Dynamic growth of tensile cracks by ductile and brittle fracture mechanisms in a viscoplastic material

In this paper, a finite element analysis of steady-state dynamic crack growth under Mode I, plane strain, small-scale yielding conditions is performed in a rate dependent plastic material characterized by the over-stress model. The main objective of the paper is to obtain theoretically the dependence of dynamic fracture toughness on crack speed. Crack propagation due to a ductile (micro-void) mechanism or a brittle (cleavage) mechanism, as well as transition from one mode to another are considered. The conversion from ductile to brittle has been observed experimentally but has received very little attention using analytical methods. Local fracture criteria based on strains and stresses are used to describe ductile and brittle fracture mechanisms. The results obtained in this paper are in general agreement with micro-structural observations of mode conversion during fracture initiation. Finally, the particular roles played by material rate sensitivity and inertia are examined in some detail.

Social and material deprivation among youth in Finland : causes, consequences, and coping.

Background: Social and material deprivation is associated with poor health, decreased subjective well-being, and limited opportunities for personal development. To date, little is known about the lived experiences of Finnish low-income youths and the general purpose of this study is to fill this gap. Despite the extensive research on socioeconomic income disparities, only a few scholars have addressed the question of how low socioeconomic position is experienced by disadvantaged people themselves. Little is known about the everyday social processes that lead to decreased well-being of economically and socially disadvantaged citizens. Data: The study is based on the data of 65 autobiographical essays written by Finnish low-income youths aged 14-29 (M=23.51, SD=3.95). The research data were originally collected in a Finnish nationwide writing contest “Arkipäivän kokemuksia köyhyydestä” [Everyday Experiences of Poverty] between June and September of 2006. The contest was partaken by 850 Finnish writers. Methods and key concepts: Autobiographical narratives (N=65) of low-income youths were analyzed based on grounded theory methodology (GTM). The analysis was not built on specific pre-conceived categorizations; it was guided by the paradigm model and so-called “sensitizing concepts”. The concepts this study utilized were based on the research literature on socioeconomic inequalities, resilience, and coping. Socioeconomic inequalities refer to unequal distribution of resources, such as income, social status, and health, between social groups. The concept of resilience refers to an individual’s capacity to cope despite existing risk factors and conditions that are harmful to health and well-being. Coping strategies can be understood as ways by which a person tries to cope with psychological stress in a situation where internal or externals demands exceed one’s resources. The ways to cope are cognitive or behavioral efforts by which individual tries to relieve the stress and gain new resources. Lack of material and social resources is associated with increased exposure to health-related stressors during the life-course. Aims: The first aim of this study is to illustrate how youths with low socioeconomic status perceive the causes and consequences of their social and material deprivation. The second aim is to describe what kind of coping strategies youths employ to cope in their everyday life. The third aim is to build an integrative conceptual framework based on the relationships between causes, consequences, and individual coping strategies associated with deprivation. The analysis was carried out through systematic coding and orderly treatment of the data based on the grounded theory methodology. Results: Finnish low-income youths attributed the primary causes of deprivation to their family background, current socioeconomic status, sudden life changes, and contextual factors. Material and social deprivation was associated with various kinds of negative psychological, social, and material consequences. Youths used a variety of coping strategies that were identified as psychological, social, material, and functional-behavioral. Finally, a conceptual framework was formulated to link the findings together. In the discussion, the results were compared and contrasted to the existing research literature. The main references of the study were: Coping: Aldwin (2007); Lazarus & Folkman (1984); Hobfoll (1989, 2001, 2002). Deprivation: Larivaara, Isola, & Mikkonen (2007); Lister (2004); Townsend (1987); Raphael (2007). Health inequalities: Dahlgren & Whitehead (2007); Lynch. et al. (2000); Marmot & Wilkinson (2006); WHO (2008). Methods: Charmaz (2006); Flick (2009); Strauss & Corbin (1990). Resilience: Cutuli & Masten (2009); Luthar (2006).

Kurkistus lapsen arkeen vuorohoidossa

Nonstandard hour child care is a subject rarely studied. From an adult's perspective it is commonly associated with a concern for child's wellbeing. The aim of this study was to view nonstandard hour child care and its everyday routines from children´s perspective. Three research questions were set. The first question dealt with structuring of physical environment and time in a kindergarten providing nonstandard hour child care. The second and third questions handled children s agency and social interaction with adults and peers. The research design was qualitative, and the study was carried out as a case study. Research material was mainly obtained through observation, but interviews, photography and written documents were used as well. The material was analysed by means of content analysis. The study suggests that the physical environment and schedule of a kindergarten providing nonstandard hour child care are similar to those of kindergartens in general. The kindergarten's daily routine enabled children s active agency especially during free play sessions for which there was plenty of time. During free play children were able to interact with both adults and peers. Children s individual day care schedules challenged interaction between children. These special features should be considered in developing and planning nonstandard hour child care. In other word, children's agency and opportunities to social interaction should be kept in mind in organising the environment of early childhood education in kindergartens providing nonstandard hour child care.

Critical phenomena in polymer solutions: Scaling of the free energy

The thermodynamics of monodisperse solutions of polymers in the neighborhood of the phase separation temperature is studied by means of Wilson’s recursion relation approach, starting from an effective ϕ4 Hamiltonian derived from a continuum model of a many‐chain system in poor solvents. Details of the chain statistics are contained in the coefficients of the field variables ϕ, so that the parameter space of the Hamiltonian includes the temperature, coupling constant, molecular weight, and excluded volume interaction. The recursion relations are solved under a series of simplifying assumptions, providing the scaling forms of the relevant parameters, which are then used to determine the scaling form of the free energy. The free energy, in turn, is used to calculate the other singular thermodynamic properties of the solution. These are characteristically power laws in the reduced temperature and molecular weight, with the temperature exponents being the same as those of the 3d Ising model. The molecular weight exponents are unique to polymer solutions, and the calculated values compare well with the available experimental data.

Interferometry with a novel composite material

An interesting application of optical phase conjugation is phase conjugate interferometry. We report here a new approach to real-time interferometry which combines the high phase conjugate efficiency of photorefractive crystals and the fast response times offered by dye-doped polymer films by using a composite structure. The ability of this material to generate two independent but overlapping phase conjugate waves. which can interfere to reveal the phase changes in a test object, is discussed and demonstrated with a specific example.

Electrical Contact Resistance in Thin (<= 0.5 mu m) Gold Plated Contacts: Effect of Gold Plating Thickness

This paper describes the electrical contact resistance (ECR) measurements made on thin gold plated (gold plating of <= 0.5 mu m with a Ni underlayer of similar to 2 mu m) oxygen free high conductivity (OFHC) Cu contacts in vacuum environment. ECR in gold plated OFHC Cu contacts is found to be slightly higher than that in bare OFHC Cu contacts. Even though gold is a softer material than copper, the relatively high ECR values observed in gold plated contacts are mainly due to the higher hardness and electrical resistivity of the underlying Ni layer. It is well known that ECR is directly related to plating factor, which increases with increasing coating thickness when the electrical resistivity of coating material is more than that of substrate. Surprisingly, in the present case it is found that the ECR decreases with increasing gold layer thickness on OFHC Cu substrate (gold has higher electrical resistivity than OFHC Cu). It is analytically demonstrated from the topography and microhardness measurements results that this peculiar behavior is associated with thin gold platings, where the changes in surface roughness and microhardness with increasing layer thickness overshadow the effect of plating factor on ECR.

Helsingin kävelykeskustan suunnittelu ydinkeskustan kadunvarsiliikeyrittäjien näkökulmasta

Aiempien tutkimusten mukaan keskustayrittäjien kielteinen asenne on olennaisesti vaikeuttanut kävelykatujen toteuttamista kaupunkikeskustoissa. Yrittäjät pelkäävät ostokykyisten asiakkaiden kaikkoavan ja liikevaihtonsa pienenevän kävelykeskustauudistusten myötä. Yrittäjien kielteiset asenteet ovat usein myös painottuneet suuriin kaupunkeihin. Etenkin ydinkeskustassa sijaitsevat kadunvarsiliikeyrittäjät ovat kokeneet kävelykadut ongelmiksi. Tämän tutkimuksen tavoitteena on selvittää, mikä on ydinkeskustan kadunvarsiliikeyrittäjien näkemys Helsingin kävelykeskustan suunnittelusta, millaisena ydinkeskustan kadunvarsiliikeyrittäjät näkevät sijaintikatunsa kävelykeskustan suunnittelupäämäärien kautta tarkasteltuna, ja onko kävelykatuyrittäjien ja kävelykatujen ulkopuolella sijaitsevien yrittäjien näkemysten välillä eroja. Taustana tälle tarkastellaan Helsingin kävelykeskustaa pohjoismaisessa kontekstissa, ja käydään läpi Helsingin kävelykeskustan suunnittelun ja rakentumisen historiaa ja päämääriä. Tutkimuksen aineisto koostuu Helsingin ydinkeskustan kadunvarsiliikeyrittäjille tehdystä kyselystä, kävelykeskustoihin liittyvistä tutkimuksista ja selvityksistä, kaupunkisuunnitteluun ja -tutkimukseen liittyvästä tutkimuskirjallisuudesta, sanomalehtiartikkeleista, ydinkeskustassa tehdystä empiirisestä havainnoinnista ja kahdesta asiantuntijahaastattelusta. Kyselyaineistoa analysoidaan tutkimuksessa tilastollisten menetelmien avulla. Helsingin kävelykeskustan suunnittelu ja rakentuminen on ollut pitkällinen prosessi. Vuoden 1 989 kävelykeskustan periaatesuunnitelmasta on konkretisoitunut Kluuvikatu ja Mikonkatu. Keskustatunnelihanke on vaakalaudalla, minkä vuoksi kävelykeskustan uuden periaatesuunnitelman toteutuminen on epävarmaa. Kävelykeskustan rakentuminen kuitenkin etenee. Keskuskatu ja Kalevankadun itäpää muutetaan kävelykaduiksi ja ydinkeskustan jalankulkuympäristöä parannetaan ja kehitetään jatkuvasti. Tällä hetkellä kävelykeskustan suunnittelun painopiste on Aleksanterinkadun kortteleiden ympäristössä, ja suunnittelun tärkeimpiä päämääriä ovat viihtyisyyden, turvallisuuden, kaupallisen vetovoimaisuuden ja saavutettavuuden parantaminen. Kyselyyn vastanneiden yrittäjien mielestä kävelykeskustaa tulisi laajentaa, sillä laajemman kävelykeskustan nähdään kasvattavan liikevaihtoa ja lisäävän yleisesti ydinkeskustan vetovoimaa. Kävelykatuyrittäjien näkemykset kävelykeskustan suunnittelusta ja kehittämisestä olivat kävelykatujen ulkopuolisia yrittäjiä kielteisempiä. Em. yrittäjien asenteisiin vaikuttavat oletettavasti tutkituilla kävelykaduilla ilmenneet ongelmat. Kyse voi myös olla siitä, että uusien kävelykatujen rakentaminen haittaa kävelykatujen saavutettavuutta. Kadunvarsiliikeyrittäjien yleinen suhtautuminen kävelykeskustan kehittämiseen ja suunnittelupäämääriin on kuitenkin pääosin positiivista. Jatkotutkimuksen kannalta olisi kiinnostavaa selvittää, onko muiden ydinkeskustassa toimivien yritysten, kuten esimerkiksi tavaratalojen ja kauppakeskusten johdon ja kiinteistösijoittajien ja -omistajien suhtautuminen kävelykeskustan kehittämiseen myös positiivista. Tämän lisäksi olisi mielenkiintoista selvittää keskustan käyttäjien ja keskustassa asuvien asenteita kävelykeskustan suunnitteluun, ja verrata tuloksia tässä tutkimuksessa selvitettyihin kadunvarsiliikeyrittäjien näkemyksiin.

Nonaxisymmetric unsteady motion over a rotating disk in the presence of free convection and magnetic field

The nonaxisymmetric unsteady motion produced by a buoyancy-induced cross-flow of an electrically conducting fluid over an infinite rotating disk in a vertical plane and in the presence of an applied magnetic field normal to the disk has been studied. Both constant wall and constant heat flux conditions have been considered. It has been found that if the angular velocity of the disk and the applied magnetic field squared vary inversely as a linear function of time (i.e. as (1??t*)?1, the governing Navier-Stokes equation and the energy equation admit a locally self-similar solution. The resulting set of ordinary differential equations has been solved using a shooting method with a generalized Newton's correction procedure for guessed boundary conditions. It is observed that in a certain region near the disk the buoyancy induced cross-flow dominates the primary von Karman flow. The shear stresses induced by the cross-flow are found to be more than these of the primary flow and they increase with magnetic parameter or the parameter ? characterizing the unsteadiness. The velocity profiles in the x- and y-directions for the primary flow at any two values of the unsteady parameter ? cross each other towards the edge of the boundary layer. The heat transfer increases with the Prandtl number but reduces with the magnetic parameter.

Non-conservatively loaded stochastic columns

A new finite element method is developed to analyse non-conservative structures with more than one parameter behaving in a stochastic manner. As a generalization, this paper treats the subsequent non-self-adjoint random eigenvalue problem that arises when the material property values of the non-conservative structural system have stochastic fluctuations resulting from manufacturing and measurement errors. The free vibration problems of stochastic Beck's column and stochastic Leipholz column whose Young's modulus and mass density are distributed stochastically are considered. The stochastic finite element method that is developed, is implemented to arrive at a random non-self-adjoint algebraic eigenvalue problem. The stochastic characteristics of eigensolutions are derived in terms of the stochastic material property variations. Numerical examples are given. It is demonstrated that, through this formulation, the finite element discretization need not be dependent on the characteristics of stochastic processes of the fluctuations in material property value.

Phase Relations in the System Cu-Gd-O and Gibbs Energy of Formation of CuGd204

The phase relations in the system Cu-Gd-O have been determined at 1273 K by X-ray diffrac- tion, optical microscopy, and electron microprobe analysis of samples equilibrated in quartz ampules and in pure oxygen. Only one ternary compound, CuGd2O4, was found to be stable. The Gibbs free energy of formation of this compound has been measured using the solid-state cell Pt, Cu2O + CuGd2O4 + Gd2O3 // (Y2O3) ZrO2 // CuO + Cu2O, Pt in the temperature range of 900 to 1350 K. For the formation of CuGd2O4 from its binary component oxides, CuO (s) + Gd2O3 (s) → CuGd2O4 (s) ΔG° = 8230 - 11.2T (±50) J mol-1 Since the formation is endothermic, CuGd2O4 becomes thermodynamically unstable with respect to CuO and Gd2O3 below 735 K. When the oxygen partial pressure over CuGd2O4 is lowered, it decomposes according to the reaction 4CuGd2O4 (s) → 4Gd2O3 (s) + 2Cu2O (s) + O2 (g) for which the equilibrium oxygen potential is given by Δμo 2 = −227,970 + 143.2T (±500) J mol−1 An oxygen potential diagram for the system Cu-Gd-O at 1273 K is presented.

Structural refinement using high-resolution powder X-ray diffraction data of Ca0.5Ti2P3O12, a low-thermal-expansion material

The structures of Ca0.5Ti2P3O12 and Sr0.5Ti2P3O12, low-thermal-expansion materials, have been refined by the Rietveld method using high-resolution powder X-ray diffraction (XRD) data. The assignment of space group R[3 with combining macron] to NASICON-type compounds containing divalent cations is confirmed. 31P magic-angle spinning nuclear magnetic resonance (MASNMR) data are presented as supporting data. A comparison of changes in the polyhedral network resulting from the cation distribution, is made with NaTi2P3O12 and Nb2P3O12. Factors that may govern thermal expansion in this family of compounds are discussed.

Microtensile testing of a free-standing Pt-aluminide bond coat

A finite element method (FEM)-based study has been carried out for the design of flat microtensile samples to evaluate tensile properties of Pt-aluminide (PtAl) bond coats. The critical dimensions of the sample have been determined using a two-dimensional elastic stress analysis. In the present testing scheme, the ratio of the dimensions of the holding length to the fillet radius of the sample was found important to achieve failure within the gage length. The effect of gage length and grip head length also has been examined. The simulation predictions have been experimentally verified by conducting microtensile test of an actual PtAl bond coat at room temperature. The sample design and testing scheme suggested in this study have also been found suitable for evaluation of tensile properties at high temperature. (C) 2010 Elsevier Ltd. All rights reserved.

A crosslinked ``polymer-gel'' rechargeable lithium-ion battery electrolyte from free radical polymerization using nonionic plastic crystalline electrolyte medium

A cross-linked polymer-gel soft matter electrolyte with superior electrochemical, thermal and mechanical properties obtained from free radical polymerization of vinyl monomers in a semi-solid organic nonionic plastic crystalline electrolyte for application in rechargeable lithium-ion batteries is discussed here.

Free convection about cylinders of elliptic cross section embedded in a porous medium

Numerical solutions are presented for the free convection boundary layers over cylinders of elliptic cross section embedded in a fluid-saturated porous medium. The transformed conservation equations of the nonsimilar boundary layers are solved numerically by an efficient finite-difference method. The theory was applied to a number of cylinders and the results compared very well with published analytical solutions. The results are of use in the design of underground electrical cables, power plant steam, and water distribution lines, among others.

Growth and extraction of flux free YBCO crystals

An improved flux draining technique for the extraction of grown YBCO crystals from its solvent is reported. This simple and efficient technique facilitates in-situ flux separation in the isothermal region of the furnace. Consequently, the crystals are spared from thermal shock and subsequent damage. Flux-free surfaces of these crystals were studied by optical microscopy. Transmission X-ray topographs of the crystals reveal the dislocations present in them as well as the stresses developed as a result of ferroelastic phase transition occurring during cooling.