MHD‐driven kinetic dissipation in the solar wind and corona

Mechanisms for the deposition of heat in the lower coronal plasma are discussed, emphasizing recent attempts to reconcile the fluid and kinetic perspectives. Structures at magnetohydrodynamic (MHD) scales may drive a nonlinear cascade, preferentially exciting high perpendicular wavenumber fluctuations. Relevant dissipative kinetic processes must be identified that can absorb the associated energy flux. The relationship between the MHD cascade and direct cyclotron absorption, including cyclotron sweep, is discussed. We conclude that for coronal and solar wind parameters the perpendicular cascade cannot be neglected and may be more rapid than cyclotron sweep. Solar wind observational evidence suggests the relevance of the ion inertial scale, which is associated with current sheet thickness during reconnection. We conclude that a significant fraction of dissipation in the corona and solar wind likely proceeds through a perpendicular cascade and small-scale reconnection, coupled to kinetic processes that act at oblique wavevectors

An in-situ pilot study to investigate the native clinical resistance of enamel to erosion

OBJECTIVES: To investigate the differences in susceptibility of the surface of native and polished enamel to dietary erosion using an in-situ model.METHODS: Thirty healthy volunteers (n = 10 per group) wore mandibular appliances containing 2 native and 2 polished enamel samples for 30 min after which, the samples were exposed to either an ex-vivo or in-vivo immersion in orange juice for 5, 10 or 15 min and the cycle repeated twice with an hour's interval between them. Samples were scanned with a non-contacting laser profilometer and surface roughness was extracted from the data, together with step height and microhardness change on the polished enamel samples.RESULTS: All volunteers completed the study. For native enamel there were no statistical difference between baseline roughness values versus post erosion. Polished enamel significantly increased mean (SD) Sa roughness from baseline for each group resulting in roughness change of 0.04 (0.03), 0.06 (0.04), 0.04 (0.03), 0.06 (0.03), 0.08 (0.05) and 0.09 (0.05) μm respectively. With statistical differences between roughness change 45 min in-vivo versus 45 min ex-vivo (p &lt; 0.05). Microhardness significantly decreased for each polished group, with statistical differences in hardness change between 30 min in-vivo versus 30 min ex-vivo (p &lt; 0.05), 45 min in-vivo versus 30 min ex-vivo (p &lt; 0.01), 45 min in-vivo versus 45 min ex-vivo (p &lt; 0.01).CONCLUSIONS: The native resistance to erosion provided clinically is a combination of the ultrastructure of outer enamel, protection from the salivary pellicle and the overall effects of the oral environment. CLINICALTRIALS.GOV IDENTIFIER: NCT03178968.CLINICAL SIGNIFICANCE: This study demonstrates that outer enamel is innately more resistant to erosion which is clinically relevant as once there has been structural breakdown at this level the effects of erosive wear will be accelerated.</p

The periodic variations of a white-light flare observed with ULTRACAM

High time resolution observations of a white-light flare on the active star EQ PegB show evidence of intensity variations with a period of ≈10 s. The period drifts to longer values during the decay phase of the flare. If the oscillation is interpreted as an impulsively-excited, standing-acoustic wave in a flare loop, the period implies a loop length of ≈3.4 Mm and ≈6.8 Mm for the case of the fundamental mode and the second harmonic, respectively. However, the small loop lengths imply a very high modulation depth making the acoustic interpretation unlikely. A more realistic interpretation may be that of a fast-MHD wave, with the modulation of the emission being due to the magnetic field. Alternatively, the variations could be due to a series of reconnection events. The periodic signature may then arise as a result of the lateral separation of individual flare loops or current sheets with oscillatory dynamics (i.e., periodic reconnection)

Welfare Challenges of Dairy Cows in India Identified Through On-Farm Observations

India has the largest population of dairy cattle in the world at over 48 million animals, yet there has been little formal assessment of their welfare reported. Through observations of dairy cows on 38 farms in Kerala, India, we aimed to investigate the welfare of these animals and the practicality of animal-based assessments within common farming systems. Substantial welfare challenges were identified. All cows were close-tied (less than 1 m length) via a halter that pierced the nasal septum when housed, which was for the entire day (50% of farms) or part thereof. When outside access was available, it was also usually restricted by close-tying, longline tether, or hobbling. Ad libitum water was only available on 22% of farms and food access was also restricted (mean of 4.3 hrs/day). Future work should focus on encouraging dairy farmers in India to improve the welfare of their dairy cattle by ceasing to tie and tether cattle or at least providing tied and tethered cattle with exercise opportunities, unlimited access to drinking water and a readier supply of food (especially quality green forage/fodder); clean housing more frequently; provide strategies to prevent heat stress; breed cattle suited to environmental conditions and with increased resistance to heat stress; carry out welfare assessments more regularly using a validated protocol; rectify the causes of poor welfare. Such changes could substantially improve the welfare of tens of millions of cattle

Factors affecting site use preference of grazing cattle studied from 2000 to 2020 through GPS tracking - A review

Understanding the behaviour of grazing animals at pasture is crucial in order to develop management strategies that will increase the potential productivity of grazing systems and simultaneously decrease the negative impact on the environment. The objective of this review is to summarize and analyse the scientific literature that has addressed the site use preference of grazing cattle using global positioning systems (GPS) collars in the past 21 years (2000-2020) to aid the development of more sustainable grazing livestock systems. The 84 studies identified were undertaken in several regions of the world, in diverse production systems, under different climate conditions and with varied methodologies and animal types. This work presents the information in categories according to the main findings reviewed, covering management, external and animal factors driving animal movement patterns. The results show that some variables such as stocking rate, water and shade location, weather conditions and pasture (terrain and vegetation) characteristics have a significant impact on the behaviour of grazing cattle. Other types of bio-loggers can be deployed in grazing ruminants to gain insights into their metabolism and its relationship with the landscape they utilise. Changing management practices based on these findings could improve the use of grasslands towards more sustainable and productive livestock systems

Kinematic model inversions of hot star recurrent DAC data - tests against dynamical CIR models

The Discrete Absorption Components (DACs) commonly observed in the ultraviolet lines of hot stars have previously been modelled by dynamical simulations of Corotating Interaction Regions (CIRs) in their fine-driven stellar winds. Here we apply the kinematic DAC inversion method of Brown et al. to the hydrodynamical CIR models and test the reliability of the results obtained. We conclude that the inversion method is able to recover valuable information on the velocity structure of the mean wind and to trace movement of velocity plateaux in the hydrodynamical data, though the recovered density profile of the stream is correct only very near to the stellar surface