Miracle-dz/UniFAR-FTUs huggingface dataset:
Refuerzo de los contenidos relacionados con las clases prácticas mediante una estrategia de aprendizaje híbrido

Resumen. Esta experiencia se planteó con el fin de reforzar el interés de los alumnos por las clases prácticas, así como de mejorar los r esultados de evaluación tras haber constatado peores resultados en las pruebas escrita rel cionadas con los contenidos prácticos. Se elaboró una estrategia de aprendizaje híbrido combinando las sesiones de laboratorio con una serie de exámenes tipo test a l os que los alumnos accedían a través de la plataforma educativa de la UPV PoliformaT. Lo s objetivos de aprendizaje de las sesiones prácticas se capturaron en una batería de 50 preguntas que serviría tanto para crear los test formativos como el examen final. Se asociaron comentarios de apoyo y corrección a las preguntas para proporcionar el fee dback necesario para la formación del alumno. La experiencia se implementó durante lo s cursos 09-10, 10-11 y 11-12. La respuesta de los alumnos fue muy positiva ya que la participación en la actividad se mantuvo alrededor del 75%, a pesar de no ser obliga tori . Los resultados mejoraron sensiblemente puesto que la media de alumnos que no superaron la prueba práctica en los últimos tres cursos fue del 3% frente al 47% in icial, y cerca del 80% obtuvieron una calificación igual o superior a 9.
Fabrication and investigation of asymmetric current-voltage characteristics of a metal/Langmuir-Blodgett monolayer/metal structure

Metal/Langmuir–Blodgett monolayer/metal devices, where the monolayer consists of the dodecyloxyphenylcarbamate of 2‐bromo, 5(2’‐hydroxyethoxy) tetracyanoquinodimethan, a donor‐σ‐acceptor molecular system, have been constructed, and dc current‐voltage (I‐V) characteristics of these devices were recorded at room temperature. For biases of ±20 mV, the I‐V characteristics are linear, changing to a nonlinear form for higher voltages. This nonlinear characteristic exhibited a ln(I)∝V1/4 dependence for both positive and negative voltages up to ±1 V. For positive voltages >+2.0 V for as‐prepared devices and >+1.5 V for annealed devices, a ln(I)∝V3 dependence was observed, revealing a very large increase in current for small voltage changes. Such behavior was not observed for corresponding negative voltages, indicating rectification across a distance approximated by the length of an individual molecule.
Sorption Isosteric Heat Determination by Thermal Analysis and Sorption Isotherms

A procedure based on thermal analysis thermogravimetry (TG) and differential-scanning calorimetry (DSC) was examined to compute isosteric heat of sorption for water. DSC measurements on samples with different moisture content allowed determining enthalpy variations due to water vaporization. Thermogravimetries performed on the same samples enabled a link to be made between enthalpic measurements and weight losses and thus compute isosteric heats. The procedure was applied to cauliflower and potato starch. From equilibrium isotherms by applying the Clausius-Clapeyron equation, the isosteric heats of sorption were calculated. The comparison of the values obtained through both procedures showed a good agreement.
Ultrafast Photoinduced Solute−Solvent Electron Transfer: Configuration Dependence

Ultrafast photoinduced electron transfer between excited oxazine-1 (OX1) dye and electron donating solvents aniline (AN) and N,N-dimethylaniline (DMA) has been studied with the femtosecond fluorescence up-conversion technique. Ultrafast and highly nonexponential fluorescence decay of OX1 is observed in AN and DMA. The fastest component observed is about 60 fs in DMA and assigned to fluorescence quenching due to an electron transfer reaction. Fluorescence decays are observed to be strongly dependent on the wavelength of observation in DMA and moderately dependent in AN. The wavelength dependence is assigned to fluorescence from different configurations of OX1 and solvent molecules. The energy parameters for electron transfer are estimated and discussed.
Influence of pH value on PbS thin films prepared by electrodeposition

Abstract PbS thin films were prepared on indium–tin oxide transparent conductive film glass substrates using a constant voltage cathodic electrodeposition method. The as deposited thin films were characterised by XRD, AFM and Fourier transform infrared spectrometer. The influence of pH value on the phase compositions, surface morphologies and optical properties of the films has been particularly investigated. Results show that cubic PbS thin films with oriented growth along (111) and (200) direction can be obtained at pH=2·4, deposition voltage=3 V, deposition time=20 min and adding EDTA as a complexing agent. The as deposited thin films exhibit a dense surface morphology. The compressive stress and optical bandgap of the PbS thin films first decrease and then increase with increasing the pH value, and the bandgap of the thin films is calculated to be 0·38–0·39 eV.
Sol−Gel Transition of Niobium Oxide Nanosheet Colloids: Hierarchical Aspect of a Novel Macroscopic Property Appearing in Colloidally Dispersed States of Layered Niobate K4Nb6O17

Colloidal suspension of exfoliated layered niobate K4Nb6O17 in water exhibited a pH-induced sol−gel transition. Viscosity of the sols drastically increased on acidification, by which thick colloids were gelated. The viscosity change depended not on the acid species (H2SO4 or HCl) added to the sols but on the pH of the colloid. Basification of the acidified colloids caused a decrease in the viscosity to the initial value, indicating reversibility of the sol−gel transition. On the other hand, optical microscope observations indicated that orientationally ordered niobate nanosheets in the sols are gathered to form domains with the size of submillimeters, indicating that the gels were hierarchically constructed. The results suggested that the niobate nanosheets were stabilized with electrical repulsion among the protonated nanosheets, which were weakly aggregated in part, to form the hydrogels. Sedimentation of the nanosheets was observed in both the sols and gels by standing them for a long time, indicating .
Energy transfer from Bi3+ to Eu3+ triggers exceptional long-wavelength excitation band in ZnWO4:Bi3+, Eu3+ phosphors

Color-tunable phosphors of ZnWO4:x mol% Bi3+, 3 mol% Eu3+ (x = 0.5, 1, 2, 3, 4, 5) were prepared through a precipitation method and their luminescence properties were investigated as a function of Bi3+ concentration. The most intense 616 nm emission indicates that Eu3+ occupies the Zn2+ sites without inversion symmetry. The spectral overlap between the emission band of Bi3+ and the excitation band of Eu3+ supports the energy transfer from Bi3+ to Eu3+, which has been demonstrated to be of a resonant type via a dipole–dipole mechanism. Energy transfer from Bi3+ to Eu3+ triggers a long-wavelength excitation band at 340 nm originating from the Bi3+ 1S0 → 3P1 transition, which makes the phosphors fit for long-wavelength radiation. The decay curves of Bi3+ and Eu3+ emission were measured to understand the energy transfer processes. Interestingly, the critical concentration of Bi3+ for Eu3+ 616 nm emission in ZnWO4:Bi3+, Eu3+ was greatly increased by 400 times compared with that for Bi3+ 560 nm emission in ZnWO4:Bi3+. Color-tunable emission in ZnWO4:Bi3+, Eu3+ phosphors can be obtained by the modulation of the excitation wavelength and the ratio of Bi3+ and Eu3+. Our work provides a novel approach to develop phosphors which can be excited effectively under long-wavelength radiation.
Hydroxyapatite Characterized by XPS

Hydroxyapatite [Ca10(PO4)6(OH)2] is commonly used as a coating material on orthopedic and dental implants. Hydroxyapatite is the major inorganic component of bone and is biocompatible with tissues when used on implants. Quality control tests are critical for the proper calcium to phosphorous ratio and also for checking for the presence of impurities. Being an important surface analytical tool used in the field of biomaterials, x-ray photoelectron spectroscopy was used to examine as-received hydroxyapatite pressed powders.
Revisiting the seemingly straightforward hydrogen cyanide/hydrogen isocyanide isomerisation

Both HCN and HNC are prominent in the interstellar medium and may have significant roles in prebiotic chemistry. Considerable attention has, therefore, been accorded to the HCN ↔ CNH isomerisation, sometimes viewed as a prototypical unimolecular process. However, detailed analysis of the potential energy of the HCN/CNH system along its intrinsic reaction coordinate, in terms of the first and second derivatives of the energy, shows that this is not a straightforward proton transfer. It appears to involve two distinct transition regions, one in which the C–H bond breaks and the other in which the N–H forms. Between these regions is a transitory state, with all vibrational frequencies being real, in which the hydrogen is situated above the C–N bond and not directly associated with either the carbon or the nitrogen. In this state, the vibrational modes of the hydrogen are, respectively, approximately parallel and perpendicular to the C–N bond.
Phenomenology and Mechanism of Antifreeze Peptide Activity

o far it has not been explained convincingly how antifreeze peptides (AFP) prevent the growth of ice crystals. Step-pinning models as proposed by DeVries, Knight, and others imply a degree of permanent adsorption which it is difficult to reconcile with the observed concentration dependence of the hysteresis gap width. We propose a novel mechanism whereby the role of the antifreeze peptide is to increase the step energy (line tension) associated with the formation of 2D nuclei thereby reducing the nucleation temperature. This is achieved by fairly strong positive adsorption on the crystal faces with reduced adsorption close to a step leading to a negative line excess. The model predicts, in excellent agreement with experiment, a linear dependence of δT on log e c where δT is the freezing point lowering and c the peptide concentration. The magnitudes of the slopes lead to reasonable values of the negative line excess and to estimates of the peptide concentration at which the amount adsorbed should be significantly below the saturation level. They also lead to estimates of adsorption free energies for isolated molecules of order 10kT. These findings provide good circumstantial evidence that the proposed mechanism is at least partially correct. The concept of positive adsorption on crystal faces with negative adsorption close to steps may have important implications not just for AFP but for the general area of additive effects on crystal growth kinetics from melts.
Reducing methyl bromide emission with a high barrier plastic film and reduced dosage

A field experiment was conducted to study the effectiveness of a high-barrier plastic film (Hytibar) and reduced methyl bromide (MeBr) application dosages in decreasing MeBr emission from soil fumigation. Comparison was made with a conventional polyethylene film (PE) and a regular application rate. MeBr emission from nine small field plots was continuously measured with two replicated active chambers. Replicated soil cores were taken to a depth of 3 m to determine MeBr degradation and to obtain a mass balance. Results indicated that about 64% of applied MeBr was lost to atmospheric emission when covered with the PE tarp for at least 5 days. The emission was reduced to 37.5% when covered with the Hytibar tarp for 5 days. MeBr emission was virtually eliminated when covering with the Hytibar tarp for more than 10 days (only 1.1-3.2% loss). The low emission rate was verified from the degradation measurements which, along with the flux measurements, produced nearly 100% mass balance. Combined use of a high-barrier plastic film such as the Hytibar with reduced application rates can significantly reduce MeBr atmospheric emission while maintaining effective pest control efficacy.
Refined ettringite (Ca6Al2(SO4)3(OH)12∙26H2O) structure for quantitative X-ray diffraction analysis

A revised structure model of ettringite is presented, in order to provide quantitative X-ray diffraction (QXRD) of this mineral in cement pastes. The model is derived from two different existing structure models, both of which are suitable for restricted use but are inferior to the refined ettringite structure presented. In the first published ettringite structure proposed by Moore and Taylor [Acta Crystallogr. B 26, 386–393 (1970)], none of the 128 positions for H are given in the unit cell, which results in reduced scattering power for use of this model for quantification purposes. For the precise quantification of ettringite in samples together with anhydrous phases, the scattering factors of all atoms including the H positions are indispensable. The revised structure model is based on the data of Moore and Taylor, supplemented by the H positions determined by Berliner (Material Science of Concrete Special Volume, The Sydney Diamond Symposium, American Ceramic, Society, 1998, pp. 127–141) on the basis of a neutron diffraction structural investigation of deuterated ettringite at 20 K. Berliner’s (Material Science of Concrete Special Volume, The Sydney Diamond Symposium, American Ceramic Society, 1998, pp. 127–141) thermal parameter should not, however, be used, since a normal application is at room temperature. In order further to improve the structure model of ettringite, Rietveld refinement with the rigid body approach for OH and H2O molecules and SO4 tetrahedra was employed. The refined and improved ettringite structure model was tested for quantitative phase analysis by the determination of actual ettringite contents in mixtures with an internal standard. Synthesized and orientation-free prepared ettringite powders were investigated by X-ray powder diffraction analysis and quantified in four different blends with zircon. The quantification results with the new structure model demonstrate the superior quality of the revised ettringite structure.
Facile synthesis of halogenated carbon quantum dots as an important intermediate for surface modification

A simple and efficient method to prepare halogenated carbon quantum dots (CQDs) through solvent-thermal reaction was reported. The halogenated CQDs were synthesized and further surface functionalization with diamines was achieved based on the halogenated CQDs as intermediates. The halogenated CQDs provide an alternative approach for surface modification of CQDs.
Solar cells utilizing small molecular weight organic semiconductors

In this review, we focus on the field of organic photovoltaic cells based on small molecular weight materials. In particular, we discuss the physical processes that lead to photocurrent generation in organic solar cells, as well as the various architectures employed to optimize device performance. These include the donor–acceptor heterojunction for efficient exciton dissociation, the exciton blocking layer, the mixed or bulk heterojunction, and the stacked or tandem cell. We show how the choice of materials with known energy levels and absorption spectra affect device performance, particularly the open‐circuit voltage and short‐circuit current density. We also discuss the typical materials and growth techniques used to fabricate devices, as well as the issue of device stability, all of which are critical for the commercialization of low‐cost and high‐performance organic solar cells. Copyright © 2007 John Wiley & Sons, Ltd.
Characterization of bacteriocin 423 produced by Lactobacillus pentosus

Lactobacillus plantarum and Lactobacillus pentosus grouped into one protein profile cluster at r ~ 0.70, separate from Lactobacillus casei, Lactobacillus sake and Lactobacillus curvatus. Similar sugar fermentation reactions were recorded for representative strains of L. plantarum and L. pentosus. Representative strains, including the type of each species, were selected from the different protein profile clusters and their genetic relatedness determined by using numerical analysis of random amplified polymorphic DNA (RAPD)-PCR. The type strains of L. plantarum (ATCC 14917) and L. pentosus (NCFB 363) displayed different RAPD profiles and grouped into two independent clusters, well separated from L. casei, L. curvatus and L. sake. Numerical analysis of RAPD-PCR proved a reliable and accurate method to distinguish between strains of L. plantarum and L. pentosus. The species Lactobacillus plantarum consists of a genetically heterogeneous collection of strains that are difficult to differentiate from Lactobacillus pentosus by simple physiological tests [3, 9]. Pentose-fermenting strains of streptobacteria were originally classified as L. pentosus [8]. However, the name L. pentosus (Fred, Peterson and Anderson) was not listed in the Approved Lists of Bacterial Names [12] and strains that fermented pentose sugars were classified as L. plantarum [9]. Dellaglio et al. [3] were the first to show that a group of pentosefermenting strains of L. plantarum, some of which were originally classified as L. pentosus by Fred et al. [8], are genotypically not closely related to L. plantarum. Extensive DNA-DNA hybridization studies [13] confirmed the results reported by Dellaglio et al. [4] and the name L. pentosus was revived. DNA similarity studies are the most reliable method to differentiate L. pentosus from L. plantarum. However, DNA-DNA hybridizations are tedious to perform and often involves the use of radioactive nucleotides. RAPD-PCR analysis, on the other hand, is a safe, rapid and Stellenbosch University http://scholar.sun.ac.za
The Formation of ? and ?'-Al2O3 from the Dehydration of Tohdite 5Al2O3H2O

The dehydration of tohdite 5Al2O3·H2O is well followed by means of the single-crystal electron-diffraction patterns, the X-ray powder patterns, differential thermal analysis, and the measurement of the density. Thermogravimetric measurements were also performed, both under a normal atmosphere and in a high vacuum. Just after the dehydration, an unstable intermediate phase was obtained; it was denoted as κ′-Al2O3(from tohdite). The mechanism of the transformation series: tohdite→κ′-Al2O3→κ-Al2O3→α-Al2O3 was discussed, and some basic data to serve as clues to elucidate the crystal structure of κ′- and κ-Al2O3 were obtained.
Polyaniline-decorated cellulose aerogel nanocomposite with strong interfacial adhesion and enhanced photocatalytic activity

Cellulose aerogel has attracted considerable attention due to its high surface area and the added advantages of being cost-effective and environmentally benign. It has been applied as supporting material for noble metal nanoparticle catalysts to prevent their agglomeration. In this paper, we have demonstrated a facile method to prepare polyaniline (PANI)-decorated cellulose aerogel via a dissolve/regeneration route using ionic liquid as solvent. Cellulose aerogel acted as a supporting material for PANI nanoparticles to prevent their agglomeration as confirmed by scanning electron microscopy. The strong interfacial interaction between PANI and cellulose aerogel was verified by Fourier transform infrared spectroscopy, differential scanning calorimetry, thermal gravimetric analysis and X-ray diffraction. PANI-cellulose aerogel exhibited excellent photocatalytic activity towards the degradation of methylene blue. The degradation efficiency reached 95% after 2 h. The approach promotes the use of renewable natural resources to prepare a variety of nanofibrillated cellulose-supported nanocomposites for catalysis, sensors, and other potential applications.
Recent advances in polybenzimidazole/phosphoric acid membranes for high-temperature fuel cells

Proton exchange membrane fuel cells are one of the most promising technologies for sustainable power generation in the future. In particular, high-temperature proton exchange membrane fuel cells (HT-PEMFCs) offer several advantages such as increased kinetics, reduced catalyst poisoning and better heat management. One of the essential components of a HT-PEMFC is the proton exchange membrane, which has to possess good proton conductivity as well as stability and durability at the required operating temperatures. Amongst the various membrane candidates, phosphoric acid-impregnated polybenzimidazole-type polymer membranes (PBI/PA) are considered the most mature and some of the most promising, providing the necessary characteristics for good performance in HT-PEMFCs. This review aims to examine the recent advances made in the understanding and fabrication of PBI/PA membranes, and offers a perspective on the future and prospects of deployment of this technology in the fuel cell market. © 2014 Society of Chemical Industry
A new method of auto‐separating thermally stimulated current

A new method of auto‐separating thermally stimulated current is presented. This method allows an easy, accurate, and quick resolution of the overall thermally stimulated current (TSC) spectrum. By comparing the individual TSC curves, plotted by microcomputer, with those obtained by the peak cleaning technique, it is believed that this method is a viable alternative to the traditional complicated test methods, and may find wide use in the separation of thermally stimulated current curves.
Sufficient condition for monotonic electron density decay in many‐electron systems

For one-electron systems, if the external potential increases monotonically from the nucleus the ground-state electron density is monotonic. For two-electron densities, similar results hold for the Kohn–Sham potential. Similarly, for many-electron systems monotonicity of the sum of the Kohn–Sham potentials and “Pauli potential” (from the correction to the Weisacker kinetic energy) is sufficient for monotonic decay of the electron density. © 2003 Wiley Periodicals, Inc. Int J Quantum Chem, 2003
Trace Determination of Copper in Foodstuffs and Biological Samples

Abstract A new heterocyclic bis-azo dye, 2,6-bis(4-sulfo-1-hydroxy-2-naphthylazo)pyridine, sodium salt (PBS), has been prepared and developed as a sensitive and highly selective chromogenic reagent for spectrophotometric determination of copper. The reagent is found to give a 1:2 (M/L) complex at pH 6.0. Beer's law is followed up to 1.8 ppm with an optimal concentration range between 0.2 and 1.4 ppm. Sandell's sensitivity of the color reaction was calculated to be 0.0013 µg cm−2 with molar absorptivity of 4.9 × 104 l·mol−1 cm−1 at 572 nm. The interfering effects of various cations and anions were also studied. The proposed method was successfully applied to the determination of copper(II) in milk, tea samples, cereals, and legume grains consumed by the Indian vegetarians and in some biological samples. Comparison of the results with those obtained using an atomic absorption spectrophotometer tested the validity of the method.
Composition and Antimicrobial Activity of Ammoides pusilla (Brot.) Breistr. Essential Oil

Abstract The essential oil of the aerial parts of Ammoides pusilla was analyzed using both GC and GC/MS. The results revealing no less than 46 constituents among which thymol (44.5%), γ-terpinene (32.9%) and p-eymene (13.5%) were the most abundant. The antimicrobial activity of A. pusilla oil was studied using the agar diffusion test on eight strains of bacteria, and against fungus and yeast. The two-fold oil solution showed an important antimicrobial activity against Serratia marcescens, Salmonella enteritidis, Escherichia coli (ATCC 25922), Pseudomonas aeruginosa (ATCC 27853), Staphyhloccus aureus (ATCC 25923), Klebsiella pneumoniae, Pseudomonas syringae pv. syringae, Pseudomonas syringae pv. mosprunorum, Aspergillus niger and Candida albicans.