350 research outputs found
Compact storage ring to search for the muon electric dipole moment
We present the concept of a compact storage ring of less than 0.5 m orbit
radius to search for the electric dipole moment of the muon () by
adapting the "frozen spin" method. At existing muon facilities a statistics
limited sensitivity of d_\mu \sim 5 \times 10^{-23} \ecm can be achieved
within one year of data taking. Reaching this precision would demonstrate the
viability of this novel technique to directly search for charged particle EDMs
and already test a number of Standard Model extensions. At a future, high-power
muon facility a statistical reach of d_\mu \sim 5 \times 10^{-25} \ecm seems
realistic with this setup.Comment: improved for submission; minor modification
Nucleation and Growth of GaN/AlN Quantum Dots
We study the nucleation of GaN islands grown by plasma-assisted
molecular-beam epitaxy on AlN(0001) in a Stranski-Krastanov mode. In
particular, we assess the variation of their height and density as a function
of GaN coverage. We show that the GaN growth passes four stages: initially, the
growth is layer-by-layer; subsequently, two-dimensional precursor islands form,
which transform into genuine three-dimensional islands. During the latter
stage, island height and density increase with GaN coverage until the density
saturates. During further GaN growth, the density remains constant and a
bimodal height distribution appears. The variation of island height and density
as a function of substrate temperature is discussed in the framework of an
equilibrium model for Stranski-Krastanov growth.Comment: Submitted to PRB, 10 pages, 15 figure
Calorimetric Evidence of Multiband Superconductivity in Ba(Fe0.925Co0.075)2As2
We report on the determination of the electronic heat capacity of a slightly
overdoped (x = 0.075) Ba(Fe1-xCox)2As2 single crystal with a Tc of 21.4 K. Our
analysis of the temperature dependence of the superconducting-state specific
heat provides strong evidence for a two-band s-wave order parameter with gap
amplitudes 2D1(0)/kBTc=1.9 and 2D2(0)/kBTc=4.4. Our result is consistent with
the recently predicted s+- order parameter [I. I. Mazin et al., Phys. Rev.
Lett. 101, 057003 (2008)].Comment: 4 pages, 3 figure
Hippocampal corticotropin releasing hormone: pre- and postsynaptic location and release by stress.
Neuropeptides modulate neuronal function in hippocampus, but the organization of hippocampal sites of peptide release and actions is not fully understood. The stress-associated neuropeptide corticotropin releasing hormone (CRH) is expressed in inhibitory interneurons of rodent hippocampus, yet physiological and pharmacological data indicate that it excites pyramidal cells. Here we aimed to delineate the structural elements underlying the actions of CRH, and determine whether stress influenced hippocampal principal cells also via actions of this endogenous peptide. In hippocampal pyramidal cell layers, CRH was located exclusively in a subset of GABAergic somata, axons and boutons, whereas the principal receptor mediating the peptide's actions, CRH receptor 1 (CRF1), resided mainly on dendritic spines of pyramidal cells. Acute 'psychological' stress led to activation of principal neurons that expressed CRH receptors, as measured by rapid phosphorylation of the transcription factor cyclic AMP responsive element binding protein. This neuronal activation was abolished by selectively blocking the CRF1 receptor, suggesting that stress-evoked endogenous CRH release was involved in the activation of hippocampal principal cells
Magnetic properties of single-crystalline CeCuGa3
The magnetic behavior of single-crystalline CeCuGa3 has been investigated.
The compound forms in a tetragonal BaAl4-type structure consisting of
rare-earth planes separated by Cu-Ga layers. If the Cu-Ga site disorder is
reduced, CeCuGa3 adopts the related, likewise tetragonal BaNiSn3-type
structure, in which the Ce ion are surrounded by different Cu and Ga layers and
the inversion symmetry is lost. In the literature conflicting reports about the
magnetic order of CeCuGa3 have been published. Single crystals with the
centrosymmetric structure variant exhibit ferromagnetic order below approx. 4 K
with a strong planar anisotropy. The magnetic behavior above the transition
temperature can be well understood by the crystal-field splitting of the 4f
Hund's rule ground-state multiplet of the Ce ions
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