A Hybrid Control Framework for Chemical Processes with Long Time Delay: Theory and Experiments.

This paper proposes a hybrid control framework based on internal model concepts, sliding mode control methodology, and fractional-order calculus theory. As a result, a modified Smith predictor (SP) is proposed for nonlinear systems with significant delays. The particular predictive approach enhances the sliding mode control (SMC) controller's transient responses for dead-time processes, and the SMC gives the predictive structure robustness for model mismatches by combining the previous methods with fractional order concepts; the result is a dynamical sliding mode controller. A numerical example is considered to evaluate the performance of the proposed approach, where a step change, external disturbance, and parametric uncertainty test are performed. A real application in the TCLab Arduino kit is presented; the proposed method presented good performance with a little amount of chattering, and in the disturbance rejection case, the overshoot increased with an aggressive response; in both cases, better tuning parameters can improve the process response and the controller action.

KLD: a program to elucidate the localization of the Fermi and Coulomb holes in molecular systems.

CONTEXT: The electron localization is a concept that allows scientists to better understand the physical and chemical properties of electronic systems. It is associated with the propensity of electron pairs with opposite spins to accumulate as well as with their response to external perturbations. This paper contains a detailed description of the design and implementation of the program KLD, which was primarily developed in our research group to elucidate electron localization in molecular systems by evaluating the information content of electron-pair density functions. KLD employs two information-based functions as a real space measure of the Fermi and Coulomb holes for same-spin electrons and shows a better resolution as compared to other methods (i.e., ELF). Information about the acceleration of the code is also included in the present work, being noticeable the reduction of wall-time calculation and the error calculation between versions. METHODS: KLD was designed to be easy to use, extend, and maintain; thus, many principles of modern software development, extensive testing, and package management were adopted. The latest version of the KLD program was created utilizing the Compute Unified Device Architecture (CUDA) version, which allows it to use the computational capacity of NVIDIA Graphics Processing Units (GPUs) for processing purposes. The electron-pair conditional density was calculated from the canonical molecular orbitals obtained at the HF/6-31G(2df,p) level, or alternatively the natural orbitals in the case of explicit correlated wavefunctions computed at the MP2/6-31G(2df,p)//HF/6-31G(2df,p) level.

Revisiting the bonding of the pentagonal-pyramidal C6H62+ and C6(CH3)62+ dications.

This work delves into the bonding nature of the pentagonal-pyramidal benzene and hexamethylbenzene dications, C6R62+ (R = H and CH3), which contain a hexacoordinate carbon. The study employs a range of methodologies to analyze a series of scalar fields, including electron density, electron localization function, local momentum representation, and the evaluation of the Coulomb hole through information theory-derived functions. The findings unveil that electron density undergoes transfer from the pentagonal ring to the apical group. As a result, the base of the complex accumulates the positive charge. Moreover, an extended electron density domain emerges between the carbon pentagon and the apical carbon atom. This phenomenon is related to the molecular orbitals with a dipolar character aligned with the principal axis of the molecule. The results also indicate an electron density polarization towards the apical carbon, coupled with an exclusion of electron density surrounding both the apical carbon and the lower portion of the pentagonal ring. These provide valuable insights into the complex bonding nature of hexacoordinate carbon and its implications for organic chemistry.

Exploring the Non-Covalent Bonding in Water Clusters.

QTAIM and source function analysis were used to explore the non-covalent bonding in twelve different water clusters (H2O)n obtained by considering n = 2-7 and various geometrical arrangements. A total of seventy-seven O-H⋯O hydrogen bonds (HBs) were identified in the systems under consideration, and the examination of the electron density at the bond critical point (BCP) of these HBs revealed the existence of a great diversity of O-H⋯O interactions. Furthermore, the analysis of quantities, such as |V(r)|/G(r) and H(r), allowed a further description of the nature of analogous O-H⋯O interactions within each cluster. In the case of 2-D cyclic clusters, the HBs are nearly equivalent between them. However, significant differences among the O-H⋯O interactions were observed in 3-D clusters. The assessment of the source function (SF) confirmed these findings. Finally, the ability of SF to decompose the electron density (ρ) into atomic contributions allowed the evaluation of the localized or delocalized character of these contributions to ρ at the BCP associated to the different HBs, revealing that weak O-H⋯O interactions have a significant spread of the atomic contributions, whereas strong interactions have more localized atomic contributions. These observations suggest that the nature of the O-H⋯O hydrogen bond in water clusters is determined by the inductive effects originated by the different spatial arrangements of the water molecules in the studied clusters.

A Theoretical Study of the C-X Bond Cleavage Mediated by Cob(II)Aloxime.

The C-X bond cleavage in different methyl halides (CH3X; X = Cl, Br, I) mediated by 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(II) (CoIICbx) was theoretically investigated in the present work. An SN2-like mechanism was considered to simulate the chemical process where the cobalt atom acts as the nucleophile and the halogen as the leaving group. The reaction path was computed by means of the intrinsic reaction coordinate method and analyzed in detail through the reaction force formalism, the quantum theory of atoms in molecules (QTAIM), and the calculation of one-electron density derived quantities, such as the source function (SF) and the spin density. A thorough comparison of the results with those obtained in the same reaction occurring in presence of 5,6-dimethylbenzimidazole-bis(dimethylglyoximate)cobalt(I) (CoICbx) was conducted to reveal the main differences between the two cases. The reactions mediated by CoIICbx were observed to be endothermic and possess higher activation energies in contrast to the reactions where the CoICbx complex is present. The latter was supported by the reaction force results, which suggest a relationship between the activation energy and the ionization potentials of the different nucleophiles present in the cleavage reaction. Moreover, the SF results indicates that the lower axial ligand (i.e., 5,6-dimethylbenzimidazole) exclusively participates on the first stage of the reaction mediated by the CoIICbx complex, while for the CoICbx case, it appears to have an important role along the whole process. Finally, the QTAIM charge analysis indicates that oxidation of the cobalt atom occurs in both cases; at the same time, it suggests the formation of an uncommon two-center one-electron bond in the CoIICbx case. The latter was confirmed by means of electron localization calculations, which resulted in a larger electron count at the Co-C interatomic region for the CoICbx case upon comparison with its CoIICbx counterpart.

Predicción del Síndrome Informático Visual mediante la adicción a videojuegos en estudiantes chinos y españoles / Prediction of computer vision syndrome by video game addiction in Chinese and Spanish students

Introducción: El uso de los videojuegos, por la extensión que ha llegado a alcanzar durante la pandemia de la COVID-19, es una variable relevante de estudio, especialmente por sus interacciones con aspectos de la salud mental y visual. Objetivo: predecir el nivel de Síndrome informático visual a partir de un índice optimizado sobre el nivel de adicción en estudiantes universitarios de dos poblaciones: española y china. Material y Métodos: Se administró un cuestionario online con tres instrumentos validados: un cuestionario para evaluar el juego con videojuegos (CHCVI), un cuestionario para evaluar la adicción a los videojuegos (CERV) y un cuestionario para detectar el síndrome visual por ordenador (CSQ). Los tres cuestionarios se aplicaron a una muestra de 253 estudiantes, tanto de universidades chinas como españolas. Para establecer las predicciones, se construyeron índices robustos basados en el análisis factorial de los instrumentos administrados. Finalmente, se aplicó una regresión logística para obtener un modelo matemático útil para predecir el Síndrome Informático Visual. Resultados: Los resultados mostraron un mayor síndrome informático visual y apetito por los videojuegos en los estudiantes españoles, y menores puntuaciones de síndrome informático visual pero una mayor alteración de la vida cotidiana en los estudiantes chinos debido a este tipo de ocio. Además, se comprobó que los estudiantes de la muestra china tenían un menor riesgo de padecer el síndrome informático visual, y que tener mayores niveles de adicción implicaba 1,4 veces más probabilidades de sufrir dicho síndrome. Conclusiones: Los presentes hallazgos demuestran una relación hasta ahora inexplorada entre la adicción a los videojuegos y los síntomas visuales relacionados con el abuso del ocio electrónico.

Introduction: The use of video games, due to the extent that it has reached during the COVID-19 pandemic, is a relevant study variable especially because of its interactions with aspects of mental and visual health. Objective: to predict the occurrence of computer vision syndrome according to the level of addiction to video games in university undergraduates during a particular period of uncertainty due to health and mobility restrictions imposed by governments as a result of the COVID-19 pandemic. Material and Methods: To accomplish this objective, an online questionnaire was administered with three validated instruments: a questionnaire to assess playing video games (CHCVI), a questionnaire to evaluate video games addiction (CERV), and a questionnaire to detect computer vision syndrome (CSQ). The three questionnaires were applied to a sample of 253 students from both Chinese and Spanish universities. To establish the predictions, robust indexes were constructed based on the Factor Analysis of the instruments administered. Finally, logistic regression was applied to predict computer vision syndrome. Results: The results showed greater computer vision syndrome and appetite for video games in Spanish students, and lower computer vision syndrome scores but a greater alteration of daily life in chinese students due to this type of leisure. Moreover, it was found that students from the Chinese sample entailed a lower risk of suffering from computer vision syndrome, and that having higher levels of addiction involved 1,4 times more likelihood of suffering from such syndrome. Conclusions: The present findings demonstrate a previously unexplored relationship between video games addiction and visual symptoms related to screen exposure.

A general justification for hybrid functionals in DFT by means of linear response theory.

In the present work, resorting to linear response theory, we examine the plausibility of postulating Kohn-Sham (KS)-type equations which contain, by definition, an effective hybrid potential made up by some arbitrary mixture of local and non-local terms. In this way a general justification for the construction of hybrid functionals is provided without resorting to arguments based on the adiabatic connection, the generalized KS theory or the Levy's constrained search (or its variations). In particular, we examine the cases of single-hybrid functionals, derived from non-local exchange and of double-hybrid functionals, emerging from non-local second-order expressions obtained from the KS perturbation theory. A further generalization for higher-order hybrid functionals is also included.

Na⋯B bond in NaBH 3 - : An induced spin-polarized bond.

The nature of the Na⋯B bond, in the recently synthesized NaBH 3 - adduct, is analyzed on the light of the Na- propensity to polarize along the bond axis as a consequence of the electric field produced by the BH3 fragment. The observed induced polarization has two consequences: (i) the energetic stabilization of the Na- , and (ii) the split of its valence electrons into two opposite lobes along the bond axis. Additionally, an analysis of the electron localization is presented using the information content of the correlated conditional pair density that reveals a significant delocalization between one lobe of the polarized Na- anion and the BH3 fragment at the equilibrium distance. Our findings reported here complement previous works on this system.

Effect of the Nucleophile's Nature on Chloroacetanilide Herbicides Cleavage Reaction Mechanism. A DFT Study.

In this study, the degradation mechanism of chloroacetanilide herbicides in the presence of four different nucleophiles, namely: Br-, I-, HS-, and S2O3-2, was theoretically evaluated using the dispersion-corrected hybrid functional wB97XD and the DGDZVP as a basis set. The comparison of computed activation energies with experimental data shows an excellent correlation (R2 = 0.98 for alachlor and 0.97 for propachlor). The results suggest that the best nucleophiles are those where a sulfur atom performs the nucleophilic attack, whereas the other species are less reactive. Furthermore, it was observed that the different R groups of chloroacetanilide herbicides have a negligible effect on the activation energy of the process. Further insights into the mechanism show that geometrical changes and electronic rearrangements contribute 60% and 40% of the activation energy, respectively. A deeper analysis of the reaction coordinate was conducted, employing the evolution chemical potential, hardness, and electrophilicity index, as well as the electronic flux. The charge analysis shows that the electron density of chlorine increases as the nucleophilic attack occurs. Finally, NBO analysis indicates that the nucleophilic substitution in chloroacetanilides is an asynchronous process with a late transition state for all models except for the case of the iodide attack, which occurs through an early transition state in the reaction.

A computational study of the reaction mechanism involved in the fast cleavage of an unconstrained amide bond assisted by an amine intramolecular nucleophilic attack.

In the present work, the fast amide bond cleavage of [3-((1R,5S,7s)-3-azabicyclo[3.3.1]nonane-7-carbonyl)-3-azabicyclo[3.3.1]nonane-7-carboxylic acid (bi-ATDO)], through an intramolecular nucleophilic attack of an amine group is evaluated. First, six possible peptide bond cleavage mechanisms, two of them including a water molecule, are described at the ωB97XD/6-311 + G(d,p)//MP2/6-311 + G(d,p) level of theory. The reaction consisting of an intramolecular nitrogen nucleophilic attack followed by a proton transfer and the amide bond cleavage is determined as the most favorable mechanism. The activation free energy computed for the latter is 20.5 kcal mol-1 , which agrees with the reported experimental result of 24.8 kcal mol-1 . Inclusion of a water molecule to assist the first step of the reaction results in an activation free energy increase of about 17 kcal mol-1 . All the steps in the most favorable mechanism are studied more in detail employing intrinsic reaction coordinate as well as the reaction force and reaction electronic flux analysis.

Two conformational polymorphs of 4-methylhippuric acid.

4-Methylhippuric acid {systematic name: 2-[(4-methylbenzoyl)amino]ethanoic acid}, a p-xylene excreted metabolite with a backbone containing three rotatable bonds (R-bonds), is likely to produce more than one stable molecular structure in the solid state. In this work, we prepared polymorph I by slow solvent evaporation (plates with Z' = 1) and polymorph II by mechanical grinding (plates with Z' = 2). Potential energy surface (PES) analysis, rotating the molecule about the C-C-N-C torsion angle, shows four conformational energy basins. The second basin, with torsion angles near -73°, agree with the conformations adopted by polymorph I and molecules A of polymorph II, and the third basin at 57° matched molecules B of polymorph II. The energy barrier between these basins is 27.5 kJ mol-1. Superposition of the molecules of polymorphs I and II rendered a maximum r.m.s. deviation of 0.398 Å. Polymorphs I and II are therefore true conformational polymorphs. The crystal packing of polymorph I consists of C(5) chains linked by N-H...O interactions along the a axis and C(7) chains linked by O-H...O interactions along the b axis. In polymorph II, two molecules (A with A or B with B) are connected by two acid-amide O-H...O interactions rendering R22(14) centrosymmetric dimers. These dimers alternate to pile up along the b axis linked by N-H...O interactions. A Hirshfeld surface analysis localized weaker noncovalent interactions, C-H...O and C-H...π, with contact distances close to the sum of the van der Waals radii. Electron density at a local level using the Quantum Theory of Atoms in Molecules (QTAIM) and the Electron Localization Function (ELF), or a semi-local level using noncovalent interactions, was used to rank interactions. Strong closed shell interactions in classical O-H...O and N-H...O hydrogen bonds have electron density highly localized on bond critical points. Weaker delocalized electron density is seen around the p-methylphenyl rings associated with dispersive C-H...π and H...H interactions.

Theoretical Description of R-X⋯NH3 Halogen Bond Complexes: Effect of the R Group on the Complex Stability and Sigma-Hole Electron Depletion.

In the present work, a number of R-X⋯NH3 (X = Cl, Br, and I) halogen bonded systems were theoretical studied by means of DFT calculations performed at the ωB97XD/6-31+G(d,p) level of theory in order to get insights on the effect of the electron-donating or electron-withdrawing character of the different R substituent groups (R = halogen, methyl, partially fluorinated methyl, perfluoro-methyl, ethyl, vinyl, and acetyl) on the stability of the halogen bond. The results indicate that the relative stability of the halogen bond follows the Cl < Br < I trend considering the same R substituent whereas the more electron-withdrawing character of the R substituent the more stable the halogen bond. Refinement of the latter results, performed at the MP2/6-31+G(d,p) level showed that the DFT and the MP2 binding energies correlate remarkably well, suggesting that the Grimme's type dispersion-corrected functional produces reasonable structural and energetic features of halogen bond systems. DFT results were also observed to agree with more refined calculations performed at the CCSD(T) level. In a further stage, a more thorough analysis of the R-Br⋯NH3 complexes was performed by means of a novel electron localization/delocalization tool, defined in terms of an Information Theory, IT, based quantity obtained from the conditional pair density. For the latter, our in-house developed C++/CUDA program, called KLD (acronym of Kullback-Leibler divergence), was employed. KLD results mapped onto the one-electron density plotted at a 0.04 a.u. isovalue, showed that (i) as expected, the localized electron depletion of the Br sigma-hole is largely affected by the electron-withdrawing character of the R substituent group and (ii) the R-X bond is significantly polarized due to the presence of the NH3 molecule in the complexes. The afore-mentioned constitutes a clear indication of the dominant character of electrostatics on the stabilization of halogen bonds in agreement with a number of studies reported in the main literature. Finally, the cooperative effects on the [Br-CN]n system (n = 1-8) was evaluated at the MP2/6-31+G(d,p) level, where it was observed that an increase of about ~14.2% on the complex stability is obtained when going from n = 2 to n = 8. The latter results were corroborated by the analysis of the changes on the Fermi-hole localization pattern on the halogen bond zones, which suggests an also important contribution of the electron correlation in the stabilization of these systems.

Adequate vegetative cover decreases nitrous oxide emissions from cattle urine deposited in grazed pastures under rainy season conditions.

A decline in pasture productivity is often associated with a reduction in vegetative cover. We hypothesize that nitrogen (N) in urine deposited by grazing cattle on degraded pastures, with low vegetative cover, is highly susceptible to losses. Here, we quantified the magnitude of urine-based nitrous oxide (N2O) lost from soil under paired degraded (low vegetative cover) and non-degraded (adequate vegetative cover) pastures across five countries of the Latin America and the Caribbean (LAC) region and estimated urine-N emission factors. Soil N2O emissions from simulated cattle urine patches were quantified with closed static chambers and gas chromatography. At the regional level, rainy season cumulative N2O emissions (3.31 versus 1.91 kg N2O-N ha-1) and emission factors (0.42 versus 0.18%) were higher for low vegetative cover compared to adequate vegetative cover pastures. Findings indicate that under rainy season conditions, adequate vegetative cover through proper pasture management could help reduce urine-induced N2O emissions from grazed pastures.

A DFT study of hydrogen and methane activation by B(C6F5)3/P(t-Bu)3 and Al(C6F5)3/P(t-Bu)3 frustrated Lewis pairs.

This contribution presents a computational study aimed at understanding factors affecting barriers associated with the activation of the H-H bond in molecular hydrogen and the H-CH3 bond in methane mediated by intermolecular Frustrated Lewis Pairs (FLPs). The classical phosphine P(t-Bu)3 Lewis base in conjunction with two Lewis acids, B(C6F5)3 and Al(C6F5)3, were used as representative models of intermolecular FLPs. DFT calculations were performed using the dispersion corrected ωB97x-D functional, including toluene as a solvent through the PCM-SMD implicit solvent scheme. The results show that, in all cases, the activation barrier is larger for methane than for hydrogen. We conclude that the observed increase in the barrier for methane activation is due primarily to a larger distortion in methane compared to hydrogen to reach the transition state. Second, a large distortion of the Lewis acid to attain a better interaction with the σ-bond in methane was observed. Finally, we found that, for both hydrogen and methane activation, a considerable reduction in the free energy activation barrier is observed when the Lewis acid Al(C6F5)3 is used. From the results extracted in this study, we propose the use of alanes acids as good candidates for methane activation.

The electron localization as the information content of the conditional pair density.

In the present work, the information gained by an electron for "knowing" about the position of another electron with the same spin is calculated using the Kullback-Leibler divergence (DKL) between the same-spin conditional pair probability density and the marginal probability. DKL is proposed as an electron localization measurement, based on the observation that regions of the space with high information gain can be associated with strong correlated localized electrons. Taking into consideration the scaling of DKL with the number of σ-spin electrons of a system (N(σ)), the quantity χ = (N(σ) - 1) DKLfcut is introduced as a general descriptor that allows the quantification of the electron localization in the space. fcut is defined such that it goes smoothly to zero for negligible densities. χ is computed for a selection of atomic and molecular systems in order to test its capability to determine the region in space where electrons are localized. As a general conclusion, χ is able to explain the electron structure of molecules on the basis of chemical grounds with a high degree of success and to produce a clear differentiation of the localization of electrons that can be traced to the fluctuation in the average number of electrons in these regions.

[Intestinal occlusion secondary to a retained surgical item]. / Oclusión intestinal secundaria a oblito quirúrgico.

BACKGROUND: Retained surgical items after a surgical procedure is a real, existing, and preventable problem that affects the safety of the surgical patient. Its incidence is not exactly known due to under-reporting of occurrence, due to the potential risk of lawsuits. CLINICAL CASE: A 31 year-old women that had an elective caesarean, apparently without complications. In the immediate post-operative period, clinical features appeared that were compatible with intestinal obstruction, such as inability to channel gas, bloating, abdominal pain and vigorous peristalsis. The diagnosis is made by the recent history of abdominal-pelvic surgery and the finding of a foreign body on a simple x-ray of the abdomen. The patient was operated upon, with a satisfactory outcome, and was discharged 5 days later. CONCLUSION: A retained surgical instrument is an under-reported event that represents a medical-legal problem, leading to various complications, including death if it is not diagnosed and treated early. It is important to know the risk factors and adopt a culture of prevention through perioperative monitoring of equipment and instruments used during the surgical act.

Design and analysis of a second and third generation biorefinery: The case of castorbean and microalgae.

In this work, a biorefinery system including castor bean seeds and microalgae is used as a case study to evaluate the integration of second and third generation biorefineries. A biorefinery concept was applied for the combined production of polyol, ethylene-glycol, omega-3 acid, biodiesel, methanol and heat and power from castor bean and microalgae. Castor bean cake and microalgae paste were used to feed a biomass-fired system (BIGCC), where part of CO2 produced in flue gas is captured and employed as substrate for microalgae growth. To evaluate the performance of this biorefinery concept three scenarios based on different levels of mass and energy integration were modeled and assessed from techno-economic and environmental points of view. The scenario with the best economic and environmental performances was the one including full mass integration, full heat integration, and cogeneration scheme.

Congenital malformations of pediatric surgical interest: prevalence, risk factors, and prenatal diagnosis between 2005 and 2012 in the capital city of a developing country. Bogotá, Colombia.

BACKGROUND: Congenital anomalies (CAs) cause nearly one third of infant deaths worldwide. Various surveillance systems have been established, such as the Bogota Congenital Malformations Surveillance Program (BCMSP). Some CAs are of special interest to pediatric surgeons: omphalocele, gastroschisis, intestinal and esophageal atresia, anorectal malformations, vascular anomalies, diaphragmatic hernias, hypospadias and cryptorchidism. The aim of this study is to determine the prevalence of such CAs, and identify possible risk factors. METHODS: Data from the BCMSP were collected between January 2005 and April 2012. CAs were classified in accordance with the ICD-10 and grouped for analysis purposes. Data on CA frequencies were obtained from the BCMSP. Association analyses were performed using the case-control methodology. RESULTS: 282,523 births were registered. 4682 (1.66%) had one or more CAs at birth. The prevalence of CAs requiring pediatric surgery was 1 in 1000. The most frequent CAs were vascular anomalies, hypospadias, and anorectal malformations. Exposure to external factors was significantly associated with selected CAs. 51% of selected birth defects were not diagnosed in prenatal ultrasound. CONCLUSIONS: This study highlights the importance of evaluating the local prevalence of congenital malformations. We propose the creation of specialized centers in Bogota to manage patients with CAs.

[Eagle's Syndrome]. / Síndrome de Eagle.

Eagle's Syndrome is an entity that is rarely clinically and anatomopathologically identified, and is defined as the elongation of the styloid process and/or the calcification of the styloid ligament. It produces intense pain in the craniocervical region and limitation of cervical movements. It can be mistaken for temporomandibular joint dysfunction. The diagnosis of this entity can be done by physical examination with palpation of the styloid process in the tonsillar fossa, and radiological studies help confirm the diagnosis.

Urea's effect on the ribonuclease A catalytic efficiency: a kinetic, 1H NMR and molecular orbital study.

Understanding of protein-urea interactions is one of the greatest challenges to modern structural protein chemistry. Based in enzyme kinetics experiments and (1)H NMR spectroscopic analysis we proposed that urea, at low concentrations, directly interacts with the protonated histidines of the active center of RNase A, following a simple model of competitive inhibition. These results were supported by theoretical analysis based on the frontier molecular orbital theory and suggest that urea might establish a favorable interaction with the cationic amino acids. Our experimental evidence and theoretical analysis indicate that the initials steps of the molecular mechanism of Urea-RNase A interaction passes through the establishment of a three center four electron adduct. Also, our results would explain the observed disruption of the (1)H NMR signals corresponding to H12 and H119 (involved in catalysis) of the RNase A studied in the presence of urea. Our interaction model of urea-amino acids (cationic) can be extended to explain the inactivation of other enzymes with cationic amino acids at the active site.