Computing the local pressure in molecular dynamics simulations

Computer simulations of inhomogeneous soft matter systems often require accurate methods for computing the local pressure. We present a simple derivation, based on the virial relation, of two equivalent expressions for the local (atomistic) pressure in a molecular dynamics simulation. One of these expressions, previously derived by other authors via a different route, involves summation over interactions between particles within the region of interest; the other involves summation over interactions across the boundary of the region of interest. We illustrate our derivation using simulations of a simple osmotic system; both expressions produce accurate results even when the region of interest over which the pressure is measured is very small.Comment: 11 pages, 4 figure

Comprehensive optical and data management infrastructure for high-throughput light-sheet microscopy of whole mouse brains

Comprehensive mapping and quantification of neuronal projections in the central nervous system requires high-throughput imaging of large volumes with microscopic resolution. To this end, we have developed a confocal light-sheet microscope that has been optimized for three-dimensional (3-D) imaging of structurally intact clarified whole-mount mouse brains. We describe the optical and electromechanical arrangement of the microscope and give details on the organization of the microscope management software. The software orchestrates all components of the microscope, coordinates critical timing and synchronization, and has been written in a versatile and modular structure using the LabVIEW language. It can easily be adapted and integrated to other microscope systems and has been made freely available to the light-sheet community. The tremendous amount of data routinely generated by light-sheet microscopy further requires novel strategies for data handling and storage. To complete the full imaging pipeline of our high-throughput microscope, we further elaborate on big data management from streaming of raw images up to stitching of 3-D datasets. The mesoscale neuroanatomy imaged at micron-scale resolution in those datasets allows characterization and quantification of neuronal projections in unsectioned mouse brains

Case studies to illustrate the rotorcraft certification by simulation process; CS 29/27 low-speed controllability

© The AuthorsThis paper is one of a set presented at the 49th European Rotorcraft Forum discussing results from the EU Clean Sky 2 project, Rotorcraft Certification by Simulation (RoCS). The process developed by the RoCS team provides guidance on the use of flight simulation in certification and features four case studies that illustrate aspects of the process using flight simulation models and flight test data provided by Leonardo Helicopters. This paper presents the case study for the low-speed controllability requirements from the relevant certification paragraphs in the EASA Certification Specifications CS-27 and CS-29. Following an introduction of the related specifications, and the motivation behind seeking compliance supported by simulation, the various phases of the RCbS process are explored in more detail. The intent is to exercise aspects of the RoCS guidance in a practical application to investigate the implementation, and the strengths and limitations, given real-world constraints. Emphasis is placed on the Validation & Verification as well as the Credibility Assessment, taking into account test and simulation uncertainties. Results from piloted simulation trials are included to illustrate possible flight simulator fidelity assessment methods

Rotorcraft flight simulation to support aircraft certification: a review of the state of the art with an eye to future applications

© The AuthorsThis paper presents the approach for Rotorcraft Certification by Simulation proposed within the RoCS project. In particular, the aspects of model validation and credibility assessment through the usage of uncertainty quantification techniques are reviewed, and some lesson learned are presented. It is shown that the increase of effort required to thoroughly evaluate the capability of the simulation model is often counterbalanced by the advantages of the insight that can be obtained and possibly exploited also for design purposes. It is shown that the numerical approaches, and in some cases even the tools required to perform the necessary uncertainty analyses are publicly available and can be directly employed. This paper is one of a set presented at the 49th European Rotorcraft Forum discussing results from the EU Clean Sky 2 project, Rotorcraft Certification by Simulation (RoCS)

Case studies to illustrate the rotorcraft certification by simulation process; CS 27/29 dynamic stability requirements

© The AuthorsThis paper is one of a set presented at the 49th European Rotorcraft Forum displaying results from the EU Clean Sky 2 project, Rotorcraft Certification by Simulation (RoCS). The process developed by the RoCS team provides guidance on the requirements for the use of simulation in certification and features four case studies that illustrate aspects of the process applied using flight simulation models and flight test data provided by Leonardo Helicopters. This paper presents the case study on Dynamic Stability, for the relevant certification paragraphs in the EASA Certification Specifications CS-27 and CS-29. The Dynamic Stability paragraphs from the Specifications are described and results from simulation model fidelity assessment, and updating compared with test data, are presented for a reference flight condition. The credibility of extrapolations of the flight simulation model results to conditions at higher altitude, different airspeeds and vertical rates of climb are then discussed. Preliminary results from piloted simulation trials, with a ‘new’ flight test manoeuvre, are included to illustrate flight simulator fidelity assessment methods and to explore the veracity of the stability margins set by the Certification Specifications