应变率效应对无铅焊锡接点跌落冲击力学行为的影响

采用应变率相关的Johnson-Cook材料模型和率无关的弹塑性模型分别计算了跌落/冲击载荷下焊锡接点的应力及应变,研究应变率对焊锡接点力学行为的影响,预测了焊锡接点的破坏情况,并与动态4点弯曲实验结果进行了比较.结果表明:焊锡材料的应变率效应对电路板的挠度几乎没有影响,但对焊锡接点的应力及应变有较大影响;不考虑应变率效应的弹塑性模型低估焊锡接点的应力值而高估等效塑性应变值;采用率相关的Johnson-Cook模型能更好地预测焊锡接点的力学行为,能较真实地预测焊锡接点的破坏情况.     

Supporting Social Interaction in Care Environments: Exploring Stakeholder Perspectives on the Potential of Interactive Technology

This article explores care stakeholders’ perspectives on how interactive technology can help form socially active environments in residential care settings. Based on participatory workshops, involving representatives from multiple stakeholder groups, the authors identify a set of considerations relevant for design of social inclusion technology for care settings. The design considerations relate to the following topics: users, places, themes, value, and role. The authors also present three mock-ups emanating from the workshops, representing the participants’ visions as to how technology can contribute to social interaction by accommodating considerations related to the above topics. The results from this study highlight the importance of social inclusion technology being firmly anchored in the local and collaboratively produced care environment. In particular, their findings illustrate how the local—i.e., the wider social context in which the care residents live, and in which activities and things gain social meaning and value—can offer a rich design space and valuable source of inspiration for social inclusion technology. Potential negative implications of social inclusion technology are also briefly discussed.

The main contribution of this article is an increased understanding of the intimate relationship between designs for social inclusion and the wider social context in which care residents live.     

Improved bispectrum based tests for Gaussianity and linearity

The classical bispectrum based tests for linearity of time series are based on Gaussian asymptotics and a suboptimal smoothing in the bispectral domain. We show that the resulting classical tests may lead to vastly incorrect significance levels for non-Gaussian time series. This implies that a non-Gaussian linear time series may incorrectly be classified as non-linear. The purpose of this paper is to propose simple yet accurate tests for Gaussianity and linearity. The improved tests are derived through: (1) an optimal hexagonal smoothing in the bispectral domain, (2) the construction of simple and intuitive bispectrum based test statistics, and (3) determination of correct significance levels through a new skewness preserving scheme for linear surrogate data. The superiority of the proposed tests is demonstrated through extensive Monte Carlo simulations using relevant synthetic data.     

On the Parameterised Complexity of String Morphism Problems

Given a source string u and a target string w, to decide whether w can be obtained by applying a string morphism on u (i. e., uniformly replacing the symbols in u by strings) constitutes an \(\mathcal {NP}\)-complete problem. We present a multivariate analysis of this problem (and its many variants) from the viewpoint of parameterised complexity theory, thereby pinning down the sources of its computational hardness. Our results show that most parameterised variants of the string morphism problem are fixed-parameter intractable and, apart from some very special cases, tractable variants can only be obtained by considering a large part of the input as parameters, namely the length of w and the number of different symbols in u.     

Building a City and a Metropolis: The Planned Development of Stockholm

The planned development of Stockholm has often been the subject of international attention, mainly because of the close integration of city planning with municipal land-ownership policy. Topographic and socio-economic factors both condition today s planning problems. The increase of population and traffic, a rising standard of living, and the relocation of city activities have emphasized the need for replanning the downtown area. A new city center is being created. Aware of the danger of overcrowding the central business district, planners are seeking the right balance of pedestrian and motor traffic. Rules governing land use patterns, dispersal of jobs within the region, and an efficient mass transportation system are regarded as guarantees for a continued balanced development.     

Melting-Temperature Measurements on alpha-Silicon Nitride to a Pressure of 37 GPa

The melting temperature of alpha-silicon nitride, up to a pressure of 37 GPa, was determined by using the diamond-anvil cell technique, together with laser heating and spectroradiometry. The melting temperature varied from 2200 ± 75 K at 3.5 GPa to 3600 ± 200 K at 37 GPa; the extrapolated temperature at 1 atm was estimated to be 2100 ± 75 K.     

No significant effect on bone mineral density by high doses of vitamin D3 given to overweight subjects for one year

Background  

In meta-analyses supplementation with vitamin D appears to reduce incidence of fractures, and in cross-sectional studies there is a positive association between serum 25-hydroxyvitamin D (25(OH)D) levels and bone mineral density (BMD). However, the effect of supplementation with high doses of vitamin D on BMD is more uncertain and could in theory have both positive and negative effects.     

Curing of Glycidyl Azide Polymer (GAP) Diol Using Isocyanate,Isocyanate‐Free,Synchronous Dual,and Sequential Dual Curing Systems

Glycidyl azide polymer (GAP) is an important energetic binder candidate for new minimum signature solid composite rocket propellants, but the mechanical properties of such GAP propellants are often limited. The mechanical characteristics of composite rocket propellants are mainly determined by the nature of the binder system and the binder‐filler interactions. In this work, we report a detailed investigation into curing systems for GAP diol with the objective of attaining the best possible mechanical characteristics as evaluated by uniaxial tensile testing of non‐plasticized polymer specimens. We started out by investigating isocyanate and isocyanate‐free curing systems, the latter by using the crystalline and easily soluble alkyne curing agent bispropargylhydroquinone (BPHQ). In the course of the presented study, we then assessed the feasibility of dual curing systems, either by using BPHQ and isophorone diisocyanate (IPDI) simultaneously (synchronous dual curing), or by applying propargyl alcohol and IPDI consecutively (sequential dual curing). The latter method, which employs propargyl alcohol as a readily available and adjustable hydroxyl‐telechelic branching agent for GAP through thermal triazole formation, gave rise to polymer specimens with mechanical characteristics that compared favorably with the best polymer specimens obtained from GAP diol and mixed isocyanate curatives. The glass transition temperature (T_g) of non‐plasticized samples was heightened when triazole‐based curing agents were included, but when plasticized with nitratoethylnitramine (NENA) plasticizer, T_g values were very similar, irrespective of the curing method.     

Linear Regression With a Sparse Parameter Vector

We consider linear regression under a model where the parameter vector is known to be sparse. Using a Bayesian framework, we derive the minimum mean-square error (MMSE) estimate of the parameter vector and a computationally efficient approximation of it. We also derive an empirical-Bayesian version of the estimator, which does not need any a priori information, nor does it need the selection of any user parameters. As a byproduct, we obtain a powerful model ("basis") selection tool for sparse models. The performance and robustness of our new estimators are illustrated via numerical examples