In a paper published today in Nature Communications, the scientists described how they drew inspiration from cephalopod skin to endow mammalian cells with tunable transparency and light-scattering characteristics.

“For millennia, people have been fascinated by transparency and invisibility, which have inspired philosophical speculation, works of science fiction, and much academic research,” said lead author Atrouli Chatterjee, a UCI doctoral student in chemical & biomolecular engineering. “Our project — which is decidedly in the realm of science — centers on designing and engineering cellular systems and tissues with controllable properties for transmitting, reflecting and absorbing light.”

Chatterjee works in the laboratory of Alon Gorodetsky, UCI associate professor of chemical & biomolecular engineering, who has a long history of exploring how cephalopods’ color-changing capabilities can be mimicked to develop unique technologies to benefit people. His team’s bioinspired research has led to breakthrough developments in infrared camouflage and other advanced materials.

For this study, the group drew inspiration from the way female Doryteuthis opalescens squids can evade predators by dynamically switching a stripe on their mantle from nearly transparent to opaque white. The researchers then borrowed some of the intercellular protein-based particles involved in this biological cloaking technique and found a way to introduce them into human cells to test whether the light-scattering powers are transferable to other animals.

This species of squid has specialized reflective cells called leucophores which can alter the how they scatter light. Within these cells are leucosomes, membrane-bound particles which are composed of proteins known as reflectins, which can produce iridescent camouflage.

In their experiments, the researchers cultured human embryonic kidney cells and genetically engineered them to express reflectin. They found that the protein would assemble into particles in the cells’ cytoplasm in a disordered arrangement. They also saw through optical microscopy and spectroscopy that the introduced reflectin-based structures caused the cells to change their scattering of light.

“We were amazed to find that the cells not only expressed reflectin but also packaged the protein in spheroidal nanostructures and distributed them throughout the cells’ bodies,” said Gorodetsky, a co-author on this study. “Through quantitative phase microscopy, we were able to determine that the protein structures had different optical characteristics when compared to the cytoplasm inside the cells; in other words, they optically behaved almost as they do in their native cephalopod leucophores.”

In another important part of the study, the team tested whether the reflectance could potentially be toggled on and off through external stimuli. They sandwiched cells in between coated glass plates and applied different concentrations of sodium chloride. Measuring the amount of light that was transmitted by the cells, they found that the ones exposed to higher sodium levels scattered more light and stood out more from the surroundings.

“Our experiments showed that these effects appeared in the engineered cells but not in cells that lacked the reflectin particles, demonstrating a potential valuable method for tuning light-scattering properties in human cells,” Chatterjee said.

While invisible humans are still firmly in the realm of science fiction, Gorodetsky said his group’s research can offer some tangible benefits in the near term.

“This project showed that it’s possible to develop human cells with stimuli-responsive optical properties inspired by leucophores in celphalopods, and it shows that these amazing reflectin proteins can maintain their properties in foreign cellular environments,” he said.

He said the new knowledge also could open the possibility of using reflectins as a new type of biomolecular marker for medical and biological microscopy applications.

The team used computer simulations to model the movement of a jet of plasma, the charged state of matter composed of electrons and atomic nuclei that makes up all the stars in the sky, including our sun. Many cosmic events can produce plasma jets, from relatively small star burps to gigantic stellar explosions known as supernovae. When fast-moving plasma jets pass through the slower plasma that exists in the void of space, it creates what is known as a collision-less shock wave.

These shocks also occur as Earth moves through the solar wind and can influence how the wind swirls into and around Earth’s magnetosphere, the protective magnetic shield that extends into space. Understanding plasma shock waves could help scientists to forecast the space weather that develops when the solar wind swirls into the magnetosphere and enable the researchers to protect satellites that allow people to communicate across the globe.

The simulations revealed several telltale signs indicating when a shock is forming, including the shock’s features, the three stages of the shock’s formation, and phenomena that could be mistaken for a shock. “By being able to distinguish a shock from other phenomena, scientists can feel confident that what they are seeing in an experiment is what they want to study in space,” said Derek Schaeffer, an associate research scholar in the Princeton University Department of Astrophysics who led the PPPL research team. The findings were reported in a paper published in Physics of Plasmas that followed up on previous research reported here and here.

The plasma shocks that occur in space, like those created by Earth traveling against the solar wind, resemble the shock waves created in Earth’s atmosphere by supersonic jet aircraft. In both occurrences, fast-moving material encounters slow or stationary material and must swiftly change its speed, creating an area of swirls and eddies and turbulence.

But in space, the interactions between fast and slow plasma particles occur without the particles touching one another. “Something else must be driving this shock formation, like the plasma particles electrically attracting or repelling each other,” Schaeffer said. “In any case, the mechanism is not fully understood.”

To increase their understanding, physicists conduct plasma experiments in laboratories to monitor conditions closely and measure them precisely. In contrast, measurements taken by spacecraft cannot be easily repeated and sample only a small region of plasma. Computer simulations then help the physicists interpret their laboratory data.

Today, most laboratory plasma shocks are formed using a mechanism known as a plasma piston. To create the piston, scientists shine a laser on a small target. The laser causes small amounts of the target’s surface to heat up, become a plasma, and move outward through a surrounding, slower-moving plasma.

Schaeffer and colleagues produced their simulation by modeling this process. “Think of a boulder in the middle of fast-moving stream,” Schaeffer said. “The water will come right up to the front of the boulder, but not quite reach it. The transition area between quick motion and zero [standing] motion is the shock.”

The simulated results will help physicists distinguish an astrophysical plasma shock wave from other conditions that arise in laboratory experiments. “During laser plasma experiments, you might observe lots of heating and compression and think they are signs of a shock,” Schaeffer said. “But we don’t know enough about the beginning stages of a shock to know from theory alone. For these kinds of laser experiments, we have to figure out how to tell the difference between a shock and just the expansion of the laser-driven plasma.”

In the future, the researchers aim to make the simulations more realistic by adding more detail and making the plasma density and temperature less uniform. They would also like to run experiments to determine whether the phenomena predicted by the simulations can in fact occur in a physical apparatus. “We’d like to put the ideas we talk about in the paper to the test,” says Schaeffer.

The study of 2,751 individuals in 14 nations identified universally valued qualities, such as intelligence and honesty, that can heighten a person’s social status. It also identified universal double-standards that socially reward men for certain sexual behaviors but punish women. The findings were published in the Journal of Personality and Social Psychology and fill an important gap in understanding the psychology behind who rises and falls within human societies.

“Humans live in a social world in which relative rank matters for nearly everything — your access to resources, your ability to attract mates, and even how long you live,” said UT Austin evolutionary psychologist David Buss, one of the study’s lead authors. “From an evolutionary perspective, reproductively relevant resources flow to those high in status and trickle slowly, if at all, to those lower on the social totem pole.”

The researchers compared people’s impressions of 240 factors — including acts, characteristics and events — to determine what increased and impaired a person’s esteem in the eyes of others. They found that certain qualities such as being honest, hard-working, kind, intelligent, having a wide range of knowledge, making sacrifices for others, and having a good sense of humor increased a person’s social value.

“From the Gypsies in Romania to the native islanders of Guam, people displaying intelligence, bravery and leadership rise in rank in the eyes of their peers,” said UT Austin psychology graduate student Patrick Durkee, who led the study with Buss. “But possessing qualities that inflict costs on others will cause your status to plummet, whether you live in Russia or Eritrea.”

Being known as a thief, as dirty or unclean, as mean or nasty, acquiring a sexually transmitted disease, and bringing shame on one’s family decreased a person’s social status or value. These status-harming actions can also lead to a person being ostracized from the group — “an action that would have meant near-certain death in ancestral environments,” the researchers said.

“Although this study was conducted prior to the current pandemic, it’s interesting that being a disease vector is universally detrimental to a person’s status,” Buss said. “Socially transmitted diseases are evolutionarily ancient challenges to human survival, so humans have psychological adaptations to avoid them. Lowering a person’s social status is an evolutionarily ancient method of social distancing from disease vectors.”

In considering universal gender differences in status criteria, the study supported that the ability and willingness to protect others — demonstrating bravery and physical formidability and taking risks to protect allies — was more status-enhancing for men than women. On the other hand, women were more valued socially for qualities relating to domestic skills and attractiveness.

Sexual strategies and mating practices also influenced status and showed strong gender differences. Being sexually promiscuous decreased the status of both genders, but hurt women’s status considerably more even in the most sexually egalitarian cultures in the study, the researchers said. Conversely, attaining a committed long-term mate increased the status of both genders, but somewhat more so for women. And fidelity increased the status of both women and men substantially and equally.

The study also identified cultural differences in qualities influencing social status. For example, practicing witchcraft damaged a person’s status in Zimbabwe and Eritrea, but has virtually no impact on status in Estonia, Russia or the United States. And although valued universally, a good sense of humor contributes to a large boost in status in Poland; a moderate boost in China, South Korea and Japan; but only a slight boost in Eritrea.

The team used the fossilized remains of ancient plant tissues to produce a new record of atmospheric CO₂ that spans 23 million years of uninterrupted Earth history. They have shown elsewhere that as plants grow, the relative amount of the two stable isotopes of carbon, carbon-12 and carbon-13 changes in response to the amount of CO₂ in the atmosphere. This research, published this week in Geology, is a next-level study measuring the relative amount of these carbon isotopes in fossil plant materials and calculating the CO₂ concentration of the atmosphere under which the ancient plants grew.

Furthermore, Schubert and colleagues’ new CO₂ “timeline” revealed no evidence for any fluctuations in CO₂ that might be comparable to the dramatic CO₂ increase of the present day, which suggests today’s abrupt greenhouse disruption is unique across recent geologic history.

Another point, important to geological readers, is that because major evolutionary changes over the past 23 million years were not accompanied by large changes in CO₂, perhaps ecosystems and temperature might be more sensitive to smaller changes in CO₂ than previously thought. As an example: The substantial global warmth of the middle Pliocene (5 to 3 million years ago) and middle Miocene (17 to 15 million years ago), which are sometimes studied as a comparison for current global warming, were associated with only modest increases in CO₂.

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