Osmotic pressure of suspensions comprised of charged microgels.

We determine the osmotic pressure of microgel suspensions using membrane osmometry and dialysis, for microgels with different softnesses. Our measurements reveal that the osmotic pressure of solutions of both ionic and neutral microgels is determined by the free ions that leave the microgel periphery to maximize their entropy and not by the translational degrees of freedom of the microgels themselves. Furthermore, up to a given concentration it is energetically favorable for the microgels to maintain a constant volume without appreciable deswelling. The concentration where deswelling starts weakly depends on the crosslinker concentration, which affects the microgel dimension; we explain this by considering the dependence of the osmotic pressure and the microgel bulk modulus on the particle size.

Coaxial nanowires as plasmon-mediated remote nanosensors.

This study reports on the plasmon-mediated remote Raman sensing promoted by specially designed coaxial nanowires. This unusual geometry for Raman study is based on the separation, by several micrometres, of the excitation laser spot, on one tip of the nanowire, and the Raman detection at the other tip. The very weak efficiency of Raman emission makes it challenging in a remote configuration. For the proof-of-concept, we designed coaxial nanowires consisting of a gold core to propagate surface plasmon polaritons and a Raman-emitting shell of poly(3,4-ethylene-dioxythiophene). The success of the fabrication was demonstrated by correlating, for the same single nanowire, a morphological analysis by electron microscopy and Raman spectroscopy analysis. Importantly for probing the remote-Raman effect, the original hard template-based process allows one to control the location of the polymer shell all along the nanowire, or only close to one or the two nanowire tips. Such all-in-one single nanowires could have applications in the remote detection of photo-degradable substances and for exploring 1D nanosources for integrated photonic and plasmonic systems.

Nota suicida y autopsia psicológica: Aspectos comportamentales asociados / Suicide note and the psychological autopsy: Associated behavioral aspects

Cuando se produce una muerte en circunstancias traumáticas, ambiguas, desconocidas o inciertas, cabe pensar en una muerte con etiología suicida. En muchas ocasiones, junto al cuerpo aparece una nota suicida que ayuda a aclarar algunos aspectos necesarios para la investigación que dilucide si realmente se trata de una muerte por suicidio o por otras causas. Hay varios tipos de nota suicida (despedida, instrucciones, acusación a otros, petición de perdón, justificación del propio suicidio) que pueden contribuir al estudio del estado psicológico de la persona y las circunstancias que condujeron a la muerte. No hay un modelo unánimemente aprobado para llevar a cabo la Autopsia Psicológica pero sí protocolos para obtener la información relevante y realizar el informe correspondiente

When a death occurs under traumatic, ambiguous, unknown, or uncertain circumstances, a death of suicidal origin can be considered. On many occasions, a suicide note is found next to body that helps to clarify certain aspects needed for the investigation to elucidate whether the death is really due to suicide or other causes. There are several types of suicide note (farewell, instructions, accusation of others, request for forgiveness, justification of one’s own suicide) that can contribute to the study of the victim’s psychological state and the circumstances that led to death. There is no unanimously approved way to conduct the psychological autopsy, but there are protocols for obtaining relevant information and preparing the report

Suicide note and the psychological autopsy: Associated behavioral aspects.

When a death occurs under traumatic, ambiguous, unknown, or uncertain circumstances, a death of suicidal origin can be considered. On many occasions, a suicide note is found next to body that helps to clarify certain aspects needed for the investigation to elucidate whether the death is really due to suicide or other causes. There are several types of suicide note (farewell, instructions, accusation of others, request for forgiveness, justification of one’s own suicide) that can contribute to the study of the victim’s psychological state and the circumstances that led to death. There is no unanimously approved way to conduct the psychological autopsy, but there are protocols for obtaining relevant information and preparing the report.

Impact of single-particle compressibility on the fluid-solid phase transition for ionic microgel suspensions.

We study ionic microgel suspensions composed of swollen particles for various single-particle stiffnesses. We measure the osmotic pressure π of these suspensions and show that it is dominated by the contribution of free ions in solution. As this ionic osmotic pressure depends on the volume fraction of the suspension ϕ, we can determine ϕ from π, even at volume fractions so high that the microgel particles are compressed. We find that the width of the fluid-solid phase coexistence, measured using ϕ, is larger than its hard-sphere value for the stiffer microgels that we study and progressively decreases for softer microgels. For sufficiently soft microgels, the suspensions are fluidlike, irrespective of volume fraction. By calculating the dependence on ϕ of the mean volume of a microgel particle, we show that the behavior of the phase-coexistence width correlates with whether or not the microgel particles are compressed at the volume fractions corresponding to fluid-solid phase coexistence.

Effective interaction in asymmetric charged binary mixtures: the non-monotonic behaviour with the colloidal charge.

In this work we study the effective force between charged spherical colloids induced by the presence of smaller charged spheres using Monte Carlo simulations. The analysis is performed for two size ratios, q = R(s)/R(b), two screened direct repulsions, κ, and two small particle packing fractions, Ø(s). We specially focus on the effect of the charge of the big colloids (Z(b)), and observe that the repulsion between big particles shows a non-monotonic behaviour: for sufficiently small charge, we find an anomalous regime where the total repulsion weakens by increasing the big colloid charge. For larger charges, the system recovers the usual behaviour and the big-big interaction becomes more repulsive increasing Z(b). This effect is linked to the existence of strong attractive depletion interactions caused by the small-big electrostatic repulsion. We have also calculated the effective force using the Ornstein-Zernike equation with the HNC closure. In general, this theory agrees with the simulation results, and is able to capture this non-monotonic behaviour.

Role of the electrostatic depletion attraction on the structure of charged liposome-polymer mixtures.

The effect of adding charged nonadsorbing polymers to electrostatically structured suspensions of charged liposomes has been experimentally studied by means of light scattering techniques. The static structure factor of the mixtures is analyzed using two polymers of different sizes. As the polymer concentration increases, the main peak of the structure factor decreases and shows an important shift to larger values of the scattering vector. Such displacement is the consequence of the electrostatic-enhanced depletion attraction induced by the polymers that counteracts the electrostatic repulsion. For the shorter polymer, the system remains stable for all studied polymer concentrations. However, for the long polymer chains, the effective attraction induced at the highest polymer density studied is strong enough to destabilize the mixture. In this case, the aggregation of the liposomes leads to clusters of nearly linear morphology. The PRISM theory is employed to calculate the effective pair potential between liposomes. The theoretical predictions are able to support the experimental observations, and provide an explanation of the interplay between the electrostatic repulsive interaction and the depletion attraction. In particular, they show that the depletion attraction is especially long ranged, and is dominated by electrostatic effects rather than entropic.

Charged colloid-polymer mixtures: a study on electrostatic depletion attraction.

In this work, light scattering methods have been used to study the effect of adding charged polymer chains on the structural and dynamic properties of a charged colloidal system. The experimental measurements of the static structure factor S(cc)(q) show that as the polymer concentration increases, the main peak moves to higher q-values, which is interpreted in terms of the electrostatically enhanced depletion attraction induced by the polymer. Moreover, we found that the shift of the peak depends on the interplay between two relevant length scales, the polymer radius of gyration, R(g), and the Debye length, κ(-1). To reach these conclusions, the polymer reference interaction site model has been employed to explain the experimental results and to study how the effective depletion attraction depends on the polymer concentration, R(g) and κ(-1). Additionally, the measurements of the dynamic structure factor f(q, τ) indicate that the colloidal diffusion increases with the polymer concentration. Both static and dynamic analysis point out that the repulsion between colloids becomes weaker as the charged polymer is added.

Evaluation of a school-based programme of universal eating disorders prevention: is it more effective in girls at risk?

There is currently controversy surrounding the effectiveness of universal versus selective prevention in eating disorders (ED). The present study aims at evaluating the effectiveness of universal school-based ED prevention administered to female secondary school students (n = 349). Students received either the full prevention programme (learning basic concepts of nutrition, criticism of aesthetic models of beauty emphasising extreme thinness, media literacy (ML)), a partial version of the programme (without nutritional education), or no prevention programme. Students were also classified on the presence or absence of distinct risk factors for ED: Early menarche, overweight, dieting, negative attitudes to food and perceived pressure to be thin. Pre-test data were collected 1 week prior to implementation of the prevention programme, and post-test data were collected on the last day of the programme. Results suggested that both the full and partial prevention programmes reduced perceived pressure to be thin and improved eating attitudes and knowledge of nutrition in all the participants (regardless of risk); however, greater effect sizes were found among particular high-risk groups (early menarche, overweight and highly influenced by aesthetic models of beauty emphasising extreme thinness). School-based programmes of universal intervention may have an important role to play in the prevention of ED.