3,705 research outputs found
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 MacKinlayās (1988) conventional variance ratio test and Jonathan Wrightās (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 ÄvrstoÄe velikih kontejnerskih brodova grednim modelom prema klasifikacijskim pravilima
Osnivanje konstrukcije velikih kontejnerskih brodova, zbog njihove male krutosti na uvijanje, trebalo bi se temeljiti na hidroelastiÄnoj analizi. BuduÄi da spomenuti problem nije dovoljno istražen joÅ” uvijek se koriste tzv. kvazi-statiÄki proraÄuni ÄvrstoÄe. Za tu svrhu, može se koristiti gredni strukturni model ili 3D FEM model uz relativno jednostavne formule za odreÄivanje presjeÄnih sila prema Pravilima. U Älanku je opisan standardni postupak za osnivanje konstrukcije velikih kontejnerskih brodova koji se koristi danas. Zatim je primjena grednog modela, razvijenog za hidroelastiÄnu analizu, ilustrirana za analizu ÄvrstoÄe, kao glavnog dijela projektnog postupka. PresjeÄne sile, odreƱene prema Pravilima su koriÅ”tene za odreÄivanje valnog optereÄenja po duljini grednog modela. Rezultati dobiveni programom DYANA za statiÄku analizu su kut uvijanja i njegov prirast, pomoÄu kojih se dalje mogu odrediti distribucije naprezanja i deformacije grotala važne za sigurnost kontejnera
EEDI kao mjera energetske uÄinkovitosti broda
U cilju poticanja razvoja suvremenih tehnoloÅ”kih rjeÅ”enja koja doprinose poboljÅ”avanju energetske uÄinkovitosti i unapreÄenju zaÅ”tite okoliÅ”a IMO Rezolucijom MEPC.203(62) donosi izmjene MARPOL-a, Prilog VI. Izmjene se odnose na obavezu ukljuÄivanja pravila za utvrÄivanje i kontrolu energetske uÄinkovitosti u nacionalna pravila registara, kojima se propisuje obavezna primjena projektnog indeksa energetske uÄinkovitosti (EEDI) i brodskog plana upravljanja energetskom uÄinkovitosti (SEEMP). DosadaÅ”nje iskustvo u primjeni formule za odreƱivanje EEDI-a pokazuje da je potrebno prilagoÄavati vrijednosti i dopunjavati broj utjecajnih faktora ovisno o tipovima brodova i o njihovim specifiÄnim projektnim i eksploatacijskim znaÄajkama. U radu su analizirani nedostaci primjene trenutno važeÄe (strukture) formule za odreƱivanje EEDI-a. Za ro-pax brodove su posebno analizirani parametri za koje se smatra da znaÄajnije utjeÄu na vrijednost EEDI-a, a proizlaze iz razliÄitih specifiÄnih projektnih i eksploatacijskih znaÄajki tih brodova
O propulziji motornoga Äamca MAESTRAL 700
TipiÄna korÄulanska pasara zadržala je svoju podvodnu formu i u izvedbi pojaÄanim poliesterom. U danaÅ”njim uvjetima nastoji joj se poveÄati brzina ugradnjom snažnijeg motora i intuitivnom modifi kacijom krme. Na primjeru MAESTRALA 700 ilustrirano je struÄno utemeljeno rjeÅ”enje na osnovi povezanosti snage motora, ploÅ”noga spojlera i primjerenog vijka
- ā¦