348 research outputs found
Recruitment of release sites underlies chemical presynaptic potentiation at hippocampal mossy fiber boutons
Synaptic plasticity is a cellular model for learning and memory. However, the expression mechanisms underlying presynaptic forms of plasticity are not well understood. Here, we investigate functional and structural correlates of presynaptic potentiation at large hippocampal mossy fiber boutons induced by the adenylyl cyclase activator forskolin. We performed 2-photon imaging of the genetically encoded glutamate sensor iGlu(u) that revealed an increase in the surface area used for glutamate release at potentiated terminals. Time-gated stimulated emission depletion microscopy revealed no change in the coupling distance between P/Q-type calcium channels and release sites mapped by Munc13-1 cluster position. Finally, by high-pressure freezing and transmission electron microscopy analysis, we found a fast remodeling of synaptic ultrastructure at potentiated boutons: Synaptic vesicles dispersed in the terminal and accumulated at the active zones, while active zone density and synaptic complexity increased. We suggest that these rapid and early structural rearrangements might enable long-term increase in synaptic strength
Increased and synchronous recruitment of release sites underlies hippocampal mossy fiber presynaptic potentiation
Synaptic plasticity is a cellular model for learning and memory. However, the expression mechanisms underlying presynaptic forms of plasticity are not well understood. Here, we investigate functional and structural correlates of long-term potentiation at large hippocampal mossy fiber boutons induced by the adenylyl cyclase activator forskolin. We performed two-photon imaging of the genetically encoded glutamate sensor iGlu(u) that revealed an increase in the surface area used for glutamate release at potentiated terminals. Moreover, time-gated stimulated emission depletion microscopy revealed no change in the coupling distance between immunofluorescence signals from calcium channels and release sites. Finally, by high-pressure freezing and transmission electron microscopy analysis, we found a fast remodeling of synaptic ultrastructure at potentiated boutons: synaptic vesicles dispersed in the terminal and accumulated at the active zones, while active zone density and synaptic complexity increased. We suggest that these rapid and early structural rearrangements likely enable long-term increase in synaptic strength
Weak Localization Effect in Superconductors by Radiation Damage
Large reductions of the superconducting transition temperature and
the accompanying loss of the thermal electrical resistivity (electron-phonon
interaction) due to radiation damage have been observed for several A15
compounds, Chevrel phase and Ternary superconductors, and in
the high fluence regime. We examine these behaviors based on the recent theory
of weak localization effect in superconductors. We find a good fitting to the
experimental data. In particular, weak localization correction to the
phonon-mediated interaction is derived from the density correlation function.
It is shown that weak localization has a strong influence on both the
phonon-mediated interaction and the electron-phonon interaction, which leads to
the universal correlation of and resistance ratio.Comment: 16 pages plus 3 figures, revtex, 76 references, For more information,
Plesse see http://www.fen.bilkent.edu.tr/~yjki
Second and Third Season QUaD Cosmic Microwave Background Temperature and Polarization Power Spectra
We report results from the second and third seasons of observation with the QUaD experiment. Angular
power spectra of the cosmic microwave background are derived for both temperature and polarization at
both 100 GHz and 150 GHz, and as cross-frequency spectra. All spectra are subjected to an extensive
set of jackknife tests to probe for possible systematic contamination. For the implemented data cuts and
processing technique such contamination is undetectable. We analyze the difference map formed between the
100 and 150 GHz bands and find no evidence of foreground contamination in polarization. The spectra are
then combined to form a single set of results which are shown to be consistent with the prevailing LCDM
model. The sensitivity of the polarization results is considerably better than that of any previous experimentâ
for the first time multiple acoustic peaks are detected in the E-mode power spectrum at high significance
Recommended from our members
Parity Violation Constraints Using Cosmic Microwave Background Polarization Spectra ïżŒfrom 2006 and 2007 Observations by the QUaD Polarimeter
We constrain parity-violating interactions to the surface of last scattering using spectra from the QUaD experimentâs second and third seasons of observations by searching for a possible systematic rotation of the polarization directions of cosmic microwave background photons. We measure the rotation angle due to such a possible ââcosmological birefringenceââ to be (random) (systematic) using QUaDâs 100 and 150 GHz temperature-curl and gradient-curl spectra over the spectra over the multipole range 200 << 2000, consistent with null, and constrain Lorentz-violating interactions to <2 10 GeV (68% conïŹdence limit). This is the best constraint to date on electrodynamic parity violation on cosmological scales.Astronom
Magnetic fields in supernova remnants and pulsar-wind nebulae
We review the observations of supernova remnants (SNRs) and pulsar-wind
nebulae (PWNe) that give information on the strength and orientation of
magnetic fields. Radio polarimetry gives the degree of order of magnetic
fields, and the orientation of the ordered component. Many young shell
supernova remnants show evidence for synchrotron X-ray emission. The spatial
analysis of this emission suggests that magnetic fields are amplified by one to
two orders of magnitude in strong shocks. Detection of several remnants in TeV
gamma rays implies a lower limit on the magnetic-field strength (or a
measurement, if the emission process is inverse-Compton upscattering of cosmic
microwave background photons). Upper limits to GeV emission similarly provide
lower limits on magnetic-field strengths. In the historical shell remnants,
lower limits on B range from 25 to 1000 microGauss. Two remnants show
variability of synchrotron X-ray emission with a timescale of years. If this
timescale is the electron-acceleration or radiative loss timescale, magnetic
fields of order 1 mG are also implied. In pulsar-wind nebulae, equipartition
arguments and dynamical modeling can be used to infer magnetic-field strengths
anywhere from about 5 microGauss to 1 mG. Polarized fractions are considerably
higher than in SNRs, ranging to 50 or 60% in some cases; magnetic-field
geometries often suggest a toroidal structure around the pulsar, but this is
not universal. Viewing-angle effects undoubtedly play a role. MHD models of
radio emission in shell SNRs show that different orientations of upstream
magnetic field, and different assumptions about electron acceleration, predict
different radio morphology. In the remnant of SN 1006, such comparisons imply a
magnetic-field orientation connecting the bright limbs, with a non-negligible
gradient of its strength across the remnant.Comment: 20 pages, 24 figures; to be published in SpSciRev. Minor wording
change in Abstrac
The QUAD Galactic Plane Survey 1: Maps and Analysis of Diffuse Emission
We present a survey of ~ 800 square degrees of the galactic plane observed with the QUaD telescope. The
primary product of the survey are maps of Stokes I, Q and U parameters at 100 and 150 GHz, with spatial
resolution 5 and 3.5 arcminutes respectively. Two regions are covered, spanning approximately 245 - 295°
and 315 - 5° in galactic longitude l, and -4 < b < +4° in galactic latitude b. At 0:02° square pixel size, the
median sensitivity is 74 and 107 kJy/sr at 100 GHz and 150 GHz respectively in I, and 98 and 120 kJy/sr for
Q and U. In total intensity, we find an average spectral index of α = 2:35+-0:01(stat)+-0:02(sys) for |b| â€1°,
indicative of emission components other than thermal dust. A comparison to published dust, synchrotron
and free-free models implies an excess of emission in the 100 GHz QUaD band, while better agreement is
found at 150 GHz. A smaller excess is observed when comparing QUaD 100 GHz data to WMAP 5-year
W band; in this case the excess is likely due to the wider bandwidth of QUaD. Combining the QUaD and
WMAP data, a two-component spectral fit to the inner galactic plane (|b| â€1°) yields mean spectral indices
of αs = -0:32+-0:03 and αd = 2:84+-0:03; the former is interpreted as a combination of the spectral indices
of synchrotron, free-free and dust, while the second is attributed largely to the thermal dust continuum. In
the same galactic latitude range, the polarization data show a high degree of alignment perpendicular to the
expected galactic magnetic field direction, and exhibit mean polarization fraction 1:38+-0:08(stat)+-0:1(sys)%
at 100 GHz and 1:70+-0:06(stat)+-0:1(sys)% at 150 GHz. We find agreement in polarization fraction between
QUaD 100 GHz and WMAP W band, the latter giving 1:1+-0:4%
Constraints on Dark Matter Annihilation in Clusters of Galaxies with the Fermi Large Area Telescope
Nearby clusters and groups of galaxies are potentially bright sources of
high-energy gamma-ray emission resulting from the pair-annihilation of dark
matter particles. However, no significant gamma-ray emission has been detected
so far from clusters in the first 11 months of observations with the Fermi
Large Area Telescope. We interpret this non-detection in terms of constraints
on dark matter particle properties. In particular for leptonic annihilation
final states and particle masses greater than ~200 GeV, gamma-ray emission from
inverse Compton scattering of CMB photons is expected to dominate the dark
matter annihilation signal from clusters, and our gamma-ray limits exclude
large regions of the parameter space that would give a good fit to the recent
anomalous Pamela and Fermi-LAT electron-positron measurements. We also present
constraints on the annihilation of more standard dark matter candidates, such
as the lightest neutralino of supersymmetric models. The constraints are
particularly strong when including the fact that clusters are known to contain
substructure at least on galaxy scales, increasing the expected gamma-ray flux
by a factor of ~5 over a smooth-halo assumption. We also explore the effect of
uncertainties in cluster dark matter density profiles, finding a systematic
uncertainty in the constraints of roughly a factor of two, but similar overall
conclusions. In this work, we focus on deriving limits on dark matter models; a
more general consideration of the Fermi-LAT data on clusters and clusters as
gamma-ray sources is forthcoming.Comment: accepted to JCAP, Corresponding authors: T.E. Jeltema and S. Profumo,
minor revisions to be consistent with accepted versio
Temas de bioética ambiental
Poner la mirada bioética en lo ambiental es plantearse radical- mente la pregunta por el origen y el sentido de todo cuanto existe, con el rigor interdisciplinario de las ciencias que incluyen el volver al mito, a la leyenda, y a las bellmsimas creencias ancestrales. Es toparse el ser humano con la alteridad, con lo otro diferente al +yo; pero hecho de lo mismo, y sentirse profundamente interpelado por las voces silentes de todos los seres que comparten con miritos pares la casa terrenal. Es descubrir con veneracisn y regocijo espiritual el Dios oculto en el mis- terio de la vida, e hincarse de rodillas para pedir su bendicisn. Es unir el Cielo con la Tierra, con la absoluta conviccisn de que no hay Cielo sin Tierra. en smntesis, la mirada bioitica de la ecologma nos hace trascender la inmediatez de lo concreto, para encontrar en ello la validez de lo universal que lo conforma. La vida humana cobra sentido al desvelar el sentido del mundo. Al descubrir felizmente la luminosa unidad del ser en la polmcroma diversidad de todo cuanto existe
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