8,006 research outputs found
Stresses in Ytterbium Silicate Multilayer Environmental Barrier Coatings
The internal stresses of plasma-sprayed multilayer ytterbium disilicate environmental barrier
coatings were measured using microfocused high-energy X-rays in a transmission geometry.
Stresses were measured for as-sprayed and ex-situ heat-treated ytterbium disilicate topcoats at
room temperature and during in-situ heating and cooling experiments. In-situ loading
experiments were also performed on the topcoat in order to establish its elastic constants. The
ytterbium disilicate was found to have a relatively low coefficient of thermal expansion resulting
in compressive stresses of approximately 100 MPa throughout the topcoat. In-situ heating
experiments revealed a statistically significant stress relaxation in the ytterbium disilicate topcoat
upon thermal cycling to temperatures above 1300°C, indicating the onset of stress relaxation but
no cracks were observed in SEM micrographs. The stress states were also modeled using a
numerical solution; measured stresses were found to be very close to the predicted stresses in
ytterbium dilisicate topcoats, while the experimentally determined stresses in the intermediate
layers were of much smaller magnitude than the calculated stresses
In Situ Melting and Revitrification as an Approach to Microsecond Time-Resolved Cryo-Electron Microscopy
Proteins typically undergo conformational dynamics on the microsecond to
millisecond timescale as they perform their function, which is much faster than
the time-resolution of cryo-electron microscopy and has thus prevented
real-time observations. Here, we propose a novel approach for microsecond
time-resolved cryo-electron microscopy that involves rapidly melting a cryo
specimen in situ with a laser beam. The sample remains liquid for the duration
of the laser pulse, offering a tunable time window in which the dynamics of
embedded particles can be induced in their native liquid environment. After the
laser pulse, the sample vitrifies in just a few microseconds, trapping
particles in their transient configurations, so that they can subsequently be
characterized with conventional cryo-electron microscopy. We demonstrate that
our melting and revitrification approach is viable and affords microsecond time
resolution. As a proof of principle, we study the disassembly of particles
after they incur structural damage and trap them in partially unraveled
configurations
Non-equilibrium dynamics and floral trait interactions shape extant angiosperm diversity.
Why are some traits and trait combinations exceptionally common across the tree of life, whereas others are vanishingly rare? The distribution of trait diversity across a clade at any time depends on the ancestral state of the clade, the rate at which new phenotypes evolve, the differences in speciation and extinction rates across lineages, and whether an equilibrium has been reached. Here we examine the role of transition rates, differential diversification (speciation minus extinction) and non-equilibrium dynamics on the evolutionary history of angiosperms, a clade well known for the abundance of some trait combinations and the rarity of others. Our analysis reveals that three character states (corolla present, bilateral symmetry, reduced stamen number) act synergistically as a key innovation, doubling diversification rates for lineages in which this combination occurs. However, this combination is currently less common than predicted at equilibrium because the individual characters evolve infrequently. Simulations suggest that angiosperms will remain far from the equilibrium frequencies of character states well into the future. Such non-equilibrium dynamics may be common when major innovations evolve rarely, allowing lineages with ancestral forms to persist, and even outnumber those with diversification-enhancing states, for tens of millions of years
Analysis of strain and stacking faults in single nanowires using Bragg coherent diffraction imaging
Coherent diffraction imaging (CDI) on Bragg reflections is a promising
technique for the study of three-dimensional (3D) composition and strain fields
in nanostructures, which can be recovered directly from the coherent
diffraction data recorded on single objects. In this article we report results
obtained for single homogeneous and heterogeneous nanowires with a diameter
smaller than 100 nm, for which we used CDI to retrieve information about
deformation and faults existing in these wires. The article also discusses the
influence of stacking faults, which can create artefacts during the
reconstruction of the nanowire shape and deformation.Comment: 18 pages, 6 figures Submitted to New Journal of Physic
The HERMES Back Drift Chambers
The tracking system of the HERMES spectrometer behind the bending magnet
consists of two pairs of large planar 6-plane drift chambers. The design and
performance of these chambers is described. This description comprises details
on the mechanical and electronical design, information about the gas mixture
used and its properties, results on alignment, calibration, resolution, and
efficiencies, and a discussion of the experience gained through the first three
years of operation.Comment: 21 pages, LaTex, 16 figures include
Recommended from our members
Standard Penetration Test-Based Probabilistic and Deterministic Assessment of Seismic Soil Liquefaction Potential
This paper presents new correlations for assessment of the likelihood of initiation (or “triggering”) of soil liquefaction. These new correlations eliminate several sources of bias intrinsic to previous, similar correlations, and provide greatly reduced overall uncertainty and variance. Key elements in the development of these new correlations are (1) accumulation of a significantly expanded database of field performance case histories; (2) use of improved knowledge and understanding of factors affecting interpretation of standard penetration test data; (3) incorporation of improved understanding of factors affecting site-specific earthquake ground motions (including directivity effects, site-specific response, etc.); (4) use of improved methods for assessment of in situ cyclic shear stress ratio; (5) screening of field data case histories on a quality/uncertainty basis; and (6) use of high-order probabilistic tools (Bayesian updating). The resulting relationships not only provide greatly reduced uncertainty, they also help to resolve a number of corollary issues that have long been difficult and controversial including: (1) magnitude-correlated duration weighting factors, (2) adjustments for fines content, and (3) corrections for overburden stress
Urinary iodine concentration during pregnancy in an area of unstable dietary iodine intake in Switzerland
We prospectively investigated urinary iodine concentration (UIC) in pregnant women and in female, non-pregnant controls in the canton of Berne, Switzerland, in 1992. Mean UIC of pregnant women [205±151 μg iodine/g creatinine (μg I/g Cr); no.=153] steadily decreased from the first (236±180 μg I/g Cr; no.=31) to the third trimester (183±111 μg I/g Cr, p<0.0001; no.=66) and differed significantly from that of the control group (91±37 μg I/g Cr, p<0.0001; no.=119). UIC increased 2.6-fold from levels indicating mild iodine deficiency in controls to the first trimester, demonstrating that high UIC during early gestation does not necessarily reflect a sufficient iodine supply to the overall population. Pregnancy is accompanied by important alterations in the regulation of thyroid function and iodine metabolism. Increased renal iodine clearance during pregnancy may explain increased UIC during early gestation, whereas increased thyroidal iodine clearance as well as the iodine shift from the maternal circulation to the growing fetal-placental unit, which both tend to lower the circulating serum levels of inorganic iodide, probably are the causes of the continuous decrease of UIC over the course of pregnancy. Mean UIC in our control group, as well as in one parallel and several consecutive investigations in the same region in the 1990s, was found to be below the actually recommended threshold, indicating a new tendency towards mild to moderate iodine deficiency. As salt is the main source of dietary iodine in Switzerland, its iodine concentration was therefore increased nationwide in 1998 for the fourth time, following increases in 1922, 1965 and 198
Intruder bands and configuration mixing in the lead isotopes
A three-configuration mixing calculation is performed in the context of the
interacting boson model with the aim to describe recently observed collective
bands built on low-lying states in neutron-deficient lead isotopes. The
configurations that are included correspond to the regular, spherical states as
well as two-particle two-hole and four-particle four-hole excitations across
the Z=82 shell gap.Comment: 20 pages, 4 figures, accepted by PRC, reference added for section 1
in this revised versio
Radiative emission of solar features in the Ca II K line: comparison of measurements and models
We study the radiative emission of various types of solar features, such as
quiet Sun, enhanced network, plage, and bright plage regions, identified on
filtergrams taken in the Ca II K line. We analysed fulldisk images obtained
with the PSPT, by using three interference filters that sample the Ca II K line
with different bandpasses. We studied the dependence of the radiative emission
of disk features on the filter bandpass. We also performed a NLTE spectral
synthesis of the Ca II K line integrated over the bandpass of PSPT filters. The
synthesis was carried out by utilizing both the PRD and CRD with the most
recent set of semi empirical atmosphere models in the literature and some
earlier atmosphere models. We measured the CLV of intensity values for various
solar features identified on PSPT images and compared the results obtained with
those derived from the synthesis. We find that CRD calculations derived using
the most recent quiet Sun model, on average, reproduce the measured values of
the quiet Sun regions slightly more accurately than PRD computations with the
same model. This may reflect that the utilized atmospheric model was computed
assuming CRD. Calculations with PRD on earlier quiet Sun model atmospheres
reproduce measured quantities with a similar accuracy as to that achieved here
by applying CRD to the recent model. We also find that the median contrast
values measured for most of the identified bright features, disk positions, and
filter widths are, on average, a factor 1.9 lower than those derived from PRD
simulations performed using the recent bright feature models. The discrepancy
between measured and modeled values decreases by 12% after taking into account
straylight effects on PSPT images. PRD computations on either the most recent
or the earlier atmosphere models of bright features reproduce measurements from
plage and bright plage regions with a similar accuracy.Comment: 14 pages, 18 figures, accepted by A&
The H1 Forward Proton Spectrometer at HERA
The forward proton spectrometer is part of the H1 detector at the HERA
collider. Protons with energies above 500 GeV and polar angles below 1 mrad can
be detected by this spectrometer. The main detector components are
scintillating fiber detectors read out by position-sensitive photo-multipliers.
These detectors are housed in so-called Roman Pots which allow them to be moved
close to the circulating proton beam. Four Roman Pot stations are located at
distances between 60 m and 90 m from the interaction point.Comment: 20 pages, 10 figures, submitted to Nucl.Instr.and Method
- …