Fast Initial Stage Research Articles

Dissolution of Sessile Microdroplets of Electrolyte and Graphene Oxide Solutions in an Ouzo System.

Manipulating the way a droplet shrinks by evaporation or dissolution is an effective approach for assembling dissolved nanomaterials. In this work, we investigate the dissolution dynamics of a submicroliter sessile droplet of electrolyte aqueous solution and of graphene oxide suspension immersed in a binary mixture of solvents, among which one is miscible and the other is immiscible with water (i.e., an Ouzo system). Our measurements reveal an interesting two-stage dissolution of the droplet: a fast initial stage and a slow second stage. The duration of the first stage is longer at a lower temperature, leading to a counterintuitive result that the dissolution completes faster at reduced temperature. The presence of graphene oxide in the droplet dramatically alters the dissolution dynamics, possibly due to its enrichment at the droplet surface. The finding from this work provides useful guideline for designing conditions to pack nanomaterials by dissolving droplets, especially for those temperature sensitive components.

Mechanism of Methylene Blue adsorption on hybrid laponite-multi-walled carbon nanotube particles

The kinetics of adsorption and parameters of equilibrium adsorption of Methylene Blue (MB) on hybrid laponite-multi-walled carbon nanotube (NT) particles in aqueous suspensions were determined. The laponite platelets were used in order to facilitate disaggregation of NTs in aqueous suspensions and enhance the adsorption capacity of hybrid particles for MB. Experiments were performed at room temperature (298K), and the laponite/NT ratio (Xl) was varied in the range of 0–0.5. For elucidation of the mechanism of MB adsorption on hybrid particles, the electrical conductivity of the system as well as the electrokinetic potential of laponite-NT hybrid particles were measured. Three different stages in the kinetics of adsorption of MB on the surface of NTs or hybrid laponite-NT particles were discovered to be a fast initial stage I (adsorption time t=0–10min), a slower intermediate stage II (up to t=120min) and a long-lasting final stage III (up to t=24hr). The presence of these stages was explained accounting for different types of interactions between MB and adsorbent particles, as well as for the changes in the structure of aggregates of NT particles and the long-range processes of restructuring of laponite platelets on the surface of NTs. The analysis of experimental data on specific surface area versus the value of Xl evidenced in favor of the model with linear contacts between rigid laponite platelets and NTs. It was also concluded that electrostatic interactions control the first stage of adsorption at low MB concentrations.

PH-responsive ordered mesoporous carbons for controlled ibuprofen release

Nitrogen-doped ordered mesoporous carbons (N-OMCs) were synthesized by nanocasting using SBA-15 silica as template and two polyaramide precursors: m-aminobenzoic acid (MABA) and p-aminobenzoic acid (PABA). The structure of the resulting materials was greatly influenced by the precursor used, since MABA yielded a CMK-3 type OMC, while PABA gave a CMK-5 one. Both carbons displayed differences in texture, structure and surface chemistry. These were reflected in a different pH dependence of ibuprofen adsorption and release. Although the two carbons exhibited a good behavior as drug adsorbents, the PABA-derived one was more efficient, in terms of drug delivery, than the carbon prepared from MABA, which was associated to the surface chemical nature and tube-like structure of the former. The desorption kinetics of both carbons presented an initial fast stage, reach the maximum ibuprofen delivery in 300min and the maximum drug concentration level remained constant up to 24h. Moreover, the carbons also exhibited a specific response toward the pH, which was associated to their different surface chemical and textural properties. This pH-responsive property was more evident for the PABA derived carbon, which allowed a sustained drug level of 10wt.% at pH=2 and of almost 40wt.% at pH=7.4.

Dynamics of spatial coherence and momentum distribution of polaritons in a semiconductor microcavity under conditions of Bose-Einstein condensation

The dynamics of spatial coherence and momentum distribution of polaritons in the regime of Bose-Einstein condensation in a GaAs microcavity with embedded quantum wells under nonresonant excitation with picosecond laser pulses are investigated. It is shown that the establishment of the condensate coherence is accompanied by narrowing of the polariton momentum distribution. At the same time, at sufficiently high excitation densities, there is significant qualitative discrepancy between the dynamic behavior of the width of the polariton momentum distribution determined from direct measurements and that calculated from the spatial distribution of coherence. This discrepancy is observed at the fast initial stage of the polariton system kinetics and, apparently, results from the strong spatial nonuniformity of the phase of the condensate wavefunction, which equilibrates on a much longer time scale.

Microstructure Variation of Pellets Containing Ferrous Dust during Carbonation Consolidation

The carbonation and microstructure characteristics of pellets containing ferrous dusts were investigated during carbonation consolidation at different reaction temperatures and CO2 partial pressures. The results indicated that green pellets had loose and network supporting structure with initial strength, and large cracks and pores existed in the pellets. The carbonation reaction was controlled by interfacial chemical reaction at the initial fast stage, which limited diffusion and thus caused the reaction rate to decrease. With increasing reaction temperature and CO2 partial pressure, the conversion rates of CaO and the number of microcrystalline CaCO3 particles increased, and the volume expansion of CaCO3 led to a decrease in the open porosity, average pore size and specific surface area of the pellets. Micro-pores were occluded, and the number of smaller pores (diameter less than 50 nm) increased, thereby resulting in the more compact and uniform structure of carbonated pellets. Simultaneously, the dense structure prevented CO2 diffusion into the product layer, affecting the increase in carbonation conversion rate.

Bioactive Glass Nanoparticles as a New Delivery System for Sustained 5‐Fluorouracil Release: Characterization and Evaluation of Drug Release Mechanism

Bioactive glass nanoparticles were synthesized and tested for the first time as a new delivery system for sustained 5‐fluorouracil (5‐FU) release. They were characterized by TEM, DTA, TGA, and FT‐IR. The porosity % and specific surface area of glass nanoparticles were 85.59% and 378.36 m2/g, respectively. The in vitro bioactivity evaluation confirmed that bioactive glass disks prepared from these nanoparticles could induce hydroxyapatite layer over their surfaces in simulated body fluid. The in vitro drug release experiment indicated that glass nanoparticles could serve as long‐term local delivery vehicles for sustained 5‐FU release. The release profile of 5‐FU showed an initial fast release stage followed by a second stage of slower release. The initial burst release of 5‐FU in the first day was about 23% (28.92 mg·L−1) of the total amount of loaded 5‐FU, while the final cumulative percentage of the 5‐FU released after 32 days was about 45.6% (57.31 mg·L−1) of the total amount of loaded 5‐FU. The application of different mathematical models indicated that 5‐FU was released by diffusion controlled mechanism and suggested that its release rate was dependent on glass particles dissolution, changes of surface area as well as diameter of glass particles, and concentration of loaded drug.

Correlation between the channel‐bottom light intensity and channel‐base current of a rocket‐triggered lightning flash

AbstractThe correlations between channel‐bottom light intensity and channel‐base current of all discharge processes of a rocket‐and‐wire‐triggered lightning flash, including initial continuous current (ICC) pulses, ICC pulse background continuing current (IBCC), return strokes, M components, and M component background continuing currents (MBCC), have been investigated. A rough linear correlation has been found between the current squared and the light intensity for ICC pulses (including peaks of different ICC pulses), IBCC, the initial rising stage (IRS) of return strokes (including current peaks of different strokes), and MBCC. The slopes of the correlation regression lines for the current squared versus light intensity of ICC pulses and IBCC are similar, but they are about 2–3 times smaller than the slopes of MBCC and 5–7 times smaller than the slopes of the IRS of return strokes. In contrast, a rough linear correlation has been found between the current and the light intensity for the later slow decay stage of return strokes and for the M components. The slopes of the correlation regression lines of the current versus the light intensity for these latter two processes are found to be similar. No simple correlation has been found between the current and the light intensity for the initial fast decay stage (IFDS) of return strokes. The duration of the IFDS of return strokes generally lasts from several microseconds to several tens of microseconds and is more or less directly proportional to the corresponding peak return stroke current squared. A time delay ranging from 12 µs to 300 µs has been found between the current and the light intensity of all ICC pulses and M components. The time delay decreases as the corresponding peak current increases.

Effect of wastewater-borne bacteria on algal growth and nutrients removal in wastewater-based algae cultivation system

Centrate, a type of nutrient-rich municipal wastewater was used to determine the effect of wastewater-borne bacteria on algal growth and nutrients removal efficiency in this study. The characteristics of algal and bacterial growth profiles, wastewater nutrient removal and effect of initial algal inoculums were systematically examined. The results showed that initial algal concentration had apparent effect on bacterial growth, and the presence of bacteria had a significant influence on algal growth pattern, suggesting symbiotic relationship between algae and bacteria at the initial stage of algae cultivation. The maximum algal biomass of 2.01g/L with 0.1g/L initial algal inoculums concentration can be obtained during algae cultivation in raw centrate medium. The synergistic effect of centrate-borne bacteria and microalgae on algae growth and nutrient removal performance at initial fast growth stage has great potential to be applied to pilot-scale wastewater-based algae wastewater system cultivated in continuous or semi-continuous mode.

Luminescence decay evaluation of long-afterglow phosphors

In the current study, the phosphorescence decays of the long-afterglow materials of SrAl2O4:Eu, Dy, Sr4Al14O25:Eu, Dy, Sr2MgSi2O7:Eu, Dy, and ZnS:Cu, Co have been measured over long time (15h to 16h). The evaluation methods of luminescence decay are analyzed and summarized. The existing formulas are in accordance with the experimental decay data in the initial fast decay stage. However, the deviation is much larger and the accuracy is much lower in the slow decay stage. Therefore, the existing formulas cannot be used to accurately describe the luminescence decay of the samples with much longer afterglow time (>80min). Moreover, certain formulas do not match the actual decay situation of long-afterglow luminescence. We suggest our solutions for this problem.

Magnetic approaches to study collective three-dimensional cell mechanics in long-term cultures (invited).

Contractile forces generated by cells and the stiffness of the surrounding extracellular matrix are two central mechanical factors that regulate cell function. To characterize the dynamic evolution of these two mechanical parameters during tissue morphogenesis, we developed a magnetically actuated micro-mechanical testing system in which fibroblast-populated collagen microtissues formed spontaneously in arrays of microwells that each contains a pair of elastomeric microcantilevers. We characterized the magnetic actuation performance of this system and evaluated its capacity to support long-term cell culture. We showed that cells in the microtissues remained viable during prolonged culture periods of up to 15 days, and that the mechanical properties of the microtissues reached and maintained at a stable state after a fast initial increase stage. Together, these findings demonstrate the utility of this microfabricated bio-magneto-mechanical system in extended mechanobiological studies in a physiologically relevant 3D environment.

Thermal decomposition of hydroxylamine: Isoperibolic calorimetric measurements at different conditions

Thermal decomposition of hydroxylamine, NH2OH, was responsible for two serious accidents. However, its reactive behavior and the synergy of factors affecting its decomposition are not being understood. In this work, the global enthalpy of hydroxylamine decomposition has been measured in the temperature range of 130–150°C employing isoperibolic calorimetry. Measurements were performed in a metal reactor, employing 30–80ml solutions containing 1.4–20g of pure hydroxylamine (2.8–40g of the supplied reagent). The measurements showed that increased concentration or temperature, results in higher global enthalpies of reaction per unit mass of reactant. At 150°C, specific enthalpies as high as 8kJ per gram of hydroxylamine were measured, although in general they were in the range of 3−5kJg−1. The accurate measurement of the generated heat was proven to be a cumbersome task as (a) it is difficult to identify the end of decomposition, which after a fast initial stage, proceeds very slowly, especially at lower temperatures and (b) the environment of gases affects the reaction rate.

Transcriptome analysis of Sacha Inchi (Plukenetia volubilis L.) seeds at two developmental stages

BackgroundSacha Inchi (Plukenetia volubilis L., Euphorbiaceae) is a potential oilseed crop because the seeds of this plant are rich in unsaturated fatty acids (FAs). In particular, the fatty acid composition of its seed oil differs markedly in containing large quantities of α-linolenic acid (18C:3, a kind of ω-3 FAs). However, little is known about the molecular mechanisms responsible for biosynthesis of unsaturated fatty acids in the developing seeds of this species. Transcriptome data are needed to better understand these mechanisms.ResultsIn this study, de novo transcriptome assembly and gene expression analysis were performed using Illumina sequencing technology. A total of 52.6 million 90-bp paired-end reads were generated from two libraries constructed at the initial stage and fast oil accumulation stage of seed development. These reads were assembled into 70,392 unigenes; 22,179 unigenes showed a 2-fold or greater expression difference between the two libraries. Using this data we identified unigenes that may be involved in de novo FA and triacylglycerol biosynthesis. In particular, a number of unigenes encoding desaturase for formation of unsaturated fatty acids with high expression levels in the fast oil accumulation stage compared with the initial stage of seed development were identified.ConclusionsThis study provides the first comprehensive dataset characterizing Sacha Inchi gene expression at the transcriptional level. These data provide the foundation for further studies on molecular mechanisms underlying oil accumulation and PUFA biosynthesis in Sacha Inchi seeds. Our analyses facilitate understanding of the molecular mechanisms responsible for the high unsaturated fatty acids (especially α-linolenic acid) accumulation in Sacha Inchi seeds.

Litterfall and litter decomposition in chestnut high forest stands in northern Portugal

This research aimed to: estimate the inputs of litterfall; model the decomposition process and assess the rates of litter decay and turnover; study the litter decomposition process and dynamics of nutrients in old chestnut high forests. This study aimed to fill a gap in the knowledge of chestnut decomposition process as this type of ecosystems have never been modeled and studied from this point of view in Portugal. The study sites are located in the mountains of Marão, Padrela and Bornes in a west-to-east transect, across northern Portugal, from a more-Atlantic-to-lessmaritime influence. This research was developed on old chestnut high forests for quality timber production submitted to a silviculture management close-to-nature. We collected litterfall using littertraps and studied decomposition of leaf and bur litter by the nylon net bag technique. Simple and double exponential models were used to describe the decomposition of chestnut litterfall incubated in situ during 559 days. The results of the decomposition are discussed in relation to the initial litter quality (C, N, P, K, Ca, Mg) and the decomposition rates. Annually, the mature chestnut high-forest stands (density 360-1,260 tree ha–1, age 55-73 years old) restore 4.9 Mg DM ha–1 of litter and 2.6 Mg ha–1 yr–1 of carbon to the soil. The two-component litter decay model proved to be more biologically realistic, providing a decay rate for the fast initial stage (46-58 yr–1for the leaves and 38-42 yr–1for the burs) and a decay rate related to the recalcitrant pool (0.45-0.60 yr–1for the leaves and 0.22-0.36 yr–1for the burs). This study pointed to some decay patterns and release of bioelements by the litterfall which can be useful for calibrating existing models and indicators of sustainability to improve both silvicultural and environmental approaches for the management of chestnut forests.

Prediction and Hydrogen Acceleration of Ordering in Iron-Vanadium Alloys

Ab initio calculations of binary metallic systems often predict ordered compounds in contrast to empirical reports of solid solutions or disordered phases. These discrepancies are usually attributed to slow kinetics that retains metastable structures at low temperatures. The Fe-V system is an example of this phenomenon, in which we predict two ordered stable ground states, Fe3V and FeV3, whereas a disordered σ phase is reported. We propose to overcome this difficulty by hydrogen absorption, which facilitates metal atom mobility through vacancy formation and separation between the two elements due to their opposite affinities towards it, thus accelerating transformation kinetics. Hydrogen also increases the relative stability of the ordered structures compared with that of the σ phase without affecting the shape of the phase diagram. The hydrogen-induced formation of the ordered structures is expressed by a reversible decrease of the electrical resistivity with increasing hydrogen pressure. Such behavior has not been reported before in thin H absorbing films. Formation of the ordered structures is further substantiated by the kinetics of the resistivity changes upon variation of the hydrogen pressure, where two stages are distinguished: a fast initial stage and a much slower subsequent process in which the resistivity changes direction, associated with hydrogen dissolution and phase transformation, respectively.

English

Kinetic behaviors of fluorine leaching from tea were studied. The leaching process of fluorine could be divided into initial fast stage and later slow stage. The duration of fast stage 1 depended on leaf particle size and temperature. The higher the temperature and the smaller the leaf particle size, the shorter the duration of initial fast stage. Based on the test results, a two-step infusion method was developed to control fluorine level in tea liquor. When the tea was infused in 50°C water for 20 s (first infusion) and then the residue leaf was re-infused in boiling water for 5 min (second infusion), more than 26% of total fluorine was removed during first infusion, but more than 80% of catechins and caffeine of the teas remained in the second infusions which had a F level 0.70 mg L-1 or less. It reflected that the two-step infusion method is an alternative to control excessive fluorine exposure for tea drinkers.   Key words: Green tea, fluorine, kinetics, diffusion coefficients, two-step infusion.

Theoretical Foundation of Carbonation Pellet Process for Ferrous Sludge Recycling

For the recycling of ferrous sludge from steel industry, the carbonation pellet process should be considered as a “green” process, since no impurities are added as well as CO 2 can be sequestrated and consumed. Through the thermodynamic calculation, the carbonation reaction can occur spontaneously and is an exothermic reaction. Based on the kinetic analysis through unreacted core model, the interfacial chemical reaction was the rate controlling step in the initial fast stage of carbonation, and the CO 2 diffusion through the CaCO 3 product layer was the rate controlling step in the following extremely slow stage. For the carbonation bonded mechanism, the pellet strength was gained by the formation and growing of CaCO 3 product layer. Since the interfacial chemical reaction was the critical stage of the entire carbonation process, the emphasizes should be focused on the improvement of sorbent activity and the optimization of process parameters, such as pore structure, pore surface area, and total pressure, CO 2 partial pressure, reaction temperature, etc to accelerate the reaction rate and to improve the quality of carbonation pellets.

In Situ Observation of Strain Development and Porosity Evolution in Nanoporous Gold Foils

AbstractThe formation of nanoporous gold by open circuit dealloying of 100 nm AgAu foils in nitric acid is investigated in situ and in real time by combining synchrotron small angle X‐ray scattering (SAXS) and X‐ray diffraction (XRD). The time dependence of the dealloying is followed as a function of acid concentration. For all concentrations, several characteristic dealloying stages are observed. Firstly, there is a fast initial dissolution stage with an increase in surface area due to pore and mound formation; this leads to strain in the nanoporous gold that results from an increase in capillary pressure. After dissolution is complete, there is rapid coarsening of the quasi‐periodic, pore–ligament morphology. During this later stage, we deduce strong strain anisotropies that can be explained by preferred crystallographic orientation of ligaments. This rapid coarsening stage is followed by a slow coarsening stage where the SAXS patterns, and hence the quasi‐periodic morphology, is self‐similar in time. There is a strong correlation between the morphology evolution and strain development, which can be explained by capillary forces.

Cyclic Oxidation Kinetics and Oxide Scale Morphologies Developed on the IN600 Superalloy

The oxidation behavior of the IN600 Ni–Cr–Fe superalloy was investigated in air at temperatures ranging from 750 to 950 °C, for up to 12 cycles. Oxidation kinetics and oxide scale morphologies were examined using weight gain measurements, SEM-EDS, and X-ray diffraction. The cyclic oxidation kinetic results suggested that the oxidation behavior of the IN600 alloy approximately followed a sub-parabolic rate and the scaling process was controlled by the formation of a chromia scale. At 850 °C, SEM-EDS observations indicated that the formed oxide scale was primarily composed of Cr2O3, and the internal oxidation of Cr and Ti occurred. At 950 °C, a fast initial stage with high weight gain was observed, followed by a steady-state stage with gradual weight gain. Additionally, a considerable change in the oxidation kinetic occurred. SEM-EDS observations and XRD results indicated that the external scale was relatively thick with a localized porous, preferential adherent, and a complex oxide scale was developed. This complex oxide scale consisted of an outermost thin layer composed of MnCr2O4–Cr2O3 mixed together with a small amount of isolated TiO2, an intermediate relatively thick layer, composed of Cr2O3, and an innermost discrete layer formed at the scale/alloy interface, which enriched by Ni/NiO mixed with Ti-, Al-, and Fe-oxides. Finally, only the Al alloying element was internally oxidized to form Al2O3 fingers, which create a discrete and narrow internal oxidation zone. Al oxide was observed as a dark area and primarily grows along the alloy grain boundaries in the vicinity of the inward chromia pegs.

Crystalline islands of semiconductor films

Silicon carbide (SiC) nucleation in the form of powder in a discharge plasma and the formation of thin film islands on a Si(100) substrate in the course of gas-phase epitaxy are simulated numerically. Models of plasma-like media and nonequilibrium processes accompanying phase transitions of the first kind (such as condensation and crystallization) in the initial fast (fluctuation) stage are described. The nonstationary evolution of nuclei size distribution functions is modeled by solving kinetic equations in partial derivatives and stochastic Ito-Stratonovich analog equations. This makes it possible to refine the formation mechanisms of microcrystalline state polytypes and calculate the nucleation rate and the initial roughness of a SiC coating.

System for time resolved spectral studies of pulsed atmospheric discharges in the visible to vacuum ultraviolet range

Vacuum ultraviolet (VUV) emission is believed to play a major role in the development of plasma streamers in pulsed atmospheric discharges, but detection of VUV light is difficult in pulsed experiments at atmospheric pressures. Since VUV light is absorbed in most standard optical materials as well, careful attention must be given to the selection of the lens and mirror optics used in these studies. Of highest interest is the VUV emission during the initial stage of pulsed atmospheric discharges, which has a typical duration in the nanosecond regime. An experiment was designed to study this fast initial stage of VUV emission coupled with fast optical imaging of streamer propagation, both with temporal resolution on the order of nanoseconds. A repetitive solid-state high voltage pulser was constructed which produces triggered flashover discharges with low jitter and consistent pulse amplitude. VUV emission is captured utilizing both photomultiplier and intensified charge-coupled device detectors during the fast stage of streamer propagation. These results are discussed in context with the streamer formation photographed in the visible wavelength regime with 3 ns exposure time.