14,199 research outputs found
Nonlinear magnetoinductive waves and domain walls in composite metamaterials
We describe novel physics of nonlinear magnetoinductive waves in left-handed
composite metamaterials. We derive the coupled equations for describing the
propagation of magnetoinductive waves, and show that in the nonlinear regime
the magnetic response of a metamaterial may become bistable. We analyze
modulational instability of different nonlinear states, and also demonstrate
that nonlinear metamaterials may support the propagation of domain walls
(kinks) connecting the regions with the positive and negative magnetization.Comment: 5 pages, 5 figure
Temperature dependent photoluminescence of single CdS nanowires
Temperature dependent photoluminescence (PL) is used to study the electronic
properties of single CdS nanowires. At low temperatures, both near-band edge
(NBE) photoluminescence (PL) and spatially-localized defect-related PL are
observed in many nanowires. The intensity of the defect states is a sensitive
tool to judge the character and structural uniformity of nanowires. As the
temperature is raised, the defect states rapidly quench at varying rates
leaving the NBE PL which dominates up to room temperature. All PL lines from
nanowires follow closely the temperature-dependent band edge, similar to that
observed in bulk CdS.Comment: 11 pages, 4 figure
Low temperature photoluminescence imaging and time-resolved spectroscopy of single CdS nanowires
Time-resolved photoluminescence (PL) and micro-PL imaging were used to study
single CdS nanowires at 10 K. The low-temperature PL of all CdS nanowires
exhibit spectral features near energies associated with free and bound exciton
transitions, with the transition energies and emission intensities varying
along the length of the nanowire. In addition, several nanowires show spatially
localized PL at lower energies which are associated with morphological
irregularities in the nanowires. Time-resolved PL measurements indicate that
exciton recombination in all CdS nanowires is dominated by non-radiative
recombination at the surface of the nanowires.Comment: 9 pages, 3 figures, to be published in Applied Physics Letter
Switchable collective pinning of flux quanta using magnetic vortex arrays
We constructed a superconducting/ferromagnetic hybrid system in which the
ordering of the pinning potential landscape for flux quanta can be manipulated.
Flux pinning is induced by an array of magnetic nanodots in the magnetic vortex
state, and controlled by the magnetic history. This allows switching on and off
the collective pinning of the flux-lattice. In addition, we observed
field-induced superconductivity that originates from the annihilation of flux
quanta induced by the stray fields from the magnetic vortices.Comment: PDF file 18 pages including 5 figures, accepted for publication in
Phys. Rev.
Mapping local optical densities of states in silicon photonic structures with nanoscale electron spectroscopy
Relativistic electrons in a structured medium generate radiative losses such
as Cherenkov and transition radiation that act as a virtual light source,
coupling to the photonic densities of states. The effect is most pronounced
when the imaginary part of the dielectric function is zero, a regime where in a
non-retarded treatment no loss or coupling can occur. Maps of the resultant
energy losses as a sub-5nm electron probe scans across finite waveguide
structures reveal spatial distributions of optical modes in a spectral domain
ranging from near-infrared to far ultraviolet.Comment: 18 pages, 4 figure
Pet ownership and cognitive decline in older people
Animals can have a positive influence on human health. However, it is not yet known whether pet ownership can prevent cognitive decline. Therefore, we aimed to investigate cross-sectional and prospective associations between pet ownership and cognitive function in a large, representative sample of older adults. Data were from the English Longitudinal Study of Ageing (ELSA) using data collected in wave 5 and six years later in wave 8. Pet ownership was categorized as no pet, dog, cat or other pet. Cognitive function was assessed using tests of verbal fluency (assessed by asking how many different animals the participants could name in 60 seconds) and memory (sum of immediate and delayed verbal recall). Multiple linear regression, adjusted for potential confounders, was used to test the associations between pet ownership and cognitive function. A total of 8291 people (mean age: 66.72 years) were included. In cross-sectional analyses, dog owners had better verbal fluency than individuals with no pet, but there was no significant difference between cat or other pet owners and those with no pet. In prospective analyses, dog owners had a significantly larger decline in recall than those with no pet, whilst cat owners had a significantly smaller decline in verbal fluency. These results provide some evidence to suggest that pet ownership may have positive effects on cognition in later life. However, benefits of pet ownership were not unilaterally observed across different types of pet and measures of cognitive function suggesting that further research is required
A Search for Early Optical Emission at Gamma-Ray Burst Locations by the Solar Mass Ejection Imager (SMEI)
The Solar Mass Ejection Imager (SMEI) views nearly every point on the sky
once every 102 minutes and can detect point sources as faint as R~10th
magnitude. Therefore, SMEI can detect or provide upper limits for the optical
afterglow from gamma-ray bursts in the tens of minutes after the burst when
different shocked regions may emit optically. Here we provide upper limits for
58 bursts between 2003 February and 2005 April.Comment: accepted for publication in ApJ, 17 pages, 8 figure
Excitation spectrum of a two-component Bose-Einstein condensate in a ring potential
A mixture of two distinguishable Bose-Einstein condensates confined in a ring
potential has numerous interesting properties under rotational and
solitary-wave excitation. The lowest-energy states for a fixed angular momentum
coincide with a family of solitary-wave solutions. In the limit of weak
interactions, exact diagonalization of the many-body Hamiltonian is possible
and permits evaluation of the complete excitation spectrum of the system.Comment: 4 pages, 1 figur
Doing more with less: the flagellar end piece enhances the propulsive effectiveness of human spermatozoa
Spermatozoa self-propel by propagating bending waves along a predominantly
active elastic flagellum. The organized structure of the "9 + 2" axoneme is
lost in the most-distal few microns of the flagellum, and therefore this region
is unlikely to have the ability to generate active bending; as such it has been
largely neglected in biophysical studies. Through elastohydrodynamic modeling
of human-like sperm we show that an inactive distal region confers significant
advantages, both in propulsive thrust and swimming efficiency, when compared
with a fully active flagellum of the same total length. The beneficial effect
of the inactive end piece on these statistics can be as small as a few percent
but can be above 430%. The optimal inactive length, between 2-18% of the total
length, depends on both wavenumber and viscous-elastic ratio, and therefore is
likely to vary in different species. Potential implications in evolutionary
biology and clinical assessment are discussed.Comment: To Appear, Physical Review Fluids. 25 pages, 14 figure
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