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Search Results: 1 - 10 of 402 matches for " Els Troost "
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Correction: Visualization of the intracavitary blood flow in systemic ventricles of Fontan patients by contrast echocardiography using particle image velocimetry
Konstantinos Lampropoulos, Werner Budts, Alexander Van de Bruaene, Els Troost, Joost P van Melle
Cardiovascular Ultrasound , 2012, DOI: 10.1186/1476-7120-10-18
Abstract: The correct legend for Figure 1 is:Sequence analysis of systemic ventricular flow during systole and diastole in Fontan patients. The vortex from the Fontan group was consistently shorter, wider and rounder. The vortices were located at the centre of the left ventricle throughout diastole and systole and did not redirect flow in a coherent, sequential fashion as in controls. The location, shape and sphericity of the main vortices differ clearly from controls in all cardiac cycle [early diastole(A), late diastole(B), ejection (C)].The correct legend for Figure 2 is:Sequence analysis of systemic ventricular flow during systole and diastole in controls. The vortex from the control group was compact, elliptically shaped, and located apically. The location, shape and sphericity of the main vortices differ clearly from the Fontan group in all cardiac cycle [early diastole(A), late diastole(B), ejection (C)].It was also noted the legends for the Additional file 1 and Addition file 2 were also incorrect:The correct legend for Additional file 1 is:The flow patterns of a 38 year old female without cardiac abnormalitiesThe correct legend for Additional file 2 is:The flow pattern of a 29 year old male with Fontan circulation.The authors would like to apologize for any inconvenience caused by this error.
Visualization of the intracavitary blood flow in systemic ventricles of Fontan patients by contrast echocardiography using particle image velocimetry
Konstantinos Lampropoulos, Werner Budts, Alexander Van de Bruaene, Els Troost, Joost P van Melle
Cardiovascular Ultrasound , 2012, DOI: 10.1186/1476-7120-10-5
Abstract: Twenty-three patients (8 Fontan and 15 normal patients) underwent echocardiography with intravenous contrast agent (Sonovue?) administration. Dedicated software was used to perform particle image velocimetry (PIV) and to visualize intracavitary flow in the systemic ventricles of the patients. Vortex parameters including vortex depth, length, width, and sphericity index were measured. Vortex pulsatility parameters including relative strength, vortex relative strength, and vortex pulsation correlation were also measured.The data from this study show that it is feasible to perform particle velocimetry in Fontan patients. Vortex length (VL) was significantly lower (0.51 ± 0.09 vs 0.65 ± 0.12, P = 0.010) and vortex width (VW) (0.32 ± 0.06 vs 0.27 ± 0.04, p = 0.014), vortex pulsation correlation (VPC) (0.26 ± 0.25 vs -0.22 ± 0.87, p = 0.05) were significantly higher in Fontan patients. Sphericity index (SI) (1.66 ± 0.48 vs 2.42 ± 0.62, p = 0.005), relative strength (RS) (0.77 ± 0.33 vs 1.90 ± 0.47, p = 0.0001), vortex relative strength (VRS) (0.18 ± 0.13 vs 0.43 ± 0.14, p = 0.0001) were significantly lower in the Fontan patients group.PIV using contrast echocardiography is feasible in Fontan patients. Fontan patients had aberrant flow patterns as compared to normal hearts in terms of position, shape and sphericity of the main vortices. The vortex from the Fontan group was consistently shorter, wider and rounder than in controls. Whether vortex characteristics are related with clinical outcome is subject to further investigation.Particle image velocimetry is a new technique of determining the velocity and the direction of fluid streams by analyzing the change in position of small particles that drift with the fluid. With the recent development of echocardiographic technology, it is now possible to apply this approach to contrast-enhanced echocardiographic imaging [1-3].The growing knowledge about the structure and function of the ventricle [4] was of high interest to us in
Willem III en de exclusion crisis, 1679-1681
W. Troost
BMGN : Low Countries Historical Review , 1992,
Abstract:
Winding strings and AdS_3 black holes
Jan Troost
Physics , 2002, DOI: 10.1088/1126-6708/2002/09/041
Abstract: We start a systematic study of string theory in AdS_3 black hole backgrounds. Firstly, we analyse in detail the geodesic structure of the BTZ black hole, including spacelike geodesics. Secondly, we study the spectrum for massive and massless scalar fields, paying particular attention to the connection between Sl(2,R) subgroups, the theory of special functions and global properties of the BTZ black holes. We construct classical strings that wind the black holes. Finally, we apply the general formalism to the vacuum black hole background, and formulate the boundary spacetime Virasoro algebra in terms of worldsheet operators. We moreover establish the link between a proposal for a ghost free spectrum for Sl(2,R) string propagation and the massless black hole background, thereby claryfing aspects of the AdS3/CFT correspondence.
Constant field strengths on T^{2n}
J. Troost
Physics , 1999, DOI: 10.1016/S0550-3213(99)00721-X
Abstract: We analyse field strength configurations in U(N) Yang-Mills theory on T^{2n} that are diagonal and constant, extending early work of Van Baal on T^4. The spectrum of fluctuations is determined and the eigenfunctions are given explicitly in terms of theta functions on tori. We show the relevance of the analysis to higher dimensional D-branes and discuss applications of the results in string theory.
Higgsed antisymmetric tensors and topological defects
J. Troost
Physics , 1999, DOI: 10.1016/S0370-2693(99)00574-2
Abstract: We find topological defect solutions to the equations of motion of a generalised Higgs model with antisymmetric tensor fields. These solutions are direct higher dimensional analogues of the Nielsen-Olesen vortex solution for a gauge field in four dimensions.
The non-abelian Born-Infeld action at order F^6
Alexander Sevrin,Jan Troost,Walter Troost
Physics , 2001, DOI: 10.1016/S0550-3213(01)00104-3
Abstract: To gain insight into the non-abelian Born-Infeld (NBI) action, we study coinciding D-branes wrapped on tori, and turn on magnetic fields on their worldvolume. We then compare predictions for the spectrum of open strings stretching between these D-branes, from perturbative string theory and from the effective NBI action. Under some plausible assumptions, we find corrections to the Str-prescription for the NBI action at order F^6. In the process we give a way to classify terms in the NBI action that can be written in terms of field strengths only, in terms of permutation group theory.
Sequential Notch Signalling at the Boundary of Fringe Expressing and Non-Expressing Cells
Tobias Troost, Thomas Klein
PLOS ONE , 2012, DOI: 10.1371/journal.pone.0049007
Abstract: Wing development in Drosophila requires the activation of Wingless (Wg) in a small stripe along the boundary of Fringe (Fng) expressing and non-expressing cells (FB), which coincides with the dorso-ventral (D/V) boundary of the wing imaginal disc. The expression of Wg is induced by interactions between dorsal and ventral cells mediated by the Notch signalling pathway. It appears that mutual signalling from dorsal to ventral and ventral to dorsal cells by the Notch ligands Serrate (Ser) and Delta (Dl) respectively establishes a symmetric domain of Wg that straddles the D/V boundary. The directional signalling of these ligands requires the modification of Notch in dorsal cells by the glycosyltransferase Fng and is based on the restricted expression of the ligands with Ser expression to the dorsal and that of Dl to the ventral side of the wing anlage. In order to further investigate the mechanism of Notch signalling at the FB, we analysed the function of Fng, Ser and Dl during wing development at an ectopic FB and at the D/V boundary. We find that Notch signalling is initiated in an asymmetric fashion on only one side of the FB. During this initial asymmetric phase, only one ligand is required, with Ser initiating Notch-signalling at the D/V and Dl at the ectopic FB. Furthermore, our analysis suggests that Fng has also a positive effect on Ser signalling. Because of these additional properties, differential expression of the ligands, which has been a prerequisite to restrict Notch activation to the FB in the current model, is not required to restrict Notch signalling to the FB.
The Geometry of Supersymmetric Sigma-Models
Alexander Sevrin,Jan Troost
Physics , 1996,
Abstract: We review non-linear sigma-models with (2,1) and (2,2) supersymmetry. We focus on off-shell closure of the supersymmetry algebra and give a complete list of (2,2) superfields. We provide evidence to support the conjecture that all N=(2,2) non-linear sigma-models can be described by these fields. This in its turn leads to interesting consequences about the geometry of the target manifolds. One immediate corollary of this conjecture is the existence of a potential for hyper-Kahler manifolds, different from the Kahler potential, which does not only allow for the computation of the metric, but of the three fundamental two-forms as well. Several examples are provided: WZW models on SU(2) x U(1) and SU(2) x SU(2) and four-dimensional special hyper-Kahler manifolds.
Off-Shell Formulation of N=2 Non-Linear Sigma-Models
Alexander Sevrin,Jan Troost
Physics , 1996, DOI: 10.1016/S0550-3213(97)00103-X
Abstract: We study d=2, N=(2,2) non-linear sigma-models in (2,2) superspace. By analyzing the most general constraints on a superfield, we show that through an appropriate choice of coordinates, there are no other superfields than chiral, twisted chiral and semi-chiral ones. We study the resulting sigma-models and we speculate on the possibility that all (2,2) non-linear sigma-models can be described using these fields. We apply the results to two examples: the SU(2) x U(1) and the SU(2) x SU(2) WZW model. Pending upon the choice of complex structures, the former can be described in terms of either one semi-chiral multiplet or a chiral and a twisted chiral multiplet. The latter is formulated in terms of one semi-chiral and one twisted chiral multiplet. For both cases we obtain the potential explicitely.
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