Ideal relaxation of the Hopf fibration

Ideal MHD relaxation is the topology-conserving reconfiguration of a magnetic field into a lower energy state where the net force is zero. This is achieved by modeling the plasma as perfectly conducting viscous fluid. It is an important tool for investigating plasma equilibria and is often used to study the magnetic configurations in fusion devices and astrophysical plasmas. We study the equilibrium reached by a localized magnetic field through the topology conserving relaxation of a magnetic field based on the Hopf fibration in which magnetic field lines are closed circles that are all linked with one another. Magnetic fields with this topology have recently been shown to occur in non-ideal numerical simulations. Our results show that any localized field can only attain equilibrium if there is a finite external pressure, and that for such a field a Taylor state is unattainable. We find an equilibrium plasma configuration that is characterized by a lowered pressure in a toroidal region, with field lines lying on surfaces of constant pressure. Therefore, the field is in a Grad-Shafranov equilibrium. Localized helical magnetic fields are found when plasma is ejected from astrophysical bodies and subsequently relaxes against the background plasma, as well as on earth in plasmoids generated by e.g.\ a Marshall gun. This work shows under which conditions an equilibrium can be reached and identifies a toroidal depression as the characteristic feature of such a configuration

Editiorial

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Comparing the pharmacokinetics of a fourth generation cephalosporin in three different age groups of New Forest ponies

REASONS FOR PERFORMING STUDY To compare the pharmacokinetics of the fourth generation cephalosporin, cefquinome, in neonatal foals, 6-week-old foals and mature New Forest ponies in order to recommend appropriate dosage regimens for use of this drug. METHODS Cefquinome was administered i.v. at 1 mg/kg bwt twice a day (q. 12 h), 1 mg/kg bwt 3 times a day (q. 8 h) or 4.5 mg/kg bwt q. 12 h to each age group (n = 6). Plasma cefquinome concentrations were analysed using high-performance liquid chromatography combined with electrospray tandem mass spectrometry. RESULTS Both foal age groups had comparable pharmacokinetic data except for the volume of distribution at a steady-state (Vss), total body clearance (CIB) and mean residence time (MRT). Both ClB and MRT decreased as the age of the foals increased. Values of area under the curve increased, in a dose dependent manner, with significant increases for all age groups following administration of 4.5 mg/kg bwt q. 12 h. Total body clearance did not have comparable dose dependency. CONCLUSIONS Cefquinome can be given at a dose of 1 mg/kg bwt q. 12 h for the treatment of infections caused by susceptible pathogens with MIC <0.125 microg/ml. A higher dose of 4.5 mg/kg bwt q. 12 h is recommended for the treatment of bacterial pathogens with minimal inhibitory concentration (MIC) 0.125-0.5 microg/ml. POTENTIAL RELEVANCE Commonly used dosing regimens should be critically evaluated in neonatal foals due to the higher volume of distribution of less lipophilic drugs in this age group

Acylcarnitine ester utilization by the hindlimb of warmblood horses at rest and following low intensity exercise and carnitine supplementation

BACKGROUND: Acylcarnitines play an important role in fuel metabolism in skeletal muscle. OBJECTIVE: To assess acylcarnitine ester utilization by the hindlimb of horses at rest and following low intensity exercise and carnitine supplementation. ANIMALS AND METHODS: Acylcarnitine ester uptake by the hindlimb was investigated using the arteriovenous difference technique. Blood from six warmblood mares (mean age 12 ± 3 (SD) years and weighing 538 ± 39 kg) was collected simultaneously from the transverse facial artery and from the caudal vena cava. Food was withheld for 12 hours prior to exercise. Exercise comprised a standardized treadmill protocol consisting of 5 minutes of walk, 20 minutes of trot and thereafter another 5 minutes of walk. At the end of the first exercise day, three horses were given carnitine supplementation (100 mg/kg bodyweight), whereas the other horses received saline. The next day the exercise was repeated and blood samples collected similarly. Free carnitine and acylcarnitines were analyzed as their butyl ester derivatives in heparinized plasma by electrospray tandem mass spectrometry. Statistical analysis was performed using a general linear mixed model. RESULTS: C3-carnitine, C6-carnitine and C14:1-carnitine showed the largest average extraction by the hindlimb at rest and C3-carnitine, C5:1-carnitine and C16-carnitine immediately after low-intensity exercise. Carnitine supplementation significantly increased free carnitine, C5-carnitine and C8-carnitine extraction. CONCLUSION: Carnitine supplementation altered the extraction of acylcarnitines by the hindlimb in horses exercising at low intensity. CLINICAL IMPORTANCE: Findings might aid in optimizing performance and myopathy prevention of the equine athlete

Effect of different head and neck positions on behaviour, heart rate variability and cortisol levels in lunged Royal Dutch Sport horses

Different head-and-neck positions (HNPs) are discussed in relation to potential welfare issues. To evaluate the effect on welfare, seven Royal Dutch Sport horses were studied in five predetermined HNPs: (1) unrestrained (HNP1); (2) neck raised, bridge of nose around the vertical (HNP2); (3) neck lowered and considerably flexed, bridge of nose pointing towards the chest (HNP4); (4) neck raised and extended, bridge of nose in front of the vertical (HNP5), and (5) neck lowered and flexed, bridge of nose pointing towards the carpus (HNP7). A standardised exercise test (SET) of 34 min consisted of trot, canter and walk. Behaviour was recorded with a pre-defined ethogram and R-R intervals measured using telemetry. Cortisol concentrations were taken at the start, 5 and 30 min after the SET. Behaviour around the SET was scored separately.Conflict behaviours increased significantly during HNP2 when compared with HNP1, HNP4 and HNP7 during the SET, and there was significant negative anticipation before HNP2 and HNP7. The heart rate variability (HRV) frequency domain for HNP2 showed a significantly increased low frequency peak (LFpeak) compared with other HNPs, and there was a decrease in very low frequency (VLF%) compared with HNP1. HNP4 showed a significant increase in LF% and decrease in VLF% compared with HNP1. Saliva cortisol concentrations were significantly increased in HNP2 at 5 and 30 min after exercise. Increased conflict behaviour was mostly observed in HNP2, but there was a raised HRV suggesting a sympathetic shift in HNP2 and HNP4, and increased cortisol concentrations during HNP2 indicated a stress response