190 research outputs found
Three-Dimensional Structure of the Magnetic Field in the Disk of the Milky Way
We present Rotation Measures (RM) of the diffuse Galactic synchrotron
emission from the Canadian Galactic Plane Survey (CGPS) and compare them to RMs
of extragalactic sources in order to study the large-scale reversal in the
Galactic magnetic field (GMF). Using Stokes Q, U and I measurements of the
Galactic disk collected with the Synthesis Telescope at the Dominion Radio
Astrophysical Observatory, we calculate RMs over an extended region of the sky,
focusing on the low longitude range of the CGPS (l=52deg to l=72deg). We note
the similarity in the structures traced by the compact sources and the extended
emission and highlight the presence of a gradient in the RM map across an
approximately diagonal line, which we identify with the well-known field
reversal of the Sagittarius-Carina arm. We suggest that the orientation of this
reversal is a geometric effect resulting from our location within a GMF
structure arising from current sheets that are not perpendicular to the
Galactic plane, as is required for a strictly radial field reversal, but that
have at least some component parallel to the disk. Examples of models that fit
this description are the three-dimensional dynamo-based model of Gressel et al.
(2013) and a Galactic scale Parker spiral (Akasofu & Hakamada 1982), although
the latter may be problematic in terms of Galactic dynamics. We emphasize the
importance of constructing three-dimensional models of the GMF to account for
structures like the diagonal RM gradient observed in this dataset.Comment: Published in Astronomy and Astrophysics, Accepted 23 April, 201
Multimode electromagnetically-induced transparency on a single atomic line
We experimentally investigate electromagnetically-induced transparency (EIT)
created on an inhomogeneously broadened 5S_1/2-5P_1/2 transition in rubidium
vapor using a control field of a complex temporal shape. A comb-shaped
transparency spectrum enhances the delay-bandwidth product and the light
storage capacity for a matched probe pulse by a factor of about 50 compared to
a single EIT line [D. D. Yavuz, Phys. Rev. A 75, 031801 (2007)]. If the
temporal mode of the control field is slowly changed while the probe is
propagating through the EIT medium, the probe will adiabatically follow,
providing a means to perform frequency conversion and optical routing
Diabetic Csf1op/op Mice Lacking Macrophages Are Protected Against the Development of Delayed Gastric Emptying
Background & AimsDiabetic gastroparesis is associated with changes in interstitial cells of Cajal (ICC), neurons, and smooth muscle cells in both animal models and humans. Macrophages appear to be critical to the development of cellular damage that leads to delayed gastric emptying (GE), but the mechanisms involved are not well understood. Csf1op/op (Op/Op) mice lack biologically active Csf1 (macrophage colony stimulating factor), resulting in the absence of Csf1-dependent tissue macrophages. We used Csf1op/op mice to determine the role of macrophages in the development of delayed GE.MethodsAnimals were injected with streptozotocin to make them diabetic. GE was determined weekly. Immunohistochemistry was used to identify macrophages and ICC networks in the gastric muscular layers. Oxidative stress was measured by serum malondialdehyde (MDA) levels. Quantitative reverse-transcription polymerase chain reaction was used to measure levels of mRNA.ResultsCsf1op/op mice had normal ICC. With onset of diabetes both Csf1op/op and wild-type Csf1+/+ mice developed increased levels of oxidative stress (75.8 ± 9.1 and 41.2 ± 13.6 nmol/mL MDA, respectively). Wild-type Csf1+/+ mice developed delayed GE after the onset of diabetes (4 of 13) whereas no diabetic Csf1op/op mouse developed delayed GE (0 of 15, P = .035). The ICC were disrupted in diabetic wild-type Csf1+/+ mice with delayed GE but remained normal in diabetic Csf1op/op mice.ConclusionsCellular injury and development of delayed GE in diabetes requires the presence of muscle layer macrophages. Targeting macrophages may be an effective therapeutic option to prevent cellular damage and development of delayed GE in diabetes
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Membrane-To-Nucleus Signaling Links Insulin-Like Growth Factor-1- and Stem Cell Factor-Activated Pathways
Stem cell factor (mouse: Kitl, human: KITLG) and insulin-like growth factor-1 (IGF1), acting via KIT and IGF1 receptor (IGF1R), respectively, are critical for the development and integrity of several tissues. Autocrine/paracrine KITLG-KIT and IGF1-IGF1R signaling are also activated in several cancers including gastrointestinal stromal tumors (GIST), the most common sarcoma. In murine gastric muscles, IGF1 promotes Kitl-dependent development of interstitial cells of Cajal (ICC), the non-neoplastic counterpart of GIST, suggesting cooperation between these pathways. Here, we report a novel mechanism linking IGF1-IGF1R and KITLG-KIT signaling in both normal and neoplastic cells. In murine gastric muscles, the microenvironment for ICC and GIST, human hepatic stellate cells (LX-2), a model for cancer niches, and GIST cells, IGF1 stimulated Kitl/KITLG protein and mRNA expression and promoter activity by activating several signaling pathways including AKT-mediated glycogen synthase kinase-3β inhibition (GSK3i). GSK3i alone also stimulated Kitl/KITLG expression without activating mitogenic pathways. Both IGF1 and GSK3i induced chromatin-level changes favoring transcriptional activation at the Kitl promoter including increased histone H3/H4 acetylation and H3 lysine (K) 4 methylation, reduced H3K9 and H3K27 methylation and reduced occupancy by the H3K27 methyltransferase EZH2. By pharmacological or RNA interference-mediated inhibition of chromatin modifiers we demonstrated that these changes have the predicted impact on KITLG expression. KITLG knock-down and immunoneutralization inhibited the proliferation of GIST cells expressing wild-type KIT, signifying oncogenic autocrine/paracrine KITLG-KIT signaling. We conclude that membrane-to-nucleus signaling involving GSK3i establishes a previously unrecognized link between the IGF1-IGF1R and KITLG-KIT pathways, which is active in both physiologic and oncogenic contexts and can be exploited for therapeutic purposes
The Global Magneto-Ionic Medium Survey: A Faraday Depth Survey of the Northern Sky Covering 1280-1750 MHz
The Galactic interstellar medium hosts a significant magnetic field, which
can be probed through the synchrotron emission produced from its interaction
with relativistic electrons. Linearly polarized synchrotron emission is
generated throughout the Galaxy, and at longer wavelengths, modified along
nearly every path by Faraday rotation in the intervening magneto-ionic medium.
Full characterization of the polarized emission requires wideband observations
with many frequency channels. We have surveyed polarized radio emission from
the Northern sky over the the range 1280-1750 MHz, with channel width 236.8
kHz, using the John A. Galt Telescope (diameter 25.6 m) at the Dominion Radio
Astrophysical Observatory, as part of the Global Magneto-Ionic Medium Survey.
The survey covered 72% of the sky, declinations -30 to +87 degrees at all right
ascensions. The intensity scale was absolutely calibrated, based on the flux
density and spectral index of Cygnus A. Polarization angle was calibrated using
the extended polarized emission of the Fan Region. Data are presented as
brightness temperatures with angular resolution 40'. Sensitivity in Stokes Q
and U is 45 mK rms in a 1.18 MHz band. We have applied rotation measure
synthesis to the data to obtain a Faraday depth cube of resolution 150 radians
per square metre and sensitivity 3 mK rms of polarized intensity. Features in
Faraday depth up to a width of 110 radians per square metre are represented.
The maximum detectable Faraday depth is +/- 20,000 radians per square metre.
The survey data are available at the Canadian Astronomy Data Centre.Comment: Accepted for publication in the Astronomical Journa
Structure in the Magnetic Field of the Milky Way Disk and Halo traced by Faraday Rotation
Magnetic fields in the ionized medium of the disk and halo of the Milky Way
impose Faraday rotation on linearly polarized radio emission. We compare two
surveys mapping the Galactic Faraday rotation, one showing the rotation
measures of extragalactic sources seen through the Galaxy (from Hutschenreuter
et al 2022), and one showing the Faraday depth of the diffuse Galactic
synchrotron emission from the Global Magneto-Ionic Medium Survey. Comparing the
two data sets in 5deg x 10deg bins shows good agreement at intermediate
latitudes, 10 < |b| < 50 deg, and little correlation between them at lower and
higher latitudes. Where they agree, both tracers show clear patterns as a
function of Galactic longitude: in the Northern Hemisphere a strong sin(2 x
longitude) pattern, and in the Southern hemisphere a sin(longitude + pi)
pattern. Pulsars with height above or below the plane |z| > 300 pc show similar
longitude dependence in their rotation measures. Nearby non-thermal structures
show rotation measure shadows as does the Orion-Eridanus superbubble. We
describe families of dynamo models that could explain the observed patterns in
the two hemispheres. We suggest that a field reversal, known to cross the plane
a few hundred pc inside the solar circle, could shift to positive z with
increasing Galactic radius to explain the sin(2xlongitude) pattern in the
Northern Hemisphere. Correlation shows that rotation measures from
extragalactic sources are one to two times the corresponding rotation measure
of the diffuse emission, implying Faraday complexity along some lines of sight,
especially in the Southern hemisphere.Comment: 37 pages, 26 figures, Ap. J. accepte
The Global Magneto-Ionic Medium Survey (GMIMS): The brightest polarized region in the Southern sky at 75cm and its implications for Radio Loop II
Using the Global Magneto-Ionic Medium Survey (GMIMS) Low-Band South (LBS)
southern sky polarization survey, covering 300 to 480 MHz at 81 arcmin
resolution, we reveal the brightest region in the Southern polarized sky at
these frequencies. The region, G150-50, covers nearly 20deg, near
(l,b)~(150 deg,-50 deg). Using GMIMS-LBS and complementary data at higher
frequencies (~0.6--30 GHz), we apply Faraday tomography and Stokes QU-fitting
techniques. We find that the magnetic field associated with G150-50 is both
coherent and primarily in the plane of the sky, and indications that the region
is associated with Radio Loop II. The Faraday depth spectra across G150-50 are
broad and contain a large-scale spatial gradient. We model the magnetic field
in the region as an expanding shell, and we can reproduce both the observed
Faraday rotation and the synchrotron emission in the GMIMS-LBS band. Using
QU-fitting, we find that the Faraday spectra are produced by several Faraday
dispersive sources along the line-of-sight. Alternatively, polarization horizon
effects that we cannot model are adding complexity to the high-frequency
polarized spectra. The magnetic field structure of Loop II dominates a large
fraction of the sky, and studies of the large-scale polarized sky will need to
account for this object. Studies of G150-50 with high angular resolution could
mitigate polarization horizon effects, and clarify the nature of G150-50.Comment: 25 pages, 14 figures. Accepted for publication in MNRA
The effects of repetitive use and pathological remodeling on channelrhodopsin function in cardiomyocytes
Aim: Channelrhodopsins (ChRs) are a large family of light-gated ion channels with distinct properties, which is of great importance in the selection of a ChR variant for a given application. However, data to guide such selection for cardiac optogenetic applications are lacking. Therefore, we investigated the functioning of different ChR variants in normal and pathological hypertrophic cardiomyocytes subjected to various illumination protocols.Methods and Results: Isolated neonatal rat ventricular cardiomyocytes (NRVMs) were transduced with lentiviral vectors to express one of the following ChR variants: H134R, CatCh, ReaChR, or GtACR1. NRVMs were treated with phenylephrine (PE) to induce pathological hypertrophy (PE group) or left untreated [control (CTL) group]. In these groups, ChR currents displayed unique and significantly different properties for each ChR variant on activation by a single 1-s light pulse (1 mW/mm(2): 470, 565, or 617 nm). The concomitant membrane potential (V-m) responses also showed a ChR variant-specific profile, with GtACR1 causing a slight increase in average V-m during illumination (V-plateau: -38 mV) as compared with a V-plateau > -20 mV for the other ChR variants. On repetitive activation at increasing frequencies (10-ms pulses at 1-10 Hz for 30 s), peak currents, which are important for cardiac pacing, decreased with increasing activation frequencies by 17-78% (p 0.05).Conclusion: Our data show that ChR variants function equally well in cell culture models of healthy and pathologically hypertrophic myocardium but show strong, variant-specific use-dependence. This use-dependent nature of ChR function should be taken into account during the design of cardiac optogenetic studies and the interpretation of the experimental findings thereof.Cardiolog
p21 produces a bioactive secretome that places stressed cells under immunosurveillance
Immune cells identify and destroy damaged cells to prevent them from causing cancer or other pathologies by mechanisms that remain poorly understood. Here, we report that the cell-cycle inhibitor p21 places cells under immunosurveillance to establish a biological timer mechanism that controls cell fate. p21 activates retinoblastoma protein (Rb)-dependent transcription at select gene promoters to generate a complex bioactive secretome, termed p21-activated secretory phenotype (PASP). The PASP includes the chemokine CXCL14, which promptly attracts macrophages. These macrophages disengage if cells normalize p21 within 4 days, but if p21 induction persists, they polarize toward an M1 phenotype and lymphocytes mount a cytotoxic T cell response to eliminate target cells, including preneoplastic cells. Thus, p21 concurrently induces proliferative arrest and immunosurveillance of cells under duress
Characterization of the John A. Galt telescope for radio holography with CHIME
The Canadian Hydrogen Intensity Mapping Experiment (CHIME) will measure the
21 cm emission of astrophysical neutral hydrogen to probe large scale structure
at redshifts z=0.8-2.5. However, detecting the 21 cm signal beneath
substantially brighter foregrounds remains a key challenge. Due to the high
dynamic range between 21 cm and foreground emission, an exquisite calibration
of instrument systematics, notably the telescope beam, is required to
successfully filter out the foregrounds. One technique being used to achieve a
high fidelity measurement of the CHIME beam is radio holography, wherein
signals from each of CHIME's analog inputs are correlated with the signal from
a co-located reference antenna, the 26 m John A. Galt telescope, as the 26 m
Galt telescope tracks a bright point source transiting over CHIME. In this work
we present an analysis of several of the Galt telescope's properties. We employ
driftscan measurements of several bright sources, along with background
estimates derived from the 408 MHz Haslam map, to estimate the Galt system
temperature. To determine the Galt telescope's beam shape, we perform and
analyze a raster scan of the bright radio source Cassiopeia A. Finally, we use
early holographic measurements to measure the Galt telescope's geometry with
respect to CHIME for the holographic analysis of the CHIME and Galt
interferometric data set
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