Effects of an intense, high-frequency laser field on the binding energy of excitons confined in a GaInNAs/GaAs quantum well

The effects of an intense, high-frequency laser field linearly polarized along the growth direction on the binding energy of excitons confined in a GaInNAs/GaAs quantum well is computed for different nitrogen and indium mole fractions by means of a variational technique within the effective-mass approximation. Our results show that such laser field creates an additional geometric confinement on the electronic and exciton states in the quantum well and the exciton binding energy depends on both the nitrogen and indium concentrations.     

Irradiation effect of low-energy ion on polyurethane nanocoating containing metal oxide nanoparticles

Irradiation effect of low-energy ion beam has been investigated on nanocoating developed with silica, titania and silica–titania core–shell nanoparticles embedded in an organic binder for nanopaint application. In this work, we have taken polyurethane as a model organic binder. Silica nanoparticles have been prepared through sol–gel synthesis with a particle size of 85?nm. Titania and core–shell nanoparticles have been prepared through both sol–gel and peptization process. Particle sizes obtained were 107?nm for titania and 240?nm for core–shell nanoparticles prepared through sol–gel process and 75?nm for TiO₂ and 144?nm for core–shell nanoparticles prepared through peptization process. The coating formulations were developed with the above nanoparticles individually and nanoparticle concentration was varied from 1 to 6?wt% and the best performance in terms of hydrophobicity was obtained with 4?wt % of the nanoparticles in polyurethane coating formulation. All the coating formulations prepared were applied on a glass substrate and dried at 100°C. The dry film thickness obtained was around 100?µm in each case. These films dried on glass substrate were irradiated by nitrogen and argon ion beam with energy of 26?keV at fluences of 10¹⁴ to 10¹⁶?ions/cm². The anti-algal property of the irradiated samples was improved and hydrophobicity was reduced.     

一种新型酰腙配体及其Sn配合物的荧光特性研究

用稳态荧光和时间分辨荧光研究了一种新型酰腙配体2-羟基甲醛-5-氯水杨酰腙(H3L)及Sn配合物(n-Bu2)Sn(HL)晶体、溶液和旋涂膜的光谱特性与分子结构的关系。实验结果表明,对H3L而言,与其稀溶液相比,晶体及旋涂膜的荧光强度依次增强,荧光峰位都有所红移,荧光寿命有所延长,其单分子跃迁能为240.2kJ.mol-1;对[(n-Bu2)Sn(HL)]而言,其晶体稳态荧光强度比在溶液中强且荧光峰位红移,旋涂膜产生了荧光猝灭,单分子跃迁能为230.4kJ.mol-1;与H3L相比较,(n-Bu2)Sn(HL)晶体的荧光强度要强接近4倍,荧光寿命变长。这些现象的物理机制是分子的共轭体系越大、分子的刚性越大其荧光强度越强,荧光寿命越长。     

Effects of an intense, high-frequency laser field on the intersubband transitions and impurity binding energy in semiconductor quantum wells

Within the framework of effective-mass approximation, using a variational method, the effect of high-frequency laser field on intersubband transitions and the binding energy of shallow-donor impurities in a semiconductor quantum well are investigated. We have found that the increase of the laser-dressing parameter leads to important effects on the electronic and optical properties of a quantum well. This gives a new degree of freedom in various device applications based on the intersubband transition of electrons.     

Photodetachment microscopy of a hydrogen negative ion in an electric field near a metal surface

According to the semi-classical theory, we study the photodetachment microscopy of H- in the electric field near a metal surface. During the photodetachment, the electron is photo-detached by a laser and the electron is drawn toward a position-sensitive detector. The electron flux distribution is measured as a function of position. Two classical paths lead the ion to any point in the classically allowed region on the detector, and waves traveling along these paths produce an interference pattern. If the metal surface perpendicular to the electric field is added, we find that the interference pattern is related not only to the electron energy and the electric-field strength, but also to the ion-surface distance. In addition, the laser polarization also has a great influence on the electron flux distribution. We present calculations predicting the interference pattern that may be seen in experiment. We hope that our study can provide a new understanding of the electron flux distribution of negative ions in an external field and surface, and can guide future experimental research on negative ion photo-detachment microscopy.     

Polaronic Effects of an Exciton in a Cylindrical Quantum Wire

The effects of exciton-optical phonon interaction on the binding energy and the total and reduced effective masses of an exciton in a cylindrical quantum wire have been investigated. We adopt a perturbative-PLL [T.D. Lee, F. Low, and D. Pines, Phys. Rev. B90 (1953) 297] technique to construct an effective Hamiltonian and then use a variational solution to deal with the exciton-phonon system. The interactions of exciton with the longitudinal-optical phonon and the surface-optical phonon have been taken into consideration. The numerical calculations for GaAs show that the influences of phonon modes on the exciton in a quasi-one-dimensional quantum wire are considerable and should not be neglected. Moreover the numerical results for heavy- and light-hole exciton are obtained, which show that the polaronic effects on two types of excitons are very different but both depend heavily on the sizes of the wire.     

Stopped-flow fluorescence studies of the interaction of a mutant form of cytochrome b5 with lipid vesicles

Cytochrome b₅ binds spontaneously to lipid vescles and also self-associates in aqueous solution. Two mutant proteins have been generated, one has a self-association constant which is less than that of the native protein, while the other has a larger self-association constant. All three proteins have Trp in the membrane-binding domain but as aqueous solutions of these proteins contain differing amounts of monomeric protein, the kinetics of fluorescence enhancement, when the proteins are mixed with lipid vesicles, are complex. Similar complex kinetics are seen when the Trp are quenched by the addition of bromolipid vesicles. The mutant which has Trp 108 and 112 both replaced by Leu does not self-associate and shows monoexponential stopped-flow fluorescence kinetics. Identical rate constants are seen with this mutant for fluorescence enhancement by POPC and fluorescence quenching by three bromolipids with bromines at the 6,7-, 9,10-, and 11,12-positions of thesn-2 acyl chain. This rate constant is only 1% of the calculated collisional rate constant and it is suggested that the reduced rate is caused by a reduction in the number of productive collisions rather than by a slow rate of penetration of the membrane-binding domain into the bilayer.     

Polaronic Effects on the Impurity Binding Energy in a Polar Crystal Slab Within an Electric Field

The effects of the interaction between electron and bulk longitudinal optical (LO) phonon and surface optical (SO) phonon on the impurity binding energy of the ground state in a polar crystal slab within an external electric field are derived by using the method of a variational wavefunction. The binding energy of the bound polaron is obtained as a function of the impurity position, the slab thickness and the electric field strength. It is found that the polaronic correction to the impurity binding energy by the SO phonon may be enhanced and that by the LO phonon may be reduced with increasing electric field strength. And the effect of the electron-phonon interaction is quite important in increasing the values of binding energy.     

Fluorescence Spectrometric Studies on the Binding of an Amino-Functionalized Ionic Liquid to Cytochrome c

The interaction of an amino-functionalized ionic liquid, 1-(2-aminoethyl)-3-butylimidazolium bromide ([NH₂C₂C₄im]Br), with cytochrome c (cyt c) at pH 7.4 was investigated using fluorescence and UV-Vis absorption spectroscopic techniques. From the experimental results, it is found that cyt c has a strong ability to quench the intrinsic fluorescence of [NH₂C₂C₄im]Br and the quenching mechanism is considered as a static quenching process. The binding constants and the number of binding sites (n) were calculated at different temperatures. The thermodynamic parameters such as free energy change (ΔG), enthalpy change (ΔH), and entropy change (ΔS) were calculated by thermodynamic equations. According to the results, the values of ΔG, ΔH, and ΔS are all negative, suggesting that interaction between [NH₂C₂C₄im]Br and cyt c is spontaneous and mainly driven by hydrogen bonding and van der Waals forces.     

Effects of high pressure on the Raman and fluorescence emission spectra of two novel 1,3,4-oxadiazole derivatives

The effects of pressure on the fluorescence emission and Raman spectra of 1,4-bis[（4-methyloxyphenyl）-1,3,4-oxadiazolyl]- 2,5-bisheptyloxyphenylene （OXD-2） and on the fluorescence emission spectra of 1,4-bis[（4-methylphenyl）- 1,3,4-oxadiazolyl]phenylene （OXD-1） are investigated using a diamond anvil cell. With the increase of pressure, the intensity of the fluorescence emission increases and reaches maxima at 13GPa for OXD-1 and at 9.6GPa for OXD-2. The effect of pressure on the peak position of the emission shows a similar trend, red shift with the increase of pressure. But at higher pressures, the intensity of emission drops down dramatically. The Raman spectra of OXD-2 indicate that there appears a structural change at ca 3GPa.     

Fluorescence intensity and anisotropy decays of the intrinsic tryptophan emission of hemoglobin measured with a 10-GHz fluorometer using front-face geometry on a free liquid surface

We measured the intensity and anisotropy decays of the intrinsic tryptophan emission from hemoglobin solutions obtained using a 10-GHz frequency-domain fluorometer and a specially designed cuvette which allows front-face excitation on a free liquid surface. The cuvette eliminates reflections and stray emissions, which become significant for low-intensity fluorescence such as in hemoglobin. Three lifetimes are detectable in the subnanosecond range. The average lifetime of hemoglobin emission is ligand dependent. The measured values of average lifetimes are 91, 174, and 184 ps for deoxy-, oxy-, and carboxyhemoglobin, respectively. Fluorescence anisotropy decays of oxy-, deoxy-, and carbonmonoxyhemoglobin can be fitted with up to three correlation times. When three components are used, the floating initial anisotropyr _o is, in each case, higher than the steady-state anisotropy of tryptophan in vitrified solution. For deoxy hemoglobin it is close to 0.4. The data are consistent with an initial loss of anisotropy from 0.4 to about 0.3 occurring in the first 2 ps.     

Effects of non-Gaussian noise on a calcium oscillation system

We investigate the effects of the non-Gaussian colored noise on a calcium oscillation system using stochastic simulation methods. It is found that the reciprocal coefficient of variance R has a maximum (R max ) with increasing noise intensity Q. The non-Gaussian noise parameter q has an important effect on the system. For some values of q (e.g., q = 0.9, q = 1.0), R has a maximum with increasing correlation time τ. Non-Gaussian noise induced spikes are more regular than Gaussian noise induced spikes when q is small and Q has large values. The R has a maximum with increasing q. Therefore, non-Gaussian noise could play more effective roles in the calcium oscillation system.     

Fluorescence Investigation on the Interaction of a Prevalent Competitive Fluorescent Probe with Entomic Odorant Binding Protein

In recent years, one prevalent competitive fluorescent probe, N-phenyl-1-naphthylamine (1-NPN), was frequently utilized to measure the binding affinity of entomic odorant binding proteins (OBPs) with diverse plant volatiles or pheromones. Nevertheless, the details and model of the binding interaction are still largely unknown, although it is vital to investigate the physiological function of OBPs. Here we studied the binding interaction between 1-NPN and OBP2, a recombinant OBP from eastern honeybee, Apis cerana, by the combination of fluorescence quenching spectra, synchronous fluorescence spectra, ultraviolet spectra, circular dichroism spectra, and molecular docking. The Stern–Volmer curve of the fluorescence quenching of OBP2 by 1-NPN indicated it was a static quenching mechanism, and the binding constants and binding number were determined, respectively. Based on the Förster theory of nonradiation energy transfer (FRET), the binding distance was calculated, and the intrinsic fluorescent energy was predicted to transfer from the donor OBP2 to the acceptor 1-NPN. Synchronous fluorescence spectra and circular dichroism spectra were used to investigate the conformational change in binding progress. The thermodynamic parameters showed that the interaction was mainly driven by hydrophobic force, which was validated by the molecular docking; meanwhile, the binding mode was revealed and one hydrogen bond was found between the nitrogen atom of 1-NPN and Glu29 of OBP2.     

激光脉冲对氢负离子在金属面附近光剥离的影响

利用闭合轨道理论和金属面附近氢负离子的双脉冲光剥离截面的计算公式,计算了氢负离子在金属面附近激光脉冲作用下的光剥离截面.计算结果表明:如果脉冲宽度远大于闭合轨道的回归周期时,它对光剥离截面的影响很小;当脉冲宽度小于闭合轨道的周期或者可以和闭合轨道的周期相比较时,光剥离截面的振荡幅度大大地减弱.光剥离截面除了与脉冲宽度有关外,还与双脉冲之间的时间延迟、相位差有关.对于某些相位差, 双脉冲光剥离截面的取值增大; 而对于另外一些相位差, 光剥离截面的取值减小.因此,可以利用脉冲激光来控制氢负离子在表面附近光剥离 关键词： 激光脉冲 光剥离截面 金属面 闭合轨道理论     

纤锌矿In_(0.19)Ga_(0.81)N/GaN量子阱中光学声子和内建电场对束缚极化子结合能的影响

用改进的Lee-Low-Pines变分方法研究纤锌矿In0.19Ga0.81N/GaN量子阱结构中束缚极化子能量和结合能等问题,给出基态结合能、不同支长波光学声子对能量和结合能的贡献随阱宽和杂质中心位置变化的数值结果.在数值计算中包括了该体系中声子频率的各向异性和内建电场对能量和结合能的影响、以及电子和杂质中心与长波光学声子的相互作用.研究结果表明,In0.19Ga0.81N/GaN量子阱材料中光学声子和内建电场对束缚极化子能量和结合能的贡献很大,它们都引起能量和结合能降低.结合能随着阱宽的增大而单调减小,窄阱中减小的速度快,而宽阱中减小的速度慢.不同支声子对能量和结合能的贡献随着阱宽的变化规律不同.没有内建电场时,窄阱中,定域声子贡献小于界面和半空间声子贡献,而宽阱中,定域声子贡献大于界面和半空间声子贡献.有内建电场时,定域声子贡献变小,而界面和半空间声子贡献变大,声子总贡献也有明显变化.在In0.19Ga0.81N/GaN量子阱中,光学声子对束缚极化子能量和结合能的贡献比GaAs/Al0.19Ga0.81As量子阱中的相应贡献(约3.2—1.8和1.6—0.3 meV)约大一个数量级.阱宽(d=8 nm)不变时,在In0.19Ga0.81N/GaN量子阱中结合能随着杂质中心位置Z0的变大而减小,并减小的速度变快.随着Z0的增大,界面和半空间光学声子对结合能的贡献缓慢减小,而定域光学声子的贡献缓慢增大.     

The influence of substrate geometry on the emission properties of a liquid metal ion source

The effect of needle radius, cone angle and shaft diameter on the threshold voltage and angular intensity — total current relationships for a Ga liquid-metal ion source (LMIS) was investigated. The variation of threshold voltage with needle geometry could be described in terms of the Taylor theory of liquid cone formation by electrostatic fields. The beam energy spread was mainly a function of total source current and was not a sensitive function of emitter geometry. Source angular intensity at a constant total current increased linearly with threshold voltage when the latter was altered due to source geometry.     

Distinct effect of xenobiotics on the metal‐binding properties of protein molecules

The X‐ray standing‐wave method was applied to study the elemental composition and molecular organization of ordered protein films of alkaline phosphatase exposed to different xenobiotics (drug compounds, lead). Binding of metal ions from triply distilled water to protein molecules has been experimentally observed. Definite differences in the arrangement of impurity metal ions in the films have been established. The considerable enhancement of protein–metal interactions is attributed to partial rearrangement of the protein native structure, induced by xenobiotics.     

Effects of positron density and temperature on ion acoustic dressed solitons in an electron–positron–ion plasma

Ion acoustic dressed solitons in a three component plasma consisting of cold ions, hot electrons and positrons are studied. Using reductive perturbation method, Korteweg–de Vries (KdV) equation and a linear inhomogeneous equation, governing respectively the evolution of first and second order potentials are derived for the system. Renormalization procedure of Kodama and Taniuti is used to obtain nonsecular solutions of these coupled equations. It is found that electron–positron–ion plasma system supports only compressive solitons. For a given amplitude of soliton on increasing the positron concentration, velocity of the KdV as well as dressed soliton increases. For any arbitrary values of soliton's amplitude and positron concentration, velocity of the dressed soliton is found to be larger than that of the KdV soliton. For small amplitude of solitons, the width of KdV as well as dressed soliton decreases as positron concentration increases and width of dressed soliton is found to be larger than that of the KdV soliton. However, for a large value of soliton's amplitude as concentration of positrons increases, instead of decreasing width of dressed soliton starts to increase.     

Generating an Inversion on a Nuclear Transition – Photopumping of 103Rh

Quite a number of proposals for a gamma-ray laser have been made over the years. One first step on the way to a gamma-ray laser is an inversion between nuclear states. For the natural isotope ¹⁰³Rh we have the favorable condition that there are two low-lying nuclear levels at energies of 357 keV and 295 keV with lifetimes of 107 ps and 9.7 ps, respectively. With two Nuclear Resonance Fluorescence (NRF) measurements the population of these low-lying levels via feeding from higher-lying levels was investigated. Altogether 26 higher-lying nuclear levels that show a branching to one or even both interesting low-lying levels have been found. Summing over all contributions from these feeding levels this results in a population inversion between the levels at 357 keV and 295 keV of ¹⁰³Rh. This revised version was published online in August 2006 with corrections to the Cover Date.