Laser action from 1,3,5,7-tetramethyl-2,6-diethyl-8-n-propyl pyrromethene-BF2

We measured spectroscopic and laser action properties of a novel 8-position substituted pyrromethene-BF2, namely 1,3,5,7-tetramethyl-2,6-diethyl-8-n-propyl pyrromethene-BF2 complex. The laser action was performed with the corresponding dye solution in ethanol, which was placed in a Littman-type laser cavity pumped by the second harmonic of a Q-switched Nd:YAG laser. The spectroscopic measurements clearly indicated that the corresponding dye solution in ethanol exhibited intense absorption in the visible spectral region with large fluorescence quantum yield. It possesses rather low triplet-triplet absorption in the spectral region 460-550 nm and almost negligible triplet-triplet absorption in the lasing spectral region. As a consequence, it lases nearly as efficiently as commercially available benchmark laser dyes such as Rhodamine-6G and outperformed them in wavelength tunability in our laser cavity and pump geometry. (C) 2002 Optical Society of America.

Serie Vídeos tutoriales para fonética. Video 6. Praat: doing phonetics by computer (Parte 2: Propiedades acústicas de los sonidos del habla observables en oscilogramas)

Esta es una colección de 10 vídeos tutoriales que pueden ser empleados como material educativo en los cursos de fonética básica en el ámbito universitario. Los vídeos 1-3 tratan aspectos relacionados con la grabación: el tipo de micrófonos que se emplean, las clases de espacios en las que se suelen llevar a cabo la captura de señales de audio y las grabadoras que se suelen emplear. El vídeo 4 explora técnicas de captura y observación de datos de flujo y presión en fonética aerodinámica. Los vídeos 5-10 presentan información sobre los principales usos que se le brindan al programa Praat (Boersma y Weenink, 2014) en los estudios actuales de fonética acústica, desde la clase de información sobre modos de articulación de las consonantes que se puede identificar en oscilogramas hasta la creación de señales sonoras sintetizadas por medio de unos procedimientos que tiene el programa para tal propósito, los cuales son susceptibles de ser empleados en experimentos de percepción auditiva.

Serie Vídeos tutoriales para fonética. Video 10. Praat: doing phonetics by computer (Parte 6: Manipulación y síntesis de señales sonoras)

Esta es una colección de 10 vídeos tutoriales que pueden ser empleados como material educativo en los cursos de fonética básica en el ámbito universitario. Los vídeos 1-3 tratan aspectos relacionados con la grabación: el tipo de micrófonos que se emplean, las clases de espacios en las que se suelen llevar a cabo la captura de señales de audio y las grabadoras que se suelen emplear. El vídeo 4 explora técnicas de captura y observación de datos de flujo y presión en fonética aerodinámica. Los vídeos 5-10 presentan información sobre los principales usos que se le brindan al programa Praat (Boersma y Weenink, 2014) en los estudios actuales de fonética acústica, desde la clase de información sobre modos de articulación de las consonantes que se puede identificar en oscilogramas hasta la creación de señales sonoras sintetizadas por medio de unos procedimientos que tiene el programa para tal propósito, los cuales son susceptibles de ser empleados en experimentos de percepción auditiva.

Synthesis of (±)-7,8-epoxy-4-basmen-6-one by a transannular cyclization strategy

The first synthesis of the cembranoid natural product (±)-7,8-epoxy-4-basmen-6- one (1) is described. Key steps of the synthetic route include the cationic cyclization of the acid chloride from 15 to provide the macrocycle 16, and the photochemical transannular radical cyclization of the ester 41 to form the tricyclic product 50. Product 50 was transformed into 1 in ten steps. Transition-state molecular modeling studies were found to provide accurate predictions of the structural and stereochemical outcomes of cyclization reactions explored experimentally in the development of the synthetic route to 1. These investigations should prove valuable in the development of transannular cyclization as a strategy for synthetic simplification.

Structural and mechanistic study of monoalkyl diazenes. Synthesis, characterization, and reactivity of 1,6-didehydro[10]annulene

Methodology for the preparation of allenes from propargylic hydrazine precursors under mild conditions is described. Oxidation of the propargylic hydrazines, which can be readily prepared from propargylic alcohols, with either of two azo oxidants, diethyl azodicarboxylate (DEAD) or 4-methyl 1,2-triazoline-3,5-dione (MTAD), effects conversion to the allenes, presumably via sigmatropic rearrangement of a monoalkyl diazene intermediate. This rearrangement is demonstrated to proceed with essentially complete stereospecificity. The application of this methodology to the preparation of other allenes, including two that are notable for their reactivity and thermal instability, is also described.

The structural and mechanistic study of a monoalkyl diazene intermediate in the oxidative transformation of propargylic hydrazines to allenes is described. The use of long-range heteronuclear NMR coupling constants for assigning monoalkyl diazene stereochemistry (E vs Z) is also discussed. Evidence is presented that all known monoalkyl diazenes are the E isomers, and the erroneous assignment of stereochemistry in the previous report of the preparation of (Z)-phenyldiazene is discussed.

The synthesis, characterization, and reactivity of 1,6-didehydro[10]annulene are described. This molecule has been recognized as an interesting synthetic target for over 40 years and represents the intersection of two sets of extensively studied molecules: nonbenzenoid aromatic compounds and molecules containing sterically compressed π-systems.The formation of 1,5-dehydronaphthalene from 1 ,6-didehydro[10]annulene is believed to be the prototype for cycloaromatizations that produce 1,4-dehydroaromatic species with the radical centers disposed anti about the newly formed single bond. The aromaticity of this annulene and the facility of its cycloaromatization are also analyzed.

1. Astronomical photometry at wavelengths of 8.5, 10.5, and 11.6 µm. 2. Infrared emission from asteroids at wavelengths of 8.5, 10.5, and 11.6 µm

The purpose of this thesis is to present new observations of thermal-infrared radiation from asteroids. Stellar photometry was performed to provide standards for comparison with the asteroid data. The details of the photometry and the data reduction are discussed in Part 1. A system of standard stars is derived for wavelengths of 8.5, 10.5 and 11.6 µm and a new calibration is adopted. Sources of error are evaluated and comparisons are made with the data of other observers.

The observations and analysis of the thermal-emission observations of asteroids are presented in Part 2. Thermal-emission lightcurve and phase effect data are considered. Special color diagrams are introduced to display the observational data. These diagrams are free of any model-dependent assumptions and show that asteroids differ in their surface properties.

On the basis of photometric models, (4) Vesta is thought to have a bolometric Bond albedo of about 0.1, an emissivity greater than 0.7 and a true radius that is close to the model value of 300^(+50)_(-30)km. Model albedos and model radii are given for asteroids 1, 2, 4, 5, 6, 7, 15, 19, 20, 27, 39, 44, 68, 80, 324 and 674. The asteroid (324) Bamberga is extremely dark with a model (~bolometric Bond) albedo in the 0.01 - 0.02 range, which is thought to be the lowest albedo yet measured for any solar-system body. The crucial question about such low-albedo asteroids is their number and the distribution of their orbits.

消色差相位匹配在光参量啁啾脉冲放大中的应用

Optical parametric chirped-pulse amplification (OPCPA) supplies broadband gain for ultrashort pulses. A new theoretic explanation of OPCPA has been obtained by introducing the concept of tilted pulse front in this paper, and the distribution of broadband amplification has been twice expanded by introducing the technology of achromatic phase matching (APM). The prospect of APM in OPCPA has been discussed in detail. Finally, a design for the amplification of chirped pulses at 1600 nm has been firstly proposed and numerically simulated. (C) 2004 Elsevier B.V. All rights reserved.

Observations of 1-6 MeV Jovian electrons at 1 AU and a study of their propagation

The 1-6 MeV electron flux at 1 AU has been measured for the time period October 1972 to December 1977 by the Caltech Electron/Isotope Spectrometers on the IMP-7 and IMP-8 satellites. The non-solar interplanetary electron flux reported here covered parts of five synodic periods. The 88 Jovian increases identified in these five synodic periods were classified by their time profiles. The fall time profiles were consistent with an exponential fall with τ ≈ 4-9 days. The rise time profiles displayed a systematic variation over the synodic period. Exponential rise time profiles with τ ≈ 1-3 days tended to occur in the time period before nominal connection, diffusive profiles predicted by the convection-diffusion model around nominal connection, and abrupt profiles after nominal connection.

The times of enhancements in the magnetic field, │B│, at 1 AU showed a better correlation than corotating interaction regions (CIR's) with Jovian increases and other changes in the electron flux at 1 AU, suggesting that │B│ enhancements indicate the times that barriers to electron propagation pass Earth. Time sequences of the increases and decreases in the electron flux at 1 AU were qualitatively modeled by using the times that CIR's passed Jupiter and the times that │B│ enhancements passed Earth.

The electron data observed at 1 AU were modeled by using a convection-diffusion model of Jovian electron propagation. The synodic envelope formed by the maxima of the Jovian increases was modeled by the envelope formed by the predicted intensities at a time less than that needed to reach equilibrium. Even though the envelope shape calculated in this way was similar to the observed envelope, the required diffusion coefficients were not consistent with a diffusive process.

Three Jovian electron increases at 1 AU for the 1974 synodic period were fit with rise time profiles calculated from the convection-diffusion model. For the fits without an ambient electron background flux, the values for the diffusion coefficients that were consistent with the data were k_x = 1.0 - 2.5 x 10²¹ cm²/sec and k_y = 1.6 - 2.0 x 10²² cm²/sec. For the fits that included the ambient electron background flux, the values for the diffusion coefficients that were consistent with the data were k_x = 0.4 - 1.0 x 10²¹ cm²/sec and k_y = 0.8 - 1.3 x 10²² cm²/sec.

光学领域里的一对奇葩——介绍2005年诺贝尔物理学奖

2005年诺贝尔物理学奖授于了光学研究领域里的两项原创性工作：1963年美国物理学家罗伊·格劳伯（R．J．Glauber 1925～）提出的“相干性量子理论”，以及1983年美国物理学家约翰·霍尔（J．L．Hall．1934～）和德国物理学家特奥多尔·亨施（T．W．Hansch．1941～）利用激光的特性对精确测量技术所作的发展。近些年来诺贝尔物理学奖频频惠顾光学研究领域。如2001年诺贝尔物理学奖授予了从事玻色一爱因斯坦凝聚的相关研究、1997年诺贝尔物理学奖授予华裔科学家朱棣文从事的激光冷却和俘获原子