Random Walk Theory and Exchange Rate Dynamics in Transition Economies

This paper investigates the validity of the random walk theory in the Euro-Serbian dinar exchange rate market. We apply Andrew Lo and Archie MacKinlay’s (1988) conventional variance ratio test and Jonathan Wright’s (2000) non-parametric ranks and signs based variance ratio tests to the daily Euro/Serbian dinar exchange rate returns using the data from January 2005 - December 2008. Both types of variance ratio tests overwhelmingly reject the random walk hypothesis over the data span. To assess the robustness of our findings, we examine the forecasting performance of a non-linear, nonparametric model in the spirit of Francis Diebold and James Nason (1990) and find that it is able to significantly improve upon the random walk model, thus confirming the existence of foreign exchange market imperfections in a small transition economy such as Serbia. In the last part of the paper, we conduct a comparative study on how our results relate to those of other transition economies in the region.Random walk, Forecasting, Exchange rates, Transition economies, Market efficiency, Artificial neural networks

The combinatorial code and the graph rules of Dale networks

We describe the combinatorics of equilibria and steady states of neurons in threshold-linear networks that satisfy the Dale's law. The combinatorial code of a Dale network is characterized in terms of two conditions: (i) a condition on the network connectivity graph, and (ii) a spectral condition on the synaptic matrix. We find that in the weak coupling regime the combinatorial code depends only on the connectivity graph, and not on the particulars of the synaptic strengths. Moreover, we prove that the combinatorial code of a weakly coupled network is a sublattice, and we provide a learning rule for encoding a sublattice in a weakly coupled excitatory network. In the strong coupling regime we prove that the combinatorial code of a generic Dale network is intersection-complete and is therefore a convex code, as is common in some sensory systems in the brain.Comment: 22 pages, 4 figures, added discussion section, corrected typos, expanded the background on convex code

Numerical Determination of Volumetric Effi ciency of High-Pressure Reciprocating Pumps

Results of experimental determination of variable-discharge high-pressure reciprocating pump performances [3, 4] show that by increasing the pressure on the pressure side of a reciprocating pump, at a constant stroke length, the discharge and volumetric effi ciency of the pump decrease. Mathematical expressions defi ning the theoretical and the actual pump discharge have been derived on the basis of the analysis of kinematic and hydrodynamic performances of a high-pressure, single-piston single-acting pump. The applied measuring system is described and examples of analysed measurement results are given. The Fourier approximation method is used to describe mathematically the experimental diagram of operating pressure p1=f(t). Assuming that physical properties of the fl uid are constant, and that geometric and kinematic characteristics of a pump have not changed, the value of volumetric effi ciency is defi ned as a function of pressure. Results of volumetric effi ciency calculation are given for a series of individually performed measurements in the range from H4T25 to H4T250. Results of the numerical determination of volumetric effi ciency confi rm that the chosen method is acceptable since calculation results differ from experimentally determined values by less than 1%

Analiza čvrstoće velikih kontejnerskih brodova grednim modelom prema klasifikacijskim pravilima

Osnivanje konstrukcije velikih kontejnerskih brodova, zbog njihove male krutosti na uvijanje, trebalo bi se temeljiti na hidroelastičnoj analizi. Budući da spomenuti problem nije dovoljno istražen još uvijek se koriste tzv. kvazi-statički proračuni čvrstoće. Za tu svrhu, može se koristiti gredni strukturni model ili 3D FEM model uz relativno jednostavne formule za određivanje presječnih sila prema Pravilima. U članku je opisan standardni postupak za osnivanje konstrukcije velikih kontejnerskih brodova koji se koristi danas. Zatim je primjena grednog modela, razvijenog za hidroelastičnu analizu, ilustrirana za analizu čvrstoće, kao glavnog dijela projektnog postupka. Presječne sile, odreñene prema Pravilima su korištene za određivanje valnog opterećenja po duljini grednog modela. Rezultati dobiveni programom DYANA za statičku analizu su kut uvijanja i njegov prirast, pomoću kojih se dalje mogu odrediti distribucije naprezanja i deformacije grotala važne za sigurnost kontejnera

EEDI kao mjera energetske učinkovitosti broda

U cilju poticanja razvoja suvremenih tehnoloških rješenja koja doprinose poboljšavanju energetske učinkovitosti i unapređenju zaštite okoliša IMO Rezolucijom MEPC.203(62) donosi izmjene MARPOL-a, Prilog VI. Izmjene se odnose na obavezu uključivanja pravila za utvrđivanje i kontrolu energetske učinkovitosti u nacionalna pravila registara, kojima se propisuje obavezna primjena projektnog indeksa energetske učinkovitosti (EEDI) i brodskog plana upravljanja energetskom učinkovitosti (SEEMP). Dosadašnje iskustvo u primjeni formule za odreñivanje EEDI-a pokazuje da je potrebno prilagođavati vrijednosti i dopunjavati broj utjecajnih faktora ovisno o tipovima brodova i o njihovim specifičnim projektnim i eksploatacijskim značajkama. U radu su analizirani nedostaci primjene trenutno važeće (strukture) formule za odreñivanje EEDI-a. Za ro-pax brodove su posebno analizirani parametri za koje se smatra da značajnije utječu na vrijednost EEDI-a, a proizlaze iz različitih specifičnih projektnih i eksploatacijskih značajki tih brodova

O propulziji motornoga čamca MAESTRAL 700

Tipična korčulanska pasara zadržala je svoju podvodnu formu i u izvedbi pojačanim poliesterom. U današnjim uvjetima nastoji joj se povećati brzina ugradnjom snažnijeg motora i intuitivnom modifi kacijom krme. Na primjeru MAESTRALA 700 ilustrirano je stručno utemeljeno rješenje na osnovi povezanosti snage motora, plošnoga spojlera i primjerenog vijka