21,078 research outputs found
A Better Definition of the Kilogram
This article reviews several recent proposed redefinitions of the kilogram,
and compares them with respect to practical realizations, uncertainties
(estimated standard deviations), and educational aspects.Comment: 10 pages, no figure
Capillary-gravity wave resistance in ordinary and magnetic fluids
Wave resistance is the drag force associated to the emission of waves by a
moving disturbance at a fluid free surface. In the case of capillary-gravity
waves it undergoes a transition from zero to a finite value as the speed of the
disturbance is increased. For the first time an experiment is designed in order
to obtain the wave resistance as a function of speed. The effect of viscosity
is explored, and a magnetic fluid is used to extend the available range of
critical speeds. The threshold values are in good agreement with the proposed
theory. Contrary to the theoretical model, however, the measured wave
resistance reveals a non monotonic speed dependence after the threshold.Comment: 12 pages, 4 figures, 1 table, submitted to Physical Review Letter
Symmetry breaking in MAST plasma turbulence due to toroidal flow shear
The flow shear associated with the differential toroidal rotation of tokamak
plasmas breaks an underlying symmetry of the turbulent fluctuations imposed by
the up-down symmetry of the magnetic equilibrium. Using experimental
Beam-Emission-Spectroscopy (BES) measurements and gyrokinetic simulations, this
symmetry breaking in ion-scale turbulence in MAST is shown to manifest itself
as a tilt of the spatial correlation function and a finite skew in the
distribution of the fluctuating density field. The tilt is a statistical
expression of the "shearing" of the turbulent structures by the mean flow. The
skewness of the distribution is related to the emergence of long-lived density
structures in sheared, near-marginal plasma turbulence. The extent to which
these effects are pronounced is argued (with the aid of the simulations) to
depend on the distance from the nonlinear stability threshold. Away from the
threshold, the symmetry is effectively restored
Interface-Induced Plasmon Nonhomogeneity in Nanostructured Metal-Dielectric Planar Metamaterial
Transformations of the electronic structure in thin silver layers in metal-dielectric (TiAlN/Ag) multilayer nanocomposite were investigated by a set of electron spectroscopy techniques. Localization of the electronic states in the valence band and reduction of electron concentration in the conduction band was observed. This led to decreasing metallic properties of silver in the thin films. A critical layer thickness of 23.5ānm associated with the development of quantum effects was determined by X-ray photoelectron spectroscopy. Scanning Auger electron microscopy of characteristic energy losses provided images of plasmon localization in the Ag layers. The nonuniformity of plasmon intensities distribution near the metal-nitride interfaces was assessed experimentally
On-chip electrically controlled routing of photons from a single quantum dot
Electrical control of on-chip routing of photons emitted by a single InAs/GaAs self-assembled quantum dot (SAQD) is demonstrated in a photonic crystal cavity-waveguide system. The SAQD is located inside an H1 cavity, which is coupled to two photonic crystal waveguides. The SAQD emission wavelength is electrically tunable by the quantum-confined Stark effect. When the SAQD emission is brought into resonance with one of two H1 cavity modes, it is preferentially routed to the waveguide to which that mode is selectively coupled. This proof of concept provides the basis for scalable, low-power, high-speed operation of single-photon routers for use in integrated quantum photonic circuits
The weakly coupled fractional one-dimensional Schr\"{o}dinger operator with index
We study fundamental properties of the fractional, one-dimensional Weyl
operator densely defined on the Hilbert space
and determine the asymptotic behaviour of
both the free Green's function and its variation with respect to energy for
bound states. In the sequel we specify the Birman-Schwinger representation for
the Schr\"{o}dinger operator
and extract the finite-rank portion which is essential for the asymptotic
expansion of the ground state. Finally, we determine necessary and sufficient
conditions for there to be a bound state for small coupling constant .Comment: 16 pages, 1 figur
Connection for conservation: The impact of counting butterflies on nature connectedness and wellbeing in citizen scientists
Biodiversity conservation is fundamentally linked to human values, attitudes, and behaviours. Nature connectedness, the strength of a person's relationship with nature, is an important determinant of pro-nature actions, and therefore vital for counteracting biodiversity loss. Citizen science may improve nature connectedness, though such outcomes are underexplored in comparison to scientific and educational results. Addressing this gap, we studied the experiences of participants in the Big Butterfly Count, a UK mass-participation citizen science activity that aims to raise awareness and gather data on the abundance of widespread butterfly and moth species. Participants completed surveys before and after the three-week Big Butterfly Count period (n = 382), and at six- to seven-week follow up (n = 345). Improvements in nature connectedness, decreased anxiety, and increased tendency to notice nature and butterflies, were found immediately after the count period, with improved wellbeing and nature noticing at follow-up. Stronger emotional responses during the butterfly count were associated with greater increases in nature connectedness and nature noticing. Qualitative data revealed mixed emotions, from sadness and concern about biodiversity loss, to feelings of hope and optimism through taking actions to help butterflies. These findings suggest that citizen science participation prompts people to notice and enjoy nature in ways that enhance their wellbeing and connection with nature, supporting the mutual health of people and the rest of the natural world. The study highlights the potential for nature-based citizen science to benefit conservation beyond the focal species or habitat, by changing how people think, feel and act towards nature more broadly
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