Relaxation time of a chiral quantum R-L circuit

We report on the GHz complex admittance of a chiral one-dimensional ballistic conductor formed by edge states in the quantum Hall regime. The circuit consists of a wide Hall bar (the inductor L) in series with a tunable resistor (R) formed by a quantum point contact. Electron interactions between edges are screened by a pair of side gates. Conductance steps are observed on both real and imaginary parts of the admittance. Remarkably, the phase of the admittance is transmission independent. This shows that the relaxation time of a chiral R -L circuit is resistance independent. A current and charge conserving scattering theory is presented that accounts for this observation with a relaxation time given by the electronic transit time in the circuit.     

Drug development: longer-lived proteins

Protein therapeutics represent a powerful class of clinically approved drugs for the prevention and treatment of various diseases. Once administered, the biological fate of protein therapeutics is governed by the body's various complex biochemical and biophysical clearance mechanisms, several of which may decrease the drug's circulation time and efficiency. In this tutorial review, we introduce the concepts of physiological protein clearance from the body, and describe several chemical modification and protein engineering approaches used to improve the life span of administered protein therapeutics.     

Subradiant split Cooper pairs

We suggest a way to characterize the coherence of the split Cooper pairs emitted by a double-quantum-dot based Cooper pair splitter (CPS), by studying the radiative response of such a CPS inside a microwave cavity. The coherence of the split pairs manifests in a strongly nonmonotonic variation of the emitted radiation as a function of the parameters controlling the coupling of the CPS to the cavity. The idea to probe the coherence of the electronic states using the tools of cavity quantum electrodynamics could be generalized to many other nanoscale circuits.     

Morphology, ionic diffusion and applicability of novel polymer gel electrolytes with LiI/I2

Novel polymer gel electrolytes have been prepared by incorporating LiI-I(2) solutions into a polyethylene oxide matrix supported by a TiO(2) filler. The gel electrolytes, based on either acetonitrile or propylene carbonate solvents are compared with liquid standard ones and are examined by (7)Li solid state nuclear magnetic resonance relaxometry and diffusion measurements. In parallel, the triiodide apparent diffusion coefficient has been determined by linear sweep voltammetry. The results are correlated with atomic force microscopic images of the electrolytes and give insight of the dynamic properties of the ions in the constrained polymer medium. Furthermore, the dissociation of the ions is estimated by relating the ionic conductivity to the ionic diffusion. As a prime application, the polymer gel electrolytes were incorporated in dye sensitized solar cells and the measured energy conversion efficiencies were successfully correlated with their morphological, diffusive and conducting properties.     

Chromium speciation by TXRF analysis

Chromium (Cr) is an element which usually occurs in two different forms, Cr(III) and Cr(VI). As Cr(VI) is much more toxic than Cr(III), no complicated analytical methods with low detection limit are needed for chromium speciation. In the present work, a new method is presented for chromium speciation at low concentrations by selective membrane collection and total Reflection x‐ray fluorescence (TXRF) analysis. Various membranes were produced on the surface of quartz reflectors containing different complexing ligands in Nafion and poly vinyl chloride (PVC) matrices. The membranes were produced on the surface of quartz glass, while the reflectors were immersed in water solutions with low concentrations of chromium salts for many hours. When the equilibration stage was achieved, the reflectors were analyzed by TXRF. Completely selective membranes for Cr(III) and Cr(VI) were prepared with minimum detection limits lower than 0.6 ng.ml^?1 (ppb) in drinking water. Copyright © 2009 John Wiley & Sons, Ltd.     

Efficient solar energy conversion using TiO2 nanotubes produced by rapid breakdown anodization – a comparison

We report on dye‐sensitization of different TiO₂ nanotube layers, their photoelectrochemical response and their efficiency for solar energy conversion. The tubes compared in this study were either grown by controlled Ti anodization in fluoride containing electrolytes or by rapid breakdown anodization (RBA) of Ti in fluoride free electrolytes. After converting the different tube layers to anatase and sensitizing with Ru‐dye (N719), clearly layers consisting of RBA‐NTs show a significantly higher photoresponse and conversion efficiencies than tubes formed under self‐ordering conditions. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reentrant Structural and Optical Properties and Large Positive Thermal Expansion in Perovskite Formamidinium Lead Iodide

The structure of the hybrid perovskite HC(NH₂)₂PbI₃ (formamidinium lead iodide) reflects competing interactions associated with molecular motion, hydrogen bonding tendencies, thermally activated soft octahedral rotations, and the propensity for the Pb²⁺ lone pair to express its stereochemistry. High‐resolution synchrotron X‐ray powder diffraction reveals a continuous transition from the cubic α‐phase (Pm m, #221) to a tetragonal β‐phase (P4/mbm, #127) at around 285 K, followed by a first‐order transition to a tetragonal γ‐phase (retaining P4/mbm, #127) at 140 K. An unusual reentrant pseudosymmetry in the β‐to‐γ phase transition is seen that is also reflected in the photoluminescence. Around room temperature, the coefficient of volumetric thermal expansion is among the largest for any extended crystalline solid.     

Shot noise in Fabry-Perot interferometers based on carbon nanotubes

We report on shot noise measurements in carbon nanotube based Fabry-Perot electronic interferometers. As a consequence of quantum interference, the noise power spectral density oscillates as a function of the voltage applied to the gate electrode. The quantum shot noise theory accounts for the data quantitatively and allows us to determine directly the transmissions of the two channels characterizing the nanotube. In the weak backscattering regime, the dependence of the noise on the backscattering current is found weaker than expected, pointing either to electron-electron interactions or to weak decoherence.     

Spin quantum bit with ferromagnetic contacts for circuit QED

We theoretically propose a scheme for a spin quantum bit based on a double quantum dot contacted to ferromagnetic elements. Interface exchange effects enable an all electric manipulation of the spin and a switchable strong coupling to a superconducting coplanar waveguide cavity. Our setup does not rely on any specific band structure and can in principle be realized with many different types of nanoconductors. This allows us to envision on-chip single spin manipulation and readout using cavity QED techniques.