Identification of mixed-symmetry states in an odd-mass nearly spherical nucleus

The low-spin structure of 93Nb has been studied using the (n,n'gamma) reaction at neutron energies ranging from 1.5 to 3 MeV and the 94Zr(p,2ngamma)93Nb reaction at bombarding energies from 11.5 to 19 MeV. States at 1779.7 and 1840.6 keV, respectively, are proposed as mixed-symmetry states associated with the pi2p(1/2)-1x(2(1),MS+,94Mo) coupling. These assignments are derived from the observed M1 and E2 transition strengths to the 2p(1/2)-1x(2(1)+,94Mo) symmetric one-phonon states, energy systematics, spins and parities, and comparison with shell model calculations.     

On Janko'S Simple Group of Order

Replace b by b⁸ throughout page 94.     

Frequency-to-electrode allocation and speech perception with cochlear implants

The hypothesis was investigated that selectively increasing the discrimination of low-frequency information (below 2600 Hz) by altering the frequency-to-electrode allocation would improve speech perception by cochlear implantees. Two experimental conditions were compared, both utilizing ten electrode positions selected based on maximal discrimination. A fixed frequency range (200-10513 Hz) was allocated either relatively evenly across the ten electrodes, or so that nine of the ten positions were allocated to the frequencies up to 2600 Hz. Two additional conditions utilizing all available electrode positions (15-18 electrodes) were assessed: one with each subject's usual frequency-to-electrode allocation; and the other using the same analysis filters as the other experimental conditions. Seven users of the Nucleus CI22 implant wore processors mapped with each experimental condition for 2-week periods away from the laboratory, followed by assessment of perception of words in quiet and sentences in noise. Performance with both ten-electrode maps was significantly poorer than with both full-electrode maps on at least one measure. Performance with the map allocating nine out of ten electrodes to low frequencies was equivalent to that with the full-electrode maps for vowel perception and sentences in noise, but was worse for consonant perception. Performance with the evenly allocated ten-electrode map was equivalent to that with the full-electrode maps for consonant perception, but worse for vowel perception and sentences in noise. Comparison of the two full-electrode maps showed that subjects could fully adapt to frequency shifts up to ratio changes of 1.3, given 2 weeks' experience. Future research is needed to investigate whether speech perception may be improved by the manipulation of frequency-to-electrode allocation in maps which have a full complement of electrodes in Nucleus implants.     

An iterative approach to novel polyamines via nucleophilic ring-opening of aziridinium ions with beta-amino alcohols

An iterative procedure for the synthesis of a novel class of synthetic polyamines has been developed, utilising the regioselective ring-opening of aziridinium ion intermediates; facile N-allyl deprotection of intermediate polyamines allows the rapid construction of high molecular weight, stereochemically defined compounds in a convergent manner.     

Efficient grating-tuned mid-infrared Cr2+:CdSe laser

Room-temperature, all-solid-state, broadly tunable laser operation of Cr(2+) -doped CdSe has been demonstrated. Pumping with a Q -switched Tm, Ho:YLF laser running at a 1-kHz repetition rate achieved broadband output of 500 mW at 2.6mum with 48% absorbed power slope efficiency. With reduced efficiency, as much as 815 mW of power was obtained. With a diffraction grating, the Cr(2+): CdSe laser was tuned from 2.3 to 2.9mum with 10-nm bandwidth (FWHM) and output power up to 350 mW.     

An efficient, preconditioned, high-order solver for scattering by two-dimensional inhomogeneous media

We consider the problem of evaluating the scattering of TE polarized electromagnetic waves by two-dimensional penetrable inhomogeneities: building upon previous work [IEEE Trans. Antennas Propag. 48 (2000) 1862] we present a practical and general fast integral equation algorithm for this problem. The contributions introduced in this text include: (1) a preconditioner that significantly reduces the number of iterations required by the algorithm in the treatment of electrically large scatterers, (2) a new radial integration scheme based on Chebyshev polynomial approximation, which gives rise to increased accuracy, efficiency and stability, and (3) an efficient and stable method for the evaluation of scaled high-order Bessel functions, which extends the capabilities of the method to arbitrarily high frequencies. These enhancements give rise to an algorithm that is much more accurate and efficient than its previous counterpart, and that allows for treatment of much larger problems than permitted by the previous approach. In one test case, for example, the present algorithm results in far-field errors of 8.9×10⁻¹³ in a 2.12s calculation (on a 1.7 GHz PC) whereas the original algorithm gave rise to far-field errors of 1.1×10⁻⁸ in 88.91s on a 400 MHz PC. In another example, the present algorithm evaluates accurately the scattering by a cylinder of acoustical size κR=256, which is of the order of 20 times larger (400 times larger in square wavelengths) than the largest scatterers that could be treated by the previous approach. Yielding, at worst, third-order far field accuracy (or substantially better, for smooth scatterers) in fast computing times ( operations for an N point mesh) even for discontinuous and complex refractive index distributions (possibly containing severe geometric singularities such as corners and cusps), the proposed approach is the highest-order solver in existence for the problem under consideration.     

Exceedingly Facile Ph?X Activation (X=Cl,Br, I) with Ruthenium(II): Arresting Kinetics,Autocatalysis, and Mechanisms

[(Ph₃P)₃Ru(L)(H)₂] (where L=H₂ ( 1 ) in the presence of styrene, Ph₃P ( 3 ), and N₂ ( 4 )) cleave the Ph X bond (X=Cl, Br, I) at RT to give [(Ph₃P)₃RuH(X)] ( 2 ) and PhH. A combined experimental and DFT study points to [(Ph₃P)₃Ru(H)₂] as the reactive species generated upon spontaneous loss of L from 3 and 4 . The reaction of 3 with excess PhI displays striking kinetics which initially appears zeroth order in Ru. However mechanistic studies reveal that this is due to autocatalysis comprising two factors: 1) complex 2 , originating from the initial PhI activation with 3 , is roughly as reactive toward PhI as 3 itself; and 2) the Ph I bond cleavage with the just‐produced 2 gives rise to [(Ph₃P)₂RuI₂], which quickly comproportionates with the still‐present 3 to recover 2 . Both the initial and onward activation reactions involve PPh₃ dissociation, PhI coordination to Ru through I, rearrangement to a η²‐PhI intermediate, and Ph I oxidative addition.     

Hypohamiltonian Planar Cubic Graphs with Girth 5

A graph is called hypohamiltonian if it is not hamiltonian but becomes hamiltonian if any vertex is removed. Many hypohamiltonian planar cubic graphs have been found, starting with constructions of Thomassen in 1981. However, all the examples found until now had 4‐cycles. In this note we present the first examples of hypohamiltonian planar cubic graphs with cyclic connectivity 5, and thus girth 5. We show by computer search that the smallest members of this class are three graphs with 76 vertices.