Ball and Spindle Convexity with respect to a Convex Body

Let $C\subset {\mathbb R}^n$ be a convex body. We introduce two notions of convexity associated to C. A set $K$ is $C$-ball convex if it is the intersection of translates of $C$, or it is either $\emptyset$, or ${\mathbb R}^n$. The $C$-ball convex hull of two points is called a $C$-spindle. $K$ is $C$-spindle convex if it contains the $C$-spindle of any pair of its points. We investigate how some fundamental properties of conventional convex sets can be adapted to $C$-spindle convex and $C$-ball convex sets. We study separation properties and Carath\'eodory numbers of these two convexity structures. We investigate the basic properties of arc-distance, a quantity defined by a centrally symmetric planar disc $C$, which is the length of an arc of a translate of $C$, measured in the $C$-norm, that connects two points. Then we characterize those $n$-dimensional convex bodies $C$ for which every $C$-ball convex set is the $C$-ball convex hull of finitely many points. Finally, we obtain a stability result concerning covering numbers of some $C$-ball convex sets, and diametrically maximal sets in $n$-dimensional Minkowski spaces.Comment: 27 pages, 5 figure

Do the rich get richer? An empirical analysis of the BitCoin transaction network

The possibility to analyze everyday monetary transactions is limited by the scarcity of available data, as this kind of information is usually considered highly sensitive. Present econophysics models are usually employed on presumed random networks of interacting agents, and only macroscopic properties (e.g. the resulting wealth distribution) are compared to real-world data. In this paper, we analyze BitCoin, which is a novel digital currency system, where the complete list of transactions is publicly available. Using this dataset, we reconstruct the network of transactions, and extract the time and amount of each payment. We analyze the structure of the transaction network by measuring network characteristics over time, such as the degree distribution, degree correlations and clustering. We find that linear preferential attachment drives the growth of the network. We also study the dynamics taking place on the transaction network, i.e. the flow of money. We measure temporal patterns and the wealth accumulation. Investigating the microscopic statistics of money movement, we find that sublinear preferential attachment governs the evolution of the wealth distribution. We report a scaling relation between the degree and wealth associated to individual nodes.Comment: Project website: http://www.vo.elte.hu/bitcoin/; updated after publicatio

Photo-Met: a non-parametric method for estimating stellar metallicity from photometric observations

Getting spectra at good signal-to-noise ratios takes orders of magnitudes more time than photometric observations. Building on the technique developed for photometric redshift estimation of galaxies, we develop and demonstrate a non-parametric photometric method for estimating the chemical composition of galactic stars. We investigate the efficiency of our method using spectroscopically determined stellar metallicities from SDSS DR7. The technique is generic in the sense that it is not restricted to certain stellar types or stellar parameter ranges and makes it possible to obtain metallicities and error estimates for a much larger sample than spectroscopic surveys would allow. We find that our method performs well, especially for brighter stars and higher metallicities and, in contrast to many other techniques, we are able to reliably estimate the error of the predicted metallicities.Comment: 5 pages, 4 figures, accepted for publication in A

Az identitás régészetének elméleti alapjai

Jelen tanulmány megkísérli röviden összefoglalni az identitásrégészet f? kutatási irányait és szempontrendszerét. Tárgyalja az identitás ? értve ezalatt a státuszokat és szerepeket, amelyek meghatározzák az egyén viszonyát, kapcsolódását közösségekhez és más egyénekhez, melyek így lényegében a társadalom összetartó és szervez? elemeit jelentik ? elvi m?ködésének, kialakulásának témakörét és csoportosítási lehet?ségeit, valamint megértésének és kifejezésének módját a kulturális memórián és az anyagi kultúrán keresztül

The accuracy of DGPS surveys on the basis of test measurements with a Leica GS20 receiver

In our article we deal with studying the accuracy of DGPS surveys. The test measurements focussed on this purpose with a LEICA GS20 GPS receiver were very useful for us for various reasons. Firstly, we got acquainted with the operation of a hand-held GIS GPS receiver which is considered to be a relatively new one on the market and the usage of the appropriate post-processing software, secondly when analyzing the results we studied the improving accuracy of our test measurements performed with a single receiver using various corrections. Accordingly, ground corrections originated from PENC control station were considered on the one hand, on the other hand EGNOS corrections were applied when we formed an opinion of the problem raised in the title of this study

Inferring the interplay of network structure and market effects in Bitcoin

A main focus in economics research is understanding the time series of prices of goods and assets. While statistical models using only the properties of the time series itself have been successful in many aspects, we expect to gain a better understanding of the phenomena involved if we can model the underlying system of interacting agents. In this article, we consider the history of Bitcoin, a novel digital currency system, for which the complete list of transactions is available for analysis. Using this dataset, we reconstruct the transaction network between users and analyze changes in the structure of the subgraph induced by the most active users. Our approach is based on the unsupervised identification of important features of the time variation of the network. Applying the widely used method of Principal Component Analysis to the matrix constructed from snapshots of the network at different times, we are able to show how structural changes in the network accompany significant changes in the exchange price of bitcoins.Comment: project website: http://www.vo.elte.hu/bitcoi

Income distribution in new (and old) EU member states

The paper, based on recent EU-SILC data, investigates the patterns of income inequalities in “old” and “new” EU member states. We describe income inequality within countries as well as income differences between states and test our results using different methodological assumptions. Our results show that the group of new member states was no less heterogeneous in terms of inequality and poverty than the EU15 at the time of EU enlargement. The most important difference between the two country groups is found in their GDP levels and in some measures that are directly related to economic development. We observed that sensitivity to changes in the equivalence scales is not systematically related to membership status; thus for overall inequality comparisons of countries, a standard scale seems appropriate. The possibility of a difference between “old” and “new” EU member states in the role of incomes in generating overall welfare of households calls, however, for caution in interpretation

First record of the eastern spadefoot toad (Pelobates syriacus Boettger, 1889) in Albania

L