Quantum graph vertices with permutation-symmetric scattering probabilities

Boundary conditions in quantum graph vertices are generally given in terms of a unitary matrix U. Observing that if U has at most two eigenvalues, then the scattering matrix S(k) of the vertex is a linear combination of the identity matrix and a fixed Hermitian unitary matrix, we construct vertex couplings with this property: For all momenta k, the transmission probability from the j-th edge to ?-th edge is independent of (j,?), and all the reflection probabilities are equal. We classify these couplings according to their scattering properties, which leads to the concept of generalized δ- and δ^′-couplings.     

Simple Synthesis of Fluorinated Graphene: Thermal Exfoliation of Fluorographite

Fluorinated graphene can be prepared directly by thermal exfoliation of fluorographite. The exfoliation was performed in a dynamic nitrogen atmosphere at various temperatures and the exfoliation products were analysed in detail by GC‐MS. The structure and properties of all prepared fluorinated graphenes with various contents of fluorine were characterized by a number of analytical techniques. The results show both the dependence of fluorine concentration on exfoliation temperature and the suitability of this method for the synthesis of graphene with controlled concentration of fluorine. The high‐temperature exfoliated fluorographite exhibits a high heterogeneous electron transfer rate and excellent catalytic properties towards the oxygen reduction reaction. These synthetic procedures can open a simple way for the synthesis of fluorinated graphene‐based devices with tailored properties.     

Solution and Solid‐State Studies on the Halide Binding Affinity of Perfluorophenyl‐Armed Uranyl–Salophen Receptors Enhanced by Anion–π Interactions

The enhancement of the binding between halide anions and a Lewis acidic uranyl–salophen receptor has been achieved by the introduction of pendant electron‐deficient arene units into the receptor skeleton. The association and the occurrence of the elusive anion–π interaction with halide anions (as tetrabutylammonium salts) have been demonstrated in solution and in the solid state, providing unambiguous evidence on the interplay of the concerted interactions responsible for the anion binding.     

Stiffening and softening of freshly prepared and aged CTA,PTMSP, and PIM-1 films exposed to volatile compounds

Glassy polymers stiffen or soften when exposed to volatile compounds, depending on the specific combination of polymer compound and the specimen history. Relevant to the long-term applicability of the separation membranes, three common membrane glassy polymers are studied in this work. Freshly prepared and 2-years aged films from cellulose triacetate (CTA), poly[1-(trimethylsilyl)-1-propyne] (PTMSP), and the archetypal polymer of intrinsic microporosity (PIM-1) were tested using isothermal Dynamic Mechanical Analysis (DMA) at varied vapor activity. Vapors of organic compounds, in which the polymers do and do not dissolve in the liquid phase (solvents and nonsolvents), were studied at 40 °C, namely: dichloromethane (DCM, solvent), p-xylene (solvent for PTMSP and PIM-1), and methanol (nonsolvent). Functional groups of the mer units sensitive to the dissolution were identified using Raman spectroscopy. All aged films were stiffer than the freshly prepared ones. Stiffening prevailed for most freshly prepared film-vapor pairs at low vapor saturations (activity < ≈0.4), except CTA and PIM-1 in nonsolvent methanol vapors. Softening prevailed for the aged films and higher vapor saturations (activity > ≈0.6). Vapors of the solvents and nonsolvents did not show the expectable prevalence of softening and stiffening, respectively. Physical aging influenced the stiffening and softening of polymer glasses expectably.     

The effect of plasma treatment on structure and properties of poly(1-butene) surface

This paper is focused on the chemical and morphology changes in the surface of poly(1-butene) (PB-1) generated by plasma treatment. The radio frequency capacitively coupled plasma (air, argon, argon then allylamine, argon containing ammonia and argon with octafluorocyclobutane) was used. Modified surface of PB-1 was characterized by contact angle measurements, X-ray photoelectron spectroscopy, and atomic force microscopy. The surface hydrophilization by air and argon with ammonia plasmas was evaluated as most sufficient. Oppositely, a high level of hydrophobicity of PB-1 surface was reached by combination of argon with octafluorocyclobutane plasma. Upon plasma modification, hydrophilicity/hydrophobicity of treated surfaces remained stable within three days under air atmosphere and then values of contact angle slowly recovered to those of unmodified PB-1. However, morphology and surface chemical composition of plasma-modified samples remained generally unchanged during observed time. Changes in surface hydrophilicity/hydrophobicity of plasma-treated PB-1 were attributed to variance of conformation of the surface molecules.     

(I)-envelopes of closed convex sets in Banach spaces

We study the notion of (I)-generating introduced by V. Fonf and J. Lindendstrauss and a related notion of (I)-envelope. As a consequence of our results we get an easy proof of the James characterization of weak* compactness in Banach spaces with weak angelic dual unit ball and an easy proof of the James characterization of reflexivity within a large class of spaces. We also show by an example that the general James theorem cannot be proved by this method. The work is a part of the research project MSM 0021620839 financed by MSMT and partly supported by the research grant GA ČR 201/06/0018.     

Sub-poissonian light in third-harmonic generation: Quantum predictions via classical trajectories

Sub-Poissonian light in the third-harmonic generation process is studied numerically and analytically. Special regime exhibiting the time-stable maximum sub-Poissonian behaviour with the Fano factorF ≈ 0.81 is found and analyzed. Theoretical prediction of the Fano factor and explanation of the extraordinary time stability of the sub-Poissonian behaviour are given using the semiclassical method of classical trajectories.     

Mercury characterisation in urban particulate matter

A five-step sequential extraction procedure was proposed in order to assess the distribution of mercury (Hg) forms in urban particulate matter (PM): exchangeable, HCl-soluble, organic-bound, elemental and other slightly soluble Hg species, mercury(II) sulphide (HgS), and residual Hg. This process was applied to the analysis of urban dust samples collected at locations in Prague (Czech Republic) with high traffic density. In addition to sequential extractions, thermal desorption analysis was performed. The differences in Hg concentrations between untreated and thermally treated samples were indicated as the thermally releasable amount of Hg. For the study of PM-adsorbing capacity, Hg vapours were passed through the samples as long as the enrichment of materials was observed. The retained elemental Hg was readily released by thermal desorption. All Hg analyses were based on the highly sensitive pyrolysis technique of atomic absorption spectrometry using the mercury analyser AMA-254.