Modal Parameter Identification of Hagia Sophia Bell-Tower via Ambient Vibration Test

Many of historical structures have degenerated in time by environmental effects, earthquakes, and winds because of the inadequate preservation. The preservation of historical heritage is considered a fundamental issue in the cultural life of modern societies. The protective measures can be supplied if the actual behaviour of the structures is known. The paper presents the results of ambient vibration test and operational modal analysis carried out on the historical masonry bell-tower of the Hagia Sophia church in Trabzon, Turkey. The bell-tower is about 23 m high and dates back to the XIII century. The study includes also the initial analytical model of the tower constituted by the geometrical survey. The experimental measurements are performed using two measurement setups in different times. In the first setup twelve uniaxial accelerometers are used, while in the second setup four triaxial accelerometers with one uniaxial reference are used with the aim of determining the bending and torsional mode shapes as well as natural frequencies and modal damping ratios of the tower. The analytical model of the tower is developed by using solid brick elements, and a relatively large number of finite elements have been used in the model to obtain a regular distribution of mass. The first five natural frequencies and corresponding mode shapes are determined from both theoretical and experimental modal analyses and compared with each other. A good harmony is attained between mode shapes, but there are some differences between natural frequencies. The sources of the differences are introduced in terms of variations in the elasticity modulus of walls, cracks on upper walls, and boundary conditions on base level.     

A methodology for the performance evaluation of an experimental desiccant cooling system

An experimental investigation was conducted in an open cycle desiccant cooling system (DCS) operating on the ventilation mode in the laboratory site [M. Yıldırım, An experimental investigation on heat and mass transfer in a desiccant cooling system, PhD thesis, Gaziantep University, Turkey (2002). [1]]. Although the operation of DCS is presumably affected by the design of primary components of rotary regenerator (RR) and desiccant wheel (DW) the methodology used in the analysis of experimental data is presented in this paper to set a different approach for the performance evaluation of similar systems.

The rotational speeds of RR and DW (N_RR and N_DW), air mass flow rate (m_a) in process and regeneration lines, and the regeneration temperature (T_R) were defined as operation parameters. Meanwhile coefficient of performance (COP) and cooling capacity (CC) of the system were called as the performance parameters. The system operation with a variety of experimental conditions resulted in an extensive data set covering the ranges of N_RR, N_DW, m_a and T_R as 5 rpm ≤ N_RR ≤ 20 rpm, 0.1 rpm ≤ N_DW ≤ 0.4 rpm, 0.05 kg/s ≤ m_a ≤ 0.139 kg/s and 60 °C ≤ T_R ≤ 90 °C, respectively. The interactive influence of the operation parameters was determined through the realization of the psychrometric cycle in deviation from an ideal cycle. A dimensional analysis based on a trial and error procedure was followed to determine the functional relationship of COP and CC.

The proposed correlations between COP and CC and the introduced system performance parameter (PP) were determined to be a sole function of m_a independent of N_RR, N_DW and T_R in their covered ranges.     

Causality between energy consumption and GDP in the U.S.: evidence from wavelet analysis

This study investigates the dynamic causal relationship between energy consumption and economic growth in the U.S. at different time scales. The main novelty of the study is that this paper complements the existing studies on the nexus between energy consumption and economic growth by employing the wavelet transformation to obtain different time scales in order to investigate causality between energy consumption and economic growth. This method is first developed by Ramsey and Lampart. Their approach consists of first decomposing the series into time scales by wavelet filters and testing causality of each time scale with the pertinent time scale of the other series separately. The data span from 1973q1 to 2012q1 on a quarterly basis. The main empirical insight is that the causal relationship is stronger at finer time scales, whereas the relationship is less and less apparent at longer time horizons. The results indicate that energy consumption causes economic growth, while the reverse is not true at the original frequency of the data. At the very finest scale the same result arises. However, at coarser scales feedback is observed. In particular, at intermediate time scales the evidence indicates that energy consumption causes economic growth, while the reverse is also true. These empirical findings are expected to be of high importance in terms of the effective design and implementation of energy and environmental policies, especially when a number of countries in the pursuit of high economic growth targets do not pay any serious attention on environmental issues.     

Influence of UV stabilizers on the weathering of PETG and PCTT films

The influence of two UV photostabilizers on the photostability of Polyethylene-co-CHDM-terephthalate (PETG) and Polycyclohexylenedimethylene-Co-TMCD-terephthalate (PCTT) copolyester films was investigated. Untreated films and films containing stabilizer were irradiated. The resulting films were analyzed by attenuated total reflectance Fourier transform infrared (ATR FTIR) spectroscopy, gel permeation chromatography (GPC), and X-ray photoelectron spectroscopy (XPS). FTIR spectra of the irradiated films containing Cyasorb 1164 showed less change in intensity of the broad peak corresponding to OH groups, than the films containing Cyasorb 3638, indicating that Cyasorb 1164 is a better photostabilizer for these films. XPS results showed that the decrease in C/O ratio, due to photodegradation, was greater in films containing Cyasorb 3638 compared to those containing Cyasorb 1164. The formation of degradation products was evident from emission spectra arising from extracts of irradiated films based on PCTT +10% Cyasorb 3638, but no degradation products were apparent in extracts from irradiated PCTT +10% Cyasorb 1164. UV-absorption spectra of Cyasorb 1164 overlap more substantially with the absorption spectra of PETG and PCTT. The results from FTIR, XPS, and GPC analyses of the irradiated PETG and PCTT films demonstrated that Cyasorb 1164 was more effective than Cyasorb 3638 in enhancing resistance to UV-induced weathering. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019 , 136, 48198.     

Mode of action of lactococcin R produced by Lactococcus lactis R

We investigated the mode of action and factors affecting adsorption of lactoccocin R produced by Lactococcus lactis R. It was found that lactococcin R adsorbed to all Gram-positive but not to the Gram-negative bacteria tested and its adsorption was dependent on pH. It was observed that the binding of lactococcin R was prevented by anions of several salts (Cl-, PO4(-3)) and lipoteichoic acid. Pretreatments of sensitive cells and cell walls with detergents, organic solvents or enzymes did not reduce subsequent binding of lactococcin R. However, treatment of cell wall preparations with methanol:chloroform and hot 20% trichloroacetic acid (TCA) caused such walls to lose their ability to adsorb lactococcin R. Sensitive cells treated with lactococcin R lost high amounts of intracellular K+ ions, UV-absorbing materials and became more permeable to o-nitrophenol-beta-D-glactopyranoside (ONPG). In addition, different lactococcin R concentrations (0-2560 AU/mL) decreased the colony counts of Listeria monocytogenes by 99% and also a reduction in the absorbance values. These results show that the mode of action of lactococcin R is bactericidal rather than bacteriostatic.     

Effects of reactive diluents on mechanical and physical properties of a UV curable acrylated urethane prepolymer

In this study, the dependence of the mechanical properties of a UV curable acrylated urethane on reactive diluent types and their amounts was investigated. The acrylated urethane prepolymer was synthesized from isophorone diisocyanate (IPDI), an aliphatic diisocyanate, and polypropylene glycol monomethacrylate (PPGMMA) by stepwise addition reaction. UV sensitive mixtures containing N-vinylpyrrolidinone (NVP), thiodiethylene glycol diacrylate (TDGDA) and isobornyl acrylate (IBoA) as reactive diluents were irradiated by UV light. An increase in reactive diluent content, either TDGDA or IBoA, caused an increase in tensile strength and a decrease in elongation values. In contrast, above a certain concentration a decrease in tensil strength was observed when NVP was used as reactive diluent. The water absorption capacities of the UV curable acrylated urethane films were observed to depend on type and amount of reactive diluent that was used. Thermooxidative properties of the films were also improved by incorporation of reactive diluents into formulations.     

Bending and tensile properties of cotton/metal wire complex yarns produced for electromagnetic shielding and conductivity applications

Recently, there has been a growing interest in protective textiles that are produced in order to reduce detrimental effects that arise from electric and magnetic fields on biological organisms and particularly on human health. The main goal of this investigation is to develop conductive metal-based yarns with desirable properties. For the purpose of this study, by using copper and stainless steel wires and cotton yarns, core spinning technique was applied in order to manufacture hybrid yarns in modified ring spinning machine. Physical behaviour of complex yarns consisting of cotton yarn and metal wire was evaluated by investigating bending rigidity, tensile and hairiness properties of the samples.