Biofouling protection for marine environmental sensors

These days, many marine autonomous environment monitoring networks are set up in the world. These systems take advantage of existing superstructures such as offshore platforms, lightships, piers, breakwaters or are placed on specially designed buoys or underwater oceanographic structures. These systems commonly use various sensors to measure parameters such as dissolved oxygen, turbidity, conductivity, pH or fluorescence. Emphasis has to be put on the long term quality of measurements, yet sensors may face very short-term biofouling effects. Biofouling can disrupt the quality of the measurements, sometimes in less than a week. <br><br> Many techniques to prevent biofouling on instrumentation are listed and studied by researchers and manufacturers. Very few of them are implemented on instruments and of those very few have been tested in situ on oceanographic sensors for deployment of at least one or two months. <br><br> This paper presents a review of techniques used to protect against biofouling of in situ sensors and gives a short list and description of promising techniques

Surface charge algebra in gauge theories and thermodynamic integrability

Surface charges and their algebra in interacting Lagrangian gauge field theories are investigated by using techniques from the variational calculus. In the case of exact solutions and symmetries, the surface charges are interpreted as a Pfaff system. Integrability is governed by Frobenius' theorem and the charges associated with the derived symmetry algebra are shown to vanish. In the asymptotic context, we provide a generalized covariant derivation of the result that the representation of the asymptotic symmetry algebra through charges may be centrally extended. Finally, we make contact with Hamiltonian and with covariant phase space methods.Comment: 40 pages Latex file, published versio

On the CFT duals for near-extremal black holes

We consider Kerr-Newman-AdS-dS black holes near extremality and work out the near-horizon geometry of these near-extremal black holes. We identify the exact U(1)_L x U(1)_R isometries of the near-horizon geometry and provide boundary conditions enhancing them to a pair of commuting Virasoro algebras. The conserved charges of the corresponding asymptotic symmetries are found to be well defined and non-vanishing and to yield central charges c_L\neq0 and c_R=0. The Cardy formula subsequently reproduces the Bekenstein-Hawking entropy of the black hole. This suggests that the near-extremal Kerr-Newman-AdS-dS black hole is holographically dual to a non-chiral two-dimensional conformal field theory.Comment: 11 page

<i>Cocconeis molesta</i> Kütz., <i>C. diaphana</i> W.Sm. and <i>C. dirupta</i> W.Greg. (Bacillariophyta): type material, ambiguities and possible synonymies

F.T. Kützing introduced Cocconeis molesta with only an uninformative description and a poor illustration: C. molesta has small, oblong valves and is an epiphyte. Another species, Cocconeis diaphana, described by William Smith, is said to have larger valves than C. molesta, with frustules that are relatively oblong. Smith described two forms: one with a distinct fascia on its raphe valve (var. β), the other without this feature. A third species, Cocconeis dirupta was described by Gregory, who expressed doubts that it differed from C. diaphana. Finally, Cocconeis molesta var. crucifera Grunow was first introduced in Van Heurck’s Atlas but was subsequently treated by Van Heurck as a synonym of C. molesta. No previous account has examined the type material of these species. In this paper, we undertake that task and examine type slides and raw material in order to discriminate these different taxa. We conclude by recognizing three species: Cocconeis molesta Kütz., C. diaphana W.Sm. and C. dirupta W.Greg. Cocconeis diaphana var. β is considered to be a synonym of C. dirupta and C. molesta var. crucifera is considered to be a synonym of C. molesta. Lectotypes are designated for C. diaphana and C. dirupta

A near-NHEK/CFT correspondence

We consider excitations around the recently introduced near-NHEK metric describing the near-horizon geometry of the near-extremal four-dimensional Kerr black hole. This geometry has a U(1)_L x U(1)_R isometry group which can be enhanced to a pair of commuting Virasoro algebras. We present boundary conditions for which the conserved charges of the corresponding asymptotic symmetries are well defined and non-vanishing and find the central charges c_L=12J/hbar and c_R=0 where J is the angular momentum of the black hole. Applying the Cardy formula reproduces the Bekenstein-Hawking entropy of the black hole. This suggests that the near-extremal Kerr black hole is holographically dual to a non-chiral two-dimensional conformal field theory.Comment: 11 pages, v2: references updated, adde

Classical central extension for asymptotic symmetries at null infinity in three spacetime dimensions

The symmetry algebra of asymptotically flat spacetimes at null infinity in three dimensions is the semi-direct sum of the infinitesimal diffeomorphisms on the circle with an abelian ideal of supertranslations. The associated charge algebra is shown to admit a non trivial classical central extension of Virasoro type closely related to that of the anti-de Sitter case.Comment: 4 sign mistakes due to a change of conventions are corrected in section 2, none of the conclusions are affected, takes precedence over published version, including corrigendu

The holographic fluid dual to vacuum Einstein gravity

We present an algorithm for systematically reconstructing a solution of the (d+2)-dimensional vacuum Einstein equations from a (d+1)-dimensional fluid, extending the non-relativistic hydrodynamic expansion of Bredberg et al in arXiv:1101.2451 to arbitrary order. The fluid satisfies equations of motion which are the incompressible Navier-Stokes equations, corrected by specific higher derivative terms. The uniqueness and regularity of this solution is established to all orders and explicit results are given for the bulk metric and the stress tensor of the dual fluid through fifth order in the hydrodynamic expansion. We establish the validity of a relativistic hydrodynamic description for the dual fluid, which has the unusual property of having a vanishing equilibrium energy density. The gravitational results are used to identify transport coefficients of the dual fluid, which also obeys an interesting and exact constraint on its stress tensor. We propose novel Lagrangian models which realise key properties of the holographic fluid.Comment: 31 pages; v2: references added and minor improvements, published versio

G2 Dualities in D=5 Supergravity and Black Strings

Five dimensional minimal supergravity dimensionally reduced on two commuting Killing directions gives rise to a G2 coset model. The symmetry group of the coset model can be used to generate new solutions by applying group transformations on a seed solution. We show that on a general solution the generators belonging to the Cartan and nilpotent subalgebras of G2 act as scaling and gauge transformations, respectively. The remaining generators of G2 form a sl(2,R)+sl(2,R) subalgebra that can be used to generate non-trivial charges. We use these generators to generalize the five dimensional Kerr string in a number of ways. In particular, we construct the spinning electric and spinning magnetic black strings of five dimensional minimal supergravity. We analyze physical properties of these black strings and study their thermodynamics. We also explore their relation to black rings.Comment: typos corrected (26 pages + appendices, 2 figures

Thermodynamics of charged and rotating black strings

We study thermodynamics of cylindrically symmetric black holes. Uncharged as well as charged and rotating objects have been discussed. We derive surface gravity and hence the Hawking temperature and entropy for all these cases. We correct some results in the literature and present new ones. It is seen that thermodynamically these black configurations behave differently from spherically symmetric objects

Microscopics of Extremal Kerr from Spinning M5 Branes

We show that the spinning magnetic one-brane in minimal five-dimensional supergravity admits a decoupling limit that interpolates smoothly between a self-dual null orbifold of AdS_3 \times S^2 and the near-horizon limit of the extremal Kerr black hole times a circle. We use this interpolating solution to understand the field theory dual to spinning M5 branes as a deformation of the Discrete Light Cone Quantized (DLCQ) Maldacena-Stominger-Witten (MSW) CFT. In particular, the conformal weights of the operators dual to the deformation around AdS_3 \times S^2 are calculated. We present pieces of evidence showing that a CFT dual to the four-dimensional extremal Kerr can be obtained from the deformed MSW CFT.Comment: 5 page