Enhancement of photoacoustic detection of inhomogeneities in polymers

We report a series of experiments on laser pulsed photoacoustic excitationin turbid polymer samples addressed to evaluate the sound speed in the samples and the presence of inhomogeneities in the bulk. We describe a system which allows the direct measurement of the speed of the detected waves by engraving the surface of the piece under study with a fiduciary pattern of black lines. We also describe how this pattern helps to enhance the sensitivity for the detection of an inhomogeneity in the bulk. These two facts are useful for studies in soft matter systems including, perhaps, biological samples. We have performed an experimental analysis on Grilon(R) samples in different situations and we show the limitations of the method.Comment: 8 pages, 7 figure

In-situ bandaged Josephson junctions for superconducting quantum processors

Shadow evaporation is commonly used to micro-fabricate the key element of superconducting qubits—the Josephson junction. However, in conventional two-angle deposition circuit topology, unwanted stray Josephson junctions are created which contribute to dielectric loss. So far, this could be avoided by shorting the stray junctions with a so-called bandage layer deposited in an additional lithography step, which may further contaminate the chip surface. Here, we present an improved shadow evaporation technique allowing one to fabricate sub-micrometer-sized Josephson junctions together with bandage layers in a single lithography step. We also show that junction aging is significantly reduced when junction electrodes are passivated in an oxygen atmosphere directly after deposition

SERS from pyridine adsorbed on electrodispersed platinum electrodes

SERS of pyridine adsorbed on electrodispersed platinum electrodes is reported. Electrodispersed platinum surfaces are obtained by electroreducing hydrous platinum oxide layers. The intensity of the Raman scattering for adsorbed pyridine is enhanced by at least one order of magnitude, after normalizing with respect to the area increase. The estimated Raman enhancement factor is lower than that reported for roughened silver electrodes but it is still sufficiently large to allow Raman scattering from adsorbates on platinum to be detectable. Surface changes (ageing) of the metal surface can be also followed by SERS.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Characterization of reference standards for dirt by Laser Ablation Induced Photoacoustics (LAIP)

Measurements of surface cleanliness and dirt characterization are important problems in a wide range of processes in industry and production. Standard methods are in most cases cumbersome laboratory procedures that must be performed out of the production lines. Instruments and methods for cleanliness determination and dirt characterization require reference standards for calibration. For that purpose we built a possible dirt reference standard (DRS) made by films of graphite grease subjected to heat treatment for mechanical stabilization. The DRS characterization was performed by Laser Ablation Induced Photoacoustics (LAIP). The measurement of the thickness of the films was made by lowcoherence interferometry.Centro de Investigaciones Óptica

Implementing EM and Viterbi algorithms for Hidden Markov Model in linear memory

<p>Abstract</p> <p>Background</p> <p>The Baum-Welch learning procedure for Hidden Markov Models (HMMs) provides a powerful tool for tailoring HMM topologies to data for use in knowledge discovery and clustering. A linear memory procedure recently proposed by <it>Miklós, I. and Meyer, I.M. </it>describes a memory sparse version of the Baum-Welch algorithm with modifications to the original probabilistic table topologies to make memory use independent of sequence length (and linearly dependent on state number). The original description of the technique has some errors that we amend. We then compare the corrected implementation on a variety of data sets with conventional and checkpointing implementations.</p> <p>Results</p> <p>We provide a correct recurrence relation for the emission parameter estimate and extend it to parameter estimates of the Normal distribution. To accelerate estimation of the prior state probabilities, and decrease memory use, we reverse the originally proposed forward sweep. We describe different scaling strategies necessary in all real implementations of the algorithm to prevent underflow. In this paper we also describe our approach to a linear memory implementation of the Viterbi decoding algorithm (with linearity in the sequence length, while memory use is approximately independent of state number). We demonstrate the use of the linear memory implementation on an extended Duration Hidden Markov Model (DHMM) and on an HMM with a spike detection topology. Comparing the various implementations of the Baum-Welch procedure we find that the checkpointing algorithm produces the best overall tradeoff between memory use and speed. In cases where sequence length is very large (for Baum-Welch), or state number is very large (for Viterbi), the linear memory methods outlined may offer some utility.</p> <p>Conclusion</p> <p>Our performance-optimized Java implementations of Baum-Welch algorithm are available at <url>http://logos.cs.uno.edu/~achurban</url>. The described method and implementations will aid sequence alignment, gene structure prediction, HMM profile training, nanopore ionic flow blockades analysis and many other domains that require efficient HMM training with EM.</p

Enhancement of photoacoustic detection of inhomogeneities in polymers

We report a series of experiments on laser pulsed photoacoustic excitation in turbid polymer samples addressed to evaluate the sound speed in the samples and the presence of inhomogeneities in the bulk. We describe a system which allows the direct measurement of the speed of the detected waves by engraving the surface of the piece under study with a fiduciary pattern of black lines. We also describe how this pattern helps to enhance the sensitivity for the detection of an inhomogeneity in the bulk. These two facts are useful for studies in soft matter systems including, perhaps, biological samples. We have performed an experimental analysis on Grilon®samples in different situations and we show the limitations of the method.Facultad de Ingenierí

Wettability, photoactivity, and antimicrobial activity of glazed ceramic tiles coated with titania films containing tungsten

Self-cleaning coatings are advanced materials for the removal of pollutants and microorganisms by combining wettability, photocatalytic degradation, and antimicrobial activity. In this work, we propose a rational design of self-cleaning films based on TiO2 synthesized by sol-gel on commercial glazed ceramic tiles for building's indoor applications. The synthesis strategy is based on hydrolysis and condensation of Ti-isopropoxide in the presence of W(VI) precursors to tune defects and crystallinity of the resulting W-TiO2 thin film. From the microstructure and surface composition analysis for different tungsten contents and annealing temperatures, we conclude that the film is composed by sintered TiO2 particles with adsorbed polytungstates (WOx) that inhibit anatase/rutile transformation. Polytungstates on TiO2 also induce surface defects that enhance water contact angle and inactivation of Escherichia coli under visible light. The presence of W(VI) has a negligible effect toward crystal violet degradation either under visible or under UV light. These results provide evidence on the existence of at least two different types of defects: (i) intrinsic defect from a sol-gel route and (ii) induced defect by tungsten species on the surface. Understanding the correlation between composition, structure, and self-cleaning properties provides a base for an efficient design of low-cost self-cleaning ceramic tiles that can be fully manufactured in an industrial plant.3121762917636Agências de fomento estrangeiras apoiaram essa pesquisa, mais informações acesse artig

SERS from pyridine adsorbed on electrodispersed platinum electrodes

SERS of pyridine adsorbed on electrodispersed platinum electrodes is reported. Electrodispersed platinum surfaces are obtained by electroreducing hydrous platinum oxide layers. The intensity of the Raman scattering for adsorbed pyridine is enhanced by at least one order of magnitude, after normalizing with respect to the area increase. The estimated Raman enhancement factor is lower than that reported for roughened silver electrodes but it is still sufficiently large to allow Raman scattering from adsorbates on platinum to be detectable. Surface changes (ageing) of the metal surface can be also followed by SERS.Instituto de Investigaciones Fisicoquímicas Teóricas y Aplicada

Photoacoustic characterization of transient defects in potassium dihydrogen phosphate crystals

Transient defects in potassium dihydrogen phosphate ͑KDP͒ were characterized by using the acoustic signals generated in the crystal when it is impinged with pulsed laser radiation. These defects are produced by simultaneous absorption of two ϭ266 nm photons and they show linear absorption in the visible and UV spectral region. The decay kinetics of the defects has been studied by a new method based on the analysis of the acoustic signal generated by visible pulses. The acoustic measurement of the decay time shows a nonexponential decay and it is free from thermal lensing or beam deformation by other causes, effects that can alter the pure optical measurements. We propose that the origin of the photoacoustic signal is the heat released by the deexcitation of the energy levels of the defects when they are excited by visible pulses. This mechanism, optical absorption and nonradiative relaxation of defects, could be the reason for some depletion in the yield of several devices based on KDP. This phenomena must be carefully taken in account, when KDP crystals are used in combination with Nd:YAG ͑YAG, yttrium aluminum garnet͒ lasers for second-harmonic generation from ϭ532 nm to ϭ266 nm

Review of Person Re-identification Techniques

Person re-identification across different surveillance cameras with disjoint fields of view has become one of the most interesting and challenging subjects in the area of intelligent video surveillance. Although several methods have been developed and proposed, certain limitations and unresolved issues remain. In all of the existing re-identification approaches, feature vectors are extracted from segmented still images or video frames. Different similarity or dissimilarity measures have been applied to these vectors. Some methods have used simple constant metrics, whereas others have utilised models to obtain optimised metrics. Some have created models based on local colour or texture information, and others have built models based on the gait of people. In general, the main objective of all these approaches is to achieve a higher-accuracy rate and lowercomputational costs. This study summarises several developments in recent literature and discusses the various available methods used in person re-identification. Specifically, their advantages and disadvantages are mentioned and compared.Comment: Published 201