Mechanism Of Hindrance Research Articles

Dynamical mechanism of fusion hindrance in heavy ion collisions

Dynamical mechanism of fusion hindrance in heavy ion collisions

Water depth resources and driving mechanism of navigation hindrance of Jingjiang Reach watershed after Three Gorges Project operation

系统解析长江中游河湖交汇区域航道水深资源的变化,可支撑“黄金航道”的可持续发展。本研究以洞庭湖-荆江交汇段为对象,研究洞庭湖分汇区域水沙条件、荆江河段滩槽演变与河湖交汇段航道水深资源的关系。研究表明:三峡工程运行以来,洞庭湖三口分流量和分沙量延续了三峡工程运行前的减少态势,伴随洞庭湖分流量减少,相对增加的长江干流径流量增强了河床冲刷强度,反馈使得洞庭湖三口分流量和分沙量均处于较低值;荆江河段河床冲刷给航道尺度提升奠定了有利基础,河湖分汇区域不满足4.5 m×200 m(水深×宽度)的长度为12.6 km,占荆江河段碍航总长度的68.35%。碍航驱动机制上:松滋口分流区段(枝城-昌门溪)的4.5 m水槽贯通但宽度不足200 m,汊道分流关系不稳定及洲滩萎缩制约航道条件稳定,枯水位下降及“坡陡流急”现象仍然严峻,不利于航道条件保障及船舶安全航行;太平口分流区段水位下降、洲滩萎缩、汊道交替发展使得枯水航路不稳定或水深不足4.5 m;藕池口分流区域的洲滩崩退、洲滩冲刷引起的向下游泥沙输移,碍航表现为航宽不足200 m或出现水深不足4.5 m的浅滩;洞庭湖入汇影响区段(熊家洲-城陵矶)受弯道冲淤特性、湖泊出流顶托作用等影响,航槽内出现水深不足4.5 m的浅滩,但顶托作用存在趋缓趋势,有利于航道条件的改善。;A systematic analysis on the effects of the changed interactive relationships between rivers and lakes on fairway depth can help to support the sustainable development of the “Gold waterway” of the Yangtze River. In this study, we investigate the variation characteristics of water and sediment, and the relationships between the evolution of shoals and channels and the fairway depth, in the Lake Dongting-Jingjiang Reach confluence of the Yangtze River. The results indicate that since the operation of the Three Gorges Project, the split ratio of watersplit and the sediment distribution of the three outlets of Lake Dongting continued to decrease. Along with the decreasing flow of Lake Dongting, the relative increase in the runoff of the Jingjiang Reach increases the riverbed erosion scouring intensity, which keep the split ratio of water split and the sediment distribution of the three outlets at a lower value. The riverbed erosion scouring of the Jingjiang Reach has created a promising foundation for an increase in the waterway dimensions. However, the length of the reach fail to meet the requirement of 4.5 m× 200 m (water depth × width) is 12.6 km in the river-lake confluence, accounting for 68.35% of the total length of obstructed navigation. The mechanisms of the obstructed navigation are as follow: at the reach affected by the first outlet (Songzikou), a 4.5 m flume has been formed, but its width is less than 200 m. The instability of water split and the shrinkage of bottomland restrict the stability of channel conditions. Moreover, the reductions of low-flow water level and the phenomenon of “steep slope and rapid current” affect the ships' safety. At the reach (Taipingkou) affected by the second outlet, the shrinkage of the bottomland, and the intersecting braided river channels make the low-flow routes unstable, the water depth being less than 4.5 m. At the reach (Ouchikou) affected by the third outlet, the shoreline of the reach has collapsed and retreated significantly. Additionally, point bar beach erosion scouring has led to the downstream movement of sediment, which have caused the downstream waterway width at the reach to be reduced to less than 200 m or formed shoals with a water depth of less than 4.5 m. Owing to the characteristics of scouring and deposition in the bends reaches and the jacking effect of the lake's outflow backwater, the water depth of some shoals are less than 4.5 m in the navigation waterway. However, the jacking effect of the lake's outflow backwater is weakening, which benefits the improvement of channel conditions.

Accelerating electrocatalytic reduction of nitrate to ammonia by utilizing steric hindrance in single boron-decorated 2H/1T-MoS2: A theoretical insight

With the increasing demand of explosives, severe burden on the environment during their use and production is seriously growing. In particular, nitrate is a potential threat to water body, which will directly endanger human health. In this work, we put forward an interesting strategy for improving the electrochemical performance of nitrate reduction reaction (NO3RR) via tuning the phase of substrate MoS2 decorated by single boron atom, denoted as B@2H-MoS2 and B@1T-MoS2. By means of DFT calculations, it is found that B@1T-MoS2 has better NO3RR activity than B@2H-MoS2 because the former (0.39 V) has smaller limiting potential than the latter (0.61 V). Meanwhile, B@1T-MoS2 can effectively alleviate H poisoning and suppress the formation of byproducts. Additionally, the underlying regulation mechanism of the steric hindrance caused by structural phase change is to promote the electron redistribution. The excellent stability of B@1T-MoS2 featured with metastable basement was confirmed by migration energy barrier and ab initio molecular dynamics (AIMD) simulations. Our work may motivate the design of various electrodes beyond element screening and offer a valuable strategy for experimental synthesis.

Survey of deep sub-barrier heavy-ion fusion hindrance phenomenon for positive and negative Q-value systems using the proximity-type potential

A systematic survey of the accurate measurements of heavy-ion fusion cross sections at extreme sub-barrier energies is performed using the coupled-channels (CC) theory that is based on the proximity formalism. This work theoretically explores the role of the surface energy coefficient and energy-dependent nucleus-nucleus proximity potential in the mechanism of the fusion hindrance of 14 typical colliding systems with negative -values, including 11B+197Au, 12C+198Pt, 16O+208Pb, 28Si+94Mo, 48Ca+96Zr, 28Si+64Ni, 58Ni+58Ni, 60Ni+89Y, 12C+204Pb, 36S+64Ni, 36S+90Zr, 40Ca+90Zr, 40Ca+40Ca, and 48Ca+48Ca, as well as five typical colliding systems with positive -values, including 12C+30Si, 24Mg+30Si, 28Si+30Si, 36S+48Ca, and 40Ca+48Ca. It is shown that the outcomes based on the proximity potential along with the above-mentioned physical effects achieve reasonable agreement with the experimentally observed data of the fusion cross sections , astrophysical factors, and logarithmic derivatives in the energy region far below the Coulomb barrier. A discussion is also presented on the performance of the present theoretical approach in reproducing the experimental fusion barrier distributions for different colliding systems.

Constraining the equation of state of nuclear matter from fusion hindrance in reactions leading to the production of superheavy elements

The mechanism of fusion hindrance, an effect preventing the synthesis of superheavy elements in the reactions of cold and hot fusion, is investigated using the Boltzmann-Uehling-Uhlenbeck equation, where Coulomb interaction is introduced. A strong sensitivity is observed both to the modulus of incompressibility of symmetric nuclear matter, controlling the competition of surface tension and Coulomb repulsion, and to the stiffness of the density-dependence of symmetry energy, influencing the formation of the neck prior to scission. The experimental fusion probabilities were for the first time used to derive constraints on the nuclear equation of state. A strict constraint on the modulus of incompressibility of nuclear matter $K_0 = 240 - 260$ MeV is obtained while the stiff density-dependences of the symmetry energy ($\gamma>1.$) are rejected.

Alteration of classical and hematopoiesis specific p53 pathway in the bone marrow hematopoietic stem/progenitor compartment facilitates leukemia progression in experimental mice

Downregulation of p53 is associated with most of the neoplasms, however it claims additional significance for hematopoietic malignancy due to its supplementary role during hematopoiesis. Apart from the classical role as tumor suppressor, p53 during steady state hematopoiesis is associated with the maintenance of quiescent cell population in bone marrow by upregulating necdin (Ndn) and Gfi-1. We felt, it is necessary to delineate its attribution towards malignant conversion of hematopoietic system during leukemogenesis from all the possible angles. The present study deals with the characterization of N-N′ Ethylnitrosourea (ENU) induced mouse model of leukemia by peripheral blood hemogram, bone marrow cytology, histology, cytochemical staining (MPO) and scanning electron microscopic study. We further investigated the alteration of conventional and hematopoiesis specific p53 pathways by flowcytometric expressional analysis of ATM, Chk-2, p53, p21, Ndn, Gfi-1 and Tie-2. The disruption of classical p53 pathway was observed in leukemic hematopoietic stem/progenitor population which involved downregulation of ATM, Chk-2, p53 and p21. Moreover, the expressional decline of Ndn and Gfi-1 hinted towards the mechanism of hindrance of hematopoietic quiescency in leukemic bone marrow. Increased expression of Tie-2 due to reverse correlation with p53 was found to be responsible for pathological angiogenesis in bone marrow together with increased blast burden in bone marrow during leukemia. The study presents the mechanistic scenario of the alteration of both classical as well as hematopoiesis specific p53 pathways in HSPC compartment triggering leukemic pathophysiology.

Mechanism of Fusion Hindrance and Predictions of SHE Production

It is shown that in the encounter of two incident ions the system quickly starts to fill out the neck crevice of the di-nucleus system to form a super-deformed mono-nucleus. The probability of forming the spherical compound nucleus is obtained, starting with the super-deformed nucleus, with the dissipation-fluctuation dynamics, which gives rise to an extremely small fusion probability. With the statistical theory of decay, survival probability of the compound nucleus is calculated. Examples of calculated excitation functions for Super-Heavy Element(SHE) are given.

DI-NUCLEUS DYNAMICS TOWARD FUSION OF HEAVY NUCLEI

The Two-Step Model for fusion of massive systems is briefly recapitulated, which clarifies the mechanism of so-called fusion hindrance. Since the neck changes the potential landscape, especially the height of the conditional saddle point, time evolution of the neck degree of freedom plays a crucial role in fusion. We analytically solve time-evolution of nuclear shape of the composite system from di-nucleus to mono-nucleus. The time-dependent distribution function of the neck is obtained, which elucidates dynamics of fusion processes in general, and thus, is useful for theoretical predictions on synthesis of the superheavy elements with various combinations of incident heavy ions.

Competition of fusion and quasifission in reactions leading to production of superheavy elements

The mechanism of fusion hindrance, an effect observed in the reactions of cold, warm, and hot fusion leading to production of superheavy elements, is investigated. A systematics of transfermium production cross sections is used to determine fusion probabilities. The mechanism of fusion hindrance is described as a competition of fusion and quasifission. Available evaporation residue cross sections in the superheavy region are reproduced satisfactorily. Analysis of the measured capture cross sections is performed and a sudden disappearance of the capture cross sections is observed at low fusion probabilities. A dependence of the fusion hindrance on the asymmetry of the projectile-target system is investigated using the available data. The most promising pathways for further experiments are suggested.

Fluoride inhibition of inorganic pyrophosphatase III. Dependence on the nature of substrate and metal ion cofactor

Studies of fluoride interaction with bakers' yeast inorganic pyrophosphatase (pyrophosphate phosphohydrolase, EC 3.6.1.1) in the presence or absence of enzyme-catalyzed reactions have revealed pronounced specificity of this inhibitor. It was found that the inhibition of the enzymic hydrolysis of PP i, ADP, ATP and tripolyphosphate in the presence of Zn 2+ and Mn 2+ at pH 6.5 is not time dependent and by far less extensive as that observed for the Mg 2+-stimulated cleavage of PP i (apparent K i values differ by three orders of magnitude). Addition of Ca 2+ to the latter reaction decreases proportionally the activity of the enzyme and the rate constant for the binding of fluoride to it, which indicates that the enzyme-substrate complexes containing both Mg 2+ and Ca 2+ are inert in the reaction with fluoride. Preincubation of pyrophosphatase with NaF and various metal cations and substrates, in conditions where the enzyme does not act as a catalyst, does not affect its activity compared to controls lacking fluoride. The results are consistent with the proposed mechanism of mutual hindrance of substrate and fluoride release from the active site of pyrophosphatase.

Studies on the mechanism of hindrance to growth of wheat in the acidified soil.

We investigated the growth and yield of 4 wheat varieties in different kind of soil, - One was soil (pH. 4.2) without lime and barnyard manure and had been given 50 Kg. of ammonium sulphate, 52 kg. calcium superphosphate and 18 kg. potassiumsulphate per 10 are every year since 1936, and the other (pH. 5.8) was the control, which had been given 6O kg. of lime per 10 are every year beside three kinds of fortilizer. In the early stage of growth, the seminal roots find much difficulty in going into the acidified soil, so they come up to surface to a degtee when the soil is frozen, but this phenomenon is scarcely caused in HIRAKIKONUGI variety. The decrease of the height of plant and the number of stem in the acidified soil is not remarkable in the early stage of growth, but conspicuous after the middie stage. This hindrance is least to HIRAKIKOMUGI. As for the growth of root, in the acidified soil, the decrease of number and weight is not great in the early stage of growth, but it seems that their sideroots do not come out. In the middle stage, the growth extremely hindered and the ratio of root weight to that of control at the latter part of March is 36% in HIRAKIKOMUGl, 17% in AKABOZU, 16% in KOMPIRA and 12% in WASEKOMUGI. the root-system at the last stage of growth in acidified soil. As to the yield, that of acidified soil is much less and the ratio of the weight of grains produced per unit area to that of control is 26% in HIRAKIKOMUGI, 5% in AKABOZU, 13% in KOMPIRA, and the harvest of WASEKOMUGI is almast nothing.