Sunspot rotation. I. A consequence of flux emergence

Context. Solar eruptions and high flare activity often accompany the rapid rotation of sunspots. The study of sunspot rotation and the mechanisms driving this motion are therefore key to our understanding of how the solar atmosphere attains the conditions necessary for large energy release. Aims. We aim to demonstrate and investigate the rotation of sunspots in a 3D numerical experiment of the emergence of a magnetic flux tube as it rises through the solar interior and emerges into the atmosphere. Furthermore, we seek to show that the sub-photospheric twist stored in the interior is injected into the solar atmosphere by means of a definitive rotation of the sunspots. Methods. A numerical experiment is performed to solve the 3D resistive magnetohydrodynamic (MHD) equations using a Lagrangian-Remap code. We track the emergence of a toroidal flux tube as it rises through the solar interior and emerges into the atmosphere investigating various quantities related to both the magnetic field and plasma. Results. Through detailed analysis of the numerical experiment, we find clear evidence that the photospheric footprints or sunspots of the flux tube undergo a rotation. Significant vertical vortical motions are found to develop within the two polarity sources after the field emerges. These rotational motions are found to leave the interior portion of the field untwisted and twist up the atmospheric portion of the field. This is shown by our analysis of the relative magnetic helicity as a significant portion of the interior helicity is transported to the atmosphere. In addition, there is a substantial transport of magnetic energy to the atmosphere. Rotation angles are also calculated by tracing selected fieldlines; the fieldlines threading through the sunspot are found to rotate through angles of up to 353 degrees over the course of the experiment

A Novel Approach for the Particle-in-Cell Modelling of Gridded Ion Engine Plume Neutralisation

The Particle-in-Cell modelling of gridded ion engine plume neutralisation has been simplified when compared to traditional methods. This results in significantly less computational resources being required. The NSTAR engine was modelled as a reference, where simulated specific impulse values were found to be 5% higher than the real engine. This method will be most suited to rapid prototyping and optimisation studies, where speed of simulations is an important factor

The influence of corotation on the high energy synchrotron emission in Crab-like pulsars

For Crab-like pulsars we consider the synchrotron mechanism influenced by relativistic effects of rotation to study the production of the very high energy (VHE) pulsed radiation. The process of quasi-linear diffusion (QLD) is applied to prevent the damping of the synchrotron emission due to extremely strong magnetic field. By examining the kinetic equation governing the QLD, apart from the synchrotron radiative force, we taken into account the the so-called reaction force, that is responsible for corotation and influences plasma processes in the nearby zone of the light cylinder (LC) surface. We have found that the relativistic effects of rotation significantly change efficiency of the quasi-linear diffusion. In particular, examining magnetospheric parameters typical for Crab-like pulsars, it has been shown that unlike the situation, where relativistic effects of rotation are not important, on the LC surface, the relativistic electrons via the synchrotron mechanism may produce photons even in the TeV domain. It is shown that the VHE radiation is strongly correlated with the relatively low frequency emission.Comment: 5 pages, 2 figure

Self-trapping of strong electromagnetic beams in relativistic plasmas

Interaction of an intense electromagnetic (EM) beam with hot relativistic plasma is investigated. It is shown that the thermal pressure brings about a fundamental change in the dynamics - localized, high amplitude, EM field structures, not accessible to a cold (but relativisic) plasma, can now be formed under well- defined conditions. Examples of the trapping of EM beams in self-guiding regimes to form stable 2D solitonic structures in a pure e-p plasma are worked out.Comment: 9 pages, 6 figure

LARGE ROOT ANGLE1, encoding OsPIN2, is involved in root system architecture in rice

Root system architecture is very important for plant growth and crop yield. It is essential for nutrient and water uptake, anchoring, and mechanical support. Root growth angle (RGA) is a vital constituent of root system architecture and is used as a parameter for variety evaluation in plant breeding. However, little is known about the underlying molecular mechanisms that determine root growth angle in rice (Oryza sativa). In this study, a rice mutant large root angle1 (lra1) was isolated and shown to exhibit a large RGA and reduced sensitivity to gravity. Genome resequencing and complementation assays identified OsPIN2 as the gene responsible for the mutant phenotypes. OsPIN2 was mainly expressed in roots and the base of shoots, and showed polar localization in the plasma membrane of root epidermal and cortex cells. OsPIN2 was shown to play an important role in mediating root gravitropic responses in rice and was essential for plants to produce normal RGAs. Taken together, our findings suggest that OsPIN2 plays an important role in root gravitropic responses and determining the root system architecture in rice by affecting polar auxin transport in the root tip

On the origin of the circular polarization in radio pulsars

Properties of circularly polarized waves are studied in the pulsar magnetosphere plasma. It is shown that some observational characteristics of the circular polarization observed in the pulsar radio emission can be qualitatively explained in the framework of the model based on anomalous Doppler resonance. Performed analysis provides that if the difference between Lorentz factors of electrons and positrons is relatively high, one of the circularly polarized waves becomes super-luminal and therefore can not be generated by cyclotron instability. We suggest that this case corresponds to the pulsars with the domination of one hand of circular polarization through the whole averaged pulse profile at all observed frequencies. For intermediate values of the difference between Lorentz factors both circularly polarized waves are generated, but the waves of one handness are much more effectively generated for high frequencies, whereas generation of another handness dominates for low frequencies. This should correspond to the pulsars with strong frequency dependence of the degree of circular polarization. The case of relatively small difference between Lorentz factors corresponds to the pulsars with sign reversal of the circular polarization in the centre of averaged pulse profiles.Comment: MNRAS, accepte

Assessment of Perivascular Space Morphometry Across the White Matter in Huntington's Disease Using MRI

BACKGROUND: Perivascular spaces (PVS) are fluid-filled cavities surrounding small cerebral blood vessels. There are limited reports of enlarged PVS across the grey matter in manifest Huntington's disease (HD). Little is known about how PVS morphometry in the white matter may contribute to HD. Enlarged PVS have the potential to both contribute to HD pathology and affect the distribution and success of intraparenchymal and intrathecally administered huntingtin-lowering therapies. OBJECTIVE: To investigate PVS morphometry in the global white matter across the spectrum of HD. Relationships between PVS morphometry and disease burden and severity measures were examined. METHODS: White matter PVS were segmented on 3T T2 W MRI brain scans of 33 healthy controls, 30 premanifest HD (pre-HD), and 32 early manifest HD (early-HD) participants from the Vancouver site of the TRACK-HD study. PVS count and total PVS volume were measured. RESULTS: PVS total count slightly increased in pre-HD (p = 0.004), and early-HD groups (p = 0.005), compared to healthy controls. PVS volume, as a percentage of white matter volume, increased subtly in pre-HD compared to healthy controls (p = 0.044), but not in early-HD. No associations between PVS measures and HD disease burden or severity were found. CONCLUSIONS: This study reveals relatively preserved PVS morphometry across the global white matter of pre-HD and early-HD. Subtle morphometric abnormalities are implied but require confirmation in a larger cohort. However, in conjunction with previous publications, further investigation of PVS in HD and its potential impact on future treatments, with a focus on subcortical grey matter, is warranted

P137 Supporting patients to get the best from their osteoporosis treatment; what works for whom, why and in what circumstance: a rapid realist review

Abstract Background/Aims For two decades, clinicians and academics have been writing about the problem of poor adherence in osteoporosis, while people with osteoporosis have identified a need for more follow up and information about medicines. We aimed to understand what works in supporting people with osteoporosis to get the best from their medicines, and specifically, to understand what mechanisms enable components of interventions to support osteoporosis medication optimisation and the underlying contextual conditions that enabled these mechanisms. Methods We conducted a Rapid Realist Review. The scope was informed by a workshop of the Effectiveness Working Group of the Royal Osteoporosis Society Osteoporosis and Bone Research Academy and the approach informed by background syntheses of qualitative literature and the Perceptions and Practicalities Approach as an underpinning conceptual framework. A primary search identified observational or interventional studies which aimed to improve medicines adherence or optimisation. Included studies were assessed for quality and data extracted relating to context, mechanism and outcomes. A supplementary second search was conducted to gain additional insight on included key papers and emerging mechanisms. Extracted data were interrogated by authors independently for patterns of context-mechanism-outcome configurations and further discussed in weekly team meetings. Recommendations for research and clinical practice were co-developed with clinical and lay stakeholders. Results 41 papers were included. We identified five contextual timepoints for the person with osteoporosis (identifying a problem; starting medicine; continuing medicine) and the practitioner and healthcare system (making a diagnosis and giving a treatment recommendation; reviewing medicine) and mechanisms relating to patient informed decision making, treatment burden, supporting routinisation and memory, supporting clinical decision making, targeting support, and approaches which were integrated and sustainable. Interventions which support patient informed decision making, improve patient knowledge and understanding, have potential to influence long-term commitment to treatment, although few studies explicitly addressed patients’ perceptions of illness and treatment as recommended in NICE guidelines. During treatment, targeting additional consultations to those most in need may be a cost and clinically effective approach to enable this. Supporting primary care clinician decision making and integration of primary and secondary care services also appears to be important, in improving rates of treatment initiation and adherence. Supporting patients’ ability to adhere (eg by lowering treatment burden and issuing reminders) may be helpful to address practical difficulties but there is little evidence to support the use of reminders alone. Conclusion For medicines optimisation for people with osteoporosis, we suggest a need for more patient-centred interventions to address patients’ perceptions of illness and treatment, and reduce treatment burden. Specialist services should consider the extent to which they integrate with, and support primary care clinical decision-making, in order to impact long-term clinical outcomes. Specific research recommendations have been co-developed, to address these knowledge gaps. Disclosure Z. Paskins: Grants/research support; NIHR, Versus Arthritis, Royal Osteoporosis Society. O. Babatunde: None. A. Sturrock: None. L. Toh: None. R. Horne: None. I. Maidment: None. </jats:sec

Properties of Flares-Generated Seismic Waves on the Sun

The solar seismic waves excited by solar flares (``sunquakes'') are observed as circular expanding waves on the Sun's surface. The first sunquake was observed for a flare of July 9, 1996, from the Solar and Heliospheric Observatory (SOHO) space mission. However, when the new solar cycle started in 1997, the observations of solar flares from SOHO did not show the seismic waves, similar to the 1996 event, even for large X-class flares during the solar maximum in 2000-2002. The first evidence of the seismic flare signal in this solar cycle was obtained for the 2003 ``Halloween'' events, through acoustic ``egression power'' by Donea and Lindsey. After these several other strong sunquakes have been observed. Here, I present a detailed analysis of the basic properties of the helioseismic waves generated by three solar flares in 2003-2005. For two of these flares, X17 flare of October 28, 2003, and X1.2 flare of January 15, 2005, the helioseismology observations are compared with simultaneous observations of flare X-ray fluxes measured from the RHESSI satellite. These observations show a close association between the flare seismic waves and the hard X-ray source, indicating that high-energy electrons accelerated during the flare impulsive phase produced strong compression waves in the photosphere, causing the sunquake. The results also reveal new physical properties such as strong anisotropy of the seismic waves, the amplitude of which varies significantly with the direction of propagation. The waves travel through surrounding sunspot regions to large distances, up to 120 Mm, without significant decay. These observations open new perspectives for helioseismic diagnostics of flaring active regions on the Sun and for understanding the mechanisms of the energy release and transport in solar flares.Comment: 12 pages, 4 figures, submitted to Ap

Plasmoid-Induced-Reconnection and Fractal Reconnection

As a key to undertanding the basic mechanism for fast reconnection in solar flares, plasmoid-induced-reconnection and fractal reconnection are proposed and examined. We first briefly summarize recent solar observations that give us hints on the role of plasmoid (flux rope) ejections in flare energy release. We then discuss the plasmoid-induced-reconnection model, which is an extention of the classical two-ribbon-flare model which we refer to as the CSHKP model. An essential ingredient of the new model is the formation and ejection of a plasmoid which play an essential role in the storage of magnetic energy (by inhibiting reconnection) and the induction of a strong inflow into reconnection region. Using a simple analytical model, we show that the plasmoid ejection and acceleration are closely coupled with the reconnection process, leading to a nonlinear instability for the whole dynamics that determines the macroscopic reconnection rate uniquely. Next we show that the current sheet tends to have a fractal structure via the following process path: tearing, sheet thinning, Sweet- Parker sheet, secondary tearing, further sheet thinning... These processes occur repeatedly at smaller scales until a microscopic plasma scale (either the ion Larmor radius or the ion inertial length) is reached where anomalous resistivity or collisionless reconnection can occur. The current sheet eventually has a fractal structure with many plasmoids (magnetic islands) of different sizes. When these plasmoids are ejected out of the current sheets, fast reconnection occurs at various different scales in a highly time dependent manner. Finally, a scenario is presented for fast reconnection in the solar corona on the basis of above plasmoid-induced-reconnection in a fractal current sheet.Comment: 9 pages, 11 figures, with using eps.sty; Earth, Planets and Space in press; ps-file is also available at http://stesun8.stelab.nagoya-u.ac.jp/~tanuma/study/shibata2001