391 research outputs found
Laser Powder-Bed Fusion as an Alloy Development Tool: Parameter Selection for In-Situ Alloying Using Elemental Powders
The design of advanced alloys specifically tailored to additive manufacturing processes is a research field that is attracting ever-increasing attention. Laser powder-bed fusion (LPBF) commonly uses pre-alloyed, fine powders (diameter usually 15–45 µm) to produce fully dense metallic parts. The availability of such fine, pre-alloyed powders reduces the iteration speed of alloy development for LPBF and renders it quite costly. Here, we overcome these drawbacks by performing in-situ alloying in LPBF starting with pure elemental powder mixtures avoiding the use of costly pre-alloyed powders. Pure iron, chromium, and nickel powder mixtures were used to perform in-situ alloying to manufacture 304 L stainless steel cube-shaped samples. Process parameters including scanning speed, laser power, beam diameter, and layer thickness were varied aiming at obtaining a chemically homogeneous alloy. The scientific questions focused on in this work are: which process parameters are required for producing such samples (in part already known in the state of the art), and why are these parameters conducive to homogeneity? Analytical modelling of the melt pool geometry and temperature field suggests that the residence time in the liquid state is the most important parameter controlling the chemical homogeneity of the parts. Results show that in-situ alloying can be successfully employed to enable faster and cost-efficient rapid alloy development
Recrystallization in non-conventional microstructures of 316L stainless steel produced via laser powder-bed fusion: effect of particle coarsening kinetics
Sum rules of codon usage probabilities
In the crystal basis model of the genetic code, it is deduced that the sum of
usage probabilities of the codons with C and A in the third position for the
quartets and/or sextets is independent of the biological species for
vertebrates. A comparison with experimental data shows that the prediction is
satisfied within about 5 %.Comment: 7 page
Atomic scale evolution of the surface chemistry in Li[Ni,Mn,Co]O2 cathode for Li-ion batteries stored in air
Layered LiMO2 (M = Ni, Co, Mn, and Al mixture) cathode materials used for Li-ion batteries are reputed to be highly reactive through their surface, where the chemistry changes rapidly when exposed to ambient air. However, conventional electron/spectroscopy-based techniques or thermogravimetric analysis fails to capture the underlying atom-scale chemistry of vulnerable Li species. To study the evolution of the surface composition at the atomic scale, here we use atom probe tomography and probed the surface species formed during exposure of a LiNi0.8Mn0.1Co0.1O2 (NMC811) cathode material to air. The compositional analysis evidences the formation of Li2CO3. Site specific examination from a cracked region of an NMC811 particle also suggests the predominant presence of Li2CO3. These insights will help to design improved protocols for cathode synthesis and cell assembly, as well as critical knowledge for cathode degradatio
Nanoporous gold thin films as substrates to analyze liquids by cryo-atom probe tomography
Cryogenic atom probe tomography (cryo-APT) is being developed to enable
nanoscale compositional analyses of frozen liquids. Yet, the availability of
readily available substrates that allow for the fixation of liquids while
providing sufficient strength to their interface, is still an issue. Here we
propose the use of 1-2 microns thick binary alloy film of gold-silver (AuAg)
sputtered onto flat silicon, with sufficient adhesion without an additional
layer. Through chemical dealloying, we successfully fabricate a nanoporous
substrate, with open-pore structure, which is mounted on a microarray of Si
posts by lift out in the focused-ion beam, allowing for cryogenic fixation of
liquids. We present cryo-APT results obtained after cryogenic sharpening,
vacuum cryo-transfer and analysis of pure water on top and inside the
nanoporous film. We demonstrate that this new substrate has the requisite
characteristics for facilitating cryo-APT of frozen liquids, with a relatively
lower volume of precious metals. This complete workflow represents an improved
approach for frozen liquid analysis, from preparation of the films to the
successful fixation of the liquid in the porous network, to cryo-atom probe
tomography
Continuous Hydrolysis and LiquidâLiquid Phase Separation of an Active Pharmaceutical Ingredient Intermediate Using a Miniscale Hydrophobic Membrane Separator
Cited2 is required for the proper formation of the hyaloid vasculature and for lens morphogenesis
Cited2 is a transcriptional modulator with pivotal roles in different biological processes. Cited2-deficient mouse embryos manifested two major defects in the developing eye. An abnormal corneal-lenticular stalk was characteristic of Cited2(â/â) developing eyes, a feature reminiscent of Petersâ anomaly, which can be rescued by increased Pax6 gene dosage in Cited2(â/â) embryonic eyes. In addition, the hyaloid vascular system showed hyaloid hypercellularity consisting of aberrant vasculature, which might be correlated with increased VEGF expression in the lens. Deletion of Hif1a (which encodes HIF-1α) in Cited2(â/â) lens specifically eliminated the excessive accumulation of cellular mass and aberrant vasculature in the developing vitreous without affecting the corneal-lenticular stalk phenotype. These in vivo data demonstrate for the first time dual functions for Cited2: one upstream of, or together with, Pax6 in lens morphogenesis; and another in the normal formation of the hyaloid vasculature through its negative modulation of HIF-1 signaling. Taken together, our study provides novel mechanistic revelation for lens morphogenesis and hyaloid vasculature formation and hence might offer new insights into the etiology of Petersâ anomaly and ocular hypervascularity
Living biointerfaces based on non-pathogenic bacteria to direct cell differentiation
Genetically modified Lactococcus lactis, non-pathogenic bacteria expressing the FNIII7-10 fibronectin fragment as a protein membrane have been used to create a living biointerface between synthetic materials and mammalian cells. This FNIII7-10 fragment comprises the RGD and PHSRN sequences of fibronectin to bind α5ÎČ1 integrins and triggers signalling for cell adhesion, spreading and differentiation. We used L. lactis strain to colonize material surfaces and produce stable biofilms presenting the FNIII7-10 fragment readily available to cells. Biofilm density is easily tunable and remains stable for several days. Murine C2C12 myoblasts seeded over mature biofilms undergo bipolar alignment and form differentiated myotubes, a process triggered by the FNIII7-10 fragment. This biointerface based on living bacteria can be further modified to express any desired biochemical signal, establishing a new paradigm in biomaterial surface functionalisation for biomedical applications
Measurement of Dijet Angular Distributions at CDF
We have used 106 pb^-1 of data collected in proton-antiproton collisions at
sqrt(s)=1.8 TeV by the Collider Detector at Fermilab to measure jet angular
distributions in events with two jets in the final state. The angular
distributions agree with next to leading order (NLO) predictions of Quantum
Chromodynamics (QCD) in all dijet invariant mass regions. The data exclude at
95% confidence level (CL) a model of quark substructure in which only up and
down quarks are composite and the contact interaction scale is Lambda_ud(+) <
1.6 TeV or Lambda_ud(-) < 1.4 TeV. For a model in which all quarks are
composite the excluded regions are Lambda(+) < 1.8 TeV and Lambda(-) < 1. 6
TeV.Comment: 16 pages, 2 figures, 2 tables, LaTex, using epsf.sty. Submitted to
Physical Review Letters on September 17, 1996. Postscript file of full paper
available at http://www-cdf.fnal.gov/physics/pub96/cdf3773_dijet_angle_prl.p
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