Affordances, constraints and information flows as ‘leverage points’ in design for sustainable behaviour

Copyright @ 2012 Social Science Electronic PublishingTwo of Donella Meadows' 'leverage points' for intervening in systems (1999) seem particularly pertinent to design for sustainable behaviour, in the sense that designers may have the scope to implement them in (re-)designing everyday products and services. The 'rules of the system' -- interpreted here to refer to affordances and constraints -- and the structure of information flows both offer a range of opportunities for design interventions to in fluence behaviour change, and in this paper, some of the implications and possibilities are discussed with reference to parallel concepts from within design, HCI and relevant areas of psychology

Piezoresistive Stress Sensors for Structural Analysis of Electronic Packages

Structural reliability of electronic packages has become an increasing concern for a variety of reasons including the advent of higher integrated circuit densities, power density levels, and operating temperatures. A powerful method for experimental evaluation of die stress distributions is the use of test chips incorporating integral piezoresistive sensors. In this paper, the theory of conduction in piezoresistive materials is reviewed and the basic equations applicable to the design of stress sensors on test chips are presented. General expressions are obtained for the stress-induced resistance changes which occur in arbitrarily oriented one-dimensional filamentary conductors fabricated out of crystals with cubic symmetry and diamond lattice structure. These relations are then applied to obtain basic results for stressed inplane resistors fabricated into thesurface of (100) and (111) oriented silicon wafers. Sensor rosettes developed by previous researchers for each of these wafer orientations are reviewed and more powerful rosettes are presented along with the equations needed for their successful application. In particular, a new sensor rosette fabricated on (111) silicon is presented which can measure the complete three-dimensional stress state at points on the surface of a die Introduction Stresses due to thermal and mechanical loadings are often produced in chips which are incorporated into electronic packages. During fabrication steps such as encapsulation and dieattachment, thermally-induced stresses are created. These occur due to nonuniform thermal expansions resulting from mismatches between the coefficients of thermal expansion of the materials comprising the package and the semiconductor die. Additional thermally-induced stresses can be produced from heat dissipated by high power density devices during operation. Finally, mechanical loadings can be transmitted to the package through contact with the printed circuit board to which it is mounted. The combination of all of the above loadings can lead to two-dimensional (biaxial) and three-dimensional (triaxial) states of stress on the surface of the die. If high-power density devices within the package are switched on and off, these stress states can be cyclic in time causing fatigue. All of these factors can lead to premature failure of the package due to such causes as fracture of the die, severing of bond connections, die attach failure, and encapsulant cracking. These reliability problems are of ever increasing concern as larger scale chips and higher temperature applications are considered. Stress analyses of electronic packages and their components have been performed using analytical, numerical, and experimental methods. Analytical investigations have been primarily concerned with finding closed-form elasticity solutions for lay- structures, while numerical studies have typically considered finite element solutions for sophisticated package geometries. Experimental approaches have included the use of test chips incorporating piezoresistive stress sensors (semiconductor strain gages), and the use of optical techniques such as holographic interferometry, moire interferometry, and photoelasticity. In this paper, the theory and design of piezoresistive stress sensors are considered in detail. Piezoresistive stress sensors are a powerful tool for experimental structural analysis of electronic packages. They are conveniently fabricated into the surface of the die as part of the normal processing procedure. In addition, they are capable of providing nonintrusive measurements of surface stress states on a chip even within encapsulated packages. If the piezoresistive sensors are calibrated over a wide temperature range, thermally induced stresses can be measured. Finally, a fullfield mapping of the stress distribution over a die's surface can be obtained using specially designed test chips which incorporate an array of sensor rosettes and multiplexing circuitry. Prior published applications of stress sensing test chips have included sensor rosettes with two and four resistors. Two element rosettes fabricated on (100) silicon have been utilized by Mathematical Theory of Piezoresistivity Anisotropic Conduction. A basic axiom of the theory of conduction of electric charge is that the current density vector is a function of the electric field vector (1) where J, and E t are the cartesian components of the current density and electric field vectors, respectively. In most solid conductors, this functional relation has been observed to be linear over a wide range of electric field magnitudes. Such conductors are referred to as ohmic materials. In an anisotropic ohmic conductor, the most general linear relationship is where K,J are the components of the conductivity tensor, and the summation convention is implied for repeated indices. This relation can be inverted to give Ei = PijJj (4) where p u are the components of the resistivity tensor. Using the reciprocity theorem derived by Onsager [1931a, 19316], it is possible to show that the conductivity and resistivity tensors are symmetric The Piezoresistive Effect. The piezoresistive effect is a stress-induced change in the components of the resistivity tensor. It is exhibited in so-called piezoresistive materials. The first observations of this phenomenon were made by Bridgman [1922, 1925, 1932] who subjected metals to tension and hydrostatic pressure. Experimental observations of the piezoresistive effect in semiconductors (silicon and germanium) were first made by The piezoresistive effect can be modeled mathematically using the series expansion where p°j are the resistivity components for the stress free material and iry«, A,j W ",", etc. are components of fourth, sixth, and higher order tensors which characterize the stress-induced resistivity change.-For sufficiently small stress levels, this relation is typically truncated so that the resistivity components are linearly related to the stress components For fixed environmental conditions (i.e. temperature), the 81 components ir iJk i of the fourth order piezoresisitvity tensor are constants. From Eq. It is also possible to model the resistivity changes in terms of the strain components using an expression such as where M ijk i are the components of the fourth order elastoresistivity tensor. In this paper, the stress-based formulation given in Eqs. The above relations are the most concise form for the fully expanded equations of the theory of piezoresistivity. They are not convenient in a notational sense since they cannot be expressed compactly in indicial notation. Historically, it has become a convention to reduce the complexities of the index labels through a renumbering scheme where index pairs are replaced by single indices which assume values of 1, 2, ..., 6 instead of 1, 2, 3. The following index conversions are typically used: 204 / Vol. 113, SEPTEMBER 1991 Transactions of the ASME Pl=Pl2> Pi- ., n 2 6 = 27r2212 A further notational simplification can be obtained by introduction of the so-called piezoresistive coefficients. They are defined by where p is the mean (hydrostatic) unstressed resistivity -P11+P22 + P33 Substitution of Eq. (19) into Eq. (14) leads to Pa^Pa + PKctpOp 7) are valid in the unprimed system (x\, x 2 , x 3 ), the appropriate expressions for the primed system are The components of the electric field vector, current density vector, resistivity tensor, stress tensor, and piezoresistivity tensor all transform from one coordinate system to the other using the standard tensor transformation relations: Transformation Relations. The basic mathematical relations for conduction and piezoresistivity found in Eqs. Crystal Symmetry. For general anisotropic materials, the equations of conduction and piezoresistivity are very complex and contain numerous terms. However, when considering crystalline materials exhibiting lattice symmetry, several simplifications can be made. These simplifications result because relationships can be established between the components of the unstressed resistivity tensor and between the components of the piezoresistivity tensor. Detailed general expositions on the ramifications of crystal symmetry on physical properties have been presented by A crystal is a solid whose local properties and structure are periodic in three dimensions. A rotation or a combination rotation/reflection of a crystal which brings its lattice structure into superposition with itself is called a symmetry operation for the crystal. The set of all symmetry operations for a given crystal defines the crystallographic point group symmetry for the crystal. All crystals with the same point group symmetry are said to be members of the same crystal class. There are 32 unique crystal classes. Silicon is a cubic crystal with diamond structure, and belongs to the crystal class denoted 32 in the international numbering system. This class has been notated several other ways including m3m and O h . The symmetry exhibited by a crystal determines the extent of anisotropy exhibited by the physical properties of the crystal. It is assumed that the physical properties of the crystalline material must possess at least the symmetry of the point group of the crystal. This is expressed mathematically by requiring the components of a physical property tensor for the crystal to be invariant under coordinate system transformations equivalent to the symmetry operations in the point group of the crystal. These relations hold when the initial coordinate system is aligned with the symmetry axes of the crystal. Therefore, using Eqs. (28, 29), the components of the unstressed resistivity tensor and the piezoresistivity tensor of a crystal must satisfy Pu = PV = a ikCjif>ii (38) *ijki = Tyki = a im aj n a ko ai p -K mnop (3 9) when the direction cosines between the two coordinate systems are chosen to be equivalent to one of the crystal's symmetry operations, and the initial coordinate system is aligned with the crystal's symmetry axes. In terms of reduced index notation, these conditions take the form The unique symmetry operations or so-called generating elements for each crystal point group have been listed by and the piezoresistivity coefficients of silicon required by its crystal symmetry are obtained by substituting each set of direction cosines in 41). If all of these calculations are considered, the following relations are found: The simplifications in the reduced index resistivity components General Conduction Equations for Stressed Materials. The governing tensor equation of conduction in a stressed anisotropic ohmic conductor is obtained by substituting Eq. The conduction equations for a stressed cubic crystal with diamond structure are more complex in an off-axis coordinate system (x\, x' 2 , x'i) rotated from the principal symmetry axes (x it x 2 , Xi) as shown in The primed piezoresistive coefficients in Eq. (53) are to be evaluated for the chosen primed coordinate system by substituting the unprimed values in Eq. (46) into the transformation relations given in Eq. (37). The expressions in Eq. (53) were first presented in the literature by Pfann and Thurston [1961]. Stress-Induced Resistance Changes in One-Dimensional Filamentary Conductors Introduction. Early applications of semiconductor strain (stress) gages which utilized the piezoresistive effect exhibited by silicon were made b

Questioning Glutamate Excitotoxicity in Acute Brain Damage: The Importance of Spreading Depolarization

Background Within 2 min of severe ischemia, spreading depolarization (SD) propagates like a wave through compromised gray matter of the higher brain. More SDs arise over hours in adjacent tissue, expanding the neuronal damage. This period represents a therapeutic window to inhibit SD and so reduce impending tissue injury. Yet most neuroscientists assume that the course of early brain injury can be explained by glutamate excitotoxicity, the concept that immediate glutamate release promotes early and downstream brain injury. There are many problems with glutamate release being the unseen culprit, the most practical being that the concept has yielded zero therapeutics over the past 30 years. But the basic science is also flawed, arising from dubious foundational observations beginning in the 1950s Methods Literature pertaining to excitotoxicity and to SD over the past 60 years is critiqued. Results Excitotoxicity theory centers on the immediate and excessive release of glutamate with resulting neuronal hyperexcitation. This instigates poststroke cascades with subsequent secondary neuronal injury. By contrast, SD theory argues that although SD evokes some brief glutamate release, acute neuronal damage and the subsequent cascade of injury to neurons are elicited by the metabolic stress of SD, not by excessive glutamate release. The challenge we present here is to find new clinical targets based on more informed basic science. This is motivated by the continuing failure by neuroscientists and by industry to develop drugs that can reduce brain injury following ischemic stroke, traumatic brain injury, or sudden cardiac arrest. One important step is to recognize that SD plays a central role in promoting early neuronal damage. We argue that uncovering the molecular biology of SD initiation and propagation is essential because ischemic neurons are usually not acutely injured unless SD propagates through them. The role of glutamate excitotoxicity theory and how it has shaped SD research is then addressed, followed by a critique of its fading relevance to the study of brain injury. Conclusions Spreading depolarizations better account for the acute neuronal injury arising from brain ischemia than does the early and excessive release of glutamate

The Critical Role of Spreading Depolarizations in Early Brain Injury: Consensus and Contention

Background: When a patient arrives in the emergency department following a stroke, a traumatic brain injury, or sudden cardiac arrest, there is no therapeutic drug available to help protect their jeopardized neurons. One crucial reason is that we have not identified the molecular mechanisms leading to electrical failure, neuronal swelling, and blood vessel constriction in newly injured gray matter. All three result from a process termed spreading depolarization (SD). Because we only partially understand SD, we lack molecular targets and biomarkers to help neurons survive after losing their blood flow and then undergoing recurrent SD. Methods: In this review, we introduce SD as a single or recurring event, generated in gray matter following lost blood flow, which compromises the Na+/K+ pump. Electrical recovery from each SD event requires so much energy that neurons often die over minutes and hours following initial injury, independent of extracellular glutamate. Results: We discuss how SD has been investigated with various pitfalls in numerous experimental preparations, how overtaxing the Na+/K+ ATPase elicits SD. Elevated K+ or glutamate are unlikely natural activators of SD. We then turn to the properties of SD itself, focusing on its initiation and propagation as well as on computer modeling. Conclusions: Finally, we summarize points of consensus and contention among the authors as well as where SD research may be heading. In an accompanying review, we critique the role of the glutamate excitotoxicity theory, how it has shaped SD research, and its questionable importance to the study of early brain injury as compared with SD theory. © 2022, The Author(s)

The Shifting Imaginaries of Corporate Crime

This article begins by setting out an analysis of the process of conventionalizing corporate crime that arises from the symbiotic relationship between states and corporations. Noting briefly the empirical characteristics of four broad categories of corporate crime and harm, the article then turns to explore the role of the state in its production and reproduction. We then problematize the role of the state in the reproduction of corporate crime at the level of the global economy, through the “crimes of globalization” and “ecocide,” warning of the tendency in the research literature to oversimplify the role of states and of international organizations. The article finishes by arguing that, as critical academics, it is our role to ensure that corporate crime is never normalized and fully conventionalized in advanced capitalist societies

Integrated Personal Health Records: Transformative Tools for Consumer-Centric Care

<p>Abstract</p> <p>Background</p> <p>Integrated personal health records (PHRs) offer significant potential to stimulate transformational changes in health care delivery and self-care by patients. In 2006, an invitational roundtable sponsored by Kaiser Permanente Institute, the American Medical Informatics Association, and the Agency for Healthcare Research and Quality was held to identify the transformative potential of PHRs, as well as barriers to realizing this potential and a framework for action to move them closer to the health care mainstream. This paper highlights and builds on the insights shared during the roundtable.</p> <p>Discussion</p> <p>While there is a spectrum of dominant PHR models, (standalone, tethered, integrated), the authors state that only the integrated model has true transformative potential to strengthen consumers' ability to manage their own health care. Integrated PHRs improve the quality, completeness, depth, and accessibility of health information provided by patients; enable facile communication between patients and providers; provide access to health knowledge for patients; ensure portability of medical records and other personal health information; and incorporate auto-population of content. Numerous factors impede widespread adoption of integrated PHRs: obstacles in the health care system/culture; issues of consumer confidence and trust; lack of technical standards for interoperability; lack of HIT infrastructure; the digital divide; uncertain value realization/ROI; and uncertain market demand. Recent efforts have led to progress on standards for integrated PHRs, and government agencies and private companies are offering different models to consumers, but substantial obstacles remain to be addressed. Immediate steps to advance integrated PHRs should include sharing existing knowledge and expanding knowledge about them, building on existing efforts, and continuing dialogue among public and private sector stakeholders.</p> <p>Summary</p> <p>Integrated PHRs promote active, ongoing patient collaboration in care delivery and decision making. With some exceptions, however, the integrated PHR model is still a theoretical framework for consumer-centric health care. The authors pose questions that need to be answered so that the field can move forward to realize the potential of integrated PHRs. How can integrated PHRs be moved from concept to practical application? Would a coordinating body expedite this progress? How can existing initiatives and policy levers serve as catalysts to advance integrated PHRs?</p