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What's the Buzz...

How aeroplane wings really work

A Cambridge University scientist has debunked the classic explanation of how wings generate lift to keep a plane or a bird in the air, saying that erroneous description could lead to misunderstanding of aerodynamics.

Many textbooks and aircraft manuals have mentioned that a wing produces lift as air travelling over the curved topside of a wing has to travel further than wind flowing around the flat underside and so has to travel faster to keep up, generating lift.

 But according to Professor Holger Babinsky, this standard explanation was proved wrong by a simple experiment where a wing is placed in an air tunnel with jets of smoke flowing over the upper and lower surfaces.

 “A wing lifts when the air pressure above it is lowered. It’s often said this happens because the airflow moving over the top, curved surface has a longer distance to travel and needs to go faster to have the same transit time as the air travelling along the lower, flat surface,” the Independent quoted Babinsky as saying.

 “But this is wrong,” said Professor Babinsky.

 “In the worst case, [this explanation] can lead to a fundamental misunderstanding of aerodynamics.”

A video of the experiment carried out at Cambridge showed that air does indeed move faster over the upper, curved surface of a wing, but this is because of the curvature of the upper surface.

 The air does not move faster so as to “catch up” with the air moving over the comparatively shorter distance of the lower wing surface, Professor Babinsky asserted.

 The slow-motion video of the smoke jets demonstrates that the air moving over the upper surface of the wing travels further in the same amount of time than wind flowing past the lower surface.

 In other words there is no “equal transit time” between the upper and lower surfaces, as stipulated by the typical explanation.

“What actually causes lift is introducing a shape into the airflow, which curves the streamlines and introduces pressure changes – lower pressure on the upper surface and higher pressure on the lower surface,” Professor Babinsky added.

Chemicals linked to lower vaccine response in children
Chemical compounds widely used in fast-food packaging, waterproof clothing and non-stick frying pans were linked in a study out Tuesday to lower immune response by young children to routine tetanus and diphtheria immunisation shots. The study, in yesterday’s Journal of the American Medical Association (JAMA), is the first to show how perfluorinated compounds can negatively affect the response to vaccines.

PFCs can be transferred to children before birth via the mother, or after birth from exposure in the environment, according to the report.

“The negative impact on childhood vaccinations from PFCs should be viewed as a potential threat to public health,” said study lead author Philippe Grandjean with the Harvard School of Public Health. Grandjean appeared alarmed because routine childhood immunisations “are a mainstay of modern disease prevention.”

Researchers “were surprised by the steep negative associations, which suggest that PFCs may be more toxic to the immune system than current dioxin exposures,” said Grandjean.

PFCs have thousands of industrial and manufacturing uses, and most Americans have traces of the chemical compounds in their bodies.

Earlier studies have shown that PFC concentrations in mice similar to those found in people suppressed immune response. The negative effects of the compounds on people however have not been well studied.

The experts studied data on infants at the National Hospital in Torshavn, on Denmark’s Faroe Islands, during 1999-2001. Of those studied, 587 children participated in follow-up examinations at ages five and seven, when they were tested for immune response to tetanus and diphtheria vaccinations. The level of PFCs were measured in maternal pregnancy blood serum, and in the blood serum of children at age five, to determine prenatal and postnatal exposure.

The results show a link between exposure to PFCs and a lower antibody response to tetanus and diphtheria vaccines than normal.

No cardiac risk with food fried in olive, sunflower oil
Food fried in olive or sunflower oil is not linked to heart disease or premature death, but the same is not true of solid or reused oils.

While eating lots of fried food can increase some heart disease risk factors such as high blood pressure, high cholesterol and obesity, a link between fried food and heart disease has not been fully investigated.

So the study authors, led by Pilar Guallar-Castillón professor at the Autonomous University of Madrid, Spain, surveyed the cooking methods of 40,757 adults aged 29 to 69 years over an 11-year period. None of them had heart disease when the study began.

Trained interviewers asked participants about their diet and cooking methods. Questions were also asked about whether food was fried, battered, crumbed or sautéed, according to an Autonomous statement. The participants’ diet was divided into ranges of fried food consumption, the first quarter related to the lowest amount of fried food consumed and the fourth indicated the highest amount. During the follow-up there were 606 events linked to heart disease and 1,134 deaths.

The authors conclude: “In a Mediterranean country where olive and sunflower oils are the most commonly used fats for frying, and where large amounts of fried foods are consumed both at and away from home, no association was observed between fried food consumption and the risk of coronary heart disease or death.”

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