Effect of substrate mismatch, orientation, and flexibility on heterogeneous ice nucleation.

Heterogeneous nucleation is the main path to ice formation on Earth. The ice nucleating ability of a certain substrate is mainly determined by both molecular interactions and the structural mismatch between the ice and the substrate lattices. We focus on the latter factor using molecular simulations of the mW model. Quantifying the effect of structural mismatch alone is challenging due to its coupling with molecular interactions. To disentangle both the factors, we use a substrate composed of water molecules in such a way that any variation on the nucleation temperature can be exclusively ascribed to the structural mismatch. We find that a 1% increase in structural mismatch leads to a decrease of ∼4 K in the nucleation temperature. We also analyze the effect of orientation of the substrate with respect to the liquid. The three main ice orientations (basal, primary prism, and secondary prism) have a similar ice nucleating ability. We finally assess the effect of lattice flexibility by comparing substrates where molecules are immobile to others where a certain freedom to fluctuate around the lattice positions is allowed. Interestingly, we find that the latter type of substrate is more efficient in nucleating ice because it can adapt its structure to that of ice.

Evaluation of watershed-derived mass loads to prioritize TMDL decision-making.

A total maximum daily load (TMDL) for oxygen demanding substances is being implemented in the San Joaquin River (SJR) in California (USA) due to frequently occurring low dissolved oxygen conditions. The SJR is a eutrophic river, heavily impacted by agriculture. A mass balance was developed to identify the sources of oxygen-demanding substances and nutrients to the river with the objective of providing a scientific basis for management actions needed to meet TMDL requirements. Data were collected for flow and water quality and mass loads calculated for sites within the main stem of the SJR, river inputs (tributaries), and diversions in the study area. Using a quadrant analysis, tributary flows and loads are ranked to identify targets for water quality improvement efforts. Additionally, all mass loads were summed (inputs minus diversions) and compared with observed loads at the downstream limit of the study area. The mass balance analysis identifies major contributors of mass loads and mass balance closure is assessed for each constituent. These analysis methods inform the TMDL process which includes a load allocation, and is useful for determining locations for implementation of improvement projects needed to improve the health of the river.

Comparison of different methods and times for reading the tuberculin skin test.

BACKGROUND: Current guidelines vary on the recommended method and time for measuring tuberculin skin test (TST) indurations. OBJECTIVE: To evaluate the best time and method for assessing TST results and which purified protein derivative (PPD) to administer. DESIGN: Standard PPD (PPD-S) and PPD-RT23 were applied concurrently on each forearm in random order in 78 nurses. MEASUREMENTS: TST induration was measured at 48, 72 and 96 h by two nurses by palpation and a ruler, palpation and a Vernier caliper, ballpoint pen and a ruler or ballpoint pen and a Vernier caliper. TST differences were assessed using mixed-effects analysis. We also assessed the rate of false-positive/-negative results and the variability of the TST measurements. RESULTS: We performed 767 TST measurements. The adjusted mean TST size was larger with PPD-S than with PPD-RT23 (12.8 vs. 10.8 mm, P < 0.001), and at 72 h than at 48 h and 96 h (13.4 vs. 11.8 vs. 10.1 mm, P < 0.05). The smallest number of false results was observed with PPD-S, the ballpoint pen-ruler and at 72 h; palpation+ruler had the least variability at 72 h. CONCLUSIONS: The TST should ideally be performed with PPD-S and measured at 72 h with the ballpoint pen+ruler or palpation+ruler methods.

Chondrocyte proliferation in a new culture system.

OBJECTIVE: This study has aimed to study different culture systems that might stimulate an increase in cell proliferation of normal and osteoarthritis chondrocytes from articular cartilage in rat model. MATERIAL AND METHODS: Three culture systems using chondrocytes embedded in alginate beads were tested: chondrocytes cultured in Dulbecco's modified Eagle's medium (DMEM) as control, a co-culture system consisting of a monolayer of de-differentiated chondrocytes as a source of mitotic factors, and an enriched medium containing culture medium obtained from a monolayer of chondrocytes and DMEM. Normal and osteoarthritis chondrocytes were stained with 5-carboxyfluorescein diacetate succinimidyl ester and were cultured in each of the three systems. After 5 days of culture cell, proliferation was detected by flow cytometry. Chondrocyte phenotype was confirmed by collagen type II and MMP-3 expression. To determine possible molecules released into the medium by the cultured chondrocyte monolayer and which would probably be involved in cell proliferation, a study of mRNA and expression of transforming growth factor-beta1 (TGF-beta1), fibroblastic growth factor-2 (FGF-2), epidermal growth factor (EGF), platelet derived growth factor-A (PDGF-A) and insulin-like growth factor-1 (IGF-1) proteins was conducted. RESULTS AND CONCLUSIONS: Chondrocytes in the co-culture system or in enriched medium showed an increase in proliferation; only when osteoarthritis chondrocytes were cultured in enriched medium would they display a statistically significant increase in their proliferation rate and in their viability. When chondrocytes from the monolayer were analysed, differential mRNA expression of TGF-beta1 and IGF-1 was found during all passages, which suggests that these two growth factors might be involved in chondrocyte proliferation.

Morphologic, biochemical and molecular mitochondrial changes during reperfusion phase following brief renal ischemia.

Ischemia/reperfusion of organs and cells induces apoptosis through a complicated series of changes in mitochondria, mainly the generation of oxygen free radicals, permeability transitions, calcium translocations, and release of apoptogenic factors such as cytochrome c and Bcl-2 family members. The liberation of these factors occurs very early after reoxygenation and it has been assumed that it takes place without any structural alteration of the mitochondrial membranes. The aim of this study was to detect ultrastructural changes of mitochondria in the initial stages of reperfusion at the time when Bcl-2 and succinic dehydrogenase, located in the outer and inner membranes, respectively, were released. Ischemia/reperfusion was produced in adult rats by clamping one renal artery for 60 min and reoxygenating for 60, 120, 180, and 240 min. A model of chemical hypoxia with intra-arterial 50 mM sodium azide served as comparison, allowing free blood flow for 30, 60, 120 and 180 min. Light and electron microscopy, immunostaining for Bcl-2, and enzyme histochemistry for succinic dehydrogenase were performed. Our results showed mitochondrial swelling, rupture of inner and outer membranes, and leakage of mitochondrial matrix into the cytoplasm in ischemia after 120 min of reperfusion. Bcl-2 immunoreactivity and focal lowering of SDH reactivity were also noted and became more pronounced at the same time that the mitochondrial ultrastructure demonstrated more evident changes including rupture of the inner and outer membranes. Our studies seem to indicate that in early ischemia-reperfusion and in chemical hypoxia-induced apoptosis, the earliest ultrastructural changes take place in mitochondria and that swelling and rupture of mitochondrial membranes occur in parallel with the loss of Bcl-2 and SDH activity.

[The role of steroids in the follicular development in mammals]. / El papel de los esteroides en el desarrollo folicular del mamífero.

The purpose of this review is to know the regulation of ovaric steroidogenesis on follicular development, ovulation and corpora lutea. The modulating endocrine mechanisms involved in the gonadotrophin secretion concomitant with the ovaric steroidogenesis and the follicular develop induce a series of endocrinologic and morphologic events in order to produce a fully mature ovocyte able to be fecundated.

[Biocompatibility of dental materials. Choice of testing methods: to do or not]. / La biocompatibilité des matériaux dentaires. Choix d'une méthode à tester: fair ou ne pas faire.

Three methods used to study the biocompatibility of dental materials are compared in this article. A glass-ionomer cement, Vitrabond, was studied, using gutta-percha as the control material. Specimens were standardized according to an original procedure. Unsterilized Vitrabond implants were used, because UV rays modify the material. Intraperitoneal Vitrabond implants increased the macrophage population in rats after 24 hrs. This was caused by the surgical trauma and indicates that this method is unreliable. The intramuscular placement of Vitrabond provoked well defined lesions after a week. The use of histochemical techniques on frozen muscle demonstrated that the concentration of succinic deshydrogenase and acid phosphatase enzymes were altered when compared to the control lesions. A comparison of enzymatic lesions and an evaluation of the areas of cellular growth inhibition during in vitro experiments using a computer image analyzer leads to quantitative conclusions that Vitrabond is a cytotoxic material. The simultaneous use of histochemical techniques on muscle tissue and cell culture in vitro enhances the validity of methods used to evaluate the biocompatibility of dental materials. These methods may be used to test the toxicity of various materials. Nevertheless, for a more complete evaluation of these materials, the allergenicity and carcinogenicity potential of these products should be evaluated, prior to the final verdict as to their biocompatibility.