Non-ideal MHD Properties of Magnetic Flux Tubes in the Solar Photosphere

Magnetic flux tubes reaching from the solar convective zone into the chromosphere have to pass through the relatively cool, and therefore non-ideal (i.e. resistive) photospheric region enclosed between the highly ideal sub-photospheric and chromospheric plasma. It is shown that stationary MHD equilibria of magnetic flux tubes which pass through this region require an inflow of photospheric material into the flux tube and a deviation from iso-rotation along the tube axis. This means that there is a difference in angular velocity of the plasma flow inside the tube below and above the non-ideal region. Both effects increase with decreasing cross section of the tube. Although for characteristic parameters of thick flux tubes the effect is negligible, a scaling law indicates its importance for small-scale structures. The relevance of this "inflow effect" for the expansion of flux tubes above the photosphere is discussed.Comment: 17 pages, 9 figures. Comments welcom

Evolution of magnetic flux in an isolated reconnection process

A realistic notion of magnetic reconnection is essential to understand the dynamics of magnetic fields in plasmas. Therefore a three-dimensional reconnection process is modeled in a region of nonvanishing magnetic field and is analyzed with respect to the way in which the connection of magnetic flux is changed. The process is localized in space in the sense that the diffusion region is limited to a region of finite radius in an otherwise ideal plasma. A kinematic, stationary model is presented, which allows for analytical solutions. Aside from the well-known flipping of magnetic flux in the reconnection process, the localization requires additional features which were not present in previous two- and 2.5-dimensional models. In particular, rotational plasma flows above and below the diffusion region are found, which substantially modify the process. (C) 2003 American Institute of Physics.</p

Information exchange with cost uncertainty: An alternative approach and new results

This paper further develops the standard modelling of information exchange between firms in the presence of cost uncertainty. In order to avoid consistency problems, we replace the normal distribution of the random variables, commonly used because of its convenient mathematical properties, by an alternative one, namely a non-symmetrically distributed random variable with a binomial positive outcome. This leads to new results concerning firms' information-disclosure policy: Confirming the empirical evidence and in contrast to the existing literature, we show that in Cournot markets firms never exchange their private information and in Bertrand markets only for very steep demand functions. --information sharing,cost uncertainty,oligopoly

The structure of current layers and degree of field line braiding in coronal loops

One proposed resolution to the long-standing problem of solar coronal heating involves the buildup of magnetic energy in the corona due to turbulent motions at the photosphere that braid the coronal field, and the subsequent release of this energy via magnetic reconnection. In this paper the ideal relaxation of braided magnetic fields modelling solar coronal loops is followed. A sequence of loops with increasing braid complexity is considered, with the aim of understanding how this complexity influences the development of small scales in the magnetic field, and thus the energy available for heating. It is demonstrated that the ideally accessible force-free equilibrium for these braided fields contains current layers of finite thickness. It is further shown that for any such braided field, if a force-free equilibrium exists then it should contain current layers whose thickness is determined by length scales in the field line mapping. The thickness and intensity of the current layers follow scaling laws, and this allows us to extrapolate beyond the numerically accessible parameter regime and to place an upper bound on the braid complexity possible at coronal plasma parameters. At this threshold level the braided loop contains $10^{26}$--$10^{28}{\rm ergs}$ of available free magnetic energy, more than sufficient for a large nanoflare.Comment: To appear in ApJ. 20 pages, 10 figure

Addressing Hxstorical Amnesia: Proactively Combating Hxstorical Amnesia as a Means of Healing in Higher Education

In a political context characterized by the desire to “Make America Great Again,” the romanticization of the past and the erasure of narratives of marginalized communities affect how students experience and navigate higher education. Institutions of higher education were built on systems of colonization and imperialism and continue to benefit from the legacy of domination and subordination; this hxstory shapes student learning. The authors introduce hxstorical amnesia, its effects on student development, and methods of actively combating hxstorical amnesia in higher education. The authors explore ways to heal from hxstorical amnesia through community-care, cogenerative dialogues, and Sentipensante Pedagogy. By discussing the contemporary impacts of hxstorical amnesia on higher education and student learning, the authors hope to (re)write the narrative of higher education to underline the importance of the hxstories of marginalized communities

Jet Shapes in Dijet Events at the LHC in SCET

We consider the class of jet shapes known as angularities in dijet production at hadron colliders. These angularities are modified from the original definitions in e+e- collisions to be boost invariant along the beam axis. These shapes apply to the constituents of jets defined with respect to either k_T-type (anti-k_T, C/A, and k_T) algorithms and cone-type algorithms. We present an SCET factorization formula and calculate the ingredients needed to achieve next-to-leading-log (NLL) accuracy in kinematic regions where non-global logarithms are not large. The factorization formula involves previously unstudied "unmeasured beam functions," which are present for finite rapidity cuts around the beams. We derive relations between the jet functions and the shape-dependent part of the soft function that appear in the factorized cross section and those previously calculated for e+e- collisions, and present the calculation of the non-trivial, color-connected part of the soft-function to O(\alpha_s). This latter part of the soft function is universal in the sense that it applies to any experimental setup with an out-of-jet p_T veto and rapidity cuts together with two tagged jets and it is independent of the choice of jet (sub-)structure measurement. In addition, we implement the recently introduced soft-collinear refactorization to resum logarithms of the jet size, valid in the region of non-enhanced non-global logarithm effects. While our results are valid for all 2 \to 2 channels, we compute explicitly for the qq' \to qq' channel the color-flow matrices and plot the NLL resummed differential dijet cross section as an explicit example, which shows that the normalization and scale uncertainty is reduced when the soft function is refactorized. For this channel, we also plot the jet size R dependence, the p_T^{\rm cut} dependence, and the dependence on the angularity parameter a.Comment: 41 pages, 4 figure

On the robustness of concealing cost information in oligopoly

Competing firms are usually better informed about their own cost parameters than about those of their rivals. Therefore, it is an important issue to study the incentives of firms to exchange private cost information. We resolve and further generalize an influential model of Raith (1996) and show that, independent of the number of firms, concealing cost information is a dominant firm strategy in heterogeneous Bertrand oligopolies with substitutive as well as with complementary goods.cost uncertainty