A truly bioinspired approach to design optimization should follow the energetically favorable natural paradigm of “minimum inventory with maximum diversity”. This study was inspired by constructive ...regression of trabecular bone – a natural process of network connectivity optimization occurring early in skeletal development. During trabecular network optimization, the original excessively connected network undergoes incremental pruning of redundant elements, resulting in a functional and adaptable structure operating at lowest metabolic cost. We have recapitulated this biological network topology optimization algorithm by first designing in silico an excessively connected network in which elements are dimension-independent linear connections among nodes. Based on bioinspired regression principles, least-loaded connections were iteratively pruned upon simulated loading. Evolved networks were produced along this optimization trajectory when pre-set convergence criteria were met. These biomimetic networks were compared to each other, and to the reference network derived from mature trabecular bone. Our results replicated the natural network optimization algorithm in uniaxial compressive loading. However, following triaxial loading, the optimization algorithm resulted in lattice networks that were more stretch-dominated than the reference network, and more capable of uniform load distribution. As assessed by 3D printing and mechanical testing, our heuristic network optimization procedure opens new possibilities for parametric design.
Display omitted
•This is a bioinspired optimization algorithm to design 3D lattice structures.•The optimized network is a scale- and material-independent design blueprint.•Properties of a developing trabecular bone network are simulated and replicated.•Iterative network topology optimization can target different convergence criteria.•Mechanical behavior of optimized networks can be fine-tuned by parametric embodiment.
Optical instruments have proved invaluable in the study of suspended matter in the sea but the measurements they provide are more closely related to the cross-sectional area of the particles in ...suspension than the mass measured by filtration or predicted by theory. In this paper, we examine the factors controlling the relationship between particle area and mass, using the fractal model of particle structure as a theoretical framework. Both theory and observation agree that the area-to-mass ratio of particles (symbol A*) decreases with increasing fractal dimension (symbol Nf) as particles hide behind each other in compact flocs. The equation A* = 0.253–0.081Nf, in which A* is in m2 g−1 explains 81% of the variance in the area:mass ratio at 151 stations in coastal waters. In contrast, the effect of floc size on A* is small. Three optical parameters – beam attenuation, diffuse attenuation and remote sensing reflectance, expressed per unit mass of suspended material, all decrease with increasing Nf. As our understanding of the flocculation process grows and it becomes possible to predict the fractal dimension of particles as a function of the environmental conditions in which the flocs form, these results will lead to improved calibration of optical instruments in terms of the mass concentration of suspended materials and to better models of sediment suspension and transport.
The first measurements of the d(gamma,p)n differential cross section at forward angles and photon energies above 4 GeV were performed at the Thomas Jefferson National Accelerator Facility (JLab). The ...results indicate evidence of an angular dependent scaling threshold. Results at straight theta(cm) = 37 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 4 GeV, while those at 70 degrees are consistent with the constituent counting rules for E(gamma) greater, similar 1.5 GeV.
Populations of the mayfly Cloeon dipterum from 48 ponds (3000 l fibre-glass tanks of 1 m depth) were monitored over the course of 1 year. To simulate possible patterns of climatic change, the ponds ...were subject to three temperature treatments: continuous heating to 3 °C above ambient; heating to 3 °C above ambient during the summer only; and no heating. Further experimental complexity included enhanced nutrient input into the ponds and the presence or absence of fish, giving a factorial combination of 3 temperature regimes × 2 nutrient levels × presence/absence of fish predation. Few nymphs were found in the presence of fish. Where fish were absent, the temperature treatments did not significantly affect nymph abundances, and only marginally influenced mean nymph body-lengths. In contrast, the nutrient treatment had significant effects on both nymph abundance and size, with greater numbers of generally larger nymphs occurring in those fish-free ponds receiving additional nutrients. Adult emergence began earlier in the year from the heated ponds, particularly those ponds receiving additional nutrients. Adult body-length differed between temperature treatments, but consistent patterns were difficult to ascertain because of interactions with nutrient treatment and seasonal effects. Our results show that during the short term at least, elevated temperature as a simulation of climate change does not have an overwhelming influence on either mayfly abundance or size. The influence of temperature is subtle and subject to complex interaction with other habitat variables. We therefore suggest that the direct consequences of small changes in temperature will likely be of little significance to C. dipterum, relative to indirect effects operating through interactions with predation and nutrient input.PUBLICATION ABSTRACT
Invertebrate offspring are usually larger in colder environments. To test for possible effects of covariates (e.g. maternal phenotype and feeding conditions) on this pattern, we performed a ...laboratory experiment to look at the effect of temperature on newborn weight in the planktonic crustacean Daphnia magna. Three temperatures (12 °C, 16 °C and 22 °C) and two food levels (10,000 cells ml-1and 150,000 cells ml-1) were used, and offspring were examined from the first five clutches of mothers that had been maintained under the constant experimental conditions for three generations. Preliminary analysis suggested that newborn weight was significantly affected by temperature although patterns in the data were not clear cut. In addition, the covariates mother weight and clutch size were positively and negatively correlated with newborn weight, respectively; and later clutches tended to contain heavier offspring. Therefore, in an effort to control for the effects of the covariates, repeated-measures analysis of covariance was performed using ratio values of newborn weight/mother weight (relative newborn weight) as the dependent variable, clutch size as the covariate and clutch number as the repeated measures term. Now, temperature as a main effect in an ANCOVA model did not significantly influence relative newborn weight. The repeated-measure term clutch number also became nonsignificant, indicating that when differences in mother weight due to age were accounted for there were no overall differences in relative newborn weight between clutches from a particular mother. Temperature effects on relative newborn weight were only significant as part of interaction terms with food concentration and with clutch number. Thus there were different weight responses to temperature within food levels, and between clutch numbers within food levels. Under the low-food conditions newborn were heaviest at 16 °C, lightest at 12 °C and intermediate at 22 °C. Conversely, under the high-food condition newborn were lightest at 16 °C, heaviest at 12 °C and again intermediate at 22 °C. However, newborn tended to be heavier under the low food condition, and food concentration was highly significant as a main effect. Mother growth rate showed no significant relationship with newborn weight. It is concluded that direct temperature effects on relative newborn weight are marginal and nonsignificant. Temperature effects through interactions with food concentration and clutch number are important determinants of newborn weight, but relatively speaking account for only a small proportion of observed variance in newborn weight (25%), compared with the direct effect of food concentration (67%).
This paper examines relationships between the inherent optical properties (IOPs) of the Irish Sea and concentrations of optically significant constituents, measured as chlorophyll (Chl), mineral ...suspended solids (MSS) and coloured dissolved organic material (CDOM). In situ measurements of IOPs at 98 stations fell into two groups with distinct characteristics. Instances include the ratio of particulate backscattering to non-water absorption at 676
nm (
b
bp676/
a
n676), the ratio of the non-water absorption coefficients at 440
nm and 676
nm (
a
n440/
a
n676) and the ratio of particulate scattering to non-water absorption (
b
p/
a
n) at 676
nm. The two groups showed corresponding differences in the proportions of their constituent concentrations with Chl/MSS values typically above 0.4
mg
g
−1 for stations with
b
bp676/
a
n676
<
0.33 and below 0.4
mg
g
−1 for stations with
b
bp676/
a
n676
>
0.33. CDOM concentrations showed no significant differences between groups. The occurrence of correlated groups in the IOP and constituent concentration data indicates the existence of identifiable sub-types of coastal water within the conventional Case 2 classification whose optical characteristics were dominated either by phytoplankton or suspended minerals. By applying linear regression analysis to the two groups we derived effective material-specific IOPs for these natural particle assemblages. The coefficients obtained enabled the successful reconstruction of total absorption, scattering and backscattering coefficients for a given water body from measurements of Chl, MSS and CDOM. This procedure may be useful for assimilating measurements of seawater composition into bio-optical models in shelf seas.
Osteopontin (OPN) is an extracellular matrix protein found in bones and teeth, where it accumulates at matrix-matrix interfaces. We postulate that OPN interacts homotypically and heterotypically in ...the adhesion of apposing matrices. Using suspensions of OPN-coupled aldehyde/sulfate latex spheres, we measured the strength of homotypic OPN-OPN binding in vitro. Doublets formed through shear-induced collisions in a cone and plate rheoscope were subjected to shear stresses >0.6 Nm(-2) and the fraction broken up determined over 60 s. Rapid initial breakup of 35% of doublets was followed by very slow breakup of the remaining 65%. Monte Carlo simulation of the breakup kinetics pointed to the existence of low and high bond strength populations of doublets. Dynamic light scattering spectroscopy of soluble OPN showed that 27% by mass existed as dimers. We postulate that OPN dimers binding to monomers account for the low strength bonds since a strong bond has already formed between the molecules of the dimer. In contrast, OPN-OPN monomer bonds had higher tensile strength than bonds between the high-affinity interaction of IgG and protein G, previously studied. Antibody blocking studies showed that the self-binding region of OPN resides in the C-terminus. These data suggest that homotypic OPN-OPN bonds have physiologically significant strength, supporting the hypothesis that OPN-OPN binding and self-assembly participate in adhesion within mineralized tissues.
The eggshell is a highly ordered structure resulting from the deposition of calcium carbonate and an organic matrix from the acellular uterine fluid. Characterization of the individual matrix ...components is necessary to determine their influence upon calcite crystal shape, size, and orientation during eggshell calcification. We have purified and sequenced a novel 32-kDa protein, ovocalyxin-32 (OCX-32), which is present at high levels in the uterine fluid during the terminal phase of eggshell formation, and is localized predominantly in the outer eggshell. Database searches identified expressed sequence tags (ESTs) whose alignment yielded the complete cDNA. OCX-32 protein possesses limited identity (32%) to two unrelated proteins: latexin, a carboxypeptidase inhibitor expressed in rat cerebral cortex and mast cells, and to a skin protein that is encoded by a retinoic acid receptor-responsive gene, TIG1. The timing of OCX-32 secretion into the uterine fluid suggests that it may play a role in the termination of mineral deposition.
PDF
