Flippers

Forsyth, J.B., Knight, K.M., Penfold, J. and Saunders, P.W. (1974) Flipper Control Unit, Rutherford Laboratory Report RL-74-114. 

Fig. 2.1 Spin history leading to the formation of the spin-echo. Longitudinally polarized neutrons enter from the left. Upper part spin motion. Lower part NSE setup, Ti/2-flipper between belonging current rings, primary main precession solenoid l symmetry scan...

The NSE principle - as described above - only works if the neutron spin is not affected by the scattering process (some exceptions hke complete spin-flip could be tolerated and would just replace the n-flipper). A related problem occurs if the scattering nuclei have a non-zero spin and their scattering power depends significantly on the relative orientation of nuclear and neutron spin. 

Fig. 2.2 A 7i/2-flipper effecively rotating the spin direction from longitudinal (S) to perpendicular to the path and to the external field. The vertical field B /2 generated inside the flipper adds to the embedding external field...

The most expensive parts of a conventional NSE instrument are the main solenoids providing the precession field. A closer look at Bloch s equation of motion for the spins (Eq. 2.11) shows that in a coordinate system that rotates with the precession frequency around Bg the spin is stationary, the coordinate system rotation is equivalent to the addition of - to all magnetic fields. By this means the large precession field inside the main coils may be transformed to zero - zero field spin-echo). The flippers are viewed as elements rotating... 

This angle is preserved in the zero field region around the sample. In a symmetric flight path between two RF-flippers (RF radio frequency) in the scat-... 

The complete instrument consists of two flippers with distance L before the sample and a symmetric set of two flippers after the sample. All flight paths between the first and the fourth (last) flipper are surrounded by magnetic shielding to yield the zero field condition that preserves the spin orientation. All RF flippers are operated synchronously, i.e. with the same current. Their field direction (i.e. rotation) is +, +. A neutron that enters the first flipper at a time... 

An interesting variant of the resonance NSE is the so-called MIEZE technique [ 19]. Using two RF-flippers that operate at different frequencies a neutron beam is prepared such that a special correlation between a time varying spin rotation co= Qi-Q2) the velocity of the neutrons is achieved. An analyser after the second RF-flipper translates the spin rotation into an intensity modulation. The... 

On Earth, manatees are large water mammals, popularly called sea cows. Their dark bodies taper to flattened tails. Their forelimbs are flippers set close to the head no external hind limbs exist. Their heads are small, with straight snouts and cleft upper lips with bristly hairs. These space manatees are similar to their Earthly counterparts. 

Figure 12-1. Types of flexing test, (a) De Mattia (b) "flipper" machine (c) Du Pont ...

ASTM has also standardised a flipper type of machine7 which uses grooved and pierced test pieces to measure crack growth. The gap between the revolving disk and the deflector bars can be varied so that the angle of deflection and, hence, the severity of test can be varied. The apparatus in contained in an oven so that tests can be made over a range of temperatures. 

Tragedy in the United States was averted by Dr. Kelsey s efforts. Her refusal to approve the thalidomide NDA without further proof of safety occurred just as news from Europe revealed that thalidomide was responsible for a birth defect that caused infants to be born with flipper-like limbs. This near miss in the United States led to passage of the 1962 Kefauver-Harris Amendments to the 1938 act. These amendments established requirements that testing for both safety and proof of drug efficacy had to be conducted in well-controlled clinical trials before an NDA could be approved and a drug allowed to reach the market (Bren, 2001). 

Specifically, thalidomide produced a characteristic stunting of limb bud tissue, apparently due to interference with normal vascularization. The result was the development of a relatively unique syndrome known as phocomelia. At least 10,000 children, most of them German, were born with flippers instead of arms or legs. Unfortunately, some thalidomide babies are still being born in South America where the drug continues to be manufactured and many people are unaware of its proper uses (it is used fairly extensively for treating certain skin lesions in leprosy patients). 

The condition of phocomelia was so rare prior to 1961 that no photographs were available and Goya s painting was used in medical texts for illustration. The term phocomelia is derived from the Greek words for seal and limb. It is characterized by the hands or feet growing directly from the main joint, like the flippers of a seal. 

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