Short timescale behavior of colliding heavy nuclei at intermediate energies

An Antisymmetrized Molecular Dynamics model is used to explore the collision of $^{114}$Cd projectiles with $^{92}$Mo target nuclei at E/A=50 MeV over a broad range in impact parameter. The atomic number (Z), velocity, and emission pattern of the reaction products are examined as a function of the impact parameter and the cluster recognition time. The non-central collisions are found to be essentially binary in character resulting in the formation of an excited projectile-like fragment (PLF$^*$) and target-like fragment (TLF$^*$). The decay of these fragments occurs on a short timescale, 100$\le$t$\le$300 fm/c. The average excitation energy deduced for the PLF$^*$ and TLF$^*$ `saturates for mid-central collisions, 3.5$\le$b$\le$6 fm, with its magnitude depending on the cluster recognition time. For short cluster recognition times (t=150 fm/c), an average excitation energy as high as $\approx$6 MeV is predicted. Short timescale emission leads to a loss of initial correlations and results in features such as an anisotropic emission pattern of both IMFs and alpha particles emitted from the PLF$^*$ and TLF$^*$ in peripheral collisions.Comment: 19 pages, 17 figure

The Burst Mode of Accretion in Primordial Star Formation

We present simulation results for the formation and long-term evolution of a primordial protostellar disk harbored by a first star. Using a 2+1D nonaxisymmetric thin disk numerical simulation, together with a barotropic relation for the gas, we are able to probe ~20 kyr of the disk's evolution. During this time period we observe fragmentation leading to loosely bound gaseous clumps within the disk. These are then torqued inward and accreted onto the growing protostar, giving rise to a burst phenomenon. The luminous feedback produced by this mechanism may have important consequences for the subsequent growth of the protostar.Comment: 3 pages, 2 figures, to appear in proceedings of First Stars IV meeting (Kyoto, Japan; 2012

Centralization and Decentralization Decisions: Multiple Contingencies for IT Governance in the Public Sector

There is often a tension in organizations between the centralization and decentralization of IT governance, as demonstrated by Sambamurthy and Zmud’s (1999) landmark paper on IT governance and contingencies. Allocation of decision rights over IT resources and capabilities is a complex governance decision, with results that vary considerably over organizations. In this paper, we conduct a conceptual replication of the well-established Centralized-Decentralized-Federal classification scheme for IT governance. Using data from the National Association of State CIOs and the Center for Digital Government, we empirically validate the three original underlying IT governance components of IT infrastructure management, IT use management and project management. We next apply a configurational approach to assess the level of centralization/decentralization of IT governance and to link them to states\u27 digital performance. Finally, we test the original theoretically derived IT governance constructs against the empirically derived ones to confirm existing and find emergent IT governance forms and their links with high and low performance. The results support the existing research but identify additional contingencies regarding the different domains of the studies (public versus private sector) and the evolution of IT architecture since the original study that have led to greater centralization over time