Inducing Features of Random Fields

We present a technique for constructing random fields from a set of training samples. The learning paradigm builds increasingly complex fields by allowing potential functions, or features, that are supported by increasingly large subgraphs. Each feature has a weight that is trained by minimizing the Kullback-Leibler divergence between the model and the empirical distribution of the training data. A greedy algorithm determines how features are incrementally added to the field and an iterative scaling algorithm is used to estimate the optimal values of the weights. The statistical modeling techniques introduced in this paper differ from those common to much of the natural language processing literature since there is no probabilistic finite state or push-down automaton on which the model is built. Our approach also differs from the techniques common to the computer vision literature in that the underlying random fields are non-Markovian and have a large number of parameters that must be estimated. Relations to other learning approaches including decision trees and Boltzmann machines are given. As a demonstration of the method, we describe its application to the problem of automatic word classification in natural language processing. Key words: random field, Kullback-Leibler divergence, iterative scaling, divergence geometry, maximum entropy, EM algorithm, statistical learning, clustering, word morphology, natural language processingComment: 34 pages, compressed postscrip

Electrical Conductivity of o-, m-, and p-Terphenyls

Many investigations have been carried out on the electrical properties of p-terphenyl1-9, and, as far as we know, only one on m-terphenyl10. In the present work, the d. c. electrical conductivities of the three isomeric terphenyls are compared to establish the influence of the molecular structure on the electrical properties and to explain the mechanism of the energy transport in organic molecules

Long-Range Order in Electronic Transport through Disordered Metal Films

Ultracold atom magnetic field microscopy enables the probing of current flow patterns in planar structures with unprecedented sensitivity. In polycrystalline metal (gold) films we observe long-range correlations forming organized patterns oriented at +/- 45 deg relative to the mean current flow, even at room temperature and at length scales orders of magnitude larger than the diffusion length or the grain size. The preference to form patterns at these angles is a direct consequence of universal scattering properties at defects. The observed amplitude of the current direction fluctuations scales inversely to that expected from the relative thickness variations, the grain size and the defect concentration, all determined independently by standard methods. This indicates that ultracold atom magnetometry enables new insight into the interplay between disorder and transport

GNSS Positioning using Android Smartphone

The possibility to manage pseudorange and carrier-phase measurements from the Global Navigation Satellite System (GNSS) chipset installed on smartphones and tablets with an Android operating system has changed the concept of precise positioning with portable devices. The goal of this work is to compare the positioning performances obtained with a smartphone and an external mass-market GNSS receiver both in real-time and post-processing. The attention is also focused not only on the accuracy and precision, but also on the possibility to determine the phase ambiguity values as integer (fixed positioning) that it is still a challenging aspect for mass-market devices: if the mass-market receiver provides good results under all points of view both for real-time and post-processing solutions (with precisions and accuracies of about 5 cm and 1 cm, respectively), the smartphone has a bad behaviour (order of magnitude of some meters) due to the noise of its measurements

Anticancer activity of cationic porphyrins in melanoma tumour-bearing mice and mechanistic in vitro studies

Background Porphyrin TMPyP4 (P4) and its C14H28-alkyl derivative (C14) are G-quadruplex binders and singlet oxygen (1O2) generators. In contrast, TMPyP2 (P2) produces 1O2 but it is not a G-quadruplex binder. As their photosensitizing activity is currently undefined, we report in this study their efficacy against a melanoma skin tumour and describe an in vitro mechanistic study which gives insights into their anticancer activity. Methods Uptake and antiproliferative activity of photoactivated P2, P4 and C14 have been investigated in murine melanoma B78-H1 cells by FACS, clonogenic and migration assays. Apoptosis was investigated by PARP-1 cleavage and annexin-propidium iodide assays. Biodistribution and in vivo anticancer activity were tested in melanoma tumour-bearing mice. Porphyrin binding and photocleavage of G-rich mRNA regions were investigated by electrophoresis and RT-PCR. Porphyrin effect on ERK pathway was explored by Western blots. Results Thanks to its higher lipophylicity C14 was taken up by murine melanoma B78-H1 cells up to 30-fold more efficiently than P4. When photoactivated (7.2 J/cm2) in B78-H1 melanoma cells, P4 and C14, but not control P2, caused a strong inhibition of metabolic activity, clonogenic growth and cell migration. Biodistribution studies on melanoma tumour-bearing mice showed that P4 and C14 localize in the tumour. Upon irradiation (660 nm, 193 J/cm2), P4 and C14 retarded tumour growth and increased the median survival time of the treated mice by ~50% (P <0.01 by ANOVA), whereas porphyrin P2 did not. The light-dependent mechanism mediated by P4 and C14 is likely due to the binding to and photocleavage of G-rich quadruplex-forming sequences within the 5\u2032-untranslated regions of the mitogenic ras genes. This causes a decrease of RAS protein and inhibition of downstream ERK pathway, which stimulates proliferation. Annexin V/propidium iodide and PARP-1 cleavage assays showed that the porphyrins arrested tumour growth by apoptosis and necrosis. C14 also showed an intrinsic light-independent anticancer activity, as recently reported for G4-RNA binders. Conclusions Porphyrins P4 and C14 impair the clonogenic growth and migration of B78-H1 melanoma cells and inhibit melanoma tumour growth in vivo. Evidence is provided that C14 acts through light-dependent (mRNA photocleavage) and light-independent (translation inhibition) mechanisms. Keywords: Melanoma B78-H1 cells; Cationic porphyrins; Biodistribution; C57/BL6 mice; Ras genes; G4-RNA; ERK pathwa

A Model Analysis of Mechanisms for Radial Microtubular Patterns at Root Hair Initiation Sites

Plant cells have two main modes of growth generating anisotropic structures. Diffuse growth where whole cell walls extend in specific directions, guided by anisotropically positioned cellulose fibers, and tip growth, with inhomogeneous addition of new cell wall material at the tip of the structure. Cells are known to regulate these processes via molecular signals and the cytoskeleton. Mechanical stress has been proposed to provide an input to the positioning of the cellulose fibers via cortical microtubules in diffuse growth. In particular, a stress feedback model predicts a circumferential pattern of fibers surrounding apical tissues and growing primordia, guided by the anisotropic curvature in such tissues. In contrast, during the initiation of tip growing root hairs, a star-like radial pattern has recently been observed. Here, we use detailed finite element models to analyze how a change in mechanical properties at the root hair initiation site can lead to star-like stress patterns in order to understand whether a stress-based feedback model can also explain the microtubule patterns seen during root hair initiation. We show that two independent mechanisms, individually or combined, can be sufficient to generate radial patterns. In the first, new material is added locally at the position of the root hair. In the second, increased tension in the initiation area provides a mechanism. Finally, we describe how a molecular model of Rho-of-plant (ROP) GTPases activation driven by auxin can position a patch of activated ROP protein basally along a 2D root epidermal cell plasma membrane, paving the way for models where mechanical and molecular mechanisms cooperate in the initial placement and outgrowth of root hairs.This work was funded by the Knut and Alice Wallenberg Foundation via grant ShapeSystems (KAW 2012.0050) to MG and HJ, the Swedish Research Council (VR2013-4632) to HJ, and the Gatsby Charitable Foundation (GAT3395/PR4) to HJ

Designing potentials by sculpturing wires

Magnetic trapping potentials for atoms on atom chips are determined by the current flow in the chip wires. By modifying the shape of the conductor we can realize specialized current flow patterns and therefore micro-design the trapping potentials. We have demonstrated this by nano-machining an atom chip using the focused ion beam technique. We built a trap, a barrier and using a BEC as a probe we showed that by polishing the conductor edge the potential roughness on the selected wire can be reduced. Furthermore we give different other designs and discuss the creation of a 1D magnetic lattice on an atom chip.Comment: 6 pages, 8 figure

Endoscopy-assisted tracheal reconstruction of post-traumatic obstruction in a cat: A case report

A domestic shorthair cat was referred with a history of dyspnoea and lethargy that had arisen gradually within the last few days. The cat had been hit by an automobile 10 days earlier. A thoracic radiograph suggested stenosis of the intrathoracic trachea, proximal to the tracheal bifurcation. Endoscopic examination confirmed a narrowing of the tracheal lumen due to the presence of a fibrotic ring, with remaining patent lumen of about 2 mm. A surgical treatment with a right lateral thoracotomy approach and resection of the narrowed portion of the trachea (a length of about 1 cm) was performed under endoscopic vision. The procedure was unsuccessful because of the size of the tissue removed and the laxity of the remaining tracheal tissue that caused dehiscence of sutures between the tracheal stump and tracheal bifurcation. After consultation with the cat\u2019s owners, an intraoperative euthanasia was performed