1,838 research outputs found
Providing adhesion for a miniture mobile intra-abdominal device based on biomimetic principles
This paper investigates the surface adhesion
characteristics required for a miniature mobile device to
move around the abdominal cavity. Such a device must
be capable of adhering to the tissue lining and move
freely across the upper surface of the insufflated
abdomen. Accordingly, the potential of utilising bioinspired
solutions to facilitate wet adhesion is assessed
A robust enhancement to the Clarke-Wright savings algorithm
We address the Clarke and Wright (CW) savings algorithm proposed for the Capacitated Vehicle Routing Problem (CVRP). We first consider a recent enhancement which uses the put first larger items idea originally proposed for the bin packing problem and show that the conflicting idea of putting smaller items first has a comparable performance. Next, we propose a robust enhancement to the CW savings formulation. The proposed formulation is normalized to efficiently solve different problems, independent from the measurement units and parameter intervals. To test the performance of the proposed savings function, we conduct an extensive computational study on a large set of well-known instances from the literature. Our results show that the proposed savings function provides shorter distances in the majority of the instances and the average performance is significantly better than previously presented enhancements
Generator Matrix Elements For II
Basis states and generator matrix elements are given for the generic
representation of in an basis.Comment: Latex, 17 pages, one figure using epsf published in J. Phys. A: Math.
Gen 28 (1995) 2581-258
Variability of Active Galactic Nuclei from the Optical to X-ray Regions
Some progress in understanding AGN variability is reviewed. Reprocessing of
X-ray radiation to produce significant amounts of longer-wavelength continua
seems to be ruled out. In some objects where there has been correlated X-ray
and optical variability, the amplitude of the optical variability has exceeded
the amplitude of X-ray variability. We suggest that accelerated particles
striking material could be linking X-ray and optical variability (as in
activity in the solar chromosphere). Beaming effects could be significant in
all types of AGN. The diversity in optical/X-ray relationships at different
times in the same object, and between different objects, might be explained by
changes in geometry and directions of motion relative to our line of sight.
Linear shot-noise models of the variability are ruled out; instead there must
be large-scale organization of variability. Variability occurs on
light-crossing timescales rather than viscous timescales and this probably
rules out the standard Shakura-Sunyaev accretion disk. Radio-loud and
radio-quiet AGNs have similar continuum shapes and similar variability
properties. This suggests similar continuum origins and variability mechanisms.
Despite their extreme X-ray variability, narrow-line Seyfert 1s (NLS1s) do not
show extreme optical variability.Comment: Invited talk given at Euro Asian Astronomical Society meeting in
Moscow, June 2002. 20 pages, 4 figures. References update
Collective dynamics of liquid aluminum probed by Inelastic X-ray Scattering
An inelastic X-ray scattering experiment has been performed in liquid
aluminum with the purpose of studying the collective excitations at wavevectors
below the first sharp diffraction peak. The high instrumental resolution (up to
1.5 meV) allows an accurate investigation of the dynamical processes in this
liquid metal on the basis of a generalized hydrodynamics framework. The
outcoming results confirm the presence of a viscosity relaxation scenario ruled
by a two timescale mechanism, as recently found in liquid lithium.Comment: 8 pages, 7 figure
Energy distribution modulation by mechanical design for electrochemical jet processing techniques
The increasing demand for optimised component surfaces with enhanced chemical and geometric complexity is a key driver in the manufacturing technology required for advanced surface production. Current methodologies cannot create complex surfaces in an efficient and scalable manner in robust engineering materials. Hence, there is a need for advanced manufacturing technologies which overcome this. Current technologies are limited by resolution, geometric flexibility and mode of energy delivery. By addressing the fundamental limitations of electrochemical jetting techniques through modulation of the current density distribution by mechanical design, significant improvements to the electrochemical jet process methods are presented. A simplified 2D stochastic model was developed with the ability to vary current density distribution to assess the effects of nozzle-tip shape changes. The simulation demonstrated that the resultant profile was found to be variable from that of a standard nozzle. These nozzle-tip modifications were then experimentally tested finding a high degree of variance was possible in the machined profile. Improvements such as an increase in side-wall steepness of 162% are achieved over a standard profile, flat bases to the cut profile and a reduction of profile to surface inter-section radius enable the process to be analogous to traditional milling profiles. Since electrode design can be rapidly modified EJP is shown to be a flexible process capable of varied and complex meso-scale profile creation. Innovations presented here in the modulation of resistance in-jet have enabled electrochemical jet processes to become a viable, top-down, single-step method for applying complex surfaces geometries unachievable by other means
Higher order glass-transition singularities in colloidal systems with attractive interactions
The transition from a liquid to a glass in colloidal suspensions of particles
interacting through a hard core plus an attractive square-well potential is
studied within the mode-coupling-theory framework. When the width of the
attractive potential is much shorter than the hard-core diameter, a reentrant
behavior of the liquid-glass line, and a glass-glass-transition line are found
in the temperature-density plane of the model. For small well-width values, the
glass-glass-transition line terminates in a third order bifurcation point, i.e.
in a A_3 (cusp) singularity. On increasing the square-well width, the
glass-glass line disappears, giving rise to a fourth order A_4 (swallow-tail)
singularity at a critical well width. Close to the A_3 and A_4 singularities
the decay of the density correlators shows stretching of huge dynamical
windows, in particular logarithmic time dependence.Comment: 19 pages, 12 figures, Phys. Rev. E, in prin
Reverberation Mapping Results from MDM Observatory
We present results from a multi-month reverberation mapping campaign
undertaken primarily at MDM Observatory with supporting observations from
around the world. We measure broad line region (BLR) radii and black hole
masses for six objects. A velocity-resolved analysis of the H_beta response
shows the presence of diverse kinematic signatures in the BLR.Comment: To appear in the Proceedings of the IAU Symposium No. 267:
Co-Evolution of Central Black Holes and Galaxies, Rio de Janeiro, 200
Pressure induced structural and dynamical changes in liquid Si. An ab-initio study
The static and dynamic properties of liquid Si at high-pressure have been
studied using the orbital free ab-initio molecular dynamics method. Four
thermodynamic states at pressures 4, 8, 14 and 23 GPa are considered. The
calculated static structure shows qualitative agreement with the available
experimental data. We analize the remarkable structural changes occurring
between 8 and 14 GPa along with its effect on several dynamic properties.Comment: 10 pages, 11 figures. Accepted for publication in Journal of Physics:
Condensed Matte
Optical Variability of Narrow-Line Seyfert 1 Galaxies
We present results of a broad-band photometric study of the optical
variability of six Narrow-Line Seyfert 1 (NLS1) galaxies observed at 172
epochs. We searched for microvariability on 33 nights. Strong evidence for
microvariability was found only for our lowest luminosity object, NGC 4051, on
one night. Weaker evidence suggests such variability on a few other nights for
two other objects, but the data are not as convincing. Intra-night variability
in NLS1s is thus concluded to be rare and of low amplitude. We give
illustrations of how variable image quality can produce spurious variability.
We find that for well-studied non-NLS1s there is a spread in the amplitude of
seasonal variability (i.e., in some years an AGN is more variable than in
others). We find that the means of the variability amplitudes of non-NLS1s over
several seasons vary from object to object (i.e., some AGNs are, on average,
more variable than others). NLS1s also show a spread in seasonal variabilities.
The best-studied NLS1, Ark 564, shows a range of amplitudes of variability from
season to season that is comparable to the range found in BLS1s, and in one
season Ark 564 was as variable as the most variable non-NLS1. The seasonal
amplitudes of variability for NLS1s are mostly in the lower half of the range
of non-BLS1 seasonal amplitudes, but the absence of a suitable control sample
makes a precise comparison difficult. However, on long timescales (weeks to
years), NLS1s as a class are not more variable than non-NLS1s. The extreme
variability seen in the X-rays was not seen in the optical. This has
consequences for the models of AGNs in general as well as NLS1s in particular.Comment: Astrophysical Journal in press (tentatively scheduled for Vol. 608,
June 2004 issue);47 pages; 19 figures. Electronic tables not included
(contact first author if needed
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