Miracle-dz/UniFAR-FTUs huggingface dataset:
Conceptual Questions and Challenge Problems

The JCE Internet Conceptual Question and Challenge Problem Web site is a source of questions and problems that can be used in teaching and assessing conceptual understanding and problem solving in chemistry. Here you can find a library of free-response and multiple-choice conceptual questions and challenge problems, tips for writing these questions and problems, and a discussion of types of conceptual questions. This site is intended to be a means of sharing conceptual questions and challenge problems among chemical educators. The Conceptual Questions and Challenge Problems Web site can be found here.
Increase in the Nitrogen Content of Soil by the Introduction of Earthworms into Soil

The contribution of an earthworm species (Amynthas vittatus) to the increase of the nitrogen content of soil was examined. Three specimens of adult earthworms were introduced into 300 g of soil (Gray Lowland soil, silty clay) supplemented with 1% carboxymethyl cellulose in a container and incubated for 32 d at 22°C in the dark. The contents of total-N, NH4-N and NO3-N, and the population of aerobic nitrogen-fixing bacteria in soil significantly increased after incubation with the earthworms, while the natural abundance of 15N (δ15N) in soil decreased. The amount of nitrogen in the earthworms did not decrease during the incubation in the microcosm. Both acetylene reduction activity of the microcosm and incorporation of 15N to soil from atmospheric 15N2 were significantly enhanced by the introduction of the earthworms into soil, though the observed increment of nitrogen in soil was much higher than the estimated one based on the nitrogen-fixing activity. The results obtained in the present study indicated that the earthworms increased the nitrogen content of soil, presumably due to the enhancement of the nitrogen-fixing activity of the soil from the microcosm by the earthworms.
Effect of Nitrate/Ammonium Ratios on Growth, Root Morphology and Nutrient Elements Uptake of Watermelon (Citrullus Lanatus) Seedlings

Nitrogen is taken up by most plant species in the form of nitrate and ammonium. The objective of this study was to investigate the effect of different nitrogen forms on the growth of watermelon seedlings. Plants were grown in hydroponic culture with five nitrate (NO3−)/ammonium (NH4+) ratios (100/0, 75/25, 50/50, 25/75, 0/100). When the proportion of NH4+ was increased, the leaf number, leaf area, shoot height, net photosynthesis, biomass, and root growth were significantly decreased. Higher concentrations of nitrogen (N) and phosphorus (P) were observed when plants were supplied with mixed NO3− and NH4+ compared to NO3− or NH4+ alone, whereas the concentrations of potassium (K), calcium (Ca), and magnesium (Mg) were decreased with increasing NH4+. The microelements concentrations were generally increased with more NH4+ added. In addition, plants fed with higher NO3−/NH4+ ratios resulted in more minerals accumulation.
Fabrication of Metal Nanowires by Electroless Plating of DNA

For the purpose of the fabrication of nanowires, the metallization of double-stranded DNA by the selective electroless plating method was investigated. Cis-platin was bound to template DNA molecules and reduced to platinum which can catalyze subsequent silver metal deposition. We have found that when DNA-amphiphile polyion complex monolayer, which was formed at the air-water interface, was transferred to a glass substrate by using the Langmuir-Blodgett (LB) method, DNA molecules could be immobilized and stretched on the glass substrate. The DNA molecules combined with the platinum clusters was also stretched and immobilized on a glass substrate by using the LB method. The electroless plating of the platinum-bound DNA molecules immobilized on the substrate by reduction of silver ion gave uniform silver nanowires (c.a. 50nm in width and height) along the stretched DNA structures. On the contrary, the electroless plating of DNA molecules without the catalyst provided inhomogeneous silver deposition. [DOI: 10.1380/ejssnt.2005. 82]
Porous aromatic frameworks: Synthesis, structure and functions

The creation of ultrahigh surface area materials are of great interest in academia and industry. In recent years, porous aromatic frameworks (PAF) were discovered and their porosity and properties were also explored. They are characterized by a rigid aromatic open-framework structure constructed by covalent bonds. The building block design, network formation method and relationship between functions and secondary building units were compiled in this highlight. In addition, advantages and challenges of predicted PAF derivatives were also discussed.
Structural position and oxidation state of nickel in SrTiO3

The properties of Ni-doped strontium titanate are studied using X-ray diffraction and XAFS spectroscopy. It is shown that regardless of the preparation conditions, the SrTi1-xNixO3 solid solution and the NiTiO3 phase are the most stable phases which can coexist. According to the EXAFS data, in the single-phase sample of SrTi0.97Ni0. 03O3, the Ni atoms substitute for the Ti ones and are on-center. The distortion of the oxygen octahedra is not observed. The XANES spectra analysis shows that the oxidation state of nickel in NiTiO3 is 2+, and in the SrTi1-xNixO3 solid solution it is close to 4+. It is shown that the strongest light absorption in doped samples is associated with the presence of tetravalent nickel in the SrTi1-xNixO3 solid solution. This doping seems the most promising one for solar energy converters that exploit the bulk photovoltaic effect.
A VUV Photoionization Aerosol Time-of-Flight Mass Spectrometer with a RF-Powered VUV Lamp for Laboratory-Based Organic Aerosol Measurements

A vacuum ultraviolet (VUV) photoionization aerosol time-of-flight mass spectrometer (VUV-ATOFMS) has been developed for real-time, quantitative chemical analysis of organic particles in laboratory environments. A nozzle of ∼ 0.12 mm orifice combined with an aerodynamic lens assembly and a three stage differential pumping system is used to sample particles at atmospheric pressure. The particles are vaporized on a thermal heater, and then the nascent vapor is photoionized by light generated with a RF-powered VUV lamp. A 0.41 V/cm electric field is used to drive the ions from the ionization region into the ion extraction region where a positive electric pulse repels the ions into a reflectron mass spectrometer. The mass resolution of the spectrometer is ∼ 350 and the detection limit is ∼ 400 μ m 3 . The signal intensities observed are linear with the mass concentration of aerosols. Oleic acid particles are well quantified with an uncertainty of 15% in mass concentrations ranging from 3.9 mg/m 3 to 392 mg/m 3 . The VUV-ATOFMS has substantial potential for the use in laboratory investigations on organic aerosol chemistry.
Synthesis and characterization of polyimide/silica hybrid waveguide materials via sol-gel technique

Polyimide (PI) /silica (SiO2) nanohybrid composite waveguide films prepared from Pyromellitic dianhydride (PMDA), 2,2-Bis(3-amino-4-hydroxyphenyl)hexafluoropropane(6FHP) , nonlinear optical (NLO) molecule, coupling agent APTES and hydrolysate of TEOS via sol-gel process and thermal imidization. The silica content in the hybrid waveguide films varied from 0 to 22.5/wt%. The PI hybrids prepared were characterized by IR, thermogravimetric analysis (TGA), X-ray diffraction (XRD), scanning electron microscopy (SEM),etc. They exhibit fair good optical transparency. The SiO2 phase is well dispersed in the polymer matrix. DSC and TGA results show that these hybrid waveguide materials have excellent thermal stability.
A facile method for the synthesis of highly monodisperse silica@gold@silica core–shell–shell particles and their use in the fabrication of three-dimensional metallodielectric photonic crystals

We report here (i) a method for the synthesis of highly monodisperse silica@gold@silica core–shell–shell (CSS) particles (<6% deviation in size) with coherent outer silica shells of directly tunable thickness and porosity, (ii) the fabrication of three unit cell thick (12 layers) metallodielectric photonic crystals (MDPCs) from these particles and (iii) their angle-resolved optical reflectance properties demonstrating the influence of dielectric contrast modification and metal plasmonic modes on photonic band gap properties. The synthetic route presented describes the use of two alkylamines, the first, 1,3-diaminopropane (DAP), as a surface manipulating agent, and the second, N,N-dimethyldodecylamine (DMDDA), as a catalyst for the outer silica shell formation, for the reproducible synthesis of monodisperse CSS particles avoiding the formation of the unwanted side-products such as core-free silica particles and aggregated particles with multiple cores. A rational chemical reaction mechanism describing the pathways involved in the formation of coherent silica shells, demonstrating the roles of both the amines, is proposed. The creation of partial wetting/de-wetting sites on gold nanoparticle surfaces by the adsorbed DAP molecules, the surface silanol modification by DAP and the slow hydrolysis–condensation reactions catalyzed by DMDDA are found to be responsible for the selective deposition of silica (heterogeneous nucleation) only onto the existing silica@gold core–shell particles leading to the formation of monodisperse CSS particles. The optical reflectance of the MDPC formed from these CSS particles shows an angle-dependent blue-shift that perfectly obeys the Bragg–Snell law predictions for photonic crystals. The dielectric contrast modification and the possible metal plasmonic mode-coupling in the MDPC also result in a high gap-to-midgap ratio (23%) as compared to the PC made of neat silica particles of comparable size (9%).
Facile diameter control of vertically aligned, narrow single-walled carbon nanotubes

Here, we report a diameter-controlled synthesis of vertically aligned (VA) single-walled carbon nanotubes (SWNTs) via catalytic chemical vapor deposition (CVD), enabled by ultrathin iron (Fe) catalysts on alumina (Al2O3) and low acetylene (C2H2) partial pressure. A long forest of sub-3-nm SWNTs up to one millimeter in height could be obtained without addition of hydrogen or moisture, and precise control of the SWNT diameters was successfully established. Key for the efficient growth of such arrays of narrow SWNTs is threefold: (a) growth temperature low enough to suppress catalyst agglomeration and Ostwald ripening, (b) C2H2 partial pressure below a certain level to extend the catalyst lifetime, and (c) size-matching at nanometer scale between Fe catalyst seeds and Al2O3 support asperities in order to mitigate the surface migration and undesirable enlargement of catalyst particles. Our findings can contribute to the facile achievement of uniform, dense arrays of high quality VA-SWNTs with narrow diameter distributions desirable for advanced nanofiltration and electronic applications.
Receptor Flexibility in Ligand Docking and Virtual Screening

It is now well recognized that receptor flexibility plays an important role in protein-ligand binding. This flexibility can concern not only the mobility and reorganization of side chains in the binding site but also conformational changes of the whole molecule, which makes modeling of ligand docking more challenging. We give here an overview of existing approaches to treating receptor flexibility in protein-ligand docking and virtual screening that range from approximate to more accurate methods, including the use of normal modes in accounting for global conformational changes of the receptor or the use of more precise force fields. In addition, we describe recent successful applications of such approaches that have led to the design or discovery of new lead compounds with therapeutic relevance. These new developments in protein-ligand docking and screening are increasingly applied for better prediction of binding affinities. In view of the ever-increasing power of machine computation, a better accounting of the flexibility of the receptor is justified in order to improve the prediction of ligand binding in the search for new drug candidates by virtual screening.
A hybrid sensorless induction motor control strategy for high performance drive applications

This paper presents a sensorless induction motor drive scheme comprising a model-based speed estimator for dynamic performance and a rotor slot harmonic estimator for speed accuracy. The slot harmonic speed estimate is used to tune the machine model, providing speed-holding accuracy comparable to a sensored drive fitted with a 10000 line encoder sampled every 0.01 sec. System performance is evaluated over the full speed and load range, with a view to its use in multi-motor, speed-synchronized drives, an application typically requiring the performance of an encodered system.
Novel zwitterionic deep eutectic solvents from trimethylglycine and carboxylic acids: characterization of their properties and their toxicity

We report the preparation and the study of the properties of novel deep eutectic solvents (DESs) formed by zwitterionic trimethylglicine and high melting point carboxylic acids. These zwitterionic DESs are liquid at room temperature or at temperatures lower than 70 °C and do not have chloride or any metal ions in their composition. These media were characterized in terms of their viscosity, conductivity, density, ionicity (via Walden plots), surface tension and thermal stability. The values observed are similar to other typical DESs, and the mixtures resulted in “poor ionic liquids” in the Walden plot. The values obtained could be correlated to the carboxylic acids' structures. The toxicity of the pure mixtures was evaluated via an FTIR-bioassay on Saccharomyces cerevisiae cells. This method allowed us to define the action of these media as dehydrating agents on eukaryotic model cells, with a mechanism highly correlated with CaCl2, a well-known dehydrating agent. The Glycolic acid/Trimethylglicine eutectic system can be considered a NADES (Natural Deep Eutectic Solvent) and resulted as the best in our set for many reasons. It is formed by natural, renewable, eco-compatible and cheap compounds (both the molecules can be derived from sugar beet) and it can be used in many applications because it has a low melting point (−36 °C) and it is colorless, and therefore suitable for spectroscopic measurements. For these reasons, the solubility of some α-L-amino acids was investigated in this DES, showing a good solubility for aromatic amino acids, which are normally scarcely soluble in water.
Raman Chirped Adiabatic Passage: a New Method for Selective Excitation of High Vibrational States

It is demonstrated that efficient and high vibrational excitation can be achieved using non-resonant stimulated Raman transitions for subsequent step by step climbing of vibrational levels. The pump laser (or both the pump and Stokes laser) frequency are to be swept in such a way that the frequency difference sweeping allows molecular anharmonicities of the final states to be matched. It is shown that amplitudes of successive Raman transitions can be quantitatively described with the help of the effective Raman two-level systems. This selective scheme of vibrational excitation, called Raman chirped adiabatic passage (RCAP), should be useful in controlling excited-state populations and chemical reactions. The limitations of another well known adiabatic scheme of population transfer, stimulated Raman adiabatic passage (STIRAP), are outlined and it is shown that RCAP is a complementary method to STIRAP. RCAP should be useful for selective excitation of highly polarizable symmetric bonds such as metal–metal bonds. © 1997 John Wiley & Sons, Ltd.
LiCoO2–MgO coaxial fibers: co-electrospun fabrication, characterization and electrochemical properties

Core–shell LiCoO2–MgO fibers for use as lithium ion batteries were prepared by co-electrospinning combined with a sol-gel process. The rheological properties and viscosity of the spinnable sols, and the pressures of the two sols during the co-electrospinning process were investigated, which had an obvious effect on the diameter and shell thickness of the core–shell fibers. The fibers had a highly crystalline LiCoO2 core composed of partially oriented nanocrystals and a poorly crystalline MgO shell. The cyclic voltammogram (CV) experiments indicated that the coaxial fiber electrode exhibited excellent reversibility, smaller impedance growth and preferable electrochemical properties with obvious improvement of cyclability compared to bare LiCoO2 fiber electrodes.
Solvation characteristics of pressurized hot water and its use in chromatography

The influence of temperature in the range 75–180 °C on the solvation properties of pressurized water is studied by use of chromatography for a varied group of compounds on a porous polymer sorbent PLRP-S 100. The solvation parameter model is used as the basis of a quantitative comparison of the influence of temperature and solvent composition variation on the elution strength and selectivity of the mobile phase. The predominant influence of increasing temperature on the solvation properties of water is to reduce its cohesion and capacity for hydrogen-bond interactions. Even at 180 °C, however, hot water retains sufficient of its room temperature properties to remain a relatively weak eluting solvent in reversed-phase chromatography compared with aqueous mixtures of miscible organic solvents. Changes in selectivity accompanying composition variation for acetonitrile, methanol, and propan-2-ol are quantitatively different from those demonstrated for temperature variation of pressurized water, indicating that for method development the two processes are complementary rather than redundant.
Intensified Effect of Reduced Pressure on the Foam Fractionation Process of Bovine Serum Albumin

A novel method to intensify the foam fractionation process by operating the column under reduced pressure was reported in this paper. It was found that a poorer foam stability, a bigger mean bubble size and a wider bubble size distribution in the foam layer, a less upward liquid flux and volumetric liquid fraction at the top of the foam layer, and a higher enrichment ratio but a lower mass recovery of the foam fractionation process were obtained under reduced pressures compared to the ones under atmospheric pressure. The most important effect of the reduced pressure on the foam layer during the foam fractionation process is the encouraged bubble coalescence process which was exhibited by those unusual foam properties discussed above. The limitations of this new method were also discussed.
Pyrolysis-GC-MS characterization of forage materials

Pyrolysis-GC-MS pyrograms from a series of alfalfa preparations, a ggrass, an angiosperm wood, a cellulose and an arabinoxylan were obtained under pyrolytic conditions optimal for aromatic components of plant cell walls. Approximately 130 pyrolytic fragments have been identified
The method of determination of sizes, rise velocities and composition of aggregates floating to froth layer

The method of analysis of bubble-solids aggregates flow inside a flotation cell, beneath froth layer, is presented. Size, shape, rise velocity and number of the aggregates were determined using a device called the Luba tube. The experiments were carried out at 25 o C in a 5.2 m diameter separation vessel used in a 100 tones per hour field pilot plant for oilsands processing. It was found that bitumen was transported to the froth layer in the form of irregular particles attached to air bubbles. A wide range of the bitumen –air aggregate sizes (from 0.13 mm to 2.84 mm) was observed with an average Feret diameter, i.e. an equivalent circular diameter of 0.68±0.35 mm. Under steady state conditions the average aggregate rise velocity was 6.8±1.8 cm/s with velocities varying from 3.0 to 12.6 cm/s. Mass of bitumen contained in a bitumen–air aggregate was determined on the basis of the experimental values of the aggregate size and rise velocity and the relationships describing velocity of unloaded contaminated (Model A) and clean (Model B) bubbles. It was found that mass of bitumen contained in a bubble-bitumen aggregate was of an order from 10 -6 to 10 -4 g depending on the aggregate dimension and the model used. The evaluated equivalent diameters of bitumen particle and air bubble making-up a bitumen–air aggregate were of a similar magnitude within ca. 0.2-1.2 mm range.
Stretch and the adiabatic burning velocity of methane- and propane-air flames

Results of measured adiabatic burning velocities of methane- and propane-air premixed laminar flames are presented, as obtained by the Heat Flux method. A comparison is made with results of the Counterflow method. The effect on the Counterflow method results of a non-linear instead of a linear correction for stretch is estimated. With a non-linear correction the agreement between both methods is good. It can be concluded that non-linear correction for stretch on the results of the Counterflow method is necessary in general. However, its effect may vary with varying fuel gas.
Isolated modes and percolation in the lattice dynamics of (Be, Zn)Se

The mixed II–VI semiconductor Zn1 − x Be x Se possesses non-trivial vibration properties, because its two constituent compounds, ZnSe and BeSe, show very different degrees of covalency and hence high elastic contrast. An anomalous Be–Se vibration line has been observed, mostly at intermediate Be content, in the Raman spectra of thin (Zn,Be)Se films. In order to explain the microscopic origin and detailed composition of these lines, a first-principles calculation of the vibration frequencies in a mixed crystal has been performed, with the frozen-phonon technique and supercell setup within the density functional theory, using the SIESTA method, which uses norm-conserving pseudopotentials and strictly localized numerical basis functions. The calculations confirmed an earlier assumption that the anomalous Be–Se line appears due to the formation of continuous chains of a more rigid Be-rich pseudo-continuous phase formed within the more soft Zn-rich host region on crossing the Be–Se bond percolation threshold (x ∼ 0.19). Different local deformations in percolated and non-percolated regions affect the interatomic elastic interactions and split the corresponding vibration lines. Besides confirming the percolation model qualitatively, the calculation provides details concerning the vibration patterns in different phonon modes.