319 research outputs found
Cutting and Welding of High-Strength Steels Using Non-Vacuum Electron Beam as a Universal Tool for Material Processing
Using a non-vacuum electron beam, a two-step process chain for plate materials is a feasible possibility. Cutting and welding can be performed in subsequent steps on the same machine for a highly productive process chain. The electron beam is a tool with high energy conversion efficiency, which is largely independent of the type of metal. Its high power density qualifies the non-vacuum electron beam as an outstanding energy source for the well-known NVEB welding as well as for high-speed cutting. Welding is possible with or without filler wire or shielding gas, depending on the application. The NVEB-cutting process employs a co-moving cutting head with a sliding seal for extremely high cutting speeds producing high quality edges. Due to direct removal of fumes and dust, NVEBC with local suction is an exceptionally clean and fast process. The NVEB welding process is possible directly after cutting, without further edge preparation. The potential directions of development of non-vacuum electron beam technologies are discussed. An exemplary two-step process chain using high-strength steel is presented to highlight possible application in industries such as general steel construction, automotive, shipbuilding, railway vehicle or crane construction. An analysis of the mechanical properties of the resulting weld seam is presented
Spectroscopic properties of a two-level atom interacting with a complex spherical nanoshell
Frequency shifts, radiative decay rates, the Ohmic loss contribution to the
nonradiative decay rates, fluorescence yields, and photobleaching of a
two-level atom radiating anywhere inside or outside a complex spherical
nanoshell, i.e. a stratified sphere consisting of alternating silica and gold
concentric spherical shells, are studied. The changes in the spectroscopic
properties of an atom interacting with complex nanoshells are significantly
enhanced, often more than two orders of magnitude, compared to the same atom
interacting with a homogeneous dielectric sphere. The detected fluorescence
intensity can be enhanced by 5 or more orders of magnitude. The changes
strongly depend on the nanoshell parameters and the atom position. When an atom
approaches a metal shell, decay rates are strongly enhanced yet fluorescence
exhibits a well-known quenching. Rather contra-intuitively, the Ohmic loss
contribution to the nonradiative decay rates for an atomic dipole within the
silica core of larger nanoshells may be decreasing when the silica core - inner
gold shell interface is approached. The quasistatic result that the radial
frequency shift in a close proximity of a spherical shell interface is
approximately twice as large as the tangential frequency shift appears to apply
also for complex nanoshells. Significantly modified spectroscopic properties
(see computer program (pending publication of this manuscript) freely available
at http://www.wave-scattering.com) can be observed in a broad band comprising
all (nonresonant) optical and near-infrared wavelengths.Comment: 20 pages plus 63 references and 11 figures, plain LaTex, for more
information see http://www.wave-scattering.com (color of D sphere in figures
2-6 altered, minor typos corrected.
Flux and Seasonality of Dissolved Organic Matter From the Northern Dvina (Severnaya Dvina) River, Russia
PanâArctic riverine dissolved organic carbon (DOC) fluxes represent a major transfer of carbon from landâtoâocean, and past scaling estimates have been predominantly derived from the six major Arctic rivers. However, smaller watersheds are constrained to northern highâlatitude regions and, particularly with respect to the Eurasian Arctic, have received little attention. In this study, we evaluated the concentration of DOC and composition of dissolved organic matter (DOM) via optical parameters, biomarkers (lignin phenols), and ultrahigh resolution mass spectrometry in the Northern Dvina River (a midsized highâlatitude constrained river). Elevated DOC, lignin concentrations, and aromatic DOM indicators were observed throughout the year in comparison to the major Arctic rivers with seasonality exhibiting a clear spring freshet and also some years a secondary pulse in the autumn concurrent with the onset of freezing. Chromophoric DOM absorbance at a350 was strongly correlated to DOC and lignin across the hydrograph; however, the relationships did not fit previous models derived from the six major Arctic rivers. Updated DOC and lignin fluxes were derived for the panâArctic watershed by scaling from the Northern Dvina resulting in increased DOC and lignin fluxes (50 Tg yrâ1 and 216 Gg yrâ1, respectively) compared to past estimates. This leads to a reduction in the residence time for terrestrial carbon in the Arctic Ocean (0.5 to 1.8 years). These findings suggest that constrained northern highâlatitude rivers are underrepresented in models of fluxes based from the six largest Arctic rivers with important ramifications for the export and fate of terrestrial carbon in the Arctic Ocean
Resolving the positions of defects in superconducting quantum bits
Solid-state quantum coherent devices are quickly progressing. Superconducting circuits, for instance, have already been used to demonstrate prototype quantum processors comprising a few tens of quantum bits. This development also revealed that a major part of decoherence and energy loss in such devices originates from a bath of parasitic material defects. However, neither the microscopic structure of defects nor the mechanisms by which they emerge during sample fabrication are understood. Here, we present a technique to obtain information on locations of defects relative to the thin film edge of the qubit circuit. Resonance frequencies of defects are tuned by exposing the qubit sample to electric fields generated by electrodes surrounding the chip. By determining the defectâs coupling strength to each electrode and comparing it to a simulation of the field distribution, we obtain the probability at which location and at which interface the defect resides. This method is applicable to already existing samples of various qubit types, without further on-chip design changes. It provides a valuable tool for improving the material quality and nano-fabrication procedures towards more coherent quantum circuits
Resolving the positions of defects in superconducting quantum bits
Solid-state quantum coherent devices are quickly progressing. Superconducting
circuits, for instance, have already been used to demonstrate prototype quantum
processors comprising a few tens of quantum bits. This development also
revealed that a major part of decoherence and energy loss in such devices
originates from a bath of parasitic material defects. However, neither the
microscopic structure of defects nor the mechanisms by which they emerge during
sample fabrication are understood. Here, we present a technique to obtain
information on locations of defects relative to the thin film edge of the qubit
circuit. Resonance frequencies of defects are tuned by exposing the qubit
sample to electric fields generated by electrodes surrounding the chip. By
determining the defect's coupling strength to each electrode and comparing it
to a simulation of the field distribution, we obtain the probability at which
location and at which interface the defect resides. This method is applicable
to already existing samples of various qubit types, without further on-chip
design changes. It provides a valuable tool for improving the material quality
and nano-fabrication procedures towards more coherent quantum circuits
Genetic and Antigenic Analysis of the First A/New Caledonia/20/99-like H1N1 Influenza Isolates Reported in the Americas
From February through May of 1999, 13 cases of Influenza A virus (FLUAV), type H1N1 were reported at a Department of Defense influenza surveillance sentinel site in Lima, Peru. Genetic and antigenic analysis by hemagglutination inhibition and direct nucleotide sequencing of the HA1 region of the hemagglutinin gene were performed on two isolates, A/Peru/1641/99 and A/Peru/1798/99. Both isolates were distinct from the Bayern/7/95-like viruses circulating in the Americas and closely related to a Beijing/262/95-like variant, A/New Caledonia/20/99. With the exception of travel-related cases, the detection of these isolates represents the first appearance of New Caledonia/20/99-like viruses in the Americas. Since the characterization of these Peru isolates, a number of New Caledonia/20/99-like viruses have been reported worldwide. For the 2000/01 and 2001/02 influenza seasons, the World Health Organization (WHO) has recommended the inclusion of A/New Caledonia/20/99 as the H1N1 vaccine component for both the southern and northern hemispheres
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