Genetical and cytological studies in the genus plantago

The totality of living organisms which comprises the plant kingdom presents an extreme diversity of form. In broad conception it may be said that the analysis and understanding of this diversity embraces the whole field of botanical study. Traditionally however plant classification has been the task of taxonomists using morphological data with ancillary considerations of geographical distribution and hybrid sterility. The primary concern of orthodox taxonomy is to supply recognizable reference points for the use of general biologists, although their classifications may be later the subject of theoretical, e.g. evolutionary, interpretation.In recent years "experimental taxonomists" have developed a different method of approach to the problems of classification. This approach is based equally on the understanding of variation in the light of modern cytogenetic study and on intensive ecological and cultivation work with the living plants. The aim of this work is not limited by the practical considerations of orthodox taxonomy.Thus Turesson (1922, 23, 25) showed that widely distributed species become differentiated into local hereditary types, naturally selected by the action of local environmental factors on the gene complex of the plant population. The local populations become morphologically distinct, since some genes are selected, others being suppressed, by different combinations of habitat factors. The local populations may remain capable of interbreeding freely (ecotypes), though, with greater differentiation, interpopulation hybrids show increasing sterility. Such populations are termed "ecospecies ". This type of analysis has been confirmed by numerous other workers.Broadly speaking the categories of experimental taxonomy as at present visualised may be conveniently grouped under two heads:(1) Infra -specific intra- fertile populations between which free gene exchange is potentially possible, though not often realised in nature, and(2) Specific populations between which gene exchange is partially or totally prevented even when opportunit is presented.The problem presented to the experimental taxonomists has two aspects; first to assess the degree of homology between the hereditary constitutions of different populations,and second to determine the gene exchange potential amongst them.The present investigation deals with certain cytological problems which have been encountered during the course of an experimental taxonomic study of Plantago maritima L. and its allies. It has already been reported, Gregor (1939), that the N. American Greenlandic and N. European sea plantain populations are diploid (n = 6); those inhabiting the region of the Alps are of two kinds (a) diploid and (b) tetraploid (n = 12). Proof was obtained that the diploids and tetraploids can be crossed, Gregor (1939), but at that time it was not known whether gene transfer from one population to the other was actually possible. Consequently the two groups were provisionally regarded as belonging to separate coenospecies (i.e. to categories incapable of exchanging genes), but with the qualification that, "if it should be found that the diploid and tetraploid groups are capable of exchanging genes then they would belong to different ecospecies of the same coenospecies ". It has therefore been the primary object of the present investigation to determine whether or not gene exchange between diploids and tetraploids has any foundation in fact and at the same time to assess the degree of relationship in and between all diploid and tetraploid populations.That restricted gene exchange between populations is not necessarily expressed as visible morphological differentiation can be readily appreciated from the fact that a specimen supplied by the Royal Botanic Garden, Edinburgh, as Plantago alpina L. proved to be tetraploid, while other specimens collected from a reputed habitat of the same species have been found to be diploid. It might be argued that the morphological criterion of chromosome number would, alone, effectively solve this problem, but such a delimitatio would, by itself, be quite inadequate as a means of recording tie evolutionary independence of diploid and tetraploid populations. In such cases, therefore, taxonomic emphasis should be transferred from the morphological characteristics to the potential evolutionary significance of the populations concerned. A classification based on information of this kind would have a far greater theoretical significance, though obviously less practical utility, than one based on morphological criteria alone

An AC electric trap for ground-state molecules

We here report on the realization of an electrodynamic trap, capable of trapping neutral atoms and molecules in both low-field and high-field seeking states. Confinement in three dimensions is achieved by switching between two electric field configurations that have a saddle-point at the center of the trap, i.e., by alternating a focusing and a defocusing force in each direction. AC trapping of 15ND3 molecules is experimentally demonstrated, and the stability of the trap is studied as a function of the switching frequency. A 1 mK sample of 15ND3 molecules in the high-field seeking component of the |J,K>=|1,1> level, the ground-state of para-ammonia, is trapped in a volume of about 1 mm^3

Stiffness and energy losses in cylindrically symmetric superconductor levitating systems

Stiffness and hysteretic energy losses are calculated for a magnetically levitating system composed of a type-II superconductor and a permanent magnet when a small vibration is produced in the system. We consider a cylindrically symmetric configuration with only vertical movements and calculate the current profiles under the assumption of the critical state model. The calculations, based on magnetic energy minimization, take into account the demagnetization fields inside the superconductor and the actual shape of the applied field. The dependence of stiffness and hysteretic energy losses upon the different important parameters of the system such as the superconductor aspect ratio, the relative size of the superconductor-permanent magnet, and the critical current of the superconductor are all systematically studied. Finally, in view of the results, we provide some trends on how a system such as the one studied here could be designed in order to optimize both the stiffness and the hysteretic losses.Comment: 8 pages; 8 figure

The Fluctuations of the Quark Number and of the Chiral Condensate

The distributions of the quark number and chiral condensate over the gauge fields are computed for QCD in Euclidean space at nonzero quark chemical potential. As both operators are non-hermitian the distributions are in the complex plane. Moreover, because of the sign problem, the distributions are not real and positive. The computations are carried out within leading order chiral perturbation theory and give a direct insight into the delicate cancellations that take place in contributions to the total baryon number and the chiral condensate.Comment: 19 pages, 2 figure

Dynamics of particles and cages in an experimental 2D glass former

We investigate the dynamics of a glass forming 2D colloidal mixture and show the existence of collective motions of the particles. We introduce a mean square displacement MSD with respect to the nearest neighbors which shows remarkable deviations from the usual MSD quantifying the individual motion of our particles. Combined with the analysis of the self part of the Van Hove function this indicates a coupled motion of particles with their cage as well as intra cage hopping processes.Comment: Submitted to EP

Mitotic chromosomes are compacted laterally by KIF4 and condensin and axially by topoisomerase IIα

© 2012 Samejima et al. This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication dateMitotic chromosome formation involves a relatively minor condensation of the chromatin volume coupled with a dramatic reorganization into the characteristic "X" shape. Here we report results of a detailed morphological analysis, which revealed that chromokinesin KIF4 cooperated in a parallel pathway with condensin complexes to promote the lateral compaction of chromatid arms. In this analysis, KIF4 and condensin were mutually dependent for their dynamic localization on the chromatid axes. Depletion of either caused sister chromatids to expand and compromised the "intrinsic structure" of the chromosomes (defined in an in vitro assay), with loss of condensin showing stronger effects. Simultaneous depletion of KIF4 and condensin caused complete loss of chromosome morphology. In these experiments, topoisomerase IIα contributed to shaping mitotic chromosomes by promoting the shortening of the chromatid axes and apparently acting in opposition to the actions of KIF4 and condensins. These three proteins are major determinants in shaping the characteristic mitotic chromosome morphology

Sphalerons, spectral flow, and anomalies

The topology of configuration space may be responsible in part for the existence of sphalerons. Here, sphalerons are defined to be static but unstable finite-energy solutions of the classical field equations. Another manifestation of the nontrivial topology of configuration space is the phenomenon of spectral flow for the eigenvalues of the Dirac Hamiltonian. The spectral flow, in turn, is related to the possible existence of anomalies. In this review, the interconnection of these topics is illustrated for three particular sphalerons of SU(2) Yang-Mills-Higgs theory.Comment: 35 pages with revtex4; invited paper for the August special issue of JMP on "Integrability, topological solitons and beyond

Molecular cloning of a human homologue of Drosophila heterochromatin protein HP1 using anti-centromere autoantibodies with anti-chromo specificity

We have identified a novel autoantibody specificity in scleroderma that we term anti-chromo. These antibodies recognize several chromosomal antigens with apparent molecular mass of between 23 and 25 kDa, as determined by immunoblots. Anti-chromo autoantibodies occur in 10-15% of sera from patients with anti-centromere antibodies (ACA). We used anti-chromo antibodies to screen a human expression library and obtained cDNA clones encoding a 25 kDa chromosomal autoantigen. DNA sequence analysis reveals this protein to be a human homologue of HP1, a heterochromatin protein of Drosophila melanogaster. We designate our cloned protein HP1Hs alpha. Epitope mapping experiments using both human and Drosophila HP1 reveal that anti-chromo antibodies target a region at the amino terminus of the protein. This region contains a conserved motif, the chromo domain (or HP1/Pc box), first recognized by comparison of Drosophila HP1 with the Polycomb gene product. Both proteins are thought to play a role in creating chromatin structures in which gene expression is suppressed. Anti-chromo thus defines a novel type of autoantibody that recognizes a conserved structural motif found on a number of chromosomal proteins

Unveiling the disc structure in ultraluminous X-ray source NGC 55 ULX-1

© 2022 The Author(s). Published by Oxford University Press on behalf of Royal Astronomical Society. This is the accepted manuscript version of an article which has been published in final form athttps://doi.org/10.1093/mnras/stac2453Despite two decades of studies, it is still not clear whether ULX spectral transitions are due to stochastic variability in the wind or variations in the accretion rate or in the source geometry. The compact object is also unknown for most ULXs. In order to place constraints onto such scenarios and on the structure of the accretion disc, we studied the temporal evolution of the spectral components of the variable source NGC 55 ULX-1. Using recent and archival data obtained with the XMM-Newton satellite, we modelled the spectra with two blackbody components which we interpret as thermal emission from the inner accretion flow and the regions around or beyond the spherization radius. The luminosity-temperature (L-T) relation of each spectral component agrees with the L proportional T^4 relationship expected from a thin disc model, which suggests that the accretion rate is close to the Eddington limit. However, there are some small deviations at the highest luminosities, possibly due to an expansion of the disc and a contribution from the wind at higher accretion rates. Assuming that such deviations are due to the crossing of the Eddington or supercritical accretion rate, we estimate a compact object mass of 6-14 Msun, favouring a stellar-mass black hole as the accretor.Peer reviewe

Breaking the limit: Super-Eddington accretion onto black holes and neutron stars

With the recent discoveries of massive and highly luminous quasars at high redshifts (z∼7; e.g. Mortlock et al. 2011), the question of how black holes (BHs) grow in the early Universe has been cast in a new light. In order to grow BHs with M_(BH) > 10^9 M⊙ by less than a billion years after the Big Bang, mass accretion onto the low-mass seed BHs needs to have been very rapid (Volonteri & Rees, 2005). Indeed, for any stellar remnant seed, the rate required would need to exceed the Eddington limit. This is the point at which the outward force produced by radiation pressure is equal to the gravitational attraction experienced by the in-falling matter. In principle, this implies that there is a maximum luminosity an object of mass M can emit; assuming spherical accretion and that the opacity is dominated by Thompson scattering, this Eddington luminosity is L_E = 1.38×10^(38)(M/M⊙) erg s^(−1). In reality, it is known that this limit can be violated, due to non-spherical geometry or various kinds of instabilities. Nevertheless, the Eddington limit remains an important reference point, and many of the details of how accretion proceeds above this limit remain unclear. Understanding how this so-called super-Eddington accretion occurs is of clear cosmological importance, since it potentially governs the growth of the first supermassive black holes (SMBHs) and the impact this growth would have had on their host galaxies (‘feedback') and the epoch of reionization, as well as improving our understanding of accretion physics more generally