845 research outputs found
Direct observation of transverse and vortex metastable magnetic domains in cylindrical nanowires
We present experimental evidence of transverse magnetic domains, previously observed only in nanostrips, in CoNi cylindrical nanowires with designed crystal symmetry and tailored magnetic anisotropy. The transverse domains are found together with more conventional vortex domains along the same cylindrical nanowire, denoting a bistable system with similar energies. The surface and the inner magnetization distribution in both types of domains are analyzed by photoemission electron microscopy with x-ray magnetic circular dichroism contrast, and hysteresis loop in individual nanowires are measured by magneto-optical Kerr effect. These experimental data are understood and compared with complementary micromagnetic simulations
Domain Wall Propagation and Pinning Induced by Current Pulses in Cylindrical Modulated Nanowires
The future developments of three-dimensional magnetic nanotechnology require
the control of domain wall dynamics by means of current pulses. While this has
been extensively studied in planar magnetic strips (planar nanowires), few
reports exist in cylindrical geometry, where Bloch point domain walls are
expected to have intriguing properties. Here we report this investigation in
cylindrical magnetic Ni nanowires with geometrical notches. Experimental work
based on synchrotron X-ray magnetic circular dichroism (XMCD) combined with
photoemission electron microscopy (PEEM) indicates that large current densities
induce domain wall nucleation while smaller currents move domain walls
preferably against the current direction. In the region where no pinning
centers are present we found domain wall velocity of about 1 km/s. The domain
wall motion along current was also detected in the vicinity of the notch
region. Pinning of domain walls has been observed not only at geometrical
constrictions but also outside of them. Thermal modelling indicates that large
current densities temporarily raise the temperature in the nanowire above the
Curie temperature leading to nucleation of domain walls during the system
cooling. Micromagnetic modelling with spin-torque effect shows that for
intermediate current densities Bloch point domain walls with chirality parallel
to the Oersted field propagate antiparallel to the current direction. In other
cases, domain walls can be bounced from the notches and/or get pinned outside
their positions. We thus find that current is not only responsible for the
domain wall propagation but is also a source of pinning due to the Oersted
field action
Performance of prototypes for the ALICE electromagnetic calorimeter
The performance of prototypes for the ALICE electromagnetic sampling
calorimeter has been studied in test beam measurements at FNAL and CERN. A
array of final design modules showed an energy resolution of about
11% / 1.7 % with a uniformity of the response
to electrons of 1% and a good linearity in the energy range from 10 to 100 GeV.
The electromagnetic shower position resolution was found to be described by 1.5
mm 5.3 mm /. For an electron identification
efficiency of 90% a hadron rejection factor of was obtained.Comment: 10 pages, 10 figure
Protection of Domestic bank Ownership in France and Germany: The Functional Equivalency of Institutional Diversity in Takeovers
We investigate the character of the market for corporate control (i.e. takeovers) in French and German banking. The key feature of this character is the marked ability of French and German banks to resist unsolicited takeover bids, especially – although not exclusively– those from foreign competitors. We present an institutional perspective to account for the restrained character of takeovers in French and German banking. Our perspective is composed of two elements. First, institutional arrangements are important since they structure power relations among firm stakeholders by providing opportunities, as well as imposing constraints, to influence the decision-making process in which takeover transactions take place. Second, institutional arrangements provide firm stakeholders with several potential opportunities, not just one, to block unsolicited bids since takeover contests are composed of sequences of decisions for which approval is needed at each stage. French and German banks have used different mixes of institutional arrangements, themselves located at different stages of takeover transactions, to secure restrained markets for corporate control. Our institutional analysis, in turn, also illustrates an important shortcoming of banking sector protectionism, namely the contribution of protection from unsolicited takeover bids to the building of banks carrying systemic risks
Charge separation relative to the reaction plane in Pb-Pb collisions at TeV
Measurements of charge dependent azimuthal correlations with the ALICE
detector at the LHC are reported for Pb-Pb collisions at TeV. Two- and three-particle charge-dependent azimuthal correlations in
the pseudo-rapidity range are presented as a function of the
collision centrality, particle separation in pseudo-rapidity, and transverse
momentum. A clear signal compatible with a charge-dependent separation relative
to the reaction plane is observed, which shows little or no collision energy
dependence when compared to measurements at RHIC energies. This provides a new
insight for understanding the nature of the charge dependent azimuthal
correlations observed at RHIC and LHC energies.Comment: 12 pages, 3 captioned figures, authors from page 2 to 6, published
version, figures at http://aliceinfo.cern.ch/ArtSubmission/node/286
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