395 research outputs found
Exact Fourier expansion in cylindrical coordinates for the three-dimensional Helmholtz Green function
A new method is presented for Fourier decomposition of the Helmholtz Green
Function in cylindrical coordinates, which is equivalent to obtaining the
solution of the Helmholtz equation for a general ring source. The Fourier
coefficients of the Helmholtz Green function are split into their half
advanced+half retarded and half advanced-half retarded components. Closed form
solutions are given for these components in terms of a Horn function and a
Kampe de Feriet function, respectively. The systems of partial differential
equations associated with these two-dimensional hypergeometric functions are
used to construct a fourth-order ordinary differential equation which both
components satisfy. A second fourth-order ordinary differential equation for
the general Fourier coefficent is derived from an integral representation of
the coefficient, and both differential equations are shown to be equivalent.
Series solutions for the various Fourier coefficients are also given, mostly in
terms of Legendre functions and Bessel/Hankel functions. These are derived from
the closed form hypergeometric solutions or an integral representation, or
both. Numerical calculations comparing different methods of calculating the
Fourier coefficients are presented
Heavy-light mesons with staggered light quarks
We demonstrate the viability of improved staggered light quarks in studies of
heavy-light systems. Our method for constructing heavy-light operators exploits
the close relation between naive and staggered fermions. The new approach is
tested on quenched configurations using several staggered actionsn combined
with nonrelativistic heavy quarks. The B_s meson kinetic mass, the hyperfine
and 1P-1S splittings in B_s, and the decay constant f_{B_s} are calculated and
compared to previous quenched lattice studies. An important technical detail,
Bayesian curve-fitting, is discussed at length.Comment: 38 pages, figures included. v2: Entry in Table IX corrected and other
minor changes, version appearing in Phys. Rev.
Novel universality class of absorbing transitions with continuously varying critical exponents
The well-established universality classes of absorbing critical phenomena are
directed percolation (DP) and directed Ising (DI) classes. Recently, the pair
contact process with diffusion (PCPD) has been investigated extensively and
claimed to exhibit a new type of critical phenomena distinct from both DP and
DI classes. Noticing that the PCPD possesses a long-term memory effect, we
introduce a generalized version of the PCPD (GPCPD) with a parameter
controlling the memory effect. The GPCPD connects the DP fixed point to the
PCPD point continuously. Monte Carlo simulations show that the GPCPD displays
novel type critical phenomena which are characterized by continuously varying
critical exponents. The same critical behaviors are also observed in models
where two species of particles are coupled cyclically. We suggest that the
long-term memory may serve as a marginal perturbation to the ordinary DP fixed
point.Comment: 13 pages + 10 figures (Full paper version
Coronal Shock Waves, EUV waves, and Their Relation to CMEs. I. Reconciliation of "EIT waves", Type II Radio Bursts, and Leading Edges of CMEs
We show examples of excitation of coronal waves by flare-related abrupt
eruptions of magnetic rope structures. The waves presumably rapidly steepened
into shocks and freely propagated afterwards like decelerating blast waves that
showed up as Moreton waves and EUV waves. We propose a simple quantitative
description for such shock waves to reconcile their observed propagation with
drift rates of metric type II bursts and kinematics of leading edges of coronal
mass ejections (CMEs). Taking account of different plasma density falloffs for
propagation of a wave up and along the solar surface, we demonstrate a close
correspondence between drift rates of type II bursts and speeds of EUV waves,
Moreton waves, and CMEs observed in a few known events.Comment: 30 pages, 15 figures. Solar Physics, published online. The final
publication is available at http://www.springerlink.co
On the structure and evolution of a polar crown prominence/filament system
Polar crown prominences are made of chromospheric plasma partially circling
the Suns poles between 60 and 70 degree latitude. We aim to diagnose the 3D
dynamics of a polar crown prominence using high cadence EUV images from the
Solar Dynamics Observatory (SDO)/AIA at 304 and 171A and the Ahead spacecraft
of the Solar Terrestrial Relations Observatory (STEREO-A)/EUVI at 195A. Using
time series across specific structures we compare flows across the disk in 195A
with the prominence dynamics seen on the limb. The densest prominence material
forms vertical columns which are separated by many tens of Mm and connected by
dynamic bridges of plasma that are clearly visible in 304/171A two-color
images. We also observe intermittent but repetitious flows with velocity 15
km/s in the prominence that appear to be associated with EUV bright points on
the solar disk. The boundary between the prominence and the overlying cavity
appears as a sharp edge. We discuss the structure of the coronal cavity seen
both above and around the prominence. SDO/HMI and GONG magnetograms are used to
infer the underlying magnetic topology. The evolution and structure of the
prominence with respect to the magnetic field seems to agree with the filament
linkage model.Comment: 24 pages, 14 figures, Accepted for publication in Solar Physics
Journal, Movies can be found at http://www2.mps.mpg.de/data/outgoing/panesar
PROTOCOL: Gender transformative approaches in agriculture for women's empowerment: a systematic review
Open Access Journal; Published online: 09 Jul 2022This is the protocol for a Campbell systematic review. The objective of this systematic review is to assess the effectiveness of interventions with gender transformative approach (GTA) components in improving women's empowerment in low- and middle-income countries, and to curate evidence on the mechanisms through which GTA works to improve women's empowerment in agriculture
What is the Nature of EUV Waves? First STEREO 3D Observations and Comparison with Theoretical Models
One of the major discoveries of the Extreme ultraviolet Imaging Telescope
(EIT) on SOHO were intensity enhancements propagating over a large fraction of
the solar surface. The physical origin(s) of the so-called `EIT' waves is still
strongly debated. They are considered to be either wave (primarily fast-mode
MHD waves) or non-wave (pseudo-wave) interpretations. The difficulty in
understanding the nature of EUV waves lies with the limitations of the EIT
observations which have been used almost exclusively for their study. Their
limitations are largely overcome by the SECCHI/EUVI observations on-board the
STEREO mission. The EUVI telescopes provide high cadence, simultaneous
multi-temperature coverage, and two well-separated viewpoints. We present here
the first detailed analysis of an EUV wave observed by the EUVI disk imagers on
December 07, 2007 when the STEREO spacecraft separation was .
Both a small flare and a CME were associated with the wave cadence, and single
temperature and viewpoint coverage. These limitations are largely overcome by
the SECCHI/EUVI observations on-board the STEREO mission. The EUVI telescopes
provide high cadence, simultaneous multi-temperature coverage, and two
well-separated viewpoints. Our findings give significant support for a
fast-mode interpretation of EUV waves and indicate that they are probably
triggered by the rapid expansion of the loops associated with the CME.Comment: Solar Physics, 2009, Special STEREO Issue, in pres
On the Nature and Genesis of EUV Waves: A Synthesis of Observations from SOHO, STEREO, SDO, and Hinode
A major, albeit serendipitous, discovery of the SOlar and Heliospheric
Observatory mission was the observation by the Extreme Ultraviolet Telescope
(EIT) of large-scale Extreme Ultraviolet (EUV) intensity fronts propagating
over a significant fraction of the Sun's surface. These so-called EIT or EUV
waves are associated with eruptive phenomena and have been studied intensely.
However, their wave nature has been challenged by non-wave (or pseudo-wave)
interpretations and the subject remains under debate. A string of recent solar
missions has provided a wealth of detailed EUV observations of these waves
bringing us closer to resolving their nature. With this review, we gather the
current state-of-art knowledge in the field and synthesize it into a picture of
an EUV wave driven by the lateral expansion of the CME. This picture can
account for both wave and pseudo-wave interpretations of the observations, thus
resolving the controversy over the nature of EUV waves to a large degree but
not completely. We close with a discussion of several remaining open questions
in the field of EUV waves research.Comment: Solar Physics, Special Issue "The Sun in 360",2012, accepted for
publicatio
The Milky Way Bulge: Observed properties and a comparison to external galaxies
The Milky Way bulge offers a unique opportunity to investigate in detail the
role that different processes such as dynamical instabilities, hierarchical
merging, and dissipational collapse may have played in the history of the
Galaxy formation and evolution based on its resolved stellar population
properties. Large observation programmes and surveys of the bulge are providing
for the first time a look into the global view of the Milky Way bulge that can
be compared with the bulges of other galaxies, and be used as a template for
detailed comparison with models. The Milky Way has been shown to have a
box/peanut (B/P) bulge and recent evidence seems to suggest the presence of an
additional spheroidal component. In this review we summarise the global
chemical abundances, kinematics and structural properties that allow us to
disentangle these multiple components and provide constraints to understand
their origin. The investigation of both detailed and global properties of the
bulge now provide us with the opportunity to characterise the bulge as observed
in models, and to place the mixed component bulge scenario in the general
context of external galaxies. When writing this review, we considered the
perspectives of researchers working with the Milky Way and researchers working
with external galaxies. It is an attempt to approach both communities for a
fruitful exchange of ideas.Comment: Review article to appear in "Galactic Bulges", Editors: Laurikainen
E., Peletier R., Gadotti D., Springer Publishing. 36 pages, 10 figure
Prostaglandin synthase 1 gene disruption in mice reduces arachidonic acid-induced inflammation and indomethacin-induced gastric ulceration
AbstractCyclooxygenases 1 and 2 (COX-1 and COX-2) are key enzymes in prostaglandin biosynthesis and the target enzymes for the widely used nonsteroidal anti-inflammatory drugs. To study the physiological roles of the individual isoforms, we have disrupted the mouse Ptgs1 gene encoding COX-1. Homozygous Ptgs1 mutant mice survive well, have no gastric pathology, and show less indomethacin-induced gastric ulceration than wild-type mice, even though their gastric prostaglandin E2 levels are about 1% of wild type. The homozygous mutant mice have reduced platelet aggregation and a decreased inflammatory response to arachidonic acid, but not to tetradecanoyl phorbol acetate. Ptgs1 homozygous mutant females mated to homozygous mutant males produce few live offspring. COX-1-deficient mice provide a useful model to distinguish the physiological roles of COX-1 and COX-2
- …