Science: Theoretically

HIV vaccine trial/ A new form of ice/ Crystal-clear laptop screens/ Helpful genes
An anti-HIV vaccine has been given approval for large-scale trials involving 7,500 healthy volunteers. The tests, which are the first for an HIV vaccine, will test its effectiveness as a vaccine over three years. The trial was approved by the US Food and Drug Administration, and will cost $20m (pounds 12.5m), most of which has come from private sources. The vaccine, called gp120, is made by VaxGen of San Francisco. It is intended to confer immunity by alerting the body to a single sub-unit protein in the virus - though critics have said the idea is "a total waste of time and money".

Ice-nine was just a plot device for Kurt Vonnegut - remember the novel Cat's Cradle, in which the US Army devised a form of ice in which water froze at room temperature, and so destroyed the world? But now scientists at University College, London, working with a team in Germany, have done something similar, taking the number of known "phases" of ice from 11 to 12. In the latest Nature they report that ice-XII seems to consist of "a mixture of five- and seven-ringed water molecules". However, it is only found in conditions of between 0.2 and 0.6 gigapascals - about a thousand times greater than atmospheric pressure - and below -10C. So the world is safe, for now.

Laptop computer screens of the future could use carbon films with the properties of diamonds, to glow more brightly, reports New Scientist. Motorola has found that depositing a very thin carbon film behind the screen leads to energetic electrons being emitted which could make laptop screens appear much more sparkling. The carbon screens are also flat and cheap - and they could be on the market in a couple of years, say the Motorola team.

Genes which don't seem to do anything positive to help an organism may actually confer some tiny advantage which in the long (evolutionary) run makes a difference, according to work by a team at the University of Utah. They took some yeast and made copies with randomly inserted foreign DNA. They then selected these "mutants" to find some which could withstand stressful environments (such as extreme temperatures). Yet when theyput the mutants back in competition with the parent yeast, the parents generally survived better. Joe Dickinson, who led the work, reckons that's because genes that survive the long haul of evolution confer a tiny but real competitive edge - even if they don't seem to do anything on their own.