Tag Archives: US

Monitoring forest soundscapes for conservation and more about whale songs

I don’t understand why anyone would publicize science work featuring soundscapes without including an audio file. However, no one from Princeton University (US) phoned and asked for my advice :).

On the plus side, my whale story does have a sample audio file. However, I’m not sure if I can figure out how to embed it here.

Princeton and monitoring forests

In addition to a professor from Princeton University, there’s the founder of an environmental news organization and someone who’s both a professor at the University of Queensland (Australia) and affiliated with the Nature Conservancy making this of the more unusual collaborations I’ve seen.

Moving on to the news, a January 4, 2019 Princeton University news release (also on EurekAlert but published on Jan. 3, 2019) by B. Rose Kelly announces research into monitoring forests,

Recordings of the sounds in tropical forests could unlock secrets about biodiversity and aid conservation efforts around the world, according to a perspective paper published in Science.

Compared to on-the-ground fieldwork, bioacoustics –recording entire soundscapes, including animal and human activity — is relatively inexpensive and produces powerful conservation insights. The result is troves of ecological data in a short amount of time.

Because these enormous datasets require robust computational power, the researchers argue that a global organization should be created to host an acoustic platform that produces on-the-fly analysis. Not only could the data be used for academic research, but it could also monitor conservation policies and strategies employed by companies around the world.

“Nongovernmental organizations and the conservation community need to be able to truly evaluate the effectiveness of conservation interventions. It’s in the interest of certification bodies to harness the developments in bioacoustics for better enforcement and effective measurements,” said Zuzana Burivalova, a postdoctoral research fellow in Professor David Wilcove’s lab at Princeton University’s Woodrow Wilson School of Public and International Affairs.

“Beyond measuring the effectiveness of conservation projects and monitoring compliance with forest protection commitments, networked bioacoustic monitoring systems could also generate a wealth of data for the scientific community,” said co-author Rhett Butler of the environmental news outlet Mongabay.

Burivalova and Butler co-authored the paper with Edward Game, who is based at the Nature Conservancy and the University of Queensland.

The researchers explain that while satellite imagery can be used to measure deforestation, it often fails to detect other subtle ecological degradations like overhunting, fires, or invasion by exotic species. Another common measure of biodiversity is field surveys, but those are often expensive, time consuming and cover limited ground.

Depending on the vegetation of the area and the animals living there, bioacoustics can record animal sounds and songs from several hundred meters away. Devices can be programmed to record at specific times or continuously if there is solar polar or a cellular network signal. They can also record a range of taxonomic groups including birds, mammals, insects, and amphibians. To date, several multiyear recordings have already been completed.

Bioacoustics can help effectively enforce policy efforts as well. Many companies are engaged in zero-deforestation efforts, which means they are legally obligated to produce goods without clearing large forests. Bioacoustics can quickly and cheaply determine how much forest has been left standing.

“Companies are adopting zero deforestation commitments, but these policies do not always translate to protecting biodiversity due to hunting, habitat degradation, and sub-canopy fires. Bioacoustic monitoring could be used to augment satellites and other systems to monitor compliance with these commitments, support real-time action against prohibited activities like illegal logging and poaching, and potentially document habitat and species recovery,” Butler said.

Further, these recordings can be used to measure climate change effects. While the sounds might not be able to assess slow, gradual changes, they could help determine the influence of abrupt, quick differences to land caused by manufacturing or hunting, for example.

Burivalova and Game have worked together previously as you can see in a July 24, 2017 article by Justine E. Hausheer for a nature.org blog ‘Cool Green Science’ (Note: Links have been removed),

Morning in Musiamunat village. Across the river and up a steep mountainside, birds-of-paradise call raucously through the rainforest canopy, adding their calls to the nearly deafening insect chorus. Less than a kilometer away, small birds flit through a grove of banana trees, taro and pumpkin vines winding across the rough clearing. Here too, the cicadas howl.

To the ear, both garden and forest are awash with noise. But hidden within this dawn chorus are clues to the forest’s health.

New acoustic research from Nature Conservancy scientists indicates that forest fragmentation drives distinct changes in the dawn and dusk choruses of forests in Papua New Guinea. And this innovative method can help evaluate the conservation benefits of land-use planning efforts with local communities, reducing the cost of biodiversity monitoring in the rugged tropics.

“It’s one thing for a community to say that they cut fewer trees, or restricted hunting, or set aside a protected area, but it’s very difficult for small groups to demonstrate the effectiveness of those efforts,” says Eddie Game, The Nature Conservancy’s lead scientist for the Asia-Pacific region.

Aside from the ever-present logging and oil palm, another threat to PNG’s forests is subsistence agriculture, which feeds a majority of the population. In the late 1990s, The Nature Conservancy worked with 11 communities in the Adelbert Mountains to create land-use plans, dividing each community’s lands into different zones for hunting, gardening, extracting forest products, village development, and conservation. The goal was to limit degradation to specific areas of the forest, while keeping the rest intact.

But both communities and conservationists needed a way to evaluate their efforts, before the national government considered expanding the program beyond Madang province. So in July 2015, Game and two other scientists, Zuzana Burivalova and Timothy Boucher, spent two weeks gathering data in the Adelbert Mountains, a rugged lowland mountain range in Papua New Guinea’s Madang province.

Working with conservation rangers from Musiamunat, Yavera, and Iwarame communities, the research team tested an innovative method — acoustic sampling — to measure biodiversity across the community forests. Game and his team used small acoustic recorders placed throughout the forest to record 24-hours of sound from locations in each of the different land zones.

Soundscapes from healthy, biodiverse forests are more complex, so the scientists hoped that these recordings would show if parts of the community forests, like the conservation zones, were more biodiverse than others. “Acoustic recordings won’t pick up every species, but we don’t need that level of detail to know if a forest is healthy,” explains Boucher, a conservation geographer with the Conservancy.

Here’s a link to and a citation for the latest work from Burivalova and Game,

The sound of a tropical forest by Zuzana Burivalova, Edward T. Game, Rhett A. Butler. Science 04 Jan 2019: Vol. 363, Issue 6422, pp. 28-29 DOI: 10.1126/science.aav1902

This paper is behind a paywall. You can find out more about Mongabay and Rhett Butler in its Wikipedia entry.

***ETA July 18, 2019: Cara Cannon Byington, Associate Director, Science Communications for the Nature Conservancy emailed to say that a January 3, 2019 posting on the conservancy’s Cool Green Science Blog features audio files from the research published in ‘The sound of a tropical forest. Scroll down about 75% of the way for the audio.***

Whale songs

Whales share songs when they meet and a January 8, 2019 Wildlife Conservation Society news release (also on EurekAlert) describes how that sharing takes place,

Singing humpback whales from different ocean basins seem to be picking up musical ideas from afar, and incorporating these new phrases and themes into the latest song, according to a newly published study in Royal Society Open Science that’s helping scientists better understand how whales learn and change their musical compositions.

The new research shows that two humpback whale populations in different ocean basins (the South Atlantic and Indian Oceans) in the Southern Hemisphere sing similar song types, but the amount of similarity differs across years. This suggests that males from these two populations come into contact at some point in the year to hear and learn songs from each other.

The study titled “Culturally transmitted song exchange between humpback whales (Megaptera novaeangliae) in the southeast Atlantic and southwest Indian Ocean basins” appears in the latest edition of the Royal Society Open Science journal. The authors are: Melinda L. Rekdahl, Carissa D. King, Tim Collins, and Howard Rosenbaum of WCS (Wildlife Conservation Society); Ellen C. Garland of the University of St. Andrews; Gabriella A. Carvajal of WCS and Stony Brook University; and Yvette Razafindrakoto of COSAP [ (Committee for the Management of the Protected Area of Bezà Mahafaly ] and Madagascar National Parks.

“Song sharing between populations tends to happen more in the Northern Hemisphere where there are fewer physical barriers to movement of individuals between populations on the breeding grounds, where they do the majority of their singing. In some populations in the Southern Hemisphere song sharing appears to be more complex, with little song similarity within years but entire songs can spread to neighboring populations leading to song similarity across years,” said Dr. Melinda Rekdahl, marine conservation scientist for WCS’s Ocean Giants Program and lead author of the study. “Our study shows that this is not always the case in Southern Hemisphere populations, with similarities between both ocean basin songs occurring within years to different degrees over a 5-year period.”

The study authors examined humpback whale song recordings from both sides of the African continent–from animals off the coasts of Gabon and Madagascar respectively–and transcribed more than 1,500 individual sounds that were recorded between 2001-2005. Song similarity was quantified using statistical methods.

Male humpback whales are one of the animal kingdom’s most noteworthy singers, and individual animals sing complex compositions consisting of moans, cries, and other vocalizations called “song units.” Song units are composed into larger phrases, which are repeated to form “themes.” Different themes are produced in a sequence to form a song cycle that are then repeated for hours, or even days. For the most part, all males within the same population sing the same song type, and this population-wide song similarity is maintained despite continual evolution or change to the song leading to seasonal “hit songs.” Some song learning can occur between populations that are in close proximity and may be able to hear the other population’s song.

Over time, the researchers detected shared phrases and themes in both populations, with some years exhibiting more similarities than others. In the beginning of the study, whale populations in both locations shared five “themes.” One of the shared themes, however, had differences. Gabon’s version of Theme 1, the researchers found, consisted of a descending “cry-woop”, whereas the Madagascar singers split Theme 1 into two parts: a descending cry followed by a separate woop or “trumpet.”

Other differences soon emerged over time. By 2003, the song sung by whales in Gabon became more elaborate than their counterparts in Madagascar. In 2004, both population song types shared the same themes, with the whales in Gabon’s waters singing three additional themes. Interestingly, both whale groups had dropped the same two themes from the previous year’s song types. By 2005, songs being sung on both sides of Africa were largely similar, with individuals in both locations singing songs with the same themes and order. However, there were exceptions, including one whale that revived two discontinued themes from the previous year.

The study’s results stands in contrast to other research in which a song in one part of an ocean basin replaces or “revolutionizes” another population’s song preference. In this instance, the gradual changes and degrees of similarity shared by humpbacks on both sides of Africa was more gradual and subtle.

“Studies such as this one are an important means of understanding connectivity between different whale populations and how they move between different seascapes,” said Dr. Howard Rosenbaum, Director of WCS’s Ocean Giants Program and one of the co-authors of the new paper. “Insights on how different populations interact with one another and the factors that drive the movements of these animals can lead to more effective plans for conservation.”

The humpback whale is one of the world’s best-studied marine mammal species, well known for its boisterous surface behavior and migrations stretching thousands of miles. The animal grows up to 50 feet in length and has been globally protected from commercial whaling since the 1960s. WCS has studied humpback whales since that time and–as the New York Zoological Society–played a key role in the discovery that humpback whales sing songs. The organization continues to study humpback whale populations around the world and right here in the waters of New York; research efforts on humpback and other whales in New York Bight are currently coordinated through the New York Aquarium’s New York Seascape program.

I’m not able to embed the audio file here but, for the curious, there is a portion of a humpback whale song from Gabon here at EurekAlert.

Here’s a link to and a citation for the research paper,

Culturally transmitted song exchange between humpback whales (Megaptera novaeangliae) in the southeast Atlantic and southwest Indian Ocean basins by Melinda L. Rekdahl, Ellen C. Garland, Gabriella A. Carvajal, Carissa D. King, Tim Collins, Yvette Razafindrakoto and Howard Rosenbaum. Royal Society Open Science 21 November 2018 Volume 5 Issue 11 https://doi.org/10.1098/rsos.172305 Published:28 November 2018

This is an open access paper.

Ouchies no more! Not from bandages, anyway.

An adhesive that US and Chinese scientists have developed shows great promise not just for bandages but wearable robotics too. From a December 14, 2018 news item on Nanowerk,

Researchers from the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) and Xi’an Jiaotong University in China have developed a new type of adhesive that can strongly adhere wet materials — such as hydrogel and living tissue — and be easily detached with a specific frequency of light.

The adhesives could be used to attach and painlessly detach wound dressings, transdermal drug delivery devices, and wearable robotics.

A December 18, 2018 SEAS news release by Leah Burrows (also on EurekAlert but published Dec. 14, 2018), which originated the news item, delves further,

“Strong adhesion usually requires covalent bonds, physical interactions, or a combination of both,” said Yang Gao, first author of the paper and researcher at Xi’an Jiaotong University. “Adhesion through covalent bonds is hard to remove and adhesion through physical interactions usually requires solvents, which can be time-consuming and environmentally harmful. Our method of using light to trigger detachment is non-invasive and painless.”

The adhesive uses an aqueous solution of polymer chains spread between two, non-sticky materials — like jam between two slices of bread. On their own, the two materials adhere poorly together but the polymer chains act as a molecular suture, stitching the two materials together by forming a network with the two preexisting polymer networks. This process is known as topological entanglement.

When exposed to ultra-violet light, the network of stitches dissolves, separating the two materials.

The researchers, led by Zhigang Suo, the Allen E. and Marilyn M. Puckett Professor of Mechanics and Materials at SEAS, tested adhesion and detachment on a range of materials, sticking together hydrogels; hydrogels and organic tissue; elastomers; hydrogels and elastomers; and hydrogels and inorganic solids.

“Our strategy works across a range of materials and may enable broad applications,” said Kangling Wu, co-lead author and researcher at Xi’an Jiaotong University in China.
While the researchers focused on using UV light to trigger detachment, their work suggests the possibility that the stitching polymer could detach with near-infrared light, a feature which could be applied to a range of new medical procedures.

“In nature, wet materials don’t like to adhere together,” said Suo. “We have discovered a general approach to overcome this challenge. Our molecular sutures can strongly adhere wet materials together. Furthermore, the strong adhesion can be made permanent, transient, or detachable on demand, in response to a cue. So, as we see it, nature is full of loopholes, waiting to be stitched.”

Here’s a link to and  a citation for the paper,

Photodetachable Adhesion by Yang Gao, Kangling Wu, Zhigang Suo. https://doi.org/10.1002/adma.201806948 First published: 14 December 2018

This paper is behind a paywall.

Two-dimensional material stacks into multiple layers to build a memory cell for longer lasting batteries

This research comes from Purdue University (US) and the December announcement seemed particularly timely since battery-powered gifts are popular at Christmas but since it could be many years before this work is commercialized, you may want to tuck it away for future reference.  Also, readers familiar with memristors might see a resemblance to the memory cells mentioned in the following excerpt. From a December 13, 2018 news item on Nanowerk,

The more objects we make “smart,” from watches to entire buildings, the greater the need for these devices to store and retrieve massive amounts of data quickly without consuming too much power.

Millions of new memory cells could be part of a computer chip and provide that speed and energy savings, thanks to the discovery of a previously unobserved functionality in a material called molybdenum ditelluride.

The two-dimensional material stacks into multiple layers to build a memory cell. Researchers at Purdue University engineered this device in collaboration with the National Institute of Standards and Technology (NIST) and Theiss Research Inc.

A December 13, 2018 Purdue University news release by Kayla Wiles, which originated the news item,  describes the work in more detail,

Chip-maker companies have long called for better memory technologies to enable a growing network of smart devices. One of these next-generation possibilities is resistive random access memory, or RRAM for short.

In RRAM, an electrical current is typically driven through a memory cell made up of stacked materials, creating a change in resistance that records data as 0s and 1s in memory. The sequence of 0s and 1s among memory cells identifies pieces of information that a computer reads to perform a function and then store into memory again.

A material would need to be robust enough for storing and retrieving data at least trillions of times, but materials currently used have been too unreliable. So RRAM hasn’t been available yet for widescale use on computer chips.

Molybdenum ditelluride could potentially last through all those cycles.
“We haven’t yet explored system fatigue using this new material, but our hope is that it is both faster and more reliable than other approaches due to the unique switching mechanism we’ve observed,” Joerg Appenzeller, Purdue University’s Barry M. and Patricia L. Epstein Professor of Electrical and Computer Engineering and the scientific director of nanoelectronics at the Birck Nanotechnology Center.

Molybdenum ditelluride allows a system to switch more quickly between 0 and 1, potentially increasing the rate of storing and retrieving information. This is because when an electric field is applied to the cell, atoms are displaced by a tiny distance, resulting in a state of high resistance, noted as 0, or a state of low resistance, noted as 1, which can occur much faster than switching in conventional RRAM devices.

“Because less power is needed for these resistive states to change, a battery could last longer,” Appenzeller said.

In a computer chip, each memory cell would be located at the intersection of wires, forming a memory array called cross-point RRAM.

Appenzeller’s lab wants to explore building a stacked memory cell that also incorporates the other main components of a computer chip: “logic,” which processes data, and “interconnects,” wires that transfer electrical signals, by utilizing a library of novel electronic materials fabricated at NIST.

“Logic and interconnects drain battery too, so the advantage of an entirely two-dimensional architecture is more functionality within a small space and better communication between memory and logic,” Appenzeller said.

Two U.S. patent applications have been filed for this technology through the Purdue Office of Technology Commercialization.

The work received financial support from the Semiconductor Research Corporation through the NEW LIMITS Center (led by Purdue University), NIST, the U.S. Department of Commerce and the Material Genome Initiative.

Here’s a link to and a citation for the paper,

Electric-field induced structural transition in vertical MoTe2- and Mo1–xWxTe2-based resistive memories by Feng Zhang, Huairuo Zhang, Sergiy Krylyuk, Cory A. Milligan, Yuqi Zhu, Dmitry Y. Zemlyanov, Leonid A. Bendersky, Benjamin P. Burton, Albert V. Davydov, & Joerg Appenzeller. Nature Materials volume 18, pages 55–61 (2019) Published: 10 December 2018 DOI: https://doi.org/10.1038/s41563-018-0234-y

This paper is behind a paywall.

An artificial synapse tuned by light, a ferromagnetic memristor, and a transparent, flexible artificial synapse

Down the memristor rabbit hole one more time.* I started out with news about two new papers and inadvertently found two more. In a bid to keep this posting to a manageable size, I’m stopping at four.

UK

In a June 19, 2019 Nanowerk Spotlight article, Dr. Neil Kemp discusses memristors and some of his latest work (Note: A link has been removed),

Memristor (or memory resistors) devices are non-volatile electronic memory devices that were first theorized by Leon Chua in the 1970’s. However, it was some thirty years later that the first practical device was fabricated. This was in 2008 when a group led by Stanley Williams at HP Research Labs realized that switching of the resistance between a conducting and less conducting state in metal-oxide thin-film devices was showing Leon Chua’s memristor behaviour.

The high interest in memristor devices also stems from the fact that these devices emulate the memory and learning properties of biological synapses. i.e. the electrical resistance value of the device is dependent on the history of the current flowing through it.

There is a huge effort underway to use memristor devices in neuromorphic computing applications and it is now reasonable to imagine the development of a new generation of artificial intelligent devices with very low power consumption (non-volatile), ultra-fast performance and high-density integration.

These discoveries come at an important juncture in microelectronics, since there is increasing disparity between computational needs of Big Data, Artificial Intelligence (A.I.) and the Internet of Things (IoT), and the capabilities of existing computers. The increases in speed, efficiency and performance of computer technology cannot continue in the same manner as it has done since the 1960s.

To date, most memristor research has focussed on the electronic switching properties of the device. However, for many applications it is useful to have an additional handle (or degree of freedom) on the device to control its resistive state. For example memory and processing in the brain also involves numerous chemical and bio-chemical reactions that control the brain structure and its evolution through development.

To emulate this in a simple solid-state system composed of just switches alone is not possible. In our research, we are interested in using light to mediate this essential control.

We have demonstrated that light can be used to make short and long-term memory and we have shown how light can modulate a special type of learning, called spike timing dependent plasticity (STDP). STDP involves two neuronal spikes incident across a synapse at the same time. Depending on the relative timing of the spikes and their overlap across the synaptic cleft, the connection strength is other strengthened or weakened.

In our earlier work, we were only able to achieve to small switching effects in memristors using light. In our latest work (Advanced Electronic Materials, “Percolation Threshold Enables Optical Resistive-Memory Switching and Light-Tuneable Synaptic Learning in Segregated Nanocomposites”), we take advantage of a percolating-like nanoparticle morphology to vastly increase the magnitude of the switching between electronic resistance states when light is incident on the device.

We have used an inhomogeneous percolating network consisting of metallic nanoparticles distributed in filamentary-like conduction paths. Electronic conduction and the resistance of the device is very sensitive to any disruption of the conduction path(s).

By embedding the nanoparticles in a polymer that can expand or contract with light the conduction pathways are broken or re-connected causing very large changes in the electrical resistance and memristance of the device.

Our devices could lead to the development of new memristor-based artificial intelligence systems that are adaptive and reconfigurable using a combination of optical and electronic signalling. Furthermore, they have the potential for the development of very fast optical cameras for artificial intelligence recognition systems.

Our work provides a nice proof-of-concept but the materials used means the optical switching is slow. The materials are also not well suited to industry fabrication. In our on-going work we are addressing these switching speed issues whilst also focussing on industry compatible materials.

Currently we are working on a new type of optical memristor device that should give us orders of magnitude improvement in the optical switching speeds whilst also retaining a large difference between the resistance on and off states. We hope to be able to achieve nanosecond switching speeds. The materials used are also compatible with industry standard methods of fabrication.

The new devices should also have applications in optical communications, interfacing and photonic computing. We are currently looking for commercial investors to help fund the research on these devices so that we can bring the device specifications to a level of commercial interest.

If you’re interested in memristors, Kemp’s article is well written and quite informative for nonexperts, assuming of course you can tolerate not understanding everything perfectly.

Here are links and citations for two papers. The first is the latest referred to in the article, a May 2019 paper and the second is a paper appearing in July 2019.

Percolation Threshold Enables Optical Resistive‐Memory Switching and Light‐Tuneable Synaptic Learning in Segregated Nanocomposites by Ayoub H. Jaafar, Mary O’Neill, Stephen M. Kelly, Emanuele Verrelli, Neil T. Kemp. Advanced Electronic Materials DOI: https://doi.org/10.1002/aelm.201900197 First published: 28 May 2019

Wavelength dependent light tunable resistive switching graphene oxide nonvolatile memory devices by Ayoub H.Jaafar, N.T.Kemp. DOI: https://doi.org/10.1016/j.carbon.2019.07.007 Carbon Available online 3 July 2019

The first paper (May 2019) is definitely behind a paywall and the second paper (July 2019) appears to be behind a paywall.

Dr. Kemp’s work has been featured here previously in a January 3, 2018 posting in the subsection titled, Shining a light on the memristor.

China

This work from China was announced in a June 20, 2019 news item on Nanowerk,

Memristors, demonstrated by solid-state devices with continuously tunable resistance, have emerged as a new paradigm for self-adaptive networks that require synapse-like functions. Spin-based memristors offer advantages over other types of memristors because of their significant endurance and high energy effciency.

However, it remains a challenge to build dense and functional spintronic memristors with structures and materials that are compatible with existing ferromagnetic devices. Ta/CoFeB/MgO heterostructures are commonly used in interfacial PMA-based [perpendicular magnetic anisotropy] magnetic tunnel junctions, which exhibit large tunnel magnetoresistance and are implemented in commercial MRAM [magnetic random access memory] products.

“To achieve the memristive function, DW is driven back and forth in a continuous manner in the CoFeB layer by applying in-plane positive or negative current pulses along the Ta layer, utilizing SOT that the current exerts on the CoFeB magnetization,” said Shuai Zhang, a coauthor in the paper. “Slowly propagating domain wall generates a creep in the detection area of the device, which yields a broad range of intermediate resistive states in the AHE [anomalous Hall effect] measurements. Consequently, AHE resistance is modulated in an analog manner, being controlled by the pulsed current characteristics including amplitude, duration, and repetition number.”

“For a follow-up study, we are working on more neuromorphic operations, such as spike-timing-dependent plasticity and paired pulsed facilitation,” concludes You. …

Here’s are links to and citations for the paper (Note: It’s a little confusing but I believe that one of the links will take you to the online version, as for the ‘open access’ link, keep reading),

A Spin–Orbit‐Torque Memristive Device by Shuai Zhang, Shijiang Luo, Nuo Xu, Qiming Zou, Min Song, Jijun Yun, Qiang Luo, Zhe Guo, Ruofan Li, Weicheng Tian, Xin Li, Hengan Zhou, Huiming Chen, Yue Zhang, Xiaofei Yang, Wanjun Jiang, Ka Shen, Jeongmin Hong, Zhe Yuan, Li Xi, Ke Xia, Sayeef Salahuddin, Bernard Dieny, Long You. Advanced Electronic Materials Volume 5, Issue 4 April 2019 (print version) 1800782 DOI: https://doi.org/10.1002/aelm.201800782 First published [online]: 30 January 2019 Note: there is another DOI, https://doi.org/10.1002/aelm.201970022 where you can have open access to Memristors: A Spin–Orbit‐Torque Memristive Device (Adv. Electron. Mater. 4/2019)

The paper published online in January 2019 is behind a paywall and the paper (almost the same title) published in April 2019 has a new DOI and is open access. Final note: I tried accessing the ‘free’ paper and opened up a free file for the artwork featuring the work from China on the back cover of the April 2019 of Advanced Electronic Materials.

Korea

Usually when I see the words transparency and flexibility, I expect to see graphene is one of the materials. That’s not the case for this paper (link to and citation for),

Transparent and flexible photonic artificial synapse with piezo-phototronic modulator: Versatile memory capability and higher order learning algorithm by Mohit Kumar, Joondong Kim, Ching-Ping Wong. Nano Energy Volume 63, September 2019, 103843 DOI: https://doi.org/10.1016/j.nanoen.2019.06.039 Available online 22 June 2019

Here’s the abstract for the paper where you’ll see that the material is made up of zinc oxide silver nanowires,

An artificial photonic synapse having tunable manifold synaptic response can be an essential step forward for the advancement of novel neuromorphic computing. In this work, we reported the development of highly transparent and flexible two-terminal ZnO/Ag-nanowires/PET photonic artificial synapse [emphasis mine]. The device shows purely photo-triggered all essential synaptic functions such as transition from short-to long-term plasticity, paired-pulse facilitation, and spike-timing-dependent plasticity, including in the versatile memory capability. Importantly, strain-induced piezo-phototronic effect within ZnO provides an additional degree of regulation to modulate all of the synaptic functions in multi-levels. The observed effect is quantitatively explained as a dynamic of photo-induced electron-hole trapping/detraining via the defect states such as oxygen vacancies. We revealed that the synaptic functions can be consolidated and converted by applied strain, which is not previously applied any of the reported synaptic devices. This study will open a new avenue to the scientific community to control and design highly transparent wearable neuromorphic computing.

This paper is behind a paywall.

Jiggly jell-o as a new hydrogen fuel catalyst

Jello [uploaded from https://www.organicauthority.com/eco-chic-table/new-jell-o-mold-jiggle-chic-holidays]

I’m quite intrigued by this ‘jell-o’ story. It’s hard to believe a childhood dessert might prove to have an application as a catalyst for producing hydrogen fuel. From a December 14, 2018 news item on Nanowerk,

A cheap and effective new catalyst developed by researchers at the University of California, Berkeley, can generate hydrogen fuel from water just as efficiently as platinum, currently the best — but also most expensive — water-splitting catalyst out there.

The catalyst, which is composed of nanometer-thin sheets of metal carbide, is manufactured using a self-assembly process that relies on a surprising ingredient: gelatin, the material that gives Jell-O its jiggle.

Two-dimensional metal carbides spark a reaction that splits water into oxygen and valuable hydrogen gas. Berkeley researchers have discovered an easy new recipe for cooking up these nanometer-thin sheets that is nearly as simple as making Jell-O from a box. (Xining Zang graphic, copyright Wiley)

A December 13, 2018 University of California at Berkeley (UC Berkeley) news release by Kara Manke (also on EurekAlert but published on Dec. 14, 2018), which originated the news item, provides more technical detail,

“Platinum is expensive, so it would be desirable to find other alternative materials to replace it,” said senior author Liwei Lin, professor of mechanical engineering at UC Berkeley. “We are actually using something similar to the Jell-O that you can eat as the foundation, and mixing it with some of the abundant earth elements to create an inexpensive new material for important catalytic reactions.”

The work appears in the Dec. 13 [2018] print edition of the journal Advanced Materials.

A zap of electricity can break apart the strong bonds that tie water molecules together, creating oxygen and hydrogen gas, the latter of which is an extremely valuable source of energy for powering hydrogen fuel cells. Hydrogen gas can also be used to help store energy from renewable yet intermittent energy sources like solar and wind power, which produce excess electricity when the sun shines or when the wind blows, but which go dormant on rainy or calm days.

A black and white image of metal carbide under high magnification.

When magnified, the two-dimensional metal carbides resemble sheets of cell[o]phane. (Xining Zang photo, copyright Wiley)

But simply sticking an electrode in a glass of water is an extremely inefficient method of generating hydrogen gas. For the past 20 years, scientists have been searching for catalysts that can speed up this reaction, making it practical for large-scale use.

“The traditional way of using water gas to generate hydrogen still dominates in industry. However, this method produces carbon dioxide as byproduct,” said first author Xining Zang, who conducted the research as a graduate student in mechanical engineering at UC Berkeley. “Electrocatalytic hydrogen generation is growing in the past decade, following the global demand to lower emissions. Developing a highly efficient and low-cost catalyst for electrohydrolysis will bring profound technical, economical and societal benefit.”

To create the catalyst, the researchers followed a recipe nearly as simple as making Jell-O from a box. They mixed gelatin and a metal ion — either molybdenum, tungsten or cobalt — with water, and then let the mixture dry.

“We believe that as gelatin dries, it self-assembles layer by layer,” Lin said. “The metal ion is carried by the gelatin, so when the gelatin self-assembles, your metal ion is also arranged into these flat layers, and these flat sheets are what give Jell-O its characteristic mirror-like surface.”

Heating the mixture to 600 degrees Celsius triggers the metal ion to react with the carbon atoms in the gelatin, forming large, nanometer-thin sheets of metal carbide. The unreacted gelatin burns away.

The researchers tested the efficiency of the catalysts by placing them in water and running an electric current through them. When stacked up against each other, molybdenum carbide split water the most efficiently, followed by tungsten carbide and then cobalt carbide, which didn’t form thin layers as well as the other two. Mixing molybdenum ions with a small amount of cobalt boosted the performance even more.

“It is possible that other forms of carbide may provide even better performance,” Lin said.

On the left, an illustration of blue spheres, representing gelatin molecules, arranged in a lattice shape. On the right, an illustration of thin sheets of metal carbide.

Molecules in gelatin naturally self-assemble in flat sheets, carrying the metal ions with them (left). Heating the mixture to 600 degrees Celsius burns off the gelatin, leaving nanometer-thin sheets of metal carbide. (Xining Zang illustration, copyright Wiley)

The two-dimensional shape of the catalyst is one of the reasons why it is so successful. That is because the water has to be in contact with the surface of the catalyst in order to do its job, and the large surface area of the sheets mean that the metal carbides are extremely efficient for their weight.

Because the recipe is so simple, it could easily be scaled up to produce large quantities of the catalyst, the researchers say.

“We found that the performance is very close to the best catalyst made of platinum and carbon, which is the gold standard in this area,” Lin said. “This means that we can replace the very expensive platinum with our material, which is made in a very scalable manufacturing process.”

Co-authors on the study are Lujie Yang, Buxuan Li and Minsong Wei of UC Berkeley, J. Nathan Hohman and Chenhui Zhu of Lawrence Berkeley National Lab; Wenshu Chen and Jiajun Gu of Shanghai Jiao Tong University; Xiaolong Zou and Jiaming Liang of the Shenzhen Institute; and Mohan Sanghasadasa of the U.S. Army RDECOM AMRDEC.

Here’s a link to and a citation for the paper,

Self‐Assembly of Large‐Area 2D Polycrystalline Transition Metal Carbides for Hydrogen Electrocatalysis by Xining Zang, Wenshu Chen, Xiaolong Zou, J. Nathan Hohman, Lujie Yang
Buxuan Li, Minsong Wei, Chenhui Zhu, Jiaming Liang, Mohan Sanghadasa, Jiajun Gu, Liwei Lin. Advanced Materials Volume30, Issue 50 December 13, 2018 1805188 DOI: https://doi.org/10.1002/adma.201805188 First published [online]: 09 October 2018

This paper is behind a paywall.

Chen Qiufan, garbage, and Chinese science fiction stories

Garbage has been dominating Canadian news headlines for a few weeks now. First, it was Canadian garbage in the Philippines and now it’s Canadian garbage in Malaysia. Interestingly, we’re also having problems with China, since December 2018, when we detained a top executive from Huawe, a China-based international telecommunicatons company, in accordance with an official request from the US government and, in accordance, with what Prime Minister Justin Trudeau calls the ‘rule of law’. All of this provides an interesting backdrop (for Canadians anyway) on the topic of China, garbage, and science fiction.

A May 16, 2019 article by Anjie Zheng for Fast Company explores some of the latest and greatest from China’s science fiction writing community,

Like any good millennial, I think about my smartphone, to the extent that I do at all, in terms of what it does for me. It lets me message friends, buy stuff quickly, and amass likes. I hardly ever think about what it actually is—a mass of copper wires, aluminum alloys, and lithium battery encased in glass—or where it goes when I upgrade.

Chen Qiufan wants us to think about that. His debut novel, Waste Tide, is set in a lightly fictionalized version of Guiyu, the world’s largest electronic waste disposal. First published in Chinese in 2013, the book was recently released in the U.S. with a very readable translation into English by Ken Liu.

Chen, who has been called “China’s William Gibson,” is part of a younger generation of sci-fi writers who have achieved international acclaim in recent years. Liu Cixin became the first Chinese to win the prestigious Hugo Award for his Three Body Problem in 2015. The Wandering Earth, based on a short story by Liu, became China’s first science-fiction blockbuster when it was released in 2018. It was the highest-grossing film in the fastest-growing film market in the world last year and was recently scooped up by Netflix.

Aynne Kokas in a March 13, 2019 article for the Washington Post describes how the hit film, The Wandering Earth, fits into an overall Chinese-led movie industry focused on the future and Hollywood-like, i. e. like US movie industry, domination,

“The Wandering Earth,” directed by Frant Gwo, takes place in a future where the people of Earth must flee their sun as it swells into a red giant. Thousands of engines — the first of them constructed in Hangzhou, one of China’s tech hubs — propel the entire planet toward a new solar system, while everyone takes refuge from the cold in massive underground cities. On the surface, the only visible reminders of the past are markers of China’s might. The Shanghai Tower, the Oriental Pearl Tower and a stadium for the Shanghai 2044 Olympics all thrust out of the ice, having apparently survived the journey’s tsunamis, deep freeze and cliff-collapsing earthquakes.

The movie is China’s first big-budget sci-fi epic, and its production was ambitious, involving some 7,000 workers and 10,000 specially-built props. Audience excitement was correspondingly huge: Nearly half a million people wrote reviews of the film on Chinese social network site Douban. Having earned over $600 million in domestic sales, “The Wandering Earth” marks a major achievement for the country’s film industry.

It is also a major achievement for the Chinese government.

Since opening up the country’s film market in 2001, the Chinese government has aspired to learn from Hollywood how to make commercially appealing films, as I detail in my book “Hollywood Made in China.” From initial private offerings for state media companies, to foreign investment in films, studios and theme parks, the government allowed outside capital and expertise to grow the domestic commercial film industry — but not at the expense of government oversight. This policy’s underlying aim was to expand China’s cultural clout and political influence.

Until recently, Hollywood films dominated the country’s growing box office. That finally changed in 2015, with the release of major local blockbusters “Monster Hunt” and “Lost in Hong Kong.” The proliferation of homegrown hits signaled that the Chinese box office profits no longer depend on Hollywood studio films — sending an important message to foreign trade negotiators and studios.

Kokas provides some insight into how the Chinese movie industry is designed to further the Chinese government’s vision of the future. As a Canadian, I don’t see that much difference between the US and China industry’s vision. Both tout themselves as the answer to everything, both target various geographic regions for the ‘bad guys’, and both tout their national moral superiority in their films. I suppose the same can be said for most countries’ film industries but both China and the US can back themselves with economic might.

Zheng’s article delves deeper into garbage, and Chen Qiufan’s science fiction while illuminating the process of changing a ‘good guy’ into a ‘bad guy’,

Chen, 37, grew up a few miles from the real Guiyu. Mountains of scrap electronics are shipped there every year from around the world. Thousands of human workers sort through the junk for whatever can be reduced to reusable precious metals. They strip wires and disassemble circuit boards, soaking them in acid baths for bits of copper, tin, platinum, and gold. Whatever can’t be processed is burned. The water in Guiyu has been so contaminated it is undrinkable; the air is toxic. The workers, migrants from poor rural areas in China, have an abnormally high rate of respiratory diseases and cancer.

For the decades China was revving its economic engine, authorities were content to turn a blind eye to the human costs of the recycling business. It was an economic win-win. For developed countries like the U.S., it’s cheaper to ship waste to places like China than trying to recycle it themselves. And these shipments create jobs and profits for the Chinese.

In recent years, however, steps have been taken to protect workers and the environment in China. …

Waste Tide highlights the danger of “throw-away culture,” says Chen, also known in English as Stanley Chan. When our personal electronics stop serving us, whether because they break or our lust for the newest specs get the better of us, we toss them. Hopefully we’re conscientious enough to bring them to local recyclers that claim they’ll dispose of them properly. But that’s likely the end of our engagement with the trash. Out of sight, out of mind.

Fiction, and science fiction in particular, is an apt medium for Chen to probe the consequences of this arrangement. “It’s not journalism,” he says. Instead, the story is an imaginative, action-packed tale of power imbalances, and the individual characters that think they’re doing good. Waste Tide culminates, expectedly, in an insurgency of the workers against their exploitative overlords.

Guiyu has been fictionalized in Waste Tide as “Silicon Isle.” (A homophone of the Chinese character “gui” translates to “Silicon,” and “yu” is an island). The waste hell is ruled by three ruthless family clans, dominated by the Luo clan. They treat workers as slaves and derisively call them “waste people.”

Technology in the near-future has literally become extensions of selves and only exacerbates class inequality. Prosthetic inner ears improve balance; prosthetic limbs respond to mental directives; helmets heighten natural senses. The rich “switch body parts as easily as people used to switch phones.” Those with fewer means hack discarded prosthetics to get the same kick. When they’re no longer needed, synthetic body parts contaminated with blood and bodily fluids are added to the detritus.

At the center of the story is Mimi, a migrant worker who dreams of earning enough money to return home and live a quiet life. She strikes up a relationship with Kaizong, a Chinese-American college graduate trying to rediscover his roots. But the good times are short-lived. The boss of the Luo clan becomes convinced that Mimi holds the key to rousing his son from his coma and soon kidnaps the hapless girl.

For all the advanced science, there is a backwards superstition that animates Silicon Isle. [emphasis mine] The clan bosses subscribe to “a simple form of animism.” They pray to the wind and sea for ample supplies of waste. They sacrifice animals (and some humans) to bring them luck, and use local witches to exorcise evil spirits. Boss Luo has Mimi kidnapped and tortured in an effort to appease the gods in the hopes of waking up his comatose son. The torture of Mimi infects her with a mysterious disease that splits her consciousness. The waste people are enraged by her violation, which eventually sparks a war against the ruling clans. [emphasis mine]

A parallel narrative involves an American, Scott Brandle, who works for an environmental company. While in town trying to set up a recycling facility, he stumbles onto the truth about the virus that may have infected Mimi: a chemical weapon developed and used by the U.S. [emphasis mine] years earlier. Invented by a Japanese researcher [emphasis mine] working in the U.S., the drug is capable of causing mass hallucinations and terror. When Brandle learns that Mimi may have been infected with this virus, he wants a piece of her [emphasis mine] too, so that scientists back home can study its effects.

Despite portraying the future of China in a less-than-positive light, [emphasis mine] Waste Tide has not been banned–a common result for works that displease Beijing; instead, the book won China’s prestigious Nebula award for science fiction, and is about to be reprinted on the mainland. …

An interview with Chen (it’s worthwhile to read his take on what he’s doing) follows the plot description in this intriguing and what seems to be a sometimes disingenuous article.

The animism and the war against the ruling class? It reminds me a little of the tales told about old Chine and Mao’s campaign to overthrow the ruling classes who had kept control of the proletariat, in part, by encouraging ‘superstitious religious belief’.

As far as I’m concerned the interpretation can go either or both ways: a critique of the current government’s policies and where they might lead in the future and/or a reference back to the glorious rising of China’s communist government. Good fiction always contains ambiguity; it’s what fuels courses in literature.

Also, the bad guys are from the US and Japan, countries which have long been allied with each other and with which China has some serious conflicts.

Interesting, non? And, it’s not that different from what you’ll see in US (or any other country’s for that matter) science fiction wiring and movies, except that the heroes are Chinese.

Getting back to the garbage in the Philippines, there are 69 containers on their way back to Canada as of May 30, 2019. As for why all this furor about Canadian garbage in the Philippines and Malaysia, it’s hard to believe that Canada is the only sinner. Of course, we are in China’s bad books due to the Huawei executive’s detention here (she is living in her home in Vancouver and goes out and about as she wishes, albeit under surveillance).

Anyway, I can’t help but wonder if indirect pressure is being exerted by China or if the Philippines and Malaysia have been incentivized in some way by China. The timing has certainly been interesting.

Political speculation aside, it’s probably a good thing that countries are refusing to take our garbage. As I’m sure more than one environmentalist would be happy to point out, it’s about time we took care of our own mess.

Two approaches to memristors

Within one day of each other in October 2018, two different teams working on memristors with applications to neuroprosthetics and neuromorphic computing (brainlike computing) announced their results.

Russian team

An October 15, 2018 (?) Lobachevsky University press release (also published on October 15, 2018 on EurekAlert) describes a new approach to memristors,

Biological neurons are coupled unidirectionally through a special junction called a synapse. An electrical signal is transmitted along a neuron after some biochemical reactions initiate a chemical release to activate an adjacent neuron. These junctions are crucial for cognitive functions, such as perception, learning and memory.

A group of researchers from Lobachevsky University in Nizhny Novgorod investigates the dynamics of an individual memristive device when it receives a neuron-like signal as well as the dynamics of a network of analog electronic neurons connected by means of a memristive device. According to Svetlana Gerasimova, junior researcher at the Physics and Technology Research Institute and at the Neurotechnology Department of Lobachevsky University, this system simulates the interaction between synaptically coupled brain neurons while the memristive device imitates a neuron axon.

A memristive device is a physical model of Chua’s [Dr. Leon Chua, University of California at Berkeley; see my May 9, 2008 posting for a brief description Dr. Chua’s theory] memristor, which is an electric circuit element capable of changing its resistance depending on the electric signal received at the input. The device based on a Au/ZrO2(Y)/TiN/Ti structure demonstrates reproducible bipolar switching between the low and high resistance states. Resistive switching is determined by the oxidation and reduction of segments of conducting channels (filaments) in the oxide film when voltage with different polarity is applied to it. In the context of the present work, the ability of a memristive device to change conductivity under the action of pulsed signals makes it an almost ideal electronic analog of a synapse.

Lobachevsky University scientists and engineers supported by the Russian Science Foundation (project No.16-19-00144) have experimentally implemented and theoretically described the synaptic connection of neuron-like generators using the memristive interface and investigated the characteristics of this connection.

“Each neuron is implemented in the form of a pulse signal generator based on the FitzHugh-Nagumo model. This model provides a qualitative description of the main neurons’ characteristics: the presence of the excitation threshold, the presence of excitable and self-oscillatory regimes with the possibility of a changeover. At the initial time moment, the master generator is in the self-oscillatory mode, the slave generator is in the excitable mode, and the memristive device is used as a synapse. The signal from the master generator is conveyed to the input of the memristive device, the signal from the output of the memristive device is transmitted to the input of the slave generator via the loading resistance. When the memristive device switches from a high resistance to a low resistance state, the connection between the two neuron-like generators is established. The master generator goes into the oscillatory mode and the signals of the generators are synchronized. Different signal modulation mode synchronizations were demonstrated for the Au/ZrO2(Y)/TiN/Ti memristive device,” – says Svetlana Gerasimova.

UNN researchers believe that the next important stage in the development of neuromorphic systems based on memristive devices is to apply such systems in neuroprosthetics. Memristive systems will provide a highly efficient imitation of synaptic connection due to the stochastic nature of the memristive phenomenon and can be used to increase the flexibility of the connections for neuroprosthetic purposes. Lobachevsky University scientists have vast experience in the development of neurohybrid systems. In particular, a series of experiments was performed with the aim of connecting the FitzHugh-Nagumo oscillator with a biological object, a rat brain hippocampal slice. The signal from the electronic neuron generator was transmitted through the optic fiber communication channel to the bipolar electrode which stimulated Schaffer collaterals (axons of pyramidal neurons in the CA3 field) in the hippocampal slices. “We are going to combine our efforts in the design of artificial neuromorphic systems and our experience of working with living cells to improve flexibility of prosthetics,” concludes S. Gerasimova.

The results of this research were presented at the 38th International Conference on Nonlinear Dynamics (Dynamics Days Europe) at Loughborough University (Great Britain).

This diagram illustrates an aspect of the work,

Caption: Schematic of electronic neurons coupling via a memristive device. Credit: Lobachevsky University

US team

The American Institute of Physics (AIP) announced the publication of a ‘memristor paper’ by a team from the University of Southern California (USC) in an October 16, 2018 news item on phys.org,

Just like their biological counterparts, hardware that mimics the neural circuitry of the brain requires building blocks that can adjust how they synapse, with some connections strengthening at the expense of others. One such approach, called memristors, uses current resistance to store this information. New work looks to overcome reliability issues in these devices by scaling memristors to the atomic level.

An October 16, 2018 AIP news release (also on EurekAlert), which originated the news item, delves further into the particulars of this particular piece of memristor research,

A group of researchers demonstrated a new type of compound synapse that can achieve synaptic weight programming and conduct vector-matrix multiplication with significant advances over the current state of the art. Publishing its work in the Journal of Applied Physics, from AIP Publishing, the group’s compound synapse is constructed with atomically thin boron nitride memristors running in parallel to ensure efficiency and accuracy.

The article appears in a special topic section of the journal devoted to “New Physics and Materials for Neuromorphic Computation,” which highlights new developments in physical and materials science research that hold promise for developing the very large-scale, integrated “neuromorphic” systems of tomorrow that will carry computation beyond the limitations of current semiconductors today.

“There’s a lot of interest in using new types of materials for memristors,” said Ivan Sanchez Esqueda, an author on the paper. “What we’re showing is that filamentary devices can work well for neuromorphic computing applications, when constructed in new clever ways.”

Current memristor technology suffers from a wide variation in how signals are stored and read across devices, both for different types of memristors as well as different runs of the same memristor. To overcome this, the researchers ran several memristors in parallel. The combined output can achieve accuracies up to five times those of conventional devices, an advantage that compounds as devices become more complex.

The choice to go to the subnanometer level, Sanchez said, was born out of an interest to keep all of these parallel memristors energy-efficient. An array of the group’s memristors were found to be 10,000 times more energy-efficient than memristors currently available.

“It turns out if you start to increase the number of devices in parallel, you can see large benefits in accuracy while still conserving power,” Sanchez said. Sanchez said the team next looks to further showcase the potential of the compound synapses by demonstrating their use completing increasingly complex tasks, such as image and pattern recognition.

Here’s an image illustrating the parallel artificial synapses,

Caption: Hardware that mimics the neural circuitry of the brain requires building blocks that can adjust how they synapse. One such approach, called memristors, uses current resistance to store this information. New work looks to overcome reliability issues in these devices by scaling memristors to the atomic level. Researchers demonstrated a new type of compound synapse that can achieve synaptic weight programming and conduct vector-matrix multiplication with significant advances over the current state of the art. They discuss their work in this week’s Journal of Applied Physics. This image shows a conceptual schematic of the 3D implementation of compound synapses constructed with boron nitride oxide (BNOx) binary memristors, and the crossbar array with compound BNOx synapses for neuromorphic computing applications. Credit: Ivan Sanchez Esqueda

Here’s a link to and a citation for the paper,

Efficient learning and crossbar operations with atomically-thin 2-D material compound synapses by Ivan Sanchez Esqueda, Huan Zhao and Han Wang. The article will appear in the Journal of Applied Physics Oct. 16, 2018 (DOI: 10.1063/1.5042468).

This paper is behind a paywall.

*Title corrected from ‘Two approaches to memristors featuring’ to ‘Two approaches to memristors’ on May 31, 2019 at 1455 hours PDT.

Unusual appetite for gold

This bacterium (bacteria being the plural) loves gold, which is lucky for anyone trying to develop artificial photosynthesis.From an October 9, 2018 news item on ScienceDaily,

A bacterium named Moorella thermoacetica won’t work for free. But UC Berkeley [University of California at Berkeley] researchers have figured out it has an appetite for gold. And in exchange for this special treat, the bacterium has revealed a more efficient path to producing solar fuels through artificial photosynthesis.

An October 5, 2018 UC Berkeley news release by Theresa Duque (also on EurekAlert but published on October 9, 2018), which originated the news item, expands on the theme,

M. thermoacetica first made its debut as the first non-photosensitive bacterium to carry out artificial photosynthesis (link is external) in a study led by Peidong Yang, a professor in UC Berkeley’s College of Chemistry. By attaching light-absorbing nanoparticles made of cadmium sulfide (CdS) to the bacterial membrane exterior, the researchers turned M. thermoacetica into a tiny photosynthesis machine, converting sunlight and carbon dioxide into useful chemicals.

Now Yang and his team of researchers have found a better way to entice this CO2-hungry bacterium into being even more productive. By placing light-absorbing gold nanoclusters inside the bacterium, they have created a biohybrid system that produces a higher yield of chemical products than previously demonstrated. The research, funded by the National Institutes of Health, was published on Oct. 1 in Nature Nanotechnology (link is external).

For the first hybrid model, M. thermoacetica-CdS, the researchers chose cadmium sulfide as the semiconductor for its ability to absorb visible light. But because cadmium sulfide is toxic to bacteria, the nanoparticles had to be attached to the cell membrane “extracellularly,” or outside the M. thermoacetica-CdS system. Sunlight excites each cadmium-sulfide nanoparticle into generating a charged particle known as an electron. As these light-generated electrons travel through the bacterium, they interact with multiple enzymes in a process known as “CO2 reduction,” triggering a cascade of reactions that eventually turns CO2 into acetate, a valuable chemical for making solar fuels.

But within the extracellular model, the electrons end up interacting with other chemicals that have no part in turning CO2 into acetate. And as a result, some electrons are lost and never reach the enzymes. So to improve what’s known as “quantum efficiency,” or the bacterium’s ability to produce acetate each time it gains an electron, the researchers found another semiconductor: nanoclusters made of 22 gold atoms (Au22), a material that M. thermoacetica took a surprising shine to.

A single nanocluster of 22 gold atoms

Figure: A single nanocluster of 22 gold atoms – Au22 – is only 1 nanometer in diameter, allowing it to easily slip through the bacterial cell wall.

“We selected Au22 because it’s ideal for absorbing visible light and has the potential for driving the CO2 reduction process, but we weren’t sure whether it would be compatible with the bacteria,” Yang said. “When we inspected them under the microscope, we discovered that the bacteria were loaded with these Au22 clusters – and were still happily alive.”

Imaging of the M. thermoacetica-Au22 system was done at UC Berkeley’s Molecular Imaging Center (link is external).

The researchers also selected Au22 ­– dubbed by the researchers as “magic” gold nanoclusters – for its ultrasmall size: A single Au22nanocluster is only 1 nanometer in diameter, allowing each nanocluster to easily slip through the bacterial cell wall.

“By feeding bacteria with Au22 nanoclusters, we’ve effectively streamlined the electron transfer process for the CO2 reduction pathway inside the bacteria, as evidenced by a 2.86 percent quantum efficiency – or 33 percent more acetate produced within the M. thermoacetica-Au22 system than the CdS model,” Yang said.

The magic gold nanocluster is the latest discovery coming out of Yang’s lab, which for the past six years has focused on using biohybrid nanostructures to convert CO2 into useful chemicals as part of an ongoing effort to find affordable, abundant resources for renewable fuels, and potential solutions to thwart the effects of climate change.

“Next, we’d like to find a way to reduce costs, improve the lifetimes for these biohybrid systems, and improve quantum efficiency,” Yang said. “By continuing to look at the fundamental aspect of how gold nanoclusters are being photoactivated, and by following the electron transfer process within the CO2 reduction pathway, we hope to find even better solutions.”

Co-authors with Yang are UC Berkeley graduate student Hao Zhang and former postdoctoral fellow Hao Liu, now at Donghua University in Shanghai, China.

Here’s a link to and a citation for the paper,

Bacteria photosensitized by intracellular gold nanoclusters for solar fuel production by Hao Zhang, Hao Liu, Zhiquan Tian, Dylan Lu, Yi Yu, Stefano Cestellos-Blanco, Kelsey K. Sakimoto, & Peidong Yang. Nature Nanotechnologyvolume 13, pages900–905 (2018). DOI: https://doi.org/10.1038/s41565-018-0267-z Published: 01 October 2018

This paper is behind a paywall.

For lovers of animation, the folks at UC Berkeley have produced this piece about the ‘gold-loving’ bacterium,