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Este trabajo tuvo como objetivo adaptar una herramienta metodológica capaz de mejorar la forma de obtener el Índice de Adopción de Innovaciones en el sistema apícola poblano. Se diseñó y aplicó un cuestionario a una muestra de 62 apicultores de donde se obtuvo información sobre el uso de innovaciones de manejo, genética, alimentación y sanidad, de la cual se definieron 32 variables originales y siete categorías de innovación. Se rediseñó y adaptó el índice de adopción de innovación (InAI) utilizando el proceso analítico jerárquico (PAJ), lo que facilitó la identificación de aspectos sociales de los apicultores y las innovaciones que contribuyen a mejorar la productividad de miel. Los resultados muestran que las innovaciones que más contribuyen a la producción son las contenidas en las categorías de ubicación del apiario y sanidad. Por otro lado, la evaluación del InAIalt, mostró ser una alternativa pertinente para la explicación del comportamiento del rendimiento por colmena, además de mostrar los porcentajes de aportación específicos sobre las innovaciones evaluadas, con lo cual se pueden calcular estimaciones más precisas y consistentes con los rendimientos esperados de la región.

Se analizaron las principales prácticas de Intensificación Sostenible (IS) que realizan pequeños y medianos productores en la camaronicultura de Sinaloa, México. Se usó el enfoque de sostenibilidad, desde el establecimiento de la granja hasta la comercialización. El estudio muestra una limitada incorporación de las prácticas de IS y los principales factores limitantes son: el deficiente marco institucional y regulatorio, la ausencia de electricidad, baja adopción de tecnologías, ineficiente manejo y suministro de alimentos y uso excesivo de antibióticos. Este trabajo contribuye al reconocimiento de limitaciones en la adopción de la IS en la camaronicultura y al avance en la sostenibilidad de esta actividad.

La comunicación del conocimiento científico es parte fundamental del progreso de la ciencia y vital para la sociedad moderna. Así, las conferencias y congresos científicos son espacios cruciales para estos procesos de comunicación. Esta investigación tiene como objetivo analizar la comunicación de trabajos científicos en un congreso agrícola; de tal forma que se añade conocimiento a la literatura en tres vertientes: uso de datos, aplicación metodológica y evidencia empírica. Para hacer esto, analizamos 316 títulos de ponencias presentadas a lo largo de cinco años. Usamos dos enfoques metodológicos: data-mining y análisis de redes sociales (ARS). Los resultados muestran que en los 316 títulos se han utilizado 1,093 términos diferentes, siguiendo una distribución power-law. A través de una red de bi-gramas, se encontró que estos términos están unidos por 1,847 relaciones dirigidas. Además, con el ARS se identificaron las palabras más importantes según distintos indicadores. Se concluye que la información existente en los archivos de congresos científicos es rica en contenido y puede ser útil para encontrar brechas de conocimiento. Además, los enfoques utilizados se complementan entre sí. Este artículo proporciona evidencia técnica y empírica sobre el campo del network mining.

La globalización está ligada al nivel de integración futuro de los países en Cadenas Globales de Valor (cgv). Utilizando el enfoque de cgv se analizó el efecto de la gobernanza en los mecanismos de aprendizaje sobre la actualización (upgrading) responsable. Se aplicaron 17 entrevistas con actores clave del sector aguacatero mexicano durante mayo y agosto del 2021, para obtener información de los principales acuerdos entre compradores, clientes y requisitos para participar en los mercados globales. La información recabada se complementó con bases de datos de organismos gubernamentales y se realizó un análisis gráfico, de nubes de palabras y estadística descriptiva. Se encontró que la gobernanza global es modular, pero al interior de la cadena fue de mercado, modular y jerárquica, basado en las características de las transacciones. Los aprendizajes por imitación están presentes en gobernanzas de mercado y jerárquica, pero en la primera es de baja tecnología y de alta en la segunda. Se concluye que al participar en cgv los conocimientos de normas y estándares permiten aumentar el volumen de ventas y acumular capital, pero no garantizan aprendizajes para lograr mejoras productivas o funcionales. La responsabilidad como práctica de la gobernanza es variable entre eslabones, depende de capacidades y voluntades individuales y colectivas, la ausencia de instrumentos validados para responsabilizar empresas dificulta su aplicación, ya que estos instrumentos deben resolver problemas reales y no solo aportar conocimiento científico.

El objetivo de esta investigación fue analizar cómo está estructurada la red de actores que hablan de productos orgánicos en Twitter y, a través de la identificación de actores clave, conocer la influencia que ejercen dentro de las redes; al hacerlo, desarrollamos ideas significativas que permitan a los usuarios de medios sociales mejorar su interacción y posición dentro de la red. Se buscaron y descargaron los datos de los términos #organico(a) y #organicos(as) por un periodo de seis meses. Para su procesamiento y estudio, se utilizó el enfoque teórico y metodológico del análisis de redes sociales (ARS). La red general se formó por 14,329 tweets únicos, publicados por 6,667 usuarios, configurando una red de 6,521 vínculos directos. Para entender con mayor detalle las interacciones, se segmentó la red con base en dos tipos de relaciones: (1) retweets y (2) menciones o respuestas, ambas redes mostraron estructuras diferentes. Se encontró que el conjunto de relaciones que estructuran la red social está asociado a productos, países y temas, así como a diversos actores clave. Además, la expresión de los orgánicos en Twitter sigue de cerca la visión general de considerarse benéficos para la salud y el medio ambiente.

Understanding how to improve the accessibility and timely dissemination of weather and market information can help farmers adapt their management to climate change impacts. Our objective is to use Social Network Analysis (SNA) as a tool to identify potential opportunities for improving weather and market advisory dissemination to rural communities and to explore the relationship between farmers’ access to information and yield and selling price. As a case study, we applied SNA to 313 farmers in Bangladesh to analyze weather and market information networks and farmers' friendship networks as a potential proxy for information exchange. Farmer access to information, dominant sources of information and potential speed of information transfer were key criteria for our analysis. Our results indicate that weather and market information networks in coastal Bangladesh depended on certain key sources of information, while the friendship network was decentralized and interconnected, with few isolated farmers. We showed that farmers networks are significantly correlated with several socio-agro-economic variables; however, there was little indication of a relationship between information access and yield and selling price. We conclude that a mixed approach of targeting central actors and broadcasting information to farmers may be a suitable strategy to reach a maximum number of farmers as well as the most isolated farmers. Our study highlights that SNA can be a promising tool to reveal hidden structures of information flows in farmer communities and provide valuable insights for developing information dissemination strategies that reach even the most remote and underserved farmers.

In this data article, we provide a dataset of 8,982,694 Twitter posts around the coronavirus health global crisis. The data were collected through the Twitter REST API search. We used the rtweet R package to download raw data. The term searched was “Coronavirus” which included the word itself and its hashtag version. We collected the data over 23 days, from January 21 to February 12, 2020. The dataset is multilingual, prevailing English, Spanish, and Portuguese. We include a new variable created from other four variables; it is called “type” of tweets, which is useful for showing the diversity of tweets and the dynamics of users on Twitter. The dataset comprises seven databases which can be analysed separately. On the other hand, they can be crossed to set other researches, among them, trends and relevance of different topics, types of tweets, the embeddedness of users and their profiles, the retweets dynamics, hashtag analysis, as well as to perform social network analysis. This dataset can attract the attention of researchers related to different fields on knowledge, such as data science, social science, network science, health informatics, tourism, infodemiology, and others.

Los objetivos fueron analizar los cambios en la adopción de buenas prácticas de producción de miel (BPPM) en productores apícolas de la Península de Yucatán, México, antes y después de haber recibido asesoría técnica y capacitación; así como la identificación de factores que inciden en la adopción de dichas prácticas. Considerando 31 BPPM agrupadas en siete categorías, se calculó el índice de adopción de BPPM (InABPPM). Se analizó información de 8,074 apicultores en dos momentos (línea base y línea final), para los estados de Yucatán (n= 3,840), Campeche (n= 3,525) y Quintana Roo (n= 709). Los apicultores se clasificaron de acuerdo al número de colmenas que poseían en: pequeños (1-22, 24 %), medianos (23-35, 27 %) y grandes (36-400, 49 %). El InABPPM global presentó un incremento significativo (P0.05). Este estudio destaca la importancia de programas para la gestión y difusión de BPPM, con la finalidad de impulsar la actividad apícola y acceder al mercado internacional cumpliendo con las normas de calidad requeridas. Los resultados sugieren impulsar la adopción de las BPPM de proceso, y posteriormente orientar la inversión de los apoyos púbicos en aquellos apiarios con mejor desempeño en cuanto al incremento en sus niveles de adopción.

México posee condiciones óptimas para el cultivo del hule natural; sin embargo, importa más del 80 % para su consumo. Para mejorar esta situación se implementó un modelo de desarrollo de proveedores a través de Agencias de Gestión de la Innovación (agi). Este trabajo analizó los logros de los servicios de asistencia técnica proporcionados por dos agi a dos agroindustrias (ai) de hule y a sus proveedores ubicados en la Cuenca del río Papaloapan, en México. De 2011 a inicios de 2014, las agi generaron informes y datos sobre parámetros técnicos, productivos, organizativos y comerciales, tanto de productores como de ai. Con la información se construyeron bases de datos globales para analizar los cambios en producción, abasto y adopción de innovaciones. Los resultados muestran que la intervención de las agi fue pertinente y eficaz en la mejora de parámetros productivos y de poscosecha. Además, se incrementó la producción de hule coagulado y la disponibilidad de materia prima para las ai. También se lograron reducir los costos de producción y mejorar la calidad del hule. No obstante, la caída del precio del hule a fines de 2013 provocó retrocesos en la adopción de innovaciones y en la integración agricultura-industria, lo que evidenció la fragilidad del desarrollo de proveedores, así como de las ai involucradas para fungir como empresas tractoras.

Based on the analysis of scientific papers published on rural extension in Colombia since 2010, an interpretive descriptive study was conducted to identify the level of collaboration between authors and institutions in the creation, systematization and dissemination of knowledge in rural extension. Information was gathered from a search in bibliographic databases to identify papers published in rural extension. 50 papers were found. They were organized in a database, and using social network analysis, a review of relational structures and indicators derived from the scientific collaboration between the authors and institutions involved in the publication conducted. Authors from 28 different institutions have participated in the 50 papers identified, 70% of them have been published by researchers working in the same institution. The findings of this study support the conclusion that actors building knowledge on rural extension in Colombia have a limited intra and interinstitutional articulation, making it urgent to strength public policies and incentives to foster relationships between research groups and institutions.

Se analizan los efectos de las interacciones, directas e indirectas, entre agricultores y otros actores relevantes en el intercambio de información y conocimiento para la innovación agrícola. Los datos se obtuvieron al preguntar a 120 agricultores «¿de quién aprende y/o a quién recurre para obtener información o conocimiento de cuestiones técnicas y productivas en torno a su unidad de producción?». Se emplean indicadores del análisis de redes sociales para proponer lineamientos que permitan catalizar la innovación agrícola. Los resultados confirman la importancia de los vínculos indirectos, pues estos permiten que los agricultores alcancen mejor información de fuentes externas. Se recomienda que los programas encaminados a promover la innovación agrícola consideren la interacción preexistente en las redes de los agricultores.

Se reconoce que los procesos de innovación suceden entre un conjunto heterogéneo de actores, donde el Análisis de Redes Sociales (ARS) es una herramienta prometedora para su análisis y comprensión y, así, diseñar intervenciones basadas en red para catalizarla. Las intervenciones en red describen el proceso a través del cual se usan datos relacionales para acelerar el flujo de información entre los actores que la conforman. Este artículo contribuye en dos vertientes: primero, proporcionar conocimiento y evidencia sobre la aplicación y utilidad del ARS en el contexto de una intervención basada en red para catalizar la innovación agrícola; segundo, añadir a la literatura del ARS el estudio de una red al inicio y al final de la intervención de un programa de extensión, mostrando los cambios en la estructura e indicadores de forma longitudinal. Se utilizaron datos de productores caprinos para generar indicadores de línea base y después se analizó la intervención con una línea final. Los resultados sustentan la utilidad del ARS para catalizar la innovación agrícola, resaltando la importancia de la selección de agricultores y actores clave para dinamizar estos procesos. Se concluye con algunas implicaciones metodológicas y de política pública para mejorar e impulsar la innovación agrícola.

La baja adopción de innovaciones en las unidades de producción agrícola es una de las causas de los ineficientes niveles de producción y por tanto es importante analizar los factores que influyen en la adopción. Este trabajo especifica un modelo para explicar el nivel de innovación de productores de cacao (Theobroma cacao L.), hule (Hevea brasiliensis Muell. Arg.) y palma de aceite (Elaeis guineensis Jacq.) en México, en función de variables cuantitativas y cualitativas de 1474 productores y sus fincas. Los resultados muestran que la edad tiene un efecto negativo sobre la adopción de innovaciones; la escolaridad, la experiencia y la importancia económica de la actividad influyen positivamente; la superficie en producción explica mayores niveles de innovación y el género no tiene efecto. De esta manera, variables del perfil del productor y de sus fincas deberían ser consideradas para plantear estrategias de intervención encaminadas a incrementar los niveles de innovación. The low adoption of innovations in the agricultural production units is one of the causes in the inefficient levels of production and therefore it is important to analyze the factors that influence in the adoption. This paper presents a model to explain the innovation adoption of cocoa (Theobroma cacao L.), rubber (Hevea brasiliensis Muell. Arg.) and oil palm (Elaeis guineensis Jacq.) producers in Mexico, in terms of quantitative and qualitative variables of 1,474 farmers and their farms. The age holds a negative effect on the adoption of innovations; school level, experience, and economic importance of the activity influence positively; the production area explains higher levels of innovation, and gender does not show any effect. Thus, the profile producers and their farms variables should be considered for intervention strategies aimed at increasing levels of innovation.

Se analizan 19 embarazos en 9 pacientes con miastenia gravis. Hubo 2 exacerbaciones de la enfermedad, una de esta asociada al uso de aminoglicósidos en el tratamiento de pielonefritis aguda. En un caso la enfermedad debutó a las 24 semanas de gestación. Hubo tres casos de miastenia gravis neonatal en la misma gestante, 2 de los recién nacidos fallecieron a los 29 y 25 días respectivamente, pese al tratamiento. Hubo un recién nacido de pretérmino y 6 casos (35%) de restricción del crecimiento intrauterinoA total of 19 pregnancies in 9 patients with myasthenia gravis are analyzed. Two exacerbations of myasthenia gravis were observed. One associated to the use of aminoglycosides to treat an acute pyelonephritis. A debut of myasthenia gravis occurred during the 24th week of gestation. There were three cases of neonatal myasthenia gravis that appeared in the same patient, two newborn died after 29 and 25 days respectively, in spite of treatment. One case of preterm childbirth was observed and six cases (35%) of intrauterine growth retardation

Ni-based catalysts with Co or Fe can potentially replace precious Ir-based catalysts for the rate-limiting oxygen evolution reaction (OER) in anion-exchange membrane (AEM) electrolyzers. In this study, density functional theory (DFT) calculations provide atomic- and electronic-level resolution on how the inclusion of Co or Fe can overcome the inactivity of NiO catalysts and even enable them to surpass IrO 2 in activating key steps to the OER. Namely, NiO resists binding the key OH* intermediate and presents a high energetic barrier to forming the O*. Co- and Fe-substitution of Ni active sites allows for the stronger binding of OH* and preferentially activates O*/O 2 * formation, with Fe-substitution increasing the OER activity substantially as compared to Co-substitution. Whereas IrO 2 requires an activation energy of 0.34-0.49 eV to form O 2 , this step is spontaneous on Fe sub -NiO. Electrodeposition of polycrystalline electrodes and synthesized nanoparticles exploit the Co or Fe presence, with Fe particularly exhibiting greater activity: Tafel slopes indicate a significant change in the mechanism as compared to pure NiO, validating the theoretical predictions of OER activation at different steps. High-performing synthesized nanoparticles of 25% Fe-Ni exhibited a 4.6 times improvement over IrO 2 and a 34% improvement over RuO 2 , showcasing that non-platinum group metal catalysts can outperform platinum group metals. High-resolution transmission electron microscopy further highlights the advantages of Fe-Ni oxide synthesized nanoparticles over commercial catalysts: small, randomly oriented nanoparticles expose greater edge sites than large nanoparticles typical of commercially available materials., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Despite the record-high efficiency of GaAs solar cells, their terrestrial application is limited due to both the particularly high costs related to the required single-crystal substrates and epitaxial growth. A water-soluble lift-off layer could reduce costs by avoiding the need for toxic and dangerous etchants, substrate repolishing, and expensive process steps. Sr 3 Al 2 O 6 (SAO) is a water-soluble cubic oxide, and SrTiO 3 (STO) is a perovskite oxide, where a SAO ≈ 4 × a STO ≈ (2√2) a GaAs . Here, the pulsed laser-deposited epitaxial growth of SrTiO 3 /Sr 3 Al 2 O 6 templates on STO and Ge substrates for epitaxial GaAs growth was investigated, where SAO works as a sacrificial layer and STO protects the hygroscopic SAO during substrate transfer between deposition chambers. We identified that the SAO film quality is strongly dependent on the growth temperature and the O 2 partial pressure, where either a high T or a high P (O 2 ) improves the quality. XRD spectra of the films with optimized deposition parameters showed an epitaxial STO/SAO stack aligned to the STO (100) substrate, and TEM analysis revealed that the grown films were epitaxially crystalline throughout the thickness. The STO/SAO growth on Ge substrates at a high T with no intentional O 2 flow resulted in some nonepitaxial grains and surface pits, likely due to partial Ge oxidation. GaAs was grown by metalorganic vapor-phase epitaxy (MOVPE) on STO/SAO/STO templates. Lift-off after dissolving the sacrificial SAO in water resulted in free-standing ⟨001⟩ preferentially oriented polycrystalline GaAs., Competing Interests: The authors declare no competing financial interest., (© 2024 The Authors. Published by American Chemical Society.)

Yttrium-doped barium zirconate (BZY) has garnered attention as a protonic conductor in intermediate-temperature electrolysis and fuel cells due to its high bulk proton conductivity and excellent chemical stability. However, the performance of BZY can be further enhanced by reducing the concentration and resistance of grain boundaries. In this study, we investigate the impact of manganese (Mn) additives on the sinterability and proton conductivity of Y-doped BaZrO 3 (BZY). By employing a combinatorial pulsed laser deposition (PLD) technique, we synthesized BZY thin films with varying Mn concentrations and sintering temperatures. Our results revealed a significant enhancement in sinterability as Mn concentrations increased, leading to larger grain sizes and lower grain boundary concentrations. These improvements can be attributed to the elevated grain boundary diffusion of zirconium (Zr) cations, which enhances material densification. We also observed a reduction in Goldschmidt's tolerance factor with increased Mn substitution, which can improve proton transport. The high proton conduction of BZY with Mn additives in low-temperature and wet hydrogen environments makes it a promising candidate for protonic ceramic electrolysis cells and fuel cells. Our findings not only advance the understanding of Mn additives in BZY materials but also demonstrate a high-throughput combinatorial thin film approach to select additives for other perovskite materials with importance in mass and charge transport applications.

Exploiting the high surface-area-to-volume ratio of nanomaterials to store energy in the form of electrochemical alloys is an exceptionally promising route for achieving high-rate energy storage and delivery. Nanoscale palladium hydride is an excellent model system for understanding how nanoscale-specific properties affect the absorption and desorption of energy carrying equivalents. Hydrogen absorption and desorption in shape-controlled Pd nanostructures does not occur uniformly across the entire nanoparticle surface. Instead, hydrogen absorption and desorption proceed selectively through high-activity sites at the corners and edges. Such a mechanism hinders the hydrogen absorption rates and greatly reduces the benefit of nanoscaling the dimensions of the palladium. To solve this, we modify the surface of palladium with an ultrathin platinum shell. This modification nearly removes the barrier for hydrogen absorption (89 kJ/mol without a Pt shell and 1.8 kJ/mol with a Pt shell) and enables diffusion through the entire Pd/Pt surface.

The accumulation of plastic waste in the environment has prompted the development of new chemical recycling technologies. A recently reported approach employed homogeneous organometallic catalysts for tandem dehydrogenation and olefin cross metathesis to depolymerize polyethylene (PE) feedstocks to a mixture of alkane products. Here, we build on that prior work by developing a fully heterogeneous catalyst system using a physical mixture of SnPt/γ-Al 2 O 3 and Re 2 O 7 /γ-Al 2 O 3 . This heterogeneous catalyst system produces a distribution of linear alkane products from a model, linear C 20 alkane, n -eicosane, and from a linear PE substrate (which is representative of high-density polyethylene), both in an n -pentane solvent. For the PE substrate, a molecular weight decrease of 73% was observed at 200 °C in 15 h. This type of tandem chemistry is an example of an olefin-intermediate process, in which poorly reactive aliphatic substrates are first activated through dehydrogenation and then functionalized or cleaved by a highly-active olefin catalyst. Olefin-intermediate processes like that examined here offer both a selective and versatile means to depolymerize polyolefins at lower severity than traditional pyrolysis or cracking conditions., Competing Interests: The authors declare no competing financial interest., (© 2021 American Chemical Society.)

Because of the complexity, high reactivity, and continuous evolution of the silicon-electrolyte interphase (SiEI), "individual" constituents of the SiEI were investigated to understand their physical, electrochemical, and mechanical properties. For the analysis of these intrinsic properties, known SiEI components (i.e., SiO 2 , Li 2 Si 2 O 5 , Li 2 SiO 3 , Li 3 SiO x , Li 2 O, and LiF) were selected and prepared as amorphous thin films. The chemical composition, purity, morphology, roughness, and thickness of prepared samples were characterized using a variety of analytical techniques. On the basis of subsequent analysis, LiF shows the lowest ionic conductivity and relatively weak, brittle mechanical properties, while lithium silicates demonstrate higher ionic conductivities and greater mechanical hardness. This research establishes a framework for identifying components critical for stabilization of the SiEI, thus enabling rational design of new electrolyte additives and functional binders for the development of next-generation advanced Li-ion batteries utilizing Si anodes.

We use thin tensile-strained AlAs layers to manage compressive strain in stacked layers of InAs/AlAsSb quantum dots (QDs). The AlAs layers allow us to reduce residual strain in the QD stacks, suppressing strain-related defects. AlAs layers 2.4 monolayers thick are sufficient to balance the strain in the structures studied, in agreement with theory. Strain balancing improves material quality and helps increase QD uniformity by preventing strain accumulation and ensuring that each layer of InAs experiences the same strain. Stacks of 30 layers of strain-balanced QDs exhibit carrier lifetimes as long as 9.7 ns. QD uniformity is further enhanced by vertical ABAB… ordering of the dots in successive layers. Strain compensated InAs/AlAsSb QD stacks show great promise for intermediate band solar cell applications.

The applicability of atom probe to the characterization of photovoltaic devices is presented with special emphasis on high efficiency III-V and low cost ITO/a-Si:H heterojunction cells. Laser pulsed atom probe is shown to enable subnanometer chemical and structural depth profiling of interfaces in III-V heterojunction cells. Hydrogen, oxygen, and phosphorus chemical profiling in 5-nm-thick a-Si heterojunction cells is also illustrated, along with compositional analysis of the ITO/a-Si interface. Detection limits of atom probe tomography useful to semiconductor devices are also discussed. Gaining information about interfacial abruptness, roughness, and dopant profiles will allow for the determination of semiconductor conductivity, junction depletion widths, and ultimately photocurrent collection efficiencies and fill factors.

We report nanocrystalline TiO2 solar cells sensitized with InAs quantum dots. InAs quantum dots of different sizes were synthesized and incorporated in solar cell devices. Efficient charge transfer from InAs quantum dots to TiO2 particles was achieved without deliberate modification of the quantum dot capping layer. A power conversion efficiency of about 1.7% under 5 mW/cm2 was achieved; this is relatively high for a nanocrystalline metal oxide solar cell sensitized with presynthesized quantum dots, but this efficiency could only be achieved at low light intensity. At one sun, the efficiency decreased to 0.3%. The devices are stable for at least weeks under room light in air.

We report an alternative synthesis and the first optical characterization of colloidal PbTe nanocrystals (NCs). We have synthesized spherical PbTe NCs having a size distribution as low as 7%, ranging in diameter from 2.6 to 8.3 nm, with first exciton transitions tuned from 1009 to 2054 nm. The syntheses of colloidal cubic-like PbSe and PbTe NCs using a PbO "one-pot" approach are also reported. The photoluminescence quantum yield of PbTe spherical NCs was measured to be as high as 52 +/- 2%. We also report the first known observation of efficient multiple exciton generation (MEG) from single photons absorbed in PbTe NCs. Finally, we report calculated longitudinal and transverse Bohr radii for PbS, PbSe, and PbTe NCs to account for electronic band anisotropy. This is followed by a comparison of the differences in the electronic band structure and optical properties of these lead salts.

We tested the hypothesis that articular cartilage adjacent to experimental osteochondral defects is not subject to unusual strains under load. A 2.5-mm drill hole was made in the medial femoral condyle of 15 knees from 10 adult rabbits. Experimental joints were loaded with simulated quadriceps force, then frozen under load and preserved by freeze-substitution fixation. Deformation in the region of the defect was evaluated by scanning electron and light microscopy and compared with nondrilled and nonloaded control knees. To simulate blood clot, alginate was placed into some defects before loading. In loaded knees, articular cartilage at the edge of the drill hole was abnormally flattened and folded into the defect. Opposing tibial cartilage or meniscus intruded into the femoral defect beyond the cement line. Alginate did not prevent incursion of opposing cartilage. In this standard drill-hole model, the articular cartilage defect is occupied by the opposing surface when a joint is loaded. Any tissue growing or surgically implanted in the defect is subject to loading and displacement, therefore complicating attempts to characterize the healing or regenerative potential in similar drill-hole models. Deformation of cartilage at the defect edge suggests load concentration or increased compliance. Either phenomenon would contribute to subsequent degeneration of the cartilage adjacent to defects.

This study characterizes the healing response of the glenoid after spherical reaming and prosthetic humeral head replacement in a canine model of glenohumeral hemiarthroplasty. The right glenoid of twelve skeletally mature female dogs was reamed to a uniform radius of curvature, removing all cartilage down to bleeding subchondral bone. The glenoid was not resurfaced. The humeral head was replaced with a stemmed metal prosthesis. Post-surgery, the operated limbs were immobilized for seven days, with motion allowed ad libitum thereafter. Fluorescent bone labels were administered to identify bone formation. These procedures were not complicated by instability, infection or death. Six animals were euthanized at 10 week and six more at 24 week. The intact glenohumeral joints were evaluated by gross examination, assessment of glenoid concavity, and light microscopy of methylmethacrylate sections. At 10 week, vascular fibrous tissue partially covered the glenoid, maintaining a concave surface congruent with the prosthetic humeral head. New bone formed at the margin of the glenoid, and the density of the periarticular trabecular bone increased. At 24 week, the healing was more advanced; thick fibrocartilaginous tissue covered the entire glenoid surface. These results demonstrate that spherical glenoid reaming produced a consistent healing response characterized by remodelling of the reamed bony concavity to a congruent, living, smooth, securely attached interface articulating with the humeral prosthesis.

Background: Exact reconstruction of an osteochondral defect by autogenous transplantation (mosaicplasty) is difficult given the variation in joint surface contour. Clinical and experimental studies do not show the extent to which incongruity can be tolerated in autografting., Hypothesis: Grafted articular cartilage will hypertrophy to correct the incongruity created by recession of the transplanted surface., Study Design: Controlled laboratory study., Methods: To test the response of grafts to incongruities, osteochondral autografts were transplanted from the trochlea to the femoral condyle in adult male sheep stifle joints. In groups of 6 animals, graft surfaces were placed flush, countersunk 1 mm or countersunk 2 mm, then histologically analyzed 6 weeks after surgery. Cartilage thickness, condition of the articular surfaces, and preservation of hyaline characteristics were the primary features compared., Results: Bony union, vascularization, and new bone formation were present in all grafts. Cartilage-to-cartilage healing did not occur. In flush specimens, cartilage changed minimally in thickness and histologic architecture. The specimens countersunk 1 mm demonstrated significant cartilage thickening (54.7% increase, P <.05). Chondrocyte hyperplasia, tidemark advancement, and vascular invasion occurred at the chondroosseous junction, and the surface remained smooth. Cartilage necrosis and fibrous overgrowth were observed in all grafts countersunk 2 mm., Conclusions: Minimally countersunk autografts possess a capacity for remodeling that can correct initial incongruities while preserving hyaline characteristics. Grafts placed deeper do not restore the contour or composition of the original articular surface., Clinical Relevance: If preservation of normal hyaline cartilage is the objective, thin grafted articular cartilage can remodel, but the tolerance for incongruity is limited and probably less than that reported for an intra-articular fracture.

Quadruple-period ordering in GaAsSb alloys is studied both theoretically and experimentally. A growth model is proposed to account for the observed three-dimensional (3D) ordered structure. The model is qualitatively different from the widely accepted surface reconstruction and dimerization-induced ordering models that strictly speaking explain only the in-plane 2D patterns. Here, we show that the already ordered substrate will affect the reconstruction of the growth front with respect to the substrate to ensure a correct stacking of the individual 2D ordered layers into the observed 3D lattice.

Previous work suggests that the labrum helps center the humeral head. We hypothesized that detachment of the labrum alone would shift the head from its centered position toward the detachment, and repair would restore its centered position. Five young shoulders were used, and glenoids were potted with the articular surfaces oriented horizontally. Unconstrained humeral heads were subjected to 30-N compressive loads and no displacing force. Using a technique with 10-micrometer resolution, we quantified head and glenoid positions before and after anteroinferior labral detachment and after three types of repair. Detachment was associated with humeral head shift toward the labral lesion in all specimens, averaging 0.74 mm (range, 0.51-1.00 mm) (P <.005). Repair to the lip restored the labrum's centering effect variably. Repair with suture anchors on the glenoid face over-reduced the humeral head, shifting it posterosuperiorly by a mean of 3.47 mm (range, 0.71-6.7 mm) (P <.05). The labrum is important for humeral head centering, even without displacing loads.

Background: The use of dopamine to protect the kidneys against hypoperfusion injury remains controversial with little clinical evidence of benefit and increasing concerns regarding safety. In this double-blind, prospective, randomised study, we investigated the effect of dopamine infusion (2.5 microg/kg/min) on glomerular filtration rate (GFR) and tubular injury in patients undergoing routine cardiopulmonary bypass (CPB)., Methods: Forty eight patients were randomly assigned to receive intravenous dopamine or saline from induction of anaesthesia until 48 hours post-operatively. There were no differences in mean age, bypass time or pre-op creatinine in the 36 patients (33 men) who completed the study. 51Cr-EDTA GFR (ml/min/1.73 m2) was measured pre-operatively and on day 5 only. Urinary markers of tubular injury (albumin, N-acetyl glucosaminidase, NAG; retinol binding protein, RBP) were measured pre-operatively, and on days 1, 2 and 5., Results: GFR was preserved equally in both groups. All patients demonstrated significant tubular injury but urinary levels of NAG and RBP were lower in the dopamine group (41%, p=0.057 and 41%, p=0.007, respectively) on the first post-operative day., Conclusion: We conclude that low dose dopamine infusion may reduce renal tubular injury following CPB in patients with normal or near normal baseline renal function.

Both the acinar and ductal cells of the pancreas secrete a near-isotonic fluid and may thus be sites of aquaporin (AQP) water channel expression. Northern blot analysis of mRNA from whole rat pancreas revealed high levels of AQP1 and AQP8 expression, whereas lower levels of AQP4 and AQP5 expression were just detectable by RT-PCR Southern blot analysis. Immunohistochemistry showed that AQP1 is localized in the microvasculature, whereas AQP8 is confined to the apical pole of the acinar cells. No labeling of acinar, ductal, or vascular tissue was detected with antibodies to AQP2-7. With immunoelectron microscopy, AQP8 labeling was observed not only at the apical membrane of the acinar cells but also among small intracellular vesicles in the subapical cytoplasm, suggesting that there may be regulated trafficking of AQP8 to the apical plasma membrane. To evaluate the contribution of AQPs to the membrane water permeability, video microscopy was used to measure the swelling of acinar cells in response to hypotonic stress. Osmotic water permeability was reduced by 90% following exposure to Hg(2+). Since AQP8 is confined to the apical membrane, the marked effect of Hg(2+) suggests that other water channels may be expressed in the basolateral membrane.

The friction coefficients measured in diarthrodial joints are small. Theories of joint lubrication attribute this efficiency to entrapment or movement of synovial fluid, yet anatomical models of the surface are based on studies of isolated fragments of cartilage, not functional joints. To investigate the functional interrelationship of joint surfaces and synovial fluid, the ultrastructure of loaded joints was examined. Twenty-four New Zealand white rabbit knee joints were loaded either statically or moved ex vivo using simulated muscle forces and then plunge-frozen under load. After fixation in the frozen/loaded state by freeze-substitution fixation, the medial joint compartments were embedded in epoxy resin while still articulated. Bone was trimmed away from the articular surfaces, permitting the cartilage to be sectioned for light and electron microscopy. These joint surfaces were then compared with controls which were not loaded, not moved or had been disarticulated prior to embedding. Articular surfaces of loaded joints were smooth at magnifications from x 35 to x 7500, whereas the tibial surfaces of nonloaded joints were irregular. Small pools of joint fluid were observed at the meniscal edge and beneath the anterior horn of the meniscus. At magnifications of x 40000, the joint surfaces were separated by a uniform 100 nm space containing fluid. An amorphous, electron dense articular surface lamina was present but, when loaded, was thicker and flatter than previously reported. No surface pits or bumps were visible in embedded, loaded joints. This is the first ultrastructural study of intact loaded joints. The findings suggest that fluid film lubrication is present in diarthrodial joints, but the fluid sequestration postulated in several models is not apparent.