New scaling relation for information transfer in biological networks

We quantify characteristics of the informational architecture of two representative biological networks: the Boolean network model for the cell-cycle regulatory network of the fission yeast Schizosaccharomyces pombe (Davidich et al. 2008 PLoS ONE 3, e1672 (doi:10.1371/journal.pone.0001672)) and that of the budding yeast Saccharomyces cerevisiae (Li et al. 2004 Proc. Natl Acad. Sci. USA 101, 4781–4786 (doi:10.1073/pnas.0305937101)). We compare our results for these biological networks with the same analysis performed on ensembles of two different types of random networks: Erdös–Rényi and scale-free. We show that both biological networks share features in common that are not shared by either random network ensemble. In particular, the biological networks in our study process more information than the random networks on average. Both biological networks also exhibit a scaling relation in information transferred between nodes that distinguishes them from random, where the biological networks stand out as distinct even when compared with random networks that share important topological properties, such as degree distribution, with the biological network. We show that the most biologically distinct regime of this scaling relation is associated with a subset of control nodes that regulate the dynamics and function of each respective biological network. Information processing in biological networks is therefore interpreted as an emergent property of topology (causal structure) and dynamics (function). Our results demonstrate quantitatively how the informational architecture of biologically evolved networks can distinguish them from other classes of network architecture that do not share the same informational properties.     

The furrows of Rhinolophidae revisited

Rhinolophidae, a family of echolocating bats, feature very baroque noseleaves that are assumed to shape their emission beam. Zhuang & Muller (Zhuang & Muller 2006 Phys. Rev. Lett. 97, 218701 (doi:10.1103/PhysRevLett.97.218701); Zhuang & Muller 2007 Phys. Rev. E Stat. Nonlin. Soft Matter Phys. 76(Pt. 1), 051902 (doi:10.1103/PhysRevE.76.051902)) have proposed, based on finite element simulations, that the furrows present in the noseleaves of these bats act as resonance cavities. Using Rhinolophus rouxi as a model species, they reported that a resonance phenomenon causes the main beam to be elongated at a particular narrow frequency range. Virtually filling the furrows reduced the extent of the main lobe. However, the results of Zhuang & Muller are difficult to reconcile with the ecological background of R. rouxi. In this report, we replicate the study of Zhuang & Muller, and extend it in important ways: (i) we take the filtering of the moving pinnae into account, (ii) we use a model of the echolocation task faced by Rhinolophidae to estimate the effect of any alterations to the emission beam on the echolocation performance of the bat, and (iii) we validate our simulations using a physical mock-up of the morphology of R. rouxi. In contrast to Zhuang & Muller, we find the furrows to focus the emitted energy across the whole range of frequencies contained in the calls of R. rouxi (both in simulations and in measurements). Depending on the frequency, the focusing effect of the furrows has different consequences for the estimated echolocation performance. We argue that the furrows act to focus the beam in order to reduce the influence of clutter echoes.     

Air motion sensing hairs of arthropods detect high frequencies at near-maximal mechanical efficiency

Using measurements based on particle image velocimetry in combination with a novel compact theoretical framework to describe hair mechanics, we found that spider and cricket air motion sensing hairs work close to the physical limit of sensitivity and energy transmission in a broad range of relatively high frequencies. In this range, the hairs closely follow the motion of the incoming flow because a minimum of energy is dissipated by forces acting in their basal articulation. This frequency band is located beyond the frequency at which the angular displacement of the hair is maximum which is between about 40 and 600 Hz, depending on hair length (Barth et al. [1] Phil. Trans. R. Soc. Lond. B 340, 445–461 (doi:10.1098/rstb.1993.0084)). Given that the magnitude of natural airborne signals is known to decrease with frequency, our results point towards the possible existence of spectral signatures in the higher frequency range that may be weak but of biological significance.     

Quantification of the passive and active biaxial mechanical behaviour and microstructural organization of rat thoracic ducts

Mechanical loading conditions are likely to play a key role in passive and active (contractile) behaviour of lymphatic vessels. The development of a microstructurally motivated model of lymphatic tissue is necessary for quantification of mechanically mediated maladaptive remodelling in the lymphatic vasculature. Towards this end, we performed cylindrical biaxial testing of Sprague–Dawley rat thoracic ducts (n = 6) and constitutive modelling to characterize their mechanical behaviour. Spontaneous contraction was quantified at transmural pressures of 3, 6 and 9 cmH₂O. Cyclic inflation in calcium-free saline was performed at fixed axial stretches between 1.30 and 1.60, while recording pressure, outer diameter and axial force. A microstructurally motivated four-fibre family constitutive model originally proposed by Holzapfel et al. (Holzapfel et al. 2000 J. Elast. 61, 1–48. (doi:10.1023/A:1010835316564)) was used to quantify the passive mechanical response, and the model of Rachev and Hayashi was used to quantify the active (contractile) mechanical response. The average error between data and theory was 8.9 ± 0.8% for passive data and 6.6 ± 2.6% and 6.8 ± 3.4% for the systolic and basal conditions, respectively, for active data. Multi-photon microscopy was performed to quantify vessel wall thickness (32.2 ± 1.60 µm) and elastin and collagen organization for three loading conditions. Elastin exhibited structural ‘fibre families’ oriented nearly circumferentially and axially. Sample-to-sample variation was observed in collagen fibre distributions, which were often non-axisymmetric, suggesting material asymmetry. In closure, this paper presents a microstructurally motivated model that accurately captures the biaxial active and passive mechanical behaviour in lymphatics and offers potential for future research to identify parameters contributing to mechanically mediated disease development.     

Workshop on Measurement Needs for Local-Structure Determination in Inorganic Materials

The functional responses (e.g., dielectric, magnetic, catalytic, etc.) of many industrially-relevant materials are controlled by their local structure—a term that refers to the atomic arrangements on a scale ranging from atomic (sub-nanometer) to several nanometers. Thus, accurate knowledge of local structure is central to understanding the properties of nanostructured materials, thereby placing the problem of determining atomic positions on the nanoscale—the so-called “nanostructure problem”—at the center of modern materials development. Today, multiple experimental techniques exist for probing local atomic arrangements; nonetheless, finding accurate comprehensive, and robust structural solutions for the nanostructured materials still remains a formidable challenge because any one of these methods yields only a partial view of the local structure. The primary goal of this 2-day NIST-sponsored workshop was to bring together experts in the key experimental and theoretical areas relevant to local-structure determination to devise a strategy for the collaborative effort required to develop a comprehensive measurement solution on the local scale. The participants unanimously agreed that solving the nanostructure problem—an ultimate frontier in materials characterization—necessitates a coordinated interdisciplinary effort that transcends the existing capabilities of any single institution, including national laboratories, centers, and user facilities. The discussions converged on an institute dedicated to local structure determination as the most viable organizational platform for successfully addressing the nanostructure problem. The proposed “institute” would provide an intellectual infrastructure for local structure determination by (1) developing and maintaining relevant computer software integrated in an open-source global optimization framework (Fig. 2), (2) connecting industrial and academic users with experts in measurement techniques, (3) developing and maintaining pertinent databases, and (4) providing necessary education and training.Open in a separate windowFig. 2A schematic representation of the complex modeling idea: integration of combined inputs from multiple experimental techniques and theory into the global optimization framework [Billinge and Levin, unpublished]. In this concept, the structural model evolves toward the correct solution as more data is provided for the fit.     

A minimum of two distinct heritable factors are required to explain correlation structures in proliferating lymphocytes

During the adaptive immune response, lymphocyte populations undergo a characteristic three-phase process: expansion through a series of cell divisions; cessation of expansion; and, finally, most of the accumulated lymphocytes die by apoptosis. The data used, thus far, to inform understanding of these processes, both in vitro and in vivo, are taken from flow cytometry experiments. One significant drawback of flow cytometry is that individual cells cannot be tracked, so that it is not possible to investigate interdependencies in the fate of cells within a family tree. This deficit in experimental information has recently been overcome by Hawkins et al. (Hawkins et al. 2009 Proc. Natl Acad. Sci. USA 106, 13 457–13 462 (doi:10.1073/pnas.0905629106)), who reported on time-lapse microscopy experiments in which B-cells were stimulated through the TLR-9 receptor. Cells stimulated in this way do not aggregate, so that data regarding family trees can be recorded. In this article, we further investigate the Hawkins et al. data. Our conclusions are striking: in order to explain the familial correlation structure in division times, death times and propensity to divide, a minimum of two distinct heritable factors are necessary. As the data show that two distinct factors are necessary, we develop a stochastic model that has two heritable factors and demonstrate that it can reproduce the key features of the data. This model shows that two heritable factors are sufficient. These deductions have a clear impact upon biological understanding of the adaptive immune response. They also necessitate changes to the fundamental premises behind the tools developed by statisticians to draw deductions from flow cytometry data. Finally, they affect the mathematical modelling paradigms that are used to study these systems, as these are widely developed based on assumptions of cellular independence that are not accurate.     

Revisiting topological properties and models of protein–protein interaction networks from the perspective of dataset evolution

Protein–protein interaction (PPI) networks are crucial for organisms. Many research efforts have thus been devoted to the study on the topological properties and models of PPI networks. However, existing studies did not always report consistent results on the topological properties of PPI networks. Although a number of PPI network models have been introduced, yet in the literature there is no convincing conclusion on which model is best for describing PPI networks. This situation is primarily caused by the incompleteness of current PPI datasets. To solve this problem, in this study, the authors propose to revisit the topological properties and models of PPI networks from the perspective of PPI dataset evolution. Concretely, they used 12 PPI datasets of Arabidopsis thaliana and 10 PPI datasets of Saccharomyces cerevisiae from different Biological General Repository for Interaction Datasets (BioGRID) database versions, and compared the topological properties of these datasets and the fitting capabilities of five typical PPI network models over these datasets.Inspec keywords: proteins, molecular biophysics, microorganisms, cellular biophysicsOther keywords: topological properties, protein‐protein interaction networks, PPI network models, PPI dataset evolution, Arabidopsis thaliana, Saccharomyces cerevisiae, Biological General Repository‐for‐Interaction Datasets database, BioGRID database     

Experimental evaluation of the viscoelasticity of porcine vitreous

This study aims to estimate the material properties of the porcine vitreous while testing it in close to its natural physiological conditions. Eighteen porcine eyes were tested within 48 h post-mortem. A custom-built computer-controlled test rig was designed to support, load and monitor the behaviour of eye globes while being subjected to dynamic rotation cycles mimicking saccade eye movement. Specimens were glued to the base of a container, surrounded by gelatin, frozen and cut in half to expose the vitreous. After thawing, the container was subjected to concentric dynamic rotations of up to 5°, 10° or 15°, while taking 50 MP photos of the specimen every 2 ms. The images were analysed by a digital image correlation algorithm to trace the movement of marked points on the vitreous surface with different radii from the centre of the posterior chamber. The initial camera image was used in building a finite-element model of the test set-up, which was used in an inverse analysis exercise to estimate the material properties of the vitreous. Angular displacements of the monitored points were up to 3.3°, 4.1° and 3.9° in response to eye rotations of 5°, 10° and 15°, respectively. With the experimental relationships between eye rotation and angular displacements used as target behaviour, the inverse analysis exercise estimated the initial shear modulus, the long-term shear modulus and the viscoelastic decay constant of the porcine vitreous as 2.10 ± 0.15 Pa, 0.50 ± 0.04 Pa and 1.20 ± 0.09 s⁻¹, respectively. Consideration of the viscoelasticity of the vitreous was essential to represent its experimental behaviour. Testing the vitreous in close to its normal physiological conditions produced estimations of the initial shear modulus and long-term shear modulus that were, respectively, smaller and larger than reported values (Zimberlin et al. 2010 Soft Matter 6, 3632–3635. (doi:10.1039/b925407b), Liu et al. 2013 J. Biomech. 46, 1321–7. (doi:10.1016/j.jbiomech.2013.02.006), Rossi et al. 2011 Invest. Ophthalmol. Vis. Sci. 52, 3994–4002. (doi:10.1167/iovs.10-6477)).     

Modelling the layer-specific three-dimensional residual stresses in arteries,with an application to the human aorta

This paper provides the first analysis of the three-dimensional state of residual stress and stretch in an artery wall consisting of three layers (intima, media and adventitia), modelled as a circular cylindrical tube. The analysis is based on experimental results on human aortas with non-atherosclerotic intimal thickening documented in a recent paper by Holzapfel et al. ( Holzapfel et al. 2007 Ann. Biomed. Eng. 35, 530–545 (doi:10.1007/s10439-006-9252-z)). The intima is included in the analysis because it has significant thickness and load-bearing capacity, unlike in a young, healthy human aorta. The mathematical model takes account of bending and stretching in both the circumferential and axial directions in each layer of the wall. Previous analysis of residual stress was essentially based on a simple application of the opening-angle method, which cannot accommodate the three-dimensional residual stretch and stress states observed in experiments. The geometry and nonlinear kinematics of the intima, media and adventitia are derived and the associated stress components determined explicitly using the nonlinear theory of elasticity. The theoretical results are then combined with the mean numerical values of the geometrical parameters and material constants from the experiments to illustrate the three-dimensional distributions of the stretches and stresses throughout the wall. The results highlight the compressive nature of the circumferential stress in the intima, which may be associated with buckling of the intima and its delamination from the media, and show that the qualitative features of the stretch and stress distributions in the media and adventitia are unaffected by the presence or absence of the intima. The circumferential residual stress in the intima increases significantly as the associated residual deformation in the intima increases while the corresponding stress in the media (which is compressive at its inner boundary and tensile at its outer boundary) is only slightly affected. The theoretical framework developed herein enables the state of residual stress to be calculated directly, serves to improve insight into the mechanical response of an unloaded artery wall and can be extended to accommodate more general geometries, kinematics and states of residual stress as well as more general constitutive models.     

Protein abundance may regulate sensitivity to external cues in polarized cells

Cell polarization is a ubiquitous process which results in cellular constituents being organized into discrete intracellular spatial domains. It occurs in a variety of cell types, including epithelial cells, immune system cells and neurons. A key player in this process is the Par protein family whose asymmetric localization to anterior and posterior parts of the cell is crucial for proper division and cell fate specification. In this paper, we explore a stochastic analogue of the temporal model of Par protein interactions first developed in Dawes & Munro (Dawes and Munro 2011 Biophys. J. 101, 1412–1422. (doi:10.1016/j.bpj.2011.07.030)). We focus on how protein abundance influences the behaviour of both the deterministic and stochastic versions of the model. In Dawes & Munro (2011), it was found that bistable behaviour in the temporal model of Par protein led to the existence of complementary domains in the corresponding spatio-temporal model. Here, we find that the corresponding temporal stochastic model permits switching behaviour (the model solution ‘jumps’ between steady states) for lower protein abundances, whereas for higher protein abundances the stochastic and deterministic models are in good agreement (the model solution evolves to one of two steady states). This led us to the testable hypothesis that cells with lower abundances of Par protein may be more sensitive to external cues, whereas cells with higher abundances of Par protein may be less sensitive to external cues. In order to gain more control over the precise abundance of Par protein, we proposed and explored a second model (again, examining both deterministic and stochastic versions) in which the total number of Par molecules is conserved. We found that this model required an additional dimerization reaction in the cytoplasm in order for bistable and switching behaviour to be found. Once this additional reaction was included, we found that both the first and second models gave qualitatively similar results but in different regions of the parameter space, suggesting a further regulatory mechanism that cells could potentially use to modulate their response to external signals.     

Non-uniform breaking of molecular bonds,peripheral morphology and releasable adhesion by elastic anisotropy in bio-adhesive contacts

Biological adhesive contacts are usually of hierarchical structures, such as the clustering of hundreds of sub-micrometre spatulae on keratinous hairs of gecko feet, or the clustering of molecular bonds into focal contacts in cell adhesion. When separating these interfaces, releasable adhesion can be accomplished by asymmetric alignment of the lowest scale discrete bonds (such as the inclined spatula that leads to different peeling force when loading in different directions) or by elastic anisotropy. However, only two-dimensional contact has been analysed for the latter method (Chen & Gao 2007 J. Mech. Phys. Solids 55, 1001–1015 (doi:10.1016/j.jmps.2006.10.008)). Important questions such as the three-dimensional contact morphology, the maximum to minimum pull-off force ratio and the tunability of releasable adhesion cannot be answered. In this work, we developed a three-dimensional cohesive interface model with fictitious viscosity that is capable of simulating the de-adhesion instability and the peripheral morphology before and after the onset of instability. The two-dimensional prediction is found to significantly overestimate the maximum to minimum pull-off force ratio. Based on an interface fracture mechanics analysis, we conclude that (i) the maximum and minimum pull-off forces correspond to the largest and smallest contact stiffness, i.e. ‘stiff-adhere and compliant-release’, (ii) the fracture toughness is sensitive to the crack morphology and the initial contact shape can be designed to attain a significantly higher maximum-to-minimum pull-off force ratio than a circular contact, and (iii) since the adhesion is accomplished by clustering of discrete bonds or called bridged crack in terms of fracture mechanics terminology, the above conclusions can only be achieved when the bridging zone is significantly smaller than the contact size. This adhesion-fracture analogy study leads to mechanistic predictions that can be readily used to design biomimetics and releasable adhesives.     

Supercritical Antisolvent Process Applied to the Pharmaceutical Industry

Pharmaceutical preparations are the final product of a technological process that gives the drugs the characteristics appropriate for easy administration, proper dosage, and enhancement of the therapeutic efficacy. The design of pharmaceutical preparations in nanoparticulate form has emerged as a new strategy for drug delivery (Pasquali, Bettini, and Giordano, 2006 Pasquali , I. , R. Bettini , and F. Giordano . 2006 . Solid-state chemistry and particle engineering with supercritical fluids in pharmaceutics . Eur. J. Pharm. Sci. 27 : 299 – 310 .[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). Particle size (PS) and particle size distribution (PSD) are critical parameters that determine the rate of dissolution of the drug in the biological fluids and, hence, have a significant effect on the bioavailability of those drugs that have poor solubility in water, for which the dissolution is the rate-limiting step in the absorption process (Perrut, Jung, and Leboeuf, 2005 Perrut , M. , J. Jung , and F. Leboeuf . 2005 . Enhancement of dissolution rate of poorly-soluble active ingredients by supercritical fluid processes: Part I: Micronization of neat particles . Int. J. Pharm. 288 : 3 – 10 .[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]; Van Nijlen et al., 2003 Van Nijlen , T., G. Van Den Mooter , R. Kinget , P. Augustijns , N. Blaton , and K. Brennan . 2003 . Improvement of the dissolution rate of artemisinin by means of supercritical fluid technology and solid dispersions . Int. J. Pharm. 254 : 173 – 181 .[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]). Supercritical antisolvent (SAS) processes have been widely used to precipitate active pharmaceutical ingredients (APIs) (Chattopadhyay and Gupta, 2001 Chattopadhyay , P. , and R. B. Gupta . 2001 . Production of antibiotic nanoparticles using supercritical CO₂ as antisolvent with enhanced mass transfer . Ind. Eng. Chem. Res. 40 : 3530 – 3539 .[Crossref], [Web of Science ®] , [Google Scholar]; Rehman et al., 2001 Rehman , M. , B. Y. Shekunov , P. York , and P. Colthorpe . 2001 . Solubility and precipitation of nicotinic acid in supercritical carbon dioxide . J. Pharm. Sci. 90 : 1570 – 1582 .[Crossref], [PubMed], [Web of Science ®] , [Google Scholar]) with a high level of purity, suitable dimensional characteristics, narrow PSD, and spherical morphologies. The SAS process is based on the particular properties of the supercritical fluids (SCFs). These fluids have diffusivities two orders of magnitude larger than those of liquids, resulting in a faster mass transfer rate SCF properties (solvent power and selectivity) can be also adjusted continuously by altering the experimental conditions (temperature and pressure). As a consequence, SCFs can be removed from the process by a simple change from the supercritical to room conditions, which avoids difficult post-treatments of waste liquid streams. Carbon dioxide (CO₂) at supercritical conditions, among all possible SCFs, is largely used because of its relatively low critical temperature (31.1°C) and pressure (73.8 bar), low toxicity, and low cost. In this article, we show some results about processed antibiotics (ampicillin and amoxicillin), two of the world's most widely prescribed antibiotics, when they are dissolved in 1-methyl-2-pyrrolidone (NMP) and carbon dioxide is used as antisolvent.     

Designing an optimal water quality monitoring network for river systems using constrained discrete optimization via simulation

The problem of designing a water quality monitoring network for river systems is to find the optimal location of a finite number of monitoring devices that minimizes the expected detection time of a contaminant spill event while guaranteeing good detection reliability. When uncertainties in spill and rain events are considered, both the expected detection time and detection reliability need to be estimated by stochastic simulation. This problem is formulated as a stochastic discrete optimization via simulation (OvS) problem on the expected detection time with a stochastic constraint on detection reliability; and it is solved with an OvS algorithm combined with a recently proposed method called penalty function with memory (PFM). The performance of the algorithm is tested on the Altamaha River and compared with that of a genetic algorithm due to Telci, Nam, Guan and Aral (2009) Telci, I. T., K. Nam, J. Guan, and M.M. Aral, 2009. “Optimal Water Quality Monitoring Network Design for River Systems.” Journal of Environmental Management, 90 (3–4): 2987–2998. doi: 10.1016/j.jenvman.2009.04.011[Crossref], [PubMed], [Web of Science ®] , [Google Scholar].     

Prediction of Concentration Distribution in Pipeline Flow of Highly Concentrated Slurry

The Kaushal and Tomita's (2002a Kaushal , D. R. , and Y. Tomita . 2002a . An improved method for predicting pressure drop along slurry pipeline . Particulate Science and Technology 20 : 1 – 20 .[Taylor & Francis Online] , [Google Scholar]) model, which has already been found satisfactory for broadly graded multisized particulate zinc tailings slurry with moderate concentration up to 26%, flow velocity up to 3.5 m/s in 105 mm diameter pipe, mean diameter 140 μm, and geometric standard deviation of particles of 4.0, is tested for concentration distribution data collected by Kaushal et al. (2005 Kaushal , D. R. , K. Sato , T. Toyota , K. Funatsu , and Y. Tomita . 2005 . Effect of particle size distribution on pressure drop and concentration profile in pipeline flow of highly concentrated slurry . International Journal of Multiphase Flow. 31 : 809 – 823 .[Crossref], [Web of Science ®] , [Google Scholar]) on two sizes of glass beads, of which mean diameter and geometric standard deviation are 440 μm and 1.2, and 125 μm and 1.15, respectively, with concentration up to 50% and flow velocity up to 5 m/s in 54.9 mm diameter pipe. Kaushal and Tomita's (2002a) model gives more asymmetric concentration distributions. A modified model is proposed by alleviating some of the restrictive assumptions used in the existing model. Comparison of experimental data by Kaushal et al. (2005 Kaushal , D. R. , K. Sato , T. Toyota , K. Funatsu , and Y. Tomita . 2005 . Effect of particle size distribution on pressure drop and concentration profile in pipeline flow of highly concentrated slurry . International Journal of Multiphase Flow. 31 : 809 – 823 .[Crossref], [Web of Science ®] , [Google Scholar]), Gillies and Shook (1994 Gillies , R. G. , and C. A. Shook . 1994 . Concentration distributions of sand slurries in horizontal pipe flow . Particulate Science Technology 12 : 45 – 69 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]), and Matousek (2009 Matousek , V. 2009 . Concentration profiles and solids transport above stationary deposit in enclosed conduit . Journal of Hydraulic Engineering 135 : 1101 – 1106 .[Crossref], [Web of Science ®] , [Google Scholar]) with the proposed model is satisfactory.     

Lagrangian relaxation based heuristic for an integrated production and maintenance planning problem

In this paper, an approach is developed to solve the joint production planning and maintenance problem. Moreover, some propositions and mathematical properties were suggested and applied in the proposed heuristic to solve this integrated problem. It is based on Lagrangian relaxation (Fisher, M.L., 1981 Fisher, M.L. 1981. Lagrangian relaxation method for solving integer programming problem. Management Science, 27(1): 1–18. [Crossref], [Web of Science ®] , [Google Scholar]. Lagrangian relaxation method for solving integer programming problem. Management Science, 27 (1), 1–18) of the capacity constraints and sub-gradient optimisation. At every step of the sub-gradient method, a smoothing procedure is applied to the solution of the Lagrangian problem to ensure the feasibility of solution and to improve it. Computational experiments are carried out to show the results obtained by our approaches and are compared to those of a commercial solver.     

A local-effective relation in planar linear elasticity

We present a relation between local and effective properties for a class of two-dimensional elastic structures. The model considered is a periodic structure, which is locally isotropic and homogeneous. The corresponding physical model is a flat two-dimensional body with traction-free holes, such as a perforated plate. We show how the effective properties of the structure depend on the local properties in a way that separates the dependence on the holes. Our result extends a result of Vigdergauz [1 S. Vigdergauz, Complete elasticity solution to the stress problem in a planar grained structure, Math. Mech. Solids, vol. 4, no. 4, pp. 407–439, 1999.[Crossref], [Web of Science ®] [Google Scholar]], which describes how effective properties depend on local properties for effectively square symmetric structures, to the case when the effective elasticity tensor is allowed to be anisotropic.     

Base Pressure Measurements under a Scale Model Stockpile: Effects of Offset Reclaim Channels and Predictive Model Developments

It has been shown (McBride, 2006 McBride , W. 2006 . Base pressure measurements under a scale model stockpile . Part. Sci. Technol. 24 : 59 – 71 .[Taylor & Francis Online], [Web of Science ®] , [Google Scholar]) that under a scale model stockpile a central pressure dip, or ‘M’ pressure, is formed during both the filling and refilling processes of a stockpile containing a central reclaim channel. This article presents the results from further experiments with a noncentral reclaim channel and clearly illustrates that a central pressure dip exists under a conical stockpile with an offset reclaim channel. Additional data were recorded regarding lateral load transfer within the stockpile on initiation of flow, although more experimental work is required to fully understand this aspect. A method for predicting conical stockpile base pressures is presented along with an overpressure theory to account for the vertical load instability induced by the onset of material discharge.     

Social insect colony as a biological regulatory system: modelling information flow in dominance networks

Social insects provide an excellent platform to investigate flow of information in regulatory systems since their successful social organization is essentially achieved by effective information transfer through complex connectivity patterns among the colony members. Network representation of such behavioural interactions offers a powerful tool for structural as well as dynamical analysis of the underlying regulatory systems. In this paper, we focus on the dominance interaction networks in the tropical social wasp Ropalidia marginata—a species where behavioural observations indicate that such interactions are principally responsible for the transfer of information between individuals about their colony needs, resulting in a regulation of their own activities. Our research reveals that the dominance networks of R. marginata are structurally similar to a class of naturally evolved information processing networks, a fact confirmed also by the predominance of a specific substructure—the ‘feed-forward loop’—a key functional component in many other information transfer networks. The dynamical analysis through Boolean modelling confirms that the networks are sufficiently stable under small fluctuations and yet capable of more efficient information transfer compared to their randomized counterparts. Our results suggest the involvement of a common structural design principle in different biological regulatory systems and a possible similarity with respect to the effect of selection on the organization levels of such systems. The findings are also consistent with the hypothesis that dominance behaviour has been shaped by natural selection to co-opt the information transfer process in such social insect species, in addition to its primal function of mediation of reproductive competition in the colony.