Structure of neutron-rich Be and C isotopes

The structure of neutron-rich beryllium isotopes has been investigated using different heavy-ion-induced transfer reactions. In neutron transfer reactions, the population of final states shows a strong sensitivity to the chosen core nucleus, i.e., the target nuclei ⁹Be or ¹⁰Be, respectively. Molecular rotational bands up to high excitation energies are observed with ⁹Be as the core due to its pronounced 2α-cluster structure, whereas only a few states at low excitation energies are populated with ¹⁰Be as the core. For ¹¹Be, a detailed investigation has been performed for the three states at 3.41, 3.89, and 3.96 MeV, which resulted in the most probable spin-parity assignments 3/2⁺, 5/2^?, and 3/2^?, respectively. Furthermore, we have studied particle-hole states of ¹⁶C using the ¹³C(¹²C, ⁹C)¹⁶C reaction and found 14 previously unknown states. Using the ¹²C(¹²C, ⁹C)¹⁵C reaction, five new states were observed for ¹⁵C.     

Fluid and diffusion limits for transient sojourn times of processor sharing queues with time varying rates

We provide an approximate analysis of the transient sojourn time for a processor sharing queue with time varying arrival and service rates, where the load can vary over time, including periods of overload. Using the same asymptotic technique as uniform acceleration as demonstrated in [12] and [13], we obtain fluid and diffusion limits for the sojourn time of the M_t/M_t/1 processor-sharing queue. Our analysis is enabled by the introduction of a “virtual customer” which differs from the notion of a “tagged customer” in that the former has no effect on the processing time of the other customers in the system. Our analysis generalizes to non-exponential service and interarrival times, when the fluid and diffusion limits for the queueing process are known.     

Biphotonic recording effect of polarization gratings based on dye-doped liquid crystal films

This study investigates a holographic recording effect of biphotonic polarization gratings (BPGs) written on dye-doped liquid crystal (DDLC) films. One linearly polarized green light (λ_G = 514.5 nm) and a polarization-modulated interference pattern formed by two mutually coherent orthogonal (±45° with respect to the polarization of the green light) polarized red lights simultaneously excite the DDLC films to generate a BPG. The formation of BPGs depends primarily on the dichroism of the dye molecules and a sequence of mechanisms: photoisomerization, anisotropic adsorption and inhibition of dye adsorption. The cis-isomer absorbance-modulated distribution associated with the red polarization-modulation pattern induces the dye adsorption-modulated pattern, in turn, yielding the permanent BPG which generates a modulated twisted nematic (TN) structure pattern in the sample. It is found that each BPG is verified to be electrically switchable and thermally erasable. The switching time is in the order of milliseconds. Additionally, the recording time to form a BPG decreases with increasing intensity of the green pump beam.     

Solid-phase synthesis of imidazo[4,5-b]pyridin-2-ones and related urea derivatives by cyclative cleavage of a carbamate linkage

A solid-phase synthesis of substituted cyclic urea derivatives as potential heterocyclic library scaffolds is described. 2-Amino-3-nitropyridine is attached to Wang resin via a carbamate linkage. Reduction of the nitro group was achieved with SnCl(2).2H(2)O. Reductive alkylation with a range of substituted benzaldehydes followed by cyclative cleavage afforded a small library of 3-substituted imidazo[4,5-b]pyridine-2-ones in 33-45% yield and 59-88% purity. Subsequently, this methodology was applied to the synthesis of 3-substituted imidazo[4,5-f]quinolin-2-ones.     

Perfluorophenyl derivatives of the elements XXVIII. Some reactions of fluoro-aromatic acetylenes

Reactions between caesium fluoride, bromine, palladium chloride, triiron dodecacarbonyl, dicobalt octacarbonyl, nickelocene, cyclopentadienylmanganese tricarbonyl or decarborane with, acetylenes containing one highly fluorinated aromatic group are described. The products mainly resembled those obtained from analogous experiments involving diphenylacetylene, although in the case of the PdCl₂ reaction no intermediate derivatives could be isolated.     

Photochemical reaction of Rh2(CO)4(μ-TPP)(TPP=tetraphenyl-porphyrinato) with pyridine (Py) in benzene. Generation of a mononuclear rhodium(II) porphyrin radical complex Rh(TPP)(Py)

Photolytic decarbonylation of Rh₂(CO)₄(TPP) (TPP=tetraphenylporphyrinato) with pyridine (Py) in benzene gives an unusual monomeric Rh^II radical complex Rh(TPP)(Py), which has been characterised by thermal and spectroscopic measurements and by vapour pressure osmosis.     

Evaluating formation and growth mechanisms of silica particles using fluorescence anisotropy decay analysis

At present, there is no direct experimental evidence that primary silica particles, which exist only transiently for a few seconds during the St?ber silica synthesis, can be stable in aqueous solutions. In the present work, we show that primary silica particles are formed spontaneously after the dissolution of diglycerylsilane (DGS) in aqueous solutions and remain stable for prolonged periods of time. By using time-resolved fluorescence anisotropy (TRFA), we demonstrate that this unique property of DGS is ascribed to the slow kinetics of silica particle growth in diluted sols at pH approximately 9.0. The anisotropy decay of the cationic dye rhodamine 6G (R6G), which strongly adsorbs to silica oligomers and nanoparticles in DGS sols, could be fit to three components: a fast (picosecond) scale component associated with free R6G, a slower (nanosecond) rotational component associated with R6G bound to primary silica particles, and a residual (nondecaying) anisotropy component associated with R6G that was bound to secondary or larger particles that were unable to rotate on the time scale of the R6G emission lifetime (4 ns). The data show that, under conditions where fast hydrolysis is obtained, the initial size of the nuclei depends on the silica concentration, with larger nuclei being present in more concentrated sols, while the rate of growth of primary particles depends on both silica concentration and solution pH. At low silica concentrations and high pHs, it was possible to observe the growth of stable, nonaggregating primary silica particles by a mechanism involving rapid nucleation followed by monomer addition. The presence of stable primary particles was confirmed by atomic force microscopy (AFM) imaging. At higher silica concentrations and lower pHs, there was an increase in the initial size of the nuclei formed, which subsequently grew to a larger radius (> 4.5 nm) or aggregated with time, and in such cases, nucleation and aggregation occurred simultaneously in the early stage of silica formation. The data clearly show the power of time-resolved fluorescence anisotropy decay measurements for probing the growth of silica colloids and show that this method is useful for elucidating the mechanism of particle formation and growth in situ.     

Serendipitous synthesis of a ditwistane: a one-step access!

4-tert-Butyl-2-cyclohexen-1-one dimerizes in THF solution via its kinetic enolate, leading to di-tert-butylditwistane 8 in up to 36% yield (−78 °C → room temp., protonolysis, flash chromatography). X-ray crystallography shows that 8 incorporates one R and one S enantiomer of the starting ketone; none of the diastereomeric ditwistanes epi-8, epi’-8 or iso-8 was isolated. This means that the formation of 8 proceeds with mutual kinetic resolution and 100% induced diastereoselectivity.