1,480 research outputs found
Enhancing the sensitivity of magnetic sensors by 3D metamaterial shells
Magnetic sensors are key elements in our interconnected smart society. Their sensitivity becomes essential for many applications in fields such as biomedicine, computer memories, geophysics, or space exploration. Here we present a universal way of increasing the sensitivity of magnetic sensors by surrounding them with a spherical metamaterial shell with specially designed anisotropic magnetic properties. We analytically demonstrate that the magnetic field in the sensing area is enhanced by our metamaterial shell by a known factor that depends on the shell radii ratio. When the applied field is non-uniform, as for dipolar magnetic field sources, field gradient is increased as well. A proof-of-concept experimental realization confirms the theoretical predictions. The metamaterial shell is also shown to concentrate time-dependent magnetic fields upto frequencies of 100 kHz
Black hole uniqueness theorems and new thermodynamic identities in eleven dimensional supergravity
We consider stationary, non-extremal black holes in 11-dimensional
supergravity having isometry group . We prove that
such a black hole is uniquely specified by its angular momenta, its electric
charges associated with the various 7-cycles in the manifold, together with
certain moduli and vector valued winding numbers characterizing the topological
nature of the spacetime and group action. We furthermore establish interesting,
non-trivial, relations between the thermodynamic quantities associated with the
black hole. These relations are shown to be a consequence of the hidden
symmetry in this sector of the solution space, and are distinct
from the usual "Smarr-type" formulas that can be derived from the first law of
black hole mechanics. We also derive the "physical process" version of this
first law applicable to a general stationary black hole spacetime without any
symmetry assumptions other than stationarity, allowing in particular arbitrary
horizon topologies. The work terms in the first law exhibit the topology of the
horizon via the intersection numbers between cycles of various dimensions.Comment: 50pp, 3 figures, v2: references added, correction in appendix B,
conclusions added, v3: reference section edited, typos removed, minor changes
in appendix
I. A 3D externally illuminated slab benchmark for dust radiative transfer
Context. The radiative transport of photons through arbitrary three-dimensional (3D) structures of dust is a challenging problem due to the anisotropic scattering of dust grains and strong coupling between different spatial regions. The radiative transfer problem in 3D is solved using Monte Carlo or Ray Tracing techniques as no full analytic solution exists for the true 3D structures. Aims. We provide the first 3D dust radiative transfer benchmark composed of a slab of dust with uniform density externally illuminated by a star. This simple 3D benchmark is explicitly formulated to provide tests of the different components of the radiative transfer problem including dust absorption, scattering, and emission. Methods. The details of the external star, the slab itself, and the dust properties are provided. This benchmark includes models with a range of dust optical depths fully probing cases that are optically thin at all wavelengths to optically thick at most wavelengths. The dust properties adopted are characteristic of the diffuse Milky Way interstellar medium. This benchmark includes solutions for the full dust emission including single photon (stochastic) heating as well as two simplifying approximations: One where all grains are considered in equilibrium with the radiation field and one where the emission is from a single effective grain with size-distribution-averaged properties. A total of six Monte Carlo codes and one Ray Tracing code provide solutions to this benchmark. Results. The solution to this benchmark is given as global spectral energy distributions (SEDs) and images at select diagnostic wavelengths from the ultraviolet through the infrared. Comparison of the results revealed that the global SEDs are consistent on average to a few percent for all but the scattered stellar flux at very high optical depths. The image results are consistent within 10%, again except for the stellar scattered flux at very high optical depths. The lack of agreement between different codes of the scattered flux at high optical depths is quantified for the first time. Convergence tests using one of the Monte Carlo codes illustrate the sensitivity of the solutions to various model parameters. Conclusions. We provide the first 3D dust radiative transfer benchmark and validate the accuracy of this benchmark through comparisons between multiple independent codes and detailed convergence tests.Peer reviewe
Multi-Center non-BPS Black Holes - the Solution
We construct multi-center, non-supersymmetric four-dimensional solutions
describing a rotating anti-D6-D2 black hole and an arbitrary number of D4-D2-D0
black holes in a line. These solutions correspond to an arbitrary number of
extremal non-BPS black rings in a Taub-NUT space with a rotating three-charge
black hole in the middle. The positions of the centers are determined by
solving a set of "bubble" or "integrability" equations that contain cubic
polynomials of the inter-center distance, and that allow scaling solutions even
when the total four-dimensional angular momentum of the scaling centers is
non-zero.Comment: 16 pages, LaTe
Balanced electric-magnetic dihole in Kaluza-Klein theory
We present a four-dimensional double-black-hole (or dihole) solution in
Kaluza-Klein theory, describing a superposition of an electrically charged and
a magnetically charged black hole. This system can be balanced for
appropriately chosen parameters, and the resulting space-time is completely
regular on and outside the event horizons. This solution was constructed using
the inverse-scattering method in five-dimensional vacuum gravity, in which it
describes a rotating black ring surrounding a static black hole on a Taub-NUT
background space. Various properties of this solution are studied, from both a
four- and five-dimensional perspective.Comment: 33 pages, 6 figures; v2: expanded discussion of phase space,
published versio
Rotating black rings on Taub-NUT
In this paper, we construct new solutions describing rotating black rings on
Taub-NUT using the inverse-scattering method. These are five-dimensional vacuum
space-times, generalising the Emparan-Reall and extremal Pomeransky-Sen'kov
black rings to a Taub-NUT background space. When reduced to four dimensions in
Kaluza-Klein theory, these solutions describe (possibly rotating) electrically
charged black holes in superposition with a finitely separated magnetic
monopole. Various properties of these solutions are studied, from both a five-
and four-dimensional perspective.Comment: 33 pages, 3 figures, LaTe
A Black Ring with two Angular Momenta in Taub-NUT
We use the recently-constructed explicit duality transformation that relates
a rotating anti-D6-D4-D2-D0 black hole solution to a rotating M5-M2-P black
string to construct a non-supersymmetric black ring in Taub-NUT that has two
angular momenta, as well as M2 charges and M5 dipole moments. This is the first
black ring solution that has both dipole charges and rotation along the S^2 of
the horizon, and hence can be thought of as the "Pomeransky-Senkov" version of
the M5-M2 black ring in Taub-NUT. Its physics should provide a testing ground
for the applicability of the blackfold approach to charged rotating black
branes, and should elucidate the phase space of charged dipole rings in various
backgrounds.Comment: 20 pages, LaTe
Hox-controlled reorganisation of intrasegmental patterning cues underlies Drosophila posterior spiracle organogenesis
10 páginas, 8 figuras. Material complementario del artículo esta disponible en http://dev.biologists.org/cgi/content/full/132/13/3093/DC1Hox proteins provide axial positional information and control segment morphology in development and evolution. Yet how they specify morphological traits that confer segment identity and how axial positional information interferes with intrasegmental patterning cues during organogenesis remain poorly understood. We have investigated the control of Drosophila posterior spiracle morphogenesis, a segment-specific structure that forms under Abdominal-B (AbdB) Hox control in the eighth abdominal segment (A8). We show that the Hedgehog (Hh), Wingless (Wg) and Epidermal Growth Factor Receptor (Egfr) pathways provide specific inputs for posterior spiracle morphogenesis and act in a genetic network made of multiple and rapidly evolving Hox/signalling interplays. A major function of AbdB during posterior spiracle organogenesis is to reset A8 intrasegmental patterning cues, first by reshaping wg and rhomboid expression patterns, then by reallocating the Hh signal and later by initiating de novo expression of the posterior compartment gene engrailed in anterior compartment cells. These changes in expression patterns confer axial specificity to otherwise reiteratively used segmental patterning cues, linking intrasegmental polarity and acquisition of segment identity.This work was supported by the `Centre National de la Recherche Scientifique' (CNRS), grants from `la Ligue Nationale Contre Le Cancer (équipe labellisée La Ligue)', `l'Association pour la Recherche contre le Cancer' (ARC), The Royal Society, The Welcome Trust, the `Minesterio de education y ciencia (BFU 2004 0 96) and ARC and EMBO long term fellowships to S. Merabet.Peer reviewe
Agency theory and performance appraisal: how bad theory damages learning and contributes to bad management practice
Performance appraisal interviews remain central to how employees are scrutinised, rewarded and sometimes penalised by managers. But they are also often castigated as ineffective, or even harmful, to both individuals and organisations. Exploring this paradox, we highlight the influence of agency theory on the (mal)practice of performance appraisal. The performative nature of human resource management increasingly reflects an economic approach within which its practices are aligned with agency theory. Such theory assumes that actors are motivated mainly or only by economic self-interest. Close surveillance is required to eliminate the risk of shirking and other deviant behaviours. It is a pessimistic mind-set about people that undermines the supportive, co-operative and developmental rhetoric with which appraisal interviews are usually accompanied. Consequently, managers often practice appraisal interviews while holding onto two contradictory mind-sets, a state of Orwellian Doublethink that damages individual learning and organisational performance. We encourage researchers to adopt a more radical critique of appraisal practices that foregrounds issues of power, control and conflicted interests between actors beyond the analyses offered to date
EVH Black Holes, AdS3 Throats and EVH/CFT Proposal
Within class of generic black holes there are extremal black holes (with
vanishing Hawking temperature T) and vanishing horizon area Ah, but with finite
Ah/T ratio,the Extremal Vanishing Horizon (EVH) black holes. We study the near
horizon limit of a four dimensional EVH black hole solution to a generic
(gauged) Einstein-Maxwell dilaton theory and show that in the near horizon
limit they develop a throat which is a pinching orbifold limit of AdS3. This is
an extension of the well known result for extremal black holes the near horizon
limit of which contains an AdS2 throat. We show that in the near EVH near
horizon limit the pinching AdS3 factor turns to a pinching BTZ black hole and
that this near horizon limit is indeed a decoupling limit. We argue that the
pinching AdS3 or BTZ orbifold is resolved if the near horizon limit is
accompanied by taking the 4d Newton constant G4 to zero such that the
Bekenstein-Hawking entropy S = Ah/(4G4) remains finite. We propose that in this
limit the near horizon EVH black hole is dual to a 2d CFT. We provide pieces of
evidence in support of the EVH/CFT correspondence and comment on its connection
to the Kerr/CFT proposal and speculations how the EVH/CFT may be used to study
generic e.g. Schwarzchild-type black holes.Comment: 31 pages, 3 figures, JHEP styl
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