938,863 research outputs found
What can be learned from binding energy differences about nuclear structure: the example of delta V_{pn}
We perform an analysis of a binding energy difference called delta
V_{pn}(N,Z) =- 1/4(E(Z,N)-E(Z,N-2)-E(Z-2,N)+ E(Z-2,N-2) in the framework of a
realistic nuclear model. Using the angular-momentum and particle-number
projected generator coordinate method and the Skyrme interaction SLy4, we
analyze the contribution brought to delta V_{pn} by static deformation and
dynamic fluctuations around the mean-field ground state. Our method gives a
good overall description of delta V_{pn} throughout the chart of nuclei with
the exception of the anomaly related to the Wigner energy along the N=Z line.
The main conclusions of our analysis are that (i) the structures seen in the
systematics of delta V_{pn} throughout the chart of nuclei can be easily
explained combining a smooth background related to the symmetry energy and
correlation energies due to deformation and collective fluctuations; (ii) the
characteristic pattern of delta V_{pn} around a doubly-magic nucleus is a
trivial consequence of the asymmetric definition of delta V_{pn}, and not due
to a the different structure of these nuclei; (iii) delta V_{pn} does not
provide a very reliable indicator for structural changes; (iv) \delta V_{pn}
does not provide a reliable measure of the proton-neutron interaction in the
nuclear EDF, neither of that between the last filled orbits, nor of the one
summed over all orbits; (v) delta V_{pn} does not provide a conclusive
benchmark for nuclear EDF methods that is superior or complementary to other
mass filters such as two-nucleon separation energies or Q values.Comment: 19 pages and 12 figure
What is "system": some decoherence-theory arguments
We discuss the possibility of making the {\it initial} definitions of
mutually different (possibly interacting, or even entangled) systems in the
context of decoherence theory. We point out relativity of the concept of
elementary physical system as well as point out complementarity of the
different possible divisions of a composite system into "subsystems", thus
eventually sharpening the issue of 'what is system'.Comment: 9 pages, no figure
Development of Heterogeneous Photosensitized Transition Metal Oxide Water-Splitting Catalysts on Silica Support
The research presented in this manuscript describes the development of photosensitized inexpensive catalysts based on readily available materials. The investigation covers synthesis and characterization of photosensitizers based on porphyrins, mechanical and thermal coating of solid support with semiconducting transition metal oxides, photosensitization of the semiconducting layer, and characterization of the photoelectrochemical properties displayed by the new materials. The process of water oxidation is of primary interest here, with little emphasis put on reduction of protons to gaseous hydrogen. Photoelectrochemically produced protons serve as a probe of effectiveness of the catalysts. Several systems are described, and two catalysts are identified as the most efficient
Signatures of orbital loop currents in the spatially resolved local density of states
Polarized neutron scattering measurements have suggested that intra-unit cell
antiferromagnetism may be associated with the pseudogap phase. Assuming that
loop current order is responsible for the observed magnetism, we calculate some
signatures of such circulating currents in the local density of states around a
single non-magnetic impurity in a coexistence phase with superconductivity. We
find a distinct C4 symmetry breaking near the disorder which is also detectable
in the resulting quasi-particle interference patterns.Comment: 5 pages, 3 figure
The photospheric solar oxygen project: III. Investigation of the centre-to-limb variation of the 630nm [OI]-NiI blend
The solar photospheric abundance of oxygen is still a matter of debate. For
about ten years some determinations have favoured a low oxygen abundance which
is at variance with the value inferred by helioseismology. Among the oxygen
abundance indicators, the forbidden line at 630nm has often been considered the
most reliable even though it is blended with a NiI line. In Papers I and Paper
II of this series we reported a discrepancy in the oxygen abundance derived
from the 630nm and the subordinate [OI] line at 636nm in dwarf stars, including
the Sun. Here we analyse several, in part new, solar observations of the the
centre-to-limb variation of the spectral region including the blend at 630nm in
order to separate the individual contributions of oxygen and nickel. We analyse
intensity spectra observed at different limb angles in comparison with line
formation computations performed on a CO5BOLD 3D hydrodynamical simulation of
the solar atmosphere. The oxygen abundances obtained from the forbidden line at
different limb angles are inconsistent if the commonly adopted nickel abundance
of 6.25 is assumed in our local thermodynamic equilibrium computations. With a
slightly lower nickel abundance, A(Ni)~6.1, we obtain consistent fits
indicating an oxygen abundance of A(O)=8.73+/-0.05. At this value the
discrepancy with the subordinate oxygen line remains. The derived value of the
oxygen abundance supports the notion of a rather low oxygen abundance in the
solar hotosphere. However, it is disconcerting that the forbidden oxygen lines
at 630 and 636nm give noticeably different results, and that the nickel
abundance derived here from the 630nm blend is lower than expected from other
nickel lines.Comment: to appear in A&
Spatially encoded light for Large-alphabet Quantum Key Distribution
Most Quantum Key Distribution protocols use a two-dimensional basis such as
HV polarization as first proposed by Bennett and Brassard in 1984. These
protocols are consequently limited to a key generation density of 1 bit per
photon. We increase this key density by encoding information in the transverse
spatial displacement of the used photons. Employing this higher-dimensional
Hilbert space together with modern single-photon-detecting cameras, we
demonstrate a proof-of-principle large-alphabet Quantum Key Distribution
experiment with 1024 symbols and a shared information between sender and
receiver of 7 bit per photon.Comment: 9 pages, 6 figures, Added references, Updated Fig. 1 in the main
text, Updated Fig.1 in supplementary material, Added section Trojan-horse
attacks in supplementary material, title changed, Added paragraphs about
final key rate and overfilling the detector to result sectio
Inducing topological order in a honeycomb lattice
We explore the possibility of inducing a topological insulator phase in a
honeycomb lattice lacking spin-orbit interaction using a metallic (or Fermi
gas) environment. The lattice and the metallic environment interact through a
density-density interaction without particle tunneling, and integrating out the
metallic environment produces a honeycomb sheet with in-plane oscillating
long-ranged interactions. We find the ground state of the interacting system in
a variational mean-field method and show that the Fermi wave vector, kF, of the
metal determines which phase occurs in the honeycomb lattice sheet. This is
analogous to the Ruderman-Kittel-Kasuya-Yosida (RKKY) mechanism in which the
metal's kF determines the interaction profile as a function of the distance.
Tuning kF and the interaction strength may lead to a variety of ordered phases,
including a topological insulator and anomalous quantum-hall states with
complex next-nearest-neighbor hopping, as in the Haldane and the Kane-Mele
model. We estimate the required range of parameters needed for the topological
state and find that the Fermi vector of the metallic gate should be of the
order of 3Pi/8a (with a being the graphene lattice constant). The net coupling
between the layers, which includes screening in the metal, should be of the
order of the honeycomb lattice bandwidth. This configuration should be most
easily realized in a cold-atoms setting with two interacting Fermionic species.Comment: 7 pages; 2 figures; Version 2 - added references; added an appendix
about screenin
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