Peak Wavenumber Research Articles

Modeling of depth‐induced wave breaking under finite depth wave growth conditions

Recent studies have shown that the spectral wind wave model SWAN (Simulating Waves Nearshore) underestimates wave heights and periods in situations of finite depth wave growth. In this study, this inaccuracy is addressed through a rescaling of the Battjes and Janssen (1978) bore‐based model for depth‐induced breaking, considering both sloping bed surf zone situations and finite depth wave growth conditions. It is found that the variation of the model error with the breaker index γBJ in this formulation differs significantly between the two types of conditions. For surf zones, clear optimal values are found for the breaker index. By contrast, under finite depth wave growth conditions, model errors asymptotically decrease with increasing values of the breaker index (weaker dissipation). Under both the surf zone and finite depth wave growth conditions, optimal calibration settings of γBJ were found to correlate with the dimensionless depth kpd (where kp is the spectral peak wave number and d is the water depth) and the local mean wave steepness. Subsequently, a new breaker index, based on the local shallow water nonlinearity, expressed in terms of the biphase of the self‐interactions of the spectral peak, is proposed. Implemented in the bore‐based breaker model of Thornton and Guza (1983), this breaker index accurately predicts the large difference in dissipation magnitudes found between surf zone conditions and finite depth growth situations. Hence, the proposed expression yields a significant improvement in model accuracy over the default Battjes and Janssen (1978) model for finite depth growth situations, while retaining good performance for sloping bed surf zones.

Raman characterization of MoS2 microtube

AbstractA MoS2 microtube synthesized by chemical transport reaction was studied by Raman line scan mapping. The Raman spectrum of the MoS2 microtube closely resembles that of a MoS2 single crystal. For the first order A1g and E2g Raman modes, the same frequencies can be observed for both MoS2 microtubes and single crystals, respectively, while line widths are slightly larger in the microtube spectrum, which can be attributed to defects. In the line scan along the tube axis, the wave numbers of first order peaks are constant, while a slight up‐shift of the Raman lines is observed in a line scan perpendicular to the tube. Possible mechanisms are discussed and the heating effect is proposed. Line scan approach over the edge of an object thus enables accurate determination of positions of first order peaks in highly absorbing materials.

SPECTROSCOPIC EFFECTS IN CH4/H2O ICES

Recent observations of CH4 in different astrophysical objects encourage laboratory research on methane/water ice mixtures. An IR spectroscopy laboratory investigation is presented on these systems. Co-deposited samples are formed by vapor deposition of CH4 and H2O on a cold substrate, in a wide range of stoichiometries, from very diluted mixtures to CH4/H2O = 2.5 values. Samples are prepared at 14 K and at 40 K, and their temperature behavior is studied when they are warmed up to 60 K. The spectroscopic analysis is centered on the methane features, and also on the water dangling bonds (DBs) that appear in the spectra of the mixtures. The IR forbidden ν1 band shows up in the spectrum (3.44 μm), indicating some form of distorted methane. The combination bands ν3 + ν4 and ν1 + ν4 are seen at 2.32 and 2.38 μm, and the ν2 + ν3 band weakly at 2.21 μm. Whereas ν3 is not shifted in spectra of mixed samples, the wavenumber peak of ν4 and its combination bands vary in a 6 cm–1 range, providing a possible estimation for the relative methane concentration in the sample. Bands in the spectra of mixtures are always broader than their counterparts in pure CH4 ice. The intensity of ν4 appears to increase in mixed samples with respect to the pure solid. Raising the temperature of the ices up to 60 K liberates part of the methane, but a fraction is retained with a maximum value of ~7% ± 2%. This limit may provide information on the temperature properties of astrophysical objects. The different spectral characteristics of water DBs with increasing methane proportion in mixed samples can also furnish information to estimate the stoichiometry of the mixture.

Theory of the evolution of 2D band in the Raman spectra of monolayer and bilayer graphene with laser excitation energy

AbstractA double‐resonance process gives rise to the 2D band in the Raman spectra of monolayer and bilayer graphene. Based on the electronic and vibrational dispersion energies of graphene, the wavenumbers of the 2D band were calculated under different laser excitation energies (from 1.0 to 4.4 eV). Calculated results are in good agreement with experimental data and reproduce the experimental dispersion slope of the 2D band very well. The calculated wavenumbers of the 2D band do not show a linear dependence on the laser excitation energies. Moreover, it is explained that the lowest wavenumber peak of the 2D band of the bilayer graphene, which is composed of four components, has the largest slope with laser excitation energy. Copyright © 2009 John Wiley & Sons, Ltd.

The Ocean Wave Height Variance Spectrum: Wavenumber Peak versus Frequency Peak

Abstract Many authors assume that the frequency peak and the wavenumber peak of an ocean wave height variance spectrum are related by the ocean wave dispersion relationship. This note shows that this is not true and that the true relationship depends on the shape of the spectrum, thereby introducing an element of randomness into the relationship.

Scaling Properties of Temperature Spectra and Heat-Flux Cospectra in the Surface Friction Layer Beneath an Unstable Outer Layer

Temperature variance and temperature power spectra in the unstable surface layer have always presented a problem to the standard Monin-Obukhov similarity model. Recently that problem has intensified with the demonstration by Smedman et al. (2007, Q J Roy Meteorol Soc 133: 37–51) that temperature spectra and heat-flux cospectra can have two distinct peaks in slightly unstable conditions, and by McNaughton et al. (2007, Nonlinear Process Geophys 14: 257–271) who showed that the wavenumber of the peak of temperature spectra in a convective boundary layer (CBL), closely above the surface friction layer (SFL), can be sensitive to the CBL depth, zi. Neither the two-peak form at slight instability nor the dependence of peak position on zi at large instability is compatible with the Monin-Obukhov model. Here we examine the properties of temperature spectra and heat-flux cospectra from between these extremes, i.e. from within the unstable SFL, in two experiments. The analysis is based on McNaughton’s model of the turbulence structure in the SFL. According to this model, heat is transported through most of the SFL by sheet plumes, created by the action of impinging outer eddies. The smallest and most effective of these outer eddies have sizes that scale on SFL depth, zs. The zs-scale eddies and plumes are organised within the overall convection pattern in the CBL, and in turn they organise the motion of smaller eddies within the SFL, whose sizes scale on height, z. The main experimental results are: (1) the peak amplitudes of the temperature spectra in the SFL are collapsed with a scaling factor \({(z_{\rm s}z)^{1/3}\varepsilon_{\rm o}^{2/3}}\) divided by the square of the surface temperature flux, where \({\varepsilon_{\rm o}}\) is the dissipation rate of turbulent energy in the outer CBL (above the SFL); (2) the peak wavenumbers of the temperature spectra are collapsed with the mixed length scale (zizs)1/2; (3) the peak wavenumbers of the heat-flux cospectra are collapsed with the doubly-mixed length scale (zizs)1/4z1/2; (4) for z/zs < 0.03, the peak in the cospectrum is replaced by another peak at a wavenumber about a magnitude larger. This peak’s position scales on z; (5) all these findings are consistent with the observations of Smedman et al.

Two-dimensional Raman correlation analysis of benzophenone

Effect of varying excitation wavelength on the Raman spectral intensity of benzophenone molecule has been examined. The overlapped bands are resolved using two-dimensional correlation method. The symmetric and asymmetric pair associated with a particular type of vibration is highly asynchronously correlated. Evidently no corresponding cross peaks are present in the synchronous spectra. This finding indicates that the succession of change of amplitude of symmetric and asymmetric vibrations related with that specific mode is not simultaneous but completely chronological. Interaction of C O group with the surroundings may be responsible for the appearance of a relatively lower wavenumber peak correspond to new type of C O stretching vibration.

Structural characterization of the ac conductivity in Ag ion conducting glasses

The material trends in various silver ion conducting glasses have been studied recently by focusing on the relationship between the first sharp diffraction peak (FSDP) wave number Q, and the fitting parameters of the ac conductivity, precisely the ratio (log A)/n, where A and n represent the pre-exponential factor and the power law exponent of Jonscher’s law, respectively. In the present paper, a model for the FSDP wave number dependence of the ratio (log A)/n has been proposed and a good agreement has been found with the experiments. By using the concept of bond fluctuation in superionic conductors, the results have been successfully explained, leading to the conclusion that the universal aspect of the power law reflects the universal pattern of the potential barrier at intermediate length scales. The result reconfirms that the ion transport in glasses is intimately related with the FSDP wave number.

Effects of dipole interaction and solvation on the C [dbnd]O stretching band of N, N-dimethylacetamide in nonpolar solutions: Infrared, isotropic and anisotropic Raman measurements

The concentration dependence of the C O stretching ( ν C O ) band of N, N-dimethylacetamide (NdMA) in cyclohexane, n-hexane, and CCl 4 has been investigated by infrared (IR) and polarized Raman spectroscopy. For the neat liquid of NdMA, the noncoincidence of the aniso- and isotropic Raman wavenumbers is evident. In the 0.47 M cyclohexane solution of NdMA, the noncoincidence effect almost disappears and the ν C O envelopes in both the Raman and IR spectra are asymmetric to the low-wavenumber side. When the concentration of NdMA decreases from 0.33 to 0.023 M, the peak of these bands slightly shifts to a higher wavenumber and the band shape becomes symmetric. The shape of the ν C O envelope does not show any significant change below 0.023 M. These results suggest that the asymmetric shape of the ν C O band observed for the 0.33 M cyclohexane solution is associated with the intermolecular interaction among NdMA molecules, which vanishes at around 0.02 M. Spectral changes for the CCl 4 solution of NdMA show a similar tendency. However, the shape and peak wavenumber of the ν C O band observed in a highly diluted CCl 4 solution (≤0.023 M) indicate that the solvation effect of CCl 4 is more complicated than those of cyclohexane and n-hexane. The analyses of the ν C O band, which is sensitive to the intermolecular interaction between solutes and between solute and solvent for NdMA dissolved in nonpolar solvents, would serve to clarify the electronic property of the molecule in a solution.

Seasonal Anisotropy in Short-Period Seismic Noise Recorded in South Asia

We present an analysis of seismic noise recorded during 1995–2004 by a medium-aperture, short-period seismic array located in Chiang Mai, Thailand (CMAR). We calculated frequency-wavenumber spectra for nearly 1000 randomly selected time windows, each with a length of 160 sec. At frequencies above about 1.4 Hz the noise is unorganized and the wavenumber spectra are isotropic and diffuse; however, at lower frequencies three robust wavenumber peaks exist. Two of the peaks have phase velocities centered near 4.0 km/sec, consistent with higher-mode Rayleigh waves, while the third peak has much higher apparent velocity (>25 km/sec), consistent with body waves that have interacted with the Earth’s core ( PKP , PcP ). All three peaks are strongly seasonal with annual power variations of 10–20 dB, and all show excellent correlation in their putative source regions with ocean wave heights derived from TOPEX/POSEIDON satellite tracks. To the best of our knowledge, this is the first time such a high-velocity component of seismic noise has been consistently observed. The presence of this high-velocity peak raises the possibility of using ambient noise to image the Earth’s lower mantle and core.

Microstructure and crystallization properties of TeO2PbF2 glasses

AbstractThe microstructures of (1 − x)(TeO2)–xPbF2, (x = 0.1, 0.15, and 0.25 mol) glasses were investigated by using the Raman spectroscopic technique. The effect of compositions on the TeO2 glass networks and the intensity ratios of the deconvoluted Raman peaks were determined. The results confirm that the addition of modifiers to the glass network former shifts the Raman intensity and the peak wavenumber values for each band in the 167–165, 652–645, and 747–755 cm−1 wavenumber regions. The structural evaluation was recognized from the Raman spectra, with the structural units described as [TeO3+1] polyhedra, [TeO3] trigonal pyramids, and [TeO4] trigonal bipyramids for this binary glass system. Heat‐treatment of the samples shows that the metastable crystalline phase of TeO2 known as γ‐TeO2 is formed only when the modifier content is 10 mol% in the glass matrix. Transparent glass properties were not realized when the TeO2 amount was decreased to less than 10 mol% content. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Terahertz time-domain spectroscopic study of the low-frequency spectra of nitrobenzene in alkanes

The low-frequency spectra of nitrobenzene in alkane solvents with different chain lengths were studied by terahertz time-domain spectroscopy (THz-TDS). The peak wavenumber of the difference spectral intensity of the absorption between the solution and the solvent was shifted to a higher wavenumber with an increase in the chain length of the alkane solvents. This feature is an evidence of the presence of a characteristic frequency of the absorption in the THz region for a particular solute–solvent interacting system. We simulate our spectra using an analytical model. The amplitudes and the time constants of different processes in the low-frequency range of our study are discussed according to results of our simulation.

Investigation of the extinction coefficient of PECVD hydrogenated amorphous silicon nitride films

In order to study the infrared absorption characteristics of hydrogenated amorphous silicon nitride (a-SiNx:H) films prepared by plasma-enhanced chemical vapor deposition (PECVD), the influence of process parameters on the extinction coefficient (EC) of a-SiNx:H films is investigated in the spectrum from 714 to 1250 cm−1. In our experiments, the EC at Si–N stretching frequency ranges from 1.32 to 2.27 and the corresponding peak wave number shifts from 828 to 890 cm−1 by adjusting process parameters. The results show that the enhanced HF power and substrate temperature are the most important parameters for increasing the EC of the film, and increased NH3/SiH4 gas flow ratio is the key to the blueshift of peak wave number. Finally, the adjusted process parameters of a-SiNx:H film for application in an infrared focal plane array are selected: SiH4:NH3:N2 = 2:3:100, HF power: 45 W, LF power: 35 W, pulse time: HF/LF pulse time = 0.6, temperature: 350 and pressure: 650 mTorr.

Sensitive Detection and Identification of Organic Liquids Using the Second Derivative of Surface Plasmon Resonance Near-Infrared Spectra

Sensitive detection of near-infrared (NIR) spectra of several organic liquids has been carried out by surface plasmon resonance (SPR) NIR spectroscopy. For all the liquids, 50- to 100-fold enhancements of the absorption peaks were obtained in the combination band region 4500-4000 cm(-1) using a gold film with a thickness of 14 nm. The SPR peak shows up as an unnecessary broadband peak or trend in an SPR-NIR spectrum, and it was difficult to separate it from the absorption signals. In order to remove the contribution of SPR from the raw SPR-NIR spectrum, the second-order derivative has been employed. The second derivative of the SPR-NIR spectrum was reasonably comparable to that of the corresponding transmittance spectrum. Two simple algorithms for sample identification from the second-derivative data have been proposed. One is similarity, which directly compares the second-derivative spectrum of an unknown sample with that of a known reference sample. The other is fitness, which is defined as a ratio of the common part of absorption peak wavenumbers of the sample and the reference. Although both methods are unfit for the identification of a minor component in a mixture, a major component can be definitely identified by choosing an informative wavenumber region. It was found that the wavenumber region 4250-4080 cm(-1) is especially useful for the identification of similar molecules such as normal alkanes.

Influence of temperature, composition, silica activity and oxygen fugacity on the H2O storage capacity of olivine at 8 GPa

Olivine crystals were grown in the presence of a hydrous silicate fluid during multi-anvil experiments at 8 GPa and 1,000–1,600°C. Experiments were conducted both in a simple system (FeO–MgO–SiO2–H2O) and in a more complex system containing additional elements (CaO–Na2O–Al2O3–Cr2O3–TiO2–FeO–MgO–SiO2–H2O). Silica activity was buffered by the presence of either pyroxene (high a SiO2) or ferropericlase (low a SiO2), and $$f_{{\text{O}}_{\text{2}} }$$ was buffered by the presence of Ni + NiO or Fe + FeO, or constrained by the presence of Fe2O3. Raman spectroscopy was used to identify pyroxene polymorphs in the run products. Clinoenstatite was present in the 1,000°C experiment, and enstatite in experiments at 1,400–1,520°C. The H2O content of olivine was measured using secondary ion mass spectroscopy, and infrared spectroscopy was used to investigate the nature of hydrous defects. The H2O storage capacity of olivine decreases with increasing temperature at 8 GPa. In contrast to previous experimental results at ≤2 GPa, no significant effect of varying oxygen fugacity is evident, but H2O storage capacity is enhanced under conditions of low silica activity. No significant growth of low wavenumber (<3,400 cm−1) peaks, generally associated with high $$f_{{\text{O}}_{\text{2}} }$$ at low pressure, was observed in the FTIR spectra of olivine from the high $$f_{{\text{O}}_{\text{2}} }$$ experiments. Our experiments show that previous high pressure H2O storage capacity measurements for olivine synthesized under more oxidizing conditions than the Earth’s mantle are not likely to be compromised by the $$f_{{\text{O}}_{\text{2}} }$$ of the experiments. However, the considerable effect of temperature on H2O storage capacity in olivine must be taken into account to avoid overestimation of the bulk upper mantle H2O storage capacity.

Temperature-dependent Raman Property of Al-doped 6H-SiC Crystals

Al-doped and un-doped 6H-SiC crystals were grown by physical vapor transport(PVT) method.Raman spectra were measured from room temperature to 400℃.The Raman frequencies were shifted to lower wavenumber and Raman peaks were broadened with increasing temperature for both samples due to thermal expansion and optical phonons decay.Free carrier concentration in Al- doped sample was increased with increasing temperature due to increasing of the plasma concentration, which correspondingly enhanced more strong coupling interactions among LO phonons,plasma,and free carriers.Therefore,the intensity of A_1(LO)mode for Al-doped sample decreased obviously and maintained unchangeable for un-doped sample.The Al activation behavior and its contribution to free carriers in high temperatures were analyzed theoretically and demonstrated experimentally.

Second‐order Raman scattering from linear carbon chains inside multiwalled carbon nanotubes

AbstractThe present investigation concerns multiwalled carbon nanotubes synthesized on graphite cathodes by arc discharge in a He atmosphere, either with the insertion of a catalytic NiCr mixture or without catalysts. The morphology of the deposited cathodes was investigated by SEM, while the amount of carbon chains inside multiwalled carbon nanotubes (C@MWCNT) in various regions of the deposited cathodes was revealed by a parallel micro‐Raman study, through the analysis of the signal from the Raman bands generated by C@MWCNT in the range 1780–1870 cm−1 (L bands). In samples obtained by using the catalyst, a very high concentration of linear carbon chains is found in some zones, as indicated by the intensity of the L band, which turns out remarkably stronger than the G band of the host nanotubes. In these zones, the second‐order Raman scattering is clearly observed, too. The experimental wavenumber values of the 2 L overtone are slightly lower than the exact doubling of the one‐phonon peak wavenumber, and this fact is discussed in terms of the existing theoretical predictions for the chain‐mode dispersion curve. Copyright © 2008 John Wiley &amp; Sons, Ltd.

Fictive temperature of GeO2 glass: Its determination by IR method and its effects on density and refractive index

A simple IR method of determining the fictive temperature of GeO2 glass, both surface and bulk, was developed using the same technique developed earlier for silica glass. Specifically, IR absorption and reflection peak wavenumbers of GeO2 structural bands were found to be correlated with the fictive temperature of the glass. Using this method structural relaxation kinetics can be investigated. Density and refractive index of GeO2 glass were also measured as a function of fictive temperature.

Deceleration of surface structural relaxation in chlorine-containing silica glass due to chlorine volatilization

Both surface and bulk fictive temperatures of chlorine-containing silica glass were measured using the IR method, after thermal, mechanical and chemical treatments. A metastable equilibrium state at 1200°C was first established for the glass by heat-treatment and a uniform fictive temperature was observed except for the sample surface created by polishing after the heat-treatment. The densified layer of the polished surface shifted the IR peak wavenumber, making the fictive temperature appear higher than the bulk. During the second heat-treatment at 950°C, the sample with the as-heat-treated surface and uniform fictive temperature of 1200°C developed non-uniform fictive temperature distribution with the bulk fictive temperature becoming lower than the surface fictive temperature. Usually, surface structural relaxation is faster than bulk structural relaxation and the surface fictive temperature becomes lower than the bulk fictive temperature when heat-treated at a lower temperature than the initial fictive temperature. The observed anomalous feature was attributed to chlorine volatilization from the glass surface layer creating a high viscosity surface layer. This conclusion was supported by the diffusion data of chlorine in the glass available in the literature.

Fictive-Temperature Mapping in Highly Ge-Doped Multimode Optical Fibers

In this paper, a Fourier transform infrared focal-plane-array detector was used to image the "bond-stretching" vibration mode observed near sigma=1120 cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-1</sup> of highly Ge-doped graded-index multimode optical fibers (GI-MMFs). We show that the distribution of the peak wavenumber sigma is nonuniform across the core and cladding of the MMF, i.e., sigma is smaller in the core due to the Ge-doping. Next, as calibration curves between sigma and the fictive temperature T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> are not available in the literature for highly Ge-doped glasses (above 7w%), we have determined calibration curves from 1w% to 30w% in Ge. Then, we have applied these corrections in order to estimate, for the first time to our knowledge, the fictive-temperature distribution within multimode-fiber cross section. Using these curves, we show that T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> is higher at the fiber edges, presumably due to faster cooling. Furthermore, there is also a T <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</sub> increase in the center of the core (i.e., higher Ge content)