530 research outputs found
On the stability limits of long nonaxisymmetric cylindrical liquid bridges
There is a self-similar solution for the stability limits of long, almost cylindrical liquid bridges between equal disks subjected to both axial and lateral accelerations. The stability limits depend on only two variables; the so-called reduced axial, and lateral Bond numbers. A novel experimental setup that involved rotating a horizontal cylindrical liquid bridge about a vertical axis of rotation was designed to test the stability limits predicted by the self-similar solution. Analytical predictions compared well with both numerical and experimental results
Black Holes in Cascading Theories: Confinement/Deconfinement Transition and other Thermal Properties
We present numerical evidence for a transition between the Klebanov-Strassler
background and a solution describing a black hole in the class of cascading
solutions in the chirally restored phase. We also present a number of
properties of this solution, including the running of the coupling constant,
the viscosity to entropy ratio and the drag force on a quark moving in this
background.Comment: 34 pages, 7 figures. Version to be published by JHE
Entanglement and topology in RG flows across dimensions: caps, bridges and corners
We quantitatively address the following question: for a QFT which is partially compactified, so as to realize an RG flow from a D-dimensional CFT in the UV to a d-dimensional CFT in the IR, how does the entanglement entropy of a small spherical region probing the UV physics evolve as the size of the region grows to increasingly probe IR physics? This entails a generalization of spherical regions to setups without full Lorentz symmetry, and we study the associated entanglement entropies holographically. We find a tight interplay between the topology and geometry of the compact space and the evolution of the entanglement entropy, with universal transitions from ‘cap’ through ‘bridge’ and ‘corner’ phases, whose features reflect the details of the compact space. As concrete examples we discuss twisted compactifications of 4d N = 4 SYM on T2, S2 and hyperbolic Riemann surfaces
Helping HELP with limited resources: The Luquillo experience
By definition the HELP approach involves the active participation of individuals from a wide range of disciplines and backgrounds, including representatives of industry, academics, natural resource managers, and local officials and community leaders. While there is considerable enthusiasm and support for the integrated HELP approach, a central problem for all HELP basins is how to effectively engage individuals and groups with few, if any financial resources. In the Luquillo HELP project we have managed this issue by focusing our efforts on holding small, public meetings and workshops with technocrats and managers who are engaged in local water resource management. To date several forums have been organised, including: technical meetings with the directors of natural resource agencies; presentations and panel discussions at the meetings of local professional societies, including the societies of Civil Engineers and Architects, the Commonwealth Association of Tourism, the Association of Builders and Developers, and the Puerto Rican Association of Lawyers. During these forums HELP specialists gave presentations and led discussions on how integrated watershed management can help resolve local problems. Because the audience are directly involved with these issues, they are quite responsive to these discussions and have often provided unique solutions to common problems. Technical workshops are co-sponsored by local municipalities – these day-long workshops are hosted by a municipality and include managers from other municipalities, the local water authority, and local community leaders. Additional activities include: technical advice on water infrastructure projects is given; there are educational exchanges between local and international students, scientists, natural resource managers, and community leaders; and synthesis publications relevant to integrated water resource management are produced. Other activities have included compiling oral environmental histories and organising watershed restoration activities. This paper describes these activities and discusses the benefits and costs of each approach
Cochleates derived from Vibrio cholerae O1 proteoliposomes : The impact of structure transformation on mucosal immunisation
Cochleates are phospholipid-calcium precipitates derived from the interaction of anionic lipid vesicles with divalent cations. Proteoliposomes from bacteria may also be used as a source of negatively charged components, to induce calcium-cochleate formation. In this study, proteoliposomes from V. cholerae O1 (PLc) (sized 160.7±1.6 nm) were transformed into larger (16.3±4.6 µm) cochleate-like structures (named Adjuvant Finlay Cochleate 2, AFCo2) and evaluated by electron microscopy (EM). Measurements from transmission EM (TEM) showed the structures had a similar size to that previously reported using light microscopy, while observations from scanning electron microscopy (SEM) indicated that the structures were multilayered and of cochleate-like formation. The edges of the AFCo2 structures appeared to have spaces that allowed penetration of negative stain or Ovalbumin labeled with Texas Red (OVA-TR) observed by epi-fluorescence microscopy. In addition, freeze fracture electron microscopy confirmed that the AFCo2 structures consisted of multiple overlapping layers, which corresponds to previous descriptions of cochleates. TEM also showed that small vesicles co-existed with the larger cochleate structures, and in vitro treatment with a calcium chelator caused the AFCo2 to unfold and reassemble into small proteoliposome-like structures. Using OVA as a model antigen, we demonstrated the potential loading capacity of a heterologous antigen and in vivo studies showed that with simple admixing and administration via intragastric and intranasal routes AFCo2 provided enhanced adjuvant properties compared with PLc
A teleoperated facility for variable gravity level fluid physics experimentation
A facility to perform experiments on fluid physics and specially on the mechanical behavior of liquid bridges has been designed and built. The facility consists of a velocity controlled centrifuge than can be rotated at speeds up to 10 rpm with and arm of 1.5 m where the experiment container (a Plateau tank in which different mechanical stimuli can be imposed to the liquid column) can be fixed at any location. The rotating system transmits out a video signal for diagnosis and besides control and monitoring signals are routed to the external data management system. The facility and its control system has been implemented in a way that it is possible to control and monitor the experiments either locally from a control workstation or the entire facility can enter in a mode to be controlled remotely. In this case, the control workstation is located far away the facility (indeed in a different city) and linked with data lines. The purpose of this exercise is to gain experience on the minimum data bandwidth needed and the impact on orbital platforms fluid science experimentation of transmission delays and data loses. The latter effects are implemented in the data stream in a way that can be simulated at a rate much higher than that will be experienced otherwise
Glueball Regge trajectories from gauge/string duality and the Pomeron
The spectrum of light baryons and mesons has been reproduced recently by
Brodsky and Teramond from a holographic dual to QCD inspired in the AdS/CFT
correspondence. They associate fluctuations about the AdS geometry with four
dimensional angular momenta of the dual QCD states. We use a similar approach
to estimate masses of glueball states with different spins and their
excitations. We consider Dirichlet and Neumann boundary conditions and find
approximate linear Regge trajectories for these glueballs. In particular the
Neumann case is consistent with the Pomeron trajectory.Comment: In this revised version we made some additional remarks on the text.
We also included 2 more references. The glueball spectrum and Regge
trajectories are unchanged. 10 pages, 2 eps figure
On a Holographic Model for Confinement/Deconfinement
We study the thermodynamics of the hard wall model, which consists in the
introduction of an infrared cut-off in asymptotically AdS spaces. This is a toy
model for confining backgrounds in the context of the gauge/gravity
correspondence. We use holographic renormalization and reproduce the existence
of a Hawking Page phase transition recently discussed by Herzog. We also show
that the entropy jumps from to , which reinforces the interpretation
of this transition as the gravity dual of confinement/deconfinement. We also
show that similar results hold for the phenomenologically motivated soft wall
model, underlining the potential universality of our analysis.Comment: 14 pages. V2: We included a new section discussing the soft wall
model and new references. V3: We clarified some points and updated the
references. Results unchanged. Version published in PR
Chaos around Holographic Regge Trajectories
Using methods of Hamiltonian dynamical systems, we show analytically that a
dynamical system connected to the classical spinning string solution
holographically dual to the principal Regge trajectory is non-integrable. The
Regge trajectories themselves form an integrable island in the total phase
space of the dynamical system. Our argument applies to any gravity background
dual to confining field theories and we verify it explicitly in various
supergravity backgrounds: Klebanov-Strassler, Maldacena-Nunez, Witten QCD and
the AdS soliton. Having established non-integrability for this general class of
supergravity backgrounds, we show explicitly by direct computation of the
Poincare sections and the largest Lyapunov exponent, that such strings have
chaotic motion.Comment: 28 pages, 5 figures. V3: Minor changes complying to referee's
suggestions. Typos correcte
-Functions in Flows Across Dimensions
We explore the notion of -functions in renormalization group flows between
theories in different spacetime dimensions. We discuss functions connecting
central charges of the UV and IR fixed point theories on the one hand, and
functions which are monotonic along the flow on the other. First, using the
geometric properties of the holographic dual RG flows across dimensions and the
constraints from the null energy condition, we construct a monotonic
holographic -function and thereby establish a holographic -theorem across
dimensions. Second, we use entanglement entropies for two different types of
entangling regions in a field theory along the RG flow across dimensions to
construct candidate -functions which satisfy one of the two criteria but not
both. In due process we also discuss an interesting connection between corner
contributions to the entanglement entropy and the topology of the compact
internal space. As concrete examples for both approaches, we holographically
study twisted compactifications of 4d SYM and compactifications
of 6d theories.Comment: 49 pages, 17 figure
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