Product Quality, Product Price, and Share Dynamics in the German Compact Car Market

The present paper examines one of the central elements of evolutionary thinking - competition formalized by the replicator dynamics mechanism. Using data on product characteristics of automobiles sold on the German domestic market over the period 2001-2006, we construct a competitiveness or fitness variable for each car model applying non-parametric efficiency measurement techniques. The basic question we intend to answer is whether cars providing a higher quality-price ratio for consumers tend to increase their market share compared to variants with lower quality-price ratios. The relationship between a car models' fitness and its market performance is empirically tested in a regression framework. The results show that the principle of `growth of the fitter' is working as suggested by evolutionary theory. In particular, we find that car models with considerably lower fitness than the market average lose, whereas models with above-average fitness gain additional market shares.Replicator Dynamics, Product Characteristics, Data Envelopment Analysis

Deterministic enhancement of coherent photon generation from a nitrogen-vacancy center in ultrapure diamond

The nitrogen-vacancy (NV) center in diamond has an optically addressable, highly coherent spin. However, an NV center even in high quality single-crystalline material is a very poor source of single photons: extraction out of the high-index diamond is inefficient, the emission of coherent photons represents just a few per cent of the total emission, and the decay time is large. In principle, all three problems can be addressed with a resonant microcavity. In practice, it has proved difficult to implement this concept: photonic engineering hinges on nano-fabrication yet it is notoriously difficult to process diamond without degrading the NV centers. We present here a microcavity scheme which uses minimally processed diamond, thereby preserving the high quality of the starting material, and a tunable microcavity platform. We demonstrate a clear change in the lifetime for multiple individual NV centers on tuning both the cavity frequency and anti-node position, a Purcell effect. The overall Purcell factor $F_{\rm P}=2.0$ translates to a Purcell factor for the zero phonon line (ZPL) of $F_{\rm P}^{\rm ZPL}\sim30$ and an increase in the ZPL emission probability from $\sim 3 \%$ to $\sim 46 \%$. By making a step-change in the NV's optical properties in a deterministic way, these results pave the way for much enhanced spin-photon and spin-spin entanglement rates.Comment: 6 pages, 4 figure

Near-unity coupling efficiency of a quantum emitter to a photonic-crystal waveguide

A quantum emitter efficiently coupled to a nanophotonic waveguide constitutes a promising system for the realization of single-photon transistors, quantum-logic gates based on giant single-photon nonlinearities, and high bit-rate deterministic single-photon sources. The key figure of merit for such devices is the $\beta$-factor, which is the probability for an emitted single photon to be channeled into a desired waveguide mode. We report on the experimental achievement of $\beta = 98.43 \pm 0.04\%$ for a quantum dot coupled to a photonic-crystal waveguide, corresponding to a single-emitter cooperativity of $\eta = 62.7 \pm 1.5$. This constitutes a nearly ideal photon-matter interface where the quantum dot acts effectively as a 1D "artificial" atom, since it interacts almost exclusively with just a single propagating optical mode. The $\beta$-factor is found to be remarkably robust to variations in position and emission wavelength of the quantum dots. Our work demonstrates the extraordinary potential of photonic-crystal waveguides for highly efficient single-photon generation and on-chip photon-photon interaction

Using planar laser-induced fluorescence to study the phase transformations of two-component liquid and suspension droplets

Using the planar laser-induced fluorescence (PLIF), we performed experiments to determine evaporation dynamics of homogeneous and heterogeneous droplets of liquids, conditions of their boiling, and explosive breakup. For the 1–2 mm water droplets, the distribution of highly non-homogeneous and non-steady temperature field was detected by highspeed cross-correlation video recording and the Tema Automotive software.We identified highly nonlinear dependences of evaporation rate on heating temperature and time as well as water droplet size. For the two-component liquids and water-based suspensions of graphite, we revealed unsteady temperature fields and established mechanisms and regimes of the explosive breakup of the heterogeneous droplets when heated. The regimes differ in the number and dimensions of the emerging gas–liquid fragments as well as the durations of the main stages. The three regimes of warming-up and evaporation of the heterogeneous droplets have been obtained. The explosive breakup of droplets enables provision for the secondary atomization of the liquid with the emergence of an aerosol cloud. The surface area of the liquid increases several-fold. The temperature variations at the water/solid or water/flammable component interfaces were determined corresponding to each boiling and breakup regime. Using the PLIF, we studied reasons and mechanism of the explosive breakup of water droplets with single large carbonaceous inclusions when heated

Excitons in InGaAs Quantum Dots without Electron Wetting Layer States

The Stranski-Krastanov (SK) growth-mode facilitates the self-assembly of quantum dots (QDs) using lattice-mismatched semiconductors, for instance InAs and GaAs. SK QDs are defect-free and can be embedded in heterostructures and nano-engineered devices. InAs QDs are excellent photon emitters: QD-excitons, electron-hole bound pairs, are exploited as emitters of high quality single photons for quantum communication. One significant drawback of the SK-mode is the wetting layer (WL). The WL results in a continuum rather close in energy to the QD-confined-states. The WL-states lead to unwanted scattering and dephasing processes of QD-excitons. Here, we report that a slight modification to the SK-growth-protocol of InAs on GaAs -- we add a monolayer of AlAs following InAs QD formation -- results in a radical change to the QD-excitons. Extensive characterisation demonstrates that this additional layer eliminates the WL-continuum for electrons enabling the creation of highly charged excitons where up to six electrons occupy the same QD. Single QDs grown with this protocol exhibit optical linewidths matching those of the very best SK QDs making them an attractive alternative to standard InGaAs QDs

Single-photon nonlinear optics with a quantum dot in a waveguide

Strong nonlinear interactions between photons enable logic operations for both classical and quantum-information technology. Unfortunately, nonlinear interactions are usually feeble and therefore all-optical logic gates tend to be inefficient. A quantum emitter deterministically coupled to a propagating mode fundamentally changes the situation, since each photon inevitably interacts with the emitter, and highly correlated many-photon states may be created . Here we show that a single quantum dot in a photonic-crystal waveguide can be utilized as a giant nonlinearity sensitive at the single-photon level. The nonlinear response is revealed from the intensity and quantum statistics of the scattered photons, and contains contributions from an entangled photon-photon bound state. The quantum nonlinearity will find immediate applications for deterministic Bell-state measurements and single-photon transistors and paves the way to scalable waveguide-based photonic quantum-computing architectures

Rational climate policy - economic demands and political obstacles

In der klimapolitischen Debatte stehen meist einzelne Instrumente und Maßnahmen im Vordergrund, wohingegen die Frage der ökonomischen Rationalität der Klimapolitik als solcher häufig vernachlässigt wird. Eine Klimapolitik wäre dann ökonomisch rational, wenn politisch vorgegebene Klimaziele mit geringstmöglichen Kosten realisiert werden würden. Notwendig hierfür ist eine umfassende und einheitliche Bepreisung der Treibhausgasemissionen. Dieser rationalen Klimapolitik wird die aktuelle deutsche und europäische Politik gegenübergestellt, die sich als ineffektiv und ineffizient erweist. Ursächlich hierfür sind die Anreize, denen die politischen Akteure unterliegen und die zu einem Widerspruch zwischen ökonomischer Rationalität und politischer Opportunität führen.The debate about climate policy is mainly concerned with particular measures and instruments. Only rarely is the economic rationality of climate policy as such discussed. Climate policy would be economically rational, if climate objectives, which are to be determined politically, are realized with minimum costs. To this end, a comprehensive and uniform price on the emission of greenhouse gases has to be established. The actual climate policy, in Germany and in Europe, is far from being economically rational: It is both ineffective and inefficient. This is due to political incentives which make inefficient policies politically more attractive than efficient ones