Kohn anomalies and electron-phonon interactions in graphite

We demonstrate that graphite phonon dispersions have two Kohn anomalies at the Gamma-E(2g) and K-A'1 modes. The anomalies are revealed by two sharp kinks. By an exact analytic derivation, we show that the slope of these kinks is proportional to the square of the electron-phonon coupling (EPC). Thus, we can directly measure the EPC from the experimental dispersions. The Gamma-E(2g) and K-A'1 EPCs are particularly large, while they are negligible for all the other modes at Gamma and K.     

Biosprayed spleen cells integrate and function in mouse models

Bio-electrospraying (BES) and aerodynamically assisted bio-jetting (AABJ), two non-contact direct cell handling approaches, have recently undergone rigorous scientific testing to assess whether cells retain chemical, physical and more importantly biological functions similarly to their unmanipulated counterparts. Previous in vitro validation of these two approaches has shown that they are inert for the direct handling and distributing of cells with great accuracy. In the present investigation we aim to validate, in vivo, that the spray techniques do not functionally or phenotypically alter splenic cells. By taking advantage of an adoptive transfer mouse model we demonstrated that the in vivo behaviour of treated cells is indistinguishable from unmanipulated cells following adoptive transfer into C57/BL6 mice. Indeed, sprayed cells survived and proliferated in response to antigen activation to similar levels observed in unmanipulated cells. In addition, in vivo sprayed cells displayed identical migratory characteristics to those observed in unmanipulated cells. Thus, demonstrating the inertness of these biosprays. Hence these biotechniques hold great potential for use in the development of three-dimensional cultures, tracking and monitoring cell-interactions and in vitro modelling of disease-states and therapeutics.     

Phase Field Approach to Multiphase Flow Modeling

We review the phase field (otherwise called diffuse interface) model for fluid flows, where all quantities, such as density and composition, are assumed to vary continuously in space. This approach is the natural extension of van der Waals?? theory of critical phenomena both for one-component, two-phase fluids and for partially miscible liquid mixtures. The equations of motion are derived, assuming a simple expression for the pairwise interaction potential. In particular, we see that a non-equilibrium, reversible body force appears in the Navier-Stokes equation, that is proportional to the gradient of the generalized chemical potential. This, so called Korteweg, force is responsible for the convection that is observed in otherwise quiescent systems during phase change. In addition, in binary mixtures, the diffusive flux is modeled using a Cahn-Hilliard constitutive law with a composition-dependent diffusivity, showing that it reduces to Fick??s law in the dilute limit case. Finally, the results of several numerical simulations are described, modeling, in particular, a) mixing, b) spinodal decomposition, c) nucleation, d) enhanced heat transport, e) liquid-vapor phase separation.     

Preparation and characterization of a silica gel-based substrate activated with a doubly attached chlorotriazine

It is shown that trichloro-1,3,5-triazine can be attached to aminated silica gel at two sites. This method of activating the silica gel for immobilization of analytical reagents is considered in relation to the typical single-site method of attachment. Diffuse-reflectance infrared and ultraviolet spectroscopic results are presented to confirm the nature of the attachment. 2,2′,4-Trihydroxyazobenzene is used as a model reagent to illustrate that better control of the immobilization reaction results from the second site of attachment of the triazine linkage to the substrate.     

Surface P and Al Distribution in P-modified ZSM-5 Zeolites

The surface composition of two commercial ZSM-5 zeolites with and without PO₄ modification was examined by X-ray photoelectron spectroscopy. Both zeolites were slightly enriched in aluminum on the surface. The surface silica/alumina ratio (SAR) was about half of that of the bulk. Calcination at 600^∘C decreased slightly this enrichment. After drying with H₃PO₄ followed by calcination, both zeolites showed surface enrichment of PO₄. The surface of the zeolite with large crystal was more enriched. Steaming resulted in enrichment of aluminum on the surface, in agreement with migration of extra-framework alumina. Increasing phosphate content decreased this enrichment. This paper was presented in the 5th Brazilian Meeting on Adsorption, held at Natal, Brazil, 18-21 July, 2004.     

Experimental evidence of the motion of a single out-of-equilibrium drop

We show experimentally that when a single, neutrally buoyant drop is injected into a binary mixture either it remains quiescent or it moves, depending on whether the composition of the drop and that of the surrounding phase coincide with the equilibrium concentrations. In general, the movement of out-of-equilibrium drops, which is called diffusiophoresis, is induced by the Korteweg body force. This force is proportional to the chemical potential gradient and is therefore nonzero only when the system is in chemical nonequilibrium. In this letter, we show experimentally that this movement occurs for a single drop as well, even when the initial condition is (almost) isotropic. This instability, although it does not have a complete analytical explanation, has been predicted in the numerical simulations by Vladimirova et al. (Vladimirova, N.; Malagoli, A.; Mauri, R. Phys. Rev. E 1999, 60, 2037).     

First principles NMR calculations of phenylphosphinic acid C6H5HPO(OH): assignments, orientation of tensors by local field experiments and effect of molecular motion

The complete set of NMR parameters for (17)O enriched phenylphosphinic acid C(6)H(5)HP( *)O(*OH) is calculated from first principles by using the Gauge Including Projected Augmented Wave (GIPAW) approach [C.J. Pickard, F. Mauri, All-electron magnetic response with pseudopotentials: NMR chemical shifts, Phys. Rev. B 63 (2001) 245101/1-245101/13]. The analysis goes beyond the successful assignment of the spectra for all nuclei ((1)H, (13)C, (17)O, (31)P), as: (i) the (1)H CSA (chemical shift anisotropy) tensors (magnitude and orientation) have been interpreted in terms of H bonding and internuclear distances. (ii) CSA/dipolar local field correlation experiments have allowed the orientation of the direct P-H bond direction in the (31)P CSA tensor to be determined. Experimental and calculated data were compared. (iii) The overestimation of the calculated (31)P CSA has been explained by local molecular reorientation and confirmed by low temperature static (1)H-->(31)P CP experiments.