Let T be an infinite locally finite tree. We say that T has exactly one end, if in T any two one-way infinite paths have a common rest (infinite subpath). The paper describes the structure of such trees and tries to formalize it by algebraic means, namely by means of acyclic monounary algebras or tree semilattices. In these algebraic structures the homomorpisms and direct products are considered and investigated with the aim of showing, whether they give algebras with the required properties. At the end some further assertions on the structure of such trees are stated, without the algebraic formalization.
With different cultures and changing times, a meaning of the same phenomena may vary. This applies also to knowledge in knowledge society: a plurality of bodies of knowledge will be preserved depending on social context, cultural significance, values and interests of the concerned groups. However, addressing the topic of the emerging knowledge society, particularly the “knowledge cultures”, implies addressing the issue of “change”: social change, socio-economic change, cultural change, changes in technology, life styles, and “environmental baselines”. A new “knowledge paradox” may appear as the rising usage of scientific principles stimulates scrutiny of knowledge and breeds uncertainty in this way. and Josef Hochgerner.
Photosynthetic pigment contents of the second sexual generation of a cybrid plant (C-18-1) resulting from Solanum nigrum genome and Solanum tuberosum plastome were compared to those of the original (S. nigrum). Chloroplast ultrastructure alterations among S. tuberosum, cybrid, and S. nigrum were also studied. Leaf segments of both the cybrid and S. nigrum plants were cultured on shoot induction medium [B5 supplemented with 0.56 g m-3 benzylaminopurine (BAP)] for one week in light, to induce adventitious bud formation. These leaf segments were then placed in darkness for 5 weeks to form a white shoot. The respective cybrid plant had the same phenotype of the fusion recipient plant (S. nigrum) and was fertile. The rate of photosynthetic pigment biosynthesis in the white cybrid shoots was lower than that of the original plant shoots after subjecting the two plants to the same conditions of different irradiation periods (0, 2, 4, 6, 8, and 10 d). At the 10-d irradiation period of two white shoot plants, the total pigment content of S. nigrum shoot increased approximately 3-fold over that of the cybrid shoot. Numbers of grana and thylakoids as well as chloroplast size were decreased in cybrid cells in comparison to those in S. tuberosum cells. Under atrazine stress, while the chloroplast ultrastructure of the cybrid cells (atrazine sensitive) was strongly influenced, the chloroplasts of S. nigrum (atrazine resistant) were not affected. and K. A. Fayez, A. M. Hassanein.
Activity of carbonic anhydrase (CA) was studied in wild type (WT) Chlamydomonas reinhardtii and five mutants distinguished only by retaining photosystem 1 (PS 1), photosystem 2 (PS 2), light-harvesting complexes (LHC) of PS 1 or PS 2 and both photosystems without LHC. Two forms of CA, soluble CA (sCA) and membrane- bound (mbCA), were found in the cells. The highest activity of mbCA was obseiwed in mutants which retained both photosystems, oř only PS 1 and PS 2. The mutants deprived of photosystems but retaining LHC almost lacked mbCA. Thus, there was a correlation between the retention of mbCA and mutant abilities to perform the photosynthesis. Photosynthetic characteristics of the high CO2 requiring mutant of C. reinhardtii CIA-3 were compared with those of WT grown at 2 % CO2 and after various times of exposure to limiting CO2 concentration (0.03 %). CIA-3 cells háve a lower photosynthetic affmity for inorganic carbon (Cj) as compared to WT when grown at high and low CO2 concentrations. Only in the WT cells the photosynthetic affmity for Cj was increased when the gas phase was changed to air. In CIA-3 the photosynthesis was inhibited by a high concentration of Cj.
Similar-aged leaflets of kidney beán plants grown either in soii or sand culture but otherwise under identical laboratory conditions, were exposed to acute O3 concentrations of 0.5 to 0.7 pmol mol"l for 1-1.5 h with a 15 to 20 min respite interval in the middle of the ozonation period. The CO2 exchange versus leaf intemal CO2 concentration relationships were determined just before ozonation, during respite period and immediately after the treatment. Under comparable absorbed O3 fluxes the calculated mesophyll conductance (gn,) and measured C02-saturated photosynthesis (Pj) in leaflets of sand-grown plants declined more rapidly than in leaflets of soil-grown plants. A rise in the CO2 compensation concentration in the sand-grown plants was also more pronounced. About 20 % greater thickness of leaves of the sand-grown plants was probably not the cause for their higher susceptíbility to absorbed O3. From the proportíonal decline in ^nd Pg, it is concluded that possible differences in patchiness of stomatal closure under O3 were also not the cause. A weaker O3 defence systém in the mesophyll cells of the sand- grown plants may be the cause of their greater sensitivity to absorbed O3.
The paper deals with derivation of the dynamical model of the turbochargers with rotor supported on the two floating ring bearings. The model respects the bearing forces acting upon the journals and floating bearing rings by means of inner and outer oil-films. The gyroscopic effects, external and internal damping of the flexible rotor shaft and the rigid turbine and compressor wheels are respected. The modal analysis and the Campbell diagram is used in the turbocharger linearized model to find the critical speeds. and Obsahuje seznam literatury
This paper explores how women’s roles and participation in resistance to Czechoslovak communism from 1968 to the Velvet Revolution serve as a base for Czech feminist thought. By examining three generations of participants through a gendered, Beauvoirian lens, the emergence of feminism can be easily charted through changing perceived gender roles and increased attention to gender issues. After the events of the Prague Spring, women from different groups of the Czechoslovak underground risked their own safety to exercise free speech and expression. Women’s struggles for greater liberties were framed by traditional gender barriers, supposed communist equality, and Western influence. To understand the experiences of female dissidents as a base for Czech feminist thought, one must examine the nature and progression of various underground communities and women’s roles within them. Since 1968, an increased emphasis on women’s freedoms and liberties has helped create a unique, local sense of femininity and feminism., Megan R. Martin., and Obsahuje bibliografii
The unsteady Hartmann flow of a conducting incompressible non-Newtonian viscoelastic fluid between two parallel horizontal insulating porous plates is studied with heat transfer. A uniform pressure gradient which decays exponentially is imposed in the axial direction. An external uniform magnetic field and uniform suction and injection through the surface of the plates are applied in the vertical direction. The two plates are kept at different but constant temperatures while the Joule and viscous dissipations are considered in the energy equation. Numerical solutions for the governing momentum and energy equations are obtained using finite differences. The effect of the magnetic field, the parameter describing the non-Newtonian behavior, and the velocity of suction and injection on both the velocity and temperature distributions is investigated. and Obsahuje seznam literatury