Tag: Japan

A vital piece of gas engines, combustors—the chambers in which the combustion powering the engine occurs—have the problem of breaking down due to fatal high-frequency oscillations during the combustion process. Now, through advanced time-series analyses based on complex systems, researchers from Tokyo University of Science and Japan Aerospace Exploration Agency have found what causes them, opening up novel paths to solving the problem.

In a breakthrough, published in Physics of Fluids, a team including Prof. Hiroshi Gotoda, Ms. Satomi Shima, and Mr. Kosuke Nakamura from Tokyo University of Science (TUS), in collaboration with Dr. Shingo Matsuyama and Dr. Yuya Ohmichi from the Japan Aerospace Exploration Agency (JAXA), have used advanced time-series analyses based on complex systems to find out.

Explaining their work, Prof. Gotoda says, “Our main purpose was to reveal the physical mechanism behind the formation and sustenance of high-frequency combustion oscillations in a cylindrical combustor using sophisticated analytical methods inspired by symbolic dynamics and complex networks.” These findings have also been covered by the American Society of Physics in their news section, and by the Institute of Physics on their news platform Physics World.

The combustor the scientists picked to simulate is one of model rocket engines. They were able to pinpoint the moment of transition from the stable combustion state to combustion oscillations and visualize it. They found that significant periodic flow velocity fluctuations in fuel injector affect the ignition process, resulting in changes to the heat release rate. The heat release rate fluctuations synchronize with the pressure fluctuations inside the combustor, and the whole cycle continues in a series of feedback loops that sustain combustion oscillations.

Additionally, by considering a spatial network of pressure and heat release rate fluctuations, the researchers found that clusters of acoustic power sources periodically form and collapse in the shear layer of the combustor near the injection pipe’s rim, further helping drive the combustion oscillations.

These findings provide reasonable answers for why combustion oscillations occur, albeit specific to liquid rocket engines. Prof. Gotoda explains, “Combustion oscillations can cause fatal damage to combustors in rocket engines, aero engines, and gas turbines for power generation. Therefore, understanding the formation mechanism of combustion oscillations is an important research subject. Our results will greatly contribute to our understanding of the mechanism of combustion oscillations generated in liquid rocket engines.”

Indeed, these findings are significant and can be expected to open doors to novel routes of
exploration to prevent combustion oscillations in critical engines.

Two-dimensional “nanosheets” made of bonds between metal atoms and organic molecules are attractive candidates for photoelectric conversion, but get corroded easily. In a new study, scientists from Japan and Taiwan present a new nanosheet design using iron and benzene hexathiol that exhibits record stability to air exposure for 60 days, signalling the commercial optoelectronic applications of these 2D materials in the future.

Converting light to electricity effectively has been one of the persistent goals of scientists in the field of optoelectronics. While improving the conversion efficiency is a challenge, several other requirements also need to be met. For instance, the material must conduct electricity well, have a short response time to changes in input (light intensity), and, most importantly, be stable under long-term exposure.

Lately, scientists have been fascinated with “coordination nanosheets” (CONASHs), that
are organic-inorganic hybrid nanomaterials in which organic molecules are bonded to metal atoms in a 2D network. The interest in CONASHs stems mainly from their ability to absorb light at multiple wavelength ranges and convert them into electrons with greater efficiency than other types of nanosheets. This feat was observed in a CONASH comprising a zinc atom bonded with a porphyrin-dipyrrin molecule. Unfortunately, the CONASH quickly became corroded due to the low stability of organic molecules in liquid electrolytes (a medium commonly used for current conduction).

“The durability issue needs to be solved to realize the practical applications of CONASH-based photoelectric conversion systems,” says Professor Hiroshi Nishihara from Tokyo University of Science (TUS), Japan, who conducts research on CONASH and has been trying to solve the CONASH stability problem.

Now, in a recent study published in Advanced Science as a result of a collaborative research between National Institute for Materials Science (NIMS), Japan and TUS, Prof. Nishihara and his colleagues, Dr. Hiroaki Maeda and Dr. Naoya Fukui from TUS, Dr. Ying-Chiao Wang and Dr. Kazuhito Tsukagoshi from NIMS, Mr. Chun-Hao Chiang and Prof. Chun-Wei Chen from National Taiwan University, Taiwan, and Dr. Chi-Ming Chang and Prof. Wen-Bin Jian from National Chiao-Tung University, Taiwan, have designed a CONASH comprising an iron (Fe) ion bonded to a benzene hexathiol (BHT) molecule that has demonstrated the highest stability under air exposure reported so far. The new FeBHT CONASH-based photodetector can retain over 94% of its photocurrent after 60 days of exposure! Moreover, the device requires no external power source.

What made such a feat possible? Put simply, the scientists made some smart choices. Firstly, they went for an all-solid architecture by replacing the liquid electrolyte with a solid-state layer of Spiro-OMeTAD, a material known to be an efficient transporter of “holes” (vacancies left behind by electrons). Secondly, they synthesized the FeBHT network from a reaction between iron ammonium sulfate and BHT, which accomplished two things: one, the reaction was slow enough to keep the sulfur group protected from being oxidized, and two, it helped the resultant FeBHT network become resilient to oxidation, as the scientists confirmed using density functional theory calculations.

In addition, the FeBHT CONASH favoured high electrical conductivity, showed an enhanced
photoresponse with a conversion efficiency of 6% (the highest efficiency previously reported was 2%), and a response time < 40 milliseconds for UV light illumination.

With these results, the scientists are thrilled about the prospects of CONASH in commercialized optoelectronic applications. “The high performance of the CONASH-based photodetectors coupled with the fact that they are self-powered can pave the way for their practical applications such as in light-receiving sensors that can be used for mobile applications and recording the light exposure history of objects,” says Prof. Nishihara excitedly.

Scientists at Tokyo University of Science, Japan, engineered a long polymer with copper-containing side units that create regions with locally high copper density, boosting the antibacterial activity of hydrogen peroxide and paving the way to a new drug design concept.

Scientists are exploring a novel approach to boost the in vivo antibacterial activity of hydrogen peroxide (H₂O₂), a commonly used disinfectant. In a recent study published in Macromolecular Rapid Communications, a team led by Assistant Professor Shigehito Osawa and Professor Hidenori Otsuka reported their success in enhancing H₂O₂ activity using
carefully tailored copper-containing polymers.

To understand their approach, it helps to know how H2O2 acts against bacteria in the first place, and the role that copper plays. H2O2 can be decomposed into a hydroxyl radical (•OH) and a hydroxide anion (OH−), the former of which is highly toxic to bacteria as it readily destroys certain biomolecules. Copper in its first oxidation state, Cu(I), can catalyze the splitting of H2O2 into a hydroxyl radical and a hydroxide anion, turning into Cu(II) in the process through oxidation (Figure 1). Curiously, H2O2 can also catalyze the reduction of Cu(II) to Cu(I), but only if this reaction is somehow facilitated. One way to achieve this is to have Cu(II)-containing complexes get close enough together.

However, when using Cu(II)-containing complexes dissolved in a solution, the only way for them to come close together is by accidentally bumping into each other, which requires an excessively high concentration of copper.

The team found a workaround to this issue by drawing inspiration from cellular chemistry, as Dr. Osawa explains: “In living organisms, copper forms complexes with proteins to efficiently catalyze redox reactions. For example, tyrosinase has two copper complex sites in close proximity to each other, which facilitates the formation of reaction intermediates between oxygen species and copper complexes. We thought we could leverage this type of mechanism in artificially produced polymers with copper complexes, even if dispersed in a solution.”

With this idea, the researchers developed a long polymer chain with dipicolylamine (DPA) as copper-containing complexes. These DPA–copper complexes were attached to the long polymer backbone as “pendant groups.” When these polymers are dispersed in a solution, the Cu(II) atoms in the pendant groups are kept in close proximity and locally high densities, vastly increasing the chances that two of them will be close enough to be reduced to Cu(I) by H2O2. Through various experiments, the scientists demonstrated that the use of these tailored polymers resulted in higher catalytic activity for the splitting of H2O2 resulting in more OH• even for lower concentrations of copper. Further tests using Escherichia coli cultures showed that these polymers greatly enhanced the antibacterial potential of H2O2.

While the results of this study open up a new design avenue for antimicrobial drugs, there may also be useful applications in the food industry as well. “Because copper is an essential
nutrient for living organisms, the antibacterial agent developed in this study holds promise as an efficient food preservative, which could contribute to increasing the variety of foods that can be preserved over long shelf times,” highlights Dr Osawa.

In the fight against COVID-19, scientists have been scanning their arsenals of previously used drugs in hopes of finding any that can be used to treat the disease. One of the contenders under scrutiny, an anti-malarial drug called mefloquine shows great promise, according to a new breakthrough study by a team of Japanese scientists, perhaps giving us a better fighting chance.

In a breakthrough study, a team of scientists—comprising Dr. Koichi Watashi, Kaho Shionoya, Masako Yamasaki, Dr. Hirofumi Ohashi, Dr. Shin Aoki, Dr. Kouji Kuramochi, and Dr. Tomohiro Tanaka from Tokyo University of Science (along with scientists from the National Institute of Infectious Diseases, Kyushu University, The University of Tokyo, Kyoto University, Japanese Foundation for Cancer Research, and Science Groove Inc.)—have identified an anti-malarial drug, mefloquine (which is incidentally a derivative of hydrochloroquine), that is effective against SARS-CoV-2. Their findings are published
in Frontiers in Microbiology.

Detailing their modus operandi, lead scientist in the team Dr. Watashi says, “To identify drugs with higher antiviral potency than existing antivirals, we first screened approved
anti-parasitic/anti-protozoal drugs. We found that mefloquine had the highest anti-SARS-CoV-2 activity among the tested compounds. Upon testing it against other quinoline derivatives, such as hydrochloroquine, in a cell line mimicking the cell-based environments of human lung cells, we found it to be better.”

The team further explored mefloquine’s mechanism of action. Dr. Watashi explains the process, “In our cell assays, mefloquine readily reduced the viral RNA levels when applied at the viral entry phase but showed no activity during virus-cell attachment. This shows that mefloquine is effective on SARS-COV-2 entry into cells after attachment on cell
surface.”

Thus, to bolster mefloquine’s anti-viral activity, the scientists looked into the possibility of combining it with a drug that inhibits the replication step of SARS-CoV-2: Nelfinavir. Interestingly, they observed that the two drugs acted in “synergy” and the drug combination showed greater anti-viral activity than either showed alone, without being toxic to the cells in the cell lines themselves.

The scientists also mathematically modelled the effectiveness of mefloquine to predict its potential real-world impact if applied to treat COVID-19. What they predicted was that mefloquine could reduce the overall viral load in affected patients to under 7% and shorten the ‘time-till-virus-elimination’ by 6.1 days.

This study must of course be succeeded by clinical trials, but the world can hope that mefloquine becomes a drug used to effectively treat patients with COVID-19.

Acrylamide, which is extensively used in industries, causes peripheral neuropathy or encephalopathy. Now, scientists from Japan examined the response against oxidative stress in acrylamide-induced neurotoxicity and found that nuclear factor erythroid 2-related factor 2 (Nrf2), a master regulator of the immune system and response to oxidative stress, was at the centre of this toxicity. They found that Nrf2 plays a protective role by increasing the expression of protective genes and decreasing that of pro-inflammatory genes.

In a recent study, a team of scientists, led by Prof. Gaku Ichihara from Tokyo University of Science, reported the role of Nrf2 in acrylamide-induced neurotoxicity. Prof. Ichihara
states, “Our study showed that Nrf2 has a protective role against neurologic damage and suggests it is through activation of antioxidant stress genes and suppression of proinflammatory cytokine genes.”

In their study published in the journal Toxicology, Prof. Gaku Ichihara, along with his colleagues Prof. Masayuki Yamamoto from Tohoku University, Prof. Ken Itoh from Hirosaki University, Associate Prof. Seiichiroh Ohsako from The University of Tokyo, and Prof. Sahoko Ichihara from Jichi Medical University, used mice models to study the role of Nrf2 in acrylamide-induced neurotoxicity.

They tested their hypothesis that when Nrf2 gene is removed, the neurotoxic effects of acrylamide will be amplified. For this, they developed “knockout” mice that could not produce Nrf2, and gave the Nrf2-knockout mice and a set of counterpart “wild-type” mice that could produce Nrf2 different concentrations of acrylamide for 4 weeks. Then, they compared the neurotoxicity between both groups of mice using various sensory and motor tests, immunohistochemistry, and protein and gene expression analyses.

The scientists found that the Nrf2-knockout mice had severe neurotoxic effects such as sensory and motor system dysfunction and axonal damage. While these mice produced fewer antioxidants and protective factors in response to acrylamide, they also showed enhanced release of pro-inflammatory chemicals, called “cytokines,” in the brain, which can potentially cause additional damage. Additionally, as different doses were given to the mice, the scientists also determined that the neurotoxicity was dose-dependent.

Previous studies have established the role of Nrf2 as a master regulator of protective genes but this study explained the specific mechanisms of immune response to acrylamide-induced toxicity, with Nrf2 at the center of it all. As Prof. Ichihara states, “The results document the first known morphological and neuro-functional evidence of the regulatory role of Nrf2 in acrylamide-induced neurotoxic effects in mice.”

The findings of this study are also immensely valuable in the field of disease biology, as recent studies have shown a link between air pollution and Alzheimer’s disease. Since the air contains other acrylamide-like chemical pollutants with similar neurotoxic effects, the study’s findings could prove useful in the prevention of Alzheimer’s disease.

Prof. Ichihara and his team’s study is certainly a timely one, as reports of acrylamide intoxication are on the rise and further research is required to better understand the specific mechanisms by which the body protects itself from harm.

Some nonpathogenic microorganisms can stimulate plant immune responses without
damaging the plants, which allows them to act like plant vaccines, but screening microorganisms for such properties has traditionally been time-consuming and expensive.

Associate Professor Toshiki Furuya and Professor Kazuyuki Kuchitsu of Tokyo University of Science and their colleagues decided to develop a screening strategy involving cultured
plant cells. A description of their method appears in a paper recently published in Scientific Reports.

The first step in this screening strategy involves incubating the candidate microorganism together with BY-2 cells, which are tobacco plant cells known for their rapid and stable growth rates. The next step is to treat the BY-2 cells with cryptogein, which is a protein secreted by fungus-like pathogenic microorganisms that can elicit immune responses from tobacco plants.

A key part of the cryptogein-induced immune responses is the production of a class of chemicals called reactive oxygen species (ROS), and scientists can easily measure cryptogein-induced ROS production and use it as a metric for evaluating the effects of the nonpathogenic microorganisms.

To put it simply, an effective pretreatment agent will increase the BY-2 cells’ ROS production levels (i.e., cause the cells to exhibit stronger immune system activation) in response to cryptogein exposure.

To test the practicability of their screening strategy, Dr. Furuya and his colleagues used the strategy on 29 bacterial strains isolated from the interior of the Japanese mustard spinach plant (Brassica rapa var. perviridis), and they found that 8 strains boosted cryptogein-induced ROS production.

They then further tested those 8 strains by applying them to the root tips of seedlings from the Arabidopsis genus, which contains species commonly used as model organisms for studies of plant biology. Interestingly, 2 of the 8 tested strains induced whole-plant resistance to bacterial pathogens.

Based on the proof-of-concept findings concerning those 2 bacterial strains, Dr Furuya proudly notes that his team’s screening method “can streamline the acquisition of microorganisms that activate the immune system of plants.”

When asked how he envisions the screening method affecting agricultural practices, he explains that he expects his team’s screening system “to be a technology that contributes to the practical application and spread of microbial alternatives to chemical pesticides.”

In time, the novel screening method developed by Dr Furuya and team may make it significantly easier for crop scientists to create greener agricultural methods that rely on the defence mechanisms that plants themselves have evolved over millions of years.