Frequency Of Fundamental Mode Research Articles

Fluorescence Spectra of 7,8-Benzoquinoline Isolated in the Supersonic Jet Expansion - An Ab Initio Analysis

The optimized equilibrium geometry of 7,8-benzoquinoline molecule in its first excited, S1, singlet state was computed with the use of ab initio RCIS/6-31G(d) method. It was found that the electronic transition to the first excited state in 7,8-benzoquinoline is not confined to the neighborhood of nitrogen atom, but is delocalized over entire aromatic rings system, much alike in the molecule of phenanthrene. With the optimized geometry of the ground and excited state of the molecule, the frequencies of the vibrational fundamental modes were computed, together with their displacement parameters (geometry changes of vibrations between the excited and the ground state). These frequencies are in good agreement with vibrational frequencies present in the fluorescence spectrum of 7,8-benzoquinoline observed recently under jet-cooling conditions in supersonic beam expansion. In comparison to the fluorescence spectrum of phenanthrene, the calculated, as well as experimental fluorescence spectra of 7,8-benzoquinoline contain much more vibrational features, and this increased vibronic activity is related to the symmetry break caused by the introduction of N-heteroatom into the aromatic ring system of phenanthrene.

Elastic stars in general relativity: III. Stiff ultrarigid exact solutions

We present an equation of state for elastic matter which allows for purely longitudinal elastic waves in all propagation directions, not just principal directions. The speed of these waves is equal to the speed of light whereas the transversal type speeds are also very high, comparable to but always strictly less than that of light. Clearly such an equation of state does not give a reasonable matter description for the crust of a neutron star, but it does provide a nice causal toy model for an extremely rigid phase in a neutron star core, should such a phase exist. Another reason for focusing on this particular equation of state is simply that it leads to a very simple recipe for finding stationary rigid motion exact solutions to the Einstein equations. In fact, we show that a very large class of stationary spacetimes with constant Ricci scalar can be interpreted as rigid motion solutions with this matter source. We use the recipe to derive a static spherically symmetric exact solution with constant energy density, regular centre and finite radius, having a nontrivial parameter that can be varied to yield a mass–radius curve from which stability can be read off. It turns out that the solution is stable down to a tenuity R/M slightly less than 3. The result of this static approach to stability is confirmed by a numerical determination of the fundamental radial oscillation mode frequency. We also present another solution with outwards decreasing energy density. Unfortunately, this solution only has a trivial scaling parameter and is found to be unstable.

Elastic stars in general relativity: II. Radial perturbations

We study radial perturbations of general relativistic stars with elastic matter sources. We find that these perturbations are governed by a second-order differential equation which, along with the boundary conditions, defines a Sturm–Liouville-type problem that determines the eigenfrequencies. Although some complications arise compared to the perfect fluid case, leading us to consider a generalization of the standard form of the Sturm–Liouville equation, the main results of Sturm–Liouville theory remain unaltered. As an important consequence we conclude that the mass–radius curve for a one-parameter sequence of regular equilibrium models belonging to some particular equation of state can be used in the same well-known way as in the perfect fluid case, at least if the energy density and the tangential pressure of the background solutions are continuous. In particular, we find that the fundamental mode frequency has a zero for the maximum mass stars of the models with solid crusts considered in paper I of this series.

High-Q single crystal silicon HARPSS capacitive beam resonators with self-aligned sub-100-nm transduction gaps

This paper reports on the fabrication and characterization of high-quality factor (Q) single crystal silicon (SCS) in-plane capacitive beam resonators with sub-100 nm to submicron transduction gaps using the HARPSS process. The resonating element is made of single crystal silicon while the drive and sense electrodes are made of trench-refilled polysilicon, yielding an all-silicon capacitive microresonator. The fabricated SCS resonators are 20-40 /spl mu/m thick and have self-aligned capacitive gaps. Vertical gaps as small as 80 nm in between 20 /spl mu/m thick silicon structures have been demonstrated in this work. A large number of clamped-free and clamped-clamped beam resonators were fabricated. Quality factors as high as 177000 for a 19 kHz clamped-free beam and 74000 for an 80 kHz clamped-clamped beam were measured under 1 mtorr vacuum. Clamped-clamped beam resonators were operated at their higher resonance modes (up to the fifth mode); a resonance frequency of 12 MHz was observed for the fifth mode of a clamped-clamped beam with the fundamental mode frequency of 0.91 MHz. Electrostatic tuning characteristics of the resonators have been measured and compared to the theoretical values. The measured Q values of the clamped-clamped beam resonators are within 20% of the fundamental thermoelastic damping limits (Q/sub TED/) obtained from finite element analysis.

Identification of reactor internals' vibration modes of a Korean standard PWR using structural modeling and neutron noise analysis

The vibration characteristics of a Korean standard PWR reactor internals have been estimated through a three-dimensional finite element analyses and verified by using the mode separated power spectral density functions obtained from the ex-core neutron noise signals. Also the natural vibration modes of the fuel assembly have been identified measuring both the ex-core and the in-core neutron noise signals which are close to each other. As a result, the fundamental bending mode frequency of the reactor internal structure is found to be around 8 Hz and the fundamental shell mode frequency 14.5 Hz, respectively. It is also shown that the fundamental bending mode frequency of the fuel assembly is 2.3 Hz and the 2nd bending mode frequency 5.8 Hz, respectively. These results can be used for the supplements of the Korean standard PWR's CVAP (Comprehensive Vibration Assessment Program) data.

Structure and Vibrational Modes of the Cyanovinyl Radical: A Study by Time-Resolved Fourier Transform IR Emission Spectroscopy

The structure and vibrational modes of the cyanovinyl radical have been characterized by using time-resolved Fourier transform IR emission spectroscopy. The cyanovinyl radical was generated with internal excitation through photodissociation of acrylonitrile. IR emission, detected with submicrosecond time resolution, from reaction products following photodissociation revealed the vibrational modes. The two vibrational modes of the cyanovinyl radical with the strongest transition strength have been identified at their fundamental transition frequencies: the CN stretch mode at 2563 cm-1 and the CH2 out-of-plane wag at 965 cm-1. The assignments were supported by experiments with deuterated acrylonitrile and ab initio calculations. Rotational contour analysis of the CN emission band indicates that the equilibrium structure is bent at the CCC angle.

Active Vibration Damping of Composite Beam using Smart Sensors and Actuators

This paper discusses active vibration control of an E-glass/epoxy-laminated composite beam using smart sensors and actua- tors. The smart sensors and actuators used in this study are piezoelectric ceramic patches. The composite beam is in a cantilevered configuration. Both theoretical and numerical ~finite-element analysis! studies of the laminated composite beam are conducted to reveal the beam's fundamental modal frequencies and modal shapes. The results based on the theoretical predication and numerical simulation are then compared with those from experimental modal testing, and a good correlation is obtained. Utilizing results from the model analysis and experimental modal testing, two control algorithms, namely, positive position feedback control and strain rate feedback control, are designed. Both single-mode vibration suppression and multimode vibration suppression are studied. An experimental appa- ratus has been developed to implement the control algorithms. The apparatus consists of a voltage amplifier and a data acquisition and real-time control system, in addition to the composite beam with bonded piezoelectric ceramic sensors and actuators. Experiments show that the proposed controllers can achieve active vibration damping of the composite beam.

Finite Element Modeling of Segmented Active Constrained Damping Layers including Bonding Layer Effect

This paper presents a new research and design finite element tool to analyze segmented active constrained layer damping treatments applied in bending. This numerical tool is based on a new five-layer beam finite element that accounts for bonding layer strain energy. Preliminary studies have confirmed that strains in the bonding layers can have a significant effect on damping ratios at the fundamental modal frequencies. This effect is particularly strong when relatively thin compliant piezo materials are used for constraining layers. The frequency-dependent stiffness and damping properties in viscoelastic materials are modeled using anelastic displacement fields (ADF). The effectiveness of the finite element model is validated experimentally for both active and passive constraining layers.

Generation of extra and very low-frequency (ELF/VLF) radiation by ionospheric electrojet modulation using high-frequency (HF) heating waves

Extra and very low-frequency (ELF/VLF) wave generation by modulated polar electrojet currents is studied numerically. Through Ohmic heating by the amplitude-modulated high-frequency heating wave, the conductivity and thus the current of the electrojet are modulated accordingly to set up the ionospheric antenna current. Stimulated thermal instability, which can further enhance the electrojet current modulation, is studied. It is first analysed analytically to determine the threshold heating power for its excitation. The nonlinear evolutions of the generated ELF/VLF waves enhanced by the instability are then studied numerically. Their spectra are also evaluated. The field intensity of the emission at the fundamental modulation frequency is found to increase with the modulation frequency in agreement with the Tromso observations. The efficiency enhancement by the stimulated thermal instability is hampered by inelastic collisions of electrons with neutral particles (mainly due to vibration excitation of N2), which cause this instability to saturate at low levels. However, the electron inelastic collision loss rate drops rapidly to a low value in the energy regime from 3.5 to 6 eV. As the heating power exceeds a threshold level, significant electron heating enhanced by the instability is shown, which indeed causes a steep drop in the electron inelastic collision loss rate. Consequently, this instability saturates at a much higher level, resulting to a near step increase (of about 10–13 dB depending on the modulation wave form) in the spectral intensity of ELF radiation. The dependence of the threshold power of the HF heating wave on the modulation frequency is determined.

Exact determination of HOM frequency in storage ring RF cavity

A formula for the determination of higher-order mode (HOM) frequency in an active storage ring RF cavity is derived, which utilizes the frequency tuning mechanism of the low-level RF feedback system. It helps us to understand the behavior of coupled bunch instabilities in a storage ring whenever we change the operating beam current, the cavity gap voltage, and the ring RF frequency as well. This analysis includes the fundamental mode frequency detuning for beam loading and Robinson damping. At any operating conditions of the RF cavity, the HOM frequencies can be precisely calculated with the low-power measurement data of the frequency shift as a function of the tuner position. The formula shows a good agreement with the measurement results.

Investigation of atypical seismic response of a base-isolated bridge

The seismic response of a base-isolated bridge is investigated with the help of acceleration data recorded during four moderate to small earthquakes. It is observed that the dynamic behavior of the bridge is not typical of base-isolated bridges as some of the transverse side-stoppers obstructed the movement of isolation bearings. Examination of the recorded transfer functions revealed that the dynamics of the bridge is dominated by the fundamental mode. Fundamental modal frequency and damping ratio of the bridge are identified and consequences of malfunctioning of isolation bearings are examined. It is found that malfunctioning of base-isolation bearings at one pier resulted in substantially unequal lateral load distribution to the substructure which signifies the attention to be devoted to such structural details for desired working of the whole system.

Raman spectra of MWCNTs and MWCNT-based H 2-adsorbing system

Raman spectra were taken with an UV–vis Raman system on two types of multiwalled carbon nanotubes (MWCNTs, CH 4-based) and MWCNTs (CO-based), grown catalytically with CH 4 and CO as the carbon sources, respectively, and their H 2-adsorbing systems. The strongest peak at 1580 cm −1 and the second-strongest band at 1416 cm −1 could be attributed to the fundamental frequency modes E 2g and D (induced by defects) analogous to those of graphite, and the bands at 2832, 2996, 3160 cm −1 and the region 4410–4422 cm −1 may be due to their second- and third-order combination frequencies: 2 D, D+ E 2g, 2 E 2g, and 2 D+ E 2g, respectively. By a comparative study with the different laser excitation lines (325 nm vs. 514 nm), it is found that the position of the D-band depends strongly on the laser excitation frequency. The Raman-spectroscopic investigation of the H 2–MWCNTs adsorption systems showed that adsorption of H 2 on the MWCNTs could occur in associative and dissociative forms. The observed Raman peaks at 2856, 2967 and 3950 cm −1 may be assigned to symmetric C–H stretch of surface C H 2, asymmetric C–H stretch of surface C H 3, and H–H stretch of molecularly adsorbed H 2(a), respectively. It was also shown that the concentration of the observed hydrogen-containing ad-species on the MWCNTs (CH 4-based) was higher than those on the MWCNTs (CO-based), and that doping of a proper amount of K + in the MWCNTs enhanced somewhat H 2 adsorption. Adsorption of trace amount of moisture on the purified MWCNTs was below the detectable limit, but pronounced on the K +-doped MWCNTs. On the H 2/K +–MWCNTs (CH 4-based) adsorption system, the observed strong Raman bands in the region 3370–3470 cm −1 may be ascribed to O–H stretching of surface hydroxyls generated from adsorption of the trace amount of moisture.

Response of tall buildings to weak long distance earthquakes

AbstractIn the last decade, two tall buildings in Singapore were instrumented with accelerometers and anemometers for the original purpose of identifying the characteristics and effects of wind loading. During the monitoring it became clear that the largest acceleration responses should result from ground motions due to earthquakes having magnitudes between 6 and 8 and epicentres at least 350 km distant. The paper describes the strategy for identifying and capturing the signals from distant tremors, which depends on tracking the RMS response levels in the second vibration mode. Characteristics of some recorded signals are given. While response levels are generally small, the frequency content coincides with the range of fundamental mode frequencies for high rise residential buildings. The validity of using a tall building as a ‘weak‐motion’ seismograph is discussed by considering the mode shape of the building and the measured transfer function between basement and roof responses. Copyright © 2001 John Wiley & Sons, Ltd.

Dispersive shear Alfvén waves on model Tsyganenko magnetic field lines

We present a theory of low- m dispersive shear Alfvén waves (SAWs) that are excited on magnetic field lines specified by the Tsyganenko 1996 magnetic field model. Our dispersive nonlinear model is applied to field lines near the midnight meridional plane and is parameterized by averaged quantities along a field line. For inner plasma sheet ambient parameters, dispersion is dominated by finite electron temperature and ion gyroradius effects that lead to a poleward propagating arc that is in general agreement with simultaneous CANOPUS and FAST satellite observations. The computed fundamental mode frequency is in the 1–4 mHz range, and is in agreement with the measured frequency of nightside magnetospheric field line resonances (FLRs). We conclude that dispersive Alfvén waves excited in a stretched magnetic topology can explain many features of FLRs observed within diffuse auroral precipitation (in H β) near the inner plasma sheet.

A temperature insensitive quartz resonator force sensor

This paper describes a novel self-temperature-sensing method andtemperature compensation of a quartz resonator force sensor based ondual-harmonic-mode oscillation. An AT-cut resonator, used as a force sensingelement, is excited at the fundamental and the third overtone modessimultaneously by a specially designed oscillator. The beat frequency betweenthree times the fundamental mode frequency and the third overtone modefrequency is linear with temperature and independent of the unknown force.Consequently, the temperature and force can be obtained simultaneously by thebeat frequency and the third overtone mode frequency, respectively. Ascompared with conventional temperature compensation using a thermistor as aseparate temperature sensor, the novel method can eliminate the temperaturemeasurement error induced by the difference in the thermal time constants andthe temperature gradient between the quartz resonator and the thermistor. Theimplementation of the dual-mode oscillating circuit is described, as well as aspecial method to reduce the frequency-temperature anomalies. Theexperimental results show that, in a dynamic temperature environment, themeasurement error of the force sensor using the self-temperature-sensingmethod decreases by 80% as compared with the method using a separatetemperature sensor.

Shear AlfvéN waves on stretched magnetic field lines near midnight in Earth's magnetosphere

The spectrum of toroidal standing shear Alfvén waves (SAWs) is derived for a stretched magnetic field line geometry that is approximated by the Tsyganenko 96 magnetic field model. The model is applied to field lines near the midnight meridional plane. It is demonstrated that the fundamental mode frequency for typical ambient parameters of Earth's magnetosphere is in the 1–4 mHz range. This frequency is in agreement with the measured frequency of magnetospheric field line resonances, and is up to an order of magnitude smaller than for a dipolar magnetic field. We conclude that stretching of Earth's magnetic field offers a possible explanation for anomalously low frequency SAWs observed within diffuse auroral emission (Hβ) produced by energetic proton precipitation in the inner plasma sheet.

Free vibration analysis of symmetric cross-ply laminated elastic plates

The present article reviews the recent research done on the free vibration analysis of multilayered laminated composite and sandwich plates using various methods available for the analysis of plates. Displacement fields of various displacement based shear deformation theories have been presented and compared. Also, some numerical results related to fundamental flexural mode frequencies of laminated composite and sandwich plates are presented using a trigonometric shear and normal deformation theory. The theory involves six unknown variables and does not require problem dependent shear correction factor. Governing differential equations and associated boundary conditions of the theory are derived by employing the dynamic version of the principle of virtual work. Navier-type closed-form solutions are obtained for simply supported laminated composite and sandwich plates. The present results are compared with exact elasticity solution and other higher order shear deformation theories wherever applicable. This article cites 391 references.

Internal flow of an electrostatically levitated droplet undergoing resonant shape oscillation

Experimental evidence of internal dc flow circulation within an electrostatically levitated, 3.4 mm diameter charged water drop oscillating in shape at a different amplitude is presented. The axisymmetric shape oscillations were excited using a continuously pulsed electrostatic field at the fundamental shape mode frequency (l=2) of the drop. It was found that the speed of the internal dc flow varied quadratically with respect to the oscillation amplitude without an observable minimum threshold. The implication of the observed internal flow is discussed with respect to the microgravity research facility and environment.

Observed Behavior of Seismically Isolated Buildings

Strong motion recordings from four seismically isolated buildings are used in time-invariant and time-variant modal identification analyses. The buildings are identified as equivalent, time-varying, linear dynamic systems characterized by their time-varying modal parameters (including fundamental-mode natural frequencies, damping ratios, and mode shapes). The identification analyses for each site are repeated using multiple earthquake recordings. In the case of one building, the inferred isolator stiffness and damping during several earthquakes is compared with experimental results. Spectral displacements of the ground motion at the effective fundamental period of the seismically isolated building are found to correlate well with two measures of isolator behavior—the maximum reduction in fundamental mode frequency during strong shaking, and the fraction of the peak total building deformation occurring within the isolators. While the recorded ground motions have much smaller amplitudes than the design basis motions, extrapolation of the observed trends in frequency reduction and relative isolator deflection to larger levels of shaking indicates performance estimates consistent with those assumed in design (which were based on laboratory testing of the isolators).

Vibrational analysis of the dioctahedral mica; 2M1muscovite

Raman spectra and lattice dynamics calculations are presented for the dioctahedral mica, muscovite. Calculated fundamental mode frequencies for the Raman-active and A g and B g species were fit to observed fundamentals assigned to features in the two polarized Raman spectra collected, so that unambiguous vibrational assignments could be made to most peaks in the Raman data. Calculated frequencies for the IR-active A u and B u modes generally fall within the frequency ranges of bands in the IR spectra for muscovite presented earlier. Factor group analysis indicates that motion from all atom types in the muscovite structure can be found in modes for all four vibrational species. Force constant values determined for muscovite are similar to equivalent values calculated for the trioctahedral mica, phlogopite. Raman and IR-active modes calculated at frequencies greater than 800 cm -1 are dominated by internal sheet T-O stretch and T-O-T bend motions, where T is a tetrahedral site. Modes between 800 and 360 cm -1 have internal tetrahedral sheet motions mixed with K and octahedral Al displacements. Modes at frequencies less than 360 cm -1 have lattice and OH motions. Inter-sheet bonding in the muscovite structure is strong enough to affect modes at frequencies as high as 824 cm -1 .