Thermal Decomposition of Cross-linked Polybutadiene and its Copolymers

Polybutadiene and two copolymers containing butadiene and styrene have been cross-linked by thermal processes, by the use of initiators in solution, and by intimately mixing an initiator with the polymer and then heating this blend. The most efficient cross-linking process is the use of an intimate blend of the initiator and polymer. Most cross-linking processes lower the onset temperature of degradation, presumably because chain scission reactions occur simultaneously with cross-linking, while also increasing the fraction of non-volatile residue which is produced. It is believed that the density of cross-links is responsible for the increased yield of non-volatile residue

Multidimensional Coherent Spectroscopy of a Semiconductor Microcavity

Rephasing and non-rephasing two-dimensional coherent spectra map the anti-crossing associated with normal-mode splitting in a semiconductor microcavity. For a 12-meV detuning range near zero detuning, it is observed that there are two diagonal features related to the intra-action of exciton-polariton branches and two off-diagonal features related to coherent interaction between the polaritons. At negative detuning, the lineshape properties of the diagonal intra-action features are distinguishable and can be associated with cavity-like and exciton-like modes. A biexcitonic companion feature is observed, shifted from the exciton feature by the biexciton binding energy. Closer to zero detuning, all features are enhanced and the diagonal intra-action features become nearly equal in amplitude and linewidth. At positive detuning the exciton- and cavity-like characteristics return to the diagonal intra-action features. Off-diagonal interaction features exhibit asymmetry in their amplitudes throughout the detuning range. The amplitudes are strongly modulated (and invert) at small positive detuning, as the lower polariton branch crosses the bound biexciton energy determined from negative detuning spectra.Comment: 13 pages, 4 figure

Real-time assembly of ribonucleoprotein complexes on nascent RNA transcripts.

Cellular protein-RNA complexes assemble on nascent transcripts, but methods to observe transcription and protein binding in real time and at physiological concentrations are not available. Here, we report a single-molecule approach based on zero-mode waveguides that simultaneously tracks transcription progress and the binding of ribosomal protein S15 to nascent RNA transcripts during early ribosome biogenesis. We observe stable binding of S15 to single RNAs immediately after transcription for the majority of the transcripts at 35 °C but for less than half at 20 °C. The remaining transcripts exhibit either rapid and transient binding or are unable to bind S15, likely due to RNA misfolding. Our work establishes the foundation for studying transcription and its coupled co-transcriptional processes, including RNA folding, ligand binding, and enzymatic activity such as in coupling of transcription to splicing, ribosome assembly or translation

Thermal degradation of Cross-Linked Polyisoprene and Polychloroprene

Polyisoprene and polychloroprene have been cross-linked either in solution or in solid state using free radical initiators. In the comparable experimental conditions higher cross-linking density was observed in the solid state process. Independent of the cross-linking method, polychloroprene tended to give a higher gel content and cross-link density than does polyisoprene. Infrared characterization of the cross-linked materials showed cis-trans isomerization occurred in the polyisoprene initiated by benzoyl peroxide, whereas no isomerization was found in the samples initiated by dicumyl peroxide. Polyisoprene does not cross-link by heating in a thermal analyzer, whereas polychloroprene easily undergoes cross-linking in such conditions. Infrared spectroscopy showed that in the case of polyisoprene, rearrangements occur upon heating which lead to the formation of terminal double bonds, while polychloroprene loses hydrogen chlorine which leads to a conjugated structure. There is apparently some enhancement of the thermal and thermal oxidative stability of polyisoprene because of the cross-linking. Cross-linked polychloroprene is less thermally stable than the virgin polymer. Cross-linking promotes polymers charring in the main step of weight loss in air, which leads to enhanced transitory char

Theoretical study of Van der Waals complexes of Al atom with N2

Al–~N2) x Van der Waals complexes have recently been produced in molecular beam experiments and studied with threshold laser photoionization.1 The ionization potential measured for the Al–N2 complex (46 821 cm21 ), combined with Al atom ionization potential (48 279 cm21 ) and Al1–N2 dissociation energy measured by Bouchard and McMahon (19246175 cm21 ) 2 leads to the estimation of the Al–N2 complex binding energy at 4666175 cm21 ~Ref. 1!. The purpose of our study is to estimate the Al–N2 and Al1–N2 binding energies using theoretical calculations and to compare them with the experimental results

Histological and immunohistochemical evaluation of mandibular bone tissue regeneration

The purpose of the study was to perform an immunohistochemical and histological evaluation of samples taken from different bone regeneration procedures in atrophic human mandible. 30 patients (15 men and 15 women, age range of 35-60 years), non-smokers, with good general and oral health were recruited in this study and divided into three groups. The first group included patients who were treated with blood Concentration Growth Factors (bCGF), the second group included patients who were treated with a mixture of bCGF and autologous bone, while the third group of patients was treated with bCGF and tricalcium phosphate/hydroxyapatite (TCP-HA). Six months after the regenerative procedures, all patients undergone implant surgery, and a bone biopsy was carried out in the site of implant insertion. Each sample was histologically and immunohistochemically examined. Histological evaluation showed a complete bone formation for group II, partial ossification for group I, and moderate ossification for group III. Immunohistochemical analysis demonstrated a statistically significant difference between the three groups, and the best clinical result was obtained with a mixture of bCGF and autologous bone

Two-step synthesis of polymer fibre material comprising indium-, bismuth-, or antimony-doped nanosized tin oxides

In this paper, we present a method of formation of polymer fibre materials comprising dispersed oxides of rare and trace elements. The results of X-ray diffraction and spectral analyses show that the optimum synthesis conditions of the antimony-doped tin oxide, indium-doped tin oxide, and bismuth-doped tin oxide particles are provided using the "reverse" hydrolytic co-precipitation of hydroxides from chloride solutions combined with the subsequent thermal treatment at 1000°C. Durable fixation of nanoparticles on the fibre surface is confirmed by the atomic emission spectrometry with inductively coupled plasma and transmission electron microscopy. The results show that spraying of a free stream of the thermoplastic polymer melt with a gas stream containing nanoparticles allows obtaining fibre materials, which possess catalytic, photosensitive, as well as heat and sound insulating properties