1,012 research outputs found
Chiral symmetry breaking in dimensionally regularized nonperturbative quenched QED
In this paper we study dynamical chiral symmetry breaking in dimensionally
regularized quenched QED within the context of Dyson-Schwinger equations. In D
< 4 dimensions the theory has solutions which exhibit chiral symmetry breaking
for all values of the coupling. To begin with, we study this phenomenon both
numerically and, with some approximations, analytically within the rainbow
approximation in the Landau gauge. In particular, we discuss how to extract the
critical coupling alpha_c = pi/3 relevant in four dimensions from the D
dimensional theory. We further present analytic results for the chirally
symmetric solution obtained with the Curtis-Pennington vertex as well as
numerical results for solutions exhibiting chiral symmetry breaking. For these
we demonstrate that, using dimensional regularization, the extraction of the
critical coupling relevant for this vertex is feasible. Initial results for
this critical coupling are in agreement with cut-off based work within the
currently achievable numerical precision.Comment: 24 pages, including 5 figures; submitted to Phys. Rev.
Regularization-independent study of renormalized non-perturbative quenched QED
A recently proposed regularization-independent method is used for the first
time to solve the renormalized fermion Schwinger-Dyson equation numerically in
quenched QED. The Curtis-Pennington vertex is used to illustrate the
technique and to facilitate comparison with previous calculations which used
the alternative regularization schemes of modified ultraviolet cut-off and
dimensional regularization. Our new results are in excellent numerical
agreement with these, and so we can now conclude with confidence that there is
no residual regularization dependence in these results. Moreover, from a
computational point of view the regularization independent method has enormous
advantages, since all integrals are absolutely convergent by construction, and
so do not mix small and arbitrarily large momentum scales. We analytically
predict power law behaviour in the asymptotic region, which is confirmed
numerically with high precision. The successful demonstration of this efficient
new technique opens the way for studies of unquenched QED to be undertaken in
the near future.Comment: 20 pages,5 figure
Truncated Schwinger-Dyson Equations and Gauge Covariance in QED3
We study the Landau-Khalatnikov-Fradkin transformations (LKFT) in momentum
space for the dynamically generated mass function in QED3. Starting from the
Landau gauge results in the rainbow approximation, we construct solutions in
other covariant gauges. We confirm that the chiral condensate is gauge
invariant as the structure of the LKFT predicts. We also check that the gauge
dependence of the constituent fermion mass is considerably reduced as compared
to the one obtained directly by solving SDE.Comment: 17 pages, 11 figures. v3. Improved and Expanded. To appear in Few
Body System
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Evidence of neutral transcriptome evolution in plants
The transcriptome of an organism is its set of gene transcripts (mRNAs) at a defined spatial and temporal locus. Because gene expression is affected markedly by
environmental and developmental perturbations, it is widely assumed that transcriptome divergence among taxa represents adaptive phenotypic selection. This assumption has been challenged by neutral theories which propose that stochastic
processes drive transcriptome evolution. To test for evidence of neutral transcriptome evolution in plants, we quantified 18 494 gene transcripts in nonsenescent leaves of 14 taxa of Brassicaceae using robust cross-species transcriptomics which includes a two-step physical and in silicobased normalization procedure based on DNA similarity among taxa. Transcriptome divergence correlates positively with evolutionary distance between taxa and with variation in gene expression among samples. Results are similar for pseudogenes and chloroplast genes evolving at different rates. Remarkably, variation in transcript abundance among root-cell samples correlates positively with
transcriptome divergence among root tissues and among taxa.
Because neutral processes affect transcriptome evolution in plants, many differences in gene expression among or within taxa may be nonfunctional, reflecting ancestral
plasticity and founder effects. Appropriate null models are required when comparing transcriptomes in space and time
On Renormalized Strong-Coupling Quenched QED in Four Dimensions
We study renormalized quenched strong-coupling QED in four dimensions in
arbitrary covariant gauge. Above the critical coupling leading to dynamical
chiral symmetry breaking, we show that there is no finite chiral limit. This
behaviour is found to be independent of the detailed choice of photon-fermion
proper vertex in the Dyson-Schwinger equation formalism, provided that the
vertex is consistent with the Ward-Takahashi identity and multiplicative
renormalizability. We show that the finite solutions previously reported lie in
an unphysical regime of the theory with multiple solutions and ultraviolet
oscillations in the mass functions. This study supports the assertion that in
four dimensions strong coupling QED does not have a continuum limit in the
conventional sense.Comment: REVTEX 3.0, 15 pages,including 4 eps files comprising 3 figures.
Submitted to Phys. Rev.
SAperI: Approaching Gender Gap Using Spatial Ability Training Week in High-School Context
The purpose of this paper is to describe the structure of a girls summer school, “SAperI – Spatial Ability per l’Ingegneria” (in English, “Knowledge – Spatial Ability for Engineering”), and to illustrate its impact on spatial ability development and future career preferences on those who participated in the week long summer school compared to a control group that did not participate.The 5 days school,organized by Politecnico di Torino (Italy), was included in a larger project addressing 17 years old high-school students. Thirtyseven girls actively took part in a summer school, while 167 students (both males and females) were tested as a controlled group.For those who attended the summer school, significant gains were observed in four measures of spatial ability - mental rotation, spatialvisualization, mental cutting and paper folding. For a minority of participants, scores on one of these tests, paper folding, were lower when measured at the end of the summer school but this was an exception. Furthermore, when tested several months after the summer school, the gains in spatial ability that were made during the course were maintained indicating stability over time with regard to the improvement in spatial ability.In terms of the experience of taking the course, the feedback provided was very positive and all but one participant would recommend the summer school to othergirls at this stage of high school
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Volumetric laser endomicroscopy and its application to Barrett's esophagus: results from a 1,000 patient registry.
Volumetric laser endomicroscopy (VLE) uses optical coherence tomography (OCT) for real-time, microscopic cross-sectional imaging. A US-based multi-center registry was constructed to prospectively collect data on patients undergoing upper endoscopy during which a VLE scan was performed. The objective of this registry was to determine usage patterns of VLE in clinical practice and to estimate quantitative and qualitative performance metrics as they are applied to Barrett's esophagus (BE) management. All procedures utilized the NvisionVLE Imaging System (NinePoint Medical, Bedford, MA) which was used by investigators to identify the tissue types present, along with focal areas of concern. Following the VLE procedure, investigators were asked to answer six key questions regarding how VLE impacted each case. Statistical analyses including neoplasia diagnostic yield improvement using VLE was performed. One thousand patients were enrolled across 18 US trial sites from August 2014 through April 2016. In patients with previously diagnosed or suspected BE (894/1000), investigators used VLE and identified areas of concern not seen on white light endoscopy (WLE) in 59% of the procedures. VLE imaging also guided tissue acquisition and treatment in 71% and 54% of procedures, respectively. VLE as an adjunct modality improved the neoplasia diagnostic yield by 55% beyond the standard of care practice. In patients with no prior history of therapy, and without visual findings from other technologies, VLE-guided tissue acquisition increased neoplasia detection over random biopsies by 700%. Registry investigators reported that VLE improved the BE management process when used as an adjunct tissue acquisition and treatment guidance tool. The ability of VLE to image large segments of the esophagus with microscopic cross-sectional detail may provide additional benefits including higher yield biopsies and more efficient tissue acquisition. Clinicaltrials.gov NCT02215291
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Pan-viral serology implicates enteroviruses in acute flaccid myelitis.
Since 2012, the United States of America has experienced a biennial spike in pediatric acute flaccid myelitis (AFM)1-6. Epidemiologic evidence suggests non-polio enteroviruses (EVs) are a potential etiology, yet EV RNA is rarely detected in cerebrospinal fluid (CSF)2. CSF from children with AFM (n = 42) and other pediatric neurologic disease controls (n = 58) were investigated for intrathecal antiviral antibodies, using a phage display library expressing 481,966 overlapping peptides derived from all known vertebrate and arboviruses (VirScan). Metagenomic next-generation sequencing (mNGS) of AFM CSF RNA (n = 20 cases) was also performed, both unbiased sequencing and with targeted enrichment for EVs. Using VirScan, the viral family significantly enriched by the CSF of AFM cases relative to controls was Picornaviridae, with the most enriched Picornaviridae peptides belonging to the genus Enterovirus (n = 29/42 cases versus 4/58 controls). EV VP1 ELISA confirmed this finding (n = 22/26 cases versus 7/50 controls). mNGS did not detect additional EV RNA. Despite rare detection of EV RNA, pan-viral serology frequently identified high levels of CSF EV-specific antibodies in AFM compared with controls, providing further evidence for a causal role of non-polio EVs in AFM
Chiral Symmetry Breaking in Quenched Massive Strong-Coupling QED
We present results from a study of subtractive renormalization of the fermion
propagator Dyson-Schwinger equation (DSE) in massive strong-coupling quenched
QED. Results are compared for three different fermion-photon proper vertex
{\it Ans\"{a}tze\/}: bare , minimal Ball-Chiu, and
Curtis-Pennington. The procedure is straightforward to implement and
numerically stable. This is the first study in which this technique is used and
it should prove useful in future DSE studies, whenever renormalization is
required in numerical work.Comment: REVTEX 3.0, 15 pages plus 7 uuencoded PostScript figure
Deep analysis of CD4 T cells in the rhesus CNS during SIV infection
Virologic suppression with antiretroviral therapy (ART) has significantly improved health outcomes for people living with HIV, yet challenges related to chronic inflammation in the central nervous system (CNS)—known as Neuro-HIV- persist. As primary targets for HIV-1 with the ability to survey and populate the CNS and interact with myeloid cells to co-ordinate neuroinflammation, CD4 T cells are pivotal in Neuro-HIV. Despite their importance, our understanding of CD4 T cell distribution in virus-targeted CNS tissues, their response to infection, and potential recovery following initiation of ART remain limited. To address these gaps, we studied ten SIVmac251-infected rhesus macaques using an ART regimen simulating suboptimal adherence. We evaluated four macaques during the acute phase pre-ART and six during the chronic phase. Our data revealed that HIV target CCR5+ CD4 T cells inhabit both the brain parenchyma and adjacent CNS tissues, encompassing choroid plexus stroma, dura mater, and the skull bone marrow. Aligning with the known susceptibility of CCR5+ CD4 T cells to viral infection and their presence within the CNS, high levels of viral RNA were detected in the brain parenchyma and its border tissues during acute SIV infection. Single-cell RNA sequencing of CD45+ cells from the brain revealed colocalization of viral transcripts within CD4 clusters and significant activation of antiviral molecules and specific effector programs within T cells, indicating CNS CD4 T cell engagement during infection. Acute infection led to marked imbalance in the CNS CD4/CD8 ratio which persisted into the chronic phase. These observations underscore the functional involvement of CD4 T cells within the CNS during SIV infection, enhancing our understanding of their role in establishing CNS viral presence. Our findings offer insights for potential T cell-focused interventions while underscoring the challenges in eradicating HIV from the CNS, particularly in the context of sub-optimal ART
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