Supercooled confined water and the Mode Coupling crossover temperature

We present a Molecular Dynamics study of the single particle dynamics of supercooled water confined in a silica pore. Two dynamical regimes are found: close to the hydrophilic substrate molecules are below the Mode Coupling crossover temperature, $T_C$, already at ambient temperature. The water closer to the center of the pore (free water) approaches upon supercooling $T_C$ as predicted by Mode Coupling Theories. For free water the crossover temperature and crossover exponent $\gamma$ are extracted from power-law fits to both the diffusion coefficient and the relaxation time of the late $\alpha$ region.Comment: To be published, Phys. Rev. Lett., 4 pages, 3 figures, revTeX, minor changes in the figures, references added, changes in the tex

Formulation Pre-screening of Inhalation Powders Using Computational Atom–Atom Systematic Search Method

The synthonic modeling approach provides a molecule-centered understanding of the surface properties of crystals. It has been applied extensively to understand crystallization processes. This study aimed to investigate the functional relevance of synthonic modeling to the formulation of inhalation powders by assessing cohesivity of three active pharmaceutical ingredients (APIs, fluticasone propionate (FP), budesonide (Bud), and salbutamol base (SB)) and the commonly used excipient, α-lactose monohydrate (LMH). It is found that FP (−11.5 kcal/mol) has a higher cohesive strength than Bud (−9.9 kcal/mol) or SB (−7.8 kcal/mol). The prediction correlated directly to cohesive strength measurements using laser diffraction, where the airflow pressure required for complete dispersion (CPP) was 3.5, 2.0, and 1.0 bar for FP, Bud, and SB, respectively. The highest cohesive strength was predicted for LMH (−15.9 kcal/mol), which did not correlate with the CPP value of 2.0 bar (i.e., ranking lower than FP). High FP–LMH adhesive forces (−11.7 kcal/mol) were predicted. However, aerosolization studies revealed that the FP–LMH blends consisted of agglomerated FP particles with a large median diameter (∼4–5 μm) that were not disrupted by LMH. Modeling of the crystal and surface chemistry of LMH identified high electrostatic and H-bond components of its cohesive energy due to the presence of water and hydroxyl groups in lactose, unlike the APIs. A direct comparison of the predicted and measured cohesive balance of LMH with APIs will require a more in-depth understanding of highly hydrogen-bonded systems with respect to the synthonic engineering modeling tool, as well as the influence of agglomerate structure on surface–surface contact geometry. Overall, this research has demonstrated the possible application and relevance of synthonic engineering tools for rapid pre-screening in drug formulation and design

Circular fl ow model from the point of view of the capital theory of Austrian School

Celem artykułu była ocena modelu obiegu okrężnego z punktu widzenia teorii austriackiej szkoły ekonomii. W artykule omówiono teorię kapitału i model struktury produkcji tej szkoły. Omawiane zagadnienia odniesiono do modelu obiegu okrężnego, który dominuje w głównym nurcie ekonomii. Model ten jest krytykowany przez szkołę austriacką z powodu zbyt dużych uproszczeń. Główne zarzuty dotyczą pominięcia: twórczej natury działania ludzkiego, problemów niedoskonałej wiedzy i przedsiębiorczości, która związana jest z ryzykiem, roli czasu w działaniu i procesie produkcji, wertykalnego charakteru produkcji w gospodarce, powiązania oszczędności i inwestycji. Szkoła austriacka wskazuje również na zbyt daleko posuniętą w modelu obiegu okrężnego agregację kategorii ekonomicznych

Fullerene-like structure of activated carbons

The structure of the commercial activated carbons AX21 and BP71 has been studied using the high-energy X-ray diffraction and molecular dynamics techniques. The diffraction measurements were carried up to a maximum value of the scattering vector K-max=24 angstrom(-1). The obtained diffraction data have been converted to a real space representation in the form of the radial distribution function. Structural models containing 2 and 4 graphene layers, approximately 16-20 angstrom in size, were computer generated and then relaxed using the reactive empirical bond order potential for carbon-carbon interactions and the Lennard-Jones potential with parameters for inter-layer interactions. The molecular dynamics simulations were performed at 300 K to account for the thermal oscillations. For Such models the intensity and radial distribution functions were computed. The correctness of the models was verified by comparison of the simulations with the experimental data both in real and reciprocal space. The effects of hydrogen, saturating dangling bonds of edge atoms, the presence of non-six membered rings and the sp(3) defects on the resulting structure were investigated

Energy relaxation and pulsed neutrons diffraction studies of carbon nanotubes

Carbon nanotubes containing non-hexagonal rings have been computer generated and relaxed by minimization of the energy using the conjugate-gradient method. Then the powder diffraction patterns have been computed and converted to a real-space representation by the Fourier transform, yielding pair correlation functions which are compared with the pulsed neutrons experimental data for the single-wall carbon nanotubes produced by catalytic chemical vapour deposition. Effects of defective graphene cylinders on the interatomic distances and the resulting structures are discussed. The obtained results are also discussed in relation to previously reported paracrystalline behaviour of the nearest-neighbours distance fluctuations. (c) 2005 Elsevier B.V. All rights reserved

Structural studies of nanodiamond by high-energy X-ray diffraction

The atomic scale structure of explosive diamond nanoparticles has been studied using high-energy X-ray diffraction. The diffraction data have been converted to the real space representation in the form of the radial distribution function. Spherical and truncated octahedron nanodiamond clusters containing from 729 to 1182 atoms have been computer generated and then relaxed using the molecular dynamics method with the reactive empirical bond order potential for carbon-carbon interaction and the Lennard-Jones potential with parameters for inter-layer interactions. Validity of such constructed models has been verified by comparison of the simulations and the experimental data in both real and reciprocal space. The obtained results show that the structure of the investigated diamond nanoparticles cannot be satisfactorily described in terms of the model based on the perfect diamond lattice. The core-shell model with an average size of 22.5-23.4 angstrom, consisting of the diamond core and the graphite-like shell, accounts very well for the experimental data

Structural studies of carbon nanotubes obtained by template deposition using high-energy X-ray scattering

High-energy X-ray diffraction has been used to study the structure of multi-wall carbon nanotubes, produced by template pyrolytic carbon deposition from thermal decomposition of propylene inside channels of an alumina membrane. X-ray diffraction intensities were measured on the powdered samples employing an image plate detector, integrated over the diffraction rings and converted to a radial distribution function by the Fourier transform. Defective hexagonal networks, generated by introducing the pentagon-heptagon pairs were rolled up to form regular cylinders and relaxed with a conjugate-gradient algorithm using the Brenner-Tersoff potential. A comparison of the simulated and experimental radial distribution functions shows that the model of the multi-wall carbon nanotubes, based on the defective nanotube structures, accounts very well for the experimental data. (c) 2005 Elsevier B.V. All rights reserved