Light driven reactions of single physisorbed azobenzenes

We present a successful attempt of decoupling a dye molecule from a metallic surface via physisorption for enabling direct photoisomerization. Effective switching between the isomers is possible by exposure to UV light via the rotation pathway.     

Pressure-volume relations for Zn,Cd, Ga,In and TI at room temperature to 30 GPa and above

Abstract

The elemental metals Zn, Cd, Ga, In and TI are studied by energy dispersive X-ray diffraction under pressures up to 30 GPa and above. Room temperature equation of state (EOS) data are derived and compared with results of earlier static and dynamic measurements at lower and higher pressures, respectively.     

Transmit-Only/Receive-Only Radiofrequency System for Hyperpolarized 13C MRS Cardiac Metabolism Studies in Pigs

Hyperpolarized ¹³C magnetic resonance spectroscopy in pig models enables metabolic activity mapping, providing a powerful tool for the study of the heart physiology, but requires the development of dedicated radiofrequency coils, capable of providing large field of view with high signal-to-noise ratio (SNR) data. This work describes the simulations and the tests of a transmit-only (TX) volume coil/receive-only (RX) surface coil both designed for hyperpolarized studies of pig heart with a clinical 3T scanner. The coil characterization is performed by developing an SNR model for coil performance in terms of coil resistance, sample-induced resistance and magnetic field pattern. In particular, coil resistances were calculated from Ohm’s law, while magnetic field patterns and sample-induced resistances were calculated using a numerical finite-difference time-domain algorithm. Experimental phantom chemical shift image, showed good agreement with the theoretical SNR-vs-depth profiles and highlighted the advantage of the novel configuration over the single transmit–receive coils throughout the volume of interest for cardiac imaging in pig. Finally, the TX-birdcage/RX-circular configuration was tested by acquiring metabolic maps with hyperpolarized [1-13C] pyruvate injected i.v. in a pig. The results of the phantom and pig experiments show the ability of the coil configuration to image well the metabolites distribution.     

Metal particles on surfaces-desorption,optical spectra,and laser-induced size manipulation

Desorption induced by electronic excitation with laser light is discussed. Emphasis is placed on nonthermal desorption where surface plasma excitation in small particles precedes the rupture of the surface chemical bond. A scenario for the mechanism underlying such a process is proposed. In this context, calculations of the electronic spectra of small sodium particles are presented and the influence of different multipole orders of the collective electron oscillation, of different shapes of the clusters and of the substrate are outlined. Furthermore, manipulation of the size distribution of metal particles on supports is described as an application of the effect. This allows the preparation of very special surfaces with novel physical and chemical properties. Methods to characterize such adsorbate-substrate combinations, especially by use of the optical spectra of the particles, are also discussed. Finally, prospects for future experiments in this field are outlined.     

On the equivalence of the parallel channel and the correlated cluster relaxation models

The question of the origins of nonexponential relaxation is addressed in terms of the probabilistic approach to relaxation. The interconnection between two differently rooted probabilistic models, i.e., between the parallel channel and the correlated cluster models, is presented. We show that clearly different probabilistic origins yield in both approaches a well-defined class of universally valid two-power-law responses with the stretched-exponential and exponential decay laws as special cases. The equivalence of both models indicates that variations in the local environment of the relaxing configurational units (parallel channel relaxation) can provide a basis for self-similar relaxation dynamics without the need for hierarchically constrained dynamics (correlated clusters relaxation).     

Density functional study of the chemisorption of O2 on the armchair surface of graphite

The reaction between O₂ and the armchair surface of a model graphite molecule has been studied using density functional calculations at the B3LYP/6-31G(d) level of theory. Both equilibrium and transition state geometries were optimized to provide a fundamental understanding of the energetics and kinetics of the chemisorption, desorption, rearrangement, and migration reactions that contribute to carbon gasification. A small barrier of 18 kJ mol⁻¹ was found for the chemisorption reaction, which is 578 kJ mol⁻¹ exothermic overall, producing a stable quinone. A number of reaction pathways with barriers below 578 kJ mol⁻¹ were characterized. Gasification of carbon occurs as CO, with barriers of 296 and 435 kJ mol⁻¹ for the first and second CO loss, respectively. The stable quinone can also undergo a rearrangement reaction to form two ketene groups, with a barrier of 260 kJ mol⁻¹. If the armchair edge is extended to include an adjacent aromatic ring, the oxide can migrate along the surface. This initially forms a furan-like bridge structure, with a barrier of just 89 kJ mol⁻¹. A further barrier of 383 kJ mol⁻¹ leads to CO desorption from the furan. The furan can also rearrange further with a barrier of 212 kJ mol⁻¹ to form a five-membered lactone, the most stable structure identified on the potential energy surface. Rearrangement and migration reactions, which have not generally been incorporated into carbon gasification models, are shown to be potentially important pathways in carbon oxidation reactions.     

Functionalization of carbon nanofibers (CNFs) through atom transfer radical polymerization for the preparation of poly(tert‐butyl acrylate)/CNF materials: Spectroscopic,thermal, morphological,and physical characterizations

Vapor‐grown carbon nanofibers (CNFs) were oxidized and functionalized for atom transfer radical polymerization (ATRP) of tert‐butyl acrylate (t‐BA) from the surface of the CNFs. The materials were characterized by solubility tests, Fourier‐transform infrared (FTIR) spectroscopy, Raman spectroscopy, thermogravimetric analysis (TGA), X‐ray diffraction (XRD), and scanning electron microscopy. The FTIR and electron microscopy results suggest that ATRP process was successfully used to graft poly(tert‐butyl acrylate) (poly(t‐BA)) chains from the surface of the fibers. Raman results strongly indicate the partial degradation of the graphitic layer of CNFs because of the chemical treatments. TGA results suggest that the presence of poly(t‐BA) leads to a decrease of the initial degradation temperature of the fibers. XRD and electron microscopy results indicate that the microstructure of fibers was not destroyed because of the oxidation and functionalization processes. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 3326–3335, 2008     

Levels in 44Ca excited by the β-decay of 44K

The β-decay of 22 min ⁴⁴K has been re-investigated with a Ge(Li) spectrometer of improved resolution and efficiency. A total of 58 γ-rays has been assigned to the decay of ⁴⁴K. Of these 53 have been incorporated into a revised decay scheme containing 20 excited states. The ⁴⁴K half-life was determined to be 22.15 ± 0.20 min.     

Vibration analysis of single curved shells by the time average reflection grating principle

If a line grating is observed via the reflective surface of a periodically vibrating object during one or more periods of its motion, an interference effect comes into existence. The interference fringes represent the slope contours of the object relative to the extreme deformation state. This principle was developed for vibration analysis of plates. It is also applicable for slope measurement of vibrating shells. The slope values again can be deduced from the arising interference effect. This interpretation is described.