Chameleon in the sun: photochromic glass

The properties characterized as photochromic?the ability to react reversibly to light?are found in various substances, both organic and inorganic. The two classes of materials are compared and the mechanism of the process is examined in each case. Of primary interest here are the inorganics, particularly the silver halide reversible photochromic glasses. Properties and ranges of properties of these are reviewed and some possible applications described.     

Modification of the pigeon's visual startle reaction by the sensory environment.

Seven experiments related amplitude and latency of 20 racing pigeons' startle response, elicited by an intense visual stimulus, to antecedent auditory and visual events in the sensory environment. Data indicate that (a) within broad limits the amplitude of the reflex was a positive function of the intensity of the sensory background prevailing at the time of startle elicitation; (b) a change in the sensory environment occurring 15-2,000 msec prior to the startle-eliciting stimulus inhibited the amplitude of the response; and (c) a change in the sensory environment less than 10 msec prior to the startle-eliciting stimulus reduced the latency of the response. Findings are consistent with previous research on acoustic elicited startle in the rat. The overall configuration of the results suggests that a pathway including the reticulospinal tract and the bulbopontine reticular nuclei could be the major mediator of startle. In these terms, latency-reduction effects would occur because of partial activation of this pathway, amplitude inhibition would occur because of cerebellar influence, and amplitude facilitation would reflect cerebral or striatal influences. (49 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of calcium antagonist, 6-(N, N-diethylamino) hexyl-3, 4, 5-trimethoxybenzoate, on digitalis-induced arrhythmias and cardiac contractions

6-(N, N-Diethylamino) hexyl-3, 4, 5-trimethylbenzoate (TMB-6) and lidocaine were equipotent (1 mg/kg) in the conversion of ectopic rhythms to normal rhythms in digoxin-toxic dogs. However, TMB-6 had fewer side effects on heart rates and dp/dt than lidocaine. TMB-6 inhibited the contractile force of electrically stimulated dog and guinea-pig atria and ventricles at concentrations ranging from 2.5 X 10(-5) to 1.7 X 10(-4) M. Elevation of extracellular Ca++ concentrations from 2.7 to 5.4 mM produced a significant increase in the ID50 of TMB-6 in atria (from 2.5 X 10(-5) to 5.0 X 10(-5) M in dogs and from 7.2 X 10(-5) to 1.0 X 10(-4) M in guinea pigs). TMB-6 (7.3 X 10(-5) to 2.4 X 10(-4) M) depressed the amplitude of Ca++-dependent action potentials in depolarized dog cardiac Purkinje fibers. These results are discussed with regard to the antagonism of TMB-6 on Ca++ availability in the myocardium which leads to the conversion of cardiac arrhythmias.     

Protein hydration in solution: experimental observation by x-ray and neutron scattering

The structure of the protein-solvent interface is the subject of controversy in theoretical studies and requires direct experimental characterization. Three proteins with known atomic resolution crystal structure (lysozyme, Escherichia coli thioredoxin reductase, and protein R1 of E. coli ribonucleotide reductase) were investigated in parallel by x-ray and neutron scattering in H2O and D2O solutions. The analysis of the protein-solvent interface is based on the significantly different contrasts for the protein and for the hydration shell. The results point to the existence of a first hydration shell with an average density approximately 10% larger than that of the bulk solvent in the conditions studied. Comparisons with the results of other studies suggest that this may be a general property of aqueous interfaces.