scholarly journals A substrate for brane shells from $$ T\overline{T} $$

2021 ◽  
Vol 2021 (5) ◽  
Author(s):  
Jeremias Aguilera-Damia ◽  
Louise M. Anderson ◽  
Evan Coleman
Keyword(s):  
Three Dimensional ◽  
Radial Position ◽  
Singular Behavior ◽  
Curvature Singularity ◽  
Closed Timelike Curves ◽  
Finite Radius ◽  
Linear Dilaton ◽  
Singularity Resolution ◽  
New Interpretation ◽  
Single Trace

Abstract A solvable current-current deformation of the worldsheet theory of strings on AdS3 has been recently conjectured to be dual to an irrelevant deformation of the spacetime orbifold CFT, commonly referred to as single-trace $$ T\overline{T} $$ T T ¯ . These deformations give rise to a family of bulk geometries which realize a non-trivial flow towards the UV. For a particular sign of this deformation, the corresponding three-dimensional geometry approaches AdS3 in the interior, but has a curvature singularity at finite radius, beyond which there are closed timelike curves. It has been suggested that this singularity is due to the presence of “negative branes,” which are exotic objects that generically change the metric signature. We propose an alternative UV-completion for geometries displaying a similar singular behavior by cutting and gluing to a regular background which approaches a linear dilaton vacuum in the UV. In the S-dual picture, a singularity resolution mechanism known as the enhançon induces this transition by the formation of a shell of D5-branes at a fixed radial position near the singularity. The solutions involving negative branes gain a new interpretation in this context.

scholarly journals Strings in irrelevant deformations of AdS3/CFT2

2020 ◽  
Vol 2020 (11) ◽  
Author(s):  
Soumangsu Chakraborty ◽  
Amit Giveon ◽  
David Kutasov
Keyword(s):  
Recent Analysis ◽  
Boundary Theory ◽  
Quantum Scattering ◽  
Closed Timelike Curves ◽  
High Energies ◽  
Scattering States ◽  
Linear Dilaton ◽  
Classical Trajectories ◽  
Single Trace ◽  
Far Future

Abstract We generalize our recent analysis [1] of probe string dynamics to the case of general single-trace $$ T\overline{T},J\overline{T} $$ T T ¯ , J T ¯ and $$ T\overline{J} $$ T J ¯ deformations. We show that in regions in coupling space where the bulk geometry is smooth, the classical trajectories of such strings are smooth and approach the linear dilaton boundary at either the far past or the far future. These trajectories give rise to quantum scattering states with arbitrarily high energies. When the bulk geometry has closed timelike curves (CTC’s), the trajectories are singular for energies above a critical value Ec. This singularity occurs in the region with CTC’s, and the value of Ec agrees with that read off from the dual boundary theory for all values of the couplings and charges.

scholarly journals $$ T\overline{T} $$ , black holes and negative strings

2020 ◽  
Vol 2020 (9) ◽  
Author(s):  
Soumangsu Chakraborty ◽  
Amit Giveon ◽  
David Kutasov
Keyword(s):  
Black Holes ◽  
String Theory ◽  
Upper Bound ◽  
Point Of View ◽  
The Other ◽  
Curvature Singularity ◽  
Asymptotically Linear ◽  
Radial Location ◽  
Linear Dilaton ◽  
Single Trace

Abstract String theory on AdS3 has a solvable single-trace irrelevant deformation that is closely related to $$ T\overline{T} $$ T T ¯ . For one sign of the coupling, it leads to an asymptotically linear dilaton spacetime, and a corresponding Hagedorn spectrum. For the other, the resulting spacetime has a curvature singularity at a finite radial location, and an upper bound on the energies of states. Beyond the singularity, the signature of spacetime is flipped and there is an asymptotically linear dilaton boundary at infinity. We study the properties of black holes and fundamental strings in this spacetime, and find a sensible picture. The singularity does not give rise to a hard ultraviolet wall for excitations -one must include the region beyond it to understand the theory. The size of black holes diverges as their energy approaches the upper bound, as does the location of the singularity. Fundamental strings pass smoothly through the singularity, but if their energy is above the upper bound, their trajectories are singular. From the point of view of the boundary at infinity, this background can be thought of as a vacuum of Little String Theory which contains a large number of negative strings.

scholarly journals Microtubules soften due to cross-sectional flattening

eLife ◽  
2018 ◽  
Vol 7 ◽  
Author(s):  
Edvin Memet ◽  
Feodor Hilitski ◽  
Margaret A Morris ◽  
Walter J Schwenger ◽  
Zvonimir Dogic ◽  
...  
Keyword(s):  
High Strain ◽  
Three Dimensional ◽  
Elastic Model ◽  
Softening Effect ◽  
Cross Sectional ◽  
Mechanical Compliance ◽  
Wide Range ◽  
Elastic Filament ◽  
New Interpretation ◽  
Effective Mechanical Properties

We use optical trapping to continuously bend an isolated microtubule while simultaneously measuring the applied force and the resulting filament strain, thus allowing us to determine its elastic properties over a wide range of applied strains. We find that, while in the low-strain regime, microtubules may be quantitatively described in terms of the classical Euler-Bernoulli elastic filament, above a critical strain they deviate from this simple elastic model, showing a softening response with increasing deformations. A three-dimensional thin-shell model, in which the increased mechanical compliance is caused by flattening and eventual buckling of the filament cross-section, captures this softening effect in the high strain regime and yields quantitative values of the effective mechanical properties of microtubules. Our results demonstrate that properties of microtubules are highly dependent on the magnitude of the applied strain and offer a new interpretation for the large variety in microtubule mechanical data measured by different methods.

Non-Dimensional Parameters for Comparing Conventional and Counter-Rotating Turbomachines

2019 ◽  
Author(s):  
J. J. Waldren ◽  
C. J. Clark ◽  
S. D. Grimshaw ◽  
G. Pullan
Keyword(s):  
High Efficiency ◽  
Three Dimensional ◽  
Relative Performance ◽  
Design Parameters ◽  
Blade Design ◽  
Finite Radius ◽  
Counter Rotation ◽  
Dimensional Parameters ◽  
Conventional Machine ◽  
Stage Efficiency

Abstract Counter-rotating turbomachines have the potential to be high efficiency, high power density devices. Comparisons between conventional and counter-rotating turbomachines in the literature make multiple and often contradicting conclusions about their relative performance. By adopting appropriate non-dimensional parameters, based on relative blade speed, the design space of conventional machines can be extended to include those with counter-rotation. This allows engineers familiar with conventional turbomachinery to transfer their experience to counter-rotating machines. By matching appropriate non-dimensional parameters the loss mechanisms directly affected by counter-rotation can be determined. A series of computational studies are performed to investigate the relative performance of conventional and counter-rotating turbines with the same non-dimensional design parameters. Each study targets a specific loss source, highlighting which phenomena are directly due to counter-rotation and which are solely due to blade design. The studies range from two-dimensional blade sections to three-dimensional finite radius stages. It is shown that, at hub-to-tip ratios approaching unity, with matched non-dimensional design parameters, the stage efficiency and work output are identical for both types of machine. However, a counter-rotating turbine in the study is shown to have an efficiency advantage over a conventional machine of up to 0.35 percentage points for a hub-to-tip ratio of 0.65. This is due to differences in absolute velocity producing different spanwise blade designs.

J0530402 Influence of Radial Position on Three-Dimensional Surface Flow on HAWT Blade

2015 ◽  
Vol 2015 (0) ◽  
pp. _J0530402--_J0530402-
Author(s):  
Tasuku MATSUNO ◽  
Yasunari KAMADA ◽  
Takao MAEDA ◽  
Junsuke MURATA ◽  
Phengpom TINNAPOB ◽  
...  
Keyword(s):  
Three Dimensional ◽  
Surface Flow ◽  
Radial Position ◽  
Dimensional Surface

The piecewise constant symmetric potential vorticity vortex in geophysical flows

2008 ◽  
Vol 614 ◽  
pp. 145-172 ◽  
Author(s):  
ÁLVARO VIÚDEZ
Keyword(s):  
Potential Vorticity ◽  
Three Dimensional ◽  
Static Stability ◽  
Geophysical Flows ◽  
Radial Dependence ◽  
Radial Solutions ◽  
Finite Radius ◽  
Piecewise Constant ◽  
Order Of Magnitude ◽  
Horizontal Cylinders

The concept of piecewise constant symmetric vortex in the context of three-dimensional baroclinic balanced geophysical flows is explored. The pressure gradients generated by horizontal cylinders and spherical balls of uniform potential vorticity (PV), or uniform material invariants, are obtained either analytically or numerically, in the general case of Boussinesq and f-plane dynamics as well as under the quasi-geostrophic and semigeostrophic dynamical approximations. Based on the order of magnitude of the different terms in the PV inversion equation, approximated PV equations are deduced. In some of these cases, radial solutions are possible and the interior and exterior solutions are found analytically. In the case of non-radial dependence, exterior solutions can be found numerically. Linear, and upper and lower bound approximations to the full PV inversion equations, and their respective solutions, are also included. However, the general solution for the pressure gradient in the vortex exterior does not have spherical symmetry and remains as an important theoretical challenge. It is suggested that, in order to maintain everywhere the inertial and static stability of the balanced geophysical flows, small balls of finite radius, rather than PV singularities, could become, specially in numerical applications, useful mathematical objects.

Integrated seismic texture segmentation and cluster analysis applied to channel delineation and chert reservoir characterization

Geophysics ◽  
2011 ◽  
Vol 76 (5) ◽  
pp. P11-P21 ◽  
Author(s):  
Marcilio Castro de Matos ◽  
Malleswar (Moe) Yenugu ◽  
Sipuikinene Miguel Angelo ◽  
Kurt J. Marfurt
Keyword(s):  
Texture Analysis ◽  
Reservoir Characterization ◽  
Three Dimensional ◽  
Seismic Survey ◽  
Self Organizing Maps ◽  
Early Introduction ◽  
Statistical Measures ◽  
Seismic Waveform ◽  
Occurrence Matrix ◽  
Single Trace

In recent years, 3D volumetric attributes have gained wide acceptance by seismic interpreters. The early introduction of the single-trace complex trace attribute was quickly followed by seismic sequence attribute mapping workflows. Three-dimensional geometric attributes such as coherence and curvature are also widely used. Most of these attributes correspond to very simple, easy-to-understand measures of a waveform or surface morphology. However, not all geologic features can be so easily quantified. For this reason, simple statistical measures of the seismic waveform such as rms amplitude and texture analysis techniques prove to be quite valuable in delineating more chaotic stratigraphy. In this paper, we coupled structure-oriented texture analysis based on the gray-level co-occurrence matrix with self-organizing maps clustering technology and applied it to classify seismic textures. By this way, we expect that our workflow should be more sensitive to lateral changes, rather than vertical changes, in reflectivity. We applied the methodology to a remote sensing image and to a 3D seismic survey acquired over Osage County, Oklahoma, USA. Our results indicate that our method can be used to delineate meandering channels as well as to characterize chert reservoirs.

A Multizone Time-Marching Technique for Unsteady Separating Three-Dimensional Boundary Layers and Its Application to the Symmetry-Plane Solution of an Impulsively Started Prolate Spheroid

1991 ◽  
Vol 113 (2) ◽  
pp. 228-239 ◽  
Author(s):  
Tzuyin Wu ◽  
Shan-Fu Shen
Keyword(s):  
Boundary Layer ◽  
Three Dimensional ◽  
Symmetry Plane ◽  
Elliptic Cylinder ◽  
Prolate Spheroid ◽  
Singular Behavior ◽  
Unsteady Separation ◽  
Stage Of Development ◽  
Dimensional Boundary ◽  
Plane Solution

Recent interest in unsteady separation and separated flows brings up the need of an accurate and efficient computational scheme for general unsteady three-dimensional boundary-layer flows. Resolution of the singular behavior at separation is a delicate problem. The task is further complicated by the geometrical singularity and the nonstationary stagnation point. The present paper proposes a numerical scheme to sidestep these difficulties. At the first stage of development, the simpler problem of the symmetry-plane solution of the laminar boundary-layer over an impulsively-started prolate spheroid is calculated. Results show that the present Eulerian calculation satisfactorily captures the singular behavior of the boundary layer when separation is approached. Comparison with Xu and Wang’s recent results and those for the two-dimensional elliptic cylinder calculated by the Lagrangian method are also made. Discussions of the results for unsteady separation at zero, small and large incidences are presented.

Lift-based paddling in diving grebe

2001 ◽  
Vol 204 (10) ◽  
pp. 1687-1696 ◽  
Author(s):  
L.C. Johansson ◽  
U. M. Lindhe Norberg
Keyword(s):  
Swimming Speed ◽  
Three Dimensional ◽  
Energetic Efficiency ◽  
Digital Analysis ◽  
Acceleration Phase ◽  
Video Images ◽  
Propulsion Mechanism ◽  
Podiceps Cristatus ◽  
New Interpretation ◽  
Great Crested Grebe

To examine the hydrodynamic propulsion mechanism of a diving great crested grebe (Podiceps cristatus), the three-dimensional kinematics was determined by digital analysis of sequential video images of dorsal and lateral views. During the acceleration phase of this foot-propelled bird, the feet move through an arc in a plane nearly normal to the bird's line of motion through the water, i.e. the toes move dorsally and medially but not caudally relative to the water. The kinematics of the grebe's lobed feet is different from that in anseriforms, whose feet move in a plane mostly parallel to the bird's line of progress through the water. Our results suggest that the foot-propelled locomotor mechanism of grebes is based primarily on a lift-producing leg and foot stroke, in contrast to the drag-based locomotion assumed previously. We suggest that the lift-based paddling of grebes considerably increases both maximum swimming speed and energetic efficiency over drag-based propulsion. Furthermore, the results implicate a new interpretation of the functional morphology of these birds, with the toes serving as a self-stabilizing multi-slotted hydrofoil during the power phase.

scholarly journals KINEMATICS OF FLOWS ON CURVED, DEFORMABLE MEDIA

2009 ◽  
Vol 06 (04) ◽  
pp. 645-666 ◽  
Author(s):  
ANIRVAN DASGUPTA ◽  
HEMWATI NANDAN ◽  
SAYAN KAR
Keyword(s):  
Hyperbolic Space ◽  
Initial Conditions ◽  
Three Dimensional ◽  
Flat Space ◽  
Singular Solutions ◽  
Geodesic Flows ◽  
Two Dimensional ◽  
Singular Behavior ◽  
Deformable Media ◽  
Raychaudhuri Equations

Kinematics of geodesic flows on specific, two-dimensional, curved surfaces (the sphere, hyperbolic space and the torus) are investigated by explicitly solving the evolution (Raychaudhuri) equations for the expansion, shear and rotation, for a variety of initial conditions. For flows on the sphere and on hyperbolic space, we show the existence of singular (within a finite value of the time parameter) as well as non-singular solutions. We illustrate our results through a phase diagram which demonstrates under which initial conditions (or combinations thereof) we end up with a singularity in the congruence and when, if at all, we can obtain non-singular solutions for the kinematic variables. Our analysis portrays the differences which arise due to positive or negative curvature and also explores the role of rotation in controlling singular behavior. Subsequently, we move on to geodesic flows on two-dimensional spaces with varying curvature. As an example, we discuss flows on a torus. Characteristic oscillatory features, dependent on the ratio of the two radii of the torus, emerge in the solutions for the expansion, shear and rotation. Singular (within a finite time) and non-singular behavior of the solutions are also discussed. Finally, we conclude with a generalization to three-dimensional spaces of constant curvature, a summary of some of the generic features obtained and a comparison of our results with those for flows in flat space.

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