104,984 research outputs found
Experimental wake survey behind Viking 75 entry vehicle at angles of attack of 0 deg, 5 deg, and 10 deg, Mach numbers from 0.20 to 1.20, and longitudinal stations from 1.50 to 11.00 body diameters
An investigation was conducted to obtain flow properties in the wake of a preliminary configuration of the Viking '75 Entry Vehicle at Mach numbers from 0.20 to 1.20 and at angles of attack of 0 deg, 5 deg, and 10 deg. The wake flow properties were calculated from total and static pressures measured with a pressure rake at longitudinal stations varying from 1.50 to 11.00 body diameters, and are presented in tabulated and plotted form. The wake properties were essentially symmetrical about the X-axis at alpha = 0 deg and the profiles were shifted away from the X-axis at angles of attack. An unexpected reduction in wake property ratios occurred as the Mach number increased from 0.60 to 1.00; these ratios then increased as the Mach number increased to 1.20. The reduction was present for all the longitudinal stations of the tests and decreased with increased longitudinal distance
An analytical and experimental assessment of flexible road ironwork support structures
This paper describes work undertaken to investigate the mechanical performance of road ironwork installations in highways, concentrating on the chamber construction. The principal aim was to provide the background research which would allow improved designs to be developed to reduce the incidence of failures through improvements to the structural continuity between the installation and the surrounding pavement. In doing this, recycled polymeric construction materials (Jig Brix) were studied with a view to including them in future designs and specifications. This paper concentrates on the Finite Element (FE) analysis of traditional (masonry) and flexible road ironwork structures incorporating Jig Brix. The global and local buckling capacity of the Jig Brix elements was investigated and results compared well with laboratory measurements. FE models have also been developed for full-scale traditional (masonry) and flexible installations in a surrounding flexible (asphalt) pavement structure. Predictions of response to wheel loading were compared with full-scale laboratory measurements. Good agreement was achieved with the traditional (masonry) construction but poorer agreement for the flexible construction. Predictions from the FE model indicated that the use of flexible elements significantly reduces the tensile horizontal strain on the surface of the surrounding asphaltic material which is likely to reduce the incidence of surface cracking
On arithmetic and asymptotic properties of up-down numbers
Let , where , and let
denote the number of permutations of whose
up-down signature , for .
We prove that the set of all up-down numbers can be expressed by
a single universal polynomial , whose coefficients are products of
numbers from the Taylor series of the hyperbolic tangent function. We prove
that is a modified exponential, and deduce some remarkable congruence
properties for the set of all numbers , for fixed . We prove a
concise upper-bound for , which describes the asymptotic behaviour
of the up-down function in the limit .Comment: Recommended for publication in Discrete Mathematics subject to
revision
Molecular dynamics simulations of reflection and adhesion behavior in Lennard-Jones cluster deposition
We conduct molecular dynamics simulations of the collision of atomic clusters
with a weakly-attractive surface. We focus on an intermediate regime, between
soft-landing and fragmentation, where the cluster undergoes deformation on
impact but remains largely intact, and will either adhere to the surface (and
possibly slide), or be reflected. We find that the outcome of the collision is
determined by the Weber number, We i.e. the ratio of the kinetic energy to the
adhesion energy, with a transition between adhesion and reflection occurring as
We passes through unity. We also identify two distinct collision regimes: in
one regime the collision is largely elastic and deformation of the cluster is
relatively small but in the second regime the deformation is large and the
adhesion energy starts to depend on the kinetic energy. If the transition
between these two regimes occurs at a similar kinetic energy to that of the
transition between reflection and adhesion, then we find that the probability
of adhesion for a cluster can be bimodal. In addition we investigate the
effects of the angle of incidence on adhesion and reflection. Finally we
compare our findings both with recent experimental results and with macroscopic
theories of particle collisions.Comment: 18 pages, 13 figure
Geometric signature of reversal modes in ferromagnetic nanowires
Magnetic nanowires are a good platform to study fundamental processes in
Magnetism and have many attractive applications in recording such as
perpendicular storage and in spintronics such as non-volatile magnetic memory
devices (MRAM) and magnetic logic devices. In this work, nanowires are used to
study magnetization reversal processes through a novel geometric approach.
Reversal modes imprint a definite signature on a parametric curve representing
the locus of the critical switching field. We show how the different modes
affect the geometry of this curve depending on the nature of the anisotropy
(uniaxial or cubic anisotropy), demagnetization and exchange effects. The
samples we use are electrochemically grown Nickel and Cobalt nanowires.Comment: 11 pages, 21 figures to submit to Europhysics Letter
Applying machine learning to the problem of choosing a heuristic to select the variable ordering for cylindrical algebraic decomposition
Cylindrical algebraic decomposition(CAD) is a key tool in computational
algebraic geometry, particularly for quantifier elimination over real-closed
fields. When using CAD, there is often a choice for the ordering placed on the
variables. This can be important, with some problems infeasible with one
variable ordering but easy with another. Machine learning is the process of
fitting a computer model to a complex function based on properties learned from
measured data. In this paper we use machine learning (specifically a support
vector machine) to select between heuristics for choosing a variable ordering,
outperforming each of the separate heuristics.Comment: 16 page
Influence of Charge Order on the Ground States of TMTTF Molecular Salts
(TMTTF)2AsF6 and (TMTTF)2SbF6 are both known to undergo a charge ordering
phase transition, though their ground states are different. The ground state of
the first is Spin-Peierls, and the second is an antiferromagnet. We study the
effect of pressure on the ground states and the charge-ordering using 13C NMR
spectroscopy. The experiments demonstrate that the the CO and SP order
parameters are repulsive, and consequently the AF state is stabilized when the
CO order parameter is large, as it is for (TMTTF)2SbF6. An extension of the
well-known temperature/pressure phase diagram is proposed.Comment: 5pages, 5 figures, Proceeding of ISCOM2003, to appear in Journal de
Physique I
Laboratory tank studies of a single species of phytoplankton using a remote sensing fluorosensor
Phytoplankton were grown in the laboratory for the purpose of testing a remote fluorosensor. The fluorosensor uses a unique four-wavelength dye laser system to excite phytoplankton bearing chlorophyll and to measure the chlorophyll fluorescence generated by this excitation. Six different species were tested, one at a time, and each was grown two to four times. Fluorescence measured by the fluorosensor provides good quantitative measurement of chlorophyll concentrations for all species tested while the cultures were in log phase growth. Fluorescene cross section ratios obtained in the single species tank tests support the hypothesis that the shape of the fluorescence cross section curve remains constant with the species (differences in fluorescence cross section ratios are a basis for determining composition of phytoplankton according to color group when a multiwavelength source of excitation is used. Linear relationships exist between extracted chlorophyll concentration and fluorescence measured by the remote fluorosensor during the log phase growth of phytoplankton cultures tested
Visible absorbance spectra: A basis for in situ and passive remote sensing of phytoplankton concentration and community composition
The concentration and composition of phytoplankton populations are measured by an optical method which can be used either in situ or remotely. This method is based upon the in vivo light absorption characteristics of phytoplankton. To provide a data base for testing assumptions relative to the proposed method, visible absorbance spectra of pure cultures of 20 marine phytoplankton were obtained under laboratory conditions. Descriptive and analytical statistics were computed for the absorbance spectra and were used to make comparisons between members of major taxonomic groups and between groups. Spectral variation between the members of the major taxonomic groups was observed to be considerably less than the spectral variation between these groups. In several cases the differences between the mean absorbance spectra of major taxonomic groups are significant enough to be detected with passive remote sensing techniques
- …