Electrostatic enhancement of coalescence of water droplets in oil: A review of the current understanding

This paper reviews the current understanding of electrocoalescence of water droplets in oil, highlighting particularly the mechanisms proposed for droplet-droplet and droplet-interface coalescence under the influence of an applied electrostatic field, as well as various factors influencing the electrocoalescence phenomenon. Generally, the coalescence behaviour can be described in three stages: droplets approaching each other, the process of film thinning/drainage, and film rupture leading to droplet-droplet coalescence. Other possible mechanisms, such as droplet chain formation, dipole-dipole coalescence, electrophoresis, dielectrophoresis and random collisions, are also presented. Experimental work and mathematical modelling of the coalescence process are both reviewed, including various models, such as molecular dynamic simulation, random collision/coalescence modelling, and linear condensation polymerisation kinetics. The type of electric field, such as alternating, direct and pulsed direct current, plays a significant role, depending on the design and set-up of the system. The concept of an optimum frequency is also discussed here, relating to the electrode design and coating. Other factors, such as the average droplet size and the residence time of the liquid mixture exposed to the electric field, are highlighted relating to coalescence efficiency. The characteristics of the emulsion system itself determine the practicality of employing a high electric field to break the emulsion. Emulsions with high aqueous phase content tend to short-circuit the electrodes and collapse the electric field. Type and concentration of surface-active components have been shown to impart stability and rheological property changes to the interfacial film, thus making the coalescence mechanism more complicated. More investigations, both experimental and by computer simulation, should be carried out to study the electrocoalescence phenomenon and to contribute to the design and operation of new electrocoalescers

Bouncing of charged droplets : an explanation using mean curvature flow

Two oppositely charged droplets of (say) water in, e.g., oil or air, will tend to drift together under the influence of their charges. As they make contact, one might expect them to coalesce and form one large droplet, and this indeed happens when the charge difference is suffi- ciently small. However, Ristenpart et al. discovered a remarkable physical phenomenon whereby for large enough charge differentials, the droplets bounce off each other as they make contact. Explanations based on minimisation of area under a volume constraint have been proposed based on the premise that consideration of surface energy cannot be sufficient. However, in this letter we explain that on the contrary, the bouncing phenomenon can be completely explained in terms of energy, including an accurate prediction of the threshold charge differential between coalescence and bouncin

LAMP assay for the detection of the Asian citrus psyllid, Diaphorina citri Kuwayama (Hemiptera: Psylloidea: Psyllidae)

Abstract Diaphorina citri Kuwayama, also known as the Asian citrus psyllid (ACP), can vector the bacterium Candidatus Liberibacter asiaticus (CLas), agent of Huanglongbing (HLB): an incurable disease affecting citrus trees worldwide. In citrus growing regions where ACP and HLB are absent, such as Australia, the risk of an incursion and consequent economic damage to citrus industries make this psyllid one of the top-priority pests. Due to ACP’s small dimensions and the generally poorly studied native psylloid fauna worldwide, morphological identification of this insect to distinguish it from harmless species is challenging, especially in the field, and with immature, partial or damaged specimens. To allow rapid and efficient detection of ACP in the field, we designed and optimised a new Loop-mediated isothermal amplification (LAMP) assay for the detection of D. citri based on the mitochondrial 16S locus. The optimised ACP 16S LAMP assay produced amplification from D. citri samples within 13.3 ± 3.6 min, with an anneal derivative of ~ 78.5 °C. A synthetic gBlock gene fragment was also developed to be used as positive control for the new LAMP assay with a different anneal derivative of ~ 83 °C. An existing commercially available LAMP assay for detection of the bacterium CLas was also tested in this study on ACP DNA. The ACP 16S LAMP assay we developed and tested here provides a valuable new in-field compatible tool that can allow early detections of ACP, enabling a quick biosecurity response, and could potentially be adopted by a wide range of users, from farmers to agronomists and from researchers to industry

Australian species of spore-feeding Thysanoptera in the genera Carientothrips and Nesothrips (Thysanoptera : Idolothripinae)

The species from Australia in the genera Carientothrips and Nesothrips are reviewed and an illustrated key is provided. Carientothrips is distinguished based on the unusual form of the maxillary palps. Two species, badius Hood comb.n. and capricornis Mound comb.n., are transferred to Nesothrips from Carientothrips; and Nesothrips melinus Mound syn.n. is synonymised with Carientothrips miskoi Mound. In Carientothrips the following six new species are described: alienatus sp.n., calami sp.n., horni sp.n., palumai sp.n., snowi sp.n., tasmanica sp.n.; while flavitibia Moulton stat.rev. is recalled from synonymy with C. mjobergi (Karny). In Nesothrips four new species are described: barrowi sp.n., brigalowi sp.n., coorongi sp.n., rossi sp.n.; while rhizophorae (Girault) syn.n. is placed as a synonym of minor Bagnall

LAMP (Loop-mediated isothermal amplification) assay for rapid identification of Varroa mites

Abstract Varroa mites are serious pests of European honeybees (Apis mellifera). For detection of Varroa mite, a new molecular LAMP-based assay has been developed, which retains the body of the mite intact for morphological identification. Six novel Varroa LAMP primers were designed from existing DNA sequences of the COI locus to target V. destructor and V. jacobsoni, providing the ability to tell them apart from other non-target beehive associated mite and insect species. This LAMP assay is specific in detecting these Varroa species and has been tested on specimens originating from multiple countries. It produces amplification of V. destructor and V. jacobsoni in 16 ± 3.4 min with an anneal derivative of 78 ± 0.5 °C whilst another Varroa species,V. underwoodi, showed late amplification. A gBlock gene fragment, used here as a positive control has a different anneal derivative of 80 °C. Three non-destructive DNA extraction methods (HotShot, QuickExtract and Xtract) were tested and found to be suitable for use in the field. The LAMP assay was sensitive to very low levels of Varroa DNA, down to 0.24 picogram (~ 1 × 10 copies/µL of Varroa gBlock). This is a new molecular tool for rapid and accurate detection and identification of Varroa mites for pest management, in areas where these mites do not occur

Propylene Glycol and Non-Destructive DNA Extractions Enable Preservation and Isolation of Insect and Hosted Bacterial DNA

Plant bio-protection and biosecurity programs worldwide use trap-based surveillance for the early detection of agricultural pests and pathogens to contain their incursions and spread. This task is reliant on effective preservation in insect traps, which is required to maintain specimen quality for extended periods under variable environmental conditions. Furthermore, with traditional morphological examinations now increasingly paired with modern molecular diagnostic techniques, insect traps are required to preserve both the specimens’ morphology and the DNA of insects and vectored bacterial pathogens. Here, we used psyllids (Hemiptera) and their hosted bacteria as a model to test the preservative ability of propylene glycol (PG): a non-flammable, easily transportable preservative agent that could be used in pitfall, suction or malaise traps. We tested preservation using various PG concentrations, at different temperatures and for multiple time periods, paired with non-destructive DNA extraction methods, which allow isolation of both insect and arbobacterial DNA while retaining a morphological voucher of the insect host specimens. PG concentrations between 40% and 100% performed best for both insect and bacterial DNA preservation up to 28 days. Ultimately, given the viscous nature of PG at high concentrations, we recommend using it at a concentration between 40% and 60% to enable insects to sink into the solution, thus enhancing DNA preservation