Generation of Alfven Waves by Magnetic Reconnection

In this paper, results of 2.5-dimensional magnetohydrodynamical simulations are reported for the magnetic reconnection of non-perfectly antiparallel magnetic fields. The magnetic field has a component perpendicular to the computational plane, that is, guide field. The angle theta between magnetic field lines in two half regions is a key parameter in our simulations whereas the initial distribution of the plasma is assumed to be simple; density and pressure are uniform except for the current sheet region. Alfven waves are generated at the reconnection point and propagate along the reconnected field line. The energy fluxes of the Alfven waves and magneto-acoustic waves (slow mode and fast mode) generated by the magnetic reconnection are measured. Each flux shows the similar time evolution independent of theta. The percentage of the energies (time integral of energy fluxes) carried by the Alfven waves and magneto-acoustic waves to the released magnetic energy are calculated. The Alfven waves carry 38.9%, 36.0%, and 29.5% of the released magnetic energy at the maximum (theta=80^\circ) in the case of beta=0.1, 1, and 20 respectively, where beta is the plasma beta (the ratio of gas pressure to magnetic pressure). The magneto-acoustic waves carry 16.2% (theta=70^\circ), 25.9% (theta=60^\circ), and 75.0% (theta=180^\circ) of the energy at the maximum. Implications of these results for solar coronal heating and acceleration of high-speed solar wind are discussed.Comment: Accepted for publication in PASJ. 24 pages, 11 figure

DETERMINATION OF INPUT LASER ENERGY FOR MELTING POWDER LAYERS OF VARIOUS THICKNESSES IN HIGH-SPEED PBF-LB/P USING NEARINFRARED LASER AND ABSORBENT

The rate of production of PBF-LB/P can be increased by increasing the layer thickness. However, this reduces the part resolution in the stacking direction. To obtain both a high rate of production and high part resolution, layer thickness adjustment in accordance with part geometry can be effective. Optimizing the input laser energy with respect to the layer thickness ensures sufficient melting and part strength. According to previous studies, the use of a nearinfrared laser and absorbent can increase penetration depth or depth of fusion. However, the optical properties of the powder bed can vary significantly depending on the layer thickness, and, therefore, the input energy that actually contributes to melting also changes with layer thickness. This study proposes a method for determining the input laser energy for various layer thickness without trial and error by estimating the amount of energy required to melt the powder layer while accounting for the optical properties of the bed.Mechanical Engineerin

Considerations of internal void generation process by observation of melting and solidification behavior in low temperature laser sintering of PEEK

Laser sintering of PEEK performed below the crystallization temperature has been achieved in previous study by low temperature process that anchors the part to a rigid base plate to suppress warpage during processing. However, significant surface roughness and large internal voids are sometimes generated in the parts built by low temperature process, and there are problems in stability of parts quality. The purpose of this study is to contribute to quality improvement of laser sintering of PEEK by low temperature process. It was attempted that clarify the process of surface roughness and void generation by observing the melting and solidification behavior of the material during process with a video camera. From these observation results, it was assumed that the amount of volume change from powder to liquid due to melting and the amount of shrinkage due to solidification affect part quality such as surface roughness and internal voids.Mechanical Engineerin

グルコースオキシダーゼ/キチン-白金修飾カーボンペースト電極におけるカーボン粉末の形状の評価

In the present study, a carbon paste electrode modified with chitin and platinum powders was constructed to evaluate features of graphite powder. Pyrolitic graphite, spherical graphite, and artificial graphite were selected to fabricate the electrode. In order to evaluate the property of the graphite powder, glucose sensor with the graphite powder was developed. After glucose oxidase was immobilized to the chitin powder on the electrode surface due to an electrostatic interaction, the electrode response of the hydrogen peroxide produced from glucose was measured. The properties of the graphite powders were monitored by the electrode response. As a result, the greatest response was obtained by the electrode with the artificial graphite. The electrode was applied to evaluate the amount of chitin, the immobilization time of the glucose oxidase, and the concentration of the enzyme. Because the chitin and platinum powders were contained in the electrode surface only, voltammetric measurements of glucose were carried out in small amounts of platinum powder

Distribution of Faraday Rotation Measure in Jets from Active Galactic Nuclei II. Prediction from our Sweeping Magnetic Twist Model for the Wiggled Parts of AGN Jets and Tails

Distributions of Faraday rotation measure (FRM) and the projected magnetic field derived by a 3-dimensional simulation of MHD jets are investigated based on our "sweeping magnetic twist model". FRM and Stokes parameters were calculated to be compared with radio observations of large scale wiggled AGN jets on kpc scales. We propose that the FRM distribution can be used to discuss the 3-dimensional structure of magnetic field around jets and the validity of existing theoretical models, together with the projected magnetic field derived from Stokes parameters. In the previous paper, we investigated the basic straight part of AGN jets by using the result of a 2-dimensional axisymmetric simulation. The derived FRM distribution has a general tendency to have a gradient across the jet axis, which is due to the toroidal component of the magnetic field generated by the rotation of the accretion disk. In this paper, we consider the wiggled structure of the AGN jets by using the result of a 3-dimensional simulation. Our numerical results show that the distributions of FRM and the projected magnetic field have a clear correlation with the large scale structure of the jet itself, namely, 3-dimensional helix. Distributions, seeing the jet from a certain direction, show a good matching with those in a part of 3C449 jet. This suggests that the jet has a helical structure and that the magnetic field (especially the toroidal component) plays an important role in the dynamics of the wiggle formation because it is due to a current-driven helical kink instability in our model.Comment: Accepted for publication in Ap

On the Origin of the Slow Speed Solar Wind: Helium Abundance Variations

The First Ionization Potential (FIP) effect is the by now well known enhancement in abundance over photospheric values of Fe and other elements with first ionization potential below about 10 eV observed in the solar corona and slow speed solar wind. In our model, this fractionation is achieved by means of the ponderomotive force, arising as Alfv\'en waves propagate through or reflect from steep density gradients in the solar chromosphere. This is also the region where low FIP elements are ionized, and high FIP elements are largely neutral leading to the fractionation as ions interact with the waves but neutrals do not. Helium, the element with the highest FIP and consequently the last to remain neutral as one moves upwards can be depleted in such models. Here, we investigate this depletion for varying loop lengths and magnetic field strengths. Variations in this depletion arise as the concentration of the ponderomotive force at the top of the chromosphere varies in response to Alfv\'en wave frequency with respect to the resonant frequency of the overlying coronal loop, the magnetic field, and possibly also the loop length. We find that stronger depletions of He are obtained for weaker magnetic field, at frequencies close to or just above the loop resonance. These results may have relevance to observed variations of the slow wind solar He abundance with wind speed, with slower slow speed solar wind having a stronger depletion of He.Comment: 28 pages, 12 figures, accepted to Ap

Magnetohydrodynamic jets from different magnetic field configurations

Using axisymmetric MHD simulations we investigate how the overall jet formation is affected by a variation in the disk magnetic flux profile and/or the existence of a central stellar magnetosphere. Our simulations evolve from an initial, hydrostatic equilibrium state in a force-free magnetic field configuration. We find a unique relation between the collimation degree and the disk wind magnetization power law exponent. The collimation degree decreases for steeper disk magnetic field profiles. Highly collimated outflows resulting from a flat profile tend to be unsteady. We further consider a magnetic field superposed of a stellar dipole and a disk field in parallel or anti-parallel alignment. Both stellar and disk wind may evolve in a pair of outflows, however, a reasonably strong disk wind component is essential for jet collimation. Strong flares may lead to a sudden change in mass flux by a factor two. We hypothesize that such flares may eventually trigger jet knots.Comment: 5 pages, 4 figures; proceedings from conference: Protostellar Jets in Context, held in Rhodes, July 7-12, 200

The role of torsional Alfven waves in coronal heating

In the context of coronal heating, among the zoo of MHD waves that exist in the solar atmosphere, Alfven waves receive special attention. Indeed, these waves constitute an attractive heating agent due to their ability to carry over the many different layers of the solar atmosphere sufficient energy to heat and maintain a corona. However, due to their incompressible nature these waves need a mechanism such as mode conversion (leading to shock heating), phase mixing, resonant absorption or turbulent cascade in order to heat the plasma. New observations with polarimetric, spectroscopic and imaging instruments such as those on board of the japanese satellite Hinode, or the SST or CoMP, are bringing strong evidence for the existence of energetic Alfven waves in the solar corona. In order to assess the role of Alfven waves in coronal heating, in this work we model a magnetic flux tube being subject to Alfven wave heating through the mode conversion mechanism. Using a 1.5-dimensional MHD code we carry out a parameter survey varying the magnetic flux tube geometry (length and expansion), the photospheric magnetic field, the photospheric velocity amplitudes and the nature of the waves (monochromatic or white noise spectrum). It is found that independently of the photospheric wave amplitude and magnetic field a corona can be produced and maintained only for long (> 80 Mm) and thick (area ratio between photosphere and corona > 500) loops. Above a critical value of the photospheric velocity amplitude (generally a few km/s) the corona can no longer be maintained over extended periods of time and collapses due to the large momentum of the waves. These results establish several constraints on Alfven wave heating as a coronal heating mechanism, especially for active region loops.Comment: 39 pages, 8 figures; http://stacks.iop.org/0004-637X/712/49

Cellular Polyamine Catalogues of the Five Classes of the PhylumProteobacteria: Distributions of Homospermidine within the ClassAlphaproteobacteria, Hydroxyputrescine within the ClassBetaproteobacteria, Norspermidine within the ClassGammaproteobacteria, and Spermine within the ClassesDeltaproteobacteria and Epsilonproteobacteria

Cellular polyamines extracted from reclassified or newly validated 47 alphaproteobacteria, 46 betaproteobacteria, 96 gammaproteobacteria, 12 deltaproteobacteria and 10 epsilonproteobacteria were analyzed by high-performance liquid chromatography. Homospermidine was widely distributed within the class Alphaproteobacteria, however, homospermidine-dominant type, spermidine-dominant type and homospermidine/spermidinedominant type were found and the three triamine profiles were genus-specific. The all genera belonging to the class Betaproteobacteria, ubiquitously contained putrescine and 2- hydroxyputrescine. Triamines were absent in almost betaproteobacteria. Many genera, including psychrophilic species, of the class Gammaproteobacteria, contained putrescine and spermidine as the major polyaminenes. Diaminopropane and norspermidine were selectively distributed in several genera of the class Gammaproteobacteria. Spermidine was the major polyamine in the classes Deltaproteobacteria and Epsilonproteobacteria. Spermine was found in some thermophiles within Betaproteobacteria, Deltaproteobacteria and Epsilonproteobacteria, suggesting that the occurrence of spermine correlate to their thermophily. Additional these polyamine catalogues serve for the classification of the phylum Proteobacteria, as a chemotaxonomic marker