4,309 research outputs found
On methods for correcting for the look-elsewhere effect in searches for new physics
The search for new significant peaks over a energy spectrum often involves a
statistical multiple hypothesis testing problem. Separate tests of hypothesis
are conducted at different locations producing an ensemble of local p-values,
the smallest of which is reported as evidence for the new resonance.
Unfortunately, controlling the false detection rate (type I error rate) of such
procedures may lead to excessively stringent acceptance criteria. In the recent
physics literature, two promising statistical tools have been proposed to
overcome these limitations. In 2005, a method to "find needles in haystacks"
was introduced by Pilla et al. [1], and a second method was later proposed by
Gross and Vitells [2] in the context of the "look elsewhere effect" and trial
factors. We show that, for relatively small sample sizes, the former leads to
an artificial inflation of statistical power that stems from an increase in the
false detection rate, whereas the two methods exhibit similar performance for
large sample sizes. We apply the methods to realistic simulations of the Fermi
Large Area Telescope data, in particular the search for dark matter
annihilation lines. Further, we discuss the counter-intutive scenario where the
look-elsewhere corrections are more conservative than much more computationally
efficient corrections for multiple hypothesis testing. Finally, we provide
general guidelines for navigating the tradeoffs between statistical and
computational efficiency when selecting a statistical procedure for signal
detection
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Preclinical translation of exosomes derived from mesenchymal stem/stromal cells.
Exosomes are nanovesicles secreted by virtually all cells. Exosomes mediate the horizontal transfer of various macromolecules previously believed to be cell-autonomous in nature, including nonsecretory proteins, various classes of RNA, metabolites, and lipid membrane-associated factors. Exosomes derived from mesenchymal stem/stromal cells (MSCs) appear to be particularly beneficial for enhancing recovery in various models of disease. To date, there have been more than 200 preclinical studies of exosome-based therapies in a number of different animal models. Despite a growing number of studies reporting the therapeutic properties of MSC-derived exosomes, their underlying mechanism of action, pharmacokinetics, and scalable manufacturing remain largely outstanding questions. Here, we review the global trends associated with preclinical development of MSC-derived exosome-based therapies, including immunogenicity, source of exosomes, isolation methods, biodistribution, and disease categories tested to date. Although the in vivo data assessing the therapeutic properties of MSC-exosomes published to date are promising, several outstanding questions remain to be answered that warrant further preclinical investigation
Type-II Bose-Mott insulators
The Mott insulating state formed from bosons is ubiquitous in solid He-4,
cold atom systems, Josephson junction networks and perhaps underdoped high-Tc
superconductors. We predict that close to the quantum phase transition to the
superconducting state the Mott insulator is not at all as featureless as is
commonly believed. In three dimensions there is a phase transition to a low
temperature state where, under influence of an external current, a
superconducting state consisting of a regular array of 'wires' that each carry
a quantized flux of supercurrent is realized. This prediction of the "type-II
Mott insulator" follows from a field theoretical weak-strong duality, showing
that this 'current lattice' is the dual of the famous Abrikosov lattice of
magnetic fluxes in normal superconductors. We argue that this can be exploited
to investigate experimentally whether preformed Cooper pairs exist in high-Tc
superconductors.Comment: RevTeX, 17 pages, 6 figures, published versio
Energy-resolved inelastic electron scattering off a magnetic impurity
We study inelastic scattering of energetic electrons off a Kondo impurity. If
the energy E of the incoming electron (measured from the Fermi level) exceeds
significantly the Kondo temperature T_K, then the differential inelastic
cross-section \sigma (E,w), i.e., the cross-section characterizing scattering
of an electron with a given energy transfer w, is well-defined. We show that
\sigma (E,w) factorizes into two parts. The E-dependence of \sigma (E,w) is
logarithmically weak and is due to the Kondo renormalization of the effective
coupling. We are able to relate the w-dependence to the spin-spin correlation
function of the magnetic impurity. Using this relation, we demonstrate that in
the absence of magnetic field the dynamics of the impurity spin causes the
electron scattering to be inelastic at any temperature. Quenching of the spin
dynamics by an applied magnetic field results in a finite elastic component of
the electron scattering cross-section. The differential scattering
cross-section may be extracted from the measurements of relaxation of hot
electrons injected in conductors containing localized spins.Comment: 15 pages, 9 figures; final version as published, minor changes,
reference adde
Nearly free electrons in the layered oxide superconductor Ag5Pb2O6
We present first measurements of quantum oscillations in the layered oxide
superconductor
Ag5Pb2O6. From a detailed angular and temperature dependent study of the dHvA
effect we determine the electronic structure and demonstrate that the electron
masses are very light, m^* is approximately equalt to 1.2 m_e. The Fermi
surface we observe is essentially that expected of nearly-free electrons -
establishing
Ag5Pb2O6 as the first known example of a monovalent, nearly-free electron
superconductor at ambient pressure.Comment: 4 pages, 3 figure
Training telescope operators and support astronomers at Paranal
The operations model of the Paranal Observatory relies on the work of
efficient staff to carry out all the daytime and nighttime tasks. This is
highly dependent on adequate training. The Paranal Science Operations
department (PSO) has a training group that devises a well-defined and
continuously evolving training plan for new staff, in addition to broadening
and reinforcing courses for the whole department. This paper presents the
training activities for and by PSO, including recent astronomical and quality
control training for operators, as well as adaptive optics and interferometry
training of all staff. We also present some future plans.Comment: Paper 9910-123 presented at SPIE 201
A Combined Geometric Morphometric and Discrete Element Modeling Approach for Hip Cartilage Contact Mechanics.
Finite element analysis (FEA) provides the current reference standard for numerical simulation of hip cartilage contact mechanics. Unfortunately, the development of subject-specific FEA models is a laborious process. Owed to its simplicity, Discrete Element Analysis (DEA) provides an attractive alternative to FEA. Advancements in computational morphometrics, specifically statistical shape modeling (SSM), provide the opportunity to predict cartilage anatomy without image segmentation, which could be integrated with DEA to provide an efficient platform to predict cartilage contact stresses in large populations. The objective of this study was, first, to validate linear and non-linear DEA against a previously validated FEA model and, second, to present and evaluate the applicability of a novel population-averaged cartilage geometry prediction method against previously used methods to estimate cartilage anatomy. The population-averaged method is based on average cartilage thickness maps and therefore allows for a more accurate and individualized cartilage geometry estimation when combined with SSM. The root mean squared error of the population-averaged cartilage geometry predicted by SSM as compared to the manually segmented cartilage geometry was 0.31 ± 0.08 mm. Identical boundary and loading conditions were applied to the DEA and FEA models. Predicted DEA stress distribution patterns and magnitude of peak stresses were in better agreement with FEA for the novel cartilage anatomy prediction method as compared to commonly used parametric methods based on the estimation of acetabular and femoral head radius. Still, contact stress was overestimated and contact area was underestimated for all cartilage anatomy prediction methods. Linear and non-linear DEA methods differed mainly in peak stress results with the non-linear definition being more sensitive to detection of high peak stresses. In conclusion, DEA in combination with the novel population-averaged cartilage anatomy prediction method provided accurate predictions while offering an efficient platform to conduct population-wide analyses of hip contact mechanics
Parallelizing Julia with a Non-Invasive DSL (Artifact)
This artifact is based on ParallelAccelerator, an embedded domain-specific language (DSL) and compiler for speeding up compute-intensive Julia programs. In particular, Julia code that makes heavy use of aggregate array operations is a good candidate for speeding up with ParallelAccelerator. ParallelAccelerator is a non-invasive DSL that makes as few changes to the host programming model as possible
Parallelizing Julia with a Non-Invasive DSL
Computational scientists often prototype software using productivity
languages that offer high-level programming abstractions. When higher
performance is needed, they are obliged to rewrite their code in a
lower-level efficiency language. Different solutions have been
proposed to address this trade-off between productivity and
efficiency. One promising approach is to create embedded
domain-specific languages that sacrifice generality for productivity
and performance, but practical experience with DSLs points to some
road blocks preventing widespread adoption. This paper proposes a
non-invasive domain-specific language that makes as few visible
changes to the host programming model as possible. We present ParallelAccelerator,
a library and compiler for high-level, high-performance scientific
computing in Julia. ParallelAccelerator\u27s programming model is aligned with existing
Julia programming idioms. Our compiler exposes the implicit
parallelism in high-level array-style programs and compiles them to
fast, parallel native code. Programs can also run in "library-only"
mode, letting users benefit from the full Julia environment and
libraries. Our results show encouraging performance improvements with very few changes to source code required. In particular, few to no additional type annotations are necessary
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