12,816 research outputs found
On-demand delivery of single DNA molecules using nanopipettes
Understanding the behavioral properties of single molecules or larger scale populations interacting with single molecules is currently a hotly pursued topic in nanotechnology. This arises from the potential such techniques have in relation to applications such as targeted drug delivery, early stage detection of disease, and drug screening. Although label and label-free single molecule detection strategies have existed for a number of years, currently lacking are efficient methods for the controllable delivery of single molecules in aqueous environments. In this article we show both experimentally and from simulations that nanopipets in conjunction with asymmetric voltage pulses can be used for label-free detection and delivery of single molecules through the tip of a nanopipet with “on-demand” timing resolution. This was demonstrated by controllable delivery of 5 kbp and 10 kbp DNA molecules from solutions with concentrations as low as 3 pM
Modelling the polarisation mode control of single quantum-dot emission in elliptical micro-pillar microcavities based on DBR mirror pairs using the FDTD method
Confined spin waves reveal an assembly of nanosize domains in ferromagnetic La(1-x)CaxMnO3 (x=0.17,0.2)
We report a study of spin-waves in ferromagnetic LaCaMnO,
at concentrations x=0.17 and x=0.2 very close to the metallic transition
(x=0.225). Below T, in the quasi-metallic state (T=150K), nearly
q-independent energy levels are observed. They are characteristic of standing
spin waves confined into finite-size ferromagnetic domains, defined in {\bf a,
b) plane for x=0.17 and in all q-directions for x=0.2. They allow an estimation
of the domain size, a few lattice spacings, and of the magnetic coupling
constants inside the domains. These constants, anisotropic, are typical of an
orbital-ordered state, allowing to characterize the domains as "hole-poor". The
precursor state of the CMR metallic phase appears, therefore, as an assembly of
small orbital-ordered domains.Comment: 4 pages, 5 figure
Resonant magnetic excitations at high energy in superconducting
A detailed inelastic neutron scattering study of the high temperature
superconductor provides evidence of new resonant
magnetic features, in addition to the well known resonant mode at 41 meV: (i) a
commensurate magnetic resonance peak at 53 meV with an even symmetry under
exchange of two adjacent layers; and (ii) high energy
incommensurate resonant spin excitations whose spectral weight is around 54
meV. The locus and the spectral weight of these modes can be understood by
considering the momentum shape of the electron-hole spin-flip continuum of
d-wave superconductors. This provides new insight into the interplay between
collective spin excitations and the continuum of electron-hole excitations.Comment: 5 figure
Vortex Polarity Switching in Magnets with Surface Anisotropy
Vortex core reversal in magnetic particle is essentially influenced by a
surface anisotropy. Under the action of a perpendicular static magnetic field
the vortex core undergoes a shape deformationof pillow- or barrel-shaped type,
depending on the type of the surface anisotropy. This deformation plays a key
point in the switching mechanism: We predict that the vortex polarity switching
is accompanied (i) by a linear singularity in case of Heisenberg magnet with
bulk anisotropy only and (ii) by a point singularities in case of surface
anisotropy or exchange anisotropy. We study in details the switching process
using spin-lattice simulations and propose a simple analytical description
using a wired core model, which provides an adequate description of the Bloch
point statics, its dynamics and the Bloch point mediated switching process. Our
analytical predictions are confirmed by spin-lattice simulations for Heisenberg
magnet and micromagnetic simulations for nanomagnet with account of a dipolar
interaction.Comment: 17 pages, 15 figure
Ultra-Low Noise Microwave Extraction from Fiber-Based Optical Frequency Comb
In this letter, we report on all-optical fiber approach to the generation of
ultra-low noise microwave signals. We make use of two erbium fiber mode-locked
lasers phase locked to a common ultra-stable laser source to generate an 11.55
GHz signal with an unprecedented relative phase noise of -111 dBc/Hz at 1 Hz
from the carrier.The residual frequency instability of the microwave signals
derived from the two optical frequency combs is below 2.3 10^(-16) at 1s and
about 4 10^(-19) at 6.5 10^(4)s (in 5 Hz bandwidth, three days continuous
operation).Comment: 12 pages, 3 figure
The helium atom in a strong magnetic field
We investigate the electronic structure of the helium atom in a magnetic
field b etween B=0 and B=100a.u. The atom is treated as a nonrelativistic
system with two interactin g electrons and a fixed nucleus. Scaling laws are
provided connecting the fixed-nucleus Hamiltonia n to the one for the case of
finite nuclear mass. Respecting the symmetries of the electronic Ham iltonian
in the presence of a magnetic field, we represent this Hamiltonian as a matrix
with res pect to a two-particle basis composed of one-particle states of a
Gaussian basis set. The corresponding generalized eigenvalue problem is solved
numerically, providing in the present paper results for vanish ing magnetic
quantum number M=0 and even or odd z-parity, each for both singlet and triplet
spin symmetry. Total electronic energies of the ground state and the first few
excitations in each su bspace as well as their one-electron ionization energies
are presented as a function of the magnetic fie ld, and their behaviour is
discussed. Energy values for electromagnetic transitions within the M=0 sub
space are shown, and a complete table of wavelengths at all the detected
stationary points with respect to their field dependence is given, thereby
providing a basis for a comparison with observed ab sorption spectra of
magnetic white dwarfs.Comment: 21 pages, 4 Figures, acc.f.publ.in J.Phys.
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