All-fiber optical supercontinuum sources in 1.7-3.2 μm range

We report supercontinuum generation in the 1.7-2.9 μm range with up to 3.08 W of output power and in the range of 1.93-3.18 μm with up to 3.8 W of output power from all-fiber MOPA pulsed systems with Tm-doped fiber mode-locked seed laser. Supercontinuum generation was demonstrated in nonlinear germanate fibers and fluoride (ZBLAN) fibers. The supercontinuum bandwidth reached 1250 nm at -10 dB level

Unsteady Aerodynamic Modeling in Roll for the NASA Generic Transport Model

Reducing the impact of loss-of-control conditions on commercial transport aircraft is a primary goal of the NASA Aviation Safety Program. One aspect in developing the supporting technologies is to improve the aerodynamic models that represent these adverse conditions. Aerodynamic models appropriate for loss of control conditions require a more general mathematical representation to predict nonlinear unsteady behaviors. In this paper, a more general mathematical model is proposed for the subscale NASA Generic Transport Model (GTM) that covers both low and high angles of attack. Particular attention is devoted to the stall region where full-scale transports have demonstrated a tendency for roll instability. The complete aerodynamic model was estimated from dynamic wind-tunnel data. Advanced computational methods are used to improve understanding and visualize the flow physics within the region where roll instability is a factor

YDFL operating in 1150-1200-nm spectral domain

A family of high-power Yb-doped fiber lasers operated in the range of 1150-1180 nm with output powers of up to 35 W and optical efficiencies up to 60% is realized. Operation at 1200 nm is also demonstrated. Amplified spontaneous emission increase with output power increase is analyzed in frames of the inhomogeneous broadening concept

Nonlinear Unsteady Aerodynamic Modeling Using Wind Tunnel and Computational Data

Extensions to conventional aircraft aerodynamic models are required to adequately predict responses when nonlinear unsteady flight regimes are encountered, especially at high incidence angles and under maneuvering conditions. For a number of reasons, such as loss of control, both military and civilian aircraft may extend beyond normal and benign aerodynamic flight conditions. In addition, military applications may require controlled flight beyond the normal envelope, and civilian flight may require adequate recovery or prevention methods from these adverse conditions. These requirements have led to the development of more general aerodynamic modeling methods and provided impetus for researchers to improve both techniques and the degree of collaboration between analytical and experimental research efforts. In addition to more general mathematical model structures, dynamic test methods have been designed to provide sufficient information to allow model identification. This paper summarizes research to develop a modeling methodology appropriate for modeling aircraft aerodynamics that include nonlinear unsteady behaviors using both experimental and computational test methods. This work was done at Langley Research Center, primarily under the NASA Aviation Safety Program, to address aircraft loss of control, prevention, and recovery aerodynamics

System Identification Applied to Dynamic CFD Simulation and Wind Tunnel Data

Demanding aerodynamic modeling requirements for military and civilian aircraft have provided impetus for researchers to improve computational and experimental techniques. Model validation is a key component for these research endeavors so this study is an initial effort to extend conventional time history comparisons by comparing model parameter estimates and their standard errors using system identification methods. An aerodynamic model of an aircraft performing one-degree-of-freedom roll oscillatory motion about its body axes is developed. The model includes linear aerodynamics and deficiency function parameters characterizing an unsteady effect. For estimation of unknown parameters two techniques, harmonic analysis and two-step linear regression, were applied to roll-oscillatory wind tunnel data and to computational fluid dynamics (CFD) simulated data. The model used for this study is a highly swept wing unmanned aerial combat vehicle. Differences in response prediction, parameters estimates, and standard errors are compared and discusse

Globalization and E-Commerce VII: Environment and Policy in the U.S.

The United States is a global leader in both Business-to-Customer (B2C) and Business-to-Business (B2B) electronic commerce. This leadership comes in part from the historical US strengths in information technology, telecommunications, financial services, and transportation - all of which are essential enabling components of e-commerce. The size and strength of the US economy, the wealth of its consumer base, and the relatively open access to venture capital creates an attractive environment for e-commerce investment. Official US Government policy toward e-commerce is to let the private sector take the lead, with government helping to make the business climate right for innovation and investment. Prior US Government investments in essential e-commerce infrastructure for military purposes (e.g., digital computing, the Internet) and for civilian purposes (e.g., interstate highways, air transport) played an important role in the US lead in e-commerce. US Government policies favoring widespread economic liberalization since the 1970\u27s in areas such as financial services, transportation, and telecommunications helped enable and stimulate private sector investment and innovation in e-commerce. The collapse of the dot.com era in the late 1990\u27s hit key sectors of e-commerce hard, suggesting that some of the more dramatic and positive predictions of e-commerce growth and impact will either be delayed substantially or will not come to pass. The strength of surviving e-commerce companies (e.g., Amazon and eBay), as well as the relative stability of the technology sector (e.g., Cisco Systems, Dell, Intel, IBM) and the continued investment of large industry sectors (e.g., autos, finance) suggest that e-commerce is still growing and is here to stay. Consumers are intrigued by B2C e-commerce, and many have used such services, but serious concerns related to privacy and transaction security remain obstacles to universal adoption of B2C e-commerce

Flat-top supercontinuum and tunable femtosecond fiber laser sources at 1.9-2.5 μm

We report the high-energy flat-top supercontinuum covering the mid-infrared wavelength range of 1.9-2.5 μm as well as electronically tunable femtosecond pulses between 1.98-2.22 μm directly from the thulium-doped fiber laser amplifier. Comparison of experimental results with numerical simulations confirms that both sources employ the same nonlinear optical mechanism - Raman soliton frequency shift occurring inside the Tm-fiber amplifier. To illustrate that, we investigate two versions of the compact diode-pumped SESAM mode-locked femtosecond thulium-doped all-silica-fiber-based laser system providing either broadband supercontinuum or tunable Raman soliton output, depending on the parameters of the system. The first system operates in the Raman soliton regime providing femtosecond pulses tunable between 1.98-2.22 μm. Wide and continuous spectral tunability over 240 nm was realized by changing only the amplifier pump diode current. The second system generates high-energy supercontinuum with the superior spectral flatness of better than 1 dB covering the wavelength range of 1.9-2.5 μm, with the total output energy as high as 0.284 μJ, the average power of 2.1 W at 7.5 MHz repetition rate. We simulate the amplifier operation in the Raman soliton self-frequency shift regime and discuss the role of induced Raman scattering in supercontinuum formation inside the fiber amplifier. We compare this system with a more traditional 1.85-2.53 μm supercontinuum source in the external highly-nonlinear commercial chalcogenide fiber using the Raman soliton MOPA as an excitation source. The reported systems1 can be readily applied to a number of industrial applications in the mid-IR, including sensing, stand-off detection, medical surgery and fine material processing

Diffusion and Impacts of E-Commerce in the United States of America: Results from an Industry Survey

The paper provides baseline conditions of U.S. e-commerce in the post-dot.com era. The article examines the key factors that act as determinants of e-commerce diffusion. It is based on qualitative analysis of U.S. industry survey data, matched to a similar data and analyses from other countries. It presents data taken from one of the most comprehensive sample surveys of U.S. firm activity in e-commerce. The paper analyzes differences among three industry sectors, and between small/medium and large firms using both qualitative interpretations and direct observations from the survey data, as well as use of structural equation modeling of e-commerce diffusion and impacts. Some differences in e-commerce orientation and experience were found across the three industry sectors studied in the survey. These differences are related largely to the nature of the tasks done in the respective industries, and to prior industry-level investment and learning related to e-commerce. There were also differences found in e-commerce attitudes and experience between small/medium sized enterprises (SMEs) and large establishments. Only modest differences were found between U.S. and non-U.S. establishments. Quantitative analysis revealed significant regression relationships with their level of statistical significance. Results show that e-commerce adoption is path dependent (i.e., establishments follow earlier investment patterns), and that each industry\u27s market and institutional context play a significant role in adoption

An Efficient and Continuous Voronoi Density Estimator

We introduce a non-parametric density estimator deemed Radial Voronoi Density Estimator (RVDE). RVDE is grounded in the geometry of Voronoi tessellations and as such benefits from local geometric adaptiveness and broad convergence properties. Due to its radial definition RVDE is moreover continuous and computable in linear time with respect to the dataset size. This amends for the main shortcomings of previously studied VDEs, which are highly discontinuous and computationally expensive. We provide a theoretical study of the modes of RVDE as well as an empirical investigation of its performance on high-dimensional data. Results show that RVDE outperforms other non-parametric density estimators, including recently introduced VDEs.Comment: 12 page

A review of trauma and orthopaedic randomised clinical trials published in high-impact general medical journals

Acknowledgements The authors are grateful for Shaun Treweek for his expert insight into the nuances of Randomised Clinical Trial design. Funding The authors did not receive support from any organisation for the submitted work.Peer reviewedPublisher PD