Patients with impaired vision because of a damaged cornea could soon regain their sight without need of a human donor transplant. Instead, such patients could be aided by an artificial but biosynthetic implant. One such implant has now been tested in patients over two years, and the results are as good as, or even better than, those achieved with donor corneas.
The transparent tissue that covers the surface of the eyes, the cornea, can be damaged by injury, infection, or inflammation, causing the eye to lose much of its ability to refract light and focus images on the retina. Such damage has caused loss of vision in millions of people around the world. The best treatment for cornea damage remains a transplant, but donor corneas are in chronically short supply.
Plastic replacements have been available for decades, but their implantation is still plagued by side effects such as infection and glaucoma. "They remain a last resort option for patients where all other options have failed, including donor transplants," says Joachim Storsberg at the Fraunhofer Institute for Applied Polymer Research in Potsdam, Germany. Storsberg is developing plastic implants but was not involved with the current work.
An anti lock breaking system(ABS) prevents the vechile wheels from locking up while breaking.
ABS ComponentsMain components to an ABS system:
Speed sensors
Pump
Valves
Controller
Speed SensorsThe ABS needs some way of knowing when a wheel is about to lock up. The speed sensors, which are located at each wheel, or in some cases in the differential, provide this information.PumpSince the valve is able to release pressure from the brakes, there has to be some way to put that pressure back. That is what the pump does; when a valve reduces the pressure in a line, the pump is there to get the pressure back up.ValvesThere is a valve in the brake line of each brake controlled by the ABS. On some systems, the valve has three positions:
In position one, the valve is open; pressure from the master cylinder is passed right through to the brake.
In position two, the valve blocks the line, isolating that brake from the master cylinder. This prevents the pressure from rising further should the driver push the brake pedal harder.
In position three, the valve releases some of the pressure from the brake.ControllerThe controller is a computer in the car. It watches the speed sensors and controls the valves.ABS at WorkThere are many different variations and control algorithms for ABS systems. We will discuss how one of the simpler systems works.
The controller monitors the speed sensors at all times. It is looking for decelerations in the wheel that are out of the ordinary. Right before a wheel locks up, it will experience a rapid deceleration. If left unchecked, the wheel would stop much more quickly than any car could. It might take a car five seconds to stop from 60 mph (96.6 kph) under ideal conditions, but a wheel that locks up could stop spinning in less than a second.
The ABS controller knows that such a rapid deceleration is impossible, so it reduces the pressure to that brake until it sees an acceleration, then it increases the pressure until it sees the deceleration again. It can do this very quickly, before the tire can actually significantly change speed. The result is that the tire slows down at the same rate as the car, with the brakes keeping the tires very near the point at which they will start to lock up. This gives the system maximum braking power.
When the ABS system is in operation you will feel a pulsing in the brake pedal; this comes from the rapid opening and closing of the valves. Some ABS systems can cycle up to 15 times per second
