Dynamics of Permanent-Magnet Biased Active Magnetic Bearings

Active magnetic radial bearings are constructed with a combination of permanent magnets to provide bias forces and electromagnets to generate control forces for the reduction of cost and the operating energy consumption. Ring-shaped permanent magnets with axial magnetization are attached to a shaft and share their magnet stators with the electromagnets. The magnet cores are made of solid iron for simplicity. A simplified magnetic circuit of the combined magnet system is analyzed with linear circuit theory by approximating the characteristics of permanent magnets with a linear relation. A linearized dynamical model of the control force is presented with the first-order approximation of the effects of eddy currents. Frequency responses of the rotor motion to disturbance inputs and the motion for impulsive forces are tested in the non-rotating state. The frequency responses are compared with numerical results. The decay of rotor speed due to magnetic braking is examined. The experimental results and the presented linearized model are similar to those of the all-electromagnetic design

Significance of Stabilometry for Assessing Postoperative Body Sway in Patients with Cervical Myelopathy

[Study Design] Prospective study. [Purpose] To examine the changes in body sway using stabilometry in patients who underwent cervical laminoplasty for cervical myelopathy. [Overview of Literature] Although the patients of cervical myelopathy complain body sway there are few report to examine body sway objectively. [Methods] Patients who received treatment for cervical myelopathy between October 2010 and February 2013 were included. Twenty-one patients underwent cervical laminoplasty (myelopathy group). Body sway was assessed using stabilometry, wherein patients stood on a stabilometer with their eyes closed for 30 seconds. The Romberg ratio, outer peripheral area (OPA) with eyes closed (cm2), and total locus length per unit area (L/A) with eyes closed (/cm) were examined. Examinations were performed preoperatively (at baseline) and at 8 weeks postoperatively. Examination results of patients in the myelopathy group were compared with those of 17 healthy individuals (control group). Clinical symptoms were evaluated using the Japanese Orthopaedic Association scale score (JOA score) and the timed up and go (TUG) test. [Results] In the myelopathy and control groups, the mean baseline Romberg ratio, OPA, and L/A were 2.3±1.2, 8.9±5.5 cm2, and 14.2±5.3/cm and 1.4±1.0, 4.3±2.8 cm2, and 23.7±10.1/cm, respectively. Eight weeks after laminoplasty, only L/A showed significant improvement from baseline in the myelopathy group (23.2±10.1 to 16.8±7.9; p=0.03). The Romberg ratio and OPA showed improvement in the myelopathy group, but the changes were not statistically significant. JOA scores and TUG test results in this group significantly improved from baseline to 8 weeks after laminoplasty (12.7 to 13.4 and 10.8 to 8.0 seconds, respectively; both p<0.05). [Conclusions] L/A is a useful parameter for measuring body sway to assess the recovery of body sway after laminoplasty

Effects of Sciatic Neurectomy on Arthritis and Bone Loss in Rats with Collagen-Induced Arthritis

We investigated the effects of sciatic neurectomy on arthritis and bone mineral density (BMD) in 7-month-old female Sprague-Dawley rats with collagen-induced arthritis (CIA). After the animals obtained a uniform mean body weight, we divided them at random into 4 groups, and treated them with the following surgical manipulations: (i) sham group (n = 8), sham surgery; (ii) CIA group (n = 9), collagen sensitization and sham surgery; (iii) NTx group (n = 9), sciatic neurectomy and (iv) CIA + NTx group (n = 9), collagen sensitization and a sciatic neurectomy. Every 2 weeks up to 8 weeks after sensitization, the arthritis score for hind paw swelling was evaluated, and BMD of the cancellous and cortical bones in the proximal tibia was measured by peripheral quantitative computed tomography (pQCT). Both the hind paw swelling and arthritis score in the CIA + NTx group were significantly lower than those in the CIA group at 6 and 8 weeks after sensitization. There was no significant difference in the cancellous BMD between the CIA and CIA + NTx groups. The cortical BMD of the tibial metaphysis was significantly lower in the NTx and CIA + NTx groups than in the sham group at 4 and 8 weeks, and in the CIA + NTx group than in the CIA group at 4 weeks after sensitization. There was no significant difference between the CIA and sham groups as well as the CIA and CIA + NTx group at 8 weeks after sensitization. It was concluded that sciatic neurectomy suppressed the severity of arthritis, but did not affect the cancellous bone loss in adult CIA rats

Influence of Diabetes Mellitus on Surgical Outcomes in Patients with Cervical Myelopathy: A Prospective, Multicenter Study

[Study Design] Multicenter, prospective study. [Purpose] To investigate the effects of diabetes mellitus (DM) on surgical outcomes in patients with cervical myelopathy. [Overview of Literature] To date, few studies have investigated the influence of postoperative blood glucose or glycated hemoglobin (HbA1c) levels on surgical outcomes. [Methods] The participants were patients who underwent surgery for the treatment of cervical spondylotic myelopathy and ossification of the posterior longitudinal ligament. The 61 cases were evaluated preoperatively and 1 year postoperatively using the Japanese Orthopaedic Association (JOA) scores and the JOA Cervical Myelopathy Evaluation Questionnaire (JOACMEQ). The study variables included fasting blood glucose and HbA1c levels measured preoperatively and at 1 week, 4 weeks, and 1 year postoperatively; the F-wave conduction velocity, latency, rate of occurrence, and M-wave latency in the ulnar and tibial nerves were measured preoperatively and at 1 year postoperatively. The patients were divided into a group without diabetes (N group, 42 patients) and a group with diabetes (DM group, 19 patients). We then assessed the associations between the surgical outcomes and each of the study variables. [Results] JOA scores significantly improved in both groups; however, no significant between-group differences were found. There was no significant improvement in the JOACMEQ scores, which assessed cervical function, upper and lower limb function, and bladder function in both groups. We then subdivided the DM group into those with a good control of HbA1c after 1 year (DMG group, 12 patients) and those with HbA1c deterioration after 1 year (DMB group, seven patients), prior to comparing the surgical outcomes. The JOACMEQ scores for upper and lower limb function significantly improved in the DMG group (p<0.01). Compared with the DMB group, there were no significant increases in upper or lower limb function scores in the DMG group. [Conclusions] Poor glycemic control might prevent postoperative functional recovery of the spinal cord

Dynamics of Active Magnetic Thrust Bearings

A linear model considering the effect of eddy currents is shown to be useful for the analysis of the dynamics of active magnetic thrust bearings in which electromagnet cores are composed of solid steel. The dynamics of the magnetic control force are modeled by the first-order time-lag system with unknown parameters : gain and time constant. The parameters are estimated from experimental results that indicate the static relation between the coil current and the magnetic control force, and the frequency response of magnetic flux for an input signal to a power amplifier. The effect of eddy currents on the dynamics is confirmed by the frequency characteristlcs of magnetic flux for the coil current. Model simulations with estimated parameters are compared with experimental results, and good agreement is obtained in frequency response in a linear range and in impulse responses with rotor displacements smaller than half the air gap

Electrochemical design of two-dimensional Au nanocone arrays using porous anodic alumina membranes with conical holes

We report step-by-step electrochemical design of two-dimensional (2D) Au nanocone arrays by using novel porous anodic alumina membranes with conical holes. The cones with desirable aspect ratios can be fabricated by using the PAA templates with different aspect ratios. The Au nanocone arrays show high potentials as SERS (Surface Enhanced Raman Scattering)-active substrates and Au electrodes with high surface area

Industrial mass-production of mesoporous silica spherical particles by a spray-drying process: investigation of synthetic conditions

A spray-drying process was applied to the mass-production of mesoporous silica particles. The applied nozzle pressure and amount of solvent in the precursor solution were varied to control the average particle size. The particle-size distribution showed a bell curve with a normal distribution. As the nozzle pressure was increased from 0.05 to 0.20 MPa, the average particle size was decreased proportionally. In addition, as the surfactant concentrations in the precursor solutions were decreased, the average particle size was decreased. Based on the results of low-angle X-ray diffraction measurements, N-2 adsorption measurements, and TEM observations, it was proven that well-ordered mesoporous structures were formed inside the particles. It is proved that the spray-drying conditions do not affect the mesoporous structures but do affect the average particle size. (C) 2009 The Ceramic society of Japan. All rights reserved