8,165 research outputs found
The PANDA Detector at FAIR
The PANDA detector is under design to be installed at the HESR storage ring
for antiproton of the future FAIR facility in Darmstadt, Germany. Fundamental
questions of hadron and nuclear physics interactions of antiprotons with
nucleons and nuclei will be pursued using a multipurpose set-up which includes
innovative detectors. Here, the FAIR facility and the PANDA detector are
described.Comment: Parallel talk at ICHEP08, Philadelphia USA, July 2008. 4 pages, 2
figure
Ultrarelativistic boost of the black ring
We investigate the ultrarelativistic boost of the five-dimensional
Emparan-Reall non-rotating black ring. Following the classical method of
Aichelburg and Sexl, we determine the gravitational field generated by a black
ring moving ``with the speed of light'' in an arbitrary direction. In
particular, we study in detail two different boosts along axes orthogonal and
parallel to the plane of the ring circle, respectively. In both cases, after
the limit one obtains a five-dimensional impulsive pp-wave propagating in
Minkowski spacetime. The curvature singularity of the original static spacetime
becomes a singular source within the wave front, in the shape of a ring or a
rod according to the direction of the boost. In the case of an orthogonal
boost, the wave front contains also a remnant of the original disk-shaped
membrane as a component of the Ricci tensor (which is everywhere else
vanishing). We also analyze the asymptotic properties of the boosted black ring
at large spatial distances from the singularity, and its behaviour near the
sources. In the limit when the singularity shrinks to a point, one recovers the
well known five-dimensional analogue of the Aichelburg-Sexl ``monopole''
solution.Comment: 10 pages, 2 figures, REVTeX 4. v2: added boost in an arbitrary
direction, one new figure, one new reference. To appear in Phys. Rev.
The generalized identification of truly interfacial molecules (ITIM) algorithm for nonplanar interfaces
We present a generalized version of the ITIM algorithm for the identification of interfacial molecules, which is able to treat arbitrarily shaped interfaces. The algorithm exploits the similarities between the concept of probe sphere used in ITIM and the circumsphere criterion used in the α-shapes approach, and can be regarded either as a reference-frame independent version of the former, or as an extended version of the latter that includes the atomic excluded volume. The new algorithm is applied to compute the intrinsic orientational order parameters of water around a dodecylphosphocholine and a cholic acid micelle in aqueous environment, and to the identification of solvent-reachable sites in four model structures for soot. The additional algorithm introduced for the calculation of intrinsic density profiles in arbitrary geometries proved to be extremely useful also for planar interfaces, as it allows to solve the paradox of smeared intrinsic profiles far from the interface. © 2013 American Institute of Physics
Molecular dissection of Phaseolus vulgaris polygalacturonase-inhibiting protein 2 reveals the presence of hold/release domains affecting protein trafficking toward the cell wall
The plant endomembrane system is massively involved in the synthesis, transport and
secretion of cell wall polysaccharides and proteins; however, the molecular mechanisms
underlying trafficking toward the apoplast are largely unknown. Besides constitutive, the
existence of a regulated secretory pathway has been proposed. A polygalacturonase
inhibitor protein (PGIP2), known to move as soluble cargo and reach the cell wall
through a mechanism distinguishable from default, was dissected in its main functional
domains (A, B, C, D), and C sub-fragments (C1–10), to identify signals essential for its
regulated targeting. The secretion patterns of the fluorescent chimeras obtained by fusing
different PGIP2 domains to the green fluorescent protein (GFP) were analyzed. PGIP2
N-terminal and leucine-rich repeat domains (B and C, respectively) seem to operate as
holding/releasing signals, respectively, during PGIP2 transit through the Golgi. The B
domain slows down PGIP2 secretion by transiently interacting with Golgi membranes.
Its depletion leads, in fact, to the secretion via default (Sp2-susceptible) of the ACD-GFP
chimera faster than PGIP2. Depending on its length (at least the first 5 leucine-rich repeats
are required), the C domain modulates B interaction with Golgi membranes allowing the
release of chimeras and their extracellular secretion through a Sp2 independent pathway.
The addition of the vacuolar sorting determinant Chi to PGIP2 diverts the path of the
protein from cell wall to vacuole, suggesting that C domain is a releasing rather than a
cell wall sorting signal
A Non-Local Mean Curvature Flow and its semi-implicit time-discrete approximation
We address in this paper the study of a geometric evolution, corresponding to
a curvature which is non-local and singular at the origin. The curvature
represents the first variation of the energy recently proposed as a variant of
the standard perimeter penalization for the denoising of nonsmooth curves.
To deal with such degeneracies, we first give an abstract existence and
uniqueness result for viscosity solutions of non-local degenerate Hamiltonians,
satisfying suitable continuity assumption with respect to Kuratowsky
convergence of the level sets. This abstract setting applies to an approximated
flow. Then, by the method of minimizing movements, we also build an "exact"
curvature flow, and we illustrate some examples, comparing the results with the
standard mean curvature flow
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