Microscope Sees with Nanoscale Resolution

first_img The collaborative team, led by Jianwei Miao and Changyong Song from the University of California at Los Angeles, also includes researchers from the Australian Synchotron, and Argonne National Laboratory in Illinois. The ultimate resolution of the x-ray images, the scientists say, is limited only by the x-ray wavelengths, and can in principle reach the near-atomic level (the diameter of an average atom is around 0.1 nanometers). The study is published in a recent issue of Physical Review Letters.“This is one of the highest resolutions obtained for x-ray microscopy,” Miao told PhysOrg.com. “It not only provides high-resolution images but also elemental specificity. For example, atomic spectroscopy only provides spectra, but not images.”The imaging technique is called resonant x-ray diffraction microscopy, and this is the first demonstration of using the technique to image buried structures (such as dopants within host elements) at such a high resolution. Resonant x-ray diffraction microscopy is different than most imaging techniques because the microscope doesn’t have a lens. By avoiding the use of a lens, the method also avoids the limitations of lenses, such as a limited depth of focus that limits the thickness of the sample under investigation.Instead of a lens, the microscope consists of a 10-micrometer-diameter pinhole that selects the most spatially coherent part of the x-ray beam, which provides the “strongest” wavelength. The x-ray beam first takes images of two x-ray diffraction patterns of a sample: one pattern just above the sample’s absorption edge, and one just below. (The absorption edge, or band edge, occurs when incident photons obtain enough energy [binding energy] to excite the atom’s electrons and produce a photoelectron.)Then, the researchers determined the difference between the two diffraction patterns to obtain the spatial distribution of the element. Knowing the spatial distribution enabled the researchers to determine not only the surface structure, but also the index of refraction of the sample, which can be used to determine its molecular contents. The researchers demonstrated the technique by mapping out bismuth (Bi) dopants that are broadly dispersed and buried inside silicon (Si) atoms. In other studies, researchers have used Bi dopants to control and manipulate the physical properties of materials in order to design advanced, highly functional materials, such as in semiconductors. Because the microscope’s CCD camera recorded thousands of diffraction patterns, the researchers developed an evolutionary algorithm to pick out the images with the best characteristics to pass on to succeeding generations and create a final spatial distribution. When analyzing the map of the Bi dopants, the researchers found that Bi atoms, which are three times larger than Si atoms, sometimes form clusters that can influence atomic growth. Insights like this may help scientists better understand the 3D self-assembly of nanostructures.“The resonant x-ray diffraction microscope can be adapted to perform electronic orbital as well as chemical state specific imaging of a broad range of systems,” said Miao. “These include magnetic materials, semiconductors, organic materials, bio-minerals, and biological specimens.”More information: Song, Changyoung, Bergstrom, Raymond, Ramunno-Johnson, Damien, Jiang, Huaidong, Paterson, David, Jonge, Martin D., McNulty, Ian, Lee, Jooyoung, Wang, Kang L., and Miao, Jianwei. “Nanoscale Imaging of Buried Structures with Elemental Specificity Using Resonant X-Ray Diffraction Microscopy.” Physical Review Letters 100, 025504 (2008).Copyright 2008 PhysOrg.com. All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com. Explore further The resonant x-ray diffraction microscope takes two diffraction patterns, above and below the element’s absorption edge. The patterns are phased to obtain high-resolution images, and the difference of the two images represents the spatial distribution of the element. Image credit: Changyoung Song, et al. Researchers have recently built an x-ray microscope that has a pixel resolution of just 15 nanometers, allowing scientists to study the properties of materials at the molecular scale and beyond. Citation: Microscope Sees with Nanoscale Resolution (2008, January 28) retrieved 18 August 2019 from https://phys.org/news/2008-01-microscope-nanoscale-resolution.html Breakthrough With Ultra-Fast Xrays This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Melanin from Jurassicera mollusk could lead to new tool for cancer diagnosis

first_img This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only. Eumelanin from the Jurassic-era fossil has a nearly identical pump-probe signature as the eumelanin from its modern counterpart, S. officinalis. The finding that eumelanin survives for millions of years opens the opportunity for pathologists to analyze the eumelanin from decades-old tissue samples of cancer patients in order to better understand the different characteristics of a melanoma that spreads versus a melanoma that does not spread. Credit: Mary Jane Simpson, et al. ©2013 American Chemical Society The researchers, Mary Jane Simpson, et al., led by Professor Warren S. Warren at Duke University in Durham, North Carolina, have published their paper on their analysis of Jurassic-aged eumelanin in a recent issue of The Journal of Physical Chemistry Letters.”Melanoma is a particularly bad cancer if it metastasizes,” Warren told Phys.org. “Unfortunately, the ‘gold standard’ of conventional diagnostic techniques (essentially, excision followed by pathology) does not do a very good job of predicting which diagnosed cancers are likely to spread. So, how do you fix a bad gold standard for a bad disease?”The best answer is retrospective studies—looking at decades-old specimens from patients, where you know the outcome—and trying to find systematic differences. That is impossible with most pathology methods because the tissue degrades. Our results show that it is possible with melanin-based diagnostics, since the melanin easily survives that long.”The researchers explain that human skin has two types of melanin, eumelanin and pheomelanin. The distribution of these two types assists in the diagnosis of melanoma skin cancer. One way to identify the types of melanin and their distribution in a given sample is to use a molecular imaging technique called pump-probe microscopy. Basically, an ultrafast laser pulse is first used to “pump,” or optically excite, the molecules. Then after a short time delay, one or more follow-up pulses are emitted to “probe” the molecules. By measuring how the probe pulses are absorbed or reflected by the molecules, researchers can obtain a pump-probe signature that reveals information on the molecules’ excitation decay process. Since eumelanin and pheomelanin have different pump-probe signatures, this technique enables scientists to distinguish between them. Citation: Melanin from Jurassic-era mollusk could lead to new tool for cancer diagnosis (2013, June 3) retrieved 18 August 2019 from https://phys.org/news/2013-06-melanin-jurassic-era-mollusk-tool-cancer.html Here, the researchers compared the pump-probe signatures of the eumelanin from the ink sack of a Jurassic-era cephalopod (an ancient molluscan marine animal) with that of a modern cephalopod, the common cuttlefish. (Despite its name, cuttlefish are mollusks, not fish.) Although the Jurassic-era cephalopod is 162 million years older than its modern counterpart, the eumelanin pump-probe signatures of the two animals are essentially identical. This finding shows that eumelanin is extremely stable, and could potentially permit researchers to image archived tissue samples from deceased cancer patients and uncover more information than could be obtained through more traditional methods that analyze other, less stable chemicals. Squid ink from Jurassic period identical to modern squid ink, study shows Journal information: Journal of Physical Chemistry Letters The researchers pointed out that they did find some variations in the eumelanin signatures from the two mollusks. However, they could trace these variations to the larger iron content in the ancient eumelanin compared with the modern sample. Eumelanin from the common cuttlefish is normally bound to a variety of transition metals such as iron, copper, and manganese, but washing the eumelanin with the solid acid EDTA removes the majority of the bound metals. When the researchers washed the ancient eumelanin with EDTA, its signature closely matched that of the modern, mostly iron-free eumelanin. Because iron affects the pump-probe signature of eumelanin, the microscopy technique could also potentially enable researchers to approximate the iron content of a sample. For example, pigmented human tissue often exhibits a wide range of pump-probe signatures, and some of the variation may be due to metal ion binding by the melanin. In the future, pathologists may use this knowledge to their advantage when investigating the molecular composition of eumelanin samples. Explore further © 2013 Phys.org. All rights reserved. More information: Mary Jane Simpson, et al. “Pump-Probe Microscopic Imaging of Jurassic-Aged Eumelanin.” The Journal of Physical Chemistry Letters. 2013, 4, 1924-1927. DOI: 10.1021/jz4008036 Common cuttlefish. ©Jarek Tuszynski / Wikimedia Commons / CC-BY-SA-3.0 & GDFL (Phys.org) —In a world where things seem to change overnight, melanin seems to stay essentially the same for more than 160 million years, a new study has found. Melanin is the biological pigment that determines an animal’s color, and is currently not very well understood. In the new study, scientists have found that a type of melanin called eumelanin from a Jurassic-era mollusk produces a signature when optically excited that is nearly identical to that of the optically excited eumelanin from its modern counterpart, Sepia officinalis, or the common cuttlefish. Because melanin survives so long, an analysis of the melanin from old cancerous tissue samples could give researchers a useful tool for predicting the spread of melanoma skin cancer in humans.last_img read more

Britains Pompeii reveals new clues about life during the Bronze Age

first_imgThought the site is no longer situated on a river, it is quite wet, which is helping to preserve artifacts. The researchers plan to remove them all because it is believed the water level in the areas is likely to fall, removing their natural protective blanket. © 2016 Phys.org Glass beads thought to have been from a necklace. More information: Press release Bronze Age textile made from plant fibres. The site was first discovered back in 2006, but it was only recently that excavations began—a joint effort between the University of Cambridge and Historic England. Items from the houses which sit approximately two meters below ground level, have been dated to approximately 1000-800 BC, which puts them near the end of the Bronze Age—a time dominated by tools and weapons made by mixing copper and tin, from roughly 2500, to 1000 BC. In Britain, the Bronze Age has been extended to approximately 800 BC—it ended when visitors from overseas introduced implements made of iron. Because of the arrangement, the researchers believe the houses were abandoned very quickly, likely due to the fire, which allowed for the preservation of objects as they existed in the everyday lives of people during that time period.Thus far, workers digging at the site have uncovered pots and pans of varying sizes, spears and daggers, exotic glass beads and even textiles that had been fashioned from tree bark. They have also uncovered the charred remains of the timbers that once served as stilts, allowing those living in the house to exist as if on their own tiny island. A human skull has also been found near one entrance, but it has not yet been studied in detail, thus it is not known if it might have belonged to one of the inhabitants of the house. The team has also identified footprints in the sediment. Detail on a 6.3m oak logboat. Close up of stilts and collapsed roof timbers. Explore further Close up of stilts and collapsed roof timbers. Close up of charred wooden bucket base. Citation: Britain’s ‘Pompeii’ reveals new clues about life during the Bronze Age (2016, January 12) retrieved 18 August 2019 from https://phys.org/news/2016-01-britain-pompeii-reveals-clues-life.html Late Iron Age baldric ring with La Tène style decoration, probably part of a shoulder belt for carrying a sword. Shifting sand dunes reveal hidden Bronze Age settlement (Phys.org)—A team of archeologists working at a dig site in Cambridgeshire in Britain has found what they are describing as Britain’s ‘Pompeii’—evidence of everyday life in an ancient society, covered by mud—and the best preserved Bronze Age dwelling ever found in that country. The find consists of two circular wooden houses that once stood atop stilts over a river—when the houses caught fire, they collapsed into the river and were covered by silt, which preserved everyday items inside, such as tables and chairs and jewelry, and even food in bowls. Glass beads thought to have been from a necklace. Bronze Age textile made from plant fibres. Late Iron Age baldric ring with La Tène style decoration, probably part of a shoulder belt for carrying a sword. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Researchers question Apolloera evidence for the Late Heavy Bombardment

first_img Journal information: Proceedings of the National Academy of Sciences Application of laser microprobe technology to Apollo samples refines lunar impact history Explore further Citation: Researchers question Apollo-era evidence for the Late Heavy Bombardment (2016, October 4) retrieved 18 August 2019 from https://phys.org/news/2016-10-apollo-era-evidence-late-heavy-bombardment.html Late Heavy Bombardment. One interpretation of lunar soil analysis suggests that four billion years ago the inner solar system was a violent place, gravitational perturbations of the orbits of the gas giants initiated a comet shower which in turn deflected many asteroids into the paths of the Earth and Moon. Erosion has removed most of the craters from the Earth but the Moon’s ancient landscape still bears the scars. Credit: Australian National University But these results are controversial—Apollo lunar samples represent only about 4 percent of the lunar surface and could thus have resulted from a single impact event rather than a more widespread bombardment episode. And due to lunar magnetism and overprinting from successive impacts, all of the Apollo-era lunar samples show evidence of 40Ar/39Ar age spectrum disturbances—in other words, the apparent ages of samples could have been “reset” by later impact events.So two researchers from the Department of Earth, Planetary and Space Sciences at the University of California, Los Angeles, recently reanalyzed the age spectra data from the Apollo samples in order to test the uniqueness of their impact histories. To do so, they used a physical model describing 40Ar* diffusive loss that accounted for age resetting of samples by subsequent impacts. The point of this reanalysis wasn’t to confirm or disconfirm the existence of the Late Heavy Bombardment, but rather to determine whether 40Ar/39Ar can even act as evidence for impact spikes. Their results, recently published in the Proceedings of the National Academy of Sciences, strongly suggest that episodic crust formation occurring more than 4 billion years ago, combined with 40Ar* loss due to a decrease in impact flux can create a bias in age compilations toward the illusion of an impact spike. “Our modeling shows that, due to the nature of declining impact rates and the early but episodic nature of crust formation on extraterrestrial bodies, apparent bombardment episodes can be a common artifact in 40Ar/39Ar plateau age histograms,” the authors write.They note that although the most widely cited evidence in favor of the LHB likely yields unreliable impact histories, their modeling does not preclude the occurrence of such events. However, determining impact histories will rely on future studies incorporating such techniques as in situ 40Ar/39Ar modeling and quantitative thermochronologic modeling. “Until such evidence is gathered,” the authors write, “we conclude that a monotonic decrease in impactor flux explains all existing 40Ar/39Ar data from both lunar and meteoritic samples.”center_img (Phys.org)—Many scientists believe that a cataclysmic series of impact events called the Late Heavy Bombardment (LHB) occurred around 4.1 to 3.9 billion years ago, during which there was a spike in asteroids colliding with the planets of the inner solar system. Among the possible explanations for the LHB is the migration of large planets to the outer solar system, disrupting objects in the asteroid belt and the Kuiper belt and flinging them toward the inner solar system.The Earth is constantly resurfaced by erosion and cratonic growth, and as a result, can’t contribute much geologic data about the existence of the LHB. Much of the evidence is therefore derived from the moon—specifically, from Apollo-era lunar samples returned to Earth in the 1960s and 1970s. Researchers used argon dating to determine age spectra of lunar rocks found in three major lunar basins. The so-called “plateau ages” of these rocks, as determined from 40Ar/39Ar age spectra, suggest a cluster of impacts approximately 3.9 billion years ago. More information: Illusory Late Heavy Bombardments. PNAS (2016). DOI: 10.1073/pnas.1611535113AbstractThe Late Heavy Bombardment (LHB), a hypothesized impact spike at ∼3.9 Ga, is one of the major scientific concepts to emerge from Apollo-era lunar exploration. A significant portion of the evidence for the existence of the LHB comes from histograms of 40Ar/39Ar “plateau” ages (i.e., regions selected on the basis of apparent isochroneity). However, due to lunar magmatism and overprinting from subsequent impact events, virtually all Apollo-era samples show evidence for 40Ar/39Ar age spectrum disturbances, leaving open the possibility that partial 40Ar* resetting could bias interpretation of bombardment histories due to plateaus yielding misleadingly young ages. We examine this possibility through a physical model of 40Ar* diffusion in Apollo samples and test the uniqueness of the impact histories obtained by inverting plateau age histograms. Our results show that plateau histograms tend to yield age peaks, even in those cases where the input impact curve did not contain such a spike, in part due to the episodic nature of lunar crust or parent body formation. Restated, monotonically declining impact histories yield apparent age peaks that could be misinterpreted as LHB-type events. We further conclude that the assignment of apparent 40Ar/39Ar plateau ages bears an undesirably high degree of subjectivity. When compounded by inappropriate interpretations of histograms constructed from plateau ages, interpretation of apparent, but illusory, impact spikes is likely. © 2016 Phys.org This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Flow apparatus samples up to 1500 chemical reactions a day

first_img Testing device for performance-enhancing drugs provides immediate results © 2018 Phys.org More information: Damith Perera et al. A platform for automated nanomole-scale reaction screening and micromole-scale synthesis in flow, Science (2018). DOI: 10.1126/science.aap9112AbstractThe scarcity of complex intermediates in pharmaceutical research motivates the pursuit of reaction optimization protocols on submilligram scales. We report here the development of an automated flow-based synthesis platform, designed from commercially available components, that integrates both rapid nanomole-scale reaction screening and micromole-scale synthesis into a single modular unit. This system was validated by exploring a diverse range of reaction variables in a Suzuki-Miyaura coupling on nanomole scale at elevated temperatures, generating liquid chromatography–mass spectrometry data points for 5760 reactions at a rate of >1500 reactions per 24 hours. Through multiple injections of the same segment, the system directly produced micromole quantities of desired material. The optimal conditions were also replicated in traditional flow and batch mode at 50- to 200-milligram scale to provide good to excellent yields. A team of researchers at Pfizer, the pharmaceutical giant, has developed an automated flow chemistry system that is capable of carrying out 1500 reactions over a 24-hour period. In their paper published in the journal Science, the group describes the system, how well it tested and its limitations. Citation: Flow apparatus samples up to 1500 chemical reactions a day (2018, January 26) retrieved 18 August 2019 from https://phys.org/news/2018-01-apparatus-samples-chemical-reactions-day.html This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.center_img Schematic depiction of the flow system. Credit: Science (2018). DOI: 10.1126/science.aap9112 Developing new drugs to treat human ailments is both expensive and profitable—researchers at pharmaceutical giants such as Pfizer are constantly looking for ways to develop new drugs that cost less which, in turn, will increase profits. In this new effort, the team at Pfizer built a machine that allows researchers to carry out and sample reactions every 45 seconds.At its most basic level, a lot of what pharmaceutical researchers do involves optimizing chemical reactions to discover which is best for scaling up for testing and producing commercial drugs—a process that is notoriously expensive because it is so time consuming. To speed things up, the researchers devised a platform that supports continuous flow of chemicals through a reactor coil for precise control of residence time, rate of flow, pressure and temperature. It also hosts two ultrahigh performance liquid chromatography devices, one for analyzing reagents, the other for analyzing the reagents as they emerge. The setup allows for pipetting reagents into solvent samples at nanoliter volumes prior to analysis with the chromatography devices.The researchers select a carrier solvent to flow through the device and then engage the sample device, which injects tiny amounts of reagents into similarly tiny samples of the solvent, and then test it to see what happens. They tested the system by carrying out 5,760 Suzuki-Miyaura coupling reactions with a host of reagents under varying conditions in just four days.The researchers note that while useful, the device is not suitable for use in commercial applications, in part because it cannot handle heterogeneous or biphasic mixes. They will continue to work with the device, hoping to expand its capabilities, and suggest other researchers might want to build similar systems for testing of their own ideas. Journal information: Science Explore furtherlast_img read more

Study suggests women in biomedical sciences have equal chance of success in

first_img Potential gender bias against female researchers in peer review of research grants © 2018 Phys.org A team of researchers at the National Institutes of Health has found that women in biomedical sciences are just as successful as men in sustaining grant funding. In their paper published in Proceedings of the National Academy of Sciences, the group describes their study of grant approval rates for men and women in the biomedical sciences. Citation: Study suggests women in biomedical sciences have equal chance of success in sustaining grant funding (2018, July 17) retrieved 18 August 2019 from https://phys.org/news/2018-07-women-biomedical-sciences-equal-chance.html Explore further Credit: CC0 Public Domaincenter_img Journal information: Proceedings of the National Academy of Sciences More information: Lisa A. Hechtman et al. NIH funding longevity by gender, Proceedings of the National Academy of Sciences (2018). DOI: 10.1073/pnas.1800615115AbstractWomen have achieved parity with men among biomedical science degree holders but remain underrepresented in academic positions. The National Institutes of Health (NIH)—the world’s largest public funder of biomedical research—receives less than one-third of its new grant applications from women. Correspondingly, women compose less than one-third of NIH research grantees, even though they are as successful as men in obtaining first-time grants. Our study examined women’s and men’s NIH funding trajectories over time (n = 34,770), exploring whether women remain funded at the same rate as men after receiving their first major research grants. A survival analysis demonstrated a slightly lower funding longevity for women. We next examined gender differences in application, review, and funding outcomes. Women individually held fewer grants, submitted fewer applications, and were less successful in renewing grants—factors that could lead to gender differences in funding longevity. Finally, two adjusted survival models that account for initial investigator characteristics or subsequent application behavior showed no gender differences, suggesting that the small observed longevity differences are affected by both sets of factors. Overall, given men’s and women’s generally comparable funding longevities, the data contradict the common assumption that women experience accelerated attrition compared with men across all career stages. Women’s likelihood of sustaining NIH funding may be better than commonly perceived. This suggests a need to explore women’s underrepresentation among initial NIH grantees, as well as their lower rates of new and renewal application submissions. Prior research has shown that despite receiving approximately half of all advanced degrees in the biomedical sciences, women are still vastly underrepresented in tenured positions at major universities. It has been suggested by some in the field that part of the reason for this disparity is the view held by many women who pursue advanced degrees that they will have limited opportunities should they pursue an academic career path. The researchers note that such a path generally involves becoming successful at applying for grants to carry out research. The researchers further suggest that many women believe this path is biased against women and thus choose to pursue careers in the corporate world as a more viable alternative. But are such beliefs justified? That is what the researchers sought to learn.To find out, the researchers ran queries on databases maintained by NIH that hold information regarding grants for the years 1991 through 2010. In so doing, they compared rates of success for first-time applicants as well as for those who apply for and receive grants repeatedly. They found that male first-time applicants far outnumbered female first-time applicants. But they also found that the rates of success for women who applied for and received grants repeatedly were much closer. And when they compared success rates by age and amount of education, they found that the rates were nearly identical for the two genders. The researchers suggest that this indicates that the so-called “leaky pipeline” is not applicable to women in the biomedical sciences. They further suggest that there is a degree of misinformation surrounding opportunities for women in the biomedical sciences and that more needs to be done to counteract it. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.last_img read more

Enhanced strength and ductility in a highentropy alloy via ordered oxygen complexes

first_img Deformation mode. a) STEM image of the TiZrHfNb base HEA at 8% tensile strain (the yellow arrows indicate the coplanar dislocation arrays). b) STEM image of O-2 HEA at 8% tensile strain (the red arrows indicate the dipolar walls). c) STEM image of N-2 HEA at 8% tensile strain (the yellow arrows indicate the planar slip bands). Typical planar slip is observed in the base HEA and in the nitrogen-doped alloy variant N-2 HEA. However, wavy slip dominates deformation of the oxygen doped variant O-2 HEA, suggesting that oxygen addition leads to a plastic deformation mode dominated by wavy slip. The beam direction in a and c is [011] while that in b is [001]. d) Dislocation spacing of the TiZrHfNb base HEA and of the interstitially doped variants O-2 and N-2 HEAs probed during in situ TEM tensile experiments. The white arrows represent the dislocation spacing. The average dislocation spacing in the O-2 HEA is much smaller than that in the base HEA and in the N-2 HEA. The error bars are standard deviations of the mean. Credit: Nature, doi: 10.1038/s41586-018-0685-y Journal information: Nature To understand the underlying mechanism of this anomalous, interstitial solid-solution strengthening effect observed with oxygen doped materials, nanostructures of materials were investigated at the atomic scale. For this, the scientists first used synchrotron high-energy X-ray diffraction (XRD) patterns of the base HEA compared with the two alloy variants of O-2 and N-2 HEA. The results showed that addition of either nitrogen or oxygen to the base HEA did not change its single-phase body-centered cubic (b.c.c) structure. This observation was confirmed by electron back-scattering diffraction mapping. In the scanning transmission electron microscope high-angle annular dark field micrograph (STEM-HAADF) images of the O-2 HEA; light atoms were represented in dark contrast, while heavy atoms were imaged bright. Mechanical properties. a) Room-temperature tensile stress–strain curves for the as-cast TiZrHfNb (denoted as base alloy), (TiZrHfNb)98O2 (denoted as O-2) and (TiZrHfNb)98N2 (denoted as N-2) HEAs. σy is the yield strength (squares), σUTS is the ultimate strength (diamonds) and ε is the elongation (circles). The inset shows the corresponding strain hardening response (dσ/dε). A higher work-hardening rate is observed for the O-2 HEA variant (TiZrHfNb)98O2 compared to the base HEA TiZrHfNb and the N-2 HEA (TiZrHfNb)98N2. b) Changes in strength and ductility observed for the HEAs introduced here, relative to several types of established high-performance alloys. The reference systems are Ti6Al4V, β-Ti alloys, niobium, vanadium, interstitial free steel and 316 austenitic stainless steels. The alloys’ interstitial oxygen or nitrogen content is indicated for comparison. Credit: Nature, doi: https://doi.org/10.1038/s41586-018-0685-y Schematic diagram illustrating the mechanism of plastic deformation in the cubic structure of the oxygen-rich high-entropy alloy (HEA). a) In the oxygen-high entropy alloys, the ordered oxygen complexes (OOCs) acted on dislocations in mechanical strain studies. b) During the initial stages of plastic deformation, the planar slip still prevailed. c) Once the dislocations encountered severely distorted interstitial-enriched OOCs, cross-slip is promoted due to their strong pinning effects. d) This results in massive dislocation multiplications. e) More and more dislocations are pinned by OOCs, and dipolar walls emerged as the strain increased to promote work hardening of the material, eventually leading to higher ductility. Credit: Nature, doi: https://doi.org/10.1038/s41586-018-0685-y Researchers present new strategy for extending ductility in a single-phase alloy Engineering strong, tough (damage-tolerant) materials traditionally requires striking a compromise between hardness and ductility. In the new study, oxygen complexes were structurally ordered in nanoscale regions within the HEA characterized by oxygen, zirconium and titanium (O, Zr, Ti)-rich atomic complexes. Formation of these complexes was promoted by chemical short-range ordering among matrix elements within the HEAs. In face-centered cubic HEAs, carbon was reported to improve strength and ductility by lowering stacking fault energy and increasing lattice friction stress. By contrast, ordered interstitial complexes described by Lei et al. mediated a strain-harvesting mechanism with potential for specific use in Ti, Zr, and Hf (Hafnium)-containing alloys. Interstitial elements are usually highly undesirable in such metal alloys due to their embrittlement effects and since tuning the stacking fault energy and exploitation of thermal transfer had not previously led to property enhancement in other alloys. The novel study results therefore provided insight to the role of interstitial solid solutions and the associated mechanisms of strengthening metallic materials. The work is now published in Nature. Explore further Citation: Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes (2018, November 27) retrieved 18 August 2019 from https://phys.org/news/2018-11-strength-ductility-high-entropy-alloy-oxygen.html Oxygen is an abundant element that can form undesired impurities or ceramic phases in metallic materials, while doping the element on metal can render substrates brittle. During interactions with metallic alloys, oxygen takes a state between oxide particles and frequently occurring random interstitials to form ordered oxygen complexes. In a new study, materials scientists Zhinfeng Lei and co-workers observed that unlike in traditional interstitial strengthening, such ordered interstitial complexes could form high-entropy alloys (HEAs) with unprecedented enhancement in strength and ductility in compositionally complex solid solutions. When the scientists doped a model TiZrHfNb HEA with 2.0 atomic percent (2 at%) oxygen, they observed substantially enhanced tensile strength and ductility, breaking a longstanding conflict on strength and ductility trade-off. This document is subject to copyright. Apart from any fair dealing for the purpose of private study or research, no part may be reproduced without the written permission. The content is provided for information purposes only.center_img Statistical analysis of STEM-HAADF and corresponding annular bright field (ABF) images conducted thereafter demonstrated that oxygen preferred interstitial positions adjacent to light-atom-rich lattice sites. Such preference was not observed in the N-2 HEA. In accordance with the solid-solution strengthening model proposed by Fleischer, the calculations for O-2 and N-2 HEAs confirmed their hardening mechanisms were of interstitial nature. Yet, unlike traditional interstitial strengthening that embrittled alloys, the presence of oxygen simultaneously increased both strength and ductility in the b.c.c TiZrHfNb HEA. The key question posed by the substructure analysis is why the addition of interstitial oxygen greatly enhanced the alloy’s work hardening capacity and ductility, compared to nitrogen-containing complexes. During plastic deformation, dislocations are typically stored and arranged in ordered patterns in metal alloys. To study such dislocation patterns in more detail, the researchers conducted high-resolution aberration-corrected STEM characterization of pre-strained specimens. At the nanoscale, oxygen-containing complexes severely distorted the local lattice, causing a large strain field around them. During deformation, the ordered oxygen complexes (OOCs) interacted with dislocations as revealed by STEM images. To further illuminate the intrinsic mechanisms at the atomic scale, the scientists conducted aberration-corrected STEM. At this point, they observed that the intrinsic features of OOCs in the O-2 HEA alloy variant enabled high work hardening due to dipolar walls that emerged with increasing stress that eventually led to higher ductility in the oxygen doped materials. Such complex-dislocation dynamics were not observed for the N-2 HEA, leading to comparatively modest ductility as a result. More information: Zhifeng Lei et al. Enhanced strength and ductility in a high-entropy alloy via ordered oxygen complexes, Nature (2018). DOI: 10.1038/s41586-018-0685-y Robert O. Ritchie. The conflicts between strength and toughness, Nature Materials (2011). DOI: 10.1038/nmat3115 Zhiming Li et al. Metastable high-entropy dual-phase alloys overcome the strength–ductility trade-off, Nature (2016). DOI: 10.1038/nature17981 Microscopic structure. a, b) Synchrotron high-energy XRD and the corresponding electron back-scattering diffraction patterns of the as-cast equiatomic TiZrHfNb and the interstitially doped solid-solution HEAs. All the as-cast HEAs have single b.c.c. lattice structure. c–e) STEM-HAADF images for the [011] b.c.c. crystal axis with differently adjusted contrast to reveal the existence of chemical short-range ordering in the O-2 HEA (TiZrHfNb)98O2, and the corresponding STEM-ABF image that reveals the ordered oxygen complexes (OOCs). Red squares represent the Zr/Ti-rich regions and yellow squares indicate the Hf/Nb-rich regions. The inset in e is an enlarged view of the OOCs, with the white arrows indicating the positions of the oxygen atom columns. f) Atom probe tomography three-dimensional reconstruction from the analysis of a specimen from the O-2 HEA. The threshold for the iso-composition surface is 3.0 at% O, highlighting the presence of OOCs. g) O composition profile as a function of the distance to the interface for a selection of particles (left axis) and evolution of the composition of the main constituents relative to their respective matrix composition (right axis). The inset shows a close-up of one such OOC, along with the {011} atomic plane imaged within the reconstruction. Ni is the number of the ith atom, while Ci and Ci, matrix are the concentrations of the ith atom in the OOCs and in the matrix, respectively. Credit: Nature, doi: https://doi.org/10.1038/s41586-018-0685-y In the study, the researchers investigated the base alloy TiZrHfNb and its optimally oxygen-doped variant (TiZrHfNb)98O2 (denoted as O-2 HEA here on) for comparison, alongside an interstitial variant with 2.0 atomic percent nitrogen (TiZrHfNb)98N2, hitherto referred as N-2 HEA. Mechanical properties of the three types of HEAs were observed using tensile stress-strain curves. A strong strengthening effect was observed for both oxygen- and nitrogen-doped HEAs. As expected from conventional interstitial strengthening, the ductility of the N-2 HEA reduced. Addition of 0.2 at% (atomic percent) oxygen to the base HEA (TiZrHfNb) improved its strength and ductility. A substantial work-hardening effect was observed for O-2 HEA compared to base-HEA and N-2 HEA, to impart an unexpected increase in ductility to the oxygen doped material. The addition of more than 3.0 at% oxygen, however, led to deterioration of the observed mechanical properties. The findings by Lei et al. showed that the strength-ductility conflict could be overcome for a class of metal alloys (HEAs), while demonstrating a completely new type of strain-hardening mechanism based on ordered interstitial complexes. The resulting high strain-hardening reserve led to increased strength and ductility. By itself, the base HEA (TiZrHfNb) is not suited for use in high-temperature applications due to oxidation problems. Alloying with antioxidant elements such as Al, Si and Cr could improve resistance to oxidation with HEAs – as also previously seen in HEA designs. The authors recommend application of such ordered interstitial strengthening mechanisms to a wider range of other alloy material classes for improved strength-ductility and strain-hardening during the development of advanced materials. Dislocation movements during deformation of the O-2 HEA. Credit: Nature, doi: 10.1038/s41586-018-0685-y © 2018 Science X Network The observations revealed regions of light atoms (Ti, Zr-rich) and regions rich in heavy atoms (Nb, Hf-rich) in the O-2 HEA. Similar zones also appeared in STEM images of the base and N-2 HEAs to confirm chemical short-range ordering among the metallic matrix elements as an inherent feature of HEAs. During deformation in any one of the three alloys, no phase transformation occurred. Ex-situ transmission electron microscopy (TEM) and in-situ mechanical testing confirmed that deformation of the three alloys occurred similarly via the process of dislocation glide. , Nature Materialslast_img read more

Music for a cause

first_imgTo create awareness about drug abuse and raise funds for addicts, seven bands from the northeast have come together to raise their voice through songs to bring about change. The bands will tour Delhi too.The music project titled ‘7×7’ will have popular artists, including two all-girl bands, from all the states of northeast. The group will bring out a music album on the theme of ‘Youth and Drug Abuse’, announced NGO BASIC, the brains behind the initiative. Also Read – ‘Playing Jojo was emotionally exhausting’‘It is an attempt to take a step towards healing, and to finding solutions to the issues… the album not only unites various bands from different northeast states but also features the diverse music talents that the region has,’ said Elvis Khevito Lee, BASIC project manager.‘We will raise funds to support people in need with special focus on HIV positive orphans,’ he added.BASIC has been supporting an orphanage for HIV positive children for more than two years in Imphal, Manipur. Also Read – Leslie doing new comedy special with Netflix‘Helping HIV positive orphans brings tremendous satisfaction knowing that not only are we supporting the suffering children but are creating a better tomorrow for them,’ said Lee.According to Lee, a concert with all the seven bands will be organsied in Delhi by November to educate the youth.‘Music, being a universal language and one of the most powerful tools to reach out to the youth, will be a great empowering force for the journey ahead,’ he said.last_img read more

For the holy river

first_imgAward winning director Lisa Sabina Harney is screening her drama documentary Satyagraha-Truth Force in the Capital.Presented by Goddess Films in association with Harvard Club Of India this drama documentary tells the story of a group of humble Indian saints who believe the sanctity of their holy river – The Ganges – is being destroyed by corruption and a powerful mining lobby.They have been threatened, beaten, jailed and bribed. Two have died. Both were murdered, or so they believe. Also Read – ‘Playing Jojo was emotionally exhausting’Satyagraha – Truth Force follows the Satyagraha or hunger strike of Swami Shivanand as he fights with his life to protect the river and attempts to find justice for his disciple whom he believes was poisoned.Harney has spent 15 years working intensively as a writer, producer and director of award winning documentaries and docu-drama. She is the recipient of a Golden Eagle and Hugo Award and has been interviewed and published by the Guerrilla Filmmakers guide as an expert in dramatized documentary.The 91-minute movie will be screened in presence of Yogesh J Karan, High Commissioner, Republic of Fiji and will be followed by a discussion about the same.When: 9th January, 6 pm onwardsWhere: Alliance Française de Delhilast_img read more

Its KPop time again

first_imgA Korean music festival, incorporating a mix of dance, ballad, electronic, rock, hip-hop and R&B among other styles of pop music is scheduled to be held in the city soon.Organised by the Korean Cultural Centre, part of the Korean Embassy the K-POP festival, which is currently in its third edition is set to be held on 30 August here according to organisers.Apart from the national capital, Mumbai, Chennai and Dimapur are the other cities, which will play host to the festival. Also Read – ‘Playing Jojo was emotionally exhausting’The festival is currently seeking applications for participation from aspiring singers and dancers who can send in videos of their performances to organisers.‘K-POP fever has amplified in India and we were overwhelmed by the enthusiasm of the people last year’, says Kim Kum Pyoung, Director, Korean Cultural Centre.He further adds, ‘It’s the ultimate platform to showcase the talent and personality of very gifted performer chosen from all corners of India!’ Meanwhile, winning teams at the upcoming festival would be awarded an all expenses paid trip to South Korea sponsored by the Korean Cultural Centre (KCC) and Korea Tourist Organization (KTO).They will also get an opportunity to perform in the K-POP World Festival in Changwon, organisers said.last_img read more