131 research outputs found
Epidemiological investigation of a case of nosocomial Legionnaires' disease in Taiwan: implications for routine environmental surveillance
AbstractAn epidemiological investigation with Legionella and molecular subtyping was conducted to determine the source of a case of nosocomial Legionnaires' disease (LD) who was hospitalized in three hospitals within a month. Legionella pneumophila serogroup 3, an uncommon serogroup for infection, was isolated from the patient's sputum. Environmental surveillance revealed Legionella colonization in all three hospitals; the patient isolate matched the isolate from the first hospital by molecular typing. Culturing the hospital water supply for Legionella is a pro-active strategy for detection of nosocomial LD even in hospitals experiencing no previous cases
Particle acceleration in three-dimensional tearing configurations
In three-dimensional electromagnetic configurations that result from unstable
resistive tearing modes particles can efficiently be accelerated to
relativistic energies. To prove this resistive magnetohydrodynamic simulations
are used as input configurations for successive test particle simulations. The
simulations show the capability of three-dimensional non-linearly evolved
tearing modes to accelerate particles perpendicular to the plane of the
reconnecting magnetic field components. The simulations differ considerably
from analytical approaches by involving a realistic three-dimensional electric
field with a non-homogenous component parallel to the current direction. The
resulting particle spectra exhibit strong pitch-angle anisotropies. Typically,
about 5-8 % of an initially Maxwellian distribution is accelerated to the
maximum energy levels given by the macroscopic generalized electric potential
structure. Results are shown for both, non-relativistic particle acceleration
that is of interest, e.g., in the context of auroral arcs and solar flares, and
relativistic particle energization that is relevant, e.g., in the context of
active galactic nuclei.Comment: Physics of Plasmas, in prin
Physics of Solar Prominences: II - Magnetic Structure and Dynamics
Observations and models of solar prominences are reviewed. We focus on
non-eruptive prominences, and describe recent progress in four areas of
prominence research: (1) magnetic structure deduced from observations and
models, (2) the dynamics of prominence plasmas (formation and flows), (3)
Magneto-hydrodynamic (MHD) waves in prominences and (4) the formation and
large-scale patterns of the filament channels in which prominences are located.
Finally, several outstanding issues in prominence research are discussed, along
with observations and models required to resolve them.Comment: 75 pages, 31 pictures, review pape
Study of flare energy release using events with numerous type III-like bursts in microwaves
The analysis of narrowband drifting of type III-like structures in radio
bursts dynamic spectra allows to obtain unique information about primary energy
release mechanisms in solar flares. The SSRT spatially resolved images and a
high spectral and temporal resolution allow direct determination not only the
positions of its sources but also the exciter velocities along the flare loop.
Practically, such measurements are possible during some special time intervals
when the SSRT (about 5.7 GHz) is observing the flare region in two high-order
fringes; thus, two 1D scans are recorded simultaneously at two frequency bands.
The analysis of type III-like bursts recorded during the flare 14 Apr 2002 is
presented. Using-muliwavelength radio observations recorded by SSRT, SBRS,
NoRP, RSTN we study an event with series of several tens of drifting microwave
pulses with drift rates in the range from -7 to 13 GHz/s. The sources of the
fast-drifting bursts were located near the top of the flare loop in a volume of
a few Mm in size. The slow drift of the exciters along the flare loop suggests
a high pitch-anisotropy of the emitting electrons.Comment: 16 pages, 6 figures, Solar Physics, in press, 201
Interchange Slip-Running Reconnection and Sweeping SEP Beams
We present a new model to explain how particles (solar energetic particles;
SEPs), accelerated at a reconnection site that is not magnetically connected to
the Earth, could eventually propagate along the well-connected open flux tube.
Our model is based on the results of a low-beta resistive magnetohydrodynamics
simulation of a three-dimensional line-tied and initially current-free bipole,
that is embedded in a non-uniform open potential field. The topology of this
configuration is that of an asymmetric coronal null-point, with a closed fan
surface and an open outer spine. When driven by slow photospheric shearing
motions, field lines, initially fully anchored below the fan dome, reconnect at
the null point, and jump to the open magnetic domain. This is the standard
interchange mode as sketched and calculated in 2D. The key result in 3D is
that, reconnected open field lines located in the vicinity of the outer spine,
keep reconnecting continuously, across an open quasi-separatrix layer, as
previously identified for non-open-null-point reconnection. The apparent
slipping motion of these field lines leads to form an extended narrow magnetic
flux tube at high altitude. Because of the slip-running reconnection, we
conjecture that if energetic particles would be traveling through, or be
accelerated inside, the diffusion region, they would be successively injected
along continuously reconnecting field lines that are connected farther and
farther from the spine. At the scale of the full Sun, owing to the super-radial
expansion of field lines below 3 solar radii, such energetic particles could
easily be injected in field lines slipping over significant distances, and
could eventually reach the distant flux tube that is well-connected to the
Earth
Recent Advances in Understanding Particle Acceleration Processes in Solar Flares
We review basic theoretical concepts in particle acceleration, with
particular emphasis on processes likely to occur in regions of magnetic
reconnection. Several new developments are discussed, including detailed
studies of reconnection in three-dimensional magnetic field configurations
(e.g., current sheets, collapsing traps, separatrix regions) and stochastic
acceleration in a turbulent environment. Fluid, test-particle, and
particle-in-cell approaches are used and results compared. While these studies
show considerable promise in accounting for the various observational
manifestations of solar flares, they are limited by a number of factors, mostly
relating to available computational power. Not the least of these issues is the
need to explicitly incorporate the electrodynamic feedback of the accelerated
particles themselves on the environment in which they are accelerated. A brief
prognosis for future advancement is offered.Comment: This is a chapter in a monograph on the physics of solar flares,
inspired by RHESSI observations. The individual articles are to appear in
Space Science Reviews (2011
Physics of Solar Prominences: I - Spectral Diagnostics and Non-LTE Modelling
This review paper outlines background information and covers recent advances
made via the analysis of spectra and images of prominence plasma and the
increased sophistication of non-LTE (ie when there is a departure from Local
Thermodynamic Equilibrium) radiative transfer models. We first describe the
spectral inversion techniques that have been used to infer the plasma
parameters important for the general properties of the prominence plasma in
both its cool core and the hotter prominence-corona transition region. We also
review studies devoted to the observation of bulk motions of the prominence
plasma and to the determination of prominence mass. However, a simple inversion
of spectroscopic data usually fails when the lines become optically thick at
certain wavelengths. Therefore, complex non-LTE models become necessary. We
thus present the basics of non-LTE radiative transfer theory and the associated
multi-level radiative transfer problems. The main results of one- and
two-dimensional models of the prominences and their fine-structures are
presented. We then discuss the energy balance in various prominence models.
Finally, we outline the outstanding observational and theoretical questions,
and the directions for future progress in our understanding of solar
prominences.Comment: 96 pages, 37 figures, Space Science Reviews. Some figures may have a
better resolution in the published version. New version reflects minor
changes brought after proof editin
Pilot Study of [18F] Fluorodeoxyglucose Positron Emission Tomography (FDG-PET)/Magnetic Resonance Imaging (MRI) for Staging of Muscle-invasive Bladder Cancer (MIBC)
Introduction: Computed tomography (CT) has limited diagnostic accuracy for staging of muscle-invasive bladder cancer (MIBC). [18F] Fluorodeoxyglucose positron emission tomography (FDG-PET)/magnetic resonance imaging (MRI) is a novel imaging modality incorporating functional imaging with improved soft tissue characterization. This pilot study evaluated the use of preoperative FDG-PET/MRI for staging of MIBC. Patients and Methods: Twenty-one patients with MIBC with planned radical cystectomy were enrolled. Two teams of radiologists reviewed FDG-PET/MRI scans to determine: (1) presence of primary bladder tumor; and (2) lymph node involvement and distant metastases. FDG-PET/MRI was compared with cystectomy pathology and computed tomography (CT). Results: Eighteen patients were included in the final analysis, most (72.2%) of whom received neoadjuvant chemotherapy. Final pathology revealed 10 (56%) patients with muscle invasion and only 3 (17%) patients with lymph node involvement. Clustered analysis of FDG-PET/MRI radiology team reads revealed a sensitivity of 0.80 and a specificity of 0.56 for detection of the primary tumor with a sensitivity of 0 and a specificity of 1.00 for detection of lymph node involvement when compared with cystectomy pathology. CT imaging demonstrated similar rates in evaluation of the primary tumor (sensitivity, 0.91; specificity, 0.43) and lymph node involvement (sensitivity, 0; specificity, 0.93) when compared with pathology. Conclusions: This pilot single-institution experience of FDG-PET/MRI for preoperative staging of MIBC performed similar to CT for the detection of the primary tumor; however, the determination of lymph node status was limited by few patients with true pathologic lymph node involvement. Further studies are needed to evaluate the potential role for FDG-PET/MRI in the staging of MIBC. © 2020 Elsevier Inc.In this pilot study, preoperative staging with [18F] fluorodeoxyglucose-positron emission tomography/magnetic resonance imaging in muscle-invasive bladder cancer detected the primary bladder tumor; however, the determination of lymph node status was limited by few patients with pathologic lymph node involvement. Additional studies are needed to evaluate the potential role for [18F] fluorodeoxyglucose-positron emission tomography/magnetic resonance imaging in the staging of bladder cancer
Microflares and the Statistics of X-ray Flares
This review surveys the statistics of solar X-ray flares, emphasising the new
views that RHESSI has given us of the weaker events (the microflares). The new
data reveal that these microflares strongly resemble more energetic events in
most respects; they occur solely within active regions and exhibit
high-temperature/nonthermal emissions in approximately the same proportion as
major events. We discuss the distributions of flare parameters (e.g., peak
flux) and how these parameters correlate, for instance via the Neupert effect.
We also highlight the systematic biases involved in intercomparing data
representing many decades of event magnitude. The intermittency of the
flare/microflare occurrence, both in space and in time, argues that these
discrete events do not explain general coronal heating, either in active
regions or in the quiet Sun.Comment: To be published in Space Science Reviews (2011
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