5,835 research outputs found
Stability of additive-free water-in-oil emulsions
We calculate ion distributions near a planar oil-water interface within
non-linear Poisson-Boltzmann theory, taking into account the Born self-energy
of the ions in the two media. For unequal self-energies of cations and anions,
a spontaneous charge separation is found such that the water and oil phase
become oppositely charged, in slabs with a typical thickness of the Debye
screening length in the two media. From the analytical solutions, the
corresponding interfacial charge density and the contribution to the
interfacial tension is derived, together with an estimate for the
Yukawa-potential between two spherical water droplets in oil. The parameter
regime is explored where the plasma coupling parameter exceeds the
crystallization threshold, i.e. where the droplets are expected to form
crystalline structures due to a strong Yukawa repulsion, as recently observed
experimentally. Extensions of the theory that we discuss briefly include
numerical calculations on spherical water droplets in oil, and analytical
calculations of the linear PB-equation for a finite oil-water interfacial
width.Comment: 9 pages, 4 figures, accepted by JPCM for proceedings of LMC
Effects of quasiparticle tunneling in a circuit-QED realization of a strongly driven two-level system
We experimentally and theoretically study the frequency shift of a driven
cavity coupled to a superconducting charge qubit. In addition to previous
studies, we here also consider drive strengths large enough to energetically
allow for quasiparticle creation. Quasiparticle tunneling leads to the
inclusion of more than two charge states in the dynamics. To explain the
observed effects, we develop a master equation for the microwave dressed charge
states, including quasiparticle tunneling. A bimodal behavior of the frequency
shift as a function of gate voltage can be used for sensitive charge detection.
However, at weak drives the charge sensitivity is significantly reduced by
non-equilibrium quasiparticles, which induce transitions to a non-sensitive
state. Unexpectedly, at high enough drives, quasiparticle tunneling enables a
very fast relaxation channel to the sensitive state. In this regime, the charge
sensitivity is thus robust against externally injected quasiparticles and the
desired dynamics prevail over a broad range of temperatures. We find very good
agreement between theory and experiment over a wide range of drive strengths
and temperatures.Comment: 25 pages, 7 figure
Dynamic parity recovery in a strongly driven Cooper-pair box
We study a superconducting charge qubit coupled to an intensive
electromagnetic field and probe changes in the resonance frequency of the
formed dressed states. At large driving strengths, exceeding the qubit
energy-level splitting, this reveals the well known Landau-Zener-Stuckelberg
(LZS) interference structure of a longitudinally driven two-level system. For
even stronger drives we observe a significant change in the LZS pattern and
contrast. We attribute this to photon-assisted quasiparticle tunneling in the
qubit. This results in the recovery of the qubit parity, eliminating effects of
quasiparticle poisoning and leads to an enhanced interferometric response. The
interference pattern becomes robust to quasiparticle poisoning and has a good
potential for accurate charge sensing.Comment: 5 pages, 4 figure
Coupling of a locally implanted rare-earth ion ensemble to a superconducting micro-resonator
We demonstrate the coupling of rare-earth ions locally implanted in a
substrate (Gd in AlO) to a superconducting NbN
lumped-element micro-resonator. The hybrid device is fabricated by a controlled
ion implantation of rare-earth ions in well-defined micron-sized areas, aligned
to lithographically defined micro-resonators. The technique does not degrade
the internal quality factor of the resonators which remain above .
Using microwave absorption spectroscopy we observe electron-spin resonances in
good agreement with numerical modelling and extract corresponding coupling
rates of the order of MHz and spin linewidths of MHz.Comment: 4 pages, 2 Figure
Delivering quality along with quantity: the challenge of teaching a large and heterogeneous engineering class
The challenges faced by a lecturer teaching large multidisciplinary engineering classes are identified. These are principally related to the size of the class, the extensive mathematical knowledge that is considered as prerequisite, as well as the heterogeneity of the class due to the diversity of studentsâ academic background and interests. In order to improve studentsâ engagement and retention in class, active learning techniques are employed and their impact on the performance of the class is captured through a questionnaire designed for this purpose. The statistics demonstrate that good teaching facilities and a well-prepared lecturer do not suffice for maximising studentsâ satisfaction, attention and retention. In order to engage the students in a large class setting, it is important to involve them in the lecture process. The employed active learning methods comprising quizzes, in class demonstration and muddiest-point cards induce a remarkably positive impact at almost no additional teaching resources
Superfluid vortex front at T -> 0: Decoupling from the reference frame
Steady-state turbulent motion is created in superfluid 3He-B at low
temperatures in the form of a turbulent vortex front, which moves axially along
a rotating cylindrical container of 3He-B and replaces vortex-free flow with
vortex lines at constant density. We present the first measurements on the
thermal signal from dissipation as a function of time, recorded at 0.2 Tc
during the front motion, which is monitored using NMR techniques. Both the
measurements and the numerical calculations of the vortex dynamics show that at
low temperatures the density of the propagating vortices falls well below the
equilibrium value, i.e. the superfluid rotates at a smaller angular velocity
than the container. This is the first evidence for the decoupling of the
superfluid from the container reference frame in the zero-temperature limit.Comment: 4 pages, 4 figure
Spontaneous Charging and Crystallization of Water Droplets in Oil
We study the spontaneous charging and the crystallization of spherical
micron-sized water-droplets dispersed in oil by numerically solving, within a
Poisson-Boltzmann theory in the geometry of a spherical cell, for the density
profiles of the cations and anions in the system. We take into account
screening, ionic Born self-energy differences between oil and water, and
partitioning of ions over the two media. We find that the surface charge
density of the droplet as induced by the ion partitioning is significantly
affected by the droplet curvature and by the finite density of the droplets. We
also find that the salt concentration and the dielectric constant regime in
which crystallization of the water droplets is predicted is enhanced
substantially compared to results based on the planar oil-water interface,
thereby improving quantitative agreement with recent experiments.Comment: 10 pages, 7 figures, submitted for publicatio
Sweet taste exposure and the subsequent acceptance and preference for sweet taste in the diet : systematic review of the published literature
Background: There are consistent, evidence-based global public health recommendations to reduce intakes of free sugars. However, the corresponding evidence for recommending reduced exposure to sweetness is less clear. Objective: Our aim was to identify and review the published evidence investigating the impact of dietary exposure to sweet-tasting foods or beverages on the subsequent generalized acceptance, preference, or choice of sweet foods and beverages in the diet. Design: Systematic searches were conducted to identify all studies testing relations of variation in exposure to sweetness through foods and beverages with subsequent variation in the generalized acceptance, preference, or choice of sweetened foods or beverages, in humans aged >6 mo. Results: Twenty-one studies met our inclusion criteria, comprising 7 population cohort studies involving 2320 children and 14 controlled trials involving 1113 individuals. These studies were heterogeneous in study design, population, exposure, and outcomes measured, and few were explicitly designed to address our research question. The findings from these were inconsistent. We found equivocal evidence from population cohort studies. The evidence from controlled studies suggests that a higher sweet taste exposure tends to lead to reduced preferences for sweetness in the shorter term, but very limited effects were found in the longer term. Conclusions: A small and heterogeneous body of research currently has considered the impact of varying exposure to sweet taste on subsequent generalized sweet taste preferences, and this evidence is equivocal regarding the presence and possible direction of a relation. Future work should focus on adequately powered studies with well-characterized exposures of sufficient duration.Peer reviewe
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