Coordinate interleaved selective coded cooperation

Çeşitleme teknikleri telsiz iletişim sistemlerinin sönümlemeli kanallardaki hata başarımlarını arttırabilmek amacıyla yaygın olarak kullanılmaktadır. Bu çalışmada telsiz iletişim sistemlerinde modülasyon çeşitlemesi ve işbirlikli çeşitleme yöntemlerini, her iki yöntemin sisteme sağladığı kazançlardan da kayıp vermeden birlikte kullanabilen yeni kodlamalı işbirlikli yapıların tasarlanması amaçlanmıştır. İletim ve/veya alım için tek antene sahip iki kullanıcılı telsiz iletişim sistemleri için klasik işbirlikli iletişim yöntemlerinden daha yüksek çeşitleme ve kodlama kazançları sağlayan bileşen serpiştirmeli seçimli kodlamalı işbirliği yöntemi önerilmiştir. Önerilen yöntem için kullanıcılarda ve hedef alıcıda işbirliği durumuna bağlı olarak verilen kararlar için çiftsel hata olasılığı üst sınırları analitik olarak elde edilmiştir. Ulaşılan çiftsel hata olasılığı üst sınır ifadelerinden önerilen işbirlikli sistemler için kullanıcılarda ve hedef alıcıda hata başarımını eniyileyecek kod tasarım ölçütleri belirlenmiştir. Bu ölçütlere dayanarak bilgisayar destekli kafes kod arama yöntemleri ile 4PSK modülasyonu için 1/2 kodlama oranına ve %50 işbirliği oranına sahip 4, 8 ve 16-durumlu yeni işbirlikli kafes kodlar tasarlanmıştır. Yeni kodların hata başarımları incelenerek kod tasarım ölçütlerinin değerlendirmesi yapılmış, yeni kodlarla eşdeğer özelliklere sahip literatürde bilinen en iyi uzay-zaman kafes kodların önerilen bileşen serpiştirmeli seçimli kodlamalı işbirlikli sistemlerde başarımları incelenerek yeni kodların üstünlükleri ortaya konmuştur. Ek olarak, önerilen işbirlikli sistem için bit hata olasılığının üst sınırı aktarım işlevleri yardımıyla çiftsel hata olasılık ifadelerinden elde edilmiş, benzetim sonuçlarıyla tutarlığı gösterilmiştir. Anahtar Kelimeler: Telsiz iletişim, işbirlikli çeşitleme, bileşen serpiştirme, kafes kodlar.Spatial diversity techniques are extensively used to enhance wireless system performance against deterioration caused by fading, since it needs neither extra transmission time nor bandwidth expansion. The link performance is enhanced by conveying the information signal to the destination over more than one ideally independent fading signal paths in space, time or frequency, through the use of a transmit antenna array. Although this is a reasonable approach for the base station, it may be impractical for the mobile unit due to the size or cost limitations which prevent the use of multiple antennas. To overcome this problem, cooperative communication is proposed with various aspects in (Laneman, 2002). In general, users with single antenna share their antennas which form a virtual antenna array. Each user transmits its own signals to both the destination and the partner(s). Each partner retransmits the received or some version of these signals to the destination to provide spatial diversity in a distributed fashion by means of a virtual multiple antennas transmission. The main difficulty compared to the classical spatial diversity is that the user-to-partner (interuser) channel is noisy and the cooperation system should be designed by taking into account that the received information by the partner may be erroneous. However, it is shown that the cooperation improves the robustness of the wireless system against fading and allows higher data rates. Two main cooperation methods are amplify-and-forward (AF) and decode-and-forward (DF). In AF, cooperating user receives the noisy signal from its partner and retransmits it after amplification. Signals from the user and its partner are combined at the destination to determine transmitted data bits. In DF, the cooperating user decodes the signal received from its partner before retransmitting using the same code. Both of these methods guarantee full diversity for two-user case when the interuser channel fading coefficients are known at the destination. It is shown that they increase the channel capacity and improve the system performance in terms of outage probability. However, these schemes can be interpreted as an instance of the repetition coding and therefore bandwidth inefficient. A different approach combining classical channel coding with cooperative diversity is the coded cooperation (Hunter et al., 2006) where instead of repeating the same codeword, the partner provides an additional redundancy to the coding scheme of the user it cooperates. Dividing the codeword of each user into two parts, the first part is transmitted by the user itself and second part by its partner after an error detection to avoid error propagation which becomes serious when the interuser signal-to-noise ratio (SNR) is low. When a user erroneously detects the first part of its partner's codeword, the second part of its own codeword will be transmitted. On the other hand, coordinates of the modulated symbols are affected from independent fading coefficients when they are suitably interleaved before transmission. In the literature, this kind of diversity and the corresponding interleaving method were named "modulation diversity" and "coordinate interleaving" (CI) (Boutros et al., 1998), respectively. For multi-dimensional modulation schemes, achievable diversity order is the minimum number of distinct coordinates of distinct symbol pairs in the constellation. With suitably rotated M-PSK constellations, both coordinates of distinct symbol pairs become different, thus the maximum modulation diversity order of two is achieved with CI. In this study, we propose a coordinate interleaved selective coded cooperation scheme based on suitable combination of the modulation and cooperative diversity techniques. We derive upper bounds on the pairwise error probability of the new scheme for each cooperation case and obtain code design criteria based on these upper bounds. 4-, 8-, 16-state QPSK cooperative trellis codes which significantly improve the system error performance compared to the corresponding best space-time trellis codes (Vucetic et al., 2003) used in cooperation with CI, are proposed. In order to upper bound the bit error probability (BEP) of the proposed schemes, the union bounding technique using generating functions is applied. As this technique produces very loose upper bounds especially for quasi-static Rayleigh fading channels, a modified upper bounding approach previously given in (Malkamaki et al., 1999)  is considered which limits the conditional union upper bound on the BEP before averaging over related fading coefficients. Keywords: Wireless communication, cooperative diversity, coordinate interleaved, trellis codes

İş Tatmini ile Tükenmişlik Düzeyi Arasında Pozitif Psikolojik Sermayeni Aracı Etkisi The Effect of Mediational Role of Positive Psychological Capital Between Job Satisfaction and Burnout Level

Bu çalışma, çalışanların iş tatmini algılarının tükenmişlik düzeyleri üzerine etkisini ve bu etkide çalışanların pozitif psikolojik sermaye durumlarının aracı rolünü belirlemeyi amaçlamaktadır. Araştırmanın amacı doğrultusunda, İstanbul ve Afyonkarahisar’da çalışan toplam 582 işgörene, kolayda örnekleme yöntemi ile anket uygulanmıştır. Anket sonuçları betimleyici analizler ve regresyon analizi kullanılarak analiz edilmiş ve yorumlanmıştır. Yapılan analizler sonucunda elde edilen sonuçlara göre, çalışanların iş tatmini düzeylerinin tükenmişlik düzeylerini negatif, pozitif psikolojik sermaye düzeylerini ise pozitif etkilediği saptanmıştır. Ayrıca, pozitif psikolojik sermayenin iş tatmini ve tükenmişlik arasında kısmi aracılık etkisine sahip olduğu tespit edilmiştir. This study aims to determine the effect of employees' job satisfaction perceptions on burnout levels and the mediating role of the positive psychological capital between job satisfaction and burnout. Using convenience sampling method, a questionnaire was conducted on 582 employees working in İstanbul and Afyonkarahisar. Results were analyzed and interpreted using descriptive analysis and regression analysis. According to the results of the analyzes, it was determined that the job satisfaction levels of the employees negatively affect their burnout levels and positively affect their positive psychological capital levels. It has also been found that the positive psychological capital has a partial mediating effect between job satisfaction and burnout

Carrier dynamics in bulk GaN

Carrier dynamics in hydride vapor phase epitaxy grown bulk GaN with very low density of dislocations, 5–8 × 105 cm−2, have been investigated by time-resolved photoluminescence (PL), free carrier absorption, and light-induced transient grating techniques in the carrier density range of 1015 to ∼1019 cm−3 under single and two photon excitation. For two-photon carrier injection to the bulk (527 nm excitation), diffusivity dependence on the excess carrier density revealed a transfer from minority to ambipolar carrier transport with the ambipolar diffusion coefficient D a saturating at 1.6 cm2/s at room temperature. An extremely long lifetime value of 40 ns, corresponding to an ambipolar diffusion length of 2.5 μm, was measured at 300 K. A nearly linear increase of carrier lifetime with temperature in the 80–800 K range and gradual decrease of D pointed out a prevailing mechanism of diffusion-governed nonradiative recombination due to carrier diffusive flow to plausibly the grain boundaries. Under single photon excitation (266 and 351 nm), subnanosecond transients of PL decay and their numerical modeling revealed fast processes of vertical carrier diffusion, surface recombination, and reabsorption of emission, which mask access to pure radiative decay

Properties of Sumac Plant and Its Importance in Nutrition

Sumac is the common name of the Anacardiaceae family, belonging to the Rhus genus, with more than 250 species of flowering plants, and the most known among these species is Rhus coriaria. When the general characteristics of the Anacardiaceae family are examined, it is seen that there are plants in the form of bush or shrub, which find themselves naturally distributed in temperate and warm climates. Sumac can also grow in areas that are not suitable for agriculture, and this shows the potential for commercialization of sumac plants without competing for land uses. Sumac, a natural source of bioactive compounds%253B It has significant potential with components that can be used in many different fields such as organic acids, fatty acids, amino acids, vitamins, minerals, anthocyanins, and phenolic acids. It also shows a strong antioxidant effect due to the phenolic compounds it contains, especially gallic acid and its derivatives. In the food industry, sumac (Rhus coriaria L.) is used as a spice and sumac sour to give aroma and flavor in many dishes. It is also considered a valuable raw material for the food industry due to its bioactive components. Today, increasing the usage areas of sumac plant in the food sector and knowing its contribution to human health are increasing the interest of consumers for sumac every day. In this review article, information is given about the properties of sumac plant and its importance in nutrition