920 research outputs found
Spin- and momentum-correlated atom pairs mediated by photon exchange and seeded by vacuum fluctuations
Engineering pairs of massive particles that are simultaneously correlated in
their external and internal degrees of freedom is a major challenge, yet
essential for advancing fundamental tests of physics and quantum technologies.
In this work, we experimentally demonstrate a mechanism for generating pairs of
atoms in well-defined spin and momentum modes. This mechanism couples atoms
from a degenerate Bose gas via a superradiant photon-exchange process in an
optical cavity, producing pairs via a single or two discernible channels. The
scheme is independent of collisional interactions, fast and tunable. We observe
a collectively enhanced production of pairs and probe inter-spin correlations
in momentum space. We characterize the emergent pair statistics, and find that
the observed dynamics is consistent with being primarily seeded by vacuum
fluctuations in the corresponding atomic modes. Together with our observations
of coherent many-body oscillations involving well-defined momentum modes, our
results offer promising prospects for quantum-enhanced interferometry and
quantum simulation experiments using entangled matter waves.Comment: 15 pages, 6 figure
Quantum Fluctuation Dynamics of Dispersive Superradiant Pulses in a Hybrid Light-Matter System
We consider theoretically a driven-dissipative quantum many-body system
consisting of an atomic ensemble in a single-mode optical cavity as described
by the open Tavis-Cummings model. In this hybrid light-matter system the
interplay between coherent and dissipative processes leads to superradiant
pulses with a build-up of strong correlations, even for systems comprising
hundreds to thousands of particles. A central feature of the mean-field
dynamics is a self-reversal of two spin degrees of freedom due to an underlying
time-reversal symmetry, which is broken by quantum fluctuations. We demonstrate
a quench protocol that can maintain highly non-Gaussian states over long time
scales. This general mechanism offers interesting possibilities for the
generation and control of complex fluctuation patterns, as suggested for the
improvement of quantum sensing protocols for dissipative spin-amplification.Comment: 7 pages, 5 figures, 4 pages supplementa
John Schuster, Descartes-agonistes: Physico-mathematics, method and corpuscular-mechanism, 1618–1633
We report on a 10 ks simultaneous Chandra/HETG-NuSTAR observation of the
Bursting Pulsar, GRO J1744-28, during its third detected outburst since
discovery and after nearly 18 years of quiescence. The source is detected up to
60 keV with an Eddington persistent flux level. Seven bursts, followed by dips,
are seen with Chandra, three of which are also detected with NuSTAR. Timing
analysis reveals a slight increase in the persistent emission pulsed fraction
with energy (from 10% to 15%) up to 10 keV, above which it remains constant.
The 0.5-70 keV spectra of the persistent and dip emission are the same within
errors, and well described by a blackbody (BB), a power-law with an exponential
rolloff, a 10 keV feature, and a 6.7 keV emission feature, all modified by
neutral absorption. Assuming that the BB emission originates in an accretion
disc, we estimate its inner (magnetospheric) radius to be about 4x10^7 cm,
which translates to a surface dipole field B~9x10^10 G. The Chandra/HETG
spectrum resolves the 6.7 keV feature into (quasi-)neutral and highly ionized
Fe XXV and Fe XXVI emission lines. XSTAR modeling shows these lines to also
emanate from a truncated accretion disk. The burst spectra, with a peak flux
more than an order of magnitude higher than Eddington, are well fit with a
power-law with an exponential rolloff and a 10~keV feature, with similar fit
values compared to the persistent and dip spectra. The burst spectra lack a
thermal component and any Fe features. Anisotropic (beamed) burst emission
would explain both the lack of the BB and any Fe components.Comment: 15 pages, 11 figures, Accepted in Ap
SIMULTANEOUS NuSTAR/CHANDRA OBSERVATIONS OF THE BURSTING PULSAR GRO J1744-28 DURING ITS THIRD REACTIVATION
We report on a 10 ks simultaneous Chandra/High Energy Transmission Grating (HETG)–Nuclear Spectroscopic Telescope Array (NuSTAR) observation of the Bursting Pulsar, GRO J1744-28, during its third detected outburst since discovery and after nearly 18 yr of quiescence. The source is detected up to 60 keV with an Eddington persistent flux level. Seven bursts, followed by dips, are seen with Chandra, three of which are also detected with NuSTAR. Timing analysis reveals a slight increase in the persistent emission pulsed fraction with energy (from 10% to 15%) up to 10 keV, above which it remains constant. The 0.5–70 keV spectra of the persistent and dip emission are the same within errors and well described by a blackbody (BB), a power-law (PL) with an exponential rolloff, a 10 keV feature, and a 6.7 keV emission feature, all modified by neutral absorption. Assuming that the BB emission originates in an accretion disk, we estimate its inner (magnetospheric) radius to be about 4 × 10[superscript 7] cm, which translates to a surface dipole field B ≈ 9 × 10[superscript 10] G. The Chandra/HETG spectrum resolves the 6.7 keV feature into (quasi-)neutral and highly ionized Fe xxv and Fe xxvi emission lines. XSTAR modeling shows these lines to also emanate from a truncated accretion disk. The burst spectra, with a peak flux more than an order of magnitude higher than Eddington, are well fit with a PL with an exponential rolloff and a 10 keV feature, with similar fit values compared to the persistent and dip spectra. The burst spectra lack a thermal component and any Fe features. Anisotropic (beamed) burst emission would explain both the lack of the BB and any Fe components
Identification of Hypoxia-Regulated Proteins Using MALDI-Mass Spectrometry Imaging Combined with Quantitative Proteomics
Hypoxia is present in most solid tumors and is clinically correlated with increased metastasis and poor patient survival. While studies have demonstrated the role of hypoxia and hypoxia-regulated proteins in cancer progression, no attempts have been made to identify hypoxia-regulated proteins using quantitative proteomics combined with MALDI-mass spectrometry imaging (MALDI-MSI). Here we present a comprehensive hypoxic proteome study and are the first to investigate changes in situ using tumor samples. In vitro quantitative mass spectrometry analysis of the hypoxic proteome was performed on breast cancer cells using stable isotope labeling with amino acids in cell culture (SILAC). MS analyses were performed on laser-capture microdissected samples isolated from normoxic and hypoxic regions from tumors derived from the same cells used in vitro. MALDI-MSI was used in combination to investigate hypoxia-regulated protein localization within tumor sections. Here we identified more than 100 proteins, both novel and previously reported, that were associated with hypoxia. Several proteins were localized in hypoxic regions, as identified by MALDI-MSI. Visualization and data extrapolation methods for the in vitro SILAC data were also developed, and computational mapping of MALDI-MSI data to IHC results was applied for data validation. The results and limitations of the methodologies described are discussed. 2014 American Chemical Societ
Tissue-Specific Target Analysis of Disease-Associated MicroRNAs in Human Signaling Pathways
MicroRNAs are a large class of post-transcriptional regulators that bind to the 3′ untranslated region of messenger RNAs. They play a critical role in many cellular processes and have been linked to the control of signal transduction pathways. Recent studies indicate that microRNAs can function as tumor suppressors or even as oncogenes when aberrantly expressed. For more general insights of disease-associated microRNAs, we analyzed their impact on human signaling pathways from two perspectives. On a global scale, we found a core set of signaling pathways with enriched tissue-specific microRNA targets across diseases. The function of these pathways reflects the affinity of microRNAs to regulate cellular processes associated with apoptosis, proliferation or development. Comparing cancer and non-cancer related microRNAs, we found no significant differences between both groups. To unveil the interaction and regulation of microRNAs on signaling pathways locally, we analyzed the cellular location and process type of disease-associated microRNA targets and proteins. While disease-associated proteins are highly enriched in extracellular components of the pathway, microRNA targets are preferentially located in the nucleus. Moreover, targets of disease-associated microRNAs preferentially exhibit an inhibitory effect within the pathways in contrast to disease proteins. Our analysis provides systematic insights into the interaction of disease-associated microRNAs and signaling pathways and uncovers differences in cellular locations and process types of microRNA targets and disease-associated proteins
Individual and school level correlates of moderate to vigorous physical activity among school-children in Germany – a multi-level analysis
Corrigendum to "Transverse extension of partons in the proton probed in the sea-quark range by measuring the DVCS cross section" [Phys. Lett. B 793 (2019) 188]
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