Optimization of Patterned Surfaces for Improved Superhydrophobicity Through Cost-Effective Large-Scale Computations

The growing need for creating surfaces with specific wetting properties, such as superhyrdophobic behavior, asks for novel methods for their efficient design. In this work, a fast computational method for the evaluation of patterned superhyrdophobic surfaces is introduced. The hydrophobicity of a surface is quantified in energy terms through an objective function. The increased computational cost led to the parallelization of the method with the Message Passing Interface (MPI) communication protocol that enables calculations on distributed memory systems allowing for parametric investigations at acceptable time frames. The method is demonstrated for a surface consisting of an array of pillars with inverted conical (frustum) geometry. The parallel speedup achieved allows for low cost parametric investigations on the effect of the fine features (curvature and slopes) of the pillars on the superhydophobicity of the surface and consequently for the optimization of superhyrdophobic surfaces.Comment: 18 pages, 18 figure

Continuous Flow vs. Static Chamber μPCR Devices on Flexible Polymeric Substrates

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Two types of μPCR devices, a continuous flow and a static chamber device, fabricated on flexible polymeric substrates are compared in the current computational study. Laminar flow, heat transfer in both solid and fluid, mass conservation of species, and reaction kinetics of PCR are coupled using COMSOL. The comparison is performed under same conditions; same material stack (based on flexible polymeric films with integrated microheaters), same species initial concentrations, amplification of the same volume of fluid sample, and implementation of the same PCR protocol. Performance is quantified in terms of DNA amplification, energy consumption, and total operating time. The calculations show that the efficiency of DNA amplification is higher in the continuous flow device. However, the continuous flow device requires (~6 times) greater energy consumption which is justified by the smaller thermal mass of the static chamber device. As regards the speed, the total time required for the static chamber μPCR is comparable to the time for the continuous flow μPCR

A Passive Micromixer for Bioanalytical Applications

This paper was presented at the 4th Micro and Nano Flows Conference (MNF2014), which was held at University College, London, UK. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute, ASME Press, LCN London Centre for Nanotechnology, UCL University College London, UCL Engineering, the International NanoScience Community, www.nanopaprika.eu.Three passive micromixers with different geometries, i.e. zigzag, spiral, and split and merge (SaM) with labyrinthine channels, are compared with respect to their mixing efficiency by means of a computational study. The specifications are imposed from flexible printed circuit (FPC) technology which is used for their fabrication and from the applications to be implemented, i.e. the mixing of biochemical reagents. The computations include the numerical solution of continuity, Navier-Stokes, and mass conservation equations in 3d by ANSYS Fluent. The highest mixing efficiency is calculated for the SaM micromixer with the labyrinthine channel. Compared to a linear micromixer, the spiral micromixer improves the mixing efficiency by 8%, the zigzag by 11%, and the SaM by 92%; the diffusion coefficient of the biomolecule is 10-10 m2/s, the Reynolds number is 0.5, and the volume of each micromixer is 2.54 μl. The best of the three designs is realized by FPC technology and is experimentally evaluated by fluorescence microscopy

Fabrication and modeling of a continuous-flow microfluidic device for on-chip DNA amplification

This paper was presented at the 3rd Micro and Nano Flows Conference (MNF2011), which was held at the Makedonia Palace Hotel, Thessaloniki in Greece. The conference was organised by Brunel University and supported by the Italian Union of Thermofluiddynamics, Aristotle University of Thessaloniki, University of Thessaly, IPEM, the Process Intensification Network, the Institution of Mechanical Engineers, the Heat Transfer Society, HEXAG - the Heat Exchange Action Group, and the Energy Institute.The fabrication process and heat transfer computations for a continuous flow microfluidic device for DNA amplification by polymerase chain reaction (PCR) are described. The building blocks are thin polymeric materials aiming at a low cost and low power consumption device. The fabrication is performed by standard pattern transfer techniques (lithography and etching) used for microelectronics fabrication. The DNA sample flows in a meander shaped microchannel formed on a 100μm thick polyimide (PI) layer through three temperature regions defined by the integrated resistive heaters. The heat transfer computations are performed in a unit cell of the device. They show that, for the fabricated device, the variation of the temperature inside the channel zones where each step (denaturation, annealing, or extension) of PCR occur is less than 1.3K. This variation increases when the thickness of the PI layer increases. The computations also show that similar Silicon-based devices lead to lower temperature difference between the heaters and the DNA sample compared to the polymer-based fabricated device. However, the power consumption is estimated much greater for Silicon-based devices.This work was co-financed by Hellenic Funds and by the European Regional Development Fund (ERDF) under the Hellenic National Strategic Reference Framework (NSRF) 2007-2013, according to Contract no. MICRO2-45 of the Project “Microelectronic Components for Lab-on-chip molecular analysis instruments for genetic and environmental applications” within the Programme "Hellenic Technology Clusters in Microelectronics – Phase-2 Aid Measure"

Prevention of fish photobacteriosis. Comparison of the efficacy of intraperitoneally administered commercial and experimental vaccines

Two commercial multivalent vaccines against vibriosis, caused by Vibrio anguillarum serotype(s) and photobacteriosis, caused by Photobacterium damsela subsp. piscicida, one with oil adjuvant (AJ) and the other,being an aqueous solution (AV), and an experimental monovalent (Ph. damselae subsp. piscicida) vaccine inactivated with formalin or heat, namely EVF and EVH, were tested in laboratory trials on sea bass (Dicentrarchus labrax) in respect to their efficacy against experimentally induced photobacteriosis. The first trial aiming at high bacterial pressure was carried out 34 days post-vaccination and resulted in 90% mortalities in the control. The relative per cent survival (RPS) of vaccinated fish was calculated at 24, 3.7, 0 and 0 for the AJ, AV, EVF and EVH formulations, respectively. The second trial aiming at medium bacterial pressure was carried out 49 days post-vaccination and resulted in 45% mortalities in the control. The relative per cent survival (RPS) of vaccinated fish was calculated at 100, 92.7, 77.8 and 66.7 for the AJ, EVF, EVH and AV, formulations, respectively. Apparently, under both these high and medium bacterial pressure conditions, the commercial vaccine AJ performed better than the commercial vaccine AV, while under medium pressure there was no statistical difference between the performance of EVF and AJ. The measurement of specific antibody titers in sera collected from all fish groups 49 days post-vaccination, showed high levels in the fish vaccinated with the AJ vaccine, almost three times lower levels for the AV and EVF vaccines and even lower levels for the EVH vaccine. Results are discussed in respect to the choices mariculture companies have in selecting a commercial vaccine against photobacteriosis and possible alternatives, which, if commercially developed, may reduce vaccine cost

Ballistic and molecular dynamics simulations of aluminum deposition in micro-trenches

Two different feature scale modeling frameworks are utilized for the study of aluminum (Al) deposition profiles inside micro-trenches. The first framework, which is applied in metal-organic chemical vapor deposition (MOCVD) of Al, couples a ballistic model for the local flux calculation, a surface chemistry model, and a profile evolution algorithm. The calculated conformity of the deposited film is compared with experimental results corresponding to Al MOCVD from dimethylethylamine alane (DMEAA). The outcome of the comparison is that the effective sticking coefficient of DMEAA is in the range of 0.1 - 1. There is also a strong indication that surface reaction kinetics follows Langmuir - Hinshelwood or Eley - Rideal mechanism. The second framework, which is applied in physical vapor deposition of Al, implements 2D molecular dynamics (MD) simulations. The simulations are performed in a "miniaturized" domain of some hundreds of Angstroms and are used to explore micro-trench filling during magnetron sputtering deposition of Al on a rotated substrate. Most of the experimental results are qualitatively reproduced by the MD simulations; the rotation, aspect ratio, and kinetic energy effects are correctly described despite the completely different length scales of simulation and experiment. The sticking probability of Al is calculated 0.6 for the conditions of the experiments

POROUS SURFACES FOR DROPLET ACTUATION AND MOBILITY MANIPULATION USING BACKPRESSURE

In this study we explore the underlying mechanisms of droplet actuation and mobility manipulation, when backpressure is applied through a porous medium under a sessile pinned droplet. Momentum conservation and continuity equations along with the Cahn-Hilliard phase-field equations in a 2D computational domain are used to shed light on the on the droplet actuation and movement mechanisms. The droplet actuation mechanism entails depinning of the receding contact line and movement, by means of a forward wave propagation reaching on the front of the droplet. Eventually, the droplet is skipping forward

Interplay between r- and K-strategists leads to phytoplankton underyielding under pulsed resource supply

Fluctuations in nutrient ratios over seasonal scales in aquatic ecosystems can result in overyielding, a condition arising when complementary life-history traits of coexisting phytoplankton species enables more complete use of resources. However, when nutrient concentrations fluctuate under short-period pulsed resource supply, the role of complementarity is less understood. We explore this using the framework of Resource Saturation Limitation Theory (r-strategists vs. K-strategists) to interpret findings from laboratory experiments. For these experiments, we isolated dominant species from a natural assemblage, stabilized to a state of coexistence in the laboratory and determined life-history traits for each species, important to categorize its competition strategy. Then, using monocultures we determined maximum biomass density under pulsed resource supply. These same conditions of resource supply were used with polycultures comprised of combinations of the isolated species. Our focal species were consistent of either r- or K-strategies and the biomass production achieved in monocultures depended on their efficiency to convert resources to biomass. For these species, the K-strategists were less efficient resource users. This affected biomass production in polycultures, which were characteristic of underyielding. In polycultures, K-strategists sequestered more resources than the r-strategists. This likely occurred because the intermittent periods of nutrient limitation that would have occurred just prior to the next nutrient supply pulse would have favored the K-strategists, leading to overall less efficient use of resources by the polyculture. This study provides evidence that fluctuation in resource concentrations resulting from pulsed resource supplies in aquatic ecosystems can result in phytoplankton assemblages' underyielding

Plug actuation and active manipulation in closed monolithic fluidics using backpressure

We explore the mechanisms to actuate and manipulate liquid plugs in monolithic closed channel fluidics with porous hydrophobic walls. Applying a small pressure, as much as 10 mbar, from the rear side of the porous wall, hereafter backpressure, the inherently pinned plug is depinned and flows through downwards the fluidic. The method is reversible in that by removing the backpressure the plug sticks back again to the fluidic. 3D numerical simulations with the volume of fluid method, presented here for the first time, show that the velocity of the plug can be manipulated by adjusting the backpressure. The movement of the plug results from deformation – displacement phases which are observed in the simulation and are corroborated by experimental results, recorded inside fluidics. A simplified model based on measurements of back and front contact angles under backpressure is developed

Proposing a Governance model for environmental crises

During August 2021, a wildfire outbreak in Evia, Greece's second largest island, resulted in a major environmental and economic crisis. Apart from biodiversity and habitat loss, the disaster triggered a financial crisis because it wiped out wood-productive forests and outdoor areas that attract visitors. This crisis highlighted the need for a new governance model in order to respond to environmental crises more effectively. The aim of this study was to investigate the acceptance and attitudes of relevant stakeholders towards establishing a Hub a proposed governance model responsible for monitoring and restoring the natural capital and biodiversity after environmental crises. Results based on quantitative data collected via questionnaires showed that most respondents were positive to the Hub and perceived that its main functions should be to recommend measures after environmental crises and to facilitate cooperation among involved stakeholders. Moreover, results pointed to preferred funding sources, stakeholder groups that should participate in the Hub and key performance indicators (KPIs) for monitoring Hub's performance. The applied methodology could guide the establishment of governance models both in the study area and other countries facing environmental crises