26,004 research outputs found
The 21st century propulsion
The prediction of future space travel in the next millennium starts by examining the past and extrapolating into the far future. Goals for the 21st century include expanded space travel and establishment of permanent manned outposts, and representation of Lunar and Mars outposts as the most immediate future in space. Nuclear stage design/program considerations; launch considerations for manned Mars missions; and far future propulsion schemes are outlined
Cargo launch vehicles to low earth orbit
There are two primary space transportation capabilities required to support both base programs and expanded mission requirements: earth-to-orbit (ETO) transportation systems and space transfer vehicle systems. Existing and new ETO vehicles required to support mission requirements, and planned robotic missions, along with currently planned ETO vehicles are provided. Lunar outposts, Mars' outposts, base and expanded model, ETO vehicles, advanced avionics technologies, expert systems, network architecture and operations systems, and technology transfer are discussed
Ambulance Emergency Response Optimization in Developing Countries
The lack of emergency medical transportation is viewed as the main barrier to
the access of emergency medical care in low and middle-income countries
(LMICs). In this paper, we present a robust optimization approach to optimize
both the location and routing of emergency response vehicles, accounting for
uncertainty in travel times and spatial demand characteristic of LMICs. We
traveled to Dhaka, Bangladesh, the sixth largest and third most densely
populated city in the world, to conduct field research resulting in the
collection of two unique datasets that inform our approach. This data is
leveraged to develop machine learning methodologies to estimate demand for
emergency medical services in a LMIC setting and to predict the travel time
between any two locations in the road network for different times of day and
days of the week. We combine our robust optimization and machine learning
frameworks with real data to provide an in-depth investigation into three
policy-related questions. First, we demonstrate that outpost locations
optimized for weekday rush hour lead to good performance for all times of day
and days of the week. Second, we find that significant improvements in
emergency response times can be achieved by re-locating a small number of
outposts and that the performance of the current system could be replicated
using only 30% of the resources. Lastly, we show that a fleet of small
motorcycle-based ambulances has the potential to significantly outperform
traditional ambulance vans. In particular, they are able to capture three times
more demand while reducing the median response time by 42% due to increased
routing flexibility offered by nimble vehicles on a larger road network. Our
results provide practical insights for emergency response optimization that can
be leveraged by hospital-based and private ambulance providers in Dhaka and
other urban centers in LMICs
Why Zimbabwe needs a long term industrial strategy
This is a paper by Boston University professor Ann Seidma
Fragmentalist Presentist Perdurantism
Perdurantists think of continuants as mereological sums of stages from different times. This view of persistence would force us to drop the idea that there is genuine change in the world. By exploiting a presentist metaphysics, Brogaard proposed a theory, called presentist four-dimensionalism, that aims to reconcile perdurantism with the idea that things undergo real change. However, her proposal commits us to reject the idea that stages must exist in their entirety. Giving up the tenet that all the stages are equally real could be a price that perdurantists are unwilling to pay. I argue that Kit Fine ’s fragmentalism provides us with the tools to combine a presentist metaphysics with a perdurantist theory of persistence without giving up the idea that reality is constituted by more than purely present stages
Treason at Quebec: British Espionage in Canada during the Winter of 1759
In the spring of 1760, the British garrison at Québec, commanded by James Murray, found itself the target of a French army intent upon the recapture of the colonial capital. Led by the exceptionally able François de Levis, the French hoped to surprise Murray’s outnumbered and isolated army, but even as the French embarked at Montreal on 20 May, Murray was writing that he had “received certain intelligence” of French preparations and had taken appropriate precautions. Much of this foreknowledge came from British spies working behind the French lines. Although prior to September 1759 the British had not possessed a single operative in Canada, Québec, now in British hands, became the base for a modest espionage organization which proved capable of scattering informants throughout the towns and countryside of New France and recruiting at least one agent in the confidence of the very highest officials of the colonial administration
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Automated Additive Construction (AAC) for Earth and Space Using In-situ Resources
Using Automated Additive Construction (AAC), low-fidelity large-scale compressive structures can be produced out of a wide variety of materials found in the environment. Compressionintensive structures need not utilize materials that have tight specifications for internal force management, meaning that the production of the building materials do not require costly methods for their preparation. Where a certain degree of surface roughness can be tolerated, lower-fidelity numerical control of deposited materials can provide a low-cost means for automating building processes, which can be utilized in remote or extreme environments on Earth or in Space. For space missions where every kilogram of mass must be lifted out of Earth’s gravity well, the promise of using in-situ materials for the construction of outposts, facilities, and installations could prove to be enabling if significant reduction of payload mass can be achieved. In a 2015 workshop sponsored by the Keck nstitute for Space Studies, on the topic of Three Dimensional (3D) Additive Construction For Space Using In-situ Resources, was conducted with additive construction experts from around the globe in attendance. The workshop explored disparate efforts, methods, and technologies and established a proposed framework for the field of Additive Construction Using In-situ Resources.
This paper defines the field of Automated Additive Construction Using In-situ Resources, describes the state-of-the-art for various methods, establishes a vision for future efforts, identifies gaps in current technologies, explores investment opportunities, and proposes potential technology demonstration missions for terrestrial, International Space Station (ISS), lunar, deep space zero-gravity, and Mars environments
Unknown chapter in Caucasian war (1848–1851): Black sea coastline and mining
The article concerns the unknown chapter in Caucasian War within the Black Sea coastline, namely mine outposts establishment and operational use
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