2,156 research outputs found
Giant magnetoresistance (GMR) in electrodeposited multilayer films: the influence of superparamagnetic regions
When preparing an alternating sequence of magnetic (Co or Ni) and non-magnetic (Cu)
layers by electrodeposition using the two-pulse plating technique, a dissolution of the lessnoble
magnetic Co and Ni atoms can take place during the deposition of the more noble and
non-magnetic Cu atoms. This process results in changes of the actual sublayer thicknesses
with respect to the nominal values and can also cause some chemical intermixing at the
magnetic/non-magnetic interfaces. As a consequence, superparamagnetic (SPM) regions
with “loose magnetic moments” can form as has been demonstrated for electrodeposited
Ni-Cu/Cu multilayers. We have also shown recently for electrodeposited Co-Cu/Cu
multilayers that if some fraction of the magnetic layers exhibits SPM behaviour then the
observed giant magnetoresistance (GMR) can be quantitatively decomposed into a
ferromagnetic (FM) and a SPM contribution. In this paper, the results of a similar GMR
decomposition study are presented for two electrodeposited Co-Cu/Cu multilayers. In the
multilayer with strongly non-saturated magnetoresistance curves, the dominant GMR term
was due to SPM regions, whereas in the other multilayer for which the magnetoresistance is
mostly saturated in magnetic fields around 1 to 2 kOe, the FM contribution to the GMR is
much larger. At the same time, magnetic measurements on the first multilayer sample have
also revealed the presence of a large SPM contribution to the magnetization
Physical Properties of Galactic Planck Cold Cores revealed by the Hi-GAL survey
Previous studies of the initial conditions of massive star formation have
mainly targeted Infrared-Dark Clouds (IRDCs) toward the inner Galaxy. This is
due to the fact that IRDCs were first detected in absorption against the bright
mid-IR background, requiring a favourable location to be observed. By
selection, IRDCs represent only a fraction of the Galactic clouds capable of
forming massive stars and star clusters. Due to their low dust temperatures,
IRDCs are bright in the far-IR and millimeter and thus, observations at these
wavelengths have the potential to provide a complete sample of star-forming
massive clouds across the Galaxy. Our aim is to identify the clouds at the
initial conditions of massive star formation across the Galaxy and compare
their physical properties as a function of their Galactic location. We have
examined the physical properties of a homogeneous galactic cold core sample
obtained with the Planck satellite across the Galactic Plane. With the use of
Herschel Hi-GAL observations, we have characterized the internal structure of
them. By using background-subtracted Herschel images, we have derived the H2
column density and dust temperature maps for 48 Planck clumps. Their basic
physical parameters have been calculated and analyzed as a function of location
within the Galaxy. These properties have also been compared with the empirical
relation for massive star formation derived by Kauffmann & Pillai (2010). Most
of the Planck clumps contain signs of star formation. About 25% of them are
massive enough to form high mass stars. Planck clumps toward the Galactic
center region show higher peak column densities and higher average dust
temperatures than those of the clumps in the outer Galaxy. Although we only
have seven clumps without associated YSOs, the Hi-GAL data show no apparent
differences in the properties of Planck cold clumps with and without star
formation.Comment: 22 pages, 11 figures, accepted for publication in A&
Three-sublattice ordering of the SU(3) Heisenberg model of three-flavor fermions on the square and cubic lattices
Combining a semi-classical analysis with exact diagonalizations, we show that
the ground state of the SU(3) Heisenberg model on the square lattice develops
three-sublattice long-range order. This surprising pattern for a bipartite
lattice with only nearest-neighbor interactions is shown to be the consequence
of a subtle quantum order-by-disorder mechanism. By contrast, thermal
fluctuations favor two-sublattice configurations via entropic selection. These
results are shown to extend to the cubic lattice, and experimental implications
for the Mott-insulating states of three-flavor fermionic atoms in optical
lattices are discussed.Comment: 4 pages, 3 figures, minor changes, references adde
Rigorous results on spontaneous symmetry breaking in a one-dimensional driven particle system
We study spontaneous symmetry breaking in a one-dimensional driven
two-species stochastic cellular automaton with parallel sublattice update and
open boundaries. The dynamics are symmetric with respect to interchange of
particles. Starting from an empty initial lattice, the system enters a symmetry
broken state after some time T_1 through an amplification loop of initial
fluctuations. It remains in the symmetry broken state for a time T_2 through a
traffic jam effect. Applying a simple martingale argument, we obtain rigorous
asymptotic estimates for the expected times ~ L ln(L) and ln() ~ L,
where L is the system size. The actual value of T_1 depends strongly on the
initial fluctuation in the amplification loop. Numerical simulations suggest
that T_2 is exponentially distributed with a mean that grows exponentially in
system size. For the phase transition line we argue and confirm by simulations
that the flipping time between sign changes of the difference of particle
numbers approaches an algebraic distribution as the system size tends to
infinity.Comment: 23 pages, 7 figure
Searching for electromagnetic counterpart of LIGO gravitational waves in the Fermi GBM data with ADWO
The Fermi collaboration identified a possible electromagnetic counterpart of
the gravitational wave event of September 14, 2015. Our goal is to provide an
unsupervised data analysis algorithm to identify similar events in Fermi's
Gamma-ray Burst Monitor CTTE data stream. We are looking for signals that are
typically weak. Therefore, they can only be found by a careful analysis of
count rates of all detectors and energy channels simultaneously. Our
Automatized Detector Weight Optimization (ADWO) method consists of a search for
the signal, and a test of its significance. We developed ADWO, a virtual
detector analysis tool for multi-channel multi-detector signals, and performed
successful searches for short transients in the data-streams. We have
identified GRB150522B, as well as possible electromagnetic candidates of the
transients GW150914 and LVT151012. ADWO is an independently developed,
unsupervised data analysis tool that only relies on the raw data of the Fermi
satellite. It can therefore provide a strong, independent test to any
electromagnetic signal accompanying future gravitational wave observations.Comment: 4 pages and 4 figures, A&A Letters accepte
Enzymatic determination of ethanol and glycerol by flow injection parallel multi-site detection
A flow injection method was developed for the sequential enzymatic determination of ethanol and glycerol in wines, using
immobilised ethanol dehydrogenase and glycerol dehydrogenase, respectively. The enzymes were immobilised separately on
alkylaminated controlled pore glass. A multi-site spectrophotometric detection system was used in parallel configuration to
monitor the absorbance change in the two independent analytical channels. A 50-fold dilution of the samples was necessary
before injection. The working range was between 0.05 and 0.5% (v/v) for the ethanol and between 0.03 and 0.3 g l−1 for the
glycerol determination, with corresponding detection limits of 2 10−3%(v/v) and 2 10−3 g l−1. Relative standard deviations
(R.S.D.) (nD9) lower than 2.3% for the ethanol and 2.1% for the glycerol determination were found. For 13 samples of different
types of table and Port wines, the results showed good agreement with the corresponding reference procedures; a two level
recovery study also showed good accuracy for the developed methods. The sampling rate was 10 h−1, corresponding to 20
determinations per hou
Extending the limits of globule detection -- ISOPHOT Serendipity Survey Observations of interstellar clouds
A faint MJysr bipolar globule was discovered with the
ISOPHOT 170 m Serendipity Survey (ISOSS). ISOSS J 20246+6541 is a cold
( K) FIR source without an IRAS pointsource counterpart.
In the Digitized Sky Survey B band it is seen as a 3\arcmin size bipolar
nebulosity with an average excess surface brightness of
mag/\arcsec . The CO column density distribution determined by
multi-isotopic, multi-level CO measurements with the IRAM-30m telescope agrees
well with the optical appearance. An average hydrogen column density of
cm was derived from both the FIR and CO data. Using a
kinematic distance estimate of 400 pc the NLTE modelling of the CO, HCO,
and CS measurements gives a peak density of cm. The
multiwavelength data characterise ISOSS 20246+6541 as a representative of a
class of globules which has not been discovered so far due to their small
angular size and low 100m brightness. A significant overabundance of
CO is found . This is likely due to
isotope selective chemical processes.Comment: 5 pages, 3 figure
Multidimensional analysis of Fermi GBM gamma-ray bursts
The Fermi GBM catalog provides a large database with many measured variables
that can be used to explore and verify gamma-ray burst classification results.
We have used Principal Component Analysis and statistical clustering techniques
to look for clustering in a sample of 801 gamma-ray bursts described by sixteen
classification variables. The analysis recovers what appears to be the Short
class and two long-duration classes that differ from one another via peak flux,
with negligible variations in fluence, duration and spectral hardness. Neither
class has properties entirely consistent with the Intermediate GRB class.
Spectral hardness has been a critical Intermediate class property. Rather than
providing spectral hardness, Fermi GBM provides a range of fitting variables
for four different spectral models; it is not intuitive how these variables can
be used to support or disprove previous GRB classification results.Comment: accepte
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