413 research outputs found
Two-loop world-sheet corrections in AdS_5 x S^5 superstring
We initiate the computation of the 2-loop quantum AdS_5 x S^5 string
corrections on the example of a certain string configuration in S^5 related by
an analytic continuation to a folded rotating string in AdS_5 in the ``long
string'' limit. The 2-loop term in the energy of the latter should represent
the subleading strong-coupling correction to the cusp anomalous dimension and
thus provide a further check of recent conjectures about the exact structure of
the Bethe ansatz underlying the AdS/CFT duality. We use the conformal gauge and
several choices of the \kappa-symmetry gauge. While we are unable to verify the
cancellation of 2d UV divergences we compute the bosonic contribution to the
effective action and also determine the non-trivial finite part of the
fermionic contribution. Both the bosonic and the fermionic contributions to the
string energy happen to be proportional to the Catalan's constant. The
resulting value for 2-loop superstring prediction for the subleading
coefficient a_2 in the scaling function matches the numerical value found in
hep-th/0611135 from the BES equation.Comment: 48 pages, 1 Figure. v3: several mistakes corrected, the finite result
for the 2-loop coefficient is found to agree with the numerical value found
by Benna et al in hep-th/061113
An evolutionarily-unique heterodimeric voltage-gated cation channel found in aphids
We describe the identification in aphids of a unique heterodimeric voltage-gated sodium channel which has an atypical ion selectivity filter and, unusually for insect channels, is highly insensitive to tetrodotoxin. We demonstrate that this channel has most likely arisen by adaptation (gene fission or duplication) of an invertebrate ancestral mono(hetero)meric channel. This is the only identifiable voltage-gated sodium channel homologue in the aphid genome(s), and the channel's novel selectivity filter motif (DENS instead of the usual DEKA found in other eukaryotes) may result in a loss of sodium selectivity, as indicated experimentally in mutagenised Drosophila channels
Infinite spin limit of semiclassical string states
Motivated by recent works of Hofman and Maldacena and Dorey we consider a
special infinite spin limit of semiclassical spinning string states in AdS5 x
S5. We discuss examples of known folded and circular 2-spin string solutions
and demonstrate explicitly that the 1-loop superstring correction to the
classical expression for the energy vanishes in the limit when one of the spins
is much larger that the other. We also give a general discussion of this limit
at the level of integral equations describing finite gap solutions of the
string sigma model and argue that the corresponding asymptotic form of the
string and gauge Bethe equations is the same.Comment: 38 pages, 3 figures; v2: comments on derivation of bound states of
magnons from discrete Bethe equations added in section 4 and appendix C,
references added, Imperial-TP-AT-6-4, HUTP-06/A002
Lassoing and corraling rooted phylogenetic trees
The construction of a dendogram on a set of individuals is a key component of
a genomewide association study. However even with modern sequencing
technologies the distances on the individuals required for the construction of
such a structure may not always be reliable making it tempting to exclude them
from an analysis. This, in turn, results in an input set for dendogram
construction that consists of only partial distance information which raises
the following fundamental question. For what subset of its leaf set can we
reconstruct uniquely the dendogram from the distances that it induces on that
subset. By formalizing a dendogram in terms of an edge-weighted, rooted
phylogenetic tree on a pre-given finite set X with |X|>2 whose edge-weighting
is equidistant and a set of partial distances on X in terms of a set L of
2-subsets of X, we investigate this problem in terms of when such a tree is
lassoed, that is, uniquely determined by the elements in L. For this we
consider four different formalizations of the idea of "uniquely determining"
giving rise to four distinct types of lassos. We present characterizations for
all of them in terms of the child-edge graphs of the interior vertices of such
a tree. Our characterizations imply in particular that in case the tree in
question is binary then all four types of lasso must coincide
Constraints on Type Ib/c and GRB Progenitors
Although there is strong support for the collapsar engine as the power source
of long-duration gamma-ray bursts (GRBs), we still do not definitively know the
progenitor of these explosions. Here we review the current set of progenitor
scenarios for long-duration GRBs and the observational constraints on these
scenarios. Examining these, we find that single-star models cannot be the only
progenitor for long-duration GRBs. Several binary progenitors can match the
solid observational constraints and also have the potential to match the trends
we are currently seeing in the observations. Type Ib/c supernovae are also
likely to be produced primarily in binaries; we discuss the relationship
between the progenitors of these explosions and those of the long-duration
GRBs.Comment: 36 pages, 6 figure
Insecticide resistance mediated 1 by an exon skipping event
Many genes increase coding capacity by alternate exon usage. The gene encoding the insect nicotinic acetylcholine receptor (nAChR) a6 subunit, target of the bio-insecticide spinosad, is one example of this and expands protein diversity via alternative splicing of mutually exclusive exons. Here, we show that spinosad resistance in the tomato leaf miner, Tuta absoluta is associated with aberrant regulation of splicing of Taa6 resulting in a novel form of insecticide resistance mediated by exon skipping. Sequencing of the a6 subunit cDNA from spinosad selected and unselected strains of T. absoluta revealed all Taa6 transcripts of the selected strain were devoid of exon 3, with comparison of genomic DNA and mRNA revealing this is a result of exon skipping. Exon skipping cosegregated with spinosad resistance in survival bioassays, and functional characterization of this alteration using modiïŹed human nAChR a7, a model of insect a6, demonstrated that exon 3 is essential for receptor function and hence spinosad sensitivity. DNA and RNA sequencing analyses suggested that exon skipping did not result from genetic alterations in intronic or exonic cis-regulatory elements, but rather was associated with a single epigenetic modiïŹcation downstream of exon 3a, and quantitative changes in the expression of trans-acting proteins that have known roles in the regulation of alternative splicing. Our results demonstrate that the intrinsic capacity of the a6 gene to generate transcript diversity via alternative splicing can be readily exploited during the evolution of resistance and identiïŹes exon skipping as a molecular alteration conferring insecticide resistance
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Limacina helicina shell dissolution as an indicator of declining habitat suitability owing to ocean acidification in the California Current Ecosystem
Few studies to date have demonstrated widespread biological impacts of ocean
acidification (OA) under conditions currently found in the natural environment.
From a combined survey of physical and chemical water properties
and biological sampling along the WashingtonâOregonâCalifornia coast in
August 2011, we show that large portions of the shelf waters are corrosive
to pteropods in the natural environment. We show a strong positive correlation
between the proportion of pteropod individuals with severe shell dissolution
damage and the percentage of undersaturated water in the top 100 m with
respect to aragonite. We found 53% of onshore individuals and 24% of offshore
individuals on average to have severe dissolution damage. Relative to pre-industrial
COâ concentrations, the extent of undersaturated waters in the top
100 m of the water column has increased over sixfold along the California Current
Ecosystem (CCE). We estimate that the incidence of severe pteropod shell
dissolution owing to anthropogenic OA has doubled in near shore habitats
since pre-industrial conditions across this region and is on track to triple by
2050. These results demonstrate that habitat suitability for pteropods in the
coastal CCE is declining. The observed impacts represent a baseline for
future observations towards understanding broader scale OA effects.Keywords: dissolution, pteropods, aragonite undersaturation, habitat reduction, ocean acidificatio
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Predicating from an early age: edusemiotics and the potential of childrenâs preconceptions
This paper aims to explain how semiotics and constructivism can collaborate in an educational epistemology by developing a joint approach to prescientific conceptions. Empirical data and findings of constructivist research are interpreted in the light of Peirceâs semiotics. Peirceâs semiotics is an anti-psychologistic logic (CP 2.252; CP 4.551; W 8:15; Pietarinen in Signs of logic, Springer, Dordrecht, 2006; Stjernfelt in Diagrammatology. An investigation on the borderlines of phenomenology, ontology and semiotics, Springer, Dordrecht, 2007) and relational logic. Constructivism was traditionally developed within psychology and sociology and, therefore, some incompatibilities can be expected between these two schools. While acknowledging the differences, we explain that constructivism and semiotics share the assumption of realism that knowledge can only be developed upon knowledge and, therefore, an epistemological collaboration is possible. The semiotic analysis performed confirms the constructivist results and provides a further insight into the teacher-student relation. Like the constructivist approach, Peirceâs doctrine of agapism infers that the personal dimension of teaching must not be ignored. Thus, we argue for the importance of genuine sympathy in teaching attitudes. More broadly, the article also contributes to the development of postmodern humanities. At the end of the modern age, the humanities are passing through a critical period of transformation. There is a growing interest in semiotics and semiotic philosophy in many areas of the humanities. Such a case, on which we draw, is the development of a theoretical semiotic approach to education, namely edusemiotics (Stables and Semetsky, Pedagogy and edusemiotics: theoretical challenge/practical opportunities, Sense Publishers, Rotterdam, 2015)
Eco-physiological responses of copepods and pteropods to ocean warming and acidification
We compare physiological responses of the crustacean copepod Calanus pacificus and pelagic pteropod mollusk Limacina helicina
to ocean temperatures and pH by measuring biomarkers of oxidative
stress, antioxidant defences, and the activity of the respiratory
electron transport system in organisms collected on the 2016 West Coast
Ocean Acidification cruise in the California Current System. Copepods
and pteropods exhibited strong but divergent responses in the same
habitat; copepods had higher oxygen-reactive absorbance capacity,
glutathione-S-transferase, and total glutathione content. The ratio
between reduced to oxidised glutathione was higher in copepods than in
pteropods, indicating lower oxidative stress in copepods. Pteropods
showed higher activities of glutathione reductase, catalase, and lipid
peroxidation, indicating increased antioxidant defences and oxidative
stress. Thus, the antioxidant defence system of the copepods has a
greater capacity to respond to oxidative stress, while pteropods already
face severe stress and show limited capacity to deal with further
changes. The results suggest that copepods have higher adaptive
potential, owing to their stronger vertical migration behaviour and
efficient glutathione metabolism, whereas pteropods run the risk of
oxidative stress and mortality under high CO2 conditions. Our
results provide a unique dataset and evidence of stress-inducing
mechanisms behind pteropod ocean acidification responses.</p
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A novel method for determination of aragonite saturation state on the continental shelf of central Oregon using multi-parameter relationships with hydrographic data
We developed a multiple linear regression model to
robustly determine aragonite saturation state (Ωarag) from
observations of temperature and oxygen (RÂČ = 0.987, RMS
error 0.053), using data collected in the Pacific Northwest
region in late May 2007. The seasonal evolution of Ωarag near
central Oregon was evaluated by applying the regression
model to a monthly (winter)/bi-weekly (summer) watercolumn
hydrographic time-series collected over the shelf and
slope in 2007. The Ωarag predicted by the regression model
was less than 1, the thermodynamic calcification/dissolution
threshold, over shelf/slope bottom waters throughout the
entire 2007 upwelling season (MayâNovember), with the
Ωarag = 1 horizon shoaling to 30 m by late summer. The
persistence of water with Ωarag < 1 on the continental shelf
has not been previously noted and could have notable
ecological consequences for benthic and pelagic calcifying
organisms such as mussels, oysters, abalone, echinoderms,
and pteropods.Keywords: aragonite saturation state, calcification, CaCO
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