Bacterial composition of commercial probiotic products as evaluated by PCR-DGGE analysis

The use of Polymerase Chain Reaction-Denaturing Gradient Gel Electrophoresis (PCR-DGGE) technique in identifying the microorganisms present in commercial probiotic yoghurts and lyophilised products was evaluated. Two reference ladders were assembled constituted by PCR-amplified V2-V3 regions of 16S rDNA from bacterial species generally used as probiotics. Identification was achieved comparing the PCR-DGGE patterns obtained from the analysed products with the ladder bands. Bands from members of the same species showed the same migration distance in denaturing gel, hence supporting the identificative value of the method. The validity of the technique was also proven confirming the PCR-DGGE identification results by sequence data analysis and by species-specific PCR. General congruence between microorganisms declared on the label and those revealed by PCR-DGGE was found for probiotic yoghurts. Conversely, some discrepancies were observed for probiotic lyophilised preparations, i.e. the incorrect identification of some Bifidobacterium and Bacillus species and the presence of not declared microorganisms. PCR-DGGE turned out to be an appropriate culture-independent approach for a rapid detection of the predominant species in mixed probiotic cultures.     

ERROR ESTIMATION AND ADAPTIVITY IN FINITE ELEMENT ANALYSIS OF CONVECTIVE HEAT TRANSFER PROBLEMS,PART I: THEORETICAL CONSIDERATIONS

Abstract

This is the first of two articles concerning error estimation and adaptive refinement techniques applied to convective heat transfer problems. This study presents the detailed development of the proposed error estimator. The error estimator takes into account the coupling effects of the dependent variables ( e.g.. velocity and temperature) on the discretization error and, consequently, on the adaptive meshes. An averaging procedure is also proposed as a substitute for the smoothing /recovery procedure used to evaluate the gradients. The implementation of the averaging technique is simple and cost effective. Numerical experiments demonstrate that the proposed methodology results in a dramatic reduction in computational costs.     

A stabilized method for transient transport equations

We present a stabilized method for the transient advective-reactive-diffusive equation. The discretization is based on Rothe’s method, which discretizes in time before the spatial discretization. The resulting steady state advective-reactive-diffusive equation is approximated by the Unusual Stabilized Finite Element Method (USFEM).     

Shape controlled spherical (0D) and rod-like (1D) silica nanoparticles in silica/styrene butadiene rubber nanocomposites: Role of the particle morphology on the filler reinforcing effect

Silica/styrene butadiene rubber (SBR) nanocomposites were prepared by blending method using shape-controlled spherical and rod-like nanoparticles with different aspect ratios as filler for the rubber reinforcement. The differently shaped silica particles were synthesized by sol–gel method using tetraethoxysilane (TEOS) and (3-mercaptopropyl) trimethoxysilane (MPTSM) as silica precursors, and cetyltrimethylammonium bromide (CTAB) as structure directing agent. This strategy allowed to study the influence of the particle morphology on the reinforcing effect independently of the silica surface chemistry and considering the aspect ratio as the only geometrical variance. Spherical and anisotropic rod-like particles, dispersed in the nanocomposites, formed a network of particles bridged by thin rubber layers throughout the SBR matrix. Moreover, differently oriented domains of aligned rods are observed when the aspect ratio of particles increases and is ≥2. Dynamic-mechanical properties demonstrated that the rod-like particles with the higher aspect ratio provided stronger reinforcement of the rubber. This was related to the self-alignment of the anisotropic particles and to the consequent larger filler/polymer interface, compared to that of spherical ones.     

Au/Pt nanoparticle systems in methanol and carbon monoxide electroxidation

Different Au/Pt bimetallic systems have been synthesised by following the approach suggested by Brust. The nanoparticles have been anchored to glassy carbon surface through a place-exchange reaction involving dithiol molecules. The resulting modified electrode consists of heterogeneous nanostructured Au and Pt patchwork. The different nanoparticles systems developed have been employed for the electroxidation of methanol and carbon monoxide in alkaline aqueous media. The results show that the electrocatalytic activity of the bimetallic systems is enhanced with respect to the single monometallic NP systems.     

Perception of tap water risks and quality: a structural equation model approach.

The present study aims to test a model of tap water risk and quality perception. A questionnaire was designed and applied to a convenience sample of 499 people in Portugal. The model includes aesthetic variables (colour, odour, and flavour), contextual indicators and risk perception. Other variables were also considered, including external information, trust in water companies, familiarity with tap water, and past water-related health problems. A behavioural outcome--drinking tap water--was also studied. Due to multivariate non-normality (Mardia's Coefficient (G2,P) = 460.3), the AGLS estimator was used for the structural equation model (SEM). A triangulation approach with multivariate regression analysis was used to explain the use of tap water to drink and to propose a more holistic model that could not be tested using SEM. Results show that perceived water quality is largely influenced by flavour. Other factors, such as perceived risk and contextual indicators, also have a role but their relevance is relatively weak. On the other hand, risk perception seems to be mainly a result of external information, past health problems, and water colour. Finally, the use of tap water to drink at home can be moderately explained and depends mostly on the ability to use alternatives (i.e. bottled water), tap water taste, and perceived risk.     

Polyphase SC IIR Hilbert transformers

A novel polyphase switched-capacitor (SC) implementation of IIR Hilbert transformers is proposed. The circuit employs fewer op-amps and has better performance than the traditional two-phase circuit. SWIT-CAP2 simulation results and phase sensitivities to capacitance mismatches are provided     

Extraction and characterisation of meat from the claws of freshwater crayfish using dense media

The purpose of this study was to investigate the effectiveness of a two‐phase (flotation and filtration) separation of claw meat from the shell of freshwater crayfish using dense media, and to evaluate modifications to physicochemical and functional properties of the recovered meat, which could be subsequently incorporated in value‐added commodities. The media used were 10% (w/w) brine, 30% glucose syrup and a 30:70 ratio of glucose syrup to 2, 5 and 10% brine, with specific gravities ranging from 1.08 to 1.16. Extraction recovery of food‐grade mince ranged between 33.3 and 43.5%, which compared favourably with that of the control (hand‐picked meat, 33.2%). Compared with the control, the meat recovered from the two phases (treated meat) was significantly firmer in texture, lower in moisture and pH and less bright in colour. Meat salt content was reflective of the salt concentration in the recovery medium used. The treated meat also had a significantly lower apparent emulsification (20%) and water‐binding (60%) capacity than the hand‐picked meat. Comparing the two extraction phases, filtration‐phase meat had a significantly lower emulsion capability, was less firm and was brighter in colour than flotation‐phase meat. © 2000 Society of Chemical Industry     

Asymmetric Fin Line and Coupler at Millimeter Waves on PBG Substrate

The photonic band gap (PBG) crystals have been used as a perfectly reflecting substrate for many millimeter wave applications. In this work the fin line directional coupler with PBG substrate is analyzed using the TTL—Transverse Transmission Line method. Compared to odder full wave methods the TTL is an efficient tool to determine the coupler characteristics, making possible a significant algebraic simplification of the equations involved in the process. In order to analyze the structure the effective dielectric constant, the attenuation constant and the coupling were determined. News results obtained for this application and the conclusions are presented.     

Spectroscopic characterization of red perylimide/surfactant nanocomposites

Novel photoluminescent materials formed by some selected surfactants, metal derivatives of bis(2-ethylhexyl) sulfosuccinate (M(AOT) _n ; M = Na⁺, Co²⁺, Er³⁺ and Yb³⁺), bis(2-ethylhexyl) amine (BEEA), bis(2-ethylhexy1) phosphoric acid (HDEHP) and a 1:1 BEEA/HDEHP mixture, doped with the red perylimide (ROT-300) have been prepared, and their optical properties have been tested by absorption spectroscopy and steady state and time-resolved fluorescence. Experimental results show spectral shifts of the typical ROT-300 absorption and fluorescence bands with respect to that in apolar solvent medium. Data analysis leads consistently to attribute this feature mainly to the freezing of the diffusive movement of the dye molecules confined in the nanodomains of the surfactant liquid crystals, whilst minor effects can be due to interaction with the surfactant polar groups. Potentialities of these novel luminescent nanostructured composites as dye lasers, optical amplifiers and solar concentrators have been highlighted. In particular, under optical pumping using a pulse laser, amplified spontaneous fluorescence emission of the ROT-300/HDEHP system above an excitation energy threshold value of about 725 mJ cm⁻² was observed.