Modified Sonine approximation for the Navier-Stokes transport coefficients of a granular gas

Motivated by the disagreement found at high dissipation between simulation data for the heat flux transport coefficients and the expressions derived from the Boltzmann equation by the standard first Sonine approximation [Brey et al., Phys. Rev. E 70, 051301 (2004); J. Phys.: Condens. Matter 17, S2489 (2005)], we implement in this paper a modified version of the first Sonine approximation in which the Maxwell-Boltzmann weight function is replaced by the homogeneous cooling state distribution. The structure of the transport coefficients is common in both approximations, the distinction appearing in the coefficient of the fourth cumulant $a_2$. Comparison with computer simulations shows that the modified approximation significantly improves the estimates for the heat flux transport coefficients at strong dissipation. In addition, the slight discrepancies between simulation and the standard first Sonine estimates for the shear viscosity and the self-diffusion coefficient are also partially corrected by the modified approximation. Finally, the extension of the modified first Sonine approximation to the transport coefficients of the Enskog kinetic theory is presented.Comment: 10 pages, 6 figures; v2: slightly shortene

Spin Orbit Coupling in Graphene Induced by Heavy Adatoms with Electrons in the Outer-Shell pp Orbitals

Many of the exotic properties proposed to occur in graphene rely on the possibility of increasing the spin orbit coupling (SOC). By combining analytical and numerical tight binding calculations, in this work we study the SOC induced by heavy adatoms with active electrons living in $p$ orbitals. Depending on the position of the adatoms on graphene different kinds of SOC appear. Adatoms located in hollow position induce spin conserving intrinsic like SOC whereas a random distribution of adatoms induces a spin flipping Rashba like SOC. The induced SOC is linearly proportional to the adatoms concentration, indicating the inexistent interference effects between different adatoms. By computing the Hall conductivity we have proved the stability of the topological quantum Hall phases created by the adatoms against inhomogeneous spin orbit coupling . For the case of Pb adatoms, we find that a concentration of 0.1 adatom per carbon atom generates SOC's of the order of $\sim$40$meV$

Foreword

Preface to the Volume by O. Rak on the Neolithic Rhyta, cult vessels distributed in most of the Balkan peninsul

Frequency division multiplex technique

A system for monitoring a plurality of condition responsive devices is described. It consists of a master control station and a remote station. The master control station is capable of transmitting command signals which includes a parity signal to a remote station which transmits the signals back to the command station so that such can be compared with the original signals in order to determine if there are any transmission errors. The system utilizes frequency sources which are 1.21 multiples of each other so that no linear combination of any harmonics will interfere with another frequency

Evaluating the social and cultural implications of the internet

Since the Internet's breakthrough as a mass medium, it has become a topic of discussion because of its implications for society. At one extreme, one finds those who only see great benefits and consider the Internet a tool for freedom, commerce, connectivity, and other societal benefits. At the other extreme, one finds those who lament the harms and disadvantages of the Internet, and who consider it a grave danger to existing social structures and institutions, to culture, morality and human relations. In between one finds the majority, those who recognize both benefits and harms in the Internet as it currently exists and who recognize its usefulness while worrying about some of its negative impacts.As an example of a positive appraisal of the Internet, consider what Esther Dyson, one of the early enthusiasts for the Internet, states in her book Release 2.0. There, she claims: "The Net offers us a chance to take charge of our own lives and to redefine our role as citizens of local communities and of a global society. It also hands us the responsibility to govern ourselves, to think for ourselves, to educate our children, to do business honestly, and to work with fellow citizens to design rules we want to live by." (Dyson, 1997). Dyson argues that the Internet offers us the chance to build exciting communities of likeminded individuals, enables people to redefine their work as they see fit, fosters truth-telling and information disclosure, helps build trust between people, and can function for people as a second home.For a negative appraisal, consider the opinion of the Council of Torah Sages, a group of leading orthodox rabbis in Israel who in 2000 issued a ruling banning the Internet from Jewish homes. The Council claimed that the Internet is "1,000 times more dangerous than television" (which they banned thirty years earlier). The Council described the Internet as "the world's leading cause of temptation" and "a deadly poison which burns souls" that "incites and encourages sin and abomination of the worst kind." The Council explained that it recognized benefits in the Internet, but saw no way of balancing these with the potential cost, which they defined as exposure to "moral pollution" and possible addiction to Internet use that could quash the motivation to learn Torah, especially among children. ( See Ha'aretz, January 7, 2000.)Even the greatest critics of the Internet, like the Council of Torah Sages, see benefits in the technology, and even the greatest advocates recognize that there are drawbacks to the medium. People have different opinions on what the benefits and disadvantages are and also differ in the way in which they balance them against each other. Underlying these different assessments of the Internet are different value systems. Esther Dyson holds a libertarian value system in which the maximization of individual freedom, property rights and free market capitalism are central values. Her positive assessment of the Internet is based on the potential she sees in this technology to promote these values. In contrast, the values Council of Torah Sages are values of Hareidi, a variety of orthodox Judaism, according to which the highest good is obedience to God's law as laid out in the Torah, and they concluded, based on these values, that the Internet is harmful.Yet, it is not just differences in value systems that determine one's appraisal of a technology like the Internet. Such an appraisal is also determined by one's empirical understanding of how the technology works and what its consequences or implications are. People often come to unduly positive or negative appraisals of technology because they assess its consequences wrongly. For instance, some people believe that Internet use increases the likelihood of social isolation, but empirical research could conceivably show that in fact the opposite is the case. Disagreements about the positive and negative aspects of the internet may therefore be either normative disagreements (disagreements about values) or empirical disagreements (disagreements about facts). Of course, it is not always easy to disentangle values and empirical facts, as these are often strongly interwoven.Next to contested benefits and harms of the Internet, there are also perceived harms and benefits that are fairly broadly acknowledged. For instance, nearly everyone agrees that the Internet has the benefit of making a large amount of useful information easily available, and nearly everyone agrees that the Internet can also be harmful by making dangerous, libelous and hateful information available. People have shared values and shared empirical beliefs by which they can come to such collective assessments.My purpose in this essay is to contribute to a better understanding of existing positive and negative appraisals of the Internet, as a first step towards a more methodical assessment of Internet technology. My focus will be on the appraisal of social and cultural implications of the Internet. Whether we like it or not, policy towards the Internet is guided by beliefs about its social and cultural benefits and harms. It is desirable, therefore, to have methods for making such beliefs explicit in order to analyze the values and empirical claims that are presupposed in them.In the next two sections (2 and 3), I will catalogue major perceived social and cultural benefits and harms of the Internet, that have been mentioned frequently in public discussions and academic studies. I will focus on perceived benefits and harms that do not seem to rest on idiosyncratic values, meaning that they seem to rest on values that are shared by most people. For instance, most people believe that individual autonomy is good, so if it can be shown that a technology enhances individual autonomy, most people would agree that this technology has this benefit. Notice, however, that even when they share this value, people may disagree on the benefits of the technology in question, because they may have different empirical beliefs on whether the technology actually enhanced individual autonomy.Cataloguing such perceived cultural benefits and harms is, I believe, an important first step towards a social and cultural technology assessment of the Internet and its various uses. An overview of perceived benefits and harms may provide a broader perspective on the Internet that could be to the benefit of both friends and foes, and can contribute to a better mutual understanding between them. More importantly, it provides a potential starting point for a reasoned and methodical analysis of benefits and harms. Ideas on how such an analysis may be possible, in light of the already mentioned facts that assessments are based on different value systems, will be developed in section 4. In a concluding section, I sketch the prospects for a future social and cultural technology assessment of the Internet

New Media and the Quality of Life

We are currently in the middle of a revolution. This revolution, sometimes called the digital revolution, is the revolutionary transformation brought about in the information and communication structure of society by the advent of the digital computer, with most of the major transformations having taken place in the past thirty years. Digital computing technology has generated the mainframe and personal computer, the multimedia computer, and computer networks. It has also transformed the telephone system and the monetary system, it is transforming all kinds of conventional products ranging from washing machines to automobiles, and it is on its way to change television as well. More than ever, contemporary society is an Information Society, in which the importance of information and communication is much greater than in past societies, and of which technologies that facilitate information and communication processes are a central societal feature. In this paper, I want to evaluate the implications of contemporary information and communication media for the quality of life, including both the new media from the digital revolution and the older media that still remain in use. My evaluation of contemporary media will proceed in three parts. In the section to follow, the benefits of contemporary media will be discussed, with special emphasis given to their immediate functional benefits. The section thereafter is devoted to a discussion of four potential threats posed by contemporary media. In a final major section, I look at the future of digital media and the possibilities available to us in shaping that future. A short concluding section ends the paper