1,169 research outputs found
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Holographic measurement of drop-on-demand drops in flight
The analysis of images of ink drops in flight can provide information about jet straightness, drop velocity and volume.
However trade-offs between field of view, optical and digital resolution and other factors such as depth of field and optical
distortion, limit the accuracy and amount of information available from a single image. In-line, digital holograms of drops in flight
can capture information from fields of view at least as large as the area of the digital sensor. Using mathematical reconstruction
techniques particularly suited to sparse, small objects of regular geometry the accuracy of measurement can potentially be submicrometer on drop position and diameter.
This paper describes our experimental apparatus, hologram reconstruction techniques and the results of experiments on
imaging drops. We also discuss techniques to improve the accuracy of the technique in the direction of the optical axis
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Aerodynamic effects in ink-jet printing on a moving web
This work was sponsored by EPSRC grant number RG5560
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Jetting, in-nozzle meniscus motion and nozzle-plate flooding in an industrial drop-on-demand print head
The state of the ink film at and near the nozzles of a drop-ondemand(DoD) print head during jetting has a direct impact on
printing performance and reliability. We have developed highspeed imaging apparatus and analytical techniques to investigate
the ink film dynamics on an industrial print head nozzle-plate in real-time. In addition to a direct correlation between the jet
emergence velocity and drive voltage, drive-dependent variations in the oscillation of the ink meniscus in adjacent nozzles were also observed. Using a ray-tracing model to analyze the meniscus shape, the meniscus oscillations for both printing and nonprinting nozzles were found to be complex and involve elements such as pre-oscillation and high-order surface waves. The flooding of non-firing nozzles, deliberately caused by the application of maximum drive voltage to a neighboring nozzle, has been recorded and analyzed dynamically. The build-up of fluid in an annulus around the nozzle (flooding rate) has been characterized and compared with models for the net ink flow
through the nozzle
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Dependence of drop speed on nozzle diameter, viscosity and drive amplitude in drop-on-demand ink-jet printing
Results of recent experiments and numerical simulations are presented, which have been used to establish empirical rules for
the dependence of drop speed on nozzle diameter and drive amplitude for Newtonian and non-Newtonian fluids printed with a
range of different ink-jet print-head technologies. Experiments were carried out with Xaar, MicroFab and Spectra Dimatix print heads and with solutions of polystyrene in diethyl phthalate as model fluids. These results are compared with
predictions from recent numerical codes developed by collaborators in the University of Leeds, and from simple models for drop-on-demand fluid jetting resulting from physical law
Extreme UV QSOs
We present a sample of spectroscopically confirmed QSOs with FUV-NUV color
(as measured by GALEX photometry) bluer than canonical QSO templates and than
the majority of known QSOs. We analyze their FUV to NIR colors, luminosities
and optical spectra. The sample includes a group of 150 objects at low redshift
(z 0.5), and a group of 21 objects with redshift 1.7z2.6. For the low
redshift objects, the "blue" FUV-NUV color may be caused by enhanced Ly
emission, since Ly transits the GALEX FUV band from z=0.1 to z=0.47.
Synthetic QSO templates constructed with Ly up to 3 times stronger than
in standard templates match the observed UV colors of our low redshift sample.
The H emission increases, and the optical spectra become bluer, with
increasing absolute UV luminosity. The UV-blue QSOs at redshift about 2, where
the GALEX bands sample restframe about 450-590A (FUV) and about 590-940A(NUV),
are fainter than the average of UV-normal QSOs at similar redshift in NUV,
while they have comparable luminosities in other bands. Therefore we speculate
that their observed FUV-NUV color may be explained by a combination of steep
flux rise towards short wavelengths and dust absorption below the Lyman limit,
such as from small grains or crystalline carbon. The ratio of Ly to CIV
could be measured in 10 objects; it is higher (30% on average) than for
UV-normal QSOs, and close to the value expected for shock or collisional
ionization. FULL VERSION AVAILABLE FROM AUTHOR'S WEB SITE:
http://dolomiti.pha.jhu.edu/papers/2009_AJ_Extreme_UV_QSOs.pdfComment: Astronomical Journal, in pres
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Imbibition dynamics of nano-particulate ink-jet drops on micro-porous media
Ink-jet printing of nano-metallic colloidal fluids on to
porous media such as coated papers has become a viable
method to produce conductive tracks for low-cost,
disposable printed electronic devices. However, the
formation of well-defined and functional tracks on an
absorbing surface is controlled by the drop imbibition
dynamics in addition to the well-studied post-impact drop
spreading behavior.
This study represents the first investigation of the realtime
imbibition of ink-jet deposited nano-Cu colloid drops
on to coated paper substrates. In addition, the same ink was
deposited on to a non-porous polymer surface as a control
substrate. By using high-speed video imaging to capture the
deposition of ink-jet drops, the time-scales of drop
spreading and imbibition were quantified and compared
with model predictions. The influences of the coating pore
size on the bulk absorption rate and nano-Cu particle
distribution have also been studied
In-shock Cooling in Numerical Simulations
We model a one-dimensional shock-tube using smoothed particle hydrodynamics
and investigate the consequences of having finite shock-width in numerical
simulations. We investigate the cooling of gas during passage through the shock
for different cooling regimes. For a shock temperature of 10^5K, the maximum
temperature of the gas is much reduced and the cooling time was reduced by a
factor of 2. At lower temperatures, we are especially interested in the
production of molecular Hydrogen and so we follow the ionization level and H_2
abundance across the shock. This regime is particularly relevent to simulations
of primordial galaxy formation for halos in which the virial temperature of the
galaxy is sufficiently high to partially re-ionize the gas. The effect of
in-shock cooling is substantial: the maximum temperature the gas reaches
compared to the theoretical temperature was found to vary between 0.15 and 0.81
for the simulations performed. The downstream ionization level is reduced from
the theoretical level by a factor of between 2.4 and 12.5, and the resulting
H_2 abundance was found to be reduced to a fraction of 0.45 to 0.74 of its
theoretical value. At temperatures above 10^5K, radiative shocks are unstable
and will oscillate. We reproduce these oscillations and find good agreement
with the previous work of Chevalier and Imamura (1982), and Imamura, Wolff and
Durisen (1984). The effect of in-shock cooling in such shocks is difficult to
quantify, but is undoubtedly present.Comment: 8 pages, LaTeX, 7 figure
A randomized controlled trial of the impact of a teacher classroom management program on the classroom behavior of children with and without behavior problems
Introducing the PRIDAL model for linking routine health and identifiable patient reported questionnaire data
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