Spectra Of Mg Research Articles

The Low-redshift Lyman Continuum Survey: Optically Thin and Thick Mg ii Lines as Probes of Lyman Continuum Escape

The Mg ii λλ2796, 2803 doublet has been suggested as a useful indirect indicator for the escape of Lyα and Lyman continuum (LyC) photons in local star-forming galaxies. However, studies to date have focused on small samples of galaxies with strong Mg ii or strong LyC emission. Here, we present the first study of Mg ii to probe a large dynamic range of galaxy properties, using newly obtained high-signal-to-noise, moderate-resolution spectra of Mg ii, for a sample of 34 galaxies selected from the Low-redshift Lyman Continuum Survey. We show that the galaxies in our sample have Mg ii profiles ranging from strong emission to P-Cygni profiles to pure absorption. We find that there is a significant trend (with a possibility of spurious correlations of ∼2%) that galaxies that are detected as strong LyC emitters (LCEs) show larger equivalent widths of Mg ii emission, while non-LCEs tend to show evidence of more scattering and absorption features in Mg ii. We then find that Mg ii strongly correlates with Lyα in both equivalent width and escape fraction, regardless of whether emission or absorption dominates the Mg ii profiles. Furthermore, we show that, for galaxies that are categorized as Mg ii emitters, one can use the information of Mg ii, metallicity, and dust to estimate the escape fraction of LyC within a factor of ∼3. These findings confirm that Mg ii lines can be used as a tool for selecting galaxies as LCEs and thus serve as an indirect indicator for the escape of Lyα and LyC.

Structure of single KL0–, double KL1–, and triple KL2 − ionization in Mg, Al, and Si targets induced by photons, and their absorption spectra

We investigated experimentally and theoretically x-ray properties of Mg, Al and Si to assess for new reliable x-ray useful quantities. We measured the KL0– diagram, and KL1– and KL2– satellite lines in Mg, Al, and Si, ionized by photon excitation, using a high-resolution anti-parallel double-crystal x-ray spectrometer. Their energy values, full width at half maxima (FWHM), and relative intensities are obtained by the multiple fitting methods and compared with those reported by other excitation processes. It was found that the relative intensity of Mg and Si KL1 and KL2 satellite lines to the KL0 diagram lines depend on the method used to produce the K hole. The evidence of a new transition between Kα3 and Kα4 in Mg, Al, and S KL1 satellite lines is suggested. These x-ray diagram and satellite lines were investigated theoretically and we found that Mg Kα1,2 diagram lines with hidden satellites are especially in very good agreement with the corresponding experimental ones. Moreover, we also determined the mass attenuation coefficients in a wide energy range covering the K-absorption edge, including a detailed evaluation of the associated uncertainties. From the absorption spectra of Mg and Al, the cross sections of the multi-electron transition processes were estimated and match the theoretical values.

Revealing physical interpretation of time constants in electrochemical impedance spectra of Mg via Tribo-EIS measurements

Tribo-electrochemical impedance spectroscopy (Tribo-EIS) measurements of pure Mg were performed to identify the origin of two time constants during standard EIS measurements in NaCl solution. The influence of abrasion introduced by tribometer on EIS spectra was investigated under different rotation speeds. Further quantitative analyses of abrasion on Mg with different surface areas were performed. The resistances associated to the two time constants on the abraded surface were deduced from the fitted results, verifying that the high frequency time constant originates from the barrier properties of the MgO-based surface film and the middle frequency time constant stems from the charge transfer process.

Transport properties and solvation state of magnesium salts dissolved in propylene carbonate and [formula omitted]-butyrolactone: A comparison with monovalent cation counterparts

We experimentally measured the conductivity and viscosity of non-aqueous solutions of magnesium electrolytes; Mg(TFSA)2 (TFSA = bis(trifluoromethanesulfonyl) amide) and Mg(ClO4)2 dissolved in propylene carbonate (PC) and γ-butyrolactone (GBL) up to the concentration of m/molkg-1=1.4-1.7 in the temperature range 288⩽T/K⩽328. With the previously obtained results, the matrix of experimental data, comprising three cations (Mg2+, Li+, Na+), two anions (ClO4-, TFSA−) and two solvents (PC, GBL), enables a systematic comparison of their transport properties. Raman spectra of Mg(TFSA)2, LiTFSA, and NaTFSA dissolved in GBL yield the solvation state of each cation, suggesting that the GBL molecules solvating Mg2+ are classified into tightly and less tightly bound states. The lattice gas Monte-Carlo simulation of conductivity quantitatively explains well the reason why the divalent cation systems are less conductive than the monovalent ones; namely, the negative effect of the strong inter-ionic interaction of Mg2+ overwhelms the positive effect of the high valence, because the former effect exponentially attenuates the conductivity while the latter is merely proportional to the harmonic mean valence of the salt. The simulation revealed that, in a hypothetical scenario wherein the long-range interactions are absent, the conductivity is dominantly determined by the solvent. Consequently, the solvent-specific upper limit of the conductivity is predicted for PC and GBL.

An Amalgam of Mg-Doped TiO2 Nanoparticles Prepared by Sol–Gel Method for Effective Antimicrobial and Photocatalytic Activity

In this study, undoped and Magnesium doped TiO2 nanoparticles (Mg-TiO2 NPs) are successfully synthesized via a simple sol–gel method cost-effectively. The prepared Mg- TiO2 NPs is characterized by UV–Vis, FTIR, PL, XRD, FESEM, TEM, and EDAX. UV–Visible Spectroscopy showed that an increase in the optical bandgap concerning the concentration of dopant Mg increases. The bandgap values were found to be 3.57–3.54 eV. FTIR spectra shows that the presence of the characteristic stretching and bending vibrational band of Ti–O bonding at 468 cm−1 and shifts in vibrational bands were observed for Mg-TiO2 NPs. PL spectra of Mg- TiO2 NPs at different concentrations exhibit a strong UV emission band. X-ray diffraction confirmed the formation of the tetragonal anatase phase. The average crystallite size of synthesized samples was found to be 22–19 nm. The average crystallite size of Mg- TiO2 NPs decreases with increasing the concentration of dopant Mg. The FESEM and TEM analysis confirmed that the spherical morphology for both TiO2 and Mg-TiO2 NPs. SAED pattern confirms the crystalline nature of prepared samples. EDAX spectra confirm the presence of Ti, O, and Mg and confirm that Mg2+ ions are present in the TiO2 lattices. The prepared samples were investigated against gram-positive and gram-negative bacteria. The prepared samples exhibit potent antibacterial activity against gram-negative bacteria than the gram-positive bacteria. The prepared samples exhibit significant photocatalytic degradation for Methylene blue (MB).

Insight into physical interpretation of high frequency time constant in electrochemical impedance spectra of Mg

Electrochemical impedance spectroscopy measurements were performed to study the evolution of surface condition, which related to the high frequency time constant of Mg, in 0.05 M NaCl solution at three different pH. Based on the assumption that the high frequency time constant originates solely from the surface film, the thickness of MgO film was calculated via fitting EIS results. The deduced results were compared with the actual surface condition, characterized by transmission electron microscopy and local measurements. The results verified that the time constant at the high frequency range originates from the barrier properties of the surface film.

Effect of the toluene content on the preparation of Mg(Al,Y)2O4:Cr3＋ nanopowders by Pechini-type hydrothermal process

Cr3＋ doped magnesia aluminum spinel has potential applications in the fields of sensing, scintillator and laser. The structure, morphology, photoluminescence and diffuse reflection spectra of Mg(Al,Y)2O4:Cr3＋ were examined as a function of toluene content during the Pechini-type hydrothermal process. Toluene solvent changed the microstructure of Mg(Al,Y)2O4:Cr3＋ nanopowders, especially for the ratio of Al:Mg in the sample. Toluene also improved the agglomeration of nanopowders, and the luminescent intensity of the sample prepared with 60% and 75% toluene was enhanced by 16%.

Impact of Small Adsorbates in the Vibrational Spectra of Mg- and Zn-MOF-74 Revealed by First-Principles Calculations.

In this work, we analyze the influence of small adsorbates on the vibrational spectra of Mg- and Zn-metal-organic framework MOF-74 by means of first-principles calculations. In particular, we consider the adsorption of four representative species of different interaction strengths: Ar, CO2, H2O, and NH3. Apart from a comprehensive characterization of the structural and energetic aspects of empty and loaded MOFs, we use a fully quantum ab initio approach to evaluate the Raman and IR activities of the normal modes, leading to the construction of the whole vibrational spectra. Under this approach, not only are we able to proceed with the complete assignment of the spectra in terms of the usual internal coordinates but also we can discern the most relevant vibrational fingerprints of the adsorbates and their impact on the whole MOF spectra. On the one hand, some of the typical vibrational modes of the small molecules are slightly shifted but still visible when adsorbed on the MOFs, especially those appearing at high wavenumbers where the empty MOFs lack IR/Raman signals. On the other hand, some bands arising from the organic ligands are affected by the presence of the absorbates, displaying non-negligible frequency shifts, in agreement with recent experiments. We find a strong correlation between all of these frequency shifts and the interaction strength of the adsorbate with the hosting framework. The findings presented in this work expand the capabilities of vibrational spectroscopy techniques to analyze porous materials and can be useful for the design of sensors and new devices based on MOF technology.

Insight into dynamic interaction of molten MgCl2-NaCl-KCl with impurity water via FPMD simulations

First principle molecular dynamics (FPMD) simulations are used to investigate the dynamic interaction of impurity water with molten MgCl2-NaCl-KCl which has emerged as one of attractive candidate salts for the generation III concentrated solar power plant. The energetic fluctuations, radial distribution functions, micro-morphologies of intermediates, vibrational characteristics, and ionic self-diffusion coefficients of hydrous MgCl2-NaCl-KCl (hMNK) systems at 773 K are demonstrated, respectively. It is concluded that the O2− will eventually tend to interact with Mg2+ regardless of the initial water distribution. Besides, the evolution of Mg–O interatomic distance over time is depicted, from which the shuttles of O2− in the coordination shell of Mg-centered polyhedrons are captured. Furthermore, the simulated stretching vibration spectra of Mg–O and H–O bonds are comparable with experimental results, suggesting the powerful predictivity of FPMD. Overall, the water in molten hMNK promotes the migration of K+ rather than Na+, and the ionic transport properties depend on the water content and spatial distribution. And these FPMD results are heuristic in understanding the structure-activity relationship of molten hMNK, which sheds insight for the development of salt purification technology.

First-principles study of rocksalt Mg x Zn1− x O: band structure and optical spectra

ABSTRACT The present work deals with electronic band structure and derived optical spectra of Mg x Zn1− x O in the hypothetical rocksalt structure. The computations are performed using full-potential linearised augmented plane wave method. The exchange–correlation potential is described using the Wu-Cohen and Tran-Blaha modified Becke–Johnson generalised gradient approximation (TB-mBJ-GGA). The calculated lattice parameter deviates by less than 1% from experiment showing a net improvement when compared with previous calculations. Moreover, its variation with respect to x does not violate Vegard's law. The TB-mBJ-GGA approach improves the magnitude of the fundamental band gap with respect to experiment. The rocksalt Mg x Zn1− x O is found to be an indirect gap semiconductor for x = 0, 0.25, 0.50 and 0.75 and a direct gap semiconductor for x = 1. The nature of the gap for rocksalt Mg x Zn1− x O is still in controversy and further investigations are required in this respect. The optical spectra of Mg x Zn1− x O are analysed and discussed. Our findings yield values of 1.55 and 1.25 for the static refractive index and 2.4 and 1.55 for the static dielectric constant for rocksalt ZnO and rocksalt MgO, respectively.

Diagnostics of the Prominence Plasma from Hα and Mg ii Spectral Observations

Abstract The goal of this paper is to derive the physical conditions of the prominence observed on 2017 March 30. To do so, we use a unique set of data in Mg ii lines obtained with the space-borne Interface Region Imaging Spectrograph (IRIS) and in Hα line with the ground-based Multi-Channel Subtractive Double Pass spectrograph operating at the Meudon solar tower. Here, we analyze the prominence spectra of Mg ii h and k lines, and the Hα line in the part of the prominence which is visible in both sets of lines. We compute a grid of 1D NLTE (i.e., departures from the local thermodynamical equilibrium) models providing synthetic spectra of Mg ii k and h, and Hα lines in a large space of model input parameters (temperature, density, pressure, and microturbulent velocity). We compare Mg ii and Hα line profiles observed in 75 positions of the prominence with the synthetic profiles from the grid of models. These models allow us to compute the relationships between the integrated intensities and between the optical thickness in Hα and Mg ii k lines. The optical thickness τ Hα is between 0.05 and 2, and is between 3 and 200. We show that the relationship of the observed integrated intensities agrees well with the synthetic integrated intensities for models with a higher microturbulence (16 km s−1) and T around 8000 K, ne = 1.5 × 1010 cm−3, p = 0.05 dyne. In this case, large microturbulence values could be a way to take into account the large mixed velocities existing in the observed prominence.

Structural studies of advanced functional materials by synchrotron-based x-ray absorption spectroscopy: BL5.2 at SLRI, Thailand**Invited talk at 5th Thailand International Nanotechnology Conference (Nano Thailand-2016), 27–29 November 2016, Nakhon Ratchasima, Thailand.

This paper highlights the use of the x-ray absorption spectroscopy (XAS) as a local structural tool unlike x-ray diffraction for selected atoms in advanced functional materials including energy storage materials, dielectric materials and thermoelectric materials. The information concerning the oxidation states and local atomic structure around probing atoms will be revealed using x-ray absorption near edge structure (XANES) and extended x-ray absorption fine structure (EXAFS). The XAS beamline: BL5.2 at the Synchrotron Light Research Institute (SLRI) (public organization), Thailand, and its characteristic including available of measured energy ranges, examples of measured spectra of Mg, S and Ti K-edge XAS are also presented. In addition, in situ XAS set up and experiment carried out at this beamline are also outlined.

Preparation of carbon microspheres coated magnesium hydroxide and its application in polyethylene terephthalate as flame retardant

A novel flame retardant, carbon microspheres coated magnesium hydroxide (Mg(OH)2@CMSs) was synthesized. The morphology and structure of Mg(OH)2@CMSs was characterized by scanning electron microscope (SEM) and fourier transform infrared spectroscopy (FTIR). Then, Mg(OH)2@CMSs was added into polyethylene terephthalate (PET) to improve the flame retardancy of PET. The prepared composite (Mg(OH)2@CMSs/PET) with only 1 wt% Mg(OH)2@CMSs obtained a LOI value of 27.5% and reached UL94 V-0 rating. The flame retardant mechanism was studied by cone calorimeter measurement, thermogravimetric analysis (TGA), SEM and FTIR. The results showed that Mg(OH)2 and CMSs had synergistic flame retardant effect on PET. And there were two effects for Mg(OH)2@CMSs to improve the flame retardancy of PET. On one hand, CMSs and MgO as the bridge supporting points were dispersed into the basic framework of char layer in order to further strengthen the three-dimensional network structure of char layer. Thus a continuous and compact protective layer was formed, resulting in the decrease of pk-HRR and pk-MLR. On the other hand, the FTIR spectra of Mg(OH)2@CMSs/PET char residues showed that Mg(OH)2@CMSs induced PET degrading into small molecules with CC, which prevented PET from further decomposition, thus increased the amount of residue and decreased the THR value.

Intrinsic Proton NMR Studies of Mg(OH)2 and Ca(OH)2

We studied the short proton free induction decay signals and the broad ^1H NMR spectra of Mg(OH)2 and Ca(OH)2 powders at 77-355 K and 42 MHz using pulsed NMR techniques. Using a Gaussian-type back extrapolation procedure for the obscured data of the proton free induction decay signals, we obtained more precise values of the second moments of the Fourier-transformed broad NMR spectra than those in a previous report [Y. Itoh and M. Isobe, J. Phys. Soc. Jpn. Vol. 84, 113601 (2015)] and compared with the theoretical second moments. The decrease in the second moment could not account for the large decrease in the magnitude of the intrinsic proton spin-lattice relaxation rate 1/T_1 from Mg(OH)2 to Ca(OH)2. The analysis of 1/T_1 $propto$ exp(-E_g/k_BT) with E_g~0.01 eV points to a local hopping mechanism, and that of 1/T_1 $propto$ T^n with n~0.5 points to an anharmonic rattling mechanism.

Preparation of high quality Mg doped ZnO nanorod arrays with enhanced optical properties by MgO passivation

Mg doped ZnO (Mg:ZnO) nanrood (NR)-arrays have been successfully fabricated onto p-type Si substrate via hydrothermal method. The photoluminescence spectra of Mg:ZnO reveal the existence of residual surface defects as deep level in the visible range. Reliable approach was used to completely remove the surface defects in order to obtain high optical quality of Mg:ZnO NR-arrays in the UV region. RF sputtering was used to deposit MgO nanoparticles around the Mg:ZnO NRs to suppress the entire surface defects. Morphological observations reveal the formation of well-aligned nanorods grown perpendicularly to substrate surface. The hexagonal structure of Mg:ZnO NR-arrays oriented along c-axis favors the formation of core-shell Mg:ZnO/MgO NR-arrays. Photoluminescence spectra of the as-fabricated core-shell Mg:ZnO/MgO exhibit an intense peak near-band-edge (NBE) emission at 375nm which completely result in the disappearance of the deep level emission at around 580nm, achieving a maximum intensity ratio (∼140) of IUV/IVIS. The Raman E2 (high) mode of Mg:ZnO NR-arrays showed a blue shift compared to ZnO NR-arrays associated with the strain arising from Mg:ZnO core.

Extrinsic Proton NMR Studies of Mg(OH)2 and Ca(OH)2

We studied narrow $^1$H NMR spectra of Mg(OH)$_2$ and Ca(OH)$_2$ powders at 100$-$355 K and 42$-$59 MHz using pulsed NMR techniques. The Fourier transformed NMR spectra of the proton free-induction signals show the superposition of broad and narrow components, which can be assigned to immobile protons and extrinsic mobile protons, respectively. We found that a narrow spectrum develops on heating above about $T_c$ = 260 K and widens above a Larmor frequency of about $f_c$ = 50 MHz for Mg(OH)$_2$. The temperature-induced NMR spectrum and the characteristic frequency $f_c$ of 50 MHz are the noteworthy features of the nuclear spin fluctuation spectra of the extrinsic protons.

Structural, morphological, optical and electrical properties of CdS thin films simultaneously doped with magnesium and chlorine

CdS thin films simultaneously doped with Mg and Cl at different doping concentrations (0, 2, 4, 6 and 8 at%) were prepared on glass substrates by spray pyrolysis technique using perfume atomizer at 400 °C. The effect of Mg and Cl doping concentration on the structural, morphological, optical and electrical properties of the deposited films were investigated using X-ray diffraction (XRD), scanning electron microscopy, UV–Vis spectroscopy and dc electrical measurements, respectively. XRD analysis showed that the undoped and doped CdS films exhibit hexagonal structure with a preferential orientation along the (0 0 2) plane. The 2θ angle position of the (0 0 2) peak of the doped films was shifted towards a higher angle with increasing Mg and Cl concentration. The UV–Vis–NIR absorption spectra of Mg and Cl doped thin films are measured and classical Tauc approach was employed to estimate their band gap energies. The increase in band gap energy from 2.46 to 2.73 eV with the reduction in crystallite size supports quantum size effect. Raman spectra implied that more defects existed in the doped samples. Electrical studies showed that all the films have resistivity in the order of 101 Ω-cm and the CdS film with 6 at% Mg and Cl concentration has a minimum resistivity of 1.332 × 101 Ω-cm.

Novel Technique for Improving the Signal-to-Background Ratio of X-ray Absorption Near-Edge Structure Spectrum in Fluorescence Mode and Its Application to the Chemical State Analysis of Magnesium Doped in GaN

A novel measurement technique for an X-ray absorption near-edge structure (XANES) for magnesium (Mg) doped in gallium nitride (GaN) has been developed. XANES spectra from Mg at very low concentrations of 1 ×1018/cm3 doped in GaN have successfully been obtained by optimizing the region of interest (ROI) and by using highly brilliant synchrotron radiation X-rays of SPring-8. The ROI is the limited energy region from an X-ray fluorescence spectrum to elicit signals of particular atoms. Using this new technique, we have investigated the effect of the annealing process for Mg-doped GaN on the XANES spectra. It has been found that the XANES spectra of Mg significantly changed as the annealing temperature increased. This indicates that the local structure around Mg atoms in GaN was modified by the annealing process.

High Sensitive Elemental Analysis of Single Yeast Cells (Saccharomyces cerevisiae) by Time-Resolved Inductively-Coupled Plasma Mass Spectrometry Using a High Efficiency Cell Introduction System

Trace elemental analysis of single yeast cells with time-resolved inductively coupled plasma mass spectrometry (ICP-MS) was successfully carried out, where a high efficiency cell introduction system (HECIS) consisting of the high performance concentric nebulizer (HPCN) and a low-volume (15 mL) on-axis spray chamber utilizing a sheath gas flow were used. Cell adsorption to the flow injector and sample tubing was reduced with the addition of a simple 4.3 mmol L(-1) of NaCl solution to the cell suspension and cell flowing liquid, allowing consecutive measurements without fear of significant contamination from previous measurements. Initially using a quadrupole mass analyzer ICP-MS (ICP-QMS) at its lowest integration time (10 ms), current spikes corresponding to separate cell events were detected for several elements (Mg, P, Ca, Mn, Fe, Cu, and Zn) on the introduction of the cell suspension. On comparing the number of peaks in the spectrum for phosphorous with the cell count using a haemocytometer, a reproducible cell transport efficiency of 75.0 ± 4.7% was achieved. Preliminary experiments into using time of flight ICP-MS (ICP-TOFMS) for single-cell analysis were carried out, allowing quasi-simultaneous multielement detection. The spectra of Mg, P, Ca, Mn, Fe, Cu, and Zn, with a time resolution of 1 ms were simultaneously obtained in one measurement. A relatively strong correlation was observed for the spectra between P and Zn (correlation factor 0.69), P and Mg (0.63), and Mg and Zn (0.63). These results indicate that the time resolved quasi-simultaneous multielement measurement may be useful for the correlation analysis of multielements in cells.

High spatial resolution X-ray spectra of Mg, Al, Si and P L-emission observed with a newly developed soft X-ray spectrometer for EPMA

Extended abstract of a paper presented at Microscopy and Microanalysis 2012 in Phoenix, Arizona, USA, July 29 – August 2, 2012.