Electronic transport in fullerene C20 bridge assisted by molecular vibrations

The effect of molecular vibrations on electronic transport is investigated with the smallest fullerene C20 bridge, utilizing the Keldysh nonequilibrium Green's function techniques combined with the tight-binding molecular-dynamics method. Large discontinuous steps appear in the differential conductance when the applied bias voltage matches particular vibrational energies. The magnitude of the step is found to vary considerably with the vibrational mode and to depend on the local electronic states besides the strength of electron-vibration coupling. On the basis of this finding, a novel way to control the molecular motion by adjusting the gate voltage is proposed.     

Precise determination of hyperfine interactions and second-order doppler shift in <Superscript>149</Superscript>Sm Mössbauer transition

We have succeeded in precisely determining the hyperfine interactions, particularly the isomer shifts, in the ¹⁴⁹Sm Mössbauer transition. The difference in the nuclear radii between the ground and excited states is critical for the determination of isomer shifts but is relatively small in ¹⁴⁹Sm. Therefore, the precise determination by ¹⁴⁹Sm Mössbauer spectroscopy is difficult. The recent development of synchrotron-radiation-based Mössbauer spectroscopy allows the isomer shifts to be determined more precisely than previously with the help of wellcollimated synchrotron radiation. In particular, the time-window effect assists the precise determination of hyperfine interactions in the ¹⁴⁹Sm Mössbauer transition because this effect enables us to measure spectra with higher energy resolution than natural linewidth determined by the lifetime of the excited states. Meanwhile, highenergy-resolution measurements to determine center shifts by SR-based Mössbauer spectroscopy enable us to observe the second-order Doppler shift, which has not been discussed, particularly for heavy Mössbauer nuclei. We have discussed the precise determination of isomer shifts and the observation of the second-order Doppler shift using ¹⁴⁹Sm synchrotron-radiation-based Mössbauer spectroscopy.     

Topological Superconductivity in Cu(x)Bi(2)Se(3)

A topological superconductor (TSC) is characterized by the topologically protected gapless surface state that is essentially an Andreev bound state consisting of Majorana fermions. While a TSC has not yet been discovered, the doped topological insulator Cu(x)Bi(2)Se(3), which superconducts below ～3 K, has been predicted to possess a topological superconducting state. We report that the point-contact spectra on the cleaved surface of superconducting Cu(x)Bi(2)Se(3) present a zero-bias conductance peak (ZBCP) which signifies unconventional superconductivity. Theoretical considerations of all possible superconducting states help us conclude that this ZBCP is due to Majorana fermions and gives evidence for a topological superconductivity in Cu(x)Bi(2)Se(3). In addition, we found an unusual pseudogap that develops below ～20 K and coexists with the topological superconducting state.     

A possible interpretation of CDF dijet mass anomaly and its realization in supersymmetry

Recently, the CDF Collaboration reports an anomaly in dijet mass distribution in association with a lepton and missing energy. We discuss a possibility that the origin of the lepton and missing energy comes not from a W boson but a new boson particle, which is also responsible for the dijet mass peak. We show that such a situation can be realized in the framework of the minimal supersymmetric standard model and the dijet anomaly can be explained.     

Tip‐heating‐assisted Raman spectroscopy at elevated temperatures

We demonstrate tip‐heating‐assisted enhanced Raman spectroscopy to investigate the temperature dependence of the carbon nanotube G‐band with nanoscale resolution. The controllable and nanoscale heat generated at the tip apex was used to thermally perturb and characterize a small volume in a carbon nanotube sample that is precisely positioned underneath the tip. The dependence of tip enhancement with temperature was also experimentally examined, which is in good agreement with the enhancement calculated from the electromagnetic model of isolated spheroids. The technique presented may open up opportunities in the study of controlled heat‐assisted biochemical reactions and physical transformations of nanostructures. It can also be used for thermal characterization of various materials requiring site‐selective and controllable nanoscale heat source and could enable the realization of new photothermal devices. Copyright © 2010 John Wiley & Sons, Ltd.     

Study of Strangeness Photoproduction on the Neutron in the Threshold Region

Photoproduction of the neutral kaon on the deuteron has been investigated at the Research Center for Electron Photon Science, Tohoku University. We constructed the Neutral Kaon Spectrometer-2 for the detection of charged particles from the decay of the neutral kaon and the hyperon. We obtained a momentum distribution of K ⁰ with the inclusive measurement. It was consistent with the previous measurement. The total cross section of γ + d → K ⁰ + Λ + p was estimated from the measured integral cross section of γ + d → Λ + X. The total cross section with respect to the photon energy was compared with the theoretical calculations. It favored the Saclay-Lyon A model calculation with the ratio of the neutral to charged coupling constants of the axial-vector meson, K ₁, as ~ ?1.5. The energy dependence and the magnitude of the total cross section were similar to the total cross section of γ + p → K ⁺ Λ.     

Detection and grading for esophageal varices in patients with chronic liver damage: comparison of gadolinium-enhanced and unenhanced steady-state coherent MR images

The purpose of this study was to compare observer interpreted steady-state coherent coronal images and gadolinium-enhanced axial images in terms of the detection and grading of esophageal varices. Magnetic resonance imaging (MRI) and gastrointestinal endoscopy were performed within 2 weeks in 90 patients with chronic liver damage, including 55 with untreated esophageal varices, for periodic screening purposes. Two blinded readers retrospectively reviewed T1- and T2-weighted images with gadolinium-enhanced (gadolinium image set) and steady-state coherent (coherent image set) images. Sensitivity for the detection of esophageal varices was higher (P<.001) in the gadolinium image set (76%) than in the coherent image set (35%); on the other hand, specificity was higher (P<.001) in the coherent image set (91%) than in the gadolinium image set (66%). Furthermore, area under the ROC curve was higher for the gadolinium image set (Az=0.823) than the coherent image set (Az=0.761) (P=.48). Moderate and weak positive correlations with endoscopic grades were found for the gadolinium image (r=0.48, P<.01) and coherent image sets (r=0.34, P=.018). The addition of steady-state coherent imaging to the current routine liver imaging protocol did not improve the detection or grading of esophageal varices, whereas gadolinium-enhanced imaging was found to be potentially valuable. Nevertheless, endoscopy was confirmed to be mandatory in patients with esophageal varices suspected by MRI of the liver.     

High-Efficiency ZnCdSe/ZnSSe/ZnMgSSe Green Light-Emitting Diodes

Green light-emitting diodes (LEDs) were fabricated employing a ZnCdSe/ZnSSe triple quantum-well (TQW) active region surrounded by ZnMgSSe cladding layers grown on an n-type (100) GaAs substrate by molecular beam epitaxy (MBE). A 3.5 mW pure green emission was observed for the surface-emitting LED device at a peak wavelength of 513.3 nm (2.415 eV) with a spectral half-width of 11.7 nm (55 meV) under a 20 mA (4.6 V) direct current at room temperature (25°C). These correspond to an external quantum efficiency of 7.2%, a power conversion efficiency of 3.8%, a luminous current efficiency of 66 lm/A, and a luminous efficiency of 14 lm/W.