Focusing fractional-order cylindrical vector beams

By numerically simulating the sharp focusing of fractional-order vector beams (0≤m≤1, with azimuthal polarization at m=1 and linear polarization at m=0), it is shown that the shape of the intensity distribution in the focal spot changes from elliptical (m=0) to round (m=0.5) and ends up being annular (m=1). Meanwhile, the distribution pattern of the longitudinal component of the Poynting vector (energy flux) in the focal spot changes in a different way: from circular (m=0) to elliptical (m=0.5) and ends up being annular (m=1). The size of the focal spot at full width at half maximum of intensity for a first-order azimuthally polarized optical vortex (m=1) and numerical aperture NA=0.95 is found to be 0.46 of the incident wavelength, whereas the diameter of the on-axis energy flux for linearly polarized light (m=0) is 0.45 of the wavelength. Therefore, the answers to the questions: when the focal spot is round and when elliptical, or when the focal spot is minimal -- when focusing an azimuthally polarized vortex beam or a linearly polarized non-vortex beam, depend on whether we are considering the intensity at the focus or the energy flow. In another run of numerical simulation, we investigate the effect of the deviation of the beam order from m=2 (when an energy backflow is observed at the focal spot center). The reverse energy flow is shown to occur at the focal spot center until the beam order gets equal to m=1.55.

A novel local impedance algorithm to guide effective pulmonary vein isolation in AF patients: 1-year outcome from the CHARISMA Study

Background Recently, a novel technology able to measure local tissue impedance (LI) providing a measure of tissue characteristics aimed at validating confidently ablation endpoints has become available for clinical use. Purpose We report the outcomes of our acute and long-term clinical evaluation of this algorithm in consecutive atrial fibrillation ablation cases. Methods Consecutive patients (pts) undergoing AF ablation at 6 Italian centers were included in the CHARISMA registry. A novel RF ablation catheter and a dedicated algorithm were used to measure LI through the distal catheter's electrode. The ablation was guided by looking at the magnitude and time course of impedance drop during RF delivery. The maximum distance between each ablation spot (center-to-center) was suggested to be ≤4 mm. RF applications were targeted to a LI drop of 10 Ω and RF applications were stopped when a maximum cutoff LI drop of <40 Ω was observed. Successful single RF ablation was defined according with a reduction of signal voltage (RedV) by at least 50% and inability to capture local tissue on pacing. Ablation endpoint was PVI as assessed by entrance and exit block. Post-ablation, all pts were monitored with ambulatory event monitoring, as well as Holter monitoring at 3, 6, and 12 months post-ablation. Additional ECG monitoring was performed as indicated by patient symptoms. Results A total of 1914 point by point first pass RF applications >10 s performed around PVs were analyzed from 98 pts (mean age = 61±11 years, 69% male, 55% paroxysmal AF, 45% persistent AF, 60% de novo procedures, 40% redo procedures). The mean LI was 105±15Ω prior to ablation and 92±13Ω after ablation (p<0.0001, mean absolute LI drop of 12.7±8Ω) during a median RF delivery time of 22 [17–31] sec. Effective ablation spots (88%) showed a higher absolute impedance drop (13.6±8Ω at effective RedV vs 6±3Ω at ineffective RedV, p<0.0001) compared with ineffective sites (12%). No steam pops or complications, including atrio-esophageal fistula or tamponade were reported during or after the procedures. At the end of the procedures all PVs were successfully isolated in all study pts. During a median follow-up of 369 [287–446] days, 13 pts (13.2%) developed an AF/AT recurrence after the 90-days blanking period (9.2% with paroxysmal vs 18% with persistent AF, p=0.239; 8.5% for de novo vs 20.5% for redo procedures, p=0.127). The time to recurrence was comparable among AF type (HR=1.97; 0.66 to 5.86; log-rank p=0.2265 for persistent vs paroxysmal AF) and procedural type (HR=2.56; 0.84 to 7.82; log-rank p=0.087 for redo vs de novo procedure) Conclusions In our experience, the magnitude of the LI drop during RF delivery was associated with effective lesion formation. An ablation strategy for PVI guided by LI technology was safe and effective, and resulted in a very low recurrence rate of AF at 1-year follow-up irrespective of paroxysmal/persistent AF type or de novo/redo procedure. Funding Acknowledgement Type of funding source: None

Laser Spot Center Location Method for Chinese Spaceborne GF-7 Footprint Camera

The Gaofen-7 (GF-7) satellite is equipped with two area array sensor footprint cameras to capture the laser altimeter spot. In order to establish a direct correspondence between the laser data and the stereo image data, a new method is proposed to fit the center of the spot using the brightness difference between the spot image and the footprint image. First, the geometric registration between the spot image and the footprint image is completed based on feature matching or template matching. Then, the brightness values between the two images are extracted from the corresponding image position to form a measurement, and the least squares adjustment method is used to calculate the parameters of the brightness conversion model between the spot image and the footprint image. Finally, according to the registration relationship, the center of the identified spots is respectively positioned in the footprint images, so that the laser spots are accurately identified in the along-track stereo footprint images. The experimental results show that the spot error of this method is less than 0.7 pixel, which has higher reliability and stability, and can be used for a GF-7 satellite footprint camera.

Calibration Technique of a Curved Zoom Compound Eye Imaging System

A calibration method for the designed curved zoom compound eye is studied in order to achieve detection and positioning of spatial objects. The structure of the curved zoom compound eye is introduced. A calibration test platform is designed and built based on the image characteristics of the compound eye, which can be constructed in the large field view for the calibration target. The spot images are obtained through image processing. The center of the spot is calculated by Gauss fitting method. This method is highly simple and intuitive, and it can be used in a zoom surface compound eye without any complex procedures. Finally, the corresponding relationship between the spot center coordinates and the incident light vector of the corresponding sub-eye is established, and the calibration of the multi vision positioning system is completed.

Optimization of thermo-hydraulic characteristics of solar cavity receiver under concentrated heat flux

It is important to study the effects of heat flux on the thermo-hydraulic characteristics in a solar cavity receiver because of the non-uniform radiation flux temporally and spatially. In this article, we presented a mathematical model of thermo-hydraulic characteristics of a solar cavity receiver, considering the effect of heat flux distribution on the energy transfer (radiation–conduction–convection). Using the model, the thermo-hydraulic characteristics under high concentrated heat flux were studied and then optimized the characteristics from two aspects: tube diameter (22, 27, 32, and 38 mm) and connection structure of the heating surface (H-type, central inlet/outlet, and vertical U-type). It was found that flow distribution changed smoothly at the diameter of 27 mm with the increase of the heat flux; when the diameter of tubes at the certain distance (1.6 σHF) from the spot center was replaced by 38 mm, the thermo-hydraulic characteristics were improved. For the evaporating surfaces, the thermo-hydraulic characteristics of working fluid (water) with the central inlet/outlet connection structure were better than those of the H-type connection structure. For the surperheated surfaces, the vertical U-type connection structure was applied to obtain the high temperature steam. These research findings are helpful for the safe and stable operation of the whole solar power system.

A numerical analysis of an energy directing method through friction heating during the ultrasonic welding of thermoplastic composites

The ultrasonic spot welding of fiber-reinforced thermoplastic laminates received a wide interest from researchers mainly in the fields of aerospace and automotive industries. This study investigated a new technique for focusing the ultrasonic vibration energy at the desired spot between two mating thermoplastic composite laminates. In this investigated method, no additional energy directing protrusions between the mating laminates were required to focus the vibration energy. It was found that by welding the laminates amid an ultrasonic horn and an anvil in which the prior had a larger contact surface with the laminate as the latter, it was possible to generate a localized friction heating. In the initial phase of the welding, the friction heating softened the interfacial layers and thus caused the focusing of the majority of the cyclic ultrasonic strain energy in the weld spot center. The assumption for the presence of the friction and its influence on the heat generation was investigated by means of finite element method (FEM) mechanical dynamic analysis. Microscopic analysis of the weld spot eventually delivered the proof for the melt initiation by friction at a ring around the weld spot and subsequent spot growth by viscoelastic heating.