Nonperturbative semiclassical stability of de Sitter spacetime for small metric deviations

We consider the linearized semiclassical Einstein equations for small deviations around de Sitter spacetime including the vacuum polarization effects of conformal fields. Employing the method of order reduction, we find the exact solutions for general metric perturbations (of scalar, vector and tensor type). Our exact (nonperturbative) solutions show clearly that in this case de Sitter is stable with respect to small metric deviations and a late-time attractor. Furthermore, they also reveal a breakdown of perturbative solutions for a sufficiently long evolution inside the horizon. Our results are valid for any conformal theory, even self-interacting ones with arbitrarily strong coupling.

Control de trajectòries òptimes en vehicles submarins : modelització d'un vehicle submarí i estudi de la seva controlabilitat i control òptim de la trajectòria sota linearització

Es modelitza un vehicle submarí i s'estudien diferents alternatives de control sota linearització sota l'assumpció d'una geometria d'elipsoide prolat, obtenint les gràfiques de l'estat i el control en un interval de temps.

Cultivation of black truffle to promote reforestation and land-use stability

Cultivation of black truffle, Tuber melanosporum Vitt., has become an important agricultural alternative in rural Mediterranean regions due to its success in relatively harsh conditions, its high market value and diminishing production in natural areas. In addition, truffle cultivation requires relatively low agricultural inputs, promotes reforestation and economic restoration of rural lands and land-use stability. However, there remain major issues regarding the management practices to ensure successful black truffle production. We therefore conducted an experiment to evaluate 3 levels of irrigation based on monthly water deficit and the effects of currently applied weed control systems and fertilization. Treatment effects were evaluated by examining the mycorrhizal status of out-planted 1-yr-old Quercus ilex L. seedlings and seedling growth parameters after 18 months in 3 distinct experimental truffle plantations located in the foothills of the Spanish Pyrenees. We found that replacing one-half of the water deficit of the driest month (moderate irrigation) promoted the proliferation of T. melanosporum mycorrhizae, while high irrigation reduced fine root production and truffle mycorrhizae. Glyphosate weed control improved seedling survival by up to 16% over control seedlings without jeopardizing truffle mycorrhizae in the first year. Fertilization did not improve seedling growth or influence its mycorrhizal status. We describe the persistent relationship between this ectomycorrhizal fungus and Q. ilex by quantifying old and new mycorrhizae and we discuss the ecological implications of the symbiosis.

Zim17/Tim15 links mitochondrial iron–sulfur cluster biosynthesis to nuclear genome stability

Genomic instability is related to a wide-range of human diseases. Here, we show that mitochondrial iron–sulfur cluster biosynthesis is important for the maintenance of nuclear genome stability in Saccharomyces cerevisiae. Cells lacking the mitochondrial chaperone Zim17 (Tim15/Hep1), a component of the iron–sulfur biosynthesis machinery, have limited respiration activity, mimic the metabolic response to iron starvation and suffer a dramatic increase in nuclear genome recombination. Increased oxidative damage or deficient DNA repair do not account for the observed genomic hyperrecombination. Impaired cell-cycle progression and genetic interactions of ZIM17 with components of the RFC-like complex involved in mitotic checkpoints indicate that replicative stress causes hyperrecombination in zim17Δ mutants. Furthermore, nuclear accumulation of pre-ribosomal particles in zim17Δ mutants reinforces the importance of iron–sulfur clusters in normal ribosome biosynthesis. We propose that compromised ribosome biosynthesis and cell-cycle progression are interconnected, together contributing to replicative stress and nuclear genome instability in zim17Δ mutants.

Thermodynamic stability of nanosized multicomponent bubbles/droplets: The square gradient theory and the capillary approach

Formation of nanosized droplets/bubbles from a metastable bulk phase is connected to many unresolved scientific questions. We analyze the properties and stability of multicomponent droplets and bubbles in the canonical ensemble, and compare with single-component systems. The bubbles/droplets are described on the mesoscopic level by square gradient theory. Furthermore, we compare the results to a capillary model which gives a macroscopic description. Remarkably, the solutions of the square gradient model, representing bubbles and droplets, are accurately reproduced by the capillary model except in the vicinity of the spinodals. The solutions of the square gradient model form closed loops, which shows the inherent symmetry and connected nature of bubbles and droplets. A thermodynamic stability analysis is carried out, where the second variation of the square gradient description is compared to the eigenvalues of the Hessian matrix in the capillary description. The analysis shows that it is impossible to stabilize arbitrarily small bubbles or droplets in closed systems and gives insight into metastable regions close to the minimum bubble/droplet radii. Despite the large difference in complexity, the square gradient and the capillary model predict the same finite threshold sizes and very similar stability limits for bubbles and droplets, both for single-component and two-component systems.

Moderately oxidized oils and dietary zinc and alpha-tocopheryl acetate supplementation: effects on the oxidative stability of rabbit plasma, liver, and meat

The aim of this study was to assess the alterations in plasma, liver, and meat oxidative stability and R-tocopherol content when moderately oxidized sunflower oils were added to feeds and when feeds were supplemented with R-tocopheryl acetate (100 mg/kg) and Zn (200 mg/kg). The effects of cooking the meat and its subsequent refrigeration were also studied. When the content of primary oxidation compounds of the oil was high, rabbit plasma, liver, and meat R-tocopherol content was reduced and meat susceptibility to oxidation increased. The addition of oil with a high content of secondary oxidation compounds (oil heated at 140 'C, 31 h) to feed also led to an increase in meat susceptibi- lity to oxidation, although it presented an R-tocopherol content similar to that of nonheated oil. Feed supplementation with R-tocopheryl acetate increased tissue R-tocopherol content and improved the oxidative stability of liver and meat. However, in the latter, it was less effective when oil heated at 55 'C was added.

Stability of hydrogenated nanocrystalline silicon thin-film transistors

Hydrogenated nanocrystalline silicon thin-films were obtained by catalytic chemical vapour deposition at low substrate temperatures (150°C) and high deposition rates (10 Å/s). These films, with crystalline fractions over 90%, were incorporated as the active layers of bottom-gate thin-film transistors. The initial field-effect mobilities of these devices were over 0.5 cm 2/V s and the threshold voltages lower than 4 V. In this work, we report on the enhanced stability of these devices under prolonged times of gate bias stress compared to amorphous silicon thin-film transistors. Hence, they are promising candidates to be considered in the future for applications such as flat-panel displays.

Protein loop compaction and the origin of the effect of arginine and glutamic acid mixtures on solubility, stability and transient oligomerization of proteins

Addition of a 50 mM mixture of l-arginine and l-glutamic acid (RE) is extensively used to improve protein solubility and stability, although the origin of the effect is not well understood. We present Small Angle X-ray Scattering (SAXS) and Nuclear Magnetic Resonance (NMR) results showing that RE induces protein compaction by collapsing flexible loops on the protein core. This is suggested to be a general mechanism preventing aggregation and improving resistance to proteases and to originate from the polyelectrolyte nature of RE. Molecular polyelectrolyte mixtures are expected to display long range correlation effects according to dressed interaction site theory. We hypothesize that perturbation of the RE solution by dissolved proteins is proportional to the volume occupied by the protein. As a consequence, loop collapse, minimizing the effective protein volume, is favored in the presence of RE.

Stability and consistency of coping in adolescence: A longitudinal study

This study analyzed stability and consistency of coping among adolescents. The objectives were twofold: a) to analyze temporal stability and cross-situational consistency of coping responses after a 17- month interval, taking into account gender, age and type of stressor. b) To analyze the relative weight of contextual versus dispositional factors in predicting future coping. A cohort of 341 adolescents (51% girls and 49% boys aged between 12 and 16) were assessed twice by means of the Coping Responses Inventory - Youth. The results indicated that the coping responses were quite stable over time at the group level, but with important within-subject differences. Girls showed slightly more stability than boys. Among the girls, Avoidance coping showed as much stability as consistency and Approach coping showed more stability than consistency. Among the boys, Avoidance coping showed more stability than consistency, and Approach coping showed both low stability and low consistency. Among the boys, the coping used at Time 1 barely predicted that used at Time 2; in contrast, among the girls, the type of coping used in the past, especially Avoidance coping, predicted the coping that would be used in the future.

First principles analysis of the stability and diffusion of oxygen vacancies in meetal oxides

Oxygen vacancies in metal oxides are known to determine their chemistry and physics. The properties of neutral oxygen vacancies in metal oxides of increasing complexity (MgO, CaO, alpha-Al2O3, and ZnO) have been studied using density functional theory. Vacancy formation energies, vacancy-vacancy interaction, and the barriers for vacancy migration are determined and rationalized in terms of the ionicity, the Madelung potential, and lattice relaxation. It is found that the Madelung potential controls the oxygen vacancy properties of highly ionic oxides whereas a more complex picture arises for covalent ZnO.

Design and physicochemical stability studies of paediatric oral formulations of sildenafil

Abstract Personalized medicine is a challenging research area in paediatric treatments. Elaborating new paediatric formulations when no commercial forms are available is a common practice in pharmacy laboratories; among these, oral liquid formulations are the most common. But due to the lack of specialized equipment, frequently studies to assure the efficiency and safety of the final medicine cannot be carried out. Thus the purpose of this work was the development, characterization and stability evaluation of two oral formulations of sildenafil for the treatment of neonatal persistent pulmonary hypertension. After the establishment of a standard operating procedure (SOP) and elaboration, the physicochemical stability parameters appearance, pH, particle size, rheological behaviour and drug content of formulations were evaluated at three different temperatures for 90 days. Equally, prediction of long term stability, as well as, microbiological stability was performed. Formulations resulted in a suspension and a solution slightly coloured exhibiting fruity odour. Formulation I (suspension) exhibited the best physicochemical properties including Newtonian behaviour and uniformity of API content above 90% to assure an exact dosification process.

Development, physical-chemical stability and release studies of four alcohol-free spironolactone suspensions for use in pediatrics

Dissolution studies have become of great significance because, in most cases, drug dissolution is the rate-limiting step in the absorption process. As occurs with solid oral dosage forms, heterogeneous disperse systems (suspensions) could also have some problems with their in vitro dissolution. The objective of this study was to evaluate influence of the excipients on the release of spironolactone from four alcohol free suspensions (pharmaceutical compounding) of spironolactone 5 mg/mL suitable for pediatric use. Also the comparison of the physical and chemical stability of the suspensions stored at 4, 25 and 40 ºC over a 60- day period has been studied. Rheological behavior, particle size, a prediction of long-term physical stability, pH and assay of spironolactone by HPLC were assessed at prefixed times. The dissolution profile of each suspension was determined and compared with that of the commercial tablets. A microbiological study of the best formula was also performed. Chemically, the four spironolactone suspensions were stable for 60 days stored at three temperatures; Suspension IV had optimum pH values and the highest recovery percentage. In terms of physical stability, sedimentation occurred in Suspension IV and flotation of spironolactone in Suspensions I, II and III. Suspension III had the highest viscosity and the slowest drug release. Suspension IV was also microbiologically stable for 60 days. In conclusion, Suspension IV had the best properties and the least suitable form was Suspension III, as its high viscosity made it difficult to achieve homogeneous redispersion, and it had the slowest dissolution profile.

Disseny de les llantes en material compòsit de les rodes davanteres i roda posterior del vehicle de baix consum "Àguila"

Durant els últims dos anys un grup d’estudiants de l’Escola Politècnica Superior de laUniversitat de Girona han construït i evolucionat un prototip per competir en la Shell EcoMarathon, una cursa de caràcter internacional que es celebra cada any a Nogaro (França) ia on l’objectiu primordial és aconseguir el mínim consum. Equips de diferents països delmón recorren amb els seus prototips la mateixa distància i el guanyador és qui en finalitzarhagi fet servir menys quantitat de combustible. La intenció de l’equip és continuar competint en aquest cursa durant els propers anys, peraquest motiu cada any es plantegen noves modificacions a realitzar per tal d’aconseguir unprototip més competitiu. Una de les modificacions consisteix en substituir les actuals llantesd’alumini equipades en el vehicle per unes llantes lenticulars fabricades en fibra de carboni.Aquestes llantes en material compòsit representen una millora en prestacions respecte lesllantes convencionals en reduir la inèrcia.Escollir la fibra de carboni com el material a emprar no ha estat a l’atzar. Els avantatges quecomporta la fibra de carboni en referència als rati rigidesa/pes i resistència/pes sónindiscutibles. La resistència a la fatiga d’aquest tipus de material és més elevada que la del’alumini, material utilitzat en les actuals llantes, a més, la voluntat d’entendre millor elcomportament i els processos de fabricació d’aquest material per part dels membres del’equip posicionen a la fibra de carboni com el material més idoni.La solució final adoptada pel disseny de les llantes consta per la unió adhesiva de duespeces iguals fabricades en fibra de carboni. La facilitat de poder fabricar dos “plats” simètricsresulta el punt fort d’aquest disseny, el qual, amb un únic motllo s’arriben a construir latotalitat de les llantes

A measure of stability as a criterion for the verification and analysis of simulation models

The aim of this study is to define a new statistic, PVL, based on the relative distance between the likelihood associated with the simulation replications and the likelihood of the conceptual model. Our results coming from several simulation experiments of a clinical trial show that the PVL statistic range can be a good measure of stability to establish when a computational model verifies the underlying conceptual model. PVL improves also the analysis of simulation replications because only one statistic is associated with all the simulation replications. As well it presents several verification scenarios, obtained by altering the simulation model, that show the usefulness of PVL. Further simulation experiments suggest that a 0 to 20 % range may define adequate limits for the verification problem, if considered from the viewpoint of an equivalence test.

Simulating fuel consumption and vehicle emissions in an Australian context

Road transport is a major source of air pollution and greenhouse gas emissions around the world. There is an increasing interest in accurate information on local vehicle emission levels for policy development and sustainable traffic management. Previous studies have shown that emission predictions for the Australian situation need to reflect both the Australian fleet and driving behaviour to avoid unreliable outcomes. This paper discusses a new Australian vehicle emission software (PΔP) and a case-study where traffic simulation software (Aimsun) is combined with PΔP to demonstrate how consistent results can be achieved for the Australian situation. The case-study is an Australian city modelled using the microscopic simulator to generate the required trajectory data of each individual vehicle for the emission model. The simulation results are used in a number of ways: to assess the impacts of urban driving behaviour on fuel consumption, to create maps showing where and when elevated emission levels occur and to compare results with another program (COPERT Australia). The paper will also discuss where further research is required.