203,892 research outputs found
Stem-root flow effect on soilâatmosphere interactions and uncertainty assessments
Abstract. Soil water can rapidly enter deeper layers via vertical redistribution of soil water through the stemâroot flow mechanism. This study develops the stemâroot flow parameterization scheme and coupled this scheme with the Simplified Simple Biosphere model (SSiB) to analyze its effects on landâatmospheric interactions. The SSiB model was tested in a single column mode using the Lien Hua Chih (LHC) measurements conducted in Taiwan and HAPEX-Mobilhy (HAPEX) measurements in France. The results show that stemâroot flow generally caused a decrease in the moisture content at the top soil layer and moistened the deeper soil layers. Such soil moisture redistribution results in significant changes in heat flux exchange between land and atmosphere. In the humid environment at LHC, the stemâroot flow effect on transpiration was minimal, and the main influence on energy flux was through reduced soil evaporation that led to higher soil temperature and greater sensible heat flux. In the Mediterranean environment of HAPEX, the stemâroot flow significantly affected plant transpiration and soil evaporation, as well as associated changes in canopy and soil temperatures. However, the effect on transpiration could either be positive or negative depending on the relative changes in the moisture content of the top soil vs. deeper soil layers due to stemâroot flow and soil moisture diffusion processes
A general multiblock Euler code for propulsion integration. Volume 1: Theory document
A general multiblock Euler solver was developed for the analysis of flow fields over geometrically complex configurations either in free air or in a wind tunnel. In this approach, the external space around a complex configuration was divided into a number of topologically simple blocks, so that surface-fitted grids and an efficient flow solution algorithm could be easily applied in each block. The computational grid in each block is generated using a combination of algebraic and elliptic methods. A grid generation/flow solver interface program was developed to facilitate the establishment of block-to-block relations and the boundary conditions for each block. The flow solver utilizes a finite volume formulation and an explicit time stepping scheme to solve the Euler equations. A multiblock version of the multigrid method was developed to accelerate the convergence of the calculations. The generality of the method was demonstrated through the analysis of two complex configurations at various flow conditions. Results were compared to available test data. Two accompanying volumes, user manuals for the preparation of multi-block grids (vol. 2) and for the Euler flow solver (vol. 3), provide information on input data format and program execution
A general multiblock Euler code for propulsion integration. Volume 3: User guide for the Euler code
This manual explains the procedures for using the general multiblock Euler (GMBE) code developed under NASA contract NAS1-18703. The code was developed for the aerodynamic analysis of geometrically complex configurations in either free air or wind tunnel environments (vol. 1). The complete flow field is divided into a number of topologically simple blocks within each of which surface fitted grids and efficient flow solution algorithms can easily be constructed. The multiblock field grid is generated with the BCON procedure described in volume 2. The GMBE utilizes a finite volume formulation with an explicit time stepping scheme to solve the Euler equations. A multiblock version of the multigrid method was developed to accelerate the convergence of the calculations. This user guide provides information on the GMBE code, including input data preparations with sample input files and a sample Unix script for program execution in the UNICOS environment
Direct measurement of the electron density of extended femtosecond laser pulse-induced filaments
We present direct time- and space- resolved measurements of the electron
density of femtosecond laser pulse-induced plasma filaments. The dominant
nonlinearity responsible for extended atmospheric filaments is shown to be
field-induced rotation of air molecules.Comment: 12 pages, 5 figure
An Improved NSGA-II and its Application for Reconfigurable Pixel Antenna Design
Based on the elitist non-dominated sorting genetic algorithm (NSGA-II) for multi-objective optimization problems, an improved scheme with self-adaptive crossover and mutation operators is proposed to obtain good optimization performance in this paper. The performance of the improved NSGA-II is demonstrated with a set of test functions and metrics taken from the standard literature on multi-objective optimization. Combined with the HFSS solver, one pixel antenna with reconfigurable radiation patterns, which can steer its beam into six different directions (ΞDOA = ± 15°, ± 30°, ± 50°) with a 5 % overlapping impedance bandwidth (S11 < â 10 dB) and a realized gain over 6 dB, is designed by the proposed self-adaptive NSGA-II
Asteroseismology of the Scuti star HD 50844
Aims. We aim to probe the internal structure and investigate more detailed
information of the Scuti star HD 50844 with asteroseismology. Methods.
We analyse the observed frequencies of the Scuti star HD 50844
obtained by Balona (2014), and search for possible multiplets based on the
rotational splitting law of g-mode. We tried to disentangle the frequency
spectra of HD 50844 by means of the rotational splitting only. We then compare
them with theoretical pulsation modes, which correspond to stellar evolutionary
models with various sets of initial metallicity and stellar mass, to find the
best-fitting model. Results. There are three multiplets including two complete
triplets and one incomplete quintuplet, in which mode identifications for
spherical harmonic degree and azimuthal number are unique. The
corresponding rotational period of HD 50844 is found to be
2.44 days. The physical parameters of HD 50844 are well
limited in a small region by three modes identified as nonradial ones
(, , and ) and by the fundamental radial mode
(). Our results show that the three nonradial modes (, ,
and ) are all mixed modes, which mainly represent the property of the
helium core. The fundamental radial mode () mainly represents the
property of the stellar envelope. In order to fit these four pulsation modes,
both the helium core and the stellar envelope must be matched to the actual
structure of HD 50844. Finally, the mass of the helium core of HD 50844 is
estimated to be 0.173 0.004 for the first time. The physical
parameters of HD 50844 are determined to be 1.81 0.01 ,
0.008 0.001. 7508 125 K, log 3.658
0.004, 3.300 0.023 , 30.98 2.39 .Comment: 11 pages, 7 figures, 6 tables, accepted for publication in A&
Double-active-layer index-guided InGaAsP-InP laser diode
A buried crescent InGaAsP-InP laser with two active layers was fabricated to study the temperature behavior of the double-carrier-confinement structure. An anomalously high characteristic temperature T0 was measured, and optical switching behavior was observed. A mode analysis and numerical calculation using a rate equation approach explained qualitatively very well the experimental results. It was revealed that both the Auger recombination in this special double-active-layer configuration and the temperature-dependent leakage current, which leads to uniform carrier distribution in both active regions, are essential to increase T0
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Studying RFID adoption by SMES in the Taiwanese IT industry
With the advent of Radio Frequency Identification (RFID), organisations have the opportunity to rethink how their organisation will operate and integrate in the supply chain. Especially for Small to Medium Sized Enterprises (SMEs), that they have limited resources adopting such an innovative technology (i.e. RFID) can be daunting. Literature indicates that SMEs that deal with implementation have so far only a few guidelines regarding specific opportunities and risks. This research is therefore trying to fill the gap by employing Exploratory Factor Analysis (EFA) techniques and utilising a questionnaire survey with the aim of exploring the factors that affect SMEsâ RFID adoption in the Taiwan Information Technology (IT) manufacturing industry. In doing so, the adoption factors which are classified into 3 different adopters categories named ready adopter (cost and management), initiator adopter (competitiveness and process efficiency) and unprepared adopter (IT management difficulties, IT implementation difficulties and cost of implementation) using EFA technique. A SMEs RFID adoption model is then proposed. It is anticipated that the findings of this research will not only enhance the research in RFID adoption in SMEs, but can also act as a reference for practitioners in the industry and researchers in the academic field
Range-Free Localization with the Radical Line
Due to hardware and computational constraints, wireless sensor networks
(WSNs) normally do not take measurements of time-of-arrival or
time-difference-of-arrival for rangebased localization. Instead, WSNs in some
applications use rangefree localization for simple but less accurate
determination of sensor positions. A well-known algorithm for this purpose is
the centroid algorithm. This paper presents a range-free localization technique
based on the radical line of intersecting circles. This technique provides
greater accuracy than the centroid algorithm, at the expense of a slight
increase in computational load. Simulation results show that for the scenarios
studied, the radical line method can give an approximately 2 to 30% increase in
accuracy over the centroid algorithm, depending on whether or not the anchors
have identical ranges, and on the value of DOI.Comment: Proc. IEEE ICC'10, Cape Town, South Africa, May, 201
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