991 research outputs found
The X10 Flare on 2003 October 29: Triggered by Magnetic Reconnection between Counter-Helical Fluxes?
Vector magnetograms taken at Huairou Solar Observing Station (HSOS) and Mees
Solar Observatory (MSO) reveal that the super active region (AR) NOAA 10486 was
a complex region containing current helicity flux of opposite signs. The main
positive sunspots were dominated by negative helicity fields, while positive
helicity patches persisted both inside and around the main positive sunspots.
Based on a comparison of two days of deduced current helicity density,
pronounced changes were noticed which were associated with the occurrence of an
X10 flare that peaked at 20:49 UT, 2003 October 29. The average current
helicity density (negative) of the main sunspots decreased significantly by
about 50. Accordingly, the helicity densities of counter-helical patches
(positive) were also found to decay by the same proportion or more. In
addition, two hard X-ray (HXR) `footpoints' were observed by the Reuven Ramaty
High Energy Solar Spectroscopic Imager (RHESSI} during the flare in the 50-100
keV energy range. The cores of these two HXR footpoints were adjacent to the
positions of two patches with positive current helicity which disappeared after
the flare. This strongly suggested that the X10 flare on 2003 Oct. 29 resulted
from reconnection between magnetic flux tubes having opposite current helicity.
Finally, the global decrease of current helicity in AR 10486 by ~50% can be
understood as the helicity launched away by the halo coronal mass ejection
(CME) associated with the X10 flare.Comment: Solar Physics, 2007, in pres
The phase transition and the Quasi-Normal Modes of black Holes
We reexamined the argument that the quasinormal modes could be a probe of the
phase transition of a topological black hole to a hairy configuration by
investigating general scalar perturbations. We found further evidence in the
quasinormal modes for this phase transition. For the general black hole
configurations, we observed that although the quasinormal modes can present us
different phases of different configurations, there is no dramatic change in
the slope of quasinormal frequencies at the critical point of the phase
transition. More detailed studies of quasinormal modes are needed to reveal the
subtle behavior of the phase transition.Comment: Revised version, accepted for publication in JHE
Role of Gallium-67 scintigraphy in the evaluation of occult sepsis in the medical ICU
Patients in intensive care units (ICUs) frequently have multiple infections or persistent fever despite management. The aim of this study was to evaluate the diagnostic contribution of gallium-67 scintigraphy in ICU patients with suspected occult sepsis. One hundred and seventeen patients (> 18 years) who had undergone gallium-67 scintigraphy in the ICU of our medical center over a 3-year period were retrospectively reviewed and analyzed. Patients were categorized into Group 1 (n = 84), those with a known infectious source, but who still had persistent fever or sepsis despite antibiotic treatment or abscess drainage; or Group 2 (n = 33), those without an evident infectious source after clinical, physical, and imaging studies. Among the 117 patients, 19 (16.2%) had a new diagnosis. In Group 1, 12 patients (14%) had a new infection, including pneumonia (4 patients), bed sore infection (2 patients), pulmonary tuberculosis (2 patients), leg cellulitis (1 patient), psoas muscle abscess (1 patient), osteomyelitis (1 patient), and infective endocarditis (1 patient). In Group 2, seven patients (21.2%) had a new infectious source, including septic arthritis (3 patients), osteomyelitis (2 patients), neck abscess (1 patient), and cholecystitis (1 patient). Significant differences were not observed between patients with positive and negative findings on gallium-67 scintigraphy in characteristics, underlying diseases, laboratory data, and outcomes. Gallium-67 scintigraphy helped to detect new or additional infectious sites, particularly bone, joint, and soft tissues. However, differences in hospital stay and mortality were not observed between patients with positive and negative findings
The CesĂ ro operator in growth Banach spaces of analytic functions
[EN] The CesA ro operator C, when acting in the classical growth Banach spaces and , for , of analytic functions on , is investigated. Based on a detailed knowledge of their spectra (due to A. Aleman and A.-M. Persson) we are able to determine the norms of these operators precisely. It is then possible to characterize the mean ergodic and related properties of C acting in these spaces. In addition, we determine the largest Banach space of analytic functions on which C maps into (resp. into ); this optimal domain space always contains (resp. ) as a proper subspace.The research of the first two authors was partially supported by the projects MTM2013-43540-P and GVA Prometeo II/2013/013.Albanese, A.; Bonet Solves, JA.; Ricker, WJ. (2016). The CesĂ ro operator in growth Banach spaces of analytic functions. Integral Equations and Operator Theory. 86(1):97-112. https://doi.org/10.1007/s00020-016-2316-zS97112861Albanese A.A., Bonet J., Ricker W.J.: Convergence of arithmetic means of operators in FrĂ©chet spaces. J. Math. Anal. Appl. 401, 160â173 (2013)Albanese, A.A., Bonet, J.,Ricker, W.J.: The CesĂ ro operator on power series spaces. Preprint (2016)Albrecht E., Miller T.L., Neumann M.M.: Spectral properties of generalized CesĂ ro operators on Hardy and weighted Bergman spaces. Archiv Math. 85, 446â459 (2005)Aleman A.: A class of integral operators on spaces of analytic functions. In: Proc. of the Winter School in Operator Theory and Complex Analysis, Univ. MĂĄlaga Secr. Publ., MĂĄlaga, pp. 3â30 (2007)Aleman A., Constantin O.: Spectra of integration operators on weighted Bergman spaces. J. Anal. Math. 109, 199â231 (2009)Aleman A., Persson A.-M.: Resolvent estimates and decomposable extensions of generalized CesĂ ro operators. J. Funct. Anal. 258, 67â98 (2010)Aleman A., Siskakis A.G.: An integral operator on H p . Complex Var. Theory Appl. 28, 149â158 (1995)Aleman A., Siskakis A.G.: Integration operators on Bergman spaces. Indiana Univ. Math. J. 46, 337â356 (1997)Bayart F., Matheron E.: Dynamics of Linear Operators. Cambridge University Press, Cambridge (2009)Bierstedt K.D., Bonet J., Galbis A.: Weighted spaces of holomorphic functions on balanced domains. Michigan Math. J. 40, 271â297 (1993)Bierstedt K.D., Bonet J., Taskinen J.: Associated weights and spaces of holomorphic functions. Studia Math. 127, 137â168 (1998)Bierstedt, K.D., Summers, W.H.: Biduals of weighted Banach spaces of analytic functions. J. Aust. Math. Soc. 54, 70â79 (1993)Bonet J., Domanski P., Lindström M.: Essential norm and weak compactness on weighted Banach spaces of analytic functions. Can. Math. Bull. 42, 139â148 (1999)Curbera G.P., Ricker W.J.: Extensions of the classical CesĂ ro operator on Hardy spaces. Math. Scand. 108, 279â290 (2011)Danikas N., Siskakis A.: The CesĂ ro operator on bounded analytic functions. Analysis 13, 295â299 (1993)Duren P.: Theory of H p Spaces. Academic Press, New York (1970)Dunford N., Schwartz J.T.:Linear Operators I: General Theory, 2nd Printing. Wiley Interscience Publ., New York (1964)Grosse-Erdmann K., Peris A.: Linear Chaos. Springer, London (2011)Harutyunyan A., Lusky W.: On the boundedness of the differentiation operator between weighted spaces of holomorphic functions. Studia Math. 184, 233â247 (2008)Hedenmalm H., Korenblum B., Zhu K.: Theory of Bergman Spaces. Grad. Texts in Math., vol. 199. Springer, New York (2000)Katzelson Y., Tzafriri L.: On power bounded operators. J. Funct. Anal. 68, 313â328 (1968)Krengel U.: Ergodic Theorems. de Gruyter Studies in Mathematics, vol. 6. Walter de Gruyter Co., Berlin (1985)Lin M.: On the uniform ergodic theorem. Proc. Am. Math. Soc. 43, 337â340 (1974)Lusky W.: On the isomorphism classes of weighted spaces of harmonic and holomorphic functions. Studia Math. 175(1), 19â40 (2006)Megginson R.E.: An Introduction to Banach Space Theory. Springer, New York (1998)Meise R., Vogt D.: Introduction to Functional Analysis. Clarendon Press, Oxford (1997)Persson A.-M.: On the spectrum of the CesĂ ro operator on spaces of analytic functions. J. Math. Anal. Appl. 340, 1180â1203 (2008)Rubel L.A., Shields A.L.: The second dual of certain spaces of analytic functions. J. Aust. Math. Soc. 11, 276â280 (1970)Shields A.L., Williams D.L.: Bounded projections, duality and multipliers in spaces of analytic functions. Trans. Am. Math. Soc. 162, 287â302 (1971)Siskakis A.: Volterra operators on spaces of analytic functionsâa survey. In: Proc. of the First Advanced Course in Operator Theory and Complex Analysis, Univ. Sevilla Serc. Publ., Seville, pp. 51â68 (2006
Global inverse optimal stabilization of stochastic nonholonomic systems
Optimality has not been addressed in existing works on control of (stochastic) nonholonomic systems.This paper presents a design of optimal controllers with respect to a meaningful cost function to globally asymptotically stabilize (in probability) nonholonomic systems affine in stochastic disturbances. The design is based on the Lyapunov direct method, the backstepping technique, and the inverse optimal control design. A class of Lyapunov functions, which are not required to be as nonlinearly strong as quadratic or quartic, is proposed for the control design. Thus, these Lyapunov functions can be applied to design of controllers for underactuated (stochastic) mechanical systems, which are usually required Lyapunov functions of a nonlinearly weak form. The proposed control design is illustrated on a kinematic cart, of which wheel velocities are perturbed by stochastic noise
Large-scale pharmacogenomic study of sulfonylureas and the QT, JT and QRS intervals: CHARGE Pharmacogenomics Working Group
Sulfonylureas, a commonly used class of medication used to treat type 2 diabetes, have been associated with an increased risk of cardiovascular disease. Their effects on QT interval duration and related electrocardiographic phenotypes are potential mechanisms for this adverse effect. In 11 ethnically diverse cohorts that included 71â857 European, African-American and Hispanic/Latino ancestry individuals with repeated measures of medication use and electrocardiogram (ECG) measurements, we conducted a pharmacogenomic genome-wide association study of sulfonylurea use and three ECG phenotypes: QT, JT and QRS intervals. In ancestry-specific meta-analyses, eight novel pharmacogenomic loci met the threshold for genome-wide significance (P<5 Ă 10â8), and a pharmacokinetic variant in CYP2C9 (rs1057910) that has been associated with sulfonylurea-related treatment effects and other adverse drug reactions in previous studies was replicated. Additional research is needed to replicate the novel findings and to understand their biological basis
A Statistical Study on Photospheric Magnetic Nonpotentiality of Active Regions and Its Relationship with Flares during Solar Cycles 22-23
A statistical study is carried out on the photospheric magnetic
nonpotentiality in solar active regions and its relationship with associated
flares. We select 2173 photospheric vector magnetograms from 1106 active
regions observed by the Solar Magnetic Field Telescope at Huairou Solar
Observing Station, National Astronomical Observatories of China, in the period
of 1988-2008, which covers most of the 22nd and 23rd solar cycles. We have
computed the mean planar magnetic shear angle (\bar{\Delta\phi}), mean shear
angle of the vector magnetic field (\bar{\Delta\psi}), mean absolute vertical
current density (\bar{|J_{z}|}), mean absolute current helicity density
(\bar{|h_{c}|}), absolute twist parameter (|\alpha_{av}|), mean free magnetic
energy density (\bar{\rho_{free}}), effective distance of the longitudinal
magnetic field (d_{E}), and modified effective distance (d_{Em}) of each
photospheric vector magnetogram. Parameters \bar{|h_{c}|}, \bar{\rho_{free}},
and d_{Em} show higher correlation with the evolution of the solar cycle. The
Pearson linear correlation coefficients between these three parameters and the
yearly mean sunspot number are all larger than 0.59. Parameters
\bar{\Delta\phi}, \bar{\Delta\psi}, \bar{|J_{z}|}, |\alpha_{av}|, and d_{E}
show only weak correlations with the solar cycle, though the nonpotentiality
and the complexity of active regions are greater in the activity maximum
periods than in the minimum periods. All of the eight parameters show positive
correlations with the flare productivity of active regions, and the combination
of different nonpotentiality parameters may be effective in predicting the
flaring probability of active regions.Comment: 20 pages, 5 figures, 4 tables, accepted for publication in Solar
Physic
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