Mechanism Of Ring Formation Research Articles

Atomistic Mechanisms of Ring Formation during Catalyzed Carbon Nanotube Growth

Atomistic Mechanisms of Ring Formation during Catalyzed Carbon Nanotube Growth

Linking Topographical Ring Features to Geochemical and Geophysical Anomalies

Circular features in forests seen from air have been studied for several decades at different locations around the world. Forest rings, as they are called in Canada’s boreal forests, express several geochemical (pH, carbonate content) and geophysical (surface potential) anomalies on their 20–30 m wide ring edges. Although it has been proposed that microbial processes may cause these anomalies, the exact mechanisms of ring formation are still unknown. We focused on the Thorn North forest ring in Ontario, Canada to correlate the surface potential anomaly to soil gas concentrations. Field measurements showed that the surface potential drop at the ring edge center is framed by peaks in CO2 production, which is linked to O2 depletion and methane generation. Carbon isotope signatures were found to drop to lighter values (down to −20‰), suggesting increased respiration. Higher concentrations of uronic acids bound to extracellular polymeric substances were found, indicating that the surface potential anomaly is linked to respiration. 16S rRNA gene sequencing of shallow soil did not indicate a dominant microbial group on the edges; instead, principal component analysis showed that the microbial composition was controlled by the substrate (clayey vs. sandy soil), therefore future studies should focus on deeper ground layers.

Investigation on the mechanism of ring formation in the process of NaCl recovery by pyrolysis of chemical waste salt using rotary kiln

Chemical waste salt is a hazardous waste generated during chemical production, and it is crucial to complete the recycling of the waste salt in a practical way. In the case of waste salt recycling by rotary kiln pyrolysis carbonization, ringing affects the pyrolysis efficiency and process running, thus a study on waste salt ringing was conducted. The results showed that the particle size is the key to the ring formation in rotary kiln, and pyrolysis temperature, pyrolysis time and temperature distribution in the rotary kiln also affect the material discharge rate during pyrolysis of waste salt in the rotary kiln. Thermogravimetric analysis and SEM images revealed that the volatilization of organic matter in the material due to pyrolysis caused a decrease in the abrasion resistance of the waste salt particle, which was the factor behind the ringing during pyrolysis in the rotary kiln. This study may provide a reference for the implementation of similar waste salt pyrolysis carbonization processes.

Research on the ring formation mechanism of magnesian flux pellets in rotary kiln

The forming of rings was a key problem of magnesian flux pellets in rotary kiln, which seriously limited production efficiency. Pellet powder and flux were the raw materials of the ring. Based on this, the bonding strength, melting behavior and microstructure of pellet powder and its mixed powder with flux were investigated. The influence of basicity (R = CaO/SiO2) on ring behavior of pellet powder was analyzed, and ring formation mechanism of magnesian flux pellets was clarified. The results showed that acid pellet powder was not easy to form rings due to lower bonding strength of briquettes. Due to changes in bonding process after mixing of flux, magnesian flux pellet powder produced ferrite and silicate liquid phase with lower melting point, which promoted diffusion and recrystallization of hematite and enhanced compressive strength of briquettes, then finally caused rings to form. Moreover, it is required to control roasting temperature below 1200 °C, which is a necessary condition for magnesian flux pellet powder to form an initial ring which was easy to be destroyed.

A First Study of Urginea maritima Rings: A Case Study from Southern Jordan

Vegetation rings are a common pattern in water-limited environments and mostly occur in clonal plants. This study presents, for the first time, rings of the geophyte species Urginea maritima. The rings, typically 40–90 cm in diameter, are abundant in the sandy environment of Little Petra and Wadi Rum, in the southern Jordanian drylands. Soil properties were studied in the rings’ center, periphery, and matrix. Soil-water volumetric content was significantly higher in the rings’ periphery than in the center and matrix. The soil organic carbon was highest in the periphery, intermediate in the center, and lowest in the matrix. At the same time, the soil texture, hydraulic conductivity, and gravimetric moisture content at the hygroscopic level were similar in the three microenvironments. According to the results, a possible ring formation mechanism is the soil-water uptake mechanism, which results in competition between the plants at the periphery and those in the center and is generally attributed to plants with large lateral root zones. Numerical simulations of a mathematical model implemented in this study support the soil-water uptake mechanism. A second possible mechanism is negative plant-soil feedback due to the accumulation of dead biomass and its consequent decomposition, with the resultant release of autotoxic compounds. It is possible that several mechanisms occur simultaneously and synergistically affect the formation of U. maritima rings.

Coal ash induced ring formation in a pilot scale rotary kiln for low-grade iron ore direct reduction process: Characterization and mechanism

For economic utilization of low grade iron ore resource, a pilot scale study of iron ore direct reduction by rotary kiln (ϕ1.5 m × 15 m) was carried out. In this work, the actual furnace burden and temperature distribution status in rotary kiln were in-situ measured. The location and typical physicochemical condition in rotary kiln for ring substances generation were verified. SEM equipped with EDX, XRD and optical microscopy were applied to analyze the characteristics of ring substances. Extra lab experiments and phase diagram calculation with the help of Factsage 7.0 were performed to reveal the ring formation mechanism. Results showed that ring substances emerged at 5 ∼ 6 m zone of rotary kiln, with high temperature, coal proportion, and metallic iron content of pellets in this region. Pellets bonded together by the sintering of metallic iron on surface, then, molten wrappage cemented them to refractory of rotary kiln forming the ring. Hedenbergite and fayalite produced by interaction of coal ash and iron ore powder developed the molten wrappage. The new understanding of ring formation promised potential for its application in coal fired rotary kiln operation.

Ring Formation in Protoplanetary Disks Driven by an Eccentric Instability

Abstract We find that, under certain conditions, protoplanetary disks may spontaneously generate multiple, concentric gas rings without an embedded planet through an eccentric cooling instability. Using both linear theory and nonlinear hydrodynamics simulations, we show that a variety of background states may trap a slowly precessing, one-armed spiral mode that becomes unstable when a gravitationally stable disk rapidly cools. The angular momentum required to excite this spiral comes at the expense of nonuniform mass transport that generically results in multiple rings. For example, one long-term hydrodynamics simulation exhibits four long-lived, axisymmetric gas rings. We verify the instability evolution and ring-formation mechanism from first principles with our linear theory, which shows remarkable agreement with the simulation results. Dust trapped in these rings may produce observable features consistent with observed disks. Additionally, direct detection of the eccentric gas motions may be possible when the instability saturates, and any residual eccentricity left over in the rings at later times may also provide direct observational evidence of this mechanism.

The Ring Formation Mechanism in Cyclization of Berberine

Berberine hydrochloride is a natural alkaloid with significant antitumor activities against many types of cancer cells, can be synthesized by cyclic reaction with hydrochloride condensate and glyoxal as raw materials and copper chloride as catalyst. In this study, the transition and energy change for the each reaction step was calculated by the density functional theory program Dmol3 in Materials Studio 2017. and the results testified that there are two ring formation in the cycliztion process, and according to the result we proposed the mechanism of this cyclization reaction. We also use infrared and ultraviolet spectroscopy to monitor the reaction process in real time and prove the ring formation process. The reaction mechanism was firstly proposed at the basic results of above.

The Ring Formation Mechanism in Cyclization of Berberine

Berberine hydrochloride is a natural alkaloid with significant antitumor activities against many types of cancer cells, can be synthesized by cyclic reaction with hydrochloride condensate and glyoxal as raw materials and copper chloride as catalyst. In this study, the transition and energy change for the each reaction step was calculated by the density functional theory program Dmol3 in Materials Studio 2017. and the results testified that there are two ring formation in the cycliztion process, and according to the result we proposed the mechanism of this cyclization reaction. We also use infrared and ultraviolet spectroscopy to monitor the reaction process in real time and prove the ring formation process. The reaction mechanism was firstly proposed at the basic results of above.

Theoretical study on a kind of cyclization mechanism of boron trichloride and hexamethyldisilazane to form the borazine ring for SiBCN ceramics precursor

Borazine rings act as a pivotal part in siliconboroncarbonitride ceramics (SiBCN) for high-temperature stability and great resistance to crystallization. A detailed investigation of the ring formation mechanism will guide the design and synthesis of SiBCN to meet application requirements under extreme conditions. Boron trichloride (BCl3) and hexamethyldisilazane (HN(SiMe3)2) are common raw materials for the synthesis of precursors for SiBCN. In this paper, quantum chemical calculation was used to study the cyclization reaction mechanism between BCl3 and HN(SiMe3)2 to form trichloroborazine (TCBZ) at the MP2/6-31G (d,p) level of theory. We discussed the structure properties, reaction pathways, energy barriers, reaction rates, and other aspects in detail. The results show that BCl3 and HN(SiMe3)2 alternately participate in the reaction process, accompanied by the release of trimethylchlorosilane (TMCS), and that the entire reaction shows an absolute advantage in terms of energy. In the Step by step reaction, lower reaction barriers are formed due to the introduction of BCl3 with more heat released compared to that for the introduction of HN(SiMe3)2. The final single-molecule cyclization and TMCS elimination steps are found to be faster compared to all previous bimolecular reactions.

From a mineralogical analytical view to a mechanism evaluation of cement kiln rings

Ring growth in cement rotary kilns is a complex and a dynamic phenomenon, where the agents responsible for their formation cannot be easily controlled. This is reflected by the mineralogical heterogeneity of the deposit material. In this context, eight samples collected from two rings, formed in the same kiln, but at different periods (during 22 and 3 days), were subjected to qualitative and quantitative mineralogical study. The consolidation of these rings was the result of the combined deposition of the carbonates and the sulphates phases. The analyzes were focused mainly on spurrite Ca5(SiO4)2CO3, calcite CaCO3, sulfospurrite Ca5(SiO4)2(SO4), Ca –Langbeinite K2Ca2(SO4)3 and chlorellestadite Ca10(SiO4)3(SO4)3Cl2. Their identifications and quantifications joined to the variation of sulfur amount and the calcination degree of the hot meal, permitted to better modulate the mechanism of ring formation in the kiln inlet.

A dynamical mechanism for the origin of nuclear rings

We develop a dynamical theory for the origin of nuclear rings in barred galaxies. In analogy with the standard theory of accretion discs, our theory is based on shear viscous forces among nested annuli of gas. However, the fact that gas follows non circular orbits in an external barred potential has profound consequences: it creates a region of reverse shear in which it is energetically favourable to form a stable ring which does not spread despite dissipation. Our theory allows us to approximately predict the size of the ring given the underlying gravitational potential. The size of the ring is loosely related to the location of the Inner Lindblad Resonance in the epicyclic approximation, but the predicted location is more accurate and is also valid for strongly barred potentials. By comparing analytical predictions with the results of hydrodynamical simulations, we find that our theory provides a viable mechanism for ring formation if the effective sound speed of the gas is low ($\cs\lesssim1\kms$), but that nuclear spirals/shocks created by pressure destroy the ring when the sound speed is high ($\cs\simeq10\kms$). We conclude that whether this mechanism for ring formation is relevant for real galaxies ultimately depends on the effective equation of state of the ISM. Promising confirmation comes from simulations in which the ISM is modelled using state-of-the-art cooling functions coupled to live chemical networks, but more tests are needed regarding the role of turbulence driven by stellar feedback. If the mechanism is relevant in real galaxies, it could provide a powerful tool to constrain the gravitational potential, in particular the bar pattern speed.

6. Human ring chromosome registry: Developing an interactive web resource for constitutional and cancer cytogenomic diagnosis

Constitutional ring chromosomes causing developmental disorders and somatic ring chromosomes in the form of double minutes, ring and marker chromosomes in various types of tumors have been documented. However, there are no organized efforts to compile and curate cytogenomic and clinical findings from ring chromosome cases. We have developed a web-based interactive Human Ring Chromosome Registry (HRCR) using a Microsoft Access based relational database to present cytogenomic and clinical findings from ring chromosome cases (http://web.gxmu.edu.cn/shengwu/HRC/home.asp). To validate the functional modules in this registry, constitutional ring chromosome cases reported in Chinese patients were compiled as a testing data set. From a total of 113 cases, relative frequencies, cytogenomic findings, and clinical features were summarized. An initial effort, focused on constitutional ring chromosome 21, classified the patients into three groups based on the cytogenomic findings and provided specific recommendations for prenatal and postnatal genetic counseling of ring chromosome 21. Furthermore, cytogenomic and genomic sequencing results from supernumerary ring chromosomes and derived giant marker chromosomes identified in liposarcoma were summarized to reveal the gene content of genomic imbalances, underlying mechanisms of ring formation, and implications for tumor classification and treatment. The development of HRCR has provided an interactive platform to compile and curate cytogenomic and clinical findings for constitutional and somatic ring chromosome cases. We propose a collaborative effort of clinical cytogeneticists and molecular geneticists to contribute to this online ring chromosome resource for establishing genotype-phenotype correlation and developing diagnostic guidelines and recommendations for genetic counseling and precise treatment.

Structural and Functional Studies of a Pyran Synthase Domain from a trans-Acyltransferase Assembly Line.

trans-Acyltransferase assembly lines possess enzymatic domains often not observed in their better characterized cis-acyltransferase counterparts. Within this repertoire of largely unexplored biosynthetic machinery is a class of enzymes called the pyran synthases that catalyze the formation of five- and six-membered cyclic ethers from diverse polyketide chains. The 1.55 Å resolution crystal structure of a pyran synthase domain excised from the ninth module of the sorangicin assembly line highlights the similarity of this enzyme to the ubiquitous dehydratase domain and provides insight into the mechanism of ring formation. Functional assays of point mutants reveal the central importance of the active site histidine that is shared with the dehydratases as well as the supporting role of a neighboring semiconserved asparagine.

回转窑处理钢铁厂含锌粉尘结圈机制的研究

针对回转窑处理含锌粉尘过程中的结圈问题，采用XRF、SEM和EDS等测试方法对窑中结圈物的化学组成和矿相组成进行分析，研究了窑中结圈物的形成机理。结果表明，结圈物的最主要的化学成分是铁和铁的氧化物，CaO、SiO2、Al2O3的含量也相对较高。内层结圈物以铁的浮氏体、钙长石为主，内层结圈以固相固结为主，液相粘结为辅。中层结圈物中液相的含量很高，铁的浮氏体和黄长石、尖晶石类物质次之。中层结圈主要是液相粘结造成的。粘结相主要是橄榄石类液相和铝酸盐类液相。外层结圈物以液相、铁的浮氏体和硅酸钙为主，主要是液相粘结，粘结相主要是金属铁液相和硅酸盐液相。导致结圈最主要的原因是煤灰的堆积和物料中各种氧化物反应形成的低熔点化合物在窑中高温的作用下形成了液相，在此基础上，提出了抑制窑内结圈的措施。 The study focuses on ring formation of rotary kiln in the process of treating Zn-bearing dusts from ironmaking and steelmaking process. The chemical composition and phase composition of the ring were analyzed using XRF, SEM and EDS. The results show that the ring consists of iron and iron oxides, and have relative high contents of CaO, SiO2, and Al2O3. The internal layer is mainly composed of iron wustite and calciclase, and mainly caused by solid phase sintering, complemented liquid phase bonding. The middle layer contains much liquid phase, and some iron wustite, the melilite and the spinel. The outer layer is mainly composed of liquid phase, iron wustite and calcium silicate. It is mainly caused by liquid phase bonding. The bond phase is predominantly liquid metallic iron and silicate liquid phase with low melting point. Based on the above results, proposing the following formation mechanism of ring: the accumulation of coal ash and the various oxides in the material form a low melting point compounds in the kiln, in turn the liquid and solid particle form high viscosity fluids adhere to the wall of rotary kiln. On the basis of the results, the measures to suppress the knot in the kiln are put forward.

Structure and composition of non‐polar (11‐20) InGaN nanorings grown by modified droplet epitaxy (Phys. Status Solidi B 5/2016)

Nitride-based quantum dots (QDs) show promise as sources for single photon emission, enabling comparably high temperature emission and access to the blue and green spectral region. Some droplets forming during modified droplet epitaxy on non-polar (11-20) surfaces of InGaN epilayers on GaN are associated with underlying ring-like structures. The work by Springbett et al. (pp. 840–844) discusses droplet etching as a possible mechanism for ring formation, whereby In and Ga atoms are incorporated into the droplet and diffuse to the edges. Thereafter, recrystallization occurs, leading to the formation of a ring. It is hypothesised that the droplet then creeps in a direction determined by the crystallographic anisotropy and the surface energetics. Once this movement halts, etching continues. The resulting structure consists of a recession enclosed by a double ring. Transmission electron microscopy (TEM) analysis shows the droplets move along the ⟨0001⟩ c-axis, and energy dispersive X-ray spectroscopy (EDXS) indicates that they have a very high In content. These studies may help reveal the underlying QD formation mechanism during modified droplet epitaxy.

Ring removal in rotary kilns used by the pulp and paper industry

Ring formation occurs in the rotary kilns used by the pulp and paper industry to regenerate the lime needed to produce white liquor. The main rings are: burning zone rings, mid-kiln rings, dust rings and/or mud balls, and mud rings. While the exact mechanisms of ring formation are not completely understood, frequent changes in the production rate and the mud solids, high soda content in the mud, and high levels of dust are believed to play a major role in ring formation. The presence of rings can restrict the movement of material through the kiln. If undetected, this can result in overheating of the refractory lining. In the worst case, the presence of rings can lead to unscheduled downtime to clean out the ring and replace damaged refractory bricks. Depending on the severity, the cost of repairs and lost production can be in excess of US$3 million for a single event. Even if the root cause of ring formation is known, from a practical standpoint, it can be difficult to eliminate rings. In mills where ring formation is a recurring problem, mechanical ring removal systems should be considered. This paper describes the use of ring removal systems as a cost effective way to mitigate the problems associated with ring formation.

Structure and composition of non‐polar (11‐20) InGaN nanorings grown by modified droplet epitaxy

Droplets grown by modified droplet epitaxy on non‐polar (11‐20) surfaces of InGaN epilayers on GaN have been seen to be associated with underlying ring‐like structures. This work discusses droplet etching as a possible mechanism for ring formation, and droplet creeping as a possible explanation for the droplets sitting askew of the ring centre. Transmission electron microscopy (TEM) analysis shows the droplets to move along the c‐axis, and indicates that they have a very high indium content.The image shows atomic force microscopy (AFM) data of a double‐ring structure, rendered in 3D.

Physicochemical Stages of Evolution: Ring-Like Structures in the Universe

This short digest is devoted to the mechanism of ring formation during the origination and evolution of planetary and satellite systems in the Universe. The appearance of these structures can be traced back to the phenomenon of spatially periodic condensation which can be observed on the Earth. The author actually posited the existence of exoplanetary systems and the cosmic scale of this phenomenon. It was accurately predicted that Uranus, Neptune and other heavenly bodies have rings. The suggested general mechanism rationalized the Titius-Bode law which, while not being a precise law, often accurately describes the tendency towards varying distances between planets (and their moons) and central bodies. The possibility of this law manifestation in exoplanetary systems had been predicted by the author long before their discovery. Many exoplanetary systems have been discovered by now and there is some evidence corroborating the mechanism of spatially periodic condensation involved in the formation of ring-like structures in these systems. The author’s hypothesis is now becoming a theory or a fact. It appears that we are now witnessing the dawn of a new extensive cosmology, taking into account general physicochemical mechanisms of space object formation.

Theoretical investigation of the chemoselectivity and synchronously pyrazole ring formation mechanism from ethoxymethylenemalononitrile and hydrazine hydrate in the gas and solvent phases: DFT, meta-GGA studies and NBO analysis

Chemoselectivity of the nucleophilic attack of nitrogen atom has been changed in the presence of the solvent due to Rds changes.