Geophysically consistent values of the perovskite to post-perovskite transition Clapeyron slope

International audienceThe doublecrossing hypothesis posits that post-perovskite bearing rock in Earth's D 00 layer exists as a layer above the core-mantle boundary bounded above and below by intersections between a curved thermal boundary layer geotherm and a relatively steep phase boundary. Increasing seismic evidence for the existence of pairs of discontinuities predicted to occur at the top and bottom of this layer motivates an examination of the consistency of this model with mineral physics constraints for the Clapeyron slope of this phase transition. Using independent constraints for a lower bound on temperature in Earth's deep mantle and the temperature of Earth's inner core boundary, we show that a post-perovskite doublecrossing is inconsistent with plausible core temperatures for a Clapeyron slope less than about 7 MPa/K, with the higher range of experimental values yielding better agreement with recent estimates of the melting temperature of Earth's core

Influence of seating styles on head and pelvic vertical movement symmetry in horses ridden at trot

Detailed knowledge of how a rider’s seating style and riding on a circle influences the movement symmetry of the horse’s head and pelvis may aid rider and trainer in an early recognition of low grade lameness. Such knowledge is also important during both subjective and objective lameness evaluations in the ridden horse in a clinical setting. In this study, inertial sensors were used to assess how different rider seating styles may influence head and pelvic movement symmetry in horses trotting in a straight line and on the circle in both directions. A total of 26 horses were subjected to 15 different conditions at trot: three unridden conditions and 12 ridden conditions where the rider performed three different seating styles (rising trot, sitting trot and two point seat). Rising trot induced systematic changes in movement symmetry of the horses. The most prominent effect was decreased pelvic rise that occurred as the rider was actively rising up in the stirrups, thus creating a downward momentum counteracting the horses push off. This mimics a push off lameness in the hindlimb that is in stance when the rider sits down in the saddle during the rising trot. On the circle, the asymmetries induced by rising trot on the correct diagonal counteracted the circle induced asymmetries, rendering the horse more symmetrical. This finding offers an explanation to the equestrian tradition of rising on the ‘correct diagonal.’ In horses with small pre-existing movement asymmetries, the asymmetry induced by rising trot, as well as the circular track, attenuated or reduced the horse’s baseline asymmetry, depending on the sitting diagonal and direction on the circle. A push off hindlimb lameness would be expected to increase when the rider sits during the lame hindlimb stance whereas an impact hindlimb lameness would be expected to decrease. These findings suggest that the rising trot may be useful for identifying the type of lameness during subjective lameness assessment of hindlimb lameness. This theory needs to be studied further in clinically lame horses

Klinisk gradering av hästens luftvägsstatus

Respiratory disease with airway inflammation as main characteristic is common in the horse. It is a syndrome that is not yet fully understood. The etiology, pathogenesis and classification into different disease states are subjects for discussion and under continuous revision. Despite a number of modern techniques, the diagnostic procedure is challenging. There is no test considered to be gold standard when diagnosing these diseases. The clinical examination remains an important approach to the horse with suspected respiratory disease. The need for a standardized clinical scoring system for the equine airways has been addressed by clinicians and researchers. The clinical scoring systems used today are of varying complexity and contain different parameters that are graded in various ways. The aim of this study was to compare different clinical scoring systems for inflammatory airway disease in the horse and their relation to measured indices of inflammation in bronchoalveolar lavage fluid (BALF) and to clinical field status. Four of the protocols used in the study were taken from publications in the field of interest and one has been developed by the author of this under graduate thesis. Data collected from 70 clinical examinations (44 horses) have been used to compare the clinical scoring systems. The registered parameters were graded according to the different protocols and a total clinical score was achieved for each examination. Pearson correlation was used to study the covariance between the clinical scores from the different protocols and their relation to neutrophil elevation in BALF and clinical status. The results show that clinical scoring systems of varying complexity were of approximately equal value in predicting overall respiratory health or disease in horses with RAO/IAD versus clinically normal horses. It appears however that none of the scoring systems examined were predictive of neutrophil elevation in BALF as an objective measure of airway inflammation. The pair-wise correlation between individual scoring systems also varied when used on the same group of horses. Future refinement of scoring systems, possibly using individual factor analysis, may aid in identifying key clinical findings of value in a scoring system that could be standardized for interlaboratory use

Buoyant melting instabilities beneath extending lithosphere: 2. Linear analysis

In a companion paper, numerical models reveal that buoyant melting instabilities can occur beneath extending lithosphere for a sufficiently small mantle viscosity, extension rate, and rate of melt percolation. However, in some cases, instabilities do not develop during extension but only occur after extension slows or stops. These results are suggestive of a critical behavior in the onset of these kinds of instabilities and motivate a linear analysis to study the onset of instability in a partially melting, passively upwelling plane layer of mantle beneath extending lithosphere. The model we employ includes the effects of buoyancy arising from thermal expansion, the presence of a retained fraction of partial melt, and depletion of the solid by melt extraction. We find a critical behavior in the onset of instability controlled by melt retention buoyancy that is characterized by a “Rayleigh” number M, such that M must exceed some critical value M_(crit) which depends on the efficiency of Stokes rise of a partially molten body relative to the rate of background percolation. Comparison of this theory to the numerical results in the companion paper yields a close quantitative agreement. We also find that solid depletion buoyancy can either stabilize or destabilize a partially melting layer, depending upon both the distribution of preexisting depletion and the magnitude of density changes with depth. This theory is compared with previous studies of buoyant melting instabilities beneath mid‐ocean ridges where similar behavior was reported, and it suggests that the stability of passively upwelling, partially melting mantle underlying both narrow and wide rift settings is controlled by similar processes

Sport surfaces in show jumping

Properties of sport surfaces influence the occurrence of injuries and the performance of equine athletes. The sports governing body seeks to develop standards for safety and performance of show jumping surfaces. Limited information is available to guide this process. Objective methods are warranted in order to define surface properties that can be associated to injury and performance data. Description of the discipline-specific interaction between the horse and the ground is important in order to display the characteristics and diversity of loading patterns applied to the sport surfaces as well as to enable understanding of the mechanical challenges that lead to injuries. The aims of this thesis were to describe the hoof-ground interaction in show jumping and to study functional properties of surfaces through rider assessments and by using a standardized biomechanical method that enables comparisons between arenas. Hoof landing characteristics of elite horses in jump landing from 1.30–1.50 m competition fences on two different surfaces were evaluated from high-speed videos. Hoof landing kinematics differed among the leading/trailing fore and hind limbs. Data increased our understanding of hoof-ground interaction and related events, which is a prerequisite for developing surface testing devices. Hoof impact was also investigated using hoof-mounted accelerometers in an experimental setup with five horses in canter, jump take-off and landing. Leading/trailing fore and hind limbs, stride types and surface affected the hoof-surface impact. The vertical deceleration at impact ranked in the same order, for three surface conditions, as when the impact from a metal hoof of a biomechanical surface testing device was measured. Subjective assessments of surface properties by riders were compared to objective in-situ measurements of the same properties with a biomechanical surface tester in 25 show jumping competition and warm-up arena surfaces at top-level events. Significant associations between the subjective and objective assessments were found. The data from this thesis contribute to the description of the discipline-specific hoof-surface interaction in show jumping. The objective method used for in-situ characterisation of functional surface properties can enable further objective comparisons which in the future can be related to injury and performance data of show jumping surfaces

Buoyant melting instabilities beneath extending lithosphere: 1. Numerical models

Buoyant decompression melting instabilities in regions of partially molten upper mantle have been proposed to be an important process that might account for some characteristics of intraplate volcanism on Earth and other terrestrial planets. The instability is driven by variations in the melting rate within a partially molten layer whenever a relative decrease in density accompanies decompression melting of ascending mantle. Here, the development of buoyant decompression melting instabilities in a plane layer of passively upwelling and partially melting mantle beneath diffusely extending lithosphere is studied using numerical convection models covering a wide range of physical parameters. We find that the occurrence and nature of these instabilities in such a scenario is strongly affected by the rate of extension and melt percolation, as well as depth distribution of solid density variations arising from melt depletion. In some cases, instabilities do not occur during extension, but only develop after extension has slowed or stopped completely. This behavior creates two pulses of magma generation due to passive upwelling accompanying extension followed by the subsequent instability and is favored by a faster rate of extension, higher mantle viscosity, higher rate of melt percolation, and smaller amount of solid residuum depletion‐derived buoyancy. Larger degrees of solid density changes accompanying melt depletion can enhance the instability of partially molten mantle during extension but decrease the cumulative volume of generated melt. This kind of behavior modifies the conventional expectation of spatially and temporally correlated volcanism and extension and may lend insight into the observed increase in localized volcanic activity following Miocene Basin and Range extension in the western United States

The Descriptions and Attitudes of Riders and Arena Owners to 656 Equestrian Sport Surfaces in Sweden

Horses in equestrian sports are commonly trained in arenas with prepared footing. Information on the number and variants of such arenas is generally unknown. This paper provides an overview of the primary construction types of riding surfaces in Sweden including details on composition, constructions principles, usage frequency, maintenance, and cost of operation as well as to investigate rider perception of the ideal arena properties using a large population of riders. Data on 656 equestrian surfaces in Sweden obtained up to 2014 are presented, of which 373 were outdoor and 283 were indoor arenas. Dressage and show-jumping were the main disciplines conducted in the arenas. Sand-mineral arenas were most common outdoors and sand-woodchips arenas most common indoors, followed by sand-fibre arenas and even fewer synthetic arenas. Comparing the three most common arena types, dragging was most often done on sand-woodchips and sand-fibre arenas. Harrowing was less often done on sand-mineral arenas compared to sand-woodchips and sand-fibre arenas. Combining dragging, harrowing, deep harrowing, and rolling, arenas with higher usage were maintained more frequently, compared to those used less frequently. It was commonly claimed that the top-layer needs renovation every other-4th year or every 5th to 10th year. Few respondents allocated more than 10,000 SEK in yearly maintenance costs, with the exception for sand-woodchips and sand-fibre arenas followed by synthetic arenas. The shortest duration perceived between required renovations was found for sand-woodchips top-layer arenas. Ideal surface properties were evaluated by 3,158 riders. Dressage and show-jumping riders differed somewhat regarding ideal spans of functional arena properties: for impact firmness, responsiveness, and grip. The current study likely included well-utilised arenas, compared to those less well-utilised. The resources necessary to keep an arena consistent over time seemed underestimated. Knowledge of maintenance and priorities for arenas are important to users and arenas managers, be they construction companies or arena managers in order to maximise the outcome of efforts for arena improvement and optimise locomotor health for horses that use them. Further, many arenas were new and research into organic arena management is important, especially if equestrians continue to build and renew arena surfaces

Performance of four equine pain scales and their association to movement asymmetry in horses with induced orthopedic pain

Objective: This study investigated the relationship between orthopedic pain experienced at rest, and degree of movement asymmetry during trot in horses with induced reversible acute arthritis. Orthopedic pain was assessed with the Horse Grimace Scale (HGS), the Equine Utrecht University Scale of Facial Assessment of Pain (EQUUS-FAP), the Equine Pain Scale (EPS), and the Composite Orthopedic Pain Scale (CPS). Reliability and diagnostic accuracy were evaluated with intraclass correlation coefficients (ICC) and area under the curve (AUC).Study design and animals: Eight healthy horses were included in this experimental study, with each horse acting as its own control.Methods: Orthopedic pain was induced by intra-articular lipopolysaccharide (LPS) administration. Serial pain assessments were performed before induction and during pain progression and regression, where three observers independently and simultaneously assessed pain at rest with the four scales. Movement asymmetry was measured once before induction and a minimum of four times after induction, using objective gait analysis.Results: On average 6.6 (standard deviation 1.2) objective gait analyses and 12.1 (2.4) pain assessments were performed per horse. The ICC for each scale was 0.75 (CPS), 0.65 (EPS), 0.52 (HGS), and 0.43 (EQUUS-FAP). Total pain scores of all scales were significantly associated with an increase in movement asymmetry (R2 values ranging from −0.0649 to 0.493); with CPS pain scores being most closely associated with movement asymmetry. AUC varied between scales and observers, and CPS was the only scale where all observers had a good diagnostic accuracy (AUC > 0.72).Conclusions and clinical relevance: This study identified significant associations between pain experienced at rest and degree of movement asymmetry for all scales. Pain scores obtained using CPS were most closely associated with movement asymmetry. CPS was also the most accurate and reliable pain scale. All scales had varying linear and non-linear relations between total pain scores and movement asymmetry, illustrating challenges with orthopedic pain assessment during rest in subtly lame horses since movement asymmetry needs to be rather high before total pain score increase