The effects of modified atmosphere gas composition on microbiological criteria, color and oxidation values of minced beef meat

This paper reports the effects of modified atmosphere gas compositions with different concentrations of CO(2)/O(2)/N(2) on color properties (L*, a* and b* values), oxidation stability (TBARS value) and microbiological properties of minced beef meat stored at +4 °C. Sampling was carried out on the 1st, 3rd, 5th, 7th, 9th, 11th and 14th day of storage. The gas mixtures used were as follows: (i) %30O(2) + %70CO(2) (MAP1), (ii) %50O(2) + %50CO(2) (MAP2), (iii) %70O(2) + %30CO(2) (MAP3), (iv) %50O(2) + %30CO(2) + %20N(2) (MAP4), and (v) %30O(2) + %30CO(2) + %40N(2) (MAP5). Control samples (AP) were packaged under atmospheric air. Pseudomonas, lactic acid bacteria, Brochothrix thermosphacta, and Enterobacteriaceae members were monitored. Among these five modified atmosphere gas compositions, the best preservation for minced beef meat was in MAP4 gas combination maintaining acceptable color together with oxidation stability and acceptable microbial loads until the end of storage period of fourteen days.     

Separability and hidden symmetries of Kerr-Taub-NUT spacetime in Kaluza-Klein theory

The Kerr-Taub-NUT spacetime in the Kaluza-Klein theory represents a localized stationary and axisymmetric object in four dimensions from the Kaluza-Klein viewpoint. That is, it harbors companion electromagnetic and dilaton fields, thereby showing up the signature of the extra fifth dimension. We explore the separability structure of this spacetime and show that the Hamilton-Jacobi equation for geodesics admits complete separation of variables only for massless geodesics. This implies the existence of hidden symmetries in the spacetime, which are generated by a conformal Killing tensor. Using a simple trick built up on a conformally related metric (an “effective” metric) with the Killing tensor, we construct an explicit expression for the conformal Killing tensor.     

Acetaldehyde migration from polyethylene terephthalate bottles into carbonated beverages in Türkiye

Polyethylene terephthalate (PET) is one of the packaging materials that is widely used for packaging of soft drinks. PET may contain acetaldehyde which is a thermal degradation product, and hence acetaldehyde may migrate into the product in the package. In this study, the migration of acetaldehyde from PET bottles into soft drinks containing carbonic acid was determined by gas chromatography without headspace instrument. Carbonated beverage samples obtained from four different firms following the filling process were stored at 5, 20 and 40 °C for 6 months and analysed periodically at 0 day, 2, 4 and 6 months. As a result, it was seen that the acetaldehyde concentrations of all samples were quite different from each other and also related to the storage temperature, and an increase in storage time raised acetaldehyde concentrations in beverages. Especially, storages at 40 °C had very serious effect on acetaldehyde concentrations in the beverages.     

Investigation of temperature,thermodynamic parameters and dielectrical properties of poly(vinylimidazole)–Na–bentonite nanocomposite

The adsorption of poly(vinylimidazole) (PVI) onto Na–Bentonite from aqueous solutions has been investigated as a function of temperature. According to the experimental results, the adsorption of PVI decreases with temperature from 25 to 55°C. The study of temperature effect has been quantified by calculating various thermodynamic parameters such as Gibbs free energy, enthalpy and entropy changes. The electrical and dielectrical properties of PVI–Na–Bentonite composite have been investigated. The current‐voltage studies show that conductivity was increased at T = 25°C. The dc conductivity was calculated at T = 25°C. The samples show typical dielectric behavior from capacitive measurements. Depending on maximum interactions at 25°C, ac conductivity and loss factors are also in high values. Especially, at frequencies over 1.5 kHz, it was seen completely clay behavior. Variation of tangent loss factor‐frequency shows decreasing of polarization density in structure in high frequency. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2011     

Effects of solution mixing temperature on dielectric properties of PMMA/Pristine bentonite nanocomposites

We examined the effects of mixing temperature on the dielectric properties of polymethylmethacrylate (PMMA)‐pristine bentonite nanocomposites by using X‐ray diffraction, FT‐IR and dielectric spectroscopies. The samples were prepared during 8 hours at temperatures 265 K, 273 K, 281 K, 289 K and 298 K without any intercalative agent and the PMMA to pristine bentonite weight ratio was chosen as 1 : 10. It was observed that with decreasing the mixing temperatures, the permittivity decreases and the dielectric relaxation displaces towards the lower frequencies with the decrease of mixing temperatures. © 2013 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 39907.     

Structural and Dielectric Properties of Two Different BaTiO3/Polyaniline Nanocomposites

Barium titanium oxide/polyaniline (BaTiO₃/PANI) nano-composites were obtained in two different processes by the use of PANI and BaTiO₃ nano-particles synthesized by the sol–gel technique. FT-IR, XRD, SEM and TGA measurements were taken for structural properties of all samples. The molecular interaction between BaTiO₃ nanoparticles and PANI was between the H atoms in the N–H bond and the OH molecules in the solution environment. The said interaction was coordinated with BaTiO₃ molecules over O atoms. XRD results confirmed that the synthesized BaTiO₃ had a characteristic cubic perovskite structure and that its structure had not changed. TGA results revealed that the composites became more stable as the BaTiO₃ amount increased. The dielectric measurement results are consistent with the structural results at higher frequencies. Dielectricity increased as BaTiO₃ ratio increased in the environment. The change in the real part of the dielectric permittivity by frequency was stable at high frequencies. According to these results, it is concluded that the composite samples could have very high electromagnetic wave absorption values at higher frequencies (GHz).     

A Novel Underlay Cognitive Radio Based on Direct Sequence Complementary Coded CDMA

In this study, we propose a spectrum sharing scheme where secondary-users (SUs) can co-exist at the same frequency band with the primary-users simultaneously. Both primary (PN) and secondary networks (SN) are considered as CDMA based networks with the same set of orthogonal complementary codes. An orthogonal complementary code set possesses both ideal auto-correlation function (ACF) of any code and ideal cross-correlation function for any two codes in the same set. In the proposed scheme, a delay is applied to the transmission of the SN which exploits ideal ACF properties of complementary codes and will not interfere the transmission of the primary user. Numerical results show that the proposed scheme enables SUs to efficiently utilize the PN’s licensed spectrum without any harmful interference.     

Performance Analysis of OFDM Repeater Networks with Spatial Fading Correlation

This paper analyzes the performance of the OFDM diversity systems with the spatial fading correlation when the network includes an RF repeater. In case of OFDM transmission, since the combining scheme is usually employed in the frequency domain, the correlation between different subchannels should be considered. In a multipath channel, correlation varies over subchannels depending on the channel delay profile and the spatial correlation between each individual delayed paths. In this study, a multipath channel is constructed by the repeated signal instead of natural multipath due to cluttered environments and the system performance with spatial correlation per subcarrier is evaluated. Previously, it is reported that the effect of correlation can be reduced by the Time Shifted Sampling (TSS) technique which relies on the multipath diversity. Numerical results indicate that the TSS technique is also effective in reducing the effect of correlation for the multipath channels constructed by the repeaters.     

Degeneration of socio-urban fabric at Yenikapı and proposals for rehabilitation

This paper aimed to discuss urban conservation challenges along the axes of two streets in the neighborhood of Yenikapı leading towards Kumkapı. The Yenikapı area of the historic peninsula of Istanbul is known to have been inhabited since prehistoric times, and it was the site of an important late antiquity port. Many cultural assets, including monuments from a number of periods and nineteenth century houses, remain in the area, but jarring changes have occurred due to newly built constructions, town planning decisions, and the development of public transport. Before any proposal for future area conservation activities, the current state of conservation was inspected through onsite analyses conducted along Paşazade, Imrahor Hamamı, and Sepetçi Selim streets. By analyzing the pressures affecting the historical peninsula, the challenges in the conservation effort of the study area were determined, followed by some proposals for its enhancement and general conservation. The paper stems from the studio of Urban Preservation-Conservation for Graduate Studies Programme, which was run between February and June 2019 under the coordination of the authors. Highlighting the value of the cultural heritage and historic importance of the area, revitalization to preserve the urban character was suggested. The current state of conservation was investigated through recent onsite analyses, one of the most important tasks in understanding the integrity and authenticity of the area.