80 research outputs found
Spatial gradients of GCR protons in the inner heliosphere derived from Ulysses COSPIN/KET and PAMELA measurements
During the transition from solar cycle 23 to 24 from 2006 to 2009, the Sun
was in an unusual solar minimum with very low activity over a long period.
These exceptional conditions included a very low interplanetary magnetic field
(IMF) strength and a high tilt angle, which both play an important role in the
modulation of galactic cosmic rays (GCR) in the heliosphere. Thus, the radial
and latitudinal gradients of GCRs are very much expected to depend not only on
the solar magnetic epoch, but also on the overall modulation level. We
determine the non-local radial and the latitudinal gradients of protons in the
rigidity range from ~0.45 to 2 GV. This was accomplished by using data from the
satellite-borne experiment Payload for Antimatter Matter Exploration and
Light-nuclei Astrophysics (PAMELA) at Earth and the Kiel Electron Telescope
(KET) onboard Ulysses on its highly inclined Keplerian orbit around the Sun
with the aphelion at Jupiter's orbit. In comparison to the previous A>0 solar
magnetic epoch, we find that the absolute value of the latitudinal gradient is
lower at higher and higher at lower rigidities. This energy dependence is
therefore a crucial test for models that describe the cosmic ray transport in
the inner heliosphere
The sandwich in the middle: using collective effects for stronger optomechanical coupling
Peer ReviewedPostprint (updated version
Non-equilibrium steady state of a driven levitated particle with feedback cooling
Laser trapped nanoparticles have been recently used as model systems to study
fundamental relations holding far from equilibrium. Here we study, both
experimentally and theoretically, a nanoscale silica sphere levitated by a
laser in a low density gas. The center of mass motion of the particle is
subjected, at the same time, to feedback cooling and a parametric modulation
driving the system into a non-equilibrium steady state. Based on the Langevin
equation of motion of the particle, we derive an analytical expression for the
energy distribution of this steady state showing that the average and variance
of the energy distribution can be controlled separately by appropriate choice
of the friction, cooling and modulation parameters. Energy distributions
determined in computer simulations and measured in a laboratory experiment
agree well with the analytical predictions. We analyse the particle motion also
in terms of the quadratures and find thermal squeezing depending on the degree
of detuning.Comment: Submitted to the New Journal of Physic
Long distance manipulation of a levitated nanoparticle in high vacuum
Accurate delivery of small targets in high vacuum is a pivotal task in many
branches of science and technology. Beyond the different strategies developed
for atoms, proteins, macroscopic clusters and pellets, the manipulation of
neutral particles over macroscopic distances still poses a formidable
challenge. Here we report a novel approach based on a mobile optical trap
operated under feedback control that enables long range 3D manipulation of a
silica nanoparticle in high vacuum. We apply this technique to load a single
nanoparticle into a high-finesse optical cavity through a load-lock vacuum
system. We foresee our scheme to benefit the field of optomechanics with
levitating nano-objects as well as ultrasensitive detection and monitoring.Comment: 12 pages 5 figure
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