Improved Magnetic Information Storage using Return-Point Memory

The traditional magnetic storage mechanisms (both analog and digital) apply an external field signal H(t) to a hysteretic magnetic material, and read the remanent magnetization M(t), which is (roughly) proportional to H(t). We propose a new analog method of recovering the signal from the magnetic material, making use of the shape of the hysteresis loop M(H). The field H, ``stored'' in a region with N domains or particles, can be recovered with fluctuations of order 1/N using the new method - much superior to the 1/sqrt{N} fluctuations in traditional analog storage.Comment: 9 pages, 15 figure

Barotropic fluid compatible parametrizations of dark energy

Parametrizations of Equation of state parameter as a function of the scale factor or redshift are frequently used in dark energy modeling. The question investigated in this paper is if parametrizations proposed in the literature are compatible with the dark energy being a barotropic fluid. The test of this compatibility is based on the functional form of the speed of sound squared, which for barotropic fluid dark energy follows directly from the function for the Equation of state parameter. The requirement that the speed of sound squared should be between 0 and speed of light squared provides constraints on model parameters using analytical and numerical methods. It is found that this fundamental requirement eliminates a large number of parametrizations as barotropic fluid dark energy models and puts strong constraints on parameters of other dark energy parametrizations.Comment: v1: 19 pages, 1 table, 4 figures. v2: minor changes, references added. v3: version accepted in EPJ

Degree Four Plane Spanners: Simpler and Better

Let P be a set of n points embedded in the plane, and let C be the complete Euclidean graph whose point-set is P. Each edge in C between two points p, q is realized as the line segment [pq], and is assigned a weight equal to the Euclidean distance |pq|. In this paper, we show how to construct in O(nlg{n}) time a plane spanner of C of maximum degree at most 4 and of stretch factor at most 20. This improves a long sequence of results on the construction of bounded degree plane spanners of C. Our result matches the smallest known upper bound of 4 by Bonichon et al. on the maximum degree while significantly improving their stretch factor upper bound from 156.82 to 20. The construction of our spanner is based on Delaunay triangulations defined with respect to the equilateral-triangle distance, and uses a different approach than that used by Bonichon et al. Our approach leads to a simple and intuitive construction of a well-structured spanner, and reveals useful structural properties of the Delaunay triangulations defined with respect to the equilateral-triangle distance

Hysteresis, Avalanches, and Noise: Numerical Methods

In studying the avalanches and noise in a model of hysteresis loops we have developed two relatively straightforward algorithms which have allowed us to study large systems efficiently. Our model is the random-field Ising model at zero temperature, with deterministic albeit random dynamics. The first algorithm, implemented using sorted lists, scales in computer time as O(N log N), and asymptotically uses N (sizeof(double)+ sizeof(int)) bits of memory. The second algorithm, which never generates the random fields, scales in time as O(N \log N) and asymptotically needs storage of only one bit per spin, about 96 times less memory than the first algorithm. We present results for system sizes of up to a billion spins, which can be run on a workstation with 128MB of RAM in a few hours. We also show that important physical questions were resolved only with the largest of these simulations

The Stretch Factor of L1L_1- and L∞L_\infty-Delaunay Triangulations

In this paper we determine the stretch factor of the $L_1$-Delaunay and $L_\infty$-Delaunay triangulations, and we show that this stretch is $\sqrt{4+2\sqrt{2}} \approx 2.61$. Between any two points $x,y$ of such triangulations, we construct a path whose length is no more than $\sqrt{4+2\sqrt{2}}$ times the Euclidean distance between $x$ and $y$, and this bound is best possible. This definitively improves the 25-year old bound of $\sqrt{10}$ by Chew (SoCG '86). To the best of our knowledge, this is the first time the stretch factor of the well-studied $L_p$-Delaunay triangulations, for any real $p\ge 1$, is determined exactly

Assessment of Influence of Traffic Intensity Increase on Collision Probability in the Gulf of Trieste

The paper presents results of researches aimed at assessing of influence of traffic intensity increase on collision probability in the Gulf of Trieste. Stochastic, simulation model working in fast time was used in the researches. Ships traffic was modeled on the basis of real data obtained from AISJRC.DG.G.4-Maritime affair

Relativistic Modification of Newtonian Gravity Law

We show how Newtonian gravity with effective (actually observed) masses, obeying the mass-energy relation of special relativity, can explain all observations used to test General relativity. Dynamics of a gravitationally coupled binary system is considered in detail and the effective masses of constituents are determined. Interpreting our results in terms of motion in a curved space-time background, we are led, using the Lagrangian formalism, to consider the exponential metric as a natural space-time metric of Newtonian gravity