Optimal Save-Then-Transmit Protocol for Energy Harvesting Wireless Transmitters

In this paper, the design of a wireless communication device relying exclusively on energy harvesting is considered. Due to the inability of rechargeable energy sources to charge and discharge at the same time, a constraint we term the energy half-duplex constraint, two rechargeable energy storage devices (ESDs) are assumed so that at any given time, there is always one ESD being recharged. The energy harvesting rate is assumed to be a random variable that is constant over the time interval of interest. A save-then-transmit (ST) protocol is introduced, in which a fraction of time {\rho} (dubbed the save-ratio) is devoted exclusively to energy harvesting, with the remaining fraction 1 - {\rho} used for data transmission. The ratio of the energy obtainable from an ESD to the energy harvested is termed the energy storage efficiency, {\eta}. We address the practical case of the secondary ESD being a battery with {\eta} < 1, and the main ESD being a super-capacitor with {\eta} = 1. The optimal save-ratio that minimizes outage probability is derived, from which some useful design guidelines are drawn. In addition, we compare the outage performance of random power supply to that of constant power supply over the Rayleigh fading channel. The diversity order with random power is shown to be the same as that of constant power, but the performance gap can be large. Furthermore, we extend the proposed ST protocol to wireless networks with multiple transmitters. It is shown that the system-level outage performance is critically dependent on the relationship between the number of transmitters and the optimal save-ratio for single-channel outage minimization. Numerical results are provided to validate our proposed study.Comment: This is the longer version of a paper to appear in IEEE Transactions on Wireless Communication

Conflicts through the lens of Chinese war photojournalists

Since the 1990s, China, as a new global power, has played an increasing role in international affairs. Chinese journalists have travelled to war and conflict zones overseas to report and file news coverage back home. This article surveys the historical development of Chinese war photography. It also critically examines the ideology and practices of four young Chinese photojournalists who work at a Chinese state news agency through semi-structured interviews and analysis of the photographs they took in conflict zones. The author argues that contemporary Chinese war photojournalists take realism as their main aesthetic and ideological doctrine in a sense to provide visual evidences and to stress the naturalism and symbolic power of war images. The visual representations of civilians’ sufferings and hope for peace correspond with China's peaceful diplomatic policy and non-intervention principles. The war images elicit sympathetic public emotions and collective memory in China. Chinese photojournalists’ depictions of wars and conflicts are influenced by internal political, organizational and individual constraints as well as the changing nature of contemporary wars

Foreign correspondents: a case study of China in the digital and globalization age

While Western foreign correspondence is retreating, Chinese central media and correspondents, resourced by the government’s financial backing for media’s role in public diplomacy, are taking the opportunities to expand overseas bureaus, hire experienced local employees, enhance the quantity and quality of international news reporting, use digital technologies in newsgathering and dissemination, and receive Western-style trainings. Against this backdrop, this paper studies the identities, media cultures, and journalistic practices of Chinese foreign correspondents, as well as the international news output, and media–audience and media–foreign policy relationships. In doing so, we propose a new six-level theoretical model: (1) journalists’ identities; (2) cultures; (3) practices; (4) news output; (5) news dissemination, reception, and audiences’ interactions; and (6) the impacts of international news coverage. Based on semi-structured interviews with Chinese resident journalists over eight years, we argue that the media–audience and media–foreign policy relationships in China have become more interactive, dynamic, and complex

Behavior of different numerical schemes for population genetic drift problems

In this paper, we focus on numerical methods for the genetic drift problems, which is governed by a degenerated convection-dominated parabolic equation. Due to the degeneration and convection, Dirac singularities will always be developed at boundary points as time evolves. In order to find a \emph{complete solution} which should keep the conservation of total probability and expectation, three different schemes based on finite volume methods are used to solve the equation numerically: one is a upwind scheme, the other two are different central schemes. We observed that all the methods are stable and can keep the total probability, but have totally different long-time behaviors concerning with the conservation of expectation. We prove that any extra infinitesimal diffusion leads to a same artificial steady state. So upwind scheme does not work due to its intrinsic numerical viscosity. We find one of the central schemes introduces a numerical viscosity term too, which is beyond the common understanding in the convection-diffusion community. Careful analysis is presented to prove that the other central scheme does work. Our study shows that the numerical methods should be carefully chosen and any method with intrinsic numerical viscosity must be avoided.Comment: 17 pages, 8 figure

On the convergence of orthogonalization-free conjugate gradient method for extreme eigenvalues of Hermitian matrices: a Riemannian optimization interpretation

In many applications, it is desired to obtain extreme eigenvalues and eigenvectors of large Hermitian matrices by efficient and compact algorithms. In particular, orthogonalization-free methods are preferred for large-scale problems for finding eigenspaces of extreme eigenvalues without explicitly computing orthogonal vectors in each iteration. For the top $p$ eigenvalues, the simplest orthogonalization-free method is to find the best rank-$p$ approximation to a positive semi-definite Hermitian matrix by algorithms solving the unconstrained Burer-Monteiro formulation. We show that the nonlinear conjugate gradient method for the unconstrained Burer-Monteiro formulation is equivalent to a Riemannian conjugate gradient method on a quotient manifold with the Bures-Wasserstein metric, thus its global convergence to a stationary point can be proven. Numerical tests suggest that it is efficient for computing the largest $k$ eigenvalues for large-scale matrices if the largest $k$ eigenvalues are nearly distributed uniformly

Mediatization of conflict in the social media era: a case study of Sino-Indian border crisis in 2017

Inspired by the concepts of Arrested War and actor–network theory, this study has traced and analyzed four main actors in the wars and conflicts in the social media age: social media platform, the mainstream news organizations, online users, and social media content. These four human and nonhuman actors associate, interact, and negotiate with each other in the social media network surrounding specific issues. Based on the case study of Sino-Indian border crisis in 2017, the central argument is that social media is playing an enabling role in contemporary wars and conflicts. Both professional media outlets and web users employ the functionalities of social media platforms to set, counter-set, or expand the public agenda. Social media platform embodies a web of technological and human complexities with different actors, factors, interests, and relations. These actor-networks and the macro social-political context are influential in the mediatization of conflict in the social media era