14,504 research outputs found
A3 Subscale Diffuser Test Article Design
This paper gives a detailed description of the design of the A3 Subscale Diffuser Test (SDT) Article Design. The subscale diffuser is a geometrically accurate scale model of the A3 altitude rocket facility. It was designed and built to support the SDT risk mitigation project located at the E3 facility at Stennis Space Center, MS (SSC) supporting the design and construction of the A3 facility at SSC. The subscale test article is outfitted with a large array of instrumentation to support the design verification of the A3 facility. The mechanical design of the subscale diffuser and test instrumentation are described her
Optimal slit orientation for long multi-object spectroscopic exposures
Historically, long-slit spectroscopic observations were carried out using the
parallactic angle for the slit orientation if slit loss was an important
consideration (either to maximize the signal-to-noise or to do
spectrophotometry). This requires periodic realignment of the slit position
angle as the parallactic angle changes. This is not possible for multi-slit
observations where one slit position angle must be chosen for the entire
exposure. Common wisdom suggests using the parallactic angle at the meridian
(HA=0). In this paper, I examine what the best strategy is for long, multi-slit
exposures. I find that in extreme cases (very long exposure time) the best
choice is to orient the slit \emph{perpendicular} to the parallactic angle at
the meridian. There are two effects to consider: the increasing dispersion with
increasing airmass and the changing angle between the parallactic angle and the
slit. In the case of \emph{traditional} slit orientation, the two effects
amplify each other, thus rendering a significant fraction of the observation
useless. Using the perpendicular orientation, the two processes work against
each other, thus most of the observation remains useful. I will use, as an
example, our 8 hour Lockman Hole observations using the Keck telescope, but
generic methods are given to evaluate a particular observation. I also make the
tools available to the community.Comment: Accepted by A&A (20/06/2005
Mg/Ca ratios in freshwater microbial carbonates: Thermodynamic, kinetic and vital effects
The ratio of magnesium to calcium (Mg/Ca) in carbonate minerals in an abiotic setting is conventionally assumed to be predominantly controlled by (Mg/Ca)solution and a temperature dependant partition coefficient. This temperature dependence suggests that both marine (e.g. foraminiferal calcite and corals) and freshwater (e.g. speleothems and surface freshwater deposits, “tufas”) carbonate deposits may be important archives of palaeotemperature data. However, there is considerable uncertainty in all these settings. In surface freshwater deposits this uncertainty is focussed on the influence of microbial biofilms. Biogenic or “vital” effects may arise from microbial metabolic activity and/or the presence of extracellular polymeric substances (EPS). This study addresses this key question for the first time, via a series of unique through-flow microcosm and agitated flask experiments where freshwater calcite was precipitated under controlled conditions. These experiments reveal there is no strong relationship between (Mg/Ca)calcite and temperature, so the assumption of thermodynamic fractionation is not viable. However, there is a pronounced influence on (Mg/Ca)calcite from precipitation rate, so that rapidly forming precipitates develop with very low magnesium content indicating kinetic control on fractionation. Calcite precipitation rate in these experiments (where the solution is only moderately supersaturated) is controlled by biofilm growth rate, but occurs even when light is excluded indicating that photosynthetic influences are not critical. Our results thus suggest the apparent kinetic fractionation arises from the electrochemical activity of EPS molecules, and are therefore likely to occur wherever these molecules occur, including stromatolites, soil and lake carbonates and (via colloidal EPS) speleothems
Luminosity Density of Galaxies and Cosmic Star Formation Rate from Lambda-CDM Hydrodynamical Simulations
We compute the cosmic star formation rate (SFR) and the rest-frame comoving
luminosity density in various pass-bands as a function of redshift using
large-scale \Lambda-CDM hydrodynamical simulations with the aim of
understanding their behavior as a function of redshift. To calculate the
luminosity density of galaxies, we use an updated isochrone synthesis model
which takes metallicity variations into account. The computed SFR and the
UV-luminosity density have a steep rise from z=0 to 1, a moderate plateau
between z=1 - 3, and a gradual decrease beyond z=3. The raw calculated results
are significantly above the observed luminosity density, which can be explained
either by dust extinction or the possibly inappropriate input parameters of the
simulation. We model the dust extinction by introducing a parameter f; the
fraction of the total stellar luminosity (not galaxy population) that is
heavily obscured and thus only appears in the far-infrared to sub-millimeter
wavelength range. When we correct our input parameters, and apply dust
extinction with f=0.65, the resulting luminosity density fits various
observations reasonably well, including the present stellar mass density, the
local B-band galaxy luminosity density, and the FIR-to-submm extragalactic
background. Our result is consistent with the picture that \sim 2/3 of the
total stellar emission is heavily obscured by dust and observed only in the
FIR. The rest of the emission is only moderately obscured which can be observed
in the optical to near-IR wavelength range. We also argue that the steep
falloff of the SFR from z=1 to 0 is partly due to the shock-heating of the
universe at late times, which produces gas which is too hot to easily condense
into star-forming regions.Comment: 25 pages, 6 figures. Accepted version in ApJ. Substantially revised
from the previous version. More emphasis on the comparison with various
observations and the hidden star formation by dust extinctio
Developing Belief in Online Teaching: Efficacy and Digital Transformation
Digital pedagogies, blended, hybrid, and online learning are not new, indeed discussions about their role in higher education are well documented. With some notable exceptions however, many of these discussions, and many more attempts at implementation, have been small in scale, operating at the level of a single course, or even single members of staff. Barriers at national, institutional and personal levels all contributed to slow uptake of digital learning. The summer of 2020 though saw institutions across the UK, and indeed the world, forced into rapid transition to online learning in the face of the COVID-19 pandemic. This paper examines our work supporting a school - which achieved high student satisfaction rates - within a large post-92 university in this transition. With specific attention to academic identity and efficacy, we examine the approaches that were taken in helping academics to climb over the digital hurdle towards good online teaching. We suggest that a three-pronged approach is needed to overcome these barriers and create the belief in digital that is needed for a successful online transition, and for continued growth. These are a collective ‘all in it together’ approach, placing curriculum, rather than technology at the heart of the work, and also ensuring solid institutional support that does not rely on early adopters
A3 Subscale Rocket Hot Fire Testing
This paper gives a description of the methodology and results of J2-X Subscale Simulator (JSS) hot fire testing supporting the A3 Subscale Diffuser Test (SDT) project at the E3 test facility at Stennis Space Center, MS (SSC). The A3 subscale diffuser is a geometrically accurate scale model of the A3 altitude simulating rocket test facility. This paper focuses on the methods used to operate the facility and obtain the data to support the aerodynamic verification of the A3 rocket diffuser design and experimental data quantifying the heat flux throughout the facility. The JSS was operated at both 80% and 100% power levels and at gimbal angle from 0 to 7 degrees to verify the simulated altitude produced by the rocket-rocket diffuser combination. This was done with various secondary GN purge loads to quantify the pumping performance of the rocket diffuser. Also, special tests were conducted to obtain detailed heat flux measurements in the rocket diffuser at various gimbal angles and in the facility elbow where the flow turns from vertical to horizontal upstream of the 2nd stage steam ejector
Post-Disaster Housing Reconstruction in Sri Lanka: What Methodology?
Research methodology is the procedural framework within which the research is conducted. This includes the overall
approach to a problem that could be put into practice in a research process, from the theoretical underpinning to the
collection and analysis of data. Choice of methodology depends on the primary drivers: topic to be researched and the
specific research questions. Hence, methodological perspectives of managing stakeholder expectations of PDHR context
are composed of research philosophies, research strategy, research design, and research techniques. This research belonged
to social constructivism or interpretivism within a philosophical continuum. The nature of the study was more toward
subjectivism where human behavior favored voluntary stance. Ontological, methodological, epistemological, and axiological
positioning carried the characteristics of idealism, ideographic, anti-positivism, and value laden, respectively. Data collection
comprises two phases, preliminary and secondary. Exploratory interviews with construction experts in the United Kingdom
and Sri Lanka were carried out to refine the interview questions and identify the case studies. Case study interviews during
the secondary phase took place in Sri Lanka. Data collected at the preliminary stage were used to assess the attributes of
power, legitimacy/proximity, and urgency of stakeholders to the project using Stakeholder Circle™ software. Moreover,
the data collected at secondary phase via case studies will be analyzed with NVivo 8. This article aims to discuss these
methodological underpinnings in detail applied in a post-disaster housing reconstruction context in Sri Lanka
Description and Operation of the A3 Subscale Facility
The purpose of this paper is to give an overview of the general design and operation of the A3 Subscale test facility. The goal is to provide the reader with a general understanding of what the major facility systems are, where they are located, and how they are used to meet the objectives supporting the design of the A3 altitude rocket test facility. This paper also provides the reader with the background information prior to reading the subsequent papers detailing the design and test results of the various systems described herein
Design, Activation, and Operation of the J2-X Subscale Simulator (JSS)
The purpose of this paper is to give a detailed description of the design, activation, and operation of the J2-X Subscale Simulator (JSS) installed in Cell 1 of the E3 test facility at Stennis Space Center, MS (SSC). The primary purpose of the JSS is to simulate the installation of the J2-X engine in the A3 Subscale Rocket Altitude Test Facility at SSC. The JSS is designed to give aerodynamically and thermodynamically similar plume properties as the J2-X engine currently under development for use as the upper stage engine on the ARES I and ARES V spacecraft. The JSS is a scale pressure fed, LOX/GH fueled rocket that is geometrically similar to the J2-X from the throat to the nozzle exit plane (NEP) and is operated at the same oxidizer to fuel ratios and chamber pressures. This paper describes the heritage hardware used as the basis of the JSS design, the newly designed rocket hardware, igniter systems used, and the activation and operation of the JSS
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