25 research outputs found
Effect of Stress Ratio on Fatigue Crack Growth Behavior of Ti-6Al-2Zr-1Mo-1V Alloy
The fatigue crack growth behaviors of Ti-6.5Al-2Zr-1Mo-1V titanium alloy at different positive stress ratios (R = 0.1, 0.3 and 0.5) were investigated at room temperature. The effects of stress ratio R on the fatigue crack growth rates and fractures morphology were discussed. The results show that with the increase of stress ratio R , the fatigue crack growth rates are increased at the given applied cyclic stress intensity factor, ÎK. Equivalently, the observed threshold stress-intensity range ÎKth and the range of stress intensity factor ÎK for fatigue crack growth are decreased as the positive stress ratio is increased. Some fatigue steps and secondary cracks are observed on the fracture surfaces of the specimens tested at the three stress ratios. In addition, with the increase of the stress ratio, the toughness of the surface is increased and the secondary cracks are decreased. However, the fatigue fracture mechanisms of Ti-6.5Al-2Zr-1Mo-1V titanium alloy tested at the three stress ratios are all the same, which the fractures are all presented in transgranular mode
Microstructure and Mechanical Properties of Friction Welding Joints with Dissimilar Titanium Alloys
Titanium alloys, which are important in aerospace application, offer different properties via changing alloys. As design complexity and service demands increase, dissimilar welding of the titanium alloys becomes a particular interest. Linear friction welding (LFW) is a relatively novel bond technique and has been successfully applied for joining titanium alloys. In this paper, dissimilar joints with Ti-6Al-4V and Ti-5Al-2Sn-2Zr-4Mo-4Cr alloys were produced by LFW process. Microstructure was studied via optical microscopy and scanning electron microscopy (SEM), while the chemical composition across the welded samples was identified by energy dispersive X-ray spectroscopy. Mechanical tests were performed on welded samples to study the joint mechanical properties and fracture characteristics. SEM was carried out on the fracture surface to reveal their fracture modes. A significant microstructural change with fine re-crystallization grains in the weld zone (WZ) and small recrystallized grains in the thermo-mechanically affected zone on the Ti-6Al-4V side was discovered in the dissimilar joint. A characteristic asymmetrical microhardness profile with a maximum in the WZ was observed. Tensile properties of the dissimilar joint were comparable to the base metals, but the impact toughness exhibited a lower value
DBSubLoc: database of protein subcellular localization
We have built a protein subcellular localization annotation database, the DBSubLoc database, which is available at http://www.bioinfo.tsinghua.edu.cn/dbsubloc.html. Annotations were taken from primary protein databases, model organism genome projects and literature texts, and then were analyzed to dig out the subcellular localization features of the proteins. The proteins are also classified into different categories. Based on sequence alignment, non-redundant subsets of the database have been built, which may provide useful information for subcellular localization prediction. The database now contains >60 000 protein sequences including âŒ30 000 protein sequences in the non-redundant data sets. Online download, search and Blast tools are also available
Elastoplastic finite element analysis for wet multidisc brake during lasting braking
Addressed to serious heat degradation problem of the braking continuously
performed in the drag brake application for a long time, finite element
analysis for bidirectional thermal-structure coupling is adopted to
investigate temperature and stress when material properties are
temperature-dependent. Based on the constitutive relations of heat transfer
and strain-stress, three-dimensional transient finite element equilibrium
equations with many kinds of boundary conditions for bidirectional
thermal-structure coupling were derived. And it was originally presented that
start time, location, severity and evolution laws of plastic deformation were
depicted using dimensionless stress distribution contour with the yield limit
related to temperature. The change laws of plastic element number and contact
area versus braking time were expressed by plasticity ratio and contact ratio
curves, respectively. The laws revealed by the numerical calculation results
are in accordance with the objective perception and reasoning
Colloidal synthesis of size-confined CsAgCl2 nanocrystals: implications for electroluminescence applications
International audienceBecause of their non-toxic properties and similar ionic radius to that of Pb2+, silver ion (Ag+)-containing perovskite derivatives have become an important class of Pb-free alternatives that are competitive for a variety of optoelectronic applications. Although great success has been achieved in producing Ag+-containing nanocrystals (NCs), such as Cs2AgInCl6 and Cs2AgBiCl6, colloidal synthesis of pure Ag-based emitters has remained challenging. Herein, we have devised a facile europium chloride (EuCl3)-based route to CsAgCl2 NCs with a tunable particle size and desirable warm white-light emission. To enhance the optical properties of CsAgCl2, we further demonstrate a trace doping strategy with Sb3+, which improves the quantum efficiency of the resulting NCs from 16% to 39%. Moreover, the addition of Sb3+ was found to significantly reduce the particle size of the CsAgCl2 NCs from a few hundred nanometers to several nanometers as a result of the reduced surface energy, paving the way for the formation of emissive layers with a well-controlled thickness and improved uniformity. Prototype electroluminescence devices fabricated using these nano-emitters exhibit favorable warm white-light (or yellow) emission, which opens up new avenues to develop single-component warm white light-emitting diodes
XLSearch: a Probabilistic Database Search Algorithm for Identifying Cross-Linked Peptides
Chemical
cross-linking combined with mass spectrometric analysis
has become an important technique for probing protein three-dimensional
structure and proteinâprotein interactions. A key step in this
process is the accurate identification and validation of cross-linked
peptides from tandem mass spectra. The identification of cross-linked
peptides, however, presents challenges related to the expanded nature
of the search space (all pairs of peptides in a sequence database)
and the fact that some peptide-spectrum matches (PSMs) contain one
correct and one incorrect peptide but often receive scores that are
comparable to those in which both peptides are correctly identified.
To address these problems and improve detection of cross-linked peptides,
we propose a new database search algorithm, XLSearch, for identifying
cross-linked peptides. Our approach is based on a data-driven scoring
scheme that independently estimates the probability of correctly identifying
each individual peptide in the cross-link given knowledge of the correct
or incorrect identification of the other peptide. These conditional
probabilities are subsequently used to estimate the joint posterior
probability that both peptides are correctly identified. Using the
data from two previous cross-link studies, we show the effectiveness
of this scoring scheme, particularly in distinguishing between true
identifications and those containing one incorrect peptide. We also
provide evidence that XLSearch achieves more identifications than
two alternative methods at the same false discovery rate (availability: https://github.com/COL-IU/XLSearch)
Filling Chlorine Vacancy with Bromine: A Two-Step Hot-Injection Approach Achieving Defect-Free Hybrid Halogen Perovskite Nanocrystals
International audienceMixed-halide (Cl and Br) perovskite nanocrystals (NCs) are of particular interest because they hold great potential for use in high-efficiency blue light-emitting diodes (LEDs). Generally, mixed-halide compounds are obtained by either a one-step synthesis with simultaneous addition of both halide precursors or a postsynthetic anion exchange using the opposite halogen. However, both strategies fail to prevent the formation of deep-level Cl vacancy defects, rendering the photoluminescence quantum yields (PLQYs) typically lower than 30%. Here, by optimizing both thermodynamic and kinetic processes, we devise a two-step hot-injection approach, which simultaneously realizes Cl vacancy filling and efficient anion exchange between Cl- and Br-. Both the identity of Br precursors and their injection temperature are revealed to be critical in transforming those highly defective CsPbCl3 NCs to defect-free CsPb(Cl/Br)(3). The optimally synthesized NCs exhibit a saturated blue emission at similar to 460 nm with a near-unity PLQY and a narrow emission bandwidth of 18 nm, which represents one of the most efficient blue emitters reported so far. The turn-on voltage of the ensuing LEDs is similar to 4.0 V, which is lower than those of most other mixed-halide perovskites. In addition, LEDs exhibit a stable electroluminescence peak at 460 nm under a high bias voltage of 8.0 V. We anticipate that our findings will provide new insights into the materials design strategies for producing high-optoelectronic-quality Cl-containing perovskites
Highly Luminescent Phase-Stable Hybrid Manganese Halides for Efficient X-ray Imaging
Mn(II)-based organic-inorganic hybrid metal halides have garnered considerable attention for their potential use in X-ray imaging due to their cost-effective solution processability and remarkable radioluminescence efficiency. However, achieving a photoluminescence quantum yield (PLQY) close to 100% across all compositions containing Cl-, Br-, and I- has been a challenge. Here, we introduce an efficient spacer cation, BDPA+ (C15H18N+), which enables all halide compounds to achieve high PLQYs of 95-98%. The high fluorescence efficiency is attributed to the passivation effect provided by Ï-conjugated aromatic groups and the long distance between emissive centers afforded by the periodic bulk structures of BDPA+. This effectively reduces energy transfer between Mn2+ ions, resulting in enhanced luminescence. Additionally, the strong hydrophobic nature of the organic component ensures that the resulting crystals maintain their stability for over 2 months in ambient air, making them suitable for a wide range of applications. A representative scintillator prepared from (BDPA)2MnBr4 exhibits impressive X-ray imaging performance with a high light yield of 44,000 ph/MeV and a low detection limit of 0.32 ÎŒGy/s, comparable to those of commercial LuAG:Ce scintillator crystals (25,000 ph/MeV, 2.32 ÎŒGy/s). These findings hold great promise for the future development of this class of materials, particularly for stable high-energy radiation detection.</p
Excitation WavelengthâDependent Fluorescence of a Lanthanide Organic Metal Halide Cluster for AntiâCounterfeiting Applications
International audienceThe achievement of significant photoluminescence (PL) in lanthanide ions (Ln3+) has primarily relied on host sensitization, where energy is transferred from the excited host material to the Ln3+ ions. However, this luminous mechanism involves only one optical antenna, namely the host material, which limits the accessibility of excitation wavelength-dependent (Ex-De) PL. Consequently, the wider application of Ln3+ ions in light-emitting devices is hindered. In this study, we present an organicâinorganic compound, (DMA)4LnCl7 (DMA+=[CH3NH2CH3]+, Ln3+=Ce3+, Tb3+), which serves as an independent host lattice material for efficient Ex-De emission by doping it with trivalent antimony (Sb3+). The pristine (DMA)4LnCl7 compounds exhibit high luminescence, maintaining the characteristic sharp emission bands of Ln3+ and demonstrating a high PL quantum yield of 90â100â%. Upon Sb3+ doping, the compound exhibits noticeable Ex-De emission with switchable colors. Through a detailed spectral study, we observe that the prominent energy transfer process observed in traditional host-sensitized systems is absent in these materials. Instead, they exhibit two independent emission centers from Ln3+ and Sb3+, each displaying distinct features in luminous color and radiative lifetime. These findings open up new possibilities for designing Ex-De emitters based on Ln3+ ions
MoistureâInsensitive, PhaseâStable IndiumâBased Metal Halides and Their LightâEmitting Applications
International audienceAbstract Ternary indium (In)âbased metal halides are gaining increased attention as promising lead (Pb)âfree alternatives for lightâemitting diodes (LEDs) owing to their broadband emission and high photoluminescence quantum yields (PLQYs). However, most of the pure Inâbased compositions suffer from instability against moisture and thermal stress, leading to a rapid degradation of material and hence their optical properties. Herein, a new kind of organicâinorganic hybrid Inâbased metal halide BA 6 InCl 9 (BA + = C 4 H 11 N + ) is presented, which exhibits stable crystal structure and material composition at both ambient (over 5 months) and heating conditions (up to 200 °C). Besides, the HuangâRhys factor of â4.94 determined for BA 6 InCl 9 is considerably smaller than most Pbâfree perovskites, which suggests a relatively weak excitonâphonon coupling in these crystals. By trace amounts of antimony (III) (Sb 3+ ) doping, the PLQY of the BA 6 InCl 9 single crystals can be markedly improved from â25% to 95%, and the ensuing downâconversion LEDs exhibit bright orangeâred emission with an external quantum efficiency of 0.12%, which retains â50% of the initial luminance after 380 min of continuous operation in ambient air. It is forseen that the study will prompt future research on Inâbased metal halides and their use in stable lightâemitting applications