Friction tensor for a pair of Brownian particles: Spurious finite-size effects and molecular dynamics estimates

In this work, we show thatin any finite system, the binary friction tensor for two Brownian particlescannot be directly estimated from an evaluation of the microscopic Green-Kubo formula, involving the time integral of force-force autocorrelation functions. This pitfall is associated with a subtle inversion of the thermodynamic and long-time limits and leads to spurious results for the estimates of the friction matrix based on molecular dynamics simulations. Starting from a careful analysis of the coupled Langevin equations for two interacting Brownian particles, we derive a method to circumvent these effects and extract the binary friction tensor from the correlation function matrix of the instantaneous forces exerted by the bath particles on the fixed Brownian particles, and from the relaxation of the total momentum of the bath in afinite system. The general methodology is applied to the case of two hard or soft Brownian spheres in a bath of light particles. Numerical estimates of the relevant correlation functions and of the resulting self and mutual components of the matrix of friction tensors are obtained by molecular dynamics simulations for various spacings between the Brownian particles. This paper is dedicated to B. Jancovici on the occassion of his 65th birthday.     

VUV photon induced fluorescence study of SF5CF3

The interaction of SF(5)CF(3) with vacuum-UV radiation has been investigated by photon induced fluorescence spectroscopy. Total fluorescence yield and dispersed fluorescence spectra of SF(5)CF(3) were recorded in the 200-1000 nm fluorescence window. In all cases, the fluorescence spectra resemble those of CF(3)X (X = H, F, Cl, and Br) molecules. At photon energies below 20 eV, the emission is attributed to the excited CF(3) and CF(2) fragments. The threshold for the CF(3) emission is 10.2 +/- 0.2 eV, giving an upper limit estimate for the SF(5)-CF(3) bond dissociation energy of 3.9 +/- 0.3 eV. The excitation functions of the CF(3) and CF(2) emissions were measured in the photon energy range 13.6-27.0 eV. The resonant structures observed in SF(5)CF(3) are attributed to electronic transitions from valence to Rydberg orbitals, following similar assignments in CF(3)X molecules. The photoabsorption spectrum of SF(5)CF(3) shows features at the same energies, indicating a strong contribution from Rydberg excitations.     

Heat conduction in transversally graded laminates with non-uniform microstructure

Two-component laminates made of conductors distributed non-periodically as laminas along one direction are considered in this note. The macroscopic properties of these laminates are described by continuous slowly-varying functions across laminas. In order to analyse heat conduction, the approach, called the tolerance modelling, is used. The aim of this note is to use averaged equations of the tolerance model for transversally graded laminates to analyse stationary heat conduction across laminas. (© 2010 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

Partitioning of atmospheric carbon dioxide over Central Europe: insights from combined measurements of CO 2 mixing ratios and their carbon isotope composition

Regular measurements of atmospheric CO ₂ mixing ratios and their carbon isotope composition (¹³C/¹²C and ¹⁴C/¹²C ratios) performed between 2005 and 2009 at two sites of contrasting characteristics (Krakow and the remote mountain site Kasprowy Wierch) located in southern Poland were used to derive fossil fuel-related and biogenic contributions to the total CO ₂ load measured at both sites. Carbon dioxide present in the atmosphere, not coming from fossil fuel and biogenic sources, was considered ‘background’ CO ₂. In Krakow, the average contribution of fossil fuel CO ₂ was approximately 3.4%. The biogenic component was of the same magnitude. Both components revealed a distinct seasonality, with the fossil fuel component reaching maximum values during winter months and the biogenic component shifted in phase by approximately 6 months. The partitioning of the local CO ₂ budget for the Kasprowy Wierch site revealed large differences in the derived components: the fossil fuel component was approximately five times lower than that derived for Krakow, whereas the biogenic component was negative in summer, pointing to the importance of photosynthetic sink associated with extensive forests in the neighbourhood of the station. While the presented study has demonstrated the strength of combined measurements of CO ₂ mixing ratios and their carbon isotope signature as efficient tools for elucidating the partitioning of local atmospheric CO ₂ loads, it also showed the important role of the land cover and the presence of the soil in the footprint of the measurement location, which control the net biogenic surface CO ₂ fluxes.     

Influence of terbium on structure and luminescence of nanocrystalline TiO2 thin films

In this work analysis of the structural and optical properties of TiO₂ thin films doped with terbium has been described. Samples were prepared by a high energy reactive magnetron sputtering process under low pressure of oxygen plasma. X-ray diffraction results have shown that different TiO₂ crystal forms have been produced, depending on the amount of Tb dopant. The undoped matrix had rutile structure with crystallites with a size of 8.7 nm, while incorporation of 0.4 at. % of Tb into the film during the sputtering process resulted in anatase structure with bigger crystallites (11.7 nm). Increasing the amount of terbium up to 2 at. % and 2.6 at. % gave rutile structure with crystallites with a size of 6.6 nm for both films. However, Raman spectroscopy has revealed that in the case of TiO₂:(2 at. % Tb), except for the rutile form, the presence of fine-crystalline anatase was observed. Moreover, the lack of Raman peaks shift attests to the lack of stress in the titania lattice of all of the TiO₂:Tb films. This fact indicates localization of Tb3+ ions on the surface of TiO₂ nanocrystals. In the case of optical investigation, results have shown that doping with terbium has a significant influence on the properties of TiO₂, but it does not decrease the high transparency of the matrix. The observed changes of the transmission characteristics were produced only due to modification of the TiO₂:Tb structure. Photoluminescence measurements have shown that emission of light from TiO₂:Tb films occurs when the amount of terbium is 2.6 at. %. Based on the obtained results a scheme of direct energy transfer from titanium dioxide matrix (with rutile structure) to Tb³⁺ ions has been proposed.     

Structural properties of transparent Ti-V oxide semiconductor thin films

Transparent oxide semiconducting thin films based on mixed Ti-V oxides were prepared using a modified reactive magnetron sputtering method. Based on structural investigations performed with the help of x-ray diffraction and transmission electron microscopy analysis, two distinct regions in the prepared thin film have been observed: a nanocrystalline TiO₂-V₂O₃-V₂O₅ mixed composition, and a thin layer consisting of amorphous phase and nanocystalline TiO₂ phase deposited directly at the substrate. Optical measurements show excellent transmission in the visible spectral range of 73%, on average. Resistivity of the thin film was found at the order of 10⁵ Ω cm at room temperature. The preparation of mixed Ti-V oxides provides a combination of high transparency and semiconducting properties.     

How To Play Two-Player Restricted Quantum Games with 10 Cards

We show that it is possible to play ‘restricted’ two-player quantum games proposed originally by Marinatto and Weber (Phys. Lett. A 272:291–303, 2000) by purely macroscopic means, in the simplest case having as the only equipment a pack of 10 cards. Our example shows also that some apparently ‘genuine quantum’ results, even those that emerge as a consequence of dealing with entangled states, can be obtained by suitable application of Kolmogorovian probability calculus and secondary-school mathematics, without application of the ‘Hilbert space machinery’.     

Temperature dependence of electric field noise above gold surfaces

Electric field noise from fluctuating patch potentials is a significant problem for a broad range of precision experiments, including trapped ion quantum computation and single spin detection. Recent results demonstrated strong suppression of this noise by cryogenic cooling, suggesting an underlying thermal process. We present measurements characterizing the temperature and frequency dependence of the noise from 7 to 100 K, using a single Sr+ ion trapped 75 mum above the surface of a gold plated surface electrode ion trap. The noise amplitude is observed to have an approximate 1/f spectrum around 1 MHz, and grows rapidly with temperature as T;{beta} for beta from 2 to 4. The data are consistent with microfabricated cantilever measurements of noncontact friction but do not extrapolate to the dc measurements with neutral atoms or contact potential probes.     

Nonadiabatic excited-state dynamics of polar pi-systems and related model compounds of biological relevance

Multireference ab initio dynamics simulations have become available as a tool for the investigation of photochemical processes, mainly for those related to nonadiabatic phenomena taking place in the sub-picosecond time scale. For organic molecules, these phenomena are in many cases deeply dependent on the relaxation of the photoexcited pi-system. We review the latest contributions of our group to this subject and report new results for systems studied previously, grouping them in single pi bonds, chains and aromatic rings. The dynamics of ethylene and substituted ethylenes is discussed mainly in connection to the competition between the two available relaxation paths in the excited states and their relation to the conical intersections in large systems. The trans-cis and the cis-trans dynamics of the pentadieniminium cation is investigated as well. Finally, we discuss the photodynamics of aminopyrimidine starting in the S1 and S2 states and the conclusions, which can be drawn from this for the interpretation of the adenine dynamics.     

Syntheses of potassium 1,1‐dioxopyrido[4,3‐e]‐1,4,2‐dithiazine‐3‐thiolate and its application to the synthesis of novel sulfonamides with potential biological activity

Potassium 1,1‐dioxopyrido[4,3‐e]‐1,4,2‐dithiazine‐3‐thiolate 2 has been synthesized and applied to the syntheses of 7H‐1,1‐dioxopyrido[4,3‐e]‐1,4,2‐dithiazolium‐3‐thiolate 3 and 3‐methylthiopyrido[4,3‐e]‐1,4,2‐dithiazine 1,1‐dioxide 4 which provided easy access to a variety of its 3‐amino derivatives 5‐10 . Hydrazinolysis of 7, 8 and 10 afforded the corresponding 3‐amino‐2‐(1,4‐dihydro‐4‐thioxopyrid‐3‐ylsulfonyl)guanidines 11‐13 . Subsequent reaction of 12 with 4‐chlorobenzaldehyde gave condensation product 14 . 1,4‐Dihydro‐2‐thioxopyridine‐3‐sulfonamide 15 was also prepared from the potassium salt 2 upon alkaline hydrolysis, whereas alkylation of 15 gave the appropriate S‐substituted derivatives 16‐19 or S,N‐disubstituted compounds 20‐21 .