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991.
George W. Barlow 《Ethology : formerly Zeitschrift fur Tierpsychologie》1968,25(3):315-318
Wie stark Fluchtstimmung (“Furcht”) das Verhalten von Versuchstieren in ethologischen Untersuchungen stören kann, ist zwar wohl vielen bekannt, wird aber selten erörtert oder in Veröffentlichungen erwähnt. Die Beobachter setzen die Tiere meist entweder der vollen Störung durch den Laborbetrieb aus oder schließen sie weitestgehend von allen möglichen Störreizen ab. Im ersten Fall fehlt die Kontrolle über wichtige Störfaktoren, im zweiten werden vor allem Wirbeltiere oft so furchtsam, daß sie das meiste Verhalten unterdrücken. In Untersuchungen an verschiedenen Fischarten hat sich folgender Ausweg sehr bewährt: Man setzt zum Versuchstier hinter eine durchsichtige Trennwand andersartige Tiere, die sich ständig gleichmäßig bewegen, für das Versuchstier aber ohne Interesse sind. 相似文献
992.
993.
George Yannopoulos 《Molecular & general genetics : MGG》1979,176(2):247-253
Summary By classical genetic experiments, evidence is provided that the male recombination factor, 31.1 MRF, has the ability to be transposed to another chromosome. The procedure by which the transposition occurs must be different from that of classical crossing over. It appears that transposition occurs only when the factor is active in male germ cells. Moreover, the factor appears to be able to undergo successive transpositions. Furthermore, the integration sites of the factor, when transposed into another chromosome, may not be completely random. Finally, the third chromosome of the 31.1/Cy
L
4 strain can also induce male recombination. 相似文献
994.
995.
996.
This paper summarises the major factors influencing the daytimevertical distribution of Daphnia hyalina var. laciutris (Sars)in two large experimental enclosures (Lund Tubes). In both tubes,the depth at which the Daphnia aggregated during the day wasclosely related to sub-surface ir-radiance. On a few occasionsaggregations of Daphnia were found in dark waterassociated with a deep chlorophyll maximum. On many occasions,however, the animals' light response per se ensured their aggregationat depths of maximum phytoplankton abundance. The most importantfactor influencing the dispersion of animals in the water columnwas the steepness of the light gradient. In turbid water verticalaggregations were well defined, whereas in clear water the animalswere widely dispersed around their depth of maximum abundance.Daphnia also tended to disperse in the water column when theirpopulation density was high or when food was scarce. A simplemodel based on surface irradiance, water turbidity and populationdensity explained the basic pattern of vertical distributionthroughout the season. The implications of these findings arediscussed in relation to the effects of zooplankton grazingand speculations on the adaptive significance of depth regulation. 相似文献
997.
Many natural and synthetic organic amphiphiles have been discovered, prepared, and/or characterized. Aggregation behavior has been studied for many of these monomers. Very few of these many amphiphiles are organometallic compounds and almost nothing is known about this novel group of amphiphiles. Under appropriate circumstances, aggregation of certain organometallic amphiphile monomers can be controlled by use of redox switching. Compounds which are not amphiphilic can be made so and amphiphilic compounds can be deprived of this property by appropriate alterations in the metal ion's oxidation state. Redox-switched aggregation-deaggregation behavior is described for bis(hexadecycloxy)-1,10-phenanthrolinium perchlorate (2), its nickel complex (3), [CH3(CH2)15NH2]2Ag+AcO− (4) and bis(hexadecylamine)copper dichloride (5), chloride acetate (6) and diacetate (7), all of the general formula: [CH3(CH2)15NH2]2Cu2+X22. Two completely new switching mechanisms are disclosed for the first time which involve electron transfer from dilute aqueous sugar solutions or from solid zinc metal which are effective in collapsing [CH3(CH2)15NH2]2Cu2+X22− vesicles. 相似文献
998.
George Karreman 《Bulletin of mathematical biology》1953,15(3):301-309
On the basis of simple physical considerations the blood flow in a branching circulatory system is studied. The case of two
groups of parallel vessels is treated. The vessels of the same group are supposed to be identical. The resistance of each
group is determined by the resistance of each vessel in the group and by the number of vessels in the group. From the dependence
of the resistance of each vessel on its radius an expression is obtained for the blood flow through each group of vessels
in terms of the numbers and sizes of the vessels in each group. The number of open vessels in an organ and the radius of each
of those vessels are assumed to depend on the metabolic rate of that organ. The relations so obtained, together with the expression
above, are applied to derive the blood flow through an organ as a function of the metabolic rate of that organ. It is indicated
that the relations obtained might describe the shifting of blood from one organ to another if the activity of one of them
changes. A way is pointed out to treat neural regulation of this phenomenon. 相似文献
999.
Han Dai Lauren Kustigian David Carney April Case Thomas Considine Basil P. Hubbard Robert B. Perni Thomas V. Riera Bruce Szczepankiewicz George P. Vlasuk Ross L. Stein 《The Journal of biological chemistry》2010,285(43):32695-32703
SIRT1 is a protein deacetylase that has emerged as a therapeutic target for the development of activators to treat diseases of aging. SIRT1-activating compounds (STACs) have been developed that produce biological effects consistent with direct SIRT1 activation. At the molecular level, the mechanism by which STACs activate SIRT1 remains elusive. In the studies reported herein, the mechanism of SIRT1 activation is examined using representative compounds chosen from a collection of STACs. These studies reveal that activation of SIRT1 by STACs is strongly dependent on structural features of the peptide substrate. Significantly, and in contrast to studies reporting that peptides must bear a fluorophore for their deacetylation to be accelerated, we find that some STACs can accelerate the SIRT1-catalyzed deacetylation of specific unlabeled peptides composed only of natural amino acids. These results, together with others of this study, are at odds with a recent claim that complex formation between STACs and fluorophore-labeled peptides plays a role in the activation of SIRT1 (Pacholec, M., Chrunyk, B., Cunningham, D., Flynn, D., Griffith, D., Griffor, M., Loulakis, P., Pabst, B., Qiu, X., Stockman, B., Thanabal, V., Varghese, A., Ward, J., Withka, J., and Ahn, K. (2010) J. Biol. Chem. 285, 8340–8351). Rather, the data suggest that STACs interact directly with SIRT1 and activate SIRT1-catalyzed deacetylation through an allosteric mechanism. 相似文献
1000.