2,787 research outputs found
FOULING DURING THE USE OF ‘FRESH’ WATER AS COOLANT- THE DEVELOPMENT OF A ‘USER GUIDE’
IHS ESDU recently published its latest ‘User Guide’ to fouling in heat exchange systems, for systems with fresh water as the coolant. ESDU 07006 [1] is the third in a group, following the development of the Crude Oil Fouling User Guide [2] issued in 2000 and the Seawater Fouling User Guide [3] issued in 2004. ESDU 07006 was developed by IHS ESDU over a period of five years under the guidance of the Oil Industry Fouling Working Party, a collaborative team of oil refiners, heat transfer equipment and services suppliers and Universities. It provides designers and operators of cooling water facilities with a practical source of guidance on the occurrence, the mechanisms and the mitigation of fresh water fouling in these systems. IHS ESDU’s Oil Industry Fouling Working Party was formed in recognition of the huge economic and environmental importance of heat exchanger fouling and the potential benefits that can accrue from better understanding of mitigation strategies. Work is now underway on reboiler and FCCU fouling. The development of the User Guide ESDU 07006 is discussed in this paper and its technical content is summarized
Effect of vessel wettability on the foamability of "ideal" surfactants and "real-world" beer heads
The ability to tailor the foaming properties of a solution by controlling its chemical composition is highly desirable and has been the subject of extensive research driven by a range of applications. However, the control of foams by varying the wettability of the foaming vessel has been less widely reported. This work investigates the effect of the wettability of the side walls of vessels used for the in situ generation of foam by shaking aqueous solutions of three different types of model surfactant systems (non-ionic, anionic and cationic surfactants) along with four different beers (Guinness Original, Banks’s Bitter, Bass No 1 and Harvest Pale). We found that hydrophilic vials increased the foamability only for the three model systems but increased foam stability for all foams except the model cationic system. We then compared stability of beer foams produced by shaking and pouring and demonstrated weak qualitative agreement between both foam methods. We also showed how wettability of the glass controls bubble nucleation for beers and champagne and used this effect to control exactly where bubbles form using simple wettability patterns
Breaking quantum linearity: constraints from human perception and cosmological implications
Resolving the tension between quantum superpositions and the uniqueness of
the classical world is a major open problem. One possibility, which is
extensively explored both theoretically and experimentally, is that quantum
linearity breaks above a given scale. Theoretically, this possibility is
predicted by collapse models. They provide quantitative information on where
violations of the superposition principle become manifest. Here we show that
the lower bound on the collapse parameter lambda, coming from the analysis of
the human visual process, is ~ 7 +/- 2 orders of magnitude stronger than the
original bound, in agreement with more recent analysis. This implies that the
collapse becomes effective with systems containing ~ 10^4 - 10^5 nucleons, and
thus falls within the range of testability with present-day technology. We also
compare the spectrum of the collapsing field with those of known cosmological
fields, showing that a typical cosmological random field can yield an efficient
wave function collapse.Comment: 13 pages, LaTeX, 3 figure
Spectral Measures and Generating Series for Nimrep Graphs in Subfactor Theory II: SU(3)
We complete the computation of spectral measures for SU(3) nimrep graphs
arising in subfactor theory, namely the SU(3) ADE graphs associated with SU(3)
modular invariants and the McKay graphs of finite subgroups of SU(3). For the
SU(2) graphs the spectral measures distill onto very special subsets of the
semicircle/circle, whilst for the SU(3) graphs the spectral measures distill
onto very special subsets of the discoid/torus. The theory of nimreps allows us
to compute these measures precisely. We have previously determined spectral
measures for some nimrep graphs arising in subfactor theory, particularly those
associated with all SU(2) modular invariants, all subgroups of SU(2), the
torus, SU(3), and some SU(3) graphs.Comment: 38 pages, 21 figure
Locality and topology with fat link overlap actions
We study the locality and topological properties of fat link clover overlap
(FCO) actions. We find that a small amount of fattening (2-4 steps of APE or 1
step of HYP) already results in greatly improved properties compared to the
Wilson overlap (WO). We present a detailed study of the localisation of the FCO
and its connection to the density of low modes of . In contrast to
the Wilson overlap, on quenched gauge backgrounds we do not find any dependence
of the localization of the FCO on the gauge coupling. This suggests that the
FCO remains local in the continuum limit. The FCO also faithfully reproduces
the zero mode wave functions of typical lattice instantons, not like the Wilson
overlap. After a general discussion of different lattice definitions of the
topological charge we also show that the FCO together with the Boulder charge
are likely to satisfy the index theorem in the continuum limit. Finally, we
present a high statistics computation of the quenched topological
susceptibility with the FCO action.Comment: 19 pages, LaTe
Density functional study of elastic and vibrational properties of the Heusler-type alloys FeVAl and FeVGa
The structural and elastic properties as well as phonon-dispersion relations
of the Heusler-type alloys FeVAl and FeVGa are computed using
density-functional and density-functional perturbation theory within the
generalized-gradient approximation. The calculated equilibrium lattice
constants agree well with the experimental values. The elastic constants of
FeVAl and FeVGa are predicted for the first time. From the elastic
constants the shear modulus, Young's modulus, Poisson's ratio, sound velocities
and Debye temperatures are obtained. By analyzing the ratio between the bulk
and shear modulii, we conclude that both FeVAl and FeVGa are brittle in
nature. The computed phonon-dispersion relation shows that both compounds are
dynamically stable in the L1 structure without any imaginary phonon
frequencies. The isomer shifts of Fe in the two compounds are discussed in
terms of the Fe s partial density of states, which reveal larger ionicity/less
hybridization in FeVGa than in FeVAl. For the same reason the Cauchy
pressure is negative in FeVAl but positive in FeVGaComment: 14 pages, 3 figure
Ab-initio study of model guanine assemblies: The role of pi-pi coupling and band transport
Several assemblies of guanine molecules are investigated by means of
first-principle calculations. Such structures include stacked and
hydrogen-bonded dimers, as well as vertical columns and planar ribbons,
respectively, obtained by periodically replicating the dimers. Our results are
in good agreement with experimental data for isolated molecules, isolated
dimers, and periodic ribbons. For stacked dimers and columns, the stability is
affected by the relative charge distribution of the pi orbitals in adjacent
guanine molecules. pi-pi coupling in some stacked columns induces dispersive
energy bands, while no dispersion is identified in the planar ribbons along the
connections of hydrogen bonds. The implications for different materials
comprised of guanine aggregates are discussed. The bandstructure of dispersive
configurations may justify a contribution of band transport (Bloch type) in the
conduction mechanism of deoxyguanosine fibres, while in DNA-like configurations
band transport should be negligible.Comment: 21 pages, 6 figures, 3 tables, to be published in Phys. Rev.
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