430 research outputs found
Quantum incompressibility of a falling Rydberg atom, and a gravitationally-induced charge separation effect in superconducting systems
Freely falling point-like objects converge towards the center of the Earth.
Hence the gravitational field of the Earth is inhomogeneous, and possesses a
tidal component. The free fall of an extended quantum object such as a hydrogen
atom prepared in a high principal-quantum-number stretch state, i.e., a
circular Rydberg atom, is predicted to fall more slowly that a classical
point-like object, when both objects are dropped from the same height from
above the Earth. This indicates that, apart from "quantum jumps," the atom
exhibits a kind of "quantum incompressibility" during free fall in
inhomogeneous, tidal gravitational fields like those of the Earth. A
superconducting ring-like system with a persistent current circulating around
it behaves like the circular Rydberg atom during free fall. Like the electronic
wavefunction of the freely falling atom, the Cooper-pair wavefunction is
"quantum incompressible." The ions of the ionic lattice of the superconductor,
however, are not "quantum incompressible," since they do not possess a globally
coherent quantum phase. The resulting difference during free fall in the
response of the nonlocalizable Cooper pairs of electrons and the localizable
ions to inhomogeneous gravitational fields is predicted to lead to a charge
separation effect, which in turn leads to a large repulsive Coulomb force that
opposes the convergence caused by the tidal, attractive gravitational force on
the superconducting system. A "Cavendish-like" experiment is proposed for
observing the charge separation effect induced by inhomogeneous gravitational
fields in a superconducting circuit. This experiment would demonstrate the
existence of a novel coupling between gravity and electricity via
macroscopically coherent quantum matter.Comment: `2nd Vienna Symposium for the Foundations of Modern Physics'
Festschrift MS for Foundations of Physic
Simultaneous Multi-band Radio & X-ray Observations of the Galactic Center Magnetar SGR 17452900
We report on multi-frequency, wideband radio observations of the Galactic
Center magnetar (SGR 17452900) with the Green Bank Telescope for 100
days immediately following its initial X-ray outburst in April 2013. We made
multiple simultaneous observations at 1.5, 2.0, and 8.9 GHz, allowing us to
examine the magnetar's flux evolution, radio spectrum, and interstellar medium
parameters (such as the dispersion measure (DM), the scattering timescale and
its index). During two epochs, we have simultaneous observations from the
Chandra X-ray Observatory, which permitted the absolute alignment of the radio
and X-ray profiles. As with the two other radio magnetars with published
alignments, the radio profile lies within the broad peak of the X-ray profile,
preceding the X-ray profile maximum by 0.2 rotations. We also find that
the radio spectral index is significantly negative between 2 and
9 GHz; during the final 30 days of our observations ,
which is typical of canonical pulsars. The radio flux has not decreased during
this outburst, whereas the long-term trends in the other radio magnetars show
concomitant fading of the radio and X-ray fluxes. Finally, our wideband
measurements of the DMs taken in adjacent frequency bands in tandem are
stochastically inconsistent with one another. Based on recent theoretical
predictions, we consider the possibility that the dispersion measure is
frequency-dependent. Despite having several properties in common with the other
radio magnetars, such as , an
increase in the radio flux during the X-ray flux decay has not been observed
thus far in other systems.Comment: 15 pages, 9 figures, 3 tables; accepted to Ap
Using Abrupt Changes in Magnetic Susceptibility within Type-II Superconductors to Explore Global Decoherence Phenomena
A phenomenon of a periodic staircase of macroscopic jumps in the admitted
magnetic field has been observed, as the magnitude of an externally applied
magnetic field is smoothly increased or decreased upon a superconducting (SC)
loop of type II niobium-titanium wire which is coated with a
non-superconducting layer of copper. Large temperature spikes were observed to
occur simultaneously with the jumps, suggesting brief transitions to the normal
state, caused by en masse motions of Abrikosov vortices. An experiment that
exploits this phenomenon to explore the global decoherence of a large
superconducting system will be discussed, and preliminary data will be
presented. Though further experimentation is required to determine the actual
decoherence rate across the superconducting system, multiple classical
processes are ruled out, suggesting that jumps in magnetic flux are fully
quantum mechanical processes which may correspond to large group velocities
within the global Cooper pair wavefunction.Comment: 13 pages, 4 figures, part of proceedings for FQMT 2011 conference in
Prague, Czech Republi
A strongly magnetized pulsar within grasp of the Milky Way's supermassive black hole
The center of our Galaxy hosts a supermassive black hole, Sagittarius (Sgr)
A*. Young, massive stars within 0.5 pc of SgrA* are evidence of an episode of
intense star formation near the black hole a few Myr ago, which might have left
behind a young neutron star traveling deep into SgrA*'s gravitational
potential. On 2013 April 25, a short X-ray burst was observed from the
direction of the Galactic center. Thanks to a series of observations with the
Chandra and the Swift satellites, we pinpoint the associated magnetar at an
angular distance of 2.4+/-0.3 arcsec from SgrA*, and refine the source spin
period and its derivative (P=3.7635537(2) s and \dot{P} = 6.61(4)x10^{-12}
s/s), confirmed by quasi simultaneous radio observations performed with the
Green Bank (GBT) and Parkes antennas, which also constrain a Dispersion Measure
of DM=1750+/-50 pc cm^{-3}, the highest ever observed for a radio pulsar. We
have found that this X-ray source is a young magnetar at ~0.07-2 pc from SgrA*.
Simulations of its possible motion around SgrA* show that it is likely (~90%
probability) in a bound orbit around the black hole. The radiation front
produced by the past activity from the magnetar passing through the molecular
clouds surrounding the Galactic center region, might be responsible for a large
fraction of the light echoes observed in the Fe fluorescence features.Comment: ApJ Letters in pres
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Intracellular \u3cem\u3eSalmonella\u3c/em\u3e delivery of an exogenous immunization antigen refocuses CD8 T cells against cancer cells, eliminates pancreatic tumors and forms antitumor immunity
Introduction: Immunotherapies have shown great promise, but are not effective for all tumors types and are effective in less than 3% of patients with pancreatic ductal adenocarcinomas (PDAC). To make an immune treatment that is effective for more cancer patients and those with PDAC specifically, we genetically engineered Salmonella to deliver exogenous antigens directly into the cytoplasm of tumor cells. We hypothesized that intracellular delivery of an exogenous immunization antigen would activate antigen-specific CD8 T cells and reduce tumors in immunized mice.
Methods: To test this hypothesis, we administered intracellular delivering (ID) Salmonella that deliver ovalbumin as a model antigen into tumor-bearing, ovalbumin-vaccinated mice. ID Salmonella delivers antigens by autonomously lysing in cells after the induction of cell invasion.
Results: We showed that the delivered ovalbumin disperses throughout the cytoplasm of cells in culture and in tumors. This delivery into the cytoplasm is essential for antigen cross-presentation. We showed that co-culture of ovalbumin-recipient cancer cells with ovalbumin-specific CD8 T cells triggered a cytotoxic T cell response. After the adoptive transfer of OT-I CD8 T cells, intracellular delivery of ovalbumin reduced tumor growth and eliminated tumors. This effect was dependent on the presence of the ovalbumin-specific T cells. Following vaccination with the exogenous antigen in mice, intracellular delivery of the antigen cleared 43% of established KPC pancreatic tumors, increased survival, and prevented tumor re-implantation.
Discussion: This response in the immunosuppressive KPC model demonstrates the potential to treat tumors that do not respond to checkpoint inhibitors, and the response to re-challenge indicates that new immunity was established against intrinsic tumor antigens. In the clinic, ID Salmonella could be used to deliver a protein antigen from a childhood immunization to refocus pre-existing T cell immunity against tumors. As an off-the-shelf immunotherapy, this bacterial system has the potential to be effective in a broad range of cancer patients
G28.17+0.05: An unusual giant HI cloud in the inner Galaxy
New 21 cm HI observations have revealed a giant HI cloud in the Galactic
plane that has unusual properties. It is quite well defined, about 150 pc in
diameter at a distance of 5 kpc, and contains as much as 100,000 Solar Masses
of atomic hydrogen. The outer parts of the cloud appear in HI emission above
the HI background, while the central regions show HI self-absorption. Models
which reproduce the observations have a core with a temperature <40 K and an
outer envelope as much as an order of magnitude hotter. The cold core is
elongated along the Galactic plane, whereas the overall outline of the cloud is
approximately spherical. The warm and cold parts of the HI cloud have a
similar, and relatively large, line width of approximately 7 km/s. The cloud
core is a source of weak, anomalously-excited 1720 MHz OH emission, also with a
relatively large line width, which delineates the region of HI self-absorption
but is slightly blue-shifted in velocity. The intensity of the 1720 MHz OH
emission is correlated with N(H) derived from models of the cold core. There is
12CO emission associated with the cloud core. Most of the cloud mass is in
molecules, and the total mass is > 200,000 Solar Masses. In the cold core the
HI mass fraction may be 10 percent. The cloud has only a few sites of current
star formation. There may be about 100 more objects like this in the inner
Galaxy; every line of sight through the Galactic plane within 50 degrees of the
Galactic center probably intersects at least one. We suggest that G28.17+0.05
is a cloud being observed as it enters a spiral arm and that it is in the
transition from the atomic to the molecular state.Comment: 35 pages, inludes 12 figure
Acceleration of Galactic Cosmic Rays in the Interstellar Medium
Challenges have arisen to diffusive shock acceleration as the primary means to accelerate galactic cosmic rays (GCRs) in the interstellar medium. Diffusive shock acceleration is also under challenge in the heliosphere, where at least the simple application of diffusive shock acceleration cannot account for observations. In the heliosphere, a new acceleration mechanism has been invented—a pump mechanism, driven by ambient turbulence, in which particles are pumped up in energy out of a low-energy core particle population through a series of adiabatic compressions and expansions—that can account for observations not only at shocks but in quiet conditions in the solar wind and throughout the heliosheath. In this paper, the pump mechanism is applied to the acceleration of GCRs in the interstellar medium. With relatively straightforward assumptions about the magnetic field in the interstellar medium, and how GCRs propagate in this field, the pump mechanism yields (1) the overall shape of the GCR spectrum, a power law in particle kinetic energy, with a break at the so-called knee in the GCR spectrum to a slightly steeper power-law spectrum. (2) The rigidity dependence of the H/He ratio observed from the PAMELA satellite instrument.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/98584/1/0004-637X_744_2_127.pd
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Dentate gyrus abnormalities in sudden unexplained death in infants: morphological marker of underlying brain vulnerability
Sudden unexplained death in infants, including the sudden infant death syndrome, is likely due to heterogeneous causes that involve different intrinsic vulnerabilities and/or environmental factors. Neuropathologic research focuses upon the role of brain regions, particularly the brainstem, that regulate or modulate autonomic and respiratory control during sleep or transitions to waking. The hippocampus is a key component of the forebrain–limbic network that modulates autonomic/respiratory control via brainstem connections, but its role in sudden infant death has received little attention. We tested the hypothesis that a well-established marker of hippocampal pathology in temporal lobe epilepsy—focal granule cell bilamination in the dentate, a variant of granule cell dispersion—is associated with sudden unexplained death in infants. In a blinded study of hippocampal morphology in 153 infants with sudden and unexpected death autopsied in the San Diego County medical examiner’s office, deaths were classified as unexplained or explained based upon autopsy and scene investigation. Focal granule cell bilamination was present in 41.2 % (47/114) of the unexplained group compared to 7.7 % (3/39) of the explained (control) group (p < 0.001). It was associated with a cluster of other dentate developmental abnormalities that reflect defective neuronal proliferation, migration, and/or survival. Dentate lesions in a large subset of infants with sudden unexplained death may represent a developmental vulnerability that leads to autonomic/respiratory instability or autonomic seizures, and sleep-related death when the infants are challenged with homeostatic stressors. Importantly, these lesions can be recognized in microscopic sections prepared in current forensic practice. Future research is needed to determine the relationship between hippocampal and previously reported brainstem pathology in sudden infant death. Electronic supplementary material The online version of this article (doi:10.1007/s00401-014-1357-0) contains supplementary material, which is available to authorized users
Ordered magnetic fields around radio galaxies: evidence for interaction with the environment
We present detailed imaging of Faraday rotation and depolarization for the
radio galaxies 0206+35, 3C 270, 3C 353 and M 84, based on Very Large Array
observations at multiple frequencies in the range 1365 to 8440 MHz. This work
suggests a more complex picture of the magneto-ionic environments of radio
galaxies than was apparent from earlier work. All of the sources show
spectacular banded rotation measure (RM) structures with contours of constant
RM perpendicular to the major axes of their radio lobes. We give a
comprehensive description of the banded RM phenomenon and present an initial
attempt to interpret it as a consequence of interactions between the sources
and their surroundings. We show that the material responsible for the Faraday
rotation is in front of the radio emission and that the bands are likely to be
caused by magnetized plasma which has been compressed by the expanding radio
lobes. A two-dimensional magnetic structure in which the field lines are a
family of ellipses draped around the leading edge of the lobe can produce RM
bands in the correct orientation for any source orientation. We also report the
first detections of rims of high depolarization at the edges of the inner radio
lobes of M 84 and 3C 270. These are spatially coincident with shells of
enhanced X-ray surface brightness, in which both the field strength and the
thermal gas density are likely to be increased by compression.Comment: 21 pages, 15 figures, accepted for publication in MNRAS. Full
resolution paper available at http://www.ira.inaf.it/~guidetti/bands/
Subjects: Astrophysics (astro-ph
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