Ball screws are robust and economical linear positioning systems widely employed in high-speed and high-precision machines. Due to precision and stability requirements, the preload force is ...considered one of the main parameters defining the axial stiffness and the maximum axial load of the ball screw feed drives. In high-speed motions, thermal effects are also considerably relevant regarding positioning precision and dynamic stability of the machine. The temperature increase and the thermal gradient between the screw, the balls and the nuts result in geometrical variations and, consequently, variations in the preload force. This paper presents a numerical modelling strategy to predict the preload variation due to temperature increase using a thermo-mechanical 3D finite element method (FEM)-based model for double nut-ball screw drives. Two different thermo-mechanical coupling strategies are compared, and the obtained results are validated with experimental measurements for different initial preload and linear speeds. In the mechanical analysis, the nut-screw ball contact interface, the offset-based preloading and the restrictions of the ball bearings are included in the model, while the thermal analysis considers heat generation and heat diffusion. The causes of the thermal preload variation are discussed considering the ball load distribution and the axial and radial thermal displacements of the contacting points.
Anatomically, viral density is greater in the nasal cavity and the nasopharynx. It is to be expected that instrumentation in or through those areas will entail a higher risk of transmission. That's ...why head and neck and otolaryngologist surgeons are among the most vulnerable health professionals.
Surgeons should essentially perform procedures they require. Surgeries should be performed with personal protective equipment suitable for the high risk of aerosolization: goggles, N95 face mask, facial mask, blood-repelling gown and gloves. It is advisable to have the cooperative COVID-19 test in all patients. Telemedicine is a useful resource if resources allow it.
Otolaryngologists and related specialists are among the groups at higher risk when performing surgeries and upper airway examinations. There are no emergencies in a pandemic. The care of health professionals is crucial to combating this health situation.
An accurate preoperative evaluation of the vascular anatomy of the abdominal wall is extremely valuable in improving the surgical strategy in abdominal perforator flaps. The multidetector-row ...computer tomography offers thin slice coverage of extended volumes with an extremely high spatial resolution. From October 2003 to December 2004, 66 female patients had breast reconstruction surgery in our department using the deep inferior epigastric artery perforator flap. Our multidetector-row computer tomography studies were performed using a 16-detector-row computer tomography scanner. The image assessment was carried out using the following protocol: we first identified the best three perforators from each side of the abdomen. Then we conducted a three-dimensional reconstruction of the abdomen by identifying exactly where the three best perforators emerged from the rectus abdominis fascia. We then transferred the data obtained from the image to the patient using a coordinate system. In addition, we also placed the dominant perforators in the patient by using a conventional hand-held Doppler. During the operation we compared intra-operative findings, Doppler results and computer tomography outcomes. Neither false positive nor false negative results were found in the computer tomography outcome. Multidetector-row computer tomography provides us with an easy method of interpreting the virtual anatomic dissection in three dimensions. It has high sensitivity and specificity and provides a good quality evaluation of the perforator vessels. This information allows reduction of operating time and safer performance of surgery. The multidetector-row computer tomography is a highly effective tool in the preoperative study of abdominal perforator flaps.
Radial fretting is defined as the damage caused by the relative motion of a ball under a variable normal load. The conducted experimental tests proved the existence of this damage even in contacting ...bodies with similar materials and elastic properties; however, the reviewed analytical methods do not predict damage under these conditions, and the numerical methods are time-consuming, especially when the investigation requires the analysis of several loading cases or during large number of cycles. The main objective of this work was to develop a fast analytical method to analyse radial fretting wear. For this purpose, a novel formulation for contact displacements under a normal variable load was built and merged to different contact mechanic formulas. For validation purposes, false brinelling in thrust bearings was used as a representative industrial example. The results were compared with a FEM model showing a relative difference under 9% and a massive reduction of the calculation time of more than 30 000 times, moreover experimental tests were carried out, showing a good agreement between the density of friction energy and the obtained fretting damage what endorse the use of this formulation for the analysis of a large number of cycles and loading cases.
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•An analytical new formulation for radial fretting wear simulation.•An experimental and numerical validation of the proposed methodology.•An industrial application to false brinelling in stationary thrust bearings under variable loading conditions.•An alternative fretting method to FEM simulations with a massive time reduction of 30 000 times.
Opioids are often the mainstay of postoperative pain management, despite strong evidence of their ill effects and potential for long-term addiction. The goal of this study was to quantify opioid use ...and contrast pain management strategies of multiple international institutions performing fibula free flap reconstruction. A retrospective multicenter cohort study was designed, including five international centers. For inclusion, the patients had to have undergone a primary fibula free flap reconstruction of the mandible. A total of 185 patients were included. The median opioid use across all centers at 72 hours was 133 oral morphine equivalents. The highest utilization was in the USA (P < 0.001), which was approximately six times that of Italy, four times that of Argentina, and twice that of India, despite all centers performing a similar procedure. Based on this study there are clear differences in prescribing practices and ideologies among surgeons from different countries.
Trivalent 2-stratifolds
X
with finite homology groups can be encoded as bicolored trivalent graphs
Γ
. We show that the homeomorphism problem for such stratifolds can be solved with complexity
O
(||
...V
||), where
V
is the set of vertices of
Γ
.
Therapy with cationic amphiphilic drugs (Amiodarone or hydroxychloroquine) may result in biochemically and ultrastructurally similar lipid inclusions in many cells also affected by Fabry disease ...(FD). In addition, it often results in similar clinical manifestations such as cornea verticillata. This may lead to a FD misdiagnosis, especially when a complete medical history is not available to the ophthalmologist confronted with cornea verticillata or to the pathologist examining a kidney biopsy. When enzymatic/genetic test or pathological studies are not conclusive, a specific biomarker may help clarify this dilemma. The plasma globotriaosylsphingosine (lyso-Gb3) assay has high sensitivity and specificity and is elevated above normal levels in FD.
We measured plasma lyso-Gb3 levels in male patients receiving Amiodarone or hydroxychloroquine and compared it with male patients with classic and late onset variant of FD.
In all Fabry patients (classic and late onset variant) α-GalA activity was deficient in dried blood spot and plasma lyso-Gb3 was above normal levels. Patients on treatment with Amiodarone or hydroxychloroquine had normal values for α-GalA activity and lyso-Gb3 in plasma.
Even when Amiodarone or hydroxychloroquine may decrease α-GalA activity in vitro or in cell culture, our results showed that in all patients lyso-Gb3 plasma levels remain normal with no evidence of reduction in α-GalA activity, confirming the specificity of this biomarker for the diagnosis of FD.
•Some drugs may result in similar lipid inclusions in cells also affected by Fabry disease.•In Fabry male patients' plasma lyso-Gb3 was above normal levels.•lyso-Gb3 plasma levels remain normal in Amiodarone and hydroxychloroquine users.•These results support the high specificity of this biomarker for the diagnosis of Fabry disease.
2-stratifolds with fundamental group Z Gómez-Larrañaga, J.C.; González-Acuña, F.; Heil, Wolfgang
Topology and its applications,
03/2021, Letnik:
290
Journal Article
Recenzirano
2-stratifolds are a generalization of 2-manifolds that occur as objects in applications such as in TDA. These spaces can be described by an associated bicoloured labelled graph. In previous papers we ...obtained a classification of 1-connected trivalent 2-stratifolds. In this paper we classify trivalent 2-stratifolds that have fundamental group Z. This classification implicitly gives an efficient algorithm that applies to a bicoloured labelled graph to decide whether the associated 2-stratifold has fundamental group Z.
Trivalent 2-stratifolds are a generalization of 2-manifolds in that there are disjoint simple closed curves where three sheets meet. We develop operations on their associated labeled graphs that will ...effectively construct from a single vertex all graphs that represent simply connected trivalent 2-stratifolds.
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