49,043 research outputs found
The role of interfaces in CoFe/IrMn exchange biased systems
A trilayer system consisting of an IrMn layer exchanged coupled to two CoFe layers of equal thickness has been studied. A single stage reversal was observed over a wide range of temperatures. Two bilayers with the same thicknesses of the pinning layer but different ferromagnetic thicknesses were also studied. By comparing the magnetic properties of these three stacks the effect of the interfacial area on the exchange field and the coercivity has been determined. We find that the interfacial area has a very minor effect on the exchange field H-ex and the blocking temperature (T-B) but causes a doubling of the coercivity (H-c). This indicates that H-c is dominated by the interface whereas the exchange bias is controlled by volumetric effects
WHO publishes the third edition of guidelines for the prevention and control of air-travel-associated tuberculosis.
Mission: Impossible (Escape from the Lyman Limit)
We investigate the intrinsic opacity of high-redshift galaxies to outgoing
ionising photons using high-quality photometry of a sample of 27
spectroscopically-identified galaxies of redshift 1.9<z<3.5 in the Hubble Deep
Field. Our measurement is based on maximum-likelihood fitting of model galaxy
spectral energy distributions-including the effects of intrinsic Lyman-limit
absorption and random realizations of intervening Lyman-series and Lyman-limit
absorption-to photometry of galaxies from space- and ground-based broad-band
images. Our method provides several important advantages over the methods used
by previous groups, including most importantly that two-dimensional sky
subtraction of faint-galaxy images is more robust than one-dimensional sky
subtraction of faint-galaxy spectra. We find at the 3sigma statistical
confidence level that on average no more than 4% of the ionising photons escape
galaxies of redshift 1.9<z<3.5. This result is consistent with observations of
low- and moderate-redshift galaxies but is in direct contradiction to a recent
result based on medium-resolution spectroscopy of high-redshift (z~3) galaxies.
Dividing our sample in subsamples according to luminosity, intrinsic
ultraviolet colour, and redshift, we find no evidence for selection effects
that could explain such discrepancy. Even when all systematic effects are
included, the data could not realistically accomodate any escape fraction value
larger than ~15%.Comment: Accepted for publication in Monthly Notices of the Royal Astronomical
Society. 8 pages, 4 b/w figures, MNRAS styl
Modeling temporal networks using random itineraries
We propose a procedure to generate dynamical networks with bursty, possibly
repetitive and correlated temporal behaviors. Regarding any weighted directed
graph as being composed of the accumulation of paths between its nodes, our
construction uses random walks of variable length to produce time-extended
structures with adjustable features. The procedure is first described in a
general framework. It is then illustrated in a case study inspired by a
transportation system for which the resulting synthetic network is shown to
accurately mimic the empirical phenomenology
The gaseous extent of galaxies and the origin of Lyman alpha absorption systems. IV: Lyman alpha absorbers arising in a galaxy group
We present new GHRS observations of Lyman alpha absorption lines associated
with a group of galaxies towards the QSO 1545+2101. We have identified eight
distinct Lyman alpha absorption features in the spectrum of QSO 1545+2101 at a
mean redshift of z=0.2648 with a velocity dispersion of 163 km/s. A group of
galaxies is detected in the vicinity of this QSO at a mean redshift of z=0.2645
and velocity dispersion 239 km/s.
The identification of discrete absorption systems indicates that they arise
in clouds of neutral hydrogen rather than in a diffuse intragroup medium. Our
analysis suggests that the Lyman alpha absorption lines are associated with
individual galaxies in the group, although a one-to-one relationship between
absorbers and galaxies is difficult to establish in such a dense environment.Comment: 16 pages, 3 figures. Accepted for publication in Ap
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