Over the past decade, major technological advances have been made, making it possible to put a wide variety of systems into this state. Mechanical vibrations oscillating between two mirrors in a resonator can be cooled to very low temperatures as far as the quantum ground state. This has not yet been possible for optical fibers in which high-frequency sound waves can propagate. Now researchers from the Stiller Research Group have taken a step closer to this goal.

In their study, recently published in Physical Review Letters, they report that they were able to lower the temperature of a sound wave in an optical fiber initially at room temperature by 219 K using laser cooling, ten times further than had previously been reported. Ultimately, the initial phonon number was reduced by 75%, at a temperature of 74 K, -194 Celsius. Such a drastic reduction in temperature was made possible by the use of laser light. Cooling of the propagating sound waves was achieved via the nonlinear optical effect of stimulated Brillouin scattering, in which light waves are efficiently coupled to sound waves. Through this effect, the laser light cools the acoustic vibrations and creates an environment with less thermal noise which is, to an extent, “disturbing” noise for a quantum communication system, for example. “An interesting advantage of glass fibers, in addition to this strong interaction, is the fact that they can conduct light and sound excellently over long distances,” says Laura Blázquez Martínez, one of the lead authors of the article and a doctoral student in the Stiller research group.

Most physical platforms previously brought to the quantum ground state were microscopic. However, in this experiment, the length of the optical fiber was 50 cm and a sound wave extending over the full 50 cm of the core of the fiber was cooled to extremely low temperatures. “These results are a very exciting step towards the quantum ground state in waveguides and the manipulation of such long acoustic phonons opens up possibilities for broadband applications in quantum technology,” according to Dr. Birgit Stiller, head of the quantum optoacoustics group.

Sound, in the day-to-day classical world, can be understood as a density wave in a medium. However, from the perspective of quantum mechanics, sound can also be described as a particle: the phonon. This particle, the sound quantum, represents the smallest amount of energy which occurs as an acoustic wave at a certain frequency. In order to see and study single quanta of sound, the number of phonons must be minimized. The transition from the classical to quantum behavior of sound is often more easily observed in the quantum ground state, where the number of phonons is close to zero on average, such that the vibrations are almost frozen and quantum effects can be measured. Stiller: “This opens the door to a new landscape of experiments that allow us to gain deeper insights into the fundamental nature of matter.” The advantage of using a waveguide system is that light and sound are not bound between two mirrors, but propagating along the waveguide. The acoustic waves exist as a continuum — not only for certain frequencies — and can have a broad bandwidth, making them promising for applications such as high-speed communication systems.

“We are very enthusiastic about the new insights that pushing these fibers into the quantum ground state will bring,” emphasizes the research group leader. “Not only from the fundamental research point of view, allowing us to peek into the quantum nature of extended objects, but also because of the applications this could have in quantum communications schemes and future quantum technologies.”

Because it requires no battery that must be recharged or replaced, and because it requires no special wiring, such a sensor could be embedded in a hard-to-reach place, like inside the inner workings of a ship’s engine. There, it could automatically gather data on the machine’s power consumption and operations for long periods of time.

The researchers built a temperature-sensing device that harvests energy from the magnetic field generated in the open air around a wire. One could simply clip the sensor around a wire that carries electricity — perhaps the wire that powers a motor — and it will automatically harvest and store energy which it uses to monitor the motor’s temperature.

“This is ambient power — energy that I don’t have to make a specific, soldered connection to get. And that makes this sensor very easy to install,” says Steve Leeb, the Emanuel E. Landsman Professor of Electrical Engineering and Computer Science (EECS) and professor of mechanical engineering, a member of the Research Laboratory of Electronics, and senior author of a paper on the energy-harvesting sensor.

In the paper, which appeared as the featured article in the January issue of the IEEE Sensors Journal, the researchers offer a design guide for an energy-harvesting sensor that lets an engineer balance the available energy in the environment with their sensing needs.

The paper lays out a roadmap for the key components of a device that can sense and control the flow of energy continually during operation.

The versatile design framework is not limited to sensors that harvest magnetic field energy, and can be applied to those that use other power sources, like vibrations or sunlight. It could be used to build networks of sensors for factories, warehouses, and commercial spaces that cost less to install and maintain.

“We have provided an example of a battery-less sensor that does something useful, and shown that it is a practically realizable solution. Now others will hopefully use our framework to get the ball rolling to design their own sensors,” says lead author Daniel Monagle, an EECS graduate student.

Monagle and Leeb are joined on the paper by EECS graduate student Eric Ponce.

A how-to guide

The researchers had to meet three key challenges to develop an effective, battery-free, energy-harvesting sensor.

First, the system must be able to cold start, meaning it can fire up its electronics with no initial voltage. They accomplished this with a network of integrated circuits and transistors that allow the system to store energy until it reaches a certain threshold. The system will only turn on once it has stored enough power to fully operate.

Second, the system must store and convert the energy it harvests efficiently, and without a battery. While the researchers could have included a battery, that would add extra complexities to the system and could pose a fire risk.

“You might not even have the luxury of sending out a technician to replace a battery. Instead, our system is maintenance-free. It harvests energy and operates itself,” Monagle adds.

To avoid using a battery, they incorporate internal energy storage that can include a series of capacitors. Simpler than a battery, a capacitor stores energy in the electrical field between conductive plates. Capacitors can be made from a variety of materials, and their capabilities can be tuned to a range of operating conditions, safety requirements, and available space.

The team carefully designed the capacitors so they are big enough to store the energy the device needs to turn on and start harvesting power, but small enough that the charge-up phase doesn’t take too long.

In addition, since a sensor might go weeks or even months before turning on to take a measurement, they ensured the capacitors can hold enough energy even if some leaks out over time.

Finally, they developed a series of control algorithms that dynamically measure and budget the energy collected, stored, and used by the device. A microcontroller, the “brain” of the energy management interface, constantly checks how much energy is stored and infers whether to turn the sensor on or off, take a measurement, or kick the harvester into a higher gear so it can gather more energy for more complex sensing needs.

“Just like when you change gears on a bike, the energy management interface looks at how the harvester is doing, essentially seeing whether it is pedaling too hard or too soft, and then it varies the electronic load so it can maximize the amount of power it is harvesting and match the harvest to the needs of the sensor,” Monagle explains.

Self-powered sensor

Using this design framework, they built an energy management circuit for an off-the-shelf temperature sensor. The device harvests magnetic field energy and uses it to continually sample temperature data, which it sends to a smartphone interface using Bluetooth.

The researchers used super-low-power circuits to design the device, but quickly found that these circuits have tight restrictions on how much voltage they can withstand before breaking down. Harvesting too much power could cause the device to explode.

To avoid that, their energy harvester operating system in the microcontroller automatically adjusts or reduces the harvest if the amount of stored energy becomes excessive.

They also found that communication — transmitting data gathered by the temperature sensor — was by far the most power-hungry operation.

“Ensuring the sensor has enough stored energy to transmit data is a constant challenge that involves careful design,” Monagle says.

In the future, the researchers plan to explore less energy-intensive means of transmitting data, such as using optics or acoustics. They also want to more rigorously model and predict how much energy might be coming into a system, or how much energy a sensor might need to take measurements, so a device could effectively gather even more data.

“If you only make the measurements you think you need, you may miss something really valuable. With more information, you might be able to learn something you didn’t expect about a device’s operations. Our framework lets you balance those considerations,” Leeb says.

The work is supported, in part, by the Office of Naval Research and The Grainger Foundation.

The African continent has seen its average monthly temperatures rise by .5 — 2 degrees Celsius over the past century, with up to another two degrees of warming projected for the next 100 years, according to the Intergovernmental Panel on Climate Change’s (IPCC) high greenhouse gas emissions scenario. It is also well known that the changing climate will disrupt historical precipitation patterns — but which of these, temperature or rainfall, will have the most impact on a species, like white and black rhinos, that have long been the target of conservation efforts?

The question is especially important for rhinos because they don’t sweat, and instead cool themselves off by bathing and finding shade.

“Generally speaking, most, if not all, species will, in one way or another, be negatively affected by the changing climate,” says lead author Hlelowenkhosi S. Mamba, who completed this research as part of her graduate studies at UMass Amherst. “It is therefore important for conservationists to conduct macroecological assessments over large areas to catch trends and model futures for some of the world’s most vulnerable species to prepare to mitigate climate change’s effects, hence minimizing global biodiversity losses.”

To understand how our changing climate will affect rhino populations, Mamba and senior author Timothy Randhir, professor of environmental conservation at UMass Amherst, focused their efforts on the five large national parks in South Africa, Namibia, Zimbabwe, Kenya, Botswana, Tanzania and eSwatini that are home to most of the rhinos. The parks represent diverse landscapes.

Mamba and Randhir then modelled two scenarios for each of the parks: the IPCC’s high-emissions scenario and a more moderate emissions scenario. They projected temperature and precipitation for each of the scenarios out to 2055 and 2085 to arrive at a probability that each park would remain suitable for the rhinos.

They found that each park will see approximately 2.2 ºC warming by 2055 and 2.5 ºC by 2085 under the moderate emissions scenario. Under the high emissions scenario, each park will be warmer by approximately 2.8 ºC in 2055 and 4.6 ºC in 2085.

Nearly every park will become increasingly drier as emissions increase, with the exception of one, Tsavo West National Park in Kenya, which will see more rainfall.

This is all very bad news for the rhinos, because the team also found that, though the change in precipitation will not be ideal for the rhinos, the changes in temperature are greater than what the species can bear.

“The temperature conditions in all study parks will become increasingly unsuitable for both species, but it is predicted that white rhinos will be affected earlier than black rhinos,” the authors write. “All the parks are showing drastic changes in the occurrence probability of rhinos.” And under the high-emissions scenarios, the probability of occurrence of either species shrinks to zero by 2085.

The worst news involves Etosha National Park, in Namibia, and Hlane National Park, in eSwatini, both of which will become too warm for rhinos in either scenario.

But to be forewarned is to be forearmed. “This paper highlights the importance of using climate predictions for both park and rhino management,” says Randhir. “We propose that park managers think now about increasing water supplies, tree cover, watching for stress and planning to allow rhino migration as the world warms.”

Antibodies that target the fusion peptide can neutralize diverse strains of HIV in vitro, that is, in a test tube or culture dish outside of a living organism. The NIAID VRC isolated a fusion peptide-directed human antibody, called VRC34.01, from a person living with HIV who donated blood samples for research. They also isolated two antibodies from rhesus macaques — a species of monkey with immune systems like humans’ — who previously had received a vaccine regimen designed to generate fusion peptide-directed antibodies. Demonstrating that these antibodies protect animals would validate the fusion peptide as a target for human vaccine design. SHIV challenge — administering an infective dose of SHIV — to rhesus macaques is a widely used animal model for assessing the performance of HIV antibodies and vaccines.

In this study, rhesus macaques in each of four groups received a single intravenous infusion of one type of antibody — a 2.5 or 10 mg/kg of bodyweight dose of VRC34.01, or one of the two vaccine-elicited rhesus macaque antibodies — and other monkeys received a placebo infusion. To determine the protective effect of the antibodies, each monkey was challenged five days after infusion with a strain of SHIV known to be sensitive to fusion peptide-directed antibodies.

All monkeys that received a placebo infusion acquired SHIV following the challenge. Among monkeys that received VRC34.01 infusions, none receiving the 10 mg/kg dose and 25% of those receiving the 2.5 mg/kg dose acquired SHIV. Of those that received the vaccine-elicited rhesus macaque antibodies, no monkeys receiving the antibody called DFPH-a.15 acquired SHIV, and 25% of those receiving the antibody called DF1W-a.01 acquired SHIV. Over time, the concentration of antibodies in the blood of animals that received DFPH-a.15 declined. Those animals were re-challenged 30 days later to see if the lower concentration of antibodies had a decreased protective effect, and half of them acquired SHIV.

The three antibodies studied each provided statistically significant protection from SHIV, and the effect was dose dependent, that is, highest in monkeys with greater antibody concentrations in their blood.

According to the authors, these findings represent the proof-of-concept that fusion peptide-directed antibodies can provide protection against SHIV and help determine the concentration of antibodies a vaccine would need to generate to be protective. They suggest that their findings on vaccine-elicited antibodies in some animals support further work to design preventive HIV vaccine concepts targeting the fusion peptide. They conclude that an effective HIV vaccine targeting the HIV fusion peptide likely will need to expand upon the concepts used in this study, by generating multiple varieties of fusion peptide-directed antibodies. This would increase the likelihood that the vaccine could maintain a preventive effect across the vastly diverse HIV variants in circulation.

In this retrospective study, the orthopaedic team at the Marshall University Joan C. Edwards School of Medicine and Marshall Health performed 25 revision knee replacements with a robotic assisted computer system. The procedure involved placing new implants at the end of the thighbone and top of the shinbone with the computer’s aid to ensure the knee was stable and balanced throughout the range of motion. Researchers then carefully compared the initial positions of the primary implants with the final planned positions of the robotic revision implants for each patient, assessing the differences in millimeters and degrees.

The analysis found that exceedingly small changes in implant position significantly influence the function of the knee replacement. Robotic assistance during revision surgery has the potential to measure these slight differences. In addition, the computer system can help the surgeon predict what size implant to use as well as help to balance the knee for stability.

“Robotic-assisted surgery has the potential to change the way surgeons think about revision knee replacement,” said Matthew Bullock, D.O., associate professor of orthopaedic surgery and co-author on the study. “The precision offered by robotic-assisted surgery not only enhances the surgical process but also holds promise for improved patient outcomes. Besides infection, knee replacements usually fail because they become loose from the bone or because they are unbalanced leading to pain and instability. When this happens patients can have difficulty with activities of daily living such as walking long distances or negotiating stairs.”

The study underscores the importance of aligning the prosthesis during revision surgery. The research also suggests potential advantages, including appropriately sized implants that can impact the ligament tension which is crucial for functional knee revisions.

“These findings open new doors in the realm of revision knee arthroplasty,” said Alexander Caughran, M.D., assistant professor of orthopaedic surgery and co-author on the study. “We continue to collect more data for future studies on patient outcomes after robotic revision knee replacement. We anticipate that further research and technological advancements in the realm of artificial intelligence will continue to shape the landscape of orthopaedic surgery.”

In addition to Bullock and Caughran, co-authors from Marshall University include Micah MacAskill, M.D., resident physician; Richard Peluso, M.D., resident physician; Jonathan Lash, M.D., resident physician; and Timothy Hewett, Ph.D., professor.