859 research outputs found
Coulombic Energy Transfer and Triple Ionization in Clusters
Using neon and its dimer as a specific example, it is shown that excited
Auger decay channels that are electronically stable in the isolated monomer can
relax in a cluster by electron emission. The decay mechanism, leading to the
formation of a tricationic cluster, is based on an efficient energy-transfer
process from the excited, dicationic monomer to a neighbor. The decay is
ultrafast and expected to be relevant to numerous physical phenomena involving
core holes in clusters and other forms of spatially extended atomic and
molecular matter.Comment: 5 pages, 1 figure, to be published in PR
Review of biorthogonal coupled cluster representations for electronic excitation
Single reference coupled-cluster (CC) methods for electronic excitation are
based on a biorthogonal representation (bCC) of the (shifted) Hamiltonian in
terms of excited CC states, also referred to as correlated excited (CE) states,
and an associated set of states biorthogonal to the CE states, the latter being
essentially configuration interaction (CI) configurations. The bCC
representation generates a non-hermitian secular matrix, the eigenvalues
representing excitation energies, while the corresponding spectral intensities
are to be derived from both the left and right eigenvectors. Using the
perspective of the bCC representation, a systematic and comprehensive analysis
of the excited-state CC methods is given, extending and generalizing previous
such studies. Here, the essential topics are the truncation error
characteristics and the separability properties, the latter being crucial for
designing size-consistent approximation schemes. Based on the general order
relations for the bCC secular matrix and the (left and right) eigenvector
matrices, formulas for the perturbation-theoretical (PT) order of the
truncation errors (TEO) are derived for energies, transition moments, and
property matrix elements of arbitrary excitation classes and truncation levels.
In the analysis of the separability properties of the transition moments, the
decisive role of the so-called dual ground state is revealed. Due to the use of
CE states the bCC approach can be compared to so-called intermediate state
representation (ISR) methods based exclusively on suitably orthonormalized CE
states. As the present analysis shows, the bCC approach has decisive advantages
over the conventional CI treatment, but also distinctly weaker TEO and
separability properties in comparison with a full (and hermitian) ISR method
Multi-component Transparent Conducting Oxides: Progress in Materials Modelling
Transparent conducting oxides (TCOs) play an essential role in modern
optoelectronic devices through their combination of electrical conductivity and
optical transparency. We review recent progress in our understanding of
multi-component TCOs formed from solid-solutions of ZnO, In2O3, Ga2O3 and
Al2O3, with a particular emphasis on the contributions of materials modelling,
primarily based on Density Functional Theory. In particular, we highlight three
major results from our work: (i) the fundamental principles governing the
crystal structures of multi-component oxide structures including (In2O3)(ZnO)n,
named IZO, and (In2O3)m(Ga2O3)l(ZnO)n, named IGZO; (ii) the relationship
between elemental composition and optical and electrical behaviour, including
valence band alignments; (iii) the high-performance of amorphous oxide
semiconductors. From these advances, the challenge of the rational design of
novel electroceramic materials is discussed.Comment: Part of a themed issue of Journal of Physics: Condensed Matter on
"Semiconducting Oxides". In Press (2011
Symmetric Informationally Complete Measurements of Arbitrary Rank
There has been much interest in so-called SIC-POVMs: rank 1 symmetric
informationally complete positive operator valued measures. In this paper we
discuss the larger class of POVMs which are symmetric and informationally
complete but not necessarily rank 1. This class of POVMs is of some independent
interest. In particular it includes a POVM which is closely related to the
discrete Wigner function. However, it is interesting mainly because of the
light it casts on the problem of constructing rank 1 symmetric informationally
complete POVMs. In this connection we derive an extremal condition alternative
to the one derived by Renes et al.Comment: Contribution to proceedings of International Conference on Quantum
Optics, Minsk, 200
Experimental manifestations of the Nb^{4+}-O^{-} polaronic excitons in KTa_{0.988}Nb_{0.012}O_{3}
The formation of the photo-polaronic excitons in ABO_{3} perovskite type
oxides has been detected experimentally by means of the photoinduced electron
paramagnetic resonance studies of KTa_{0.998}Nb_{0.012}O_{3} crystals. The
corresponding microwave X-band spectrum at T < 10 K consists of a narrow,
nearly isotropic signal located at g ~ 2 and a strongly anisotropic component.
The first signal, which has a rich structure due to hyperfine interactions with
the lattice nuclei, is attributed to the single trapped charge carriers: the
electrons and/or the holes. The anisotropic spectrum is caused by the axial
centers oriented along the C_{4} pseudo-cubic principal crystalline axes. The
spectrum angular dependence can be described well by an axial center with S =
1, g_{\parallel) = 0.82, g_{\perp} = 0.52 and D = 0.44 cm^{-1}. The anisotropic
spectrum is attributed to the Nb^{4+}-O^{-} polaronic excitons. The temperature
dependence of the anisotropic component is characterized by two activation
energies: the internal dynamics activation E_{a1} = 3.7\pm0.5 meV, which makes
the EPR spectrum unobservable above 10 K, and the destruction energy E_{a2} =
52\pm4 meV. By comparing the anisotropic photo-EPR spectrum and the
photoinduced optical absorption temperature dependencies, we found that the
Nb^{4+}-O^{-} polaronic excitons also manifested themselves via the ~0.7 eV
wide absorption band arising under UV light excitation in the weakly
concentrated KTaO_{3}:Nb crystals.Comment: PDF, 15 pages, 6 figures (submitted to Physical review B
280 one-opposition near-Earth asteroids recovered by the EURONEAR with the <i>Isaac Newton</i> Telescope
Context. One-opposition near-Earth asteroids (NEAs) are growing in number, and they must be recovered to prevent loss and mismatch risk, and to improve their orbits, as they are likely to be too faint for detection in shallow surveys at future apparitions.
Aims. We aimed to recover more than half of the one-opposition NEAs recommended for observations by the Minor Planet Center (MPC) using the Isaac Newton Telescope (INT) in soft-override mode and some fractions of available D-nights. During about 130 h in total between 2013 and 2016, we targeted 368 NEAs, among which 56 potentially hazardous asteroids (PHAs), observing 437 INT Wide Field Camera (WFC) fields and recovering 280 NEAs (76% of all targets).
Methods. Engaging a core team of about ten students and amateurs, we used the THELI, Astrometrica, and the Find_Orb software to identify all moving objects using the blink and track-and-stack method for the faintest targets and plotting the positional uncertainty ellipse from NEODyS.
Results. Most targets and recovered objects had apparent magnitudes centered around V ~ 22.8 mag, with some becoming as faint as V ~ 24 mag. One hundred and three objects (representing 28% of all targets) were recovered by EURONEAR alone by Aug. 2017. Orbital arcs were prolonged typically from a few weeks to a few years; our oldest recoveries reach 16 years. The OâC residuals for our 1854 NEA astrometric positions show that most measurements cluster closely around the origin. In addition to the recovered NEAs, 22â000 positions of about 3500 known minor planets and another 10â000 observations of about 1500 unknown objects (mostly main-belt objects) were promptly reported to the MPC by our team. Four new NEAs were discovered serendipitously in the analyzed fields and were promptly secured with the INT and other telescopes, while two more NEAs were lost due to extremely fast motion and lack of rapid follow-up time. They increase the counting to nine NEAs discovered by the EURONEAR in 2014 and 2015.
Conclusions. Targeted projects to recover one-opposition NEAs are efficient in override access, especially using at least two-meter class and preferably larger field telescopes located in good sites, which appear even more efficient than the existing surveys
Transkingdom Networks: A Systems Biology Approach to Identify Causal Members of Host-Microbiota Interactions
Improvements in sequencing technologies and reduced experimental costs have
resulted in a vast number of studies generating high-throughput data. Although
the number of methods to analyze these "omics" data has also increased,
computational complexity and lack of documentation hinder researchers from
analyzing their high-throughput data to its true potential. In this chapter we
detail our data-driven, transkingdom network (TransNet) analysis protocol to
integrate and interrogate multi-omics data. This systems biology approach has
allowed us to successfully identify important causal relationships between
different taxonomic kingdoms (e.g. mammals and microbes) using diverse types of
data
CARS: the CFHTLS-Archive-Research Survey; I. Five-band multi-colour data from 37 sq. deg. CFHTLS-Wide observations
We present the CFHTLS-Archive-Research Survey (CARS). It is a virtual
multi-colour survey based on public archive images from the CFHT-Legacy-Survey.
Our main scientific interests in CARS are optical searches for galaxy clusters
from low to high redshift and their subsequent study with photometric and
weak-gravitational lensing techniques. As a first step of the project we
present multi-colour catalogues from 37 sq. degrees of the CFHTLS-Wide
component. Our aims are to create astrometrically and photometrically well
calibrated co-added images. Second goal are five-band (u*, g', r', i', z')
multi-band catalogues with an emphasis on reliable estimates for object
colours. These are subsequently used for photometric redshift estimates. The
article explains in detail data processing, multi-colour catalogue creation and
photometric redshift estimation. Furthermore we apply a novel technique, based
on studies of the angular galaxy cross-correlation function, to quantify the
reliability of photo-z's. The accuracy of our high-confidence photo-z sample
(10-15 galaxies per sq. arcmin) is estimated to up to i'<24 with typically only 1-3% outliers. Interested users can
obtain access to our data by request to the authors.Comment: 31 pages, 18 figures, 6 tables; accepted for publication by A&A main
journa
The dynamical Green's function and an exact optical potential for electron-molecule scattering including nuclear dynamics
We derive a rigorous optical potential for electron-molecule scattering
including the effects of nuclear dynamics by extending the common many-body
Green's function approach to optical potentials beyond the fixed-nuclei limit
for molecular targets. Our formalism treats the projectile electron and the
nuclear motion of the target molecule on the same footing whereby the dynamical
optical potential rigorously accounts for the complex many-body nature of the
scattering target. One central result of the present work is that the common
fixed-nuclei optical potential is a valid adiabatic approximation to the
dynamical optical potential even when projectile and nuclear motion are
(nonadiabatically) coupled as long as the scattering energy is well below the
electronic excitation thresholds of the target. For extremely low projectile
velocities, however, when the cross sections are most sensitive to the
scattering potential, we expect the influences of the nuclear dynamics on the
optical potential to become relevant. For these cases, a systematic way to
improve the adiabatic approximation to the dynamical optical potential is
presented that yields non-local operators with respect to the nuclear
coordinates.Comment: 22 pages, no figures, accepted for publ., Phys. Rev.
- âŠ