Investigation of Transitional Shock-Wave/Boundary Layer Interactions Using Direct Numerical Simulations

Interaction of a transitional boundary layer with a normal-shock is investigated using unstructured tetrahedral meshes under the numerical framework of the space-time conservation element, solution element (CESE) method. The computations mimic recent experimental efforts at the University of Tennessee Space Institute, where a Mach 2.0 flow interacts with a tall cylinder attached to a flat plate. The location of the cylinder with respect to the flat plate leading edge determines if the incoming boundary layer is laminar, transitional or fully turbulent. Four representative flow conditions exemplifying laminar and transitional boundary layers are analyzed by direct numerical simulations. Similar to what was observed in the experiments for the case of transitional interaction, the computations reveal an intermittent upstream influence (UI) shock that repeatedly travels upstream from the lambda-foot toward the leading edge before vanishing. Through detailed unsteady flow analysis obtained using Fourier analysis and dynamic mode decomposition techniques, the presence of disturbances with similar frequencies as those measured in experiments were identified in the flow along with locations that appear to influence the dynamics of the flow

Costing-out the Big Bang: Impact of external shocks on the Armenian economy at the outset of transition

This paper explores factors of economic decline in the small republican economies of the former USSR. It develops quantitative estimates of the costs of major transitional shocks for Armenia during the early transition, including the direct impact of terms of trade shock (price shock), direct impact of external demand shock (market loss), direct impact of fiscal shock (loss of transfers), as well as secondary effects of all the above shocks, defined as a further decline in macroeconomic aggregates due to a weakening of the overall domestic demand. These estimates are obtained within a single framework, built on a detailed input-output model for Armenia, and using the actual 1987 data. Our estimates suggest that the cumulative impact of the external shocks of the early 90-s amounted to the equivalent of 85 percent of the pre-transition GDP, and both price and demand shocks were highly significant. At the same time, the fiscal shock was much less important in Armenia due to its lower dependence on transfers from the union budget. The actual economic decline in Armenia in the first part of the 90-s was less severe than the model’s projections. We attribute this difference to a positive impact of market reforms on economic incentives.Armenia, costs of transition, USSR collapse, external shock

The Aid of Optical Studies in Understanding Millisecond Pulsar Binaries

A large number of new "black widow" and "redback" energetic millisecond pulsars with irradiated stellar companions have been discovered through radio and optical searches of unidentified \textit{Fermi} sources. Synchrotron emission, from particles accelerated up to several TeV in the intrabinary shock, exhibits modulation at the binary orbital period. Our simulated double-peaked X-ray light curves modulated at the orbital period, produced by relativistic Doppler-boosting along the intrabinary shock, are found to qualitatively match those observed in many sources. In this model, redbacks and transitional pulsar systems where the double-peaked X-ray light curve is observed at inferior conjunction have intrinsically different shock geometry than other millisecond pulsar binaries where the light curve is centered at superior conjunction. We discuss, and advocate, how current and future optical observations may aid in constraining the emission geometry, intrabinary shock and the unknown physics of pulsar winds.Comment: 7 pages, 1 figure. Conference proceedings of SALT Science Conference 2015. Accepted for publication in PoS SSC201

Physical aspects of computing the flow of a viscous fluid

One of the main themes in fluid dynamics at present and in the future is going to be computational fluid dynamics with the primary focus on the determination of drag, flow separation, vortex flows, and unsteady flows. A computation of the flow of a viscous fluid requires an understanding and consideration of the physical aspects of the flow. This is done by identifying the flow regimes and the scales of fluid motion, and the sources of vorticity. Discussions of flow regimes deal with conditions of incompressibility, transitional and turbulent flows, Navier-Stokes and non-Navier-Stokes regimes, shock waves, and strain fields. Discussions of the scales of fluid motion consider transitional and turbulent flows, thin- and slender-shear layers, triple- and four-deck regions, viscous-inviscid interactions, shock waves, strain rates, and temporal scales. In addition, the significance and generation of vorticity are discussed. These physical aspects mainly guide computations of the flow of a viscous fluid

Behaviors and housing inertia are key factors in determining the consequences of a shock in transportation costs

This paper investigates the consequences of a sudden increase in transportation costs when households behaviors and buildings inertia are accounted for. A theoretical framework is proposed, capturing the interactions between behaviors, transportation costs and urban structure. It is found that changes in households consumption and housing choices reduce significantly the long-term adverse effects of a shock in transportation costs. Indeed, the shock translates, over the long-run, into a more concentrated housing that limits households utility losses and maintains landowners' income. But, because of buildings inertia, the shock leads first to a long transition, during which the adjustment is constrained by a suboptimal housing-supply structure. Then, households support larger losses than in the final stage, though lower than with no adjustment at all, and landowners experience a large decrease in their aggregate income and an important redistribution of wealth. Negative transitional effects grow as the shock becomes larger. Thus, behaviors and buildings inertia are key factors in determining the vulnerability to transportation price variability and to the introduction of climate policies. Our policy conclusions are that: (i) if a long-term increase in transportation costs is unavoidable because of climate change or resource scarcity, a smooth change, starting as early as possible, must be favored; and (ii) fast-growing cities of the developing world can reduce their future vulnerability to shocks in transportation costs through the implementation of policies that limit urban sprawl.City, Housing, Transportation

The Impact of Socialist Imprinting and Search for Knowledge on Resource Change: An Empirical Study of Firms in Lithuania

In this paper we examine how firms change their resources in response to exogenous shocks in their business environment. Building on core ideas from the literatures on organizational imprinting and firm resources, we suggest that founding conditions differentially imprint firm resources. These initial imprinting differentials in turn influence the search for knowledge required to adapt or change firm resources in the face of external change in their business environment. We also suggest that the level of imprinting and the location of search independently and jointly influence the success with which firms are able to change their resources. We use survey-based data from a set of firms in Central Europe that experienced an exogenous shock in 1989-1991 to test our arguments. We develop a measure of pre-shock imprinting (called socialist imprinting) on resources and use it to predict where firms will search for knowledge to undertake change in the post-shock period and how successful that change will be. We find that the level of socialist imprinting influences the search location for knowledge to change key resources and activities following the shock. In terms of the success of change undertaken, we see that distant search for knowledge is positively linked to it. We also observe that the level of imprinting and search location jointly impact the success of change; for resources with higher socialist imprinting, distant search was more effective than local search. This research makes three important contributions in the context of existing research on organizational imprinting and firm level change. One, it focuses on firm-level resources to examine the impact of imprinting. Two, we examine how differences in resource level imprinting influence the search for new knowledge required to transform these resources. Three, we demonstrate that the interaction between the level of imprinting and the nature of search has important influences on firm performance. Our findings also provide insights to practitioners and policy makers who deal with firms in transitional economies. Practitioners can better understand how to undertake firm level change more effectively in the context of sudden exogenous shock. For policy makers, both of domestic and international institutions, understanding the change process can help formulate assistance programs more effectively.http://deepblue.lib.umich.edu/bitstream/2027.42/39830/3/wp446.pd