A brief review of the Siesta project is presented in the context of linear-scaling density-functional methods for electronic-structure calculations and molecular-dynamics simulations of systems with a large number of atoms. Applications of the method to different systems are reviewed, including carbon nanotubes, gold nanostructures, adsorbates on silicon surfaces, and nucleic acids. Also, progress in atomic-orbital bases adapted to linear-scaling methodology is presented.
In the present study, an innovative method to produce cellulose nanocrystals is proposed. The conventional production of nanocrystals uses concentrated solutions of strong acids to promote the hydrolysis of cellulose amorphous regions and hemicelluloses. However, in the conventional method, long duration washing steps and the nanocrystals low temperature resistance still limit their larger industrialization and some applications in processes or end-uses that require heat resistance, like extrusion. In this context, the use of subcritical water (120 °C and 20.3 MPa for 60 min) allows higher diffusion, activity, and ionization of water. With that, partial hydrolysis of cellulose can be attended (with 21.9 wt % NCC yield). The cellulose source, the hydrolyzed cellulose, and a commercial nanocellulose were submitted to different analytical techniques to evaluate their morphology and physicochemical characteristics. The obtained cellulose nanocrystals presented a high crystallinity index (79.0% by XRD), rod-like shape with a similar aspect ratio as those known for classic cellulose nanocrystals but also a higher thermal stability even when compared with the original cellulosic source (onset around 300 °C). The exclusive use of water as a reagent is a promising process not only for its green characteristics but also for its low corrosion, low and cleaner effluent, and low cost of reagents.
Abstract:The aim of the study was deepening the knowledge of livestock innovations knowledge on small-scale farms in developing countries. First, we developed a methodology focused on identifying potential appropriate livestock innovations for smallholders and grouped them in innovation areas, defined as a set of well-organized practices with a business purpose. Finally, a process management program (PMP) was evaluated according to the livestock innovation level and viability of the small-scale farms. Logistic regression was used to evaluate the impact of PMP on the economic viability of the farm. Information from 1650 small-scale livestock farms in Mexico was collected and the innovations were grouped in five innovation areas: A1. Management, A2. Feeding, A3. Genetic, A4. Reproduction and A5. Animal Health. The resulting innovation level in the system was low at 45.7% and heterogeneous among areas. This study shows the usefulness of the methodology described and confirms that implementing a PMP allows improving the viability an additional 21%, due to a better integration of processes, resulting in more efficient management.
The bπ.aσ charge-transfer complex formed by ethyne and chlorine monofluoride has been studied with various approximate pure and hybrid density functional methods and the second-order Møller-Plesset (MP2) theory.The calculations demonstrate that one hybrid method, namely, the so-called B3LYP, leads to reasonably good estimates of the experimentally measured rotational constants. Accordingly, the predicted B3LYP intermolecular distance is found to be also close to the experimental value. This enables us to estimate reliably the intermolecular interaction energy, which is found to be 3.43 kcal/mol. The performance of the various approximate density functionals and the MP2 theory is compared and discussed. Finally, we comment on the analysis of the natural bond orbitals, which has been found to be very valuable to shed light on the nature of the weak intermolecular interaction.
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