Performance of multilevel‐turbo codes with blind/non‐blind equalization over WSSUS multipath channels

In this paper, in order to improve error performance, we introduce a new type of turbo codes, called ‘multilevel‐turbo codes (ML‐TC)’ and we evaluate their performance over wide‐sense stationary uncorrelated scattering (WSSUS) multipath channels. The basic idea of ML‐TC scheme is to partition a signal set into several levels and to encode each level separately by a proper component of the turbo encoder. In the considered structure, the parallel input data sequences are encoded by our multilevel scheme and mapped to any modulation type such as MPSK, MQAM, etc. Since WSSUS channels are very severe fading environments, it is needed to pass the received noisy signals through non‐blind or blind equalizers before turbo decoders. In ML‐TC schemes, noisy WSSUS corrupted signal sequence is first processed in equalizer block, then fed into the first level of turbo decoder and the first sequence is estimated from this first Turbo decoder. Subsequently, the other following input sequences of the frame are computed by using the estimated input bit streams of previous levels. Here, as a ML‐TC example, 4PSK 2 level‐turbo codes (2L‐TC) is chosen and its error performance is evaluated in WSSUS channel modelled by COST 207 (Cooperation in the field of Science & Technology, Project #207). It is shown that 2L‐TC signals with equalizer blocks exhibit considerable performance gains even at lower SNR values compared to 8PSK‐turbo trellis coded modulation (TTCM). The simulation results of the proposed scheme have up to 5.5 dB coding gain compared to 8PSK‐TTCM for all cases. It is interesting that after a constant SNR value, 2L‐TC with blind equalizer has better error performance than non‐blind filtered schemes. We conclude that our proposed scheme has promising results compared to classical schemes for all SNR values in WSSUS channels. Copyright © 2005 John Wiley & Sons, Ltd.     

A comparative study of borided pure niobium, tungsten and chromium

Pure niobium (Nb), tungsten (W) and chromium (Cr) were boronized at 940 °C for 2, 4 and 8 h. The borided samples were characterized by X-ray diffraction, Scanning electron microscope and microhardness tests. Tribological investigation was conducted. X-ray study showed the presence of NbB₂, WB, and CrB. The hardnesses of boride layers formed on the pure Nb, W and Cr were 2500, 2500 and 1700 HV, respectively, whereas the hardnesses of the pure Nb, pure W and pure Cr were 110, 445 and 115 HV, respectively. Nb boride layers ranged in thickness from 8 to 22 μm, whereas W boride layers ranged in thickness from 10 to 42 μm, and the thickness of Cr boride layer varied from 4 to 12 μm with boronizing time. The boriding of W resulted in thicker boride layer compared to the boriding of Nb and Cr at given time. The frictional behaviour and wear mechanicms differ in modes and scales.     

Real-time X-ray studies of the growth of Mo-seeded Si nanodots by low-energy ion bombardment

Silicon surface evolution during room temperature low-energy (300, 500 and 1000 eV) normal incidence Ar⁺ ion bombardment in the presence of Mo seed atoms has been studied with real-time grazing-incidence small-angle X-ray scattering and ex situ atomic force microscopy. When a small amount of Mo atoms was supplied to the Si surface during ion bombardment, the development of correlated structures with two different characteristic length scales was observed. The shorter length scale features (“dots”) coarsened with time until they reached a constant spatial wavelength. The longer length scale corrugations associated with kinetic roughening, however, continued to grow in amplitude during bombardment. The overall roughness is dominated by different corrugations at different times in the kinetic evolution, showing a complex behavior. The evolution of the kinetic roughening can be described by the Family-Vicsek scaling hypothesis, but measured scaling exponents are not in agreement with those of existing models.     

The electrical measurements in poly(2-chloroaniline) based thin film sandwich devices

Al/P2ClAn(CH₃COOH)/p-Si/Al structure has been obtained by evaporation of the polymer P2ClAn(CH₃COOH) on the front surface of p-type silicon substrate, P2ClAn: the poly(2-chloroaniline). The P2ClAn emeraldine salt was chemically synthesized by using acetic acid (CH₃COOH). It has been seen that the current-voltage characteristics of the heterojunction obey to space charge-limited current model. Furthermore, P2ClAn(CH₃COOH) was characterized by using Fourier Transform Infrared (FTIR) and Ultraviolet-Visible (UV-Vis) spectroscopies. An average value of μ, 2.43 × 10^− 5 cm² V^− 1 s^− 1, was obtained for the mobility of the P2ClAn(CH₃COOH); this value is in agreement with the value of about 10^− 4 cm² V^− 1 s^− 1 given for the conjugated polymeric thin films in the literature. Low capacitance-voltage-frequency and conductance-frequency measurements have been made at the voltages of 0.00, 0.02 and 0.30 V in the frequency range of 100 Hz-2.0 MHz. An average value of 7.91 × 10¹¹ cm^− 2 eV^− 1 for interface state density has been obtained from the frequency-capacitance characteristics.     

Removal of ammonium ion from aqueous solution by natural Turkish (Yildizeli) zeolite for environmental quality

The purposes of this study were to investigate the removal efficiency of ammonium (NH(4)(+)) ion from aqueous solution using the natural Turkish (Yildizeli) zeolite and to characterize equilibrium isotherms. Experiments were carried out using batch method as a function of the solution pH, shaking time, dosage of adsorbent, and temperature. All these factors affected NH(4)(+) ion removal from aqueous solution. Equilibrium modelling data were fitted to linear Langmuir and Freundlich models. Dubinin-Redushckevich (D-R) isotherm was applied to describe the nature of ion exchange of NH(4)(+) and found that it occurred physically. Thermodynamics parameters such as change in free energy (DeltaG degrees ), enthalpy (DeltaH degrees ) and entropy (DeltaS degrees ) were also calculated. These parameters confirmed that ion exchange of NH(4)(+) by the zeolite was feasible, spontaneous and exothermic in nature. Based on the results, it can be concluded that the natural Turkish (Yildizeli) zeolite is suitable for the removal of NH(4)(+) ions in wastewater treatments and agricultural purposes to in terms of sustainability of environmental quality.     

CCB-based encapsulation of pyrite for remediation of acid mine drainage

Acid mine drainage (AMD) from abandoned coal mines continues to be one of the most significant environmental problems. Remediation of AMD requires an addition of lime source to decrease the acidity, and grouting the entire mine and encapsulating the pyrite by calcium-rich additives is often employed. Utilization of alkaline coal combustion by-products (CCBs) has gained acceptance in such remediation applications because of their cost-effectiveness. A study was conducted to investigate the effectiveness of CCBs to abate acid mine drainage by encapsulation of pyrite. Geomechanical, hydraulic, and environmental tests were performed on grouts prepared with various ratios of CCBs as well as an alternative free lime source, lime kiln dust (LKD). The results indicated that the mechanical properties of grouts were dependent on their free lime contents. Hydraulic conductivities of pyrite-grout columns were relatively high due to the coating of the pyrite rock with the grout rather than the filling of all of the void spaces, as commonly experienced in field applications. The leaching tests indicated that the presence of high amounts of lime in a grout is not solely sufficient to improve the quality of AMD, since the rate of dissolution of a high lime content grout may be slow due to its rapid hardening. Therefore, it is recommended that grouts be selected with consideration of their hardening capacities, as well as the percentage of lime content present in the mixture.     

Application of nonlinear regression analysis for ammonium exchange by natural (Bigadiç) clinoptilolite

The experimental data of ammonium exchange by natural Bigadiç clinoptilolite was evaluated using nonlinear regression analysis. Three two-parameters isotherm models (Langmuir, Freundlich and Temkin) and three three-parameters isotherm models (Redlich–Peterson, Sips and Khan) were used to analyse the equilibrium data. Fitting of isotherm models was determined using values of standard normalization error procedure (SNE) and coefficient of determination (R²). HYBRID error function provided lowest sum of normalized error and Khan model had better performance for modeling the equilibrium data. Thermodynamic investigation indicated that ammonium removal by clinoptilolite was favorable at lower temperatures and exothermic in nature.     

T6热处理对触变锻造加低过热铸造制备的A356和A380铝合金的影响（英文）

研究T6热处理对触变锻造A356和A380铝合金的影响。采用低过热铸造(LSC)技术制备用于触变锻造的样品。为了获得等轴晶粒并防止枝晶生长,将样品在高于液相温度20°C时进行浇铸,将浇铸坯料再加热不同时间(20~80 min)后进行触变锻造,变形量为50%,再将触变锻造后的A356和A380铝合金样品进行T6热处理。用光学显微镜、能量弥散X射线谱仪、扫描电镜和布氏硬度仪对经触变锻造、固溶处理和时效处理后样品的显微组织和硬度变化进行检测。结果表明,T6热处理后合金的显微组织更均匀,并分别在A356和A380坯料中形成了新的析出相Mg_2Si和Al_2Cu。相应地,经过人工时效后,样品的硬度大幅度提高,A356铝合金的硬度达到HB 93,A380铝合金的硬度达到HB 120。     

Analysis of diversity schemes employing antenna selection in the presence of channel estimation errors and feedback delay

The main objective of this paper is to provide an extensive and complete examination on the effect of practical impairments such as channel estimation errors (CEEs) and feedback delay (FD) on the performance of diversity schemes over Nakagami‐m fading channels. Under erroneous channel estimation and outdated feedback cases, statistical expressions and several performance metrics related to the post‐processing signal‐to‐noise ratio (SNR) are derived for four different diversity schemes: transmit antenna selection (TAS)/orthogonal space–time block coding, TAS/maximal‐ratio transmission (MRT), MRT/receive antenna selection (RAS), and joint transmit and RAS. Exact analytical expressions for outage probability and average error rates of M‐ary modulations are derived in order to provide insightful perspectives on the capacity and error performance of diversity schemes that experience both CEE and FD. The asymptotic diversity order of the investigated diversity schemes are derived via a high‐SNR approximation approach. In order to assess the real‐world performance of the investigated diversity schemes and to observe their robustness or sensitivities in practical imperfections, various configurations are considered together with several performance comparisons. Also, Monte Carlo simulations are performed in order to validate the theoretical results. Copyright © 2014 John Wiley & Sons, Ltd.     

Reformulation of bone china body for the reduction of pyroplastic deformation

This work is aimed to decrease the pyroplastic deformation using sodium feldspar and potassium feldspar in bone china revealing the viscosity and crystalline phase effect. For this, we reformulated the traditional bone china recipe considering the amount and ratio of fluxing agents. In the first group, sodium feldspar (coded as Na-F) and potassium feldspar (coded as K-F) were introduced individually into the body from 20 to 35 wt.%. In the second group, we fixed the feldspar amount to 35 wt.% but changed the Na-F/K-F ratio to 1/3–1/2–1/1–2/1–3/1. Optical dilatometry measurements revealed that K-feldspar reduced the sintering temperature by about 50°C compared to Na-feldspar. Densified 35% K-F and 35% Na-F bodies showed very low pyroplastic index (PI) such as 5.36 × 10^–6 cm⁻¹ (at 1150°C) and 7.46 × 10⁻⁶ cm⁻¹ (at 1200°C), respectively, whereas Na-F/K-F 1/3 sample exhibited the lowest PI (3.58 × 10⁻⁶ cm⁻¹) at very low sintering temperature (at 1150°C). Microstructural analysis showed that the dissolution of residual quartz grains and the homogeneity of the distribution of the crystal phases support decrease in pyroplastic deformation.