Lifeboat Foundation

Scientists develop an energy-efficient strategy to reversibly change ‘spin orientation’ or magnetization direction in magnetite at room temperature.

Over the last few decades, conventional electronics has been rapidly reaching its technical limits in computing and information technology, calling for innovative devices that go beyond the mere manipulation of electron current. In this regard, spintronics, the study of devices that exploit the “spin” of electrons to perform functions, is one of the hottest areas in applied physics. But, measuring, altering, and, in general, working with this fundamental quantum property is no mean feat.

Current spintronic devices — for example, magnetic tunnel junctions — suffer from limitations such as high-power consumption, low operating temperatures, and severe constraints in material selection. To this end, a team of scientists at Tokyo University of Science and the National Institute for Materials Science (NIMS), Japan, has published a study in ACS Nano, in which they present a surprisingly simple yet efficient strategy to manipulate the magnetization angle in magnetite (Fe₃O₄), a typical ferromagnetic material.

Advanced uses of time in image rendering and reconstruction have been the focus of much scientific research in recent years. The motivation comes from the equivalence between space and time given by the finite speed of light c. This equivalence leads to correlations between the time evolution of electromagnetic fields at different points in space. Applications exploiting such correlations, known as time-of-flight (ToF)¹ and light-in-flight (LiF)² cameras, operate at various regimes from radio^3,4 to optical⁵ frequencies. Time-of-flight imaging focuses on reconstructing a scene by measuring delayed stimulus responses via continuous wave, impulses or pseudo-random binary sequence (PRBS) codes¹. Light-in-flight imaging, also known as transient imaging⁶, explores light transport and detection^2,7. The combination of ToF and LiF has recently yielded higher accuracy and detail to the reconstruction process, especially in non-line-of-sight images with the inclusion of higher-order scattering and physical processes such as Rayleigh–Sommerfeld diffraction⁸ in the modeling. However, these methods require experimental characterization of the scene followed by large computational overheads that produce images at low frame rates in the optical regime. In the radio-frequency (RF) regime, 3D images at frame rates of 30 Hz have been produced with an array of 256 wide-band transceivers³. Microwave imaging has the additional capability of sensing through optically opaque media such as walls. Nonetheless, synthetic aperture radar reconstruction algorithms such as the one proposed in ref. ³ required each transceiver in the array to operate individually thus leaving room for improvements in image frame rates from continuous transmit-receive captures. Constructions using beamforming have similar challenges⁹ where a narrow focused beam scans a scene using an array of antennas and frequency modulated continuous wave (FMCW) techniques.

In this article, we develop an inverse light transport model¹⁰ for microwave signals. The model uses a spatiotemporal mask generated by multiple sources, each emitting different PRBS codes, and a single detector, all operating in continuous synchronous transmit-receive mode. This model allows image reconstructions with capture times of the order of microseconds and no prior scene knowledge. For first-order reflections, the algorithm reduces to a single dot product between the reconstruction matrix and captured signal, and can be executed in a few milliseconds. We demonstrate this algorithm through simulations and measurements performed using realistic scenes in a laboratory setting. We then use the second-order terms of the light transport model to reconstruct scene details not captured by the first-order terms.

We start by estimating the information capacity of the scene and develop the light transport equation for the transient imaging model with arguments borrowed from basic information and electromagnetic field theory. Next, we describe the image reconstruction algorithm as a series of approximations corresponding to multiple scatterings of the spatiotemporal illumination matrix. Specifically, we show that in the first-order approximation, the value of each pixel is the dot product between the captured time series and a unique time signature generated by the spatiotemporal electromagnetic field mask. Next, we show how the second-order approximation generates hidden features not accessible in the first-order image. Finally, we apply the reconstruction algorithm to simulated and experimental data and discuss the performance, strengths, and limitations of this technique.

And they say computers can’t create art.

In 1642, famous Dutch painter Rembrandt van Rijn completed a large painting called Militia Company of District II under the Command of Captain Frans Banninck Cocq — today, the painting is commonly referred to as The Night Watch. It was the height of the Dutch Golden Age, and The Night Watch brilliantly showcased that.

The painting measured 363 cm × 437 cm (11.91 ft × 14.34 ft) — so big that the characters in it were almost life-sized, but that’s only the start of what makes it so special. Rembrandt made dramatic use of light and shadow and also created the perception of motion in what would normally be a stationary military group portrait. Unfortunately, though, the painting was trimmed in 1715 to fit between two doors at Amsterdam City Hall.

Continue reading “An AI algorithm just completed a famous Rembrandt painting” »

Photo: Stark Ackerman.

To understand how the clones can create millions of copies of themselves and yet remain functional, Oldroyd and his team compared the genomes of Cape honeybee workers with those of their queen and her offspring.

After forcing the Cape queen to reproduce asexually by fitting her with surgical tape that prevented her from mating, the team examined certain DNA sequences of both the Cape queen and the 25 larvae she produced. Then, they did the same for four Cape honeybee workers and their 63 larvae.

The team discovered that the asexually reproduced offspring of the queen had levels of recombination (DNA mixing) 100 times greater than the genetically identical cloned offspring of the workers — a finding that suggests the Cape worker bees have evolved a mutation that prevents recombination. Without the risk of a one-third loss of genetic material caused by the asexual reshuffling process, the workers are free to continually create perfect copies of themselves.

Genome-embedded ribonucleotides arrest replicative DNA polymerases (Pols) and cause DNA breaks. Whether mammalian DNA repair Pols efficiently use template ribonucleotides and promote RNA-templated DNA repair synthesis remains unknown. We find that human Polθ reverse transcribes RNA, similar to retroviral reverse transcriptases (RTs). Polθ exhibits a significantly higher velocity and fidelity of deoxyribonucleotide incorporation on RNA versus DNA. The 3.2-Å crystal structure of Polθ on a DNA/RNA primer-template with bound deoxyribonucleotide reveals that the enzyme undergoes a major structural transformation within the thumb subdomain to accommodate A-form DNA/RNA and forms multiple hydrogen bonds with template ribose 2′-hydroxyl groups like retroviral RTs. Last, we find that Polθ promotes RNA-templated DNA repair in mammalian cells. These findings suggest that Polθ was selected to accommodate template ribonucleotides during DNA repair.

Polymerase θ (Polθ) is a unique DNA polymerase-helicase fusion protein in higher eukaryotes whose A-family polymerase domain evolved from Pol I enzymes (Fig. 1A) (1, 2). However, contrary to most Pol I enzymes, Polθ is highly error-prone and promiscuous (3–6), performs translesion synthesis (TLS) opposite DNA lesions (3, 7, 8), and facilitates microhomology-mediated end-joining (MMEJ) of double-strand breaks (DSBs) by extending partially base-paired 3′ single-stranded DNA (ssDNA) overhangs at DSB repair junctions (5, 9–12). Polθ is not expressed in most tissues but is highly expressed in many cancer cells, which corresponds to a poor clinical outcome (13, 14). Furthermore, Polθ confers resistance to genotoxic cancer therapies and promotes the survival of cells deficient in DNA damage response pathways (11, 13–16). Thus, Polθ represents a promising cancer drug target.

Intriguingly, Polθ has an inactive proofreading domain due to acquired mutations (Fig. 1A) (2). Inactivating the 3′-5′ proofreading function of closely related A-family bacterial Pol I Klenow fragment (KF) enables this polymerase to reverse transcribe RNA like retroviral reverse transcriptases (RTs), which lack proofreading activity (fig. S1A) (17, 18). Because Polθ is highly error-prone and promiscuous and contains an inactive proofreading domain, we hypothesized that it has RNA-dependent DNA synthesis activity. Given that ribonucleotides are the most frequently occurring nucleotide lesion in genomic DNA that arrest replicative Pols and cause DNA breaks (19, 20), we also envisaged that Polθ would tolerate template ribonucleotides during its DNA repair activities and thus promote RNA-templated DNA repair synthesis (RNA-DNA repair). Although RNA-DNA repair mechanisms have been demonstrated in genetically engineered yeast cells (21, 22), they remain obscure in mammalian cells.

## GENERAL FUSION (VANCOUVER) • JUN 16, 2021.

# General Fusion to build its Fusion Demonstration Plant in the UK, at the UKAEA Culham Campus.

*Unlike conventional nuclear power, which involves fission or splitting atoms, the emerging fusion technology promises clean energy where the only emission would be helium, and importantly, no radioactive waste.*

Continue reading “General Fusion to build its Fusion Demonstration Plant in the UK, at the UKAEA Culham Campus” »

## FUTURE TENSE RN ABC (AUDIO 29 MIN) • JUN 27, 2021.

# Some foresight about.
the future of foresight.

*Trying to predict the future is a timeless and time-consuming pursuit.*

Continue reading “Some foresight about the future of foresight” »

Fusion energy has the potential to supply safe, clean, and nearly limitless power. Although fusion reactions can occur for light nuclei weighting less than iron, most elements will not fuse unless they are in the interior of a star. To create burning plasmas in experimental fusion power reactors such as tokamaks and stellarators, scientists seek a fuel that is relatively easy to produce, store, and bring to fusion. The current best bet for fusion reactors is deuterium-tritium fuel. This fuel reaches fusion conditions at lower temperatures compared to other elements and releases more energy than other fusion reactions.

Deuterium and tritium are isotopes of hydrogen, the most abundant element in the universe. Whereas all isotopes of hydrogen have one proton, deuterium also has one neutron and tritium has two neutrons, so their ion masses are heavier than protium, the isotope of hydrogen with no neutrons. When deuterium and tritium fuse, they create a helium nucleus, which has two protons and two neutrons. The reaction releases an energetic neutron. Fusion power plants would convert energy released from fusion reactions into electricity to power our homes, businesses, and other needs.

Fortunately, deuterium is common. About 1 out of every 5000 hydrogen atoms in seawater is in the form of deuterium. This means our oceans contain many tons of deuterium. When fusion power becomes a reality, just one gallon of seawater could produce as much energy as 300 gallons of gasoline.