Laser-induced quenched phosphorescence detection in capillary electrophoresis.

The feasibility of laser-based excitation for quenched phosphorescence detection in capillary electrophoresis (CE) was explored for the first time by using a small-size, quadrupled Nd-YAG laser emitting 266 nm pulses (duration, 0.4 ns) at a repetition rate of 7.8 kHz. To provide a continuous phosphorescence background, the phosphorophore 1-bromo-4-naphthalene sulfonic acid (BrNS) was added to the separation buffer. Both experiments and theory show that in laser-induced phosphorescence (LIP) - in contrast with lamp-excited phosphorescence - one normally deals with such high triplet-state phosphorophore concentrations that triplet-triplet annihilation is the major deactivation pathway. This results in a lower quantum yield of the analyte-induced bimolecular quenching interaction and, thus, the observed quenching signal. The situation can be improved by using a cylindrical lens for excitation in order to reduce the irradiance. In this case limits of detection (LODs) similar to those obtained using lamp excitation (1x10(-8) M) were achieved, while the width of the detection window was reduced from about 4 mm to 1 mm. Even under exclusion of triplet-triplet annihilation, i.e., under conditions of low irradiance, for our setup the quenching yields in LIP were smaller than in lamp-based phosphorescence detection. This is due to the repetition rate of the laser (7.8 kHz), which is too high in view of the phosphorescence lifetime (ca. 300 micros at low irradiance). Theory shows that this disadvantageous effect will be fully eliminated if the repetition rate is decreased to 1 kHz.     

Constructive influence of noise-flatness in correlation ratchets

The influence of noise-flatness on overdamped motion of Brownian particles in a 1D periodic system with a simple sawtooth potential subjected to both unbiased thermal noise and three-level telegraph noise is considered. The exact formula for the stationary probability flux (current) is presented. The phenomenon of multiple current reversals and some topological properties of the hypersurface of zero current in the parameter space of noises are investigated and illustrated by phase diagrams. The conditions for the existence of four current reversals versus the switching rate of nonequilibrium noise are given. An alternative interpretation of the results in terms of cross-correlation between two dichotomous noises is presented.     

The Physical Tourist¶Vienna: A Random Walk in Science

I provide a guided tour of sites of scientific interest in Vienna with particular reference to the history of physics.     

Switching layer stability in a polymer bilayer by thickness variation

We use optical and scanning force microscopy to explore the possibility of switching the stability of a bilayer of poly(methyl methacrylate) (PMMA) on polystyrene by simply changing the film thickness. We show that for thin PMMA layers on thicker polystyrene films the PMMA layer is unstable to thickness fluctuations. However, polystyrene layers are unstable when they are substantially thinner than the now stable PMMA film. Dewetting morphologies are cataloged as a function of the thickness of individual polymer layers by identifying which layer is unstable by which mechanism, be it spinodal dewetting or heterogeneous thermal nucleation. Our results are in good agreement with a linear stability analysis of the influence of long-range dispersion forces, but also indicate the influence of film preparation and small variations of material properties.     

Optimal finite-time processes in stochastic thermodynamics

For a small system like a colloidal particle or a single biomolecule embedded in a heat bath, the optimal protocol of an external control parameter minimizes the mean work required to drive the system from one given equilibrium state to another in a finite time. In general, this optimal protocol obeys an integro-differential equation. Explicit solutions both for a moving laser trap and a time-dependent strength of such a trap show finite jumps of the optimal protocol to be typical both at the beginning and at the end of the process.     

Akkommodationskoeffizienten von Edelgasen an Pt im Temperaturbereich von 80 K bis 450 K

Zusammenfassung Die Akkommodationskoeffizienten von He, Ne und Ar wurden von 80 K bis 450 K, die von Kr und Xe von 250 K bis 450 K an gasbedeckten und teilweise gereinigten Pt-Oberflächen gemessen. Zur Anwendung kam die stationäre Hitzdrahtmethode bei sehr niedrigen Drucken.Der Fehler in den Bestimmungen an der gasbedeckten Oberfläche wird auf 2–3% geschätzt. Die Messungen an der teilweise gereinigten Oberfläche wurden extrapoliert aus dem zeitlichen Anstieg des Akkommodationskoeffizienten nach einer Aufheizung des Hitzdrahtes auf 900 K. Diese Ergebnisse sind mit einem wesentlich höheren Fehler behaftet.

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Accommodation coefficients of noble gases on Pt-surfaces from 80 K up to 450 K

Accommodation coefficients of He, Ne and Ar have been measured from 80 K up to 450 K, those of Kr and Xe from 250 K up to 450 K on gas covered and partially cleaned Pt-surfaces by the stationary hot wire method at very low pressures.The error of determinations on gas covered surfaces is estimated to be about 2 or 3%. The measurements on partially cleaned surfaces were extrapolated from the increase of the accommodation coefficient with time after a heating of the Pt-wire up to 900 K. In this case the error will be considerably higher.

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Bezeichnungen A Apparaturkonstante - a_i Konstante - C_v Molwärme bei konstantem Volumen - F Oberfläche des Meßdrahtes aus Pt - f_i Druckexpansionsfaktor - g (T) Korrekturfunktion, die die thermomolekulare Druck-differenz in verschieden temperierten Teilen des Versuchsraumes berücksichtigt - I Heizstrom im Pt-Draht - l Länge des Pt-Drahtes - M Molmasse - p Druck - q_D vom Pt-Draht durch Drahtwärmeleitung abgeführte Leistung - q_E dem Pt-Draht zugeführte elektrische Leistung - q_G vom Pt-Draht durch Gaswärmeleitung abgeführte Leistung - q_s vom Pt-Draht durch Strahlung abgeführte Leistung - R allgemeine Gaskonstante - R_i Widerstand des Pt-Drahtes - r Radius des Pt-Drahtes - T Gastemperatur - t₀ Raumtemperatur - T Differenz der Temperatur des Meßdrahtes und der Gas-temperatur - t Zeit - t_A charakteristische Adsorptionszeit - V_i Volumina - z Koordinate in Längsrichtung des Pt-Drahtes - Akkommodationskoeffizient (AK) - ₀ AK der teilweise gereinigten Pt-Oberfläche - _G AK der gasbedeckten Pt-Oberfläche - mittlere freie Weglänge - _Pt Wärmeleitfähigkeit des Pt     

Application of the Tris(acetylacetonato)iron(III)/(II) Redox Couple in p‐Type Dye‐Sensitized Solar Cells

An electrolyte based on the tris(acetylacetonato)iron(III)/(II) redox couple ([Fe(acac)₃]^0/1?) was developed for p‐type dye‐sensitized solar cells (DSSCs). Introduction of a NiO blocking layer on the working electrode and the use of chenodeoxycholic acid in the electrolyte enhanced device performance by improving the photocurrent. Devices containing [Fe(acac)₃]^0/1? and a perylene–thiophene–triphenylamine sensitizer (PMI–6T–TPA) have the highest reported short‐circuit current (J_SC=7.65 mA cm^?2), and energy conversion efficiency (2.51 %) for p‐type DSSCs coupled with a fill factor of 0.51 and an open‐circuit voltage V_OC=645 mV. Measurement of the kinetics of dye regeneration by the redox mediator revealed that the process is diffusion limited as the dye‐regeneration rate constant (1.7×10⁸ M ^?1 s^?1) is very close to the maximum theoretical rate constant of 3.3×10⁸ M ^?1 s^?1. Consequently, a very high dye‐regeneration yield (>99 %) could be calculated for these devices.     

Supramolecularly engineered phospholipids constructed by nucleobase molecular recognition: upgraded generation of phospholipids for drug delivery

Despite of great advances of phospholipids and liposomes in clinical therapy, very limited success has been achieved in the preparation of smart phospholipids and controlled-release liposomes for in vivo drug delivery and clinical trials. Here we report a supramolecular approach to synthesize novel supramolecularly engineered phospholipids based on complementary hydrogen bonding of nucleosides, which greatly reduces the need of tedious chemical synthesis, including reducing the strict requirements for multistep chemical reactions, and the purification of the intermediates and the amount of waste generated relative more traditional approaches. These upgraded phospholipids self-assemble into liposome-like bilayer structures in aqueous solution, exhibiting fast stimuli-responsive ability due to the hydrogen bonding connection. In vitro and in vivo evaluations show the resulted supramolecular liposomes from nucleoside phospholipids could effectively transport drug into tumor tissue, rapidly enter tumor cells, and controllably release their payload in response to an intracellular acidic environment, thus resulting in a much higher antitumor activity than conventional liposomes. The present supramolecularly engineered phospholipids represent an important evolution in comparison to conventional covalent-bonded phospholipid systems.