1,722,622 research outputs found
Analysis of high capacity short reach optical links
Full text linkOver the last few years, the global Internet traffic has grown exponentially due to the advent of the social networks, high definition streaming, online gaming, high performance computing and cloud services. The network is saturating, facing a challenge to provide enough capacity to such ever-demanding bandwidth expensive applications. Fiber optic communications is the only technology capable of dealing such high demands due to its advantages over the traditional electrical transmission technology. The short haul transmissions currently rely on direct detection due to low cost, low power and low complexity as compared to the coherent detection schemes. In order to increase the bit rate, several advance modulation formats are under investigation for short reach transmissions. Such links mostly use intensity modulation direct detection (IMDD) schemes providing a simple system when compared with the coherent receivers. In this thesis the performance of Multilevel Pulse Amplitude Modulation (MPAM) is studied using IMDD, providing good spectral efficiency as well as able to deal with the limited electronic devices bandwidth. MPAM can address the typical optical channel without the need to go with more complex and higher power modulation schemes. It provides a trade off between sensitivity and the complexity. So a simple communication system using MPAM is implemented using an external modulated laser transmitted over a distance of 2 km. In order to reduce the cost, single laser and single receiver technique is being adopted. The performance of the MPAM system in a bandwidth limited scenarios is studied with a possibility to use equalization techniques to improve the sensitivity. The utility of Forward Error Correction codes is also studied to improve the performance without increasing the latency. By increasing the number of bits per symbol, the system becomes more sensitive to the impairments. Moreover, the components and the connectors in the transmission system also introduces multipath interference (MPI) that is a key limitation to the use of advance modulation formats. Hence a detailed study is carried out to investigate the MPI effects. At the end, a novel idea based on reflective Mach-Zehnder modulator (MZM) is presented that reuses the modulated wavelength eliminating the need for a laser. As a consequent, the cost and power consumption specifically targeted for the optical interconnect environment is reduced. In a nutshell, the thesis provides an overview of the direct detection system targeted to the short optical links. It includes the studies related to the optical transmission systems and provides an insight of the available advance modulation formats and the detection schemes. Finally, the simulations and laboratory results are provided showing that adoption of MPAM is a viable solution that should be employed in high capacity short reach optical links
액체 금속 에멀젼의 열물리적 물성치에 대한 연구
No full text학위논문(석사) - 한국과학기술원 : 기계공학과, 2022.8,[iv, 33 p. :]Improving the cooling performance of a system is of importance for renewable energy and energy sustainability. Herein as a novel coolant, we present Galinstan-ethylene glycol emulsion having up to a volume fraction φ of 0.1 obtained from an ultrasonication method. We subsequently characterized its properties including emulsion size, density, viscosity, specific heat capacity, and thermal conductivity. For the hydrodynamic characteristics, we observed that the volume fraction φ = 0.01 was the critical value to distinguish the regime of Newtonian and non-Newtonian fluid behaviors (i.e., shear-thinning behaviors). Regarding the thermal properties, we found that the specific heat capacity decreased with increasing φ while density changed linearly. On the contrary, it turns out that overall thermal conductivity increases with φ. In particular, for φ > 0.01, the thermal conductivity increased linearly but for φ < 0.01 it dramatically increased depending on the concentration of galinstan. In this work, we will explain this main reason by taking into account the aggregation of the particles, nanoconvection and interfacial thermal resistance. Finally, we compared the thermophyiscal properties of emulsion with the base fluid using figure of merit (FOM) and showed that the proposed coolant, Galinstan-ethylene glycol emulsion, can be considered as a new working fluid.한국과학기술원 :기계공학과
Speckle-noise reduction in knee articular cartilage ultrasound image using anisotropic diffusion / Muhammad Shoaib Ali
Full text linkKnee arthritis is the most common type of arthritis which effects the people and may cause severe pain to the patient and can lead to joint effusion. Ultrasound (US) imaging is an appropriate and consistent substitute for other imaging techniques like magnetic resonance imaging or X-rays in the investigation or screening of knee injury. Nevertheless, one of the major problems in US images which make the analysis of these images hard is the presence of speckle noise. For the reduction of speckle noise, the performance of the anisotropic method is found much better over other approaches. In removing the speckle noise, mostly used methods diffuse the edges during the diffusion of the homogenous region of US images. Therefore, the very critical task is to preserve the edges during the diffusion process. In this research, a method based on Anisotropic Diffusion (AD) is proposed to reduce the speckle noise. The proposed variation in the AD method not only reduces the speckle noise but also preserves the edges and other important detail of images efficiently. Four gradient thresholds are proposed instead of one to have comprehensive information of all neighbouring pixels. A new diffusivity function is also proposed to preserve the edges by stopping diffusion abruptly nears edges. Four different evaluation metrics i.e. Peak Signal-to-Noise Ratio (PSNR), Structure Similarity Index Measurement (SSIM), Figure of Merit (FOM), and Equivalent Number of Looks (ENL) are used to evaluate the performance of the proposed method. Numerical results attained by simulations show that the proposed method reduces the speckle noise very effectively and preserves the edges as well
<b>Supplemental Material - Effects of Occupational Stress, Self-Efficacy and Mental Health During the Pandemic on Hospital Sanitation Workers in Malaysia</b>
No full textSupplemental Material for Effects of Occupational Stress, Self-Efficacy and Mental Health During the Pandemic on Hospital Sanitation Workers in Malaysia by Ayesha Nawal, Muhammad Shoaib, Roman Zámečník, and Asad Ur Rehman in Evaluation & the Health Professions</p
Performance Assessment of Short-Reach Multi-Level PAM Transmission Exploiting LMS Equalization
Full text linkStress analysis and buckling stability of imperfect pressure vessel heads with geometric variations
Full text linkThis study provided a comprehensive analysis of geometry, imperfections, and material distribution affecting the structural performance of HDPE pressure vessels. The findings contribute valuable insights for designing more resilient and efficient pressure tanks, bridging the gap between theoretical models and practical engineering applications. This work emphasizes the importance of geometric optimization, advanced stress analysis, and targeted reinforcement in advancing the reliability of HDPE pressure tanks in real-world scenarios
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