3,415 research outputs found
On the cusp of cusps: a universal model for extreme scattering events in the ISM
The scattering structures in the ISM responsible for so-called ``extreme
scattering events" (ESEs), observed in quasars and pulsars, remain enigmatic.
Current models struggle to explain the high-frequency light curves of ESEs, and
a recent analysis of a double lensing event in PSR\,B0834+06 reveals features
of ESEs that may also be challenging to accommodate via existing models. We
propose that these features arise naturally when the lens has a cusp-like
profile, described by the elementary cusp catastrophe. This is an
extension of previous work describing pulsar scintillation as arising from
fold catastrophes in thin, corrugated plasma sheets along the line of
sight. We call this framework of describing the lens potentials via elementary
catastrophes ``doubly catastrophic lensing", as catastrophes (e.g. folds and
cusps) have long been used to describe universal features in the light curves
of lensing events that generically manifest, regardless of the precise details
of the lens. Here, we argue that the lenses themselves may be described by
these same elementary structures. If correct, the doubly catastrophic lensing
framework would provide a unified description of scintillation and ESEs, where
the lenses responsible for these scattering phenomena are universal and can be
fully described by a small number of unfolding parameters. This could enable
their application as giant cosmic lenses for precision measurements of coherent
sources, including FRBs and pulsars.Comment: 10 pages, 10 figure
Universal analytic properties of noise. Introducing the J-Matrix formalism
We propose a new method in the spectral analysis of noisy time-series data
for damped oscillators. From the Jacobi three terms recursive relation for the
denominators of the Pad\'e Approximations built on the well-known Z-transform
of an infinite time-series, we build an Hilbert space operator, a J-Operator,
where each bound state (inside the unit circle in the complex plane) is simply
associated to one damped oscillator while the continuous spectrum of the
J-Operator, which lies on the unit circle itself, is shown to represent the
noise. Signal and noise are thus clearly separated in the complex plane. For a
finite time series of length 2N, the J-operator is replaced by a finite order
J-Matrix J_N, having N eigenvalues which are time reversal covariant. Different
classes of input noise, such as blank (white and uniform), Gaussian and pink,
are discussed in detail, the J-Matrix formalism allowing us to efficiently
calculate hundreds of poles of the Z-transform. Evidence of a universal
behaviour in the final statistical distribution of the associated poles and
zeros of the Z-transform is shown. In particular the poles and zeros tend, when
the length of the time series goes to infinity, to a uniform angular
distribution on the unit circle. Therefore at finite order, the roots of unity
in the complex plane appear to be noise attractors. We show that the
Z-transform presents the exceptional feature of allowing lossless undersampling
and how to make use of this property. A few basic examples are given to suggest
the power of the proposed method.Comment: 14 pages, 8 figure
Considering Vermont\u27s Future in a Changing Climate: The First Vermont Climate Assessment
The Vermont Climate Assessment (VCA) paints a vivid picture of a changing climate in Vermont and calls for immediate strategic planning to sustain the social, economic and environmental fabric of our state. The VCA is the first state-scale climate assessment in the country and speaks directly to the impacts of climate change as they pertain to our rural towns, cities and communities, including impacts on Vermont tourism and recreation, agriculture, natural resources and energy
Scintillated microlensing: measuring cosmic distances with fast radio bursts
We propose a novel means of directly measuring cosmological distances using
scintillated microlensing of fast radio bursts (FRBs). In standard strong
lensing measurements of cosmic expansion, the main source of systematic
uncertainty lies in modeling the mass profile of galactic halos. Using
extra-galactic stellar microlensing to measure the Hubble constant avoids this
systematic uncertainty as the lens potential of microlenses depends only on a
single parameter: the mass of the lens. FRBs, which may achieve nanosecond
precision on lensing time delays, are well-suited to precision measurements of
stellar microlensing, for which the time delays are on the order of
milliseconds. However, typical angular separations between the microlensed
images on the order of microarcseconds make the individual images impossible to
spatially resolve with ground-based telescopes. We propose leveraging
scintillation in the ISM to resolve the microlensed images, effectively turning
the ISM into an astrophysical-scale interferometer. Using this technique, we
estimate a 6\% uncertainty on from a single observed scintillated
microlensing event, with a sub-percent uncertainty on achievable with
only 30 such events. With an optical depth for stellar microlensing of
, this may be achievable in the near future with upcoming FRB
telescopes
When the magic closes: Examining how Disney fans coped with theme park and resort closures amid the COVID-19 pandemic
This essay discusses a qualitative investigation we conducted with fans of the Disney parks and resorts during the summer of 2020 regarding the company’s handling of the COVID-19 pandemic. Specifically, 22 people responded to open-ended questions from an online survey to discuss their views of the closures and planned reopenings of the Disney parks and resorts amid the early days of the pandemic. Using social identity theory (Tajfel, 1978) and the theory of planned behavior (Ajzen, 1991), we discuss how fans react to and cope with the temporary loss of a favorite activity and how companies in the themed entertainment industry can work to engage customers during such times. Along with implications for practitioners working in themed entertainment, we also introduce areas of future investigation important to further understanding of fan behavior amid uncertainty
Computational identification and experimental characterization of substrate binding determinants of nucleotide pyrophosphatase/phosphodiesterase 7
<p>Abstract</p> <p>Background</p> <p>Nucleotide pyrophosphatase/phosphodiesterase 7 (NPP7) is the only member of the mammalian NPP enzyme family that has been confirmed to act as a sphingomyelinase, hydrolyzing sphingomyelin (SM) to form phosphocholine and ceramide. NPP7 additionally hydrolyzes lysophosphatidylcholine (LPC), a substrate preference shared with the NPP2/autotaxin(ATX) and NPP6 mammalian family members. This study utilizes a synergistic combination of molecular modeling validated by experimental site-directed mutagenesis to explore the molecular basis for the unique ability of NPP7 to hydrolyze SM.</p> <p>Results</p> <p>The catalytic function of NPP7 against SM, LPC, platelet activating factor (PAF) and para-nitrophenylphosphorylcholine (pNPPC) is impaired in the F275A mutant relative to wild type NPP7, but different impacts are noted for mutations at other sites. These results are consistent with a previously described role of F275 to interact with the choline headgroup, where all substrates share a common functionality. The L107F mutation showed enhanced hydrolysis of LPC, PAF and pNPPC but reduced hydrolysis of SM. Modeling suggests this difference can be explained by the gain of cation-pi interactions with the choline headgroups of all four substrates, opposed by increased steric crowding against the sphingoid tail of SM. Modeling also revealed that the long and flexible hydrophobic tails of substrates exhibit considerable dynamic flexibility in the binding pocket, reducing the entropic penalty that might otherwise be incurred upon substrate binding.</p> <p>Conclusions</p> <p>Substrate recognition by NPP7 includes several important contributions, ranging from cation-pi interactions between F275 and the choline headgroup of all substrates, to tail-group binding pockets that accommodate the inherent flexibility of the lipid hydrophobic tails. Two contributions to the unique ability of NPP7 to hydrolyze SM were identified. First, the second hydrophobic tail of SM occupies a second hydrophobic binding pocket. Second, the leucine residue present at position 107 contrasts with a conserved phenylalanine in NPP enzymes that do not utilize SM as a substrate, consistent with the observed reduction in SM hydrolysis by the NPP7-L107F mutant.</p
Age validation of Red Snapper, Lutjanus campechanus, and Red Drum, Sciaenops ocellatus, from the northern Gulf of Mexico using 210Po/226Ra Disequilibria in Otoliths
The effect of regular exercise on insulin sensitivity in type 2 diabetes mellitus: A systematic review and meta-analysis
The purpose of this study was to examine the effect of regular exercise training on insulin sensitivity in adults with type 2 diabetes mellitus ( T2DM ) using the pooled data available from randomised controlled trials. In addition, we sought to determine whether short-term periods of physical inactivity diminish the exercise-induced improvement in insulin sensitivity. Eligible trials included exercise interventions that involved ≥3 exercise sessions, and reported a dynamic measurement of insulin sensitivity. There was a significant pooled effect size ( ES ) for the effect of exercise on insulin sensitivity ( ES, –0.588; 95% confidence interval [CI], –0.816 to –0.359; P < 0.001 ). Of the 14 studies included for meta-analyses, nine studies reported the time of data collection from the last exercise bout. There was a significant improvement in insulin sensitivity in favour of exercise versus control between 48 and 72 hours after exercise ( ES, –0.702; 95% CI, –1.392 to –0.012; P=0.046 ); and this persisted when insulin sensitivity was measured more than 72 hours after the last exercise session ( ES, –0.890; 95% CI, –1.675 to –0.105; P=0.026 ). Regular exercise has a significant benefit on insulin sensitivity in adults with T2DM and this may persist beyond 72 hours after the last exercise session
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