502 research outputs found
Sensitization of Gold Dust in 430 Grade Stainless Steel
\u27Gold dusting\u27 is a surface defect that is sometimes observed on cold-rolled AISI type 430 stainless steel. Gold dusting is characterized by a sparkling appearance, which results from small flakes of metal on the cold rolled surface, the flakes are mostly elongated in the rolling direction. The processing steps include continuous casting, hot rolling, continuous annealing, and pickling. One possibility is that the flakes of metal are grains that had been undercut by intergranular corrosion such intergranular corrosion may occur during pickling after the annealing step (which itself follows hot rolling). If intergranular corrosion does occur during this pickling step, the intergranular cavities would be elongated by subsequent cold rolling; this can account for the observed morphology of gold dusting. If the steel has been sensitized, intergranular corrosion may occur during pickling. Pickling is commonly carried out by electrolytic descaling in a neutral sodium sulphate solution followed by immersion in a nitric acid/hydrofluoric acid bath. The sensitized type 430 stainless steel does, indeed, suffer intergranular corrosion in a nitric acid/hydrofluoric acid bath, while it is largely unaffected during electrolytic pickling. Hence, sensitization is a possible cause of gold dusting
Transient downflows associated with the intensification of small-scale magnetic features and bright point formation
Small-scale magnetic features are present everywhere in the solar
photosphere. Theoretical models, numerical calculations, and simulations
describing the formation of these features have existed for a few decades, but
there are only a few observational studies in direct support of the
simulations. In this study we present the evolution of small-scale magnetic
features with a spatial resolution close to 0.15 arcsecond and compare these
observations with those predicted by numerical simulations and also with
previous observational work of a similar nature. We analyze a 40 min time
sequence of full Stokes spectropolarimetric 630.25 nm data from a plage region
near the Sun center. We use line-of-sight velocities and magnetic field
measurements obtained using Milne-Eddington inversion techniques with and
without stray-light compensation along with measured continuum and line minimum
intensities. We discuss the results in relation to earlier observations and
simulations. We present eight cases involving strong downflows and magnetic
field intensification. All cases studied are associated with the formation of a
bright point in the continuum. In three out of the eight cases we find the
presence of weak opposite polarity field in close proximity to the downflow.
Our data are consistent with earlier simulations describing flux tube collapse,
but the transition to a state with stronger field appears transient and
short-lived, rather than resulting in a permanent field intensification. Three
cases of weak opposite polarity field found adjacent to the downflows do not
appear related to reconnection but may be related to overturning convection
pulling down some field lines and leading to up/down "serpentine" field, as
seen in some simulations.Comment: Accepted for publication in Astronomy & Astrophysic
Criteria for Flux Rope Eruption: Non Equilibrium versus Torus Instability
The coronal magnetic configuration of an active region typically evolves
quietly during few days before becoming suddenly eruptive and launching a
coronal mass ejection (CME). The precise origin of the eruption is still
debated. Among several mechanisms, it has been proposed that a loss of
equilibrium, or an ideal magneto-hydrodynamic (MHD) instability such as the
torus instability, could be responsible for the sudden eruptivity. Distinct
approaches have also been formulated for limit cases having circular or
translation symmetry. We revisit the previous theoretical approaches, setting
them in the same analytical framework. The coronal field results from the
contribution of a non-neutralized current channel added to a background
magnetic field, which in our model is the potential field generated by two
photospheric flux concentrations. The evolution on short Alfvenic time scale is
governed by ideal MHD. We show analytically first that the loss of equilibrium
and the stability analysis are two different views of the same physical
mechanism. Second, we identify that the same physics is involved in the
instability of circular and straight current channels. Indeed, they are just
two particular limiting case of more general current paths. A global
instability of the magnetic configuration is present when the current channel
is located at a coronal height, h, large enough so that the decay index of the
potential field, (d ln |Bp|) / (d ln h) is larger than a critical value. At the
limit of very thin current channels, previous analysis found a critical decay
index of 1.5 and 1 for circular and straight current channels, respectively.
However, with current channels being deformable and as thick as expected in the
corona, we show that this critical index has similar values for circular and
straight current channels, typically in the range [1.1,1.3].Comment: 12 pages, 4 figure
Speed of CMEs and the Magnetic Non-Potentiality of their Source Active Regions
Most fast coronal mass ejections (CMEs) originate from solar active regions (ARs). Non-potentiality of ARs plausibly determines the speed of CMEs in the outer corona. Several other unexplored parameters might be important as well. To find out the relation between the intial speed of CMEs and the non-potentiality of source ARs, we identified over a hundred of CMEs with source ARs via their co-produced flares. The speed of the CMEs are collected from the SOHO LASCO CME catalog. We have used vector magnetograms obtained with HMI/SDO, to evaluate various magnetic non-potentiality parameters, e.g. magnetic free-energy proxies, twist, shear angle, signed shear angle, net current etc. We have also included several other parameters e.g. total unsigned flux, magnetic area of ARs, area of sunspots, to investigate their correlation, if any, with the initial speeds of CMEs. Our preliminary results show that the ARs with larger non-potentiality and area produce faster CMEs but they can also produce slow ones. The ARs with lesser non-potentiality and area generally produce only slower CMEs
Solar flares with and without SOHO/LASCO coronal mass ejections and type II shocks
We analyse of a set of radio rich (accompanied by type IV or II bursts) solar
flares and their association with SOHO/LASCO Coronal Mass Ejections in the
period 1998 2000. The intensity, impulsiveness and energetics of these events
are investigated. We find that, on the average, flares associated both with
type IIs and CMEs are more impulsive and more energetic than flares associated
with type IIs only (without CME reported), as well as flares accompanied by
type IV continua but not type II shocks. From the last two classes, flares with
type II bursts (without CMEs reported) are the shortest in duration and the
most impulsive.Comment: Advances in Space Research, Volume 38, Issue 5, p. 1007-101
Spial: analysis of subtype-specific features in multiple sequence alignments of proteins
Motivation: Spial (Specificity in alignments) is a tool for the comparative analysis of two alignments of evolutionarily related sequences that differ in their function, such as two receptor subtypes. It highlights functionally important residues that are either specific to one of the two alignments or conserved across both alignments. It permits visualization of this information in three complementary ways: by colour-coding alignment positions, by sequence logos and optionally by colour-coding the residues of a protein structure provided by the user. This can aid in the detection of residues that are involved in the subtype-specific interaction with a ligand, other proteins or nucleic acids. Spial may also be used to detect residues that may be post-translationally modified in one of the two sets of sequences
Glycan analysis of human neutrophil granules implicates a maturation-dependent glycosylation machinery
Protein glycosylation is essential to trafficking and immune functions of human neutrophils. During granulopoiesis in the bone marrow, distinct neutrophil granules are successively formed. Distinct receptors and effector proteins, many of which are glycosylated, are targeted to each type of granule according to their time of expression, a process called "targeting by timing." Therefore, these granules are time capsules reflecting different times of maturation that can be used to understand the glycosylation process during granulopoiesis. Herein, neutrophil subcellular granules were fractionated by Percoll density gradient centrifugation, andN- andO-glycans present in each compartment were analyzed by LC-MS. We found abundant paucimannosidicN-glycans and lack ofO-glycans in the early-formed azurophil granules, whereas the later-formed specific and gelatinase granules and secretory vesicles contained complexN-andO-glycans with remarkably elongatedN-acetyllactosamine repeats with Lewis epitopes. Immunoblotting and histochemical analysis confirmed the expression of Lewis X and sialyl-Lewis X in the intracellular granules and on the cell surface, respectively. Many glycans identified are unique to neutrophils, and their complexity increased progressively from azurophil granules to specific granules and then to gelatinase granules, suggesting temporal changes in the glycosylation machinery indicative of "glycosylation by timing" during granulopoiesis. In summary, this comprehensive neutrophil granule glycome map, the first of its kind, highlights novel granule-specific glycosylation features and is a crucial first step toward a better understanding of the mechanisms regulating protein glycosylation during neutrophil granulopoiesis and a more detailed understanding of neutrophil biology and function
Pseudo-transient Continuation, Solution Update Methods, and CFL Strategies for DG Discretizations of the RANS-SA Equations
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/106459/1/AIAA2013-2686.pd
- …