The physics of chemical waves and disease

Waves come and go, but a study of chemical waves by US physicists could improve our understanding of how pathogens flow around the body and how mutant genes spread through invading populations of viruses. The research might ultimately help medicine find a way to control the rate of viral mutation and so block the spread of retroviruses, such as HIV, which rely on mutations to overcome the body’s immune defences.

Boyd Edwards of West Virginia University has analysed the motion of chemical wavefronts through a filled tube with a fluid moving in the opposite direction through the tube. Intriguingly, he discovered that the chemical wavefront is not slowed by the liquid, which one would imagine contravenes at least one of the laws of nature. We’ve learned chemical waves are like pedestrians in a hurry, explains Edwards. Head winds don’t slow them down but may bend them out of shape. Tail winds, on the other hand, speed them along.

Edwards analysis - going against the flow

Edwards analysis – going against the flow

Edwards has previously published research on the critical wavelength needed for a river to meander and the dynamics of falling raindrops, but this current research focuses on a more esoteric phenomenon: chemical waves.

Chemical waves thrive on the diffusion and mixing of interacting ingredients. One of the most beautiful examples is the Belousov-Zhabotinsky (BZ) (BZ Ref 1 and BZ Ref 2) reaction in which a wave of changing colour sweeps through the reaction mixture. The reaction involves the interchange of a chemical by a reduction-oxidation (redox) reaction. Each step generates a catalyst that speeds up the counter reaction. Therefore, as the reduction proceeds, for instance, it produces more and more catalyst to speed up the oxidation and vice versa. The reduced state reaction is red while the oxidised state is a pale brown.

BZ reaction

BZ reaction

It takes just a tiny fluctuation in the ingredients favourable to either the reduction or the oxidation to trigger a chain of reactive events that spread outwards from the centre like ripples on a pool. The BZ reaction left unstirred produces striking geometric growth patterns. Such patterns are reminiscent of animal patterns, such as those of water snails, leopards and zebras and indeed chemical waves were first implicated in how the leopard got its spots by Cambridge mathematician and cryptography expert Alan Turing (Turing homepage and Turing reference). As one reagent diffuses and is used up, it meets its counterpart so the reaction product diffuses ‘behind’ it and meets with its counterpart propagating the counter-reaction.

The BZ reactions and its chemical cousins bring together the reaction between ingredients and how they diffuse through the reaction mixture. Edwards has used trusted fluid mechanics equations to look at a simpler version of the BZ reaction that also involves a moving chemical wavefront. He predicted that a chemical wave front moving through a tube filled with fluid moving in the opposite direction would develop a trailing spike at the centre of the tube. The spike consumes just enough extra fluid to compensate for the flow, thereby allowing the wave front to travel at its usual speed. In contrast, a chemical wave moving in the same direction as the flow is carried along by the flow, and travels faster than one would intuitively anticipate.

Edwards says that experiments are already under way at WVU to test his predictions, while doctoral student Robert Spangler is investigating the deeper theoretical implications.

Research in chemical waves may prove to be useful in medicine, since chemical waves are similar to biological waves found in the body, Edwards explains. One example is electrical waves that cause the heart muscle to contract. Research on chemical waves might lead to the design of pacemakers which can better respond to life-threatening fibrillation. The spread of pathogens, toxins and poisons through the bloodstream might also be investigated using the fundamentals of the study.

Edwards confesses to not being an expert in genetic mutation and that is research is at a scientifically fundamental level, but he says, there may indeed be eventual ties to these biological areas. The research may also have something to say about the molecular diffusion of a pathogen into uninfected blood in the bloodstream. Non-uniform fluid flow (advection) can increase the diffusion rate of a pathogen, as some portions of the chemical wavefront are carried forward faster than others by the nonuniform fluid flow.

Further reading

Phys. Rev. Lett. 89, 104501 (2002)
http://dx.doi.org/10.1103/PhysRevLett.89.104501

Boyd Edwards
http://physics.wvu.edu/people/boyd_edwards

Turing homepage
http://www.turing.org.uk/

Turing reference
http://www.ma.hw.ac.uk/~painter/research/pigmentation/fish.html

Suggested searches

Belousov Zhabotinsky reaction
Fluid mechanics
Redox reactions

Scientists conscripted in war on terrorism

The US National Academies of Science and Engineering and the Institute of Medicine are calling for the country to take full advantage of its scientific and engineering strengths to detect, thwart, and respond to terrorist attacks more effectively.

Science and technology have always provided humanity with a double-edge sword from our first crackling fires to the computer chip. But, as technology has become increasingly sophisticated the benefits of its and threats of its abuse have concomitantly grown. The Academies have released a report that now identifies actions, including deployment of available technologies, that can be taken immediately, and it points to the urgent need to initiate research and development activities in critical areas to prevent the USA, and putatively its allies from succumbing to terrorist attack.

Lewis Branscomb

Lewis Branscomb

The scientific and engineering community is aware that it can make a critical contribution to protecting the nation from catastrophic terrorism, said Lewis Branscomb, co-chair of the committee that wrote the report, and emeritus professor of the John F. Kennedy School of Government, at Harvard University, Cambridge, Massachusetts. Our report gives the government a blueprint for using current technologies and creating new capabilities to reduce the likelihood of terrorist attacks and the severity of their consequences.

The Academies’ report suggests that action can be taken now to protect and control nuclear weapons and radioactive material, to produce adequate vaccine and antibody supplies to combat biological weapons, to secure shipping containers and electric power grids, and to improve ventilation systems and emergency communications. The authors list literally dozens of specific recommendations for research and development activities that could lessen vulnerabilities to terrorism.

Richard Klausner

Richard Klausner

Biomedical research know-how, for instance, might be harnessed to develop drugs to fight pathogens for which there are currently no treatments. Electrical engineers could generate smart power grids and adaptive systems that can cope even when sections are sabotaged or seriously damaged.

Critically, the report points to the opportunity new computer programs provide in data-mining and scanning information to make it easier for the intelligence services to join the dots between seemingly unrelated snippets of information.

Research is also to be encouraged in the development of new emergency equipment, such as better protective gear for rescue workers and sensors to alert them to radiological or chemical contamination and other hazards when they enter a disaster area. These opportunities will go unrealised unless the government is able to establish and execute a coherent strategy for taking advantage of the nation’s scientific and technical capabilities, adds co-chair Richard Klausner (Gates Foundation team), Executive Director of the Global Health Program, at the Bill and Melinda Gates Foundation in Seattle. The federal agencies with science and engineering expertise are not necessarily the same as the agencies responsible for deploying systems to protect the nation, and they all must work together to discover and implement the best counter-terrorism technologies.

The report is aimed squarely at the US federal government, but many institutions from cities and states to private companies and universities will have to work together to discover and deploy anti-terrorism solutions.

It appears that it will hit home, Branscomb told Spotlight. At a hearing before the House Science Committee and the Senate subcommittee for Science, with some eighteen members present, both the senior senator (a democrat) and the senior congressman (a republican) endorsed the two key institutional recommendations. Since they are responsible for marking up that part of the Bill establishing the new department and dealing with science and technology it seems likely that the Academies’ study will influence the legislation that creates the department, he adds.

Making the Nation Safer: The Role of Science and Technology in Countering Terrorism will be available from the National Academy Press.

Further reading

Lewis Branscomb
http://belfercenter.ksg.harvard.edu/experts/125/lewis_m_branscomb.html

Bill and Melinda Gates Foundation
http://www.gatesfoundation.org/Pages/home.aspx

Making the Nation Safer: The Role of Science and Technology in Countering Terrorism
http://www.nap.edu/catalog.php?record_id=10415

Suggested searches

USA science policy

Evolutionary materials revolution

Quantum mechanics and biological evolution could be combined to make a host of new materials, such as tough, lightweight superalloys.

Jens Norskov and his colleagues at the Technical University of Denmark are coupling revolutionary quantum mechanical techniques with an evolutionary search algorithm inspired by natural selection to find new super alloys. Their method, however, could be used in the discovery of new materials for use in everything from electrical batteries to catalysts for chemical reactions as well as the more traditional stamping ground of superalloys – the aerospace and rocketry components that can withstand protracted exposure to temperature above 650 Celsius while in operation.

Jens Norskov

Jens Norskov

Until recently, predicting the properties of a particular blend of metals without actually creating the alloy has required incredibly unwieldy computational techniques. Moreover, the characteristics of new alloys tend to reveal themselves fully only experimentally once the material has been made. After all, even a handful of metals can be combined with each other in hundreds of thousands of possible arrangements. The hunt for better alloys has typically required patience and luck.

Norksov’s team, however, wanted to bring a more rational approach to bear on the design of novel alloys. They have now identified twenty promising alloys from a possible two hundred thousand combinations, without making a single alloy in the laboratory.

An array of combinations

An array of combinations

Their method is based in part on a modelling technique known as density functional theory (DFT), which was the subject of the 1998 Nobel Prize for Chemistry. DFT can help predict material properties by modelling the way electrons change depending on how the atoms in the material are hooked together.

Norskov and his team could have simply applied DFT to the myriad possible alloys, but instead they began investigating alloys containing four metals and used a process of natural selection to pick out the fittest. To start, they generated a population of alloys – on the computer – each consisted of the possible combinations of four metals selected from thirty-two candidate metals. They then mutated and randomly bred the metals to create offspring. They then picked out the most stable materials and allowed the offspring to breed with each other to make a new generation and so on until they had selected the fittest group of combinations.

They tried to bias the result by starting with several different initial alloy populations but each time the same final group of alloys survived. Interestingly, the generation game spawned several super alloys that were already known, which lent great credence to the approach. But, more importantly, other survivors included a number of super alloys that are yet to be investigated experimentally. The researchers hope believe these materials may just as good if not better than the known super alloys produced.

Norskov points out that stability is not the only criterion for choosing an alloy for a particular application but picking out unstable materials is pointless, so it is a crucial first step in a process of discovery that will greatly cut down on expensive and time-consuming laboratory work.

Further reading

Phys. Rev. Lett., 88, 255506 (2002)
http://link.aps.org/abstract/PRL/v88/e255506

DOI: 10.1103/PhysRevLett.88.255506

Jens Norskov
http://www.camd.dtu.dk/Medarbejdere/Jens_cv.aspx

1998 Nobel Prize for Chemistry
http://nobelprize.org/nobel_prizes/chemistry/laureates/1998/

Suggested searches

Super alloys
Density functional theory