Franck-Condon Factors to High Vibrational Quantum Numbers I: N2 and [... formula ...]

Franck-Condon factor arrays have been computed numerically to high vibrational quantum numbers for the band systems N2:C3II−B3II(Second Positive)N2:B3II−A3∑(First Positive)N2:A3∑−X1∑(Vegard Kaplan)N2:a1II−X1∑(Lyman-Birge-Hopfield)N2+;A2II−X2∑(Meinel)N2+:B2∑−X2∑(First Negative)and for the following ionization transitions N2X1∑→N2+X2∑N2X1∑→N2+A2IIN2X1∑→N2+B2∑     

Vibrational Spectroscopy at High Pressures in CF4: Implications to the Phase Diagram

The molecular analogue of methane CF₄ is the most fundamental saturated perfluorocarbon, exhibiting complex optical behavior that is highly unusual for such a simple molecular system. We present Raman measurements in solid CF₄ over a wide range in pressure from 1.6 to over 30 GPa at room temperature. The Raman spectra exhibit polarization-dependent intensity variations and history-dependent absence or presence of high pressure modes. Our results compellingly demonstrate that previously identified phase transitions in CF₄ based on Raman signatures need to be reconsidered. Though our data suggest possible new high-pressure transitions, we do not identify new phases because of spectral complexity. Finally, we used the measured longitudinal and transverse optical mode splitting to estimate the dipole moment derivative at high pressures and find it close to that of gaseous CF₄.     

Quantum Key Distribution: from Principles to Practicalities

We review the main protocols for key distribution based on principles of quantum mechanics, describing the general underlying ideas, discussing implementation requirements and pointing out directions of current experiments. The issue of security is addressed both from a principal and real-life point of view. Received: October 15, 1998; revised version: June 8, 1999     

Broken Symmetry Phase Transition in Solid HD: Quantum Behavior at Very High Pressures

The broken symmetry phase (BSP) transition in solid HD has been shown to be an example of quantum orientational melting. Anomalous features observed for the transition are a consequence of the symmetry properties of the system, namely, the fact that in HD all rotational states and transitions between them are allowed, in contrast to the behavior of the homonuclear H₂ and D₂.     

High Aspect Ratio Microcolumns to Manipulate Single Electrons on a Liquid Helium Surface for Quantum Logic Bits

Electrons are bound to the surface of liquid helium by the image potential due to the induced polarization of the helium. The potential varies as the reciprocal of the distance of the electron from the surface so that the energy levels for the electron motion perpendicular to the surface are those of a one-dimensional hydrogen atom with very small charge. In order to make quantum logic elements (qubits) using the ground state and first excited state in this potential, individual electrons must be confined over microelectrodes which are individually connected to variable voltage sources so that the electron energy levels can be shifted in and out of resonance with applied microwave radiation. The electrodes consist of an array of gold columns, about 1.2$muhbox m$tall and 200 nm in diameter, separated by 500 nm. These are grown by electroplating on the ends of leads deposited on a silicon substrate by e-beam lithography. The leads are covered by a dielectric layer and then a metal ground plane, so that the electric field from the leads is screened. We describe, here, our technique for fabricating this system and present the numerical computations of the electric fields from the electrodes.     

超高周疲劳的影响因素及疲劳机理的研究进展

超高周疲劳的研究可以满足某些特殊零部件极高循环周次的要求。综述了近年来超高周疲劳的研究进展,从S-N曲线的特征、断面上的鱼眼形貌以及裂纹的萌生与扩展特征等方面介绍了超高周疲劳的典型特征。分析了影响超高周疲劳的若干因素,如氢的作用、加载频率、应力比和晶粒尺寸等。进而提出了一些今后超高周疲劳的研究方向:超高周疲劳裂纹扩展的微观机理、扩展速率尤其是微观、宏观上的控制参量的研究以及确定鱼眼与ODA区边缘的应力强度因子范围对内部裂纹扩展门槛值的影响作用。     

Use of modulated excitation signals in medical ultrasound. Part III: High frame rate imaging

This paper, the last from a series of three papers on the application of coded excitation signals in medical ultrasound, investigates the possibility of increasing the frame rate in ultrasound imaging by using modulated excitation signals. Linear array-coded imaging and sparse synthetic transmit aperture imaging are considered, and the trade-offs between frame rate, image quality, and SNR are discussed. It is shown that FM codes can be used to increase the frame rate by a factor of two without a degradation in image quality and by a factor of 5, if a slight decrease in image quality can be accepted. The use of synthetic transmit aperture imaging is also considered, and it is here shown that Hadamard spatial encoding in transmit with FM emission signals can be used to increase the frame rate by 12 to 25 times with either a slight or no reduction in signal-to-noise ratio and image quality. By using these techniques a complete ultrasound-phased array image can be created using only two emissions.     

Thermodynamic and kinetic properties of indium- implanted silicon III: High temperature diffusion in oxidizing atmospheres

To a first approximation, indium diffusion in silicon is characterized by the same diffusion coefficient in an oxidizing atmosphere as in an inert atmosphere.Chemical etching of oxidized wafers has revealed unusual etch patterns and a bimodal stacking fault distribution for samples implanted at 10¹² ions cm^-2.The segregation between silicon and SiO₂ markedly favours silicon. However, in the first stages of oxidation indium can be incorporated in the SiO₂ layer because of the high growth rate of the oxide compared with the low indium diffusivity. After that, the “snowplough” effect gives rise to indium accumulation at the silicon surface.     

Recent Advances on Graphene Quantum Dots: From Chemistry and Physics to Applications

Graphene quantum dots (GQDs) that are flat 0D nanomaterials have attracted increasing interest because of their exceptional chemicophysical properties and novel applications in energy conversion and storage, electro/photo/chemical catalysis, flexible devices, sensing, display, imaging, and theranostics. The significant advances in the recent years are summarized with comparative and balanced discussion. The differences between GQDs and other nanomaterials, including their nanocarbon cousins, are emphasized, and the unique advantages of GQDs for specific applications are highlighted. The current challenges and outlook of this growing field are also discussed.     

A continuum approach to magnon-phonon couplings—III: Numerical results

The present final part of this work is devoted to the numerical evaluation of the various effects which were studied, both analytically and qualitatively, in Part II insofar as coupled magnetoelastic waves in ferromagnets are concerned. The case of four typically deformable ferromagnets (Cobalt, Nickel Ferrite, YIG and Iron) is examined. The graphs of practical interest which are obtained provide quantitative results pertaining to the repulsion of coupled modes in crossover regions of the dispersion diagram, the magnetoacoustic resonance effect in the absence of dissipation, the magnetoacoustic Faraday effect and the exchange of relaxation between coupled modes in the neighborhood of the coupling point when viscosity and spin-lattice relaxation are accounted for. The latter effect occurs slightly before, slightly after, or practically at the coupling point, depending on the material considered.