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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.
Electron transport through molecular quantum dots coupled to a single vibrational mode is studied in the Kondo regime. We apply a generalized Schrieffer-Wolff transformation to determine the effective low-energy spin-spin-vibron interaction. From this model we calculate the nonlinear conductance and find Kondo sidebands located at bias voltages equal to multiples of the vibron frequency. Because of selection rules, the side peaks are found to have strong gate-voltage dependences, which can be tested experimentally. In the limit of weak electron-vibron coupling, we employ a perturbative renormalization group scheme to calculate analytically the nonlinear conductance. 相似文献
125.
We develop the general nonequilibrium theory of transport through a quantum dot, including Coulomb blockade effects via a 1/N expansion, where N is the number of scattering channels. At lowest order we recover the Landauer formula for the current plus a self-consistent equation for the dot potential. We obtain the leading corrections and compare with earlier approaches. Finally, we show that to leading and to next leading order in 1/N there is no interaction correction to the weak localization, in contrast to previous theories, but consistent with experiments by Huibers et al. [Phys. Rev. Lett. 81, 1917 (1998)], where N=4. 相似文献
126.
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
127.
Hsieh HT Psaltis D Beyer O Maxein D von Korff Schmising C Buse K Sturman B 《Optics letters》2005,30(17):2233-2235
Spatial gratings are recorded holographically by two femtosecond pump pulses at 388 nm in lithium niobate (LiNbO3) crystals and read out by a Bragg-matched, temporally delayed probe pulse at 776 nm. We claim, to our knowledge, the first holographic pump-probe experiments with subpicosecond temporal resolution for LiNbO3. An instantaneous grating that is due mostly to the Kerr effect as well as a long-lasting grating that results mainly from the absorption caused by photoexcited carriers was observed. The Kerr coefficient of LiNbO3 for our experimental conditions, i.e., pumped and probed at different wavelengths, was approximately 1.0 x 10(-5) cm2/GW. 相似文献
128.
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
129.
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
130.
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