3,923 research outputs found
Spatial characterization of the magnetic field profile of a probe tip used in magnetic resonance force microscopy
We have developed the experimental approach to characterize spatial
distribution of the magnetic field produced by cantilever tips used in magnetic
resonance force microscopy (MRFM). We performed MRFM measurements on a well
characterized diphenyl-picrylhydrazyl (DPPH) film and mapped the 3D field
profile produced by a Nd2Fe14B probe tip. Using our technique field profiles of
arbitrarily shaped probe magnets can be imaged.Comment: 10 pages, 5 figure
Selective addressing of high-rank atomic polarization moments
We describe a method of selective generation and study of polarization
moments of up to the highest rank possible for a quantum state with
total angular momentum . The technique is based on nonlinear magneto-optical
rotation with frequency-modulated light. Various polarization moments are
distinguished by the periodicity of light-polarization rotation induced by the
atoms during Larmor precession and exhibit distinct light-intensity and
frequency dependences. We apply the method to study polarization moments of
Rb atoms contained in a vapor cell with antirelaxation coating. Distinct
ultra-narrow (1-Hz wide) resonances, corresponding to different multipoles,
appear in the magnetic-field dependence of the optical rotation. The use of the
highest-multipole resonances has important applications in quantum and
nonlinear optics and in magnetometry.Comment: 5 pages, 6 figure
Gpr126/Adgrg6 has Schwann cell autonomous and nonautonomous functions in peripheral nerve injury and repair
Schwann cells (SCs) are essential for proper peripheral nerve development and repair, although the mechanisms regulating these processes are incompletely understood. We previously showed that the adhesion G protein-coupled receptor Gpr126/Adgrg6 is essential for SC development and myelination. Interestingly, the expression of Gpr126 is maintained in adult SCs, suggestive of a function in the mature nerve. We therefore investigated the role of Gpr126 in nerve repair by studying an inducible SC-specific Gpr126 knock-out mouse model. Here, we show that remyelination is severely delayed after nerve-crush injury. Moreover, we also observe noncell-autonomous defects in macrophage recruitment and axon regeneration in injured nerves following loss of Gpr126 in SCs. This work demonstrates that Gpr126 has critical SC-autonomous and SC-nonautonomous functions in remyelination and peripheral nerve repair. SIGNIFICANCE STATEMENT Lack of robust remyelination represents one of the major barriers to recovery of neurological functions in disease or following injury in many disorders of the nervous system. Here we show that the adhesion class G protein-coupled receptor (GPCR) Gpr126/Adgrg6 is required for remyelination, macrophage recruitment, and axon regeneration following nerve injury. At least 30% of all approved drugs target GPCRs; thus, Gpr126 represents an attractive potential target to stimulate repair in myelin disease or following nerve injury
Formation of hydrogen impurity states in silicon and insulators at low implantation energies
The formation of hydrogen-like muonium (Mu) has been studied as a function of
implantation energy in intrinsic Si, thin films of condensed van der Waals
gases (N2, Ne, Ar, Xe), fused and crystalline quartz and sapphire. By varying
the initial energy of positive muons (mu+) between 1 and 30 keV the number of
electron-hole pairs generated in the ionization track of the mu+ can be tuned
between a few and several thousand. The results show the strong suppression of
the formation of those Mu states that depend on the availability of excess
electrons. This indicates, that the role of H-impurity states in determining
electric properties of semiconductors and insulators depends on the way how
atomic H is introduced into the material.Comment: 4 pages, 4 enscapulated postscript figures, uses revtex4 twocolumn
style to be published in Physical Review Letter
Cosmogenic rare gases and 10-Be in a cross section of Knyahinya
The concentrations of cosmogenic nuclides were studied as a function of shielding on samples from a cross section of the 293 kg main fragment of the L5 chondrite Knyahinya. The stone broke into two nearly symmetrical parts upon its fall in 1866. The planar cross section has diameters between 40 and 55 cm. He, Ne, and Ar were measured on about 20 samples by mass spectrometry and the 10-Be activities on aliquots of 10 selected samples were determined by AMS. The 10-Be data are presented and the abundances of spallogenic nuclides are compared with the model calculations reported by Reedy for spherical L chondrites. The 10-Be production rates in Knyahinya are shown versus the shielding parameter 22-Ne/21-Ne
Observation of non-exponential magnetic penetration profiles in the Meissner state - A manifestation of non-local effects in superconductors
Implanting fully polarized low energy muons on the nanometer scale beneath
the surface of a superconductor in the Meissner state enabled us to probe the
evanescent magnetic field profile B(z)(0<z<=200nm measured from the surface).
All the investigated samples [Nb: kappa \simeq 0.7(2), Pb: kappa \simeq 0.6(1),
Ta: kappa \simeq 0.5(2)] show clear deviations from the simple exponential B(z)
expected in the London limit, thus revealing the non-local response of these
superconductors. From a quantitative analysis within the Pippard and BCS models
the London penetration depth lambda_L is extracted. In the case of Pb also the
clean limit coherence length xi0 is obtained. Furthermore we find that the
temperature dependence of the magnetic penetration depth follows closely the
two-fluid expectation 1/lambda^2 \propto 1-(T/T_c)^4. While B(z) for Nb and Pb
are rather well described within the Pippard and BCS models, for Ta this is
only true to a lesser degree. We attribute this discrepancy to the fact that
the superfluid density is decreased by approaching the surface on a length
scale xi0. This effect, which is not taken self-consistently into account in
the mentioned models, should be more pronounced in the lowest kappa regime
consistently with our findings.Comment: accepted in PRB 14 pages, 17 figure
Charge degree of freedom and single-spin fluid model in YBa_2Cu_4O_8
We present a 17O nuclear magnetic resonance study in the stoichiometric
superconductor YBa_2Cu_4O_8. A double irradiation method enables us to show
that, below around 180 K, the spin-lattice relaxation rate of plane oxygen is
not only driven by magnetic, but also significantly by quadrupolar
fluctuations, i.e. low-frequency charge fluctuations. In the superconducting
state, on lowering the temperature, the quadrupolar relaxation diminishes
faster than the magnetic one. These findings show that, with the opening of the
pseudo spin gap, a charge degree of freedom of mainly oxygen character is
present in the electronic low-energy excitation spectrum.Comment: 4 pages, 3 figures, REVTE
Retrospective analysis of esophageal imaging features in brachycephalic vs. non-brachycephalic dogs based on videofluoroscopic swallowing studies
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