1,018 research outputs found
A class of diagonal preconditioners for limited memory BFGS method.
A major weakness of the limited memory BFGS (LBFGS) method is that it may converge very slowly on
ill-conditioned problems when the identity matrix is used for initialization. Very often, the LBFGS method
can adopt a preconditioner on the identity matrix to speed up the convergence. For this purpose, we propose
a class of diagonal preconditioners to boost the performance of the LBFGS method. In this context, we find
that it is appropriate to use a diagonal preconditioner, in the form of a diagonal matrix plus a positive multiple
of the identity matrix, so as to fit information of local Hessian as well as to induce positive definiteness for
the diagonal preconditioner at a whole. The property of hereditary positive definiteness is maintained by
a careful choice of the positive scalar on the scaled identity matrix while the local curvature information
is carried implicitly on the other diagonal matrix through the variational techniques, commonly employed
in the derivation of quasi-Newton updates. Several preconditioning formulae are then derived and tested
on a large set of standard test problems to access the impact of different choices of such preconditioners
on the minimization performance
Resonant inelastic x-ray scattering study of holon-antiholon continuum in SrCuO2
We report a resonant inelastic x-ray scattering study of charge excitations
in the quasi-one-dimensional Mott insulator SrCuO2. We observe a continuum of
low-energy excitations, in which a highly dispersive feature with a large
sinusoidal dispersion (~1.1 eV) resides. We have also measured the optical
conductivity, and studied the dynamic response of the extended Hubbard model
with realistic parameters, using a dynamical density-matrix renormalization
group method. In contrast to earlier work, we do not find a long-lived exciton,
but rather these results suggest that the excitation spectrum comprises a
holon-antiholon continuum together with a broad resonance.Comment: Final version to be published in Phys. Rev. Let
Chembench: A Publicly Accessible, Integrated Cheminformatics Portal
The enormous increase in the amount of publicly available chemical genomics data and the growing emphasis on data sharing and open science mandates that cheminformaticians also make their models publicly available for broad use by the scientific community. Chembench is one of the first publicly accessible, integrated cheminformatics Web portals. It has been extensively used by researchers from different fields for curation, visualization, analysis, and modeling of chemogenomics data. Since its launch in 2008, Chembench has been accessed more than 1 million times by more than 5000 users from a total of 98 countries. We report on the recent updates and improvements that increase the simplicity of use, computational efficiency, accuracy, and accessibility of a broad range of tools and services for computer-assisted drug design and computational toxicology available on Chembench. Chembench remains freely accessible at https://chembench.mml.unc.ed
Factors that influence excessive gestational weight gain: Moving beyond assessment and counselling
One in four Canadian adults is obese, and more women are entering pregnancy with a higher body mass index (BMI) than in the past. Pregnant women who are overweight or obese have a higher risk of pregnancy-related complications than women of normal weight. Gestational weight gain (GWG) is also associated with childhood obesity. Although the factors influencing weight gain during pregnancy are multifaceted, little is known about the social inequality of GWG. This review will address some of the socioeconomic factors and maternal characteristics influencing weight gain and the impact that excessive GWG has on health outcomes such as post-partum weight retention. The effects of an overweight or obese pre-pregnancy BMI on GWG and neonatal outcomes will also be addressed. The timing of weight gain is also important, as recommendations now include trimester-specific guidelines. While not conclusive, preliminary evidence suggests that excessive weight gain during the first trimester is most detrimental
Cardiovascular magnetic resonance of the charcoal heart
We report a case of malignant melanoma metastasis to the heart presenting as complete heart block. The highlight of the case is to demonstrate that silent cardiac metastasis is not uncommon and CMR has the potential to characterize these cardiac metastases and should be used routinely as a screening tool for those cancers with a high chance of cardiac involvement
Alternative splicing of coq-2 controls the levels of rhodoquinone in animals
Parasitic helminths use two benzoquinones as electron carriers in the electron transport chain. In normoxia, they use ubiquinone (UQ), but in anaerobic conditions inside the host, they require rhodoquinone (RQ) and greatly increase RQ levels. We previously showed the switch from UQ to RQ synthesis is driven by a change of substrates by the polyprenyltransferase COQ-2 (Del Borrello et al., 2019; Roberts Buceta et al., 2019); however, the mechanism of substrate selection is not known. Here, we show helminths synthesize two coq-2 splice forms, coq-2a and coq-2e, and the coq-2e-specific exon is only found in species that synthesize RQ. We show that in Caenorhabditis elegans COQ-2e is required for efficient RQ synthesis and survival in cyanide. Importantly, parasites switch from COQ-2a to COQ-2e as they transit into anaerobic environments. We conclude helminths switch from UQ to RQ synthesis principally via changes in the alternative splicing of coq-2.Agencia Nacional de Investigación e InnovaciónCanadian Institutes of Health Researc
Alternative splicing of coq-2 controls the levels of rhodoquinone in animals
Parasitic helminths use two benzoquinones as electron carriers in the electron transport chain. In normoxia, they use ubiquinone (UQ), but in anaerobic conditions inside the host, they require rhodoquinone (RQ) and greatly increase RQ levels. We previously showed the switch from UQ to RQ synthesis is driven by a change of substrates by the polyprenyltransferase COQ-2 (Del Borrello et al., 2019; Roberts Buceta et al., 2019); however, the mechanism of substrate selection is not known. Here, we show helminths synthesize two coq-2 splice forms, coq-2a and coq-2e, and the coq-2e-specific exon is only found in species that synthesize RQ. We show that in Caenorhabditis elegans COQ-2e is required for efficient RQ synthesis and survival in cyanide. Importantly, parasites switch from COQ-2a to COQ-2e as they transit into anaerobic environments. We conclude helminths switch from UQ to RQ synthesis principally via changes in the alternative splicing of coq-2.Agencia Nacional de Investigación e InnovaciónCanadian Institutes of Health Researc
Deletion of the gabra2 gene results in hypersensitivity to the acute effects of ethanol but does not alter ethanol self administration
Human genetic studies have suggested that polymorphisms of the GABRA2 gene encoding the GABA(A) α2-subunit are associated with ethanol dependence. Variations in this gene also convey sensitivity to the subjective effects of ethanol, indicating a role in mediating ethanol-related behaviours. We therefore investigated the consequences of deleting the α2-subunit on the ataxic and rewarding properties of ethanol in mice. Ataxic and sedative effects of ethanol were explored in GABA(A) α2-subunit wildtype (WT) and knockout (KO) mice using a Rotarod apparatus, wire hang and the duration of loss of righting reflex. Following training, KO mice showed shorter latencies to fall than WT littermates under ethanol (2 g/kg i.p.) in both Rotarod and wire hang tests. After administration of ethanol (3.5 g/kg i.p.), KO mice took longer to regain the righting reflex than WT mice. To ensure the acute effects are not due to the gabra2 deletion affecting pharmacokinetics, blood ethanol concentrations were measured at 20 minute intervals after acute administration (2 g/kg i.p.), and did not differ between genotypes. To investigate ethanol's rewarding properties, WT and KO mice were trained to lever press to receive increasing concentrations of ethanol on an FR4 schedule of reinforcement. Both WT and KO mice self-administered ethanol at similar rates, with no differences in the numbers of reinforcers earned. These data indicate a protective role for α2-subunits, against the acute sedative and ataxic effects of ethanol. However, no change was observed in ethanol self administration, suggesting the rewarding effects of ethanol remain unchange
Multilevel Interventions Targeting Obesity: Research Recommendations for Vulnerable Populations
The origins of obesity are complex and multifaceted. To be successful, an intervention aiming to prevent or treat obesity may need to address multiple layers of biological, social, and environmental influences
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