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801.
Jari Oksanen 《Plant Ecology》1987,72(1):51-57
Joint plots of species and site scores in correspondence analysis can be interpreted so that points which are in the same
direction from the origin are closely associated. Species and site scores can thus be compared. Within each set of scores
the location of points is also meaningful. Owing to the unimodal species response model which can be recovered by the correspondence
analysis, the location of the species points in respect to the site points indicates the location of the optimum when direct
weighted averages are used. However, when the eigenvalue of the solution is low, very different joint plots are derived when
the set which is used for computing the weighted averages for the other set is changed. This makes the interpretation of the
between-set proximities in the joint plot vague. Generally, it is not possible to deduce the species composition of a site
or sites where a species occurs from the joint plot, although for some pairs of species and sites this is justified. Although
the proximity interpretation is not possible in every case, a joint plot display can greatly enhance the interpretation of
results. 相似文献
802.
Development of a neural phenotype in differentiating ganglion cell-derived human neuroblastoma cells 总被引:6,自引:0,他引:6
Ian G. Scott Karl E. O. kerman Jari E. Heikkil Kai Kaila Leif C. Andersson 《Journal of cellular physiology》1986,128(2):285-292
Human neuroblastoma cells (clone SHSY-5Y) induced to differentiate by 12-O-tetradecanoylphorbol-13-acetate (TPA) are shown to possess properties characteristic of mature ganglion cells. Elevation of the external K+ concentration, exposure to Ca2+ ionophore A23187, and acetylcholine all stimulate the release of preloaded 3H-noradrenaline in the presence but not in the absence of added Ca2+. Acetylcholine causes a fall in the 86Rb+ or 14C-TPMP equilibrium potential across the plasma membrane and stimulates 86Rb+ efflux. These responses are prevented by atropine. Acetylcholine and muscarine but not nicotine stimulate an increase in 45Ca2+ influx, an effect blocked by atropine. None of these responses have been observed in nondifferentiating cells. Muscarinic receptors, however, as measured by the binding of tritiated quinuclidinyl benzilate (3H-QNB), were present to a similar extent in control and differentiated cells. Both cell types also exhibit an accelerated release of Ca2+ in response to acetylcholine, but the control cells were at least 1 order of magnitude more sensitive to the agonist. 相似文献
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806.
Esa Koskela Pinja Juutistenaho Tapio Mappes Tuula A. Oksanen 《Evolutionary ecology》2000,14(2):99-109
According to parental investment theory, nest defence activity should be related to the reproductive value of the offspring.
Alternative hypotheses suggest that defence activity may, for example, depend upon the conspicuousness of the young. Studies
concerning this topic have been carried out almost exclusively on birds and experimental data on the diversity of organisms
is lacking. Bank voles Clethrionomys glareolus were used to study the effects of the number and age of offspring upon the pup defence activity of mothers. Male bank voles
are infanticidal and thus an adult male was used as a predator. Defence trials were conducted in the laboratory and filmed
for subsequent analysis. Litter sizes were divided into three treatment groups: reduced (−2 pups), control (±0 pups) and enlarged
(+2 pups). In order to study the effect of offspring age upon maternal defence activity the trials were conducted twice: when
the pups were 3 and 8 days old. Defence activity increased with the number of offspring and enlarged litters were most actively
defended. This result supports parental investment theory and conclusions drawn by earlier studies of birds. However, in contrast
to the conclusions of earlier studies, older offspring were defended less than the younger ones. Whilst new-born pups are
totally defenceless against predators their vulnerability decreases as they age. Therefore, we suggest that maternal aggression
in female bank voles is related to the value as well as to the vulnerability of the offspring. The validity of this explanation
and the determinants of parental investment decisions in small mammals in general deserve further study.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
807.
Lotta J. Happonen Esko Oksanen Lassi Liljeroos Adrian Goldman Tommi Kajander Sarah J. Butcher 《Journal of virology》2013,87(15):8388-8398
Biochemical reactions powered by ATP hydrolysis are fundamental for the movement of molecules and cellular structures. One such reaction is the encapsidation of the double-stranded DNA (dsDNA) genome of an icosahedrally symmetric virus into a preformed procapsid with the help of a genome-translocating NTPase. Such NTPases have been characterized in detail from both RNA and tailed DNA viruses. We present four crystal structures and the biochemical activity of a thermophilic NTPase, B204, from the nontailed, membrane-containing, hyperthermoacidophilic archaeal dsDNA virus Sulfolobus turreted icosahedral virus 2. These are the first structures of a genome-packaging NTPase from a nontailed, dsDNA virus with an archaeal host. The four structures highlight the catalytic cycle of B204, pinpointing the molecular movement between substrate-bound (open) and empty (closed) active sites. The protein is shown to bind both single-stranded and double-stranded nucleic acids and to have an optimum activity at 80°C and pH 4.5. The overall fold of B204 places it in the FtsK-HerA superfamily of P-loop ATPases, whose cellular and viral members have been suggested to share a DNA-translocating mechanism. 相似文献
808.
Kati Pasanen Jari Parkkari Matti Pasanen Hannele Hiilloskorpi Tanja M?kinen Markku J?rvinen Pekka Kannus 《BMJ (Clinical research ed.)》2008,337(7661):96-99
Objective To investigate whether a neuromuscular training programme is effective in preventing non-contact leg injuries in female floorball players.Design Cluster randomised controlled study.Setting 28 top level female floorball teams in Finland.Participants 457 players (mean age 24 years)—256 (14 teams) in the intervention group and 201 (14 teams) in the control group—followedup for one league season (six months).Intervention A neuromuscular training programme to enhance players’ motor skills and body control, as well as to activate and prepare their neuromuscular system for sports specific manoeuvres.Main outcome measure Acute non-contact injuries of the legs.Results During the season, 72 acute non-contact leg injuries occurred, 20 in the intervention group and 52 in the control group. The injury incidence per 1000 hours playing and practise in the intervention group was 0.65 (95% confidence interval 0.37 to 1.13) and in the control group was 2.08 (1.58 to 2.72). The risk of non-contact leg injury was 66% lower (adjusted incidence rate ratio 0.34, 95% confidence interval 0.20 to 0.57) in the intervention group.Conclusion A neuromuscular training programme was effective in preventing acute non-contact injuries of the legs in female floorball players. Neuromuscular training can be recommended in the weekly training of these athletes.Trial registration Current Controlled Trials ISRCTN26550281. 相似文献
809.
The electrostatic contribution to spontaneous membrane curvature is calculated within Poisson-Boltzmann theory under a variety of assumptions and emphasizing parameters in the physiological range. Asymmetrical surface charges can be fixed with respect to bilayer midplane area or with respect to the lipid-water area, but induce curvatures of opposite signs. Unequal screening layers on the two sides of a vesicle (e.g., multivalent cationic proteins on one side and monovalent salt on the other) also induce bending. For reasonable parameters, tubules formed by electrostatically induced bending can have radii in the 50-100-nm range, often seen in many intracellular organelles. Thus membrane associated proteins may induce curvature and subsequent budding, without themselves being intrinsically curved. Furthermore, we derive the previously unexplored effects of respecting the strict conservation of charge within the interior of a vesicle. The electrostatic component of the bending modulus is small under most of our conditions and is left as an experimental parameter. The large parameter space of conditions is surveyed in an array of graphs. 相似文献