New worlds: The intricate beauty of cracked glass

Researchers have long pondered the origin of the delicate, criss-cross faceted patterns that are commonly found on the surfaces of broken material. Typical “crack speeds” in glass easily surpass a kilometer per second, and broken surface features may be well smaller than a millimeter. Since the formation of surface structure lasts a tiny fraction of a second, the processes generating these patterns have largely remained a mystery. Now there is a way around this problem. Replacing hard glass with soft but brittle gels makes it possible to slow down the cracks that trigger fracture to mere meters per second. This novel technique, reported recently in Nature Materials, has enabled researchers Itamar Kolvin, Gil Cohen and Prof. Jay Fineberg at the Hebrew University of Jerusalem's Racah Institute of Physics to unravel the complex physical processes that take place during fracture in microscopic detail and in real time. Their work sheds new light on how broken surface patterns are formed. Surface facets bounded by steps are formed due to a special “topological” arrangement of the crack that cannot easily be undone, much as a knot along a string cannot be unraveled without pulling the whole length of the string through it. These “crack knots” increase the surface formed by a crack, thereby creating a new venue for dissipating the energy required for material failure, and thereby making materials harder to break. “The complex surfaces that are commonly formed on any fractured object have never been entirely understood,” said Fineberg. “While a crack could form perfectly flat, mirror-like fracture surfaces (and sometimes does), generally complex faceted surfaces are the rule, even though they require much more energy to form.” EASY MULTIPLICATION Elementary school teachers devote many lessons and children spend much time doing homework to master the multiplication tables; but it really doesn't have to be difficult to get it down pat. A lovely new hardcover book for children by Schocken Publishers (www.schocken.co.il) with 10 double pages provides all the exercises up to 12X12 using pullouts to reveal the answers. Called Luah Hakefel, the colorful NIS 58 book begins with a regular table showing all the permutations. Each page has a question mark in a cardboard “hole” that reveals the answer when its tab is pulled. On the final page, there is an empty table to be filled in by the much-more-mathematical child that results from using the book. Congratulation to the publishers for their imaginative product. FIGHTING THE AFLATOXIN Ground nuts such as peanuts are nutritious and relatively cheap, but a fungus called aflatoxin can make them and other plant species dangerous. But now, scientists at the Danforth Plant Science Center in St. Louis, Missouri, and their collaborators at Louisiana University, the US Department of Agriculture and the International Crops Research Institute for the Semi-Arid Tropics in Hyderabad, India have made a significant research breakthrough by suppressing the aflatoxin-producing fungus in groundnut. The discovery has the potential to drastically improve food safety and reduce losses caused by the contamination from the poisonous carcinogen, aflatoxin. The discovery was recently published in the Plant Biotechnology Journal. Aflatoxins pose a major risk to human and animal health worldwide and result in an enormous amount of food waste. The molds, Aspergillus flavus and Aspergillus parasiticus, which infect groundnut, maize and cottonseed produce these toxins which suppress the immune system, hinder growth in children and even cause liver cancer. The fungus that produces these toxins can lay dormant in soil for years. It infects maize and ground nut during drought and heat stress. Contamination also happens when grain is stored in hot, humid and poorly- ventilated conditions. Since aflatoxins are potent carcinogens, the US authorities do not allow the sale and export of food with aflatoxin levels exceeding 20 parts per billion (ppb). European Union standards are more stringent at 2 ppb. “Plant defensins [proteins active against bacteria, fungi and many viruses] exhibit potent antifungal activity against several economically important fungal pathogens. It is exciting to see the successful application of this technology for reducing the pre-harvest infection by Aspergillus and alleviating the burden of mycotxins in genetically modified ground nut. “If deployed commercially, this technology has significant potential to contribute to food safety in the under-developed and developing countries where mycotoxin contamination of groundnut, maize, chili and cottonseed pose a major threat to human and animal health,” said Dr. Dilip Shah of Danforth. World peanut production totals about 29 million metric tons per year. The US is the world's third-largest producer, after China and India. Two complementary approaches are being deployed to address the issue. Shah and his team transferred defensins from alfalfa and the Mediterranean clover to the DNA of an Aspergillus-susceptible peanut variety widely grown in Africa and India which allowed the groundnut to stop the fungus from infecting the plant. The team transferred small RNA molecules from the Aspergillus fungus that are involved in the aflatoxin synthetic pathway. The nuts produced these RNA molecules during fungal attacks and inactivated target genes responsible for aflatoxin synthesis. The technology is also translatable to maize. animal feed, pistachios and almonds.

New worlds: The intricate beauty of cracked glass

Jay Fineberg at the Hebrew University of Jerusalem’s Racah Institute of Physics to unravel the complex physical processes that take place during fracture in microscopic detail and in real time.

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