Ice growth rate: Temperature dependence and effect of heat dissipation.

The transformation of liquid water into solid ice is arguably the most important phase transition on Earth. A key aspect of such transformation is the speed with which ice grows once it is nucleated. There are contradictory experimental results as to whether the ice growth rate shows a maximum on cooling. Previous simulation results point to the existence of such a maximum. However, simulations were performed at constant temperature with the aid of a thermostat that dissipates the heat released at the ice-water interface unrealistically fast. Here, we perform simulations of ice growth without any thermostat. Large systems are required to perform these simulations at constant overall thermodynamic conditions (pressure and temperature). We obtain the same growth rate as in previous thermostatted simulations. This implies that the dynamics of ice growth is not affected by heat dissipation. Our results strongly support the experiments predicting the existence of a maximum in the ice growth rate. By using the Wilson-Frenkel kinetic theory, we argue that such maximum is due to a competition between an increasing crystallization thermodynamic driving force and a decreasing molecular mobility on cooling.

Cosmological Signature of the Standard Model Higgs Vacuum Instability: Primordial Black Holes as Dark Matter.

For the current central values of the Higgs boson and top quark masses, the standard model Higgs potential develops an instability at a scale of the order of 10^{11} GeV. We show that a cosmological signature of such instability could be dark matter in the form of primordial black holes seeded by Higgs fluctuations during inflation. The existence of dark matter might not require physics beyond the standard model.

Cosmological implications of Higgs near-criticality.

The Standard Model electroweak (EW) vacuum, in the absence of new physics below the Planck scale, lies very close to the boundary between stability and metastability, with the last option being the most probable. Several cosmological implications of this so-called 'near-criticality' are discussed. In the metastable vacuum case, the main challenges that the survival of the EW vacuum faces during the evolution of the Universe are analysed. In the stable vacuum case, the possibility of implementing Higgs inflation is critically examined.This article is part of the Theo Murphy meeting issue 'Higgs cosmology'.

Primordial black holes from Higgs vacuum instability: avoiding fine-tuning through an ultraviolet safe mechanism.

We have recently proposed the idea that dark matter in our universe is formed by primordial black holes generated by Standard Model Higgs fluctuations during inflation and thanks to the fact that the Standard Model Higgs potential develops an instability at a scale of the order of 10 11 GeV. In this sense, dark matter does not need any physics beyond the Standard Model, although the mechanism needs fine-tuning to avoid the overshooting of the Higgs into the dangerous AdS vacuum. We show how such fine-tuning can be naturally avoided by coupling the Higgs to a very heavy scalar with mass ≫ 10 11 GeV that stabilises the potential in the deep ultraviolet, but preserving the basic feature of the mechanism which is built within the Standard Model.

A potential model for sodium chloride solutions based on the TIP4P/2005 water model.

Despite considerable efforts over more than two decades, our knowledge of the interactions in electrolyte solutions is not yet satisfactory. Not even one of the most simple and important aqueous solutions, NaCl(aq), escapes this assertion. A requisite for the development of a force field for any water solution is the availability of a good model for water. Despite the fact that TIP4P/2005 seems to fulfill the requirement, little work has been devoted to build a force field based on TIP4P/2005. In this work, we try to fill this gap for NaCl(aq). After unsuccessful attempts to produce accurate predictions for a wide range of properties using unity ionic charges, we decided to follow recent suggestions indicating that the charges should be scaled in the ionic solution. In this way, we have been able to develop a satisfactory non-polarizable force field for NaCl(aq). We evaluate a number of thermodynamic properties of the solution (equation of state, maximum in density, enthalpies of solution, activity coefficients, radial distribution functions, solubility, surface tension, diffusion coefficients, and viscosity). Overall the results for the solution are very good. An important achievement of our model is that it also accounts for the dynamical properties of the solution, a test for which the force fields so far proposed failed. The same is true for the solubility and for the maximum in density where the model describes the experimental results almost quantitatively. The price to pay is that the model is not so good at describing NaCl in the solid phase, although the results for several properties (density and melting temperature) are still acceptable. We conclude that the scaling of the charges improves the overall description of NaCl aqueous solutions when the polarization is not included.

On the calculation of solubilities via direct coexistence simulations: Investigation of NaCl aqueous solutions and Lennard-Jones binary mixtures.

Direct coexistence molecular dynamics simulations of NaCl solutions and Lennard-Jones binary mixtures were performed to explore the origin of reported discrepancies between solubilities obtained by direct interfacial simulations and values obtained from the chemical potentials of the crystal and solution phases. We find that the key cause of these discrepancies is the use of crystal slabs of insufficient width to eliminate finite-size effects. We observe that for NaCl crystal slabs thicker than 4 nm (in the direction perpendicular to the interface), the same solubility values are obtained from the direct coexistence and chemical potential routes, namely, 3.7 ± 0.2 molal at T = 298.15 K and p = 1 bar for the JC-SPC/E model. Such finite-size effects are absent in the Lennard-Jones system and are likely caused by surface dipoles present in the salt crystals. We confirmed that µs-long molecular dynamics runs are required to obtain reliable solubility values from direct coexistence calculations, provided that the initial solution conditions are near the equilibrium solubility values; even longer runs are needed for equilibration of significantly different concentrations. We do not observe any effects of the exposed crystal face on the solubility values or equilibration times. For both the NaCl and Lennard-Jones systems, the use of a spherical crystallite embedded in the solution leads to significantly higher apparent solubility values relative to the flat-interface direct coexistence calculations and the chemical potential values. Our results have broad implications for the determination of solubilities of molecular models of ionic systems.

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.

Cosmological Higgs-Axion Interplay for a Naturally Small Electroweak Scale.

Recently, a new mechanism to generate a naturally small electroweak scale has been proposed. It exploits the coupling of the Higgs boson to an axionlike field and a long era in the early Universe where the axion unchains a dynamical screening of the Higgs mass. We present a new realization of this idea with the new feature that it leaves no sign of new physics at the electroweak scale, and up to a rather large scale, 10^{9} GeV, except for two very light and weakly coupled axionlike states. One of the scalars can be a viable dark matter candidate. Such a cosmological Higgs-axion interplay could be tested with a number of experimental strategies.

Homogeneous ice nucleation evaluated for several water models.

In this work, we evaluate by means of computer simulations the rate for ice homogeneous nucleation for several water models such as TIP4P, TIP4P/2005,TIP4P/ICE, and mW (following the same procedure as in Sanz et al. [J. Am. Chem. Soc. 135, 15008 (2013)]) in a broad temperature range. We estimate the ice-liquid interfacial free-energy, and conclude that for all water models γ decreases as the temperature decreases. Extrapolating our results to the melting temperature, we obtain a value of the interfacial free-energy between 25 and 32 mN/m in reasonable agreement with the reported experimental values. Moreover, we observe that the values of γ depend on the chosen water model and this is a key factor when numerically evaluating nucleation rates, given that the kinetic prefactor is quite similar for all water models with the exception of the mW (due to the absence of hydrogens). Somewhat surprisingly the estimates of the nucleation rates found in this work for TIP4P/2005 are slightly higher than those of the mW model, even though the former has explicit hydrogens. Our results suggest that it may be possible to observe in computer simulations spontaneous crystallization of TIP4P/2005 at about 60 K below the melting point.

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.

Homogeneous ice nucleation at moderate supercooling from molecular simulation.

Among all of the freezing transitions, that of water into ice is probably the most relevant to biology, physics, geology, or atmospheric science. In this work, we investigate homogeneous ice nucleation by means of computer simulations. We evaluate the size of the critical cluster and the nucleation rate for temperatures ranging between 15 and 35 K below melting. We use the TIP4P/2005 and the TIP4P/ice water models. Both give similar results when compared at the same temperature difference with the model's melting temperature. The size of the critical cluster varies from ∼8000 molecules (radius = 4 nm) at 15 K below melting to ∼600 molecules (radius = 1.7 nm) at 35 K below melting. We use Classical Nucleation Theory (CNT) to estimate the ice-water interfacial free energy and the nucleation free-energy barrier. We obtain an interfacial free energy of 29(3) mN/m from an extrapolation of our results to the melting temperature. This value is in good agreement both with experimental measurements and with previous estimates from computer simulations of TIP4P-like models. Moreover, we obtain estimates of the nucleation rate from simulations of the critical cluster at the barrier top. The values we get for both models agree within statistical error with experimental measurements. At temperatures higher than 20 K below melting, we get nucleation rates slower than the appearance of a critical cluster in all water of the hydrosphere during the age of the universe. Therefore, our simulations predict that water freezing above this temperature must necessarily be heterogeneous.

Variables psicosociales y de personalidad asociadas a la cervicalgia recurrente / Psychosocial and personality variables related to recurrent cervicalgia

El objetivo del presente estudio es evaluar la relación existente entre variables de personalidad y bienestar en pacientes diagnosticados de cervicalgia. Para ello, se seleccionó una muestra de sujetos con diagnóstico y baja laboral por cervicalgia procedentes de dos mutuas de accidentes de trabajo de la ciudad de Murcia. Los resultados indican que la mitad de los sujetos de la muestra tiene una estructura de personalidad desadaptativa, con un claro perfil “neurótico”. Este perfil se caracteriza por inestabilidad emocional, escasos recursos para afrontar las situaciones de estrés y dificultades para adaptarse e implicarse activamente en el trabajo. El 61,9% de los participantes muestra una estructura de personalidad inapropiada para tener éxito laboral. Así mismo, el 49,1% perciben claramente un malestar psicológico que se focaliza en la presencia de síntomas somáticos. La presencia de sintomatología ansioso-depresiva es un indicador de mal pronóstico con relación a la duración de la baja. El perfil de personalidad “neurótica” y la presencia de cuadros depresivos se relacionan con la recurrencia de los cuadros cervicálgicos. Con respecto a la prevención, los resultados sugieren que la evaluación y el tratamiento de aspectos psicopatológicos serían importantes para reducir las bajas laborales, minimizar su duración y evitar las recurrencias

The objective of the present work is to evaluate the relationship between personality variables and wellness among patients diagnosed with cervicalgia. A sample of subjects with cervicalgia and on sick-leave was recruited from two sickness and accident insurance companies at the city of Murcia. About half of the sample showed not to have a well-adapted personality, with a clear “neurotic” profile. This profile was characterised by emotional instability, poor resources to cope with stress and difficulties to be adapted and involved into the work life. 61.9% of participants showed a personality structure non-efficient to achieve work success. In this way, 49.1% reported some psychological discomfort, which was often expressed in soma to form symptoms. Regarding the sick-leave length, the presence of anxious- depressive symptoms was an indicator of worse prognosis. The “neurotic” personality profile and the depressive symptoms were related to the neck pain recurrence. With relation to prevention, our results suggest that taking into account the evaluation and treatment of psychopathological aspects may be of help to minimize the number of sick-leaves, reduce their length and prevent their recurrence

New supersymmetric source of neutrino masses and mixings.

Conventionally, neutrino masses in a supersymmetric theory arise from nonrenormalizable lepton-number (L)-violating operators in the superpotential. The alternative possibility of having such operators in the Kähler potential as the dominant source of neutrino masses has very interesting implications and differences with respect to the standard scenario: first, the scale of L violation can be lowered dramatically; second, the renormalization of these operators has remarkable properties: in many cases it improves drastically the stability of neutrino textures against radiative corrections, while in others it makes it possible to generate radiatively large mixing angles in a natural way.

Relación entre la calidad del sueño, el burnout y el bienestar psicológico en profesionales de la seguridad ciudadana / Relation between the quality sleep, burnout and psychological well-being in policemen

La mala calidad del sueño es un síntoma que con frecuencia aparece asociado a fatiga, disminución de las capacidades cognitivas y motoras durante el día y una mayor incidencia de accidentes de tráfico y laborales. Las consecuencias de una pobre calidad del sueño tiene una relevancia especial en diversos colectivos de trabajadores, involucrados en condiciones laborales estresantes tales como: profesionales sanitarios, de la seguridad, etc. El objetivo de este estudio se centra en evaluar la calidad del sueño, el burnout y el bienestar psicológico en una muestra de policías locales, así como la posible relación de estas medidas con variables laborales, tales como turnos de trabajo, bajas laborales, etc.La información se recogió por medio de pruebas estandarizadas, tales como la Escala de Somnolencia Diurna de Epworth (ESS; Murray, 1991), el Cuestionario de Salud General (GHQ-28; Goldberg, 1970) y la Escala de Burnout de Maslach (MBI-GS; Schaufeli, 1996), así como mediante un protocolo estructurado, que recogía las principales variables sociolaborales objeto de estudio. La muestra estuvo compuesta por 252 sujetos que contestaron el protocolo. Los resultados muestran relaciones significativas entre las tres variables principales, de forma que los sujetos con más problemas de sueño presentan menor bienestar y mayor burnout. También aparecen relaciones significativas entre burnout y bienestar psicológico, de modo que quienes tienen mayor burnout presentan un menor bienestar (AU)

ACTH and prolactin deficiency.

A 35 year old woman suffering from ACTH and prolactin (Prl) deficiency is described. Her symptoms of adrenal insufficiency appeared gradually after her first pregnancy in 1970; however, she conceived twice more and delivered healthy babies in 1972 and 1974, which she could not breast feed due to lack of milk. During an episode of pneumonia in 1977 she suffered acute adrenal insufficiency, after which she began treatment with hydrocortisone. Her pituitary reserve for TSH, GH, LH and FSH was normal, but her ACTH and Prl levels were undectable and did not respond to acute iv challenges of corticotrophin-releasing factor (CRF) and TRH, respectively. Autoantibodies, including antilactotroph titres, were negative, except for a positive pituitary immunofluorescence to ACTH. There was also no ACTH stimulation to a prolonged infusion of CRF followed by an acute iv bolus. These results, together with the gradual onset of symptoms which worsened after each pregnancy, suggest a possible autoimmune aetiology of her pituitary ACTH and Prl deficiencies.