Nonlinear dynamics of attractive magnetic bearings

The nonlinear dynamics of a ferromagnetic shaft suspended by the force of attraction of 1, 2, or 4 independent electromagnets is presented. Each model includes a state variable feedback controller which has been designed using the pole placement method. The constitutive relationships for the magnets are derived analytically from magnetic circuit theory, and the effects of induced eddy currents due to the rotation of the journal are included using Maxwell's field relations. A rotor suspended by four electro-magnets with closed loop feedback is shown to have nine equilibrium points within the bearing clearance space. As the rotor spin speed increases, the system is shown to pass through a Hopf bifurcation (a flutter instability). Using center manifold theory, this bifurcation can be shown to be of the subcritical type, indicating an unstable limit cycle below the critical speed. The bearing is very sensitive to initial conditions, and the equilibrium position is easily upset by transient excitation. The results are confirmed by numerical simulation

A constitutive model for the forces of a magnetic bearing including eddy currents

A multiple magnet bearing can be developed from N individual electromagnets. The constitutive relationships for a single magnet in such a bearing is presented. Analytical expressions are developed for a magnet with poles arranged circumferencially. Maxwell's field equations are used so the model easily includes the effects of induced eddy currents due to the rotation of the journal. Eddy currents must be included in any dynamic model because they are the only speed dependent parameter and may lead to a critical speed for the bearing. The model is applicable to bearings using attraction or repulsion

FPGA based secure and noiseless image transmission using LEA and optimized bilateral filter

In today’s world, the transmission of secured and noiseless image is a difficult task. Therefore, effective strategies are important to secure the data or secret image from the attackers. Besides, denoising approaches are important to obtain noise-free images. For this, an effective crypto-steganography method based on Lightweight Encryption Algorithm (LEA) and Modified Least Significant Bit (MLSB) method for secured transmission is proposed. Moreover, a bilateral filter-based Whale Optimization Algorithm (WOA) is used for image denoising. Before image transmission, the secret image is encrypted by the LEA algorithm and embedded into the cover image using Discrete Wavelet Transform (DWT) and MLSB technique. After the image transmission, the extraction process is performed to recover the secret image. Finally, a bilateral filter-WOA is used to remove the noise from the secret image. The Verilog code for the proposed model is designed and simulated in Xilinx software. Finally, the simulation results show that the proposed filtering technique has superior performance than conventional bilateral filter and Gaussian filter in terms of Peak Signal to Noise Ratio (PSNR) and Structural Similarity Index Measure (SSIM)

Sliding wear studies of microwave clad versus unclad surface of stainless steel 304

Small and large scale (gas power plant, hydro power plant), automobile industries are suffering by failure of component. Sometimes, it is also observed that the component which was failed due to these reasons are very much costly and replacement of those also very difficult due to the complex geometry. By using Microwave hybrid heating, WC-12Co based clads were developed on austenitic stainless steel (SS304). Microwave clads were developed by introducing the preplaced, preheated powder for a duration of 15 min to microwave radiation at 2.45GHz frequency and 900 W power in domestic microwave applicator. By using optical microscope and scanning electron microscope (SEM), the developed clads were characterized. By using pin-on-disk, wear performance of the WC-12Co based clads and unclad samples were tested. It is observed that developed clad samples performed superior wear resistance than unclad samples

Congenital unilateral diaphragmatic eventration in adults – a case series with a brief literature review

Objective: The aim of this article was to present the results of thoracotomy performed in three symptomatic adult patients with congenital diaphragm eventration in the light of current literature data. Methods: Along with representation of the surgical management of each case, a brief review of literature was performed. Results and Conclusion:  Diaphragmatic eventration is a rare clinical entity that may be congenital or acquired. Surgery, which may be open or endoscopic, is the primary treatment modality for symptomatic patients

A Case of Hip Chondrosarcoma Metastasis to the Right Ventricle

Background. While primary cardiac tumors occur rarely, it is observed that cardiac metastases are almost 20 times more common. These are, however, observed during autopsy and seldom missed in living patients. Patients with cardiac metastases present commonly with dyspnea on exertion or pleuritic chest pain. Most common site of intracardiac metastases is right atrium. Case presentation. Here we present a case of a 21-year-old male who presented for a routine check-up to the cardiac outpatient department for assessment of fitness for chemotherapy. He was a known case of right hip chondrosarcoma for 2 years, being treated with Ayurvedic medications. He had no symptoms related to the respiratory or cardiac system. He was afebrile during the examination, however, was restricted to a bed due to the pain in his right hip. On evaluation, the patient was diagnosed with a right ventricular thrombus extending to the pulmonary artery (PA) causing an impending pulmonary embolism. On opening the right atrium and PA, we found a loose, whitish-grey mass, adherent to the right ventricular papillary muscle, entangling the chordae. The tricuspid valve leaflets were also found to be tethered to this mass. The mass was found to extend to the PA beyond the leaflets, however, the leaflets were free of the tissue. The mass was extracted piece-meal through right atrium and PA approach. Histopathology revealed metastatic chondrosarcoma tissue. Conclusion. Cardiac metastases of chondrosarcoma are a rare condition, and can be often asymptomatic. Such patients often present with dyspnea, and imaging may not be able to rightly identify the cause. A high index of suspicion is necessary in patients with a known current or prior malignancy before committing to surgical intervention

Left atrial myxoma as a rare cause of acute hemiplegia in an 8-year-old child

Objective: Myxomas are uncommon in the pediatric age group. However, acute cerebral infarcts in children are most often secondary to a myxoma. Early diagnosis is essential in such cases to prevent further such episodes, thereby decreasing the risk of permanent neurological deficits. In the pediatric age group, a high index of suspicion is required to diagnose such rare causes. Most myxomas are benign in nature, and hence surgery can offer complete curative resection and also help avoiding further incidents of cerebrovascular accidents (CVA). Here, we present an interesting case of an 8-year-old female child who presented with acute right-sided hemiplegia and was incidentally detected with a left atrial myxoma. Case presentation: An 8-year-old female presented to the emergency department with the complaint of loss of consciousness for 1 hour. There was no preceding history of trauma and no associated seizures.Computed tomography and magnetic resonance imaging of brain revealed an acute thalamic infarct and 2D echocardiography showed a mass lesion in the left atrium. Mass was excised, and histopathology confirmed it as a benign myxoma. Conclusion: Myxomas are a rare cause of CVA in children, making the diagnosis challenging. A high index of suspicion with a multidisciplinary approach is necessary for early diagnosis and appropriate management of such cases

Panoramic radiological study to identify locally displaced maxillary canines in Bangladeshi population

PURPOSE: This study was performed to determine the prevalence of maxillary canine impaction on a basis of a single panoramic radiograph in Bangladeshi population. MATERIALS AND METHODS: A random sample of seven hundred panoramic radiographs was collected from the patient record of a dental clinic. All the selected panoramic radiographs were taken from January 2009 to August 2010 by a single panoramic radiograph machine with the same exposure time (19 seconds) for all radiographs. One hundred and twenty panoramic radiographs were excluded to minimize the selection bias. In a dim lit room, an observer assessed the radiographs on a standard radiographic light box. The position of the impacted maxillary canine was recorded in line with the longitudinal axis of a tooth using the edge of a metal ruler. Data were subsequently put on SPSS 11.5 software and chi-square (χ(2)) tests were applied to find out the association. RESULTS: Among 580 panoramic radiographs it was found that impacted maxillary canines were present in only 7 (1.2%) radiographs. A statistical significant difference was found between the age of the patients and the vertical position of the impacted canines (p=0.000) and between the age of the patients and the horizontal position of the impacted canines (p=0.003). CONCLUSION: The prevalence was found to be low compared with the present study from the limitation of panoramic image. Further study needs to include three-dimensional imaging modality