Wave pinning in competition-diffusion models in variable environments.

Numerical results on conditions for the emergence of propagation failure of diffusive fronts in two-species competition models for populations with either logistic growth or strong Allee effect are presented. Particularly, the stability against environmental perturbations is investigated. Two different density dependencies of the noise intensities are considered. They mimic a differential functional response of the competitors to the variable environment. Assuming classical linearly density-dependent noise intensities, stochastic wave pinning can occur. This is an ecologically important finding regarding biological invasion as it means that the invasion speed can be reduced by environmental perturbations even yielding a reversal of the invasion wave. However, this depends on the form of the functional per-capita noise response.

Disease-induced chaos, coexistence, oscillations, and invasion failure in a competition-model with strong Allee effect.

Biological invasions have impacts on diverse social, ecological, and economic issues. Among others, invasion success can be determined by epidemiological aspects, intraspecific dynamics as, e.g., Allee effects, and interspecific interactions as, e.g., competition. In this study, a process-based model describing competitive eco-epidemiological dynamics of two species, which are both subject to an Allee effect, is developed. Only one of the species can be infected by an infectious disease which is transmitted both, horizontally and vertically. The local dynamics of the disease-free competition model, the competition-free SI-model, and the full eco-epidemiological model are considered. In particular, it is shown that an outbreak of a disease is more likely in the absence of a competitor. Thus, competition and species richness can increase disease resistance of particular species in a community. The complete partial differential equation model is investigated both, analytically and numerically in order to determine possible impacts of the disease on the invasion dynamics. It is shown that in case of strong competition, invasion fronts are always slowed down or even reversed due to the infection for parameter regimes in which the invader is the stronger competitor in the absence of the disease while in case of weak competitive pressure, the dynamics are more complex. Besides slowing down of the invasion front, disease-induced chaos, coexistence (i.e., coexistence in a regime in which coexistence without disease would not be possible), and oscillations can occur. Furthermore, spatial spread can temporarily prevent an infected population from going extinct with potentially detrimental impacts for the resident. This happens via a (replicating) traveling pulse which pushes the competitor out of the domain. The results are discussed in order to enhance the understanding of mechanisms underlying biological invasions and to develop better management strategies for biological invasions as, e.g., selective infections.

[Invasion of an intermediate predator: the dynamics of fish populations in the mathematical model of a trophic chain (as applied to the Syamozero lake)].

We present a mathematical model of the dynamics of a spatially heterogeneous predator-prey population system. A prototype of the model system is the Syamozero lake fish community. We study the impact of the invader, an intermediate predator, on the dynamics of the fish community. We show that the invasion can lead to the appearance of chaotic oscillations in the population density. We show also that different dynamical regimes resulting from the invasion, i.e., stationary, non-chaotic oscillatory and chaotic ones, can coexist. The "choice" of a specific regime therewith depends on the initial invader density. Our analysis of solutions of the mathematical models shows that the successful invasion of the alien species takes place solely in the absence of the competition between the invaders and the native species.

[Evolution of rotifer population dynamics in a heterogeneous habitat: mathematical modeling].

We present the results of mathematical modeling of a rotifer species inhabiting two coupled habitats with different environmental conditions. We use the modified Consensus model and show that the exchange between the habitats can lead to chaotization of originally regular plankton dynamics and synchronization of plankton biomass oscillations. As a result, the invasion of a chaotic regime takes place.

A randomized, double-blind, placebo-controlled trial of olsalazine for active Crohn's disease.

SUMMARY: : Olsalazine, consisting of two salicylate radicals linked by an azo-bond, is effective in the treatment of active ulcerative colitis. To test its effect in patients with mild to moderate attacks of Crohn's disease, the International Organization for the Study of Inflammatory Bowel Disease (IOIBD) designed a multicentre, randomised, double-blind, placebo-controlled study. Ninety-one patients from four centres were randomised to receive either olsalazine, 1 g b.i.d., or matching placebo tablets. Twenty-six patients had ileal disease; 43, ileocolonic; and 22, colonic. Thirty-five of 46 patients taking olsalazine and 24 of 45 patients taking placebo were withdrawn before the end of the 4-month study. Diarrhoea was the most common reason for withdrawal from the olsalazine group, accounting for 22% of the patients, as compared with 4% in the placebo group. No other side effects were reported. There was no difference in the remission rate or withdrawal rate for active disease in the two groups. However, when an intent-to-treat analysis was performed, only eight of the 46 (17%) olsalazine-treated patients were considered to have entered remission or improved their symptoms compared with 22 of the 45 (49%) placebo-treated patients (p < 0.03). This study was unable to show that patients with mild to moderate attacks of Crohn's disease were significantly improved by treatment with olsalazine at a dose of 1 g daily. However, the potential benefit of a higher dose cannot be excluded.

A new mesalazine foam enema (Claversal Foam) compared with a standard liquid enema in patients with active distal ulcerative colitis.

BACKGROUND: Rectally administered mesalazine (5-aminosalicylic acid) is a recognized therapy for distal ulcerative colitis. It is frequently applied as a liquid enema. However, there are reasons (acceptability to the patient, more uniform topical dispersion and effective adhesion) to prefer a foam-based enema. AIM: This study compared a foam enema (2 g mesalazine per day, Claversal Foam) with a standard liquid enema (4 g mesalazine per day, Salofalk enema). METHODS: Patients with active distal ulcerative colitis, diagnosed according to standardized criteria, were treated for 4 weeks. The primary goal was clinical remission; endoscopic remission, histological changes, global assessment and standard safety measures were also analysed. A major subset of the patients also provided quality-of-life data. RESULTS: Both foam and liquid enema gave good rates of clinical and endoscopic remission. The foam enema was shown to be as efficacious as the reference, even though the daily dose in the foam treatment contained only half as much active drug as in the reference treatment. Minor regional differences in efficacy were seen. The tolerabilities of the two formulations were comparable. CONCLUSIONS: The foam enema offers a safe, efficacious and acceptable treatment for distal ulcerative colitis.

Chaos and regular dynamics in model multi-habitat plankton-fish communities.

This work is focused on the role of diffusive interaction between separate habitats in a patchy environment in plankton pattern formation. We demonstrate that conceptual reaction-diffusion mathematical models constitute an appropriate tool for searching and understanding basic mechanisms of plankton pattern formation and complex spatio-temporal plankton dynamics

Biological factors underlying regularity and chaos in aquatic ecosystems: simple models of complex dynamics.

This work is focused on the processes underlying the dynamics of spatially inhomogeneous plankton communities. We demonstrate that reaction-diffusion mathematical models are an appropriate tool for searching and understanding basic mechanisms of complex spatio-temporal plankton dynamics and fractal properties ofplanktivorous fish school walks

Endoscopic and bioptic study of the upper gastrointestinal tract in Crohn's disease patients.

In the present study, virtually all of 225 patients suffering from Crohn's disease of the lower gastrointestinal tract (small and/or large bowel) were subjected to endoscopic examination of the upper gastrointestinal tract (esophagus, stomach, duodenum); while histologic examination of the upper gastrointestinal tract was performed in a portion of the patients (54 initial esophageal, 221 initial gastric and 210 initial duodenal examinations). Statistical evaluation of the findings from the upper gastrointestinal tract revealed that: Endoscopic lesions were observed in the esophagus of 15%, the stomach of 49%, and the duodenum of 34% of the 225 Crohn's disease patients. Of the 54 patients from which esophageal biopsies were taken, 31 (57%) revealed histopathologic alterations. Of the 221 patients from which gastric biopsies were obtained, 60% revealed histopathologic alterations; the rate was 53% in the 210 patients from which duodenal biopsies were taken. Calculated from the present data, noncaseating granulomas, i.e., Crohn's disease, were present only in the stomach of 29.4% of the patients, only in the duodenum in 3.4% of patients, and in both the stomach and duodenum in 4.9% of patients. Gastric granulomas were confined to the region of the stomach body and fundus in 3.4% of the patients from which gastric biopsies were obtained and to the antrum in 15.6% of the respective patients. Both gastric regions were involved in 8.3% of the respective patients. The incidence of gastric granulomas was significantly increased in young patients, patients with enterocolic manifestations of Crohn's disease, and those with brief duration of disease. Patient sex or previous drug therapy had no effect on the incidence of granulomas. The most frequent endoscopic findings in the stomach of patients with Crohn's disease were mucosal edema, mucosal redness, and acute or chronic erosions. Only chronic erosions were of significant predictive value for the presence of granulomas, i.e., diagnosis of Crohn's disease. The most frequent endoscopic lesion in the duodenum was mucosal redness, followed by mucosal edema and aphthous lesions. Ulcers, stenosis, and mucosal redness had significant predictive values for the presence of granulomas.

The granuloma in Crohn's disease. A bioptical study.

Serial sections of 1434 colonic and rectal biopsies of 347 patients with Crohn's disease were performed. The relationship between the incidence of granulomas and the inflammatory alterations of the mucosa and some clinical parameters was studied. The presence of granulomas depends on the severity of inflammatory alterations and not on the site of the biopsy. The number of granulomas per mm3 increases from caecum to rectum. The incidence of granulomas decreases with age, duration of illness and under a conservative therapy. If several biopsies, taken at the same or at different times, are studied, granulomas can be found in 40-50% of these patients.

Patchy environment as a factor of complex plankton dynamics.

We study the role of the diffusive interaction in plankton dynamics in a patchy environment. We use a minimal reaction-diffusion model of the nutrient-plankton-fish food chain to simulate the diffusive interaction between fish-populated and fish-free habitats. We show that such interaction can give rise to spatiotemporal plankton patterns. The plankton dynamics depend on the fish predation rate and can exhibit both regular and chaotic behavior. We show that limit cycle and chaotic attractor coexist in the system. The entire basin of attraction of the limit cycles is found to be riddled with "holes" leading to the competitive chaotic attractors. The chaotic dynamics is typical of a wide range of the fish predation rates.

[The radiological and endoscopic appearances of Crohn's disease of the upper gastro-intestinal tract (author's transl)]. / Morbus Crohn des oberen Gastrointestinaltraktes im radiologischen und endoskopischen Bild.

Involvement of the upper gastrointestinal tract (oesophagus, stomach, duodenum, jejunum) accounted for 13% of endoscopically proven Crohn's disease in patients at the University Clinic, Tübingen between 1973 and 1980. The basis for the diagnosis was the presence of epitheloid granulomas. The diagnosis was suspected in 26% of patients on endoscopic appearances alone. In these two groups, the appearances were similar, consisting of atypical or linear ulcers, cobble-stone lesions, chronic erosions, aphthous ulcers, stenoses, coarsening of the mucosa and areas of engorgement and granularity. Most patients were also examined radiologically. The radiological findings correspond with the endoscopic observations. Using a double contrast technique, mucosal changes could be demonstrated which, up to now, were only seen by endoscopy. If these findings are observed either radiologically or endoscopically, it is essential to examine the distal portions of the gut.

Evaluation of the Crohn's Disease Activity Index (CDAI) and the Dutch Index for severity and activity of Crohn's disease. An analysis of the data from the European Cooperative Crohn's Disease Study.

In the European Cooperative Crohn's Disease Study a general documentation of clinical and laboratory data was made at the entry into the study in 452 patients. These patients were in different states of their disease from quiescent to very active. In all patients the Crohn's Disease Activity Index of Best (CDAI) and the Dutch Index of van Hees was calculated. Three gastroenterologists did a global clinical rating and a separate laboratory rating without knowledge of the indices. The ratings were then correlated with the indices in the individual patients. The clinical rating correlated well with the CDAI (r = 0.88) and less with the Dutch Index (r = 0.672). On the other hand the laboratory rating showed a better correlation with the Dutch Index (r = 0.742) than with the CDAI (r = 0.573). This demonstrates that the CDAI preferably is an estimate of the clinical severity of the disease and not of the activity of inflammation. Vice versa the Dutch Index is mainly reflecting the activity of the inflammatory process.

[Interdependence of plankton spatial distribution and plancton biomass temporal oscillations: mathematical simulation]. / Vzaimozavisimost' raspredeleniia planktona v prostranstve i izmenenii biomassy planktona vo vremeni: matematicheskoe modelirovanie.

The dynamics of aquatic biological communities in a patchy environment is of great interest in respect to interrelations between phenomena at various spatial and time scales. To study the complex plankton dynamics in relation to variations of such a biologically essential parameter as the fish predation rate, we use a simple reaction-diffusion model of trophic interactions between phytoplankton, zooplankton, and fish. We suggest that plankton is distributed between two habitats one of which is fish-free due to hydrological inhomogeneity, while the other is fish-populated. We show that temporal variations in the fish predation rate do not violate the strong correspondence between the character of spatial distribution of plankton and changes of plankton biomass in time: regular temporal oscillations of plankton biomass correspond to large-scale plankton patches, while chaotic oscillations correspond to small-scale plankton patterns. As in the case of the constant fish predation rate, the chaotic plankton dynamics is characterized by coexistence of the chaotic attractor and limit cycle.

[Effect of the rate of phytoplankton growth on the spaced-time dynamics of plankton communities in an homogeneous environment]. / Vliianie skorosti rosta fitoplanktona na prostranstvenno-vremennuiu dinamiku planktonnykh soobshchestv v neodnorodnoi srede obitaniia.

We use a conceptual mathematical reaction-diffusion model to investigate the mechanisms of spatial structure formation and complex temporal dynamics of plankton in a heterogeneous environment. We take into account basic trophic interactions, namely, "prey-predator" interactions between phytoplankton, zooplankton, and fish in upper layers of natural waters. We consider plankton as a passive contaminant in turbulent waters. We show that plankton structure formation can result from the difference in phytoplankton growth rate in neighboring habitats. Phytoplankton and zooplankton biomass is shown to undergo both regular and chaotic oscillations. The fish predation rate substantially affects the spatial and temporal dynamics of plankton in a heterogeneous environment.

[The role of carnivorous zooplankton in dynamics of trophic interaction of fish and plankton]. / Rol' plotoiadnogo zooplanktona v dinamike troficheskikh vzaimodeistvii ryby i planktona.

A conceptual (minimal) model of the aquatic community is proposed, which includes phytoplankton, zooplankton, fish and fish larvae. It is shown that carnivorous zooplankton increases the system stability when the fish predation changes. As a result, the system collapse followed by algal bloom becomes less probable.

[Dependence of the fish school movement and plankton special distribution on the phytoplankton growth rate]. / Zavisimost' dvizheniia rybnykh kosiakov i prostranstvennogo raspredeleniia planktona ot skorosti rosta fitoplanktona.

In this paper we investigate the spontaneous emergence and the dynamics of patchiness in spatially distributed communities of plankton, which plays a key role in the matter rotation on earth. Patchiness is often supposed to be due to hydrodynamical factors (diffusion and advection). In contrast to this approach, we consider the formation of plankton patches as a result of interactions in the trophic chain nutrient--phytoplankton--zooplankton-fish. We present a mathematical model of such interactions, which combines a continuous description of the plankton spatio-temporal dynamics and a discrete description of the fish school movement. We show that the fish school can give rise to plankton patches. In turn, fish school walks are shown to depend on phytoplankton growth rate. We show also that the Hurst exponent characterizing the fish school movement in the diffusion approximation depends on phytoplankton growth rate.

Epidemiology of inflammatory bowel disease in the county of Tübingen (West Germany).

The incidence and prevalence of Crohn's disease (CD) and ulcerative colitis (UC) were investigated retrospectively for 1970-1980 and prospectively for 1981-1984 in the predominantly rural county of Tübingen (FRG). Eight hundred and twenty-eight patients with CD and 376 patients with UC were detected. Point prevalence at the end of 1984 was 54.6 for CD and 24.8 for UC, respectively. The occurrence of UC was stable during the period of investigation. The annual incidence of CD rose during the end of the seventies and afterwards reached a plateau of about 4 new cases per 100,000 inhabitants per annum. The prevalence of IBD was markedly greater in the cities than in the rural areas of the county.

Comparative study with ranitidine and cimetidine on gastric secretion.

The inihibitory effect of various doses of ranitidine and cimetidine on pentagastrin stimulated volume, acid, and pepsin secretion was studied in 8 healthy volunteers. Both compounds inhibited all three variables in a dose dependent manner with an average ID50 of approximately 5 mg for ranitidine and of approximately 41 mg for cimetidine. On a molar basis ranitidine is about 11 times more potent than cimetidine. The duration of action of both compounds appears to be equally long.