394,265 research outputs found
Statistical study of free magnetic energy and flare productivity of solar active regions
Photospheric vector magnetograms from Helioseismic and Magnetic Imager on
board the Solar Dynamic Observatory are utilized as the boundary conditions to
extrapolate both non-linear force-free and potential magnetic fields in solar
corona. Based on the extrapolations, we are able to determine the free magnetic
energy (FME) stored in active regions (ARs). Over 3000 vector magnetograms in
61 ARs were analyzed. We compare FME with ARs' flare index (FI) and find that
there is a weak correlation () between FME and FI. FME shows slightly
improved flare predictability relative to total unsigned magnetic flux of ARs
in the following two aspects: (1) the flare productivity predicted by FME is
higher than that predicted by magnetic flux and (2) the correlation between FI
and FME is higher than that between FI and magnetic flux. However, this
improvement is not significant enough to make a substantial difference in
time-accumulated FI, rather than individual flare, predictions.Comment: The paper was submitted to ApJ and it is accepted no
Exponential Decay for Damped Klein-Gordon Equations on Asymptotically Cylindrical and Conic Manifolds
We study the decay of the global energy for the damped Klein-Gordon equation
on non-compact manifolds with finitely many cylindrical and subconic ends up to
bounded perturbation. We prove that under the Geometric Control Condition, the
decay is exponential, and that under the weaker Network Control Condition, the
decay is logarithmic, by developing the global Carleman estimate with multiple
weights
Recommended from our members
Can the persistence of a currency crisis be explained by fundamentals? Markov switching models for exchange market pressure
This paper investigates the contribution of fundamentals to the persistence of currency crises by identifying the determinants of high volatility in the exchange market pressure index (empi) for some new EU member states. The Markov switching model is utilised to identify the high volatility of empi, and a linear regression analysis is conducted to find the sources of the transition probability of the high volatility regime. The evidence does not seem to provide strong support for macroeconomic fundamentals, whereas it highlights the adverse movement of interest rates as the major determinant of the persistence of the currency crisis
Recommended from our members
Learning occupants’ indoor comfort temperature through a Bayesian inference approach for office buildings in United States
A carefully chosen indoor comfort temperature as the thermostat set-point is the key to optimizing building energy use and occupants’ comfort and well-being. ASHRAE Standard 55 or ISO Standard 7730 uses the PMV-PPD model or the adaptive comfort model that is based on small-sized or outdated sample data, which raises questions on whether and how ranges of occupant thermal comfort temperature should be revised using more recent larger-sized dataset. In this paper, a Bayesian inference approach has been used to derive new occupant comfort temperature ranges for U.S. office buildings using the ASHRAE Global Thermal Comfort Database. Bayesian inference can express uncertainty and incorporate prior knowledge. The comfort temperatures were found to be higher and less variable at cooling mode than at heating mode, and with significant overlapped variation ranges between the two modes. The comfort operative temperature of occupants varies between 21.9 and 25.4 °C for the cooling mode with a median of 23.7 °C, and between 20.5 and 24.9 °C for the heating mode with a median of 22.7 °C. These comfort temperature ranges are similar to the current ASHRAE standard 55 in the heating mode but 2–3 °C lower in the cooling mode. The results of this study could be adopted as more realistic thermostat set-points in building design, operation, control optimization, energy performance analysis, and policymaking
Composite fermi liquids in the lowest Landau level
We study composite fermi liquid (CFL) states in the lowest Landau level (LLL)
limit at a generic filling . We begin with the old
observation that, in compressible states, the composite fermion in the lowest
Landau level should be viewed as a charge-neutral particle carrying vorticity.
This leads to the absence of a Chern-Simons term in the effective theory of the
CFL. We argue here that instead a Berry curvature should be enclosed by the
fermi surface of composite fermions, with the total Berry phase fixed by the
filling fraction . We illustrate this point with the CFL of
fermions at filling fractions and (single and two-component) bosons
at . The Berry phase leads to sharp consequences in the transport
properties including thermal and spin Hall conductances, which in the RPA
approximation are distinct from the standard Halperin-Lee-Read predictions. We
emphasize that these results only rely on the LLL limit, and do not require
particle-hole symmetry, which is present microscopically only for fermions at
. Nevertheless, we show that the existing LLL theory of the composite
fermi liquid for bosons at does have an emergent particle-hole
symmetry. We interpret this particle-hole symmetry as a transformation between
the empty state at and the boson integer quantum hall state at .
This understanding enables us to define particle-hole conjugates of various
bosonic quantum Hall states which we illustrate with the bosonic Jain and
Pfaffian states. The bosonic particle-hole symmetry can be realized exactly on
the surface of a three-dimensional boson topological insulator. We also show
that with the particle-hole and spin rotation symmetries, there is no
gapped topological phase for bosons at .Comment: 16 pages, 1 figure, new version with minor change
- …