A Neural Network model with Bidirectional Whitening

We present here a new model and algorithm which performs an efficient Natural gradient descent for Multilayer Perceptrons. Natural gradient descent was originally proposed from a point of view of information geometry, and it performs the steepest descent updates on manifolds in a Riemannian space. In particular, we extend an approach taken by the "Whitened neural networks" model. We make the whitening process not only in feed-forward direction as in the original model, but also in the back-propagation phase. Its efficacy is shown by an application of this "Bidirectional whitened neural networks" model to a handwritten character recognition data (MNIST data).Comment: 16page

Does Scientific Progress Consist in Increasing Knowledge or Understanding?

Bird argues that scientific progress consists in increasing knowledge. Dellsén objects that increasing knowledge is neither necessary nor sufficient for scientific progress, and argues that scientific progress rather consists in increasing understanding. Dellsén also contends that unlike Bird’s view, his view can account for the scientific practices of using idealizations and of choosing simple theories over complex ones. I argue that Dellsén’s criticisms against Bird’s view fail, and that increasing understanding cannot account for scientific progress, if acceptance, as opposed to belief, is required for scientific understanding

Fast and dense magneto-optical traps for Strontium

We improve the efficiency of sawtooth-wave-adiabatic-passage (SWAP) cooling for strontium atoms in three dimensions and combine it with standard narrow-line laser cooling. With this technique, we create strontium magneto-optical traps with $6\times 10^7$ bosonic $^{88}$Sr ($1\times 10^7$ fermionic $^{87}$Sr) atoms at phase-space densities of $2\times 10^{-3}$ ($1.4\times 10^{-4}$). Our method is simple to implement and is faster and more robust than traditional cooling methods.Comment: 9 pages, 6 figure

Comments on "Entropy of 2D Black Holes from Counting Microstates"

In a recent letter, Cadoni and Mignemi proposed a formulation for the statistical computation of the 2D black holes entropy. We present a criticism about their formulation.Comment: 5 pages, Latex, no figure

Local spectroscopy of a proximity superconductor at very low temperature

We performed the local spectroscopy of a Normal-metal--Superconductor (N-S) junction with the help of a very low temperature (60 mK) Scanning Tunneling Microscope (STM). The spatial dependence of the local density of states was probed locally in the vicinity of the N-S interface. We observed spectra with a fully-developed gap in the regions where a thin normal metal layer caps the superconductor dot. Close to the S metal edge, a clear pseudo-gap shows up, which is characteristic of the superconducting proximity effect in the case of a long normal metal. The experimental results are compared to the predictions of the quasiclassical theory.Comment: 7 pages, 3 figure

Shuttling of Spin Polarized Electrons in Molecular Transistors

Shuttling of electrons in single-molecule transistors with magnetic leads in the presence of an external magnetic field is considered theoretically. For a current of partially spin-polarized electrons a shuttle instability is predicted to occur for a finite interval of external magnetic field strengths. The lower critical magnetic field is determined by the degree of spin polarization and it vanishes as the spin polarization approaches 100%. The feasibility of detecting magnetic shuttling in a $C_{60}$-based molecular transistor with magnetic (Ni) electrodes is discussed [A.~N.~Pasupathy et al., Science 306, 86 (2004)].Comment: Submitted to a special issue of "Synthetic Metals" to appear in March 201

Aspects of Horava-Lifshitz cosmology

We review some general aspects of Horava-Lifshitz cosmology. Formulating it in its basic version, we extract the cosmological equations and we use observational data in order to constrain the parameters of the theory. Through a phase-space analysis we extract the late-time stable solutions, and we show that eternal expansion, and bouncing and cyclic behavior can arise naturally. Concerning the effective dark energy sector we show that it can describe the phantom phase without the use of a phantom field. However, performing a detailed perturbation analysis, we see that Horava-Lifshitz gravity in its basic version suffers from instabilities. Therefore, suitable generalizations are required in order for this novel theory to be a candidate for the description of nature.Comment: 10 pages, 4 figures, invited talk given at the 2nd International Workshop on Dark Matter, Dark Energy and Matter-Antimatter Assymetry, National Tsing Hua University, Hsinchu, Taiwan, November 5-6, 201

The quantization of the chiral Schwinger model based on the BFT-BFV formalism II

We apply an improved version of Batalin-Fradkin-Tyutin (BFT) Hamiltonian method to the a=1 chiral Schwinger Model, which is much more nontrivial than the a>1.$one. Furthermore, through the path integral quantization, we newly resolve the problem of the non-trivial$\delta$function as well as that of the unwanted Fourier parameter$\xi$ in the measure. As a result, we explicitly obtain the fully gauge invariant partition function, which includes a new type of Wess-Zumino (WZ) term irrelevant to the gauge symmetry as well as usual WZ action.Comment: 17 pages, To be published in J. Phys.

Mechanically Induced Thermal Breakdown in Magnetic Shuttle Structures

A theory of a thermally induced single-electron "shuttling" instability in a magnetic nanomechanical device subject to an external magnetic field is presented in the Coulomb blockade regime of electron transport. The model magnetic shuttle device considered comprises a movable metallic grain suspended between two magnetic leads, which are kept at different temperatures and assumed to be fully spin polarized with antiparallel magnetizations. For a given temperature difference shuttling is found to occur for a region of external magnetic fields between a lower and an upper critical field strength, which separate the shuttling regime from normal small-amplitude "vibronic" regimes. We find that (i) the upper critical magnetic field saturates to a constant value in the high temperature limit and that the shuttle instability domain expands with a decrease of the temperature, (ii) the lower critical magnetic field depends not only on the temperature independent phenomenological friction coefficient used in the model but also on intrinsic friction (which vanishes in the high temperature limit) caused by magnetic exchange forces and electron tunneling between the quantum dot and the leads. The feasibility of using thermally driven magnetic shuttle systems to harvest thermal breakdown phenomena is discussed.Comment: 9 pages, 2 figure