Dynamics of matter-wave solitons in a ratchet potential

We study the dynamics of bright solitons formed in a Bose-Einstein condensate with attractive atomic interactions perturbed by a weak bichromatic optical lattice potential. The lattice depth is a biperiodic function of time with a zero mean, which realizes a flashing ratchet for matter-wave solitons. We find that the average velocity of a soliton and the soliton current induced by the ratchet depend on the number of atoms in the soliton. As a consequence, soliton transport can be induced through scattering of different solitons. In the regime when matter-wave solitons are narrow compared to the lattice period the dynamics is well described by the effective Hamiltonian theory.     

Formation of a chiral NPPN ligand via metallation of acyclic NPNCN systems

A new type of bidentate N,N'-chelating ligand containing a chiral phosphorus centre has been synthesized via the metallation of an acyclic NPNCN species. The zwitterionic ligand backbone contains a phosphenium centre stabilised by an imido phosphine fragment.     

Synthesis and characterization of [ButNSn(mu-NBut)2TeNBut](mu3-SnTe), a stannanetellurone with four-coordinate tin

Treatment of [Li2Te(NBut)3]2 with Sn(O3SCF3)2 or SnCl2 in diethyl ether generates the stannanetellurone [ButNSn(mu-NBut)2 TeNBut](mu3-SnTe) involving four-coordinate tin with d(Sn=Te) = 2.589(1) A; the two Sn and two Te atoms are in different oxidation states (+II/+IV and +IV/-II, respectively).     

Broadband measurements on ultrasonic tank lining materials

The need for good absorbing materials in ultrasonic test tanks is described, although few systematic measurements appear to have been reported to date. Measurements of transmission and reflection on neoprene, paraffin wax, rubber car mat and plastic door mat are reported in the frequency range 1 – 5 MHz and for angles of incidence up to 45°. Neoprene and paraffin wax appear to have excellent characteristics. The paper includes a discussion of experimental problems, a brief comparison with similar techniques in audio acoustics, and identifies two important areas for further work.     

Ranges in silicon of ions with atomic numbers 62 ⩽ Z1 ⩽ 66 at 100 keV

The ranges of ions with atomic numbers 62 ? Z₁ ? 66 at 100 keV in silicon have been measured. Both the projected range and standard deviation are found to vary smoothly with Z₁.     

Proton magnetic resonance studies of compounds with bridgehead nitrogen atoms—XXIV: The stereochemistry of octahydroimidazo [1,5-a] pyridine and of some N-acetyloctahydroimidazo [1,5-a] pyridines

Octahydroimidazo[1,5-a]pyridine is shown to preferentially adopt the trans-fused ring conformation in solution at room temperature. The NMR spectra of the rotational isomers of some N-acetyloctahydroimidazo[1,5-a]pyridines and N-acetyloctahydro-1H-pyrido[1,2-c]pyrimidine are described, and the stereochemistry about the N-acetyl bonds and the cis or trans nature of the ring fusion defined.     

Estimation of critical and viscous frequencies for Biot theory in cancellous bone

The use of Biot theory for modelling ultrasonic wave propagation in porous media involves the definition of a "critical frequency" above which both fast and slow compressional waves will, in principle, propagate. Critical frequencies have been evaluated for healthy and osteoporotic cancellous bone filled with water or marrow, using data from the literature. The range of pore sizes in bone gives rise to a critical frequency band rather than a single critical frequency, the mean of which is lower for osteoporotic bone than normal bone. However, the critical frequency is a theoretical concept and previous researchers considered a more realistic "viscous frequency" above which both fast and slow waves may be experimentally observed. Viscous frequencies in bone are found to be several orders of magnitude greater than calculated critical frequencies. Whereas two waves may well be observed at all ultrasonic frequencies for water-filled cancellous bone at 20 degrees C, it is probable megahertz frequencies would be needed for observation of two waves in vivo.     

The sonocrystallisation of ice in sucrose solutions: primary and secondary nucleation

Two investigations of the sonocrystallisation of ice are reported for solutions in the concentration range of 0-45 wt.% sucrose. The first, carried out at 20 kHz using a commercial sonicator shows clear evidence of the stimulation of primary nucleation, by increasing the temperature at which nucleation takes place. The nucleation temperature is also increased as the ultrasonic power output level or duty cycles are increased. The second uses a novel measurement cell which permits the direct visualisation of the crystallisation and cavitation with a light microscope while different levels of alternating pressures at a frequency of 67 kHz are applied to the sample, whose heating and cooling is carefully controlled and monitored. This provides confirmation of the fragmentation of ice dendrites growing in a sucrose solution to produce smaller new ice crystals (secondary nucleation). These observations show that the primary and secondary nucleation of ice are both possible during the sonocrystallisation of ice.     

Calculations of the backscattering and radiation force functions of spherical targets for use in ultrasonic beam assessment

Knowledge of the frequency dependence of the backscattering from spherical targets, or of the associated radiation force function Y_p, is of considerable practical importance for the choice of material and size of sphere for transducer beam profiling. The former is often employed in a pulse-echo situation to define iso-echo contours, while the latter is used in absolute measurements of intensity.The present paper contains the graphical results of the calculation of the backscattering from 43 materials and the radiation force function for 48 materials, all of which were assumed to be immersed in water. The range of ka values displayed is from 0 to 20, calculations being performed in ka steps of 0.05. It is shown that the frequency behaviour of the radiation force function is an unreliable index of the frequency behaviour of the backscattering.