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991.
Amarian M Auerbach L Averett T Berthot J Bertin P Bertozzi W Black T Brash E Brown D Burtin E Calarco J Cates G Chai Z Chen JP Choi S Chudakov E Cisbani E de Jager CW Deur A DiSalvo R Dieterich S Djawotho P Finn JM Fissum K Fonvieille H Frullani S Gao H Gao J Garibaldi F Gasparian A Gilad S Gilman R Glamazdin A Glashausser C Goldberg E Gomez J Gorbenko V Hansen JO Hersman B Holmes R Huber GM Hughes E Humensky B Incerti S Iodice M Jensen S Jiang X Jones C Jones G Jones M Jutier C Ketikyan A 《Physical review letters》2004,93(15):152301
The generalized forward spin polarizabilities gamma(0) and delta(LT) of the neutron have been extracted for the first time in a Q2 range from 0.1 to 0.9 GeV2. Since gamma(0) is sensitive to nucleon resonances and delta(LT) is insensitive to the Delta resonance, it is expected that the pair of forward spin polarizabilities should provide benchmark tests of the current understanding of the chiral dynamics of QCD. The new results on delta(LT) show significant disagreement with chiral perturbation theory calculations, while the data for gamma(0) at low Q2 are in good agreement with a next-to-leading-order relativistic baryon chiral perturbation theory calculation. The data show good agreement with the phenomenological MAID model. 相似文献
992.
For the active control of the transformer noise, a newly developed adaptive algorithm based on waveform synthesis was proposed in [19], where a comparison of the performance of the proposed algorithm with the FXLMS algorithm made on a single channel system showed the feasibility of the algorithm. This paper describes the implementation of the proposed algorithm on a multiple channel adaptive control system, which is used to control the noise radiated by a small transformer in an anechoic chamber. The implementation shows that the proposed algorithm requires less memory and less computation load than a typical implementation of the FXLMS algorithm and that a controller realised with the proposed algorithm can effectively reduce transformer noise and be quite robust. 相似文献
993.
Nielsen SK Brandbyge M Hansen K Stokbro K Van Ruitenbeek JM Besenbacher F 《Physical review letters》2002,89(6):066804
We present an experimental study of current-voltage (I-V) curves on atomic-sized Au and Pt contacts formed under cryogenic vacuum (4.2 K). Whereas I-V curves for Au are almost Ohmic, the conductance G=I/V for Pt decreases with increasing voltage, resulting in distinct nonlinear I-V behavior. The experimental results are compared with first principles density functional theory calculations for Au and Pt, and good agreement is found. The difference in conductance properties for Pt vs Au can be explained by the underlying electron valence structure: Pt has an open d shell while Au has not. 相似文献
994.
Ahrens J Altieri S Annand JR Anton G Arends HJ Aulenbacher K Beck R Bradtke C Braghieri A Degrande N D'Hose N Drechsel D Dutz H Goertz S Grabmayr P Hansen K Harmsen J Von Harrach D Hasegawa S Hasegawa T Heid E Helbing K Holvoet H Van Hoorebeke L Horikawa N Iwata T Jahn O Jennewein P Kageya T Kamalov S Kiel B Klein F Kondratiev R Kossert K Krimmer J Lang M Lannoy B Leukel R Lisin V Matsuda T McGeorge JC Meier A Menze D Meyer W Michel T Naumann J Panzeri A Pedroni P Pinelli T Preobrajenski I 《Physical review letters》2002,88(23):232002
The helicity dependence of the gamma-->p-->-->ppi(0) reaction has been measured for the first time in the photon-energy range from 550 to 790 MeV. The experiment, performed at the Mainz microtron MAMI, used a 4pi-detector system, a circularly polarized, tagged photon beam, and a longitudinally polarized frozen-spin target. These data are predominantly sensitive to the D13(1520) resonance and are used to determine its helicity amplitudes. 相似文献
995.
A general NMR method is presented that allows a precise determination of the second-order rate constant, k(ese), for the electron self-exchange in blue copper proteins, from the longitudinal relaxation rates of the nuclei in the protein. The method relies on the use of partly oxidized (paramagnetic) samples of the protein. In contrast to previous NMR approaches for the determination of electron self-exchange rates, the applicability of the method extends beyond the slow-exchange limit, k(ese)c < R(ip), i = 1, 2, where c is the protein concentration, and R(ip) is the paramagnetic relaxation enhancement of the observed nuclei. 相似文献
996.
A new experiment for selective determination of the relaxation rates of fast relaxing NMR signals is presented. The experiment is derived from the conventional inversion recovery experiment by substituting the 180 degrees inversion pulse of this experiment with a signal eliminating relaxation filter (SERF) consisting of three 180 degrees pulses separated by two variable delays, Delta1 and Delta2. The SERF experiment allows a selective suppression of signals with relaxation rates below a given limit while monitoring the relaxation of faster relaxing signals. The experiment was tested on a sample of 20% oxidized plastocyanin from Anabaena variabilis, where the fast exchange of an electron between the reduced (diamagnetic) and the oxidized (paramagnetic) form results in a series of average signals with widely different relaxation rates. To ensure an optimum extraction of information from the experimental data, the relaxation rates were obtained from the SERF experiment by a simultaneous analysis of all the FIDs of the experiment using a fast linear prediction model method developed previously. The reliability of the relaxation rates obtained from the SERF experiment was confirmed by a comparison of the rates with the corresponding rates obtained from a conventional inversion recovery experiment. 相似文献
997.
A. V. Bobylev Alex Hansen J. Piasecki E. H. Hauge 《Journal of statistical physics》2001,102(5-6):1133-1150
We consider a system of non-interacting charged particles moving in two dimensions among fixed hard scatterers, and acted upon by a perpendicular magnetic field. Recollisions between charged particles and scatterers are unavoidable in this case. We derive from the Liouville equation for this system a generalized Boltzmann equation with infinitely long memory, but which still is analytically solvable. This kinetic equation has been earlier written down from intuitive arguments. 相似文献
998.
Hansen H Aichele T Hettich C Lodahl P Lvovsky AI Mlynek J Schiller S 《Optics letters》2001,26(21):1714-1716
A pulsed, balanced homodyne detector has been developed for precise measurement of the electric field quadratures of pulsed optical quantum states. A high level of common mode suppression (>85 dB) and low electronic noise (730 electrons per pulse) provide a signal-to-noise ratio of 14 dB for measurement of the quantum noise of individual pulses. Measurements at repetition rates as high as 1 MHz are possible. As a test, quantum tomography of the coherent state was performed, and the Wigner function and the density matrix were reconstructed with 99.5% fidelity. The detection system can be used for ultrarsensitive balanced detection in cw mode, e.g., for weak absorption measurements. 相似文献
999.
1000.
W. Hansen 《Mathematische Annalen》2001,319(3):539-551
It is shown that any continuous bounded function f on such that
, is constant provided r is a strictly positive real function on satisfying
The proof is based on a minimum principle exploiting that and on a study of -stable sets, i.e., sets A such that the circle of radius r(x) centered at x is contained in A whenever . The latter reveals that there is no disjoint pair of non-empty closed -stable subsets in unless (taking spheres this holds for any , ). A counterexample is given where .
Received November 24, 1999 / Published online December 8, 2000 相似文献