双级动叶调节轴流式一次风机振动分析及处理

某电厂三期1 000MW机组一次风机投产初期振动故障较为突出,风机无法正常运行。为彻底解决一次风机振动问题,检修人员使用PI系统及实时频谱分析仪对风机运行状态及振动频谱进行了综合分析,并对风机进行了全面解体检修,最终查明了导致风机振动异常的原因是机壳结构刚性不足,制定了改造方案,成功解决了风机振动异常的问题。

Strategies and challenges in treatment of varicose veins and venous insufficiency

Patients with varicose veins can be treated with conservative or surgical approaches based on the clinical conditions and patient preferences.In the recent decade,the recommendations for managing symptomatic varicose veins have changed dramatically due to the rise of minimally invasive endovascular techniques.The literature was systematically searched on Medline without language restrictions.All papers on the treatment of varicose veins and venous insufficiency with different procedures were included and reviewed.Endovenous laser ablation(EVLA)and radiofrequency ablation(RFA)both are same safe and effective in terms of occlusion rate,and time to return to normal activity.In comparison with RFA or EVLT,Cure conservatrice et Hemodynamique de l’Insufficience Veineuse en Ambulatoire(CHIVA)may cause more bruising and make little or no difference to rates of limb infection,superficial vein thrombosis,nerve injury,or hematoma.In terms of recurrence of varicose veins,there is little or no difference between CHIVA and stripping,RFA,or EVLT.Great saphenous vein recanalization is highest in the ultrasound-guided foam sclerotherapy(FS)group(51%)during 1 year of follow-up.The 2013 National Institute for Health and Care Excellence clinical guidelines recommend surgery as a third-line therapeutic option after EVLA or RFA and sclerotherapy.Although the mechanochemical endovenous ablation(MOCA)is a non-thermal,non-tumescent option and appears to be of similar efficacy to stab avulsion with no potential risk of nerve damage,the overall success rate of MOCA is lower than those of other procedures such as EVLA,RFA,or high ligation and stripping.EVLA is the most cost-effective therapeutic option,with RFA being a close second for the treatment of patients with varicose veins.Endovenous thermal ablation(EVLA or RFA)is recommended as a first-line treatment for varicose veins and has substituted the high ligation of saphenofemoral junctional reflux and stripping of varicose veins.Ultrasound-guided FS is associated with a high recurrence rate and can be used in conjunction with other procedures.MOCA and cyanoacrylate embolization appear promising,but evidence of their effectiveness is required.

Brachiocephalic artery stenting through the carotid artery: A case report and review of the literature

BACKGROUND As the population ages and people’s living standards gradually improve,the incidence of cerebrovascular disease in China is increasing annually,posing a serious threat to people’s health.The incidence of brachiocephalic artery stenosis in ischemic cerebrovascular disease is relatively low,accounting for 0.5% to 2% of patients,but its consequences are very serious.Herein,we report a case of brachiocephalic artery stenting through the carotid artery.CASE SUMMARY The patient was a 66-year-old man.He came to our hospital because of repeated dizziness and was diagnosed with ischemic cerebrovascular disease (stenosis at the beginning of the brachiocephalic artery).Cerebral angiography suggested that the stenosis of the brachiocephalic artery had almost occluded it.Contrast agent threaded a line through the stenosis,and there was reversed blood flow through the right vertebral artery to compensate for the subclavian steal syndrome in the right subclavian artery.To improve the symptoms,we placed an Express LD (8 mm × 37 mm) balloon expanding stent in the stenosis section.After the operation,the patient’s dizziness significantly improved.However,after 6 mo,the patient was re-admitted to the hospital due to dizziness.A computed tomography scan of the head revealed multiple cerebral infarctions in bilateral basal ganglia and the right lateral ventricle.An auxiliary examination including computerized tomography angiography of the vessels of the head and cerebral angiography both showed severe stenosis in the brachiocephalic artery stent.During the operation,the guidewire and catheter were matched to reach the opening of the brachiocephalic artery.Therefore,we decided to use a right carotid artery approach to complete the operation.We sutured the neck puncture point with a vascular stapler and then ended the operation.After the operation,the patient recovered well,his symptoms related to dizziness disappeared,and his right radial artery pulsation could be detected.CONCLUSION In patients with brachial artery stenosis,when the femoral artery approach is difficult,the carotid artery is an unconventional but safe and effective approach.At the same time,the use of vascular suturing devices to suture a carotid puncture point is also commendable.Although it is beyond the published scope of the application,when used cautiously,it can effectively avoid cerebral ischemia caused by prolonged artificial compression,and improper suturing can lead to stenosis of the puncture site and improper blood pressure,resulting in the formation of a hematoma.Finally,satisfactory hemostasis can be achieved.

Strategies and challenges in the treatment of chronic venous leg ulcers

Evaluating patients with chronic venous leg ulcers(CVLUs)is essential to find the underlying etiology.The basic tenets in managing CVLUs are to remove the etiological causes,to address systemic and metabolic conditions,to examine the ulcers and artery pulses,and to control wound infection with debridement and eliminating excessive pressure on the wound.The first-line treatments of CVLUs remain wound care,debridement,bed rest with leg elevation,and compression.Evidence to support the efficacy of silver-based dressings in healing CVLUs is unavailable.Hydrogen peroxide is harmful to the growth of granulation tissue in the wound.Surgery options include a high ligation with or without stripping or ablation of the GSVs depending on venous reflux or insufficiency.Yet,not all CVLUs are candidates for surgical treatment because of comorbidities.When standard care of wound for 4 wk failed to heal CVLUs effectively,use of advanced wound care should be considered based on the available evidence.Negative pressure wound therapy facilitates granulation tissue development,thereby helping closure of CVLUs.Autologous split-thickness skin grafting is still the gold standard approach to close huge CVLUs.Hair punch graft appears to have a better result than traditional hairless punch graft for CVLUs.Application of adipose tissue or placenta-derived mesenchymal stem cells is a promising therapy for wound healing.Autologous platelet-rich plasma provides an alternative strategy for surgery for safe and natural healing of the ulcer.The confirmative efficacy of current advanced ulcer therapies needs more robust evidence.

Multi-objective optimization design of deviation-correction trajectory considering the production loss in shale gas cluster well

In shale gas mining,the inter-fracture interference effect will significantly occur if the actual well deviates from the planned trajectory.To reduce production loss,operators want to get back on the planned trajectory economically and safely.Based on this,a multi-objective optimization model of deviationcorrection trajectory is established considering the production loss evaluation.Firstly,the functional relationship between the production envelope and the fracturing depth is constructed,and the production loss is obtained by combining the calculation method of volume flow.Based on the proposed“double-arc”trajectory design method,the production loss of the fracture on the deviation-correction trajectory is obtained.Finally,combined with the well profile energy evaluation,a new optimization model of deviation-correction trajectory is established.The results demonstrate that after optimizing the fracturing depth,the production loss of the deviation-correction trajectory is reduced by 13.2%.The maximum curvature value results in a trajectory with a minimum production loss yet a maximum well profile energy.The proposed model reduces the well profile energy by 15.6%compared with the existing model.It is proved that the proposed model can reduce the probability of drilling accidents and achieve high gas production in the later mining stage.This study fully considers various factors affecting horizontal wells in the fracturing area,which can provide theoretical guidance for the design of deviationcorrection trajectory.

Low temperature ferromagnetism in CaCu_(3)Ti_(4)O_(12)

The low-temperature magnetic order behaviors of perovskite oxide CaCu_(3)Ti_(4)O_(12)(CCTO)ceramics prepared by different methods are discussed.X-ray diffraction,scanning electron microscope,x-ray photoelectron spectroscopy,and direct current(DC)magnetization are used to characterize the structures,microscopic morphologies,valence states,and magnetic properties of the samples.The results show that the magnetic behaviors of CCTO ceramics are very sensitive to the preparation process.The quenched CCTO ceramic and CCTO powders grown in a molten salt crystal,which contain much more oxygen vacancies and Ti^(3+),show the coexistence of weak ferromagnetic order and antiferromagnetic order below the Neel temperature.It suggests that the bound magnetopolaron formed by oxygen vacancies and Ti^(3+)ion composite defects are responsible for the weak ferromagnetic order at low temperature.

Microstructure and properties of 3D-printed alumina ceramics with different heating rates in vacuum debinding

The effect of heating rates during vacuum debinding on the microstructure and mechanical properties of alumina ceramics are discussed in this paper.The threedimensional(3D)-printed alumina ceramics examined in this study were found to have a layered structure,and interlayer spacing increased as the heating rate increased The pore diameter,shrinkage,flexural strength and hardness were found to decrease as the heating rate increased due to weak interfacial bonding between alumina particles Shrinkage was found to be much larger along the Z direction than along the X or Y directions due to the layer-bylayer forming mode during 3D printing.0.5°C·min-1is considered the optimum heating rate,yielding ceramics with interlayer spacing of 0.65 lm,shrinkage of 2.6%2.3%and 4.0%along the X,Y and Z directions,respectively,flexural strength of 27.5 MPa,hardness of29.8 GPa,Vickers hardness of HV 266.5,pore diameter of356.8 nm,bulk density of 2.5 g·cm-3,and open porosity of38.4%.The debinding procedure used in this study could be used to produce a high-quality ceramic which can be used for fabricating alumina ceramic cores.

Microstructure and mechanical properties of 3D printed ceramics with different vinyl acetate contents

Stereolithography(SL)-based three-dimensional(3D) printing technique is an efficient method for the fabrication of alumina ceramics.The alumina slurry is difficult to obtain due to the barrier between hydrophilic alumina and oleophilic resin.It not only requires that the ceramic slurry possessed low viscosity and uniformity,but also requires that the slurry could complete the photocuring process.In this study,vinyl acetate was added in the ceramic slurry as a bridge to connect alumina and resin,and the effects of vinyl acetate content on the microstructure and mechanical properties of the alumina ceramics were systematically investigated.The results showed that the alumina ceramics were composed of three types of particles which included large aggregates,individual particles,and long-columnshaped particles.The shrinkage,bulk density,and crystallite size of the ceramics increased with the increase in vinyl acetate content.The open porosity decreased with the increase in vinyl acetate content.The flexural strength of the ceramics first increased and subsequently decreased with the increase in vinyl acetate content.The shrinkage in Z direction was much greater than that in X or Y direction.Based on the above results,the optimum vinyl acetate content for alumina slurry was 10 wt%,which resulted in sintered ceramic with the shrinkage of 15.6% in X direction,13.5% in Ydirection,21.9% in Z direction,bulk density of 1.9 g·cm^(-3),open porosity of 50.1%,and flexural strength of 24.4 MPa.The sintered ceramics satisfy the requirement of alumina ceramic cores.