Demiarcs,creaons and genons

Useful insights into the representation of natural systems can be gained by decomposing directed graphs (digraphs) into elementary components. Arcs of digraphs can be split into male demiarcs (outarcs) which leave vertices and female demiarcs (inarcs) which enter demiarcs. Likewise, a vertex can be split into an input perceiving side called the creaon and an output generating side called the genon. Digraphs can be regarded as being hierarchically organized because each vertex in a level-1 digraph can be expanded into a level-2 digraph. In general, each vertex of a level-i digraph can be expanded into a level-(i+1) digraph. Arcs of a level-i digraph can be regarded as bundles of level-(i + 1) arcs which are split at the vertex boundary. These elementary graphical components are shown to be useful for depicting input-output systems such as organisms, ecosystems and societies.     

Comportement desFormica devant un obstacle «infranchissable»

Summary Formica polyctena can send information along their path about an obstacle. A simple mechanism (abnormal workers agitation) help the ants to find another way behind the obstacle.Formica rufa can dig a tunnel under a large circular wall that blocks all accesses to the nest. They can also open a hole in the wall, passing building materials through. These materials can be carried also underground, to repair the central part of the nest whose access is blocked. That is another proof of the extreme plasticity of the building activity among red ants.     

On the distribution of the general irreversiblen-compartmental model having time-dependent transition probabilities

The cumulant generating function and first two moments are derived for the stochastic distribution of units in a general irreversiblen-compartment model with time-dependent transition probabilities. In this model, a unit in the first compartment can transfer to any one of the remainingn−1 compartments and a unit in the second compartment can transfer to any of the remainingn−2 compartments and so on. In addition, a unit can enter or leave the system through any compartment. The work is related to previous research and a numerical example is given.     

Connectivity and information transfer in flow networks: Two magic numbers in ecology?

An ecosystem can be visualized as a graph of certain preassigned trophic compartments; these nodes are then mutually connected through the internal exchanges of material and energy. The mathematical theory of information can be applied to such a graph in order to define two relevant indices: a measure of connectivity (the entropy H of the connections) and a measure of the degree of the “energetic” specialization (the internal transfer of informationI). The computation of these indices in stationary real cases suggests that the observed complexity of ecosystems is conditioned by two competing effects. The first can be interpreted as a “thermodynamical” principle related to the unavoidable irreversibility taking place inside the system, whereas the second can be taken as a “biological” principle concerned with the selection of some particular interactions: those which maximize the information circulating between the compartments.     

Selective alkylation of cycloheptaamylose

The verification of a number of assumptions made about cycloamylose structure, substrate binding and catalysis is dependent on the ability to 3-O-alkylate selectively these oligosaccharides. In the presence of barium oxide and barium hydroxide octahydrate, cycloheptaamylose reacts with 3-bromopropene in dimethylformamide and dimethyl sulfoxide to produce a high yield of tetradecakis-2,6-O-allylcycloheptaamylose, a compound which can serve as a highly versatile intermediate in the preparation of heptakis-3-O-alkylated cycloheptamyloses. Depending on the nature of the substituent to be introduced at the C-3 hydroxyl position, the intermediate allyl ether can be 3-O-alkylated and the allyl ether can be isomerized to the vinyl ether and cleaved; or, alternatively, the allyl ether can be first subjected to isomerization followed by alkylation, and then cleavage.     

Excitotoxic Stimulation of Brain Microslices as an In vitro Model of Stroke

Examining molecular mechanisms involved in neuropathological conditions, such as ischemic stroke, can be difficult when using whole animal systems. As such, primary or ''neuronal-like'' cell culture systems are commonly utilized. While these systems are relatively easy to work with, and are useful model systems in which various functional outcomes (such as cell death) can be readily quantified, the examined outcomes and pathways in cultured immature neurons (such as excitotoxicity-mediated cell death pathways) are not necessarily the same as those observed in mature brain, or in intact tissue. Therefore, there is the need to develop models in which cellular mechanisms in mature neural tissue can be examined. We have developed an in vitro technique that can be used to investigate a variety of molecular pathways in intact nervous tissue. The technique described herein utilizes rat cortical tissue, but this technique can be adapted to use tissue from a variety of species (such as mouse, rabbit, guinea pig, and chicken) or brain regions (for example, hippocampus, striatum, etc.). Additionally, a variety of stimulations/treatments can be used (for example, excitotoxic, administration of inhibitors, etc.). In conclusion, the brain slice model described herein can be used to examine a variety of molecular mechanisms involved in excitotoxicity-mediated brain injury.     

Nanoelectromechanics of Methylated DNA in a Synthetic Nanopore

Methylation of cytosine is a covalent modification of DNA that can be used to silence genes, orchestrating a myriad of biological processes including cancer. We have discovered that a synthetic nanopore in a membrane comparable in thickness to a protein binding site can be used to detect methylation. We observe a voltage threshold for permeation of methylated DNA through a <2 nm diameter pore, which we attribute to the stretching transition; this can differ by >1 V/20 nm depending on the methylation level, but not the DNA sequence.     

The hidden variables of leadership

The dynamics of a collective move can be untangled into three components: initiation, following and cancellation. Varying the response function parameters attached to one individual can switch the collective phenomenology from an absence of well identified leader (“distributed leadership”) to the emergence of a “despotic regime”, i.e. this individual leading more often the collective moves. I show that not all parameters have the same impact but rather that only a large increase of the initiation rate can empower an obvious leader, up to the “despotic” regime. Being more readily followed, or cancelling less often can enhance the leader's prominence only up to a limited level. To overtake this limit would then further require to affect also the parameters attached to the others (e.g. to lower their eagerness to initiate group motion as well as their probability to be followed when they do).     

Implications of immune-mediated metastatic growth on metastatic dormancy,blow-up,early detection,and treatment

Metastatic seeding of distant organs can occur in the very early stages of primary tumor development. Once seeded, these micrometastases may enter a dormant phase that can last decades. Curiously, the surgical removal of the primary tumor can stimulate the accelerated growth of distant metastases, a phenomenon known as metastatic blow-up. Recent clinical evidence has shown that the immune response can have strong tumor promoting effects. In this work, we investigate if the pro-tumor effects of the immune response can have a significant contribution to metastatic dormancy and metastatic blow-up. We develop an ordinary differential equation model of the immune-mediated theory of metastasis. We include both anti- and pro-tumor immune effects, in addition to the experimentally observed phenomenon of tumor-induced immune cell phenotypic plasticity. Using geometric singular perturbation analysis, we derive a rather simple model that captures the main processes and, at the same time, can be fully analyzed. Literature-derived parameter estimates are obtained, and model robustness is demonstrated through a time dependent sensitivity analysis. We determine conditions under which the parameterized model can successfully explain both metastatic dormancy and blow-up. The results confirm the significant active role of the immune system in the metastatic process. Numerical simulations suggest a novel measure to predict the occurrence of future metastatic blow-up in addition to new potential avenues for treatment of clinically undetectable micrometastases.

     

A rapid technique for evaluating the biodeterioration potential of polyurethane elastomers

Summary The technique described provides a rapid method for screening thermoplastic polyurethanes against deteriogenic micro-organisms using thin films (0.4–0.5 mm thick) of plastic prepared in an electric plantens press. The films are inoculated with a spore suspension of Gliocladium roseum and can be viewed directly under the light microscope for evaluation of surface effects; selective staining can be used to reveal fungal mycelium. Results can be obtained within a week which correlate with longer term tests using commercial samples. The technique can also be used to isolate potential polyurethane deteriorating micro-organisms from the environment and to confirm their biodeteriogenic activities.     

Viable populations in a prey–predator system

 Lotka–Volterra equations are considered a dynamical game, where the phenotypes of the predator and of the prey can vary. This differs from the usual procedure of specifying as a priori laws according to which strategies are supposed to change. The question at stake is the survival of each of the species, instead of the maximization of a given pay-off by each player, as it is commonly discussed in games. The predator needs the prey, while the prey can survive without the predator. These obvious and simplistic constraints are enough to shape the regulation of the system: notably, the largest closed set of initial conditions can be delineated, from which there exists at least one evolutionary path where the population can avoid extinction forever. To these so-called viable trajectories, viable strategies are associated, respectively for the prey or for the predator. A coexistence set can then be defined. Within this set and outside the boundary, strategies can vary arbitrarily within given bounds while remaining viable, whereas on the boundary, only specific strategies can guarantee the viability of the system. Thus, the largest set can be determined, outside of which strategies will never be flexible enough to avoid extinction. Received 2 May 1995; received in revised form 15 August 1995     

Moment Aberrations of Magnetoelectrostatic Plasma Lenses

The moment and geometric aberrations of magnetoelectrostatic plasma lenses are studied by computer modeling. Conditions are determined such that these aberrations can be made substantially lower, in which case the cross-sectional area of a focused beam can be reduced by a factor of 10⁵ and the ion current density at the focus of a lens can amount to 10³ A/cm².     

On the theory of microwave discharges excited on the surface of a dielectric antenna

Microwave gas discharges excited near a dielectric surface are investigated. Such discharges can exist over a broad range of gas pressures and thereby can be used to solve a wide variety of applied problems. The wave dispersion properties favorable for discharge excitation are analyzed, and a kinetic discharge model is considered that can be used to calculate the discharge parameters. A model of a steady discharge at gas pressures of 10²–10⁴ Pa is constructed.     

Cooperative Regulation of Cellular Proliferation by Intercellular Diffusion

A theoretical model for the cooperative control of cellular kinetics is investigated. A critical substance A is produced by the cells whose concentration in a given cell determines whether that cell can divide. The substance A can leak out of the cells into the surrounding medium as well as be reabsorbed by the cells. This feature then implies communication between the cells since all concentrations will be functions of the population density. The substance A also has a lifetime, i.e. decays, for example, by denaturation. This system can be described by three coupled nonlinear differential equations which can be solved analytically in certain limiting cases and can, of course, be studied in detail by computer techniques. Our investigations have shown that (a) there is a critical initial cell population density below which cell proliferation will not occur, (b) cell proliferation can be stimulated by supplying substance A to the medium and there is a critical initial concentration in the medium for initiating proliferation when the cell population density is subcritical, and (c) a well-defined induction period prior to exponential growth may exist whose length depends on the system parameters and initial conditions.     

Somatic embryogenesis and in vitro flowering inBrassica nigra

Summary This report describes a protocol for regeneration ofBrassica nigra in vitro from unorganized callus to a highly differentiated stage of flowering. Callus is initiated from seedling hypocotyl, and root explants and plantlets are obtained via somatic embryogenesis. Shoot cultures can be established from these plantlets. These shoots can either be induced to flower in vitro or rooted to produce plants which flower ex vitro. Each stage of development is marked with a specific growth regulator requirement. This has potential as a model system to understand the cellular and molecular mechanisms involved in morphogenesis, and it can be used to understand the mechanism of change of phase from vegetative to reproductive. An advantage of this system is that in vitro flowering can be obtained repeatedly in the shoots raised from the axillary buds of the flowering shoots. The protocol can also be used to procureB. nigra gametes under aseptic condition.     

Sequencing and expression of two arsenic resistance operons with different functions in the highly arsenic-resistant strain <Emphasis Type="Italic">Ochrobactrum tritici</Emphasis> SCII24<Superscript>T</Superscript>

Background  

Arsenic (As) is a natural metalloid, widely used in anthropogenic activities, that can exist in different oxidation states. Throughout the world, there are several environments contaminated with high amounts of arsenic where many organisms can survive. The most stable arsenical species are arsenate and arsenite that can be subject to chemically and microbiologically oxidation, reduction and methylation reactions. Organisms surviving in arsenic contaminated environments can have a diversity of mechanisms to resist to the harmful effects of arsenical compounds.     

UPTAKE AND RELEASE OF NIPECOTIC ACID BY RAT BRAIN SLICES

—Nipecotic acid, a potent inhibitor of GABA uptake, is taken up by slices of rat cerebral cortex by a sodium-dependent, ‘high affinity’ system (K_m 11 μM), and can be released from these slices by an increased potassium ion concentration in a calcium-dependent manner. Nipecotic acid and GABA appear to be taken up by the same osmotically-sensitive structures. GABA and substances which inhibit GABA uptake also inhibit the uptake of nipecotic acid. GABA can release preloaded nipecotic acid from brain slices, and nipecotic acid can release preloaded GABA. This indicates that GABA and nipecotic acid can be counter-transported using the same mobile carrier. Nipecotic acid appears to have a higher affinity than GABA for this carrier.     

Shame and HIV: Strategies for addressing the negative impact shame has on public health and diagnosis and treatment of HIV

There are five ways in which shame might negatively impact upon our attempts to combat and treat HIV.

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Development and differentiation of haploid Lycopersicon esculentum (tomato)

Summary Haploid callus cultures of selected races of Lycopersicon (tomato) species can be obtained from anther culture. This is a further demonstration of a proposed general method of haploid culture developed with Arabidopsis thaliana. Differentiation of haploid callus of Lycopersicon esculentum can be controlled both in the dark and the light by hormones added to defined minimal media. Development to plantlets is achieved only in the light. Callus cells can be induced to develop into seedless pseudo-fruits. Chromosome counts on callus cells or root-tip cells establishes haploidy (n=12).Haploidy can be maintained in culture on defined minimal media for at least one year.