Carlos Alexandre R. Fernandes

Evaluation of Regional Bond Strength of Resin Cement to Endodontic Surfaces

The purpose of this study was to test the feasibility of adapting a new microtensile testing technique to measure resin cement bond strengths to the cervical, middle, and apical thirds of root canals. Post spaces were created in extracted human teeth, and the roots were ground flat on one side to expose the canal and permit ideal placement of one of two resin cements (Panavia 21 or C&B Metabond). After 48 h of storage, serial 1-mm-thick cross-sections were cut to create 6-10 specimens per root. The first three specimens were from the cervical third, the next three were from the middle third, and the last three were from the apical third of the root. Each 1 x 1 x 8 mm specimen was pulled to failure in a miniature testing machine. The results indicated that both resin cements produced high bond strengths (12-23 MPa), and that bond strengths to the apical third were significantly higher (p < 0.05) than to the cervical or middle third with either cement. This new method shows promise for evaluating resin bond strengths within root canals.

Decision directed adaptive blind equalization based on the constant modulus algorithm

In this paper, new decision directed algorithms for blind equalization of communication channels are presented. These algorithms use informations about the last decided symbol to improve the performance of the constant modulus algorithm (CMA). The main proposed technique, the so called decision directed modulus algorithm (DDMA), extends the CMA to non-CM modulations. Assuming correct decisions, it is proved that the decision directed modulus (DDM) cost function has no local minima in the combined channel-equalizer system impulse response. Additionally, a relationship between the Wiener and DDM minima is established. The other proposed algorithms can be viewed as modifications of the DDMA. They are divided into two families: stochastic gradient algorithms and recursive least squares (RLS) algorithms. Simulation results allow to compare the performance of the proposed algorithms and to conclude that they outperform well-known methods.

Efficient immobilization of fructose-6-phosphate aldolase in layered double hydroxide: improved stereoselective synthesis of sugar analogues

Fructose-6-phosphate aldolase immobilized on layered double hydroxide (FSA@LDH) has been characterized and evaluated as a biocatalyst in aldol reactions. The versatile FSA@LDH showed a comparable activity to the free FSA and can be reused several times without a notable loss of activity.

Genome Mining for Innovative Biocatalysts: New Dihydroxyacetone Aldolases for the Chemist’s Toolbox

Stereoselective carboligating enzymes were discovered by a genome mining approach to extend the biocatalysis toolbox. Seven hundred enzymes were selected by sequence comparison from diverse prokaryotic species as representatives of the aldolase (FSA) family diversity. The aldol reaction tested involved dihydroxyacetone (DHA) and glyceraldehyde‐3‐phosphate. The hexose‐6‐phosphate formation was monitored by mass spectrometry. Eighteen enzymes annotated either as transaldolases or aldolases were found to exhibit a DHA aldolase activity. Remarkably, six of them proven as aldolases, and not transaldolases, shared very limited similarities with those currently described. Multiple sequence alignment performed on all enzymes revealed a Tyr in the new DHA aldolases as found in FSAcoli instead of a Phe usually found in transaldolases. Four of these DHA aldolases were biochemically characterised in comparison with FSAcoli. In particular, an aldolase from Listeria monocytogenes exhibited interesting catalytic properties.

PARAFAC-based channel estimation and data recovery in nonlinear MIMO spread spectrum communication systems

In this paper, a new tensorial modeling is first proposed for nonlinear multiple-input multiple-output (MIMO) direct sequence spread spectrum communication systems. The channel is modeled as an instantaneous MIMO Volterra system. Then, a direct data approach for joint blind channel estimation and data recovery is developed using the parallel factor (PARAFAC) decomposition of a third-order tensor composed of received signals, exploiting space, time and code diversities. A blind channel estimation method based on the PARAFAC decomposition of a fifth-order tensor composed of covariances of the received signals is also proposed, considering phase shift keying (PSK) modulated transmitted signals. The proposed estimation algorithms are evaluated by simulating a nonlinear uplink MIMO radio over fiber (ROF) communication system.

Blind identification of multiuser nonlinear channels using tensor decomposition and precoding

This paper presents two blind identification methods for nonlinear memoryless channels in multiuser communication systems. These methods are based on the parallel factor (PARAFAC) decomposition of a tensor composed of channel output covariances. Such a decomposition is possible owing to a new precoding scheme developed for phase-shift keying (PSK) signals modeled as Markov chains. Some conditions on the transition probability matrices (TPM) of the Markov chains are established to introduce temporal correlation and satisfy statistical correlation constraints inducing the PARAFAC decomposition of the considered tensor. The proposed blind channel estimation algorithms are evaluated by means of computer simulations.

Microtensile bond strength of resin-based composites to Ti-6Al-4V

OBJECTIVE The purpose of this study was to determine the microtensile bond strength of various resin composite/adhesive systems to alumina particle abraded Ti-6Al-4V substrate after aging for 24h, 10 days, and 30 days in distilled water at 37 degrees C. METHODS Four laboratory resin composite veneering systems (Gradia, GR; Solidex, SOL; Ceramage, CER; and Sinfony, SF) were bonded to 25 mm diameter machined disks of Ti-6Al-4V with their respective adhesive and methodology, according to the manufacturers instructions. Microtensile bars of approximate dimensions 1 mm x 1 mm x 6 mm were prepared for each resin composite/adhesive system. After cutting, groups (n=12) from each adhesive system were separated and either stored in water at 37 degrees C for 24h (baseline) or aged for 10 or 30 days prior to loading to failure under tension at a cross head speed of 1.0mm/min. Failure modes were determined by means of scanning electron microscopy (SEM). Statistical analysis was performed through one-way ANOVA and Tukeys test at 95% level of significance. RESULTS Significant variation in microtensile bond strength was observed for the different systems and aging times. SOL and GR showed the highest mean bond strength values followed by SF and CER at baseline. Aging specimens in water had an adverse effect on bond strength for SOL and CER but not for the SF and GR groups. SIGNIFICANCE In vitro bond strength of laboratory resin composites to Ti-6Al-4V suggests that strong bonds can be achieved and are stable for certain systems, making them useful as an alternative for esthetic fixed prosthetic restorations.

Blind source separation and identification of nonlinear multiuser channels using second order statistics and modulation codes

In this paper, a Blind Source Separation (BSS) and channel identification method using second order statistics is proposed for nonlinear multiuser communication channels. It is based on the joint diagonalization of a set of covariance matrices. Modulation codes (constrained codes) are used to ensure the orthogonality of nonlinear combinations of the transmitted signals, allowing the application of a joint diagonalization based estimation algorithm. This constitutes a new application of modulation codes, used to introduce temporal redundancy and to ensure some statistical constraints. Identifiability conditions for the problem under consideration are addressed and some simulation results illustrate the performance of the proposed method.

Analysis and Power Diversity-Based Cancellation of Nonlinear Distortions in OFDM Systems

One of the main drawbacks of orthogonal frequency division multiplexing (OFDM) systems is the high peak-to-average power ratio (PAPR) of the transmitted signals, which can cause the introduction of intercarrier interference (ICI) due to the presence of nonlinear power amplifiers (PAs). In this paper, a theoretical analysis of the ICI in nonlinear OFDM systems with polynomial PAs is made. Contrary to other works, this analysis provides an exact description of the nonlinear ICI. Moreover, three receivers for channel estimation and ICI cancellation in OFDM systems with polynomial PAs are proposed, based on the concept of power diversity that consists in retransmitting the information symbols several times with a different transmission power each time. The transmission powers that minimize the sum of the residual mean square errors (MSEs) provided by the proposed receivers are derived in the case of a third-degree polynomial PA. An important advantage of the proposed receivers is that the optimal transmission powers do not depend on the channel and the PA coefficients.

A trilinear decompositionD approach fof Space-Time-Frequency multiple-access wireless systems

A new multiple-antenna transmission framework is proposed for multicarrier multiple-access wireless communication systems. The trilinear tensor (PARAFAC) decomposition is used to model a multiple-input multiple-output (MIMO) space-time-frequency (STF) scheme which consists in jointly multiplexing and spreading multiple data streams across space (transmit antennas), time (chips) and frequency (subcarriers) using a trilinear spreading code. The proposed framework affords a variable degree of diversity across the three signal dimensions by adjusting the dimensions of the trilinear spreading code. It also allows blind detection at the receiver by means of the alternating least squares algorithm.