Using time delay in the nonlinear oscillations of magnetic levitation for simultaneous energy harvesting and vibration suppression

In this paper, the nonlinear oscillations of magnetic levitation in the presence of a time delay is investigated, with the purpose of simultaneous energy harvesting and vibration suppression. To harvest energy, a coil with seven layers of 36 gauge wire wound around the outer casing is utilized. Although the proposed control feedback consumes some power, the results show the harvestable power can be much larger than the consumed power, which makes the proposed concept feasible. The first-order perturbation method is utilized to examine the possibility of energy harvesting and vibration suppression for different selections of the delay parameters, the distances between the magnets and the external load resistances. In addition, the stability map of the time-delayed control is analytically determined. The influence of the time delay parameters chosen from Single Periodic Solutions (SPS) and Multiple Periodic Solutions (MPS) on the vibration and power amplitudes is studied. It is shown that a point chosen from the MPS region enables the system to harvest power over a broad range of excitation frequencies. Also, the effect of the distance between the magnets on the frequency response of the system is examined. In addition, to select the optimum value for the distance between the magnets for different values of the time delay parameters, a parameter called the Perfection Rate (PR), which reflects both the electrical and mechanical behavior of the system, is used. Finally, it is shown that the presence of the time delay and a point chosen from the MPS region enables the system to harvest more power over a broad range of excitation frequency and to suppress higher levels of vibration, than for a point chosen from the SPS region and without time delay

Finding the buckling load of non-uniform columns using the iteration perturbation method

The aim of this study is to calculate the critical load of variable inertia columns. The example studied in this paper can be used as a paradigm for other non-uniform columns. The wavelength of equivalent vibratory system is used to calculate the critical load of the trigonometrically varied inertia column. In doing so, the equilibrium equation of the column is theoretically studied using the perturbation method. Accuracy of the calculated results is evaluated by comparing the solution with numerical results. Effect of improving the initial guess on the solution accuracy is investigated. Effects of varying parameters of the trigonometrically varied inertia and the uniformly tapered columns on their stability behavior are studied. Finally, using the so-called “perfectibility” parameter, two design goals, i.e., being lightweight and being strong, are studied for the discussed columns

Undifferentiated Pleomorphic Sarcoma Presenting as Abdominal Pain with a Pulsatile Mass

Malignant fibrous histiocytoma (MFH) is a rare tumor that mostly involves adults aged 50 to 70. The most common anatomic location is the lower extremities. MFH of the retroperitoneum usually manifests late in its course and may be initially mistaken with other more common diagnosis. Here, the authors describe a 60-year-old man that was brought to the emergency department with a chief complaint of periumbilical abdominal pain. Our patient presented with symptoms consistent with a symptomatic aortic aneurysm, but a mass was encountered during surgery. In such circumstances the diagnosis of malignant sarcoma must be kept in mind and attempts at full resection with tumor-free margins are necessary

Embolectomy For Acute Lower Limb Ischemia

In this prospective descriptive study, all patients with acute lower limb ischemia who presented to Shohada Tajrish Hospital (STH) between July 2001 and July 2003 were analyzed and followed for 6 months. The total population of 109 patients, with no significant difference in sexual distribution had a mean age of 64±16 years. 23% had AF and 31% had a history of MI, but in the ECG of 30%, no pathologic finding had been detected. Pain and coolness were the two most prevalent symptoms. Only one-third of the patients had normal sensory and motor examination in their limb and the rest had different degrees of impairment. More than 70% of the patients arrived here after 12 hours from the onset of the symptoms. Fasciotomy was done in 29%, and amputation in 23.5%. The mortality rate was 12.2%. Surgical site infection occurred in 11% and 14.1% underwent re-embolectomy. There was no pseudoaneurysms. The time interval from the onset, sensory and motor findings, and calf tenderness a! ffected the prognosis. Prognosis was better in smokers. The iatrogenic group which consisted of 13.7% of our patient population had the best prognosis (no mortality or morbidity). 4% of the patients who had first undergone embolectomy in other centers, all lost their limbs. In cases of late embolectomies, venotomy and heparin flush has lowered the amputation level without increasing mortality. Early referral by a cardiologist, receiving heparin rapidly and smoking are among the factors which improve prognosis

Necrolytic Migratory Erythema as the First Manifestation of Glucagonoma

Necrolytic migratory erythma (NME) as a rare skin disorder that can affected Perineum, distal extremities, lower abdomen and face are the most commonly affected sites.It can be as a part of Glucagonoma syndrome that is defined as an association of glucagonoma with NME, hyperglucagonemia, glucose intolerance, anemia and weight loss. Here, Authors describe a woman admitted to the dermatology ward with NME which was later found to be associated with glucagonoma and multiple hepatic lesions