Lithium–sulfur (Li–S) batteries with high energy density and long cycle life are considered to be one of the most promising next-generation energy-storage systems beyond routine lithium-ion batteries. Various approaches have been proposed to break down technical barriers in Li–S battery systems. The use
of nanostructured metal oxides and sulfides for high sulfur utilization and long life span of Li–S batteries is reviewed here. The relationships between the intrinsic properties of metal oxide/sulfide hosts and electrochemical performances of Li–S batteries are discussed. Nanostructured metal oxides/ sulfides hosts used in solid sulfur cathodes, separators/interlayers, lithium- metal-anode protection, and lithium polysulfides batteries are discussed respectively. Prospects for the future developments of Li–S batteries with nanostructured metal oxides/sulfides are also discussed.
Abstract—In the future communication applications, users
may obtain their messages that have different importance levels
distributively from several available sources, such as distributed
storage or even devices belonging to other users. This
scenario is the best modeled by the multilevel diversity coding
systems (MDCS). To achieve perfect (information-theoretic)
secrecy against wiretap channels, this paper investigates the
fundamental limits on the secure rate region of the asymmetric
MDCS (AMDCS), which include the symmetric case as a special
case. Threshold perfect secrecy is added to the AMDCS model.
The eavesdropper may have access to any one but not more than
one subset of the channels but know nothing about the sources,
as long as the size of the subset is not above the security level.
The question of whether superposition (source separation) coding
is optimal for such an AMDCS with threshold perfect secrecy
is answered. A class of secure AMDCS (S-AMDCS) with an
arbitrary number of encoders is solved, and it is shown that linear
codes are optimal for this class of instances. However, in contrast
with the secure symmetric MDCS, superposition is shown to
be not optimal for S-AMDCS in general. In addition, necessary
conditions on the existence of a secrecy key are determined as a
design guideline.
In recent years, cellular voice networks have transformed into powerful packet-switched
access networks for both voice communication and Internet access. Evolving Universal
Mobile Telecommunication System (UMTS) networks and first Long Term Evolution
(LTE) installations now deliver bandwidths of several megabits per second to individual
users, and mobile access to the Internet from handheld devices and notebooks is no
longer perceived as slower than a Digital Subscriber Line (DSL) or cable connection.
Bandwidth and capacity demands, however, keep rising because of the increasing number
of people using the networks and because of bandwidth-intensive applications such as
video streaming. Thus, network manufacturers and network operators need to find ways
to continuously increase the capacity and performance of their cellular networks while
reducing the cost.
Today’s wireless services have come a long way since the roll out of the
conventional voice-centric cellular systems. The demand for wireless access
in voice and high rate data multi-media applications has been increasing.
New generation wireless communication systems are aimed at accommodating
this demand through better resource management and improved transmission
technologies.
Cooperation is not a natural characteristic attributed to humans. The typical human horizon is focused
on short-term gains, which might be due to our instinct-driven subconscious occupying a grander
importance than we dare to admit [1]. Cooperating with other individuals or entities, however, usually
means that short-term losses may translate into long-term gains – something history has proved to
hold true but humans for some reason rarely ever understand.
It is commonly accepted today that optical fiber communications have revolutionized
telecommunications. Indeed, dramatic changes have been induced in the way we interact
with our relatives, friends, and colleagues: we retrieve information, we entertain and
educate ourselves, we buy and sell, we organize our activities, and so on, in a long list
of activities. Optical fiber systems initially allowed for a significant curb in the cost of
transmission and later on they sparked the process of a major rethinking regarding some,
generation-old, telecommunication concepts like the (OSI)-layer definition, the lack of
cross-layer dependency, the oversegmentation and overfragmentation of telecommunica-
tions networks, and so on.
Cellular communications is one of the fastest growing and most challenging telecom-
munication applications ever. Today, it represents a large and continuously increasing
percentage of all new telephone subscribers around the world. In the long term,
cellular digital technology may become the universal way of communication.
The motivation to write about the History of Wireless comes from Auguste
Comte (1798-1857), a French philosopher who is termed the father of positivism
and modem sociology [Les Maximes d'Auguste Comte (Auguste Comte's
Mottos), http://www.membres.lycos.fr/clotilde/l:
On ne connaitpas complgtement une science tant qu'on n'en saitpas l'histoire.
(One does not know completely a science as long as one does not know its
history.)
