Friction and Stiffness Dependent Dynamics of Accumulation Landslides with Delayed Failure

We propose a new model for landslide dynamics under the assumption of a delay failure mechanism. Delay failure is simulated as a delayed interaction between adjacent blocks, which mimics the relationship between the accumulation and feeder part of the accumulation slope. The conducted research consisted of three phases. Firstly, the real observed movements of the landslide were examined to exclude the existence or the statistically significant presence of background noise. Secondly, we propose a new mechanical model of an accumulation landslide dynamics, with introduced delay failure, and with variable friction law. Results obtained indicate the onset of a transition from an equilibrium state to an oscillatory regime if delayed failure is assumed for different cases of slope stiffness and state of homogeneity/heterogeneity of the slope. At the end, we examine the influence of different frictional properties (along the sliding surface) on the conditions for the onset of instability. Results obtained indicate that the increase of friction parameters leads to stabilization of sliding for homogeneous geological environment. Moreover, increase of certain friction parameters leads to the occurrence of irregular aperiodic behavior, which could be ascribed to the regime of fast irregular sliding along the slope.

Triggered dynamics in a model of different fault creep regimes

The study is focused on the effect of transient external force induced by a passing seismic wave on fault motion in different creep regimes. Displacement along the fault is represented by the movement of a spring-block model, whereby the uniform and oscillatory motion correspond to the fault dynamics in post-seismic and inter-seismic creep regime, respectively. The effect of the external force is introduced as a change of block acceleration in the form of a sine wave scaled by an exponential pulse. Model dynamics is examined for variable parameters of the induced acceleration changes in reference to periodic oscillations of the unperturbed system above the supercritical Hopf bifurcation curve. The analysis indicates the occurrence of weak irregular oscillations if external force acts in the post-seismic creep regime. When fault motion is exposed to external force in the inter-seismic creep regime, one finds the transition to quasiperiodic- or chaos-like motion, which we attribute to the precursory creep regime and seismic motion, respectively. If the triggered acceleration changes are of longer duration, a reverse transition from inter-seismic to post-seismic creep regime is detected on a larger time scale.

Predictions of experimentally observed stochastic ground vibrations induced by blasting

In the present paper, we investigate the blast induced ground motion recorded at the limestone quarry “Suva Vrela” near Kosjerić, which is located in the western part of Serbia. We examine the recorded signals by means of surrogate data methods and a determinism test, in order to determine whether the recorded ground velocity is stochastic or deterministic in nature. Longitudinal, transversal and the vertical ground motion component are analyzed at three monitoring points that are located at different distances from the blasting source. The analysis reveals that the recordings belong to a class of stationary linear stochastic processes with Gaussian inputs, which could be distorted by a monotonic, instantaneous, time-independent nonlinear function. Low determinism factors obtained with the determinism test further confirm the stochastic nature of the recordings. Guided by the outcome of time series analysis, we propose an improved prediction model for the peak particle velocity based on a neural network. We show that, while conventional predictors fail to provide acceptable prediction accuracy, the neural network model with four main blast parameters as input, namely total charge, maximum charge per delay, distance from the blasting source to the measuring point, and hole depth, delivers significantly more accurate predictions that may be applicable on site. We also perform a sensitivity analysis, which reveals that the distance from the blasting source has the strongest influence on the final value of the peak particle velocity. This is in full agreement with previous observations and theory, thus additionally validating our methodology and main conclusions.

[The effect of alphacalcidol on calcium and phosphate metabolism in patients treated with hemodialysis]

The purpose of these studies was to assess the effect of 6 month calcidol treatment on Ca and PO4 metabolism in haemodialyzed patients. During 3 and 6 month on alpha calcidol therapy, there was significant increase of total and ionized Ca (p < 0.05; p < 0.01 respectively). After 6 months on alpha calcidol therapy there was significant decrease of alkaline phosphatase level (p < 0.05) and increase in bone density (up to 82%, p < 0.05). The study has shown that appropriate use of alpha calcidol could be effective in treatment of Ca and PO4 disbalance in haemodialyzed patients.

[Anatomic and physiologic characteristics of the peritoneal cavity with reference to peritoneal dialysis]

Most common complications of peritoneal dialysis are those related to anatomic defect of the abdominal wall and peritoneum. The aim of this investigation was to examine the frequency of congenital and acquired wall defects in patients on CAPD treatment causing complications. Fifty patients, 32 women and 18 men, on CAPD treatment for more than two years, were investigated. Most common was a defect in the anterior-lateral abdominal wall predisposing to hernias in 14% of patients. Umbilical and pericatheteral hernias were more common than other, with a mean time of 21 months for the appearance. Persistence of vaginal process of peritoneum related to scrotal oedema was documented in 4% of patients. Communication of peritoneal cavity with the abdominal ostium of tuba uterina was found not to be an important factor for peritonitis.

[The effect of frequent peritonitis on parameters of efficacy of peritoneal dialysis]

The estimation of CAPD efficacy presents a complex problem in the patients treated by this method. The most important parameters are: clinical indications, biochemical parameters, Kt/v, PCT, PET indexes, and others. Numerous factors may influence CAPD efficacy. Peritonitis, particularly the frequent episodes, significantly affects permeability and ultrafiltration capacity of the peritoneal membrane. The aim of this paper is to investigate the peritonitis incidence and its influence on some parameters of CAPD efficacy. Forty-four CAPD patients of both sexes, aged 55.7 +/- 13.5 yrs, dialysis duration 19.6 +/- 15 months, were studied. The influence of peritonitis incidence was studied using urea, creatinine, hemoglobin, hematocrit parameters and K t/v, PET indexes. Statistically significant low K t/v values were found in the patients who had four or more peritonitis episodes. Our results, as well as those in the literature, indicate that frequent peritonitis episodes significantly decrease the peritoneal membrane permeability.

[Our protocol in the treatment of peritonitis in patients on continuous ambulatory peritoneal dialysis]

Peritonitis is a very serious complication in patients treated by CAPD. The frequent and grave episodes are the main cause for CAPD withdrawal. The effective prevention and adequate therapy of peritonitis are very important for a successful CAPD treatment. The aim of this study was to present our results of peritonitis therapy in CAPD patients using the following protocol: Vancomycin 1.0 g.i.p. immediately after the admission to the unit, 250 mg Ceftriaxon (Longaceph) after a bag exchange for seven days, and the 1.0 g Vancomycin. Using this protocol we treated 97 peritonitis episodes; 74 of them (80%) were treated successfully by this antibiotics combination. The clearness of peritoneal fluid was attained 1-3 days within 56.7% of cases, and 4-6 days within the 29.7% peritonitis episodes (86.4%). A common cause of peritonitis was Staphylococcus epidermidis episodes (28.4%), Staphylococcus aureus (13.5%), and in 39.1% episodes the cultures were sterile. Uneffective antibiotic application according to this protocol was found in cases of pseudomonas and fungal peritonitis. The mentioned antibiotic therapy had no effect in a small number of peritonitides provoked by S. epidermidis (8.7%) and S. aureus (13.0%) This required the application of a third antibiotic. It could be concluded that this antibiotic combination in treatment of peritonitis in patients on CAPD was very effective.

[The effect of parathormone on arterial blood pressure in patients on hemodialysis]

We evaluated the effect of PTH on blood pressure in haemodialysed patients. The correlation was found between systolic, diastolic pressure and PTH. The results have shown that PTH might have the influence on regulation of arterial blood pressure in these patients.

[Nutrition and physical activity of obese and properly nourished children]

The aim of the study which included 2297 children (aged 5-18), was to determine the role of nutrition and physical activity in the occurrence of obesity in this population. Nutritional status of children was estimated by body mass index. In order to examine nutrition we used a quantitative questionnaire, and physical activity was examined by a specially designed questionnaire (made according to the WHO recommendations). The obtained results showed that abundant nutrition and insufficient physical activity played a significant role in the occurrence of child obesity.

Design, synthesis and properties of several heterocyclic dopaminergic ligands

Two series of non-catechol dopamine (DA) bioisosteres with the hydroxyl groups on the benzene ring replaced by N-H groups were synthesized using phenethylamine as a parent molecule. Compounds from the first series (1-9) contained a primary amine group, while those from the second one (10-19) had a N,N-di-propylamino group introduced into the side chain of the phenethylamine. The affinity and selectivity of these compounds for the D-1 and D-2 subtypes of the DA receptor were determined in competition binding assays using synaptosomal membranes from bovine caudate nuclei and [3H]SCH 23390 (D-1 selective) and [3H]spiperone (D-2 selective) as radioligands. None of the 19 compounds examined expressed significant affinity for D-1 receptors, while compounds 15, 17 and 19, in this order of potency, strongly competed with [3H]spiperone binding to D-2 receptors under conditions that prevented radioligand binding to serotonin 5HT2 receptors. Varying affinities of the compounds examined for the DA receptors can be ascribed to different acidity of the N-H groups introduced at meta- and para-positions of the phenethylamine molecule.

Chronic biofiltration therapy

Long-term follow-up evaluation of biofiltration treatment in 7 patients is presented. These patients experienced frequent episodes of hypotension during acetate hemodialysis. A 3-year biofiltration treatment reduced by 43% episodes of symptomatic hypotension and produced a significant increase in the pretreatment pH and plasma bicarbonate levels. The beta 2-microglobulin level was significantly reduced during biofiltration therapy. The mean systolic and diastolic blood pressures slightly increased during biofiltration. Uremic polyneuropathy, as demonstrated by an increase in motor nerve conduction velocity, slightly improved. The patients reported increased comfort during biofiltration therapy.