The understanding of the interplay of electron correlations and randomness in solids is enhanced by demonstrating that particle-hole ( p−h) symmetry plays a crucial role in determining the effects... Show moreThe understanding of the interplay of electron correlations and randomness in solids is enhanced by demonstrating that particle-hole ( p−h) symmetry plays a crucial role in determining the effects of disorder on the transport and thermodynamic properties of the half-filled Hubbard Hamiltonian. We show that the low-temperature conductivity decreases with increasing disorder when p−h symmetry is preserved, and shows the opposite behavior, i.e., conductivity increases with increasing disorder, when p−h symmetry is broken. The Mott insulating gap is insensitive to weak disorder when there is p−h symmetry, whereas in its absence the gap diminishes with increasing disorder. Show less
An optical single-molecule study is reported of a quickly frozen solution of 2.3,8.9-dibenzanthanthrene (DBATT) in n-tetradecane at 1.4 K. The orientation has been measured of several hundreds of... Show moreAn optical single-molecule study is reported of a quickly frozen solution of 2.3,8.9-dibenzanthanthrene (DBATT) in n-tetradecane at 1.4 K. The orientation has been measured of several hundreds of DBATT molecules within a confocal detection volume of similar to 10 mum(3) as a function of their resonance frequency in the range of the two 0-0 bands in the fluorescence-excitation spectrum. Each band is found to correspond to a distinct distribution of orientations of DBATT molecules. A particular resonance frequency within a band is not correlated with a specific molecular orientation. (C) 2001 Elsevier Science B.V. All rights reserved. Show less
Decreased phosphorylation of focal adhesion kinase (FAK) is associated with loss of focal adhesions and actin stress fibers and precedes the onset of apoptosis in renal epithelial cells caused by... Show moreDecreased phosphorylation of focal adhesion kinase (FAK) is associated with loss of focal adhesions and actin stress fibers and precedes the onset of apoptosis in renal epithelial cells caused by nephrotoxicants (Van de Water, B., Nagelkerke, J. F., and Stevens, J. L. (1999) J. Biol. Chem. 274, 13328-13337). The role of FAK in the control of apoptosis caused by nephrotoxicants was further investigated in LLC-PK1 cells that were stably transfected with either green fluorescent protein (GFP)-FAK or dominant negative acting deletion mutants of FAK, GFP-FAT, and GFP-FRNK. GFP-FAT and GFP-FRNK delayed the formation of focal adhesions and prevented the localization of endogenous (phosphorylated) FAK at these sites. GFP-FAT and GFP-FRNK overexpression potentiated the onset of apoptosis caused by the nephrotoxicant dichlorovinyl-cysteine. This was associated with an increased activation of caspase-3. GFP-FAT also potentiated apoptosis caused by doxorubicin but not cisplatin. The potentiation of apoptosis by GFP-FAT was related to an almost complete dephosphorylation of FAK; this did not occur in cells overexpressing only GFP. This dephosphorylation was associated with a pronounced loss of focal adhesion organization in GFP-FAT cells, in association with loss of tyrosine phosphorylation of paxillin. In conclusion, the data indicate an important role of cell-matrix signaling in the control of chemically induced apoptosis; loss of FAK activity caused by toxic chemicals results in perturbations of focal adhesion organization with a subsequent inactivation of associated (signaling) molecules and loss of survival signaling. Show less
