Search

In various chemical systems enthalpy-entropy compensation (EEC) is a well-known rule of behavior, although the physical roots of it are still not completely understood. It has been frequently questioned whether EEC is a truly physical phenomenon or a coincidence due to trivial mathematical connections between statistical-mechanical parameters - or even simpler: A phantom effect resulting from the misinterpretation of experimental data. Here, we review EEC from a new standpoint using the notion of correlation which is essential for the method of factor analysis, but is not conventional in physics and chemistry. We conclude that the EEC may be rationalized in terms of hidden (not directly measurable with the help of the current experimental set-up) but physically real factors, implying a Carnot-cycle model in which a micro-phase transition (MPT) plays a crucial role. Examples of such MPTs underlying physically valid EEC should be typically cooperative processes in supramolecular aggregates, like changes of structured water at hydrophobic surfaces, conformational transitions upon ligand-biopolymer binding, and so on, so forth. The MPT notion could help rationalize the occurrence of EEC in connection with hydration and folding of proteins,enzymatic reactions, functioning of molecular motors, DNA de- and rehybridization, as well as similar phenomena., Comment: 8 pages, 2 Figures, Submitted for publication

The name of George Augustus Linhart is in fact "widely unknown". In effect, he was a Viennese-born USA-American physicist-chemist, partially associated with the Gilbert Newton Lewis' school of thermodynamics at the University of California in Berkeley. As a lone small boy, he had arrived (from Austria via Hamburg) at New York in 1896, but was officially USA-naturalized only in 1912. He was able to pick up English in the streets of New York and Philadelphia, when occasionally working as a waiter and/or as a tailor - just to somehow survive. But, nonetheless, he could successfully graduate a high school in about one year - and then went to the universities for his further education. After obtaining his BS from the University of Pennsylvania, he could manage getting both MA and then PhD from the Yale University, Kent Chemical Laboratory. George Augustus Linhart was afterwards definitely able to successfully work out the true foundations of thermodynamics and could thus outdistance many famous thermodynamicists of his time and even the later ones. Linhart's view of the Second Law of Thermodynamics was and is extremely fruitful. The interconnection of Linhart's ideas with those of Gilbert Newton Lewis, as well as with the modern standpoints are discussed here in detail., Comment: Submitted

Some 80-90 years ago, George A. Linhart, unlike A. Einstein, P. Debye, M. Planck and W. Nernst, has managed to derive a very simple, but ultimately general mathematical formula for heat capacity vs. temperature from the fundamental thermodynamical principles, using what we would nowadays dub a "Bayesian approach to probability". Moreover, he has successfully applied his result to fit the experimental data for diverse substances in their solid state in a rather broad temperature range. Nevertheless, Linhart's work was undeservedly forgotten, although it does represent a valid and fresh standpoint on thermodynamics and statistical physics, which may have a significant implication for academic and applied science., Comment: submitted

The controlled fabrication of actively switchable atomic-scale devices, in particular transistors, has remained elusive to date. Here we explain operation of an atomic-scale three-terminal device by a novel switching mechanism of bistable, self-stabilizing reconstruction of the electrode contacts at the atomic level: While the device is manufactured by electrochemical deposition, it operates entirely on the basis of mechanical effects of the solid-liquid interface. We analyze mechanically and thermally stable metallic junctions with a predefined quantized conductance of 1-5 G_0 in experiment and atomistic simulation. Atomistic modeling of structural and conductance properties elucidates bistable electrode reconstruction as the underlying mechanism of the device. Independent room-temperature operation of two transistors at low voltage demonstrates intriguing perspectives for quantum electronics and logics on the atomic scale.

The controlled fabrication of well-ordered atomic-scale metallic contacts is of great interest: it is expected that the experimentally observed high percentage of point contacts with a conductance at non-integer multiples of the conductance quantum G_0 = 2e^2/h in simple metals is correlated to defects resulting from the fabrication process. Here we demonstrate a combined electrochemical deposition and annealing method which allows the controlled fabrication of point contacts with pre-selectable integer quantum conductance. The resulting conductance measurements on silver point contacts are compared with tight-binding-like conductance calculations of modeled idealized junction geometries between two silver crystals with a predefined number of contact atoms.

We numerically investigate quantum diffusion of an electron in a model of poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers with fluctuation of the parameters due to the impact of colored noise. The randomness is introduced by fluctuations of distance between two consecutive bases along the stacked base pairs. We demonstrate that in the model the decay time of the correlation can control the spread of the electronic wavepacket. Furthermore it is shown that in a motional narrowing regime the averaging over fluctuation causes ballistic propagation of the wavepacket, and in the adiabatic regime the electronic states are affected by localization., Comment: 17pages, 8figures

Recent papers have considered moving breathers (MBs) in DNA models including long range interaction due to the dipole moments of the hydrogen bonds. We have recalculated the value of the charge transfer when hydrogen bonds stretch using quantum chemical methods which takes into account the whole nucleoside pairs. We explore the consequences of this value on the properties of MBs, including the range of frequencies for which they exist and their effective masses. They are able to travel through bending points with fairly large curvatures provided that their kinetic energy is larger than a minimum energy which depends on the curvature. These energies and the corresponding velocities are also calculated in function of the curvature., Comment: 4 pages and 4 figures

This paper has been withdrawn due to some inconsistency of the results discovered after the submission. We apologize for it., Comment: This paper has been withdrawn

We investigate the charge transport in synthetic DNA polymers built up from single types of base pairs. In the context of a polaron-like model, for which an electronic tight-binding system and bond vibrations of the double helix are coupled, we present estimates for the electron-vibration coupling strengths utilizing a quantum-chemical procedure. Subsequent studies concerning the mobility of polaron solutions, representing the state of a localized charge in unison with its associated helix deformation, show that the system for poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers, respectively possess quantitatively distinct transport properties. While the former supports unidirectionally moving electron breathers attributed to highly efficient long-range conductivity the breather mobility in the latter case is comparatively restrained inhibiting charge transport. Our results are in agreement with recent experimental results demonstrating that poly(dG)-poly(dC) DNA molecules acts as a semiconducting nanowire and exhibits better conductance than poly(dA)-poly(dT) ones., Comment: 11 pages, 5 figures