Computers Math

Stanford University computer science graduate student Mackenzie Leake has been quilting since age 10, but she never imagined the craft would be the focus of her doctoral dissertation. Included in that work is new prototype software that can facilitate pattern-making for a form of quilting called foundation paper piecing, which involves using a backing made of foundation paper to lay out and sew a quilted design.
Developing a foundation paper piece quilt pattern — which looks similar to a paint-by-numbers outline — is often non-intuitive. There are few formal guidelines for patterning and those that do exist are insufficient to assure a successful result.
“Quilting has this rich tradition and people make these very personal, cherished heirlooms but paper piece quilting often requires that people work from patterns that other people designed,” said Leake, who is a member of the lab of Maneesh Agrawala, the Forest Baskett Professor of Computer Science and director of the Brown Institute for Media Innovation at Stanford. “So, we wanted to produce a digital tool that lets people design the patterns that they want to design without having to think through all of the geometry, ordering and constraints.”
A paper describing this work is published and will be presented at the computer graphics conference SIGGRAPH 2021 in August.
Respecting the craft
In describing the allure of paper piece quilts, Leake cites the modern aesthetic and high level of control and precision. The seams of the quilt are sewn through the paper pattern and, as the seaming process proceeds, the individual pieces of fabric are flipped over to form the final design. All of this “sew and flip” action means the pattern must be produced in a careful order. More

So-called quantum dots are a new class of materials with many applications. Quantum dots are realized by tiny semiconductor crystals with dimensions in the nanometre range. The optical and electrical properties can be controlled through the size of these crystals. As QLEDs, they are already on the market in the latest generations of TV flat screens, where they ensure particularly brilliant and high-resolution colour reproduction. However, quantum dots are not only used as “dyes,” they are also used in solar cells or as semiconductor devices, right up to computational building blocks, the qubits, of a quantum computer.
Now, a team led by Dr. Annika Bande at HZB has extended the understanding of the interaction between several quantum dots with an atomistic view in a theoretical publication.
Annika Bande heads the “Theory of Electron Dynamics and Spectroscopy” group at HZB and is particularly interested in the origins of quantum physical phenomena. Although quantum dots are extremely tiny nanocrystals, they consist of thousands of atoms with, in turn, multiples of electrons. Even with supercomputers, the electronic structure of such a semiconductor crystal could hardly be calculated, emphasises the theoretical chemist, who recently completed her habilitation at Freie Universität. “But we are developing methods that describe the problem approximately,” Bande explains. “In this case, we worked with scaled-down quantum dot versions of only about a hundred atoms, which nonetheless feature the characteristic properties of real nanocrystals.”
With this approach, after a year and a half of development and in collaboration with Prof. Jean Christophe Tremblay from the CNRS-Université de Lorraine in Metz, we succeeded in simulating the interaction of two quantum dots, each made of hundreds of atoms, which exchange energy with each other. Specifically, we have investigated how these two quantum dots can absorb, exchange and permanently store the energy controlled by light. A first light pulse is used for excitation, while the second light pulse induces the storage.
In total, we investigated three different pairs of quantum dots to capture the effect of size and geometry. We calculated the electronic structure with highest precision and simulated the electronic motion in real time at femtosecond resolution (10-15 s).
The results are also very useful for experimental research and development in many fields of application, for example for the development of qubits or to support photocatalysis, to produce green hydrogen gas by sunlight. “We are constantly working on extending our models towards even more realistic descriptions of quantum dots,” says Bande, “e.g. to capture the influence of temperature and environment.”
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Materials provided by Helmholtz-Zentrum Berlin für Materialien und Energie. Note: Content may be edited for style and length. More

Quantum computers with their promises of creating new materials and solving intractable mathematical problems are a dream of many physicists. Now, they are slowly approaching viable realizations in many laboratories all over the world. But there are still enormous challenges to master. A central one is the construction of stable quantum bits — the fundamental unit of quantum computation called qubit for short — that can be networked together.
In a study published in Nature Materials and led by Daniel Jirovec from the Katsaros group at IST Austria in close collaboration with researchers from the L-NESS Inter-university Centre in Como, Italy, scientists now have created a new and promising candidate system for reliable qubits.
Spinning Absence
The researchers created the qubit using the spin of so-called holes. Each hole is just the absence of an electron in a solid material. Amazingly, a missing negatively charged particle can physically be treated as if it were a positively charged particle. It can even move around in the solid when a neighboring electron fills the hole. Thus, effectively the hole described as positively charged particle is moving forward.
These holes even carry the quantum-mechanical property of spin and can interact if they come close to each other. “Our colleagues at L-NESS layered several different mixtures of silicon and germanium just a few nanometers thick on top of each other. That allows us to confine the holes to the germanium-rich layer in the middle,” Jirovec explains. “On top, we added tiny electrical wires — so-called gates — to control the movement of holes by applying voltage to them. The electrically positively charged holes react to the voltage and can be extremely precisely moved around within their layer.”
Using this nano-scale control, the scientists moved two holes close to each other to create a qubit out of their interacting spins. But to make this work, they needed to apply a magnetic field to the whole setup. Here, their innovative approach comes into play.
Linking Qubits
In their setup, Jirovec and his colleagues cannot only move holes around but also alter their properties. By engineering different hole properties, they created the qubit out of the two interacting hole spins using less than ten millitesla of magnetic field strength. This is a weak magnetic field compared to other similar qubit setups, which employ at least ten times stronger fields.
But why is that relevant? “By using our layered germanium setup we can reduce the required magnetic field strength and therefore allow the combination of our qubit with superconductors, usually inhibited by strong magnetic fields,” Jirovec says. Superconductors — materials without any electrical resistance — support the linking of several qubits due to their quantum-mechanical nature. This could enable scientists to build new kinds of quantum computers combining semiconductors and superconductors.
In addition to the new technical possibilities, these hole spin qubits look promising because of their processing speed. With up to one hundred million operations per second as well as their long lifetime of up to 150 microseconds they seem particularly viable for quantum computing. Usually, there is a tradeoff between these properties, but this new design brings both advantages together.
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Materials provided by Institute of Science and Technology Austria. Note: Content may be edited for style and length. More

The impact of deploying Artificial Intelligence (AI) for radiation cancer therapy in a real-world clinical setting has been tested by Princess Margaret researchers in a unique study involving physicians and their patients.
A team of researchers directly compared physician evaluations of radiation treatments generated by an AI machine learning (ML) algorithm to conventional radiation treatments generated by humans.
They found that in the majority of the 100 patients studied, treatments generated using ML were deemed to be clinically acceptable for patient treatments by physicians.
Overall, 89% of ML-generated treatments were considered clinically acceptable for treatments, and 72% were selected over human-generated treatments in head-to-head comparisons to conventional human-generated treatments.
Moreover, the ML radiation treatment process was faster than the conventional human-driven process by 60%, reducing the overall time from 118 hours to 47 hours. In the long term this could represent a substantial cost savings through improved efficiency, while at the same time improving quality of clinical care, a rare win-win.
The study also has broader implications for AI in medicine. More

Researchers have demonstrated “giant flexoelectricity” in soft elastomers that could improve robot movement range and make self-powered pacemakers a real possibility. In a paper published this month in the Proceedings of the National Academy of Sciences, scientists from the University of Houston and Air Force Research Laboratory explain how to engineer ostensibly ordinary substances like silicone rubber into an electric powerhouse.
What do the following have in common: a self-powered implanted medical device, a soft human-like robot and how we hear sound? The answer as to why these two disparate technologies and biological phenomena are similar lies in how the materials they are made of can significantly change in size and shape — or deform — like a rubber band, when an electrical signal is sent.
Some materials in nature can perform this function, acting as an energy converter that deforms when an electrical signal is sent through or supplies electricity when manipulated. This is called piezoelectricity and is useful in creating sensors and laser electronics, among several other end uses. However, these naturally occurring materials are rare and consist of stiff crystalline structures that are often toxic, three distinct drawbacks for human applications.
Human-made polymers offer steps toward alleviating these pain points by eliminating material scarcity and creating soft polymers capable of bending and stretching, known as soft elastomers, but previously those soft elastomers lacked significant piezoelectric attributes.
In a paper published this month in the Proceedings of the National Academy of Sciences, Kosar Mozaffari, graduate student at the Cullen College of Engineering at the University of Houston; Pradeep Sharma, M.D. Anderson Chair Professor & Department Chair of Mechanical Engineering at the University of Houston and Matthew Grasinger, LUCI Postdoctoral Fellow at the Air Force Research Laboratory, offer a solution.
“This theory engineers a connection between electricity and mechanical motion in soft rubber-like materials,” said Sharma. “While some polymers are weakly piezoelectric, there are no really soft rubber like materials that are piezoelectric.”
The term for these multifunctional soft elastomers with increased capability is “giant flexoelectricity.” In other words, these scientists demonstrate how to boost flexoelectric performance in soft materials. More

A new formula from Army scientists is leading to new insights on how to build an energy-efficient legged teammate for dismounted warfighters.
In a recent peer-reviewed PLOS One paper, the U.S. Army Combat Capabilities Development Command, known as DEVCOM, Army Research Laboratory’s Drs. Alexander Kott, Sean Gart and Jason Pusey offer new insights on building autonomous military robotic legged platforms to operate as efficiently as any other ground mobile systems.
Its use could lead to potentially important changes to Army vehicle development. Scientists said they may not know exactly why legged, wheeled and tracked systems fit the same curve yet, but they are convinced their findings drive further inquiry.
“If vehicle developers find a certain design would require more power than is currently possible given a variety of real-world constraints, the new formula could point to specific needs for improved power transmission and generation, or to rethink the mass and speed requirements of the vehicle,” Gart said.
Inspired by a 1980s formula that shows relationships between the mass, speed and power expenditure of animals, the team developed a new formula that applied to a very broad range of legged, wheeled and tracked systems — such as motor vehicles and ground robots.
Although much of the data has been available for 30 years, this team believes they are the first to actually assemble it and study the relationships that emerge from this data. Their findings show that legged systems are as efficient as wheeled and tracked platforms. More

Scientists have created a cybersecurity technology called Shadow Figment that is designed to lure hackers into an artificial world, then stop them from doing damage by feeding them illusory tidbits of success.
The aim is to sequester bad actors by captivating them with an attractive — but imaginary — world.
The technology is aimed at protecting physical targets — infrastructure such as buildings, the electric grid, water and sewage systems, and even pipelines. The technology was developed by scientists at the U.S. Department of Energy’s Pacific Northwest National Laboratory.
The starting point for Shadow Figment is an oft-deployed technology called a honeypot — something attractive to lure an attacker, perhaps a desirable target with the appearance of easy access.
But while most honeypots are used to lure attackers and study their methods, Shadow Figment goes much further. The technology uses artificial intelligence to deploy elaborate deception to keep attackers engaged in a pretend world — the figment — that mirrors the real world. The decoy interacts with users in real time, responding in realistic ways to commands.
“Our intention is to make interactions seem realistic, so that if someone is interacting with our decoy, we keep them involved, giving our defenders extra time to respond,” said Thomas Edgar, a PNNL cybersecurity researcher who led the development of Shadow Figment. More

The myriad processes occurring in biological cells may seem unbelievably complex at first glance. And yet, in principle, they are merely a logical succession of events, and could even be used to form digital circuits. Researchers have now developed a molecular switching circuit made of DNA, which can be used to mechanically alter gels, depending on the pH. DNA-based switching circuits could have applications in soft robotics, say the researchers in their article in Angewandte Chemie.
DNA is a long molecule that can be folded and twisted in various ways. It has a backbone and bases that stick out from the backbone and pair up with counterparts in other DNA strands. When a series of these matching pairs comes together, they form a twisted, ladder-like double strand — the familiar DNA double helix. The flexibility of DNA, which makes it possible to produce bends, loops, and a wide variety of other shapes, has inspired researchers to build DNA switches. These switches change shape after receiving an input, and can then affect their surroundings.
Hao Pei from Shanghai Key Laboratory of Green Chemistry and Chemical Processes at the East China Normal University in Shanghai, China, and colleagues have now developed a configurable, multi-mode logic switching network that reacts differently with its surroundings depending on pH and DNA input. All the components of the switching circuit were produced from DNA.
The team developed a series of four DNA switches, each with slightly different lengths and combinations of bases. These variations meant they reacted differently with a single DNA strand depending on the pH of their surroundings. For example, at a slightly alkaline pH of 8, two of the switches formed triple-stranded DNA (triplexes), while the others remained loosely stretched out. These reactions and folds led to secondary reactions, which were utilized by the researchers as logic functions in the switching circuit. The result was, for example, a fluorescent signal that could be read as an output.
To demonstrate the use of the switching circuit in a real mechanical system, the team incorporated the DNA switches into polyacrylamide gels. The DNA acted as a crosslinker, joining the polymer molecules in the gel together. The shorter the crosslinker, or the more folded the DNA, the denser the gel became. Once a piece of DNA with matching bases was added as an input, a logic circuit was set in place, causing the DNA switches to unfold, form triplexes, or relax. The reaction circuit was also dependent on the pH. As a result, certain combinations of DNA input and pH range caused the DNA crosslinker to grow longer and the gel to swell up, in some cases nearly doubling in size.
As DNA switches have almost infinite possibilities for combinations of twists and folds, the researchers consider their switching circuits to be a vital step toward soft matter robotics, where controllable, miniaturized logic functional networks are important.
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Materials provided by Wiley. Note: Content may be edited for style and length. More