5,818 research outputs found
Flow properties of concentrated suspensions
The viscosity and flow behavior of a concentrated suspension, with special emphasis on fresh concrete containing a superplasticizer, is analyzed according to Newton's law of viscosity. The authors interpreted Newton's law in a new way, and explain non-Newton flow from Newton's law. The outline of this new theory is given. Viscosity of suspensions, and the effect of dispersants are analyzed
Descent strategy comparisons for TNAV-equipped aircraft under airplane-preferred operating conditions
Three 4-D descent strategies were evaluated which were employed by TNAV-equipped aircraft in an advanced metering air traffic control environment. The Flow Management Evaluation Model (FMEM) was used to assess performance using three criteria when traffic enters the simulation under preferred cruise operating conditions (altitude and speed): throughput, fuel usage, and conflict probability. In comparison to an evaluation previously performed under NASA contract, the current analysis indicates that the optimal descent strategy is preferred over the clean-idle and constant descent angle (CFPA) strategies when all three criteria are considered
Particle production in models with helicity-0 graviton ghost in de Sitter spacetime
We revisit the problem of the helicity-0 ghost mode of massive graviton in
the de Sitter background. In general, the presence of a ghost particle, which
has negative energy, drives the vacuum to be unstable through pair production
of ghost particles and ordinary particles. In the case that the vacuum state
preserves the de Sitter invariance, the number density created by the pair
production inevitably diverges due to unsuppressed ultra-violet(UV)
contributions. In such cases one can immediately conclude that the model is not
viable. However, in the massive gravity theory we cannot construct a vacuum
state which respects the de Sitter invariance. Therefore the presence of a
ghost does not immediately mean the breakdown of the model. Explicitly
estimating the number density and the energy density of particles created by
the pair production of two conformal scalar particles and one helicity-0 ghost
graviton, we find that these densities both diverge. However, since models with
helicity-0 ghost graviton have no de Sitter invariant vacuum state, it is
rather natural to consider a UV cutoff scale in the three-dimensional momentum
space. Then, even if we take the cutoff scale as large as the Planck scale, the
created number density and energy density are well suppressed. In many models
the cutoff scale is smaller than the Planck scale. In such models the created
number density and the energy density are negligiblly small as long as only the
physics below the cutoff scale is concerned.Comment: 7 pages, 1 figur
No de Sitter invariant vacuum in massive gravity theory with ghost
In this letter we point out that the massive gravity theory with a graviton
ghost mode in de Sitter background cannot possess a de Sitter invariant vacuum
state. In order to avoid a negative norm state, we must associate the creation
operator of the ghost mode with a negative-energy mode function instead of a
positive-energy one as the mode function. Namely, we have to adopt a different
procedure of quantization for a ghost. When a theory has a symmetry mixing a
ghost mode with ordinary non-ghost modes, the choice of a ghost mode is not
unique. However, quantization of a ghost is impossible without specifying a
choice of ghost mode, which breaks the symmetry. For this reason, the vacuum
state cannot respect the symmetry. In the massive gravity theory with a
graviton ghost mode in de Sitter background, the ghost is the helicity-0 mode
of the graviton. This ghost mode is mixed with the other helicity graviton
modes under the action of de Sitter symmetry. Therefore, there is no de Sitter
invariant vacuum in such models. This leads to an interesting possibility that
non-covariant cutoff of the low energy effective theory may naturally arise. As
a result, the instability due to the pair production of a ghost and normal
non-ghost particles gets much milder and that the model may escape from being
rejected.Comment: 5 page
A conflict analysis of 4D descent strategies in a metered, multiple-arrival route environment
A conflict analysis was performed on multiple arrival traffic at a typical metered airport. The Flow Management Evaluation Model (FMEM) was used to simulate arrival operations using Denver Stapleton's arrival route structure. Sensitivities of conflict performance to three different 4-D descent strategies (clear-idle Mach/Constant AirSpeed (CAS), constant descent angle Mach/CAS and energy optimal) were examined for three traffic mixes represented by those found at Denver Stapleton, John F. Kennedy and typical en route metering (ERM) airports. The Monte Carlo technique was used to generate simulation entry point times. Analysis results indicate that the clean-idle descent strategy offers the best compromise in overall performance. Performance measures primarily include susceptibility to conflict and conflict severity. Fuel usage performance is extrapolated from previous descent strategy studies
Superluminal Propagation and Acausality of Nonlinear Massive Gravity
Massive gravity is an old idea: trading geometry for mass. Much effort has
been expended on establishing a healthy model, culminating in the current
ghost-free version. We summarize here our recent findings -- that it is still
untenable -- because it is locally acausal: CTC solutions can be constructed in
a small neighborhood of any event.Comment: Contribution to Conference in Honour of the 90th Birthday of Freeman
Dyson -- To Appear in Proceeding. v2: Explicit CTC example, and other
improvements, adde
NMR relaxation of quantum spin chains in magnetic fields
We investigate NMR relaxation rates 1/T_1 of quantum spin chains in magnetic
fields. Universal properties for the divergence behavior of 1/T_1 are obtained
in the Tomonaga-Luttinger-liquid state. The results are discussed in comparison
with experimental results.Comment: 5 pages, 3 figure
Hsp90 picks PIKKs via R2TP and Tel2
Phosphatidylinositol-3 kinase-like kinases (PIKKs) are dependent on Hsp90 for their activation via the R2TP complex and Tel2. In this issue of Structure, Pal and colleagues present the molecular mechanism by which PIKKs are recruited to Hsp90
Effects of slopes and spaces of protrusions in fish ladder for eels on migration rate of Anguilla japonica
In recent year, populations of Anguilla japonica have been decreasing sharply. This decrease is partly because it is estimated to be overfishing of Anguilla japonica, the deterioration of the river environment and so on. Migrating fishes are impeded by weirs and dams in the river. Fishways have been constructed to swimming fish like Plecoglossus altivelis altivelis in order to solve this problem. On the other hand, it is thought that special fishway is necessary for demersal fish like eels. Furthermore, studies on fish ladder for eels haven’t been conducted. In the present study, an investigation on migration rate of Anguilla japonica was conducted under the condition that slope of fish ladder for eels and spaces of protrusions are changed. It was found that migration rates decreased with the increase of slopes and spaces of protrusions. Besides, Anguilla japonica migrated while using protrusions by serpentine movement.The 11th Pacific Symposium on Flow Visualization and Image Processing, 2017, 1-3 December, Kumamoto, Japa
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