Robert J. Brecha

Renewable Energy in the Context of Sustainable Development

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Quantum interference and collapse of the wavefunction in cavity QED

Abstract We calculate the delayed coincidence rate for photons transmitted by a driven cavity containing N two-level atoms. Under cavity QED conditions (strong dipole coupling) the coincidence rate shows a nonclassical dependence on delay. This novel behavior illustrates the interference of probability amplitudes and the collapse of the wavefunction in quantum mechanics.

Analyzing Major Challenges of Wind and Solar Variability in Power Systems

Ambitious policy targets together with current and projected high growth rates indicate that future power systems will likely show substantially increased generation from renewable energy sources. A large share will come from the variable renewable energy (VRE) sources wind and solar photovoltaics (PV); however, integrating wind and solar causes challenges for existing power systems. In this paper we analyze three major integration challenges related to the structural matching of demand with the supply of wind and solar power: low capacity credit, reduced utilization of dispatchable plants, and over-produced generation. Based on residual load duration curves we define corresponding challenge variables and estimate their dependence on region (US Indiana and Germany), penetration and mix of wind and solar generation. Results show that the impacts of increasing wind and solar shares can become substantial, and increase with penetration, independently of mix and region. Solar PV at low penetrations is much easier to integrate in many areas of the US than in Germany; however, some impacts (e.g. over-production) increase significantly with higher shares. For wind power, the impacts increase rather moderately and are fairly similar in US Indiana and Germany.

Economics of nuclear power and climate change mitigation policies.

The events of March 2011 at the nuclear power complex in Fukushima, Japan, raised questions about the safe operation of nuclear power plants, with early retirement of existing nuclear power plants being debated in the policy arena and considered by regulators. Also, the future of building new nuclear power plants is highly uncertain. Should nuclear power policies become more restrictive, one potential option for climate change mitigation will be less available. However, a systematic analysis of nuclear power policies, including early retirement, has been missing in the climate change mitigation literature. We apply an energy economy model framework to derive scenarios and analyze the interactions and tradeoffs between these two policy fields. Our results indicate that early retirement of nuclear power plants leads to discounted cumulative global GDP losses of 0.07% by 2020. If, in addition, new nuclear investments are excluded, total losses will double. The effect of climate policies imposed by an intertemporal carbon budget on incremental costs of policies restricting nuclear power use is small. However, climate policies have much larger impacts than policies restricting the use of nuclear power. The carbon budget leads to cumulative discounted near term reductions of global GDP of 0.64% until 2020. Intertemporal flexibility of the carbon budget approach enables higher near-term emissions as a result of increased power generation from natural gas to fill the emerging gap in electricity supply, while still remaining within the overall carbon budget. Demand reductions and efficiency improvements are the second major response strategy.

Cavity induced transparency

We consider a two-level atom inside a cavity. We find that the absorption spectrum of the atom may exhibit a hole at line center for a weak probe. This hole appears when the cavity linewidth is small compared to the atom-field coupling strength, which is itself smaller than the atoms free space linewidth. In the weak-field limit, this system is analogous to a three-level atom, where similar absorption holes at line center occur due to electromagnetically induced transparency (EIT). In EIT, a strong field is required to strongly mix the upper two levels, whereas in the system we consider, it is the atom-field coupling strength that plays this role. An alternate explanation in terms of interference between the cavity field and atomic polarization is given. We also examine the driven cavity case.

Hydroxyl (OH) distributions and temperature profiles in a premixed propane flame obtained by laser deflection techniques

OH-concentration distributions and temperature profiles have been measured on a premixed propane–air flame by laser deflection techniques. Photothermal deflection spectroscopy has been utilized for the measurement of the OH radical. Both a low-spatial-resolution (near collinear) and high-spatial-resolution (crossed-beam) scheme were used to profile the premixed flame. An optoacoustic deflection technique was utilized for thermometry. Both average-temperature profiles and probability distribution functions were determined by this technique. A comparison with data obtained by the CARS technique demonstrated that no significant flame perturbation was occurring.

Dipolar oscillations in a quantum degenerate Fermi–Bose atomic mixture

We study the dynamics of coupled dipolar oscillations in a Fermi–Bose mixture of 40K and 87Rb atoms. This low-energy collective mode is strongly affected by the interspecies interactions. Measurements are performed in the classical and quantum degenerate regimes and reveal the crucial role of the statistical properties of the mixture. At the onset of quantum degeneracy, we investigate the role of Pauli blocking and superfluidity for K and Rb atoms, respectively, resulting in a change in the collisional interactions.

Analysis of imperfect polarizer effects in magnetic rotation spectroscopy

Small amounts of ellipticity in the nominally linearly polarized light used in magnetic rotation spectroscopy play an important role in determining the character of the signals developed in these experiments. For example, ellipticity introduced by stress-induced birefringence can easily influence such signals more than does a nonzero polarizer extinction ratio. In addition, for nearly-crossed polarizers, an initial ellipticity allows one to probe magnetic circular dichroism instead of the more commonly investigated magnetic circular birefringence. A general expression for the magnetic rotation spectroscopy signal is derived and compared to experimental results. An expression for the detection sensitivity is developed by taking shot noise and rms laser power uctuations to be the dominant noise sources.

Cooling Atoms in an Optical Trap by Selective Parametric Excitation

We demonstrate the possibility of energy-selective removal of cold atoms from a tight optical trap by means of parametric excitation of the trap vibrational modes. Taking advantage of the anharmonicity of the trap potential, we either selectively remove the most energetic trapped atoms or excite those at the bottom of the trap by tuning the parametric modulation frequency. This process, which had been previously identified as a possible source of heating, also appears to be a robust way for forcing evaporative cooling in anharmonic traps.

Will economic growth and fossil fuel scarcity help or hinder climate stabilization? Overview of the RoSE multi-model study

We investigate the extent to which future energy transformation pathways meeting ambitious climate change mitigation targets depend on assumptions about economic growth and fossil fuel availability. The analysis synthesizes results from the RoSE multi-model study aiming to identify robust and sensitive features of mitigation pathways under these inherently uncertain drivers of energy and emissions developments. Based on an integrated assessment model comparison exercise, we show that economic growth and fossil resource assumptions substantially affect baseline developments, but in no case they lead to the significant greenhouse gas emission reduction that would be needed to achieve long-term climate targets without dedicated climate policy. The influence of economic growth and fossil resource assumptions on climate mitigation pathways is relatively small due to overriding requirements imposed by long-term climate targets. While baseline assumptions can have substantial effects on mitigation costs and carbon prices, we find that the effects of model differences and the stringency of the climate target are larger compared to that of baseline assumptions. We conclude that inherent uncertainties about socio-economic determinants like economic growth and fossil resource availability can be effectively dealt with in the assessment of mitigation pathways.