Reversible Dynamic Behavior of Condensation-Cured Silicone Elastomers Caused by a Catalyst

This study demonstrates that dibutyltin-dilaurate (DBTL), commonly used to catalyze condensation-cured silicone elastomers, causes dynamic behavior in the silicone network, which is attributed to the catalyst finding a way to become part of the elastomer network. Furthermore, it establishes that by choosing an appropriate silanol-terminated polydimethylsiloxane (HO-PDMS-OH) chain length, the catalyst causes the gelation of the system without a cross-linker. To the best of authors' knowledge, this is the first time that the DBTL catalyst is shown, apart from the catalytic effect, to have the ability to act as a cross-linker.     

Shunting operations at flat yards: retrieving freight railcars from storage tracks

OR Spectrum - In this paper, we study the railcar retrieval problem (RRT) in which specified numbers of certain types of railcars must be withdrawn from the storage tracks of a flat yard. This task...     

Nanofibers prepared by needleless electrospinning technology as scaffolds for wound healing

Electrospun gelatin and poly-ε-caprolactone (PCL) nanofibers were prepared using needleless technology and their biocompatibility and therapeutic efficacy have been characterized in vitro in cell cultures and in an experimental model of a skin wound. Human dermal fibroblasts, keratinocytes and mesenchymal stem cells seeded on the nanofibers revealed that both nanofibers promoted cell adhesion and proliferation. The effect of nanofibers on wound healing was examined using a full thickness wound model in rats and compared with a standard control treatment with gauze. Significantly faster wound closure was found with gelatin after 5 and 10 days of treatment, but no enhancement with PCL nanofibers was observed. Histological analysis revealed enhanced epithelialisation, increased depth of granulation tissue and increased density of myofibroblasts in the wound area with gelatin nanofibers. The results show that gelatin nanofibers produced by needleless technology accelerate wound healing and may be suitable as a scaffold for cell transfer and skin regeneration.     

cNTnC and fYTnC2, Genetically Encoded Green Calcium Indicators Based on Troponin C from Fast Animals

NTnC-like green fluorescent genetically encoded calcium indicators (GECIs) with two calcium ion binding sites were constructed using the insertion of truncated troponin C (TnC) from Opsanus tau into green fluorescent proteins (GFPs). These GECIs are small proteins containing the N- and C-termini of GFP; they exert a limited effect on the cellular free calcium ion concentration; and in contrast to calmodulin-based calcium indicators they lack undesired interactions with intracellular proteins in neurons. The available TnC-based NTnC or YTnC GECIs had either an inverted response and high brightness but a limited dynamic range or a positive response and fast kinetics in neurons but lower brightness and an enhanced but still limited dF/F dynamic range. Here, we solved the crystal structure of NTnC at 2.5 Å resolution. Based on this structure, we developed positive NTnC2 and inverted iNTnC2 GECIs with a large dF/F dynamic range in vitro but very slow rise and decay kinetics in neurons. To overcome their slow responsiveness, we swapped TnC from O. tau in NTnC2 with truncated troponin C proteins from the muscles of fast animals, namely, the falcon, hummingbird, cheetah, bat, rattlesnake, and ant, and then optimized the resulting constructs using directed molecular evolution. Characterization of the engineered variants using purified proteins, mammalian cells, and neuronal cultures revealed cNTnC GECI with truncated TnC from Calypte anna (hummingbird) to have the largest dF/F fluorescence response and fast dissociation kinetics in neuronal cultures. In addition, based on the insertion of truncated TnCs from fast animals into YTnC2, we developed fYTnC2 GECI with TnC from Falco peregrinus (falcon). The purified proteins cNTnC and fYTnC2 had 8- and 6-fold higher molecular brightness and 7- and 6-fold larger dF/F responses to the increase in Ca²⁺ ion concentration than YTnC, respectively. cNTnC GECI was also 4-fold more photostable than YTnC and fYTnC2 GECIs. Finally, we assessed the developed GECIs in primary mouse neuronal cultures stimulated with an external electric field; in these conditions, cNTnC had a 2.4-fold higher dF/F fluorescence response than YTnC and fYTnC2 and was the same or slightly slower (1.4-fold) than fYTnC2 and YTnC in the rise and decay half-times, respectively.     

Selected Simple Natural Antimicrobial Terpenoids as Additives to Control Biodegradation of Polyhydroxy Butyrate

In this experimental research, different types of essential oils (EOs) were blended with polyhydroxybutyrate (PHB) to study the influence of these additives on PHB degradation. The blends were developed by incorporating three terpenoids at two concentrations (1 and 3%). The mineralization rate obtained from CO₂ released from each sample was the factor that defined biodegradation. Furthermore, scanning electron microscope (SEM), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA) were used in this research. The biodegradation percentages of PHB blended with 3% of eucalyptol, limonene, and thymol after 226 days were reached 66.4%, 73.3%, and 76.9%, respectively, while the rate for pure PHB was 100% after 198 days, and SEM images proved these results. Mechanical analysis of the samples showed that eucalyptol had the highest resistance level, even before the burial test. The other additives showed excellent mechanical properties although they had less mechanical strength than pure PHB after extrusion. The samples’ mechanical properties improved due to their crystallinity and decreased glass transition temperature (Tg). DSC results showed that blending terpenoids caused a reduction in Tg, which is evident in the DMA results, and a negligible reduction in melting point (Tm).     

SPE and MSPD as pre-separation techniques for HPLC of tetracyclines in meat, milk and cheese

 Solid phase extraction (SPE) and Matrix solid phase dispersion (MSPD) have been tested as pre-separation procedures for high-performance liquid chromatography (HPLC) determination of tetracycline antibiotics in milk, meat and cheese. The extraction recoveries ranged from 48% to 86% for SPE and from 89% to 93% for MSPD at concentration levels of the maximal residual limits (MRL) recommended by the European Union to be 100 ng/g for the tetracyclines oxytetracycline (OTC), tetracycline (TC) and chlortetracycline (CTC). The detection limits were 15 – 22 ng/g for SPE and 30 ng/g for MSPD. Following the relatively simple SPE procedure we used a Lichrosorb RP-18 column and a diode array detector for HPLC. Results dealing with analysis of tetracyclines HPLC in cheese are published for the first time. Received: 7 March 1997     

Relaxation capacity and cracking resistance of nitrous coating produced by electron-beam facing of 0.6C-24Cr-0.7N-16Mn steel powder during wear by hard abrasive under heavy loads

Specific features of the topography of friction tracks formed during the sliding of a WCo6 ball over an austenitic nitrous coating at various velocities of sliding under various loads using the ball-on-disc arrangement are studied and compared with those for the WCo6 ball-110Mn13 steel pair. It has been found that the wear resistance of nitrous austenite is due to its capacity to relax frictional stresses. The correlation between the H ₃/E ₂ parameter of the friction surface and the wear rate has been shown.