933 research outputs found
Imaging Pulsed Laser Deposition oxide growth by in-situ Atomic Force Microscopy
To visualize the topography of thin oxide films during growth, thereby
enabling to study its growth behavior quasi real-time, we have designed and
integrated an atomic force microscope (AFM) in a pulsed laser deposition (PLD)
vacuum setup. The AFM scanner and PLD target are integrated in a single support
frame, combined with a fast sample transfer method, such that in-situ
microscopy can be utilized after subsequent deposition pulses. The in-situ
microscope can be operated from room temperature (RT) up to 700C and at
(process) pressures ranging from the vacuum base pressure of 10 mbar up
to 1 mbar, typical PLD conditions for the growth of oxide films. The
performance of this instrument is demonstrated by resolving unit cell height
surface steps and surface topography under typical oxide PLD growth conditions.Comment: 8 pages, 8 figure
Determining the energetics of vicinal perovskite oxide surfaces
The energetics of vicinal SrTiO(001) and DyScO(110), prototypical
perovskite vicinal surfaces, has been studied using topographic atomic force
microscopy imaging. The kink formation and strain relaxation energies are
extracted from a statistical analysis of the step meandering. Both perovskite
surfaces have very similar kink formation energies and exhibit a similar
triangular step undulation. Our experiments suggest that the energetics of
perovskite oxide surfaces is mainly governed by the local oxygen coordination.Comment: 16 pages, 4 figure
Lifshitz transition in the phase diagram of two-leg - ladder systems at low filling
We use a combination of numerical matrix product states (MPS) and analytical
approaches to investigate the phase diagram of the two-leg - ladder in
the region of low to intermediate fillings. We choose the same coupling
strength along the leg- and rung-directions, but study the effect of adding a
nearest-neighbor repulsion . We observe a rich phase diagram and
analytically identify a Lifshitz-like band filling transition, which can be
associated to a numerically observed crossover from s-wave to d-wave like
superconducting quasi-long range order (QLRO). Due to the strong interactions,
the Lifshitz transition is smeared into a crossover region which separates two
distinct Luttinger theories with unequal physical meaning of the Luttinger
parameter. Our numerically exact MPS results spotlight deviations from standard
Luttinger theory in this crossover region and is consistent with Luttinger
theory sufficiently far away from the Lifshitz transition. At very low
fillings, studying the Friedel-like oscillations of the local density
identifies a precursor region to a Wigner crystal at small values of the
magnetic exchange interaction . We discuss analytically how tuning
parameters at these fillings modifies the phase diagram, and find good
agreement with MPS results.Comment: 14 pages, 4 appendices, 17 figure
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Reversion reporters in Arabidopsis thaliana to detect all six base substitution pathways
Maintaining genome integrity is essential for an organism, as mutation
accumulation can lead to cancer, reduced fitness, and heritable diseases in offspring.
Therefore the study of mutations, how they are induced, and how they are prevented is
vital. Biomonitor systems are useful for understanding the relevant biological effects
of a given mutagen, and depending on the system, can even provide information on
specific molecular changes induced by the mutagen. Plants are ideal biomonitors, as a
sedentary lifestyle allows measurement of mutagens in air, soil, and water, even at low
doses. We constructed mutation reporters in Arabidopsis designed to restore β-
glucuronidase (GUS) activity through one of six base substitution reversions. All six
mutant constructs contained inactivating base substitutions in the same codon, which
minimized sequence context effects. An AcV5 epitope tag sequence was fused to the
3' end of GUS to allow detection of the inactive protein and selection of sublines
based on levels of GUS protein expression. Initial characterization of these reversion
reporters with or without UV-C treatment and exposure to heavy metal ions (Cd²⁺ and
Zn²⁺) supports the ability of the lines to measure different mutations. UV-C radiation
induced T to C and C to T reversions, as well as T to G and T to A to a lesser extent.
Heavy-metal-ion-mutation induction was inconsistent, showing variable increases in G to T and G to C, and no induction of T to C reversion. Of key interest is the G to T
reporter line, as this is the first such reporter in higher eukaryotes. This line showed a
large increase in spontaneous mutation as well as potential germinal mutations when
compared to the other reporter lines, most likely due to endogenous oxidative damage
(i.e. 8-oxoguanine). Further experiments to test the reporter lines with various
mutagens as well as ways to improve the ability of the reporters to detect mutation are discussed
Ecological determinants of extrapair fertilizations and egg dumping in Alpine water pipits (Anthus spinoletta)
Behavioral ecology has successfully explained the diversity in social mating systems through differences in environmental conditions, but diversity in genetic mating systems is poorly understood. The difference is important in situations where parents care for extrapair young (EPY) originating from extrapair paternity (EPP), extrapair maternity (EPM), and intraspecific brood parasitism (IBP). In birds, IBP and EPM are rare, but EPP is widespread and highly variable among species and populations. Explanations for this variability are controversial, mainly because detailed ecological information is usually lacking in paternity studies. Here we present results of the first study to identify the ecological determinants of extrapair activities for both sexes of the same species, the water pipit (Anthus spinoletta). DNA fingerprints of 1052 young from 258 nests revealed EPP in 5.2% of the young from 12.4% of the nests. EPM and IBP, both involving egg dumping (EDP), each occurred in 0.5% of the young from 1.9% of the nests. Nests with and without EPY could not be distinguished by traits of the breeders and by reproductive succcess, but they differed with respect to ecology: nests with EPP young were characterized by asynchronous clutch initiation, nests with EPM and IBP young were characterized by higher overlap with neighboring territories and closer proximity to communal feeding sites. We suggest that chance events, resulting from the temporal and spatial distribution of broods, offer a better explanation for the occurence of extrapair activities than female search for genetic or phenotypic benefits. This possibility of "accidental” extrapair reproduction as an "ecological epiphenomenon” with low potential for selection should also be considered for species other than the water pipi
Minimal invasive surgery for coronoid fracture: technical note
Operative treatment of coronoid fracture often requires a large dissection of soft tissue, resulting in elbow stiffness and functional limitation. The authors present a minimal invasive, safe technique, useful in the case of isolated coronoid fracture associated with elbow dislocation. This technique does not require soft tissue dissection and allows an early unlimited resumption of sports activitie
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Control of Visually Guided Behavior by Distinct Populations of Spinal Projection Neurons
A basic question in the field of motor control is how different actions are represented by activity in spinal projection neurons. We used a new behavioral assay to identify visual stimuli that specifically drive basic motor patterns in zebrafish. These stimuli evoked consistent patterns of neural activity in the neurons projecting to the spinal cord, which we could map throughout the entire population using in vivo two-photon calcium imaging. We found that stimuli that drive distinct behaviors activated distinct subsets of projection neurons, consisting, in some cases, of just a few cells. This stands in contrast to the distributed activation seen for more complex behaviors. Furthermore, targeted cell by cell ablations of the neurons associated with evoked turns abolished the corresponding behavioral response. This description of the functional organization of the zebrafish motor system provides a framework for identifying the complete circuit underlying a vertebrate behavior.Molecular and Cellular Biolog
Grain boundary energies and cohesive strength as a function of geometry
Cohesive laws are stress-strain curves used in finite element calculations to
describe the debonding of interfaces such as grain boundaries. It would be
convenient to describe grain boundary cohesive laws as a function of the
parameters needed to describe the grain boundary geometry; two parameters in 2D
and 5 parameters in 3D. However, we find that the cohesive law is not a smooth
function of these parameters. In fact, it is discontinuous at geometries for
which the two grains have repeat distances that are rational with respect to
one another. Using atomistic simulations, we extract grain boundary energies
and cohesive laws of grain boundary fracture in 2D with a Lennard-Jones
potential for all possible geometries which can be simulated within periodic
boundary conditions with a maximum box size. We introduce a model where grain
boundaries are represented as high symmetry boundaries decorated by extra
dislocations. Using it, we develop a functional form for the symmetric grain
boundary energies, which have cusps at all high symmetry angles. We also find
the asymptotic form of the fracture toughness near the discontinuities at high
symmetry grain boundaries using our dislocation decoration model.Comment: 12 pages, 19 figures, changed titl
A Precision Measurement of pp Elastic Scattering Cross Sections at Intermediate Energies
We have measured differential cross sections for \pp elastic scattering with
internal fiber targets in the recirculating beam of the proton synchrotron
COSY. Measurements were made continuously during acceleration for projectile
kinetic energies between 0.23 and 2.59 GeV in the angular range deg. Details of the apparatus and the data analysis are
given and the resulting excitation functions and angular distributions
presented. The precision of each data point is typically better than 4%, and a
relative normalization uncertainty of only 2.5% within an excitation function
has been reached. The impact on phase shift analysis as well as upper bounds on
possible resonant contributions in lower partial waves are discussed.Comment: 23 pages 29 figure
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