Distribution by Scientific Domains

Terms modified by Fourier

  • fourier analysis
  • fourier coefficient
  • fourier descriptor
  • fourier map
  • fourier methods
  • fourier series
  • fourier synthesis
  • fourier transform
  • fourier transform infrared
  • fourier transform infrared analysis
  • fourier transform infrared spectrometry
  • fourier transform infrared spectroscopy
  • fourier transform infrared spectroscopy analysis
  • fourier transform infrared spectrum
  • fourier transform ion cyclotron resonance
  • fourier transform ion cyclotron resonance mass spectrometer
  • fourier transform ion cyclotron resonance mass spectrometry
  • fourier transform ir
  • fourier transform ir spectroscopy
  • fourier transform mass spectrometry
  • fourier transform method
  • fourier transform raman spectroscopy
  • fourier transform spectroscopy
  • fourier transform technique
  • fourier transformation
  • fourier velocity encoding

  • Selected Abstracts

    Living labour and the labour of living: a little tractate for looking forward in the twenty-first century

    CRITICAL QUARTERLY, Issue 1 2004
    Darko Suvin
    An approach to the insights of Marx indispensable for looking forward today understands them as a fusion of three domains and horizons (cognition, liberty, and pleasure), with a set of regulative principles (dialectic, measure, absolute swerve), and a focus on living labour. The discussion progresses from Epicure and Fourier to Marx's form-giving fire of living labour. Against this horizon, capitalism is discussed as a cultural revolution based on measuring labour by means of quantitative time, opposed to use-value qualities, as well as through the metaphors from horror fantasy which Marx found to be appropriate to such a revolution. Its alliance with entropy leads to alienation and loneliness, and finally to a death-bringing economy. An Appendix on political economy and entropy discusses the situation today and a minimum program of counter-measures, beginning with the rejection of GNP as is. [source]

    Synthesis and Characterization of MWNTs/Au NPs/HS(CH2)6Fc Nanocomposite: Application to Electrochemical Determination of Ascorbic Acid

    ELECTROANALYSIS, Issue 16 2008
    Jian-Ding Qiu
    Abstract In this article, a detailed electrochemical study of a novel 6-ferrocenylhexanethiol (HS(CH2)6Fc) self-assembled multiwalled carbon nanotubes-Au nanoparticles (MWNTs/Au NPs) composite film was demonstrated. MWNTs/Au NPs were prepared by one-step in situ synthesis using linear polyethyleneimine (PEI) as bifunctionalizing agent. HS(CH2)6Fc, which acted as the redox mediator, was self-assembled to MWNTs/Au NPs via Au-S bond. Transmission electron microscopy (TEM), energy-dispersive X-ray analysis (EDX), Fourier transformed infrared absorption spectroscopy (FT-IR), UV-visible absorption spectroscopy, and cyclic voltammetry were used to characterize the properties of the MWNTs/Au NPs/HS(CH2)6Fc nanocomposite. The preparation of the nanocomposite was very simple and effectively prevented the leakage of the HS(CH2)6Fc mediator during measurements. The electrooxidation of AA could be catalyzed by Fc/Fc+ couple as a mediator and had a higher electrochemical response due to the unique performance of MWNTs/Au NPs. The nanocomposite modified electrode exhibited excellent catalytic efficiency, high sensitivity, good stability, fast response (within 3,s) and low detection limit toward the oxidation of AA at a lower potential. [source]

    A Versatile System for Arbitrary Function Large-Amplitude Fourier Transformed Voltammetry

    ELECTROANALYSIS, Issue 13 2007
    Lishi Wang
    Abstract A novel low-cost instrument for arbitrary function large-amplitude Fourier transformed voltammetry was developed. Description of both hardware and software was given in detail in this paper. A micro-control-unit (MCU) in combination with a field programmable gate array (FPGA) was designed to act as the controller of the instrument. Profiting from the built-in USB2.0 standard interface of the MCU, vast amount of data to/from the high resolution digital-to-analog converter (DAC)/analog-to-digital converter (ADC) then could be exchanged with computer in real-time, instead of being temporarily stored at the capacity limited memory of the instrument which always restricted the length of sampling time and the size of the collected data set. In the [Fe(CN)6]4+/3+ system, by superimposing a sinusoidal waveform with an amplitude of 120,mV onto a triangular potential and then applying to a macro electrode through the instrument, voltammograms up to the eighth harmonic could be well resolved by FT-IFT method. Excellent agreement was attained with Bond's similar experiment [Anal. Chem. 76 (2004) 3619] in respect of the shape and relative peak height of each harmonic. With the simply structured instrument, stable performance, flexible and versatile function was achieved. Arbitrary forms of AC perturbation which may not necessarily be sinusoidal or square-wave or other regular formed periodic signal could be synthesized and superimposed onto a DC potential as the excitation signal with this instrument. Some more useful electrode process information was expected to unveil by utilizing the FT-IFT algorithm to dissect the response signal. [source]

    Fourier Transformed Large Amplitude Square-Wave Voltammetry as an Alternative to Impedance Spectroscopy: Evaluation of Resistance, Capacitance and Electrode Kinetic Effects via an Heuristic Approach

    ELECTROANALYSIS, Issue 15-16 2005

    Abstract A detailed simulation of Fourier transformed large amplitude square-wave voltammetry is presented in the frequency domain for the process Red,Ox+e,. The simulation takes into account the influence of the electrode kinetics (Butler,Volmer model), uncompensated resistance (Ru) and double layer capacitance (Cdl). Of particular significance is the prediction that the even harmonic responses are only detected in the presence of quasi-reversibility or uncompensated resistance, and also are essentially devoid of charging current. In contrast, the DC and odd harmonic AC components exhibit much larger faradaic currents and also contain charging current. Conveniently, detailed analysis of the simulated DC and AC harmonic components reveals the presence of readily recognised patterns of behaviour with unique levels of sensitivity to electrode kinetics, Ru and Cdl, that facilitate quantitative analysis of these terms. These electrochemical parameters are generally calculated by small amplitude impedance spectroscopy and utilisation of linear analysis of equivalent circuits. Experimental studies on the one electron oxidation of ferrocene in dichloromethane (0.1,M Bu4NPF6) and the one electron reduction of [Fe(CN)6]3, in aqueous 0.5,M KCl electrolyte analysed via heuristic forms of data analysis based on recognition of patterns of behaviour, are presented as examples of a reversible process with significant uncompensated resistance and a quasi-reversible process with minimal ohmic drop, respectively. Results demonstrate the advantages of a more intuitively implemented form of data analysis than presently available with conventional forms of impedance spectroscopy. [source]

    Biomimetic Carbonate,Hydroxyapatite Nanocrystals Prepared by Vapor Diffusion,

    Michele Iafisco
    Abstract Biomimetic carbonate,hydroxyapatite (HA) nanocrystals have been synthesized by using the sitting drop vapor diffusion technique, for the first time. The method consists of diffusing vapors of an aqueous solution of NH4HCO3 through drops containing an aqueous mixture of (CH3COO)2Ca and (NH4)2HPO4 in order to increase slowly their pH. This synthesis has been performed in a crystallization mushroom, a glass device developed for protein and small molecules crystallization. The concentrations of the reagents, the final pH and the crystallization time have been optimized to produce pure carbonate,HA as a single phase. X-Ray diffraction, Fourier transformed infrared spectroscopy, and transmission electron microscopy have been utilized to characterize the synthesized carbonated substituted HA crystals which display nanometric dimensions, plate-like morphology, and low crystallinity degree, closely resembling the inorganic phase of bones, teeth, and many pathological calcifications. This novel method may prove to be suitable for the study of the interactions and/or the co-crystallization of hydroxyapatite with minute amounts of biomolecules, polymers, or drugs. [source]

    Biophysical studies of the development of amyloid fibrils from a peptide fragment of cold shock protein B

    FEBS JOURNAL, Issue 9 2000
    Deborah K. Wilkins
    The peptide CspB-1, which represents residues 1,22 of the cold shock protein CspB from Bacillus subtilis, has been shown to form amyloid fibrils when solutions containing this peptide in aqueous (50%) acetonitrile are diluted in water [M. Großet al. (1999) Protein Science8, 1350,1357] We established conditions in which reproducible kinetic steps associated with the formation of these fibrils can be observed. Studies combining these conditions with a range of biophysical methods reveal that a variety of distinct events occurs during the process that results in amyloid fibrils. A CD spectrum indicative of ,,structure is observed within 1 min of the solvent shift, and its intensity increases on a longer timescale in at least two kinetic phases. The characteristic wavelength shift of the amyloid-binding dye Congo Red is established within 30 min of the initiation of the aggregation process and corresponds to one of the phases observed by CD and to changes in the Fourier transform-infrared spectrum indicative of ,,structure. Short fibrillar structures begin to be visible under the electron microscope after these events, and longer, well-defined amyloid fibrils are established on a timescale of hours. NMR spectroscopy shows that there are no significant changes in the concentration of monomeric species in solution during the events leading to fibril formation, but that soluble aggregates too large to be visible in NMR spectra are present throughout the process. A model for amyloid formation by this peptide is presented which is consistent with these kinetic data and with published work on a variety of disease-related systems. These findings support the concept that the ability to form amyloid fibrils is a generic property of polypeptide chains, and that the mechanism of their formation is similar for different peptides and proteins. [source]

    Metabolic fingerprinting allows discrimination between Ulmus pumila and U. minor, and between U. minor clones of different susceptibility to Dutch elm disease

    FOREST PATHOLOGY, Issue 4 2008
    J. A. Martin
    Summary Experiments were conducted to test whether Fourier transform-infrared (FT-IR) spectroscopy, coupled with chemometric methods, can distinguish healthy xylem tissues collected from elms known to differ significantly in their susceptibility to Ophiostoma novo-ulmi Brasier. Twig samples from resistant Ulmus pumila L., susceptible U. minor Mill. and resistant U. minor clones were harvested on 1 May, 15 May, 1 June, 1 July and 1 September 2004, and subjected to FT-IR analysis. The application of principal component analysis to the spectral data, followed by discriminant function analysis, discriminated between the three groups of samples in all harvesting dates. The examination of the DF-loading plots allowed the identification of key regions within the spectra for the separation between clusters. The chemical assignments of these key regions allowed the following interpretations to be made: (i) U. pumila tissues contained enhanced levels of starch, cellulose and lignin with respect to U. minor tissues and (ii) resistant U. minor tissues contained enhanced levels of starch, cellulose and pectic polysaccharides with respect to susceptible U. minor tissues. The possible roles of the compositional differences in disease resistance, as well as the potential use of FT-IR spectroscopy and chemometrics as a tool for screening resistant elms are discussed. [source]


    ABSTRACT. Six millennial proxy records of temperature in the northern hemisphere were analysed using both the Fourier and wavelet approaches. We found that the analysed temperature proxies have appreciable synchrony at multidecadal and centennial time scales. These data also show evidence for the presence of a roughly regular large-scale rhythm with a periodicity of 50,130 years in the climate of the northern hemisphere over the last millennium. It is shown that the amplitude of this variation might reach 0.20,0.28°C and contribute appreciably to the rise of global temperature over the first part of the 20th century. Possible origins of the global centennial climatic cycles are discussed. [source]

    Seismic data reconstruction using multidimensional prediction filters

    M. Naghizadeh
    ABSTRACT In this paper we discuss a beyond-alias multidimensional implementation of the multi-step autoregressive reconstruction algorithm for data with missing spatial samples. The multi-step autoregressive method is summarized as follows: vital low-frequency information is first regularized adopting a Fourier based method (minimum weighted norm interpolation); the reconstructed data are then used to estimate prediction filters that are used to interpolate higher frequencies. This article discusses the implementation of the multi-step autoregressive method to data with more than one spatial dimension. Synthetic and real data examples are used to examine the performance of the proposed method. Field data are used to illustrate the applicability of multidimensional multi-step autoregressive operators for regularization of seismic data. [source]

    On the Origin of Green Emission in Polyfluorene Polymers: The Roles of Thermal Oxidation Degradation and Crosslinking,

    W. Zhao
    Abstract The green emission of poly(9,9,,-dioctylfluorenyl-2,7,,-diyl), end-capped by polyhedral oligomeric silsequioxanes, (PFO-POSS) has been investigated by photoluminescence (PL) and photoexcitation (PE), gel permeation chromatography (GPC), and transmission Fourier transform infrared (FTIR) spectroscopy. The green emission is closely correlated with thermal oxidation degradation and crosslinking of the polymer and is enhanced by annealing at elevated temperatures. The green-to-blue emission intensity ratio, used to assess the emission properties of thin (90,nm) films, was 3.70, 4.35, and 1.54 for an air-annealed film, its insoluble residue (crosslinked), and a film cast from its soluble portion, respectively. For thick (5,6,,m) film, the ratios are 13.33, 13.33, and 0.79, respectively. However, FTIR spectroscopy of thick films leads to the conclusion that the carbonyl-to-aromatic ring concentration ratio are 0.018, 0.015, and 0.032, respectively. Focusing on the recast films, the green emission is relatively low while the carbonyl concentration is relatively high. This suggests that the energy traps at crosslinked chains play an important role in green emission. It is likely that the crosslinking enhances the excitation energy migration and energy transfer to the defects by hindering chain segment twisting. [source]

    Analytical solution of the harmonic waves diffraction by a cylindrical lined cavity in poroelastic saturated medium

    Y. S. Karinski
    Abstract This paper presents a model for the analysis of plane waves diffraction at a cavity in an infinite homogeneous poroelastic saturated medium, lined by a lining composed of four equal segments. An elastic boundary layer is placed between the cavity lining and the infinite porous medium. The boundary layer is simulated by ,elastic boundary conditions' in which the bulk matrix stress is proportional to the relative displacement between the lining and the surrounding medium matrix boundary. In addition, fluid impermeability through the intermediate layer is assumed. For the frequencies, that differ from the pseudoresonanse frequencies, the problem was reduced to the problem of an ideal elastic medium. A closed-form analytical solution of the problem was obtained using Fourier,Bessel series, the convergence of which was proven. It was shown that the number of series terms required to obtain a desired level of accuracy can be determined in advance. The influence of the medium porosity on the medium dynamic stress concentration was studied. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Development of a class of multiple time-stepping schemes for convection,diffusion equations in two dimensions

    R. K. Lin
    Abstract In this paper we present a class of semi-discretization finite difference schemes for solving the transient convection,diffusion equation in two dimensions. The distinct feature of these scheme developments is to transform the unsteady convection,diffusion (CD) equation to the inhomogeneous steady convection,diffusion-reaction (CDR) equation after using different time-stepping schemes for the time derivative term. For the sake of saving memory, the alternating direction implicit scheme of Peaceman and Rachford is employed so that all calculations can be carried out within the one-dimensional framework. For the sake of increasing accuracy, the exact solution for the one-dimensional CDR equation is employed in the development of each scheme. Therefore, the numerical error is attributed primarily to the temporal approximation for the one-dimensional problem. Development of the proposed time-stepping schemes is rooted in the Taylor series expansion. All higher-order time derivatives are replaced with spatial derivatives through use of the model differential equation under investigation. Spatial derivatives with orders higher than two are not taken into account for retaining the linear production term in the convection,diffusion-reaction differential system. The proposed schemes with second, third and fourth temporal accuracy orders have been theoretically explored by conducting Fourier and dispersion analyses and numerically validated by solving three test problems with analytic solutions. Copyright © 2006 John Wiley & Sons, Ltd. [source]

    Les fards rouges cosmétiques et rituels a base de cinabre et d'ocre de l'époque punique en Tunisie: analyse, identification et caractérisation

    A. Alatrache
    Synopsis Natural antique colorants include mainly red pigments such as cinnabar and ochre. These archeological pigments were used especially as funeral and cosmetic makeup and are a material proof of handicraft activities and exchanges. The identification and characterization of a group of punic colorants, corresponding to samples discovered during excavations at several Tunisian archeological sites (Cartage, Ksour Essef, Kerkouane, Bekalta, Makthar, Bou Arada), were conducted using the least destructive analysis techniques such us scanning electron microscopy coupled to X-ray fluorescence microprobe, direct current plasma emission spectroscopy, atomic absorption spectrometry, Fourier transform infrared spectrometry and X-ray diffraction. Eleven natural red colorants from punic period were subject to this investigation and were compared to contemporary substances. Five colorants were cinnabar and the other six were ochre. Résumé Les colorants antiques naturels comportent principalement les pigments rouges tels que le cinabre et l'ocre. Ces pigments archéologiques ont été utilisés spécialement comme fards funéraires et cosmétiques, qui sont des témoins matériels d'activités artisanales et d'échanges. La caractérisation et l'identification d'un ensemble de colorants puniques correspondant à des échantillons découverts lors des fouilles sur divers sites de Tunisie (Carthage, Ksour Essef, Kerkouane, Bekalta, Makthar, Bou Arada) ont été conduites en employant des techniques d'analyse les moins destructives possibles telles que la microscopie électronique à balayage (MEB) couplée à une microsonde de fluorescence X (XRF), les spectrométries d'émission plasma à courant direct (DCP), d'absorption atomique (SAA) et infrarouge à transformée de Fourier (FTIR) et la diffraction aux rayons X (RX). Onze colorants naturels rouges puniques ont été soumis à l'étude et comparés avec des matières contemporaines. Cinq d'entre eux sont des composés de cinabre, les six autres des ocres. [source]

    Characteristic analysis of reverse-L-shaped microstrip-fed large-bandwidth printed slot antenna

    Yong-Woong Jang
    Abstract The characteristics of a reverse-L-shaped microstrip-fed structure is analyzed using the finite difference time domain method, and the characteristics of the proposed antenna are compared with a conventional antenna. The return loss, radiation resistance, and voltage,standing wave ratio in the frequency domain are calculated by Fourier transforming the time domain results. When the proposed feed structure is used, the bandwidth is extended in proportion to the slot width and the radiation resistance has the low value. When the slot width is 16 mm, the experimental bandwidth is approximately 50% (,10 dB , S11) at the center frequency of 2.3 GHz. In addition, the experimental data for the impedance and radiation pattern of the antenna are described. They are in good agreement with the calculated results. © 2002 Wiley Periodicals, Inc. Int J RF and Microwave CAE 12, 496,502, 2002. Published online in Wiley InterScience ( DOI 10.1002/mmce.10055 [source]

    Characterization and biodegradability of amphoteric superabsorbent polymers

    Dan Wang
    Abstract Novel amphoteric superabsorbent polymers (SAPs) based on carboxymethyl cellulose, acrylic acid, acrylamide, and [2-(methylacryloyloxy)ethyl]trimethylammonium chloride were prepared by inverse suspension copolymerization. The SAPs were characterized by Fourier transforms infrared spectroscopy, thermogravimetric analysis, and scanning electron microscopy. The absorbency or swelling behaviors in deionized water, saline solutions, and pH value solutions were investigated. Experimental results indicate that the absorbency in various solutions decreases with an increase of the ion concentration, which was attributed to osmotic pressure of water and ions between the polymeric gel and the external solutions. Biodegradability of the amphoteric SAPs was also reported. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Preconcentration and matrix elimination for the determination of Pb(II), Cd(II), Ni(II), and Co(II)by 8-hydroxyquinoline anchored poly(styrene-divinylbenzene) microbeads

    Hakan A
    Abstract Poly(styrene-divinylbenzene), PS-DVB, microbeads were modified with 8-hydroxyquinoline (8-HQ) following nitration, reduction of NO2 to NH2, and conversion of NH2 to diazonium salt. Characterization of pristine, NO2, NH2, NN+Cl,, and 8-QH functional groups modified microbeads was made by Fourier transform-infrared spectrometry (FTIR) and porosimetry. Total reflectron-X-ray florescence spectrometer (TXRF) was used to test the affinity of the 8-HQ modified microbeads to toxic metal ions. 8-HQ-modified microbeads were used to examine the adsorption capacity, recovery, preconcentration, and the matrix elimination efficiency for Pb(II), Cd(II), Ni(II), and Co(II) ions as a function of changing pH, initial metal-ion concentrations, and also equilibrium adsorption time of the studied metal ions. Preconcentration factors for the studied toxic metal ions were found to be more than 500-fold and recovery between 93.8% and 100.6%. Ultratrace toxic metal-ion concentrations in sea water were determined easily by using modified microbeads. Reference sea-water sample was used for the validation of the method, and it was found that recovery, preconcentration, and the matrix elimination were performed perfectly. For the desorption of the toxic metal ions, 3M of HNO3 was used and desorption ratio shown to be more than 96%. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008 [source]

    Physicochemical characterization and antioxidant activity of quercetin-loaded chitosan nanoparticles

    Yuying Zhang
    Abstract Quercetin is an abundant flavonoid in food plants with numerous biological activities and widely used as a potent antioxidant. Being sparingly soluble in water and subject to degradation in aqueous intestinal fluids, the absorption of quercetin is limited upon oral administration. In the present study, chitosan nanoparticles and quercetin-loaded nanoparticles were prepared based on the ionic gelation of chitosan with tripolyphosphate anions. The encapsulation of quercetin in the chitosan nanoparticles were confirmed by differential scanning calorimetry, X-ray powder diffractometry, Fourier transformed infrared spectroscopy, ultraviolet-visible spectrum, and fluorescence spectrum. The morphology of the nanoparticles was characterized by atomic force microscopy. The antioxidant activity of the quercetin-nanoparticles was also evaluated in vitro by two different methods (free radical scavenging activity test and reducing power test), which indicates that inclusion of quercetin in chitosan nanopaticles may be useful in improving the bioavailabilty of quercetin. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 2008 [source]

    Microwave accelerated synthesis and characterization of poly(acrylamide)

    Vandana Singh
    Abstract Poly(acrylamide) (PAM) was efficiently synthesized under microwave (MW) irradiation using catalytic amount of potassium persulfate. The synthesis does not require any inert atmosphere and could be accomplished in very short time. Microwave power, exposure time, concentration of persulfate, and concentration of the acrylamide were varied to optimize the polymerization in terms of the % conversion (%C). The maximum %C that could be achieved was in 98.5%. The average molecular weight of the synthesized PAM samples ranged from 4.11 × 104 to 1.30 × 105, depending upon the MW power used for their synthesis. The representative PAM was characterized by Fourier transform-infrared, SEM, and X-ray diffraction studies. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 3702,3707, 2007 [source]

    Chemical characteristics and cytocompatibility of collagen-based scaffold reinforced by chitin fibers for bone tissue engineering

    Xiaoming Li
    Abstract Chitin is a kind of seemly material to match PLLA for a scaffold, which may create an appropriate environment for the regeneration of tissues. In this study, we prepared and evaluated a new nano-hydroxyapatite/collagen/PLLA (nHACP) scaffold reinforced by chitin fibers for bone-tissue engineering. The chitin fibers were crosslinked with PLLA by dicyclohexylcarbodimide (DCC). The chemical characteristics were evaluated by Fourier transformed infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS). The mechanical strength was measured by compressive tests. The fibers, crosslinked with PLLA, could enhance the compressive strength of the scaffold about four times. Human marrow mesenchymal stem cells (MSCs) culture showed that the reinforced nHACP scaffolds were more cytocompatible than that without reinforcement. The crosslinks hardly affected the cytocompatibility of the reinforced scaffolds. The results suggested that the reinforced scaffolds (DCC crosslinked) might be a promising candidate for bone-tissue engineering. © 2005 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2006 [source]

    Fourier transformation of arterial Doppler waveforms of the lower extremity

    Hong Gi Lee MD
    Abstract Purpose Although it is well known that the normal, triphasic pulsatile arterial Doppler waveform changes in shape as flow is impaired, interpretation of the waveform has largely been subjective. We aimed to describe the Doppler waveforms of the lower extremity objectively using Fourier transformation. Methods Sixty-eight zero-crossing detector arterial recordings from 25 lower extremities were grouped as follows: group 1, no ischemic symptoms with an ankle-brachial index (ABI) > 0.9 (n = 17, 8 limbs); group 2, no ischemic symptoms with ABI < 0.9 (n = 18, 5 limbs); group 3, symptoms of claudication (n = 19, 7 limbs); group 4, rest pain or tissue loss (n = 14, 5 limbs). The waveforms were Fourier transformed and their amplitudes and phases were compared up to the third harmonic (H3). Results Amplitudes of both the fundamental (H1) and second harmonic (H2) were predominant in group 1. In contrast, amplitudes of the H2 and H3 decreased with altered flow (p < 0.0001 for group 1 versus others). The phases of the H1 and H2 were delayed with altered flow (p < 0.05 for group 1 versus others). Phases of the H1 were different between group 2 and 4 (p < 0.05). The difference of phase between the H3 and H1 was shortened with altered flow (p < 0.05 for group 1 or 2 versus group 4). Multivariate analysis revealed that the relative amplitudes of the H2 and H3, the phases of the H1 and H2, and the relative phase of the H3 were significant discriminators among the groups. Conclusion Abnormal waveforms could be characterized by the predominant amplitude of the H1, phase delay of the H1 and H2, and shortening of the relative phase of the H3. These parameters may be useful in the evaluation of Doppler waveforms in patients with peripheral arterial disease. © 2004 Wiley Periodicals, Inc. J Clin Ultrasound 32:277,285, 2004 [source]

    Elimination and exchange of trifluoroacetate counter-ion from cationic peptides: a critical evaluation of different approaches

    Stéphane Roux
    Abstract Most synthesized peptides are nowadays produced using solid-phase procedures. Due to cleavage and purification conditions, they are mainly obtained in the presence of trifluoroacetic acid (TFA) and, for cationic peptides, as trifluoroacetate (TF-acetate) salts. However, TF-acetate interferes with physicochemical characterizations using infrared spectroscopy and might significantly affect the in vivo studies. Thus, TF-acetate exchange by another counter-ion is often required. Up to now, the classical procedure has consisted of freeze-drying the peptide several times in the presence of an excess of a stronger acid than TFA (pKa ,0): generally HCl (pKa = , 7). This approach means that working at pH < 1 can induce peptide degradation. We therefore tested three different approaches to exchange the tightly bound TF-acetate counter-ion from the dicationic octapeptide lanreotide: (i) reverse-phase HPLC, (ii) ion-exchange resin, and (iii) deprotonation/reprotonation cycle of the amino groups. The first two approaches allow the partial to almost complete exchange of the TF-acetate counter-ion by another ion from an acid weaker than TFA, such as acetic acid (pKa = 4.5), and the third requires a basic solution that permits the complete removal of TF-acetate counter-ion. The efficiency of these three procedures was tested and compared by using different analytical techniques such as 19F-NMR, 1H-NMR and attenuated total reflectance Fourier transformed infrared spectroscopy (ATR FT-IR). We also show that ATR-IR can be used to monitor the TFA removal. The counter-ion exchange procedures described in this study are easy to carry out, fast, harmless and reproducible. Moreover, two of them offer the very interesting possibility of exchanging the initial TF-acetate by any other counter-ion. Copyright © 2007 European Peptide Society and John Wiley & Sons, Ltd. [source]

    Piroxicam/2-hydroxypropyl-,-cyclodextrin inclusion complex prepared by a new fluid-bed coating technique

    Xingwang Zhang
    Abstract This work was aimed at investigating the feasibility of fluid-bed coating as a new method to prepare cyclodextrin inclusion complex. The inclusion complex of the model drug piroxicam (PIX) and 2-hydroxypropyl-,-cyclodextrin (HPCD) in aqueous ethanol solution was sprayed and deposited onto the surface of the pellet substrate upon removal of the solvent. The coating process was fluent with high coating efficiency. Scanning electron microscopy revealed a coarse pellet surface, and a loosely packed coating structure. Significantly enhanced dissolution, over 90% at 5 min, was observed at stoichiometric PIX/HPCD molar ratio (1/1) and at a ratio with excessive HPCD (1/2). Differential scanning calorimetry and powder X-ray diffractometry confirmed absence of crystallinity of PIX at PIX/HPCD molar ratio of 1/1 and 1/2. Fourier transform-infrared spectrometry and Raman spectrometry revealed interaction between PIX and HPCD adding evidence on inclusion of PIX moieties into HPCD cavities. Solid-state 13C NMR spectrometry indicated possible inclusion of PIX through the pyridine ring. It is concluded that fluid-bed coating has potential to be used as a new technique to prepare cyclodextrin inclusion complex. © 2008 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 98:665,675, 2009 [source]

    Analysis of structure and vibrational spectra of 2,5-dihydroxybenzoicacid based on density functional theory calculations

    V. Krishnakumar
    Abstract The spectra of 2,5-dihydroxybenzoic acid (DHBA) have been recorded using Fourier transform-infrared spectroscopy (FT-IR) and FT-Raman measurements. The total energy calculations of DHBA were evaluated for various possible conformers. The spectra were interpreted with the help of normal coordinate analysis based on density functional theory (DFT) using standard B3LYP/6,31G* method for the most optimized geometry. The effect of intramolecular hydrogen bonding was discussed. Normal coordinate calculations were performed with the DFT force field corrected by a recommended set of scaling factors, yielding fairly good agreement between observed and calculated frequencies. On the basis of the comparison between calculated and experimental results, assignments of fundamental modes were examined. Copyright © 2009 John Wiley & Sons, Ltd. [source]

    Structural conformations and electronic interactions of the natural product, oroxylin: a vibrational spectroscopic study

    Jose P. Abraham
    Abstract The oroxylin, 5,7-dihydroxy 6-methoxy flavone is a potent natural product extracted from ,Vitex peduncularis'. Density functional theory (DFT) at B3LYP/6-311G(d,p) level has been used to compute energies of different conformers of oroxylin to find out their stability, the optimized geometry of the most stable conformer and its vibrational spectrum. The conformer ORLN-1 with torsion angles 0, 180, 180 and 0 degrees, respectively, for H13O12C6C5, H14O10C4C5, H13O12C6C5 and H14O10C4C5 is found to be most stable. The optimized geometry reveals that the dihedral angle , between phenyl ring B and the chrome part of the molecule in , 19.21° is due to the repulsive force due to steric interaction between the ortho-hydrogen atom H29 of the B ring and H18 of the ring C (H29·H18 = 2.198 Å). A vibrational analysis based on the near-infrared Fourier transform(NIR-FT) Raman, Fourier transform-infrared (FT-IR) and the computed spectrum reveals that the methoxy group is influenced by the oxygen lone pair-aryl pz orbital by back donation. Hence the stretching and bending vibrational modes of the methoxy group possess the lowest wavenumber from the normal values of methyl group. The carbonyl stretching vibrations have been lowered due to conjugation and hydrogen bonding in the molecules. The intramolecular H-bonding and nonbonded intramolecular interactions shift the band position of O10H14 and O12H13 stretching modes, which is justified by DFT results. Copyright © 2008 John Wiley & Sons, Ltd. [source]


    ABSTRACT On five separate occasions, eight volunteers were asked to consume five edible gels with known texture and flavour properties. The electrical activity of their temporal and masseter muscles was recorded using electromyography (EMG). The electrode voltages were sampled at a rate of 1 kHz, starting when each volunteer began to masticate, and terminating when the volunteer indicated that the gel's flavour could no longer be perceived. Data from the mastication phase (first 20 s) were Fourier transformed to give a power spectrum in the frequency domain. Upon visual examination, the low frequency (< 10 Hz) region was found to contain spectral features that differ between volunteers, and the differences were generally consistent between sessions. Principal component analysis (PCA) supported this finding, by showing some clustering of the scores from different volunteers. However, when PCA was applied to the whole of the frequency range, the clustering became much more pronounced, indicating that higher frequencies also contribute to the distinction between volunteers. Clusters of readings from each volunteer were almost entirely separated using internally cross-validated canonical variate analysis (CVA), showing that each individual demonstrated characteristic and consistent mastication behaviour. Finally, a statistically significant association was found between the integrated power spectrum and the concentration of flavour compound in the gels; however, a similar relationship was discovered to exist between the flavour and the texture, as determined by cutting and compression. Hence, it was not possible to determine conclusively whether flavour alone has an effect on mastication characteristics. [source]

    Phase Evolution During Formation of SrAl2O4 from SrCO3 and ,-Al2O3/AlOOH

    Yu-Lun Chang
    Through the execution of experimental investigation, thermogravimetry, X-ray diffractometry, Fourier transform-infrared spectrometry, transmission electron microscopy, and energy-dispersive spectrometry, a variant reaction mechanism model was proposed for the solid-state reaction between SrCO3 and Al2O3/AlOOH for formation of SrAl2O4 material. The solid-state reaction is observed to be dependent on the calcination temperature. At temperatures lower than the transformation temperature of SrCO3 from orthorhombic to hexagonal (920°C), the reaction is attributed to the interfacial reaction between SrCO3 and alumina. Conversely, at temperatures higher than that, the solid-state reaction is dominated by the diffusion of Al3+ ions into the SrCO3 lattice. In this mechanism, two metastable species, hexagonal SrCO3 and hexagonal SrAl2O4, were observed. The activation energies of SrCO3 decomposition in the solid-state reaction also support these results. The interfacial reaction at low temperatures is characterized by a high activation energy of ,130 kJ/mol; whereas, in the reaction at higher temperatures, the activation energy of SrCO3 decomposition decreases to 34 kJ/mol. [source]

    A penalized likelihood approach to image warping

    C. A. Glasbey
    A warping is a function that deforms images by mapping between image domains. The choice of function is formulated statistically as maximum penalized likelihood, where the likelihood measures the similarity between images after warping and the penalty is a measure of distortion of a warping. The paper addresses two issues simultaneously, of how to choose the warping function and how to assess the alignment. A new, Fourier,von Mises image model is identified, with phase differences between Fourier-transformed images having von Mises distributions. Also, new, null set distortion criteria are proposed, with each criterion uniquely minimized by a particular set of polynomial functions. A conjugate gradient algorithm is used to estimate the warping function, which is numerically approximated by a piecewise bilinear function. The method is motivated by, and used to solve, three applied problems: to register a remotely sensed image with a map, to align microscope images obtained by using different optics and to discriminate between species of fish from photographic images. [source]

    Wavelet processes and adaptive estimation of the evolutionary wavelet spectrum

    G. P. Nason
    This paper defines and studies a new class of non-stationary random processes constructed from discrete non-decimated wavelets which generalizes the Cramér (Fourier) representation of stationary time series. We define an evolutionary wavelet spectrum (EWS) which quantifies how process power varies locally over time and scale. We show how the EWS may be rigorously estimated by a smoothed wavelet periodogram and how both these quantities may be inverted to provide an estimable time-localized autocovariance. We illustrate our theory with a pedagogical example based on discrete non-decimated Haar wavelets and also a real medical time series example. [source]

    Characterisation of lubricants on ball bearings by FT-IR using an integrating sphere

    K.W. Street
    Abstract Fourier transform-infrared reflectance microspectroscopy has been used extensively for the examination of coatings on non-planar surfaces such as ball bearings. While this technique offers considerable advantages, practical application has many drawbacks, some of which are easily overcome by the use of integrating sphere technology. This paper described the use of an integrating sphere for the quantification of thin layers of lubricant on the surface of ball bearings and the parameters that require optimisation in order to obtain reliable data. Several applications of the technique were discussed including determination of lubricant load on 12.7mm steel ball bearings and the examination of degraded lubricant on post-mortem specimens. Copyright © 2007 John Wiley & Sons, Ltd. [source]

    Generalized MRI reconstruction including elastic physiological motion and coil sensitivity encoding

    Freddy Odille
    Abstract This article describes a general framework for multiple coil MRI reconstruction in the presence of elastic physiological motion. On the assumption that motion is known or can be predicted, it is shown that the reconstruction problem is equivalent to solving an integral equation,known in the literature as a Fredholm equation of the first kind,with a generalized kernel comprising Fourier and coil sensitivity encoding, modified by physiological motion information. Numerical solutions are found using an iterative linear system solver. The different steps in the numerical resolution are discussed, in particular it is shown how over-determination can be used to improve the conditioning of the generalized encoding operator. Practical implementation requires prior knowledge of displacement fields, so a model of patient motion is described which allows elastic displacements to be predicted from various input signals (e.g., respiratory belts, ECG, navigator echoes), after a free-breathing calibration scan. Practical implementation was demonstrated with a moving phantom setup and in two free-breathing healthy subjects, with images from the thoracic-abdominal region. Results show that the method effectively suppresses the motion blurring/ghosting artifacts, and that scan repetitions can be used as a source of over-determination to improve the reconstruction. Magn Reson Med, 2008. © 2008 Wiley-Liss, Inc. [source]