On the free vibration behavior of cylindrical shell structures

Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student-submitted PDF version of thesis.Includes bibliographical references (p. 105-106).Shell structures, especially cylindrical shells, are widely used in aerospace and naval architectural industries. Submarine hulls and aircraft bodies can be idealized as cylindrical shell structures. The study of vibrations of cylindrical shells is an important aspect in the successful applications of the cylindrical shells. The free vibration characteristics of a submarine hull have an important influence on the noise signature of the submarine. That makes the free vibration problem of the submarine hull a particular interest for the submarine community. The natural frequencies of cylindrical shells are clustered in a very narrow band and they are thus more prone to becoming involved in resonant vibrations. The determination and control of these frequencies is significant to manage the acoustic signature of the submarine. This thesis focuses on the free vibration characteristics of stiffened and unstiffened cylindrical shells. The analysis is carried out mainly in two parts. First, the unstiffened cylindrical shell is modeled and the free vibration problem is analyzed as the shell thickness decreases. Then the cylindrical shell is stiffened with ring stiffeners and the free vibration problem of the stiffened cylindrical shell is studied. The vibration modes of the unstiffened cylindrical shell are studied for four shells with different thicknesses. Initial tensile and compressive membrane stresses are applied separately to the shells to study the effect of the initial stresses on the free vibration modes. The vibration modes of the stiffened cylindrical shell are studied in two steps. First, the influence of the positions of two ring stiffeners on the fundamental frequencies is studied; second, the free vibration modes of the stiffened cylindrical shell are studied. Two cylindrical shells with different thicknesses are used and they are stiffened with different numbers of ring stiffeners, which are uniformly distributed along the longitudinal axis of the shell. The results are compared with available analytical results and finite element solutions of similar problems from the literature.by Burak Ustundag.S.M

3D Propolis-Sodium Alginate Scaffolds: Influence on Structural Parameters, Release Mechanisms, Cell Cytotoxicity and Antibacterial Activity

FEN-C-YLP-130319-0065 BAPKO Project. UID/CTM/50025/2019In this study, the main aim was to fabricate propolis (Ps)-containing wound dressing patches using 3D printing technology. Different combinations and structures of propolis (Ps)-incorporated sodium alginate (SA) scaffolds were developed. The morphological studies showed that the porosity of developed scaffolds was optimized when 20% (v/v) of Ps was added to the solution. The pore sizes decreased by increasing Ps concentration up to a certain level due to its adhesive properties. The mechanical, swelling-degradation (weight loss) behaviors, and Ps release kinetics were highlighted for the scaffold stability. An antimicrobial assay was employed to test and screen antimicrobial behavior of Ps against Escherichia coli and Staphylococcus aureus strains. The results show that the Ps-added scaffolds have an excellent antibacterial activity because of Ps compounds. An in vitro cytotoxicity test was also applied on the scaffold by using the extract method on the human dermal fibroblasts (HFFF2) cell line. The 3D-printed SA-Ps scaffolds are very useful structures for wound dressing applications.publishersversionpublishe

Paroxysmal Atrial Fibrillation After Smokeless Tobacco (Maras Powder) Use

Use of cigarettes and smokeless tobacco is a considerable public health problem. In Turkey, a type of smokeless tobacco called Maras powder (MP) is widely used in the Southeastern region. We present a case of paroxysmal atrial fibrillation that was suspected to be caused by the use of MP, which has never previously been noted in the literature. A 46-year-old man was admitted to our emergency department with angina pectoris and palpitation. He was a long time cigarette smoker and had begun using MP the fortnight before. Electrocardiography showed atrial fibrillation with rapid ventricular response. The patient had no medical history of alcohol use, surgery, palpitation, coronary arterial illness, hypertension or chronic bronchitis. Atrial fibrillation was converted to sinus rhythm after antiarrhythmic medication. Our patient was discharged from the emergency department with a suggestion to quit MP usage immediately. In conclusion, the use of MP may lead to the occurrence of paroxysmal atrial fibrillation

Brain Inspired Cortical Coding Method for Fast Clustering and Codebook Generation

A major archetype of artificial intelligence is developing algorithms facilitating temporal efficiency and accuracy while boosting the generalization performance. Even with the latest developments in machine learning, a key limitation has been the inefficient feature extraction from the initial data, which is essential in performance optimization. Here, we introduce a feature extraction method inspired by energy–entropy relations of sensory cortical networks in the brain. Dubbed the brain-inspired cortex, the algorithm provides convergence to orthogonal features from streaming signals with superior computational efficiency while processing data in a compressed form. We demonstrate the performance of the new algorithm using artificially created complex data by comparing it with the commonly used traditional clustering algorithms, such as Birch, GMM, and K-means. While the data processing time is significantly reduced—seconds versus hours—encoding distortions remain essentially the same in the new algorithm, providing a basis for better generalization. Although we show herein the superior performance of the cortical coding model in clustering and vector quantization, it also provides potent implementation opportunities for machine learning fundamental components, such as reasoning, anomaly detection and classification in large scope applications, e.g., finance, cybersecurity, and healthcare

Front-end blocks of a w-band Dicke radiometer in SiGe BiCMOS technology

In this paper, design methodology and measurement results of W-Band Dicke radiometer blocks are presented. The Dicke radiometer blocks are implemented in IHPs 0.13-μm SiGe BiCMOS technology. All the implemented blocks, namely the SPDT switch, LNA and the power detector demonstrate the state of the art performance at W-Band. The SPDT has a measured IL of 1.8 dB and 20 dB isolation. The LNA achieves a peak gain of 22.3 dB and 4.2 dB NF and the PD has a NEP better than 0.5 pW/Hz. To achieve the minimum NETD, all the blocks are designed to be as wideband as possible. Using the measurement and simulation results, the achievable NETD of the radiometer is calculated to be better than 0.5 K

Clinical and histopathological characteristics of primary focal segmental glomerulosclerosis in Turkish adults

Abstract The data regarding primary FSGS (pFSGS) from different parts of the world differ. While the prevalence of pFSGS has been increasing in Western countries like the USA, it follows an inconsistent trend in Europe and Asia and a decreasing trend in Far Eastern countries such as China in the last two decades. There are undetermined factors to explain those national and geographic discrepancies. Herein, we aimed to reveal the current prevalence with clinical and histopathological characteristics of pFSGS in Turkish adults. This study includes the biopsy-proven pFSGS patients data recorded between 2009 and 2019, obtained from the national multicenter primary glomerulonephritis registry system of the Turkish Society of Nephrology Glomerular Diseases (TSN-GOLD) database. 850 of the 3875 primer glomerulonephritis patients(21.9%) have pFSGS. The mean age is 40.5 ± 14.2 and 435 (51.2%) of patients are male. Nephrotic syndrome is the most common biopsy indication (59.2%). 32.6% of patients have hematuria, 15.2% have leukocyturia and 7.8% have both. Serum creatinine, albumin, and proteinuria are 1.0 mg/dL (IQR = 0.7–1.4) mg/dl, 3.4 ± 0.9 g/dl, 3400 mg/day(IQR, 1774–5740), respectively. Females have lower mean arterial pressure (− 2.2 mmHg), higher eGFR (+ 10.0 mL/min/1.73 m2), and BMI (+ 1.6 kg/m2) than males. Thickened basal membrane(76.6%) and mesangial proliferation (53.5%) on light microscopy are the major findings after segmental sclerosis. IgM (32.7%) and C3 (32.9%) depositions are the most common findings on immunofluorescence microscopy. IgM positivity is related to lower eGFR, serum albumin, and higher proteinuria. The prevalence of pFSGS is stable although slightly increasing in Turkish adults. The characteristics of the patients are similar to those seen in Western countries