1,347 research outputs found
Effect of engine, tank and propellant specific cost on single stage recoverable booster economics
Reusable first stages using hydrogen-oxygen, hydrogen-fluorine
and kerosine-oxygen are compared with non-reusable stages using a solid
in addition to the liquid combinations. The criterion used for comparison
is the minimum specific cost of the "loaded and ready for launch"
stage cost per unit of stage payload mass. A closed form relationship
is used in which the empty stage mass without payload is taken to scale
in part proportional to propellant mass, and in part to mass flow rate.
The stage specific cost is proportional to specific cost of engine (or
nozzle) tank and propellant. In the second part the hydrogen-oxygen
combination is consiaered,in more detail. The sensitivity of the
results to changes in various specific costs including that of refurbishing
are described.
Throughout, the stage velocity increments are compared in the
3000-6000 metres/second range with losses
Regular and First Order List Functions
We define two classes of functions, called regular (respectively, first-order) list functions, which manipulate objects such as lists, lists of lists, pairs of lists, lists of pairs of lists, etc. The definition is in the style of regular expressions: the functions are constructed by starting with some basic functions (e.g. projections from pairs, or head and tail operations on lists) and putting them together using four combinators (most importantly, composition of functions). Our main results are that first-order list functions are exactly the same as first-order transductions, under a suitable encoding of the inputs; and the regular list functions are exactly the same as MSO-transductions
Atmosphere breathing engines in astronautics
The contents of this note fall into two sections. Part I considers
the possibilities and problems involved in using ramjets as a power source
for one of the stages of a satellite launching vehicle or similar project.
In comparing such a system with rocket powered vehicles, consideration is
given to both performance and mass of the various systems. Various trajectories
are considered. This work includes a reassessment of projects that have been
suggested elsewhere.
The second part examines the possibility of using forms of ramjet in
the atmosphere of other planets. Because there is insufficient knowledge
of these atmospheres, a study has been carried out to determine the approximate
performance of a chemical ramjet in atmospheres of Methane, Ammonia, Hydrogen
and Carbon Dioxide at Mach 3. The work in Part II is original, there being
no previously reported papers on the subject known.
These studies, which are necessarily based on several simplifying
assumptions, indicate that applications for these engines may be expected
to arise in astronautics, and that this is a fruitful field for further
studies
Green's Relations in Finite Transformation Semigroups
We consider the complexity of Green's relations when the semigroup is given
by transformations on a finite set. Green's relations can be defined by
reachability in the (right/left/two-sided) Cayley graph. The equivalence
classes then correspond to the strongly connected components. It is not
difficult to show that, in the worst case, the number of equivalence classes is
in the same order of magnitude as the number of elements. Another important
parameter is the maximal length of a chain of components. Our main contribution
is an exponential lower bound for this parameter. There is a simple
construction for an arbitrary set of generators. However, the proof for
constant alphabet is rather involved. Our results also apply to automata and
their syntactic semigroups.Comment: Full version of a paper submitted to CSR 2017 on 2016-12-1
Traduction et validation française du Questionnaire de Répression de Weinberger
International audienceL'objectif de ce travail a été de réaliser une étude préliminaire de validation de la version française d'un questionnaire de répression émotionnelle (WAI, Weinberger Adjustment Inventory, 1989). Ses relations ont été explorées avec des évaluations de l'anxiété, de la dépression et de l'alexithymie
The impact of organizational performance on the emergence of Asian American leaders
Despite remarkably high levels of education and income, Asian Americans remain underrepresented at the top of the organizational hierarchy. Existing work suggests that a mismatch between the prototypical characteristics of business leaders (e.g., dominance) and stereotypes associated with Asian Americans (e.g., submissiveness) lowers the likelihood that Asian Americans will emerge as leaders. We predict that this reluctance to appoint Asian Americans will be attenuated when organizations experience performance decline because decision makers believe Asian Americans are inclined to sacrifice their self-interest to improve the welfare of others. We found support for these predictions using a multimethod approach. In an archival study of 4,951 CEOs across five decades, we find that Asian Americans were appointed almost two-and-a-half times more often during decline than nondecline (Study 1). Then, in three studies, we show that this pattern occurs because evaluators (a) prefer self-sacrificing leaders more when organizations are experiencing decline than success (Study 2); (b) expect Asian Americans leaders to behave in self-sacrificing ways in general (Study 3); and, consequently, (c) perceive that Asian Americans are better equipped to be leaders during decline than success (Study 4). We consider these findings in tandem with a set of exploratory analyses. This includes our finding that organizations experience decline only 12% of the time, suggesting that evaluators deem Asian Americans to be suitable leaders in circumstances that occur infrequently and are short-lived
Aspects of slurry management on pig farms.
End of Project ReportThe objectives of manure or slurry management on intensive pig farms
are the provision of adequate slurry storage capacity and the efficient
recycling of the slurry nutrients for crop production. However, recent
surveys of pig slurry dry matter suggest there is excessive dilution of
raw pig slurry with water. This has two important implications for
management. The first is greater storage capacity will be required due
to the increased volume of slurry generated. Slurry storage is expensive.
For example, a 350 sow unit adding 10 weeks storage needs to
invest £50,000. Secondly, evidence from the literature indicates an
improved slurry nitrogen efficiency with the more dilute manure. The results of field trials showed that higher dry matter pig slurries
reduced the relative efficiency of pig slurry nitrogen for second cut
silage production. This is probably linked to reduced ammonia volatilisation
losses, consequent to the less viscous nature of dilute slurry
which permits a more rapid infiltration of the ammonium nitrogen into
the soil. The use of a band spreader or shallow injection rather than
the conventional splash plate were shown to increase the efficiency of
pig slurry nitrogen for grass silage production. Therefore, the potential
for the higher pig slurry dry matter, required for cost effective storage/
handling costs, to reduce the efficiency of its nitrogen for grass
silage production can be partially offset by using band spreaders or
shallow injection spreading systems. These have the added advantage
of reducing odour emissions from the land spreading operation.Teagasc Walsh Fellowship Programm
Satellite Evidence of Hurricane-Induced Phytoplankton Blooms in an Oceanic Desert
The physical effects of hurricanes include deepening of the mixed layer and decreasing of the sea surface temperature in response to entrainment, curl-induced upwelling, and increased upper ocean cooling. However, the biological effects of hurricanes remain relatively unexplored. In this paper, we examine the passages of 13 hurricanes through the Sargasso Sea region of the North Atlantic during the years 1998 through 2001. Remotely sensed ocean color shows increased concentrations of surface chlorophyll within the cool wakes of the hurricanes, apparently in response to the injection of nutrients and/or biogenic pigments into the oligotrophic surface waters. This increase in post-storm surface chlorophyll concentration usually lasted 2-3 weeks before it returned to its nominal pre-hurricane level
Определение оптимальных параметров источника рентгеновского излучения на базе малогабаритного ускорителя электронов
Проведено моделирование спектров рентгеновского излучения, генерируемого электронами с энергией 4…10 МэВ в мишенях из различных материалов и разной толщины. Определены оптимальные параметры мишени-конвертора для использования ее в медицинских источниках монохроматического рентгеновского излучения на базе малогабаритных электронных ускорителей. Проведены оценки интенсивности излучения и сравнение источников на базе разных ускорителей
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