From Solar and Stellar Flares to Coronal Heating: Theory and Observations of How Magnetic Reconnection Regulates Coronal Conditions

There is currently no explanation of why the corona has the temperature and density it has. We present a model which explains how the dynamics of magnetic reconnection regulates the conditions in the corona. A bifurcation in magnetic reconnection at a critical state enforces an upper bound on the coronal temperature for a given density. We present observational evidence from 107 flares in 37 sun-like stars that stellar coronae are near this critical state. The model may be important to self-organized criticality models of the solar corona.Comment: 13 pages, 2 figures, accepted to Ap. J. Lett., February 200

Waves and instabilities in an anisotropic universe

The excitation of low frequency plasma waves in an expanding anisotropic cosmological model which contains a magnetic field frozen into the matter and pointing in the longitudinal direction is discussed. Using the exact equations governing finite-amplitude wave propagation in hydromagnetic media within the framework of general theory of relativity, we show that a spectrum of magnetized sound waves will be excited and form large scale ``\textit{damped oscillations}'' on the expanding universe. The characteristic frequency of the excited waves is slightly shifted away from the sound frequency and the shift depends on the strength of the primordial magnetic field. This magnetic field dependent shift may have an effect on the acoustic peaks of the CM

Akt in the pathogenesis of COPD

In this review we consider the therapeutic potential of targeting Akt for the treatment of COPD. Akt is a serine/threonine protein kinase that functions as a signaling intermediate linked to multiple signaling programs involved in survival, inflammation, and growth. Akt is closely associated with key membrane-bound receptors and represents a convergent integration point for multiple stimuli implicated in COPD pathogenesis. Persistent activation of Akt secondary to somatic mutations in regulatory oncogenes, such as PTEN, may explain why inflammation in COPD does not resolve when smoking is ceased. Akt is also implicated in the systemic manifestations of COPD such as skeletal muscle wasting and metabolic disturbances. Furthermore, targeting Akt may provide a useful means of limiting the severity and duration of disease exacerbations in COPD. As such, Akt represents a particularly attractive therapeutic target for the treatment of COPD. Interestingly, current knowledge suggests that both inhibitors and activators of Akt may be useful for treating different clinical subpopulations of COPD patients

Random walk through fractal environments

We analyze random walk through fractal environments, embedded in 3-dimensional, permeable space. Particles travel freely and are scattered off into random directions when they hit the fractal. The statistical distribution of the flight increments (i.e. of the displacements between two consecutive hittings) is analytically derived from a common, practical definition of fractal dimension, and it turns out to approximate quite well a power-law in the case where the dimension D of the fractal is less than 2, there is though always a finite rate of unaffected escape. Random walks through fractal sets with D less or equal 2 can thus be considered as defective Levy walks. The distribution of jump increments for D > 2 is decaying exponentially. The diffusive behavior of the random walk is analyzed in the frame of continuous time random walk, which we generalize to include the case of defective distributions of walk-increments. It is shown that the particles undergo anomalous, enhanced diffusion for D_F < 2, the diffusion is dominated by the finite escape rate. Diffusion for D_F > 2 is normal for large times, enhanced though for small and intermediate times. In particular, it follows that fractals generated by a particular class of self-organized criticality (SOC) models give rise to enhanced diffusion. The analytical results are illustrated by Monte-Carlo simulations.Comment: 22 pages, 16 figures; in press at Phys. Rev. E, 200

Glutathione Peroxidase-1 Primes Pro-Inflammatory Cytokine Production after LPS Challenge In Vivo

Reactive oxygen species produced during the innate immune response to LPS are important agents of anti-pathogen defence but may also cause oxidative lung damage. Glutathione peroxidase-1 (gpx-1) is an anti-oxidant enzyme that may protect lungs from such damage. We assessed the in vivo importance of gpx-1 in LPS-induced lung inflammation. Male wild-type (WT) or gpx-1 deficient (gpx-1−/−) mice were treated intranasally with PBS or 10 µg LPS and killed 3 and 24 h post LPS. Lungs were lavaged with PBS and then harvested for inflammatory marker expression. LPS caused an intense neutrophilia in WT BALF evident 3 and 24 h post challenge that was reduced in gpx-1−/− mice. In addition, LPS-treated gpx-1−/− mice had significantly fewer macrophages than LPS-treated WT mice. To understand the basis for this paradoxical reduction we assessed inflammatory cytokines and proteases at protein and transcript levels. MMP-9 expression and net gelatinase activity in BALF of gpx-1−/− mice treated with LPS for 3 and 24 h was no different to that found in LPS-treated WT mice. BALF from LPS-treated gpx-1−/− mice (3 h) had less TNF-α, MIP-2 and GM-CSF protein than LPS-treated WT mice. In contrast, LPS-induced increases in TNF-α, MIP-2 and GM-CSF mRNA expression in WT mice were similar to those observed in gpx-1−/− mice. These attenuated protein levels were unexpectedly not mirrored by reduced mRNA transcripts but were associated with increased 20S proteasome expression. Thus, these data suggest that gpx-1 primes pro-inflammatory cytokine production after LPS challenge in vivo

Apocynin and ebselen reduce influenza A virus-induced lung inflammation in cigarette smoke-exposed mice

Influenza A virus (IAV) infections are a common cause of acute exacerbations of chronic obstructive pulmonary disease (AECOPD). Oxidative stress is increased in COPD, IAV-induced lung inflammation and AECOPD. Therefore, we investigated whether targeting oxidative stress with the Nox2 oxidase inhibitors and ROS scavengers, apocynin and ebselen could ameliorate lung inflammation in a mouse model of AECOPD. Male BALB/c mice were exposed to cigarette smoke (CS) generated from 9 cigarettes per day for 4 days. On day 5, mice were infected with 1 × 104.5 PFUs of the IAV Mem71 (H3N1). BALF inflammation, viral titers, superoxide production and whole lung cytokine, chemokine and protease mRNA expression were assessed 3 and 7 days post infection. IAV infection resulted in a greater increase in BALF inflammation in mice that had been exposed to CS compared to non-smoking mice. This increase in BALF inflammation in CS-exposed mice caused by IAV infection was associated with elevated gene expression of pro-inflammatory cytokines, chemokines and proteases, compared to CS alone mice. Apocynin and ebselen significantly reduced the exacerbated BALF inflammation and pro-inflammatory cytokine, chemokine and protease expression caused by IAV infection in CS mice. Targeting oxidative stress using apocynin and ebselen reduces IAV-induced lung inflammation in CS-exposed mice and may be therapeutically exploited to alleviate AECOPD

Local re-acceleration and a modified thick target model of solar flare electrons

The collisional thick target model (CTTM) of solar hard X-ray (HXR) bursts has become an almost 'Standard Model' of flare impulsive phase energy transport and radiation. However, it faces various problems in the light of recent data, particularly the high electron beam density and anisotropy it involves.} {We consider how photon yield per electron can be increased, and hence fast electron beam intensity requirements reduced, by local re-acceleration of fast electrons throughout the HXR source itself, after injection.} {We show parametrically that, if net re-acceleration rates due to e.g. waves or local current sheet electric (${\cal E}$) fields are a significant fraction of collisional loss rates, electron lifetimes, and hence the net radiative HXR output per electron can be substantially increased over the CTTM values. In this local re-acceleration thick target model (LRTTM) fast electron number requirements and anisotropy are thus reduced. One specific possible scenario involving such re-acceleration is discussed, viz, a current sheet cascade (CSC) in a randomly stressed magnetic loop.} {Combined MHD and test particle simulations show that local ${\cal E}$ fields in CSCs can efficiently accelerate electrons in the corona and and re-accelerate them after injection into the chromosphere. In this HXR source scenario, rapid synchronisation and variability of impulsive footpoint emissions can still occur since primary electron acceleration is in the high Alfv\'{e}n speed corona with fast re-acceleration in chromospheric CSCs. It is also consistent with the energy-dependent time-of-flight delays in HXR features.Comment: 8 pages, 2 figure

Feed and nutrition in organic aquaculture

publishedVersio

The role of antihydrogen formation in the radial transport of antiprotons in positron plasmas

Simulations of the behaviour of antiprotons in positron clouds during antihydrogen formation.The work added to our understanding of the underlying processes, including the dominant role played by antihydrogen formation itself

'TaxTrack': Introducing a Democratic Innovation for Taxation

In this article we introduce an input-oriented democratic innovation – that we term ‘TaxTrack’ – which offers individual taxpayers the means to engage with their political economies in three ways. After joining the TaxTrack program, an individual can: (1) see and understand how much, and what types, of taxes they have contributed, (2) see and understand how their tax contributions are, or have been, used, and (3) control what their tax contributions can, or cannot, be spent on. We explain this democratic innovation in two ways. The first is through evocation to prefigure what the innovation could look like in future practise which raises the prospects for both good and problematic outcomes. The second is through formal theory to produce a detailed model of the innovation to assist theory building. We conclude by discussing three interactive outcomes of ‘TaxTrack’ through the democratic innovations literature to establish the beginnings of a theory for the model. This theory tells us that ‘TaxTrack’ can return benefits to its users and the democratic regimes in which they are located but it may also place restrictions on output-oriented innovations like Participatory Budgeting