744 research outputs found
The strange-quark mass from QCD sum rules in the pseudoscalar channel
QCD Laplace transform sum rules, involving the axial-vector current
divergences, are used in order to determine the strange quark mass. The
two-point function is known in QCD up to four loops in perturbation theory, and
up to dimension-six in the non-perturbative sector. The hadronic spectral
function is reconstructed using threshold normalization from chiral symmetry,
together with experimental data for the two radial excitations of the kaon. The
result for the running strange quark mass, in the scheme at a scale
of 1 is: .Comment: 10 pages. Latex file. 2 Figures obtained from author CAD upon reques
Determination of the strange-quark mass from QCD pseudoscalar sum rules
A new determination of the strange-quark mass is discussed, based on the
two-point function involving the axial-vector current divergences. This Green
function is known in perturbative QCD up to order O(alpha_s^3), and up to
dimension-six in the non-perturbative domain. The hadronic spectral function is
parametrized in terms of the kaon pole, followed by its two radial excitations,
and normalized at threshold according to conventional chiral-symmetry. The
result of a Laplace transform QCD sum rule analysis of this two-point function
is: m_s(1 GeV^2) = 155 pm 25 MeV.Comment: Invited talk given by CAD at QCD98, Montpellier, July 1998. To appear
in Nucl.Phys.B Proc.Suppl. Latex File. Four (double column) page
Reachability analysis for neural agent-environment systems
We develop a novel model for studying agent-environment systems, where the agents are implemented via feed-forward ReLU neural networks. We provide a semantics and develop a method to verify automatically that no unwanted states are reached by the system during its evolution. We study several reachability problems for the system, ranging from one-step reachability, to fixed multi-step and arbitrary-step to study the system evolution. We also study the decision problem of whether an agent, realised via feed-forward ReLU networks will perform an action in a system run. Whenever possible, we give tight complexity bounds to decision problems intro- duced. We automate the various reachability problems stud- ied by recasting them as mixed-integer linear programming problems. We present an implementation and discuss the ex- perimental results obtained on a range of test cases
Comparative transcriptomics reveals commonalities and differences in the genetic underpinnings of a floral dimorphism
Distyly, a floral dimorphism associated with heteromorphic self-incompatibility and controlled by the S-locus supergene, evolved independently multiple times. Comparative analyses of the first transcriptome atlas for the main distyly model, Primula veris, with other distylous species produced the following findings. A set of 53 constitutively expressed genes in P. veris did not include any of the housekeeping genes commonly used to normalize gene expression in qPCR experiments. The S-locus gene CYP acquired its role in controlling style elongation via a change in expression profile. Comparison of genes differentially expressed between floral morphs revealed that brassinosteroids and auxin are the main hormones controlling style elongation in P. veris and Fagopyrum esculentum, respectively. Furthermore, shared biochemical pathways might underlie the expression of distyly in the distantly related P. veris, F. esculentum and Turnera subulata, suggesting a degree of correspondence between evolutionary convergence at phenotypic and molecular levels. Finally, we provide the first evidence supporting the previously proposed hypothesis that distyly supergenes of distantly related species evolved via the recruitment of genes related to the phytochrome-interacting factor (PIF) signaling network. To conclude, this is the first study that discovered homologous genes involved in the control of distyly in distantly related taxa
Stability of sub-surface oxygen at Rh(111)
Using density-functional theory (DFT) we investigate the incorporation of
oxygen directly below the Rh(111) surface. We show that oxygen incorporation
will only commence after nearly completion of a dense O adlayer (\theta_tot =
1.0 monolayer) with O in the fcc on-surface sites. The experimentally suggested
octahedral sub-surface site occupancy, inducing a site-switch of the on-surface
species from fcc to hcp sites, is indeed found to be a rather low energy
structure. Our results indicate that at even higher coverages oxygen
incorporation is followed by oxygen agglomeration in two-dimensional
sub-surface islands directly below the first metal layer. Inside these islands,
the metastable hcp/octahedral (on-surface/sub-surface) site combination will
undergo a barrierless displacement, introducing a stacking fault of the first
metal layer with respect to the underlying substrate and leading to a stable
fcc/tetrahedral site occupation. We suggest that these elementary steps,
namely, oxygen incorporation, aggregation into sub-surface islands and
destabilization of the metal surface may be more general and precede the
formation of a surface oxide at close-packed late transition metal surfaces.Comment: 9 pages including 9 figure files. Submitted to Phys. Rev. B. Related
publications can be found at http://www.fhi-berlin.mpg.de/th/paper.htm
HO distribution in the disc of HD 100546 and HD 163296: the role of dust dynamics and planet--disc interaction
[Abridged] Far-infrared observations with Herschel revealed a surprisingly
low abundance of cold-water reservoirs in protoplanetary discs. On the other
hand, a handful of discs show emission of hot water transitions excited at
temperatures above a few hundred Kelvin. In particular, the protoplanetary
discs around the Herbig Ae stars HD 100546 and HD 163296 show opposite trends
in terms of cold versus hot water emission: in the first case, the ground-state
transitions are detected and the high-J lines are undetected, while the trend
is opposite in HD 163296. We performed a spectral analysis using the
thermo-chemical model DALI. We find that HD 163296 is characterised by a
water-rich (abundance ) hot inner disc (within the snowline)
and a water-poor () outer disc: the relative abundance may be due
to the thermal desorption of icy grains that have migrated inward. Remarkably,
the size of the HO emitting region corresponds to a narrow dust gap visible
in the millimeter continuum at au with ALMA. The low-J lines detected
in HD 100546 instead imply an abundance of a few in the cold outer
disc ( au). The emitting region of the cold HO transitions is
spatially coincident with that of the HO ice previously seen in the
near-infrared. Notably, millimetre observations with ALMA reveal the presence
of a large dust gap between nearly 40 and 150 au, likely opened by a massive
embedded protoplanet. In both discs, we find that the warm molecular layer in
the outer region (beyond the snow line) is highly depleted of water molecules,
implying an oxygen-poor chemical composition of the gas. We speculate that
gas-phase oxygen in the outer disc is readily depleted and its distribution in
the disc is tightly coupled to the dynamics of the dust grains.Comment: Accepted for publication on A&
Adlayer core-level shifts of random metal overlayers on transition-metal substrates
We calculate the difference of the ionization energies of a core-electron of
a surface alloy, i.e., a B-atom in a A_(1-x) B_x overlayer on a
fcc-B(001)-substrate, and a core-electron of the clean fcc-B(001) surface using
density-functional-theory. We analyze the initial-state contributions and the
screening effects induced by the core hole, and study the influence of the
alloy composition for a number of noble metal-transition metal systems. Data
are presented for Cu_(1-x)Pd_x/Pd(001), Ag_(1-x) Pd_x/Pd(001), Pd_(1-x)
Cu_x/Cu(001), and Pd_(1-x) Ag_x/Ag(001), changing x from 0 to 100 %. Our
analysis clearly indicates the importance of final-state screening effects for
the interpretation of measured core-level shifts. Calculated deviations from
the initial-state trends are explained in terms of the change of inter- and
intra-atomic screening upon alloying. A possible role of alloying on the
chemical reactivity of metal surfaces is discussed.Comment: 4 pages, 2 figures, Phys. Rev. Letters, to appear in Feb. 199
Vastus Lateralis Muscle's Characterization on bedridden patients: a Time Domain fNIRS study
The vastus lateralis muscle was characterized by means of time-domain near infrared spectroscopy on 28 bedridden elderly patients. Optical and hemodynamics parameters were evaluated together with age, adipose tissue thickness and pennation angle
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