关键词： Stability   Delays   Torque   Galerkin method   Weight (Mass)   Rocks   Modeling   Trajectories (Physics)   Cutting   Drill strings   Equations of motion   Polycrystalline diamond compact bits   Vibration  

摘要： This work describes an alternative formulation of a system of nonlinear state-dependent delay differential equations (SDDDEs), which governs the coupled axial-torsional vibrations of a 2 DOF drillstring model with a realistic representation of polycrystalline diamond compact (PDC) bits. The regenerative effect associated with the complex cutter layout for such bits can introduce up to 100 state-dependent delays in the equations of motion. This large number of state-dependent delays renders the computational efficiency of conventional solution strategies unacceptable. The regeneration of the bottom-hole surface can alternatively be described by the bit trajectory function, whose evolution is governed by a partial differential equation (PDE). Thus the original system of SDDDEs can be replaced by a nonlinear coupled system of a PDE and ordinary differential equations (ODEs). Via the application of the Galerkin Method, this system of PDE-ODEs is transformed into a system of coupled ODEs, which can readily be solved. The algorithm is further extended to perform a linear stability analysis of the bit motion. The resulting stability boundaries are verified with time-domain simulations. The reported algorithm could, in principle, be applied to a more realistic drillstring model, which may lead to an in-depth understanding of the mitigation of self-excited vibrations through PDC bit designs.

关键词： adipofascial tissue   bridge principle   digital artery perforator flaps   digital propria artery   dorsal perforators   indirect transfer  

摘要： Background Dorsal digital soft tissue defects are considered among the most challenging to reconstruct. Numerous treatment options are proposed, including advancement flaps, antegrade, retrograde flow flaps, adipofascial flaps, and digital artery perforator flaps. However, the optimal treatment remains controversial. The concept of the "bridge principle," consisting of the indirect transfer of the flap to the defect area through a muscular bridge, has recently introduced by authors for medial canthal reconstruction. The aim of the study was to examine the feasibility of its application in digital reconstruction for dorsal defects and the development of a new flap. The utilization of the dorsal subcutaneous adipofascial digital or toe tissue as a "bridge" led to description and development of bridged digital artery perforator flaps as an alternative treatment of such defects. Methods From November 2017 to September 2019, a series of 14 patients (mean age of 57.1 years) suffered from dorsal digital or toe soft tissue defects of different dimensions and sustained reconstruction with this new technique. Results Twelve digits and 2 toes have been concerned. The mean size of the defects was 1.3 x 1.1 cm. All flaps survived without a sign of venous congestion. No functional digital or toe problems were observed during the follow-up period (mean of 11.6 months). Minor wound dehiscence presented in 2 cases (2 of 14 [14.3%]) and a transient skin swelling around the flap in 1. Conclusions A new concept was introduced to resolve a challenging problem. Initial outcomes are very encouraging. These flaps could be a valuable and reliable reconstructive option.

关键词： Aerosols  

摘要： Penetration of 3-10 nm particles through a metal grid has been measured using different experimental methodologies. Two basic schemes have been compared: (i) the upstream-downstream (UD), where particle penetration is determined from comparison between the aerosol number concentrations measured at two sampling points, one placed upstream, the other downstream, of the filter;and (ii) the filter-dummy (FD), in which penetration is determined from comparison of number concentrations measured at the outlet of two geometrically identical chambers, one empty and the other containing the filter. The test aerosol facing the grid was either monodisperse (MONO) or polydisperse (POLY). The UD method requires the additional measurement of particle penetration (without filter) through the flow path between the two sampling points and it is thus a more time consuming strategy, but it has the advantage that fabrication of an additional dummy holder is not needed. UD + MONO and FD + MONO gave results in good agreement with the well-established fan filter model theory of Cheng and Yeh. The results obtained with the FD + POLY method, the fastest one, were less precise and accurate. As far as diffusional capture of particles is concerned, the MONO method (using either the UD or FD basic schemes) should be preferred for accurate measurement of filter efficiency;the POLY method should perhaps be more suitable for a quick evaluation of the overall performance of a given filtration system.

关键词： Boron source   Boronizing mixture   SAE 1020   Microhardness   Wear resistance  

摘要： In this study, SAE 1020 steel samples were boronized at 850 degrees C for 4 h with different boronizing mixtures by powder-pack boronizing method. H3BO3 or Na2B8O13 was used as the boron source, KBF4 or NaBF4 was used as the activator and SiC was used as the diluent. Thus, 4 different boronizing mixtures (M1-M4) were prepared. Thickness, morphology and phase structure of the formed boride layers were studied by X-ray diffraction and microstructural analyzes. The single phase (Fe2B) boride layer with saw-tooth morphology was formed on surface of the samples. The thickest boride layers were obtained by using M1 and M2 boronizing mixtures. Microhardness measurements were performed to determine hardness of the 3 zones (core, transition zone and boride layer). The means of boride layer hardness of the samples were compared according to 95% Confidence Intervals analysis. It was determined that the average hardness value of the boride layers was about 1475 HV. Wear tests were fulfilled by ball on disc type wear test method under dry sliding condition and at 25 degrees C. According to the friction coefficient and specific wear rate values of boronized samples, it was identified that the sample S-M4 boronized with M4 boronizing mixture has the lowest wear rate (1.64 mm(3)/N.m) and friction coefficient value (0.63). Graphic

关键词： Multisystem inflammatory syndrome in children (MIS-C)   Pediatric inflammatory multisystem syndrome   COVID-19   SARS-COV-2  

摘要： Purpose of Review The novel coronavirus disease 2019 (COVID-19) is caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) and has developed into a pandemic. A unique challenge of this pandemic has been the emergence of multisystem inflammatory syndrome in children (MIS-C), a rare post-infectious hyperinflammatory disorder associated with SARS-CoV-2. This syndrome is characterized by overwhelming systemic inflammation, fever, hypotension, and cardiac dysfunction. This disorder may also have features overlapping with Kawasaki disease (KD), macrophage activation syndrome (MAS), and toxic shock syndrome (TSS). The goal of this review is to outline the presenting features, presumed immunopathogenesis, management, and outcomes of patients with MIS-C. Recent Findings Patients with MIS-C present with characteristics that fall within a wide clinical spectrum. Main features include fever, gastrointestinal symptoms such as abdominal pain and diarrhea, and cardiac complications such as myocarditis and coronary artery aneurysms, although various other features have been reported. Younger children may present with features of Kawasaki-like disease, and older children are often admitted to the intensive care unit with cardiogenic shock. Current treatment guidelines recommend intravenous immunoglobulins (IVIG) and glucocorticoids, with utilization of biologics in refractory cases. Fortunately, the majority of patients recover, with resolution of the systemic inflammation and cardiac abnormalities. Mortality from MIS-C is rare. This review provides an overview of the presenting features, proposed pathogenesis, suggested therapies, and outcomes of MIS-C. Clinicians must have a high clinical suspicion for this disorder in children who have had recent COVID-19 infection or exposure and present with a significant inflammatory response. Understanding of this disorder continues to evolve, and prompt diagnosis and treatment allow for the best possible outcome for patients w

摘要： Retraction: Songsong Zhao, Xinyi Han, Bin Liu, Wenqiang Guan, Quanyu Dai, Different effects of continuous and intermittent alternative magnetic field on inhibiting chilling injury of bananas 2021, 44(11) e13834 (). The above article, published online on 12 August, 2021, in Wiley Online Library (), has been retracted by agreement between the journal Editor in Chief, V.M Balasubramaniam and Wiley Periodicals LLC. The retraction has been agreed due to major overlap with a previously published Chinese-language version of this article from the same group of authors.