76 research outputs found
On the worldsheet theory of the type IIA AdS(4) x CP(3) superstring
We perform a detailed study of the type IIA superstring in AdS(4) x CP(3).
After introducing suitable bosonic light-cone and fermionic kappa worldsheet
gauges we derive the pure boson and fermion SU(2|2) x U(1) covariant light-cone
Hamiltonian up to quartic order in fields.
As a first application of our derivation we calculate energy shifts for
string configurations in a closed fermionic subsector and successfully match
these with a set of light-cone Bethe equations. We then turn to investigate the
mismatch between the degrees of freedom of scattering states and oscillatory
string modes. Since only light string modes appear as fundamental Bethe roots
in the scattering theory, the physical role of the remaining massive
oscillators is rather unclear. By continuing a line of research initiated by
Zarembo, we shed light on this question by calculating quantum corrections for
the propagators of the bosonic massive fields. We show that, once loop
corrections are incorporated, the massive coordinates dissolve in a continuum
state of two light particles.Comment: 40 pages, 2 figures. v3: Minor clarifications made and reference list
updated. Published version
On Non-linear Action for Gauged M2-brane
We propose a non-linear extension of U(1) \times U(1) (abelian) ABJM model
including T_{M2} (higher derivative) corrections. The action proposed here is
expected to describe a single M2-brane proving C^4/Z_k target space. The model
includes couplings with the 3-form background in the eleven-dimensional
supergravity which is consistent with the orbifold projection. We show that the
novel higgs mechanism proposed by Mukhi and Papageorgakis does work even in the
presence of higher derivative corrections and couplings with the background
field, giving the correct structure of the Dirac-Born-Infeld action with
Wess-Zumino term for a D2-brane. We also find half BPS solutions in the full
non-linear theory which is interpreted as an another M2-brane intersecting with
the original M2-brane. A possible generalization to U(N) \times U(N) gauge
group is briefly discussed.Comment: 19 pages, no figure, references added, typos correcte
Charged particle-like branes in ABJM
We study the effect of adding lower dimensional brane charges to the 't Hooft
monopole, di-baryon and baryon vertex configurations in . We show that these configurations capture the background fluxes
in a way that depends on the induced charges, and therefore, require additional
fundamental strings in order to cancel the worldvolume tadpoles. The study of
the dynamics reveals that the charges must lie inside some interval in order to
find well defined configurations, a situation familiar from the baryon vertex
in with charges. For the baryon vertex and the di-baryon the
number of fundamental strings must also lie inside an allowed interval. Our
configurations are sensitive to the flat -field recently suggested in the
literature. We make some comments on its possible role. We also discuss how
these configurations are modified in the presence of a non-zero Romans mass.Comment: 31 pages, 14 figures, discussion of charges improved, published
versio
Worldvolume Superalgebra Of BLG Theory With Nambu-Poisson Structure
Recently it was proposed that the Bagger-Lambert-Gustavsson theory with
Nambu-Poisson structure describes an M5-brane in a three-form flux background.
In this paper we investigate the superalgebra associated with this theory. We
derive the central charges corresponding to M5-brane solitons in 3-form
backgrounds. We also show that double dimensional reduction of the superalgebra
gives rise to the Poisson bracket terms of a non-commutative D4-brane
superalgebra. We provide interpretations of the D4-brane charges in terms of
spacetime intersections.Comment: 23 pages; references added, section 4 clarification
Deformation of half-BPS solution in ABJM model and instability of supermembrane
It is well-known that a supermembrane in the light-cone gauge has a
continuous spectrum and is unstable. Physical interpretation of this
instability is that a supermembrane can have a long thin tube without cost of
energy and consequently it becomes a spiky configuration in which multiple
membranes are connected by thin tubes. On the other hand, the ABJM model was
proposed as a low-energy description of multiple M2-branes in the static gauge.
It is natural that an M2-brane is also unstable in this gauge if we believe the
physical picture in the light-cone gauge. In order to examine this, we
construct a BPS solution explicitly both in the Nambu-Goto action of a
supermembrane in the static gauge and in the U(1){\times}U(1) ABJM model, which
represents intersecting M2-branes. Since this configuration is regarded as a
single M2-brane emitting another one, we study the instability of an M2-brane
by analyzing fluctuations around it. We show that a zero mode exists which can
deform the configuration. For comparison, we also examine a similar
configuration on the D2-brane and check that it does not have such zero modes
under a fixed string charge. Furthermore we confirm that the novel Higgs
mechanism translates our BPS solution in the ABJM model into that in the
D2-brane world volume theory, where the winding number of the former around the
fixed point of the orbifold becomes the number of strings ending on the
D2-brane in the latter.Comment: 27 page
Effect of haemoglobin concentration on the clinical outcomes in patients with acute myocardial infarction and the factors related to haemoglobin
<p>Abstract</p> <p>Background</p> <p>The impact of haemoglobin concentrations on clinical outcomes is still a controversial issue. To determine the association between haemoglobin concentrations on admission and clinical outcomes and the related factors, this study was performed in a Chinese hospital.</p> <p>Findings</p> <p>We conducted a retrospective study on 1394 Chinese patients with acute myocardial infarction. Patients were categorized according to the haemoglobin concentration on admission, and data were evaluated to determine whether there was an association between the haemoglobin concentrations on admission and 30-day in-hospital MACEs (major cardiovascular events). Patients with hemoglobin values between 141 and 150 g/L were used as the reference, the MACEs increased as hemoglobin concentrations fell below 140 g/L or rose > 150 g/L, with an adjusted OR (odds ratio) of 5.96[95% CI (confidence interval) 2.00 to 17.68, p = 0.0013], 4.39(1.37 to 14.08, p = 0.0128), 3.99(1.46 to 10.92, p = 0.0071), 3.19(1.27 to 8.05, p = 0.0139), 2.37(0.94 to 6.01, p = 0.0687), 2.11(0.66 to 6.74, p = 0.2065), 2.01(0.60 to 6.68, p = 0.2559) in patients with haemoglobin concentrations <100 g/L, 101-110 g/L, 111-120 g/L, 121-130 g/L, 131-140 g/L, 151-160 g/L, and >160 g/L respectively. Partial correlation analysis showed that age, albumin and creatinine were significantly associated with hemoglobin concentration.</p> <p>Conclusions</p> <p>Our results demonstrated that haemoglobin concentration affected MACEs in patients with acute myocardial infarction, and that haemoglobin concentration was associated with age, albumin and creatinine.</p
Reticulate evolution: frequent introgressive hybridization among chinese hares (genus lepus) revealed by analyses of multiple mitochondrial and nuclear DNA loci
<p>Abstract</p> <p>Background</p> <p>Interspecific hybridization may lead to the introgression of genes and genomes across species barriers and contribute to a reticulate evolutionary pattern and thus taxonomic uncertainties. Since several previous studies have demonstrated that introgressive hybridization has occurred among some species within <it>Lepus</it>, therefore it is possible that introgressive hybridization events also occur among Chinese <it>Lepus </it>species and contribute to the current taxonomic confusion.</p> <p>Results</p> <p>Data from four mtDNA genes, from 116 individuals, and one nuclear gene, from 119 individuals, provides the first evidence of frequent introgression events via historical and recent interspecific hybridizations among six Chinese <it>Lepus </it>species. Remarkably, the mtDNA of <it>L. mandshuricus </it>was completely replaced by mtDNA from <it>L. timidus </it>and <it>L. sinensis</it>. Analysis of the nuclear DNA sequence revealed a high proportion of heterozygous genotypes containing alleles from two divergent clades and that several haplotypes were shared among species, suggesting repeated and recent introgression. Furthermore, results from the present analyses suggest that Chinese hares belong to eight species.</p> <p>Conclusion</p> <p>This study provides a framework for understanding the patterns of speciation and the taxonomy of this clade. The existence of morphological intermediates and atypical mitochondrial gene genealogies resulting from frequent hybridization events likely contribute to the current taxonomic confusion of Chinese hares. The present study also demonstrated that nuclear gene sequence could offer a powerful complementary data set with mtDNA in tracing a complete evolutionary history of recently diverged species.</p
BPS solutions in ABJM theory and Maximal Super Yang-Mills on RxS^2
We investigate BPS solutions in ABJM theory on RxS^2. We find new BPS
solutions, which have nonzero angular momentum as well as nontrivial
configurations of fluxes. Applying the "Higgsing procedure" of arxiv:0803.3218
around a 1/2-BPS solution of ABJM theory, one obtains N=8 super Yang-Mills
(SYM) on RxS^2. We also show that other BPS solutions of the SYM can be
obtained from BPS solutions of ABJM theory by this higgsing procedure.Comment: 33 pages, v2: minor corrections, references adde
Landscape history, time lags and drivers of change : urban natural grassland remnants in Potchefstroom, South Africa
The history of the landscape directly affects biotic assemblages, resulting in time lags in species response to disturbances. In highly fragmented environments, this phenomenon often causes extinction debts. However, few studies have been carried out in urban settings. To determine if there are time lags in the response of temperate natural grasslands to urbanization. Does it differ for indigenous species and for species indicative of disturbance and between woody and open grasslands? Do these time lags change over time? What are the potential landscape factors driving these changes? What are the corresponding vegetation changes? In 1995 and 2012 vegetation sampling was carried out in 43 urban grassland sites. We calculated six urbanization and landscape measures in a 500 m buffer area surrounding each site for 1938, 1961, 1970, 1994, 1999, 2006, and 2010. We used generalized linear models and model selection to determine which time period best predicted the contemporary species richness patterns. Woody grasslands showed time lags of 20-40 years. Contemporary open grassland communities were, generally, associated with more contemporary landscapes. Altitude and road network density of natural areas were the most frequent predictors of species richness. The importance of the predictors changed between the different models. Species richness, specifically, indigenous herbaceous species, declined from 1995 to 2012. The history of urbanization affects contemporary urban vegetation assemblages. This indicates potential extinction debts, which have important consequences for biodiversity conservation planning and sustainable future scenarios.Peer reviewe
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