Radijalne zaptivače - uloga i značaj u održavanju mašina

Appropriate choice of sealing elements is one of essential tasks of sealing related with problem of working fluids loosening. In that way cost of maintenance are decreasing and reliability of machinery couples is improving. Radial sealers are used for sealing of different types of axles and shafts, primary in motor and vehicles industries as well as productions of machinery and equipment. This paper presents basical types of radial sealers with accent on material type used for their production, physical and chemical factors of material properties as well as some tribology characteristics. Influence of working conditions on strength of radial sealers is also shown as well as reliability on chemical reagents.Pravilan izbor zaptivnih elemenata kvalitetno rešava problem gubitka radnog fluida što je jedan od suštinskih zadataka zaptivanja. Na taj način smanjuju se troškovi održavanja a povećava pouzdanost mašinskih sklopova. Radijalne zaptivače se koriste za zaptivanje kod različitih osovina i vratila, prvenstveno u motornoj i vozilskoj industriji, mašinskoj industriji, industriji opreme. U radu su prikazane osnovne vrste radijalnih zaptivača, pri čemu je naglasak dat na vrste materijala koji se koriste za njihovu izradu, uticaj fizičko-hemijskih faktora na osobine materijala, kao i neke tribološke karakteristike. Takođe, prikazan je i uticaj radnih uslova na izdržljivost radijalnih zaptivača, kao i postojanost na hemijske reagense

Razmatranje potrošnje motornog ulja dizel motora

From aspect of regulation strict ecological regulations of exgsauts emissions from diesel engines as well imroving maintenace of diesel enigine, today reducing of consumption from motor lubricant is primary goal in construction of engine. In that way important role in that feature is researching in the level of consumption of oil and influencing factors. Date obtained in this field give consumers the costs of exploitation using adequate engine lubricant for certified engine. In this paper work it is evaluated problem of consumption of engine lubricant from several influencing parameters like construction of engine, condition of exploitation and quality parameters of measured lubricant.Sa aspekta zadovoljenja strogih ekoloških propisa izduvne emisije dizel motora kao i poboljšanja dizel motora sa stanovišta održavanja, danas smanjenje potrošnje motornog ulja predstavlja jedan od primarnih zadataka konstruktora motora. U tom kontekstu značajno mesto zauzima istraživanje nivoa potrošnje motornog ulja i uticajnih faktora. Rezultati istraživanja daju smernice i korisnicima koji mogu da projektuju troškove eksploatacije koji su ogledaju u korišćenju odgovarajućeg motornog ulja za odgovarajući motor. U radu je razmatran problem potrošnje motornog ulja sa stanovišta uticaja konstrukcije motora, uslova eksploatacije, kao i parametra kvaliteta motornog ulja

Fluoride bioavailability in saliva and plaque

<p>Abstract</p> <p>Background</p> <p>Different fluoride formulations may have different effects on caries prevention. It was the aim of this clinical study to assess the fluoride content, provided by NaF compared to amine fluoride, in saliva and plaque.</p> <p>Methods</p> <p>Eight trained volunteers brushed their teeth in the morning for 3 minutes with either NaF or amine fluoride, and saliva and 3-day-plaque-regrowth was collected at 5 time intervals during 6 hours after tooth brushing. The amount of collected saliva and plaque was measured, and the fluoride content was analysed using a fluoride sensitive electrode. All subjects repeated all study cycles 5 times, and 3 cycles per subject underwent statistical analysis using the Wilcoxon-Mann-Whitney test.</p> <p>Results</p> <p>Immediately after brushing the fluoride concentration in saliva increased rapidly and dropped to the baseline level after 360 minutes. No difference was found between NaF and amine fluoride. All plaque fluoride levels were elevated after 30 minutes until 120 minutes after tooth brushing, and decreasing after 360 minutes to baseline. According to the highly individual profile of fluoride in saliva and plaque, both levels of bioavailability correlated for the first 30 minutes, and the fluoride content of saliva and plaque was back to baseline after 6 hours.</p> <p>Conclusions</p> <p>Fluoride levels in saliva and plaque are interindividually highly variable. However, no significant difference in bioavailability between NaF and amine fluoride, in saliva, or in plaque was found.</p

The spectroabsorptiometric and voltammetric behavior of malvin in buffered solutions and its antioxidant properties

In the present work the structural transformations of malvin in aqueous acetate buffer solutions were investigated over a wide pH range under in vitro conditions using electronic absorption spectroscopy. In addition to the spectroabsorptiometric investigation, the voltammetric behavior and the mechanism of the redox process of this molecule were studied, in order to define its antioxidant properties. The electronic absorption spectra reveal that the structural changes of malvin, caused by changes in the pH of the medium, lead to changes in the voltammetric behaviour of this molecule. The dependence of the oxidation potential of malvin on pH, which can be explained by the presence of different electroactive molecular structures of malvin at different pH values, indicates different mechanisms of the electrode process. The voltammetric activity of malvin is compared semiquantitatively with the voltammetric activity of a standard synthetic antioxidant, BHA, and a natural antioxidant, quercetin

The characteristics of nucleobase transport and metabolism by the perfused sheep choroid plexus

Abstract The uptake of nucleobases was investigated across the basolateral membrane of the sheep choroid plexus perfused in situ. The maximal uptake (U ) for hypoxanthine and adenine, was 35.5161.50% and 30.7160.49% and for guanine, thymine and uracil was max 12.0060.53%, 13.0760.48% and 12.3060.55%, respectively with a negligible backflux, except for that of thymine (35.1165.37% of the U ). HPLC analysis revealed that the purine nucleobase hypoxanthine and the pyrimidine nucleobase thymine can pass intact through max the choroid plexus and enter the cerebrospinal fluid CSF so the lack of backflux for hypoxanthine was not a result of metabolic trapping in the cell. Competition studies revealed that hypoxanthine, adenine and thymine shared the same transport system, while guanine and uracil were transported by a separate mechanism and that nucleosides can partially share the same transporter. HPLC analysis of sheep CSF collected in vivo revealed only two nucleobases were present adenine and hypoxanthine; with an R 0.1960.02 and 3.4360.20, CSF / Plasma respectively. Xanthine and urate, the final products of purine catabolism, could not be detected in the CSF even in trace amounts. These results suggest that the activity of xanthine oxidase in the brain of the sheep is very low so the metabolic degradation of purines is carried out only as far as hypoxanthine which then accumulates in the CSF. In conclusion, the presence of saturable transport systems for nucleobases at the basolateral membrane of the choroidal epithelium was demonstrated, which could be important for the distribution of the salvageable nucleobases, adenine and hypoxanthine in the central nervous system

Hepcidin Is a Reliable Marker of Iron Deficiency Anemia in Newly Diagnosed Patients with Inflammatory Bowel Disease

Background and Aim. Differentiating iron deficiency anemia (IDA) from anemia of chronic disease (ACD) in patients with inflammatory bowel disease (IBD) represents a clinical challenge. Hepcidin is a polypeptide synthetized in the liver, and iron levels or inflammation mostly regulate hepcidin production. Our aim was to determine serum hepcidin levels in patients with inflammatory bowel disease (IBD) as well to investigate whether hepcidin levels correlate with disease activity. Material and Methods. A case-control study was preformed among newly diagnosed IBD patients and same number age- and sex-matched healthy controls. All patients underwent a total ileocolonoscopy. Complete blood count was obtained in addition to inflammatory markers (CRP, erythrocyte sedimentation rate-ESR). Serum levels of hepcidin were determined with commercially available enzyme-linked immunosorbent assay (DRG Instruments Marburg, Germany). Serum iron, TIBC, and UIBC were assessed with an electrochemiluminesence immunoassay, and soluble transferrin receptor (sTfR) was assessed using an immunoturbidimetric method. Mayo score and CDAI, respectively, were calculated for each patient. Statistical analyses were performed using the SPSS software version 20.0 for Windows. Results. There was a high statistically significant difference between IBD patients and controls in levels of hepcidin (P0.05). However, we have found a statistically significant negative correlation of sTfR and TIBC with hepcidin (P<0.01). Conclusion. Results of our study suggest that hepcidin is a reliable marker of IDA in patients with IBD, and it could be used in routine clinical practice when determining adequate therapy in these patients