Role of transport performance on neuron cell morphology

The compartmental model is a basic tool for studying signal propagation in neurons, and, if the model parameters are adequately defined, it can also be of help in the study of electrical or fluid transport. Here we show that the input resistance, in different networks which simulate the passive properties of neurons, is the result of an interplay between the relevant conductances, morphology and size. These results suggest that neurons must grow in such a way that facilitates the current flow. We propose that power consumption is an important factor by which neurons attain their final morphological appearance.Comment: 9 pages with 3 figures, submitted to Neuroscience Letter

Some constructions of almost para-hyperhermitian structures on manifolds and tangent bundles

In this paper we give some examples of almost para-hyperhermitian structures on the tangent bundle of an almost product manifold, on the product manifold $M\times\mathbb{R}$, where $M$ is a manifold endowed with a mixed 3-structure and on the circle bundle over a manifold with a mixed 3-structure.Comment: 10 pages; This paper has been presented in the "4th German-Romanian Seminar on Geometry" Dortmund, Germany, 15-18 July 200

Optimal spatial transportation networks where link-costs are sublinear in link-capacity

Consider designing a transportation network on $n$ vertices in the plane, with traffic demand uniform over all source-destination pairs. Suppose the cost of a link of length $\ell$ and capacity $c$ scales as $\ell c^\beta$ for fixed $0<\beta<1$. Under appropriate standardization, the cost of the minimum cost Gilbert network grows essentially as $n^{\alpha(\beta)}$, where $\alpha(\beta) = 1 - \frac{\beta}{2}$ on $0 < \beta \leq {1/2}$ and $\alpha(\beta) = {1/2} + \frac{\beta}{2}$ on ${1/2} \leq \beta < 1$. This quantity is an upper bound in the worst case (of vertex positions), and a lower bound under mild regularity assumptions. Essentially the same bounds hold if we constrain the network to be efficient in the sense that average route-length is only $1 + o(1)$ times average straight line length. The transition at $\beta = {1/2}$ corresponds to the dominant cost contribution changing from short links to long links. The upper bounds arise in the following type of hierarchical networks, which are therefore optimal in an order of magnitude sense. On the large scale, use a sparse Poisson line process to provide long-range links. On the medium scale, use hierachical routing on the square lattice. On the small scale, link vertices directly to medium-grid points. We discuss one of many possible variant models, in which links also have a designed maximum speed $s$ and the cost becomes $\ell c^\beta s^\gamma$.Comment: 13 page

Effect of substrate thermal resistance on space-domain microchannel

In recent years, Fluorescent Melting Curve Analysis (FMCA) has become an almost ubiquitous feature of commercial quantitative PCR (qPCR) thermal cyclers. Here a micro-fluidic device is presented capable of performing FMCA within a microchannel. The device consists of modular thermally conductive blocks which can sandwich a microfluidic substrate. Opposing ends of the blocks are held at differing temperatures and a linear thermal gradient is generated along the microfluidic channel. Fluorescent measurements taken from a sample as it passes along the micro-fluidic channel permits fluorescent melting curves to be generated. In this study we measure DNA melting temperature from two plasmid fragments. The effects of flow velocity and ramp-rate are investigated, and measured melting curves are compared to those acquired from a commercially available PCR thermocycler

Direct measurements of OH and other product yields from the HO2 + CH3C(O)O2 reaction

The reaction CH3C(O)O2 + HO2 → CH3C(O)OOH+O2 (Reaction R5a), CH3C(O)OH+O3 (Reaction R5b), CH3+CO2+OH+O2 (Reaction R5c) was studied in a series of experiments conducted at 1000 mbar and (293±2)K in the HIRAC simulation chamber. For the first time, products, (CH3C(O)OOH, CH3C(O)OH, O3 and OH) from all three branching pathways of the reaction have been detected directly and simultaneously. Measurements of radical precursors (CH3OH, CH3CHO), HO2 and some secondary products HCHO and HCOOH further constrained the system. Fitting a comprehensive model to the experimental data, obtained over a range of conditions, determined the branching ratios α(R5a) = 0.37±0.10, α(R5b) =0.12±0.04 and α(R5c) =0.51±0.12 (errors at 2σ level). Improved measurement/model agreement was achieved using k(R5) =(2.4±0.4)×10-11 cm3 molecule-1 s-1, which is within the large uncertainty of the current IUPAC and JPL recommended rate coefficients for the title reaction. The rate coefficient and branching ratios are in good agreement with a recent study performed by Groß et al. (2014b); taken together, these two studies show that the rate of OH regeneration through Reaction (R5) is more rapid than previously thought. GEOS-Chem has been used to assess the implications of the revised rate coefficients and branching ratios; the modelling shows an enhancement of up to 5% in OH concentrations in tropical rainforest areas and increases of up to 10% at altitudes of 6-8 km above the equator, compared to calculations based on the IUPAC recommended rate coefficient and yield. The enhanced rate of acetylperoxy consumption significantly reduces PAN in remote regions (up to 30 %) with commensurate reductions in background NOx

Leaf Shapes and Venation Patterns

We present an analysis of leaf shapes and venation patterns based on a new assumption of the way how water flows in plants, together with the assumption that leaf shapes and leaf venation patterns have evolved in time such as to provide easier and easier access to its internal currents (Constructal Law). Then, by minimizing the global resistance to flow we anticipate the number of veins in relation to leaf shape (slenderness and vein insertion angle) and prevalent environmental conditions (represented by the potential for leaf water intake from the atmosphere). We also anticipate that leaves in dry climates will be slender and shorter, and with more veins as compared with those of plants adapted to wet environments. We finish by showing some cases in which the theory describes the characteristic of real leaves closely

Thermodynamic optimization of steady-flow industrial chemical processes

© 2018, The Author(s). Industrial steady-flow chemical processes are generally organised as a sequence of individually optimised operations. However, this may not achieve overall optimization since material (as recycle), heat and work transfers overall may not be well balanced. We introduce the idea of a preliminary overall thermodynamic balance to produce a reversible process, with the objective of minimising, for both economic and environmental reasons, the quality and quantity of energy used. This balance may later require adjustment to account for the realities of available materials and equipment. For this purpose, we introduce (i) a Carnot temperature, TCarnot, by which a Carnot machine (an engine which can operate as either a heat pump or a turbine) can supply the required heat at the correct temperature for a process to operate reversibly, that is with least energy, and (ii) the GH Diagram on which Carnot temperature-based processes are plotted in ?G–?H space. We demonstrate the utility of this analysis by simple application to the Haber–Bosch process for ammonia synthesis and by a sequence of operations for the synthesis of methanol. We also briefly introduce the state function exergy, which uses the natural environment as the reference base for energy in place of pure elements under standard conditions

Optimal Counter-current exchange networks

We present a general analysis of exchange devices linking their efficiency to the geometry of the exchange surface and supply network. For certain parameter ranges, we show that the optimal exchanger consists of densely packed pipes which can span a thin sheet of large area (an “active layer”), which may be crumpled into a fractal surface and supplied with a fractal network of pipes. We derive the efficiencies of such exchangers, showing the potential for significant gains compared to regular exchangers (where the active layer is flat), using parameters relevant to biological systems

Enhancing surface heat transfer by carbon nanofins: towards an alternative to nanofluids?

Background: Nanofluids are suspensions of nanoparticles and fibers which have recently attracted much attention because of their superior thermal properties. Nevertheless, it was proven that, due to modest dispersion of nanoparticles, such high expectations often remain unmet. In this article, by introducing the notion of nanofin, a possible solution is envisioned, where nanostructures with high aspect-ratio are sparsely attached to a solid surface (to avoid a significant disturbance on the fluid dynamic structures), and act as efficient thermal bridges within the boundary layer. As a result, particles are only needed in a small region of the fluid, while dispersion can be controlled in advance through design and manufacturing processes. Results: Toward the end of implementing the above idea, we focus on single carbon nanotubes to enhance heat transfer between a surface and a fluid in contact with it. First, we investigate the thermal conductivity of the latter nanostructures by means of classical non-equilibrium molecular dynamics simulations. Next, thermal conductance at the interface between a single wall carbon nanotube (nanofin) and water molecules is assessed by means of both steady-state and transient numerical experiments. Conclusions: Numerical evidences suggest a pretty favorable thermal boundary conductance (order of 107 W·m-2·K-1) which makes carbon nanotubes potential candidates for constructing nanofinned surface