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In a material with both a piezoelectric effect and the capability to form a photocurrent, photostriction can be observed - the deformation of the crystal by light. When studying photostriction, a potential method is to use x-rays to probe the unit cell in response to another light source as a stimulus, such as a laser or a diode. Given that x-rays are also photons it is plausible that they themselves produce some effect. An experiment was carried out to investigate how significant the effects of the x-rays are in producing photostriction in the absence of any other source of illumination. The material studied in this example was bismuth iron oxide, BiFeO3. A thin film with electrodes was used and it was found that the photocurrent generated by a laboratory x-ray source on the sample was of comparable level to that of a laser or diode used in the study of the bulk photoelectric effect. Using a novel, time dependent crystallographic approach, the intrinsic effect of synchrotron x-ray light on a photoferroelectric thin film has been investigated. Furthermore, we have simultaneously collected diffraction and photoelectric data, and the correlation between the electronic and structural properties will be discussed. These results could suggest that caution is necessary when interpreting photostriction data obtained with the use of x-rays.
abstracts
The average age of people is increasing continuously thanks to the progress in the medicinal sciences and further social advances. As a consequence, however, diseases which affect people more likely at a higher age also increase. In this course Alzheimer's disease (AD) and related brain disorders distribute rapidly and have to be taken more serious. One of the most frequently applied drugs against AD is donepezil®. Its function is a reversible inhibition of acetylcholinesterase (AChE), thereby reducing the deficit of acetylcholine associated with the occurrence of AD. As one result from the charge density (CD) of the small-molecule structure containing the donepezilium cation comparable electronic interactions were identified as in the macromolecular TcAChE-donepezil complex which were made visible by electrostatic potential and Hirshfeld surfaces.[1] Two newer developments of Alzheimer agents are bexarotene and methylene blue. For the first one a therapeutic effect on AD in a mouse model was recently reported. From a comparative CD study on bexarotene and its disila analogue differences in the electrostatic potentials were identified, while the spherical structures showed no significant differences. The second one, methylene blue, targets the abnormal tangle type tau protein aggregation inside the nerve cells in the brain and stops its spread. The molecule is positively charged with various counterions. From the CD an answer to the not yet understood question is expected whether the formal positive charge is localized or delocalized.
