Magnetic helicity in magnetohydrodynamic turbulence with a mean magnetic field

A computational investigation of magnetic helicity of the fluctuatingmagnetic fieldHm in ideal and freely decaying three‐dimensional (3‐D) magnetohydrodynamics (MHD) in the presence of a uniform mean magnetic field is performed. It is shown that for ideal 3‐D MHDHm, which is a rugged invariant in the absence of a mean magnetic field [Frisch et al., J. Fluid Mech. 77, 796 (1975)], decays from its initial value and proceeds to oscillate about zero. The decay of Hm is shown to result from the presence of a new ‘‘generalized’’ helicity invariant, which includes contributions from the uniform magnetic field. The loss of invariance of Hm will diminish the effects of inverse transfer of Hm on freely decaying turbulence. This is demonstrated in a discussion of the selective decay relaxation process

An Evaluation of Max-Flex Fast Fence™ for Reducing Deer Damage to Crops

A 2-year study was undertaken to assess the effectiveness of Max-Flex Fast Fence™ electric fencing materials (polytape) for reducing damage to crops. Specifically, our goal was to look at the efficacy of this product for the home gardener. In the first phase of the project, plots of approximately 1/40 acre were established in areas of historically high deer densities. Each plot was planted with soybeans and randomly assigned to 1 of 4 fencing configurations or to the open control group. Within each plot, 6\u27 wide strips were tilled across the length. These tilled areas were checked for the presence of deer tracks. The study design was replicated 3 times to produce 12 treatment plots (3 of each fence configuration) and 3 open controls. Fences were charged via a New Zealand-type high voltage, low-impedance charger. The open controls were fed on heavily by deer and soon were almost void of foliage. Results suggest that under these conditions even a single strand of polytape 2 1/2\u27 high was successful in preventing deer from entering the plots. Phase 2 of the study used a single strand of polytape 2 1/2\u27 feet from the ground to exclude deer from plots ranging in size from 0.025 acres to 1 acre. Each exclosure was planted with soybeans. Three replication areas were selected and plots randomly established within the replicates. The effectiveness of the single strand was much less conclusive than in Phase I, with deer entering all plots at some time during the study. However, there does appear to be a direct relationship between plot size and number of deer tracks observed in the plot. In addition, there were significant differences in fence effectiveness between replicates. We concluded that a single strand of polytape electric fencing, if properly installed, could be a suitable deterrent to deer in a small garden situation

Successful recruitment to trials: findings from the SCIMITAR plus Trial

BACKGROUND: Randomised controlled trials (RCT) can struggle to recruit to target on time. This is especially the case with hard to reach populations such as those with severe mental ill health. The SCIMITAR+ trial, a trial of a bespoke smoking cessation intervention for people with severe mental ill health achieved their recruitment ahead of time and target. This article reports strategies that helped us to achieve this with the aim of aiding others recruiting from similar populations. METHODS: SCIMITAR+ is a multi-centre pragmatic two-arm parallel-group RCT, which aimed to recruit 400 participants with severe mental ill health who smoke and would like to cut down or quit. The study recruited primarily in secondary care through community mental health teams and psychiatrists with a smaller number of participants recruited through primary care. Recruitment opened in October 2015 and closed in December 2016, by which point 526 participants had been recruited. We gathered information from recruiting sites on strategies which led to the successful recruitment in SCIMITAR+ and in this article present our approach to trial management along with the strategies employed by the recruiting sites. RESULTS: Alongside having a dedicated trial manager and trial management team, we identified three main themes that led to successful recruitment. These were: clinicians with a positive attitude to research; researchers and clinicians working together; and the use of NHS targets. The overriding theme was the importance of relationships between both the researchers and the recruiting clinicians and the recruiting clinicians and the participants. CONCLUSIONS: This study makes a significant contribution to the limited evidence base of real-world cases of successful recruitment to RCTs and offers practical guidance to those planning and conducting trials. Building positive relationships between clinicians, researchers and participants is crucial to successful recruitment

Understanding Helical Magnetic Dynamo Spectra with a Nonlinear Four-Scale Theory

Recent MHD dynamo simulations for magnetic Prandtl number $>1$ demonstrate that when MHD turbulence is forced with sufficient kinetic helicity, the saturated magnetic energy spectrum evolves from having a single peak below the forcing scale to become doubly peaked with one peak at the system (=largest) scale and one at the forcing scale. The system scale field growth is well modeled by a recent nonlinear two-scale nonlinear helical dynamo theory in which the system and forcing scales carry magnetic helicity of opposite sign. But a two-scale theory cannot model the shift of the small-scale peak toward the forcing scale. Here I develop a four-scale helical dynamo theory which shows that the small-scale helical magnetic energy first saturates at very small scales, but then successively saturates at larger values at larger scales, eventually becoming dominated by the forcing scale. The transfer of the small scale peak to the forcing scale is completed by the end of the kinematic growth regime of the large scale field, and does not depend on magnetic Reynolds number $R_M$ for large $R_M$. The four-scale and two-scale theories subsequently evolve almost identically, and both show significant field growth on the system and forcing scales that is independent of $R_M$. In the present approach, the helical and nonhelical parts of the spectrum are largely decoupled. Implications for fractionally helical turbulence are discussed.Comment: 19 Pages, LaTex, (includes 4 figs at the end), in press, MNRA

Standard smoking cessation services in sites participating in the SCIMITAR+ trial for people with severe mental ill health

Aims and methodThe SCIMITAR+ trial was commissioned to evaluate the effectiveness of a bespoke smoking cessation intervention for people with severe mental ill health compared with usual services. It is difficult to define what constitutes usual care in smoking cessation services. We aimed to define what this was during the trial. Twenty-two National Health Service healthcare providers participated in a bespoke survey asking about usual care in their area. RESULTS: All sites offered smoking cessation support; however, service provider and service type varied substantially. In some cases services were not streamlined, meaning that people received smoking cessation counselling from one organisation and smoking cessation medication from another.Clinical implicationsTo better implement the National Institute for Health and Care Excellence guideline PH48, clearer referral pathways need to be implemented and communicated to patients, staff and carers. People with severe mental ill health need to be able to access services that combine nicotine replacement therapy and behavioural support in a streamlined manner.Declaration of interestNone

Turbulent Dynamos and Magnetic Helicity

It is shown that the turbulent dynamo $\alpha$-effect converts magnetic helicity from the turbulent field to the mean field when the turbulence is electromagnetic while the magnetic helicity of the mean-field is transported across space when the turbulence is electrostatic or due to the electron diamagnetic effect. In all cases, however, the dynamo effect strictly conserves the total helicity except for resistive effects and a small battery effect. Implications for astrophysical situations, especially for the solar dynamo, are discussed.Comment: 5 pages, 1 figur

Universal Sequence Replication, Reversible Polymerization and Early Functional Biopolymers: A Model for the Initiation of Prebiotic Sequence Evolution

Many models for the origin of life have focused on understanding how evolution can drive the refinement of a preexisting enzyme, such as the evolution of efficient replicase activity. Here we present a model for what was, arguably, an even earlier stage of chemical evolution, when polymer sequence diversity was generated and sustained before, and during, the onset of functional selection. The model includes regular environmental cycles (e.g. hydration-dehydration cycles) that drive polymers between times of replication and functional activity, which coincide with times of different monomer and polymer diffusivity. Template-directed replication of informational polymers, which takes place during the dehydration stage of each cycle, is considered to be sequence-independent. New sequences are generated by spontaneous polymer formation, and all sequences compete for a finite monomer resource that is recycled via reversible polymerization. Kinetic Monte Carlo simulations demonstrate that this proposed prebiotic scenario provides a robust mechanism for the exploration of sequence space. Introduction of a polymer sequence with monomer synthetase activity illustrates that functional sequences can become established in a preexisting pool of otherwise non-functional sequences. Functional selection does not dominate system dynamics and sequence diversity remains high, permitting the emergence and spread of more than one functional sequence. It is also observed that polymers spontaneously form clusters in simulations where polymers diffuse more slowly than monomers, a feature that is reminiscent of a previous proposal that the earliest stages of life could have been defined by the collective evolution of a system-wide cooperation of polymer aggregates. Overall, the results presented demonstrate the merits of considering plausible prebiotic polymer chemistries and environments that would have allowed for the rapid turnover of monomer resources and for regularly varying monomer/polymer diffusivities