143 research outputs found
Effects of the low lying Dirac modes on excited hadrons in lattice QCD
Chiral symmetry breaking in Quantum Chromodynamics is associated with the low
lying spectral modes of the Dirac operator according to the Banks-Casher
relation. Here we study how removal of a variable number of low lying modes
from the valence quark sector affects the masses of the ground states and first
excited states of baryons and mesons in two flavor lattice QCD.Comment: 6 pages, 2 figures. Contribution to proceedings of "Excited QCD
2012", May 6-12, 2012, Peniche, Portuga
More effects of Dirac low-mode removal
In previous studies we have shown that hadrons, except for a pion, survive
the removal of the lowest lying Dirac eigenmodes from the valence quark
propagators. The low-modes are tied to the dynamical breaking of chiral
symmetry and we found chiral symmetry to be restored by means of matching
masses of chiral partners, like, e.g., the vector and axial vector currents.
Here we investigate the influence of removing the lowest part of the Dirac
spectrum on the locality of the Dirac operator. Moreover, we analyze the
influence of low-mode truncation on the quark momenta and thereupon on the
hadron spectrum and, finally, introduce a reweighting scheme to extend the
truncation to the sea quark sector.Comment: 7pages, 4 figures. Proceedings of the 31st International Symposium on
Lattice Field Theory, July 29 - August 3, 2013, Mainz, German
Symmetries of hadrons after unbreaking the chiral symmetry
We study hadron correlators upon artificial restoration of the spontaneously
broken chiral symmetry. In a dynamical lattice simulation we remove the lowest
lying eigenmodes of the Dirac operator from the valence quark propagators and
study evolution of the hadron masses obtained. All mesons and baryons in our
study, except for a pion, survive unbreaking the chiral symmetry and their
exponential decay signals become essentially better. From the analysis of the
observed spectroscopic patterns we conclude that confinement still persists
while the chiral symmetry is restored. All hadrons fall into different chiral
multiplets. The broken U(1)_A symmetry does not get restored upon unbreaking
the chiral symmetry. We also observe signals of some higher symmetry that
includes chiral symmetry as a subgroup. Finally, from comparison of the \Delta
- N splitting before and after unbreaking of the chiral symmetry we conclude
that both the color-magnetic and the flavor-spin quark-quark interactions are
of equal importance.Comment: 12 pages, 14 figures; final versio
Unbreaking chiral symmetry
In Quantum Chromodynamics (QCD) the eigenmodes of the Dirac operator with
small absolute eigenvalues have a close relationship to the dynamical breaking
of the chiral symmetry. In a simulation with two dynamical quarks, we study the
behavior of meson propagators when removing increasingly more of those modes in
the valence sector, thus partially removing effects of chiral symmetry
breaking. We find that some of the symmetry aspects are restored (e.g., the
masses of and approach each other) while confining properties
persist.Comment: 5 pages, 5 figures (figure added, references updated
Three-dimensional reconstruction of painted human interphase chromosomes: active and inactive X chromosome territories have similar volumes but differ in shape and surface structure.
Melanosomes in pigmented epithelia maintain eye lens transparency during zebrafish embryonic development
Altered levels of trace elements are associated with increased oxidative stress that is eventually responsible for pathologic conditions. Oxidative stress has been proposed to be involved in eye diseases, including cataract formation. We visualized the distribution of metals and other trace elements in the eye of zebrafish embryos by micro X-ray fluorescence (μ-XRF) imaging. Many elements showed highest accumulation in the retinal pigment epithelium (RPE) of the zebrafish embryo. Knockdown of the zebrafish brown locus homologues tyrp1a/b eliminated accumulation of these elements in the RPE, indicating that they are bound by mature melanosomes. Furthermore, albino (slc45a2) mutants, which completely lack melanosomes, developed abnormal lens reflections similar to the congenital cataract caused by mutation of the myosin chaperon Unc45b, and an in situ spin trapping assay revealed increased oxidative stress in the lens of albino mutants. Finally transplanting a wildtype lens into an albino mutant background resulted in cataract formation. These data suggest that melanosomes in pigment epithelial cells protect the lens from oxidative stress during embryonic development, likely by buffering trace elements
An annotated checklist of bryophytes of Europe, Macaronesia and Cyprus
Introduction. Following on from work on the European bryophyte Red List, the taxonomically and nomenclaturally updated spreadsheets used for that project have been expanded into a new checklist for the bryophytes of Europe. Methods. A steering group of ten European bryologists was convened, and over the course of a year, the spreadsheets were compared with previous European checklists, and all changes noted. Recent literature was searched extensively. A taxonomic system was agreed, and the advice and expertise of many European bryologists sought. Key results. A new European checklist of bryophytes, comprising hornworts, liverworts and mosses, is presented. Fifteen new combinations are proposed. Conclusions. This checklist provides a snapshot of the current European bryophyte flora in 2019. It will already be out-of-date on publication, and further research, particularly molecular work, can be expected to result in many more changes over the next few years.Peer reviewe
Multicolour-banding fluorescence in situ hybridisation (mbanding-FISH) to identify recurrent chromosomal alterations in breast tumour cell lines
Recurrent chromosome breakpoints in tumour cells may point to cancer genes, but not many have been molecularly characterised. We have used multicolour-banding fluorescence in situ hybridisation (mbanding-FISH) on breast tumour cell lines to identify regions of chromosome break created by inversions, duplications, insertions and translocations on chromosomes 1, 5, 8, 12 and 17. We delineate a total of 136 regions of break, some of them occurring with high frequency. We further describe two examples of dual-colour FISH characterisation of breakpoints, which target the 1p36 and 5p11–12 regions. Both breaks involve genes whose function is unknown to date. The mbanding-FISH strategy constitutes an efficient first step in the search for potential cancer genes
Chromosomal analysis of non-small-cell lung cancer by multicolour fluorescent in situ hybridisation
- …