199 research outputs found
BRST Anomaly and Superspace Constraints of the Pure Spinor Heterotic String in a Curved Background
The pure spinor heterotic string in a generic super Yang-Mills and
supergravity background is considered. We determine the one-loop BRST anomaly
at the cohomological level. We prove that it can be absorbed by consistent
corrections of the classical constraints due to Berkovits and Howe, in
agreement with the Green-Schwarz cancelation mechanism.Comment: harvmac-big, 18 pages; references added; minor correction
Taxonomic resolution refinement does not improve understanding of invertebrate's role on leaf litter breakdown
Abstract
The invertebrate biodiversity of subtropical streams depends on the seasonal input of organic matter, as much as the leaf decomposition process on stream system. However, one of the challenges in determining the importance of invertebrates for leaf breakdown in subtropical streams is the low taxonomic resolution applied in most studies. To overcome this limitation, here we used litter bags with senescent leaves to evaluate the impact of different taxonomic resolutions of trophic group classification to assess the seasonal importance of invertebrate community for leaf litter breakdown in a subtropical stream (Atlantic Forest in western of Paraná state, Brazil). Litterfall was quarterly measured over a year. The leaf litter accumulated in an interval of 30 days was retrieved, weighed, and used for the leaf breakdown experiments (by litter bags). We found a lower importance of invertebrate community richness and density (shredders and scrapers) in leaf breakdown process irrespective of the taxonomic resolution (family or genus level used). Hyphomycetes biomass and fungi sporulation also did not present changes among sample times, and consecutively, importance for leaf breakdown. However, the richness and density of Chironomidae taxa respond differently depending on the taxonomic resolution used. Low litter breakdown may be explained by the increase of consumption of microorganisms, due to high density of Chironomidae scrapers evaluated at the genus level. Moreover, temperature is the main factor responsible for breakdown over the year, in a positive way. Therefore, our results indicated the family level as the taxonomic resolution sufficient to assess the role of shredders and scrapers in the leaf litter breakdown process of this subtropical stream system
A New First Class Algebra, Homological Perturbation and Extension of Pure Spinor Formalism for Superstring
Based on a novel first class algebra, we develop an extension of the pure
spinor (PS) formalism of Berkovits, in which the PS constraints are removed. By
using the homological perturbation theory in an essential way, the BRST-like
charge of the conventional PS formalism is promoted to a bona fide
nilpotent charge , the cohomology of which is equivalent to the
constrained cohomology of . This construction requires only a minimum number
(five) of additional fermionic ghost-antighost pairs and the vertex operators
for the massless modes of open string are obtained in a systematic way.
Furthermore, we present a simple composite "-ghost" field which
realizes the important relation , with the
Virasoro operator, and apply it to facilitate the construction of the
integrated vertex. The present formalism utilizes U(5) parametrization and the
manifest Lorentz covariance is yet to be achieved.Comment: 38 pages, no figure. Proof of triviality of delta-homology improved
and a reference adde
Relating Green-Schwarz and Extended Pure Spinor Formalisms by Similarity Transformation
In order to gain deeper understanding of pure-spinor-based formalisms of
superstring, an explicit similarity transformation is constructed which
provides operator mapping between the light-cone Green-Schwarz (LCGS) formalism
and the extended pure spinor (EPS) formalism, a recently proposed
generalization of the Berkovits' formalism in an enlarged space. By applying a
systematic procedure developed in our previous work, we first construct an
analogous mapping in the bosonic string relating the BRST and the light-cone
formulations. This provides sufficient insights and allows us to construct the
desired mapping in the more intricate case of superstring as well. The success
of the construction owes much to the enlarged field space where pure spinor
constraints are removed and to the existence of the ``B-ghost'' in the EPS
formalism.Comment: 37pages, no figur
Superbrane Actions and Geometrical Approach
We review a generic structure of conventional (Nambu-Goto and
Dirac-Born-Infeld-like) worldvolume actions for the superbranes and show how it
is connected through a generalized action construction with a doubly
supersymmetric geometrical approach to the description of super-p-brane
dynamics as embedding world supersurfaces into target superspaces.Comment: Based on talks given by the authors at the Volkov Memorial Seminar
"Supersymmetry and Quantum field Theory" (Kharkov, January 5-7, 1997), LaTeX
file, 11 pages Misprints corrected, references adde
Evidence for the classical integrability of the complete AdS(4) x CP(3) superstring
We construct a zero-curvature Lax connection in a sub-sector of the
superstring theory on AdS(4) x CP(3) which is not described by the
OSp(6|4)/U(3) x SO(1,3) supercoset sigma-model. In this sub-sector worldsheet
fermions associated to eight broken supersymmetries of the type IIA background
are physical fields. As such, the prescription for the construction of the Lax
connection based on the Z_4-automorphism of the isometry superalgebra OSp(6|4)
does not do the job. So, to construct the Lax connection we have used an
alternative method which nevertheless relies on the isometry of the target
superspace and kappa-symmetry of the Green-Schwarz superstring.Comment: 1+26 pages; v2: minor typos corrected, acknowledgements adde
A low-background γγ-coincidence spectrometer for radioisotope studies
The performance of a new, low-background NaI(Tl) spectrometer, based on γγ-coincidence counting, is discussed. We present experimental coincidence efficiencies, timing resolutions, background count rates, and minimum detectable activities. The spectrometer has been simulated using Geant4, and the results are used for estimating coincidence efficiencies for volume sources. To test the device, we measured the cosmogenic 26Al activity in a small (17.7 g) meteorite fragment. We find a value of 52.9±7.8dpm∕kg, in agreement with the activity measured previously in a much larger fragment of the same meteorite using a HPGe detector
Influence of monolayer, spheroid, and tumor growth conditions on chromosome 3 gene expression in tumorigenic epithelial ovarian cancer cell lines
<p>Abstract</p> <p>Background</p> <p>Expression microarray analyses of epithelial ovarian cancer (EOC) cell lines may be exploited to elucidate genetic and epigenetic events important in this disease. A possible variable is the influence of growth conditions on discerning candidates. The present study examined the influence of growth conditions on the expression of chromosome 3 genes in the tumorigenic EOC cell lines, OV-90, TOV-21G and TOV-112D using Affymetrix GeneChip<sup>® </sup>HG-U133A expression microarray analysis.</p> <p>Methods</p> <p>Chromosome 3 gene expression profiles (n = 1147 probe sets, representing 735 genes) were extracted from U133A expression microarray analyses of the EOC cell lines OV-90, TOV-21G and TOV-112D that were grown as monolayers, spheroids or nude mouse xenografts and monolayers derived from these tumors. Hierarchical cluster analysis was performed to compare chromosome 3 transcriptome patterns of each growth condition. Differentially expressed genes were identified and characterized by two-way comparative analyses of fold-differences in gene expression between monolayer cultures and each of the other growth conditions, and between the maximum and minimum values of expression of all growth conditions for each EOC cell line.</p> <p>Results</p> <p>An overall high degree of similarity (> 90%) in gene expression was observed when expression values of alternative growth conditions were compared within each EOC cell line group. Two-way comparative analysis of each EOC cell line grown in an alternative condition relative to the monolayer culture showed that overall less than 15% of probe sets exhibited at least a 3-fold difference in expression profile. Less than 23% of probe sets exhibited greater than 3-fold differences in gene expression in comparisons of the maximum and minimum value of expression of all growth conditions within each EOC cell line group. The majority of these differences were less than 5-fold. There were 17 genes in common which were differentially expressed in all EOC cell lines. However, the patterns of expression of these genes were not necessarily the same for each growth condition when one cell line was compared with another.</p> <p>Conclusion</p> <p>The various alternative <it>in vivo </it>and <it>in vitro </it>growth conditions of tumorigenic EOC cell lines appeared to modestly influence the global chromosome 3 transcriptome supporting the notion that the <it>in vitro </it>cell line models are a viable option for testing gene candidates.</p
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