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Intensity Ratio (intensity + ratio)
Kinds of Intensity Ratio Selected AbstractsRaman and Rayleigh scattering study of crystalline polyoxyethyleneglycolsCRYSTAL RESEARCH AND TECHNOLOGY, Issue 4-5 2005M. Kozielski Abstract Results of the study of Raman and Rayleigh scattering in crystalline polyoxyethyleneglycols (PEG) and PEG 1500 aqueous solution are reported. The conformational changes of the polymer chain have been studied as a function of PEG water solution concentration and molecular weight. Intensity ratios of the gauche and trans conformation around C,C and C,O bonds have been estimated from the Raman spectra. Moreover, from the Raman band parameters the values of the order parameters versus aqueous solution concentration have been determined. The influence of an external electric field on these parameters has been analysed. Mutual orientation of polyoxyethyleneglycol chains in the crystalline and liquid state has been studied on the basis of the angular correlation parameters obtained from the Rayleigh band intensity as a function of aqueous solution concentration and molecular weight. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] A Ratiometric Fluorescent Probe for Hypochlorite Based on a Deoximation ReactionCHEMISTRY - A EUROPEAN JOURNAL, Issue 10 2009Weiying Lin Prof. Abstract The first ratiometric fluorescent probe for hypochlorite has been developed through regulation of the electron-withdrawing ability of the electron acceptor in an intramolecular charge-transfer (ICT) system by a deoximation reaction (see figure; EWG=electron-withdrawing group). In this work, we have successfully provided a novel strategy for the rational design and synthesis of a ratiometric fluorescent probe for hypochlorite. The strategy is based on the deoximation reaction, which has not yet been used in the fluorescent hypochlorite probe design. Interestingly, the probe showed a ratiometric fluorescent response to hypochlorite with the emission intensities ratio (I509/I439) increasing from 0.28 to 2.74. Furthermore, the probe displayed high selectivity for hypochlorite over other species due to the distinct deoximation conditions. The probe developed herein represents the first ratiometric fluorescent probe for hypochlorite. [source] Effect of organic matter applications on 13C-NMR spectra of humic acids of soilEUROPEAN JOURNAL OF SOIL SCIENCE, Issue 3 2008S. Dou Summary Much attention has been paid to improving soil fertility with organic matter (OM) application, which not only deals with organic wastes and protects the environment, but also maintains soil fertility and increases crop yields. Much research has also been on the effects of OM applications on the soil's physical, chemical and biological properties, but relatively less attention has been spent on humic substance (HS). In order to clarify the mechanism of improving soil fertility by applying OM, we analysed the changes of structural characteristics of humic acid (HA) from OM applications to soils by 13C-NMR, chemical analysis, thermal analysis, optical properties, IR and fluorescence spectroscopy. Samples of a brown soil (Paleudalf) and a paddy soil (an anthropogenic soil originating from Udifluvents) were collected from the plough layer of the long-term field experiment at Shenyang Agricultural University and Liaoning Provincial Alkali-Saline Soil Institute, respectively. Both field experiments included three treatments each: (i) brown soil, zero-treatment (CKbr) and two pig manure (PM) applications (O1 and O2) at annual rates of 0.9 t ha,1 and 1.8 t ha,1 of organic carbon, respectively; and (ii) paddy soil, zero-treatment (CKpad), pig manure (Op) and rice straw (Or) at annual rates of 2.62 t ha,1 and 1.43 t ha,1 of organic carbon, respectively. An incubation experiment was also carried out to test the field experiment on the brown soil, namely four treatments: zero-treatment (CKc), and three pig manure applications at rates of 30 g kg,1 (C1), 50 g kg,1 (C2) and 70 g kg,1 (C3), respectively. The total incubation was 180 days. The results indicated that number-average molecular weights (Mn), total acidity, aromaticity, excitation maximum wavelength (,Exmax), and the heat ratio of the high to moderate temperature exothermic regions (H3/H2) of the HA all decreased after OM application. The degree of activation (AD), the absorption intensity ratio of 2920 cm,1 to 1720 cm,1 in infrared spectra (IR2920/1720), alkyl C and O-alkyl C of the HA increased. The HA structure tended to become simpler and more aliphatic. [source] Characterization, Cathodoluminescence, and Field-Emission Properties of Morphology-Tunable CdS Micro/NanostructuresADVANCED FUNCTIONAL MATERIALS, Issue 15 2009Tianyou Zhai Abstract High-quality, uniform one-dimensional CdS micro/nanostructures with different morphologies,microrods, sub-microwires and nanotips,are fabricated through an easy and effective thermal evaporation process. Their structural, cathodoluminescence and field-emission properties are systematically investigated. Microrods and nanotips exhibit sharp near-band-edge emission and broad deep-level emission, whereas sub-microwires show only the deep-level emission. A significant decrease in a deep-level/near-band-edge intensity ratio is observed along a tapered nanotip towards a smaller diameter part. This behavior is understood by consideration of defect concentrations in the nanotips, as analyzed with high-resolution transmission electron microscopy. Field-emission measurements show that the nanotips possess the best field-emission characteristics among all 1D CdS nanostructures reported to date, with a relatively low turn-on field of 5.28,V µm,1 and the highest field-enhancement factor of 4,819. The field-enhancement factor, turn-on and threshold fields are discussed related to structure morphology and vacuum gap variations under emission. [source] Superparamagnetic iron oxide,enhanced magnetic resonance images of hepatocellular carcinoma: Correlation with histological gradingHEPATOLOGY, Issue 2 2000Ph.D., Yasuharu Imai M.D. Superparamagnetic iron oxide (SPIO),enhanced magnetic resonance (MR) imaging has been used for the detection of hepatic tumors. However, little is known about this technique in relation to hepatocellular carcinoma (HCC). The aim of this study was to investigate whether SPIO,enhanced MR imaging can be useful in assessing histological grades of HCC. The authors studied histologically proven tumors including 31 HCCs and 6 dysplastic nodules. The ratio of the Kupffer-cell count in the tumorous tissue relative to that in the nontumorous tissue (Kupffer-cell,count ratio) decreased as HCCs became less well differentiated. The ratio of the intensity of the tumorous lesion to that of the nontumorous area on SPIO,enhanced MR images (SPIO intensity ratio) correlated inversely with Kupffer-cell,count ratio in HCCs and dysplastic nodules (r = ,.826, P< .001) and increased as the degree of differentiation of HCCs decreased, indicating that the uptake of SPIO in HCCs decreased as the degree of differentiation of HCCs declined. All of the dysplastic nodules and some well-differentiated HCCs showed hypointense or isointense enhancement, relative to the surrounding liver parenchyma, indicating greater or similar uptake of SPIO in the tumor when compared with nontumorous areas. These results suggest that SPIO,enhanced MR imaging reflects Kupffer-cell numbers in HCCs and dysplastic nodules, and is useful for estimation of histological grading in HCCs, although uncertainties persist in differentiating dysplastic nodules from well-differentiated HCCs. [source] FULLPAT: a full-pattern quantitative analysis program for X-ray powder diffraction using measured and calculated patternsJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2002Steve J. Chipera FULLPAT is a quantitative X-ray diffraction methodology that merges the advantages of existing full-pattern fitting methods with the traditional reference intensity ratio (RIR) method. Like the Rietveld quantitative analysis method, it uses complete diffraction patterns, including the background. However, FULLPAT can explicitly analyze all phases in a sample, including partially ordered or amorphous phases such as glasses, clay minerals, or polymers. Addition of an internal standard to both library standards and unknown samples eliminates instrumental and matrix effects and allows unconstrained analyses to be conducted by direct fitting of library standard patterns to each phase in the sample. Standard patterns may include data for any solid material including glasses, and calculated patterns may also be used. A combination of standard patterns is fitted to observed patterns using least-squares minimization, thereby reducing user intervention and bias. FULLPAT has been coded into Microsoft EXCEL using standard spreadsheet functions. [source] MRI and S-MRCP findings in patients with suspected chronic pancreatitis: Correlation with endoscopic pancreatic function testing (ePFT)JOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 3 2010N. Cem Balci MD Abstract Purpose: To review magnetic resonance imaging (MRI) and secretin stimulated magnetic resonance cholangiopancreatography (S-MRCP) findings of patients with suspected chronic pancreatitis and compare them with endoscopic pancreatic function testing (ePFT). Materials and Methods: MRI and S-MRCP findings of 36 patients with clinically suspected chronic pancreatitis were reviewed. Baseline ductal changes, duodenal filling grades, and pancreatic duct caliber change (PDC) on S-MRCP, mean values of pancreatic anteroposterior (AP) diameter, signal intensity ratio (SIR) between pancreas and the spleen on T1-weighted fat saturated images, and arterial to venous (A/V) enhancement ratios were compared between groups of normal and abnormal pancreatic exocrine function determined by ePFT. Results: All patients (n = 24) with normal ePFT (HCO3 >80 mEq/L) had grade 3 normal duodenal filling. Patients with abnormal ePFT (HCO3 <80 mEq/L) (n = 12) had grade 1 (n = 1) and grade 2 (n = 11) diminished duodenal filling (P < 0.0001). PDC was 1.51 in the normal ePFT group versus 1.27 in the abnormal ePFT group (P = 0.01). No significant differences were found in terms of mean pancreatic AP diameter (21.8 vs. 19.8 cm), SIR (1.59 vs. 1.44), and A/V (1.08 vs. 1.01) between groups of normal/abnormal pancreatic exocrine function. Conclusion: Despite discrepancies between pancreatic exocrine function and the findings on standard MRI/MRCP, the S-MRCP findings are comparable to ePFT in the evaluation of chronic pancreatitis. J. Magn. Reson. Imaging 2010;31:601,606. © 2010 Wiley-Liss, Inc. [source] Monitoring of unfolding of metallo-proteins by electrospray ionization mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 5 2003Vincenzo Cunsolo Abstract An electrospray ionisation (ESI) mass spectrometric method for the determination of the equilibrium constant and free energy (,G) of protein unfolding was used to monitor the denaturation process at different pH of three metallo-proteins, i.e. wild-type copper azurin, zinc azurin and wild-type amicyanin. The time course of the unfolding process was followed by dissolving the proteins under denaturing conditions (methanol,water (1 : 1, v/v)) at different pH (2.5, 3.0, 3.5) and recording ESI spectra at time intervals. The spectra showed two series of peaks, corresponding to the native holo-protein and the unfolded apo-protein. From the intensity ratio of these two series of peaks at increasing time and at equilibrium, the equilibrium constants for the unfolding process for the three proteins could be determined. From these equilibrium constants a ,G° derivation was attempted. The ,G° values obtained decrease with decrease in pH, in agreement with the expected reduction of conformational stability of proteins at lower pH. The results obtained confirm that ESI-MS can be used for monitoring of unfolding process and to derive quantitative thermodynamic data. Copyright © 2003 John Wiley & Sons, Ltd. [source] Discrimination between pentose oligosaccharides containing D -xylopyranose or L -arabinofuranose as non-reducing terminal residue using fast atom bombardment mass spectrometry,JOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 4 2001Vladimír Ková Abstract Collisional-induced dissociation (CID) mass spectra of the [M + H]+ and [M , H], ions obtained under fast atom bombardment conditions of a number of methyl glycoside di-, tri- and tetrasaccharides, containing D -xylopyranosyl and/or L -arabinofuranosyl residues at the non-reducing terminus, do not provide information about their ring size. This information could only be obtained from a careful comparison of the intensity ratio of the [M + Na , 90]+ and [M + Na , 104]+ ions (0,2Xt/1,5Xt) in the high-energy CID spectra of the sodium-cationized di-, tri- and probably also tetrasaccharide compounds. Copyright © 2001 John Wiley & Sons, Ltd. [source] Ageing of calcium silicate cements for endodontic use in simulated body fluids: a micro-Raman studyJOURNAL OF RAMAN SPECTROSCOPY, Issue 12 2009Paola Taddei Abstract To evaluate bioactivity properties, a calcium silicate experimental cement (wTC) and a phosphate-doped wTC cement (wTC-TCP) were aged for different times (1,180 days) at 37 °C in two simulated body fluids, i.e. Dulbecco's phosphate buffered saline (DPBS) and Hank's balanced salt solution (HBSS). The cements were analyzed by micro-Raman spectroscopy to investigate the presence of calcium phosphate deposits and the composition changes as a function of the storage time (hydration of anhydrite/gypsum and formation of ettringite; hydration of belite/alite and formation of hydrated silicates). After 1 day of ageing in DPBS, the two cements already showed a different behavior: only the surface of wTC-TCP cement showed the band at 965 cm,1, suggesting the formation of a detectably thick calcium phosphate deposit. The trend of the I965/I990 Raman intensity ratio indicated the formation of a meanly thicker apatite deposit on the wTC-TCP cement until 90 days. After 60 days of ageing in DPBS, the thickness of the apatite deposit on wTC and wTC-TCP was about 200 and 500 µm, respectively, whereas at 180 days, the two cements did not appear significantly different (thickness of about 900 µm). The bioactivity of both cements in HBSS was less pronounced than in DPBS, according to the lower phosphate concentration of HBSS; at the same time, higher amounts of calcite were found on the surface of both cements. The wTC-TCP cement showed a higher bioactivity in this medium also; after 180 days, the thickness of the apatite deposit on wTC and wTC-TCP was < 50 µm and about 100 µm, respectively. Copyright © 2009 John Wiley & Sons, Ltd. [source] Characterisation of carbonaceous materials using Raman spectroscopy: a comparison of carbon nanotube filters, single- and multi-walled nanotubes, graphitised porous carbon and graphiteJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2009H. M. Heise Abstract Multi-walled carbon nanotube (MWCNT) filters have been recently synthesised which have specific molecular filtering capabilities and good mechanical strength. Optical and scanning electron microscopy (SEM) reveals the formation of highly aligned arrays of bundles of carbon nanotubes having lengths up to 500 µm. The Raman spectra of this material along with four other carbonaceous materials, commercially available single-walled carbon nanotubes (SWCNTs) and MWCNTs, graphitised porous carbon (Carbotrap) and graphite have been recorded using two-excitation wavelengths, 532 and 785 nm, and analysed for band positions and shape with special emphasis paid to the D-, G- and G,-bands. A major difference between the different MWCNT varieties analysed is that G-bands in the MWCNT filters exhibit almost no dispersion, whereas the other MWCNTs show a noticeable dispersive behaviour with a change in the excitation wavelength. Spectral features similar to those of the MWCNT filter varieties were observed for the Carbotrap material. From the line shape analysis, the intensity ratio, ID/IG, of the more ordered MWCNT filter material using the integral G-band turns out to be two times lower than that of the less ordered MWCNT filter product at both excitation wavelengths. This parameter can, therefore, be used as a measure of the degree of MWCNT alignment in filter varieties, which is well supported also by our SEM study. Copyright © 2008 John Wiley & Sons, Ltd. [source] Ultraviolet and visible Raman spectroscopic investigations of nanocrystalline carbon thin films grown by bias-assisted hot-filament chemical vapor depositionJOURNAL OF RAMAN SPECTROSCOPY, Issue 3 2003S. Gupta Abstract The structural bonding in a series of nanocrystalline carbon thin films grown under different substrate biasing conditions was analyzed using Raman spectroscopy in both the visible and ultraviolet (uv) regimes of the spectrum. The nanocrystalline carbon thin films studied were deposited by the hot-filament chemical vapor deposition (HFCVD) technique using a 2% concentration of methane in hydrogen. The films were deposited on molybdenum substrates under various substrate biasing conditions. A positive bias (forward) produced a continuous flow of electrons from the filament on to the substrate, whereas a negative bias (negative) caused the substrate to be bombarded with positive ions. Films were also grown under no bias, for comparison. Differences in the Raman spectra obtained with visible (,L = 514.5 nm) and uv (,L = 244.0 nm) excitation sources were investigated. Apart from the basic features consisting of D and G bands at around 1360 and 1580 cm,1 in the case of visible Raman spectra, an extra feature at around 1060 cm,1, denoted a T band, appeared in the uv Raman spectra only. Hence, uv Raman scattering measurements clearly revealed the presence of sp3 -bonded carbon atoms. The position and its intensity ratio with respect to the G peak [(I(T)/I(G)] were used to provide a reliable means to measure the sp3 C bonding fraction, which is both semi-quantitative and non-destructive. The sp3 content estimated within the microstructure of n-C thin films was found to be around 60,80%. Further, probing the samples with two different photons (visible and uv) allowed us to estimate qualitatively the amount and clustering of sp2 sites. This technique provided a fast and reliable microstructural characterization of disordered carbons. The dispersion in the Raman features is specific to each carbon system and, therefore, can be used as a fingerprint. These findings point at the similarities of bias-assisted HFCVD nanocrystalline carbon (n-C) materials and the tetrahedrally bonded amorphous carbon (ta -C) materials grown by ion-beam assisted deposition (IBAD). Copyright © 2003 John Wiley & Sons, Ltd. [source] Enhanced Blue Emission from Transparent Oxyfluoride Glass,Ceramics Containing Pr3+:BaF2 NanocrystalsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 4 2010Kaushik Biswas Transparent glass,ceramics containing Pr3+:BaF2 nanocrystals in the chemical composition of SiO2,BaF2,K2CO3,La2O3,Sb2O3 oxyfluoride glass systems have been prepared from melt quenching and with a subsequent heat-treatment method. The luminescence and structural properties of these materials have been evaluated and the results are reported. Rietveld analysis of X-ray diffraction patterns and investigation of transmission electron microscopy confirmed the presence of BaF2 nanocrystals dispersed in the heat-treated glass matrices. Measured UV-Vis-NIR absorption spectra exhibited nine bands of the transitions 3H4,3P2, (1I6, 3P1), 3P0, 1D2, 1G4, 3F3, 3F2, 3H6, and 3H5 from all the samples with nondegenerated 1I6 and 3P1 levels in the glass,ceramics. The photoluminescence spectra show an enhancement in the intensities upon ceramization, indicating the incorporation of Pr3+ ions into BaF2 nanocrystals that possess a low phonon energy (346 cm,1). This has further been corroborated from the observation of a significant threefold increase in the relative intensity ratio of blue (3P0,3H4) to red (1D2,3H4, 3P0,3H6) emissions from glass,ceramics compared with the glass. This is due to a significant decrease of multiphonon nonradiative relaxation from the 3P0 to the 1D2 level of Pr3+ in glass,ceramics. Time-resolved spectra exhibit 3P0 -level decays faster than the 1D2 level. [source] Hydrogen bonds and local symmetry in the crystal structure of gibbsiteMAGNETIC RESONANCE IN CHEMISTRY, Issue 11 2010Anastasia Vyalikh Abstract First-principles quantum mechanical calculations of NMR chemical shifts and quadrupolar parameters have been carried out to assign the 27Al MAS NMR resonances in gibbsite. The 27Al NMR spectrum shows two signals for octahedral aluminum revealing two aluminum sites coordinated by six hydroxyl groups each, although the crystallographic positions of the two Al sites show little difference. The presence of two distinguished 27Al NMR resonances characterized by rather similar chemical shifts but quadrupolar coupling constants differing by roughly a factor of two is explained by different character of the hydrogen bonds, in which the hydroxyls forming the corresponding octahedron around each aluminum site, are involved. The Al-I site characterized by a CQ = 4.6 MHz is surrounded by OHgroups participating in four intralayer and two interlayer hydrogen bonds, while the Al-II site with the smaller quadrupolar constant (2.2 MHz) is coordinated by hydroxides, of which two point toward the intralayer cavities and four OH-bonds are aligned toward the interlayer gallery. In high-resolution solid-state 1H CRAMPS (combination of rotation and multiple-pulse spectroscopy) four signals with an intensity ratio of 1:2:2:1 are resolved which allow to distinguish six nonequivalent hydrogen sites reported in the gibbsite crystal structure and to ascribe them to two types of structural OH groups associated with intralayer and interlayer hydrogen bonds. This study can be applied to characterize the gibbsite-like layer,intergallery interactions associated with hydrogen bonding in the more complex systems, such as synthetic aluminum layered double hydroxides. Copyright © 2010 John Wiley & Sons, Ltd. [source] The effects of MRI signal intensity changes and clinical manifestations on prognosis after surgical intervention for cervical spondylotic myelopathyORTHOPAEDIC SURGERY, Issue 2 2009Ying-ze Zhang MD Objective:, To investigate whether the magnetic resonance (MR) T2 image signal intensity ratio and clinical manifestations can predict the prognosis in patients with cervical spondylotic myelopathy (CSM). Methods:, A total of 73 patients treated with anterior, posterior, or posterior-anterior combined surgery for compressive cervical myelopathy were enrolled retrospectively in this study. 1.5 T magnetic resonance imaging (MRI) was performed on all patients before surgery. T2-weighted images (T2WI) of sagittal signal intensity were obtained of the cervical spinal cord, and the regions of interest (ROI) were taken by 0.05 cm2. MR T2WI of sagittal normal cord signal at the C7-T1 disc level were also obtained, and the ROI were taken by 0.3 cm2. Signal value was measured by computer and the signal ratio between regions 0.05 cm2 and 0.3 cm2 calculated. Where no intramedullary high signal intensity was noted on MR T2WI, the ROI were taken by 0.05 cm2 of the region of most severe spinal cord compression. The 73 patients were divided into three groups by hierarchical clustering analysis with signal intensity ratio (group 1: low signal intensity ratio; group 2: middle signal intensity ratio; group 3: high signal intensity ratio). Statistical analyses were performed with SPSS 11.0. Results:, There were significant differences between the three groups according to the recovery rate (P < 0.001), age (P= 0.003), duration of disease (P= 0.001), Babinski sign (P < 0.001), pre- and postoperative Japanese Orthopaedic Association (JOA) score (P= 0.006). With increases in both signal intensity ratio grade and age, the recovery rate and pre- and postoperative JOA scores gradually decreased, and the incidence of Babinski sign increased. There was no significant difference in sex among the three groups (P= 0.387). Multiple comparison tests further supported the above-mentioned results. Conclusion:, Patients with light or no intramedullary signal changes on T2WI had a good surgical outcome. However, increase of signal intensity ratio and occurrence of the pyramidal sign were associated with a poor prognosis after surgery. [source] Structural order on different length scales in amorphous silicon investigated by Raman spectroscopyPHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 3 2010S. Muthmann Abstract Parameters for the structural short (SRO) and medium range order (MRO) of hydrogenated amorphous silicon (a-Si:H) films on the edge of the microcrystalline silicon (µc-Si:H) phase transition were studied with Raman spectroscopy. The observed samples were deposited using radio frequency plasma enhanced chemical vapor deposition. The studied films were grown with various constant and non-constant silane concentrations (SCs). A substrate dependent correlation of SC to the intensity ratio (IMRO) of the transversal acoustical (TA) and the transversal optical (TO) phonon bands was found. A strong correlation between width and position of the (TO) phonon band was observed. These two easily accessible parameters show an increase of SRO when IMRO decreases. [source] Surface morphology effects on the optical phonon modes in InAsxSb1,x epilayers on GaAs(001)PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 4 2006P. Jayavel Abstract We have studied Raman scattering from longitudinal- and transverse-optical (LO and TO) phonon modes in InAsxSb1,x epilayers grown on GaAs(001) substrates with various arsenic compositions (x). InSb-like and InAs-like LO and TO phonon modes of the epilayers are observed. We find that the peak intensity ratio of the InAs-like LO to TO-mode decreases for x < 0.6 while it increases for x > 0.6. This intensity ratio change is attributed to two- and three-dimensional (2D and 3D) growth mode of the epilayers using atomic force microscopy. Further, the intensity ratio depends on the root mean square surface roughness of the alloy. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Improvement of the optical properties of GaN epilayers on Si(111): Impact of GaAs layer thickness on Si and pre-growth strategyPHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 7 2003Bablu K. Ghosh Abstract This paper reports the effect of the GaN coating layer on the optical properties of GaN epilayers grown on GaAs/Si(111). Almost crack free GaN epilayers are found to be grown when a thin (,25 nm) GaN coating layer is inserted on 0.5 and 2 ,m GaAs layers at 550 °C. Then nitridation of the GaAs layer is done through the coating layer by NH3 flow while the substrate temperature is ramped at 1000 °C for epilayer growth. An attempt has also been made by implementing an additional GaN interlayer at 800 °C while growth is continued for epilayer growth. For this growth strategy, cracks also happened without improvement of the epilayer quality. PL measurements show high excitonic peak energy and high excitonic to yellow band intensity ratio for GaN epilayers grown on the 0.5 ,m GaAs converted layer (CL) using a thin GaN coating layer. Those values are also found to be comparable/ better than for epilayers grown on 2 ,m CL. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] Risk of silicosis in cohorts of Chinese tin and tungsten miners and pottery workers (II): Workplace-specific silica particle surface composition,,AMERICAN JOURNAL OF INDUSTRIAL MEDICINE, Issue 1 2005J. Harrison Abstract Background It is hypothesized that surface occlusion by alumino-silicate affects the toxic activity of silica particles in respirable dust. In conjunction with an epidemiological investigation of silicosis disease risk in Chinese tin and tungsten mine and pottery workplaces, we analyzed respirable silica dusts using a multiple-voltage scanning electron microscopy,energy dispersive X-ray spectroscopy (MVSEM-EDS). Methods Forty-seven samples of respirable sized dust were collected on filters from 13 worksites and were analyzed by MVSEM-EDS using high (20 keV) and low (5 keV) electron beam accelerating voltages. Changes in the silicon-to-aluminum X-ray line intensity ratio between the two voltages are compared particle-by-particle with the 90th percentile value of the same measurements for a ground glass homogeneous control sample. This provides an index that distinguishes a silica particle that is homogeneously aluminum-contaminated from a clay-coated silica particle. Results The average sample percentages of respirable-sized silica particles alumino-silicate occlusion were: 45% for potteries, 18% for tin mines, and 13% for tungsten mines. The difference between the pottery and the metal mine worksites accounted for one third of an overall chi-square statistic for differences in change in measured silicon fraction between the samples. Conclusion The companion epidemiological study found lower silicosis risk per unit cumulative respirable silica dust exposure for pottery workers compared to metal miners. Using these surface analysis results resolves differences in risk when exposure is normalized to cumulative respirable surface-available silica dust. Am. J. Ind. Med. 48:10,15, 2005. Published 2005 Wiley-Liss, Inc. [source] Influence of substituent groups at the 3-position on the mass spectral fragmentation pathways of cephalosporinsRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 14 2010Jin Li The structural fragment ions of nine cephalosporins were studied by electrospray ionization quadrapole trap mass spectrometry (Q-Trap MSn) in positive mode. The influence of substituent groups in the 3-position on fragmentation pathway B, an ,-cleavage between the C7C8 single bond, coupled with a [2,4]-trans-Diels-Alder cleavage simultaneously within the six-membered heterocyclic ring, was also investigated. It was found that when the substituent groups were methyl, chloride, vinyl, or propenyl, fragmentations belonging to pathway B were detected; however, when the substituents were heteroatoms such as O, N, or S, pathway B fragmentation was not detected. This suggested that the [M,R3]+ ion, which was produced by the bond cleavage within the substituent group at the 3-position, had a key influence on fragmentation pathway B. This could be attributed to the strong electronegativity of the heteroatoms (O, N, S) that favors the production of the [M,R3]+ ion. Moreover, having the positive charge of the [M,R3]+ ion localized on the nitrogen atom in the 1-position changed the electron density distribution of the heterocyclic structure, which prohibits a [2,4]-reverse-Diels-Alder fragmentation and as a result fragmentation pathway B could not occur. The influence of the substituent group in the 3-position was determined by the intensity ratio (e/d) of ions produced by fragmentation pathway A, a [2,2]-trans-Diels-Alder cleavage within the quaternary lactam ring, including the breaking of the amide bond and the C6C7 single bond (ion d), and fragmentation pathway B (ion e). The results indicate that the electronegativity of the substituent group was a key influencing factor of pathway B fragmentation intensity, because the intensity ratio (e/d) is higher for a chlorine atom, a vinyl, or a propenyl group than that of a methyl group. This study provided some theoretical basis for the identification of cephalosporin antibiotics and structural analysis of related substances in drugs. Copyright © 2010 John Wiley & Sons, Ltd. [source] Analysis of human tear fluid by Fourier transform infrared spectroscopyBIOPOLYMERS, Issue 1 2005Yasushi Nagase Abstract The purpose of this research is to find some useful spectroscopic factors in human tear fluid contents to monitor diurnal changes of the physicochemical ocular conditions noninvasively. All tear fluid samples were collected with glass microcapillary tubes from both eyes of three donors and analyzed by Fourier transform infrared spectroscopy with attenuated total reflectance (FTIR,ATR). We measured the peak intensities at 2852, 1735, 1546, and 1242 cm,1, and the peak intensity ratios among those peaks in the second derivative spectra. We found significant diurnal and individual variations in those peak intensities for tear fluid obtained from right and left eyes. Among these variations, we observed significant changes in tear samples between right and left eyes. In this case the peak intensity ratio between 1242 (phosphate ester) and 2852 cm,1 (fatty acid methylene) of right eye tear fluid was increased in the afternoon (1600 to 1900 h), while that of left eye tear fluid did not change significantly. In the ratio between 1242 (phosphate ester) and 1546 cm,1 (amide II), the difference was not observed between both eyes. We conclude that the difference in diurnal variations of biochemical constituents between right and left eye tear fluids could be monitored noninvasively and nondestructively by FTIR technique and this method could be useful in the future for tear diagnoses.© 2005 Wiley Periodicals, Inc. Biopolymers 79: 18,27, 2005 This article was originally published online as an accepted preprint. The "Published Online" date corresponds to the preprint version. You can request a copy of the preprint by emailing the Biopolymers editorial office at biopolymers@wiley.com [source] New structural insights from Raman spectroscopy of proteins and their assembliesBIOPOLYMERS, Issue 4-5 2002George J. Thomas Jr.Article first published online: 9 MAY 200 Abstract Protein structure and stability are sensitive to and dependent on the local interactions of amino acid side chains. A diverse and important type of side-chain interaction is the hydrogen bond. Although numerous hydrogen bonds are resolved in protein 3-dimensional structures, those of the cysteine sulfhydryl group (S H) are elusive to high-resolution X-ray and NMR methods. However, the nature and strength of sulfhydryl hydrogen bonds (SH,X) are amenable to investigation by Raman spectroscopy. The power of the Raman method for characterizing SH,X interactions is illustrated by resolving the Raman SH stretching band for each of the eight cysteines per 666-residue subunit in the trimeric tailspike of icosahedral bacteriophage P22. The Raman sulfhydryl signatures of the wild-type tailspike and eight single-site cysteine to serine mutants reveal a heretofore unrecognized diversity of SH hydrogen bonds in a native protein. The use of Raman spectroscopy to identify the non-hydrogen-bonded state of the tyrosine phenoxyl group is also described. This unusual and unexpected state occurs for all tyrosines in the assembled capsids of filamentous viruses Ff and Pf1. The Raman spectral signature of the non-hydrogen-bonded tyrosine phenoxyl, which is characterized by an extraordinary Raman Fermi doublet intensity ratio (I850/I830 = 6.7), extends and refines the existing correlation for hydrogen-bonded tyrosines. Finally, a novel Raman signature for tryptophan in the Pf3 filamentous virus is identified, which is proposed as diagnostic of "cation,, interaction" involving the guanidinium group of Arg 37 as a cation donor and the indolyl ring of Trp 38 as a ,-electron acceptor. These studies demonstrate the power of Raman spectroscopy for investigating the interactions of key side chains in native protein assemblies. © 2002 Wiley Periodicals, Inc. Biopolymers (Biospectroscopy) 67: 214,225, 2002 [source] MOCVD of Platinum Films from (CH3)3CH3CpPt and Pt(acac)2: Nanostructure, Conformality, and Electrical Resistivity,CHEMICAL VAPOR DEPOSITION, Issue 4 2003J. Goswami Abstract A potentially manufacturable liquid-source MOCVD process was applied to deposit platinum (Pt) films (12,140,nm) on thermally oxidized Si substrates. The deposition of Pt films was carried out at a substrate temperature of 350,°C by oxygen-assisted pyrolysis of complex precursors in a low-pressure, hot-wall reactor. The effects of two different metal,organic precursors, a) trimethyl methyl cyclopentadienyl platinum [(CH3)3CH3CpPt], and b) platinum acetylacetonate [Pt(acac)2], on the properties of Pt films were studied. Although the polycrystalline Pt films deposited from Pt(acac)2 exhibited a preferred (111) orientation with a X-ray intensity ratio of I(111)/I(200),=,40, the films deposited from (CH3)3CH3CpPt were highly (111) oriented with I(111)/I(200),=,270. The following properties were typical of Pt films from Pt(acac)2 as compared to Pt films from (CH3)3CH3CpPt: finer grain size (25,nm vs. 50,nm), smaller root mean square (rms) surface roughness (5,nm vs. 15,nm), and better step coverage (95,% vs. 35,%). These experimental findings indicated that growth of Pt films from Pt(acac)2 occurred under the kinetically-limited regime, whereas the deposition of Pt from (CH3)3CH3CpPt was limited by the mass transport rate. Additionally, the temperature (4.2,293,K) dependence of the electrical resistivities (,) of Pt films was measured and the electron mean free paths were estimated. It was observed that ,(T) deviated from Matthiessen's rule. [source] The use of X-ray crystallography to determine absolute configurationCHIRALITY, Issue 5 2008H. D. Flack Abstract Essential background on the determination of absolute configuration by way of single-crystal X-ray diffraction (XRD) is presented. The use and limitations of an internal chiral reference are described. The physical model underlying the Flack parameter is explained. Absolute structure and absolute configuration are defined and their similarities and differences are highlighted. The necessary conditions on the Flack parameter for satisfactory absolute-structure determination are detailed. The symmetry and purity conditions for absolute-configuration determination are discussed. The physical basis of resonant scattering is briefly presented and the insights obtained from a complete derivation of a Bijvoet intensity ratio by way of the mean-square Friedel difference are exposed. The requirements on least-squares refinement are emphasized. The topics of right-handed axes, XRD intensity measurement, software, crystal-structure evaluation, errors in crystal structures, and compatibility of data in their relation to absolute-configuration determination are described. Characterization of the compounds and crystals by the physicochemical measurement of optical rotation, CD spectra, and enantioselective chromatography are presented. Some simple and some complex examples of absolute-configuration determination using combined XRD and CD measurements, using XRD and enantioselective chromatography, and in multiply-twinned crystals clarify the technique. The review concludes with comments on absolute-configuration determination from light-atom structures. Chirality, 2008. © 2007 Wiley-Liss, Inc. [source] Fluctuating Helium Emission in Optically Thick Divertor PlasmasCONTRIBUTIONS TO PLASMA PHYSICS, Issue 1-3 2008F. B. Rosmej Abstract Simulations of the helium radiative properties carried out with the recently developed multi-level meta-stable resolved collisional-radiative code SOPHIA discovered new unique emission lines to analyze optically thick divertor plasmas relevant for ITER. The comparison of their time dependent line emission obtained from the NAGDIS-II plasma simulator experiments with time dependent temperature probe measurements shows a strong correlation. This indicates that line intensity fluctuations can be transformed to the important quantities of density and temperature fluctuations. A transformation method based on integral line intensity ratios which can be recorded with high time resolution is discussed. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source] An Approach to the Synthesis of Silicon Carbide Nanowires by Simple Thermal Evaporation of Ferrocene onto Silicon WafersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 25 2007Jun-Jie Niu Abstract Scales of silicon carbide nanowires (SiC-NWs) with high quality were synthesized by direct thermal evaporation of ferrocene onto silicon wafers at high temperature. Ferrocene decomposed into iron and carbon, which was subsequently treated with silicon to form SiC-NWs at high temperature. The SiC-NWs possess small diameters of , 20 nm and lengths of several ,ms. Furthermore, the samples show a uniform morphology, crystalline structure, and a very thin oxide layer. The main crystal direction of [111] was confirmed by high-resolution field-emission-transmission electron microscopy (HR-FETEM). The Raman scattering spectra showed two peaks at , 796 (TO) and , 980 cm,1 (LO) with varying intensity ratios at different positions. The band line fluctuation was contributed to the Raman selection rules. With reference to the experimental results, we suggested a tentative growth model according to the vapor,liquid,solid (VLS) mechanism. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Outcomes of the International Union of Crystallography Commission on Powder Diffraction Round Robin on Quantitative Phase Analysis: samples 1a to 1hJOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 4 2001Ian C. Madsen The International Union of Crystallography (IUCr) Commission on Powder Diffraction (CPD) has sponsored a round robin on the determination of quantitative phase abundance from diffraction data. Specifically, the aims of the round robin were (i) to document the methods and strategies commonly employed in quantitative phase analysis (QPA), especially those involving powder diffraction, (ii) to assess levels of accuracy, precision and lower limits of detection, (iii) to identify specific problem areas and develop practical solutions, (iv) to formulate recommended procedures for QPA using diffraction data, and (v) to create a standard set of samples for future reference. Some of the analytical issues which have been addressed include (a) the type of analysis (integrated intensities or full-profile, Rietveld or full-profile, database of observed patterns) and (b) the type of instrument used, including geometry and radiation (X-ray, neutron or synchrotron). While the samples used in the round robin covered a wide range of analytical complexity, this paper reports the results for only the sample 1 mixtures. Sample 1 is a simple three-phase system prepared with eight different compositions covering a wide range of abundance for each phase. The component phases were chosen to minimize sample-related problems, such as the degree of crystallinity, preferred orientation and microabsorption. However, these were still issues that needed to be addressed by the analysts. The results returned indicate a great deal of variation in the ability of the participating laboratories to perform QPA of this simple three-component system. These differences result from such problems as (i) use of unsuitable reference intensity ratios, (ii) errors in whole-pattern refinement software operation and in interpretation of results, (iii) operator errors in the use of the Rietveld method, often arising from a lack of crystallographic understanding, and (iv) application of excessive microabsorption correction. Another major area for concern is the calculation of errors in phase abundance determination, with wide variations in reported values between participants. Few details of methodology used to derive these errors were supplied and many participants provided no measure of error at all. [source] A new molecular mechanics force field for the oxidized form of blue copper proteinsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 7 2002Peter Comba Abstract A molecular mechanics force field for blue copper proteins has been developed, based on a rigid potential energy surface scan of the CuII/His/His/Cys/Met chromophore, using DFT (B3LYP) calculations and the AMBER force field for the protein backbone. The strain,energy-minimized structures of the model chromophore alone are in excellent agreement with the DFT-optimized structure, and those of the entire set of cupredoxins (five structures are considered) are, within the experimental error limits, in good agreement with the single crystal structural data. However, the structural variation in the computed structures is much smaller than those in the experimental structures. It is shown that, due to the large error limits in the experimental data, a validation of the force field with experimental structural data is impossible because, within the error limits, all experimental structures considered are virtually identical. A validation on the basis of spectroscopic data and their correlation with experimental and computed structural data is proposed, and, as a first example, the correlation of intensity ratios of the charge transfer transitions with a specific distortion mode is presented. The quality of the correlation, using the computed structures, is higher than that with the X-ray structures, and this indicates that the computed structures are meaningful. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 697,705, 2002 [source] Proton spectroscopic metabolite signal relaxation times in preterm infants: A prerequisite for quantitative spectroscopy in infant brainJOURNAL OF MAGNETIC RESONANCE IMAGING, Issue 6 2003Harald Kugel PhD Abstract Purpose To determine relaxation times of metabolite signals in proton magnetic resonance (MR) spectra of immature brain, which allow a correction of relaxation that is necessary for a quantitative evaluation of spectra acquired with long TE. Proton MR spectra acquired with long TE allow a better definition of metabolites as N-acetyl aspartate (NAA) and lactate especially in children. Materials and Methods Relaxation times were determined in the basal ganglia of 84 prematurely born infants at a postconceptional age of 37.8 ± 2.2 (mean ± SD) weeks. Metabolite resonances were investigated using the double-spin-echo volume selection method (PRESS) at 1.5 T. T1 was determined from intensity ratios of signals obtained with TRs of 1884 and 6000 msec, measured at 3 TEs (25 msec, 136 msec, 272 msec). T2 was determined from signal intensity ratios obtained with TEs of 136 msec and 272 msec, measured at 2 TR. Taking only long TEs reduced baseline distortions by macromolecules and lipids. For myo-inositol (MI), an apparent T2 for short TE was determined from the ratio of signals obtained with TE = 25 msec and 136 msec. Intensities were determined by fitting a Lorentzian to the resonance, and by integration. Results Relaxation times were as follows: trimethylamine-containing compounds (Cho): T1 = 1217 msec/T2 = 273 msec; total creatine (Cr) at 3.9 ppm: 1010 msec/111 msec; Cr at 3.0 ppm: 1388 msec/224 msec; NAA: 1171 msec/499 msec; Lac: 1820 msec/1022 msec; MI: 1336 msec/173 msec; apparent T2 at short TE: 68 msec. Conclusion T1 and T2 in the basal ganglia of premature infants do not differ much from previously published data from basal ganglia of older children and adults. T2 of Cho was lower than previous values. T2 of Cr at 3.9 ppm and Lac have been measured under different conditions before, and present values differ from these data. J. Magn. Reson. Imaging 2003;17:634,640. © 2003 Wiley-Liss, Inc. [source] Oligosaccharide sequences in Quillaja saponins by electrospray ionization ion trap multiple-stage mass spectrometryJOURNAL OF MASS SPECTROMETRY (INCORP BIOLOGICAL MASS SPECTROMETRY), Issue 6 2004Susanna Broberg Abstract Ten different samples with 13 previously identified saponin structures from Quillaja saponaria Molina were investigated by electrospray ionization ion trap multiple-stage mass spectrometry (ESI-ITMSn) in positive and negative ion modes. Both positive and negative ion mode MS1,MS4 spectra were analyzed, showing that structural information on the two oligosaccharide parts in the saponin can be obtained from positive ion mode spectra whereas negative ion mode spectra mainly gave information on one of the oligosaccharide parts. Analysis of MS1,MS4 spectra identified useful key fragment ions important for the structural elucidation of Quillaja saponins. A flowchart involving a stepwise procedure based on key fragments from MS1,MS3 spectra was constructed for the identification of structural elements in the saponin. Peak intensity ratios in MS3 spectra were found to be correlated with structural features of the investigated saponins and are therefore of value for the identification of terminal monosaccharide residues. Copyright © 2004 John Wiley & Sons, Ltd. [source] | ||||||||||||||||||||||