2,505 research outputs found
Efficient pathway for early detection of prostate cancer concluded from a 5-year prospective study
Enzyme activities in liver and muscle biopsy specimens from thyrotoxic and hypothyroid patiens
Pre main sequence: Accretion & Outflows
Low-mass pre-main sequence (PMS) stars are strong X-ray sources, because they
possess hot corona like their older main-sequence counterparts. Unique to young
stars, however, are X-rays from accretion and outflows, and both processes are
of pivotal importance for star and planet formation. We describe how X-ray data
provide important insight into the physics of accretion and outflows. First,
mass accreted from a circumstellar disk onto the stellar surface reaches
velocities up to a few hundred km/s, fast enough to generate soft X-rays in the
post-shock region of the accretion shock. X-ray observations together with
laboratory experiments and numerical simulations show that the accretion
geometry is complex in young stars. Specifically, the center of the accretion
column is likely surrounded by material shielding the inner flow from view but
itself also hot enough to emit X-rays. Second, X-rays are observed in two
locations of protostellar jets: an inner stationary emission component probably
related to outflow collimation and outer components, which evolve withing years
and are likely related to working surfaces where the shock travels through the
jet. Jet-powered X-rays appear to trace the fastest jet component and provide
novel information on jet launching in young stars. We conclude that X-ray data
will continue to be highly important for understanding star and planet
formation, because they directly probe the origin of many emission features
studied in other wavelength regimes. In addition, future X-ray missions will
improve sensitivity and spectral resolution to probe key model parameters (e.g.
velocities) in large samples of PMS stars.Comment: Invited chapter for the "Handbook of X-ray and Gamma-ray
Astrophysics" (Eds. C. Bambi and A. Santangelo, Springer Nature, 2022),
accepted (34 pages, 11 figures
Far-Ultraviolet Activity Levels of F, G, K, and M dwarf Exoplanet Host Stars
We present a survey of far-ultraviolet (FUV; 1150 - 1450 Ang) emission line
spectra from 71 planet-hosting and 33 non-planet-hosting F, G, K, and M dwarfs
with the goals of characterizing their range of FUV activity levels,
calibrating the FUV activity level to the 90 - 360 Ang extreme-ultraviolet
(EUV) stellar flux, and investigating the potential for FUV emission lines to
probe star-planet interactions (SPIs). We build this emission line sample from
a combination of new and archival observations with the Hubble Space
Telescope-COS and -STIS instruments, targeting the chromospheric and transition
region emission lines of Si III, N V, C II, and Si IV.
We find that the exoplanet host stars, on average, display factors of 5 - 10
lower UV activity levels compared with the non-planet hosting sample; this is
explained by a combination of observational and astrophysical biases in the
selection of stars for radial-velocity planet searches. We demonstrate that UV
activity-rotation relation in the full F - M star sample is characterized by a
power-law decline (with index ~ -1.1), starting at rotation periods
>~3.5 days. Using N V or Si IV spectra and a knowledge of the star's bolometric
flux, we present a new analytic relationship to estimate the intrinsic stellar
EUV irradiance in the 90 - 360 Ang band with an accuracy of roughly a factor of
~2. Finally, we study the correlation between SPI strength and UV activity in
the context of a principal component analysis that controls for the sample
biases. We find that SPIs are not a statistically significant contributor to
the observed UV activity levels.Comment: ApJS, accepted. 33 pages in emulateapj, 13 figures, 10 table
Bench-to-bedside review: Latest results in hemorrhagic shock
Hemorrhagic shock is a leading cause of death in trauma patients worldwide. Bleeding control, maintenance of tissue oxygenation with fluid resuscitation, coagulation support, and maintenance of normothermia remain mainstays of therapy for patients with hemorrhagic shock. Although now widely practised as standard in the USA and Europe, shock resuscitation strategies involving blood replacement and fluid volume loading to regain tissue perfusion and oxygenation vary between trauma centers; the primary cause of this is the scarcity of published evidence and lack of randomized controlled clinical trials. Despite enormous efforts to improve outcomes after severe hemorrhage, novel strategies based on experimental data have not resulted in profound changes in treatment philosophy. Recent clinical and experimental studies indicated the important influences of sex and genetics on pathophysiological mechanisms after hemorrhage. Those findings might provide one explanation why several promising experimental approaches have failed in the clinical arena. In this respect, more clinically relevant animal models should be used to investigate pathophysiology and novel treatment approaches. This review points out new therapeutic strategies, namely immunomodulation, cardiovascular maintenance, small volume resuscitation, and so on, that have been introduced in clinics or are in the process of being transferred from bench to bedside. Control of hemorrhage in the earliest phases of care, recognition and monitoring of individual risk factors, and therapeutic modulation of the inflammatory immune response will probably constitute the next generation of therapy in hemorrhagic shock. Further randomized controlled multicenter clinical trials are needed that utilize standardized criteria for enrolling patients, but existing ethical requirements must be maintained
Activated partial thromboplastin time waveform analysis as specific sepsis marker in cardiopulmonary bypass surgery
Throughout the last years, several new diagnostic biomarkers have been introduced into clinical routine to identify a systemic inflammatory response syndrome (SIRS) or a septic state and to discriminate between these two entities. According to studies in selected patients, measurement of these biomarkers may be advantageous under certain clinical conditions. On an individual basis, however, these sepsis markers usually lack an adequate negative or positive predictive power. Therefore, physicians in charge still have to rely on a combination of personal experience and results from clinical or laboratory tests when deciding on a patient's therapy. For surgical patients, a key problem consists of the time delay which is associated with the diagnosis of serious postoperative infections and which may negatively affect outcome. It is in this context where the activated partial thromboplastin time waveform analysis may represent a promising new method to discriminate between SIRS and sepsis, thereby shortening the time to therapy. Nevertheless, studies involving large patient populations will be necessary to prove the efficacy of this new diagnostic concept either as a single tool or in combination with the measurement of other biomarkers
Probing UV-sensitive Pathways for CN and HCN Formation in Protoplanetary Disks with the Hubble Space Telescope
The UV radiation field is a critical regulator of gas-phase chemistry in surface layers of disks around young stars. In an effort to understand the relationship between photocatalyzing UV radiation fields and gas emission observed at infrared and submillimeter wavelengths, we present an analysis of new and archival Hubble Space Telescope (HST), Spitzer, ALMA, IRAM, and SMA data for five targets in the Lupus cloud complex and 14 systems in Taurus-Auriga. The HST spectra were used to measure Lyα and far-UV (FUV) continuum fluxes reaching the disk surface, which are responsible for dissociating relevant molecular species (e.g., HCN, Nâ). Semi-forbidden C II] λ2325 and UV-fluorescent Hâ emission were also measured to constrain inner disk populations of Câș and vibrationally excited H2. We find a significant positive correlation between 14 ÎŒm HCN emission and fluxes from the FUV continuum and C II] λ2325, consistent with model predictions requiring Nâ photodissociation and carbon ionization to trigger the main CN/HCN formation pathways. We also report significant negative correlations between submillimeter CN emission and both C II] and FUV continuum fluxes, implying that CN is also more readily dissociated in disks with stronger FUV irradiation. No clear relationships are detected between either CN or HCN and Lyα or UV-Hâ emission. This is attributed to the spatial stratification of the various molecular species, which span several vertical layers and radii across the inner and outer disk. We expect that future observations with the James Webb Space Telescope will build on this work by enabling more sensitive IR surveys than were possible with Spitzer
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