Laputan Logic
Thursday, June 26, 2003
  Eclipses and Pinhole Sundials

Pinhole sundials are just the sort of wonderful devices that one might find in a cathedral built during the Renaissance.

The sundial works by focussing the sun's rays into a bright spot on the church's floor. The movement of this spot marks the course of the day.

The interesting aspect here is that the shape of the spot is not simply due to the shape of the hole that it passes through. The hole is so small that it actually acts like a lens and what is displayed is really an inverted image of the sun itself. It works just like a giant pinhole camera.

This becomes more apparent when the spot is observed during a solar eclipse...


reposted for the Collaboratory
  MEMS Pinball

Scientists in Sweden have developed a novel technique for making micromachines and demonstrated its potential by making a micro pinball table in which silicon cantilevers acted as the 'flippers', magnetic beads 150 microns in diameter were the balls, and the table measured 25 millimetres square.The table was tilted at an angle of 20 degrees to the horizon.

They found that the speed of a ball could reach up to 0.75 kilometres per hour - or 210 000 microns per second. This is equivalent to a football having an almost supersonic speed of 1125 km per hour (see a movie of the action).

"The pinball games are used for demonstrating this simple and easy process," says researcher Martin Bring. "It also demonstrates some of the effects that occur on the micrometer level, such as small apparent inertia."

Tuesday, June 24, 2003
  View morphing

I'm sorry but I just happen to think that this is really really cool.

Image morphing techniques can generate compelling 2D transitions between images. However, differences in object pose or viewpoint often cause unnatural distortions in image morphs that are difficult to correct manually. Using basic principles of projective geometry, this paper introduces a simple extension to image morphing that correctly handles 3D projective camera and scene transformations. The technique, called view morphing, works by prewarping two images prior to computing a morph and then postwarping the interpolated images. Because no knowledge of 3D shape is required, the technique may be applied to photographs and drawings, as well as rendered scenes. The ability to synthesize changes both in viewpoint and image structure affords a wide variety of interesting 3D effects via simple image transformations.

A different side to Mona
Here is an animation of the complete rotation in 20 frames (64K MPEG). Those eyes really follow you around the room, don't they?

You might also like to check out La Gioconda in 3D! This image was made by taking two adjacent frames from the animation and putting them side-by-side. You'll need to cross your eyes to get the three dimensional effect.  

Sunday, June 22, 2003
  Update: Oded Golan's fakes

The Israel Antiquities Authority declares that the James Ossuary and the Jehoash Inscription are both forgeries.

James Ossuary

  • Epigraphical experts divided on authenticity of inscription

  • Ossuary is made of local limestone

  • Ossuary surface covered with a natural rock varnish overlaid by patina in places

  • Inscription carved through the varnish

  • "Patina" coating only the inscription was made from a solution of hot water and chalk

Conclusion: At some time long after the natural processes of varnish and patination in a damp cave environment had been completed, someone carved a series of letters through the natural varnish on the ossuary. Then he or she covered the freshly cut letters with an imitation patina made from water and ground chalk.

Jehoash Inscription

  • Numerous mistakes in grammar and eccentric letter forms

  • Made of a metamorphic stone found in western Cyprus and points west, not local sandstone

  • Patina covering inscription made from a solution of hot water, clay, chalk, carbonized particles, and micron-sized globules of metal--possibly gold


Conclusion: An obvious forgery

Nothing too surprising here but there are lots of things of interest in this article both about the artfulness of 21st century forgers and the techniques used by experts in order to expose them.  IAA scientific panel member, Yuval Goren of Tel-Aviv University, had already expressed skepticism about the authenticity of Jehoash inscription before this current investigation. His skepticism focussed on the nature of the patina, a natural coating that forms on rocks over long periods of time. If an inscription can be shown to have been made prior to when the patina had formed then this implies that it is very old. However, as Goren has demonstrated, it's not all that hard for forgers to fake a convincing looking patina. By directly examining both of these artifacts, Goren and Avner Ayalon (of the Geological Survey of Israel) were able to determine that this kind of faking had in fact occurred.
Calcite (calcium carbonate, CaCO3) is the primary component of naturally formed patina on buried archaeological artifacts in calcareous areas, such as the Jerusalem region. This is due to the fact that calcite dissolves in groundwater. With the loss of CO2 from the groundwater by evaporation, the calcite crystallizes again on the stone's surface (just like the "stone" that collects inside a tea kettle). The oxygen within this recrystallized calcareous coating--the patina--has the same isotopic ratio as the water from which it was produced. And that value can even be used to determine the temperature at which the crystallization took place.

Ayalon determined in his analysis that while the calcite of the patina from the uninscribed surface of the James ossuary, and indeed the surfaces and inscriptions of other authentic ossuaries that he examined, had ratios that were normal for average ground temperature of the Jerusalem vicinity, the ratios of the "James Bond"--that strange mixture that covered only the letters of the inscription--was entirely different. In fact, they suggested that the crystallization took place in heated water, not the "cave environment" that the earlier geologists had claimed. The evidence pointed to an intentional faking of the patina over the letters of the "James, son of Joseph, brother of Jesus" inscription--and nowhere else.

...the fake patina on the Jehoash Inscription shared the most telltale characteristics of the "James Bond" on the James Ossuary." The presence of undissolved microfossils in the mixture showed that it was made from powdered chalk, not natural crystallization and its isotopic ratios of oxygen for the calcite in the fake patina of the Jehoash inscription indicated again the crystallization was produced in hot water--not in the ground.

Incidentally, isotopic analysis of calcium carbonate is an powerful technique which has some other interesting uses. For example, in the study of long term climate change. Sea temperatures over periods of millions of years can be determined simply by analyzing the ratios of the oxygen isotopes trapped in the shells of molluscs.
Water, the compound making up the oceans of the Earth, is composed of the elements oxygen and hydrogen. These elements have several similar forms, known as isotopes. For example, the isotopes of oxygen are oxygen-16, oxygen-17 and oxygen-18, where the number refers to the number of protons and neutrons in the nucleus.

...In the hydrologic cycle, evaporation preferentially removes water with oxygen-16 (i.e. light oxygen). This oxygen isotope is therefore rich in the gas phase of water in clouds. Precipitation and runoff returns water with high oxygen-16 to the Earth's surface. During glacial epochs, this precipitated oxygen-16 is preferentially stored in polar icecaps and continental ice sheets. This leaves the oceans enriched in oxygen-18. In the opposite case, when the cliamte is very hot, icecaps do not exist, and oceans are no longer enriched in oxygen-18.

The stable isotopes of oxygen are used to reconstruct palaeoclimates. The abundance of oxygen-18 compared to oxygen-16 is displayed in a ratio of the the two isotopes. The relative value of this ratio is compared to a standard so that the climate change with respect to time can be measured.

The ratio of isotopes (signatures) can be recorded in the rocks that are forming at that time. For example, forams create their shell of calcium carbonate from the water and food they consume. When they die and their body sinks to the bottom of the ocean, this isotope signature is preserved in these shells. Sediment accumulates and eventually forms a rock which can become uplifted and be available for study.

Update: Rochelle Altman comments on the IAA finding. She disagrees that the entire inscription of the James Ossuary is a forgery, instead she says that the first part "Jacob son of Jospeh" is authentic while the "his brother of Yeshua" was a later addition.

She concludes with this parting shot at Hershel Shanks ("And just who is this Rochelle Altman anyway? Has anyone ever heard of her?")

On October 21, 2002, Mr. Hershel Shanks, lawyer turned publisher and managing editor of the Biblical Archaeological Review (BAR), a glossy popular pulp magazine, announced to a group of journalists, assembled for the purpose of a media circus...
Update: The Geological Survey of Israel (GSI) clarifies its position regarding the Jehoash Inscription which it had earlier this year declared as authentic. Despite this error, it's worth recalling that the GSI provided the services of Avner Ayalon whose work was of critical importance to the IAA finding.

Update: Hershel Shanks remains the optimist: Why I Am Not Yet Convinced the Ossuary Inscription Is a Forgery. Yuval Goren replies

Fanciful. Preposterous. Absurd.

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