Accurate Chemical Composition Research Articles

Galaxy simulations in the Gaia era

AbstractWe live in an age where an enormous amount of astrometric, photometric, asteroseismic, and spectroscopic data of Milky Way stars are being acquired, many orders of magnitude larger than about a decade ago. Thanks to the Gaia astrometric mission and followup ground-based spectroscopic surveys in the next 5-10 years about 10-20 Million stars will have accurate 6D kinematics and chemical composition measurements. KEPLER-2, PLATO, and TESS will provide asteroseismic ages for a good fraction of those. In this article we outline some outstanding problems concerning the formation and evolution of the Milky Way and argue that, due to the complexity of physical processes involved in the formation of disk galaxies, numerical simulations in the cosmological context are needed for the interpretation of Milky Way observations. We also discuss in some detail the formation of the Milky Way thick disk, chemodynamical models, and the effects of radial migration.

Beryllium-distribution in metallic glass matrix composite containing beryllium

The morphologies, sizes, compositions and volume fractions of dendritic phases in in situ Ti-based metallic glass matrix composites (MGMCs) containing beryllium (Be) with the nominal composition of Ti47Zr19Cu5V12Be17 (mole fraction, %) were investigated using XRD, SEM, EBSD, TEM, EDS and three-dimensional reconstruction method. Moreover, visualized at the nanoscale, Be distribution is confirmed to be only present in the matrix using scanning transmission electron microscopy–electron energy loss spectroscopy (STEM–EELS). Based on these findings, it has been obtained that the accurate chemical compositions are Ti28.3Zr19.7Cu8V6.4Be37.6 (mole fraction, %) for glass matrix and Ti62.4Zr18.4Cu2.6V16.6 (mole fraction, %) for the dendritic phases, and the volume fractions are 38.5% and 61.5%, respectively. It is believed that the results are of particular importance for the designing of Be-containing MGMCs.

Sol–gel preparation of Li-rich layered cathode material for lithium ion battery with polymer polyacrylic acid + citric acid chelators

The sol–gel method was improved to synthesize the layered Li-rich cathode material Li1.2Ni0.13Co0.13Mn0.54O2 by employing the mixture of polymer polyacrylic acid (PAA) and citric acid as the mixed chelator. The crystal structure, particle morphology and electrochemical performance of the prepared layered Li-rich cathode material are extensively studied by X-ray diffraction spectrometry, scanning electron microscopy, charge–discharge test, cyclic voltammetry and electrochemical impedance spectroscopy techniques. The results show that the Li-rich cathode materials prepared with the new method present explicit layer structure, low level of Li+/Ni2+ disordering, large specific surface area and accurate chemical composition. When measured with electrochemical test system, the prepared material exhibits a high capacity of 274.8 mAh g−1. The excellent performances of the prepared material could be ascribed to the fact that the novel approach combines the advantages of the two chelating agents of PAA and citric acid.

Fourier plane colorimetric sensing using broadband imaging of surface plasmons and application to biosensing

We demonstrate an optical technique for refractive index and thickness sensing of sub-wavelength-thick dielectric analytes. The technique utilizes the broadband, multimode, directional leakage radiation arising from the excitation of hybrid mode surface plasmons (SP) on low aspect ratio periodic plasmonic substrates with period ≈λ. The approach requires relaxed fabrication tolerances compared to extra ordinary transmission-based sensing techniques, wherein minor shifts in the fabricated dimensions result in a very large change from the designed resonant wavelength. We show that refractive index perturbations due to about 10-nm-thick dielectric can be captured optically by the usage of carefully designed plasmonic substrates, a halogen lamp source, free-space optical components, polarizers, and a low-end, consumer-grade charge coupled device camera. The plasmonic substrates were designed for converting the signature of hybrid mode SP excitation into a transmission peak by utilizing a thin homogeneous metal layer sandwiched between the periodic plasmonic structures and the substrate. The resonance is highly sensitive to the refractive index and thickness of the analyte superstrate. The excitation of hybrid mode SP results in a polarization rotation of 90° of the leaked radiation at resonant wavelength. In order to eliminate the problem of image registration (i.e., placing the same feature in the same pixel of the image, for comparison before and after a change in refractive index) for sensing, we perform the color analysis in the Fourier plane. The change in color of the bright emitted spot with highest momentum, corresponding to the leakage of fundamental SP mode, was used to measure the changes in refractive index, whereas the number and color of spots of lower momenta, corresponding to higher-order Fabry Perot modes, was used to measure the variation in thickness. We further show that the Fourier plane analysis can also be used to sense the index of thicker dielectrics, where real plane image analysis may fail to sense index perturbations, simply due to superposition of different modes in the real plane images of such substrates. Control experiments and analysis revealed a refractive index resolution of 10–5 RIU. The results were correlated with simulations to establish the physical origin of the change in the fundamental mode and higher-order modes due to the refractive index and thickness of analyte. As a demonstration of an application and to test the limits of sensing, the substrates were used to image the surface functionalization using 2-nm-thick 11-mercaptoundecanoic acid and immobilization of 7-nm-thick mouse anti-human IgG antibody. In biological systems, where a priori knowledge about a process step is available, where accurate chemical composition testing is not necessary or possible, the presented method could be used to study the surface changes using a label-free sensing mechanism.

On the chemistry of the carbides in a molybdenum base Mo-Hf-C alloy produced by powder metallurgy

The main focus of the present work is on the investigation of carbides present after sintering in the molybdenum base alloy MHC (Mo-Hf-C) which is produced via a powder route. The alloy has a nominal content of 0.65 at.% hafnium and 0.65 at.% carbon and can be hardened by precipitation of nm-sized hafnium carbides. The assessment of the molybdenum-rich corner of the ternary (quaternary) Mo-Hf-C(-O) phase diagram is required to exploit the full precipitation potential of the alloy. Thus, it is important to gain information about the accurate chemical composition of all individual phases. Therefore, the chemistry and structure of hafnium and molybdenum carbides were analyzed by means of X-ray diffraction, energy dispersive spectroscopy and atom probe tomography. The analysis of hexagonal molybdenum carbides revealed a significant amount of hafnium (∼1 at.%) in addition to molybdenum and carbon. The face centered cubic hafnium carbide phase on the other hand contains high amounts of oxygen (∼4.4 at.%) and molybdenum (∼2 at.%) in addition to small amounts of zirconium and nitrogen. In order to understand the high oxygen content in the hafnium carbide, energies of formation and lattice parameters for hafnium carbides with different contents of oxygen and molybdenum were calculated theoretically using an ab initio approach. Subsequently, the theoretically calculated lattice parameter of hafnium carbide was compared to the experimentally determined one of the carbide present in the MHC alloy. The experimental and modeling results are in good agreement. Finally, the formation mechanism of hafnium carbide during the sintering process is discussed.

Revealing the morphology and chemical distribution of nodes in wheat straw

Morphology and chemical distribution of wheat straw stem, including nodes and internodes, were profiled and thoroughly analysed through a combination of qualitative and quantitative analytical techniques. It was found that the morphology across node area has great variety when the longitudinal profile was investigated in the upwards direction to the grain head; the node core morphology revealed a very dense zone with elliptical shaped rings organised in order to provide the mechanical strength to the overall stem. ATR-FTIR results for the chemical functional groups of outer and inner surfaces of node and internode also showed differences in terms of concentration of functional groups present in each section. It was revealed that the outer surface of wheat straw stem has a higher concentration of aliphatic fraction of waxes compared to the inner surface, with the highest being in the node area. EDX-SEM results were averaged for node and internode and also for inner and outer surfaces for quantitative comparison. It was found that the outer surface of wheat straw had considerable higher Si contents than the inner surface. Also higher content of C in the node outer surface is an indication of high quantity of wax which is in agreement with ATR-FTIR results. The crystallinity of node and internode was investigated using XRD; it was found that node is more amorphous than internode with the crystallinity index of 34.73% compared to 45.00% of internode. The profile of wheat straw morphology in the nodes has never been reported; the results of the quantitative and qualitative structural analysis through in-depth microstructure interpretation, and detailed and accurate chemical composition improved the understanding of straw biomass.

Rapid analysis of composition and reactivity in cellulosic biomass feedstocks with near-infrared spectroscopy.

BackgroundObtaining accurate chemical composition and reactivity (measures of carbohydrate release and yield) information for biomass feedstocks in a timely manner is necessary for the commercialization of biofuels. Our objective was to use near-infrared (NIR) spectroscopy and partial least squares (PLS) multivariate analysis to develop calibration models to predict the feedstock composition and the release and yield of soluble carbohydrates generated by a bench-scale dilute acid pretreatment and enzymatic hydrolysis assay. Major feedstocks included in the calibration models are corn stover, sorghum, switchgrass, perennial cool season grasses, rice straw, and miscanthus.ResultsWe present individual model statistics to demonstrate model performance and validation samples to more accurately measure predictive quality of the models. The PLS-2 model for composition predicts glucan, xylan, lignin, and ash (wt%) with uncertainties similar to primary measurement methods. A PLS-2 model was developed to predict glucose and xylose release following pretreatment and enzymatic hydrolysis. An additional PLS-2 model was developed to predict glucan and xylan yield. PLS-1 models were developed to predict the sum of glucose/glucan and xylose/xylan for release and yield (grams per gram). The release and yield models have higher uncertainties than the primary methods used to develop the models.ConclusionIt is possible to build effective multispecies feedstock models for composition, as well as carbohydrate release and yield. The model for composition is useful for predicting glucan, xylan, lignin, and ash with good uncertainties. The release and yield models have higher uncertainties; however, these models are useful for rapidly screening sample populations to identify unusual samples.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0222-2) contains supplementary material, which is available to authorized users.

Segregation during Metal Sampling

In order to obtain accurate chemical compositions in as-cast billets and ingots the sampling methods for the analysis have to give reproducible results with high precision. OES analysis made on samples at certain milling depths does not always show the desired nominal composition, and especially the segregation profiles within the samples can show significant variations. The present work examine the influence of main sampling parameters, such as the volume of the melt, the melt temperature, the mould design and the method of filling the mould, on the segregation. The results point out the importance of the convection in the mould during solidification, and thus the technique of pouring the melt into the sampling mould.

Direct Quantification of Molar Masses of Copolymers by Online Liquid Chromatography under Critical Conditions–Nuclear Magnetic Resonance and Size Exclusion Chromatography–Nuclear Magnetic Resonance

Online LCCC-NMR and SEC-NMR are compared regarding the determination of molar masses of block copolymers. Two different direct referencing methods are particularly demonstrated in LCCC-NMR for a detailed characterization of diblock copolymers and their co-monomers. First, an intramolecular reference group was used for the direct determination of block lengths and molar masses. For the first time, it was shown that LCCC-NMR can be used for an accurate determination of Mw and Mn of copolymers. These data were in perfect agreement with SEC-NMR measurements using the same intramolecular referencing method. In contrast, the determination of molar masses with common relative methods based on calibrations with homopolymers delivered inaccurate results for all investigated diblock copolymers due to different hydrodynamic volumes of the diblock copolymer compared to their homopolymers. The intramolecular referencing method provided detailed insights in the co-monomer behavior during the chromatographic separation of LCCC. Especially, accurate chain lengths and chemical compositions of the "invisible" and "visible" blocks were quantified during the elution under critical conditions and provided new aspects to the concept of critical conditions. Second, an external reference NMR signal was used to directly determine concentrations and molar masses of the block copolymers from the chromatographic elution profile. Consequently, the intensity axes of the resulting chromatograms were converted to molar amounts and masses, allowing for determination of the amount of polymer chains with respect to elution volume, the evaluation of the limiting magnitude of concentration for LCCC-NMR, and determination of the molar masses of copolymers.

Chemical composition dispersion in bi-metallic nanoparticles: semi-automated analysis using HAADF-STEM

We present a method using high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) to determine the chemical composition of bi-metallic nanoparticles. This method, which can be applied in a semi-automated way, allows large scale analysis with a statistical number of particles (several hundreds) in a short time. Once a calibration curve has been obtained, e.g., using energy-dispersive X-ray spectroscopy (EDX) measurements on a few particles, the HAADF integrated intensity of each particle can indeed be directly related to its chemical composition. After a theoretical description, this approach is applied to the case of iron–palladium nanoparticles (expected to be nearly stoichiometric) with a mean size of 8.3 nm. It will be shown that an accurate chemical composition histogram is obtained, i.e., the Fe content has been determined to be 49.0 at.% with a dispersion of 10.4 %. HAADF-STEM analysis represents a powerful alternative to fastidious single particle EDX measurements, for the compositional dispersion in alloy nanoparticles.

Distances to galaxies from the brightest stars in the Universe

Blue Supergiants (BSGs) are the brightest stars in the universe at visual light with absolute magnitudes up to M V =−10 mag. They are ideal stellar objects for the determination of extragalactic distances, in particular, because the perennial uncertainties troubling most of the other stellar distance indicators, interstellar extinction and metallicity, do not affect them. The quantitative spectral analysis of low resolution spectra of individual BSGs provides accurate stellar parameters and chemical composition, which are then used to determine accurate reddening and extinction from photometry for each individual object. Accurate distances can be determined from stellar gravities and effective temperatures using the “Flux Weighted Gravity–Luminosity Relationship (FGLR)”.Most recent results of the quantitative spectral analysis of BSGs in galaxies within and beyond the Local Group based on medium and low resolution spectra obtained with the ESO VLT and the Keck telescopes on Mauna Kea are presented and distances obtained with the FGLR-method are discussed together with the effects of patchy extinction and abundance gradients in galaxies. BSG metallicities and metallicity gradients are compared with results from strong-line H ii region studies and the consequences for the empirical calibration of the metallicity dependence of the Cepheid period–luminosity relationship are pointed out. The perspectives of future work are discussed, the use of the giant ground-based telescopes of the next generation such as the TMT on Mauna Kea and the E-ELT and the tremendous value of the GAIA mission to allow for the ultimate calibration of the FGLR using galactic BSGs.

Atom Probe Tomography of Zinc Oxide Nanowires

Wide-bandgap zinc oxide (ZnO) semiconductors and nanowires have become important materials for electronic and photonic device applications. In this work, we report the growth of well-aligned single-crystal ZnO nanowire arrays on sapphire substrates by chemical vapor deposition and the development of atom probe tomography, an emerging nanoscale characterization method capable of providing deeper insight into the three-dimensional distribution of atoms and impurities within its structure. Using a metal-catalyst-free approach, the influence of the growth parameters on the orientation and density of the nanowires were studied. The resulting ZnO nanowires were determined to be single crystalline, with diameter on the order of 50 nm to 150 nm and length that could be controlled between 0.5 μm to 20 μm. Their density was on the order of high 108 cm−2 to low 109 cm−2. In addition to routine characterizations using scanning and transmission electron microscopy, x-ray diffraction, photoluminescence, and Raman spectroscopy, we developed the atom probe tomography technique for ZnO nanowires, comparing the voltage pulse and laser pulse modes. In-depth analysis of the data was carried out to determine the accurate chemical composition of the nanowires and reveal the incorporation of nitrogen impurities. The current–voltage characteristics of individual nanowires were measured to determine their electrical properties.

Sizer for Neutral Weakly Bound Ultrafine Aerosol Particles Based on Sodium Doping and Mass Spectrometric Detection

The determination of accurate size distributions and chemical composition of volatile and semivolatile ultrafine aerosol particles with sizes in the subnanometer to several tens of nanometers range is a problem that plagues many studies in aerosol research. We propose to employ sodium-doping of the aerosol particles with subsequent photoionization in the ultraviolet combined with mass spectrometric detection to solve this problem. Comparison with “soft” EUV ionization demonstrates that this technique can determine size distributions and to some extent the chemical composition of weakly bound ultrafine aerosol particles largely destruction-free. We also discuss how sodium-doping can be turned into a viable quantitative technique for the sizing of ultrafine aerosol particles.

Effects of laser pulsing on analysis of steels by atom probe tomography

When performing atom probe tomography analysis, laser pulsing was found very helpful for some types of steels, which are prone to premature sample failure under voltage pulsing. Rather accurate chemical compositions for both matrix and precipitates were obtained by voltage- and laser-pulsed mode. Some special issues on the effects of laser are discussed. A simple correction based on the (13)C(n+) and (10)B(n+) peak was used to quantify C in the carbide (M(23)C(6), M = Fe, Cr, Mo) and B in the boride (M(3)B(2), M = Mo, Fe, Cr, V). The mass resolution in laser mode is sufficient to resolve (56)Fe(2+) and (14)N(2)(1+) at 28Da. Small peak shifts were found in the spectrum due to reflectron aberrations.

THE MICROSTRUCTURE, CHEMICAL CHARACTERISTIC AND CRYSTALLIZATION BEHAVIOR OF THE POLYMER DERIVED Si-B-C-N AMORPHOUS CERAMIC

Amorphous materials of the Si -( B )- C - N system have recently attracted considerable interest because of its hardness, low density, durability at extremely high temperature and easy to be prepared from precursor compounds by polymer route. The materials show a great potential to be used in the field of the Thermal Protective System (TPS) for the aircrafts, while the microstructure and chemical configuration are still not clearly revealed due to its complicated covalent character for this multi-component amorphous material. This paper focused on the characterization of polymer derived Si -( B )- C - N amorphous ceramic, various method were employed in order to obtain accurate information about the microstructure, chemical composition, bonding mode of components, such as TEM, EPMA, NMR and FT-IR. SiC crystalline was found existing in the amorphous glass, which indicates the preparation process was achieved accompanied by crystallization of SiC from polymer precursor. The microstructure of the researched material was analyzed and relative accurate chemical composition was obtained on the basis of characterization result, furthermore the covalent character of the amorphous material was deduced according to the characterization results obtained.

COMMISSION 29: STELLAR SPECTRA

The members of IAU Commission 29 Stellar Spectra are actively engaged in the quantitative analysis of spectra of various types of stars. With large and medium size telescopes equipped with high resolution spectrographs LTE and Non-LTE analysis of spectra of all types stars are being carried out. Spectra of stars in our Galaxy, in globular and open clusters, stars in LMC and SMC and in nearby galaxies are being studied. Accurate chemical composition analysis of various types of stars has been carried out during the past three years. Now the analysis of stellar spectra covers the wavelength range from X-ray region to IR and sub-millimeter range. Recently stellar spectra are being analysed using time-dependent, 3D, hydrodynamical model atmospheres to derive accurate stellar abundances.

Optimum phantum material for dosimetric evaluation of low energy brachytherapy sources

Purpose: The updated TG-43U1 recommends determination of the consensus of low energy brachytherapy source parameters using experimental and Monte Carlo Simulated data. As per this recommendation, the measured parameters in water equivalent materials are converted into water data for clinical application by using appropriate conversion factors. Various investigators quoted different chemical composition of phantom materials utilized in Monte Carlo and experimental determinations. Impact of different phantom materials and accurate chemical composition on dose rate constant and radial dose function needs to be evaluated for low energy brachytherapy sources.

Determination of VOC source signature of vehicle exhaust in a traffic tunnel

This study describes the methodology used to obtain the volatile organic compound (VOC) source signature of vehicle exhaust. To accomplish this, C 2–C 9 VOCs were measured in a traffic tunnel located in Seoul, South Korea. The effect of VOC concentrations from the outside ambient air was considered in the determination of the source signature. To examine the effects of ambient air on VOC concentrations inside the tunnel, the ratio of propane to the total VOC concentrations was compared between the entrance and middle sites in the tunnel. Propane was used as a standard not only because of its insignificant contribution to vehicle exhaust gas, but also the fact that propane is the most abundant VOC in the atmosphere of Seoul. The ratio of propane to the total VOC concentrations was higher at the entrance site than at the middle location by, on average, 60%. This suggests that ambient air affects the inside tunnel air to a greater extent at the entrance site as compared to the middle site. The contribution of ambient air to the air inside the tunnel at the entrance location varied from 30% to 67%, with an average of 55%. This is 1.5 times higher than the value measured at the middle location, which ranged from 20% to 48%, with an average of 36%. This shows that ambient air substantially affects the inside air of the tunnel. Excluding the effects of ambient air on the air inside the tunnel can provide an improved chemical composition for vehicle exhaust using tunnel measurements. We believe that the concentration difference between the two sites within the tunnel provides a more accurate chemical composition of vehicle exhaust as compared to that obtained from a measurement taken at only one point inside the tunnel.

New Chromatographic and Hyphenated Techniques for Hydrophilic Copolymers

AbstractMost synthetic polymers are distributed in more than one parameter of molecular heterogeneity. For hydrophobic copolymers there are different chromatographic techniques available to analyse these distributions. As a result of the increasing interest in hydrophilic polymers and copolymers new chromatographic techniques are developed for the characterization of these polymers as well. However, very frequently these polymers contain highly polar or charged functional groups making them soluble only in aqueous mobile phases. There are several problems related to the use of aqueous mobile phases in polymer chromatography. Even the SEC analysis of such copolymers is not straightforward. As for HPLC in aqueous mobile phases, there are only a few applications in the literature so far. In addition to the fact that only a very limited number of stationary phases is available for aqueous HPLC of polymers, the interactions of polyelectrolytes in such chromatographic systems are not well understood.The present paper addresses the problems related to the application of SEC and HPLC in aqueous mobile phases. For graft copolymers with a polyethylene oxide backbone, e.g. PEG‐g‐polymethacrylic acid and PEG‐g‐polyvinyl alcohol, it will be shown that methods can be developed that give accurate molar mass and chemical composition information. Two‐dimensional chromatography where aqueous HPLC and SEC are coupled on‐line will be shown to be the most powerful analysis tool for the analysis of such copolymers. The hyphenation of the chromatographic separation techniques with spectroscopic detection techniques provides further insight into the molecular complexity of these copolymers.

Equations of state of Na?K?Al host phases and implications for MORB density in the lower mantle

We report equations of state (EoS) of two important silicate phases known to store Na, K, and Al, at pressures and temperatures prevailing in the Earth’s lower mantle. Using laser heated diamond anvil cell, we produced the Ca-ferrite type (CF) and the new aluminum rich (NAL) phases using different synthetic and natural starting materials, at pressures ranging from 23 to 65 GPa. Unit cell volumes were investigated by means of angle dispersive X-ray diffraction at the ID30 beamline of the ESRF synchrotron ring (Grenoble, France). CF-phases were synthesized in NaAlSiO 4 –MgAl 2 O 4 and NaAlSiO 4 –(Mg,Fe) 2 SiO 4 systems, and for a natural mid-ocean ridge basalt (MORB). The insertion of MgAl 2 O 4 in the NaAlSiO 4 -based lattice has reduced effects on the CF-phase EoS, whereas that of (Mg,Fe) 2 SiO 4 is mainly to increase the room pressure volume. CF-phases most relevant to the Earth’s mantle show compression behavior comparable to the pure NaAlSiO 4 -CF-phase, with bulk moduli values close to K 0 =190 GPa and K 0 ′=4. We also synthesized (NAL) phases in NaAlSiO 4 –MgAl 2 O 4 system, and using CaNa- and K-rich silicate glasses as starting materials. All NAL-compounds investigated show similar compression behavior, except for one anomalously NaAlSiO 4 -rich composition. For NAL-phase with the most “natural” conditions relevant composition, we refine bulk moduli of K 0 =182 GPa and K 0 ′=6. We then model the density profiles expected for the CF and NAL-phases, using our newly determined EoS and the most accurate chemical compositions reported in the literature. These two phases appear significantly less dense than a pyrolitic type material at all lower mantle pressures and 300 K. However, the density profiles calculated for mineral assemblages corresponding to typical MORB compositions point out to denser MORBs compared to the pyrolite. This is due to the high Fe-content in MORB, yielding a densest Fe-rich perovskite that counterbalances the lower densities of the CF and NAL-phases. The density gap is calculated between 0.4 and 4.0% depending on the starting MORB composition and pressure.