Diels-Alder reactions of masked o-benzoquinones: new experimental findings and a theoretical study of the inverse electron demand case

Diels-Alder reactions of the masked o-benzoquinone (MOB) 2 with vinylene carbonate (3), the bicyclic derivatives 4, 5, and 6, and the intramolecular version of the 2-hydroxymethylfuran-MOB Diels-Alder reaction are described. In addition, a theoretical study of the Diels-Alder reactions of MOBs with enol and thioenol ethers is presented.     

Indirect methods of collocation: Trefftz‐Herrera collocation

A nonstandard collocation method (TH‐collocation) is presented, where collocation is used to construct specialized weighting functions instead of the solution itself, as it is usual, so that in this sense it is an indirect method. TH‐collocation is shown to be as accurate as standard collocation, but computationally far more efficient. The present article is the first of a series devoted to explore thoroughly collocation methods. The following classification of collocation methods is introduced: direct‐nonoverlapping; indirect‐nonoverlapping; direct‐overlapping; and indirect‐overlapping. Most of the effort reported in the literature has gone to direct‐nonoverlapping methods. The procedure presented in this article falls into the indirect‐nonoverlapping category and it is based on Trefftz‐Herrera formulation. © 1999 John Wiley & Sons, Inc. Numer Methods Partial Differential Eq 15: 709–738, 1999     

Development and implementation of the k0-standardization and other parametric methods of INAA in Cuba. Part I

This paper explains chronologically the implementation of thek ₀-standardization and other parametric methods in Cuba. Fundamental and applied results in the determination of the most important parameters are obtained, using the IBR-2 at Dubna and Triga Mark III at Mexico reactor facilities. Some modifications in the Stoughton-Halpering convention, and its comparison with the modified Westcott and Høgdahl method are presented. The application of the described methods at the CS-ISCTN low flux facility, using the big samples techniques, is presented.     

Implementing Complementary Approaches to Shape the Mechanism of α-Synuclein Oligomerization as a Model of Amyloid Aggregation

The aggregation of proteins into amyloid fibers is linked to more than forty still incurable cellular and neurodegenerative diseases such as Parkinson’s disease (PD), multiple system atrophy, Alzheimer’s disease and type 2 diabetes, among others. The process of amyloid formation is a main feature of cell degeneration and disease pathogenesis. Despite being methodologically challenging, a complete understanding of the molecular mechanism of aggregation, especially in the early stages, is essential to find new biological targets for innovative therapies. Here, we reviewed selected examples on α-syn showing how complementary approaches, which employ different biophysical techniques and models, can better deal with a comprehensive study of amyloid aggregation. In addition to the monomer aggregation and conformational transition hypothesis, we reported new emerging theories regarding the self-aggregation of α-syn, such as the alpha-helix rich tetramer hypothesis, whose destabilization induce monomer aggregation; and the liquid-liquid phase separation hypothesis, which considers a phase separation of α-syn into liquid droplets as a primary event towards the evolution to aggregates. The final aim of this review is to show how multimodal methodologies provide a complete portrait of α-syn oligomerization and can be successfully extended to other protein aggregation diseases.     

The Active Gravitational Mass of a Heat Conducting Sphere Out of Hydrostatic Equilibrium

We obtain an expression for the activegravitational mass of a relativistic heat conductingfluid, just after its departure from hydrostaticequilibrium, on a time scale of the order of relaxationtime. It is shown that an increase of acharacteristic parameter leads to larger (smaller)values of active gravitational mass of collapsing(expanding) spheres, enhancing thereby the instabilityof the system.     

Determination of alpha-tocopherol and alpha-tocopherol acetate in diets of experimental animals. Study of stability in the diets.

A simple method is described which permits, avoiding saponification, alpha-tocopherol and alpha-tocopheryl acetate measurement in semi-synthetic diets for experimental animals by HPLC, with both UV and fluorescence detection. Phenyldodecane was chosen as internal standard with remarkable performances, and EDTA and BHT were added to prevent oxidation in aqueous and non-aqueous phases respectively. The mobile phase was methanol-water (94:6 v/v) at a flow-rate of 2 ml/min. Samples were homogenized and extracted twice with n-hexane by probe sonication. Extracts were evaporated to dryness and redissolved with chloroform-methanol (1:1, v/v). Validation parameters were studied between 25 ng and 6 micrograms for alpha-tocopherol and between 3 and 24.2 micrograms for alpha-tocopheryl acetate, which corresponds to the range of values in the existing diets. Results had correlation coefficients > 0.99; recoveries > 85%; R.S.D. < 6%, so the method is adequate to control vitamin E intake in animals as well as vitamin E stability in food during storage.     

Identification of surgical practice patterns using evolutionary cluster analysis

Modern data analysis and machine learning are strongly dependent on efficient search techniques. However, in general, further exploration into high-dimensional and multi-modal spaces is needed, and moreover, many real-world problems exhibit inaccurate, noisy, discrete and complex data. Thus, robust methods of optimization are often required to generate results suitable for these data. Some algorithms that imitate certain natural principles, namely the so-called evolutionary algorithms, have been used in different fields with great success. In this paper, we apply a variant of Particle Swarm Optimization (PSO), recently introduced by the authors, to partitional clustering of a real-world data set to distinguish between perioperative practices and associate them with some unknown relevant facts. Our data were obtained from a survey conducted in Spain based on a pool of colorectal surgeons. The PSO derivative we consider here: (i) is adapted to consider mixed discrete-continuous optimization, with statistical clustering criteria arranged to take these types of mixed measures; (ii) is able to find optimum or near-optimum solutions much more efficiently and with considerably less computational effort because of the richer population diversity it introduces; and (iii) is able to select the right parameter values through self-adaptive dynamic parameter control, thus overcoming the cumbersome aspect common to all metaheuristics.     

Incoherent recovering of the spatial resolution in digital holography

We report on a technique to recover the spatial resolution of digitally recorded and reconstructed holograms of large objects. Due to the high-contrast speckle noise diminishes the spatial resolution in coherent imaging systems our proposal is based on the reduction of the contrast of it. This aim is achieved through the superposition on an intensity basis of digitally reconstructed holograms of the same static scene. We show a theoretical justification of the procedure and experimentally-obtained results of applying the technique with digitally reconstructed holograms of an object with very poor optical contrast.     

Optimisation of 40 Gb/s wavelength converters based on four-wave mixing in a semiconductor optical amplifier

The optimum operating powers and wavelengths for a 40 Gb/s wavelength converter based on four-wave mixing in a semiconductor optical amplifier are inferred from experimental results. From these measurements, some general rules of thumb are derived for this kind of devices. Generally, the optimum signal power should be 10 dB lower than the pump power (−16 dB conversion efficiency) whereas the wavelength separation between the signal and the pump carrier should not be lower than about four times the signal bitrate (1.3 nm for 40 Gb/s RZ signals).