Dynamic analysis of integrally geared compressors with varying workloads

Integrally geared compressors are characterized by compact and high efficiency machines, which are widely used in modern processing industries. As an important part of integrally geared compressors, a geared rotor-bearing system exhibits complicated dynamic behaviors. When running at rated speeds, a coupling system likely produces resonance with an adjusted workload, and a critical load phenomenon occurs. The dynamic coefficients of bearings, axial force and torque, and gear meshing stiffness vary with workload because of the interaction between rotors. In this study, a dynamic model of a geared rotor-bearing system influenced by the dynamic coefficients of bearings, axial force and torque, and gear meshing stiffness is developed. The dynamic responses of the coupling system are calculated and analyzed by using a typical five-shaft integrally geared compressor as an example. The effects of different parameters on the dynamic behaviors of the proposed system are also considered in the discussion. The geared rotor-bearing system is further investigated to examine the failure mechanism of the critical load

Mutual coupling reduction of two PIFAs with a T-shape slot impedance transformer for MIMO mobile terminals

Abstract in UndeterminedAn efficient technique is introduced to reduce mutual coupling between two closely spaced PIFAs for MIMO mobile terminals. The proposed mutual coupling reduction method is based on a T-shape slot impedance transformer and can be applied to both single-band and dual-band PIFAs. For the proposed single-band dual PIFAs, the 10 dB impedance bandwidth covers the 2.4 GHz WLAN band (2.4–2.48 GHz), and within the WLAN band an isolation of over 20 dB is achieved. Moreover, the dual-band version covers both the WLAN band and the WiMAX band of 3.4–3.6 GHz, with isolations of over 19.2 dB and 22.8 dB, respectively. The efficiency, gain and radiation patterns of the two-PIFA prototypes are verified in measurements. Due to very low pattern correlation and very good matching and isolation characteristics, the capacity performances are mainly limited by radiation efficiency. The single-band and dual-band PIFAs are also studied with respect to their locations on the ground plane. An eight-fold increase in the bandwidth of one PIFA is achieved, when the single-band PIFAs are positioned at one corner of the ground plane, with the bandwidth of the other PIFA and the good isolation unchanged

An Automated Over-the-Air Radiated Testing Platform for Reconfigurable Intelligent Surface

In the relentless quest to enhance wireless communicationcapabilities, reconfigurable intelligent surface (RIS)has emerged as a technology of immense promise. Armed withthe beamforming capabilities, RIS can intelligently engineerand control wireless propagation environments. Consequently,an in-depth knowledge of RIS radiation characteristics hasbecome important. This paper presents an automated over-theair(OTA) radiated testing platform designed for characterizingRIS radiation. Operating in an anechoic chamber setup in afully automated manner, the platform system utilizes multipleprobes to expedite testing and employs a vector network analyzer(VNA) for testing signal measurement and recording. Controlledby a programmed controller, the system efficiently manages RISoperation with predefined code-book while the controller directsthe system to conduct radiation measurements. To validate thedesigned testing platform system, RIS beam steering radiationmeasurements were conducted using a 2-bit 10 × 10 RIS. Themeasured results demonstrate the capabilities and reliability ofthe automated testing system

Efficiency of different annuloplasty in treating functional tricuspid regurgitation and risk factors for recurrence

AbstractBackgroundFunctional tricuspid regurgitation (FTR) is frequent in patients with mitral valve disease. Untreated tricuspid regurgitation (TR) may cause poor clinical outcomes. The surgical factors involved in annuloplasty for FTR remain controversial. Our objective was to compare effectiveness of different tricuspid annuloplasty (TVP), and reveal the risk factors of recurrence.MethodsWe analyzed the clinical details of 399 consecutive patients who underwent mitral surgery with concomitant TVP, from 2006 to 2011, in two Chinese single-centers. Three methods were used for TVP: De Vega surgery was completed in 242 patients; annuloplasty using a flexible band was completed in 98 patients; and surgery with a rigid ring was performed in 59 patients.ResultsThe operative mortality rate was 2.3%. After surgery, the TR grade of all patients decreased significantly. At three years postoperatively, 13.7% of patients were diagnosed with recurrent FTR. At the three year time point, severe TR in the De Vega group was 18%, which was higher than those in the flexible (8.4%) and rigid planner ring groups (5.2%). During follow-up, the recurrent rates in the rigid group were significantly lower than in the flexible group. Multivariate analysis revealed that pre-operative atrial fibrillation, severe TR, large left atrial, ejection fraction (EF)<40%, De Vega annuloplasty, and postoperative permanent pacemaker installation were independent risk factors for severe recurrent TR.ConclusionsRigid ring annuloplasty efficaciously improved post-operative tricuspid valve function in patients with FTR. Atrial fibrillation, a large left atrium, low EF and postoperative permanent pacemaker installation were independent risk factors for severe recurrent TR