22 research outputs found
Astrophysical and Dark Matter Interpretations of Extended Gamma-Ray Emission from the Galactic Center
We construct empirical models of the diffuse gamma-ray background toward the
Galactic Center. Including all known point sources and a template of emission
associated with interactions of cosmic rays with molecular gas, we show that
the extended emission observed previously in the Fermi Large Area Telescope
data toward the Galactic Center is detected at high significance for all
permutations of the diffuse model components. However, we find that the fluxes
and spectra of the sources in our model change significantly depending on the
background model. In particular, the spectrum of the central Sgr A
source is less steep than in previous works and the recovered spectrum of the
extended emission has large systematic uncertainties, especially at lower
energies. If the extended emission is interpreted to be due to dark matter
annihilation, we find annihilation into pure -quark and -lepton
channels to be statistically equivalent goodness of fits. In the case of the
pure -quark channel, we find a dark matter mass of
$39.4\left(^{+3.7}_{-2.9}\rm\ stat.\right)\left(\pm 7.9\rm\ sys.\right)\rm\
GeV\tau^{+} \tau^{-}9.43\left(^{+0.63}_{-0.52}\rm\ stat.\right)(\pm 1.2\rm\ sys.)\
GeV$. Alternatively, if the extended emission is interpreted to be
astrophysical in origin such as due to unresolved millisecond pulsars, we
obtain strong bounds on dark matter annihilation, although systematic
uncertainties due to the dependence on the background models are significant.Comment: 14 pages, 11 figures; v3: matches version in Phys. Rev.
Testing for New Physics: Neutrinos and the Primordial Power Spectrum
We test the sensitivity of neutrino parameter constraints from combinations
of CMB and LSS data sets to the assumed form of the primordial power spectrum
(PPS) using Bayesian model selection. Significantly, none of the tested
combinations, including recent high-precision local measurements of
and cluster abundances, indicate a signal for massive neutrinos
or extra relativistic degrees of freedom. For PPS models with a large, but
fixed number of degrees of freedom, neutrino parameter constraints do not
change significantly if the location of any features in the PPS are allowed to
vary, although neutrino constraints are more sensitive to PPS features if they
are known a priori to exist at fixed intervals in . Although there is
no support for a non-standard neutrino sector from constraints on both neutrino
mass and relativistic energy density, we see surprisingly strong evidence for
features in the PPS when it is constrained with data from Planck 2015, SZ
cluster counts, and recent high-precision local measurements of .
Conversely combining Planck with matter power spectrum and BAO measurements
yields a much weaker constraint. Given that this result is sensitive to the
choice of data this tension between SZ cluster counts, Planck and
measurements is likely an indication of unmodeled systematic
bias that mimics PPS features, rather than new physics in the PPS or neutrino
sector.Comment: 23 pages, 9 figures, 8 tables; matches version published in JCA
Discovery of a New Galactic Center Excess Consistent with Upscattered Starlight
We present a new extended gamma ray excess detected with the Fermi Satellite
Large Area Telescope toward the Galactic Center that traces the morphology of
infrared starlight emission. Combined with its measured spectrum, this new
extended source is approximately consistent with inverse Compton emission from
a high-energy electron-positron population with energies up to about 10 GeV.
Previously detected emissions tracing the 20 cm radio, interpreted as
bremsstrahlung radiation, and the Galactic Center Extended emission tracing a
spherical distribution and peaking at 2 GeV, are also detected. We show that
the inverse Compton and bremsstrahlung emissions are likely due to the same
source of electrons and positrons. All three extended emissions may be
explained within the framework of a model where the dark matter annihilates to
leptons or a model with unresolved millisecond pulsars in the Galactic Center.Comment: 13 pages and 5 figures. Version 2 was expanded to include tests to
demonstrate the robustness of results against background systematics.
Conclusions unchanged. Version 3 includes more checks and matches the
published versio
Decision Criteria for Large Vessel Occlusion Using Transcranial Doppler Waveform Morphology
Background: The current lack of effective tools for prehospital identification of Large Vessel Occlusion (LVO) represents a significant barrier to efficient triage of stroke patients and detriment to treatment efficacy. The validation of objective Transcranial Doppler (TCD) metrics for LVO detection could provide first responders with requisite tools for informing stroke transfer decisions, dramatically improving patient care.Objective: To compare the diagnostic efficacy of two such candidate metrics: Velocity Asymmetry Index (VAI), which quantifies disparity of blood flow velocity across the cerebral hemispheres, and Velocity Curvature Index (VCI), a recently proposed TCD morphological biomarker. Additionally, we investigate a simple decision tree combining both metrics.Methods: We retrospectively compare accuracy/sensitivity/specificity (ACC/SEN/SPE) of each method (relative to standard CT-Angiography) in detecting LVO in a population of 66 subjects presenting with stroke symptoms (33 with CTA-confirmed LVO), enrolled consecutively at Erlanger Southeast Regional Stroke Center in Chattanooga, TN.Results: Individual VCI and VAI metrics demonstrated robust performance, with area under receiver operating characteristic curve (ROC-AUC) of 94% and 88%, respectively. Additionally, leave-one-out cross-validation at optimal identified thresholds resulted in 88% ACC (88% SEN) for VCI, vs. 79% ACC (76% SEN) for VAI. When combined, the resultant decision tree achieved 91% ACC (94% SEN).Discussion: We conclude VCI to be superior to VAI for LVO detection, and provide evidence that simple decision criteria incorporating both metrics may further optimize.Performance: Our results suggest that machine-learning approaches to TCD morphological analysis may soon enable robust prehospital LVO identification.Registration: Was not required for this feasibility study
Model Selection and Parameter Estimation in Neutrino Cosmology and High Energy Astrophysics Around the Galactic Center
Understanding the particle nature of dark matter and determining the properties of neutrinos remain two of the most important questions within the physics community. Both problems lie within the intersection between astrophysics and particle physics, a fact which gives rise to a rich set of independent and complementary approaches to making progress on both fronts. This thesis presents three works that attempt to construct models and constrain the properties of these particles using empirical data from a large host of astronomical observations. The first work uses observations from the Fermi Gamma-ray Space Telescopeâs Large Area Telescope (Fermi LAT) to construct empirical models of the diffuse gamma-ray background in the Galactic Center (GC). A new template associated with cosmic rays interacting with molecular gas is detected with high significance. Using this new template along with other known sources of gamma-ray emission in the GC, I find that the previously detected extended gamma-ray excess is still detected for all permutations of the background model, although its properties vary significantly within the observed range of models. The second work presents a detection of a new source of gamma-ray emission in the GC that traces the morphology of infrared starlight, again using observations from the Fermi LAT. I argue that this emission is likely due to the same source of cosmic rays responsible for producing the emission associated with the molecular gas template in the previous work, and further make the case that this population of cosmic rays could be produced by the same source responsible for the GC excess. The last work explores how derived neutrino parameter constraints depend on the assumed form of the primordial power spectrum, using constraints derived from a host of cosmological data sets, including cosmic microwave background, baryon acoustic oscillation, power spectrum, cluster counts, and hubble constant measurements. I find that for a model independent reconstruction of the primordial power spectrum, neutrino parameter constraints are robust. In addition, certain data sets suggest evidence for non-standard cosmological parameters, though this could also be attributed to systematics within the data
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Identification of Pulse Onset on Cerebral Blood Flow Velocity Waveforms: A Comparative Study.
The low cost, simple, noninvasive, and continuous measurement of cerebral blood flow velocity (CBFV) by transcranial Doppler is becoming a common clinical tool for the assessment of cerebral hemodynamics. CBFV monitoring can also help with noninvasive estimation of intracranial pressure and evaluation of mild traumatic brain injury. Reliable CBFV waveform analysis depends heavily on its accurate beat-to-beat delineation. However, CBFV is inherently contaminated with various types of noise/artifacts and has a wide range of possible pathological waveform morphologies. Thus, pulse onset detection is in general a challenging task for CBFV signal. In this paper, we conducted a comprehensive comparative analysis of three popular pulse onset detection methods using a large annotated dataset of 92,794 CBFV pulses-collected from 108 subarachnoid hemorrhage patients admitted to UCLA Medical Center. We compared these methods not only in terms of their accuracy and computational complexity, but also for their sensitivity to the selection of their parameters values. The results of this comprehensive study revealed that using optimal values of the parameters obtained from sensitivity analysis, one method can achieve the highest accuracy for CBFV pulse onset detection with true positive rate (TPR) of 97.06% and positive predictivity value (PPV) of 96.48%, when error threshold is set to just less than 10 ms. We conclude that the high accuracy and low computational complexity of this method (average running time of 4ms/pulse) makes it a reliable algorithm for CBFV pulse onset detection
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Testing for new physics: neutrinos and the primordial power spectrum
We test the sensitivity of neutrino parameter constraints from combinations
of CMB and LSS data sets to the assumed form of the primordial power spectrum
(PPS) using Bayesian model selection. Significantly, none of the tested
combinations, including recent high-precision local measurements of
and cluster abundances, indicate a signal for massive neutrinos
or extra relativistic degrees of freedom. For PPS models with a large, but
fixed number of degrees of freedom, neutrino parameter constraints do not
change significantly if the location of any features in the PPS are allowed to
vary, although neutrino constraints are more sensitive to PPS features if they
are known a priori to exist at fixed intervals in . Although there is
no support for a non-standard neutrino sector from constraints on both neutrino
mass and relativistic energy density, we see surprisingly strong evidence for
features in the PPS when it is constrained with data from Planck 2015, SZ
cluster counts, and recent high-precision local measurements of .
Conversely combining Planck with matter power spectrum and BAO measurements
yields a much weaker constraint. Given that this result is sensitive to the
choice of data this tension between SZ cluster counts, Planck and
measurements is likely an indication of unmodeled systematic
bias that mimics PPS features, rather than new physics in the PPS or neutrino
sector
Analyse de séances « ordinaires » intégrant l'histoire des sciences. Regards croisés sur quatre pratiques enseignantes en sciences et en mathématiques
International audienceAs history of science appears ever more significantly in the latest high-school curricula, we present an analysis of «ordinary» sessions integrating historical elements, for 4 different teachers and in 3 school disciplines (mathematics, physics-chemistry, life-and-earth-sciences). In particular, we seek to determine what motivates these teachers to integrate history of science into their teaching, what the function they assign to it, how the historical and scientific elements are intertwined in the tasks assigned to the students, and what the type of knowledge construction is aimed for in tasks integrating historical elements. For this purpose, we use the DADE theoretical framework (Robert & Rogalski, 2002) to study the empirical data (recordings of the sessions, pre- and post-interviews with the teachers).Ă lâheure oĂč lâhistoire des sciences fait une entrĂ©e remarquĂ©e dans les programmes dâenseignement scientifique du cycle terminal, nous prĂ©sentons ici une analyse de sĂ©ances « ordinaires » intĂ©grant des Ă©lĂ©ments historiques pour quatre enseignants diffĂ©rents relevant de trois disciplines scolaires (les mathĂ©matiques, la physique-chimie et les sciences de la vie et de la Terre). Nous cherchons en particulier Ă dĂ©terminer ce qui incite ces enseignants Ă intĂ©grer de lâhistoire des sciences dans leurs cours, les fonctions quâils lui attribuent, le degrĂ© dâimbrication des Ă©lĂ©ments historiques et scientifiques dans les tĂąches proposĂ©es aux Ă©lĂšves et le type de connaissances que ces tĂąches permettent de construire lorsquâelles intĂšgrent des Ă©lĂ©ments historiques. Nous mobilisons pour cela le cadre de la double approche didactique et ergonomique (Robert & Rogalski, 2002) et nous nous appuyons dâune part, sur les enregistrements vidĂ©os de ces sĂ©ances et dâautre part, sur des entretiens ante et post sĂ©ance, ainsi que sur des entretiens dâauto-confrontation