5,650 research outputs found
Water as a Solvent for Life
"Follow the water" is our basic strategy in searching for life in the universe. The universality of water as the solvent for living systems is usually justified by arguing that water supports the rich organic chemistry that seeds life, but alternative chemistries are possible in other organic solvents. Here, other, essential criteria for life that have not been sufficiently considered so far, will be discussed
A Simulation of Snow on Antarctic Sea Ice Based on Satellite Data and Climate Reanalyses
Although snow plays an important role in the energy and mass balance of sea ice, it is little studied in the Southern Ocean. We present a Lagrangian model of snow on sea ice, CASSIS, that simulates the daily creation and drift of floes. Drifting floes accumulate snow from the atmosphere and the Antarctic ice sheet, and lose snow to the ocean and snow-ice formation. The depth of snow on Southern Ocean sea ice increases in all sectors between autumn and spring 1981ā2021, reaching 40 cm in much of the Weddell Sea, coastal Amundsen Sea and south east Indian Ocean. The root mean square difference between seasonally-averaged model and ship-based snow depths is 13.1 cm, and between modeled and airborne snow depths from Operation IceBridge is 13.5 cm. Our model offers an alternative long-term snow depth record to that from passive microwave (PM) radiometry, which does not capture the seasonal growth of the snow cover. We find that although the average circumpolar snow layer thickness has increased by 16 mm between 1981 and 2021 (P = 0.004), there has been a decrease of 13 mm in the Southern Pacific Ocean (P = 0.133, but significant in spring and autumn), driven by a reduction of summer sea ice extent in this region. Our model paves the way for improved satellite-based estimates of Antarctic sea ice thickness
Dark matter halos in the multicomponent model. II. Density profiles of galactic halos
The multicomponent dark matter model with self-scattering and
inter-conversions of species into one another is an alternative dark matter
paradigm that is capable of resolving the long-standing problems of
CDM cosmology at small scales. In this paper, we have studied in
detail the properties of dark matter halos with obtained in -body cosmological simulations with the simplest
two-component (2cDM) model. A large set of velocity-dependent cross-section
prescriptions for elastic scattering and mass conversions, and , has been explored and the results
were compared with observational data. The results demonstrate that
self-interactions with the cross-section per particle mass evaluated at
km s being in the range of
cmg robustly suppress central cusps, thus resolving the core-cusp
problem. The core radii are controlled by the values of and the DM
cross-section's velocity-dependent power-law indices , but are
largely insensitive to the species' mass degeneracy. These values are in full
agreement with those resolving the substructure and too-big-to-fail problems.
We have also studied the evolution of halos in the 2cDM model with cosmic time.Comment: 17 pages, 13 figure
Facile Protocol for Water-Tolerant āFrustrated Lewis Pairā-Catalyzed Hydrogenation
Despite rapid advances in the field of metal-free, āfrustrated Lewis pairā (FLP)-catalyzed hydrogenation, the need for strictly anhydrous reaction conditions has hampered wide-scale uptake of this methodology. Herein, we report that, despite the generally perceived moisture sensitivity of FLPs, 1,4-dioxane solutions of B(C6F5)3 actually show appreciable moisture tolerance and can catalyze hydrogenation of a range of weakly basic substrates without the need for rigorously inert conditions. In particular, reactions can be performed directly in commercially available nonanhydrous solvents without subsequent drying or use of internal desiccants
Equality of Effort via Algorithmic Recourse
This paper proposes a method for measuring fairness through equality of
effort by applying algorithmic recourse through minimal interventions. Equality
of effort is a property that can be quantified at both the individual and the
group level. It answers the counterfactual question: what is the minimal cost
for a protected individual or the average minimal cost for a protected group of
individuals to reverse the outcome computed by an automated system? Algorithmic
recourse increases the flexibility and applicability of the notion of equal
effort: it overcomes its previous limitations by reconciling multiple treatment
variables, introducing feasibility and plausibility constraints, and
integrating the actual relative costs of interventions. We extend the existing
definition of equality of effort and present an algorithm for its assessment
via algorithmic recourse. We validate our approach both on synthetic data and
on the German credit dataset
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Investigating the impact of occupant response time on computer simulations of the WTC North Tower evacuation
This work explores the impact of response time distributions on high-rise building evacuation.
The analysis utilises response times extracted from printed accounts and interviews of evacuees from the
WTC North Tower evacuation of 11 September 2001. Evacuation simulations produced using these
ārealā response time distributions are compared with simulations produced using instant and engineering
response time distributions. Results suggest that while typical engineering approximations to the
response time distribution may produce reasonable evacuation times for up to 90% of the building
population, using this approach may underestimate total evacuation times by as much as 61%. These
observations are applicable to situations involving large high-rise buildings in which travel times are
generally expected to be greater than response time
Change in multimodal MRI markers predicts dementia risk in cerebral small vessel disease.
OBJECTIVE: To determine whether MRI markers, including diffusion tensor imaging (DTI), can predict cognitive decline and dementia in patients with cerebral small vessel disease (SVD). METHODS: In the prospective St George's Cognition and Neuroimaging in Stroke study, multimodal MRI was performed annually for 3 years and cognitive assessments annually for 5 years in a cohort of 99 patients with SVD, defined as symptomatic lacunar stroke and confluent white matter hyperintensities (WMH). Progression to dementia was determined in all patients. Progression of WMH, brain volume, lacunes, cerebral microbleeds, and a DTI measure (the normalized peak height of the mean diffusivity histogram distribution) as a marker of white matter microstructural damage were determined. RESULTS: Over 5 years of follow-up, 18 patients (18.2%) progressed to dementia. A significant change in all MRI markers, representing deterioration, was observed. The presence of new lacunes, and rate of increase in white matter microstructural damage on DTI, correlated with both decline in executive function and global functioning. Growth of WMH and deterioration of white matter microstructure on DTI predicted progression to dementia. A model including change in MRI variables together with their baseline values correctly classified progression to dementia with a C statistic of 0.85. CONCLUSIONS: This longitudinal prospective study provides evidence that change in MRI measures including DTI, over time durations during which cognitive change is not detectable, predicts cognitive decline and progression to dementia. It supports the use of MRI measures, including DTI, as useful surrogate biomarkers to monitor disease and assess therapeutic interventions
Comparison of higher-order mode suppression and Q-switched laser performance in thulium-doped large mode area and photonic crystal fibers
We report the influence of higher order modes (HOMs) in large mode fibers operation in Q-switched oscillator configurations at similar to 2 mu m wavelength. S-2 measurements confirm guiding of LP11 and LP02 fiber modes in a large mode area (LMA) step-index fiber, whereas a prototype photonic crystal fiber (PCF) provides nearly single-mode performance with a small portion of light in the LP11 mode. The difference in HOM content leads to a significant difference in Q-switched oscillator performance. In the step-index fiber, the percentage of cladding light increases by 20% to \u3e 40% with increasing pulse energy to similar to 250 mu J. We accredit this degradation to saturation of the gain in the fundamental mode leading to more light generated in the HOMs, which is eventually converted into cladding light. No such degradation is seen in PCF laser system for \u3e 400 mu J energies
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