Wavenumber Band Research Articles

Chemometric Resolution for Baseline Identification of <i>Amomum subulatum</i> Roxb. Essential Oils through FT-IR Spectroscopy Technique

Essential oil of Amomum subulatum is the complex mixture of various alkyl, alkanes, sulfonates, amines, alcohols, sulfoxides, trans RCH≡CHR and aromatic bending compounds. The FT-IR analysis of aromatic bending occurs on 845 cm-1 with para C-H bend. A strong absorption band between 900 cm-1 - 675 cm-1 indicated the presence of aromatic C=C. The alcoholic stretching detected on 1080 cm-1 and 1169 cm-1 with C-O stretching molecular motion in large cardamom. In our investigation, the frequency of 2943 cm-1 and 2934 cm-1 the C-H stretching occurred in alkyl group. The wave numbers of bands 2966 (C=CH2), 1358 (S=O Stretch), 1215 (C-N Stretch), 1053 (S=O Stretch) and 984 (C-H Bending) the functional group specify vinyl, sulfonates, amines, sulfoxides and trans RCH-CHR, respectively.

Subwavelength elastic joints connecting torsional waveguides to maximize the power transmission coefficient

Joints with slowly varying tapered shapes, such as linear or exponential profiles, are known to transmit incident wave power efficiently between two waveguides with dissimilar impedances. This statement is valid only when the considered joint length is longer than the wavelengths of the incident waves. When the joint length is shorter than the wavelengths, however, appropriate shapes of such subwavelength joints for efficient power transmission have not been explored much. In this work, considering one-dimensional torsional wave motion in a cylindrical elastic waveguide system, optimal shapes or radial profiles of a subwavelength joint maximizing the power transmission coefficient are designed by a gradient-based optimization formulation. The joint is divided into a number of thin disk elements using the transfer matrix approach and optimal radii of the disks are determined by iterative shape optimization processes for several single or bands of wavenumbers. Due to the subwavelength constraint, the optimized joint profiles were found to be considerably different from the slowly varying tapered shapes. Specifically, for bands of wavenumbers, peculiar gourd-like shapes were obtained as optimal shapes to maximize the power transmission coefficient. Numerical results from the proposed optimization formulation were also experimentally realized to verify the validity of the present designs.

The Ring Monstrance from the Loreto treasury in Prague: handheld Raman spectrometer for identification of gemstones.

A miniature lightweight portable Raman spectrometer and a palm-sized device allow for fast and unambiguous detection of common gemstones mounted in complex jewels. Here, complex religious artefacts and the Ring Monstrance from the Loreto treasury (Prague, Czech Republic; eighteenth century) were investigated. These discriminations are based on the very good correspondence of the wavenumbers of the strongest Raman bands of the minerals. Very short laser illumination times and efficient collection of scattered light were sufficient to obtain strong diagnostic Raman signals. The following minerals were documented: quartz and its varieties, beryl varieties (emerald), corundum varieties (sapphire), garnets (almandine, grossular), diamond as well as aragonite in pearls. Miniature Raman spectrometers can be recommended for common gemmological work as well as for mineralogical investigations of jewels and cultural heritage objects whenever the antiquities cannot be transported to a laboratory.This article is part of the themed issue 'Raman spectroscopy in art and archaeology'.

Nonlinear self-adapting wave patterns

We propose a new type of traveling wave pattern, one that can adapt to the size of physical system in which it is embedded. Such a system arises when the initial state has an instability for a range of wavevectors, k, that extends down to k = 0, connecting at that point to two symmetry modes of the underlying dynamical system. The Min system of proteins in E. coli is such a system with the symmetry emerging from the global conservation of two proteins, MinD and MinE. For this and related systems, traveling waves can adiabatically deform as the system is increased in size without the increase in node number that would be expected for an oscillatory version of a Turing instability containing an allowed wavenumber band with a finite minimum.

Parametric decay of wide band Langmuir wave spectra

Previous results obtained for modulational instability of a Langmuir wave spectrum are extended to account also for the Langmuir wave decay. The general model is tested by considering first the parametric decay of single-mode Langmuir waves, and also two-wave models, where several combinations are considered: one wave is modulationally unstable, another decay unstable and one where both waves are unstable with respect to decay. For the general case with continuous wave spectra it is found that distribution of the Langmuir wave energy over a wide wavenumber band reduces the decay rate when the correlation length for the spectrum becomes comparable to the wavelength of the most unstable sound wave among the possible decay products.

SERS characterization of neuropeptide Y and its C-terminal fragments deposited onto colloidal gold nanoparticle surface

It has been suggested that the family of neuropeptide Y (NPY) peptides is a promising target for the neuroprotective therapy; therefore, knowledge of the structure of these biologically active compounds and their behavior at solid/liquid interface is important in order to design new analogues. Because there is still a lack of detailed information on the behavior of NPY and its mutated analogues at the solid/liquid interfaces, in this work surface-enhanced Raman spectroscopy (SERS) analysis was used to investigate NPY and its native NPY3–36, NPY13–36, and NPY22–36 and mutated acetyl-(Leu28,31)-NPY24–36C-terminal fragments, acting on Y2 receptors (Y2R), in order to determine their possible metal surface/molecule interactions. In these studies, colloidal gold nanoparticle surface served as a solid surface, whereas an aqueous solution was used as a liquid medium. The observed differences in the band intensities, wavenumbers, and widths allowed us to draw conclusions on an adsorption mode of NPY and on changes in this mode upon the shortening of the peptide chain and increase in solution pH (from pH 3 to pH 11). Briefly, three different species of Tyr were identified onto the colloidal gold surface depending upon the length of the peptide chain and solution pH. Tyrosine (TyrOH) is present in a basic medium. Tyrosinate (TyrO−) is present in an acidic solution, whereas phenoxyl radical (Tyr*) appears at neutral pH for peptides having relatively short peptide chain (acetyl-(Leu28,31)-NPY24–36). The elongation of the peptide chain partially (NPY13–36 and NPY22–36) or completely (NPY3–36 and NPY) protects the Tyr residue against conversion to the radical form.

High pressure Raman spectra of DL-lysine hydrochloride

DL-lysine hydrochloride crystals were studied by Raman spectroscopy under hydrostatic pressure using a diamond anvil cell from ambient pressure up to 9.8GPa in the spectral range from 1150 to 40cm−1. Changes in the Raman spectrum were observed in all spectral regions analyzed. In particular, modifications in the lattice modes indicate that the crystal undergoes a phase transition. The classification of the vibrational modes, the behavior of their band wavenumber as a function of the pressure and the reversibility of the phase transitions are also discussed.

Structural evolution of poly(lactic acid) upon uniaxial stretching investigated by in situ infrared spectroscopy

Structural evolution of poly(lactic acid) (PLA) upon uniaxial stretching was studied with in-situ polarized infrared spectroscopy measurements, and its structural change affected by annealing was also investigated. Band shifting was used to reflect the structural ordering process. It was found that the band at 1302cm−1 always moves to low wavenumbers before crystallization, indicating the occurrence of intermolecular packing ordering. However, the band at 869cm−1 shifts to high wavenumbers, which is related to the transition from the amorphous phase to the ordered phase. Interestingly, during stretching, the shifting for the band at 1302cm−1 always occurs before that for the lower wavenumber band, whereas these two band shifts take place simultaneously under annealing. Based on the different characteristics of the structural evolution under stretching and annealing processes, a critical temperature was found at around 63°C, which influences the effect weight of kinetic and thermodynamic factors to the crystallization behavior. The effect of the drawing temperature on crystallization and mechanical property of PLA films was also analyzed.

Simulation of the 2014 Anomalous Warming in the Northeast Pacific

ABSTRACTThe Nucleus for European Modelling of the Ocean (NEMO) numerical model was used to simulate the North Pacific Ocean beginning in January 1960. The model had a horizontal resolution of 0.25o, 46 vertical levels, and employed a spectral nudging assimilation scheme that, unlike standard nudging, nudges only specific frequency and wavenumber bands. This simulation was nudged to the mean and monthly Levitus climatology of potential temperature and salinity. The model was forced with mean monthly winds, net heat flux, and precipitation from the National Centers for Environmental Prediction (NCEP). The simulation was used to study a recent intrusion of much warmer and less saline water than normal from the west into the Gulf of Alaska, beginning in December 2013 and lasting until at least the early summer of 2014. The observed surface temperature anomalies were more than 4 standard deviations above normal. The model reproduced these anomalies in both a qualitative and quantitative manner, reproducing the same scale of anomalies over the region. An anomalous increase in the North Pacific Current (NPC) was found in the model in 2012 and the beginning of 2013, in agreement with observations. This increase in the NPC is associated with the positive phase of the North Pacific Gyre Oscillation. The causes of the temperature anomalies in the Gulf of Alaska could be due to three key factors: (i) an anomalously high, positive, surface heat flux in 2013 over the greater North Pacific; (ii) a significant decrease in the eastward flow of the NPC starting in late 2013 (with an accompanying decrease in cold water advection) after a period of historically strong eastward flow; and (iii) weaker winds throughout most of 2013 accompanied, however, by a shift to stronger northward winds (with an accompanying increase in warm water advection) in late 2013.

Response and receptivity of the hypersonic boundary layer past a wedge to free-stream acoustic, vortical and entropy disturbances

This paper analyses the response and receptivity of the hypersonic boundary layer over a wedge to free-stream disturbances including acoustic, vortical and entropy fluctuations. Due to the presence of an attached oblique shock, the boundary layer is known to support viscous instability modes whose eigenfunctions are oscillatory in the far field. These modes acquire a triple-deck structure. Any of three elementary types of disturbance with frequency and wavelength on the triple-deck scales interacts with the shock to generate a slow acoustic perturbation, which is reflected between the shock and the wall. Through this induced acoustic perturbation, vortical and entropy free-stream disturbances drive significant velocity and temperature fluctuations within the boundary layer, which is impossible when the shock is absent. A quasi-resonance was identified, due to which the boundary layer exhibits a strong response to a continuum of high-frequency disturbances within a narrow band of streamwise wavenumbers. Most importantly, in the vicinity of the lower-branch neutral curve the slow acoustic perturbation induced by a disturbance of suitable frequency and wavenumbers is in exact resonance with a neutral eigenmode. As a result, the latter can be generated directly by each of three types of free-stream disturbance without involving any surface roughness element. The amplitude of the instability mode is determined by analysing the disturbance evolution through the resonant region. The fluctuation associated with the eigenmode turns out to be much stronger than the free-stream disturbances due to the resonant nature of excitation, and in the case of acoustic disturbances, to the well-known amplification effect of a strong shock. Moreover, excitation at the neutral position means that the instability mode grows immediately without undergoing any decay, or missing any portion of the unstable region. All these indicate that this new mechanism is particularly efficient. The boundary-layer response and coupling coefficients are calculated for typical values of parameters.

Raman study of thaumasite Ca3Si(OH)6(SO4)(CO3)⋅12H2O at high pressure

Thaumasite, Ca3Si(OH)6(SO4)(CO3)⋅12H2O, is an extraordinary mineral that possibly plays a special role in the carbonate–sulfate–silicate balance of the Earth's crust. Thaumasite, an undesirable component in concrete, remains a material poorly studied at high pressures in various media except for He medium (M. Ardit et al., Mineral. Mag., 2014). In the present Raman study, thaumasite samples were compressed in alcohol–water and KBr media at high pressures up to ~7 GPa: several phase transformations were identified. In samples compressed in alcohol–water, the wavenumbers of intense Raman bands of SO and СО symmetric stretching vibrations at 991 and 1074 cm−1 proved to exhibit similar dependences on pressure: during a first transition I → II at 4.4 GPa, the wavenumbers of both bands exhibited a downward jump; at a second transition II → III, which occurred at 4.9 GPa, each band split in a doublet; and then, at a third transition III → IV, which was observed at 5.4 GPa, each doublet band transformed in a singlet. In KBr medium, these and other Raman bands of thaumasite showed similar (to those in thaumasite at compression in alcohol–water) dependences on pressure, revealing several phase transitions with slightly shifted transition points, the first transition I → II, however, being not distinguished. Taking into account the similar behaviors in both media, the transitions are assumed to be polymorphic: no noticeable overhydration in thaumasite compressed in water–alcohol occurred. In phase IV, gradual widening and weakening of each band were observed; those changes can be attributed to amorphization of the material. Considerable hysteresis was observed at thaumasite decompression. Copyright © 2016 John Wiley & Sons, Ltd.

Mitigation of Methane Selectivity on Pt/KL-Zeolite Aromatization Catalysts by Ag Promotion

Silver addition, in low amounts (0.0054 or 0.013 %), to a 1 %Pt/KL catalysts prepared by a sequential CVD procedure using acetylacetonates resulted in improved benzene selectivity at similar conversion levels compared to the undoped 1 %Pt/KL CVD catalyst. Both hydrogenolysis and aromatization require an ensemble of atoms to constitute the active site, but hydrogenolysis is more structure sensitive. Silver, which is a relatively inert metal catalyst, blocks a fraction of Pt surface sites, lowering the overall n-hexane rate. When added in low levels, silver disrupts to a greater degree the Pt ensembles responsible for hydrogenolysis relative to those required for aromatization. This was confirmed by DRIFTS of adsorbed CO measurements, which showed that higher wavenumber bands attributed to larger Pt ensembles were suppressed to a greater extent relative to lower wavenumber bands (i.e., arising from smaller ensembles).

Effects of spin-coating speed on the morphology and photovoltaic performance of the diketopyrrolopyrrole-based terpolymer

Polymer solar cells (PSCs) were fabricated by combining a diketopyrrolopyrrole-based terpolymer (PTBT-HTID-DPP) as the electron donor, and [6,6]-phenyl C 61 butyric acid methyl ester (PC 61 BM) as the electron acceptor, and the power conversion efficiency (PCE) of 4.31% has been achieved under AM 1.5 G (100 mW cm -2 ) illumination condition via optimizing the polymer/PC 61 BM ratio, the variety of solvent and the spin-coating speed. The impact of the spin-coating speed on the photovoltaic performance of the PSCs has been investigated by revealing the effects of the spin-coating speed on the morphology and the absorption spectra of the polymer/PC 61 BM blend films. When the thickness of the blend films are adjusted by spin-coating a fixed concentration with different spin-coating speeds, the blend film prepared at a lower spin-coating speed shows a stronger absorption per unit thickness, and the correspond device shows higher IPCE value in the longer-wavelength region. Under the conditions of similar thickness, the blend film prepared at a lower spin-coating speed forms a more uniform microphase separation and smaller domain size which leads to a higher absorption intensity per unit thickness of the blend film in long wavenumber band, a larger short-circuit current density ( J sc ) and a higher power conversion efficiency (PCE) of the PSC device. Noteworthily, it was found that spin-coating speed is not only a way to control the thickness of active layer but also an influencing factor on morphology and photovoltaic performance for the diketopyrrolopyrrole-based terpolymer.

Explicitly Solvable Nonlocal Eigenvalue Problems and the Stability of Localized Stripes in Reaction‐Diffusion Systems

The transverse stability of localized stripe patterns for certain singularly perturbed two‐component reaction‐diffusion (RD) systems in the asymptotic limit of a large diffusivity ratio is analyzed. In this semi‐strong interaction regime, the cross‐sectional profile of the stripe is well‐approximated by a homoclinic pulse solution of the corresponding 1‐D problem. The linear instability of such homoclinic stripes to transverse perturbations is well known from numerical simulations to be a key mechanism for the creation of localized spot patterns. However, in general, owing to the difficulty in analyzing the associated nonlocal and nonself‐adjoint spectral problem governing stripe stability for these systems, it has not previously been possible to provide an explicit analytical characterization of these instabilities, including determining the growth rate and the most unstable mode within the band of unstable transverse wave numbers. Our focus is to show that such an explicit characterization of the transverse instability of a homoclinic stripe is possible for a subclass of RD system for which the analysis of the underlying spectral problem reduces to the study of a rather simple algebraic equation in the eigenvalue parameter. Although our simplified theory for stripe stability can be applied to a class of RD system, it is illustrated only for homoclinic stripe and ring solutions for a subclass of the Gierer–Meinhardt model and for a three‐component RD system modeling patterns of criminal activity in urban crime.

Solvatochromic study on chlortetracycline in binary and ternary solutions

Molecular modeling of chlortetracycline was performed based on DFT approach implemented in Gaussian software. The differences between simulated electronic spectra and those recorded experimentally were analyzed. Experimental investigations were carried out using electronic absorption spectra as well as fluorescence ones. Spectral shift to the changing of solvent polarity was measured in various solvents (binary solutions) and graphical correlations were evidenced between the electronic band wavenumbers and some theoretical functions on solvent electro-optical macroscopic parameters (refractive index and dielectric constant); interpretation was done based on the solvatochromic theory dedicated to universal interaction forces. Fluorescence spectra, studied in mixture of solvents (ternary solutions), evidenced also specific interactions in water-alcohols not considered in the classical solvatochromic approach.

Spectroscopic characteristic (FT-IR, FT-Raman, UV, 1H and 13C NMR), theoretical calculations and biological activity of alkali metal homovanillates

The structural and vibrational properties of lithium, sodium, potassium, rubidium and cesium homovanillates were investigated in this paper. Supplementary molecular spectroscopic methods such as: FT-IR, FT-Raman in the solid phase, UV and NMR were applied. The geometrical parameters and energies were obtained from density functional theory (DFT) B3LYP method with 6-311++G** basis set calculations. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibrations were assigned. Geometric and magnetic aromaticity indices, atomic charges, dipole moments, HOMO and LUMO energies were also calculated. The microbial activity of investigated compounds was tested against Bacillus subtilis (BS), Pseudomonas aeruginosa (PA), Escherichia coli (EC), Staphylococcus aureus (SA) and Candida albicans (CA). The relationship between the molecular structure of tested compounds and their antimicrobial activity was studied. The principal component analysis (PCA) was applied in order to attempt to distinguish the biological activities of these compounds according to selected band wavenumbers. Obtained data show that the FT-IR spectra can be a rapid and reliable analytical tool and a good source of information for the quantitative analysis of the relationship between the molecular structure of the compound and its biological activity.

Stability Of Superposed Fluids Through Magnetic Field With Suspended Particles Of Different Permeability Saturated Through Porous Layer

The instability of plane interface between two superposed Rivlin-Ericksen elastico-viscous fluids saturated through a porous medium has been studied to include the suspended (dust) particles effect. Following the linearized stability theory and normal mode analysis the dispersion relation is obtained. For stationary convection, the Rivlin-Ericksen elastico-viscous fluid behaves like Newtonian fluids. It found that for a potentially stable arrangement the Rivlin-Ericksen elastico-viscous fluid of different permeabilities in the presence of suspended particles in a porous medium is stable, whereas in a potentially unstable case instability of the system occurs. In the presence of a magnetic field for a potentially stable arrangement the system is always stable and for the potentially unstable arrangement, the magnetic field succeeds in stabilizing certain wave-number band which was unstable in the absence of the magnetic field.

Coexistence of stable branched patterns in anisotropic inhomogeneous systems

A new class of pattern forming systems is identified and investigated: anisotropic systems that are spatially inhomogeneous along the direction perpendicular to the preferred one. By studying the generic amplitude equation of this new class and a model equation, we show that branched stripe patterns emerge, which for a given parameter set are stable within a band of different wave numbers and different numbers of branching points (defects). Moreover, the branched patterns and unbranched ones (defect-free stripes) coexist over a finite parameter range. We propose two systems where this generic scenario can be found experimentally, surface wrinkling on elastic substrates and electroconvection in nematic liquid crystals, and relate them to the findings from the amplitude equation.

Magnonic crystals—Prospective structures for shaping spin waves in nanoscale

We have investigated theoretically band structure of spin waves in magnonic crystals with periodicity in one- (1D), two- (2D) and three-dimensions (3D). We have solved Landau–Lifshitz equation with the use of plane wave method, finite element method in frequency domain and micromagnetic simulations in time domain to find the dynamics of spin waves and spectrum of their eigenmodes. The spin wave spectra were calculated in linear approximation. In this paper we show usefulness of these methods in calculations of various types of spin waves. We demonstrate the surface character of the Damon–Eshbach spin wave in 1D magnonic crystals and change of its surface localization with the band number and wavenumber in the first Brillouin zone. The surface property of the spin wave excitation is further exploited by covering plate of the magnonic crystal with conductor. The band structure in 2D magnonic crystals is complex due to additional spatial inhomogeneity introduced by the demagnetizing field. This modifies spin wave dispersion, makes the band structure of magnonic crystals strongly dependent on shape of the inclusions and type of the lattice. The inhomogeneity of the internal magnetic field becomes unimportant for magnonic crystals with small lattice constant, where exchange interactions dominate. For 3D magnonic crystals, characterized by small lattice constant, wide magnonic band gap is found. We show that the spatial distribution of different materials in magnonic crystals can be explored for tailored effective damping of spin waves.

Analysis of soda-lime glasses using non-negative matrix factor deconvolution of Raman spectra

Novel statistical analysis and machine learning algorithms are proposed for the deconvolution and interpretation of Raman spectra of silicate glasses in the Na2O–CaO–SiO2 system. Raman spectra are acquired along diffusion profiles of three pairs of glasses centered around an average composition of 69.9wt.% SiO2, 12.7wt.% CaO, and 16.8wt.% Na2O. The shape changes of the Raman spectra across the compositional domain are analyzed using a combination of principal component analysis (PCA) and sparse non-negative matrix factorization (NMF). This procedure yields components accounting for the observed changes, as well as their mixing proportions, without any direct prior assumption as to their actual shape, number or position. These methods are applied separately to the Q band (wavenumbers in the range 850–1400cm−1), the main band (200–850cm−1), and to the whole spectra (200–1400cm−1). Compositional profiles obtained by Electron Probe Micro-Analysis (EPMA) are then used to relate spectral components to structural entities. Spectral components extracted from a Q band analysis and a complete spectral analysis show significant similarities both in terms of shape of the components and their mixing proportions. This result implies a link between Qn species and the shift of the medium-range network features in the main band of the Raman spectra. To illustrate the possibilities of the method, a linear regression model is used to relate the proportions of spectral components derived from the Raman spectra to chemical composition. This model can be used to determine the composition of different glasses inside the investigated compositional domain with reasonable accuracy.