1,164 research outputs found
Dynamics of Water Entry
The hydrodynamics associated with water-entry of spheres can be highly
variable with respect to the material and kinematic properties of the sphere.
This series of five fluid dynamics videos illustrates several subtle but
interesting variations. The first series of videos contrasts the nature of
impact between a hydrophilic and hydrophobic sphere, and illustrates how
surface coating can affect whether or not an air cavity is formed. The second
video series illustrates how spin and surface treatments can alter the splash
and cavity formation following water entry. The spinning sphere causes a wedge
of fluid to be drawn into the cavity due to the no-slip condition and follows a
curved trajectory. The non-spinning sphere has two distinct surface treatments
on the left and right hemispheres: the left hemisphere is hydrophobic and the
right hemisphere is hydrophilic . Interestingly, the cavity formation for the
half-and-half sphere has many similarities to that of the spinning sphere
especially when viewed from above. The third video series compares two
millimetric nylon spheres impacting at slightly different impact speeds (Uo =
40 and 45 cm/s); the faster sphere fully penetrates the free surface, forming a
cavity, whereas the slower sphere does not. The fourth series shows the
instability of an elongated water-entry cavity formed by a millimetric steel
sphere with a hydrophobic coating impacting at Uo = 600 cm/s. The elongated
cavity forms multiple pinch-off points along its decent. Finally, a millimetric
steel sphere with a hydrophobic coating breaks the free surface with an impact
speed of Uo = 350 cm/s. The cavity pinches-off below the surface, generating a
Worthington jet that pinches into droplets owing to the Rayleigh-Plateau
instability.Comment: American Physical Society Division of Fluid Dynamics Gallery of Fluid
Motion Video Entry Replaced previous version because abstract had LaTex
markup and was too lon
Observation of transverse interference fringes on an atom laser beam
Using the unique detection properties offered by metastable
helium atoms we have produced high resolution images of the transverse
spatial profiles of an atom laser beam. We observe fringes on the beam,
resulting from quantum mechanical interference between atoms that start
from rest at different transverse locations within the outcoupling surface
and end up at a later time with different velocities at the same transverse
position. Numerical simulations in the low output-coupling limit give good
quantitative agreement with our experimental data
How effective is school-based deworming for the community-wide control of soil-transmitted helminths?
Background: The London Declaration on neglected tropical diseases was based in part on a new World Health Organization roadmap to “sustain, expand and extend drug access programmes to ensure the necessary supply of drugs and other interventions to help control by 2020”. Large drug donations from the pharmaceutical industry form the backbone to this aim, especially for soil-transmitted helminths (STHs) raising the question of how best to use these resources. Deworming for STHs is often targeted at school children because they are at greatest risk of morbidity and because it is remarkably cost-effective. However, the impact of school-based deworming on transmission in the wider community remains unclear.
Methods: We first estimate the proportion of parasites targeted by school-based deworming using demography, school enrolment, and data from a small number of example settings where age-specific intensity of infection (either worms or eggs) has been measured for all ages. We also use transmission models to investigate the potential impact of this coverage on transmission for different mixing scenarios.
Principal Findings: In the example settings <30% of the population are 5 to <15 years old. Combining this demography with the infection age-intensity profile we estimate that in one setting school children output as little as 15% of hookworm eggs, whereas in another setting they harbour up to 50% of Ascaris lumbricoides worms (the highest proportion of parasites for our examples). In addition, it is estimated that from 40–70% of these children are enrolled at school.
Conclusions: These estimates suggest that, whilst school-based programmes have many important benefits, the proportion of infective stages targeted by school-based deworming may be limited, particularly where hookworm predominates. We discuss the consequences for transmission for a range of scenarios, including when infective stages deposited by children are more likely to contribute to transmission than those from adults
Reflective Journeys Toward Culturally Relevant Pedagogy
In this qualitative case study we used Bronfenbrenner’s ecological systems theory methodologically and theoretically to investigate the reflections of three elementary pre-service teachers as they were learning about teaching culturally and linguistically diverse students. Data sources included a questionnaire, interview transcripts, course documents, and individual written records. Cross and within case analyses were conducted using a priori and open coding for all data utilizing the analytic strategy of relying on theoretical propositions. Findings suggested that participants’ reflected beyond the classroom on influences that impact the education of diverse students and there were program specific factors that encouraged critical reflectivity across systems of influence. This study offers insights about using critical reflectivity in developing pre-service teachers’ understandings of culturally relevant pedagogy. In this qualitative case study we used Bronfenbrenner’s ecological systems theory methodologically and theoretically to investigate the reflections of three elementary pre-service teachers as they were learning about teaching culturally and linguistically diverse students. Data sources included a questionnaire, interview transcripts, course documents, and written records. Cross and within case analyses were conducted using a priori and open coding for all data utilizing the analytic strategy of relying on theoretical propositions. Findings suggested that participants’ reflected beyond the classroom on influences that impact the education of diverse students and there were program specific factors that encouraged critical reflectivity across systems of influence. This study offers insights about using critical reflectivity in developing pre-service teachers’ understandings of culturally relevant pedagogy
Approaching the adiabatic timescale with machine-learning
The control and manipulation of quantum systems without excitation is
challenging, due to the complexities in fully modeling such systems accurately
and the difficulties in controlling these inherently fragile systems
experimentally. For example, while protocols to decompress Bose-Einstein
condensates (BEC) faster than the adiabatic timescale (without excitation or
loss) have been well developed theoretically, experimental implementations of
these protocols have yet to reach speeds faster than the adiabatic timescale.
In this work, we experimentally demonstrate an alternative approach based on a
machine learning algorithm which makes progress towards this goal. The
algorithm is given control of the coupled decompression and transport of a
metastable helium condensate, with its performance determined after each
experimental iteration by measuring the excitations of the resultant BEC. After
each iteration the algorithm adjusts its internal model of the system to create
an improved control output for the next iteration. Given sufficient control
over the decompression, the algorithm converges to a novel solution that sets
the current speed record in relation to the adiabatic timescale, beating out
other experimental realizations based on theoretical approaches. This method
presents a feasible approach for implementing fast state preparations or
transformations in other quantum systems, without requiring a solution to a
theoretical model of the system. Implications for fundamental physics and
cooling are discussed.Comment: 7 pages main text, 2 pages supporting informatio
Customised patient implants : future lifeline of the medical industry
Published ArticleLong-term growth in the additive fabrication industry will come from designs that are difficult, time-consuming, costly, or impossible to produce using standard techniques. Growth will occur with advances in the current additive processes, coupled with breakthroughs in new materials, which are expected to emerge over the next five to 10 years. These advanced materials will better satisfy the design requirements of many new products. The paper considers currently available technologies and discusses recent advancements in direct metal freeform fabrication and its potential of revolutionising the medical industry
Excitable media in open and closed chaotic flows
We investigate the response of an excitable medium to a localized
perturbation in the presence of a two-dimensional smooth chaotic flow. Two
distinct types of flows are numerically considered: open and closed. For both
of them three distinct regimes are found, depending on the relative strengths
of the stirring and the rate of the excitable reaction. In order to clarify and
understand the role of the many competing mechanisms present, simplified models
of the process are introduced. They are one-dimensional baker-map models for
the flow and a one-dimensional approximation for the transverse profile of the
filaments.Comment: 14 pages, 16 figure
Paired atom laser beams created via four-wave mixing
A method to create paired atom laser beams from a metastable helium atom
laser via four-wave mixing is demonstrated. Radio frequency outcoupling is used
to extract atoms from a Bose Einstein condensate near the center of the
condensate and initiate scattering between trapped and untrapped atoms. The
unequal strengths of the interactions for different internal states allows an
energy-momentum resonance which leads to the creation of pairs of atoms
scattered from the zero-velocity condensate. The resulting scattered beams are
well separated from the main atom laser in the 2-dimensional transverse atom
laser profile. Numerical simulations of the system are in good agreement with
the observed atom laser spatial profiles, and indicate that the scattered beams
are generated by a four-wave mixing process, suggesting that the beams are
correlated.Comment: 5 pages, 3 figure
Three-Fluid Description of the Sympathetic Cooling of a Boson-Fermion Mixture
We present a model for sympathetic cooling of a mixture of fermionic and
bosonic atomic gases in harmonic traps, based on a three-fluid description. The
model confirms the experimentally observed cooling limit of about 0.2 T_F when
only bosons are pumped. We propose sequential cooling -- first pumping of
bosons and afterwards fermions -- as a way to obtain lower temperatures. For
this scheme, our model predicts that temperatures less than 0.1 T_F can be
reached.Comment: 9 pages, 6 figure
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