bluuebunny/crossref_metadata_2025 huggingface dataset:
La Expedición Hidrográfica del Atlas de la América septentrional, 1792-1805
Authors: Martín-Merás Luisa
Published: March 2008

The study deals with the hydrographic expeditions to make maps of the Gulf of Mexico and the Antilles, organized by the Spanish navy at the end of the eighteenth century, within the framework of a program to confirm and recognize the Spanish American colonies in opposition to the other European powers, principally Great Britain. This expedition that traversed Venezuela, Colombia and Panama and its islands, as well as the Lesser Antilles, is less-known than that of Malaspina, but of equal importance, and produced an important cartographic documentation.
Malaria, Landscape, and Society in Northwest Argentina in the Early Twentieth Century
Authors: Carter Eric D.
Published: March 2008

Although mostly forgotten, malaria was once widespread in Argentina’s Northwest region and had a dramatic impact on public health and social development. This paper explores the malaria problem in the social, demographic, and environmental context of Argentina in the early 1900s, when prevalence of the disease was at its height. Using a diverse range of sources and a mixture of historical demographic, spatial analytical, and qualitative methods, the geographical distribution of malaria and its association with social and environmental factors is analyzed. Examination of the general epidemiology of malaria in the Northwest is complemented by case studies that demonstrate the complex dynamics of malaria in the city of Salta and the agricultural hinterland of Tucumán province. Although malaria was a widespread and commonplace illness in the region, and garnered much political attention, it was neither a leading cause of mortality nor a cause of demographic stagnation. Improvements in sanitary infrastructure and drainage helped facilitate the decline of malaria in urban centers, although the relationship of the disease with wetland hazards remains unclear. In rural areas, the tenuous and impoverished conditions of agricultural laborers helped to sustain malaria transmission, but permanent workers in sugar mills enjoyed better health conditions, generally. Overall, this paper demonstrates the utility of historical statistical and spatial analysis, complemented by more fine-grained qualitative research, in drawing out the social and environmental dimensions of past disease complexes.
Mise en valeur de la Guyane française et peuplement blanc: les espoirs déçus du baron de Laussat (1819-1823)
Authors: Puyo Jean-Yves
Published: March 2008

Au XVIIe siècle, à savoir au plus fort des revendications territoriales françaises sur le bassin de l’Amazone, la France se trouve favorisée par la possession d’un vaste territoire dénommé la France Equinoxiale, s’étendant au Sud, de la rivière des Amazones jusqu’à l’Orénoque, et au Nord, jusqu’au fleuve Maroni. Ce droit d’exploitation demeurait néanmoins très théorique, la présence française au début du XIXe siècle se limitant aux environs de Cayenne ainsi qu’à l’embouchure des principaux fleuves compris entre l’Oyapok et le Maroni. Or, malgré le désastre passé de l’expédition de Kourou (1763), les projets de colonisation de ce vaste “désert démographique” ne manquèrent pas en ce même début de siècle. Notre recherche, reposant en grande partie sur l’étude des archives de la colonie guyanaise, a pour objectif d’analyser la pensée antinomique, à propos de l’aménagement du territoire, du baron de Laussat, gouverneur de la Guyane de 1819 à 1823. Homme des Lumières, doté d’une vraie pensée aménagiste élaborée au gré de ses postes précédents en Louisiane puis en Martinique, il fut toutefois démis de ses fonctions suite à l’échec de Laussadelphie, à savoir un périmètre de colonisation créé initialement pour accueillir des settlers nord-américains. Néanmoins, il demeura jusqu’à sa mort un fervent partisan du peuplement blanc en estimant possible l’acclimatation des colons blancs aux conditions extrêmes de la colonie tropicale. Quant à sa pensée, elle inspira nombre de projets et réalisations qui fleurirent en Guyane française durant la première moitié du XIXe siècle, avant sa transformation en une colonie de transportation (1851).
Posibles Controles Hidrogeológicos de Impacto Ambiental por la Extracción de Agua Subterránea en Xochimilco, México
Authors: Angeles-Serrano Gabriela , Perevochtchikova María , Carrillo-Rivera J. Joel
Published: March 2008

Since the middle of the last century through an inefficient water handling in several sites of the country different environmental impacts related to groundwater extraction have appeared. Thus, the National Protected Area of Xochimilco (ANP-X), located in the southeast area of the Basin of Mexico, has been affected by differential soil consolidation, and changes in the quality and amount of the groundwater extracted by boreholes. These boreholes partially supply Mexico City. In the present study an interdisciplinary approach to the water resources of Basin of Mexico was applied to achieve an understanding of the natural functioning of the flow systems through a flow system analysis. The main causes, effects and possible controls of environmental impacts due to intensive groundwater abstraction are discussed.
Who Will Work the Land? National Integration, Cash Economies, and the Future of Shifting Cultivation in the Honduran Mosquitia
Authors: Jr. David M. Cochran
Published: March 2008

This article describes how shifting cultivation is being marginalized in the Honduran Mosquitia as the region becomes more tied to national society. For much of the past four centuries, the Mosquitia has been a commercial frontier whose residents balanced subsistence with participation in external markets. In recent decades, colonization and greater integration with national society have transformed much of the region. I analyze the impacts of this change on shifting cultivation in three Miskito-Ladino communities on the Río Patuca. Few households specialize in land-based subsistence. Most combine subsistence with cash work. A few focus on professional and commercial activities and have no direct ties to the land. Many young adults pursue cash work at the expense of subsistence activities, suggesting that shifting cultivation may decline as older generations die out. In this sense, the long-term viability of shifting cultivation in the Mosquitia may largely be a factor of its performance relative to other economic activities.
The Mesquite Economy in the Mexican-American Borderlands
Authors: Taylor Matthew J.
Published: March 2008

Scrubby mesquite trees infest large regions of the Mexican-American borderland. In this same area, demand for mesquite wood and charcoal places pressure on mature trees. This paper examines consumption of this biomass fuel on both sides of the Sonora-Arizona border and the demands that consumption places on the environment in Northern Sonora. In Sonora multi-stemmed trees provide wood for heating homes and cooking stoves upon which coffee pots bubble and large, flat tortillas cook to perfection. At the opposite extreme, large, mature trees fall to the chainsaw and charcoal pits to provide North American restaurants and backyard cooks with a chic and flavorful grilling fuel. This research in northern Sonora reveals details of this hidden industry. This study provides important information and discussion about biomass use in a dry region. Studies like this, which consider direct use of biomass resources, are important, especially in light of present and future industrial, population, and urban growth along the border, which all place additional pressure on natural resources.
Market integration, perceived wealth and household consumption of river turtles ( Podocnemis spp.) in eastern lowland Bolivia
Authors: Conway-Gómez Kristen
Published: March 2008

Written records indicate that humans in the Bolivian Amazon have utilized Podocnemis river turtles in their diets since at least the 16 th century, resulting in their decline. This study examines the potential effects of market pressures and the perception of wealth on human consumption patterns of Podocnemis unifilis and P. expansa . The hypotheses tested were: 1) there is greater market consumption of turtle protein closer to market and greater subsistence consumption of turtle protein farther away; 2) there is a negative relationship between wealth and turtle protein sale/trade such that as personal wealth increases, the consumption of turtle protein decreases. Findings suggest proximity to market does not lead to greater turtle consumption and the relationship between turtle consumption and perception of wealth is negative. The fi ndings also suggest that improved roads into communities may reduce pressure on the turtles; poorest households pose the greatest risks to turtle abundance; and culturally-specific attitudes must be addressed for effective turtle conservation and management.
Explaining Variations in Environmental Activism on the United State-Mexico Border
Authors: Verduzco Basilio
Published: March 2008

This paper analyzes levels of environmental activism observed during a two year period in the early 1990s in the municipalities of the six Mexican states located in the United States-Mexico border. By focusing on a short period of time, it aims to capture the relevance of opportunities for mobilization. It uses multivariate statistical methods to relate variations in conflict rates to economic and political conditions in the area. It shows that even when using aggregate data it is possible to identify a pattern of concentration of activism following the geographical distribution of economic growth. The paper identifies that in this region the two important factors shaping the patterns of environmental activism are the influence of border dynamics and the presence of environmental groups with the experience and capacity to form international coalitions. The analysis demonstrates that these patterns of activism may eventually influence the geography of environmental pollution in the region.
Different Fear-Regulation Behaviors in Toddlerhood: Relations to Preceding Infant Negative Emotionality, Maternal Depression, and Sensitivity
Authors: Glöggler Bettina , Pauli-Pott Ursula
Published: March 2008

In the study presented, the development of different fear regulation behaviors and their associations with preceding maternal sensitivity and depression is addressed. A sample of 64 mother-child pairs was examined at the children's ages of 4, 12, and 30 months. Four-month negative reactivity and 12- and 30- month behavioral inhibition and fear regulation behaviors were assessed using laboratory routines. Maternal sensitivity and depression were assessed by behavior observations and questionnaires, respectively. Four-month negative emotionality preceded 30-month behavioral inhibition. Passive fear-regulation behaviors showed significant continuity between 12 and 30 months but no relations with maternal characteristics. In contrast, active fear-regulation behaviors were significantly related to less maternal depression and high sensitivity but showed no continuity. These associations might reflect a more stable disposition underlying passive fear behaviors and a higher dependence on experience for the active fear behaviors.
The AIDS Memorial Quilt and the Contemporary Culture of Public Commemoration
Authors: Blair Carole , Michel Neil
Published: March 2008

This essay situates the NAMES Project AIDS Memorial Quilt within the vigorous culture of national commemorative building in the late twentieth-century United States, a culture that found its first articulation in the Vietnam Veterans Memorial. We begin with an assessment of ways in which the AIDS Memorial Quilt appropriated and extended the rhetoric of the VVM in terms of the two memorials' modes of democratic representation, their troubling of the boundaries between contexts of invention and reception, and their differential coding of the public and private. We take up later memorial projects, specifically the Oklahoma City National Memorial and the September 11, 2001, commemorative projects, to suggest how the rhetoric of the AIDS Quilt can be marked as a harbinger of practices to come and how its progressive rhetoric has been turned in some later commemorative works to very different ends.
The Politics of Loss and Its Remains in Common Threads: Stories from the Quilt
Authors: Yep Gust A
Published: March 2008

Using Judith Butler's notion of the "ungrievable life," this project examines the politics of loss and its remains in Common Threads: Stories from the Quilt, an award-winning documentary featuring five diverse lives, represented by panels in the AIDS Memorial Quilt, and their subsequent loss. The essay is divided into four sections. The first discusses the notion of loss and its remains. The second provides a brief overview of the film and situates it in the political and historical context in which it was produced and circulated. Using the concepts of bodily, spatial, and ideal remains, the third section analyzes the politics of loss in the film. The essay concludes by examining these politics two decades after the AIDS Memorial Quilt was originally displayed.
From San Francisco to Atlanta and Back Again: Ideologies of Mobility in the AIDS Quilt's Search for a Homeland
Authors: Brouwer Daniel C.
Published: March 2008

In this essay, I examine two key controversies about the NAMES Project AIDS Memorial Quilt that span the years 2001–7. Specifically, these controversies are the relocation of the Quilt from San Francisco to Atlanta and the firing of NAMES Project founder and spokesperson Cleve Jones. These controversies bring to the forefront the importance of ideologies about place and movement. Embedded in these controversies is an assumption about the nature of the Quilt—that it does its work best when it engages in "promiscuous mobility." Yet this assumption stands alongside an equally strong assumption about the Quilt's need to rest in an appropriate homeland. Thus, these controversies nominate mobility as both a key topic for analysis and a conceptual resource. I employ mobility as a conceptual framework for exploring themes of movement, space, place, homeland, and ownership in these two controversies and for exploring the intersections of these themes with sexuality and race.
Q.U.I.L.T.: A Patchwork of Reflections
Authors: DeLuca Kevin Michael , Harold Christine , Rufo Kenneth
Published: March 2008

This essay, through an interrelated patchwork of "thought panels," explores the themes of visuality, representation, and trauma in the AIDS Memorial Quilt. We argue that as a text visually representing the magnitude of the global AIDS crisis, the Quilt fails miserably. However, this failure to represent is precisely why the Quilt succeeds as a gathering point for AIDS awareness and compassion, where traditional memorials might not. Indeed, to understand the rhetorical function of the Quilt, we argue that the Quilt must not be conceived as a "monument" to the crisis, but as an "archive." Whereas a monument enshrines an event in a particular place and time, an archive records and makes accessible a (partial, contingent) history, a history that is more than the sum of the parts on its timeline.
Repeated Remembrance: Commemorating the AIDS Quilt and Resuscitating the Mourned Subject
Authors: Rand Erin J
Published: March 2008

This essay examines the twentieth anniversary of the NAMES Project AIDS Memorial Quilt as a moment of doubled memorialization through which the nation's relationship to AIDS and homosexuality is renegotiated. Considering both the processes of national identity formation and the constitution of subjectivity and subject positions, I contend that a "mourned subject" position is produced by the discourses of the Quilt and is necessary to a specific national identity forged in relation to AIDS. That is, as we remember the origins of the Quilt project, the "mourned subject"—a position through which gay men were granted social recognition and therefore a certain kind of agency during the early years of the AIDS crisis, but from which legitimate mourning and militant activism were prohibited—is reconstituted. Ultimately, by considering the possibilities for developing activism through mourning and/or militancy, I suggest that the commemoration of the Quilt conserves a limiting form of social recognition that severely constrains its potential as a site for activating social change.
A Vision of the Quilt
Authors: Jones Cleve
Published: March 2008

In two chapters from his memoir Stitching a Revolution, Cleve Jones details the vision for the AIDS Quilt in the extraordinary epidemic context from which it emerged. Jones takes us through the complicated, sometimes frustrating but also heartening process of creation, coordination, and negotiation as that vision became realized. Here we experience the mourning ritual and spectacle of that first display in Washington, D.C., in 1987, as well some of the meaningful responses the AIDS Quilt elicited.
The First Displays: D.C. and S.F., 1987
Authors: Jones Cleve
Published: March 2008

In two chapters from his memoir Stitching a Revolution, Cleve Jones details the vision for the AIDS Quilt in the extraordinary epidemic context from which it emerged. Jones takes us through the complicated, sometimes frustrating but also heartening process of creation, coordination, and negotiation as that vision became realized. Here we experience the mourning ritual and spectacle of that first display in Washington, D.C., in 1987, as well some of the meaningful responses the AIDS Quilt elicited.
Since Black into White: Thomas Skidmore on Brazilian Race Relations
Authors: Dávila Jerry , Morgan Zachary R.
Published: March 2008

In the 40 years since he published Politics in Brazil, 1930-1964: An Experiment in Democracy, Thomas Skidmore has simultaneously been a leading U.S. scholar of Latin American history and a prominent public figure in Brazil. Balancing these roles, Skidmore has written and commented extensively on recent Brazilian political and economic history. But he is also the author of an influential intellectual history of racial thought in Brazil, Black into White: Race and Nationality in Brazilian Thought (1974). Black into White examines what Skidmore calls the “whitening thesis” by which Brazilian intellectuals of the late nineteenth and early twentieth centuries managed their racial and nationalist anxieties by interpreting miscegenation as a dynamic process that would dilute Brazil’s black population.
Defending Corporate Identity on New Spain's Northeastern Frontier: San Esteban de Nueva Tlaxcala, 1780-1810
Authors: Offutt Leslie S.
Published: March 2008

In 1808, confronted with the latest in a lengthy series of legal challenges to its corporate landholdings, the municipal council of the Indian town of San Esteban de Nueva Tlaxcala, in the northeastern province of Coahuila in New Spain, dispatched a blistering note to its counterpart in the adjoining Spanish town of Saltillo. The question of the moment concerned the right of Saltillo residents José Miguel and Juan González to route water they claimed in one place to property San Esteban had earlier allowed them to farm in another. But to do so meant that the water would be directed across lands belonging to San Esteban. When the Indian town denied them this right, the brothers protested vigorously. They contended that agriculture was, after all, the mainstay of the local economy. It benefited the public, the king, the church, and particularly the families of the pueblo itself. To deny these two farmers access to their water was to jeopardize agricultural production in the area. Further, they argued, San Esteban possessed much uncultivated arid land; perhaps the pueblo should consider renting some of the Gonzálezes' water as it flowed across the town's properties. Implicit in this suggestion was the assumption that San Esteban residents could not deal with what they had, that they were wasteful in utilizing their resources, and that Spaniards, in this particular case the brothers González, were better equipped to exploit the resources of the community.
Bishop Martínez Compañón's Practical Utopia in Enlightenment Peru
Authors: Berquist Emily
Published: March 2008

“Bishops, because they are bishops, cannot stop being vassals of their kings, and functionaries of their states. Nor are they exempt from practicing with all those around them, especially with their diocesans, works of mercy, physically as well as spiritually.

I gave [the miners] as proof of this truth one of the soliloquies of the Emperor Marcus Aurelius, in which he said: “You are a man, you are a citizen of the world.”—Bishop Martínez Compañón recounting his experiences with the Hualgayoc miner's guild in a letter to Viceroy Teodoro de Croix of Peru, May 1786.
Picturing Prints in Early Modern New Spain
Authors: Donahue-Wallace Kelly
Published: March 2008

In an anonymouscirca1754 portrait (Figure 1), fray Francisco de Santa Ana stands in a flowered crown and the brown and white habit of the Carmelite first order. The image commemorates the occasion of his final vows as a mendicant friar, and he is a rare if not unique example of a monk within the genre of the so-called crowned nuns. With eyes cast down, fray Francisco appears next to a table bearing an hourglass, skull, and book, symbols of his devotion and of his meditation on his own mortality. Painted as if tacked to the wall beside him is a print of the Virgin Mary, representing the Carmelite order's fervent Marian devotion. While she seems to gaze down at her follower, fray Francisco humbly looks away.
Painting by the Numbers: The Digital Intermediate
Authors: Belton John
Published: March 2008

This essay looks at the digital manipulation of color in such films as Pleasantville and Sin City in terms of their consequences for thinking about the “wholeness” and homogeneity of the image.
Structural studies of diamond thin films grown from dc arc plasma
Authors: Nistor L. C. , Landuyt J. Van , Ralchenko V. G. , Smolin A. A. , Korotushenko K. G. , Obraztsova E. D.
Published: March 2008

Diamond thin films grown from a dc-arc discharge in CH4/H2mixtures on Si wafers were examined by transmission electron microscopy and Raman spectroscopy. This deposition method provides good diamond crystallinity at high CH4concentrations (3%–9%). Seeding the substrate with 5 nm diamond particles at a density of 2 × 1012cm−1followed by argon laser irradiation to reduce their agglomeration gives, just after starting deposition, a density of growth centers of 1010cm−2. At 3% CH4concentration the film grows with almost perfect crystallites. Richer CH4mixtures (5% and 9%) produce crystallites with twins and stacking faults. An amorphous 20–70 nm SiC interlayer is present at these CH4concentrations, which was not observed at 3% CH4. Amorphoussp3- andsp2-bonded carbon was detected by Raman spectroscopy at all CH4concentrations and correlated with TEM data.
Phase instability in ZrO2–NiAl functionally graded materials
Authors: He Yi-Rong , Subramanian Vidya , Lannutti John J.
Published: March 2008

Sedimentation in organic solvents was followed by hot-pressing to produce 2 mole % yttria stabilized zirconia-NiAl functionally graded materials (FGM's). These FGM's were better able to accommodate high levels of residual stress than alumina-NiAl FGM's; this is possibly due to enhanced tetragonal phase retention. However, we found that the zirconia layer in these FGM's subsequently experiences room temperature transformation of t-ZrO2 to m-ZrO2.
In situ mass spectrometry during diamond chemical vapor deposition using a low pressure flat flame
Authors: Wolden C. A. , Davis R. F. , Sitar Z. , Prater J. T.
Published: March 2008

A combination of experiments and detailed kinetic modeling was used to investigate diamond deposition chemistry in low pressure combustion synthesis. Microprobe sampling was employed to provide in situ, quantitative measurements of the stable gas-phase species impinging the growth surface. The reactant gas ratio was found to be the most critical experimental variable. A detailed kinetic model was developed for the stagnation flow system. Comparison of experimental measurements showed very good agreement with model predictions. The model was then used to predict the concentration of radical species and analyze the sensitivity of predictions to γH, the probability of atomic hydrogen recombination on the surface. It was shown that γH dramatically affects the distribution of radical species near the diamond surface. The analysis also indicates that atomic carbon may be an important gas-phase precursor in this system. Comparison of mole fraction measurements and observations of film morphology were used to draw conclusions on the growth mechanism.
Camber development during cofiring Ag-based low-dielectric-constant ceramic package
Authors: Jean Jau-Ho , Chang Chia-Ruey
Published: March 2008

Camber (curvature) development during cofiring a two-layered structure of Ag film/low-dielectric-constant, low-temperature cofired ceramic (LTCC) green tape has been investigated. At a given thickness of Ag film, both the camber and camber rate decrease linearly with increasing the square thickness of LTCC. Densification mismatch between Ag and LTCC is attributed to be the root cause for the camber generation during cofiring. Mathematical analysis is made to theoretically describe the camber development, and the results show a fairly good agreement with experimental observations.
Studies on age-hardening characteristics of ceramic particle/matrix interfaces in Al–Cu–SiCp composites using ultra low-load-dynamic microhardness measurements
Authors: Dutta B. , Surappa M. K.
Published: March 2008

Ultra low-load-dynamic microhardness testing facilitates the hardness measurements in a very low volume of the material and thus is suited for characterization of the interfaces in MMC's. This paper details the studies on age-hardening behavior of the interfaces in Al–Cu–5SiCp composites characterized using this technique. Results of hardness studies have been further substantiated by TEM observations. In the solution-treated condition, hardness is maximum at the particle/matrix interface and decreases with increasing distance from the interface. This could be attributed to the presence of maximum dislocation density at the interface which decreases with increasing distance from the interface. In the case of composites subjected to high temperature aging, hardening at the interface is found to be faster than the bulk matrix and the aging kinetics becomes progressively slower with increasing distance from the interface. This is attributed to the dislocation density gradient at the interface, leading to enhanced nucleation and growth of precipitates at the interface compared to the bulk matrix. TEM observations reveal that the sizes of the precipitates decrease with increasing distance from the interface and thus confirms the retardation in aging kinetics with increasing distance from the interface.
An alternative analysis of water vapor and gas transport in polyimide films
Authors: Ouyang H. , Lee Sanboh
Published: March 2008

The water vapor and gas transport in polyimide films were analyzed using Harmon's model with accounts for case I transport and case II transport. Harmon's model was in good agreement with the experimental data. The diffusion coefficient obtained by Harmon's model was smaller than that obtained by using the short-time slope of mass uptake versus time with the exception of CO2 in polyimide. A comparison of the present model and the dual-mode sorption model, in which populations follow Henry's law and Langmuir type, was made.
Conductors with controlled grain boundaries: An approach to the next generation, high temperature superconducting wire
Authors: Goyal A. , Norton D. P. , Kroeger D. M. , Christen D. K. , Paranthaman M. , Specht E. D. , Budai J. D. , He Q. , Saffian B. , List F. A. , Lee D. F. , Hatfield E. , Martin P. M. , Klabunde C. E. , Mathis J. , Park C.
Published: March 2008

Much of the conductor development effort in the last decade has focused on optimizing the processing of (Bi, Pb)2Sr2Ca2Cu3Ox oxide-powder-in-tube conductors and (Bi, Pb)2Sr2CaCu2O8 (Bi-2212) and TlBa2Ca2Cu3Ox thick film conductors. It is demonstrated that in each of these conductors, critical current densities are dictated by the grain boundary misorientation distributions (GBMD's). Percolative networks of low-angle boundaries with fractions consistent with the active cross-sectional area of the conductor exist in each of these conductors. Further enhancements in the properties require increased numbers of small-angle grain boundaries. Given the processing methods used to fabricate these materials, no clear route employing a simple modification of the established processing method is apparent. To address this need, conductors with controlled or predetermined GBMD's are necessary. Development of biaxial texture appears to be the only possible way to increase the number of small-angle boundaries in a practical and controllable manner. We summarize in this paper recent results obtained on epitaxial superconducting films on rolling-assisted-biaxially-textured-substrates (RABiTS). This technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield structurally and chemically compatible surfaces. Epitaxial YBa2Cu3O7–δ films grown using laser ablation on such substrates have critical current densities exceeding 106 A/cm2 at 77 K in zero field and have a field dependence similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of the next generation high temperature superconducting (HTS) wire capable of carrying high currents in high magnetic fields and at elevated temperatures.
Surface nucleation, domain growth mechanisms, and factors dominating superconducting properties in seeded melt grown YBa2Cu3Ox
Authors: Shi Donglu , Lahiri K. , Qu D. , Sagar S. , Solovjov V. F. , Pan V. M.
Published: March 2008

Using a seeded melt growth (SMG) method, we have produced single-domain YBa2Cu3Ox with high levitation forces and trapped magnetic fields. A threshold temperature TL has been found above which extraneous nucleation does not occur. Surface nucleation has been suppressed when the top sample surface is coated with low melting compounds. The planar growth rates along the a- and c-axes have been found to be comparable within the undercooling range used in this study, and agree well with the current model. Major factors that strongly influence the levitation force have been studied in detail including domain geometry and orientation. Current physical models have been used to interpret the observed levitation force behaviors.
Effect of filament architecture on magnetic flux distributions in multifilamentary (Bi, Pb)2Sr2Ca2Cu3Ox/Ag composites
Authors: Kaiser Debra L. , Turchinskaya Marina , Riley Gilbert N. , Christopherson Craig
Published: March 2008

Multifilamentary (Bi, Pb)2Sr2Ca2Cu3Ox/Ag composites have been studied by a nondestructive magneto-optical imaging technique in order to determine the effect of filament architecture on the local magnetic flux distribution. The images reveal the homogeneity of the flux distribution in the upper layer filaments under magnetizing and demagnetizing conditions, and the alignment and morphology of these filaments in tapes with nine different composite structures. Certain types of filament arrangements led to homogeneous flux distributions, while other types caused localized inhomogeneities in the flux distribution. Nonuniform filament thickness also resulted in a highly inhomogeneous flux distribution. These results are useful in selecting optimal composite structures for power applications.
Growth and characterization of semiconductor nanoparticles in porous sol-gel films
Authors: Dawnay E. J. C. , Fardad M. A. , Green Mino , Yeatman E. M.
Published: March 2008

Two methods for the preparation of semiconductor doped sol-gel films, for applications in nonlinear optics, have been studied and compared. In the first, porous films are spun from sols containing the cation precursor, and then reacted with H2S gas, and in the second, the cation is adsorbed onto the pore surfaces of passive films from aqueous solution before the gas reaction. Extensive results for CdS doping are given, and preliminary results are reported for other semiconductor species. It is shown that a sputtered silica layer can seal the structure to allow further heat treatment without loss of dopant. The effects of heat treatment of doped films are described, and the limitation of crystallite growth by pore size is shown.
New hybrid nanocomposites based on an organophilic clay and poly(styrene-b-butadiene) copolymers
Authors: Laus Michele , Francescangeli Oriano , Sandrolini Franco
Published: March 2008

The preparation, by direct melt intercalation, and the properties of new hybrid organic-inorganic nanocomposites, consisting of a commercial sample of poly(styrene-b-butadiene) copolymer (SBS) and a commercial organophilic clay containing the dioctadecyl dimethyl ammonium salt are described. In addition, several mixtures between the same copolymer and an unfunctionalized clay were prepared and studied. XRD spectra showed a partial insertion of the SBS block copolymer segments in the interlayers of the organophilic clay, accompanied by a loss of correlation within the layers. The degree of insertion increased by annealing the nanocomposites at 120 °C for increasing time periods. No interaction between the polymer matrix and the unfunctionalized clay was found. The storage modulus value, in the plateau region between the glass transition processes of the polybutadiene and the polystyrene blocks, and the glass transition temperature of the polystyrene block domain increase as both the organophilic clay content and the annealing time increase. The glass transition process of the polybutadiene block domain is practically unaffected by the filler content and the annealing treatments. These data are most promising for upgrading the thermo-mechanical behavior and the application temperature window of the SBS thermoplastic elastomers through the preparation of nanocomposites employing suitably designed organophilic clays.
Adhesion mechanisms of copper films deposited onto laser-irradiated alumina
Authors: Park Jae-Won , Pedraza Anthony J. , Lowndes Douglas H. , Allen William R.
Published: March 2008

Strong adhesion between a deposited copper film and an alumina substrate takes place when the substrate is laser-irradiated prior to deposition. A post-deposition annealing is required to achieve the strong bonding. In this work, the interfacial region between the copper film and the alumina substrate was analyzed using Auger Electron Spectroscopy (AES). It was found that a transitional region is always present in couples that have a high adhesion strength, while little or no transitional region was found in weakly bonded couples. The transitional region depends on the laser irradiation atmosphere. In the case of laser irradiation in air, oxygen excess was found on the surface of the alumina substrate, and in the copper/alumina couple the transitional region consists of a copper oxide and a Cu–Al double oxide. When the laser irradiation was performed in a reducing atmosphere (Ar–4% H2), substoichiometric alumina and metallic aluminum were found on the surface of the substrate and also a reaction between copper and the substoichiometric aluminum oxide was detected in the subsurface. Although the substoichiometric alumina is formed on the surface irradiated in Ar–4% H2, a stable Al2O3 thin layer is formed on the outmost surface because the irradiated substrate is exposed to the atmosphere before deposition. This reoxidized layer remains whole at the interface of the couple upon low temperature (at least up to 300 °C) annealing, while it is ruptured upon higher temperature annealing (500 °C in this work). In the latter case, the copper film can contact and react with the substoichiometric alumina formed in the subsurface of the substrate irradiated in the Ar–4% H2 atmosphere. It is concluded that the Cu–Al–O interfacial compound formed in the transitional region causes the strong adhesion between the copper film and the alumina substrate.
Effect of sintering temperature and cooling rate on microstructure, phase formation, and critical current density of Ag-sheathed Bi1.8Pb0.4Sr2Ca2Cu3Ox superconducting tapes
Authors: Singh J. P. , Vasanthamohan N.
Published: March 2008

Silver-sheathed Bi–Pb–Sr–Ca–Cu–O (2223) superconducting tapes (with a starting composition of Bi1.8Pb0.4Sr2Ca1Cu2O8, calcium cuprate, and CuO) were fabricated by the powder-in-tube technique. The tapes were sintered at various temperatures to optimize the formation of Bi1.8Pb0.4Sr2Ca2Cu3O10 phase within the tape. The results show that sintering within the temperature range of 815–825 °C can produce tapes with high critical current density (Jc). The Jc of samples sintered at the higher temperature of 825 °C, where more liquid is present, depended markedly on the rate at which tapes were cooled from the sintering temperature; samples sintered at lower temperatures did not exhibit such a cooling-rate effect. The optimum combination of phase purity and microstructure that yielded an average transport Jc of ≥ 2.5 × 104 A/cm2 was obtained when the tapes were sintered at 825 °C for 150 h and cooled at a rate of 25 °C/h from the sintering temperature. Quenching studies indicate that the Bi-2223 phase becomes unstable below 700 °C during slow cooling. This result may have important implications for processing Bi–Sr–Ca–Cu–O tapes with high Jc. Addition of 15 vol.% Ag flakes to the monolithic core exerted no significant effect on Jc.
Anisotropic growth morphology and platelet formation in large grain Y–Ba–Cu–O grown by seeded peritectic solidification
Authors: Lo Wai , Cardwell D. A. , Chow J. C. L.
Published: March 2008

The characteristic platelet-like structure of large grain superconducting Y–Ba–Cu–O fabricated using peritectic solidification techniques has been documented widely as a key microstructural feature of this material. The platelet formation mechanism is investigated via a detailed comparison of the difference in morphology of YBa2Cu3O7–δ (123) growth fronts propagating along different lattice directions. The development of YBa2Cu3O7–δ dendrites between the growth front and local Y2BaCuO5 (211) particles is observed to be a key feature of the growth mechanism along all directions. Dendrites broaden rapidly for growth fronts propagating along the c-axis due to the enhanced growth rate of Y–Ba–Cu–O in the a-b plane to yield a uniform, regular growth morphology. Dendrite broadening is inhibited for grain growth along the a-b directions, however, due to the slower growth rate along the c-axis, which yields an irregular extended growth front. Growth along the a/b direction commonly results in the formation of regions consisting of 123 dendrites which may connect 211 particles. Continued solidification of the 123 phase in such regions results in the development of platelet structures perpendicular to the crystallographic c-axis in the YBa2Cu3O7–δ phase matrix which may impede the flow of current through the grain in the superconducting state.
Cu films by partially ionized beam deposition for ultra large scale integration metallization
Authors: Kim Ki-Hwan , Jang Hong-Gui , Han Sung , Jung Hyung-Jin , Koh Seok-Keun , Choi Doo-Jin
Published: March 2008

Highly (111) oriented Cu films with a thickness around 1800 Å were prepared on Si(100) at room temperature by partially ionized beam deposition (PIBD) at pressure of 8 × 10-7-1 × 10-6 Torr. Effects of acceleration voltage (Va) between 0 and 4 kV on such properties as crystallinity, surface roughness, resistivity, etc. of the films have been investigated. The Cu films deposited by PIBD had only (111) and (200) planes, and the relative intensity ratio, I(111)/I(200) of the Cu films increased from 6.8 at Va = 0 kV to 37 at Va = 4 kV. There was no indication of impurities in the system from Auger electron spectroscopy (AES) analyses. A large increase in grain size of the films occurred with Va up to Va = 1 kV, but little increase occurred with Va > 1 kV. Surface roughness of the Cu films decreased with Va, and resistivity showed the same trends as that of the surface roughness. In the Cu films by PIBD, it is considered that changes of resistivity are mainly due to a surface scattering rather than a grain boundary scattering. The via holes, dimensions of which are 0.5 μm in diameter and 1.5 μm in depth, in the Cu films made at Va = 4 kV were completely filled without voids. Interface adhesion of the Cu film on Si(100) deposited at Va = 3 kV was five times greater than that of Cu film deposited at Va = 0 kV, as determined by a scratch test.
Intercalation of cyclic amines in α–hafnium bis(hydrogen phosphate) monohydrate
Authors: Suáarez M. , Llavona R. , Rodríguez M. L. , Barcina L. M. , Anillo A. , Rodríguez J.
Published: March 2008

The intercalation in vapor phase of cyclic amines (aniline, benzylamine, cyclohexylamine, piperidine, and pyridine) in α–hafnium bis(hydrogen phosphate) monohydrate (α–HfP) has been investigated. Elemental and thermal analysis lead to the establishment of the intercalate composition. The general formula is x[Hf(HPO4)2 · y amine H2O] (1 - x) α–HfP where y = 2, 1 and x ≤ 1. When y = 1 (piperidine and pyridine) the amines form a monomolecular layer. When y = 2 (aniline, benzylamine, and cyclohexylamine) the arrangement is bimolecular. The results are compared to those described for α–ZrP.
Effect of (La0.5Sr0.5)CoO3 and Pt intermediate layers on improving the stability of Pb1–xLaxTi1–x/4O3 films
Authors: Wang J. P. , Ling Y. C. , Tseng Y. K. , Liu K. S. , Lin I. N.
Published: March 2008

Deposition of a (La0.5Sr0.5)CoO3 (LSCO) layer on top of Pt/Ti/Si substrates was observed to substantially improve the stability of the subsequently deposited Pb1−xLaxTi1−x/4O3 (PLT) films. Platinum coating of silicon substrates by itself is known to enhance the formation of PLT phase. In this paper, the elemental depth profile examined by secondary ion mass spectroscopy (SIMS) and the structural profile examined by grazing angle incident x-ray diffractometry (GIXD) reveals that the Ti species precoated underneath the Pt layer diffuses outward through the Pt layer at high temperature, forming a rutile TiO2 layer on top of Pt coating. It is this outermost TiO2 layer which promotes the transformation kinetics of the PLT species adhered onto substrates into the perovskite phase. Thus obtained films (PLT/Pt/Ti/Si) are, however, not stable enough to survive subsequent high-temperature processing. On the other hand, the PLT/LSCO/Pt/Ti/Si films, which incorporate LSCO as buffer layer, can survive 650 °C without significant deterioration.
Enhancing adhesion between metals or epoxy and polytetrafluoroethylene by ion assisted reaction
Authors: Koh S. K. , Seok J. W. , Choi S. C. , Choi W. K. , Jung H. J.
Published: March 2008

Ion irradiation on polytetrafluoroethylene (PTFE) has been carried out to improve adhesions to metals and to adhesive cements. Argon ions were irradiated on the polymer, by varying the amount of Ar+ from 1 × 1014 ions/cm2 to 1 × 1017 ions/cm2 at 1 keV, and 4 ml/min of oxygen gas flowed near the polymer surface during the ion irradiation. The wetting angle of water on the PTFE surface was changed from 100° to 70–150°, depending on the ion beam condition. The changes of the wetting angle and effects of Ar+ irradiation in oxygen environment were explained by the changes in surface morphology due to the ion beam irradiation onto PTFE, and formation of a hydrophilic group due to a reaction between the irradiated polymer chain and the blown oxygen. Strongly enhanced adhesion is explained by interlock mechanism, formation of electron acceptor groups on the modified PTFE, and interfacial chemical reactions between the irradiated surface and the deposited materials.
Phase formation sequence induced by deposition temperatures in Nb/Si multilayers
Authors: Zhang Ming , Wang W. K.
Published: March 2008

The phase formation sequence in Nb/Si multilayers formed at different deposition temperatures was investigated by x-ray diffraction (XRD) and transmission electron microscopy (TEM). The amorphous phases were found to form in Nb/Si multilayers deposited at room temperature and 560 °C, but the compositions of these two amorphous phases were different. The crystalline Nb3Si and Nb5Si3 were formed in Nb/Si multilayers deposited at 180–500 °C. The interfacial energy and modified heat of formation are adopted to explain our obtained results. The occurrence of crystalline Nb5Si3, NbSi2, and amorphous silicide phase was found when the Nb/Si multilayers with Nb3Si phase were annealed at 550 °C, while only NbSi2 was found to form when annealing this sample at 700 °C. The mobility of Si takes an important role in phase formation in Nb/Si multilayers.
Morphologies and Related Electronic Properties of Carbon Nanotubes
Authors: Charlier J-C.
Published: March 2008

The electronic structures of different morphologies of carbon nanotubes are investigated within either tight-binding or ab initio frameworks. After a brief description of the electronic properties of the “perfect” rolled-up graphene sheet, nanotubes containing pentagon-heptagon pairs, tips (hemispherical caps), sp3-like lines responsible for polygonization, multishell and solid-state packings (bundles) are studied in order to point out the influence of such defects on the electronic states of the “perfect” cylinders. Most of the time, a structural optimization was performed on the atomic topology, prior to the calculation of the electronic properties. Connections with experimental facts are indicated as frequently as possible.
Compensating for elastic deformation of the indenter in hardness tests of very hard materials
Authors: Lo Roger Yu , Bogy David B.
Published: March 2008

The current method of analysis for hardness measurements by indentation is examined. Although the method is based on Sneddon's solution for an elastic stress field within a homogeneous half space indented by an elastically deformable indenter, it implicitly assumes a fixed indenter geometry. Therefore, if indentations are made on materials whose hardness or elastic modulus are close to those of the indenter, this method underestimates the contact area and, thus, overestimates the hardness and modulus values of the indented materials. A new method, based on the Hertz contact theory, is proposed that accounts for the elastic deformation of the indenter and provides a simple way to calculate the tip radius. The restrictions of this method are also indicated and discussed. Finally, the hardness and modulus for two recently developed films are measured by this method, and the results are compared with published finite element method (FEM) results.
Micro/nanomechanical and tribological characterization of ultrathin amorphous carbon coatings
Authors: Li Xiaodong , Bhushan Bharat
Published: March 2008

Micro/nanomechanical and tribological characterization of ultrathin amorphous carbon coatings, deposited by filtered cathodic arc (FCA), direct ion beam (IB), electron cyclotron resonance plasma chemical vapor deposition (ECR-CVD), and sputter (SP) deposition processes on Si substrate have been conducted using a nanoindenter with a nanoscratch attachment and an accelerated ball-on-flat tribometer. Coating thicknesses of 20, 10, 5 nm and, for the first time, 3.5 nm coatings have been investigated. It was found the FCA coating exhibits the highest hardness and elastic modulus, followed by the ECR-CVD, IB, and SP coatings. In general, the thicker coatings exhibited better scratch/wear performance than the thinner coatings due to their better load-carrying capacity as compared to the thinner coatings. At 20 nm, the FCA and ECR-CVD coatings show the best scratch and wear resistance, while the IB and ECR-CVD coatings show the best scratch and wear resistance at 10 nm. Five nanometer thick coatings show reasonable scratch and wear resistance, while 3.5 nm thick coatings show extremely low load-carrying capacity and poor scratch and wear resistance. It appears that the 3.5 nm coatings studied are unfeasible for scratch and wear resistance applications as of now.