Shape transitions in developing organisms can be driven by active stresses, notably, active contractility generated by myosin motors. The mechanisms generating tissue folding are typically studied in epithelia. There, the interaction between cells is also coupled to an elastic substrate, presenting a major difficulty for studying contraction induced folding. Here we study the contraction and buckling of active, initially homogeneous, thin elastic actomyosin networks isolated from bounding surfaces. The network behaves as a poroelastic material, where a flow of fluid is generated during contraction. Contraction starts at the system boundaries, proceeds into the bulk, and eventually leads to spontaneous buckling of the sheet at the periphery. The buckling instability resulted from system self-organization and from the spontaneous emergence of density gradients driven by the active contractility. The buckling wavelength increases linearly with sheet thickness. Our system offers a well-controlled way to study mechanically induced, spontaneous shape transitions in active matter.
Microscopic FTIR spectroscopy was used to investigate the spectral differences between normal cells in culture and cells infected with various members of the herpes family of viruses [Herpes simplex (HSV) and Varicella zoster (VZV)]. The main objective of this study is to evaluate the possibility of developing microscopic FTIR spectroscopy as a sensitive assay for the detection of herpetic infections at their early stages. The advantage of this method over conventional FTIR spectroscopy is that it facilitates inspection of restricted regions of tissue. Our results showed significant and consistent differences between all normal and HSV or VZV infected cells that were tested. Detectable and significant spectral differences between normal and infected cells are seen as early as 24 h postinfection, but the damage of the cells (cytopathic effect), caused by the infecting virus, can be seen by optical microscope observations at only 3 days postinfection. An impressive increase in the levels of vital cellular metabolites was seen in the herpes virus infected cells compared to normal cells. It seems that this spectral behavior is unique for infection with herpes viruses, because when these cells were infected with other viruses from different families like retroviruses, a considerable decrease in the levels of vital cellular metabolites was seen in infected cells compared to normal cells. Cluster analysis performed on FTIR mass chromatography yielded 100% accuracy in classifying control uninfected and VZV or HSV infected cells. Our data strongly support the possibility of developing FTIR microscopy as a diagnostic method for early detection of herpetic infections.
FTIR and RAMAN spectroscopic methods were used to study the ordering of non-stoichiometric nano-magnesium aluminate spinels (MgOnAl 2 O 3 , 0.4 < n < 12) synthesized using a combustion synthesis method. It was established that the degree of structural disorder (i.e., the inversion parameter, i) can be quantified using the intensities of the γ 1 and γ 5 IR modes or 670 and 723 cm -1 Raman shifts. The results indicated that the as-synthesized materials were heavily disordered and obey earlier conclusions that the defect chemistry of non-stoichiometric spinels is dominated by clusters formed from anti-site defects. Analysis of the temperature dependency of cation distribution in the Mg-and Alrich samples showed that the spinel phase moved toward equilibrium upon increases in temperature. Where decomposition occurred, the disordered level decreased at temperatures up to 1000 °C. Above this temperature, the order level dropped far below the expected equilibrium value and the γ 3 mode (a mode that is characterized for ordered structures, such as a natural spinel) that appears. These findings, together with Raman results of partly decomposed Al-rich samples, support the hypothesis that a MgAl 2 O 4 -γ-Al 8/3 o 1/3 O 4 solid solution comprises of series of complex micro-phases with considerable short-range order.
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