25,495 research outputs found
The ITS-90 after definition of neon isotopic reference composition. Extent of the isotopic effect on previous inter-comparison results
Starting from the end of the past century, the importance has been recognized
of the effect of isotopic composition on some of the temperature fixed points
for the most accurate realizations of the ITS-90. In the original definition of
the latter, dating back to 1990, only a generic reference was made to natural
composition of the substances used for the realization of the fixed points,
except for helium. The definition of a reference isotopic composition for three
fixed points, e-H2, Ne and H2O, while eliminating the non-uniqueness of the
Scale in this respect, induced detectable differences in the present and future
realizations of the Scale, at the highest accuracy level, with respect to the
previous realizations, when they affected the results of past key comparisons,
namely the K1 and K1.1, and K2 and K2.1 to K2.5 and the related regional and
supplementary ones. The paper provides evidence of the extent of this effect by
using the results of the relevant key comparisons for Neon archived in the BIPM
KCDB, and of other comparisons existing in the literature: 1979-1984, 2007-2012
and 2009-2010 sealed cell comparisons; and discusses the meaning and the
outcomes of this evaluation.Comment: 19 pages, 4 figures, 4 tables. BIPM, Doc. CCT/17-1
Parametric entry corridors for lunar/Mars aerocapture missions
Parametric atmospheric entry corridor data are presented for Earth and Mars aerocapture. Parameter ranges were dictated by the range of mission designs currently envisioned as possibilities for the Human Exploration Initiative (HEI). This data, while not providing a means for exhaustive evaluation of aerocapture performance, should prove to be a useful aid for preliminary mission design and evaluation. Entry corridors are expressed as ranges of allowable vacuum periapse altitude of the planetary approach hyperbolic orbit, with chart provided for conversion to an approximate flight path angle corridor at entry interface (125 km altitude). The corridor boundaries are defined by open-loop aerocapture trajectories which satisfy boundary constraints while utilizing the full aerodynamic control capability of the vehicle (i.e., full lift-up or full lift-down). Parameters examined were limited to those of greatest importance from an aerocapture performance standpoint, including the approach orbit hyperbolic excess velocity, the vehicle lift to drag ratio, maximum aerodynamic load factor limit, and the apoapse of the target orbit. The impact of the atmospheric density bias uncertainties are also included. The corridor data is presented in graphical format, and examples of the utilization of these graphs for mission design and evaluation are included
On the heating of source of the Orion KL hot core
We present images of the J=10-9 rotational lines of HC3N in the vibrationally
excited levels 1v7, 1v6 and 1v5 of the hot core (HC) in Orion KL. The images
show that the spatial distribution and the size emission from the 1v7 and 1v5
levels are different. While the J=10-9 1v7 line has a size of 4''x 6'' and
peaks 1.1'' NE of the 3 mm continuum peak, the J=10--9 1v5 line emission is
unresolved (<3'') and peaks 1.3'' south of the 3 mm peak. This is a clear
indication that the HC is composed of condensations with very different
temperatures (170 K for the 1v7 peak and K for the 1v5 peak). The
temperature derived from the 1v7 and 1v5 lines increases with the projected
distance to the suspected main heating source I. Projection effects along the
line of sight could explain the temperature gradient as produced by source I.
However, the large luminosity required for source I, >5 10^5 Lsolar, to explain
the 1v5 line suggests that external heating by this source may not dominate the
heating of the HC. Simple model calculations of the vibrationally excited
emission indicate that the HC can be internally heated by a source with a
luminosity of 10^5 Lsolar, located 1.2'' SW of the 1v5 line peak (1.8'' south
of source I). We also report the first detection of high-velocity gas from
vibrationally excited HC3N emission. Based on excitation arguments we conclude
that the main heating source is also driving the molecular outflow. We
speculate that all the data presented in this letter and the IR images are
consistent with a young massive protostar embedded in an edge-on disk.Comment: 13 pages, 3 figures, To be published in Ap.J. Letter
Sensory Difference of Bio-Dynamically, Organically and Conventionally Produced Wheat from the DOK Long-Term Field Trial
There is a need of scientific evidence on the differentiation of organic from conventional produce concerning health, nutrition and sensory related qualities (Leifert et al., 2007). Analysis of wheat from the DOK long-term system comparison trial near Basel, Switzerland (Mäder et al., 2002) showed that organic wheat differed in contents of 16 “diagnostic” proteins from conventional wheat (Zörb et al., 2009a), had higher concentrations of K+ and Mg2+ cations and lower concentrations of six amino acids, and a different seed ripening metabolism (Zörb et al., 2009b). In a previous sensory test with cooked porridge of wheat (cv. Tamaro) from the DOK trial (harvest 1999), the biodynamic samples had been preferred (Arncken et al., 2007). In the present work we aimed to corroborate these results with dry samples of three harvest years
Bell's experiment with intra- and inter-pair entanglement: Single-particle mode entanglement as a case study
Theoretical considerations of Bell-inequality experiments usually assume
identically prepared and independent pairs of particles. Here we consider pairs
that exhibit both intra- and inter-pair entanglement. The pairs are taken from
a large many-body system where all the pairs are generally entangled with each
other. Using an explicit example based on single mode entanglement and an
ancillary Bose-Einstein condensate, we show that the Bell-inequality violation
in such systems can display statistical properties that are remarkably
different from those obtained using identically prepared, independent pairs. In
particular, one can have probabilistic violation of Bell's inequalities in
which a finite fraction of all the runs result in violation, even though there
could be no violation when averaging over all the runs. Whether or not a
particular run of results will end up being local realistically explainable is
"decided" by a sequence of quantum (random) outcomes.Comment: 7 pages (two column), 5 figure
Can the effects of anthropogenic pressures and environmental variability on nekton fauna be detected in fishery data? Insights from the monitoring of the artisanal fishery within the Venice lagoon
Nekton communities in transitional ecosystems are naturally adapted to stressful conditions associated with high environmental variability. Human activities in these systems are likely to determine additional stress with a possible effect on fish fauna, hence on fisheries. In order to test the relative importance of natural and anthropogenic factors in determining changes in nekton community, catches (incl. bycatch) from artisanal fisheries (fyke nets) were monitored seasonally in different areas of the Venice lagoon (Italy) between 2001 and 2013. Changes in nekton community composition and in the biomass of target and non-target species/groups were analysed, and the results were related to temporal factors, environmental characteristics and to the variability in anthropogenic pressures. Statistical tests were carried out using a model-based analysis of both univariate and multivariate data. Results highlighted that temporal factors and environmental conditions (i.e. the main chemico-physical descriptors) are more relevant than anthropogenic pressures in explaining spatial and temporal changes in the lagoon nekton assemblage, but that several characteristics of the assemblage, in particular the biomass of some particular categories and of the whole assemblage, are sensitive to human impacts. A particularly negligible effect seemed to be associated with fishing effort, thus suggesting that the monitoring of the local artisanal fishery is suitable also to provide useful information on the evaluation of the status of nekton assemblage
Optical Properties of Graphene Nanoflakes: Shape Matters
In recent years there has been significant debate on whether the edge type of
graphene nanoflakes (GNF) or graphene quantum dots (GQD) are relevant for their
electronic structure, thermal stability and optical properties. Using computer
simulations, we have proven that there is a fundamental difference in the
calculated absorption spectra between samples of the same shape, similar size
but different edge type, namely, armchair or zigzag edges. These can be
explained by the presence of electronic structures near the Fermi level which
are localized on the edges. These features are also evident from the dependence
of band gap on the GNF size, which shows three very distinct trends for
different shapes and edge geometries.Comment: 8 pages, 9 figures. Submitted to The Journal of Chemical Physic
Surface Josephson plasma waves in layered superconductors
We predict the existence of surface waves in layered superconductors in the
THz frequency range, below the Josephson plasma frequency . This wave
propagates along the vacuum-superconductor interface and dampens in both
transverse directions out of the surface (i.e., towards the superconductor and
towards the vacuum). This is the first prediction of propagating surface waves
in any superconductor. These predicted surface Josephson plasma waves are
important for different phenomena, including the complete suppression of the
specular reflection from a sample (Wood's anomalies) and a huge enhancement of
the wave absorption (which can be used as a THz detector).Comment: 4 pages, 2 figure
On Dimer Models and Closed String Theories
We study some aspects of the recently discovered connection between dimer
models and D-brane gauge theories. We argue that dimer models are also
naturally related to closed string theories on non compact orbifolds of \BC^2
and \BC^3, via their twisted sector R charges, and show that perfect
matchings in dimer models correspond to twisted sector states in the closed
string theory. We also use this formalism to study the combinatorics of some
unstable orbifolds of \BC^2.Comment: 1 + 25 pages, LaTeX, 11 epsf figure
D-brane Instantons as Gauge Instantons in Orientifolds of Chiral Quiver Theories
Systems of D3-branes at orientifold singularities can receive
non-perturbative D-brane instanton corrections, inducing field theory operators
in the 4d effective theory. In certain non-chiral examples, these systems have
been realized as the infrared endpoint of a Seiberg duality cascade, in which
the D-brane instanton effects arise from strong gauge theory dynamics. We
present the first UV duality cascade completion of chiral D3-brane theories, in
which the D-brane instantons arise from gauge theory dynamics. Chiral examples
are interesting because the instanton fermion zero mode sector is topologically
protected, and therefore lead to more robust setups. As an application of our
results, we provide a UV completion of certain D-brane orientifold systems
recently claimed to produce conformal field theories with conformal invariance
broken only by D-brane instantons.Comment: 50 pages, 32 figures. v2: version published in JHEP with references
adde
- …