Effects of vertical grid discretization in infrared transmission modeling

The vertical spacing of a discretization used to model transmission in the mid-infrared spectral range was investigated. The forward model employed in this study is a part of an algorithm used to retrieve trace gas profiles from high-resolution ground-based solar absorption Fourier transform infrared (FTIR) spectra, however, the results have general applicability. A finely spaced retrieval grid was constructed and made progressively more sparse in the troposphere and in the stratosphere. The effect was quantified in terms of transmission differences with respect to the most fine discretization for a suite of molecules (H₂O, O₃, CO, CO₂, CH₄, N₂O, NO, NO₂, HCl, HF, HNO₃, ClONO₂, and N₂) in microwindows commonly used in FTIR spectroscopy. Systematic differences in modeled transmissions are apparent when coarser grid schemes are used for all species and microwindows, though some are below random noise levels typical of spectra recorded at Toronto. The most significant are H₂O and O₃ at 0.30-0.73% and 0.10-0.34%, respectively. CO (0.13%), ClONO₂ (0.84%), and HF (1.03%) are also influenced by the interference of H₂O, which is sensitive to temperature interpolation errors via the lower state energy of the particular H₂O transition. O₃ is a significant interference in CO (0.42%) and ClONO₂ (0.31%) microwindows, but its influence is felt primarily via interpolation errors in the O₃ number concentration profile introduced by the coarser grids. HCl and HF themselves show the next most significant response in transmission to coarser stratospheric grids (∼0.18%). Finally, considering transmission differences >0.1% as significant in typical measurements, we identify maximum tropospheric and stratospheric layer widths that still lead to negligible transmission errors as, respectively, 0.6 and 2.0 km. These numbers can vary depending on the band or transition of interest, the signal-to-noise ratio of the measurement and the use of significantly different a priori volume mixing ratio profiles.     

Surface modification of carbon nanotubes for enhancing BTEX adsorption from aqueous solutions

Carbon nanotubes (CNTs) were fabricated by the catalytic chemical vapor deposition method and oxidized by HCl, H₂SO₄, HNO₃ and NaOCl solutions for enhancing benzene, toluene, ethylbenzene and p-xylene (BTEX) adsorption in an aqueous solution. The surface nature of CNTs was changed after the H₂SO₄, HNO₃ and NaOCl oxidation, which makes CNTs that adsorb more BTEX. The NaOCl-oxidized CNTs show the greatest enhancement in BTEX adsorption, followed by the HNO₃-oxidized CNTs, and then the H₂SO₄-oxidized CNTs. The adsorption mechanism of BTEX via CNTs is mainly attributed to the π-π electron-donor-acceptor interaction between the aromatic ring of BTEX and the surface carboxylic groups of CNTs. The NaOCl-oxidized CNTs have superior adsorption performance of BTEX as compared to many types of carbon and silica adsorbents reported in the literature. This suggests that the NaOCl-oxidized CNTs are efficient BTEX adsorbents and that they possess good potential applications for BTEX removal in wastewater treatment.     

Calibration method for ESR signal intensity of calcitic shells

A practical method of calibrating intensities of ESR signals with a single crystal of copper pentahydrate (CuSO₄ · 5H₂O) has been developed for calcitic shells containing a large amount of manganese (Mn²⁺). A sample holder is designed to insert the crystal from the bottom of the cavity for use as a standard sample. The signal of Cu²⁺ in the standard does not interfere with the Mn²⁺ signals. The Cu²⁺ signal and dating signal of the shell are recorded simultaneously; the ratio of their intensities is the basis for calibration. It is shown that this calibration method reduces the errors attributed to both coupling and unloadedQ factors of the cavity resonator to within 2%.     

Dissolution patterns caused by chemical etching of Al–Co–Cu and Al–Co–Ni decagonal quasicrystals with a HF–HNO3–H2O solution

Dissolution patterns essential for Al–Co–Cu and Al–Co–Ni decagonal quasicrystals (d-QCs) have been investigated in detail by chemical etching using a HF–HNO₃–H₂O solution followed by scanning electron microscopy (SEM) observations. The chemical etching of definite surface areas of the samples, which are either normal or parallel to the tenfold axes, using a solution with HF–HNO₃–H₂O (1?:?5?:?4 in volume ratio; 0°C; 5–10?min), produces a large number of microfacet pits of decagonal prismatic shape. In addition, the same etching test in combination with SEM observations was carried out on a deformed sample of the Al–Co–Ni d-QC, which had been subjected to concentrated mechanical stress at an elevated temperature of 850°C by means of the Vickers indentation technique. The morphological features of the resulting micropits and their possible origins are discussed on the basis of results obtained by SEM observations.     

Thermal properties of graphite intercalation compounds with acids

This work is devoted to systematic thermal analysis of first to fifth stages of binary graphite intercalation compounds (GIC) with HNO₃ and ternary GICs with HNO₃–R (R=CH₃COOH, H₃PO₄) by simultaneous TG–DSC thermoanalyses (Netzsch). Thermolysis of GIC leads to the full deintercalation of acid and significant expansion of samples. The thermal properties of co-intercalated GICs-HNO₃-R and the thermal expanding coefficient of GIC depend on the nature of the intercalate. The endopeak at 110–150 °C corresponds to the loss of nitric acid was observed in DSC- curve of binary second to fifth stages of GICs with HNO₃. A wide endopeak which is characterized by the increasing of decomposition temperature in comparison with GIC-HNO₃ was observed in DSC—curve of ternary GIC with HNO₃–CH₃COOH. Thus, acetic acid stabilizes the graphite nitrate matrix. Two endoeffects due to the deintercalation of HNO₃ (110–180 °C) and H₃PO₄ (450–800 °C) were observed in the DSC-curves of co-intercalated GICs with HNO₃–H₃PO₄ of second and third stages. The value of decomposition heat (ΔH) and weight loss decrease with the increasing of the stage number of GICs. The values of ΔH are equal to 0.40–14.8 kJ/g-at C.     

New approach for understanding the fundamental chemistry of the oxidative sample digestion in spectrochemical analysis

The process known as “wet digestion” is widely used in analytical chemistry as the most common way of dissolving solid samples for elemental spectrochemical analysis. Wet digestion involves the use of oxidizing reagents and acids–mainly HNO₃, H₂O₂, H₂SO₄, HClO₄, and other complementary acid reagents such as HF, HCl, or their mixtures. Wet digestion has become popular and attractive to users in part owing to the application of modern equipment with new technologies such as temperature-controlled heating blocks, microwave systems, and automated digestion systems, among others. Nonetheless, the use of modern, sophisticated instruments does not change the physical and chemical foundations of the classic chemical process. Until now, simplified equations have been used to explain this process. However, fundamental chemical mechanisms and thermodynamic concepts have been commonly left aside. In this work, the acid digestion of samples has been approached based on the chemical reactions, detailing the role and the effect of main reagents and intermediaries. The reactions that can occur during the digestion process have been specified considering the fundamental thermodynamic properties of the reagents used, especially the oxidizing reagents HNO₃ and H₂O₂. This article will be a beneficial resource for students, instructors, and professionals alike.     

Oxidation of Activated Carbon in Liquid Phase. Study by FT-IR

Surface chemistry of a commercial activated carbon (AC) and of products oxidized in liquid phase using aqueous solutions of a series of oxidizing agents (H₂SO₄, HNO₃, HClO₄, H₂O₂, O₃, ClO₂, KlO₄ and KMnO₄) has been studied by FT-IR. Oxidation led to surface groups and structures which, and also the extend of formation, depended on the oxidizing agent and the pH and concentration of the solution used. Most oxidizing agents proved to be effective for the formation of surface C[dbnd]O groups. Variations in pH of solutions of H₂O₂, KlO₄ and KMnO₄ unequally affected the oxidation of AC. This was unfavourable with the increase in concentration of the solutions of HNO₃ and KMnO₄. The reverse was noted with KlO₄.     

Stable,metastable and unstable solutions of a spin-1 Ising system in the presence of magnetic fields due to the dipole and quadrupole moments

The spin-1 Ising model with bilinear (J) and biquadratic (K) interactions is studied for magnetic fields H_s and H_Q representing dipole and quadrupole moments, respectively, by using the lowest approximation of the cluster variation method. The influence of H_s, H_Q and α = J/K on metastable and unstable solutions, which are very important for many theoretical and experimental works, is investigated and it is found that metastable and unstable solutions occur at high temperatures when α and H_Q are increased. However if H_S is increased, metastable and unstable solutions can be found only at low temperatures.     

Laser Ablation of Titanium in Cryogenic and Room-Temperature Liquids

The results of processing of an OT4-0 titanium plate surface in media of C₂H₅OH + H₂O and liquid argon by radiation of a pulse-periodic Nd:YAG laser with subnanosecond pulses are presented. A change in current-carrying properties of structures synthesized in C₂H₅OH + H₂O is studied. The effect of subsequent influence of HNO₃ + HF acid solution on laser-induced structures is considered.     

Density functional calculation of K-shell spectra of small molecules

Both ΔE_KS and time-dependent density functional theory (TD-DFT) methods, with approximations for the singlet–triplet splitting and for the relativistic corrections, were tested for the calculation of K-shell spectra of Ne, HF, H₂O, NH₃, CH₄, and CO. Results from several exchange-correlation functionals as well as diffuse basis sets were compared with available experimental data. Excellent core excitation and core-electron ionization energies for Ne, HF, H₂O, NH₃, CH₄, and CO can be obtained from ΔE with Perdew–Wang 1986 exchange and Perdew–Wang 1991 correlation functionals; and reasonable intensities for singlet excitations, from TD-DFT with exchange-correlation potential known as statistical average of orbital potentials. The dependence of the quality of ΔE on basis set is as expected: excitations to higher Rydberg levels requiring more diffuse functions. However, the oscillator strength seems to be more sensitive to the quality of the basis set. Suggestions are made for extending the procedure to larger systems.     

Index of a family of Dirac operators on loop space

We use methods of constructive field theory to generalize index theory to an infinite-dimensional setting. We study a family of Dirac operatorsQ on loop space. These operators arise in the context of supersymmetric nonlinear quantum field models with HamiltoniansH=Q ². In these modelsQ is self-adjoint and Fredholm. A natural grading operator Γ exists such that ΓQ+QΓ=0. We studyQ ₊=P _? QP ₊, whereP _±=1/2 (1±Γ) are the orthogonal projections onto the eigenspaces of Γ. We calculate the indexi(Q ₊) for Wess-Zumino models defined by a superpotentialV(ω). HereV is a polynomial of degreen≧2. We establish thati(Q ₊)=n?1=degδV. In particular, the field theory models have unbroken supersymmetry, and (forn≧3) they have degenerate vacua. We believe that this is the first index theorem for a Dirac operator that couples infinitely many degrees of freedom.     

Excitation transfer and quenching induced in inelastic collisions of Zn 41P1 and 43P1 atoms

Quenching of excited Zn(4¹P₁) and Zn(4³P₁) atoms by collisions with Ar, N₂, H₂, CO and CO₂ has been investigated using methods of fluorescence spectroscopy. Mixtures of Zn vapor and quenching gases topped-up with Ar to maintain constant pressure were irradiated in a quartz cell with 2139 or 3076 Å resonance radiation which excited the 4¹P₁ or the 4³P₁ state, respectively. The resulting resonance fluorescence and sensitized fluorescence were monitored in relation to the gas density. Intensity measurements yielded the following cross sections Q_tot for the overall collisional deexcitation of the ¹P₁ state, Q₃ for quenching of the ³P₁ state, and Q₁₃ for ¹P₁→³P_J excitation transfer.For N₂: Q_tot = 26, Q₃ = 4.4, Q₁₃ = 5.8; for H₂: Q_tot = 12, Q₃ = 21, Q₁₃ < 5 × 10^-3; for CO: Q_tot = 28, Q₃ = 14, Q₁₃ = 17; for CO₂: Q_tot = 76, Q₃ = 23. All values are in Ų.     

Atomic and molecular fluorescence as a stratospheric species monitor

The results of an extensive evaluation are presented assessing the potential of atomic and molecular fluorescence as a stratospheric monitor of the concentrations of any one of eighteen minor species. These include Cl, Cl₂, ClO, ClO₂, CO, H₂, HCHO, HCl, HNO₂, HNO₃, H₂S, NH₃, NO, NO₂, N₂O, O, OH and SO₂. All spectral regions from the vacuum u.v. through to the i.r. have been included. Where appropriate, detection limits (signal/noise ratio of unity) are presented for each species under various sample pressure conditions and are based on practical systems that could be constructed using current technology.The most promising systems, with typical detection limits indicated either as parts per million, billion or trillion by volume, are for CO(5ppb), NO₂(<1ppb), OH(0.2ppt) and O(50–200ppt). The fluorescence sensitivities for Cl(0.5–1 ppt), H₂(0.2 ppm at 10 torr sample pressure) and SO₂(1–10 ppb) are marginally insufficient at present for such a stratospheric application. Likewise HCHO(10 ppb) and NO(100 ppb) fluorescence detection may be of interest in other applications where sensitivity demands are not as severe. There are no promising analytical possibilities using direct fluorescence techniques for Cl₂, ClO₂, HCl, HNO₂, HNO₃, H₂S, NH₃ or N₂O. ClO fluorescence has not yet been characterized.It has been noted, for various reasons, that i.r. fluorescence techniques in general cannot be exploited in the development of sensitive analyzers. However, by far the most surprising outcome of this study has been the recognition of the analytical potential of vacuum u.v. fluorescence. For some species, under certain conditions, extremely high sensitivities are possible even with samples in air at atmospheric pressure.     

Effect of different electrolytes on porous GaN using photo-electrochemical etching

This article reports the properties and the behavior of GaN during the photoelectrochemical etching process using four different electrolytes. The measurements show that the porosity strongly depends on the electrolyte and highly affects the surface morphology of etched samples, which has been revealed by scanning electron microscopy (SEM) images. Peak intensity of the photoluminescence (PL) spectra of the porous GaN samples was observed to be enhanced and strongly depend on the electrolytes. Among the samples, there is a little difference in the peak position indicating that the change of porosity has little influence on the PL peak shift, while it highly affecting the peak intensity. Raman spectra of porous GaN under four different solution exhibit phonon mode E₂ (high), A₁ (LO), A₁ (TO) and E₂ (low). There was a red shift in E₂ (high) in all samples, indicating a relaxation of stress in the porous GaN surface with respect to the underlying single crystalline epitaxial GaN. Raman and PL intensities were high for samples etched in H₂SO₄:H₂O₂ and KOH followed by the samples etched in HF:HNO₃ and in HF:C₂H₅OH.     

Electrochemical behaviors of the magnesium alloy substrates in various pretreatment solutions

Interface reactions and film features of AZ91D magnesium alloy in pickling, activation and zinc immersion solutions have been investigated. The surface morphologies of the specimens were observed with scanning electron microscope (SEM). Electrochemical behaviors of AZ91D magnesium alloy in the baths of pickling, activation and zinc immersion were analyzed based on the open circuit potential (OCP) - time curves in various solutions. The results show that the corrosive rate in HNO₃ + CrO₃ or HNO₃ + H₃PO₄ pickling solution was more rapid than in KMnO₄ pickling-activation solution. Both α phase and β phase of the substrates were uniformly corroded in HNO₃ + CrO₃ or HNO₃ + H₃PO₄ pickling solution, the coarse surface can augment the mechanical occlusive force between the subsequent coatings and the substrates, so coatings with good adhesion can be obtained. In HF activation solution, the chromic compound formed via HNO₃ + CrO₃ pickling was removed and a compact MgF₂ film was formed on the substrate surface. In K₄P₂O₇ activation solution, the corrosion products formed via HNO₃ + H₃PO₄ pickling were removed, a new thin film of oxides and hydroxides was formed on the substrate surface. In KMnO₄ pickling-activation solution, a film of manganic oxides and phosphates was adhered on the substrate surface. Zinc film was symmetrically produced via K₄P₂O₇ activation or KMnO₄ pickling-activation, so it was good interlayer for Ni or Cu electroplating. Asymmetrical zinc film was produced because the MgF₂ film obtained in the HF activation solution had strong adhesive attraction and it was not suitable for interlayer for electroplating. However, the substrate containing compact MgF₂ film without zinc immersion was fit for direct electroless Ni-P plating.     

Single orbital relaxations accompanying core ionization in the isoelectronic series CH4, NH3, H2O,HF and Ne

Single orbital contributions to the total relaxation energy accompanying core ionization are computed by means of non-empirical LCAO MO SCF calculations within the ΔSCF formalism for the isoelectronic series CH₄, NH₃, H₂O, HF and Ne. Individual contributions to the total relaxation energy associated with the valence levels of essentially core-like 2s character are also presented.     

Molecular field theory analysis of R3Co11B4 compounds

The temperature dependence of magnetization of the R₃Co₁₁B₄ compounds has been analysed using the two-sublattice molecular field theory. The molecular field coefficients, n_CoCo, n_RCo, n_RR, have been calculated by a numerical fitting process. The analytic form of the exchange field H_R(T) varying with temperature for each of the R₃Co₁₁B₄ compounds is presented, and some results are discussed.     

Functionalization of carbon encapsulated iron nanoparticles

Carbon-encapsulated magnetic nanoparticles are a new class of materials where the core magnetic nanoparticle is protected from reactions with its environment by graphite shells. Having a structure similar to carbon nanotubes, these nanoparticles could be potentially functionalized using methods which are already applied to those structures. We present the effects of acidic treatments based on HCl, HNO₃, and H₂SO₄ on these nanoparticles highlighting the impact on their magnetic and surface properties. We show that acidic treatments based on HNO₃ can be successfully applied for the generation of carboxylic groups on the surface of the nanoparticles. Using methylamine as a model, we demonstrate that these functional groups can be used for further functionalization with amino-containing biomolecules via diimide-activated amidation.     

Further investigation on the formation mechanisms of (NH4)2SiF6 synthesized by dry etching technique

The validity of two formation mechanisms of ammonium silicofluoride (ASF), which are proposed to take place when a silicon surface is exposed to the vapor of HNO₃/HF acid mixture is investigated. Of the two proposed mechanisms regarding the synthesis of ASF on silicon surface, validity of the first predicting the release of hydrofluosilicic acid (H₂SiF₆) at the intermediate stage is examined by FTIR spectroscopy and the second mechanism suggesting O₂ release is investigated using the Winkler technique. IR absorbance bands of SiF₆²⁺ are observed on the fresh samples prepared at low (1/100) HNO₃/HF volume fractions. No significant amount of oxygen is detected during the synthesis of ASF films on silicon surface by dry etching technique. These two observations together provide firmer support for the validity of the second mechanism.