739 research outputs found
Stability of a hard-sphere binary quasicrystal
The stability of a quasicrystalline structure, recently obtained in a
molecular-dynamics simulation of rapid cooling of a binary melt, is analyzed
for binary hard-sphere mixtures within a density-functional approach. It is
found that this quasicrystal is metastable relative to crystalline and fluid
phases for diameter ratios above 0.83. Such trend is partially reversed for
lower diameter ratios, since the quasicrystal becomes stable with respect to
the crystal but does not reach a coexistence with the fluid.Comment: 14 pages, 6 eps figures included. Revised version to appear in Phil.
Mag.
Rescaled density expansions and demixing in hard-sphere binary mixtures
The demixing transition of a binary fluid mixture of additive hard spheres is
analyzed for different size asymmetries by starting from the exact low-density
expansion of the pressure. Already within the second virial approximation the
fluid separates into two phases of different composition with a lower consolute
critical point. By successively incorporating the third, fourth, and fifth
virial coefficients, the critical consolute point moves to higher values of the
pressure and to lower values of the partial number fraction of the large
spheres. When the exact low-density expansion of the pressure is rescaled to
higher densities as in the Percus-Yevick theory, by adding more exact virial
coefficients a different qualitative movement of the critical consolute point
in the phase diagram is found. It is argued that the Percus-Yevick factor
appearing in many empirical equations of state for the mixture has a deep
influence on the location of the critical consolute point, so that the
resulting phase diagram for a prescribed equation has to be taken with caution.Comment: 5 pages, 1 figure; to be published in The Journal of Chemical Physic
Structure of Madrid basin (NE zone) derived from gravity data
[Abstract] Modelling of five profiles in the NE area of Madrid Basin shows that low anomalies are related to both the thicker sediments infill of the Basin and the
basement rocks like gneiss and granites. The highs are related to thick sequences
ofalternating slates and quarzites, outcropping or underlaying a thin cover. The
main gradients are related to the marginal faults of the Basin. The existence of
a granitic body and a NE-SW striking fault, was also detected. Out of the data
obtained in the models, an isobaths map has been depicted of Madrid Basin which shows a fault bounded structure
Stability of the hard-sphere icosahedral quasilattice
The stability of the hard-sphere icosahedral quasilattice is analyzed using
the differential formulation of the generalized effective liquid approximation.
We find that the icosahedral quasilattice is metastable with respect to the
hard-sphere crystal structures. Our results agree with recent findings by
McCarley and Ashcroft [Phys. Rev. B {\bf 49}, 15600 (1994)] carried out using
the modified weighted density approximation.Comment: 15 pages, 2 figures available from authors upon request, (revtex),
submitted to Phys. Rev.
Impact of droop and scarf on the aerodynamic performance of compact aero-engine nacelles
Future turbofan engines will operate with larger engine bypass-ratios and lower specific thrust than current in-service architectures to reduce the specific fuel consumption. This will be achieved by increasing the fan diameter which will incur in an increment in nacelle size and a concomitant larger nacelle drag, weight and interaction effects with the airframe. Therefore, it is required to design compact nacelles which will not counteract the benefits obtained from the new engine cycles. Nacelle design is based on a set of aero-lines that in combination with droop and scarf result in a 3D design. Traditionally, this process was performed by the design of axisymmetric aero-lines. Nevertheless, there is an emerging need to carry out the design process for full 3D configurations to have a better understanding of the effect of droop and scarf angles on the nacelle drag characteristics. This paper presents a numerical method for the multi-objective optimisation of drooped and scarfed non-axisymmetric nacelle aero-engines. It uses intuitive Class Shape Tranformations (iCSTs) for the aero-engine geometry definition, multi-point aerodynamic simulation, a near-field nacelle drag extraction method and the NSGA-II genetic algorithm. The process has been employed to perform independent multi-objective optimisations of compact architectures at selected droop and scarf angle combinations. The multi-objective optimisation framework was successfully demonstrated for the new nacelle design challenge and the overall system was shown to enable the identification of the effects of droop and scarf on compact aero-engines. The proposed tool complements a set of technologies for the design, analysis and optimisation of future civil turbofans aiming at reduction of specific fuel consumption
Phase behaviour of additive binary mixtures in the limit of infinite asymmetry
We provide an exact mapping between the density functional of a binary
mixture and that of the effective one-component fluid in the limit of infinite
asymmetry. The fluid of parallel hard cubes is thus mapped onto that of
parallel adhesive hard cubes. Its phase behaviour reveals that demixing of a
very asymmetric mixture can only occur between a solvent-rich fluid and a
permeated large particle solid or between two large particle solids with
different packing fractions. Comparing with hard spheres mixtures we conclude
that the phase behaviour of very asymmetric hard-particle mixtures can be
determined from that of the large component interacting via an adhesive-like
potential.Comment: Full rewriting of the paper (also new title). 4 pages, LaTeX, uses
revtex, multicol, epsfig, and amstex style files, to appear in Phys. Rev. E
(Rapid Comm.
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