Dynamical Mass Generation and Confinement in Maxwell-Chern-Simons Planar Quantum Electrodynamics

We study the non-perturbative phenomena of Dynamical Mass Generation and Confinement by truncating at the non-perturbative level the Schwinger-Dyson equations in Maxwell-Chern-Simons planar quantum electrodynamics. We obtain numerical solutions for the fermion propagator in Landau gauge within the so-called rainbow approximation. A comparison with the ordinary theory without the Chern-Simons term is presented.Comment: 9 pages, 9 figures; prepared for the XIV Mexican School of Particles and Fields, 4-12 November 2010, Morelia, Michoacan, Mexic

Chiral Symmetry Breaking and Confinement Beyond Rainbow-Ladder Truncation

A non-perturbative construction of the 3-point fermion-boson vertex which obeys its Ward-Takahashi or Slavnov-Taylor identity, ensures the massless fermion and boson propagators transform according to their local gauge covariance relations, reproduces perturbation theory in the weak coupling regime and provides a gauge independent description for dynamical chiral symmetry breaking (DCSB) and confinement has been a long-standing goal in physically relevant gauge theories such as quantum electrodynamics (QED) and quantum chromodynamics (QCD). In this paper, we demonstrate that the same simple and practical form of the vertex can achieve these objectives not only in 4-dimensional quenched QED (qQED4) but also in its 3-dimensional counterpart (qQED3). Employing this convenient form of the vertex \emph{ansatz} into the Schwinger-Dyson equation (SDE) for the fermion propagator, we observe that it renders the critical coupling in qQED4 markedly gauge independent in contrast with the bare vertex and improves on the well-known Curtis-Pennington construction. Furthermore, our proposal yields gauge independent order parameters for confinement and DCSB in qQED3.Comment: 8 pages, 6 figure

A review of therapeutic effects of mesenchymal stem cell secretions and induction of secretory modification by different culture methods

The mesenchymal stem cell (MSC) is being broadly studied in clinical trials. Contrary to the early paradigm of cell replacement and differentiation as a therapeutic mechanism of action, evidence is mounting that the secretions of the cells are responsible for their therapeutic effects. These secretions include molecules and extracellular vesicles that have both local and distant effects. This review summarizes the up- and down-regulation of MSC anti-inflammatory, immune modulating, anti-tumor, and regenerative secretions resulting from different stimuli including: a) hypoxia, which increases the production of growth factors and anti-inflammatory molecules; b) pro-inflammatory stimuli that induce the secretion of immune modulating and anti-inflammatory factors; and c) 3 dimensional growth which up regulates the production of anti-cancer factors and anti-inflammatory molecules compared to monolayer culture. Finally we review in detail the most important factors present in conditioned medium of MSC that can be considered protagonists of MSC physiological effects including HGF, TGF-b, VEGF, TSG-6, PGE2 and galectins 1, and 9. We conclude that there is potential for the development of acellular therapeutic interventions for autoimmune, inflammatory, and malignant diseases and tissue regeneration from cellular secretions derived from MSCs cultured under the appropriate conditions.The mesenchymal stem cell (MSC) is being broadly studied in clinical trials. Contrary to the early paradigm of cell replacement and differentiation as a therapeutic mechanism of action, evidence is mounting that the secretions of the cells are responsible for their therapeutic effects. These secretions include molecules and extracellular vesicles that have both local and distant effects. This review summarizes the up- and down-regulation of MSC anti-inflammatory, immune modulating, anti-tumor, and regenerative secretions resulting from different stimuli including: a) hypoxia, which increases the production of growth factors and anti-inflammatory molecules; b) pro-inflammatory stimuli that induce the secretion of immune modulating and anti-inflammatory factors; and c) 3 dimensional growth which up regulates the production of anti-cancer factors and anti-inflammatory molecules compared to monolayer culture. Finally we review in detail the most important factors present in conditioned medium of MSC that can be considered protagonists of MSC physiological effects including HGF, TGF-b, VEGF, TSG-6, PGE2 and galectins 1, and 9. We conclude that there is potential for the development of acellular therapeutic interventions for autoimmune, inflammatory, and malignant diseases and tissue regeneration from cellular secretions derived from MSCs cultured under the appropriate conditions

Effects of Algal Diversity on the Production of Biomass in Homogeneous and Heterogeneous Nutrient Environments: A Microcosm Experiment

BACKGROUND: One of the most common questions addressed by ecologists over the past decade has been--how does species richness impact the production of community biomass? Recent summaries of experiments have shown that species richness tends to enhance the production of biomass across a wide range of trophic groups and ecosystems; however, the biomass of diverse polycultures only rarely exceeds that of the single most productive species in a community (a phenomenon called 'transgressive overyielding'). Some have hypothesized that the lack of transgressive overyielding is because experiments have generally been performed in overly-simplified, homogeneous environments where species have little opportunity to express the niche differences that lead to 'complementary' use of resources that can enhance biomass production. We tested this hypothesis in a laboratory experiment where we manipulated the richness of freshwater algae in homogeneous and heterogeneous nutrient environments. METHODOLOGY/PRINCIPAL FINDINGS: Experimental units were comprised of patches containing either homogeneous nutrient ratios (16:1 nitrogen to phosphorus (N:P) in all patches) or heterogeneous nutrient ratios (ranging from 4:1 to 64:1 N:P across patches). After allowing 6-10 generations of algal growth, we found that algal species richness had similar impacts on biomass production in both homo- and heterogeneous environments. Although four of the five algal species showed a strong response to nutrient heterogeneity, a single species dominated algal communities in both types of environments. As a result, a 'selection effect'--where diversity maximizes the chance that a competitively superior species will be included in, and dominate the biomass of a community--was the primary mechanism by which richness influenced biomass in both homo- and heterogeneous environments. CONCLUSIONS/SIGNIFICANCE: Our study suggests that spatial heterogeneity, by itself, is not sufficient to generate strong effects of biodiversity on productivity. Rather, heterogeneity must be coupled with variation in the relative fitness of species across patches in order for spatial niche differentiation to generate complementary resource use

Gauge invariance of a critical number of flavours in QED3

The fermion propagator in an arbitrary covariant gauge can be obtained from the Landau gauge result via a Landau-Khalatnikov-Fradkin transformation. This transformation can be written in a practically useful form in both configuration and momentum space. It is therefore possible to anticipate effects of a gauge transformation on the propagator's analytic properties. These facts enable one to establish that if a critical number of flavours for chiral symmetry restoration and deconfinement exists in noncompact QED3, then its value is independent of the gauge parameter. This is explicated using simple forms for the fermion-photon vertex and the photon vacuum polarisation. The illustration highlights pitfalls that must be avoided in order to arrive at valid conclusions. Landau gauge is seen to be the covariant gauge in which the propagator avoids modification by a non-dynamical gauge-dependent exponential factor, whose presence can obscure truly observable features of the theory.Comment: 7 pages, 3 figure

High resolution HLA-A, -B, -C and -DRB1 allele and haplotype frequencies in the Costa Rica Central Valley population

The Costa Rica Central Valley population (CCVP) is the major population in this country, accounting for over 60% of the Costa Rican inhabitants concentrated since colonial times in a 2,500 km2 intermontane region. Interesting historic, demographic and genetic characteristics of this hybrid population have attracted researchers interested in testing genetic associations for various diseases. However, no study describing Human Leukocyte Antigen (HLA) frequencies by molecular methods had been performed. We have recently described low resolution HLA allele group and haplotype frequencies in a sample of this population. In this report, we extend our study to high resolution by sequence-based typing of exons 2, 3 and 4 for class I, and exon 2 for HLA-DRB1. DNA was extracted from blood or saliva samples from a cohort of 205 non-related healthy donors recruited as part of the University of Costa Rica’s Centre for Research in Hematology and Related Disorders (CIHATA) DNA bank. All participants were born in the CCVP and gave informed consent. A total of 37 HLA-A, 61 HLA-B, 24 HLA-C and 38 HLA-DRB1 alleles were seen in this sample. The five most frequent alleles for these genes are HLA-A*02:01:01, HLA-A*24:02:01, HLA-A*03:01:01, HLA-A*01:01:01, HLA-A*68:01:02, HLA-B*07:02:01, HLA-B*40:02:01, HLA-B*35:01:01, HLA-B*44:02:01, HLA-B*14:02:01, HLA-C*04:01:01, HLA-C*07:02:01, HLA-C*03:05, HLA-C*06:02:01, HLA-C*07:01:01, HLA-DRB1*13:01:01G, HLA-DRB1*04:07:01G, HLA-DRB1*15:01:01G, HLA-DRB1*03:01:01G, and HLA-DRB1*07:01:01G. Preliminary haplotype estimation results show, as a proxy for admixture proportions, that 68% of the extended haplotypes are Caucasian, while 23% are Amerindian in origin and 9% are clearly Sub-Saharan African. Principal coordinates analysis based on HLA-A and –B allele group frequencies reveals that this population clusters among other admixed groups with strong Caucasian component that lie closely to Iberian populations