Low-noise 0.8-0.96- and 0.96-1.12-THz superconductor-insulator-superconductor mixers for the Herschel Space Observatory

Heterodyne mixers incorporating Nb SIS junctions and NbTiN-SiO/sub 2/-Al microstrip tuning circuits offer the lowest reported receiver noise temperatures to date in the 0.8-0.96- and 0.96-1.12-THz frequency bands. In particular, improvements in the quality of the NbTiN ground plane of the SIS devices' on-chip microstrip tuning circuits have yielded significant improvements in the sensitivity of the 0.96-1.12-THz mixers relative to previously presented results. Additionally, an optimized RF design incorporating a reduced-height waveguide and suspended stripline RF choke filter offers significantly larger operating bandwidths than were obtained with mixers that incorporated full-height waveguides near 1 THz. Finally, the impact of junction current density and quality on the performance of the 0.8-0.96-THz mixers is discussed and compared with measured mixer sensitivities, as are the relative sensitivities of the 0.8-0.96- and 0.96-1.12-THz mixers

RIFT’ing the Waves: Developing and applying an algorithm to infer properties of gravitational wave sources

With the Advanced LIGO and Virgo ground-based detectors consistently identifying more compact binary coalesces, the need for fast, reliable, and unbiased parameter inference is ever more vital. To that end, we introduce RIFT: an algorithm to perform Rapid parameter inference on gravitational wave sources via Iterative FiTting. To demonstrate RIFT can recover the correct parameters of coalescing compact binary systems, we compare results to the well-tested LALInference parameter inference software. We provide several examples where the unique speed and flexibility of RIFT enables otherwise intractable or awkward parameter inference analyses, such as (a) adopting costly and novel models for outgoing gravitational waves and (b) mixed-model result, each suitable to different parts of the compact binary parameter space and allowing one to use more sophisticated approximations where valid but still producing a complete posterior distribution. We also demonstrate how RIFT can be applied specifically to binary neutron stars, both for parameter inference and direct constraints on the nuclear equation of state. We also show that two precessing models often used in inferring the properties of coalescing black hole binaries disagree substantially when sources have modestly large spins and modest mass ratios. We demonstrate these disagreements using standard figures of merit and the parameters inferred for some detections of binary black holes from O1 and O2. By comparing to numerical relativity, we confirm these disagreements reflect systematic errors. We provide concrete examples to demonstrate that these systematic errors can significantly impact inferences about astrophysically significant binary parameters. In response to LIGO\u27s observation of GW170104, a series of full numerical simulations of binary black holes were performed, each designed to replicate likely realizations of its dynamics and radiation. These simulations have been performed at multiple resolutions and with two independent techniques to solve Einstein\u27s equations. For both the nonprecessing and precessing simulations, we demonstrate the two techniques agree at a precision substantially in excess of statistical uncertainties in current LIGO\u27s observations. Conversely, we demonstrate that these full numerical solutions contain information which is not accurately captured with the approximate phenomenological models. To quantify the impact of these differences on parameter inference for GW170104 specifically, we compare the predictions of our simulations and these approximate models to LIGO\u27s observations of GW170104. Using one of the novel numerical relativity surrogate models, we also investigate the importance of higher order modes when inferring the parameters of coalescing compact binaries. We focus on examples relevant to the current three-detector network of observatories with a detector-frame mass set to 120$M_\odot$ and with signal amplitudes values that are consistent with plausible candidates for the next few observing runs. We show that for such systems the higher mode content will be important for interpreting coalescing binary black holes, reducing systematic bias, and computing properties of the remnant object. Using similar tools, we finally use RIFT to analyze many real data events. This includes the loudest marginal intermediate mass binary black hole trigger from the 1st and 2nd Observing Runs as well as a subset of the events from the first half of the 3rd Observing Run. This includes both 15 binary black hole candidates and 1 binary neutron star candidate

Directly comparing synthetic and real binary black hole coalescence sources with numerical solutions of Einstein’s equation

We compare real and synthetic data directly to complete numerical relativity simulations of binary black holes. Even though our method largely agrees with \cite{PEPaper}, our method goes beyond the existing semi-analytic models that were used. Comparisons with only the quadrupole modes constrain the redshifted mass $M_{z}\in[64 M_{\bigodot}-82 M_{\bigodot}]$, mass ratio $1/q=m_2/m_1\in[0.6,1]$, effective aligned spin $\chi_{eff}\in[-0.3,0.2]$, where $\chi_{eff}=(\mathbf{S}_1/m_1+\mathbf{S_2}/m_2)\cdot\mathbf{\hat{L}}/M$. If we include the octopole modes, we can constrain the mass ratio even better. Even though the spins are correlated, both magnitude and directions are not significantly constrained by the data. We determine that an upper limit for the spin magnitudes up to at least 0.8 but with random orientations. When we interpolate between nonprecessing binaries and reconstruct the posterior distribution, we find it is consistent with the results in \cite{PEPaper}. We found a final total black hole redshifted mass is consistent with $M_{f,z}$ in the range $64.0 M_{\bigodot}-73.5 M_{\bigodot}$, and we found a final dimensionless spin parameter to be constrained to $a_f=0.62-0.73$. To better understand and quantify the impact of potential sources of error, we calculated mismatches between waveforms and the KL Divergence($D_{KL}$) between PDFs derived from fits to our \lnLmarg from our \textit{integrate\_likelihood\_extrinsic} code (called \textit{ILE}). The error due to Monte Carlo integration was found to have a insignificant effect on the PDFs giving $D_{KL}\sim10^{-5}$. The impact of extracting the waveform was also found to be minimal assuming a high enough extraction radius is possible; we found $D_{KL}\sim10^{-2}-10^{-3}$ for PDFs corresponding to sources with different extraction radii. The resolution of a simulation was also found to have an extremely low impact with $D_{KL}\sim10^{-4}$. Our most noticeable source of error was the low frequency cutoffs, which produced $D_{KL}\sim2$ for two PDFs with the biggest differences; however, this effect becomes less significant after marginalizing over all dimensions. We also use different sources for three end-to-end runs: zero spin, equal mass; aligned spin, unequal mass; and precessing, unequal mass. For all three cases, we were able to constrain the same parameters as with the analysis of the real event. For all three cases, the true system parameters lied within our reconstructed posterior. For the aligned case, we ran comparisons using the octopole modes and found, as in the real event analyses, we could further constrain the mass ratio

For wind turbines in complex terrain, the devil is in the detail

Abstract The cost of energy produced by onshore wind turbines is among the lowest available; however, onshore wind turbines are often positioned in a complex terrain, where the wind resources and wind conditions are quite uncertain due to the surrounding topography and/or vegetation. In this study, we use a scale model in a three-dimensional wind-testing chamber to show how minor changes in the terrain can result in significant differences in the flow at turbine height. These differences affect not only the power performance but also the life-time and maintenance costs of wind turbines, and hence, the economy and feasibility of wind turbine projects. We find that the mean wind, wind shear and turbulence level are extremely sensitive to the exact details of the terrain: a small modification of the edge of our scale model, results in a reduction of the estimated annual energy production by at least 50% and an increase in the turbulence level by a factor of five in the worst-case scenario with the most unfavorable wind direction. Wind farm developers should be aware that near escarpments destructive flows can occur and their extent is uncertain thus warranting on-site field measurements.</jats:p

Banning the bulb: institutional evolution and the phased ban of incandescent lighting in Germany

Much academic attention has been directed at analysing energy efficiency investments through the lens of ‘behavioural failure’. These studies have challenged the neoclassical framing of regulation which emphasises the efficiency benefits of price based policy, underpinned by the notion of rational individual self-mastery. The increasing use of a regulatory ban on electric lamps in many countries is one of the most recent and high profile flash points in this dialectic of ‘freedom-versus-the-state’ in the public policy discourse. This paper interrogates this debate through a study of electric lamp diffusion in Germany. It is argued that neoclassical theory and equilibrium analysis is inadequate as a tool for policy analysis as it takes the formation of market institutions, such as existing regulations, for granted. Further still, it may be prone to encourage idealistic debates around such grand narratives which may in practice simply serve those who benefit most from the status quo. Instead we argue for an evolutionary approach which we suggest offers a more pragmatic framing tool which focuses on the formation of market institutions in light of shifting social norms and political goals—in our case, progress towards energy efficiency and environmental goals