Band-selective measurements of electron dynamics in VO2 using femtosecond near-edge x-ray absorption

We report on the first demonstration of femtosecond x-ray absorption spectroscopy, made uniquely possible by the use of broadly tunable bending-magnet radiation from "laser-sliced" electron bunches within a synchrotron storage ring. We measure the femtosecond electronic rearrangements that occur during the photoinduced insulator-metal phase transition in VO2. Symmetry- and element-specific x-ray absorption from V2p and O1s core levels (near 500 eV) separately measures the filling dynamics of differently hybridized V3d-O2p electronic bands near the Fermi level.     

Evidence of the kappa1-1 law in a high-Reynolds-number turbulent boundary layer

Dimensional analysis and overlap arguments lead to a prediction of a region in the streamwise velocity spectrum of wall-bounded turbulent flows in which the dependence on the streamwise wave number, kappa(1), is given by kappa(1)(-1). Some recent experiments have questioned the existence of this region. In this Letter, experimental spectra are presented which support the existence of the kappa(1)(-1) law in a high-Reynolds-number boundary layer. This Letter presents the experimental results and discusses the theoretical and experimental issues involved in examining the existence of the kappa(1)(-1) law and the reasons why it has proved so elusive.     

Pulsed laser deposition of oriented barium ferrite (BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript>) thin films

Barium ferrite (BaFe₁₂O₁₉) thin films have been deposited by pulsed laser deposition at 900 °C in 250 mTorr oxygen on Si substrates with Pt(111) underlayers. The barium ferrite films contained platelet grains and a small amount of acicular grains, with sizes of 300 nm and 80×300 nm, respectively, and had a surface roughness of 11 nm. Vibrating-sample magnetometer measurements indicated that the BaFe₁₂O₁₉ films have some perpendicular orientation, with a perpendicular squareness of 0.64 and an in-plane squareness of 0.28. The saturation magnetization is about 190 emu/cc. The perpendicular and in-plane coercivities are 2.1 kOe and 1.6 kOe, respectively. PACS 75.50.Ss; 75.60.Ej; 75.70.Ak; 68.55.Ik     

Even-tempered Slater-type orbitals revisited: from hydrogen to krypton

Even-tempered Slater-type orbital basis sets were developed in 1973, based on total atomic energy optimization. Here, we revisit ET STOs and propose new sets based on past experience and recent computational studies. From preliminary atomic and molecular tests, these sets are shown to be very well balanced and to perform, at lower cost, almost as well as a very large (close to complete) basis set.     

Deep-notch, ultracompact long-period grating in a large-mode-area photonic crystal fiber

An extremely short long-period grating (LPG) with strong resonance has been developed in a large-mode-area photonic crystal fiber (PCF) by use of the heat source of a CO2 laser. We believe that such a LPG in pure silica PCF is the first example to be obtained with the point-by-point technique. The fabrication method is simple and repeatable. The resulting LPG has 8 periods, written by a CO2 laser, within a 2.8-mm length of fiber, which yields a deep notch of core-cladding mode coupling of -31.5 dB at the telecommunication wavelength of 1529.2 nm, with a FWHM of approximately 0.7 nm. The principal advantages of this LPG are that it is practical, cost effective, and compact.     

Pulsed-laser-deposited epitaxial aluminum nitride films on (111) Si for surface acoustic-wave applications

Epitaxial (001) aluminum nitride (AlN) thin films on (111) Si substrates are prepared using pulsed-laser deposition. The epitaxial structure of the as-prepared thin films is characterized by checking the X-ray-diffraction θ-2 θ scan and pole-figure, using scanning electron microscopy, infrared radiation (IR) spectroscopy and Raman spectroscopy. The surface acoustic-wave resonance at 345 MHz for a 1.5 μm thick AlN film on a (111) Si substrate is observed using an inter-digital electrode. Received: 18 September 2001 / Accepted: 29 January 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +86-25/359-5535, E-mail: liujm@nju.edu.cn     

圆形面偶极层的静电势

讨论了圆形面偶极层静电势问题的正确解法,阐明了对于延拓法的正确理解,给出了有限间距时圆形平行板（分别带有异性面电荷）的静电势问题。     

Solid phase synthesis of carbocyclic l-2'-deoxynucleosides

[reaction: see text] Carbocyclic L-2'deoxynucleosides 17 were synthesized on solid phase in four steps from the appropriately protected intermedate 11. The Mitsunobu reaction was used as a condensation method between the carbocyclic moiety and heterocyclic bases. The regioselectivity of the carbocyclic nucleosides was compared between the solid and solution phase syntheses.     

Experimental study of sound propagation in a flexible duct

Propagation of sound in a flexible duct is investigated both theoretically and experimentally. Strong coupling of sound and flexural waves on the duct wall is found when the wall-to-air mass ratio is of the order of unity. The axial phase speed of sound approaches the in vacuo speed of flexural waves (subsonic in this case) at low frequencies. However, a speed higher than the isentropic sound speed in free space (340 m/s) is found beyond a critical frequency which is a function of the mass ratio. Experiments using a duct with a finite section of tensioned membrane are compared with the propagating modes pertaining to the infinite membrane model. Satisfactory quantitative agreement is obtained and the measured phase speed ranges from 8.3 to 1348 m/s. In the moderate frequency range, the theory predicts high spatial damping rate for the subsonic waves, which is consistent with the experimental observation that subsonic waves become increasingly undetectable as the frequency increases. Substantial sound reflection is observed at the interface between the rigid and the flexible segments of the duct without cross-section discontinuity, which, together with the high spatial damping, could form a basis for passive control of low-frequency duct noise.     

基于DSP的新一代液晶光电图形发生器

液晶光电图形发生器选用先进的液晶显示器件,在计算机的控制下可根据实际测量的需求产生出各种所需的目标图形。针对第一代光电图形发生器数据传输速度过慢等问题,研制了新一代基于DSP的光电图形发生器,采用通用异步接收/发送通信外设的接口方式,通过高性能DSP与FPGA进行图形传输,利用专用的液晶驱动芯片完成图形显示。结果表明,该装置提高了传统光学测量中对目标更换的效率和图形传输速度,实现了从目标到探测的全光电化测量。