Journal Staff

We investigate the performance of delay constrained data transmission over wireless networks without end-to-end feedback. Forward error-correction coding (FEC) is performed at the bit level to combat channel distortions and random linear network coding (RLNC) is performed at the packet level to recover from packet erasures. We focus on the scenario where RLNC re-encoding is performed at intermediate nodes and we assume that any packet that contains bit errors after FEC decoding can be detected and erased. To facilitate explicit characterization of data transmission over network-coded wireless systems, we propose a generic two-layer abstraction of a network that models both bit/symbol-level operations at the lower layer (termed PHY-layer) over several heterogeneous links and packet-level operations at the upper layer (termed NET-layer). Based on this model, we propose a network reduction method to characterize the throughput-reliability function of the end-to-end transmission. Our approach not only reveals an explicit tradeoff between data delivery rate and reliability, but also provides an intuitive visualization of the bottlenecks within the underlying network. We illustrate our approach via a point-to-point link and a relay network and highlight the advantages of this method over capacity-based approaches.Accepted for publication in IEEE Globecom 2014. Copyright will be transferred to IEEE without notice.QS22014</p

Analysis of Biases in Corporate Income Tax-CIT

This paper analyzes the biases in CIT in some countries around the world. Most corporate tax systems are found in the Tax Codes. The sample covers the Tax Codes in force in ten countries in Africa, America, Asia and Europe. Assuming that corporate tax is the cost of using public capital, the analysis of the content of these tax codes relating to corporate income taxation, has made it possible to identify several biases or differences in taxation and/or tax treatment. The biases in CIT identified relate to financing, investment, result, rate and tax base. This paper is one of the first to expand the literature by analyzing the biases in CIT, likely to affect tax behavior and, by extension, the financial behavior of firms

Distributed Quantization for Sparse Time Sequences

Analog signals processed in digital hardware are quantized into a discrete bit-constrained representation. Quantization is typically carried out using analog-to-digital converters (ADCs), operating in a serial scalar manner. In some applications, a set of analog signals are acquired individually and processed jointly. Such setups are referred to as distributed quantization. In this work, we propose a distributed quantization scheme for representing a set of sparse time sequences acquired using conventional scalar ADCs. Our approach utilizes tools from secure group testing theory to exploit the sparse nature of the acquired analog signals, obtaining a compact and accurate representation while operating in a distributed fashion. We then show how our technique can be implemented when the quantized signals are transmitted over a multi-hop communication network providing a low-complexity network policy for routing and signal recovery. Our numerical evaluations demonstrate that the proposed scheme notably outperforms conventional methods based on the combination of quantization and compressed sensing tools

Fabrication and Optical Properties of a Fully Hybrid Epitaxial ZnO-Based Microcavity in the Strong Coupling Regime

In order to achieve polariton lasing at room temperature, a new fabrication methodology for planar microcavities is proposed: a ZnO-based microcavity in which the active region is epitaxially grown on an AlGaN/AlN/Si substrate and in which two dielectric mirrors are used. This approach allows as to simultaneously obtain a high-quality active layer together with a high photonic confinement as demonstrated through macro-, and micro-photoluminescence ({\mu}-PL) and reflectivity experiments. A quality factor of 675 and a maximum PL emission at k=0 are evidenced thanks to {\mu}-PL, revealing an efficient polaritonic relaxation even at low excitation power.Comment: 12 pages, 3 figure

Distribution of monocarboxylate transporters in the peripheral nervous system suggests putative roles in lactate shuttling and myelination.

Lactate, a product of glycolysis, has been shown to play a key role in the metabolic support of neurons/axons in the CNS by both astrocytes and oligodendrocytes through monocarboxylate transporters (MCTs). Despite such importance in the CNS, little is known about MCT expression and lactate function in the PNS. Here we show that mouse MCT1, MCT2, and MCT4 are expressed in the PNS. While DRG neurons express MCT1, myelinating Schwann cells (SCs) coexpress MCT1 and MCT4 in a domain-specific fashion, mainly in regions of noncompact myelin. Interestingly, SC-specific downregulation of MCT1 expression in rat neuron/SC cocultures led to increased myelination, while its downregulation in neurons resulted in a decreased amount of neurofilament. Finally, pure rat SCs grown in the presence of lactate exhibited an increase in the level of expression of the main myelin regulator gene Krox20/Egr2 and the myelin gene P0. These data indicate that lactate homeostasis participates in the regulation of the SC myelination program and reveal that similar to CNS, PNS axon-glial metabolic interactions are most likely mediated by MCTs

LO-phonon assisted polariton lasing in a ZnO based microcavity

Polariton relaxation mechanisms are analysed experimentally and theoretically in a ZnO-based polariton laser. A minimum lasing threshold is obtained when the energy difference between the exciton reservoir and the bottom of the lower polariton branch is resonant with the LO phonon energy. Tuning off this resonance increases the threshold, and exciton-exciton scattering processes become involved in the polariton relaxation. These observations are qualitatively reproduced by simulations based on the numerical solution of the semi-classical Boltzmann equations

Robustness in large-scale random networks

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2003.Includes bibliographical references (p. 73-76).This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.We consider the issue of protection in very large networks displaying randomness in topology. We employ random graph models to describe such networks, and obtain probabilistic bounds on several parameters related to various protection schemes. In particular, we take the case of random regular networks for simplicity, where the degree of each node is the same, and consider the length of primary and backup paths in terms of the number of hops. First, for a randomly picked pair of nodes, we derive a lower bound on the average distance between the pair and discuss the tightness of the bound. In addition, noting that primary and protection paths form cycles, we obtain a lower bound on the average length of the shortest cycle around the pair. Finally, we show that the protected connections of a given maximum finite length are rare. We then generalize our network model so that different degrees are allowed according to some arbitrary distribution. Notably, we derive an upper bound on the mean number of non-finite length cycles in generalized random networks. More importantly, we show that most of the results in regular networks carry over with minor modifications, which significantly broadens the scope of networks to which our approach applies. Our main contributions are the following. First, we take an analytical approach by bringing the concept of randomness into network topologies that can provide concise rules to relate basic network parameters to robustness. Second, we establish analytical results for the length of backup paths for path and link-based protection schemes rather than for the efficiency of backup capacity, upon which most studies concentrate. Finally, we develop a unified framework for studying the issue of robustness in very general random networks with arbitrary degree distributions.by Minkyu Kim.S.M

The ethics of (not) giving back

Recent concerns with academic research 'giving back' and 'having impact' are encouraging the adoption of various practices through which academics are able to share research findings with host communities. While we support the laudable principles behind these efforts, in this contribution we reflect on the viability of such practices in relation to overseas, undergraduate fieldclasses. Drawing on our experiences of leading and teaching on a range of international fieldclasses, we explore the complexities of giving back and caution against a drift towards universalising such practices in specific ways. Instead we call for greater critical honesty as to the potential for fieldclasses to give back in multiple ways and the need to avoid inadvertently doing harm when seeking to engage in ethical practices