113 research outputs found
New Higgs Transitions between Dual N=2 String Models
We describe a new kind of transition between topologically distinct
type II Calabi--Yau vacua through points with enhanced non-abelian gauge
symmetries together with fundamental charged matter hypermultiplets. We connect
the appearance of matter to the local geometry of the singularity and discuss
the relation between the instanton numbers of the Calabi--Yau manifolds taking
part in the transition. In a dual heterotic string theory on the
process corresponds to Higgsing a semi-classical gauge group or equivalently to
a variation of the gauge bundle. In special cases the situation reduces to
simple conifold transitions in the Coulomb phase of the non-abelian gauge
symmetries.Comment: 22 pages, harvmac, references adde
Mirror Symmetry and the Moduli Space for Generic Hypersurfaces in Toric Varieties
The moduli dependence of superstring compactifications based on
Calabi--Yau hypersurfaces in weighted projective space has so far only been
investigated for Fermat-type polynomial constraints. These correspond to
Landau-Ginzburg orbifolds with whose potential is a sum of -type
singularities. Here we consider the generalization to arbitrary
quasi-homogeneous singularities at . We use mirror symmetry to derive the
dependence of the models on the complexified K\"ahler moduli and check the
expansions of some topological correlation functions against explicit genus
zero and genus one instanton calculations. As an important application we give
examples of how non-algebraic (``twisted'') deformations can be mapped to
algebraic ones, hence allowing us to study the full moduli space. We also study
how moduli spaces can be nested in each other, thus enabling a (singular)
transition from one theory to another. Following the recent work of Greene,
Morrison and Strominger we show that this corresponds to black hole
condensation in type II string theories compactified on Calabi-Yau manifolds.Comment: 54 pages, use harvmac and epsf, one uuencoded figur
Mirror Symmetry for Hypersurfaces in Weighted Projective Space and Topological Couplings
By means of toric geometry we study hypersurfaces in weighted projective
space of dimension four. In particular we compute for a given manifold its
intrinsic topological coupling. We find that the result agrees with the
calculation of the corresponding coupling on the mirror model in the large
complex structure limit.Comment: 28p, use harvmac. A new derivation of the Yukawa coupling in the
large complex structure limit has been added to section 5.
Periods for Calabi--Yau and Landau--Ginzburg Vacua
The complete structure of the moduli space of \cys\ and the associated
Landau-Ginzburg theories, and hence also of the corresponding low-energy
effective theory that results from (2,2) superstring compactification, may be
determined in terms of certain holomorphic functions called periods. These
periods are shown to be readily calculable for a great many such models. We
illustrate this by computing the periods explicitly for a number of classes of
\cys. We also point out that it is possible to read off from the periods
certain important information relating to the mirror manifolds.Comment: 54pp. Use harvmac; WARNING: option l does not work. (Replaces
unTeXable version.
Special Geometry and Automorphic Forms
We consider special geometry of the vector multiplet moduli space in
compactifications of the heterotic string on or the type IIA
string on -fibered Calabi-Yau threefolds. In particular, we construct a
modified dilaton that is invariant under T-duality
transformations at the non-perturbative level and regular everywhere on the
moduli space. The invariant dilaton, together with a set of other coordinates
that transform covariantly under , parameterize the moduli space.
The construction involves a meromorphic automorphic function of ,
that also depends on the invariant dilaton. In the weak coupling limit, the
divisor of this automorphic form is an integer linear combination of the
rational quadratic divisors where the gauge symmetry is enhanced classically.
We also show how the non-perturbative prepotential can be expressed in terms of
meromorphic automorphic forms, by expanding a T-duality invariant quantity both
in terms of the standard special coordinates and in terms of the invariant
dilaton and the covariant coordinates.Comment: 21 pages, plain LaTeX. Minor changes, references adde
Transcriptomics and adaptive genomics of the asymptomatic bacteriuria Escherichia coli strain 83972
Escherichia coli strains are the major cause of urinary tract infections in humans. Such strains can be divided into virulent, UPEC strains causing symptomatic infections, and asymptomatic, commensal-like strains causing asymptomatic bacteriuria, ABU. The best-characterized ABU strain is strain 83972. Global gene expression profiling of strain 83972 has been carried out under seven different sets of environmental conditions ranging from laboratory minimal medium to human bladders. The data reveal highly specific gene expression responses to different conditions. A number of potential fitness factors for the human urinary tract could be identified. Also, presence/absence data of the gene expression was used as an adaptive genomics tool to model the gene pool of 83972 using primarily UPEC strain CFT073 as a scaffold. In our analysis, 96% of the transcripts filtered present in strain 83972 can be found in CFT073, and genes on six of the seven pathogenicity islands were expressed in 83972. Despite the very different patient symptom profiles, the two strains seem to be very similar. Genes expressed in CFT073 but not in 83972 were identified and can be considered as virulence factor candidates. Strain 83972 is a deconstructed pathogen rather than a commensal strain that has acquired fitness properties
Exploring de Sitter Space and Holography
We explore aspects of the physics of de Sitter (dS) space that are relevant
to holography with a positive cosmological constant. First we display a
nonlocal map that commutes with the de Sitter isometries, transforms the
bulk-boundary propagator and solutions of free wave equations in de Sitter onto
the same quantities in Euclidean anti-de Sitter (EAdS), and takes the two
boundaries of dS to the single EAdS boundary via an antipodal identification.
Second we compute the action of scalar fields on dS as a functional of boundary
data. Third, we display a family of solutions to 3d gravity with a positive
cosmological constant in which the equal time sections are arbitrary genus
Riemann surfaces, and compute the action of these spaces as a functional of
boundary data from the Einstein gravity and Chern-Simons gravity points of
view. These studies suggest that if de Sitter space is dual to a Euclidean
conformal field theory (CFT), this theory should involve two disjoint, but
possibly entangled factors. We argue that these CFTs would be of a novel form,
with unusual hermiticity conditions relating left movers and right movers.
After exploring these conditions in a toy model, we combine our observations to
propose that a holographic dual description of de Sitter space would involve a
pure entangled state in a product of two of our unconventional CFTs associated
with the de Sitter boundaries. This state can be constructed to preserve the de
Sitter symmetries and and its decomposition in a basis appropriate to antipodal
inertial observers would lead to the thermal properties of static patch.Comment: LaTeX, v2: references adde
Harmful algal blooms and their effects in coastal seas of Northern Europe
Highlights
• Fish mortalities due to harmful algae cause substantial economic and social costs for the fish farming industry in the northeastern Atlantic, North Sea and adjacent European waters
• Toxin syndromes associated with Diarrhetic Shellfish Toxins and Paralytic Shellfish Toxins and their regulation have the most profound effect on the bivalve aquaculture industry in the northeastern Atlantic region
• Cyanobacteria and cyanotoxins are mainly problems in brackish water areas, particularly in the Baltic Sea
• Emerging threats to the shellfish and finfish industries include the known presence of the phycotoxins azaspiracids and goniodomins
• The IOC-ICES-PICESHAEDAT contains time-series baseline information on harmful algal events in EuropeHarmful algal blooms (HAB) are recurrent phenomena in northern Europe along the coasts of the Baltic Sea, Kattegat-Skagerrak, eastern North Sea, Norwegian Sea and the Barents Sea. These HABs have caused occasional massive losses for the aquaculture industry and have chronically affected socioeconomic interests in several ways. This status review gives an overview of historical HAB events and summarises reports to the Harmful Algae Event Database from 1986 to the end of year 2019 and observations made in long term monitoring programmes of potentially harmful phytoplankton and of phycotoxins in bivalve shellfish. Major HAB taxa causing fish mortalities in the region include blooms of the prymnesiophyte Chrysochromulina leadbeateri in northern Norway in 1991 and 2019, resulting in huge economic losses for fish farmers. A bloom of the prymesiophyte Prymnesium polylepis (syn. Chrysochromulina polylepis) in the Kattegat-Skagerrak in 1988 was ecosystem disruptive. Blooms of the prymnesiophyte Phaeocystis spp. have caused accumulations of foam on beaches in the southwestern North Sea and Wadden Sea coasts and shellfish mortality has been linked to their occurrence. Mortality of shellfish linked to HAB events has been observed in estuarine waters associated with influx of water from the southern North Sea. The first bloom of the dictyochophyte genus Pseudochattonella was observed in 1998, and since then such blooms have been observed in high cell densities in spring causing fish mortalities some years. Dinoflagellates, primarily Dinophysis spp., intermittently yield concentrations of Diarrhetic Shellfish Toxins (DST) in blue mussels, Mytilus edulis, above regulatory limits along the coasts of Norway, Denmark and the Swedish west coast. On average, DST levels in shellfish have decreased along the Swedish and Norwegian Skagerrak coasts since approximately 2006, coinciding with a decrease in the cell abundance of D. acuta. Among dinoflagellates, Alexandrium species are the major source of Paralytic Shellfish Toxins (PST) in the region. PST concentrations above regulatory levels were rare in the Skagerrak-Kattegat during the three decadal review period, but frequent and often abundant findings of Alexandrium resting cysts in surface sediments indicate a high potential risk for blooms. PST levels often above regulatory limits along the west coast of Norway are associated with A. catenella (ribotype Group 1) as the main toxin producer. Other Alexandrium species, such as A. ostenfeldii and A. minutum, are capable of producing PST among some populations but are usually not associated with PSP events in the region. The cell abundance of A. pseudogonyaulax, a producer of the ichthyotoxin goniodomin (GD), has increased in the Skagerrak-Kattegat since 2010, and may constitute an emerging threat. The dinoflagellate Azadinium spp. have been unequivocally linked to the presence of azaspiracid toxins (AZT) responsible for Azaspiracid Shellfish Poisoning (AZP) in northern Europe. These toxins were detected in bivalve shellfish at concentrations above regulatory limits for the first time in Norway in blue mussels in 2005 and in Sweden in blue mussels and oysters (Ostrea edulis and Crassostrea gigas) in 2018. Certain members of the diatom genus Pseudo-nitzschia produce the neurotoxin domoic acid and analogs known as Amnesic Shellfish Toxins (AST). Blooms of Pseudo-nitzschia were common in the North Sea and the Skagerrak-Kattegat, but levels of AST in bivalve shellfish were rarely above regulatory limits during the review period. Summer cyanobacteria blooms in the Baltic Sea are a concern mainly for tourism by causing massive fouling of bathing water and beaches. Some of the cyanobacteria produce toxins, e.g. Nodularia spumigena, producer of nodularin, which may be a human health problem and cause occasional dog mortalities. Coastal and shelf sea regions in northern Europe provide a key supply of seafood, socioeconomic well-being and ecosystem services. Increasing anthropogenic influence and climate change create environmental stressors causing shifts in the biogeography and intensity of HABs. Continued monitoring of HAB and phycotoxins and the operation of historical databases such as HAEDAT provide not only an ongoing status report but also provide a way to interpret causes and mechanisms of HABs
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