14,780 research outputs found
Apollo experience report: Development of guidance targeting techniques for the command module and launch vehicle
The development of the guidance targeting techniques for the Apollo command module and launch vehicle is discussed for four types of maneuvers: (1) translunar injection, (2) translunar midcourse, (3) lunar orbit insertion, and (4) return to earth. The development of real-time targeting programs for these maneuvers and the targeting procedures represented are discussed. The material is intended to convey historically the development of the targeting techniques required to meet the defined target objectives and to illustrate the solutions to problems encountered during that development
Corrigendum to "Assessment of China's virtual air pollution transport embodied in trade by using a consumption-based emission inventory" published in Atmos. Chem. Phys., 15, 5443-5456, 2015
No abstract available
Assessment of China's virtual air pollution transport embodied in trade by using a consumption-based emission inventory
Substantial anthropogenic emissions from China have resulted in serious air pollution, and this has generated considerable academic and public concern. The physical transport of air pollutants in the atmosphere has been extensively investigated; however, understanding the mechanisms how the pollutant was transferred through economic and trade activities remains a challenge. For the first time, we quantified and tracked China's air pollutant emission flows embodied in interprovincial trade, using a multiregional input - output model framework. Trade relative emissions for four key air pollutants (primary fine particle matter, sulfur dioxide, nitrogen oxides and non-methane volatile organic compounds) were assessed for 2007 in each Chinese province. We found that emissions were significantly redistributed among provinces owing to interprovincial trade. Large amounts of emissions were embodied in the imports of eastern regions from northern and central regions, and these were determined by differences in regional economic status and environmental policy. It is suggested that measures should be introduced to reduce air pollution by integrating cross-regional consumers and producers within national agreements to encourage efficiency improvement in the supply chain and optimize consumption structure internationally. The consumption-based air pollutant emission inventory developed in this work can be further used to attribute pollution to various economic activities and final demand types with the aid of air quality models
Complexity-based learning and teaching: a case study in higher education
This paper presents a learning and teaching strategy based on complexity science and explores its impacts on a higher education game design course. The strategy aimed at generating conditions fostering individual and collective learning in educational complex adaptive systems, and led the design of the course through an iterative and adaptive process informed by evidence emerging from course dynamics. The data collected indicate that collaboration was initially challenging for students, but collective learning emerged as the course developed, positively affecting individual and team performance. Even though challenged, students felt highly motivated and enjoyed working on course activities. Their perception of progress and expertise were always high, and the academic performance was on average very good. The strategy fostered collaboration and allowed students and tutors to deal with complex situations requiring adaptation
Sterile Neutrinos as Dark Matter
The simplest model that can accomodate a viable nonbaryonic dark matter
candidate is the standard electroweak theory with the addition of right-handed
or sterile neutrinos. We reexamine this model and find that the sterile
neutrinos can be either hot, warm, or cold dark matter. Since their only direct
coupling is to left-handed or active neutrinos, the most efficient production
mechanism is via neutrino oscillations. If the production rate is always less
than the expansion rate, then these neutrinos will never be in thermal
equilibrium. However, enough of them may be produced so that they provide the
missing mass necessary for closure. We consider a single generation of neutrino
fields with a Dirac mass, , and a Majorana
mass for the right-handed components only, . For we show that the
number density of sterile neutrinos is proportional to so that the
energy density today is {\it independent of} . However is crucial in
determining the large scale structure of the Universe. In particular, leads to warm dark matter and a structure formation
scenario that may have some advantages over both the standard hot and cold dark
matter scenarios.Comment: 10 pages (1 figure available upon request) phyzzx,
FERMILAB-Pub-93/057-
A Single Scale Theory for Cold and Hot Dark Matter
We show that a recently proposed extension of the MSSM can provide a scenario
where both the cold and hot dark matter of the universe owe their origin to a
single scale connected with the breakdown of the global B-L symmetry. The susy
partner of the majoron and the light Majorana neutrinos are the cold and hot
dark matter candidates respectively in this model and their desired relative
abundances emerge when the scale of B-L symmetry breaking is in the TeV range.Comment: UMD-PP-94-102 (latex file; 15 pages
Dissecting X-ray-emitting Gas around the Center of our Galaxy
Most supermassive black holes (SMBHs) are accreting at very low levels and
are difficult to distinguish from the galaxy centers where they reside. Our own
Galaxy's SMBH provides a uniquely instructive exception, and we present a
close-up view of its quiescent X-ray emission based on 3 mega-second of Chandra
observations. Although the X-ray emission is elongated and aligns well with a
surrounding disk of massive stars, we can rule out a concentration of low-mass
coronally active stars as the origin of the emission based on the lack of
predicted Fe Kalpha emission. The extremely weak H-like Fe Kalpha line further
suggests the presence of an outflow from the accretion flow onto the SMBH.
These results provide important constraints for models of the prevalent
radiatively inefficient accretion state.Comment: 18 pages, 5 PDF figures, pdflatex format; Final version, published in
Scienc
How do intrahousehold dynamics change when assets are transferred to women? Evidence from BRACâs âTargeting the Ultra Poorâ program in Bangladesh
BRACâs Challenging the Frontiers of Poverty Reduction Targeting the Ultra Poor (CFPR ÂŹâ TUP) program aims to assist the ultra poor in rural Bangladesh to rise out of extreme poverty and access mainstream development programming. CFPRâTUP Phase 2 âthe focus of the Gender, Agriculture, and Assets Projectâs study â operated from 2007 to 2011 in the poorest regions of Bangladesh. The program provided female members of ultra poor households with assets that could be maintained at home (primarily livestock such as cattle, goats, and poultry birds), as well as intensive training on how to use the assets for income -generating activities. Training subject matter included management practices and how to use improved technology. The GAAP studyâs aim was to explore how CFPRÂŹâTUP affected intrahousehold dynamics in beneficiary households, including menâs and womenâs ownership of and control over various assets (the transferred asset, as well as other assets) and roles in intrahousehold decision making. It also aimed to understand menâs and womenâs perceptions of these changes
On Active Current Selection for Lagrangian Profilers
Autonomous Lagrangian profilers are now widely used as measurement and monitoring platforms, notably in observation programs as Argo. In a typical mode of operation, the profilers drift passively at their parking depthbefore making a vertical profile to go back to the surface. This paperpresents simple and computationally-efficient control strategies to activelyselect and use ocean currents so that a profiler can autonomously reach adesired destination. After briefly presenting a typical profiler andpossible mechanical modifications for a coastal environment, we introducesimple mathematical models for the profiler and the currents it will use. Wethen present simple feedback controllers that, using the direction of thecurrents and taking into account the configuration of the environment(coastal or deep-sea), is able to steer the profiler to any desiredhorizontal location. To illustrate the approach, a few results are presentedusing both simulated currents and real current velocity profiles from theNorth Sea
- âŠ