The electronic properties of glasses in the Cux(As0.4Se0.6)100−x system with x between 5 and 30

Data are presented on the dc conductivity, thermopower and optical absorption of glasses in the CuAs₂Se₃ system. The electronic properties of the alloys differ markedly from those of As₂Se₃, but variations in composition do not introduce significant changes in properties, until the atomic percent of copper is greater than 25. The results are interpreted in terms of small polaron transport.     

Surface enhanced Raman scattering of water on an Ag electrode

Surface enhanced Raman scattering of adsorbates on an Ag electrode in various electrolytes (e.g., 0.1–1.0 M KF, KCl, KBr, KI, K₃PO₄, and NaN₃) has been investigated in an effort to elucidate the mechanism of the enhancement of water compared to that for other adsorbates. (It is well known, for example, that pyridine exhibits large enhancement in 0.1 M KCl while SERS from water is not detectable unless the salt concentration is raised to almost 1 M.) Use of an optical multichannel analyzer allowed rapid recording of Raman spectra, and SERS intensities of adsorbates could therefore be monitored simultaneously during a continuous oxidation-reduction cycle. Potential dependencies of SERS intensities when the electrode potential is cycled in a non-faradiac potential range immediately following oxidation and reduction indicate that adatoms are partially responsible for the Raman enhancement. Furthermore, the anions in the electrolyte play an important role in stabilizing these “active sites.” For this reason, the degree of enhancement is influenced by the solubility of the Ag compound formed during oxidation and the specific adsorption of the anions to the Ag surface. Preferential alignment of H₂O molecules with their oxygen ends facing the surface at positive potentials, the tendency of anions in the electrolyte to disrupt hydrogen bonding with the water network, and the weak hydrogen bonding of H₂O with the anions give rise to a SERS lineshape from adsorbed H₂O molecules which is narrower than, and thus distinguishable from, the Raman line of bulk water. Thus, the degree to which the particular anions in the electrolyte disrupt hydrogen bonding among water molecules and reform hydrogen bonding between the anions and H₂O molecules influences the SERS lineshape and the apparent enhancement of the H₂ Raman emission.     

Metal-metal charge transfer and solvatochromism in cyanomanganese carbonyl complexes of ruthenium and osmium

The complexes [(H3N)5Ru(II)(mu-NC)Mn(I)Lx]2+, prepared from [Ru(OH2)(NH3)5]2+ and [Mn(CN)L(x)] {L(x) = trans-(CO)2{P(OPh)3}(dppm); cis-(CO)2(PR3)(dppm), R = OEt or OPh; (PR3)(NO)(eta-C5H4Me), R = Ph or OPh}, undergo two sequential one-electron oxidations, the first at the ruthenium centre to give [(H3N)5Ru(III)(mu-NC)Mn(I)Lx]3+; the osmium(III) analogues [(H3N)5Os(III)(mu-NC)Mn(I)Lx]3+ were prepared directly from [Os(NH3)5(O3SCF3)]2+ and [Mn(CN)Lx]. Cyclic voltammetry and electronic spectroscopy show that the strong solvatochromism of the trications depends on the hydrogen-bond accepting properties of the solvent. Extensive hydrogen bonding is also observed in the crystal structures of [(H3N)5Ru(III)(mu-NC)Mn(I)(PPh3)(NO)(eta-C5H4Me)][PF6]3.2Me2CO.1.5Et2O, [(H3N)5Ru(III)(mu-NC)Mn(I)(CO)(dppm)2-trans][PF6]3.5Me2CO and [(H3N)5Ru(III)(mu-NC)Mn(I)(CO)2{P(OEt)3}(dppm)-trans][PF6]3.4Me2CO, between the amine groups (the H-bond donors) at the Ru(III) site and the oxygen atoms of solvent molecules or the fluorine atoms of the [PF6]- counterions (the H-bond acceptors).     

Observations of slow electron holes at a magnetic reconnection site

We report in situ observations of high-frequency electrostatic waves in the vicinity of a reconnection site in the Earth's magnetotail. Two different types of waves are observed inside an ion-scale magnetic flux rope embedded in a reconnecting current sheet. Electron holes (weak double layers) produced by the Buneman instability are observed in the density minimum in the center of the flux rope. Higher frequency broadband electrostatic waves with frequencies extending up to f(pe) are driven by the electron beam and are observed in the denser part of the rope. Our observations demonstrate multiscale coupling during the reconnection: Electron-scale physics is induced by the dynamics of an ion-scale flux rope embedded in a yet larger-scale magnetic reconnection process.     

Dual-mode transducers for ultrasound imaging and thermal therapy

Medical imaging is a vital component of high intensity focused ultrasound (HIFU) therapy, which is gaining clinical acceptance for tissue ablation and cancer therapy. Imaging is necessary to plan and guide the application of therapeutic ultrasound, and to monitor the effects it induces in tissue. Because they can transmit high intensity continuous wave ultrasound for treatment and pulsed ultrasound for imaging, dual-mode transducers aim to improve the guidance and monitoring stages. Their primary advantage is implicit registration between the imaging and treatment axes, and so they can help ensure before treatment that the therapeutic beam is correctly aligned with the planned treatment volume. During treatment, imaging signals can be processed in real-time to assess acoustic properties of the tissue that are related to thermal ablation. Piezocomposite materials are favorable for dual-mode transducers because of their improved bandwidth, which in turn improves imaging performance while maintaining high efficiency for treatment. Here we present our experiences with three dual-mode transducers for interstitial applications. The first was an 11-MHz monoelement designed for use in the bile duct. It had a aperture that was cylindrically focused to 10 mm. The applicator motion was step-wise rotational for imaging and therapy over a 360°, or smaller, sector. The second transducer had 5-elements, each measuring for a total aperture of . It operated at 5.6 MHz, was cylindrically focused to 14 mm, and was integrated with a servo-controlled oscillating probe designed for sector imaging and directive therapy in the liver. The last transducer was a 5-MHz, 64-element linear array designed for beam-formed imaging and therapy. The aperture was with a pitch of 0.280 mm. Characterization results included conversion efficiencies above 50%, pulse-echo bandwidths above 50%, surface intensities up to , and axial imaging resolutions to 0.2 mm. The second transducer was evaluated in vivo using porcine liver, where coagulation necrosis was induced up to a depth of 20 mm in 120 s. B-mode and M-mode images displayed a hypoechoic region that agreed well with lesion depth observed by gross histology. These feasibility studies demonstrate that the dual-mode transducers had imaging performance that was sufficient to aid the guidance and monitoring of treatment, and could sustain high intensities to induce coagulation necrosis in vivo.