Characterization of building stones from the ancient Tyana aqueducts,Central Anatolia,Turkey: implications on the factors of deterioration processes

Many archaeological and historical monuments constructed by different civilizations over the last 5500 years can be observed in the Ni?de region located in central Anatolia. The Tyana aqueduct as a continuation of the Roman Pool is one such important historical monument. The aqueducts that carried the water of the Roman Pool to the ancient city of Tyana were constructed during the time of the Roman emperors Trajan, Hadrian and Marcus Aurelius Antoninus. Half of the total length of the aqueducts (3 km) is on the surface and the rest is buried. The engineering properties of the rocks used in such archaeological and historical buildings are very important in terms of conserving these structures for future generations. In this study, the geomechanical and geotechnical features of the Tyana aqueducts were investigated to understand the rock types, deterioration in the stones over time and problems originating from these features. Also, for restoration purposes, the ancient stone quarry areas for the aqueducts were identified, and the chemical, petrographical and geomechanical properties of fresh travertine blocks from these quarries were determined. The main rock type used as building stones in the aqueducts is Mio-Pliocene travertine. Laboratory studies were performed to determine the mineralogical, petrographic and petrophysical properties of the building stone samples. Fresh and used travertine samples were composed exclusively of calcite crystal. The results of chemical analyses were similar for fresh and used travertine samples. To determine the geomechanical properties of the travertines, dry unit weight, water absorption, effective porosity, P-wave velocity, Böhme abrasion test, capillary water absorption and uniaxial compressive strength experiments were conducted. In addition, Schmidt hammer hardness measurements were performed on site for the different levels and different textural characteristics of the belts on the travertines. According to the experimental data obtained, higher strength was displayed by samples with fine grains, massive texture and low porosity. The deterioration effects in most of the travertines used in the original structure are very low. In addition to human effects, the use of small stone dimensions (especially the stones used in belts as keystones) and the use of stone from the same quarry but with features that differ or are inferior are thought to be factors in the destruction of the Tyana aqueducts.     

屏蔽电机定子端部氮气腔温度场计算方法分析

核主泵屏蔽电机的热设计是涉及核电发展的一个关键因素,直接关系到电机能否安全运行60年。针对某屏蔽电机结构紧凑、内部损耗大,特别是氮气腔内散热条件差,定子绕组容易超温等特点,本文基于有限体积法,根据计算流体动力学(CFD)原理,分别进行了常规不考虑与考虑辐射换热两种算法时的电机内温度场数值模拟,获得了电机内的三维温度分布,并分析了定子端部氮气腔内的自然对流换热系数和热流密度等传热特性。此外,还对比了两种计算方法电机内温度分布的差异。计算结果表明,两种计算方法的峰值数值模拟结果与实验数据的相对误差分别是+3.6%、-4.2%。所得结论为对我国开发具有自主知识产权的同类电机产品具有重要参考价值。     

Reproducible surface-enhanced Raman scattering spectra of bacteria on aggregated silver nanoparticles

Surface-enhanced Raman scattering (SERS) is proven to be a powerful technique for rapid identification and discrimination of microorganisms. However, due to the heterogeneous nature of the samples, the acquisition of reproducible spectra hinders the further development of the technique. In this study, we demonstrate the influence of the experimental conditions on SERS spectra. Then, we report a simple sample preparation method coupled with a light microscope attached to a Raman spectrometer to find a proper spot on the sample to acquire reproducible SERS spectra. This method utilizes the excited surface plasmons of the aggregated silver nanoparticles to visualize the spots on the sample. The samples are prepared using the concentrated silver colloidal solutions. The collection time for one spectrum is 10 s and each spectrum is a very good representative of the other spectra acquired from the same sample. The nature of the surface charge of the silver nanoparticles influences the spectral features by determining the strength of the interactions between nanoparticles and bacteria and the aggregation properties of the nanoparticles. Although increasing the colloid concentration in the sample resulted in reproducible spectra from arbitrary points on the sample, a great variation from sample to sample prepared with the different colloidal solution concentrations is observed.     

Investigation of Sm → Ca substitution in Bi(Pb)SrCaCuO high temperature superconductor by low field AC magnetic susceptibility

We have investigated the effect of Sm substitution in Bi(Pb)SrCaCuO system by performing AC susceptibility ( ), XRD (X Ray Diffraction) and SEM (Scanning Electron Microscopy) measurements. The Sm → Ca substitution (Bi_1.6Pb_0.4Sr₂Ca_2−x Sm _x Cu₃O_y) was carried out by conventional solid-state reaction method. The susceptibility measurements were carried out at different values of the AC field amplitudes. The imaginary part of susceptibility is used to estimate the intergranular critical current density by means of the Bean’s model. The intergranular critical current density (J _c) of pure sample is found to be about 68 A/cm² at 95 K. The intergranular J _c is seen to decrease with increasing Sm substitution. XRD pattern and SEM micrographs are given to provide information about Bi-2223 phase and grain size respectively.     

Removal of boron from aqueous solution by using neutralized red mud

The adsorptive removal of boron from aqueous solution by using the neutralized red mud was studied in batch equilibration technique. The effects of pH, adsorbent dosage, initial boron concentration and contact time on the adsorption were investigated. The experiments demonstrated that boron removal was of a little fluctuation in pH range of 2-7 and it takes 20 min to attain equilibrium. The adsorption data was analyzed using the Langmuir and the Freundlich isotherm models and it was found that the Freundlich isotherm model represented the measured sorption data well.     

Equilibrium, kinetic and thermodynamic studies of adsorption of Pb(II) from aqueous solution onto Turkish kaolinite clay

The adsorption of Pb(II) onto Turkish (Bandirma region) kaolinite clay was examined in aqueous solution with respect to the pH, adsorbent dosage, contact time, and temperature. The linear Langmuir and Freundlich models were applied to describe equilibrium isotherms and both models fitted well. The monolayer adsorption capacity was found as 31.75 mg/g at pH 5 and 20 degrees C. Dubinin-Radushkevich (D-R) isotherm model was also applied to the equilibrium data. The mean free energy of adsorption (13.78 kJ/mol) indicated that the adsorption of Pb(II) onto kaolinite clay may be carried out via chemical ion-exchange mechanism. Thermodynamic parameters, free energy (deltaG degrees ), enthalpy (deltaH degrees ) and entropy (deltaS degrees ) of adsorption were also calculated. These parameters showed that the adsorption of Pb(II) onto kaolinite clay was feasible, spontaneous and exothermic process in nature. Furthermore, the Lagergren-first-order, pseudo-second-order and the intraparticle diffusion models were used to describe the kinetic data. The experimental data fitted well the pseudo-second-order kinetics.     

Effect of ZrSiO4 on the Friction Performance of Automotive Brake Friction Materials

Friction-wear properties of the ZrSiO4 reinforced samples were measured and compared with those of plain bronze based ones. For this purpose, density, hardness, friction coefficient wear behaviour of the samples were tested. Microstructures of samples before and after sintering and worn surfaces were also investigated by scanning electron microscopy （SEM）, and the wear types were determined. The optimum friction-wear behaviour was obtained in the sample compacted at 500 MPa and sintered at 820℃. Density of the final samples decreased with increasing the amount of reinforcing elements （ZrSiO4） before pre-sintering. However after sintering, there is no change in density of the samples including reinforcing elements （ZrSiO4）. With increasing friction surface temperature, a reduction in the friction coefficient of the samples was observed. However, the highest reductions in the friction coefficients were observed in the as-received samples containing 0. 5% reinforced ZrSiO4. The SEM images of the sample indicated that while bronze-based break lining material without ZrSiO4 showed abrasive wear behaviour, increasing the amount of ZrSiO4 resulted a change in abrasive to adhesive wear mechanism. All samples exhibited friction-wear values, which were within the values shown in SAE-J661 standard. With increasing the amount of reinforcing ZrSiO4, wear resistance of the samples was increased. However samples reinforced with 5% and 6% ZrSiO4 showed the best results.     

The application of solar distillation technique as a mean for olive mill wastewater management

The present study was conducted on a pilot scale level using a solar still unit to separate olive mill wastewater (OMW) into condensate and solid residue. The prevailing conditions inside the solar still, rates of distillation and a number of quality parameters for condensate [pH, electrical conductivity (EC), turbidity, chemical oxygen demand (COD), total organic carbon (TOC), total nitrogen (TN) and total‐phenols] were evaluated to assess the system performance. The solid residue was evaluated as well for its utility as a potential biofuel. The condensate is acidic (pH 3.8), colourless, transparent and free of suspended solids. The turbidity and EC were reduced in the condensate by 100 and 99%, respectively, while the loads of COD, TOC, TN and T‐phenols were reduced by 90, 98, 99.9 and 99.96%, respectively. Almost 0.04% of initial total phenols found in OMW were recovered in the condensate. High calorific value (23.5 kJ/g) and combustible portion (84%) of solid residue suggests its applicability as a potential biofuel     

Kinetics of plasma paste boronized AISI 8620 steel in borax paste mixtures

In the present study, AISI 8620 steel was plasma paste boronized by using various borax paste mixtures. The plasma paste boronizing process was carried out in a dc plasma system at a temperature of 973, 1023 and 1073 K for 2, 5 and 7 h respectively in a gas mixture of 70% H₂-30% Ar under a constant pressure of 10 mbar. The properties of the boride layer were evaluated by optical microscopy, X-ray diffraction, the micro-Vickers hardness tester and the growth kinetics of the boride layers. The thickness of the boride layers varied from 14 to 91 μm depending on the boronizing time and temperature. X-ray diffraction analysis of boride layers on the surface of the steel revealed the formation of FeB and Fe₂B phases. Depending on the temperature and layer thickness, the activation energies of boron in steel were found to be 99.773 kJ/mol for 100% borax paste.