16,778 research outputs found
Properties of the first excited state of 9Be derived from (gamma,n) and (e,e') reactions
Properties of the first excited state of the nucleus 9Be are discussed based
on recent (e,e') and (gamma,n) experiments. The parameters of an R-matrix
analysis of different data sets are consistent with a resonance rather than a
virtual state predicted by some model calculations. The energy and the width of
the resonance are deduced. Their values are rather similar for all data sets,
and the energy proves to be negative. It is argued that the disagreement
between the extracted B(E1) values may stem from different ways of integration
of the resonance. If corrected, fair agreement between the (e,e') and one of
the (gamma,n) data sets is found. A recent (gamma,n) experiment at the HIgS
facility exhibits larger cross sections close to the neutron threshold which
remain to be explained.Comment: 5 pages, accepted fro publication in Phys. Rev.
Thermopower of a superconducting single-electron transistor
We present a linear-response theory for the thermopower of a single-electron
transistor consisting of a superconducting island weakly coupled to two
normal-conducting leads (NSN SET). The thermopower shows oscillations with the
same periodicity as the conductance and is rather sensitive to the size of the
superconducting gap. In particular, the previously studied sawtooth-like shape
of the thermopower for a normal-conducting single-electron device is
qualitatively changed even for small gap energies.Comment: 9 pages, 3 figure
Excitation of the electric pygmy dipole resonance by inelastic electron scattering
To complete earlier studies of the properties of the electric pygmy dipole
resonance (PDR) obtained in various nuclear reactions, the excitation of the
1 states in Ce by scattering for momentum transfers
~fm is calculated within the plane-wave and distorted-wave
Born approximations. The excited states of the nucleus are described within the
Quasiparticle Random Phase Approximation (QRPA), but also within the
Quasiparticle-Phonon Model (QPM) by accounting for the coupling to complex
configurations. It is demonstrated that the excitation mechanism of the PDR
states in reactions is predominantly of transversal nature for
scattering angles . Being thus mediated by the
convection and spin nuclear currents, the like the
reaction, may provide additional information to the one obtained from Coulomb-
and hadronic excitations of the PDR in , , and
heavy-ion scattering reactions. The calculations predict that the
cross sections for the strongest individual PDR states are in general about
three orders of magnitude smaller as compared to the one of the lowest
state for the studied kinematics, but that they may become dominant at extreme
backward angles.Comment: Prepared for the special issue of EPJA on the topic "Giant, Pygmy,
Pairing Resonances and related topics" dedicated to the memory of Pier
Francesco Bortigno
Concentration of Vacancies at Metal Oxide Surfaces: Case Study of MgO (100)
We investigate effects of doping on formation energy and concentration of
oxygen vacancies at a metal oxide surface, using MgO (100) as an example. Our
approach employs density-functional theory, where the performance of the
exchange-correlation functional is carefully analyzed, and the functional is
chosen according to a fundamental condition on DFT ionization energies. The
approach is further validated by CCSD(T) calculations for embedded clusters. We
demonstrate that the concentration of oxygen vacancies at a doped oxide surface
is largely determined by formation of a macroscopically extended space charge
region
Observation of a Chiral State in a Microwave Cavity
A microwave experiment has been realized to measure the phase difference of
the oscillating electric field at two points inside the cavity. The technique
has been applied to a dissipative resonator which exhibits a singularity --
called exceptional point -- in its eigenvalue and eigenvector spectrum. At the
singularity, two modes coalesce with a phase difference of We
conclude that the state excited at the singularity has a definitiv chirality.Comment: RevTex 4, 5 figure
Absence of long-range order in a spin-half Heisenberg antiferromagnet on the stacked kagome lattice
We study the ground state of a spin-half Heisenberg antiferromagnet on the
stacked kagome lattice by using a spin-rotation-invariant Green's-function
method. Since the pure two-dimensional kagome antiferromagnet is most likely a
magnetically disordered quantum spin liquid, we investigate the question
whether the coupling of kagome layers in a stacked three-dimensional system may
lead to a magnetically ordered ground state. We present spin-spin correlation
functions and correlation lengths. For comparison we apply also linear spin
wave theory. Our results provide strong evidence that the system remains
short-range ordered independent of the sign and the strength of the interlayer
coupling
Zigzag spin-S chain near ferromagnet-antiferromagnet transition point
The properties of the ferromagnetic frustrated spin-S one-dimensional
Heisenberg model in the vicinity of the transition point from the ferromagnetic
to the singlet ground state is studied using the perturbation theory (PT) in
small parameter characterizing the deviation from the transition point. The
critical exponents defining the behavior of the ground state energy and spin
correlation functions are determined using scaling estimates of infrared
divergencies of the PT. It is shown that the quantum fluctuations for
are sufficiently strong to change the classical critical exponents, while for
spin systems with the critical exponents remain classical. The
dimerization in the singlet phase near the transition point is discussed.Comment: 13 pages, 3 figure
Decoherence vs entanglement in coined quantum walks
Quantum versions of random walks on the line and cycle show a quadratic
improvement in their spreading rate and mixing times respectively. The addition
of decoherence to the quantum walk produces a more uniform distribution on the
line, and even faster mixing on the cycle by removing the need for
time-averaging to obtain a uniform distribution. We calculate numerically the
entanglement between the coin and the position of the quantum walker and show
that the optimal decoherence rates are such that all the entanglement is just
removed by the time the final measurement is made.Comment: 11 pages, 6 embedded eps figures; v2 improved layout and discussio
Resistance Breeding in Apple at Dresden-Pillnitz
Resistance breeding in apple has a long tradition at the Institute of Fruit Breeding now Julius Kuehn-institute in Dresden-Pillnitz. The breeding was aimed at the production of multiple resistance cultivars to allow a more sustainable and environmentally friendly production of apple. In the last decades a series of resistant cultivars (Re®-cultivars) bred in Dresden-Pillnitz has been released, ‘Recolor’ and ‘Rekarda’ in 2006. The main topic in the resistance breeding programme was scab resistance and the donor of scab resistance in most cultivars was Malus x floribunda 821. Due to the development of strains that are able to overcome resistance genes inherited by M. x floribunda 821 and due to the fact that single resistance genes can be broken easily, pyramiding of resistance genes is necessary. Besides scab, fire blight and powdery mildew are the main disease for which a pyramiding of genes is aspired in Pillnitz. Biotechnical approaches are necessary for the early detection of pyramided resistance genes in breeding clones. This paper will give an overview of the resistance breeding of apple in Pillnitz and the methods used
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