Oblique propagation of solitary electrostatic waves in magnetized plasmas with cold ions and nonthermal electrons

Oblique propagation of large amplitude electrostatic waves and solitary structures is investigated in magnetized plasmas, comprising cold fluid ions and Cairns nonthermally distributed electrons, by using a Sagdeev pseudopotential formalism. To perform the analysis, quasineutrality is assumed, so that in normalized variables the electrostatic potential and the occurrence of solitary structures are governed by three parameters: the Mach number M, the typical Cairns parameter beta, and the angle theta between the directions of propagation and the static magnetic field. Below a critical beta, only positive compressive solitons are possible, and their amplitudes increase with increasing beta, M, and theta. Above the critical b, there is coexistence between negative rarefactive and positive compressive solitons, and the range of negative solitons, at increasing M, ends upon encountering a double layer or a singularity. The double layer amplitudes (in absolute value) increase with beta but are independent of theta. Roots of the Sagdeev pseudopotential beyond the double layer are not accessible from the undisturbed conditions, because of an intervening singularity where the pseudopotential becomes infinite. Recent claims of finding supersolitons beyond a double layer appear to be based on a misinterpretation of the nature of the singularity

First-principles investigation of the Ni-Fe-Al system

By combining ab-initio electron theory and statistical mechanics, the physical properties of the ternary intermetallic system Ni-Fe-Al in the ground state and at finite temperatures were investigated. The Ni-Fe-Al system is not only of high technological interest, but exhibits also rich physics, e.g., a delicate interplay between structure and magnetism over a wide composition range and substantial electronic correlations which is challenging for modern electronic structure methods. The new Stuttgart ab-initio mixed-basis pseudopotential code in the generalized gradient approximation (GGA) was used to determine the energetics in the ground state. Therewith, in combination with the cluster expansion (CE) method a representation of the energy landscape at $T$=0 over the whole Gibbs triangle was elaborated. At finite temperatures, the cluster variation method (CVM) in tetrahedron approximation was employed in order to calculate the ab-initio ternary phase diagram on the bcc and fcc lattice. Thereby, a miscibility gap in the ternary B2 phase was theoretically verified.Comment: 27 page

Denomination, Religious Context, and Suicide: Neo-Durkheimian Multilevel Explanations Tested with Individual and Contextual Data

In Suicide, Durkheim found that involvement in religious communities is inversely related to suicide risk. In this article, two explanations for this relationship are examined. One is that religious networks provide support. The other is that religious communities prohibit suicide. To examine these hypotheses, individual-level data on suicide in the Netherlands from 1936 to 1973 are used. The results show that with an increase in the proportion of religious persons in a municipality, the chances of committing suicide decrease for every denomination in that municipality, as well as among nonchurch members. Furthermore, along with the secularization of Dutch society, the impact of religious composition on suicide wanes. These results contradict the network-support mechanism and confirm the notion that religious communities have a general protective effect against suicide.

Head-on collisions of electrostatic solitons in nonthermal plasmas

In contrast to overtaking interactions, head-on collisions between two electrostatic solitons can only be dealt with by an approximate method, which limits the range of validity but offers valuable insights. Treatments in the plasma physics literature all use assumptions in the stretching of space and time and in the expansion of the dependent variables that are seldom if ever discussed. All models force a separability to lowest order, corresponding to two linear waves with opposite but equally large velocities. A systematic exposition of the underlying hypotheses is illustrated by considering a plasma composed of cold ions and nonthermal electrons. This is general enough to yield critical compositions that lead to modified rather than standard Korteweg-de Vries equations, an aspect not discussed so far. The nonlinear evolution equations for both solitons and their phase shifts due to the collision are established. A Korteweg-de Vries description is the generic conclusion, except when the plasma composition is critical, rendering the nonlinearity in the evolution equations cubic, with concomitant repercussions on the phase shifts. In the latter case, the solitons can have either polarity, so that combinations of negative and positive solitons can occur, contrary to the generic case, where both solitons necessarily have the same polarity

Anskuelsens ophævelse i metaforens spil

I artiklen udfolder Manfred Frank en polyhistors tour de force igennem de sidste 200 års æstetik-, litteratur- og erkendelsesteori. Udgangspunktet er en kritisk kommentar fra Nietzsche vendt mod æstetikken, som han beskylder for ’sanseløshed’. Men hvordan forholder det sig overhovedet med den moderne æstetik, der først og fremmest er en teori om ’det skønnes omfattende rige’ (Hegel), snarere end en teori om sanseligheden (aisthesis), som man stadig finder spor af hos Kant? Imellem anskuelse og begreb opererer indbildningskraften og det imaginære, som det skønne appellerer til. Så vidt er Kant helt med. Men det er samtidig – utilsigtet – Kants historiske bidrag til metaforteorien, at han foretager sin berømte – og principielle – adskillelse mellem anskuelse og begreb. Dermed bliver anskuelsen frisat, og den finder som sådan hurtigt sin vej ind i den romantisk-moderne poesi. Hermed kommer grænserne for repræsentationernes traditionelle skema i fare. Ansatsen bliver derfor for Frank at tage den udfordring op, der stilles som idéhistorisk novum med romantikernes omkalfatring af anskuelsestingen til noget, der pludseligt forekommer uden indre retning mod en idé. Men der er også konsekvenser på begrebssiden. Det virkeligt værende er det, som vi anskuer via sanserne, og begrebet er den funktion, der bringer sandhedsbegrebet i spil, i forhold til det, som vi anskuer. Derfor ligger der en stor udfordring for sandhedsbegrebet i, at Nietzsche og hans følge (Derrida m.fl.) ophæver verdens umiddelbare anskuelighed i begrebsligt formidlede metaforspil. Metaforen er sproglig af natur og væsensbestemt som over-føring af billeddannelser mellem heterogene zoner. Idet sandheden for Nietzsche er afsløret som illusion og en hær af sproglige troper, tenderer metaforen til at blive en autonom størrelse. Nietzsches problematisering af sandhedsbegrebet har siden ført til tesen om subjektets død. Subjektet var bare en fiktion – og dem er der så mange af. Men dette bliver, taget i sin fulde konsekvens, aldeles problematisk. Og Nietzsche er selv den første til at se det. Så på trods af kongeniale udlægninger af pointer hos bl.a. Derrida stiller subjektivitetsteoretikeren Manfred Frank sig ikke tilfreds med neostrukturalismens (som Frank selv har døbt den) ophævelse af anskuelsen i metaforens spil. Hos Frank er der mere på spil end blot og bar fiktion

Mennyi történelemre van szüksége a filozófiának?

Translation of Franks study