Spatial alternation

Levin ED, Bowman RE. 1989. Long-term effects of chronic postnatal lead exposure on delayed spatial alternation in monkeys. Neurotoxicol Teratol 10 505-510. 

Interperitoneal injection of rats at doses insufficient to produce clinical signs of neurotoxicity did cause reduction in T-maze spatial alternation scores. The authors concluded that acute TPP administration has a persistent effect on the neural systems required for spatial alternation learning in rats. ... 

Levin ED, Christopher NC, Abou-DoniaMB Triphenyl phosphite-induced impairment of spatial alternation learning. J Toxicol Environ Health 44(4) 461-467, 1995... 

Levin ED, Schantz SL, Bowman RE. 1988. Delayed spatial alternation deficits resulting from perinatal PCB exposure in monkeys. Arch Toxicol 62 267-273. 

An interdigital transducer deposited on the surface of a piezoelectric substrate (i.e., hthium niobate) launches a surface acoustic wave (Fig. 3.13). The interdigital transducer has a combhke structure that establishes an alternating electric field whose polarity is spatially alternating. This alternation produces an electrically induced strain in the medium via the piezoelectric effect that excites an acoustic wave. The acoustic wave modulates the index of refraction of the medium that diffracts the optical beam. Note that this diffraction effect is not only due to the modification of the index of refraction, but also to the physical deformation of the medium produced by the acoustic wave. 

An alternative perspective is as follows. A 5-frmction pulse in time has an infinitely broad frequency range. Thus, the pulse promotes transitions to all the excited-state vibrational eigenstates having good overlap (Franck-Condon factors) with the initial vibrational state. The pulse, by virtue of its coherence, in fact prepares a coherent superposition of all these excited-state vibrational eigenstates. From the earlier sections, we know that each of these eigenstates evolves with a different time-dependent phase factor, leading to coherent spatial translation of the wavepacket. 

FIGURE 7 16 Poly mers of propene The mam chain IS shown in a zigzag conformation Every other carbon bears a methyl sub stituent and is a chirality center (a) All the methyl groups are on the same side of the carbon chain in isotactic polypropylene (b) Methyl groups alternate from one side to the other in syndiotactic polypropy lene (c) The spatial orienta tion of the methyl groups IS random in atactic polypropylene... 

The success of quinine inspired the search for other antimalarials. The greatest impetus for the development of synthetic dmgs came this century when the two World Wars intermpted the supply of cinchona bark to the combatants. A stmcturally related 4-quinolinemethanol is mefloquine (65, Lariam [51773-92-3]) which now serves as an effective alternative agent for chloroquine-resistant P. falciparum. This is a potent substance that requires less than one-tenth the dose of quinine to effect cures. There are some untoward side effects associated with this dmg such as gastrointestinal upset and dizziness, but they tend to be transient. Mefloquine is not recommended for use by those using beta-blockers, those whose job requires fine coordination and spatial discrimination, or those with a history of epilepsy or psychiatric disorders. A combination of mefloquine with Fansidar (a mixture of pyrimethamine and sulfadoxine) is known as Fansimef but its use is not recommended. Resistance to mefloquine has been reported even though the compound has not been in wide use. 

The im< e mode produces an image of the illuminated sample area, as in Figure 2. The imj e can contain contrast brought about by several mechanisms mass contrast, due to spatial separations between distinct atomic constituents thickness contrast, due to nonuniformity in sample thickness diffraction contrast, which in the case of crystalline materials results from scattering of the incident electron wave by structural defects and phase contrast (see discussion later in this article). Alternating between imj e and diffraction mode on a TEM involves nothing more than the flick of a switch. The reasons for this simplicity are buried in the intricate electron optics technology that makes the practice of TEM possible. 

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