Experimental study of drop-interface coalescence in the presence of polymer stabilisers

An experimental study has been carried out to characterise the performance of polymer stabilisers, partially hydrolysed polyvinyl acetate (PVAc), used in suspension polymerisation processes. The stabilisers are ranked by their ability to stabilise the dispersion characterised by the median coalescence time of a single drop with its homophase at a planar liquid/liquid interface. Results show that the stability of the dispersion relates closely to the molecular properties of the PVAcs. Other conditions being equal, PVAcs with higher molecular weights or lower degrees of hydrolysis can better stabilise a liquid-liquid dispersion. The stability of the dispersion also depends strongly on where the PVAc resides. The presence of a PVAc in the dispersed phase significantly reduces stability. Consistent with results reported in the literature, considerable scatter has been observed on the coalescence times of identical drops under the same conditions. An explanation for the scatter is also proposed in the paper, based on the classical Reynolds model for film thinning. (C) 2002 Elsevier Science B.V. All rights reserved.

Effect of solute lipophilicity on penetration through canine skin

Objective To investigate the effect of lipophilicity on the percutaneous penetration of a homologous series of alcohols through canine skin Design Skin harvested from Greyhound thorax was placed in Franz-type diffusion cells and the in vitro passage of radio-labelled (C-14) alcohols (ethanol, butanol, hexanol and octanol (Log P 0.19 - 3.0)) through separate skin sections was measured in replicates of five. Permeability coefficient (k(P), cm/h), maximum flux (J(max), mol/cm(2)/h) and residue remaining within the skin were determined. Results The k(P) increased with increasing lipophilicity (6.2 x 10(-4) +/- 1.6 x 10(-4) cm/h for ethanol to 1.8 x 10(-2) 3.6 x 10(-3) cm/h for octanol). Alcohol residues remaining within each skin sample followed a similar pattern. An exponential decrease in Jmax with increasing lipophilicity was observed. Conclusion Changes in canine skin permeability occur with increasing alcohol lipophilicity. This finding has practical consequences for the design of topical formulations and optimisation of drug delivery through animal skin.

Transdermal penetration of vasoconstrictors - Present understanding and assessment of the human epidermal flux and retention of free bases and ion-pairs

Purpose. As reductions in dermal clearance increase the residence time of solutes in the skin and underlying tissues we compared the topical penetration of potentially useful vasoconstrictors (VCs) through human epidermis as both free bases and ion-pairs with salicylic acid (SA). Methods. We determined the in vitro epidermal flux of ephedrine, naphazoline, oxymetazoline, phenylephrine, and xylometazoline applied as saturated solutions in propylene glycol: water (1: 1) and of ephedrine, naphazoline and tetrahydrozoline as 10% solutions of 1: 1 molar ratio ion-pairs with SA in liquid paraffin. Results. As free bases, ephedrine had the highest maximal flux, Jmax = 77.4 +/- 11.7 mug/cm(2)/h, being 4-fold higher than tetrahydrozoline and xylometazoline, 6-fold higher than phenylephrine, 10-fold higher than naphazoline and 100-fold higher than oxymetazoline. Stepwise regression of solute physicochemical properties identified melting point as the most significant predictor of flux. As ion-pairs with SA, ephedrine and naphazoline had similar fluxes (11.5 +/- 2.3 and 12.0 +/- 1.6 mug/cm(2)/h respectively), whereas tetrahydrozoline was approximately 3-fold slower. Corresponding fluxes of SA from the ion-pairs were 18.6 +/- 0.6, 7.8 +/- 0.8 and 1.1 +/- 0.1 respectively. Transdermal transport of VC's is discussed. Conclusions. Epidermal retention of VCs and SA did not correspond to their molar ratio on application and confirmed that following partitioning into the stratum corneum, ion-pairs separate and further penetration is governed by individual solute characteristics.

Penetration resistance in a latosol under different moisture and penetration speeds

The soil penetration resistance has been used to represent the compaction situation and several authors have attempted to relate the cone index (CI) with the bulk density. The importance of using the CI as source of information for decisions in agricultural activities, livestock and forestry manner, has become increasingly larger, which requires more knowledge about the penetrometers and penetrographs behavior. This study aimed to verify, in controlled laboratory conditions, the influence of soil water content and cone penetration rate to obtain the cone index, when density variation occurs. The soil was compacted by compression through a universal press cylinder which was specially designed to produce the test specimens. Bulk densities were determined from samples taken from the test specimens and their moisture content. The CI values obtained were between 0.258 and 4.776 MPa, measured in 4 moistures and 7 soil densities with 3 penetration speeds. It was concluded that the determination of IC is strongly influenced by the soil moisture but the penetration speed variation, used in this study, was not sufficient to influence the IC determination. However, the decrease in soil water content may increase the sensitiveness to detect a variation in bulk density by the use of cone index.

Development of a penetration test for timber impregnation products for use in old buildings

This paper studies the application of commercial biocides to old maritime pine timber structures (Pinus pinaster Ait.) that have previously been impregnated with other products. A method was developed in the laboratory to be used in situ to determine the impregnation depth achieved by a new generation biocide product applied to timber from an old building. This timber had once been treated with an unknown product difficult to characterize without extensive analysis. The test was initially developed in laboratory conditions and later tested on elements of the roof structure of an 18th century building. In both cases the results were promising and mutually consistent with penetration depths for some treatments reaching 2.0 cm. The application in situ proved the tests viability and simplicity of execution giving a clear indication on the feasibility of possible re-treatments.

Development of an in situ penetration test for the uptake of preservatives in applied wood

This paper concerns the study of biocides application in old timber structures of maritime pine (Pinus pinaster Ail.), previously impregnated with other products. A method was developed in laboratory to determine in situ the penetration depth of a product applied superficially. As initial treatment, three traditional products for sawn timber for buildings were used and, for new treatments, two newer, more environmentally benign products were used. Their ability to penetrate the pre-treated surfaces was evaluated after 1, 2 and 3 applications at 24 hours intervals and the results obtained are presented. Finally, the applicability of the developed test to the in-situ evaluation of timber structures is also discussed.

Real-time energy resources scheduling considering intensive wind penetration

The use of distributed energy resources, based on natural intermittent power sources, like wind generation, in power systems imposes the development of new adequate operation management and control methodologies. A short-term Energy Resource Management (ERM) methodology performed in two phases is proposed in this paper. The first one addresses the day-ahead ERM scheduling and the second one deals with the five-minute ahead ERM scheduling. The ERM scheduling is a complex optimization problem due to the high quantity of variables and constraints. In this paper the main goal is to minimize the operation costs from the point of view of a virtual power player that manages the network and the existing resources. The optimization problem is solved by a deterministic mixedinteger non-linear programming approach. A case study considering a distribution network with 33 bus, 66 distributed generation, 32 loads with demand response contracts and 7 storage units and 1000 electric vehicles has been implemented in a simulator developed in the field of the presented work, in order to validate the proposed short-term ERM methodology considering the dynamic power system behavior.

ANN-Based LMP forecasting in a distribution network with large penetration of DG

In recent years, power systems have experienced many changes in their paradigm. The introduction of new players in the management of distributed generation leads to the decentralization of control and decision-making, so that each player is able to play in the market environment. In the new context, it will be very relevant that aggregator players allow midsize, small and micro players to act in a competitive environment. In order to achieve their objectives, virtual power players and single players are required to optimize their energy resource management process. To achieve this, it is essential to have financial resources capable of providing access to appropriate decision support tools. As small players have difficulties in having access to such tools, it is necessary that these players can benefit from alternative methodologies to support their decisions. This paper presents a methodology, based on Artificial Neural Networks (ANN), and intended to support smaller players. In this case the present methodology uses a training set that is created using energy resource scheduling solutions obtained using a mixed-integer linear programming (MIP) approach as the reference optimization methodology. The trained network is used to obtain locational marginal prices in a distribution network. The main goal of the paper is to verify the accuracy of the ANN based approach. Moreover, the use of a single ANN is compared with the use of two or more ANN to forecast the locational marginal price.

Maximum penetration of microgeneration photovoltaic panels in distribution network

In smart grids context, the distributed generation units based in renewable resources, play an important rule. The photovoltaic solar units are a technology in evolution and their prices decrease significantly in recent years due to the high penetration of this technology in the low voltage and medium voltage networks supported by governmental policies and incentives. This paper proposes a methodology to determine the maximum penetration of photovoltaic units in a distribution network. The paper presents a case study, with four different scenarios, that considers a 32-bus medium voltage distribution network and the inclusion storage units.

The development and optimization of a modified single-drop microextraction method for organochlorine pesticides determination by gas chromatography-tandem mass spectrometry

We have developed a new method for single-drop microextraction (SDME) for the preconcentration of organochlorine pesticides (OCP) from complex matrices. It is based on the use of a silicone ring at the tip of the syringe. A 5 μL drop of n-hexane is applied to an aqueous extract containing the OCP and found to be adequate to preconcentrate the OCPs prior to analysis by GC in combination with tandem mass spectrometry. Fourteen OCP were determined using this technique in combination with programmable temperature vaporization. It is shown to have many advantages over traditional split/splitless injection. The effects of kind of organic solvent, exposure time, agitation and organic drop volume were optimized. Relative recoveries range from 59 to 117 %, with repeatabilities of <15 % (coefficient of variation) were achieved. The limits of detection range from 0.002 to 0.150 μg kg−1. The method was applied to the preconcentration of OCPs in fresh strawberry, strawberry jam, and soil.

Square-wave voltametric method for determination of molinate concentration in a biological process using a hanging mercury drop electrode

A square-wave voltammetric (SWV) method using a hanging mercury drop electrode (HMDE) has been developed for determination of the herbicide molinate in a biodegradation process. The method is based on controlled adsorptive accumulation of molinate for 10 s at a potential of -0.8 V versus AgCl/Ag. An anodic peak, due to oxidation of the adsorbed pesticide, was observed in the cyclic voltammogram at ca. -0.320 V versus AgCl/Ag; a very small cathodic peak was also detected. The SWV calibration plot was established to be linear in the range 5.0x10-6 to 9.0x10-6 mol L-1; this corresponded to a detection limit of 3.5x10-8 mol L-1. This electroanalytical method was used to monitor the decrease of molinate concentration in river waters along a biodegradation process using a bacterial mixed culture. The results achieved with this voltammetric method were compared with those obtained by use of a chromatographic method (HPLC–UV) and no significant statistical differences were observed.

Add/drop filters based on SiC technology for optical interconnects

In this paper we demonstrate an add/drop filter based on SiC technology. Tailoring of the channel bandwidth and wavelength is experimentally demonstrated. The concept is extended to implement a 1 by 4 wavelength division multiplexer with channel separation in the visible range. The device consists of a p-i'(a-SiC:H)-n/p-i(a-Si: H)-n heterostructure. Several monochromatic pulsed lights, separately or in a polychromatic mixture illuminated the device. Independent tuning of each channel is performed by steady state violet bias superimposed either from the front and back sides. Results show that, front background enhances the light-to-dark sensitivity of the long and medium wavelength channels and quench strongly the others. Back violet background has the opposite behaviour. This nonlinearity provides the possibility for selective removal or addition of wavelengths. An optoelectronic model is presented and explains the light filtering properties of the add/drop filter, under different optical bias conditions.

Optical nonlinearity in Tandem SI-C photodetectors

The behavior of tandem pin heterojunctions based on a-SiC: H alloys is investigated under different optical and electrical bias conditions. The devices are optimized to act as optically selective wavelength filters. Depending on the device configuration (optical gaps, thickness, sequence of cells in the stack structure) and on the applied voltage (positive or negative) and optical bias (wavelength, intensity, frequency) it is possible to combine the wavelength discrimination function with the self amplification of the signal. This wavelength nonlinearity allows the amplification or the rejection of a weak signal-impulse. The device works as an active tunable optical filter for wavelength selection and can be used as an add/drop multiplexer (ADM) which enables data to enter and leave an optical network bit stream without having to demultiplex the stream. Results show that, even under weak transient input signals, the background wavelength controls the output signal. This nonlinearity, due to the transient asymmetrical light penetration of the input channels across the device together with the modification on the electrical field profile due to the optical bias, allows tuning an input channel without demultiplexing the stream. This high optical nonlinearity makes the optimized devices attractive for the amplification of all optical signals. Transfer characteristics effects due to changes in steady state light, control d.c. voltage and applied light pulses are presented. Based on the experimental results and device configuration an optoelectronic model is developed. The transfer characteristics effects due to changes in steady state light, dc control voltage or applied light pulses are simulated and compared with the experimental data. A good agreement was achieved.

Experimental assessment of pressure drop in air stripping columns

One important step in the design of air stripping operations for the removal of VOC is the choice of operating conditions, which are based in the phase ratio. This parameter sets on directly the stripping factor and the efficiency of the operation. Its value has an upper limit determined by the flooding regime, which is previewed using empirical correlations, namely the one developed by Eckert. This type of approach is not suitable for the development of algorithms. Using a pilot scale column and a convenient solution, the pressure drop was determined in different operating conditions and the experimental values were compared with the estimations. This particular research will be incorporated in a global model for simulating the dynamics of air stripping using a multi variable distributed parameter system.