4,327 research outputs found
Scale Model Acoustic Test Validation of IOP-SS Water Prediction using Loci-STREAM-VoF
The Scale Model Acoustic Test (SMAT) is a 5% scale test of the Space Launch System (SLS), which is currently being designed at Marshall Space Flight Center (MSFC). SMAT consists of a 5% scale representation of the ignition overpressure sound-suppression system (IOP-SS) that is being tested to quantify the water flow and induced air entrainment in and around the mobile launcher exhaust hole. This data will be compared with computational fluid dynamics (CFD) simulations using the newly developed Loci-STREAM Volume of Fluid (VoF) methods. Compressible and incompressible VoF methods have been formulated, and are currently being used to simulate the water flow of SMAT IOP-SS. The test data will be used to qualitatively and quantitatively assess and validate the VoF methods
Saprolegnia diclina IIIA and S. parasitica employ different infection strategies when colonizing eggs of Atlantic salmon, Salmo salar L.
Acknowledgements The work has been funded by the European Commission through the EU Marie Curie ITN project SAPRO (238550) (MMS, AW). We would also like to acknowledge support from the BBSRC and the University of Aberdeen (PvW) and Landcatch and AquaGen for providing salmon eggs. Elin Rolen's assistance with sequencing of the strains is highly appreciated.Peer reviewedPublisher PD
Multi-party entanglement in graph states
Graph states are multi-particle entangled states that correspond to
mathematical graphs, where the vertices of the graph take the role of quantum
spin systems and edges represent Ising interactions. They are many-body spin
states of distributed quantum systems that play a significant role in quantum
error correction, multi-party quantum communication, and quantum computation
within the framework of the one-way quantum computer. We characterize and
quantify the genuine multi-particle entanglement of such graph states in terms
of the Schmidt measure, to which we provide upper and lower bounds in graph
theoretical terms. Several examples and classes of graphs will be discussed,
where these bounds coincide. These examples include trees, cluster states of
different dimension, graphs that occur in quantum error correction, such as the
concatenated [7,1,3]-CSS code, and a graph associated with the quantum Fourier
transform in the one-way computer. We also present general transformation rules
for graphs when local Pauli measurements are applied, and give criteria for the
equivalence of two graphs up to local unitary transformations, employing the
stabilizer formalism. For graphs of up to seven vertices we provide complete
characterization modulo local unitary transformations and graph isomorphies.Comment: 22 pages, 15 figures, 2 tables, typos corrected (e.g. in measurement
rules), references added/update
Computational Fluid Dynamics Study on the Effects of RATO Timing on the Scale Model Acoustic Test
The Scale Model Acoustic Test (SMAT) is a 5% scale test of the Space Launch System (SLS), which is currently being designed at Marshall Space Flight Center (MSFC). The purpose of this test is to characterize and understand a variety of acoustic phenomena that occur during the early portions of lift off, one being the overpressure environment that develops shortly after booster ignition. The SLS lift off configuration consists of four RS-25 liquid thrusters on the core stage, with two solid boosters connected to each side. Past experience with scale model testing at MSFC (in ER42), has shown that there is a delay in the ignition of the Rocket Assisted Take Off (RATO) motor, which is used as the 5% scale analog of the solid boosters, after the signal to ignite is given. This delay can range from 0 to 16.5ms. While this small of a delay maybe insignificant in the case of the full scale SLS, it can significantly alter the data obtained during the SMAT due to the much smaller geometry. The speed of sound of the air and combustion gas constituents is not scaled, and therefore the SMAT pressure waves propagate at approximately the same speed as occurs during full scale. However, the SMAT geometry is much smaller allowing the pressure waves to move down the exhaust duct, through the trench, and impact the vehicle model much faster than occurs at full scale. To better understand the effect of the RATO timing simultaneity on the SMAT IOP test data, a computational fluid dynamics (CFD) analysis was performed using the Loci/CHEM CFD software program. Five different timing offsets, based on RATO ignition delay statistics, were simulated. A variety of results and comparisons will be given, assessing the overall effect of RATO timing simultaneity on the SMAT overpressure environment
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Quantile forecasts of daily exchange rate returns from forecasts of realized volatility
Quantile forecasts are central to risk management decisions because of the widespread
use of Value-at-Risk. A quantile forecast is the product of two factors: the model used to
forecast volatility, and the method of computing quantiles from the volatility forecasts. In
this paper we calculate and evaluate quantile forecasts of the daily exchange rate returns
of five currencies. The forecasting models that have been used in recent analyses of the
predictability of daily realized volatility permit a comparison of the predictive power of
different measures of intraday variation and intraday returns in forecasting exchange rate
variability. The methods of computing quantile forecasts include making distributional
assumptions for future daily returns as well as using the empirical distribution of predicted
standardized returns with both rolling and recursive samples. Our main findings are that the
Heterogenous Autoregressive model provides more accurate volatility and quantile forecasts
for currencies which experience shifts in volatility, such as the Canadian dollar, and that
the use of the empirical distribution to calculate quantiles can improve forecasts when there
are shifts
A 2-dimensional Geometry for Biological Time
This paper proposes an abstract mathematical frame for describing some
features of biological time. The key point is that usual physical (linear)
representation of time is insufficient, in our view, for the understanding key
phenomena of life, such as rhythms, both physical (circadian, seasonal ...) and
properly biological (heart beating, respiration, metabolic ...). In particular,
the role of biological rhythms do not seem to have any counterpart in
mathematical formalization of physical clocks, which are based on frequencies
along the usual (possibly thermodynamical, thus oriented) time. We then suggest
a functional representation of biological time by a 2-dimensional manifold as a
mathematical frame for accommodating autonomous biological rhythms. The
"visual" representation of rhythms so obtained, in particular heart beatings,
will provide, by a few examples, hints towards possible applications of our
approach to the understanding of interspecific differences or intraspecific
pathologies. The 3-dimensional embedding space, needed for purely mathematical
reasons, allows to introduce a suitable extra-dimension for "representation
time", with a cognitive significance.Comment: Presented in an invited Lecture, conference "Biologie e selezioni
naturali", Florence, December 4-8, 200
Sex differences in health at ages 11, 13 and 15
This paper tests the hypothesis of an emerging or increasing female excess in general ill-health and physical symptoms, as well as psychological distress, during early to mid-adolescence. Self-reported data on general health (longstanding illness and health in the last 12 months), recent symptoms (classified as ‘physical’ and ‘malaise’) and depressive mood were obtained from a large, Scottish, school-based cohort at ages 11, 13 and 15. Generally high levels of health problems at age 11 tended to increase with age, these increases being greater for females than males, not only in respect of depression and ‘malaise’ symptoms, but also limiting illness, ‘poor’ self-rated health, headaches, stomach problems and dizziness. The consequence, by age 15, is the emergence of a female excess in general ill-health and depressive mood, and a substantial strengthening of the small excess in both ‘physical’ and ‘malaise’ symptoms already apparent at 11 years. These findings are discussed in relation to explanations for the adult female excess in poorer health, and the emergence of a female excess of depression during adolescence
Computational equivalence of the two inequivalent spinor representations of the braid group in the Ising topological quantum computer
We demonstrate that the two inequivalent spinor representations of the braid
group \B_{2n+2}, describing the exchanges of 2n+2 non-Abelian Ising anyons in
the Pfaffian topological quantum computer, are equivalent from computational
point of view, i.e., the sets of topologically protected quantum gates that
could be implemented in both cases by braiding exactly coincide. We give the
explicit matrices generating almost all braidings in the spinor representations
of the 2n+2 Ising anyons, as well as important recurrence relations. Our
detailed analysis allows us to understand better the physical difference
between the two inequivalent representations and to propose a process that
could determine the type of representation for any concrete physical
realization of the Pfaffian quantum computer.Comment: 9 pages, 2 figures, published versio
Application of homogeneously precipitated nanosized Fe-doped alumina powders to carbon nanotube growth.
Homogeneous precipitation of hydroxides was investigated as an alternative method to synthesize Fe-doped aluminum oxide (α-Al2−2xFe2xO3) particles over which carbon nanotubes (CNTs) were grown via a catalytic chemical vapor deposition (CCVD) method. Performance of the homogeneously precipitated particles for CNT growth was quantitatively compared with that of the combustion-synthesized particles. The main advantage of the homogeneous precipitation of hydroxides and subsequent calcination process against to the combustion synthesis and other commonly practiced chemical routes is the ability to tailor the Fe-doped Al2O3 precursor powder characteristics such as size and specific surface area (SSA) without requiring any milling step and also to control the phase composition of the oxide powder with high Fe content, and subsequently the quality and quantity of CNTs during CCVD process. The particle size of the precipitated and calcined α-Al2−2xFe2xO3 powders varies between ∼50 and 400 nm for 5–10 cat.% Fe-containing systems. The monodispersed particle size distribution and optimum phase composition of the homogeneously precipitated powders, particularly for a 10 cat.% Fe content in the starting oxide, and their much higher SSA than similar materials prepared by other chemical routes lead to production of high amounts of good quality CNTs
Quantum Computing with Continuous-Variable Clusters
Continuous-variable cluster states offer a potentially promising method of
implementing a quantum computer. This paper extends and further refines
theoretical foundations and protocols for experimental implementation. We give
a cluster-state implementation of the cubic phase gate through photon
detection, which, together with homodyne detection, facilitates universal
quantum computation. In addition, we characterize the offline squeezed
resources required to generate an arbitrary graph state through passive linear
optics. Most significantly, we prove that there are universal states for which
the offline squeezing per mode does not increase with the size of the cluster.
Simple representations of continuous-variable graph states are introduced to
analyze graph state transformations under measurement and the existence of
universal continuous-variable resource states.Comment: 17 pages, 5 figure
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