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Are you ready for mood-altering drugs precisely inserted into your brain?

To directly probe the relationship between prefrontal cortex circuitry (PFC), limbic network oscillatory dysfunction, and the emergence of depression-related behavior, the researchers implanted mice with microwire recording electrodes in PFC and three relevant limbic brain regions implicated in major depressive disorder: nucleus accumbens (NAC), amygdala (AMY), and ventral tegmental area (VTA). Shown below: representative local field potential traces of neural signals. In the overlaid traces below, note that PFC oscillations (blue) tended to precede AMY oscillations (red). (credit: Rainbo Hultman et al./Neuron)

Imagine if doctors could precisely insert a tiny amount of a custom drug into a specific circuit in your brain and improve your depression (or other mood problems) — instead of treating the entire brain.

That’s exactly what Duke University researchers have explored in mice. Stress-susceptible animals that appeared depressed or anxious were restored to relatively normal behavior this way, according to a study appearing in the forthcoming July 20 issue of Neuron.

The plan was to define specific glitches in the neural circuits and then use a drug to fix them. The ambitious goal: go from a protein, to a signaling activity, to a cell, to a circuit, to activity that happens across the whole brain, to actual behavior.

1. Identify the key neurons in the prefrontal cortex

The researchers first determined how the prefrontal cortex is used as a pacemaker for the limbic system, said lead researcher Kafui Dzirasa, an assistant professor of psychiatry and behavioral sciences, and neurobiology.

The team started by precisely placing arrays of 32 electrodes in four brain areas of the mice (see illustration above). Then they recorded brain activity as these mice were subjected to a stressful situation called chronic social defeat.* This allowed the researchers to observe the activity between the prefrontal cortex and three areas of the limbic system that are implicated in major depression.

To interpret the complicated data coming from the electrodes, the team used machine learning algorithms — identifying which parts of the data seemed to be the timing control signal between the prefrontal cortex and the limbic system— and then zeroed in on the individual neurons involved in that cortical signal and its corresponding circuit.

2. Inject a drug to restore function

They then applied engineered molecules called DREADD (Designer Receptors Exclusively Activated by Designer Drug), developed by University of North Carolina at Chapel Hill pharmacologist Bryan Roth, in very tiny amounts (0.5 microliter). A drug that attaches only to that DREADD is then administered to give the researchers control over the circuit.

They found that direct stimulation of PFC-amygdala neural circuitry with DREADDs normalized PFC-dependent limbic synchrony in stress-susceptible animals and restored normal behavior.

The researchers suggest that their findings also demonstrate an interdisciplinary approach that can be used to identify the large-scale network changes that underlie complex emotional pathologies and the specific network nodes that can be used to develop targeted interventions.

“These subcortical circuits are the key regulators of our emotional life,” said Helen Mayberg, a professor of psychiatry, neurology and radiology at Emory University who was not involved in this research. “What’s great about this paper is that they use different approaches to see a circuit that’s relevant to a lot of disorders,” said Mayberg, who has been pioneering deep-brain stimulation of very specific sites in the human prefrontal cortex to treat mood disorders.

But she cautions that to assess anything like “mood” in a mouse, one can only infer from its behaviors. “It’s hard to do, even in a human,” she said.

This work was supported by funding from National Institutes of Mental Health and a research incubator award from the Duke Institute for Brain Sciences.

* The mice were repeatedly exposed to larger aggressive animals for 10–15 consecutive days. At the end of this protocol, animals exhibit multiple depressive endophenotypes including hedonic dysfunction, circadian dysregulation, anxiety, and psychomotor retardation.

Abstract of Dysregulation of Prefrontal Cortex-Mediated Slow-Evolving Limbic Dynamics Drives Stress-Induced Emotional Pathology

Circuits distributed across cortico-limbic brain regions compose the networks that mediate emotional behavior. The prefrontal cortex (PFC) regulates ultraslow (<1 Hz) dynamics across these networks, and PFC dysfunction is implicated in stress-related illnesses including major depressive disorder (MDD). To uncover the mechanism whereby stress-induced changes in PFC circuitry alter emotional networks to yield pathology, we used a multi-disciplinary approach including in vivo recordings in mice and chronic social defeat stress. Our network model, inferred using machine learning, linked stress-induced behavioral pathology to the capacity of PFC to synchronize amygdala and VTA activity. Direct stimulation of PFC-amygdala circuitry with DREADDs normalized PFC-dependent limbic synchrony in stress-susceptible animals and restored normal behavior. In addition to providing insights into MDD mechanisms, our findings demonstrate an interdisciplinary approach that can be used to identify the large-scale network changes that underlie complex emotional pathologies and the specific network nodes that can be used to develop targeted interventions.

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The top 10 emerging technologies of 2016

(credit: WEF)

The World Economic Forum’s annual list of this year’s breakthrough technologies, published today, includes “socially aware” openAI, grid-scale energy storage, perovskite solar cells, and other technologies with the potential to “transform industries, improve lives, and safeguard the planet.” The WEF’s specific interest is to “close gaps in investment and regulation.”

“Horizon scanning for emerging technologies is crucial to staying abreast of developments that can radically transform our world, enabling timely expert analysis in preparation for these disruptors. The global community needs to come together and agree on common principles if our society is to reap the benefits and hedge the risks of these technologies,” said Bernard Meyerson, PhD, Chief Innovation Officer of IBM and Chair of the WEF’s Meta-Council on Emerging Technologies.

The list also provides an opportunity to debate human, societal, economic or environmental risks and concerns that the technologies may pose — prior to widespread adoption.

One of the criteria used by council members during their deliberations was the likelihood that 2016 represents a tipping point in the deployment of each technology. So the list includes some technologies that have been known for a number of years, but are only now reaching a level of maturity where their impact can be meaningfully felt.

The top 10 technologies that make this year’s list are:

  1. Nanosensors and the Internet of Nanothings  — With the Internet of Things expected to comprise 30 billion connected devices by 2020, one of the most exciting areas of focus today is now on nanosensors capable of circulating in the human body or being embedded in construction materials. They could use DNA and proteins to recognize specific chemical targets, store a few bits of information, and then report their status by changing color or emitting some other easily detectable signal.
  2. Next-Generation Batteries — One of the greatest obstacles holding renewable energy back is matching supply with demand, but recent advances in energy storage using sodium, aluminum, and zinc based batteries makes mini-grids feasible that can provide clean, reliable, around-the-clock energy sources to entire villages.
  3. The Blockchain — With venture investment related to the online currency Bitcoin exceeding $1 billion in 2015 alone, the economic and social impact of blockchain’s potential to fundamentally change the way markets and governments work is only now emerging.
  4. 2D Materials — Plummeting production costs mean that 2D materials like graphene are emerging in a wide range of applications, from air and water filters to new generations of wearables and batteries.
  5. Autonomous Vehicles — The potential of self-driving vehicles for saving lives, cutting pollution, boosting economies, and improving quality of life for the elderly and other segments of society has led to rapid deployment of key technology forerunners along the way to full autonomy.
  6. Organs-on-chips — Miniature models of human organs could revolutionize medical research and drug discovery by allowing researchers to see biological mechanism behaviors in ways never before possible.
  7. Perovskite Solar Cells — This new photovoltaic material offers three improvements over the classic silicon solar cell: it is easier to make, can be used virtually anywhere and, to date, keeps on generating power more efficiently.
  8. Open AI Ecosystem — Shared advances in natural language processing and social awareness algorithms, coupled with an unprecedented availability of data, will soon allow smart digital assistants to help with a vast range of tasks, from keeping track of one’s finances and health to advising on wardrobe choice.
  9. Optogenetics — Recent developments mean light can now be delivered deeper into brain tissue, something that could lead to better treatment for people with brain disorders.
  10. Systems Metabolic Engineering — Advances in synthetic biology, systems biology, and evolutionary engineering mean that the list of building block chemicals that can be manufactured better and more cheaply by using plants rather than fossil fuels is growing every year.

To compile this list, the World Economic Forum’s Meta-Council on Emerging Technologies, a panel of global experts, “drew on the collective expertise of the Forum’s communities to identify the most important recent technological trends. By doing so, the Meta-Council aims to raise awareness of their potential and contribute to closing gaps in investment, regulation and public understanding that so often thwart progress.”

You can read 10 expert views on these technologies here or download the series as a PDF.

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How to convert graphene into a semiconductor for scalable production

Progressively magnified images (left to right; scale bars: 400, 10, and 1 nm) of graphene nanoribbons grown on germanium semiconductor wafers.  (credit: Michael Arnold/University of Wisconsin-Madison)

Graphene can be transformed in the lab from a semimetal into a semiconductor if it is confined into nanoribbons narrower than 10 nm (with controlled orientation and edges), but scaling it up for commercial use has not been possible. Until now.

University of Wisconsin-Madison scientists have discovered how to synthesize narrow, long “one-dimensional” (1-D) nanoribbons (sub-10 nanometers wide) directly on a conventional germanium semiconductor wafer.

That narrow width is not possible with the optical and electron-beam lithography techniques conventionally used in making chips, and integrating graphene nanoribbons onto insulating or semiconducting wafers has also been difficult.

The breakthrough was extremely slow growth (under 5 nanometers per hour), using a new variation of a technique called chemical vapor deposition (CVD), allowing nanoribbons with length-to-width aspect ratios greater than 70 to grow on the surface of a germanium wafer (and with the required smooth “armchair” edges — see the image on the right above).

In addition, this new fabrication process is compatible with existing semiconductor fabrication infrastructure. Appears promising. Let’s see which chipmakers go for it.

The research is described in an open-access article just published in Nature Communications.

Abstract of Direct oriented growth of armchair graphene nanoribbons on germanium

Graphene can be transformed from a semimetal into a semiconductor if it is confined into nanoribbons narrower than 10 nm with controlled crystallographic orientation and well-defined armchair edges. However, the scalable synthesis of nanoribbons with this precision directly on insulating or semiconducting substrates has not been possible. Here we demonstrate the synthesis of graphene nanoribbons on Ge(001) via chemical vapour deposition. The nanoribbons are self-aligning 3° from the Geleft fence110right fence directions, are self-defining with predominantly smooth armchair edges, and have tunable width to <10 nm and aspect ratio to >70. In order to realize highly anisotropic ribbons, it is critical to operate in a regime in which the growth rate in the width direction is especially slow, <5 nm h−1. This directional and anisotropic growth enables nanoribbon fabrication directly on conventional semiconductor wafer platforms and, therefore, promises to allow the integration of nanoribbons into future hybrid integrated circuits.

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First self-driving ‘cognitive’ vehicle uses IBM Watson Internet of Things

Olli (credit: Local Motors)

Local Motors, creator of the world’s first 3D-printed cars, has developed the first self-driving “cognitive” vehicle, using IBM Watson Internet of Things (IoT) for Automotive.

The vehicle, dubbed “Olli,” can carry up to 12 people. It uses IBM Watson and other systems to improve the passenger experience and allow natural interaction with the vehicle. Olli will be used on public roads locally in Washington DC and later this year in Miami-Dade County.

Olli is the first vehicle to use the cloud-based cognitive computing capability of IBM Watson IoT to analyze and learn from high volumes of transportation data, produced by more than 30 sensors embedded throughout the vehicle. Sensors will be added and adjusted continually as passenger needs and local preferences are identified.

Four Watson developer APIs — Speech to Text, Natural Language Classifier, Entity Extraction and Text to Speech — will enable passengers to interact conversationally with Olli while traveling from point A to point B, discussing topics about how the vehicle works, where they are going, and why Olli is making specific driving decisions.

Watson empowers Olli to understand and respond to passengers’ questions as they enter the vehicle, such as destinations (“Olli, can you take me downtown?”) or specific vehicle functions (“how does this feature work?” or even “are we there yet?”). Passengers can also ask for recommendations on local destinations such as popular restaurants or historical sites based on analysis of personal preferences.

“Cognitive computing provides incredible opportunities to create unparalleled, customized experiences for customers, taking advantage of the massive amounts of streaming data from all devices connected to the Internet of Things, including an automobile’s myriad sensors and systems,” said Harriet Green, General Manager, IBM Watson Internet of Things, Commerce & Education.

Miami-Dade County and Las Vegas are also exploring a pilot program in which several autonomous vehicles would be used to transport people around Miami and Las Vegas.


IBM Internet of Things | Local Motors Debuts “Olli,” the First Self-driving Vehicle to Tap the Power of IBM Watson


IBM Internet of Things | Harnessing vehicle safety data with analytics

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Ultra-flexible solar cells thin enough to wrap around a glass stirring rod

Ultra-thin solar cells flexible enough to bend around small objects, such as this 6-mm-diameter glass rod (credit: Juho Kim, et al./APL)

Scientists in South Korea have designed ultra-thin photovoltaics that are flexible enough to wrap around a thin glass rod. The new solar cells could power wearable electronics like smart watches and fitness trackers.

“Our photovoltaic is about 1 micrometer thick” (the thinnest human hair is about 17 micrometers), said Jongho Lee, an engineer at the Gwangju Institute of Science and Technology in South Korea. Standard photovoltaics are usually hundreds of times thicker, and most other thin photovoltaics are 2 to 4 times thicker, he explained.

Fabrication procedure of the flexible vertical ultra-thin gallium-arsenide solar microcells.* (credit: Juho Kim, et al./APL)

The researchers made the ultra-thin solar cells from the semiconductor gallium arsenide. They stamped the cells directly onto a flexible substrate without using an adhesive (which would add to the material’s thickness).

The cells were then “cold welded” to the electrode on the substrate by applying pressure at 170 degrees Celsius and melting a top layer of material called photoresist, which acted as a temporary adhesive. The photoresist was later peeled away, leaving the direct metal-to-metal bond.

The metal bottom electrode layer also serves as a reflector to direct stray light back to the solar cells (to increase current output). The researchers tested the efficiency of the device at converting sunlight to electricity and found that it was comparable to thicker photovoltaics.

The team performed bending tests and found the cells could wrap around a radius as small as 1.4 millimeters. They also performed numerical analysis of the cells, finding that they experience one-fourth the amount of strain of similar cells that are 3.5 micrometers thick.

A few other groups have reported solar cells with thicknesses of around 1 micrometer, but have produced the cells in different ways, for example, by removing the whole subtrate by etching. By transfer-printing instead of etching, the new method developed by Lee and his colleagues could be used to make very flexible photovoltaics with a smaller amount of materials, according to Lee.

The thin cells can also be integrated onto glasses frames or fabric and might power the next wave of wearable electronics, Lee said.

The researchers report the results in an open-access paper in the journal Applied Physics Letters, from AIP Publishing.

* (a) Schematic illustration of a film stamp with vertical gallium-arsenide microcells fabricated and isolated from the epitaxially grown source wafers. The photoresist (PR) temporarily holds the solar microcells on the source wafers. (b) The bottom electrode, which also serves as a back reflector, is deposited onto the backside of the ultra-thin vertical GaAs microcells. (c) After the film stamp is brought into contact with the receiver substrate, heat (∼170 °C) and pressure (∼80 kPa) are applied to melt the PR to serve as an adhesive. (d) Cross-sectional scanning electron microscope (SEM) image of the microcell covered with the adhesive (PR) on the receiver substrate after the printing process. The bottom electrode is in direct contact with the Au layer on the receiver substrate. (e) Peeling the film stamp leaves the vertical ultra-thin solar microcells on the receiver substrate. (h) An optical image of the microcell wrapped on a glass slide with a radius of 1 mm. The microcell is encapsulated with a thin epoxy layer (thickness ∼2 μm).

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A low-cost ‘electronic nose’ spectrometer for home health diagnosis

Current experimental design of transmitter radio-frequency front end for a rotational spectrometer. Using integrated circuits (such as the one below “CHIP1”) in an electronic nose promises to make the future device more affordable. (credit: UT Dallas)

UT Dallas researchers have designed an affordable “electronic nose” radio-frequency front end for a rotational spectrometer — used for detecting chemical molecules in human breath for health diagnosis.

Current breath-analysis devices are bulky and too costly for commercial use, said Kenneth O, PhD, a principal investigator of the effort and director of Texas Analog Center of Excellence (TxACE). Instead, the researchers used CMOS integrated circuits technology, which promises to make the device compact and affordable.

A rotational spectrometer generates and transmits electromagnetic waves over a wide range of frequencies, and analyzes how the waves are attenuated (absorbed) to determine what chemicals are present, as well as their concentrations in a sample. The system can detect low levels of chemicals present in human breath.

A breath test contains information about practically every part of a human body, but an electronic nose can detect gas molecules with more specificity and sensitivity than breathalyzers, which can confuse acetone for ethanol (the active ingredient of alcoholic drinks) in the breath, for example. This is important for patients with Type 1 diabetes, who have high concentrations of acetone in their breath.

The current research focuses on the design of a 200–280 GHz transmitter radio-frequency front end.

Future home use predicted

The researchers envision that the CMOS-based device will first be used in industrial settings, and then in doctors’ offices and hospitals. As the technology matures, the devices could be used in homes. Dr. O said the need for blood work and gastrointestinal tests, for example, could be reduced, and diseases could be detected earlier, lowering the costs of health care.

The researchers plan to have a prototype programmable electronic nose available for beta testing in early 2018.

The research is supported by the Semiconductor Research Corporation, Texas Instruments, and Samsung Global Research Outreach. The research team includes members at UT Southwestern, Ohio State University, and Wright State University.

The research was presented Wednesday in an open-access paperat the 2016 IEEE Symposia on VLSI Technology and Circuits in Honolulu, Hawaii.

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Built-in miniaturized micro-supercapacitor powers silicon chip

In-chip porous silicon-titanium nitride supercapacitor. (a) Scanning electron microscopy (SEM) inset of the trenches separating the electrodes (dark gray). (b) Rotated schematic illustration of the cross-section of two opposite electrodes of a device (titanium nitride-coated porous silicon layer with aluminum contact pads on the back side), with electrolyte shown in orange. (c) Higher-magnification SEM picture of the porous silicon regions. (d) Device trench side. (e) metallization side containing aluminum contacts for electrodes. (f) 3D illustration of two atomic-layer-deposition cycles of titanium-nitride growth. (credit: adapted from Kestutis Grigoras et al./Nano Energy)

Finnish researchers have developed a method for building highly efficient miniaturized micro-supercapacitor energy storage directly inside a silicon microcircuit chip, making it possible to power autonomous sensor networks, wearable electronics, and mobile internet-of-things (IoT) devices.

Supercapacitors function similar to standard batteries, but store electrostatic energy instead of chemical energy.

The researchers at VTT Technical Research Centre of Finland have developed a hybrid nano-electrode that’s only a few nanometers thick. It consists of porous silicon coated with a titanium nitride layer formed by atomic layer deposition.

The nano-electrode design features the highest-ever conductive surface-to-volume ratio. That combined with an ionic liquid (in a microchannel formed in between two electrodes), results in an extremely small form factor and efficient energy storage. That design makes it possible for a silicon-based micro-supercapacitor to achieve higher energy storage (energy density) and faster charge/discharge (power density) than the leading carbon- and graphene-based supercapacitors, according to the researchers.

The micro-supercapacitor can store 0.2 joule (55 microwatts of power for one hour) on a one-square-centimeter silicon chip. This design also leaves the surface of the chip available for active integrated microcircuits and sensors.

Micro-supercapacitors can also be integrated directly with active microelectronic devices to store electrical energy generated by thermal, light, and vibration energy harvesters to supply electrical energy (see, for example, Wireless device converts ‘lost’ microwave energy into electric power).

An open-access paper on the research has been published in Nano Energy journal.

Abstract of Conformal titanium nitride in a porous silicon matrix: A nanomaterial for in-chip supercapacitors

Today’s supercapacitor energy storages are typically discrete devices aimed for printed boards and power applications. The development of autonomous sensor networks and wearable electronics and the miniaturization of mobile devices would benefit substantially from solutions in which the energy storage is integrated with the active device. Nanostructures based on porous silicon (PS) provide a route towards integration due to the very high inherent surface area to volume ratio and compatibility with microelectronics fabrication processes. Unfortunately, pristine PS has limited wettability and poor chemical stability in electrolytes and the high resistance of the PS matrix severely limits the power efficiency. In this work, we demonstrate that excellent wettability and electro-chemical properties in aqueous and organic electrolytes can be obtained by coating the PS matrix with an ultra-thin layer of titanium nitride by atomic layer deposition. Our approach leads to very high specific capacitance (15 F cm−3), energy density (1.3 mWh cm−3), power density (up to 214 W cm−3) and excellent stability (more than 13,000 cycles). Furthermore, we show that the PS–TiN nanomaterial can be integrated inside a silicon chip monolithically by combining MEMS and nanofabrication techniques. This leads to realization of in-chip supercapacitor, i.e., it opens a new way to exploit the otherwise inactive volume of a silicon chip to store energy.

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How creating defective nanodiamonds could revolutionize nanotechnology and quantum computing

This electron microscope image shows a hybrid nanoparticle consisting of a nanodiamond (roughly 50 nanometers wide) covered in smaller silver nanoparticles that enhance the diamond’s optical properties. (credit: Min Ouyang)

University of Maryland researchers have developed a method to quickly and inexpensively assemble diamond-based hybrid nanoparticles from the ground up in large quantities while avoiding many of the problems with current methods.

These hybrid nanoparticles could speed the design of room-temperature qubits for quantum computers and create brighter dyes for biomedical imaging or highly sensitive magnetic and temperature sensors, for example.

When impurities are better

Synthetic diamonds of various colors (from defects) grown by the high-pressure high-temperature technique (credit: Wikipedia/
public domain)

The basic trick in creating a interesting or useful diamond is, ironically: Add a defect in the diamond’s crystal lattice. It’s similar to doping silicon to give it special electronic properties (such as making it work as a transistor).

Pure diamonds consist of an orderly lattice of carbon atoms and are completely transparent. However, pure diamonds are quite rare in natural diamond deposits; most have defects resulting from non-carbon impurities such as nitrogen, boron and phosphorus. Such defects create the subtle and desirable color variations seen in gemstone diamonds.

This altered bond is also the source of the optical, electromagnetic, and quantum physical properties that will make a nanodiamond useful when paired with other nanomaterials.

Nitrogen vacancy impurity

Model of nitrogen-vacancy center in diamond (credit: Wikipedia/public domain)

The most useful impurity — and used in the Maryland study — is the famous “nitrogen vacancy” defect: Sticking in a single nitrogen atom where a carbon atom should be, with an empty space right next to it.

As KurzweilAI has shown in several articles, a nitrogen vacancy in a diamond (or other crystalline materials) can lead to a variety of interesting new properties, such as a highly sensitive way to detect neural signals, an ultrasensitive real-time magnetic field detector, and importantly, making a nanodiamond behave as a quantum bit (qubit) for use in quantum computing and other applications.

Nearly all qubits studied to date require ultra-cold temperatures to function properly. A qubit that works at room temperature would represent a significant step forward, helping use quantum circuits in industrial, commercial and consumer-level electronics. That’s of special interest to Ougang’s team.

Volume production of hybrid nanoparticles

A synthetic route for hybrid nanodiamond nanoparticles. (a) Different growth stages, ending in (S6) growth of metal nanoparticles on the nanodiamond surface. (b) Transmission electron microscope image showing hybrid nanodiamond-silver nanostructures made by following the synthetic scheme in (a). Scale bar, 200 nm. (credit: J. Gong et al./Nature Communications)

Ougang’s and colleagues’ main breakthrough, though, is their method for constructing the hybrid nanoparticles. Other researchers have paired nanodiamonds with complementary nanoparticles using relatively imprecise methods, such as manually installing the diamonds and particles next to each other onto a larger surface one by one.

These top-down methods are costly, time consuming, and introduce a host of complications. “Our key innovation is that we can now reliably and efficiently produce these freestanding hybrid particles in large numbers,” explained Ouyang, who also has appointments in the UMD Center for Nanophysics and Advanced Materials and the Maryland NanoCenter, with an affiliate professorship in the UMD Department of Materials Science and Engineering.

His team’s method also enables precise control of the hybrid particles’ properties, such as the composition and total number of non-diamond particles.

“A major strength of our technique is that it is broadly useful and can be applied to a variety of diamond types and paired with a variety of other nanomaterials,” Ouyang said. “It can also be scaled up fairly easily. We are interested in studying the basic physics further, but also moving toward specific applications.”

Abstract of Nanodiamond-based nanostructures for coupling nitrogen-vacancy centres to metal nanoparticles and semiconductor quantum dots

The ability to control the interaction between nitrogen-vacancy centres in diamond and photonic and/or broadband plasmonic nanostructures is crucial for the development of solid-state quantum devices with optimum performance. However, existing methods typically employ top-down fabrication, which restrict scalable and feasible manipulation of nitrogen-vacancy centres. Here, we develop a general bottom-up approach to fabricate an emerging class of freestanding nanodiamond-based hybrid nanostructures with external functional units of either plasmonic nanoparticles or excitonic quantum dots. Precise control of the structural parameters (including size, composition, coverage and spacing of the external functional units) is achieved, representing a pre-requisite for exploring the underlying physics. Fine tuning of the emission characteristics through structural regulation is demonstrated by performing single-particle optical studies. This study opens a rich toolbox to tailor properties of quantum emitters, which can facilitate design guidelines for devices based on nitrogen-vacancy centres that use these freestanding hybrid nanostructures as building blocks.

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Implanted neuroprosthesis improves walking ability in stroke patient

Left: multichannel implantable gait-assist system. Right: participant walking with the system. (credit: N.S. Makowski et al./Am. J. Phys. Med. Rehabil.)

A surgically implanted neuroprosthesis has led to substantial improvement in walking speed and distance in a patient with limited mobility after a stroke, according to a single-patient study in the American Journal of Physical Medicine & Rehabilitation.

The system, programmed to stimulate coordinated activity of hip, knee, and ankle muscles, “is a promising intervention to provide assistance to stroke survivors during daily walking,” write Nathaniel S. Makowski, PhD, and colleagues of the Louis Stokes Cleveland Veterans Affairs Medical Center.

With technical refinements and further research, such implanted neuroprosthesis systems might help to promote walking ability for at least some patients with post-stroke disability.

Clinically relevant gait improvements

The researchers report their experience with an implanted neuroprosthesis in a 64-year-old man with impaired motion and sensation of his left leg and foot after a hemorrhagic (bleeding) stroke. After thorough evaluation, he underwent surgery to place an implanted pulse generator and intramuscular stimulating electrodes in seven muscles of the hip, knee, and ankle.*

Makowski and colleagues then created a customized electrical stimulation program to activate the muscles, with the goal of restoring a more natural gait pattern. The patient went through extensive training in the researchers’ laboratory for several months after neuroprosthesis placement.

With training without muscle stimulation, gait speed only increased from 0.29 meters per second (m/s) before surgery, to 0.35 m/s after training, a non-significant improvement. But when muscle stimulation was turned on, gait speed increased dramatically: to 0.72 m/s, with “more symmetrical and dynamic gait.”

In addition, the patient was able to walk much farther. When first evaluated, he could walk only 76 meters before becoming fatigued. After training but without stimulation, he could walk about 300 meters (in 16 minutes). With stimulation, the patient’s maximum walking distance increased to more than 1,400 meters (in 41 minutes) with stimulation.

Even though the patient wasn’t walking with stimulation outside the laboratory, his walking ability in daily life improved significantly. He went from “household-only” ambulation to increased walking outside in the neighborhood.

“The therapeutic effect is likely a result of muscle conditioning during stimulated exercise and gait training,” according to the authors. “Persistent use of the device during walking may provide ongoing training that maintains both muscle conditioning and cardiovascular health.”

While the results of this initial experience in a single patient are encouraging, the researchers emphasize that large-scale studies will be needed to demonstrate the wider applicability of a neuroprosthesis for multi-joint control. If the benefits are confirmed, Makowski and colleagues conclude, “daily use of an implanted system could have significant clinical relevance to a portion of the stroke population.”

* Tensor fasciae latae (hip flexor), sartorius (hip and knee flexor), gluteus maximus (hip extensor), short head of biceps femoris (knee flexor), quadriceps (knee extensor), tibialis anterior/peroneus longus (ankle dorsiflexors), and gastrocnemius.

Abstract of Improving Walking with an Implanted Neuroprosthesis for Hip, Knee, and Ankle Control After Stroke.

Objective: The objective of this work was to quantify the effects of a fully implanted pulse generator to activate or augment actions of hip, knee, and ankle muscles after stroke.

Design: The subject was a 64-year-old man with left hemiparesis resulting from hemorrhagic stroke 21 months before participation. He received an 8-channel implanted pulse generator and intramuscular stimulating electrodes targeting unilateral hip, knee, and ankle muscles on the paretic side. After implantation, a stimulation pattern was customized to assist with hip, knee, and ankle movement during gait.

The subject served as his own concurrent and longitudinal control with and without stimulation. Outcome measures included 10-m walk and 6-minute timed walk to assess gait speed, maximum walk time, and distance to measure endurance, and quantitative motion analysis to evaluate spatial-temporal characteristics. Assessments were repeated under 3 conditions: (1) volitional walking at baseline, (2) volitional walking after training, and (3) walking with stimulation after training.

Results: Volitional gait speed improved with training from 0.29 m/s to 0.35 m/s and further increased to 0.72 m/s with stimulation. Most spatial-temporal characteristics improved and represented more symmetrical and dynamic gait.

Conclusions: These data suggest that a multijoint approach to implanted neuroprostheses can provide clinically relevant improvements in gait after stroke.

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Diamonds closer to becoming ideal power semiconductors

A diode array bonded to a natural single crystalline diamond plate. Inset: deposited anode metal on top of doped silicon nanomembrane. (credit: Jung-Hun Seo)

Researchers have developed a new method for doping (integrating elements to change a semiconductor’s properties) single crystals of diamond with boron at relatively low temperatures, without degradation.

Diamonds have properties that could make them ideal semiconductors for power electronics. They can handle high voltages and power, and electrical currents also flow through diamonds quickly, meaning the material would make for energy-efficient devices. And they are thermally conductive, which means diamond-based devices would dissipate heat quickly and easily (no need for bulky, expensive cooling methods). However. diamond’s rigid crystalline structure makes doping difficult.*

Doping a diamond with boron

Zhengqiang (Jack) Ma, a University of Wisconsin-Madison electrical and computer engineering professor, and his colleagues describe a solution in the Journal of Applied Physics, from AIP Publishing.

They discovered that if you bond a single-crystal diamond with a piece of silicon doped with boron, and heat it to 800 degrees Celsius (low compared to conventional techniques), the boron atoms will migrate from the silicon to the diamond. It turns out that the boron-doped silicon has defects such as vacancies, where an atom is missing in the lattice structure. Carbon atoms from the diamond will fill those vacancies, leaving empty spots for boron atoms.

This technique also allows for selective doping, which means more control when making devices. You can choose where to dope a single-crystal diamond simply by bonding the silicon to that spot.

The new method currently only works for P-type doping, where the semiconductor is doped with an element that provides positive charge carriers (in this case, the absence of electrons, called holes). The researchers are already working on a simple device using P-type single-crystal diamond semiconductors.

But to make electronic devices like transistors, you need N-type doping, which gives the semiconductor negative charge carriers (electrons). And other barriers remain: diamond is expensive and single crystals are very small.

Still, Ma says, achieving P-type doping is an important step, and might inspire others to find solutions for the remaining challenges. Eventually, he said, single-crystal diamond could be useful everywhere — perfect, for instance, for controlling power in the electrical grid.

* Currently, you can dope diamond by coating the crystal with boron and heating it to 1450 degrees Celsius. But it’s difficult to remove the boron coating at the end. This method only works on diamonds consisting of multiple crystals stuck together. Because such polydiamonds have irregularities between the crystals, single crystals would be superior semiconductors. You can dope single crystals by injecting boron atoms while growing the crystals artificially. The problem is the process requires powerful microwaves that can degrade the quality of the crystal.

Abstract of Thermal diffusion boron doping of single-crystal natural diamond

With the best overall electronic and thermal properties, single crystal diamond (SCD) is the extreme wide bandgap material that is expected to revolutionize power electronics and radio-frequency electronics in the future. However, turning SCD into useful semiconductors requires overcoming doping challenges, as conventional substitutional doping techniques, such as thermal diffusion and ion implantation, are not easily applicable to SCD. Here we report a simple and easily accessible doping strategy demonstrating that electrically activated, substitutional doping in SCD without inducing graphitization transition or lattice damage can be readily realized with thermal diffusion at relatively low temperatures by using heavily dopedSi nanomembranes as a unique dopant carrying medium. Atomistic simulations elucidate a vacancyexchange boron doping mechanism that occurs at the bonded interface between Si and diamond. We further demonstrate selectively doped high voltage diodes and half-wave rectifier circuits using such dopedSCD. Our new doping strategy has established a reachable path toward using SCDs for future high voltage power conversion systems and for other novel diamond based electronic devices. The novel dopingmechanism may find its critical use in other wide bandgap semiconductors.