35,800 research outputs found
Nucleon Spin in QCD: Old Crisis and New Resolution
We discuss the shortfalls of existing resolutions of the long-standing gauge
invariance problem of the canonical decomposition of the nucleon spin to the
spin and angular momentum of quarks and gluons. We provide two logically
flawless expressions of nucleon spin which have different physical meanings,
using the gauge independent Abelian decomposition. The first one is based on
the assumption that all gluons (binding and valence gluons) contribute to the
nucleon spin, but the second one is based on the assumption that only the
binding gluons (and the quarks) contribute to it. We propose the second
expression to be the physically correct one
Strong 3p -T1u Hybridization in Ar@C60
Multilayers of fullerenes with and without endohedral Ar units, C60 and
Ar@C60, were investigated by photoemission and density functional theory. The
stoichiometry and the endohedral nature of Ar is checked by x-ray photoelectron
spectroscopy and x-ray photoelectron diffraction. Valence band ultraviolet
photoemission spectra show a strong hybridisation of the Ar 3p valence shell
with the 6T1u molecular orbital of C60. A hybridisation gap of 1.6 +/- 0.2 eV
is found. This is in agreement with density functional theory (DFT) that
predicts 1.47 eV, and indicates Ar@C60 to be a noble gas compound with a strong
coupling between Ar and the C60 cage. No giant Ar photoemission cross section
as predicted for the gas phase in [Phys. Rev. Lett. 99, 243003 (2007)] was
found
Reconfiguration on sparse graphs
A vertex-subset graph problem Q defines which subsets of the vertices of an
input graph are feasible solutions. A reconfiguration variant of a
vertex-subset problem asks, given two feasible solutions S and T of size k,
whether it is possible to transform S into T by a sequence of vertex additions
and deletions such that each intermediate set is also a feasible solution of
size bounded by k. We study reconfiguration variants of two classical
vertex-subset problems, namely Independent Set and Dominating Set. We denote
the former by ISR and the latter by DSR. Both ISR and DSR are PSPACE-complete
on graphs of bounded bandwidth and W[1]-hard parameterized by k on general
graphs. We show that ISR is fixed-parameter tractable parameterized by k when
the input graph is of bounded degeneracy or nowhere-dense. As a corollary, we
answer positively an open question concerning the parameterized complexity of
the problem on graphs of bounded treewidth. Moreover, our techniques generalize
recent results showing that ISR is fixed-parameter tractable on planar graphs
and graphs of bounded degree. For DSR, we show the problem fixed-parameter
tractable parameterized by k when the input graph does not contain large
bicliques, a class of graphs which includes graphs of bounded degeneracy and
nowhere-dense graphs
Power-law tails from multiplicative noise
We show that the well-known Langevin equation, modeling the Brownian motion
and leading to a Gaussian stationary distribution of the corresponding
Fokker-Planck equation, is changed by the smallest multiplicative noise. This
leads to a power-law tail of the distribution at large enough momenta. At
finite ratio of the correlation strength for the multiplicative and additive
noise the stationary energy distribution becomes exactly the Tsallis
distribution.Comment: 4 pages, LaTeX, revtex4 style, 2 figure
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