Collective dynamics in optomechanical arrays

Optomechanical systems couple light stored inside an optical cavity to the motion of a mechanical mode. Recent experiments have demonstrated setups, such as photonic crystal structures, that in principle allow one to confine several optical and vibrational modes on a single chip. Here we start to investigate the collective nonlinear dynamics in arrays of coupled optomechanical cells. We show that such "optomechanical arrays" can display synchronization, and that they can be described by an effective Kuramoto-type model.     

Steady-state solutions in a nonlinear pool boiling model

We consider a relatively simple model for pool boiling processes. This model involves only the temperature distribution within the heater and describes the heat exchange with the boiling fluid via a nonlinear boundary condition imposed on the fluid–heater interface. This results in a standard heat equation with a nonlinear Neumann boundary condition on part of the boundary. In this paper, we analyse the qualitative structure of steady-state solutions of this heat equation. It turns out that the model allows both multiple homogeneous and multiple heterogeneous solutions in certain regimes of the parameter space. The latter solutions originate from bifurcations on a certain branch of homogeneous solutions. We present a bifurcation analysis that reveals the multiple-solution structure in this mathematical model. In the numerical analysis a continuation algorithm is combined with the method of separation-of-variables and a Fourier collocation technique. For both the continuous and discrete problem a fundamental symmetry property is derived that implies multiplicity of heterogeneous solutions. Numerical simulations of this model problem predict phenomena that are consistent with laboratory observations for pool boiling processes.     

Measurement of Dipolar Couplings for Methylene and Methyl Sites in Weakly Oriented Macromolecules and Their Use in Structure Determination

A simple and effective method is described for simultaneously measuring dipolar couplings for methine, methylene, and methyl groups in weakly oriented macromolecules. The method is aJ-modulated 3D version of the well-known [¹H-¹³C] CT-HSQC experiment, from which theJand dipolar information are most accurately extracted by using time-domain fitting in the third, constant-time dimension. For CH₂-sites, the method generally yields only the sum of the two individual¹³C-¹H couplings. Structure calculations are carried out by minimizing the deviation between the measured sum, and the sum predicted for each methylene on the basis of the structure. For rapidly spinning methyl groups the dipolar contribution to the splitting of the outer¹³C quartet components can be used directly to constrain the orientation of the C-CH₃bond. Measured sidechain dipolar couplings are in good agreement with an ensemble of NMR structures calculated without use of these couplings.     

Die Hysteresisschleifen auf den Dampfdruck-Konzentrations-Isothermen des Systems Menschenhaar—Wasser und ihr Verschwinden bei sorgfältiger Entfernung der Fremdgase

Zusammenfassung Die Dampfdruck-Konzentrations-Isothermen des Systemes Menschenhaar-Wasser zeigen, nach der Methode van Bemmelen's in Luft untersucht, ausgesprochene Hysteresisschleifen. Doch lie? sich zeigen, da? in Luft nach einigen Wochen definitive Gleichgewichte sicher noch nicht erreicht waren. Durch sorgf?ltige Entfernung der Luft im Hochvakuum kann man die Hysteresis glatt zum verschwinden bringen, in übereinstimmung mit Befunden von Fricke und Lüke am gleichen, sowie von McGavack und Patrick, sowie Gregg an anderen Systemen. Der Notgemeinschaft der Deutschen Wissenschaft danken wir bestens für die Bereitstellung eines Teiles der verwandten Apparate.     

Ein neues Verdickungsmittel der Mineralschmier?le

Ohne Zusammenfassung     

The absorption spectra of anisole-h8, anisole-d3 and anisole-d8. The assignment of fundamental vibrations in the S0 and the S1 states

The REMPI spectra of anisole-h8, anisole-d3 and anisole-d8 have been measured. The assignment of the fundamental vibrations of anisole in the S(1) state is supported by quantum chemical model calculations, the isotopic shifts, the comparison with the frequencies of corresponding vibrations in other monosubstituted benzenes, especially phenol, and the overtones, combinations and progressions observed in the spectrum of anisole-h8. The frequencies of the 42 fundamental vibrations of anisole in the S(1) state are evaluated and compared with the frequencies of the corresponding vibrations in the electronic ground state. Some assignments given earlier in the literature have been revised.     

Atmospheric channel characteristics for quantum communication with continuous polarization variables

We investigate the properties of an atmospheric channel for free space quantum communication with continuous polarization variables. In our prepare-and-measure setup, coherent polarization states are transmitted through an atmospheric quantum channel of 100 m length on the flat roof of our institute’s building. The signal states are measured by homodyne detection with the help of a local oscillator (LO) which propagates in the same spatial mode as the signal, orthogonally polarized to it. Thus the interference of signal and LO is excellent and atmospheric fluctuations are auto-compensated. The LO also acts as a spatial and spectral filter, which allows for unrestrained daylight operation. Important characteristics for our system are atmospheric channel influences that could cause polarization, intensity and position excess noise. Therefore we study these influences in detail. Our results indicate that the channel is suitable for our quantum communication system in most weather conditions.     

Correlation-induced resonances in transport through coupled quantum dots

We investigate the effect of local electron correlations on transport through parallel quantum dots. The linear conductance as a function of gate voltage is strongly affected by the interplay of the interaction U and quantum interference. We find a pair of novel correlation-induced resonances separated by an energy scale that depends exponentially on U. The effect is robust against a small detuning of the dot energy levels and occurs for arbitrary generic tunnel couplings. It should be observable in experiments on the basis of presently existing double-dot setups.