54,819 research outputs found
Aggregates of two-dimensional vesicles: Rouleaux and sheets
Using both numerical and variational minimization of the bending and adhesion
energy of two-dimensional lipid vesicles, we study their aggregation, and we
find that the stable aggregates include an infinite number of vesicles and that
they arrange either in a columnar or in a sheet-like structure. We calculate
the stability diagram and we discuss the modes of transformation between the
two types of aggregates, showing that they include disintegration as well as
intercalation.Comment: 4 figure
Transform-limited X-ray pulse generation from a high-brightness self-amplified spontaneous-emission free-electron laser
A method to achieve high-brightness self-amplified spontaneous emission (HB-SASE) in the free-electron laser (FEL) is described. The method uses repeated nonequal electron beam delays to delocalize the collective FEL interaction and break the radiation coherence length dependence on the FEL cooperation length. The method requires no external seeding or photon optics and so is applicable at any wavelength or repetition rate. It is demonstrated, using linear theory and numerical simulations, that the radiation coherence length can be increased by approximately 2 orders of magnitude over SASE with a corresponding increase in spectral brightness. Examples are shown of HB-SASE generating transform-limited FEL pulses in the soft x-ray and near transform-limited pulses in the hard x-ray. Such pulses may greatly benefit existing applications and may also open up new areas of scientific research
Non-linear effect of uniaxial pressure on superconductivity in CeCoIn5
We study single-crystal CeCoIn5 with uniaxial pressure up to 3.97 kbar
applied along the c-axis. We find a non-linear dependence of the
superconducting transition temperature Tc on pressure, with a maximum close to
2 kbar. The transition also broadens significantly as pressure increases. We
discuss the temperature dependence in terms of the general trend that Tc
decreases in anisotropic heavy-fermion compounds as they move towards
three-dimensional behavior.Comment: 6 pages, 4 figure
A Completely Covariant Approach to Transformation Optics
We show that the Plebanski based approach to transformation optics overlooks
some subtleties in the electrodynamics of moving dielectrics that restricts its
applicability to a certain class of transformations. An alternative, completely
covariant, approach is developed that is more generally applicable and provides
a clearer picture of transformation optics.Comment: 10 pages. This version: Additional references added, corrected a
small error in Eq. (28) (Eq. (29) in present version), some revision of the
text, appendix content moved to the main body of the text, figure removed.
Corresponds more closely to published version. Prepared for a special issue
on transformation optics published by Journal of Optic
General Relativistic Contributions in Transformation Optics
One potentially realistic specification for devices designed with
transformation optics is that they operate with high precision in curved
space-time, such as Earth orbit. This raises the question of what, if any, role
does space-time curvature play in determining transformation media?
Transformation optics has been based on a three-vector representation of
Maxwell's equations in flat Minkowski space-time. I discuss a completely
covariant, manifestly four-dimensional approach that enables transformations in
arbitrary space-times, and demonstrate this approach for stable circular orbits
in the spherically symmetric Schwarzschild geometry. Finally, I estimate the
magnitude of curvature induced contributions to satellite-borne transformation
media in Earth orbit and comment on the level of precision required for
metamaterial fabrication before such contributions become important.Comment: 14 pages, 3 figures. Latest version has expanded analysis,
corresponds to published versio
Quasiparticles in Neon using the Faddeev Random Phase Approximation
The spectral function of the closed-shell Neon atom is computed by expanding
the electron self-energy through a set of Faddeev equations. This method
describes the coupling of single-particle degrees of freedom with correlated
two-electron, two-hole, and electron-hole pairs. The excitation spectra are
obtained using the Random Phase Approximation, rather than the Tamm-Dancoff
framework employed in the third-order algebraic diagrammatic contruction
[ADC(3)] method. The difference between these two approaches is studied, as
well as the interplay between ladder and ring diagrams in the self-energy.
Satisfactory results are obtained for the ionization energies as well as the
energy of the ground state with the Faddeev-RPA scheme that is also appropriate
for the high-density electron gas.Comment: Revised manuscript. The working equations of the Faddeev-RPA method
are included in the Appendi
The Hudson Bay Lithospheric Experiment (HuBLE) : Insights into Precambrian Plate Tectonics and the Development of Mantle Keels
The UK component of HuBLE was supported by Natural Environment Research Council (NERC) grant NE/F007337/1, with financial and logistical support from the Geological Survey of Canada, Canada–Nunavut Geoscience Office, SEIS-UK (the seismic node of NERC), and First Nations communities of Nunavut. J. Beauchesne and J. Kendall provided invaluable assistance in the field. Discussions with M. St-Onge, T. Skulski, D. Corrigan and M. Sanborne-Barrie were helpful for interpretation of the data. D. Eaton and F. A. Darbyshire acknowledge the Natural Sciences and Engineering Research Council. Four stations on the Belcher Islands and northern Quebec were installed by the University of Western Ontario and funded through a grant to D. Eaton (UWO Academic Development Fund). I. Bastow is funded by the Leverhulme Trust. This is Natural Resources Canada Contribution 20130084 to its Geomapping for Energy and Minerals Program. This work has received funding from the European Research Council under the European Unions Seventh Framework Programme (FP7/2007-2013)/ERC Grant agreement no. 240473 ‘CoMITAC’.Peer reviewedPublisher PD
SPEAR-1: An experiment to measure current collection in the ionosphere by high voltage biased conductors
An experiment is described in which a high electrical potential difference, up to 45 kV, was applied between deployed conducting spheres and a sounding rocket in the ionosphere. Measurements were made of the applied voltage and the resulting currents for each of 24 applications of different high potentials. In addition, diagnostic measurements of optical emissions in the vicinity of the spheres, energetic particle flow to the sounding rocket, dc electric field and wave data were made. The ambient plasma and neutral environments were measured by a Langmuir probe and a cold cathode neutral ionization gauge, respectively. The payload is described and examples of the measured current and voltage characteristics are presented. The characteristics of the measured currents are discussed in terms of the diagnostic measurements and the in-situ measurements of the vehicle environment. In general, it was found that the currents observed were at a level typical of magnetically limited currents from the ionospheric plasma for potentials less than 12 kV, and slightly higher for larger potentials. However, due to the failure to expose the plasma contactor, the vehicle sheath modified the sphere sheaths and made comparisons with the analytic models of Langmuir-Blodgett and Parker-Murphy less meaningful. Examples of localized enhancements of ambient gas density resulting from the operation of the attitude control system thrusters (cold nitrogen) were obtained. Current measurements and optical data indicated localized discharges due to enhanced gas density that reduced the vehicle-ionosphere impedance
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