A Lagrangian kinetic model for collisionless magnetic reconnection

A new fully kinetic system is proposed for modeling collisionless magnetic reconnection. The formulation relies on fundamental principles in Lagrangian dynamics, in which the inertia of the electron mean flow is neglected in the expression of the Lagrangian, rather then enforcing a zero electron mass in the equations of motion. This is done upon splitting the electron velocity into its mean and fluctuating parts, so that the latter naturally produce the corresponding pressure tensor. The model exhibits a new Coriolis force term, which emerges from a change of frame in the electron dynamics. Then, if the electron heat flux is neglected, the strong electron magnetization limit yields a hybrid model, in which the electron pressure tensor is frozen into the electron mean velocity.Comment: 15 pages, no figures. To Appear in Plasma Phys. Control. Fusio

Quantitative Imaging of Protein-Protein Interactions by Multiphoton Fluorescence Lifetime Imaging Microscopy using a Streak camera

Fluorescence Lifetime Imaging Microscopy (FLIM) using multiphoton excitation techniques is now finding an important place in quantitative imaging of protein-protein interactions and intracellular physiology. We review here the recent developments in multiphoton FLIM methods and also present a description of a novel multiphoton FLIM system using a streak camera that was developed in our laboratory. We provide an example of a typical application of the system in which we measure the fluorescence resonance energy transfer between a donor/acceptor pair of fluorescent proteins within a cellular specimen.Comment: Overview of FLIM techniques, StreakFLIM instrument, FRET application

Narrating resistant citizenships through two pandemics

Covid has intensified inequalities in the UK, particularly for those already living with structural disadvantage, and despite community and popular resistance to those losses. Covid has also disproportionately affected people with HIV, especially those already living with multi-dimensional inequalities. However, many people with HIV have, as they have done before, made strong and often successful efforts to resist and to restore or reconstruct their citizenships, in opposition to dominant, dispossessing discourses during Covid times. A narrative approach offers a means of mapping these citizenly technologies. This article draws on a 2020 study conducted with 16 people living with HIV in the UK. The study explored, through telephone semi-structured interviews, the health, economic, and psychosocial resources with which these participants lived with HIV and how Covid has impacted those resources. Narrative analysis showed losses of HIV and other health resources, constituting reductions in health citizenship, resisted largely by reconstitutions of alternatives within the HIV sector; losses of economic citizenship, despite oppositional, anti-political attempts to retain it, and of psychosocial citizenship, in spite of family and friendship networks; resistant, ‘alter’ development of renewed HIV citizenships; and across fields, resistance by complaint. This study indicates that ‘de-citizening’ citizenship losses are likely to also affect other groups with long-term conditions, illnesses, and disabilities. Resistant ‘re-citizening’ technologies, while important, had limited effects. The study suggests potential future resistant effects of repeated ‘complaint’ about Covid-era citizenship losses, and the more general significance of histories of dissent for future effective resistance

A simple interpretation of quantum mirages

In an interesting new experiment the electronic structure of a magnetic atom adsorbed on the surface of Cu(111), observed by STM, was projected into a remote location on the same surface. The purpose of the present paper is to interpret this experiment with a model Hamiltonian, using ellipses of the size of the experimental ones, containing about 2300 atoms. The charge distribution for the different wavefunctions is analyzed, in particular, for those with energy close to the Fermi energy of copper Ef. Some of them show two symmetric maxima located on the principal axis of the ellipse but not necessarily at the foci. If a Co atom is adsorbed at the site where the wavefunction with energy $E_F$ has a maximum and the interaction is small, the main effect of the adsorbed atom will be to split this particular wavefunction in two. The total charge density will remain the same but the local density of states will present a dip at Ef at any site where the charge density is large enough. We relate the presence of this dip to the observation of quantum mirages. Our interpretation suggests that other sites, apart from the foci of the ellipses, can be used for projecting atomic images and also indicates the conditions for other non magnetic adsorbates to produce mirages.Comment: 3 pages, 3 Fig

Under pressure: Psychological perspectives on letterpress, craft and well-being

12 months embargo appliedAbstract Arts and crafts are widely considered to be psychologically beneficial. Letterpress, as a traditional method of printing, was made redundant by computers in the later twentieth century but has enjoyed a 'rebirth' in recent years. There are a growing number of independent presses, and universities who are recognizing its potential as a pedagogical tool. As a printing method, it is no longer a necessity, so what is its role going forward? The techniques are not lost, but their value has changed. As a craft, letterpress has several distinctive qualities, particularly when compared to digital alternatives. When working with letterpress, students are no longer alone at their desks. Rather, the letterpress workshop is a social, communal space. In this article we reflect on the resurgence of letterpress as a celebration of culture and heritage: a coming together of like-minded individuals in a community of action. What is the value of enabling students to immerse themselves in letterpress, and what are the effects of this immersion on the practitioner and their well-being? There is a shift in focus of letterpress from output ‐ mass-produced printed media ‐ to process. We analyse the unique qualities of this process ‐ its physicality, the restrictions it imposes and the latitude it allows ‐ and explore links to mental and physical health and well-being. This position paper explores the practical, conceptual and emotional dimensions of letterpress as a craft. It draws upon personal reflection, observation and anecdotal accounts collected over years of teaching (V. S.), while offering psychological perspectives on the links between letterpress, craft and well-being (S. R. H.).</jats:p

Plasma Heating Simulation in the VASIMR System

The paper describes the recent development in the simulation of the ion-cyclotron acceleration of the plasma in the VASIMR experiment. The modeling is done using an improved EMIR code for RF field calculation together with particle trajectory code for plasma transport calculat ion. The simulation results correlate with experimental data on the p lasma loading and predict higher ICRH performance for a higher density plasma target. These simulations assist in optimizing the ICRF anten na so as to achieve higher VASIMR efficiency

Genome analysis of Clostridium difficile PCR ribotype 014 lineage in Australian pigs and humans reveals a diverse genetic repertoire and signatures of long-range interspecies transmission

Clostridium difficile PCR ribotype (RT) 014 is well-established in both human and porcine populations in Australia, raising the possibility that C. difficile infection (CDI) may have a zoonotic or foodborne etiology. Here, whole genome sequencing and high-resolution core genome phylogenetics were performed on a contemporaneous collection of 40 Australian RT014 isolates of human and porcine origin. Phylogenies based on MLST (7 loci, STs 2, 13, and 49) and core orthologous genes (1260 loci) showed clustering of human and porcine strains indicative of very recent shared ancestry. Core genome single nucleotide variant (SNV) analysis found 42 % of human strains showed a clonal relationship (separated by ≤ 2 SNVs in their core genome) with one or more porcine strains, consistent with recent inter-host transmission. Clones were spread over a vast geographic area with 50 % of the human cases occurring without recent healthcare exposure. These findings suggest a persistent community reservoir with long-range dissemination, potentially due to agricultural recycling of piggery effluent. We also provide the first pan-genome analysis for this lineage, characterizing its resistome, prophage content, and in silico virulence potential. The RT014 is defined by a large “open” pan-genome (7587 genes) comprising a core genome of 2296 genes (30.3 % of the total gene repertoire) and an accessory genome of 5291 genes. Antimicrobial resistance genotypes and phenotypes varied across host populations and ST lineages and were characterized by resistance to tetracycline [tetM, tetA(P), tetB(P) and tetW], clindamycin/erythromycin (ermB), and aminoglycosides (aph3-III-Sat4A-ant6-Ia). Resistance was mediated by clinically important mobile genetic elements, most notably Tn6194 (harboring ermB) and a novel variant of Tn5397 (harboring tetM). Numerous clinically important prophages (Siphoviridae and Myoviridae) were identified as well as an uncommon accessory gene regulator locus (agr3). Conservation in the pathogenicity locus and S-layer correlated with ST affiliation, further extending the concept of clonal C. difficile lineages. This study provides novel insights on the genetic variability and strain relatedness of C. difficile RT014, a lineage of emerging One Health importance. Ongoing molecular and genomic surveillance of strains in humans, animals, food, and the environment is imperative to identify opportunities to reduce the overall CDI burden

Capture of particles of dust by convective flow

Interaction of particles of dust with vortex convective flows is under theoretical consideration. It is assumed that the volume fraction of solid phase is small, variations of density due to nonuniform distribution of particles and those caused by temperature nonisothermality of medium are comparable. Equations for the description of thermal buoyancy convection of a dusty medium are developed in the framework of the generalized Boussinesq approximation taking into account finite velocity of particle sedimentation. The capture of a cloud of dust particles by a vortex convective flow is considered, general criterion for the formation of such a cloud is obtained. The peculiarities of a steady state in the form of a dust cloud and backward influence of the solid phase on the carrier flow are studied in detail for a vertical layer heated from the sidewalls. It is shown that in the case, when this backward influence is essential, a hysteresis behavior is possible. The stability analysis of the steady state is performed. It turns out that there is a narrow range of governing parameters, in which such a steady state is stable.Comment: 14 pages, 10 figures, published in Physics of Fluid

Attenuation and directional spreading of ocean wave spectra in the marginal ice zone

A theoretical model is used to study wave energy attenuation and directional spreading of ocean wave spectra in the marginal ice zone (MIZ). The MIZ is constructed as an array of tens of thousands of compliant circular ice floes, with randomly selected positions and radii determined by an empirical floe size distribution. Linear potential flow and thin elastic plate theories model the coupled water–ice system. A new method is proposed to solve the time-harmonic multiple scattering problem under a multidirectional incident wave forcing with random phases. It provides a natural framework for tracking the evolution of the directional properties of a wave field through the MIZ. The attenuation and directional spreading are extracted from ensembles of the wave field with respect to realizations of the MIZ and incident forcing randomly generated from prescribed distributions. The averaging procedure is shown to converge rapidly so that only a small number of simulations need to be performed. Far-field approximations are investigated, allowing efficiency improvements with negligible loss of accuracy. A case study is conducted for a particular MIZ configuration. The observed exponential attenuation of wave energy through the MIZ is reproduced by the model, while the directional spread is found to grow linearly with distance. The directional spreading is shown to weaken when the wavelength becomes larger than the maximum floe size.Fabien Montiel, V. A. Squire, and L. G. Bennett

Evolution of directional wave spectra through finite regular and randomly perturbed arrays of scatterers

A method is proposed to solve the full linear problem of wave scattering by a large finite array of circular inclusions in two spatial dimensions and compute the concomitant evolution of directional wave properties through the array. The method decomposes the array into slabs. Interactions between adjacent slabs are calculated using a representation of the wave fields scattered by each slab as integrals of plane waves over the directional spectrum plus exponentially decaying branches. The method is applied to the canonical problem of acoustic sound-hard scatterers. Validation is sought for (i) regular arrays via comparison with solutions of corresponding infinite, periodic single- and multiple row arrays and (ii) random arrays via comparison with Foldy's approximation for the effective field. A numerical investigation is conducted to determine the effect of introducing random perturbations into regular arrays on the directional properties of the reflected and transmitted fields.Fabien Montiel, Vernon A. Squire, and Luke G. Bennett