832 research outputs found
The Kontsevich constants for the volume of the moduli of curves and topological recursion
We give an Eynard-Orantin type topological recursion formula for the
canonical Euclidean volume of the combinatorial moduli space of pointed smooth
algebraic curves. The recursion comes from the edge removal operation on the
space of ribbon graphs. As an application we obtain a new proof of the
Kontsevich constants for the ratio of the Euclidean and the symplectic volumes
of the moduli space of curves.Comment: 37 pages with 20 figure
The Compositional Structure of the Asteroid Belt
The past decade has brought major improvements in large-scale asteroid
discovery and characterization with over half a million known asteroids and
over 100,000 with some measurement of physical characterization. This explosion
of data has allowed us to create a new global picture of the Main Asteroid
Belt. Put in context with meteorite measurements and dynamical models, a new
and more complete picture of Solar System evolution has emerged. The question
has changed from "What was the original compositional gradient of the Asteroid
Belt?" to "What was the original compositional gradient of small bodies across
the entire Solar System?" No longer is the leading theory that two belts of
planetesimals are primordial, but instead those belts were formed and sculpted
through evolutionary processes after Solar System formation. This article
reviews the advancements on the fronts of asteroid compositional
characterization, meteorite measurements, and dynamical theories in the context
of the heliocentric distribution of asteroid compositions seen in the Main Belt
today. This chapter also reviews the major outstanding questions relating to
asteroid compositions and distributions and summarizes the progress and current
state of understanding of these questions to form the big picture of the
formation and evolution of asteroids in the Main Belt. Finally, we briefly
review the relevance of asteroids and their compositions in their greater
context within our Solar System and beyond.Comment: Accepted chapter in Asteroids IV in the Space Science Series to be
published Fall 201
On Optimizing the Conditional Value-at-Risk of a Maximum Cost for Risk-Averse Safety Analysis
The popularity of Conditional Value-at-Risk (CVaR), a risk functional from
finance, has been growing in the control systems community due to its intuitive
interpretation and axiomatic foundation. We consider a non-standard optimal
control problem in which the goal is to minimize the CVaR of a maximum random
cost subject to a Borel-space Markov decision process. The objective takes the
form , where is a
risk-aversion parameter representing a fraction of worst cases, is a
stage or terminal cost, and is the length of a finite
discrete-time horizon. The objective represents the maximum departure from a
desired operating region averaged over a given fraction of worst
cases. This problem provides a safety criterion for a stochastic system that is
informed by both the probability and severity of the potential consequences of
the system's trajectory. In contrast, existing safety analysis frameworks apply
stage-wise risk constraints (i.e., must be small for all , where
is a risk functional) or assess the probability of constraint violation
without quantifying its possible severity. To the best of our knowledge, the
problem of interest has not been solved. To solve the problem, we propose and
study a family of stochastic dynamic programs on an augmented state space. We
prove that the optimal CVaR of a maximum cost enjoys an equivalent
representation in terms of the solutions to this family of dynamic programs
under appropriate assumptions. We show the existence of an optimal policy that
depends on the dynamics of an augmented state under a measurable selection
condition. Moreover, we demonstrate how our safety analysis framework is useful
for assessing the severity of combined sewer overflows under precipitation
uncertainty.Comment: A shorter version is under review for IEEE Transactions on Automatic
Control, submitted December 202
What Do We Know About What to Do With Dams? How Knowledge Shapes Public Opinion About Their Removal in New Hampshire
In this brief, authors Simone Chapman, Catherine Ashcraft, Lawrence Hamilton, and Kevin Gardner report the results of an October 2018 Granite State Poll that asked 607 New Hampshire residents how much they have heard, and their thoughts, concerning the question of whether older dams on New Hampshire rivers should be removed for ecological or safety reasons, or whether the dams should be kept.
Most people admitted they have not heard or read about this issue, but at the same time they agreed that dams could be removed in at least some cases. The more people heard or read about the issue of dam removal, the more likely they were to support removal in some or most cases. These survey results highlight the need for communicating sound information to the public concerning the costs and benefits of possible dam management options— whether doing nothing, repairs and maintenance, or removal
DATA SHARING TO DRIVE THE IMPROVEMENT OF TEACHER PREPARATION PROGRAMS
Background/Context: Teacher preparation programs (TPPs) face increasing pressure from the federal government, states, and accreditation agencies to improve the quality of their practices and graduates, yet they often do not possess enough data to make evidence-based reforms. Purpose/Objective: This manuscript has four objectives: (a) to present the strengths and shortcomings of accountability-based TPP evaluation systems; (b) to detail the individual-level data being shared with TPPs at public universities in North Carolina; (c) to describe how data sharing can lead to TPP improvement and the challenges that programs will need to overcome; and (d) to detail how three TPPs are using the data for program improvement. Setting: North Carolina public schools and schools of education at public universities in North Carolina. Importantly, this individual-level data sharing system can be instituted among TPPs in other states. Population/Participants/Subjects: Teachers initially-prepared b
Orbital Dimer Model for Spin-Glass State in YMoO
The formation of a spin glass usually requires both structural disorder and
frustrated magnetic interactions. Consequently, the origin of spin-glass
behaviour in YMoO in which magnetic Mo ions occupy a
frustrated pyrochlore lattice with minimal compositional disorder has been
a longstanding question. Here, we use neutron and X-ray pair-distribution
function (PDF) analysis to develop a disorder model that resolves apparent
incompatibilities between previously-reported PDF, EXAFS and NMR studies and
provides a new and physical mechanism for spin-glass formation. We show that
Mo ions displace according to a local "2-in/2-out" rule on each Mo
tetrahedron, driven by orbital dimerisation of Jahn-Teller active Mo
ions. Long-range orbital order is prevented by the macroscopic degeneracy of
dimer coverings permitted by the pyrochlore lattice. Cooperative O
displacements yield a distribution of MoOMo angles, which in turn
introduces disorder into magnetic interactions. Our study demonstrates
experimentally how frustration of atomic displacements can assume the role of
compositional disorder in driving a spin-glass transition.Comment: 6 pages, 3 figure
Recommended from our members
Continuous Spikes and Waves during Sleep: Electroclinical Presentation and Suggestions for Management
Continuous spikes and waves during sleep (CSWS) is an epileptic encephalopathy characterized in most patients by (1) difficult to control seizures, (2) interictal epileptiform activity that becomes prominent during sleep leading to an electroencephalogram (EEG) pattern of electrical status epilepticus in sleep (ESES), and (3) neurocognitive regression. In this paper, we will summarize current epidemiological, clinical, and EEG knowledge on CSWS and will provide suggestions for treatment. CSWS typically presents with seizures around 2–4 years of age. Neurocognitive regression occurs around 5-6 years of age, and it is accompanied by subacute worsening of EEG abnormalities and seizures. At approximately 6–9 years of age, there is a gradual resolution of seizures and EEG abnormalities, but the neurocognitive deficits persist in most patients. The cause of CSWS is unknown, but early developmental lesions play a major role in approximately half of the patients, and genetic associations have recently been described. High-dose benzodiazepines and corticosteroids have been successfully used to treat clinical and electroencephalographic features. Corticosteroids are often reserved for refractory disease because of adverse events. Valproate, ethosuximide, levetiracetam, sulthiame, and lamotrigine have been also used with some success. Epilepsy surgery may be considered in a few selected patients
NMP-7 inhibits chronic inflammatory and neuropathic pain via block of Cab3.2 T-type calcium channels and activation of CB2 receptors
Background: T-type calcium channels and cannabinoid receptors are known to play important roles in chronic pain, making them attractive therapeutic targets. We recently reported on the design, synthesis and analgesic properties of a novel T-type channel inhibitor (NMP-7), which also shows mixed agonist activity on CB1 and CB2 receptors in vitro. Here, we analyzed the analgesic effect of systemically delivered NMP-7 (intraperitoneal (i.p.) or intragstric (i.g.) routes) on mechanical hypersensitivity in inflammatory pain induced by Complete Freund’s Adjuvant (CFA) and neuropathic pain induced by sciatic nerve injury.
Results: NMP-7 delivered by either i.p. or i.g. routes produced dose-dependent inhibition of mechanical hyperalgesia in mouse models of inflammatory and neuropathic pain, without altering spontaneous locomotor activity in the open-field test at the highest active dose. Neither i.p. nor i.g. treatment reduced peripheral inflammation per se, as evaluated by examining paw edema and myeloperoxidase activity. The antinociception produced by NMP-7 in the CFA test was completely abolished in CaV3.2-null mice, confirming CaV3.2 as a key target. The analgesic action of intraperitoneally delivered NMP-7 was not affected by pretreatment of mice with the CB1 antagonist AM281, but was significantly attenuated by pretreatment with the CB2 antagonist AM630, suggesting that CB2 receptors, but not CB1 receptors are involved in the action of NMP-7 in vivo.
Conclusions: Overall, our work shows that NMP-7 mediates a significant analgesic effect in a model of persistent inflammatory and chronic neuropathic pain by way of T-type channel modulation and CB2 receptor activation. Thus, this study provides a novel therapeutic avenue for managing chronic pain conditions via mixed CB ligands/ T-type channel blockers
The 3-D kinematics of water masers around the semiregular variable RT Virginis
We report observations of water masers around the semiregular variable RT
Virginis (RT Vir), which have been made with the Very Long Baseline Array
(VLBA) of the National Radio Astronomy Observatory (NRAO) at five epochs, each
separated by three weeks of time. We detected about 60 maser features at each
epoch. Overall, 61 features, detected at least twice, were tracked by their
radial velocities and proper motions. The 3-D maser kinematics exhibited a
circumstellar envelope that is expanding roughly spherically with a velocity of
about 8 km/s. Asymmetries in both the spatial and velocity distributions of the
maser features were found in the envelope, but less significant than that found
in other semiregular variables. Systematic radial-velocity drifts of individual
maser features were found with amplitudes of <= 2 km/s/yr. For one maser
feature, we found a quadratic position shift with time along a straight line on
the sky. This apparent motion indicates an acceleration with an amplitude of 33
km/s/yr, implying the passage of a shock wave driven by the stellar pulsation
of RT Vir. The acceleration motion is likely seen only on the sky plane because
of a large velocity gradient formed in the accelerating maser region. We
estimated the distance to RT Vir to be about 220 pc on the basis of both the
statistical parallax and model-fitting methods for the maser kinematics.Comment: 18 pages, 8 figures. Accepted to appear in the Astrophysical Journa
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