A semi-grand canonical Monte Carlo simulation model for ion binding to ionizable surfaces: Proton binding of carboxylated latex particles as a case study

In this paper, we present a computer simulation study of the ion binding process at an ionizable surface using a semi-grand canonical Monte Carlo method that models the surface as a discrete distribution of charged and neutral functional groups in equilibrium with explicit ions modelled in the context of the primitive model. The parameters of the simulation model were tuned and checked by comparison with experimental titrations of carboxylated latex particles in the presence of different ionic strengths of monovalent ions. The titration of these particles was analysed by calculating the degree of dissociation of the latex functional groups vs. pH curves at different background salt concentrations. As the charge of the titrated surface changes during the simulation, a procedure to keep the electroneutrality of the system is required. Here, two approaches are used with the choice depending on the ion selected to maintain electroneutrality: counterion or coion procedures. We compare and discuss the difference between the procedures. The simulations also provided a microscopic description of the electrostatic double layer (EDL) structure as a function of pH and ionic strength. The results allow us to quantify the effect of the size of the background salt ions and of the surface functional groups on the degree of dissociation. The non-homogeneous structure of the EDL was revealed by plotting the counterion density profiles around charged and neutral surface functional groups. © 2011 American Institute of Physics.

Relaxation and derelaxation of pure and hydrogenated amorphous silicon during thermal annealing experiments

The structural relaxation of pure amorphous silicon a-Si and hydrogenated amorphous silicon a-Si:H materials, that occurs during thermal annealing experiments, has been analyzed by Raman spectroscopy and differential scanning calorimetry. Unlike a-Si, the heat evolved from a-Si:H cannot be explained by relaxation of the Si-Si network strain but it reveals a derelaxation of the bond angle strain. Since the state of relaxation after annealing is very similar for pure and hydrogenated materials, our results give strong experimental support to the predicted configurational gap between a-Si and crystalline silicon.

RNA interference is ineffective as a routine method for gene silencing in chick embryos as monitored by fgf8 silencing.

The in vivo accessibility of the chick embryo makes it a favoured model system for experimental developmental biology. Although the range of available techniques now extends to miss-expression of genes through in ovo electroporation, it remains difficult to knock out individual gene expression. Recently, the possibility of silencing gene expression by RNAi in chick embryos has been reported. However, published studies show only discrete quantitative differences in the expression of the endogenous targeted genes and unclear morphological alterations. To elucidate whether the tools currently available are adequate to silence gene expression sufficiently to produce a clear and specific null-like mutant phenotype, we have performed several experiments with different molecules that trigger RNAi: dsRNA, siRNA, and shRNA produced from a plasmid coexpressing green fluorescent protein as an internal marker. Focussing on fgf8 expression in the developing isthmus, we show that no morphological defects are observed, and that fgf8 expression is neither silenced in embryos microinjected with dsRNA nor in embryos microinjected and electroporated with a pool of siRNAs. Moreover, fgf8 expression was not significantly silenced in most isthmic cells transformed with a plasmid producing engineered shRNAs to fgf8. We also show that siRNA molecules do not spread significantly from cell to cell as reported for invertebrates, suggesting the existence of molecular differences between different model systems that may explain the different responses to RNAi. Although our results are basically in agreement with previously reported studies, we suggest, in contrast to them, that with currently available tools and techniques the number of cells in which fgf8 gene expression is decreased, if any, is not sufficient to generate a detectable mutant phenotype, thus making RNAi useless as a routine method for functional gene analysis in chick embryos.

Recommendations for malaria prevention in moderate to low risk areas: travellers' choice and risk perception.

BACKGROUND: The considerable malaria decline in several countries challenges the strategy of chemoprophylaxis for travellers visiting moderate- to low-risk areas. An international consensus on the best strategy is lacking. It is essential to include travellers' opinions in the decision process. The preference of travellers regarding malaria prevention for moderate- to low-risk areas, related to their risk perception, as well as the reasons for their choices were investigated. METHODS: Prior to pre-travel consultation in the Travel Clinic, a self-administered questionnaire was given to travellers visiting moderate- to low-risk malaria areas. Four preventive options were proposed to the traveller, i.e., bite prevention only, chemoprophylaxis, stand-by emergency treatment alone, and stand-by emergency treatment with rapid diagnostic test. The information was accompanied by a risk scale for incidence of malaria, anti-malarial adverse drug reactions and other travel-related risks, inspired by Paling palettes from the Risk Communication Institute. RESULTS: A total of 391 travellers were included from December 2012 to December 2013. Fifty-nine (15%) opted for chemoprophylaxis, 116 (30%) for stand-by emergency treatment, 112 (29%) for stand-by emergency treatment with rapid diagnostic test, 100 (26%) for bite prevention only, and four (1%) for other choices. Travellers choosing chemoprophylaxis justified their choice for security reasons (42%), better preventive action (29%), higher efficacy (15%) and easiness (15%). The reasons for choosing stand-by treatment or bite prevention only were less medication consumed (29%), less adverse drug reactions (23%) and lower price (9%). Those who chose chemoprophylaxis were more likely to have used it in the past (OR = 3.0 (CI 1.7-5.44)), but were not different in terms of demographic, travel characteristics or risk behaviour. CONCLUSIONS: When travelling to moderate- to low-risk malaria areas, 85% of interviewees chose not to take chemoprophylaxis as malaria prevention, although most guidelines recommend it. They had coherent reasons for their choice. New recommendations should include shared decision-making to take into account travellers' preferences.

Sterolin valmistus selluprosessin yhteydessä

Työssä tutkittiin UPM-Kymmene Oyj Kaukaan kemiallisella tehtaalla käytössä olevia steroliprosesseja. Steroleita erotetaan sulfaattiselluloosan keitossa syntyvasta suovasta uutetusta neutraaliainejakeesta. Neutraaliaine sisältää β-sitosterolia, α-sitosterolia ja kampesterolia yhteensä noin 20 p-%. Primal-laadun valmistus perustuu neste-nesteuuttoon sekä kiteytykseen ja Ultra-laadun kaksivaiheiseen suorakiteytykseen. Työn kirjallisessa osassa perehdytään sterolien kemiaan sekä neste-nesteuuttoon ja kiteytykseen erotus- ja puhdistusmenetelminä. Laboratoriokokeissa tutkittiin kolmen eri alkoholin ja kahden eri hiilivetyliuottimen soveltuvuutta Primal-sitosterolin uuttoon ja kiteytykseen. Lisaksi tutkittiin liuotinseoksen vesipitoisuuden vaikutusta. Tavoitteena oli löytää uuttoliuottimien koostumus, jolla uuton sterolisaanto ja sterolikiteiden puhtaus olisivat mahdollisimman korkeat. Havaittiin, että uuton sterolisaanto voitiin maksimoida pitämällä uuttoalkoholin vesipitoisuus niin alhaisena, että faasit juuri ja juuri erottuvat toisistaan. Laboratoriokokeissa saatujen tulosten perusteella tehtiin tehdasmittakaavan koeajo Primal-sitosterolin valmistuslaitteistolla UPM-Kymmene Oyj Kaukaan kemiallisella tehtaalla. Talloin uutossa saavutettiin noin 50 %:n sterolisaanto. Ultra-sitosterolin laboratoriomittakaavaisissa kiteytyskokeissa vertailtiin neljän eri alkoholin ja kahden muun orgaanisen liuottimen soveltuvuutta kiteytysliuoksen komponenteiksi. Lisaksi tutkittiin vesipitoisuuden liuotinseoksen vaikutusta. Tarkoituksena oli löytää se liuotinkoostumus, jolla sterolikiteiden saanto ja puhtaus olisivat mahdollisimman korkeat. Sopivalla kiteytysliuoksen koostumuksella saavutettiin melko hyvä sterolisaanto ja lähes 98 %:n puhtaus.

Biologisen jätevedenpuhdistuksen ilmastuksen tehostaminen

Työssä tutkittiin, mikä on kustannustehokkain tapa lisätä ilmastuskapasiteettia ja selvitettiin, saostaako vesilaitokselta flotaatioaltaasta poistettava ferrisulfaattisakka jäteveden fosforia esiselkeyttimessä. Työssä määritettiin teoreettinen hapentarve ilmastusaltaassa maksimikuormituksen aikana ja hapensiirtonopeus jäteveteen olemassa olevalla laitteistolla. Hapensiirtonopeuden funktion korjauskertoimet  ja  sekä kokonaishapensiirtokerroin määritettiin laboratorio-olosuhteissa. Lisäksi laskettiin kuinka paljon nykyisten ilmastimien kautta saadaan happea jäteveteen liukenemaan ja verrattiin tätä lukua teoreettiseen hapentarpeeseen. Jälkimmäistä menettelytapaa käyttäen arvioitiin lisähapen tarve. Tulokseksi saatiin, että maksimi BOD-kuormituksen aikana happea tarvitsee saada jäteveteen liuotettua 5200 m³/d lisää. Ilmastuskapasiteetin lisäyksen kustannuslaskelmassa verrattiin neljää vaihtoehtoa: puhdasta happea liuotettuna happimattojen kautta tai OKI-ilmastimen kautta, onsite-happilaitoksen puhdasta happea liuotettuna OKI-ilmastimen kautta tai ilman happea liuotettuna jäteveteen EDI-ilmastimien kautta. Laskelmat osoittivat uusien EDI-ilmastimien hankinnan olevan edullisin vaihtoehto pitkällä aikavälillä. Vaikka EDI-ilmastimien investointikustannukset ovat korkeat, tulevat ne käyttökustannuksiltaan kaikkein edullisimmaksi. Vesilaitokselta tulevan rautasuolasakan fosforia saostavaa vaikutusta tutkittiin laboratoriossa astiakokein. Näytteet otettiin vesilaitokselta jätevesilaitokselle menevästä rautasuolasakasta sekä esiselkeyttimen kirkasteesta. Näitä eri suhteissa keskenään sekoittamalla saatiin selville, että rautasuolasakka ja sakan mukana tuleva reagoimaton rautasuola saostavat liukoista ja kokonaisfosforia esiselkeytyksessä.

Probabilistic electrical resistivity tomography of a CO2 sequestration analog

Electrical resistivity tomography (ERT) is a well-established method for geophysical characterization and has shown potential for monitoring geologic CO2 sequestration, due to its sensitivity to electrical resistivity contrasts generated by liquid/gas saturation variability. In contrast to deterministic inversion approaches, probabilistic inversion provides the full posterior probability density function of the saturation field and accounts for the uncertainties inherent in the petrophysical parameters relating the resistivity to saturation. In this study, the data are from benchtop ERT experiments conducted during gas injection into a quasi-2D brine-saturated sand chamber with a packing that mimics a simple anticlinal geological reservoir. The saturation fields are estimated by Markov chain Monte Carlo inversion of the measured data and compared to independent saturation measurements from light transmission through the chamber. Different model parameterizations are evaluated in terms of the recovered saturation and petrophysical parameter values. The saturation field is parameterized (1) in Cartesian coordinates, (2) by means of its discrete cosine transform coefficients, and (3) by fixed saturation values in structural elements whose shape and location is assumed known or represented by an arbitrary Gaussian Bell structure. Results show that the estimated saturation fields are in overall agreement with saturations measured by light transmission, but differ strongly in terms of parameter estimates, parameter uncertainties and computational intensity. Discretization in the frequency domain (as in the discrete cosine transform parameterization) provides more accurate models at a lower computational cost compared to spatially discretized (Cartesian) models. A priori knowledge about the expected geologic structures allows for non-discretized model descriptions with markedly reduced degrees of freedom. Constraining the solutions to the known injected gas volume improved estimates of saturation and parameter values of the petrophysical relationship. (C) 2014 Elsevier B.V. All rights reserved.

Robust Estimates of the Negative Binomial Model

We consider robust parametric procedures for univariate discrete distributions, focusing on the negative binomial model. The procedures are based on three steps: ?First, a very robust, but possibly inefficient, estimate of the model parameters is computed. ?Second, this initial model is used to identify outliers, which are then removed from the sample. ?Third, a corrected maximum likelihood estimator is computed with the remaining observations. The final estimate inherits the breakdown point (bdp) of the initial one and its efficiency can be significantly higher. Analogous procedures were proposed in [1], [2], [5] for the continuous case. A comparison of the asymptotic bias of various estimates under point contamination points out the minimum Neyman's chi-squared disparity estimate as a good choice for the initial step. Various minimum disparity estimators were explored by Lindsay [4], who showed that the minimum Neyman's chi-squared estimate has a 50% bdp under point contamination; in addition, it is asymptotically fully efficient at the model. However, the finite sample efficiency of this estimate under the uncontaminated negative binomial model is usually much lower than 100% and the bias can be strong. We show that its performance can then be greatly improved using the three step procedure outlined above. In addition, we compare the final estimate with the procedure described in

The gender-based stereotype about food is on the table. Food choice also depends on co-eater's gender

Previous research has shown that different foods are stereotypically associated with gender and that eating in a role-congruent way fulfills an impression management function. On the other hand, other studies revealed that adapting one's food consumption to that of the co-eaters is a means to gain social approval as well. In the present study, we bridge these two distinct lines of research by studying what happens when the two norms (conforming to the gender-based stereotype and imitating the co-eater) conflict, that is with opposite-sex co-eaters. Results indicated that the tendency to match the co-eaters' supposed consumption generally appeared over and above one's gender-congruent choice. In addition, as expected, gender differences also emerged: while men were always willing to adapt to the co-eaters, women's intention to eat the feminine food was independent from the co-eaters' gender.

Spatial radial maze procedures and setups to dissociate local and distal relational spatial frameworks in humans.

BACKGROUND: Radial maze tasks have been used to assess optimal foraging and spatial abilities in rodents. The spatial performance was based on a capacity to rely on a configuration of local and distant cues. We adapted maze procedures assessing the relative weight of local cues and distant landmarks for arm choice in humans. NEW METHOD: The procedure allowed testing memory of places in four experimental setups: a fingertip texture-groove maze, a tactile screen maze, a virtual radial maze and a walking size maze. During training, the four reinforced positions remained fixed relative to local and distal cues. During subsequent conflict trials, these frameworks were made conflictive in the prediction of reward locations. RESULTS: Three experiments showed that the relative weight of local and distal relational cues is affected by different factors such as cues' nature, visual access to the environment, real vs. virtual environment, and gender. A fourth experiment illustrated how a walking maze can be used with people suffering intellectual disability. COMPARISON WITH EXISTING METHODS: In our procedure, long-term (reference) and short-term (working) memory can be assessed. It is the first radial task adapted to human that enables dissociating local and distal cues, to provides an indication as to their relative salience. Our mazes are moveable and easily used in limited spaces. Tasks are performed with realistic and spontaneous though controlled exploratory movements. CONCLUSION: Our tasks enabled highlighting the use of different strategies. In a clinical perspective, considering the use of compensatory strategies should orient towards adapted behavioural rehabilitation.