3,892 research outputs found
Irreducible Killing Tensors from Third Rank Killing-Yano Tensors
We investigate higher rank Killing-Yano tensors showing that third rank
Killing-Yano tensors are not always trivial objects being possible to construct
irreducible Killing tensors from them. We give as an example the Kimura IIC
metric were from two rank Killing-Yano tensors we obtain a reducible Killing
tensor and from third rank Killing-Yano tensors we obtain three Killing
tensors, one reducible and two irreducible.Comment: 10 page
Energy levels and decoherence properties of single electron and nuclear spins in a defect center in diamond
The coherent behavior of the single electron and single nuclear spins of a
defect center in diamond and a 13C nucleus in its vicinity, respectively, are
investigated. The energy levels associated with the hyperfine coupling of the
electron spin of the defect center to the 13C nuclear spin are analyzed.
Methods of magnetic resonance together with optical readout of single defect
centers have been applied in order to observe the coherent dynamics of the
electron and nuclear spins. Long coherence times, in the order of microseconds
for electron spins and tens of microseconds for nuclear spins, recommend the
studied system as a good experimental approach for implementing a 2-qubit gate.Comment: 4 pages, 4 figure
Isotopic evidence for biogenic molecular hydrogen production in the Atlantic Ocean
Oceans are a net source of molecular hydrogen (H2) to the atmosphere. The production of marine H2 is assumed to be mainly biological by N2 fixation, but photochemical pathways are also discussed. We present measurements of mole fraction and isotopic composition of dissolved and atmospheric H2 from the southern and northern Atlantic between 2008 and 2010. In total almost 400 samples were taken during five cruises along a transect between Punta Arenas (Chile) and Bremerhaven (Germany), as well as at the coast of Mauretania.
The isotopic source signatures of dissolved H2 extracted from surface water are highly deuterium-depleted and correlate negatively with temperature, showing ÎŽD values of (â629 ± 54) â° for water temperatures at (27 ± 3) °C and (â249 ± 88) â° below (19 ± 1) °C. The results for warmer water masses are consistent with biological production of H2. This is the first time that marine H2 excess has been directly attributed to biological production by isotope measurements. However, the isotope values obtained in the colder water masses indicate that beside possible biological production a significant different source should be considered.
The atmospheric measurements show distinct differences between both hemispheres as well as between seasons. Results from the global chemistry transport model TM5 reproduce the measured H2 mole fractions and isotopic composition well. The climatological global oceanic emissions from the GEMS database are in line with our data and previously published flux calculations. The good agreement between measurements and model results demonstrates that both the magnitude and the isotopic signature of the main components of the marine H2 cycle are in general adequately represented in current atmospheric models despite a proposed source different from biological production or a substantial underestimation of nitrogen fixation by several authors
Ab initio nucleon-nucleus elastic scattering with chiral effective field theory uncertainties
Background: Effective interactions for nucleon-nucleus () elastic
scattering from first principles require the use of the same nucleon-nucleon
() interaction in the structure and reaction calculations, and a consistent
treatment of the relevant operators at each order.
Purpose: Truncation uncertainties of chiral forces have been studied for
scattering observables in few-body systems and for bound state properties of
light nuclei. We extend this to elastic scattering.
Methods: With the spectator expansion of multiple scattering theory and the
no-core shell model, we use a chiral interaction from the LENPIC collaboration
to consistently calculate the leading order effective interaction up to
third chiral order (N2LO) and extract elastic scattering observables. We
quantify the chiral truncation error using pointwise and correlated methods.
Results: We analyze proton-O and neutron-C elastic scattering
observables between 65 and 185 MeV projectile kinetic energy. We find
qualitatively similar results for the chiral truncation uncertainties as in
few-body systems, which we assess using similar diagnostic tools. The
order-by-order convergence of the scattering observables for O and
C is reasonable near 100 MeV, but for higher energies the expansion
parameter becomes too large to converge. We find a near-perfect correlation
between the neutron differential cross section and the Wolfenstein
amplitudes for small momentum transfers.
Conclusions: The tools used to study the convergence of a chiral
interaction in few-body systems can be applied to scattering with minor
changes. The interaction used here gives a good description of O
and C scattering observables as low as 65 MeV. The very forward
direction of the neutron differential cross section mirrors the behavior of the
interaction amazingly well.Comment: 17 pages, 13 figures, 1 tabl
Nuclear structure and elastic scattering observables obtained consistently with different NN interactions
Nucleon-nucleon () interactions based on chiral effective theories are
commonly used in ab initio calculations of light nuclei. Here we present a
study based on three different NN interactions (up to next-to-next-to-leading
order) for which structure and elastic proton scattering observables are
consistently calculated for He, C, and O. The interactions
are compared at the two-body level in terms of Wolfenstein amplitudes, and
their predictions for ground state energies, point-proton radii, and charge
form factors, as well as proton elastic scattering observables in the
leading-order spectator expansion in the energy range between 65 and 160 MeV
projectile energy are presented. To gain further insight into differences
visible in elastic scattering observables, we investigate the behavior of the
calculated effective nucleon-nucleus interactions for the C nucleus
based on the different interactions.Comment: 17 pages, 17 figure
Little âWeâsâ: how common identities improve behavior differently for ethnic majority and minority children
This field experiment tested whether inducing common inclusive representations (i.e., one group, dual identity) during contact influences intergroup relations differently for ethnic majority and minority children by changing their metaperceptions and intergroup emotions differently. White (N = 113) and Black (N = 111) 8- to 10-year-old children were exposed to interactive mixed-ethnicity sessions in schools emphasizing either categorization as one group (national group), dual identity (national group with ethnic subgroups), or two ethnic groups. Overall, as predicted, for White children, one-group, but not dual-identity perceptions, improved behavioral intentions by influencing metaperceptions. For Black children, dual-identity, but not one-group, perceptions improved behavioral intentions through metaperceptions. Contrary to the expected, both dual-identity and one-group perceptions were associated with White and Black childrenâs intergroup emotions.info:eu-repo/semantics/acceptedVersio
Showing Their True Colors? How EU Flag Display Affects Perceptions of Party Elitesâ European Attachment
Evidence suggests that incidental national flag exposure activates nationalistic feelings and that incidental exposure to the EU flag can affect citizen attachments to Europe. However, we know little about what inferences citizens make based on the EU flag when they see it displayed by parties in an electoral context. To test the expectation that this display affects citizensâ evaluations of party elitesâ EU attachment, we conducted a large-scale experiment embedded in a Swedish survey in which respondents were exposed to communications from one of the two main Swedish parties, containing or not containing the image of the flag. We find that simple visual display does little to move perceptions. However, if citizens perceive that a particular party displayed the flag, then they are more likely to evaluate its party elites as more attached to Europe
Do Search for Dibaryonic De - Excitations in Relativistic Nuclear Reactions
Some odd characteristics are observed in the single particle distributions
obtained from interactions at momenta which are
explained as the manifestation of a new mechanism of strangeness production via
dibaryonic de-excitations. A signature of the formation of hadronic and
baryonic clusters is also reported. The di-pionic signals of the dibaryonic
orbital de-excitations are analyzed in the frame of the MIT - bag Model and a
Monte Carlo simulation.The role played by the dibaryonic resonances in
relativistic nuclear collisions could be a significant one.
Key words: Relativistic nuclear interactions negative pions, negative kaons,
di-pions , streamer chamber, dibaryons, MIT - bag model
PACS codes: 25.75.+r,14.40.Aq,14.20.Pt,12.40.AsComment: 17 pages,LATEX, preprint ICTP -243 1993,figures available by reques
NLTE analysis of the methylidyne radical (CH) molecular lines in metal-poor stellar atmospheres
An analysis of the CH molecule in non-local thermodynamic equilibrium (NLTE)
is performed for the physical conditions of cool stellar atmospheres typical of
red giants (log g = 2.0, Teff = 4500 K) and the Sun. The aim of the present
work is to explore whether the G-band of the CH molecule, which is commonly
used in abundance diagnostics of Carbon-Enhanced Metal-Poor (CEMP) stars, is
sensitive to NLTE effects. LTE and NLTE theoretical spectra are computed with
the MULTI code. We use one-dimensional (1D) LTE hydrostatic MARCS model
atmospheres with parameters representing eleven red giant stars with
metallicities ranging from [Fe/H] = -4.0 to [Fe/H] = 0.0 and carbon-to-iron
ratios [C/Fe] = 0.0, +0.7, +1.5, and +3.0. The CH molecule model is represented
by 1981 energy levels, 18377 radiative bound-bound transitions, and 932
photo-dissociation reactions. The rates due to transitions caused by collisions
with free electrons and hydrogen atoms are computed using classical recipes.
Our calculations suggest that NLTE effects in the statistical equilibrium of
the CH molecule are significant and cannot be neglected for precision
spectroscopic analysis of C abundances. The NLTE effects in the G-band increase
with decreasing metallicity. We show that the C abundances are always
under-estimated if LTE is assumed. The NLTE corrections to C abundance inferred
from the CH feature range from +0.04 dex for the Sun to +0.21 dex for a red
giant with metallicity [Fe/H] = -4.0. Departures from the LTE assumption in the
CH molecule are non-negligible and NLTE effects have to be taken into account
in the diagnostic spectroscopy based on the CH lines. We show here that the
NLTE effects in the optical CH lines are non-negligible for the Sun and red
giant stars, but further calculations are warranted to investigate the effects
in other regimes of stellar parameters.Comment: Accepted for publication in Astronomy & Astrophysic
Generation of single colour centers by focussed nitrogen implantation
Single defect centers in diamond have been generated via nitrogen
implantation. The defects have been investigated by single defect center
fluorescence microscopy. Optical and EPR spectra unambiguously show that the
produced defect is the nitrogen-vacancy colour center. An analysis of the
nitrogen flux together with a determination of the number of nitrogen-vacancy
centers yields that on average two 2 MeV nitrogen atoms need to be implanted
per defect center.Comment: 6 pages, 3 figure
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