Taste is important for food intake. The fetus first experiences taste through amniotic fluid, and later via mother’s milk. Early human experience with taste has a key importance for later acceptance of food. Dietary behavior is determined by the interaction of many different factors. The development of the olfactory and taste receptors begins at 7-8 weeks of gestation. An early sensitive period probably exists when flavor preference is established. Sweet taste is preferred in early childhood; this is the reason why children are at increased risk of over-consuming saccharides. Gustatory sensitivity declines with age. The threshold for the perception of each basic taste differs, and is established genetically. In this review, we summarize published data on taste preferences and its development and changes during life., Š. Podzimek, M. Dušková, Z. Broukal, B. Rácz, L. Stárka, J. Dušková., and Obsahuje bibliografii
The formation of ring species might provide an explanation of how speciation can occur despite ongoing gene flow. However, few species fit all of the criteria of a classic ring species that formed via isolation by distance around a barrier. Population genetic analyses and ecological niche models were used to examine a ring of song sparrow (Melospiza melodia) subspecies that surround the Sierra Nevada in North America. Eight models were compared that included both geography-based and ecology-based scenarios of ring formation. Song sparrows do fit some aspects of a classic ring species that formed via expansion around a barrier; however, admixture rather than complete reproductive isolation occurred when populations met at the terminus of the ring in southern California. Nichemodels show that variation among subspecies is likely to reflect adaptation to local conditions coupled with current limitations to gene flow across ecotones and that birds are likely to have expanded from a refugium in the southwestern United States. Given that simple isolation-based models often fail to explain many ring species patterns, alternative models that incorporate ecological factors might provide a better explanation of how most ring species formed. Isolation and subsequent partitioning of populations by ecotones can be important drivers of geographic variability in ring species.
Modern studies on the Be star population of young open clusters point towards the presence of an evolutionary enhancement of the Be phenomenon in the second half of the B stars main sequence lifetime. However, in the galactic field, Be stars are equally present in luminosity classes V to III, indicating that there is no evolutionary trend. To investigate these diverging results we have studied samples of main sequence B stars in the galactic field and in theh and ¬ Per clusters. From the analysis of the HR diagrams it is shown that there is no segregation between class V and class III stars, both groups being evenly distributed along the whole main sequence. We conclude that luminosity classes of main sequence B stars are not related to the evolutionary status of the stars. We propose a scenario of evolutionary enhancement of the rotational velocity to explain both the lack of relation between the evolutionary status and the luminosity classes and the evolutionary enhancement of the Be phenomenon.
Most of the work on exact models representing gravitational waves in general relativity has been concerned with spacetimes which are,at least in some directions, asymptotically flat. Here we treat gravitational waves in one of the simplest but everywhere curved cosmological model. We give the physical interpretation of exact "type - N solutions" of Einstein´s equations with cosmological constant presented recently by García Días and Plebanski. We show that some of these solutions may be interpreted as gravitational waves propagating in the de Sitter universe. (According to present consensus, this unvierse represents the inflationary stage of our Universe.) The analysis also reveals that tha solutions can serve as the illustration of the cosmological no-hair theorem: they approach the de Sitter space-time asymptotically in time.
In this paper, the feedback control for a class of bilinear control systems with a small parameter is proposed to guarantee the existence of limit cycle. We use the perturbation method of seeking in approximate solution as a finite Taylor expansion of the exact solution. This perturbation method is to exploit the "smallness" of the perturbation parameter ε to construct an approximate periodic solution. Furthermore, some simulation results are given to illustrate the existence of a limit cycle for this class of nonlinear control systems.
Effect algebras are very natural logical structures as carriers of probabilities and states. They were introduced for modeling of sets of propositions, properties, questions, or events with fuzziness, uncertainty or unsharpness. Nevertheless, there are effect algebras without any state, and questions about the existence (for non-modular) are still unanswered. We show that every Archimedean atomic lattice effect algebra with at most five blocks (maximal MV-subalgebras) has at least one state, which can be obtained by "State Smearing Theorem'' from a state on its sharp elements.
This paper deals with an experimental study of lubricant film in an experimental device (tribometer). Lubricating film is formed between a glass disc and steel ball on which modification for friction surfaces have been made. The experiment is aimed at both fully flooded EHL lubrication regime as well as the starved. This document also deals with a comparison of micro dents passage through a contact at different degrees of slip. and Obsahuje seznam literatury