Photographs of a liquid drop hitting a smooth dry substrate.

Everyone has seen water droplets splash off a surface but this phenomenon is more complicated than it first appears, as recent experiments at the University of Chicago have demonstrated. Not surprisingly, the experiments show that the viscosity of the liquid plays a critical role, but so does the pressure and molecular weight of the gas that the drop falls through, PhysicsWeb.org said.
Scientists have been interested in splashes since at least the late 19th century when A M Worthington photographed what happens when drops of milk or mercury hit a smooth surface. Harold Edgerton and colleagues also photographed drops hitting thin layers of fluid in the 1950s. In general, when a drop hits a solid surface it spreads out and breaks up, creating a splash of smaller droplets.
Sidney Nagel and colleagues at Chicago have now seen something that no one has seen before by releasing drops of alcohol from various heights onto a glass microscope slide inside a vacuum chamber and recording what happens with a high-speed video camera. The team used three liquids with different viscosities (methanol, ethanol and 2-propanol) and four gases with different molecular weights (helium, air, krypton and sulphur fluoride) inside the vacuum chamber. Moreover, they varied the pressure in the chamber from just 1 kilopascal up to 100 kilopascals (atmospheric pressure).
To their surprise, the Chicago physicists found that the surrounding gas played a key role in the splashing process. In particular, they found fewer droplets were ejected from the surface as the pressure was lowered, and that no droplets emerged below a threshold pressure (see figure). They also found that the threshold pressure scaled with the molecular weight of the surrounding gas. Moreover, they found that 2-propanol, which has the largest viscosity of the three liquids, had the lowest threshold pressure.

Larger babies have higher risk of developing certain cancers in adulthood, research suggests.
According to BBC News website, UK and Swedish researchers found higher rates of digestive and lymphatic cancer among people who were big at birth.
Bigger female babies went on to have significantly higher rates of breast cancer--but much lower rates of cancer of the womb lining.
The researchers, from the London School of Hygiene and Tropical Medicine and the Universities of Uppsala and Stockholm examined the records of 11,166 babies born between 1915 and 1929 in Sweden.
Of these one in four was diagnosed with cancer between 1960 and 2001.
The researchers found that each increase in birth weight of 450g was associated with a 17% increase in lympathic cancers, and a 13% increase in digestive cancers, including stomach, colorectal and pancreatic cancer.
Women in the highest category of birth weight (4kg or greater) were four times as likely to get breast cancer before age 50, than those who weighed less than 3kg.
In contrast, women who were large at birth were only half as likely to get endometrial cancer as their smallest counterparts.
The researchers accept that some of their findings may have arisen by chance.
They also stress that birth weight only seems to be associated with an increased risk of certain cancers--and by no means all forms of the disease.
However, they speculate that the conditions inside the womb--for instance the levels of circulating hormones--may have a direct impact on the later chances of developing cancer.

Exhaust fumes from traffic could be turning airborne proteins into more powerful allergens, explaining why asthma and other allergies are on the rise in urban areas, nature.com said.
Researchers have found that the mixture of nitrogen dioxide and ozone produced by vehicles can add the chemical group nitrate to the protein molecules that account for up to 5% of the particles in our air.
Nitration could boost the power of existing allergens, or even make benign proteins allergenic, says Ulrich P?schl, an atmospheric chemist from the Technical University of Munich, Germany, who worked on the study. Previous research has shown that nitrated proteins bind more strongly to the antibodies that cause allergic reactions.
Medical studies have shown a link between air pollution and rising allergy rates. But scientists have not been able to pin down how one causes the other. Nitration is now a prime suspect, P?schl says.
The team collected samples of urban dust. Up to 0.1% of the proteins in the dust had been nitrated by traffic smog, they found.
But for allergenic proteins from birch pollen left at a busy Munich road junction for a few days, that figure rises to 10%. And for allergenic proteins exposed to smog in the laboratory, nitration rose to 20%, they report in Environmental Science and Technology1.
The smog reacts with the amino acid tyrosine, a common component of proteins. Birch-pollen protein has seven tyrosine components and was readily nitrated by traffic smog. Proteins that are easiest to nitrate might trigger the strongest allergic reaction, says P?schl.
It's not clear how nitrate groups increase the allergic response, he adds, but previous studies have suggested that the body uses tyrosine nitration as a marker to attract antibodies to inflamed tissue.
P?schl thinks that the finding could help to develop drugs that stop nitrated proteins disrupting our immune systems. And it strengthens the case for reducing nitrogen-dioxide emissions, he adds.