Experimental analyses of the performance of metal-organic frameworks (MOFs) for the separation of propane and propene under real-world conditions revealed that the most commonly used theory to predict the selectivity does not yield accurate estimates, and also that water as an impurity does not have a detrimental effect on the material’s performance.

Short chain hydrocarbons are produced in mixtures after treatment of crude oil in refineries and need to be separated in order to be industrially useful. For example, propane is used as a fuel and propene as a raw material for chemical synthesis such as the production of polymers. However, the separation process usually requires high temperatures and pressures, and additionally the removal of other impurities such as water makes the process costly and energy-consuming.

The structure of the studied MOF offers a long-lived, adaptable, and most importantly efficient separation alternative at ambient conditions. They build on the fact that unsaturated molecules such as propene can be complexed with the material’s exposed metal atoms, while saturated ones such as propane fail to do so. While research has focused on developing different metal-organic frameworks for different separation processes, the feasibility of using these materials on industrial-scale applications is commonly only gauged by relying on a theory that makes many idealizing assumptions on both the material and the purity of the gasses. Thus, it has not been clear whether these predictions hold under more complicated but also more realistic conditions.

A team of Hokkaido University researchers around Professor Shin-ichiro Noro in collaboration with Professor Roland A. Fischer’s group at the Technical University of Munich conducted a series of measurements on the performance of a prototypical MOF to ascertain the material’s real-world selectivity, for both completely dry frameworks and ones pre-exposed to water.

Their results recently published in ACS Applied Materials & Interfaces show that the predicted selectivities of the material are too high compared to the real-world results. It also demonstrated that water does not drastically decrease the selectivity, although it does reduce the material’s capacity to adsorb gas. The team then performed quantum-chemical computations to understand why and realized that the water molecules themselves offer new binding sites to unsaturated hydrocarbons, such as propene (but not propane), thus retaining the material’s functionality.

The researchers state: “We showed the power of multi-component adsorption experiments to analyze the feasibility of using an MOF system.” They thus want to raise awareness of the shortcomings of commonly used theories and motivate other groups to also use a combination of different real-world measurements.

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Materials provided by Hokkaido University. Note: Content may be edited for style and length.

A team from the University of Cambridge used the mass, radius, and atmospheric data of the exoplanet K2-18b and determined that it’s possible for the planet to host liquid water at habitable conditions beneath its hydrogen-rich atmosphere. The results are reported in The Astrophysical Journal Letters.

The exoplanet K2-18b, 124 light-years away, is 2.6 times the radius and 8.6 times the mass of Earth, and orbits its star within the habitable zone, where temperatures could allow liquid water to exist. The planet was the subject of significant media coverage in the autumn of 2019, as two different teams reported detection of water vapour in its hydrogen-rich atmosphere. However, the extent of the atmosphere and the conditions of the interior underneath remained unknown.

“Water vapour has been detected in the atmospheres of a number of exoplanets but, even if the planet is in the habitable zone, that doesn’t necessarily mean there are habitable conditions on the surface,” said Dr Nikku Madhusudhan from Cambridge’s Institute of Astronomy, who led the new research. “To establish the prospects for habitability, it is important to obtain a unified understanding of the interior and atmospheric conditions on the planet — in particular, whether liquid water can exist beneath the atmosphere.”

Given the large size of K2-18b, it has been suggested that it would be more like a smaller version of Neptune than a larger version of Earth. A ‘mini-Neptune’ is expected to have a significant hydrogen ‘envelope’ surrounding a layer of high-pressure water, with an inner core of rock and iron. If the hydrogen envelope is too thick, the temperature and pressure at the surface of the water layer beneath would be far too great to support life.

Now, Madhusudhan and his team have shown that despite the size of K2-18b, its hydrogen envelope is not necessarily too thick and the water layer could have the right conditions to support life. They used the existing observations of the atmosphere, as well as the mass and radius, to determine the composition and structure of both the atmosphere and interior using detailed numerical models and statistical methods to explain the data.

The researchers confirmed the atmosphere to be hydrogen-rich with a significant amount of water vapour. They also found that levels of other chemicals such as methane and ammonia were lower than expected for such an atmosphere. Whether these levels can be attributed to biological processes remains to be seen.

The team then used the atmospheric properties as boundary conditions for models of the planetary interior. They explored a wide range of models that could explain the atmospheric properties as well as the mass and radius of the planet. This allowed them to obtain the range of possible conditions in the interior, including the extent of the hydrogen envelope and the temperatures and pressures in the water layer.

“We wanted to know the thickness of the hydrogen envelope — how deep the hydrogen goes,” said co-author Matthew Nixon, a PhD student at the Institute of Astronomy. “While this is a question with multiple solutions, we’ve shown that you don’t need much hydrogen to explain all the observations together.”

The researchers found that the maximum extent of the hydrogen envelope allowed by the data is around 6% of the planet’s mass, though most of the solutions require much less. The minimum amount of hydrogen is about one-millionth by mass, similar to the mass fraction of the Earth’s atmosphere. In particular, a number of scenarios allow for an ocean world, with liquid water below the atmosphere at pressures and temperatures similar to those found in Earth’s oceans.

This study opens the search for habitable conditions and bio-signatures outside the solar system to exoplanets that are significantly larger than Earth, beyond Earth-like exoplanets. Additionally, planets such as K2-18b are more accessible to atmospheric observations with current and future observational facilities. The atmospheric constraints obtained in this study can be refined using future observations with large facilities such as the upcoming James Webb Space Telescope.

As a result, the ability to precisely assess the extent of MS-related disability and disease advancement is critical to effective treatment. In a new study, published in the February 26, 2020 online issue of Annals of Clinical and Translational Neurology, an international team of scientists, led by researchers at University of California San Diego School of Medicine, describe a new, multi-sensor tool that measures subtle changes in MS patients, allowing physicians to more frequently and more quickly respond to changes in symptoms or patient condition.

“We currently lack reliable measures of subtle MS disability progression over short time intervals,” said senior study author Jennifer Graves, MD, PhD, a neurologist at UC San Diego Health and associate professor of neurosciences at UC San Diego School of Medicine.

“For example, a patient may tell us that that she can no longer play piano, but our 150-year-old bedside neurological exam techniques can’t quantify this. In a standard clinical trial, this patient would be rated stable and not progressing. Developing tools that can capture MS progression reliably within six to 12 months instead of three to five years will drive faster drug development for the most disabling forms of MS.”

MS affects approximately 1 million persons in the United States and 2.5 million worldwide. The cause is unknown, but the condition, which typically appears between the ages of 20 and 40, is more common in women. MS is one of the most common causes of non-traumatic disability among young and middle-aged adults.

Traditional assessment of MS has involved periodic clinical exams, which may only produce actionable findings over the course of several years. There are no tools to measure smaller, more subtle changes in the disease that may happen in shorter intervals.

The new device employs a combination of sensors, such as accelerometers, gyroscopes and surface electromyography (which records nerve electrical impulses using electrodes placed on the skin), that have been repurposed from commercial uses.

“The use of multi-sensors allows for use of complementary data-types that can be employed for a more comprehensive view of the movement,” said Graves. “The types of sensors we used are widely available in different hardware products. We used a product that could be purchased off Amazon and was originally used for gaming and other gesture control tasks. The critical steps in our work involved the data processing and analyses, including use of artificial intelligence approaches.”

The device involves wearing a small, sensor-laden band on the forearm or calf, then completing 20 finger or foot taps. Data is wirelessly downloaded to a computer in real-time. The procedure is repeated on all four limbs of the patient, and takes less than five minutes.

“A great advantage is potential use by non-experts and even non-clinicians, such as medical assistants or research coordinators,” Graves said. The researchers are now preparing to publish a longitudinal analysis demonstrating the device’s sensitivity to within patient changes over short time periods. Subsequent steps include validation in a multi-site study and development of commercial grade software to allow more expansive dissemination.

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Materials provided by University of California – San Diego. Original written by Scott LaFee. Note: Content may be edited for style and length.