3,948 research outputs found
Off-equilibrium corrections to energy and conserved charge densities in the relativistic fluid in heavy-ion collisions
Dissipative processes in relativistic fluids are known to be important in the
analyses of the hot QCD matter created in high-energy heavy-ion collisions. In
this work, I consider dissipative corrections to energy and conserved charge
densities, which are conventionally assumed to be vanishing but could be
finite. Causal dissipative hydrodynamics is formulated in the presence of those
dissipative currents. The relation between hydrodynamic stability and transport
coefficients is discussed. I then study their phenomenological consequences on
the observables of heavy-ion collisions in numerical simulations. It is shown
that particle spectra and elliptic flow can be visibly modified.Comment: 10 pages, 5 figures; title changed, references added, conclusions
unchange
Metrological characterization of a vision-based system for relative pose measurements with fiducial marker mapping for spacecrafts
An improved approach for the measurement of the relative pose between a target and a chaser spacecraft is presented. The selected method is based on a single camera, which can be mounted on the chaser, and a plurality of fiducial markers, which can be mounted on the external surface of the target. The measurement procedure comprises of a closed-form solution of the Perspective from n Points (PnP) problem, a RANdom SAmple Consensus (RANSAC) procedure, a non-linear local optimization and a global Bundle Adjustment refinement of the marker map and relative poses. A metrological characterization of the measurement system is performed using an experimental set-up that can impose rotations combined with a linear translation and can measure them. The rotation and position measurement errors are calculated with reference instrumentations and their uncertainties are evaluated by the Monte Carlo method. The experimental laboratory tests highlight the significant improvements provided by the Bundle Adjustment refinement. Moreover, a set of possible influencing physical parameters are defined and their correlations with the rotation and position errors and uncertainties are analyzed. Using both numerical quantitative correlation coefficients and qualitative graphical representations, the most significant parameters for the final measurement errors and uncertainties are determined. The obtained results give clear indications and advice for the design of future measurement systems and for the selection of the marker positioning on a satellite surface
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β-cell dedifferentiation in diabetes is important, but what is it?
This commentary discusses the concept of β-cell dedifferentiation in diabetes, which is important but not well defined. A broad interpretation is that a state of differentiation has been lost, which means changes in gene expression as well as in structural and functional elements. Thus, a fully mature healthy β cell will have its unique differentiation characteristics, but maturing cells and old β cells will have different patterns of gene expression and might therefore be considered as dedifferentiated. The meaning of dedifferentiation is now being debated because β cells in the diabetic state lose components of their differentiated state, which results in severe dysfunction of insulin secretion. The major cause of this change is thought to be glucose toxicity (glucotoxicity) and that lowering glucose levels with treatment results in some restoration of function. An issue to be discussed is whether dedifferentiated β cells return to a multipotent precursor cell phenotype or whether they follow a different pathway of dedifferentiation
Observations of Reduced Electron Gyroscale Fluctuations in National Spherical Torus Experiment H-Mode Plasmas with Large E X B Flow Shear
Electron gyroscale fluctuation measurements in National Spherical Torus Experiment H-mode plasmas with large toroidal rotation reveal fluctuations consistent with electron temperature gradient (ETG) turbulence. Large toroidal rotation in National Spherical Torus Experiment plasmas with neutral beam injection generates ExB flow shear rates comparable to ETG linear growth rates. Enhanced fluctuations occur when the electron temperature gradient is marginally stable with respect to the ETG linear critical gradient. Fluctuation amplitudes decrease when the ExB flow shear rate exceeds ETG linear growth rates. The observations indicate that ExB flow shear can be an effective suppression mechanism for ETG turbulence.X1129sciescopu
Dark Matter and Pseudo-flat Directions in Weakly Coupled SUSY Breaking Sectors
We consider candidates for dark matter in models of gauge mediated
supersymmetry breaking, in which the supersymmetry breaking sector is weakly
coupled and calculable. Such models typically contain classically flat
directions, that receive one-loop masses of a few TeV. These pseudo-flat
directions provide a new mechanism to account for the cold dark matter relic
abundance. We discuss also the possibility of heavy gravitino dark matter in
such models.Comment: 16 pages, 2 figures. v2: comments, refs adde
Chiral Rings, Anomalies and Electric-Magnetic Duality
We study electric-magnetic duality in the chiral ring of a supersymmetric
U(N_c) gauge theory with adjoint and fundamental matter, in presence of a
general confining phase superpotential for the adjoint and the mesons. We find
the magnetic solution corresponding to both the pseudoconfining and higgs
electric vacua. By means of the Dijkgraaf-Vafa method, we match the effective
glueball superpotentials and show that in some cases duality works exactly
offshell. We give also a picture of the analytic structure of the resolvents in
the magnetic theory, as we smoothly interpolate between different higgs vacua
on the electric side.Comment: 54 pages, harvmac. v2: typos correcte
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