102 research outputs found
Stability of Impurities with Coulomb Potential in Graphene with Homogeneous Magnetic Field
Given a 2-dimensional no-pair Weyl operator with a point nucleus of charge Z,
we show that a homogeneous magnetic field does not lower the critical charge
beyond which it collapses.Comment: J. Math. Phys. (in press
Complementary Domains of Retinoic Acid Production and Degradation in the Early Chick Embryo
AbstractExcess retinoids as well as retinoid deprivation cause abnormal development, suggesting that retinoid homeostasis is critical for proper morphogenesis. RALDH-2 and CYP26, two key enzymes that carry out retinoic acid (RA) synthesis and degradation, respectively, were cloned from the chick and show significant homology with their orthologs in other vertebrates. Expression patterns of RALDH-2 and CYP26 genes were determined in the early chick embryo by in situ hybridization. During gastrulation and neurulation RALDH-2 and CYP26 were expressed in nonoverlapping regions, with RALDH-2 transcripts localized to the presumptive presomitic and lateral plate mesoderm and CYP26 mRNA to the presumptive mid- and forebrain. The two domains of expression were separated by an approximately 300-μm-wide gap, encompassing the presumptive hindbrain. In the limb region, a similar spatial segregation of RALDH-2 and CYP26 expression was found at stages 14 and 15. Limb region mesoderm expressed RALDH-2, whereas the overlying limb ectoderm expressed CYP26. RA-synthesizing and -degrading enzymatic activities were measured biochemically in regions expressing RALDH-2 or CYP26. Regions expressing RALDH-2 generated RA efficiently from precursor retinal but degraded RA only inefficiently. Conversely, tissue expressing CYP26 efficiently degraded but did not synthesize RA. Localized regions of RA synthesis and degradation mediated by these two enzymes may therefore provide a mechanism to regulate RA homeostasis spatially in vertebrate embryos
A semiclassical approach to the Dirac equation
We derive a semiclassical time evolution kernel and a trace formula for the
Dirac equation. The classical trajectories that enter the expressions are
determined by the dynamics of relativistic point particles. We carefully
investigate the transport of the spin degrees of freedom along the trajectories
which can be understood geometrically as parallel transport in a vector bundle
with SU(2) holonomy. Furthermore, we give an interpretation in terms of a
classical spin vector that is transported along the trajectories and whose
dynamics, dictated by the equation of Thomas precession, gives rise to
dynamical and geometric phases every orbit is weighted by. We also present an
analogous approach to the Pauli equation which we analyse in two different
limits
Impact of exercise interventions on physical fitness in breast cancer patients and survivors: a systematic review
Background: This systematic review aims to identify the effects of exercise interventions in patients with breast cancer (BCP) and survivors (BCS) on selected variables of physical fitness. Methods: A comprehensive literature search was conducted using Medline and Scopus. Randomized controlled trials with isolated exercise interventions in BCP and BCS women (< 5 years from therapy completion) were included. The risk of bias (RoB) assessment was conducted using the Cochrane RoB-2-tool. Variables regarding cardiorespiratory fitness (CRF), strength (ST), fatigue (F) and health-related quality of life (HRQoL) were discussed. Results: Of the 336 studies initially identified, 22 met all the inclusion criteria and were deemed eligible. RoB assessment indicated that the studies had predominantly “some concerns” or had “low RoB”, with only 3 studies presenting a “high RoB”. The mean duration and frequency of exercise interventions were 19 weeks and 3 sessions/week, performed at moderate intensity (65% VO2max and 66% 1RM, for aerobic and resistance-training interventions, respectively). Conclusions: Exercise interventions seem to be a valuable strategy in BCP to avoid the decline of CRF, ST, F and HRQoL. Conversely, improved physical function among BCS is observed for the same variables. Resistance training and combined interventions seem to provide the most encouraging variations of the selected outcomes. PROSPERO registration ID: CRD42021237917
Zitterbewegung and semiclassical observables for the Dirac equation
In a semiclassical context we investigate the Zitterbewegung of relativistic
particles with spin 1/2 moving in external fields. It is shown that the
analogue of Zitterbewegung for general observables can be removed to arbitrary
order in \hbar by projecting to dynamically almost invariant subspaces of the
quantum mechanical Hilbert space which are associated with particles and
anti-particles. This not only allows to identify observables with a
semiclassical meaning, but also to recover combined classical dynamics for the
translational and spin degrees of freedom. Finally, we discuss properties of
eigenspinors of a Dirac-Hamiltonian when these are projected to the almost
invariant subspaces, including the phenomenon of quantum ergodicity
Quarkonium and hydrogen spectra with spin dependent relativistic wave equation
A non-linear non-perturbative relativistic atomic theory introduces spin in
the dynamics of particle motion. The resulting energy levels of Hydrogen atom
are exactly same as the Dirac theory. The theory accounts for the energy due to
spin-orbit interaction and for the additional potential energy due to spin and
spin-orbit coupling. Spin angular momentum operator is integrated into the
equation of motion. This requires modification to classical Laplacian operator.
Consequently the Dirac matrices and the k operator of Dirac's theory are
dispensed with. The theory points out that the curvature of the orbit draws on
certain amount of kinetic and potential energies affecting the momentum of
electron and the spin-orbit interaction energy constitutes a part of this
energy. The theory is developed for spin 1/2 bound state single electron in
Coulomb potential and then further extended to quarkonium physics by
introducing the linear confining potential. The unique feature of this
quarkonium model is that the radial distance can be exactly determined and does
not have a statistical interpretation. The established radial distance is then
used to determine the wave function. The observed energy levels are used as the
input parameters and the radial distance and the string tension are predicted.
This ensures 100% conformance to all observed energy levels for the heavy
quarkonium.Comment: 14 pages, v7: Journal reference adde
Digitale Erschließung und Sicherung von aktuellen archäologischen Befunden
Bei Projekten zur Digitalisierung in Geisteswissenschaften ist heute die Realisierung größerer, überregionaler und über das World Wide Web abfragbarer Lösungen erforderlich. Die Beiträge dieses Bandes wurden auf der Tagung des Staatsarchivs Hamburg und des Zentrums "Geisteswissenschaften in der digitalen Welt" an der Universität Hamburg am 10. und 11. April 2006 gehalten. Sie leisten einen interdisziplinären Beitrag zur erforderlichen Standardisierung dieser Angebote, die erst den dringend notwendigen Austausch erleichtern und die gemeinsame Nutzung strukturierter Daten ermöglichen kann.Today, digitization projects in the Humanities require the implementation of larger, supraregional solutions. The contributions in this volume were presented at the conference of the Hamburg State Archives and the Center for the Humanities in the Digital World at the University of Hamburg on April 10 and 11, 2006. They make an interdisciplinary contribution to the required standardisation of corresponding services which can only facilitate the urgently needed exchange of information and make it possible to share structured data
Salmonella Strains Isolated from Galápagos Iguanas Show Spatial Structuring of Serovar and Genomic Diversity
It is thought that dispersal limitation primarily structures host-associated bacterial populations because host distributions inherently limit transmission opportunities. However, enteric bacteria may disperse great distances during food-borne outbreaks. It is unclear if such rapid long-distance dispersal events happen regularly in natural systems or if these events represent an anthropogenic exception. We characterized Salmonella enterica isolates from the feces of free-living Galápagos land and marine iguanas from five sites on four islands using serotyping and genomic fingerprinting. Each site hosted unique and nearly exclusive serovar assemblages. Genomic fingerprint analysis offered a more complex model of S. enterica biogeography, with evidence of both unique strain pools and of spatial population structuring along a geographic gradient. These findings suggest that even relatively generalist enteric bacteria may be strongly dispersal limited in a natural system with strong barriers, such as oceanic divides. Yet, these differing results seen on two typing methods also suggests that genomic variation is less dispersal limited, allowing for different ecological processes to shape biogeographical patterns of the core and flexible portions of this bacterial species' genome
Genome-wide linkage analysis of inguinal hernia in pigs using affected sib pairs
BACKGROUND: Inguinal and scrotal hernias are of great concern to pig producers, and lead to poor animal welfare and severe economic loss. Selection against these conditions is highly preferable, but at this time no gene, Quantitative Trait Loci (QTL), or mode of inheritance has been identified in pigs or in any other species. Therefore, a complete genome scan was performed in order to identify genomic regions affecting inguinal and scrotal hernias in pigs. Records from seedstock breeding farms were collected. No clinical examinations were executed on the pigs and there was therefore no distinction between inguinal and scrotal hernias. The genome scan utilised affected sib pairs (ASP), and the data was analysed using both an ASP test based on Non-parametric Linkage (NPL) analysis, and a Transmission Disequilibrium Test (TDT). RESULTS: Significant QTLs (p < 0.01) were detected on 8 out of 19 porcine chromosomes. The most promising QTLs, however, were detected in SSC1, SSC2, SSC5, SSC6, SSC15, SSC17 and SSCX; all of these regions showed either statistical significance with both statistical methods, or convincing significance with one of the methods. Haplotypes from these suggestive QTL regions were constructed and analysed with TDT. Of these, six different haplotypes were found to be differently transmitted (p < 0.01) to healthy and affected pigs. The most interesting result was one haplotype on SSC5 that was found to be transmitted to hernia pigs with four times higher frequency than to healthy pigs (p < 0.00005). CONCLUSION: For the first time in any species, a genome scan has revealed suggestive QTLs for inguinal and scrotal hernias. While this study permitted the detection of chromosomal regions only, it is interesting to note that several promising candidate genes, including INSL3, MIS, and CGRP, are located within the highly significant QTL regions. Further studies are required in order to narrow down the suggestive QTL regions, investigate the candidate genes, and to confirm the suggestive QTLs in other populations. The haplotype associated with inguinal and scrotal hernias may help in achieving selection against the disorder
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