Counterions and water molecules in charged silicon nanochannels: the influence of surface charge discreteness

In order to detect the effect of the surface charge discreteness on the properties at the solid-liquid interface, molecular dynamics simulation model taking consideration of the vibration of wall atoms was used to investigate the ion and water performance under different charge distributions. Through the comparison between simulation results and the theoretical prediction, it was found that, with the degree of discreteness increasing, much more counterions were attracted to the surface. These ions formed a denser accumulating layer which located much nearer to the surface and caused charge inversion. The ions in this layer were non-hydrated or partially hydrated. When a voltage was applied across the nanochannel, this dense accumulating layer did not move unlike the ions near uniformly charged surface. From the water density profiles obtained in nanochannels with different surface charge distributions, the influence of the surface charge discreteness on the water distributions could be neglected

Challenges of Alternatives Educational Policy for Enrolling Children to School in Tanzania

Considering the substantial growth of educational policy research in providing quality education, many nations including Tanzania have adopted strategic initiatives to improve education. As the implementation of initiatives or programs require different stakeholders, it is associated with the practical utility of the country's progress in providing and evaluating quality and accessible education and the efficacy of economic growth of rural livelihood. Such evaluation is carried out at several separate stages by distinct stakeholders engaged in educational policy making on the effects to the people.  Evaluation as a method of assessing the progress or failure of the pre-existing policies can be often daunting for several participants in the educational sector. The evaluation of alternative and pre-policies, however, has an essential part of the progress of national policy. This also appears to be somewhat evident in the context of the Tanzanian National Educational Policy. Nevertheless, assessment-based policy making in Tanzania and many countries has not yet been widely applied in this regard. This is particularly true in developing countries whose public sector capacity is not yet fully developed. In these countries, the utilization of policy evaluation results in the process of efficient learning process a supreme clumsy. Evaluation usually encompasses a judgement of interventions as per their results, potential impact and needs they aim to satisfy. It is a systematic control mechanism which generates a stringent evidence base to inform decision-making and contributing to making Local government activities more effective, concise, useful, relevant and efficient. Evaluation also enhances accountability, learning and transparency. To reach this, the evaluation requirements of the Local authority strive to guarantee appropriate and timely evaluations of high quality and to communicate the outcomes of the evaluation in a clear and transparent manner to decision-makers and other appropriate stakeholders to promote the use of evaluation outcomes on educational policy

On creep fatigue interaction of components at elevated temperature

The accurate assessment of creep-fatigue interaction is an important issue for industrial components operating with large cyclic thermal and mechanical loads. An extensive review of different aspects of creep fatigue interaction is proposed in this paper. The introduction of a high temperature creep dwell within the loading cycle has relevant impact on the structural behaviour. Different mechanisms can occur, including the cyclically enhanced creep, the creep enhanced plasticity and creep ratchetting due to the creep fatigue interaction. A series of crucial parameters for crack initiation assessment can be identified, such as the start of dwell stress, the creep strain and the total strain range. A comparison between the ASME NH and R5 is proposed, and the principal differences in calculating the aforementioned parameters are outlined. The Linear Matching Method framework is also presented and reviewed, as a direct method capable of calculating these parameters and assessing also the steady state cycle response due to creep and cyclic plasticity interaction. Two numerical examples are presented, the first one is a cruciform weldment subjected to cyclic bending moment and uniform high temperature with different dwell times. The second numerical example considers creep fatigue response on a long fibre reinforced Metal Matrix Composite (MMC), which is subjected to a cycling uniform thermal field and a constant transverse mechanical load. All the results demonstrate that the Linear Matching Method is capable of providing accurate solutions, and also relaxing the conservatisms of the design codes. Furthermore, as a direct method it is more efficient than standard inelastic incremental finite element analysis

Influences of T-stress on constraint effect in mismatched modified boundary layer model for creep crack

Constraint effect plays an important role in assessing the stress field and the growth rate of creep crack in components under high temperature. The mismatched modified boundary layer (MMBL) model is extended to creep crack in this paper. For the MMBL model, the Q-parameters for different mismatch factors are studied under different T-stresses. The variation of the dimensionless T-stress in creep zone is given. The variations of open stresses with creep time for different mismatch factors are presented under different T-stresses. The comparisons of Q-parameter between homogeneous material and mismatched materials are made. The influences of mismatch factor on the constraint parameter are discussed. The influence of creep exponent on the open stress is also discussed

Creep-fatigue behaviour of aluminum alloy-based metal matrix composite

Metal Matrix Composite (MMC) represents a valuable option as structural material for different type of structures and components. Despite this they struggle to become widely adopted due to expensive manufacturing process and complex microstructural behaviour. When subjected to cyclic load conditions the structural response of MMC is not trivial, and becomes even more difficult when high temperature load is involved. Different failure mechanisms would happen and they are originated by the different material properties between the fibre and surrounding matrix. Among all, the mismatch of thermal expansion coefficient is recognized to be the dominant one. The significantly differing coefficients of thermal expansion between ceramic and metal give rise to micro thermal stresses, which enhance the initiation of matrix micro cracks. Their performance under varying load and high temperature is complex, and hence it is difficult to have a clear understanding of the structural responses, especially when fatigue and creep damages become the main failures of MMCs. To improve current understanding of the relationship between creep fatigue interaction of MMCs, the history of thermal and mechanical loading, and the creep dwell period, a highly accurate but robust direct simulation technique on the basis of the Linear Matching Method (LMM) framework has been proposed in this paper, and been applied to model the fatigue and creep behaviour of MMCs. A homogenised FE model is considered in all analyses, which consist of continuous silicon carbide fibres embedded in a square 2024T3 aluminium alloy matrix array. Various factors that affect creep and fatigue behaviours of composites are analysed and discussed, including effects of the applied load level, dwell period and temperature on the MMC’s performance. The effects of reversed plasticity on stress relaxation and creep deformation of MMC are investigated, and the behaviours of cyclically enhanced creep and elastic followup are presented. A detailed study of the creep ratchetting mechanism is also performed with the concentration on the impact of temperature and different loading conditions. The accuracy of the proposed method has been verified by detailed incremental finite element analyses using the commercial finite element solver Abaqus. Such verifications further improve the understanding of the failure mechanisms identified and discussed in this work

In-group favoritism or black sheep effect? The moderating role of norm strength on destination residents’ responses towards deviant behaviors

Drawing on social identity theory and focus theory of norms, this study investigated differences in how destination residents respond to deviant behaviors by other residents—members of their in-group—and similar behavior by tourists, who they see as the out-group. We proposed and tested a conceptual model of the transition between in-group favoritism and the black sheep effect under the moderating effect of norm strength. A mixed-method approach, including a secondary data study and three scenario-based experiments, was applied. Findings of this study revealed that focal residents showed in-group favoritism for other residents\u27 deviant behavior compared with tourists. The contagion effect of deviant behavior was stronger among in-groups than out-groups. However, with respect to behaviors about which norms are tight, the black sheep effect comes into play, as focal residents hold a higher desire to punish in-groups’ deviant behavior than the out-group. This study has theoretical and practical implications for destination marketing organizations

Ionic Behavior in Highly Concentrated Aqueous Solutions Nanoconfined between Discretely Charged Silicon Surfaces

Through molecular dynamics simulations considering thermal vibration of surface atoms, ionic behaviors in concentrated NaCl solutions confined between discretely charged silicon surfaces have been investigated. The electric double layer structure was found sensitive to the density and distribution of surface charges. Due to the surface charge discreteness, slight charge inversion appeared which depended on the surface charge density, bulk concentration and confinement. In the nanoconfined NaCl solutions differently concentrated from 0.2 M to 4.0 M, the locations of accumulation layers for Na+ and Cl- ions kept stable, but their peak values increased. The higher the concentration was, the more obvious charge inversion appeared. In 4.0 M NaCl solution, Na+ and Cl- ions show obvious alternating layered distributions which may be corresponding to the solidification found in experiments. By changing surface separation, the confinement had a large effect on ionic distributions. As both surfaces approached each other, many ions and water molecules were squeezed out of the confined space. Two adjacent layers in ion or water distribution profiles can be forced to closer to each other and merge together. From ionic hydration analysis, the coordination number of Na+ ions in highly-confined space was much lower than that in the bulk.Comment: 26 pages, 9 figure

The influence of tourists\u27 monetary and temporal sunk costs on destination trust and visit intention

Although the phenomenon of sunk costs is common in tourism situations, tourism research has largely ignored its effect on tourists. Drawing on prospect theory, cognitive dissonance theory, and signal theory, this study proposed that monetary sunk cost and temporal sunk cost both have significant impact on potential tourists\u27 visit intention. Four scenario-based experiments were performed to test hypothesized relationships. Findings revealed that monetary sunk cost has a negative effect on visit intention, while temporal sunk cost has a positive effect. Good destination reputation attenuates the effects, and destination trust mediates the relationship between sunk cost and visit intention. These studies extend existing theoretical applications by identifying the conditions under which sunk cost can influence tourists\u27 visit intention, and provides relevant practical suggestions for tourism product suppliers and local government departments

The Cost Implications of Primary School Educational Policy Shift Toward Free Education at Point of Delivery for Primary School Children: The Case Study of Nyamagana District

One of the fundamental issues in the educational sector in Tanzania is on how to increase and promote equipoise in education to the indigenous. The study encapsulates many of the central outcomes on educational policy change. It stipulates that, there are more children being enrolled in primary schools due to free education. This has consequently led educational sector to encounter encumbrance to the national budget either directly or indirectly. The impacts have mostly affected educational stakeholders including students, teachers, parents and policy implementers. This study is both quantitative and qualitative and was conducted in Nyamagana district. The study used population set to gather data from Mwanza region in Nyamagana District-Tanzania. The researcher limited himself to the respondents who were from Local Government Authorities that encompassed Education Officer of Mwanza Region, District Secretary Education as well as head teachers, teachers, students and parents who had children at primary schools. Keywords: Implications, Policy, Education, Tanzania, Primary, School DOI: 10.7176/JEP/10-15-21 Publication date:May 31st 201