377 research outputs found
Full phase stabilization of a Yb:fiber femtosecond frequency comb via high-bandwidth transducers
We present full phase stabilization of an amplified Yb:fiber femtosecond
frequency comb using an intra-cavity electro-optic modulator and an
acousto-optic modulator. These transducers provide high servo bandwidths of 580
kHz and 250 kHz for frep and fceo, producing a robust and low phase noise fiber
frequency comb. The comb was self-referenced with an f - 2f interferometer and
phase locked to an ultra-stable optical reference used for the JILA Sr optical
clock at 698 nm, exhibiting 0.21 rad and 0.47 rad of integrated phase errors
(over 1 mHz - 1 MHz) respectively. Alternatively, the comb was locked to two
optical references at 698 nm and 1064 nm, obtaining 0.43 rad and 0.14 rad of
integrated phase errors respectively
Broadband Phase-Noise Suppression in a Yb-Fiber Frequency Comb
We report a simple technique to suppress high frequency phase noise of a
Yb-based fiber optical frequency comb using an active intensity noise servo.
Out-of-loop measurements of the phase noise using an optical heterodyne beat
with a continuous wave (cw) laser show suppression of phase noise by \geq7 dB
out to Fourier frequencies of 100 kHz with a unity-gain crossing of -700 kHz.
These results are enabled by the strong correlation between the intensity and
phase noise of the laser. Detailed measurements of intensity and phase noise
spectra, as well as transfer functions, reveal that the dominant phase and
intensity noise contribution above -100 kHz is due to amplified spontaneous
emission (ASE) or other quantum noise sources.Comment: 4 pages, 3 figure
International energy agency ocean energy systems task 10 wave energy converter modeling verification and validation
This is the first joint reference paper for the Ocean
Energy Systems (OES) Task 10 Wave Energy Converter modeling
verification and validation group. The group is established
under the OES Energy Technology Network program under the
International Energy Agency. OES was founded in 2001 and
Task 10 was proposed by Bob Thresher (National Renewable
Energy Laboratory) in 2015 and approved by the OES Executive
Committee EXCO in 2016. The kickoff workshop took place in
September 2016, wherein the initial baseline task was defined.
Experience from similar offshore wind validation/verification
projects (OC3-OC5 conducted within the International Energy
Agency Wind Task 30) [1], [2] showed that a simple test
case would help the initial cooperation to present results in
a comparable way. A heaving sphere was chosen as the first
test case. The team of project participants simulated different
numerical experiments, such as heave decay tests and regular
and irregular wave cases. The simulation results are presented
and discussed in this paper.IEA-OES Task 1
Computational modelling and experimental tank testing of the multi float WaveSub under regular wave forcing
A submerged wave device generates energy from the relative motion of floating bodies. In WaveSub, three floats are joined to a reactor; each connected to a spring and generator. Electricity generated damps the orbital movements of the floats. The forces are non-linear and each float interacts with the others. Tuning to the wave climate is achieved by changing the line lengths, so there is a need to understand the performance trade-offs for a large number of configurations. This requires an efficient, large displacement, multidirectional, multi-body numerical scheme. Results from a 1/25 scale wave basin experiment are described. Here, we show that a time domain linear potential flow formulation (Nemoh, WEC-Sim) can match the tank testing provided that suitably tuned drag coefficients are employed. Inviscid linear potential models can match some wave device experiments; however, additional viscous terms generally provide better accuracy. Scale experiments are also prone to mechanical friction, and we estimate friction terms to improve the correlation further. The resulting error in mean power between numerical and physical models is approximately 10%. Predicted device movement shows a good match. Overall, drag terms in time domain wave energy modelling will improve simulation accuracy in wave renewable energy device design
Computational modelling and experimental tank testing of the multi float WaveSub under regular wave forcing
A submerged wave device generates energy from the relative motion of floating bodies. In 1 WaveSub, three floats are joined to a reactor; each connected to a spring and generator. Electricity generated 2 damps the orbital movements of the floats. The forces are non-linear and each float interacts with the others. 3 Tuning to the wave climate is achieved by changing the line lengths so there is a need to understand the 4 performance trade-offs for a large number of configurations. This requires an efficient, large displacement, 5 multidirectional, multi-body numerical scheme. Results from a 1/25 scale wave basin experiment are described. 6 Here we show that a time domain linear potential flow formulation (Nemoh, WEC-Sim) can match the tank 7 testing provided that suitably tuned drag coefficients are employed. Inviscid linear potential models can match 8 some wave device experiments, however, additional viscous terms generally provide better accuracy. Scale 9 experiments are also prone to mechanical friction and we estimate friction terms to improve the correlation 10 further. The resulting error in mean power between numerical and physical models is approximately 10%. 11 Predicted device movement shows a good match. Overall, drag terms in time domain wave energy modelling 12 will improve simulation accuracy in wave renewable energy device design
Quantitative Characterization of the T Cell Receptor Repertoire of Naive and Memory subsets Using an Integrated experimental and Computational Pipeline Which Is Robust, economical, and Versatile
The T cell receptor (TCR) repertoire can provide a personalized biomarker for infectious and non-infectious diseases. We describe a protocol for amplifying, sequencing, and analyzing TCRs which is robust, sensitive, and versatile. The key experimental step is ligation of a single-stranded oligonucleotide to the 3′ end of the TCR cDNA. This allows amplification of all possible rearrangements using a single set of primers per locus. It also introduces a unique molecular identifier to label each starting cDNA molecule. This molecular identifier is used to correct for sequence errors and for effects of differential PCR amplification efficiency, thus producing more accurate measures of the true TCR frequency within the sample. This integrated experimental and computational pipeline is applied to the analysis of human memory and naive subpopulations, and results in consistent measures of diversity and inequality. After error correction, the distribution of TCR sequence abundance in all subpopulations followed a power law over a wide range of values. The power law exponent differed between naïve and memory populations, but was consistent between individuals. The integrated experimental and analysis pipeline we describe is appropriate to studies of T cell responses in a broad range of physiological and pathological contexts
Using Heat to Characterize Streambed Water Flux Variability in Four Stream Reaches
Estimates of streambed water fl ux are needed for the interpretation of streambed chemistry and reactions. Continuous temperature and head monitoring in stream reaches within four agricultural watersheds (Leary Weber Ditch, IN; Maple Creek, NE; DR2 Drain, WA; and Merced River, CA) allowed heat to be used as a tracer to study the temporal and spatial variability of fluxes through the streambed. Synoptic methods (seepage meter and differential discharge measurements) were compared with estimates obtained by using heat as a tracer. Water flux was estimated by modeling one-dimensional vertical flow of water and heat using the model VS2DH. Flux was influenced by physical heterogeneity of the stream channel and temporal variability in stream and ground-water levels. During most of the study period (April–December 2004), flux was upward through the streambeds. At the IN, NE, and CA sites, high-stage events resulted in rapid reversal of flow direction inducing short-term surface-water flow into the streambed. During late summer at the IN site, regional ground-water levels dropped, leading to surface-water loss to ground water that resulted in drying of the ditch. Synoptic measurements of flux generally supported the model flux estimates. Water flow through the streambed was roughly an order of magnitude larger in the humid basins (IN and NE) than in the arid basins (WA and CA). Downward flux, in response to sudden high streamflows, and seasonal variability in flux was most pronounced in the humid basins and in high conductivity zones in the streambed
Calibration of the Logarithmic-Periodic Dipole Antenna (LPDA) Radio Stations at the Pierre Auger Observatory using an Octocopter
An in-situ calibration of a logarithmic periodic dipole antenna with a
frequency coverage of 30 MHz to 80 MHz is performed. Such antennas are part of
a radio station system used for detection of cosmic ray induced air showers at
the Engineering Radio Array of the Pierre Auger Observatory, the so-called
Auger Engineering Radio Array (AERA). The directional and frequency
characteristics of the broadband antenna are investigated using a remotely
piloted aircraft (RPA) carrying a small transmitting antenna. The antenna
sensitivity is described by the vector effective length relating the measured
voltage with the electric-field components perpendicular to the incoming signal
direction. The horizontal and meridional components are determined with an
overall uncertainty of 7.4^{+0.9}_{-0.3} % and 10.3^{+2.8}_{-1.7} %
respectively. The measurement is used to correct a simulated response of the
frequency and directional response of the antenna. In addition, the influence
of the ground conductivity and permittivity on the antenna response is
simulated. Both have a negligible influence given the ground conditions
measured at the detector site. The overall uncertainties of the vector
effective length components result in an uncertainty of 8.8^{+2.1}_{-1.3} % in
the square root of the energy fluence for incoming signal directions with
zenith angles smaller than 60{\deg}.Comment: Published version. Updated online abstract only. Manuscript is
unchanged with respect to v2. 39 pages, 15 figures, 2 table
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