Spot-like Structures of Neutron Star Surface Magnetic Fields

There is growing evidence, based on both X-ray and radio observations of isolated neutron stars, that besides the large--scale (dipolar) magnetic field, which determines the pulsar spin--down behaviour, small--scale poloidal field components are present, which have surface strengths one to two orders of magnitude larger than the dipolar component. We argue in this paper that the Hall--effect can be an efficient process in producing such small--scale field structures just above the neutron star surface. It is shown that due to a Hall--drift induced instability, poloidal magnetic field structures can be generated from strong subsurface toroidal fields, which are the result of either a dynamo or a thermoelectric instability acting at early times of a neutron star's life. The geometrical structure of these small--scale surface anomalies of the magnetic field resembles that of some types of ``star--spots''. The magnetic field strength and the length--scales are comparable with values that can be derived from various observations.Comment: 4 pages, 2 figures, accepted by Astronomy & Astrophysics Letters; language improved, 2nd para of Sect. 3 change

Stimulating Cooperation in Self-Organized Vehicular Networks

A Vehicular Ad-hoc NETwork (VANET) is a special form of Mobile Ad-hoc Network designed to provide communications among nearby vehicles and between vehicles and nearby fixed roadside equipment. Its main goal is to improve safety and comfort for passengers, but it can also be used for commercial applications. In this latter case, it will be necessary to motivate drivers to cooperate and contribute to packet forwarding in Vehicle-to-Vehicle and Vehicle-to-Roadside communications. This paper examines the problem, analyzes the drawbacks of known schemes and proposes a new secure incentive scheme to stimulate cooperation in VANETs, taking into account factors such as time and distance

Interrelation between radio and X-ray signatures of drifting subpulses in pulsars

We examined a model of partially screened gap region above the polar cap, in which the electron-positron plasma generated by sparking discharges coexists with thermionic flow ejected by the bombardment of the surface beneath these sparks. Our special interest was the polar cap heating rate and the subpulse drifting rate, both phenomena presumably associated with sparks operating at the polar cap. We investigated correlation between the intrinsic drift rate and polar cap heating rate and found that they are coupled to each other in such a way that the thermal X-ray luminosity $L_x$ from heated polar cap depends only on the observational tertiary subpulse drift periodicity $\hat{P}_3$ (polar cap carousel time). Within our model of partially screened gap we derived the simple formula relating $L_x$ and $\hat{P}_3$, and showed that it holds for PSRs B0943$+$10 and B1133+16, which are the only two pulsars in which both $L_x$ and $\hat{P}_3$ are presently known.Comment: 4 page

A simple algorithm based on fluctuations to play the market

In Biology, all motor enzymes operate on the same principle: they trap favourable brownian fluctuations in order to generate directed forces and to move. Whether it is possible or not to copy one such strategy to play the market was the starting point of our investigations. We found the answer is yes. In this paper we describe one such strategy and appraise its performance with historical data from the European Monetary System (EMS), the US Dow Jones, the german Dax and the french Cac40.Comment: 8 pages 14 figure

The Need for Governmental Inefficiency in Plato’s Republic

In book II of Plato’s Republic, Socrates discusses the cities of necessity and luxury (372d-373a). Discussions of these cities have often focused on citizens desiring more than they need, which creates a demand for luxury. Yet the second part of the equation, which is not usually recognized, is that there must be sufficient supply to meet this demand. The focus of this article is on the importance of supply in the discussion of the first two cities in book II of the Republic. This article argues that the way Plato models the cities makes it the case that a surplus above levels of necessity will be generated from time to time. That the unwanted surplus cannot be spontaneously disposed of entails that the first two cities are institutionally incomplete. A government is needed in order to coordinate the disposal of the surplus supply the city will produce

Three Puzzles on Mathematics, Computation, and Games

In this lecture I will talk about three mathematical puzzles involving mathematics and computation that have preoccupied me over the years. The first puzzle is to understand the amazing success of the simplex algorithm for linear programming. The second puzzle is about errors made when votes are counted during elections. The third puzzle is: are quantum computers possible?Comment: ICM 2018 plenary lecture, Rio de Janeiro, 36 pages, 7 Figure

No Theory-Free Lunches in Well-Being Policy

Generating an account that can sidestep the disagreement among substantive theories of well-being, while at the same time still providing useful guidance for well-being public policy, would be a significant achievement. Unfortunately, the various attempts to remain agnostic regarding what constitutes well-being fail to either be an account of well-being, provide useful guidance for well-being policy, or avoid relying on a substantive well-being theory. There are no theory-free lunches in well-being policy. Instead, I propose an intermediate account, according to which well-being is constituted by endorsed veridical experiences. This account refers back to theories of well-being but does so as agnostically as possible. An intermediate account of well-being is meant as a policy guiding compromise between the different theories of well-being that make claims regarding what constitutes well-being. An intermediate account does as well as can be hoped for in providing a basis for well-being policy

The Narrowed Domain of Disagreement for Well-Being Policy

in recent years, policy makers have shown increasing interest in implementing policies aimed at promoting individual well-being. But how should policy makers choose their well-being policies? a seemingly reasonable first step is to settle on an agreed-upon definition of well-being. yet there currently is significant disagreement on how well-being ought to be characterized, and agreement on the correct view of well-being does not appear to be forthcoming. Nevertheless, i argue in this paper that there are several reasons to think that the domain of well-being in the public policy context is narrower than that of well-being in general, which makes agreement on how to understand well-being in the public policy context more likely