In this work, we address the problem of damage diagnosis on the railway pantograph mechanism including nonlinear behaviour and sample-induced uncertainties. In particular, we discuss an experimental ...campaign in which investigation pursued the analysis of frequency response functions estimated by a dedicated inspection robot that we intentionally developed for vibration tests on pantographs. Special focus is pointed to the inherent nonlinear behaviour of the pantograph for which we estimated the damage index for different levels of the input excitation. The investigation is carried out on a population of pantographs of the same type and studying three kinds of damages. Results highlight the relevance of including several excitation levels and encourage investigation in a real operational scenario.
Abstract Management of non-emergent, non-acute subdural hematomas (SDHs) ranges from observation to burr-hole evacuation or craniotomy, but recurrence rates are high. We evaluated the safety and ...efficacy of tranexamic acid (TXA) for the treatment of residual SDHs following bedside twist-drill evacuation. We performed a retrospective analysis of a prospectively maintained database from November 2013 to November 2014 for all patients who underwent placement of a bedside Subdural Evacuating Port System (SEPS) followed by treatment with oral TXA (650 mg daily). All demographics, evidence of VTE and volumes of pertinent CTs were obtained. Twenty subdural hematomas in 14 patients met the inclusion criteria for this study. The majority of SDHs were mixed density. Mean SDH volume on presentation was 145.96 cm3 +/- 40.22 with a mean midline shift of 9.44 mm +/- 4.84. Mean volumes decreased to 80.00 cm3 +/- 31.96, and midline shift improved to 4.44 mm +/- 3.29, after SEPS placement (p < 0.0001 and p = 0.0046). All patients were placed on TXA after their procedure. Mean follow-up with CT was 92.1 days +/- 27.5, and mean SDH volume at last follow-up was 7.41 cm3 +/- 15.54 with a mean midline shift of 0.19 mm +/- 0.69 (p < 0.0001 and p = 0.0002). Percent volume reduction was significantly higher after TXA than after SEPS (91.31% versus 40.74%, p < 0.0001). No increase or delayed recurrence of the SDH was noted during TXA treatment. All but one clinical presenting symptom improved at follow-up. No venous thromboembolisms were noted amongst the patients. In our pilot study, chronic SDH volumes were reduced by 40.74% after SEPS drainage. The residual volume was reduced by an additional 91.31% during oral TXA treatment. No patients developed delayed recurrence or expansion of their SDHs. Further prospective studies are needed to evaluate the role of TXA for adjunctive treatment of chronic SDHs.
This paper presents a novel method based on screw theory for the analysis of position accuracy in spatial parallel manipulators with revolute joint clearances. The method is general, and can tackle ...with an arbitrary pose error function, expressed as a quadratic function of the end-effector displacement.
The method performs a maximization of the pose error function, based on a 2-step computational procedure. The first computational step is analytical and leads to a sub-optimal estimate of the maximum pose error. This analytical solution represents the exact maximum pose error for the calculus of the angular accuracy in the special case of fully translational parallel mechanisms. The second computational step is numerical, and starting from the previous solution, can converge to the exact maximum pose error in a limited number of iterations.
The relevance of the method is demonstrated through some application examples, where the worst-case angular and linear position accuracy in translating fully parallel manipulators is determined. As a further contribution, this paper shows how the position accuracy due to joint clearances in parallel manipulators is strictly dependent of the mechanism pose and its association to kinematic isotropy.
► Position accuracy in parallel manipulators with revolute joint clearances. ► Analysis by screw theory of joint clearances in parallel manipulators. ► Analytical solution of angular accuracy in translational parallel mechanisms. ► Effect of kinematic isotropy on the position accuracy of parallel manipulators.
This paper presents a novel haptic device providing both kinesthetic and cutaneous cues informative of shape geometry at the contact point. The system is composed of a supporting kinesthetic haptic ...interface and an innovative fingertip haptic display that can instantaneously orient a small plate along the tangent plane at the contact point with a virtual shape and bring it in contact with the fingertip. We show how this local augmentation of displayed haptic information can improve human performance in shape exploration, by assessing perception thresholds in curvature discrimination. When kinesthetic feedback was enriched with cutaneous cues, we found a significantly lower threshold for curvature discrimination (1.51 ± 0.2 m
vs. 2.62 ± 0.61 m
,
< .05) for stimuli constituted of spheres with curvature ranging in the interval from 4–6 m
. This confirms the importance in haptic perception of the stimulation of cutaneous mechanoreceptors at the fingertip.
An approach to the dynamic analysis of parallel manipulators is presented. The proposed method, based on the theory of screws and on the principle of virtual work, allows a straightforward ...calculation of the actuator forces as a function of the external applied forces and the imposed trajectory. In order to show the generality of such a methodology, two case studies are developed, a 2-DOF parallel spherical mechanism and a Gough–Stewart platform.
The anterior and posterior communicating arteries are natural connections between arteries that enable different adjacent circulations to redistribute blood flow instantly in response to changing ...supply and demand. An analogous communication does not exist in the middle cerebral circulation. A middle communicating artery (MCoA) can be created microsurgically between separate middle cerebral artery (MCA) trunks, enabling flow to redistribute in response to changing supply and demand. The MCoA would draw blood flow from an adjacent circulation such as the external carotid circulation. The MCoA requires the application of fourth-generation techniques to reconstruct bi- and trifurcations after occluding complex MCA trunk aneurysms. In this report, the authors describe two recent cases of complex MCA bi- and trifurcation aneurysms in which the occluded efferent trunks were revascularized by creating an MCoA. The first MCoA was created with a "double-barrel" superficial temporal artery-M2 segment bypass and end-to-end reimplantation of the middle and inferior MCA trunks. The second MCoA was created with an external carotid artery-radial artery graft-M2 segment interpositional bypass and end-to-side reimplantation of the inferior trunk onto the superior trunk. Both aneurysms were occluded, and both patients experienced good outcomes. This report introduces the concept of the MCoA and demonstrates two variations. Angioarchitectural and technical elements include the donation of flow from an adjacent circulation, a communicating bypass, the application of fourth-generation bypass techniques, and a minimized ischemia time. The MCoA construct is ideally suited for rebuilding bi- and trifurcated anatomy after trapping or distally occluding complex MCA aneurysms.
The discriminating ability and relevance of clinical risk factors, quantitative ultrasound (QUS) variables, X-ray-based bone mineral density (BMD) and hip axis length (HAL) measurements to evaluate ...the risk of osteoporotic fracture in elderly Brazilian women were examined in this study. QUS at the calcaneus (Achilles +, Lunar), HAL and BMD measurements (DPX-L, Lunar) at several anatomical sites were performed in 275 postmenopausal Caucasian women. Patients with suspected secondary osteoporosis were excluded. One hundred twenty-two (44.4%) women had had previous osteoporotic fracture. All of the subjects were over 50 years old (range 53-93) and answered a questionnaire that included details concerning aspects of lifestyle, diet, hormonal factors and drug use. Lateral thoracic and lumbar radiographs were taken and an independent radiologist reviewed the X-rays for the presence of vertebral fractures. After adjustments for age, the most relevant risk factors to discriminate patients with osteoporotic fracture from normal non-fracture controls were Stiffness index (OR 2.8 per standard deviation; 95% confidence interval 2.3, 8.7), familial history of hip fracture (OR 2.6 per standard deviation; 95% confidence interval 2.2, 5.4), femoral neck BMD (OR 2.3 per standard deviation; 95% confidence interval 1.9, 4.2), age (OR 2.1 per standard deviation; 95% confidence interval 1.6, 2.8) and weight (OR 1.9 per standard deviation; 95% confidence interval 1.5, 2.6). HAL measurements did not associate significantly with the risk of hip fracture in this population. The ability of QUS measurements discriminate between patients with fractures from those without was similar to, if not better, than X-ray-based BMD measurements. However, a combination of QUS and BMD measurements did not significantly improve fracture discrimination compared with either technique alone. Association of clinical risk factors with QUS or BMD measurements seems, on the other hand, to increase the sensibility to identify patients at risk of osteoporotic fractures.
Methods. In a randomized, double-blind, placebo-controlled clinical trial, we evaluated the effect of a 2-year treatment with nandrolone decanoate (ND) on bone mineral density (BMD) of lumbar spine, ...femoral neck, and trochanter and on vertebral fracture rate, muscle mass, and hemoglobin levels. Sixty-five osteoporotic women older than 70 years were studied. Thirty-two patients received injections of 50 mg ND, and 33 received placebos every 3 weeks. All patients received 500 mg calcium tablets daily. Results. Compared to baseline, ND increased the BMD of the lumbar spine (3.4% ± 6.0 and 3.7% ± 7.4; p <.05) and femoral neck (4.1% ± 7.3 and 4.7% ± 8.0; p <.05) after 1 and 2 years, respectively. The BMD of trochanter increased significantly only after the first year (4.8% ± 9.3, p <.05). Compared to the placebo group, the ND group presented with significantly increased BMD of the trochanter and neck. ND significantly reduced incidence of new vertebral fractures (21% vs 43% in the placebo group; p <.05). ND showed a significant statistical increase in lean body mass after the first (6.2% ± 5.8; p <.01) and second years (11.9% ± 29.2; p <.01). In addition, a 2-year treatment with ND significantly increased hemoglobin levels compared to baseline (14.3%; p <.01) and placebo (p <.01). Conclusions. ND increased BMD, hemoglobin levels, and muscle mass, and reduced the vertebral fracture rate of elderly osteoporotic women.
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