On some aspects of the dynamics of a monoatomic Lennard-Jones liquid

Summary On the basis of the results obtained by methods of molecular dynamics by Rahman on liquid Ar, it is empirically shown that the harmonic spectrum of the atomic motion can be interpreted as a sum of two contributions. A ?preliminary? frequency spectrum, obtained by considering every possible (practically harmonic) motion of an atom in the field of its nearest neighbours, duly transformed to take account of the very short duration of the single monochromatic oscillations, constitutes one of the contributions interpretable as a superposition of disordered ?local oscillations?. The other contribution, interpretable as a superposition of travelling waves, is given by a sum of two bands having some analogy with Rayleigh-Debye bands, but having the customary cut replaced by a factor of the form exp [−(ω/ω₀)²] whose physical meaning is that only oscillations having an amplitude larger than a minimal value appear as travelling waves. These bands come into evidence when the spectrum of the local oscillations is subtracted from the harmonic spectrum. The lower frequency band is quite small (area about 2% of the total area of the spectrum) and suggests the existence of transverse waves (in the field of 10¹² Hz.)

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Riassunto Sulla base dei risultati ottenuti con metodi di dinamica molecolare applicati da Rahman al caso dell’argon liquido, si mostra empiricamente che lo spettro armonico dei moti atomici in questo liquido si può interpretare come somma di due contributi. Uno spettro di frequenza ?preliminare? ottenuto considerando tutti i possibili moti di un atomo nel campo dei suoi vicini piú prossimi, debitamente transformato per tener conto della brevissima durata delle singole oscillazioni, costituisce uno dei contributi, interpretabile come sovrapposizione disordinata di ?oscillazioni locali?. L’altro contributo, interpretabile come sovrapposizione di onde viaggianti, risulta formato da due bande aventi una certa analogia con le bande di Rayleigh-Debye nelle quali però l’abituale taglio discontinuon è sostituito da un fattore exp [−(ω/ω₀)²] il cui significato fisico è che soltanto oscillazioni con un’ampiezza superiore ad un minimo (legato al valore di ω₀) appaiono come onde viaggianti. Queste bande di onde viaggianti si evidenziano quando lo spettro delle oscillazioni locali è sottratto dallo spettro atomico. La banda di frequenza minore è molto piccola (area di circa il 2% dell’area totale dello spettro) e suggerisce l’esistenza di onde trasversali (nel campo di 10¹² Hz).

     

Advances in Microwave-Assisted Combinatorial Chemistry Without Polymer-Supported Reagents

Summary Combinatorial methodologies have dramatically changed the chemical research and discovery process, offering an unlimited source of new molecule entities to be screened for activity. The application of microwave irradiation in Combinatorial Chemistry and high-throughput synthesis has become increasingly popular. By taking advantage of this energy source, compound libraries for lead generation can be assembled in a fraction of time required by conventional thermal heating. This review focuses on the advances in developing synthetic methodologies in microwave without polymer-supported reagents suitable for combinatorial chemistry, including the advances in microwave-assisted fluorous synthesis technology.     

Off-axis phase-only holograms of 3D objects using accelerated point-based Fresnel diffraction algorithm

A method for calculating off-axis phase-only holograms of three-dimensional (3D) object using accelerated point-based Fresnel diffraction algorithm (PB-FDA) is proposed. The complex amplitude of the object points on the z-axis in hologram plane is calculated using Fresnel diffraction formula, called principal complex amplitudes (PCAs). The complex amplitudes of those off-axis object points of the same depth can be obtained by 2D shifting of PCAs. In order to improve the calculating speed of the PB-FDA, the convolution operation based on fast Fourier transform (FFT) is used to calculate the holograms rather than using the point-by-point spatial 2D shifting of the PCAs. The shortest recording distance of the PB-FDA is analyzed in order to remove the influence of multiple-order images in reconstructed images. The optimal recording distance of the PB-FDA is also analyzed to improve the quality of reconstructed images. Numerical reconstructions and optical reconstructions with a phase-only spatial light modulator (SLM) show that holographic 3D display is feasible with the proposed algorithm. The proposed PB-FDA can also avoid the influence of the zero-order image introduced by SLM in optical reconstructed images.     

氩-氮混合气电感耦合等离子体在元素和同位素分析中的应用进展

在传统Ar等离子体中引入其他活性气体(如氮气等)已经成为拓展其分析性能的一种重要手段。本文较系统的阐述了Ar-N₂混合气体电感耦合等离子体的基本物理化学性质,从N₂气引入引起传统Ar-ICP基本物理化学参数变化的层面出发探讨了Ar-N₂混合气等离子体特殊性质产生的机制,回顾了Ar-N₂混合气电感耦合等离子体在质谱分析中近40年的应用成果,并且展望了该技术在未来元素和同位素分析领域的应用前景。     

Accelerating the calculations of binary detour phase method by integrating both CUDA and Matlab programming for GPU's parallel computations

The availability of state of art GPGPU cards can play a promising role in accelerating the calculations of computer generated holograms (CGH) where one of the main problems of generating such holograms is the need for massive amount of calculations. Both CUDA and Matlab can be used alone to fulfill this purpose but using both at the same time gives a number of benefits. This paper is dedicated to present a performance study of applying Fermi-Architecture CUDA-enabled GPGPU card for speeding up the calculations of binary detour phase holograms using both Matlab and CUDA programming.     

Use of 4-bromo pyridazine 3,6-dione for building 3-amino pyridazine libraries

An efficient method for preparation of 4,6 or 5,6 disubstituted 3-aminopyridazines was easily carried out starting from easily available 4-bromo-pyridazine-3,6-dione, and using combination of both amination and Pd(0) cross-coupling reactions under microwave irradiation.     

Combinatorial computational chemistry approach of tight-binding quantum chemical molecular dynamics method to the design of the automotive catalysts

Recently, we have developed a new tight-binding quantum chemical molecular dynamics program “Colors” for combinatorial computational chemistry approach. This methodology is based on our original tight-binding approximation and realized over 5000 times acceleration compared to the conventional first-principles molecular dynamics method. In the present study, we applied our new program to the simulations on various realistic large-scale models of the automotive three-way catalysts, ultrafine Pt particle/CeO₂(111) support. Significant electron transfer from the Pt particle to the CeO₂(111) surface was observed and it was found to strongly depend on the size of the Pt particle. Furthermore, our simulation results suggest that the reduction of the Ce atom due to the electron transfer from the Pt particle to the CeO₂ surface is a main reason for the strong interaction of the Pt particle and CeO₂(111) support.     

High-throughput screening of fuel cell electrocatalysts

The drawbacks of our earlier report of preparing fuel cell catalyst arrays by borohydride reduction of inkjet prepared arrays of metal salts are discussed along with the need for inclusion of state-of-the-art metrics in all array screening. An alternative method for screening of hydrogen/air cathode catalysts, direct methanol fuel cell (DMFC) anode catalysts, and catalyst loading studies is provided. State-of-the-art Johnson Matthey catalysts were used in control experiments to demonstrate the utility of the array fuel cell for high throughput screening of fuel cell catalysts in the 3-4 mg/cm² range. This report lays out hard learned rules for high throughput screening and demonstrates that the array fuel cell can be used for very precise screening of libraries of membrane electrode assembly (MEA) components without the pitfalls discussed in the introduction.     

光学空间滤波过程的计算机仿真

提出了一种利用MATLAB软件并通过计算机仿真光学空间滤波实验过程的新方法.其特点是:既可以随意改变所设计滤波器的参量,又可以对输入图象进行振幅、相位或复合滤波,并且可实现傅里叶变换频谱中相位信息的提取、存储和利用,因而能够完成一般光学实验中往往难以实现的某些操作.并分别给出了网格滤波、低通、高通及相位滤波等仿真实验结果.这种仿真实验给光学滤波器的设计和图象处理带来很大方便,同时也为相关器件的设计提供了一条新的途径.