139 research outputs found
The Magnetic Properties of Heating Events on High-Temperature Active Region Loops
Understanding the relationship between the magnetic field and coronal heating
is one of the central problems of solar physics. However, studies of the
magnetic properties of impulsively heated loops have been rare. We present
results from a study of 34 evolving coronal loops observed in the Fe XVIII line
component of AIA/SDO 94 A filter images from three active regions with
different magnetic conditions. We show that the peak intensity per unit
cross-section of the loops depends on their individual magnetic and geometric
properties. The intensity scales proportionally to the average field strength
along the loop () and inversely with the loop length () for a
combined dependence of . These loop properties are
inferred from magnetic extrapolations of the photospheric HMI/SDO line-of-sight
and vector magnetic field in three approximations: potential and two Non Linear
Force-Free (NLFF) methods. Through hydrodynamic modeling (EBTEL model) we show
that this behavior is compatible with impulsively heated loops with a
volumetric heating rate that scales as .Comment: Astrophysical Journal, in pres
Transition region and chromospheric signatures of impulsive heating events. II. Modeling
Results from the Solar Maximum Mission showed a close connection between the hard X-ray (HXR) and transition
region (TR) emission in solar flares. Analogously, the modern combination of RHESSI and IRIS data can inform
the details of heating processes in ways that were never before possible. We study a small event that was observed
with RHESSI, IRIS, SDO, and Hinode, allowing us to strongly constrain the heating and hydrodynamical properties
of the flare, with detailed observations presented in a previous paper. Long duration redshifts of TR lines observed
in this event, as well as many other events, are fundamentally incompatible with chromospheric condensation on a
single loop. We combine RHESSI and IRIS data to measure the energy partition among the many magnetic strands
that comprise the flare. Using that observationally determined energy partition, we show that a proper
multithreaded model can reproduce these redshifts in magnitude, duration, and line intensity, while simultaneously
being well constrained by the observed density, temperature, and emission measure. We comment on the
implications for both RHESSI and IRIS observations of flares in general, namely that: (1) a single loop model is
inconsistent with long duration redshifts, among other observables; (2) the average time between energization of
strands is less than 10 s, which implies that for a HXR burst lasting 10 minutes, there were at least 60 strands
within a single IRIS pixel located on the flare ribbon; (3) the majority of these strands were explosively heated with
an energy distribution well described by a power law of slope »-1.6; (4) the multi-stranded model reproduces the
observed line profiles, peak temperatures, differential emission measure distributions, and densities
Towards a Quantitative Comparison of Magnetic Field Extrapolations and Observed Coronal Loops
It is widely believed that loops observed in the solar atmosphere trace out
magnetic field lines. However, the degree to which magnetic field
extrapolations yield field lines that actually do follow loops has yet to be
studied systematically. In this paper we apply three different extrapolation
techniques - a simple potential model, a NLFF model based on photospheric
vector data, and a NLFF model based on forward fitting magnetic sources with
vertical currents - to 15 active regions that span a wide range of magnetic
conditions. We use a distance metric to assess how well each of these models is
able to match field lines to the 12,202 loops traced in coronal images. These
distances are typically 1-2". We also compute the misalignment angle between
each traced loop and the local magnetic field vector, and find values of
5-12. We find that the NLFF models generally outperform the potential
extrapolation on these metrics, although the differences between the different
extrapolations are relatively small. The methodology that we employ for this
study suggests a number of ways that both the extrapolations and loop
identification can be improved.Comment: Accepted for publication in Ap
Global Burden of Invasive Nontyphoidal Salmonella Disease, 2010
Nontyphoidal Salmonella is a major cause of bloodstream infections worldwide, and HIV-infected persons and malaria-infected and malnourished children are at increased risk for the disease. We conducted a systematic literature review to obtain age groupâspecific, population-based invasive nontyphoidal Salmonella (iNTS) incidence data. Data were categorized by HIV and malaria prevalence and then extrapolated by using 2010 population data. The case-fatality ratio (CFR) was determined by expert opinion consensus. We estimated that 3.4 (range 2.1â6.5) million cases of iNTS disease occur annually (overall incidence 49 cases [range 30â94] per 100,000 population). Africa, where infants, young children, and young adults are most affected, had the highest incidence (227 cases [range 152â341] per 100,000 population) and number of cases (1.9 [range 1.3â2.9] million cases). An iNTS CFR of 20% yielded 681,316 (range 415,164â1,301,520) deaths annually. iNTS disease is a major cause of illness and death globally, particularly in Africa. Improved understanding of the epidemiology of iNTS is needed
Febrile Illness Evaluation in a Broad Range of Endemicities (FIEBRE): protocol for a multisite prospective observational study of the causes of fever in Africa and Asia.
INTRODUCTION NlmCategory: BACKGROUND content:
Fever commonly leads to healthcare seeking and hospital
admission in sub-Saharan Africa and Asia. There is only limited
guidance for clinicians managing non-malarial fevers, which
often results in inappropriate treatment for patients.
Furthermore, there is little evidence for estimates of disease
burden, or to guide empirical therapy, control measures,
resource allocation, prioritisation of clinical diagnostics or
antimicrobial stewardship. The Febrile Illness Evaluation in a
Broad Range of Endemicities (FIEBRE) study seeks to address
these information gaps. - Label: METHODS AND ANALYSIS
NlmCategory: UNASSIGNED content: FIEBRE investigates febrile
illness in paediatric and adult outpatients and inpatients using
standardised clinical, laboratory and social science protocols
over a minimum 12-month period at five sites in sub-Saharan
Africa and Southeastern and Southern Asia. Patients presenting
with fever are enrolled and provide clinical data, pharyngeal
swabs and a venous blood sample; selected participants also
provide a urine sample. Laboratory assessments target infections
that are treatable and/or preventable. Selected point-of-care
tests, as well as blood and urine cultures and antimicrobial
susceptibility testing, are performed on site. On day 28,
patients provide a second venous blood sample for serology and
information on clinical outcome. Further diagnostic assays are
performed at international reference laboratories. Blood and
pharyngeal samples from matched community controls enable
calculation of AFs, and surveys of treatment seeking allow
estimation of the incidence of common infections. Additional
assays detect markers that may differentiate bacterial from
non-bacterial causes of illness and/or prognosticate illness
severity. Social science research on antimicrobial use will
inform future recommendations for fever case management.
Residual samples from participants are stored for future use. -
Label: ETHICS AND DISSEMINATION NlmCategory: UNASSIGNED content:
Ethics approval was obtained from all relevant institutional and
national committees; written informed consent is obtained from
all participants or parents/guardians. Final results will be
shared with participating communities, and in open-access
journals and other scientific fora. Study documents are
available online (https://doi.org/10.17037/PUBS.04652739)
Typhoid Fever and Invasive Nontyphoid Salmonellosis, Malawi and South Africa
To determine the prevalence of invasive nontyphoid salmonellosis and typhoid fever in Malawi and South Africa, we compared case frequency and patient age distribution. Invasive nontyphoid salmonellosis showed a clear bimodal age distribution; the infection developed in women at a younger age than in men. Case frequency for typhoid fever was lower than for salmonellosis
Modelling acquired resistance to DOT1L inhibition exhibits the adaptive potential of KMT2A-rearranged acute lymphoblastic leukemia
In KMT2A-rearranged acute lymphoblastic leukemia (ALL), an aggressive malignancy, oncogenic KMT2A-fusion proteins inappropriately recruit DOT1L to promote leukemogenesis, highlighting DOT1L as an attractive therapeutic target. Unfortunately, treatment with the first-in-class DOT1L inhibitor pinometostat eventually leads to non-responsiveness. To understand this we established acquired pinometostat resistance in pediatric KMT2A::AFF1+ B-ALL cells. Interestingly, these cells became mostly independent of DOT1L-mediated H3K79 methylation, but still relied on the physical presence of DOT1L, HOXA9 and the KMT2A::AFF1 fusion. Moreover, these cells selectively lost the epigenetic regulation and expression of various KMT2A-fusion target genes such as PROM1/CD133, while other KMT2A::AFF1 target genes, including HOXA9 and CDK6 remained unaffected. Concomitantly, these pinometostat-resistant cells showed upregulation of several myeloid-associated genes, including CD33 and LILRB4/CD85k. Taken together, this model comprehensively shows the adaptive potential of KMT2A-rearranged ALL cells upon losing dependency on one of its main oncogenic properties
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