Microscopic theory of thermal phase slips in clean narrow superconducting wires

We consider structure of a thermal phase-slip center for a simple microscopic model of a clean one-dimensional superconductors in which superconductivity occurs only within one conducting channel or several identical channels. Surprisingly, the Eilenberger equations describing the saddle-point configuration allow for exact analytical solution in the whole temperature and current range. This solution allows us to derive a closed expression for the free-energy barrier, which we use to compute its temperature and current dependences

Frequency dependent polarizability of small metallic grains

We study the dynamic electronic polarizability of a single nano-scale spherical metallic grain using quantum mechanical approach. We introduce the model for interacting electrons bound in the grain allowing us numerically to calculate the frequency dependence of the polarizability of grains of different sizes. We show that within this model the main resonance peak corresponding to the surface plasmon mode is blue-shifted and some minor secondary resonances above and below the main peak exist. We study the behavior of blue shift as a function of grain size and compare our findings with the classical polarizability and with other results in the literature.Comment: 8 pages, 3 figure

Nonlinear properties of left-handed metamaterials

We analyze nonlinear properties of microstructured materials with negative refraction, the so-called left-handed metamaterials. We consider a two-dimensional periodic structure created by arrays of wires and split-ring resonators embedded into a nonlinear dielectric, and calculate the effective nonlinear electric permittivity and magnetic permeability. We demonstrate that the hysteresis-type dependence of the magnetic permeability on the field intensity allows changing the material from left- to right-handed and back. These effects can be treated as the second-order phase transitions in the transmission properties induced by the variation of an external field.Comment: 4 pages, 3 figure

Molecular transport in thiacalix[4]arene-modified nanoporous colloidal films

The surface of nanopores in colloidal films assembled from 200 nm silica spheres was modified with thiacalix[4]arene moieties and transport of two redox-active species, ferrocene dimethanol and iron tris(bipyridyl) hexafluorophosphate, through the films has been studied using cyclic voltammetry. Evidence for two different molecular transport mechanisms was observed. Ferrocene dimethanol is transported via a simple diffusive mechanism while iron tris(bipyridyl) is transported via a surface-hopping mechanism. The difference in transport mechanisms is believed to result from different interaction strength between the diffusing species and the surface-bound organic moieties, and sheds light on transport mechanisms in nanoporous systems

Solvent extraction and self-assembly of nanosized aggregates of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by tertiary amide groups and monocharged metal cations in the organic phase

New p-tert-butyl thiacalix[4]arenes functionalized with morpholide and pyrrolidide groups at the lower rim in cone, partial cone, and 1,3-alternate conformations were synthesized, and their receptor properties for monocharged cations (alkali metal and silver ions) were studied using the picrate extraction method and dynamic light scattering (DLS). To evaluate the ability of the p-tert-butyl thiacalix[4]arene derivatives to recognize metal ions, liquid-liquid extraction of their picrate salts has been carried out in a mutually saturated water-dichloromethane system. The degrees of extraction and the extraction constants for monocharged metal cations (Li+, Na+, K+, Cs+) have been determined. The ability of the systems, consisting of host and guest molecules, to self-assembly was proved by DLS using a Zetasizer Nano ZS particle size analyzer. It was shown that all the investigated thiacalix[4]arenes are able to form nanoscale particles with silver cations under the experimental conditions. The pyrrolidide derivative in the cone conformation showed both self-association and aggregation processes with lithium cations. The degree of extraction for all the investigated systems that formed nanoscale aggregates in the organic phase was more than 67% and the extraction constants, log Kex determined by the picrate extraction method, more than 6. © 2008 Elsevier Ltd. All rights reserved

The synthesis of p-tert-butyl thiacalix[4]arenes functionalized with secondary amide groups at the lower rim and their extraction properties and self-assembly into nanoscale aggregates

In this work, the synthesis of novel p-tert-butyl thiacalix[4]arenes functionalized with the secondary amide groups at the lower rim in cone, partial cone, and 1,3-alternate conformations is described. The ability of novel thiacalixarene derivatives to form dimeric associates held together by hydrogen bonds of p-tert-butyl thiacalixarenes and to recognize metal ions of s (Li+, Na+, K+, Cs+, Mg2+, Ca2+, Ba2+), p (Al3+, Pb2+), and d (Fe3+, Co3+, Ni2+, Cu2+, Ag+, Cd2+, Hg2+) elements was investigated by the picrate extraction method and dynamic light scattering (DLS). As was established, the thiacalix[4]arenes investigated are poor extractants for all the metal ions. Meanwhile they self-associate to form dimers of similar size (1.1-2.7 nm) and nanoscale particles consisting of p-tert-butyl thiacalix[4]arenes and silver cations with hydrodynamic diameters of 70-170 nm. © 2008 Elsevier Ltd. All rights reserved

Silica nanoparticles surface-modified with thiacalixarenes selectively adsorb oligonucleotides and proteins

We prepared silica nanospheres 360 nm in diameter surface-modified with p-tert-butylthiacalix[4]arenes containing amine, carboxyl, and guanidinium groups. We found that these silica nanoparticles selectively adsorb model oligonucleotides and proteins. The particles modified with the macrocycle containing guanidinium fragments selectively adsorbed long-chain oligonucleotides and those modified with the macrocycle containing amine groups adsorbed BSA and hemoglobin with pH-dependent selectivity. We compared this behavior with that of silica nanoparticles carrying amine and carboxyl groups, and concluded that both electrostatic interactions and specific binding are responsible for the observed selectivity. © 2013 Springer Science+Business Media Dordrecht

Self-assembly of stereoisomers of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by a tertiary amide group with cations of p- and d-elements in the organic phase

The ability of p-tert-butyl thiacalix[4]arenes tetrasubstituted at the lower rim by morpholide and pyrrolidide groups in cone, partial cone, and 1,3-alternate conformations to recognize cations of p- (Al3+, Pb 2+) and d- (Fe3+, Co3+, Ni2+, Cu2+, Cd2+, Hg2+) elements has been studied by the picrate extraction method, dynamic light scattering (DLS), and atomic force microscopy (AFM). The hydrodynamic diameters of supramolecular associates, polydispersity index of host-guest systems, and molecular weight of nanoscale aggregates consisting of p-tert-butyl thiacalix[4]arenes and metal nitrates have been determined by the correlation spectroscopy method. It was shown that the investigated macrocycles are effective extractants for metal cations. All the investigated thiacalix[4]arenes are able to form dimers of about 1 nm with metal cations and nanoscale particles of 238 and 212 nm with Ni2+ and Pb2+ cations, respectively. © 2009 American Chemical Society