Miracle-dz/UniFAR-FTUs huggingface dataset:
Key role of oxygen at zinc oxide varistor grain boundaries

The electrical transport properties of zinc oxide varistors are correlated with the chemistry of their grain boundaries. An adsorbed layer of bismuth, about 5 A thick, is necessary to create potential barriers at the grain boundaries. The height of these potential barriers depends sensitively on the excess amount of oxygen (∼1 monolayer) present at the interfaces between grains. This oxygen enrichment is influenced by thermal processing and by electrical degradation.
Poly(ortho‐toluidine) Modified Carbon Paste Electrode: A Sensor for Electrocatalytic Reduction of Nitrite

The electrocatalytic reduction of nitrite has been studied by poly(ortho-toluidine) films modified carbon paste electrode (P-OT/MCPE). Cyclic voltammetry and chronoamperometry techniques were used to investigate the suitability of poly(ortho-toluidine) as a mediator for the electrocatalytic nitrite reduction in aqueous solution with various pH. Results showed that pH 0.00 is the most suitable for this purpose. In the optimum pH, the reduction of nitrite occurs at a potential about 600 mV more positive than unmodified carbon paste electrode. The catalytic reaction rate constant, (kh), was calculated 8.68×102 M−1 s−1 by the data of chronoamperometry. The catalytic reduction peak current was linearly dependent on the nitrite concentration and the linearity range obtained was 5.00×10−4 M–1.90×10−2 M. Detection limit has been found to be 3.38×10−4 M (2σ). This method has been successfully employed for quantification of nitrite in real sample.
An Agar Gel Technique Demonstrates Diffusion Limitations to Cadmium Uptake by Higher Plants

Environmental Context. Toxic effects of trace metals are often related to the amount of metal that is internalized by the organism. Uptake of metals by biota is usually predicted with equilibrium models, which assume that transport of the metal from the solution to the biosurface does not limit uptake. In this study, uptake of cadmium by higher plants is shown to be limited by the transport of the free ions to the root surface under a range of conditions. Abstract. Uptake of cadmium (Cd) by spinach and wheat was higher in the presence of fast-dissociating complexes than in unbuffered solutions with the same free ion concentration. This contribution of metal complexes to metal uptake cannot be explained by equilibrium free-ion-based models, which assume that transport of the free ion to the biosurface is not limiting the uptake. To demonstrate diffusion limitations to metal uptake, we used an agar gel technique in which Cd and Zn concentrations around the roots, after 6 h of uptake, were compared with bulk concentrations. Metal depletion around the roots was clearly observed in agar where the ion activities were not buffered by complexes, whereas the depletion was less pronounced in buffered agar. Metal uptake by the plants in unbuffered media was greater as the degree of agitation increased (stirred solution > unstirred solution > agar), while no such dependence on hydrodynamic conditions was found in buffered media, which is in agreement with theoretical predictions.
Composición química volátil del aceite esencial de Eryngium foetidum L. colombiano y determinación de

Introduction: culantro (Eryngium foetidum L., Apiaceae) is a herb native to Tropical America and the West Indies. Although widely used in dishes throughout the Caribbean, Latin America, and the Far East. The herb is reportedly rich in calcium, iron, carotene, and riboflavin and its harvested leaves are widely used as a food flavoring and seasoning herb for meat and many other foods. Their medicinal values include its use as a tea for flu, diabetes, constipation, and fevers. One of its most popular uses is in chutneys as an appetite stimulant. Species of E. foetidum from several countries have shown a variable composition of its essential oil, particularly, in their leaves. Objective: to establish the volatile chemical composition of the essential oil obtained from fresh leaves and stems of E. foetidum and to evaluate its antioxidant activity. Methods: the essential oil was isolated by hydrodistillation. The volatile chemical composition was analyzed by Gas Chromatography coupled to flame ionization detector (GC-FID) and Mass Spectrometry (GC-MS). The antioxidant activity was determined using the test radical DPPH decoloration. (2,2-diphenyl-1-picryl hidrazyl). Results: the essential oil from E. foetidum showed a high percentage of aliphatic aldehydes (E-2-dodecenal, 5-dodecene, tetradecanal, tetradecenal) and aromatic (2,3,5-trimethylbenzaldehyde, trimethylphenol). The antioxidant activity was expressed as percentage inhibition of DPPH radical (89.39 %). Conclusions: in the essential oil from Colombian E. foetidum predominant aliphatic aldehydes and aromatic compounds. The DPPH test showed that AE has antioxidant capacity, this makes it an important source of natural antioxidants.
Considerations for the measurement of spectrophotometric pH for ocean acidification and other studies

Indicator‐based spectrophotometric pH is commonly used for the analysis of seawater because of its high precision and long‐term reproducibility. Users come from an increasingly diverse range of disciplines, primarily motivated by studies focused on the causes and effects of ocean acidification. While the analysis is readily implemented and straightforward, there are many variables that must be predetermined or measured, all of which can contribute uncertainty to the measurement. The indicator equilibrium constant and molar absorption coefficient ratios are available in the literature, but for various reasons, the conditions of analysis can be different, creating errors. Most of the parameters are temperature, salinity, and pressure dependent, posing potential additional errors. Indicator impurities and indicator perturbation of the sample pH also create uncertainties. We systematically evaluate all of the sources of error and compute how the errors propagate into CO2 equilibrium calculations of the partial pressure of CO2 (pCO2) and calcium carbonate saturation states (Ω). The primary sources of uncertainty originate from wavelength and absorbance errors in low quality or poorly functioning spectrophotometers (0.007 to 0.020 pH units) and indicator impurities (0.000 to >0.040 pH units). These errors generate pCO2 and Ω uncertainties of 11‐200 µatm and 0.08‐0.38, respectively, depending upon the pH value and its uncertainty.
Studies on VaR Estimation of China’s Agricultural Product Futures Market Based on GARCH Models

ABSTRACT Taking China Agricultural Products Futures Index (CAFI) as an example, this paper makes descriptive statistics and analysis on the logarithm yield of CAFI, discusses the calculation of VaR under the assumption that the residual is subject to the normal distribution, t-distribution, and generalized error distribution (GED), and tests the accuracy of VaR calculated by each model by Kupiec backtest. The results show that the yield of the CAFI index has the characteristics of "peak and fat tail", volatility aggregation, and asymmetric effect. GARCH (1,1) model under the assumption of normal distribution and GED distribution can truly reflect and measure the risk of the agricultural futures market.
Synthesis and Photoelectrochemical Property of Urchin-like Zn/ZnO Core−Shell Structures

An urchin-like Zn/ZnO core-shell structure was synthesized and deposited directly on an indium tin oxide (ITO) glass substrate by using a thermal evaporation method. Structural characterization reveals that the hybrid material is composed of a micrometer scale sphere-shaped metallic Zn core and a shell made up of numerous radially protruding single-crystalline ZnO nanorods. It was found that the Zn core makes direct contact with the ITO layer, which enhances the interface bonding and conductance between the Zn/ZnO structure and the substrate. Desirable photoelectrochemical properties of such Zn/ZnO core-shell structures aredemonstrated.Theirsuperiorphotoelectricalresponseperformancecanbeattributedtothemetal-semiconductor core-shell structure, unique urchin-like configuration, and favorable combination between the active material and the substrate.
Fenton-like Chemistry in Water: Oxidation Catalysis by Fe(III) and H2O2

The formation of active intermediates from the Fenton-like reagent (a mixture of iron(III) ions and hydrogen peroxide) in aqueous solution has been investigated using static DFT calculations and Car−Parrinello molecular dynamics simulations. We show the spontaneous formation of the iron(III) hydroperoxo intermediate in a first step. The Fenton-like reaction thus proceeds very differently compared to Fenton's reagent (i.e., the FeII/H2O2 mixture), for which we have recently shown that the first step is the spontaneous O−O lysis of hydrogen peroxide when coordinated to iron(II) in water. For the second step in the reaction mechanism of the Fenton-like reagent, we compare the possibilities of homolysis and heterolysis of the O−O bond and the Fe−O bond of the produced [(H2O)5FeIIIOOH]2+ intermediate. We find that concomitant hydrolysis of the reacting species plays a crucial role and, taking this into account, that O−O homolysis ([(H2O)4(OH)FeIIIOOH]+ → [(H2O)4(OH)FeIVO]+ + OH•) in vacuo is a likely second st.
Marandu Palisadegrass Mineral Nutrition and Production Related to Nitrogen and Potassium Supply

Nitrogen (N) and potassium (K) fertilization play a key role in forage crops and can significantly increase yields of ‘Marandu’ palisadegrass [Brachiaria brizantha (Hochst. exA. Rich.) Stapf. ], one of the most important forage crops in Brazil. This study aimed to identify the concentrations of total N and K, nitrate (NO3−), and ammonium (NH4+), chlorophyll meter readings (SPAD), and nitrate reductase activity (At-RNA) required to maximize yield. Plants were grown in quartz substrate and treated with nutrient solutions that ranged from 2 to 33 mmol L−1 for N and 0.5 to 11 mmol L−1 for K. Dry matter production and At-RNA increased with increasing N and K supplies. SPAD readings correlated strongly with N leaf concentration and dry matter production and can be used to assess the N status of this species. The supply of N and K in the fertilization promoted high yield and adequate N and K concentration for plant metabolism.
Structural Variations and Ordering Conditions for the Self-Assembled Monolayers of HS(CH2CH2O)3-6CH3

The structure and ordering conditions of the self-assembled monolayers (SAMs) of HS(EO)xR, where R = CH3, EO = CH2CH2O, and x = 3−6, on polycrystalline gold (Au) were determined by reflection−absorption infrared spectroscopy (RAIRS), spectroscopic ellipsometry (SE), and electrochemical impedance spectroscopy (EIS). For x = 5 and 6, RAIRS and SE data show that the 1-thiaoligo(ethylene oxide) [TOEO] segments adopt the highly ordered helical structure of the folded-chain crystal polymorph of crystalline poly(ethylene oxide) and are oriented normal to the substrate. RAIRS and SE data obtained as a function of immersion time show that x = 6 attains the highly ordered, all helical conformation faster than x = 5. For x = 3 and 4, RAIRS and SE data indicate largely disordered structures, with some all-trans conformation but little evidence of the helical conformation. EIS measurements, in an aqueous environment, indicate a significant presence of water in all SAMs with x < 6 while x = 6 remains essentially free o.
The Significance of the Points of Zero Charge of Zirconium (Hydr)Oxide Reported in the Literature

ABSTRACT The points of zero charge (PZC) of zirconium (hydr)oxide reported in the literature range from 4 to 8.6. A set of seventy-six PZC of zirconium (hydr)oxide was used to explore the effect of the origin and crystalline structure on the one hand and of the choice of the experimental method on the other. The average and median PZC was found at pH 6.5 when the entire data set was taken into account. Among the synthetic samples, monoclinic zirconium oxide has substantially higher PZC than other crystallographic forms of zirconium oxide, mixtures of different forms, and amorphous zirconium (hydr)oxide (or samples of unknown structure). But with commercially available samples, the effect of the crystalline form on the PZC was rather insignificant. The PZC obtained by means of titration (the common intersection point [CIP] of titration curves for three or more ionic strengths is identified with the PZC) and the PZC obtained by means of electroacoustic methods are substantially higher than the IEP from classical electrokinetic measurements. Interestingly, a few PZC of zirconium oxide obtained as matching CIP and IEP are very scattered, thus their significance as the “most reliable PZC” is rather limited.
On-membrane digestion of ?-casein for determination of phosphorylation sites by matrix-assisted laser desorption/ionization quadrupole/time-of-flight mass spectrometry

This article discusses the features of a newly developed matrix-assisted laser desorption/ionization quadrupole/time-of-flight (MALDI-QqTOF) mass spectrometer that is useful in the analysis of phosphorylated peptides. Aliquots of β-casein, a commonly used phosphorylated protein standard, were digested with trypsin directly on a non-porous polyurethane membrane used as sample support in MALDI-QqTOF mass spectrometry (MS) experiments. Although a complete peptide map was obtained, it was difficult to obtain sequence information for some of the tryptic fragments, in particular T1-2, which bears four phosphate groups and is thus difficult to ionize in positive mode. This article focuses on the sequencing of this particular fragment by comparing MS/MS spectra obtained using different precursor ions. These precursors associated with T1-2 were [M + H]+, [M + H]2+, and [M + H − nH3PO4]+ ions. Typically, phosphorylated ions showed facile unimolecular losses of phosphoric acid moieties, and produced limited backbone fragmentation. The abundance of [M + H]2+ ions of T1-2 in the full mass spectrum was low relative to that of [M + H]+. [M + H − 4H3PO4]+ ions as MS/MS precursors underwent backbone fragmentations, with phosphoserine residues transformed into dehydroalanines or serines. Unusual b + 18 u fragments were observed, although only for segments with previously phosphorylated serines. These partly interfered with c-ions, and were noticeable due to overlapping isotopic envelopes. It was possible to establish the sequence of phosphorylated tryptic fragment T1-2 and the location of phosphate groups using the mass of dehydroalanine residues (69 Da) and b + 18 u fragments as markers. All MS and MS/MS spectra obtained with fully phosphorylated β-casein were compared with spectra acquired with dephosphorylated β-casein obtained commercially. These comparisons helped assess the spectral differences caused by the presence of phosphate groups. Also, they highlighted the potential usefulness of conducting dephosphorylation directly on the probe prior to MALDI analysis in future studies. Copyright © 2001 John Wiley & Sons, Ltd.
The characterization of heterogeneous catalysts by XPS based on geometrical probability 1: Monometallic catalysts

Geometrical probability can be used as a basis for the quantification of XPS-signals stemming from random samples such as, for instance, supported heterogeneous catalysts. From a study of three ideal cases, namely extended layers of constant thickness, equally sized spheres and hemispheres on a randomly oriented support, it has been established that the effects of angular and layer thickness averaging are interconnected in such a way that a general model can be derived. It has been found that signal ratios as measured by XPS for convex particles are determined by the surface/volume ratios of the supported phases, nearly independent of particle shape.
Impurities in multicrystalline silicon wafers for solar cells detected by synchrotron micro-beam X-ray fluorescence analysis

We report on the trace analysis of copper and iron impurities in multicrystalline silicon wafers with the microbeam X-ray fluorescence (μ-XRF) technique. The efficiency of solar cells, which are based on multicrystalline silicon wafers, is strongly influenced by minor contamination with metals such as copper and iron. Application of compound refractive lenses (CRLs) in μ-XRF allows versatile two-dimensional mapping of relevant contaminations and localization of their sites of deposition. In this context, the measured bulk average limit of detection (LOD) was one picogram of iron and copper per gram of silicon. We suggest that μ-XRF is a valuable tool for non-destructive spatial (3D) quantification of metal impurities in a wide range of materials and devices whose functioning could be critically affected by impurities.
Behavior of evanescent fields in the periodic scattering system

We study the problem of scattering by a thin and conducting screen perforated periodically with square apertures, when the screen is illuminated by an electromagnetic wave in subwavelength regime. Our formulation extends the monomodal approximation technique up to the second-order Floquet modes, which enable us to investigate not only propagation mode, but also nonpropagation mode in the low-frequency regime. We also study dispersion relation of the principal Floquet modes and show the behavior of electromagnetic fields in the periodic system at the extremely low frequency, the resonance frequency and Wood’s anomaly frequency. The interesting characteristics of the fields can be found in these specific frequencies.
Spectral analysis, molecular orbital calculations and antimicrobial activity of PMF-G fraction extracted from PM-701.

PM701 is a natural product and it is free of toxicity. The extracted fraction which coded PMF-G was found in 150 mg /g of lyophilized PM- 701 and it was able to inhibit significantly the proliferation of cancer cells without affect the normal cells at cell culture level. The PMF fraction has been fractionated from PM-701 sample and it has been concluded that this fractionated sample has anticarcinogenic effect on lung cancer and Leukemic cells. The elemental analysis, mass, infrared, atomic absorption and electronic spectra had been done for this sample and it has been concluded that the main constituent is amino acid and some salts. The structural studies were done by DFT method in the bases set B3LYP/6-31G** using Gaussian 98 to calculate the ionization energies, electron affinities and dipole moments in comparison to those of nucleic acid bases and AMP. The different values of low ionization energies and high electron affinities permit the electron transfer between these amino acids and the nucleic acid bases to excess or loss of an electron in the DNA of the human being cell. It has been concluded from the mass spectra that the major component of the PMF is cysteine and from the atomic absorption it has been concluded that it contains some elements mainly K, Na, Zn, Fe, Cu, Br and Cl. The antimicrobial activities of the PM701 and pure fraction PMF were detected against four dermatophytic fungi (Aspergillus fumigatus, Epidermophyton floccosum, Microsporum canis and Trichophyton rubrum), two Gram-positive bacteria (Staphylococcus citrus and Bacillus subtilis) and two Gram–negative bacteria (Escherchia coli and Salmonella typhi). The crude extract PMF showed the higher antimicrobial activity up to 32 mm inhibition zone with MIC<100 µ g/ml, compared with the low antimicrobial activity (<10 mm inhibition zone) accompanied with MIC in the range of 100- 150 µ g/ml of the pure extract of PM7. The maximum toxicity (40-85 % cell mortality) was observed with addition of 100% crude extract of PM 701.
Potentiometric Selectivity Coefficients of Ion-Selective Electrodes. Part I. Inorganic Cations (Technical Report)

Abstract Potentiometric selectivity coefficients have been collected for ionophore-based ion-selective electrodes (ISEs) for inorganic cations reported from 1988-1997. In addition to numerical values of K(A,B)pot together with the methods and conditions for their determination, response slopes, linear concentration ranges, chemical compositions, and ionophores structures for the ISE membranes are tabulated.
Ligand-Enhanced Aliphatic Carbon−Carbon Bond Activation of Nitroxides by Rhodium(II) Porphyrin

Rh(tmp) underwent Ph3P-enhanced aliphatic carbon−carbon bond activation with various nitroxides. (Ph3P)Rh(tmp), rapidly formed from Rh(tmp) and Ph3P, enhanced the rate, selectivity, and yield in comparison to Rh(tmp). From kinetic studies, the rate of reaction showed a first-order dependence on both Rh(tmp) and TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine-1-oxyl) and saturation kinetics on Ph3P. The rate enhancement of (Ph3P)Rh(tmp) over Rh(tmp) was estimated to be about 11 at 70 °C.
Organic−Inorganic Hybrid Materials Incorporating Phosphorus-Containing Dendrimers

Phosphorus-containing dendrimers of first, second, and third generation with various peripheral functional groups and bearing a hydrolyzable Si(OEt)3 group at the core have been prepared. Two synthetic routes were used: either the Si(OEt)3 group was introduced from the start by reaction of (EtO)3Si(CH2)3PPh2 with an azide according to the Staudinger reaction (A series of dendrimers) or the Si(OEt)3 group was grafted to the core in the last step by reaction of 3-aminopropyltriethoxysilane with a vinyl group at the core (B series of dendrimers). The silylated dendrimers were characterized by elemental analyses and 1H, 13C, 31P, and 29Si NMR spectroscopies. The cohydrolysis and polycondensation of these macromolecules with a defined and varying number of equivalents of tetraethoxysilane (TEOS) was carried out via sol−gel protocol, giving rise to dendrimer−silica xerogels. It was proven by 31P NMR spectroscopy that the dendrimers were not damaged during the sol−gel process, and it was shown by 29Si NMR spect.
Kinetic and thermodynamic study of the adsorption of Pb (II) from aqueous solution to the natural and treated bentonite

Lead (Pb) is one of the major environmental pollutants. Adsorption appears to be the most widely used for the removal of heavy metals. The aim of this work is to investigate the adsorption potential of commercial natural bentonite (NB) in the removal of Pb (II) ions from aqueous solution. The effect of different variables, such as, concentration of Pb, mass of NB, pH, time, NB washing and heat treatment and temperature was investigated. The bentonite sample under the heat and washed treatment are labeled as CB and WB respectively. The adsorption experiments were carried out using batch process. The equilibrium time for Pb (II) adsorption on NB was 5 min, the processes conforming to second order kinetics. NB had a much higher adsorption capacity for Pb (II) with the Langmuir monolayer capacity (qm) of 107, 110 and 120 mg g− 1 at 293, 313 and 333 K respectively compared to others adsorbents. Thermodynamic parameters such as ΔH°, ΔS° and ΔG° were calculated. The adsorption process was found to be endothermic and spontaneous. The enthalpy change for Pb (II) by NB adsorption has been estimated as 33 kJ mol−1, indicating that the adsorption of Pb (II) by NB corresponds to a physical reaction. The adsorption capacity of washed bentonite WB was very high compared to NB and CB Key word: Adsorption, clay minerals, bentonite, lead, wastewater treatment