Low-temperature detectors often use mechanical coolers as part of the cooling chain in order to reach sub-Kelvin operating temperatures. The microphonic noise caused by the mechanical coolers is a ...general and inherent issue for these detectors. We have observed this effect in the ground test data obtained with the
Resolve
instrument to be flown on the XRISM satellite.
Resolve
is a cryogenic X-ray microcalorimeter spectrometer with a required energy resolution of 7 eV at 6 keV. Five mechanical coolers are used to cool from ambient temperature to
∼
4 K: four two-stage Stirling coolers (STC) driven nominally at 15 Hz and a Joule–Thomson cooler (JTC) driven nominally at 52 Hz. In 2019, we operated the flight-model instrument for two weeks, in which we also obtained accelerometer data inside the cryostat at a low-temperature stage (He tank). X-ray detector and accelerometer data were obtained continuously while changing the JTC drive frequency, which produced a unique data set for investigating how the vibration from the cryocoolers propagates to the detector. In the detector noise spectra, we observed harmonics of both STCs and JTC. More interestingly, we also observed the low (
<
20
Hz) frequency beat between the 4th JTC and 14th STC harmonics and the 7th JTC and the 23–24th STC harmonics. We present here a description and interpretation of these measurements.
One of the most enduring and intensively studied problems of x-ray astronomy is the disagreement of state-of-the art theory and observations for the intensity ratio of two Fe XVII transitions of ...crucial value for plasma diagnostics, dubbed 3C and 3D. We unravel this conundrum at the PETRA III synchrotron facility by increasing the resolving power 2.5 times and the signal-to-noise ratio thousandfold compared with our previous work. The Lorentzian wings had hitherto been indistinguishable from the background and were thus not modeled, resulting in a biased line-strength estimation. The present experimental oscillator-strength ratio R_{exp}=f_{3C}/f_{3D}=3.51(2)_{stat}(7)_{sys} agrees with our state-of-the-art calculation of R_{th}=3.55(2), as well as with some previous theoretical predictions. To further rule out any uncertainties associated with the measured ratio, we also determined the individual natural linewidths and oscillator strengths of 3C and 3D transitions, which also agree well with the theory. This finally resolves the decades-old mystery of Fe XVII oscillator strengths.
Highly charged iron (Fe super(16+), here referred to as Fexvii) produces some of the brightest X-ray emission lines from hot astrophysical objects, including galaxy clusters and stellar coronae, and ...it dominates the emission of the Sun at wavelengths near 15 angstroms. The Fexvii spectrum is, however, poorly fitted by even the best astrophysical models. A particular problem has been that the intensity of the strongest Fexvii line is generally weaker than predicted. This has affected the interpretation of observations by the Chandra and XMM-Newton orbiting X-ray missions, fuelling a continuing controversy over whether this discrepancy is caused by incomplete modelling of the plasma environment in these objects or by shortcomings in the treatment of the underlying atomic physics. Here we report the results of an experiment in which a target of iron ions was induced to fluoresce by subjecting it to femtosecond X-ray pulses from a free-electron laser; our aim was to isolate a key aspect of the quantum mechanical description of the line emission. Surprisingly, we find a relative oscillator strength that is unexpectedly low, differing by 3.6 sigma from the best quantum mechanical calculations. Our measurements suggest that the poor agreement is rooted in the quality of the underlying atomic wavefunctions rather than in insufficient modelling of collisional processes.
ABSTRACT We have measured the energies of the strongest 1s-2 transitions in He- through Ne-like silicon and sulfur ions to an accuracy of using the Lawrence Livermore National Laboratory's electron ...beam ion traps, EBIT-I and SuperEBIT, and the NASA/GSFC EBIT Calorimeter Spectrometer (ECS). We identify and measure the energies of 18 and 21 X-ray features from silicon and sulfur, respectively. The results are compared to new Flexible Atomic Code calculations and to semi-relativistic Hartree-Fock calculations by Palmeri et al. (2008). These results will be especially useful for wind diagnostics in high-mass X-ray binaries, such as Vela X-1 and Cygnus X-1, where high-resolution spectral measurements using Chandra's high-energy transmission grating has made it possible to measure Doppler shifts of . The accuracy of our measurements is consistent with that needed to analyze Chandra observations, exceeding Chandra's limit. Hence, the results presented here not only provide benchmarks for theory, but also accurate rest energies that can be used to determine the bulk motion of material in astrophysical sources. We show the usefulness of our results by applying them to redetermine Doppler shifts from Chandra observations of Vela X-1.
Abstract Cholesterol is an essential component of cellular membranes that is required for normal lipid organization and cell signaling. While the mechanisms associated with maintaining cholesterol ...homeostasis in the plasma and peripheral tissues have been well studied, the role and regulation of cholesterol biosynthesis in normal brain function and development have proven much more challenging to investigate. Smith–Lemli–Opitz syndrome (SLOS) is a disorder of cholesterol synthesis characterized by mutations of 7-dehydrocholesterol reductase (DHCR7) that impair the reduction of 7-dehydrocholesterol (7DHC) to cholesterol and lead to neurocognitive deficits, including cerebellar hypoplasia and austism behaviors. Here we have used a novel mass spectrometry-based imaging technique called cation-enhanced nanostructure-initiator mass spectrometry (NIMS) for the in situ detection of intact cholesterol molecules from biological tissues. We provide the first images of brain sterol localization in a mouse model for SLOS ( Dhcr7−/− ). In SLOS mice, there is a striking localization of both 7DHC and residual cholesterol in the abnormally developing cerebellum and brainstem. In contrast, the distribution of cholesterol in 1-day old healthy pups was diffuse throughout the cerebrum and comparable to that of adult mice. This study represents the first application of NIMS to localize perturbations in metabolism within pathological tissues and demonstrates that abnormal cholesterol biosynthesis may be particularly important for the development of these brain regions.
It has been suggested that fjord geometry could be an important contributor to the observed mass loss variability in Greenland by modulating the flow of warm water to marine-terminating glaciers. New ...gravity-derived bathymetry of Greenlandic fjords confirms the link between the grounding line depth and rates of glacier mass loss, a relationship previously predicted only in ice models. We focus on two neighboring glaciers to minimize differences in external forcing and therefore isolate the role of the fjord bathymetry. Tracy Glacier has a deeper grounding line and has been retreating since 1892 with a contemporary mass budget of −1.63 Gt a−1. Heilprin Glacier has a shallower grounding line depth, a stable ice terminus, and a mass budget of only −0.53 Gt a−1. Because of its deeper grounding line, Tracy has more ice in contact with warm subsurface water, leaving it more vulnerable to changes in ocean forcing and therefore mass loss.
•We focus on a pair of neighboring glaciers in NW Greenland with similar forcings.•Lidar data indicate Tracy Glacier is losing three times more mass than Heilprin.•Aerogravity data is inverted to obtain new bathymetry of these fjords.•A deeper grounding line exposes more ice to warm subsurface water.•For this pair, the glacier with a deeper grounding line is losing more mass.
At NASA Goddard Space Flight Center, we have previously demonstrated a kilo-pixel array of transition-edge sensor (TES) microcalorimeters capable of meeting the energy resolution requirements of the ...future X-ray Integral Field Unit (X-IFU) instrument that is being developed for the Advanced Telescope for High ENergy Astrophysics (ATHENA) observatory satellite. The TES design in this array was a square device with side length of <inline-formula><tex-math notation="LaTeX">50 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula>. Here, we describe studies of TES designs with small variations of the dimensions, exploring lengths, parallel to the current direction, ranging from <inline-formula><tex-math notation="LaTeX">75 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">50 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> and widths, perpendicular to the current direction, ranging from <inline-formula><tex-math notation="LaTeX">50 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> to <inline-formula><tex-math notation="LaTeX">15 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula>. We describe how these changes impact transition properties, thermal conductance and magnetic field sensitivity. In particular, we show that using a TES with a length of <inline-formula><tex-math notation="LaTeX">50 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> and width of <inline-formula><tex-math notation="LaTeX">30 \,\mathrm{\upmu }\mathrm{m}</tex-math></inline-formula> may be a promising route to reduce the maximum time-derivative of the TES current in an X-ray pulse and reduce the sensitivity of the TES to magnetic field.
Data from massively parallel sequencing or ‘Next Generation Sequencing’ of the human exome has reached a critical mass in both public and private databases, in that these collections now allow ...researchers to critically evaluate population genetics in a manner that was not feasible a decade ago. The ability to determine pathogenic allele frequencies by evaluation of the full coding sequences and not merely a single nucleotide polymorphism (SNP) or series of SNPs will lead to more accurate estimations of incidence. For demonstrative purposes, we analyzed the causative gene for the disorder Smith–Lemli–Opitz Syndrome (SLOS), the 7‐dehydrocholesterol reductase (DHCR7) gene and determined both the carrier frequency for DHCR7 mutations, and predicted an expected incidence of the disorder. Estimations of the incidence of SLOS have ranged widely from 1:10,000 to 1:70,000 while the carrier frequency has been reported as high as 1 in 30. Using four exome data sets with a total of 17,836 chromosomes, we ascertained a carrier frequency of pathogenic DHRC7 mutations of 1.01%, and predict a SLOS disease incidence of 1/39,215 conceptions. This approach highlights yet another valuable aspect of the exome sequencing databases, to inform clinical and health policy decisions related to genetic counseling, prenatal testing and newborn screening.
Neutrophil chemotaxis plays an essential role in innate immunity, but the underlying cellular mechanism is still not fully characterized. Here, using a small-molecule functional screening, we ...identified NADPH oxidase-dependent reactive oxygen species as key regulators of neutrophil chemotactic migration. Neutrophils with pharmacologically inhibited oxidase, or isolated from chronic granulomatous disease (CGD) patients and mice, formed more frequent multiple pseudopodia and lost their directionality as they migrated up a chemoattractant concentration gradient. Knocking down NADPH oxidase in differentiated neutrophil-like HL60 cells also led to defective chemotaxis. Consistent with the in vitro results, adoptively transferred CGD murine neutrophils showed impaired in vivo recruitment to sites of inflammation. Together, these results present a physiological role for reactive oxygen species in regulating neutrophil functions and shed light on the pathogenesis of CGD.
Previous research has established that social work practitioners are especially vulnerable to work-related psychological distress and burnout due to the high-stress nature of the profession, yet less ...research has focused on examining factors are associated with social worker retention. Emerging research on compassion satisfaction suggests that this factor could mitigate professional burnout, yet there is a gap in research focusing explicitly on examining compassion satisfaction among social workers. To address this gap in knowledge, this quantitative study collected survey data on practicing social workers who were alumni from a large southeastern university (n = 120) to examine individual and organizational factors associated with compassion satisfaction. Multiple regression analyses revealed that higher levels of emotional intelligence, perceived work autonomy, and perceived work-life balance were associated with an increase in compassion satisfaction among experienced, licensed social work practitioners. Findings have implications for how social work employers can promote compassion satisfaction through cultivating emotional intelligence among practitioners, allowing social workers autonomy in decision making, and providing supportive work environments. Recommended directions for future research include longitudinal studies with large sample sizes that expound research on compassion satisfaction by examining the role of additional factors, such as client population, job role characteristics, and supervisor support.
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