Composing JSON-based Web APIs

International audienceThe development of Web APIs has become a discipline that companies have to master to succeed in the Web. The so-called API economy is pushing companies to provide access to their data by means of Web APIs, thus requiring web developers to study and integrate such APIs into their applications. The exchange of data with these APIs is usually performed by using JSON, a schemaless data format easy for computers to parse and use. While JSON data is easy to read, its structure is implicit, thus entailing serious problems when integrating APIs coming from di erent vendors. Web developers have therefore to understand the domain behind each API and study how they can be composed. We tackle this issue by presenting an approach able to both discover the domain of JSON-based Web APIs, and identify composition links among them. Our approach allows developers to easily visualize what is behind APIs and how they can be composed to be used in their applications

RG flow of transport quantities

The RG flow equation of various transport quantities are studied in arbitrary spacetime dimensions, in the fixed as well as fluctuating background geometry both for the Maxwellian and DBI type of actions. The regularity condition on the flow equation of the conductivity at the horizon for the DBI action reproduces naturally the leading order result of {\it Hartnoll et al.}, [{\it JHEP}, {\bf 04}, 120 (2010)]. Motivated by the result of {\it van der Marel et al.}, [{\it science}, {\bf 425}, 271 (2003], we studied, analytically, the conductivity versus frequency plane by dividing it into three distinct parts: $\omega T$ and $\omega >> T$. In order to compare, we choose 3+1 dimensional bulk spacetime for the computation of the conductivity. In the $\omega <T$ range, the conductivity does not show up the Drude like form in any spacetime dimensions. In the $\omega > T$ range and staying away from the horizon, for the DBI action with unit dynamical exponent, non-zero magnetic field and charge density, the conductivity goes as $\omega^{-2/3}$, whereas the phase of the conductivity, goes as, $ArcTan(Im\sigma^{xx}/Re\sigma^{xx})=\pi/6$ and $ArcTan(Im\sigma^{xy}/Re\sigma^{xy})=-\pi/3$. There exists a universal quantity at the horizon that is the phase angle of conductivity, which either vanishes or an integral multiple of $\pi$. Furthermore, we calculate the temperature dependence to the thermoelectric and the thermal conductivity at the horizon. The charge diffusion constant for the DBI action is studied.Comment: 1+68 pages, 12 figures and 4 appendices; V2: The charge diffusion constant is calculated for arbitrary spacetime dimensions and related references added; v3: Connection with the RG flow of 1010.4036 is made; v4: Several corrections, typos fixed and a ref. adde

Quantum Hall Effect in a Holographic Model

We consider a holographic description of a system of strongly coupled fermions in 2+1 dimensions based on a D7-brane probe in the background of D3-branes, and construct stable embeddings by turning on worldvolume fluxes. We study the system at finite temperature and charge density, and in the presence of a background magnetic field. We show that Minkowski-like embeddings that terminate above the horizon describe a family of quantum Hall states with filling fractions that are parameterized by a single discrete parameter. The quantization of the Hall conductivity is a direct consequence of the topological quantization of the fluxes. When the magnetic field is varied relative to the charge density away from these discrete filling fractions, the embeddings deform continuously into black-hole-like embeddings that enter the horizon and that describe metallic states. We also study the thermodynamics of this system and show that there is a first order phase transition at a critical temperature from the quantum Hall state to the metallic state.Comment: v2: 27 pages, 12 figures. There is a major revision in the quantitative analysis. The qualitative results and conclusions are unchanged, with one exception: we show that the quantum Hall state embeddings, which exist for discrete values of the filling fraction, deform continuously into metallic state embeddings away from these filling fraction

Striped instability of a holographic Fermi-like liquid

We consider a holographic description of a system of strongly-coupled fermions in 2+1 dimensions based on a D7-brane probe in the background of D3-branes. The black hole embedding represents a Fermi-like liquid. We study the excitations of the Fermi liquid system. Above a critical density which depends on the temperature, the system becomes unstable towards an inhomogeneous modulated phase which is similar to a charge density and spin wave state. The essence of this instability can be effectively described by a Maxwell-axion theory with a background electric field. We also consider the fate of zero sound at non-zero temperature.Comment: 16 pages, 9 figures; v2: added discussion and one figure. Typos correcte

Holographic Conformal Window - A Bottom Up Approach

We propose a five-dimensional framework for modeling the background geometry associated to ordinary Yang-Mills (YM) as well as to nonsupersymmetric gauge theories possessing an infrared fixed point with fermions in various representations of the underlying gauge group. The model is based on the improved holographic approach, on the string theory side, and on the conjectured all-orders beta function for the gauge theory one. We first analyze the YM gauge theory. We then investigate the effects of adding flavors and show that, in the holographic description of the conformal window, the geometry becomes AdS when approaching the ultraviolet and the infrared regimes. As the number of flavors increases within the conformal window we observe that the geometry becomes more and more of AdS type over the entire energy range.Comment: 20 Pages, 3 Figures. v2: references adde

Prison reform in Serbia: a case for mental health?

This article outlines the findings of the recent research in the field of prison mental health care in Serbia, in light of the recent developments in the Serbian criminal justice system and the development of community mental health care services. The article notes paucity of research in this area, which is a reflection of the unfavorable position of offender care on the Serbian prison agenda. The authors emphasize the need for dedicated mental health legislation as well as the development of mental health services in prisons, which would mirror the developments in the community. Other suggestions for the development of prison mental health care are discussed in the text

Fluctuations of a holographic quantum Hall fluid

We analyze the neutral spectrum of the holographic quantum Hall fluid described by the D2-D8' model. As expected for a quantum Hall state, we find the system to be stable and gapped and that, at least over much of the parameter space, the lowest excitation mode is a magneto-roton. In addition, we find magneto-rotons in higher modes as well. We show that these magneto-rotons are direct consequences of level crossings between vector and scalar modes.Comment: 20 pages, 8 figures; v.2 figures improved, 2 figures added, and text clarified particularly in Sec. 5, to appear in JHE

Thermodynamics of deformed AdS5_5 model with a positive/negative quadratic correction in graviton-dilaton system

By solving the Einstein equations of the graviton coupling with a real scalar dilaton field, we establish a general framework to self-consistently solve the geometric background with black-hole for any given phenomenological holographic models. In this framwork, we solve the black-hole background, the corresponding dilaon field and the dilaton potential for the deformed AdS$_5$ model with a positive/negative quadratic correction. We systematically investigate the thermodynamical properties of the deformed AdS$_5$ model with a positive and negative quadratic correction, respectively, and compare with lattice QCD on the results of the equation of state, the heavy quark potential, the Polyakov loop and the spatial Wilson loop. We find that the bulk thermodynamical properties are not sensitive to the sign of the quadratic correction, and the results of both deformed holographic QCD models agree well with lattice QCD result for pure SU(3) gauge theory. However, the results from loop operators favor a positive quadratic correction, which agree well with lattice QCD result. Especially, the result from the Polyakov loop excludes the model with a negative quadratic correction in the warp factor of ${\rm AdS}_5$.Comment: 26 figures,36 pages,V.3: an appendix,more equations and references added,figures corrected,published versio

Improved Holographic QCD

We provide a review to holographic models based on Einstein-dilaton gravity with a potential in 5 dimensions. Such theories, for a judicious choice of potential are very close to the physics of large-N YM theory both at zero and finite temperature. The zero temperature glueball spectra as well as their finite temperature thermodynamic functions compare well with lattice data. The model can be used to calculate transport coefficients, like bulk viscosity, the drag force and jet quenching parameters, relevant for the physics of the Quark-Gluon Plasma.Comment: LatEX, 65 pages, 28 figures, 9 Tables. Based on lectures given at several Schools. To appear in the proceedinds of the 5th Aegean School (Milos, Greece

On thermodynamics of N=6 superconformal Chern-Simons theory

We study thermodynamics of N=6 superconformal Chern-Simons theory by computing quantum corrections to the free energy. We find that in weakly coupled ABJM theory on R(2) x S(1), the leading correction is non-analytic in the 't Hooft coupling lambda, and is approximately of order lambda^2 log(lambda)^3. The free energy is expressed in terms of the scalar thermal mass m, which is generated by screening effects. We show that this mass vanishes to 1-loop order. We then go on to 2-loop order where we find a finite and positive mass squared m^2. We discuss differences in the calculation between Coulomb and Lorentz gauge. Our results indicate that the free energy is a monotonic function in lambda which interpolates smoothly to the N^(3/2) behaviour at strong coupling.Comment: 29 pages. v2: references added. v3: minor changes, references added, published versio