Synthesis of cyclophellitol utilizing a palladium chloride mediated-Ferrier-II rearrangement

Cyclophellitol and its C3-epimer have been synthesized from5-enoglucopyranoside and 5-enomannopyranoside, respectively. The carbocyclic skeletonwas constructed through a Ferrier-II reaction meditated by PdCl2.     

Tailored sinc pulses for uniform excitation and artifact-free radio frequency time-domain EPR imaging

A method to generate shaped radiofrequency pulses for uniform excitation of electron spins in time-domain radio frequency (RF) electron paramagnetic resonance (EPR) imaging is presented. A commercial waveform generator was integrated with the transmit arm of the existing time-domain RF-EPR spectrometer to generate tailored excitation pulses with sub-nano second resolution for excitation with a 90 degrees flip-angle. A truncated sinc [sin(x)/x] pulse, tailored to compensate for the Q-profile (RF frequency response) of the resonator, was shown to yield images from phantom objects as well as in vivo images, with minimal distortion. These studies point to the advantages in using shaped sinc pulses to achieve improved uniform excitation over a relatively wide bandwidth region in time-domain RF-EPR imaging (RF-FT-EPRI).     

Mathematical models for the apparent masses of standing subjects exposed to vertical whole-body vibration

Linear lumped parameter models of the apparent masses of human subjects in standing positions when exposed to vertical whole-body vibration have been developed. Simple models with a single degree-of-freedom (d.o.f.) and with two (d.o.f.) were considered for practical use. Model parameters were optimised using both the mean apparent mass of 12 male subjects and the apparent masses of individual subjects measured in a previous study. The calculated responses of two (d.o.f.) models with a massless support structure showed best agreement with the measured apparent mass and phase, with errors less than 0.1 in the normalised apparent mass (i.e., corresponding to errors less than 10% of the static mass) and errors less than 5° in the phase for a normal standing posture. The model parameters obtained with the mean measured apparent masses of the 12 subjects were similar to the means of the 12 sets of parameters obtained when fitting to the individual apparent masses. It was found that the effects of vibration magnitude and postural changes on the measured apparent mass could be represented by changes to the stiffness and damping in the two (d.o.f.) models.     

Role of structural fluctuation in a surface reaction studied by scanning tunneling microscopy: the CO+O-->CO2 clean-off reaction on Ag(110)-(2x1)-O

The kinetics of the clean-off reaction of O adatoms by CO on Ag(110)-(2x1)-O is investigated by scanning tunneling microscopy. The reaction is accelerated in the lower O coverage range where AgO chains with (nx1) (n> or =4) configurations show significant structural fluctuation. Simulations based on the Ising model are used to provide a quantitative understanding of the acceleration, which originates from the dynamical formation of active O adatoms by fluctuation of AgO chains.     

Visualization and numerical analysis of stress waves in blasting process

Visualization studies were performed both experimentally and theoretically to observe stress wave propagation in a material and its interaction with the free surface of the material in a blasting process. PMMA (polymethyl-methacrylate) plates were used as a transparent material. The stress wave was generated by initiation of an electric detonator. The stress waves in the PMMA specimen with the right-angled corner were observed by means of the shadowgraph system using a Q switched ruby laser as a light source. In addition to the experiment, a numerical analysis using smoothed particle hydrodynamics (SPH) was also carried out to clarify the dynamic behavior of stress waves in the blasting process. Transmittance and reflection of the stress wave at the free surface could be visualized by both the experiment and the numerical analysis.     

Isolation, characterization, and reaction of activated iodosylbenzene monomer hydroxy(phenyl)iodonium ion with hypervalent bonding: supramolecular complex PhI+OH.18-crown-6 with secondary I...O interactions

The isolation, characterization, and reaction of the active species hydroxy(phenyl)iodonium ion with hypervalent bonding are reported. Reaction of iodosylbenzene with HBF(4)-Me(2)O in the presence of equimolar 18-crown-6 in dichloromethane afforded the hydroxy-lambda(3)-iodane complex PhI(OH)BF(4).18-crown-6 as stable yellow prisms. X-ray structure analysis indicated that both the close contacts between the iodine(III) and the three adjacent oxygen atoms of 18-crown-6, and the hydrogen bonding OH.O(crown ether) will be responsible for the increased stability of the complex as compared to the uncomplexed PhI(OH)BF(4). The crown ether complex is highly reactive and serves as a versatile oxidant even in water: thus, the complex undergoes oxidative transformations of a variety of functional groups such as olefins, alkynes, enones, silyl enol ethers, sulfides, and phenols under mild conditions.     

Multireference configuration interaction calculations for positronium halides

Multireference configuration interaction (MRCI) calculations of the positronium halides, PsF, PsCl, PsBr, and PsI, are carried out, to give positron ionization energies, positronium binding energies, and two-photon annihilation rates. All CI calculations consider only valence correlation effect with a frozen-core approximation, and use the orbitals with angular momentum up to 8. To incorporate the effects of many-body correlations in the energies and two-photon annihilation rates, the MRCI calculations are repeated with increasing reference configurations, and the full CI limits of these energies and annihilation rates are estimated. The contribution from orbitals having angular momentum greater than 8 to those values is also estimated. Relative to our previous single reference CI calculations, many-body correlation effects significantly increase the positron ionization energies, positronium binding energies, and two-photon annihilation rates. The structures of the positronium halides are also discussed.     

Large optical nonlinearity of semiconducting single-walled carbon nanotubes under resonant excitations

We measured third-order nonlinear susceptibility (chi(3)) spectra in semiconducting single-walled carbon nanotubes (SWNTs) by the Z-scan method. |Imchi(3)| is remarkably enhanced under resonant excitation to the lowest interband transition, reaching 4.2 x 10(-6) esu and 1.5 x 10(-7) esu in SWNTs grown by the laser ablation and HiPco methods, respectively. A comparison of the transient absorption changes evaluated by degenerate and nondegenerate pump-probe measurements suggests that the resonant enhancement of |Imchi(3)| is dominated by a coherent process rather than by saturation of absorption.     

Phase-locked widely tunable optical single-frequency generator based on a femtosecond comb

We present an arbitrary optical single-frequency generator based on a femtosecond optical frequency comb. The functions of this device are comparable to those of a radio-frequency synthesizer. However, this device operates at hundreds of terahertz. The absolute frequency accuracy of this synthesizer is approximately 1 kHz at a 282 THz carrier frequency. The stability is approximately 2 x 10(-14) at 100 s, and the tuning speed exceeds 30 GHz/s. This source demonstrates the integration of a phase-locked optical comb into a versatile and easy-to-use system for the generation of tunable, absolute optical frequencies. By using downconversion, one could generate tunable terahertz frequencies that are phase locked to a microwave reference, such as a Cs atomic clock, and high-precision interferometry could benefit greatly from the stability and accuracy of this widely tunable source.