Showing papers on "Resonance published in 1994"
TL;DR: In this article, the spectral ratio between horizontal and vertical components (H/V ratio) and its sensitivity to various parameters were investigated for sedimentary soil profiles, and it was shown that the amplitude of this peak exhibits a poor correlation with the ground motion amplification of S waves at resonance frequency.
Abstract: Numerical simulation of noise is used to investigate the characteristics of the spectral ratio between horizontal and vertical components (H/V ratio) and its sensitivity to various parameters in order to better appreciate the reliability of the technique proposed by Nakamura (1989) to estimate site amplification effects from single station noise recordings. Noise is simulated as the signal produced at a single site by a set of superficial sources (unidirectional forces or dipoles) disposed all around with random amplitude and time delay. Individual signals from a single source are computed by the discrete wave number technique. Synthetic calculations for 15 soil profiles show that this ratio exhibits a single, clear peak, the location of which is independent of the source excitation function, but strongly correlated with the local geological structure: its frequency is very close to the S wave resonance frequency. This peak appears to be mainly controlled by the polarization curve of the fundamental Rayleigh waves, which in turn exhibits a sharp peak around the fundamental resonance mode of the sedimentary structure. A similar result is found for the H/V ratio obtained for incident plane SV waves. In contrast, the amplitude of this peak exhibits a poor correlation with the ground motion amplification of S waves at resonance frequency. It is shown to be related with a high sensitivity on the value of the Poisson's ratio in the uppermost layer presumed to be the noise source layer, and, though to a much lesser extent, on the mean distance between site and noise sources. It is concluded that Nakamura's method can clearly allow the resonance frequency of a given sedimentary site to be measured very efficiently and very cheaply, but that its use for deriving the amplification at resonance frequency seems still premature from a theoretical point of view.
624 citations
487 citations
TL;DR: In this paper, a double-quantum homonuclear rotary resonance (2Q•HORROR) was established by fulfilling the condition ωr=2ω1, where ω r is the sample rotation frequency and ω 1 is the nutation frequency around an applied resonant radio frequency (RF) field.
Abstract: We describe an efficient method for the recovery of homonuclear dipole–dipole interactions in magic‐angle spinning NMR. Double‐quantum homonuclear rotary resonance (2Q‐HORROR) is established by fulfilling the condition ωr=2ω1, where ωr is the sample rotation frequency and ω1 is the nutation frequency around an applied resonant radio frequency (rf) field. This resonance can be used for double‐quantum filtering and measurement of homonuclear dipolar interactions in the presence of magic‐angle spinning. The spin dynamics depend only weakly on crystallite orientation allowing good performance for powder samples. Chemical shift effects are suppressed to zeroth order. The method is demonstrated for singly and doubly 13C labeled L‐alanine.
423 citations
TL;DR: In this article, the design, modelling and performance characteristics of electrostatically driven vacuum-encapsulated polysilicon resonators are addressed, and an expression for the pull-in voltage of a beam is given.
Abstract: In this paper, the design, modelling and performance characteristics of electrostatically driven vacuum-encapsulated polysilicon resonators are addressed. A one-port configuration is preferably employed for excitation and detection of the vibration. Mechanical instability (pull-in) is discussed on the basis of the energy minimum principle. An expression for the pull-in voltage of a beam is given. The electromechanical behaviour in a limited frequency regime around the fundamental resonance is accurately modelled by an electric circuit consisting of a (static) capacitor shunted by a series (dynamic) RLC branch. The d.c. bias dependence of the circuit components and of the series resonance frequency has been experimentally investigated and is compared with the theory. The large-amplitude behaviour is discussed as well. The plate modulus and residual strain of boron-doped polysilicon are estimated from the resonance frequencies of microbridges of varying lengths. The feasibility of their application as resonant strain gauges is investigated. The 210 m long beams typically have an unloaded fundamental frequency of 324 kHz, a gauge factor of 2400 and an uncompensated temperature coefficient of -135 ppm 0C-1.
417 citations
TL;DR: In this article, a comparative analysis of the vibrational and structural properties of carbon nanotubes is presented, where the first-order Raman spectrum exhibits two lines at 1582 cm −1 and at 1350 cm−1.
350 citations
TL;DR: In this article, a time-dependent quantum wave packet calculation for the combustion reaction H+O2 using the DMBE IV potential energy surface has been presented, which has a deep well and supports long-lived resonances.
Abstract: We show in this paper a time‐dependent (TD) quantum wave packet calculation for the combustion reaction H+O2 using the DMBE IV (double many‐body expansion) potential energy surface which has a deep well and supports long‐lived resonances. The reaction probabilities from the initial states of H+O2(3Σ−g) (v=0–3, j=1) for total angular momentum J=0 are obtained for scattering energies from threshold up to 2.5 eV, which show numerous resonance features. Our results show that, by carrying out the wave packet propagation to several picoseconds, one can resolve essentially all the resonance features for this reaction. The present TD results are in good agreement with other time‐independent calculations. A particular advantage of the time‐dependent approach to this reaction is that resonance structures—strong energy dependence of the reaction probability—can be mapped out in a single wave packet propagation without having to repeat scattering calculations for hundreds of energies. We also report calculations of some low‐lying vibrational energies of the hydroperoxyl radical HO2(2A‘) and their spectroscopic assignments. The vibrational frequencies of HO2(2A‘) on the DMBE IV potential energy surface are lower than experimental values, indicating the need to further improve the accuracy of the potential energy surface.
261 citations
228 citations
TL;DR: It is shown that ideal reflection filters can be designed by combining guided-mode resonance effects in waveguide gratings with antireflection effects of thin-film structures and a single-layer filter with multilayer design.
Abstract: We show that ideal reflection filters can be designed by combining guided-mode resonance effects in waveguide gratings with antireflection effects of thin-film structures. Since the guided-mode resonance effect overrides the antireflection effect this filter provides a symmetrical line shape with near-zero reflectivity over appreciable wavelength bands adjacent to the resonance wavelength. In the single-layer filter the same layer functions as the waveguide grating supporting the resonance and as the antireflection layer suppressing reflection around the resonance. A multilayer design allows the filter resonance peak to have a wide surrounding region of low reflectance. The central resonance wavelength, the filter linewidth, the range of the low sidebands, and the resonance line shape are all under the control of the designer.
205 citations
TL;DR: In this article, the -1, -2, and -3 anions of C[sub 60] were generated electrochemically in 4:1 toluene-acetonitrile.
Abstract: The -1, -2, and -3 anions of C[sub 60] were generated electrochemically in 4:1 toluene-acetonitrile. The visible/near-IR spectra were monitored in situ. Square wave voltammograms and electronic spectra showed that after bulk electrolysis to produce the anions, the following percentages of the starting C[sub 60] concentration could be reoxidized to neutral C[sub 60] in typical data sets: -1 anion, 75%; -2 anion, 66%; -3 anion, 46%. Continuous wave (CW) electron paramagnetic resonance (EPR) spectra of the -1 and -3 anions exhibited broad signals that were temperature dependent. The averaging of anisotropy of the signals between 15 and 60 K is attributed to dynamic Jahn-Teller distortion. Electron spin-echo and saturation recovery EPR data for the -1 anion at 10 and 16 K showed that the electron spin relaxation rates are dependent upon position in the spectrum, which is attributed to variations in the Jahn-Teller distortion. For both the -1 and -3 anion above about 70 K the CW line shape of the EPR signal is electron spin-lattice relaxation rate determined. The EPR data indicate that the -2 anion is diamagnetic. 53 refs., 14 figs.
144 citations
TL;DR: In this article, the authors examined atom transfer resulting from coherent multiple excitation of the adsorbate-substrate bond caused by inelastic tunneling of a single electron (or hole) via a negative- (or positive-) ion resonance.
Abstract: We examine atom transfer resulting from coherent multiple excitation of the adsorbate-substrate bond caused by inelastic tunneling of a single electron (or hole) via a negative- (or positive-) ion resonance. At low biases and in particular for the transitions resulting in atom transfer, the rates of coherent multiple excitation are nonlinear and also highly asymmetrical with respect to the polarity of the bias. We establish a simple criterion for the regime in which this mechanism dominates over earlier proposed mechanisms for atom transfer resulting from vibrational heating by sequential (incoherent) inelastic resonance tunneling. In the case of the atomic switch, where a Xe atom is transferred between a Ni surface and a tip, the vibrational heating mechanism is found to dominate over the coherent mechanism. For other systems, such as Na adsorption on Cu or ${\mathrm{O}}_{2}$ adsorbed on Pt, the coherent mechanism is argued to play a role in bond breaking.
139 citations
TL;DR: In this article, the authors introduce a new concept in vibrating quartz sensors, where the vibrational characteristics of such a compound resonator, namely the nominal frequency and vibrational amplitude, are correlated to the physical characteristics of the medium vibrating synchronously with the quartz resonator as a compound Resonator.
Abstract: This paper reviews the original contributions in the development of vibrating quartz sensors, loaded with whatever medium: solid, liquid or gas. The common feature of such a loading is its ability to vibrate synchronously with the quartz resonator as a compound resonator. The paper introduces a new concept in vibrating quartz sensors, where the vibrational characteristics of such a compound resonator, namely the nominal frequency and vibrational amplitude, are correlated to the physical characteristics of the medium vibrating synchronously with the quartz resonator as a compound resonator. The energy transfer model is introduced to explain the microweighing capability of quartz resonators. Further, it is proved that microweighing is a common feature of all quartz resonators, whatever their vibrational mode. It is also proved that other piezoelectric resonators exhibit the same capability. Damping of quartz-resonator vibrations at certain temperatures during a temperature sweep is correlated with the deposited film morphology. Resonance of the gas within a cavity is used for the development of tunable gas sensors. Examples are given for hydrogen and methane detection without using a catalyst. An experiment called ‘Nanobalance’ is also presented, which was performed in outer space.
TL;DR: In this article, the authors reported the existence of a previously unsuspected peak in the [sup 1]H magic angle spinning spectrum of commercially available HZSM-5 samples.
Abstract: We report the existence of a previously unsuspected peak in the [sup 1]H magic angle spinning spectrum of commercially available HZSM-5 samples. At 298 K, this resonance is a broad shoulder on the downfield side of the Bronsted acid signal at 4.3 ppm. Cooling the sample caused the line to narrow, and a clear peak at 6.9 ppm was visible at 123 K. This technique resulted in selective broadening of the 4.3 and 6.9 ppm resonances as a result of conflicting averaging of the [sup 1]H-[sup 27]Al dipolar coupling. We conclude that the 6.9 ppm resonance corresponds to a novel aluminum-containing site in zeolite HZSM-5 and is not an artifact due to exchange with the Bronsted site or an aluminum-rich impurity phase. A possible interpretation of these results is a second Bronsted site for the zeolite. 49 refs., 8 figs.
TL;DR: Experimental results are the first to support in detail the validity of the fundamental relationships embodied in the IPR model.
Abstract: A companion paper describes a predictive ion parametric resonance (IPR) model of magnetic field interactions with biological systems based on a selective relation between the ratio of the flux density of the static magnetic field to the AC magnetic field and the charge-to-mass ratio of ions of biological relevance. Previous studies demonstrated that nerve growth factor (NGF)-stimulated neurite outgrowth (NO) in PC-12 cells can be inhibited by exposure to magnetic fields as a function of either magnetic field flux density or AC magnetic field frequency. The present work examines whether the PC-12 cell response to magnetic fields is consistent with the quasiperiodic, resonance-based predictions of the IPR model. We tested changes in each of the experimentally controllable variables [flux densities of the parallel components of the AC magnetic field (Bac) and the static magnetic field (Bdc) and the frequency of the AC magnetic field] over a range of exposure conditions sufficient to determine whether the IPR model is applicable. A multiple-coil exposure system independently controlled each of these critical quantities. The perpendicular static magnetic field was controlled to less than 2 mG for all tests. The first set of tests examined the NO response in cells exposed to 45 Hz Bac from 77 to 468 mG(rms) at a Bdc of 366 mG. Next, we examined an off-resonance condition using 20 mG Bdc with a 45 Hz AC field across a range of Bac between 7.9 and 21 mG(rms). Finally, we changed the AC frequency to 25 Hz, with a corresponding change in Bdc to 203 mG (to tune for the same set of ions as in the first test) and a Bac range from 78 to 181 mG(rms). In all cases the observed responses were consistent with predictions of the IPR model. These experimental results are the first to support in detail the validity of the fundamental relationships embodied in the IPR model. © 1994 Wiley-Liss, Inc.
TL;DR: In this paper, a coupled-channel theory that starts from the full scattering Hamiltonian and a more general S-matrix approach is used to identify the causes of asymmetric resonance.
Abstract: that cause this phenomenon are identified in this paper using first a coupled-channel theory that starts from the full scattering Hamiltonian, and secondly a more general S-matrix approach. The latter is model-independent and thus yields predictions for the possible lineshapes in a wide variety of systems. Modelindependent results are desirable because knowledge of the microstructure potentials is often incomplete. We show for the most general multiprobe, multisubband structure that the total transmssion never varies by more than unity on resonance, generalizing a result previously known only for resonant tunneling structures. The role of symmetry is investigated to clarify which features (e.g. reflection zeros) are a consequence of special invariance properties and which are robust in the unsymmetric case. The eect of a resonance is found to decrease with increasing number of leads in a rotationally symmetric structure. Only in a two-probe geometry can zeros in transmission and reflection occur together for a single resonance. The known result that resonances in symmetric resonant tunneling devices always display exactly unit variation of the transmission is shown to be violated in structures where the nonresonant transmission exceeds one. Time reversal invariance is not required in the present treatment. Two model systems displaying asymmetric resonances are discussed. Their advantage is that the resonance lifetime can be tuned externally, making it possible to test a scaling property of the Fano lineshape that we derive below.
TL;DR: In this paper, the Raman spectra of the primary electron donor (a bacteriochlorophyll dimer known as P) and of the monomeric accessory bacterio chlorophyll (B) in the bacterial photosynthetic reaction center of Rb. spkaeroides have been obtained using a shifted excitation Raman difference technique with excitation at 850 nm for P spectrum and 800 nm for B spectrum.
Abstract: Rapid-flow resonance Raman spectra of the primary electron donor (a bacteriochlorophyll dimer known as P) and of the monomeric accessory bacteriochlorophylls (B) in the bacterial photosynthetic reaction center of Rb. spkaeroides have been obtained at 5 OC. The spectra were obtained using a shifted excitation Raman difference technique with excitation at 850 nm for the P spectrum and 800 nm for the B spectrum. Raman bands at 187, 204,332,564,684,730, 899, and 1163 cm-l are found in common in the P and B spectra, while unique modes appear in the low-frequency region of the special pair at 34,71,95,128, and 484 cm-l. The remaining strongly Raman-active monomer modes at 353,385,621,761,1010,1114, and 1132 cm-l were not detected in the dimer spectrum. No substantial resonance Raman activity is observed above 1200 cm-I for either chromophore, indicating that high-frequency modes are not strongly coupled to the optical excitation in the Qy absorptions of B or P. The Raman spectrum shows that the electronic excitation of P is coupled to at least 14 vibrational degrees of freedom, including low-frequency modes at 34, 71,95, and 128 cm-l. The Raman scattering cross sections for the modes of B are approximately an order of magnitude larger than those for analogous modes of P. This difference suggests that the excited electronic state of P is damped by rapid vibronic relaxation processes that are not present in B. The complete analysis of these resonance Raman results will lead to the development of specific multimode models for the excited-state structural dynamics and relaxation of the chromophores in reaction centers.
TL;DR: The Brownian oscillator model for the coupling of solvent motions to a solute's electronic transitions is applied to the calculation of absorption, relaxed fluorescence, and unrelaxed total emission (Raman and fluorescence) band shapes of a diatomic molecule in solution.
Abstract: The Brownian oscillator model for the coupling of solvent motions to a solute's electronic transitions is applied to the calculation of absorption, relaxed fluorescence, and unrelaxed total emission (Raman and fluorescence) band shapes of a diatomic molecule in solution. The band shapes and the ratios of sharp scattering to broad fluorescence are explored as a function of the laser detuning from resonance, the parameters describing the solvent oscillator, and the excited-state lifetime, and direct comparisons with the stochastic theory, which does not contain the solvent-induced Stokes shift, are made. The relationship between the optical band shapes and the nuclear Franck- Condon factor for nonphotochemical electron transfer processes is also discussed within the Brownian oscillator model for the solvation coordinate. The limits of applicability of the "high-temperature" limit for the Brownian oscillator are established.
TL;DR: In this article, the authors show that the cesium atom exhibits a two-fold sign reversal of a crossover resonance, under various polarization configurations with and without applied magnetic fields.
Abstract: The complex magnetic structure of the cesium atom is responsible for the interesting behaviour of its saturated absorption spectra, e.g., a two-fold sign reversal of a crossover resonance, under various polarization configurations with and without applied magnetic fields. We show that this morphology is a result of optical pumping processes including coherent population trapping which, under normal laboratory conditions, prevent the atoms from reaching an equilibrium situation. Our interpretation is useful for an intuitive and rapid understanding of this important tool in high-resolution spectroscopy.
TL;DR: In this article, the authors have grown and characterized BaTiO3 doped with Rh and showed that the resulting blue-green color is probably due to charge-transfer optical transitions involving Rh4+ and/or Rh3+ centers.
Abstract: We have grown and characterized crystals of BaTiO3 doped with Rh. These crystals have a blue-green color that is probably due to charge-transfer optical transitions involving Rh4+ and/or Rh3+. Electron paramagnetic resonance spectroscopy confirmed the presence of Rh4+ centers. Self-pumped phase-conjugation measurements were performed at wavelengths between 776 and 990 nm. Reflectivities near 80% were obtained throughout this wavelength range. In addition, self-pumped phase-conjugation buildup times were measured as a function of input power at 851 nm and are significantly faster than in undoped or Co-doped crystals studied previously. BaTiO3:Rh is therefore a promising material for near-infrared photorefractive applications.
TL;DR: In this article, the optical Stark effect of a two-level system coupled to a Brownian oscillator is studied using equations of motion for a reduced density matrix, which can be used to study the combined effects of strong fields and dephasing processes at finite temperature and interpolate continuously from the coherent to the overdamped limits where they reduce to the stochastic Gaussian-Markovian equation.
Abstract: The optical Stark effect of a two-level system coupled to a Brownian oscillator (i.e. a harmonic mode which in turn is coupled to a heat bath) is studied using equations of motion for a reduced density matrix. These equations, derived using path integral techniques, can be used to study the combined effects of strong fields and dephasing processes at finite temperature, and interpolate continuously from the coherent to the overdamped limits where they reduce to the stochastic Gaussian-Markovian equation. Numerical calculations of probe absorption spectra for various pump intensities are presented, and show dynamical Stark splitting. In contrast to the Bloch equations which contain an infinite-temperature dephasing, we find that at finite temperature, the Stark peaks may have different heights even when the pump pulse is on resonance.
TL;DR: In this article, the concept of resonance wave discharge was introduced to explain the high absorption efficiency of inductively coupled helicon plasma sources, supported by long-scale weakly damped eigenmodes excited in a plasma resonator.
Abstract: The concept of the 'resonance' wave discharge is introduced to explain the high absorption efficiency of inductively coupled helicon plasma source. This discharge is supported by long-scale weakly damped eigenmodes excited in plasma resonator. The RF power absorbed in it is inversely proportional to electron collision frequency. The fields excited by simple single-loop inner antenna and its impedance are calculated in a cylindrical metal resonator. At low collision frequencies the field amplitudes and antenna resistance are shown to peak sharply near the helicon dispersion branches.
TL;DR: In this paper, the authors studied the relationship between the average unimolecular decay rate and the resonance width in the regime of overlapping resonances and showed that the rate becomes independent of the average resonance width.
Abstract: Unimolecular decay processes are studied in the regime of overlapping resonances with the goal of elucidating how unimolecular reaction rates depend on resonances widths (the imaginary part of the Siegert eigenvalues). As illustrated analytically for one‐dimensional models and numerically for a more general random matrix version of Feshbach’s optical model, transition state theory (TST, Rice–Ramsperger–Kassel–Marcus) provides the correct average unimolecular decay rate whether the resonances are overlapping or not. For all studied cases, the explicit ‘‘universal’’ dependence of the TST average rate on the average resonance width (for a given energy, or an energy interval) is that of a saturation curve: in the regime of nonoverlapping resonances (i.e., weak coupling) the standard relation ‘‘unimolecular decay rate=resonance width /ℏ’’ holds, but as the resonance overlap increases (strong coupling) the rate saturates, becoming practically independent of the average resonance width in the strong overlapping ...
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TL;DR: In this article, the triple coincidence of 8He and two neutrons was measured by measuring the triple coincidences of eightHe + n + n. Experimental data show a peak that can be explained as a resonance 10He, which is unbound by 1.2± 0.3 MeV and its width is less than 1.5 MeV.
TL;DR: A laser technique for analysis of carbon-13:carbon-12 ratios with the specificity of laser resonance spectroscopy and the sensitivity and accuracy typical of isotope ratio mass spectrometers is reported.
Abstract: A laser technique for analysis of carbon-13:carbon-12 ratios with the specificity of laser resonance spectroscopy and the sensitivity and accuracy typical of isotope ratio mass spectrometers is reported. The technique is based on laser optogalvanic effect spectroscopy, in which an electrical (galvanic) signal is detected in response to the optical stimulation of a resonance transition in a gas discharge species. Carbon dioxide molecular gas lasers are used, with the probed transitions being identical to the lasing transitions. Measurements for carbon dioxide samples with 100-second averaging times yield isotopic ratios with a precision of better than 10 parts per million.
TL;DR: Spin relaxation of optically trapped atoms that is due to light scattering from the trap laser is studied to observe enhancement in atomic ground-state lifetime due to an interference effect in spontaneous Raman scattering far from atomic resonance.
Abstract: We study spin relaxation of optically trapped atoms that is due to light scattering from the trap laser. We observe relaxation times greater than 2 s for ground-state hyperfine-level populations of 85Rb atoms trapped in an optical dipole force trap operating as much as 65 nm to the red of the D1 line. The measured relaxation rate can be more than 100 times slower than the atoms’ total spontaneous scatter rate from the trap laser. This enhancement in atomic ground-state lifetime is due to an interference effect in spontaneous Raman scattering far from atomic resonance.
Patent•
17 Feb 1994
TL;DR: In this article, a method of assaying for a ligand in a sample involves incubating the sample in contact with a specific binding partner for the ligand carried on one surface of an optical structure, irradiating the structure at a suitable angle or range of angles to the normal such that the resonance and total internal reflection of the radiation occurs within the optical structure and/or the layer of specific binding partners.
Abstract: A method of assaying for a ligand in a sample involves incubating the sample in contact with a specific binding partner for the ligand carried on one surface of an optical structure, irradiating the structure at a suitable angle or range of angles to the normal such that the resonance and/or total internal reflection of the radiation occurs within the optical structure and/or the layer of specific binding partner, and analyzing the radiation in order to determine whether, and if desired the extent to which and/or rate at which the generated radiation and/or optical characteristics of the optical structure are altered by complex formation.
TL;DR: In this paper, the authors show that the energy absorption profile for ions subjected to resonance excitation broadens with the amplitude of ion oscillation and shifts to higher frequencies, an observation consistent with behavior predicted for ion motion in a quadrupole electric field with relatively small higher-order field components.
Abstract: Mass resolution obtained with the commonly employed stretched quadrupole ion trap geometry is shown to be dependent upon scan direction when resonance ejection is used as the mass analysis method. Data are also presented showing that the energy absorption profile for ions subjected to resonance excitation broadens with the amplitude of ion oscillation and shifts to higher frequencies, an observation consistent with behavior predicted for ion motion in a quadrupole electric field with relatively small higher-order field components. The observed effect of scan direction on mass resolution is therefore reasoned to arise from an effect analogous to Doppler focusing or defocusing, depending on scan direction relative to the direction of the ion frequency shift with oscillatory amplitude. 15 refs., 7 figs.
TL;DR: In this article, the authors presented the guided-mode resonance characteristics of dielectric waveguide gratings and experimentally observed them in the microwave region (4-18 GHz) and were shown to be in agreement with theory.
Abstract: The guided-mode resonance characteristics of dielectric waveguide gratings are presented. The sharp resonance features predicted theoretically are experimentally observed in the microwave region (4-18 GHz) and are shown to be in agreement with theory. >
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TL;DR: In this article, the conduction electron spin resonance (ESR) of carbon nanotubes at various stages of purification has been measured between 4 and 296 K and the results imply that metallic and/or narrow gap semiconducting nanotube are actually present as predicted by theory.
TL;DR: In this paper, the results of wave-dispersed third harmonic generation measurements in sublimed C60 thin films are reported and discussed within a three-level model, and two strong resonant enhancements in cubic susceptibility χ(3)(−3ω; ω, ω and ω) are observed.