Phasing of dragonfly wings can improve aerodynamic efficiency by removing swirl

Dragonflies are dramatic, successful aerial predators, notable for their flight agility and endurance. Further, they are highly capable of low-speed, hovering and even backwards flight. While insects have repeatedly modified or reduced one pair of wings, or mechanically coupled their fore and hind wings, dragonflies and damselflies have maintained their distinctive, independently controllable, four-winged form for over 300 Myr. Despite efforts at understanding the implications of flapping flight with two pairs of wings, previous studies have generally painted a rather disappointing picture: interaction between fore and hind wings reduces the lift compared with two pairs of wings operating in isolation. Here, we demonstrate with a mechanical model dragonfly that, despite presenting no advantage in terms of lift, flying with two pairs of wings can be highly effective at improving aerodynamic efficiency. This is achieved by recovering energy from the wake wasted as swirl in a manner analogous to coaxial contra-rotating helicopter rotors. With the appropriate fore–hind wing phasing, aerodynamic power requirements can be reduced up to 22 per cent compared with a single pair of wings, indicating one advantage of four-winged flying that may apply to both dragonflies and, in the future, biomimetic micro air vehicles

Single-incision videolaparoscopic appendectomy with conventional videolaparoscopy equipment

Background : Acute appendicitis is the most common surgical emergency in daily practice, and is approached laparoscopically in many centers. Efforts have been undertaken for the development of minimally invasive techniques that reduce tissue trauma and offer improved cosmetic results, one of such being the single-incision laparoscopic surgery (SILS). Aim : To present a minimally invasive technique for appendectomy (SILS) undertaken with conventional instruments. Method : Eleven patients were treated in the emergency care center presenting abdominal pain in the right iliac fossa that was suggestive of appendicitis. Diagnostic investigation was subsequently conducted, including physical examination, laboratory and imaging exams (CT scan with intravenous contrast or total abdominal ultrasound), and the results were consistent with acute appendicitis. Thus, after consent, these patients underwent SILS appendectomy under general anesthesia with three trocars (two 10 mm and one 5 mm), using conventional and optical laparoscopic tweezers (10 mm, 30º). The base and pedicle of the appendix were ligated with titanium LT 400 clips. The procedure occurred uneventfully. Inclusion criteria were absence of diffuse peritonitis, BMI (body mass index) less than 35 and absence of serious comorbidities or sepsis. Results : Seven men and four women were operated with average age of 25.7 years and underwent appendectomy through this technique. Mean procedure duration was of 37.2 min. Regarding surgical findings, three had appendicitis in stage 1, four in stage 2 and four in stage 3. All patients improved well, without surgical complications, and did not require conversion to open surgery or conventional laparoscopy technique. Conclusion : Appendectomy conducted through Single Incision Laparoscopic Surgery is a feasible and promising technique that can be performed with conventional laparoscopic instruments