Author: Shalini Saxena

Enlarge (credit: Joe Murphy)

Most of us are accustomed to the comfort of an air-conditioned or heated shelter, providing temporary relief from an outdoor climate that's often less than desirable. Such heating and cooling actually dominates residential and commercial energy consumption, accounting for a whopping 12.3 percent of total US energy use. As a result, emissions from maintaining our indoor environment affect the global climate outdoors.

But what if we heated or cooled people rather than spaces? Researchers exploring “personal thermal management” focus on providing heating or cooling directly to the human body. This approach reduces energy consumption that is largely wasted when providing climate control for an entire building, resulting in higher energy efficiency. Recently, scientists have developed a cost-effective textile that, when made into clothes, could provide a personal thermal management system.

Basic system requirements

Personal thermal management systems require careful control of the process of heat dissipation from the human body. At normal skin temperatures (typically 34 degrees Celsius), the human body emits infrared radiation (IR) with a peak emission at a 9.5µm wavelength. Dissipation of this radiative heat accounts for more than 50 percent of total body heat loss indoors.

Enlarge / A forest of false-colored silicon nanowires.

Flexible electronics, which could be used to control flexible robots, depend on the ability to produce electrical circuits that can be repeatedly stretched and bent while remaining operational. Silicon is obviously one of the most important building blocks of modern electronics, but even when it's shaped into wires, it isn't very stretchy.

Recently, theoretical calculations have indicated that it may be possible to stretch silicon nanowire by as much as 23 percent, depending on its structure and the stretch direction. This raises an obvious question: why haven't we been able to do so?

Recently, an international team of scientists and engineers has directly probed the elastic strain limit of single-crystalline Si nanowires. The team found that stretching the Si nanowires almost to their theoretical limit is possible.

(credit: Kim et al., Science (2016))

Touchscreens have transformed the way we interact with electronics, enabling the development of elegant handheld devices. But currently, their screens are limited to a fixed size. As flexible and wearable electronics are in development, the touchscreens we'll need in the future will have to be both flexible and biocompatible. In an investigation recently published in Science, researchers have designed an ionic touchscreen that boasts stretchability and biocompatibility, allowing easy integration with the human body.

The team selected a hydrogel-based material for their work. Hydrogels are soft, water-filled polymer networks; their mechanical properties are similar to those of certain tissues, and they can be made of biocompatible materials. As an added bonus, they’re highly transparent. In this case, the scientists selected an ionic hydrogel—a polyacrylamide base containing lithium chloride salts.

For a gel to function as a touchscreen panel, it has to conduct electricity, which is why there's lithium chloride present. To produce a uniform electrostatic field across the panel, voltage was applied at all the panel corners. When a person touches the panel with their finger, the finger acts as a conductor that is grounded. As a result, a potential difference is generated between the electrode and the touch point causing the current to flow from the electrode through the finger.

(credit: Julius Nielsen)

At four to five meters in length, the Greenland shark (Squaliformes, Somniosus microcephalus) is the largest fish native to the Arctic waters. Getting that big must take a while, and scientists have long known that these sharks grow less than one cm per year. So these sharks probably live a very long time, but little was known about their longevity and maturation.

In an investigation recently published in Science, a team of researchers used radiocarbon dating to put together a timeline of the Greenland shark's lifespan.

Because Greenland sharks lack bones—they’re cartilaginous fish—conventional methods of tracking growth, like carbon dating of bones, won't work. Instead, the team used a modified radiocarbon dating technique that has worked before on other boneless animals: tracking the chronology of the eye lens. The eye lens nucleus is composed of inert proteins. The central portion of the lens is formed during prenatal development, and during growth, the tissue retains the original proteins, which were largely made before birth.

Some may like it hot, but probably not quite this hot. (credit: Climate.gov)

This summer has been particularly hot across the US, and scorching temperatures have forced most of us to take refuge somewhere with air-conditioning. This leads to high electricity demand, especially in the hottest regions. As climate change continues, we are likely to experience similar hot temperatures more frequently.

Climate change modeling also forecasts that these increased temperatures will result in increased storm intensity and flooding. These types of extreme weather-related events could have a profound impact on the population distribution, if populations shift away from regions affected by extreme storms.

Combined, the change in weather and population movement can present regional infrastructure challenges due to significant changes in electricity demand. Understanding where electricity service is most vulnerable is of utmost importance if we're going to plan ahead for these future challenges. In an investigation recently published in Nature Energy, researchers have predicted how this combination of climate and population stresses will influence electricity demand using high-resolution, spatially explicit tools.

Salt water, a sheet of molybdenum disulfide, and a pore is all you need to produce current. (credit: Mohammad Heiranian, U of Illinois )

It's possible to generate energy using nothing but the difference between fresh and salt water. When fresh and salt water are separated by a membrane that blocks the passage of certain ions, there is a force that drives the freshwater into the salt water to even out the salt concentration. That force can be harvested to produce energy, an approach termed osmotic power.

But the generation of osmotic power is highly dependent on how quickly ions can cross the membrane—the thicker (and more robust) the membrane, the slower the ions will flow. Theoretically, the most efficient osmotic power generation would come from an atomically thin membrane layer. But can this theoretical system be achieved here in reality?

Recently, scientists answered that question using atomically-thin membranes composed of molybdenum-disulfide (MoS₂). In the paper that resulted, they describe a two-dimensional MoS₂ membrane containing a single nanopore, which was used to separate reservoirs containing two solutions with different concentrations of salt in order to generate osmotic power.

Battery research focuses on balancing three competing factors: performance, lifetime, and safety. Typically, you have to sacrifice one of these factors to get gains in the other two. But for applications like electric vehicles, we'd really like to see all three improved.

In an investigation recently published in Nature Energy, scientists demonstrated the ability to use a magnetic field to align graphite flakes within electrodes as they're manufactured. The alignment gives lithium ions a clearer path to transit the battery, leading to improved performance.

The electrodes of Lithium-ion batteries are often composed of graphite, which balances attributes such as a high energy density with non-toxicity, safety, and low cost. Graphite, composed of stacked sheets of carbon atoms, is often incorporated into these electrodes in the form of flake-like particles.

Because of its popularity, a great deal of research has been devoted to understanding the impact of chocolate on our health and well-being. There are several positive effects of chocolate. Cocoa has been found to be a rich source of antioxidants, and certain types of chocolate (eaten in moderation) reduce blood pressure and positively affect the circulatory system.

Sadly, most chocolates on the market today are also rather unhealthy due to their extremely high fat content. Rising obesity rates worldwide make it hard to recommend chocolate as a health food. Reducing the fat levels in chocolate would help address this concern.

Unfortunately, no adequate solution has ever been found. In a new study recently published in Proceedings of the National Academy of Sciences, researchers investigated the basic science behind liquid chocolate suspensions that makes it so difficult to get rid of the fat.

Chameleons have the seemingly impossible ability to capture their prey while remaining motionless simply through the flick of their tongue. This sensationalized predatory ability depends in part on a sophisticated ballistic projection of the chameleon’s tongue. The chameleon is able to extend its tongue as far as two body lengths away during a predatory attack, sending it towards its victim using accelerations that range from 300 to 1500 m/s².

Given the forces involved, what happens next is a bit surprising: the victim sticks to the tongue, even in cases where the prey is up to 30 percent of the chameleon's own body weight. Recently, a team of scientists investigated how this works.

It all depends on extremely viscous spit. The team characterized the viscosity of the mucus that's present on the chameleon's tongue by rolling small steel beads over a thin mucus film. During the rolling, the viscous forces of the mucus produce a drag force on the beads, which can be used to indirectly measure the viscosity. The scientists determined that the mucus viscosity (0.4 ± 0.1 Pa-s) is roughly 400 times larger than that of human saliva (~10^-3 Pa-s).

Most life depends on the Sun. Through photosynthesis, plants and other organisms harness the energy of the Sun to convert water and CO­₂ into sugars, forming the base of the food chain. Scientists and engineers around the world are trying to develop processes that are as sustainable and elegant as photosynthesis.

But it’s really not that easy to make use of natural systems as an energy source. When such organisms are transplanted into bioreactors, the overall efficiency of the photosynthesis achieved is typically quite low, less than five percent. But there have been attempts to improve on this low efficiency.

Recently, a team of scientists developed a hybrid inorganic-biological system capable of driving an artificial photosynthetic process. Their system relies on an "artificial leaf" as well as some bacteria to power carbon fixation into biomass and liquid fuels.