Flow separation in shock wave boundary layer interactions at hypersonic speeds

An assessment is presented for the experimental data on separated flow in shock wave turbulent boundary layer interactions at hypersonic and supersonic speeds. The data base consists mainly of two dimensional and axisymmetric interactions in compression corners or cylinder-flares, and externally generated oblique shock interactions with boundary layers over flat plates or cylindrical surfaces. The conditions leading to flow separation and the subsequent changes in the flow empirical correlations for incipient separation are reviewed. The effects of the Mach number, Reynolds number, surface cooling and the methods of detecting separation are discussed. The pertinent experimental data for the separated flow characteristics in separated turbulent boundary layer shock interaction are also presented and discussed

From spring to summer? Revolutionary change in Tunisia, Egypt and Libya

This article offers an analysis of the early stages of the revolutions that have been taking place in Tunisia, Egypt and Libya. Here we consider the early stages of the revolutions from winter 2010-11 up until the summer of 2012 and offers a comparative study of the experiences of the early stage of the revolutions in each case study. In particular this study considers the roles of six variables on the process of regime change and transition as follows: 1) duration of the uprising up to regime change; 2) the initial outcome of the revolution/uprising; 3) the number of deaths and casualties; 4) the post-regime change status of key members of the former governing elite; 5) the existence and nature of post-regime change elections; and 6) levels of international involvement. This study finds that in all three case studies, considering these variables offers insight into the nature and effect of the early stages of the revolutions. Furthermore, in each case there are key similarities in some of these variables but significant differences in others which suggest that the processes of transition are not directly comparable with each other. This article also offers some thoughts on how the early stages of these revolutions could affect the direction and pace of change in each state

Libya after the civil war: regime change and democratisation

This article examines changes in Libya’s internal security, politics, economy and international relations since the start of the revolution in February 2011. Our main argument is that in order to transition from authoritarianism to democracy significant change in each of these four, mutually reinforcing, areas is needed. Drawing on data collected through media analysis and field work, we offer a discussion of the nature of change in Libya and how far the country has democratised. We claim that significant changes in Libya’s political system and foreign relations have taken place since 2011 that reinforce the process of democratisation. Within the political system these changes include the conduct of free and fair elections, the formation of new political parties, the reinforcement of civil rights and liberties, governmental accountability and the emergence of a participant political culture. Within foreign relations they include deeper cooperation with regional and international actors, reintegration into the Arab League, and rapprochement with Western states. However, we also observe that structural economic changes, in particular raising personal incomes and lowering poverty, and the normalisation of security provision are moving forward more slowly. We conclude that democratisation in Libya is taking place and there is a solid possibility that embedded democracy will emerge in Libya in the medium to long-term

Optimality of Orthogonal Access for One-dimensional Convex Cellular Networks

It is shown that a greedy orthogonal access scheme achieves the sum degrees of freedom of all one-dimensional (all nodes placed along a straight line) convex cellular networks (where cells are convex regions) when no channel knowledge is available at the transmitters except the knowledge of the network topology. In general, optimality of orthogonal access holds neither for two-dimensional convex cellular networks nor for one-dimensional non-convex cellular networks, thus revealing a fundamental limitation that exists only when both one-dimensional and convex properties are simultaneously enforced, as is common in canonical information theoretic models for studying cellular networks. The result also establishes the capacity of the corresponding class of index coding problems

On the Tuning Condition of Split Supersymmetry

Split Supersymmetry does not attempt to solve the hierarchy problem, but it assumes a tuning condition for the electroweak scale. We clarify the meaning of this condition and show how it is related to the underlying parameters. Simple assumptions on the structure of the soft terms lead to predictions on tan beta and on the physical Higgs mass.Comment: 9 pages, 6 figures, latex2

Retrospective Interference Alignment

We explore similarities and differences in recent works on blind interference alignment under different models such as staggered block fading model and the delayed CSIT model. In particular we explore the possibility of achieving interference alignment with delayed CSIT when the transmitters are distributed. Our main contribution is an interference alignment scheme, called retrospective interference alignment in this work, that is specialized to settings with distributed transmitters. With this scheme we show that the 2 user X channel with only delayed channel state information at the transmitters can achieve 8/7 DoF, while the interference channel with 3 users is able to achieve 9/8 DoF. We also consider another setting where delayed channel output feedback is available to transmitters. In this setting the X channel and the 3 user interference channel are shown to achieve 4/3 and 6/5 DoF, respectively

Bi-metric theory of gravity from the non-chiral Plebanski action

We study a modification of the Plebanski action for general relativity, which leads to a modified theory of gravity with eight degrees of freedom. We show how the action can be recasted as a bi-metric theory of gravity, and expanding around a bi-flat background we identify the six extra degrees of freedom with a second, massive graviton and a scalar mode.Comment: 28 pages. v2 minor typos correcte

Constructing Gravitational Dimensions

It would be extremely useful to know whether a particular low energy effective theory might have come from a compactification of a higher dimensional space. Here, this problem is approached from the ground up by considering theories with multiple interacting massive gravitons. It is actually very difficult to construct discrete gravitational dimensions which have a local continuum limit. In fact, any model with only nearest neighbor interactions is doomed. If we could find a non-linear extension for the Fierz-Pauli Lagrangian for a graviton of mass mg which does not break down until the scale Lambda_2=(mg Mpl)^(1/2), this could be used to construct a large class of models whose continuum limit is local in the extra dimension. But this is shown to be impossible: a theory with a single graviton must break down by Lambda_3 = (mg^2 Mpl)^(1/3). Next, we look at how the discretization prescribed by the truncation of the KK tower of an honest extra diemsinon rasies the scale of strong coupling. It dictates an intricate set of interactions among various fields which conspire to soften the strongest scattering amplitudes and allow for a local continuum limit. A number of canditate symmetries associated with locality in the discretized dimension are also discussed.Comment: 21 pages, 6 diagrams, 1 figur