Editorial v. 8, n. 2, jul./dez., 2019

Vol. 8, No. 2 , 2019

v 1 2 8 N ov 1 99 8 Spacetime Exterior to a Star

In many circumstances the perfect fluid conservation equations can be directly integrated to give a Geometric-Thermodynamic equation: typically that the lapse N is the reciprocal of the enthalphy h, (N = 1/h). This result is aesthetically appealing as it depends only on the fluid conservation equations and does not depend on specific field equations such as Einstein’s. Here the form of the Geom...

Editorial, Volume 8, Issue 1

A new vocabulary item has been added to English dictionaries: Covid-19. For linguists, the addition of a meaningful linguistic element to any language should change the whole language as, for T. S. Eliot, a new poem changes the whole literature of a nation. But let us see how seriously the addition of the vocabulary item Covid-19 might change the English language. According to Cambridge online ...

$n$-cocoherent rings‎, ‎$n$-cosemihereditary rings and $n$-V-rings

 Let $R$ be a ring‎, ‎and let $n‎, ‎d$ be non-negative integers‎. ‎A right $R$-module $M$ is called $(n‎, ‎d)$-projective if $Ext^{d+1}_R(M‎, ‎A)=0$ for every $n$-copresented right $R$-module $A$‎. ‎$R$ is called right $n$-cocoherent if every $n$-copresented right $R$-module is $(n+1)$-coprese-nted‎, ‎it is called a right co-$(n,d)$-ring if every right $R$-module is $(n‎, ‎d)$-projective‎. ‎$R$...

v 2 2 8 Ja n 20 02 Multifractal nature of stock exchange prices

The multifractal structure of the temporal dependence of the Deutsche Aktienindex (DAX) is analyzed. The q-th order moments of the structure functions and the singular measures are calculated. The generalized Hurst exponent H(q) and the h(γ(q)) curve indicate a hierarchy of power law exponents. This approach leads to characterizing the nonstationarity and intermittency pertinent to such financi...