EUV telescope for a Cubesat nanosatellite.

This paper describes in detail a compact (2U format) telescope operating in the extreme ultraviolet range for studying the solar corona at a wavelength of 17.14 nm. The telescope objective has been built according to the Ritchey-Chrétien scheme with the following parameters: effective focal length of 381.3 mm, field of view of 2×2∘, and angular resolution of 11 in. Reflective multilayer Al/Be coatings were used, having 55% reflectance and a 0.4 nm spectral bandwidth. The wavefront rms error is 30 nm. An interferometric technique for controlling the shapes of the substrates and for adjusting the optical system and detector of the telescope assembly is described in detail.

Sliding tracheoplasty of complete tracheal cartilage rings in children.

INTRODUCTION: Complete tracheal rings are a rare malformation that occurs in 1 out of 100,000 live births. It is rare, isolated tracheal or tracheobronchial anomaly developed due to abnormal cartilage growth with formation of complete ring and often resulting in airway stenosis. Slide tracheoplasty, as it was originally described by Tsang et al. and popularized by Grillo et al., overlaps stenotic segments of trachea, shortening trachea itself, thus, doubling the circumference and diameter of the stenotic area. MATERIALS AND METHODS: We have performed slide tracheoplasty in 12 children during the period of 2019-2021 in thoracic surgery department of our center. Median age was 15 ± 21,1 months (2 months-6 years),median weight - 8,04 ± 4,75 kg (3-20,7 kg),tracheal lumen varied from 2.5 to 3.0 mm, stenosis length - from 40 to 70% of the trachea length. RESULTS: Slide tracheoplasty was performed using central veno-arterial extracorporeal membrane oxygenation in 7 cases and using cardiopulmonary bypass in 5 cases. Concomitant heart disease was revealed in 5 children (pulmonary artery sling in 3 cases, ventricular septal defects - 1, aberrant subclavian artery -1). 5 children underwent one-stage correction of VSD: plastic VSD -1; left pulmonary artery reimplantation - 3; subclavian artery reimplantation - 1. All patients were on mechanical ventilation for 4,3 ± 2,78 days at postoperative period. Patients were discharged 16,3 ± 5,14 days after surgery. Satisfactory result of treatment in the form of respiratory failure relief was achieved in 10 patients. It was possible to increase the trachea lumen from 1.5 to 2 times in all cases. There were 2 (16,6%) fatal cases due to sepsis and multi-organ failure development. CONCLUSIONS: Children with complete tracheal rings are very complicated patients with various comorbidities. Despite the advances in medicine, sometimes it is impossible to save lives of these children. The use of extracorporeal circulation (ECMO and bypass) allows us to safely perform reconstructive surgery on the trachea and save the child from respiratory failure manifestations. If needed, simultaneous correction of heart and tracheal defects is possible. Slide tracheoplasty allows to increase trachea lumen at least in 1.5-2 times. Mechanical ventilation is an unfavorable predictive factor for the outcomes of congenital tracheal stenosis management. LEVEL OF EVIDENCE: III.

Modeling flow into horizontal wells in a Dupuit-Forchheimer model.

Horizontal wells or radial collector wells are used in shallow aquifers to enhance water withdrawal rates. Groundwater flow patterns near these wells are three-dimensional (3D), but difficult to represent in a 3D numerical model because of the high degree of grid refinement needed. However, for the purpose of designing water withdrawal systems, it is sufficient to obtain the correct production rate of these wells for a given drawdown. We developed a Cauchy boundary condition along a horizontal well in a Dupuit-Forchheimer model. Such a steady-state 2D model is not only useful for predicting groundwater withdrawal rates but also for capture zone delineation in the context of source water protection. A comparison of our Dupuit-Forchheimer model for a radial collector well with a 3D model yields a nearly exact production rate. Particular attention is given to horizontal wells that extend underneath a river. A comparison of our approach with a 3D solution for this case yields satisfactory results, at least for moderate-to-large river bottom resistances.