A University of British Columbia astronomer with an international team has discovered the largest structures of dark matter ever seen. Measuring 270 million light-years across, these dark matter structures criss-cross the night sky, each spanning an area that is eight times larger than the full moon.

“The results are a major leap forward since the presence of a cosmic dark matter web that extends over such large distances has never been observed before,” says Ludovic Van Waerbeke, an assistant professor in the Dept. of Physics and Astronomy.

To glimpse the unseen structures, the team of French and Canadian scientists “X-rayed” the dark matter, an invisible web that makes up more than 80 per cent of the mass of the universe.

The team used a recently developed technique called “weak gravitational lensing,” which is similar to taking an X-ray of the body to reveal the underlying skeleton. The study relied on data gathered from the world’s largest digital camera.

“This new knowledge is crucial for us to understand the history and evolution of the cosmos,” says Van Waerbeke. “Such a tool will also enable us to glimpse a little more of the nature of dark matter.”

The astronomers observed how light from distant galaxies is bent and distorted by webs of dark matter as it travels toward Earth. They then mapped dark matter structures by measuring the distortions seen in these galaxy light patterns.

The study involved 19 researchers from 11 institutions and was led by UBC, the Institut d’Astrophysique de Paris, the Universite Pierre and Marie Curie (UPMC) and the University of Victoria. Van Waerbeke and his co-authors will publish their findings in a forthcoming issue of the journal Astronomy and Astrophysics. The submission can be seen at: http://arxiv.org/abs/0712.0884.

The team spent several years developing the gravitational lensing tool, which is one of the major goals of the Canada-France-Hawaii-Telescope (CFHT) Legacy Survey.

The gravitational lensing technique also played a pivotal role in another recent UBC first: UBC astrophysicist Catherine Heymans and Van Waerbeke produced jointly with an international team the highest resolution map ever of dark matter.

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The mystery over the identity of the woman behind Leonardo da Vinci’s “Mona Lisa” painting has been solved once and for all, German academics at Heidelberg University announced on Tuesday.

Mona Lisa is “undoubtedly” Lisa Gherardini del Giocondo, according to Veit Probst, director of the Heidelberg University Library.

Conclusive evidence came from notes written in October 1503 in the margin of a book.

Discovered two years ago in the library’s collection by manuscript expert Armin Schlechter, the notes were made by Florentine city official Agostino Vespucci, an acquaintance of Leonardo da Vinci, in an edition of letters by the Roman orator, Cicero.

In his annotations, Vespucci wrote that Leonardo was working on three paintings at the time, including a portrait of Lisa del Giocondo.

“All doubts about the identity of the ‘Mona Lisa’ have been eliminated,” the university said in a statement.

Vespucci’s notes also “establish more precisely the year the painting was done,” the university said.

Until now, the only other source to have identified the sitter in Leonardo’s masterpiece as Lisa Gherardini, was the 16th century painter and art historian Giorgio Vasari.

In his work “Lives of the Artists,” Vasari named Lisa Gherardini, the wife of the wealthy Florentine silk merchant Francesco del Giocondo as the subject of the portrait and concluded that the portrait was painted between 1503 and 1506.

But doubts about Vasari’s attribution have always abounded since he was known to rely on anecdotal evidence.

The work is unsigned, undated and bears nothing to indicate the sitter’s name. Attempts to solve the mystery surrounding her famous smile as well as her identity have included theories that she was the artist’s mother, a noblewoman, a courtesan, even a prostitute.

There have also been theories that the sitter was happily pregnant, or affected by various diseases ranging from facial paralysis to the compulsive gnashing of teeth.

“The German finding confirms that Vasari is indeed a reliable source,” Giuseppe Pallanti, the author of two books on the “Mona Lisa,” told Discovery News.

Pallanti was the first historian to identify the sitter in Leonardo’s portrait as Lisa Gherardini, following 25 years of research.

“Indeed, I found documents showing that Leonardo’s father — a local notary, Ser Piero da Vinci — and Lisa’s family were neighbors, living about 10 feet away from each other in Via Ghibellina,” Pallanti said. “Leonardo met a pregnant Lisa in 1500 in Florence. In December 1502 she gave birth again.”

According to Pallanti’s research, Lisa Gherardini, a member of a minor noble family of rural origins, was born on June 15, 1479, in a rather ugly house in Via Sguazza in Florence.

In 1495, when she was 16 years old, she married the merchant Francesco del Giocondo. Ser Francesco was 14 years her senior and had lost his first wife, Camilla Rucellai, the previous year.

The girl moved to Del Giocondo’s house, located in today’s San Lorenzo market quarter. Though the house was big and beautiful, the surroundings were less than ideal. Prostitutes populated the area, which was a sort of Renaissance red light district.

In that house, Lisa gave birth to five children: Piero, Andrea, Giocondo, Camilla and Marietta.

Pallanti was also able to reconstruct Lisa’s last years. She died four years after her husband’s death on July 15, 1542, at age 63, and was buried in the convent Saint Orsola.

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In a study that could open up the field of virology to an entirely new suite of possibilities and that paves the way for future drug research, scientists at Rockefeller University and the Aaron Diamond AIDS Research Center have pinned down a molecule on the surface of human cells that helps keep particles of mutant strains of HIV from spreading. Rather than floating off to infect more cells, the protein contains the virus particles by keeping them attached to the parent cell’s outer membrane, as if stuck there with glue.

Two years ago, Paul Bieniasz — head of the Laboratory of Retrovirology and ADARC scientist — discovered that normal HIV-1 particles are able to extricate themselves from the sticky membrane surface using a protein called Vpu. Bieniasz has been searching for the source of the glue itself ever since. Now, in an advanced online publication in Nature, he and his colleagues report that they found it: a protein they dubbed “tetherin” for its ability to keep viruses tied to a cell.

“All we knew when we started this two and a half years ago was that a virus lacking Vpu was released less efficiently from cells.” Bieniasz says. “And we had some electron micrographs that showed virus particles stuck there on the surface and clustered inside cells.” Once they started looking carefully at the reasons behind this, they found an antiviral mechanism keeping the HIV-1 mutant particles tethered to the cell. And it wasn’t just HIV — the glue appeared to interfere with the spread of other membrane-encapsulated (or “enveloped”) viruses, too.

To track down the cause of stickiness — and the likely reason HIV evolved Vpu — Bieniasz and his team looked at gene activity across all known human genes, making comparisons between cells that require Vpu for HIV-1 release and those that don’t. Ultimately, they narrowed it down to one very likely candidate. And the candidate, the tetherin protein, passed all the tests the researchers threw at it: When Vpu was not present but tetherin was, large numbers of virus particles piled up on the cell surface. When tetherin was missing, however, even the Vpu-deficient viruses were able to escape.

“We’ve discovered a new way that cells defend themselves against viruses,” Bieniasz says. “I think this will open up a new area of study in virology: how this protein antagonizes other viruses, and how viruses learn to get around it.” Going forward, his lab will focus on how broad tetherin’s antiviral activity is, and whether variations of it exist that might confer additional immunity or sensitivity to HIV and other viruses. And, he notes, if drug researchers are able to interfere with the interaction between tetherin and Vpu, their newly discovered protein might even provide a potential therapeutic target.

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