822 research outputs found
Conservative effects in spin-transfer-driven magnetization dynamics
It is shown that under appropriate conditions spin-transfer-driven
magnetization dynamics in a single-domain nanomagnet is conservative in nature
and admits a specific integral of motion, which is reduced to the usual
magnetic energy when the spin current goes to zero. The existence of this
conservation law is connected to the symmetry properties of the dynamics under
simultaneous inversion of magnetisation and time. When one applies an external
magnetic field parallel to the spin polarization, the dynamics is transformed
from conservative into dissipative. More precisely, it is demonstrated that
there exists a state function such that the field induces a monotone relaxation
of this function toward its minima or maxima, depending on the field
orientation. These results hold in the absence of intrinsic damping effects.
When intrinsic damping is included in the description, a competition arises
between field-induced and damping-induced relaxations, which leads to the
appearance of limit cycles, that is, of magnetization self-oscillations.Comment: 5 pages, 3 figure
Tunneling magnetic force microscopy
We have developed a powerful new tool for studying the magnetic patterns on magnetic recording media. This was accomplished by modifying a conventional scanning tunneling microscope. The fine-wire probe that is used to image surface topography was replaced with a flexible magnetic probe. Images obtained with these probes reveal both the surface topography and the magnetic structure. We have made a thorough theoretical analysis of the interaction between the probe and the magnetic fields emanating from a typical recorded surface. Quantitative data about the constituent magnetic fields can then be obtained. We have employed these techniques in studies of two of the most important issues of magnetic record: data overwrite and maximizing data-density. These studies have shown: (1) overwritten data can be retrieved under certain conditions; and (2) improvements in data-density will require new magnetic materials. In the course of these studies we have developed new techniques to analyze magnetic fields of recorded media. These studies are both theoretical and experimental and combined with the use of our magnetic force scanning tunneling microscope should lead to further breakthroughs in the field of magnetic recording
The Radio-to-Submm Spectral Index as a Redshift Indicator
We present models of the 1.4 GHz to 350 GHz spectral index, alpha(350/1.4),
for starburst galaxies as a function of redshift. The models include a
semi-analytic formulation, based on the well quantified radio-to-far infrared
correlation for low redshift star forming galaxies, and an empirical
formulation, based on the observed spectrum of the starburst galaxies M82 and
Arp 220. We compare the models to the observed values of alpha(350/1.4) for
starburst galaxies at low and high redshift. We find reasonable agreement
between the models and the observations, and in particular, that an observed
spectral index of alpha(350/1.4) > +0.5 indicates that the target source is
likely to be at high redshift, z > 1. The evolution of alpha(350/1.4) with
redshift is mainly due to the very steep rise in the Raleigh-Jeans portion of
the thermal dust spectrum shifting into the 350 GHz band with increasing
redshift. We also discuss situations where this relationship could be violated.
We then apply our models to examine the putative identifications of submm
sources in the Hubble Deep Field, and conclude that the submm sources reported
by Hughes et al. are likely to be at high redshifts, z > 1.5.Comment: standard LATEX file plus 1 postscript figure. Added references and
revised figure. second figure revision. Final Proof version. to appear in
Astrophysical Journal Letter
Terminal complement activation is increased and associated with disease severity in CIDP
Chronic inflammatory demyelinating polyneuropathy (CIDP) is the most common
chronic autoimmune neuropathy. While both cell-mediated and humoral mechanisms
contribute to its pathogenesis, the rapid clinical response to plasmapheresis
implicates a circulating factor responsible for peripheral nerve injury. We
report that treatment-naĂŻve patients with CIDP show increased serum and CSF
levels of the anaphylatoxin C5a and the soluble terminal complement complex
(sTCC). Systemic terminal complement activation correlates with clinical
disease severity as determined by the Inflammatory Neuropathy Cause and
Treatment (INCAT) disability scale. These data indicate that complement
activation contributes to peripheral nerve injury and suggest that complement
inhibition should be explored for its potential therapeutic merit in CIDP
On finitely ambiguous B\"uchi automata
Unambiguous B\"uchi automata, i.e. B\"uchi automata allowing only one
accepting run per word, are a useful restriction of B\"uchi automata that is
well-suited for probabilistic model-checking. In this paper we propose a more
permissive variant, namely finitely ambiguous B\"uchi automata, a
generalisation where each word has at most accepting runs, for some fixed
. We adapt existing notions and results concerning finite and bounded
ambiguity of finite automata to the setting of -languages and present a
translation from arbitrary nondeterministic B\"uchi automata with states to
finitely ambiguous automata with at most states and at most accepting
runs per word
A Study of CO Emission in High Redshift QSOs Using the Owens Valley Millimeter Array
Searches for CO emission in high-redshift objects have traditionally suffered
from the accuracy of optically-derived redshifts due to lack of bandwidth in
correlators at radio observatories. This problem has motivated the creation of
the new COBRA continuum correlator, with 4 GHz available bandwidth, at the
Owens Valley Radio Observatory Millimeter Array. Presented here are the first
scientific results from COBRA. We report detections of redshifted CO(J=3-2)
emission in the QSOs SMM J04135+10277 and VCV J140955.5+562827, as well as a
probable detection in RX J0911.4+0551. At redshifts of z=2.846, z=2.585, and
z=2.796, we find integrated CO flux densities of 5.4 Jy km/s, 2.4 Jy km/s, and
2.9 Jy km/s for SMM J04135+10277, VCV J140955.5+562827, and RX J0911.4+0551,
respectively, over linewidths of Delta(V_{FWHM}) ~ 350 km/s. These
measurements, when corrected for gravitational lensing, correspond to molecular
gas masses of order M(H_2) ~ 10^{9.6-11.1} solar masses, and are consistent
with previous CO observations of high-redshift QSOs. We also report 3-sigma
upper limits on CO(3-2) emission in the QSO LBQS 0018-0220 of 1.3 Jy km/s. We
do not detect significant 3mm continuum emission from any of the QSOs, with the
exception of a tentative (3-sigma) detection in RX J0911.4+0551 of S_{3mm}=0.92
mJy/beam.Comment: 18 pages, 5 figures, 2 tables, accepted to ApJ. Changes made for
version 2: citations added, 2 objects added to Table 2 and Figure
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