123 research outputs found
Magnetic remanent states in antiferromagnetically coupled multilayers
In antiferromagnetically coupled multilayers with perpendicular anisotropy
unusual multidomain textures can be stabilized due to a close competition
between long-range demagnetization fields and short-range interlayer exchange
coupling.
In particular, the formation and evolution of specific topologically stable
planar defects within the antiferromagnetic ground state, i.e. wall-like
structures with a ferromagnetic configuration extended over a finite width,
explain configurational hysteresis phenomena recently observed in
[Co/Pt(Pd)]/Ru and [Co/Pt]/NiO multilayers.
Within a phenomenological theory, we have analytically derived the
equilibrium sizes of these "ferroband" defects as functions of the
antiferromagnetic exchange, a bias magnetic field, and geometrical parameters
of the multilayers. In the magnetic phase diagram, the existence region of the
ferrobands mediates between the regions of patterns with sharp
antiferromagnetic domain walls and regular arrays of ferromagnetic stripes.
The theoretical results are supported by magnetic force microscopy images of
the remanent states observed in [Co/Pt]/Ru.Comment: Paper submitted by the Joint European Magnetics Symposia 2008, Dublin
(4 pages, 3 figures
Synteza i badanie właściwości fizykochemicznych związków makrocyklicznych zawierających atomy siarki oraz tlenu lub azotu
Macrocyclic compounds from the family of crown ethers are subject of an enduring interest
due to their interesting properties and numerous applications. The most characteristic feature of
chemical compounds belonging to this class is their ability to form complexes with metal cations
from I and II group, and the dependence of stability of these complexes on the matching of a cation
diameter and the size of the cavity in a macrocyclic ring. The changing of part or all oxygen atoms
in the crown ether ring by other heteroatoms (for example sulfur or nitrogen atoms) allows the
obtaining of macrocyclic compounds with differentiated complexing properties.
During the research, a number of new macrocyclic compounds containing sulfur and oxygen
or nitrogen atoms were synthesized. Each of the synthesized macrocyclic compounds also
possesses an aromatic moiety in its structure. Complexes of the part of obtained macrocycles with
chosen transition metal cations were also synthesized. Obtained compounds were characterized by
means of instrumental analytical methods such as NMR, FTIR, UV-Vis spectrometry. Single
crystals obtained during research were used to determine crystal structures of large part of obtained
compounds by means of the XRD method.
Conducted research aims in broadening of fundamental knowledge in the field of described
group of macrocyclic compounds, with emphasis on their crystal structures and crystal structures of
their complexes with transition metal cations
Crystal structure of sparteinium tetrachlorocuprate monohydrate‑packing polymorph
A new polymorph of sparteinium tetrachlorocuprate monohydrate [(C15H28N2)CuCl4·H2O] is reported. The structure of
the analyzed crystal was solved in the orthorhombic P212121 space group with the following unit cell parameters at 295 K:
a = 9.7722(2) Å; b = 13.4582(3) Å; c = 15.1582(3) Å. The various types of hydrogen bonding interactions existing in the
crystal structure of this salt were compared with the data of the previously reported polymorph. XRPD measurement proved
that our salt consists of a pure phase of the new polymorph. Cooling down the salt to ca. 230 K caused its color to change
from orange-brown to yellow. DSC experiments revealed that during the cooling an endothermic process takes place corresponding
to the mentioned color change of the salt
Crystal structures and other properties of ephedrone (methcathinone) hydrochloride, N‑acetylephedrine and N‑acetylephedrone
Purpose Three compounds obtained from ephedrine were identified and characterized by various instrumental analytical
methods. Ephedrone (methcathinone) hydrochloride and its fundamental derivatives N-acetylephedrine and N-acetylephedrone
were analyzed as precursors of a cathinone derivative.
Methods The obtained samples were analyzed by gas chromatography coupled with mass spectrometry, nuclear magnetic
resonance spectroscopy, infrared and Raman spectroscopy, and X-ray crystallography.
Results The three compounds were confirmed as: N-methyl-2-amino-1-phenylpropan-1-one (methcathinone) hydrochloride,
N-acetyl-N-methyl-2-amino-1-phenylpropan-1-one (cathinone derivative), and N-acetyl-N-methyl-2-amino-1-phenylpropan-
1-ol (acetyl derivative of ephedrine).
Conclusions X-ray crystallography is especially useful for identifying the new designer drugs and their different precursor
forms
Topological defects in antiferromagnetically coupled multilayers with perpendicular anisotropy
A rich variety of specific multidomain textures recently observed in
antiferromagnetically coupled multilayers with perpendicular anisotropy include
regular (equilibrium) multidomain states as well as different types of
topological magnetic defects. Within a phenomenological theory we have
classified and analyzed the possible magnetic defects in the antiferromagnetic
ground state and determine their structures. We have derived the optimal sizes
of the defects as functions of the antiferromagnetic exchange, the applied
magnetic field, and geometrical parameters of the multilayer. The calculated
magnetic phase diagrams show the existence regions for all types of magnetic
defects. Experimental investigations of the remanent states (observed after
different magnetic pre-history) in [Co/Pt]/Ru multilayers with wedged Co layers
reveal a corresponding succession of different magnetic defect domain types.Comment: 3 pages, 4 figure
Muon Track Reconstruction and Data Selection Techniques in AMANDA
The Antarctic Muon And Neutrino Detector Array (AMANDA) is a high-energy
neutrino telescope operating at the geographic South Pole. It is a lattice of
photo-multiplier tubes buried deep in the polar ice between 1500m and 2000m.
The primary goal of this detector is to discover astrophysical sources of high
energy neutrinos. A high-energy muon neutrino coming through the earth from the
Northern Hemisphere can be identified by the secondary muon moving upward
through the detector. The muon tracks are reconstructed with a maximum
likelihood method. It models the arrival times and amplitudes of Cherenkov
photons registered by the photo-multipliers. This paper describes the different
methods of reconstruction, which have been successfully implemented within
AMANDA. Strategies for optimizing the reconstruction performance and rejecting
background are presented. For a typical analysis procedure the direction of
tracks are reconstructed with about 2 degree accuracy.Comment: 40 pages, 16 Postscript figures, uses elsart.st
Sensitivity of the IceCube Detector to Astrophysical Sources of High Energy Muon Neutrinos
We present the results of a Monte-Carlo study of the sensitivity of the
planned IceCube detector to predicted fluxes of muon neutrinos at TeV to PeV
energies. A complete simulation of the detector and data analysis is used to
study the detector's capability to search for muon neutrinos from sources such
as active galaxies and gamma-ray bursts. We study the effective area and the
angular resolution of the detector as a function of muon energy and angle of
incidence. We present detailed calculations of the sensitivity of the detector
to both diffuse and pointlike neutrino emissions, including an assessment of
the sensitivity to neutrinos detected in coincidence with gamma-ray burst
observations. After three years of datataking, IceCube will have been able to
detect a point source flux of E^2*dN/dE = 7*10^-9 cm^-2s^-1GeV at a 5-sigma
significance, or, in the absence of a signal, place a 90% c.l. limit at a level
E^2*dN/dE = 2*10^-9 cm^-2s^-1GeV. A diffuse E-2 flux would be detectable at a
minimum strength of E^2*dN/dE = 1*10^-8 cm^-2s^-1sr^-1GeV. A gamma-ray burst
model following the formulation of Waxman and Bahcall would result in a 5-sigma
effect after the observation of 200 bursts in coincidence with satellite
observations of the gamma-rays.Comment: 33 pages, 13 figures, 6 table
On the selection of AGN neutrino source candidates for a source stacking analysis with neutrino telescopes
The sensitivity of a search for sources of TeV neutrinos can be improved by
grouping potential sources together into generic classes in a procedure that is
known as source stacking. In this paper, we define catalogs of Active Galactic
Nuclei (AGN) and use them to perform a source stacking analysis. The grouping
of AGN into classes is done in two steps: first, AGN classes are defined, then,
sources to be stacked are selected assuming that a potential neutrino flux is
linearly correlated with the photon luminosity in a certain energy band (radio,
IR, optical, keV, GeV, TeV). Lacking any secure detailed knowledge on neutrino
production in AGN, this correlation is motivated by hadronic AGN models, as
briefly reviewed in this paper.
The source stacking search for neutrinos from generic AGN classes is
illustrated using the data collected by the AMANDA-II high energy neutrino
detector during the year 2000. No significant excess for any of the suggested
groups was found.Comment: 43 pages, 12 figures, accepted by Astroparticle Physic
Limits on the high-energy gamma and neutrino fluxes from the SGR 1806-20 giant flare of December 27th, 2004 with the AMANDA-II detector
On December 27th 2004, a giant gamma flare from the Soft Gamma-ray Repeater
1806-20 saturated many satellite gamma-ray detectors. This event was by more
than two orders of magnitude the brightest cosmic transient ever observed. If
the gamma emission extends up to TeV energies with a hard power law energy
spectrum, photo-produced muons could be observed in surface and underground
arrays. Moreover, high-energy neutrinos could have been produced during the SGR
giant flare if there were substantial baryonic outflow from the magnetar. These
high-energy neutrinos would have also produced muons in an underground array.
AMANDA-II was used to search for downgoing muons indicative of high-energy
gammas and/or neutrinos. The data revealed no significant signal. The upper
limit on the gamma flux at 90% CL is dN/dE < 0.05 (0.5) TeV^-1 m^-2 s^-1 for
gamma=-1.47 (-2). Similarly, we set limits on the normalization constant of the
high-energy neutrino emission of 0.4 (6.1) TeV^-1 m^-2 s^-1 for gamma=-1.47
(-2).Comment: 14 pages, 3 figure
Detection of Atmospheric Muon Neutrinos with the IceCube 9-String Detector
The IceCube neutrino detector is a cubic kilometer TeV to PeV neutrino
detector under construction at the geographic South Pole. The dominant
population of neutrinos detected in IceCube is due to meson decay in cosmic-ray
air showers. These atmospheric neutrinos are relatively well-understood and
serve as a calibration and verification tool for the new detector. In 2006, the
detector was approximately 10% completed, and we report on data acquired from
the detector in this configuration. We observe an atmospheric neutrino signal
consistent with expectations, demonstrating that the IceCube detector is
capable of identifying neutrino events. In the first 137.4 days of livetime,
234 neutrino candidates were selected with an expectation of 211 +/-
76.1(syst.) +/- 14.5(stat.) events from atmospheric neutrinos
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