86 research outputs found
Role of Drosophila Rab5 during endosomal trafficking at the synapse and evoked neurotransmitter release
The X-ray Telescope of the CAST Experiment
The CERN Axion Solar Telescope (CAST) searches for solar axions employing a 9
Tesla superconducting dipole magnet equipped with 3 independent detection
systems for X-rays from axion-photon conversions inside the 10 m long magnetic
field. Results of the first 6 months of data taking in 2003 imply a 95 % CL
upper limit on the axion-photon coupling constant of 1.16x10(-10) GeV(-1) for
axion masses < 0.02 eV. The most sensitive detector of CAST is a X-ray
telescope consisting of a Wolter I type mirror system and a fully depleted
pn-CCD as focal plane detector. Exploiting the full potential of background
suppression by focussing X-rays emerging from the magnet bore, the axion
sensitivity obtained with telescope data taken in 2004, for the first time in a
controlled laboratory experiment, will supersede axion constraints derived from
stellar energy loss arguments.Comment: 5 pages, 9 figure
Understanding and Controlling Cu-Catalyzed Graphene Nucleation: The Role of Impurities, Roughness, and Oxygen Scavenging
The mechanism by which Cu catalyst pretreatments control graphene nucleation density in scalable chemical vapor deposition (CVD) is systematically explored. The intrinsic and extrinsic carbon contamination in the Cu foil is identified by time-of-flight secondary ion mass spectrometry as a major factor influencing graphene nucleation and growth. By selectively oxidizing the backside of the Cu foil prior to graphene growth, a drastic reduction of the graphene nucleation density by 6 orders of magnitude can be obtained. This approach decouples surface roughness effects and at the same time allows us to trace the scavenging effect of oxygen on deleterious carbon impurities as it permeates through the Cu bulk. Parallels to well-known processes in Cu metallurgy are discussed. We also put into context the relative effectiveness and underlying mechanisms of the most widely used Cu pretreatments, including wet etching and electropolishing, allowing a rationalization of current literature and determination of the relevant parameter space for graphene growth. Taking into account the wider CVD growth parameter space, guidelines are discussed for high-throughput manufacturing of "electronic-quality" monolayer graphene films with domain size exceeding 1 mm, suitable for emerging industrial applications, such as electronics and photonics.This research was supported by the ERC under grant InsituNANO (279342), the EPSRC under grant GRAPHTED (EP/K016636/1), and the Innovation R&D programme of the National Measurement System of the U.K. Department of Business, Innovation and Skills (project number 118616)
Magnetic Field tuning of low energy spin dynamics in the single-atomic magnet Li(LiFe)N
We present a systematic 57Fe-Moessbauer study on highly diluted Fe centers in
Li2(Li1-xFex)N single-crystals as a function of temperature and magnetic field
applied transverse and longitudinal with respect to the single-ion anisotropy
axis. Below 30 K the Fe centers exhibit a giant magnetic hyperfine field of E_A
= 70.25(2)T parallel to the axis of strongest electric field gradient Vzz =
-154.0(1) V/A2. Fluctuations of the magnetic hyperfine field are observed
between 50K and 300K and described by the Blume two-level relaxation model.
From the temperature dependence of the uctuation rate an Orbach spin-lattice
relaxation process is deduced. An Arrhenius analysis yields a single thermal
activation barrier of E_A = 570(6)K and an attempt frequency nu_0 = 309(10)
GHz. Moessbauer spectroscopy studies with applied transverse magnetic fields up
to 5T reveal a large increase of the uctuation rate by more than one order of
magnitude. In longitudinal magnetic fields a splitting of the uctuation rate
into two branches is observed consistent with a Zeeman induced modifcation of
the energy levels. The experimental observations are qualitatively reproduced
by a single-ion effective spin Hamiltonian analysis assuming a Fe1+ d7 charge
state with unquenched orbital moment and a J = 7=2 ground state. It is
demonstrated that a weak axial single-ion anisotropy D of the order of a few
Kelvin can cause a two orders of magnitude larger energy barrier for
longitudinal spin fluctuations.Comment: 19 pages, 17 figures
Constraining General Two Higgs Doublet Models by the Evolution of Yukawa Couplings
We study how general two Higgs doublet models can be constrained by
considering their properties under renormalization group evolution of the
Yukawa couplings. We take into account both the appearance of a Landau pole as
well as off-diagonal Yukawa couplings leading to flavour changing neutral
currents in violation with experimental constraints at the electroweak scale.
We find that the latter condition can be used to limit the amount of Z2
symmetry breaking allowed in a given model.Comment: 28 pages, 10 figures, added discussion of evolution from high to low
scales, to be published in JHE
Engineering high charge transfer n-doping of graphene electrodes and its application to organic electronics.
Using thermally evaporated cesium carbonate (Cs2CO3) in an organic matrix, we present a novel strategy for efficient n-doping of monolayer graphene and a ∼90% reduction in its sheet resistance to ∼250 Ohm sq(-1). Photoemission spectroscopy confirms the presence of a large interface dipole of ∼0.9 eV between graphene and the Cs2CO3/organic matrix. This leads to a strong charge transfer based doping of graphene with a Fermi level shift of ∼1.0 eV. Using this approach we demonstrate efficient, standard industrial manufacturing process compatible graphene-based inverted organic light emitting diodes on glass and flexible substrates with efficiencies comparable to those of state-of-the-art ITO based devices.Funding via EU FP7 programme Grafol (Grant No. 285275) and EPSRC programme GRAPHTED (Grant No. EP/K016636/1) is acknowledged. P.R.K. acknowledges the Lindemann Trust Fellowship. J.A.A.-W. acknowledges a Research Fellowship from Churchill College, Cambridge. A.C.V. acknowledges the Conacyt Cambridge Scholarship and Roberto Rocca Fellowship.This is the author accepted manuscript. The final version is available from the Royal Society of Chemistry via http://dx.doi.org/10.1039/C5NR03246
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