Enforcing Temporal Consistency in Physically Constrained Flow Field Reconstruction with FlowFit by Use of Virtual Tracer Particles

Processing techniques for particle based optical flow measurement data such as 3D Particle Tracking Velocimetry (PTV) or the novel dense Lagrangian Particle Tracking method Shake-The-Box (STB) can provide time-series of velocity and acceleration information scattered in space. The following post-processing is key to the quality of space-filling velocity and pressure field reconstruction from the scattered particle data. In this work we describe a straight-forward extension of the recently developed data assimilation scheme FlowFit, which applies physical constraints from the Navier-Stokes equations in order to simultaneously determine velocity and pressure fields as solutions to an inverse problem. We propose the use of additional artificial Lagrangian tracers (virtual particles), which are advected between the flow fields at single time instants to achieve meaningful temporal coupling. This is the most natural way of a temporal constraint in the Lagrangian data framework. Not FlowFit's core method is altered in the current work, but its input in form of Lagrangian tracks. This work shows that the introduction of such particle memory to the reconstruction process significantly improves the resulting flow fields. The method is validated in virtual experiments with two independent DNS test cases. Several contributions are revised to explain the improvements, including correlations of velocity and acceleration errors in the reconstructions and the flow field regularization within the inverse problem

Pressure reconstruction from Lagrangian particle tracking with FFT integration

Volumetric time-resolved pressure gradient fields in unsteady flows can be estimated through flow measurements of the material acceleration in the fluid and the assumption of the governing momentum equation. In order to derive pressure, almost exclusively two numerical methods have been used to spatially integrate the pressure gradient until now: first, direct path integration in the spatial domain, and second, the solution of the Poisson equation with numerical methods. We propose an alternative method by integrating the pressure gradient field directly in Fourier space with a standard FFT function. The method is fast and easy to implement. We demonstrate the accuracy of the integration scheme on a synthetic pressure field and apply it to an experimental example based on acceleration data from Lagrangian particle tracking with high seeding density (Shake-The-Box method)

Self-reported muscle pain in adolescents with migraine and tension-type headache

Aim: To identify possible associations between muscular pain and headache in adolescents in a large population-based sample. Methods: Grammar school students were invited to fill in a questionnaire on headache and associated lifestyle factors. Headache was classified according to the German version of the International Classification of Headache Disorders (2nd edition). Muscular pain was assessed via denoting affected areas in schematic drawings of a body and via provoked muscular pain on controlled movements of head, neck and shoulder regions. Results: Prevalence of any headache within the previous 6 months exceeded 80%. In all subjects muscular pain or pain on movement was most prominent in the neck and shoulder region, ranging from 9% to 27% in the non-headache population to up to 63% for individuals with migraine or mixed migraine and tension-type headache (TTH). Frequency of muscular pain increased significantly with growing chronicity of TTH. Interpretation: A strong association between muscle pain in the neck/shoulder region and headache was observed, pointing to the importance of muscular pain for headache in adolescents. Also, in this age group muscular pain appears to be of particular importance in chronic TTH and – unexpectedly – in migraine, which is the most important new finding in our study

Geochemistry and mineralogy of Western Australian salt lake sediments: Implications for Meridiani Planum on Mars

Hypersaline lakes are characteristic for Western Australia and display a rare combination of geochemical and mineralogical properties which make these lakes potential analogues for past conditions on Mars. In our study we focused on the geochemistry and mineralogy of Lake Orr and Lake Whurr. While both lakes are poor in organic carbon (<1%) the sediments’ pH values differ and range from 3.8 to 4.8 in Lake Orr and from 5.4 to 6.3 in Lake Whurr sediments. Lake Whurr sediments were dominated by orange and red sediment zones in which the main Fe minerals were identified as hematite, goethite, and tentatively jarosite and pyrite. Lake Orr was dominated by brownish and blackish sediments where the main Fe minerals were goethite and another paramagnetic Fe(III)-phase that could not be identified. Furthermore, a likely secondary Fe(II)-phase was observed in Lake Orr sediments. The mineralogy of these two salt lakes in the sampling area is strongly influenced by events such as flooding, evaporation and desiccation, processes that explain at least to some extent the observed differences between Lake Orr and Lake Whurr. The iron mineralogy of Lake Whurr sediments and the high salinity make this lake a suitable analogue for Meridiani Planum on Mars and in particular the tentative identification of pyrite in Lake Whurr sediments has implications for the interpretation of the Fe mineralogy of Meridiani Planum sediments

Large-scale volumetric flow measurement in a pure thermal plume by dense tracking of helium-filled soap bubbles

We present a spatially and temporally highly resolved flow measurement covering a !arge volume (~o.6 m3) in a pure thermal plume in air. The thermal plume develops above an extended heat source and is characterized by moderate velocities (U~0.35 m/s) with a Reynolds number of Re~500 and a Rayleigh number of Ra~100000. We demonstrate the requirements and capa bilities of the measurement equipment and the particle tracking approach to be able to probe measurement volumes up to and beyond one cubic meter. The use of !arge tracer particles (300 µm), helium-filled soap bubbles (HFSBs), is crucial and yields high particle image quality over large-volume depths when illuminated with arrays of pulsed high-power LEDs. The experimental limitations of the HFSBs-their limited lifetime and their intensity loss over time-are quantified. The HFSBs' uniform particle images allows an accurate reconstruction of the flow using Shake-The-Box particle tracking with high partlcle concentrations up to 0.1 particles per pixel. This enables tracking of up to 275,000 HFSBs simultaneously. After interpolating the scattered data onto a regular grid with a Navier-Stokes regularization, the velocity field of the thermal plume reveals a multitude of vortices with a smooth temporal evolution and a remarkable coherence in time (see animation, supplementary data). Acceleration fields are also derived from interpolated particle tracks and complement the flow measurement. Additionally, the flow map, the basis of a !arge dass of Lagrangian coherent structures, is computed directly from observed particle tracks. We show entrainment regions and coherent vortices of the thermal plume in the flow map and compute fields of the finite-time Lyapunov exponent

Investigation of universal small-scale structures in turbulence using Shake-The-Box Lagrangian Particle Tracking and FlowFit

A characteristic property of turbulent flows is the presence of a universal small-scale structure consisting of a shear layer separated by two stretched vortices. This pattern becomes visible by averaging the velocity sampled in the eigenframe of the local strain rate tensor. In this contribution, the structure is detected and tracked over time to investigate its formation and decay. For this purpose, experimental data of a von Karman flow at ReÄ = 370 is used, which is analyzed with Shake-The-Box (STB) Lagrangian Particle Tracking (LPT) and the data assimilation method FlowFit. The universal structure is characterized by the time-resolved mean distribution of dissipation and pressure in the strain rate eigenframe. Using the average power balance terms along all particle trajectories passing through the direct vicinity of conditioned high-dissipation (> 7.5 ) and enstrophy (> 7.5 ) events during the time-span from -4 < t < 4 the Lagrangian energy transport mechanism through such intermittent events can be discovered, at least in a mean sense. It is shown how the impact of the particles in a high dissipative event leads to a part of the energy being converted into heat and another part into rotation in a time period of approximately 2r,;. This finding is consistent with the existence of the universal structure. Thus, a connection of Eulerian universal structures with their underlying energy exchange processes is proposed. Furthermore, instantaneous high dissipative events and the Lagrangian tracks that constitute them are shown and related to the Statistical results

Recasting Tomo-PIV reconstruction as constrained and L1-regularized nonlinear least squares problem

Abstract. Tomo-PIV is a volumetric flow measurement system. It is able to obtain instantaneous 3D-3C velocity fields using multiple cameras that observe the same volume of two subsequently illuminated particle distributions from different angles. Part of the measurement technique is the 3D reconstruction of the particle volume from 2D images. This work presents a promising alternative approach to the popular reconstruction algorithms MART and SMART. Simulations and experimental data of a turbulent free jet at Ma = 0.7 are used in order to assess and demonstrate the performance of the newly developed reconstruction algorithm based on constrained least squares strategies and L1-regularization

Complete genome sequence, lifestyle, and multi-drug resistance of the human pathogen Corynebacterium resistens DSM 45100 isolated from blood samples of a leukemia patient

Schröder J, Maus I, Meyer K, et al. Complete genome sequence, lifestyle, and multi-drug resistance of the human pathogen Corynebacterium resistens DSM 45100 isolated from blood samples of a leukemia patient. BMC Genomics. 2012;13(1): 141.BACKGROUND: Corynebacterium resistens was initially recovered from human infections and recognized as a new coryneform species that is highly resistant to antimicrobial agents. Bacteremia associated with this organism in immunocompromised patients was rapidly fatal as standard minocycline therapies failed. C. resistens DSM 45100 was isolated from a blood culture of samples taken from a patient with acute myelocytic leukemia. The complete genome sequence of C. resistens DSM 45100 was determined by pyrosequencing to identify genes contributing to multi-drug resistance, virulence, and the lipophilic lifestyle of this newly described human pathogen. RESULTS: The genome of C. resistens DSM 45100 consists of a circular chromosome of 2,601,311 bp in size and the 28,312-bp plasmid pJA144188. Metabolic analysis showed that the genome of C. resistens DSM 45100 lacks genes for typical sugar uptake systems, anaplerotic functions, and a fatty acid synthase, explaining the strict lipophilic lifestyle of this species. The genome encodes a broad spectrum of enzymes ensuring the availability of exogenous fatty acids for growth, including predicted virulence factors that probably contribute to fatty acid metabolism by damaging host tissue. C. resistens DSM 45100 is able to use external L-histidine as a combined carbon and nitrogen source, presumably as a result of adaptation to the hitherto unknown habitat on the human skin. Plasmid pJA144188 harbors several genes contributing to antibiotic resistance of C. resistens DSM 45100, including a tetracycline resistance region of the Tet W type known from Lactobacillus reuteri and Streptococcus suis. The tet(W) gene of pJA144188 was cloned in Corynebacterium glutamicum and was shown to confer high levels of resistance to tetracycline, doxycycline, and minocycline in vitro. CONCLUSIONS: The detected gene repertoire of C. resistens DSM 45100 provides insights into the lipophilic lifestyle and virulence functions of this newly recognized pathogen. Plasmid pJA144188 revealed a modular architecture of gene regions that contribute to the multi-drug resistance of C. resistens DSM 45100. The tet(W) gene encoding a ribosomal protection protein is reported here for the first time in corynebacteria. Cloning of the tet(W) gene mediated resistance to second generation tetracyclines in C. glutamicum, indicating that it might be responsible for the failure of minocycline therapies in patients with C. resistens bacteremia

Measurements of the energy dissipation rate in homogeneous turbulence using dense 3D Lagrangian Particle Tracking and FlowFit

We present measurements of the full velocity gradient tensor and all volumetric dissipation rate elements based on dense fields of fluid particle trajectories in homogeneous turbulence at Re ~270 and ~370 in a Kármán flow between two counter-rotating disks with impellers. Applying the Shake-The-Box (STB) Lagrangian Particle Tracking (LPT) algorithm, we are able to instantaneously track up to 80.000 particles in a volume of 40 x 40 x 15 mm³. The mean interparticle distance is lower than 7 Kolmogorov lengths for the Re_lambda ~270 case. A data assimilation scheme (FlowFit) with continuity and Navier-Stokes- constraints is used to interpolate the scattered velocity and acceleration data by a continuous 3D B-Spline representation, enabling to recover (locally) the smallest flow scales. In the presentation, we show Lagrangian velocity and acceleration statistics, as well as the Eulerian counterparts on velocity gradients and pressure fields. We compute the energy dissipation rate directly by making use of quadruples of particle trajectories in close proximity (r < 3 eta) and compare it to indirect approaches using second-order velocity- and velocityacceleration structure functions in the inertial subrange