High-amplitude Modes Research Articles

The 2003–2004 multisite photometric campaign for the β Cephei and eclipsing star 16 (EN) Lacertae with an appendix on 2 Andromedae, the variable comparison star

A multisite photometric campaign for the Beta Cephei and eclipsing variable 16 Lacertae is reported. 749 h of high-quality differential photoelectric Stromgren, Johnson and Geneva time-series photometry were obtained with ten telescopes during 185 nights. After removing the pulsation contribution, an attempt was made to solve the resulting eclipse light curve by means of the computer program EBOP. Although a unique solution was not obtained, the range of solutions could be constrained by comparing computed positions of the secondary component in the Hertzsprung-Russell diagram with evolutionary tracks. For three high-amplitude pulsation modes, the uvy and the Geneva UBG amplitude ratios are derived and compared with the theoretical ones for spherical-harmonic degrees l <= 4. The highest degree, l = 4, is shown to be incompatible with the observations. One mode is found to be radial, one is l = 1, while in the remaining case l = 2 or 3. The present multisite observations are combined with the archival photometry in order to investigate the long-term variation of the amplitudes and phases of the three high-amplitude pulsation modes. The radial mode shows a non-sinusoidal variation on a time-scale of 73 yr. The l = 1 mode is a triplet with unequal frequency spacing, giving rise to two beat-periods, 720.7 d and 29.1 yr. The amplitude and phase of the l = 2 or 3 mode vary on time-scales of 380.5 d and 43 yr. The light variation of 2 And, one of the comparison stars, is discussed in the Appendix.

Mechanism of displacement of a catalytically essential loop from the active site of mammalian fructose-1,6-bisphosphatase.

AMP triggers a 15° subunit-pair rotation in fructose-1,6-bisphosphatase (FBPase) from its active R state to its inactive T state. During this transition, a catalytically essential loop (residues 50-72) leaves its active (engaged) conformation. Here, the structures of Ile(10) → Asp FBPase and molecular dynamic simulations reveal factors responsible for loop displacement. The AMP/Mg(2+) and AMP/Zn(2+) complexes of Asp(10) FBPase are in intermediate quaternary conformations (completing 12° of the subunit-pair rotation), but the complex with Zn(2+) provides the first instance of an engaged loop in a near-T quaternary state. The 12° subunit-pair rotation generates close contacts involving the hinges (residues 50-57) and hairpin turns (residues 58-72) of the engaged loops. Additional subunit-pair rotation toward the T state would make such contacts unfavorable, presumably causing displacement of the loop. Targeted molecular dynamics simulations reveal no steric barriers to subunit-pair rotations of up to 14° followed by the displacement of the loop from the active site. Principal component analysis reveals high-amplitude motions that exacerbate steric clashes of engaged loops in the near-T state. The results of the simulations and crystal structures are in agreement: subunit-pair rotations just short of the canonical T state coupled with high-amplitude modes sterically displace the dynamic loop from the active site.

Highly correlated ab initio study of the low frequency modes of propane and various monosubstituted isotopologues containing D and 13C

With the purpose of providing some clues that could encourage the spectral recordings of propane and various monodeuterated and (13)C isotopologues and also to explore their far infrared spectra at low temperatures, the energy levels corresponding to their three lowest frequency modes are determined variationally using a flexible model in three dimensions. Five vibrationally corrected potential energy surfaces are computed using CCSD(T) ab initio calculations. In spite of the quality of these highly correlated potentials in molecules with similar structures, it was proven that an empirical adjustment of the surfaces would enclose accurately the experimental and theoretical frequency residuals and therefore it is also used in the present work. Interacting terms, energy levels and tunneling splittings are provided for CH3CH2CH3, CH3(13)CH2CH3, (13)CH3CH2CH3, CH2DCH2CH3 and CH3CHDCH3. Infrared and Raman transitions of CH3CH2CH3 are assigned. Correlation between symmetry species of the five isotopologue symmetry groups (G36, G36, G18, G6 and G'18, respectively) is established for the classification of the levels and torsional splittings. The rotational constants are determined with CCSD(T)/CBS (A0 = 29263.46 MHz, B0 = 8454.10 MHz and C0 = 7466.64 MHz) using a non-relativistic procedure. Fundamental anharmonic frequencies corresponding to the high and medium amplitude modes are computed for all the isotopologues. The adjusted parameters are accurate enough to be employed in further spectral analysis.

Vibrational dynamics of bio- and nano-filaments in viscous solution subjected to ultrasound: implications for microtubules

In this paper, using a new analytical method, we solved the beam equation for a uniform bio- and nano-filament in a viscous solution. The filament is assumed to be attached at its two ends and driven by ultrasound plane waves. To obtain analytical solutions, we converted the beam equation to an equation that allows us the use of the method of separation of variables. We then reconstructed the solution of the original beam equation from the solution of the converted equation. Subsequently, we have used the parametric equations derived in this paper to investigate the resonance condition for a microtubule (MT) in an aqueous solution. We show that by using ultrasound plane waves, one cannot satisfy a resonance condition for MTs treated as rigid rods. In order to achieve resonance, a single mode of the MT vibration must be excited with a harmonic number larger than a threshold value found here. Single mode excitation not only helps to transfer a minimum amount of energy to the surrounding medium compared with multi-mode excitation, but it also allows for a simultaneous high amplitude and high mode quality that is impossible using plane waves. In order to overcome this difficulty, we propose to use an ultrasound generation device as a potential technical solution characterized by both frequency control and optimized energy transfer to the MT. Finally, the minimum required intensity of the ultrasound at the location of the MT in order to break it is shown to be on the order of 10(5)W/m(2), which corresponds to 170dB.

Update and Additional Frequencies for Kepler Star KIC 9700322

Breger et al. (2011) reported on the discovery of 76 frequencies for the star KIC 9700322 from one month (Sept.-Oct. 2009) of short-cadence (1-minute sampling rate) photometric data during Quarter 3 of the NASA Kepler mission. Here we report on a reanalysis combining an additional month (June-July 2009) obtained during Quarter 2 as part of the Kepler Guest Observer program. This analysis confirms all but two of the earlier frequencies > 0.5 c/d, and in addition finds six new combination frequencies of the 8 highest amplitude modes, and three frequencies that are not combinations of these modes. Since we do not know the parents of 12 of the 83 frequencies, additional astrophysical discoveries may await in continued study of this star. The rotational modulations of the two radial modes and the &#x1D4C1; = 2 quintuplet are confirmed. For the two radial modes (f1, f2) and the central (m = 0) mode of the &#x1D4C1; = 2 quintuplet, f6, amplitude variability and/or close frequencies were found. The additional data do not reveal more of the &#x1D4C1;=0, 1, 2 or higher-degree p modes that were expected, and this result is still a mystery.

Multicolour photometry of EO Ceti (PB 8783)

We present the first-look analysis of the high-speed multicolour photometry of the bright V361 Hya-type star EO Ceti (m V=12.3). The observations were gathered with the three-channel ULTRACAM instrument attached to the 4.2-m William Herschel Telescope. The data set has a total time span of 6.2 d and consists of 31 h simultaneous three colour photometry. The main power regions in all three colours are the same as previously reported in the white light photometric campaigns on EO Ceti. We calculate the frequencies, amplitudes and phases of the significant modes in three colours of the SDSS system, r′, g′ and u′. The amplitudes of the detected modes are the highest in the u′ lightcurve, and the phases are the same in all three colours within the measurement accuracy. The amplitudes of the highest signal-to-noise modes show time variability in all three colours. We analyse the amplitude and phase variations of the five highest signal-to-noise modes in different colours. Even though the amplitudes show variations from night to night, the amplitude ratios are found to be constant to within 2σ level. This result is promising as it allows us to compare the observed amplitude ratios with theoretically calculated amplitude ratios. This may further constrain the mode identification of the highest amplitude modes in EO Ceti and let us test the proposed seismic and binary evolution models.

RAT0455+1305: another pulsating hybrid sdB star

RAT0455+1305 was discovered during the Rapid Temporal Survey which aims in finding any variability on timescales of a few minutes to several hours. The star was found to be another sdBV star with one high amplitude mode and relatively long period. These features along with estimation of T_eff and log g makes this star very similar to Balloon 090100001. Encouraged by prominent results obtained for the latter star we have decided to perform white light photometry on RAT0455+1305. In 2009 we used the 1.5m telescope located in San Pedro Martir Observatory in Mexico. Fourier analysis confirmed the dominant mode found in the discovery data, uncovered another peak close to the dominant one, and three peaks in the low frequency region. This shows that RAT0455+1305 is another hybrid sdBV star pulsating in both p- and g-modes.

Characterizing the pulsations of the ZZ Ceti star KUV 02464+3239

We present the results on period search and modeling of the cool DAV star KUV 02464+3239. Our observations resolved the multiperiodic pulsational behaviour of the star. In agreement with its position near the red edge of the DAV instability strip, it shows large amplitude, long period pulsation modes, and has a strongly non-sinusoidal light curve. We determined 6 frequencies as normal modes and revealed remarkable short-term amplitude variations. A rigorous test was performed for the possible source of amplitude variation: beating of modes, effect of noise, unresolved frequencies or rotational triplets. Among the best-fit models resulting from a grid search, we selected 3 that gave l=1 solutions for the largest amplitude modes. These models had masses of 0.645, 0.650 and 0.680 M_Sun. The 3 `favoured' models have M_H between 2.5x10^-5 - 6.3x10^-6 M_* and give 14.2 - 14.8 mas seismological parallax. The 0.645 M_Sun (11400 K) model also matches the spectroscopic log g and T_eff within 1 sigma. We investigated the possibility of mode trapping and concluded that while it can explain high amplitude modes, it is not required.

Multimode Pulsations of the λ Bootis Star 29 Cygni: The 1995 and 1996 Multisite Campaigns

In this paper we present the results of multisite photometric and spectroscopic campaigns, carried out during the years 1995 and 1996, to study the pulsations of a typical λ Bootis star, 29 Cyg. During the 1995 campaign we found well-defined multiperiodicity in 29 Cyg, which was studied in detail during a multilongitude campaign covering a 65 day time interval in 1996. The frequency analysis of the 1996 campaign's data easily revealed 11 excited low l degree modes with frequencies of oscillation ranging from 20.3 to 37.4 cycles day-1 and mean photometric amplitudes ranging from 10.65 to 0.96 mmag in the V filter. After removing the well-identified frequencies, the discrete Fourier transform of the residuals showed excess power in the 20-40 cycle day-1 domain, which indicates the probable existence of unresolved rich p-mode spectra with photometric V amplitudes below 0.5 mmag. We found a regular spacing of 2.41 cycles day-1 within the modes of 29 Cyg, which was interpreted as the spacing of consecutive even and odd l-values. The asteroseismic luminosity log L/L⊙ = 1.12, calculated from the frequency spacing, is in good agreement with the Hipparcos luminosity log L/L⊙ = 1.16 and with luminosities from photometric and spectroscopic calibrations. Using our multicolor photometry we tentatively identified the dominant f1 = 37.425 cycle day-1 mode as an l = 2, n = 5 mode, and made radial overtone identification for all frequencies. These ranged from n = 2 to 5. Analysis of the photometric data shows the long-term (years) and probable short-term (days) variability of amplitudes for all of these modes in 29 Cyg. Using our multicolor WBVR filter photometry, we found the wavelength dependence of the pulsation amplitudes for the five highest amplitude modes. Based on the Hα line radial velocity observations of 29 Cyg, we detected multiperiodic radial velocity variations with frequencies of 38.36 and 29.99 cycles day-1 and semiamplitudes of 1.0 and 0.8 km s-1, respectively. These frequencies coincide within the errors with the photometric frequencies of the two highest amplitude modes, 37.425 and 29.775 cycles day-1. For the highest amplitude l = 2, n = 5 mode (37.425 cycles day-1), the radial velocity-to-light amplitude ratio and velocity-to-light phase shift are equal to 2K(Hα)/ΔV = 94 km mag-1 s-1 and Φf1 = - V = +0.08 ± 0.01, respectively, and are in good agreement with values for δ Scuti stars. The rich multiperiodic spectrum makes 29 Cyg a promising target for future multisite campaigns.

低速デルタ翼フラッタ現象における大変形振動流れ場の解析

The problem of low subsonic delta wing flutter was studied experimentally and numerically. Two kinds of oscillation: low- and high-amplitude oscillation modes were observed in experiment. Moreover, the transition velocity between the two modes significantly depends on angle of attack. When angle of attack is high, the transition from low- to high-amplitude mode is made more suddenly. The flutter velocity obtained in the present experiment shows good agreement with other experimental data as well as results of the present computation. In addition, the flow field around an oscillating delta wing with large deformation is made clear, where vortex motion is coupled with wing motion. It is found that aerodynamic force produced by the vortex near the wing leading edge is closely related with the large amplitude wing oscillation.

Effects of Dissolved and Ambient Gases on Sonochemical Degradation of Methylene Blue in High-Amplitude Resonant Mode

In this paper, we show the dominant contribution of an ambient gas to sonochemical reactions in a high-amplitude acoustic resonant mode. A high-amplitude resonant mode in the solution was predicted by the three-layer resonator model, which showed an acoustic amplitude higher than the standard amplitude by a factor of 5. The high-amplitude resonance mode was used to decompose methylene blue in water. The effects of the dissolved gases and the ambient gases of argon, oxygen, and helium on the degradation efficiency were systematically studied using a closed resonant reactor. The maximum efficiency was achieved when the ambient gas was argon regardless of the dissolved gases. The replacement of dissolved gas with ambient gas is enhanced with high-amplitude ultrasonic irradiation.

A detailed structural characterization of quartz on heating through the α–β phase transition

AbstractTotal neutron scattering measurements, analysed using a modification of the reverse Monte Carlo modelling method to account for long-range crystallographic order, have been used to describe the temperature-dependent behaviour of the structure of quartz. Two key observations are reported. First, the symmetry change associated with the displacive α–β phase transition is observed in both the long-range and short-range structural correlations. Secondly, some aspects of the structure, such as the Si–O bond length and the thermally-induced dynamic disorder, the latter of which sets in significantly below the transition, are relatively insensitive to the phase transition. These results are used to show that the α-domain model of the β-phase disorder is inappropriate and that the classical soft-mode picture of the phase transition is too simplistic. Instead, it is argued that the structural behaviour is best described in terms of its ability to respond to low-frequency, high-amplitude vibrational modes. This view is supported by additional single-crystal diffuse neutron scattering measurements.

Dynamics of molecules in crystals from multi-temperature anisotropic displacement parameters. II. Application To benzene (C6D6) and urea

The temperature evolution of atomic anisotropic displacement parameters (ADP's) of perdeuterobenzene and of urea in the temperature range between 12 and 123 K is investigated in terms of the model presented in paper I. For the benzene molecule, the temperature-dependent contributions to the ADP's are well described by three molecular librations and three molecular translations. For the urea molecule, the analysis revealed a low-frequency high-amplitude normal mode ( approximately 64 cm(-1)), which combines out-of-plane deformations of the NH(2) groups with molecular libration. The pyramidalization motion allows the hydrogen-bonding pattern to be retained quite well, whereas this pattern is heavily distorted in the higher-frequency molecular librations. The results presented for urea go a step beyond those obtainable in a conventional rigid-body or segmented-rigid-body analysis because they show how correlations of atomic displacements in molecular crystals can be determined from the temperature evolution of ADP's. For both molecules, the analysis reveals temperature-independent contributions to the ADP's accounting for the high-frequency internal vibrations. It is the first time that such contributions have been extracted directly from single-crystal diffraction data for light atoms like hydrogen and deuterium as well as for heavier atoms like carbon, nitrogen and oxygen. These contributions agree well with those calculated from independent spectroscopic information.

Open inflationary universes in the induced gravity theory

The induced gravity theory is a variant of Jordan--Brans--Dicke theory where the `dilaton' field possesses a potential. It has the unusual feature that in the presence of a false vacuum there is a {\em stable} static solution with the dilaton field displaced from the minimum of its potential, giving perfect de Sitter expansion. We demonstrate how this solution can be used to implement the open inflationary universe scenario. The necessary second phase of inflation after false vacuum decay by bubble nucleation is driven by the dilaton rolling from the static point to the minimum of its potential. Because the static solution is stable whilst the false vacuum persists, the required evolution occurs for a wide range of initial conditions. As the exterior of the bubble is perfect de Sitter space, there is no problem with fields rolling outside the bubble, as in one of the related models considered by Linde and Mezhlumian, and the expansion rates before and after tunnelling may be similar which prevents problematic high-amplitude super-curvature modes from being generated. Once normalized to the microwave background anisotropies seen by the COBE satellite, the viable models form a one-parameter family for each possible $\Omega_0$.

The influence of soft mode adsorbate vibrations on NEXAFS analyses: NO on Pd{110}

Near-edge X-ray absorption fine structure (NEXAFS) measurements have been performed on NO adsorbed on Pd“110” using a polarized light source at a range of incidence angles. An analysis of intensities of σ and π resonance features is made which includes both the average orientation of the molecule and contributions arising from a low frequency, in-plane hindered-translation mode. The analysis indicates that at all coverages NO is upright, with a hindered-translation mode frequency of 68 cm −1 directed along the <001> azimuth. The normal frozen-molecule analysis would, incorrectly, yield a tilt angle of 22°; adsorbate molecular orientation cannot be reliably obtained from NEXAFS data at 300 K without including the effect of these high-amplitude modes.

Thermodynamics and structure in nonelectrolyte solutions

Abstract

The EOFs of the Geopotential Eddies at 500 mb in Winter and Their Probability Density Distributions

In this paper we examine the empirical orthogonal functions (EOFs) of the geopotential eddies at 500 mb in the northern extratropical atmosphere during the cold season, and discuss the time variability of the EOF coefficients and their probability density distributions. Our data sample includes 1152 5-day mean fields derived from 32 years of NMC and ECMWF analyses. The first EOF is representative of the wintertime stationary eddies: the second and the fourth show good similarity to the PNA and WA teleconnection patterns, respectively. The pattern of the fifth EOF resembles a zonal wavenumber-3 with a latitudinally confined amplitude. The probability density distributions, estimated by means of nonparametric statistical techniques, have been computed both for the time-dependent amplitudes of individual EOFs and for indices of the spatial variance explained by more than one pattern. The EOF-5 appeared to be particularly relevant in this analysis; its amplitude shows a bimodal distribution, and bimodality is also found in the distribution of the combined amplitude of the first few EOFs when the fifth is included. The difference between the composite map computed averaging the fields classified in the high-amplitude mode (according to EOFs 1–5) and the corresponding map for the low-amplitude mode shows a large-scale pattern with positive maxima in regions known to be preferred locations for blocking centers.

Further Observational Characteristics of Bimodal Planetary Waves: Mean Structure and Transitions

Further results concerning the mean gates of the bimodal wavnumber 2 to 4 amplitude probability density distribution are presented followed by composites of transitions from one side of this distribution to the other. The data used are ECMWF analyses from the four winters from 1980/81 to 1983/84. Cross sections of the mean states associated with the two modes reveal that both modes exhibit a baroclinic vertical structure, but that the difference between the two is more nearly equivalent barotropic. The composite transitions between the low-amplitude and high-amplitude states indicate that the transition time for the onset or decay of the large amplitude waves is about 4 days. The kinetic energy and available potential energy of wavenumbers 2 to 4 increases (or decreases) by 50 percent in this same time interval during the onset (or decay) of the large amplitude state. Nonlinear interaction with intermediate-scale waves is the only apparent source for the observed kinetic energy tendency during the transition from the low amplitude to the high amplitude mode. Thus, the growth of the 1arge amplitude events does not strictly resemble that of a classical baroclinic instability. During the decay of the large amplitude waves, nonlinear interaction between the wavenumber 2 to 4 ensemble and wavenumber 1 accounts for the decline in kinetic energy, while nonlinear interaction between wavenumbers 2 to 4 and smaller-scale waves accounts for the decline in available potential energy. Examples of individual cases are presented to corroborate the composite results. Finally, a case study of the synoptic evolution of a large-amplitude event is presented to illustrate the event's life cycle.

The adsorption of CO on Pt(111) studied by infrared reflection—Absortion spectroscopy

The interaction CO with a clean Pt(111) surface at adsorption temperatures between 85 and 300 K has been studied with infrared reflection-absorption spectroscpy (IRAS) as well as with TPD and LEED. In accordance with electron energy loss data, bands due to the C-O stretch are found in both the linear and bridging regions. The high resolution of IRAS shows, however, that there are two distinct bands in the bridging region which can be assigned to CO in two-fold bridge and three-fold hollow sites. The results suggest a facile interconversion between the two species which is promoted by the occupation of excited states of the low frequency high-amplitude bending modes (frustrated translations). This accounts in turn for the increasing disorder observed with LEED at higher adsorption temperatures. For coverages above Φ=0.5, where a continous splitting of the extra LEED features is observed, the relative intensities of bands in the bridging and linear regions favour the “fault-line” description of Avery rather than the incommensurate layer model.