Non-Parametric Regression Methods

The nature of the financial time series is complex, continuous interchange of stochastic and deterministic regimes. Therefore, it is difficult to forecast with parametric techniques. Instead of parametric models, we propose three techniques and compare with each other. Neural networks and support vector regression (SVR) are two universally approximators. They are data-driven non parametric models. ARCH/GARCH models are also investigated. Our assumption is that the future value of Istanbul Stock Exchange 100 index daily return depends on the financial indicators although there is no known parametric model to explain this relationship. This relationship comes from the technical analysis. Comparison shows that the multi layer perceptron networks overperform the SVR and time series model (GARCH).     

Body waves in fractured porous media saturated by two immiscible newtonian fluids

A study of body waves in fractured porous media saturated by two fluids is presented. We show the existence of four compressional and one rotational waves. The first and third compressional waves are analogous to the fast and slow compressional waves in Biot's theory. The second compressional wave arises because of fractures, whereas the fourth compressional wave is associated with the pressure difference between the fluid phases in the porous blocks. The effects of fractures on the phase velocity and attenuation coefficient of body waves are numerically investigated for a fractured sandstone saturated by air and water phases. All compressional waves except the first compressional wave are diffusive-type waves, i.e., highly attenuated and do not exist at low frequencies.Now at Izmir Institute of Technology, Faculty of Engineering, Gaziosmanpasa Bulvari, No.16, Cankaya, Izmir, Turkey.     

Classical density functional theory of orientational order at interfaces: application to water

A classical density functional formalism has been developed to predict the position-orientation number density of structured fluids. It is applied to the liquid-vapor interface of pure water, where it consists of a classical term, a gradient correction, and an anisotropic term that yields order through density gradients. The model is calibrated to predict that water molecules have their dipole moments almost parallel to a planar interface, while the molecular plane is parallel to it on the liquid side and perpendicular to it on the vapor side. For a planar interface, the surface tension obtained is twice its experimental value, while the surface potential is in qualitative agreement with that calculated by others. The model is also used to predict the orientation of water molecules near the surface of droplets, as well as the dependence of equilibrium vapor pressure around them on their size.     

A measure of dependence for stable distributions

A distance based measure of dependence is proposed for stable distributions that completely characterizes independence for a bivariate stable distribution. Properties of this measure are analyzed, and contrasted with the covariation and co-difference. A sample analog of the measure is defined and demonstrated on simulated and real data, including time series and distributions in the domain of attraction of a stable law.     

Distress among disaster-affected populations: delay in relief provision

Central to humanitarian logistics is the minimization of distress among impacted populations in the aftermath of a disaster. In this paper, we characterize two levels of distress, termed criticality and destitution, with respect to the delay provision of relief items. Delay in provision of a relief item will lead to destitution for a tolerable number of days, beyond which it will lead to criticality. We develop a mixed-integer goal program that quantifies these two metrics with respect to the number of days without provision of each of a set of relief items. The model determines the allocation of resources and the distribution of available relief items in a manner that minimizes criticality and destitution in affected population segments. The use of the model is demonstrated for the aftermath of a catastrophic earthquake in Istanbul, expected to occur by 2030.     

New fatty acid derivatives based on barbiturates and other cyclic β-dicarbonyl compounds and an acyl migration

The use of DCC, triethylamine and 4-dimethylaminopyridine in dichloromethane provides a general and standard one-pot procedure for the O-acylation of cyclic β-dicarbonyl compound derivatives (1) with palmitic and stearic acids which have long hydrocarbon tails, to synthesis of new type of fatty acid derivative in good to excellent yields. Structure elucidation was carried out by FT-IR, ¹H NMR and ¹³C NMR spectroscopy techniques. The acyl migration was also found in results and the corresponding structure was characterized by X-ray crystallography. A proposed mechanism was discussed for the formation of products.     

Peripherally and Axially Carboxylic Acid Substituted Subphthalocyanines for Dye‐Sensitized Solar Cells

A series of subphthalocyanines (SubPcs) bearing a carboxylic acid group either at the peripheral or axial position have been designed and synthesized to investigate the influence of the COOH group positions on the dye‐sensitized solar cell (DSSC) performance. The DSSC devices based on SubPcs with axially substituted carboxylic acid groups showed low photovoltaic performance, whereas peripherally substituted one exhibited higher power conversion efficiency owing to improved injection from LUMO of SubPcs to the TiO₂ conduction band.     

Excitation pulse deconvolution in luminescence lifetime analysis for oxygen measurements in vivo

Oxygen-dependent quenching of phosphorescence has been proven to be a valuable tool for the measurement of oxygen concentrations both in vitro and in vivo. For biological measurements the relatively long lifetimes of phosphorescence have promoted time-domain-based devices using xenon arc flashlamps as the most common excitation light source. The resulting complex form of the excitation pulse leads to complications in the analysis of phosphorescence lifetimes and ultimately to errors in the recovered pO2 values. Although the problem has been recognized, the consequences on in vivo phosphorescence lifetime measurements have been neglected so far. In this study, the consequences of finite excitation flash duration are analyzed using computer simulations, and a method for the recovery of phosphorescence decay times from complex photometric signals is presented. The analysis provides an explanation as to why different calibration constants are reported in the literature and presents a unified explanation whereby calibration constants are not solely a property of the dye but also of the measuring device. It is concluded that complex excitation pulse patterns without appropriate analysis methods lead to device-specific calibration constants and nonlinearity and can be a potent source of errors when applied in vivo. The method of analysis presented in this article allows reliable phosphorescence lifetime measurements to be made for oxygen pressure measurements and can easily be applied to existing phosphorimeters.     

Impacts of pH and molecular structure on ultrasonic degradation of azo dyes

Sonochemical bleaching of monoazo dyes was investigated by irradiating 30 microM solutions of two "aryl-azo-naphthol" type model dyes in acidic, neutral and basic conditions using a 300 kHz emitter. It was found that the rate of bleaching in all cases was first order with respect to the maximum absorption of the dye in the visible band, and accelerated with increased acidity. The inhibition observed at alkaline conditions was attributed to the formation of anionic dye structures and their competition with the dye and its intermediate oxidation products for hydroxyl radicals, which are the major precursors of azo dye oxidation in sonicated water. Decolorization of the dyes was also related to the size of the molecule and the type or position of substituents about azo bonds. Comparison of color decay rates at similar conditions showed that the dye with a simple structure, low molecular mass and one ortho-substituent (hydroxyl) about the azo bond bleached considerably faster than the one having a more complicated structure (higher mass) and an additional o-substituent to the azo bond other than the OH group.