A Numerical Study of Several Species Population Models

This work considers a special case of Lotka-Volterra equations, which means that in the system of two ordinary differential equations, we take the four parameters equal to one. The reason is that we want just to illustrate the procedure to reduce that system to only one ordinary differential equation, such that we know its analytical solution. This idea will be applied to study the relations between a system of three ordinary differential equations, and a couple of partial differential equations. Lotka-Volterra equations are solved numerically by a fourth-order predictor-corrector method, which is initialized by an improved Euler method with a rather small time step because it is only a second-order algorithm. Then, it is proposed a model with three species, defined by ordinary differential equations.

Effect of Sleep Hygiene Orientation on Social Cognition Impairments Due to Chronic Sleep Restriction in Mexican Medical Residents

Introduction: Sleep is critical to human physiological function, cognitive performance, and emotional regulation. Healthcare personnel, especially physicians, are chronically exposed to long working hours, which are often accompanied by decreased sleep time. Clinical evidence indicates that these conditions affect their cognitive function and professional practice, but researchers in the field have not sufficiently explored the possible effects of reductions in sleep time on social cognition. Objective: The aim of this is to further explore the effects of sleep restriction among medical residents, the specific impairments in social cognition that it produces, and the effects of a sleep hygiene orientation on those impairments. Method: There were 124 medical residents (50 males, 74 females) who completed a daily sleep/work log, a battery of sleep tests/questionnaires, and neuropsychological evaluations. The participants then received a short course (8 hours) on basic concepts of sleep hygiene and sleep psychoeducation. Once the course was completed, participants filled out the questionnaires again. Results: The results indicate that sleep disturbances in medical residents were associated with severe neurocognitive and social cognition impairments. After the sleep hygiene intervention, neuropsychological function and sleep parameters improved, awareness increased, and social cognition performance significantly improved. Conclusion: Using sleep psychoeducation and sleep hygiene intervention in medical residents is a simple strategy to mitigate the effects of sleep restriction.

Suitability of the Composite Made of Multi Wall Carbon Nanotubes-Polyvinylpyrrolidone for Culturing Invertebrate <i>Helix aspersa</i>Neurons

Carbon nanotubes have been used as scaffolds for tissue engineering. However, the identification of these nanomaterials disperses in biological solutions and their direct interaction with nerve cells is still controversial. The aim of this work is to characterize the topographic and ultra-structural distribution of the composite made of multi wall carbon nanotubes-polyvinylpyrrolidone (MWCNTs-PVP) deposited on the Helix aspersa neurons and over glass coverslip. Scanning Electron Microscopy (SEM) and Confocal Microscopy (CM) studies were done to analyze the properties of such MWCNTs-PVP composite. The cerebral ganglion of Helix aspersa was treated and incubated with MWCNTs-PVP, fixing it in paraformaldehyde at 4% and was observed with SEM and CM. Although the nanotubes were not labeled or stained with fluorescent compounds, the MWCNTs-PVP deposited on glass and on nerve cells, was observed by the confocal microscope in the reflection mode. In SEM studies, it was observed that MWCNTs-PVP was attached to the surface on neurons. Moreover, in CM studies, it was possible to observe that MWCNTs-PVP was attached to the neuronal membrane, crossing the cell membrane and getting into the cytoplasm. These results support the hypothesis that carbon nanotubes interact with the neuronal cell membrane and can be useful for neuronal tissue engineering. In addition, these results open new alternatives for toxicological studies, in order to elucidate the cytotoxicity of MWCNTs-PVP composite in neurons and other excitable cells.

Two New Species of the Genus Dictyota (Phaeophyceae: Dictyotales) from the Mexican Caribbean

During a molecular characterization of the genus Dictyota J. V. Lamouroux (Phaeophyceae, Dictyotales) along the Mexican coasts of the Gulf of Mexico and the Mexican Caribbean, using psbA and cox1 genes, it was found that two particular collections did not match with the sequences published for a total of 39 species of Dictyota. For each gene, both collections diverged in high-uncorrected “p” distance values with respect to other related species. This high genetic divergence was corroborated by morphological analysis. Hence, we proposed Dictyota mayae J. Lozano-Orozco & Sentíes and Dictyota pedrochei J. Lozano-Orozco & Sentíes as new species.

Absence of Fruit Mexican Fly (<i>Anastrepha ludens</i>) in Pitaya de Mayo (<i>Stenocereus pruinosus</i>)

Pitaya de mayo (Stenocereus pruinosus) exportation is considered feasible especially to the United States of America (USA) using the adequate preservation and transportation techniques. One of the exportation requirements is that pitayas, as well as any other tropical fruits, have to be free from Mexican fruit fly contamination and certified by the Food National Sanitary, Iniquity, and Quality Service. This review proved that this fruit is not attacked by the Mexican fruit fly A. ludens or any other Anastrepha species. The fruit fly may be found in some States of Mexican Republic such as some tropical regions but not in the semi-arid regions where cacti fruits are grown.

Reproductive performance of the Mesa silverside(Chirostoma jordani Woolman,1894)under natural and controlled photoperiods

Chirostoma jordani is a native annual species inhabiting lacustrine waters of the Central Mexico Plateau.It is widely distributed and is currently facing high environmental pressures.Five experi-ments were performed to study the reproductive performance of this species.Four of the experiments were conducted in 270-L indoor recirculation tanks.Two males and one female at the first stage of reproduction were included in each test.A photoperiod of 14 light hours and 10 dark hours was used.In a fifth experiment,10 females and 15 males were kept in an outdoor 3,000-L recirculation tank under natural photoperiod.The number of spawns,fertilised eggs and 30-day-old juveniles were counted and the survival rate was calculated.The results indicated significant differences(P<0.05)between treatments.Higher spawn numbers and greater egg production were observed under controlled photoperiod,and higher numbers of juveniles and a higher survival rate were observed under natural photoperiod.The trials exhibited different patterns of egg produc-tion during the experiment.The egg production in the natural-photoperiod trials followed a polynomial curve model.In contrast,the trials under the controlled photoperiod showed an irregular pattern of increases and decreases in egg production.

Clusters in Macroscopic Traffic Flow Models

This paper concerns the traveling wave formation in macroscopic traffic flow models. The dynamics involved in this problem is described following a close analogy to compressible fluid dynamics. It is well known that vehicle clusters appear along a highway when the homogenous steady state taken as a reference is linearly unstable. The cluster properties are determined in an approximate way in terms of the parameters proper to each model and are compared between them.

The Explicitly Covariant Stress-Energy-Momentum Balance Equation for Electromagnetism in Material Media

Beginning with the explicitly covariant Maxwell equations in media, we deduce an explicitly covariant stress-energy-momentum balance equation in material media. Proceeding in this way we avoid mixing external fields and self fields, as occurs if one begins with Lorentz＇s law, the most usual approach appearing in textbooks. Indeed our deduction implies a generalized force density in which the total fields appear. As an application of the present deduction, we discuss briefly the Abraham-Minkowski controversy, showing its relation to open or closed electromagnetic systems. This approach will be interesting for scholars as well as graduate students interested in conceptual problems of relativistic electromagnetism.

Performance of Brooders,Fry and Growth of the Nile Tilapia(Oreochromis niloticus)Cultured in an Experimental Recirculating Aquaculture System

We present results of a long-term study aimed to optimize Nile tilapia O. niloticus production in a recirculating aquaculture system (RAS) in México City. Three experiments were evaluated: 1) fry production;2) production of masculinized fries;and 3) assessment of growth under three different densities (10, 30 and 75 fish/m3). The broodstock produced on average 2400 ± 600 fry every 15 days during six months, with a total production of 28,800 ± 2000. One hundred percent males were produced in 274-L raceways in an eight-week period. The obtained results in fish production in the RAS system indicated variations related to density. A daily growth rate of 3.6 g/day was registered with a density of 10 fish/m3, 0.9 g/day in 30 fish/m3 and 0.4 g/day in 75 fish/m3. This information could be useful for production purposes in this type of systems.

Evaluation of Growth Performance of a Genetically Characterized F1 Rainbow Trout,Oncorhynchus mykiss in a Recirculating Aquaculture System

The growth performance of a selected F1 rainbow trout genetically characterized as polymorphic with locus Omy207UoG (NA = 13, PIC = 0.891, HE = 0.9003) was evaluated in a recirculating aquaculture system (RAS). A set of 157 rainbow trout of 37.8 g of mean body weight and 14.6 cm mean total length per tank, were introduced in each of six fish tank of 5 m3 connected to a recirculating aquaculture system (RAS). The trout was rearing during 317 days. Growth performance indicators and water quality were evaluated during the experiment. The genetically selected F1 rainbow trout showed a tendency towards homogeneity in growth performance along the culture period, reaching a mean total weight of 552.2 g. The length-weight relationship indicated an isometric growth (>3.0). This study presents the basis to establish a long-term marker-assisted selection program for rainbow trout culture in a subtropical region.

Isolation and Characterization of 26 Microsatellite Loci for the Shortfin Silverside Fish <i>Chirostoma humboldtianum</i>Valenciennes1835 (Atherinopsidae: Menidiinae) Derived from Next Generation Sequencing and Their Cross-Amplification in Central Mexican Atherinopsids

The endemic silverside fish C. humboldtianum is of great ichtyologycal, economical and cultural relevance in central Mexico and it has been suggested that it is among a group of other “peces blancos”, the most ancestral species. Here we characterized a set of 26 microsatellite loci from the species in order to further assess population and phylogeographic issues that aid in evaluating their highly impacted populations. From 58 primer pairs tested on specimens from Villa Victoria dam (Rio Balsas Basin), 26 loci positively amplified on the species and cross-primed on specimens of the closely related and threatened Poblana alchichica, C. promelas and C. riojai. Loci resolved medium and high genetic variation (mean NA = 14.3, SD = 9.38;mean HO & HE = 0.47, SD = 0.32 and 0.58, SD = 0.32, respectively) and it is expected that these polymorphic loci are also useful in studing threatened atherinopsid species.