Particle energisation in a collapsing magnetic trap model : the relativistic regime

The authors acknowledge financial support by the UK’s Science and Technology Facilities Council through a Doctoral Training Grant (SEO) and Consolidated Grant ST/K000950/1 (SEO and TN).Context. In solar flares, a large number of charged particles is accelerated to high energies. By which physical processes this is achieved is one of the main open problems in solar physics. It has been suggested that during a flare, regions of the rapidly relaxing magnetic field can form a collapsing magnetic trap (CMT) and that this trap may contribute to particle energisation. Aims. In this Research Note we focus on a particular analytical CMT model based on kinematic magnetohydrodynamics. Previous investigations of particle acceleration for this CMT model focused on the non-relativistic energy regime. It is the specific aim of this Research Note to extend the previous work to relativistic particle energies. Methods. Particle orbits were calculated numerically using the relativistic guiding centre equations. We also calculated particle orbits using the non-relativistic guiding centre equations for comparison. Results. For mildly relativistic energies the relativistic and non-relativistic particle orbits mainly agree well, but clear deviations are seen for higher energies. In particular, the final particle energies obtained from the relativistic calculations are systematically lower than the energies reached from the corresponding non-relativistic calculations, and the mirror points of the relativistic orbits are systematically higher than for the corresponding non-relativistic orbits. Conclusions. While the overall behaviour of particle orbits in CMTs does not differ qualitatively when using the relativistic guiding centre equations, there are a few systematic quantitative differences between relativistic and non-relativistic particle dynamics.Publisher PDFPeer reviewe

Agricultural mechanisation systems analysis: tractor power selection for tillage operations

Primary tillage largely dictates the power requirement on an arable farm. As power and machinery costs continue to rise, it is important to provide a sound management base for the optimum selection of tractor size. A tractor power selection programme has been developed by examining a single operation for a single crop, namely, ploughing for cereals.The tractor power selection programme comprises seven essential sections each of which an be used separately and independently depending on the type of the output required. The even major steps are the prediction of soil moisture, soil workability, soil strength, tractor performance, plough draught and system cost and the selection of a limited number of suitable tractor plough combinations.For the prediction of daily fluctuations of soil moisture content, the amount of water rained by the soil is balanced against the amount of water lost. Water added to the soil in he form of precipitation and irrigation is lost by means of evapotranspiration, drainage and surface run -off. Potential evaporation is calculated by means of an empirical equation sing mean monthly air temperature and converted to actual evaporation from the soil and transpiration from vegetation where present. Factors are incorporated to correct for the dryness of the soil, the duration and intensity of precipitation and the stage of the crop which is covering the soil. Daily values of drainage flux was calculated from the hydraulic conductivicies and moisture content of the soil at saturation and field capacity and soil moisture content prior to commencement of drying. Existing empirical procedures were utilised to calculate run -off.By analysing the predicted soil moisture contents, each calendar day can be assigned as suitable for farm work (a work day) or unsuitable for a given operation (non -work day). As oil workability varies from soil to soil, machine to machine and farm manager to farm manager, the adoption of a unique soil moisture value to differentiate between soil workability and unworkability is unrealistic. A procedure has therefore been adopted to enable the number if work days to be calculated at different levels of soil moisture content or workability criteria. The data is analysed for a number of years (up to 20) and then the cumulated number years on which a given day was a work day or a non -work day with a given workability criterion was determined for different probability levels. This data is of direct relevance lot only to machinery planning but also to irrigation planning and for timeliness penalty evaluation.Soil strength in terms of the cone penetrometer resistance or cone index of the soil at a given soil workability criterion level is predicted by an empirical equation containing soil bulk density. The cone index influences the pull produced by the tractor for a given set of tyre and deflection data and the tractor power required. It also affects the draught requirements of the plough of given dimensions, tail angle, number of bodies and depth of cut.The cost of owning a machinery system is calculated in the form of the present annual cost, taking into account the effect of inflation and interest rate by using discounted cash flows. the purchase prices of tractors and implements were related to the average price per unit of power and per unit width of plough, respectively. Crop loss or timeliness penalties through delayed operations are also determined.Finally, the various different ploughing systems with different sizes of tractors and Ploughs and at different operations speeds are examined and a small number of suitable systems are presented in a form which enables the farmer or farm manager to take into account other critique management parameters of his particular farm business

Evidence for braggoriton excitations in opal photonic crystals infiltrated with highly polarizable dyes

Journal ArticleWe studied angle-dependent reflectivity spectra of opal photonic crystals infiltrated with cyanine dye aggregates, which are highly polarizable media with very large Rabi frequency. We show that, at resonance condition between the exciton-polariton of the dye aggregate and the Bragg gap, the Bragg stop band decomposes into two reflectivity bands with a semitransparent spectral range in between, that is due to propagation of braggoritons inside the gap

Excitations in opal photonic crystals infiltrated with polarizable media

Journal ArticlePhotonic crystals (PC) are a class of artificial structures with a periodic dielectric function. PCs can be a laboratory for testing fundamental processes involving interactions of radiation with matter in novel conditions. We have studied the optical properties of opal PCs that are infiltrated with highly polarizable media such as J-aggregates of cyanine dyes. Opals are self-assembled structures of silica (Si02) spheres. We report our studies on clarifying the relationship between a polaritonic gap and a photonic stop band (Bragg gap) when they resonantly coexist in the same structure. Infiltration of opal with polarizable molecules combines the polaritonic and Bragg diffractive effects. Both effects exist independently when the Bragg (at ω = ωB) and polaritonic (at ω = ωT) resonances are well separated in frequency. A completely different situation occurs when ωT ~ ωB- Such a condition was achieved in opals that were infiltrated with J-aggregates of cyanine dyes that have large Rabi frequency. Our measurements show some dramatic changes in the shape of the reflectivity plateaus, which are due to the interplay between the photonic band gap and the polaritonic gap. The experimental results on reflectivity and its dependence on the light propagation angle and concentration of the cyanine dyes are in agreement with the theoretical calculations

Laser properties of luminescent conducting polymers in open resonators

Journal ArticleWe have investigated the lasing properties of several luminescent conducting polymers, i.e. DOO-PPV and the bi-substituted polyacetylenes PDPA-nBu, and PHJPA, dissolved in various polar and non-polar solvents. PP V polymers emit with high quantum efficiencies in broad emission bands centered in the orange/red region of the spectrum, depending on the solvent, and the PDPA polymers emit in the blue/green region. Our tested laser resonators include polymer solutions excited with 100 ps pulses from a regeneratively amplified mode-locked Nd: YAG laser. We obtain pulsed, low- threshold (uJ-level) laser operation with repetition rate of up to 1 kHz. Resulting mainly from recent refinements in material quality, the DOO-PPV laser characteristics appear to be significantly improved compared to laser results reported originally in the literature. The dependencies of threshold pump energy and output versus input power characteristics on material parameters (type of solvent, polymer concentration) are investigated for a fixed optical gain length. The results are compared with the standard Rhodamine 590 organic dye system used in the same wavelength regions. We have observed that the well known phenomenon of "concentration quenching" in dye molecules does not happen in polymers. Spectral narrowing in PDPA-nBu solution, emitting near 500 nm, is also obtained for the first time

New aspects of particle acceleration in collapsing magnetic traps

Collapsing magnetic traps (CMTs) have been suggested as one of the mechanisms that could contribute to particle energisation in solar flares. The basic idea behind CMTs is that charged particles will be trapped on the magnetic field lines below the reconnection region of a flare. This thesis discusses a number of important new aspects in particle energisation processes in CMTs, based on the model by Giuliani et al. (2005). In particular, we extend previous studies of particle acceleration in this CMT model to the relativistic regime and compare our results obtained using relativistic guiding centre theory with results obtained using the non-relativistic guiding centre theory. The similarities and differences found are discussed. We then present a detailed study of the question, what leads to the trapping or escape of particle orbits from CMTs. The answer to this question is investigated by using results from the non-relativistic orbit calculations with guiding centre theory and a number of simple models for particle energy gain in CMTs. We find that there is a critical pitch angle dividing trapped particle orbits from the escaping particle orbits and that this critical pitch angle does not coincide with the initial loss cone angle. Furthermore, we also present a calculation of the time evolution of an anisotropic pressure tensor and of the plasma density under the assumptions that they evolve in line with our kinematic MHD CMT model and that the pressure tensor satisfies the double-adiabatic Chew-Goldburger-Low (CGL) theory. Finally, we make a first step to introduce Coulomb scattering by a Maxwellian background plasma into our guiding centre equations by changing them into a set of stochastic differential equations. We study the influence of a static background plasma onto selected particle orbits by pitch angle scattering and energy losses, and look at its effect on the particle energy and the trapping conditions

Evidence for Braggoriton Excitations in Opal Photonic Crystals Infiltrated with Highly Polarizable Dyes

We studied angle-dependent reflectivity spectra of opal photonic crystals infiltrated with cyanine dyes, which are highly polarizable media with very large Rabi frequency. We show that when resonance conditions between the exciton-polariton of the infiltrated dye and Bragg frequencies exist, then the Bragg stop band decomposes into two reflectivity bands with a semi-transparent spectral range in between that is due to light propagation inside the gap caused by the existence of braggoriton excitations. These novel excitations result from the interplay interaction between the Bragg gap with spatial modulation origin and the polariton gap due to the excitons, and may lead to optical communication traffic inside the gap of photonic crystals via channel waveguiding.Comment: LaTex, 5 pages, 3 figures include

TCL1B (T-cell leukemia/lymphoma 1B)

Review on TCL1B (T-cell leukemia/lymphoma 1B), with data on DNA, on the protein encoded, and where the gene is implicated