Mechanical Evidence of the Orbital Angular Momentum to Energy Ratio of Vortex Beams

We measure, in a single experiment, both the radiation pressure and the torque due to a wide variety of propagating acoustic vortex beams. The results validate, for the first time directly, the theoretically predicted ratio of the orbital angular momentum to linear momentum in a propagating beam. We experimentally determine this ratio using simultaneous measurements of both the levitation force and the torque on an acoustic absorber exerted by a broad range of helical ultrasonic beams produced by a 1000-element matrix transducer array. In general, beams with helical phase fronts have been shown to contain orbital angular momentum as the result of the azimuthal component of the Poynting vector around the propagation axis. Theory predicts that for both optical and acoustic helical beams the ratio of the angular momentum current of the beam to the power should be given by the ratio of the beam’s topological charge to its angular frequency. This direct experimental observation that the ratio of the torque to power does convincingly match the expected value (given by the topological charge to angular frequency ratio of the beam) is a fundamental result

Combustion of hydrogen-air jets in local chemical equilibrium: A guide to the CHARNAL computer program

A guide to a computer program, written in FORTRAN 4, for predicting the flow properties of turbulent mixing with combustion of a circular jet of hydrogen into a co-flowing stream of air is presented. The program, which is based upon the Imperial College group's PASSA series, solves differential equations for diffusion and dissipation of turbulent kinetic energy and also of the R.M.S. fluctuation of hydrogen concentration. The effective turbulent viscosity for use in the shear stress equation is computed. Chemical equilibrium is assumed throughout the flow

Multidimensional collaboration; reflections on action research in a clinical context

This paper reflects on the challenges and benefits of multidimensional collaboration in an action research study to evaluate and improve preoperative education for patients awaiting colorectal surgery. Three cycles of planning, acting,observing and reflecting were designed to evaluate practice and implement change in this interactive setting, calling for specific and distinct collaborations. Data collection includes: observing educational interactions; administering patient evaluation questionnaires; interviewing healthcare staff, patients and carers; patient and carer focus groups; and examining written and audiovisual educational materials. The study revolves around and depends on multi-dimensional collaborations. Reflecting on these collaborations highlights the diversity of perspectives held by all those engaged in the study and enhances the action research lessons. Successfully maintaining the collaborations recognises the need for negotiation, inclusivity, comprehension, brokerage,and problem-solving. Managing the potential tensions is crucial to the successful implementation of changes introduced to practice and thus has important implications for patients’ well-being. This paper describes the experiences from an action research project involving new and specific collaborations, focusing on a particular healthcare setting. It exemplifies the challenges of the collaborative action research process and examines how both researchers and practitioners might reflect on the translation of theory into educational practices within a hospital colorectal department. Despite its context-specific features, the reflections on the types of challenges faced and lessons learned provide implications for action researchers in diverse healthcare settings across the world

State of the art: noninvasive imaging and management of neurovascular trauma

Neurotrauma represents a significant public health problem, accounting for a significant proportion of the morbidity and mortality associated with all traumatic injuries. Both blunt and penetrating injuries to cervicocerebral vessels are significant and are likely more common than previously recognized. Imaging of such injuries is an important component in the evaluation of individuals presenting with such potential injuries, made all the more important since many of the vascular injuries are clinically silent. Management of injuries, particularly those caused by blunt trauma, is constantly evolving. This article addresses the current state of imaging and treatment of such injuries

Simultaneous Water Vapor and Dry Air Optical Path Length Measurements and Compensation with the Large Binocular Telescope Interferometer

The Large Binocular Telescope Interferometer uses a near-infrared camera to measure the optical path length variations between the two AO-corrected apertures and provide high-angular resolution observations for all its science channels (1.5-13 $\mu$m). There is however a wavelength dependent component to the atmospheric turbulence, which can introduce optical path length errors when observing at a wavelength different from that of the fringe sensing camera. Water vapor in particular is highly dispersive and its effect must be taken into account for high-precision infrared interferometric observations as described previously for VLTI/MIDI or the Keck Interferometer Nuller. In this paper, we describe the new sensing approach that has been developed at the LBT to measure and monitor the optical path length fluctuations due to dry air and water vapor separately. After reviewing the current performance of the system for dry air seeing compensation, we present simultaneous H-, K-, and N-band observations that illustrate the feasibility of our feedforward approach to stabilize the path length fluctuations seen by the LBTI nuller.Comment: SPIE conference proceeding

Cortical bony thickening of the lateral intercondylar wall : the functional attachment of the anterior cruciate ligament

Background: The anatomy of the anterior cruciate ligament (ACL) has become the subject of much debate. There has been extensive study into attachment points of the native ligament, especially regarding the femoral attachment. Some of these studies have suggested that fibers in the ACL are of differing functional importance. Fibers with higher functional importance would be expected to exert larger mechanical stress on the bone. According to Wolff’s law, cortical thickening would be expected in these areas. Purpose: To examine cortical thickening in the region of the ACL footprint (ie, the functional footprint of the ACL). Study Design: Descriptive laboratory study. Methods: Using micro–computed tomography with resolutions ranging from 71 to 91 μm, the cortical thickness of the lateral wall of the intercondylar notch in 17 cadaveric knees was examined, along with surface topography. After image processing, the relationship between the cortical thickening and surface topology was visually compared. Results: A pattern of cortical thickening consistent with the functional footprint of the ACL was found. On average, this area was 3 times thicker than the surrounding bone and significantly thicker than the remaining lateral wall (P < .0001). This thickening was roughly elliptical in shape (with a mean centroid at 23.5 h:31 t on a Bernard and Hertel grid) and had areas higher on the wall where greater thickness was present. The relationship to previously reported osseous landmarks was variable, although the patterns were broadly consistent with those reported in previous studies describing direct and indirect fibers of the ACL. Conclusion: The findings of this study are consistent with those of recent studies describing fibers in the ACL of differing functional importance. The area in which the thickening was found has been defined and is likely to represent the functional footprint of the ACL

Exoplanet science with the LBTI: instrument status and plans

The Large Binocular Telescope Interferometer (LBTI) is a strategic instrument of the LBT designed for high-sensitivity, high-contrast, and high-resolution infrared (1.5-13 $\mu$m) imaging of nearby planetary systems. To carry out a wide range of high-spatial resolution observations, it can combine the two AO-corrected 8.4-m apertures of the LBT in various ways including direct (non-interferometric) imaging, coronagraphy (APP and AGPM), Fizeau imaging, non-redundant aperture masking, and nulling interferometry. It also has broadband, narrowband, and spectrally dispersed capabilities. In this paper, we review the performance of these modes in terms of exoplanet science capabilities and describe recent instrumental milestones such as first-light Fizeau images (with the angular resolution of an equivalent 22.8-m telescope) and deep interferometric nulling observations.Comment: 12 pages, 6 figures, Proc. SPI

Meniscal transplantation and its effect on osteoarthritis risk : an abridged protocol for the MeTEOR study : a comprehensive cohortstudy incorporating a pilot randomised controlled trial

Objectives: Subtotal or total meniscectomy in the medial or lateral compartment of the knee results in a high risk of future osteoarthritis. Meniscal allograft transplantation has been performed for over thirty years with the scientifically plausible hypothesis that it functions in a similar way to a native meniscus. It is thought that a meniscal allograft transplant has a chondroprotective effect, reducing symptoms and the long-term risk of osteoarthritis. However, this hypothesis has never been tested in a high-quality study on human participants. This study aims to address this shortfall by performing a pilot randomised controlled trial within the context of a comprehensive cohort study design. Methods: Patients will be randomised to receive either meniscal transplant or a non-operative, personalised knee therapy program. MRIs will be performed every four months for one year. The primary endpoint is the mean change in cartilage volume in the weight-bearing area of the knee at one year post intervention. Secondary outcome measures include the mean change in cartilage thickness, T2 maps, patient-reported outcome measures, health economics assessment and complications. Results: This study is expected to report its findings in 2016

The HOSTS Survey for Exozodiacal Dust: Preliminary results and future prospects

[abridged] The presence of large amounts of dust in the habitable zones of nearby stars is a significant obstacle for future exo-Earth imaging missions. We executed an N band nulling interferometric survey to determine the typical amount of such exozodiacal dust around a sample of nearby main sequence stars. The majority of our data have been analyzed and we present here an update of our ongoing work. We find seven new N band excesses in addition to the high confidence confirmation of three that were previously known. We find the first detections around Sun-like stars and around stars without previously known circumstellar dust. Our overall detection rate is 23%. The inferred occurrence rate is comparable for early type and Sun-like stars, but decreases from 71% [+11%/-20%] for stars with previously detected mid- to far-infrared excess to 11% [+9%/-4%] for stars without such excess, confirming earlier results at high confidence. For completed observations on individual stars, our sensitivity is five to ten times better than previous results. Assuming a lognormal luminosity function of the dust, we find upper limits on the median dust level around all stars without previously known mid to far infrared excess of 11.5 zodis at 95% confidence level. The corresponding upper limit for Sun-like stars is 16 zodis. An LBTI vetted target list of Sun-like stars for exo-Earth imaging would have a corresponding limit of 7.5 zodis. We provide important new insights into the occurrence rate and typical levels of habitable zone dust around main sequence stars. Exploiting the full range of capabilities of the LBTI provides a critical opportunity for the detailed characterization of a sample of exozodiacal dust disks to understand the origin, distribution, and properties of the dust.Comment: To appear in SPIE Astronomical Telescopes + Instrumentation 2018 proceedings. Some typos fixed, one reference adde

Rotational dynamics and heating of trapped nanovaterite particles

We synthesize, optically trap, and rotate individual nanovaterite crystals with a mean particle radius of 423 nm. Rotation rates of up to 4.9 kHz in heavy water are recorded. Laser-induced heating due to residual absorption of the nanovaterite particle results in the superlinear behavior of the rotation rate as a function of trap power. A finite element method based on the Navier-Stokes model for the system allows us to determine the residual optical absorption coefficient for a trapped nanovaterite particle. This is further confirmed by the theoretical model. Our data show that the translational Stokes drag force and rotational Stokes drag torque need to be modified with appropriate correction factors to account for the power dissipated by the nanoparticle