Dust yields in clumpy SN shells: SN 1987A revisited

We present a study of the effects of clumping on the emergent spectral energy distribution (SED) from dusty supernova (SN) shells illuminated by a diffuse radiation source distributed throughout the medium. (...) The fully 3D radiation transport problem is solved using a Monte Carlo code, MOCASSIN, and we present a set of models aimed at investigating the sensitivity of the SEDs to various clumping parameters. We find that, contrary to the predictions of analytical prescriptions, the combination of an optical and IR observational data set is sufficient to constrain dust masses even in the case where optically thick clumps are present. Using both smoothly varying and clumped grain density distributions, we obtain new estimates for the mass of dust condensed by the Type II SN 1987A by fitting the optical and infrared spectrophotometric data of Wooden et al. (1993) at two epochs (day 615 and day 775). (...) From our numerical models we derive dust masses for SN 1987A that are comparable to previous analytic clumped graphite grain mass estimates, and at least two orders of magnitude below the 0.1-0.3 Msol that have been predicted to condense as dust grains in primordial core collapse supernova ejecta. This low condensation efficiency for SN 1987A is in contrast to the case of SN 2003gd, for which a dust condensation efficiency as large as 0.12 has recently been estimated. (Abridged)Comment: accepted for publication in MNRAS. The paper contains 15 figures and 1 tabl

PVLAS experiment, star cooling and BBN constraints: Possible interpretation with temperature dependent gauge symmetry breaking

It is known that the kinetic mixing of photon and another U(1)_ex gauge boson can introduce millicharged particles. Millicharged particles $f$ of mass 0.1 eV can explain the PVLAS experiment. We suggest a temperature dependent gauge symmetry breaking of U(1)_ex for this idea to be consistent with astrophysical and cosmological constraints.Comment: 9 pages, 3 figue

Matching Conditions in Atomistic-Continuum Modeling of Materials

A new class of matching condition between the atomistic and continuum regions is presented for the multi-scale modeling of crystals. They ensure the accurate passage of large scale information between the atomistic and continuum regions and at the same time minimize the reflection of phonons at the interface. These matching conditions can be made adaptive if we choose appropriate weight functions. Applications to dislocation dynamics and friction between two-dimensional atomically flat crystal surfaces are described.Comment: 6 pages, 4 figure

Knives and the Second Amendment

This Article is the first scholarly analysis of knives and the Second Amendment. Under the Supreme Court’s standard in District of Columbia v. Heller, knives are Second Amendment “arms” because they are “typically possessed by law-abiding citizens for lawful purposes,” including self-defense. There is no knife that is more dangerous than a modern handgun; to the contrary, knives are much less dangerous. Therefore, restrictions on carrying handguns set the upper limit for restrictions on carrying knives. Prohibitions on carrying knives in general, or of particular knives, are unconstitutional. For example, bans of knives that open in a convenient way (e.g., switchblades, gravity knives, and butterfly knives) are unconstitutional. Likewise unconstitutional are bans on folding knives that, after being opened, have a safety lock to prevent inadvertent closure

Criticality experiments with planar arrays of three-liter bottles containing plutonium nitrate solution

The objective of these experiments was to provide benchmark data to validate calculational codes used in critically safety assessments of plant configurations. Arrays containing up to as many as sixteen three-liter bottles filled with plutonium nitrate were used in the experiments. A split-table device was used in the final assembly of the arrays. Ths planar arrays were reflected with close fitting plexiglas on each side and on the bottom but not the top surface. The experiments addressed a number of factors effecting criticality: the critical air gap between bottles in an array of fixed number of bottles, the number of bottles required for criticality if the bottles were touching, and the effect on critical array spacing and critical bottle number due to the insertion of an hydrogeneous substance into the air gap between bottles. Each bottle contained about 2.4l of Pu(NO{sub 3}){sub 4} solution at a Pu concentration of 105g Pu/l, with the {sup 240}Pu content being 2.9 wt% at a free acid molarity H{sup +} of 5.1. After the initial series of experiments were performed with bottles separated by air gaps, plexiglas shells of varying thicknesses were placed around each bottle to investigate how moderation between bottles affects both the number of bottles required for criticality and the critical spacing between each bottle. The minimum of bottles required for criticality was found to be 10.9 bottles, occurring for a square array with bottles in contact. As the bottles were spaced apart, the critical number increased. For sixteen bottles in a square array, the critical separation between surfaces in both x and y direction was 0.96 cm. The addition of plexiglas around each bottle decreased the critical bottle number, compared to those separated in air, but the critical bottle number, even with interstitial plastic in place was always greater than 10.9 bottles. The most reactive configuration was a tightly packed array of bottles with no intervening material

Calculating Chemical Evolution on the Web

We have constructed a web site that may be of interest to cosmochemists seeking to under-stand the evolution of isotopes in the Galaxy. The URL is http://photon.phys.clemson.edu/gce.html. It is fully interactive and uses IDL on the Net (ION) to construct tables and graphs dynamically. The resulting tables may be downloaded as text files while the graphs may be downloaded as gif or postscript files. The present ab-stract presents a brief tutorial on using the “GCE tool” on this site and illustrates some of its capabilities. Ques-tions or comments should be addressed to either of the first two authors

Abundances of Linear Carbon-Chain Molecules in Supernovae

This paper continues our effort to under-stand the condensation of carbon solids in a gas of pure C and O atoms when these exist within the interior of an expanding young supernova. This setting has a sufficiently large number of energetic electrons that the CO molecule is disrupted with a lifetime of a few months, causing the abundance of CO to be no greater than 1% or so of the C abundance. As a consequence, the CO molecule cannot consume the available C atoms, even when the O abundance exceeds that of

High-resolution spectroscopy of the R Coronae Borealis and Other Hydrogen Deficient Stars

High-resolution spectroscopy is a very important tool for studying stellar physics, perhaps, particularly so for such enigmatic objects like the R Coronae Borealis and related Hydrogen deficient stars that produce carbon dust in addition to their peculiar abundances. Examples of how high-resolution spectroscopy is used in the study of these stars to address the two major puzzles are presented: (i) How are such rare H-deficient stars created? and (ii) How and where are the obscuring soot clouds produced around the R Coronae Borealis stars?Comment: 16 pages, 9 figures, Astrophysics and Space Science Proceedings, Springer-Verlag, Berlin, 201