Infrared spectra and transport properties of Li-doped La214 system

The microstructure, charge transport and phonon vibration of polycrystalline samples of Li-doped La214 system have been studied by X-ray diffraction, resistivity and transmission infrared (IR) spectra. It is found that the doping of Li in La₂Cu_1−xLi_xO_y (0x0.5) and La_1.85+xSr_0.15−xCu_1−xLi_xO_y shows different effects on the crystal structure and resistivity. The change of resistivity with Li doping can be interpreted based on the variation of carrier concentration and impurity scattering. The shift of two IR vibration modes around 512 and 683 cm⁻¹, which are referred to the vibrations of apical oxygen and planar oxygen, is analyzed in detail. The change of the intensity for the mode around 683 cm⁻¹ is interpreted in terms of the screened effect of charge carrier in CuO₂ plane. The relation among crystal microstructure, carrier concentration, transport properties and phonon vibration is analyzed and discussed based on the experiment results.     

139La NQR relaxation and μSR study of La2Cu1−x Zn x O4

Il Nuovo Cimento D - 139La NQR spectra, μSR precessional frequencies and NQR relaxation rates W driven by the Cu2+ spin fluctuations are used to study the static magnetic properties and the...     

An NQR study of the polymorphism of triphenylchloromethane

This work is a study of the polymorphic transformations of triphenylchloromethane (TPCM) as well as the structure and dynamics of this molecular solid. Crystalline TPCM has been studied by a variety of techniques and many of its physical properties have been characterized. Previous crystallographic studies have reported the existence of two crystalline phases. Phase II, stable above 372 K, is trigonal with space group P3; and Z = 6. The compound associates pairwise (halogen-to-halogen and triphenylmethyl-to-triphenylmethyl) and linearly with all carbon-halogen bonds aligned with C3 and S6 axes of the lattice. Below 372 K, a triclinic modification (phase III) is found (P1;, Z = 10) where the molecules are also aligned pairwise with close Cl cdots, three dots, centered Cl interactions. However, the C-Cl bonds were no longer parallel. On the other hand, DTA studies have also reported a phase transition at 381 K (to phase I) that can been obtained from slow evaporation of pentane or ether solutions. Crystallographic information about these phases has not been obtained in the literature.Five NQR lines have been observed from liquid nitrogen temperature to 372 K in good agreement with phase III that has Z = 10. Above 372 K, three lines are observed which are related to phase II. Any effort to observe phase I through NQR failed; phase II remains until the sample is melted. Instead, if phase II is cooled down, a second-order phase transition to a new phase at 259 K is observed through NQR studies. The temperature dependence of experimental data in the phase transition region is well explained assuming the transitions occur when molecules in the crystal lattice change their direction uniformly with a change in temperature and the liberational modes, coupled in an anharmonic way with the uniform mode, change their frequencies in such a way that entropy compensates the unfavorable potential energy increase due to the uniform angular tilt.     

EXAFS study of copper complexes with azomethinic ligand environment

A series of copper metallochelates C₂₂H₁₈CuN₄O₂ X (X = Se, S, O) as models of active centers of natural metalloproteins have been synthesized on the basis of new azomethine ligand systems. The structure of the complexes has been studied by extended X-ray absorption fine-structure spectroscopy. It is shown that, in the metallochelates with X = Se or S, one azomethine chalcogen-containing ligand undergoes tridentate interaction with copper ions, while the other ligand is an acetate group. As a result, a complex with the N₂O₂ X environment is formed, where one of the oxygen atoms of the acetate group is at a large distance from the metal ion: R = 2.56–2.68 Å. For the metallochelate with X = O, coordination of the acetate group by a copper ion is found to be absent, and only interaction with azomethine ligands having average Cu-N/O distances R = 1.96–2.04 Å is observed.     

La NMR and As NQR study of the As-based filled skutterudite LaOs4As12

We report experimental results of nuclear magnetic resonance (NMR) at the La site and nuclear quadrupole resonance (NQR) at the As site in the normal state of the superconducting compound LaOs₄As₁₂. Measurements have been performed on powder sample obtained from high quality single crystals. The temperature dependences of the nuclear spin-lattice relaxation rates, 1/T₁, of ⁷⁵As and ¹³⁹La nuclei were measured. No scaling between them was found indicating a local character of relaxation processes. The relaxation of ⁷⁵As nuclei can consistently be understood in terms of antiferromagnetic spin fluctuations, as deduced from the T-dependence of (1/T₁T)=C/(T−θ)^1/2.     

A metallographic and electron microscopic study of the structure of copper after dynamic pressing

Structural changes in copper samples subjected to severe plastic deformation with the use of the dynamic loading technique were studied. The deformation was caused by pressing blanks through two or three channels situated at an angle with respect to one another. The velocity of a blank before it got into the first channel was 280–450 m/s. Pressure in samples did not exceed 3–7 GPa. The microstructure of copper changed under the simultaneous action of high-velocity deformation and temperature increase. The formation of cellular dislocation structures, systems of microtwins, dynamic polygonization subgranular structures, and new recrystallized grains was observed. After two passes, the major part of a sample had a structure that consisted of thin fibers containing submicrodisperse (50–100 nm) grains.     

Copper resinate: an XPS study of degradation

In this paper, we describe an X-ray photoelectron spectroscopy (XPS) study of copper resinate, a transparent green glaze that is coloured by copper salts of resin acids. This pigment was used in Europe in the fifteenth and sixteenth centuries, but it does not seem to be a usual feature of the palette anywhere after the end of the sixteenth century, because its tendency to discolour was already widely known by artists. An essential prerequisite for the restoration of works of art is the understanding of the effects of various climatic parameters on the deterioration process. For this reason, pictorial models of copper resinate in linseed oil, capable of simulating the ancient paintings on mobile supports, were prepared and aged in a climatic chamber, under different conditions such as exposure to UV radiations, humidity and different concentration of chemical pollutants (NO₂ and SO₂).All the samples were investigated by XPS and the data obtained were evaluated in order to estimate aging effects as well as mechanisms of degradation. On these paint layers damage induced by X-ray irradiation was also verified. PACS 79.60.-i; 61.80.Cb; 81.40.Cd     

NQR application to the study of hydrogen dynamics in hydrogen-bonded molecular dimers

The temperature dependences of ¹H NMR as well as ³⁵Cl NQR spin-lattice relaxation times T ₁ were investigated in order to study the hydrogen transfer dynamics in carboxylic acid dimers in 3,5-dichloro- and 2,6-dichlorobenzoic acids. The asymmetry energy A/ k _B and the activation energy V/ k _B for the hydrogen transfer were estimated to be 240 K and 900 K, and 840 K and 2500 K, respectively, for these compounds. In spite of a large asymmetric potential the quantum nature of hydrogen transfer is recognized in the slope of the temperature dependence of T ₁ on the low-temperature side of the T ₁ minimum. The NQR T ₁ measurements was revealed to be a good probe for the hydrogen transfer dynamics.     

Use of the Bohr Principle for Detecting NQR Signals from Mines

Principles of message transfer in telecommunication systems are considered when a wide transmission band is required, which can result in tuning away from the transmitting station if the signal-to-noise ratio (SNR) is insufficiently high. Based on a solution of the Fokker-Planck-Kolmogorov equation, it is demonstrated that a signal below noise is broadened 20 times for SNR = 0.05. This makes signal accumulation difficult. The matrix pencil method of information theory is used to demonstrate that the broadening of a signal below noise and shift of its frequency detuning interfere with reliable signal detection for SNR ≤ 0.05. An analog of the Bohr complementarity principle is used to analyze the NQR detector. In addition, performance of the NQR-mine detector used to clear of mines territories of former military actions is examined.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 40–46, February, 2005.     

Cu NQR study of the stripe phase local structure in the lanthanum cuprates

Using Cu nuclear quadrupole resonance (NQR) in Eu-doped La2-xSrxCuO4 we find the evidence of the pinned stripe phase at 1.3 K for 0. 080.18 correlating with the onset of bulk superconductivity corresponds to the depinning of the stripe phase.     

声波作用下铜球传热特性实验*

针对频率为500 Hz～3000 Hz和声压级为110 d B～133 d B的声场作用对铜球在空气中自然冷却的传热特性的影响,通过热电偶测温的方法,分析铜球温度梯度的分布与声场声压级、频率以及铜球直径的关系。结果表面,当频率f一定时,随着声压级的增加,铜球的传热效果得到明显增强,对于直径为5 mm的铜球,在133 d B声场中传热系数最大增加了25%。当声压级一定时,在频率范围中存在某一频率,此时铜球的传热系数最大,此特殊频率随着声压级的增大而增大。当铜球的直径为5 mm时,可以在低频段观测到声流效应的影响,而当铜球的直径为10 mm、15mm时,很难在低频段辨别出声流效应的影响。所得结论为声波应用于电站锅炉中,强化煤颗粒燃烧提供了依据。     

14N NQR study of the structural phase transitions in NH4NO3

The temperature dependences of the¹⁴N nuclear quadrupole resonance frequencies have been measured in phases II, III, IV and V of ammonium nitrate with the help of the¹H–¹⁴H nuclear quadrupole double resonance technique. The experimental results are related to the proposed crystal structures and disorder in the various crystallographic phases.     

高噪声背景下的孤立词语音识别方法研究及系统实现

对高噪声背景下的语音特点进行了分析,提出了适应于高噪声背景下孤立词语音识别的全套方法,进行了系统实现。对本方法和系统进行了详细的实验比较和测试,证明系统在80dB左右接近同类无噪声识别系统的精度,最高可以抵抗100dB的噪声。     

Study on the method and system implementation of an isolated word recognition system used in noisy environment

I.IntroductionRecentlytherearemanykindsofsystemsandproductsforspeechrecognition,butalmostallofthemareworkinginquietenvironment,theperformancearedegradedorevencan'tworkwhenitisoperatedinhighnoisyenvironmentssuchasincockpits,vehicle,workshopsetc.SonoiserobustnesshasbecomeoneofthemainobstaclesfortherealaPplicationsoftheautomaticspeechrecognizersanditattractstheattentionofresearchersinspeechtechnologyareas.Since1978,substantialeffortshavebeendevotedtotestandevaluatethespeechrecognizersusedinfight…     

EPR study of exchange interactions in the nonmagnetic Kondo system La1−x CexCu6

The EPR of paramagnetic impurities Gd³⁺ and Mn²⁺ was studied in nonmagnetic Kondo system La_1−x Ce_xCu₆ containing in the 1.6–200 K range. The exchange interaction parameters of gadolinium and manganese ions with conduction electrons, of cerium ions with conduction electrons and with one another, the Kondo temperature of cerium ions, and the temperature behavior of cerium-ion spin-fluctuation rate have been determined. A pseudogap in the density of states at the Fermi level has been detected in the CeCu₆ regular system, which is apparently due to s-f hybridization. This pseudogap can be destroyed by introducing an aluminum impurity, which induces strong conduction-electron scattering. It was also found that RKKY interaction among manganese ions in CeCu_6−y Mn_y is considerably stronger than it is in LaCu_6−y Mn_y, which implies enhancement of nonlocal spin susceptibility due to an f band contribution to conduction-electron states. Fiz. Tverd. Tela (St. Petersburg) 40, 593–599 (April 1998)