Differences In Formation Mechanisms Research Articles

Hematite (α-Fe2O3) with Oxygen Defects: The Effect of Heating Rate for Photocatalytic Performance.

Hematite (α-Fe2O3) emerges as an enticing material for visible-light-driven photocatalysis owing to its remarkable stability, low toxicity, and abundance. However, its inherent shortcomings, such as a short hole diffusion length and high recombination rate, hinder its practical application. Recently, oxygen vacancies (Vo) within hematite have been demonstrated to modulate its photocatalytic attributes. The effects of Vo can be broadly categorized into two opposing aspects: (1) acting as electron donors, enhancing carrier conductivity, and improving photocatalytic performance and (2) acting as surface carrier traps, accelerating excited carrier recombination, and deteriorating performance. Critically, the generation rate, distribution, role, and behavior of Vo significantly differ for synthesis methods due to differences in formation mechanisms and oxygen diffusion. This complexity hampers simplified discussions of Vo, necessitating careful investigation and nuanced discussion tailored to the specific method and conditions employed. Among various approaches, hydrothermal synthesis offers a simple and cost-effective route. Here, we demonstrate a hydrothermal synthesis method for Vo introduction to hematite using a carbon source, where variations in the heating rate have not been previously explored in terms of their influence on Vo generation. The analyses revealed that the concentration of Vo was maximized at a heating rate of 16 °C/min, indicative of a high density of surface defects. With regard to photocatalytic performance, elevated heating rates (16 °C/min) fostered the formation of Vo primarily on the hematite surface. The photocatalytic activity was 7.1 times greater than that of the sample prepared at a low heating rate (2 °C/min). These findings highlight the crucial role of surface defects, as opposed to bulk defects, in promoting hematite photocatalysis. Furthermore, the facile control over Vo concentration achievable via manipulating the heating rate underscores the promising potential of this approach for optimizing hematite photocatalysts.

PH-Regulated host-guest architecture in molybdenum Dioxide/Carbon sphere composites for flexible solid-state supercapacitors

Compositing molybdenum dioxide (MoO2) with carbon sphere (CS) can greatly enhance the conductivity and structural instability to achieve its high theoretical capacitances. The controllable regulation of local architecture and host–guest interaction in the two-phase composites is highly desirable, but commonly hindered by the significant difference in formation mechanism between MoO2 and CS. Herein, a pH-regulated pre-intervention strategy was developed to provide control over the MoO2/CS architecture by adjusting the interplay between the precipitation kinetics of MoO2 and the polymerization effect of hydrochar precursor. By varying the pre-synthesis pH from 10.0 to 0.1, the corresponding dominant formation process of precursor changes from inside-out Ostwald ripening to protonation-induced electrostatic interactions, resulting in the structural evolution of MoO2/CS from hollow CS-encapsulating MoO2 nanosheets and solid CS-supporting MoO2 nanoparticles. The electrochemical test proved the former architecture possesses faster electrode kinetics, lower charge/ion-transfer resistance, and better electrochemical stability. An extended oxidation-etching method was further introduced to prepare mesoporous CS with excellent supercapacitive properties. A flexible solid-state asymmetric supercapacitor composed of optimal MoO2/CS structure as the positive electrode and mesoporous CS as the negative electrode delivers a high energy density of 52.3 W h kg−1 and power density of 14500 W kg−1, and good cycling stability with 89.7 % retention of the initial capacitance after 8000 cycles.

Structures and formation mechanism of borides with varied morphologies in cast γ-TiAl alloys

Borides with varied morphologies and structures obtained by changing B content in as-cast Ti-45Al-2Mn-2Nb alloys are investigated. With the increase of B content, morphologies of borides change from curved to straight, and flake shape, ribbon shape, needle/rod shape, and blocky appear in turn. Curved boride particles have a lamellar structure composed of TiB2 and B2 layers, accompanied by the random appearance and distribution of Ti3B4 and Bf-TiB layers. Except for the absence of the B2 layer, straight needle-like and blocky boride particles have roughly the same structure as curved boride particles, revealing that the formation of curved boride particles is accompanied by divorced eutectic with the matrix and internal irregular eutectic, while no eutectics occurs in straight boride particles. The lack of B atoms during solidification in alloys with lower B content results in a less regular structure and higher stacking fault density of curved boride particles compared to straight boride particles in alloys with higher B content. In addition, some needle-like boride particles are observed to have pure B27-TiB structure without intergrowth. The difference in morphologies and structures can be attributed to the difference in formation mechanism and crystallographic structures of the borides.

Differences in Formation Mechanisms of Phenolic Off-Flavor Compounds among Yeast Species

Phenolic off-flavor compounds such as 4-vinylguaiacol (4-VG) affect the quality of fermented foods. In Saccharomyces cerevisiae, 4-VG production requires prenylated FMN (flavin mononucleotide) produced by the mitochondrial protein Pad1. To examine this mechanism further, we expressed Escherichia coli ubiX, whose gene product prenylates FMN in E. coli, in an S. cerevisiae Δpad1 strain, which recovered the ability to produce 4-VG. Because E. coli UbiX is expected to localize to the cytoplasm in the transformed yeast, next, we expressed a truncated Pad1 (tPad1) variant lacking the mitochondrial translocation signal sequence in S. cerevisiae Δpad1. The transformed strain also recovered the ability to produce 4-VG; furthermore, it produced a larger amount of 4-VG than wild-type S. cerevisiae, indicating that 4-VG production in S. cerevisiae may be mediated by the partial mislocalization of Pad1 to the cytoplasm. We also expressed the gene encoding Dekkera (Brettanomyces) bruxellensis phenolic acid decarboxylase (DbPAD) in S. cerevisiae Δpad1. The transformed yeast recovered the ability to produce 4-VG, indicating that the D. bruxellensis phenolic acid decarboxylation reaction does not require prenylated FMN. Sequencing of the cloned DbPAD gene showed that the translation start codon differs from previous reports; therefore, we recloned the DbPAD gene from the position predicted to be the translation initiation point (designated DbPADs). Transformation of S. cerevisiae Δpad1 with DbPADs further increased the amount of 4-VG produced. Collectively, these findings provide insight into the mechanism of off-flavor production by different yeast species.

Stress-Induced Polyploid Giant Cancer Cells: Unique Way of Formation and Non-Negligible Characteristics.

Polyploidy is a conserved mechanism in cell development and stress responses. Multiple stresses of treatment, including radiation and chemotherapy drugs, can induce the polyploidization of tumor cells. Through endoreplication or cell fusion, diploid tumor cells convert into giant tumor cells with single large nuclei or multiple small nucleuses. Some of the stress-induced colossal cells, which were previously thought to be senescent and have no ability to proliferate, can escape the fate of death by a special way. They can remain alive at least before producing progeny cells through asymmetric cell division, a depolyploidization way named neosis. Those large and danger cells are recognized as polyploid giant cancer cells (PGCCs). Such cells are under suspicion of being highly related to tumor recurrence and metastasis after treatment and can bring new targets for cancer therapy. However, differences in formation mechanisms between PGCCs and well-accepted polyploid cancer cells are largely unknown. In this review, the methods used in different studies to induce polyploid cells are summarized, and several mechanisms of polyploidization are demonstrated. Besides, we discuss some characteristics related to the poor prognosis caused by PGCCs in order to provide readers with a more comprehensive understanding of these huge cells.

Significant contrasts in aerosol acidity between China and the United States.

Aerosol acidity governs several key processes in aerosol physics and chemistry, thus affecting aerosol mass and composition and ultimately climate and human health. Previous studies have reported aerosol pH values separately in China and the United States (USA), implying different aerosol acidity between these two countries. However, there is debate about whether mass concentration or chemical composition is the more important driver of differences in aerosol acidity. A full picture of the pH difference and the underlying mechanisms responsible is hindered by the scarcity of simultaneous measurements of particle composition and gaseous species, especially in China. Here we conduct a comprehensive assessment of aerosol acidity in China and the USA using extended ground-level measurements and regional chemical transport model simulations. We show that aerosols in China are significantly less acidic than in the USA, with pH values 1-2 units higher. Based on a proposed multivariable Taylor series method and a series of sensitivity tests, we identify major factors leading to the pH difference. Compared to the USA, China has much higher aerosol mass concentrations (gas + particle, by a factor of 8.4 on average) and a higher fraction of total ammonia (gas + particle) in the aerosol composition. Our assessment shows that the differences in mass concentrations and chemical composition play equally important roles in driving the aerosol pH difference between China and the USA - increasing the aerosol mass concentrations (by a factor of 8.4) but keeping the relative component contributions the same in the USA as the level in China increases the aerosol pH by ~1.0 units and further shifting the chemical composition from US conditions to China's that are richer in ammonia increases the aerosol pH by ~0.9 units. Therefore, China being both more polluted than the USA and richer in ammonia explains the aerosol pH difference. The difference in aerosol acidity highlighted in the present study implies potential differences in formation mechanisms, physicochemical properties, and toxicity of aerosol particles in these two countries.

In situ energy-dispersive X-ray diffraction of local phase dynamics during solvothermal growth of Cu4O3

Using in situ methods to characterize the state of a system during reactions is critical to understanding and improving solvothermal syntheses. This work demonstrates the use of in situ energy-dispersive X-ray diffraction (EDXRD) to investigate the local dynamics during solvothermal formation of Cu4O3 using a general-purpose full-sized laboratory oven. This allows for direct comparison of in situ data with laboratory-based reactions. Using in situ EDXRD, changes in the local amounts of Cu4O3, Cu2O and CuO within approximately 100 × 100 × 700 µm gauge volumes during solvothermal Cu4O3 formation were recorded. Fast conversion between Cu2O and CuO was observed in the solvothermal environment, whereas Cu4O3 was found to be chemically stable against disturbances once formed. The observed differences in local dynamics give further support to the differences in formation mechanisms between Cu4O3 and Cu2O/CuO proposed here.

Methods to determine the upper limits of petrophysical properties in tight oil reservoirs: Examples from the Ordos and Songliao Basins

In large petroliferous basins, tight and conventional reservoirs are widely distributed. These reservoirs have significant differences in formation mechanisms, enrichment rules, and development modes. Only when a reservoir petrophysical property is less than a certain upper limit can a large area of tight oil accumulation be formed. Therefore, it is necessary to scientifically define the petrophysical property boundary between tight and conventional reservoirs. In the past, the determination of petrophysical property boundaries between tight and conventional reservoirs was based mainly on the statistics of a large number of measured petrophysical property data of typical tight oil basins and lacked theoretical research. Taking the Ordos and Songliao Basins as examples, this paper studies the petrophysical upper limits of tight reservoirs, starting with the reservoir-forming mechanism and characteristics of tight and conventional reservoirs. Based on four methods—the mechanical balance method assuming that the buoyancy and capillary pressure are equal, petrophysical simulation of an oil accumulation in sandstone, analysis of the distribution characteristics of the current petrophysical properties of conventional and tight oil reservoirs, and mercury injection porosimetry tests to determine the change in reservoir porosity and permeability with displacement pressure—this research determines that basically the same upper limits of tight reservoir properties are found among these methods. Obtained synthetically, the upper limit of permeability is approximately 1 md, corresponding to the upper limit of porosity of approximately 12%. These research results provide new ideas and methods to distinguish tight oil from conventional oil accumulations in petroliferous basins in different stages of exploration.

Catalogue of new Herbig Ae/Be and classical Be stars

Context. The intermediate-mass pre-main sequence Herbig Ae/Be stars are key to understanding the differences in formation mechanisms between low- and high-mass stars. The study of the general properties of these objects is hampered by the lack of a well-defined, homogeneous sample, and because few and mostly serendipitously discovered sources are known. Aims. Our goal is to identify new Herbig Ae/Be candidates to create a homogeneous and well defined catalogue of these objects. Methods. We have applied machine learning techniques to 4 150 983 sources with data from Gaia DR2, 2MASS, WISE, and IPHAS or VPHAS+. Several observables were chosen to identify new Herbig Ae/Be candidates based on our current knowledge of this class, which is characterised by infrared excesses, photometric variabilities, and Hα emission lines. Classical techniques are not efficient for identifying new Herbig Ae/Be stars mainly because of their similarity with classical Be stars, with which they share many characteristics. By focusing on disentangling these two types of objects, our algorithm has also identified new classical Be stars. Results. We have obtained a large catalogue of 8470 new pre-main sequence candidates and another catalogue of 693 new classical Be candidates with a completeness of 78.8 ± 1.4% and 85.5 ± 1.2%, respectively. Of the catalogue of pre-main sequence candidates, at least 1361 sources are potentially new Herbig Ae/Be candidates according to their position in the Hertzsprung-Russell diagram. In this study we present the methodology used, evaluate the quality of the catalogues, and perform an analysis of their flaws and biases. For this assessment, we make use of observables that have not been accounted for by the algorithm and hence are selection-independent, such as coordinates and parallax based distances. The catalogue of new Herbig Ae/Be stars that we present here increases the number of known objects of the class by an order of magnitude.

Difference in formation mechanism of inclusion complex between configuration isomers of gallate-type catechin and β-cyclodextrin

The formation mechanism of inclusion complex between (-)-epigallocatechin gallate (EGCg), which is the main catechin in tea leaves, or (-)-gallocatechin gallate (GCg), which is an isomer of EGCg, and β-cyclodextrin (βCD) was studied by isothermal titration microcalorimetry (ITC), NMR and molecular modeling calculation (MMC). ITC measurements revealed that EGCg or GCg interacted with βCD at 1:1 molar ratio driven by enthalpy. Comparing the values of binding constant (7.2 × 103 1/M for EGCg with βCD and 3.9 × 104 1/M for GCg with βCD), it was suggested that GCg interacted with βCD more strongly rather than EGCg. In their ROESY NMR spectra, the cross-peaks were observed between the protons of A, B and B′ ring of EGCg and the protons in the cavity of βCD, and between the protons of B and B′ ring of GCg and the protons in the cavity of βCD. MMC in water showed that EGCg had one kind and GCg had two kinds of most stable conformation (GCg(E) and GCg(A)) in energy. In the stable conformation of EGCg, B ring was coordinated equatorially to C ring, and B′ ring was axially coordinated to C ring. On the other hand, in GCg (E), the coordination of B ring and B′ ring to C ring was both equatorial, and in GCg (A), the coordination of B ring and B′ ring was both axial. MMC also revealed B or B′ ring of GCg(A) was easy to be included in the cavity of βCD more deeply than each ring of EGCg or GCg(E) since the steric hindrance of B ring or B′ ring was small. Therefore, it was found that the difference of B ring’s configuration of gallate-type catechin greatly affected the formation of inclusion complex with βCD.

Quantitative depth distribution analysis of elements in high alloy steel using MCs+-SIMS approach

Elemental composition analysis in alloy samples using secondary ion mass spectrometry (SIMS) suffers from matrix effects which hamper the analytical results. These matrix effects arise due to numerous factors like change in surface work function due to primary ion beam implantation, presence of reactive chemical species in the samples or on the sample surface, sample composition, chamber pressure etc. which changes the ionization probability of secondary ion species and hence produces non-linear effects in the production of secondary ions. In order to minimize these effects, Cs+ primary ion beam in conjunction with MCs+ (M being the element of interest) secondary ion monitoring (MCs+-SIMS) approach has been used. The MCs+-SIMS approach has been extensively used for quantitative depth distribution analysis in semiconductor samples but limited reports are available for the analysis of alloys sample. In the present work, the MCs+-SIMS approach has been utilized to determine the chemical composition and quantitative depth distribution of multiple elements (C, Si, Ni, Mn, Cr, Co, Mo and Fe) in high alloy steel samples. Quantitative depth distribution analysis revealed a non-homogenous distribution of elements on the steel surface which can be due to the presence of surface oxide layers. The minor and major constituents such as Cr, Mo; Mn, Ni; and Si; were determined with relative error of <2%, 6% and 5%, respectively. Surface distribution analyses of these elements were also carried out using both Cs+ and O2+ primary ion beams. An interesting and contrasting feature has been observed for surface distribution analysis carried out with MCs+ as compared to M+ secondary ion detection mode. It was observed that the surface distribution patterns of non-homogenous elements showed homogenous distribution patterns in case of MCs+ secondary ion monitoring approach. This anomaly can be attributed to the difference in formation mechanism of MCs+ and M+ secondary ions.

Morphology of Upper and Lower Bainite with 0.7 Mass Pct C

There has been an on-going discussion on the difference in formation mechanisms of upper and lower bainite. Various suggestions have been supported by reference to observed morphologies and illustrated with idealized sketches of morphologies. In order to obtain a better basis for discussions about the difference in mechanism, the morphology of bainite in an Fe-C alloy with 0.7 mass pct carbon was now studied in some detail from 823 K to 548 K (550 °C to 275 °C) at temperature intervals of 50 K or less. The work focused on bainite seen to start from a grain boundary in the plane of polish and showing an advancing tip in the remaining austenite. The results indicate that there is no essential difference with temperature regarding the ferritic skeleton of feathery bainite. The second stage of bainite formation, which involves the formation of both ferrite and cementite, was regarded as a eutectoid transformation and the resulting morphologies were analyzed in terms of two modes, degenerate and cooperative eutectoid transformation. There was no sharp difference between upper and lower bainite. Ways to define the difference were discussed.

Herbig Ae/Be stars with TGAS parallaxes in the HR diagram

AbstractThe intermediate mass Herbig Ae/Be stars are young stars approaching the Main Sequence and are key to understanding the differences in formation mechanisms between magnetic low mass stars and non-magnetic high mass stars. A large fraction of known Herbig Ae/Be stars have TGAS parallaxes, which were used to derive luminosities and place 107 of these objects in the HR diagram, increasing the number of objects using directly determined parallaxes by a factor of 5. We also studied the characteristics of the infrared excesses of this set of Herbig Ae/Be stars and we linked our results to an evolutionary analysis.

Unified theory of nucleation of folded-chain crystals (FCCs) and extended-chain crystals (ECCs) of linear-chain polymers: 2. Origin of FCC and ECC

An improved formulation for the nucleation rate j of a generalized sequential process is presented. The topological nature of linear chains was formulated by introducing activation energy for chain sliding diffusion within crystals. It is shown that when chain sliding diffusion is easy extended chain crystals (ECC) will be formed from folded chain crystals (FCC) by lamellar thickening, whereas when it is difficult FCCs will be formed, which shows the origin of ECC and FCC. It indicates that there is no essential difference in formation mechanism between FCC and ECC. It is predicted that polymers crystallized from the melt into hexagonal form will change continuously from FCC to ECC with increasing crystallization temperature.

Plasma polymerization of some simple saturated hydrocarbons

Methane, ethane, propane, and n-butane were polymerized in a plasma created by a radio-frequency glow discharge. It was found that the kinetics of polymer deposition were similar for all monomers but methane. It is suggested that the deviation from “normal” behavior of methane may be due to the difference in mechanism of formation of reaction intermediates. The “characteristic map” for the plasma polymerization of ethane was determined. It was shown that, in addition to transparent films, powders may be formed at low pressures and low monomer flow rates and unstable discharges at high pressures and low flow rates. With increasing power input, the unstable regions are decreased while the powdery regions are increased. The rates of polymer deposition were found to depend on pressure, flow rate, and power. An empirical equation is proposed that relates the rates of deposition for ethane, propane, and n-butane to these parameters.

The formation of various ash flows in Indonesia

A thorough analysis of the mode of occurrence of various ash flows deposits in Indonesia confirms the present author’s belief in an important difference in mechanism of formation between ash-flow tuff sheets abundantly found in the island of Sumatra and those minor ash flows of nuee ardentes type produced by orogenic volcanic activity such as displayed by Mt Merapi and Mt Agung in Java and Bali.