The U.S. Science and Technology Workforce

[Excerpt] In the 21st century, global competition and rapid advances in science and technology will challenge the scientific and technical proficiency of the U.S. workforce. Policymakers often discuss policy actions that could enhance the nation’s science and technology (S&T) workforce— deemed by some as essential to both meet U.S. workforce demands as well as to generate the new ideas that lead to improved and new industries that create jobs. The America COMPETES Act (P.L. 110-69) addresses concerns regarding the S&T workforce and STEM education, and the 111th Congress is debating funding for the programs authorized within it. Policymaker discussions tend to focus on three issues: demographic trends and the future S&T talent pool, the current S&T workforce and changing workforce needs, and the influence of foreign S&T students and workers on the U.S. S&T workforce. Many perspectives exist, however, on the supply and demand of scientists and engineers. Some question the fundamental premise that any action is necessary at all regarding U.S. competitiveness. They question whether or not the S&T workforce and STEM education are problems at all. The first issue of demographic trends and the future S&T talent pool revolves around whether the quality of science, technology, engineering and mathematics (STEM) education received by all Americans at the pre-college level is of sufficient quality that workers are available to satisfy current and future workforce needs. In response, some policymakers propose taking actions to increase the number of Americans interested in the S&T workforce. These policies are motivated by demographic trends that indicate the pool of future workers will be far more diverse than the current STEM workforce. Proposed policies would take actions to enhance the quality of STEM education these Americans receive so they are able to consider S&T careers, and to recruit them into the S&T workforce. The second issue regarding the current S&T workforce and changing workforce needs tend to focus on whether or not the number of Americans pursuing post-secondary STEM degrees is sufficient to meet future workforce needs compared to students in countries considered to be U.S. competitors. The goal of proposed policies responding to this concern to reinvigorate and retrain Americans currently trained in science and engineering who voluntarily or involuntarily are no longer part of the current STEM workforce. The third issue focuses on whether or not the presence of foreign S&T students and workers is necessary to meet the nation’s workforce needs and attract the best and brightest to bring their ideas to the United States, or if the presence of such individuals adversely affects the U.S. S&T students and workers. Policy discussions focus on immigration policy, primarily increasing the ability of foreign STEM students currently in U.S. universities to more easily obtain permanent admission, and increasing the number of temporary worker visas available so more talent from abroad can be recruited to the United States. The challenge facing policymakers when making decisions regarding the S&T workforce is that science, engineering, and economic conditions are constantly changing, both in terms of workforce needs as well as the skills the STEM workforce needs to be marketable relative to demand

An HI Imaging Survey of Asymptotic Giant Branch Stars

We present an imaging study of a sample of eight asymptotic giant branch (AGB) stars in the HI 21-cm line. Using observations from the Very Large Array, we have unambiguously detected HI emission associated with the extended circumstellar envelopes of six of the targets. The detected HI masses range from M_HI ~ 0.015-0.055 M_sun. The HI morphologies and kinematics are diverse, but in all cases appear to be significantly influenced by the interaction between the circumstellar envelope and the surrounding medium. Four stars (RX Lep, Y UMa, Y CVn, and V1942 Sgr) are surrounded by detached HI shells ranging from 0.36 to 0.76 pc across. We interpret these shells as resulting from material entrained in a stellar outflow being abruptly slowed at a termination shock where it meets the local medium. RX Lep and TX Psc, two stars with moderately high space velocities (V_space>56 km/s), exhibit extended gaseous wakes (~0.3 and 0.6 pc in the plane of the sky), trailing their motion through space. The other detected star, R Peg, displays a peculiar "horseshoe-shaped" HI morphology with emission extended on scales up to ~1.7 pc; in this case, the circumstellar debris may have been distorted by transverse flows in the local interstellar medium. We briefly discuss our new results in the context of the entire sample of evolved stars that has been imaged in HI to date.Comment: Accepted to AJ. A version with full resolution figures is available at http://www.haystack.mit.edu/hay/staff/lmatthew/matthews_HI_survey.pd

New Measurements of the Radio Photosphere of Mira based on Data from the JVLA and ALMA

We present new measurements of the millimeter wavelength continuum emission from the long period variable Mira ($o$ Ceti) at frequencies of 46 GHz, 96 GHz, and 229 GHz ($\lambda$~7 mm, 3 mm, and 1 mm) based on observations obtained with the Jansky Very Large Array (JVLA) and the Atacama Large Millimeter/submillimeter Array (ALMA). The measured millimeter flux densities are consistent with a radio photosphere model derived from previous observations, where flux density, $S_{\nu}\propto\nu^{1.86}$. The stellar disk is resolved, and the measurements indicate a decrease in the size of the radio photosphere at higher frequencies, as expected if the opacity decreases at shorter wavelengths. The shape of the radio photosphere is found to be slightly elongated, with a flattening of ~10-20%. The data also reveal evidence for brightness non-uniformities on the surface of Mira at radio wavelengths. Mira's hot companion, Mira B was detected at all three observed wavelengths, and we measure a radius for its radio-emitting surface of $\approx2.0\times10^{13}$ cm. The data presented here highlight the power of the JVLA and ALMA for the study of the atmospheres of evolved stars.Comment: Accepted to ApJ; 27 pages, 7 figure

Galactic Center Youth: Orbits and Origins of the Young Stars in the Central Parsec

We present new proper motions for the massive, young stars at the Galactic Center, based on 10 years of diffraction limited data from the Keck telescopes. Our proper motion measurements now have uncertainties of only 1-2 km/s and allow us to explore the origin of the young stars that reside within the sphere of inflience of the supermassive black hole whose strong tidal forces make this region inhospitable for star formation. Their presence, however, may be explained either by in situ star formation in an accretion disk or as the remnants of a massive stellar cluster which spiraled in via dynamical friction. Earlier stellar velocity vectors were used to postulate that all the young stars resided in two counter-rotating stellar disks, which is consistent with both of the above formation scenarios. Our precise proper motions allow us, for the frst time, to determine the orbital parameters of each individual star and thereby to test the hypothesis that the massive stars reside in two stellar disks. Of the 26 young stars in this study that were previously proposed to lie on the inner, clockwise disk, we find that nearly all exhibit orbital constraints consistent with such a disk. On the other hand, of the 7 stars in this study previously proposed to lie in the outer, less well-defhed counter-clockwise disk, 6 exhibit inclinations that are inconsistent with such a disk, bringing into question the existence of the outer disk. Furthermore, for stars in the inner disk that have eccentricity constraints, we find several that have lower limits to the eccentricity of more than 0.4, implying highly eccentric orbits. This stands in contrast to simple accretion disk formation scenarios which typically predict predominantly circular orbits

Fluxon analogues and dark solitons in linearly coupled Bose-Einstein condensates

Two effectively one-dimensional parallel coupled Bose-Einstein condensates in the presence of external potentials are studied. The system is modelled by linearly coupled Gross-Pitaevskii equations. In particular, grey-soliton-like solutions representing analogues of superconducting Josephson fluxons as well as coupled dark solitons are discussed. Theoretical approximations based on variational formulations are derived. It is found that the presence of a magnetic trap can destabilize the fluxon analogues. However, stabilization is possible by controlling the effective linear coupling between the condensates.Comment: 14 pages, 7 figures, The paper is to appear in Journal of Physics

HI Observations of the Asymptotic Giant Branch Star X Herculis: Discovery of an Extended Circumstellar Wake Superposed on a Compact High-Velocity Cloud

We report HI 21-cm line observations of the AGB star X Her obtained with the Green Bank Telescope (GBT) and the Very Large Array (VLA). We have detected HI emission totaling M_HI=2.1e-03 M_sun associated with the circumstellar envelope of the star. The HI distribution exhibits a head-tail morphology, similar to those previously observed around Mira and RS Cnc. The tail extends ~6.0' (0.24 pc) in the plane of the sky, along the direction of the star's space motion. We also detect a velocity gradient of ~6.5 km/s across the envelope, consistent with the HI tracing a turbulent wake that arises from the motion of a mass-losing star through the ISM. GBT mapping of a 2x2deg region around X Her reveals that the star lies (in projection) near the periphery of a much larger HI cloud that also exhibits signatures of ISM interaction. The properties of the cloud are consistent with those of compact high-velocity clouds. Using CO observations, we have placed an upper limit on its molecular gas content of N_H2<1.3e20 cm^-2. Although the distance to the cloud is poorly constrained, the probability of a chance coincidence in position, velocity, and apparent position angle of space motion between X Her and the cloud is extremely small, suggesting a possible physical association. However, the large HI mass of the cloud (~>2.4~M_sun) and the blueshift of its mean velocity relative to X Her are inconsistent with an origin tied directly to stellar ejection. (abridged)Comment: Accepted to AJ; 47 pages, 15 figures; version with full resolution figures available at http://www.haystack.mit.edu/hay/staff/lmatthew/matthews_XHer.pd