Phase field theory modeling of CH4/CO2 gas hydrates in gravity fields

Natural gas hydrates in reservoirs are thermodynamically unstable due to the interactions with surrounding fluids (aqueous, gas) and mineral surfaces. Depending on the local flow hydrate will dissociate as well as reform. If the dissociation rate is faster than the capacity of the surrounding fluids to dissolve the released gas, the gas will form bubbles. Depending on the rate of released gas and possible fracture patterns this may lead to venting of gas. The proper implementation of hydrodynamics will provide a deeper insight of the hydrate kinetics involved during dissociation and formation processes which involve hydrate former phase as smaller or larger bubbles or even continuous gas phase. In this work the phase field theory coupled with hydrodynamics model is implemented with variable density using the relative composition, phase field parameter and flow, which is an extension of our previous work which considers a constant density.publishedVersio

Phase field theory of crystal nucleation in hard sphere liquid

The phase field theory of crystal nucleation described in [L. Granasy, T. Borzsonyi, T. Pusztai, Phys. Rev. Lett. 88, 206105 (2002)] is applied for nucleation in hard--sphere liquids. The exact thermodynamics from molecular dynamics is used. The interface thickness for phase field is evaluated from the cross--interfacial variation of the height of the singlet density peaks. The model parameters are fixed in equilibrium so that the free energy and thickness of the (111), (110), and (100) interfaces from molecular dynamics are recovered. The density profiles predicted without adjustable parameters are in a good agreement with the filtered densities from the simulations. Assuming spherical symmetry, we evaluate the height of the nucleation barrier and the Tolman length without adjustable parameters. The barrier heights calculated with the properties of the (111) and (110) interfaces envelope the Monte Carlo results, while those obtained with the average interface properties fall very close to the exact values. In contrast, the classical sharp interface model considerably underestimates the height of the nucleation barrier. We find that the Tolman length is positive for small clusters and decreases with increasing size, a trend consistent with computer simulations.Comment: 7 pages, 7 figure

Modernisation of the Norwegian Tide Gauge Network

The modernization of the Norwegian Tide Gauge Network using technologies of the 1980s is presented. Technical and organizational challenges are described in detail together with cost-estimates and possible future developments

Body mass index and mortality in elderly men and women: the Tromsø and HUNT studies

The impact of body mass index (BMI; kg/m2) and waist circumference (WC) on mortality in elderly individuals is controversial and previous research has largely focused on obesity. With special attention to the lower BMI categories, associations between BMI and both total and cause-specific mortality were explored in 7604 men and 9107 women aged ≥65 years who participated in the Tromsø Study (1994–1995) or the North-Trøndelag Health Study (1995–1997). A Cox proportional hazards model adjusted for age, marital status, education and smoking was used to estimate HRs for mortality in different BMI categories using the BMI range of 25–27.5 as a reference. The impact of each 2.5 kg/m2 difference in BMI on mortality in individuals with BMI<25.0 and BMI≥25.0 was also explored. Furthermore, the relations between WC and mortality were assessed. We identified 7474 deaths during a mean follow-up of 9.3 years. The lowest mortality was found in the BMI range 25–29.9 and 25–32.4 in men and women, respectively. Mortality was increased in all BMI categories below 25 and was moderately increased in obese individuals. U-shaped relationships were also found between WC and total mortality. About 40% of the excess mortality in the lower BMI range in men was explained by mortality from respiratory diseases. BMI below 25 in elderly men and women was associated with increased mortality. A modest increase in mortality was found with increasing BMI among obese men and women. Overweight individuals (BMI 25–29.9) had the lowest mortality

Risk of malnutrition and health-related quality of life in community-living elderly men and women: The Tromsø study

Purpose To explore the association between risk of malnutrition as well as current body mass index (BMI) and health-related quality of life (HRQoL) in elderly men and women from the general population. Methods In a cross-sectional population survey including 1,632 men and 1,654 women aged 65 to 87 years from the municipality of Tromsø, Norway, we assessed HRQoL by using the EuroQol (EQ-5D) instrument in three risk groups of malnutrition and in different categories of BMI. The Malnutrition Universal Screening Tool (‘MUST’) was used to evaluate the risk of malnutrition. Results We found a significant reduction in HRQoL with an increasing risk of malnutrition, and this was more pronounced in men than in women. The relationship between BMI and HRQoL was dome shaped, with the highest score values in the BMI category being 25–27.5 kg/m2. Conclusions HRQoL was significantly reduced in elderly men and women at risk of malnutrition. The highest HRQoL was seen in moderately overweight individuals

Excessive Daytime Sleepiness in Obstructive Sleep Apnea Patients Treated With Continuous Positive Airway Pressure: Data From the European Sleep Apnea Database

Excessive daytime sleepiness (EDS) is a symptom of obstructive sleep apnea (OSA) that resolves under treatment with continuous positive airway pressure (CPAP). In some patients, sleepiness persists despite CPAP treatment. We retrospectively analyzed data on subjective residual EDS, assessed as an Epworth Sleepiness Scale score (ESS) &gt;10, in patients from the European Sleep Apnea Database (n = 4,853, mean age ± SD 54.8 ± 11.8 years, 26.1% females), at baseline and at the first visit (median follow-up: 5 months, interquartile range 3–13). An ESS &gt; 10 occurred in 56% of patients at baseline and in 28.2% of patients at follow-up. Residual EDS was analyzed in 2,190 patients (age: 55.1 ± 12.0 years, 26.1% females) with sleep monitoring data (median follow-up: 3 months, interquartile range 1–15). Sleep studies during CPAP use were obtained in 58% of these patients; EDS was reported by 47.2% of patients at baseline and by 30.3% at follow-up. Residual OSA, defined as an apnea–hypopnea index &gt;10/h, and insufficient CPAP adherence, defined as nightly use &lt;4 h, occurred with similar frequency in patients with and without EDS at follow-up. Prevalence of residual EDS was highest (40%) in patients with a first follow-up visit at 0–3 months, then it was 13–19% in patients with a first follow-up visit after 4 months to 2 years. The change in ESS (n = 2,190) was weakly correlated with CPAP use (R2 = 0.023, p &lt; 0.0001). Logistic regression showed that an ESS score &gt;10 at the first follow-up visit was associated directly with ESS at baseline and inversely with duration of follow-up, and CPAP use (R2 of the model: 0.417). EDS showed heterogeneity in different European countries both at baseline and at the first follow-up visit, suggesting modulation by cultural and lifestyle factors. In conclusion, residual EDS in CPAP-treated OSA occurred in approximately one in four patients at follow-up; its prevalence was highest (40%) in the first 3 months of treatment and subsequently decreased. The finding of residual EDS in a significant percentage of optimally treated OSA patients suggests that wake-promoting agents may be useful, but their indication should be evaluated after at least 3 months of treatment

Reading religion in Norwegian textbooks: are individual religions ideas or people?

Different religions are treated in different ways in Norwegian sixth form textbooks. We carried out an exhaustive content analysis of the chapters devoted to individual religions in textbooks for the Religion and Ethics course currently available in Norway, using rigorous indicators to code each word, image and question according to whether they were treated the religion as a set of ideas or a group of people. After adjusting for trends in the different kinds of data (word, image, question), we found that Buddhism and Christianity receive significantly more attention for their ideas than Hinduism, Islam and Judaism, which are treated more as people. This difference cannot be explained by the national syllabus or the particularities of the individual religions. The asymmetry also has implications for the pupils’ academic, moral and pedagogical agency for which teachers play a critical role in compensating.acceptedVersio

Methods for specifying the target difference in a randomised controlled trial : the Difference ELicitation in TriAls (DELTA) systematic review

Peer reviewedPublisher PD