Forecasting Home Sales in the Four Census Regions and the Aggregate US Economy Using Singular Spectrum Analysis

Accurate forecasts of home sales can provide valuable information for not only, policy makers, but also financial institutions and real estate professionals. Given this, our analysis compares the ability of two different versions of singular spectrum analysis (SSA) methods, namely recurrent SSA (RSSA) and vector SSA (VSSA), in univariate (UV) and multivariate (MV) frameworks, in forecasting seasonally unadjusted home sales for the aggregate US economy and its four census regions (Northeast, Midwest, South and West). We compare the performance of the SSA-based models with classical and Bayesian variants of the autoregressive (AR) and vector AR models. Using an out-of-sample period of 1979:8–2014:6, given an in-sample period of 1973:1–1979:7, we find that the UVVSSA is the best performing model for the aggregate US home sales, while the MV versions of the RSSA is the outright favorite in forecasting home sales for all the four census regions. Our results highlight the superiority of the nonparametric approach of the SSA, which in turn, allows us to handle any statistical process: linear or nonlinear, stationary or non-stationary, Gaussian or non-Gaussian.     

Effects of bed-load movement on flow resistance over bed forms

The effect of bed-load transport on flow resistance of alluvial channels with undulated bed was experimentally investigated. The experiments were carried out in a tilting flume 250mm wide and 12.5m long with glass-sides of rectangular cross-section and artificial dune shaped floor that was made from Plexi-glass. Steady flow of clear as against sediment-laden water with different flow depths and velocities were studied in the experiments with a fine sand (d ₅₀ = 0.5mm). The results indicate that the transport of fine particles (d ₅₀ = 0.5mm) can decrease the friction factor by 22% and 24% respectively for smooth and rough beds. Increasing the bed-load size (d ₅₀ = 2.84 mm) can decrease the friction factor by 32% and 39% respectively for smooth and rough beds. The decrease in flow resistance is due to filling up of the troughs of dunes. This separation zone is responsible for increasing the flow resistance. On the upstream side of dunes condition is similar to plane bed. Presence of bed-load causes to increase the shear velocity and hence increasing flow resistance. But decreasing in flow resistance is more and it causes to decrease the total flow resistance. Grains saturated the troughs in the bed topography, effectively helping in smoothening of bed irregularities.     

A modification on ECAP process by incorporating torsional deformation

In the present study, integration of equal channel angular pressing (ECAP), as a well known severe plastic deformation (SPD) technique, and torsion deformation, is studied by using three dimensional finite element analysis. This process is to be named as torsional-equal channel angular pressing (T-ECAP). In this modification a part of the exit channel in the ECAP die is rotating around its axis, to impose extra shear strains to the samples. To study deformation behavior in the T-ECAP process, three-dimensional finite element analysis (FEA) was carried out by using the elasto-plastic finite element analysis ABAQUS/Explicit Simulation. To investigate the validity of the simulation results, experimental studies were furthermore performed on commercially pure aluminum (AA 1050). Vickers hardness test was used to determine the distribution of hardness on both normal and longitudinal sections of the deformed samples with respect to the exit channel of the die. The hardness test results showed more uniform distribution of hardness in both sections of the T-ECAP processed samples regarding the ones produced by ECAP process. The load requirement comparison for performing both processes showed lower value for the T-ECAP with respect to the ECAP process. The simulation results for the strain values showed higher magnitude and more uniform distribution for the T-ECAP with respect to the ECAP process.     

Steam gasification of bitumen oil in presence of Ni/dolomite catalysts

An important step in developing clean energy and reducing greenhouse gas emissions is the use of clean technologies such as gasification. In this work, we were used a bubbling fluidized bed (BFB) to convert the bitumen oil into a clean syngas in presence of three kinds of Ni/dolomite catalysts. While all three catalysts were acceptable in the process of tar elimination, but DN-22 was more successful in eliminating tar than the other two samples, which might be due to the higher amount of CaO in the composition DN-22. With increase in Ni, the amount of eliminated tars in the tar cracking process was also increased due to the delay in the deactivation of the dolomite catalyst.     

Schauder fixed point theorem based existence of periodic solution for the response of Duffing’s oscillator

An initial-boundary value problem that is Duffing’s oscillator with time varying coefficients will be studied. Using Banach’s fixed-point theorem, the existence of periodic solution of the equation will be predicted. The method applied in this paper is the Schauder second fixed point theorem, which includes the response of structures under vibratory force systems. As an example, the dynamics of nonlinear simply supported rectangular thin plate under influence of a relatively moving mass is studied. By expansion of the solution as a series of mode functions, the governing equations of motion are reduced to an ordinary differential equation for time development vibration amplitude, which is Duffing’s oscillator. Finally, a parametric study is developed, after that some numerical examples are solved, and the validity of the present analysis is clearly shown. This paper was recommended for publication in revised form by Associate Editor Maenghyo Cho Hossein Ali Sepiani received his B.S. degree in Mechanical Engineering from University of Kashan, Iran, in 2003. He then received his M.S. degree from University of Tehran, in 2006. Currently, Hossein is continuing his research at University of Tehran. His research interests include new materials (FGMs, Nano-materials, SMAs, SMPs, etc), Composites (Woven Fabrics and Fiber Metal Laminates), Smart Materials (Shape Memory Alloy, Magnet/Electro-rheological and Piezoelectric Sensors and Actuators), Intelligent structures (Structures integrated with smart materials), Vibration and control of Intelligent Structures and their application. Ahmad Feyz Dizaji got his B.S. degree from University of Tehran, Iran, in 1970. Then he continued his study in U.S. and received his PhD. degree from Michigan State University in 1983, in Applied Mathematics under the supervision of Professor Shui-ni Chow and Professor J. Mallet-Paret. Since then he has been a member of the Faculty of Engineering in University of Tehran, teaching mathematics in both undergraduate and graduate levels.     

A solidification model for prediction of castability in the precipitation-strengthened nickel-based superalloys

The Scheil equation was used to model the solidification path, microsegregation of alloying elements in the interdendritic regions, solidification temperature ranges, and to predict the formation of secondary structures and the castability behavior of as-cast superalloys. 4 experimental alloys with pre-specified γ-Ti,Nb,Al,Mo composition containing different Nb, Ti and Al contents were designed using vacuum induction melting furnace. The produced as-cast superalloys were characterized using optical and scanning electron microscopy equipped with energy dispersive X-ray spectrometer and TG–DSC analysis. The experiments showed logic conformity to the modeling results. The model and experiment confirmed the highest segregation behavior for Ti and Nb. All the experimental superalloys indicated the remarkable tendency to form secondary eutectic structures at the last stages of solidification. Superalloy with chemical composition of γ-3.5%Mo,1.8%Al,4%Ti,2.9%Nb showed the shorter solidification temperature range and the best castability.     

On the use of multi-path inductorless TIAs for larger transimpedance limit

This paper discusses the use of mutli-path inductorless transimpedance amplifiers (TIAs), consisting of several different second-order shunt-feedback sub-TIAs (SF-sTIAs) driven by the photodiode, to break the single-stage technology-dependent transimpedance limit. The advantage of the MP-TIA that is explored in this work is in its third-order transfer function, which provides additional degrees of freedom in tailoring the performance. Pole and zero locations of the MP-TIA transfer function are examined and verified with behavioural simulations. The theoretical transimpedance limit for MP-TIAs based on two SF-sTIAs is derived. The possibility of further increasing the transimpedance limit vs bandwidth trade-off by combining three and four sub-TIAs is investigated with simulations. A transistor-level design example of an MP-TIA is presented. The 0.13-μm CMOS MP-TIA achieves the largest figure-of-merit among published TIAs.     

A genetic programming model for bankruptcy prediction: Empirical evidence from Iran

Prediction of corporate bankruptcy is a phenomenon of increasing interest to investors/creditors, borrowing firms, and governments alike. Timely identification of firms’ impending failure is indeed desirable. By this time, several methods have been used for predicting bankruptcy but some of them suffer from underlying shortcomings. In recent years, Genetic Programming (GP) has reached great attention in academic and empirical fields for efficient solving high complex problems. GP is a technique for programming computers by means of natural selection. It is a variant of the genetic algorithm, which is based on the concept of adaptive survival in natural organisms. In this study, we investigated application of GP for bankruptcy prediction modeling. GP was applied to classify 144 bankrupt and non-bankrupt Iranian firms listed in Tehran stock exchange (TSE). Then a multiple discriminant analysis (MDA) was used to benchmarking GP model. Genetic model achieved 94% and 90% accuracy rates in training and holdout samples, respectively; while MDA model achieved only 77% and 73% accuracy rates in training and holdout samples, respectively. McNemar test showed that GP approach outperforms MDA to the problem of corporate bankruptcy prediction.     

An innovative method of die design and evaluation of flow balance for thermoplastics extrusion profiles

In this article, a computational and experimental method for flow balancing of a U‐shaped die profile with nonuniform thicknesses is presented. The approach was to implement a flow restricting mechanism along the melt flow path. A parametric study based on the restrictor dimensions was carried out to attain a preliminary optimal design. Simulations were performed using Fluent software to analyze the flow velocity at the die exit. Experimental study was then carried out at various restrictor positions for the purpose of attaining a desirable flow balance. The velocity at various segments of the die exit was measured utilizing an innovative procedure by implementing the “separating blades.” Experimental findings were compared with those of simulations which showed an acceptable agreement. The results suggest that a flexible die can be designed to achieve a flow balance under various processing conditions. POLYM. ENG. SCI., 2009. © 2009 Society of Plastics Engineers