Negative incremental bulk modulus in foams

Negative incremental stiffness is known to occur in structures such as post-buckled flexible tubes and single-cell models. A single foam cell under uniaxial loading buckles and exhibits a non-monotonic S-shaped deformation curve, which is indicative of negative incremental stiffness. Negative stiffness is not observed in bulk materials. For example, individual foam cells display negative stiffness but foams tested in uniaxial compression exhibit a plateau in the stress–strain curve because the buckled cells localize in bands. This behaviour is consistent with the continuum view in which strong ellipticity and, hence, a positive shear modulus G and positive C ₁₁ modulus are required for stability, even for a constrained object. It is hypothesized that a solid with negative bulk modulus can be stabilized by control of the surface displacement. Experimentally, foams were hydrostatically compressed by controlled injections of small volumes of water into a plastic chamber, causing volumetric deformation. A negative incremental bulk modulus was observed in a foam with 0.4-mm cell size beyond about 20% volumetric strain. A foam with large cells, 2.5–4?mm in size, was anisotropic and did not exhibit the cell buckling required for negative modulus.     

Juggling with bubbles in cylindrical ferrofluid foams

Monodisperse foams in long cylinders exhibit ordered spiral structures. We have made ferrofluid foams of this kind and find that they can be manipulated in a variety of ways by an external magnetic field. Effects include morphological changes, twisting of structures and size control in the bubble formation process. This offers a promising technique for the efficient transport, switching and combining of samples in fluidic networks, possibly on the microfluidic scale.     

Dynamic instabilities as mechanisms for emergence

That competences may emerge given appropriate environmental and behavioral context is a long-standing theme in developmental research. Work in the motor domain, but also in cognitive development, has made it possible to transform this idea into a mechanistic account closely linked to empirical evidence. In dynamic systems thinking, such capacities as keeping a motor goal in mind, remembering a location, or resisting a motor habit, are all understood in terms of the generation of stable patterns of neuronal activation. These may be input-driven, but also be stabilized by interactions within neuronal representations. A key theoretical insight is that whether a particular pattern of activation is stable or not is not determined by any single factor, learning process, or structural parameter. Instead, ongoing activity, recent activation history, current input, all may affect when a particular dynamic regime is reachable. In spite of such broad interdependence, sharp transitions may characterize the onset of a skill in any given context. Dynamic instabilities are the mechanistic basis for this phenomenon and thus form the basis for understanding development in terms of emergence. We exemplify the concepts of instability and emergence around the phenomenon of infant perseverative reaching and discuss implications for identifying key markers of development and their link to neuronal processes.     

Nonlocal effects in the continuum theory of shear localisation in 2d foams

Goyon et al. [J. Goyon, A. Colin, G. Ovarlez, A. Ajdari and L. Bocquet, Nature 454 (2008) p. 84] have shown that nonlocal effects in the rheology of foams may be accounted for by a modification of the standard (Herschel–Bulkley) model. Here we consider the effects of this modification on the continuum theory of 2d shear localisation. We compute results for various examples, showing that the localisation length is increased, and explore the limiting cases of zero and infinite nonlocality length ξ. Velocity profiles are shown to take an exponential form in the case where ξ is large. As the formulation of the nonlocal continuum model presented in this article is general, it may also be directly applicable to other complex fluids.     

A bifurcation theory for the instabilities of optimization and design

The world I grew up in believed that change and development in life are part of a continuous process of cause and effect, minutely and patiently sustained throughout the millenniums. With the exception of the initial act of creation ..., the evolution of life on earth was considered to be a slow, steady and ultimately demonstrable process. No sooner did I begin to read history, however, than I began to have my doubts. Human society and living beings, it seemed to me, ought to be excluded from so calm and rational a view. The whole of human development, far from having been a product of steady evolution, seemed subject to only partially explicable and almost invariably violent mutations. Entire cultures and groups of individuals appeared imprisoned for centuries in a static shape which they endured with long-suffering indifference, and then suddenly, for no demonstrable cause, became susceptible to drastic changes and wild surges of development. It was as if the movement of life throughout the ages was not a Darwinian caterpillar but a startled kangaroo, going out towards the future in a series of unpredictable hops, stops, skips and bounds. Indeed, when I came to study physics I had a feeling that the modern concept of energy could perhaps throw more light on the process than any of the more conventional approaches to the subject. It seemed that species, society and individuals behaved more like thunder-clouds than scrubbed, neatly clothed and well-behaved children of reason. Throughout the ages life appeared to build up great invisible charges, like clouds and earth of electricity, until suddenly in a sultry hour the spirit moved, the wind rose, a drop of rain fell acid in the dust, fire flared in the nerve, and drums rolled to produce what we call thunder and lightening in the heavens and chance and change in human society and personality.LAURENS VAN DER POST, The Lost World of the Kalahari     

Effect of crystallization on the surface area of porous Ni-based metallic glass foams

The change of the specific surface area in porous Ni₅₉Zr₂₀Ti₁₆Si₂Sn₃ metallic glass (MG) upon partial crystallization was investigated. The observed increase in the surface area of the annealed Ni-based MG foams is due to the formation of homogeneously distributed Ni₁₀(Zr,Ti)₇ rod-shape intermetallic phases with nominal diameters around 250?nm and ～800?nm length on the surface of MG struts during the crystallization. For longer annealing, the specific surface area decreases again due to a change of the morphology of the crystals from rod-like to disc-like appearance, thus suggesting an optimum regime for increasing the specific surface area upon isothermal annealing at a given temperature.     

Certification in Testing in Canada

This article presents a brief outline of a program developed by the Canada Employment and Immigration Commission (CEIC) for certifying employment counselors to use tests in Canada Employment Centres (CECs).     

儿童Graves'病研究进展

Grave's病(GD)是导致儿童甲亢最常见的病因,其易感性80%决定于基因因素.ATD治疗是最常推荐的初始治疗手段,但长期缓解率仅为30%.ATD诱导儿童GD缓解的合适用药时间尚不明确.最佳治疗方式(ATD、RAI或手术)的选择还存在重大争议.药物治疗复发的预测非常重要,最近建立了一种复发风险评分,通过种族、年龄、诊断时FT4、TRAb水平、ATD预期治疗持续时间将GD儿童分成低中高三类风险人群,对其复发风险作出评估,对于确定GD儿童在初始治疗时选择何种方案更为适合意义重大.     

Occupational Stress in Workers and Managers in Steelworks in China

Occupational stressors and strains of 121 Chinese steelwork employees and 122 managers were measured using the Chinese version of the Occupational Stress Indicator (OSI). It was found that factors intrinsic to the job, Type A behavior, logic, and organizational structure and climate were the main predictors of mental ill-health and physical ill-health in managers. Organizational structure and climate and relationships with other people were important predictors for workers. Management processes and organizational forces were the strongest predicting factors of job satisfaction in both samples. On certain OSI scales and subscales, managers scored statistically higher than workers. It is proposed that these results reflect the enormous economic and social changes currently taking place in China, together with certain features inherent in Chinese organizational and managerial processes.     

Sex differences in relational aggression in preschool children in Iran

The purpose of this study was to compare scores on a Relational Aggression Questionnaire for preschool boys and girls in Iran. The questionnaire was developed here, and its reliability and validity were assessed. Teachers' reports of relational aggression in 258 children ages 3 to 7 years was studied. Sex differences in relational aggression were not observed and was not significantly different across age groups.     

Studies in analytic philosophy in China

This essay explores the history of studies in analytical philosophy in China since the beginning of the last century, by dividing into three phases. It shows that, in these phases, analytic philosophy was always at a disadvantage in confronting serious challenges coming from both Chinese traditional philosophy and modern philosophical trends. The authors argue that Chinese philosophers have both done preliminary studies and offered their own analyses of various problems as well as some new applications of analytic philosophy especially in the latest period. Meanwhile, Chinese traditional philosophy was always trying to adjust its cultural mentality in the struggle with analytic philosophy, and accommodated in its own way the rationalistic spirit and scientific method represented in analytic philosophy.     

Persistence in seminary and in ministry

A follow-up study of 672 seminary students from 14 seminaries who took the Theological School Inventory in 1962 and 574 from 10 seminaries who took it in 1973 investigated factors involved in persistence in seminary and in ministry. Among those found were definiteness of decision, interest in parish ministry, a supportive spouse, unambivalent resolution of the authority problem, good role models in father and ministers. Motivations included redemptive outreach, pastoral care, Christian insight and scholarship, the encouragement of other people and a sense of effectiveness in ministry.Dr. Cardwell is Assistant Professor of Psychology and Counseling at Christian Theological Seminary, 1000 W. 42nd St., Indianapolis, Indiana 46208. This study was the basis for her Ph.D. dissertation, Indiana University, June, 1978. TSI data for the 1973 subjects were made available by Richard A. Hunt, Ph.D., Professor of Psychology, Southern Methodist University, and Director of Ministry Inventories, P.O. Box 8265, Dallas, Texas 75205. TSI data for the 1962 subjects were coded and made available by Edgar W. Mills. Ph.D., presently visiting Associate Professor of Sociology, University of Texas, San Antonio, formerly Director, Ministry Studies Board. Special credit is due the 16 seminaries who cooperated by furnishing follow-up data.     

Women in advertisements in medical journals

To determine the images of women in picture advertisements, a stratified random sample of 32 medical journals, representing approximately 12% of medical journals published in the United States that are directed toward physicians in clinical practice, was subjected to content analysis. The sample consists of 209 different ads. The subjects of the ads included men, women, and children representing a variety of ethnic, racial, and socioeconomic groups. Notable, however, was the preponderance of Caucasian males pictured as physicians and the absence of women and people of color in this role. Women are pictured as 68.1% of consumers and men as 31.9%, a significant difference. Statistically significant differences also occur in the images of men and women as consumers. Most of the workers are men (68.2%), another significant difference. When women depicted are workers, they are secretaries and waitresses. Portrayals of women in medical advertisements continue to be stereotyped and outdated.