An Impossibility Result for High Dimensional Supervised Learning

We study high-dimensional asymptotic performance limits of binary supervised classification problems where the class conditional densities are Gaussian with unknown means and covariances and the number of signal dimensions scales faster than the number of labeled training samples. We show that the Bayes error, namely the minimum attainable error probability with complete distributional knowledge and equally likely classes, can be arbitrarily close to zero and yet the limiting minimax error probability of every supervised learning algorithm is no better than a random coin toss. In contrast to related studies where the classification difficulty (Bayes error) is made to vanish, we hold it constant when taking high-dimensional limits. In contrast to VC-dimension based minimax lower bounds that consider the worst case error probability over all distributions that have a fixed Bayes error, our worst case is over the family of Gaussian distributions with constant Bayes error. We also show that a nontrivial asymptotic minimax error probability can only be attained for parametric subsets of zero measure (in a suitable measure space). These results expose the fundamental importance of prior knowledge and suggest that unless we impose strong structural constraints, such as sparsity, on the parametric space, supervised learning may be ineffective in high dimensional small sample settings.Comment: This paper was submitted to the IEEE Information Theory Workshop (ITW) 2013 on April 23, 201

The value of Big Data in government: The case of 'smart cities'

The emergence of Big Data has added a new aspect to conceptualizing the use of digital technologies in the delivery of public services and for realizing digital governance. This article explores, via the ‘value-chain’ approach, the evolution of digital governance research, and aligns it with current developments associated with data analytics, often referred to as ‘Big Data’. In many ways, the current discourse around Big Data reiterates and repeats established commentaries within the eGovernment research community. This body of knowledge provides an opportunity to reflect on the ‘promise’ of Big Data, both in relation to service delivery and policy formulation. This includes, issues associated with the quality and reliability of data, from mixing public and private sector data, issues associated with the ownership of raw and manip- ulated data, and ethical issues concerning surveillance and privacy. These insights and the issues raised help assess the value of Big Data in government and smart city environments

Policy Innovation, Convergence and Divergence: Considering the Policy Transfer Regulating Privacy and Data Protection in Three European Countries

This article examines policy activity surrounding the implementation of privacy regulations in three European countries, Denmark, Sweden and the UK, following the ratification of the 1995 European Union Directive on Data Protection. It highlights the convergence and divergence of policy embedded in the policy transfer process and stresses not only the complexity of policy transfer, but also the degree to which policy innovation is shaped by existing institutional settings and the processes associated with policy implementation. The article uses Dolowitz and Marsh’s ‘Policy Transfer Model’ as an analytical tool to unpack the regulatory environment surrounding the governance of privacy. This illuminates the main features of the policy process in each of the three case study countries and also the tendency to focus on policy formation at the expense of policy implementation. In the case of the 1995 European Union Directive on Data Protection the three cases examined here demonstrate that multiple regulatory regimes and policy divergence are embedded in the harmonisation (or convergence) process, and that different countries approach the regulation of privacy and data protection in quite different ways

Mach-Zehnder Interferometry in a Strongly Driven Superconducting Qubit

We demonstrate Mach-Zehnder-type interferometry in a superconducting flux qubit. The qubit is a tunable artificial atom, whose ground and excited states exhibit an avoided crossing. Strongly driving the qubit with harmonic excitation sweeps it through the avoided crossing two times per period. As the induced Landau-Zener transitions act as coherent beamsplitters, the accumulated phase between transitions, which varies with microwave amplitude, results in quantum interference fringes for n=1...20 photon transitions. The generalization of optical Mach-Zehnder interferometry, performed in qubit phase space, provides an alternative means to manipulate and characterize the qubit in the strongly-driven regime.Comment: 14 pages, 6 figure

Relações filogenéticas entre espécies de "Flectonotus" (Anura: Hemiphractidae) isoladas geograficamente reveladas por dados moleculares, de comportamento e morfológicos

Phylogenetic analyses of data derived from one mitochondrial gene and one nuclear gene show that the five species of small marsupial frogs currently recognized as Flectonotus are in fact two distinct and not closely related lineages. This conclusion is strongly supported by reproductive behavior and morphological characters. Thus, we recognize the genus Fritziana Mello-Leitão for the three species in southeastern Brazil and Flectonotus Miranda-Ribeiro for the two species in northern South America.Análises filogenéticas de dados derivados de um gene mitocondrial e um gene nuclear mostram que as cinco espécies de pererecas-marsupiais de pequeno porte atualmente incluídas no gênero Flectonotus pertencem, na verdade, a duas linhagens distintas e não intimamente aparentadas. Essa conclusão é fortemente sustentada por caracteres morfológicos e características do comportamento reprodutivo. Dessa forma, reconhecemos os gêneros Fritziana Mello-Leitão, para as três espécies do sudeste do Brasil, e Flectonotus Miranda-Ribeiro, para as duas espécies do norte da América do Sul

Nonlinear resonant behavior of the dispersive readout scheme for a superconducting flux qubit

A nonlinear resonant circuit comprising a SQUID magnetometer and a parallel capacitor is studied as a readout scheme for a persistent-current (PC) qubit. The flux state of the qubit is detected as a change in the Josephson inductance of the SQUID magnetometer, which in turn mediates a shift in the resonance frequency of the readout circuit. The nonlinearity and resulting hysteresis in the resonant behavior are characterized as a function of the power of both the input drive and the associated resonance peak response. Numerical simulations based on a phenomenological circuit model are presented which display the features of the observed nonlinearity.Comment: 9 pages, 9 figure

Resonant Readout of a Persistent Current Qubit

We have implemented a resonant circuit that uses a SQUID as a flux-sensitive Josephson inductor for qubit readout. In contrast to the conventional switching current measurement that generates undesired quasi-particles when the SQUID switches to the voltage state, our approach keeps the readout SQUID biased along the supercurrent branch during the measurement. By incorporating the SQUID inductor in a high-Q resonant circuit, we can distinguish the two flux states of a niobium persistent-current (PC) qubit by observing a shift in the resonant frequency of both the magnitude and the phase spectra. The readout circuit was also characterized in the nonlinear regime to investigate its potential use as a nonlinear amplifier.Comment: 4 pages, 2004 ASC Proceeding

Lunar hand tools

Tools useful for operations and maintenance tasks on the lunar surface were determined and designed. Primary constraints are the lunar environment, the astronaut's space suit and the strength limits of the astronaut on the moon. A multipurpose rotary motion tool and a collapsible tool carrier were designed. For the rotary tool, a brushless motor and controls were specified, a material for the housing was chosen, bearings and lubrication were recommended and a planetary reduction gear attachment was designed. The tool carrier was designed primarily for ease of access to the tools and fasteners. A material was selected and structural analysis was performed on the carrier. Recommendations were made about the limitations of human performance and about possible attachments to the torque driver

The Three-Dimensional Structure of Cassiopeia A

We used the Spitzer Space Telescope's Infrared Spectrograph to map nearly the entire extent of Cassiopeia A between 5-40 micron. Using infrared and Chandra X-ray Doppler velocity measurements, along with the locations of optical ejecta beyond the forward shock, we constructed a 3-D model of the remnant. The structure of Cas A can be characterized into a spherical component, a tilted thick disk, and multiple ejecta jets/pistons and optical fast-moving knots all populating the thick disk plane. The Bright Ring in Cas A identifies the intersection between the thick plane/pistons and a roughly spherical reverse shock. The ejecta pistons indicate a radial velocity gradient in the explosion. Some ejecta pistons are bipolar with oppositely-directed flows about the expansion center while some ejecta pistons show no such symmetry. Some ejecta pistons appear to maintain the integrity of the nuclear burning layers while others appear to have punched through the outer layers. The ejecta pistons indicate a radial velocity gradient in the explosion. In 3-D, the Fe jet in the southeast occupies a "hole" in the Si-group emission and does not represent "overturning", as previously thought. Although interaction with the circumstellar medium affects the detailed appearance of the remnant and may affect the visibility of the southeast Fe jet, the bulk of the symmetries and asymmetries in Cas A are intrinsic to the explosion.Comment: Accepted to ApJ. 54 pages, 21 figures. For high resolution figures and associated mpeg movie and 3D PDF files, see http://homepages.spa.umn.edu/~tdelaney/pape