Comment on "On an identity for the volume integral of the square of a vector field"

Stewart has provided a position-space derivation of an identity for the volume integral of the square of a vector field that was quoted by Gubarev, Stodolsky and Zakharov. In this comment, I provide a momentum-space derivation of this result, generalized to the scalar product of two complex vector fields. This approach demonstrates the effective use of the Fourier transform technique in the context of vector analysis at a level suitable for undergraduate instruction.Comment: 5 page

Migration and Children\u27s School and Labor: Evidence from El Salvador

This paper examines the impact of parental migration on schooling outcomes for children left behind in El Salvador. Using cross sectional data collected in 2012, outcomes for children are observed for children with migrant parents. The outcomes are also analyzed by gender of the migrant parent who left his or her child behind. Results are observed using instrumental variable estimations, as well as a seemingly unrelated regression to estimate the impact of migration on a child’s time allocation. Outcomes are also analyzed measuring the impact of remittances. Results show that children with at least one migrant parent will complete more years of school. The gender of that migrant parent has no significant impact. Also, parental migration has no significant influence on time allocation, but the presence of remittances in the child’s household does. This paper studies the impact of both migration and remittances on a child’s schooling behavior. Results suggest that the same factors that affect schooling may have a strong correlation with the propensity to migrate as well

The investigation of flow instabilities on a rotating disk with curvature in the radial direction

The major objective is to explore any visible differences of the flow field with wall curvature of the test body, including possible interaction between Taylor-Gortler instabilities present along concave walls and the inflexional instabilities investigated here. An experimental study was conducted with emphasis placed on making visual observations and recording photographically the flow instabilities present under three different rotating bodies: a flat disk, a concave paraboloid, and a convex paraboloid. The data collected for the three test bodies lead to the conclusion that the wall curvature of the concave and convex paraboloids did not alter the observed flow field significantly from that observed on the flat disk

The New Particles in High-Energy Physics: What Do They Mean?

Since the earliest of times man has searched for an underlying unity to the rich diversity observed in nature. That search has taken him from the world of atoms and molecules to the domain of sub-nuclear particles and quarks as powerful accelerators have enabled physicists to probe smaller and smaller distances with higher and higher energies. The last six years have been especially significant in high-energy physics. During this brief period there have been unexpected discoveries of matter described by such whimsical names as \u27\u27charm\u27\u27 and \u27\u27beauty.\u27\u27 These recent developments are reviewed for the purpose of explaining the role which these new particles may play in attempts to identify the fundamental building blocks of matter

Developing benzobisazole-containing conjugated polymers for semiconducting applications

Benzobisazoles are electron deficient moieties whose polymers are known to possess high thermal and mechanical strength. To date, howeverm they have not been well developed for semiconducting applications due to their poor solubility in organic solvents and an inability to functionalize these materials. This thesis describes the synthesis and properties of a variety of new benzobisazole-containing conjugated polymers and reports their performance in organic light-emitting diodes. The new polymers are soluble in common organic solvents and have been synthetically tuned to possess a wide variety of properties by copolymerizing benzobisazole with an assortment of different comonomers. Furthermore, the first examples of benzobisoxazole-containing polymers with backbone connectivity at the 4 and 8-position are reported. This change in connectivity is shown to decrease the optical bandgap of these materials as well as improve their performance in guest-host light-emitting diodes

The New Particles in High-Energy Physics: What Do They Mean?

Since the earliest of times man has searched for an underlying unity to the rich diversity observed in nature. That search has taken him from the world of atoms and molecules to the domain of sub-nuclear particles and quarks as powerful accelerators have enabled physicists to probe smaller and smaller distances with higher and higher energies. The last six years have been especially significant in high-energy physics. During this brief period there have been unexpected discoveries of matter described by such whimsical names as \u27\u27charm\u27\u27 and \u27\u27beauty.\u27\u27 These recent developments are reviewed for the purpose of explaining the role which these new particles may play in attempts to identify the fundamental building blocks of matter

Correcting for bias due to categorisation based on cluster analysis using multiple continuous error-prone exposures

The association between multidimensional exposure patterns and outcomes is commonly investigated by first applying cluster analysis algorithms to derive patterns and then estimating the associations. However, errors in the underlying continuous, possibly skewed, exposure variables lead to misclassified exposure patterns and therefore to biased effect estimates. This is often the case for lifestyle exposures in epidemiology, e.g. for dietary variables measured on daily basis. We introduce three new algorithms for correcting the biased effect estimates, which are based on regression calibration (RC), simulation extrapolation (SIMEX) and multiple imputation (MI). In addition, the naive method ignoring the measurement error structure is considered for comparison. These methods are combined with the k-means cluster algorithm and the Gaussian mixture model to derive exposure patterns. The performance of the correction methods is compared in a simulation study regarding absolute, maximum and relative bias. The simulated data mimic a typical situation in nutritional epidemiology when diet is assessed using repeated 24-hour dietary recalls. Continuous and binary outcomes are considered. Simulation results show, that the correction method based on RC and MI perform better than the naive and the SIMEX-based method. Furthermore, the MI-based approach, which can use outcome information in the error model, is superior to the RC-based approach in most scenarios. Therefore, we recommend using the MI-based approach.Comment: 25 pages, 2 figures; supplementary material attache

Escalera: stairway to better education, evidence from rural Mexico

As a basic input to human capital development, access to quality education remains a significant barrier to growth in most developing countries. Today’s blog looks at evidence of an innovative NGO approach that has been tested in Chiapas, Mexico’s poorest state

Subsonic high-angle-of-attack aerodynamic characteristics of a cone and cylinder with triangular cross sections and a cone with a square cross section

Experiments were conducted in the 12-Foot Pressure Wind Tunnel at Ames Research Center on three models with noncircular cross sections: a cone having a square cross section with rounded corners and a cone and cylinder with triangular cross sections and rounded vertices. The cones were tested with both sharp and blunt noses. Surface pressures and force and moment measurements were obtained over an angle of attack range from 30 deg to 90 deg and selected oil-flow experiments were conducted to visualize surface flow patterns. Unit Reynolds numbers ranged from 0.8x1,000,000/m to 13.0x1,000,000/m at a Mach number of 0.25, except for a few low-Reynolds-number runs at a Mach number of 0.17. Pressure data, as well as force data and oil-flow photographs, reveal that the three dimensional flow structure at angles of attack up to 75 deg is very complex and is highly dependent on nose bluntness and Reynolds number. For angles of attack from 75 deg to 90 deg the sectional aerodynamic characteristics are similar to those of a two dimensional cylinder with the same cross section