A modified Oster-Murray-Harris mechanical model of morphogenesis

There are two main modeling paradigms for biological pattern formation in developmental biology: chemical prepattern models and cell aggregation models. This paper focuses on an example of a cell aggregation model, the mechanical model developed by Oster, Murray, and Harris [Development, 78 (1983), pp. 83--125]. We revisit the Oster--Murray--Harris model and find that, due to the infinitesimal displacement assumption made in the original version of this model, there is a restriction on the types of boundary conditions that can be prescribed. We derive a modified form of the model which relaxes the infinitesimal displacement assumption. We analyze the dynamics of this model using linear and multiscale nonlinear analysis and show that it has the same linear behavior as the original Oster--Murray--Harris model. Nonlinear analysis, however, predicts that the modified model will allow for a wider range of parameters where the solution evolves to a bounded steady state. The results from both analyses are verified through numerical simulations of the full nonlinear model in one and two dimensions. The increased range of boundary conditions that are well-posed, as well as a wider range of parameters that yield bounded steady states, renders the modified model more applicable to, and more robust for, comparisons with experiments

Water reuse for irrigated agriculture in Jordan: challenges of soil sustainability and the role of management strategies

Reclaimed water provides an important contribution to the water balance in water-scarce Jordan, but the quality of this water presents both benefits and challenges. Careful management of reclaimed water is required to maximize the nutrient benefits while minimizing the salinity risks. This work uses a multi-disciplinary research approach to show that soil response to irrigation with reclaimed water is a function of the management strategies adopted on the farm by the water user. The adoption of management methods to maintain soil productivity can be seen to be a result of farmers’ awareness to potentially plant-toxic ions in the irrigation water (70% of Jordan Valley farmers identified salinization as a hazard from irrigation with reclaimed water). However, the work also suggests that farmers’ management capacity is affected by the institutional management of water. About a third (35%) of farmers in the Jordan Valley claimed that their ability to manage salinization was limited by water shortages. Organizational interviews revealed that institutional awareness of soil management challenges was quite high (34% of interviewees described salinization as a risk from water reuse), but strategies to address this challenge at the institutional level require greater development

Efeito do KMnO4 e 1-MCP com atmosfera modificada na conservação pós-colheita de melão Cantaloupe.

O trabalho teve como objetivo avaliar o efeito do uso de permanganato de potássio (KMnO) e 1-metilciclopropeno (1-MCP), associados à atmosfera modificada passiva (AMP), na conservação pós-colheita de melão Cantaloupe (Cucumis melon L.)

Eficiência de métodos alternativos utilizando atmosfera modificada passiva, no controle da podridão de melão Cantaloupe.

Este trabalho avalia a eficiência do permanganato de potássio (KMnO4) e outras alternativas no controle da podridão do melão, associados a atmosfera modificada (AM). Este foi conduzido na Embrapa Agroindústria Tropical em Fortaleza com melões Cantaloupe ?Vera Cruz` provenientes de fazenda comercial Dinamarca, localizada em Mossoró-RN. Os frutos foram selecionados, lavados com álcool 70%, inoculados com Fusarium pallidoroseum e separados por tratamentos. Foram acondicionados 5 frutos por caixa, sendo cada caixa uma repetição. Os sachês de vermiculita impregnados com KMnO4 foram distribuídos de acordo com o peso de frutos por caixa. Foram armazenados em câmara fria na temperatura de 3 ± 2°C e UR de 85 ± 2%, onde permaneceram por 14 dias. A pós esse período foram retiradas as embalagens e as caixas a rmazenadas em temperatura ambiente de 23 ± 2°C e URde 90 ±2%. A partir daí foram feitas avaliações de perda de massa e escalas de notas aos 15 e 18 dias de arma zenamento. O delineamento experimental utilizado foi inteiramente casualizado em esquema fatorial 5x2, sendo 5 tratamentos (1-MCP, KMnO4, Cera de Carnaúba, Funginat e frutos testemunha) e duas AM (com e sem X-tend). Os resultados das notas referentes à incidência de doenças foram expressos em percentagem por caixa. Foi observada diferença significativa principalmente com relação à utilização de embalagens, provando que o armazenamento de melão sem AM afeta a qualidade do mesmo, diminuindo assim sua vida útil. E se associado a outros métodos de conservação pós-colheita, pode aumentar a eficiência de ambos os métodos

Serotonin-3 Receptors in the Posterior Ventral Tegmental Area Regulate Ethanol Self-Administration of Alcohol-Preferring (P) Rats

Several studies indicated the involvement of serotonin-3 (5-HT 3 ) receptors in regulating alcohol- drinking behavior. The objective of this study was to determine the involvement of 5-HT 3 receptors within the ventral tegmental area (VTA) in regulating ethanol self-administration by alcohol-preferring (P) rats. Standard two-lever operant chambers were used to examine the effects of 7 consecutive bilateral micro-infusions of ICS205-930 (ICS), a 5-HT 3 receptor antagonist, directly into the posterior VTA on the acquisition and maintenance of 15% (v/v) ethanol self- administration. P rats readily acquired ethanol self-administration by the 4 th session. The three highest doses (0.125, 0.25 and 1.25 ug) of ICS prevented acquisition of ethanol self- administration. During the acquisition post-injection period, all rats treated with ICS demonstrated higher responding on the ethanol lever, with the highest dose producing the greatest effect. In contrast, during the maintenance phase, the 3 highest doses (0.75, 1.0 and 1.25 ug) of ICS significantly increased responding on the ethanol lever; following the 7-day dosing regimen, responding on the ethanol lever returned to control levels. Micro-infusion of ICS into the posterior VTA did not alter the low responding on the water lever, and did not alter saccharin (0.0125% w/v) self-administration.. Micro-infusion of ICS into the anterior VTA did not alter ethanol self- administration. Overall, the results of this study suggest that 5-HT 3 receptors in the posterior VTA of the P rat may be involved in regulating ethanol self-administration. In addition, chronic operant ethanol self-administration, and/or repeated treatments with a 5-HT 3 receptor antagonist may alter neuronal circuitry within the posterior VTA

An Empirical Model for the Radio Emission from Pulsars

A model for slow radio pulsars is proposed which involves the entire magnetosphere in the production of the observed radio emission. It is argued that observations of pulsar profiles suggest that a feedback mechanism exists between the star surface and the null charge surface, requiring particle flow in both directions. In their flow to and from the surface the particles execute an azimuthal drift around the magnetic pole, thereby creating a ring of discrete `emission nodes' close to the surface. Motion of the nodes is observed as the well-known subpulse `drift', but is interpreted here as a small residual component of the real particle drift. The nodes can therefore move in either direction, or even remain stationary. A precise fit is found for the pulsar PSR0943+10. Azimuthal interactions between different regions of the magnetosphere depend on the angle between the magnetic and rotation axes and influence the conal type, as observed. The requirement of intermittent weak pair-production in an outergap suggests a natural evolutionary link between radio and gamma-ray pulsars.Comment: 17 pages 8 figure

Fluctuation theorem for currents and Schnakenberg network theory

A fluctuation theorem is proved for the macroscopic currents of a system in a nonequilibrium steady state, by using Schnakenberg network theory. The theorem can be applied, in particular, in reaction systems where the affinities or thermodynamic forces are defined globally in terms of the cycles of the graph associated with the stochastic process describing the time evolution.Comment: new version : 16 pages, 1 figure, to be published in Journal of Statistical Physic

Effects of Alcohol and Saccharin Deprivations on Concurrent Ethanol and Saccharin Operant Self-Administration by Alcohol-Preferring (P) Rats

Consumption of sweet solutions has been associated with a reduction in withdrawal symptoms and alcohol craving in humans. The objective of the present study was to determine the effects of EtOH and saccharin (SACC) deprivations on operant oral self-administration. P rats were allowed to lever press concurrently self-administer EtOH (15% v/v) and SACC (0.0125% g/v) for 8 weeks. Rats were then maintained on daily operant access (non-deprived), deprived of both fluids (2 weeks), deprived of SACC and given 2 ml of EtOH daily, or deprived of EtOH and given 2 ml of SACC daily. All groups were then given two weeks of daily operant access to EtOH and SACC, followed by an identical second deprivation period. P rats responded more for EtOH than SACC. All deprived groups increased responding on the EtOH lever, but not on the SACC lever. Daily consumption of 2 ml EtOH decreased the duration of the ADE. Home cage access to 2 ml SACC also decreased the ADE but to a lesser extent than access to EtOH. A second deprivation period further increased and prolonged the expression of an ADE. These results show EtOH is a more salient reinforcer than SACC. With concurrent access to EtOH and SACC, P rats do not display a saccharin deprivation effect. Depriving P rats of both EtOH and SACC had the most pronounced effect on the magnitude and duration of the ADE, suggesting that there may be some interactions between EtOH and SACC in their CNS reinforcing effects

Reachability in Biochemical Dynamical Systems by Quantitative Discrete Approximation (extended abstract)

In this paper, a novel computational technique for finite discrete approximation of continuous dynamical systems suitable for a significant class of biochemical dynamical systems is introduced. The method is parameterized in order to affect the imposed level of approximation provided that with increasing parameter value the approximation converges to the original continuous system. By employing this approximation technique, we present algorithms solving the reachability problem for biochemical dynamical systems. The presented method and algorithms are evaluated on several exemplary biological models and on a real case study.Comment: In Proceedings CompMod 2011, arXiv:1109.104