482 research outputs found
Hardy type spaces on certain noncompact manifolds and applications
In this paper we consider a complete connected noncompact Riemannian manifold
M with Ricci curvature bounded from below, positive injectivity radius and
spectral gap b. We introduce a sequence X^1(M), X^2(M), ... of new Hardy spaces
on M, the sequence Y^1(M/, Y^2(M), ... of their dual spaces, and show that
these spaces may be used to obtain endpoint estimates for purely imaginary
powers of the Laplace-Beltrami operator and for more general spectral
multipliers associated to the Laplace--Beltrami operator L on M. Under the
additional condition that the volume of the geodesic balls of radius r is
controlled by C r^a e^{2\sqrt{b} r} for some real number a and for all large r,
we prove also an endpoint result for first order Riesz transforms D L^{-1/2}.
In particular, these results apply to Riemannian symmetric spaces of the
noncompact type.Comment: 27 pages, v2: the first version has been revised and rearranged, with
additions, in two papers, of which this new version is the first. The second
paper is posted as arXiv:1002.1161v
Phase transitions and phase diagram of the ferroelectric perovskite NBT-BT by anelastic and dielectric measurements
The complex elastic compliance and dielectric susceptibility of
(Na_{0.5}Bi_{0.5})_{1-x}Ba_{x}TiO_{3} (NBT-BT) have been measured in the
composition range between pure NBT and the morphotropic phase boundary
included, 0 <= x <= 0.08. The compliance of NBT presents sharp peaks at the
rhombohedral/tetragonal and tetragonal/cubic transitions, allowing the
determination of the tetragonal region of the phase diagram, up to now
impossible due to the strong lattice disorder and small distortions and
polarizations involved. In spite of ample evidence of disorder and structural
heterogeneity, the R-T transition remains sharp up to x = 0.06, whereas the T-C
transition merges into the diffuse and relaxor-like transition associated with
broad maxima of the dielectric and elastic susceptibilities. An attempt is made
at relating the different features in the anelastic and dielectric curves to
different modes of octahedral rotations and polar cation shifts. The
possibility is also considered that the cation displacements locally have
monoclinic symmetry, as for PZT near the morphotropic phase boundary.Comment: 11 pages, 9 figures, submitted to Phys. Rev.
Low-temperature phase transformations of PZT in the morphotropic phase-boundary region
We present anelastic and dielectric spectroscopy measurements of
PbZr(1-x)Ti(x)O(3) with 0.455 < x < 0.53, which provide new information on the
low temperature phase transitions. The tetragonal-to-monoclinic transformation
is first-order for x < 0.48 and causes a softening of the polycrystal Young's
modulus whose amplitude may exceed the one at the cubic-to-tetragonal
transformation; this is explainable in terms of linear coupling between shear
strain components and tilting angle of polarization in the monoclinic phase.
The transition involving rotations of the octahedra below 200 K is visible both
in the dielectric and anelastic losses, and it extends within the tetragonal
phase, as predicted by recent first-principle calculations.Comment: 4 pages, 4 figure
Smart Textile: Exploration of Wireless Sensing Capabilities
This is the author accepted manuscript. The final version is available from IEEE via the DOI in this recordE-textile is a developing technology joining the advantages of material science and information and communication technologies. In this work, we present the development and assessment of smart textile system containing sensing, processing and wireless communication capabilities. We demonstrate a wearable temperature sensing system based on resistance temperature detection approach utilizing graphene technology, which allows high flexibility and robustness of the electronic textile. The developed sensing system demonstrates experimental sensitivity as high as 80Ω/°C within the temperature detection range from 24 °C to 35 °C, which is the highest reported to date for wearable temperature sensors. In terms of wireless communication, the system operates at 2.4 GHz supporting Bluetooth low energy technology and securely transmits the measured data for up to 10 m which is proved by received signal strength and link quality indicators
Biomolecule-polymer hybrid compartments: combining the best of both worlds
Compartmentalization is a fundamental principle in biology that is needed for the temporal and spatial separation of chemically incompatible reactions and biomolecules. Nano- or micro-sized compartments made of synthetic polymers are used to mimick this principle. The self-assembly of these polymers into vesicular objects is highly compatible with the integration of biomolecules, either into the lumen, the membrane or onto the surface of the vesicles. Thus, a great variety of biohybrid nano- and microscaled compartments has been developed exploiting the specific function and properties of targeting peptides, antibodies, enzymes, nucleic acids or lipids. Such biohybrid compartments have moved from simple systems encapsulating e.g. a model protein into complex multicompartmentalized structures that are able to combine the activity of different biomolecular cargos getting closer to the realization of artifical organelles or cells. Encapsulation of medically relevant cargos combined with careful design of the polymeric scaffold and specific surface functionalization have led to a significant progress in therapeutical applications such as targeted drug delivery or enzyme replacement therapy
Hydrogen tunneling in the perovskite ionic conductor BaCe(1-x)Y(x)O(3-d)
We present low-temperature anelastic and dielectric spectroscopy measurements
on the perovskite ionic conductor BaCe(1-x)Y(x)O(3-x/2) in the protonated,
deuterated and outgassed states. Three main relaxation processes are ascribed
to proton migration, reorientation about an Y dopant and tunneling around a
same O atom. An additional relaxation maximum appears only in the dielectric
spectrum around 60 K, and does not involve H motion, but may be of electronic
origin, e.g. small polaron hopping. The peak at the lowest temperature,
assigned to H tunneling, has been fitted with a relaxation rate presenting
crossovers from one-phonon transitions, nearly independent of temperature, to
two-phonon processes, varying as T^7, to Arrhenius-like. Substituting H with D
lowers the overall rate by 8 times. The corresponding peak in the dielectric
loss has an intensity nearly 40 times smaller than expected from the classical
reorientation of the electric dipole associated with the OH complex. This fact
is discussed in terms of coherent tunneling states of H in a cubic and
orthorhombically distorted lattice, possibly indicating that only H in the
symmetric regions of twin boundaries exhibit tunneling, and in terms of
reduction of the effective dipole due to lattice polarization.Comment: submitted to Phys. Rev.
Homogeneously Bright, Flexible, and Foldable Lighting Devices with Functionalized Graphene Electrodes.
Alternating current electroluminescent technology allows the fabrication of large area, flat and flexible lights. Presently the maximum size of a continuous panel is limited by the high resistivity of available transparent electrode materials causing a visible gradient of brightness. Here, we demonstrate that the use of the best known transparent conductor FeCl3-intercalated few-layer graphene boosts the brightness of electroluminescent devices by 49% compared to pristine graphene. Intensity gradients observed for high aspect ratio devices are undetectable when using these highly conductive electrodes. Flat lights on polymer substrates are found to be resilient to repeated and flexural strains.S. Russo and M.F. Craciun acknoweldge
financial support from EPSRC (Grant no. EP/J000396/1, EP/K017160/1, EP/K010050/1,
EPG036101/1, EP/M001024/1, EPM002438/1) and from the Leverhulme Trust (Research grant
title Quantum Drums)
Strong Correlations in Electron Doped Phthalocyanine Conductors Near Half Filling
We propose that electron doped nontransition metal-phthalocyanines (MPc) like
ZnPc and MgPc, similar to those very recently reported, should constitute novel
strongly correlated metals. Due to orbital degeneracy, Jahn-Teller coupling and
Hund's rule exchange, and with a large on-site Coulomb repulsion, these
molecular conductors should display, particularly near half filling at two
electrons/molecule, very unconventional properties, including Mott insulators,
strongly correlated superconductivity, and other intriguing phases.Comment: 4 pages, 1 figure, submited to PR
2D WS2 liquid crystals: tunable functionality enabling diverse applications
This is the final version. Available on open access from Royal Society of Chemistry via the DOI in this recordThe first observation of liquid crystalline dispersions of liquid phase-exfoliated tungsten disulfide flakes is reported in a range of organic solvents. The liquid crystals demonstrate significant birefringence as observed in the linear and circular dichroism measurements respectively. In particular, linear dichroism is observed throughout the visible range while broad-band circular dichroism can be observed in the range from 500-800 nm. Under an applied magnetic field of ±1.5 T the circular dichroism can be switched ON/OFF, while the wavelength range for switching can be tuned from large to narrow range by the proper selection of the host solvent. In combination with photoluminescence capabilities of WS2, this opens a pathway to a wide variety of applications, such as deposition of highly uniform films over large areas for photovoltaic and terahertz devices.Engineering and Physical Sciences Research Council (EPSRC)Royal Societ
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