Neural network aided diffractive metagratings for efficient beam splitting at terahertz frequencies

The merge of neural network with metasurfaces is a rising subject in photonics design, which offers an abstract bridge between the geometry of the subwavelength element and the optical response. The commonly involved optical response is the transmission or reflection spectrum, while here we focus on metasurfaces with superwavelength elements and predict multiple diffraction spectra in all the possible orders and orthogonal polarization modes given the geometry. This is achieved by parallel arrangement of several fully connected neural networks with shared input and diverse output diffraction spectra. As an application example, the model is used to find a metagrating as a 1:1 beam splitter in TE mode and 1:1:1 beam splitter in TM mode. The design is taken into fabrication and experimentally tested at 0.14 THz with highly consistent results to the prediction.

Melt electro-written scaffolds with box-architecture support orthogonally-oriented collagen

Melt Electro-Writing (MEW) is a state-of-the-art technique that supports fabrication of 3D, precisely controlled and reproducible fiber structures. A standard MEW scaffold design is a box-structure, where a repeat layer of 90° boxes is produced from a single fiber. In 3D form (i.e., multiple layers), this structure has the potential to mimic orthogonal arrangements of collagen, as observed in the corneal stroma. In this study, we determined the response of human primary corneal stromal cells and their deposited fibrillar collagen (detected using a CNA35 probe) following 6-weeks in vitro culture on these box-structures made from poly(ε-caprolactone). Comparison was also made to glass substrates (topography-free) and electrospun poly(ε-caprolactone) fibers (aligned topography). Cell orientation and collagen deposition were non-uniform on glass substrates. Electrospun scaffolds supported an excellent parallel arrangement of cells and deposited collagen to the underlying architecture of aligned fibers, but there was no evidence of bidirectional collagen. In contrast, MEW scaffolds encouraged the formation of a dense, interconnected cellular network and deposited fibrillar collagen layers with a distinct orthogonal-arrangement. Collagen fibrils were particularly dominant through the middle layers of the MEW scaffolds’ total thickness and closer examination revealed these fibrils to be concentrated within the pores’ central regions. With the demand for donor corneas far exceeding the supply - leaving many with visual impairment - the application of MEW as a potential technique to recreate the corneal stroma with spontaneous, bidirectional collagen organization warrants further study.

Effect of series and parallel combination of photovoltaic thermal collectors on the performances of integrated active solar still

In this paper, an analytical expression for hourly yield, electrical energy and overall exergy of self-sustained solar still integrated with series and parallel combination of photovoltaic thermal-compound parabolic concentrator (PVT-CPC) collectors have been derived. Based on numerical computations, it has been observed that the yield is maximum for all self-sustained PVT-CPC collectors are connected in series [case (i)]. Further, the daily yield and exergy increase with the increase of water depth unlike passive solar still for all collectors connected in series. However, overall exergy decreases with an increase of water depth for all collectors connected in parallel [case (iv)]. For numerical simulations, the total numbers of self-sustained PVT-CPC collectors has been considered as constant. Further, an effect of series and parallel combination of PVT-CPC collectors on daily yield, electrical energy and overall exergy have also been carried out. Following additional conclusions have also been drawn: (i) The daily yield of the proposed active solar still decreases with the increase of packing factor of semi-transparent PV module for a given water depth and electrical energy and overall exergy increase with water depth for case (i) as expected due to low operating temperature range at higher water depth in the basin. (i) The daily yield, electrical energy and overall exergy increase with the increase of water depth for all combination of series and parallel arrangement of PVT-CPC collectors for a packing factor of 0.22 as per our expectation.

A First Assessment of an Aerodynamic Barrier Layer for Filtering Airborne Hygroscopic Particles

In this work consideration is given to an aerodynamic concept for filtration of small water droplets such as those caused by an infected person when coughs or sneezes and including airborne hygroscopic particle, and with particular application to medical masks. Nowadays, the efficiency of such masks is strongly reduced for airborne particles and increasing the efficiency implies either increasing the thickness of the filtering layers or decreasing the aerodynamic equivalent diameter of the pore, both measures in clear detriment of its breathability. Here, a novel strategy is proposed in which efficiency is increased, not by decreasing the diameter of the pore but actually by increasing the diameter of the water droplet itself. We called this concept as the aerodynamic barrier layer. In this concept a layer with parallel arrangement of micro fibers in the direction of the flow is located just before the traditional filtering layer and being able to promote lift forces which induce clustering, coalescence and growth of water droplets at the center of the aerodynamic channel. The enlarged drop after passing though the aerodynamic barrier layer is now easy captured by a conventional filtering layer. Utilizing a simplified geometrical model, an expression for the required length of the aerodynamic barrier layer was derived.

Experimental and numerical investigations of ventilated acoustic metamaterial based in-parallel arrangement of Helmholtz resonator for façade screen

Understanding urban noise as a serious environmental problem in urban centers, the development and application of noise control strategies have demanded a recent effort by several researches. In this case, the development of acoustic metamaterial artificially designed to manipulate the wave phenomena has become a recent topic, aiming at optimized responses, and enables the development of subwavelength devices with potential application in passive ventilation and noise mitigation, providing better environmental conditions in buildings. The present paper intends to contribute to the knowledge in this field by investigating the concept of an acoustic metamaterial with negative bulk modulus based in a parallel arrangement of Helmholtz Resonators. Experimental and numerical investigations are carried out to determine the acoustic potential of the proposed meta structure in terms of sound absorption and sound transmission loss. The developed concept exhibits significant benefits in the properties of sound transmission loss, and seems a potential application for noise control at specific frequency bands (mainly at low to middle frequency) in building façades.

Impact of a motorcycle on cyclist aerodynamic drag in parallel and staggered arrangements

Cycling races contain a multitude of motorcycles for various activities including television broadcasting. During parts of the race, these motorcycles can ride in close proximity of cyclists. Earlier studies focused on the impact of a nearby motorcycle on cyclist drag for in-line arrangements. It was shown that not only a motorcycle in front of a cyclist but also a motorcycle closely behind a cyclist can substantially reduce cyclist drag. However, there appears to be no information in the scientific literature about the impact of the motorcycle on cyclist drag for parallel and staggered arrangements. This paper presents wind tunnel measurements of cyclist drag for 32 different parallel and staggered cyclist-motorcycle arrangements. It is shown that the parallel arrangement leads to a drag increase for the cyclist, in the range of 5 to about 10% for a lateral distance of 2 to 1 m. The staggered arrangement can lead to either a drag increase or a drag decrease, where the latter is about 2% for most positions analyzed. For one of the parallel arrangements, computational fluid dynamics simulations were performed to provide insight into the reasons for the drag increase. A cyclist power model was used to convert the drag changes into potential time gains or losses. Compared to a lone cyclist riding at a speed of 46.8 km/h (13 m/s) on level road in calm weather, the time loss by a drag increase of 10%, 4% and − 2% was 2.16, 0.76 s and − 0.80 s per km, respectively. These time differences are large enough to influence the outcome of cycling races.

Chopstick technique used in laparoendoscopic single site radical hysterectomy for early stage cervical cancer

Laparoendoscopic single-site surgery (LESS) further minimizes the invasiveness of traditional laparoscopic surgery. However, the "chopstick" effect caused by the parallel arrangement of the instruments in the umbilicus is considered an obstacle indelicate operations. The purpose of this study was to introduce a new technique characterized by a double fulcrum formed by instruments, named the "chopstick" technique, which facilitates the expedient accomplishment of complicated surgeries such as LESS radical hysterectomy (LESS-RH). Seventy-three patients who underwent LESS-RH using the "chopstick" technique were retrospectively analyzed. The procedure was performed successfully in 72 patients. The median operative duration was 225 min, and the median intraoperative blood loss was 200 ml. Among the operations in the first 20 patients, intraoperative vascular injuries and bladder injury occurred in two patients and were repaired by LESS. Patients responded positively regarding minimal postoperative pain control. The score of satisfaction with the cosmetic outcome expressed by the patients was eight at discharge and nine 30 days later. In conclusion, this study presents the feasibility of accomplishing complicated procedures, such as radical hysterectomy, by LESS using the “chopstick” technique. This approach provides more options for both selected patients and surgeons.