共查询到20条相似文献,搜索用时 62 毫秒
1.
Andrei V. Astashkin Asako Kawamori 《Journal of magnetic resonance (San Diego, Calif. : 1997)》1998,135(2):406-417
The intense line in Mims and Davies electron-nuclear double resonance (ENDOR) spectra due to the hyperfine interactions of an unpaired electron with distant matrix nuclei is shown to originate from a simultaneous inversion of a large number of nuclear spins by a radiofrequency pulse. Theoretical expressions describing the matrix ENDOR effect are derived and verified experimentally. 相似文献
2.
Kulik LV Grishin YA Dzuba SA Grigoryev IA Klyatskaya SV Vasilevsky SF Tsvetkov YD 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2002,157(1):61-68
The use of a rapid stepping of the magnetic field for investigation of electron dipole-dipole ESEEM in pulsed X-band ELDOR is described. The magnetic field jump, synchronized with a microwave pumping pulse, is positioned between the second and the third pulses of the stimulated echo pulse sequence. This echo is measured as a function of the delay between the first and the second pulses. The data are analyzed for a Fourier transform resulting in a Pake resonance pattern. To remove the electron-nuclear contributions to ESEEM, time traces with pumping were divided by those without. This resulted in complete elimination of electron-nuclear contributions, which is seen from the absence of peaks at nuclear frequencies and the similarity of results for protonated and deuterated solvents. For increasing the electron-electron modulation depth, a scanning of the magnetic field during the microwave pumping is proposed. The interspin distances and their distribution are determined for two long-chained (ca. 2 nm) nitroxide biradicals in glassy toluene and in frozen nematic liquid crystal 4-cyano-4'-pentyl-biphenyl. For the latter solvent, the alignment of the axis connecting two nitroxides in biradicals is quantitatively analyzed. 相似文献
3.
Kaminker I Florent M Epel B Goldfarb D 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2011,208(1):95-102
High resolution pulse EPR methods are usually applied to resolve weak magnetic electron-nuclear or electron-electron interactions that are otherwise unresolved in the EPR spectrum. Complete information regarding different magnetic interactions, namely, principal components and orientation of principal axis system with respect to the molecular frame, can be derived from orientation selective pulsed EPR measurements that are performed at different magnetic field positions within the inhomogeneously broadened EPR spectrum. These experiments are usually carried out consecutively, namely a particular field position is chosen, data are accumulated until the signal to noise ratio is satisfactory, and then the next field position is chosen and data are accumulated. Here we present a new approach for data acquisition of pulsed EPR experiments referred to as parallel acquisition. It is applicable when the spectral width is much broader than the excitation bandwidth of the applied pulse sequence and it is particularly useful for orientation selective pulse EPR experiments. In this approach several pulse EPR measurements are performed within the waiting (repetition) time between consecutive pulse sequences during which spin lattice relaxation takes place. This is achieved by rapidly changing the main magnetic field, B(0), to different values within the EPR spectrum, performing the same experiment on the otherwise idle spins. This scheme represents an efficient utilization of the spectrometer and provides the same spectral information in a shorter time. This approach is demonstrated on W-band orientation selective electron-nuclear double resonance (ENDOR), electron spin echo envelope modulation (ESEEM), electron-electron double resonance (ELDOR)--detected NMR and double electron-electron resonance (DEER) measurements on frozen solutions of nitroxides. We show that a factors of 3-6 reduction in total acquisition time can be obtained, depending on the experiment applied. 相似文献
4.
This mini-review focuses on various aspects of the application of radio frequency (rf) irradiation in electron paramagnetic resonance (EPR). The development of the electron-nuclear double resonance (ENDOR) technique is briefly described, and we highlight the use of circularly polarized rf fields and pulse ENDOR methodology in one- and two-dimensional experiments. The capability of pulse ENDOR at Q-band is illustrated with interesting experimental examples. Electron spin echo envelope modulation effects induced by an rf field in liquid samples demonstrate another role which rf fields can play. Technical achievements in the design of ENDOR resonators are illustrated by the example of a bridged loop-gap resonator. Finally, the influence of longitudinal rf fields on the dynamics of EPR transitions is explained using a dressed spin resonance treatment. 相似文献
5.
A high-field continuous-wave (CW) and pulse electron paramagnetic resonance spectrometer operating at 122 and 244 GHz is described. The instrument is based on a millimeter-wave bridge built from quasi-optical components. To improve the sensitivity, a cryo-cooled detector/mixer is used. The magnetic field is generated using a cryogen-free superconducting 12 T magnet (warm bore, 88 mm) equipped with a helium-flow cryostat for sample cooling. The advantages of this spectrometer are described and first results (obtained in CW mode) on different types of samples at 122 and 244 GHz are presented. The extensions to pulse operation as well as double resonance techniques (electron-electron and electron-nuclear) are briefly discussed. 相似文献
6.
本文通过求解一维含时薛定谔方程, 比较研究了H2+和HD+分子离子体系的高次谐波发射效率. 数值计算结果表明, 在相同激光条件下, 不对称分子体系能产生更高强度的谐波谱. 此外, 借助时频分布, 电离几率和电子-核波包密度概率分布图, 对计算结果做出了合理的解释. 相似文献
7.
N. M. Galeeva 《Russian Physics Journal》1980,23(3):246-250
The nuclear spin-phonon interaction Hamiltonian for Van Vleck paramagnets is derived in general form with allowance for rotational vibrations of the crystal lattice. The specific form of the Hamiltonian is given for tetragonal crystal symmetry in the cases S=1/2 and S > 1/2. The coefficient of sound absorption at the electron-nuclear levels as well as the electron spin system is calculated. It is verified that the contribution of rotational lattice vibrations can in a number of cases turn out to be an order of magnitude greater than the contribution depending on the shear and compressive strain.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 80–85, March, 1980. 相似文献
8.
使用不同声源利用矢量传声器对毛毡材料进行现场吸声系数测试,研究了不同背景下不同声源的抗噪能力。矢量传声器可以同时测得声压和质点振速信号,进而可计算得到阻抗,利用自由空间和材料表面的阻抗可计算得到材料的吸声系数。在此次实验中,使用不同声源分别在无干扰和有一白噪声干扰源的两种情况下进行测试。结果表明,使用对数扫频脉冲和巴特沃斯脉冲测试所得的吸声系数曲线更平滑,说明脉冲声可以有效降低环境反射的影响,在高噪声背景下使用对数扫频脉冲测试所得的结果基本没有受到背景噪声的影响,说明对数扫频脉冲的抗噪能力更强。因此,使用对数扫频脉冲作为声源进行测试可有效减弱环境反射和背景噪声的影响。 相似文献
9.
We report a measurement of the spin-echo decay of a single electron spin confined in a semiconductor quantum dot. When we tip the spin in the transverse plane via a magnetic field burst, it dephases in 37 ns due to the Larmor precession around a random effective field from the nuclear spins in the host material. We reverse this dephasing to a large extent via a spin-echo pulse, and find a spin-echo decay time of about 0.5 micros at 70 mT. These results are in the range of theoretical predictions of the electron spin coherence time governed by the electron-nuclear dynamics. 相似文献
10.
11.
Voronovich AG 《The Journal of the Acoustical Society of America》2008,123(5):2480-2483
When a "massless" one-dimensional sound pulse (mass of a sound pulse is defined as an integral of the perturbation of density over the pulse length) reflects from a pressure-release boundary, its momentum changes sign. This obviously violates momentum conservation. However, in contrast to the case of an unbounded medium, calculation of the momentum in a bounded region includes a second-order term as well. Apparently, the second-order correction to the linear solution ensures momentum conservation in this case. The purpose of this Letter is to find a concrete form of this second-order correction. It appears that, as a result of the nonlinear interaction of the pulse with a pressure-release boundary, the latter experiences second-order net shift. This leads to the generation of a massive second-order rarefaction pulse whose momentum is directed opposite to the direction of propagation of the pulse itself. Appearance of this pulse ensures total momentum conservation. 相似文献
12.
D. I. Abubakirov V. V. Naletov M. S. Tagirov D. A. Tayurskii A. N. Yudin 《JETP Letters》2002,76(10):633-636
Resonant transitions predicted earlier between low-lying electron-nuclear sublevels of the Tm3+ ground state were observed at frequencies up to 700 MHz in a dielectric Van Vleck paramagnet—thulium ethylsulfate single crystal. It is shown that, due to the distortion of the 4f-electron shell of a rare-earth ion in an applied magnetic field, the parameters of electron-nuclear interaction become field-dependent. 相似文献
13.
In this paper we discuss the relevance of electron-nuclear double transitions for the problem of the amplification of gamma
rays. We consider the electron-nuclear coupled system of 151Eu in a CaF2 lattice, in the presence of a strong static magnetic field. We analyze the possibility of pumping this electron-nuclear coupled
system from the ground atomic electron Zeeman level to a higher electron level with the aid of a microwave magnetic field,
while the nucleus is simultaneously undergoing a gamma-ray transition to the nuclear ground state. It is shown that an overall
inversion condition can be satisfied even in the absence of inversion of the nuclear populations, provided that the ratio
of the electron populations in the excited and ground electron Zeeman states has a sufficiently small value.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
14.
In this paper a new mechanism for the production of impulsive noise in impact forming machines is proposed; namely the sudden radial expansion of the billet at the instant of impact. First of all a mathematical model of a forging machine is described which, though simplified in order to render it amenable to calculation, contains the essential features necessary for a realistic calculation of the sound pulse. A theory then is developed which enables the sound pulse to be computed given the rate of expansion of the billet surface.It is shown that the main part of the pulse from this source is produced during the first few microseconds of impact, the remaining few milliseconds of impact time producing a relatively small pulse. It being assumed, then, that the acceleration of the billet surface is essentially a delta function, the sound pulse produced by such an acceleration is computed and shown to constitute a significant part of the peak pressure measured. Finally the variation of pulse height with billet dimensions and impact velocity are given. 相似文献
15.
The propagation of a heat pulse into a perfect bcc crystal is studied by means of molecular dynamical calculations. We observe second sound waves associated with the heat pulse as well as with longitudinal and transverse elastic pulses. Our results explain a number of features observed in second sound experiments and suggest that second sound is a phenomenon of general occurrence. 相似文献
16.
17.
I.IntroductionTomeasurethesound1evelofanundcrwatersoundpulsewithunknownamplitudeisofimportanceinunderwaterapp1ication.Forinstancc,asimu1ationsystemusedtointerfcresomesonarmusthavesuchfunction,whichhastobeabIctomeasurethesoundlcvelatreceivingpointandretransmitasimulatcdsignalwithrequircdsoundlcvelafterpropcrprocessing.Itisdifficultforanorma1peakorthresho1ddetectortocompletethistask.Thereasonforthisisthattherangeofthesignalamp1itudercaches7O-8odBandthereissomedistortionofsignalwaveform,inaddit… 相似文献
18.
R. Reibold 《Ultrasonics》1980,18(2):85-89
The investigation of ultrasonically produced liquid-surface relief by means of double-exposure holography to determine the sound intensity has been extended to pulsed ultrasonic waves and the transient behaviour of the surface relief. The rise time and height of the surface elevation varies considerably with pulse duration, sound field structure, and sound pressure amplitude. For pulse repetition frequencies higher than 200 Hz a steady-state condition is achieved. 相似文献
19.
Suppression of reverberation distortions of a receiver signal using the water tank transfer function
The paper considers a method for suppressing the reverberant distortions of an underwater sound receiver signal during receiver calibration in a laboratory water tank. The method is based on using the water tank transfer function, which is a complex frequency-dependent coefficient that establishes, for the point of signal reception, the relation between the sound pressures in the reverberant sound field of the water tank and in the free sound field. The procedure for experimentally obtaining the water tank transfer function is considered. Examples of suppressing reverberant distortions during noise and pulse sound reception are presented. 相似文献
20.
Yurchenko SN Patchkovskii S Litvinyuk IV Corkum PB Yudin GL 《Physical review letters》2004,93(22):223003
We solve the time-dependent Schr?dinger equation in three dimensions for H+2 in a one-cycle laser pulse of moderate intensity. We consider fixed nuclear positions and Coulomb electron-nuclear interaction potentials. We analyze the field-induced electron interference and diffraction patterns. To extract the ionization dynamics we subtract the excitations to low-lying bound states explicitly. We follow the time evolution of a well-defined wave packet that is formed near the first peak of the laser field. We observe the fragmentation of the wave packet due to molecular focusing. We show how to retrieve a diffraction molecular image by taking the ratio of the momentum distributions in the two lateral directions. The positions of the diffraction peaks are well described by the classical double slit diffraction rule. 相似文献