Flip-flop jet nozzle extended to supersonic flows

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/76991/1/AIAA-11725-757.pd

Reconstructing the calibrated strain signal in the Advanced LIGO detectors

Advanced LIGO's raw detector output needs to be calibrated to compute dimensionless strain h(t). Calibrated strain data is produced in the time domain using both a low-latency, online procedure and a high-latency, offline procedure. The low-latency h(t) data stream is produced in two stages, the first of which is performed on the same computers that operate the detector's feedback control system. This stage, referred to as the front-end calibration, uses infinite impulse response (IIR) filtering and performs all operations at a 16384 Hz digital sampling rate. Due to several limitations, this procedure currently introduces certain systematic errors in the calibrated strain data, motivating the second stage of the low-latency procedure, known as the low-latency gstlal calibration pipeline. The gstlal calibration pipeline uses finite impulse response (FIR) filtering to apply corrections to the output of the front-end calibration. It applies time-dependent correction factors to the sensing and actuation components of the calibrated strain to reduce systematic errors. The gstlal calibration pipeline is also used in high latency to recalibrate the data, which is necessary due mainly to online dropouts in the calibrated data and identified improvements to the calibration models or filters.Comment: 20 pages including appendices and bibliography. 11 Figures. 3 Table

Calibration Uncertainty for Advanced LIGO's First and Second Observing Runs

Calibration of the Advanced LIGO detectors is the quantification of the detectors' response to gravitational waves. Gravitational waves incident on the detectors cause phase shifts in the interferometer laser light which are read out as intensity fluctuations at the detector output. Understanding this detector response to gravitational waves is crucial to producing accurate and precise gravitational wave strain data. Estimates of binary black hole and neutron star parameters and tests of general relativity require well-calibrated data, as miscalibrations will lead to biased results. We describe the method of producing calibration uncertainty estimates for both LIGO detectors in the first and second observing runs.Comment: 15 pages, 21 figures, LIGO DCC P160013

Water relations and irrigation requirements of onion (Allium Cepa L.): a review of yield and quality impacts

The results of international research on the water relations and irrigation needs of onions have been synthesized in an attempt to link fundamental studies on crop physiology to irrigation practices, and consequent impacts on crop yield, quality and storage. Following a brief introduction on its origins and centres of production, a synthesis of research on crop development including plant water relations, crop water requirements, yield response to water, irrigation systems and scheduling are presented. Most of the evidence stems from research conducted in arid and semi-arid regions notably the USA, India, Spain and Turkey. The findings confirm that onion seasonal water requirements are highly variable depending on agroclimate, location and season, as are the crop coefficients (Kc) which range from 0.4 to 0.7 (initial stage), 0.85 to 1.05 (middle development) and 0.6 to 0.75 (final stage). Seasonal irrigation needs are reported to vary from 225 to 1040 mm to produce between 10 and 77 t ha-1. The most sensitive stages for water stress are at emergence, transplanting and bulb formation. Final crop quality can also be affected by water excess. Water stress at specific stages can negatively impact on quality leading to reduced size and multi-centred bulbs. In recent years, pressure on water resources, retailer demands for quality assurance and rising production costs have meant that onion irrigation has switched from traditional low efficiency (furrow) methods to more efficient advanced (sprinkler and drip) technologies. For scheduling, optimal soil water potential thresholds for triggering irrigation were found to be between -17 kPa and -27 kPa for drip and furrow irrigation. Research is underway to maximize water use efficiency in onions, but the deficit irrigation regimes being tested under experimental conditions have yet to be adopted commercially

First narrow-band search for continuous gravitational waves from known pulsars in advanced detector data

Spinning neutron stars asymmetric with respect to their rotation axis are potential sources of continuous gravitational waves for ground-based interferometric detectors. In the case of known pulsars a fully coherent search, based on matched filtering, which uses the position and rotational parameters obtained from electromagnetic observations, can be carried out. Matched filtering maximizes the signalto- noise (SNR) ratio, but a large sensitivity loss is expected in case of even a very small mismatch between the assumed and the true signal parameters. For this reason, narrow-band analysis methods have been developed, allowing a fully coherent search for gravitational waves from known pulsars over a fraction of a hertz and several spin-down values. In this paper we describe a narrow-band search of 11 pulsars using data from Advanced LIGO’s first observing run. Although we have found several initial outliers, further studies show no significant evidence for the presence of a gravitational wave signal. Finally, we have placed upper limits on the signal strain amplitude lower than the spin-down limit for 5 of the 11 targets over the bands searched; in the case of J1813-1749 the spin-down limit has been beaten for the first time. For an additional 3 targets, the median upper limit across the search bands is below the spin-down limit. This is the most sensitive narrow-band search for continuous gravitational waves carried out so far

Metric Assisted Stochastic Sampling (MASS) search for gravitational waves from binary black hole mergers

We present a novel gravitational wave detection algorithm that conducts amatched filter search stochastically across the compact binary parameter spacerather than relying on a fixed bank of template waveforms. This technique iscompetitive with standard template-bank-driven pipelines in both computationalcost and sensitivity. However, the complexity of the analysis is simplerallowing for easy configuration and horizontal scaling across heterogeneousgrids of computers. To demonstrate the method we analyze approximately onemonth of public LIGO data from July 27 00:00 2017 UTC - Aug 25 22:00 2017 UTCand recover eight known confident gravitational wave candidates. We also injectsimulated binary black hole (BBH) signals to demonstrate the sensitivity.<br

Characterization of systematic error in Advanced LIGO calibration

The raw outputs of the detectors within the Advanced Laser Interferometer Gravitational-Wave Observatory need to be calibrated in order to produce the estimate of the dimensionless strain used for astrophysical analyses. The two detectors have been upgraded since the second observing run and finished the year-long third observing run. Understanding, accounting, and/or compensating for the complex-valued response of each part of the upgraded detectors improves the overall accuracy of the estimated detector response to gravitational waves. We describe improved understanding and methods used to quantify the response of each detector, with a dedicated effort to define all places where systematic error plays a role. We use the detectors as they stand in the first half (six months) of the third observing run to demonstrate how each identified systematic error impacts the estimated strain and constrain the statistical uncertainty therein. For this time period, we estimate the upper limit on systematic error and associated uncertainty to be $< 7\%$ in magnitude and $< 4$ deg in phase ($68\%$ confidence interval) in the most sensitive frequency band 20-2000 Hz. The systematic error alone is estimated at levels of $< 2\%$ in magnitude and $< 2$ deg in phase