Gas vesicle formation and buoyancy regulation in Pelodictyon phaeoclathratiforme (Green sulfur bacteria)

Gas vesicle formation and buoyancy regulation in Pelodictyon phaeoclathratiforme strain BU1 (Green sulfur bacteria) was investigated under various laboratory conditions. Cells formed gas vesicles exclusively at light intensities below 5 mol · m-2 · s-1 in the stationary phase. No effect of incubation temperature or nutrient limitation was observed. Gas space of gas vesicles occupied always less than 1.2% of the total cell volume. A maximum cell turgor pressure of 330 kPa was determined which is comparable to values determined for cyanobacterial species. Since a pressure of at least 485 kPa was required to collapse the weakest gas vesicles in Pelodictyon phaeoclathratiforme, short-term regulation of cell density by the turgor pressure mechanism can be excluded. Instead, regulation of the cell density is accomplished by the cease of gas vacuole production and accumulation of carbohydrate at high light intensity. The carbohydrate content of exponentially growing cells increased with light intensity, reaching a maximum of 35% of dry cell mass above 10 mol · m-2 · s-1. Density of the cells increased concomitantly. At maximum density, protein and carbohydrate together accounted for 62% of the total cell ballast. Cells harvested in the stationary phase had a significantly lower carbohydrate content (8–12% of the dry cell mass) and cell density (1010–1014 kg · m-3 with gas vesicles collapsed) which in this case was independent of light intensity. Due to the presence of gas vesicles in these cultures, the density of cells reached a minimum value of 998.5 kg · m-3 at 0.5 mol · m-2 · s-1. The cell volume during the stationary phase was three times higher than during exponential growth, leading to considerable changes in the buoyancy of Pelodictyon phaeoclathratiforme. Microscopic observations indicate that extracellular slime layers may contribute to these variations of cell volume

Driven quantum transport on the nanoscale

We explore the prospects to control by use of time-dependent fields quantum transport phenomena in nanoscale systems. In particular, we study for driven conductors the electron current and its noise properties. We review recent corresponding theoretical descriptions which are based on Floquet theory. Alternative approaches, as well as various limiting approximation schemes are investigated and compared. The general theory is subsequently applied to different representative nanoscale devices, like the non-adiabatic pumps, molecular gates, molecular quantum ratchets, and molecular transistors. Potential applications range from molecular wires under the influence of strong laser fields to microwave-irradiated quantum dots.Comment: 82 pages, 19 figures, elsart.cls, solved LaTeX/hyperref problem

Sequential Tunneling through Molecular Spin Rings

We consider electrical transport through molecules with Heisenberg-coupled spins arranged in a ring structure in the presence of an easy-axis anisotropy. The molecules are coupled to two metallic leads and a gate. In the charged state of the ring, a Zener double-exchange mechanism links transport properties to the underlying spin structure. This leads to a remarkable contact-site dependence of the current, which for an antiferromagnetic coupling of the spins can lead to a total suppression of the zero-bias conductance when the molecule is contacted at adjacent sites.Comment: 4 pages, 3 figure

Digital Commons as a Model for Digital Sovereignty: The Case of Cultural Heritage

This contribution looks at cultural heritage institutions and their digital assets from a commons perspective. Since the beginning of digitization in the late 1990s and with the change of the medium from the analogue to the digital, the role and mission of cultural heritage institutions has changed. Challenges for managing their assets in the sense of a commons arise, on the one hand, due to the current legislation on copyright and intellectual property rights, and, on the other, because of the availability of digital cultural heritage as Big Data, which opens up possibilities for economic exploitation of these assets by private companies. Should digital assets be available open access, or should access and use be regulated? This short paper discusses the possibilities for this model of sovereign data governance within the legal regimes of intellectual property rights and the public domain

Rectification of laser-induced electronic transport through molecules

We study the influence of laser radiation on the electron transport through a molecular wire weakly coupled to two leads. In the absence of a generalized parity symmetry, the molecule rectifies the laser induced current, resulting in directed electron transport without any applied voltage. We consider two generic ways of dynamical symmetry breaking: mixing of different harmonics of the laser field and molecules consisting of asymmetric groups. For the evaluation of the nonlinear current, a numerically efficient formalism is derived which is based upon the Floquet solutions of the driven molecule. This permits a treatment in the non-adiabatic regime and beyond linear response.Comment: 12 pages, 10 figures, REVTeX

CENDARI Archival Research Guide

This Archival Research Guide is dedicated to different forms of women’s participation in the war effort and associationism during the First World War: these two strands include active participation of women in battles; war relief associations, peace movements and women’s employment in the war industry. Contemporary historiography has recognized the crucial role that women played in sustaining the war effort by replacing the labour of men who were engaged on the front. On the other hand, the role of women was crucial in those years for a variety of reasons and occupations: in fact, their commitment to organize in soldier’s relief and peace associations represents an important part of the historiography of the WW1. Moreover, the First World War was the first major belligerent event in which women could wear a military uniform: while this didn’t happen in every country, it was probably a first step toward the inclusion of women in sectors which once were exclusively occupied by men

Numerical evaluation of convex-roof entanglement measures with applications to spin rings

We present two ready-to-use numerical algorithms to evaluate convex-roof extensions of arbitrary pure-state entanglement monotones. Their implementation leaves the user merely with the task of calculating derivatives of the respective pure-state measure. We provide numerical tests of the algorithms and demonstrate their good convergence properties. We further employ them in order to investigate the entanglement in particular few-spins systems at finite temperature. Namely, we consider ferromagnetic Heisenberg exchange-coupled spin-1/2 rings subject to an inhomogeneous in-plane field geometry obeying full rotational symmetry around the axis perpendicular to the ring through its center. We demonstrate that highly entangled states can be obtained in these systems at sufficiently low temperatures and by tuning the strength of a magnetic field configuration to an optimal value which is identified numerically.Comment: 13 pages, 5 figure

Vibrational effects in laser driven molecular wires

The influence of an electron-vibrational coupling on the laser control of electron transport through a molecular wire that is attached to several electronic leads is investigated. These molecular vibrational modes induce an effective electron-electron interaction. In the regime where the wire electrons couple weakly to both the external leads and the vibrational modes, we derive within a Hartree-Fock approximation a nonlinear set of quantum kinetic equations. The quantum kinetic theory is then used to evaluate the laser driven, time-averaged electron current through the wire-leads contacts. This novel formalism is applied to two archetypical situations in the presence of electron-vibrational effects, namely, (i) the generation of a ratchet or pump current in a symmetrical molecule by a harmonic mixing field and (ii) the laser switching of the current through the molecule.Comment: 12 pages, 7 figures, RevTeX4 require