Improved signal-to-noise ratio in spectral-domain compared with time-domain optical coherence tomography

A signal-to-noise ratio (SNR) analysis is presented for optical coherence tomography (OCT) signals in which time-domain performance is compared with that of the spectral domain. A significant SNR gain of several hundredfold is found for acquisition in the spectral domain. The SNR benefit is demonstrated experimentally in a hybrid time-domain-spectral-domain OCT system.     

De Rham and Infinitesimal Cohomology in Kapranov's Model for Non commutative Algebraic Geometry

The title refers to the nilcommutative or NC-schemes introduced by M. Kapranov in Noncommutative Geometry Based on Commutator Expansions, J. Reine Angew. Math 505 (1998) 73–118. The latter are noncommutative nilpotent thickenings of commutative schemes. We also consider the parallel theory of nil-Poisson or NP-schemes, which are nilpotent thickenings of commutative schemes in the category of Poisson schemes. We study several variants of de Rham cohomology for NC- and NP-schemes. The variants include nilcommutative and nil-Poisson versions of the de Rham complex as well as of the cohomology of the infinitesimal site introduced by Grothendieck in Crystals and the de Rham Cohomology of Schemes, Dix exposés sur la cohomologie des schémas, Masson, Paris (1968), pp. 306–358. It turns out that each of these noncommutative variants admits a kind of Hodge decomposition which allows one to express the cohomology groups of a noncommutative scheme Y as a sum of copies of the usual (de Rham, infinitesimal) cohomology groups of the underlying commutative scheme X (Theorems 6.1, 6.4, 6.7). As a byproduct we obtain new proofs for classical results of Grothendieck (Corollary 6.2) and of Feigin and Tsygan (Corollary 6.8) on the relation between de Rham and infinitesimal cohomology and between the latter and periodic cyclic homology.     

Low Dimension Dynamics in the EPRB Experiment with Random Variable Analyzers

The Einstein–Podolsky–Rosen–Bohm (EPRB) experiment performed with random variable and spatially separated analyzers is a milestone test in the controversy between Objective Local Theories (OLT) and Quantum Mechanics (QM). Only a few OLT are still possible. Some of the surviving OLT (specifically, the so called non-ergodic theories) would be undetectable in the averaged statistical values, but they may leave their trace in the time dynamics. For, while QM predicts random processes, the OLT of this kind predict the existence of regularities that may be revealed as a low dimensional object in the phase space. We perform a numerical analysis of the time-resolved data recorded in that experiment to unveil any hypothetical low dimensional dynamics that may be present. We find no consistent indication of such dynamics except for one data file, the longest of all in the real time. The possible causes of these dynamics are discussed.      

Atomistic modeling of segregation and bulk ordering in Ag-Au alloys

The bulk and surface properties of Ag-Au alloys, for the whole range of concentration and as a function of temperature, is studied by means of a simple modeling scheme using the Bozzolo-Ferrante-Smith method for alloys. Evidence for short-range order is found and explained, as well as its relationship with the experimentally observed segregation behavior.     

Determination of β-glucosidase activity in soils with a bioanalytical sensor modified with multiwalled carbon nanotubes

Soil microorganisms and enzymes are the primary mediators of soil biological processes, including organic matter degradation, mineralization, and nutrient recycling. They play an important role in maintaining soil ecosystem quality and functional diversity. Moreover, enzyme activities can provide an indication of quantitative changes in soil organic matter. β-Glucosidase (β-Glu) activity has been found to be sensitive to soil management and has been proposed as a soil quality indicator because it provides an early indication of changes in organic matter status and its turnover. The aims of the present study were to test and use a simple and convenient procedure for the assay of β-Glu activity in agricultural soil. The method described here is based on the enzymatic degradation of cellobiose by β-Glu present in the soil sample and the subsequent determination of glucose produced by the enzymatic reaction using screen-printed carbon electrodes modified with multiwalled carbon nanotubes (SPCE-CNT) equipped with coimmobilized glucose oxidase and horseradish peroxidase enzymes. The potential applied to the SPCE-CNT detection was −0.15 V versus a Ag/AgCl pseudo-reference electrode. A linear calibration curve was obtained in the range 2.7–11.3 mM with a correlation coefficient. In the present study, an easy and effective SPCE-CNT-modified electrode allowed an improved amperometric response to be achieved and this is attributed to the increased surface area upon electrode modification.     

A Theoretical and Computational Framework for Isometry Invariant Recognition of Point Cloud Data

Point clouds are one of the most primitive and fundamental manifold representations. Popular sources of point clouds are three-dimensional shape acquisition devices such as laser range scanners. Another important field where point clouds are found is in the representation of high-dimensional manifolds by samples. With the increasing popularity and very broad applications of this source of data, it is natural and important to work directly with this representation, without having to go through the intermediate and sometimes impossible and distorting steps of surface reconstruction. A geometric framework for comparing manifolds given by point clouds is presented in this paper. The underlying theory is based on Gromov-Hausdorff distances, leading to isometry invariant and completely geometric comparisons. This theory is embedded in a probabilistic setting as derived from random sampling of manifolds, and then combined with results on matrices of pairwise geodesic distances to lead to a computational implementation of the framework. The theoretical and computational results presented here are complemented with experiments for real three-dimensional shapes.     

Synthesis of novel indenoquinolines and indenopyridazines via photoisomerization of benzotropolone derivatives

We describe the photoisomerization of hetero Diels-Alder adducts of tetramethylpurpurogallin bearing β,γ-unsaturated ketone chromophores and endocyclic -N-O- or -N-N- groups. Based on spectroscopic and crystallographic data, our results indicate that the outcome of the reaction for the two types of substrates can be correlated with the difference in the stabilities of the radical intermediates generated in each case. For oxazines, the photoisomerization involves both the β,γ-unsaturated ketone and -N-O- moieties, and proceeds through the formation of allyl, benzoyl, phenyl, and α-carbonyl radical intermediates. While the same allylic and benzoyl radicals are formed in adducts with an -N-N- group, the hydrazine does not participate in the reaction and the product is a simple rearrangement of the initial intermediate.     

Selecting an Effective Entropy Estimator for Short Sequences of Bits and Bytes with Maximum Entropy

Entropy makes it possible to measure the uncertainty about an information source from the distribution of its output symbols. It is known that the maximum Shannon’s entropy of a discrete source of information is reached when its symbols follow a Uniform distribution. In cryptography, these sources have great applications since they allow for the highest security standards to be reached. In this work, the most effective estimator is selected to estimate entropy in short samples of bytes and bits with maximum entropy. For this, 18 estimators were compared. Results concerning the comparisons published in the literature between these estimators are discussed. The most suitable estimator is determined experimentally, based on its bias, the mean square error short samples of bytes and bits.     

Scattering in Terms of Bohmian Conditional Wave Functions for Scenarios with Non-Commuting Energy and Momentum Operators

Without access to the full quantum state, modeling quantum transport in mesoscopic systems requires dealing with a limited number of degrees of freedom. In this work, we analyze the possibility of modeling the perturbation induced by non-simulated degrees of freedom on the simulated ones as a transition between single-particle pure states. First, we show that Bohmian conditional wave functions (BCWFs) allow for a rigorous discussion of the dynamics of electrons inside open quantum systems in terms of single-particle time-dependent pure states, either under Markovian or non-Markovian conditions. Second, we discuss the practical application of the method for modeling light–matter interaction phenomena in a resonant tunneling device, where a single photon interacts with a single electron. Third, we emphasize the importance of interpreting such a scattering mechanism as a transition between initial and final single-particle BCWF with well-defined central energies (rather than with well-defined central momenta).