Wax secretion in worker honeybees is significantly related to the age of the worker and, while the secretion pattern remains the same, the absolute amount of wax secreted varies seasonally. Comb building festoons, previously thought to be the site of wax secretion, contain only a fraction of the newly-secreted wax in the nest. Festooning behaviour was also found to be seasonal. The amount of wax secreted by workers was significantly affected by hive. Although age-related changes in behaviour and physiology of worker honeybees appears to be modulated by juvenile hormone (JH), wax secretion is not dependent on JH. Manipulating JH III titres by injecting the hormone and manipulating the only source of the hormone (the corpora allata: CA) did not affect wax secretion. Increasing haemolymph JH titre shortly after ec1osion did not affect the amount of wax produced by workers aged 3 to 21 days, nor could a critical period be found during which elevated hormone titres would affect the rate of wax secretion. Allatectomy of newly eclosed workers did not affect wax production. Removing the putative neural feedback inhibition on the CA did not result in a change in wax production. Implanting CA from older workers into younger workers had no significant effect. Methoprene, a widely-used JH analog, caused reduced wax secretion in workers. It is suggested that methoprene poisons worker honeybees. The results obtained are consistent with an alternative model for wax secretion proposed by Butler (1954). The methodological problems found in this work are present in many other studies. When viewed in this light, the role of JH in polyethism appears dubious and there are alternative models of polyethism that do not have these shortcomings.

The main aim of this project was to examine the effects of introducing hierarchy into honeycombs and determining the variables that preside over the global response of the structure. Specifically to understand how the in and out-of-plane elastic and non-linear plastic properties of honeycombs were affected by hierarchy. Analytical analysis of hierarchical honeycombs has been used to explain and predict the response of finite element simulations validated by experimental investigations. The early stage of the investigation focused on finding if the elastic modulus could be maintained or improved on an equal density basis due to the introduction of hierarchy. It is clear that honeycombs are sensitive to hierarchical sub-structures, particularly the fraction of mass shared between the super-and sub-structures. Introduction of an additional level of hierarchy without reducing performance is difficult, but was possible by functional grading. Another original result was that it was determined when the sub-structure could be assumed to be a continuum of the super-structure. Meaning the material properties from a single unit sub-cell could be used as the constituent material properties of the super-structure, as in previous work by (Lakes 1993) and (Carpinteri et al 2009) for example. Work investigating the in-plane, non-linear plastic response of hierarchical honeycombs showed that the introduction of hierarchy into honeycombs can have the effect of delaying the onset of elastic buckling, which is a common failure mechanism for low relative density structures. As such it was possible to achieve a marked increase in the recoverable energy absorbed by hierarchical honeycombs prior to elastic buckling or plastic yield. The potential benefits are less apparent in higher relative density structures due to the onset of plasticity becoming the first mode of failure. The out-of-plane properties also investigated showed no increase in the elastic properties due to the introduction of hierarchy, but showed a marked increase in the out-of-plane elastic buckling stress of 60% when compared to a conventional hexagonal honeycomb of the same relative density.

No description available.

Size effects in out-of-plane bending stiffness of honeycomb cellular materials were studied using analytical mechanics of solids modeling, fabrication of samples and mechanical testing. Analysis predicts a positive size-effect relative to continuum model predictions in the flexure stiffness of a honeycombed beam loaded in out-of-plane bending. A method of determining the magnitude of that effect for several different methods of constructing or assembling square-celled and hexagonal-celled materials, using both single-walled and doubled-walled construction methods is presented. Hexagonal and square-celled honeycombs, with varying volume fractions were fabricated in Nylon 12 using Selective Laser Sintering. The samples were mechanically tested in three-point and four point-bending to measure flexure stiffness. The results from standard three-point flexure tests, did not agree with predictions based on a mechanics of solids model for either square or hexagonal-celled samples. Results for four-point bending agreed with the mechanics of solids model for the square-celled geometries but not for the hexagonal-celled geometries. A closed form solution of an elasticity model for the response of the four-point bending configuration was developed, which allows interpretation of recorded displacement data at two points and allows separation the elastic bending from the localized, elastic/plastic deformation that occurs between the loading rollers and the specimen’s surface. This localized deformation was significant in the materials tested. With this analysis, the four-point bending data agreed well with the mechanics of solids predictions. / text

Ceramic cellular solids, mainly honeycombs and foams, are a novel class of composite materials where one phase is an interconnected network of solid struts or plates and the other one an empty phase or possibly a fluid. Honeycombs are an array of two dimensional prismatic cells whereas in foams the arrangements of cells are three dimensional polyhedral cells. Unlike solids, the properties of honeycombs are based on three major variables i.e. a) relative density (p* /p s where p* is the density of the cellular material and ps that of the solid of which it is made) b) cell wall material and c) geometry of the cells. Because of the flexibility in tailoring these variables, cellular solids can be engineered to exhibit a unique combination of mechanical and thermal properties for diversified thermostructural applications. Ceramic based honeycombs fabricated out of cordierite (2MgO.2Al2O35SiO2), mullite (3Al2O32SiO2), cordierite: mullite (2MgO.2Al2O35SiO2) with specific configurations are the leading candidates for many of the applications such as substrates for catalytic converters, molten metal filters, air heaters and heat exchangers etc. Zirconia by the virtue of its high fracture toughness and low thermal conductivity and high refractoriness is an interesting ceramic material and explored for versatile applications. However, no significant efforts have been reported to produce zirconia/alumina and their composite based honeycomb structures and also they have not been explored for their thermo-mechanical and energy absorption based applications. In the present study, looking at the possible potential applications of the honeycombs of Zirconia/alumina and their composites such as solid oxide fuel cells, high temperature filters, blast protection tiles etc., attempts are made to fabricate honeycomb structures. Chapter 1 of the thesis describes the detailed literature survey that has been carried out using advanced search packages regarding the evolution of ceramic honeycomb structures and their properties followed by the advantages of zirconia/alumina and their composites as candidate materials for targeted applications. Literature survey also covers the various processing techniques, characterization procedures with special emphasis on the thermo-mechanical properties. Chapter II describes attempts on developing an optimum scheme of processing of zirconia honeycomb which includes selection of precursor oxides, mixing of formulations, dough making based on viscosity measurements, shaping by extrusion, microwave drying, debinding and sintering to obtain the defect free monolithic structures keeping in view of the scale up possibilities. The chapter also describes a specially developed die fabrication process with innovative machining procedures. (Patent no. 198045). Sintered honeycombs were also characterized for their critical physiochemical properties. In chapter III mechanical characterization of honeycomb samples is reported after subjecting them to compression testing with varying cell channel orientation, compositions and configurations. It is observed that all honeycombs, irrespective of the composition and configuration exhibited anisotropic behavior. In addition, the anisotropy increases with the rib thickness and decreases with increase in the unit cell length. Thermal conductivity measurement studies of the honeycombs are reported in chapter IV. Two types of measurement techniques viz. laser diffraction and monotonic heating technique have confirmed the reduction of thermal conductivity of the honeycomb samples as compared to their solid counterpart. It is observed that the finer channel honeycombs offer low thermal conductivity as compared to the coarser channel when tested across the channel direction. For equivalent relative density, the thermal conductivity value for triangular channel is found to be more as compared to the square channel. Also, the thermal conductivity values were found less when measured across the channel as compared to the values when measured along the channels. The thermal conductivity value for fine channel zirconia-alumina composite honeycombs was found much less than the thermal conductivity of the alumina matrix. Chapter V summarises the implications of the study, conclusions and the target applications.

The thesis deals with moisture transport in porous medium of quartz sandstone. Capillary water and its movement is crucial for processes such as salt and frost weathering, growth of organisms and development of honeycombs and tafone. However, moisture transport is still not well described. I focused particularly on two new methods applied to sandstone investigation. In the laboratory I studied moisture transport in sandstone samples by means of repeated injection of uranine solution. I observed the evolution of evaporation front based on the changes in solution concentration indicated by difference in color of uranine solution. Additionally I investigated moisture content in the shallow subsurface of sandstone outcrops in the field using suction pressure and moisture content measurements by microtensiometers and TDR in three locations in the Bohemian Cretaceous Basin. Uranine proved to be an excellent tracer for visualization of the evaporation front geometry and its evolution in time. The results suggest that moisture transport is considerably affected by the presence of biofilms which are hydrophobic and retain moisture transport to surface. In addition, the values of suction pressure measured in honeycombs and a tafone are in agreement with the salt weathering model proposed by Huinink et al. (2004).

Aluminum hexagonal honeycombs loaded in their tubular direction have extremely good mechanical properties, including high stiffness to weight and energy absorption capacities. The corresponding load-displacement curve exhibits a long plateau accompanied by small fluctuations. These fluctuations are due to the propagation of a folding front through the studied sample, which is due to the creation of folds. This plateau load makes honeycombs the perfect candidates for use as energy-dissipative devices such as bumpers. Previous studies have largely focused on the study of the plateau load with less attention given to the length of the folds. However, it will be seen that this parameter is crucial for both the complete understanding of the mechanics of the folding and the derivation of the plateau load. We present first an introduction to the thematic of honeycomb. Then, the first model focuses precisely on the fold length. Two hypotheses are considered, a correlation between elastic buckling and folding first and a local propagation of the existing fold secondly. The second hypothesis is found to be correct, and the results are good for thin foils. For thick foils, a geometric limitation occurs, which makes the results less precise. Then, we are able to use the previous kinematics for the folding and derive a new set of formulas for the plateau load. The results are compared with experimental results and past formulas, and are found to be good, especially for thin foils, where our results for the fold length are more precise.

The main goal of this thesis was to find and compare salt-forming ions from samples of a subsurface zone of sandstone and other porous rocks. The surveyed samples came from different environments (humid and arid climate) from different locations in the Czech Republic, Jordan and the United States of America. Identification of various types of salt was based on evaluation of chemical analyzes of leached samples. Furthermore a laboratory experiment in which I used a fluorescein dye to observe the capillary rise and evaporation in unsaturated samples of sandstone was carried out. The salt content in the Czech Republic humid environment locations is generally lower than the one in foreign arid climate locations. Halit dominates in the locations Petra and Crystal Peak. In the other locations sulphate minerals dominate. The salts containing aluminum - alums were determined in the Czech Republic in the area of Czech Paradise and the surrounding. Relatively high concentrations of nitrate mineral nitratine were identified in the Devil's Pulpit location in Pilsen, the Czech Republic. From the observation of capillary rising experiments performed with artificially created honeycombs, I conclude that the height of the capillary rise is crucial for the transport of solution, and at a certain capillary height,...

<p dir="ltr">The natural honeycomb made from beeswax is an engineering marvel. Modern-day engineering has taken several inspirations from it in the form of hexagonal panels and cells made of various materials such as polymers, ceramics, and metals for light-weighting without compromising on its mechanical properties. Previously, characterizing this structure has relied on two-dimensional (2D) surface observations on the macroscale which have an inherently limited scope in understanding complex three-dimensional (3D) structures. As a result, several seminal features of the honeycomb that would have shed light on how it is constructed and what makes it so mechanically robust are left out of reach and overlooked. X-ray microscopy (XRM) is a powerful tool to characterize these complex structures non-destructively, yielding insights that are not possible without three-dimensional (3D) datasets. Further, when a time-resolved approach is adopted, where an external stimulus is interrupted for an XRM scan, one can obtain four-dimensional (4D) datasets. This provides unrivaled information on how complex 3D structures evolve over time when a stimulus is applied.</p><p dir="ltr">In this work, a time-resolved approach towards understanding how bees build out their hexagonal cells, both under normal and abnormal conditions was developed. Several previously unreported, but seminal features of the honeycomb such as the “coping” and porosity at well-defined locations yielded insights into how the comb is constructed. The corrugated spine is seen to be the foundation on which all hexagonal cells are built on. Additionally, this work also explores how bees accommodate distortions within the ordered lattice during the merger of two combs. Behaviorally they are seen to reduce the distortion within cells to minimize the wastage of wax and to keep the cells usable. A 3D parameter using automated image processing was developed to quantify how distortions are accommodated in an ordered lattice.</p><p dir="ltr">This work will further shed light on the mechanical behavior of the natural honeycomb arising from the corrugated nature of the spine and the gradient in its wall thickness which plays a role in crack deflection when the honeycomb is loaded under tension. When loaded under compression, the honeycomb lattice crumples in a manner to limit the damage to very local regions thereby forming a damage-tolerant crumple zone.</p>

Forms of cavernous weathering - tafoni and honeycombs - belong to long-term investigated and discussed phenomena in geology. The reason for the difference in size between few centimetres- long honeycombs and the several-metres-long tafoni has not been yet studied. In my master thesis I compared the hydraulic properties of rocks with developed honeycombs and tafoni. The research consists of field measurements (measurement of suction pressures and capillary water absorption using Karsten tube) and laboratory measurements on tafoni and honeycomb samples (retention curve measurement, capillary water absorption, water vapour diffusion rate and saturated hydraulic conductivity). I have been studing honeycombs from various sites in the Bohemian Cretaceous Basin and tafoni from three different sites: Carbon Arkoses near Kralupy nad Vltavou, Cambrian Sandstone in Petra (Jordan) and Tunnel Spring Tuff in Crystal Peak (Utah). The measurements showed that values of suction pressure are far higher inside tafoni than inside honeycombs. This observation corresponds to different retention curves of studied rocks: steeper retention curve for honeycomb's quartz sandstone than for fine-grained arkosic sandstones to arkoses with tafoni. In the other part of my research I have compared the properties of hydrophobic...