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1
Denisov, Artem, Anton Bubis, Stanislau Piatrusha, Nadezhda Titova, Albert Nasibulin, Jonathan Becker, Julian Treu i in. "Heat-Mode Excitation in a Proximity Superconductor". Nanomaterials 12, nr 9 (25.04.2022): 1461. http://dx.doi.org/10.3390/nano12091461.
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Mesoscopic superconductivity deals with various quasiparticle excitation modes, only one of them—the charge-mode—being directly accessible for conductance measurements due to the imbalance in populations of quasi-electron and quasihole excitation branches. Other modes carrying heat or even spin, valley etc. currents populate the branches equally and are charge-neutral, which makes them much harder to control. This noticeable gap in the experimental studies of mesoscopic non-equilibrium superconductivity can be filled by going beyond the conventional DC transport measurements and exploiting spontaneous current fluctuations. Here, we perform such an experiment and investigate the transport of heat in an open hybrid device based on a superconductor proximitized InAs nanowire. Using shot noise measurements, we investigate sub-gap Andreev heat guiding along the superconducting interface and fully characterize it in terms of the thermal conductance on the order of Gth∼e2/h, tunable by a back gate voltage. Understanding of the heat-mode also uncovers its implicit signatures in the non-local charge transport. Our experiments open a direct pathway to probe generic charge-neutral excitations in superconducting hybrids.
2
Denisov, Artem, Anton Bubis, Stanislau Piatrusha, Nadezhda Titova, Albert Nasibulin, Jonathan Becker, Julian Treu i in. "Heat-Mode Excitation in a Proximity Superconductor". Nanomaterials 12, nr 9 (25.04.2022): 1461. http://dx.doi.org/10.3390/nano12091461.
Pełny tekst źródłaStreszczenie:
Mesoscopic superconductivity deals with various quasiparticle excitation modes, only one of them—the charge-mode—being directly accessible for conductance measurements due to the imbalance in populations of quasi-electron and quasihole excitation branches. Other modes carrying heat or even spin, valley etc. currents populate the branches equally and are charge-neutral, which makes them much harder to control. This noticeable gap in the experimental studies of mesoscopic non-equilibrium superconductivity can be filled by going beyond the conventional DC transport measurements and exploiting spontaneous current fluctuations. Here, we perform such an experiment and investigate the transport of heat in an open hybrid device based on a superconductor proximitized InAs nanowire. Using shot noise measurements, we investigate sub-gap Andreev heat guiding along the superconducting interface and fully characterize it in terms of the thermal conductance on the order of Gth∼e2/h, tunable by a back gate voltage. Understanding of the heat-mode also uncovers its implicit signatures in the non-local charge transport. Our experiments open a direct pathway to probe generic charge-neutral excitations in superconducting hybrids.
3
Denisov, Artem, Anton Bubis, Stanislau Piatrusha, Nadezhda Titova, Albert Nasibulin, Jonathan Becker, Julian Treu i in. "Heat-Mode Excitation in a Proximity Superconductor". Nanomaterials 12, nr 9 (25.04.2022): 1461. http://dx.doi.org/10.3390/nano12091461.
Pełny tekst źródłaStreszczenie:
Mesoscopic superconductivity deals with various quasiparticle excitation modes, only one of them—the charge-mode—being directly accessible for conductance measurements due to the imbalance in populations of quasi-electron and quasihole excitation branches. Other modes carrying heat or even spin, valley etc. currents populate the branches equally and are charge-neutral, which makes them much harder to control. This noticeable gap in the experimental studies of mesoscopic non-equilibrium superconductivity can be filled by going beyond the conventional DC transport measurements and exploiting spontaneous current fluctuations. Here, we perform such an experiment and investigate the transport of heat in an open hybrid device based on a superconductor proximitized InAs nanowire. Using shot noise measurements, we investigate sub-gap Andreev heat guiding along the superconducting interface and fully characterize it in terms of the thermal conductance on the order of Gth∼e2/h, tunable by a back gate voltage. Understanding of the heat-mode also uncovers its implicit signatures in the non-local charge transport. Our experiments open a direct pathway to probe generic charge-neutral excitations in superconducting hybrids.
4
CAO, LI-GANG, i ZHONG-YU MA. "SOFT DIPOLE MODES IN NEUTRON-RICH Ni-ISOTOPES IN QRRPA". Modern Physics Letters A 19, nr 38 (14.12.2004): 2845–56. http://dx.doi.org/10.1142/s0217732304015233.
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The soft dipole modes in neutron-rich even–even Ni-isotopes are investigated in the quasiparticle relativistic random phase approximation. We study the evolution of strengths distribution, centroid energies of dipole excitation in low-lying and normal GDR regions with the increase of the neutron excess. It is found in the present study that the centroid energies of the soft dipole strengths strongly depend on the thickness of neutron skin along with the neutron-rich even–even Ni-isotopes.
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Tang, Deman, i Earl H. Dowell. "Reduced Order Model Analysis for Two-Dimensional Molecular Dynamic Chain Structure Attached to an Atomic Force Microscope". Journal of Dynamic Systems, Measurement, and Control 126, nr 3 (1.09.2004): 531–46. http://dx.doi.org/10.1115/1.1789969.
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Dynamic analysis and numerical simulation of a protein-ligand chain structure connected to a moving atomic force microscope (AFM) has been conducted. The elements of the chain are free to extend and rotate relative to each other in a two-dimensional plane. Sinusoidal base excitation of the cantilevered beam of the AFM is considered in some detail. Reduced order (dynamic) models are constructed using global modes for both linear and nonlinear dynamic systems with and without the “nearest neighbor assumption.” The agreement between the original and reduced order models (ROM) is very good even when only one global mode is included in the ROM for either the linear case or for the nonlinear case, provided the excitation frequency is lower than the fundamental natural frequency of the linear system. For higher excitation frequencies, more global modes are required. The computational advantage of the reduced order model is clear from the results presented.
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Liu, Kaicheng, i Cheng Yan. "Investigation of the Influence of Splitter Blades on the Resonance Conditions of Impellers". Applied Sciences 9, nr 10 (18.05.2019): 2051. http://dx.doi.org/10.3390/app9102051.
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The conventional resonance conditions are derived based on the conventionally designed impellers without splitter blades. This paper proposes the resonance conditions for impellers under the excitation from the impeller–diffuser interaction with attention paid on the influence of splitter blades. A lumped parameter model is established and the modal analysis is carried out. The blade-based representative modal vector (RMV) is defined. The influence of splitter blades on the impeller’s traits of modes is investigated by analyzing the spatial harmonic contents of the RMV. Then, given the specific form of the diffuser-induced engine order excitation acting on the main and splitter blades, the resonance conditions are derived. Tuned and mistuned cases are provided for a practical impeller. The resonance conditions are verified by harmonic response calculations. The applications of the proposed resonance conditions in resonance identification and hazard evaluation of different excitations are given. The differences between the proposed resonance conditions and the conventional ones are discussed. The research indicates that even the RMV of the tuned impeller contains two harmonic components due to the existence of splitter blades. When the excitation frequency equals the natural frequency of the impeller and the excitation order matches with either harmonic index of the two harmonics, the resonance occurs. The results of case studies show that the harmfulness of various engine orders of excitation can be exactly evaluated by the joint use of the spatial harmonic contents analysis result and the proposed resonance conditions; however, analyzing based on the conventional resonance conditions may lead to the misjudgment of the harmfulness of the excitations.
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Al-Khudair, Falih H. "Investigation of isospin excited and mixed-symmetry states in even–even N = Z nuclei". International Journal of Modern Physics E 27, nr 08 (sierpień 2018): 1850065. http://dx.doi.org/10.1142/s0218301318500659.
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Mixed-symmetry and isospin excited states are typical of the interacting boson model with isospin (IBM-3). With a view to look for such states, levels scheme of the IBM-3 dynamical symmetry is discussed. A systematic investigation in the proton and neutron degrees of freedom of the energy levels has been carried out. A sequence of isospin excitation bands has been identified. We have analyzed the wave functions and given the symmetrical labeling of the states. The transition probabilities between the isospin excitation states of model limits are analyzed in terms of isoscalar and isovector decompositions. The present calculations suggest that a combination of isospin excitation and mixed-symmetry states can provide substantial information on the structure of nuclear states. Calculations for [Formula: see text] and [Formula: see text] nuclei are presented and compared with the results of the shell model and available experimental data.
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Han, Jian Ping, i Pei Juan Zheng. "Modal Parameter Identification of a Rigid Frame-Continuous Girders Bridge under Ambient Excitation by Fast Bayesian FFT Method". Advanced Materials Research 639-640 (styczeń 2013): 985–91. http://dx.doi.org/10.4028/www.scientific.net/amr.639-640.985.
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Bayesian theory is adopted in modal parameter identification, finite element model updating and residual capacity evaluation of the structures recently. Fast Bayesian FFT modal identification approach provides a rigorous way to obtain modal parameters and well-separated modes using the fast Fourier transform under ambient excitation. Moreover, it avoids choosing the modal order or removing false modes based on the stable diagram and has its obvious advantages. In this paper, modal parameters of a rigid frame-continuous girders bridge under ambient excitation are identified by this approach. Comparison with stochastic subspace identification (SSI) method indicates that Fast Bayesian FFT is a good approach to identify the modal parameters even for a large number of measurement channels.
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Waluk, Jacek. "Non-classical effects in proton or hydrogen transfer". Pure and Applied Chemistry 88, nr 10-11 (1.11.2016): 1063–71. http://dx.doi.org/10.1515/pac-2016-0706.
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AbstractResults of thorough investigations of tautomerism in the ground and excited electronic states performed for various organic molecules under different regimes: condensed phases, isolated and single molecules, with a special emphasis on porphycene, a porphyrin isomer, demonstrate that, in order to precisely describe the proton/hydrogen transfer path, one has to explicitly consider tunneling. Tautomerization is a multidimensional process, controlled by excitation of specific vibrational modes. Vibrational excitation can both enhance or hinder the reaction. The role of specific vibrational modes can now be assessed, even at the level of single molecules.
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Wang, Zuo-Cai, Chun-Yang Huang, Zhi-Chao He i Yong-Ping Wang. "Strain modes identification using cross-correlation function of measured dynamic strain". Advances in Structural Engineering 20, nr 1 (28.07.2016): 96–104. http://dx.doi.org/10.1177/1369433216646008.
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Strain modes of structures reflect the distribution rule of dynamic strain and can be of service to structural health monitoring. This article presents a new method to estimate the strain modes of beam structures based on the measured dynamic strain. Since the cross-correlation matrix of the modal coordinates is a diagonal matrix, thus, the cross-correlation matrix of the measured dynamic strain is also a diagonal matrix, and the strain modes can be obtained to find the eigenvectors of the strain cross-correlation matrix. The strain modes of a simply support beam and a continuous beam subjected to various impulsive excitations are identified from the numerical simulations using the proposed method. The noise effect is also investigated in this article. The numerical results show that the proposed method can effectively identify the strain modes even with noise effect. Finally, the method is verified through the experiment of a simply supported beam under hammering excitation. The test results also show that the proposed method can estimate the strain modes of beam structures with a high accuracy.
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Smith, Craig C., i Forrest L. Staffanson. "Frequency and Spatial Shaping of Inputs for Multiaxis Shaker Testing". Shock and Vibration 3, nr 6 (1996): 393–401. http://dx.doi.org/10.1155/1996/919032.
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Controlled amplitude and phase relationships between multiaxial shaker inputs (i.e., spatial shaping) provides for more realistic simulation of a service environment than does conventional frequency shaping alone. Spatial shaping is described in terms of a basic mathematical model relating test article response (absolute and relative motions) to excitation by the shaker. Advantages and objectives are viewed through spectral relationships. The objective of simulating dynamic responses as in service is shown to be the duplication of the resultant cross-modal response for all important modes, even if the sources of excitation in service are unknown.
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Liu, H., Agne Ciuciulkaite, Vassilios Kapaklis, D. Karaiskaj i D. A. Arena. "Enhanced optical mode coherence in exchange coupled soft magnetic multilayers". Journal of Applied Physics 131, nr 21 (7.06.2022): 213902. http://dx.doi.org/10.1063/5.0093827.
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We report on an all-optical investigation of coupled spin excitation modes in a series of magnetic trilayer structures. Using time-resolved magneto-optic Kerr effect (tr-MOKE) magnetometry, we observe multi-mode coherent spin excitations in [Formula: see text]/Ru/[Formula: see text] multilayers even though the tr-MOKE optical detection is sensitive only to the [Formula: see text] magnetization dynamics. Frequency shifts of the different modes indicate that the coupling between the [Formula: see text] and [Formula: see text] layers varies from anti-ferromagnetic to ferromagnetic to uncoupled as the Ru spacer layer thickness is increased from 8 Å to 200 Å. The lifetime of the high frequency coherent oscillations in the [Formula: see text] layer increases by over 200%–300% even in the case of uncoupled [Formula: see text] and [Formula: see text] layers with a 200 Å thick Ru spacer. The results suggest an additional method to decrease the damping of high-moment alloys in layered magnetic nanostructures.
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Haga, Akihiro, Hiroshi Toki, Setsuo Tamenaga i Yataro Horikawa. "Relativistic mean-field model and random-phase approximation with vacuum polarization". Modern Physics Letters A 21, nr 31n33 (30.10.2006): 2447–54. http://dx.doi.org/10.1142/s0217732306022092.
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The collective multipole excitations are studied in the framework of relativistic random-phase approximation with the vacuum polarization. First, we show for the nuclear ground state that the leading order of derivative expansion of the effective action arising from the vacuum correction agrees with the exact calculation using the Green function method very well. The derivative expansion makes us easy to perform a fully self-consistent calculation, even for the random-phase approximation. A remarkable effect of the inclusion of the vacuum polarization is the increase of the effective mass meff/mN ~ 0.9, which gives, for all multipole modes, smaller energy-weighted sum rule values than those of the typical relativistic model. Also, the large effective mass constrained by the vacuum polarization can give an excellent agreement with experimental data on the excitation energy for the isoscalar quadrupole resonances. It is shown, further, that the change of the shell structure due to the vacuum polarization plays an important role in the dipole compression modes.
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Habenicht, Bradley F., Svetlana V. Kilina i Oleg V. Prezhdo. "Comparative analysis of electron-phonon relaxation in a semiconducting carbon nanotube and a PbSe quantum dot". Pure and Applied Chemistry 80, nr 7 (1.01.2008): 1433–48. http://dx.doi.org/10.1351/pac200880071433.
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The key features of the phonon-induced relaxation of electronic excitations in the (7,0) zig-zag carbon nanotube (CNT) and the Pb16Se16 quantum dot (QD) are contrasted using a time-domain ab initio density functional theory (DFT) simulation. Upon excitation from the valence to the conduction band (CB), the electrons and holes nonradiatively decay to the band-edge in both materials. The paper compares the electronic structure, optical spectra, important phonon modes, and decay channels in the CNT and QD. The relaxation is faster in the CNT than in the QD. In the PbSe QD, the electronic energy decays by coupling to low-frequency acoustic modes. The decay is nonexponential, in agreement with non-Lorentzian line-shapes observed in optical experiments. In contrast to the QD, the excitation decay in the CNT occurs primarily via high-frequency optical modes. Even though the holes have a higher density of states (DOS), they relax more slowly than the electrons, due to better coupling to low-frequency vibrations. Further, the expected phonon bottleneck is not observed in the QD, as rationalized by a high density of optically dark states. The same argument applies to the CNT. The computed results agree well with experimentally measured ultrafast relaxation time-scales and provide a unique atomistic picture of the electron-phonon relaxation processes.
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Soheibi, Nahid, Mahdi Eshghi, Mohsen Bigdeli i Majid Hamzavi. "Phenomenological and analytical solution of the Bohr model for even–even and odd–even nuclei with Mie potential". International Journal of Modern Physics E 28, nr 08 (sierpień 2019): 1950059. http://dx.doi.org/10.1142/s0218301319500599.
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In this paper, analytical solution of the Bohr model with Mie potential for even–even and odd–even nuclei are evaluated in the Bose alone symmetry [Formula: see text] and a new class of Bose–Fermi dynamical symmetry [Formula: see text], respectively. The excitation energy spectra as well as electromagnetic transition strengths, quadrupole moments and dipole moments are investigated near the critical point of shape phase transition between the spherical and deformed [Formula: see text]-unstable nuclei. To show our results are compatible with experiment, some examples are tested.
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Hugenberg, Nicholas R., Tuhin Roy, Hadiya Harrigan, Margherita Capriotti, Hyoung-Ki Lee, Murthy Guddati, James F. Greenleaf, Matthew W. Urban i Wilkins Aquino. "Toward improved accuracy in shear wave elastography of arteries through controlling the arterial response to ultrasound perturbation in-silico and in phantoms". Physics in Medicine & Biology 66, nr 23 (26.11.2021): 235008. http://dx.doi.org/10.1088/1361-6560/ac38fe.
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Abstract Dispersion-based inversion has been proposed as a viable direction for materials characterization of arteries, allowing clinicians to better study cardiovascular conditions using shear wave elastography. However, these methods rely on a priori knowledge of the vibrational modes dominating the propagating waves induced by acoustic radiation force excitation: differences between anticipated and real modal content are known to yield errors in the inversion. We seek to improve the accuracy of this process by modeling the artery as a fluid-immersed cylindrical waveguide and building an analytical framework to prescribe radiation force excitations that will selectively excite certain waveguide modes using ultrasound acoustic radiation force. We show that all even-numbered waveguide modes can be eliminated from the arterial response to perturbation, and confirm the efficacy of this approach with in silico tests that show that odd modes are preferentially excited. Finally, by analyzing data from phantom tests, we find a set of ultrasound focal parameters that demonstrate the viability of inducing the desired odd-mode response in experiments.
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Godart, Melanie, Arlette Grotsch-Noels i Marc-Antoine Dupret. "Pulsations in hot supergiants". Proceedings of the International Astronomical Union 9, S301 (sierpień 2013): 313–20. http://dx.doi.org/10.1017/s1743921313014518.
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AbstractMassive stars are the cosmic engines that shape and drive our Universe. Many issues such as their formation, their stability and the mass loss effects, are far from being completely understood. Recent ground-based and space observations have shown pulsations in massive MS and post-MS stars, such as acoustic and gravity modes excited by the κ-mechanism and even solar-like oscillations. Theoretical studies emphasized the presence of strange modes in massive models, and recent theoretical analyses have shown that hot supergiants can pulsate in oscillatory convective modes. We review the instability domains of massive stars as well as their excitation mechanisms and present the latest results.
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Sutherland, Bruce R. "Excitation of superharmonics by internal modes in non-uniformly stratified fluid". Journal of Fluid Mechanics 793 (16.03.2016): 335–52. http://dx.doi.org/10.1017/jfm.2016.108.
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Theory and numerical simulations show that the nonlinear self-interaction of internal modes in non-uniform stratification results in energy being transferred to superharmonic disturbances forced at twice the horizontal wavenumber and frequency of the parent mode. These disturbances are not in themselves a single mode, but a superposition of modes such that the disturbance amplitude is largest where the change in the background buoyancy frequency with depth is largest. Through weakly nonlinear interactions with the parent mode, the disturbances evolve to develop vertical-scale structures that distort and modulate the parent mode. Because pure resonant wave triads do not exist in non-uniformly stratified fluid, parametric subharmonic instability (PSI) is not evident even though noise is superimposed upon the initial state. The results suggest a new mechanism for energy transfer to dissipative scales (from large to small vertical scale and with frequencies larger and smaller than that of the parent mode) through forcing superharmonic rather than subharmonic disturbances.
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Torkanpouri, K. E., H. Zohoor i M. H. Korayem. "Effects of Tip Mass and Interaction Force on Nonlinear Behavior of Force Modulation FM-AFM Cantilever". Journal of Mechanics 33, nr 2 (23.06.2016): 257–68. http://dx.doi.org/10.1017/jmech.2016.44.
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AbstractInfluences of the tip mass, excitation mode of Frequency Modulated Atomic Force Microscope (FM-AFM) on the resonance frequency shift in force modulation (FM) mode are studied. Governing equations of motion are determined based on Timoshenko beam model with concentrated end mass. Approach point and base amplitude are set such that the FM-AFM remains just in FM mode. Either the linearized and nonlinear Derjaguin-Muller-Toporov (DMT) model are investigated. Then frequency shifts are determined for various interaction force regimes. It is showed the effect of tip mass on frequency shift is significant even for small tips. Nonlinear model shows lower frequency shifts in comparison with linearized model. It is showed that the amplitude of response is increased by increasing the tip mass and order of base excitation. Deviation of frequency shift between linearized and nonlinear solution are studied. It is declared that the error between linearized and nonlinear model is complicated. A deviation index is used for explaining behavior of error while tip mass and excitation mode are changed. It is showed, this index predicts the trend of error in all excitation modes and force cases. Behavior of system is linearizing by increasing the order of excitation, generally.
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Thuvanismail, Nasar, Sannasiraj Sannasi i Sundar Vallam. "Liquid sloshing dynamics in a barge carrying container subjected to random wave excitation". Journal of Naval Architecture and Marine Engineering 9, nr 1 (17.06.2012): 43–65. http://dx.doi.org/10.3329/jname.v9i1.7600.
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The sloshing phenomenon of liquid in a partially filled tank mounted rigidly on a barge exposed to random beam waves has been investigated through a well controlled experimental program. Four relative liquid depths, (liquid depth, hs/ length of tank, l) of 0.163, 0.325, 0.488 and 0.585 were considered for the tests. The sloshing oscillation was measured along the length of the tank at predefined locations. The effect of variation of the peak wave excitation frequency on the sloshing oscillation in the frequency domain is studied. The dominant energy is found to be concentrated around lowest nth sloshing mode frequency and, secondary peaks are observed at higher order sloshing frequencies. Odd modes contributions are dominating even modes irrespective of the excitation peak frequency. The sacrifice of second mode is observed while the excitation peak frequency is closer to its primary resonance. DOI: http://dx.doi.org/10.3329/jname.v9i1.7600 Journal of Naval Architecture and Marine Engineering 9(2012) 43-65
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WRZOSEK-LIPSKA, K., M. ZIELIŃSKA, K. HADYŃSKA-KLȨK, Y. HATSUKAWA, J. IWANICKI, J. KATAKURA, M. KISIELIŃSKI i in. "SHAPE EVOLUTION IN HEAVIEST STABLE EVEN-EVEN MOLYBDENUM ISOTOPES STUDIED VIA COULOMB EXCITATION". International Journal of Modern Physics E 20, nr 02 (luty 2011): 443–50. http://dx.doi.org/10.1142/s0218301311017831.
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The quadrupole shape evolution in heaviest stable Mo isotopes is studied in terms of the shape coexistence phenomenon occurrence in this region of nuclear chart. Quadrupole deformation parameters of the 96,98,100 Mo isotopes in the low-lying (ground and excited) 0+ states were deduced using Coulomb excitation method. In all cases rich sets of electromagnetic reduced matrix elements were determined using the GOSIA code and then analysed using the Quadrupole Sum Rules formalism. Discussion of the experimental results in comparison with the predictions of microscopic calculations within the general quadrupole collective Bohr Hamiltonian model is presented for 100 Mo .
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Radeș, Mircea. "Modal analysis of a simple cyclic system". Journal of Engineering Sciences and Innovation 4, nr 2 (30.05.2019): 115–30. http://dx.doi.org/10.56958/jesi.2019.4.2.115.
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Cyclic systems have double modes with identical natural frequencies. Using the theory of circulants, independent eigenvectors can be exactly determined without slightly perturbing the eigenvalues. The paper presents the contribution of the double modes to the frequency response functions (FRFs) of cyclic systems with proportional damping. The mode indicator functions UMIF and CoMIF, based on the left singular vectors of a matrix encompassing all available FRFs as columns, are applied to simulated noise-free data. It is shown that they can reveal double modes even using FRFs from single point excitation.
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Park, I. W., J. S. Kim i F. Ma. "Characteristics of Modal Coupling in Nonclassically Damped Systems Under Harmonic Excitation". Journal of Applied Mechanics 61, nr 1 (1.03.1994): 77–83. http://dx.doi.org/10.1115/1.2901425.
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The normal coordinates of a nonclassically damped system are coupled by nonzero off-diagonal elements of the modal damping matrix. The purpose of this paper is to study the characteristics of modal coupling, which is amenable to a complex representation. An analytical formulation is developed to facilitate the evaluation of modal coupling. Contrary to widely accepted beliefs, it is shown that enhancing the diagonal dominance of the modal damping matrix or increasing the frequency separation of the natural modes need not diminish the effect of modal coupling. The effect of modal coupling may even increase. It is demonstrated that, within the practical range of engineering applications, neither diagonal dominance of the modal damping matrix nor frequency separation of the natural modes would be sufficient for neglecting modal coupling.
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Lozeva, Radomira. "New nuclear structure data beyond 136Sn". EPJ Web of Conferences 178 (2018): 02020. http://dx.doi.org/10.1051/epjconf/201817802020.
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Exotic nuclei beyond the 132Sn double shell-closure are influenced by both the Sn superfluity and the evolving collectivity only few nucleons away. Toward even more neutron-rich nuclei, especially at intermediate mass number, the interplay between single-particle and collective particle-hole excitations competes. In some cases with the extreme addition of neutrons also other effects as the formation of neutron skin, stabilization as sub-shell gaps or orbital crossings may be expected. The knowledge of nuclear ingredients is especially interesting beyond 132Sn and little is known on how the excitation modes develop with the addition of both protons and neutrons and for example systematic prompt and decay studies can be such very sensitive probe. Recently, we have approached this region of nuclei in several experimental measurements following 238U projectile fission on 9Be and n-induced fission on 241Pu and 235U. Consistent data analysis allows to access various spins and excitation energies and provide new input to theory. Examples from these studies on several nuclei in the A~140 region were presented during the conference together with the possible interpretation of the new data. Here, we will illustrate one example on 136I using two complementary data sets.
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Mendes, Ricardo Ugliara, Kátia Lucchesi Cavalca i Luiz Otávio Saraiva Ferreira. "Analysis of a complete model of rotating machinery excited by magnetic actuator system". Proceedings of the Institution of Mechanical Engineers, Part C: Journal of Mechanical Engineering Science 227, nr 1 (17.04.2012): 48–64. http://dx.doi.org/10.1177/0954406212444510.
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Rotating machines have a wide range of application involving shafts rotating at high speeds that must have high confidence levels of operation. Therefore, the dynamic behavior analysis of such rotating systems is required to establish operational patterns of the equipment, providing the basis for controller development in order to reduce vibrations or even to control oil instabilities in lubricated bearings. A classical technique applied in parameter identification of machines and structures is the modal analysis, which consists of applying a perturbation force into the system and then to measure its response. However, there are mainly two problems in modal analysis concerning the excitation of rotating systems. First, there are limitations to the excitation of systems with rotating shafts when using impact hammers or shakers, due to friction, undesired tangential forces, and noise that can be introduced in the system response. The second problem relies in the difficulty of exciting backward whirl modes, an inherent characteristic from these systems. Therefore, the study of a non-contact technique of external excitation, also capable of exciting backward whirl modes, becomes of high interest. In this sense, this article deals with the study and modeling of a magnetic actuator, used as an external excitation source for a rotating machine, mainly in backward whirl mode. Special attention is given to the actuator model and its interaction with the rotor system. Differently from previous works with similar proposal, which uses current and air gap measurements, here the external excitation force control is based on the magnetic field directly measured by hall sensor positioned in the pole center of the magnetic actuator core. The magnetic actuator design was completely developed for this purpose, opening different paths to experimental application of this device, for example, fault detection analysis based on directional modes. It is also presented a comparison between the numerical simulations and practical tests obtained from a rotor test rig and an experimental evidence of the backward whirl was accomplished based on the numerical simulation results.
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Pillarisetti, Lalith Sai Srinivas, Cliff J. Lissenden i Parisa Shokouhi. "Control of low-frequency guided elastic wave modes in a hollow pipe using a meta-surface". AIP Advances 12, nr 8 (1.08.2022): 085027. http://dx.doi.org/10.1063/5.0098576.
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A locally resonant meta-surface for preferential excitation of a guided mode in a hollow pipe can improve ultrasonic guided wave inspection of pipelines. The proposed meta-surface comprises a periodic arrangement of bonded prismatic rod-like resonators in the circumferential and axial directions of the pipe. We demonstrate the presence of bandgaps for the low-frequency axisymmetric longitudinal modes L(0,1) and L(0,2) and the torsional mode T(0,1). The generated bandgaps can be used to filter the higher harmonics associated with the system nonlinearity to improve nonlinear ultrasonic measurements on pipes. These bandgaps exist even for the non-axisymmetric flexural modes but with their hybridized dispersion curves exhibiting mode-coupling for higher circumferential orders. Moreover, a “partial” bandgap is obtained where preferential transmission of the L(0,2) mode over L(0,1) is possible. We discuss the potential advantages of this partial bandgap to improve pipeline inspections using the L(0,2) mode. Time-domain finite element analyses are used to validate the presence of these bandgaps under radial, circumferential, and axial excitation that mimics the excitation using a ring of piezoelectric transducers. Finally, we discuss the influence of resonator spacing, filling fraction, and the number of resonator rings on the bandgaps for an informed meta-surface design.
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Paşca, H., A. V. Andreev, G. G. Adamian i N. V. Antonenko. "Role of the excitation energy of the compound nucleus in binary decay processes". EPJ Web of Conferences 169 (2018): 00015. http://dx.doi.org/10.1051/epjconf/201816900015.
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Employing the improved scission-point model, the isotopic and excitation energy trends of the charge distribution of fission fragments are studied in fission of even-even Th isotopes at low and high excitation energies.
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Prudnikov, I. R. "Guiding hard X-rays by means of a periodic multilayer waveguide with an air clearance: a numerical study". Journal of Applied Crystallography 40, nr 3 (15.05.2007): 427–35. http://dx.doi.org/10.1107/s0021889807012253.
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A periodic multilayer waveguide for X-rays with an air gap serving as a guiding layer is considered. The propagation of hard X-ray guided modes through such a waveguide has been investigated with the help of numerical modeling. The propagation lengths of the guided modes are analyzed thoroughly with respect to their dependence on the reflectivity of the periodic multilayers forming the waveguide. It is shown that the guided modes can be generated even in a waveguide composed of low-reflectivity multilayers. The influence of a standing wave inside the reflecting multilayers on the transmission of the guided waves by the waveguide is demonstrated. Conditions which are favorable for the excitation of the guided modes are discussed.
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Inci, I., i H. Sonkaya. "Coupling of a j = 3/2 nucleon to an even–even core with Davidson potential". International Journal of Modern Physics E 27, nr 10 (październik 2018): 1850085. http://dx.doi.org/10.1142/s0218301318500854.
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The properties of odd nuclei have been investigated within the collective model by assuming the system is composed of a single nucleon in the [Formula: see text] single particle orbit coupled to a [Formula: see text]-unstable even-core. The Davidson potential has been used in the corresponding Bohr Hamiltonian for the even core. The excitation energy spectrum and the electric quadrupole transition ratios have been obtained. The results have been used to predict the experimental data of the some selected odd isotopes.
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Arora, Nishta, i Akshay K. Naik. "Qualitative effect of internal resonance on the dynamics of two-dimensional resonator". Journal of Physics D: Applied Physics 55, nr 26 (5.04.2022): 265301. http://dx.doi.org/10.1088/1361-6463/ac5bc8.
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Abstract Nonlinear modal interactions and associated internal resonance phenomena have recently been used to demonstrate improved oscillator performance and enhanced sensing capabilities. Here, we show tunable modal interaction in a molybdenum disulfide (MoS2) resonator. We achieve the tunability of coupling between these initially uncoupled modes by using electrostatic gate voltages. This tunable coupling enables us to make the modes commensurate and observe energy exchange between the modes. We attribute the strong energy exchange between the vibrational modes to 1:2 internal resonance. This interaction strongly impacts the dynamics of the modal response of such resonators. We observe peak splitting, a signature of energy exchange between the modes even when the modal response is in the linear regime. We model our device to explain the observed effect of excitation, detuning of modal frequencies, and intermodal coupling strength on the resonator dynamics. MoS2 resonators explored in this work are ideal for understanding the rich dynamics offered through the intermodal coupling.
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Hong, Wenjia, i Yasushi Horii. "Contribution of Even/Odd Sound Wave Modes in Human Cochlear Model on Excitation of Traveling Waves and Determination of Cochlear Input Impedance". Acoustics 4, nr 1 (21.02.2022): 168–83. http://dx.doi.org/10.3390/acoustics4010011.
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Based on the Navier–Stokes equation for compressible media, this work studies the acoustic properties of a human cochlear model, in which the scala vestibuli and scala tympani are filled with compressible perilymph. Since the sound waves propagate as a compression wave in perilymph, this model can precisely handle the wave–based phenomena. Time domain analysis showed that a sound wave (fast wave) first propagates in the scala vestibuli and scala tympani, and then, a traveling wave (slow wave) is generated by the sound wave with some delay. Detailed studies based on even and odd mode analysis indicate that an odd mode sound wave, that is, the difference in the sound pressures between the scala vestibuli and scala tympani, excites the Békésy’s traveling wave, while an even mode sound determines the input impedance of the cochlea.
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ITO, MAKOTO. "ASYMMETRIC CLUSTERS IN EVEN Be ISOTOPES". Modern Physics Letters A 25, nr 21n23 (30.07.2010): 1862–65. http://dx.doi.org/10.1142/s0217732310000502.
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The generalized two-center cluster model (GTCM), which can treat various single particle configurations in general two center systems, is applied to light neutron-rich systems, Be isotopes (α+α+ X N). We discuss the change of the neutrons' configuration around two α-cores as a variation of an excitation energy. We show that the asymmetric clusters, which correspond to the atomic or ionic configurations, appear in the unbound region above the α particle-decay threshold systematically.
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Kareem, Noor M., i Ali A. Alzubadi. "Study of the Nuclear Structure for Some Nuclei Using Self-Consistent RPA Calculations with Skyrme-Type Interaction". East European Journal of Physics, nr 4 (6.12.2022): 57–71. http://dx.doi.org/10.26565/2312-4334-2022-4-04.
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In the present research, some static and dynamic nuclear properties of the closed-shell nuclei; 58Ni, 90Zr, 116Sn, and 144Sm nuclei have been studied using the Random Phase Approximation (RPA) method framework and different Skyrme parameterizations, particularly SyO-, Sk255, SyO+, SLy4, BSk17, and SLy5. In particular, in studies of static properties such as nuclear densities for neutrons, protons, mass, and charge densities with their corresponding rms radii, the single-particle nuclear density distributions All the obtained results agreed well with the relevant experimental data. Concerning the dynamic properties, the excitation energy, transition density, and giant resonance modes for the excitation to the low-lying negative partite excited states 1–, 3–, 5–, and 7– have also been studied. The findings indicate that estimates of RPA with Skyrme-type interactions are a good way to describe the properties of the structure of even-even, closed-shell nuclei.
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Wu, Yingxin, Aoxue Li, Feng Pan, Lianrong Dai i Jerry P. Draayer. "The Rotor-Vibrator Plus Multi-Particle-Hole Description of 154Gd". Symmetry 14, nr 12 (10.12.2022): 2620. http://dx.doi.org/10.3390/sym14122620.
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Based on the well-known rotor-vibrator model and the particle-plus-rotor model, multi-particle-hole excitations from a collective even-even core described by the rotor-vibrator is considered to describe well-deformed even-even nuclei. Like the particle-plus-rotor model, the intrinsic Vierergruppe (D2) symmetry is still preserved in the rotor-vibrator plus multi-particle-hole description. It is shown that a series of experimentally observed 0+ states in these nuclei may be interpreted as the multi-particle-hole excitations in a complementary manner to the beta and gamma vibrations described by the rotor-vibrator model. As a typical example of the model application, low-lying positive parity level energies below 1.990 MeV in the eight experimentally identified positive parity bands; a series of 0+ excitation energies up to 016+; and some experimentally known B(E2) values, E2 branching ratios, and E2/M1 and E0/E2 mixing ratios of 154Gd are fitted and compared to the experimental data. The results suggest that the multi-particle-hole-pair configuration mixing may play a role in these 0+ states.
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Chaplin, W. J., Y. Elsworth, G. R. Isaak, C. P. McLeod, B. A. Miller i R. New. "Excitation of Oscillations - An Update of Bison Data". Symposium - International Astronomical Union 185 (1998): 221–22. http://dx.doi.org/10.1017/s0074180900238667.
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BiSON is a 6-station, world-wide network of instruments which observe low-degree solar oscillations.Theory (Goldreich & Keeley, 1977) predicts that the probability distribution of the mode powers is expected to follow negative exponential statistics under the condition that the interval of time for which the modes are averaged is less than the lifetime of the mode. Simulations (Chaplin et al, 1997) confirm this. The first publication of such an analysis for real data (Elsworth et al., 1995) showed that the oscillations largely follow the predictions with a small excess of the very largest power in the modes. In this paper we extend the previous observations of BiSON data to 80 months of data taken during the declining phase of the solar cycle. The data span the period January 1990 to August 1996. The data have been analysed using Fourier transforms each about 1/2 day in length. The minimum data fill accepted in any one period was 0.7 (Elsworth et al, 1995). Below this fill the data were discarded. The resolution of such short transforms is insufficient to distinguish between the components of the even and odd mode pairs. The mode powers are calculated for mode pairs ℓ = 0 & 2 and ℓ=1&3.Comparison with theoretical predictions show that, as seen previously, there is still an excess of very high excitations which can be seen throughout the 80 months.
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EßLER, FABIAN H. L., i VLADIMIR E. KOREPIN. "SPECTRUM OF LOW-LYING EXCITATIONS IN A SUPERSYMMETRIC EXTENDED HUBBARD MODEL". International Journal of Modern Physics B 08, nr 23 (20.10.1994): 3243–79. http://dx.doi.org/10.1142/s0217979294001366.
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We continue the study of the u(2|2)-supersymmetric extension of the Hubbard model in one dimension. We determine the excitation spectrum at zero temperature even in the sectors where the ground states are u(2|2)-descendants of Bethe states. The excitations include spinons, holons, electrons, localons (local electron pairs, moving coherently through the lattice) and their bound states. The spectra are found to be very different for repulsive and attractive on-site interaction. We also study the thermodynamics of the model.
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Trumper, A. E., L. Capriotti i S. Sorella. "Low-lying spin-wave spectrum of the triangular anti-ferromagnet: A finite-size study". Canadian Journal of Physics 79, nr 11-12 (1.12.2001): 1537–42. http://dx.doi.org/10.1139/p01-084.
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We developed a finite-size spin-wave calculation on the Heisenberg anti-ferromagnet on the triangular lattice, which, to order 1/s, favors a singlet (for an even number of sites) ground state. Furthermore, we implement the computation of the low-energy excitation spectrum E (S) where S is the total spin. For s=1/2, the good agreement with the exact diagonalization and quantum Monte Carlo results strengthens the validity of the spin-wave expansion to describe the low-energy spin excitations of the Heisenberg model even in the presence of frustration. PACS No.: 75.10-b
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Bonatsos, Dennis, Andriana Martinou, Spyridon K. Peroulis, Theodoros J. Mertzimekis i Nikolay Minkov. "Shape Coexistence in Even–Even Nuclei: A Theoretical Overview". Atoms 11, nr 9 (30.08.2023): 117. http://dx.doi.org/10.3390/atoms11090117.
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The last decade has seen a rapid growth in our understanding of the microscopic origins of shape coexistence, assisted by the new data provided by the modern radioactive ion beam facilities built worldwide. Islands of the nuclear chart in which shape coexistence can occur have been identified, and the different microscopic particle–hole excitation mechanisms leading to neutron-induced or proton-induced shape coexistence have been clarified. The relation of shape coexistence to the islands of inversion, appearing in light nuclei, to the new spin-aligned phase appearing in N=Z nuclei, as well as to shape/phase transitions occurring in medium mass and heavy nuclei, has been understood. In the present review, these developments are considered within the shell-model and mean-field approaches, as well as by symmetry methods. In addition, based on systematics of data, as well as on symmetry considerations, quantitative rules are developed, predicting regions in which shape coexistence can appear, as a possible guide for further experimental efforts that can help in improving our understanding of the details of the nucleon–nucleon interaction, as well as of its modifications occurring far from stability.
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Panigrahi, P. K., i S. Acharya. "Multi-Modal Forcing of the Turbulent Separated Shear Flow Past a Rib". Journal of Fluids Engineering 126, nr 1 (1.01.2004): 22–31. http://dx.doi.org/10.1115/1.1637634.
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Experiments have been conducted to study the development of flow behind a surface mounted rib under different phase controlled excitation. Single mode excitation and multi-mode excitation with different relative phases are studied. The results presented include the coherent and random components of the turbulent energy and shear stresses, the energy exchange with the mean flow and between the modes, and the phase decorrelation of the coherent components. The fundamental-subharmonic excitation does not provide any significant improvements in the shear layer growth over the fundamental excitation. The shear layer growth correlates with the subharmonic mode development. The large scale structures are significant even after the reattachment region as evident from the magnitude of the coherent components of the turbulent energy and the shear stress. The binary exchange terms are significant in the near-field region whose sign is phase dependent, i.e., it reverses its sign based on the phase difference between the fundamental and 1st subharmonic mode. The location of the fundamental and subharmonic peaks are different from the peak location of their respective energy exchange with the mean flow; this is attributed to the significance of the binary energy exchange between the fundamental and the subharmonic mode in this region. The excitation regularizes the flow leading to low phase jitter in the near field region. The origin and development of phase decorrelation is attributed primarily to the subharmonic instability.
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Mikola, P. V., Z. M. Kenzhegulova i R. S. Surovtsev. "Analysis of the pulse signal propagation in a turn of a meander line of two segments based on lattice diagrams". Journal of Physics: Conference Series 2291, nr 1 (1.07.2022): 012030. http://dx.doi.org/10.1088/1742-6596/2291/1/012030.
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Abstract The analysis of the propagation of a pulse signal in a turn of a meander line of two segments is carried out. For this purpose, the plotting of lattice diagrams for the even and odd modes is carried out, as well as their subsequent comparison with the time responses to the pulse excitation in each node of the line. A complete coincidence of the amplitudes and arrival times of pulses obtained by different methods was obtained.
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Papadopoulos, C. A., i A. D. Dimarogonas. "Coupled Vibration of Cracked Shafts". Journal of Vibration and Acoustics 114, nr 4 (1.10.1992): 461–67. http://dx.doi.org/10.1115/1.2930285.
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The coupling of vibration modes of vibration of a clamped-free circular cross-section Timoshenko beam with a transverse crack is investigated in this paper. A 6 × 6 local flexibility matrix is used to simulate the crack. The nondiagonal terms of this matrix cause coupling between the longitudinal, torsional, and bending vibrations. Coupling is apparent in all spectra obtained with a harmonic sweeping excitation throughout the frequency range. The method is very sensitive even for small cracks.
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Hussain, A. K. M. F., i M. A. Z. Hasan. "Turbulence suppression in free turbulent shear flows under controlled excitation. Part 2. Jet-noise reduction". Journal of Fluid Mechanics 150 (styczeń 1985): 159–68. http://dx.doi.org/10.1017/s0022112085000076.
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It is shown that reduction of broadband (even total) far-field jet noise can be achieved via controlled excitation of a jet at a frequency in the range 0.01 < Stθ < 0.02, where Stθ is the Strouhal number based on the exit momentum thickness of the shear layer. Hot-wire measurements in the noise-producing region of the jet reveal that the noise suppression is a direct consequence of turbulence suppression, produced by early saturation and breakdown of maximally growing instability modes.
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Li, Dongkang, Tao Wang i Feng Pan. "Shape Phase Transitions in Even–Even 176–198Pt: Higher-Order Interactions in the Interacting Boson Model". Symmetry 14, nr 12 (9.12.2022): 2610. http://dx.doi.org/10.3390/sym14122610.
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Dynamical symmetry plays a dominant role in the interacting boson model in elucidating nuclear structure, for which group theoretical or algebraic techniques are powerful. In this work, the higher-order interactions required in describing triaxial deformation in the interacting boson model are introduced to improve the fitting results to low-lying level energies, B(E2) values and electric quadrupole moments of even–even nuclei. As an example of the model application, the low-lying excitation spectra and the electromagnetic transitional properties of even–even 176−198Pt are fitted and compared to the experimental data and the results of the consistent-Q formalism. It is shown that the results obtained from the model are better than those of the original consistent-Q formalism, indicating the importance of the higher-order interactions in describing the structure and the shape phase evolution of these nuclei.
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Howie, A., F. J. Garcia de Abajo i N. Yamamoto. "Quantitative Low Loss and Ultra Low Loss Spectroscopy in the STEM". Microscopy and Microanalysis 7, S2 (sierpień 2001): 190–91. http://dx.doi.org/10.1017/s1431927600027021.
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Many of the topics in valence spectroscopy originally pioneered with TEM equipment have now been taken over by STEM. Notable exceptions are the studies by J. Silcox and his colleagues of plasmon dispersion and of the guided modes in thin slabs where retardation and other relativistic effects arise. The growing use of STEM valence EELS on increasingly complex nanostructures and the development of dielectric excitation theory for quantitative interpretation of the results were recently reviewed. The spatial resolution approaches the atomic scale, exceeding by orders of magnitude the capability of near field spectroscopy. By using the cathodoluminescence (CDL) signal, optical precision in STEM energy loss measurement can also be achieved, particularly in the difficult region below 5 eV or even 1 eV. High spatial resolution can be preserved provided that an intermediate stage of carrier diffusion is not involved in the radiative decay of excitations.Figure 1 shows STEM CDL images of an Ag particle obtained from the dipole l=1 and quadrupole l=2 surface plasmon excitations
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Terradas, Jaume, Adolfo F. Viñas i Jaime A. Araneda. "Excitation of ion-acoustic waves by non-linear finite-amplitude standing Alfvén waves". Astronomy & Astrophysics 660 (kwiecień 2022): A24. http://dx.doi.org/10.1051/0004-6361/202141914.
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We investigate, using a multi-fluid approach, the main properties of standing ion-acoustic modes driven by non-linear standing Alfvén waves. The standing character of the Alfvénic pump is due to the superposition of two identical circularly polarised counter-propagating waves. We consider parallel propagation along the constant magnetic field and we find that left- and right-handed modes generate via ponderomotive forces the second harmonic of standing ion-acoustic waves. We demonstrate that parametric instabilities are not relevant in the present problem and the secondary ion-acoustic waves attenuate by Landau damping in the absence of any other dissipative process. Kinetic effects are included in our model where ions are considered as particles and electrons as a massless fluid, and hybrid simulations are used to complement the theoretical results. Analytical expressions are obtained for the time evolution of the different physical variables in the absence of Landau damping. From the hybrid simulations we find that the attenuation of the generated ion-acoustic waves follows the theoretical predictions even under the presence of an Alfvénic pump. Due to the non-linear induced ion-acoustic waves the system develops density cavities and an electric field parallel to the magnetic field. Theoretical expressions for this density and electric field fluctuations are derived. The implications of these results in the context of standing slow mode oscillations in coronal loops is discussed.
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Nadirbekov, M. S., S. N. Kudiratov, F. N. Temirov i N. Minkov. "Vibrational-rotational spectra of even–even nuclei with quadrupole and octupole deformations". International Journal of Modern Physics E 29, nr 06 (czerwiec 2020): 2050031. http://dx.doi.org/10.1142/s0218301320500317.
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Vibrational-rotation levels of the yrast and first nonyrast alternating-parity bands of the lanthanide [Formula: see text]Nd, [Formula: see text]Sm, [Formula: see text]Gd, [Formula: see text]Er and actinide [Formula: see text]Th, [Formula: see text]U, [Formula: see text]Pu nuclei are studied in the framework of a nonadiabatic collective model of even–even nuclei with quadrupole and octupole deformations. The theoretical spectra are obtained through the use of Gauss and harmonic-oscillator (HO) potentials in the radial part of the Schrödinger equation which is taken in polar coordinates. The change of the surface deformation of the nucleus with the collective excitation energy is taken into account. The [Formula: see text] staggering structure of the yrast alternating-parity bands is also considered. The theoretically obtained energy bands and staggering diagrams are in good agreement with the corresponding experimental data and point out the soft character of the collective quadrupole–octupole deformation mode manifesting in these nuclei.
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Jasim, Mahdi Hadi. "The effect of deformation parameter of heavy nuclei on level density parameter". Iraqi Journal of Physics (IJP) 12, nr 25 (12.02.2019): 38–43. http://dx.doi.org/10.30723/ijp.v12i25.302.
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The possible effect of the collective motion in heavy nuclei has been investigated in the framework of Nilson model. This effect has been searched realistically by calculating the level density, which plays a significant role in the description of the reaction cross sections in the statistical nuclear theory. The nuclear level density parameter for some deformed radioisotopes of (even- even) target nuclei (Dy, W and Os) is calculated, by taking into consideration the collective motion for excitation modes for the observed nuclear spectra near the neutron binding energy. The method employed in the present work assumes equidistant spacing of the collective coupled state bands of the considered isotopes. The present calculated results for first excited rotational band have been compared with the accumulated values from the literature for s-wave neutron resonance data, and were in good agreement with those data.
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Desbiolles, Benoit X. E., Gabriela Furlan, Adam M. Schwartzberg, Paul D. Ashby i Dominik Ziegler. "Electrostatically actuated encased cantilevers". Beilstein Journal of Nanotechnology 9 (8.05.2018): 1381–89. http://dx.doi.org/10.3762/bjnano.9.130.
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Background: Encased cantilevers are novel force sensors that overcome major limitations of liquid scanning probe microscopy. By trapping air inside an encasement around the cantilever, they provide low damping and maintain high resonance frequencies for exquisitely low tip–sample interaction forces even when immersed in a viscous fluid. Quantitative measurements of stiffness, energy dissipation and tip–sample interactions using dynamic force sensors remain challenging due to spurious resonances of the system. Results: We demonstrate for the first time electrostatic actuation with a built-in electrode. Solely actuating the cantilever results in a frequency response free of spurious peaks. We analyze static, harmonic, and sub-harmonic actuation modes. Sub-harmonic mode results in stable amplitudes unaffected by potential offsets or fluctuations of the electrical surface potential. We present a simple plate capacitor model to describe the electrostatic actuation. The predicted deflection and amplitudes match experimental results within a few percent. Consequently, target amplitudes can be set by the drive voltage without requiring calibration of optical lever sensitivity. Furthermore, the excitation bandwidth outperforms most other excitation methods. Conclusion: Compatible with any instrument using optical beam deflection detection electrostatic actuation in encased cantilevers combines ultra-low force noise with clean and stable excitation well-suited for quantitative measurements in liquid, compatible with air, or vacuum environments.
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MATTIS, DANIEL C. "ABSENCE OF A GAP IN THE EXCITATION SPECTRUM (PHONONS) OF ANHARMONIC SOLIDS". Modern Physics Letters B 01, nr 01n02 (maj 1987): 1–5. http://dx.doi.org/10.1142/s0217984987000028.
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Acoustic phonons are the suitably quantized low-lying normal modes of elastic solids. Their energies ε(k) are given by ε(k)=ħω(k), where the frequencies ω(k) are proportional to k (k=wavevector, or inverse wavelength) and vanish as w=sk (s=speed of sound) in the limit k→0. Here we prove a similar result for a reasonably general class of anharmonic solids, applicable even to such solids as the various He4 phases, H2 molecular solid, etc., which are in the extreme quantum limit. We show that the spectrum of elementary excitations in the harmonic solid provides an upper bound to the spectrum of elementary excitations in the similar anharmonic solid having the same ground state interatomic spring constantsK.
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MESSING, RALF, i MARKUS J. KLOKER. "Investigation of suction for laminar flow control of three-dimensional boundary layers". Journal of Fluid Mechanics 658 (30.06.2010): 117–47. http://dx.doi.org/10.1017/s0022112010001576.
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Direct numerical simulations are employed to investigate the effects of discrete suction orifices at the wall on the disturbance evolution in laminar three-dimensional boundary-layer flows with favourable pressure gradient. Suction panels with many suction orifices can excite unstable crossflow (CF) modes even if the orifice spacing is smaller than the chordwise/spanwise wavelengths of unstable modes, caused by imperfections in the orifice order or suction strength. It has been found that the most unstable steady vortex mode leads to strong CF vortices that invoke turbulence by secondary instability even on the active suction panel. The deliberate excitation and support of stabilizing vortices that have less than two-thirds of the spanwise wavelength of the most amplified ones – known from the upstream flow deformation or micrometre-sized roughness elements technique – by the orifice order on the panel can secure the desired stabilizing effect of suction and lower the necessary suction amount significantly.