ‘cell-level’ diagnosis data, shedding more light on the statistical rules that should govern the routine practice in examination of e.g., thin blood smear samples. This framework could be generalized for various other tele-pathology needs, and can be used by trained experts within an efficient tele-medicine platform. 相似文献
4.
E Schulte N A Dimitrova G V Dimitrov G Rau C Disselhorst-Klug 《Journal of electromyography and kinesiology》2005,15(3):290-299
Changes in muscle fibre length and surface electrode position with respect to the muscle fibres affect the amplitude and frequency characteristics of surface electromyography (SEMG) in different ways. Knowledge of changes in muscle fibre length would help towards a better interpretation of the signals. The possibility of estimating the length through SEMG during voluntary contractions was checked in this study. The fibres' semi-length was estimated from the product of the conduction velocity and conduction time during which the wave of excitation propagated from the end-plate region to the ends of the fibres. Short (10 s), moderate (30% of maximum voluntary contraction) isometric contractions were performed by 10 subjects at different elbow joint angles (80-140 degrees in steps of 20 degrees ). Monopolar signals were detected non-invasively, using a two-dimensional electrode array. High spatial resolution EMG and a decomposition technique were utilised to extract single motor unit activities for triggered averaging and to estimate conduction velocity. A significant increase with joint angle was found in conduction time and estimated fibre semi-length. Changes in conduction velocity with joint angle were found to be not significant. The methodology described allows the relative changes in fibres' semi-length to be estimated from SEMG data. 相似文献
5.
Summary According to Nagl and Fusenig (1979) the structure and ultrastructure of plant nuclei is species-specific and is determined by the DNA (2C) value and the amount of the repetitive DNA. Light and electron microscopic observations ofZea mays L.,Pisum sativum L., andPhaseolus vulgaris L. nuclei led us to define their organization as chromonematic, chronomeric and chromocentric, respectively. Nuclear proteins, soluble in 0.4N H2SO4 and 0.74M HC1O4, were extracted from isolated nuclei and resolved according to their solubility and mobility in SDS and acetic acid-urea PAGE and 2D-Triton X 100 PAGE. Differences in the variants (and modifications) of the H 1 histone class and the nucleosomal H 2 A, H 2 B, and H 3 isoforms probably reflect that species-specific nuclear ultrastructure is based, not only on the heterogeneity and the quantity of DNA, but also on the diversity of the protein component of chromatin.Abbreviations MES
Morpholinoethane sulfonic acid
- PMSF
phenylmethylsulphonyl fluoride
- DMSO
dimethylsulfoxid
- SDS
sodium dodecylsulfate
- TEMED N, N, N
N-tetramethylethylen-diamin
- PAGE
polyacrylamide gel electrophoresis 相似文献
6.
Laser-induced crosslinking of histones to DNA in chromatin and core particles: implications in studying histone-DNA interactions. 总被引:5,自引:4,他引:1
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Stefanovsky VYu S I Dimitrov V R Russanova D Angelov I G Pashev 《Nucleic acids research》1989,17(23):10069-10081
UV laser irradiation has been used to covalently crosslink histones to DNA in nuclei, chromatin and core particles and the presence of the different histone species in the covalently linked material was detected immunochemically. When nuclei were irradiated and then trypsinized to cleave the N- and C- terminal histone tails, no histones have been found covalently linked to DNA. This finding shows that UV laser-induced crosslinking of histones to DNA is accomplished via the non-structured domains only. This unexpected way of crosslinking operated in chromatin, H1-depleted chromatin and core particles, i.e. independently of the chromatin structure. The efficiency of crosslinking, however, showed such a dependence: whilst the yield of crosslinks was similar in total and H1-depleted chromatin, in core particles the efficiency was 3-4 times lower for H2A, H2B and H4 and 10-12 times lower for H3. The decreased crosslinking efficiency, especially dramatic in the case of H3, is attributed to a reduced number of binding sites, and, respectively, is considered as a direct evidence for interaction of nonstructured tails of core histones with linker DNA. 相似文献
7.
The enhancers and promoters of the Xenopus laevis ribosomal spacer are associated with histones upon active transcription of the ribosomal genes 总被引:4,自引:2,他引:2
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S I Dimitrov Stefanovsky VYu L Karagyozov D Angelov I G Pashev 《Nucleic acids research》1990,18(21):6393-6397
The presence of histones on the enhancer-promoter region of the X.laevis ribosomal spacer has been studied in embryos at stage 40, where the ribosomal genes are actively transcribed. Isolated tadpole nuclei were either fixed with formaldehyde or irradiated with UV laser to crosslink histones to DNA. The purified protein-DNA complexes were immunoprecipitated with antibodies to the histones H1, H2A and H4 and the DNA fragments carrying the respective histones were analyzed for the presence of spacer enhancer-promoter sequences by hybridization to specific DNA probe. The two independent crosslinking procedures revealed the presence of these DNA sequences in the precipitated DNA. The quantitative analysis of the UV laser-crosslinked complexes showed that histones H2A and H4 were associated with enhancer-promoter DNA in amounts similar to those found for bulk DNA, whilst the content of H1 was reduced. 相似文献
8.
9.
D. S. Dimitrov 《The Journal of membrane biology》1984,78(1):53-60
Summary A simple viscoelastic film model is presented, which predicts a breakdown electric potential having a dependence on the electric pulse length which approximates the available experimental data for the electric breakdown of lipid bilayers and cell membranes (summarized in the reviews of U. Zimmermann and J. Vienken, 1982,J. Membrane Biol.
67:165 and U. Zimmermann, 1982,Biochim. Biophys. Acta
694:227). The basic result is a formula for the time of membrane breakdown (up to the formation of pores): =(/C)/(
m
2
0
2
U
4/24Gh
3+T
2/Gh–1), where is a proportionality coefficient approximately equal to ln(h/20),h being the membrane thickness and 0 the amplitude of the initial membrane surface shape fluctuation ( is usually of the order of unity), represents the membrane shear viscosity,G the membranes shear elasticity modules,
m
the membrane relative permittivity, 0=8.85×10–12
Fm,U the electric potential across the membrane, the membrane surface tension andT the membrane tension. This formula predicts a critical potentialU
c
;U
c
=(24Gh
3/
m
2
0
2
)1/4 (for = andT=0). It is proposed that the time course of the electric field-induced membrane breakdown can be divided into three stages: (i) growth of the membrane surface fluctuations, (ii) molecular rearrangements leading to membrane discontinuities, and (iii) expansion of the pores, resulting in the mechanical breakdown of the membrane. 相似文献
10.
The life-cycle of Catatropis verrucosa (Frölich, 1789) Odhner, 1905 has been completed experimentally starting from infected snails collected along the River Danube in Europe. Each stage of the life-cycle is redescribed. Taxonomic problems are discussed and the main features of the species are listed. Synonyms for C. verrucosa are Fasciola verrucosa Frölich, 1789, F. anseris Gmelin, 1790, Monostoma verrucosa (Frölich, 1789) Zeder, 1800, and Catatropis charadrii Skrjabin, 1915. Other names, such as Notocotylus triserialis Diesing, 1839, Notocotyle triseriale (Diesing, 1839) Diesing, 1850, Monostoma verrugueux Dujardin, 1845, “Monostoma sp. du canard” of Blanchard (1847), Notocotyle verrucosum (Frölich, 1789) Monticelli, 1892, N. verruqueux Railliet, 1895, and Distoma verrucosum (Frölich, 1789) Wolffhugel, 1900, were found to represent adults and/or larvae of C. verrucosa. Conversely, but less often, adults and larvae of other species were found described and illustrated as C. verrucosa. One of these, C. verrucosa of Joyeux (1922), was renamed Pseudocatatropis joyeuxi Kanev & Vassilev, 1986. Occasionally, authors actually working with C. verrucosa ascribed their results to different species. Based on experimental life-cycle studies, the following facts were demonstrated. (1) The first intermediate hosts are the prosobranch freshwater snails Bithynia tentaculata (Linnaeus, 1758) and B. leachi (Leach, 1818). (2) The same snails are also first intermediate hosts for Notocotylus imbricatus (Looss, 1893) Szidat, 1935, N. parviovatus Yamaguti, 1934, and N. ponticus Tschiaberaschvili, 1966. In all these species, the species characteristics are expressed by the adult morphology only, and the larvae cannot be identified by morphological criteria. It is proposed that tri-oculate monostome cercariae found in naturally infected B. tentaculata and B. leachi be referred to as “Cercaria imbricata group”. These cercariae include Cercaria imbricata Looss, 1893, C. helvetica I Dubois, 1928, C. triophthalmia Faust, 1930, C. fennica I Wikgren, 1956; C. ephemera of Lutta (1934); C. monostomi of Mathias (1925), Lutta (1934) and Zdun (1961), Cercaria Notocotylus attenuatus of Francalanci & Manfredini (1969), and Monostome cercaria I Emmel, 1943. (3) There is no second intermediate snail host in the life-cycle of C. verrucosa. (4) The final hosts are birds. (5) The adult worms possess, on the ventral body surface, a median ridge and two lateral rows of 12 (range 11–14) papillae per row. 相似文献