The present paper discusses processes in our world embedded in a dense net of causes and effects. The role of laws of nature is discussed using classical mechanics as an example to demonstrate that the behavior of objects is not determined by laws of nature on their own. Natural processes rather depend on the environment that implies forces and conditions under which these processes occur. These conditions are usually described in mathematical terms using suitable initial or boundary conditions or further constrains. This analysis may seem trivial but has an important consequence. Divine intervention appears not to violate natural laws, rather, new causes are introduced that lead to results that otherwise would not have occurred. A further consequence arises from the complexity of causal nets and the presence of probabilistic processes in our world as one may not be able to determine the causes that led to a certain effect., Příspěvek pojednává o procesech v našem světě v husté síti příčin a následků. Role zákonů přírody je diskutována pomocí klasické mechaniky jako příklad, který demonstruje, že chování objektů není samo o sobě určeno zákony přírody. Přírodní procesy spíše závisí na prostředí, které implikuje síly a podmínky, za kterých tyto procesy probíhají. Tyto podmínky jsou obvykle popsány v matematických termínech za použití vhodných počátečních nebo okrajových podmínek nebo dalších omezení. Tato analýza se může zdát triviální, ale má důležitý důsledek. Zdá se, že božské zásahy neporušují přírodní zákony, spíše se zavádějí nové příčiny, které vedou k výsledkům, ke kterým by jinak nedošlo., and Ralf B. Bergmann
We hypothesized that decreased stomatal conductance (gs) at elevated CO2 might decrease transpiration (E), increase leaf water potential (ΨW), and thereby protect net photosynthesis rate (PN) from heat damage in maize (Zea mays L) seedlings. To separate long-term effects of elevated CO2, plants grew at either ambient CO2 or elevated CO2. During high-temperature treatment (HT) at 45°C for 15 min, leaves were exposed either to ambient CO2 (380 μmol mol-1) or to elevated CO2 (560 μmol mol-1). HT reduced PN by 25 to 38% across four CO2 combinations. However, the gs and E did not differ among all CO2 treatments during HT. After returning the leaf temperature to 35°C within 30 min, gs and E were the same or higher than the initial values. Leaf water potential (ΨW) was slightly lower at ambient CO2, but not at elevated CO2. This study highlighted that elevated CO2 failed in protecting PN from 45°C via decreasing gs and ΨW., M. N. Qu, J. A. Bunce, Z. S. Shi., and Obsahuje bibliografii
Melatonin has been shown to play a role in antioxidative defence. We therefore studied its effect on oxidative damage to the rat cerebral cortex evoked by painful stimulation and immobilization-induced stress. Moreover, the effect of melatonin on chronic pain perception was examined. Rats were injected with either a high dose of melatonin (100 mg/kg i.p.) or a vehicle for five days and were subjected to painful stimulation or immobilization stress 30 min after the treatment. To determine the degree of oxidative stress, the levels of free radicals, thiobarbituric acid reactive substances (TBARS) as indicators of lipid peroxidation and glutathione peroxidase (GSHPx) were estimated in somatosensory cortex. Pain perception was measured by the tail-flick and plantar test. Melatonin reduced the level of TBARS previously increased by painful stimulation. Melatonin also exhibited a slight analgesic effect in those animals exposed to painful stimulation but its role in free radical scavenging did not contribute to this effect., I. Pekárková, S. Parara, V. Holeček, P. Stopka, L. Trefil, J. Racek, R. Rokyta., and Obsahuje bibliografii