Proučavanje mogućnosti mikrotalasne polimerizacije monomera na osnovu obnovljivih sirovina

Polylactide belongs to the biodegradable and biocompatible polymers, and degrade to harmless component, lactic acid, which allows their use in various areas. The development of new methods for the synthesis of polylactide can further extend the application of this polymer and makes its use more economical. The use of microwaves in the synthesis of the polymer can reduce the polymerization time of only 10 to 30 minutes and save a large amount of energy. In this paper, polylactide is synthesized in a microwave reactor, using a frequency of 2,45 GHz and a power of 150 W. FITR analysis confirmed the structure of the resulting polylactide and the thermal properties were studied using differential scanning calorimetry.Polilaktid spada u grupu biorazgradivih i biokompatibilnih polimera i može se razložiti na neškodljivu komponentu, mlečnu kiselinu, što omogućava njegovu primenu u najrazličitijim oblastima. Razvoj novih metoda sinteze polilaktida može proširiti područje primene ovog polimera i učiniti njegovu upotrebu ekonomičnijom. Upotreba mikrotalasa u sintezi polimera može skratiti vreme polimerizacije na svega 10 do 30 minuta štedeći veliku količinu energiju. U ovom radu polilaktid je sintetisan u mikrotalasnom reaktoru, koristeći frekvenciju od 2.45 GHz i snagu od 150 W. FTIC analiza je potvrdila strukturu dobijenog polilaktida, a toplotna svojstva su proučavana metodom diferencijalne skenirajuće kalorimetrije.Vrednost temperatura prelaska u staklasto stanje i temperatura kristalizacije dobijenog polimera zavise od molskog odnosa monomera (L-laktida) i katalizatora (kalaj-oktoata)

Strukturiranje ekološki prihvatljivih elastomernih kompozitnih materijala

For the waste rubber recycling, it is obligative to know the chemical composition of the waste products, if it is to be used in the new composite elastomeric material formulation. The composite elastomeric materials obtained from the waste rubber powder have a very diverse application (farm floors, sports stadiums, tyres production, in construction as a vibration protection material). The aim of this work was to prepare elastomeric composites based on recycled elastomer powder (REP). A few types of elastomeric materials were synthesized based on natural rubber, polybutadiene rubber, styrene-butadiene rubber, (NR/BR/SBR, 40/40/20 phr), carbon black and recycled elastomer powder were synthesized. It was assessed that composites NR/BR/SBR/REP have shorter optimum curing time tc90 than samples without REP. By increasing the REP content the tc90 value and tensile strength are decreasing, but the abrasion resistance is increasing.Kod recikliranja otpadne gume neophodno je poznavati hemijski sastav otpadnog proizvoda, ukoliko će se on koristiti u recepturama za nove hibridne elastomerne materijale. Kompozitni elastomerni materijali dobijeni od praha otpadne gume imaju veoma raznovrsnu primenu (podovi na farmama, sportski stadioni, dobijanje pneumatika, u građevinarstvu kao materijali za zaštitu od vibracija itd). Cilj ovog rada je bio da se dobiju elastomerni kompoziti na osnovu reciklirane gume. Sintetisano je nekoliko tipova elastomernih materijala na osnovu prirodnog kaučuka, stiren-butadienskog kaučuka i polibutadienskog kaučuka (NR/BR/SBR, 40/40/20 phr), čestica čađi i recikliranog gumenog praha. Ustanovljeno je da kompoziti NR/BR/SBR/REP imaju kraće optimalno vreme umrežavanja u poređenju sa uzorcima NR/BR/SBR bez REP. Porastom količine REP smanjuje se vreme optimalnog umrežavanja i prekidna črstoća, a povećava se otpornost na abraziju

Navigation-assisted suture anchor insertion for arthroscopic rotator cuff repair

Background: Suture anchor placement for subscapularis repair is challenging. Determining the exact location and optimum angle relative to the subscapularis tendon direction is difficult because of the mismatch between a distorted arthroscopic view and the actual anatomy of the footprint. This study aimed to compare the reliability and reproducibility of the navigation-assisted anchoring technique with conventional arthroscopic anchor fixation. Methods: Arthroscopic shoulder models were tested by five surgeons. The conventional and navigation-assisted methods of suture anchoring in the subscapularis footprint on the humeral head were tested by each surgeon seven times. Angular results and anchor locations were measured and compared using the Wilcoxon signed rank test. Interobserver intraclass correlation coefficients (ICCs) were analyzed among the surgeons. Results: The mean angular errors of the targeted anchor fixation guide without and with navigation were 17° and 2° (p < 0.05), respectively, and the translational errors were 15 and 3 mm (p < 0.05), respectively. All participants showed a narrow range of anchor fixation angular and translational errors from the original target. Among the surgeons, the interobserver reliabilities of angular errors for ICCs of the navigation-assisted and conventional methods were 0.897 and 0.586, respectively, and the interobserver ICC reliabilities for translational error were 0.938 and 0.619, respectively. Conclusions: The navigation system may help surgeons be more aware of the surrounding anatomy and location, providing better guidance for anchor orientation, including footprint location and anchor angle. © 2019 The Author(s).1

A hybrid randomized initialization protocol for TDMA in single-hop wireless networks

Although collision free TDMA schemes have been proposed and used for more than two decades, an important ingredient of these schemes, the initialization of stations (that is, assigning ID numbers 1,2,...,n) was not investigated until recently. Binary and n-ary partitioning algorithms were recently proposed for the case of stations with collision detection capability. The main contribution of this paper is a new randomized hybrid initialization protocol which combines the two partitioning algorithms into a more efficient one. The new scheme optimizes the binary partition protocol for small values of n (e.g. n=2, 3, 4). The hybrid scheme then applies n-ary partition protocol on the whole set, followed by binary partition on the stations that caused collision. We proved analytically that the expected number of time slots in the hybrid algorithm with known number of users is <2.20 n. Performance of these algorithms was also evaluated experimentally by comparing it with existing algorithms, and an improvement from e n to approximately 2.15 n was obtained

Biosynthesis and Characterization of Polyhydroxyalkanoates with Controlled Composition and Microstructure

Volatile fatty acids (VFA) C2:0 to C6:0 were used as the sole carbon source for poly­(3-hydroxybutyrate-<i>co</i>-3-hydroxyvalerate) (PHBV) production with controllable composition and microstructure in <i>Haloferax mediterranei</i>. Feeding carbon-even VFA gave >90 mol % poly­(3-hydroxybutyrate) (3HB) PHBV, while carbon-odd VFA generated >87 mol % poly­(3-hydroxyvalerate) (3HV) PHBV. Bespoke random, block, and blend copolymers with 0–100 mol % 3HV were synthesized using C4:0/C5:0 mixtures. The copolymer 3HV fraction is proportional to the Å:0 in the feed mixture, allowing control over copolymer composition. Microstructure depends on the substrate addition order: cofeeding generated random copolymers, while sequential feeding created block and blend copolymers. On average, the PHBV had an ultrahigh molecular weight of 3 × 10⁶ g/mol. 3HV rich copolymers showed lower melting temperatures, enhanced elasticity, and ductility. <i>H. mediterranei</i> is ideal for large-scale production of PHBV due to its inherent bioprocessing advantages, while control over the composition and microstructure of PHBV will facilitate the production of biopolymers capable of meeting industrial criteria for specific applications