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101.
102.
Galarza M De Mesel K Baets R Martínez A Aramburu C López-Amo M 《Applied optics》2003,42(24):4841-4846
We propose a concept for InGaAsP-InP 1.55-microm lasers integrated with spot-size converters based on modal interference between the modes of the structure formed by an active waveguide and an underlying fiber-matched antiresonant reflecting optical waveguide. Simulation results show that the spot-size converters exhibit low transformation loss, and narrowed far-field emission patterns (10 degrees x 20 degrees) and reduce the coupling loss to standard single-mode fibers from 8 to 2.6 dB over lengths approximately 200 microm shorter than the adiabatic concept. A tolerant design to fabrication variations is also proposed, which could be realized by standard processing techniques. 相似文献
103.
The Hydrogeochemistry of Arsenic in
the Clara Mine,Germany 总被引:1,自引:1,他引:0
Yinian?Zhu Broder?J.?MerkelEmail author Ingrid?Stober Kurt?Bucher 《Mine Water and the Environment》2003,22(3):110-117
Abstract.
The oxidative dissolution of primary arsenic-bearing
sulfide minerals in barite-fluorite veins is a potential source
of arsenic in the Clara Mine. Geological structures, especially
the mineral veins, provide potential pathways for the water. The
highest arsenic concentrations are found in ground water within
the eastern part of the mine. Arsenic and major ions are
positively correlated and provide evidence that arsenic is
likely derived locally from the water-vein/water-rock
interaction. Geochemical modeling with PHREEQC shows all the
arsenate mineral phases to be significantly undersaturated,
although secondary arsenate minerals are common in the oxidized
part of the deposit. The mine waters plot near the boundary of
Fe(OH)3 and
Fe2+ in the pH-Eh diagram for the
As-Fe-S-H2O-system. Arsenic occurs as the
5-valent species
and
. Statistical analysis
illustrates a strong association between As, Fe, pH, and
HCO3. Oxidation of the primary As-bearing
minerals, such as pyrite and arsenopyrite, and the subsequent
behavior of the oxyanion, arsenate, generally controls the
distribution and speciation of arsenic. The low concentrations
of dissolved As is due to co-precipitation and adsorption of
arsenate by Fe, Al, and Mn (oxy)hydroxides. 相似文献
104.
Wang Y Metzger K Stephens DN Williams G Brownlie S O'Donnell M 《IEEE transactions on ultrasonics, ferroelectrics, and frequency control》2003,50(7):805-823
In this paper, a scheme called coded excitation with spectrum inversion (CEXSI) is presented. An established optimal binary code whose spectrum has no s and possesses the least variation is encoded as a burst for transmission. Using this optimal code, the decoding filter can be derived directly from its inverse spectrum. Various transmission techniques can be used to improve energy coupling within the system pass-band. We demonstrate its potential to achieve excellent decoding with very low (<80 dB) side-lobes. For a 2.6 /spl mu/s code, an array element with a center frequency of 10 MHz and fractional bandwidth of 38%, range side-lobes of about 40 dB have been achieved experimentally with little compromise in range resolution. The signal-to-noise ratio (SNR) improvement also has been characterized at about 14 dB. Along with simulations and experimental data, we present a formulation of the scheme, according to which CEXSI can be extended to improve SNR in sparse array imaging in general. 相似文献
105.
Sepiolite of Turkish origin was used as Si precursor in the syntheses of silicon nitride (Si3N4) powders by carbothermal reduction-nitridation (CRN) by mixing with several reducing agents i.e. charcoal, carbon black and petroleum coke as discrete particles and acrylonitrile as an intercalation medium. Purified sepiolite samples with a pre-determined C/SiO2 ratio of 4 yielded Si3N4 powders after firing at temperatures 1300–1475°C under continuous nitrogen flow. The various sepiolite-reducing agent combinations were evaluated. The / ratio and secondary phase content of the powders after CRN were found to depend on temperature, time, heating rate and on the physicochemical properties of the precursor used such as, surface area and mixing of the reactants. 相似文献
106.
Sepiolite-PAN intercalation used as Si3N4 forming precursor 总被引:2,自引:0,他引:2
Silicon nitride (Si3N4) formation was investigated using sepiolite and polyacrylonitrile as silicon and carbon source, respectively. It was found that purified sepiolite could readily adsorb a sufficient amount of acrylonitrile (AN) reagent without pre-treatment. Polymerisation of sepiolite-AN mixtures and subsequent cyclization of the polymerised complex yielded a precursor, which was found ideal as a starting material in carbothermal reduction-nitridation (CRN) for the formation of silicon nitride powders. The quantity of silicon nitride, grain size and morphology were found to be dependent on the reaction conditions and starting reagent. Fine grain size, high surface area (up to approx. 12.4 m2/g) powders of mainly -Si3N4 were obtained via pyrolysis of sepiolite-PAN complex after 4 h heating at 1400°C in 1000 ml/min nitrogen flow with a heating rate of 300°C/h. Mg retained in the molecular structure of the mineral must have promoted the formation of -grains in CRN process. 相似文献
107.
Cory J. Rupp Anton Evgrafov Kurt Maute Martin L. Dunn 《Structural and Multidisciplinary Optimization》2007,34(2):111-121
We develop a topology optimization approach to design two- and three-dimensional phononic (elastic) materials, focusing primarily
on surface wave filters and waveguides. These utilize propagation modes that transmit elastic waves where the energy is contained
near a free surface of a material. The design of surface wave devices is particularly attractive given recent advances in
nano- and micromanufacturing processes, such as thin-film deposition, etching, and lithography, which make it possible to
precisely place thin film materials on a substrate with submicron feature resolution. We apply our topology optimization approach
to a series of three problems where the layout of two materials (silicon and aluminum) is sought to achieve a prescribed objective:
(1) a grating to filter bulk waves of a prescribed frequency in two and three dimensions, (2) a surface wave device that uses
a patterned thin film to filter waves of a single or range of frequencies, and (3) a fully three-dimensional structure to
guide a wave generated by a harmonic input on a free surface to a specified output port on the surface. From the first to
the third example, the resulting topologies increase in sophistication. The results demonstrate the power and promise of our
computational framework to design sophisticated surface wave devices. 相似文献
108.
This paper proposes a system architecture, related design approaches for autonomous mobile systems and guidelines for self-sufficient autonomy. Development of a tiered layout for a hybrid-state control in a series of stages as well as the integration of such a controller in the overall autonomy structure are proposed and demonstrated as part of multiple examples, including The Ohio State University participation in DARPA Urban Challenge 2007. The hierarchical layout and the iterative design methodology enable a certain level of design flexibility for the overall system and preparation for various contingencies, as illustrated on specific development cycles. 相似文献
109.
Location-based applications such as Facebook Places, Foursquare, or Loopt typically use location services to manage mobile object positions. However, exposing precise user positions raises user privacy concerns, especially if location service providers are not fully trusted. To enable the secure management of private user positions in non-trusted systems, we present two novel position sharing approaches based on the concept of multi-secret sharing. We improve existing geometric position sharing approaches by Dürr et al. [2] and Skvortsov et al. [3] by considering continuous position updates and by increasing the robustness against various attacks. Furthermore, we present the first position sharing approach for symbolic location models. 相似文献
110.
Michel A Junger A Benson M Brammen DG Hempelmann G Dudeck J Marquardt K 《Computer methods and programs in biomedicine》2003,70(1):71-79
The major intent of this article was to describe the design principles of the drug-therapy documentation module of the Patient Data Management System (PDMS) ICUData, in routine use at the intensive care unit (ICU) of the Department of Anesthesiology and Intensive Care Medicine at the University Hospital of Giessen, Germany, since February 1999. The new drug management system has been in routine use since March 2000. Until 8 January 2001, 1140 patients have been documented using this approach. It could be demonstrated that it was possible to transform the formerly unstructured text-based documentation into a detailed and structured model. The mediated benefit resulted in the automatic calculation of fluid balance. Further, detailed statistical analyses of therapeutic behavior in drug administration are now possible. 相似文献