Comparative study of tapered versus conventional cylindrical balloon for stent implantation in stenotic tapered artery

The natural tapering of coronary arteries often creates a dilemma for optimal balloon sizing during stenting. The influence of different balloon types, namely, a tapered balloon and a conventional cylindrical balloon, on the mechanical performance of the stent as well as arterial mechanics was investigated via the finite element method. Stent free-expansion and stent deployment in a stenotic tapered artery were investigated numerically. The biomechanical behavior of the two balloon types was compared in terms of stent foreshortening, stent deformation, stent stress distribution, and arterial wall stress distribution. Results indicate that balloon types affect the transient behavior of the stent and the arterial mechanics. Specifically, a tapered balloon could maintain the natural tapering of the coronary artery after stent expansion. In contrast to a cylindrical balloon, tapered balloon also mitigated the foreshortening of the stent (7.69%) as well as the stress concentration in the stent and artery (8.61% and 4.17%, respectively). Hence, tapered balloons should be used in tapered arteries as they may result in low risk of artery injury. This study might provide insights for improved balloon choice and presurgical planning

Angular deviation and diffraction efficiency of Littrow-configuration ECDL for three-dimensional diffraction

We consider in this paper the angular deviation and diffraction efficiency of the reflection gratings in Littrow-configuration for applications of external cavity diode laser (ECDL) using the rigorous coupled-wave analysis (RCWA) method. We consider the three-dimensional diffraction case in general, where the incidence plane is un-parallel with the grating vector (i.e. conical diffraction). The angular tolerance of arbitrary gratings under plane and conical diffraction are thus derived and presented. A typical blazed grating is chosen as an example to calculate its diffraction efficiency (DE) using RCWA. {Furthermore}, we point out that the angular tolerance and reflection efficiency can be improved if the appropriate parameter settings are selected for Littrow-configuration ECDL, including incidence angle, diffraction order, grating period and blazed angle. Otherwise, a tiny slanting angle of the grating vector deviated from the incidence plane will {deviate the feedback light away from} entering the LD-chip and halt laser oscillation in the external cavity. Finally, a general rule for the parameter settings in Littrow-configuration is provided as a benchmark.Comment: 9 pages,11 figure

Capacitor Voltage Ripple and Harmonics Analysis in MMC

[Introduction] The rapid development of VSC-HVDC provides practical support for MMC (Modular Multi-Level Converter) topology. Takes a half bridge MMC converter as an example, the relationship between steady-state capacitor voltage fluctuation, harmonic interaction, and bridge arm switching function of MMC is studied in order to provide theoretical support for MMC system design and control strategy. [Method] By establishing analytical expressions for the sub module capacitor voltage and bridge arm switch function, the mathematical approximate expressions for the energy fluctuation and capacitor voltage fluctuation of the upper and lower bridge arms of the MMC converter were obtained. Furthermore, the distribution law of harmonics in the upper and lower bridge arms current, AC (Alternating Current ) valve side, and DC (Direct Current) side, as well as the positive and negative sequence relationship of inter phase circulation were studied. Based on the harmonic formula, an estimation method for the secondary circulation was obtained; Furthermore, the variable comparison method was used to study the relationship between the switching function of the bridge arm and the voltage of the submodule capacitance with the valve side power factor and the size of the submodule capacitance. Finally, a detailed PSCAD/EMTDC model was built based on actual engineering parameters, and a consistency comparison between theoretical analysis and offline simulation was conducted. [Result] The research has shown that the inter phase circulating current of MMC only contains even harmonics, with 6k+2 circulating currents exhibiting negative sequence, 6k+4 circulating currents exhibiting positive sequence, and 6k circulating currents exhibiting zero sequence characteristics. At the same time, under steady-state conditions, the AC voltage and current flow at the outlet of MMC valve side only contains odd harmonics, while the DC voltage and current flow at MMC DC side only contains even harmonics, and at the power factor angle φ<0, the peak value of the bridge arm switch function will be greater than 1, and the peak voltage fluctuation of the module capacitor at low power factor is greater than that at high power factor. [Conclusion] Based on this, we can select and design capacitor for MMC inverters and carry out the transient stability strategies, also, master the operational characteristics of MMC topology through theoretical analysis

Effect of Ge Nanocrystals on 1.54 μm Photoluminescence Enhancement in Er2O3:ZnO and Ge Co-Sputtered Films

Photoluminescence (PL) of Er and Ge co-doped ZnO films synthesized by radio frequency magnetron co-sputtering was investigated. X-ray diffraction (XRD) patterns showed that the annealing process at 400–800 °C led to the formation of nanocrystal (nc) Ge. Samples containing nc-Ge showed a strong visible PL with a peak at 582–593 nm, which was consistent with the calculated energy of the exciton of the ~5 nm-sized nc-Ge, according to the quantum confinement effect. The formation of nc-Ge could greatly enhance the 1.54 μm emission, and it is considered that the 1.54 μm PL enhancement may come from a joint effect of both the energy transfer from nc-Ge to Er3+ and the local environment change of Er3+

Energy Storage Overflow-Aware Data Delivery Scheme for Energy Harvesting Wireless Sensor Networks

In Energy-Harvesting Wireless Sensor Networks (EH-WSNs), energy storage with limited capacity is used in the nodes to store the harvested energy. Energy storage overflow (ESO) happens when the energy storage is full, which causes the nodes to be unable to store the newly harvested energy. In traditional data delivery schemes, there is the problem of &#8220;energy hungry and surplus coexistence&#8222;, meaning that some nodes in the network are hungry for energy while some other nodes continue to waste energy due to ESO. To alleviate this problem, in this paper, we present the ESO-aware multiple path (EAMP) data delivery scheme so that more data can be delivered to the sink. With the EAMP, multiple disjoint paths from the source node to the sink are constructed, and the source node splits data into multiple pieces with each going through one of the paths, which helps in mitigating ESO. Simulation results show that the proposed EAMP scheme can deliver more data than the existing ones

Numerical Investigations of a Non-Uniform Stator Dihedral Design Strategy for a Boundary Layer Ingestion (BLI) Fan

A distributed propulsion system has the advantage of saving 5&ndash;15% fuel burn through ingesting the fuselage boundary layer of an aircraft by fan or compressor. However, due to boundary layer ingestion (BLI), the fan stage will continuously operate under serious inlet distortion. This will lead to a circumferentially non-uniform flow separation distribution on the stator blade suction surface along the annulus, which significantly decreases the fan&rsquo;s adiabatic efficiency. To solve this problem, a non-uniform stator dihedral design strategy has been developed to explore its potential of improving BLI fan performance. First, the stator full-annulus blade passages were divided into blade dihedral design regions and baseline design regions on the basis of the additional aerodynamic loss distributions caused by BLI inlet distortion. Then, to find the appropriate dihedral design parameters, the full-annulus BLI fan was discretized into several portions according to the rotor blade number and the dihedral design parameter investigations for dihedral depth and dihedral angle were conducted at the portion with the largest inflow distortion through a single-blade-passage computational model. The optimal combinational dihedral design parameter (dihedral depth 0.3, dihedral angle 6 deg) was applied to the blade passages with notable flow loss which were mainly located in the annulus positions from &minus;120 to 60 degrees suffering from inlet distortion, while the blades in the low-loss annulus locations were unchanged. In this way, a non-uniform stator dihedral design scheme was achieved. In the end, the effectiveness of the non-uniform stator dihedral design was validated by analyzing the internal flow fields of the BLI fan. The results show that the stator dihedral design in distorted regions can increase the inlet axial velocity and reduce the aerodynamic load near the blade trailing edge, which are beneficial for suppressing the flow separations and reducing aerodynamic loss. Specifically, compared with the baseline design, the non-uniform stator dihedral design has achieved a reduction of aerodynamic loss of about 7.7%. The fan stage has presented an improvement of adiabatic efficiency of about 0.48% at the redesigned point without sacrificing the total pressure ratio. In the entire operating range, the redesigned fan has also shown a higher adiabatic efficiency than the baseline design with no reduction of the total pressure ratio, which provides a probable guideline for future BLI distortion-tolerant fan design