Photographic Memory

A wearable video camera may be able to slow the ravages of Alzheimer’s disease.

Hopes for new drugs that would slow or stop the inexorable decline of Alzheimer’s patients have repeatedly foundered in recent years. In one example, Eli Lilly had to halt the trial of a drug designed to prevent the production of toxic proteins in the brain because patients’ cognition actually worsened while they were taking it. Scientists are now looking to the computer industry for alternative ways to help patients. One approach is centered on a small camera called SenseCam, worn like a necklace, that snaps photographs automatically throughout the day. The idea is to use the images not to replace memory but to stimulate it. Each photograph can serve as a cue, like Marcel Proust’s madeleine, tapping into the web of remembrances that collectively defines a person’s identity. SenseCam, developed by Microsoft and now marketed by a company called Vicon, uses a fish-eye lens to capture a wide-angle view. At regular intervals—say, every 30 seconds—a new image gets stored in the one-gigabyte solid-state memory. When the wearer moves from one room to another, a sensor that picks up the change in light triggers SenseCam to take a new photograph. Further, if a person walks by, an

infrared sensor detects the body heat and signals that it is time for another photo. The result is a thumbnail chronology of the minutiae of the wearer’s daily life. Later, patients or their caregivers pipe this electronic thumbnail record into a PC to display the images either individually or in chronological sequence.

HERE COME THE DRONES

These popular, unmanned aircraft will eventually fall into the hands of hostile nations and terrorists.

Some are as large and fast as commercial airplanes. Some are blimps that sit in the sky, surveying broad swaths of territory. Others flit around imperceptibly, like birds or insects, recording videos and landing themselves. Unmanned aircraft have transformed the way the U.S. wages war, making it possible to gather unprecedented amounts of aerial imagery using nearly undetectable platforms and to strike at targets without putting pilots at risk. But it would be naive to assume drones will only be used to safeguard U.S. interests. As they continue to become smaller, cheaper and more numerous, drones will become easier for hostile nations, and perhaps even terrorists, to get their hands on. To think otherwise would be to disregard the history of military technology. Many countries, including Israel, China and Iran, are developing, using and selling drones, and global spending on drones is expected to approach $100 billion over the next 10 years. Should a terrorist group deploy a drone in the U.S., it could be very hard to detect. Drones can fly right over fences and walls and are invisible to traditional radar systems. Because they can be transported in the trunk of a car or in a backpack, they can be launched from virtually any publicly accessible spot. We might also be worried about our own government, or private companies, using drones to peer into our lives. In 1986 the U.S. Supreme Court ruled that law-enforcement agencies could use a private plane to view otherwise hidden marijuana plants because the police observations were made from “public navigable airspace.” This may suggest that the government will enjoy broad latitude to use drones for surveillance.

Tightening access to drones is very difficult. The core information technologies used in small drones— extremely small video cameras, chips to process video and high-speed wireless communications systems—are routinely found in inexpensive consumer electronics. This does not mean that there is nothing we can do. Drones could be equipped with kill switches and hidden tracking software that could help disable or trace them if they go missing. A combination of domestic regulation and international nonproliferation efforts could reduce the possibility that drones would fall into the wrong hands. It may be possible to equip sensitive government buildings or areas with new systems to detect and, if appropriate, electromagnetically or kinetically engage low-flying incoming drones. Yet despite these efforts, in the future we will no longer have the luxury of assuming that the skies above us are free of pilotless machines. —John Villasenor

Uniform flow past a circular cylinder at R=0.16

That the flow is from left to right can scarcely be deduced from the streamline pattern, because in the limit of zero Reynolds number the flow past a solid body is reversible, and hemce symmetric about a symmetric shape. It resembles superficially the pattern of potencial flow in figure Hele-Shaw flow past a circle, but disturbances to the uniform stream die off much more slowly. The flow of water is shown by aluminum dust Photograph by Sadatoshi Taneda.

Hele-Shaw flow past a rectangular block on a plate

The analogy faithfully simulates the unseparated potential flow into the stagnation region of a concave corner, and the infinite velocities over an outside corner. The water takes much longer to travel through the system if it follows a streamline that passes close to a stagnation point. This allows a greater diffusion of dye, which is seen in the slight blurring of streamlines at the lower right-hand corner. Photograph by D. H. Peregrine.

Hele-Shaw flow past an inclined airfoil

Dye in oil shows the streamlines of plane potential flow past an NACA 64A015 airfoil at 13° angle of attack. However, because the Hele-Shaw flow cannot show circulation, the Kutta condition is not enforced at the trailing edge. Hence infinite velocities are represented there. The model is between glass plates 1 mm apart. Wale 1973. Reproduced, with permission, from the Annual Review of Fluid Mechanics, Volume 5. 1973 by Annual Reviews Inc. 

Hele-Shaw flow past an inclined plate.

The Hele-Shaw analogy cannot represent a flow with circulation. It  therefore shows the streamlines of potential flow past an inclined plate with zero lift. Dye flows in water between glass plates spaced 1 mm apart. Photograph by D. H. Peregrine 

Hele-shaw flow past a Rankine half-body

A viscous fluid is introduced through the orifice at the left into a uniform stream of the same fluid flowing between glass plates spaced 0.5 mm apart. Dye shows both the external and internal streamlines for plane potencial flow past a semi-infinite body. The streamlines are slightly blurred because the rate of delivery of  fluid to the source was changing as the photograph was made. Taylor 1972.

Hele-Shaw flow past a circle

Dye shows the streamlines in water flowing at 1 mm per second  between glass plates spaced 1 mm apart. It is a first sight paradoxical that  the best way of producing the unseparated pattern of plane potencial flow past  a bluff object, which would be spoiled by separation in a real fluid of even the slightest viscosity , is to go to the opposite extreme  of creeping flow in a narrow gap, which is dominate by viscous forces. Photograph by D. H. Peregrine.

Kármán Vortex Streetbehind a circularcylinder

Smoke filaments in a wind tunnel show de periodic shedding of vortices. The Reynolds number is about 300, which is near the observed upper limit for stability; and the pattern seems to be desintegrating at the downstream edge of the photograph. This is an intermediate stage in the remarkable variety of partners that succeed one another as the Reynolds number is increased. Photograph by Peter Bradshaw