35 research outputs found
Newly identified properties of surface acoustic power
The cause of enhanced acoustic power surrounding active regions, the acoustic
halo, is not as yet understood. We explore the properties of the enhanced
acoustic power observed near disk center from 21 to 27 January 2002, including
AR 9787. We find that (i) there exists a strong correlation of the enhanced
high frequency power with magnetic-field inclination, with greater power in
more horizontal fields, (ii) the frequency of the maximum enhancement increases
along with magnetic field strength, and (iii) the oscillations contributing to
the halos show modal ridges which are shifted to higher wavenumber at constant
frequency in comparison to the ridges of modes in the quiet-Sun.Comment: 16 pages, 10 figures, submitted to solar physic
Surface-focused Seismic Holography of Sunspots: I. Observations
We present a comprehensive set of observations of the interaction of p-mode
oscillations with sunspots using surface-focused seismic holography. Maps of
travel-time shifts, relative to quiet-Sun travel times, are shown for incoming
and outgoing p modes as well as their mean and difference. We compare results
using phase-speed filters with results obtained with filters that isolate
single p-mode ridges, and further divide the data into multiple temporal
frequency bandpasses. The f mode is removed from the data. The variations of
the resulting travel-time shifts with magnetic-field strength and with the
filter parameters are explored. We find that spatial averages of these shifts
within sunspot umbrae, penumbrae, and surrounding plage often show strong
frequency variations at fixed phase speed. In addition, we find that positive
values of the mean and difference travel-time shifts appear exclusively in
waves observed with phase-speed filters that are dominated by power in the
low-frequency wing of the p1 ridge. We assess the ratio of incoming to outgoing
p-mode power using the ridge filters and compare surface-focused holography
measurements with the results of earlier published p-mode scattering
measurements using Fourier-Hankel decomposition.Comment: Solar Physics, accepte
Helioseismology of Sunspots: A Case Study of NOAA Region 9787
Various methods of helioseismology are used to study the subsurface
properties of the sunspot in NOAA Active Region 9787. This sunspot was chosen
because it is axisymmetric, shows little evolution during 20-28 January 2002,
and was observed continuously by the MDI/SOHO instrument. (...) Wave travel
times and mode frequencies are affected by the sunspot. In most cases, wave
packets that propagate through the sunspot have reduced travel times. At short
travel distances, however, the sign of the travel-time shifts appears to depend
sensitively on how the data are processed and, in particular, on filtering in
frequency-wavenumber space. We carry out two linear inversions for wave speed:
one using travel-times and phase-speed filters and the other one using mode
frequencies from ring analysis. These two inversions give subsurface wave-speed
profiles with opposite signs and different amplitudes. (...) From this study of
AR9787, we conclude that we are currently unable to provide a unified
description of the subsurface structure and dynamics of the sunspot.Comment: 28 pages, 18 figure
Advances in Global and Local Helioseismology: an Introductory Review
Helioseismology studies the structure and dynamics of the Sun's interior by
observing oscillations on the surface. These studies provide information about
the physical processes that control the evolution and magnetic activity of the
Sun. In recent years, helioseismology has made substantial progress towards the
understanding of the physics of solar oscillations and the physical processes
inside the Sun, thanks to observational, theoretical and modeling efforts. In
addition to the global seismology of the Sun based on measurements of global
oscillation modes, a new field of local helioseismology, which studies
oscillation travel times and local frequency shifts, has been developed. It is
capable of providing 3D images of the subsurface structures and flows. The
basic principles, recent advances and perspectives of global and local
helioseismology are reviewed in this article.Comment: 86 pages, 46 figures; "Pulsation of the Sun and Stars", Lecture Notes
in Physics, Vol. 832, Rozelot, Jean-Pierre; Neiner, Coralie (Eds.), 201
An Observational Overview of Solar Flares
We present an overview of solar flares and associated phenomena, drawing upon
a wide range of observational data primarily from the RHESSI era. Following an
introductory discussion and overview of the status of observational
capabilities, the article is split into topical sections which deal with
different areas of flare phenomena (footpoints and ribbons, coronal sources,
relationship to coronal mass ejections) and their interconnections. We also
discuss flare soft X-ray spectroscopy and the energetics of the process. The
emphasis is to describe the observations from multiple points of view, while
bearing in mind the models that link them to each other and to theory. The
present theoretical and observational understanding of solar flares is far from
complete, so we conclude with a brief discussion of models, and a list of
missing but important observations.Comment: This is an article for a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Human Ciliary Muscle Cell Responses to FP-Class Prostaglandin Analogs: Phosphoinositide Hydrolysis, Intracellular Ca 2+
Agonist Activity of Bimatoprost, Travoprost, Latanoprost, Unoprostone Isopropyl Ester and Other Prostaglandin Analogs at the Cloned Human Ciliary Body FP Prostaglandin Receptor
A library of AuNPs modified by RAFT polymers of different charge and chain length: high throughput synthesis and synchrotron XFM imaging using a zebrafish larvae model
Gold nanoparticles (AuNPs) have been widely investigated in drug delivery and imaging. However, for such biomedical applications, the modification of AuNPs is necessary to improve their aqueous dispersion stability and biocompatibility, especially in a salt environment. Here, we report a simple and highly efficient method to create a library of polymer-modified gold nanoparticles (PAuNPs) and screen their dispersion stability utilizing high-throughput facilities (in total 1000 experiments). Three types of water soluble polymers with different charge and chain length were prepared using Reversible Addition-Fragmentation chain Transfer (RAFT) polymerization technology. The polymers were then converted into thiol-capped polymers by aminolysis and coated on AuNPs via thiol–gold binding to improve aqueous dispersion stability as well as the biocompatibility of AuNPs. Remarkably, we present the first report of imaging zebrafish embryos injected with a PAuNPs sample (selected from our PAuNPs library) using synchrotron X-ray fluorescence microscopy (XFM) beamline. The selected PAuNPs sample, which has been evaluated to be non-cytotoxic to L929 cells and biocompatible to zebrafish larvae in a wide range of concentrations, was injected into zebrafish larvae via the cardinal vein and could be clearly visualized in the whole circulatory system including both peripheral blood vessels and the head region by XFM. The result indicates that zebrafish larvae could be a potential animal model for probing the ability of AuNPs to cross the blood–brain barrier (BBB) and therefore hold promise for investigating AuNPs in biomedical applications such as detecting cancer and Alzheimer's disease (AD).Bao Luan, Timo Friedrich, Jiali Zhai, Victor A. Streltsov, Benjamin W. Lindsey ... Timothy C. Hughes ... et al