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Power Sector Reform and Corruption: Evidence from Sub-Saharan Africa
In order to reduce the influence of corruption on electricity sector performance, most Sub-Saharan African countries have implemented sector reforms. However, after nearly two and half decades of reforms, there is no evidence whether these reforms have mitigated or exacerbated corruption. Neither is there evidence of performance improvements of reforms in terms of technical, economic or welfare impact. This paper aims to fill this gap. We use a dynamic panel estimator with a novel panel data set of 47 Sub-Saharan African countries from 2002 to 2013. We analyse the impact of corruption and two key aspects of electricity reform model - creations of independent regulatory agencies and private sector participation - on three performance indicators: technical efficiency, access to electricity and income. We find that corruption can significantly reduce technical efficiency of the sector and constrain the efforts to increase access to electricity and national income. However, these adverse effects are reduced where independent regulatory agencies are established and privatisation is implemented. Our results suggest that well-designed reforms not only boost economic performance of the sector directly, but also indirectly reduce the negative effects of macro level institutional deficiencies such as corruption on micro and macro indicators of performance
Broadcast Caching Networks with Two Receivers and Multiple Correlated Sources
The correlation among the content distributed across a cache-aided broadcast
network can be exploited to reduce the delivery load on the shared wireless
link. This paper considers a two-user three-file network with correlated
content, and studies its fundamental limits for the worst-case demand. A class
of achievable schemes based on a two-step source coding approach is proposed.
Library files are first compressed using Gray-Wyner source coding, and then
cached and delivered using a combination of correlation-unaware cache-aided
coded multicast schemes. The second step is interesting in its own right and
considers a multiple-request caching problem, whose solution requires coding in
the placement phase. A lower bound on the optimal peak rate-memory trade-off is
derived, which is used to evaluate the performance of the proposed scheme. It
is shown that for symmetric sources the two-step strategy achieves the lower
bound for large cache capacities, and it is within half of the joint entropy of
two of the sources conditioned on the third source for all other cache sizes.Comment: in Proceedings of Asilomar Conference on Signals, Systems and
Computers, Pacific Grove, California, November 201
Caching and Coded Multicasting: Multiple Groupcast Index Coding
The capacity of caching networks has received considerable attention in the
past few years. A particularly studied setting is the case of a single server
(e.g., a base station) and multiple users, each of which caches segments of
files in a finite library. Each user requests one (whole) file in the library
and the server sends a common coded multicast message to satisfy all users at
once. The problem consists of finding the smallest possible codeword length to
satisfy such requests. In this paper we consider the generalization to the case
where each user places requests. The obvious naive scheme consists
of applying times the order-optimal scheme for a single request, obtaining
a linear in scaling of the multicast codeword length. We propose a new
achievable scheme based on multiple groupcast index coding that achieves a
significant gain over the naive scheme. Furthermore, through an information
theoretic converse we find that the proposed scheme is approximately optimal
within a constant factor of (at most) .Comment: 5 pages, 1 figure, to appear in GlobalSIP14, Dec. 201
Duplex and superduplex stainless steels: microstructure and properties evolution by surface modification processes
The paper presents an overview of diffusion surface treatments, especially nitriding processes, applied to duplex and superduplex stainless steels in the last five years. Research has been done mainly to investigate different nitriding processes in order to optimize parameters for the most appropriate procedure. The scope has been to improve mechanical and wear resistance without prejudice to the corrosion properties of the duplex and superduplex stainless steels. Our investigation also aimed to understand the effect of the nitriding layer on the precipitation of secondary phases after any heating step.Peer ReviewedPostprint (published version
Dynamic Cloud Network Control under Reconfiguration Delay and Cost
Network virtualization and programmability allow operators to deploy a wide
range of services over a common physical infrastructure and elastically
allocate cloud and network resources according to changing requirements. While
the elastic reconfiguration of virtual resources enables dynamically scaling
capacity in order to support service demands with minimal operational cost,
reconfiguration operations make resources unavailable during a given time
period and may incur additional cost. In this paper, we address the dynamic
cloud network control problem under non-negligible reconfiguration delay and
cost. We show that while the capacity region remains unchanged regardless of
the reconfiguration delay/cost values, a reconfiguration-agnostic policy may
fail to guarantee throughput-optimality and minimum cost under nonzero
reconfiguration delay/cost. We then present an adaptive dynamic cloud network
control policy that allows network nodes to make local flow scheduling and
resource allocation decisions while controlling the frequency of
reconfiguration in order to support any input rate in the capacity region and
achieve arbitrarily close to minimum cost for any finite reconfiguration
delay/cost values.Comment: 15 pages, 7 figure
Optimal Control of Wireless Computing Networks
Augmented information (AgI) services allow users to consume information that
results from the execution of a chain of service functions that process source
information to create real-time augmented value. Applications include real-time
analysis of remote sensing data, real-time computer vision, personalized video
streaming, and augmented reality, among others. We consider the problem of
optimal distribution of AgI services over a wireless computing network, in
which nodes are equipped with both communication and computing resources. We
characterize the wireless computing network capacity region and design a joint
flow scheduling and resource allocation algorithm that stabilizes the
underlying queuing system while achieving a network cost arbitrarily close to
the minimum, with a tradeoff in network delay. Our solution captures the unique
chaining and flow scaling aspects of AgI services, while exploiting the use of
the broadcast approach coding scheme over the wireless channel.Comment: 30 pages, journa
Joint Service Placement and Request Routing in Multi-cell Mobile Edge Computing Networks
The proliferation of innovative mobile services such as augmented reality,
networked gaming, and autonomous driving has spurred a growing need for
low-latency access to computing resources that cannot be met solely by existing
centralized cloud systems. Mobile Edge Computing (MEC) is expected to be an
effective solution to meet the demand for low-latency services by enabling the
execution of computing tasks at the network-periphery, in proximity to
end-users. While a number of recent studies have addressed the problem of
determining the execution of service tasks and the routing of user requests to
corresponding edge servers, the focus has primarily been on the efficient
utilization of computing resources, neglecting the fact that non-trivial
amounts of data need to be stored to enable service execution, and that many
emerging services exhibit asymmetric bandwidth requirements. To fill this gap,
we study the joint optimization of service placement and request routing in
MEC-enabled multi-cell networks with multidimensional
(storage-computation-communication) constraints. We show that this problem
generalizes several problems in literature and propose an algorithm that
achieves close-to-optimal performance using randomized rounding. Evaluation
results demonstrate that our approach can effectively utilize the available
resources to maximize the number of requests served by low-latency edge cloud
servers.Comment: IEEE Infocom 201
An Efficient Coded Multicasting Scheme Preserving the Multiplicative Caching Gain
Coded multicasting has been shown to be a promis- ing approach to
significantly improve the caching performance of content delivery networks with
multiple caches downstream of a common multicast link. However, achievable
schemes proposed to date have been shown to achieve the proved order-optimal
performance only in the asymptotic regime in which the number of packets per
requested item goes to infinity. In this paper, we first extend the asymptotic
analysis of the achievable scheme in [1], [2] to the case of heterogeneous
cache sizes and demand distributions, providing the best known upper bound on
the fundamental limiting performance when the number of packets goes to
infinity. We then show that the scheme achieving this upper bound quickly loses
its multiplicative caching gain for finite content packetization. To overcome
this limitation, we design a novel polynomial-time algorithm based on random
greedy graph- coloring that, while keeping the same finite content
packetization, recovers a significant part of the multiplicative caching gain.
Our results show that the order-optimal coded multicasting schemes proposed to
date, while useful in quantifying the fundamental limiting performance, must be
properly designed for practical regimes of finite packetization.Comment: 6 pages, 7 figures, Published in Infocom CNTCV 201
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