86,645 research outputs found
Comparing Thermal Stability of NbTi and NbSn Wires
No full textThe investigation of quenching in low temperature superconducting wires is of great relevance for a proper design of superconductive cables and magnets. This paper reports the experimental results of a vast measurement campaign of quench induced by laser pulses on NbTi and NbSn wires in pool boiling Helium I. A comparison of the quench behavior of two typical NbTi and NbSn wires is shown from different standpoints. Different qualitative behaviors of the voltage traces recorded during quenches and recoveries on NbTi and NbSn wires are reported and analyzed. It is shown that the NbSn wire exhibits a quench or no-quench behavior, whereas quenches and recoveries are exhibited by the NbTi wire. The two wires are also compared considering the behaviors of the two main parameters describing quench, i.e. quench energies and quench velocities, with respect to operation current and pulse duration and magnetic field. It is shown that the NbSn wire exhibits a ‘kink’ of the quench energy vs current curve that makes the quench energy of NbSn lower than that of NbTi at some intermediate current levels. Both the qualitative differences of the voltage traces and the different behaviors of quench energies and velocities are interpreted through a coupled electromagnetic- thermal model, with special emphasis on the detailed description of heat exchange with liquid helium
Effects of the Nb3Sn Wire Cross Section Configuration on the Thermal Stability Performance
No full textThe thermal and electrical conductivities of the normal matrix of LTS wires have a remarkable influence on the wire stability. In particular, in Nb3Sn wires, a bronze matrix in the region of the superconducting filaments may act as a thermal and electrical barrier between the filaments and the copper matrix. This phenomenon is analyzed here through a numerical model accounting for these thermal and electrical transverse resistances. The model is applied to a parametric analysis of the effect of the main properties of the wire matrix on the quench energy
and velocity. A 2D analysis of the wire cross section is applied to
investigate how a configuration change could improve the wire
stability
A nanostructural study of Raney-type nickel catalysts
No full textRaney-type nickel catalysts have been applied in commercial hydrogenation reactions for decades. They are relatively cheap and have proven to be very efficient in hydrogenation. The preparation process is relatively simple, but it appears that many parameters have an influence on the performance of the final catalyst. Consequently, the manufacturing of Raney-type nickel catalyst with an absolute control of the preparation process is hard to accomplish, leading to unpredictable variation in the catalyst selectivity and activity. A lot of information can be found in literature about characterization of Raney-type nickel catalysts, but many discrepancies exist so that general conclusions are hard to draw. It was the goal of this project to predict the catalytic properties from structure - catalytic performance relationships. Understanding the mechanism of transformation of starting alloys into Raney-type nickel catalysts was then required. To achieve this goal, a detailed characterization at different stages of the leaching process, coupled with the determination of the catalytic properties was performed (chapters 3 and 4). The usual starting alloy used in the preparation of Raney-type nickel catalysts is a 50-50 wt % Ni-Al alloy. As the addition of a second component to metal catalysts is widely used in order to enhance activity and/or selectivity, the effect of Mo, and a combination of Cr and Fe promoters on the performance of Raney-type nickel catalysts has also been investigated (chapter 5). Two extra different approaches in studying Raney-type nickel catalysts have been considered: a rapid solidification technique (melt spinning) to prepare the starting alloy (chapter 6) and the use of cryo-ultramicrotomy to prepare specimens For TEM/HREM characterization (chapter 7).Applied Science
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
[Newspaper Clipping: Author Claims Evidence of Second JFK Assassin #1]
No full textNewspaper article titled "Author Claims Evidence of Second JFK Assassin." The article states that author Richard J. Whalen concluded "that there is circumstantial evidence to support the theory of a second assassin in the shooting of President John F. Kennedy.
Stability of Nb3Sn superconducting wires: the role of the normal matrix
No full textThe stability of ���� superconducting wires is
a crucial issue in the design and operation of reliable superconducting
magnets. High current density magnets, such as those
presently developed for future accelerator projects, may be subject
to premature quenches due to local releases of energy. In
this paper we study the results of stability experiments that have
been performed using a single mode Diode Laser with an optical
fiber to illuminate the superconducting strand surface and trigger
fast quenches. The development and propagation of laser-induced
quenches have been measured on Nb3Sn strands in LHe bath by
means of three voltage taps. This paper deals with the numerical
analysis of the experimental results. A coupled electric and
thermal model has been developed to study the quench propagation.
The experimental evidence of a different qualitative behavior
of the voltage traces recorded on ���� strands with respect to
NbTi strands is explained by means of a more detailed physical
model of ���� strands, that takes into account electrical and
thermal transverse resistances
Also By The Same Author: AKTiveAuthor, a Citation Graph Approach to Name Disambiguation
No full textThe desire for definitive data and the semantic web drive for inference over heterogeneous data sources requires co-reference resolution to be performed on those data. In particular, name disambiguation is required to allow accurate publication lists, citation counts and impact measures to be determined. This paper describes a graph-based approach to author disambiguation on large-scale citation networks. Using self-citation, co-authorship and document source analyses, AKTiveAuthor clusters papers, achieving precision of 0.997 and recall of 0.818 over a test group of eight surname clusters
John F. Kennedy telegram to Roosevelt
No full textJersey Homesteads (later the Borough of Roosevelt) was established in the 1930s as an agro-industrial cooperative community. It was established specifically for urban Jewish garment workers, many of whom had emigrated from Europe. President John F. Kennedy sent a telegram to the citizens of Roosevelt, New Jersey, apologizing for not being able to attend the memorial dedication in honor of former President Franklin Delano Roosevelt. (Jersey Homesteads became Roosevelt in 1945 in honor of the president.) President Kennedy expressed his gratitude to the people of Roosevelt for constructing the memorial, and commented that it will serve as a constant reminder of Roosevelt's good works
Minimum Quench Energy and Early Quench Development in NbTi Superconducting Strands
No full textThe stability of superconducting wires is a crucial task in the design of safe and reliable superconducting magnets. These magnets are prone to premature quenches due to local releases of energy. In order to simulate these energy disturbances, various heater technologies have been developed, such as coated tips, graphite pastes, and inductive coils. The experiments studied in the present work have been performed using a single-mode diode laser with an optical fiber to illuminate the superconducting strand surface. Minimum quench energies and voltage traces at different magnetic flux densities and transport currents have been measured on an LHC-type, Cu/NbTi wire bathed in pool boiling helium I. This paper deals with the numerical analysis of the experimental data. In particular, a coupled electromagnetic and thermal model has been developed to study quench development and propagation, focusing on the influence of heat exchange with liquid helium
Logarithmic variance profiles and the corresponding f-1 spectra of temperature fluctuations in turbulent Rayleigh-Bénard convection
No full textWe report experimental results for the temperature variance 2(z) and the corresponding frequency spectra P(f) in turbulent Rayleigh-Bénard convection (RBC) in a cylindrical sample of aspect ratioT= D/L = 1:00 (D = 1:12 m is the diameter and L = 1:12 m the height). The measurements were conducted in the Rayleigh-number range 1011 < Ra < 1:35 1014 and Pr ' 0:8. For Ra = 1:35x1014, 2(z) could be described well by a logarithmic dependence on the vertical position z in a range of z 1 < z < z 2 with z 1 ' 70 and z 2 = 0:1L. Here L=(2Nu) is the thickness of a thin thermal sublayer adjacent to the horizontal plate where the heat flux (denoted by the Nusselt number Nu) is carried mostly by thermal diffusion. In the log layer, we found that the temperature spectra had a significant frequency range over which P(f) f with close to 1. As Ra decreased, increased so that the log layer became thinner. At Ra = 2:05 1011, z 2 < z 1 and therefore there was no range for a log layer. Correspondingly, the temperature spectrum near the horizontal plate did not have the f1 scaling form either
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