The Cooling of Coronal Plasmas. iv: Catastrophic Cooling of Loops

We examine the radiative cooling of coronal loops and demonstrate that the recently identified catastrophic cooling (Reale and Landi, 2012) is due to the inability of a loop to sustain radiative / enthalpy cooling below a critical temperature, which can be > 1 MK in flares, 0.5 - 1 MK in active regions and 0.1 MK in long tenuous loops. Catastrophic cooling is characterised by a rapid fall in coronal temperature while the coronal density changes by a small amount. Analytic expressions for the critical temperature are derived and show good agreement with numerical results. This effect limits very considerably the lifetime of coronal plasmas below the critical temperature

Enthalpy-based Thermal Evolution of Loops: II. Improvements to the Model

This paper develops the zero-dimensional (0D) hydrodynamic coronal loop model "Enthalpy-based Thermal Evolution of Loops" (EBTEL) proposed by Klimchuk et al (2008), which studies the plasma response to evolving coronal heating, especially impulsive heating events. The basis of EBTEL is the modelling of mass exchange between the corona and transition region and chromosphere in response to heating variations, with the key parameter being the ratio of transition region to coronal radiation. We develop new models for this parameter that now include gravitational stratification and a physically motivated approach to radiative cooling. A number of examples are presented, including nanoflares in short and long loops, and a small flare. The new features in EBTEL are important for accurate tracking of, in particular, the density. The 0D results are compared to a 1D hydro code (Hydrad) with generally good agreement. EBTEL is suitable for general use as a tool for (a) quick-look results of loop evolution in response to a given heating function, (b) extensive parameter surveys and (c) situations where the modelling of hundreds or thousands of elemental loops is needed. A single run takes a few seconds on a contemporary laptop

A Relationship Between Spin and Geometry

In a recent paper, algebraic descriptions for all non-relativistic spins were derived by elementary means directly from the Lie algebra \specialorthogonalliealgebra{3}, and a connection between spin and the geometry of Euclidean three-space was drawn. However, the details of this relationship and the extent to which it can be developed by elementary means were not expounded. In this paper, we will reveal the geometric content of the spin algebras by realising them within a novel, generalised form of Clifford-like algebra. In so doing, we will demonstrate a natural connection between spin and non-commutative geometry, and discuss the impact of this on the measurement of hypervolumes and on quantum mechanics.Comment: 12 pages, includes work presented at the 13th Annual Conference on Clifford Algebras and Their Applications in Mathematical Physics (ICCA13

IDENTIFICATION OF FLOOR AND VAULTING APTITUDE IN 8·14 YEAR OLD TALENT-SELECTED FEMALE GYMNASTS

Training programs can be designed and monitored to maximise high aptitude for floor and vault when the key attributes are identified, and then used to recognize apparatus ability in talent-selected gymnasts. The aim of this study was to identify the anthropometric and physical prerequisites for high difficulty floor tumbling and vaulting. Twenty female gymnasts performed handstand push-offs, single and multiple jumps on a portable Kistler force plate. The gymnasts were also examined when sprinting, vaulting, and performing broad jumps. Each gymnast's best vault, three best noor tumbling skills and their anthropometric characteristics were also recorded. High squat jump force and power, vault take-off velocity, and sprinting speed indicated vaulting talent. High vault running speed and reduced handstand push-off ground contact time indicated high floor ability

BIOLOGICAL MOVEMENT VARIABILITY DURING THE SPRINT START

The current study proposed a method for estimating biological movement variability in order to examine its effect on 10 m sprinting performance. Two 250 Hz cameras recorded the sprinters (male, n=10) action across four trials to enable the kinematics of their block start and initial strides to be obtained using motion analysis software (APAS). Infra-red timing lights were utilised to measure the 10 m sprinting times. The coefficient of variation (CV %) calculation was adjusted in order to separate biological movement variability (BCV %) from variability induced by measurement error (SEE %). This adjustment revealed that measurement error highly inflated traditional measures of movement variability (CV %) by up to 72%,. Variability in task outcome kinematics was considerably lower than that observed in joint rotation patterns. Few biological variability measures had a direct relationship with reduced sprinting time

NOVEL INSIGHTS ON LOWER LIMB MUSCULOSKELETAL HEALTH AND PERFORMANCE IN PRE-ADOLESCENT AND ADOLESCENT GYMNASTS

New analyses are presented from the data of Bradshaw and Le Rossignol (2004) to examine the relationship between musculoskeletal health, and physical and performance qualities, with measures of leg stiffness in a group of female gymnasts. A gymnasts leg stiffness can be assessed through continuous jump (straight & bent legged) series tests, as well as from rebound jumps. Although the observations are retrospective, the study revealed a potential safe zone for ankle extensor stiffness. The gymnast with low stiffness had previously suffered a landing ankle injury; whilst four gymnasts with high stiffness had histories of take-off ankle injuries. Aside from profiling physical performance qualities, biomechanical (kinetic) testing has the potential to also aid in the assessment and management of the athlete’s functional musculoskeletal health (rehabilitation, injury risk)

The Effects of Blast Exposure on Protein Deimination in the Brain

Oxidative stress and calcium excitotoxicity are hallmarks of traumatic brain injury (TBI). While these early disruptions may be corrected over a relatively short period of time, long-lasting consequences of TBI including impaired cognition and mood imbalances can persist for years, even in the absence of any evidence of overt injury based on neuroimaging. This investigation examined the possibility that disordered protein deimination occurs as a result of TBI and may thus contribute to the long-term pathologies of TBI. Protein deimination is a calcium-activated, posttranslational modification implicated in the autoimmune diseases rheumatoid arthritis and multiple sclerosis, where aberrant deimination creates antigenic epitopes that elicit an autoimmune attack. The present study utilized proteomic analyses to show that blast TBI alters the deimination status of proteins in the porcine cerebral cortex. The affected proteins represent a small subset of the entire brain proteome and include glial fibrillary acidic protein and vimentin, proteins reported to be involved in autoimmune-based pathologies. The data also indicate that blast injury is associated with an increase in immunoglobulins in the brain, possibly representing autoantibodies directed against novel protein epitopes. These findings indicate that aberrant protein deimination is a biomarker for blast TBI and may therefore underlie chronic neuropathologies of head injury

A solar active region loop compared with a 2D MHD model

We analyzed a coronal loop observed with the Normal Incidence Spectrometer (NIS), which is part of the Coronal Diagnostic Spectrometer (CDS) on board the Solar and Heliospheric Observatory (SOHO). The measured Doppler shifts and proper motions along the selected loop strongly indicate unidirectional flows. Analysing the Emission Measure Curves of the observed spectral lines, we estimated that the temperature along the loop was about 380000 K. We adapted a solution of the ideal MHD steady equations to our set of measurements. The derived energy balance along the loop, as well as the advantages/disadvantages of this MHD model for understanding the characteristics of solar coronal loops are discussed.Comment: A&A in press, 10 pages, 6 figure