37,437 research outputs found
A hybrid boundary for the prediction of intake wave dynamics in IC engines
This paper concerns the calculation of wave dynamics in the intake systems of naturally aspirated internal combustion (I.C.) engines. In particular it presents a method for improving the boundary conditions required to solve the one-dimensional Euler equations that are commonly used to describe the wave dynamics in time and space.
A number of conclusions are reached in this work. The first relates to the quasi-steady state inflow boundary specified in terms of ingoing and outgoing characteristics that is commonly adopted for engine simulation. This is correctly specified by using the pair of primitive variables pressure (p) and density (ρ) but will be unrealistic at frequencies above a Hemholtz number of 0.1 as only stagnation values po, ρo are used. For the case of I.C. engine intake simulations this sets a maximum frequency of around 300Hz. Above that frequency the results obtained will become increasingly unrealistic.
Secondly, a hybrid time and frequency domain boundary has been developed and tested against linear acoustic theory. This agrees well with results obtained using a quasi-steady state boundary at low frequencies (Helmholtz number less than 0.1) and should remain realistic at higher frequencies in the range of Helmholtz number 0.1 - 1.84.
Thirdly, the cyclic nature of the operation of the IC engine has been exploited to make use of the inverse Fourier transform to develop an analytical hybrid boundary that functions for non-sinusoidal waves in ducts. The method is self starting, does not rely on iterations over complete cycles and is entirely analytical and therefore is an improvement over earlier hybrid boundaries
Heart catheter cable and connector
Ultraminiature catheter cables that are stiff enough for intravenous insertion yet flexible at the tip, sterilizable, and economical are fabricated entirely from commercially available parts. Assembly includes air passageway for reference pressures and coaxial cable for transmission of signals from the tip of catheter
Fully Constrained Majorana Neutrino Mass Matrices Using
In 2002, two neutrino mixing ansatze having trimaximally-mixed middle
() columns, namely tri-chi-maximal mixing () and
tri-phi-maximal mixing (), were proposed. In 2012, it was
shown that with as well as
with leads to the solution,
, consistent with the
latest measurements of the reactor mixing angle, . To obtain
and
, the type~I see-saw
framework with fully constrained Majorana neutrino mass matrices was utilised.
These mass matrices also resulted in the neutrino mass ratios,
.
In this paper we construct a flavour model based on the discrete group
and obtain the aforementioned results. A Majorana neutrino
mass matrix (a symmetric matrix with 6 complex degrees of freedom)
is conveniently mapped into a flavon field transforming as the complex 6
dimensional representation of . Specific vacuum alignments
of the flavons are used to arrive at the desired mass matrices.Comment: 20 pages, 1 figure. arXiv admin note: substantial text overlap with
arXiv:1402.085
Deviations from Tribimaximal Neutrino Mixing using a Model with Symmetry
We present a model of neutrino mixing based on the flavour group
in order to account for the observation of a non-zero reactor mixing angle
(). The model provides a common flavour structure for the
charged-lepton and the neutrino sectors, giving their mass matrices a
`circulant-plus-diagonal' form. Mass matrices of this form readily lead to
mixing patterns with realistic deviations from tribimaximal mixing, including
non-zero . With the parameters constrained by existing
measurements, our model predicts an inverted neutrino mass hierarchy. We obtain
two distinct sets of solutions in which the atmospheric mixing angle lies in
the first and the second octants. The first (second) octant solution predicts
the lightest neutrino mass, ()
and the phase, (), offering the possibility of large observable violating
effects in future experiments.Comment: 9 pages, 3 figure
Spatial Relationship between Solar Flares and Coronal Mass Ejections
We report on the spatial relationship between solar flares and coronal mass
ejections (CMEs) observed during 1996-2005 inclusive. We identified 496
flare-CME pairs considering limb flares (distance from central meridian > 45
deg) with soft X-ray flare size > C3 level. The CMEs were detected by the Large
Angle and Spectrometric Coronagraph (LASCO) on board the Solar and Heliospheric
Observatory (SOHO). We investigated the flare positions with respect to the CME
span for the events with X-class, M-class, and C-class flares separately. It is
found that the most frequent flare site is at the center of the CME span for
all the three classes, but that frequency is different for the different
classes. Many X-class flares often lie at the center of the associated CME,
while C-class flares widely spread to the outside of the CME span. The former
is different from previous studies, which concluded that no preferred flare
site exists. We compared our result with the previous studies and conclude that
the long-term LASCO observation enabled us to obtain the detailed spatial
relation between flares and CMEs. Our finding calls for a closer flare-CME
relationship and supports eruption models typified by the CSHKP magnetic
reconnection model.Comment: 7 pages; 4 figures; Accepted by the Astrophysical Journa
Positive selection underlies Faster-Z evolution of gene expression in birds.
The elevated rate of evolution for genes on sex chromosomes compared to autosomes (Fast-X or Fast-Z evolution) can result either from positive selection in the heterogametic sex, or from non-adaptive consequences of reduced relative effective population size. Recent work in birds suggests that Fast-Z of coding sequence is primarily due to relaxed purifying selection resulting from reduced relative effective population size. However, gene sequence and gene expression are often subject to distinct evolutionary pressures, therefore we tested for Fast-Z in gene expression using next-generation RNA-sequencing data from multiple avian species. Similar to studies of Fast-Z in coding sequence, we recover clear signatures of Fast-Z in gene expression, however in contrast to coding sequence, our data indicate that Fast-Z in expression is due to positive selection acting primarily in females. In the soma, where gene expression is highly correlated between the sexes, we detected Fast-Z in both sexes, although at a higher rate in females, suggesting that many positively selected expression changes in females are also expressed in males. In the gonad, where inter-sexual correlations in expression are much lower, we detected Fast-Z for female gene expression, but crucially, not males. This suggests that a large amount of expression variation is sex-specific in its effects within the gonad. Taken together, our results indicate that Fast-Z evolution of gene expression is the product of positive selection acting on recessive beneficial alleles in the heterogametic sex. More broadly, our analysis suggests that the adaptive potential of Z chromosome gene expression may be much greater than that of gene sequence, results which have important implications for the role of sex chromosomes in speciation and sexual selection
Oscillating Neutrinos from the Galactic Center
It has recently been demonstrated that the -ray emission spectrum of
the EGRET-identified, central Galactic source 2EG J1746-2852 can be well fitted
by positing that these photons are generated by the decay of 's produced
in p-p scattering at or near an energizing shock. Such scattering also produces
charged pions which decay leptonically.The ratio of -rays to neutrinos
generated by the central Galactic source may be accurately determined and a
well-defined and potentially-measurable high energy neutrino flux at Earth is
unavoidable. An opportunity, therefore, to detect neutrino oscillations over an
unprecedented scale is offered by this source. In this paper we assess the
prospects for such an observation with the generation of neutrino \v{C}erenkov
telescopes now in the planning stage. We determine that the next generation of
detectors may find an oscillation signature in the Galactic Center (GC) signal.Comment: 45 pages, LaTeX, uses ApJ style, some minor revisions, this final
version to be published in ApJ
Accommodating repair actions into gas turbine prognostics
Elements of gas turbine degradation, such as compressor
fouling, are recoverable through maintenance actions like
compressor washing. These actions increase the usable engine
life and optimise the performance of the gas turbine.
However, these maintenance actions are performed by a separate
organization to those undertaking fleet management operations,
leading to significant uncertainty in the maintenance
state of the asset. The uncertainty surrounding maintenance
actions impacts prognostic efficacy. In this paper, we adopt
Bayesian on-line change point detection to detect the compressor
washing events. Then, the event detection information
is used as an input to a prognostic algorithm, advising an
update to the estimation of remaining useful life. To illustrate
the capability of the approach, we demonstrated our on-line
Bayesian change detection algorithms on synthetic and real
aircraft engine service data, in order to identify the compressor
washing events for a gas turbine and thus provide demonstrably
improved prognosis
Gamma-Ray Burst Spectral Features: Interpretation as X-ray Emission From A Photoionized Plasma
Numerous reports have been made of features, either in emission or
absorption, in the 10 - 1000 keV spectra of some gamma-ray bursts. Originally
interpreted in the context of Galactic neutron star models as cyclotron line
emission and annihilation features, the recent demonstration that
the majority of GRBs lie at cosmological distances make these explanations
unlikely. In this letter, we adopt a relativistic fireball model for
cosmological GRBs in which dense, metal rich blobs or filaments of plasma are
entrained in the relativistic outflow. In the context of this model, we
investigate the conditions under which broadband features, similar to those
detected, can be observed. We find a limited region of parameter space capable
of reproducing the observed GRB spectra. Finally, we discuss possible
constraints further high-energy spectral observations could place on fireball
model parameters.Comment: Accepted for publication in Astrophysical Journal Letters Four pages,
2 figure
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