Lithium–sulfur batteries are a promising energy-storage technology due to their relatively low cost and high theoretical energy density. However, one of their major technical problems is the shuttling of soluble polysulfides between electrodes, resulting in rapid capacity fading. Here, we present a metal–organic framework (MOF)-based battery separator to mitigate the shuttling problem. We show that the MOF-based separator acts as an ionic sieve in lithium–sulfur batteries, which selectively sieves Li+ ions while e ciently suppressing undesired polysulfides migrating to the anode side. When a sulfur-containing mesoporous carbon material (approximately 70 wt% sulfur content) is used as a cathode composite without elaborate synthesis or surface modification, a lithium–sulfur battery with a MOF-based separator exhibits a low capacity decay rate (0.019% per cycle over 1,500 cycles). Moreover, there is almost no capacity fading after the initial 100 cycles. Our approach demonstrates the potential for MOF-based materials as separators for energy-storage applications.
上传时间： 2017-11-23
上传用户：653357637
The working title of this book was Channel Equalization for Everyone. Channel equalization for everyone? Well, for high school students, channel equalization provides a simple, interesting example of how mathematics and physics can be used to solve real-world problems.
标签： Equalization Channel
上传时间： 2020-05-26
上传用户：shancjb
This book is an entry-level text on the technology of telecommunications. It has been crafted with the newcomer in mind. The eighteen chapters of text have been prepared for high-school graduates who understand algebra, logarithms, and basic electrical prin- ciples such as Ohm’s law. However, many users require support in these areas so Appen- dices A and B review the essentials of electricity and mathematics through logarithms.
标签： Telecommunications Fundamentals 1st of ed
上传时间： 2020-05-27
上传用户：shancjb
This book is an entry-level text on the technology of telecommunications. It has been crafted with the newcomer in mind. The twenty-one chapters of text have been prepared for high-school graduates who understand algebra, logarithms, and the basic principles of electricity such as Ohm’s law. However, it is appreciated that many readers require support in these areas. Appendices A and B review the essentials of electricity and mathematics up through logarithms. This material was placed in the appendices so as not to distract from the main theme, the technology of telecommunication systems. Another topic that many in the industry find difficult is the use of decibels and derived units. Appendix C provides the reader a basic understanding of decibels and their applications. The only mathematics necessary is an understanding of the powers of ten
标签： Telecommunications Fundamentals 2nd of ed
上传时间： 2020-05-27
上传用户：shancjb
Soon after Samuel Morse’s telegraphing device led to a deployed electri- cal telecommunications system in 1843, waiting lines began to form by those wanting to use the system. At this writing queueing is still a significant factor in designing and operating communications services, whether they are provided over the Internet or by other means, such as circuit switched networks.
标签： Telecommunication Queueing Packet Theory with
上传时间： 2020-05-31
上传用户：shancjb
It is more than a decade since GSM was first commercially available. After some unexpected delay, it seems that finally UMTS is here to stay as a 3G system standardised by 3GPP, at least for another ten years. UMTS will enable multi-service, multi-rate and flexible IP native-based mobile technologies to be used in wide area scenarios and also pave the way for a smooth transition from circuit switched voice networks to mobile packet services.
标签： Management Strategies Resource Radio
上传时间： 2020-06-01
上传用户：shancjb
When 3GPP started standardizing the IMS a few years ago, most analysts expected the number of IMS deploymentsto grow dramatically as soon the initial IMS specifications were ready (3GPP Release 5 was functionallyfrozenin the first half of 2002and completedshortly after that). While those predictions have proven to be too aggressive owing to a number of upheavals hitting the ICT (Information and Communications Technologies) sector, we are now seeing more and more commercial IMS-based service offerings in the market. At the time of writing (May 2008), there are over 30 commercial IMS networks running live traffic, addingup to over10million IMS users aroundthe world; the IMS is beingdeployedglobally. In addition, there are plenty of ongoing market activities; it is estimated that over 130 IMS contracts have been awarded to all IMS manufacturers. The number of IMS users will grow substantially as these awarded contracts are launched commercially. At the same time, the number of IMS users in presently deployed networks is steadily increasing as new services are introduced and operators running these networks migrate their non-IMS users to their IMS networks.
标签： Multimedia Subsystem The IMS 3G IP
上传时间： 2020-06-01
上传用户：shancjb
The first practical examples of mobile communications were used in many countries like the USA, the UK and Germany in military services, and played a significant role in the First World War to transfer important information from the front to headquarters to take further actions. Good and secure wireless communications were an important need for all military services – army, navy and air force. In this respect, the Second World War was a big experimental battlefield for the development and evolution of mobile radio. It was in the interests of governments that after the Second World War the military investment should be paid back by civilian use, and all western European countries started their so-called first generation of mobile communication networks.
标签： Multimedia Business Mobile The
上传时间： 2020-06-01
上传用户：shancjb
n the first part of this book, we give an introduction to the basic applications of wireless com- munications, as well as the technical problems inherent in this communication paradigm. After a brief history of wireless, Chapter 1 describes the different types of wireless services, and works out their fundamental differences. The subsequent Section 1.3 looks at the same problem from a different angle: what data rates, ranges, etc., occur in practical systems, and especially, what combination of performance measures are demanded (e.g., what data rates need to be transmitted over short distances; what data rates are required over long distances?) Chapter 2 then describes the technical challenges of communicating without wires, putting special emphasis on fading and co-channel interference. Chapter 3 describes the most elementary problem of designing a wireless system, namely to set up a link budget in either a noise-limited or an interference-limited system. After studying this part of the book, the reader should have an overview of different types of wireless services, and understand the technical challenges involved in each of them. The solutions to those challenges are described in the later parts of this book.
标签： Communications Wireless Edition 2nd
上传时间： 2020-06-01
上传用户：shancjb
It has been over a decade since the Chinese publication of Line Loss in Electric Power Systems. To keep pace with technological developments, I started a revision as early as 2002, following the main principles that the theoretical framework and characteristics of the first edition should be retained, with new contents added according to new problems after the reform of electric power systems and the new requirements for line loss management practices and in combination with practical experience.
上传时间： 2020-06-07
上传用户：shancjb
