4,678 research outputs found
Commercial Mortgage Prepayments Under Heterogeneous Prepayment Penalty Structures
Much of the literature on pricing commercial mortgages and commercial mortgage-backed securities has assumed homogeneity in prepayment penalty structure. In this paper, we provide evidence that such an assumption is inappropriate and examine the effect of penalty structures observed in actual contracts. After conducting preliminary simulations, we present hazard models estimated from data on 1,165 multifamily mortgage loans to show how empirical prepayment rates vary with alternative penalty structures. While yield maintenance and lockout provisions are relatively more effective than fixed or step down structures in reducing or postponing prepayment, none completely eliminates the risk. Our empirical results generally confirm the theoretical findings of Kelly and Slawson (2001).
Switching the magnetic configuration of a spin valve by current induced domain wall motion
We present experimental results on the displacement of a domain wall by
injection of a dc current through the wall. The samples are 1 micron wide long
stripes of a CoO/Co/Cu/NiFe classical spin valve structure.
The stripes have been patterned by electron beam lithography. A neck has been
defined at 1/3 of the total length of the stripe and is a pinning center for
the domain walls, as shown by the steps of the giant magnetoresistance curves
at intermediate levels (1/3 or 2/3) between the resistances corresponding to
the parallel and antiparallel configurations. We show by electric transport
measurements that, once a wall is trapped, it can be moved by injecting a dc
current higher than a threshold current of the order of magnitude of 10^7
A/cm^2. We discuss the different possible origins of this effect, i.e. local
magnetic field created by the current and/or spin transfer from spin polarized
current.Comment: 3 pages, 3 figure
Thermal Effects on the Magnetic Field Dependence of Spin Transfer Induced Magnetization Reversal
We have developed a self-aligned, high-yield process to fabricate CPP
(current perpendicular to the plane) magnetic sensors of sub 100 nm dimensions.
A pinned synthetic antiferromagnet (SAF) is used as the reference layer which
minimizes dipole coupling to the free layer and field induced rotation of the
reference layer. We find that the critical currents for spin transfer induced
magnetization reversal of the free layer vary dramatically with relatively
small changes the in-plane magnetic field, in contrast to theoretical
predictions based on stability analysis of the Gilbert equations of
magnetization dynamics including Slonczewski-type spin-torque terms. The
discrepancy is believed due to thermal fluctuations over the time scale of the
measurements. Once thermal fluctuations are taken into account, we find good
quantitative agreement between our experimental results and numerical
simulations.Comment: 14 pages, 4 figures, Submitted to Appl. Phys. Lett., Comparison of
some of these results with a model described by N. Smith in cond-mat/040648
Chiral nature of magnetic monopoles in artificial spin ice
Micromagnetic properties of monopoles in artificial kagome spin ice systems
are investigated using numerical simulations. We show that micromagnetics
brings additional complexity into the physics of these monopoles that is, by
essence, absent in spin models: besides a fractionalized classical magnetic
charge, monopoles in the artificial kagome ice are chiral at remanence. Our
simulations predict that the chirality of these monopoles can be controlled
without altering their charge state. This chirality breaks the vertex symmetry
and triggers a directional motion of the monopole under an applied magnetic
field. Our results also show that the choice of the geometrical features of the
lattice can be used to turn on and off this chirality, thus allowing the
investigation of chiral and achiral monopoles.Comment: 10 pages, 4 figure
Sparse aperture masking at the VLT II. Detection limits for the eight debris disks stars Pic, AU Mic, 49 Cet, Tel, Fomalhaut, g Lup, HD181327 and HR8799
Context. The formation of planetary systems is a common, yet complex
mechanism. Numerous stars have been identified to possess a debris disk, a
proto-planetary disk or a planetary system. The understanding of such formation
process requires the study of debris disks. These targets are substantial and
particularly suitable for optical and infrared observations. Sparse Aperture
masking (SAM) is a high angular resolution technique strongly contributing to
probe the region from 30 to 200 mas around the stars. This area is usually
unreachable with classical imaging, and the technique also remains highly
competitive compared to vortex coronagraphy. Aims. We aim to study debris disks
with aperture masking to probe the close environment of the stars. Our goal is
either to find low mass companions, or to set detection limits. Methods. We
observed eight stars presenting debris disks ( Pictoris, AU
Microscopii, 49 Ceti, Telescopii, Fomalhaut, g Lupi, HD181327 and
HR8799) with SAM technique on the NaCo instrument at the VLT. Results. No close
companions were detected using closure phase information under 0.5 of
separation from the parent stars. We obtained magnitude detection limits that
we converted to Jupiter masses detection limits using theoretical isochrones
from evolutionary models. Conclusions. We derived upper mass limits on the
presence of companions in the area of few times the diffraction limit of the
telescope around each target star.Comment: 7 pages, All magnitude detection limits maps are only available in
electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr
(130.79.128.5
A giant planet imaged in the disk of the young star Beta Pictoris
Here we show that the ~10 Myr Beta Pictoris system hosts a massive giant
planet, Beta Pictoris b, located 8 to 15 AU from the star. This result confirms
that gas giant planets form rapidly within disks and validates the use of disk
structures as fingerprints of embedded planets. Among the few planets already
imaged, Beta Pictoris b is the closest to its parent star. Its short period
could allow recording the full orbit within 17 years.Comment: 4 pages, 2 figures. Published online 10 June 2010;
10.1126/science.1187187. To appear in Scienc
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