Optical trapping of nonspherical particles in the T-matrix formalism

The theory of the trapping of nonspherical particles in the focal region of a high-numerical-aperture optical system is formulated in the framework of the transition matrix approach. Both the case of an unaberrated lens and the case of an aberrated one are considered. The theory is applied to single latex spheres of various sizes and, when the results are compared with the available experimental data, a fair agreement is attained. The theory is also applied to binary clusters of spheres of latex with a diameter of 220 nm in various orientations. Although, in this case we have no experimental data to which our results can be compared, we get useful indications for the trapping of nonspherical particles. In particular, we find substantial agreement with recent results on the trapping of prolate spheroids in aberrated gaussian fields [S. H. Simpson and S. Hanna, J. Opt. Soc. Am. A 24, 430 (2007)]

Radiation torque on nonspherical particles in the transition matrix formalism: erratum

An erratum is presented to correct the errors in two equations in Sect. 3 of [Opt. Express 14, 9508--9521 (2006)]

On the rotational stability of nonspherical particles driven by the radiation torque

We calculate the radiation torque exerted by a monochromatic plane wave, either unpolarized or linearly polarized, on aggregates of spheres and investigate the stability of the resulting rotational motion. In fact, neglecting any braking momenta we calculate the component of the electromagnetic torque orthogonal to the principal axis of maximum moment of inertia through the center of mass (transverse torque), as a function of the direction of propagation of the incident field. The aggregates we study are composed of homogeneous spheres, possibly of different materials. The electromagnetic torque is calculated through the transition matrix approach along the lines of the theory reported in our recent paper [F. Borghese, P. Denti, R. Saija and M. A. Iati, Opt. Express 14, 9508 (2006)]. When the transverse component of the electromagnetic torque is small or vanishes the rotational motion driven by the component along the principal axis of inertia may be nearly stable

Multi-disciplinary approach in engineering education: learning with additive manufacturing and reverse engineering

Purpose - The purpose of this paper is to report an interdisciplinary, cooperative-learning project in a second-year course within the "Enzo Ferrari" Master of Science Degree in Mechanical Engineering. The work aims to raise awareness of the educational impact of additive manufacturing and reverse engineering. Design/methodology/approach - Students are asked to develop, concurrently, the design and the manufacturing solution for an eye-tracker head mount. A digital head model is reverse engineered from an anatomical mannequin and used as an ergonomic mock-up. The project includes prototype testing and cost analysis. The device is produced using additive manufacturing techniques for hands-on evaluation by the students. Findings - Results of the presented case study substantiate the authors' belief in the tremendous potential of interdisciplinary project-based learning, relying on innovative technologies to encourage collaboration, motivation and dynamism. Originality/value - The paper confirms a spreading conviction that the soon-to-be engineers will need new practice-oriented capabilities to cope with new competitive scenarios. Engineering education must adapt to the social, rather than industrial, revolution that is being brought about by additive fabrication

Optical trapping calculations for metal nanoparticles. Comparison with experimental data for Au and Ag spheres.

We calculate the optical forces on Au and Ag nanospheres through a procedure based on the Maxwell stress tensor. We compare the theoretical and experimental force constants obtained for gold and silver nanospheres finding good agreement for all particles with r < 80 nm. The trapping of the larger particles recently demonstrated in experiments is not foreseen by our purely electromagnetic theory based on fixed dielectric properties. Since the laser power produces a heating that may be large for the largest spheres, we propose a model in which the latter particles are surrounded by a steam bubble. This model foresees the trapping of these particles and the results turn out to be in reasonable agreement with the experimental data

Direct access transcatheter mitral annuloplasty with a sutureless and adjustable device: preclinical experience†

OBJECTIVES The aim of the study was to evaluate the technical feasibility and performance of a transcatheter mitral annuloplasty system. METHODS Adult swines (n=15) underwent left thoracotomy through the 4th-5th intercostal space. A transcatheter device (CardioBand, Valtech-Cardio Ltd) was introduced through an 18F sheath through the left atrium and attached to the annulus between the posterior and anterior commissures using echocardiographic and fluoroscopic guidance, on the beating heart. The sutureless device was implanted using a steerable delivery system to deploy sequential fixation elements. Following implantation, the device length was adjusted on the beating heart to reduce the intercommissural and septolateral dimension, under echocardiographic guidance. Finally, the flexible adjustment tool was withdrawn from the working sheath and the atrial purse-string closed. All but five animals were sacrificed acutely by intent, while the others were sacrificed at 90 days. RESULTS All animals survived the acute implant. One animal died at the third post-operative day due to bleeding. The annuloplasty system was successfully implanted in all animals. A mean of 12±3 fixation elements were deployed. The band length was reduced up to 20% after implantation in each animal. At necropsy, the location of the implant was within a few millimetres of the annulus (3.5±4mm). In three animals, fixation elements were implanted inadvertently in the leaflets, but no coronary lesions were observed. All animals survived the acute implant. One animal died on the third post-operative day due to bleeding. In the four long-term survivors, the implanted annuloplasty device showed satisfactory healing and no ring dehiscence. CONCLUSIONS Transcatheter minimally invasive, beating-heart implantation of an adjustable annuloplasty band is feasible in the animal model. This approach may be an alternative to open surgical procedures in high-risk patient

A Deep Learning-Based Fully Automated Pipeline for Regurgitant Mitral Valve Anatomy Analysis From 3D Echocardiography

Three-dimensional transesophageal echocardiography (3DTEE) is the recommended imaging technique for the assessment of mitral valve (MV) morphology and lesions in case of mitral regurgitation (MR) requiring surgical or transcatheter repair. Such assessment is key to thorough intervention planning and to intraprocedural guidance. However, it requires segmentation from 3DTEE images, which is timeconsuming, operator-dependent, and often merely qualitative. In the present work, a novel workflow to quantify the patient-specific MV geometry from 3DTEE is proposed. The developed approach relies on a 3D multi-decoder residual convolutional neural network (CNN) with a U-Net architecture for multi-class segmentation of MV annulus and leaflets. The CNN was trained and tested on a dataset comprising 55 3DTEE examinations of MR-affected patients. After training, the CNN is embedded into a fully automatic, and hence fully repeatable, pipeline that refines the predicted segmentation, detects MV anatomical landmarks and quantifies MV morphology. The trained 3D CNN achieves an average Dice score of 0.82 +/- 0.06, mean surface distance of 0.43 +/- 0.14 mm and 95% Hausdorff Distance (HD) of 3.57 +/- 1.56 mm before segmentation refinement, outperforming a state-of-the-art baseline residual U-Net architecture, and provides an unprecedented multi-class segmentation of the annulus, anterior and posterior leaflet. The automatic 3D linear morphological measurements of the annulus and leaflets, specifically diameters and lengths, exhibit differences of less than 1.45 mm when compared to ground truth values. These measurements also demonstrate strong overall agreement with analyses conducted by semi-automated commercial software. The whole process requires minimal user interaction and requires approximately 15 seconds

(User-friendly) formal requirements verification in the context of ISO26262

Abstract In order to achieve the highest safety integrity levels, ISO26262 recommends the use of formal methods for various verification activities, throughout the lifecycle of safety-related embedded systems for road vehicles. Since formal methods are known to be difficult to use, one of the main challenges raised by these ISO26262 requirements is to find cost-effective approaches for being compliant with them. This paper proposes an approach for requirements formal verification where formal methods, languages, and tools are only minimally exposed to the user, and are integrated into one of the commonly used system modeling environments based on SysML. This approach does not require particular expertise in formal methods still allowing to apply them. Hence, personnel training costs and development costs should be kept limited. The proposed approach has been implemented as a plugin of the Topcased environment. Although it is limited to discrete system models, it has been successfully experimented on an industrial use case

Optical Properties of Composite Interstellar Grains: A Morphological Analysis

In the framework of the transition matrix approach, we calculate the relevant optical properties of cosmic dust grains of amorphous carbon and astronomical silicates, modeled as aggregates of spherical monomers. Two mechanisms of aggregation were considered, producing clusters with different structure and degree of fluffiness: ballistic particle-cluster aggregation (BPCA) and ballistic cluster-cluster aggregation (BCCA). Our results are very different from those obtained through computational approaches based on effective medium theories and might have major implications both on the modeling procedure and on the dust-mass balance in the interstellar medium

Ultraviolet Radiation inside Interstellar Grain Aggregates. I. The Density of Radiation

We study the distribution of energy density inside dust grain aggregates through an approach based on the multipole expansion of the electromagnetic fields. A significant fraction of the energy of the impinging wave is found throughout the interiors of grains. Implications for extraterrestrial prebiotic chemistry are discussed