Growth and characterization of materials for tunable lasers in the near infrared spectral region

During this reporting period, work proceeded in two directions. The first was the development of crystal growth procedures for rare earth doped LiYF4 crystals. The procedures for growth and pre-growth treatment of starting materials for undoped LiYF4 crystals were established and good optical quality materials were grown. A significant amount of time was spent trying to establish the optimum growth parameters for Yb(3+)-doped crystals. Unfortunately, it has proven difficult to obtain large size boules of high optical quality crystals of LiYF4 with doping concentrations of Yb(3+) of several percent. Because of these problems, this research is to be changed to attempt doping with other trivalent rare earth ions such as Ho, Er, and Tm. The second research area was investigating the potential of LiNbO3:Mg,Cr and LiNbO3:Mg,Cr,Yb as possible laser materials. The results are summarized

A CRITIQUE OF THE CONSTANT ELASTICITY OF TRANSFORMATION (CET) LINEAR SUPPLY SYSTEM

An elusive restriction maintained in earlier CET supply models with three or more products is shown to result in a potentially serious misspecification. Its impact on empirical estimates is found to be substantial, and an alternative formulation is presented which overcomes the problem while still maintaining the CET hypothesis.Research Methods/ Statistical Methods,

Growth and characterization of tunable solid state lasers in the near infrared spectral region

This research resulted in the publication of two major papers. The major results include the development of improved crystal growth techniques for rare earth-doped LiYF4 crystals and the determination of laser-pumped laser characteristics of Tm:Ho:Y3Al5O12 crystals

The effect of interplanetary trajectory options on a manned Mars aerobrake configuration

Manned Mars missions originating in low Earth orbit (LEO) in the time frame 2010 to 2025 were analyzed to identify preferred mission opportunities and their associated vehicle and trajectory characteristics. Interplanetary and Mars atmospheric trajectory options were examined under the constraints of an initial manned exploration scenario. Two chemically propelled vehicle options were considered: (1) an all propulsive configuration, and (2) a configuration which employs aerobraking at Earth and Mars with low lift/drag (L/D) shapes. Both the interplanetary trajectory options as well as the Mars atmospheric passage are addressed to provide a coupled trajectory simulation. Direct and Venus swingby interplanetary transfers with a 60 day Mars stopover are considered. The range and variation in both Earth and Mars entry velocity are also defined. Two promising mission strategies emerged from the study: (1) a 1.0 to 2.0 year Venus swingby mission, and (2) a 2.0 to 2.5 year direct mission. Through careful trajectory selection, 11 mission opportunities are identified in which the Mars entry velocity is between 6 and 10 km/sec and Earth entry velocity ranges from 11.5 to 12.5 km/sec. Simulation of the Earth return aerobraking maneuver is not performed. It is shown that a low L/D configuration is not feasible for Mars aerobraking without substantial improvements in the interplanetary navigation system. However, even with an advanced navigation system, entry corridor and aerothermal requirements restrict the number of potential mission opportunities. It is also shown that for a large blunt Mars aerobrake configuration, the effects of radiative heating can be significant at entry velocities as low as 6.2 km/sec and will grow to dominate the aerothermal environment at entry velocities above 8.5 km/sec. Despite the additional system complexity associated with an aerobraking vehicle, the use of aerobraking was shown to significantly lower the required initial LEO weight. In comparison with an all propulsive mission, savings between 19 and 59 percent were obtained depending upon launch date

Making BEASTies: dynamical formation of planetary systems around massive stars

Exoplanets display incredible diversity, from planetary system architectures around Sun-like stars that are very different to our Solar System, to planets orbiting post-main sequence stars or stellar remnants. Recently the B-star Exoplanet Abundance STudy (BEAST) reported the discovery of at least two super-Jovian planets orbiting massive stars in the Sco Cen OB association. Whilst such massive stars do have Keplerian discs, it is hard to envisage gas giant planets being able to form in such hostile environments. We use N-body simulations of star-forming regions to show that these systems can instead form from the capture of a free-floating planet, or the direct theft of a planet from one star to another, more massive star. We find that this occurs on average once in the first 10Myr of an association's evolution, and that the semimajor axes of the hitherto confirmed BEAST planets (290 and 556au) are more consistent with capture than theft. Our results lend further credence to the notion that planets on more distant (>100au) orbits may not be orbiting their parent star.Comment: 5 pages, 4 figures, published in MNRAS Letter

Growth and characteristics of materials for tunable lasers in the near infrared spectral region

A method for growing crystals of LiYF4 using an HF pretreatment and purification system is described. In addition, spectrum analyses were performed on eight crystals of type LiNbO3:Mg,Cr,RE, which were grown in order to investigate the use of lithium niobate as a laser host material

Alternate cyclin D1 mRNA splicing modulates P27\u3csup\u3eKlP1\u3c/sup\u3e binding and cell migration

Cyclin D1 is an important cell cycle regulator but in cancer its overexpression also increases cellular migration mediated by p27KlP1 stabilization and RhoA inhibition. Recently, a common polymorphism at the exon 4-intron 4 boundary of the human cyclin D1 gene within a splice donor region was associated with an altered risk of developing cancer. Altered RNA splicing caused by this polymorphism gives rise to a variant cyclin D1 isoform termed cyclin D1b, which has the same N-terminus as the canonical cyclin D1a isoform but a distinct C-terminus. In this study we show that these different isoforms have unique properties with regard to the cellular migration function of cyclin D1. Whereas they displayed little difference in transcriptional co-repression assays on idealized reporter genes, microarray cDNA expression analysis revealed differential regulation of genes including those that influence cellular migration. Additionally, while cyclin D1a stabilized p27KIP1 and inhibited RhoA-induced ROCK kinase activity, promoting cellular migration, cyclin D1b failed to stabilize p27KIP1 or inhibit ROCK kinase activity and had no effect on migration. Our findings argue that alternate splicing is an important determinant of the function of cyclin D1 in cellular migration

Improving Referrals for HIV Care Through Organizational Network Analysis

Context: The link between testing for HIV and obtaining antiretroviral therapy (ART) is central to the HIV/AIDS control strategies of UNAIDS (the “90-90-90” goals) and the International Association of Providers of AIDS Care (“Test and Start”). To ensure that 90% of those diagnosed with HIV/AIDS begin ART and 90% of those on ART achieve viral suppression, service providers not providing all services need to refer patients to other organizations. Setting: Homa Bay, Kenya. Objective: Homa Bay county’s HIV/AIDS prevalence is one of the country’s highest.We identified the organizations providing some aspect of HIV/AIDS care and investigatedways in which theywork together, or do not, to cover the comprehensive needs of those they serve. Design and Participants: We identified 56 organizations and interviewed a representative from each about his or her organization’s services and its connections with the other 55, with particular interest in referrals from sites that test for HIV but do not treat infections to sites that do treat infections. Main Outcome Measure: Referral connections. Results: Referral connections among the 56 in the past 30 dayswere relatively rare, averaging fewer than 2; 13 organizations made no referrals at all. Notably, 5 facilities that test for HIV did not refer their clients to an ART provider. We found 2 distinct clusters of connected organizations: one in Homa Bay Township and the other in Rangwe subcounty. When we convened the organizations and presented our results to them, they expressed interest in establishing better connections and referrals. Conclusions: Homa Bay has an opportunity to improve care for people with HIV/AIDS, in particular ensuring that those testing positive receive treatment, simply by making better use of the services already available. This can be achieved by informing each organization of the services provided by each of the others and by bringing the organizations together to plan and monitor the services’ coordination. These steps could be implemented separately in each of the 2 organizational clusters