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排序方式: 共有382条查询结果,搜索用时 15 毫秒
1.
2.
Relative apparent synapomorphy analysis (RASA). I: The statistical measurement of phylogenetic signal 总被引:10,自引:9,他引:1
We have developed a new approach to the measurement of phylogenetic signal
in character state matrices called relative apparent synapomorphy analysis
(RASA). RASA provides a deterministic, statistical measure of natural
cladistic hierarchy (phylogenetic signal) in character state matrices. The
method works by determining whether a measure of the rate of increase of
cladistic similarity among pairs of taxa as a function of phenetic
similarity is greater than a null equiprobable rate of increase. Our
investigation of the utility and limitations of RASA using simulated and
bacteriophage T7 data sets indicates that the method has numerous
advantages over existing measures of signal. A first advantage is
computational efficiency. A second advantage is that RASA employs known
methods of statistical inference, providing measurable sensitivity and
power. The performance of RASA is examined under various conditions of
branching evolution as the number of characters, character states per
character, and mutations per branch length are varied. RASA appears to
provide an unbiased and reliable measure of phylogenetic signal, and the
general approach promises to be useful in the development of new techniques
that should increase the rigor and reliability of phylogenetic estimates.
相似文献
3.
Six non-pregnant cows were allocated into 3 groups. Group 1 comprised a pair of lactating cows, whereas groups 2 and 3 each comprised a pair of non-lactating cows. The cows in groups 1 and 2 were dosed intraruminally by stomach tube with zinc oxide at 120 mg Zn per kg of bodyweight at weekly intervals for a period of 33 days. Each cow received a total of 4 doses of zinc oxide. Group 3 served as non-treated control group. Blood samples were collected from all 6 cows daily. Serum was analysed for concentration of calcium. Within 12–24 h of each zinc oxide administration the serum calcium of the lactating cows dropped dramatically indicating the existence of an antagonistic effect between Zn and Ca. The first Zn induced hypocalcaemic episode in the lactating cows was followed by a rise in serum calcium to a level above the pre-dosing level and above the mean value of the control group. The depth of the hypocalcaemic response decreased with the number of zinc oxide dosings. This effect was explained as a response from the stimulation of the calcium homeostatic mechanisms. In the Zn dosed non-lactating cows responses were similar but less clear. The perspective of these findings is discussed in relation to resistance towards parturient hypocalcaemia. 相似文献
4.
Three main preventive principles against milk fever were evaluated in this literature review, and the efficacy of each principle was estimated from the results of controlled investigations. Oral calcium drenching around calving apparently has a mean efficacy of 50%–60% in terms of milk fever prevention as well as prevention of milk fever relapse after intravenous treatment with calcium solutions. However, some drenches have been shown to cause lesions in the forestomacs. When using the DCAD (dietary cation-anion difference) principle, feeding rations with a negative DCAD (measured as (Na + K) – (Cl + S)) significantly reduce the milk fever incidence. Calculating the relative risk (RR) of developing milk fever from controlled experiments results in a mean RR between 0.19 and 0.35 when rations with a negative versus positive DCAD are compared. The main drawback from the DCAD principle is a palatability problem. The principle of feeding rations low in calcium is highly efficient in milk fever prevention provided the calcium intake in the dry period is kept below 20 g per day. Calculating the relative risk (RR) of developing milk fever from controlled experiments results in a very low mean RR (between 0 and 0.20) (daily calcium intake below versus above 20 g/d). The main problem in implementing the low-Ca principle is difficulties in formulating rations sufficiently low in calcium when using commonly available feeds. The use of large doses of vitamin D metabolites and analogues for milk fever prevention is controversial. Due to toxicity problems and an almost total lack of recent studies on the subject this principle is not described in detail. A few management related issues were discussed briefly, and the following conclusions were made: It is important to supply the periparturient cow with sufficient magnesium to fulfil its needs, and to prevent the dry cows from being too fat. Available information on the influence of carbohydrate intake, and on the effect of the length of the dry period and prepartum milking, is at present insufficient to include these factors in control programmes. 相似文献
5.
Gösta Nachman 《Experimental & applied acarology》1988,5(3-4):293-318
Phytoseiid mites are efficient predators capable of completely destroying colonies of spider mites. Thus, coexistence of phytoseiids
and their tetranychid prey at a local scale (typically an individual plant) is not likely for more than a single predator/prey
cycle. However, the species may coexist at a regional scale, i.e. in a complex environment consisting of many plants, provided
local colonisations, extinctions and recolonisations occur asynchronously. This review investigates some of the factors responsible
for establishing and maintaining spatial asynchrony between local populations of prey and predators, such as dispersal, environmental
heterogeneity and demographic stochasticity. Existing predator/prey models are considered in order to find agreement between
theory and empirical data. Based on our current knowledge of spatial processes and their importance for the overall dynamics
and persistence of predator/prey interactions, some consequences and aspects for biological control of crop pests by means
of natural enemies are outlined. 相似文献
6.
Activation of immobilized plasminogen by tissue activator. Multimolecular complex formation 总被引:12,自引:0,他引:12
R L Silverstein R L Nachman L L Leung P C Harpel 《The Journal of biological chemistry》1985,260(18):10346-10352
Ternary complex formation of tissue plasminogen activator (TPA) and plasminogen (Plg) with thrombospondin (TSP) or histidine-rich glycoprotein (HRGP) has been demonstrated using an enzyme-linked immunosorbent assay, an affinity bead assay, and a rocket immunoelectrophoresis assay. The formation of these complexes was specific, concentration dependent, saturable, lysine binding site-dependent, and inhibitable by fluid phase plasminogen. Apparent Kd values were approximately 12-36 nM for the interaction of TPA with TSP-Plg complexes and 15-31 nM with HRGP-Plg complexes. At saturation the relative molar stoichiometry of Plg:TPA was 3:1 within the TSP-containing complexes and 1:1 within HRGP-containing complexes. The activation of Plg to plasmin by TPA on TSP- and HRGP-coated surfaces was studied using a synthetic fluorometric plasmin substrate (D-Val-Leu-Lys-7-amino-4-trifluoromethyl coumarin). Kinetic analysis demonstrated a marked increase in the affinity of TPA for plasminogen in the presence of surface-associated TSP or HRGP. Compared to fluid phase activation or activation on fibronectin- or Factor VIII-related antigen-coated surfaces there was a 35-fold increase in efficiency of plasmin generation. A substantial amount (up to 71%) of the plasmin formed remained surface-associated and was found to be protected from inhibition by alpha 2-plasmin inhibitor. Greater than 200-fold increase in inhibitor concentration was required to effect 50% inhibition. Complex formation of locally released tissue plasminogen activator with Plg immobilized on TSP or HRGP surfaces may thus play an important role in effecting proteolytic events in nonfibrin-containing microenvironments. 相似文献
7.
Active fragments and analogs of the insect neuropeptide leucopyrokinin: structure-function studies 总被引:3,自引:0,他引:3
R J Nachman G M Holman B J Cook 《Biochemical and biophysical research communications》1986,137(3):936-942
Evaluation of analogs of the blocked insect myotropic neuropeptide leucopyrokinin (LPK) has demonstrated its relative insensitivity to amino acid substitution in the N-terminal in contrast to the C-terminal region. Truncated analogs of LPK without the first, second, and third N-terminal amino acids retain a significant 144%, 59% and 30% of the activity of the parent octapeptide, respectively. The [2-8]LPK analog is the first fragment of an insect neuropeptide to exhibit greater activity than the parent hormone. In contrast, truncated analogs of the insect myotropic, proctolin, exhibit little or no activity. The pentapeptide fragment Phe-Thr-Pro-Arg-Leu-NH2 has been identified as the active core of LPK. 相似文献
8.
Meleah D. Boyle Devon C. Payne-Sturges Thurka Sangaramoorthy Sacoby Wilson Keeve E. Nachman Kelsey Babik Christian C. Jenkins Joshua Trowell Donald K. Milton Amir Sapkota 《PloS one》2016,11(1)
The recent growth of unconventional natural gas development and production (UNGDP) has outpaced research on the potential health impacts associated with the process. The Maryland Marcellus Shale Public Health Study was conducted to inform the Maryland Marcellus Shale Safe Drilling Initiative Advisory Commission, State legislators and the Governor about potential public health impacts associated with UNGDP so they could make an informed decision that considers the health and well-being of Marylanders. In this paper, we describe an impact assessment and hazard ranking methodology we used to assess the potential public health impacts for eight hazards associated with the UNGDP process. The hazard ranking included seven metrics: 1) presence of vulnerable populations (e.g. children under the age of 5, individuals over the age of 65, surface owners), 2) duration of exposure, 3) frequency of exposure, 4) likelihood of health effects, 5) magnitude/severity of health effects, 6) geographic extent, and 7) effectiveness of setbacks. Overall public health concern was determined by a color-coded ranking system (low, moderately high, and high) that was generated based on the overall sum of the scores for each hazard. We provide three illustrative examples of applying our methodology for air quality and health care infrastructure which were ranked as high concern and for water quality which was ranked moderately high concern. The hazard ranking was a valuable tool that allowed us to systematically evaluate each of the hazards and provide recommendations to minimize the hazards. 相似文献
9.
Wang Qiaochun Mawassi Munir Sahar Nachman Li Ping Violeta Colova-Tsolova Gafny Ron Sela Ilan Tanne Edna Perl Avihai 《Plant Cell, Tissue and Organ Culture》2004,77(3):267-275
Embryogenic cell suspensions of two grapevine rootstocks: 110 Ritcher (V. berlandieri × V. rupestris), 41B (V. vinifera × V. berlandieri) and several table grape and wine cultivars (Vitis vinifera) were successfully cryopreserved by the encapsulation–vitrification method. Embryogenic cell suspensions were precultured for 3 days in liquid MGN medium supplemented with daily increasing sucrose concentrations of 0.25, 0.5, 0.75 M. Precultured cells were encapsulated and directly dehydrated with a highly concentrated vitrification solution prior to immersion in liquid nitrogen for 1 h. After rewarming at 40 °C for 3 min, cryopreserved cells were post-cultured on solid MGN medium supplemented with 2.5 g l–1 activated charcoal. Surviving cells were transferred to solid MGN medium for regrowth or solid MG medium for embryo development and then to solid WPM for plant regeneration. Optimal viability was 42–76% of cryopreserved cells when cell suspensions were precultured with a final sucrose concentration of 0.75 M and dehydrated with PVS2 at 0 °C for 270 min. Biochemical analysis showed that sucrose preculture caused changes in levels of total soluble protein and sugars in cell suspensions. Although the increase in fresh weight was significantly lower in cryopreserved cells than in control cells, the growth pattern of the cryopreserved cells and control cells was the same after two subcultures, following re-establishment in cell suspensions. Protocol developed in this study suggests a universal and highly efficient cryopreservation system suitable for several genetically diversed Vitis species. 相似文献
10.
The study of cell responses to environmental changes poses many experimental challenges: cells need to be imaged under changing conditions, often in a comparative manner. Multiwell plates are routinely used to compare many different strains or cell lines, but allow limited control over the environment dynamics. Microfluidic devices, on the other hand, allow exquisite dynamic control over the surrounding conditions, but it is challenging to image and distinguish more than a few strains in them. Here we describe a method to easily and rapidly manufacture a microfluidic device capable of applying dynamically changing conditions to multiple distinct yeast strains in one channel. The device is designed and manufactured by simple means without the need for soft lithography. It is composed of a Y-shaped flow channel attached to a second layer harboring microwells. The strains are placed in separate microwells, and imaged under the exact same dynamic conditions. We demonstrate the use of the device for measuring protein localization responses to pulses of nutrient changes in different yeast strains. 相似文献