Dehydration of biological membranes in a non-condensing environment.

The study of the dehydration process in a cell membrane allows a better understanding of how water is bound to it. While in prior studies, cell dehydration was commonly analyzed under osmotic stress conditions, in the present work, we focus on the dehydration driven by evaporation in a restricted condensing environment. Using a thermogravimetry method, we studied the dehydration of Escherichia coli through isothermal evaporation in the presence of a gas flux. To figure out the loss of mass in this situation, we first evaluated the dynamics of water evaporation of a suspension of multilamellar liposomes. We found that the evaporation of liposomal suspensions composed of individual lipids is constant, although slightly restricted by the presence of liposomes, while the evaporation of liposomal suspensions composed of a mixture of different lipids follows an exponential decay. This is explained considering that the internal pressure at the air-water interface is proportional to the amount of bound water. The evaporation of water from a biomass sample follows this latter behaviour.

On the evolution of the exclusion zone produced by hydrophilic surfaces: A contracted description.

After exciting scientific debates about its nature, the development of the exclusion zone, a region near hydrophilic surfaces from which charged colloidal particles are strongly expelled, has been finally traced back to the diffusiophoresis produced by unbalanced ion gradients. This was done by numerically solving the coupled Poisson equation for electrostatics, the two stationary Stokes equations for low Reynolds numbers in incompressible fluids, and the Nernst-Planck equation for mass transport. Recently, it has also been claimed that the leading mechanism behind the diffusiophoretic phenomenon is electrophoresis [Esplandiu et al., Soft Matter 16, 3717 (2020)]. In this paper, we analyze the evolution of the exclusion zone based on a one-component interaction model at the Langevin equation level, which leads to simple analytical expressions instead of the complex numerical scheme of previous works, yet being consistent with it. We manage to reproduce the evolution of the exclusion zone width and the mean-square displacements of colloidal particles we measure near Nafion, a perfluorinated polymer membrane material, along with all characteristic time regimes, in a unified way. Our findings are also strongly supported by complementary experiments using two parallel planar conductors kept at a fixed voltage, mimicking the hydrophilic surfaces, and some computer simulations.

The effect of green light on the motility of mouse sperm at two different temperatures.

Photo-modulation with visible light has been used to induce gains in the motility of the sperms of rabbits, boars, buffalo, bulls, fish, and humans. Although different hypotheses have been proposed to explain such an effect, the origin and mechanisms by which visible light affects sperm motility are still far from being completely understood. Several groups have observed changes in the intracellular Ca2+ concentration and significant differences in the production of ROS, which are attributed to specific photosensitizers. Also, it has been reported that blue light induces nitric oxide production in sperm cells, which plays a vital role in acrosome reaction and capacitation leading to an augmentation in the fertilisation probability. In the present work, we study the effects of green light (490-540 nm) on the sperm motility of mice. Firstly, we carried out experiments at 37 °C to confirm what previous researchers have observed before using red and blue light: that the overall sperm motility increases. Secondly, we studied the effects of green light at 10 °C and found that the motility drastically diminishes. In order to understand this opposing outcome, we carried out fluorescence measurements to evaluate reactive oxygen species production induced by green light at both temperatures. Our results suggest that the balance between the use and generation of ROS at 37 °C is favorable to the cells, while at 10 °C it is harmful.

Experimental device to measure the electrical and optical properties of radiochromic films as a function of temperature.

In the last decade, radiochromic films (RCF) have been used extensively in medical physics for evaluating uniformity of radiation beams and dose distributions. These films are very sensitive to changes in temperature; therefore, one needs to know its thermal behavior to use them efficiently. Normally, the thermal assessment is done using optical methods on previously irradiated samples. Here, we report the use of a complementary dielectric method. We designed an experimental device that allows us to measure, simultaneously, the dielectric and optical properties as a function of temperature. We performed the measurements in real-time to temperature increases from 27 to 48 degrees C of EBT and MD-55 RCF previously exposed to UV. We found for both films a decrease in the real part of the dielectric permittivity as the temperature increases, but an increment and decrease in the dielectric loss factor for the EBT and MD-55 film, respectively.

Thermoluminescent response of LiF:Mg,Ti to 20 keV electrons.

The thermoluminescence response of LiF:Mg,Ti (TLD-100) to 20 keV electrons from a scanning electron microscope has been measured. Radiochromic dye films previously calibrated were used to determine the fluence incident on TLD-100 chips. The procedure for irradiation and glow curve deconvolution was adhered to the protocols previously determined in our laboratory for gamma rays and heavy charged particles. The response at electron fluences higher than 4 x 10(10) cm(-2) is supralinear, due to the increasingly relevant contribution of the high temperature peaks. The relative contribution of the high temperature peaks to the TL signal is abnormally small, about half that observed in gamma irradiation and four times smaller than what has been measured in low-energy X ray exposure.

The use of a reflective scanner to study radiochromic film response.

GafChromic MD-55-2 film response was studied using a flatbed, reflective Microtek ScanMaker E3 scanner, under different conditions to optimize its use. Irradiations were performed using 60Co gamma rays in a 0-300 Gy dose interval to produce a calibrated step wedge. A 24-bit colour-scale mode along with image splitting into its red, green and blue components is suggested as an improved dosimetry method over a 256 grey level (8-bit) mode, extending the dynamic range for this film. Diverse film orientation and positioning, a black or a white background, and individual step film scanning were evaluated. Unwanted normalization is overcome by adding reference black and white steps adjacent to the radiochromic film, ensuring reproducibility. The use of a red filter was found to be equivalent to the use of the red component of the image after image colour splitting. The useful range for MD-55-2 film is extended up to 300 Gy if colour components, other than red, are used to evaluate the response. Comparisons with optical density measurements show that inexpensive commercial scanners might be a good alternative to densitometers.