207 research outputs found
INTEGRAL/RossiXTE high-energy observation of a state transition of GX 339-4
On 2004 August 15, we observed a fast (shorter than 10 hours) state
transition in the bright black-hole transient GX 339-4 simultaneously with
RossiXTE and INTEGRAL. This transition was evident both in timing and spectral
properties. Combining the data from PCA, HEXTE and IBIS, we obtained good
quality broad-band (3-200 keV) energy spectra before and after the transition.
These spectra indicate that the hard component steepened. Also, the high-energy
cutoff that was present at ~70 keV before the transition was not detected after
the transition. This is the first time that an accurate determination of the
broad-band spectrum across such a transition has been measured on a short time
scale. It shows that, although some spectral parameters do not change abruptly
through the transition, the high-energy cutoff increases/disappears rather
fast. These results constitute a benchmark on which to test theoretical models
for the production of the hard component in these systems.Comment: Accepted for publication in MNRAS (9 pages, 6 figures
Synthesizing Political Zero-Shot Relation Classification via Codebook Knowledge, NLI, and ChatGPT
Recent supervised models for event coding vastly outperform pattern-matching
methods. However, their reliance solely on new annotations disregards the vast
knowledge within expert databases, hindering their applicability to
fine-grained classification. To address these limitations, we explore zero-shot
approaches for political event ontology relation classification, by leveraging
knowledge from established annotation codebooks. Our study encompasses both
ChatGPT and a novel natural language inference (NLI) based approach named ZSP.
ZSP adopts a tree-query framework that deconstructs the task into context,
modality, and class disambiguation levels. This framework improves
interpretability, efficiency, and adaptability to schema changes. By conducting
extensive experiments on our newly curated datasets, we pinpoint the
instability issues within ChatGPT and highlight the superior performance of
ZSP. ZSP achieves an impressive 40% improvement in F1 score for fine-grained
Rootcode classification. ZSP demonstrates competitive performance compared to
supervised BERT models, positioning it as a valuable tool for event record
validation and ontology development. Our work underscores the potential of
leveraging transfer learning and existing expertise to enhance the efficiency
and scalability of research in the field.Comment: Preprin
-NMR of Isolated Li Implanted into a Thin Copper Film
Depth-controlled -NMR was used to study highly spin-polarized Li
in a Cu film of thickness 100 nm deposited onto a MgO substrate. The positive
Knight Shifts and spin relaxation data show that Li occupies two sites at
low temperatures, assigned to be the substitutional () and octahedral ()
interstitial sites. Between 50 to 100 K, there is a site change from to
. The temperature dependence of the Knight shifts and spin-lattice
relaxation rates at high temperatures, i.e. when all the Li are in the
site, is consistent with the Korringa Law for a simple metal.Comment: Accepted for publication in Phys. Rev.
Hyperfine Fields in an Ag/Fe Multilayer Film Investigated with 8Li beta-Detected Nuclear Magnetic Resonance
Low energy -detected nuclear magnetic resonance (-NMR) was used
to investigate the spatial dependence of the hyperfine magnetic fields induced
by Fe in the nonmagnetic Ag of an Au(40 \AA)/Ag(200 \AA)/Fe(140 \AA) (001)
magnetic multilayer (MML) grown on GaAs. The resonance lineshape in the Ag
layer shows dramatic broadening compared to intrinsic Ag. This broadening is
attributed to large induced magnetic fields in this layer by the magnetic Fe
layer. We find that the induced hyperfine field in the Ag follows a power law
decay away from the Ag/Fe interface with power , and a field
extrapolated to T at the interface.Comment: 5 pages, 4 figure. To be published in Phys. Rev.
The role of the chemokine receptor CXCR4 in infection with feline immunodeficiency virus
Infection with feline immunodeficiency virus (FIV) leads to the development of a disease state similar to AIDS in man. Recent studies have identified the chemokine receptor CXCR4 as the major receptor for cell culture-adapted strains of FIV, suggesting that FIV and human immunodeficiency virus (HIV) share a common mechanism of infection involving an interaction between the virus and a member of the seven transmembrane domain superfamily of molecules. This article reviews the evidence for the involvement of chemokine receptors in FIV infection and contrasts these findings with similar studies on the primate lentiviruses HIV and SIV (simian immunodeficiency virus)
Local Magnetic Properties of a Monolayer of Mn12 Single Molecule Magnets
The magnetic properties of a monolayer of Mn12 single molecule magnets
grafted onto a Si substrate have been investigated using depth-controlled
-detected nuclear magnetic resonance. A low energy beam of spin
polarized radioactive 8Li was used to probe the local static magnetic field
distribution near the Mn12 monolayer in the Si substrate. The resonance
linewidth varies strongly as a function of implantation depth as a result of
the magnetic dipolar fields generated by the Mn12 electronic magnetic moments.
The temperature dependence of the linewidth indicates that the magnetic
properties of the Mn12 moments in this low dimensional configuration differ
from bulk Mn12.Comment: 6 pages, 4 figure
Giant Vortices Below the Surface of NbSe Detected Using Low Energy -NMR
A low energy radioactive beam of polarized Li has been used to observe
the vortex lattice near the surface of superconducting NbSe. The
inhomogeneous magnetic field distribution associated with the vortex lattice
was measured using depth-resolved -detected NMR. Below one
observes the characteristic lineshape for a triangular vortex lattice which
depends on the magnetic penetration depth and vortex core radius. The size of
the vortex core varies strongly with magnetic field. In particular in a low
field of 10.8 mT the core radius is much larger than the coherence length. The
possible origin of these giant vortices is discussed.Comment: 5 pages, 3 figures. Submitted to Phys. Rev. Let
Observation of slow order parameter fluctuations in superconducting films using beta-detected NMR
We report beta-NMR investigations of polarized 8Li implanted in thin Pb and
Ag/Nb films. At the critical superconducting temperature, we observe a singular
peak in the spin relaxation rate in small longitudinal magnetic fields, which
is attributed to fluctuations in the superconducting order parameter. However,
the peak is more than an order of magnitude larger than the prediction based on
the enhancement of the dynamic electron spin susceptibility by superconducting
fluctuations and reflects the presence of unexpected slow fluctuations.
Furthermore the fluctuations are rapidly suppressed in a small magnetic field,
which may explain why they have not been observed previously with conventional
NMR or NQR.Comment: 5 pages, 2 figure
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