131 publications from this institution
In this study, the Y358 phase, the newest high-temperature superconductor member of the yttrium barium copper oxide family, was produced using the solid-state reaction technique. The Y358 superconductor exhibited the Meissner effect at low temperature (77 K). The X-ray diffraction spectra indicated that the crystal structure was almost identical to that of Y123, but with some impurity peaks. An X-ray peak broadening analysis was applied to determine the lattice strain, and the medial crystallite size was calculated perpendicular to the surface of the superconductor specimens. As a result of the analyses, it was determined that the crystallite size of the Y358 superconductor was about 1.125 times larger than that of the Y123 superconductor.
The Smart Grid (SG) initiative introduces a two-way communication between utility companies and the consumers thanks to Advanced Metering Infrastructure (AMI) networks. One of the most crucial components that constitute an AMI network is smart meters (SMs). SMs execute some programs called firmware to rule the hardware. The firmware occasionally needs to be updated to fix bugs and improve the services. Since the SM firmware is proprietary, the update file should be communicated to the SMs in a secure way. In addition, the firmware update can target a specific subgroup of the SMs rather than all of them. In this paper, we address the problem of multicasting the firmware update securely in an IEEE 802.11s-based SG AMI network and develop a secure and reliable multicast-over-broadcast protocol by making use of ciphertext-policy attribute-based signcryption (CP-ABSC) to provide not only confidentiality and access control but also message authentication. A hash of the firmware update is signcrypted based on an access tree such that the hash can be designcrypted only by the SMs possessing the attributes that can satisfy the access tree. In this paper, we propose an attribute-based multicast-over-broadcast protocol called Broadcast-Alarm (Bcast-Alarm) which is both secure and reliable. We assessed its performance under ns-3 network simulator. The simulation results have shown that Bcast-Alarm protocol can complete downloading a firmware update file by consuming comparable amount of bandwidth compared to unicasting.
Abstract The ternary alloy Zn-27Al-1Cu was produced by permanent mold casting. As-cast alloy was aged for different periods after being subjected to solution treatment followed by water quenching. The microstructure, mechanical properties and fatigue behavior of as-cast and heat-treated alloy were then investigated. The quench-aging eliminated the as-cast dendritic structure and produced a uniform microstructure consisting of large grains combined with precipitates. The hardness and tensile strength generally increased, whereas the ductility slightly decreased with aging time. Under all conditions, the longest fatigue life was obtained from the alloy that had been aged for 0.5 h, while the alloy which had been aged for 10 h exhibited the shortest. The fatigue properties were found to be more dependent on impact toughness and elongation, rather than tensile strength.
Çığ olayı, kar yağışının fazla olduğu genellikle orta ve yukarı enlemlerin dağlık alanlarında görülür. Yüksek eğimli yamaçlar üzerine biriken karlar gök gürlemesi, deprem ve benzeri doğal etmenlerle ya da insan kaynaklı titreşimlerle yerlerinden koparak hızla yamaç aşağı harekete geçerler. Bu sırada önlerine çıkan canlı, cansız birçok unsuru da beraberinde sürüklerler. Bu nedenle özellikle yerleşim alanlarını etkileyen çığ olayları zaman zaman can ve mal kayıplarına sebep olur. Türkiye'nin Doğu Anadolu ve Karadeniz bölgeleri çığ olaylarının en çok yaşandığı alanlardır. Bu çalışmada Karadeniz Bölgesi'nin Doğu Karadeniz Bölümü'nde yer alan Karaçam Deresi Havzası’nın çığ riski incelenmiştir. Havzanın ana bölümü Trabzon ili sınırları içinde, diğer küçük parçaları ise Gümüşhane ve Bayburt illeri sınırları içinde yer alır. Çalışmada 1/25000 ölçekli topografya haritaları altlık olarak kullanılmış, uzaktan algılama ve saha çalışmalarıyla toplanan veriler CBS yöntemlerinden yararlanılarak değerlendirilmiştir. Havzanın çığ risk haritasının ve çığ etki düzey haritasının üretiminde entegre risk haritaları oluşturan Afet ve Acil Durum Yönetimi Kurumu'nun puanlama kriterleri kullanılmıştır. Bu haritaya göre, çok yüksek ve yüksek çığ riski olan alanlar havzanın orta kesiminde yoğunlaşmakta ve havza alanının %37'sini kaplamaktadır. Havzanın yukarı bölümünde daha fazla kar yağmasına rağmen, çığ riskinin daha düşük olması, 25 derecenin altındaki eğim değerleriyle dikkati çeken yüksek aşınım düzlükleriyle ilişkili bulunmuştur. Sahada, yöre sakinleriyle yapılan görüşmelerde çığ oluşumu konusunda endişe taşıdıkları ve çığ oluşumunu azaltmaya dönük olarak çığ önleme çitleri gibi bazı önlemler aldıkları görülmüştür. Bununla birlikte Köknar, Seyrantepe, Şekersu ve Yeşilkaya gibi bazı yerleşim birimlerinde birçok evin halen çığ yolları üzerinde bulunduğu belirlenmiş; bunların bir an önce güvenli yerlere taşınmasının hayati önem taşıdığı değerlendirilmiştir.
We have investigated the magnetostriction of type II superconductors under the viscous flux‐flow. The critical state approach was employed to obtain the magnetostriction loops versus applied field. The flux profile equations in the time dependent form have been introduced for both exponential model and Anderson‐Kim model. Both shape and scale of the curves are dependent on the frequency of applied field.
Bu çalışmada, YBCO (358) süperiletkeninin manyetik-moment sıcaklık ölçümleri ve teorik analizleri araştırıldı. Manyetik Moment-Sıcaklık (M-T) eğrilerinin teorik analizi sinterleme sırasında verilen oksijen oranına bağlılığı olarak yapıldı. Elde edilen deneysel sonuçlarda, oksijen oranının değişiminin Moment-Sıcaklık eğrileri deseninde değişikliğe sebep olduğu görüldü. Deneysel sonuçlar, kritik hal modeli çerçevesinde nitel olarak tartışıldı. Oksijen oranının miktarının artmasıyla (%0, 50, 100), kritik akım yoğunluğunun (J c ) büyüklüğünün sırasıyla 50, 100 ve 0 olarak değiştiği bulundu. Her numune için teorik ve deneysel en iyi uyum eğrilerinden kritik akım yoğunluğunun alan ve sıcaklık bağlılığı belirlendi. M-T verilerine göre en iyi uyum eğrileri elde edildi ve kullanılan parametrik değerler her bir numune için karşılaştırıldı. Sonucun literatürle uyumlu olduğu görüldü.
Ceramic glass is a multipurpose solid-state material that merges the high thermal stability, mechanical strength, and chemical durability of ceramics with the transparency, light transmission, and aesthetic benefits of glass. Because of these qualities, ceramic glass can be used in both industrial and scientific settings, especially when radiation protection, high-temperature endurance, heat resistance to thermal fluctuations, and optical clarity are required. Radiation shielding properties of five distinct ceramic glass samples with the chemical formula B2O3-ZnO-K2CO3-PbO (abbreviated as BZKP) were comprehensively assessed in this study. The radiation protection parameters of B2O3-ZnO-K2CO3-PbO glass-ceramic systems, including gamma-ray kerma coefficients (kγ), half-value layer (HVL), radiation shielding efficiency (RPE), mean free path (MFP), fast neutron macroscopic cross section ΣR (cm−1), and effective atomic number (Zeff), were theoretically examined using Monte Carlo EGS4 and WinXCOM software. The radiation shielding characteristics at 20 discrete photon energies, ranging from 0.05 MeV to 2 MeV, were theoretically calculated using the EGS4 simulation code and subsequently compared with data obtained from the XCOM program. The results of this study provide solid and valuable information regarding the improved design of high-performance ceramic glasses for radiation shielding applications. To create effective shielding solutions, a comprehensive understanding of the interactions between various materials and ionizing radiation, such as neutrons and gamma rays, is essential. By combining these discoveries, scientists can create new shielding materials that make the most of materials in these critical areas while improving radiation protection.
The chapter presents a review of proactive Moving Target Defense (MTD) paradigm and investigates the feasibility and potential of specific MTD approaches for the resource-constrained Internet of Things (IoT) applications. The aim is not only to provide taxonomy of various MTD approaches but also to advocate MTD techniques in the dynamic network domain in conjunction with the emerging Software Defined Networking (SDN) for more effective proactive IoT defense. The Internet of Battlefield Things (IoBT) and Industrial IoT (IIoT), which subject to more attacks, are identified as two critical IoT domains that can reap from the SDN-based MTD approaches. Finally, the chapter also discusses potential future research challenges of the MTD approaches in the IoT domain.
Despite the potential benefits of smart meters as part of the Smart Grid initiative, the deployment of smart meters has aroused several concerns on consumer privacy. To address such concerns, various solutions are proposed in recent years under a variety of assumptions. Nonetheless, all of these solutions require a trust relationship between the consumers and utilities or third-party service providers which still does not convince some of the consumers for using smart meters. An ultimate solution is to hide the data from utilities or third-parties by using fully homomorphic encryption (FHE) systems while still allowing them to do processing on the encrypted data for their needs. However, the FHE systems are recently started to be realized and their wider deployment for certain applications has not been explored yet. In this paper, we investigate the feasibility of using FHE systems on an IEEE 802.11s-based Advanced Metering Infrastructure (AMI) application when preserving the privacy of the consumers. We design and adapt one of the existing FHE schemes for AMI and test its overhead under a variety of conditions on an 802.11s-based wireless mesh network using ns-3 network simulator. Compared to traditional encryption and partially homomorphic systems, FHE comes with significant overhead in terms of data size and delay. Nevertheless, the results indicate that such delay and data size overhead are still in acceptable limits that can be handled by the existing meters and networks.
Accurate precursor calculation is essential for the successful synthesis of oxide-based superconductors. This study compares two commonly used methods stoichiometric balance and conversion factor (CF) approaches in the synthesis of YBa2Cu3O7-δ (Y123) and Y3Ba5Cu8O18+δ (Y358) superconductors. The analysis reveals that CF methods introduce substantial systematic errors, particularly for Y2O3, with deviations reaching 21.2% in Y123. These errors are exacerbated in Y358 due to its increased stoichiometric complexity. Unlike stoichiometric methods, CF approaches neglect volatile losses such as CO2 and fail to adjust for oxygen non-stoichiometry (δ variations), leading to misestimations in precursor masses. Statistical tests (χ2 < 0.001, RMSE) and experimental data confirm that these inaccuracies can negatively impact phase purity and crystallographic quality. A strong correlation (R2 = 0.847) between stoichiometric accuracy and phase formation quality emphasizes the importance of rigorous calculation. This study highlights the inherent limitations of CF-based shortcuts and underscores the necessity of comprehensive stoichiometric modeling, especially in complex oxide systems. The findings also provide an educational framework to address common misconceptions in materials synthesis, particularly for early-stage researchers in solid-state chemistry and materials science.
Computational fluid dynamics (CFD) is widely used in device design to determine gas flow patterns and turbulence levels. CFD is also used to simulate particles and droplets, which are subjected to various forces, turbulence and wall interactions. These studies can now be performed routinely because of the availability of commercial software containing high quality turbulence and particle models. In order to understand how the gas is brought down to wafer, it is necessary to have a knowledge of the gas flow behavior very early in the design spiral of the Tantalum nitride-Atomic layer deposition (TaN-ALD) chamber by undertaking parametric investigation of the interaction effect between gas flow and the funnel structure. This paper presents such a parametric investigation on a generic TaN-ALD chamber using CFD. The results presented have been analyzed for a total of 11 different cases by varying neck and nozzle angles for a process gas. The gas flow was mainly investigated for the nozzle angles of 4.5, 9, 12 and 20 and the film thickness results were compared with numerical flow patterns. CFD simulations using the turbulence model in ANSYS Fluent v.13 are undertaken. The parametric study has demonstrated that CFD is a powerful tool to study the problem of gas flow-structure interaction on funnel and is capable of providing a means of visualizing the path of the gas under different operating conditions.
