FORM. In the most general sense: shape (contour, the variation of some attribute of a thing in space or time), and structure (the disposition of parts, relations of part to part, and of part to whole). In music, shape is the result of changes in some attribute or parameter of sound, in time, while structure has to do with various relations between sounds and sound-configurations, at the same or...

A generic assumption of ionization models of quasar absorption systems is that radiation from local sources is negligible compared with the cosmological background. We test this assumption and find that it is unlikely to hold for absorbers as rare as H I Lyman limit systems. Assuming that the absorption systems are gas clouds centered on sources of radiation, we derive analytic estimates for th...

The number of magnetoelectric multiferroic materials reported to date is scarce, as magnetic structures that break inversion symmetry and induce an improper ferroelectric polarization typically arise through subtle competition between different magnetic interactions. The (NH4)2[FeCl5(H2O)] compound is a rare case where such improper ferroelectricity has been observed in a molecular material. We...

This paper studies inference about the values of the parameters in the threshold model in a generalized method of moments (GMM) framework. First, we establish that the extensively studied least squares method leads to substantially oversized tests and confidence intervals when the coeffi cient change is not large. Second, by re-ordering the data to recast the threshold model as a structural bre...

The first self-consistent three-dimensional magnetohydrodynamical simulations of convergingmagnetic flux events associated with the formation of coronal X-ray bright points are presented. The initial magnetic field results from two magnetic dipoles located below the photosphere at positions r1 and r2, respectively, and an additional horizontal magnetic field parallel to the line r1r2. Both dipo...

A typical course in “abstract algebra” starts with groups, and then moves on to rings, vector spaces, fields, etc. This sequence may give the impression that fields form an advanced and arcane subject. In fact, however, fields are rather simpler than other structures, by virtue of being more constrained. This holds particularly for the case of finite fields, which arise in many areas of compute...