Gaussian Bands Research Articles

Ultrasonic Flaw Detection in Composite Materials Using SSP-MPSD Algorithm

Due to the inherent inhomogeneous and anisotropy nature of the composite materials, the detection of internal defects in these materials with non-destructive techniques is an important requirement both for quality checks during the production phase and in service inspection during maintenance operations. The estimation of the time-of-arrival (TOA) and/or time-of-flight (TOF) of the ultrasonic echoes is essential in ultrasonic non-destructive testing (NDT). In this paper, we used split-spectrum processing (SSP) combined with matching pursuit signal decomposition (MPSD) to develop a dedicated ultrasonic detection system. SSP algorithm is used for Signal-to-Noise Ratio (SNR) enhancement, and the MPSD algorithm is used to decompose backscattered signals into a linear expansion of chirplet echoes and estimate the chirplet parameters. Therefore, the combination of SSP and MPSD (SSP-MPSD) presents a powerful technique for ultrasonic NDT. The SSP algorithm is achieved by using Gaussian band pass filters. Then, MPSD algorithm uses the Maximum Likelihood Estimation. The good performance of the proposed method is experimentally verified using ultrasonic traces acquired from three specimens of carbon fibre reinforced polymer multi-layered composite materials (CFRP).

Structural features and gasification reactivity of coal chars formed in Ar and CO2 atmospheres at elevated pressures

The structural features and gasification reactivity of chars derived from pyrolysis of a bituminous coal under Ar (Ar char) and CO2 atmosphere (CO2 char) have been investigated, respectively. The pyrolysis was performed in a fixed bed reactor at a final temperature of 700 °C and pressures ranging from 0.1 to 1.5 MPa. It was found that CO2 affect the char yield, pore structure and surface area. The N2 surface area of the CO2 char at ambient pressure increased by nearly 42 times compared to the Ar char. The chemical structure features were characterized by using Raman spectroscopy. The recorded spectra between 800 and 1800 cm−1 were curve-fitted with 10 Gaussian bands representing typical structural features of chars to quantitatively compare the char structure difference. The ratio I(Gr+Vl+Vr)/ID between the band intensities of amorphous char structures with small aromatic ring (3–5 rings) systems and condensed aromatic ring systems (>6 rings) is seen to decrease with increasing pyrolysis pressure. The I(Gr+Vl+Vr)/ID of CO2 char is always lower than that of Ar char in the whole pressure range. The non-isothermal CO2 gasification from 700 to 1000 °C in a TGA (thermogravimetric analyzer) indicates that the char prepared under Ar atmosphere was more reactive.

Biodegradable and thermostable synthetic hyperbranched poly(urethane-urea)s as advanced surface coating materials

Abstract Aliphatic hyperbranched poly(urethane-urea)s with different weight percentages of branch generating moiety were synthesized by a one pot A2 + BC2 approach. Isophorone diisocyanate was used as the A2 type monomer, while a tri-functional dihydroxyamine compound synthesized from ɛ-caprolactam and diethanol amine acted as the BC2 monomer. Evidence supporting the hyperbranched structure of the synthesized poly(urethane-urea) was obtained from 1H NMR spectra. FTIR study confirmed the nature and extent of hydrogen bonding present in this novel macromolecule. A Gaussian band fitting procedure of the IR band at amide-I region showed that the extent of hydrogen bonding increases with the increase of weight percentage of the tri-functional compound. The tensile strength, elongation at break, impact resistance, scratch hardness and gloss followed an increasing trend with the same. The thermal degradation of the hyperbranched poly(urethane-urea) was found to be dependent on the weight percentage of the BC2 type moiety. The kinetics of thermal degradation studied by the Ozawa method showed that the activation energy required for thermal degradation of hyperbranched polymer is higher than its linear polyurethane analog. The synthesized polymer was found to be biodegradable by Pseudomonas aeruginosa bacteria. The study showed superiority of the hyperbranched structure over the linear one. Thus the results indicated the potential usage of the studied hyperbranched poly(urethane-urea) as an advanced surface coating material.

Assessing the performance of curtain flow first generation silica monoliths

Analytical scale active flow technology first generation silica monolithic columns kitted out in curtain flow mode of operation were studied for the first time. A series of tests were undertaken assessing the column efficiency, peak asymmetry and detection sensitivity. Two curtain flow columns were tested, one with a fixed outlet ratio of 10% through the central exit port, the other with 30%. Tests were carried out using a wide range in inlet flow segmentation ratios. The performance of the curtain flow columns were compared to a conventional monolithic column. The gain in theoretical plates achieved in the curtain flow mode of operation was as much as 130%, with almost Gaussian bands being obtained. Detection sensitivity increased by as much as 250% under optimal detection conditions. The permeability advantage of the monolithic structure together with the active flow technology makes it a priceless tool for high throughput, sensitive, low detection volume analyses.

Emission variation in infrared (CdSeTe)/ZnS quantum dots conjugated to antibodies

The paper presents the photoluminescence (PL) and Raman scattering investigations of infrared CdSeTe/ZnS quantum dots (QDs) with emission at 800nm (1.60eV) in nonconjugated states and after the conjugation to the anti-papilloma virus antibodies (Ab). The Raman scattering study has shown that the CdSeTe core includes two layers with different material compositions such as: CdSe0.5Te0.5 and CdSe0.7Te0.3.PL spectra of nonconjugated CdSeTe/ZnS QDs are characterized by two Gaussian shape PL bands related to exciton emission in the CdSeTe core and in intermediate layer at the core/shell interface. PL spectra of bioconjugated QDs have changed essentially: the main PL band related to the core emission shifts into high energy and become asymmetric. The energy diagram of double core/shell CdSeTe/ZnS QDs has been analyzed to explain the PL spectrum of nonconjugated QDs and its transformation at the bioconjugation to the papiloma virus antibodies. It is shown that the PL spectrum transformation in bioconjugated QDs can be a powerful technique for biology and medicine.

Effects of charging on the chromophores of dissolved organic matter from the Rio Negro basin

This study demonstrates that the deprotonation of dissolved organic matter (DOM) originating from a small creek characteristic for DOM-rich waters located in the Rio Negro basin can be quantified based on measurements of pH effects on its absorbance spectra. The method was ascertained by the data of Near-Edge X-Ray Absorbance Spectroscopy (NEXAFS), potentiometric titration to quantify the structural and compositional differences between the colloidal and hydrophobic fractions that contribute 91% of black-water creek DOM. Changes in the absorbance spectra of the DOM fractions caused by deprotonation quantified via numeric deconvolution which indicated the presence of six well-resolved Gaussian bands in the differential spectra. The emergence of these bands was determined to be associated with the engagement of carboxylic and phenolic functionalities and changes of inter-chromophore interactions in DOM molecules. Interpretation of the data based on the NICA-Donnan approach showed that behavior of DOM chromophores was consistent with results of potentiometric titrations. Similar trends were observed for changes of the spectral slope of the DOM absorbance spectra in the range of wavelengths 325–375 nm (DSlope325–375). The behavior of DSlope325–375 values was modeled based on the NICA-Donnan approach and correlated with potentiometrically-estimated charges attributed to the carboxylic and phenolic groups. The correlations between DSlope325–375 and charges of low- and high-affinity protonation-active groups in DOM were monotonic but not linear and had important differences between the colloidal and hydrophobic fractions.

On the Second Mixed Moment of the Characteristic Polynomials of 1D Band Matrices

We consider the asymptotic behavior of the second mixed moment of the characteristic polynomials of 1D Gaussian band matrices, i.e., of the Hermitian N × N matrices H N with independent Gaussian entries such that 〈H ij H lk 〉 = δ ik δ jl J ij , where $${J=(-W^2\triangle+1)^{-1}}$$ . Assuming that $${W^2=N^{1+\theta}}$$ , $${0 < \theta \leq 1}$$ , we show that the moment’s asymptotic behavior (as $${N\to\infty}$$ ) in the bulk of the spectrum coincides with that for the Gaussian Unitary Ensemble.

Comparative Examination of Effects of Binding of Different Metals on Chromophores of Dissolved Organic Matter

This study quantified the binding of dissolved organic matter (DOM) from Suwannee River with nine metals, Ca(II), Mg(II), Fe(III), Al(III), Cu(II), Cd(II), Cr(III), Eu(III), and Th(IV), using a differential absorbance approach. The differential spectra of DOM were closely fitted with six Gaussian bands that were present for all of the metals at varying pH values. Their maxima were located at ca. 200, 240, 276, 316, 385, and 547 nm (denoted as A0, A1, A2, A3, A4, and A5, respectively). The relative contributions and signs of the Gaussian bands were metal-specific and correlated to some degree with the covalent-bonding index of the ions and applicable complexation constants of the NICA-Donnan model. The intensity of band A4 was linearly proportional to the concentration of DOM-complexed metal, although these correlations formed two groups with different slopes, reflecting the nature of DOM-metal interactions. The results demonstrate that differential spectra yield results indicative of the nature and extent of metal and DOM interactions.

Studies on shallow traps in Li2B4O7:Eu,Mn

Li2B4O7 (LTB) single crystals doped with 0.5 mol% Mn and 0.005 mol% Eu have been grown by the Czochralski method. The presence of Eu3+ has been confirmed by photoluminescence spectra of non-irradiated crystals, whereas the presence of Mn2+ by absorption spectra of gamma-irradiated ones, as well as by EPR measurements. Unlike in most thermoluminescence studies on pure and doped LTB, performed usually above 300 K, glow curves have been recorded between 10 and 300 K in order to focus the attention on shallow traps. A broad, intense glow peak is observed around 80 K, with three weaker peaks at 205, 255, and 280 K. Based on supplementary Tmax − Tstop experiments, the trap parameters have been derived assuming that the glow curve is in fact formed by a superposition of a double Gaussian band related to a quasi-continuous distribution of trapping levels, and several glow peaks produced by discrete traps. The nature of the traps is also discussed.

Aromatic and aliphatic organic materials on Iapetus: Analysis of Cassini VIMS data

We present a quantitative analysis of the hydrocarbon and other organic molecular inventory as a component of the low-albedo material of Saturn’s satellite Iapetus, based on a revision of the calibration of the Cassini VIMS instrument. Our study uses hyperspectral data from a mosaic of Iapetus’ surface (Pinilla-Alonso, N., Roush, T.L., Marzo, G.A., Cruikshank, D.P., Dalle Ore, C.M. [2011]. Icarus 215, 75–82) constructed from VIMS data on a close fly-by of the satellite. We extracted 2235 individual spectra of the low-albedo regions, and with a clustering analysis tool (Dalle Ore, C.M., Cruikshank, D.P., Clark, R.N. [2012]. Icarus 221, 735–743), separated them into two spectrally distinct groups, one concentrated on the leading hemisphere of Iapetus, and the other group on the trailing. This distribution is broadly consistent with that found from Cassini ISS data analyzed by Denk et al. (Denk, T. et al. [2010]. Science 327, 435–439). We modeled the average spectra of the two geographic regions using the materials and techniques described by Clark et al. (Clark, R.N., Cruikshank, D.P., Jaumann, R., Brown, R.H., Stephan, K., Dalle Ore, C.M., Livio, K.E., Pearson, N., Curchin, J.M., Hoefen, T.M., Buratti, B.J., Filacchione, G., Baines, K.H., Nicholson, P.D. [2012]. Icarus 218, 831–860), and after dividing the Iapetus spectrum by the model for each case, we extracted the resulting spectra in the interval 2.7–4.0μm for analysis of the organic molecular bands. The spectra reveal the CH stretching modes of aromatic hydrocarbons at ∼3.28μm (∼3050cm−1), plus four blended bands of aliphatic CH2 and CH3 in the range ∼3.36–3.52μm (∼2980–2840cm−1). In these data, the aromatic band, probably indicating the presence of polycyclic aromatic hydrocarbons (PAH), is unusually strong in comparison to the aliphatic bands, as was found for Hyperion (Dalton, J.B., Cruikshank, D.P., Clark, R.N. [2012]. Icarus 220, 752–776; Dalle Ore, C.M., Cruikshank, D.P., Clark, R.N. [2012], op. cit.) and Phoebe (Dalle Ore, C.M., Cruikshank, D.P., Clark, R.N. [2012], op. cit.). Our Gaussian decomposition of the organic band region suggests the presence of molecular bands in addition to those noted above, specifically bands attributable to cycloalkanes, olefinic compounds, CH3OH, and N-substituted PAHs, as well as possible Hn-PAHs (PAHs with excess peripheral H atoms). In a minimalist interpretation of the Gaussian band fitting, we find the ratio of aromatic CH to aliphatic CH2+CH3 functional groups for both the leading and trailing hemispheres of Iapetus is ∼10, with no clear difference between them. In the aliphatic component of the surface material, the ratio CH2/CH3 is 4.0 on the leading hemisphere and 3.0 on the trailing; both values are higher than those found in interstellar dust and other Solar System materials and the difference between the two hemispheres may be statistically significant. The superficial layer of low-albedo material on Iapetus originated in the interior of Phoebe and is being transported to and deposited on Iapetus (and Hyperion) in the current epoch via the Phoebe dust ring (Tosi, F., Turrini, D., Coradini, A., Filacchione, G., and the VIMS Team [2010]. Mon. Not. R. Astron. Soc. 403, 1113–1130; Tamayo, D., Burns, J.A., Hamilton, D.P., Hedman, M.M. [2011]. Icarus 215, 260–278). The PAHs on Iapetus exist in a H2O-rich environment, and consequently are subject to UV destruction by hydrogenation on short time-scales. The occurrence of this material is therefore consistent with the assertion that the deposition of the PAH-bearing dust is occurring at the present time. If the organic inventory we observe represents the interior composition of Phoebe, we may be sampling the original material from a region of the solar nebula beyond Neptune where Phoebe formed prior to its capture by Saturn (Johnson, T.V., Lunine, J.I. [2005]. Nature 435, 69–71).

Growth of β-Ga&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;3&lt;/sub&gt; Nanoparticles Doped with Tin by Ni&lt;sup&gt;2+&lt;/sup&gt; Catalyzed Chemical Vapor Deposition

Sn-doped monoclinic β-Ga2O3 nanoparticles were successfully fabricated on Si (111) substrates with NiCl2 as a catalyst by chemical vapor deposition using metallic gallium and oxygen as sources. The composition, crystal structure, morphology, and optical properties were characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectrophotometry (FTIR), and photoluminescence, respectively. The results demonstrate that the sample was monoclinic β-Ga2O3 nanoparticles with diameters approximately ranging from 200~300 nm. Well-defined prominent absorption bands located at 458 and 671 cm-1 in the FTIR spectra corresponded to Ga-O vibrations. The photoluminescence spectrum shows that the Ga2O3 nanoparticles have a broad and strong emission band ranging from 300 nm to 650 nm with four Gaussian bands centered at approximately 346 (UV), 416 (blue), 473 (dark blue), and 529 nm (green), which may be attributed to defects such as oxygen vacancies and galliumoxygen vacancy pairs. The growth mechanism of β-Ga2O3 nanoparticles is discussed in brief.

Support vector regression with digital band pass filtering for the quantitative analysis of near‐infrared spectra

This paper proposes a novel calibration technique based on combining support vector regression with a digital band pass (DBP) filter for the quantitative analysis of near‐infrared spectra. The efficacy of the proposed method is investigated and validated in the determination of glucose from near‐infrared spectra of a mixture composed of urea, triacetin and glucose. In this paper, the DBP filtering was implemented as a pre‐processing technique in the frequency domain as a Gaussian band pass filter and in the time domain as a Chebyshev filter. The grid‐search optimization method was used to optimize the filter parameters. The results demonstrate that utilization of the optimized DBP filters as a pre‐processing technique improved the performance of the predictive models. Copyright © 2013 John Wiley &amp; Sons, Ltd.

Influences of magmatic intrusion on the macromolecular and pore structures of coal: Evidences from Raman spectroscopy and atomic force microscopy

Magmatic intrusion into coal-bearing sequences can significantly affect the rank of the intruded coal and change the macromolecular and pore structures. Here, we use Raman microscope and Atomic force microscope (AFM) to obtain quantitative information on these transformations. Six coal samples of different ranks taken from a magmatic intrusion zone of Huainan Coalfield, China, were studied. The Raman spectra were fitted with a combination of 8 Lorentzian bands and 1 Gaussian band. We found that the macromolecular structures in coals of different ranks have significant relationships with Raman spectral parameters, particularly the band area ratios (ID1/IG, ID2/IG, ID3/IG, ID4/IG and IG/IAll). With the increase of coal rank, ID1/IG, ID2/IG, ID3/IG and ID4/IG show trends of decreasing intensity, suggesting an enhanced orientation of aromatic hydrocarbons. Observations by Atomic force microscopy indicate that the pore parameters (e.g. amount, size, shape) are quite different for different ranks of coals. The pore size of low-rank bituminous coal is much larger than high-rank anthracite and pore abundance is higher in the former. In addition, there is also good correspondence between the surface topography of coal grains and coal rank.

Abnormal broadband photoluminescence from Yb3+/Mn2+ codoped barium octaborate

Abstract Concentration-dependent anomalous broadband down- and upconversion luminescence of Yb 3+ /Mn 2+ codoped barium octaborate have been demonstrated. Upon ultraviolet (UV) excitation, dual Gaussian emission bands depend on the Mn 2+ concentration located at 550 and 656 nm were respectively ascribed to the Mn 2+ pairs and single Mn 2+ ion. Moreover, abnormal broadband upconversion luminescence at room temperature in BaB 8 O 13 :Yb 3+ , Mn 2+ under near-infrared (NIR) excitation of Yb 3+ at 976 nm was demonstrated by the cooperative sensitization luminescence process. The experimental results could provide new insights into developing lighting and display systems, and biomedical imaging.

Size-dependent spectral linewidth narrowing of H-bands in organic nanoparticles of pentamethine cyanine dye

Abstract Considering that cationic polymethine cyanine dyes such as 3,3′-diethylthiadicarbocyanine (DTDC) are used for near-IR (NIR) probes of biological tissues such as mitochondria, we synthesize DTDC organic nanoparticles based on ion association between the dye cation and hydrophobic tetrakis(4-fluorophenyl)borate (TFPB) anion in the presence of neutral stabilizing polymer. Size tuning of the dye nanoparticles is successful by varying the molar ratio of the loaded anion to the dye cation. Binding of DTDC with TFPB results in the prominent appearance of a broad electronic absorption band at 580–590 nm, which we assign to an H-aggregate of DTDC chromophore. The dye nanoparticles show an interesting size-dependent spectroscopic property; linewidth narrowing of H-bands. Spectral deconvolution analysis in terms of a linear combination of Gaussian bands reveals the existence of three types of H-aggregates possessing different transition energies, and the linewidth narrowing of all H-bands is detected as a function of particle size. Meanwhile, monomer bandwidths are almost unchanged. The results suggest that H-aggregates of DTDC dye are readily subject to inhomogeneous broadening that is associated with size-dependent stochastic fluctuations or conformational heterogeneity in the nanoparticles.

Effects of gasification atmosphere and temperature on char structural evolution during the gasification of Collie sub-bituminous coal

Char structure is one of the important factors influencing the char reactivity during gasification. The purpose of this study is to investigate the effects of gasification atmosphere and temperature on the changes of char structure during gasification. In this study, a Collie sub-bituminous coal from Western Australia was gasified in a fluidised-bed/fixed-bed reactor at 800–900°C in three gasification atmospheres: pure CO2, 15% H2O balanced with Ar and 15% H2O balanced with CO2. The structural features of the chars produced from the gasification of Collie sub-bituminous coal at varying levels of gasification conversion were characterised with FT-Raman spectroscopy. The recorded Raman spectra between 800 and 1800cm−1 were deconvoluted into 10 Gaussian bands in order to obtain quantitative information about the key structural features of these chars. The total Raman area and the band area ratio of small and large aromatic ring systems are two important indices to study evolution of char structure during gasification. It is shown that the char structure changes drastically during gasification. The reaction pathways for char-CO2 reaction and char-H2O reaction are different. CO2 and H2O compete for active sites most likely on the char surface. For the same gasification atmospheres, the reaction pathway does not change with the gasification temperature between 800 and 900°C.

Effect of Al doping on the structural, optical and photoluminescence properties of ZnS nanoparticles

Un-doped and Al doped ZnS nanoparticles were prepared via an efficient and low cost chemical co-precipitation method using Poly Ethylene Glycol (PEG) as stabilizer. In the present study effect of Al concentration on the morphological, structural, and optical properties is studied using X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), Raman analysis, Fourier transform infrared spectroscopy (FTIR), diffuse reflectance spectroscopy (DRS) and photoluminescence (PL) studies. XRD, TEM, FTIR and Raman analysis indicated the formation of impurity-free nanocrystals with cubic structure. DRS studies revealed that as the Al dopant concentration increases the band gap increases in the range of 3.73–4.01 eV. The PL spectra of all samples exhibit a broad emission band in the range of 350–650 nm. The Gaussian fitting emission bands for ZnS are located at 382, 398, 417 and 445 nm. For Al doped ZnS nanoparticles in addition to the pure ZnS peaks two extra peaks are observed at 472 and 493 nm. Further, enhanced photoluminescence was observed with increasing Al content up to 8 at.% and beyond this photoluminescence quenching was noticed.

Spectroscopic Study of Charge Transfer Complexes of Biphenyl

Biphenyl is a well-known photoconductor with a band gap of 0.16 eV lying in the infrared range. In the present work, the charge transfer complexes of biphenyl with the acceptors such as 7,7,8,8-tetracyano-p-quinodimethane, N,N,N′,N′-tetracyanoethylene (TCNE), 2,3-dichloro-5,6-dicyano-p-benzoquinone (DDQ), Chloranil, and iodine have been studied with ultraviolet-visible near infrared and infrared spectroscopy. Biphenyl-TCNE and biphenyl-DDQ show spin-orbit splitting of valence band and consequently show three optical transitions. Biphenyl-iodine and biphenyl-chloranil show nondegenerate semiconducting nature. The charge transfer complexes (CTCs) show an asymmetric Gaussian band associated with small polaron model. Many of the CTCs also show a scattering of charge carriers by light particles as expected in photoconductors.

KrF- and ArF-excimer-laser-induced absorption in silica glasses produced by melting synthetic silica powder

KrF- and ArF-excimer-laser-induced absorption of silica glasses produced by electric melting and flame fusion of synthetic silica powder were investigated. The growth of KrF-laser-induced absorption was more gradual than that of ArF-laser-induced absorption. Induced absorption spectra exhibited a peak at about 5.8 eV, of which the position and width differed slightly among samples and laser species. Widths of ArF-laser-induced absorption spectra were wider than those of KrF-laser-induced spectra. KrF-laser-induced absorption is reproducible by two Gaussian absorption bands peaking at 5.80 eV with full width at half maximum (FWHM) of 0.62 eV and at 6.50 eV with FWHM of 0.74 eV. For reproduction of ArF-laser-induced absorption, Gaussian bands at 5.41 eV with FWHM of 0.62 eV was necessary in addition to components used for reproducing KrF-laser-induced absorption. Based on the discussion of the change of defect structures evaluated from change of absorption components, we proposed that the precursor of the 5.8-eV band ascribed to E′ center (≡Si·) is ≡Si−H HO−Si≡ structures formed by the reaction between strained Si−O−Si bonds and interstitial H2 molecules during the irradiation.

Delayed fluorescence spectra of intact leaves photoexcited by sunlight measured with a multichannel Fourier-transform chemiluminescence spectrometer

Delayed fluorescence spectra of intact leaves of Green pak choi (Brassica rapa var. chinensis) were measured with a multichannel Fourier-transform chemiluminescence spectrometer, which we developed recently. The intact samples, photoexcited by sunlight without artificial light sources, showed delayed fluorescence around 740nm with a lifetime of ∼6s. The observed spectra were deconvoluted into two Gaussian bands: the delayed fluorescence from photosystem II and photosystem I complexes. Their relative intensities depended on the chlorophyll concentration, but their wavelengths were unchanged.