Improving robustness of tuned vibration absorbers using shape memory alloys

Abstract. A conventional passive tuned vibration absorber (TVA) is effective when it is precisely tuned to the frequency of a vibration mode; otherwise, it may amplify the vibrations of the primary system. In many applications, the frequency often changes over time. For example, adding or subtracting external mass on the existing primary system results in changes in the system's natural frequency. The frequency changes of the primary system can significantly degrade the performance of TVA. To cope with this problem, many alternative TVAs (such as semiactive, adaptive, and active TVAs) have been studied. As another alternative, this paper investigates the use of Shape Memory Alloys (SMAs) in passive TVAs in order to improve the robustness of the TVAs subject to mass change in the primary system. The proposed SMA-TVA employs SMA wires, which exhibit variable stiffness, as the spring element of the TVA. This allows us to tune effective stiffness of the TVA to adapt to the changes in the primary system's natural frequency. The simulation model, presented in this paper, contains the dynamics of the TVA along with the SMA wire model that includes phase transformation, heat transfer, and the constitutive relations. Additionally, a PID controller is included for regulating the applied voltage to the SMA wires in order to maintain the desired stiffness. The robustness analysis is then performed on both the SMA-TVA and the equivalent passive TVA. For our robustness analysis, the mass of the primary system is varied by ± 30% of its nominal mass. The simulation results show that the SMA-TVA is more robust than the equivalent passive TVA in reducing peak vibrations in the primary system subject to change of its mass

Application of Magneto-Rheological Fluids for Investigating the Effect of Skin Properties on Arterial Tonometry Measurements

Accurate, non-invasive measurements of blood pressure and its continuous monitoring are extremely important for personal health care. Arterial tonometry, a method that is used to provide a detailed image of a patient's cardiovascular health, shows promise for being a non-invasive alternative to current blood pressure measurement methods. However, its measurement accuracy is sensitive to patient variations such as the stiffness of the skin. Thus, this project intends to investigate the effect of skin properties (i.e., stiffness) on the accuracy of tonometric blood pressure measurements. To this end, a test platform, consisting of a pulsatile system and a tunable skin stiffness apparatus (or MR apparatus), is constructed. The cam-follower pulsatile system built based on in vivo testing of human pulses is used to generate realistic pulse waveforms. The MR apparatus is able to adjust its stiffness using Magneto-Rheological (MR) fluid whose apparent viscosity changes with applied magnetic fields. Placed at the surface of the MR apparatus, a cylinder with a frictionless plunger simulates a variable applanation force or “hold-down pressure” of tonometry by adjusting the added weights atop the cylinder. Using this test setup, a series of tests were performed by varying the input magnetic field and the weights, which effectively adjusts the skin stiffness and the hold-down pressure, respectively. The vertical displacement of the plunger caused by the internal pulse pressure was measured using a laser displacement sensor. The output displacement waveforms were analyzed with the focus on the peak amplitude difference of the waveforms, which is related to the augmentation index (a surrogate measure of arterial stiffness). The results show that there exists an “optimal” plunger weight or “hold-down pressure” that provides the most distinct output pulse waveforms. The results further show that the difference in the first two peak values decreases as the skin stiffness increases, indicating that the stiffer the skin property, the less the “hold-down pressure” effects on the accuracy of the tonometry measurements

Femoral Head Fracture without Dislocation by Low-Energy Trauma in a Young Adult

We describe the case of a healthy young man with a femoral head fracture by low-energy trauma that occurred without evidence of hip dislocation. While plain radiographs showed no definite fracture or dislocation, computed tomography (CT) and magnetic resonance imaging (MRI) revealed a femoral head fracture with a wedge-shaped cortical depression at the superomedial aspect of the femoral head. Our patient reported feeling that the right hip had been displaced from its joint for a moment. This probably represented subluxation with spontaneous relocation. The characteristic findings and possible mechanisms of this fracture were postulated on the basis of the sequential 3 dimensional-CT and MRI. The clinical results of conservative treatment were better than those of previously reported indentation fractures

Fate of untreated asymptomatic osteonecrosis of the femoral head

BACKGROUND: Magnetic resonance imaging has made it possible to detect asymptomatic lesions of osteonecrosis of the femoral head before abnormalities appear on plain radiographs. The extent of a necrotic lesion is known to be an important prognostic factor. In this study, we evaluated the fate of untreated asymptomatic osteonecrosis of the femoral head with an emphasis on the size of the lesion. We hypothesized that a lesion smaller than a certain size would not progress to symptomatic disease. METHODS: One hundred and five initially asymptomatic hips of patients with bilateral nontraumatic osteonecrosis of the femoral head who had been followed without any treatment for at least five years or until pain developed were enrolled in this study. The extent of a lesion was estimated according to the area of the lesion based on a two-dimensional analysis on magnetic resonance images or on plain radiographs at the time of diagnosis. RESULTS: Sixty-two hips became symptomatic, and forty-three hips remained asymptomatic for more than five years (average, eight years and seven months). Of the twenty-one hips with a small necrotic lesion (50% of the area of the femoral head), fifty became painful. Forty-six of the sixty-two hips that became symptomatic required surgery. Pain developed within five years after the diagnosis in fifty-eight (94%) of the sixty-two symptomatic hips. CONCLUSIONS: No treatment appears to be necessary for asymptomatic necrotic lesions with an area smaller than 30% of the femoral head, as the vast majority of these lesions will remain asymptomatic for more than five years

Isolated fracture of the ceramic head after third-generation alumina-on-alumina total hip arthroplasty

BACKGROUND: While most reports of component fracture following alumina-on-alumina total hip arthroplasty have involved the acetabular liner, few have involved fracture of the alumina femoral head. In the present multicenter study, we investigated ceramic head fractures in a cohort of patients who underwent third-generation alumina-on-alumina total hip arthroplasty. METHODS: We performed a retrospective study of 312 patients (367 hips) who underwent alumina-on-alumina total hip arthroplasty without cement at four participating centers with the use of a 28-mm BIOLOX forte femoral head and a BIOLOX forte liner from July 2001 to October 2003. Three hundred and five patients (359 hips) were evaluated at a mean of forty-five months postoperatively. Clinical follow-up with use of the Harris hip score and radiographic evaluation were performed at six weeks; at three, six, and twelve months; and every six months thereafter. Retrieved ceramic implants were examined by means of visual inspection. RESULTS: Five hips (1.4%) in five patients were revised because of a ceramic head fracture during the follow-up period. The ceramic head fractures occurred during normal daily activities at a mean of 22.6 months postoperatively. A short neck had been used in all five hips in which a fracture occurred, compared with 121 (34.2%) of the 354 hips in which a fracture did not occur (p = 0.009). The fracture involved a circular crack along the circumference of the thinnest portion of the head component at the proximal edge of the bore. The fracture also involved multiple vertical cracks extending radially along the longitudinal axis from the circumference of the circular crack line to the lower edge of the head component. CONCLUSIONS: In the present study, the rate of ceramic head fracture associated with one design of a short-neck modular alumina femoral head was 1.4% (five of 359). The extent to which these findings are generalizable to other designs that utilize this type of femoral head is unknown

Alumina-on-Alumina Total Hip Arthroplasty A Concise Follow-up, at a Minimum of Ten Years, of a Previous Report

We previously reported the five-to-six-year results of the use of third-generation alumina-on-alumina bearings in a consecutive series of 100 primary cementless total hip arthroplasties. This report presents the longer-term outcomes of these same bearings, at a minimum of ten years postoperatively. Eighty-six of eighty-eight hips available for the study retained the original bearings at the time of the latest follow-up. Thirteen hips were associated with noise, and six hips demonstrated fretting of the femoral neck on radiographs. Two hips required a change of the bearings because of a ceramic head fracture. The ten-year survival rate of the alumina-on-alumina total hip prostheses, with revision of any implant for any reason as the end point, was 99.0%. On the basis of those results, we concluded that the rate of survival of primary cementless total hip prostheses with third-generation alumina-on-alumina bearings is excellent at ten years. However, the risk of ceramic fracture, noise, and impingement between the metal neck and the ceramic liner should be a concern to surgeons, and patients should be informed of these risks before surgery.Koo KH, 2008, J BONE JOINT SURG AM, V90A, P329, DOI 10.2106/JBJS.F.01489Sugano N, 2007, J BONE JOINT SURG BR, V89B, P455Yoo JJ, 2005, J BONE JOINT SURG AM, V87A, P530, DOI 10.2106/JBJS.D01753Allain J, 1998, J BONE JOINT SURG AM, V80A, P1355Joshi RP, 1998, J BONE JOINT SURG BR, V80B, P585MARTELL JM, 1993, J BONE JOINT SURG AM, V75A, P554MALONEY WJ, 1990, J BONE JOINT SURG AM, V72A, P1025BELLAMY N, 1988, J RHEUMATOL, V15, P1833ENGH CA, 1987, J BONE JOINT SURG BR, V69, P45SARMIENTO A, 1985, J BONE JOINT SURG AM, V67A, P48GRUEN TA, 1979, CLIN ORTHOP RELAT R, P17DELEE JG, 1976, CLIN ORTHOP RELAT R, P20HARRIS WH, 1969, J BONE JOINT SURG AM, VA 51, P737KAPLAN EL, 1958, J AM STAT ASSOC, V53, P457

Alumina-on-alumina total hip arthroplasty. A five-year minimum follow-up study

BACKGROUND: Ceramic-on-ceramic couplings are attractive alternative bearing surfaces that have been reported to eliminate or reduce problems related to polyethylene wear debris. Disappointing experiences with alumina ceramic bearings in the past have led to many improvements in the manufacture and design of ceramic implants. The purpose of the present study was to report the results of contemporary alumina-on-alumina total hip arthroplasties with regard to wear, osteolysis, and fracture of the ceramic after a minimum duration of follow-up of five years. METHODS: We evaluated the results of a consecutive series of 100 primary alumina-on-alumina total hip arthroplasties that had been performed with use of a metal-backed socket and a cementless stem in eighty-four patients. All of the patients were sixty-five years of age or younger (mean age, forty-one years), and a single surgeon performed all of the procedures. After a minimum duration of follow-up of sixty months, one patient (one hip) had died and four patients (six hips) had been lost to follow-up, leaving a total of seventy-nine patients (ninety-three hips) available for study. All of these patients were evaluated clinically and radiographically with special attention to wear, periprosthetic osteolysis, and ceramic failure. RESULTS: The mean Harris hip score was 97 points at the time of the latest follow-up evaluation. All prostheses demonstrated radiographic evidence of bone ingrowth. No implant was loose radiographically, and no implant was revised. Ceramic wear was not detectable in the thirty-seven hips in which the femoral head could be differentiated from the cup on radiographs. Periprosthetic osteolysis was not observed in any hip. A fracture of the alumina femoral head and a peripheral chip fracture of the alumina insert occurred in one hip following a motor-vehicle accident. CONCLUSIONS: The results of contemporary alumina-on-alumina total hip arthroplasty with a metal-backed socket and a cementless stem were encouraging after a minimum duration of follow-up of five years. We believe that these improved alumina-on-alumina bearing implants offer a promising option for younger, active patients

Liver-Specific Deletion of Mouse CTCF Leads to Hepatic Steatosis via Augmented PPARγ Signaling

Background & Aims: The liver is the major organ for metabolizing lipids, and malfunction of the liver leads to various diseases. Nonalcoholic fatty liver disease is rapidly becoming a major health concern worldwide and is characterized by abnormal retention of excess lipids in the liver. CCCTC-binding factor (CTCF) is a highly conserved zinc finger protein that regulates higher-order chromatin organization and is involved in various gene regulation processes. Here, we sought to determine the physiological role of CTCF in hepatic lipid metabolism. Methods: We generated liver-specific, CTCF-ablated and/or CD36 whole-body knockout mice. Overexpression or knockdown of peroxisome proliferator-activated receptor (PPAR)γ in the liver was achieved using adenovirus. Mice were examined for development of hepatic steatosis and inflammation. RNA sequencing was performed to identify genes affected by CTCF depletion. Genome-wide occupancy of H3K27 acetylation, PPARγ, and CTCF were analyzed by chromatin immunoprecipitation sequencing. Genome-wide chromatin interactions were analyzed by in situ Hi-C. Results: Liver-specific, CTCF-deficient mice developed hepatic steatosis and inflammation when fed a standard chow diet. Global analysis of the transcriptome and enhancer landscape revealed that CTCF-depleted liver showed enhanced accumulation of PPARγ in the nucleus, which leads to increased expression of its downstream target genes, including fat storage-related gene CD36, which is involved in the lipid metabolic process. Hepatic steatosis developed in liver-specific, CTCF-deficient mice was ameliorated by repression of PPARγ via pharmacologic blockade or adenovirus-mediated knockdown, but hardly rescued by additional knockout of CD36. Conclusions: Our data indicate that liver-specific deletion of CTCF leads to hepatosteatosis through augmented PPARγ DNA-binding activity, which up-regulates its downstream target genes associated with the lipid metabolic process. © 2021 The Authors1