An algorithm for modeling the sinusoidal input/steady-state response behavior of nonlinear systems over a set of frequencies and amplitudes

An algorithm for constructing a black box model of the sinusoidal input/steady-state response behavior of nonlinear time-invariant systems over a set of frequencies and amplitudes is presented. It is assumed that the steady-state response is periodic of the same fundamental frequency as the excitation, and that the Fourier coefficients are continuous functions of amplitude and square-integrable functions of frequency. The algorithm converges, in a mean-square sense, to an exact representation of the first N harmonics of the steady-state response minus its d.c. component. The model constructed by the algorithm admits a relatively simple physical realization characterized by 2NM+1 linear dynamic elements, and N(2M+1)+1 nonlinear static elements. The underlying mathematical structure of the model is an orthogonal series expansion relative to time whose coefficients are themselves truncated orthogonal expansions relative to frequency. Here M, the number of harmonics used for frequency interpolation, is determined by the algorithm. Of the N(2M+1)+1 memoryless nonlinearities which characterize the model, N of these are specified ahead of time (Tchebysheff polynomials), and 2NM+1 are parameters which mold the representation to the specific system being modeled. Each of these functions of a single variable can be obtained in a pointwise manner directly from steady-state measurements. The algorithm was implemented on a digital computer, and forced versions of the classic equations of van der Pol and Duffing were run as examples. An additional analytic example of a frequency multiplier of prescribed bandwidth was also presented.     

The difficult bridge between university and industry: a case study in computer science teaching

Recently, there has been increasing criticism concerning academic computer science education. This paper presents a new approach based on the principles of constructivist learning design as well as the ideas of knowledge transfer in communities of practice. The course ‘High‐tech Entrepreneurship and New Media’ was introduced as an interdisciplinary project management lab in which students collaborate in groups to develop software solutions for authentic problems. Main goals were the tighter integration of university and local start‐up companies, an intense knowledge transfer on software engineering methods, as well as the implementation of constructivist learning principles in academic teaching. This paper presents the background and structure of the course as well as the results of a formative evaluation. While being successful in introducing a course based on digital‐media assisted, constructivist learning arrangements, establishing lasting communities of practice between university and industry is still an open issue. After discussing several reasons, the paper concludes with a list of general recommendations on how to improve the approach and its implementation.     

CAD-VR geometry and meta data synchronization for design review applications

INTRODUCTION The first phases of the product life cycle are almost completely digitalized nowadays. Single parts or complete product models are modeled with 3D CAD solutions. Assembling single parts to digital mockups (DMUs) is important for checking the de- pendencies between the parts and detecting conflicts. Due to their complexity, such data is managed in specialized Product Data Management (PDM) sys- tems. They gained an increasing importance in many industries during the last d…     

纸条检测法对第85窟壁画空鼓灌浆脱盐效果的评估

实验得出不损伤壁画的纸条检测法与壁画表面盐分含量的关系,并以此为根据,采用纸条法测定壁画表面盐分的含量状态,评价壁画空鼓灌浆后脱盐的效果.结果表明壁画空鼓灌浆所带人的水分激活了地仗中的盐分,使盐分运移并大量地富集到壁画的表面.保护笔的脱盐效果十分显著,纸条法测得保护笔脱盐后Cl-浓度降低约10个ppm,相当于保护笔脱盐可以减少了壁画表面地仗中所含1.6%的Cl-的量,即可以去除掉未灌浆区域壁画表面盐分的80%.实验证明纸条法可以应用于壁画脱盐效果的检验.     

Soreness-related changes in three-dimensional running biomechanics following eccentric knee extensor exercise

Runners often experience delayed onset muscle soreness (DOMS), especially of the knee extensors, following prolonged running. Sagittal knee joint biomechanics are altered in the presence of knee extensor DOMS but it is unclear how muscle soreness affects lower limb biomechanics in other planes of motion. The purpose of this study was to assess the effects of knee extensor DOMS on three-dimensional (3D) lower limb biomechanics during running. Thirty-three healthy men (25.8?±?6.8 years; 84.1?±?9.2?kg; 1.77?±?0.07?m) completed an isolated eccentric knee extensor damaging protocol to elicit DOMS. Biomechanics of over-ground running at a set speed of 3.35?m?s^?1±5% were measured before eccentric exercise (baseline) and, 24?h and 48?h following exercise in the presence of knee extensor DOMS. Knee flexion ROM was reduced at 48?h (P?=?0.01; d?=?0.26), and peak knee extensor moment was reduced at 24?h (P?=?0.001; d?=?0.49) and 48?h (P?<?0.001; d?=?0.68) compared to baseline. Frontal and transverse plane biomechanics were unaffected by the presence of DOMS (P?>?0.05). Peak positive ankle and knee joint powers and, peak negative knee joint power were all reduced from baseline to 24?h and 48?h (P?<?0.05). These findings suggest that knee extensor DOMS greatly influences sagittal knee joint angular kinetics and, reduces sagittal power production at the ankle joint. However, knee extensor DOMS does not affect frontal and transverse plane lower limb joint biomechanics during running.     

An Examination of Resilience Processes in Context: The Case of Tasha

This research examined resilience processes in context through a narrative case study of Tasha, a young African-American woman who grew up in a poverty-ridden area of a mid-sized city in the Southeast. Personal and external data are analyzed and interpreted in terms of contextually defined themes of adversity (i.e., intersectionality of social identities, lack of attachment to her primary caregiver, and teenage pregnancy); adaptation (i.e., high school graduation, career goal-setting, commitment to her children, and “street” competence); and, protective processes (i.e., individual attributes, natural mentors, and extended family support). The importance of external sources of support and Tasha as an active agent in her development is highlighted. Research and practical implications are discussed.