Bowl-Shaped Symmetric and Non-symmetric Bis-functionalized Indacenopicenes.

Regioselective arrangement of two groups of orthogonal reactivity in bowl-shaped as-indaceno[3,2,1,8,7,6-pqrstuv]picene (Idpc) was key for the synthesis of hetero-bis-functionalized Idpc derivatives. Halogen and methyl groups were positioned at specific positions in the rim area of Idpc at an early stage during the synthesis by functionalization of suitable precursors. Regioselective functionalization of the bowl's rim was then finally achieved either via consecutive Cu(I)-catalyzed azide-alkyne coupling (CuAAC) and C-C cross-coupling reactions or by C-C cross-coupling alone, giving access to either symmetric or non-symmetric bis-functionalized Idpc derivatives. The self-aggregation behavior of 9c in solution was investigated by recording a series of concentration-dependent NMR spectra. The aggregation constant of 9c was determined by a nonlinear least-squares treatment of the 1H NMR shift data to be 2.9 ± 0.2 M-1, and the formation of dimers was found to be the prevailing process.

Controlled emission time statistics of a dynamic single-electron transistor.

Quantum technologies involving qubit measurements based on electronic interferometers rely critically on accurate single-particle emission. However, achieving precisely timed operations requires exquisite control of the single-particle sources in the time domain. Here, we demonstrate accurate control of the emission time statistics of a dynamic single-electron transistor by measuring the waiting times between emitted electrons. By ramping up the modulation frequency, we controllably drive the system through a crossover from adiabatic to nonadiabatic dynamics, which we visualize by measuring the temporal fluctuations at the single-electron level and explain using detailed theory. Our work paves the way for future technologies based on the ability to control, transmit, and detect single quanta of charge or heat in the form of electrons, photons, or phonons.

Spectral Properties of Stochastic Resonance in Quantum Transport.

We investigate theoretically and experimentally stochastic resonance in a quantum dot coupled to electron source and drain via time-dependent tunnel barriers. A central finding is a transition visible in the current noise spectrum as a bifurcation of a dip originally at zero frequency. The transition occurs close to the stochastic resonance working point and relates to quantized pumping. For the evaluation of power spectra from measured waiting times, we generalize a result from renewal theory to the ac-driven case. Moreover, we develop a master equation method to obtain phase-averaged current noise spectra for driven quantum transport.

Geodesic-Planar Conjugates: Substituted Buckybowls-Synthesis, Photoluminescence and Electrochemistry.

C-C cross coupling products of bowl-shaped as-indaceno[3,2,1,8,7,6-pqrstuv]picene (Idpc) and different planar arenes and ethynyl-arenes were synthesized. Photoluminescence as well as electrochemical properties of all products were investigated and complemented by time-dependent quantum chemical calculations. UV/Vis spectroelectrochemistry investigations of the directly linked (Idpc)2 indicated the absence of any intramolecular charge-transfer transition of intermittently formed (Idpc)2 .- . All coupling products showed fluorescence. Ferrocene-1-yl-Idpc was structurally characterized by X-ray diffraction and is a rare example of a ferrocene-containing buckybowl exhibiting luminescence.

Strong suppression of shot noise in a feedback-controlled single-electron transistor.

Feedback control of quantum mechanical systems is rapidly attracting attention not only due to fundamental questions about quantum measurements, but also because of its novel applications in many fields in physics. Quantum control has been studied intensively in quantum optics but progress has recently been made in the control of solid-state qubits as well. In quantum transport only a few active and passive feedback experiments have been realized on the level of single electrons, although theoretical proposals exist. Here we demonstrate the suppression of shot noise in a single-electron transistor using an exclusively electronic closed-loop feedback to monitor and adjust the counting statistics. With increasing feedback response we observe a stronger suppression and faster freezing of charge current fluctuations. Our technique is analogous to the generation of squeezed light with in-loop photodetection as used in quantum optics. Sub-Poisson single-electron sources will pave the way for high-precision measurements in quantum transport similar to optical or optomechanical equivalents.

Fractional photothermolysis for the treatment of facial wrinkles - searching for optimal treatment parameters in a randomized study in the split-face design.

BACKGROUND: Fractionated photothermolysis (FP) is used for the treatment of facial wrinkles. OBJECTIVES: Investigation of effects of different FP treatment parameters in the treatment of facial wrinkles. PATIENTS AND METHODS: In a randomized split-face controlled study 11 patients received 3 FP sessions in 4-week intervals. Keeping the total energy input for each facial side constant, one side was treated with 6 mJ/MTZ with relatively high MTZ density (up to 2,625 MTZ/cm(2) ) and the contralateral side with 70 mJ/MTZ with lower MTZ density (up to 230 MTZ/cm(2) ). Follow-up (FU) visits were performed 1, 3, and 6 months after the last treatment. The cosmetic evaluation was done by the patient self-assessments and by assessment of standardized photographs by 3 independent, blinded investigators. Post-treatment side effects were documented daily in a patient diary up to 7 days after the procedure. RESULTS: After 6 months, the patient self-assessments indicated significant improvements (p < 0.005) in wrinkle severity from 5.2 ± 1.5 to 3.8 ± 1.3 and 3.7 ± 1.3 for 6 and 70 mJ/MTZ, respectively, but without significant difference between the energy levels. In contrast, the photographic evaluation by the blinded investigators showed that wrinkle severity was rated significantly better at the sites treated with 70 mJ/MTZ than at the sites treated with 6 mJ/MTZ (p < 0.01). Treatment with 70 mJ/MTZ was significantly more painful than treatment with 6 mJ/MTZ. The typical local reactions to FP, erythema and edema, were also significantly more intense after 70 mJ/MTZ and lasted longer. CONCLUSIONS: FP with higher energy per MTZ at constant total energy input is more effective in the treatment of facial wrinkles than lower energy. The gain in effectiveness is, nonetheless, accompanied by an increase in adverse reactions. The treating physician may use this information to adjust treatment to the preferences of the individual patient.

Neurite branch retraction is caused by a threshold-dependent mechanical impact.

Recent results indicate that, in addition to chemical cues, mechanical stimuli may also impact neuronal growth. For instance, unlike most other cell types, neurons prefer soft substrates. However, the mechanisms responsible for the neuronal affinity for soft substrates have not yet been identified. In this study, we show that, in vitro, neurons continuously probe their mechanical environment. Growth cones visibly deform substrates with a compliance commensurate with their own. To understand the sensing of stiff substrates by growth cones, we investigated their precise temporal response to well-defined mechanical stress. When the applied stress exceeded a threshold of 274 +/- 41 pN/microm(2), neurons retracted and re-extended their processes, thereby enabling exploration of alternative directions. A calcium influx through stretch-activated ion channels and the detachment of adhesion sites were prerequisites for this retraction. Our data illustrate how growing neurons may detect and avoid stiff substrates--as a mechanism involved in axonal branch pruning--and provide what we believe is novel support of the idea that mechanics may act as guidance cue for neuronal growth.

DNA microelectrophoresis using double focus fluorescence correlation spectroscopy.

Double focus fluorescence correlation spectroscopy (dfFCS) was used to determine electrophoretic mobilities of short double-stranded DNA (dsDNA)-fragments (75 base pairs (bp) -1019 bp) in microfluidic channels. The electrokinetic flow profile across a microchannel was measured with 1 microm spatial resolution and separated in electroosmotic and electrophoretic contributions. Experiments show that the free solution mobility is independent of DNA length. The diffusion constant is additionally determined by FCS and follows a length dependent rod-diffusion model. We interpret the electrophoretic mobilities using a modified Nernst Einstein relation, which additionally takes Manning condensation and counterion induced hydrodynamic retardation forces into account. In 3% w/v polyethylene oxide (PEO)-network (M(r) 3 .10(5) Dalton) the electrophoretic velocities become size-dependent with a power-law exponent be-tween 0.28 and 0.31. Mixtures of dsDNA-fragments exhibit distinguishable peaks in the dfFCS cross-correlation function. The potential of dfFCS for realtime micro-analysis in terms of speed and spatial resolution is discussed.