A low-complexity time-domain MMSE channel estimator for space-time/frequency block-coded OFDM systems

Focusing on transmit diversity orthogonal frequency-division multiplexing (OFDM) transmission through frequency-selective channels, this paper pursues a channel estimation approach in time domain for both space-frequency OFDM (SF-OFDM) and space-time OFDM(ST-OFDM) systems based on AR channel modelling. The paper proposes a computationally efficient, pilot-aided linear minimum mean-square-error (MMSE) time-domain channel estimation algorithm for OFDM systems with transmitter diversity in unknown wireless fading channels. The proposed approach employs a convenient representation of the channel impulse responses based on the Karhunen-Loeve (KL) orthogonal expansion and finds MMSE estimates of the uncorrelated KL series expansion coefficients. Based on such an expansion, no matrix inversion is required in the proposed MMSE estimator. Subsequently, optimal rank reduction is applied to obtain significant taps resulting in a smaller computational load on the proposed estimation algorithm. The performance of the proposed approach is studied through the analytical results and computer simulations. In order to explore the performance, the closed-form expression for the average symbol error rate (SER)probability is derived for the maximum ratio receive combiner(MRRC). We then consider the stochastic Cramer-Rao lower bound(CRLB) and derive the closed-form expression for the random KL coefficients, and consequently exploit the performance of the MMSE channel estimator based on the evaluation of minimum Bayesian MSE. We also analyze the effect of a modelling mismatch on the estimator performance. Simulation results confirm our theoretical analysis and illustrate that the proposed algorithms are capable of tracking fast fading and improving overall performance. Copyright © 2006 Hindawi Publishing Corporation. All rights reserved

Prevalence of and risk factors for low back pain among healthcare workers in Denizli

Objectives: The purpose of this study was to examine personal, occupational, and psychosocial risk factors affecting prevalence of low back pain in healthcare workers. Methods: Study included total of 1682 participants (1010 female, 672 male) working at Denizli State Hospital. Low back pain section of Standardized Nordic Musculoskeletal Questionnaire (SNMA) was used to evaluate recent occurrence, pain experienced within previous year, and over lifetime. Perceived Stress Scale and Job Satisfaction Scale were also administered. Results: Prevalence of lifetime low back pain in healthcare workers was determined to be 53% based on SNMA. It was observed that low back pain was most common among medical secretaries (56.9%). Advanced age, female gender, high body mass index (p=0.002), being married (p=0.0001), lack of regular exercise (p=0.009), working for more than 4 hours while standing (p=0.012) or sitting at desk (p=0.021), using computer for more than 4 hours (p=0.0001), greater number of years of service (p=0.001), and low job satisfaction (p=0.001) were found to be factors increasing low back pain risk. Conclusion: Our study demonstrated that healthcare workers are among group with high risk of low back pain. © 2017 Turkish Society of Algology

Biogas potential of hazelnut shells and hazelnut wastes in Giresun City

In recent years, the world's natural energy resources unable to meet the increasing energy needs. In Turkey and in the world, there is an increasing need for renewable energy. One of the renewable energy sources is biogas energy. In this study, the biogas potential of Giresun, which is also known as coastal city, can be formed from 2 different organic wastes are experimentally calculated. Organic wastes included in the calculation; hazelnut shells (HS) and hazelnut wastes (HW). Production experiments were investigated in two ways: untreated and thermal pretreatment. In addition, biogas yield was examined at room temperature (23 °C), at mesophilic temperature (39 °C), and at thermophilic temperature (60 °C). As a result, the highest biogas yield was found at temperatures of 60 °C and under thermal pretreatment conditions. Under these conditions, annual biogas production potential of Giresun city was found as 38.21 GW h/yr. © 201

Temperature and Pressure Dependence of the Linewidth for an Internal Mode in the Solid Phases of Benzene

The pressure dependence of the Raman linewidths for the $ν_1$ breathing mode is analyzed using the experimental data from the literature for the solid phases (I, II, III and III') in benzene. Increase (I, III and III') and decrease (II) in the Raman linewidths are described by a power-law analysis with the critical exponent β. The β values we find, which characterize the phase transition are in favour of the first order among those phases considered in benzene. The temperature and pressure dependence of the frequencies and linewidths of various Raman modes can be analyzed using a power-law formula, as studied here for the solid phases (I, II, III and III') in benzene when the experimental data are available in the literature