The Impact of Government Policy on Technology Transfer: An Aircraft Industry Case Study

This case study explores the interaction between domestic and foreign governmental policy on technology transfer with the goal of exploring the long-term impacts of technology transfer. Specifically, the impact of successive licensing of fighter aircraft manufacturing and design to Japan in the development of Japan’s aircraft industry is reviewed. Results indicate Japan has built a domestic aircraft industry through sequential learning with foreign technology transfers from the United States, and design and production on domestic fighter aircraft. This process was facilitated by governmental policies in both Japan and the United States

Andreev Reflection in Heavy-Fermion Superconductors and Order Parameter Symmetry in CeCoIn_5

Differential conductance spectra are obtained from nanoscale junctions on the heavy-fermion superconductor CeCoIn$_5$ along three major crystallographic orientations. Consistency and reproducibility of characteristic features among the junctions ensure their spectroscopic nature. All junctions show a similar conductance asymmetry and Andreev reflection-like conductance with reduced signal (~ 10%-13%), both commonly observed in heavy-fermion superconductor junctions. Analysis using the extended Blonder-Tinkham-Klapwijk model indicates that our data provide the first spectroscopic evidence for $d_{x^2-y^2}$ symmetry. To quantify our conductance spectra, we propose a model by considering the general phenomenology in heavy fermions, the two-fluid behavior, and an energy-dependent density of states. Our model fits to the experimental data remarkably well and should invigorate further investigations.Comment: 4 pages, 4 figures; Phys. Rev. Lett., published versio

Machine Learning Using U-Net Convolutional Neural Networks for the Imaging of Sparse Seismic Data

Machine learning using convolutional neural networks (CNNs) is investigated for the imaging of sparsely sampled seismic reflection data. A limitation of traditional imaging methods is that they often require seismic data with sufficient spatial sampling. Using CNNs for imaging, even if the spatial sampling of the data is sparse, good imaging results can still be obtained. Therefore, CNNs applied to seismic imaging have the potential of producing improved imaging results when spatial sampling of the data is sparse. The imaged model can then be used to generate more densely sampled data and in this way be used to interpolate either regularly or irregularly sampled data. Although there are many approaches for the interpolation of seismic data, here seismic imaging is performed directly with sparse seismic data once the CNN model has been trained. The CNN model is found to be relatively robust to small variations from the training dataset. For greater deviations, a larger training dataset would likely be required. If the CNN is trained with a sufficient amount of data, it has the potential of imaging more complex seismic profiles

Analysis of Local Seismic Events near a Large-N Array for Moho Reflections

Local seismic events recorded by the large-N IRIS Community Wavefield Experiment in Oklahoma are used to estimate Moho reflections near the array. For events within 50 km of the center of the array, normal moveout corrections and receiver stacking are applied to identify the PmP and SmS Moho reflections on the vertical and transverse components. Corrections for the reported focal depths are applied to a uniform event depth. To stack signals from multiple events, further static corrections of the envelopes of the Moho reflected arrivals from the individual event stacks are applied. The multiple-event stacks are then used to estimate the pre-critical PmP and SmS arrivals, and an average Poisson\u27s ratio of 1.77±.02 was found for the crust near the array. Using a modified Oklahoma Geological Survey (OGS) velocity model with this Poisson\u27s ratio, the time-to-depth converted PmP and SmS arrivals resulted in a Moho depth of 41±.6 km. The modeling of wide-angle Moho reflections for selected events at epicenter-to-station distances of 90 to 135 km provides additional constraints, and assuming the modified OGS model, a Moho depth of 40±1 km was inferred. The difference between the pre-critical and wide-angle Moho estimates could result from some lateral variability between the array and the wide-angle events. However, both estimates are slightly shallower than the original OGS model Moho depth of 42 km, and this could also result from a somewhat faster lower crust. This study shows that local seismic events, including induced events, can be utilized to estimate properties and structure of the crust, which in turn can be used to better understand the tectonics of a given region. The recording of local seismicity on large-N arrays provides increased lateral phase coherence for the better identification of pre-critical and wide-angle reflected arrivals

Simultaneous Spin-Charge Relaxation in Double Quantum Dots

We investigate phonon-induced spin and charge relaxation mediated by spin-orbit and hyperfine interactions for a single electron confined within a double quantum dot. A simple toy model incorporating both direct decay to the ground state of the double dot and indirect decay via an intermediate excited state yields an electron spin relaxation rate that varies non-monotonically with the detuning between the dots. We confirm this model with experiments performed on a GaAs double dot, demonstrating that the relaxation rate exhibits the expected detuning dependence and can be electrically tuned over several orders of magnitude. Our analysis suggests that spin-orbit mediated relaxation via phonons serves as the dominant mechanism through which the double-dot electron spin-flip rate varies with detuning.Comment: 5 pages, 3 figures, Supplemental Material (2 pages, 2 figures

Universal phase shift and non-exponential decay of driven single-spin oscillations

We study, both theoretically and experimentally, driven Rabi oscillations of a single electron spin coupled to a nuclear spin bath. Due to the long correlation time of the bath, two unusual features are observed in the oscillations. The decay follows a power law, and the oscillations are shifted in phase by a universal value of ~pi/4. These properties are well understood from a theoretical expression that we derive here in the static limit for the nuclear bath. This improved understanding of the coupled electron-nuclear system is important for future experiments using the electron spin as a qubit.Comment: Main text: 4 pages, 3 figures, Supplementary material: 2 pages, 3 figure

Impacts of stratospheric sulfate geoengineering on tropospheric ozone

A range of solar radiation management (SRM) techniques has been proposed to counter anthropogenic climate change. Here, we examine the potential effects of stratospheric sulfate aerosols and solar insolation reduction on tropospheric ozone and ozone at Earth's surface. Ozone is a key air pollutant, which can produce respiratory diseases and crop damage. Using a version of the Community Earth System Model from the National Center for Atmospheric Research that includes comprehensive tropospheric and stratospheric chemistry, we model both stratospheric sulfur injection and solar irradiance reduction schemes, with the aim of achieving equal levels of surface cooling relative to the Representative Concentration Pathway 6.0 scenario. This allows us to compare the impacts of sulfate aerosols and solar dimming on atmospheric ozone concentrations. Despite nearly identical global mean surface temperatures for the two SRM approaches, solar insolation reduction increases global average surface ozone concentrations, while sulfate injection decreases it. A fundamental difference between the two geoengineering schemes is the importance of heterogeneous reactions in the photochemical ozone balance with larger stratospheric sulfate abundance, resulting in increased ozone depletion in mid-A nd high latitudes. This reduces the net transport of stratospheric ozone into the troposphere and thus is a key driver of the overall decrease in surface ozone. At the same time, the change in stratospheric ozone alters the tropospheric photochemical environment due to enhanced ultraviolet radiation. A shared factor among both SRM scenarios is decreased chemical ozone loss due to reduced tropospheric humidity. Under insolation reduction, this is the dominant factor giving rise to the global surface ozone increase. Regionally, both surface ozone increases and decreases are found for both scenarios; that is, SRM would affect regions of the world differently in terms of air pollution. In conclusion, surface ozone and tropospheric chemistry would likely be affected by SRM, but the overall effect is strongly dependent on the SRM scheme. Due to the health and economic impacts of surface ozone, all these impacts should be taken into account in evaluations of possible consequences of SRM

Seismic Interferometry using Seismic Noise from Wind Turbines and other Anthropogenic Sources

We investigate seismic noise from anthropogenic sources, in particular wind turbines, for seismic interferometry. The data is from the 17-station Autocorr Seismic Array located in the Midwestern United States. The array has a linear component that extends about 30 km from north to south and a subarray to the south with a diameter of 10 km. The array was deployed from August 2019 to July 2020, which included the initial months of the Covid-19 pandemic. The northernmost seismic stations of the array are located within the southern end of one of the largest onshore wind farms in the world. To the south of the array there are regularly occurring east-west running trains. However even during times when trains are present, the frequency signatures of the wind turbines are dominant over much of the array, including seismic stations well to the south of the wind farm. Although there is vehicle traffic in the region, time windows in the late evening and early morning were chosen to reduce its effect. Shallow refraction data are available nearby individual seismic stations of the array, and since the spectral peaks do not vary for stations with differing basement depths, they are inferred to be source effects of wind turbines. When utilizing seismic interferometry, coherent Rayleigh wave signals are observed for time windows of seismic noise as short as 15 minutes. There are also concurrent estimates of average hourly wind speeds and wind gusts at the locations of the seismic stations. These data show that for ambient noise correlations, clear south propagating Rayleigh waves are observed for moderate to large average hourly wind speeds. For lower wind speeds, less coherent Rayleigh wave signals are observed in the one-hour ambient noise correlations. For seismic stations within the wind farm, both north and south propagating Rayleigh waves are observed in the correlations. However, for seismic stations to the south of the wind farm, only south propagating waves are observed, which are inferred to be coming from the wind farm