242 research outputs found
Stability of zero modes in parafermion chains
One-dimensional topological phases can host localized zero-energy modes that
enable high-fidelity storage and manipulation of quantum information. Majorana
fermion chains support a classic example of such a phase, having zero modes
that guarantee two-fold degeneracy in all eigenstates up to exponentially small
finite-size corrections. Chains of `parafermions'---generalized Majorana
fermions---also support localized zero modes, but, curiously, only under much
more restricted circumstances. We shed light on the enigmatic zero mode
stability in parafermion chains by analytically and numerically studying the
spectrum and developing an intuitive physical picture in terms of domain-wall
dynamics. Specifically, we show that even if the system resides in a gapped
topological phase with an exponentially accurate ground-state degeneracy,
higher-energy states can exhibit a splitting that scales as a power law with
system size---categorically ruling out exact localized zero modes. The
transition to power-law behavior is described by critical behavior appearing
exclusively within excited states.Comment: 15 pages, 8 figures; substantial improvements to chiral case,
coauthor added. Published 7 October 201
KELT-9 and its ultra-hot Jupiter: stellar parameters, composition, and planetary pollution
KELT-9b is an ultra-hot Jupiter observed to be undergoing extreme mass loss.
Its A0-type host star has a radiative envelope, which makes its surface layers
prone to retaining recently accreted material. To search for potential signs of
planetary material polluting the stellar surface, we carry out the most
comprehensive chemical characterisation of KELT-9 to-date. New element
detections include Na and Y, which had previously been detected in the
ultra-hot Jupiter but not studied in the star; these detections complete the
set of nine elements measured in both star and planet. In comparing KELT-9 with
similar open cluster stars we find no strong anomalies. This finding is
consistent with calculations of photospheric pollution accounting for stellar
mixing and using observationally estimated KELT-9b mass loss rates. We also
rule out recent, short-lived intensive mass transfer such as the stellar
ingestion of an Earth-mass exomoon.Comment: 7 pages, 7 figures, accepted for publication in MNRA
Coupled Oscillators with Chemotaxis
A simple coupled oscillator system with chemotaxis is introduced to study
morphogenesis of cellular slime molds. The model successfuly explains the
migration of pseudoplasmodium which has been experimentally predicted to be
lead by cells with higher intrinsic frequencies. Results obtained predict that
its velocity attains its maximum value in the interface region between total
locking and partial locking and also suggest possible roles played by partial
synchrony during multicellular development.Comment: 4 pages, 5 figures, latex using jpsj.sty and epsf.sty, to appear in
J. Phys. Soc. Jpn. 67 (1998
Abundant Refractory Sulfur in Protoplanetary Disks
Sulfur is one of the most abundant elements in the Universe, with important
roles in astro-, geo-, and biochemistry. Its main reservoirs in planet-forming
disks have previously eluded detection: gaseous molecules only account for
\% of total elemental sulfur, with the rest likely in either ices or
refractory minerals. Mechanisms such as giant planets can filter out dust from
gas accreting onto disk-hosting stars. For stars above 1.4 solar masses, this
leaves a chemical signature on the stellar photosphere that can be used to
determine the fraction of each element that is locked in dust. Here, we present
an application of this method to sulfur, zinc, and sodium. We analyse the
accretion-contaminated photospheres of a sample of young stars and find
\% of elemental sulfur is in refractory form in their disks. The
main carrier is much more refractory than water ice, consistent with sulfide
minerals such as FeS
Macroscopic Optical Imaging Technique for Wide-Field Estimation of Fluorescence Depth in Optically Turbid Media for Application in Brain Tumor Surgical Guidance
A diffuse imaging method is presented that enables wide-field estimation of the depth of fluorescent molecular markers in turbid media by quantifying the deformation of the detected fluorescence spectra due to the wavelength-dependent light attenuation by overlying tissue. This is achieved by measuring the ratio of the fluorescence at two wavelengths in combination with normalization techniques based on diffuse reflectance measurements to evaluate tissue attenuation variations for different depths. It is demonstrated that fluorescence topography can be achieved up to a 5 mm depth using a near-infrared dye with millimeter depth accuracy in turbid media having optical properties representative of normal brain tissue. Wide-field depth estimates are made using optical technology integrated onto a commercial surgical microscope, making this approach feasible for real-world applications
Cell-type specific RNA-Seq reveals novel roles and regulatory programs for terminally differentiated Dictyostelium cells
Abstract Background A major hallmark of multicellular evolution is increasing complexity by the evolution of new specialized cell types. During Dictyostelid evolution novel specialization occurred within taxon group 4. We here aim to retrace the nature and ancestry of the novel âcupâ cells by comparing their transcriptome to that of other cell types. Results RNA-Seq was performed on purified mature spore, stalk and cup cells and on vegetative amoebas. Clustering and phylogenetic analyses showed that cup cells were most similar to stalk cells, suggesting that they share a common ancestor. The affinity between cup and stalk cells was also evident from promoter-reporter studies of newly identified cell-type genes, which revealed late expression in cups of many stalk genes. However, GO enrichment analysis reveal the unexpected prominence of GTPase mediated signalling in cup cells, in contrast to enrichment of autophagy and cell wall synthesis related transcripts in stalk cells. Combining the cell type RNA-Seq data with developmental expression profiles revealed complex expression dynamics in each cell type as well as genes exclusively expressed during terminal differentiation. Most notable were nine related hssA-like genes that were highly and exclusively expressed in cup cells. Conclusions This study reveals the unique transcriptomes of the mature cup, stalk and spore cells of D. discoideum and provides insight into the ancestry of cup cells and roles in signalling that were not previously realized. The data presented in this study will serve as an important resource for future studies into the regulation and evolution of cell type specialization
Young Women and Consumer Culture
This article is presented as an intervention in the field of feminist media and cultural studies with particular reference to consumer culture. It is concerned with the seeming evasion of critique which can be detected in a number of recent feminist responses to the way in which modalities of âpopular feminismâ have found themselves incorporated into women's genres of television, such as, in particular, the US series Sex in the City. This usage or instrumentalization of feminism (in its most conventionally liberal feminist guise) also provides corporate culture with the means of presenting itself to young women as their ally and even champion of âgirlsâ while at the same time earning seeming approval for adopting the mantle of social responsibility, which makes the concept of popular feminism more problematic than it first appeared. Such appropriation of popular feminist discourse by the commercial domain prompts a self-critique on the part of the author alongside an analysis of recent approaches toward consumer culture in cultural studies. The article continues by presenting a schematic account of how the commercial domain increasingly supplants state and public sector institutions in the intensity and dedication of its address to girls and young women. Whilst some may argue that the intersection of youthful femininity and the commercial sphere is not a new phenomenon, what is being explored here is the connection between this intensification of attention and the logic of current neo-liberal economic rationalities. The argument is, therefore, that it is by these means including the instrumentalization of a specific modality of âfeminismâ that there emerges into existence a neo-liberal culture, with global aspirations, which has as its ideal subject the category of âgirlâ
âIt makes me feel aliveâ: the socio-motivational impact of drama and theatre on marginalised young people
An in-depth, longitudinal, idiographic study examined the impact of theatre and drama involvement on marginalised young people. Semi-structured interviews, at three separate time points over 2 years, were conducted with four young people (15â21 years of age) involved in a theatre project. Interpretative phenomenological analysis suggested that drama and theatre create space and support for the authentic self, and provide optimal conditions for promoting growth and resilience through voluntary engagement in a positive activity. In particular, the analysis highlighted the pivotal role of interpersonal relationships and a nurturing environment in re-engaging young people. Some participantsâ accounts also suggested that drama provides a uniquely engaging and therapeutic way to reflect on, express and explore experiences. The results are discussed in relation to core psychological processes underpinning self-development and key directions for further research
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