Infrared spectral study of molecular vibrations in amorphous, nanocrystalline and AlO(OH) · αH2O bulk crystals

Amorphous, nanocrystalline, and bulk AlO(OH) · xH₂O crystals have six fundamental modes (FM) of vibration in a nonlinear AlO(OH) molecular structure. Most of them appear in groups of four IR and Raman bands. Their positions and relative intensities differ significantly in three specimens. The nanocrystals (monoclinic structure with z=8 molecules per unit cell) have four OH stretching bands at values enhanced by up to 360 cm⁻¹ at 3120, 3450, 3560 cm⁻¹ in comparison to those in bulk crystals or amorphous specimens. The first two bands are broad, bandwidth Δν_1/2200 to 350 cm⁻¹, while the other two are sharp, Δν_1/290 cm⁻¹. The sharp bands shift to 3525 and 3595 cm⁻¹ after heating the sample at 100°C. They no longer appear after heating at 300 or 500°C for 2 h (the specimen decomposes to Al₂O₃), leaving behind only two bands at 3100 and 3400 cm⁻¹. A Δν_1/2 value of 500 cm⁻¹ appears in the 3400 cm⁻¹ in a delocalized distribution of H atoms. Two bands also occur at 3098 and 3300 cm⁻¹ in bulk crystals (orthorhombic structure with z=4) or at 2990 and 3515 cm⁻¹ in an amorphous sample. More than one bands appear in a FM vibration in occurrence of sample in more than one conformers. The amorphous sample has approximately the same conformer structure as the bulk crystals. An amorphous surface structure exists in nanocrystals with a group of three bands at 1420, 1510 and 1635 cm⁻¹ in an interconnected network structure. It encapsulates the nanocrystals in an amorphous shell. Its volume fraction, 33% estimated from the integrated intensity in three bands, determines 2.2 nm thickness in the shell in spherical shape of nanocrystals in 35 nm diameter.     

Noise Stability of SIS Receivers

There is a strong interest in the submillimeter astronomy community to increase the IF bandwidth of SIS receivers in order to better facilitate broad spectral linewidth and continuum observations of extragalactic sources. However, with an increase in receiver IF bandwidth there is a decrease in the mixer stability. This in turn effects the integration efficiency and quality of the measurement. In order to better understand the noise mechanisms responsible for reducing the receiver stability, we employed a technique first described by D.W. Allan and later elaborated upon by Schieder et al. In this paper we address a variety of factors that degrade the noise stability of SIS receivers. The goal of this exercise is to make recommendations aimed at maximizing SIS receiver stability.     

利用微扰法分析两个相互耦合的参量四波混频过程

利用微扰法在旋转波近似下分析了铷原子中两个独立的参量四波混频过程和一个耦合的参量四波混频过程.当用超短激光脉冲相干激发这两个参量四波混频过程时,两个过程就会同时出现并且存在相互耦合作用.微扰分析表明,耦合的参量四波混频信号中可以观察到量子拍,量子拍幅度的大小不仅取决于超短脉冲的特性,而且依赖于两个耦合的参量四波混频过程中的相位匹配.     

The S-FFT calculation of Collins formula and its application in digital holography

We study analytically and numerically the properties of one-dimensional chain of cold ions placed in a periodic potential of optical lattice and global harmonic potential of a trap. In close similarity with the Frenkel-Kontorova model, a transition from sliding to pinned phase takes place with the increase of the optical lattice potential for the density of ions incommensurate with the lattice period. We show that at zero temperature the quantum fluctuations lead to a quantum phase transition and melting of pinned instanton glass phase at large values of dimensional Planck constant. After melting the ion chain can slide in an optical lattice. The obtained results are also relevant for a Wigner crystal placed in a periodic potential.     

Defect identification in rods subject to forced vibrations using the spatial wavelet transform

Use of the wavelet transform (WT) to study the forced vibrations in a rod in order to detect the presence of a defect is proposed. The axial vibrations in an inhomogeneous rod, produced by the application of different forces, are simulated by the Network Simulation Method and the obtained response is analyzed with the WT. An analysis of the detection and location of defects for several applied forces and defects generated by locally changing density or stiffness of the rod is presented. A noise test was carried out to check the robustness of the technique in real situations.     

Three‐dimensional computation for flow‐induced vibrations in in‐line and cross‐flow directions of a circular cylinder

We present numerical results for in‐line and cross‐flow vibrations of a circular cylinder, which is immersed in a uniform flow and is elastically supported by damper‐spring systems to compute vibrations of a rigid cylinder. In the case of a circular cylinder with a low Scruton number, it is well‐known that two types of self‐excited vibrations appear in the in‐line direction in the range of low reduced velocities. On the other hand, a cross‐flow vibration of the circular cylinder can be excited in the range of high reduced velocities. Therefore, we compute the flow‐induced vibrations of the circular cylinder in the wide range of the reduced velocities at low and high Scruton numbers and discuss about excitation mechanisms in the in‐line and cross‐flow directions. Copyright © 2011 John Wiley & Sons, Ltd.     

Remarks on maximal meanstandard devition ratio in undiscounted mdps

In the steady state of an undiscounted Markov decision process, we consider the problem to find an optimal stationary probability distribution that maximizes the mean standard deviation ratio among all the stationary probability distributions. The problem injects considerations in MDPs from the relative point of view     

Statistical energy analysis by finite elements for middle frequency vibration

Statistical energy analysis (SEA) is commonly used in industry to predict high-frequency vibrational response of structures. Since only local modes are used in SEA, only high-frequency responses can be predicted. This study extends SEA to the middle-frequency region by additionally using global modes. Methods using impedance matrices that can be found by NASTRAN are developed. Then the results are post processed to determine coupling loss factors.     

HREELS investigation of hydrogenated and deuterated GaN{0001} surfaces

The vibrational properties of clean, H- and D-covered GaN{0001} surfaces were investigated by high-resolution electron energy-loss spectroscopy. Auger electron spectroscopy and low-energy electron diffraction were utilized to monitor the surface cleanliness and structure, respectively. At the clean surface the Fuchs-Kliewer surface phonon frequency was determined to 700 cm^-1 (86.8 meV). For the adsorbate-covered surfaces current structure models predict only Ga-H vibrations for surfaces of either polarity. Despite of this, the HREEL-spectra of the hydrogenated sample show a new loss structure at 3255 cm^-1 (403.6 meV) and a shoulder at 1900 cm^-1 (235.6 meV) which are attributed to N-H and Ga-H stretching vibrations, respectively. After deuterium exposure an isotope shift occurs. Again, a N-adsorbate vibration is clearly resolved. A Ga-D bending mode is observed at 390 cm^-1 (48.4 meV), indicating that vibrations of both species are present. Received 1 February 2000     

Phonon anomalies in Co−Ni alloys

Summary A detailed experimental analysis of the inelastic crosssection along the [111]-direction in Co−Ni alloys is presented. Using a simple model and studying the cross-section as a function of both composition and temperature, it is shown that interesting information about the h.c.p.-f.c.c. transition can be gained in these alloys.

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Riassunto Nel presente lavoro si describe un’analisi sperimentale dettagliata della sezione d’urto anelastica dei neutroni lungo la direzione [111] in leghe Co−Ni. Impiegando un modello relativamente semplice e studiando la sezione d’urto in funzione di temperatura e concentrazione, si mostra che si possono ottenere utili informazioni riguardanti la transizione h.c.p.-f.c.c.