Studies of the quantum Hall to quantum Hall insulator transition in InSb-based 2DESs

The temperature dependence of ρ_xx is studied in the vicinity of the quantum Hall to quantum Hall insulator transition (ν=1→0) in InSb/InAlSb based 2DESs. ρ_xx displays a symmetric temperature dependence about the transition with on the QH side and on the insulating side. A plot of 1/T₀ for successive ν displays power-law divergence with 1/T₀∝|ν−ν_c|^−γ,² with γ=2.2±0.3. This critical behavior in addition to the behavior expected of the quantum transport regime confirms that the QH/QHI transition is indeed a good quantum phase transition.     

Nuclear matter properties and relativistic mean-field theory

Nuclear matter properties are calculated in the relativistic mean-field theory by using a number of different parameter sets. The result shows that the volume energy a₁ and the symmetry energy J are around the acceptable values 16MeV and 30MeV, respectively; the incompressibility K₀ is unacceptably high in the linear model, but assumes reasonable value if nonlinear terms are included; the density symmetry L is around 100MeV for most parameter sets, and the symmetry incompressibility K _s has positive sign which is opposite to expectations based on the nonrelativistic model. In almost all parameter sets there exists a critical point (,), where the minimum and the maximum of the equation of state are coincident and the incompressibility equals zero, falling into ranges 0.014fm^-3 < < 0.039fm^-3 and 0.74 < ≤0.95; for a few parameter sets there is no critical point and the pure neutron matter is predicted to be bound. The maximum mass M _NS of neutron stars is predicted in the range 2.45M ?M _NS? 3.26M , the corresponding neutron star radius R _NS is in the range 12.2km ?R _NS? 15.1km. Received: 5 May 2000 / Accepted: 28 November 2000     

Fission experiments with secondary beams

Nuclear fission from excitation energies around 11 MeV was studied at GSI, Darmstadt for 76 neutron-deficient actinides and pre-actinides by use of relativistic secondary beams. The characteristics of multimodal fission of nuclei around ²²⁶Th are systematically investigated and related to the influence of shell effects on the potential-energy and on the level density between saddle point and scission. A systematic view on the large number of elemental yields measured gave rise to a new interpretation of the enhanced production of even elements in nuclear fission and allowed for a new understanding of pair breaking in fission.     

A Pyrene-based Highly Selective Turn-on Fluorescent Sensor for Copper(II) Ion and its Application in Live Cell Imaging

A new pyrene derivative (chemosensor 1) containing a picolinohydrazide moiety exhibits high selectivity for Cu²⁺ ion detection in mixed aqueous media (CH₃OH:H₂O = 7:3). Significant fluorescence enhancement was observed with chemosensor 1 in the presence of Cu²⁺. However, the metal ions Ag⁺, Ca²⁺, Cd²⁺, Co²⁺, Cu²⁺, Fe²⁺, Fe³⁺, Hg²⁺, K⁺, Mg²⁺, Mn²⁺, Ni²⁺, Pb²⁺, and Zn²⁺ produced only minor changes in fluorescence for the system. The apparent association constant (K _a) of Cu²⁺ binding in chemosensor 1 was found to be 2.75*10³ M⁻¹. The maximum fluorescence enhancement caused by Cu²⁺ binding in chemosensor 1 was observed over the pH range 5–8. Moreover, by means of fluorescence microscopy experiments, it is demonstrated that 1 can be used as a fluorescent probe for detecting Cu²⁺ in living cells.     

Measurement of the neutrino mass splitting and flavor mixing by MINOS

Measurements of neutrino oscillations using the disappearance of muon neutrinos from the Fermilab NuMI neutrino beam as observed by the two MINOS detectors are reported. New analysis methods have been applied to an enlarged data sample from an exposure of 7.25×10(20) protons on target. A fit to neutrino oscillations yields values of |Δm(2)|=(2.32(-0.08)(+0.12))×10(-3) eV(2) for the atmospheric mass splitting and sin(2)(2θ)>0.90 (90% C.L.) for the mixing angle. Pure neutrino decay and quantum decoherence hypotheses are excluded at 7 and 9 standard deviations, respectively.     

Nonlinear optical characteristics of monolayer MoSe2

In this study, we utilized picosecond pulses from an Nd:YAG laser to investigate the nonlinear optical characteristics of monolayer MoSe₂. Two‐step growth involving the selenization of pulsed‐laser‐deposited MoO₃ film was employed to yield the MoSe₂ monolayer on a SiO₂/Si substrate. Raman scattering, photoluminescence (PL) spectroscopy, and atomic force microscopy verified the high optical quality of the monolayer. The second‐order susceptibility χ⁽²⁾ was calculated to be ～50 pm V^?1 at the second harmonic wavelength ～810 nm, which is near the optical gap of the monolayer. Interestingly, our wavelength‐dependent second harmonic scan can identify the bound excitonic states including negatively charged excitons much more efficiently, compared with the PL method at room temperature. Additionally, the MoSe₂ monolayer exhibits a strong laser‐induced damage threshold ～16 GW cm^?2 under picosecond‐pulse excitation_. Our findings suggest that monolayer MoSe₂ can be considered as a promising candidate for high‐power, thin‐film‐based nonlinear optical devices and applications.     

Interaction of Ag with the Si(1 1 1)1 × 1–H surface

Synchrotron radiation based photoemission spectroscopy (SRPES) and low energy electron diffraction (LEED) are used to study the interaction between Ag atoms and the Si(1 1 1)1 × 1–H surface. At an Ag coverage of 0.063 monolayers (ML) on the Si(1 1 1)1 × 1–H surface, the Si 2p component corresponding to Si–H bonds decreases, and an additional Si 2p component appears which shifts to a lower binding energy by 109 meV with respect to the Si bulk peak. The new Si 2p component is also observed for 0.25 ML Ag on the Si(1 1 1)7 × 7 surface. These findings suggest that Ag atoms replace the H atoms of the Si(1 1 1)1 × 1–H surface and form direct Ag–Si bonds. Contrary to the widely accepted view that there is no chemical interaction between Ag particles and the H-passivated Si surface, these results are in good agreement with recent first-principles calculations.     

In-situ study of the catalytic oxidation of CO on a Pt(1 1 0) surface using ambient pressure X-ray photoelectron spectroscopy

CO and O₂ co-adsorption and the catalytic oxidation of CO on a Pt(1 1 0) surface under various pressures of CO and O₂ (up to 250 mTorr) are studied using ambient pressure X-ray photoelectron spectroscopy (APXPS) and mass spectrometry. There is no surface oxide formation on Pt under our reaction conditions. CO oxidation in this pressure (<500 mTorr), O₂ to CO ratio (<10), and temperature (150 °C) regime is consistent with the Langmuir-Hinshelwood reaction mechanism. Our findings provide in-situ surface chemical composition data of the catalytic oxidation of CO on Pt(1 1 0) at total pressures below 1 Torr.