Efficiency of Fish Propulsion

It is shown that the system efficiency of a self-propelled flexible body is ill-defined unless one considers the concept of quasi-propulsive efficiency, defined as the ratio of the power needed to tow a body in rigid-straight condition over the power it needs for self-propulsion, both measured for the same speed. Through examples we show that the quasi-propulsive efficiency is the only rational non-dimensional metric of the propulsive fitness of fish and fish-like mechanisms. Using two-dimensional viscous simulations and the concept of quasi-propulsive efficiency, we discuss the efficiency two-dimensional undulating foils. We show that low efficiencies, due to adverse body-propulsor hydrodynamic interactions, cannot be accounted for by the increase in friction drag

Optimized kinematics enable both aerial and aquatic propulsion from a single three-dimensional flapping wing

Flapping wings in nature demonstrate a large force envelope, with capabilities far beyond the traditional limits of static airfoil section coefficients. Puffins, murres, and other auks particularly showcase this effect, as they are able to generate both enough thrust to swim and enough lift to fly, using the same wing, purely by changing the wing motion trajectory. The wing trajectory is therefore an additional design criterion to be optimized along with traditional aircraft parameters and could open the door to dual aerial-aquatic robotic vehicles. In this paper we showcase one realization of a three-dimensional flapping-wing actuation system that reproduces the force coefficients necessary for dual aerial-aquatic flight. The wing apparatus oscillates by the root and employs an active upstream and downstream sweep degree of freedom. We analyze two types of motions in detail: aerial motions where the wing tip moves upstream during the power stroke of each flapping cycle and aquatic motions where the wing tip moves downstream during the power stroke. We design these aerial and aquatic flapping-wing trajectories using an experiment-coupled optimization routine, allowing control of the unsteady forces throughout each flapping cycle. Additionally, we elucidate the wakes of these complex wing trajectories using dye visualization, correlating the wake vortex structures with simultaneous experiment force measurements. After optimization, the wing trajectories generate the large force envelope necessary for propulsion in both fluid media and furthermore demonstrate improved control over the unsteady wake

Gradient-Free Stochastic Sensitivity Analysis of the Shipboard Power System

Sensitivity analysis results are useful both for the early design stage – where the parametric space can be substantially reduced – but also in operating conditions, e.g. of the future electric ship, resulting in reduced operational costs and increased reliability. Here we discuss variance-based methods to analyze the sensitivity of stochastic electro-mechanical systems with multirate dynamics. We present results for an illustrative example and for a model of an integrated power system.United States. Office of Naval Research (N00014-02-1-0623); United States. Office of Naval Research (N00014-07-1-0846); Massachusetts Institute of Technology. Sea Grant College Program (NA060AR4170019 NOAA/DOC

Swimming kinematics and efficiency of entangled North Atlantic right whales

© The Author(s), 2017. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Endangered Species Research 32 (2017): 1-17, doi:10.3354/esr00781.Marine mammals are streamlined for efficient movement in their relatively viscous fluid environment and are able to alter their kinematics (i.e. fluke stroke frequency, amplitude, or both) in response to changes in force balance. Entanglement in fishing gear adds significant drag and buoyant forces that can impact swimming behaviors across a range of timescales. We deployed biologging tags during the disentanglement of 2 North Atlantic right whales Eubalaena glacialis to (1) examine how their kinematics changed in response to drag and buoyancy from entanglement in fishing gear, and (2) calculate resultant changes in swimming efficiency for one individual. We observed variable responses in dive behavior, but neither whale appeared to exploit added buoyancy to reduce energy expenditure. While some of the observed changes in behavior were individually specific, some swimming kinematics were consistently modulated in response to high drag and buoyancy associated with entangling gear, affecting thrust production. In high drag and buoyancy conditions, fluke strokes were significantly shorter and more variable in shape, and gliding was less frequent. Thrust and efficiency significantly differed among dive phases. Disentanglement reduced thrust coefficients ~4-fold, leading to 1.2 to 1.8-fold lower power (W). Ideal propulsive efficiency was significantly lower when entangled, though we detected no difference in observed propulsive efficiency between the conditions. Similar to carrying heavy objects or changing shoes, we present another condition where animals perceive unique movement constraints over seconds to minutes and develop compensatory strategies, altering their movement accordingly.J.M.v.d.H was supported by a postgraduate scholarship from the Natural Sciences and Engineering Research Council of Canada, the MIT Martin Family for Sustainability Fellowship, the Herrington Fitch Family Foundation, a NOAA Award #NA14OAR4320158 to The Cooperative Institute for the North Atlantic Region, and a WHOI-Duke Fellowship through the WHOI Marine Mammal Center

Design of the All-Electric Ship: Focus on Integrated Power System Coupled to Hydrodynamics

We present a detailed model of the integrated power system coupled to hydrodynamics that allows us to study global sensitivities in the All-Electric Ship. A novel element of our formulation is the stochastic modeling of the coupled system to account for uncertainty in the parameters or operating conditions. This new computational framework is applied to a model of the DDG- 51 destroyer that involves a 19 MW 15-phase induction machine and an indirect field oriented controller. In particular, we simulate extreme events corresponding to propeller emergence and firing of pulsed power weapons.United States. Office of Naval Research (N00014-02-1-0623 ESRD Consortium); United States. Office of Naval Research (N00014-07-1-0846); Massachusetts Institute of Technology. Sea Grant College Program (NA060AR4170019 NOAA/DOC

An Image Analysis System for the Assessment of Retinal Microcirculation in Hypertension and Its Clinical Evaluation

Abstract — A system for the assessment of hypertension through the measurement of retinal vessels in fundoscopy images, is presented. The proposed approach employs multiple image analysis methods, in an integrated system that is used in clinical practice. Automating the measurement process enables the conduct of a clinical study that, for the first time, shows the correlation between macrovascular and microvascular al-terations, based on numerous measurements acquired by this system. Experience and perspectives gained from clinical usage and evaluation are reported. I

From Biological Cilia to Artificial Flow Sensors: Biomimetic Soft Polymer Nanosensors with High Sensing Performance

We report the development of a new class of miniature all-polymer flow sensors that closely mimic the intricate morphology of the mechanosensory ciliary bundles in biological hair cells. An artificial ciliary bundle is achieved by fabricating bundled polydimethylsiloxane (PDMS) micro-pillars with graded heights and electrospinning polyvinylidenefluoride (PVDF) piezoelectric nanofiber tip links. The piezoelectric nature of a single nanofiber tip link is confirmed by X-ray diffraction (XRD) and Fourier transform infrared spectroscopy (FTIR). Rheology and nanoindentation experiments are used to ensure that the viscous properties of the hyaluronic acid (HA)-based hydrogel are close to the biological cupula. A dome-shaped HA hydrogel cupula that encapsulates the artificial hair cell bundle is formed through precision drop-casting and swelling processes. Fluid drag force actuates the hydrogel cupula and deflects the micro-pillar bundle, stretching the nanofibers and generating electric charges. Functioning with principles analogous to the hair bundles, the sensors achieve a sensitivity and threshold detection limit of 300 mV/(m/s) and 8 μm/s, respectively. These self-powered, sensitive, flexible, biocompatibale and miniaturized sensors can find extensive applications in navigation and maneuvering of underwater robots, artificial hearing systems, biomedical and microfluidic devices.Singapore. National Research Foundation (Singapore-MIT Alliance for Research and Technology)Singapore-MIT Alliance for Research and Technology (SMART) (Innovation Grants ING148079- ENG

Endoscopic ultrasound fine-needle biopsy vs fine-needle aspiration for lymph nodes tissue acquisition: A systematic review and meta-Analysis

Background: Endoscopic ultrasound (EUS)-guided tissue acquisition represents the choice of methods for suspected lymph nodes (LNs) located next to the gastrointestinal tract. This study aimed to compare the pooled diagnostic performance of EUS-guided fine-needle biopsy (EUS-FNB) and fine-needle aspiration (EUS-FNA) for LNs sampling. Methods: We searched PubMed/MedLine and Embase databases through August 2021. Primary outcome was diagnostic accuracy; secondary outcomes were sensitivity, specificity, sample adequacy, optimal histological core procurement, number of passes, and adverse events. We performed a pairwise meta-Analysis using a random-effects model. The results are presented as odds ratio (OR) or mean difference along with 95% confidence interval (CI). Results: We identified nine studies (1,276 patients) in this meta-Analysis. Among these patients, 66.4% were male; the median age was 67 years. Diagnostic accuracy was not significantly different between the two approaches (OR, 1.31; 95% CI, 0.81-2.10; P = 0.270). The accuracy of EUS-FNB was significantly higher when being performed with newer end-cutting needles (OR, 1.87; 95% CI, 1.17-3.00; P = 0.009) and in abdominal LNs (OR, 2.48; 95% CI, 1.52-4.05; P < 0.001) than that of EUS-FNA. No difference in terms of sample adequacy was observed between the two approaches (OR, 1.40; 95% CI, 0.46-4.26; P = 0.550); however, histological core procurement and diagnostic sensitivity with EUS-FNB were significantly higher than those with EUS-FNA (OR, 6.15; 95% CI, 1.51-25.07; P = 0.010 and OR, 1.87; 95% CI, 1.27-2.74, P = 0.001). The number of needle passes needed was significantly lower in the EUS-FNB group than in the EUS-FNA group (mean difference,-0.54; 95% CI,-0.97 to-0.12; P = 0.010). Conclusions: EUS-FNA and EUS-FNB perform similarly in LN sampling; however, FNB performed with end-cutting needles outperformed FNA in terms of diagnostic accuracy

Association between pancreatic intraductal papillary mucinous neoplasms and extrapancreatic malignancies: A systematic review with meta-analysis

Background: It is unclear whether patients with intraductal papillary mucinous neoplasia harbor a higher risk of developing extrapancreatic malignancies. Aims: We performed a pooled estimate of the incidence of extrapancreatic malignancies in patients with intraductal papillary mucinous neoplasia, with a particular focus on the comparison to the general population. Methods: Computerized bibliographic search of main databases was performed through February 2021. The primary endpoint was the pooled incidence of extrapancreatic malignancies in patients with intraductal papillary mucinous neoplasms. Additional outcome was the comparison between intraductal papillary mucinous neoplasia patients and the general population, expressed in terms of standardized incidence ratio along with 95% confidence intervals. Results: Eighteen studies with 8709 patients were included. The pooled rate of metachronous extrapancreatic malignancies was 10 (6e13)/1000 persons-year. No difference was observed according to intraductal papillary mucinous neoplasia histology and sex, whereas a significantly superior incidence of extrapancreatic malignancies was observed in patients with main-duct (36.7%, 25.4ä8%) as compared to branch-duct intraductal papillary mucinous neoplasia (26.2%, 17.6ã4.8%; p 1⁄4 0.03). Pooled standardized incidence ratio comparing expected rates in the general population was 1.01 (0.79e1.29); no difference was observed concerning rates of metachronous gastric cancer (standardized incidence ratio 1.60, 0.72e3.54) and colorectal cancer (1.29, 0.92e1.18), whereas biliary cancer was observed more frequently in intraductal papillary mucinous neoplasia patients (2.29, 1.07e4.93). Conclusion: Patients with intraductal papillary mucinous neoplasia harbor an overall rate of extrapancreatic malignancies as high as 27.3%. The rate of metachronous extrapancreatic malignancies is not superior to the general population