Study shows how water dissolves stone, molecule by molecule
International team uses supercomputers, experiments to better predict chemical dissolution Scientists from Rice University and the University of Bremen's Center for Marine Environmental Sciences (MARUM) in Germany have combined cutting-edge experimental techniques and computer simulations to find a new way of predicting how water dissolves crystalline structures like those found in natural stone and...
Berkeley Lab researchers create a nonlinear light-generating zero-index metamaterial
The Information Age will get a major upgrade with the arrival of quantum processors many times faster and more powerful than today's supercomputers. For the benefits of this new Information Age 2.0 to be fully realized, however, quantum computers will need fast and efficient multi-directional light sources. While quantum technologies remain grist for science fiction, a team of researchers with...
Laser light at useful wavelengths from semiconductor nanowires
Thread-like semiconductor structures called nanowires, so thin that they are effectively one-dimensional, show potential as lasers for applications in supercomputing, communications, and sensing. Scientists at the Technische Universitaet Muenchen (TUM) have demonstrated laser action in semiconductor nanowires that emit light at technologically useful wavelengths and operate at room temperature....
- Written by Tyler O'Neal
- Published: 06 December 2013
International team uses supercomputers, experiments to better predict chemical dissolution
Scientists from Rice University and the University of Bremen's Center for Marine Environmental Sciences (MARUM) in Germany have combined cutting-edge experimental techniques and computer simulations to find a new way of predicting how water dissolves crystalline structures like those found in natural stone and cement.
In a new study featured on the cover of the Nov. 28 issue of the Journal of Physical Chemistry C, the team found their method was more efficient at predicting the dissolution rates of crystalline structures in water than previous methods. The research could have wide-ranging impacts in diverse areas, including water quality and planning, environmental sustainability, corrosion resistance and cement construction.
"We need to gain a better understanding of dissolution mechanisms to better predict the fate of certain materials, both in nature and in man-made systems," said lead investigator Andreas Lüttge, a professor of mineralogy at MARUM and professor emeritus and research professor in Earth science at Rice. His team specializes in studying the thin boundary layer that forms between minerals and fluids.
Boundary layers are ubiquitous in nature; they occur when raindrops fall on stone, water seeps through soil and the ocean meets the sea floor. Scientists and engineers have long been interested in accurately explaining how crystalline materials, including many minerals and stones, interact with and are dissolved by water. Calculations about the rate of these dissolution processes are critical in many fields of science and engineering.
In the new study, Lüttge and lead author Inna Kurganskaya, a research associate in Earth science at Rice, studied dissolution processes using quartz, one of the most common minerals found in nature. Quartz, or silicon dioxide, is a type of silicate, the most abundant group of minerals in Earth's crust.
At the boundary layer where quartz and water meet, multiple chemical reactions occur. Some of these happen simultaneously and others take place in succession. In the new study, the researchers sought to create a supercomputerized model that could accurately simulate the complex chemistry at the boundary layer.
"The new model simulates the dissolution kinetics at the boundary layer with greater precision than earlier stochastic models operating at the same scale," Kurganskaya said. "Existing simulations rely on rate constants assigned to a wide range of possible reactions, and as a result, the total material flux from the surface have an inherent variance range -- a plus or minus factor that is always there."
One reason the team's simulations more accurately represent real processes is that its models incorporate actual measurements from cutting-edge instruments and from high-tech materials, including glass ceramics and nanomaterials. With a special imaging technique called "vertical scanning interferometry," which the group at MARUM and Rice helped to develop, the team scanned the crystal surfaces of both minerals and manufactured materials to generate topographic maps with a resolution of a just a few nanometers, or billionths of a meter.
"We found that dissolution rates that were predicted using rate constants were sometimes off by as much as two orders of magnitude," Lüttge said.
The new method for more precisely predicting dissolution processes could revolutionize the way engineers and scientists make many calculations related to a myriad of things, including the stability of building materials, the longevity of materials used for radioactive waste storage and more, he said.
"Further work is needed to prove the broad utility of the method," he said. "In the next phase of research, we plan to test our simulations on larger systems and over longer periods."
- Written by Tyler O'Neal
- Published: 06 December 2013
Having the sense to cut office energy bills
Office buildings have an enormous carbon footprint, but often energy is being wasted maintaining empty rooms and spaces at a comfortable temperature. Research to be published in the International Journal of Communication Networks and Distributed Systems shows how the ubiquity of smart phones connected to the office network could be used to monitor occupancy and reduce heating or air conditioning for unused spaces.
Bruce Nordman of the Lawrence Berkeley National Laboratory, plus Ken Christensen of the Department of Computer Science and Engineering at the University of South Florida, and other colleagues from those institutions and the University of Puerto Rico at Arecibo, explain how implicit occupancy sensing can be undertaken using existing IT infrastructure. The infrastructure includes networked smart phones, devices on the local IP network like computers, and others – and avoids installing dedicated sensors in every space in a building. Their approach is to continually monitor the network addresses associated with every device, or data flowing to or from the devices.
The implicit sensing approach uses the network identity and other data and how devices are accessing specific wireless access points and other network equipment in the building and then correlates them with the assumed location of the users of those devices when mapped against the building's floor plans, or location of the access points. Unoccupied and frequently unused spaces can then have their temperature control and air-conditioning adjusted to lower power consumption, at least until the space is once again occupied. Controls could be put in place to allow temperature of a given space to be adjusted in advance for schedule occupancy.
The team describes three main advantages of their approach over dedicated monitoring equipment. First, there is no additional hardware cost in terms of devices, installation, operation, or maintenance. Secondly, sensor readings can be obtained readily over an existing network. Finally, the system can drill down to occupancy number, identity and activity, information that would not be available for dedicated sensors. Such information can be coupled to management systems or can simply be used to ensure that cleaning staff are not blasted with heat while working nor office workers chilled too drastically in a meeting room.