Modulational Instability of Fast Sausage Mode as One of the Possible Mechanisms for Quasiperiodic Pulsations during Solar Flares

Quasiperiodic pulsations (QPPs) are frequently observed in the entire range of the electromagnetic spectrum during solar flares, and there can be many possible mechanisms leading to this phenomenon. In the present work, we demonstrate the possibility of the generation of QPPs by a nonlinear fast sausage mode in a coronal loop. The coronal loop itself is represented by an infinitely long homogenous magnetic flux tube, which in many cases is a good approximation, and the nonlinearity of the fast sausage mode is modeled by the nonlinear Schrödinger equation (NSE) with a cubic nonlinearity. We have shown that the frequency-renormalized plane wave solution, which happens to be an exact solution of the NSE, transforms into a series of quasiperiodic oscillations (QPOs) due to the so-called modulational instability or the Benjamin–Feir instability. Our numerical solutions show that such QPOs evolve at almost every point above a certain height along the magnetic flux tube, which represents the coronal loop. As the fast sausage mode perturbs the plasma density strongly, the density perturbations caused by the QPOs of the nonlinear fast sausage mode correspondingly modulate the radiation throughout the electromagnetic spectrum, resulting in the emergence of the corresponding QPPs. This mechanism should therefore be able to describe some of the observed QPPs.

Reflection and Evolution of Torsional Alfvén Pulses in Zero-beta Flux Tubes

We model the behavior of a torsional Alfvén pulse, assumed to propagate through the chromosphere. Building on our existing model, we utilize the zero-beta approximation appropriate for plasma in an intense magnetic flux tube, e.g., a magnetic bright point. The model is adapted to investigate the connection between these features and chromospheric spicules. A pulse is introduced at the lower, photospheric boundary of the tube as a magnetic shear perturbation, and the resulting propagating Alfvén waves are reflected from an upper boundary, representing the change in density found at the transition region. The induced upward mass flux is followed by the reversal of the flux that may be identified with the rising and falling behavior of certain lower solar atmospheric jets. The ratio of the transmitted and reflected mass flux is estimated and compared with the relative total mass of spicules and the solar wind. An example is used to study the properties of the pulse. We also find that the interaction between the initial and reflected waves may create a localized flow that persists independently from the pulse itself.

The Electron Structure of the Solar Wind

Time-series measurements of the number density ncore and temperature Tcore of the core-electron population of the solar wind are examined at 1 AU and at 0.13 AU using measurements from the WIND and Parker Solar Probe spacecraft, respectively. A statistical analysis of the ncore and Tcore measurements at 1 AU finds that the core-electron spatial structure of the solar wind is related to the magnetic-flux-tube structure of the solar wind; this electron structure is characterized by jumps in the values of ncore and Tcore when passing from one magnetic flux tube into the next. The same types of flux-tube jumps are seen for Tcore at 0.13 AU. Some models of the interplanetary electrical potential of the heliosphere predict that Tcore is a direct measure of the local electrical potential in the heliosphere. If so, then jumps seen in Tcore represent jumps in the electrical potential from flux tube to flux tube. This may imply that the interplanetary electrical potential (and its effect on the radial evolution away from the Sun of solar-wind ions and electrons) independently operates in each flux tube of the heliosphere.

Magnetic nulls in interacting dipolar fields

The prominence of nulls in reconnection theory is due to the expected singular current density and the indeterminacy of field lines at a magnetic null. Electron inertia changes the implications of both features. Magnetic field lines are distinguishable only when their distance of closest approach exceeds a distance $\varDelta _d$ . Electron inertia ensures $\varDelta _d\gtrsim c/\omega _{pe}$ . The lines that lie within a magnetic flux tube of radius $\varDelta _d$ at the place where the field strength $B$ is strongest are fundamentally indistinguishable. If the tube, somewhere along its length, encloses a point where $B=0$ vanishes, then distinguishable lines come no closer to the null than $\approx (a^2c/\omega _{pe})^{1/3}$ , where $a$ is a characteristic spatial scale of the magnetic field. The behaviour of the magnetic field lines in the presence of nulls is studied for a dipole embedded in a spatially constant magnetic field. In addition to the implications of distinguishability, a constraint on the current density at a null is obtained, and the time required for thin current sheets to arise is derived.

Coronal loops in a box: 3D models of their internal structure, dynamics and heating

<p>The corona of the Sun, and probably also of other stars, is built up by loops defined through the magnetic field. They vividly appear in solar observations in the extreme UV and X-rays. High-resolution observations show individual strands with diameters down to a few 100 km, and so far it remains open what defines these strands, in particular their width, and where the energy to heat them is generated.</p><p>The aim of our study is to understand how the magnetic field couples the different layers of the solar atmosphere, how the energy generated by magnetoconvection is transported into the upper atmosphere and dissipated, and how this process determines the scales of observed bright strands in the loop.</p><p>To this end, we conduct 3D resistive MHD simulations with the MURaM code. We include the effects of heat conduction, radiative transfer and optically thin radiative losses.<br>We study an isolated coronal loop that is rooted with both footpoints in a shallow convection zone layer. To properly resolve the internal structure of the loop while limiting the size of the computational box, the coronal loop is modelled as a straightened magnetic flux tube. By including part of the convection zone, we drive the evolution of the corona self-consistently by magnetoconvection.</p><p>We find that the energy injected into the loop is generated by internal coherent motions within strong magnetic elements. <br>The resulting Poynting flux is channelled into the loop in vortex tubes forming a magnetic connection between the photosphere and corona, where it is dissipated and heats the upper atmosphere.</p><p>The coronal emission as it would be observed in solar extreme UV or X-ray observations, e.g. with AIA or XRT, shows transient bright strands.<br>The widths of these strands are consistent with observations. From our model we find that the width of the strands is governed by the size of the individual photospheric magnetic field concentrations where the field lines through these strands are rooted. Essentially, each coronal strand is mainly rooted in a single magnetic patch in the photosphere, and the energy to heat the strand is generated by internal motions within this magnetic concentration.</p><p>With this model we can build a coherent picture of how energy and matter are transported into the upper solar atmosphere and how these processes structure the interior of coronal loops.</p>

Improved Method for Distributed Parameter Model of Solenoid Valve Based on Kriging Basis Function Predictive Identification Program

In this paper, a method for the improvement of the calculation accuracy of the distributed parameter model (DPM) of electromagnetic devices is proposed based on the kriging basis function predictive identification program (PIP). Kriging is mainly an optimal interpolation method which uses spatial self-covariance, and takes a polynomial as the basis function. The accuracy of the kriging-based surrogate model can be improved by adjusting the related functions and hyperparameters. Based on the DPM of a solenoid valve, there exist certain errors in the estimation. They can be summarized as follows: Firstly, the estimation error of magnetic flux leakage (MFL) permeance is caused directly by the deviation of the magnetic flux tube due to the segmented magnetic field line. Secondly, the estimation error of soft magnetic resistance because of the nonlinearity of the permeability of soft magnetic material leads to the change of soft magnetic resistance alongside the magnetic flux. In this paper, an improved kriging error correction method is applied to modify the leak permeance and soft magnetic resistance calculation. The kriging basis function is adjusted to adapt to the data curve of the MFL permeance error data. The calculated MFL permeance data are compared with the error variation data to select the appropriate basis function. To improve the computational efficiency, the PIP is proposed to select the appropriate basis function. The modified MFL permeance data and soft magnetic resistance are substituted into the DPM for improving the computational accuracy and efficiency of the solenoid valve.

DNA bioelectric field: a futuristic bioelectric marker of cancer, aging and death – A working hypothesis

Telomeres are associated with the ends of DNA double strands. The lengths of the telomeres are controlled by the telomerase enzyme. The shortening of the telomeres is known to relate to aging. In cancers, telomere lengths are abnormally short. Telomeres could act as buffers shielding the part of DNA coding for the proteins. For cancer cells, germ cells and stem cells the length of the telomeres is not varying. There is an analogy with microtubules, which are highly dynamical and carry a longitudinal electric field, whose strength correlates with the microtubule length. Could sticky ends generate a longitudinal field along DNA double strand with strength determined by the lengths of the sticky ends? In the standard picture the flux of the longitudinal electric field would be proportional to the difference of the negative charges associated with the sticky ends. In TGD framework, DNA strands are accompanied by the dark analog of DNA with codons realized as 3-proton units at magnetic flux tubes parallel to DNA strands and neutralizing the negative charge of ordinary DNA except at the sticky ends. This allows considering the possibility that opposite sticky ends carry opposite charges generating a longitudinal electric field along the magnetic flux tube associated with the system. DNA/Telomere bioelectric field could serve as a novel bioelectric marker to be used for prognostic and diagnostic purposes in researches of cancer, aging, surgery grafts and rejuvenation. We propsed that DNA bioelectric field can be used as a futuristic bioelectric marker of cancer, aging and death.