15,088 research outputs found
Effect of Bilayer Thickness on Membrane Bending Rigidity
The bending rigidity of bilayer vesicles self-assembled from
amphiphilic diblock copolymers has been measured using single and
dual-micropipet techniques. These copolymers are nearly a factor of 5 greater
in hydrophobic membrane thickness than their lipid counterparts, and an
order of magnitude larger in molecular weight . The macromolecular
structure of these amphiphiles lends insight into and extends relationships for
traditional surfactant behavior. We find the scaling of with thickness to
be nearly quadratic, in agreement with existing theories for bilayer membranes.
The results here are key to understanding and designing soft interfaces such as
biomembrane mimetics
Modeling of grating assisted standing wave microresonators for filter applications in integrated optics
A wide, multimode segment of a dielectric optical waveguide, enclosed by Bragg reflectors and evanescently coupled to adjacent port waveguides, can constitute the cavity in an integrated optical microresonator. It turns out that the device can be described adequately in terms of an approximate coupled mode theory model which involves only a few guided modes as basis fields. By reasoning along the coupled mode model, we motivate a simple design strategy for the resonator device. Rigorous two dimensional mode expansion simulations are applied to verify the predictions of the approximate model. The results exemplify the specific spectral response of the standing wave resonators. As refinements we discuss the single resonance of a device with nonsymmetrically detuned Bragg reflectors, and the cascading of two Fabry-Perot cavities, where the coupling across an intermediate shorter grating region establishes a power transfer characteristic that is suitable for an add-drop filter
Low-energy p-d scattering and He-3 in pionless EFT
We calculate low-energy proton--deuteron scattering in the framework of
pionless effective field theory. In the quartet channel, we calculate the
elastic scattering phase shift up to next-to-next-to-leading order in the power
counting. In the doublet channel, we perform a next-to-leading order
calculation. We obtain good agreement with the available phase shift analyses
down to the scattering threshold. The phase shifts in the region of
non-perturbative Coulomb interactions are calculated by using an optimised
integration mesh. Moreover, the Coulomb contribution to the 3He-3H binding
energy difference is evaluated in first order perturbation theory. We comment
on the implications of our results for the power counting of subleading
three-body forces.Comment: 27 pages, 13 figures, typos corrected in Sec. V.A (trinucleon wave
functions
Pion-mass dependence of three-nucleon observables
We use an effective field theory (EFT) which contains only short-range
interactions to study the dependence of a variety of three-nucleon observables
on the pion mass. The pion-mass dependence of input quantities in our
``pionless'' EFT is obtained from a recent chiral EFT calculation. To the order
we work at, these quantities are the 1S0 scattering length and effective range,
the deuteron binding energy, the 3S1 effective range, and the binding energy of
one three-nucleon bound state. The chiral EFT input we use has the inverse 3S1
and 1S0 scattering lengths vanishing at mpi_c=197.8577 MeV. At this
``critical'' pion mass, the triton has infinitely many excited states with an
accumulation point at the three-nucleon threshold. We compute the binding
energies of these states up to next-to-next-to-leading order in the pionless
EFT and study the convergence pattern of the EFT in the vicinity of the
critical pion mass. Furthermore, we use the pionless EFT to predict how doublet
and quartet nd scattering lengths depend on mpi in the region between the
physical pion mass and mpi=mpi_c.Comment: 24 pages, 9 figure
Vaporization response of evaporating drops with finite thermal conductivity
A numerical computing procedure was developed for calculating vaporization histories of evaporating drops in a combustor in which travelling transverse oscillations occurred. The liquid drop was assumed to have a finite thermal conductivity. The system of equations was solved by using a finite difference method programmed for solution on a high speed digital computer. Oscillations in the ratio of vaporization of an array of repetitivity injected drops in the combustor were obtained from summation of individual drop histories. A nonlinear in-phase frequency response factor for the entire vaporization process to oscillations in pressure was evaluated. A nonlinear out-of-phase response factor, in-phase and out-of-phase harmonic response factors, and a Princeton type 'n' and 'tau' were determined. The resulting data was correlated and is presented in graphical format. Qualitative agreement with the open literature is obtained in the behavior of the in-phase response factor. Quantitatively the results of the present finite conductivity spray analysis do not correlate with the results of a single drop model
Three-body problem in heteronuclear mixtures with resonant interspecies interaction
We use the zero-range approximation to study a system of two identical bosons
interacting resonantly with a third particle. The method is derived from
effective field theory. It reduces the three-body problem to an integral
equation which we then solve numerically. We also develop an alternative
approach which gives analytic solutions of the integral equation in coordinate
representation in the limit of vanishing total energy. The atom-dimer
scattering length, the rates of atom-dimer relaxation and three-body
recombination to shallow and to deep molecular states are calculated either
analytically or numerically with a well controlled accuracy for various
energies as functions of the mass ratio, scattering length, and three-body
parameter. We discuss in detail the relative positions of the recombination
loss peaks, which in the universal limit depend only on the mass ratio. Our
results have implications for ongoing and future experiments on Bose-Bose and
Bose-Fermi atomic mixtures.Comment: 13 pages, 8 figures, minor changes, published versio
Skylab mission planning support through the use of a hybrid simulation
The manner in which a hybrid simulation was used in support of Skylab operations in the area of dynamics and control is described. Simulation results were used in the development of acceptable vehicle maneuvers and in the verification of acceptability when the maneuvers were integrated into daily flight plans. The criterion of acceptability was based on vehicle controllability and the minimization of thruster system propellant usage. A simulation of a representative daily flight plan containing three experimental maneuvers is included, along with thruster attitude control system propellant usage tables which show predicted and actual usage for each mission. The inherent characteristics of quick turnaround and flexibility afforded by the hybrid computer proved invaluable in the operations support required throughout the Skylab mission
Droplet vaporization with liquid heat conduction Final report
Mathematical model for droplet vaporization with liquid heat conductio
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