f Electron contribution to the change of electronic structure in CeRu2Si2 with temperature: a Compton scattering study

High resolution Compton profiles have been measured in the single crystal of CeRu(2)Si(2) above and below the Kondo temperature to elucidate the change of the Ce-4f electron from localized to itinerant states. Two-dimensional electron occupation number densities projected on the first Brillouin zone, which are obtained after a series of analyses, clearly specify the difference between itinerant and localized states. The contribution of Ce-4f electrons to the electronic structure is discussed by contrast with a band calculation.     

变价稀土元素L,M,N内壳层电子束缚能量的变化

变价稀土元素的4f电子占有数可以随不同的温度、压力或者组成(为化合物时)而作“连续”或不连续的变化,对于不同的4f电子占有数,其内壳层电子的束缚能量也将有所不同,本文应用相对论性原子自洽场理论计算由“变价”而引起的束缚能移动。 关键词：     

4f delocalization in Gd: inelastic x-ray scattering at ultrahigh pressure

We present resonant inelastic x-ray scattering and x-ray emission spectroscopy results on Gd metal to 113 GPa which suggest Kondo-like aspects in the delocalization of 4f electrons. Analysis of the resonant inelastic x-ray scattering data reveals a prolonged and continuous delocalization with volume throughout the entire pressure range, so that the volume-collapse transition at 59 GPa is only part of the phenomenon. Moreover, the Lgamma1 x-ray emission spectroscopy spectra indicate no apparent change in the bare 4f moment across the collapse, suggesting that Kondo screening is responsible for the expected Pauli-like behavior in magnetic susceptibility.     

A two-band model for intermediate valence compounds

The change of valence as a function of pressure in intermediate valence rare-earth compounds is computed in a two hybridized band model: a conduction band and a 4f-band, being V the hybridization parameter. A Coulomb interaction G between 4f and conduction electrons is also included. For different values of G/V we obtain first or second order transitions from a semiconductor to a metallic state.     

Hyperfine fields for119Sn in laves phases Rt2 (R=rare earth: T=Fe,Co, Ni)

The hyperfine fields acting on¹¹⁹Sn nuclei in the RT₂ (R=Sm?Lu; T=Fe, Co, Ni) have been measured by Mössbauer spectroscopy. It has been found that the hyperfine fields acting on¹¹⁹Sn nuclei in the RT₂ compounds are changed at some electronic occupation of the 4f shell of the R-component. The occupation of 4f shell is varied with the T-component. The sharp change of the hyperfine fields are connected with the change of the electronic band structure.     

Acoustic distortion products in humans: systematic changes in amplitudes as a function of f2/f1 ratio

The effects of primary-tone separation on the amplitude of distortion-product emissions (DPEs) at the 2f1-f2 frequency were systematically examined in ten ears of five subjects. All individuals had normal hearing and middle-ear function based upon standard clinical measures. Acoustic-distortion products were elicited at 1, 2.5, and 4 kHz by equilevel primaries at 65, 75, and 85 dB SPL, while f2/f1 ratios were varied in 0.02 increments from 1.01-1.41 (4 kHz), 1.01-1.59 (2.5 kHz), or 1.01-1.79 (1 kHz). A principal outcome reflected in the detailed structure of both average and individual ratio functions was a nonmonotonic change in DPE amplitude as the ratio of f2/f1 increased. Despite the presence of amplitude nonmonotonicities, there was clearly a region of f1 and f2 separation that generated a maximum DPE. The effects of primary-tone separation on DPE amplitudes were systematically related to DPE frequency and primary-tone level. For all three levels of stimulation, the f2/f1 ratio was inversely related to DPE frequency. Thus larger ratios reflecting a greater separation of f1 and f2 were more effective in generating DPEs at 1 kHz rather than at 4 kHz. The optimal ratio for 2.5 kHz fell at an intermediate value. Conversely, acoustic distortion-product amplitude as a function of primary-tone level was directly related to the frequency separation of the primary tones. Regardless of the frequency region of the primary tones, smaller f2/f1 ratios were superior in generating DPEs in response to 65-dB stimuli, whereas larger ratios elicited bigger DPEs with primaries at 75 and 85 dB SPL. Within any specific stimulus-parameter combination, individual variability in DPE amplitude was noted. When all stimulus conditions describing the variations in frequency and level were considered, an f2/f1 ratio of 1.22 was most effective in maximizing DPE amplitude.     

A magnetoelectric laminate based passive micro‐displacement sensor

A passive micro‐displacement sensor (for ～μm displacement) was fabricated based on a magnetoelectric laminate, in which the displacement change can result in a change of the magnetic flux around the magnetoelectric sensor. The displacement measurement was realized by measuring the magnetoelectric output voltage. The displacement detecting coefficient was ～2.5 mV/μm at a frequency of ～1 kHz. This passive displacement sensor possesses the advantages of low cost, high resolution, low energy consumption and good linearity and has potential for application in future displacement detectors.

     

Density of states and the problem of Sm valence

Density of states for Sm metal has been calculated in DFT/GGA approximation using the same treatment for f and s-d bands. It is concluded that the 4f electrons of Sm must be considered as valence electrons, not shallow core states. Therefore the 4f-5d transition cannot change the valence of Sm, which may be characterized (if necessary) by the sum of all electrons in the s-d-f valence bands. The possibility of alternative interpretation of UPS spectra of Sm adsorbed films is illustrated by calculations of DOS (density of states) for oxygen-contaminated Sm crystal.     

Gas challenge-blood oxygen level-dependent (GC-BOLD) MRI in the rat Novikoff hepatoma model

Purpose

The purpose of the study was to investigate the relationship between gas challenge-blood oxygen level-dependent (GC-BOLD) response angiogenesis and tumor size in rat Novikoff hepatoma model.

Materials and Methods

Twenty adult male Sprague-Dawley rats (weighting 301-325 g) were used for our Animal Care and Use Committee-approved experiments. N1-S1 Novikoff hepatomas were grown in 14 rats with sizes ranging from 0.42 to 2.81 cm. All experiments were performed at 3.0 T using a custom-built rodent receiver coil. A multiple gradient-echo sequence was used for R2^? measurements, first during room air (78% N₂/20% O₂) breathing and then after 10 min of carbogen (95% O₂/5% CO₂) breathing. After image acquisition, rats were euthanized, and the tumors were harvested for histological evaluation.

Results

The R2^? change between air and carbogen breathing for small hepatomas was positive; R2^? changes changed to negative values for larger hepatomas. We found a significant positive correlation between tumor R2^? change and tumor microvessel density (MVD) (r=0.798, P=.001) and a significant inverse correlation between tumor R2^? change and tumor size (r=−0.840, P<.0001).

Conclusions

GC-BOLD magnetic resonance imaging measurements are well correlated to MVD levels and tumor size in the N1-S1 Novikoff hepatoma model; GC-BOLD measurements may serve as noninvasive biomarkers for evaluating angiogenesis and disease progression and/or therapy response.     

Structural and electronic relationships between the lanthanide and actinide elements

The similarity and difference between the solid state properties of the 4f and 5f transition metals are pointed out. The heavier 5f elements show properties which have direct correspondence to the early 4f transition metals, suggesting a localized behaviour of the 5f electrons for those metals. On the other hand, the fact that Pu metal has a 30% lower volume than its neighbour heavier element, Am, suggests a tremendous difference in the properties of the 5f electrons for this element relative to the heavier actinides. This change in behaviour between Pu and Am can be viewed as a Mott transition within the 5f shell as a function of the atomic number Z. On the metallic 5f side of the Mott transition (i.e., early actinides), the elements show most unusual crystal structures, the common feature being their low symmetry. An analogous behaviour for the lanthanides is found in cerium metal under compression, where structures typical for the light actinides have been observed experimentally. A generalized phase diagram for the actinides is shown to contain features comparable to the individual phase diagram of Ce metal. The crystal structure behaviour of the lanthanides and heavier actinides is determined by the number of 5d (or 6d) electrons in the metallic state, since for these elements the f electrons are localized and nonbonding. For the earlier actinide metals electronic structure calculations - where the 5f orbitals are treated as part of the valence bands - account very well for the observed ground state crystal structures. The distorted structures can be understood as Peierls distortions away from the symmetric bcc structure and originate from strongly bonding 5f electrons occupying relatively narrow 5f states. High pressure is an extremely useful experimental tool to demonstrate the interrelationship between the lanthanides and the actinides. This revised version was published online in July 2006 with corrections to the Cover Date.     

New spectroscopy solves an old puzzle: the Kondo scale in heavy fermions

Resonant inelastic x-ray scattering (RIXS) yields clear evidence of spectroscopic Kondo scales in heavy fermions. In YbInCu4 and YbAgCu4 RIXS probes the Yb2+ component of the hybrid ground state and the temperature dependence of the Yb 4f occupation. We report a sudden valence change at a phase transition in YbInCu4, but a continuous temperature dependence in YbAgCu4, consistent with the predictions of the Anderson impurity model, for a Kondo temperature T(K) = 70 K. These results solve a long-standing controversy and establish RIXS as a quantitative probe of the electronic structure of strongly correlated electron systems.     

Decomposition of an azo dye in aqueous solution by combination of ultrasound and visible light

The degradation of Acid Orange 7 in aqueous solution has been investigated under the irradiation of ultrasound and visible light respectively and simultaneously. We have observed that the maximum removal percentage K increases from 4% to 35% when the ultrasonic frequency f and power P change from f=20 KHz and P=3 W to f=1 MHz and P=40 W. On the other hand, the K-value is approximately 3% under the irradiation of visible light at 632 nm and 100 mW/mm(2). Under the simultaneous irradiation of ultrasound (1 MHz, 40 W) and visible light (632 nm, 100 mW/mm(2)), the K-value reaches to approximately 65%, indicating a synergistic effect of ultrasound and visible light irradiations. A simple model based on the band gap theory and cavitation theory is proposed to explain the synergistic phenomenon.     

LED用荧光粉Sr（S1-xSex）：Eu^2＋的合成和光谱性质研究

采用高温固相法合成了Sr(S1-xSex)系列硫属化合物掺Eu2 荧光粉.XRD表明荧光粉的组成为单相,而且体系Sr(Sl-xSex):0.005Eu2 中晶胞参数随着组成的变化呈现良好的线性关系,遵守韦加定律.漫反射光谱与激发光谱吻合,说明荧光粉吸收的能量能够有效地激发发光中心而发光,激发光谱中较低能量区域覆盖了400～500 nm的光谱范围,与蓝光LED芯片的发射光匹配.发射光谱呈现的是Eu2 离子的5d→4f特征跃迁发射带,当x由0增加到1.0的过程中,发射峰值波长由617 nm逐渐蓝移到571 nm.不同基质中掺杂的Eu2 离子的荧光寿命均为微秒数量级,与Eu2 离子的4f65d1→4f7跃迁相符合.将荧光粉封装在发蓝色光(λ=460 nm)的GaN芯片上制作了LED器件,测量了器件的发光强度、色纯度和色坐标等参数.Sr(S1-xSex):Eu2 系列硫属化合物掺铕荧光粉能够有效地被GaN芯片发出的蓝色光激发,发出从橙色到红色的可见光,是一类较好的LED用荧光粉.     

Cd2SnO4薄膜光致发光某些性质的研究

本文研究了Cd2SnO4薄膜光致发光的某些性质.Cd2SnO4膜是利用Cd-Sn合金靶在Ar+O2气氛中反应溅射而成的.实验研究表明,Cd2SnO4膜的发光峰值随着氧浓度的增加移向长波方向.这是因为氧浓度的增加,减少了膜中的氧空位,导致了导带中电子浓度的减小,致使Burstein-Moss效应和电子散射作用相对减弱,从而改变了带隙宽度.     

Magnetocaloric effect in

In this work, it is discussed the magnetocaloric effect in the doped compound (Tb_1-zDy_z)Co₂. To this end, it is used a model Hamiltonian of interacting 4f-spins coupled with 3d-itinerant electrons. In the model are also included the crystalline electrical field and the magnetoelastic interaction. The 4f spin–spin interaction is treated in the mean field approximation taking into account the type of rare earth ion is occupying the neighborhood of a given site. The theoretically calculated isothermal entropy change upon variation of the applied magnetic field shows the good trend of the available experimental data.     

紫外激发的LiCaPO_4:Eu~(2+)蓝色发光粉的发光特性

采用高温固相法合成了LiCaPO4:Eu2+蓝色发光粉,并对其发光特性进行了研究。该发光粉发射峰值位于470nm,属于Eu2+的4f65d1→4f的特征跃迁发射,与结构相似的LiSrPO4:Eu2+和NaBaPO4:Eu2+相比其峰值有明显红移。Eu2+在LiCaPO4晶体中可被250～440nm光有效激发,这与紫外发光二极管的发射光谱(350～410nm)匹配。考察了Eu2+的掺杂浓度对发光强度的影响,最佳掺杂摩尔分数为5%,摩尔分数超过5%后发生猝灭现象。浓度猝灭机理为电多极-电多极的交互作用。LiCaPO4:Eu2+是适合UV-LED管芯激发的白光发光二极管用高亮度蓝色发光粉。     

Active dielectric metasurface based on phase‐change medium

We propose all‐dielectric metasurfaces that can be actively re‐configured using the phase‐change material Ge₂Sb₂Te₅ (GST) alloy. With selectively controlled phase transitions on the composing GST elements, metasurfaces can be tailored to exhibit varied functionalities. Using phase‐change GST rod as the basic building block, we have modelled metamolecules with tunable optical response when phase change occurs on select constituent GST rods. Tunable gradient metasurfaces can be realized with variable supercell period consisting of different patterns of the GST rods in their amorphous and crystalline states. Simulation results indicate a range of functions can be delivered, including multilevel signal modulating, near‐field coupling of GST rods, and anomalous reflection angle controlling. This work opens up a new space in exploring active meta‐devices with broader applications that cannot be achieved in their passive counterparts with permanent properties once fabricated.

     

Optimization of phase objects in 4f coherent imaging system for nonlinear refraction measurements

We numerically analyze the effects of radius and phase shift of phase objects on the diffraction image of the 4f coherent imaging system, a system used for measuring the third-order nonlinear refractive index. The selection of the aperture radius is discussed. We prove that when the phase object radius is 0.1 time of the aperture radius and the phase change of the phase object is 0.57π, one can get the highest sensitivity for nonlinear refraction measurement.     

Magnetic properties and magnetocaloric effect of the Cr-based spinel sulfides Co_(1-x)Cu_xCr_2S_4

Crystallographic structure, magnetic properties, and magnetic entropy change of the Cr-based spinel sulfides Co_(1-x)Cu_xCr_2S_4(x = 0–0.8) have been investigated. All these compounds crystallize into the cubic spinel structure, the Cu substitution shrinks linearly the lattice constant at a ratio of 0.0223 per Cu atom in the unit cell, and enhances linearly the Curie temperature and the spontaneous magnetization at the rates of 18K and 0.33 μB/f.u. per Cu atom in the unit cell,respectively. All these compounds show a typical behavior of second order magnetic transition, and a room temperature magnetic entropy change of 2.57 J/kg·K is achieved for Co_(0.4)Cu_(0.6)Cr_2S_4.     

A study on a primitive artificial esterase model: reactivity of a calix[4]resorcinarene bearing carboxyl groups

The host molecule octacarboxymethyl calix[4]resorcinarene 1 catalyses the hydrolysis of substituted phenyl N‐methylpyridinium‐4‐carboxylate esters 3a–f by complexation followed by intracomplex reaction via an anhydride intermediate. The reactivity in the presence of 1 is higher than that of the background at low pH; at high pH an inversion of reactivity occurs, the background becomes predominant since the host inhibits hydrolysis of the esters. The reactivity of esters 3a–f complexed with the host suffers little change in effective charge on the phenolic oxygen (?0.15 units) in contrast with the changes observed in alkaline hydrolysis (?0.28 units) and in the hydrolysis of the model monoaryl glutarate esters (‐1.02 units). The less negative effective charge in the transition state for host 1 catalysis compared with that in the glutarate case is ascribed to stronger solvation by water molecules in the complex compared with that due to water molecules in the bulk solvent.