Two-dimensional correlation analysis of polyimide films using attenuated total reflection-based dynamic compression modulation step-scan Fourier transform infrared spectroscopy

Attenuated total reflection (ATR)-based dynamic compression modulation two-dimensional (2D) correlation study of poly(p-phenylene biphenyltetracarboximide) film is carried out in combination with spectral simulation analysis by density functional theory (DFT). The dynamic 2D infrared (IR) correlation spectra in the region of imide I (C=O stretching mode) show three distinct correlation peaks located around 1777, 1725, and 1708 cm(-1). The band at 1708 cm(-1) is the lower wavenumber shift component of 1777 or 1735 cm(-1) peaks and is attributed to the results from intermolecular interactions, according to the DFT analysis. The 1708 cm(-1) band also shows the largest dynamic response, suggesting that these intermolecular interactions may enhance the dynamic response. The dynamic 2D IR correlation spectra in the region of imide II (C-N-C axial stretching mode) vibrations also show three correlation peaks located around 1335, 1355, and 1370 cm(-1), although the imide II band is shown to consist substantially of one component by the DFT analysis. These multiple peaks may be attributed to the compression-induced wavenumber shift of the band in the backbone structures. The sequential analysis of 2D correlation data show that, upon applying the dynamic compression, the response of the backbone regions (imide II) occurs first, followed by that of the side-chain regions (imide I, C=O).     

Characterization of attenuated total reflection infrared spectral intensity variations of immature and mature cotton fibers by two-dimensional correlation analysis

Two-dimensional (2D) correlation analysis was applied to characterize the attenuated total reflection (ATR) spectral intensity fluctuations of immature and mature cotton fibers. Prior to 2D analysis, the spectra were leveled to zero at the peak intensity of 1800 cm(-1) and then were normalized at the peak intensity of 660 cm(-1) to subjectively correct the variations resulting from ATR sampling. Next, normalized spectra were subjected to principal component analysis (PCA), and two clusters of immature and mature fibers were confirmed on the basis of the first principal component (PC1) negative and positive scores, respectively. The normalized spectra clearly demonstrated the intensity increase or decrease of the bands ascribed to different C-O confirmations of primary alcohols in the 1050-950 cm(-1) region, which was not apparent from raw ATR spectra. The PC1 increasing-induced 2D correlation analysis revealed remarkable differences between the immature and mature fibers. Of interest were that: (1) Both intensity increase of two bands at 968 and 956 cm(-1) and the shifting of 968 cm(-1) in immature fibers to 956 cm(-1) in mature fibers, together with the intensity decreasing and shifting of the 1048 and 1042 cm(-1) bands, are the characteristics of cotton fiber development and maturation. (2) Intensities of most bands in the 1800-1200 cm(-1) region decreased with the fiber growth, suggesting they are from either noncellulosic components or CH and OH fractions in amorphous celluloses. (3) The reverse sequence of intensity variations of the bands in the 1100-1000 cm(-1) and 1000-900 cm(-1) region of asynchronous spectra indicated a different mechanism of compositional and structural changes in developing cotton fibers at different growth stages.     

Influential Factors on Electromagnetic Properties of Selected 3D Reticulated Ceramics

3D reticulated ceramics (3DRCs) with the composition containing SrFe12O19-SiC-TiO2 were prepared by a replication process with polyurethane sponges as the template in ceramic slurry. The electrical conductivity, dielectric and magnetic parameters of 3D reticulated ceramics (3DRCs) were measured with changes in cell size of the sponges, contents in the slurry and sintering temperature in this paper. Discussions about the influential factors of those parameters were focused on their electrical conductivity. The experimental results indicated that the electrical conductivity of 3DRCs raised with the increase of cell size, SiC/SrO.6Fe2O3 with weight ratio and sintering temperature. X-ray diffractions and SEM were used to investigate the relationship between electrical conductivity and sintering temperature. Deoxidizing reactions of SrO.6Fe2O3 caused the increasing electrical conductivity. The real part of permittivity (ε′) and imaginary part of permeability (μ") raised with the increase of electrical conductivity (σ). The imaginary part of permittivity (ε") has a maximum at 10° S/cm with the increase of σ, and the real part of permeability (μ′)changes slightly with the increase of σ. When σ is at the range of 10-4 S/cm to 100 S/cm (a semi conductive state),both the imagine part of permittivity and permeability raises with increasing σ, therefore, the 3DRCs present their high electromagnetic loss properties.     

尿素-过氧化氢混合模板法合成介孔二氧化硅

以尿素-过氧化氢为混合模板、正硅酸乙酯为硅源,在酸性条件下,通过溶胶-凝胶过程合成二氧化硅介孔材料。采用煅烧法除去模板剂,用红外光谱、XRD、N2吸附-脱附、HRTEM等分析测试手段对介孔材料的结构和形态进行了表征。结果表明:与以尿素为单一模板相比,采用混合模板剂所合成介孔材料为蠕虫状,孔径分布基本保持不变、比表面积相近(分别为445、431m2/g)、孔径(分别为7.04、8.11nm)和孔体积(分别为0.783、0.874cm3/g)明显增大。     

Gas-phase databases for quantitative infrared spectroscopy

The National Institute of Standards and Technology (NIST) and the Pacific Northwest National Laboratory (PNNL) are each creating quantitative databases containing the vapor-phase infrared spectra of pure chemicals. The digital databases have been created with both laboratory and remote-sensing applications in mind. A spectral resolution of approximate, equals 0.1 cm(-1) was selected to avoid degrading sharp spectral features, while also realizing that atmospheric broadening typically limits line widths to 0.1 cm(-1). Calculated positional (wave- number, cm(-1)) uncertainty is /=9) path length-concentration burdens and fitting a weighted Beer's law plot to each wavenumber channel. The two databases include different classes of compounds and were compared using 12 samples. Though these 12 samples span a range of polarities, absorption strengths, and vapor pressures, the data agree to within experimental uncertainties with only one exception.     

A method to accurately determine the extent of solid-phase reactions by monitoring an intermediate in a nondestructive manner

The application of Fourier transform infrared (FT-IR) spectroscopy to the quantitation of effective nucleoside loading on a solid support, via detection of a reaction intermediate, was developed. 4,5-Dicyanoimidazole (DCI) activator is reacted with a known amount of polystyrene-bound phosphoramidite to form a diisopropylamine-DCI salt complex that is detected by FT-IR spectroscopy at a unique wavenumber of 1104 cm(-1). Based on a linear standard curve, the species' absorbance at 1104 cm(-1) is then directly translated into an appropriate concentration. This concentration characterizes the number of active phosphoramidite sites on the solid support. This method consistently determines the loading extent of nucleosides (deoxy-A/T/G/C) on the solid support to the nearest 0.02 mmol/g. The coupling reaction extent of a deoxy-T derivative with the support-bound phosphoramidite compares well with the nucleoside loading, as determined by the FT-IR-based analytical method. The nucleoside loading was further verified by phosphorus elemental analysis of the 3'-phosphate linker concentration.     

Two-dimensional attenuated total reflection infrared correlation spectroscopy study of the desorption process of water-soaked cotton fibers

Two-dimensional (2D) correlation analysis was applied to characterize the attenuated total reflection (ATR) spectral intensity fluctuations of native cotton fibers with various water contents. Prior to 2D analysis, the spectra were leveled to zero at the peak intensity of 1800 cm(-1) and then were normalized at the peak intensity of 660 cm(-1) to subjectively correct the changes resulting from water diffusion in fibers and resultant density dilution. Next, a new spectral set was subjected to principal component analysis (PCA) and two clusters of hydrated (≥13.3%) and dehydrated (<13.3%) fibers were obtained. Synchronous and asynchronous 2D correlation spectra from individual ATR spectral sets enhanced spectral resolution and provided insights about water-content-dependent intensity variations not readily accessible from one-dimensional ATR spectra. The 2D results revealed remarkable differences corresponding to water loss between the hydrated and dehydrated fibers. Of interest were that: (1) the intensity of the 1640 cm(-1) water band remains in a steady state for hydrated fibers but decreases for dehydrated fibers; (2) during the desorption process of adsorbed water, small and water-soluble carbonyl species (i.e., esters, acids, carboxylates, and proteins) begin to accumulate on the cotton surface, resulting in possible changes in the coloration and surface chemistry of native cotton fibers that were rained on prior to harvesting; (3) intensities of bands in the 1200 to 950 cm(-1) region exhibit a more apparent intensity increase than those in the 1500 to 1200 cm(-1) region, indicating the sensitivity of the 1200 to 950 cm(-1) infrared (IR) region to intra- and inter-molecular hydrogen bonding in fiber celluloses; and (4) the 750 cm(-1) band, ascribed to the unstable I(α) phase in amorphous regions, might originate from the cellulose-water complex through hydrogen bonding.     

Automated Fourier transform infrared analysis of urinary stones: technical aspects and example of procedures applied to carbapatite/weddellite mixtures

New software (ScanLith) was developed to provide an automated procedure for identifying and quantifying crystalline species in urinary calculi. The first step was to strictly define operative conditions of sample preparation because they have a significant influence on the stability of various crystalline phases. Second, we determined the quantification coefficients of a polynomial curve required to develop the automated procedure. This was illustrated by the study of carbapatite and weddellite, as both constituents represent one of the most frequent associations found in stones analyzed in our laboratory. The following quadratic equation was obtained with a correlation coefficient r2 = 0.9997: Y = -0.5144x2 + 1.5239x - 0.0141, where Y is the absorbance ratio carbapatite/weddellite and x is the percentage of carbapatite in the mixture. The absorbance of carbapatite and weddellite was measured at 1035 cm(-1) and 1325 cm(-1), respectively. The third step was to validate the ScanLith procedure in routine analysis by comparing computed results with those of an expert. Concordance (r2 = 0.9824) was better than that previously reported using various computerized systems with a mean deviation of 4%. Algorithms developed in ScanLith to identify main and minor components found in urinary stones, even in complex mixtures containing up to seven constituents, allowed us to lower the detection threshold down to 1 to 10% depending on the main component.     

Development of a multi-Fourier-transform interferometer: imaging experiments in millimeter and submillimeter wave bands

We have developed a millimeter and submillimeter Michelson-type bolometric interferometer based on a Martin-Puplett-type Fourier-transform spectrometer named multi-Fourier-transform interferometer (MuFT). We have succeeded in proving that the MuFT is capable of performing broadband imaging observations as theoretically proposed by our previous paper (OHM) [Appl. Opt. 45, 2576 (2006)]. We succeeded in acquiring the mutual coherence signal for an extended source in broadband. By analyzing the obtained mutual coherence signal following the formula proposed in OHM, 2D source images for each wavenumber from 5 cm(-1) (150 GHz) to 35 cm(-1) (1.05 THz) with a wavenumber interval of 0.4 cm(-1) (12 GHz) were successfully extracted. The large dynamic range advantage of the MuFT proposed in OHM was confirmed experimentally.     

Solvent interactions in methanol/N, N-dimethylamide binary systems studied by Fourier transform infrared-attenuated total reflection (FT-IR/ATR) and two-dimensional correlation spectroscopy (2D-COS)

The interaction of N,N-dimethyl formamide (DMF) and N,N-dimethyl acetamide (DMA) with methanol in solution mixtures was studied using Fourier transform infrared-attenuated total reflection (FT-IR/ATR) spectroscopy. The concentration-dependent FT-IR/ATR spectra of DMF/methanol and DMA/methanol mixtures were recorded in the wavenumber range 4000-650 cm(-1) to investigate wavenumber shifts as a consequence of hydrogen bonding interactions. In combination with two-dimensional correlation spectroscopy (2D-COS), the positional fluctuations observed in the ν(C=O) and ν(O-H) regions of DMF/DMA and methanol, respectively, have been discussed in terms of changing populations of differently hydrogen-bonded and interacting species of the same and different component molecules.     

Statistical and generalized two-dimensional correlation spectroscopy of multiple ionization States. Fluorescence of neurotransmitter serotonin

Fluorescence spectra of neurotransmitter serotonin are analyzed with generalized and statistical two-dimensional correlation spectroscopy. A comparison is provided for these two emerging data analysis techniques. Both methods reveal correlations between spectral variables and demonstrate enhanced sensitivity in detecting the dynamic spectral changes over conventional one-dimensional spectroscopy. Both statistical and generalized 2D correlation analysis emphasize simultaneous spectral changes in response to external perturbations. Generalized 2D correlation spectroscopy further reveals the difference in rates of these dynamic changes. Using 2D correlation analysis, a third ionization species of serotonin is identified using pH and excitation wavelength perturbation. This species is a doubly deprotonated serotonin with very low fluorescence quantum yield, confirmed by using a laser excitation at longer wavelength and at higher pH. Taking advantage of the spectral differences between excitation of serotonin and tryptophan, as low as 3.8 nM serotonin can be detected in the presence of 20 microM tryptophan, with long-wavelength excitation. This represents the sensitive detection of serotonin in 5000-fold excess of tryptophan.     

Generation of 224-nm radiation by stimulated Raman scattering of ArF excimer laser radiation in a mixture of H2 and D2

Raman shifting of tunable ArF excimer laser radiation in a mixture of H(2) and D(2) produces tunable radiation in the 224-nm region as a result of Stokes shifting the frequency of the fundamental radiation (193 nm) once in both H(2) and D(2). At a total pressure of 25 bars, a 19% H(2) in D(2) mixture is found to provide a maximum conversion efficiency (2.5%) to the 224-nm range. Both fundamental and 224-nm radiation were used to record laser-induced fluorescence excitation spectra of nitric oxide produced in an oxyacetylene flame. From the excitation spectra, we determined the tuning range of the 224-nm radiation to be 270 cm(-1) with a linewidth of 0.9 cm(-1), which is similar to the fundamental laser radiation. We derived the exact Raman shift of the generated radiation by comparing both excitation spectra which was found to be 7142.3(5) cm(-1).     

Absorption Anomalies in Ratio and Subtraction FT-IR Spectroscopy

Subtraction and ratioing of strong absorption bands in Fourier transform infrared (FT-IR) spectroscopy produces anomalous absorption errors. One source of error is the instability in the wavenumber scale of the FT-IR spectra. The possible causes of this error are explored. The thermal expansion and contraction of the cavity of the HeNe reference laser from a typical commercial instrument was found to produce changes in the laser wavenumber of ±0.034 cm(-)(1). Changes of this size are shown to introduce errors into the wavenumber scales of FT-IR spectra which are sufficient to produce the observed anomalies. The dependence of the error on instrumental and spectroscopic parameters is explored. Solutions to the problem are proposed.     

Optical evaluation on Nd3+-doped phosphate glasses for O-band amplification

We have fabricated and characterized optically Nd3+-doped phosphate [Li2O-CaO-BaO-Al2O3-La2O3-P2O5 (LCBALP)] glasses for drawing single-mode glass fiber. The 4F3/2→4I13/2 transition emission from the Nd3+ is at the 1.327?μm wavelength with a full width at half-maximum of 43?nm, and the spontaneous transition probability and quantum efficiency are calculated to be 1836?s-1 and 52%, respectively. The maximum stimulated emission cross sections for 4F3/2→4I11/2 and 4F3/2→4I13/2 transitions are derived to be 1.82×10(-20)?cm2 and 6.97×10(-21)?cm2, respectively, and the theoretical gain coefficient at the 1.327?μm wavelength is evaluated to be 0.182?dB/cm when the fractional factor of the excited neodymium ions equals 0.6, which indicates that Nd3+-doped LCBALP phosphate glasses are potential candidates in developing O-band optical fiber amplifiers.     

Two-dimensional correlation analysis and waterfall plots for detecting positional fluctuations of spectral changes

In this study, we demonstrate the potentials and pitfalls of using various waterfall plots, such as conventional waterfall plots, two-dimensional (2D) gradient maps, moving window two-dimensional analysis (MW2D), perturbation-correlation moving window two-dimensional analysis (PCMW2D), and moving window principal component analysis two-dimensional correlation analysis (MWPCA2D), in the detection of the existence of band position shifts. Waterfall plots of the simulated spectral datasets are compared with conventional 2D correlation spectra. Different waterfall plots give different features in differentiating the behaviors of frequency shift versus two overlapped bands. Two-dimensional correlation spectra clearly show the very characteristic cluster pattern for both band position shifts and two overlapped bands. The vivid pattern differences are readily detectable in various waterfalls plots. Various types of waterfall plots of temperature-dependent infrared (IR) spectra of ethylene glycol, which does not have the actual band shift but only two overlapped bands, and of Fourier transform infrared (FT-IR) spectra of 2 wt% acetone in a mixed solvent of CHCl(3)/CCl(4) demonstrate that waterfall plots are not able to unambiguously detect the difference between real band shift and two overlapped bands. Thus, the presence or lack of the asynchronous 2D butterfly pattern seems like the most effective diagnostic tool for band shift detection.     

On the normalization method in two-dimensional correlation spectra when concentration is used as a perturbation parameter

Data pretreatment is of importance in two-dimensional (2D) correlation analysis when composition is used as a perturbation parameter. For composition-oriented studies, different normalization methods based on both external parameters (i.e., concentration) and internal parameters (i.e., absorbance from individual components) have been compared. It was found that when there is no overlapping between absorption bands of interest, no normalization is needed for data pretreatment. When overlapped bands must be used for 2D correlation analysis, the mean-centered normalization method could be used to obtain correct signs in synchronous spectra for a transformation process in the specific form of A-->kC. The intensity of the 2D spectrum, however, may not accurately reflect quantitative information of the overall extent of spectral intensity variation observed during experiments.     

Two-dimensional correlation analysis of nuclear magnetic resonance metabonomics data

Two-dimensional (2D) correlation analysis has been used in this study to identify changes in complex nuclear magnetic resonance (NMR) metabonomics spectra of rat urine samples obtained during a study in which vasculitis (vascular injury), an important safety element in preclinical trials, was induced. Two types of correlation analysis were performed, along the variables and along the samples, and both 2D covariance and correlation coefficient maps were calculated. The binned and 'raw' NMR spectra were analyzed (0.04 and 0.001 ppm resolution, respectively). Good correlation was found among the major peaks of the binned spectra, and two groups of samples were identified using sample-sample 2D correlation maps. Much more complex correlation features were obtained from the 'raw' spectra, in which the specific, butterfly-like patterns were obtained in the covariance map but with only a few significant correlation coefficients in the corresponding 2D correlation maps. In terms of classification, the same group of the last nine spectra that indicated the end of the process and clustered in the 2D sample-sample covariance map of the binned data was also found in the 2D sample-sample covariance map of the raw NMR spectra but, again, not in the 2D correlation coefficient map. A discussion is given on the details of the application of the correlation analysis with regard to spectral data resolution, alignment, the effect of actual intensities of the NMR signal, and reference to various results from 2D correlation analysis of vibrational spectra.     

TiO2/CuInS2复合纳米棒阵列的制备及其光电性能

采用两步溶剂热法在氧化氟锡(FTO)导电玻璃基底上制备了CuInS2敏化TiO2纳米棒阵列复合薄膜光阳极.利用X射线衍射仪(XRD)和扫描电子显微镜(SEM)表征了复合阵列薄膜的晶体结构和表面形貌,同时采用紫外可见吸收分光光度计(UV-Vis)及光电流电压(I-V)曲线研究了CuInS2敏化TiO2纳米阵列薄膜的光学及光电化学性质.研究结果表明,TiO2纳米棒阵列薄膜被CuInS2敏化后在可见光区的吸收有明显的增强.在模拟太阳光照射下(100 mW/cm2),利用这种复合薄膜作为光阳极组装的量子点敏化太阳能电池的开路电压为0.29 V,短路电流密度为0.15 mA/cm2,具有一定的光电转换能力.     

The scattering of 3D sound sources by rigid barriers in the vicinity of tall buildings

The acoustic scattering of a three-dimensional (3D) sound source by an infinitely long rigid barrier in the vicinity of a tall building is analyzed using the boundary element method (BEM). The acoustic barrier is modeled using boundary elements, and is assumed to be non-absorbing, while the image source method is used to model the tall building as an infinite vertical barrier. A frequency domain BEM formulation is used, and time domain responses are then obtained by applying an inverse Fourier transformation.Since the geometry of the problem does not vary along one direction, the 3D solution can be calculated as the summation of a sequence of 2D problems, each solved for a different spatial wavenumber, k_z. To obtain the 3D solution, a discrete form wavenumber transform is performed by considering an infinite number of virtual point sources equally spaced along the z axis. Complex frequencies are used to minimize the influence of these neighboring fictitious sources.Numerical simulations are performed using barriers of varying sizes, evaluating the attenuation of the sound pressure level in the vicinity of the building façade. The creation of shadow zones by the barriers is analyzed and time responses are presented to better understand the sound propagation around these obstacles.