Meson multiplicity in nucleus-nucleus collisions above 4 GeV/amu

Dependence of meson multiplicity on energy for 1486 cosmic ray nucleus-emulsion nucleus interactions is examined. Comparison is made to predictions of the Multi-Chain Model

The charge and energy spectra of heavy cosmic ray nuclei

A charged particle detector array flown in a high altitude balloon detected and measured some 30,000 cosmic ray nuclei with Z greater than or equal to 12. The charge spectrum at the top of the atmosphere for nuclei with E greater than 650 MeV/n and the energy spectrum for 650 less than or equal to E less than 1800 MeV/n are reported and compared with previously published results. The charge spectrum at the source of cosmic rays is deduced from these data and compared with a recent compilation of galactic abundances

Stopping relativistic Xe, Ho, Au and U nuclei in nuclear emulsions

Nuclei of Xe-54, Ho-67, Au-79 and U-92 accelerated at the Bevalac to energies between 1200 and 900 MeV/n were stopped in nuclear emulsions. The observed residual ranges were compared with those calculated from various models of energy loss and shown to be most consistent with a calculation that includes those higher order correction terms proposed previously to describe the energy loss of highly charged particles, for which the first Born approximation is not valid

Gamma ray emission from the region of the galactic center

A combination nuclear emulsion-spark chamber gamma ray (E=100 MeV) telescope was used to study the region of sky that includes the Galactic Center. 95% confidence upper limits on the flux from the reported sources G gamma 2 - 3 and Sgr gamma-1 were placed at 4.4 and 8.8 x 10 to the minus 5th power protons/sq cm-sec, and a similar limit on the emission from the Galactic Center as a point source (plus or minus .75 degrees) was placed at 3.3 x 10 to the minus 5th power protons/sq cm-sec. No enhanced emission was observed from the Galactic Plane (plus or minus 6 degrees) and an upper limit of 2 x 10 to the minus 4th power protons/sq cm-sec rad/ was obtained

Analytical description of finite size effects for RNA secondary structures

The ensemble of RNA secondary structures of uniform sequences is studied analytically. We calculate the partition function for very long sequences and discuss how the cross-over length, beyond which asymptotic scaling laws apply, depends on thermodynamic parameters. For realistic choices of parameters this length can be much longer than natural RNA molecules. This has to be taken into account when applying asymptotic theory to interpret experiments or numerical results.Comment: 10 pages, 13 figures, published in Phys. Rev.

Electrostatics in wind-blown sand

Wind-blown sand, or "saltation," is an important geological process, and the primary source of atmospheric dust aerosols. Significant discrepancies exist between classical saltation theory and measurements. We show here that these discrepancies can be resolved by the inclusion of sand electrification in a physically based saltation model. Indeed, we find that electric forces enhance the concentration of saltating particles and cause them to travel closer to the surface, in agreement with measurements. Our results thus indicate that sand electrification plays an important role in saltation.Comment: 4 journal pages, 5 figures, and supplementary material. Article is in press at PR

At Our Own Peril: DoD Risk Assessment in a Post-Primacy World

The U.S. Department of Defense (DoD) faces persistent fundamental change in its strategic and operating environments. This report suggests this reality is the product of the United States entering or being in the midst of a new, more competitive, post-U.S. primacy environment. Post-primacy conditions promise far-reaching impacts on U.S. national security and defense strategy. Consequently, there is an urgent requirement for DoD to examine and adapt how it develops strategy and describes, identifies, assesses, and communicates corporate-level risk. This report takes on the latter risk challenge. It argues for a new post-primacy risk concept and its four governing principles of diversity, dynamism, persistent dialogue, and adaptation. The authors suggest that this approach is critical to maintaining U.S. military advantage into the future. Absent change in current risk convention, the report suggests DoD exposes current and future military performance to potential failure or gross under-performance.https://press.armywarcollege.edu/monographs/1410/thumbnail.jp

Statistical mechanics of secondary structures formed by random RNA sequences

The formation of secondary structures by a random RNA sequence is studied as a model system for the sequence-structure problem omnipresent in biopolymers. Several toy energy models are introduced to allow detailed analytical and numerical studies. First, a two-replica calculation is performed. By mapping the two-replica problem to the denaturation of a single homogeneous RNA in 6-dimensional embedding space, we show that sequence disorder is perturbatively irrelevant, i.e., an RNA molecule with weak sequence disorder is in a molten phase where many secondary structures with comparable total energy coexist. A numerical study of various models at high temperature reproduces behaviors characteristic of the molten phase. On the other hand, a scaling argument based on the extremal statistics of rare regions can be constructed to show that the low temperature phase is unstable to sequence disorder. We performed a detailed numerical study of the low temperature phase using the droplet theory as a guide, and characterized the statistics of large-scale, low-energy excitations of the secondary structures from the ground state structure. We find the excitation energy to grow very slowly (i.e., logarithmically) with the length scale of the excitation, suggesting the existence of a marginal glass phase. The transition between the low temperature glass phase and the high temperature molten phase is also characterized numerically. It is revealed by a change in the coefficient of the logarithmic excitation energy, from being disorder dominated to entropy dominated.Comment: 24 pages, 16 figure