Miracle-dz/UniFAR-FTUs huggingface dataset:
Molecular field effect passivation: Quinhydrone/methanol treatment of n-Si(100)

The quinhydrone/methanol treatment has been reported to yield outstanding passivation of the H-terminated Si(100) surface. Here, we report on the mechanism of this process by comparing the resulting surface to that of freshly etched H-terminated Si, of Si with chemically grown oxide, and of Si treated with hydroquinone/methanol solution of the same concentration. We find that the benzoquinone moieties of the quinhydrone react with the surface to yield a Si-hydroquinone surface termination, while the methanol molecules bind as well to form methoxy-terminated Si. The slightly negative-charged benzene ring of the hydroquinone acts to repel majority carrier electrons from the surface and inhabits the surface recombination. The higher the ratio of surface-bound hydroquinone to surface-bound methoxy species, the larger the minority carrier life-time measured by microwave photoconductivity. Thus, our results lead us to conclude that this treatment results in field effect passivation; remarkably, this effect is c.
Binding of Monovalent Ions to PEO in Solution: Relevant Parameters and Structural Transitions

We present a comparative small-angle neutron scattering and theoretical study of the charging effects of poly(ethylene oxide) (PEO) in the presence of monovalent ions as a function of the solvent characteristics and cation strength, and we demonstrate that the classical “salting-in” condition is constituted by distinct subregimes depending on salt and solvent characteristics. In solvents with moderate dielectric constant and moderate hydrogen- bonding capacity, two distinct regimes can be distinguished: (1) at low ionic strengths, the addition of salts primarily results in the formation of polymer−cation association complexes and thus in charging of the polymer chain (binding regime); (2) at higher salt concentrations, the binding of ions becomes increasingly unfavorable, resulting in the screening of electrostatic interactions and neutral polymer-like characteristics of PEO are observed (screening regime). The extent of ion-binding is compared to predictions based on mean-field theory in the thermodynam.
CO2 absorption by aqueous NH3 solutions: speciation of ammonium carbamate, bicarbonate and carbonate by a 13C NMR study

The absorption of CO2 in aqueous NH3 solutions occurs with high efficiency and loading capacity at room temperature and atmospheric pressure producing the ammonium salts of bicarbonate (HCO3−), carbonate (CO32−), and carbamate (NH2CO2−) anions. 13C NMR spectroscopy at room temperature has been proven to be a simple and reliable method to investigate the speciation in solution of these three ionic species. Fast equilibration of HCO3−/CO32− anions results in a single NMR peak whose chemical shift depends on the relative concentration of the two species. A method has been developed to correlate the chemical shift of this carbon resonance to the ratio of the two anionic species. Integration of the carbamate carbon peak provided the relative amount of this species with respect to HCO3−/CO32− pair. No other species was detected in solution by 13C NMR, and no solid compounds separated out under our experimental conditions. Finally, the relative amount of HCO3−, CO32−, and NH2CO2− in solution have been correlated to the molar ratio between free ammonia in solution and absorbed CO2.
Evaluation of Avulsion Potential on Active Alluvial Fans in Central and Western Arizona

An avulsion is the process by which flow is diverted out of an established channel into a new course on the adjacent floodplain. Occurrences of avulsions are what makes an alluvial fans “active. ” Avulsions give the alluvial fan the ability to distribute water and sediment over the surface of the landform, which results in a radial “fan” shape. Avulsions influence flood hazards on an alluvial fan landform by changing the location, concentration and severity of flooding on the fan surface. Avulsions have been observed on several alluvial fans in central and western Arizona. The avulsion history of several fan evaluation sites are documented and described. It is likely that there are other examples of major avulsions in Arizona, but no comprehensive evaluation of avulsion frequency or occurrences has been made. Historical records clearly indicate that avulsions do occur on the types of alluvial fans found in central and western Arizona. The cursory data summarized above indicate that it is likely that avulsions are relatively rare events, and that they are often associated with the occurrence of large floods. However, further documentation of the avulsion history of local alluvial fans is warranted to better assess the recurrence interval and frequency of avulsions. Almost all of the known causative factors for avulsions exist on alluvial fans in central and western Arizona, and thus it is likely that avulsions will continue to occur in the future.
What causes iron-sulphur bonds in active sites of one-iron superoxide reductase and two-iron superoxide reductase to differ?

The electronic and vibrational properties of [Fe(NHis)4(SCys)] sites responsible for the catalysis of superoxide reduction in two types of superoxide reductase (SOR), one-iron superoxide reductase (1Fe-SOR) and two-iron superoxide reductase (2Fe-SOR), were compared previously (Clay et al., 2003); the differences between these two classes of SOR, examined by UV-VIS and NIR absorption, VTMCD, and vibrational spectroscopy techniques, were interpreted as being indicative of weaker Fe-S bonds in 2Fe-SOR in comparison with 1Fe-SOR. Here, we report on density functional (DFT) and semi-empirical (ZINDO/S-CI) calculations exploring the extent of this difference in bonding between the two classes of SOR. The differences observed experimentally between the electronic spectra of the two SORs are shown to probably arise either from different degrees of torsion between the Fe—ligand bonds or from differences in length of the Fe—carboxylate bond, but are shown to be incompatible with any significant differences in Fe—S bond lengths. The differences observed in the vibrational spectra between the two SORs are shown to correlate with differences in the Fe-S bond length of no more than 0.01 Å, which in turn arise from slight differences in the polarity of the medium surrounding the iron active site in the two proteins.
The indirect determination of chlorine atom concentration in the troposphere from changes in the patterns of non-methane hydrocarbons

About 200 measurements of C 2 –C 9 hydrocarbons were made during a ship cruise (NATAC 91) in the western Mediterranean Sea, the eastern Mid- and North Atlantic and the North Sea in April and May 1991. The changes in the ratios of several pairs of hydrocarbons are used to investigate the possible impact of Cl-atom reactions on the atmospheric removal processes of hydrocarbons. In order to minimize the potential bias from atmospheric mixing processes, a careful selection of suitable hydrocarbon sets is essential. The NMHC mixing ratios observed during NATAC 91 are generally well above those typical for air in the remote marine background and the observed changes in the hydrocarbon patterns agree very well with those predicted from OH-radical chemistry. No significant evidence for an impact of chlorine atoms could be found in this data set. The best estimate for the average [Cl]/[OH] ratio is in the range of 10 −3 . However, within the various uncertainties associated with such estimates, this value is not significantly different from zero. The upper limit is in the range of 2–7·10 −3 . Based on an average OH-radical concentration of 10 6 cm −3 , this corresponds to some 10 3 Cl-atoms cm −3 . This is far below the Cl-atom concentrations found during the tropospheric ozone depletion events in arctic spring. Our values are also far below those derived in some other studies for the marine boundary layer but are still compatible with recent model calculations. Our findings support the conclusion of Rudolph and coworkers that on average, Cl-atoms are of limited importance for the chemistry of the troposphere. It is important that the major part of the uncertainty of the Cl-atom concentration estimates results from errors in the rate constants for the reactions of the hydrocarbons with OH-radicals. A reliable and consistent set of the relevant rate constants would further improve the accuracy of the Cl-atom concentration estimates or their upper limits derived from changes in the hydrocarbon patterns. DOI: 10.1034/j.1600-0889.49. issue5.13. x
The profile distribution of zinc in arable alluvial soils with naturally elevated content of calcium carbonate

The objective of the study was to analyze profile spatiation of total and DTPA-extractable zinc forms in alluvial arable soils. Six soil profiles located in the Unislaw Basin were analyzed. The soils were classified as alluvial black earths. The alluvial material of the examined soils was overlying calcareous sinter situated 100 cm deep into the ground. Soil samples were analyzed for the grain size composition, reaction, Corg and the CaCO3 content. The total zinc concentration was assessed after mineralization in HF+ HClO4 mixture according to Crock and Severson (1980), while zinc forms extractable with DTPA were assayed with ASA as described by Lindsay and norveLL (1978). The soils did not show symptoms of zinc pollution. Its total, Zn concentrations ranged between 6.25 and 18.78 mg kg–1, while an average content was 11.16 mg kg–1. The analyzed soil samples contained zinc forms extractable with DTPA in amounts fluctuating between 0.32 and 2.6 mg kg–1. The highest concentrations of total and available zinc were noted in the surface horizons of the soils and in the horizons enriched with organic carbon.
A Transition in the Ni2+ Complex Structure from Six- to Four-Coordinate upon Formation of Ion Pair Species in Supercritical Water: An X-ray Absorption Fine Structure, Near-Infrared, and Molecular Dynamics Study

The coordination structure about Ni2+ in water at temperatures up to 525 °C was measured by the X-ray absorption fine structure (XAFS) technique. Solutions containing 0.2 m NiBr2 and 0.2 m NiBr2/0.8 m NaBr were explored at pressures up to 720 bar. For certain systems, both Ni and Br XAFS data were acquired and a global model was used to fit the two independent sets of XAFS data. These two independent measurements gave excellent agreement on the coordination structure of the Ni2+/Br- contact-ion pairing. The result is a complete picture of the coordination structure of the contact-ion pairing including the coordination numbers, distances for the water−ion and ion−ion associations, and also a high-quality measurement of the binding strength and amount of disorder (Debye−Waller factor and the anharmonicity) of the Ni2+/Br- association. The XAFS measurements strongly indicate a transitional change in the coordination of Ni2+ from the octahedral Ni2+(H2O)6 species at room temperature to the 4-coordinate struct.
The Selection of Thymus vulgaris Cultivars to Grow in Canada.

Abstract Five different cultivars of Thymus vulgaris originating from various geographical sources (Canada, Germany, former GDR and Spain) were organically cultivated in the fields in Quebec, Canada. The oils obtained through steam distillation of the dried leaves from each cultivar varied from 1.38% to 2.04%, depending on the cultivarused. The highest oil content was obtained from cv “Madrid” followed by “RH-1” and “Laval-1. ” More than 95% of the oil, with a total of approximately 22 components were identified in the samples. Oxygenated monoterpenes were the main group of constituents in all cultivars. Cultivar “Laval-1,” recentiy developed in Quebec, “Madrid” from Spain and “RH-1” from Germany were established to belong to thymol-chemotypes. Cultivar “QDLB” characterized by its content of thymol (approximately 39%), carvacrol (17%) and linalool (3.5%) in the oil, was also found to belong to “thymol”-chemotypes, while “RH-2” with carvacrol (40%) was found to be a carvacrol-chemotype. Though none of the c.
Calculating the annual input of organic matter to soil from measurements of total organic carbon and radiocarbon

Summary Measurements of total organic C, δ13C and δ14C are given for topsoils taken from six experimental sites in southern England. At each site, some of the samples were collected before and some after the thermonuclear tests of the early 1960s, so that pre- and post-bomb samples could be compared for radiocarbon content. The current Rothamsted model for the turnover of organic C in soil gave an acceptable fit to the data from five of the sites, apart from one aberrant radiocarbon measurement. The annual input of C to the topsoil was calculated for the five sites from these fits; the values obtained were: 0.15 t C ha−1 a−l for a site on silty clay loam, kept bare by hand weeding since 1870; 0.2 for unmanured spring barley growing on a sandy loam; 2.95 for a fertilized all-arable rotation on a loamy sand; 1.9 for the same fertilized all-arable rotation on a silty loam and 2.5 from this rotation on a calcareous silty loam. The corresponding values for Net Primary Production at the five sites were 0.15, 0.76, 5.16, 5.71 and 5.46 t C ha−1 a−l. In fitting the model to the radiocarbon data it was necessary to postulate that all these sites contained substantial quantities of biologically-inert organic matter, ranging from 2.2 to 10.0 t C ha−1.
Chemical and microbial investigation of drinking water sources from Kohat, Pakistan

Safe drinking water is one of the basic human rights and essential need for healthy life. In Pakistan, the quality of drinking water is not being managed properly and various studies provide evidence that most of the drinking-water supplies are contaminated. In this study, 60 drinking water samples from both urban and rural areas of district Kohat were analyzed chemically and microbiologically, to find out their suitability for drinking purposes. Fifty-four samples were collected from hand pumps, streams, tanks, wells and tube wells, at 15 main population zones selected. Six bottled water samples were also taken from the open market for analysis. These were investigated for various chemical parameters including sodium (Na+), potassium (K+), sulfate (SO42-), phosphate (PO4-3), nitrate (NO3-), and nitrite (NO2-), using standard methods of analysis recommended by American Public Health Association (APHA). Microbiological analysis was also carried out for Escherichia coli, to find out any fecal contamination. The results of parameters showed variations from the WHO and Pakistan standard values for drinking water (Table 1). The K+ and NO2− of 3%, SO42− of 7%, Na+ of 9% and NO3− of 16% samples were found to be higher than the WHO/Pakistan recommended values for drinking water. E. coli were found present in 70% of samples. From the results it was confirmed that majority of water sources are not safe to drink. Therefore, proper measures by the concerned authorities are required, to avoid health hazards. Key words: Drinking water, Kohat, chemical, Escherichia coli, American Public Health Association (APHA).
Sensitive and Facile Determination of Catechol and Hydroquinone Simultaneously Under Coexistence of Resorcinol with a Zn/Al Layered Double Hydroxide Film Modified Glassy Carbon Electrode

A stable dihydroxybenzene sensor was fabricated by electrochemical deposition of Zn/Al layered double hydroxide film on glassy carbon electrode (LDHf/GCE). The sensitive and facile electrochemical method for the simultaneous determination of catechol (CA) and hydroquinone (HQ) under coexistence of resorcinol (RE) has been achieved at the LDHf/GCE in phosphate buffer solution (pH 6.5). Under the optimized conditions, the differential pulse voltammetry response of the modified electrode to CA (or HQ) shows a linear concentration range of 0.6 μM to 6.0 mM (or 3.2 μM to 2.4 mM) with a correlation coefficient of 0.9987 (or 0.9992) and the calculated limit of detection is 0.1 μM (or 1.0 μM) at a signal-to-noise ratio of 3. In the presence of 50 μM isomer, the linear concentration ranges for CA and HQ are 3.0 μM to 1.5 mM and 12.0 μM to 0.8 mM, respectively. The detection limits are 1.2 μM and 9.0 μM. Further, the proposed method has been performed to successfully detect dihydroxybenzene isomers in analysis of real samples, such as water and tea.
Atomic and molecular adsorption on Ir(111)

The chemisorption of atomic (H, O, N, S, C), molecular (N2, CO, NO, NH3), and radical (CH3, OH, NOH) species on Ir(111) has been systematically studied. Self-consistent, periodic, density functional theory (DFT-GGA) calculations, using PW91 and RPBE functionals, have been used to determine preferred binding sites, chemisorbed structures, binding energies, vibrational frequencies, and the effect of surface relaxation for the above species at 0.25 ML surface coverage. The following order in binding energies from least to most strongly bound was determined: N2 < NH3 < NO < CH3 < CO < OH < H < NOH < O < N < S < C. A preference for 3-fold sites for the atomic adsorbates was observed, with the exception of atomic H, which prefers top sites. Molecular species showed a preference for top sites with the exception of NOH; this species preferred fcc sites. Surface relaxation had only a small effect on energetics in most cases. Calculated vibrational frequencies, in general, were in good agreement with experimental .
Estimation of L-glutaminase and L-asparaginase activities in soils by the indophenol method

Abstract A simple and rapid method was developed for determining L-glutaminase and L-asparaginase activities in soils. It involved colorimetric estimation of NH4 + released by the activity of L-glutaminase and L-asparaginase when soil was incubated with 0.25 M L-glutamine or L-asparagine in 0.1 M phosphate buffer (pH 7.6) and toluene used as a germicide. The indophenol method was applied to the assay of NH4 + for soil L-glutaminase and L-asparaginase activities. Color development in the indophenol method required one hour. The color development was stable for 2 d and was not appreciably affected by the presence of L-glutamine, L-glutamic acid, L-asparagine, and L-aspartic acid. In addition, no turbidity nor precipitate appeared in the presence of a high concentration (10 μg) of NH4 +-N. The L-glutaminase activity was estimated in three soil samples differing in pH, organic-C content, and land use. The L-glutaminase activity in the three soils ranged from 28 to 1,470 mU (10-9 mol min-1 g-1 of dry soil at 3.
Enhancement of Mechanical Properties of Emulsion Copolymers by Gradual Variation in Feed Composition. I: Effect of Particle Size in the Butyl Acrylate-Styrene System

Using a semicontinuous seeded emulsion polymerization process with a gradual variation in feed composition, butyl acrylate (BA)/styrene copolymers were obtained (variable composition copolymers, VCCs). BA seed particles of two different diameters were used to prepare copolymer materials with 50–85 wt. % styrene. In each reaction, cumulative copolymer composition was followed by 1H-NMR; with such data, a histogram showing the relative content of copolymer chains corresponding to each composition interval was built. The VCCs presented higher moduli and ultimate mechanostatical properties than their equivalent core-shell type polymers. The mechanical performance of VCC materials was explained considering the respective histograms.
Assessment of the impact of simulated acid rain and alkaline effluent discharge on pond biota with respect to larvae of Amphibian Rana tigrina

The metamorphosing tadpoles of amphibian Rana tigrina were grown in simulated environments of urban ponds perturbed or unperturbed by acid rain and alkaline wastewater. The impacts were studied in terms of behavioural responses, food consumption, growth, and computer‐aided mortality analysis. The studies reveal that the pH range of 6.5–9.0 recommended by regulatory agencies, such as United States Environmental Protection Agency for the protection of aquatic life in water bodies receiving acidic or alkaline pollutants, is only partially adequate; the upper limit of pH 9.0 appears too liberal and may need to be lowered. The pH standards for irrigation and domestic waters may also need revision.
Combustion mechanism of HMX

The combustion wave structure and thermal decomposition process of HMX were examined in order to elucidate the burning rate characteristics of HMX. The combustion wave can be divided into three zones: nonreactive solid-phase, surface reaction, and gas-phase reaction zones. Measurements with micro-thermocouples revealed that the heat flux produced in the surface reaction zone is approximately equal to the heat flux transferred back from the gas phase to the burning surface. Accordingly, the reaction process in the suface reaction and the gas phase zones plays a dominant role in the burning rate of HMX. The gas phase reaction zone consists of a two-stage reaction process: the first stage is the exothermic rapid reaction process between NO2 and aldchydes, and the second stage is the exothermic slow reaction process between NO and N2O and remaining fuel species. The luminous flame zone which is determined to be the second stage reaction process approaches rapidly the burning surface as pressure increases. However, the luminous flame reaction appears to be little responsible for the burning rate of HMX. Examinations of the quenched burning surface of HMX samples revealed that the burning surface melts and forms a noncrystallized intermediate material. The surface structure appears to be different from the structure of thermally degraded HMX samples which were obtained by a thermogravnmetric analysis.
Plastic Deformation of the γ Phase in Isotactic Polypropylene in Plane-Strain Compression

Morphology and deformation behavior of samples of iPP homopolymer containing exclusively γ-modification with only minor traces of α-crystals, obtained by isothermal crystallization at high pressure of 200 MPa, were investigated. It was found that the growth of γ-lamellae is initiated on “seeds” consisting of a spine of single α-lamella and several shorter α-lamellae branching at the angle of 80°. Epitaxial growth of γ-lamellae on (010) faces of α-parent and daughter lamellae of the seed leads to the formation of immature spherulites, which eventually fill completely the sample volume. The plane-strain and uniaxial compression tests demonstrated higher modulus, higher yield stress and flow stress, yet slightly lower ultimate strain of γ-iPP as compared to α−iPP. During plastic deformation numerous fine shear bands, initiated by the interlamellar shear of the amorphous layers start to develop already at the yield point. Their propagation across the sample causes a limited destruction of γ-lamellae oriented .