There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

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Table Of Integrals Series And Products

Brian Thompson is a Senior Nutrition Officer at the Food and Agriculture Organization of the United Nations (FAO). FAO is an intergovernmental organization, it has 191 Member Nations, two associate members and one member organization, the European Union. As a knowledge organization, FAO creates and shares critical information about food, agriculture and natural resources in the form of global public goods. FAO plays a connector role, through identifying and working with different partners with established expertise, and facilitating a dialogue between those who have the knowledge and those who need it. By turning knowledge into action, FAO links the field to national, regional and global initiatives in a mutually reinforcing cycle. Its mandate is to raise levels of nutrition and standards of living. What is the size of the malnutrition problem and what regions are most affected? There are persistently high levels of undernutrition. Nearly 870 million people in the world go to bed hungry (1 in 8 people) according to the recently released report of The State of Food Insecurity in the World 2012 (SOFI) and 2 billion have some form of micronutrient malnutrition – this constitutes a crime against humanity and is a responsibility for all of us. Prevalence of undernourishment in developing countries has declined over the past two decades, from 23 to 15 percent. In terms of total numbers in 1990– 92, around 980 million individuals were estimated to be undernourished. The number dropped to 901 million in 1999– 2001, to 885 million in 2006–06 and to 852 million in 2007–09. The financial crisis, economic downturn, persistent food price volatility, drought and other repercussions of climate change since 2006–08 may have prevented any further significant improvements in the number of people who are undernourished in developing countries since then. Africa has by far the highest prevalence, at around 23 percent in 2010–12 but though it is down from what it was in 1990–92 (27 percent) the numbers have risen from 175 million to 239 million with nearly 20 million added in the past four years. In subSaharan Africa, the modest progress achieved in recent years up to 2007 was reversed, with hunger rising 2 percent per year since then. In Asia, both prevalence and numbers dropped over the same period from 24 percent (739 million) to 14 percent (563 million). Latin America and the Caribbean (LAC) boasts the lowest rate of undernourishment (8 percent) among developing country regions but the rate of progress has slowed recently. Countries considered as leastdeveloped countries and lowincome economies have the highest prevalence rates of all around 30 percent but down from the 40 percent levels of twenty years ago.

Interview ラン・ラン

The fifth generation (5G) mobile communication systems will be in use around 2020. The aim of 5G systems is to provide anywhere and anytime connectivity for anyone and anything. Several new technologies are being researched for 5G systems, such as massive multiple-input multiple-output communications, vehicle-to-vehicle communications, high-speed train communications, and millimeter wave communications. Each of these technologies introduces new propagation properties and sets specific requirements on 5G channel modeling. Considering the fact that channel models are indispensable for system design and performance evaluation, accurate and efficient channel models covering various 5G technologies and scenarios are urgently needed. This paper first summarizes the requirements of the 5G channel modeling, and then provides an extensive review of the recent channel measurements and models. Finally, future research directions for channel measurements and modeling are provided.

A Survey of 5G Channel Measurements and Models

High-speed railway (HSR) brings convenience to peoples' lives and is generally considered as one of the most sustainable developments for ground transportation. One of the important parts of HSR construction is the signaling system, which is also called the “operation control system,” where wireless communications play a key role in the transmission of train control data. We discuss in detail the main differences in scientific research for wireless communications between the HSR operation scenarios and the conventional public land mobile scenarios. The latest research progress in wireless channel modeling in viaducts, cuttings, and tunnels scenarios are discussed. The characteristics of nonstationary channel and the line-of-sight (LOS) sparse and LOS multiple-input-multiple-output channels, which are the typical channels in HSR scenarios, are analyzed. Some novel concepts such as composite transportation and key challenging techniques such as train-to-train communication, vacuum maglev train techniques, the security for HSR, and the fifth-generation wireless communications related techniques for future HSR development for safer, more comfortable, and more secure HSR operation are also discussed.

Challenges Toward Wireless Communications for High-Speed Railway

The future development of the railway is highly desired to evolve into a new era where infrastructure, trains, travelers, and goods will be increasingly interconnected to provide high comfort, with optimized door-to-door mobility at higher safety. For this vision, it is required to realize seamless high data rate wireless connectivity for railways. To improve the safety and comfort of future railways, wireless communications for railways are required to evolve from only voice and traditional train control signaling services to various high data rate services including critical high-definition (HD) video and other more bandwidth-intensive passenger services, such as onboard and wayside HD video surveillance, onboard real-time high data rate services, train multimedia dispatching video streaming, railway mobile ticketing, and the Internet of Things for railways. Corresponding mobile communications network architecture under various railway scenarios including inter-car, intra-car, inside station, train-to-infrastructure and infrastructure- to-infrastructure are proposed in this article. Wireless coverage based on massive MIMO for railway stations and train cars is proposed to fulfill the requirement of high-data-rate and high spectrum efficiency. The technical challenges brought by the massive MIMO technique are discussed as well.

Future railway services-oriented mobile communications network

This paper focuses on the shadow fading characteristic in viaduct scenario of the High-speed Railway. Measurement is done on Beijing to Shanghai High-speed Railway. Based on the measurement data, distribution and autocorrelation of the shadow fading are researched. Statistical values of the shadow fading standard deviation and the decorrelation distance are analyzed. It is shown that the lognormal distribution suits most groups of the measurement data well. Evaluation of the exponential shadow fading autocorrelation model and the double exponential shadow fading autocorrelation model are made in terms of mean error, standard deviation and correlation coefficient of the residuals between the models and the measurement data. Simulation results show better performance of the double exponential model compared with the exponential model.

Study on the shadow fading characteristic in viaduct scenario of the High-speed Railway

As a very important parameter in link budget and channel modeling, the Ricean K factor in the viaduct and cutting scenarios along the high speed railway is estimated by using a moment-based estimator. The practical measurement is taken in the train at a speed of more than 250 km/h. The measured distributions are compared with the Ricean distributions and it's seen that the estimation of Kis accurate. Channel conditions of the two special scenarios are analyzed based on the measurement and estimation results.

Estimation of the Ricean factor in K the high speed railway scenarios

The fifth generation (5G) communication has recently attracted much interest. In this paper we present radio channel measurements on campus at 3.5 GHz, which is the candidate frequency band for the 5G communications. The measurement setup is based on software radio units with a bandwidth of 30 MHz, and the measurements were conducted on campus of Beijing Jiaotong University, China. We discuss the power delay profile, path loss, shadowing, and delay spread. It is found that the path loss exponent is up to 6.16 due to high carrier frequency. A lognormal distribution is used to model the shadowing effect, and the standard deviation is 4.21 dB. Furthermore, the root-mean-square delay spread is around 45 ns in the measured campus environments. The results can be applied to the 5G communication system design.

Lei Xiong

Papers

Challenges Toward Wireless Communications for High-Speed Railway

Future railway services-oriented mobile communications network

Study on the shadow fading characteristic in viaduct scenario of the High-speed Railway

Estimation of the Ricean factor in K the high speed railway scenarios

Channel measurements and modeling for 5G communication systems at 3.5 GHz band