The main aim of this paper is to forecast gold and silver daily returns with advanced regression analysis using various linear and non-linear models.
ARMA models are used as a linear benchmark for comparison purposes with established non-linear models such as Nearest Neighbours and MultiLayer Perceptron (MLP), and Higher Order Neural Networks (HONN) whose application to financial markets is quite new. All models are assessed using statistical criteria such as correct directional change as well as financial criteria such as risk adjusted return. The main aim is to find which of these models generate the best returns and if nonlinear models can be used for generating excess returns in the precious metals market. This is achieved by implementing a trading simulation where the forecast is translated into a trading signal. Profit statistics are calculated taking into account transaction costs.
It is concluded that, for the January 2000-May 2006 period under review, nonlinear models like MLPs and HONNs did outperform the linear ARMA models. In the end, the performance of both MLP and HONN models showed the presence of nonlinearities in the gold and silver prices as it was found that nonlinear models can be effectively used for generating excess returns in these markets.
Vermiculite (V) from Brazil with aqueous solutions AgNO3 and/or Cu(NO3)2 was used for preparation of nanocomposites V/Ag, V/Cu, V/AgCu and V/CuAg using two procedures and their effect on bacteria was compared. Structural changes were evaluated using X-ray diffraction (XRD) analysis, Infrared spectroscopy (IRS) and Scanning electron microscopy (SEM). Elemental chemical composition was determined using X-ray fluorescence (XRF) analysis and the solutions were analyzed by Atomic emission spectroscopy with inductively coupled plasma (AES-ICP). Antibacterial properties of Ag- and Cu-vermiculites and combined Ag/Cu-vermiculites were tested on two bacteria groups: (1) Gram-positive, G+, (Staphylococcus aureus and Enterococcus faecalis) and (2) Gram-negative, G-, (Pseudomonas aeruginosa and Klebsiella pneumoniae). The samples under antibacterial testing showed different effective times and minimum inhibitory concentration (MIC) values. The Gram-negative bacteria showed higher sensitivity to the prepared samples than Gram-positive bacteria. The combined Cu/Ag vermiculites stopped the bacterial growth at lower MIC value., Marianna Hundáková, Marta Valášková, Vladimír Tomášek, Erich Pazdziora and Kateřina Matějová., and Obsahuje bibliografii
V práci jsou prezentovány archeologické nálezy dokládající metalurgii neželezných kovů raně středověkého stáří získané při výzkumech na Malé Straně v Praze. Patří k nim zejména tavicí kelímky (tyglíky) a miskovité střepy běžné keramiky využité druhotně v metalurgii. Méně běžné jsou další druhy nálezů a situace svědčící o práci s neželeznými kovy (prubířské kameny, kadlub ad.). Část souboru byla podrobena EDS–SEM analýzám. Vyhodnocení jejich výsledků přispělo k poznání druhů získávaných a zpracovávaných neželezných kovů, resp. jejich slitin, i k částečnému objasnění postupů využívaných při jejich výrobě či testování kvality rudních surovin a hutnických meziproduktů. and The work presents archaeological finds documenting the metallurgy of non-ferrous metals of early medieval age acquired during excavations in Prague’s Lesser Quarter. These in particular include melting crucibles and bowl-shaped potsherds of common ceramics used secondarily in metallurgy. Other types of finds and situations documenting work with non-ferrous metals are less frequent (touchstones, a mould, etc.). Part of the assemblage was subjected to EDS–SEM analyses. An evaluation of their results contributed to an understanding of the types of non-ferrous metals (and their alloys) acquired and processed, to a partial clarification of the methods used in their production or the testing of the quality of their ores and their intermediate metallurgical products.