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Strictly Speaking

When the Same is Different

IMPELLER

An impeller is a mechanical device involving curved concentrically arranged blades that function by rotating around an axis to which they are attached in order to convert the gravitational and kinetic energy of moving fluids, such as water and air, into other forms of energy.

Affixed in various numbers to a shaft or rotor, an impeller may look identical to a propeller, but a propeller employs an internal source of energy (as in prop driven aircraft or nuclear submarine) to propel an attached object through a fluid that is discharged behind it. By contrast, impellers in hydroelectic plants simply rotate on a shaft by resisting the direct gravitational descent of water that would otherwise make a waterfall.

Similarly, a wind turbine does not have a propeller, but an impeller. Since the relative motion (of fluids past the blades) is independent of end use, it would be theoretically possible to place a powerful engine inside a cowling affixed to the wind turbine and, on a windless day, propel it free of its pylon. The force generated by reversing the intended use would, as in submarines, be all backward, with no upward component. Read More 
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Identity

IDENTITY

Identity is the recognition of an object or person as what it is. At best, the claim of identity is supported by a process that provides an accuracy (see “accuracy”) and precision (see “precision”) suitable for the purpose required. Admission to an entertainment event requires only one’s identity as a ticket holder.

Admission to a public zoo requires only recognition as the only species not behind bars. Admission to a penal institution requires identity as guilty beyond reasonable doubt, conviction by a jury of your peers and a sentence imposed by the court. Prisons are human zoos, yet in some unfairness to other species, none are admitted to view the captive animals.

The strictures of recognition become increasingly severe as the advantages of access grow, and often as the peril of the admitting person or institution increase. Hence in personal access, matters of retinal scans and minute details like x-rays to reveal shrapnel remaining from combat action increase confidence. But if the matter of confirming identity is put in the hands of software recognition program, such programs, as others, can be hacked, sometimes easily. Identity theft (more accurately misrepresentation) is the largest growing crime in the United States.

Only identical twins can claim that their identity is not unique, and DNA evidence (if not contaminated or mishandled, or mislabeled or misreported) implicates only one of two identical twins. In these cases, the chances of error (assuming rigorous procedures have been followed) is not one in eight billion, but one in two. As always, context counts.

Parts of your identity can be stolen without other parts being lost. If you are a bone marrow donor, the donated marrow replaces the sick patients, and your blood type then becomes his or hers. If it changes the recipient’s blood type during the procedure, then typing blood at the crime will point away from a criminal whose blood type has been changed. These sorts of scientific torpedoes get even more devastating when with extremely rare conditions like chimeras. So as much as everyone loves a sure thing, in reality there is never such a thing. Ergo one can never reach a certainty beyond a reasonable doubt. And reasonable doubt can only emerge when all of the facts and evidence and interpretive assumptions are presented. Read More 
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