Friction in inflaton equations of motion

The possibility of a friction term in the equation of motion for a scalar field is investigated in non-equilibrium field theory. The results obtained differ greatly from existing estimates based on linear response theory, and suggest that dissipation is not well represented by a term of the form $\eta\dot{\phi}$.Comment: 4 pages, 2 figures, RevTex4. An obscurity in the original version has been clarifie

Scrambled and Unscrambled Turbulence

The linked fluid dynamics videos depict Rayleigh-Taylor turbulence when driven by a complex acceleration profile involving two stages of acceleration interspersed with a stage of stabilizing deceleration. Rayleigh-Taylor (RT) instability occurs at the interface separating two fluids of different densities, when the lighter fluid is accelerated in to the heavier fluid. The turbulent mixing arising from the development of the miscible RT instability is of key importance in the design of Inertial Confinement Fusion capsules, and to the understanding of astrophysical events, such as Type Ia supernovae. By driving this flow with an accel-decel-accel profile, we have investigated how structures in RT turbulence are affected by a sudden change in the direction of the acceleration first from destabilizing acceleration to deceleration, and followed by a restoration of the unstable acceleration. By studying turbulence under such highly non-equilibrium conditions, we hope to develop an understanding of the response and recovery of self-similar turbulence to sudden changes in the driving acceleration.Comment: 3 pages article, Two videos are include

Perturbative nonequilibrium dynamics of phase transitions in an expanding universe

A complete set of Feynman rules is derived, which permits a perturbative description of the nonequilibrium dynamics of a symmetry-breaking phase transition in $\lambda\phi^4$ theory in an expanding universe. In contrast to a naive expansion in powers of the coupling constant, this approximation scheme provides for (a) a description of the nonequilibrium state in terms of its own finite-width quasiparticle excitations, thus correctly incorporating dissipative effects in low-order calculations, and (b) the emergence from a symmetric initial state of a final state exhibiting the properties of spontaneous symmetry breaking, while maintaining the constraint $\equiv 0$. Earlier work on dissipative perturbation theory and spontaneous symmetry breaking in Minkowski spacetime is reviewed. The central problem addressed is the construction of a perturbative approximation scheme which treats the initial symmetric state in terms of the field $\phi$, while the state that emerges at later times is treated in terms of a field $\zeta$, linearly related to $\phi^2$. The connection between early and late times involves an infinite sequence of composite propagators. Explicit one-loop calculations are given of the gap equations that determine quasiparticle masses and of the equation of motion for $$ and the renormalization of these equations is described. The perturbation series needed to describe the symmetric and broken-symmetry states are not equivalent, and this leads to ambiguities intrinsic to any perturbative approach. These ambiguities are discussed in detail and a systematic procedure for matching the two approximations is described.Comment: 22 pages, using RevTeX. 6 figures. Submitted to Physical Review

Alpacas and Ecosystems Management

Alpacas are a species that present physiological, anatomical, morphological and behavioural distinctive characteristics compared to other species used in animal production. Empirical observation of a herd, grazing under time management controlled conditions, allowed to approximate some initial observations about the effect of alpacas in the management of ecosystems. Larger green matter availability in the paddocks grazed by alpacas, evident natural weed control, better plants distribution and increasing stocking capacity were the relevant observed issues. It is considered that the special behavioural characteristics of alpacas in terms of excretion habits, low hoof pressure, food conversion efficiency and grazing habits should be factors to be rigourously studied to explore the value of alpacas as an environmentally friendly species.Sustainable farm management, farming systems research, alpacas, Environmental Economics and Policy, Livestock Production/Industries,

Dissipation in equations of motion of scalar fields

The methods of non-equilibrium quantum field theory are used to investigate the possibility of representing dissipation in the equation of motion for the expectation value of a scalar field by a friction term, such as is commonly included in phenomenological inflaton equations of motion. A sequence of approximations is exhibited which reduces the non-equilibrium theory to a set of local evolution equations. However, the adiabatic solution to these evolution equations which is needed to obtain a local equation of motion for the expectation value is not well defined; nor, therefore, is the friction coefficient. Thus, a non-equilibrium treatment is essential, even for a system that remains close to thermal equilibrium, and the formalism developed here provides one means of achieving this numerically.Comment: 17 pages, 5 figure

Strong Purifying Selection at Synonymous Sites in D. melanogaster

Synonymous sites are generally assumed to be subject to weak selective constraint. For this reason, they are often neglected as a possible source of important functional variation. We use site frequency spectra from deep population sequencing data to show that, contrary to this expectation, 22% of four-fold synonymous (4D) sites in D. melanogaster evolve under very strong selective constraint while few, if any, appear to be under weak constraint. Linking polymorphism with divergence data, we further find that the fraction of synonymous sites exposed to strong purifying selection is higher for those positions that show slower evolution on the Drosophila phylogeny. The function underlying the inferred strong constraint appears to be separate from splicing enhancers, nucleosome positioning, and the translational optimization generating canonical codon bias. The fraction of synonymous sites under strong constraint within a gene correlates well with gene expression, particularly in the mid-late embryo, pupae, and adult developmental stages. Genes enriched in strongly constrained synonymous sites tend to be particularly functionally important and are often involved in key developmental pathways. Given that the observed widespread constraint acting on synonymous sites is likely not limited to Drosophila, the role of synonymous sites in genetic disease and adaptation should be reevaluated

CHEMISTRY EDUCATION COMMUNITY OF PRACTICE DISCIPLINE DAY WORKSHOP

Gwendolyn Lawrie, representing the RACI Chemical Education Division Committee ZOOM WORKSHOP ACTIVITIES This workshop will include 3 sessions to catalyse conversations. Activities will be facilitated by members of the RACI Chemical Education Division Committee and the wider chemistry education community. Zoom will be used to facilitate activities including breakout rooms for ‘round table’ discussions, polling and collaborative creation of content. 1. A landscape view of chemistry educators’ experiences: ‘successes’ and ‘unsuccesses’ The recent transition to emergency remote teaching due to the COVID-19 pandemic has resulted in adoption, adaptation and creation of chemistry pedagogies, practices and assessment in online learning environments. The opportunities and challenges in teaching will be distilled to inform the next session. 2. Defining, curating and disseminating exemplars of TPACK in practice In this session, participants will be encouraged to contribute to a co-constructed repository of shared resources for teaching and learning of chemistry online. The first step will be to re-establish shared understanding of technological pedagogical content knowledge (TPACK) to assist in collation of resources. 3. Ensuring and widening access and participation in learning chemistry online The transition of learning into online environments has amplified potential barriers that students face in accessing learning. In this session, inclusive practices will be identified to develop recommendations for practice. ANTICIPATED OUTCOMES • Strengthening networks and communities of practice in chemistry education • An open access resource bank of online teaching and assessment exemplars for the community to share • Recommendations for inclusive learning and teaching practices Submissions for this workshop session by community members have been invited through the ChemNet June newsletter. The repository will be hosted at http://chemnet.edu.au/node/37

Nonequilibrium perturbation theory for complex scalar fields

Real-time perturbation theory is formulated for complex scalar fields away from thermal equilibrium in such a way that dissipative effects arising from the absorptive parts of loop diagrams are approximately resummed into the unperturbed propagators. Low order calculations of physical quantities then involve quasiparticle occupation numbers which evolve with the changing state of the field system, in contrast to standard perturbation theory, where these occupation numbers are frozen at their initial values. The evolution equation of the occupation numbers can be cast approximately in the form of a Boltzmann equation. Particular attention is given to the effects of a non-zero chemical potential, and it is found that the thermal masses and decay widths of quasiparticle modes are different for particles and antiparticles.Comment: 15 pages using RevTeX; 2 figures in 1 Postscript file; Submitted to Phys. Rev.

Targeting Vascular Remodeling to Treat Pulmonary Arterial Hypertension

Pulmonary arterial hypertension (PAH) describes a group of conditions with a common hemodynamic phenotype of increased pulmonary artery pressure, driven by progressive remodeling of small pulmonary arteries, leading to right heart failure and death. Vascular remodeling is the key pathological feature of PAH, but treatments targeting this process are lacking. In this review, we summarize important advances in our understanding of PAH pathogenesis from novel genetic and epigenetic factors, to cell metabolism and DNA damage. We show how these processes may integrate and highlight exploitable targets that could alter the relentless vascular remodeling in PAH