6,289 research outputs found
Polytopal Bier spheres and Kantorovich-Rubinstein polytopes of weighted cycles
The problem of deciding if a given triangulation of a sphere can be realized
as the boundary sphere of a simplicial, convex polytope is known as the
"Simplicial Steinitz problem". It is known by an indirect and non-constructive
argument that a vast majority of Bier spheres are non-polytopal. Contrary to
that, we demonstrate that the Bier spheres associated to threshold simplicial
complexes are all polytopal. Moreover, we show that all Bier spheres are
starshaped. We also establish a connection between Bier spheres and
Kantorovich-Rubinstein polytopes by showing that the boundary sphere of the
KR-polytope associated to a polygonal linkage (weighted cycle) is isomorphic to
the Bier sphere of the associated simplicial complex of "short sets"
Testing Invisible Momentum Ansatze in Missing Energy Events at the LHC
We consider SUSY-like events with two decay chains, each terminating in an
invisible particle, whose true energy and momentum are not measured in the
detector. Nevertheless, a useful educated guess about the invisible momenta can
still be obtained by optimizing a suitable invariant mass function. We review
and contrast several proposals in the literature for such ansatze: four
versions of the M_T2-assisted on-shell reconstruction (MAOS), as well as
several variants of the on-shell constrained M_2 variables. We compare the
performance of these methods with regards to the mass determination of a new
particle resonance along the decay chain from the peak of the reconstructed
invariant mass distribution. For concreteness, we consider the event topology
of dilepton ttbar events and study each of the three possible subsystems, in
both a ttbar and a SUSY example. We find that the M_2 variables generally
provide sharper peaks and therefore better ansatze for the invisible momenta.
We show that the performance can be further improved by preselecting events
near the kinematic endpoint of the corresponding variable from which the
momentum ansatz originates.Comment: 38 pages, 15 figure
Quantum adaptation of noisy channels
Probabilistic quantum filtering is proposed to properly adapt sequential
independent quantum channels in order to stop sudden death of entanglement. In
the adaptation, the quantum filtering does not distill or purify more
entanglement, it rather properly prepares entangled state to the subsequent
quantum channel. For example, the quantum adaptation probabilistically
eliminates the sudden death of entanglement of two-qubit entangled state with
isotropic noise injected into separate amplitude damping channels. The result
has a direct application in quantum key distribution through noisy channels.Comment: 6 pages, 4 figure
Evolution of twin-beam in active optical media
We study the evolution of twin-beam propagating inside active media that may
be used to establish a continuous variable entangled channel between two
distant users. In particular, we analyze how entanglement is degraded during
propagation, and determine a threshold value for the interaction time, above
which the state become separable, and thus useless for entanglement based
manipulations. We explicitly calculate the fidelity for coherent state
teleportation and show that it is larger than one half for the whole range of
parameters preserving entanglemenent.Comment: several misprints correcte
Spin injection and spin accumulation in permalloy-copper mesoscopic spin valves
We study the electrical injection and detection of spin currents in a lateral
spin valve device, using permalloy (Py) as ferromagnetic injecting and
detecting electrodes and copper (Cu) as non-magnetic metal. Our multi-terminal
geometry allows us to experimentally distinguish different magneto resistance
signals, being 1) the spin valve effect, 2) the anomalous magneto resistance
(AMR) effect and 3) Hall effects. We find that the AMR contribution of the Py
contacts can be much bigger than the amplitude of the spin valve effect, making
it impossible to observe the spin valve effect in a 'conventional' measurement
geometry. However, these 'contact' magneto resistance signals can be used to
monitor the magnetization reversal process, making it possible to determine the
magnetic switching fields of the Py contacts of the spin valve device. In a
'non local' spin valve measurement we are able to completely isolate the spin
valve signal and observe clear spin accumulation signals at T=4.2 K as well as
at room temperature. We obtain spin diffusion lengths in copper of 1 micrometer
and 350 nm at T=4.2 K and room temperature respectively.Comment: 8 pages (incl. figures), 7 figures, RevTex, conferenc
Unusual cause of mechanical ileus: abdominal cocoon syndrome
A 38-year-old black male patient was admitted with diarrhea and nausea over two days and aggravating pain in the meso- and epigastium that resolved after urination. He had no surgical history and only an episode of pulmonary tuberculosis five years earlier, for which he was properly treated. Physical examination revealed a tender and distended abdomen with clangorous sounds. His temperature was 36.1°C. Routine laboratory blood analyses were normal. An abdominal ultrasound revealed diffuse distention of the small intestine. A computed tomography (CT) scan showed a conglomerate of dilated small bowel loops in the meso- and hypogastrium, suggestive for a supravesical mechanical small bowel obstruction. Peritoneal thickening was seen in the right epigastrium (Figure A, white arrow). An explorative laparoscopy revealed a whitish, thickened membrane encapsulating the small bowels as a ‘cocoon’ (Figure B). Extensive adhesiolysis released an intestinal kinking in the lower abdomen, just above the bladder. No resection was needed. Histopathology of the membrane showed fibrocollagenous tissue with mixed inflammatory infiltrate
Improving the sensitivity of stop searches with on-shell constrained invariant mass variables
The search for light stops is of paramount importance, both in general as a
promising path to the discovery of beyond the standard model physics and more
specifically as a way of evaluating the success of the naturalness paradigm.
While the LHC experiments have ruled out much of the relevant parameter space,
there are "stop gaps", i.e., values of sparticle masses for which existing LHC
analyses have relatively little sensitivity to light stops. We point out that
techniques involving on-shell constrained M_2 variables can do much to enhance
sensitivity in this region and hence help close the stop gaps. We demonstrate
the use of these variables for several benchmark points and describe the effect
of realistic complications, such as detector effects and combinatorial
backgrounds, in order to provide a useful toolkit for light stop searches in
particular, and new physics searches at the LHC in general.Comment: 49 pages, 28 figures, revised version published in JHEP, references
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