Emma Sanders, Author at New �Ӱ�ԭ��

Planting season grows with spray-on coats for crops

Emma Sanders — Sat, 18 Nov 1995 00:00:00 +0000

SHRINK-WRAPPED fruit and vegetables are a common sight in the local supermarket. But now some farmers are to go one step further and shrink-wrap seeds to grow their crops. Researchers in the US are wrapping seeds in a new type of plastic called Intellicoat which protects them from fungal attack in cold, wet soil and then disintegrates when the weather improves and the soil warms up enough for the seeds to germinate.

According to Ray Stewart, who invented the coating, it will solve the problem farmers have in deciding on the best time to plant. “At the moment the farmer has a dilemma,” says Stewart. “Plant seeds too late and he’ll have a short growing season and yields will suffer. Plant seeds too early and he has the possibility of producing more crop, but the seeds will be susceptible to fungal attack in the cold, wet soil.” Intellicoat avoids the problem by keeping the seeds dry until the soil is warm enough for germination.

Crops grown from treated soya bean and sweetcorn seeds have just been harvested in Iowa and Nebraska. Spring was particularly cold and wet in these regions, delaying planting for most farmers. But the plastic-coated seeds were planted early and gave a significant increase in yields – up to 50 per cent in some cases. Stewart now wants to try planting seeds in the late autumn to avoid spring planting altogether.

Research is underway to investigate the coating on other crops. Cotton, which suffers a lot from cold injuries, and rice, which is particularly susceptible to fungal attack, are both on the list.

Unlike food in the supermarket, the seeds do not have to be wrapped individually. “We produce our plastic in a water-based suspension like a paint and then spray this onto the seeds, which are being agitated.” The process has now been given approval by the US Environmental Protection Agency.

Stewart works for Landec Corporation of Menlo Park, California. The company specialises in side-chain crystallisable polymers. These abruptly change their characteristics at a threshold temperature. Below the threshold, the structure is crystalline, but above it, the polymer becomes an amorphous mass. The key lies in hydrocarbon side chains that branch off the central, fatty polymer. By adjusting the length of the hydrocarbon side-chains, the Landec researchers can control the temperature at which the switch occurs to within 1 °C. The longer the carbon chain, the higher the plastic’s transition temperature.

Dwarf galaxy gives life to neighbour

Emma Sanders — Fri, 31 Mar 1995 23:00:00 +0000

FOR the first time, a British astronomer has shown that a gravitational interaction between two neighbouring galaxies could have “activated” the larger of the two. A small proportion of galaxies have extremely dense centres called active galactic nuclei which emit huge amounts of radiation. These dense central regions are thought to form when vast quantities of material falls towards a black hole at the core of a galaxy. When so much material accumulates in a relatively small space, it causes an explosive release of energy;

For some time astronomers have suspected that gravitational interactions between neighbouring galaxies could trigger active galactic nuclei. Galactic interactions can cause vast upheavals of gas, dust and stars, and so could easily send material spiralling towards the black hole at the centre of a galaxy; Until now, however, there has been no hard evidence linking such interactions with the formation of active galactic nuclei.

Carole Mundell of the University of Manchester’s Jodrell Bank observatory;, made the new observations using the Very Large Array (VLA), a network of 27 radio dishes in the New Mexico desert. Many active galaxies are very distant, but Mundell looked at a relatively nearby example called NGC3227, which lies 50 million light years from the Earth.

Mundell knew that NGC3227 was interacting with another galaxy; because two huge plumes of gas have been pulled from its core in opposite directions out into space. Each plume is about 150 000 light years long. This distortion was thought to be caused by the gravitational pull of another galaxy called NGC3226. But Mundell’s new observations reveal that both the plumes and NGC3227’s active nucleus were probably caused by a more subtle galactic interaction.

The VLA images of the galaxy’s core clearly show the star-filled disc at its centre, but there is also a strange rotating blob of gas with about one tenth of the mass of NGC3227. Mundell believes this is a dwarf galaxy which is merging with NGC3227. Over millions of years, this dwarf galaxy may have wandered back and forth, forming the two plumes by pulling gas from NGC3227. More importantly, the dwarf has enough mass to have disturbed the central region of NGC3227, causing material to fall towards the black hole that is thought to lurk in the galaxy’s core and form the active galactic nucleus.

Mundell described her new results in London last month, at a meeting of the Royal Astronomical Society.

Birth of a barred spiral galaxy

Emma Sanders — Sat, 19 Nov 1994 00:00:00 +0000

SOME spiral galaxies have an elongated “bar” of stars in their centre. Now
astronomers have found that a galaxy known as NGC 3359, has a bar that has
only recently formed. According to Pierre Martin at Steward University and
Jean-Rene´ Roy at Laval University in Quebec, the galaxy provides an
unprecedented opportunity to observe one evolving from a normal spiral into a
barred spiral.

Bars are composed of dense clusters of dust and stars. The gas, churned up
by their formation, can be swallowed by the hungry black holes thought to lurk
in the heart of many galaxies. This may trigger the formation of some of the
Universe’s most energetic objects such as quasars. About 30 per cent of all
galaxies are barred spirals.

Bars are created in a similar way to spiral arms in galaxies, such as our
Milky Way. Stars circling the centre of galaxies are disturbed in their motion
by the passage of a so-called density wave that propagates out from the centre
of the galaxy The formation of a bar in a spiral galaxy is thought to trigger
a knock-on effect right to the outer regions of the galaxy. Evidence for this
theory lies in the observation of chemical abundances in galaxies.

In most spiral galaxies the concentration of elements heavier than hydrogen
and helium decreases with distance from the centre of the galaxy. This is
because the heavy elements that stars create by fusion are blown out into
space, where they provide the raw material for making a new generation of
stars. The rate of star formation is greatest in the centre of a spiral
galaxy, where stars are most concentrated. But in barred spirals the bar mixes
up the elements throughout the galaxy. As a result, the concentration of heavy
elements drops off less sharply with distance from the galaxy’s centre.

Using spectroscopic analysis, Martin and Roy found that the concentration
of heavy elements in NGC 3359 decreases with radius as it does in normal
spiral galaxies. This implies that little mixing has taken place. The
astronomers believe this is because the bar formed only recently. It is so
young that the gas flows created by the bar are only just starting to disturb
neighbouring stars in the galaxy and mix the chemicals.

When Martin and Roy examined chemical abundances within the bar, they found
evidence of a gas flow that they attribute to material falling into the centre
of the galaxy.

This is what would be expected if there is a massive black hole at the
galaxy’s core. The centre of our own Galaxy is itself very active but
observations are hampered by the large amount of dust that lies between it and
the Earth.

These latest observations of the young bar in NGC 3359 may have important
implications for determining the processes at the heart of many galaxies.