Frequency-Dependent Responses in 3rd Generation Gravitational-Wave Detectors

Interferometric gravitational wave detectors are dynamic instruments. Changing gravitational-wave strains influence the trajectories of null geodesics and therefore modify the interferometric response. These effects will be important when the associated frequencies are comparable to the round-trip light travel time down the detector arms. The arms of advanced detectors currently in operation are short enough that the strain can be approximated as static, but planned 3$^\mathrm{rd}$ generation detectors, with arms an order of magnitude longer, will need to account for these effects. We investigate the impact of neglecting the frequency-dependent detector response for compact binary coalescences and show that it can introduce large systematic biases in localization, larger than the statistical uncertainty for 1.4-1.4$M_\odot$ neutron star coalescences at $z\lesssim1.7$. Analysis of $3^\mathrm{rd}$ generation detectors therefore must account for these effects.Comment: 6 pages, 5 figure

Resonant Dampers for Parametric Instabilities in Gravitational Wave Detectors

Advanced gravitational wave interferometric detectors will operate at their design sensitivity with nearly 1MW of laser power stored in the arm cavities. Such large power may lead to the uncontrolled growth of acoustic modes in the test masses due to the transfer of optical energy to the mechanical modes of the arm cavity mirrors. These parametric instabilities have the potential of significantly compromising the detector performance and control. Here we present the design of "acoustic mode dampers" that use the piezoelectric effect to reduce the coupling of optical to mechanical energy. Experimental measurements carried on an Advanced LIGO-like test mass shown a 10-fold reduction in the amplitude of several mechanical modes, thus suggesting that this technique can greatly mitigate the impact of parametric instabilities in advanced detectors

'Snapshots of repression and resistance' [Review] Richard Pithouse (2016) Writing the decline: on the struggle for South Africa’s democracy

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Relationships between estimated autozygosity and complex traits in the UK Biobank

<div><p>Inbreeding increases the risk of certain Mendelian disorders in humans but may also reduce fitness through its effects on complex traits and diseases. Such inbreeding depression is thought to occur due to increased homozygosity at causal variants that are recessive with respect to fitness. Until recently it has been difficult to amass large enough sample sizes to investigate the effects of inbreeding depression on complex traits using genome-wide single nucleotide polymorphism (SNP) data in population-based samples. Further, it is difficult to infer causation in analyses that relate degree of inbreeding to complex traits because confounding variables (e.g., education) may influence both the likelihood for parents to outbreed and offspring trait values. The present study used runs of homozygosity in genome-wide SNP data in up to 400,000 individuals in the UK Biobank to estimate the proportion of the autosome that exists in autozygous tracts—stretches of the genome which are identical due to a shared common ancestor. After multiple testing corrections and controlling for possible sociodemographic confounders, we found significant relationships in the predicted direction between estimated autozygosity and three of the 26 traits we investigated: age at first sexual intercourse, fluid intelligence, and forced expiratory volume in 1 second. Our findings corroborate those of several published studies. These results may imply that these traits have been associated with Darwinian fitness over evolutionary time. However, some of the autozygosity-trait relationships were attenuated after controlling for background sociodemographic characteristics, suggesting that alternative explanations for these associations have not been eliminated. Care needs to be taken in the design and interpretation of ROH studies in order to glean reliable information about the genetic architecture and evolutionary history of complex traits.</p></div

Regulating Electricity-Market Manipulation: A Proposal for a New Regulatory Regime to Proscribe All Forms of Manipulation

Congress broadly authorized the Federal Energy Regulatory Commission (“FERC”) to protect consumers of electricity from all forms of manipulation in the electricity markets, but the regulations that FERC passed are not nearly so expansive. As written, FERC’s Anti-Manipulation Rule covers only instances of manipulation involving fraud. This narrow scope is problematic, however, because electricity markets can also be manipulated by nonfraudulent activity. Thus, in order to reach all forms of manipulation, FERC is forced to interpret and apply its Anti-Manipulation Rule in ways that strain the plain language and accepted understanding of the rule and therefore constitute an improper extension of the fraud-based regulations to nonfraudulent activity. This Note argues that FERC ought to fix the current anti-manipulation regulatory regime, both as a matter of sound governmental regulation and to ensure fair notice to the regulated entities. In particular, this Note contends that FERC should redraft its Anti-Manipulation Rule and that, in doing so, it should use the Commodity Futures Trading Commission (“CFTC”)’s rules as a model. By adopting the CFTC’s rules, FERC could design a new anti-manipulation regulation that would properly and flexibly encompass all forms of potential manipulation in the electricity markets—a solution that would allow the law adequately to respond to future attempts at manipulation

Modal Analysis to Minimize Gearbox Induced Noise of General Electric Wind Turbines

With the current global emphasis on alternative green energy sources, wind turbine technologies have seen significant growth in recent years. Today, wind turbines are being produced and constructed at unprecedented levels with their sites inching closer and closer to residential communities. With that, wind turbine companies have been receiving growing complains about the noise emitted from these turbines during operation. To resolve this issue, many of these companies are spending more resources to design and manufacture quieter wind turbines. In particular, General Electric (GE) intends to reduce the noise created by their 2.5 MW CGDT wind turbines. Previous studies showed that noise starts in the gearbox due to the transmission error between the meshing gears which creates extensive vibrations. These vibrations resonate with the gearbox housing causing energy to propagate from the housing to the bedplate and then to the nacelle. Vibrations are then transmitted from the nacelle to the rotating blades which produce a humming sound (noise) in the surroundings. GE researchers have theorized that noise can be eliminated if the gearbox housing is designed such that its modal frequencies are far from the excitation frequencies resulting from the transmission error. In order to achieve this goal, this thesis aims to develop a computational model which captures the modal response of the gearbox housing. Once this model is developed and validated against experimental data, alterations to the design can be implemented to shift the trouble frequencies. Two computational models are developed using the commercial softwares ANSYS and MASTA. The ANSYS model, which imposes several simplifying assumptions on the dynamics, is shown to lack the accuracy necessary to capture the modal response of the gearbox housing. The MASTA model, on the other hand, includes the interactions between the gearbox dynamics and the housing and is shown to produce modal responses that match the experimental data. The model and techniques provided in this thesis will provide the springboard upon which future design improvements and noise reduction techniques of GE wind turbines are launched