The Influence of Cerebral Blood Flow and Carbon Dioxide on Neuromuscular Responses During Environmental Stress

Although reductions in cerebral blood flow (CBF) may be implicated in the development of central fatigue during environmental stress, the contribution from hypocapnia-induced reductions in CBF versus reductions in CBF per se has yet to be isolated. The current research program examined the influence of CBF, with and without consequent hypocapnia, on neuromuscular responses during hypoxia and passive heat stress. To this end, neuromuscular responses, as indicated by motor evoked potentials (MEP), maximal M-wave (Mmax) and cortical voluntary activation (cVA) of the flexor carpi radialis muscle during isometric wrist flexion, was assessed in three separate projects: 1) hypocapnia, independent of concomitant reductions in CBF; 2) altered CBF during severe hypoxia and; 3) thermal hyperpnea-mediated reductions in CBF, independent of hypocapnia. All projects employed a custom-built dynamic end-tidal forcing system to control end-tidal PCO2 (PETCO2), independent of the prevailing environmental conditions, and cyclooxygenase inhibition using indomethacin (Indomethacin, 1.2 mg·Kg-1) to selectively reduce CBF (estimated using transcranial Doppler ultrasound) without changes in PETCO2. A primary finding of the present research program is that the excitability of the corticospinal tract is inherently sensitive to changes in PaCO2, as demonstrated by a 12% increase in MEP amplitude in response to moderate hypocapnia. Conversely, CBF mediated reductions in cerebral O2 delivery appear to decrease corticospinal excitability, as indicated by a 51-64% and 4% decrease in MEP amplitude in response to hypoxia and passive heat stress, respectively. The collective evidence from this research program suggests that impaired voluntary activation is associated with reductions in CBF; however, it must be noted that changes in cVA were not linearly correlated with changes in CBF. Therefore, other factors independent of CBF, such as increased perception of effort, distress or discomfort, may have contributed to the reductions in cVA. Despite the functional association between reductions in CBF and hypocapnia, both variables have distinct and independent influence on the neuromuscular system. Therefore, future studies should control or acknowledge the separate mechanistic influence of these two factors.

Standardization of cytokine flow cytometry assays

Affiliation: Faculté de médecine, Université de Montréal & CANVAC

Autocrine loop in the purinergic control of airway surface liquid volume : monitoring with a novel side-view imaging technique

La Fibrose Kystique (FK) est une maladie dégénérative qui entraine une dégénération des poumons dû au problème de clairance mucociliaire (CMC). Le volume de surface liquide (SL) couvrant les cellules pulmonaires est essentiel à la clairance de mucus et au combat contre les infections. Les nucléotides extracellulaires jouent un rôle important dans la CMC des voies aériennes, en modifiant le volume de la SL pulmonaire. Cependant, les mécanismes du relâchement de l’ATP et de leurs déplacements à travers la SL, restent inconnus. Des études ultérieures démontrent que l’exocytose d’ATP mécano-sensible et Ca2+-dépendant, dans les cellules A549, est amplifié par les actions synergétiques autocrine/paracrine des cellules avoisinantes. Nous avions comme but de confirmer la présence de la boucle purinergique dans plusieurs modèles de cellules épithéliales et de développer un système nous permettant d’observer directement la SL. Nous avons démontrés que la boucle purinergique est fonctionnelle dans les modèles de cellules épithéliales examinés, mis appart les cellules Calu-3. L’utilisation de modulateur de la signalisation purinergique nous a permis d’observer que le relâchement d’ATP ainsi que l’augmentation du [Ca2+]i suivant un stress hypotonique, sont modulés par le biais de cette boucle purinergique et des récepteurs P2Y. De plus, nous avons développé un système de microscopie qui permet d’observer les changements de volume de SL en temps réel. Notre système permet de contrôler la température et l’humidité de l’environnement où se trouvent les cellules, reproduisant l’environnement pulmonaire humain. Nous avons démontré que notre système peut identifier même les petits changements de volume de SL.

Copyright is an Impediment to the Free Flow of Ideas

"Sur un ton humoristique, les auteurs avouent être des voleurs… d’idées. À quoi riment les lois sur le droit d’auteur demandent-ils ? À l’origine, ce ne sont pas les droits des créateurs que le souverain ou l’État voulait protéger, mais bien les privilèges des éditeurs. Et d’où vient qu’on ait ainsi accordé à ces derniers le droit exclusif de publier ? C’est que dès l’invention de l’imprimerie, les hommes de pouvoir ont bien vu la menace que représentait pour eux la dissémination des idées : le calcul qu’ils ont fait a profité aux imprimeurs. Le phénomène n’est pas étranger à l’existence des permis de radiodiffusion / télévision existant de nos jours dans nos États démocratiques ; et l’histoire se répète comme on l’observe aujourd’hui quant à la régulation du réseau Internet. Quand les éditeurs se rendirent compte qu’ils ne pouvaient plus avoir la main haute sur tout ce qui se publiait, ils ont pris prétexte du droit des créateurs pour protéger leurs propres intérêts. Ni l’éthique ni l’esthétique ne motivaient les éditeurs , mais bien leurs seuls intérêts commerciaux, légitimes au demeurant. Deux factions s’opposent aujourd’hui quant à la question du droit des auteurs à l’ère numérique. La vieille garde se bat pour préserver à peu de choses près le statu quo tandis que ses vis-à-vis proclament la mort du droit d’auteur tel qu’il a existé. Et quel modèle nouveau préconisent ces derniers ? En fait, ils ne s’opposent pas à toute forme de protection pour ceux qui traditionnellement en ont bénéficié, mais songent à des mécanismes nouveaux …, de sorte que la vieille garde n’a pas à s’en faire outre mesure. Le fond du problème est ailleurs soutiennent MM. Benyekhlef et Tresvant : même si les avocats plaideront que ce ne sont pas les idées, mais bien la forme particulière qu’un créateur a choisie pour les exprimer qu’on protège par les lois sur le droit d’auteur, cela ne change rien. Dès qu’une idée est exprimée et fixée d’une certaine manière, il devient plus difficile de l’exprimer à nouveau puisqu’une partie du champ virtuel qu’elle pouvait occuper est déjà conquise, à bon droit selon le droit actuel. Il faut en conclure que le droit d’auteur nouveau, comme le droit d’auteur traditionnel, est une entrave à la libre circulation des idées."

Qualitative air flow modelling and analysis of data centre air conditioning as multiple jet array

This work identifies the importance of plenum pressure on the performance of the data centre. The present methodology followed in the industry considers the pressure drop across the tile as a dependant variable, but it is shown in this work that this is the only one independent variable that is responsible for the entire flow dynamics in the data centre, and any design or assessment procedure must consider the pressure difference across the tile as the primary independent variable. This concept is further explained by the studies on the effect of dampers on the flow characteristics. The dampers have found to introduce an additional pressure drop there by reducing the effective pressure drop across the tile. The effect of damper is to change the flow both in quantitative and qualitative aspects. But the effect of damper on the flow in the quantitative aspect is only considered while using the damper as an aid for capacity control. Results from the present study suggest that the use of dampers must be avoided in data centre and well designed tiles which give required flow rates must be used in the appropriate locations. In the present study the effect of hot air recirculation is studied with suitable assumptions. It identifies that, the pressure drop across the tile is a dominant parameter which governs the recirculation. The rack suction pressure of the hardware along with the pressure drop across the tile determines the point of recirculation in the cold aisle. The positioning of hardware in the racks play an important role in controlling the recirculation point. The present study is thus helpful in the design of data centre air flow, based on the theory of jets. The air flow can be modelled both quantitatively and qualitatively based on the results.

Exploiting non-Markovianity for quantum control

Quantum technology, exploiting entanglement and the wave nature of matter, relies on the ability to accurately control quantum systems. Quantum control is often compromised by the interaction of the system with its environment since this causes loss of amplitude and phase. However, when the dynamics of the open quantum system is non-Markovian, amplitude and phase flow not only from the system into the environment but also back. Interaction with the environment is then not necessarily detrimental. We show that the back-flow of amplitude and phase can be exploited to carry out quantum control tasks that could not be realized if the system was isolated. The control is facilitated by a few strongly coupled, sufficiently isolated environmental modes. Our paradigmatic example considers a weakly anharmonic ladder with resonant amplitude control only, restricting realizable operations to SO(N). The coupling to the environment, when harnessed with optimization techniques, allows for full SU(N) controllability.

Stereo-Based Head Pose Tracking Using Iterative Closest Point and Normal Flow Constraint

In this text, we present two stereo-based head tracking techniques along with a fast 3D model acquisition system. The first tracking technique is a robust implementation of stereo-based head tracking designed for interactive environments with uncontrolled lighting. We integrate fast face detection and drift reduction algorithms with a gradient-based stereo rigid motion tracking technique. Our system can automatically segment and track a user's head under large rotation and illumination variations. Precision and usability of this approach are compared with previous tracking methods for cursor control and target selection in both desktop and interactive room environments. The second tracking technique is designed to improve the robustness of head pose tracking for fast movements. Our iterative hybrid tracker combines constraints from the ICP (Iterative Closest Point) algorithm and normal flow constraint. This new technique is more precise for small movements and noisy depth than ICP alone, and more robust for large movements than the normal flow constraint alone. We present experiments which test the accuracy of our approach on sequences of real and synthetic stereo images. The 3D model acquisition system we present quickly aligns intensity and depth images, and reconstructs a textured 3D mesh. 3D views are registered with shape alignment based on our iterative hybrid tracker. We reconstruct the 3D model using a new Cubic Ray Projection merging algorithm which takes advantage of a novel data structure: the linked voxel space. We present experiments to test the accuracy of our approach on 3D face modelling using real-time stereo images.

Numerical Simulation of Electroosmotic Flow with Step Change in Zeta Potential

Electroosmotic flow is a convenient mechanism for transporting polar fluid in a microfluidic device. The flow is generated through the application of an external electric field that acts on the free charges that exists in a thin Debye layer at the channel walls. The charge on the wall is due to the chemistry of the solid-fluid interface, and it can vary along the channel, e.g. due to modification of the wall. This investigation focuses on the simulation of the electroosmotic flow (EOF) profile in a cylindrical microchannel with step change in zeta potential. The modified Navier-Stoke equation governing the velocity field and a non-linear two-dimensional Poisson-Boltzmann equation governing the electrical double-layer (EDL) field distribution are solved numerically using finite control-volume method. Continuities of flow rate and electric current are enforced resulting in a non-uniform electrical field and pressure gradient distribution along the channel. The resulting parabolic velocity distribution at the junction of the step change in zeta potential, which is more typical of a pressure-driven velocity flow profile, is obtained.

Admission Control for TCP Flows Using Packet Classes and Edge-to-edge Measurements of Aggregates

TCP flows from applications such as the web or ftp are well supported by a Guaranteed Minimum Throughput Service (GMTS), which provides a minimum network throughput to the flow and, if possible, an extra throughput. We propose a scheme for a GMTS using Admission Control (AC) that is able to provide different minimum throughput to different users and that is suitable for "standard" TCP flows. Moreover, we consider a multidomain scenario where the scheme is used in one of the domains, and we propose some mechanisms for the interconnection with neighbor domains. The whole scheme uses a small set of packet classes in a core-stateless network where each class has a different discarding priority in queues assigned to it. The AC method involves only edge nodes and uses a special probing packet flow (marked as the highest discarding priority class) that is sent continuously from ingress to egress through a path. The available throughput in the path is obtained at the egress using measurements of flow aggregates, and then it is sent back to the ingress. At the ingress each flow is detected using an implicit way and then it is admission controlled. If it is accepted, it receives the GMTS and its packets are marked as the lowest discarding priority classes; otherwise, it receives a best-effort service. The scheme is evaluated through simulation in a simple "bottleneck" topology using different traffic loads consisting of "standard" TCP flows that carry files of varying sizes

Estado del arte del control en sistemas organizacionales y técnicos

La perdurabilidad empresarial es una de las preocupaciones sectoriales, regionales y nacionales estudiada desde diferentes ámbitos (económico, social y académico), convirtiéndose en uno de los objetivos multinivel que impulsa el desarrollo y crecimiento de un país. De otro lado, una de las metodologías que está orientada a garantizar el cumplimiento de los objetivos o comportamientos planificados se denomina “sistemas de control” cuya aplicación es interdisciplinaria, tiene su origen en los sistemas técnicos y se traslada a los sistemas organizacionales. Este trabajo desarrolla una revisión bibliográfica del control, desde la en los sistemas técnicos y desde la Psicología, Sociología y disciplinas sociales a los sistemas organizacionales, identificando dos corrientes. La primera corriente, denominada “clásica” en sistemas causales y la segunda, llamada “inteligente”. El trabajo describe en cada corriente la conceptualización, los propósitos, las metodologías, la estructura, la taxonomía y las críticas en los sistemas de control. El control es abordado con diferentes metodologías, dependiendo de la corriente y de la naturaleza de cada sistema, pero tiene un propósito transversal o interdisciplinario que consiste en generar comportamientos esperados o deseables en el sistema, incluyendo alcanzar objetivos establecidos. En cuanto al desarrollo y comprensión, hay un mayor avance en los sistemas técnicos enfocados básicamente hacia la autonomía del sistema, mientras que en los sistemas organizacionales se ha generado la inquietud de evolucionar o generar controles diferentes o eliminar el control, pero las organizaciones continúan aplicando los controles clásicos y generando resultados de no perdurabilidad empresarial.

Admission control schemes for TCP elastic traffic in class-based networks

En aquesta tesi proposem dos esquemes de xarxa amb control d'admissió per al trànsit elàstic TCP amb mecanismes senzills. Ambdós esquemes són capaços de proporcionar throughputs diferents i aïllament entre fluxos, on un "flux" es defineix com una seqüència de paquets relacionats dins d'una connexió TCP. Quant a l'arquitectura, ambdós fan servir classes de paquets amb diferents prioritats de descart, i un control d'admissió implícit, edge-to-edge i basat en mesures. En el primer esquema, les mesures són per flux, mentre que en el segon, les mesures són per agregat. El primer esquema aconsegueix un bon rendiment fent servir una modificació especial de les fonts TCP, mentre que el segon aconsegueix un bon rendiment amb fonts TCP estàndard. Ambdós esquemes han estat avaluats satisfactòriament a través de simulació en diferents topologies de xarxa i càrregues de trànsit.

Development of an air-scour control system for membrane bioreactors

The thesis involves the development and implementation of a new and robust control system based on permeability trends but at the same time capable of reducing aeration proportionally to permeate flux. Permeability was made a key parameter for directly comparing temporary changes in membrane performance. Transmembrane pressure and flux were gathered every 10 seconds and permeability values were automatically calculated; different mathematical algorithms were applied for the signal filtering of on-line data. Short term and long term permeability trends were compared once a day, and a control action was applied proportionally to the short term/long term permeability ratio without exceeding the aeration flow recommended by the membrane suppliers.

A regime-dependent balanced control variable based on potential vorticity

In this paper it is argued that rotational wind is not the best choice of leading control variable for variational data assimilation, and an alternative is suggested and tested. A rotational wind parameter is used in most global variational assimilation systems as a pragmatic way of approximately representing the balanced component of the assimilation increments. In effect, rotational wind is treated as a proxy for potential vorticity, but one that it is potentially not a good choice in flow regimes characterised by small Burger number. This paper reports on an alternative set of control variables which are based around potential vorticity. This gives rise to a new formulation of the background error covariances for the Met Office's variational assimilation system, which leads to flow dependency. It uses similar balance relationships to traditional schemes, but recognises the existence of unbalanced rotational wind which is used with a new anti-balance relationship. The new scheme is described and its performance is evaluated and compared to a traditional scheme using a sample of diagnostics.

Flow controls on lowland river macrophytes: A review

We review the current status of knowledge regarding the role that flow parameters play in controlling the macrophyte communities of temperate lowland rivers. We consider both direct and indirect effects and the interaction with other factors known to control macrophyte communities. Knowledge gaps are identified and implications for the management of river systems considered. The main factors and processes controlling the status of macrophytes in lowland rivers are velocity (hence also discharge), light, substrate, competition, nutrient status and river management practices. We suggest that whilst the characteristics of any particular macrophyte community reflect the integral effects of a combination of the factors, fundamental importance can be attributed to the role of discharge and velocity in controlling instream macrophyte colonisation, establishment and persistence. Velocity and discharge also appear to control the relative influence of some of the other controlling factors. Despite the apparent importance of velocity in determining the status of macrophyte communities in lowland rivers, relatively little is understood about the nature of the processes controlling this relationship. Quantitative knowledge is particularly lacking. Consequently, the ability to predict macrophyte abundance and distribution in rivers is still limited. This is further complicated by the likely existence of feedback effects between the growth of macrophytes and velocity. Demand for water resources increases the pressure on lowland aquatic ecosystems. Despite growing recognition of the need to allocate water for the needs of instream biota, the inability to assess the flow requirements of macrophyte communities limits the scope to achieve this. This increases the likelihood of overexploitation of the water resource as other users, whose demands are quantifiable, are prioritised. (C) 2008 Elsevier B.V. All rights reserved.

Modeling the mechanisms that control in-stream dissolved organic carbon dynamics in upland and forested catchments

[1] We present a new, process-based model of soil and stream water dissolved organic carbon (DOC): the Integrated Catchments Model for Carbon (INCA-C). INCA-C is the first model of DOC cycling to explicitly include effects of different land cover types, hydrological flow paths, in-soil carbon biogeochemistry, and surface water processes on in-stream DOC concentrations. It can be calibrated using only routinely available monitoring data. INCA-C simulates daily DOC concentrations over a period of years to decades. Sources, sinks, and transformation of solid and dissolved organic carbon in peat and forest soils, wetlands, and streams as well as organic carbon mineralization in stream waters are modeled. INCA-C is designed to be applied to natural and seminatural forested and peat-dominated catchments in boreal and temperate regions. Simulations at two forested catchments showed that seasonal and interannual patterns of DOC concentration could be modeled using climate-related parameters alone. A sensitivity analysis showed that model predictions were dependent on the mass of organic carbon in the soil and that in-soil process rates were dependent on soil moisture status. Sensitive rate coefficients in the model included those for organic carbon sorption and desorption and DOC mineralization in the soil. The model was also sensitive to the amount of litter fall. Our results show the importance of climate variability in controlling surface water DOC concentrations and suggest the need for further research on the mechanisms controlling production and consumption of DOC in soils.