Compressive properties of pristine and SiC-Te-added MgB2 powders,green compacts and spark-plasma-sintered bulks

Pristine and (SiC+Te)-added MgB₂ powders, green and spark plasma sintered (SPS) compacts were investigated from the viewpoint of quasi-static and dynamic (Split-Hopkinson Pressure Bar, SHPB) compressive mechanical properties The amount of the additive (SiC+Te) was selected to be the optimum one for maximization of the superconducting functional parameters. Pristine and added MgB₂ show very similar compressive parameters (tan δ, fracture strength, Vickers hardness, others) and fragment size in the SHPB test. However, for the bulk SPSed samples the ratio of intergranular to transgranular fracturing changes, the first one being stronger in the added sample. This is reflected in the quasi-static K_IC that is higher for the added sample. Despite this result, sintered samples are brittle and have roughly similar fragmentation behavior as for brittle engineering ceramics. In the fragmentation process, the composite nature of our samples should be considered with a special focus on MgB₂ blocks (colonies) that show the major contribution to fracturing. The Glenn-Chudnovsky model of fracturing under dynamic load provides the closest values to our experimental fragment size data.     

Compatibility of polysaccharide/maleic copolymer blends. IV. Thermal behavior of hydroxypropyl cellulose‐containing blends

The compatibility of the hydroxypropyl cellulose (HPC) with maleic acid–vinyl acetate copolymer in the solid state was studied by thermogravimetry, thermo‐optical analysis, differential scanning calorimetry (DSC), Fourier transform infrared spectroscopy (FTIR), and optical microscopy. It was established that physical interactions are prevalent in blends with a high content of HPC, whereas chemical interactions predominate in blends with a medium and low content of HPC. By increasing the temperature, the thermochemical reactions are favored. Thermal properties are dependent on the mixing ratio of the components. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 88: 2585–2597, 2003     

Enzymatic degradation of thermoresponsive poly(N‐isopropylacrylamide) grafted to carboxymethylcellulose copolymers

The enzymatic degradation of poly(N‐isopropyl acrylamide) (PNIPAM) grafted to carboxymethylcellulose (CMC) copolymers with a cellulasic preparation (Trichoderma viride) was studied. The enzymatic activity of the cellulasic preparation against CMC and the grafted copolymers was determined by the Petterson–Porath method, while their reduced viscosity variation in the presence of the same preparation was also followed. It has been shown that the enzymatic degradation behavior depends on the copolymer composition and the reaction temperature. Reducing sugars analysis showed that the experimental values for the grafted copolymers were higher than the calculated ones. At 50°C, the enzymatic reaction is completed in about 20 min for the copolymers, whereas for CMC it takes more than 40 min. It can be concluded that their enzymatic degradation is facilitated by the presence of the PNIPAM grafts. © 2002 Wiley Periodicals, Inc. J Appl Polym Sci 87: 1383–1386, 2003     

Characterization of microdevices for ferrous chloride separation for biosensing applications

Ferrous chloride has a variety of applications such as a reducing flocculation agent in waste-water treatment, especially for wastes containing chromate, in the laboratory synthesis of iron complexes and it is employed as a reducing agent in many organic syntheses. The device used for experiment was fabricated on the silicon wafer as support for two electrodes in a SU8 polymer microchannel with an inlet, for the injection of aqueous solution of ferrous chloride, and two outlets, for the two by-products of separated solutions. The various parameters of the device were measured by White Light Interferometer (WLI) and Scanning Electron Microscopy (SEM). The magnetic field created by applying different types of potential between two electrodes determined ferrous chloride to separate in ferrous oxide and chlorine (in gaseous form). If a protein is added in this solution we have the possibility to immobilize the protein on the iron particles and on the channel area. The electrical results were collected using a semiconductor system analyzer Keithley and were examined subsequently. The Fe complexes deposited on the electrodes were characterized by XRD analyses.     

pH and heat-induced structural changes of bovine apo-α-lactalbumin

The effects of pH and thermal treatments on conformation and association state of Ca²⁺-depleted bovine α-lactalbumin (apo-α-LA) have been studied by fluorescence spectroscopy, and molecular modelling. The experimental results demonstrate a third-state model for heat-induced unfolding of apo-α-LA, at pH 2.0, and an all-or-none transition of apo-α-LA, at pH 4.5 and 7.0, respectively. The heat-induced changes in the secondary and tertiary structure of α-LA were outlined after running molecular dynamics simulations at 25 °C and 80 °C, at neutral pH, therefore supporting the experimental observations. Our data provides insight into the mechanism of pH- and heat-dependent structural changes and oligomerization of α-LA, and will be helpful in understanding the ability of this protein to interact with certain compounds of biological interest.     

Synthesis and characterization of a titanium phosphate-tellurite glass for Faraday rotators

This work is focused on investigation of thermal, structural, optical, magnetic, and magneto-optical properties of novel titanium phosphate-tellurite glass applied as Faraday rotators. The glass belonging to the system 35Li₂O–10Al₂O₃–5TiO₂–45P₂O₅–5TeO₂ was prepared by a nonconventional wet route of raw materials processing, followed by melting-quenching-annealing steps. Some important physical properties of the investigated glass have been measured and calculated, providing knowledge related to glass compactness, electronic structure, glass forming capability, etc. XRD analysis evidenced an amorphous network structure of the investigated glass. The optical absorption in the Vis domain is mainly due to Ti³⁺ ions and Te₂ clusters formed during the glass melting process. A relatively low optical absorption is noticed over 600 nm that activates a significant Faraday magneto-optical effect. Photoluminescence bands in the blue, red, and infrared domains are observed, caused by Te₂ clusters formed during the glass melting process. The magnetization in dependency on applied magnetic field reveals a complex behavior of the glass, depending on temperature. Thus, it is found a ferromagnetic behavior up to 2000 Oe, a paramagnetic component up to 40 000 Oe, followed by a diamagnetic one over 40 000 Oe. Faraday rotation angle and Verdet constant values in the visible domain are correlated with the reduced TeO₂ content of the glass.     

Unconventional method used in synthesis of polyphosphoesters

Polyphosphonates, polyphosphates, polyarylazophosphonates and polyarylazophosphates were synthesized by a new alternative to the classical phase transfer catalysis, respectively, the modified inverse phase transfer catalysis (IPTC) polycondensation of various phenylphosphonic (phosphoric) dichlorides (phenylphosphonic dichloride, phenylphosphoric dichloride, p-chlorophenylphosphoric dichloride) with bisphenols: bisphenol A, tetrabromobisphenol A, bis-(4-hydroxyphenyl)methane (bisphenol F), 4,4′-dihydroxyazobenzene. The polymers were characterized by infrared spectroscopy and magnetic resonance (¹H-NMR, ³¹P-NMR, ¹³C-NMR) spectroscopy. Yields in the range of 63.5–85% and molecular weights (M _w) of ~2,000–8,200 g mol^?1 were obtained. Polyphosphonates were stable up 210–270 °C and polyphosphates up 190–220 °C in air atmosphere. For a correct estimation of the thermal behavior of similar compounds, a kinetic analysis using a modified version of Non Parametric Kinetic method for representative polyphosphonate and polyphosphate was realized. The studies made on the hydrolytic degradation of the synthesized polyphosphates show that the most stable polymer under alkali-catalyzed degradation is the polyphosphate obtained by IPTC of phenylphosphoric dichloride and bisphenol A.     

Melanocytes Affect Nodal Expression and Signaling in Melanoma Cells: A Lesson from Pediatric Large Congenital Melanocytic Nevi

Expression of Nodal, a Transforming Growth Factor-beta (TGF-β) related growth factor, is associated with aggressive melanoma. Nodal expression in adult dysplastic nevi may predict the development of aggressive melanoma in some patients. A subset of pediatric patients diagnosed with giant or large congenital melanocytic nevi (LCMN) has shown increased risk for development of melanoma. Here, we investigate whether Nodal expression can help identify the rare cases of LCMN that develop melanoma and shed light on why the majority of these patients do not. Immunohistochemistry (IHC) staining results show varying degree of Nodal expression in pediatric dysplastic nevi and LCMN. Moreover, median scores from Nodal IHC expression analysis were not significantly different between these two groups. Additionally, none of the LCMN patients in this study developed melanoma, regardless of Nodal IHC levels. Co-culture experiments revealed reduced tumor growth and lower levels of Nodal and its signaling molecules P-SMAD2 and P-ERK1/2 when melanoma cells were grown in vivo or in vitro with normal melanocytes. The same was observed in melanoma cells cultured with melanocyte conditioned media containing pigmented melanocyte derived melanosomes (MDM). Since MDM contain molecules capable of inactivating radical oxygen species, to investigate potential anti-oxidant effect of MDM on Nodal expression and signaling in melanoma, melanoma cells were treated with either N-acetyl-l-cysteine (NAC), a component of the anti-oxidant glutathione or synthetic melanin, which in addition to providing pigmentation can also exert free radical scavenging activity. Melanoma cells treated with NAC or synthetic melanin showed reduced levels of Nodal, P-SMAD2 and P-ERK1/2 compared to untreated melanoma cells. Thus, the potential role for Nodal in melanoma development in LCMN is less evident than in adult dysplastic nevi possibly due to melanocyte cross-talk in LCMN capable of offsetting or delaying the pro-melanoma effects of Nodal via anti-oxidant effects of MDM.