Optical artefacts in transflection mode FTIR microspectroscopic images of single cells on a biological support: the effect of back-scattering into collection optics

Infrared microspectroscopic imaging data of single human prostate cancer cells, on an artificial extracellular matrix (Matrigel) thin-film surface, are presented. The spectral intensity maps, obtained in reflection mode, appear to show that the protein intensity distribution observed at the location of a cell changes dramatically depending on the concentration and/or thickness of the underlying Matrigel layer. Specifically, cells adhered to a low protein concentration or thin surface exhibit a higher protein intensity signal than the surrounding layer whereas those on a high protein concentration or thick surface exhibit a lower protein intensity signal. These results are qualitatively explained by a simple model that takes into account the fact that radiation scattered from cells can enter the collection optics of the microscope without passing through the Matrigel layer. This leads to an apparent reduction in absorption at the cell.     

Anomalous transport in molecularly confined spaces

We develop a novel theory to predict the density dependence of the diffusivity of simple fluids in a molecularly sized nanopore with diffusely reflecting walls, incorporating nearest neighbor intermolecular interactions within the framework of the recent oscillator model of low density transport arising from this laboratory. It is shown that when the pore width is about two molecular diameters, at sufficiently high densities these interactions lead to a repulsive inner core, as a result of which the diffusing molecules undergo more frequent reflections at the wall. This leads to a reduction in diffusivity with increase in density, which is consistent with molecular dynamics simulation results, and contrasts with the behavior in larger pores where the transport coefficient has previously been shown to increase with increase in density due to viscouslike intermolecular interactions. At low densities the behavior is opposite, with the inner core becoming more attractive with increase in density, which can lead to an increase in diffusivity. The theory consistently explains molecular dynamics simulation results when the inhomogeneous pair distribution function of moving particles in the pore is axially periodic, suggesting concerted motion of neighboring molecules. It is also shown that a potential of mean force concept is inadequate for describing the influence of intermolecular interactions on transport.     

Energy convexity as a consequence of decoherence and pair-extensive interactions in many-electron systems

Using the concept of self-entanglement, through which a pure state constructed in an augmented Hilbert space can describe a mixed state and through which the effects of physical decoherence can be mapped onto systems separated by an infinite distance, with the role of environmental states assumed by system states in disjoint Hilbert spaces, we show that expectation values of Hamiltonians subscribing to decoherence and satisfying the condition of extensivity, defined in the text, obey the energy convexity relation. The analysis based on self-entanglement also leads to a surprising interpretation of the failure of the convexity relation for model Hamiltonians such as the Hubbard model: The failure is due to the existence of self-entangled states with lower energies than the ground state so that in such models decoherence, i.e., disentangling from the self-entangled states, would cost energy and disallow the observation of the state through measurement. The Hubbard model is discussed extensively in an appendix where we also discuss and resolve some of the counterarguments to the convexity relation that have been advanced in the literature.     

Competing pairing symmetries in a generalized two-orbital model for the pnictide superconductors

We introduce and study an extended "t-U-J" two-orbital model for the pnictides that includes Heisenberg terms deduced from the strong coupling expansion. Including these J terms explicitly allows us to enhance the strength of the (π,0)-(0,π) spin order which favors the presence of tightly bound pairing states even in the small clusters that are here exactly diagonalized. The A(1g) and B(2g) pairing symmetries are found to compete in the realistic spin-ordered and metallic regime. The dynamical pairing susceptibility additionally unveils low-lying B(1g) states, suggesting that small changes in parameters may render any of the three channels stable.     

A critical assessment of capillary condensation and evaporation equations: a computer simulation study

Nonaqueous reverse micelles of brij surfactants are prepared in benzene and ethylammonium nitrate (EAN). The effect of polar head group bulk on reverse micellar size was studied with brij-52, brij-56 and brij-58 whereas the effect of polarity of hydrocarbon chain was investigated taking brij-52 and brij-93 with varying W(s) (W(s)=[EAN]/[surfactant]). Dynamic light scattering (DLS) has been employed to reveal the size and shape of the reverse micelles. Micropolarities of these reverse micelles were investigated by visible spectroscopy using methylene blue (MB) and methyl orange (MO) as molecular optical probes. It has been revealed from the experimental results that with increase in polar head group size reverse micellar size increases. Moreover, it is also observed that with increasing polarity of the hydrocarbon chain the average size of the reverse micelles decreases. It can be concluded that polar head group size and polarity of hydrocarbon chain play important roles in determining reverse micellar size of the brij surfactants apart from the W(s) ratio, nature of the solvent medium, and concentration of the surfactants.     

Modeling mixture transport at the nanoscale: departure from existing paradigms

We present a novel theory of mixture transport in nanopores, which represents wall effects via a species-specific friction coefficient determined by its low density diffusion coefficient. Onsager coefficients from the theory are in good agreement with those from molecular dynamics simulation, when the nonuniformity of the density distribution is included. It is found that the commonly used assumption of a uniform density in the momentum balance is in serious error, as is also the traditional use of a mixture center of mass based frame of reference.     

ChemInform Abstract: First‐Principles Screening of Complex Transition Metal Hydrides for High Temperature Applications.

Semi‐automated thermodynamic and phase diagram calculations based on DFT and grand canonical linear programming (GCLP) methods are used to screen 102 ternary and quaternary complex transition metal hydrides (CTMHs) and 26 ternary saline hydrides in a library of over 260 metals, intermetallics, binary, and higher hydrides to identify materials that release H₂ at higher temperatures than the associated binary hydrides and at elevated temperatures (T < 1000 K, 1 bar H₂ overpressure).