News Article | April 17, 2017
A new technique that computes the eigenmodes of the eddy-current problem provides an aid to classification using broadband electromagnetic induction sensors. Electromagnetic induction (EMI) sensors excel at detecting even small fragments of metal that are buried underground. The sensors work according to the principle that time-varying magnetic fields cause electrical currents to flow in conductive media. These electrical currents, called eddy currents because of their circular path, produce a secondary magnetic field that signals the presence of nearby metal. This mechanism is shown in Figure 1. For many applications, such as landmine detection, establishing the presence of metal alone is not useful because of the ubiquity of metallic clutter. Broadband sensors, which transmit and receive signals over a large frequency band, provide a way around this problem. The additional data collected by these sensors can be used to determine whether a metal target is of interest or not. The broadband data can also be used to estimate the target's orientation and position underground.1, 2 The main challenge is to make effective use of the broadband data collected by the sensor. The target is characterized by how the flow of eddy currents changes when it is excited at different frequencies. However, the flow of eddy currents also depends on the target's positioning relative to the sensor and its orientation. Creating a dictionary for the responses of each target of interest at each position and orientation is not computationally feasible. A much more attractive approach is to perform a modal analysis of the target so that its frequency response is interpreted as the contribution of several eddy-current modes, each with a corresponding relaxation frequency.3 This is analogous to characterizing the vibration of a string as an excitation of different standing waves. In order to perform the modal analysis of a specific target type, first a linear system that describes the eddy-current response of the target to a magnetic field is constructed. This system is then decomposed using an eigenvalue solver to find its natural modes and their corresponding relaxation frequencies. Because the linear system is treated as an eigenvalue problem, the nature of the excitation does not factor in the analysis. Once the modes of the problem are known, it is possible to easily find the response of the target to any excitation, at any of the possible orientations of the target relative to the sensor. Since the relaxation frequencies of the target are independent of the excitation, they do not change as the sensor moves over a target. This is an important property that is used for target classification. Additionally, the magnetic dipole moment of each particular eddy-current mode captures all of its scattering behavior within six scalar values.4 We chose to use the finite integration technique (FIT) to model the electromagnetic interactions. FIT is a differential method where Maxwell equations in integral form are applied to a set of staggered grids.5 The linear systems that are constructed are very large and sparse, often with many millions of unknowns. This is because the analysis is three dimensional and because differential methods require that, in addition to the target, a large region surrounding it must be discretized as well. Finding the eigenmodes of these systems is challenging because of the size and structure of the system matrices. The nature of the problem requires that the smallest eigenvalues of the system be found. Storage and computational constraints mean that finding all the eigenmodes of the system is not possible. Additionally, the formulation of the linear system introduces a large, non-physical null space, which complicates the computation of the system's smallest eigenvalues. Traditionally, these types of problems are solved using a factorization of the system matrices and the application of a Lanczos-based eigensolver that computes only a subset of the eigenmodes. This is not a feasible strategy in this case because of the storage requirements of such a factorization. Instead, we implemented a Jacobi–Davidson eigensolver, which requires no factorization and which employs a special strategy to avoid the linear system's null space.6, 7 The approach taken also employs a form of domain decomposition that eliminates the degrees of freedom associated with fields exterior to the target. This is a necessary step to avoid the system's null space but it conveniently also reduces the storage requirements for the eigenmodes. Figure 2 shows cross sections of the computed magnetic induction associated with the first eddy-current modes of a spherical and cubical conductor. Using this approach, we decomposed the eddy-current response of arbitrarily shaped conductors into their fundamental modes. Using this approach, we decomposed the eddy-current response of arbitrarily shaped conductors into their fundamental modes. Such a decomposition is valuable because it captures a fundamental aspect of the conducting target's geometry and material properties. This aspect is independent of excitation and provides a reliable signature for targets of its type. The obtained compact signature allows for position and orientation inversion that jointly utilizes measurements that were taken at different positions over the target. With this Jacobi–Davidson-based approach, we can derive physical broadband models for conducting objects that can be used for both the detection and classification of buried objects. The use of broadband models greatly aids in minimizing the number of false alarms triggered by benign metallic clutter. In the future, we would like to improve the accuracy of the computed field interactions on the target's exterior, and we would also like to extend this work to permeable targets. This material is based upon work supported in part by the US Office of Naval Research as a Multi-disciplinary University Research Initiative on Sound and Electromagnetic Interacting Waves under grant N00014-10-1-0958, in part by the US Army REDCOM CERDEC Night Vision and Electronic Sensors Directorate, Science and Technology Division, Countermine Branch, and in part by the US Army Research Office under grant W911NF-11-1-0153.
News Article | April 19, 2017
Researchers at Columbia University have made a significant step toward breaking the so-called "color barrier" of light microscopy for biological systems, allowing for much more comprehensive, system-wide labeling and imaging of a greater number of biomolecules in living cells and tissues than is currently attainable. The advancement has the potential for many future applications, including helping to guide the development of therapies to treat and cure disease. In a study published online April 19 in Nature, the team, led by Associate Professor of Chemistry Wei Min, reports the development of a new optical microscopy platform with drastically enhanced detection sensitivity. Additionally, the study details the creation of new molecules that, when paired with the new instrumentation, allow for the simultaneous labeling and imaging of up to 24 specific biomolecules, nearly five times the number of biomolecules that can be imaged at the same time with existing technologies. "In the era of systems biology, how to simultaneously image a large number of molecular species inside cells with high sensitivity and specificity remains a grand challenge of optical microscopy," Min said. "What makes our work new and unique is that there are two synergistic pieces - instrumentation and molecules - working together to combat this long-standing obstacle. Our platform has the capacity to transform understanding of complex biological systems: the vast human cell map, metabolic pathways, the functions of various structures within the brain, the internal environment of tumors, and macromolecule assembly, to name just a few." All existing methods of observing a variety of structures in living cells and tissues have their own strengths, but all are also hindered by fundamental limitations, not the least of which is the existence of a "color barrier." Fluorescence microscopy, for example, is extremely sensitive and, as such, is the most prevalent technique used in biology labs. The microscope allows scientists to monitor cellular processes in living systems by using proteins that are broadly referred to as "fluorescent proteins" with usually up to five colors. Each of the fluorescent proteins has a target structure that it applies a "tag," or color to. The five fluorescent proteins, or colors, typically used to tag these structures are BFP (Blue Fluorescent Protein), ECFP (Cyan Fluorescent Protein), GFP (Green Fluorescent Protein), mVenus (Yellow Fluorescent Protein), and DsRed (Red Fluorescent Protein). Despite its strengths, fluorescence microscopy is impeded by the "color barrier," which limits researchers to seeing a maximum of only five structures at a time because the fluorescent proteins used emit a range of indistinguishable shades that, as a result, fall into five broad color categories. If a researcher is trying to observe all of the hundreds of structures and different cell types in a live brain tumor tissue sample, for example, she would be restricted to seeing only up to five structures at a time on a single tissue sample. If she wanted to see more than those five, she would have to clean the tissue of the fluorescent labels she used to identify and tag the last five structures in order to use those same fluorescent labels to identify another set of up to five structures. She would have to repeat this process for every set of up to five structures she wants to see. Not only is observing a maximum of five structures at a time labor intensive, but in cleaning the tissue, vital components of that tissue could be lost or damaged. "We want to see them all at the same time to see how they're operating on their own and also how they're interacting with each other," said Lu Wei, lead author on the study and a postdoctoral researcher in the Min lab. "There are lots of components in a biological environment and we need to be able to see everything simultaneously to truly understand the processes." In addition to fluorescence microscopy, there are currently a variety of Raman microscopy techniques in use for observing living cell and tissue structures that work by making visible the vibrations stemming from characteristic chemical bonds in structures. Traditional Raman microscopy produces the highly-defined colors lacking in fluorescence microscopy, but is missing the sensitivity. As such, it requires a strong, concentrated vibrational signal that can only be achieved through the presence of millions of structures with the same chemical bond. If the signal from the chemical bonds is not strong enough, visualizing the associated structure is near impossible. To address this challenge, Min and his team, including Profs. Virginia Cornish in chemistry and Rafael Yuste in neuroscience, pursued a novel hybrid of existing microscopy techniques. They developed a new platform called electronic pre-resonance stimulated Raman scattering (epr-SRS) microscopy that combines the best of both worlds, bringing together a high level of sensitivity and selectivity. The innovative technique identifies, with extreme specificity, structures with significantly lower concentration - instead of millions of the same structure needed to identify the presence of that structure in traditional Raman microscopy, the new instrument requires only 30 for identification. The technique also utilizes a novel set of tagging molecules designed by the team to work synergistically with the ultramodern technology. The amplified "color palette" of molecules broadens tagging capabilities, allowing for the imaging of up to 24 structures at a time instead of being limited by only five fluorescent colors. The researchers believe there's potential for even further expansion in the future. The team has successfully tested the epr-SRS platform in brain tissue. "We were able to see the different cells working together," Wei said. "That's the power of a larger color palette. We can now light up all these different structures in brain tissue simultaneously. In the future we hope to watch them function in real time." Brain tissue is not the only thing the researchers envision this technique being used for, she added. "Different cell types have different functions, and scientists usually study only one cell type at a time. With more colors, we can now start to study multiple cells simultaneously to observe how they interact and function both on their own and together in healthy conditions versus in disease states." The new platform has many potential applications, Min said, adding that it is possible the technique could one day be used in the treatment of tumors that are hard to kill with available drugs. "If we can see how structures are interacting in cancer cells, we can identify ways to target specific structures more precisely," he said. "This platform could be game-changing in the pursuit of understanding anything that has a lot of components." Funding: NIH Director's New Innovator Award (1DP2EB016573), R01 (EB020892), the US Army Research Office (W911NF-12-1-0594), the Alfred P. Sloan Foundation and the Camille and Henry Dreyfus Foundation. R.Y. is supported by the NEI (EY024503, EY011787) and NIMH (MH101218, MH100561)
News Article | October 26, 2016
In a paradigm shift from conventional electronic devices, exploiting the quantum properties of superlattices holds the promise of developing new technologies Researchers at the Nanoscale Transport Physics Laboratory from the School of Physics at the University of the Witwatersrand have found a technique to improve carbon superlattices for quantum electronic device applications. Superlattices are made up of alternating layers of very thin semiconductors, just a few nanometers thick. These layers are so thin that the physics of these devices is governed by quantum mechanics, where electrons behave like waves. In a paradigm shift from conventional electronic devices, exploiting the quantum properties of superlattices holds the promise of developing new technologies. The group, headed by Professor Somnath Bhattacharyya has been working for the past 10 years on developing carbon-based nano-electronic devices. "Carbon is the future in the electronics field and it soon will be challenging many other semiconductors, including silicon," says Bhattacharyya. The physics of carbon superlattices is more complex than that of crystalline superlattices (such as gallium arsenide), since the material is amorphous and carbon atoms tend to form chains and networks. The Wits group, in association with researchers at the University of Surrey in the UK, has developed a detailed theoretical approach to understand the experimental data obtained from carbon devices. The paper has been published in Scientific Reports (Nature Publishing Group) on 19 October. "This work provides an understanding of the fundamental quantum properties of carbon superlattices, which we can now use to design quantum devices for specific applications," says lead author, Wits PhD student, Ross McIntosh. "Our work provides strong impetus for future studies of the high-frequency electronic and optoelectronic properties of carbon superlattices". Through their work, the group reported one of the first theoretical models that can explain the fundamental electronic transport properties in disordered carbon superlattices. Bhattacharyya started looking at the use of carbon for semiconductor applications almost 10 years ago, before he joined Wits University, when he and co-authors from the University of Surrey developed and demonstrated negative differential resistance and excellent high-frequency properties of a quantum device made up of amorphous carbon layers. This work was published in Nature Materials in 2006. McIntosh undertook the opportunity at honours level to measure the electrical properties of carbon superlattice devices. Now, as a PhD student and having worked extensively with theoretician Dr. Mikhail V. Katkov, he has extended the theoretical framework and developed a technique to calculate the transport properties of these devices. Bhattacharyya believes this work will have immense importance in developing Carbon-based high-frequency devices. "It will open not only fundamental studies in Carbon materials, but it will also have industrial applications in the electronic and optoelectronic device sector," he says. Superlattices are currently used as state of the art high frequency oscillators and amplifiers and are beginning to find use in optoelectronics as detectors and emitters in the terahertz regime. While the high frequency electrical and optoelectronic properties of conventional semiconductors are limited by the dopants used to modify their electronic properties, the properties of superlattices can be tuned over a much wider range to create devices which operate in regimes where conventional devices cannot. Superlattice electronic devices can operate at higher frequencies and optoelectronic devices can operate at lower frequencies than their conventional counterparts. The lack of terahertz emitters and detectors has resulted in a gap in that region of the electromagnetic spectrum (known as the "terahertz gap"), which is a significant limitation, as many biological molecules are active in this regime. This also limits terahertz radio astronomy. Amorphous Carbon devices are extremely strong, can operate at high voltages and can be developed in most laboratories in the world, without sophisticated nano-fabrication facilities. New Carbon-based devices could find application in biology, space technology, science infrastructure such as the Square Kilometre Array (SKA) telescope in South Africa, and new microwave detectors. "What was lacking earlier was an understanding of device modelling. If we have a model, we can improve the device quality, and that is what we now have," says Bhattacharyya. The Wits Nanoscale Transport Physics Laboratory (NSTPL) was established in 2009 under the leadership of Bhattacharyya when Professor João Rodrigues was the Head of the School of Physics at the University of the Witwatersrand, South Africa. The department is known as a leading Physics school in the African continent, having one of the largest academic staff complements on a single campus. Since the opening of the laboratory, the NSTPL has gone from strength to strength in establishing a facility that houses world class fabrication and measurement equipment, an initiative strongly supported by research entities such as the NRF, CSIR, Wits Research Office and DST/NRF Centre of Excellence in Strong Materials. The NSTPL is well equipped with various sophisticated synthesis facilities, as well as a cryogenic micro-manipulated probe station to conduct sensitive quantum transport measurements at temperatures near absolute zero. The NSTPL also houses a fully operational electron beam lithography scanning electron microscope, used to fabricate nanoscale devices based on these carbon materials. Some noteworthy current projects include the fabrication of spintronic devices using supramolecular Gd-functionalized carbon nanotubes, the fabrication of graphene field effect transistors and most recently the study of the unconventional superconductivity observed in boron-doped diamond. The NSTPL group has also published a number of papers on theoretical investigations, led by Dr Mikhail Katkov and Dr Dmitry Churochkin, on the role of disorder on the quantum transport in carbon systems. These various topics form part of the broader direction the group has taken, that being, investigating the physics of carbon materials in the hopes of finding application in quantum information systems as well as detector devices valuable for space exploration.
News Article | February 28, 2017
Infants with a genetic polymorphism of the serotonin transporter gene may be more susceptible to a psychosocial intervention designed to promote maternal-infant attachment in South Africa, according to a study in PLOS Medicine. In a study led by Mark Tomlinson from Stellenbosch University, South Africa, with lead author Barak Morgan from the University of Cape Town, South Africa and colleagues, data from a randomized controlled trial were reanalysed in light of new genetic data. In the study, researchers reanalysed data from a randomized controlled trial that was originally published in 2009. This had found that infants whose mothers were visited by lay community workers to provide support and guidance in parenting were significantly more likely to be securely attached to their primary caregiver after 18 months. Using genetic data collected from 220 participants when they were 13 years of age (approximately half of those who participated in the original trial) the researchers were able to compare attachment rates for participants with different polymorphisms of the serotonin transporter gene. Individuals with the short form of the gene, which is involved in nerve signalling in the brain, have previously been found to be sensitive to psychosocial interventions. The researchers found that, for those with the short allele of the serotonin transporter gene, the probability of secure attachment being observed for those who received the intervention was 84% (95% CI [73%, 94%]), compared to 58% (95% CI [43%, 72%]) in the control group. For those with two copies of the long allele of the serotonin transporter gene, the probability of secure attachment being observed for those who received the intervention was 70% (95% CI [59%, 81%]), compared to 71% (95% CI [60%, 82%]) of infants in the control group. The researchers note, "[b]eyond illuminating the role of genetic differential susceptibility in early childhood development, the current finding also speaks to a fundamental issue in the quest to understand and mitigate the developmental effects of poverty through psychosocial intervention. The near large effect size reported here for the intervention in children with susceptible genotypes [...] is at variance with the general conclusion that psychosocial interventions in the context of poverty produce only small to medium effect sizes [...] Without taking account of genetic susceptibility, it is possible that other intervention studies have, at least in some subpopulations, underestimated the impact of their interventions, as we originally did. By the same token [...] other studies might also have underestimated the negative impact on susceptible subpopulations of not receiving an intervention [...] In short, averaging outcomes across all participants may well lead to an invalid conclusion about the efficacy of an intervention. The researchers also note, "[a]n important limitation of this study is that we were not able to follow-up all cases of the individuals from the original trial, and there were missing data for attachment and genotype. In total, our primary analysis included 49% (220/449) of the original sample of children whose mothers were randomized to treatment and control conditions. Although the intervention and control groups were highly similar in our follow-up sample, and the follow-up sample was generally very similar to the original sample, there was some evidence of selective loss to follow-up on two variables [...] This means that randomization within our follow-up subsample may have been imperfect. Attribution of the primary outcome to causal effects of treatment in the present subsample should therefore be treated with caution. This study was supported by a grant from Grand Challenges Canada, grant reference #0066-03). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. MT is a member of the Editorial Board of PLOS Medicine. PF received an honorarium for providing a workshop on attachment at the Meeting of Minds Conference, organised by Shire Pharmaceuticals. Morgan B, Kumsta R, Fearon P, Moser D, Skeen S, Cooper P, et al. (2017) Serotonin transporter gene (SLC6A4) polymorphism and susceptibility to a home-visiting maternal-infant attachment intervention delivered by community health workers in South Africa: Reanalysis of a randomized controlled trial. PLoS Med 14(2): e1002237. doi:10.1371/journal.pmed.1002237 Global Risk Governance Program, Department of Public Law, University of Cape Town, Rondebosch, South Africa NRF Centre of Excellence in Human Development, DVC Research Office, University of Witwatersrand, Johannesburg, South Africa Neonatal Unit, Department of Women's and Children's Health, Karolinska Institute, Stockholm, Sweden Department of Genetic Psychology, Faculty of Psychology, Ruhr University Bochum, Bochum, Germany Research Department of Clinical, Educational and Health Psychology, Faculty of Brain Sciences, University College London, London, United Kingdom Department of Psychology, Stellenbosch University, Stellenbosch, South Africa School of Psychology and Clinical Language Sciences, University of Reading, Reading, United Kingdom Department of Psychology, University of Cape Town, Rondebosch, South Africa Department of Psychology, Western University, London, Ontario, Canada IN YOUR COVERAGE PLEASE USE THIS URL TO PROVIDE ACCESS TO THE FREELY AVAILABLE PAPER: http://journals.
News Article | February 15, 2017
CAMBRIDGE, MA - Sequencing messenger RNA molecules from individual cells offers a glimpse into the lives of those cells, revealing what they're doing at a particular time. However, the equipment required to do this kind of analysis is cumbersome and not widely available. MIT researchers have now developed a portable technology that can rapidly prepare the RNA of many cells for sequencing simultaneously, which they believe will enable more widespread use of this approach. The new technology, known as Seq-Well, could allow scientists to more easily identify different cell types found in tissue samples, helping them to study how immune cells fight infection and how cancer cells respond to treatment, among other applications. "Rather than trying to pick one marker that defines a cell type, using single-cell RNA sequencing we can go in and look at everything a cell is expressing at a given moment. By finding common patterns across cells, we can figure out who those cells are," says Alex K. Shalek, the Hermann L.F. von Helmholtz Career Development Assistant Professor of Health Sciences and Technology, an assistant professor of chemistry, and a member of MIT's Institute for Medical Engineering and Science. Shalek and his colleagues have spent the past several years developing single-cell RNA sequencing strategies. In the new study, he teamed up with J. Christopher Love, an associate professor of chemical engineering at MIT's Koch Institute for Integrative Cancer Research, to create a new version of the technology that can rapidly analyze large numbers of cells, with very simple equipment. "We've combined his technologies with some of ours in a way that makes it really accessible for researchers who want to do this type of sequencing on a range of different clinical samples and settings," Love says. "It overcomes some of the barriers that are facing the adoption of these techniques more broadly." Love and Shalek are the senior authors of a paper describing the new technique in the Feb. 13 issue of Nature Methods. The paper's lead authors are Research Associate Todd Gierahn and graduate students Marc H. Wadsworth II and Travis K. Hughes. Most cells in the human body express only a fraction of the genes found in their genome. Those genes are copied into molecules of messenger RNA, also known as RNA transcripts, which direct the cells to build specific proteins. Each cell's gene expression profile varies depending on its function. Sequencing the RNA from many individual cells of a blood or tissue sample offers a way to distinguish the cells based on patterns of gene expression. This gives scientists the opportunity to determine cell functions, including their roles in disease or response to treatment. Key to sequencing large populations of cells is keeping track of which RNA transcripts came from which cell. The earliest techniques for this required sorting the cells into individual tubes or compartments of multiwell plates, and then separately transforming each into a sequencing library. That process works well but can't handle large samples containing thousands of cells, such as blood samples or tissue biopsies, and costs between $25 and $35 per cell. Shalek and others have recently developed microfluidic techniques to help automate and parallelize the process considerably, but the amount of equipment required makes it impossible to be easily transported. Shalek and Love, who have worked on other projects together, realized that technology Love had previously developed to analyze protein secretions from single cells could be adapted to do single-cell RNA sequencing rapidly and inexpensively using a portable device. Over the past several years, Love's lab has developed a microscale system that can isolate individual cells and measure the antibodies and other proteins that each cell secretes. The device resembles a tiny ice cube tray, with individual compartments for each cell. Love also developed a process known as microengraving that uses these trays, which can hold tens of thousands of cells, to measure each cell's protein secretions. To use this approach for sequencing RNA, the researchers created arrays of nanowells that each capture a single cell plus a barcoded bead to capture the RNA fragments. The nanowells are sealed with a semipermeable membrane that allows the passage of chemicals needed to break the cells apart, while the RNA stays contained. After the RNA binds to the beads, it is removed and sequenced. Using this process, the cost per cell is less than $1. Similar to previous single-cell RNA sequencing techniques, the Seq-Well process captures and analyzes about 10 to 15 percent of the total number of RNA transcripts per cell. "That is still a very rich set of information that maps to several thousand genes," Love says. "If you look at sets of these genes, you can start to understand the identity of those cells based on the sets of genes that are expressed in common." In this paper, the researchers used Seq-Well to analyze immune cells called macrophages, which were infected with tuberculosis, allowing them to identify different pre-existing populations and responses to infection. Shalek and members of his lab also brought the technology to South Africa and analyzed tissue samples from TB- and HIV-infected patients there. "Having a simple system that can go everywhere I think is going to be incredibly empowering," Shalek says. Love's lab is now using this approach to analyze immune cells from people with food allergies, which could help researchers determine why some people are more likely to respond well to therapies designed to treat their allergies. "There are still a lot of unknowns in chronic diseases, and these types of tools help you uncover new insights," Love says. The research team has also joined forces with clinical investigators at Dana-Farber/Harvard Cancer Center to apply this technology toward the discovery of new combination immunotherapies to treat cancer as part of the Bridge Project partnership. The research was funded by the Searle Scholars Program, the Beckman Young Investigator Program, an NIH New Innovator Award, the Bill and Melinda Gates Foundation, the Ragon Institute, the Burroughs Wellcome Foundation, the W.M. Keck Foundation, the U.S. Army Research Office through MIT's Institute for Soldier Nanotechnologies, and the Koch Institute Support Grant from the National Cancer Institute.
News Article | November 2, 2016
Researchers at North Carolina State University have developed a new technique for creating NV-doped single-crystal nanodiamonds, only four to eight nanometers wide, which could serve as components in room-temperature quantum computing technologies. These doped nanodiamonds also hold promise for use in single-photon sensors and nontoxic, fluorescent biomarkers. Currently, computers use binary logic, in which each binary unit - or bit - is in one of two states: 1 or 0. Quantum computing makes use of superposition and entanglement, allowing the creation of quantum bits - or qubits - which can have a vast number of possible states. Quantum computing has the potential to significantly increase computing power and speed. A number of options have been explored for creating quantum computing systems, including the use of diamonds that have "nitrogen-vacancy" centers. That's where this research comes in. Normally, diamond has a very specific crystalline structure, consisting of repeated diamond tetrahedrons, or cubes. Each cube contains five carbon atoms. The NC State research team has developed a new technique for creating diamond tetrahedrons that have two carbon atoms; one vacancy, where an atom is missing; one carbon-13 atom (a stable carbon isotope that has six protons and seven neutrons); and one nitrogen atom. This is called the NV center. Each NV-doped nanodiamond contains thousands of atoms, but has only one NV center; the remainder of the tetrahedrons in the nanodiamond are made solely of carbon. It's an atomically small distinction, but it makes a big difference. "That little dot, the NV center, turns the nanodiamond into a qubit," says Jay Narayan, the John C. Fan Distinguished Chair Professor of Materials Science and Engineering at NC State and lead author of a paper describing the work. "Each NV center has two transitions: NV0 and NV-. We can go back and forth between these two states using electric current or laser. These nanodiamonds could serve as the basic building blocks of a quantum computer." To create these NV-doped nanodiamonds, the researchers start with a substrate, such as such as sapphire, glass or a plastic polymer. The substrate is then coated with amorphous carbon - elemental carbon that, unlike graphite or diamond, does not have a regular, well-defined crystalline structure. While depositing the film of amorphous carbon, the researchers bombard it with nitrogen ions and carbon-13 ions. The carbon is then hit with a laser pulse that raises the temperature of the carbon to approximately 4,000 Kelvin (or around 3,727 degrees Celsius) and is then rapidly quenched. The operation is completed within a millionth of a second and takes place at one atmosphere - the same pressure as the surrounding air. By using different substrates and changing the duration of the laser pulse, the researchers can control how quickly the carbon cools, which allows them to create the nanodiamond structures. "Our approach reduces impurities; controls the size of the NV-doped nanodiamond; allows us to place the nanodiamonds with a fair amount of precision; and directly incorporates carbon-13 into the material, which is necessary for creating the entanglement required in quantum computing," Narayan says. "All of the nanodiamonds are exactly aligned through the paradigm of domain matching epitaxy, which is a significant advance over existing techniques for creating NV-doped nanodiamonds." "The new technique not only offers unprecedented control and uniformity in the NV-doped nanodiamonds, it is also less expensive than existing techniques," Narayan says. "Hopefully, this will enable significant advances in the field of quantum computing." The researchers are currently talking with government and private sector groups about how to move forward. One area of interest is to develop a means of creating self-assembling systems that incorporate entangled NV-doped nanodiamonds for quantum computing. The paper, "Novel synthesis and properties of pure and NV-doped nanodiamonds and other nanostructures," is published in the journal Materials Research Letters. The paper was co-authored by Anagh Bhaumik, a Ph.D. student at NC State. The work was supported by the U.S. Army Research Office under grant W911NF-12-R-0012-03.
News Article | October 7, 2016
Home > Press > Exotic property confirmed in natural material could lead to fundamental studies Abstract: Auxetic Black Phosphorus: A 2D Material with Negative Poisson's Ratio Yuchen Du1,3, Jesse Maassen1,3,4,*, Wangran Wu1,3, Zhe Luo2,3, Xianfan Xu2,3,*, and Peide D. Ye1,3,* 1 School of Electrical and Computer Engineering, Purdue University, West Lafayette, Indiana 2 School of Mechanical Engineering, Purdue University 3 Birck Nanotechnology Center, Purdue University 4 Department of Physics and Atmospheric Science, Dalhousie University, Halifax, Nova Scotia, Canada, * Address correspondence to: (P.D.Y.); (X.X.); (J.M.) The Poisson's ratio of a material characterizes its response to uniaxial strain. Materials normally possess a positive Poisson's ratio - they contract laterally when stretched, and expand laterally when compressed. A negative Poisson's ratio is theoretically permissible but has not, with few exceptions of man-made bulk structures, been experimentally observed in any natural materials. Here, we show that the negative Poisson's ratio exists in the low-dimensional natural material black phosphorus, and that our experimental observations are consistent with first principles simulations. Through applying uniaxial strain along armchair direction, we have succeeded in demonstrating a cross-plane interlayer negative Poisson's ratio on black phosphorus for the first time. Meanwhile, our results support the existence of a cross-plane intralayer negative Poisson's ratio in the constituent phosphorene layers under uniaxial deformation along the zigzag axis, which is in line with a previous theoretical prediction. The phenomenon originates from the puckered structure of its in-plane lattice, together with coupled hinge-like bonding configurations. Researchers have confirmed the existence of a naturally occurring exotic property in which a material becomes thicker when stretched - the opposite of most materials - a discovery that could lead to new studies into the fundamental science of nano-materials behavior. The counterintuitive phenomenon, called auxetic behavior, has been extensively studied in engineered structures that have potential applications in medicine, tissue engineering, body armor and "fortified armor enhancement." However, until now the behavior has not been confirmed in natural materials, said Peide Ye, Purdue University's Richard J. and Mary Jo Schwartz Professor of Electrical and Computer Engineering. The auxetic behavior was discovered in a material called black phosphorous. The phenomenon is governed by a fundamental mechanical property of materials called the Poisson's ratio, which characterizes how a material behaves when stretched. Most materials when stretched become thinner and when compressed become thicker, and they are said to have a positive Poisson's ratio. "A negative Poisson's ratio is theoretically possible but until now has not, with few exceptions of man-made structures, been experimentally observed in any natural materials," Ye said. "Here, we show that the negative Poisson's ratio exists in the natural material black phosphorus." Findings are detailed in a research paper that appeared on Sept. 23 in the journal Nano Letters. "Until now, there has been a lack of experimental evidence since the measurement of internal deformation in auxetic materials, in particular at the atomic level, is extremely difficult," Ye said. Researchers used a technique called Raman spectroscopy to document the negative Poisson's ratio in extremely thin, individual layers of black phosphorous called phosphorene. The research was based at the Birck Nanotechnology Center in Purdue's Discovery Park. The Nano Letters paper was authored by doctoral student Yuchen Du; former postdoctoral research associate Jesse Maassen; graduate students Wangran Wu and Zhe Luo; Xianfan Xu, the James J. and Carol L. Shuttleworth Professor of Mechanical Engineering and professor of electrical and computer engineering; and Ye. Du carried out most of the experiments. Maassen performed the theoretical work critical to the research. He is now an assistant professor of physics at Dalhousie University in Nova Scotia, Canada. The researchers focused on the material's uniquely puckered crystal structure in which atoms are arranged in a wavy pattern. Like silicon, the material possesses a bandgap, a trait essential for a semiconductor's ability to switch on and off in electronic circuits. The material also has a relatively high "carrier mobility," meaning it is very conductive and could be useful for technological applications. Future research will include work to investigate whether the negative Poisson's ratio exists in other so-called "two-dimensional" materials, including extremely thin layers of graphite called graphene. The research was funded by the National Science Foundation, U.S. Air Force Office of Scientific Research, the U.S. Army Research Office, and the Natural Sciences and Engineering Research Council of Canada. For more information, please click If you have a comment, please us. Issuers of news releases, not 7th Wave, Inc. or Nanotechnology Now, are solely responsible for the accuracy of the content.
News Article | February 28, 2017
BROOKLYN, New York - Colloidal particles, used in a range of technical applications including foods, inks, paints, and cosmetics, can self-assemble into a remarkable variety of densely-packed crystalline structures. For decades, though, researchers have been trying to coax colloidal spheres to arranging themselves into much more sparsely populated lattices in order to unleash potentially valuable optical properties. These structures, called photonic crystals, could increase the efficiency of lasers, further miniaturize optical components, and vastly increase engineers' ability to control the flow of light. A team of engineers and scientists from the NYU Tandon School of Engineering Department of Chemical and Biomolecular Engineering, the NYU Center for Soft Matter Research, and Sungkyunkwan University School of Chemical Engineering in the Republic of Korea report they have found a pathway toward the self-assembly of these elusive photonic crystal structures never assembled before on the sub-micrometer scale (one micrometer is about 100 times smaller than the diameter of a strand of human hair). The research, which appears in the journal Nature Materials, introduces a new design principle based on preassembled components of the desired superstructure, much as a prefabricated house begins as a collection of pre-built sections. The researchers report they were able to assemble the colloidal spheres into diamond and pyrochlore crystal structures - a particularly difficult challenge because so much space is left unoccupied. The team, comprising Etienne Ducrot, a post-doctoral researcher at the NYU Center for Soft Matter Research; Mingxin He, a doctoral student in chemical and biomolecular engineering at NYU Tandon; Gi-Ra Yi of Sungkyunkwan University; and David J. Pine, chair of the Department of Chemical and Biomolecular Engineering at NYU Tandon School of Engineering and a NYU professor of physics in the NYU College of Arts and Science, took inspiration from a metal alloy of magnesium and copper that occurs naturally in diamond and pyrochlore structures as sub-lattices. They saw that these complex structures could be decomposed into single spheres and tetrahedral clusters (four spheres permanently bound). To realize this in the lab, they prepared sub-micron plastic colloidal clusters and spheres, and employed DNA segments bound to their surface to direct the self-assembly into the desired superstructure. "We are able to build those complex structures because we are not starting with single spheres as building blocks, but with pre-assembled parts already 'glued' together," Ducrot said. "We fill the structural voids of the diamond lattice with an interpenetrated structure, the pyrochlore, that happens to be as valuable as the diamond lattice for future photonic applications." Ducrot said open colloidal crystals, such as those with diamond and pyrochlore configurations, are desirable because, when composed of the right material, they may possess photonic band gaps -- ranges of light frequency that cannot propagate through the structure -- meaning that they could be for light what semiconductors are for electrons. "This story has been a long time in the making as those material properties have been predicted 26 years ago but until now, there was no practical pathway to build them," he said. "To achieve a band gap in the visible part of the electromagnetic spectrum, the particles need to be on the order of 150 nanometers, which is in the colloidal range. In such a material, light should travel with no dissipation along a defect, making possible the construction of chips based on light." Pine said that self-assembly technology is critical to making production of these crystals economically feasible because creating bulk quantities of crystals with lithography techniques at the correct scale would be extremely costly and very challenging. "Self-assembly is therefore a very appealing way to inexpensively create crystals with a photonic band gap in bulk quantities," Pine said. This research was funded by the U.S. Army Research Office under a Multidisciplinary University Research Initiative (MURI) grant. About the New York University Tandon School of Engineering The NYU Tandon School of Engineering dates to 1854, the founding date for both the New York University School of Civil Engineering and Architecture and the Brooklyn Collegiate and Polytechnic Institute (widely known as Brooklyn Poly). A January 2014 merger created a comprehensive school of education and research in engineering and applied sciences, rooted in a tradition of invention and entrepreneurship and dedicated to furthering technology in service to society. In addition to its main location in Brooklyn, NYU Tandon collaborates with other schools within NYU, the country's largest private research university, and is closely connected to engineering programs at NYU Abu Dhabi and NYU Shanghai. It operates Future Labs focused on start-up businesses in downtown Manhattan and Brooklyn and an award-winning online graduate program. For more information, visit http://engineering. .
News Article | February 15, 2017
CAMBRIDGE, Mass. -- Determining the exact configuration of proteins and other complex biological molecules is an important step toward understanding their functions, including how they bind with receptors in the body. But such imaging is difficult to do. It usually requires the molecules to be crystallized first so that X-ray diffraction techniques can be applied -- and not all such molecules can be crystallized. Now, a new method developed by researchers at MIT could lead to a way of producing high-resolution images of individual biomolecules without requiring crystallization, and it could even allow zoomed-in imaging of specific sites within the molecules. The technique could also be applied to imaging other kinds of materials, including two-dimensional materials and nanoparticles. The findings are reported this week in the Proceedings of the National Academy of Sciences, in a paper by Paola Cappellaro, the Esther and Harold E. Edgerton Associate Professor of Nuclear Science and Engineering at MIT, and others at MIT and at the Singapore University of Technology and Design. "There are advantages to being able to see at the level of single protein molecules," Cappellaro says, because that allows imaging of some molecules that can't be imaged using the conventional X-ray method. "There are some types of molecules, such as membrane proteins, that are quite difficult to crystallize." The method uses a type of defect in diamond crystals known as a nitrogen vacancy center -- a place where one of the carbon atoms in the crystal has been replaced by a nitrogen atom. Such defects, which can give diamonds a pink tinge, make the crystal extremely sensitive to changes in magnetic and electric fields, making the nitrogen vacancy center an efficient detector for such variations. When a molecule is close to the crystal, nitrogen vacancies near the crystal surface will respond to the nuclear spins within that molecule, and this response can be detected. But these sensors have been severely limited by the sampling rate of the microwave pulses used to probe them. Now, the research team has found that this limitation can be overcome using a method they call "quantum interpolation," which improves the resolving power of such systems by more than a hundredfold, Cappellaro says. In order to reveal the tiny variations of the magnetic fields associated with some atoms in the molecule whose configuration is being analyzed, it's necessary to observe changes that take place within a few picoseconds, or trillionths of a second. In principle, such tiny increments of time can be resolved using large, specialized instruments, but these are very expensive and not available to most researchers. So Cappellaro and her students, not having access to such systems, set out to find a lower-cost, simpler approach to making such observations. The new scheme is similar to the way some mobile phone cameras provide better resolution by taking multiple images of the same scene, with slightly different exposures, and then adding the images together. It's also similar to sophisticated techniques used by astronomers and NASA researchers to improve the resolution of images taken by planetary rovers or the Hubble Space Telescope. "We try to mimic what the human eye does automatically," which is to move constantly and build up detail through multiple images of the same area, which the brain knits together into a single picture, Cappellaro says. In this case, the technique is applied to variations in the strength of a magnetic field, rather than variations in light intensity and color, but the underlying principles are similar. And, whereas the classical technique involves taking a series of images and adding them together, in this method the researchers take a single image but vary the separation of microwave pulses during the acquisition of that image. By applying microwave pulses that are separated by time increments on a scale of nanoseconds -- more than 100 times longer than the desired time resolution -- the team was able to achieve the higher resolution that would be needed to get detailed structural information about the spin-state of individual atoms in biological molecules. The data could be used to help unravel the complex shapes of some biologically important proteins and other molecules, as well as other kinds of materials. So far, the team's proof-of-principle experiments produced images of just the nuclear spin associated with the sensor itself -- the nitrogen vacancy center within a diamond crystal. The next step, which Cappellaro says should be within reach now that the principle has been validated, will be to try the method on actual biomolecules. "All the various pieces have been demonstrated" to enable molecular imaging, she says. "So combining the different techniques should be a straightforward, though difficult to reach, goal." The next step, she says, is to see "if we can measure a single protein in its natural environment," which may help reveal important features such as binding sites. The research team included Ashok Ajoy PhD '16 , MIT graduate student Yixiang Liu, former postdocs Kasturi Saha, Luca Marseglia, Jean-Christophe Jaskula, and Ulf Bissbort. It was supported by the National Science Foundation and the U.S. Army Research Office. ARCHIVE: Diamonds could help bring proteins into focus http://news.
News Article | February 15, 2017
Determining the exact configuration of proteins and other complex biological molecules is an important step toward understanding their functions, including how they bind with receptors in the body. But such imaging is difficult to do. It usually requires the molecules to be crystallized first so that X-ray diffraction techniques can be applied — and not all such molecules can be crystallized. Now, a new method developed by researchers at MIT could lead to a way of producing high-resolution images of individual biomolecules without requiring crystallization, and it could even allow zoomed-in imaging of specific sites within the molecules. The technique could also be applied to imaging other kinds of materials, including two-dimensional materials and nanoparticles. The findings are reported this week in the Proceedings of the National Academy of Sciences, in a paper by Paola Cappellaro, the Esther and Harold E. Edgerton Associate Professor of Nuclear Science and Engineering at MIT, and others at MIT and at the Singapore University of Technology and Design. “There are advantages to being able to see at the level of single protein molecules,” Cappellaro says, because that allows imaging of some molecules that can’t be imaged using the conventional X-ray method. “There are some types of molecules, such as membrane proteins, that are quite difficult to crystallize.” The method uses a type of defect in diamond crystals known as a nitrogen vacancy center — a place where one of the carbon atoms in the crystal has been replaced by a nitrogen atom. Such defects, which can give diamonds a pink tinge, make the crystal extremely sensitive to changes in magnetic and electric fields, making the nitrogen vacancy center an efficient detector for such variations. When a molecule is close to the crystal, nitrogen vacancies near the crystal surface will respond to the nuclear spins within that molecule, and this response can be detected. But these sensors have been severely limited by the sampling rate of the microwave pulses used to probe them. Now, the research team has found that this limitation can be overcome using a method they call “quantum interpolation,” which improves the resolving power of such systems by more than a hundredfold, Cappellaro says. In order to reveal the tiny variations of the magnetic fields associated with some atoms in the molecule whose configuration is being analyzed, it’s necessary to observe changes that take place within a few picoseconds, or trillionths of a second. In principle, such tiny increments of time can be resolved using large, specialized instruments, but these are very expensive and not available to most researchers. So Cappellaro and her students, not having access to such systems, set out to find a lower-cost, simpler approach to making such observations. The new scheme is similar to the way some mobile phone cameras provide better resolution by taking multiple images of the same scene, with slightly different exposures, and then adding the images together. It’s also similar to sophisticated techniques used by astronomers and NASA researchers to improve the resolution of images taken by planetary rovers or the Hubble Space Telescope. “We try to mimic what the human eye does automatically,” which is to move constantly and build up detail through multiple images of the same area, which the brain knits together into a single picture, Cappellaro says. In this case, the technique is applied to variations in the strength of a magnetic field, rather than variations in light intensity and color, but the underlying principles are similar. And, whereas the classical technique involves taking a series of images and adding them together, in this method the researchers take a single image but vary the separation of microwave pulses during the acquisition of that image. By applying microwave pulses that are separated by time increments on a scale of nanoseconds — more than 100 times longer than the desired time resolution — the team was able to achieve the higher resolution that would be needed to get detailed structural information about the spin-state of individual atoms in biological molecules. The data could be used to help unravel the complex shapes of some biologically important proteins and other molecules, as well as other kinds of materials. So far, the team’s proof-of-principle experiments produced images of just the nuclear spin associated with the sensor itself — the nitrogen vacancy center within a diamond crystal. The next step, which Cappellaro says should be within reach now that the principle has been validated, will be to try the method on actual biomolecules. “All the various pieces have been demonstrated” to enable molecular imaging, she says. “So combining the different techniques should be a straightforward, though difficult to reach, goal.” The next step, she says, is to see “if we can measure a single protein in its natural environment,” which may help reveal important features such as binding sites. The research team included Ashok Ajoy PhD ’16 , MIT graduate student Yixiang Liu, former postdocs Kasturi Saha, Luca Marseglia, Jean-Christophe Jaskula, and Ulf Bissbort. It was supported by the National Science Foundation and the U.S. Army Research Office.