1,721,058 research outputs found
Upgrading the Frozen Sonic Flow Method for Arc-Jet Facilities
No full textThe arc-jet facilities are used to simulate the aero-heating environment during the high speed planetary entry. The most important parameter to be reproduced is the flow total enthalpy that is highest at the nozzle centerline and decreases toward the nozzle walls. The assessment of the ratio of the centerline enthalpy (i.e. the total enthalpy at the core of the free jet) to the mass–averaged enthalpy is important for an accurate evaluation of the heat flux on the tested model. In fact, this is proportional to the centerline enthalpy; on the other hand the mass–averaged enthalpy is usually measured in the arc-jet facilities.
The assessment of the centerline enthalpy in arc-heated flows expanding from high pressure reservoirs, i.e. from equilibrium conditions, relies on the Winovich “sonic flow method”. This method assumes that the flow at the sonic point of a nozzle can be represented by a one-dimensional, isentropic expansion in equilibrium conditions. Jorgensen suggested applying the Winovich method to flows that are in equilibrium through a reservoir up to the beginning of expansion and suddenly freeze at that point (the so-called “frozen sonic point method”). Finally Pope verified that this method can be applied also to high-enthalpy flows freezing upstream the beginning of expansion, provided that the chemical composition of the frozen flow is known.
The equation for equilibrium or frozen flow, allowing the evaluation of total temperature (Tt) at the beginning of expansion, reads:
mg/ptA*=CF(γ)/(ZTt)1/2 (1)
where C=m/R0 and F(γ)=[(2/+1)(+1)/(-1)]1/2. The chemical composition (ci) is evaluated by the measurement of the mass–averaged enthalpy and pressure in the reservoir. The compressibility factor (Z) is computed as Z=1+ then the isentropic exponent (γ) can be evaluated for a chemically frozen mixture of atomic and diatomic species, with frozen vibrational energy, by γ=(4+3Z)/(4+Z), while mg and pt are measured during the test.
Once known Tt and the chemical composition, from the JANAF thermo-chemical data, the centerline enthalpy can be calculated by:
HCL=Σci(HT+ΔHf,T)i (2)
To simplify the data reduction, Pope correlated the values of (HT+ΔHf,T)i in terms of temperature by:
(HT+ΔHf,T)i=B1T+B2 (3)
Park, for one operating condition of the Interaction Heating Facility (IHF) at NASA Ames Research Center (HN=44.5 MJ/Kg, pt=4.7105 Pa), compared five methods for evaluating enthalpy; two experimental methods for the mass-averaged enthalpy, two experimental methods for the centerline enthalpy and a fully numerical method for both enthalpies. All methods gave values of the centerline to mass-averaged enthalpy ratio of about 1.41.
The Small Planetary Entry Simulator (SPES) in Naples is an arc-jet facility operating with simulated air, i.e. a mixture of 80% Nitrogen and of 20% Oxygen. Nitrogen is processed by the arc-heater while cold Oxygen is injected into a reservoir downstream the arc-heater. The reservoir pressure is less than 7.5104 (Pa), therefore the sonic flow method, as modified by Pope, can be applied to evaluate the centerline enthalpy.
A rational base, making the results from SPES comparable with those from IHF, is that the enthalpy profile across the nozzle of all arc-heated facilities is characterized by a maximum at the center line. This is basically due to the fact that the arc is concentrate at the center line (argon in IHF and nitrogen in SPES) while the arc flow is surrounded by a cold gas (air in IHF and oxygen in SPES). As for both IHF and SPES the nozzles are water-cooled and the area ratios (A/A*) are similar, you can expect a similar boundary layer development and therefore a similar enthalpy profile across the nozzle exit. Moreover, SPES has been used in the past as pilot facility for SCIROCCO, a 70 MW arc-driven wind tunnel (based on a segmented arc-heater similar to the IHF one).
The aim of the present note is upgrading the Pope procedure by:
1) using the most updated version of thermochemical JANAF tables (1998 edition);
2) including the formation of nitric oxide in the air chemical model,
3) considering low-to-moderate enthalpy levels
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe 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
Experimental and numerical simulation, by an arc-jet facility, of hypersonic flow in Titan's atmosphere
No full textThis paper summarizes experimental and numerical results on high enthalpy hypersonic flows in nitrogen–methane mixtures. The experimental results have been obtained by the Small Planetary Entry Simulator (SPES), an arc-jet hypersonic wind tunnel in operation at the University of Naples “Federico II”. The facility has been used in the past to simulate entry conditions into Earth’s and Mars’ atmosphere and has recently been upgraded to simulate entry into Titan’s atmosphere. Numerical simulations of the flow field in the facility, for a nitrogen–methane mixture in chemical nonequilibrium have been performed. The chemical species and the heat flux distributions on a calorimeter located in the arc-jet test chamber have been computed.
The ability to perform a numerical rebuilding of the facility, by comparing numerical and experimental results has been investigated. The paper also highlights the importance of the wall catalyticity for the characterization of the thermal response of materials in high enthalpy flow
Variations on the Author
Full text link“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
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Dispelling the Myths Behind First-author Citation Counts
Full text linkWe 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
koamabayili/VECTRON-author-checklist: VECTRON author checklist
No full textWe have done our best to complete the author checklist relating to the use of animals in the hut study. Note that the objective for the hut study was to evaluate the IRS treatment applications for residual efficacy against Anopheles mosquitoes, including the local An. coluzzii mosquito population. Cows were only used to attract mosquitoes into the huts and no tests were carried out directly on the cows. The author checklist is intended for use with studies where experiments are carried out on animals, which is why we have had such difficulty in completing this for the hut study, as many of the questions do not relate to how the cows were used
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