Mechanical and chemical behavior of spruce wood modified by heat

In this study the effects of heat treatment on compression strength (CS) of spruce wood (Picea orientalis) were examined and changes in the chemical structure of the treated wood were determined by analyzing contents of cellulose, hemicellulose and lignin.

Heat treatment was applied on the test samples in an oven at four different temperatures (130, 150, 180 and 200 °C) and three different durations (2, 6 and 10 h) under atmospheric pressure.

The results indicate that the effects of heat treatment on CS values generally exhibited a decrease with increased duration and temperature. It was seen that hemicelluloses were the wood-cell components most degraded by the heat treatment.     

Removal copper,chromium and arsenic from CCA-treated yellow pine by oleic acid

Removal of Cu, Cr and As metals from chromated copper arsenate (CCA) treated yellow pine wood samples with three different dimensions were investigated by extraction with oleic acid at four different pH levels. The concentrations of Cu, Cr and As were determined by XRF. The effects of pH, dimension and duration on remediation of CCA-treated wood samples were determined. Oleic acid was found to be very effective to remove copper, chromium and arsenic from CCA-treated wood samples especially at lower pH levels (pH=2.00 and 2.50). In addition, the best models estimate copper, chromium and arsenic leaching from CCA-treated wood samples by oleic acid remediation were determined by step-wise regression analysis.     

Climatic effect in the formation of vernacular houses in the Eastern Black Sea region

Climate is one of the many factors such as socio-cultural structure, economy, materials, and technology that influence architectural forms. The resolutions that exist as a result of the effect of climate on architecture differ according to regions, cultures, time and technology. The climate in the Eastern Black Sea region, which lies in the north of Turkey, plays an active role in the formation and diversity of the vernacular houses in the region. Climatic factors such as rain, wind, humidity and sunlight in the region, which has a warm-humid climate and which gets excessive rain, have different effects on the spaces, elements and annexes of the vernacular houses. This study explains climatic approaches that are evident in the architecture of the vernacular houses in the Eastern Black Sea region. The aim of this study is to give information about the vernacular architecture in the Eastern Black Sea region and to investigate the relationship between the architectural products and the climate that plays a very important role in the formation of this architecture. Thus, the effects of climatic factors, such as rain, wind, humidity and sunlight, on vernacular houses are explained in the topics as plan, external walls, roof and exterior of buildings.     

Experimental and Numerical Modal Characterization for Additively Manufactured Triply Periodic Minimal Surface Lattice Structures: Comparison between Free-Size and Homogenization-Based Optimization Methods

Homogenization-based topology optimization (HMTO) is one of the most extensively used grading methods to generate functionally graded lattice structures (FGLs). However, it requires a precharacterization of the lattices, which is time-consuming. As a remedy, free-size optimization-based graded lattice generation (FOGLG) is explored as an alternative method to generate the FGLs. This article builds on the authors’ previous work in which the HMTO and FOGLG approaches are studied to improve the dynamic characteristic of a design by using a single lattice type, namely, double gyroid (DG) structure. To show applicability of the proposed methods, different lattice types including diamond (D), gyroid (G), and I-WP are employed to create FGLs herein. The frequency response analysis is performed, and the results from HMTO and FOGLG are compared in terms of their accuracy and efficiency. The optimized designs are then reconstructed by relative density mapping (RDM) and enhanced relative density mapping (ERDM) methods. The fabricated test samples made of cobalt–chromium using the direct metal laser melting (DMLM) technique are then experimentally validated using a laser vibrometer. The results reveal that HMTO and FOGLG can be used on the lattice types with a variety of configurations and relative densities.     

Performance Comparison of 2.4 and 5 GHz WiFi Signals and Proposing a New Method for Mobile Indoor Positioning

Wireless Personal Communications - Nowadays, the location information of people and objects is a necessity for indoor environments. Therefore, many technologies, methods, and algorithms have been...     

Simulation of an efficient silicon heterostructure solar cell concept featuring molybdenum oxide carrier‐selective contact

Transition metal oxides/silicon heterocontact solar cells are the subject of intense research efforts owing to their simpler processing steps and reduced parasitic absorption as compared with the traditional silicon heterostructure counterparts. Recently, molybdenum oxide (MoO_x, x < 3) has emerged as an integral transition metal oxide for crystalline silicon (cSi)‐based solar cell based on carrier‐selective contacts (CSCs). In this paper, we physically modelled the CSC‐based cSi solar cell featuring MoO_x/intrinsic a‐Si:H/n‐type cSi/intrinsic a‐Si:H/n⁺‐type a‐Si:H for the first time using Silvaco technology computer‐aided design simulator. To analyse the optical and electrical properties of the proposed solar cell, several technological parameters such as work function and thickness of MoO_x contact layer, intrinsic a‐Si:H band gap, interface recombination, series resistance, and temperature coefficient have been evaluated. It has been shown that higher work function of MoO _x induces the formation of a favourable Schottky barrier height as well as an inversion at the front interface, stimulating least resistive path for holes. Utilising thinner MoO_x layer implies reduced tunnelling of minority charge carriers, thus enabling the device to numerically attain 25.33% efficiency. With an optimised interface recombination velocity and reduced parasitic absorption, the proposed device exhibited higher V_oc of 752 mV, J_sc of 38.8 mA/cm², fill‐factor of 79.0%, and an efficiency of 25.6%, which can be termed as the harbinger for industrial production of next‐generation efficient solar cell technology.     

Electrical analysis of a hybrid photovoltaic-hydrogen/fuel cell energy system in Denizli, Turkey

In recent years, hybrid photovoltaic-hydrogen/fuel cell energy systems have been popular as energy production systems that are clean, environmental-friendly, modular, and independent from fossil fuels. In February 2007, a clean energy research facility consisting of a 5 kWp photovoltaic system and a 2.4 kWp hydrogen-fuel cell system was built to investigate these energy production technologies at Pamukkale University in Denizli, Turkey. In this hybrid energy system, electricity is generated by photovoltaic panels. Generated electrical energy is stored chemically in batteries and metal hydride hydrogen canisters. Hydrogen electrolyzed from water is transformed to DC electrical energy by two fuel cells in the case of its necessity. DC electricity produced by photovoltaic panels and fuel cells is converted to AC by two inverters for the requirements of the building. In this study, an electrical energy analysis of the building, in terms of energy efficiency, harmonics, voltage changes, voltage and current sags, voltage and current swells, transients, power outage, frequency changes etc., is performed to evaluate the power quality of the hybrid energy system. In addition, some measurements such as insulation resistance, loop impedance, line impedance, grounding resistance, and specific resistance of the ground are measured to obtain the electrical characteristics of the system.     

桥梁结构状态参数监测技术研究现状

桥梁的自然老化、劣化将会影响其安全与正常使用,甚至造成重大的人员伤亡和财产损失,已成为交通运输部门关注的问题。为了有效维护桥梁和确保其安全运行,监测桥梁结构的关键状态参数对于全面及时反映桥梁工作状态和进一步开展安全性评估极为重要。综述了桥梁结构的应变、挠度、振动等关键状态参数监测技术的研究进展,并分析了这些监测技术的基本原理、性能、应用范围,同时,对未来桥梁结构状态参数监测的发展提出了建议。     

Attention based hybrid parametric and neural network models for non-stationary time series prediction

This paper investigates non-stationary time series analysis and forecasting techniques for financial datasets. We focus on the use of a popular non-stationary parametric model namely GARCH and neural network model LSTM, with an attention mechanism to capture the complex temporal dynamics and dependencies in the data. We propose a hybrid GARCH-ATT-LSTM model where the GARCH model is employed for volatility forecasting, attention mechanism is applied to capture the more important parts of the data sequence and enhance the interpretability of the model, and the LSTM model is used for price forecasting. Our experiments are conducted on real-world financial datasets, that is, Apple stock price, Dow Jones index, and gold futures price. We compare the performance of GARCH-ATT-LSTM against the sole LSTM model, ATT-LSTM model, and LSTM-GARCH model. Our results show that GARCH-ATT-LSTM outperforms the baseline methods and achieves high accuracy in price forecasting. It implies the effectiveness of the attention mechanism in improving the interpretability and stability of the model and the success of combining parametric models with neural network models. The findings suggest that GARCH-ATT-LSTM can be a valuable tool for non-stationary time series analysis and forecasting in financial applications.