265 research outputs found
Nuclear Octupole Correlations and the Enhancement of Atomic Time-Reversal Violation
We examine the time-reversal-violating nuclear ``Schiff moment'' that induces
electric dipole moments in atoms. After presenting a self-contained derivation
of the form of the Schiff operator, we show that the distribution of Schiff
strength, an important ingredient in the ground-state Schiff moment, is very
different from the electric-dipole-strength distribution, with the Schiff
moment receiving no strength from the giant dipole resonance in the
Goldhaber-Teller model. We then present shell-model calculations in light
nuclei that confirm the negligible role of the dipole resonance and show the
Schiff strength to be strongly correlated with low-lying octupole strength.
Next, we turn to heavy nuclei, examining recent arguments for the strong
enhancement of Schiff moments in octupole-deformed nuclei over that of 199Hg,
for example. We concur that there is a significant enhancement while pointing
to effects neglected in previous work (both in the octupole-deformed nuclides
and 199Hg) that may reduce it somewhat, and emphasizing the need for
microscopic calculations to resolve the issue. Finally, we show that static
octupole deformation is not essential for the development of collective Schiff
moments; nuclei with strong octupole vibrations have them as well, and some
could be exploited by experiment.Comment: 25 pages, 4 figures embedded in tex
Enhanced T-odd P-odd Electromagnetic Moments in Reflection Asymmetric Nuclei
Collective P- and T- odd moments produced by parity and time invariance
violating forces in reflection asymmetric nuclei are considered. The enhanced
collective Schiff, electric dipole and octupole moments appear due to the
mixing of rotational levels of opposite parity. These moments can exceed
single-particle moments by more than two orders of magnitude. The enhancement
is due to the collective nature of the intrinsic moments and the small energy
separation between members of parity doublets. In turn these nuclear moments
induce enhanced T- and P- odd effects in atoms and molecules. First a simple
estimate is given and then a detailed theoretical treatment of the collective
T-, P- odd electric moments in reflection asymmetric, odd-mass nuclei is
presented and various corrections evaluated. Calculations are performed for
octupole deformed long-lived odd-mass isotopes of Rn, Fr, Ra, Ac and Pa and the
corresponding atoms. Experiments with such atoms may improve substantially the
limits on time reversal violation.Comment: 28 pages, Revte
Proteins and their peptide motifs in acellular apatite mineralization of scaffolds for tissue engineering
Many proteins in the inorganic=organic matrix of bone induce or modulate or inhibit mineralization of apatite
in vivo. Many attempts have been made to mimic and understand this mechanism as part of bone formation, and
ectopic mineralization and control thereof. Many attempts have also been made to use such proteins or protein
fragments to harness their potential for improved mineralization. Such proteins and peptide motifs have also been
the inspiration for attempts of making mimics of their structures and motifs using chemical or biological synthesis.
The aim of this review is to highlight how proteins and (poly)peptides themselves impact mineralization
in the human body, and how those could be used and have been used for improving apatite mineralization, for
example, on or in materials that by themselves do not induce apatite mineralization but otherwise have interesting
properties for use as bone tissue engineering scaffolds.J. Benesch wishes to acknowledge the financial support from FCT, postdoctoral fellowship scholarship SFRH/BPD/17584/2004. This work was carried out under the scope of the European Union NoE EXPERTISSUES (NMP3-CT-2004500283) and partially funded by the European Union FP6 STREP Project HIPPOCRATES (NMP3-CT-2003-505758) and FCT project ProteoLight (PTDC/FIS/68517/2006)
Elastic interactions of active cells with soft materials
Anchorage-dependent cells collect information on the mechanical properties of
the environment through their contractile machineries and use this information
to position and orient themselves. Since the probing process is anisotropic,
cellular force patterns during active mechanosensing can be modelled as
anisotropic force contraction dipoles. Their build-up depends on the mechanical
properties of the environment, including elastic rigidity and prestrain. In a
finite sized sample, it also depends on sample geometry and boundary conditions
through image strain fields. We discuss the interactions of active cells with
an elastic environment and compare it to the case of physical force dipoles.
Despite marked differences, both cases can be described in the same theoretical
framework. We exactly solve the elastic equations for anisotropic force
contraction dipoles in different geometries (full space, halfspace and sphere)
and with different boundary conditions. These results are then used to predict
optimal position and orientation of mechanosensing cells in soft material.Comment: Revtex, 38 pages, 8 Postscript files included; revised version,
accepted for publication in Phys. Rev.
Affective Man-Machine Interface: Unveiling human emotions through biosignals
As is known for centuries, humans exhibit an electrical profile. This profile is altered through various psychological and physiological processes, which can be measured through biosignals; e.g., electromyography (EMG) and electrodermal activity (EDA). These biosignals can reveal our emotions and, as such, can serve as an advanced man-machine interface (MMI) for empathic consumer products. However, such a MMI requires the correct classification of biosignals to emotion classes. This chapter starts with an introduction on biosignals for emotion detection. Next, a state-of-the-art review is presented on automatic emotion classification. Moreover, guidelines are presented for affective MMI. Subsequently, a research is presented that explores the use of EDA and three facial EMG signals to determine neutral, positive, negative, and mixed emotions, using recordings of 21 people. A range of techniques is tested, which resulted in a generic framework for automated emotion classification with up to 61.31% correct classification of the four emotion classes, without the need of personal profiles. Among various other directives for future research, the results emphasize the need for parallel processing of multiple biosignals
Genome-wide association analysis identifies variants associated with nonalcoholic fatty liver disease that have distinct effects on metabolic traits
Nonalcoholic fatty liver disease (NAFLD) clusters in families, but the only known common genetic variants influencing risk are near PNPLA3. We sought to identify additional genetic variants influencing NAFLD using genome-wide association (GWA) analysis of computed tomography (CT) measured hepatic steatosis, a non-invasive measure of NAFLD, in large population based samples. Using variance components methods, we show that CT hepatic steatosis is heritable (∼26%-27%) in family-based Amish, Family Heart, and Framingham Heart Studies (n = 880 to 3,070). By carrying out a fixed-effects meta-analysis of genome-wide association (GWA) results between CT hepatic steatosis and ∼2.4 million imputed or genotyped SNPs in 7,176 individuals from the Old Order Amish, Age, Gene/Environment Susceptibility-Reykjavik study (AGES), Family Heart, and Framingham Heart Studies, we identify variants associated at genome-wide significant levels (p<5×10(-8)) in or near PNPLA3, NCAN, and PPP1R3B. We genotype these and 42 other top CT hepatic steatosis-associated SNPs in 592 subjects with biopsy-proven NAFLD from the NASH Clinical Research Network (NASH CRN). In comparisons with 1,405 healthy controls from the Myocardial Genetics Consortium (MIGen), we observe significant associations with histologic NAFLD at variants in or near NCAN, GCKR, LYPLAL1, and PNPLA3, but not PPP1R3B. Variants at these five loci exhibit distinct patterns of association with serum lipids, as well as glycemic and anthropometric traits. We identify common genetic variants influencing CT-assessed steatosis and risk of NAFLD. Hepatic steatosis associated variants are not uniformly associated with NASH/fibrosis or result in abnormalities in serum lipids or glycemic and anthropometric traits, suggesting genetic heterogeneity in the pathways influencing these traits.Peer reviewe
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