Acceleration is the key to drag reduction in turbulent flow.

A turbulent pipe flow experiment was conducted where the surface of the pipe was oscillated azimuthally over a wide range of frequencies, amplitudes, and Reynolds numbers. The drag was reduced by as much as 35%. Past work has suggested that the drag reduction scales with the velocity amplitude of the motion, its period, and/or the Reynolds number.

An energy-efficient pathway to turbulent drag reduction.

Simulations and experiments at low Reynolds numbers have suggested that skin-friction drag generated by turbulent fluid flow over a surface can be decreased by oscillatory motion in the surface, with the amount of drag reduction predicted to decline with increasing Reynolds number. Here, we report direct measurements of substantial drag reduction achieved by using spanwise surface oscillations at high friction Reynolds numbers ([Formula: see text]) up to 12,800. The drag reduction occurs via two distinct physical pathways.

A simple method to monitor hemolysis in real time.

Blood damage (hemolysis) can occur during clinical procedures, e.g. dialysis, due to human error or faulty equipment, and it can cause significant harm to the patient or even death.

Swimmers' wake structures are not reliable indicators of swimming performance.

The structure of swimmers' wakes is often assumed to be an indicator of swimming performance, that is, how momentum is produced and energy is consumed. Here, we discuss three cases where this assumption fails. In general, great care should be taken in deriving any conclusions about swimming performance from the wake flow pattern.

How smooth is a dolphin? The ridged skin of odontocetes.

Dolphin skin has long been an inspiration for research on drag reduction mechanisms due to the presence of skin ridges that could reduce fluid resistance. We gathered in vivo three-dimensional surface data on the skin from five species of odontocetes to quantitatively examine skin texture, including the presence and size of ridges. We used these data to calculate k values, which relate surface geometry to changes in boundary layer flow.

Efficient cruising for swimming and flying animals is dictated by fluid drag.

Many swimming and flying animals are observed to cruise in a narrow range of Strouhal numbers, where the Strouhal number [Formula: see text] is a dimensionless parameter that relates stroke frequency f, amplitude A, and forward speed U. Dolphins, sharks, bony fish, birds, bats, and insects typically cruise in the range [Formula: see text], which coincides with the Strouhal number range for maximum efficiency as found by experiments on heaving and pitching airfoils. It has therefore been postulated that natural selection has tuned animals to use this range of Strouhal numbers because it confers high efficiency, but the reason why this is so is still unclear.

Structure identification in pipe flow using proper orthogonal decomposition.

The energetic motions in direct numerical simulations of turbulent pipe flow at Re=685 are investigated using proper orthogonal decomposition. The procedure is extended such that a pressure component is identified in addition to the three-component velocity field for each mode. The pressure component of the modes is shown to align with the streamwise velocity component associated with the large-scale motions, where positive pressure coincides with positive streamwise velocity, and vice versa.

Impact of global Fxr deficiency on experimental acute pancreatitis and genetic variation in the FXR locus in human acute pancreatitis.

Background: Infectious complications often occur in acute pancreatitis, related to impaired intestinal barrier function, with prolonged disease course and even mortality as a result. The bile salt nuclear receptor farnesoid X receptor (FXR), which is expressed in the ileum, liver and other organs including the pancreas, exhibits anti-inflammatory effects by inhibiting NF-κB activation and is implicated in maintaining intestinal barrier integrity and preventing bacterial overgrowth and translocation. Here we explore, with the aid of complementary animal and human experiments, the potential role of FXR in acute pancreatitis.

Different cutoff values for thyroid transcription factor-1 antibodies in the diagnosis of lung adenocarcinoma.

With the use of more specific treatments and targeted therapies for non-small cell lung carcinoma, distinction between adenocarcinoma (ADC) or squamous cell carcinoma (SCC) becomes increasingly important. For this, the key technique is an immunohistochemical panel in which a thyroid transcription factor-1 (TTF-1) antibody is often used. Two different TTF-1 clones (8G7G3/1 and SPT24) are used in daily practice, which appear to have different sensitivities and specificities.

Flexible propulsors in ground effect.

We present experimental evidence for the hydrodynamic benefits of swimming 'in ground effect', that is, near a solid boundary. This situation is common to fish that swim near the substrate, especially those that are dorsoventrally compressed, such as batoids and flatfishes. To investigate flexible propulsors in ground effect, we conduct force measurements and particle image velocimetry on flexible rectangular panels actuated at their leading edge near the wall of a water channel.

The estimation of tumor cell percentage for molecular testing by pathologists is not accurate.

Molecular pathology is becoming more and more important in present day pathology. A major challenge for any molecular test is its ability to reliably detect mutations in samples consisting of mixtures of tumor cells and normal cells, especially when the tumor content is low. The minimum percentage of tumor cells required to detect genetic abnormalities is a major variable.

EGFR and KRAS mutations in lung carcinomas in the Dutch population: increased EGFR mutation frequency in malignant pleural effusion of lung adenocarcinoma.

Background: Frequencies of EGFR and KRAS mutations in non-small cell lung cancer (NSCLC) have predominantly been determined in East Asian and North American populations, showing large differences between these populations. The aim of the present study was to determine the frequency of EGFR and KRAS mutations in NSCLC in the West European Dutch population in primary carcinomas and different metastatic locations.

Methods: EGFR (exons 19, 20 and 21) and KRAS (exons 2 and 3) mutation test results of NSCLC samples of patients in 13 hospitals were collected.

Wake structures behind a swimming robotic lamprey with a passively flexible tail.

A robotic lamprey, based on the silver lamprey, Ichthyomyzon unicuspis, was used to investigate the influence of passive tail flexibility on the wake structure and thrust production during anguilliform swimming. A programmable microcomputer actuated 11 servomotors that produce a traveling wave along the length of the lamprey body. The waveform was based on kinematic studies of living lamprey, and the shape of the tail was taken from a computer tomography scan of the silver lamprey.

Model of accommodation: contributions of lens geometry and mechanical properties to the development of presbyopia.

Purpose: To determine the relative importance of lens geometry and mechanical properties for the mechanics of accommodation and the role of these elements in the causes and potential correction of presbyopia.

Setting: Department of Mechanical and Aerospace Engineering, Princeton University, Princeton, New Jersey, USA.

Design: Experimental study.

Using hyperbolic Lagrangian coherent structures to investigate vortices in bioinspired fluid flows.

We use direct Lyapunov exponents to identify Lagrangian coherent structures (LCSs) in a bioinspired fluid flow: the wakes of rigid pitching panels with a trapezoidal planform geometry chosen to model idealized fish caudal fins. When compared with commonly used Eulerian criteria, the Lagrangian method has previously exhibited the ability to define structure boundaries without relying on a preselected threshold. In addition, qualitative changes in the LCS have previously been shown to correspond to physical changes in the vortex structure.

Effects of three-dimensionality on thrust production by a pitching panel.

To understand the fluid dynamics of a biologically inspired unsteady low-aspect-ratio propulsor, unsteady pressure distributions were measured and compared with time-averaged thrust performance and wake visualizations. The experiments were performed on rigid rectangular panels with different aspect ratios, pitching in a uniform flow. Panel aspect ratio and pitching amplitude were shown to affect the magnitude and time dependence of the pressure distribution on the panel surface, the vorticity generation on the panel, and thrust production.

Thrust performance of unsteady propulsors using a novel measurement system, and corresponding wake patterns.

An apparatus is described for the measurement of unsteady thrust and propulsive efficiency produced by biologically inspired oscillating hydrodynamic propulsors. Force measurement is achieved using a strain-gauge-based force transducer, augmented with a lever to amplify or attenuate the applied force and control the measurement sensitivity and natural frequency of vibration. The lever can be used to tune the system to a specific application and it is shown that, using the lever, the stiffness can be made to increase more rapidly than the measurement sensitivity decreases.

The wake structure and thrust performance of a rigid low-aspect-ratio pitching panel.

Thrust performance and wake structure were investigated for a rigid rectangular panel pitching about its leading edge in a free stream. For Re(C) = O(10(4)), thrust coefficient was found to depend primarily on Strouhal number St and the aspect ratio of the panel AR. Propulsive efficiency was sensitive to aspect ratio only for AR less than 0.

Flowfield measurements in the wake of a robotic lamprey.

Experiments are reported on the hydrodynamics of a swimming robotic lamprey under conditions of steady swimming and where the thrust exceeds the drag. The motion of the robot was based on the swimming of live lampreys, which is described by an equation similar to that developed for the American eel by Tytell and Lauder (J Exp Biol 207:1825-1841, 2004). For steady swimming, the wake structure closely resembles that of the American eel, where two pairs of same sign vortices are shed each tail beat cycle, giving the wake a 2P structure.

On the evolution of the wake structure produced by a low-aspect-ratio pitching panel.

Flow visualization is used to interrogate the wake structure produced by a rigid flat panel of aspect ratio (span/chord) 0.54 pitching in a free stream at a Strouhal number of 0.23.