10,622 research outputs found
NK cells as effectors of acquired immune responses: effector CD4+ T cell-dependent activation of NK cells following vaccination.
We characterized vaccine-induced cellular responses to rabies virus in naive adult volunteers. Contrary to current paradigms, we observed potent and prolonged in vitro NK cell cytokine production and degranulation responses after restimulation of PBMCs with inactivated rabies virus in vaccinated, but not in unvaccinated, individuals. This "recall" NK cell response was absolutely dependent on Ag-specific IL-2 from CD45RO(+) CD4(+) T cells as well as IL-12 and IL-18 from accessory cells. Importantly, NK cells represented over 70% of all IFN-gamma-secreting and degranulating cells in the first 12-18 h after virus rechallenge indicating they may be required for rapid control of infection after vaccination. Activation of NK cells may be a critical function of IL-2-secreting effector memory T cells. Although IL-2-dependent postvaccination NK cell activation has been reported previously, this is the first time the magnitude of this effect and its contribution to the overall vaccine-induced response has been appreciated and the mechanisms of NK activation postvaccination have been elucidated. Our data will allow standard protocols for evaluating vaccine-induced immunity to be adapted to assess NK cell effector responses
Orbital electron capture by the nucleus
The theory of nuclear electron capture is reviewed in the light of current understanding of weak interactions. Experimental methods and results regarding capture probabilities, capture ratios, and EC/Beta(+) ratios are summarized. Radiative electron capture is discussed, including both theory and experiment. Atomic wave function overlap and electron exchange effects are covered, as are atomic transitions that accompany nuclear electron capture. Tables are provided to assist the reader in determining quantities of interest for specific cases
Two-Body B Meson Decays to η and η': Observation of B â η'K
In a sample of 6.6Ă10^6 produced B mesons we have observed decays BâηâČK, with branching fractions B(B^+âηâČK^+) = (6.5_(-1.4)^(+1.5)±0.9)Ă10^(-5) and B(B^0âηâČK^0) = (4.7_(-2.0)^(+2.7)±0.9)Ă10^(-5). We have searched with comparable sensitivity for 17 related decays to final states containing an η or ηâČ meson accompanied by a single particle or low-lying resonance. Our upper limits for these constrain theoretical interpretations of the BâηâČK signal
Combined analysis of KamLAND and Borexino neutrino signals from Th and U decays in the Earth's interior
The KamLAND and Borexino experiments have detected electron antineutrinos
produced in the decay chains of natural thorium and uranium (Th and U
geoneutrinos). We analyze the energy spectra of current geoneutrino data in
combination with solar and long-baseline reactor neutrino data, with
marginalized three-neutrino oscillation parameters. We consider the case with
unconstrained Th and U event rates in KamLAND and Borexino, as well as cases
with fewer degrees of freedom, as obtained by successively assuming for both
experiments a common Th/U ratio, a common scaling of Th+U event rates, and a
chondritic Th/U value. In combination, KamLAND and Borexino can reject the null
hypothesis (no geoneutrino signal) at 5 sigma. Interesting bounds or
indications emerge on the Th+U geoneutrino rates and on the Th/U ratio, in
broad agreement with typical Earth model expectations. Conversely, the results
disfavor the hypothesis of a georeactor in the Earth's core, if its power
exceeds a few TW. The interplay of KamLAND and Borexino geoneutrino data is
highlighted.Comment: 12 pages, including 6 figure
Characterization of red wines aged with oak chip in the SĂŁo Francisco Valley, Brazil.
This research aimed to characterize the physicochemical composition of Syrah tropical wines aged with oak chip addition
Electron beam profile imaging in the presence of coherent optical radiation effects
High-brightness electron beams with low energy spread at existing and future
x-ray free-electron lasers are affected by various collective beam
self-interactions and microbunching instabilities. The corresponding coherent
optical radiation effects, e.g., coherent optical transition radiation, render
electron beam profile imaging impossible and become a serious issue for all
kinds of electron beam diagnostics using imaging screens. Furthermore, coherent
optical radiation effects can also be related to intrinsically ultrashort
electron bunches or the existence of ultrashort spikes inside the electron
bunches. In this paper, we discuss methods to suppress coherent optical
radiation effects both by electron beam profile imaging in dispersive beamlines
and by using scintillation imaging screens in combination with separation
techniques. The suppression of coherent optical emission in dispersive
beamlines is shown by analytical calculations, numerical simulations, and
measurements. Transverse and longitudinal electron beam profile measurements in
the presence of coherent optical radiation effects in non-dispersive beamlines
are demonstrated by applying a temporal separation technique.Comment: 12 pages, 11 figures, submitted to Phys. Rev. ST Accel. Beam
Probing Low Energy Neutrino Backgrounds with Neutrino Capture on Beta Decaying Nuclei
We study the interaction of low energy neutrinos on nuclei that spontaneously
undergo beta decay showing that the product of the cross section times neutrino
velocity takes values as high as 10^{-42} cm^2 c for some specific nuclei that
decay via allowed transitions. The absence of energy threshold and the value of
the cross section single out these processes as a promising though very
demanding approach for future experiments aimed at a direct detection of low
energy neutrino backgrounds such as the cosmological relic neutrinos.Comment: Includes a discussion of local relic neutrino density effect on
neutrino capture rate. Accepted for publication in JCA
Finite-Difference Time-Domain Simulation for Three-dimensional Polarized Light Imaging
Three-dimensional Polarized Light Imaging (3D-PLI) is a promising technique
to reconstruct the nerve fiber architecture of human post-mortem brains from
birefringence measurements of histological brain sections with micrometer
resolution. To better understand how the reconstructed fiber orientations are
related to the underlying fiber structure, numerical simulations are employed.
Here, we present two complementary simulation approaches that reproduce the
entire 3D-PLI analysis: First, we give a short review on a simulation approach
that uses the Jones matrix calculus to model the birefringent myelin sheaths.
Afterwards, we introduce a more sophisticated simulation tool: a 3D Maxwell
solver based on a Finite-Difference Time-Domain algorithm that simulates the
propagation of the electromagnetic light wave through the brain tissue. We
demonstrate that the Maxwell solver is a valuable tool to better understand the
interaction of polarized light with brain tissue and to enhance the accuracy of
the fiber orientations extracted by 3D-PLI.Comment: 13 pages, 5 figure
Entorhinal and ventromedial prefrontal cortices abstract and generalize the structure of reinforcement learning problems
Knowledge of the structure of a problem, such as relationships between stimuli, enables rapid learning and flexible inference. Humans and other animals can abstract this structural knowledge and generalize it to solve new problems. For example, in spatial reasoning, shortest-path inferences are immediate in new environments. Spatial structural transfer is mediated by cells in entorhinal and (in humans) medial prefrontal cortices, which maintain their co-activation structure across different environments and behavioral states. Here, using fMRI, we show that entorhinal and ventromedial prefrontal cortex (vmPFC) representations perform a much broader role in generalizing the structure of problems. We introduce a task-remapping paradigm, where subjects solve multiple reinforcement learning (RL) problems differing in structural or sensory properties. We show that, as with space, entorhinal representations are preserved across different RL problems only if task structure is preserved. In vmPFC and ventral striatum, representations of prediction error also depend on task structure
Observation of Flux Reversal in a Symmetric Optical Thermal Ratchet
We demonstrate that a cycle of three holographic optical trapping patterns
can implement a thermal ratchet for diffusing colloidal spheres, and that the
ratchet-driven transport displays flux reversal as a function of the cycle
frequency and the inter-trap separation. Unlike previously described ratchet
models, the approach we describe involves three equivalent states, each of
which is locally and globally spatially symmetric, with spatiotemporal symmetry
being broken by the sequence of states.Comment: 4 pages, 2 figures, submitted for publication in Physical Review
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