In this paper we give a new set of verifiable conditions for the existence of average optimal stationary policies in discrete-time Markov decision processes with Borel spaces and unbounded reward/cost functions. More precisely, we provide another set of conditions, which only consists of a Lyapunov-type condition and the common continuity-compactness conditions. These conditions are imposed on the primitive data of the model of Markov decision processes and thus easy to verify. We also give two examples for which all our conditions are satisfied, but some of conditions in the related literature fail to hold.
During a survey of 23 wet heathland sites in Flanders (north Belgium) in 1999 and 2000, using both manual nest searching and pitfall traps as sampling techniques, we found 28 ant species. One species (Myrmica lonae) was new to the Belgian fauna and several rare species were encountered. Three ecological groups could be distinguished based on soil preference: the first group of species was characteristic of sandy soil, the second contained species that were more numerous on peat soil (with Sphagnum spp.), and the third group of species had no soil preference. Ant nest numbers increased strongly between 1999 and 2000, especially on the plots that were inundated during the winter of 1999-2000, but the number of ant species did not differ significantly between years. Ant nest density showed an optimum at a Purple Moor-grass (Molinia caerulea) cover of about 45%; the number of species did not show such an optimum. Pitfall traps yielded more species than manual nest searching; in particular temporary social parasites, species with a large foraging range and winged females from the surrounding habitats were missed by the latter technique. Finally, we give some recommendations for the conservation of, and suitable management measures for, ants on wet heathland.
The sugarcane borer Diatraea saccharalis is an important pest of sugarcane and ants are one of its main predators. The practice of burning sugarcane straw in situ after harvest has been gradually replaced in Brazil by other practices. However, it is unknown whether ants can control the abundance of this borer in the presence of straw. In this study, we assessed the diversity and species composition of ants attacking different stages of the pest’s life cycle. Specifically, we asked whether the species richness and abundance of ants varies during the course of day and a year. We established one-hectare plots at random locations in a sugarcane plantation. Once a month, we collected 20 samples of each stage of the D. saccharalis life cycle and randomly distributed these samples as bait on plants spaced 20 m apart within a plot. Ants were collected daily in the morning and afternoon over a period of 12 months. We identified several aspects of ant feeding behaviour that may affect their biological control of the borer: (1) the greatest number of ants were collected from baits consisting of the immature stages of the sugarcane borer, (2) ants were most active in the morning and (3) their activity varied from month to month. Solenopsis saevissima and morphotypes of Crematogaster sp.7 and Pheidole sp.35 are potentially important predators of borers in sugarcane crops in which the straw is not burnt., Roseli de Fatima de Oliveira ... [et al.]., and Obsahuje seznam literatury
Investigations of the interactions between aphids and ants in multispecies ant communities and an experimental investigation of some ethological aspects of ant-aphid interactions were carried out in mixed forests at Novosibirsk Academic Centre, from 1998-2002. The eight species of ants investigated were characterized by different levels of territorial organization and interaction with aphids, which were associated with different degrees of specialization of the worker ants. The most myrmecophilous species of aphids (24 out of 33 species identified) were associated with the red wood ants. By placing Coccinella septempunctata Linnaeus (Coleoptera: Coccinellidae) in aphid colonies it was shown that only ants with large protected territories attacked the adults and larvae of the predator. Other species of ants either protected aphids only from adult ladybirds or did not guard them at all. Moreover, only individuals of Formica s. str., which has specialized workers, did not switch to collecting protein food. However, aphids make up a considerable part of the prey of ants, in which non-myrmecophilous aphids predominate (about 60-100% of the aphid prey). Moreover, ants only killed unattended or damaged myrmecophilous aphids. Formica s. str., which has the highest level of social and territorial organization, provides aphids with the most services and is the dominant species forming symbiotic relationships with aphids in the communities studied.
Blokátory angiotenzinových receptorů typu 1 (AT1-blokátory, sartany) patří mezi základní antihypertenzní látky vhodné pro monoterapii i kombinační léčbu hypertenze. AT1-blokátory mají srovnatelné účinky s dalšími hlavními třídami antihypertenziv včetně ACE-inhibitorů. Dle současných doporučení České společnosti pro hypertenzi jsou sartany spolu s ACE-inhibitory a blokátory kalciových kanálů považovány za tzv. univerzální antihypertenziva. Mají ze všech antihypertenziv nejméně nežádoucích účinků a nemocní léčení sartany vykazují nejlepší dlouhodobou perzistenci k léčbě. V článku jsou diskutovány mechanizmy antihypertenzního účinku jakož i srovnání antihypertenzních účinků sartanů s dalšími antihypertenzními látkami. Jsou uvedeny výsledky větších klinických studií se sartany a indikace u arteriální hypertenze., Angiotensin receptor antagonists (AT1-blockers) are considered as one of the major classes of antihypertensive drugs suitable for monotherapy as well as for combination treatment. AT1-blockers have comparable antihypertensive efficacy with other major classes of antihypertensive drugs. AT1-blockers are considered by current guidelines of Czech society of hypertension altogether with ACE-inhibitors and calcium channel blockers as universal antihypertensive drug class. AT1-blockers has the lowest profile of side-effects among all antihypertensive drug classes and thus very high persistence to therapy. Mechanisms of antihypertensive effects of AT1-blockers are discussed altogether with the results of large clinical trials and indications in the treatment of hypertension., and Jiří Widimský Jr.
Male rats received estradiol benzoate in a long acting microcrystalline suspension (1 mg/rat i.m., twice a week), methylene blue (MB) 0.5 % in the food and the combination of estradiol and MB. After three weeks, MB partially inhibited the growth response of the anterior pituitary to estradiol and it partially inhibited the increase of cAMP content in anterior pituitary. The increase of anterior pituitary cGMP content was not modified by MB, neither the ratio cAMP/cGMP in the anterior pituitary which, however, decreased after estradiol. This decrease was not modified by MB. On the other hand, the prolactin (PRL) increase in the blood after estradiol was inhibited by MB, although the prolactin content in the anterior pituitary was not. Methylene blue alone did not change blood prolactin concentration, but it unexpectedly elevated blood thyroxine levels and this effect was partially inhibited by simultaneous estradiol treatment.
Seven Gymnura altavela (Linnaeus, 1758) (Elasmobranchii, Myliobatiformes) caught off the Tunisian coast were examined for endoparasites during a three-year period (1995-1998). A phyllobothriid cestode new to science was found in the spiral intestine of all host specimens. The presence of a tetrabothridiate scolex, bothridia lacking an apical sucker, laciniate strobila, and possession of postvaginal testes are sufficient to place this species in the genus Anthobothrium Van Beneden, 1850. In this genus, we consider that only two species, both previously reported from carcharhiniform sharks, are valid: Anthobothrium cornucopia Van Beneden, 1850 and A. laciniatum Linton, 1890. Anthobothrium altavelae sp. n. can be distinguished from its congeners by its length, strobila morphology, and the number of testes. The taxonomic position of the species attributed to Anthobothrium parasitic in gymnurids is discussed.