Myalgic encephalomyelitis/chronic fatigue syndrome (ME/CFS)

ME/CFS is a debilitating condition hardly discussed in the Maltese Islands, and was only recognized in 2009 as a neurological disease in our archipelago despite it being recognized by WHO in 1969. The authors discuss the origin of the combined terminology ME/CFS, the importance of recognizing the condition at an early stage, the appropriate treatment and the potential role of the health services. The authors also highlight the lack of official statistical data available in the Maltese archipelago.peer-reviewe

Multiple equilibria in a simple elastocapillary system

We consider the elastocapillary interaction of a liquid drop placed between two flexible sheets, which are both clamped at one end to a rigid substrate. This is a simple model system relevant to the problem of surface tension-induced collapse of flexible micro-channels that has been observed in the manufacture of microelectromechanical systems(MEMS). We determine the conditions under which the flexible sheets remain separated, touch at a point, or stick along a portion of their length. Surprisingly, we show that in many circumstances multiple equilibrium states are possible. We develop a lubrication-type model for the flow of liquid out of equilibrium and thereby investigate the stability of the multiple equilibria. We demonstrate that for given material properties two stable equilibria may exist and show through numerical solutions of the dynamic model that it is the initial state of the system that determines which stable equilibrium is reached by the system; the system does not simply choose the equilibrium state of lowest energy

Switch on, switch off: stiction in nanoelectromechanical switches

We present a theoretical investigation of stiction in nanoscale electromechanical contact switches. We develop a mathematical model to describe the deflection of a cantilever beam in response to both electrostatic and van der Waals forces. Particular focus is given to the question of whether adhesive van der Waals forces cause the cantilever to remain in the ‘ON’ state even when the electrostatic forces are removed. In contrast to previous studies, our theory accounts for deflections with large slopes (i.e. geometrically nonlinear). We solve the resulting equations numerically to study how a cantilever beam adheres to a rigid electrode: transitions between free, ‘pinned’ and ‘clamped’ states are shown to be discontinuous and to exhibit significant hysteresis. Our findings are compared to previous results from linearized models and the implications for nanoelectromechanical cantilever switch design are discussed

The Liquid Blister Test

We consider a thin elastic sheet adhering to a stiff substrate by means of the surface tension of a thin liquid layer. Debonding is initiated by imposing a vertical displacement at the centre of the sheet and leads to the formation of a delaminated region, or `blister'. This experiment reveals that the perimeter of the blister takes one of three different forms depending on the vertical displacement imposed. As this displacement is increased, we observe first circular, then undulating and finally triangular blisters. We obtain theoretical predictions for the observed features of each of these three families of blisters. The theory is built upon the F\"{o}ppl-von K\'{a}rm\'{a}n equations for thin elastic plates and accounts for the surface energy of the liquid. We find good quantitative agreement between our theoretical predictions and experimental results, demonstrating that all three families are governed by different balances between elastic and capillary forces. Our results may bear on micrometric tapered devices and other systems where elastic and adhesive forces are in competition.Comment: 23 pages, 11 figs approx published versio

A simple microscopic model for the dynamics of adhesive failure

We consider a microscopic model for the failure of soft adhesives in tension based on ideas of bond rupture under dynamic loading. Focusing on adhesive failure under loading at constant velocity, we demonstrate that bi-modal curves of stress against strain may occur due to effects of finite polymer chain or bond length and characterise the loading conditions under which such bi-modal behaviour is observed. The results of this analysis are in qualitative agreement with experiments performed on unconfined adhesives in which failure does not occur by cavitation.Comment: 11 pages, 5 figure

Metallurgy of armour exhibited at the Palace Armoury, Valletta, Malta

The metallurgy of ten armour pieces from the Palace Armoury Collection in Malta was examined. Results showed that out of ten artefacts examined, six were produced in low carbon steel, one from a high carbon steel and three were made from wrought iron. One of the wrought iron armour pieces was fabricated from a phosphoric iron, an unusual material for these artefacts. All the steel artefacts exhibited a ferrite-pearlite microstructure. In their manufacture, no attempts had been made at producing martensite by full or slack quenching. All metal fragments contained slag inclusions. The elongated nature of the latter suggested that these artefacts were forged into shape.peer-reviewe

The sensitivity of Graphene ‘Snap-through’ to substrate\ud geometry

We study theoretically the deposition of Few Layer Graphene sheets onto a grooved substrate incorporating adhesion between substrate and sheet. We develop a model to understand the equilibrium of the sheet allowing for partial conformation of sheet to substrate. This model gives new insight into recent observations of ‘snap-through’ from flat to conforming states and emphasizes the crucial role of substrate shape in determining the nature of this transition. Our analytical results are consistent with numerical simulations using a van der Waals-like interaction . Finally we propose a novel substrate shape that should exhibit a continuous, rather than ‘snap-through’, transition

Floating carpets and the delamination of elastic sheets

We investigate the deformation of a thin elastic sheet floating on a liquid surface and subject to a uniaxial compression. We show that at a critical compression the sheet delaminates from the liquid over a finite region forming a delamination ‘blister’. This blistering regime adds to the wrinkling and localized folding regimes that have been studied previously. The transition from wrinkled to blistered states occurs when delamination becomes energetically favourable compared to wrinkling. We determine the initial blister size and the evolution of blister size with continuing compression before verifying our theoretical results with experiments at a macroscopic scale

Indentation of ellipsoidal and cylindrical elastic shells

Thin shells are found in nature at scales ranging from viruses to hens’ eggs; the stiffness of such shells is essential for their function. We present the results of numerical simulations and theoretical analyses for the indentation of ellipsoidal and cylindrical elastic shells, considering both pressurized and unpressurized shells. We provide a theoretical foundation for the experimental findings of Lazarus et al. [Phys. Rev. Lett. (submitted)] and for previous work inferring the turgor pressure of bacteria from measurements of their indentation stiffness; we also identify a new regime at large indentation. We show that the indentation stiffness of convex shells is dominated by either the mean or Gaussian curvature of the shell depending on the pressurization and indentation depth. Our results reveal how geometry rules the rigidity of shells

The effect of a concentration-dependent viscosity on\ud particle transport in a channel flow with porous walls

We analyse the transport of a dilute suspension of particles through a channel with porous walls accounting for the concentration dependence of the viscosity. Two cases of leakage flow of fluid through the porous channel walls are studied: (i) constant flux, and (ii) dependent on the pressure drop across the wall. The effect of mixing the suspension first compared with point injection is examined by considering inlet concentration distributions of different widths. We find that a pessimal distribution width exists that maximizes the required hydrodynamic pressure for a constant fluid influx. We also show that the presence of an osmotic pressure may lead to fluid being sucked into the channel. We consider how the application of an external hydrodynamic pressure affects this observation and discuss the significance of our results for water filtration