High-frequency response and acoustic phonon contribution of the linear electro-optic effect in DAST

We present a simple method to measure the contribution from acoustic phonons to the linear electro-optic effect. A step voltage with a short rise time (600 ps) is applied to the sample, and the electro-optic response is measured in the time domain. For the organic salt 4-N, N-dimethylamino-4(?)-N(?)-methyl-stilbazolium tosylate (DAST), we obtained a negative contribution of r(a)(111) = -1.0 +/- 0.1 pm/V to the overall electro-optic coefficient of r(111) = 48 +/- 5 pm/V (lambda = 1535 nm). The electro-optic response was limited only by the rise time of the applied voltage, which corresponds to a frequency of 1 GHz.     

Studies of the out-of-plane emission of pions in symmetric heavy-ion collisions

Triple differential cross-sections of midrapidity pions from ²⁰⁹Bi+²⁰⁹Bi collisions were measured with the Kaon Spectrometer at SIS at incident energies of 400, 700 and 1000 AMeV. The azimuthal emission pattern of the pions has been investigated in dependence of beam energy and impact parameter. An enhanced emission of pions perpendicular to the reaction plane is observed. The strength of the anisotropy increases with beam energy and pion transverse momentum. In contrast to the nucleons the anisotropy varies only little with the impact parameter. No difference in the behaviour of positive and negative pions is observed.     

人工神经网络方法预测八面体六卤化物MX^n—6的v1和v2模的振…

利用ＡＮＮ－ＢＰ算法，采用逐步改变训练步长和两个惯性项的权重系数惯性调整策略，分别以单目标和双目标的三层网络对八面体六卤化物ＭＸ＾ｎ－６的八面体ｖ１和ｖ２模振动频率进行了预测，发现单，双目标下预测的结果相差不大，双目标时权重系数调整科较快，（ＭｏＦ６）＾２－（ＢｉＦ６）＾－和（ＡｕＦ６）＾２－的振动频率文献值与网络的计算值或预测值相差偏大。     

Spin-lattice relaxation in multiple-pulse experiments as contrast parameter in NMR imaging of solids

The molecular motion contrast parameter for NMR imaging of solids and quasi-solids based on the spin-lattice relaxation (T _leff) in multiple-pulse experiments is discussed. For Ostroff-Waugh multiple-pulse sequence theT _leff contrast parameter is evaluated in slow and fast molecular motion regime and compared with spin-lattice relaxation in the rotating frame contrast parameter. It is shown thatT _leff is offering a good molecular motion contrast in NMR imaging of polymer systems. The radio-frequency pulse scheme forT _leff-imaging using magic-echo phase-encoding procedure for recording spatial distribution in solids is introduced. A method forT _leff-weighted imaging using gradient spin-echo valid for weak dipolar solids is also discussed. The one-dimensional protonT _leff image using Ostroff-Waugh pulse sequence in combination with frequency-encoding imaging procedure is presented for a phantom of poly(ethyleneoxide) and poly(methylmethacrylate). The distribution of mechanical stresses in a acrylate film on glass is investigated by protonT _leff-imaging. A proton spin-density image weighted byT _leff, for a mixture of two elastomers with different crosslink density is also shown.     

Single-particle enhancement of heavy-element production

Fusion barriers are calculated in a macroscopic-microscopic model for several cold-fusion heavy-ion reactions leading to heavy and superheavy elements. The results obtained in such a picture are very different from those obtained in a purely macroscopic model. For reactions on ²⁰⁸Pb targets, shell effects in the entrance channel result in fusion-barrier energies at the touching point that are only a few MeV higher than the ground state for compound systems near Z = 110. The entrance-channel fragment-shell effects remain far inside the touching point, almost to configurations only slightly more elongated than the ground-state configuration, where the fusion barrier has risen to about 10 MeV above the ground-state energy. Calculated single-particle level diagrams show that few level crossings occur until the peak in the fusion barrier very close to the ground-state shape is reached, which indicates that dissipation is negligible until very late in the fusion process. Whereas the fission valley in a macroscopic picture is several tens of MeV lower in energy than is the fusion valley, we find in the macroscopic-microscopic picture that the fission valley is only about 5 MeV lower than the fusion valley for cold-fusion reactions leading to compound systems near Z = 110. These results show that no significant “extra-extrapush” energy is needed to bring the system inside the fission saddle point and that the typical reaction energies for maximum cross section in heavy-element synthesis correspond to only a few MeV above the maximum in the fusion barrier.     

Superdeformed bands and ‘shears’ bands in 197Pb and 198Pb

Excited states in ¹⁹⁷Pb and ¹⁹⁸Pb, produced in the ¹⁸⁶W (¹⁸O,xn) reaction, were studied using the EUROGAM phase 2 γ ray spectrometer array. Two new superdeformed bands have been observed in ¹⁹⁷Pb, and the existence of a superdeformed band in ¹⁹⁸Pb has been confirmed. The increased statistics provided by the latest generation of arrays has resulted in the reordering of some of the previous known cascades of magnetic dipole transitions, with the first observation of the extremely weak E2 crossover transitions.     

Charge transfer from ammonia physisorbed on nanotubes

We report the use of nanotube field-effect transistor devices for chemical sensing in a conducting liquid environment. Detection of ammonia occurs through the shift of the gate voltage dependence of the source-drain current. We attribute this shift to charge transfer from adsorbed ammonia molecules, with the amount of charge estimated to be as small as 40 electrons for the smallest shift detected. Using the concentration dependence of the response as an adsorption isotherm, we are able to measure the amount of charge transfer to be 0.04 electron per ammonia molecule.     

Asymmetric Landau-Zener tunneling in a periodic potential

Using a simple model for nonlinear Landau-Zener tunneling between two energy bands of a Bose-Einstein condensate in a periodic potential, we find that the tunneling rates for the two directions of tunneling are not the same. Tunneling from the ground state to the excited state is enhanced by the nonlinearity, whereas in the opposite direction it is suppressed. These findings are confirmed by numerical simulations of the condensate dynamics. Measuring the tunneling rates for a condensate of rubidium atoms in an optical lattice, we have found experimental evidence for this asymmetry.     

Advanced flicker spectroscopy of fluid membranes

The bending elasticity of a fluid membrane is characterized by its modulus and spontaneous curvature. We present a new method, advanced flicker spectroscopy of giant nonspherical vesicles, which makes it possible to simultaneously measure both parameters for the first time. Our analysis is based on the generation of a large set of reference data from Monte Carlo simulations of randomly triangulated surfaces. As an example of the potential of the procedure, we monitor thermal trajectories of vesicle shapes and discuss the elastic response of zwitterionic membranes to transmembrane pH gradients. Our technique makes it possible to easily characterize membrane curvature as a function of environmental conditions.     

Measurement of X-ray production cross-sections of Ti,V, Cr,Mn, Fe,Co, Ni and Cu molecules

K shell X-ray production cross-sections in the Ti, V, Cr, Mn, Fe, Co, Ni, and Cu in the molecules were studied at 59.5 keV excitation energy by using a Si(Li) detector ( FWHM = 155 eV at 5.96 keV). The present results are compared with other theoretical values.