Understanding flame extinction in timber under external heating using high-activation energy asymptotics

The present study analyses the flame extinction of timber under different levels of external heating and oxygen contents in the surrounding atmosphere. An existing theoretical framework conceived initially for the analysis of a counter-flow diffusion flame established above the surface of a condensed fuel is extended for charring materials to deliver a fundamental understanding of the self-extinction of timber. This study shows that the energy balance at the burning surface is influenced primarily by the magnitude of external heating conditions, which directly influences the evolution of bulk properties such as flame temperature, location, and stagnation plane position. Variations in the oxygen content had a lesser influence over these bulk properties. For all investigated conditions, the limits of the strain rate range where a flame can be sustained were shown to vary substantially, and critical Damköhler number (Da) analyses were conducted. Blow-off at high strain rates (low Da) occurs for all investigated conditions. The value of this critical Da decreases when increasing either the magnitude of the external heating or the oxygen content as flame temperature increases. Quenching at low strain rates (high Da) is only found for sufficiently low magnitudes of external heating. There, the associated critical Da increases when increasing either the external heating or the oxygen content. Above a certain degree of external heating, the flame can be theoretically sustained even at infinitely-low strain rates. By comparing these results to experimental data, the experimental critical Da at quenching was found to behave like the theoretical results but with a lower sensitivity to variations in the parameters studied. To account for this discrepancy, a fuel dilution parameter is introduced to incorporate the complex dependencies of timber decomposition and surface reactions not captured by the theoretical framework

IMPORTANCIA DE LA NUTRICIÓN EN EL PLAN DE ESTUDIOS DE ENFERMERÍA DE LA FESI UNAM

Introduction: In Mexico there are some regions with starvation and undernourishment, therefore the medical research has to be increased. The Nursing Major program at Facultad de Estudios Superiores Iztacala of Universidad Nacional Autónoma de México (2006) includes the study of nutrition. This one is divided in different modules but not as an specific subject, however we have observed that students are not able to incorporate all the nutrition fundamental aspects. Currently the basic theory of nutrition takes 56 hours and 50 minutes, but this one is included such as a section in different courses. “Nutrition and Health care” is an elective subject and it takes 80 hours, nevertheless there are two disadvantages. The first one is that students are allowed to take it up to the fourth semester, and the second one is that there is a lack of time (23 hours), since nutrition is a wide topic. We need to get qualified people related to this topic in order to teach efficiently. We have noticed that students need to learn more about nutrition, for that reason it is necessary to assign the nutrition topic as a compulsory subject, otherwise not all the students will be able to take the course. Material and Method: Qualitative and quantitative methods were used for the current research. For the quantitative method was used a nominal scale that allowed to sort the 34 programs reviewed from mexican institutions which have the nursing major. Two researches (done by the students) were considerated to find out that only 70% of students enrolled in seventh semester had taken the nutrition subject. Regarding the qualitative method, 10 students proposed that nutrition must be included as a compulsory subject. Results: There was a study focused on the nursing major programs from mexican universities, in which 34 was the number of programs reviewed. 28 universities have already included nutrition topic in their programs and 6 universities have not considered this matter in their programs yet. According to the results from the qualitative research, nutrition must be considered as an essential subject on the programs. Discussion: As a result of a quantitative and qualitative research, it is important to take into account, in the next evaluation of the subject’s curriculum, the opportunity to reincorporate the nutrition topic in basic semesters, and emphasize this point on all the study programs. Conclusion: In an effort to improve the topics related to nutrition and health care, it is very important to reorganize and focus on study plans at Iztacala University.Introducción: México tiene algunas regiones con hambre y desnutrición. También la producción en investigación clínica en México se debe incrementar. El Plan de Estudios de la Licenciatura en Enfermería de la Facultad de Estudios Superiores Iztacala de la Universidad Nacional Autónoma de México (2006) sí contempla el estudio de la Nutrición pero de manera fraccionada en diferentes módulos. Hemos observado que las y los estudiantes no han integrado todos los aspectos fundamentales de Nutrición. El tiempo empleado para abordar la temática teórica básica sobre Nutrición es de 56 horas con 50 minutos. Como optativa de “Nutrición y Salud” se imparten 80 horas. El primer inconveniente es que la optativa la pueden llevar hasta el 4° semestre; el segundo, es que hay un déficit de 23 horas de trabajo en el aula, si restamos las horas asignadas al módulo optativo con respecto a las horas de trabajo en los módulos obligatorios. Si México tiene problemas de nutrición, necesitamos contar con personal preparado en el tema. Vemos que no estamos aportándoles suficientemente estas herramientas, por lo que es necesario que no se estudie en forma de materia optativa, porque no todos los estudiantes la van a cursar. Material y Método: Es una investigación evaluativa cuanti-cualitativa. La parte cuantitativa empleó el nivel de escala nominal que permitió clasificar los 34 programas revisados de Instituciones de Educación Superior que imparten la Licenciatura en Enfermería en México. Se tomaron en cuenta los resultados de 2 investigaciones realizadas por estudiantes que encontraron que sólo el 70% de la matrícula de séptimo semestre han llevado Nutrición. En la parte cualitativa, 10 estudiantes sugirieron que Nutrición fuera un módulo obligatorio. Resultados: 28 Programas de los 34 revisados de Universidades de México SÍ tienen especificado en su Plan de Estudios el abordaje de Nutrición. Mientras que 6 Programas de los 34 revisados NO tienen especificado en su Plan de Estudios el abordaje de Nutrición. Los resultados cualitativos fueron constantes en cuanto a que “la optativa de Nutrición debería pasar a módulo obligatorio”. Discusión: Hay un peso cuantitativo y cualitativo que se pronuncia hacia revisar en una próxima Evaluación Curricular, la pertinencia de reincorporar en los primeros semestres obligatorios la temática de Nutrición de un manera más explícita en nuestro Plan de Estudios. Conclusión: Hay que reorganizar los contenidos programáticos en materia de Nutrición y Salud dentro de nuestro Plan de Estudios

Challenges and New Approaches to Proving the Existence of Muscle Synergies of Neural Origin

Muscle coordination studies repeatedly show low-dimensionality of muscle activations for a wide variety of motor tasks. The basis vectors of this low-dimensional subspace, termed muscle synergies, are hypothesized to reflect neurally-established functional muscle groupings that simplify body control. However, the muscle synergy hypothesis has been notoriously difficult to prove or falsify. We use cadaveric experiments and computational models to perform a crucial thought experiment and develop an alternative explanation of how muscle synergies could be observed without the nervous system having controlled muscles in groups. We first show that the biomechanics of the limb constrains musculotendon length changes to a low-dimensional subspace across all possible movement directions. We then show that a modest assumption—that each muscle is independently instructed to resist length change—leads to the result that electromyographic (EMG) synergies will arise without the need to conclude that they are a product of neural coupling among muscles. Finally, we show that there are dimensionality-reducing constraints in the isometric production of force in a variety of directions, but that these constraints are more easily controlled for, suggesting new experimental directions. These counter-examples to current thinking clearly show how experimenters could adequately control for the constraints described here when designing experiments to test for muscle synergies—but, to the best of our knowledge, this has not yet been done

Carbon-fiber tips for scanning probe microscopes and molecular electronics experiments

We fabricate and characterize carbon-fiber tips for their use in combined scanning tunneling and force microscopy based on piezoelectric quartz tuning fork force sensors. An electrochemical fabrication procedure to etch the tips is used to yield reproducible sub-100-nm apex. We also study electron transport through single-molecule junctions formed by a single octanethiol molecule bonded by the thiol anchoring group to a gold electrode and linked to a carbon tip by the methyl group. We observe the presence of conductance plateaus during the stretching of the molecular bridge, which is the signature of the formation of a molecular junction.Comment: Conference Proceeding (Trends in NanoTechnology 2011, Tenerife SPAIN); Nanoscale Research Letters, (2012) 7:25

Discrete breathers in ϕ4\phi^4 and related models

We touch upon the wide topic of discrete breather formation with a special emphasis on the the $\phi^4$ model. We start by introducing the model and discussing some of the application areas/motivational aspects of exploring time periodic, spatially localized structures, such as the discrete breathers. Our main emphasis is on the existence, and especially on the stability features of such solutions. We explore their spectral stability numerically, as well as in special limits (such as the vicinity of the so-called anti-continuum limit of vanishing coupling) analytically. We also provide and explore a simple, yet powerful stability criterion involving the sign of the derivative of the energy vs. frequency dependence of such solutions. We then turn our attention to nonlinear stability, bringing forth the importance of a topological notion, namely the Krein signature. Furthermore, we briefly touch upon linearly and nonlinearly unstable dynamics of such states. Some special aspects/extensions of such structures are only touched upon, including moving breathers and dissipative variations of the model and some possibilities for future work are highlighted

What traits are carried on mobile genetic elements, and why?

Although similar to any other organism, prokaryotes can transfer genes vertically from mother cell to daughter cell, they can also exchange certain genes horizontally. Genes can move within and between genomes at fast rates because of mobile genetic elements (MGEs). Although mobile elements are fundamentally self-interested entities, and thus replicate for their own gain, they frequently carry genes beneficial for their hosts and/or the neighbours of their hosts. Many genes that are carried by mobile elements code for traits that are expressed outside of the cell. Such traits are involved in bacterial sociality, such as the production of public goods, which benefit a cell's neighbours, or the production of bacteriocins, which harm a cell's neighbours. In this study we review the patterns that are emerging in the types of genes carried by mobile elements, and discuss the evolutionary and ecological conditions under which mobile elements evolve to carry their peculiar mix of parasitic, beneficial and cooperative genes

Population genomics provide insights into the global genetic structure of Colletotrichum graminicola, the causal agent of maize anthracnose

Understanding the genetic diversity and mechanisms underlying genetic variation in pathogen populations is crucial to the development of effective control strategies. We investigated the genetic diversity and reproductive biology of Colletotrichum graminicola isolates which infect maize by sequencing the genomes of 108 isolates collected from 14 countries using restriction site-associated DNA sequencing (RAD-seq) and whole-genome sequencing (WGS). Clustering analyses based on single-nucleotide polymorphisms revealed three genetic groups delimited by continental origin, compatible with short-dispersal of the pathogen and geographic subdivision. Intra- and intercontinental migration was observed between Europe and South America, likely associated with the movement of contaminated germplasm. Low clonality, evidence of genetic recombination, and high phenotypic diversity were detected. We show evidence that, although it is rare (possibly due to losses of sexual reproduction- and meiosis-associated genes) C. graminicola can undergo sexual recombination. Our results support the hypotheses that intra- and intercontinental pathogen migration and genetic recombination have great impacts on the C. graminicola population structure

Perspectives on the Trypanosoma cruzi-host cell receptor interaction

Chagas disease is caused by the parasite Trypanosoma cruzi. The critical initial event is the interaction of the trypomastigote form of the parasite with host receptors. This review highlights recent observations concerning these interactions. Some of the key receptors considered are those for thromboxane, bradykinin, and for the nerve growth factor TrKA. Other important receptors such as galectin-3, thrombospondin, and laminin are also discussed. Investigation into the molecular biology and cell biology of host receptors for T. cruzi may provide novel therapeutic targets

Learning curves of basic laparoscopic psychomotor skills in SINERGIA VR simulator

Purpose: Surgical simulators are currently essential within any laparoscopic training program because they provide a low-stakes, reproducible and reliable environment to acquire basic skills. The purpose of this study is to determine the training learning curve based on different metrics corresponding to five tasks included in SINERGIA laparoscopic virtual reality simulator. Methods: Thirty medical students without surgical experience participated in the study. Five tasks of SINERGIA were included: Coordination, Navigation, Navigation and touch, Accurate grasping and Coordinated pulling. Each participant was trained in SINERGIA. This training consisted of eight sessions (R1–R8) of the five mentioned tasks and was carried out in two consecutive days with four sessions per day. A statistical analysis was made, and the results of R1, R4 and R8 were pair-wise compared with Wilcoxon signed-rank test. Significance is considered at P value <0.005. Results: In total, 84.38% of the metrics provided by SINERGIA and included in this study show significant differences when comparing R1 and R8. Metrics are mostly improved in the first session of training (75.00% when R1 and R4 are compared vs. 37.50% when R4 and R8 are compared). In tasks Coordination and Navigation and touch, all metrics are improved. On the other hand, Navigation just improves 60% of the analyzed metrics. Most learning curves show an improvement with better results in the fulfillment of the different tasks. Conclusions: Learning curves of metrics that assess the basic psychomotor laparoscopic skills acquired in SINERGIA virtual reality simulator show a faster learning rate during the first part of the training. Nevertheless, eight repetitions of the tasks are not enough to acquire all psychomotor skills that can be trained in SINERGIA. Therefore, and based on these results together with previous works, SINERGIA could be used as training tool with a properly designed training program