Thesis (M.A.)--Mahāwitthayālai Sīnakharintharawirōt, 1976. / In Thai. Typescript. Appendices : p. 324-356. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (p. 314-323).

Aluminium alloys with Si as the major alloying element form a class of material providing the most significant part of all casting manufactured materials. These alloys have a wide range of applications in the automotive and aerospace industries due to an excellent combination of castability and mechanical properties, as well as good corrosion resistance and wear resistivity. Additions of minor alloying elements such as Cu and Mg improve the mechanical properties and make the alloy responsive to heat treatment. The aim of this work is studying the role of size and morphology of microstructural constituents (e.g SDAS, Si-particles and intermetalics) on mechanical properties of Al-Si based casting alloy at room temperatures up to 500 ºC. The cooling rate controls the secondary dendrite arm spacing (SDAS), size and distribution of secondary phases. As SDAS becomes smaller, porosity and second phase constituents are dispersed more finely and evenly. This refinement of the microstructure leads to substantial improvement in tensile properties (e.g. Rm and εF). Addition of about 280 ppm Sr to EN AC- 46000 alloy yields fully modified Si-particles (from coarse plates to fine fibres) regardless of the cooling conditions. Depression in eutectic growth temperature as a result of Sr addition was found to be strongly correlated to the level of modification irrespective of coarseness of microstructure. Modification treatment can improve elongation to failure to a great extent as long as the intermetallic compounds are refined in size. Above 300 ºC, tensile strength, Rp0.2 and Rm, of EN AC-46000 alloys are dramatically degraded while the ductility was increased. The fine microstructure (SDAS 10 μm) has superior Rm and ductility compared to the coarse microstructure (SDAS 25 μm) at all test temperature (from room to 500 ºC). Concentration of solutes (e.g. Cu and Mg) in the dendrites increases at 300 ºC and above where Rp0.2 monotonically decreased. The brittleness of the alloy below 300 ºC was related to accumulation of a high volume fraction damaged particles such as Cu- Fe-bearing phases and Si-particles. The initiation rate of damage in the coarse particles was significantly higher, which enhances the probability of failure and decreasing both Rm and εF compared to the fine microstructure. A physically-based model was adapted, improved and validated in order to predict the flow stress behaviour of EN AC- 46000 cast alloys at room temperature up to 400 ºC for various microstructures. The temperature dependant variables of the model were quite well correlated to the underlying physics of the material

The scattering of H2 from Si(100) has been studied using pulsed molecular beam techniques and quantum state-specific detection methods. These studies can be used to test theoretical calculations and give insight into new theories of molecule-surface interactions, a fundamental study in a diverse field of science and technology. In this work, time-of-flight (TOF) spectra of the elastic scattering of H2(v=1. J=1) and H2(v=0, J=1) from clean Si were recorded over a wide range of surface temperatures. Two data processing strategies were developed to extract rich kinematic information from the scattering experiments, e.g., mean translational energy exchange, absolutely survival probability, and angular and speed distribution of the scattered molecules. No such set of quantitative results has been reported before for this system. Compared with close packed metal surfaces, these scattering experiments from a covalently bonded semiconductor surface showed a completely distinct dynamics, e.g. the finding of energy gain instead of loss from the substrate, much broader angular distribution and some counterintuitive surface temperature effects. From the studies of molecules/surface scattering experiments, the thermal excitation on Si(100) surface which depends on surface temperature can substantially alter the adsorption barrier and its distribution, and therefore changes the kinematics of scattered molecules. As a result, even the most basic understanding of the dynamics has to include phonon excitation and deexcitation of the silicon substrate. / text

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Pb-free piezoelectric materials have grown in importance through increased environmental concern related to the presence of Pb and the subsequent legislation that has arisen including directives such as Waste Electrical and Electronic Equipment (WEEE) and the Restriction of Hazardous Substances Directive (RoHS). While much progress has been made on producing Pb-free bulk materials, the need to integrate these next generation Pb-free piezoelectric materials with substrates to form functional micro devices has received less attention and raises a number of challenges. With respect to the high temperature mixed oxide synthesis method, a simple, cost effective and robust low temperature molten hydroxide synthesis (MHS) method derived from the molten salt synthesis (MSS) method, has been developed to produce K0.5Na0.5NbO3 (KNN) small grain powders and is a method that lends itself easily to industrial scale up. A powder/sol gel composite ink film forming technique has been used to produce KNN thick films on silicon substrates. Characterisation of the produced films has shown the films to exhibit piezoelectric coefficients for un-doped material in the region of 30pC/N. The work will report on the Na ion favouring mechanism of the MSS and the related mechanism of the MHS. The work will also report on the dielectric and piezoelectric characteristics of initial KNN thick films produced and an investigation into use of dopants and process modification to improve the KNN thick film’s characteristics.

As highly important personal and social approach, the choice of professional studies and policy is essential at the age of teens or in the early youth. In the same breath, it is the most relevant question among the students with special needs (SNS) as they are in need of help to key their intentions and desires to their possibilities according to their knowledge, skills and state of health, as well as to embrace the right occupation. This work is focused on ventilation of students’ familiarization with the professions, vocational training and development of their purposeful motivation in choosing the occupation. The basis of purposeful development into career education is general education, vocational training, practical work, as well as analysis of its results in the context of impersonal self-evaluation. The objective of the research is to investigate the purposeful career education of students with special needs. The goals of the research: 1. To analyses scientific pedagogical and psychological literature on investigative matter. 2. To ascertain how pre-career education and training of students with special needs is implement at comprehensive school. 3. To investigate the professional choice of students with special needs. 4. To work up a purposeful career model of students with special needs. 5. To give recommendations for the purposeful career training of students with special needs. Qualitative type of research – (the survey of experts, interview). Fifteen assistant... [to full text]

Life alteration stipulates the changing of education ideas, the search of new teaching and learning theories and methods is going on. For a contempory pupil it is not enough to have only formal knowledge and abilities. He/she must become an initiative person having a critical way of thinking and being able to work and create in this constantly changing world. A modern person should be able to learn continually and improve himself/herself as well as his/her activities. From this point of view it is important to understand that studies for each person are not over when he finishes school or any other educational institution, he is an active learner in everyday life and activities. In order to estimate our unique experience, to improve our knowledge and to see what else we need for our improvement we must master modern methods of active teaching which deliberately help to plan learning activity. Such learning activity should be full of sense. In the documents regulating the content of education at comprehensive schools in Lithuania the constructive direction of education is encouraged, the creation of the system of valuable rules is underlined, the importance of educating different kinds of abilities is mentioned, by various methods teachers are stimulated to encourage pupils’ self-dependence and to create auspicious conditions for this at the lessons. Searching to combine these two spheres it is relevant to encourage cognitive processes employing interactive learning strategies... [to full text]

Lifelong learning became a must skill in Europe and all over the World that are affected by rapid social, technological and economical changes in nowadays. Qualitative training and learning process is influenced by many factors that should be carefully examined during the curriculum design phases, as well as during the learning/ teaching process. Distance learning and teaching is the efficient means to implement strategic aims of the system of education: to create learning possibilities for all society members, to contribute to designing effective learning/ teaching process, as well as to ensure more flexile organization of learning activities. While new distance learning/ teaching forms are getting more and more popular, they should be reviewed regularly applying a consistent quality evaluation methodology based on quality criteria and indicators, and distance learning/ teaching curriculum quality should be examined before each learning/ teaching process. There are some examples of quality assessment methodology prepared for distance learning/ teaching curriculum assessment in Lithuania on practical level allowing assessing distance learning/ teaching curriculum quality before accreditation procedure, however, such factors as analysis of other existing resources for realisation of curriculum online, effectiveness of chosen curriculum design and factors, influencing learning/ teaching process having the current design options, are not assessed at all. Quality assessment... [to full text] / Sparčių socialinių, technologinių ir ekonominių pokyčių veikiamoje Europoje mokymasis visą gyvenimą tapo būtinybe. Nuotolinis mokymas(-is) (NM) puikiai sprendžia strateginių švietimo sistemos siekių įgyvendinimą, sukuriant mokymosi galimybes ir efektyvesnį mokymo(-si) procesą, užtikrinant lankstesnį mokymo(-si) veiklos organizavimą. Naujai atsirandančioms NM formoms turi būti taikoma kokybės kriterijų bei rodiklių sistema, o NM turinio kokybė turi būti įvertinama prieš kiekvieną mokymo(-si) organizavimą. Lietuvoje parengtos NM turinio kokybės vertinimo metodikos leidžia įvertinti jo kokybę prieš jo akreditaciją, tačiau pasirinktų NM turinio realizavimo formų ir NM turinio projektavimo strategijos efektyvumas ir poveikis mokymo(-si) organizavimo procesui lieka neįvertinti. Mokymo(-si) turinio kokybės vertinimo proceso metu neužtikrinama konstruktyvaus mokymo(-si) samprata, nes nėra įvertinama, ar NM turinys leis mokymo(-si) organizatoriams savarankiškai veikti individualiose, nenumatytose situacijose mokymo(-si) organizavimo metu. Tačiau kokybės vertinimo metodika negali būti parengta kol nėra nustatyti ir apibendrinti veiksniai, įtakojantys NM turinio kokybę Disertacijoje projektuojamas NM turinio kokybės reflektyvus vertinimo modelis sujungia NM turinio projektavimo ir mokymo(-si) organizavimo procesus. Tyrime nagrinėjamos NM turinio projektavimo teorijos, identifikuojamos turinio kokybės vertinimo dimensijos, operacionalizuojami kokybės vertinimo veiksniai, kurių... [toliau žr. visą tekstą]

A new technique based on the study of the transmitted neutron beam has been developed to study the low-temperature decomposition of austenite in a 0.4 wt.% C–3 wt.% Mn–2 wt.% Si steel. Experiments were conducted in which the neutron beam continuously passed through a specially designed layered sample, the temperature of which could be controlled to allow for a high-temperature austenization treatment followed by accelerated cooling to an isothermal transformation temperature in the range of 275–450 °C. It was possible to measure the volume fraction of the face-centred cubic (fcc) and body-centred cubic (bcc) phases and the carbon concentration of the fcc phase by characterizing the neutron Bragg edges in the transmitted beam. This provides a technique for in situ continuous measurements on the decomposition of austentite. The technique has been validated by comparing the data with other experimental techniques such as dilatometry, quantitative optical metallography and room temperature X-ray diffraction.

In this work, we have investigated the internal stress contribution to the flow stress for a commercial 6xxx aluminium alloy (AA6111). In contrast to stresses from forest and precipitation hardening, the internal stress cannot be assessed properly with a uniaxial tensile test. Instead, tension-compression tests have been used to measure the Bauschinger stress and produce a comprehensive study which examines its evolution with i) the precipitation structure and ii) a wide range of applied strain. A large set of ageing conditions was investigated to explore the effect of the precipitation state on the development of internal stress within the material. It is shown that the Bauschinger stress generally increases with the applied strain and critically depends on the precipitate average radius and is thus linked to the shearable/non shearable transition. Further work in the case of non-shearable particles shows that higher strain eventually lead to particle fracture and the Bauschinger stress then rapidly decreases. Following the seminal work of Brown et al, a physically based approach including plastic relaxation and particle fracture is developed to predict the evolution of the internal stress as a function of the applied strain. Knowing the precipitation structure main characteristics –such as the average precipitate radius, length and volume fraction– allows one to estimate accurately the internal stress contribution to the flow stress with this model.