SCIENCE & TECHNOLOGY


Concrete advances in nanotech
By Gurvinder Singh Bedi
Nanotechnology is usually associated with high profile biomedical, telecommunication and military applications. But for most of us, one of the main ways this science at nanometre-level is revolutionising our daily lives is right under our feet – concrete. Researchers are helping lead the way in understanding the nanoscale properties of concrete and using this knowledge to create stronger and more durable concrete in a more sustainable manner.

Stem-cell based heart valves for children
By Delthia Ricks
Doctors say they are a significant step closer to producing stem-cell-generated heart valves for children, structures that can grow with the child, eliminating the need for repeat surgeries as now is the case when conventional methods are used. Medical researchers at Children’s Hospital in Boston say they can create the valves from stem cells derived from the bone marrow and coax those cells in the lab to grow into a complete, functioning heart valve.

Prof Yash Pal

Prof Yash Pal

THIS UNIVERSE
PROF YASH PAL
Rain falls in drops. Why does it not flow down  like a river?
This is a beautiful question. I am sure you would agree that it would be a bit unpleasant if a river were to descend on us unexpectedly in the middle of the night, as rain often does.





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Concrete advances in nanotech
By Gurvinder Singh Bedi

Nanotechnology is usually associated with high profile biomedical, telecommunication and military applications. But for most of us, one of the main ways this science at nanometre-level is revolutionising our daily lives is right under our feet – concrete.

Researchers are helping lead the way in understanding the nanoscale properties of concrete and using this knowledge to create stronger and more durable concrete in a more sustainable manner.

A quick overview of the scope of the global concrete industry and its environmental impact makes it clear why R&D advances in nanotechnology will have enormous economic, social and environmental impact. Concrete has the largest production of all man-made materials with an annual global production of about one cubic metre for every person on earth.

Concrete is a composite mixture containing a binding phase, a cement paste, and aggregates. The paste, composed of hydrated Portland cement and water, coats the surface of the fine and coarse aggregates. Through a chemical reaction called hydration, the paste hardens and gains strength to form the rock-like mass known as concrete.

Portland cement is manufactured by igniting, at 1300-1500 degree centigrade, a mixture of raw materials, mainly composed of limestone (calcium carbonate) and other aluminium silicates such as clays and shale. The combination of energy use and carbon dioxide output makes cement production a leading contributor to green house gas production, accounting for six per cent of the annual global total.

Nanoscience has a central role to play in producing innovative concretes for the 21st century. Nanoscience enables scientists to work at the molecular level – atom by atom – to develop new materials with fundamentally new physical and chemical properities.

Nanotechnology is already used in a variety of ways to produce innovative construction materials. Nanoarticulate additives are now widely used as fillers in protective paints, coatings, and clean-up systems for buildings and monuments exposed to radioactive materials.

Other applications of nanotechnology in construction include its use in steel reinforcement, fibre-reinforced plastics, nanofibre additives and nanoporous ceramics for environmental applications.

The researchers’ interests lie primarily in developing new cements, concretes, admixtures (concrete performance-enhancing additives) and innovations based on these discoveries. Initial research has concentrated on such areas as low energy cements, nano-composites, improved particle packing, and novel approaches for the controlled release of chemical admixtures.

Hydrated cement is porous with a pore size distribution that ranges from the nanometres to millimetres. However, the pores are also a core weakness: they are a pathway for chloride salts and other chemicals to seep into concrete causing cracking and deterioration that costs the economy annually.

The addition of nanoscale particles to concrete is expected to improve control of concrete porosity beyond what is presently possible with silica fume.

The performance of concrete can also be improved by adding nanofibres. Carbon nanotubes have the potential to enhance the strength, to effectively hinder crack propagation in cement composites, and to act as nucleating agents. Reinforcing concrete with nanofibres will produce tougher concretes by interrupting crack formation as soon as it is initiated.

Development of efficient nucleating agents and low energy cements will contribute to increased use of supplementary cementing materials, such as fly ash and slag, while making concrete production more environmentally sustainable.

While the exploration for various applications of nanotechnology to develop innovative construction materials continues, it is already clear that the science of the very small in making big changes, with numerous economic benefits for the construction industry.
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Stem-cell based heart valves for children
By Delthia Ricks

Doctors say they are a significant step closer to producing stem-cell-generated heart valves for children, structures that can grow with the child, eliminating the need for repeat surgeries as now is the case when conventional methods are used.

Medical researchers at Children’s Hospital in Boston say they can create the valves from stem cells derived from the bone marrow and coax those cells in the lab to grow into a complete, functioning heart valve. The process is called tissue-engineering, an area of science in which investigators are attempting to develop replacement parts for structures damaged by disease and age.

Dr. John Mayer said the valves should be available for clinical trials within the next three years. “These are stem cells derived from the bone marrow,” Mayer said. “They are not embryonic stem cells.”

Mayer and his collaborators report their work in this week’s edition of Circulation, a journal of the American Heart Association. “We had published other work on this two years ago in the same journal where we actually implanted them in sheep for periods up to eight months,” he said.

Tissue engineers at Wake Forest University in North Carolina already have grown a functioning human bladder derived from stem cells. The new work involving heart valves, which provide one-way blood flow from the heart’s right ventricle into the pulmonary artery, are more complex. They have three “leaflets” – flaps – that must open and close in synchrony.

Dr. David Martin, director of research and development at Tepha Inc., a Boston-area biotechnology company, has aided previous experiments at Children’s Hospital, providing the complex material on which the valves are grown.

“The scaffold is biodegradable, but it mimics the shape and size of a heart valve,” Martin said, adding that when stem cells are introduced to the scaffold in the laboratory “they invade it.” Growth is encouraged through a soup of cellular nutrients.

“We are fine-tuning the technique to make this whole process work better,” Mayer said. Surgeons have long been able to repair congenital heart defects in children by implanting artificial valves made of synthetic materials, or they have used valves from pigs. Either way, children grow and need replacements, which means at least two or three repeat surgeries.

Mayer, a pediatric heart surgeon, said there are several pediatric heart conditions that lend themselves to repair with a tissue-engineered valve.

By arrangement with LA Times-Washington Post

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THIS UNIVERSE
PROF YASH PAL

Rain falls in drops. Why does it not flow down like a river?

This is a beautiful question. I am sure you would agree that it would be a bit unpleasant if a river were to descend on us unexpectedly in the middle of the night, as rain often does.

As you know, rain is made up of moisture that is evaporated from large bodies of water. The amount of water vapour in the atmosphere increases when the water bodies are hot. Moisture laden air moves towards land when it becomes hotter than the sea. When this air rises, say by going over a mountain, it cools. Cool air cannot hold as much vapour as hot air. Therefore the vapour condenses into clouds.

Clouds are made up of tiny drops of water suspended in the air. An upward motion of the clouds cools them and the tiny droplets join each other to become bigger. Sometimes these droplets freeze into tiny crystals of ice. Large drops and ice crystals become too heavy to float around in the atmosphere. They start descending. In our part of the world the ice crystals melt and the water droplets get bigger while coming down.

But they come down only as drops and not torrents of water as if a tap had been opened. Various parts of the cloud do not act in unison while rising up to colder regions. No air mass is capable of suddenly removing all the heat from the vapour in the atmosphere to turn it into a lake of liquid water that might fall or flow onto the earth as a river.

Incidentally, even if there were a large tank of water very high in the atmosphere and a tap was used to bring a stream down to the earth, the result would be a thick shower and not a steady connected stream.

Just try it by opening the tap of a water jug held over the ledge of a roof. Here I will not go into the explanation for breaking up of the stream while descending.

The fact that cool air cannot hold as much moisture as hot air is easily proved by a simple experiment.

Put some ice in a metal glass and leave it on the table. After some time you would notice that the glass is wet on the outside. This is due to the moisture that warm air has shed on being cooled by touching the cold glass.
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