The effect of different microstructural factors on crack growth and fatigue fracture mechanisms in dual‐phase (DP) steels has yet to be fully understood. The present research examines the ...relationship between crack growth, microstructure, and fracture mechanisms. The samples were intercritically annealed at different temperatures to produce three different martensite volume fractions (MVFs). The results show that the mechanical incompatibility of ferrite and martensite promotes continuous crack tip deflection. MVF increases are associated with elevated fracture tortuosity, more significant fracture energy surface formation, and higher Paris law exponent m values. The interaction of the microstructure with the crack tip, the strain energy density, and the softening caused by secondary microcrack propagation are all illustrated by Electron backscatter diffraction (EBSD) maps. Increasing MVF promotes slow crack growth and a fracture energy increase of 22.9% between the as‐received and heat‐treated steels.
Highlights
Martensite content in dual‐phase steels generate greater crack propagation resistance.
Martensite volume increase produces a more significant number and extension of secondary microcracks.
Differences in ferrite and martensite phases promote continuous crack tip deflection.
This article assesses the effect of mix design parameters on the compressive strength and thermal performance of alkali silicate-activated blends of metakaolin (MK) and granulated blast furnace slag ...(GBFS). A strong interrelationship between the effects of activator composition and the GBFS/(GBFS + MK) ratio is identified through statistical analysis of compressive strength data. Pastes formulated with higher SiO
2
/Al
2
O
3
molar ratios show improvements in mechanical strength with increasing GBFS addition, associated with the formation of a structure comprising coexisting aluminosilicate ‘geopolymer’ gel and Ca-rich Al-substituted silicate hydrate (C-(A)-S-H) reaction products. The inclusion of GBFS in MK-based geopolymers seems also to improve their performance when exposed to high temperatures, as higher residual compressive strengths are reported for these mixtures compared to solely MK-based systems. Only slight differences in shrinkage behaviour are observed at temperatures of up to 600 °C with the inclusion of GBFS; however, slag-blended pastes exhibit enhanced stability at temperatures exceeding 800 °C, as no variation in the compressive strength and no additional shrinkage are identified. These results suggest that nanostructural modifications are induced in the gel by the inclusion of GBFS into MK-based geopolymers, improving the overall performance of these materials.
Ray fish were caught, filleted, and stored in ice. Fillets were analysed for 18
days to determine the chemical, biochemical and physical changes and their relation to the muscle eating quality. ...Trimethylamine (TMA-N), total volatile bases (TVB-N), ATP content and breakdown products,
K value, pH, texture, water-holding capacity (WHC) and colour changes were monitored. At the beginning of the study, the ray fish muscle showed a low concentration of ATP and a high value of inosine 5′-monophosphate (IMP). Regarding to the signs of freshness and deterioration,
K value presented an exponential increase (
r2
=
0.95) with an initial value of 4.7% and a final value of 47.5%. Furthermore, the TBV-N and TMA-N significantly increased (
P
<
0.05) during the storage in ice. As for the physical analysis whereas the texture changed (
P
<
0.05); pH and the WHC were not affected (
P
<
0.05). The overall results of this study indicated that the edible quality of ray fish muscle was maintained during at least 15
days of ice storage.
Briarellins, a subset of C2–C11 cyclized cembranoids, were proposed to contain a C3–C14 ether or lactone bridge, similar to asbestinins. However, the total synthesis of the proposed structure of ...briarellin J revealed a misassignment. We revisited briarellins, computationally, with the help of a recently developed hybrid DFT/parametric method, DU8+, and revised the structures of briarellin C14–C3 ε-lactones to new structural types containing either a C14–C11 or C14–C12 lactone bridge. The original structures of briarellin and asbestinin ethers were confirmed.
Context.
The formation of planets is expected to be enhanced around snowlines in protoplanetary disks, in particular around the water snowline. Moreover, freeze-out of abundant volatile species in ...disks alters the chemical composition of the planet-forming material. However, the close proximity of the water snowline to the host star combined with the difficulty of observing water from Earth makes a direct detection of the water snowline in protoplanetary disks challenging. HCO
+
is a promising alternative tracer of the water snowline. The destruction of HCO
+
is dominated by gas-phase water, leading to an enhancement in the HCO
+
abundance once water is frozen out.
Aims.
Following earlier observed correlations between water and H
13
CO
+
emission in a protostellar envelope, the aim of this research is to investigate the validity of HCO
+
and the optically thin isotopologue H
13
CO
+
as tracers of the water snowline in protoplanetary disks and the required sensitivity and resolution to observationally confirm this.
Methods.
A typical Herbig Ae disk structure is assumed, and its temperature structure is modelled with the thermochemical code
DALI
. Two small chemical networks are then used and compared to predict the HCO
+
abundance in the disk: one without water and one including water. Subsequently, the corresponding emission profiles are modelled for the
J
= 2−1 transition of H
13
CO
+
and HCO
+
, which provides the best balance between brightness and the optical depth effects of the continuum emission and is less affected by blending with complex molecules. Models are then compared with archival ALMA data.
Results.
The HCO
+
abundance jumps by two orders of magnitude over a radial range of 2 AU outside the water snowline, which in our model is located at 4.5 AU. We find that the emission of H
13
CO
+
and HCO
+
is ring-shaped due to three effects: destruction of HCO
+
by gas-phase water, continuum optical depth, and molecular excitation effects. Comparing the radial emission profiles for
J
= 2−1 convolved with a 0′′.05 beam reveals that the presence of gas-phase water causes an additional drop of only ~13 and 24% in the centre of the disk for H
13
CO
+
and HCO
+
, respectively. For the much more luminous outbursting source V883 Ori, our models predict that the effects of dust and molecular excitation do not limit HCO
+
as a snowline tracer if the snowline is located at radii larger than ~40 AU. Our analysis of recent archival ALMA band 6 observations of the
J
= 3−2 transition of HCO
+
is consistent with the water snowline being located around 100 AU, further out than was previously estimated from an intensity break in the continuum emission.
Conclusions.
The HCO
+
abundance drops steeply around the water snowline, when water desorbs in the inner disk, but continuum optical depth and molecular excitation effects conceal the drop in HCO
+
emission due to the water snowline. Therefore, locating the water snowline with HCO
+
observations in disks around Herbig Ae stars is very difficult, but it is possible for disks around outbursting stars such as V883 Ori, where the snowline has moved outwards.
Abstract
We introduce the Automatic Learning for the Rapid Classification of Events (ALeRCE) broker, an astronomical alert broker designed to provide a rapid and self-consistent classification of ...large etendue telescope alert streams, such as that provided by the Zwicky Transient Facility (ZTF) and, in the future, the Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST). ALeRCE is a Chilean-led broker run by an interdisciplinary team of astronomers and engineers working to become intermediaries between survey and follow-up facilities. ALeRCE uses a pipeline that includes the real-time ingestion, aggregation, cross-matching, machine-learning (ML) classification, and visualization of the ZTF alert stream. We use two classifiers: a stamp-based classifier, designed for rapid classification, and a light curve–based classifier, which uses the multiband flux evolution to achieve a more refined classification. We describe in detail our pipeline, data products, tools, and services, which are made public for the community (see
https://alerce.science
). Since we began operating our real-time ML classification of the ZTF alert stream in early 2019, we have grown a large community of active users around the globe. We describe our results to date, including the real-time processing of 1.5 × 10
8
alerts, the stamp classification of 3.4 × 10
7
objects, the light-curve classification of 1.1 × 10
6
objects, the report of 6162 supernova candidates, and different experiments using LSST-like alert streams. Finally, we discuss the challenges ahead in going from a single stream of alerts such as ZTF to a multistream ecosystem dominated by LSST.
Abstract
We present Atacama Large Millimeter/sub-millimeter Array Cycle-2 observations of the HBC 494 molecular outflow and envelope. HBC 494 is an FU Ori-like object embedded in the Orion A cloud ...and is associated with the reflection nebulae Re50 and Re50N. We use 12CO, 13CO and C18O spectral line data to independently describe the outflow and envelope structures associated with HBC 494. The moment-1 map of the 12CO emission shows the widest outflow cavities in a Class I object known to date (opening angle ∼150°). The morphology of the wide outflow is likely to be due to the interaction between winds originating in the inner disc and the surrounding envelope. The low-velocity blueshifted and redshifted 13CO and C18O emission trace the rotation and infall motion of the circumstellar envelope. Using molecular line data and adopting standard methods for correcting optical depth effects, we estimate its kinematic properties, including an outflow mass of the order of 10−1 M⊙. Considering the large estimated outflow mass for HBC 494, our results support recent theoretical work suggesting that wind-driven processes might dominate the evolution of protoplanetary discs via energetic outflows.
Summary
In self‐incompatible Solanaceae, the pistil protein S‐RNase contributes to S‐specific pollen rejection in conspecific crosses, as well as to rejecting pollen from foreign species or whole ...clades. However, S‐RNase alone is not sufficient for either type of pollen rejection. We describe a thioredoxin (Trx) type h from Nicotiana alata, NaTrxh, which interacts with and reduces S‐RNase in vitro. Here, we show that expressing a redox‐inactive mutant, NaTrxhSS, suppresses both S‐specific pollen rejection and rejection of pollen from Nicotiana plumbaginifolia. Biochemical experiments provide evidence that NaTrxh specifically reduces the Cys155‐Cys185 disulphide bond of SC10‐Rnase, resulting in a significant increase of its ribonuclease activity. This reduction and increase in S‐RNase activity by NaTrxh helps to explain why S‐RNase alone could be insufficient for pollen rejection.
Significance Statement
S‐RNase is very well known for its role in S‐RNase‐based self‐incompatibility and in some types of interspecific pollen rejection. Through a dominant‐negative approach, we show that a thioredoxin (Trx) type h from Nicotiana alata, NaTrxh, is required for both types of pollen rejection. This is a significant advance, although what sets our new contribution apart is that we show that NaTrxh reduces an S‐RNase disulphide and increases its activity, providing a remarkable level of insight into the biochemical mechanism of S‐RNase‐dependent pollen rejection.
Previous studies demonstrated that laminar separation bubbles (LSBs) in the absence of external disturbances or forcing are intrinsically unstable with respect to a three-dimensional instability of ...centrifugal nature. This instability produces topological modifications of the recirculation region with the introduction of streamwise vorticity in an otherwise purely two-dimensional time-averaged flows. Concurrently, the existence of spanwise inhomogeneities in LSBs have been reported in experiments in which the amplification of convective instability waves dominates the physics. The co-existence of the two instability mechanisms is investigated herein by means of three-dimensional parabolised stability equations. The spanwise waviness of the LSB on account of the primary instability is found to modify the amplification of incoming disturbance waves in the linear regime, resulting in a remarkable enhancement of the amplitude growth and a three-dimensional arrangement of the disturbance waves in the aft portion of the bubble. Present findings suggest that the oblique transition scenario should be expected in LSBs dominated by the convective instability, unless high-amplitude disturbances are imposed.
PDF
