Time operators for quantum walks

Letters in Mathematical Physics - We study time operators for discrete-time quantum systems. Quantum walks are typical examples. We construct time operators for one-dimensional homogeneous quantum...     

Opposed type double stage cell for Mbar pressure experiment with large sample volume

ABSTRACT

A new opposed type double-stage large volume cell has been developed to compress large volume samples to more than 100?GPa (Mbar) pressure. A pair of second-stage diamond anvils is introduced into the first-stage Paris–Edinburgh press. The double-stage large volume cell allows the generation of ultrahigh pressures using a large culet diameter of the second-stage diamond anvils (diameters of 0.5–1.2?mm). Pressure generation up to 131?GPa has been achieved by using the culet diameter of 0.5?mm. Sample volume of the double-stage large volume cell can be more than ～100 times larger than that of conventional Mbar experiment using a diamond anvil cell. The double-stage large volume cell has a large opening in the horizontal plane for X-ray measurements, which is particularly suited for the multi-angle energy dispersive X-ray diffraction measurement, thus opening a new way of in situ structural determinations of amorphous materials at Mbar pressures.     

Acousto-induced structural change in amorphous As2S3

The acoustic flux injection method was applied to amorphous As₂S₃. The velocity and the attenuation constant for shear wave at ～ 100MHz were measured through the observation of the Brillouin scattering of the light beam from a He-Ne laser. The optical transmission around absorption edge was found to change after the injection of acoustic fluxes. It was also found that the sound velocity decreased with increasing injection time of acoustic fluxes and the amount of the change of the sound velocity reached ～ 20% after 10⁵ injections. The changes in the optical transmission and the sound velocity tended to be erased by annealing below the glass transition temperature. These phenomena are considered to be due to structural changes caused by the injection of strong acoustic fluxes.     

Quality factor of vibration of aluminum alloy disks

The quality factor Q of a quadrupole vibration at 20 kHz has been measured for circular disks of several aluminum alloys in the temperature range 4–300 K. Q = 4 × 10⁷ is obtained with disks of the 5056 alloy below 20 K.     

Heat capacities of copper(II) formate tetrahydrate and tetradeuterate: A comparative study of phase transitions in layer hydrate crystals

The heat capacities of copper(II) formate tetrahydrate and tetradeuterate have been measured from 12 to 300 K with an adiabatic calorimeter. They have sigmoidal temperature dependence except near the antiferroelectric-paraelectric transition temperatures, 235.78 ± 0.05 K and 245.64 ± 0.05 K, respectively. The corresponding enthalpy changes are 836.0 ± 1.0 J mol^?1 and 936.9 ± 0.5 J mor^?1. The entropy changes are 3.546 ± 0.005 JK^?1mol^?1 and 3.814 ± 0.002 JK^?1 mol^?1. The heat capacities are larger in the high temperature phase than in the low temperature phase, the difference amounting to 5.74 JK^?1 mol^?1 and 7.15 JK^?1 mol^?1 for the hydrate and the deuterate, respectively. The heat capacity anomaly is compared with those in tin(II) chloride dihydrate and potassium hexacyanoferrate trihydrate and discussed in relation to the structure of the hydrogen bond networks in these substances. The discussion is extended to include possible properties of the hydrogen bond frameworks in ices I_h and II.     

Short-range part of the NN interaction: Lowest-order relativistic corrections to equivalent local potentials from quark exchange kernels

The full Breit hamiltonian, including the Darwin term and relativistic kinetic-energy correction, has been used to construct resonating group kernels in analytic form for the six-quark NN system. The nonlocal kernels have been converted to equivalent local potentials using the WKB approximation based on their Wigner transforms. The equivalent local potentials have been confirmed to be rather insensitive to a choice of parameters and to be fairly accurate by comparing with the phase shifts and the wave functions obtained with the RGM equation. The results indicate the importance of the Darwin term. The term leads to a large reduction of the strong repulsive cores given by the color magnetic interaction and makes the resulting potentials less repulsive than those which neglect this term. The relative importance of the various components in the Breit interaction and of the quark-gluon exchange diagrams is made clear.     

Multiwalled carbon nanotubes mass-produced by dc arc discharge in He–H2 gas mixture

Uniform cathode deposits (longer than 15 mm), containing multiwalled carbon nanotubes (MWNTs) inside, were produced by dc arc discharge evaporation with a computer-controlled feeder of a pure-carbon electrode without a metal catalyst in a He–H₂ gas mixture. The purification of MWNTs was carried out to remove amorphous carbon and carbon nanoparticles. High-resolution transmission electron microscopy observations and Raman scattering studies show that the MWNTs possess a high crystallinity and a mean outermost diameter of ∼ ∼10 nm. It has been confirmed that the current density in the electron field emission from a purified MWNT mat can reach 77.92 mA/cm², indicating that the purified MWNTs are a promising candidate electron source in a super high-luminance light-source tube or a miniature X-ray source.