Cells respond to topographical, mechanical and biochemical characteristics of the surrounding environment. Capability to reconstruct these factors individually, and also acting in accord, would facilitate systematic investigations of a multitude of related biological and tissue engineering questions. The subject of the present review is a group of technologies allowing realization of customized cell-culture matrices. These methods utilize photochemistry induced by multiphoton absorption and are carried out using essentially identical equipment. Fabrication of 2D microstructured substrates, complex 3D scaffolds, containing actively induced topographies, and immobilization of biomolecules in a spatially defined manner was demonstrated with these techniques. The reviewed reports indicate that multiphoton processing is a promising technology platform for the development of standard biomimetic microenvironments for 3D cell culture.
The history of literacy in Russia may be divided into four periods: 1) the Kievan, from the tenth to the thirteenth centuries (before the Mongol invasion); 2) the medieval (Muscovite), from the middle of the thirteenth to the end of the seventeenth centuries; 3) the imperial, from the eight eenth century to 1917; and 4) the Soviet, after 1917. For each of these periods distinctive sources have been preserved that call for special han dling and methodologies. Before the 1950s historians of literacy in Kievan Rus had recourse primarily to archaeological material, especially writing paraphernalia, as well as to signatures on handicrafts, shoe lasts, and church walls. The earliest archaeological findings and graffiti of this sort derive from the tenth and eleventh centuries. 1 In 1951, during archaeological excavations at Novgorod, the first birch-bark charters were unearthed. These were notations of a mundane character-household lists, records, letters, requests, school exercises, and so forth-on beresta, the outer layer of the bark of the birch tree. Some seven hundred birch-bark charters, dating from the eleventh to the fifteenth centuries, have been discovered in nine ancient Russian towns. Excavations at virtually every other site have uncovered instruments for writing on birch bark. The discoveries indicate that literacy was not a monopoly of the clergy, feudal lords, and clerks, as was earlier thought, but extended as well to the urban population engaged in handicrafts and trade. The findings provide evidence of the spread of literacy and show Boris N. Mironov is a senior research associate at the Leningrad branch of the Institute of History of the USSR Academy of Sciences. The editors of the HEQ are extremely grateful to Professor Ben Eklof of Indiana University for his careful translation and editing of this article.
Time-resolved electron microscopy is based on the excitation of a sample by pulsed laser radiation and its probing by synchronized photoelectron bunches in the electron microscope column. With femtosecond lasers, if probing pulses with a small number of electrons—in the limit, single-electron wave packets—are used, the stroboscopic regime enables ultrahigh spatiotemporal resolution to be obtained, which is not restricted by the Coulomb repulsion of electrons. This review article presents the current state of the ultrafast electron microscopy (UEM) method for detecting the structural dynamics of matter in the time range from picoseconds to attoseconds. Moreover, in the imaging mode, the spatial resolution lies, at best, in the subnanometer range, which limits the range of observation of structural changes in the sample. The ultrafast electron diffraction (UED), which created the methodological basis for the development of UEM, has opened the possibility of creating molecular movies that show the behavior of the investigated quantum system in the space-time continuum with details of sub-Å spatial resolution. Therefore, this review on the development of UEM begins with a description of the main achievements of UED, which formed the basis for the creation and further development of the UEM method. A number of recent experiments are presented to illustrate the potential of the UEM method.
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