40,111 research outputs found
"Ladder" structure in tonal noise generated by laminar flow around an airfoil
The presence of a âladderâ structure in the airfoil tonal noise was discovered in the 1970s, but its mechanism hitherto remains a subject of continual investigation in the research community. Based on the measured noise results and some numerical analysis presented in this letter, the variations of four types of airfoil tonal noise frequencies with the flow velocity were analyzed individually. The ladder structure is proposed to be caused by the acoustic/hydrodynamic frequency lag between the scattering of the boundary layer instability noise and the discrete noise produced by an aeroacoustic feedback loop
Application of EFT at Thermal Energies
We have been evaluated some observables of n-d systems by using pionless
Effective Field Theory(\EFTNoPion) and insertion of the three-body force up to
next-to-next to leading order(NLO). The evaluated data has been compared
with experimental and the three-nucleon calculation of the total cross section
with modern realistic two- and three-nucleon forces AV18/UrbIX potential models
calculations.Comment: 3 pages, 1 figure and 1 table. Talk given at 20th European Conference
on Few-Body Problems in Physics (EFB 20), Pisa, Italy, 10-14 Sep 200
Towards sympathetic cooling of large molecules: Cold collisions between benzene and rare gas atoms
This paper reports on calculations of collisional cross sections for the complexes Z-CDH6 (X = 3He, 4He, Ne) at temperatures in the range 1)ÎŒK - 10K and shows that relatively large cross sections in the 103-105Ă
2 range are available for collisional cooling. Both elastic and inelastic processes are considered in this temperature range. The calculations suggest that sympathetically cooling benzene to microkelvin temperatures is feasible using these co-trapped rare gas atoms in an optical trap. © IOP Publishing Ltd and Deutsche Physikalische Gesellschan
The propositional nature of human associative learning
The past 50 years have seen an accumulation of evidence suggesting that associative learning depends oil high-level cognitive processes that give rise to propositional knowledge. Yet, many learning theorists maintain a belief in a learning mechanism in which links between mental representations are formed automatically. We characterize and highlight the differences between the propositional and link approaches, and review the relevant empirical evidence. We conclude that learning is the consequence of propositional reasoning processes that cooperate with the unconscious processes involved in memory retrieval and perception. We argue that this new conceptual framework allows many of the important recent advances in associative learning research to be retained, but recast in a model that provides a firmer foundation for both immediate application and future research
Self-noise produced by an airfoil with nonflat plate trailing-edge serrations
This paper represents the results of an experimental study aimed at reducing the airfoil self-noise by the trailing edge serration of four different sawtooth geometries (defined in the serration angle and length). These serrations have a common feature: all of the sawtooth patterns are cut directly into the trailing edge of a realistic airfoil. This configuration offers better structural strength and integrity. For the sawtooth trailing edges investigated here, the radiation of the extraneous vortex shedding noise in a narrowband frequency due to the partial bluntness at the serration roots is unavoidable. However, this narrowband component tends to be less significant provided that the serration angle is large and the serration length is moderate. Sound power was measured, and some of the sawtooth geometries have been shown to afford significant boundary-layer instability tonal noise and moderate turbulent broadband noise reductions across a fairly large velocity range. This paper demonstrates that a nonflat plate serrated trailing edge can also be effective in the self-noise reduction. Some experimental results are also presented in order to explain the self-noise mechanisms.This work is partly supported by the Brunel Research Initiative and Enterprise fun
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Modular assembly with postponement to improve health, safety & productivity in construction
This paper presents the outcome of an engineering study as part of the design and development of a lean and agile construction system and in particular its supply chain component. This combines modular assembly with a postponement function to be tested on a case study project (not reported here), the objective of which is to improve health, safety and productivity for the company sponsoring the research.
The contribution to research is the combination of countermeasures described in this paper that have been developed and incorporated into a wider construction system, in the same way that manufacturing has used this strategy with great success. Also, a further output is the development and use of an innovative method for assembling, transporting and installing mechanical and electrical modules, whereby modularization can be achieved with or without offsite manufacturing capability. The research forecasts a reduction of onsite labor of 35% compared to using traditional methods of construction, with less onsite operatives at risk of injury carrying out simpler assembly tasks within ergonomic mobile work cells. Further research is proposed to measure the benefits of the construction system following its implementation on a case study project
Vacuum Alignment in SUSY A4 Models
In this note we discuss the vacuum alignment in supersymmetric models with
spontaneously broken flavour symmetries in the presence of soft supersymmetry
(SUSY) breaking terms. We show that the inclusion of soft SUSY breaking terms
can give rise to non-vanishing vacuum expectation values (VEVs) for the
auxiliary components of the flavon fields. These non-zero VEVs can have an
important impact on the phenomenology of this class of models, since they can
induce an additional flavour violating contribution to the sfermion soft mass
matrix of right-left (RL) type. We carry out an explicit computation in a class
of SUSY A4 models predicting tri-bimaximal mixing in the lepton sector. The
flavour symmetry breaking sector is described in terms of flavon and driving
supermultiplets. We find non-vanishing VEVs for the auxiliary components of the
flavon fields and for the scalar components of the driving fields which are of
order m_{SUSY} x and m_{SUSY}, respectively. Thereby, m_{SUSY} is the
generic soft SUSY breaking scale which is expected to be around 1 TeV and
is the VEV of scalar components of the flavon fields. Another effect of these
VEVs can be the generation of a mu term.Comment: 23 pages; added a new section on the relation to Supergravity;
version accepted for publication in JHE
On the birational section conjecture with local conditions
A birationally liftable Galois section s of a hyperbolic curve X/k over a
number field k yields an adelic point x(s) in the smooth completion of X. We
show that x(s) is X-integral outside a set of places of Dirichlet density 0, or
s is cuspidal. The proof relies on -quotients of for
some open U of X.
If k is totally real or imaginary quadratic, we prove that all birationally
adelic, non-cuspidal Galois sections come from rational points as predicted by
the section conjecture of anabelian geometry. As an aside we also obtain a
strong approximation result for rational points on hyperbolic curves over Q or
imaginary quadratic fields.Comment: Theorem C (and Section 7) of the original version have been deleted
due to a gap in the proof. This is the journal versio
Asymptotic boundary forms for tight Gabor frames and lattice localization domains
We consider Gabor localization operators defined by two
parameters, the generating function of a tight Gabor frame
, parametrized by the elements of a
given lattice , i.e. a discrete cocompact subgroup
of , and a lattice localization domain
with its boundary consisting of line segments connecting points of .
We find an explicit formula for the boundary form
, the normalized limit of the projection
functional
,
where are the eigenvalues of the localization
operators applied to dilated domains , is an
integer and is the area of the fundamental domain of the
lattice .Comment: 35 page
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