390,468 research outputs found
Analysis of quasi-hybrid solid rocket booster concepts for advanced earth-to-orbit vehicles
A study was conducted to assess the feasibility of quasi-hybrid solid rocket boosters for advanced Earth-to-orbit vehicles. Thermochemical calculations were conducted to determine the effect of liquid hydrogen addition, solids composition change plus liquid hydrogen addition, and the addition of an aluminum/liquid hydrogen slurry on the theoretical performance of a PBAN solid propellant rocket. The space shuttle solid rocket booster was used as a reference point. All three quasi-hybrid systems theoretically offer higher specific impulse when compared with the space shuttle solid rocket boosters. However, based on operational and safety considerations, the quasi-hybrid rocket is not a practical choice for near-term Earth-to-orbit booster applications. Safety and technology issues pertinent to quasi-hybrid rocket systems are discussed
Breaking Dense Structures: Proving Stability of Densely Structured Hybrid Systems
Abstraction and refinement is widely used in software development. Such
techniques are valuable since they allow to handle even more complex systems.
One key point is the ability to decompose a large system into subsystems,
analyze those subsystems and deduce properties of the larger system. As
cyber-physical systems tend to become more and more complex, such techniques
become more appealing.
In 2009, Oehlerking and Theel presented a (de-)composition technique for
hybrid systems. This technique is graph-based and constructs a Lyapunov
function for hybrid systems having a complex discrete state space. The
technique consists of (1) decomposing the underlying graph of the hybrid system
into subgraphs, (2) computing multiple local Lyapunov functions for the
subgraphs, and finally (3) composing the local Lyapunov functions into a
piecewise Lyapunov function. A Lyapunov function can serve multiple purposes,
e.g., it certifies stability or termination of a system or allows to construct
invariant sets, which in turn may be used to certify safety and security.
In this paper, we propose an improvement to the decomposing technique, which
relaxes the graph structure before applying the decomposition technique. Our
relaxation significantly reduces the connectivity of the graph by exploiting
super-dense switching. The relaxation makes the decomposition technique more
efficient on one hand and on the other allows to decompose a wider range of
graph structures.Comment: In Proceedings ESSS 2015, arXiv:1506.0325
Constraining strangeness in dense matter with GW170817
Particles with strangeness content are predicted to populate dense matter,
modifying the equation of state of matter inside neutron stars as well as their
structure and evolution. In this work, we show how the modeling of strangeness
content in dense matter affects the properties of isolated neutrons stars and
the tidal deformation in binary systems. For describing nucleonic and hyperonic
stars we use the many-body forces model (MBF) at zero temperature, including
the mesons for the description of repulsive hyperon-hyperon
interactions. Hybrid stars are modeled using the MIT Bag Model with vector
interaction (vMIT) in both Gibbs and Maxwell constructions, for different
values of bag constant and vector interaction couplings. A parametrization with
a Maxwell construction, which gives rise to third family of compact stars (twin
stars), is also investigated. We calculate the tidal contribution that adds to
the post-Newtonian point-particle corrections, the associated love number for
sequences of stars of different composition (nucleonic, hyperonic, hybrid and
twin stars), and determine signatures of the phase transition on the
gravitational waves in the accumulated phase correction during the inspirals
among different scenarios for binary systems. On the light of the recent
results from GW170817 and the implications for the radius of
stars, our results show that hybrid stars can
only exist if a phase transition takes place at low densities close to
saturation
Composition of Stochastic Transition Systems Based on Spans and Couplings
Conventional approaches for parallel composition of stochastic systems relate probability measures of the individual components in terms of product measures. Such approaches rely on the assumption that components interact stochastically independent, which might be too rigid for modeling real world systems. In this paper, we introduce a parallel-composition operator for stochastic transition systems that is based on couplings of probability measures and does not impose any stochastic assumptions. When composing systems within our framework, the intended dependencies between components can be determined by providing so-called spans and span couplings. We present a congruence result for our operator with respect to a standard notion of bisimilarity and develop a general theory for spans, exploiting deep results from descriptive set theory. As an application of our general approach, we propose a model for stochastic hybrid systems called stochastic hybrid motion automata
Assessment of the Thermal Conductivity of BN-C Nanostructures
Chemical and structural diversity present in hexagonal boron nitride ((h-BN)
and graphene hybrid nanostructures provide new avenues for tuning various
properties for their technological applications. In this paper we investigate
the variation of thermal conductivity () of hybrid graphene/h-BN
nanostructures: stripe superlattices and BN (graphene) dots embedded in
graphene (BN) are investigated using equilibrium molecular dynamics. To
simulate these systems, we have parameterized a Tersoff type interaction
potential to reproduce the ab initio energetics of the B-C and N-C bonds for
studying the various interfaces that emerge in these hybrid nanostructures. We
demonstrate that both the details of the interface, including energetic
stability and shape, as well as the spacing of the interfaces in the material
exert strong control on the thermal conductivity of these systems. For stripe
superlattices, we find that zigzag configured interfaces produce a higher
in the direction parallel to the interface than the armchair
configuration, while the perpendicular conductivity is less prone to the
details of the interface and is limited by the of h-BN. Additionally,
the embedded dot structures, having mixed zigzag and armchair interfaces,
affects the thermal transport properties more strongly than superlattices.
Though dot radius appears to have little effect on the magnitude of reduction,
we find that dot concentration (50% yielding the greatest reduction) and
composition (embedded graphene dots showing larger reduction that h-BN dot)
have a significant effect
Mutual maintenance of di- and triploid Pelophylax esculentus hybrids in R-E systems: results fro
Background: Interspecies animal hybrids can employ clonal or hemiclonal reproduction modes where one or all
parental genomes are transmitted to the progeny without recombination. Nevertheless, some interspecies
hybrids retain strong connection with the parental species needed for successful reproduction. Appearance of
polyploid hybrid animals may play an important role in the substitution of parental species and in the
speciation process.
Results: To establish the mechanisms that enable parental species, diploid and polyploid hybrids coexist we
have performed artificial crossing experiments of water frogs of Pelophylax esculentus complex. We identified
tadpole karyotypes and oocyte genome composition in all females involved in the crossings. The majority of
diploid and triploid hybrid frogs produced oocytes with 13 bivalents leading to haploid gametes with the
same genome as parental species hybrids usually coexist with. After fertilization of such gametes only diploid
animals appeared. Oocytes with 26 bivalents produced by some diploid hybrid frogs lead to diploid gametes,
which give rise to triploid hybrids after fertilization. In gonads of all diploid and triploid hybrid tadpoles we
found DAPI-positive micronuclei (nucleus-like bodies) involved in selective genome elimination. Hybrid male
and female individuals produced tadpoles with variable karyotype and ploidy even in one crossing owing to
gametes with various genome composition.
Conclusions: We propose a model of diploid and triploid hybrid frog reproduction in R-E population systems.
Triploid Pelophylax esculentus hybrids can transmit genome of parental species they coexist with by producing
haploid gametes with the same genome composition. Triploid hybrids cannot produce triploid individuals
after crossings with each other and depend on diploid hybrid females producing diploid eggs. In contrast to
other population systems, the majority of diploid and triploid hybrid females unexpectedly produced gametes
with the same genome as parental species hybrids coexist with
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