1,854 research outputs found
Low-Mach-number turbulence in interstellar gas revealed by radio polarization gradients
The interstellar medium of the Milky Way is multi-phase, magnetized and
turbulent. Turbulence in the interstellar medium produces a global cascade of
random gas motions, spanning scales ranging from 100 parsecs to 1000
kilometres. Fundamental parameters of interstellar turbulence such as the sonic
Mach number (the speed of sound) have been difficult to determine because
observations have lacked the sensitivity and resolution to directly image the
small-scale structure associated with turbulent motion. Observations of linear
polarization and Faraday rotation in radio emission from the Milky Way have
identified unusual polarized structures that often have no counterparts in the
total radiation intensity or at other wavelengths, and whose physical
significance has been unclear. Here we report that the gradient of the Stokes
vector (Q,U), where Q and U are parameters describing the polarization state of
radiation, provides an image of magnetized turbulence in diffuse ionized gas,
manifested as a complex filamentary web of discontinuities in gas density and
magnetic field. Through comparison with simulations, we demonstrate that
turbulence in the warm ionized medium has a relatively low sonic Mach number,
M_s <~ 2. The development of statistical tools for the analysis of polarization
gradients will allow accurate determinations of the Mach number, Reynolds
number and magnetic field strength in interstellar turbulence over a wide range
of conditions.Comment: 5 pages, 3 figures, published in Nature on 13 Oct 201
Global marine bacterial diversity peaks at high latitudes in winter.
Genomic approaches to characterizing bacterial communities are revealing significant differences in diversity and composition between environments. But bacterial distributions have not been mapped at a global scale. Although current community surveys are way too sparse to map global diversity patterns directly, there is now sufficient data to fit accurate models of how bacterial distributions vary across different environments and to make global scale maps from these models. We apply this approach to map the global distributions of bacteria in marine surface waters. Our spatially and temporally explicit predictions suggest that bacterial diversity peaks in temperate latitudes across the world's oceans. These global peaks are seasonal, occurring 6 months apart in the two hemispheres, in the boreal and austral winters. This pattern is quite different from the tropical, seasonally consistent diversity patterns observed for most macroorganisms. However, like other marine organisms, surface water bacteria are particularly diverse in regions of high human environmental impacts on the oceans. Our maps provide the first picture of bacterial distributions at a global scale and suggest important differences between the diversity patterns of bacteria compared with other organisms
Annual Modulation of Dark Matter in the Presence of Streams
In addition to a smooth component of WIMP dark matter in galaxies, there may
be streams of material; the effects of WIMP streams on direct detection
experiments is examined in this paper. The contribution to the count rate due
to the stream cuts off at some characteristic energy. Near this cutoff energy,
the stream contribution to the annual modulation of recoils in the detector is
comparable to that of the thermalized halo, even if the stream represents only
a small portion (~5% or less) of the local halo density. Consequently the total
modulation may be quite different than would be expected for the standard halo
model alone: it may not be cosine-like and can peak at a different date than
expected. The effects of speed, direction, density, and velocity dispersion of
a stream on the modulation are examined. We describe how the observation of a
modulation can be used to determine these stream parameters. Alternatively, the
presence of a dropoff in the recoil spectrum can be used to determine the WIMP
mass if the stream speed is known. The annual modulation of the cutoff energy
together with the annual modulation of the overall signal provide a "smoking
gun" for WIMP detection.Comment: 27 pages, 9 figures. v2: Added reference and minor revisions to match
PRD versio
The inverse-Compton ghost HDF 130 and the giant radio galaxy 6C 0905+3955: matching an analytic model for double radio source evolution
We present new GMRT observations of HDF 130, an inverse-Compton (IC) ghost of
a giant radio source that is no longer being powered by jets. We compare the
properties of HDF 130 with the new and important constraint of the upper limit
of the radio flux density at 240 MHz to an analytic model. We learn what values
of physical parameters in the model for the dynamics and evolution of the radio
luminosity and X-ray luminosity (due to IC scattering of the cosmic microwave
background (CMB)) of a Fanaroff-Riley II (FR II) source are able to describe a
source with features (lobe length, axial ratio, X-ray luminosity, photon index
and upper limit of radio luminosity) similar to the observations. HDF 130 is
found to agree with the interpretation that it is an IC ghost of a powerful
double-lobed radio source, and we are observing it at least a few Myr after jet
activity (which lasted 5--100 Myr) has ceased. The minimum Lorentz factor of
injected particles into the lobes from the hotspot is preferred to be
for the model to describe the observed quantities well,
assuming that the magnetic energy density, electron energy density, and lobe
pressure at time of injection into the lobe are linked by constant factors
according to a minimum energy argument, so that the minimum Lorentz factor is
constrained by the lobe pressure. We also apply the model to match the features
of 6C 0905+3955, a classical double FR II galaxy thought to have a low-energy
cutoff of in the hotspot due to a lack of hotspot
inverse-Compton X-ray emission. The models suggest that the low-energy cutoff
in the hotspots of 6C 0905+3955 is , just slightly above
the particles required for X-ray emission.Comment: 9 pages, 3 figure
The inverse-Compton X-ray-emitting lobes of the high-redshift giant radio galaxy 6C 0905+39
We present new XMM-Newton data of the high-redshift (z=1.883), Mpc-sized
giant radio galaxy 6C 0905+39. The larger collecting area and longer
observation time for our new data means that we can better characterise the
extended X-ray emission, in particular its spectrum, which arises from cosmic
microwave background photons scattered into the X-ray band by the energetic
electrons in the spent synchrotron plasma of the (largely) radio-quiet lobes of
6C 0905+39. We calculate the energy that its jet-ejected plasma has dumped into
its surroundings in the last 3 X 10^7 years and discuss the impact that
similar, or even more extreme, examples of spent, radio-quiet lobes would have
on their surroundings. Interestingly, there is an indication that the emission
from the hotspots is softer than the rest of the extended emission and the
core, implying it is due to synchrotron emission. We confirm our previous
detection of the low-energy turnover in the eastern hotspot of 6C 0905+39.Comment: 7 pages, 7 figures, accepted by MNRA
The Dynamics and Stability of Circumbinary Orbits
We numerically investigate the dynamics of orbits in 3D circumbinary
phase-space as a function of binary eccentricity and mass fraction. We find
that inclined circumbinary orbits in the elliptically-restricted three-body
problem display a nodal libration mechanism in the longitude of the ascending
node and in the inclination to the plane of the binary. We (i) analyse and
quantify the behaviour of these orbits with reference to analytical work
performed by Farago & Laskar (2010) and (ii) investigate the stability of these
orbits over time. This work is the first dynamically aware analysis of the
stability of circumbinary orbits across both binary mass fraction and binary
eccentricity. This work also has implications for exoplanetary astronomy in the
existence and determination of stable orbits around binary systems.Comment: Monthly Notices of the Royal Astronomical Society. in pres
Blockade ofthe negative co-stimulatory molecules PD-1 and CTLA-4 improves survival in primary and secondary fungal sepsis
INTRODUCTION: Fungal sepsis is an increasingly common problem in intensive care unit patients.Mortality from fungal sepsis remains high despite antimicrobial therapy that is highly active against most fungal pathogens, a finding consistent with defective host immunity that is present in many patients with disseminated fungemia.One recently recognized immunologic defect that occurs in patients with sepsis is T cell "exhaustion" due to increased expression of programmed cell death -1 (PD-1).This study tested the ability of anti-PD-1 and anti-programmed cell death ligand -1 (anti-PD-L1) antagonistic antibodies to improve survival and reverse sepsis-induced immunosuppression in two mouse models of fungal sepsis. METHODS: Fungal sepsis was induced in mice using two different models of infection, that is, primary fungal sepsis and secondary fungal sepsis occurring after sub-lethal cecal ligation and puncture (CLP).Anti-PD-1 and anti-PD-L1 were administered 24 to 48 h after fungal infection and effects on survival, interferon gamma production, and MHC II expression were examined. RESULTS: Anti-PD-1 and anti-PD-L1 antibodies were highly effective at improving survival in primary and secondary fungal sepsis.Both antibodies reversed sepsis-induced suppression of interferon gamma and increased expression of MHC II on antigen presenting cells.Blockade of cytotoxic T-lymphocyte antigen-4 (CTLA-4), a second negative co-stimulatory molecule that is up-regulated in sepsis and acts like PD-1 to suppress T cell function, also improved survival in fungal sepsis. CONCLUSIONS: Immuno-adjuvant therapy with anti-PD-1, anti-PD-L1 and anti-CTLA-4 antibodies reverse sepsis-induced immunosuppression and improve survival in fungal sepsis.The present results are consistent with previous studies showing that blockade of PD-1 and CTLA-4 improves survival in bacterial sepsis.Thus, immuno-adjuvant therapy represents a novel approach to sepsis and may have broad applicability in the disorder.Given the relative safety of anti-PD-1 antibody in cancer clinical trials to date, therapy with anti-PD-1 in patients with life-threatening sepsis who have demonstrable immunosuppression should be strongly considered
Dysregulated Amino Acid Sensing Drives Colorectal Cancer Growth and Metabolic Reprogramming Leading to Chemoresistance
BACKGROUND & AIMS: Colorectal cancer (CRC) is a devastating disease that is highly modulated by dietary nutrients. Mechanistic target of rapamycin complex 1 (mTORC1) contributes to tumor growth and limits therapy responses. Growth factor signaling is a major mechanism of mTORC1 activation. However, compensatory pathways exist to sustain mTORC1 activity after therapies that target oncogenic growth factor signaling. Amino acids potently activate mTORC1 via amino acid-sensing GTPase activity towards Rags (GATOR). The role of amino acid-sensing pathways in CRC is unclear.
METHODS: Human colon cancer cell lines, preclinical intestinal epithelial-specific GATOR1 and GATOR2 knockout mice subjected to colitis-induced or sporadic colon tumor models, small interfering RNA screening targeting regulators of mTORC1, and tissues of patients with CRC were used to assess the role of amino acid sensing in CRC.
RESULTS: We identified loss-of-function mutations of the GATOR1 complex in CRC and showed that altered expression of amino acid-sensing pathways predicted poor patient outcomes. We showed that dysregulated amino acid-sensing induced mTORC1 activation drives colon tumorigenesis in multiple mouse models. We found amino acid-sensing pathways to be essential in the cellular reprogramming of chemoresistance, and chemotherapeutic-resistant patients with colon cancer exhibited de-regulated amino acid sensing. Limiting amino acids in in vitro and in vivo models (low-protein diet) reverted drug resistance, revealing a metabolic vulnerability.
CONCLUSIONS: Our findings suggest a critical role for amino acid-sensing pathways in driving CRC and highlight the translational implications of dietary protein intervention in CRC
The Effect of Two Elementary School-Based Prevention Interventions on Being Offered Tobacco and the Transition to Smoking
Aims: This study sought to more precisely delineate the mechanisms by which two early elementary school-based, universal (i.e., applied to the entire population regardless of risk status) preventive interventions increased survival to first tobacco cigarette smoked. Specifically, we examined whether the interventions\u27 effect on survival to first use was via the reduction of offers to smoke and/or through preventing the transition from first offer to smoking. Methods: A total of 678 urban first-graders were assigned randomly to the classroom-centered (CC), or the family-school partnership (FSP), or a control classroom condition. Youth were followed annually until 1 year beyond their anticipated high school graduation (mean age ∼18 years). Discrete-time survival analyses on 628 youth evaluated the impact of the CC and FSP interventions on first tobacco offer and initial tobacco smoking once offered. Findings: The risk of being offered tobacco was reduced among both CC and FSP intervention groups relative to the control group, although the reduction was only statistically significant for the CC intervention. Neither intervention condition reduced the transition to smoking once offered tobacco to smoke. Conclusion: The CC intervention appeared to have its effect on survival to first cigarette smoked by delaying the first offer to smoke. Preventive interventions focused on refusal skills during the middle school years may be necessary to reduce the likelihood of the transition to smoking once offered
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