Excited-state absorption in a terpyridyl platinum(II) pentynyl complex

The singlet excited-state lifetime of a terpyridyl platinum(II) pentynyl complex was determined to be 268+/-87 ps by fitting femtosecond transient absorption data, the triplet excited-state lifetime was found to be 62 ns by fitting nanosecond transient absorption decay data, and the triplet quantum yield was measured to be 0.16. A ground-state absorption cross section of 2.5 x 10(-19) cm(2) at 532 nm was deduced from UV-vis absorption data. Excited-state absorption cross sections of 3.5 x 10(-17) cm(2) (singlet) and 4.5 x 10(-17) cm(2) (triplet) were obtained by using a five-level dynamic model to fit open-aperture Z scans at picosecond and nanosecond pulse widths and a variety of pulse energies.     

时间分辨傅氏变换红外光谱方法中的定时直流成分

在常规的傅里叶变换红外光谱学中，干涉图的直流成分为∫＾∞０Ｂ（σ）ｄσ，而在时间分辨ＦＴＩＲ中，直流成分Ｉｄｅ成为∫（∞，０）Ｂ（σ，τ）ｄσ，即与信号出现的时间τ有关，称为定量直流成分。     

Efficient ternary organic solar cells with high absorption coefficient DIB-SQ as the third component

A series of organic solar cells(OSCs) are prepared with PTB7:PC_(71) BM as the host materials and DIB-SQ as the third component. The power conversion efficienty(PCE) of OSCs can be improved from 6.79% to 7.92% by incorporating 6 wt%DIB-SQ into donors, resulting from the enhanced short circuit current density(J_(SC) and fill factor(FF). The increased JSCof the optimized ternary OSCs should be attributed to the enhanced photon harvesting of teranry active layer by incorporating DIB-SQ. Meanwhile, FF of the optimized ternary OSCs should be due to the optimied phase separation. The open circuit voltage(V_(OC)) of tenray OSCs can be maintained at a constant of 0.75 V, indicating that all photogenerated holes willl be transported along the channels formed by PTB7.     

Effects of Particle Shape and Microstructure on Effective Nonlinear Response

We consider a binary granular composite medium, in which two materials have high-order nonlinearities. The effect of particle shape on effective nonlinear response (ENR) is investigated by assuming all the particles to be shaped as uniaxial ellipsoid. We discuss two types of arrangements of particles: 1) parallel axes (Case I); 2) random axes (Case II). During the process of numerical calculation, one component material is assumed to be linear, and two kinds of conductors are assumed to be at high conducting contrast. We find that: 1) the shape effect on ENR is possibly strong; 2) the enhanced ENR can even be obtained by choosing particles of appropriate ellipsoidal shapes; 3) the ENR enhancement predicted by Case I is much stronger than that by Case II.     

六硼酸钡Ba3B6O9(OH)6热力学性质研究

本文通过水热法合成了六硼酸钡Ba3B6O9(OH)6,并通过 X射线衍射(XRD)、红外光谱(FT-IR)、综合热分析法(TG-DSC) 和扫描电子显微镜(SEM)对其进行了表征。通过微量热仪测定了Ba3B6O9(OH)6在 0.9995mol·dm-3HCl(aq) 的摩尔溶解焓为(32.34±0.58) kJ·mol-1,并计算了其标准摩尔生成焓为-(7130.664±4.2) kJ·mol-1。此外,通过基团贡献法估算了[B6O9(OH)6]6- 的摩尔生成焓为-5517.744 kJ·mol-1。     

应用NMR技术确证5-(R)-(1-孟氧基)-2(5H)-呋喃酮与苯甲醛肟1,3-偶极环加成产物的结构

5-(R)-(l-孟氧基)-2(5H)-呋喃酮(A)与苯甲醛肟(B)进行1,3-偶极环加成反应时得到两个产物, 我们应用NOE及HMBC技术确证了它们的结构. 由于反应物(A)的绝对构型已经X-射线单晶衍射法确证, 因此通过NMR研究产物呋喃酮环上各手性碳的关系, 最终确立产物的绝对构型.     

Equilibrium time correlation functions in the low-density limit

We consider a system of hard spheres in thermal equilibrium. Using Lanford's result about the convergence of the solutions of the BBGKY hierarchy to the solutions of the Boltzmann hierarchy, we show that in the low-density limit (Boltzmann-Grad limit): (i) the total time correlation function is governed by the linearized Boltzmann equation (proved to be valid for short times), (ii) the self time correlation function, equivalently the distribution of a tagged particle in an equilibrium fluid, is governed by the Rayleigh-Boltzmann equation (proved to be valid for all times). In the latter case the fluid (not including the tagged particle) is to zeroth order in thermal equilibrium and to first order its distribution is governed by a combination of the Rayleigh-Boltzmann equation and the linearized Boltzmann equation (proved to be valid for short times).Supported in part by NSF Grant PHY 78-22302.     

Rate measurement of D(0)-->K+pi(-)pi(0) and constraints on D(0) -- D(0) mixing

We present an observation and time-integrated rate measurement of the decay D(0)-->K(+)pi(-)pi(0) produced in 9 fb(-1) of e(+)e(-) collisions near the Upsilon(4S) resonance. The signal is inconsistent with an upward fluctuation of the background by 4.9 standard deviations. We measured the time-integrated rate of D(0)-->K(+)pi(-)pi(0) normalized to the rate of D(0)-->K(+)pi(-)pi(0) to be 0.0043(+0.0011)(-0.0010) (stat)+/-0.0007 (syst). This decay can be produced by doubly Cabibbo-suppressed decays or by the D(0) evolving into a D(0) through mixing, followed by a Cabibbo-favored decay to K(+)pi(-)pi(0). We also found the CP asymmetry A = (9(+25)(-22))% be consistent with zero.     

Metal-insulator transition in SrTiO(3-x) thin films induced by frozen-out carriers

We report optical, electrical and magnetotransport properties of oxygen deficient SrTiO(3) (SrTiO(3-x)) thin films fabricated by pulsed laser deposition technique. The oxygen vacancies (O(vac)) in the thin film are expected to be uniform. By comparing its electrical properties to those of bulk SrTiO(3-x), it was found that O(vac) in bulk SrTiO(3-x) is far from uniform over the whole material. The metal-insulator transition (MIT) observed in the SrTiO(3-x) film was found to be induced by the carrier freeze-out effect. The low temperature frozen state can be reexcited by Joule heating, electric and intriguingly magnetic field.     

Galactic-cosmic-ray-produced 3He in a ferromanganese crust: any supernova 60Fe excess on earth?

An excess of 60Fe in 2.4-3.2 x 10(6) year old ferromanganese crust (237 KD) from the deep Pacific Ocean has been considered as evidence for the delivery of debris from a nearby supernova explosion to Earth. Extremely high ;{3}He/;{4}He (up to 6.12 x 10(-3)) and 3He concentrations (up to 8 x 10(9) atoms/g) measured in 237 KD cannot be supernova-derived. The helium is produced by galactic cosmic rays (GCR) and delivered in micrometeorites that have survived atmospheric entry to be trapped by the crust. 60Fe is produced by GCR reactions on Ni in extraterrestrial material. The maximum (3)He/(60)Fe of 237 KD (80-850) is comparable to the GCR (3)He/(60)Fe production ratio (400-500) predicted for Ni-bearing minerals in iron meteorites. The excess 60Fe can be plausibly explained by the presence of micrometeorites trapped by the crust, rather than injection from a supernova source.     

Detection and characterization of boric acid and borate ion binding to cytochrome c using multiple quantum filtered NMR

The application of multiple quantum filtered (MQF) NMR to the identification and characterization of the binding of ligands containing quadrupolar nuclei to proteins is demonstrated. Using relaxation times measured by MQF NMR multiple binding of boric acid and borate ion to ferri and ferrocytochrome c was detected. Borate ion was found to have two different binding sites. One of them was in slow exchange, k(diss) = 20 +/- 3 s(-1) at 5 degrees C and D(2)O solution, in agreement with previous findings by (1)H NMR (G. Taler et al., 1998, Inorg. Chim. Acta 273, 388-392). The triple quantum relaxation of the borate in this site was found to be governed by dipolar interaction corresponding to an average B-H distance of 2.06 +/- 0.07 A. Other, fast exchanging sites for borate and boric acid could be detected only by MQF NMR. The binding equilibrium constants at these sites at pH 9.7 were found to be 1800 +/- 200 M(-1) and 2.6 +/- 1.5 M(-1) for the borate ion and boric acid, respectively. Thus, detection of binding by MQF NMR proved to be sensitive to fast exchanging ligands as well as to very weak binding that could not be detected using conventional methods.     

用X射线衍射法测定氮化镓马赛克结构中的面内扭转角

Ⅲ-Ⅴ族氮化物半导体材料在发光二极管、激光器和探测器方面有着广泛的应用,采用高分辨X射线衍射来测定用金属有机化学气相沉淀法在蓝宝石衬底上生长的氮化镓外延层马赛克结构的扭转角,分别研究了(0002)、(1013)、(1012)、(1011)、(2021)五个面的X射线摇摆曲线,并且用Pseudo-Voigt方程拟合每一个面的摇摆曲线,我们利用外推法很方便地测得氮化镓外延薄膜的面内扭转角。另外我们采用同步辐射X射线掠入射衍射对样品进行(1100)面反射φ扫描直接测得面内扭转角,对第一种方法进行验证,两种方法测量结果相同。从而提供一种简单、方便的GaN外延层的面内扭转角的测试方法,为深入研究GaN材料奠定良好基础。     

Fluorescence Correlation Spectroscopy of Gold Nanoparticles

Diffusion dynamics of gold nanoparticles (GNPs) was studied by fluorescence correlation spectroscopy (FCS). The fluorescence was studied by exciting the particles by green laser (532 nm), which is far from longitudinal plasmon band of nanorods. Transmission electron microscope (TEM) and UV-Vis-NIR spectrometer were used to characterize the gold nanoparticles. Despite their low quantum yields, GNPs possess the native fluorescence. The excellent antiphotobleaching behavior of gold nanorods leads to prospects of using FCS for its detailed studies. Using FCS, dynamic information can be extracted from the fluorescence fluctuations in the system by autocorrelation function. Maximum entropy method (MEMFCS) was used to identify the number of distinct components present in the system. The particle sizes obtained from FCS were found to be higher (by few orders of magnitude) compared to TEM analysis. This might be due to the possible contributions from cetyltrimethyl ammonium bromide (CTAB) capping in the system.     

Compensating for frequency shifts in modulation transfer spectroscopy caused by residual amplitude modulation

Residual amplitude modulation (RAM) distorts saturated absorption signals, limiting the accuracy of optical frequency references based on modulation transfer spectroscopy (MTS). Described here are two independent means by which RAM is produced in these references: (1) by the modulator and (2) when the overlap of the optical fields in the saturable absorber is asymmetric. Methods to vary RAM generated by either mechanism will be outlined and these will be used to show how RAM arising from one effect can be cancelled by the other. A theoretical treatment of MTS signals in references containing RAM is given and used to evaluate the level of signal distortion allowing the conditions for RAM cancellation to be determined. This technique is applied to improve the frequency accuracy of a reference by an order of magnitude.     

插入电荷控制层对蓝色OLED发光性能的提高

用蓝色有机荧光材料N⁶,N⁶,N¹²,N¹²-tetrap-tolylchrysene-6,12-diamine （DNCA）作为发光层,在发光层中间以及发光层与电子传输层之间插入2-methyl-9,10-di（2-napthyl）anthracene （MADN） 和9,10-di（2-naphthyl）anthracene （ADN） 作为电荷控制层,制备了结构为ITO/NPB（40 nm）/DNCA（15 nm）/MADN（3 nm）/DNCA（15 nm）/ADN（3 nm）/Bphen（30 nm）/LiF（0.8 nm）/Al（120 nm）的蓝色有机电致发光器件（OLED）。该器件的最大电流效率和最大亮度分别为5.6 cd/A和23 310 cd/m²。与传统的单发光层器件相比,最大电流效率和最大亮度分别提高了70%和87%。器件发光性能的提高可归结于两个电荷控制层在整个器件中的协同作用。第一电荷控制层MADN的作用主要是将发光层区域分成两个部分,从而扩大了激子在发光层中的复合区域;第二电荷控制层ADN可以有效地将空穴限制在发光层中,避免了激子在电子传输层中形成的无辐射跃迁从而提高了器件的发光性能。     

Electromagnetic Resonance of Astigmatic Gaussian Beam to the High Frequency Gravitational Waves

The high frequency gravitational waves(around 10~8-10~(12) Hz) could interact with a specially designed electromagnetic resonance system.It is found that the power of transverse perturbative photon flux(PPF) of an electromagnetic resonance system can be improved significantly by virtue of an astigmatic Gaussian beam.Correspondingly the signal-to-noise ratio(SNR) would also be improved.When the eccentric ratio of waist satisfying w_(0x):w_(0y)1,the peak value of signal photon flux could be raised by 2-4 times with typical systematic parameters,while the background photon flux would be depressed.Therefore,the ratio of transverse PPF to background photon flux(i.e.,SNR)can be further improved 3-8 times with dimensionless amplitude of relic gravitational wave h_t=10~(-36).     

Validation of computations by high pressure measurements: Solutions to problems that experiments cannot solve

Abstract

Calculations of the properties of condensed matter systems can be crucially tested by comparison with their experimental pressure behavior. When validated by such a comparison theoretical models become reliable computer experiments and can be used to explore properties of the system which are intrinsically unobservable by experiment alone.

Three examples are given of such methods:

(i) The behavior of wurtzite indium nitride under pressure which is shown to be due to a second-order isostructural phase transition.

(ii) The instability of tetrahedrally bonded semiconductors (Ge) under pressure which turns out to be related to a second-order process.

(iii) The explanation of the lattice dynamics of a-boron at ambient conditions which can be understood only by comparison of its high pressure behavior with calculations.     

Cosmic ray test for a T0 detector

The endcap of time-of-flight (ETOF) detector in BES (Beijing Spectrometer) III is planned to be upgraded by using multi-gap resistive plate chambers (MRPCs) and the designed time resolution of the MRPCs is around 50 ps. Thus a time-zero (T0) detector needs to be built to offer a high quality reference time for the MRPCs beam test. So a T0 detector is built using plastic scintillator tiles (BC420) to couple with four fast phototubes (PMTs, Hamamatsu H6533). The timing properties of the detector is studied by using a cosmic ray test and factors related to the time resolution, such as plastic scintillator size, readout mode and angle effects, are discussed. T0 detector timing resolutions of ～41-62 ps are achieved, which means that the T0 detector can be used in the MRPC beam test.     

Suppression of antiferromagnetic interactions through Cu vacancies in Mn-substituted CuInSe2 chalcopyrites

Stoichiometric and Cu-poor Cu(0.95-x)Mn(0.05)InSe(2) (x = 0-0.20) compounds were synthesized by high-temperature, solid-state reactions. The presence of copper vacancies is revealed by Rietveld refinements of combined neutron and x-ray powder diffraction data. The antiferromagnetic interaction is depressed by the copper deficiency, which may be explained as the competition between the antiferromagnetic Mn-Se-Mn superexchange interaction and the hole-mediated ferromagnetic exchange induced by the copper vacancy. The introduction of copper vacancies is proposed to be a viable route to impart carrier-mediated ferromagnetic exchange in the chalcopyrite-based dilute magnetic semiconductors.     

The OPCL control method for entrainment,model-resonance,and migration actions on multiple-attractor systems

A survey is given of three different control objectives that can be achieved with the use of the Open-Plus-Closed-Loop (OPCL) control method, developed by Jackson and Grosu. For a system that can be characterized by N first-order ordinary differential equations, these objectives are: (1) the asymptotic entrainment of the system's dynamics to a prescribed "goal" dynamics, g(t); (2) an experimental-search method to determine an approximate dynamic model; (3) the transferal of the system from one attractor to any "target" attractor. For one class of systems, this may be accomplished without a model, by using only a short-duration record of the natural dynamics in the target attractor, as demonstrated experimentally using the Chua system. (c) 1997 American Institute of Physics.