Abstract
Externally bonded carbon fiber–reinforced polymer (CFRP) composites have been instrumental in the flexural strengthening of concrete structures. However, intermediate crack debonding from ...the concrete substrate is a governing failure mode in most externally bonded CFRP applications, limiting the composite strength utilization and deformability of a strengthened member. The addition of transverse U-wrap anchorage for longitudinally oriented CFRP sheet tension reinforcement can improve performance in terms of both deformability and ultimate strength. Due to the scarcity of experimental data, design guidance for U-wrap anchorage to mitigate intermediate crack debonding is lacking. The results of flexural tests on large-scale reinforced concrete beams strengthened in flexure with externally bonded CFRP anchored with U-wraps are reported in this paper. Test results indicate that U-wraps can increase the strain utilization of longitudinal CFRP between 40% and 57%, while also mitigating the intermediate crack debonding failure mode. Varying the ratio of the area of U-wrap anchorage to area of flexural CFRP had little effect on the beams’ flexural capacity.
The sources of ultra-high energy (UHE) cosmic rays, which can have energies up to 1020 eV, remain a mystery. UHE neutrinos may provide important clues to understanding the nature of cosmic-ray ...sources. ARIANNA aims to detect UHE neutrinos via radio (Askaryan) emission from particle showers when a neutrino interacts with ice, which is an efficient method for neutrinos with energies between 1016 eV and 1020 eV. The ARIANNA radio detectors are located in Antarctic ice just beneath the surface. Neutrino observation requires that radio pulses propagate to the antennas at the surface with minimum distortion by the ice and firn medium. Using the residual hole from the South Pole Ice Core Project, radio pulses were emitted from a transmitter located up to 1.7 km below the snow surface. By measuring these signals with an ARIANNA surface station, the angular and polarization reconstruction abilities are quantified, which are required to measure the direction of the neutrino. After deconvolving the raw signals for the detector response and attenuation from propagation through the ice, the signal pulses show no significant distortion and agree with a reference measurement of the emitter made in an anechoic chamber. Furthermore, the signal pulses reveal no significant birefringence for our tested geometry of mostly vertical ice propagation. The origin of the transmitted radio pulse was measured with an angular resolution of 0.37ˆ indicating that the neutrino direction can be determined with good precision if the polarization of the radio-pulse can be well determined. In the present study we obtained a resolution of the polarization vector of 2.7ˆ. Neither measurement show a significant offset relative to expectation.
Ultra high energy neutrinos (Eν>1016.5eV) are efficiently measured via radio signals following a neutrino interaction in ice. An antenna placed1 (15 m) below the ice surface will measure two signals ...for the vast majority of events (90% at Eν=1018 eV): a direct pulse and a second delayed pulse from a reflection off the ice surface. This allows for a unique identification of neutrinos against backgrounds arriving from above. Furthermore, the time delay between the direct and reflected signal (D'n'R) correlates with the distance to the neutrino interaction vertex, a crucial quantity to determine the neutrino energy. In a simulation study, we derive the relation between time delay and distance and study the corresponding experimental uncertainties in estimating neutrino energies. We find that the resulting contribution to the energy resolution is well below the natural limit set by the unknown inelasticity in the initial neutrino interaction. We present an in-situ measurement that proves the experimental feasibility of this technique. Continuous monitoring of the local snow accumulation in the vicinity of the transmit and receive antennas using this technique provide a precision of (1 mm) in surface elevation, which is much better than that needed to apply the D'n'R technique to neutrinos.
We report on the development, installation, and operation of the first three of seven stations deployed at the ARIANNA site's pilot Hexagonal Radio Array (HRA) in Antarctica. The primary goal of the ...ARIANNA project is to observe ultrahigh energy ( > 100 PeV) cosmogenic neutrino signatures using a large array of autonomous stations, each 1 km apart on the surface of the Ross Ice Shelf. Sensing radio emissions of 100 MHz to 1 GHz, each station in the array contains RF antennas, amplifiers, 1.92 G-sample/s, 850 MHz bandwidth signal acquisition circuitry, pattern-matching trigger capabilities, an embedded CPU, 32 GB of solid-state data storage, and long-distance wireless and satellite communications. Power is provided by the sun and buffered in LiFePO 4 storage batteries, and each station consumes an average of 7 W of power. Operation on solar power has resulted in ≥58% per calendar-year live-time. The station's pattern-trigger capabilities reduce the trigger rates to a few milli-Hertz with 4-sigma voltage thresholds while retaining good stability and high efficiency for neutrino signals. The timing resolution of the station has been found to be 0.049 ns, RMS, and the angular precision of event reconstructions of signals bounced off of the sea-ice interface of the Ross Ice Shelf ranged from 0.14 to 0.17 ° .
The primary mission of the ARIANNA ultra-high energy neutrino telescope is to uncover astrophysical sources of neutrinos with energies greater than 1016 eV. A pilot array, consisting of seven ARIANNA ...stations located on the surface of the Ross Ice Shelf in Antarctica, was commissioned in November 2014. We report on the search for astrophysical neutrinos using data collected between November 2014 and February 2019. A straight-forward template matching analysis yielded no neutrino candidates, with a signal efficiency of 79%. We find a 90% confidence upper limit on the diffuse neutrino flux of E2Φ=1.7×10−6GeV cm−2s−1sr−1 for a decade wide logarithmic bin centered at a neutrino energy of 1018,eV, which is an order of magnitude improvement compared to the previous limit reported by the ARIANNA collaboration. The ARIANNA stations, including purpose built cosmic-ray stations at the Moore's Bay site and demonstrator stations at the South Pole, have operated reliably. Sustained operation at two distinct sites confirms that the flexible and adaptable architecture can be deployed in any deep ice, radio quiet environment. We show that the scientific capabilities, technical innovations, and logistical requirements of ARIANNA are sufficiently well understood to serve as the basis for large area radio-based neutrino telescope with a wide field-of-view.
Ongoing experimental efforts in Antarctica seek to detect ultra-high energy neutrinos by measurement of radio-frequency (RF) Askaryan radiation generated by the collision of a neutrino with an ice ...molecule. An array of RF antennas, deployed either in-ice or in-air, is used to infer the properties of the neutrino. To evaluate their experimental sensitivity, such experiments require a refractive index model for ray tracing radio-wave trajectories from a putative in-ice neutrino interaction point to the receiving antennas; this gives the degree of signal absorption or ray bending from source to receiver. The gradient in the density profile over the upper 200 meters of Antarctic ice, coupled with Fermat's least-time principle, implies ray "bending" and the existence of "forbidden" zones for predominantly horizontal signal propagation at shallow depths. After re-deriving the formulas describing such shadowing, we report on experimental results that, somewhat unexpectedly, demonstrate the existence of electromagnetic wave transport modes from nominally shadowed regions. Finally, the fact that this shadow-signal propagation is observed both at South Pole and the Ross Ice Shelf in Antarctica suggests that the effect may be a generic property of polar ice, with potentially important implications for experiments seeking to detect neutrinos.
•A 2D FEM approach is developed for strength of post-tensioned beams with unbonded and bonded tendons.•The approach predicts ultimate flexural strength, failure mode, and tendon stress ...accurately.•Displacement of members with both bonded and unbonded tendons was predicted within 15%.•In comparisons with experimental work, the FEM approach demonstrates good representation of the development of the plastic hinge region.
Tendon filler materials serve as a critical layer, protecting a post-tensioned bridge’s steel reinforcement against corrosion and subsequent strength loss. Recent adoption of flexible filler materials in post-tensioning tendons in bridge construction – an alternative to the more typical cementitious grout which is currently common in the U.S. – has implications on member flexural behavior. This paper describes the development and experimental validation of a simplified, computationally inexpensive finite element modeling (FEM) approach for unbonded tendons. Flexural members containing both unbonded post-tensioned steel and bonded pretensioned steel, or “mixed tendons”, were modeled. FEM results were then validated against experimentally obtained ultimate strength, tendon stress, and plastic hinge length data. The developed analytical approach described herein was found to predict the ultimate flexural strength, failure mode and tendon stress with good accuracy, within 5%. Prediction of the ultimate displacement was fairly accurately modeled (within 15%) for the mixed tendon beams.
Abstract
The ARIANNA experiment is an Askaryan radio detector designed to measure high-energy neutrino induced cascades within the Antarctic ice. Ultra-high-energy neutrinos above 10
16
eV have an ...extremely low flux, so experimental data captured at trigger level need to be classified correctly to retain as much neutrino signal as possible. We first describe two new physics-based neutrino selection methods, or “cuts”, (the updown and dipole cut) that extend the previously published analysis to a specialized ARIANNA station with 8 antenna channels, which is double the number used in the prior analysis. For a standard trigger with a threshold signal to noise ratio at 4.4, the new cuts produce a neutrino efficiency of > 95% per station-year of operation, while rejecting 99.93% of the background (corresponding to 53 remaining experimental background events). When the new cuts are combined with a previously developed cut using neutrino waveform templates, all background is removed at no change of efficiency. In addition, the neutrino efficiency is extrapolated to 1,000 station-years of operation, obtaining 91%. This work then introduces a new selection method (the deep learning cut) to augment the identification of neutrino events by using deep learning methods and compares the efficiency to the physics-based analysis. The deep learning cut gives 99% signal efficiency per station-year of operation while rejecting 99.997% of the background (corresponding to 2 remaining experimental background events), which are subsequently removed by the waveform template cut at no significant change in efficiency. The results of the deep learning cut were verified using measured cosmic rays which shows that the simulations do not introduce artifacts with respect to experimental data. The paper demonstrates that the background rejection and signal efficiency of near surface antennas meets the requirements of a large scale future array, as considered in baseline design of the radio component of IceCube-Gen2.
Abstract
The ARIANNA detector is designed to detect neutrinos with energies above 10
17
eV. Due to the similarities in generated radio signals, cosmic rays are often used as test beams for neutrino ...detectors. Some ARIANNA detector stations are equipped with antennas capable of detecting air showers. Since the radio emission properties of air showers are well understood, and the polarization of the radio signal can be predicted from the arrival direction, cosmic rays can be used as a proxy to assess the reconstruction capabilities of the ARIANNA neutrino detector. We report on dedicated efforts of reconstructing the polarization of cosmic-ray radio pulses. After correcting for difference in hardware, the two stations used in this study showed similar performance in terms of event rate and agreed with simulation. Subselecting high quality cosmic rays, the polarizations of these cosmic rays were reconstructed with a resolution of 2.5° (68% containment), which agrees with the expected value obtained from simulation. A large fraction of this resolution originates from uncertainties in the predicted polarization because of the contribution of the subdominant Askaryan effect in addition to the dominant geomagnetic emission. Subselecting events with a zenith angle greater than 70° removes most influence of the Askaryan emission, and, with limited statistics, we found the polarization uncertainty is reduced to 1.3° (68% containment).
Abstract
The ARIANNA experiment is an Askaryan detector designed to
record radio signals induced by neutrino interactions in the
Antarctic ice. Because of the low neutrino flux at high energies
(E_ν> ...10^16 eV), the physics output is limited by
statistics. Hence, an increase in sensitivity significantly improves
the interpretation of data and offers the ability to probe new
parameter spaces. The amplitudes of the trigger threshold are
limited by the rate of triggering on unavoidable thermal noise
fluctuations. We present a real-time thermal noise rejection
algorithm that enables the trigger thresholds to be lowered, which
increases the sensitivity to neutrinos by up to a factor of two
(depending on energy) compared to the current ARIANNA
capabilities. A deep learning discriminator, based on a
Convolutional Neural Network (CNN), is implemented to identify and
remove thermal events in real time. We describe a CNN trained on MC
data that runs on the current ARIANNA microcomputer and retains 95%
of the neutrino signal at a thermal noise rejection factor of
10^5, compared to a template matching procedure which reaches only
10^2 for the same signal efficiency. Then the results are verified
in a lab measurement by feeding in generated neutrino-like signal
pulses and thermal noise directly into the ARIANNA data acquisition
system. Lastly, the same CNN is used to classify cosmic-rays events
to make sure they are not rejected. The network classified 102 out
of 104 cosmic-ray events as signal.
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