373 research outputs found
Parent Actions, Dualities and New Weyl-invariant Actions of Bosonic p-branes
By using the systematic approach of parent action method, we derive one
Weyl-noninvariant and two Weyl-invariant actions of bosonic -branes () starting from the Nambu-Goto action, and establish the duality symmetries
in this set of four actions. Moreover, we discover a new bosonic -brane
action (including the string theory) and deduce two corresponding
Weyl-invariant formulations by proposing a new special parent action. We find
that the same duality symmetries as those mentioned above exist in this new set
of actions. The new -brane actions are also briefly analyzed.Comment: 19 pages, 14 figures. The first section is modified slightly, and
references are adde
Direct evidende of sex and a hypothesis about meiosis in Symbiodiniaceae
Dinoflagellates in the family Symbiodiniaceae are obligate endosymbionts of diverse marine invertebrates, including corals, and impact the capacity of their hosts to respond to climate change-driven ocean warming. Understanding the conditions under which increased genetic variation in Symbiodiniaceae arises via sexual recombination can support efforts to evolve thermal tolerance in these symbionts and ultimately mitigate coral bleaching, the breakdown of the coral-Symbiodiniaceae partnership under stress. However, direct observations of meiosis in Symbiodiniaceae have not been reported, despite various lines of indirect evidence that it occurs. We present the first cytological evidence of sex in Symbiodiniaceae based on nuclear DNA content and morphology using Image Flow Cytometry, Cell Sorting and Confocal Microscopy. We show the Symbiodiniaceae species, Cladocopium latusorum, undergoes gamete conjugation, zygote formation, and meiosis within a dominant reef-building coral in situ. On average, sex was detected in 1.5% of the cells analyzed (Nâ=â10,000â40,000 cells observed per sample in a total of 20 samples obtained from 3 Pocillopora colonies). We hypothesize that meiosis follows a two-step process described in other dinoflagellates, in which diploid zygotes form dyads during meiosis I, and triads and tetrads as final products of meiosis II. This study sets the stage for investigating environmental triggers of Symbiodiniaceae sexuality and can accelerate the assisted evolution of a key coral symbiont in order to combat reef degradation
Dirac Quantisation Conditions and Kaluza-Klein Reduction
We present the form of the Dirac quantisation condition for the p-form
charges carried by p-brane solutions of supergravity theories. This condition
agrees precisely with the conditions obtained in lower dimensions, as is
necessary for consistency with Kaluza-klein dimensional reduction. These
considerations also determine the charge lattice of BPS soliton states, which
proves to be a universal modulus-independent lattice when the charges are
defined to be the canonical charges corresponding to the quantum supergravity
symmetry groups.Comment: 40 pages, Late
Conformal p-branes as a Source of Structure in Spacetime
We discuss a model of a conformal p-brane interacting with the world volume
metric and connection. The purpose of the model is to suggest a mechanism by
which gravity coupled to p-branes leads to the formation of structure rather
than homogeneity in spacetime. Furthermore, we show that the formation of
structure is accompanied by the appearance of a multivalued cosmological
constant, i.e., one which may take on different values in different domains, or
cells, of spacetime. The above results apply to a broad class of non linear
gravitational lagrangians as long as metric and connection on the p-brane
manifold are treated as independent variables.Comment: 10 pages, ReVTeX, no figure
Symbiont Community Diversity is More Variable in Corals That Respond Poorly to Stress
Coral reefs are declining globally as climate change and local water quality press environmental conditions beyond the physiological tolerances of holobiontsâthe collective of the host and its microbial symbionts. To assess the relationship between symbiont composition and holobiont stress tolerance, community diversity metrics were quantified for dinoflagellate endosymbionts (Family: Symbiodiniaceae) from eight Acropora millepora genets that thrived under or responded poorly to various stressors. These eight selected genets represent the upper and lower tails of the response distribution of 40 coral genets that were exposed to four stress treatments (and control conditions) in a 10-day experiment. Specifically, four âbest performerâ coral genets were analyzed at the end of the experiment because they survived high temperature, high pCO2, bacterial exposure, or combined stressors, whereas four âworst performerâ genets were characterized because they experienced substantial mortality under these stressors. At the end of the experiment, seven of eight coral genets mainly hosted Cladocopium symbionts, whereas the eighth genet was dominated by both Cladocopium and Durusdinium symbionts. Symbiodiniaceae alpha and beta diversity were higher in worst performing genets than in best performing genets. Symbiont communities in worst performers also differed more after stress exposure relative to their controls (based on normalized proportional differences in beta diversity), than did best performers. A generalized joint attribute model estimated the influence of host genet and treatment on Symbiodiniaceae community composition and identified strong associations among particular symbionts and host genet performance, as well as weaker associations with treatment. Although dominant symbiont physiology and function contribute to host performance, these findings emphasize the importance of symbiont community diversity and stochasticity as components of host performance. Our findings also suggest that symbiont community diversity metrics may function as indicators of resilience and have potential applications in diverse disciplines from climate change adaptation to agriculture and medicine
Instanton Cosmology and Domain Walls from M-theory and String Theory
The recent proposal by Hawking and Turok for obtaining an open inflationary
universe from singular instantons makes use of low-energy effective Lagrangians
describing gravity coupled to scalars and non-propagating antisymmetric
tensors. In this paper we derive some exact results for Lagrangians of this
type, obtained from spherical compactifications of M-theory and string theory.
In the case of the S^7 compactification of M-theory, we give a detailed
discussion of the cosmological solutions. We also show that the
lower-dimensional Lagrangians admit domain-wall solutions, which preserve one
half of the supersymmetry, and which approach AdS spacetimes near their
horizons.Comment: 51 pages, Latex (3 times). Discussion and references adde
An experimental study of the flow-induced noise created by a wall-mounted finite length airfoil
AIAA 2014-3290This paper presents the results of an experimental investigation of the sound produced by flow interaction with a wall-mounted finite length airfoil at low-to-moderate Reynolds number. Acoustic measurements have been taken in an anechoic wind tunnel at a range of Reynolds numbers, angles of attack and for a variety of airfoil aspect ratios (airfoil length to chord ratio) with a single microphone and two perpendicular planar microphone arrays. For comparison, measurements have also been taken with a semi-infinite or two- dimensional airfoil and a half-span airfoil with tip flow but no boundary layer impingement. The experimental data is used to examine changes in wall-mounted finite airfoil noise production as a function of Reynolds number, angle of attack and airfoil aspect ratio. Additionally, the data gives insight into the airfoil noise generation mechanisms and the influence of flow at the airfoil tip and wall junction on noise productionDanielle J. Moreau , Zebb Prime and Con J. Doola
Supergravity Solutions for BI Dyons
We construct partially localized supergravity counterpart solutions to the
1/2 supersymmetric non-threshold and the 1/4 supersymmetric threshold bound
state BI dyons in the D3-brane Dirac-Born-Infeld theory. Such supergravity
solutions have all the parameters of the BI dyons. By applying the IIA/IIB
T-duality transformations to these supergravity solutions, we obtain the
supergravity counterpart solutions to 1/2 and 1/4 supersymmetric BIons carrying
electric and magnetic charges of the worldvolume U(1) gauge field in the
Dirac-Born-Infeld theory in other dimensions.Comment: 17 pages, REVTeX, revised version to appear in Phys. Rev.
Superextendons with a modified measure
For superstrings, the consequences of replacing the measure of integration
in the Polyakov's action by where is
a density built out of degrees of freedom independent of the metric
defined in the string are studied. As in Siegel reformulation of
the Green Schwarz formalism the Wess-Zumino term is the square of
supersymmetric currents. As opposed to the Siegel case, the compensating fields
needed for this do not enter into the action just as in a total derivative.
They instead play a crucial role to make up a consistent dynamics. The string
tension appears as an integration constant of the equations of motion. The
generalization to higher dimensional extended objects is also studied using in
this case the Bergshoeff and Sezgin formalism with the associated additional
fields, which again are dynamically relevant unlike the standard formulation.
Also unlike the standard formulation, there is no need of a cosmological term
on the world brane.Comment: typos corrected, references adde
Comparisons of Supergranule Characteristics During the Solar Minima of Cycles 22/23 and 23/24
Supergranulation is a component of solar convection that manifests itself on
the photosphere as a cellular network of around 35 Mm across, with a turnover
lifetime of 1-2 days. It is strongly linked to the structure of the magnetic
field. The horizontal, divergent flows within supergranule cells carry local
field lines to the cell boundaries, while the rotational properties of
supergranule upflows may contribute to the restoration of the poloidal field as
part of the dynamo mechanism that controls the solar cycle. The solar minimum
at the transition from cycle 23 to 24 was notable for its low level of activity
and its extended length. It is of interest to study whether the convective
phenomena that influences the solar magnetic field during this time differed in
character to periods of previous minima. This study investigates three
characteristics (velocity components, sizes and lifetimes) of solar
supergranulation. Comparisons of these characteristics are made between the
minima of cycles 22/23 and 23/24 using MDI Doppler data from 1996 and 2008,
respectively. It is found that whereas the lifetimes are equal during both
epochs (around 18 h), the sizes are larger in 1996 (35.9 +/- 0.3 Mm) than in
2008 (35.0 +/- 0.3 Mm), while the dominant horizontal velocity flows are weaker
(139 +/- 1 m/s in 1996; 141 +/- 1 m/s in 2008). Although numerical differences
are seen, they are not conclusive proof of the most recent minimum being
inherently unusual.Comment: 22 pages, 5 figures. Solar Physics, in pres
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