Monday, September 24, 2007

 

Reactance

Reactance is the invented part of electrical impedance, a measure of opposition to a sinusoidal alternating current. Reactance arises from the occurrence of inductance and capacitance within a circuit, and the SI unit is the ohm. The value of the reactance is a lower maximum value on the amount of the impedance. A positive reactance implies that the phase of the voltage leads the phase of the current, while a harmful reactance implies that the phase of the voltage lags the phase of the current. A reactance of zero implies the current and voltage are in phase and equally if the reactance is non-zero then there is a phase distinction between the voltage and current

Wednesday, September 05, 2007

 

Inca Rope bridge

Inca Rope bridges were simple suspension bridges over canyons and gorges to present access for the Inca Empire. Bridges of this type were suitable for use since the Inca people did not use wheeled transport - traffic was incomplete to pedestrians and livestock. These bridges were an intrinsic part on the Inca road scheme and are an excellent example of Inca innovation in engineering. They were frequently used by Chasqui runners delivering messages throughout the Inca Empire.
The construction of these bridges amounted to a pair of stone anchors on each side of the canyon with immense cables of woven ichu grass linking these two pylons together. Adding to this construction, two additional cables acted as guardrails. The cables which supported the foot-path were unbreakable with plaited branches. This multi-structure system made these bridges strong enough to even carry the Spaniards while riding horses after they indoors. However, these massive bridges were so heavy that they tended to sag in the middle, and this caused them to bend in high winds.

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