Numerical stability for finite difference approximations of Einstein's equations

We extend the notion of numerical stability of finite difference approximations to include hyperbolic systems that are first order in time and second order in space, such as those that appear in Numerical Relativity. By analyzing the symbol of the second order system, we obtain necessary and sufficient conditions for stability in a discrete norm containing one-sided difference operators. We prove stability for certain toy models and the linearized Nagy-Ortiz-Reula formulation of Einstein's equations. We also find that, unlike in the fully first order case, standard discretizations of some well-posed problems lead to unstable schemes and that the Courant limits are not always simply related to the characteristic speeds of the continuum problem. Finally, we propose methods for testing stability for second order in space hyperbolic systems.Comment: 18 pages, 9 figure

THE RISKS ASSOCIATED TO THE HOARFROST PHENOMENON IN THE REGHIN HILLS

Hoarfrost, being a hydrometeor which is produced only in the presence of frost, represents a major risk factor to agriculture especially when it appears early in autumn, 2-3 weeks earlier then the average date of appearance and late in spring, in the second decade of April and the first decade of May. This paper shows an analysis of the parameters which define the hoarfrost phenomenon in order to highlight the vulnerability of the analysed area regarding this phenomenon. In a first phase, in order to identify the periods of high vulnerability, we analysed the frequency of the days with minimum temperatures ≤ 0C, and in order to highlight the vulnerability of the studied area regarding the hoarfrost phenomenon we analysed the parameters which define the hoarfrost phenomenon: the medium annual number of days with hoarfrost and their multiannual variation, the frequency of the annual deviations from the multiannual average, the monthly and season variation of the days with hoarfrost, the medium and extreme dates of hoarfrost production and the frequency and degree of assurance of the monthly number of hoarfrost days of different lengths. The analysis of the parameters which define the hoarfrost phenomenon was realized on the basis of the information recorded at the two metorological stations present in the studied area, the Târgu Mureş Metorological Station and the Batoş Metorological Station and the Eremitu and Gurghiu rainfall stations for the 1978-2008 period

Shortening the length of stay and mechanical ventilation time by using positive suggestions via MP3 players for ventilated patients

Long stay in intensive care unit (ICU) and prolonged ventilation are deleterious for subsequent quality of life and surcharge financial capacity. We have already demonstrated the beneficial effects of using suggestive communication on recovery time during intensive care. The aim of our present study was to prove the same effects with standardized positive suggestive message delivered by an MP3 player. Patients ventilated in ICU were randomized into a control group receiving standard ICU treatment and two groups with a standardized pre-recorded material delivered via headphones: a suggestive message about safety, self-control, and recovery for the study group and a relaxing music for the music group. Groups were similar in terms of age, gender, and mortality, but the SAPS II scores were higher in the study group than that in the controls (57.8 ± 23.6 vs. 30.1 ± 15.5 and 33.7 ± 17.4). Our post-hoc analysis results showed that the length of ICU stay (134.2 ± 73.3 vs. 314.2 ± 178.4 h) and the time spent on ventilator (85.2 ± 34.9 vs. 232.0 ± 165.6 h) were significantly shorter in the study group compared to the unified control. The advantage of the structured positive suggestive message was proven against both music and control groups

The Activation of the Fibrodysplasia Ossificans Progressiva-Inducing ALK2-R206H Mutant Depends on the Distinct Homo-Oligomerization Patterns of ACVR2B and ACVR2A

Mutations in activin-like kinase 2 (ALK2), e.g., ALK2-R206H, induce aberrant signaling to SMAD1/5/8, leading to Fibrodysplasia Ossificans Progressiva (FOP). In spite of extensive studies, the underlying mechanism is still unclear. Here, we quantified the homomeric and heteromeric interactions of ACVR2A, ACVR2B, ALK2-WT, and ALK2-R206H by combining IgG-mediated immobilization of one receptor with fluorescence recovery after photobleaching (FRAP) measurements on the lateral diffusion of a co-expressed receptor. ACVR2B formed stable homomeric complexes that were enhanced by Activin A (ActA), while ACVR2A required ActA for homodimerization. ALK2-WT, but not ALK2-R206H, exhibited homomeric complexes unaffected by ActA. ACVR2B formed ActA-enhanced heterocomplexes with ALK2-R206H or ALK2-WT, while ACVR2A interacted mainly with ALK2-WT. The extent of the homomeric complex formation of ACVR2A or ACVR2B was reflected in their ability to induce the oligomerization of ALK2-R206H and ALK2-WT. Thus, ACVR2B, which forms dimers without ligand, induced ActA-independent ALK2-R206H clustering but required ActA for enhancing the oligomerization of the largely dimeric ALK2-WT. In contrast, ACVR2A, which undergoes homodimerization in response to ActA, required ActA to induce ALK2-R206H oligomerization. To investigate whether these interactions are translated into signaling, we studied signaling by the FOP-inducing hyperactive ALK2-R206H mutant, with ALK2-WT signaling as control. The activation of SMAD1/5/8 signaling in cells expressing ALK2-R206H alone or together with ACVR2A or ACVR2B was measured by blotting for pSMAD1/5/8 and by transcriptional activation assays using BRE-Luc reporter. In line with the biophysical studies, ACVR2B activated ALK2-R206H without ligand, while activation by ACVR2A was weaker and required ActA. We propose that the homodimerization of ACVR2B or ACVR2A dictates their ability to recruit ALK2-R206H into higher complexes, enabling the homomeric interactions of ALK2-R206H receptors and, subsequently, their activation

Synthesis, physico-chemical characterization and bacteriostatic study of Pt complexes with substituted amine ligands

Three complexes of general formula PtCl2R2 were synthesized, where R is the amine ligand with aromatic substituents. Coordination compounds [Pt(an)2Cl2] (1), [Pt(pa)2Cl2] (2) and [Pt(aph)2Cl2] (3), where an = 2-aminonaphthalene, pa = 2-aminopyrimidine, aph = 4-anilinophenol, were characterized by on-line coupled TG/DTA-MS, powder XRD and spectroscopic techniques (FTIR, ESI–MS and NMR), and tested against selected Gram(+) and Gram(–) bacteria. The thermal data show that all three compounds contain lattice or absorbed water, and the stability of the anhydrous compounds in nitrogen decreases in the order 2 > 1 > 3. Above 200 °C, the complexes loose characteristic fragments of their ligands. The spectroscopic data are in accordance with the thermal properties of the samples and prove their composition. The compounds are more effective inhibitors of Gram(+) than Gram(−) bacteria. © 2016 Akadémiai Kiadó, Budapest, Hungar