100 research outputs found
Shell-model interactions from chiral effective field theory
We construct valence-space Hamiltonians for use in shell-model calculations,
where the residual two-body interaction is based on symmetry principles and the
low-momentum expansion from chiral effective field theory. In addition to the
usual free-space contact interactions, we also include novel
center-of-mass--dependent operators that arise due to the Galilean invariance
breaking by in-medium effects. We fitted the low-energy constants to 441
ground- and excited-state energies in the sd shell and obtained a
root-mean-square derivation of 1.8 MeV at leading order and of 0.5 MeV at
next-to-leading order, with natural low-energy constants in all cases. The
developed chiral shell-model interactions enable order-by-order uncertainty
estimates and show promising predictions for neutron-rich isotopes beyond the
fitted data set.Comment: 19 pages, 12 figures, published versio
Significantly improved precision of cell migration analysis in time-lapse video microscopy through use of a fully automated tracking system
<p>Abstract</p> <p>Background</p> <p>Cell motility is a critical parameter in many physiological as well as pathophysiological processes. In time-lapse video microscopy, manual cell tracking remains the most common method of analyzing migratory behavior of cell populations. In addition to being labor-intensive, this method is susceptible to user-dependent errors regarding the selection of "representative" subsets of cells and manual determination of precise cell positions.</p> <p>Results</p> <p>We have quantitatively analyzed these error sources, demonstrating that manual cell tracking of pancreatic cancer cells lead to mis-calculation of migration rates of up to 410%. In order to provide for objective measurements of cell migration rates, we have employed multi-target tracking technologies commonly used in radar applications to develop fully automated cell identification and tracking system suitable for high throughput screening of video sequences of unstained living cells.</p> <p>Conclusion</p> <p>We demonstrate that our automatic multi target tracking system identifies cell objects, follows individual cells and computes migration rates with high precision, clearly outperforming manual procedures.</p
Assessment of Automated Analyses of Cell Migration on Flat and Nanostructured Surfaces
Motility studies of cells often rely on computer software that analyzes time-lapse recorded movies and establishes cell trajectories fully automatically. This raises the question of reproducibility of results, since different programs could yield significantly different results of such automated analysis. The fact that the segmentation routines of such programs are often challenged by nanostructured surfaces makes the question more pertinent. Here we illustrate how it is possible to track cells on bright field microscopy images with image analysis routines implemented in an open-source cell tracking program, PACT (Program for Automated Cell Tracking). We compare the automated motility analysis of three cell tracking programs, PACT, Autozell, and TLA, using the same movies as input for all three programs. We find that different programs track overlapping, but different subsets of cells due to different segmentation methods. Unfortunately, population averages based on such different cell populations, differ significantly in some cases. Thus, results obtained with one software package are not necessarily reproducible by other software
Spontaneous Dissociation of Co2(CO)8 and Autocatalytic growth of Co on SiO2 : A Combined Experimental and Theoretical Investigation
We present experimental results and theoretical simulations of the adsorption
behavior of the metal-organic precursor Co2(CO)8 on SiO2 surfaces after
application of two different pre-treatment steps, namely by air plasma cleaning
or a focused electron beam pre-irradiation. We observe a spontaneous
dissociation of the precursor molecules as well as auto-deposition of cobalt on
the pre-treated SiO2 surfaces. We also find that the differences in metal
content and relative stability of these deposits depend on the pre-treatment
conditions of the substrate. Transport measurements of these deposits are also
presented. We are led to assume that the degree of passivation of the SiO2
surface by hydroxyl groups is an important controlling factor in the
dissociation process. Our calculations of various slab settings using
dispersion corrected density functional theory support this assumption. We
observe physisorption of the precursor molecule on a fully hydroxylated SiO2
surface (untreated surface) and chemisorption on a partially hydroxylated SiO2
surface (pre-treated surface) with a spontaneous dissociation of the precursor
molecule. In view of these calculations, we discuss the origin of this
dissociation and the subsequent autocatalysis.Comment: 22 pages, 8 Figures, In Press Article, Beilstein Journal of
Nanotechnology, 201
Meta-Analysis of the INSIG2 Association with Obesity Including 74,345 Individuals: Does Heterogeneity of Estimates Relate to Study Design?
The INSIG2 rs7566605 polymorphism was identified for obesity (BMIâ„30 kg/m2) in one of the first genome-wide association studies, but replications were inconsistent. We collected statistics from 34 studies (nâ=â74,345), including general population (GP) studies, population-based studies with subjects selected for conditions related to a better health status (âhealthy populationâ, HP), and obesity studies (OB). We tested five hypotheses to explore potential sources of heterogeneity. The meta-analysis of 27 studies on Caucasian adults (nâ=â66,213) combining the different study designs did not support overall association of the CC-genotype with obesity, yielding an odds ratio (OR) of 1.05 (p-valueâ=â0.27). The I2 measure of 41% (p-valueâ=â0.015) indicated between-study heterogeneity. Restricting to GP studies resulted in a declined I2 measure of 11% (p-valueâ=â0.33) and an OR of 1.10 (p-valueâ=â0.015). Regarding the five hypotheses, our data showed (a) some difference between GP and HP studies (p-valueâ=â0.012) and (b) an association in extreme comparisons (BMIâ„32.5, 35.0, 37.5, 40.0 kg/m2 versus BMI<25 kg/m2) yielding ORs of 1.16, 1.18, 1.22, or 1.27 (p-values 0.001 to 0.003), which was also underscored by significantly increased CC-genotype frequencies across BMI categories (10.4% to 12.5%, p-value for trendâ=â0.0002). We did not find evidence for differential ORs (c) among studies with higher than average obesity prevalence compared to lower, (d) among studies with BMI assessment after the year 2000 compared to those before, or (e) among studies from older populations compared to younger. Analysis of non-Caucasian adults (nâ=â4889) or children (nâ=â3243) yielded ORs of 1.01 (p-valueâ=â0.94) or 1.15 (p-valueâ=â0.22), respectively. There was no evidence for overall association of the rs7566605 polymorphism with obesity. Our data suggested an association with extreme degrees of obesity, and consequently heterogeneous effects from different study designs may mask an underlying association when unaccounted for. The importance of study design might be under-recognized in gene discovery and association replication so far
Density functional theory based screening of ternary alkali-transition metal borohydrides: A computational material design project
The dissociation of molecules, even the most simple hydrogen molecule, cannot be described accurately within density functional theory because none of the currently available functionals accounts for strong on-site correlation. This problem led to a discussion of properties that the local Kohn-Sham potential has to satisfy in order to correctly describe strongly correlated systems. We derive an analytic expression for the nontrivial form of the Kohn-Sham potential in between the two fragments for the dissociation of a single bond. We show that the numerical calculations for a one-dimensional two-electron model system indeed approach and reach this limit. It is shown that the functional form of the potential is universal, i.e., independent of the details of the two fragments.We acknowledge funding by the Spanish MEC (Grant No. FIS2007-65702-C02-01), âGrupos Consolidados UPV/EHU del Gobierno Vascoâ (Grant No. IT-319-07), and the European Community through e-I3 ETSF project (Grant Agreement No. 211956).Peer reviewe
Meta-Analysis of the INSIG2 Association with Obesity Including 74,345 Individuals: Does Heterogeneity of Estimates Relate to Study Design?
The INSIG2 rs7566605 polymorphism was identified for obesity (BMIâ„30 kg/m2) in one of the first genome-wide association studies, but replications were inconsistent. We collected statistics from 34 studies (n = 74,345), including general population (GP) studies, population-based studies with subjects selected for conditions related to a better health status (âhealthy populationâ, HP), and obesity studies (OB). We tested five hypotheses to explore potential sources of heterogeneity. The meta-analysis of 27 studies on Caucasian adults (n = 66,213) combining the different study designs did not support overall association of the CC-genotype with obesity, yielding an odds ratio (OR) of 1.05 (p-value = 0.27). The I2 measure of 41% (p-value = 0.015) indicated between-study heterogeneity. Restricting to GP studies resulted in a declined I2 measure of 11% (p-value = 0.33) and an OR of 1.10 (p-value = 0.015). Regarding the five hypotheses, our data showed (a) some difference between GP and HP studies (p-value = 0.012) and (b) an association in extreme comparisons (BMIâ„32.5, 35.0, 37.5, 40.0 kg/m2 versus BMI<25 kg/m2) yielding ORs of 1.16, 1.18, 1.22, or 1.27 (p-values 0.001 to 0.003), which was also underscored by significantly increased CC-genotype frequencies across BMI categories (10.4% to 12.5%, p-value for trend = 0.0002). We did not find evidence for differential ORs (c) among studies with higher than average obesity prevalence compared to lower, (d) among studies with BMI assessment after the year 2000 compared to those before, or (e) among studies from older populations compared to younger. Analysis of non-Caucasian adults (n = 4889) or children (n = 3243) yielded ORs of 1.01 (p-value = 0.94) or 1.15 (p-value = 0.22), respectively. There was no evidence for overall association of the rs7566605 polymorphism with obesity. Our data suggested an association with extreme degrees of obesity, and consequently heterogeneous effects from different study designs may mask an underlying association when unaccounted for. The importance of study design might be under-recognized in gene discovery and association replication so far
Search for dark matter produced in association with bottom or top quarks in âs = 13 TeV pp collisions with the ATLAS detector
A search for weakly interacting massive particle dark matter produced in association with bottom or top quarks is presented. Final states containing third-generation quarks and miss- ing transverse momentum are considered. The analysis uses 36.1 fbâ1 of protonâproton collision data recorded by the ATLAS experiment at âs = 13 TeV in 2015 and 2016. No significant excess of events above the estimated backgrounds is observed. The results are in- terpreted in the framework of simplified models of spin-0 dark-matter mediators. For colour- neutral spin-0 mediators produced in association with top quarks and decaying into a pair of dark-matter particles, mediator masses below 50 GeV are excluded assuming a dark-matter candidate mass of 1 GeV and unitary couplings. For scalar and pseudoscalar mediators produced in association with bottom quarks, the search sets limits on the production cross- section of 300 times the predicted rate for mediators with masses between 10 and 50 GeV and assuming a dark-matter mass of 1 GeV and unitary coupling. Constraints on colour- charged scalar simplified models are also presented. Assuming a dark-matter particle mass of 35 GeV, mediator particles with mass below 1.1 TeV are excluded for couplings yielding a dark-matter relic density consistent with measurements
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