175 research outputs found
The string partition function in Hull's doubled formalism
T-duality is one of the essential elements of string theory. Recently, Hull
has developed a formalism where the dimension of the target space is doubled so
as to make T-duality manifest. This is then supplemented with a constraint
equation that allows the connection to the usual string sigma model. This paper
analyses the partition function of the doubled formalism by interpreting the
constraint equation as that of a chiral scalar and then using holomorphic
factorisation techniques to determine the partition function. We find there is
quantum equivalence to the ordinary string once the topological interaction
term is included.Comment: 16 pages, latex, v2 typos corrected, v3 some comments adde
Laser-Doppler Measurements of the Decay of Velocity Fluctuations in Dilute Polymer Solutions
Finite disturbances were generated in a pipe containing water or a 20 ppm solution of Separan AP-30 in water by oscillating a sleeve at the wall. The sleeve amplitude in the axial direction varied from 0.5 to 2.0 inches and the frequency from 0.25 to 1.0 Hz. Downstream of the sleeve oscillations in the fluid velocity were measured with a laser Doppler flowmeter at various axial and radial positions to determine behavior at the lower frequency part of the stability curve for water. The response amplitude, phase angle and the mean velocities were measured for both fluids at Reynolds numbers from 500 to 2100. The water response was frequency dependent in the experimental range. Transitions from well defined velocity fluctuations following the disturbance frequency to random responses were noted as the frequency changed from 0.25 Hz to 1.0 Hz. The dilute polymer solutions showed reduced response amplitudes and always had well defined fluctuations indicating that the stability limit is at a higher frequency than that for water
A note on the M2-M5 brane system and fuzzy spheres
This note covers various aspects of recent attempts to describe membranes
ending on fivebranes using fuzzy geometry. In particular, we examine the
Basu-Harvey equation and its relation to the Nahm equation as well as the
consequences of using a non-associative algebra for the fuzzy three-sphere.
This produces the tantalising result that the fuzzy funnel solution
corresponding to Q coincident membranes ending on a five-brane has
degrees of freedom.Comment: 17 pages, late
Five-brane Calibrations and Fuzzy Funnels
We present a generalisation of the Basu-Harvey equation that describes
membranes ending on intersecting five-brane configurations corresponding to
various calibrated geometries.Comment: 20 pages, latex, v2: typos fixed and refs adde
Background Field Equations for the Duality Symmetric String
This paper describes the background field equations for strings in T-duality
symmetric formalisms in which the dimension of target space is doubled and the
sigma model supplemented with constraints. These are calculated by demanding
the vanishing of the beta-functional of the sigma model couplings in the
doubled target space. We demonstrate the equivalence with the background field
equations of the standard string sigma model.Comment: 26 pages, latex, v2 typos correcte
A Double Sigma Model for Double Field Theory
We define a sigma model with doubled target space and calculate its
background field equations. These coincide with generalised metric equation of
motion of double field theory, thus the double field theory is the effective
field theory for the sigma model.Comment: 26 pages, v1: 37 pages, v2: references added, v3: updated to match
published version - background and detail of calculations substantially
condensed, motivation expanded, refs added, results unchange
Reframing noncommunicable diseases and injuries for the poorest Malawians: the Malawi National NCDI Poverty Commission
Noncommunicable diseases and injuries (NCDIs) account for nearly 70% of deaths worldwide, with an estimated 75% of these deaths occurring in low- and middle-income countries. Globally, the burden of disease from noncommunicable diseases (NCDs) is most often caused by the âbig 4,â namely: diabetes, cardiovascular diseases, cancer, and chronic lung diseases. However, in Malawi, these 4 conditions account for only 29% of the NCDI disease burden.The Malawi National NCDI Poverty Commission was launched in November 2016 and will describe and evaluate the current NCDI situation in Malawi, with a focus on the poorest populations. The National Commission will investigate which NCDIs cause the biggest burden, which are more present in the young, and which interventions are available to avert death and disability from NCDIs in Malawi, particularly among the poorest segments of the population.The evidence gained through the work of this Commission will help inform research, policy, and programme interventions, all through an advocacy lens, as we strive to address the impact of NCDIs among all populations in Malawi
Possible Transport of Basal Debris to the Surface of a Mid-Latitude Glacier on Mars
International audience<p><strong>Introduction:</strong> We observe internal flow structures within a viscous flow feature (VFF; 51.24&#176;W, 42.53&#176;S) interpreted as a debris-covered glacier in Nereidum Montes, Mars. The structures are exposed in the wall of a gully that is incised through the VFF, parallel to its flow-direction. They are near to the glacier terminus and appear to connect its deep interior (and possibly its bed) to arcuate flow-transverse foliations on its surface. Such foliations are common on VFF surfaces, but their relation to VFF-internal structures and ice flow is poorly understood. The VFF-internal structures we observe are reminiscent of up-glacier dipping shear structures that transport basal debris to glacier surfaces on Earth.</p><p>Subglacial environments on Mars are of astrobiological interest due to the availability of water ice and shelter from Mars&#8217; surface radiation environment. However, current limitations in drilling technology prevent their direct exploration. If debris on VFF surfaces contains a component of englacial and/or subglacial debris, those materials could be sampled without access to the subsurface. This could reduce the potential cost and complexity of future missions that aim to explore englacial and subglacial environments on Mars.</p><p><strong>Methods: </strong>We use a 1&#160;m/pixel digital elevation model (DEM) derived from 25&#160;cm/pixel High Resolution Imaging Science Experiment (HiRISE) stereo-pair images, and a false-colour (merged IRB) HiRISE image. We measured the dip and strike of the VFF-internal structures using ArcGIS 10.7 and QGIS software. We also input the DEM (and an inferred glacier bed topography derived from it) into ice flow simulations using the Ice Sheet System Model, assuming no basal sliding and present-day mean annual surface temperature (210K).</p><p><strong>Results and Discussion: </strong>The VFF-internal structures dip up-glacier at ~20&#176; from the bed. This is inconsistent with their formation by bed-parallel ice-accumulation layering without modification by ice flow. The VFF-internal structures and surface foliations are spectrally &#8216;redder&#8217; than adjacent VFF portions, which appear &#8216;bluer&#8217;. This could result from differences in debris concentration and/or surficial dust trapping between the internal structures and the bulk VFF. Modelling experiments suggest that the up-glacier-dipping structures occur at the onset of a compressional regime as ice flow slowed towards the VFF terminus.</p><p>In cold-based glaciers on Earth, up-glacier-dipping folds are common approaching zones of enhanced ice rigidity near the glacier margin. Where multiple folds co-exist, the outermost typically comprises basal ice with a component of subglacial debris entrained in the presence of interfacial films of liquid water at sub-freezing temperatures. In polythermal glaciers, debris-rich up-glacier-dipping thrust faults form where sliding wet-based ice converges with cold-based ice.</p><p><strong>Conclusions: </strong>We propose that the observed up-glacier-dipping VFF-internal structures are englacial shear zones formed by compressional ice flow. They could represent transport pathways for englacial and subglacial material to the VFF surface. The majority of extant mid-latitude VFF on Mars are thought to have been perennially cold-based; thus we favour the hypothesis that the VFF-internal structures are folds formed under a cold-based thermal regime. Under this mechanism, the outermost surface foliation, and its corresponding VFF-internal structure, is the most likely to contain subglacial debris.</p>
Nonabelian (2,0) Tensor Multiplets and 3-algebras
Using 3-algebras we obtain a nonabelian system of equations that furnish a
representation of the (2,0)-supersymmetric tensor multiplet. The on-shell
conditions are quite restrictive so that the system can be reduced to
five-dimensional gauge theory along with six-dimensional abelian (2,0) tensor
multiplets. We briefly discuss possible applications to D4-branes using a
spacelike reduction and M5-branes using a null reduction.Comment: 17 pages, Latex; v2: Typos corrected and references adde
Internal Structure of a Glacier on Mars Revealed by Gully Incision
International audienceDebris transport from / A Mars glacier bed to / Flowlines on surface
- âŠ