552 research outputs found
Comparison between two mobile absolute gravimeters: optical versus atomic interferometers
We report a comparison between two absolute gravimeters: the LNE-SYRTE cold
atoms gravimeter and FG5#220 of Leibniz Universit\"at of Hannover. They rely on
different principles of operation: atomic and optical interferometry. Both are
movable which enabled them to participated to the last International Comparison
of Absolute Gravimeters (ICAG'09) at BIPM. Immediately after, their bilateral
comparison took place in the LNE watt balance laboratory and showed an
agreement of 4.3 +/- 6.4 {\mu}Gal
Perturbations of the local gravity field due to mass distribution on precise measuring instruments: a numerical method applied to a cold atom gravimeter
We present a numerical method, based on a FEM simulation, for the
determination of the gravitational field generated by massive objects, whatever
geometry and space mass density they have. The method was applied for the
determination of the self gravity effect of an absolute cold atom gravimeter
which aims at a relative uncertainty of 10-9. The deduced bias, calculated with
a perturbative treatment, is finally presented. The perturbation reaches (1.3
\pm 0.1) \times 10-9 of the Earth's gravitational field.Comment: 12 pages, 7 figure
Charge fluctuations in nano-scale capacitors
The fluctuations of the charge on an electrode contain information on the
microscopic correlations within the adjacent fluid and their effect on the
electronic properties of the interface. We investigate these fluctuations using
molecular dynamics simulations in a constant-potential ensemble with histogram
reweighting techniques. This approach offers in particular an efficient,
accurate and physically insightful route to the differential capacitance that
is broadly applicable. We demonstrate these methods with three different
capacitors: pure water between platinum electrodes, and a pure as well as a
solvent-based organic electrolyte each between graphite electrodes. The total
charge distributions with the pure solvent and solvent-based electrolytes are
remarkably Gaussian, while in the pure ionic liquid the total charge
distribution displays distinct non-Gaussian features, suggesting significant
potential-driven changes in the organization of the interfacial fluid
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SAR image segmentation with GMMs
This paper proposes a new approach for Synthetic Aperture Radar (SAR) image segmentation. Segmenting SAR images can be challenging because of the blurry edges and the high speckle. The segmentation proposed is based on a machine learning technique. Gaussian Mixture Models (GMMs) were already used to segment images in the visual field and are here adapted to work with single channel SAR images. The segmentation suggested is designed to be a first step towards feature and model based classification. The recall rate is the most important as the goal is to retain most target's features. A high recall rate of 88%, higher than for other segmentation methods on the Moving and Stationary Target Acquisition and Recognition (MSTAR) dataset, was obtained. The next classification stage is thus not affected by a lack of information while its computation load drops. With this method, the inclusion of disruptive features in models of targets is limited, providing computationally lighter models and a speed up in further classification as the narrower segmented areas foster convergence of models and provide refined features to compare. This segmentation method is hence an asset to template, feature and model based classification methods. Besides this method, a comparison between variants of the GMMs segmentation and a classical segmentation is provided
The electric double layer has a life of its own
Using molecular dynamics simulations with recently developed importance
sampling methods, we show that the differential capacitance of a model ionic
liquid based double-layer capacitor exhibits an anomalous dependence on the
applied electrical potential. Such behavior is qualitatively incompatible with
standard mean-field theories of the electrical double layer, but is consistent
with observations made in experiment. The anomalous response results from
structural changes induced in the interfacial region of the ionic liquid as it
develops a charge density to screen the charge induced on the electrode
surface. These structural changes are strongly influenced by the out-of-plane
layering of the electrolyte and are multifaceted, including an abrupt local
ordering of the ions adsorbed in the plane of the electrode surface,
reorientation of molecular ions, and the spontaneous exchange of ions between
different layers of the electrolyte close to the electrode surface. The local
ordering exhibits signatures of a first-order phase transition, which would
indicate a singular charge-density transition in a macroscopic limit
Rotation symmetry axes and the quality index in a 3D octahedral parallel robot manipulator system
The geometry of a 3D octahedral parallel robot manipulator system is specified in terms of two rigid octahedral structures (the fixed and moving platforms) and six actuation legs. The symmetry of the system is exploited to determine the behaviour of (a new version of) the quality index for various motions. The main results are presented graphically
Probabilistic analysis of the upwind scheme for transport
We provide a probabilistic analysis of the upwind scheme for
multi-dimensional transport equations. We associate a Markov chain with the
numerical scheme and then obtain a backward representation formula of
Kolmogorov type for the numerical solution. We then understand that the error
induced by the scheme is governed by the fluctuations of the Markov chain
around the characteristics of the flow. We show, in various situations, that
the fluctuations are of diffusive type. As a by-product, we prove that the
scheme is of order 1/2 for an initial datum in BV and of order 1/2-a, for all
a>0, for a Lipschitz continuous initial datum. Our analysis provides a new
interpretation of the numerical diffusion phenomenon
Performance evaluation of parallel manipulators for milling application
This paper focuses on the performance evaluation of the parallel manipulators
for milling of composite materials. For this application the most significant
performance measurements, which denote the ability of the manipulator for the
machining are defined. In this case, optimal synthesis task is solved as a
multicriterion optimization problem with respect to the geometric, kinematic,
kinetostatic, elastostostatic, dynamic properties. It is shown that stiffness
is an important performance factor. Previous models operate with links
approximation and calculate stiffness matrix in the neighborhood of initial
point. This is a reason why a new way for stiffness matrix calculation is
proposed. This method is illustrated in a concrete industrial problem
Variations in 123I-metaiodobenzylguanidine (MIBG) late heart mediastinal ratios in chronic heart failure: a need for standardisation and validation
BACKGROUND: There is lack of validation and standardisation of acquisition parameters for myocardial (123)I-metaiodobenzylguanidine (MIBG). This lack of standardisation hampers large scale implementation of (123)I-MIBG parameters in the evaluation of patients with chronic heart failure (CHF). METHODS: In a retrospective multi-centre study (123)I-MIBG planar scintigrams obtained on 290 CHF patients (82% male; 58% dilated cardiomyopathy; New York Heart Association [NYHA classification] > I) were reanalysed to determine the late heart-to-mediastinum ratio (H/M). RESULTS: There was a large variation in acquisition parameters. Multivariate forward stepwise regression showed that a significant proportion (31%, p < 0.001) of the variation in late H/M could be explained by a model containing patient-related variables and acquisition parameters. Left ventricular ejection fraction (p < 0.001), type of collimation (p < 0.001), acquisition duration (p = 0.001), NYHA class (p = 0.028) and age (p = 0.034) were independent predictors of late H/M. CONCLUSIONS: Acquisitions parameters are independent contributors to the variation of semi-quantitative measurements of cardiac (123)I-MIBG uptake. Improved standardisation of cardiac (123)I-MIBG imaging parameters would contribute to increased clinical applicability for this procedur
Monotherapy with the PCSK9 inhibitor alirocumab versus ezetimibe in patients with hypercholesterolemia:Results of a 24week, double-blind, randomized Phase 3 trial
Background:Efficacy and safety of alirocumab were compared with ezetimibe in hypercholesterolemic patients at moderate cardiovascular risk not receiving statins or other lipid-lowering therapy. Methods In a Phase 3, randomized, double-blind, double-dummy study (NCT01644474), patients (low-density lipoprotein cholesterol [LDL-C] 100â190 mg/dL, 10-year risk of fatal cardiovascular events = 1%â<5% [systemic coronary risk estimation]) were randomized to ezetimibe 10 mg/day (n = 51) or alirocumab 75 mg subcutaneously (via 1ÂmL autoinjector) every 2 weeks (Q2W) (n = 52), with dose up-titrated to 150 mg Q2W (also 1 mL) at week 12 if week 8 LDL-C was = 70 mg/dL. Primary endpoint was mean LDL-C % change from baseline to 24 weeks, analyzed using all available data (intent-to-treat approach, ITT). Analyses using on-treatment LDL-C values were also conducted.Results: Mean (SD) baseline LDL-C levels were 141.1 (27.1) mg/dL (alirocumab) and138.3 (24.5) mg/dL (ezetimibe). The 24-week treatment period was completed by 85% of alirocumab and 86% of ezetimibe patients. Least squares mean (SE) LDL-C reductions were 47 (3)% with alirocumab versus 16 (3)% with ezetimibe (ITT; p < 0.0001) and 54 (2)% versus 17 (2)% (on-treatment; p < 0.0001).At week 12, before up-titration, alirocumab 75 mg Q2W reduced LDL-C by 53 (2)% (on-treatment). Injection site reactions were infrequent (< 2% and < 4% of alirocumab and ezetimibe patients, respectively). Conclusions: Alirocumab demonstrated significantly greater LDL-C lowering versus ezetimibe after 24 weeks with the lower 75 mg Q2W dose sufficient to provide = 50% LDL-C reduction in the majority of the patients. Adverse events were comparable between groups.</p
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