Liquid marble formation using hydrophobic powders

This work aims to investigate and quantitatively measure “liquid marble” phenomena using hydrophobic powders (granules). The hydrophobic powders based on a copper substrate were prepared by a silver deposition technique of particle sizes 9 µm, 20 µm and 320 µm and of contact angle with water approaching 160°. The hydrophobic powder poly-methylmethacralate (PMMA) particle size 42 µm and contact angle of 120° was also used to determine the effect of powder density on liquid marble stability. The experimental investigations indicated that for successful formation of liquid marbles a number of variables in addition to hydrophobicity need to be considered, namely: powder density; powder particle size; powder shape; liquid marble formation technique. It was found that liquid marbles were formed using all four powders to varying extents, with a low powder particle size forming more stable liquid marbles. In a series of gravimetric tests, adhered powder mass on liquid marbles was found to be directly proportional to the water droplet surface area. A more complete coverage of the water drops were found with PMMA powder than the hydrophobic granules. Moreover, a further procedure was developed to increase the mechanical strength of the liquid marble, by polymerising methylmethacrylate (MMA) on the surface of a PMMA powder – liquid marble, with the aim of maintaining water within a more robust PMMA – liquid marble shell. This technique may prove to be a novel way of encapsulating drug compounds, such as gentamicin sulphate, for PMMA bone cement.

LIQUID MARBLES GRANULATED USING SUPER-HYDROPHOBIC METAL POWDERS

Superhydrophobic (SH) particles based on a copper substrate were prepared by a silver deposition technique of different particle sizes from 10µm to 425µm. Such SH particles were found to be pH-responsive and liquid marbles formed using the SH copper substrate destabilised under certain pH conditions. The exposure to high concentrations of acidic or basic gases caused immediate collapse of the liquid marble. However, low concentrations of acidic and basic gases could diffuse across the shell of liquid marbles without adversely affecting the structure. Liquid marbles formed with large SH particles (425
µm) did not fully form a mono-layer around the liquid droplet. This phenomenon, whereby SH particles slide down the surface of the water droplet until an equilibrium position is reached, was studied using a mathematical approach, which related the angle to the vertical axis of the SH particles at t
he equilibrium F, to the shape of liquid marble and the contact angle, ?.

Rocking behaviour of multi-block columns subjected to pulse-type ground motion accelerations

Ancient columns, made with a variety of materials such as marble, granite, stone or masonry are an important part of the
European cultural heritage. In particular columns of ancient temples in Greece and Sicily which support only the architrave are
characterized by small axial load values. This feature together with the slenderness typical of these structural members clearly
highlights as the evaluation of the rocking behaviour is a key aspect of their safety assessment and maintenance. It has to be noted
that the rocking response of rectangular cross-sectional columns modelled as monolithic rigid elements, has been widely investigated
since the first theoretical study carried out by Housner (1963). However, the assumption of monolithic member, although being
widely used and accepted for practical engineering applications, is not valid for more complex systems such as multi-block columns
made of stacked stone blocks, with or without mortar beds. In these cases, in fact, a correct analysis of the system should consider
rocking and sliding phenomena between the individual blocks of the structure. Due to the high non-linearity of the problem, the
evaluation of the dynamic behaviour of multi-block columns has been mostly studied in the literature using a numerical approach
such as the Discrete Element Method (DEM). This paper presents an introductory study about a proposed analytical-numerical
approach for analysing the rocking behaviour of multi-block columns subjected to a sine-pulse type ground motion. Based on the
approach proposed by Spanos (2001) for a system made of two rigid blocks, the Eulero-Lagrange method to obtain the motion
equations of the system is discussed and numerical applications are performed with case studies reported in the literature and with a
real acceleration record. The rocking response of single block and multi-block columns is compared and considerations are made
about the overturning conditions and on the effect of forcing function’s frequency.
.

The Terrace Structure: Trenches I, II and XV

The Settlement at Dhaskalio is the first volume in the series The Sanctuary on Keros: Excavations at Dhaskalio and Dhaskalio Kavos, 2006-2008, edited by Colin Renfrew, Olga Philaniotou, Neil Brodie, Giorgos Gavalas and Michael Boyd. Here the findings are presented from the well-stratified settlement of Dhaskalio, today an islet near the Cycladic island of Keros, Greece. A series of radiocarbon dates situates the duration of the settlement from around 2750 to 2300 BC. The volume begins with a discussion of the geological setting of Keros and of sea-level change, concluding that Dhaskalio was in the third millennium BC linked to Keros by a narrow causeway. The excavation and finds (excluding the pottery, discussed in later volumes) are fully documented, with consideration of stratigraphy, geomorphology, organic remains, and the evidence for metallurgy. It is concluded that there was a small permanent population of around 20, increased periodically by up to 400 visitors who would have participated in the rituals of deposition occurring at the Sanctuary at Kavos, situated opposite, on Keros itself, for which the detailed evidence (including abundant fragmented pottery, marble vessels and sculptures) will be presented in Volumes II and III