High-Throughput Prediction of the Thermal and Electronic Transport Properties of Large Physical and Chemical Spaces Accelerated by Machine Learning: Charting the ZT of Binary Skutterudites.

Thermal and electronic transport properties are the keys to many technological applications of materials. Thermoelectric, TE, materials can be considered a singular case in which not only one but three different transport properties are combined to describe their performance through their TE figure of merit, ZT. Despite the availability of high-throughput experimental techniques, synthesizing, characterizing, and measuring the properties of samples with numerous variables affecting ZT are not a cost- or time-efficient approach to lead this strategy. The significance of computational materials science in discovering new TE materials has been running in parallel to the development of new frameworks and methodologies to compute the electron and thermal transport properties linked to ZT. Nevertheless, the trade-off between computational cost and accuracy has hindered the reliable prediction of TE performance for large chemical spaces. In this work, we present for the first time the combination of new ab initio methodologies to predict transport properties with machine learning and a high-throughput framework to establish a solid foundation for the accurate prediction of thermal and electron transport properties. This strategy is applied to a whole family of materials, binary skutterudites, which are well-known as good TE candidates. Following this methodology, it is possible not only to connect ZT with the experimental synthetic (carrier concentration and grain size) and operando (temperature) variables but also to understand the physical and chemical phenomena that act as driving forces in the maximization of ZT for p-type and n-type binary skutterudites.

Cytomegalovirus infection and disease in pediatric liver transplantation: Burden of disease under a preemptive therapy approach.

BACKGROUND: CMV remains a frequent complication after liver transplantation. Few studies exist in children reporting the epidemiology and outcomes of CMV after LT with current prevention strategies. Our goal is to report the incidence of CMV infection and disease in pediatric LT recipients under preemptive therapy, identify risk factors, complications, and adverse reactions to treatment. METHODS: All pediatric LT recipients from a single center (1998-2018) were included. Antigenemia pp65 (1998-2003) and QNAT or both were used to inform preemptive therapy. Cutoff value for starting treatment was Agpp65 > 10 + cells/200 000 or QNAT >1500 copies/ml or any value in high-risk recipients (D+/R-). RESULTS: One hundred eighteen LT were analyzed. CMV infection was detected in 67% of patients, only 44 (37%) required treatment, and 5 (4%) developed CMV disease. All patients responded well to treatment, and no graft or patients were lost to CMV effects. There were no differences in mortality, CMV indirect effects, or other complications between those who required treatment and those who did not. Thirty-two percent of the patients who received antivirals developed an adverse hematological reaction. Risk factors associated with CMV infection requiring treatment were D+/R- (OR 13.9, p = .01) and fulminant hepatitis (OR 4.8, p = .02). CONCLUSIONS: Preemptive therapy for CMV in children is safe and effective, yields low CMV infection rates that require treatment, and minimal rates of CMV disease, without increasing CMV-related complications. Using this strategy, 63% of our patients did not receive treatment. Therefore, drug exposure, adverse reactions, and resistance risk were minimized.

High-Throughput Screening of the Thermoelastic Properties of Ultrahigh-Temperature Ceramics.

Ultrahigh-temperature ceramics (UHTCs) are a group of materials with high technological interest because of their applications in extreme environments. However, their characterization at high temperatures represents the main obstacle for their fast development. Obstacles are found from an experimental point of view, where only few laboratories around the world have the resources to test these materials under extreme conditions, and also from a theoretical point of view, where actual methods are expensive and difficult to apply to large sets of materials. Here, a new theoretical high-throughput framework for the prediction of the thermoelastic properties of materials is introduced. This approach can be systematically applied to any kind of crystalline material, drastically reducing the computational cost of previous methodologies up to 80% approximately. This new approach combines Taylor expansion and density functional theory calculations to predict the vibrational free energy of any arbitrary strained configuration, which represents the bottleneck in other methods. Using this framework, elastic constants for UHTCs have been calculated in a wide range of temperatures with excellent agreement with experimental values, when available. Using the elastic constants as the starting point, other mechanical properties such a bulk modulus, shear modulus, or Poisson ratio have been also explored, including upper and lower limits for polycrystalline materials. Finally, this work goes beyond the isotropic mechanical properties and represents one of the most comprehensive and exhaustive studies of some of the most important UHTCs, charting their anisotropy and thermal and thermodynamical properties.

Accidente cerebrovascular de la arteria basilar: cannabis como factor de riesgo en jóvenes / Cerebrovascular accident of basilar artery: Cannabis as a risk factor in young people / Acidente Vascular Cerebral (AVC) da artéria basilar: cannabis como fator de risco em jovens

Introducción. La arteria basilar se forma de las arterias vertebrales, cursa sobre el puente y se bifurca originando las arterias cerebrales posteriores. Irriga parte del tronco encefálico, cerebelo, tálamo y los lóbulos occipitales y temporales cerebrales. Su obstrucción es rara (1% de los accidentes isquémicos), puede ocurrir en cualquier parte de su trayecto, con cuadro clínico diverso. En jóvenes se añaden otros factores de riesgo distintos a los cardiovasculares, se incluye el consumo de sustancias psicoactivas. El objetivo de este artículo es presentar el caso de un adulto joven, su evolución posterior a la intervención endovascular y la asociación, pasada por alto, al consumo de cannabinoides. Caso clínico. Individuo de 23 años con 14 horas de parálisis facial periférica derecha, diplopía, disartria, hemiparesia e hiperreflexia izquierda, disfagia, náuseas y emesis. Tomografía Axial Computarizada de cráneo simple sin alteraciones. Posteriormente, al realizarse resonancia magnética nuclear, se evidencia isquemia pontomesencefálica y focos isquémicos agudos lacunares en lóbulos cerebelosos. Se consideró comprometido el territorio de la arteria basilar, por lo que se realizó angiotomografía que evidenció una obstrucción crítica de dicho vaso a nivel del tercio distal. Se realizó trombectomía con stent-retriever con recanalización total de la arteria basilar con flujo en toda su extensión. Al egreso fue clasificado como TOAST idiopático. Conclusiones. Las escalas etiológicas para stroke creadas para adultos mayores sobreestiman la etiología idiopática en pacientes jóvenes, lo cual puede ocasionar que el consumo de cannabis sea pasado por alto como causante pese a la asociación reportada por la literatura.

Introduction. The basilar artery is formed from the vertebral arteries, runs over the pons and bifurcates, originating the posterior cerebral arteries. It irrigates part of the brainstem, cerebellum, thalamus, and the occipital and temporal lobes of the brain. Its obstruction is rare (1% of ischemic accidents), it can occur in any part of its path, with a diverse clinical condition. In young people, other risk factors other than cardiovascular ones are added; psychoactive substance use is included. The objective of this article is to present the case of a young adult, his evolution after endovascular intervention and the association, overlooked, to the consumption of cannabinoids. Clinical case. 23-year-old man with 14 hours of right peripheral facial paralysis, diplopia, dysarthria, left hyperreflexia and hemiparesis, dysphagia, nausea and emesis. Simple skull Computerized Axial Tomography without alterations. Subsequently, when a nuclear magnetic resonance was performed, pontomesencephalic ischemia and acute lacunar ischemic foci in the cerebellar lobes were evidenced. The basilar artery territory was considered compromised, so a CT angiography was performed, which revealed a critical obstruction of said artery at the level of the distal third. A stent-retriever thrombectomy was performed with total recanalization of the basilar artery with flow in its entirety. Upon discharge, he was classified as "idiopathic" according to the TOAST classification. Conclusions. The etiological scales for stroke created for older adults overestimate idiopathic etiology in young patients, which may cause cannabis use to be overlooked as a cause despite the association reported in the literature.

Introdução. A artéria basilar é formada pelas artérias vertebrais, passa pela ponte e se bifurca, originando as artérias cerebrais posteriores. Irriga parte do tronco cerebral, cerebelo, tálamo e os lobos occipital e temporal do cérebro. Sua obstrução é rara (1% dos acidentes isquêmicos), podendo ocorrer em qualquer parte de seu trajeto, com quadro clínico diverso. Nos jovens, são adicionados outros fatores de risco além dos cardiovasculares, incluindo o consumo de substâncias psicoativas. O objetivo deste artigo é apresentar o caso de um adulto jovem, sua evolução após a intervenção endovascular e a associação, despercebida, ao consumo de canabinoides. Caso clínico. Indivíduo de 23 anos com 14 horas de paralisia facial periférica direita, diplopia, disartria, hemiparesia e hiperreflexia esquerda, disfagia, náuseas e vômitos. Tomografia axial computadorizada de crânio simples sem alterações. Posteriormente, quando foi realizada a ressonância magnética nuclear, foram evidenciados isquemia pontomesencefálica e focos agudos de isquemia lacunar nos lobos cerebelares. O território da artéria basilar foi considerado comprometido, por isso foi realizada uma angiotomografia, que revelou uma obstrução crítica do referido vaso no terço distal. Foi realizada trombectomia stent-retriever com recanalização total da artéria basilar com fluxo em sua totalidade. No momento da alta, foi classificado como TOAST idiopática. Conclusões.As escalas etiológicas para AVC criadas para idosos superestimam a etiologia idiopática em pacientes jovens, o que pode fazer com que o uso de cannabis seja negligenciado como causa, apesar da associação relatada na literatura.

Improving the activity of gold nanoparticles for the water-gas shift reaction using TiO2-Y2O3: an example of catalyst design.

In the last ten years, there has been an acceleration in the pace at which new catalysts for the water-gas shift reaction are designed and synthesized. Pt-based catalysts remain the best solution when only activity is considered. However, cost, operation temperature, and deactivation phenomena are important variables when these catalysts are scaled in industry. Here, a new catalyst, Au/TiO2-Y2O3, is presented as an alternative to the less selective Pt/oxide systems. Experimental and theoretical techniques are combined to design, synthesize, characterize and analyze the performance of this system. The mixed oxide demonstrates a synergistic effect, improving the activity of the catalyst not only at large-to-medium temperatures but also at low temperatures. This effect is related to the homogeneous dispersion of the vacancies that act both as nucleation centers for smaller and more active gold nanoparticles and as dissociation sites for water molecules. The calculated reaction path points to carboxyl formation as the rate-limiting step with an activation energy of 6.9 kcal mol-1, which is in quantitative agreement with experimental measurements and, to the best of our knowledge, it is the lowest activation energy reported for the water-gas shift reaction. This discovery demonstrates the importance of combining experimental and theoretical techniques to model and understand catalytic processes and opens the door to new improvements to reduce the operating temperature and the deactivation of the catalyst.

Ag2S Quantum Dot-Sensitized Solar Cells by First Principles: The Effect of Capping Ligands and Linkers.

Quantum dots solar cells, QDSCs, are one of the candidates for being a reliable alternative to fossil fuels. However, the well-studied CdSe and CdTe-based QDSCs present a variety of issues for their use in consumer-goods applications. Silver sulfide, Ag2S, is a promising material, but poor efficiency has been reported for QDSCs based on this compound. The potential influence of each component of QDSCs is critical and key for the development of more efficient devices based on Ag2S. In this work, density functional theory calculations were performed to study the nature of the optoelectronic properties for an anatase-TiO2(101) surface sensitized with different silver sulfide nanoclusters. We demonstrated how it is possible to deeply tune of its electronic properties by modifying the capping ligands and linkers to the surface. Finally, an analysis of the electron injection mechanism for this system is presented.

Effects of the capping ligands, linkers and oxide surface on the electron injection mechanism of copper sulfide quantum dot-sensitized solar cells.

Quantum dot-sensitized solar cells, QDSCs, are a clean and effective alternative to fossil fuels to reduce CO2 emissions. However, the different components that constitute the QDSCs and the difficulty of isolating experimentally their effects on the performance of the whole system slow down the development of more efficient devices. In this work, DFT calculations are combined with a bottom-up approach to differentiate the effect of each component on the electronic structure and absorption spectra. First, Cu2S QDs were built including a U parameter to effectively describe the localization of electrons. The effect of capping agents is addressed using ligands with different electron-donating/withdrawing groups. The role of linkers and their adsorption on the oxide surface are also examined. Finally, we propose a main indirect electron injection mechanism based on the position of the peaks of the spectra.

IL1B-CGTC haplotype is associated with colorectal cancer in admixed individuals with increased African ancestry.

Single-nucleotide polymorphisms (SNPs) in cytokine genes can affect gene expression and thereby modulate inflammation and carcinogenesis. However, the data on the association between SNPs in the interleukin 1 beta gene (IL1B) and colorectal cancer (CRC) are conflicting. We found an association between a 4-SNP haplotype block of the IL1B (-3737C/-1464G/-511T/-31C) and CRC risk, and this association was exclusively observed in individuals with a higher proportion of African ancestry, such as individuals from the Coastal Colombian region (odds ratio, OR 2.06; 95% CI 1.31-3.25; p < 0.01). Moreover, a significant interaction between this CRC risk haplotype and local African ancestry dosage was identified in locus 2q14 (p = 0.03). We conclude that Colombian individuals with high African ancestry proportions at locus 2q14 harbour more IL1B-CGTC copies and are consequently at an increased risk of CRC. This haplotype has been previously found to increase the IL1B promoter activity and is the most frequent haplotype in African Americans. Despite of limitations in the number of samples and the lack of functional analysis to examine the effect of these haplotypes on CRC cell lines, our results suggest that inflammation and ethnicity play a major role in the modulation of CRC risk.

First principles thermodynamical modeling of the binodal and spinodal curves in lead chalcogenides.

High-throughput ab initio calculations, cluster expansion techniques, and thermodynamic modeling have been synergistically combined to characterize the binodal and the spinodal decompositions features in the pseudo-binary lead chalcogenides PbSe-PbTe, PbS-PbTe, and PbS-PbSe. While our results agree with the available experimental data, our consolute temperatures substantially improve with respect to previous computational modeling. The computed phase diagrams corroborate that in ad hoc synthesis conditions the formation of nanostructure may occur justifying the low thermal conductivities in these alloys. The presented approach, making a rational use of online quantum repositories, can be extended to study thermodynamical and kinetic properties of materials of technological interest.

Charting the complete elastic properties of inorganic crystalline compounds.

The elastic constant tensor of an inorganic compound provides a complete description of the response of the material to external stresses in the elastic limit. It thus provides fundamental insight into the nature of the bonding in the material, and it is known to correlate with many mechanical properties. Despite the importance of the elastic constant tensor, it has been measured for a very small fraction of all known inorganic compounds, a situation that limits the ability of materials scientists to develop new materials with targeted mechanical responses. To address this deficiency, we present here the largest database of calculated elastic properties for inorganic compounds to date. The database currently contains full elastic information for 1,181 inorganic compounds, and this number is growing steadily. The methods used to develop the database are described, as are results of tests that establish the accuracy of the data. In addition, we document the database format and describe the different ways it can be accessed and analyzed in efforts related to materials discovery and design.

Genetic ancestry is associated with colorectal adenomas and adenocarcinomas in Latino populations.

Colorectal cancer rates in Latin American countries are less than half of those observed in the United States. Latin Americans are the resultant of generations of an admixture of Native American, European, and African individuals. The potential role of genetic admixture in colorectal carcinogenesis has not been examined. We evaluate the association of genetic ancestry with colorectal neoplasms in 190 adenocarcinomas, 113 sporadic adenomas and 243 age- and sex-matched controls enrolled in a multicentric case-control study in Colombia. Individual ancestral genetic fractions were estimated using the STRUCTURE software, based on allele frequencies and assuming three distinct population origins. We used the Illumina Cancer Panel to genotype 1,421 sparse single-nucleotide polymorphisms (SNPs), and Northern and Western European ancestry, LWJ and Han Chinese in Beijing, China populations from the HapMap project as references. A total of 678 autosomal SNPs overlapped with the HapMap data set SNPs and were used for ancestry estimations. African mean ancestry fraction was higher in adenomas (0.13, 95% confidence interval (95% CI)=0.11-0.15) and cancer cases (0.14, 95% CI=0.12-0.16) compared with controls (0.11, 95% CI=0.10-0.12). Conditional logistic regression analysis, controlling for known risk factors, showed a positive association of African ancestry per 10% increase with both colorectal adenoma (odds ratio (OR)=1.12, 95% CI=0.97-1.30) and adenocarcinoma (OR=1.19, 95% CI=1.05-1.35). In conclusion, increased African ancestry (or variants linked to it) contributes to the increased susceptibility of colorectal cancer in admixed Latin American population.

Communication: improving the density functional theory+U description of CeO2 by including the contribution of the O 2p electrons.

Density functional theory (DFT) based approaches within the local-density approximation or generalized gradient approximation frameworks fail to predict the correct electron localization in strongly correlated systems due to the lack of cancellation of the Coulomb self-interaction. This problem might be circumvented either by using hybrid functionals or by introducing a Hubbard-like term to account for the on site interactions. This latter DFT+U approach is less expensive and therefore more practical for extensive calculations in solid-state computational simulations. By and large, the U term only affects the metal electrons, in our case the Ce 4f ones. In the present work, we report a systematic analysis of the effect of adding such a U term also to the oxygen 2p electrons. We find that using a set of U(f) = 5 eV and U(p) = 5eV effective terms leads to improved description of the lattice parameters, band gaps, and formation and reduction energies of CeO(2).

Comparative Study on the Performance of Hybrid DFT Functionals in Highly Correlated Oxides: The Case of CeO2 and Ce2O3.

The outstanding catalytic properties of cerium oxides rely on the easy Ce(3+) ↔ Ce(4+) redox conversion, which however constitutes a challenge in density functional based theoretical chemistry due to the strongly correlated nature of the 4f electrons present in the reduced materials. In this work, we report an analysis of the performance of five exchange-correlation functionals (HH, HHLYP, PBE0, B3LYP, and B1-WC) implemented in the CRYSTAL06 code to describe three properties of ceria: crystal structure, band gaps, and reaction energies of the CeO2 → Ce2O3 process. All five functionals give values for cell parameters that are in fairly good agreement with experiment, although the PBE0 hybrid functional is found to be the most accurate. Band gaps, 2p-4f-5d in the case of CeO2 and 4f-5d in the case of Ce2O3, are found to be, in general, overestimated and drop off when the amount of Hartree-Fock exchange in the exchange-correlation functional decreases. In contrast, the reaction energies are found to be underestimated, and increase when the amount of HF exchange lowers. Overall, at its standard formulation, the B1-WC functional seems to be the best choice as it provides good band gaps and reaction energies, and very reasonable crystal parameters.

Carcinoma de células acinares del páncreas: reporte de un caso / Acinar cell carcinoma of the pancreas: a case report

Reportar el caso de una paciente con carcinoma de células acinares de pancreas como una entidad clínico-patológica infrecuente. Presentación del caso clínico y revisión de la literatura. Servicio de Cirugía General del Hospital Universitario de Los Andes Mérida Estado Mérida-Venezuela. Paciente femenino de 21 años de edad que refiere enfermedad actual de 12 meses de evolución, caraterizada por aumento de volumen en epigastrio e hipocondrio izquierdo y sensación de plenitud postprandial. Por estudios imagenológicos se evidencia una tumoración en cuerpo y cola pancreática. Se realiza laparotomía subcostal bilateral, encontrando tumoración de 20x15x10 cm en cuerpo y cola pancreática, encapsulada, con áreas sólidas y quísticas, no adherida a órganos vecinos y de 850 gr de peso; se realizó pancreatectomía córporocaudal, sin preservacion esplénica. El reporte histopatológico fue carcinoma acinar del pancreas. Actualmente sin complicaciones de la función endocrina, sin evidencias de recidiva y recibiendo quimioterapia adyuvante. El carcinoma de células acinares es una entidad poco frecuente que representa del 1 al 2% de los tumores pancreáticos exocrinos. Ocurre con mayor frecuencia en hombres de edad media o mayores. Clinicamente cursan con dolor difuso y aumento del volumen abdominal. Por lo general afectan al cuerpo y cola del pancreas, son tumores encapsulados, de gran tamaño, que presentan distintos patrones de crecimiento. La supervivencia es variable, entre 1 a 3 años, dependiendo de la presencia o no de metástasis.

To report a case of a patient with acinar cell carcinoma of the pancreas as no frequent clinical pathological entity. Presentatin of clinical case and literature review. General Surgery Service of the Hospital Universitario de Los Andes. Mérida State Merida-Venezuela. A 21-year-old female patient presented to out hospital with a 12 month history of a increasing tumor in epigastrium and left hipocondrio and complaining of early satiety. Image studies evidenced a tumor in head and tail of pancreas. Chevron's laparotomy was performed, finding a 20x15x10 cm tumor in head and tail of pancreas, capsuled, with cystic and solid areas, not adherent to other tissues, with a weight of 850 grams. Corpocaudal pancreatectomy with splenectomy was performed. Histological report showed an acinar cell carcinoma of the pancreas. Patient actually with no endocrine disfuntions, no tumor recidive evidence, in adyuvant chemotherapy. Acinar cell carcinoma of the páncreas is a rare tumor that constitutes 1-2 of exocrine neoplasms. Ocurrs most frequently in elder male patients. Clinically presented with diffuse abdominal pain and tumors. Head and tail of pancreas are the most involved, as large capsiled tumors with different grow partterns. Survival is variable, from 1 to 3 years depending on presence or absence of metastases.

A theoretical insight into the catalytic effect of a mixed-metal oxide at the nanometer level: the case of the highly active metal/CeOx/TiO2(110) catalysts.

The structural and electronic properties of CeO(x) species supported on the rutile TiO(2)(110) surface have been examined by means of periodic density-functional calculations that use a generalized gradient approximation functional including a Hubbard-like type correction. Deposition of Ce atoms leads in a first step to Ce(3+) ions bound to the surface through bridge and in-plane oxygen atoms, the released electrons occupying the Ti 3d empty orbitals. Further addition of Ce and molecular oxygen gives place to Ce(2)O(3) dimers diagonally arranged on the surface, in agreement with the spots observed in the scanning tunnel microscope images. The formation process of CeO(x) nanoparticles (NPs) on the TiO(2) surface is highly exothermic and our calculations show that the redox properties of the Ce(III)-Ce(IV) couple are significantly altered when it is supported on TiO(2). In particular the reactivity against CO/O(2) indicates that on the surface the presence of Ce(III) is favored over Ce(IV) species. Our results also indicate that the CeO(x)/TiO(2) interface should be seen like a real mixed-metal oxide rather than a supported NP of ceria. Finally, in the context of the high catalytic activity of the M/CeO(x)/TiO(2) (M=Au,Cu,Pt) systems in the water-gas shift reaction, we have examined the dissociation of water on the CeO(x)/TiO(2) surface and estimated a barrier as small as 0.04 eV, i.e. approximately 8 times smaller than that computed for a TiO(2) oxygen vacancy. This result agrees with the experimental superior catalytic activity of the M/CeO(x)/TiO(2) systems over M/TiO(2).

Unnecessary gastric decompression in distal elective bowel anastomoses in children: a randomized study.

BACKGROUND: The goal of this study was to investigate the role of nasogastric drainage in preventing postoperative complications in children with distal elective bowel anastomosis. Nasogastric drainage has been used as a routine measure after gastrointestinal surgery in children and adults to hasten bowel function, prevent postoperative complications, and shorten hospital stay. However, there has been no study that shows in a scientific manner the benefit of nasogastric drainage in children. METHODS: We performed a clinical, controlled, randomized trial comprising 60 children who underwent distal elective bowel anastomoses and compared postoperative complications between a group with nasogastric tube in place (n = 29) and one without it (n = 31). RESULTS: Demographic data and diagnoses were comparable in both groups (P = NS). No anastomotic leaks or enterocutaneous fistulae were found in any patient. There were no significant differences between the two groups with respect to abdominal distension, infection, or hospital stay. Only one patient in the experimental group required placement of the nasogastric tube due to persistent abdominal distension (3.2%). CONCLUSIONS: The routine use of nasogastric drainage after distal elective intestinal surgery in children can be eliminated. Its use should depend on the individual patient's situation.

Carcinoma de células acinares del páncreas: reporte de un caso / Acinar cell carcinoma of the pancreas: case report

Objetivo: Reportar el caso de una paciente con carcinoma de células acinares de páncreas como una entidad clinico-patológica infrecuente. Método: Presentación del caso clínico y revisión de la literatura. Ambiente: Servicio de Cirugía General del Hospital Universitario de Los Andes. Mérida. Estado Mérida. Venezuela. Resultados: Paciente femenino de 21 años de edad, que refiere enfermedad actual de 12 meses de evolución, caracterizada por aumento de volumen en epigastrio e hipocondrio izquierdo y sensación de plenitud postprandial. Por estudios imagenológicos se evidencia tumoración en cuerpo y cola pancreática. Se realiza laparotomía subcostal bilateral, encontrando tumoración de 20 x 15 x 10 cm en cuerpo y cola pancreática, encapsulada, con áreas sólidas y quísticas, no adherida a órganos vecinos y de 850 gr de peso; se realizó pancreatectomía corporocaudal, sin preservación esplénica. El reporte histopatológico fue carcinoma acinar de páncreas. Actualmente sin complicaciones de la función endocrina y sin evidencias de recidiva. Discusión: El carcinoma de células acinares es una entidad poco frecuente que representa del 1 al 2 por ciento de los tumores pancreáticos exocrinos. Ocurre con mayor frecuencia en hombres de edad media o mayores. Clínicamente cursan con dolor difuso y aumento del volumen abdominal. Por lo general afectan al cuerpo y cola del páncreas, son tumores encapsulados, de gran tamaño, que presentan distintos patrones de crecimiento. La supervivencia es variable, entre 1 y 3 años, dependiendo de la presencia o no de metástasis.

We report a 21 years old female presenting with a history of 12 months of a lump located in the epigastrium. An abdominal CAT scan showed a tumor located in the pancreatic body and tail. The patient was operated, and during the laparotomy an encapsulated tumor of the pancreas measuring 20 x 15 x 10 cm was found. The body and tail of the pancreas were excised and the pathological study of the surgical piece disclosed an acinar cell carcinoma. In the postoperative period the patient received chemotherapy with gemcitabine and oxaliplatin. After three years of follow up, she is in good conditions and without evidences of tumor relapse.

Vinyl acetate synthesis on homogeneous and heterogeneous Pd-based catalysts: a theoretical analysis on the reaction mechanisms.

Vinyl acetate can be synthetized by both homogeneous and heterogeneous processes involving Pd atoms as reaction centers. We have determined the reaction mechanisms by means of density functional theory applied to molecular models for the homogeneous catalyst and to slabs that model the most active heterogeneous ensemble to unravel the similarities and differences in the reaction networks under these different conditions. We find that although the reaction network is similar, the rate determining step is different. Thus, direct extrapolations from organometallic chemistry to gas-phase heterogeneous catalysis should be handled with care.

Pancreaticoyeyunostomía ducto-seromuscular término-lateral en la operación whipple: experiencia en 27 casos / Seromuscular end pancreaticojejunostomy-duct-side in the whipple operation: experience with 27 cases

Presentar la experiencia con la anastomosis ductoserosa termino-lateral en la pancreaticoyeyunostomía del Whipple, en el Servicio de Cirugía General del Instituto Autónomo Hospital Universitario de Los Andes, Mérida-Venezuela. Estudio prospectivo, descriptivo en pacientes sometidos a duodenopancreatectomía por patología maligna a nivel pancreático y región periampular entre los años 2003 a 2007. En todos los casos se realizó preservación pilórica con anastomosis ducto-serosa termino-lateral del remanente pancreático, con colocación de stent intraductal, excepto en un caso donde se realizó la técnica invaginante término-terminal. Se evaluaron las complicaciones postoperatorias inherentes a la técnica quirúrgica, haciendo especial énfasis en la fístula pancreática. Un total de 27 pacientes durante el período 2003 a 2007 fueron sometidos a duodenopancreatectomía cefálica en forma electiva por etiología maligna tales como: ampuloma II casos, colangiocarcinoma distal 2 casos, cáncer de páncreas 12 casos, tumor neuroendocrino 1 caso, adenoma velloso malignizado de colédoco 1 caso. Las edades estuvieron comprendidas entre 42-81 años con promedio de 61 años, predominantemente del sexo femenino en una proporción 4:1. Entre las complicaciones posquirúrgicas relacionadas con la técnica encontramos 4 casos (14.8 por ciento) dado por: 2 fístulas pancreáticas (una de ellas por la ligadura accidental del stent intraductal), 1 dehiscencia de la duodenopancreatectomía, siendo la causa de muerte, y finalmente un caso de atonía gástrica manejado médicamente en forma satisfactoria. La anastomosis ducto-serosa en el manejo del remanente pancreático del Whipple constituye una técnica de fácil ejecución y con buenos resultados, ya que ofrece menos morbimortalidad.

Adenoma velloso del colédoco con transformación maligna hacia adenocarcinoma bien diferenciado / Coledochal vellous adenoma with malignant transformation

Informar el caso de una paciente de 55 años de edad con diagnóstico de adenoma velloso del colédoco con transformación maligna. Descripción del caso clínico y revisión de la literatura. Servicio de Cirugía General del Instituto Autónomo Hospital Universitario de Los Andes. Mérida-Venezuela. Se realizó operación de Whipple modificada obteniéndose diagnóstico histológico de adenoma velloso en colédoco con transformación maligna hacia adenocarcinoma bien diferenciado. El adenoma velloso del colédoco es una entidad clínica patológica inusual, y su abordaje puede verse dificultado por ser poco documentado. Obtener un diagnostico definitivo previo es necesario para realizar el procedimiento quirúrgico apropiado.