4,796 research outputs found
Reionization history constraints from neural network based predictions of high-redshift quasar continua
Observations of the early Universe suggest that reionization was complete by
, however, the exact history of this process is still unknown. One
method for measuring the evolution of the neutral fraction throughout this
epoch is via observing the Ly damping wings of high-redshift quasars.
In order to constrain the neutral fraction from quasar observations, one needs
an accurate model of the quasar spectrum around Ly, after the spectrum
has been processed by its host galaxy but before it is altered by absorption
and damping in the intervening IGM. In this paper, we present a novel machine
learning approach, using artificial neural networks, to reconstruct quasar
continua around Ly. Our QSANNdRA algorithm improves the error in this
reconstruction compared to the state-of-the-art PCA-based model in the
literature by 14.2% on average, and provides an improvement of 6.1% on average
when compared to an extension thereof. In comparison with the extended PCA
model, QSANNdRA further achieves an improvement of 22.1% and 16.8% when
evaluated on low-redshift quasars most similar to the two high-redshift quasars
under consideration, ULAS J1120+0641 at and ULAS J1342+0928 at
, respectively. Using our more accurate reconstructions of these two
quasars, we estimate the neutral fraction of the IGM using a homogeneous
reionization model and find at
and at . Our
results are consistent with the literature and favour a rapid end to
reionization
A model for cost analysisâapplication to clinical laboratory test economics using computer facilities
The Kabua 1 cranium: Virtual anatomical reconstructions
Our current knowledge of the emergence of anatomically modern humans, and the human lineage in general, is limited, in large part because of the lack of a well preserved and well dated fossil record from Pleistocene Africa. Thus, the primary aim of our research is to partly relieve this problem by virtually reconstructing and analyzing the hominin cranial remains of Kabua 1, found in Kenya in the 1950s. Most scholars have argued that Kabua 1 represents an anatomically modern Homo sapiens, although the fragmentary nature of the remains and lack of a chronometric date hinder robust phylogenetic and taxonomic assessments. This manuscript presents the first steps taken to resolve this issue, namely a set of reconstructions of the specimen that would allow comparison with the fossil record. First, we virtually removed sediment and laboratory adhesives from ÎŒct scans of the fragments. Subsequently, all fragments were separated by segmentation of the ÎŒct data and described. Finally, virtual surface projections were used in the creation of several anatomical reconstructions, based on separate reference crania. These first steps provide a framework that will be used for quantitative shape analyses that aim to more firmly place these remains in the context of human evolution
The formation of CO through consumption of gas-phase CO on vacuum-UV irradiated water ice
[Abridged] Observations of protoplanetary disks suggest that they are
depleted in gas-phase CO. It has been posed that gas-phase CO is chemically
consumed and converted into less volatile species through gas-grain processes.
Observations of interstellar ices reveal a CO component within HO ice
suggesting co-formation. The aim of this work is to experimentally verify the
interaction of gas-phase CO with solid-state OH radicals above the sublimation
temperature of CO. Amorphous solid water (ASW) is deposited at 15 K and
followed by vacuum-UV (VUV) irradiation to dissociate HO and create OH
radicals. Gas-phase CO is simultaneously admitted and only adsorbs with a short
residence time on the ASW. Products in the solid state are studied with
infrared spectroscopy and once released into the gas phase with mass
spectrometry. Results show that gas-phase CO is converted into CO, with an
efficiency of 7-27%, when interacting with VUV irradiated ASW. Between 40 and
90 K, CO production is constant, above 90 K, O production takes over.
In the temperature range of 40-60 K, the CO remains in the solid state,
while at temperatures 70 K the formed CO is released into the gas
phase. We conclude that gas-phase CO reacts with solid-state OH radicals above
its sublimation temperature. This gas-phase CO and solid-state OH radical
interaction could explain the observed CO embedded in water-rich ices. It
may also contribute to the observed lack of gas-phase CO in planet-forming
disks, as previously suggested. Our experiments indicate a lower water ice
dissociation efficiency than originally adopted in model descriptions of
planet-forming disks and molecular clouds. Incorporation of the reduced water
ice dissociation and increased binding energy of CO on a water ice surfaces in
these models would allow investigation of this gas-grain interaction to its
full extend.Comment: Accepted for publication in Astronomy & Astrophysic
Mixed-Integer MPC Strategies for Fueling and Density Control in Fusion Tokamaks
Model predictive control (MPC) is promising for fueling and core density
feedback control in nuclear fusion tokamaks, where the primary actuators,
frozen hydrogen fuel pellets fired into the plasma, are discrete. Previous
density feedback control approaches have only approximated pellet injection as
a continuous input due to the complexity that it introduces. In this letter, we
model plasma density and pellet injection as a hybrid system and propose two
MPC strategies for density control: mixed-integer (MI) MPC using a conventional
mixed-integer programming (MIP) solver and MPC utilizing our novel modification
of the penalty term homotopy (PTH) algorithm. By relaxing the integer
requirements, the PTH algorithm transforms the MIP problem into a series of
continuous optimization problems, reducing computational complexity. Our novel
modification to the PTH algorithm ensures that it can handle path constraints,
making it viable for constrained hybrid MPC in general. Both strategies perform
well with regards to reference tracking without violating path constraints and
satisfy the computation time limit for real-time control of the pellet
injection system. However, the computation time of the PTH-based MPC strategy
consistently outpaces the conventional MI-MPC strategy
Sound localization with bilateral bone conduction devices
Purpose To investigate sound localization in patients bilaterally fitted with bone conduction devices (BCDs). Additionally, clinically applicable methods to improve localization accuracy were explored. Methods Fifteen adults with bilaterally fitted percutaneous BCDs were included. At baseline, sound localization, (un)aided pure-tone thresholds, device use, speech, spatial and qualities of hearing scale (SSQ) and York hearing-related quality of life (YHRQL) questionnaire were measured. Settings to optimize sound localizing were added to the BCDs. At 1 month, sound localization was assessed again and localization was practiced with a series of sounds with visual feedback. At 3 months, localization performance, device use and questionnaire scores were determined again. Results At baseline, one patient with congenital hearing loss demonstrated near excellent localization performance and four other patients (three with congenital hearing loss) localized sounds (quite) accurately. Seven patients with acquired hearing loss were able to lateralize sounds, i.e. identify whether sounds were coming from the left or right side, but could not localize sounds accurately. Three patients (one with congenital hearing loss) could not even lateralize sounds correctly. SSQ scores were significantly higher at 3 months. Localization performance, device use and YHRQL scores were not significantly different between visits. Conclusion In this study, the majority of experienced bilateral BCD users could lateralize sounds and one third was able to localize sounds (quite) accurately. The localization performance was robust and stable over time. Although SSQ scores were increased at the last visit, optimizing device settings and a short practice session did not improve sound localization
Changes in Blood Cell Deformability in Chorea-Acanthocytosis and Effects of Treatment With Dasatinib or Lithium
Misshaped red blood cells (RBCs), characterized by thorn-like protrusions known as acanthocytes, are a key diagnostic feature in Chorea-Acanthocytosis (ChAc), a rare neurodegenerative disorder. The altered RBC morphology likely influences their biomechanical properties which are crucial for the cells to pass the microvasculature. Here, we investigated blood cell deformability of five ChAc patients compared to healthy controls during up to 1-year individual off-label treatment with the tyrosine kinase inhibitor dasatinib or several weeks with lithium. Measurements with two microfluidic techniques allowed us to assess RBC deformability under different shear stresses. Furthermore, we characterized leukocyte stiffness at high shear stresses. The results showed that blood cell deformabilityâincluding both RBCs and leukocytes - in general was altered in ChAc patients compared to healthy donors. Therefore, this study shows for the first time an impairment of leukocyte properties in ChAc. During treatment with dasatinib or lithium, we observed alterations in RBC deformability and a stiffness increase for leukocytes. The hematological phenotype of ChAc patients hinted at a reorganization of the cytoskeleton in blood cells which partly explains the altered mechanical properties observed here. These findings highlight the need for a systematic assessment of the contribution of impaired blood cell mechanics to the clinical manifestation of ChAc
Off hour admission to an intensivist-led ICU is not associated with increased mortality
Introduction: Caring for the critically ill is a 24-hour-a-day responsibility, but not all resources and staff are available during off hours. We evaluated whether intensive care unit (ICU) admission during off hours affects hospital mortality. Methods: This retrospective multicentre cohort study was carried out in three non-academic teaching hospitals in the Netherlands. All consecutive patients admitted to the three ICUs between 2004 and 2007 were included in the study, except for patients who did not fulfil APACHE II criteria (readmissions, burns, cardiac surgery, younger than 16 years, length of stay less than 8 hours). Data were collected prospectively in the ICU databases. Hospital mortality was the primary endpoint of the study. Off hours was defined as the interval between 10 pm and 8 am during weekdays and between 6 pm and 9 am during weekends. Intensivists, with no responsibilities outside the ICU, were present in the ICU during daytime and available for either consultation or assistance on site during off hours. Residents were available 24 hours a day 7 days a week in two and fellows in one of the ICUs. Results: A total of 6725 patients were included in the study, 4553 (67.7%) admitted during daytime and 2172 (32.3%) admitted during off hours. Baseline characteristics of patients admitted during daytime were significantly different from those of patients admitted during off hours. Hospital mortality was 767 (16.8%) in patients admitted during daytime and 469 (21.6%) in patients admitted during off hours (P < 0.001, unadjusted odds ratio 1.36, 95%CI 1.20-1.55). Standardized mortality ratios were similar for patients admitted during off hours and patients admitted during daytime. In a logistic regression model APACHE II expected mortality, age and admission type were all significant confounders but off-hours admission was not significantly associated with a higher mortality (P = 0.121, adjusted odds ratio 1.125, 95%CI 0.969-1.306). Conclusions: The increased mortality after ICU admission during off hours is explained by a higher illness severity in patients admitted during off hours
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