3,507 research outputs found
Characterization of fatigue damage in A36 steel specimens using nonlinear Rayleigh surface waves
A36 steel is a commonly used material in civil engineering structures where fatigue damage can lead to catastrophic failure. In this research, nonlinear Rayleigh surface waves are used to characterize damage in A36 steel specimens caused by monotonic tension and low cycle fatigue. Fatigue damage produces the increased acoustic nonlinearity that leads to the generation of measurable higher harmonics in an initially monochromatic Rayleigh wave signal. One specimen is subjected to static tension and four specimens are used for low cycle fatigue tests in the tension-tension mode with a constant stress amplitude. The fatigue tests are interrupted at
different numbers of cycles for the nonlinear ultrasonic measurements. Tone burst Rayleigh wave signals are generated and detected using a pair of oil coupled wedge transducers. The amplitudes of the first and second harmonic are measured at varying propagation distances to obtain the nonlinearity parameter for a given damage state.
The experimental results show an increase of acoustic nonlinearity in the early stages of fatigue life. Furthermore, a close relationship between plastic deformation and the acoustic nonlinearity is found, which indicates that the acoustic nonlinearity is indeed a measure of microplasticity in this material.MSCommittee Chair: Jacobs, Laurence; Committee Member: Kim, Jin-Yeon; Committee Member: Qu, Jianmi
Overview of radio experiments for UHE cosmic particles detection
Radio-detection is a mature technique that has gained large momentum over the
past decades. Its physical detection principle is mainly driven by the
electromagnetic part of the shower, and is therefore not too sensitive to
uncertainties on hadronic interactions. Furthermore its technical detection
principle allows for a 100% duty cycle, and large surface coverage thanks to
the low cost of antennas. Various detection methods of UHE particles now rely
on the radio signal as main observable. For instance, ground based experiments
such as AERA on the Pierre Auger Observatory or LOFAR detect the radio emission
from air-showers induced by high-energy particles in the atmosphere; in-ice
experiment such as ARA, IceCube, or ARIANNA benefits from a detection in denser
media which reduces the interaction lengths; finally, balloon experiments such
as ANITA allow for very sensitive UHE neutrino detection with only a few
antennas. Radio-detection is now focused on building increasingly large-scale
radio experiments to enhance the detector sensitivity and address the low
fluxes at UHE. In this proceeding we give an overview of the past, current and
future experiments for the detection of UHE cosmic particles using the radio
technique in air (AERA, Auger-Prime, GRAND), in balloon (ANITA, PUEO) or in
other media (IceCube-Gen2, BEACON, RNO-G).Comment: 12 pages, 8 figures, Rencontres de Moriond 2022: conference
proceeding; section 4.2 and acknowkedgements update
Spiral waves triggered by shadows in transition disks
Circumstellar asymmetries such as central warps have recently been shown to
cast shadows on outer disks. We investigate the hydrodynamical consequences of
such variable illumination on the outer regions of a transition disk, and the
development of spiral arms. Using 2D simulations, we follow the evolution of a
gaseous disk passively heated by the central star, under the periodic forcing
of shadows with an opening angle of 28. With a lower pressure
under the shadows, each crossing results in a variable azimuthal acceleration,
which in time develops into spiral density waves. Their pitch angles evolve
from at the onset, to 11-14,
over 65~AU to 150~AU. Self-gravity enhances the density contrast of the
spiral waves, as also reported previously for spirals launched by planets. Our
control simulations with unshadowed irradiation do not develop structures,
except for a different form of spiral waves seen at later times only in the
gravitationally unstable control case. Scattered light predictions in the
-band show that such illumination spirals should be observable. We suggest
that spiral arms in the case-study transition disk HD~142527 could be explained
as a result of shadowing from the tilted inner disk.Comment: 6 pages, 4 figures, 1 table. Accepted for publication in ApJ
The Impact of Riser-induced Slugs on the Downstream Deoiling Efficiency
In Oil and gas productions, the severe slug is an undesired flow regime due to the negative impact on the production rate and facility safety. This study examines the severe riser-induced slugs’ influence on a typical separation process, consisting of a 3-phase gravity separator physically linked to a deoiling hydrocyclone. Four inflow scenarios are compared: Uncontrolled, open-loop, feasible, and infeasible closed-loop anti-slug control, respectively. Three PID controllers’ coefficients are kept constant for all the tests: The separator pressure, water level, and hydrocyclone pressure-drop-ratio (PDR) controllers. The simulation results show that the separation efficiency is significantly larger in the closed-loop configuration, probably due to the larger production rates which provide a preferable operation condition for the hydrocyclone. It is concluded that both slug elimination approaches improve the separation efficiency consistency, but that the closed-loop control provides the best overall separation performance
Double tungstate lasers: From bulk toward on-chip integrated waveguide devices
It has been recognized that the monoclinic double tungstates , , and possess a high potential as rare-earth-ion-doped solid-state laser materials, partly due to the high absorption and emission cross sections of rare-earth ions when doped into these materials. Besides, their high refractive indexes make these materials potentially suitable for applications that require optical gain and high power in integrated optics, with rather high integration density. We review the recent advances in the field of bulk lasers in these materials and present our work toward the demonstration of waveguide lasers and their integration with other optical structures on a chip
The oil and gas industry will need to scale back much faster to limit warming to 1.5°C
If global temperature increase is to be limited to 1.5°C, CO2 emissions must reach net zero in 2050, if not sooner. Consumption of oil must begin to fall in the next few years and fall substantially thereafter – far from the gentle plateauing expected by many in the industry. Gas consumption, considered by the industry to be a “growth engine”, must begin to decline by 2030. Most European oil and gas companies have responded to investor pressure by updating their emission targets, describing them as being consistent with net zero. Research shows that this is not the case. Dan Gardiner, Rory Sullivan, Simon Dietz, and Valentin Jahn say that oil and gas companies will have to go much further to genuinely claim 1.5C/net-zero alignment. For most, this is likely to require a substantial scaling back of investment in exploration and production activities, particularly for oil
The oil and gas industry will need to scale back much faster to limit warming to 1.5oC
If global temperature increase is to be limited to 1.5oC, CO2 emissions must reach net zero in 2050, if not sooner. Consumption of oil must begin to fall in the next few years and fall substantially thereafter – far from the gentle plateauing expected by many in the industry. Gas consumption, considered by the industry to be a “growth engine”, must [...
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