Asymmetric quantum shot noise in quantum dots

We analyze the frequency-dependent noise of a current through a quantum dot which is coupled to Fermi leads and which is in the Coulomb blockade regime. We show that the asymmetric shot noise, as a function of detection frequency, shows steps and becomes super-Poissonian. This provides experimental access to the quantum fluctuations of the current. We present an exact calculation of the noise for a single dot level and a perturbative evaluation of the noise in Born approximation (sequential tunneling regime but without Markov approximation) for the general case of many levels with charging interaction.     

Photon counting with a loop detector

We propose a design for a photon-counting detector that is capable of resolving multiphoton events. The basic element of the setup is a fiber loop, which traps the input field with the help of a fast electro-optic switch. A single weakly coupled avalanche photodiode is used to detect small portions of the signal field extracted from the loop. We analyze the response of the loop detector to an arbitrary input field and discuss both the reconstruction of the photon-number distribution of an unknown field from the count statistics measured in the setup and the application of the detector in conditional-state preparation.     

Coupled LC-GC: The capacity of silica gel (HP)LC columns for retaining fat

Many applications of coupled LC-GC in food analysis require that LC separates large quantities of triglycerides from the components of interest. The capacities of silica gels to retain triglycerides have been determined for n-hexane as mobile phase as well as some eluent mixtures. Conclusions are drawn for practical applications.     

On-line solvent evaporator for coupled LC systems

The mobile phase of a fraction eluted from a first LC column is removed by an on-line evaporator in order to reconcentrate the solute material or to exchange the eluent before performing a subsequent LC separation. Evaporation essentially occurs by concurrent evaporation, i.e. the solvent evaporates at a rate equal to the flow rate of the incoming eluent, and is driven by the overflow principle, i.e. vapors leave the tube as a result of the expansion resulting from evaporation. The liquid is introduced into a small tube (e.g., 4 cm × 1.3 mm i.d.) which is packed, e.g., with a coarse silica gel. The outlet of the evaporator is connected to vacuum in order to enable evaporation at reduced temperature and to increase retention of the volatile components. With normal phase eluents, evaporation rates may approach 1 ml/min; n-dodecane was the most volatile n-alkane fully retained by the evaporator.     

Untersuchung der Iouenassoziation im System Natriummetavanadat-Natriumchlorid-Wasser mit der Ultrazentrifuge

Zusammenfassung Am Beispiel des Systems Na₄(VO₃)₄-NaCl-H₂O wird untersucht, in welcher Weise Ultrazentrifugenmessungen im Sedimentationsgleichgewicht durchgeführt werden müssen, um die molare Masse und die Ladungszahl von Polymerelektrolyten in ternären Systemen unter der Bedingung von nicht vernachlässigbaren Wechselwirkungen zwischen Polymerund Fremdelektrolyt zu bestimmen. Es erweist sich, daß die experimentellen scheinbaren molaren Massen nicht nur auf die Polymerkonzentration Null extrapoliert werden müssen, sondern auch auf die Fremdelektrolytkonzentration Null. Es gelingt, die Ableitung (alnyPX_z/amBx)mPX_z an der StellemPX_z = 0 mol kg_-1 mit einer scheinbaren mittleren Ladungszahlz _app des Polymeranions zu korrelieren. Zwischen dieser und der stöchiometrischen Ladungszahlz des Polymeranions besteht die Beziehungz _app = Z =az, so daß die Dissoziationskonstante des Polymerelektrolyten für die summarische Dissoziation berechnet werden kann. Die aus dieser Korrelation folgenden Abhängigkeiten der scheinbaren mittleren Ladungszahlen und der Ableitung (alnypx _z /amBX)Mpx _z = 0 von der Konzentration des Fremdelektrolyten werden experimentell bestätigt.

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Summary The system Na₄(VO₃)₄-NaCl-H₂0 is taken as an example for ultracentrifugal measurements at sedimentation equilibrium to determine the molar mass and the valency of a polymer electrolyte in a ternary system when interactions exist between the polymer and the supporting electrolyte. The experimental apparent molar mass is obtained by extrapolation to zero value of concentration of both the polymeric and supporting electrolyte. It is possible to correlate the quantity (alnyPX _z /amBX)^mPX_z at the point ^m PX _z = 0 mole kg^-1 with the apparent valency _zapp of the polymeric anion.z _app is related to the stoichiometric valency by the equationz _app = _z =a.Z. Thus the dissociation constant can be calculated for complete dissociation of the polymer electrolyte. The dependence of _zapp and (aln _y PX _z /a ^m _BX ) ^m PX _z = 0 on concentration of the supporting electrolyte called for in the correlation is verified experimentally.

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Mit 4 Abbildungen und 4 Tabellen     

A Facile Conversion of Tertiary Amines into [2-(dialkylamino)vinyl]triphenylphosphonium salts

Halogenation of Et₃N, (i-Pr)₂EtN, and N-ethylmorpholine or of enamines with dichlorotriphenylphosphorane gives in up to 75% yield the corresponding [2-(dialkylamino)vinyl]triphenylphosphonium chlorides, which can be readily converted into the corresponding stable crystalline tetraphenylborates (Schemes 2 and 3).