1,540 research outputs found
Sy Montgomery and Matt Patterson: 2024 Cook Prize Gold Medal Winners
No full textAuthor Sy Montgomery and illustrator Matt Patterson\u27s video for The Book of Turtles (Clarion)https://educate.bankstreet.edu/cook/1012/thumbnail.jp
Ice Particles Sink below the Water Surface Due to a Balance of Salt, van der Waals, and Buoyancy Forces
No full textAccording to the classical Archimedes’ principle, ice floats in water and has a fraction of its volume above the water surface. However, for very small ice particles, other competing forces such as van der Waals forces due to fluctuating charge distributions and ionic forces due to salt ions and charge on the ice surface also contribute to the force balance. The latter crucially depends on both the pH of the water and the salt concentration. We show that a bulge in the air–water interface due to interaction of surface tension with the rising ice particle becomes significant when the particle radius is greater than 50–100 μm. The role of these forces in governing the initial stages of ice condensation has never been considered. Here, we show that small ice particles can only form below an exclusion zone, from 2 nm (in high salt concentrations) up to 1 μm (in pure water at pH 7) thick, under the water surface. This distance is defined by an equilibrium of upward buoyancy forces and repulsive van der Waals forces. Ionic forces due to salt and ice surface charge push this zone further down. Only after growing to a radius larger than 10 μm, will the ice particles eventually float toward the water surface in agreement with the simple intuition based on Archimedes’ principle. Our result is the first prediction of observable repulsive van der Waals forces between ice particles and the water surface outside a laboratory setting. We posit that it has consequences on the biology of ice water as we predict an exclusion zone free of ice particles near the water surface which is sufficient to support the presence of bacteria
Non-perturbative theory of dispersion interactions
No full textSome open questions exist with fluctuation-induced forces between extended dipoles. Conventional intuition derives from large-separation perturbative approximations to dispersion force theory. Here, we present a full non-perturbative theory. In addition, we discuss how one can take into account finite dipole size corrections. It is of fundamental value to investigate the limits of validity of the perturbative dispersion force theory
Trends of CO2 adsorption on cellulose due to van der Waals forces
No full textThe non-retarded van der Waals and Casimir–Polder forces on a CO2 molecule in water near a single surface and between surfaces are explored. We observe preferential adsorption and desorption of CO2 molecules depending on the material of the surfaces. We also find a potential mechanism of capture and storage of CO2 molecules in a geometry consisting of a cellulose surface coated by a thin film of water and then by air
Effects of van der Waals forces and salt ions on the growth of water films on ice and the detachment of CO2 bubbles
No full textWe study the effect of salts on the thickness of wetting films on melting ice and interactions acting on CO2 bubble near ice-water and vapor-water interfaces. Governing mechanisms are the Lifshitz and the double-layer interactions in the respective three-layer geometries. We demonstrate that the latter depend on the Casimir-Polder interaction of the salt ions dissolved in water with the respective ice, vapor and CO2 interfaces, as calculated using different models for their effective polarizability in water. Significant variation in the predicted thickness of the equilibrium water film is observed for different salt ions and when using different models for the ions' polarizabilities. We find that CO2 bubbles are attracted towards the ice-water interface and repelled from the vapor-water interface
Photometric study of a marginal contact binary SY Hor
No full text32nd International Physics Congress of Turkish-Physical-Society (TPS) -- SEP 06-09, 2016 -- Bodrum, TURKEYIn this study, we present light curve analysis of a southern contact binary SY lior. Photometric parameters of the system and its components are derived using the Wilson and Devinney code based on the data taken from the SuperWASP public data archive. Photometric solutions indicate that SY Hai is a marginal contact binary system with a mass ratio of q = 1.59 and a contact degree of f = 6%.Turkish Phys So
Effective Polarizability Models
No full textTheories for the effective polarizability of a small particle in a medium are presented using different levels of approximation: we consider the virtual cavity, real cavity, and the hard-sphere models as well as a continuous interpolation of the latter two. We present the respective hard-sphere and cavity radii as obtained from density-functional simulations as well as the resulting effective polarizabilities at discrete Matsubara frequencies. This enables us to account for macroscopic media in van der Waals interactions between molecules in water and their Casimir–Polder interaction with an interface
The study of CMOS based VCO with active inductor and its design methodology
No full textActive Inductors are useful in reducing the large chip area typically consumed by spiral inductors, as well as providing larger inductance values and higher quality factors that otherwise cannot be achieved by spiral inductors. Integrated inductors find application in many radio frequency (RF) front end integrated circuits, including impedance matching, filtering, biasing and in oscillator circuits. Nonetheless, because of the interdependent relationship of the self-resonant frequency and quality factor it is often difficult to meet desired circuit requirements. Additionally, active devices pose problems of higher power consumption , noise figure and potential instability. This thesis begins with the study of active inductors, the Wu active inductor in particular, and considers tuning methods based on the Wu active inductor topology. Starting with the small-signal model, the emulated inductance and quality factor expressions are derived. Next, the operation of active inductors under large-signal is closely examined. Comparisons between a passive and an active VCO are made. The active inductor based voltage-controlled oscillator (Active VCO) is studied extensively, and the methods of improving the performance under large signal-behavior are discussed. Then a design procedure based on gm/ID methodology is proposed. A Matlab script that can be applied to gyrator-C based active inductors is developed to determine the sizing of the transistors for a desired inductance and resonant frequency. Cadence Virtuoso is used for simulations, and extraction based on an IBM 8RF technology file. Finally, a low power active VCO is designed, simulated and laid out.M.S.Includes bibliographical referencesby Sy-Min Chuen
Dynamical Casimir-Polder force between an excited atom and a conducting wall
No full textWe consider the dynamical atom-surface Casimir-Polder force in the nonequilibrium configuration of an atom near a perfectly conducting wall, initially prepared in an excited state with the field in its vacuum state. We evaluate the time-dependent Casimir-Polder force on the atom and find that it shows an oscillatory behavior from attractive to repulsive both in time and in space. We also investigate the asymptotic behavior in time of the dynamical force and of related local field quantities, showing that the static value of the force, as obtained by a time-independent approach, is recovered for times much longer than the time scale of the atomic self-dressing but shorter than the atomic decay time. We then discuss the evolution of global quantities such as atomic and field energies and their asymptotic behavior. We also compare our results for the dynamical force on the excited atom with analogous results recently obtained for an initially bare ground-state atom. We show that new relevant features are obtained in the case of an initially excited atom, for example, much larger values of the dynamical force with respect to the static one, allowing for an easier way to single out and observe the dynamical Casimir-Polder effect
Bothaville en sy mense
No full textHierdie boek bet sy verskyning te danke aan 'n begeerte by histories-bewuste
mense van Bothaville om die bonderjarige bestaan van die dorp feesvierend in
1991 te herdenk. Daardeur het Bothaville aangesluit by die talle ander dorpe
en gemeenskappe/organisasies/instansies wat veral in die jongste twee tot drie
dekades dié verboogde en groeiende historiese bewussyn openbaar.
Aanvanklik is beplan dat publikasie nog in die feesjaar sou geskied, maar dit
was spoedig duidelik: dat dié doelwit nie binne so 'n kort tydsbestek haalbaar
was nie. Finansiele bronne was boonop ook nie voldoende om die
onvoorspelbare eskalerende navorsing te finansier nie en 'n groot deel van die
werk moes noodgedwonge by die reeds druk akademiese programme van die
twee skrywers ingepas word. Hierdie toedrag van sake bet beduidend
vertragend op die projek ingewerk.
Hierdie boek is nie 'n wetenskaplike werk in die normale sin van die woord
nie. Met inagneming van die genoemde beperkinge ten opsigte van tyd en
finansies, is die navorsing wat die boek ten grondslag lê, asook die
bevindinge en gevolgtrekkinge waartoe geraak is, egter ten volle
wetenskaplik-gefundeerd
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