Propagación in vitro del platanero y el bananero en Puerto Rico

Some 7,000 plantlets were produced in vitro from six plantain cultivars (Enano Común, Congo Enano, Maricongo, Congo, Clone 12 and Clone 7), and from three banana cultivars (Grand Nain, Valerie and Ziv) by supplementing Murashige and Skoog (MS) basal medium with 0.5 mg/L kinetin and 0.5 mg/L 6-benzylamino purine. Calli were induced by supplementing the MS basal medium with 0.05 mg/L 2,4-D, 0.1 mg/L NAA, 0.5 mg/L BA, 15% coconut water and 20 mg/L ascorbic acid (filter sterilized). Data obtained from a replicated field trial at the Corozal Substation with the above-mentioned plantain cultivars indicated that the bunch weight from plantain cultivar Congo Enano, regenerated from axillary meristem with in vitro culture, was significantly greater than that from plantains derived from conventional suckers in the plant crop (P = 0.1). Similarly, the individual fruit weight from Congo Enano derived from meristem culture was significantly greater than that from plantains derived from the conventional planting materials (P = 0.5).Alrededor de 7,000 plántulas de plátano de 6 cultivares (Enano común, Congo enano, Maricongo, Congo, Clon 12 y Clon 7) se obtuvieron por cultivo de tejidos, suplementando el medio basal de Murashige y Skoog (MS) con cinetina (KIN) 0.5 mg./l. y benzilaminopurina (BA) 0.5 mg./l. Se obtuvo la inducción de callo suplementando el medio basal de MS con ácido 2,4-diclorofenoxiacético (2,4-D) 0.05 mg./l. , ácido naftalenoacético (NAA) 0.1 mg./l. benzilaminopurina (BA) 0.5 mg./l., agua de coco 15% (v/v) ácido ascórbico (filtrado por esterilización) 20 mg./l. Los datos obtenidos del experimento de campo realizado en la Subestación de Corozal, con las variedades de plátano arriba mencionadas, indicaron que el peso del racimo de la cultivar Congo enano propagado por cultivo de tejidos fue significativamente (P = 0.1) mayor que el del racimo propagado por el método corriente. Similarmente, el peso de las frutas individuales del Congo enano provenientes de plátanos propagados por tejido meristemático fue significativamente mayor ( P = 0.5) que el de los que provenían del método corriente

Prediction of Mechanical Properties of Polymers With Various Force Fields

The effect of force field type on the predicted elastic properties of a polyimide is examined using a multiscale modeling technique. Molecular Dynamics simulations are used to predict the atomic structure and elastic properties of the polymer by subjecting a representative volume element of the material to bulk and shear finite deformations. The elastic properties of the polyimide are determined using three force fields: AMBER, OPLS-AA, and MM3. The predicted values of Young s modulus and shear modulus of the polyimide are compared with experimental values. The results indicate that the mechanical properties of the polyimide predicted with the OPLS-AA force field most closely matched those from experiment. The results also indicate that while the complexity of the force field does not have a significant effect on the accuracy of predicted properties, small differences in the force constants and the functional form of individual terms in the force fields determine the accuracy of the force field in predicting the elastic properties of the polyimide

COVID-19 Models for Hospital Surge Capacity Planning: A Systematic Review

Objective: Health system preparedness for coronavirus disease (COVID-19) includes projecting the number and timing of cases requiring various types of treatment. Several tools were developed to assist in this planning process. This review highlights models that project both caseload and hospital capacity requirements over time. Methods: We systematically reviewed the medical and engineering literature according to Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. We completed searches using PubMed, EMBASE, ISI Web of Science, Google Scholar, and the Google search engine. Results: The search strategy identified 690 articles. For a detailed review, we selected 6 models that met our predefined criteria. Half of the models did not include age-stratified parameters, and only 1 included the option to represent a second wave. Hospital patient flow was simplified in all models; however, some considered more complex patient pathways. One model included fatality ratios with length of stay (LOS) adjustments for survivors versus those who die, and accommodated different LOS for critical care patients with or without a ventilator. Conclusion: The results of our study provide information to physicians, hospital administrators, emergency response personnel, and governmental agencies on available models for preparing scenario-based plans for responding to the COVID-19 or similar type of outbreak

Shape: automatic conformation prediction of carbohydrates using a genetic algorithm

<p>Abstract</p> <p>Background</p> <p>Detailed experimental three dimensional structures of carbohydrates are often difficult to acquire. Molecular modelling and computational conformation prediction are therefore commonly used tools for three dimensional structure studies. Modelling procedures generally require significant training and computing resources, which is often impractical for most experimental chemists and biologists. <monospace>Shape</monospace> has been developed to improve the availability of modelling in this field.</p> <p>Results</p> <p>The <monospace>Shape</monospace> software package has been developed for simplicity of use and conformation prediction performance. A trivial user interface coupled to an efficient genetic algorithm conformation search makes it a powerful tool for automated modelling. Carbohydrates up to a few hundred atoms in size can be investigated on common computer hardware. It has been shown to perform well for the prediction of over four hundred bioactive oligosaccharides, as well as compare favourably with previously published studies on carbohydrate conformation prediction.</p> <p>Conclusion</p> <p>The <monospace>Shape</monospace> fully automated conformation prediction can be used by scientists who lack significant modelling training, and performs well on computing hardware such as laptops and desktops. It can also be deployed on computer clusters for increased capacity. The prediction accuracy under the default settings is good, as it agrees well with experimental data and previously published conformation prediction studies. This software is available both as open source and under commercial licenses.</p

Application of Enzymes in Regioselective and Stereoselective Organic Reactions

Nowadays, biocatalysts have received much more attention in chemistry regarding their potential to enable high efficiency, high yield, and eco-friendly processes for a myriad of applications. Nature’s vast repository of catalysts has inspired synthetic chemists. Furthermore, the revolutionary technologies in bioengineering have provided the fast discovery and evolution of enzymes that empower chemical synthesis. This article attempts to deliver a comprehensive overview of the last two decades of investigation into enzymatic reactions and highlights the effective performance progress of bio-enzymes exploited in organic synthesis. Based on the types of enzymatic reactions and enzyme commission (E.C.) numbers, the enzymes discussed in the article are classified into oxidoreductases, transferases, hydrolases, and lyases. These applications should provide us with some insight into enzyme design strategies and molecular mechanisms

Solid-State and Gas-Phase Structures and Energetic Properties of the Dangerous Methyl and Fluoromethyl Nitrates

Reichel M, Krumm B, Vishnevskiy Y, et al. Solid-State and Gas-Phase Structures and Energetic Properties of the Dangerous Methyl and Fluoromethyl Nitrates. Angewandte Chemie (International ed. in English). 2019;58(51):18557-18561.An improved synthesis of the simplest nitric acid ester, methyl nitrate, and a new synthesis of fluoromethyl nitrate use the metathesis of the corresponding iodomethanes with silver nitrate. Both compounds were identified by spectroscopy and the structures determined for in situ grown crystals by X-ray diffraction as well as in the gas phase by electron diffraction. Fluorination leads to structures with shorter C-O and N-O bonds, has an energetically destabilizing effect and increases friction sensitivity, but decreases detonation performance. © 2019 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA

Nucleation and growth kinetics for intercalated islands during deposition on layered materials with isolated point-like surface defects

Theory and stochastic lattice-gas modeling is developed for the formation of intercalated metal islands in the gallery between the top layer and the underlying layer at the surface of layered materials. Our model for this process involves deposition of atoms, some fraction of which then enter the gallery through well-separated point-like defects in the top layer. Subsequently, these atoms diffuse within the subsurface gallery leading to nucleation and growth of intercalated islands nearby the defect point source. For the case of a single point defect, continuum diffusion equation analysis provides insight into the nucleation kinetics. However, complementary tailored lattice-gas modeling produces a more comprehensive and quantitative characterization. We analyze the large spread in nucleation times and positions relative to the defect for the first nucleated island. We also consider the formation of subsequent islands and the evolution of island growth shapes. The shapes reflect in part our natural adoption of a hexagonal close-packed island structure. Motivation and support for the model is provided by scanning tunneling microscopy observations of the formation of intercalated metal islands in highly-ordered pyrolytic graphite at higher temperatures

The interlayer cohesive energy of graphite from thermal desorption of polyaromatic hydrocarbons

We have studied the interaction of polyaromatic hydrocarbons (PAHs) with the basal plane of graphite using thermal desorption spectroscopy. Desorption kinetics of benzene, naphthalene, coronene and ovalene at sub-monolayer coverages yield activation energies of 0.50 eV, 0.85 eV, 1.40 eV and 2.1 eV, respectively. Benzene and naphthalene follow simple first order desorption kinetics while coronene and ovalene exhibit fractional order kinetics owing to the stability of 2-D adsorbate islands up to the desorption temperature. Pre-exponential frequency factors are found to be in the range $10^{14}$-$10^{21} s^{-1}$ as obtained from both Falconer--Madix (isothermal desorption) analysis and Antoine's fit to vapour pressure data. The resulting binding energy per carbon atom of the PAH is $52\pm$5 meV and can be identified with the interlayer cohesive energy of graphite. The resulting cleavage energy of graphite is $61\pm5$~meV/atom which is considerably larger than previously reported experimental values.Comment: 8 pages, 4 figures, 2 table

A new model for predicting relative nonwetting phase permeability from soil water retention curves

Relative permeability of the nonwetting phase in a multiphase flow in porous media is a function of phase saturation. Specific expressions of this function are commonly determined by combining soil water retention curves with relative nonwetting phase permeability models. Experimental evidence suggests that the relative permeability of the nonwetting phase can be significantly overestimated by the existing relative permeability models. A new model for the prediction of relative nonwetting phase permeability from soil water retention curves is proposed in this paper. A closed form expression can be obtained in combination with soil water retention curves. The model is mathematically simple and can easily and efficiently be implemented in numerical models of multiphase flow processes in porous media. The predicting capability of the proposed model is contrasted with well-supported models by comparing the measured and predicted relative air permeability data for 11 soils, representing a wide range of soil textures, from sand to silty clay loam. In most of the cases the proposed model improves the agreement between the predicted relative air permeability and the measured data. Copyright 2011 by the American Geophysical Union.published_or_final_versio