Page 970 – Physics World

Home » Page 970

Nanostructured semiconductors become superabsorbers

Nanostructuring a thin layer of the semiconductor germanium using a technique called nanoimprinting lithography can greatly boost the amount of light it absorbs across the visible to near-infrared wavelengths. The broadband absorption comes from the strong interplay between Brewster and photonic crystal modes in the material and the effect could benefit optoelectronics applications such as photovoltaics and telecommunications.

Designing ultrathin semiconducting materials that absorb light over a broad range of wavelengths is crucial for making improved optoelectronics devices that more efficiently convert light into active electrons. One way of achieving this is to increase the thickness of the semiconductor layer so that it can capture the maximum number of photons across the optical spectrum.

Researchers at the Institut de Ciència de Materials de Barcelona in Spain have taken a different approach to this one by employing different light-trapping strategies so that a reduced amount of semiconductor is still able to strongly absorb light. In the photonic metastructure they studied, incoming light is coupled to different types of light resonant modes: Brewster and hybrid photonic-plasmonic resonant modes. It is these resonances that are responsible for concentrating the light electric field in small volumes and so allow the material to absorb light over the visible to the NIR range (400–1500–nm).

Two effective thicknesses of germanium for light to interact with

A Brewster mode is a photonic mode in which there is no light reflected from the surface, explains team leader Agustin Mihi. “A thin layer of semiconductor, like the one we used in our study, on a noble metal substrate sustains this type of mode thanks to the high refractive index of the semiconductor and the non-ideal behaviour of noble metals in the visible part of the optical spectrum. In this mode, light is strongly confined in the thin film at wavelengths determined by its thickness.

“Because of the nanostructuring of the germanium (Ge) film in our sample, there are two effective thicknesses of Ge that light can interact with: the thinner one with the Brewster mode and the thicker one with the plasmonic-photonic mode.”

The metastructure made by the researchers comprises a Ge 2D square array of cylindrical holes built on top of a gold film using soft lithography – a scalable technique that has the advantage of being compatible with mass production processes such as roll to roll.

Metasurface exhibits a series of photonic resonances

“It is challenging to achieve broadband light absorption through photonic resonances alone because each resonance amplifying light absorption acts only over a specific wavelength range,” says Mihi. “In our experiments, we make a metasurface that exhibits a series of photonic resonances from the NIR to the visible, increasing the light absorption of the Ge layer at all energies above its electronic bandgap.”

The broadband absorption in fact comes from the simultaneous excitation of the different resonances throughout the entire absorption spectra of the Ge layer, he tells nanotechweb.org. “In the visible, our photonic architecture sustains a broad Fabry Perot resonance, which is enhanced by coupling with a Brewster mode, as mentioned. In the NIR, there are multiple absorption peaks coming from the plasmonic-photonic modes excited in the photonic crystal fabricated on top of the metal substrate.

Applications in photovoltaics and telecommunications

“The photonic crystal provides ways to couple the light in the in-plane direction of the ultrathin Ge film, allowing it to confine long wavelength photons (up to 1400 nm),” he adds. “We also carefully design the metasurface to couple this light to slow light modes, which combine photonic crystal and plasmonic effects, resulting in strong absorption peaks.”

Such strong broadband absorption could be useful for making more efficient photovoltaics devices and the NIR absorption in particular (which reaches 100% over the important telecommunications window) could benefit applications such as photodetectors, he says.

The team, reporting its work in Advanced Materials DOI: 10.1002/adma.201705876, is now busy designing different optoelectronics devices using its nanostructured Ge. “These include third-generation solar cells (based on perovskite materials). We hope to improve their efficiency and make them competitive with established silicon technology.”

Concentration of small air pollution particles has risen by more than one-third

Air pollution is a major global issue. In the city of London, for example, more than 9000 deaths each year are attributed to air pollution, with around 3500 of those associated with long-term exposure to PM_2.5. Now a study has shown that globally PM_2.5 concentrations have increased by more than one-third since 1960, and that the number of deaths attributable to long-term exposure to PM_2.5 has increased by nearly 90%.

Pollution particles are inhaled deep into the lungs, with smaller particles (PM_2.5) penetrating the furthest and having the most serious effect. Those exposed to higher levels of particulate pollution are more likely to suffer from respiratory and cardiovascular diseases, and have a shorter average life expectancy.

Today, nearly 90% of the global population lives in areas exceeding the World Health Organisation’s air-quality guidelines for annual mean PM_2.5. A number of studies have investigated the impact of present-day air pollution on health, but few have looked at how air pollution has affected health over the last few decades; a period where air quality changed rapidly.

To rectify this, Edward Butt from the University of Leeds, UK, and his colleagues used the HadGEM3-UKCA coupled chemistry-climate model, along with demographic and disease data, to estimate the changes in global and regional air pollution PM_2.5 and the attributable health burden over the period 1960 to 2009.

The team found that global mean population-weighted PM_2.5 concentrations increased by 38%, dominated by increases in China and India. The global attributable deaths from particulate pollution, meanwhile, rose by 89% to 124% over the same period, again dominated by large increases in China and India. These large increases were not only a result of regional growth in particulate air pollution levels, but were heavily influenced by rapid population growth and ageing.

“These changes resulted in significant increases in attributable deaths in China and India year-on-year because more people were being exposed to high levels of air pollution, which is further exacerbated by an ageing population, who are more vulnerable to the effects of particulate air pollution,” said Butt.

In contrast, the study showed that air-quality regulation and emission controls in Europe and the US reduced air pollution PM_2.5 concentrations over the same time period. There was a significant drop in the number of attributable deaths – by 65.7% for Europe and 47.9% in the US. In 1960 the US and Europe accounted for 27% of the global attributable deaths; this fell to around 1% by 2009.

Butt and his colleagues hope that understanding the changes in particulate air pollution deaths over the past few decades can help policy makers make sound decisions on future air quality policy. They also note that projected demographic changes in Asia will pose a challenge for policy makers aiming to reduce the total number of deaths due to particulate air pollution in the near future.

The team reported the findings in Environmental Research Letters (ERL).

How well did subsidies for solar panels on US homes work?

Have subsidies for domestic solar panels installed in the US been worthwhile? To find out, researchers analyzed data for 540,000 systems with a total installed capacity of 6 GW.

“We hope that the study will give policymakers, utilities and solar businesses the ability to fine-tune their offers so that the costs of PV [photovoltaics] more closely match its benefits,” Parth Vaishnav and colleagues Nathaniel Horner and Inês Azevedo of Carnegie Mellon University told environmentalresearchweb. “We’d also like to highlight the geographical variation that exists in the costs of systems and the benefits they produce.”

It’s estimated that 2.5 GW of distributed PV installations were added across the US in 2015, followed by another 3.4 GW in 2016. Driving this capacity growth is a reduction in system prices, plus a range of federal, state and local subsidies as well as net metering programmes offered by some utility providers.

Looking at the financial benefits, data from 2014 point to a much wider range of the population receiving incentives for adopting rooftop solar than back in 2006. But the study concludes that PV subsidies still flow disproportionately to areas with higher incomes.

Other observations include the importance of generous net metering policies for the financial viability of rooftop systems. In US states where customers can sell excess power to the grid at retail prices, the private benefits of solar PV typically exceed private costs. However, if marginal pricing is applied, then customers need to be in locations with abundant sunshine such as California, Nevada or Texas to make the numbers add up. But that’s not the only factor, as the calculation is also sensitive to the financing terms of purchasing a rooftop system – even in sunny states.

While the study estimates that the total upfront subsidy per kilowatt of installed capacity has fallen from, on average, $5200 in 2006 to $1400 in 2014, the absolute magnitude has soared as the number of rooftop systems in operation has rocketed. This public investment has helped to grow jobs – the number of installers in the dataset rose from 514 in 2006 to 2900 in 2015 – as well as stimulate a regulatory environment for firms to operate in.

The scientists touch on other plus points too, adding that the increase in installed capacity also contributes to understanding how best to integrate distributed PV into the electric grid.

However, when considering the public benefit in terms of pollution cuts, such as avoided carbon dioxide emissions and improvements in air quality, the group recognizes the difficulty in determining appropriate monetary values. As a result, the researchers caution against defining public benefits too narrowly.

Renewable energy sources such as solar and wind have a crucial role to play in reaching climate goals, and success will be felt on a global scale. It follows that the benefits of technologies such as rooftop solar PV need to be priced accordingly.

The team reported their work in Environmental Research Letters (ERL).

Intel unveils 49-qubit superconducting chip

Intel has announced the design and fabrication of a 49-qubit superconducting quantum-processor chip at the Consumer Electronics Show in Las Vegas. Speaking at the conference, Intel chief executive Brian Krzanich introduced “Tangle Lake”; a quantum-processor chip that operates at extremely low temperatures. The device takes its name from the Tangle Lakes, a frigid chain of lakes in Alaska, and is a nod to quantum entanglement.

Tangle Lake is designed to store and process quantum information in qubits that are superconducting circuits. Krzanich said that the chip is an important step towards developing quantum computers that could quickly solve mathematical problems involved in some of society’s most pressing issues – from drug development to climate forecasting.

Large-scale integration

He also announced progress in Intel’s research on spin qubits, which have qubits based on the spin states of single electrons. While superconducting chips tend to be relatively large, the spin-qubits could be miniaturized using well-established silicon-chip fabrication processes. This means that it may be possible to manufacture quantum processors containing large numbers of spin qubits. This large-scale integration would be could be more difficult for superconducting qubits.

However, there is some scepticism in the physics community regarding Intel’s silence about the performance and quality specifications of Tangle Lake and their spin qubit chips. Intel is also facing fierce competition. IBM has itself announced quantum computers with 20 and 50 superconducting qubits in recent months, and companies including Google and Rigetti are also securing footholds in the nascent market.

Commercial quest

“In the quest to deliver a commercially viable quantum computing system, it’s anyone’s game,” confesses Mike Mayberry, managing director at Intel Labs. “We expect it will be five to seven years before the industry gets to tackling engineering-scale problems, and it will likely require one million or more qubits to achieve commercial relevance.”

X-ray ‘GPS’ unveiled by NASA

A GPS-like navigation system for spacecraft that uses X-ray signals from pulsars could soon be a reality because of an experiment done on the International Space Station (ISS). NASA engineers have shown that the ISS-based SEXTANT system can use signals from four pulsars to determine the location of the ISS to within 15 km. A pulsar-based navigation system would make it much easier for spacecraft to travel throughout the solar system, and beyond – according to NASA.

SEXTANT makes use of the NICER X-ray telescope. NICER was installed on the ISS in June 2017 and is designed to probe the interior of X-ray pulsars, which are spinning neutron stars that emit X-rays. This is done by making very precise measurements of the energy of the X-rays as well as the frequency of the pulses – which typically fall between 1 and 800 Hz.

Concentrating X-rays

NICER is an array of 52 X-ray concentrators – each a set of concentric cylindrical mirrors – that focus incoming X-rays on to silicon-drift detectors. These detectors record the energy and arrival times of individual X-ray photons from distant neutron stars.

The SEXTANT measurement was done over the course of two days using four pulsars with millisecond periods. The arrival times of the pulses are measured to within 300 ns and by comparing the arrival times of pulses from the four different sources, Sextant was able to track the position of the ISS as it travelled around Earth at nearly 28,000 km/h. The spatial resolution of the system is about 15 km, but NASA’s Jason Mitchell says this could be reduced to about 100 m in deep space.

Beyond the solar system

According to NASA, a future spacecraft could use pulsars to navigate deep space autonomously without having to communicate with Earth to workout its position. “This successful demonstration firmly establishes the viability of X-ray pulsar navigation as a new autonomous navigation capability,” says Mitchell. We have shown that a mature version of this technology could enhance deep-space exploration anywhere within the solar system and beyond.”

Following on from this early success, the SEXTANT team is updating on-board and ground-based software for a second test later this year.

Stem cell exosomes repair cartilage damage

Researchers in Singapore have investigated the use of mesenchymal stem cell (MSC) exosomes to improve cartilage regeneration. They observed an increase in cartilage cell proliferation and infiltration, enhanced matrix synthesis, and an immunologic response matching with an appropriate healing mechanism (Biomaterials 156 16).

Cartilage repair is a challenging issue due to the poor intrinsic regenerative capacity of cartilage and the fibrous tissue formation (fibroblast proliferation) that results from injury. MSC therapy has shown great promise in addressing both of these problems. However, several papers have reported that the beneficial effects of MSC rely on a paracrine secretion mechanism (in which cells synthesize molecules that they then secrete), rather than MSC differentiation into cartilage cells (chondrocytes), as first hypothesized.

Among these secreted paracrine factors, increasing attention has been given to extracellular vesicles, particularly the exosomes. Endogenously formed by almost every cell, exosomes are a type of extracellular vesicle that play an important role in cell-to-cell communication. Exosomes contain complex cargo components including proteins, RNA, microRNA, DNA and lipids. MSC exosomes are postulated to be the mediator of MSCs in tissue repair as they deliver biomolecules with immunomodulatory and regenerative capacity.

Wei Seong Toh and his team at the National University of Singapore reported the mechanism underlying exosome-mediated cartilage regeneration of a damaged femur in rats with functional immune systems. The regeneration process is composed of multiple aspects, each of which was studied by the researchers. They reported encouraging results for both the gross appearance and histological analysis using this treatment compared with the control, phosphate buffered saline solution.

Chondrocyte proliferation

Following injection of the MSC exosomes, the chondrocytes rapidly transported the exosomes into the cell, where they localized in the cytoplasm. Chondrocyte proliferation, metabolism and migration were enhanced in a dose-dependent manner.

Experiment design and exosomes uptake (click to zoom)

Exosome treatment also increased cartilage extracellular matrix (ECM) components: collagen type II and sulphated glycosaminoglycan (s-GAG), indicating an enhanced matrix synthesis. This finding, combined with the increased expression of mRNA levels of cartilage matrix protein (COMP) and chondrogenic factor TGF-β1, confirms the capacity of those exosomes to maintain the chondrocyte phenotype, for an optimal cartilage healing.

Favourable immune response

Immune response is an important aspect in the regeneration process. Macrophages (white blood cells) play key roles in healing. M1 macrophages exhibit an inflammatory response, which jeopardizes the healing process, while M2 macrophages are associated to anti-inflammatory response. In this study, the team observed an increase of M2 macrophages and a decrease of M1 macrophages in both cartilage and synovial tissues (connective tissue between the cartilage and tendon), suggesting that healing is promoted by restraining inflammation.

M1 and M2 macrophages in cartilage and synovium

This multi-parameter study confirms the potential of MSC exosomes for cartilage regeneration and suggests great promise for this clinical application, which is also under consideration for treatment of other disorders.

Graphene makes good VUV photodetector

New generation semiconductor-based vacuum-ultraviolet (VUV) detectors that replace traditional heavy and energy-hungry microchannel detection systems could be used to better study how stars form and evolve. Making such detectors is proving to be no easy task, but a novel heterojunction device based on highly-crystalline, multi-step epitaxially-grown aluminium nitride (AlN) and p-type graphene shows promise here. The new detector has an encouraging VUV photoresponse and high external quantum efficiency (EQE). It is also extremely fast with a response time of just 80 nm, which makes it 10⁴ to 10⁶ times faster than current VUV photoconductive devices.

VUV photodetectors work in the 10–200 nm wavelength range and are widely employed in cosmic chemistry and space science – for example, to study how nebulas expand and to monitor solar storms. Today, satellites and spacecraft mainly carry violet chromatographs and microchannel plates. These are not only heavy, and so contribute to increased launch costs, but they are also power-hungry and require thousands of volts to operate.

Researchers have made much progress in developing photoconductive-type VUV photodetectors in recent years, but photovoltaic-type ones would be better, since they require zero power. Their charge signals also linearly increase with light intensity and they are fast and highly sensitive. The problem here, however, is that good transparent electrode materials for use in such detectors that allow VUV light to pass through unheeded are still lacking.

A new heterojunction device based on p-type graphene, which, according to new work by researchers in China, transmits up to 96% of VUV light, represents a breakthrough for this type of detector. It consists of a highly-crystalline AlN film, which acts as the VUV absorbing layer for photogenerated charge carriers, covered with p-type graphene as the transport electrode that collects excited holes.

Studying ultrafast dynamic celestial processes

The team, led by Feng Huang of the School of Materials at Sun Yat-Sen University in Guangzhou found that when illuminated with 180 nm VUV light, the device forms a 1.7 V open-circuit voltage and (in the absence of bias) produces a photocurrent with a high EQE of over 42%. This high value comes thanks to graphene’s high charge mobility and the fact that it collects holes with high efficiency, say the researchers. And that is not all: under nanosecond VUV pulse irradiation its response time is only 80 ns, which is 10⁴ to 10⁶ times faster than that of existing photoconductive-type VUV devices. Such high speed could come in useful for studying ultrafast dynamic celestial processes – for example, to determine the chemical composition of coronal jets in a solar storm, says Huang.

“The new VUV-light-detecting device, being much lighter than existing detectors, could also help lower launch costs of the spacecraft carrying it,” he tells nanotechweb.org.

The detector is described in ACS Nano DOI: 10.1021/acsnano.7b06633.

UC Davis group reports progress on total-body PET/CT

Researchers at the University of California, Davis (UC Davis) report continued progress on their development of a total-body PET/CT scanner designed to image patients in less than one minute, in an article in the January issue of the Journal of Nuclear Medicine (J. Nucl. Med. 59 3).

The key component of the work-in-progress Explorer is the half-million PET detectors that line the entire PET camera bore. That additional capacity is designed to result in much less radiation dose for a patient because the device would capture almost all available signal from a radiotracer. The CT scan is acquired as the patient moves into the PET scanner.

Explorer will have “the ability to detect throughout the whole body the location of focal pathologies, including cancer, infection, and inflammation at considerably lower levels of disease activity than is currently possible,” said study co-author and co-developer Terry Jones, a clinical professor of diagnostic radiology at UC Davis, in a press statement.

The journey to create Explorer was buoyed in October 2015 by a five-year, $15.5 million grant from the US National Institutes of Health (NIH). In addition, United Imaging Healthcare America, a North American subsidiary of Shanghai United Imaging Healthcare, and SensL Technologies of Cork, Ireland, joined the Explorer project in January 2017.

By reducing total-body scan time to less than one minute, the PET/CT device would be particularly beneficial for imaging paediatric patients without anaesthesia or sedation, as well as adult patients who cannot withstand prolonged scanning. Explorer is also expected to help with the development of new therapeutic agents.

“The applications of nuclear medicine will expand considerably across internal medicine … and will become more evenly distributed across the age spectrum,” Jones said. “There will be a considerable stimulus/investment to develop new imaging biomarkers especially within immunology and endocrinology.”

The Explorer team is expected to test the technology soon with a scaled-down prototype to perform total-body PET imaging on nonhuman primates.

This article was originally published on AuntMinnie.com.
© 2018 by AuntMinnie.com. Any copying, republication or redistribution of AuntMinnie.com content is expressly prohibited without the prior written consent of AuntMinnie.com.

New satellites set to eye up Earth’s ice and water

It is essential that scientists closely track ongoing changes in Earth’s cryosphere, including the surface area covered by ice, which is both affected by climate change and contributes to it. Two previous satellite observation missions will be succeeded and significantly upgraded in 2018, NASA reported at the American Geophysical Union (AGU) meeting in New Orleans in December.

NASA plans to launch ICESat-2 (Ice, Cloud, and Land Elevation Satellite-2) into polar orbit in September 2018. Its multibeam micro pulse laser will fire 5000 times every half second, taking 30,000 measurements over a surface distance of around three kilometres.

Its predecessor, ICESat, was launched in 2003 and operated until early 2010 with but one objective: to quantify contributions to sea-level change by melting from the Antarctic and Greenland ice sheets. It discovered that most of “the action” is on the sloped glaciers around the margins of those ice sheets, said Thorsten Markus of NASA’s Goddard Space Flight Center. Markus is the new mission’s project scientist.

“We need to do better than what ICESat-1 was able to do,” Markus said at the AGU meeting. ICESat-2 will also quantify regional signatures of ice-sheet changes, to help improve predictive ice-sheet models.

ICESat-2 has an additional new objective – to estimate the thickness of Arctic sea-ice, which has been declining. Thirty years of satellite data have provided a good understanding of the decreasing surface area of the ice, Markus said, but we do not have an adequate understanding of its thickness.

The second 2018 mission is the GRACE-FO, scheduled for launch in the spring, with first data release in June. GRACE-FO (Gravity Recovery and Climate Experiment Follow-On) is a pair of satellites produced jointly by NASA’s Jet Propulsion Laboratory (JPL), and the German Research Centre for Geosciences (GFZ), with participation by Deutsches Zentrum für Luft und Raumfahrt (DLR), the German Aerospace Center.

The original GRACE satellites functioned from 2002 to 2017, flying in tandem polar orbit 220 km apart and racking up scores of discoveries about Earth’s water cycle. The new version, crammed with more sophisticated equipment, will, like its predecessor, measure gravity changes alone to determine such factors as aquifer depletion, the impact of seismic activity, and changes in deep ocean currents, as well as water storage globally.

There is no direct measurement to the ground, only between the satellites. A microwave ranging instrument will constantly assess variations in their distance of just a few nanometres—the size of a large virus—said Felix Landerer of JPL, GRACE-FO deputy project scientist, at AGU.

“We’re very excited about these missions,” Landerer said. “I think the great thing is also that these are going to fly together concurrently and it’s really the combination of these multiple observations, these multiple angles that we have on the ice sheets, on our water cycle, that will enable us to track the health, the status of Earth’s ice…and Earth’s water cycle as it evolves and quite dramatically changes in these decades.”

The man behind the machine

Photograph of a young Alan Turing — Enigmatic. (Courtesy: REX/Shutterstock)

As a practising computer scientist, I thought I had a fairly good grasp of Alan Turing’s many contributions to the field. But The Turing Guide, by Jack Copeland, Jonathan Bowen, Mark Sprevak and Robin Wilson, has opened up a universe of Turing’s other pursuits I knew nothing about, inflating my admiration for him and his work by several orders of magnitude. I doubt that there exists a more complete book about Turing’s life and work – 33 contributing authors explore every biographical, historical, theoretical and practical aspect one could possibly wish for, in a thorough rendering and analysis of one man’s extraordinary life. Weighing in at a mere 1.24 kg, this tome does justice not only to Turing’s impact on the evolution of computing and the defeat of the Axis powers in the Second World War, but also to the wide-ranging and deep thought that characterized Turing’s approach to pretty much everything.

The writing of this book is a story in itself – the scale of the project and its reach are testament to the zeal of its authors and their determination to leave no aspect unaccounted for. But reading this eight-part book is a project as well, as you work your way through 42 chapters. (I couldn’t help but immediately think of Douglas Adams’ The Hitchhiker’s Guide to the Galaxy, where the number 42 is “the answer to the ultimate question of life, the universe and everything”, as calculated by the ultimate supercomputer, called Deep Thought.) In fact, it is not surprising that Turing’s life and influence could not be captured in anything less than that.

For readers daunted by the size of this book, the first chapter on “Life and work” contains an extraordinarily detailed timeline of key milestones in Turing’s life, which is a real eye-opener. In a few pages, we learn of Turing’s early accomplishments; his wide-ranging intellectual contributions including the concepts of the universal computing machine (“Turing machine”) and artificial intelligence, mechanical code-breaking strategies and tactics; complexity theory; practical computer design; computational biology and even artificial life. Turing also developed innovative computational mathematics – such as computing the Riemann zeta function, Mersenne primes and L/U (Lower/Upper) methods for solving matrix equations. In addition, he explored ideas for using software to check other software (verification methods) and evolutionary algorithms.

The book details as well the many giants of computing and mathematics whom Turing worked with over the course of his career, including Claude Shannon, John von Neumann, Alonzo Church, Ludwig Wittgenstein and Maxwell Newman among many others. The diversity of these interactions serves to underscore the remarkable range of Turing’s interests and, more importantly, his capacity to make (sometimes truly seminal) contributions in so many areas.

British philosopher Jack Copeland – who has written seven other books on Turing, and is the primary author of this one – offers an important summary of Turing’s work on the theoretical universal computing machine. Copeland also describes Turing’s time at Bletchley Park, where he wrestled with the decryption of German and Japanese encryption algorithms and devices. A strong case is made that Turing’s work on universal computing and stored-program concepts predates the work done by other giants in the field, including Konrad Zuse and Von Neumann. Copeland also explores the details of how Turing’s pursuit of his universal computing machine emerged from his attack on German mathematician David Hilbert’s Entscheidungsproblem or the “decision problem”. In a later chapter, titled “Decidability and the Entscheidungsproblem”, computer scientist Robin Whitty from Queen Mary University of London, provides a fully accessible explanation of the Turing Machine and its function.

Brian Randell, emeritus professor of computing science at Newcastle University, takes us on a journey of discovery in his chapter on “Turing and the origins of digital computers”. Randell takes us back in time to 1873, as he discusses the earliest foundations of “automatic calculating engines” with the work done by Charles Babbage and Ada Lovelace, before moving forward to the period of the 1940s, as he talks about the development of early computing systems such as ENIAC, EDVAC and the Manchester “Baby” machine. In subsequent chapters, we learn more of the details of the work Turing and others undertook at Bletchley and the breaking of German cryptographic codes.

Along with the many chapters on his research, the book also presents a comprehensive view of Turing as a human being, and not only an icon of brilliance. This is particularly well illustrated in two chapters: one is penned by his nephew John Dermot Turing, titled “The man with the terrible trousers”, and the other – “Meeting a genius” – by his Bletchley Park colleague Peter Hilton. Turing is portrayed as a warm and approachable person, far less concerned with sartorial appearances and far more interested in diverse intellectual concepts. He was also eager to help others understand his ideas. In Hilton’s words “he was a fundamentally serious person, but never unduly severe”. One thing characteristic of Turing’s approach to new areas was to start from first principles and not with the assumptions made by or conclusions reached by others. This tactic surely contributed to the originality of so much of his work.

The Turing Guide does not shy away from the painful consequences of his sexual orientation – Turing was gay and in the mid-20th century this was a crime in the UK. Copeland elaborates on the sequence of events leading up to Turing’s conviction and sentence to be “treated” chemically for his “condition”. Turing died of cyanide poisoning and his death was officially ruled to be suicide, but Copeland makes a very strong case that Turing’s state of mind in the weeks prior to his death was not consistent with such a conclusion. I now believe, despite the conventional wisdom and official pronouncement, that Turing’s death was in fact accidental.

It is nearly impossible to do justice to the monumental content of this book in a short review. Turing’s ideas for artificial intelligence, neural networks, computer music, computer chess and morphogenesis all receive attention. There is an unexpected chapter on Turing’s interest and belief in parapsychology and extrasensory perception. Turing evidently believed that there was clear statistical evidence of the ability of one person to receive information from another purely through the mind. My reaction to this is that perhaps someone as brilliant as Turing should have the freedom to hold some quirky views!

The book continues with an exploration of the proposition that the universe is computing itself and finishes with “Turing’s legacy” by Jonathan Bowen, who is emeritus professor of computing at London Southbank University, and Copeland. The duo present a succinct summary of the hundreds of pages that precede this section, detailing the many ways in which Turing has touched our society, in what is a well-researched and catalogued final section. A towering figure in the history of computing, but also in history itself, we come to know Turing with a completeness unattained by any preceding work.