Time filter

Source Type

Karlsruhe, Germany

Mel'nikov V.V.,Institute of Technical Physics
Journal of Applied Mechanics and Technical Physics | Year: 2010

An axisymmetric thermoelastic problem for a sphere with conical cuts in the poles under the action of a quasi-stationary temperature field depending on the meridional angle and on the sphere radius is solved by a method based on the Castigliano variational principle. Orthonormalized systems of polynomials are used as the coordinate functions. Results of numerical calculations of the stress state of a spherical solid are presented. © 2009 Springer Science+Business Media, Inc. Source

Doroftei C.,Institute of Technical Physics | Doroftei C.,Al. I. Cuza University
Materials Chemistry and Physics | Year: 2015

Lanthanum perovskite LaFeO3 (LFO) is a semi-conducting oxide and it has been extensively studied with reference to several potential applications, such as gas sensors, humidity sensors and catalysts. This oxide crystallizes in an orthorhombic perovskite structure. This work is dedicated to the study of the structural, electric and humidity sensitivity properties of some thin films obtained through rf magnetron sputtering using as targets La0.8Pb0.2FeO3 (LPFO) perovskites in which Fe-ions were partially substituted by Zn-ions. The effects of substitutions, substrate (quartz and alumina) and its temperature during deposition, as well as of working gas composition (O2/(O2 + Ar)) and subsequent heat treatments have been investigated. Electrical behavior of the deposited layers is that of a p-type semiconductor. Thermal activation energy (Ea) is around 0.5 eV and increases to 0.62 eV with the increase of zinc ions content (from 0 to 0.2) in LPFO target. The influence of the environmental humidity on the electric resistivity of the obtained films was determined within the 0%-98% RH interval. By increasing the amount of zinc ions which substitute the iron in LPFO target, films much more sensitive to humidity between 53% and 98% RH were obtained. © 2015 Elsevier B.V. All rights reserved. Source

Doroftei C.,Al. I. Cuza University | Iacomi F.,Al. I. Cuza University | Popa P.D.,Institute of Technical Physics
Journal of Optoelectronics and Advanced Materials | Year: 2013

The structural and electric properties of some thin films obtained through rf magnetron sputtering using as target the La0.8Pb 0.2FeO3 perovskite have been studied. We have investigated the effects of the quartz and alumina substrate, its temperature during deposition, as well as of sputtering gas composition (Ar/O2 ratio) and subsequent heat treatments. The thin films microstructure was characterized by XRD, SEM, EDX and AFM analyses. The XRD patterns indicate the generation of perovskite phase and the increase of its crystallinity after a heat treatment at 750°C/30min. The micrographs indicate the formation of a uniformly clustered structure of the films after the heat treatment. From the resistivity standpoint, the layers are practically insensitive to environmental humidity up to a value of about 53% RH and presents a good sensitivity to humidity within the range 53% - 98% RH. Source

News Article
Site: http://www.rdmag.com/rss-feeds/all/rss.xml/all

By converting sunlight into usable energy, solar thermal devices could become an important part of a sustainable future. To that end, researchers have developed a new solar-light-absorbing surface that can have almost any design, pattern, and color – useful for turning building facades and roofs into energy-capturing exteriors without sacrificing aesthetics. Since they also use similar materials as existing solar absorbers, this new kind of solar absorber could lead to wider use of solar thermal technology and more energy efficiency, said Shao-Wei Wang, Shanghai Institute of Technical Physics, China. Wang and his colleagues describe their design in Optics Express, a journal of The Optical Society (OSA). "A significant amount of energy might come from our building facades and roofs," he said.   One of the most common uses of solar thermal technology is to heat water, allowing for an enjoyable hot shower or a dip in a warm swimming pool. Hot water could also heat buildings during winter. Additionally, solar thermal technology can generate electricity. While solar panels convert sunlight directly into electricity, solar thermal devices use sunlight to first boil a liquid like water, producing gas or steam that drives power generators.   At the heart of this technology are layered surfaces called solar selective absorbers, which, as their name implies, are made from materials that absorb sunlight. To be efficient and hold onto heat, the emission of infrared light must be minimal. The problem with conventional absorbers is that the best ones are always black or dark blue. If you're hoping to incorporate the technology into a building, such a dark color doesn't always fit with the architecture and aesthetics. "A colorful world is much better than a monotonous dark one," Wang said.   Previous attempts at colorful solar absorbers have been limited. For example, the materials either couldn't absorb all wavelengths of sunlight or they emitted a lot of infrared. Each absorber also had to be the same color, making it expensive and difficult to design a façade with an image or a complex pattern.   The new absorber is covered with multiple layers of transparent dielectric materials, which can reflect light of a particular color. By changing the thickness of these layers, the researchers can tune the absorber to reflect light of almost any shade required. Some parts of the absorbing layer can be covered with a thicker transparent dielectric layer than other parts, allowing the researchers to create a single absorber with a rainbow of hues. And, it works almost as well as the best conventional ones.   In particular, the researchers made a square absorber 60 mm on each side. They covered the absorber with a mosaic of dielectric materials, forming a grid of 16 tiles. Each tile was of a different thickness – and thus a different color. Each tile, which could be made as small as one millimeter on each side, acts like a pixel on the absorber.   Using this methodology, an absorber with up to a thousand of these pixel-like color units – which would be virtually impossible with conventional absorbers – can be built and form almost any pattern you want, Wang said. For example, you could make a camouflage pattern, which would be useful for making solar thermal devices for the military.     While the technology isn't market-ready yet, he said that with enough industry investment, the methods could be commercialized in the near future.

News Article | April 19, 2016
Site: http://motherboard.vice.com/

Image of the embryos having developed to the blastocyst stage 80 hours after launch. Image: Enkui Duan Chinese scientists are creeping a tiny bit closer to the future dream of humans colonizing and reproducing in space. They’ve succeeded, reports the Chinese Academy of Sciences, in developing early-stage mouse embryos aboard the SJ-10, a satellite that was launched into orbit on April 6 from the Jiuquan Satellite Launch Center in northwest China’s Gansu Province. “This research is a very first step for [we humans] to make interstellar travel and planet colonization come true,” Enkui Duan, the principal investigator of the space mouse embryos project and a researcher at the State Key Laboratory of Stem Cell and Reproductive Biology in Beijing told me over email. I caught Duan as he spent a sleepless night travelling to retrieve the mouse embryos (some of which survived) from Sizi Wangqi in Inner Mongolia—where the SJ-10 satellite landed on April 18—and back again to his team’s lab in Beijing for further analysis. “The experiment we have proposed in space was a big challenge. We boarded more than 6,000 mouse embryos on China’s SJ-10 recoverable satellites by using our newly developed large scale mammalian embryo freezing and thawing technology,” said Duan. The embryos before launch, at the two-cell stage (not yet developed to blastocysts). Image: Enkui Duan The team developed an embryo culture system and placed it within a small enclosed chamber that provides the ideal conditions for the embryos to develop in space. While the chamber was in orbit, a camera attached to the experiment took photographs of the embryos as they developed in microgravity, and sent these images back to Earth. With the aid of their imaging technology, the researchers were able to observe how the mammalian two-cell stage embryos developed into blastocysts under microgravity after four days. Blastocysts are structures formed in the very early development of mammals. In humans blastocysts begin to form five days after fertilization. The researchers will now compare their space-developed embryos to those cultured in normal laboratory environments on Earth to see what differences there are between the two at both a cellular and molecular level. In the long run, the researchers are tying their research into the more broader issues of whether humans could survive and live healthily in space, whether they could have healthy offspring in space, and if short or long-term travel in space could affect human fertility owing to exposure to harsh space environments. In other words, they’re dreaming big. “The question we focused on is whether humans could achieve the dream of surviving and reproducing in outer space in the future,” said Duan. “Now, we have finally proven that the most crucial step in our reproduction—early embryo development—is possible in outer space.” L-R Zheng WB (designer of embryo cultural box), Enkui Duan, Lei XH (embryo researcher) at the payload transfer area. Image: Enkui Duan Duan and his team have been working on space reproductive technologies for the last couple of years, and they first attempted to develop mouse embryos in space back in 2006. That time, the team placed four-cell stage mouse embryos in the SJ-8 satellite, which beamed back high-resolution images of how those embryos were getting on. “Unfortunately, all embryos failed to develop because of the high temperature in the culture system according to the data and images transmitted from the SJ-8 satellite,” said Duan, who didn’t give up. He and his team spent the next few years persuading Chinese state officials that “failure is inevitable in the path of such space exploration,” and that the team was set on succeeding if it was given a second chance. In the meantime, Duan also collaborated with researchers from the Shanghai Institute of Technical Physics in order to improve their space-faring equipment and in-lab culture systems. Though Duan admitted that humans still had a long way to go before they can could colonize space, he was adamant that his team’s project was a leap in the right direction. “As we know, after the embryo develops to blastocyst, it must implant into the uterus then develop into a fetus. Next, we want to see whether the embryo developed in outer space could implant into the uterus correctly and develop into the final step—the fetus,” said Duan. “We will further still focus on the possibility of mammalian embryo implantation and subsequent development as well as human pregnant ability in outer space. Our final conquest, is the sea of stars.”

Discover hidden collaborations