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Boundaries
Kinds of Boundaries Terms modified by Boundaries Selected AbstractsTHE FALL LINE: A PHYSIOGRAPHIC-FOREST VEGETATION BOUNDARY,GEOGRAPHICAL REVIEW, Issue 4 2007David Shankman ABSTRACT. The range boundaries for many tree species in the southeastern United States correspond to the Fall Line that separates the Coastal Plain from the Appalachian Highlands. Trees in the Coastal Plain with northern range boundaries corresponding to the Fall Line occur exclusively in alluvial valleys created by lateral channel migration. These species grow mostly on lower bottomland sites characterized by a high water table, soils that are often saturated, and low annual water fluctuation. In contrast to the Coastal Plain, the southern Appalachian Highlands are occupied mostly by bedrock streams that have few sites suitable for the regeneration of these species. The Fall Line is also an approximate southern boundary for trees common in the southern Appalachians that typically occur on either dry, rocky ridgetops or in narrow stream valleys, habitats that are uncommon on the relatively flat Coastal Plain. The ranges for many trees in eastern North America are controlled by large-scale climatic patterns. Tree species with range boundaries corresponding to the Fall Line, however, are not approaching their physiological limits caused by progressively harsher climatic conditions or by competition. Instead, the Fall Line represents the approximate boundary of habitats suitable for regeneration. [source] ,SETTING A PRINCIPLED BOUNDARY'?BIOETHICS, Issue 3 2007EUTHANASIA AS A RESPONSE TO, LIFE FATIGUE' ABSTRACT The Dutch case of Brongersma presents novel challenges to the definition and evaluation of voluntary euthanasia since it involved a doctor assisting the suicide of an individual who was (merely?) ,tired of life'. Legal officials had called on the courts to ,set a principled boundary', excluding such cases from the scope of permissible voluntary euthanasia, but they arguably failed. This failure is explicable, however, since the case seems justifiable by reference to the two major principles in favour of that practice, respect for autonomy and beneficence. Ultimately, it will be argued that those proponents of voluntary euthanasia who are wary of its use in such circumstances may need to draw upon ,practical' objections, in order to erect an otherwise arbitrary perimeter. Furthermore, it will be suggested that the issues raised by the case are not peculiarly Dutch in nature and that, therefore, there are lessons here for other jurisdictions too. [source] Potential of Marine Reserves to Cause Community-Wide Changes beyond Their BoundariesCONSERVATION BIOLOGY, Issue 2 2007PAOLO GUIDETTI arrecifes rocosos templados; cambios a nivel comunitario; cascadas tróficas; estados comunitarios alternativos; exceso de pesca; reservas marinas Abstract:,Fishing and other human activities can alter the abundances, size structure, and behavior of species playing key roles in shaping marine communities (e.g., keystone predators), which may in turn cause ecosystem shifts. Despite extensive evidence that cascading trophic interactions can underlie community-wide recovery inside no-take marine reserves by protecting high-level predators, the spatial extent of these effects into adjacent fished areas is unknown. I examined the potential for community-wide changes (i.e., the transition from overgrazed coralline barrens to macroalgal beds) in temperate rocky reefs within and around a no-take marine reserve. For this purpose I assessed distribution patterns of predatory fishes, sea urchins, and barrens across the reserve boundaries. Predatory fishes were significantly more abundant within the reserve than in adjacent locations, with moderate spillover across the reserve edges. In contrast, community-wide changes of benthic assemblages were apparent well beyond the reserve boundaries, which is consistent with temporary movements of predatory fishes (e.g., foraging migration) from the reserve to surrounding areas. My results suggest that no-take marine reserves can promote community-wide changes beyond their boundaries. Resumen:,La pesca y otras actividades humanas pueden alterar la abundancia, tamaño, estructura y comportamiento de las especies que juegan papeles clave en el modelado de las comunidades marinas (e.g., depredadores clave), que a su vez pueden causar cambios en los ecosistemas. No obstante la evidencia extensiva de que las interacciones tróficas en cascada pueden subyacer en la recuperación de la comunidad dentro de reservas marinas que no permiten la pesca mediante la protección de depredadores de nivel alto, se desconoce la extensión espacial de estos efectos en áreas adyacentes. Examiné el potencial de los cambios a nivel comunidad (i.e., la transición de áreas coralinas sobre pastoreadas a lechos de microalgas) en arrecifes rocosos templados dentro y alrededor de una reserva marina sin pesca. Para este propósito, evalué los patrones de distribución de peces depredadores, erizos de mar y áreas sobre pastoreadas en los límites de la reserva. Los peces depredadores fueron significativamente más abundantes dentro de la reserva que en localidades adyacentes, con un excedente moderado en los bordes de la reserva. En contraste, los cambios a nivel de comunidad en los ensambles bénticos fueron aparentes más allá de los límites de la reserva, lo que es consistente con los movimientos temporales de los peces depredadores (e.g., migración de forrajeo) desde la reserva hacia las áreas circundantes. Mis resultados sugieren que las reservas que no permiten la pesca pueden promover cambios a nivel comunidad más allá de sus límites. [source] Drifters and the Dancing Mad: The Public School Music Curriculum and the Fabrication of Boundaries for ParticipationCURRICULUM INQUIRY, Issue 3 2008RUTH GUSTAFSON ABSTRACT Recent reforms in the general music curriculum have, for the most part, failed to lessen the attrition rates of African Americans from public school music programs. In this article I assert that an embodied ideal of cultural nobility, exemplified by Auguste Rodin's famous statue, The Thinker, has unconsciously operated as a template for participation. As a model comportment in the Western musical tradition, The Thinker has a broader relevance insofar as other school subjects emerged from similar cultural ideals. Beginning with the early period of public music instruction up to the present, I examine the construction of racial boundaries by linking a specific body comportment hailed as worthy by the music curriculum to historically constructed notions of Whiteness. This issue has been underexplored in research in both music and general education. For that reason, this article examines overlapping systems of reasoning about music, comportment, class, religion, language, nationality, and race in professional and popular texts from the early 1800s to the present. This positions public music instruction as authored, not by pedagogical insight alone, but through changes in musical taste, social practices, strategies of governing populations, and definitions of worthy citizenship. There are three levels of analysis. The first is a personal account of the early manifestations of attrition of African Americans from school music programs. The second level of analysis brings the problem of equity into proximity with the tradition of genteel comportment that permeated the training of the good ear or listener and the fabrication of the bona fide citizen. These, I argue are congruent with the historical construction of Whiteness as a standard mark of worthiness. At the third level of analysis, I take up present-day curriculum designs. This section discusses how the language of the music curriculum continues to draw boundaries for participation through protocols that regulate musical response. Here, I argue that the exclusion of popular genres such as hip-hop should be rethought in light of the evidence that shifting historical definitions for music fabricated an overly restrictive template for comportment, recognizing the prototype of Whiteness as the sole embodiment of merit. [source] Shifting Boundaries on the Professional Knowledge Landscape: When Teacher Communications Become Less SafeCURRICULUM INQUIRY, Issue 4 2004CHERYL J. CRAIG ABSTRACT Researched in the narrative-inquiry tradition, this article continues to map the terrain of teachers' professional knowledge landscapes by distinguishing knowledge communities from other teacher groups. It brings to light a bridging space in which the boundaries of teachers' landscapes may shift, and their transactions may become less safe, particularly when hotly contested matters reach narrative plateaus that are difficult to surmount. This personal experience study conducted in relationship with African-American teachers, Hope and Lorne, makes these distinctions known amid the unexamined narrative freight that pervaded their school contexts and against the backdrop of the historical African-American neighborhood within which their campuses were located. [source] Border Practices, Boundaries, and the Control of Resource Access: A Case from China, Thailand and BurmaDEVELOPMENT AND CHANGE, Issue 3 2004Janet C. Sturgeon This article traces border practices along boundaries that China and Thailand share with Burma. It portrays a spectrum of small border polities, from principalities on the fringes of Southeast Asian kingdoms, through Nationalist troops in Burma following their defeat in China, to ,drug lords' and ,rebel armies'. The focus here is on Akha village heads who have worked their connections in multiple directions, including into Burma, to position themselves as patrons controlling local resource access. With state appointment as border guardians, village heads become chiefs of new kinds of small border entities, protecting the border for the homeland while enabling certain illicit information, people, and goods to cross. In regions with a history of complex patronage relations, state efforts to control peripheral people, resources, and territories have in fact produced small border chiefs, with practices similar to those of frontier princes in the past. [source] On the Boundaries of New and Old Historicisms: Thomas Harman and the Literature of RogueryENGLISH LITERARY RENAISSANCE, Issue 2 2003Lee Beier First page of article [source] Governing by Managing Identity Boundaries: The Case of Family BusinessesENTREPRENEURSHIP THEORY AND PRACTICE, Issue 3 2008Chamu Sundaramurthy In this paper we illustrate how boundary theory can be a useful perspective to understand the dynamics of family businesses. We integrate insights from the family business literature with the work,family and identity boundary literatures to describe degrees of integration between the family and business identities in family firms and outline contingencies that influence this integration. We also develop the notion of "differential permeability" as a state of being both integrated and segmented on various aspects of identity and articulate costs and benefits to this state, as well as to high integration and high segmentation. Finally, we invoke the research on "boundary work" as a means of managing family business boundaries and conclude by outlining additional avenues of research that stem from using such a boundary theory lens. [source] European Integration: Popular Sovereignty and a Politics of BoundariesEUROPEAN LAW JOURNAL, Issue 3 2000Hans Lindahl The problem raised by popular sovereignty in the framework of the EU is not whether it is relevant to European integration; it is. The problem is another, namely the identity and, thus, the boundary of a democratic polity. The very idea of ,European' integration suggests that integration is only imaginable by reference to the closure provided by an identity, a boundary that is normative rather than merely geographical. In this minimal sense, a European people is the necessary presupposition of integration, not merely its telos. Bluntly, there is no integration without inclusion and, also, no integration without exclusion. This, then, is the real problem raised by popular sovereignty in a European context: if there is no such thing as non-exclusionary integration, how can a reflection on the boundedness of European integration be more than a rationalisation of exclusion? [source] Sister-to-Sister Talk: Transcending Boundaries and Challenges in Qualitative Research With Black Women,FAMILY RELATIONS, Issue 3 2003April L. Few Our purpose is to discuss the challenges that Black women researchers face when doing qualitative research with Black women on sensitive topics. From a Black feminist perspective, we explore the dynamics of race, class, and gender in the informant-researcher relationship between Black women. We also share five recommendations for conducting ethical qualitative research with Black women: contextualizing research, contextualizing subjectivity, triangulating multiple sources, monitoring symbolic power, and caring in the research process. [source] Boundaries, defects and Frobenius algebrasFORTSCHRITTE DER PHYSIK/PROGRESS OF PHYSICS, Issue 7-8 2003J. Fuchs The interpretation of D-branes in terms of open strings has lead to much interest in boundary conditions of two-dimensional conformal field theories (CFTs). These studies have deepened our understanding of CFT and allowed us to develop new computational tools. The construction of CFT correlators based on combining tools from topological field theory and non-commutative algebra in tensor categories, which we summarize in this contribution, allows e.g. to discuss, apart from boundary conditions, also defect lines and disorder fields. [source] Microtexture and Grain Boundaries in Freestanding CVD Diamond Films: Growth and Twinning MechanismsADVANCED FUNCTIONAL MATERIALS, Issue 24 2009Tao Liu Abstract Three groups of free-standing chemical vapor deposition (CVD) diamond films formed with variations in substrate temperature, methane concentration, and film thickness are analyzed using high-resolution electron back-scattering diffraction. Primarily {001}, {110}, and {111} fiber textures are observed. In addition, corresponding primary and higher order twinning components are found. As interfaces, high angle, low angle, primary twin, and secondary twin boundaries are observed. A growth and a twinning model are proposed based on the sp3 hybridization of the bond in the CH4 molecule that is used as the deposition medium. [source] Diaspora as Process: (De)Constructing BoundariesGEOGRAPHY COMPASS (ELECTRONIC), Issue 3 2007Elizabeth Mavroudi This article discusses different conceptualisations of diaspora, as bounded, unbounded and as a process, in order to help highlight the useful role diaspora can play in explorations and (de)constructions of nation-state, community and identity boundaries. There are two main ways in which diaspora has been theorised. The first theorises diaspora in relation to defined homeland-orientated ethnic groups and identities and the second theorises diaspora in relation to fluid, non-essentialised, nomadic identities. This article argues that it is necessary to look beyond such conceptualisations of diaspora as nomadic/fluid (unbounded) or homeland-centred/ethnic-religious (bounded). This article advocates a flexible use of diaspora as process that is able to examine the dynamic negotiations of collective, strategic and politicised identities based around constructions of ,sameness' and the homeland, as well as individual identities that are malleable, hybrid and multiple. It stresses that it is within this notion of diaspora as process that geographers, with their emphasis on place, space and time, have an important role to play. [source] Globalization and the Boundaries of the State: A Framework for Analyzing the Changing Practice of SovereigntyGOVERNANCE, Issue 1 2001Edward S. Cohen The impact of globalization on the sovereignty of the modern state has been a source of great controversy among political scientists. In this article, I offer a framework for understanding the state as a boundary-setting institution, which changes shape and role over time and place. I argue that, rather than undermining the state, globalization is a product of a rearrangement of the purposes, boundaries, and sovereign authority of the state. Focusing on the United States, the article traces the changing shape of state sovereignty through a study of the patterns of immigration policy and politics over the past three decades. Immigration policy, I argue, provides a unique insight into the continuities and changes in the role of the state in an era of globalization. [source] Geomorphic controls and transition zones in the lower Sabine RiverHYDROLOGICAL PROCESSES, Issue 14 2008Jonathan D. Phillips Abstract Instream flow science and management requires identification of characteristic hydrological, ecological, and geomorphological attributes of stream reaches. This study approaches this problem by identifying geomorphic transition zones along the lower Sabine River, Texas and Louisiana. Boundaries were delineated along the lower Sabine River valley based on surficial geology, valley width, valley confinement, network characteristics (divergent versus convergent), sinuousity, slope, paleomeanders, and point bars. The coincidence of multiple boundaries reveals five key transition zones separating six reaches of distinct hydrological and geomorphological characteristics. Geologic controls and gross valley morphology play a major role as geomorphic controls, as does an upstream-to-downstream gradient in the importance of pulsed dam releases, and a down-to-upstream gradient in coastal backwater effects. Geomorphic history, both in the sense of the legacy of Quaternary sea level changes, and the effects of specific events such as avulsions and captures, are also critical. The transition zones delineate reaches with distinct hydrological characteristics in terms of the relative importance of dam releases and coastal backwater effects, single versus multi-channel flow patterns, frequency of overbank flow, and channel-floodplain connectivity. The transitional areas also represent sensitive zones which can be expected to be bellwethers in terms of responses to future environmental changes. Copyright © 2007 John Wiley & Sons, Ltd. [source] Polymer Charge Transport: Charge-Transport Anisotropy Due to Grain Boundaries in Directionally Crystallized Thin Films of Regioregular Poly(3-hexylthiophene) (Adv. Mater.ADVANCED MATERIALS, Issue 16 200916/2009) Grain boundaries can be engineered in directionally oriented thin films of poly(3-hexylthiophene) report Alberto Salleo and co-workers on p. 1568. Charge-transport studies coupled with X-ray and AFM characterization indicate that intergrain transport is greatly facilitated when neighboring grains can be bridged by relatively straight polymer chains. [source] Charge-Transport Anisotropy Due to Grain Boundaries in Directionally Crystallized Thin Films of Regioregular Poly(3-hexylthiophene)ADVANCED MATERIALS, Issue 16 2009Leslie H. Jimison P3HT films that are highly anisotropic in-plane are produced using a directional crystallization technique, and the charge-transport properties of grain bourdaries between different orientations of crystallites are studied. Boundaries along the fiber provide a small barrier to charge transport when compared to fiber-to-fiber grain boundaries. The films allow a correlation to be drawn between the grain-boundary type and charge-transport behavior in P3HT. [source] Direct Observation of Inversion Domain Boundaries of GaN on c -Sapphire at Sub-ångstrom Resolution,ADVANCED MATERIALS, Issue 11 2008Fude Liu Inversion domain boundaries (IDBs) of GaN are studied by a high-resolution technique. The IDB separates adjacent domains of opposite polarity. The image shows a GaN IDB in the [bar;2110] projection. The theoretical IDB structure fits the experimentally obtained structure well. The inset is an image acquired from a very thin region on the right side of the IDB. It can indicate the polarity of GaN directly. [source] Multimedia in the Art Curriculum: Crossing BoundariesINTERNATIONAL JOURNAL OF ART & DESIGN EDUCATION, Issue 3 2001Steve Long Art educators, like those in other areas of the curriculum, are under pressure from various directions to use digital technology in the classroom. Whilst some of this pressure is politically motivated I believe there are also what could be described as more legitimate educational reasons for using computers; what is lacking at this stage is a coherent body of knowledge amongst art educators as to what happens when we do use them. This article focuses on a development project which took place last year in a secondary school involving a Year 10 class in the use of multimedia software. The project was collaborative in nature and was carried out by Miles Jefcoate, an art teacher at Beacon Community College in East Sussex, a group of Year 10 students at Beacon and myself as a member of the teaching team on the Art and Design PGCE course at the University of Brighton. Supported by research funding from the University, the school was provided with multimedia software which was installed into its computer network. The design and delivery of the students' project was undertaken by Miles whilst I evaluated the impact of the digital technology on the learning taking place, with an emphasis on how Miles and the students experienced and evaluated their activities. [source] Guest Editorial: ,Boundaries and barriers': redefining older people nursing in the 21st centuryINTERNATIONAL JOURNAL OF OLDER PEOPLE NURSING, Issue 4 2009Sarah H. Kagan PhD No abstract is available for this article. [source] Space, Boundaries, and the Problem of Order: A View from Systems TheoryINTERNATIONAL POLITICAL SOCIOLOGY, Issue 3 2007Jan Helmig The idea our global polity is chiefly divided by territorially organized nation-states captures contemporary constellations of power and authority only insufficiently. Through a decoupling of power and the state, political spaces no longer match geographical spaces. Instead of simply acknowledging a challenge to the state, there is the need to rethink the changing meaning of space for political processes. The paper identifies three aspects, a reconceptualization of the spatial assumptions that IR needs to address: the production of space, the constitutive role of boundaries, and the problem of order. With this contribution, we argue that one avenue in understanding the production of space and the following questions of order is by converging systems theory and critical geopolitics. While the latter has already developed a conceptual apparatus to analyze the production of space, the former comes with an encompassing theoretical background, which takes "world society" as the starting point of analysis. In this respect, nation states are understood as a form of internal differentiation of a wider system, namely world society. [source] Setting Boundaries: Can International Society Exclude "Rogue States"?,INTERNATIONAL STUDIES REVIEW, Issue 1 2006ELIZABETH N. SAUNDERS This essay addresses a prominent post-Cold War issue to which political scientists have paid relatively little attention: the status of so-called rogue states in international politics. The war in Iraq crystallized transatlantic disagreement over whether "rogue states" exist and how they should be treated, but the debate raged throughout the 1990s. This essay brings international relations theory to bear on the issue of "rogue states," but it does so with a theoretical twist. It argues that we must first identify the entity from which these states are allegedly excluded as well as who gets to set the membership criteria. If we stipulate that the international system includes all states, then international society can be defined according to various shared ideas and many realizations of international society are possible. Powerful states may try to act as "norm entrepreneurs," promoting their ideas as the basis of international society. But states, including great powers, may genuinely disagree over the basis and boundaries of this society. It is thus vital not only to take both power and shared ideas seriously, but also to describe the origins and limits of shared ideas. The limits to shared ideas can be termed"bounded intersubjectivity." This essay uses the debate over "rogue states" and the transatlantic crisis over confronting Iraq to underscore these theoretical issues. [source] Crossing Disciplinary Boundaries: International Relations Meets International LawINTERNATIONAL STUDIES REVIEW, Issue 1 2000Sonia Cardenas Book reviewed: Byers, Michael Custom, Power and the Power of Rules [source] Governance ,to Go': Domestic Actors, Institutions and the Boundaries of the PossibleJCMS: JOURNAL OF COMMON MARKET STUDIES, Issue 4 2001Laura Cram How to ,bring Europe closer to the people' has long been a preoccupation of the policy-maker at the EU level and has recently been restated as a goal of the member governments in the Treaty of Nice. Currently, the Commission is addressing this issue through the White Paper on European Governance. Here, it is argued that the focus on ,governance' as a strategy for inclusion was ill founded and underestimated the likely conflict with existing ,governance' regimes at the domestic level. Moreover, the pursuit of ,heroic' Europeanism with a concomitant emergence of a sense of ,Europeanness' or a European ,identity' as advocated in the Commission's work programme for the White Paper on European Governance was misguided. Drawing on empirical research into the activities of women's organizations in Greece, Ireland and the UK, it is argued that the extent to which EU level action may [source] Boundaries of Britishness in British Indian and Pakistani young adultsJOURNAL OF COMMUNITY & APPLIED SOCIAL PSYCHOLOGY, Issue 6 2009Kiren Vadher Abstract This study explored what it means to be British from the perspective of young British Indian and Pakistani adults. Fifteen respondents were interviewed using a semi-structured schedule in order to explore their self-descriptions and self-categorizations, how different contexts influence their identifications as British and as Indian/Pakistani, their sense of patriotism, and their perceptions of racism, discrimination and multiculturalism. Grounded theory methodology was used to analyse the interviews. The respondents' identifications and the role of context, threat and racism were studied in detail, and a model of how these individuals defined the boundaries of Britishness, and how they positioned themselves in relationship to these boundaries, was derived from the data. Six boundaries of Britishness were identified, these being the racial, civic/state, instrumental, historical, lifestyle and multicultural boundaries. Participants used these boundaries flexibly, drawing on different boundaries depending on the particular context in which Britishness was discussed. The implications of these multiple boundaries for the conceptualization of national identification are discussed. Copyright © 2009 John Wiley & Sons, Ltd. [source] Boundaries and barriers: a history of district nursing management in regional QueenslandJOURNAL OF NURSING MANAGEMENT, Issue 1 2008WENDY MADSEN BA Aim, To explore administrative constraints of district nursing during the latter part of the 20th century in regional Queensland, Australia. Background, A greater understanding of the evolution of district nursing can illuminate why present conditions and circumstances exist. Method, Thirteen interviews undertaken and analysed historically in association with other documentary evidence from the time period 1960,90. Findings, District nursing services of regional Queensland were initially established by voluntary organizations that had very lean budgets. Throughout the study period, government funding became increasingly available, but this coincided with increased regulation of the services. Conclusions, District nurses have worked within considerable boundaries and barriers associated with either a lack of funds or imposed regulations. While greater government funding solved some working conditions, it did so by imposing greater administrative responsibilities on the nurses and services that were not always seen as advantageous for clients or as professionally satisfying for the nurses. [source] Crossing Age and Generational Boundaries: Exploring Intergenerational Research EncountersJOURNAL OF SOCIAL ISSUES, Issue 4 2007Amanda M. Grenier Academics and professionals who aim to understand and plan for aging societies are most often younger than study participants and the benefactors of social programs themselves. However, the appropriateness of such intergenerational practice is beginning to be questioned. It has been suggested that only older people should conduct research, consult on and plan programs for older people. To understand the benefits and pitfalls of such an approach, research encounters between younger and older people will be used as examples from which to explore the question: what happens when individuals attempt to reach across age and generational boundaries? Situating age and generation as organizing principles, insights will be gleaned from the anthropological insider,outsider debate, linguistic work on age-based differences, and emotional associations and identification across age and generational boundaries. This paper argues that the ways older and younger people relate to each other may hold the potential for connection and/or conflict between the generations. Results suggest that age and generation be considered one of the many social locations that may impact the research process and outcomes. Researchers and policy makers of all ages must begin to reflect on their involvement with age and generational boundaries. [source] Simulation of Thermoelectric Performance of Bulk SrTiO3 with Two-Dimensional Electron Gas Grain BoundariesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 6 2010Rui-zhi Zhang Density functional theory calculations and Boltzmann transport theory are used to simulate the thermoelectric properties of SrTiO3 ceramics with two-dimensional electron gas grain boundaries (GBs). This material can achieve a large thermoelectric figure of merit (ZT>1 at room temperature) by utilizing quantum confinement and energy filtering at GBs. The latter causes the ZT value to reach a maximum before decreasing with an increasing GB barrier height. The optimum barrier height was approximately 0.06 eV higher than the Fermi energy of the grain interior. Our results may aid the design of materials with environmentally benign thermoelectric oxides. [source] Cation Ordering and Domain Boundaries in Ca[(Mg1/3Ta2/3)1,xTix]O3 Microwave Dielectric CeramicsJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 8 2008Mao Sen Fu Cation ordering and domain boundaries in perovskite Ca[(Mg1/3Ta2/3)1,xTix]O3 (x=0.1, 0.2, 0.3) microwave dielectric ceramics were investigated by high-resolution transmission electron microscopy (HRTEM) and Rietveld analysis. The variation of ordering structure with Ti substitution was revealed together with the formation mechanism of ordering domains. When x=0.1, the ceramics were composed of 1:2 and 1:1 ordered domains and a disordered matrix. The 1:2 cation ordering could still exist until x=0.2 but the 1:1 ordering disappeared. Neither 1:2 nor 1:1 cation ordering could exist at x=0.3. The space charge model was used to explain the cation ordering change from 1:2 to 1:1 and then to disorder. A comparison between the space charge model and random layer model was also conducted. HRTEM observations showed an antiphase boundary inclined to the (111)c plane with a projected displacement vector in the ,001,c direction and ferroelastic domain boundaries parallel to the ,100,c direction. [source] Direct Observation of Multilayer Adsorption on Alumina Grain BoundariesJOURNAL OF THE AMERICAN CERAMIC SOCIETY, Issue 3 2007Shen J. Dillon Grain-boundary films 0.6 nm in size have been observed on the grain boundaries of neodymia (Nd2O3)-doped alumina (,-Al2O3) sintered at 1800°C. Direct observation by high-angle annular dark-field imaging in the aberration-corrected scanning transmission electron microscope shows that this type of grain-boundary structure is the result of multilayer adsorption. Neodymium cations adsorb onto the faces of each of the two grains that comprise the grain boundary by substituting for aluminum cations. The positions of these cations are slightly distorted relative to the perfect lattice, and a third atomic layer in the core of the grain-boundary resides between these two layers. The measurements also confirm that the thickness deduced from high-resolution transmission electron microscopy lattice images are accurate. [source] | |||||||||||||||||||||||||||||||||||||||||||