456 research outputs found
Concentration of rocuronium in cerebrospinal fluid of patients undergoing cerebral aneurysm clippingâ
Background. This study assessed the concentration of rocuronium in the cerebrospinal fluid (CSF) of patients undergoing cerebral aneurysm clipping, and investigated whether the mode of administration (single bolus vs continuous infusion) influenced the CSF concentration. Methods. Twenty patients with subarachnoid haemorrhage were randomly allocated to receive a bolus dose (bolus group), or a bolus followed by a continuous infusion of rocuronium (infusion group) (n=10 for each group). Arterial blood and ventricular CSF were sampled 2 h after the rocuronium bolus. Samples were analysed by liquid chromatography electrospray ionizationâtandem mass spectrometry. Results. Rocuronium could be detected in all the CSF samples. The mean (range) CSF concentration was 2.2 (0.9-4.6) ng ml-1 in the bolus group and 12.4 (2.4-34.6) ng ml-1 in the infusion group; P<0.01. Conclusions. This study demonstrated that rocuronium, normally not considered to cross the blood-brain barrier, is regularly found in the CSF of patients undergoing cerebral clipping; continuous infusion of the drug led to higher plasma and CSF concentrations than after a single bolus dose. Br J Anaesth 2004; 92: 419-2
Chemical Doppelgangers in GALAH DR3: the Distinguishing Power of Neutron-Capture Elements Among Milky Way Disk Stars
The observed chemical diversity of Milky Way stars places important
constraints on Galactic chemical evolution and the mixing processes that
operate within the interstellar medium. Recent works have found that the
chemical diversity of disk stars is low. For example, the APOGEE "chemical
doppelganger rate," or the rate at which random pairs of field stars appear as
chemically similar as stars born together, is high, and the chemical
distributions of APOGEE stars in some Galactic populations are well-described
by two-dimensional models. However, limited attention has been paid to the
heavy elements (Z > 30) in this context. In this work, we probe the potential
for neutron-capture elements to enhance the chemical diversity of stars by
determining their effect on the chemical doppelganger rate. We measure the
doppelganger rate in GALAH DR3, with abundances rederived using The Cannon, and
find that considering the neutron-capture elements decreases the doppelganger
rate from 2.2% to 0.4%, nearly a factor of 6, for stars with -0.1 < [Fe/H] <
0.1. While chemical similarity correlates with similarity in age and dynamics,
including neutron-capture elements does not appear to select stars that are
more similar in these characteristics. Our results highlight that the
neutron-capture elements contain information that is distinct from that of the
lighter elements and thus add at least one dimension to Milky Way abundance
space. This work illustrates the importance of considering the neutron-capture
elements when chemically characterizing stars and motivates ongoing work to
improve their atomic data and measurements in spectroscopic surveys.Comment: 23 pages, 16 figures, 1 table. Submitted to AAS Journals, comments
welcome. Associated catalog of high precision, Cannon-rederived abundances
for GALAH giants to be made publicly available upon acceptance and available
now upon request. See Walsen et al. 2023 for a complementary, high precision,
Cannon-rederived abundance catalog for GALAH solar twin
BICEP3: a 95 GHz refracting telescope for degree-scale CMB polarization
BICEP3 is a 550 mm-aperture refracting telescope for polarimetry of radiation
in the cosmic microwave background at 95 GHz. It adopts the methodology of
BICEP1, BICEP2 and the Keck Array experiments - it possesses sufficient
resolution to search for signatures of the inflation-induced cosmic
gravitational-wave background while utilizing a compact design for ease of
construction and to facilitate the characterization and mitigation of
systematics. However, BICEP3 represents a significant breakthrough in
per-receiver sensitivity, with a focal plane area 5 larger than a
BICEP2/Keck Array receiver and faster optics ( vs. ).
Large-aperture infrared-reflective metal-mesh filters and infrared-absorptive
cold alumina filters and lenses were developed and implemented for its optics.
The camera consists of 1280 dual-polarization pixels; each is a pair of
orthogonal antenna arrays coupled to transition-edge sensor bolometers and read
out by multiplexed SQUIDs. Upon deployment at the South Pole during the 2014-15
season, BICEP3 will have survey speed comparable to Keck Array 150 GHz (2013),
and will significantly enhance spectral separation of primordial B-mode power
from that of possible galactic dust contamination in the BICEP2 observation
patch.Comment: 12 pages, 5 figures. Presented at SPIE Astronomical Telescopes and
Instrumentation 2014: Millimeter, Submillimeter, and Far-Infrared Detectors
and Instrumentation for Astronomy VII. To be published in Proceedings of SPIE
Volume 915
Chasing the impact of the Gaia-Sausage-Enceladus merger on the formation of the Milky Way thick disc
We employ our Bayesian Machine Learning framework BINGO (Bayesian INference for Galactic archaeOlogy) to obtain high-quality stellar age estimates for 68 360 red giant and red clump stars present in the 17th data release of the Sloan Digital Sky Survey, the APOGEE-2 high-resolution spectroscopic survey. By examining the denoised age-metallicity relationship of the Galactic disc stars, we identify a drop in metallicity with an increase in [Mg/Fe] at an early epoch, followed by a chemical enrichment episode with increasing [Fe/H] and decreasing [Mg/Fe]. This result is congruent with the chemical evolution induced by an early-epoch gas-rich merger identified in the Milky Way-like zoom-in cosmological simulation Auriga. In the initial phase of the merger of Auriga 18 there is a drop in metallicity due to the merger diluting the metal content and an increase in the [Mg/Fe] of the primary galaxy. Our findings suggest that the last massive merger of our Galaxy, the Gaia-Sausage-Enceladus, was likely a significant gas-rich merger and induced a starburst, contributing to the chemical enrichment and building of the metal-rich part of the thick disc at an early epoch
Differentiation Between Type I and Type II Substrate Binding to Cytochrome P450 by Temperature Studies
The binding reactions of type J and type II substances to
cytochrome P450 solubilized from phenobarbital induced rat liver
microsomes show different dependence on temperature. With increasing
temperature the type II binding is lowered whereas the
stability of type I substrate complexes increases. The binding enthalpies
were calculated from the van\u27t Hoff plots and discussed
in connection with the entropy and Gibbs energy of substrate
binding to cytochrome P450. Our data on temperature dependence
provide further evidence pointing to a difference between the
binding sites of the two classes of substrates, and support the view
that the type I binding site is located in a hydrophobic part of the
cytochrome P450 molecule
Many Roads Lead to Lithium: Formation Pathways For Lithium-Rich Red Giants
Stellar models predict that lithium (Li) inside a star is destroyed during
the first dredge-up phase, yet 1.2% of red giant stars are Li-rich. We aim to
uncover possible origins of this population, by analysing 1155 Li-rich giants
(A(Li) 1.5) in GALAH DR3. To expose peculiar traits of Li-rich stars, we
construct a reference sample of Li-normal (doppelg\"anger) stars with matched
evolutionary state and fiducial supernova abundances. Comparing Li-rich and
doppelg\"anger spectra reveals systematic differences in the H- and
Ca-triplet line profiles associated with the velocity broadening measurement.
We also find twice as many Li-rich stars appear to be fast rotators (2% with
km s) compared to doppelg\"angers. On
average, Li-rich stars have higher abundances than their doppelg\"angers, for a
subset of elements, and Li-rich stars at the base of RGB have higher mean
process abundances ( dex for Ba, Y, Zr), relative to their
doppelg\"angers. External mass-transfer from intermediate-mass AGB companions
could explain this signature. Additional companion analysis excludes binaries
with mass ratios 0.5 at 7 AU. We also discover that highly
Ba-enriched stars are missing from the Li-rich population, possibly due to
low-mass AGB companions which preclude Li-enrichment. Finally, we confirm a
prevalence of Li-rich stars on the red clump that increases with lithium, which
supports an evolutionary state mechanism for Li-enhancement. Multiple culprits,
including binary spin-up and mass-transfer, are therefore likely mechanisms of
Li-enrichment.Comment: 29 pages, 19 figures, 6 tables. Submitted to Ap
Gaia FGK Benchmark stars: Opening the black box of stellar element abundance determination
Gaia and its complementary spectroscopic surveys combined will yield the most comprehensive database of kinematic and chemical information of stars in the Milky Way. The Gaia FGK benchmark stars play a central role in this matter as they are calibration pillars for the atmospheric parameters and chemical abundances for various surveys. The spectroscopic analyses of the benchmark stars are done by combining different methods, and the results will be affected by the systematic uncertainties inherent in each method. In this paper, we explore some of these systematic uncertainties. We determined line abundances of Ca, Cr, Mn and Co for four benchmark stars using six different methods. We changed the default input parameters of the different codes in a systematic way and found, in some cases, significant differences between the results. Since there is no consensus on the correct values for many of these default parameters, we urge the community to raise discussions towards standard input parameters that could alleviate the difference in abundances obtained by different methods. In this work, we provide quantitative estimates of uncertainties in elemental abundances due to the effect of differing technical assumptions in spectrum modelling
First Season QUIET Observations: Measurements of CMB Polarization Power Spectra at 43 GHz in the Multipole Range 25 <= ell <= 475
The Q/U Imaging ExperimenT (QUIET) employs coherent receivers at 43GHz and
95GHz, operating on the Chajnantor plateau in the Atacama Desert in Chile, to
measure the anisotropy in the polarization of the CMB. QUIET primarily targets
the B modes from primordial gravitational waves. The combination of these
frequencies gives sensitivity to foreground contributions from diffuse Galactic
synchrotron radiation. Between 2008 October and 2010 December, >10,000hours of
data were collected, first with the 19-element 43GHz array (3458hours) and then
with the 90-element 95GHz array. Each array observes the same four fields,
selected for low foregrounds, together covering ~1000deg^2. This paper reports
initial results from the 43GHz receiver which has an array sensitivity to CMB
fluctuations of 69uK sqrt(s). The data were extensively studied with a large
suite of null tests before the power spectra, determined with two independent
pipelines, were examined. Analysis choices, including data selection, were
modified until the null tests passed. Cross correlating maps with different
telescope pointings is used to eliminate a bias. This paper reports the EE, BB
and EB power spectra in the multipole range ell=25-475. With the exception of
the lowest multipole bin for one of the fields, where a polarized foreground,
consistent with Galactic synchrotron radiation, is detected with 3sigma
significance, the E-mode spectrum is consistent with the LCDM model, confirming
the only previous detection of the first acoustic peak. The B-mode spectrum is
consistent with zero, leading to a measurement of the tensor-to-scalar ratio of
r=0.35+1.06-0.87. The combination of a new time-stream double-demodulation
technique, Mizuguchi-Dragone optics, natural sky rotation, and frequent
boresight rotation leads to the lowest level of systematic contamination in the
B-mode power so far reported, below the level of r=0.1Comment: 19 pages, 14 figures, higher quality figures are available at
http://quiet.uchicago.edu/results/index.html; Fixed a typo and corrected
statistical error values used as a reference in Figure 14, showing our
systematic uncertainties (unchanged) vs. multipole; Revision to ApJ accepted
version, this paper should be cited as "QUIET Collaboration et al. (2011)
The QUIET Instrument
The Q/U Imaging ExperimenT (QUIET) is designed to measure polarization in the
Cosmic Microwave Background, targeting the imprint of inflationary
gravitational waves at large angular scales (~ 1 degree). Between 2008 October
and 2010 December, two independent receiver arrays were deployed sequentially
on a 1.4 m side-fed Dragonian telescope. The polarimeters which form the focal
planes use a highly compact design based on High Electron Mobility Transistors
(HEMTs) that provides simultaneous measurements of the Stokes parameters Q, U,
and I in a single module. The 17-element Q-band polarimeter array, with a
central frequency of 43.1 GHz, has the best sensitivity (69 uK sqrt(s)) and the
lowest instrumental systematic errors ever achieved in this band, contributing
to the tensor-to-scalar ratio at r < 0.1. The 84-element W-band polarimeter
array has a sensitivity of 87 uK sqrt(s) at a central frequency of 94.5 GHz. It
has the lowest systematic errors to date, contributing at r < 0.01. The two
arrays together cover multipoles in the range l= 25-975. These are the largest
HEMT-based arrays deployed to date. This article describes the design,
calibration, performance of, and sources of systematic error for the
instrument
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