74 research outputs found
Can a supernova be located by its neutrinos?
A future core-collapse supernova in our Galaxy will be detected by several
neutrino detectors around the world. The neutrinos escape from the supernova
core over several seconds from the time of collapse, unlike the electromagnetic
radiation, emitted from the envelope, which is delayed by a time of order
hours. In addition, the electromagnetic radiation can be obscured by dust in
the intervening interstellar space. The question therefore arises whether a
supernova can be located by its neutrinos alone. The early warning of a
supernova and its location might allow greatly improved astronomical
observations. The theme of the present work is a careful and realistic
assessment of this question, taking into account the statistical significance
of the various neutrino signals. Not surprisingly, neutrino-electron forward
scattering leads to a good determination of the supernova direction, even in
the presence of the large and nearly isotropic background from other reactions.
Even with the most pessimistic background assumptions, SuperKamiokande (SK) and
the Sudbury Neutrino Observatory (SNO) can restrict the supernova direction to
be within circles of radius and , respectively. Other
reactions with more events but weaker angular dependence are much less useful
for locating the supernova. Finally, there is the oft-discussed possibility of
triangulation, i.e., determination of the supernova direction based on an
arrival time delay between different detectors. Given the expected statistics
we show that, contrary to previous estimates, this technique does not allow a
good determination of the supernova direction.Comment: 11 pages including 2 figures. Revised version corrects typos, adds
some brief comment
Cosmological Perturbations Generated in the Colliding Bubble Braneworld Universe
We compute the cosmological perturbations generated in the colliding bubble
braneworld universe in which bubbles filled with five-dimensional anti-de
Sitter space (AdS5)expanding within a five dimensional de Sitter space (dS5) or
Minkowski space (M5) collide to form a (3+1) dimensional local brane on which
the cosmology is virtually identical to that of the Randall-Sundrum model. The
perturbation calculation presented here is valid to linear order but treats the
fluctuations of the expanding bubbles as (3+1) dimensional fields localized on
the bubble wall. We find that for bubbles expanding in dS5 the dominant
contribution to the power spectrum is `red' but very small except in certain
cases where the fifth dimension is not large or the bubbles have expanded to
far beyond the dS5 apparent horizon length. This paper supersedes a previous
version titled "Exactly Scale-Invariant Cosmological Perturbations From a
Colliding Bubble Braneworld Universe" in which we erroneously claimed that a
scale-invariant spectrum results for the case of bubbles expanding in M5. This
present paper corrects the errors of the previous version and extends the
analysis to the more interesting and general case of bubbles expanding in dS5.Comment: 29 pages Latex with eps figures. Major errors in the original version
of the paper corrected and analysis extended to bubbles expanding in dS
Evidence for the existence of powder sub-populations in micronized materials : Aerodynamic size-fractions of aerosolized powders possess distinct physicochemical properties
This article is distributed under the terms of the Creative Commons Attribution License which permits any use, distribution, and reproduction in any medium, provided the original author(s) and the source are credited.Purpose: To investigate the agglomeration behaviour of the fine ( 12.8 µm) particle fractions of salmeterol xinafoate (SX) and fluticasone propionate (FP) by isolating aerodynamic size fractions and characterising their physicochemical and re-dispersal properties. Methods: Aerodynamic fractionation was conducted using the Next Generation Impactor (NGI). Re-crystallized control particles, unfractionated and fractionated materials were characterized for particle size, morphology, crystallinity and surface energy. Re-dispersal of the particles was assessed using dry dispersion laser diffraction and NGI analysis. Results: Aerosolized SX and FP particles deposited in the NGI as agglomerates of consistent particle/agglomerate morphology. SX particles depositing on Stages 3 and 5 had higher total surface energy than unfractionated SX, with Stage 5 particles showing the greatest surface energy heterogeneity. FP fractions had comparable surface energy distributions and bulk crystallinity but differences in surface chemistry. SX fractions demonstrated higher bulk disorder than unfractionated and re-crystallized particles. Upon aerosolization, the fractions differed in their intrinsic emission and dispersion into a fine particle fraction (< 5.0 µm). Conclusions: Micronized powders consisted of sub-populations of particles displaying distinct physicochemical and powder dispersal properties compared to the unfractionated bulk material. This may have implications for the efficiency of inhaled drug deliveryPeer reviewe
Brane Big-Bang Brought by Bulk Bubble
We propose an alternative inflationary universe scenario in the context of
Randall-Sundrum braneworld cosmology. In this new scenario the existence of
extra-dimension(s) plays an essential role. First, the brane universe is
initially in the inflationary phase driven by the effective cosmological
constant induced by small mismatch between the vacuum energy in the
5-dimensional bulk and the brane tension. This mismatch arises since the bulk
is initially in a false vacuum. Then, the false vacuum decay occurs, nucleating
a true vacuum bubble with negative energy inside the bulk. The nucleated bubble
expands in the bulk and consequently hits the brane, bringing a hot big-bang
brane universe of the Randall-Sundrum type. Here, the termination of the
inflationary phase is due to the change of the bulk vacuum energy. The bubble
kinetic energy heats up the universe. As a simple realization, we propose a
model, in which we assume an interaction between the brane and the bubble. We
derive the constraints on the model parameters taking into account the
following requirements: solving the flatness problem, no force which prohibits
the bubble from colliding with the brane, sufficiently high reheating
temperature for the standard nucleosynthesis to work, and the recovery of
Newton's law up to 1mm. We find that a fine tuning is needed in order to
satisfy the first and the second requirements simultaneously, although, the
other constraints are satisfied in a wide range of the model parameters.Comment: 20pages, 5figures, some references added, the previous manuscript has
been largely improve
Neuropeptide S-Mediated Facilitation of Synaptic Transmission Enforces Subthreshold Theta Oscillations within the Lateral Amygdala
The neuropeptide S (NPS) receptor system modulates neuronal circuit activity in
the amygdala in conjunction with fear, anxiety and the expression and extinction
of previously acquired fear memories. Using in vitro brain
slice preparations of transgenic GAD67-GFP (Δneo) mice, we investigated the
effects of NPS on neural activity in the lateral amygdala as a key region for
the formation and extinction of fear memories. We are able to demonstrate that
NPS augments excitatory glutamatergic synaptic input onto both projection
neurons and interneurons of the lateral amygdala, resulting in enhanced spike
activity of both types of cells. These effects were at least in part mediated by
presynaptic mechanisms. In turn, inhibition of projection neurons by local
interneurons was augmented by NPS, and subthreshold oscillations were
strengthened, leading to their shift into the theta frequency range. These data
suggest that the multifaceted effects of NPS on amygdaloid circuitry may shape
behavior-related network activity patterns in the amygdala and reflect the
peptide's potent activity in various forms of affective behavior and
emotional memory
Functional Clustering Drives Encoding Improvement in a Developing Brain Network during Awake Visual Learning
Sensory experience drives dramatic structural and functional plasticity in developing neurons. However, for single-neuron plasticity to optimally improve whole-network encoding of sensory information, changes must be coordinated between neurons to ensure a full range of stimuli is efficiently represented. Using two-photon calcium imaging to monitor evoked activity in over 100 neurons simultaneously, we investigate network-level changes in the developing Xenopus laevis tectum during visual training with motion stimuli. Training causes stimulus-specific changes in neuronal responses and interactions, resulting in improved population encoding. This plasticity is spatially structured, increasing tuning curve similarity and interactions among nearby neurons, and decreasing interactions among distant neurons. Training does not improve encoding by single clusters of similarly responding neurons, but improves encoding across clusters, indicating coordinated plasticity across the network. NMDA receptor blockade prevents coordinated plasticity, reduces clustering, and abolishes whole-network encoding improvement. We conclude that NMDA receptors support experience-dependent network self-organization, allowing efficient population coding of a diverse range of stimuli.Canadian Institutes of Health Researc
M-CSF Induces Monocyte Survival by Activating NF-κB p65 Phosphorylation at Ser276 via Protein Kinase C
Macrophage colony-stimulating factor (M-CSF) promotes mononuclear phagocyte survival and proliferation. The transcription factor Nuclear Factor-kappaB (NF-κB) is a key regulator of genes involved in M-CSF-induced mononuclear phagocyte survival and this study focused at identifying the mechanism of NF-κB transcriptional activation. Here, we demonstrate that M-CSF stimulated NF-κB transcriptional activity in human monocyte-derived macrophages (MDMs) and the murine macrophage cell line RAW 264.7. The general protein kinase C (PKC) inhibitor Ro-31-8220, the conventional PKCα/β inhibitor Gö-6976, overexpression of dominant negative PKCα constructs and PKCα siRNA reduced NF-κB activity in response to M-CSF. Interestingly, Ro-31-8220 reduced Ser276 phosphorylation of NF-κBp65 leading to decreased M-CSF-induced monocyte survival. In this report, we identify conventional PKCs, including PKCα as important upstream kinases for M-CSF-induced NF-κB transcriptional activation, NF-κB-regulated gene expression, NF-κB p65 Ser276 phosphorylation, and macrophage survival. Lastly, we find that NF-κB p65 Ser276 plays an important role in basal and M-CSF-stimulated NF-κB activation in human mononuclear phagocytes
Inflation and Braneworlds: Degeneracies and Consistencies
Scalar and tensor perturbations arising in an inflationary braneworld
scenario driven by a single scalar field are considered, where the bulk on
either side of the brane corresponds to Anti-de Sitter spaces with different
cosmological constants. A consistency relation between the two spectra is
derived and found to have an identical form to that arising in standard
single-field inflation based on conventional Einstein gravity. The dS/CFT
correspondence may provide further insight into the origin of this degeneracy.
Possible ways of lifting such a degeneracy are discussed.Comment: 10 page
The Inflationary Energy Scale in Braneworld Cosmology
Upper bounds on the energy scale at the end of inflation in the
Randall-Sundrum type II braneworld scenario are derived. The analysis is made
exact by introducing new parameters that represent extensions of the Hubble
flow parameters. Only very weak assumptions about the form of the inflaton
potential are made. In the high energy and slow roll regime the bounds depend
on the amplitude of gravitational waves produced during inflation and become
stronger as this amplitude increases.Comment: 10 pages, 3 figure
Supplement: "Localization and broadband follow-up of the gravitational-wave transient GW150914" (2016, ApJL, 826, L13)
This Supplement provides supporting material for Abbott et al. (2016a). We briefly summarize past electromagnetic (EM) follow-up efforts as well as the organization and policy of the current EM follow-up program. We compare the four probability sky maps produced for the gravitational-wave transient GW150914, and provide additional details of the EM follow-up observations that were performed in the different bands
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