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121.
S.P. Belov L.I. Gershstein A.F. Krupnov A.V. Maslovskij Š. Urban V. Špirko D. Papoušek 《Journal of Molecular Spectroscopy》1980,84(1):288-304
Using the vibration-inversion-rotation Hamiltonian for ammonia [V. ?pirko, J. M. R. Stone, and D. Papou?ek, J. Mol. Spectrosc.60, 159–178 (1976)], a modified theory is worked out for the Δk = ±3n interactions between the inversion-rotation energy levels of NH3 which takes into account the large amplitude inversion motion. Eighty frequencies of inversion and inversion-rotation transitions and two perturbation-allowed transitions in the ν2 state of 14NH3 are measured in the far-infrared region around 1 THz (≈33 cm?1), mostly with the microwave accuracy, by the radiofrequency spectrometer with acoustic detector. By a least-squares fit of these data and the data of the infrared-microwave two-photon and infrared heterodyne measurements of the ν2 band, a set of molecular constants for the ν2 state of 14NH3 is obtained which reproduces the submillimeterwave data with the accuracy of the experiment. 相似文献
122.
123.
Luuk H. Karsten 《Physics letters. [Part B]》1981,104(4):315-319
A very short proof of a no-go theorem for putting fermions on a lattice is given using the Poincaré-Hopf theorem. The no-go theorem forbids the lattice formulation of theories with handed fermions without species doubling. Examples of such theories are chiral invariant QCD and the Weinberg-Salam-Glashow model. We give arguments why it could be possible to circumvent the no-go theorem by relaxing one of the assumptions, viz. bilinearity of the action in the fermion fields. 相似文献
124.
Urban MW Kinnick RR Greenleaf JF 《The Journal of the Acoustical Society of America》2005,118(6):3465-3472
Detection of calcifications in breast is an important problem in the diagnosis of breast cancer. Vibro-acoustography is a recently developed method that uses the radiation force of ultrasound to create images of the mechanical response of an object at a low frequency using the magnitude or phase of the response. Small spheres are used to explore the use of the phase of vibration as a contrast modality for use in detection and identification of calcifications in breast tissue. An experiment is presented to measure the magnitude and phase of vibration at different frequencies. The theoretical and experimental results are compared for spheres of two different sizes. Phase images are shown in which five spheres of different density can be clearly distinguished from each other. With phase measurements and images, it is demonstrated that predictable image contrast exists for spheres of different density embedded in a viscoelastic medium. 相似文献
125.
Using electron holography in a transmission electron microscope, we obtained direct evidence for the reduction of negative charge at grain boundary dislocations in Ca-doped YBa2Cu3O7 (YBCO) when compared to undoped YBCO. Because of the finite width of the valence band in the superconducting CuO2 planes, the negative grain boundary charge can lead to a depletion of electron holes available for superconductivity. A significant reduction in the size of the perturbed region in the Ca-doped samples appears to be the principal mechanism for the improved interfacial superconductivity. 相似文献
126.
E. O. Podsvirova R. M. Lieder A. A. Pasternak S. Chmel W. Gast Ts. Venkova H. M. Jäger L. Mihailescu G. de Angelis D. R. Napoli A. Gadea D. Bazzacco R. Menegazzo S. Lunardi W. Urban Ch Droste T. Morek T. Rzaca-Urban G. Duchêne 《The European Physical Journal A - Hadrons and Nuclei》2004,21(1):1-6
Lifetimes have been measured for dipole bands in 141Eu using DSAM. The deduced B(M1) and B(E2) values as well as B(M1)/B(E2) ratios are compared with calculations in the framework of the TAC (Tilted Axis Cranking) and SPAC (Shears mechanism with Principal Axis Cranking) models. The dipole bands can be interpreted as magnetic rotational bands.Received: 6 April 2004, Revised: 14 May 2004, Published online: 13 July 2004PACS:
21.10.-k Properties of nuclei; nuclear energy levels - 21.10.Re Collective levels - 21.10.Tg Lifetimes - 27.60. + j
相似文献
127.
Johannes?Winkler Ernst?Urban Christian R.?NoeEmail author 《Monatshefte für Chemie / Chemical Monthly》2004,135(1):109-116
Summary. A synthesis of the amino sugar 2-amino-2,3-didesoxyribose is described. Starting from D-glucosamine, -methylfuranoside was obtained in eight steps in 20% yield. This carbohydrate is a novel building block for nucleosides and for backbone modified antisense oligonucleotides with 2–5 amide linkages. 相似文献
128.
Using a Bayesian approach a general method is developed to assess error bars on predictions made by models fitted to data. The error bars are estimated from fluctuations in ensembles of models sampling the model-parameter space with a probability density set by the minimum cost. The method is applied to the development of interatomic potentials for molybdenum using various potential forms and databases based on atomic forces. The calculated error bars on elastic constants, gamma-surface energies, structural energies, and dislocation properties are shown to provide realistic estimates of the actual errors for the potentials. 相似文献
129.
We show that frequency and intensity noise in a Nd:YAG laser are correlated to a high degree and can be traced to the same underlying cause, namely, power fluctuations of the pump source. Because of this correlation, simultaneous suppression of frequency and intensity noise by 30 dB is achieved by means of a single actuator, the pump power. 相似文献
130.
Joachim Urban 《Journal of Quantitative Spectroscopy & Radiative Transfer》2003,76(2):145-178
Present and near future limb-sounding heterodyne instruments operating at millimeter or sub-millimeter wavelengths will be capable to gather profile information on a variety of stratospheric trace gases with relatively strong spectral features such as O3, H2O, O2 (temperature), N2O, HCl, ClO, HNO3, CH3Cl, and CO. Some species however, which are of particular interest for the understanding of stratospheric ozone chemistry, have only very weak spectral signatures, either due to their very small abundances and/or spectroscopic properties. These are amongst others the radical BrO, the potential bromine reservoir HBr, HOCl as a member of the chlorine family, and the hydroperoxyl radical HO2. Often, these target species are very difficult to detect and profiles have not yet been measured by space-borne sensors at all, even considering other spectral ranges and observation techniques. A study was therefore dedicated to the investigation of the retrieval of species with spectral features close to the detection limit of a typical state-of-the-art space-borne heterodyne receiver. A survey of the millimeter- and sub-millimeter spectral range was performed in order to identify appropriate spectral bands, followed by retrieval simulations for a representative atmospheric and instrumental scenario in order to explore the relative merits of the pre-selected bands and to derive associated parameters as measurement precision, altitude range and resolution. The feasibility of retrieving profile information from limb observations at sub-millimeter wavelengths of the “weak line” species under investigation is demonstrated. Optimal dedicated bands are recommended for HBr , BrO , and HOCl . For HO2 five more or less equivalent bands between 585 and are identified. 相似文献