1,489 research outputs found
The sensitivity of Northern Hemisphere ice sheets to atmospheric forcing during the last glacial cycle using PMIP3 models
The evolution of Northern Hemisphere ice sheets through the last glacial cycle is simulated with the glacial index method by using the climate forcing from one General Circulation Model, COSMOS. By comparing the simulated results to geological reconstructions, we first show that the modelled climate is capable of capturing the main features of the ice-sheet evolution. However, large deviations exist, likely due to the absence of nonlinear interactions between ice sheet and other climate components. The model uncertainties of the climate forcing are examined using the output from nine climate models from the Paleoclimate Modelling Intercomparison Project Phase III. The results show a large variability in simulated ice sheets between the different models. We find that the ice-sheet extent pattern resembles summer surface air temperature pattern at the Last Glacial Maximum, confirming the dominant role of surface ablation process for high-latitude Northern Hemisphere ice sheets. This study shows the importance of the upper boundary condition for ice-sheet modelling, and implies that careful constraints on climate output is essential for simulating realistic glacial Northern Hemisphere ice sheets
Naming Game on Adaptive Weighted Networks
We examine a naming game on an adaptive weighted network. A weight of
connection for a given pair of agents depends on their communication success
rate and determines the probability with which the agents communicate. In some
cases, depending on the parameters of the model, the preference toward
successfully communicating agents is basically negligible and the model behaves
similarly to the naming game on a complete graph. In particular, it quickly
reaches a single-language state, albeit some details of the dynamics are
different from the complete-graph version. In some other cases, the preference
toward successfully communicating agents becomes much more relevant and the
model gets trapped in a multi-language regime. In this case gradual coarsening
and extinction of languages lead to the emergence of a dominant language,
albeit with some other languages still being present. A comparison of
distribution of languages in our model and in the human population is
discussed.Comment: 22 pages, accepted in Artificial Lif
Nuclear binding near a quantum phase transition
How do protons and neutrons bind to form nuclei? This is the central question
of ab initio nuclear structure theory. While the answer may seem as simple as
the fact that nuclear forces are attractive, the full story is more complex and
interesting. In this work we present numerical evidence from ab initio lattice
simulations showing that nature is near a quantum phase transition, a
zero-temperature transition driven by quantum fluctuations. Using lattice
effective field theory, we perform Monte Carlo simulations for systems with up
to twenty nucleons. For even and equal numbers of protons and neutrons, we
discover a first-order transition at zero temperature from a Bose-condensed gas
of alpha particles (4He nuclei) to a nuclear liquid. Whether one has an
alpha-particle gas or nuclear liquid is determined by the strength of the
alpha-alpha interactions, and we show that the alpha-alpha interactions depend
on the strength and locality of the nucleon-nucleon interactions. This insight
should be useful in improving calculations of nuclear structure and important
astrophysical reactions involving alpha capture on nuclei. Our findings also
provide a tool to probe the structure of alpha cluster states such as the Hoyle
state responsible for the production of carbon in red giant stars and point to
a connection between nuclear states and the universal physics of bosons at
large scattering length.Comment: Published version to appear in Physical Review Letters. Main: 5
pages, 3 figures. Supplemental material: 13 pages, 6 figure
Synthesis and characterization of tungsten trioxide powders prepared from tungstic acids
WO3 powders were prepared by the thermal decomposition of tungstic acids (WO3 nH2O, n ¼ 1/3, 1, 2). The
tungstic acids were synthesized from WO4
2 aqueous solutions under a variety of conditions of pH, temperature
and W(VI) concentrations. The thermal decomposition of the tungstic acids into WO3 was analysed by TG and
DSC methods. Nano-sized WO3 powders with different morphological characteristics were obtained by thermal
treatment of the tungstic acids at 500 8C in air atmosphere. The morphologies of WO3 powders were
characterised by scanning electron microscopy and infrared absorption spectroscopy. Patterns of infrared spectra
were related with distinct powder morphologies
Hidden spin-isospin exchange symmetry
The strong interactions among nucleons have an approximate spin-isospin
exchange symmetry that arises from the properties of quantum chromodynamics in
the limit of many colors, . However this large- symmetry is well
hidden and reveals itself only when averaging over intrinsic spin orientations.
Furthermore, the symmetry is obscured unless the momentum resolution scale is
close to an optimal scale that we call . We show
that the large- derivation requires a momentum resolution scale of
MeV. We derive a set of spin-isospin
exchange sum rules and discuss implications for the spectrum of P and
applications to nuclear forces, nuclear structure calculations, and
three-nucleon interactions.Comment: 5 pages (main) + 3 pages (supplemental materials), 1 figure (main) +
4 figures (supplemental materials), final version to appear in Phys. Rev.
Let
Analysis of Incomplete Compound Variables
This is the peer reviewed version of the following article: Zhao, J., Cook, R. J. and Wu, C. (2015), Multiple imputation for the analysis of incomplete compound variables. Can J Statistics, 43: 240–264. doi: 10.1002/cjs.11249, which has been published in final form at http://dx.doi.org/10.1002/cjs.11249. This article may be used for non-commercial purposes in accordance With Wiley Terms and Conditions for self-archiving'In many settings interest lies in modelling a compound variable defined as a function of two or more component variables. When one or more of the components are missing, the compound variable is not observed and a strategy for handling incomplete data is required. Analyses based on individuals with complete data are inefficient and yield potentially inconsistent estimators.We develop a multiple imputation strategy in this setting with an auxiliary model for imputing the compound variable directly, and one based on a multivariate imputation model for the component variables. Asymptotic properties of the imputation-based estimators are presented for the case in which the imputation model is correctly specified, and a shrinkage estimator is proposed to reduce the bias arising from misspecification of the imputation model. Finite sample properties of the various estimators are examined through simulations. An application to data from the Cana- dian Youth Smoking Survey involving a study of body mass index illustrates the approach.Natural Sciences and Engineering Research Council of Canada (RJC RGPIN 155849, CW RGPIN 05613); Canadian Institutes for Health Research (RJC FRN 13887
Glycaemic Response to a Nut-Enriched Diet in Asian Chinese Adults with Normal or High Glycaemia: The TÅ« Ora RCT
\ua9 2024 by the authors. Nut-based products are a good source of high-quality plant protein in addition to mono- and polyunsaturated fatty acids, and may aid low-glycaemic dietary strategies important for the prevention of type 2 diabetes (T2D). In particular, they may be advantageous in populations susceptible to dysglycaemia, such as Asian Chinese. The present study aimed to compare effects of a higher-protein nut bar (HP-NB, also higher in total fibre and unsaturated fats, comprising mixed almonds and peanuts) vs. an isoenergetic higher-carbohydrate cereal bar (HC-CB) within the diet of 101 Chinese adults with overweight and normo- or hyperglycaemia. Ectopic pancreas and liver fat were characterised using magnetic resonance imaging and spectroscopy (MRI/S) as a secondary outcome. Participants were randomized to receive HP-NB or HC-CB daily as a 1 MJ light meal or snack replacement, in addition to healthy eating advice. Anthropometry and clinical indicators of T2D risk were assessed fasted and during an oral glucose tolerance test (OGTT), pre- and post-intervention. No significant difference was observed between diet groups for body weight, body mass index, waist or hip circumference, blood pressure, glucoregulatory markers, lipid profile or inflammatory markers over 12 weeks (all, p > 0.05). No difference was observed between glycaemic subgroups or those with normal versus high ectopic organ fat. Although HP-NB can attenuate postprandial glycaemia following a meal, no effects were observed for either fasting or glucose-mediated outcomes following longer-term inclusion in the habitual diet of Chinese adults with overweight, including at-risk subgroups
Ab initio alpha-alpha scattering
Processes involving alpha particles and alpha-like nuclei comprise a major
part of stellar nucleosynthesis and hypothesized mechanisms for thermonuclear
supernovae. In an effort towards understanding alpha processes from first
principles, we describe in this letter the first ab initio calculation of
alpha-alpha scattering. We use lattice effective field theory to describe the
low-energy interactions of nucleons and apply a technique called the adiabatic
projection method to reduce the eight-body system to an effective two-cluster
system. We find good agreement between lattice results and experimental phase
shifts for S-wave and D-wave scattering. The computational scaling with
particle number suggests that alpha processes involving heavier nuclei are also
within reach in the near future.Comment: 6 pages, 6 figure
Reversal of left-right asymmetry induced by aberrant nodal signaling in the node of mouse embryos
The node at the anterior tip of the primitive streak serves as an initial generator of the left-right (L-R) axis in mammalian embryos. We now show that a small disturbance in molecular signaling at the node is responsible for the L-R reversal of visceral organs in the inv mutant mouse. In the node of wild-type embryos, the expression of Nodal and Cerl2 (Dand5), which encodes an inhibitor of Nodal, is asymmetric, with the level of Nodal expression being higher on the left side and that of Cerl2 expression higher on the right. In inv/inv embryos, however, a localized reduction in the level of Cerl2 expression results in upregulation of the Nodal signal and a consequent induction of Lefty expression in the node. The ectopic expression of Lefty1 delays the onset of Nodal expression in the lateral plate mesoderm. L-R asymmetry of Cerl2 expression in the node also becomes reversed in a manner dependent on the Nodal signal. Nodal expression in the lateral plate mesoderm then appears on the right side, probably reflecting the balance between Nodal and Cerl2 in the node. The inhibition of Cerl2 expression by the Nodal signal suggests a mechanism for amplification of the cue for L-R asymmetry provided by nodal flow and for stabilization of asymmetric gene expression around the node. In inv/inv embryos, this system may function in reverse as a result of ectopic production of Lefty, which inhibits the Nodal signal on the left side in a manner dependent on leftward nodal flow.Ministry of Education, Culture, Sports, Science, and Technology of Japan; CREST; Kyushu University; Naito Foundationinfo:eu-repo/semantics/publishedVersio
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