323,023 research outputs found
Multiphysics Analysis of High-power Vacuum Feedthrough for DTT ICRH System
No full textIn the framework of the Divertor Tokamak Test (DTT) facility, which aims at the validation of an integrated solution for the power exhaust moving to the DEMOnstration power plant (DEMO), an Ion Cyclotron Resonance Heating (ICRH) system is under development. Its final configuration, which comprises two independent modules, shall couple 6MW to the DTT
plasma, in a pulsed regime (pulse length 50 s, duty cycle 1.4%), in the 60-90MHz frequency range. The Vacuum Feedthrough (VFT), usually made with one or two alumina windows, assures the reliable separation between the pressurized Main Transmission Line (MTL) and Vacuum Transmission Line (VTL) sections, which is located close to the plasma-facing antenna. It is one of the most critical components of the ICRH system because it must protect the tokamak
vacuum and withstand a high RF voltage in a resonant transmission line (RTL) based on rigid coaxial cable. Results of RF, thermodynamic, and mechanical simulations of RTLs, constituted by an impedance transformer, an RF divider (T-junction), and two output branches, each with a VFT, are reported.
In our simulations, the effective antenna impedance is substituted with an equivalent resistive load (Rs), representing the coupling resistance locating the RTL outputs in a voltage node.
Thermodynamic and mechanical simulations of matched RTLs, with two windows for each branch, were conducted in the worst condition, i.e., imposing the maximum working frequency (90 MHz) and the minimum value of Rs (0.5 Ohm). In all analyses, an RF power of 1.2MW (600kW each VFT) for a pulse of 50 s has been injected into the RTL. VFTs with conical and disk geometry types with Alumina 99 windows were studied.
Considering only the unforced convection of the outer conductor, significant temperature and thermal stresses were obtained for both window types. The conical window reaches a maximum thermal stress of 140MPa, more than half of the Ultimate Tensile Strength of Alumina 99, i.e., 260MPa. Instead, given the same boundary conditions, the disk window reaches a maximum thermal stress of 35MPa. The thermal difference between the edges and the center obtained for both windows exceeds 30 degrees. The leading cause is the ohmic loss of the metals. The mechanical design is preliminary, but Multiphysics simulations already allow us to choose materials, geometry, and cooling method of VFT
Waveguide-to-Microstrip Nonbinary Power Dividers
No full textA novel spatial power combiner (SPC), exploiting nonbinary and odd power divisions and working in full Ka-band, is designed and measured in this letter. Starting from the theory that rules the power division captured by the waveguide-to-microstrip transitions with different power division factors, a full 3-D EM model has been created and simulated along with a working manufactured prototype. The measurements demonstrated how all the broadband transmission characteristics of the Finline transitions (S11 > 10 dB and minimum losses) are preserved, also avoiding any resonant behavior possibly introduced by the nonsymmetry of the structure. This is the first example of a non-TEM and non-Radial SPC with nonbinary power division. In this case, a power division/recombination by five has been performed
Perturbative Approach For Mass Varying Neutrinos Coupled To The Dark Sector In The Generalized Chaplygin Gas Scenario
No full textWe suggest a perturbative approach for generic choices for the universe equation of state and introduce a novel framework for studying mass varying neutrinos (MaVaN's) coupled to the dark sector. For concreteness, we examine the coupling between neutrinos and the underlying scalar field associated with the generalized Chaplygin gas (GCG), a unification model for dark energy and dark matter. It is shown that the application of a perturbative approach to MaVaN mechanisms translates into a constraint on the coefficient of a linear perturbation, which depends on the ratio between a neutrino energy dependent term and scalar field potential terms. We quantify the effects on the MaVaN sector by considering neutrino masses generated by the seesaw mechanism. After setting the GCG parameters in agreement with general cosmological constraints, we find that the squared speed of sound in the neutrino-scalar GCG fluid is naturally positive. In this scenario, the model stability depends on previously set up parameters associated with the equation of state of the universe. Our results suggest that the GCG is a particularly suitable candidate for constructing a stable MaVaN scenario. © 2008 The American Physical Society.778Riess, A.G., (1998) Astron. J., 116, p. 1009. , ANJOAA 0004-6256 10.1086/300499Perlmutter, S., (1999) Astrophys. J., 517, p. 565. , ASJOAB 0004-637X 10.1086/307221Astier, P., (2006) Astron. Astrophys., 447, p. 31. , AAEJAF 0004-6361 10.1051/0004-6361:20054185Burles, S., (2001) Astrophys. J., 552, p. 1. , ASJOAB 0004-637X 10.1086/320251De Bernardis, P., (2000) Nature (London), 404, p. 955. , NATUAS 0028-0836 10.1038/35010035Bennett, C.L., (2003) Astrophys. J. Suppl. Ser., 148, p. 1. , APJSA2 0067-0049 10.1086/377253Spergel, D.N., (2003) Astrophys. J. Suppl. 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A quantitative NLTE analysis of visual and ultraviolet spectra of four helium-rich subdwarf O stars
No full textAims. Hot subdwarf stars represent a poorly understood late phase of stellar evolution. While binary evolution plays an important role for the formation of B-Type subdwarfs (sdB), the origin of the helium dominated subclass of O-Type subdwarfs (He-sdO) is still unknown. We search for chemical signatures of their genesis by means of quantitative spectral analyses of high-quality visual and ultraviolet spectra. Methods. Four prototypical He-sdO stars, one belonging to the nitrogen-rich and three to the C-rich subclass, were selected for which archival far-ultraviolet spectra from the FUSE satellite as well as high-resolution visual and UVA spectra taken with the ESO-UVES/FEROS spectrographs are available. Using Ta LUSTY200/Sa YNSPEC49 to compute line blanketed-non-local thermodynamic equilibrium (NLTE) model atmospheres and synthetic spectra, atmospheric parameters and the abundances patterns have been derived. The final models included H, He, C, N, O, Ne, Mg, Al, Si, P, S, Fe, and Ni represented by the most detailed model atoms available. Because of the enrichment of either nitrogen or carbon, it turned out, that models including these elements at the appropriate high abundance provide sufficiently accurate approximations to the temperature stratification of full models. Results. No indications for binarity were found, neither radial velocity variations nor photometric evidence for the presence of a companion could be detected. All stars have helium-dominated atmospheres almost free of hydrogen and temperatures between 42 000 K and 47 000 K while their surface gravities lie between log g = 5.4 and 5.7. The abundance pattern of CD-31°4800 displays the signatures of CNO burning, while heavier elements are subsolar by about 0.4 dex, except for Ne and Si which are close to solar. The abundance patterns of the C-rich He-sdOs are more complex. A slightly subsolar metallicity is accompanied by N-enrichment and O-deficiency, less pronounced than in CD-31°4800. Neon is mildly to strongly enriched, up to a factor of ten with respect to the sun in LS IV +10° 9. The nickel-To-iron ratio is significantly super-solar. Using spectral energy distributions and Gaia parallaxes the masses of the stars were determined. They are found to scatter around the canonical mass for the core helium flash, although the uncertainties are large. Conclusions. The abundance pattern observed for CD-31°4800 is consistent with predictions of models for slow (cold) mergers of pairs of equal mass helium WDs except for the low oxygen abundance observed. Models for composite mergers were considered for the C-rich stars, but predict abundance pattern dissimilar to those determined. [CW83] 0904-02, though, may be a candidate for a composite He-WD merger, as it rotates and appears to be more massive than the other program stars. New evolutionary models for the hot flasher scenario predict abundance patterns similar to those determined for the C-rich stars. Hence, C-rich He-sdO may well result from late He flashes with deep-mixing episodes.Fil: Schindewolf, M.. Universitat Erlangen-Nuremberg; AlemaniaFil: Németh, P.. Universitat Erlangen-Nuremberg; AlemaniaFil: Heber, U.. Universitat Erlangen-Nuremberg; AlemaniaFil: Battich, Tiara. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Miller Bertolami, Marcelo Miguel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Irrgang, A.. Universitat Erlangen-Nuremberg; AlemaniaFil: Latour, M.. Universitat Erlangen-Nuremberg; Alemani
Comprehensive Analysis of a Slow Wave Structure for an X-band MILO
No full textMagnetically Insulated transmission Line Oscillator (MILO) is a relatively new
High Power Microwave (HPM) device that has recently received increasing attention because it
does not require an external magnetic ̄eld and can generate gigawatt (GW) of power from L to
Ku bands. Furthermore, it is a compact and lightweight tube and can operate at low impedance
(» 10 ). The most signi ̄cant element in a magnetically insulated transmission line oscillator
(MILO) is a slow wave structure (SWS) in which the interaction between the RF ̄eld and par-
ticles occurs. This study aimed to design an SWS for an X-band MILO using a High-Frequency
Structure Simulator (HFSS) and Particle in Cell (PIC) Simulator (CST-PS). HFSS was used to
obtain the structure's dispersion relation and investigate the resonant mode frequencies through
EigenmodeSolver. Previous investigations demonstrate that a MILO oscillates in the 1⁄4-mode,
which is the spatial harmonic associated with the SWS with the highest Q. The ̄eld distri-
bution associated with this mode produces the strongest coupling to the electron °ow. In our
studies, parameter optimization was investigated, and particular attention was focused on the
phenomenon of mode competition observed during di®erent simulations. The simulations dis-
played remarkable performance in sizes and weight terms and the potential to produce very high
output power. Dispersion diagrams will be shown, highlighting the interaction between modes
propagating in the structure and beamline as the input voltage varies. An X-band MILO with
the simulated SWS was designed, and a PIC simulation was done to con ̄rm our proper design. A
pulse signal of 500 kV and 100 ns pulse length in PIC simulations generate the relativistic beam.
TEM mode and high-order modes are evaluated. A peak power of 450MW and frequency of
9.4 GHz is observed. Conclusions and possible future developments will be discussed
Diffusive author(s), cohesive author: Analysis of S/N (1994)
No full textThis study indicates the ways in which various aspects of the author(s) are brought forth in Dumb type’s performance art, the S/N production. Previous research has suggested a non-hierarchical organization of Dumb type and the absence of a “privileged author” in Dumb type’s collaborative work, S/N. However, the results that I have investigated from member’s interviews on the creative process of S/N along with my analysis of the recorded images of S/N, indicate a different aspect of the author(s). First, S/N was created through, so to speak, the collective ideas of the members of Dumb type. Further, S/N has at least nine quotations from previous performances, installations, and printed writings, besides the work-in-progress technique. Explicating one of the “author functions” as given by Michel Foucault, each text has plural subjects of the author. However, it has been revealed from members’ interviews that Teiji Furuhashi had a decision-making role in selecting the members’ ideas within the performance. Since then, S/N has had plural subjects of creation; however, Furuhashi is one of the subjects of creation along with the “privileged author.” S/N has plural authors (diffusive authors) yet at the same time, it has a “privileged author,” Teiji Furuhashi (cohesive author)
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Exploring Multiple Benefits of Urban and Energy Regeneration Projects: A Stakeholder-Centred Methodological Approach
No full textAn effective way to promote energy transition while tackling climate change involves redefining cities from being part of the problem to integral parts of the solution. Positive energy districts and climate positive circular communities are excellent examples of how this is feasible. But how do we understand which are the multiple benefits that these projects can bring to the local territory and relative community? This article aims to answer this question by developing a specific engagement and evaluation methodology. Our approach involves consulting with project partners to explore the multiple benefits of each case study. Subsequently, it plans to engage the stakeholders through the submission of a questionnaire to gather information regarding the relative importance of different benefits as perceived by each stakeholder. The questionnaire is based on the best–worst scaling method, which is a survey technique for determining people’s priorities. The preliminary findings of the study conducted on project partners of two European projects, ARV and ProLight, indicate a strong alignment with current European policy priorities. The involvement of other stakeholders in the study will serve to assess whether bottom-up priorities coincide with broader perspectives or whether adaptations to project strategies and dissemination approaches are needed
Dispelling the Myths Behind First-author Citation Counts
No full textWe conducted a full-scale evaluative citation analysis study of scholars in the XML research field to explore just how different from each other author rankings resulting from different citation counting methods actually are, and to demonstrate the capability of emerging data and tools on the Web in supporting more realistic citation counting methods. Our results contest some common arguments for the continued
use of first-author citation counts in the evaluation of scholars, such as high correlations between author rankings by first-author citation counts and other citation
counting methods, and high costs of using more realistic citation counting methods that are not well-supported by the ISI databases. It is argued that increasingly available digital full text research papers make it possible for citation analysis studies to go beyond what the ISI databases have directly supported and to employ more
sophisticated methods
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