Kolmogorov and scalar spectral regimes in numerical turbulence

Velocity and passive-scalar spectra for turbulent fields generated by a forced three-dimensional simulation and Taylormicroscale Reynolds numbers up to 83 are shown to have distinct spectral regimes, including a Kolmogorov inertial subrange. Both one- and three-dimensional spectra are shown for comparison with experiment and theory, respectively. When normalized by the Kolmogorov dissipation scales velocity spectra collapse to a single curve and a high-wavenumber bulge is seen. The bulge leads to an artificially high Kolmogorov constant, but is consistent with recent measurements of the velocity spectrum in the dissipation regime and the velocity-derivative skewness. Scalar spectra, when normalized by the Oboukov-Corrsin scales, collapse to curves which depend only on Prandtl number and show a universal inertial-convective subrange, independent of Prandtl number. When normalized by the Batchelor scales, the scalar spectra show a universal dissipation regime which is independent of Prandtl numbers from 0.1 to 1.0. The time development of velocity spectra is illustrated by energy-transfer spectra in which distinct pulses propagate to high wavenumbers

U.S. ethnic scientists and entrepreneurs

Immigrants are exceptionally important for U.S. technology development, accounting for almost half of the country’s Ph.D. workforce in science and engineering. Most notably, the contribution of Chinese and Indian scientists and entrepreneurs in U.S. high-technology sectors increased dramatically in the 1990s. These ethnic scientific communities in the United States further help transfer new technologies back to their home countries.Immigrants ; Technological innovations

The Agglomeration of US Ethnic Inventors

The ethnic composition of US inventors is undergoing a significant transformation - with deep impacts for the overall agglomeration of US innovation. This study applies an ethnic-name database to individual US patent records to explore these trends with greater detail. The contributions of Chinese and Indian scientists and engineers to US technology formation increase dramatically in the 1990s. At the same time, these ethnic inventors became more spatially concentrated across US cities. The combination of these two factors helps stop and reverse long-term declines in overall inventor agglomeration evident in the 1970s and 1980s. The heightened ethnic agglomeration is particularly evident in industry patents for high-tech sectors, and similar trends are not found in institutions constrained from agglomerating (e.g., universities, government).Agglomeration, Innovation, Research and Development, Patents, Scientists, Engineers, Inventors, Ethnicity, Immigration.

On signal and noise level estimation in a coherent PCM channel

Joint maximum likelihood estimates for signal amplitude and noise power density in coherent pulse code modulation channel with white Gaussian noise and correlation receive

Higher-order derivative correlations and the alignment of small-scale structures in isotropic numerical turbulence

In a three dimensional simulation higher order derivative correlations, including skewness and flatness factors, are calculated for velocity and passive scalar fields and are compared with structures in the flow. The equations are forced to maintain steady state turbulence and collect statistics. It is found that the scalar derivative flatness increases much faster with Reynolds number than the velocity derivative flatness, and the velocity and mixed derivative skewness do not increase with Reynolds number. Separate exponents are found for the various fourth order velocity derivative correlations, with the vorticity flatness exponent the largest. Three dimensional graphics show strong alignment between the vorticity, rate of strain, and scalar-gradient fields. The vorticity is concentrated in tubes with the scalar gradient and the largest principal rate of strain aligned perpendicular to the tubes. Velocity spectra, in Kolmogorov variables, collapse to a single curve and a short minus 5/3 spectral regime is observed

Ethnic Scientific Communities and International Technology Diffusion

This study explores the importance of knowledge transfer for international technology diffusion by examining ethnic scientific and entrepreneurial communities in the US and their ties to their home countries. US ethnic research communities are quantified by applying an ethnic-name database to individual patent records. International patent citations con.rm knowledge diffuses through ethnic networks, and manufacturing output in foreign countries increases with an elasticity of 0.1-0.3 to stronger scientific integration with the US frontier. To address reverse-causality concerns, reduced-form specifications exploit exogenous changes in US immigration quotas. Consistent with a model of sector reallocation, output growth in less developed economies is facilitated by employment gains, while more advanced economies experience sharper increases in labor productivity. The ethnic transfer mechanism is especially strong in high-tech industries and among Chinese economies. The findings suggest channels for transferring codified and tacit knowledge partly shape the effective technology frontiers of developing and emerging economies.Technology Transfer, Tacit Knowledge, Productivity, Patents, Innovation, Research and Development, Entrepreneurship, Immigration, Networks.

Breakthrough Inventions and Migrating Clusters of Innovation

We investigate the speed at which clusters of invention for a technology migrate spatially following breakthrough inventions. We identify breakthrough inventions as the top one percent of US inventions for a technology during 1975-1984 in terms of subsequent citations. Patenting growth is significantly higher in cities and technologies where breakthrough inventions occur after 1984 relative to peer locations that do not experience breakthrough inventions. This growth differential in turn depends on the mobility of the technology's labor force, which we model through the extent that technologies depend upon immigrant scientists and engineers. Spatial adjustments are faster for technologies that depend heavily on immigrant inventors. The results qualitatively con.rm the mechanism of industry migration proposed in models like [Duranton, G., 2007. Urban evolutions: The fast, the slow, and the still. American Economic Review 97, 197.221].Agglomeration, Clusters, Entrepreneurship, Invention, Mobility, Reallocation, R&D, Patents, Scientists, Engineers, Immigration.