Publications

Ab initio calculations have been performed on novel compounds that may greatly expand the scope of rare gas chemistry. These molecules are insertion compounds of xenon into unsaturated hydrocarbons, including acetylene, benzene, and phenol. We present computational evidence that molecules such as H-Xe-C2H, H-Xe-C6H5, and H-Xe-OC6H5 exist. Computational results suggest also the existence of a series of xenon-insertion compounds for larger hydrocarbons of these types. The predictions are not restricted to molecules p with only one xenon atom inserted in them but molecules such as H-Xe-C-2-Xe-H and H-Xe-C-2-XeC2-Xe-H are computationally stable as well. This suggests the existence of linear polymers H-(Xe-C-2)(n)-H for arbitrary large n. All predicted xenon-insertion molecules form a new class of possible precursors and intermediates for synthetic organic and organoelement chemistry.

This perspective examines quantum dot (QD) superlattices as model systems for achieving a general understanding of the electronic structure of solids and devices built from nanoscale components. QD arrays are artificial two-dimensional solids, with novel optical and electric properties, which can be experimentally tuned. The control of the properties is primarily by means of the selection of the composition and size of the individual QDs and secondly, through their packing. The freedom of the architectural design is constrained by nature insisting on diversity. Even the best synthesis and separation methods do not yield dots of exactly the same size nor is the packing in the self-assembled array perfectly regular. A series of experiments, using both spectroscopic and electrical probes, has characterized the effects of disorder for arrays of metallic dots. We review these results and the corresponding theory. In particular, we discuss temperature-dependent transport experiments as the next step in the characterization of these arrays.

The Classical Separable Potential (CSP) method, which is a mean-field approximation to multidimensional quantum dynamics, is applied to the dephasing process of a vibrationally excited HArF molecule in an argon cluster at low temperatures. Dephasing timescales of the order of 1 ps are estimated for dynamics following fundamental excitation of either the H-Ar or the Ar-F stretching mode of HArF. The CSP approach is valid over such timescales, and it is thus a viable approach to quantum simulations of dephasing at low temperatures. Vibrational relaxation is much slower: Quasi-classical molecular dynamics simulations yield a relaxation time around 100 ps for the initial v = 1 Ar-F stretching excitation. Such timescales are beyond the validity range of CSP; therefore, this or similar separable methods are inapplicable for vibrational energy decay.

We present the real-space block renormalization group equations for fermion systems described by a Hubbard Hamiltonian on a triangular lattice with hexagonal blocks. The conditions that keep the equations from proliferation of the couplings are derived. Computational results are presented including the occurrence of a first-order metal-insulator transition at the critical value of U/t approximate to 12.5.

We assessed the role of the cell labile iron pool in mediating oncogene-induced cell proliferation via repression of ferritin expression. When HEK-293 cells, engineered to inducibly express either active (+) or dominant-negative (-) forms of the H-ras oncogene, were treated with antisense nucleotides to ferritin subunits they displayed (a) decreased ferritin levels, (b) increased labile iron pool and either (c) faster growth in cells induced to express H-Ras (+) or (d) recovery from growth retardation in dominant-negative H-Ras-induced cells. Our studies support the view that the role of down-modulation of ferritin expression by some oncogene-evoked proliferation proceeds via expansion of the cellular labile iron pool.

This study looks at the competition over news exposure during political waves. Political waves are sudden and significant changes in the political environment that are characterized by a substantial increase in the amount of public attention centered on a political issue or event. Four research questions are raised in an attempt to better understand this issue from the perspective of political actors. 1) Which political actors are in the best position to initiate political waves? 2) Which actors are in the best position to exploit political waves? 3) What types of waves provide the greatest news opportunities for political actors? 4) Which types of actors are in the best position to exploit different types of political waves? [ABSTRACT FROM AUTHOR]

Oncogene amplification is an important process in human tumorigenesis, but its underlying mechanism is currently unknown. Cytogenetic analysis indicates that amplification of drug-selected genes in rodent cells is driven by recurrent breaks within chromosomal common fragile sites (CFSs), via the breakage-fusion-bridge (BFB) mechanism. Here we show that BFB cycles drive the intrachromosomal amplification of the MET oncogene in a human gastric carcinoma. Our molecular evidence includes a "ladder-like" structure and inverted repeat organization of the MET amplicons. Furthermore, we show that the breakpoints, setting the centromeric amplicon boundaries, are within the CFS FRA7G region. Upon replication stress, this region showed perturbed chromatin organization, predisposing it to breakage. Thus, in vivo induction of CFSs can play an important role in human oncogenesis.

Lipoteichoic acid (LTA) is a surface-associated adhesion amphiphile from Gram-positive bacteria and regulator of autolytic wall enzymes (muramidases). It is released from the bacterial cells mainly after bacteriolysis induced by lysozyme, cationic peptides from leucocytes, or beta-lactam antibiotics. It binds to target cells either non-specifically, to membrane phospholipids, or specifically, to CD14 and to Toll-like receptors. LTA bound to targets can interact with circulating antibodies and activate the complement cascade to induce a passive immune kill phenomenon. It also triggers the release from neutrophils and macrophages of reactive oxygen and nitrogen species, acid hydrolases, highly cationic proteinases, bactericidal cationic peptides, growth factors, and cytotoxic cytokines, which may act in synergy to amplify cell damage. Thus, LTA shares with endotoxin (lipopolysaccharide) many of its pathogenetic properties. In animal studies, LTA has induced arthritis, nephritis, uveitis, encephalomyelitis, meningeal inflammation, and periodontal lesions, and also triggered cascades resulting in septic shock and multiorgan failure. Binding of LTA to targets can be inhibited by antibodies, phospholipids, and specific antibodies to CD14 and Toll, and in vitro its release can be inhibited by non-bacteriolytic antibiotics and by polysulphates such as heparin, which probably interfere with the activation of autolysis. From all this evidence, LTA can be considered a virulence factor that has an important role in infections and in postinfectious sequelae caused by Gram-positive bacteria. The future development of effective antibacteriolitic drugs and multidrug strategies to attenuate LTA-induced secretion of proinflammatory agonists is of great importance to combat septic shock and multiorgan failure caused by Gram-positive bacteria.

No abstract is available for this item.

Transport properties of arrays of metallic quantum dots are governed by the distance-dependent exchange coupling between the dots. It is shown that the effective value of the exchange coupling, as measured by the charging energy per dot, depends monotonically on the size of the array. The effect saturates for-hexagonal arrays of over 7(5) unit cells. The discussion uses a multistage block renormalization group approach applied to the Hubbard Hamiltonian. A first-order phase transition occurs upon compression of the lattice, and the size dependence is qualitatively different for the two phases.