Direct Optical Coupling to an Unoccupied Dirac Surface State in the Topological Insulator Bi2_2Se3_3

We characterize the occupied and unoccupied electronic structure of the topological insulator Bi$_2$Se$_3$ by one-photon and two-photon angle-resolved photoemission spectroscopy and slab band structure calculations. We reveal a second, unoccupied Dirac surface state with similar electronic structure and physical origin to the well-known topological surface state. This state is energetically located 1.5 eV above the conduction band, which permits it to be directly excited by the output of a Ti:Sapphire laser. This discovery demonstrates the feasibility of direct ultrafast optical coupling to a topologically protected, spin-textured surface state.Comment: Accepted to Physical Review Letter

Understanding the Nonlinear Dynamics Governing Vertical-Lift Vehicles with Variable-Speed, Fixed Rotors

Problem: Traffic significantly limits travel in urban areas. • The NASA Urban Air Mobility Project is developing an air taxi as an alternative mean of transportation (Fig. 1). Challenge: Operating rotors at different frequencies may cause the cabin to vibrate at high amplitudes. Such effects are currently unknown. Objective: Understand the effect of variable speed rotors on passenger comfort. From the reduced-order modeling simulations, it can be assumed that counteracting the rotor speed in-balances can reduce the displacement and vibrations experienced at the center of the wing. In other words, should a rotor not maintain its optimal operation speed, reducing the motor on the other side of the wing can reduce the vibrations that passengers would experience

Storying Addiction with Youth in Recovery: A Critical Affective Literacies Approach

This qualitative research study analyzes data gathered through a nine-week literacy collective with eight young people at a recovery high school in the US Mountain West region taught by Dan. During the literacy collective, Dan and the youth he worked alongside drew on critical affective literacies and storying practices to analyze the social label addict in an attempt to understand how the label is imbued with power and redefine the meanings associated with the label. This dissertation is framed through affect theory and uses thinking with theory and narrative inquiry as research methods to outline six plateaus of thought. Plateau one creates a new model of addiction by connecting youth’s stories with Newton’s Three Laws of Physics. Plateau two develops an emotional lens of disgust to analyze a social text that attempts to create categories of normativity and non-normativity and then works to marginalize those who fall into the non-normative category. Plateau three develops the idea of metaphors of emergence and then considers how the youth’s metaphors can help shed the social connotations of deviance associated with addiction. Plateau four analyzes a full transcript of one day’s engagement through the process of critical witnessing as a critical affective literacy practice. Plateau five looks at how youth use previous literacy learning to feel with and analyze young adult literature texts about addiction. Plateau six examines embodied literacies of the youth in the literacy collective. Each plateau connects with the research questions that guided this dissertation and provides implications for literacy learning with youth in recovery from addictions

The measured effect magnitude of co-morbidities on burn injury mortality

The ability to better prognosticate burn injury outcome is challenging and historically, most center use the Baux or revised Baux score to help prognosticate burn outcome, however, the weighted contribution of comorbidity on burn mortality has traditionally not been accounted for nor adequately studied. We therefore sought to determine the effect of comorbidities, using the Charlson comorbidity index (CCI) on burn mortality

Key influencing factors of information systems quality and success in Jamaican organizations

Despite major strides in information technology, the Information Systems (IS) community generally continues to suffer fromthe delivery of low quality and failed systems. The situation in the English-speaking Caribbean and in Jamaica in particular,is even more stark because interventions such as software process improvement (SPI) processes are neither well known norused. There is therefore a glaring need to understand the fundamentals of quality determinants in this domain to be able toprovide useful insights for improvement. A recent study has indicated that Jamaican developers are unaware of SPIapproaches and consequently the potential impact and role of process and people on IS quality. We have also included theperception of quality as a probable determinant of the success of even high quality IS. In this research in progress, we havedeveloped and proposed a research model and propositions to explore the impact of process, people and perception on ISquality and success. We hope to use it in Caribbean studies to provide much needed insights

Identifying Key Software Development Practices in the English-Speaking Caribbean Using the Nominal Group Technique

This paper explains how a simplified process improvement framework was developed with practices from the capability maturity model integration (CMMI) model using the nominal group technique (NGT). The NGT was used to generate consensus on key software process improvement practices that are likely to lead to the improvement of the quality of information systems (IS) in the English-speaking Caribbean (ESC). We present the approach taken, the results derived, and the benefits of using this approach. NGT sessions, involving 30 IS professionals were conducted in four ESC territories to reduce and finalize a list of key software development practices that would be more suitable for ESC nations to focus on

Aeroelastic Tailoring of the NASA Common Research Model via Novel Material and Structural Configurations

This work explores the use of tow steered composite laminates, functionally graded metals (FGM), thickness distributions, and curvilinear rib/spar/stringer topologies for aeroelastic tailoring. Parameterized models of the Common Research Model (CRM) wing box have been developed for passive aeroelastic tailoring trade studies. Metrics of interest include the wing weight, the onset of dynamic flutter, and the static aeroelastic stresses. Compared to a baseline structure, the lowest aggregate static wing stresses could be obtained with tow steered skins (47% improvement), and many of these designs could reduce weight as well (up to 14%). For these structures, the trade-off between flutter speed and weight is generally strong, although one case showed both a 100% flutter improvement and a 3.5% weight reduction. Material grading showed no benefit in the skins, but moderate flutter speed improvements (with no weight or stress increase) could be obtained by grading the spars (4.8%) or ribs (3.2%), where the best flutter results were obtained by grading both thickness and material. For the topology work, large weight reductions were obtained by removing an inner spar, and performance was maintained by shifting stringers forward and/or using curvilinear ribs: 5.6% weight reduction, a 13.9% improvement in flutter speed, but a 3.0% increase in stress levels. Flutter resistance was also maintained using straightrotated ribs although the design had a 4.2% lower flutter speed than the curved ribs of similar weight and stress levels were higher. These results will guide the development of a future design optimization scheme established to exploit and combine the individual attributes of these technologies

BAFFLES: Bayesian Ages for Field Lower-mass Stars

Funding: R.D. acknowledges support from the Fonds de Recherche du Québec. Supported by NSF grants AST-1411868 (E.L.N., B.M.), and AST-1518332 (R.J.D.R.). Supported by NASA grants NNX14AJ80G (E.L.N., B.M.), NNX15AC89G and NNX15AD95G (B.M., R.J.D.R.), 80NSSC17K0535 (B.M., E.L.N., R.J.D.R), and NASA Hubble Fellowship grant HST-HF2-51405.001-A (I.C.).Age is a fundamental parameter of stars, yet in many cases, ages of individual stars are presented without robust estimates of the uncertainty. We have developed a Bayesian framework, BAFFLES, to produce the age posterior for a star from its calcium emission strength (log(R′HK)) or lithium abundance (Li EW) and B − V color. We empirically determine the likelihood functions for calcium and lithium as functions of age from literature measurements of stars in benchmark clusters with well-determined ages. We use a uniform prior on age, which reflects a uniform star formation rate. The age posteriors we derive for several test cases are consistent with literature ages found from other methods. BAFFLES represents a robust method to determine the age posterior probability distribution for any field star with 0.45 ≤ B − V ≤ 0.9 and a measurement of R′HK and/or 0.35 ≤ B − V ≤ 1.9 and measured Li EW. We compile colors, R′HK, and Li EW from over 2630 nearby field stars from the literature, and present the derived BAFFLES age posterior for each star.PostprintPeer reviewe

SeaWiFS Technical Report Series

The Sea-viewing Wide Field-of-view Sensor (SeaWiFS) mission will provide operational ocean color that will be superior to the previous Coastal Zone Color Sensor (CZCS) proof-of-concept mission. An algorithm is needed that exploits the full functionality of SeaWiFS whilst remaining compatible in concept with algorithms used for the CZCS. This document describes the theoretical rationale of radiance band-ratio methods for determining chlorophyll-a and other important biogeochemical parameters, and their implementation for the SeaWIFS mission. Pigment interrelationships are examined to explain the success of the CZCS algorithms. In the context where chlorophyll-a absorbs only weakly at 520 nm, the success of the 520 nm to 550 nm CZCS band ratio needs to be explained. This is explained by showing that in pigment data from a range of oceanic provinces chlorophyll-a (absorbing at less than 490 nm), carotenoids (absorbing at greater than 460 nm), and total pigment are highly correlated. Correlations within pigment groups particularly photoprotectant and photosynthetic carotenoids are less robust. The sources of variability in optical data are examined using the NIMBUS Experiment Team (NET) bio-optical data set and bio-optical model. In both the model and NET data, the majority of the variance in the optical data is attributed to variability in pigment (chlorophyll-a), and total particulates, with less than 5% of the variability resulting from pigment assemblage. The relationships between band ratios and chlorophyll is examined analytically, and a new formulation based on a dual hyperbolic model is suggested which gives a better calibration curve than the conventional log-log linear regression fit. The new calibration curve shows the 490:555 ratio is the best single-band ratio and is the recommended CZCS-type pigment algorithm. Using both the model and NET data, a number of multiband algorithms are developed; the best of which is an algorithm based on the 443:555 and 490:555 ratios. From model data, the form of potential algorithms for other products, such as total particulates and dissolved organic matter (DOM), are suggested