1,721,151 research outputs found
Il piacere della carne, tra scienza e arte
No full textLibro pubblicato dalla casa editrice Segni e Suoni di Ancon
Laboratory customized online measurements for the prediction of the key-parameters of biomass quality control
No full textEmpathes: A general code for nudged elastic band transition states search
Full text linkAn easy and flexible interface, Empathes (Extensible Minimum PATH EStimator), that allows to perform Nudged Elastic Band calculation for the determination of transition states is presented. The code is designed to be easily modified, in order to be associated with the user's preferred calculation software, even with those which implement composite approaches. In particular, the interfaces to Gaussian and Siesta programs are discussed in details, being the former only used for testing purpose, while the latter can be productively employed for transition states search with that commonly used density functional theory software for periodic calculations. Program summary: Program Title: Empathes CPC Library link to program files: https://doi.org/10.17632/v525mwf3cc.1 Developer's repository link: https://github.com/marberti/empathes Code Ocean capsule: https://codeocean.com/capsule/2394233 Licensing provisions: GPLv3 Programming language: Fortran 08 Nature of problem: The search for the structure of transition states through computational methods, essentially based on Density Functional Theory, is of overwhelming importance for the determination of the elementary steps forming a reaction mechanism. Allowing to develop basic knowledge, these investigations can be used to direct experimentalists towards a more efficient realization of chemical compounds synthetic processes. In cases where it is necessary to describe the reactive system through periodic calculations, which is very common in heterogeneous catalysis, this research must be done through the use of non-analytical methods. Solution method: In case of lacking of analytical procedures, the search for the transition states associated with the elementary stages that make up chemical reactions must take place through numerical methods. The Nudged Elastic Band (NEB) approach is, together with its variants, one of the most used for this purpose. In accordance with the NEB algorithm, a chain of geometric structures, generated by interpolating between the reactant and product geometries and joined by fictitious springs, is relaxed on the minimum energy path, allowing the association of the transition state to the maximum along this path. The NEB method involves the determination of molecular energies and forces acting on the nuclei of the system, which is generally carried out through a program for electronic structure calculation. The present code is a useful general interface
Hydrogen Arrangements on Defective Quasi-Molecular BN Fragments
Full text linkConsidering the ever-increasing interest in metal-free materials, some potential chemical applications of quasi-molecular boron nitride (BN) derivatives were tested. Specifically, the behavior of BN fragments was analyzed when given defects, producing local electron density changes, were introduced by using topological engineering approaches. The inserted structural faults were Schottky-like divacancy (BN-d) defects, assembled in the fragment frame by the subtraction of one pair of B and N atoms or Stone-Wales (SW) defects. This study is aimed at highlighting the role of these important classes of defects in BN materials hypothesizing their future use in H-2-based processes, related to either (i) H-2 activation or (ii) H-2 production, from preadsorbed hydrogenated molecular species on BN sites. Here, it has been observed that BN species, embodying SW defects, are characterized by endothermic H-2 adsorption and fragmentation phenomena in order to guess their potential use in processes based on the transformation or production of hydrogen. On the contrary, in the presence of BN-d defects, and for reasons strictly related to local structural changes occurring along with the hydrogen rearrangements on the defective BN fragments, a possible use can be inferred. Precautions must be however taken to decrease the material rigidity that could actually decrease the ability of the BN fragment to flatten. This conversely seems to be a necessary requirement to have strong exothermic effects, following the rearrangements of the H-2 molecules
Computational investigation of isoeugenol transformations on a platinum cluster – I: Direct deoxygenation to propylcyclohexane
Full text linkThe growing demand for renewable and sustainable fuels, protagonists of an increasingly important research
area due to the exhaustion of fossil resources, has oriented our investigation towards the computational
mechanistic analysis of the catalytic hydrodeoxygenation (HDO) reaction of isoeugenol. Having the most com
mon functional groups, the isoeugenol molecule is actually considered as an experimental and computational
model for typical species of biomass origin. The reported computational investigation outlines the energy bar
riers and the intermediates along the path for the conversion of isoeugenol to propylcyclohexane through a direct
deoxygenation mechanims, catalyzed by a subnanometric metal cluster. For this purpose, the Pt10 platinum
cluster was chosen as the catalyst model, being this noble metal a reference for hydrogenation reaction. The
results obtained rule the formation of the 4-propylphenol intermediate as the rate determining step for the
considered branch of the mechanim, and as the pivotal point for further ramifications. The present is the first of a
series of studies aimed to a complete mapping of isoeugenol HDO on a Pt cluster, to be used as reference for
further, more focused, investigations, such as those regarding the effects of the support and of the metal particle
size, as well as the HDO reaction of biomass-derived compounds similar to isoeugenol
Biomass Energy Resources: Feedstock Quality and Bioenergy Sustainability
Full text linkA relationship is also emerging between sustainability and raw material or biofuel quality. The most representative parameter of this ratio is moisture content. This factor has always limited the biomass supply chains by reducing the combustible product’s energy density, undermining the sustainability of the logistic processes of a supply chain.
An excellent example of a virtuous supply chain and an exercise in the application of sustainability is the vine pruning pellets produced using a mobile pelletising machine. The use of residual biomass and densification close to the origin of the raw material represents an effective combination in making this solid biofuel sustainable and of higher quality than the raw material, which is removed from polluting combustion in the field with harmful effects on human health.
Although we can obtain biomass through forest management, overexploitation leads to serious environmental issues. In contrast to the widespread idea that unmanaged woods and forests guarantee a high biodiversity, regular coppice management can lead to increased biodiversity due to the inclusion of species associated with different habitats, such as pasture. This potential relationship between mild forest resource management and biomass production was highlighted in one study. However, this topic has not been thoroughly investigated.
The response to the SI can be considered satisfactory because the published papers contribute by adding specific information on different bioenergy production chains. Still, it is also evident how difficult it is to couple sustainability assessment with biomass and biofuel quality analysis in the same work
Mechanisms of plant response to salt and drought stress and their alteration by rhizobacteria,
No full textBackground Soil salinity and drought are an enormous worldwide problem for agriculture, horticulture and silviculture. The initial responses of plants to drought and salinity are similar; both are attributed to water deficit
which inhibits plant growth and development.
Scope In this review, an overview of the major physiological and biochemical changes that occur in plants as a
consequence of salt and drought stress is presented. In addition, the role of beneficial plant growth-promoting
bacteria in ameliorating many of the deleterious consequences of salt and drought stress is discussed. Mechanisms used by plant growth-promoting bacteria to ameliorate the effects of these stresses include the production of cytokinin, indoleacetic acid, ACC deaminase, abscisic acid, trehalose, volatile organic compounds, and exopolysaccharides.
Conclusion Given the fundamental understanding of many of the mechanisms operating in plant-bacterial
interactions, it is expected that the practical use of beneficial bacteria in agriculture, horticulture and silviculture
will grow dramatically in the coming years
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
PUMICE-SUPPORTED PALLADIUM CATALYSTS .2. SELECTIVE HYDROGENATION OF 1,3-CYCTOOCTADIENE
No full textTwo series of pumice-supported palladium catalysts (W and U) have been tested in the liquid-phase selective hydrogenation of 1,3-cyclooctadiene (1,3-COD) to cyclooctene (COE). The two series of catalysts, obtained via organometallic precursors, differ in the preparation procedure. In the W series the reduced metal derives only from Pd intermediates anchored to pumice; in the U series the metal originates also from unreacted Pd(allyl)(2) species in solution. The U catalysts present agglomerated metal particles. The hydrogenations, free of any diffusion problems, were performed at constant pressure of hydrogen (1 at-m). Analysis of the data suggests that the rate-determining step is a surface reaction involving activated 1,3-COD. Selectivity is very high since cyclooctane (COA) is detected only when all 1,3-COD is consumed. The turnover frequencies (TOF1) of the first semihydrogenation do not change with palladium dispersion, determined from the Pored diameter D-p up to D-x < 35%, but thereafter they slowly decrease. Experimental evidence, such as the absence of oxidation when exposed to air and the negative shift of binding energy of the Pd 3d level in WS measurements, indicate a different behavior of the present catalysts in comparison with other supported palladium catalysts. These differences are attributed to the presence of alkali metal ions (Na+, K+) on the pumice surface and are explained on the basis of the change in electron density and/or in the ensemble size of the supported palladium. Several interesting features and differences in activity and selectivity between the two series of catalysts can be accounted for by the presence of agglomerated palladium particles in the U series and are discussed in terms of the evolution of parameters with dispersio
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