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Resonance Frequency (resonance + frequency)
Terms modified by Resonance Frequency Selected AbstractsAdvanced resonant ultrasound spectroscopy for measuring anisotropic elastic constants of thin filmsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2005H. OGI ABSTRACT This paper presents an advanced resonant ultrasound spectroscopy (RUS) method to determine the elastic constants Cij of thin films. Polycrystalline thin films often exhibit elastic anisotropy between the film growth direction and the in-plane direction, and they macroscopically show five independent elastic constants. Because all of the Cij of a deposited thin film affect the mechanical resonance frequencies of the film/substrate layer specimen, measuring resonance frequencies enables one to determine the Cij of the film with known density, dimensions and the Cij of the substrate. Resonance frequencies have to be measured accurately because of low sensitivity of the Cij of films to them. We achieved this by a piezoelectric tripod. Mode identification has to be made unambiguously. We made this measuring displacement,amplitude distributions on the resonated specimen surface by laser Doppler interferometry. We applied our technique to copper thin film and diamond thin film. They show elastic anisotropy and the Cij smaller than bulk values of Cij. Micromechanics calculations indicate the presence of incohesive bonded regions. [source] Resonance frequency of hexagonal and half hexagonal microstrip antennasMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 2 2009K. P. Ray Abstract Closed form expressions for the accurate calculation of the resonance frequency of a hexagonal and half hexagonal microstrip antennas, based on their equivalence with rectangular microstrip antenna, have been presented. These proposed empirical formulae have been validated using simulations and experiments. Design curves, for the input impedance variation along the feed axis, have been presented for hexagonal and half hexagonal patches for two feed positions. © 2008 Wiley Periodicals, Inc. Microwave Opt Technol Lett 51: 448,452, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.24087 [source] Positive effect of early loading on implant stability in the bi-cortical guinea-pig modelCLINICAL ORAL IMPLANTS RESEARCH, Issue 4 2005Els De Smet Abstract: Loading, early after implant placement, has gained rapid interest in dentistry. Primary implant stability, as e.g. defined by resonance frequency instrumentation, has been isolated as a predicator when immediate and early implant loading is applied. The aim of this study was to investigate the effect of early (after 7 days) mechanical loading on the establishment of osseointegration by means of resonance frequency analysis (RFA). Percutaneous titanium implants were installed in both tibiae of 10 guinea-pigs. One week after implant installation, one implant (test) was loaded daily for 6 weeks, while the contra-lateral served as the unloaded one (control). A sinusoidally varying bending moment was applied at a frequency of 3 Hz and a force amplitude of 5 N, for 1800 cycli. Resonance frequency was measured at implant installation and from then on weekly using the RFA-device (Osstell®). Contrary to control implants, that showed a decrease in stability 1 week after installation, reaching a minimum at 3 weeks (,200 Hz), test implants showed a progressive increase in stability over time. After 6 weeks, the mean resonance frequency of test and control implants reached the same values. As confirmed by recent literature, early loading does not have to endanger the establishment of osseointegration of titanium implants. On the contrary, controlled loading is beneficial to maintain the implant stability during the early critical healing period as determined by RFA-measurements. Résumé La mise en charge précoce après l'insertion de l'implant acquière beaucoup d'intérêt en médecine dentaire. La stabilité primaire de l'implant, qui est par exemple définie par l'instrumentation de fréquence de résonnance RFA, a été isolée comme un annonciateur lorsque la mise en charge de l'implant était précoce ou immédiate. Le but de cette étude a été d'étudier l'effet d'une mise en charge précoce (sept jours) sur l'établissement de l'ostéïntégration à l'aide de RFA (Osstell®). Des implants titane percutanés ont été insérés dans les deux tibias de dix cobayes. Une semaine après le placement des implants, un implant test a été mis en charge tous les jours pendant six semaines tandis que le contralatéral servait de contrôle et n'était pas mis en charge. Un moment sinusoïdal a été appliquéà une fréquence de trois hertz et une amplitute d'une force de 5 N pour 1 800 cycles. La fréquence de résonnance a été mesurée lors de l'insertion de l'implant et ensuite hebdomadairement en utilisant le RFA. Contrairement aux implants contrôles, qui accusaient une diminution de la stabilité une semaine après leur insertion atteignant un minimum après trois semaines (,200 Hz), les implants tests ont montré une augmentation progressive de la stabilité avec le temps. Après six semaines, la fréquence de résonnance moyenne des implants tests et contrôles atteignaient les mêmes valeurs. Comme décrit dans la littérature récente, la mise en charge précoce ne met pas en danger l'établissement de l'ostéoïntégration des implants en titane. Au contraire, une mise en charge contrôlée est bénéfique au maintien de la stabilité implantaire durant la période de guérison critique précoce comme déterminée par les mesures RFA. Zusammenfassung Die Belastung kurz nach der Implantatplatzierung hat in der Zahnmedizin schnell an Interesse gewonnen. Die Primärstabilität der Implantate, bestimmt z.B. durch Messung der Resonanzfrequenz, hat sich als Voraussagewert herauskristallisiert, wenn eine Sofort-oder Frühbelastung der Implantate durchgeführt wird. Das Ziel dieser Studie war, den Einfluss der frühen (nach 7 Tagen) mechanischen Belastung auf die Ausbildung der Osseointegration mittels Resonanzfrequenzanalyse (RFA) zu untersuchen. In die beiden Tibias von 10 Meerschweinchen wurden perkutane Titanimplantate eingesetzt. Eine Woche nach der Implantation wurde ein Implantat (Test) während 6 Wochen täglich belastet, während das kontralaterale Implantat unbelastet blieb (Kontrolle). Es wurde ein Biegemoment mit sinusoidalen Schwankungen mit einer Frequenz von 3 Hz und einer Kraftamplitude von 5 N in 1800 Zyklen appliziert. Die Resonanzfrequenz wurde nach der Implantation und dann wöchentlich mit einem RFA-Gerät (Osstell®) gemessen. Im Gegensatz zu den Kontrollimplantaten, welche eine Woche nach dem Setzen eine Stabilitätsabnahme zeigten und das Minimum nach drei Wochen (,200 Hz) erreichten, konnte bei den Testimplantaten eine progressive Zunahme der Stabilität über die Zeit beobachtet werden. Nach sechs Wochen erreichten die mittleren Resonanzfrequenzen der Test-und Kontrollimplantate dieselben Werte. Die frühe Belastung gefährdet die Ausbildung einer Osseointegration bei Titanimplantaten nicht, was auch durch die neuere Literatur bestätig wird. Im Gegenteil, eine kontrollierte Belastung ist von Vorteil für den Erhalt der Implantatstabilität während der kritischen frühen Einheilphase. Dies konnte mittels RFA Messungen ermittelt werden. Resumen La carga temprana tras la colocación del implante ha ganado rápidamente interesen odontología. Se ha aislado como predictor, la estabilidad primaria del implante, definida por instrumentación de frecuencia de resonancia, cuando se aplica la carga temprana al implante. La intención del estudio fue investigar el efecto de carga mecánica temprana (tras 7 días) en el establecimiento de la osteointegración por medio del análisis de la frecuencia de resonancia (RFA). Se instalaron implantes de titanio percutaneos en ambas tibias de 10 conejos de indias. Una semana tras la instalación, un implante (prueba) se cargó diariamente durante 6 semanas, mientras que el contralateral sirvió como el implante sin carga (control). Se aplicó un momento de flexión variante sinusoidalmente a una frecuencia de 3 Hz y una amplitud de la fuerza de 5 N, durante 1899 ciclos. Se midió la frecuencia de resonancia al instalar el implante y a partir de ahí semanalmente usando el dispositivo RFA (Ostell®). Contrariamente a los implantes de control, que mostraron una disminución de la estabilidad una semana después de la instalación, alcanzando un mínimo a las tres semanas (,200 Hz), los implantes de prueba mostraron un incremento progresivo de la estabilidad a lo largo del tiempo. Tras seis semanas, la frecuencia de resonancia de los implantes de prueba y de control alcanzaron los mismos valores. Tal como se confirma por la literatura reciente, la carga temprana no debe hacer peligrar el establecimiento de la osteointegración de los implantes de titanio. Por lo contrario, la carga controlada es beneficiosa para mantener la estabilidad de los implantes durante el periodo crítico de la cicatrización determinado por las mediciones de RFA. [source] NMR diffusion measurements under chemical exchange between sites involving a large chemical shift differenceCONCEPTS IN MAGNETIC RESONANCE, Issue 2 2010S. Leclerc Abstract This study concerns the thallium-205 cation in aqueous solution in the presence of a calixarene molecule. Although the measurement of the self-diffusion coefficient of pure thallium (without calixarene in the aqueous solution) does not pose any particular problem, major difficulties are encountered with the standard method using gradient strength increment as soon as thallium is partly complexed by calixarene. With static magnetic field gradients, the NMR signal is so weak that it prevents any reliable measurement, whereas radio frequency (rf) field gradients lead to an unrealistic value of the diffusion coefficient. This failure is explained by the fact that thallium is in fast exchange between two sites (complexed and free thallium) thus exhibiting a single NMR signal although, in the course of the experiment, two signals, with an important difference in resonance frequencies (due to the large thallium chemical shift range), are effectively involved. With the objective to understand these quite unexpected observations, the theory underlying NMR diffusion experiments is first reviewed, and criteria of fast exchange are discussed for three parameters: chemical shifts, relaxation rates, and diffusion coefficients. It turns out that off-resonance effects are responsible for unwanted defocusing due to rf pulses in the static magnetic field gradient method and for time-dependent gradients in the rf field gradient method. Concerning the latter, a remedy is proposed which consists in applying the stronger gradient and incrementing the gradient pulse durations. After correction for relaxation, the expected value of the diffusion coefficient is retrieved. © 2010 Wiley Periodicals, Inc. Concepts Magn Reson Part A 36A: 127,137, 2010. [source] Nuclear magnetic moments from NMR spectra,Experimental gas phase studies and nuclear shielding calculationsCONCEPTS IN MAGNETIC RESONANCE, Issue 5 2007Karol Jackowski Abstract NMR spectra of gaseous compounds and quantum chemical calculations are combined to determine new accurate values of magnetic dipole moments for a series of nuclei. We have analyzed shielding constants, resonance frequencies, and nuclear magnetic moments for a group of simple molecules. The chemical shifts and resonance frequencies are measured at 300 K and extrapolated to the zero-density limit in order to remove all the intermolecular effects from the experimental parameters. The absolute shielding constants in the studied molecules are obtained from ab initio calculations. Assuming the proton magnetic moment as the reference, we determine the nuclear magnetic moments of 13C, 14N, 15N, 17O, 19F, 29Si, 31P, 33S, and 73Ge. The new nuclear magnetic moments are consistent with the experimental NMR parameters, and using these new values one can for the first time predict successfully the shielding constant of a nucleus in a molecule when the corresponding resonance frequency is known. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 246,260, 2007. [source] Maximum likelihood constrained deconvolution.CONCEPTS IN MAGNETIC RESONANCE, Issue 2 2003II: Application to experimental two-, three-dimensional NMR spectra Abstract The maximum likelihood method (MLM) and related protocols were applied to the experimental 2-D nuclear Overhauser effect (NOE) spectrum of a 24-nucleotide RNA hairpin loop molecule. The output becomes more valuable when diagonal symmeterization is followed by MLM. This symmeterized maximum likelihood (SML) protocol restores the original spectral information with high fidelity by accurately partitioning components from overlapped peaks and provides substantial improvements in line shape and spectral resolution, in particular in the F1 dimension. These advantages lead to a simpler interpretation of the resonance frequencies, intensities, multiplet fine structure, and J -coupling values from a heavily overlapped peak region. This promises a more effective tool for peak picking, assignment, and integration. Also, application of MLM and related protocols to the 2-D NOE proton spectrum of a 24-mer RNA dramatically increases the number of NOE-based distance constraints that can be used for determination of its 3-D molecular structure. By application of 3-D MLM to a simple 3-D spectrum, the spectral resolution and signal-to-noise (S/N) ratio was greatly improved by effective line sharpening and reduction of cross-talk between planes. © 2003 Wiley Periodicals, Inc. Concepts Magn Reson 18A: 146,156, 2003 [source] Maximum likelihood constrained deconvolution.CONCEPTS IN MAGNETIC RESONANCE, Issue 6 2002I: Algorithm, qualitative, quantitative enhancement in synthetic two-dimensional NMR spectra Abstract The maximum likelihood method is a constrained iterative spectral deconvolution technique in which a spectral fitting model is determined by minimizing the variance of fit in the time domain in a nonlinear iterative manner. Application of this method to synthetic 2-dimensional (2-D) NMR spectra, which have heavily overlapped multiplets associated with low signal to noise ratios, yields contrast-enhanced spectra with simultaneous noise suppression and resolution improvement. This protocol greatly facilitates peak recognition and often partitions overlapping multiplets into individual components, leading to a more accurate interpretation of resonance frequencies, coupling constants, and multiplets than does the conventional apodization or Fourier transform method. These advantages are useful for constructing reliable 3-D molecular structures for complex molecular systems. © 2002 Wiley Periodicals, Inc. Concepts Magn Reson 14: 402,415, 2002 [source] The effects of torsion and motion coupling in site response estimationEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 5 2003Mohammad R. Ghayamghamian Abstract Soil amplification characteristics are investigated using data from the Chibaken-Toho-Oki earthquake and its aftershocks recorded at Chiba dense array in Japan. The frequency-dependent amplification function of soil is calculated using uphole-to-downhole spectral ratio analysis, considering the horizontal components of shear wave. The identified spectral ratios consistently demonstrate the splitting of peaks in their resonance frequencies and low amplification values in comparison with a 1D model. The torsional behaviour and horizontal ground motion coupling are clarified as the reasons for these phenomena at the site. To prove the hypothesis, the torsional motion is directly evaluated using the data of the horizontal dense array in different depths at the site. The comparison between Fourier spectra of torsional motion and identified transfer functions reveals the peaks at the same frequencies. The wave equation including torsion and horizontal motion coupling is introduced and solved for the layered media by applying wave propagation theory. Using the developed model, the effects of torsional motion with horizontal motion coupling on soil transfer function are numerically examined. Splitting and low amplification at resonance frequencies are confirmed by the results of numerical analysis. Furthermore, the ground motion in two horizontal directions at the site is simulated using site geotechnical specification and optimizing the model parameters. The simulated and recorded motions demonstrate good agreement that is used to validate the hypothesis. In addition, the spectral density of torsional ground motions are compared with the calculated one and found to be well predicted by the model. Finally, the results are used to explain the overestimation of damping in back-calculation of dynamic soil properties using vertical array data in small strain level. Copyright © 2003 John Wiley & Sons, Ltd. [source] An experimental evaluation of ice cover effects on the dynamic behaviour of a concrete gravity damEARTHQUAKE ENGINEERING AND STRUCTURAL DYNAMICS, Issue 12 2002Patrick Paultre Abstract An extensive forced-vibration testing programme has been carried out on an 84-m concrete gravity dam located in northeastern Québec, Canada. The dam was subjected to a harmonic load on the crest in summer and severe winter conditions with temperatures ranging from ,10°C to ,15°C and a 1.0,1.5m ice cover. Acceleration and hydrodynamic frequency responses were obtained in different locations on the dam and in the reservoir. The main objective of the repeated tests was to investigate the effects of the ice cover on the dynamic behaviour of the dam,reservoir,foundation system, by comparing summer and winter results. Modifications in damping and resonance frequencies were observed, as well as an additional resonance that was attributed to an interaction of the dam with the ice cover. These findings provided a reliable and unique database for the investigations of dam,reservoir,foundation interaction and, in particular, the ice-cover effects for dams located in northern regions. Copyright © 2002 John Wiley & Sons, Ltd. [source] Recognition of resonance in long radial transmission lines with static VAR compensation using travelling wavesEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 1 2005Ljubivoje M. Popovi Abstract This paper presents an analytical procedure for estimation of resonance frequencies in long-distance radial transmission lines with static VAR compensation. The development of the procedure is based on a new approach in solving this problem. It employs the fact that the phenomenon is characterized by an algebraic sum of travelling current waves at the beginning of the line. Relatively simple analytical expressions are obtained by considering the phase angles of only one direct and only one corresponding reflected wave. Besides enabling a simpler and faster solution of the problem under various realistic conditions, the obtained analytical expressions also offer more direct analytical insight into the interplay of basic parameters. Copyright © 2005 John Wiley & Sons, Ltd. [source] A wide-band lumped circuit model of the terminal and internal electromagnetic response of coaxially insulated windings mounted on a coreEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 3 2003P. Holmberg This paper presents a wide-band lumped circuit model of coaxially insulated windings mounted on a core. The polyphase model can be used to simulate the terminal and internal electromagnetic response in DryformerTM, a new oil-free power transformer, and similar electromagnetic power devices. The circuit parameters are based on geometrical and material data. The simulated frequency and transient response of the lumped circuit is compared to measurements on a 20 MVA 140/6.6 kV three-phase transformer of the DryformerTM type. The comparison shows that the model can be used to estimate resonance frequencies and transient overvoltages in the transformer, although the damping is not accurately modelled. The influence of the core is discussed and investigated. [source] Advanced resonant ultrasound spectroscopy for measuring anisotropic elastic constants of thin filmsFATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 8 2005H. OGI ABSTRACT This paper presents an advanced resonant ultrasound spectroscopy (RUS) method to determine the elastic constants Cij of thin films. Polycrystalline thin films often exhibit elastic anisotropy between the film growth direction and the in-plane direction, and they macroscopically show five independent elastic constants. Because all of the Cij of a deposited thin film affect the mechanical resonance frequencies of the film/substrate layer specimen, measuring resonance frequencies enables one to determine the Cij of the film with known density, dimensions and the Cij of the substrate. Resonance frequencies have to be measured accurately because of low sensitivity of the Cij of films to them. We achieved this by a piezoelectric tripod. Mode identification has to be made unambiguously. We made this measuring displacement,amplitude distributions on the resonated specimen surface by laser Doppler interferometry. We applied our technique to copper thin film and diamond thin film. They show elastic anisotropy and the Cij smaller than bulk values of Cij. Micromechanics calculations indicate the presence of incohesive bonded regions. [source] Geophysical investigation and dynamic modelling of unstable slopes: case-study of Kainama (Kyrgyzstan)GEOPHYSICAL JOURNAL INTERNATIONAL, Issue 1 2008G. Danneels SUMMARY The presence of massive Quaternary loess units at the eastern border of the Fergana Basin (Kyrgyzstan, Central Asia) makes this area particularly prone to the development of catastrophic loess earthflows, causing damages and injuries almost every year. Efficient disaster management requires a good understanding of the main causes of these mass movements, that is, increased groundwater pressure and seismic shaking. This paper focuses on the Kainama earthflow, mainly composed of loess, which occurred in 2004 April. Its high velocity and the long run-out zone caused the destruction of 12 houses and the death of 33 people. In summer 2005, a field survey consisting of geophysical and seismological measurements was carried out along the adjacent slope. By combination and geostatistical analysis of these data, a reliable 3-D model of the geometry and properties of the subsurface layers, as shown in the first part of the paper, was created. The analysis of the seismological data allowed us to point out a correlation between the thickness of the loess cover and the measured resonance frequencies and associated amplification potential. The second part of this paper is focused on the study of the seismic response of the slope by numerical simulations, using a 2-D finite difference code named FLAC. Modelling of the seismic amplification potential along the slope confirmed the results obtained from the seismological survey,strong amplifications at the crest and bottom of the slope where there is a thick loess cover and almost no amplification in the middle part of the slope. Furthermore, dynamic slope stability analyses were conducted to assess the influence of local amplifications and increased groundwater pressures on the slope failure. The results of the dynamic modelling, although preliminary, show that a combination of seismic and hydrologic origin (pore pressure build-up during the seismic shaking) is the most probable scenario responsible for the 2004 failure. [source] Resonance behaviour of viscoelastic fluid in Poiseuille flow in the presence of a transversal magnetic fieldINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 8 2005Muhammad R. Mohyuddin Abstract The oscillatory flow of a viscoelastic fluid in a circular pipe under the influence of a transversal magnetic field is studied. Exact solutions for the axial velocity and flow rate are presented. The velocity enhancement and the resonance behaviour are analysed both numerically and asymptotically in the case of small pipe radii. Approximations for the resonance frequencies and the achievable velocity enhancements are derived. Copyright © 2005 John Wiley & Sons, Ltd. [source] Adaptive repetitive control for resonance cancellation of a distributed solar collector fieldINTERNATIONAL JOURNAL OF ADAPTIVE CONTROL AND SIGNAL PROCESSING, Issue 4 2009J. D. Álvarez Abstract This paper deals with modelling and control of the outlet temperature in a distributed solar collector field. The resonance dynamics characteristics of this kind of system are similar to those of tubular heat exchangers in the closed-loop system bandwidth when fast responses are required. Simple low-order rational models are unable to capture the resonance dynamics, which can be excited by changes in both the heat transfer fluid flow and solar irradiation. This paper proposes a new model derived from a similar model for a tubular heat exchanger. This model allows the use of low-order controllers, which can be extended to an adaptive control scheme to account for varying resonance frequencies, as a new functionality achieving fast, well-damped responses. Copyright © 2008 John Wiley & Sons, Ltd. [source] Nordic rattle: the hoarse vocalization and the inflatable laryngeal air sac of reindeer (Rangifer tarandus)JOURNAL OF ANATOMY, Issue 2 2007Roland Frey Abstract Laryngeal air sacs have evolved convergently in diverse mammalian lineages including insectivores, bats, rodents, pinnipeds, ungulates and primates, but their precise function has remained elusive. Among cervids, the vocal tract of reindeer has evolved an unpaired inflatable ventrorostral laryngeal air sac. This air sac is not present at birth but emerges during ontogenetic development. It protrudes from the laryngeal vestibulum via a short duct between the epiglottis and the thyroid cartilage. In the female the growth of the air sac stops at the age of 2,3 years, whereas in males it continues to grow up to the age of about 6 years, leading to a pronounced sexual dimorphism of the air sac. In adult females it is of moderate size (about 100 cm3), whereas in adult males it is large (3000,4000 cm3) and becomes asymmetric extending either to the left or to the right side of the neck. In both adult females and males the ventral air sac walls touch the integument. In the adult male the air sac is laterally covered by the mandibular portion of the sternocephalic muscle and the skin. Both sexes of reindeer have a double stylohyoid muscle and a thyroepiglottic muscle. Possibly these muscles assist in inflation of the air sac. Head-and-neck specimens were subjected to macroscopic anatomical dissection, computer tomographic analysis and skeletonization. In addition, isolated larynges were studied for comparison. Acoustic recordings were made during an autumn round-up of semi-domestic reindeer in Finland and in a small zoo herd. Male reindeer adopt a specific posture when emitting their serial hoarse rutting calls. Head and neck are kept low and the throat region is extended. In the ventral neck region, roughly corresponding to the position of the large air sac, there is a mane of longer hairs. Neck swelling and mane spreading during vocalization may act as an optical signal to other males and females. The air sac, as a side branch of the vocal tract, can be considered as an additional acoustic filter. Individual acoustic recognition may have been the primary function in the evolution of a size-variable air sac, and this function is retained in mother,young communication. In males sexual selection seems to have favoured a considerable size increase of the air sac and a switch to call series instead of single calls. Vocalization became restricted to the rutting period serving the attraction of females. We propose two possibilities for the acoustic function of the air sac in vocalization that do not exclude each other. The first assumes a coupling between air sac and the environment, resulting in an acoustic output that is a combination of the vocal tract resonance frequencies emitted via mouth and nostrils and the resonance frequencies of the air sac transmitted via the neck skin. The second assumes a weak coupling so that resonance frequencies of the air sac are lost to surrounding tissues by dissipation. In this case the resonance frequencies of the air sac solely influence the signal that is further filtered by the remaining vocal tract. According to our results one acoustic effect of the air sac in adult reindeer might be to mask formants of the vocal tract proper. In other cervid species, however, formants of rutting calls convey essential information on the quality of the sender, related to its potential reproductive success, to conspecifics. Further studies are required to solve this inconsistency. [source] Dynamic resonances in ultra-short laser pulsesLASER PHYSICS LETTERS, Issue 6 2007N.V. Bordyug Abstract Dynamic multiphoton resonances in ultra-short superintense laser pulses consisting of 50,200 field periods are considered numerically for a two-level system. The impact of nonresonant (Bloch-Siegert) and carrier-envelope effects on the dynamics of a two-level system was studied numerically, and conditions for complete population inversion were derived. The widths of multiphoton resonances increase with the increasing of the laser field. Results do not depend practically on the pulse duration. Effective resonance frequencies for multiphoton resonances increases strongly in a super-intense field. Multiphoton resonances are shifted and unified with each other in super-intense laser fields. (© 2007 by Astro Ltd., Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA) [source] Electronic structure and biological activity of chosen DDT-type insecticides studied by 35Cl-NQRMAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2009Maciej Jad Abstract A correlation between the electronic structure and biological activity of chosen dichlorodiphenyltrichloroethane (DDT)-type insecticides: 1,1,1-trichloro-2,2-bis(4-chlorophenyl)ethane, 1,1-dichloro-2,2-bis(4-chlorophenyl)ethane, 2,2-bis(p-chlorophenyl)-1,1-dichloroethylene, 2,2-bis(4-chlorophenyl)ethanoic acid and 4,4,-dichlorobenzophenone (used in agriculture) has been analysed on the basis of the 35Cl-nuclear quadrupole resonance (NQR) spectroscopy. The 35Cl-NQR resonance frequencies measured at 77 K have been correlated with the lethal dose (LD50) parameter that characterises the biological activity of these insecticides. Copyright © 2008 John Wiley & Sons, Ltd. [source] Shaping and timing gradient pulses to reduce MRI acoustic noise,MAGNETIC RESONANCE IN MEDICINE, Issue 2 2010Marcel Segbers MSc Abstract A method to reduce the acoustic noise generated by gradient systems in MRI has been recently proposed; such a method is based on the linear response theory. Since the physical cause of MRI acoustic noise is the time derivative of the gradient current, a common trapezoid current shape produces an acoustic gradient coil response mainly during the rising and falling edge. In the falling edge, the coil acoustic response presents a 180° phase difference compared to the rising edge. Therefore, by varying the width of the trapezoid and keeping the ramps constant, it is possible to suppress one selected frequency and its higher harmonics. This value is matched to one of the prominent resonance frequencies of the gradient coil system. The idea of cancelling a single frequency is extended to a second frequency, using two successive trapezoid-shaped pulses presented at a selected interval. Overall sound pressure level reduction of 6 and 10 dB is found for the two trapezoid shapes and a single pulse shape, respectively. The acoustically optimized pulse shape proposed is additionally tested in a simulated echo planar imaging readout train, obtaining a sound pressure level reduction of 12 dB for the best case. Magn Reson Med, 2010. © 2010 Wiley-Liss, Inc. [source] Generalized early-time/late-time evolutionary programming-based CLEANMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 1 2008In-Sik Choi Abstract A novel method, which is called generalized early-time/late-time evolutionary programming (EP)-based CLEAN algorithm, is proposed for simultaneous extraction of the scattering centers and natural resonance frequencies of a radar target. This algorithm uses a duality between the temporal late-time response and spectral early-time response. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 50: 208,210, 2008; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.23032 [source] Miniaturized microstrip meander-line antenna with very high-permittivity substrate for sensor applicationsMICROWAVE AND OPTICAL TECHNOLOGY LETTERS, Issue 10 2007Haiwen Liu Abstract This article presents a compact microstrip meander-line antenna for sensor network applications in the 290 MHz band. The antenna is fed by coplanar waveguide and its dimension is 15 mm × 15 mm × 2 mm. Because of the use of a very high relative permittivity substrate (,r = 90) and meander-line structure simultaneously, the side length of the designed antenna is about ,g/12 (,g is the guided wavelength) so that the circuit size is reduced greatly. Measurements verify that the proposed antenna has bandwidth of 12% at the resonant frequency of 293 MHz. Also, the radiation patterns measured at resonance frequencies are very close to omnidirectional in the E-plane. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 2438,2440, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22798 [source] Estimation of screened plasma resonance frequencies of a layered semiconductor using a single oblique incidence reflectance spectrumPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 4 2007O. Foltin Abstract The second derivative of a simulated oblique incidence specular reflectance spectrum of infrared radiation, polarized parallel to the plane of incidence, shows the possibility of estimating the values of two screened plasma resonance frequencies of an optically uniaxial semiconductor by knowledge of a single spectrum. The use of a basal plane reflection surface enables us, in a case of a layered semiconductor, to avoid a troublesome production and a poor spectroscopic quality of the reflection surface oriented normal to the easy cleavage plane, otherwise needed for one of the normal incidence reflectance measurements. For the calculations the parameters of a Bi2Se3 crystal were used. (© 2007 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Einstein Lecture , Passion for precision,ANNALEN DER PHYSIK, Issue 9 2006T.W. Hänsch Abstract Optical frequency combs from mode-locked femtosecond lasers have link optical and microwave frequencies in a single step, and they provide the long missing clockwork for optical atomic clocks. By extending the limits of time and frequency metrology, they enable new tests of fundamental physics laws. Precise comparisons of optical resonance frequencies of atomic hydrogen and other atoms with the microwave frequency of a cesium atomic clock are establishing sensitive limits for possible slow variations of fundamental constants. Optical high harmonic generation is extending frequency comb techniques into the extreme ultraviolet, opening a new spectral territory to precision laser spectroscopy. Frequency comb techniques are also providing a key to attosecond science by offering control of the electric field of ultrafast laser pulses. In our laboratories at Stanford and Garching, the development of new instruments and techniques for precision laser spectroscopy has long been motivated by the goal of ever higher resolution and measurement accuracy in optical spectroscopy of the simple hydrogen atom which permits unique confrontations between experiment and fundamental theory. This lecture recounts these adventures and the evolution of laser frequency comb techniques from my personal perspective. [source] High-speed serial-kinematic SPM scanner: design and drive considerations,ASIAN JOURNAL OF CONTROL, Issue 2 2009Kam K. Leang Abstract This paper describes the design of a flexure-guided, two-axis nanopositioner (scanner) driven by piezoelectric stack actuators. The scanner is specifically designed for high-speed scanning probe microscopy (SPM) applications, such as atomic force microscopy (AFM). A high-speed AFM scanner is an essential component for acquiring high-resolution, three-dimensional, time-lapse images of fast processes such as the rapid movement of cells and the diffusion of DNA molecules. A two-axis SPM scanner is proposed, where the slow and fast scanning axes are serially connected and flexure guided to minimize runout. The scanner's achievable scan range is approximately 10µm × 10µm. Finite element analysis is utilized to optimize the mechanical resonance frequencies of the scanner. Experimental results show a first major resonance in the slow and fast axis at 1.5 and 29,kHz, respectively. This paper also discusses the various tradeoffs between speed, range, electrical requirements, and scan trajectory design for high-speed nanopositioning. Copyright © 2009 John Wiley and Sons Asia Pte Ltd and Chinese Automatic Control Society [source] High-Resolution Solid-State NMR Studies on Uniformly [13C,15N]-Labeled UbiquitinCHEMBIOCHEM, Issue 9 2005Karsten Seidel Abstract Understanding of the effects of intermolecular interactions, molecular dynamics, and sample preparation on high-resolution magic-angle spinning NMR data is currently limited. Using the example of a uniformly [13C,15N]-labeled sample of ubiquitin, we discuss solid-state NMR methods tailored to the construction of 3D molecular structure and study the influence of solid-phase protein preparation on solid-state NMR spectra. A comparative analysis of13C,,13C,, and13C, resonance frequencies suggests that13C chemical-shift variations are most likely to occur in protein regions that exhibit an enhanced degree of molecular mobility. Our results can be refined by additional solid-state NMR techniques and serve as a reference for ongoing efforts to characterize the structure and dynamics of (membrane) proteins, protein complexes, and other biomolecules by high-resolution solid-state NMR. [source] Nuclear magnetic moments from NMR spectra,Experimental gas phase studies and nuclear shielding calculationsCONCEPTS IN MAGNETIC RESONANCE, Issue 5 2007Karol Jackowski Abstract NMR spectra of gaseous compounds and quantum chemical calculations are combined to determine new accurate values of magnetic dipole moments for a series of nuclei. We have analyzed shielding constants, resonance frequencies, and nuclear magnetic moments for a group of simple molecules. The chemical shifts and resonance frequencies are measured at 300 K and extrapolated to the zero-density limit in order to remove all the intermolecular effects from the experimental parameters. The absolute shielding constants in the studied molecules are obtained from ab initio calculations. Assuming the proton magnetic moment as the reference, we determine the nuclear magnetic moments of 13C, 14N, 15N, 17O, 19F, 29Si, 31P, 33S, and 73Ge. The new nuclear magnetic moments are consistent with the experimental NMR parameters, and using these new values one can for the first time predict successfully the shielding constant of a nucleus in a molecule when the corresponding resonance frequency is known. © 2007 Wiley Periodicals, Inc. Concepts Magn Reson Part A 30A: 246,260, 2007. [source] NMR nomenclature: Nuclear spin properties and conventions for chemical shifts (IUPAC recommendations 2001),CONCEPTS IN MAGNETIC RESONANCE, Issue 5 2002Robin K. Harris Abstract A unified scale is recommended for reporting the NMR chemical shifts of all nuclei relative to the 1H resonance of tetramethylsilane. The unified scale is designed to provide a precise ratio, ,, of the resonance frequency of a given nuclide to that of the primary reference, the 1H resonance of tetramethylsilane (TMS) in dilute solution (volume fraction, , < 1%) in chloroform. Referencing procedures are discussed, including matters of practical application of the unified scale. Special attention is paid to recommended reference samples and values of , for secondary references on the unified scale are listed, many of which are the results of new measurements. Some earlier recommendations relating to the reporting of chemical shifts are endorsed. The chemical shift, ,, is redefined to avoid previous ambiguities but to leave practical usage unchanged. Relations between the unified scale and recently published recommendations for referencing in aqueous solutions (for specific use in biochemical work) are discussed, as well as the special effects of working in the solid state with magic-angle spinning. In all, nine new recommendations relating to chemical shifts are made. Standardized nuclear spin data are also presented in tabular form for the stable (and some unstable) isotopes of all elements with non-zero quantum numbers. The information given includes quantum numbers, isotopic abundances, magnetic moments, magnetogyric ratios and receptivities, together with quadrupole moments and linewidth factors (where appropriate). © 2001 IUPAC. Concepts Magn Reson 14:326,346, 2002 [source] Tuning Nanotubes: Beam to String Transition of Vibrating Carbon Nanotubes Under Axial Tension (Adv. Funct.ADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Mater. On page 1753, the vibration properties of carbon nanotubes (CNTs) under axial tension are quantificationally studied by X. L. Wei et al. through a novel in situ method for precise and simultaneous measurement of the resonance frequency, the axial tension applied to individual CNTs, and the tube geometry. A gradual beam-to-string transition from multiwalled CNTs to singlewalled CNTs is observed; the CNTs can be tuned like a zither! [source] Beam to String Transition of Vibrating Carbon Nanotubes Under Axial TensionADVANCED FUNCTIONAL MATERIALS, Issue 11 2009Xianlong Wei Abstract State-of-the-art nanoelectromechanical systems have been demonstrated in recent years using carbon nanotube (CNT) based devices, where the vibration of CNTs is tuned by tension induced through external electrical fields. However, the vibration properties of CNTs under axial tension have not been quantitatively determined in experiments. Here, a novel in situ method for precise and simultaneous measurement of the resonance frequency, the axial tension applied to individual CNTs and the tube geometry is demonstrated. A gradual beam-to-string transition from multi-walled CNTs to single-walled CNTs is observed with the crossover from bending rigidity dominant regime to extensional rigidity dominant regime occur much larger than that expected by previous theoretical work. Both the tube resonance frequency under tension and transition of vibration behavior from beam to string are surprisingly well fitted by the continuum beam theory. In the limit of a string, the vibration of a CNT is independent of its own stiffness, and a force sensitivity as large as 0.25,MHz (pN),1 is demonstrated using a 2.2,nm diameter single-walled CNT. These results will allow for the designs of CNT resonators with tailored properties. [source] Increasing the vertical resolution of conventional sub-bottom profilers by parametric equalizationGEOPHYSICAL PROSPECTING, Issue 2 2002P. Cobo ABSTRACT Vertical resolution, i.e. the ability to resolve two close reflectors, is a crucial aspect of pulses used in geo-acoustic exploration of sea sub-bottoms. This paper deals with the problem of exploring the shallowest unconsolidated layers of the seafloor with conventional piezo-electric sonar pulses. Such transducers do not have a sufficiently broad transmission response to enable them to radiate short high-resolution pulses. Therefore, some kind of equalization process must be applied to broaden the transmission response. Here, inverse filtering is used to calculate the transducer driving waveform so that the subsequent acoustic pulse has a zero-phase cosine-magnitude nature. Within a specified bandwidth, this pulse has minimum length, i.e. maximum resolution. The method has been applied to compress the acoustic pulses radiated by two piezo-electric transducers. In conventional performance, these transducers radiate narrowband pulses which contain several cycles at the natural resonance frequency. Under equalized driving, both transducers emit broadband pulses, with resolving power greatly increased, at the cost of some amplitude loss. That is, the pulses radiated by both transducers have been shortened from 1 ms (low-frequency transducer) and 0.274 ms (high-frequency transducer) in conventional performance to 0.13 ms and 0.038 ms in equalized mode, with amplitude losses of 33% and 56%, respectively. The great improvement in the resolution of this technique is demonstrated by comparing the synthetic echograms that should be obtained when exploring a wedge model using zero-phase cosine-magnitude pulses with conventional ping pulses. [source] | |||||||||||||||||||||||||||||||||||||||||||