Dynamical behavior of generic quintessence potentials: constraints on key dark energy observables

We perform a comprehensive study of a class of dark energy models - scalar field models where the effective potential can be described by a polynomial series - exploring their dynamical behavior using the method of flow equations that has previously been applied to inflationary models. Using supernova, baryon oscillation, CMB and Hubble constant data, and an implicit theoretical prior imposed by the scalar field dynamics, we find that the LCDM model provides an excellent fit to the data. Constraints on the generic scalar field potential parameters are presented, along with the reconstructed w(z) histories consistent with the data and the theoretical prior. We propose and pursue computationally feasible algorithms to obtain estimates of the principal components of the equation of state, as well as parameters w_0 and w_a. Further, we use the Monte Carlo Markov Chain machinery to simulate future data based on the Joint Dark Energy Mission, Planck and baryon acoustic oscillation surveys and find that the inverse area figure of merit improves nearly by an order of magnitude. Therefore, most scalar field models that are currently consistent with data can be potentially ruled out by future experiments. We also comment on the classification of dark energy models into "thawing'" and "freezing" in light of the more diverse evolution histories allowed by this general class of potentials.Comment: 22 pages and 12 figures, minor clarifications and a new Figure (#9) added in v3, matches the published PRD version. Chains and high-res figures are available at http://kicp.uchicago.edu/~dhuterer/DE_FLOWROLL/de_flowroll.htm

Fast approximation of centrality and distances in hyperbolic graphs

We show that the eccentricities (and thus the centrality indices) of all vertices of a $\delta$-hyperbolic graph $G=(V,E)$ can be computed in linear time with an additive one-sided error of at most $c\delta$, i.e., after a linear time preprocessing, for every vertex $v$ of $G$ one can compute in $O(1)$ time an estimate $\hat{e}(v)$ of its eccentricity $ecc_G(v)$ such that $ecc_G(v)\leq \hat{e}(v)\leq ecc_G(v)+ c\delta$ for a small constant $c$. We prove that every $\delta$-hyperbolic graph $G$ has a shortest path tree, constructible in linear time, such that for every vertex $v$ of $G$, $ecc_G(v)\leq ecc_T(v)\leq ecc_G(v)+ c\delta$. These results are based on an interesting monotonicity property of the eccentricity function of hyperbolic graphs: the closer a vertex is to the center of $G$, the smaller its eccentricity is. We also show that the distance matrix of $G$ with an additive one-sided error of at most $c'\delta$ can be computed in $O(|V|^2\log^2|V|)$ time, where $c'< c$ is a small constant. Recent empirical studies show that many real-world graphs (including Internet application networks, web networks, collaboration networks, social networks, biological networks, and others) have small hyperbolicity. So, we analyze the performance of our algorithms for approximating centrality and distance matrix on a number of real-world networks. Our experimental results show that the obtained estimates are even better than the theoretical bounds.Comment: arXiv admin note: text overlap with arXiv:1506.01799 by other author

Periglacial Relief Phenomena on Mount Vardenik (Southeastern Serbia)

In the medium-high mountains of Serbia (1,000-2,000 m.a.s.l), sporadic periglacial relief forms occur, which is also the case with Mount Vardenik (1,876 m.high), a mountain in the southeast of Serbia. During reconnaissance, certain relict and sub-recent periglacial phenomena and landforms in the highest part of the mountain have been identified: block slides, rock flows, thermogenic landslides in springs, nivation-induced relief and in one location cryoplanation terraces. Sparsely clustered and individual occurrences of frost splitting and solifluction of the land surface and small areas with grass turf indicate contemporary signs of sporadically present seasonal frost and freeze-thaw cycles. Periglacial morphology and its processes have been recorded and investigated using a qualitative geomorphological procedure. The main problem is the origin of periglacial phenomena (occurrences and landforms) of the relief, considering that the analysis of the contemporary climate, geoecological properties and anthropogenic activities indicate that there are no condi-tions for the existence and development of a contemporary periglacial environment on the mountain. The problem was analyzed considering the climate change in general and, in particular, geoecological conditions created under the influence of human activities. Due to the observed sporadic relict and sub-recent periglacial relief on Mount Vardenik, in contemporary conditions the periglacial environment of this area can be consid-ered as relict or as a phenomenon bordering the limits of differentiation. The relict property also results from the fact that on the mountain, due to the contemporary climate and changed geoecological conditions, the transition zone of the periglacial environment cannot be distinguished

Water Distribution Modeling

To effectively use water distribution models, the engineer must be able to link knowledge of basic hydraulic theory and the mechanics of the program with that of the operation of real-world systems. Water Distribution Modeling does just that. Written by industry experts, it provides a practical resource for engineers and modelers that goes well beyond being a how-to guide for typing data into a computer program. It contains straightforward answers to common questions related both to modeling and to distribution systems in general. This textbook walks the practicing engineer or student through the modeling process from start to finish — from data collection and field-testing to using a model for system design and complex operational tasks

Design of class 4 cross section in axial compression according to EUROCODE 3

In this paper theoretic basis of design of class 4 cross section in axial compression according to EN1993-1-5 is given. Design procedure is given as an flow chart and ilustrated with an worked example. Plate buckling is treated localy and globaly through the concept of effective cross sections. Interaction between plate-like and column-like behaviour of panels is carried out thought buckling reduction factors and final effective area of cross section

Wind towers - design of flange ring connection

Today, wind power is second largest available renewable resource of energy, with 870 TW (terawatts). Large wind farms, with hundreds of wind towers are big opportunity for steel production industry. Designers and manufacturers of wind towers pay special attention on every single detail, always looking for some new solutions, trying to reduce price of wind towers. Some of the most interesting design and manufacturing details are connections used to assemble sections of tubular steel towers supporting wind turbins. There is traditional and actually more used flange ring connection and on the other side, as a new proposal which is used more and more, friction connection. In this paper theoretic basis of design of flange ring connection of wind towers is give

Wind towers - design of flange ring connection

Today, wind power is second largest available renewable resource of energy, with 870 TW (terawatts). Large wind farms, with hundreds of wind towers are big opportunity for steel production industry. Designers and manufacturers of wind towers pay special attention on every single detail, always looking for some new solutions, trying to reduce price of wind towers. Some of the most interesting design and manufacturing details are connections used to assemble sections of tubular steel towers supporting wind turbins. There is traditional and actually more used flange ring connection and on the other side, as a new proposal which is used more and more, friction connection. In this paper theoretic basis of design of flange ring connection of wind towers is give

Design of class 4 cross section in axial compression according to EUROCODE 3

In this paper theoretic basis of design of class 4 cross section in axial compression according to EN1993-1-5 is given. Design procedure is given as an flow chart and ilustrated with an worked example. Plate buckling is treated localy and globaly through the concept of effective cross sections. Interaction between plate-like and column-like behaviour of panels is carried out thought buckling reduction factors and final effective area of cross section