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.

Beyond lectures and practical courses: Teaching pharmacology using imaginative pedagogical tools

Pharmacology has broadened its scope considerably in recent decades. Initially, it was of interest to chemists, doctors and pharmacists. In recent years, however, it has been incorporated into the teaching of biologists, molecular biologists, biotechnologists, chemical engineers and many health professionals, among others. Traditional teaching methods, such as lectures or laboratory work, have been superseded by the use of new pedagogical approaches to enable a better conceptualization and understanding of the discipline. In this article, we present several new methods that have been used in Spanish universities. Firstly, we describe a teaching network that has allowed the sharing of pedagogical innovations in Spanish universities. A European experience to improve prescribing safety is described in detail. The use of popular films and medical TV series in biomedical students shows how these audiovisual resources can be helpful in teaching pharmacology. The use of virtual worlds is detailed to introduce this new approach to teaching. The increasingly important area of the social aspects of pharmacology is also considered in two sections, one devoted to social pharmacology and the other to the use of learning based on social services to improve understanding of this important area. Finally, the use of Objective Structured Clinical Evaluation in pharmacology allows to know how this approach can help to better evaluate clinical pharmacology students. In conclusion, this article allows to know new pedagogical methods resources used in some Spanish universities that may help to improve the teaching of pharmacology.

Growth rate of CO2 and CH4 hydrates by means of molecular dynamics simulations

CO2 and CH4 hydrates are of great importance both from an energetic and from an environmental point of view. It is therefore highly relevant to quantify and understand the rate with which they grow. We use molecular dynamics simulations to shed light on the growth rate of these hydrates. We put the solid hydrate phase in contact with a guest aqueous solution in equilibrium with the pure guest phase and study the growth of both hydrates at 400 bars with temperature. We compare our results with previous calculations of the ice growth rate. We find a growth rate maximum as a function of the supercooling in all cases. The incorporation of guest molecules into the solid structure strongly decelerates hydrate growth. Consistently, ice grows faster than either hydrate and the CO2 hydrate grows faster than the CH4 one because of the higher solubility of CO2. We also quantify the molecular motion required to build the solids under study and find that the distance traveled by liquid molecules exceeds by orders of magnitude that advanced by any solid. Less molecular motion is needed in order for ice to grow as compared to the hydrates. Moreover, when temperature increases, more motion is needed for solid growth. Finally, we find a good agreement between our growth rate calculations and experiments of hydrate growth along the guest-solution interface. However, more work is needed to reconcile experiments of hydrate growth toward the solution among each other and with simulations.

Homogeneous nucleation rate of methane hydrate formation under experimental conditions from seeding simulations

In this work, we shall estimate via computer simulations the homogeneous nucleation rate for the methane hydrate at 400 bars for a supercooling of about 35 K. The TIP4P/ICE model and a Lennard-Jones center were used for water and methane, respectively. To estimate the nucleation rate, the seeding technique was employed. Clusters of the methane hydrate of different sizes were inserted into the aqueous phase of a two-phase gas-liquid equilibrium system at 260 K and 400 bars. Using these systems, we determined the size at which the cluster of the hydrate is critical (i.e., it has 50% probability of either growing or melting). Since nucleation rates estimated from the seeding technique are sensitive to the choice of the order parameter used to determine the size of the cluster of the solid, we considered several possibilities. We performed brute force simulations of an aqueous solution of methane in water in which the concentration of methane was several times higher than the equilibrium concentration (i.e., the solution was supersaturated). From brute force runs, we infer the value of the nucleation rate for this system rigorously. Subsequently, seeding runs were carried out for this system, and it was found that only two of the considered order parameters were able to reproduce the value of the nucleation rate obtained from brute force simulations. By using these two order parameters, we estimated the nucleation rate under experimental conditions (400 bars and 260 K) to be of the order of log₁₀ (J/(m³ s)) = -7(5).

Homogeneous nucleation of NaCl in supersaturated solutions

The seeding method is an approximate approach to investigate nucleation that combines molecular dynamics simulations with classical nucleation theory. Recently, this technique has been successfully implemented in a broad range of nucleation studies. However, its accuracy is subject to the arbitrary choice of the order parameter threshold used to distinguish liquid-like from solid-like molecules. We revisit here the crystallization of NaCl from a supersaturated brine solution and show that consistency between seeding and rigorous methods, like Forward Flux Sampling (from previous work) or spontaneous crystallization (from this work), is achieved by following a mislabelling criterion to select such threshold (i.e. equaling the fraction of the mislabelled particles in the bulk parent and nucleating phases). This work supports the use of seeding to obtain fast and reasonably accurate nucleation rate estimates and the mislabelling criterion as one giving the relevant cluster size for classical nucleation theory in crystallization studies.

Mortality risk in cardiogenic shock depending on aetiology in a Mediterranean cohort. Prognostic accuracy of CardShock vs IABP score: the Shock CAT study

Background

Mortality in cardiogenic shock (CS) remains very high. Several risk scores have been purposed to early stratification, although the CS aetiology could influence in this prediction.

Purpose

The aim is to investigate in-hospital prognosis and mortality risk in CS patients depending on the CS aetiology comparing the prognostic accuracy of CardShock and IABP scores in a Mediterranean cohort.

Method

Shock CAT study was a multicentre, prospective, observational study conducted between December 2018 and December 2019 in eight public University hospitals in Catalonia (Spain), including CS patients due to acute coronary syndrome (ACS) and other aetiologies. Data on clinical presentation, biomarkers, management, including mechanical assistance support were analyzed comparing ACS and non-ACS patients. Cardshock and IABP score have been compared to assess 90-days mortality risk in both groups.

Results

A total of 382 CS patients were included, mean age was 65.3 (SD 13.9) years and 75.1% were men. Patient were classified in ACS (n=232, 60.7%) and non-ACS (n=150, 39.3%). In ACS group, 77.6% were STEMI, reperfussion in 84.7% of cases, all with primary angioplasty, 9% developed mechanical complications and 19.4% primary ventricular fibrillation. Main non-ACS aetiologies were severe heart failure (36.2%), malignant arrhythmias (22.1%), valve disease (8.0%) and myocarditis (7.4%). ACS group had less prevalence of women (17.7% vs 36%, p=0.001) and previous myocardial infarction (13.9% vs 24.8%, p=0.007). Mechanical assistance device was implanted more in ACS patients (43.1% vs 16.7%, p<0.001, mainly intraaortic balloon pump (35.6% vs 9.8%, p<0.001) and ECMO (10.7% vs 3%, p=0.01). Both shock risk scores were higher in ACS patients, Cardshock (4.5 vs 4.0, p=0.006) and IABP (2.4 vs 1.9, p=0.005). In-hospital mortality was higher in ACS (37.1 vs 26.7%, p=0.035) although this difference loss the significance at 90-days (40.9 vs 31.8%, p=0.074) and 6-months (45.2 vs 35.8%, p=0.176). Receiver-operating characteristic curves demonstrated that IABP shock score had superior prognostic power for predicting 90-days mortality when compared with Cardshock score in ACS patients (area under the curve -AUC- 0.74 vs 0.66) respectively, p=0.047, although both scores were similar in non-ACS (AUC 0.64 vs 0.62, p=0.693), Figures 1–2.

Conclusions

Cardiogenic shock due to ACS had higher in-hospital mortality than non-ACS CS, although this difference decreased at 90 days and 6 months. IABP score provided better 90-days mortality risk prediction than CardShock score in ACS patients, but both scores are similar in non-ACS cardiogenic shock.

Funding Acknowledgement

Type of funding sources: None. Figure 1Figure 2

Mortality risk in cardiogenic shock: head to head comparision CardShock vs IABP score in a Mediterranean cohort: the Shock CAT study

Background

Mortality in cardiogenic shock (CS) remains very high. Several risk scores have been purposed to early stratification.

Purpose

The aim is to investigate in-hospital prognosis and mortality risk in CS patients comparing the prognostic accuracy of CardShock and IABP scores in a Mediterranean cohort.

Method

Shock CAT study was a multicentre, prospective, observational study conducted between December 2018 and December 2019 in eight public University hospitals in Catalonia (Spain), including CS patients due to acute coronary syndrome (ACS) and other aetiologies. Data on clinical presentation, biomarkers, management, including mechanical assistance support were analyzed. Cardshock and IABP score have been compared to assess 90-days mortality risk in a Mediterranean cohort.

Results

A total of 382 CS patients were included, mean age was 65.3 (SD 13.9) years and 75.1% were men. The most common cause of CS was ACS (61%, n=233); of them, 77.6% were STEMI, 9% developed mechanical complications and 19.4% primary ventricular fibrillation. STEMI patients were reperfused in 84.7% of cases, all with primary angioplasty. Main non-ACS aetiologies were severe acute heart failure, malignant arrhythmias and myocarditis. Mechanical assistance device was implanted in one third of patients (n=119), mainly intraaortic balloon pump (26.1%), ECMO in 7.8% and Impella in 4.5%. Average Cardshock score was 4.3 (SD 1.74) and mean IABP score was 2.2 (SD 1.61). In-hospital mortality was 33% (126 patients) and 90-days mortality was 37.3% (141 patients). Receiver-operating characteristic curves demonstrated that IABP shock score had superior prognostic power for predicting 90-days mortality when compared with Cardshock score (area under the curve 0.72 vs 0.66) respectively, p=0.042; Figure 1.

Conclusions

Even though invasive management with STEMI reperfusion and mechanical assistance devices, cardiogenic shock in-hospital mortality remains 33% in a contemporary Mediterranean cohort. In this population, IABP shock score provided better 90-days mortality risk prediction than CardShock score

Funding Acknowledgement

Type of funding sources: None.

Generalized Structure Functions and Multifractal Detrended Fluctuation Analysis Applied to Vegetation Index Time Series: An Arid Rangeland Study

Estimates suggest that more than 70% of the world’s rangelands are degraded. The Normalized Difference Vegetation Index (NDVI) is commonly used by ecologists and agriculturalists to monitor vegetation and contribute to more sustainable rangeland management. This paper aims to explore the scaling character of NDVI and NDVI anomaly (NDVIa) time series by applying three fractal analyses: generalized structure function (GSF), multifractal detrended fluctuation analysis (MF-DFA), and Hurst index (HI). The study was conducted in four study areas in Southeastern Spain. Results suggest a multifractal character influenced by different land uses and spatial diversity. MF-DFA indicated an antipersistent character in study areas, while GSF and HI results indicated a persistent character. Different behaviors of generalized Hurst and scaling exponents were found between herbaceous and tree dominated areas. MF-DFA and surrogate and shuffle series allow us to study multifractal sources, reflecting the importance of long-range correlations in these areas. Two types of long-range correlation appear to be in place due to short-term memory reflecting seasonality and longer-term memory based on a time scale of a year or longer. The comparison of these series also provides us with a differentiating profile to distinguish among our four study areas that can improve land use and risk management in arid rangelands.

Equivalence between condensation and boiling in a Lennard-Jones fluid

Condensation and boiling are phase transitions highly relevant to industry, geology, and atmospheric science. These phase transitions are initiated by the nucleation of a drop in a supersaturated vapor and of a bubble in an overstretched liquid, respectively. The surface tension between both phases, liquid and vapor, is a key parameter in the development of such nucleation stage. Whereas the surface tension can be readily measured for a flat interface, there are technical and conceptual limitations to obtain it for the curved interface of the nucleus. On the technical side, it is quite difficult to observe a critical nucleus in experiments. From a conceptual point of view, the interfacial free energy depends on the choice of the dividing surface, being the surface of tension the one relevant for nucleation. We bypass the technical limitation by performing simulations of a Lennard-Jones fluid where we equilibrate critical nuclei (both drops and bubbles). Regarding the conceptual hurdle, we find the relevant cluster size by searching the radius that correctly predicts nucleation rates and nucleation free energy barriers when combined with Classical Nucleation Theory. With such definition of the cluster size we find the same value of the surface tension for drops and bubbles of a given radius. Thus, condensation and boiling can be viewed as two sides of the same coin. Finally, we combine the data coming from drops and bubbles to obtain, via two different routes, estimates of the Tolman length, a parameter that allows describing the curvature dependence of the surface tension in a theoretical framework.

[COVID-19 Pandemic: Impact and rapid reaction of Urology]

The COVID-19 pandemic caused by the SARS-CoV-2 virus has caused tens of thousands of deaths in Spain and has managed to breakdown the healthcare system hospitals in the Community of Madrid, largely due to its tendency to cause severe pneumonia, requiring ventilatory support. This fact has caused our center to collapse, with 130% of its beds occupied by COVID-19 patients, thus causing the absolute cessation of activity of the urology service, the practical disappearance of resident training programs, and the incorporation of a good part of the urology staff into the group of medical personnel attending these patients. In order to recover from this extraordinary level of suspended activity, we will be obliged to prioritize pathologies based on purely clinical criteria, for which tables including the relevance of each pathology within each area of urology are being proposed. Technology tools such as online training courses or surgical simulators may be convenient for the necessary reestablishment of resident education.

Necesidades de información en las empresas: estudio de un caso

El estudio de las necesidades de información en las empresas es una tarea compleja y urgente que se está acometiendo desde distintas vertientes, con el fin de ir completando el conocimiento que se tiene de este tipo de usuario de información. En este sentido, en el trabajo se estudian las necesidades de información de las empresas norteamericanas del estado de Indiana, a partir de una serie de entrevistas con responsables de centros de información y servicios de desarrollo, que atendían las distintas demandas de las empresas. Asimismo, en el trabajo se ha utilizado una encuesta realizada por la Universidad del Estado de Indiana sobre el uso y los tipos de información más demandados por las empresas.

Seeding approach to nucleation in the NVT ensemble: The case of bubble cavitation in overstretched Lennard Jones fluids

Simulations are widely used to study nucleation in first order phase transitions due to the fact that they have access to the relevant length and time scales. However, simulations face the problem that nucleation is an activated process. Therefore, rare event simulation techniques are needed to promote the formation of the critical nucleus. The Seeding method, where the simulations are started with the nucleus already formed, has proven quite useful in efficiently providing estimates of the nucleation rate for a wide range of orders of magnitude. So far, Seeding has been employed in the NPT ensemble, where the nucleus either grows or redissolves. Thus, several trajectories have to be run in order to find the thermodynamic conditions that make the seeded nucleus critical. Moreover, the nucleus lifetime is short and the statistics for obtaining its properties is consequently poor. To deal with these shortcomings we extend the Seeding method to the NVT ensemble. We focus on the problem of bubble nucleation in a metastable Lennard Jones fluid. We show that, in the NVT ensemble, it is possible to equilibrate and stabilise critical bubbles for a long time. The nucleation rate inferred from NVT-Seeding is fully consistent with that coming from NPT-Seeding. The former is quite suitable to obtain the nucleation rate along isotherms, whereas the latter is preferable if the dependence of the rate with temperature at constant pressure is required. Care should be taken with finite size effects when using NVT-Seeding. Further work is required to extend NVT seeding to other sorts of phase transitions.

Seeding approach to bubble nucleation in superheated Lennard-Jones fluids

We investigate vapor homogeneous nucleation in a superheated Lennard-Jones liquid with computer simulations. Special simulation techniques are required to address this study since the nucleation of a critical vapor bubble-one that has an equal chance to grow or shrink-in a moderately superheated liquid is a rare event. We use the Seeding method, which combines Classical Nucleation Theory with computer simulations of a liquid containing a vapor bubble to provide bubble nucleation rates in a wide temperature range. Seeding has been successfully applied to investigate the nucleation of crystals in supercooled fluids, and here we apply it to the liquid-to-vapor transition. We find that the Seeding method provides nucleation rates that are consistent with independent calculations not based on the assumptions of Classical Nucleation Theory. Different criteria to determine the radius of the critical bubble give different rate values. The accuracy of each criterion depends of the degree of superheating. Moreover, seeding simulations show that the surface tension depends on pressure for a given temperature. Therefore, using Classical Nucleation Theory with the coexistence surface tension does not provide good estimates of the nucleation rate.

On the time required to freeze water

By using the seeding technique the nucleation rate for the formation of ice at room pressure will be estimated for the TIP4P/ICE model using longer runs and a smaller grid of temperatures than in the previous work. The growth rate of ice will be determined for TIP4P/ICE and for the mW model of water. Although TIP4P/ICE and mW have a similar melting point and melting enthalpy, they differ significantly in the dynamics of freezing. The nucleation rate of mW is lower than that of TIP4P/ICE due to its higher interfacial free energy. Experimental results for the nucleation rate of ice are between the predictions of these two models when obtained from the seeding technique, although closer to the predictions of TIP4P/ICE. The growth rate of ice for the mW model is four orders of magnitude larger than for TIP4P/ICE. Avrami's expression is used to estimate the crystallization time from the values of the nucleation and growth rates. For mW the minimum in the crystallization time is found at approximately 85 K below the melting point and its value is of about a few ns, in agreement with the results obtained from brute force simulations by Moore and Molinero. For the TIP4P/ICE the minimum is found at about 55 K below the melting point, but its value is about ten microseconds. This value is compatible with the minimum cooling rate required to avoid the formation of ice and obtaining a glass phase. The crossover from the nucleation controlled crystallization to the growth controlled crystallization will be discussed for systems of finite size. This crossover could explain the apparent discrepancy between the values of J obtained by different experimental groups for temperatures below 230 K and should be considered as an alternative hypothesis to the two previously suggested: internal pressure and/or surface freezing effects. A maximum in the compressibility was found for the TIP4P/ICE model in supercooled water. The relaxation time is much smaller than the crystallization time at the temperature at which this maximum occurs, so this maximum is a real thermodynamic feature of the model. At the temperature of minimum crystallization time, the crystallization time is larger than the relaxation time by just two orders of magnitude.

The function of national journals in disseminating applied science

This paper considers the problem of national versus inter national journals. The practice in certain countries of giving 'recognition' only to Science Citation Index journals, per se, does a disservice to national journals. These journals serve an important role in local diffusion of applied infor mation. Sixty papers were studied: half published in a local Spanish journal and the other half in international journals. They were written by the same groups of researchers. Indicators designed to discriminate the type of research published in both sets were used. The analysis indicated that the type of research published in the Spanish journals is applied, whereas that published abroad is basic. Apparently, the Spanish journal is nearer to the industrial sector. However, to disregard the local journal for evalua tive purposes may be a disservice to scientists who are trying to help in the transfer of information to the indus trial sector.

The mold integration method for the calculation of the crystal-fluid interfacial free energy from simulations

The interfacial free energy between a crystal and a fluid, γcf, is a highly relevant parameter in phenomena such as wetting or crystal nucleation and growth. Due to the difficulty of measuring γcf experimentally, computer simulations are often used to study the crystal-fluid interface. Here, we present a novel simulation methodology for the calculation of γcf. The methodology consists in using a mold composed of potential energy wells to induce the formation of a crystal slab in the fluid at coexistence conditions. This induction is done along a reversible pathway along which the free energy difference between the initial and the final states is obtained by means of thermodynamic integration. The structure of the mold is given by that of the crystal lattice planes, which allows to easily obtain the free energy for different crystal orientations. The method is validated by calculating γcf for previously studied systems, namely, the hard spheres and the Lennard-Jones systems. Our results for the latter show that the method is accurate enough to deal with the anisotropy of γcf with respect to the crystal orientation. We also calculate γcf for a recently proposed continuous version of the hard sphere potential and obtain the same γcf as for the pure hard sphere system. The method can be implemented both in Monte Carlo and Molecular Dynamics. In fact, we show that it can be easily used in combination with the popular Molecular Dynamics package GROMACS.

Field-induced sublimation in perfect two-dimensional colloidal crystals

Phase transitions in two-dimensional (2D) systems are of considerable fundamental and practical importance. However, the kinetics of these processes are difficult to predict and understand, even in simple systems for which equilibrium states are properly described, owing to the difficulty of studying crystallites with single-particle resolution and free of defects. Here we introduce an alternative method for the sublimation of 2D colloidal crystallites by a sudden induction of repulsive forces between the particles. The sublimation kinetics, studied in real space by microscopy and by computer simulations, shows a scaling behavior that suggests a universal mechanism fundamentally different from the one usually accepted for thermal sublimation. The universal behavior found for the early stages of the process may be useful for understanding the dynamic features of particle systems at liquid interfaces and for designing technological applications without the need of performing extensive experimental studies.

Species differentiation of slipper orchids using color image analysis

Una gran cantidad de sistemas de reconocimiento automático de especies se han desarrollado en los últimos años, como ayuda a aquellas personas que no son especialistas en la identificación de especies. Estos sistemas han utilizado sistemas de reconocimiento automático basados en geometría morfométrica, sin embargo existen límites debido a la necesidad de encontrar puntos de georreferenciación en los diferentes organismos. En este artículo investigamos el uso de los colores para diferenciar especies en los géneros Paphiopedilum y Phragmipedium, ambos con gran importancia en la horticultura. La capacidad de discriminación varía entre los grupos taxonómicos, dependiendo del tamaño del taxón, la variedad de colores entre las especies y el fondo de las imágenes. En este estudio el análisis de imágenes se ha llevado a cabo con fotografías de flores individuales. No obstante dado que las flores son órganos efímeros, en el futuro esta investigación incluirá partes vegetativas, ya que es en estado vegetativo la forma en la que se suele comerciar internacionalmente más a menudo.

[Steps towards the institutionalization of health impact assessment in Spain: perception of public health professionals]

BACKGROUND

The current normative reform of public health policy in Spain envisages the inclusion of Health Impact Assessment (HIA). This study contributes the vision of public health and planning professionals on the usefulness and applicability of HIA in their daily work and thus reflects on how best to institutionalize it.

METHODOLOGY

Three training workshop were carried out with public health professionals. Participants were specialists in different branches: epidemiological surveillance, environmental health, food safety and health promotion. In this HIA workshop, a questionnaire was given to the attendees to be completed.

RESULTS

Forty-one percent of the people attending answered the questionnaire; 92% of the staff considered that the model of social determinants of health is useful in the field of public health. The principal routes for introducing HIA were: mandatory rules (85%), integration into other existing assessment tools (65%) and the systematization of this methodology (40%). Concerning the applicability of HIA, specific strategies ere proposed for its introduction into the different branches of public health.

CONCLUSIONS

The successful institutionalization of HIA will require the opinion and collaboration of the technical personnel. A widespread approval of this tool for its utilization in the administration was verified. To guarantee the viability of its implementation, it will be necessary to raise the awareness of professionals about the model of the social determinants of health, as well as to attend to their demands and suggestions.

Cytological features of ossifying fibromyxoid tumor of soft parts

A case of ossifying fibromyxoid tumor (OFMT) evaluated during an intraoperative pathological consultation is presented. The patient, a 70-year-old woman was being followed because of a tumor in the left buttock. Cytological smears were obtained after scrapping the tumoral cut surface and revealed a myxoid background with fragments composed of a denser, fibrillar metachromatic stroma with accompanying round to oval tumoral nuclei and no vessels. Single cells were predominantly monomorphic with a round to oval morphology and scarce cytoplasm. The most relevant feature of the tumor was its peripheral, plaque-like, calcified consistency. The review of the cytological descriptions of four cases revealed similar findings that can be presumed as those of a low-grade myxoid tumor of round to oval cells. A specific recognition of OFMT based solely on cytological features seems difficult. However, when such features are coupled with characteristic radiological findings (peripheral calcification) this entity must be considered.

Crystallization and aging in hard-sphere glasses

We report new results from our programme of molecular dynamics simulation of hard-sphere systems, focusing on crystallization and glass formation at high concentrations. First we consider a much larger system than hitherto, N = 86 400 equal-sized particles. The results are similar to those obtained with a smaller system, studied previously, showing conventional nucleation and growth of crystals at concentrations near melting and crossing over to a spinodal-like regime at higher concentrations where the free energy barrier to nucleation appears to be negligible. Second, we investigate the dependence on the initial state of the system. We have devised a Monte Carlo 'constrained aging' method to move the particles in such a way that crystallization is discouraged. After a period of such aging, the standard molecular dynamics programme is run. For a system of N = 3200, we find that constrained aging encourages caging of the particles and slows crystallization somewhat. Nevertheless, both aged and unaged systems crystallize at volume fraction φ = 0.61 whereas neither system shows full crystallization in the duration of the simulation at φ = 0.62, a concentration still significantly below that of random close packing.

Patterns of corpora lutea growth and progesterone secretion in sows with thrifty genotype and leptin resistance due to leptin receptor gene polymorphisms (Iberian pig)

The current study aimed to compare luteal function, as measured by corpora lutea dynamics and progesterone secretion, in 10 sows with obesity/leptin resistance genotype (Iberian pig) and 10 females of lean commercial crosses (Large White × Landrace). In all the animals, the oestrous cycle was synchronized with progestagens, and ovulation was induced by exogenous gonadotrophins. Thereafter, number and size of follicles and plasma oestradiol concentration were determined at oestrus detection, and number and size of corpora lutea and progesterone concentration were evaluated from Day 4 to 12 of the cycle. There were no differences between genotypes in follicle population and oestradiol concentration, and ovulation rate (15.2±1.3 in Iberian vs 12.7±1.8 in LWxL sows); however, there was a higher percentage of Iberian than control sows showing luteal cysts (66.7% vs 30%, respectively; p<0.05). In both breeds, both total luteal area and plasma progesterone concentration grew linearly from Day 4 to 8 (p<0.01) and remained more stable between Days 8 and 12, without significant differences between genotypes. In conclusion, current study supports that ovulatory processes and luteal functionality are not the main limiting factors for prolificacy in a pig model of leptin resistance and obesity.

Preovulatory follicle dynamics and ovulatory efficiency in sows with thrifty genotype and leptin resistance due to leptin receptor gene polymorphisms (Iberian pig)

This study compares follicular function and ovulatory efficiency in 20 sows with obesity/leptin resistance genotype (Iberian pig) and 20 females of lean commercial crosses (Large White × Landrace; LW×L). Estrous cycle was synchronized with progestagens; ovulation was induced with eCG and hCG, in half of the females of each group, to determine its effect. In females of both breeds not treated with gonadotropins, the number of follicles larger than 4.9 mm and the estradiol secretion increased throughout the follicular phase (P<0.05); estradiol values were similar at estrus detection (22.5±1.2 vs. 26.5±0.6 pg/ml respectively, for Iberian and LW×L sows). Moreover, ovulation rate was higher in Iberian pigs (15.3±1.3 CLs) than in LW×L (10.2±1.3 CLs; P<0.05), with mean progesterone values being 18.1±0.7 ng/ml in Iberian and 16.8±0.6 ng/ml in LW×L pigs. Thus, the preovulatory follicular growth and the ovulatory efficiency seem not to be the main limiting factors for reproductive efficiency in Iberian swine. The gonadotropins induced a significant increase, when compared to untreated females (P<0.05), in the number of follicles larger than 4.9 mm growing throughout the follicular phase; however, estradiol values at estrus were lower (P<0.05) in both breeds (9.2±0.7 pg/ml in Iberian vs. 8.6±0.8 pg/ml in LW×L), when compared with the nontreated animals, which suggests defective follicular function after gonadotropin stimulation. There were also no differences between genotypes in ovulation rate (15.2±1.3 vs. 12.7±1.8) and progesterone secretion (21.2±0.8 ng/ml in Iberian and 20.9±0.7 ng/ml in LW×L sows) in the treated animals. In conclusion, the current findings indicate that preovulatory follicular growth and ovulatory efficiency are not main limiting factors for prolificacy in a pig model of leptin resistance and obesity.

Hard spheres: crystallization and glass formation

Motivated by old experiments on colloidal suspensions, we report molecular dynamics simulations of assemblies of hard spheres, addressing crystallization and glass formation. The simulations cover wide ranges of polydispersity s (standard deviation of the particle size distribution divided by its mean) and particle concentration. No crystallization is observed for s>0.07. For 0.02<s<0.07, we find that increasing the polydispersity at a given concentration slows down crystal nucleation. The main effect here is that polydispersity reduces the supersaturation since it tends to stabilize the fluid but to destabilize the crystal. At a given polydispersity (<0.07), we find three regimes of nucleation: standard nucleation and growth at concentrations in and slightly above the coexistence region; 'spinodal nucleation', where the free-energy barrier to nucleation appears to be negligible, at intermediate concentrations; and, at the highest concentrations, a new mechanism, still to be fully understood, which only requires small rearrangement of the particle positions. The cross-over between the second and third regimes occurs at a concentration, approximately 58 per cent by volume, where the colloid experiments show a marked change in the nature of the crystals formed and the particle dynamics indicate an 'ideal' glass transition.

Crystallization of hard-sphere glasses

We study by molecular dynamics the interplay between arrest and crystallization in hard spheres. For state points in the plane of volume fraction (0.54 <or= varphi <or= 0.63) and polydispersity (0 <or= s <or= 0.085), we delineate states that spontaneously crystallize from those that do not. For noncrystallizing (or precrystallization) samples we find isodiffusivity lines consistent with an ideal glass transition at varphi_{g} approximately 0.585, independent of s. Despite this, for s < 0.05, crystallization occurs at varphi > varphi_{g}. This happens on time scales for which the system is aging, and a diffusive regime in the mean square displacement is not reached; by those criteria, the system is a glass. Hence, contrary to a widespread assumption in the colloid literature, the occurrence of spontaneous crystallization within a bulk amorphous state does not prove that this state was an ergodic fluid rather than a glass.

Irreducible finite-size effects in the surface free energy of NaCl crystals from crystal-nucleation data

In this Letter we report a simulation study in which we compare the solid-liquid interfacial free energy of NaCl at coexistence, gamma_{LS}, with the value that follows from the height of the homogeneous nucleation barrier. The two estimates differ by more than 100%. Smaller discrepancies are found for gamma_{LS} of hard-sphere and of Lennard-Jones particles. We consider a variety of possible causes for this discrepancy and conclude that it is due to a finite-size effect that cannot be corrected for by any simple thermodynamic procedure. By taking into account the finite-size effects of gamma_{LS} obtained in real nucleation experiments, we obtain quantitative agreement between gamma_{LS} estimated in the simulations and derived from the experiments. Our finding suggests that most published solid-liquid surface free energies derived from nucleation experiments will have to be revised.

Arsenic speciation in rice, straw, soil, hair and nails samples from the arsenic-affected areas of Middle and Lower Ganga plain

In the present study, pressurised liquid extraction and ultrasound probe sonication, for the latter in combination with a mixed enzymatic treatment in case of rice and straw samples, were applied as sample preparation prior to arsenic speciation analysis by high pressure liquid chromatography coupled to inductively coupled plasma mass spectrometric detection (HPLC-ICP-MS). A significant number of samples as different as rice, straw, soil, nail and hair, all coming from the heavily arsenic-contaminated Middle and Lower Ganga plain area, could be investigated with validated methods, supported by high speed extraction methods. For rice and paddy samples, inorganic arsenic counted up to 70-98% of the total arsenic content, being the major species As (III). The levels of arsenic obtained from straw and soil samples are significantly higher than the background levels, being the major species As (V), thus increasing human exposure to arsenic via the soil-plant-animal-human pathway. Concentrations found in hair and nails were significantly higher than their background levels: 39- and 20-fold for hair and nails, respectively. These samples contained mainly inorganic arsenic in its tri- and pentavalent forms. Results indicate that, under the local frame conditions, arsenic mainly enters into the food chain via its more problematic inorganic forms. Arsenic speciation analysis proves to be a powerful tool for a complete analytical assessment in epidemiological studies covering the endemic areas.