Semigroups for flows in infinite networks

Inspired by previous work of M. Kramar and E. Sikolya (Math. Z. 249, 139–162, [2005]), we study transport processes on infinite networks. These “flows” can be modeled by operator semigroups on a suitable Banach space. Using functional analytical and graph theoretical methods, we investigate its spectral properties to determine the long time behavior of the system, and finally characterize uniform convergence of the semigroup to a periodic group under appropriate assumptions on the network.     

Resonant infrared laser-induced desorption of methane condensed on NaCl(100): isotope mixture experiments

Resonantly enhanced infrared laser-induced desorption of methane condensed on a single-crystal NaCl(100) surface is observed after excitation with the widely tunable infrared laser output of the free-electron laser at the free-electron laser for infrared experiments facility using mass spectroscopic detection and time-of-flight analysis. Desorption of methane is observed only when the exciting light is in resonance with an internal vibrational mode of the molecule. Different intramolecular modes of the three methane isotopologues under study--CH(4), CD(4), and CD(3)H--are excited; the degenerate deformation mode nu(4) is observed for CH(4) and CD(4) at 7.69 and 10.11 microm, respectively, as well as the nu(2) and nu(4) modes of CD(3)H at 7.79, 9.75, and 9.98 microm. The desorption signals for the pure layers of these different methane isotopologues as well as for different mixtures of two of these are investigated as a function of the infrared wavelength and the laser fluence. The desorption behavior for pure and mixed layers is compared and the underlying desorption mechanism is discussed.     

Polarization‐dependent Raman spectroscopy of LiBH4 single crystals and Mg(BH4)2 powders

The phonons and the crystal structure of the complex hydride LiBH₄ are studied on single crystals using micro‐Raman spectroscopy. The symmetry of the modes is determined by polarization‐dependent measurements at liquid helium temperature, allowing a better comparison and a more reliable assignment to the computed phonon wavenumbers. This has led to the revision of some former assignments made from Raman measurements on polycrystalline samples. In addition, a higher integration time allowed the detection of very weak lines, so that 35 out of 36 predicted Raman lines have been identified. We have also performed explorative Raman measurements on Mg(BH₄)₂ powders. In contrast to LiBH₄, the very poor crystallinity of this material inhibits the exploitation of the full potential of Raman spectroscopy. Only broad lines are observed, which we compare to phonon wavenumbers calculated for various possible structures using density functional theory. Copyright © 2011 John Wiley & Sons, Ltd.     

Nanofibrillated cellulose/nanographite composite films

Though research into nanofibrillated cellulose (NFC) has recently increased, few studies have considered co-utilising NFC and nanographite (NG) in composite films, and, it has, however been a challenge to use high-yield pulp fibres (mechanical pulps) to produce this nanofibrillar material. It is worth noting that there is a significant difference between chemical pulp fibres and high-yield pulp fibres, as the former is composed mainly of cellulose and has a yield of approximately 50 % while the latter is consist of cellulose, hemicellulose and lignin, and has a yield of approximately 90 %. NFC was produced by combining TEMPO (2,2,6,6-tetramethypiperidine-1-oxyl)-mediated oxidation with the mechanical shearing of chemi-thermomechanical pulp (CTMP) and sulphite pulp (SP); the NG was produced by mechanically exfoliating graphite. The different NaClO dosages in the TEMPO system differently oxidised the fibres, altering their fibrillation efficiency. NFC–NG films were produced by casting in a Petri dish. We examine the effect of NG on the sheet-resistance and mechanical properties of NFC films. Addition of 10 wt% NG to 90 wt% NFC of sample CC2 (5 mmol NaClO CTMP-NFC homogenised for 60 min) improved the sheet resistance, i.e. from that of an insulating pure NFC film to 180 Ω/sq. Further addition of 20 (CC3) and 25 wt% (CC4) of NG to 80 and 75 wt% respectively, lowered the sheet resistance to 17 and 9 Ω/sq, respectively. For the mechanical properties, we found that adding 10 wt% NG to 90 wt% NFC of sample HH2 (5 mmol NaClO SP-NFC homogenised for 60 min) improved the tensile index by 28 %, tensile stiffness index by 20 %, and peak load by 28 %. The film’s surface morphology was visualised using scanning electron microscopy, revealing the fibrillated structure of NFC and NG. This methodology yields NFC–NG films that are mechanically stable, bendable, and flexible.     

An Anti‐angiogenic Reverse Thermal Gel as a Drug‐Delivery System for Age‐Related Wet Macular Degeneration

Reverse thermal gels have numerous biomedical implications, as they undergo physical gelation upon temperature increases and can incorporate biomolecules to promote tissue repair. Such a material is developed for the sustained release of bevacizumab (Avastin), a drug used to treat age‐related macular degeneration. The polymer, poly(ethylene glycol)‐poly(serinol hexamethylene urethane) (ESHU), forms a physical gel when heated to 37 °C and shows good cytocompatibility with ocular cells. ESHU is capable of sustaining bevacizumab release over 17 weeks in vitro, and the release kinetics can be altered by changing the drug dose and the ESHU concentration. These results suggest that ESHU is biologically safe, and suitable for ocular drug delivery.

     

Optical polariton properties in ZnSe-based planar and pillar structured microcavities

Strong coupling is demonstrated in monolithic ZnSe-based microcavities. Under nonresonant excitation the polariton dispersion has been investigated in dependence on the photon-exciton detuning for different excitation densities at low temperatures. For zero detuning indications of a polariton lasing threshold are observed like a k-space and energy dispersion narrowing of the lower polariton branch with increasing excitation density. Furthermore, it is observed that this effect is hampered for measurements at negative detunings as a result of the less effective polariton relaxation to the ground state. Latter results in the formation of a discrete polariton distribution at finite k values as known for the polariton bottleneck. In order to investigate the influence of a three-dimensional optical confinement on the polariton relaxation, pillar structured microcavities were fabricated. The formation of discrete polariton states in the k-space distribution is observed. Furthermore, indications for a softening of the k-conservation arising from the structural confinement are found leading to a more effective polariton relaxation. This process would be beneficial for the realization of efficient polariton lasing processes.     

Synthesis and Qualitative Olfactory Evaluation of Benzodioxepine Analogues

Marine fragrances, particularly Calone 1951^® (=7‐methyl‐2H‐1,5‐benzodioxepin‐3(4H)‐one; 1 ) has carved a minor but distinct niche in the broad field of fragrance chemistry. By focusing on the polar structure fragment of the benzodioxepinone parent compound, we set out to determine the molecular influence on the dominant marine note attributed to the Calone 1951^® structure. A selection of one‐step modifications of the ketone 1 resulted in a range of odor‐active conformers with diverse olfactory attributes. The synthesis of a range of benzodioxepine analogues, i.e., of 3 – 11 , is presented alongside olfactory evaluation (Tables 2 and 3). Removal of the carbonyl group of 1 and increasing the size of the aliphatic ring portion (see 6 and 7 ) introduced sweetness and a predominant loss of the marine character.     

Hydrogen-induced transition from dissociative to molecular chemisorption of CO on vanadium clusters

We report on the size-dependent interaction of carbon monoxide molecules with hydrogen covered vanadium clusters containing between 5 and 20 atoms. Structural information on these hydrogen covered vanadium clusters and their complexes with CO is obtained from infrared multiple photon dissociation spectroscopy, complemented with density functional theory calculations for the V5 to V9 cluster sizes. The non-dissociative or dissociative binding of CO on the metal clusters is detected by the presence or absence of the nu(CO) stretching band in the infrared spectra. It is found that the CO molecule dissociates on bare vanadium clusters, while it adsorbs intact on all saturated hydrogen covered V5-20+ clusters, with the distinctive exceptions of V5+, V9+, V11+, and V19+. We show that dissociative chemisorption is prevented when the potential binding sites of atomic C and O atoms are blocked by H atoms.