Natural frequencies of two bubbles in a compliant tube: analytical, simulation, and experimental results

Motivated by various clinical applications of ultrasound contrast agents within blood vessels, the natural frequencies of two bubbles in a compliant tube are studied analytically, numerically, and experimentally. A lumped parameter model for a five degree of freedom system was developed, accounting for the compliance of the tube and coupled response of the two bubbles. The results were compared to those produced by two different simulation methods: (1) an axisymmetric coupled boundary element and finite element code previously used to investigate the response of a single bubble in a compliant tube and (2) finite element models developed in comsol Multiphysics. For the simplified case of two bubbles in a rigid tube, the lumped parameter model predicts two frequencies for in- and out-of-phase oscillations, in good agreement with both numerical simulation and experimental results. For two bubbles in a compliant tube, the lumped parameter model predicts four nonzero frequencies, each asymptotically converging to expected values in the rigid and compliant limits of the tube material.     

Unraveling the stability of polypeptide helices: critical role of van der Waals interactions

Folding and unfolding processes are important for the functional capability of polypeptides and proteins. In contrast with a physiological environment (solvated or condensed phases), an in?vacuo study provides well-defined "clean room" conditions to analyze the intramolecular interactions that largely control the structure, stability, and folding or unfolding dynamics. Here we show that a proper consideration of van der Waals (vdW) dispersion forces in density-functional theory (DFT) is essential, and a recently developed DFT+vdW approach enables long time-scale ab?initio molecular dynamics simulations at an accuracy close to "gold standard" quantum-chemical calculations. The results show that the inclusion of vdW interactions qualitatively changes the conformational landscape of alanine polypeptides, and greatly enhances the thermal stability of helical structures, in agreement with gas-phase experiments.     

Theory of 2D transport in graphene for correlated disorder

We theoretically revisit graphene transport properties as a function of carrier density, taking into account possible correlations in the spatial distribution of the Coulomb impurity disorder in the environment. We find that the charged impurity correlations give rise to a density-dependent graphene conductivity, which agrees well qualitatively with the existing experimental data. We also find, quite unexpectedly, that the conductivity could increase with increasing impurity density if there is sufficient interimpurity correlation present in the system. In particular, the linearity (sublinearity) of graphene conductivity at lower (higher) gate voltage is naturally explained as arising solely from impurity correlation effects in the Coulomb disorder.     

Application of factor analysis to XPS valence band of superparamagnetic iron oxide nanoparticles

X-Ray photoelectron spectra of nano-sized superparamagnetic iron oxide nanoparticles were examined with the aim to discriminate the different degree of iron oxidation. Careful analysis of the valence band regions reveals the presence of both Fe₃O₄ and Fe₂O₃. The application of factor analysis enabled us to extract the relative molar concentrations of these oxides in the nanoparticles. This is of particular interest in improving the magnetic properties of iron oxide nanoparticles whose superparamagnetic character can be optimized to obtain better contrast in images from nuclear magnetic resonance. As a result, the factor analysis allows tuning the nanoparticle synthesis conditions in order to obtain the optimal magnetic properties for imaging. Results obtained by the XPS valence band analysis were compared to the transmission electron microscopy, X-ray diffraction and Raman measurements.     

InCl3-assisted one-pot synthesis of 1-aminocarbazoles

A novel InCl₃-mediated one-pot reaction leading to 1-aminocarbazoles is reported. Starting from easily available 2-acetyl-1H-indole, the reaction involves the alkylation of C-3 with a prop-2-yn-1-ol followed by a domino aminobenzannulation reaction in the presence of a secondary amine. The indium salt is most likely involved as catalyst in all three steps of the one-pot reaction. Starting from 2-acetyl-1H-indole and a series of prop-2-yn-1-ols and secondary amines a small library of products has been obtained.     

Synthesis of carbolines by photostimulated cyclization of anilinohalopyridines

A general synthetic route to prepare all four carboline regioisomers by photostimulated cyclization of anilinohalopyridines is described. The methodology affords various substituted carbolines in good to excellent yields. In the case of α-carbolines, the S(RN)1 methodology complements previously reported palladium-catalyzed cyclization approaches.     

Fluorous materials in microbubble engineering science and technology—Design and development of new bubble preparation and sizing technologies

Microbubbles are being used in ultrasound diagnosis imaging, could serve as contrast agents for multiple imaging modalities and for parenteral oxygen delivery, and have potential in materials science as new multi-scale materials for magnetic, optical and magneto-optical devices. We designed new procedures for the preparation of narrowly size-distributed, monomodal microbubble populations, as well as a new multifrequency acoustical device for microbubble sizing. Methods for microbubble stabilization using fluorinated gases and surfactants are also discussed. Prospects include further use of fluorinated amphiphiles for bubble stabilization and size control, and decoration of bubble surface with functional particles (e.g. magnetic iron oxide nanoparticles).     

Ab-initio crystal structure prediction. A case study: NaBH4

Crystal structure prediction from first principles is still one of the most challenging and interesting issue in condensed matter science. we explored the potential energy surface of NaBH₄ by a combined ab-initio approach, based on global structure optimizations and quantum chemistry. In particular, we used simulated annealing (SA) and density functional theory (DFT) calculations. The methodology enabled the identification of several local minima, of which the global minimum corresponded to the tetragonal ground-state structure (P4₂/nmc), and the prediction of higher energy stable structures, among them a monoclinic (Pm) one was identified to be 22.75 kJ/mol above the ground-state at T=298 K. In between, orthorhombic and cubic structures were recovered, in particular those with Pnma and symmetries.     

Interactions of Proteins with the Acidic Components of the Electrolyte Solution and Their Role in the Performance of Separations by CZE

This paper reports the results of a study performed to investigate the dependence of the performance of protein separation by capillary zone electrophoresis (CZE) on the anionic component of the electrolyte solutions consisting of 20 mM N,N,N′,N′-tetramethyl-1,3-butanediamine (TMBD) titrated to either pH 4.0 or pH 6.5 with either a monoprotic or a polyprotic acid. With the exception of hydrochloric acid, the acids were selected among those commonly used as the constituents of the solutions employed for protein analysis by either HPLC or CZE. TMBD was chosen for its effectiveness at preventing the interactions of proteins with the inner wall of bare fused-silica capillaries. The performance of separations was evaluated using four basic model proteins having pI value and molecular mass ranging from 9.5 to 11.0 and from 12,400 to 25,000 Da, respectively. It is shown that the different acids used as the components of the background electrolyte solutions, all containing the same concentration of TMBD, affect to different extents both migration time and peak shape of the tested proteins. The performance displayed by the BGE containing phosphate ions is enhanced using TMBD in combination with diethylenetriamine, an aliphatic vicinal triamine having effective buffering capacity at pH 4.0 and capability at minimizing protein–capillary wall interactions. The reported experimental evidences are discussed based on the possible interactions that the phosphate ions are known to establish with both the protein molecules and the surface of bare fused-silica capillaries.     

A new study of 25Mg(\alpha,n) 28Si angular distributions at E_{\alpha} =3-5 MeV

Heavy neutron-rich nuclei close to N = 126 were produced by fragmentation of a 1A GeV ²⁰⁸Pb beam at the FRS at GSI. The β-decay half-lives of 7 nuclides have been determined using a novel numerical analysis method. The half-lives of ^202,199Ir, ^200,199Os and ¹⁹⁶Re are reported for the first time. The comparison of the data with model calculations provides indications on the importance of first-forbidden transitions on the β-decay of nuclei around N = 126 and Z < 82.