3,029 research outputs found
Size-dependent Auger spectra and two-hole Coulomb interaction of small supported Cu-clusters
Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Auger (L3M4,5M4,5) and X-ray photoionization spectra (2p, 3d) of mass-selected CuN-clusters supported by a thin natural silica layer are presented in the size range N = 8–55 atoms per cluster. The Auger spectra of all clusters are shifted to a lower kinetic energy with respect to the spectrum of the bulk. Furthermore the Auger energy decreases systematically with decreasing cluster size. The binding energies of the 2p and 3d valence states are higher than the corresponding bulk values. Using the energy of the Auger main line, the corresponding core hole peak and the centroid of the self-convoluted 3d valence band the on-site Coulomb interaction energy Udd of the two-hole final state as a function of cluster size has been determined
Photoelectron Soft X-Ray Fluorescence Coincidence Spectroscopy on Free Molecules
A technique for measuring core-level photoemission from free molecules in coincidence with the soft x-ray fluorescence decay is presented. Zero-kinetic-energy photoelectrons are detected in a time-of-flight electron spectrometer, and photons are collected in a large solid angle by a detector situated close to the interaction region. The coincidence spectrum of N2 shows an adiabatic 1s line, free from electron-electron postcollision interaction effects. The results open up new aspects on core-hole excitation-emission dynamics
On Binary Matroid Minors and Applications to Data Storage over Small Fields
Locally repairable codes for distributed storage systems have gained a lot of
interest recently, and various constructions can be found in the literature.
However, most of the constructions result in either large field sizes and hence
too high computational complexity for practical implementation, or in low rates
translating into waste of the available storage space. In this paper we address
this issue by developing theory towards code existence and design over a given
field. This is done via exploiting recently established connections between
linear locally repairable codes and matroids, and using matroid-theoretic
characterisations of linearity over small fields. In particular, nonexistence
can be shown by finding certain forbidden uniform minors within the lattice of
cyclic flats. It is shown that the lattice of cyclic flats of binary matroids
have additional structure that significantly restricts the possible locality
properties of -linear storage codes. Moreover, a collection of
criteria for detecting uniform minors from the lattice of cyclic flats of a
given matroid is given, which is interesting in its own right.Comment: 14 pages, 2 figure
The formation of Uranus and Neptune among Jupiter and Saturn
The outer giant planets, Uranus and Neptune, pose a challenge to theories of
planet formation. They exist in a region of the Solar System where long
dynamical timescales and a low primordial density of material would have
conspired to make the formation of such large bodies ( 15 and 17 times as
massive as the Earth, respectively) very difficult. Previously, we proposed a
model which addresses this problem: Instead of forming in the trans-Saturnian
region, Uranus and Neptune underwent most of their growth among proto-Jupiter
and -Saturn, were scattered outward when Jupiter acquired its massive gas
envelope, and subsequently evolved toward their present orbits. We present the
results of additional numerical simulations, which further demonstrate that the
model readily produces analogues to our Solar System for a wide range of
initial conditions. We also find that this mechanism may partly account for the
high orbital inclinations observed in the Kuiper belt.Comment: Submitted to AJ; 38 pages, 16 figure
Q value and half-life of double-electron capture in Os-184
Os-184 has been excluded as a promising candidate for the search of
neutrinoless double-electron capture. High-precision mass measurements with the
Penning-trap mass spectrometer TRIGA-TRAP resulted in a marginal resonant
enhancement with = -8.89(58) keV excess energy to the 1322.152(22) keV 0+
excited state in W-184. State-of-the-art energy density functional calculations
are applied for the evaluation of the nuclear matrix elements to the excited
states predicting a strong suppression due to the large deformation of mother
and daughter states. The half-life of the transition in Os-184 exceeds T_{1/2}
> 1.3 10^{29} years for an effective neutrino mass of 1 eV.Comment: accepted in Phys. Rev.
Origin of the reduced exchange bias in epitaxial FeNi(111)/CoO(111) bilayer
We have employed Soft and Hard X-ray Resonant Magnetic Scattering and
Polarised Neutron Diffraction to study the magnetic interface and the bulk
antiferromagnetic domain state of the archetypal epitaxial
NiFe(111)/CoO(111) exchange biased bilayer. The combination of
these scattering tools provides unprecedented detailed insights into the still
incomplete understanding of some key manifestations of the exchange bias
effect. We show that the several orders of magnitude difference between the
expected and measured value of exchange bias field is caused by an almost
anisotropic in-plane orientation of antiferromagnetic domains. Irreversible
changes of their configuration lead to a training effect. This is directly seen
as a change in the magnetic half order Bragg peaks after magnetization
reversal. A 30 nm size of antiferromagnetic domains is extracted from the width
the (1/2 1/2 1/2) antiferromagnetic magnetic peak measured both by neutron and
x-ray scattering. A reduced blocking temperature as compared to the measured
antiferromagnetic ordering temperature clearly corresponds to the blocking of
antiferromagnetic domains. Moreover, an excellent correlation between the size
of the antiferromagnetic domains, exchange bias field and frozen-in spin ratio
is found, providing a comprehensive understanding of the origin of exchange
bias in epitaxial systems.Comment: 8 pages, 5 figures, submitte
Water in Comet 2/2003 K4 (LINEAR) with Spitzer
We present sensitive 5.5 to 7.6 micron spectra of comet C/2003 K4 (LINEAR)
obtained on 16 July 2004 (r_{h} = 1.760 AU, Delta_{Spitzer} = 1.409 AU, phase
angle 35.4 degrees) with the Spitzer Space Telescope. The nu_{2} vibrational
band of water is detected with a high signal-to-noise ratio (> 50). Model
fitting to the best spectrum yields a water ortho-to-para ratio of 2.47 +/-
0.27, which corresponds to a spin temperature of 28.5^{+6.5}_{-3.5} K. Spectra
acquired at different offset positions show that the rotational temperature
decreases with increasing distance from the nucleus, which is consistent with
evolution from thermal to fluorescence equilibrium. The inferred water
production rate is (2.43 +/- 0.25) \times 10^{29} molec. s^{-1}. The spectra do
not show any evidence for emission from PAHs and carbonate minerals, in
contrast to results reported for comets 9P/Tempel 1 and C/1995 O1 (Hale-Bopp).
However, residual emission is observed near 7.3 micron the origin of which
remains unidentified.Comment: 33 pages, including 11 figures, 2 tables, ApJ 2007 accepte
Superfluid Helium Tanker (SFHT) study
Replenishment of superfluid helium (SFHe) offers the potential of extending the on-orbit life of observatories, satellite instruments, sensors and laboratories which operate in the 2 K temperature regime. A reference set of resupply customers was identified as representing realistic helium servicing requirements and interfaces for the first 10 years of superfluid helium tanker (SFHT) operations. These included the Space Infrared Telescope Facility (SIRTF), the Advanced X-ray Astrophysics Facility (AXAF), the Particle Astrophysics Magnet Facility (Astromag), and the Microgravity and Materials Processing Sciences Facility (MMPS)/Critical Point Phenomena Facility (CPPF). A mixed-fleet approach to SFHT utilization was considered. The tanker permits servicing from the Shuttle cargo bay, in situ when attached to the OMV and carried to the user spacecraft, and as a depot at the Space Station. A SFHT Dewar ground servicing concept was developed which uses a dedicated ground cooling heat exchanger to convert all the liquid, after initial fill as normal fluid, to superfluid for launch. This concept permits the tanker to be filled to a near full condition, and then cooled without any loss of fluid. The final load condition can be saturated superfluid with any desired ullage volume, or the tank can be totally filed and pressurized. The SFHT Dewar and helium plumbing system design has sufficient component redundancy to meet fail-operational, fail-safe requirements, and is designed structurally to meet a 50 mission life usage requirement. Technology development recommendations were made for the selected SFHT concept, and a Program Plan and cost estimate prepared for a phase C/D program spanning 72 months from initiation through first launch in 1997
Sex or cannibalism: Polyphenism and kin recognition control social action strategies in nematodes
Resource polyphenisms, where single genotypes produce alternative feeding strategies in response to changing environments, are thought to be facilitators of evolutionary novelty. However, understanding the interplay between environment, morphology, and behavior and its significance is complex. We explore a radiation of Pristionchus nematodes with discrete polyphenic mouth forms and associated microbivorous versus cannibalistic traits. Notably, comparing 29 Pristionchus species reveals that reproductive mode strongly correlates with mouth-form plasticity. Male-female species exhibit the microbivorous morph and avoid parent-offspring conflict as indicated by genetic hybrids. In contrast, hermaphroditic species display cannibalistic morphs encouraging competition. Testing predation between 36 co-occurring strains of the hermaphrodite P. pacificus showed that killing inversely correlates with genomic relatedness. These empirical data together with theory reveal that polyphenism (plasticity), kin recognition, and relatedness are three major factors that shape cannibalistic behaviors. Thus, developmental plasticity influences cooperative versus competitive social action strategies in diverse animals
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